Chemical Process Technology [First Edition] 9789354667305

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Chemical Process Technology

Chemical Process Technology Indra Deo Mall phd fie (i) fiiche lm ippta

Former Professor and Head Department of Chemical Engineering Indian Institute of Technology, Roorkee Uttrakhand, India Distinguished Professor Department of Chemical Engineering University of Petroleum and Energy Studies, Dehradun Uttrakhand, India

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Representatives Hyderabad Pune Nagpur Manipal Vijayawada Patna

to my parents, teachers and students

Foreword

T

he developing nations, in their quest for economic growth, have been revamping, modernizing and expanding the chemical industry. However, thesedays, the industry has been facing various challenges, including the wide variation in the raw materials and its costs, besides complying with stringent environmental standards and enhanced quality of products required. To remain competitive, the chemical industry has to look at various cost cutting and conservation measures including those for raw materials, energy, and other utilities. The book Chemical Process Technology by Prof ID Mall covers various inorganic and organic chemical industries including fertilizers, pulp and paper, soap and detergents, sugar and alcohol, cement, glass and refractory, dyes and paints, pharmaceutical and metallurgical industries. Prof Mall has also discussed some details of petroleum and petrochemical processes. The issues of specific energy consumption, corrosion, environment and safety also have been widely covered in the last few chapters. I congratulate Prof Mall for his efforts in detailing various aspects of chemical process industries, and I am sure this compilation will help the students, faculty and practicing engineers and scientists. I wish Prof Mall all success in his future endeavors.

SJ Chopra Chancellor University of Petroleum and Energy Studies (UPES) Dehradun

Preface

C

hemical industry is one of the most important sectors of economy and plays vital role in the industrialization and urbanization which meet basic needs of mankind through supplying fertilizers, synthetic fiber, synthetic rubber, polymers, sugar and alcohol, paper dyes and intermediates, explosives, agrochemicals, dyes, paints, etc. Globally, it processes more material than any other industry. With expected population of 7.6 billion by 2020, huge increase in demand for chemicals in various forms is expected and offers the huge scope for the growth. The chemical industry in India accounts for about 2.11% of gross domestic product (GDP) and is the third largest producer in Asia and sixth largest in the world in terms of volume. Indian chemical industry has been expected to grow from $118 billion in 2014 to $214 billion in 2019.The diversification within chemical industry is very large, as it includes more than eighty thousand commercial products. The size of Indian chemical industry in terms of value of output in year 2013–14 was 839,460 crore. The production of total major chemicals and petrochemicals in 2014–15 was 21,226 kilo tons. Due to present epidemic all predicted figures are going to change in spite of steps which are being taken globally. Chemical technology is the one of the important courses in chemical engineering curriculum. Chemical industry is knowledge intensive as well as capital intensive industry. Knowledge of chemical process industries is of great importance to chemical engineers. The book contains 28 Chapters. Chapter 1 deals with introduction to chemical process industries dealing with technological development, major challenges, issues and weakness of Indian chemical industry, global and Indian scenario. Chapter 2 deals with basic principles for chemical processes, unit processes and unit operations in chemical industries. Chapter 3 deals with industrial gases. Chapter 4 deals with chlor-caustic and soda ash industry while Chapter 5 discusses sulfur and sulfuric acid. Chapter 6 deals with introduction to fertilizer industry, nitric acid and ammonia. Chapters 7 and 8 describe nitrogenous and phosphorous and phosphatic fertilizer industry. Chapter 9 describes cement and lime industries while Chapter 10 deals with glass and refractories. Chapter 11 describes oils and fats industries while Chapter 12 describes explosives and miscellaneous chemicals. Chapter 13 describes about metallurgical industry. Chapter 14 describes leather industries while in Chapter 15, coal and coal as chemical feedstock has been discussed. Chapter 16 describes pulp and paper industries. Chapter 17 describes about sugar and alcohol industries while Chapter 18 describes about soap and detergent. Chapters 19 and 20 deal with petroleum and petrochemical industries. Chapter 21 describes polymer, elastomer and

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Chemical Process Technology

synthetic fiber. Chapter 22 deals with agrochemicals while Chapters 23 and 24 deal with dyestuff industry and paint, varnish and lacquers, respectively. Chapter 25 deals with pharmaceutical industry. Chapter 26 describes corrosion and material of construction in chemical industries. Chapters 27 and 28 deal with energy management in chemical industry and environment, health and safety in chemical process industry. In appendices, a list of various petroleum, petrochemical, chemical and fertilizer industry has been given. Cost of some important chemicals and utility is also given. A list of commmonly used abbreviations in chemcial process industries is also provided in the begining of the book.

Indra Deo Mall

Acknowledgments would like to express my sincere thanks to Dr SJ Chopra, Chancellor, University of Petroleum and Energy Studies for his encouragement, inspiration and valuable comments, as well as for providing foreword in this book. I am greatly indebted to Dr SN Upadhyaya, Former Director, Indian Institute of Technology, Banaras Hindu University who has always a source of inspiration and encouragement. I would like to offer my sincere gratitude to Dr Prem Vrat, Former Director, Indian Institute of Technology, Roorkee, and Vice Chancellor, UP Technical University and Dr SC Saxena, Former Director, Indian Institute of Technology, Roorkee and Vice Chancellor, JP University. I would like to offer my sincere gratitude to Prof MM Sharma and Dr RA Mashelkar who are source of inspiration to chemical engineers. I would also like to pay my sincere gratitude to all my teachers at IIT, BHU, Varanasi and rich tribute to those who are not with us for their inspiration and guidance. I am thankful to my friend IM Mishra, Ex-Professor and Head, Chemical Engineering IIT Roorkee, and Emeritus Professor, ISM Dhanbad, for his help and support. Thanks are also due to Dr Vimal Chandra Srivastava, Head, Chemical Engineering, IIT Roorkee for his support and sincere efforts and contribution. The author pays rich tribute to late Shri Dhiru Bhai Ambani, great visionary who has brought India on the world petroleum and petrochemical map and revolutionized petroleum and petrochemical sector. The author also pays rich tribute to late Prof AP Mall and Prof YD Upadhyay who had been a source of inspiration and moral support. I would like to offer my sincere gratitude to NPTEL, Reliance Industries Ltd., Indian Oil Corporation Ltd, Panipat Refinery, Gas Authority of India Ltd, New Delhi; Indian Petrochemical Corporation Ltd (Now Reliance Industries), Vadodara, and CPCL for providing important technical information and Dr RP Verma, Former Executive Director, IOC, R&D Centre, Faridabad, Dr SN Kaul, Former Acting Director, NERI, Mr RK Ghosh, Former Director, Refineries, IOCL, Mr Sanjeev Singh, Director Refineries, Former Chairman and MD, IOCL and Paradip Refinery, Mr A Basu, Former CMD, CPCL, Chennai and presently, Head, Refineries HPCL, Dr MO Garg, Former Director General, CSIR, late Sri Anand Kumar, Director Petrotech, Mr NP Rao DGM IFFCO Bareilly, Dr Karuna, Head, Chemical Engineering Rohilkhand University, and Late Sri DK Karwal, Former DGM, IOC Panipat Refinery, and Dr Sushil Kumar, Former President, Reliance Industries. I would like to express my sincere thanks to Dr Chandrakant Thakur, Assistant Professor, NIT, Raipur, for his untiring efforts in preparation of manuscript. Sincere thanks are due to Dr V Subaramaiah, Assistant Professor, MNIT, Jaipur,

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Chemical Process Technology

Dr SK Nanda, Professor, UPES, Dr M Gopinath, Assistant Professor, UPES, Dr Murali Pujari, Assistant Professor, UPES, Dehradun. I also acknowledge the contribution of my student, Saurabh Singh, Bokaro Steel Plant and some of my other students Anang Swapnesh, Nitin Kumar, Dr Seema, Bhawna Bajpai, Dr Priyanka, Sanjay Gautam, Shailendra, Karthikeyan Shukla, Rohit, Anirudh Jindal, Shamira Khatoon, Shrey Jain and Rudraksh Rai and Sumit Shrma for designing cover page and flow diagram and other computational work. Last but not the least, I sincerely acknowledge the patience, support and understanding of my wife Indira who is standing behind me during ups and down of my life. I also acknowledge the support of Vishal and Pallavi, Kavim, Gunjan and Sanjay, Priyansh and Shagun. Indra Deo Mall

Contents Foreword vii Preface ix Acknowledgments xi Abbreviations xv 1. Chemical Process Industries 1 2. Basic Principles of Chemical Processes and Unit Operations in 16 Chemical Industries 3. Industrial Gases 46 4. Chlor-caustic and Soda Ash Industry 57 5. Sulfur and Sulfuric Acid 82 6. Fertilizer Industry 93 7. Nitrogenous Fertilizer and Nitric Acid 110 8. Phosphorus, Phosphatic, Potassium and Mixed Fertilizers 133 9. Cement and Lime Industries 148 10. Glass and Refractories 162 11. Oil and Fats 176 12. Explosives and Miscellaneous Chemicals 186 13. Metallurgical Industry in India 195 14. Leather Industries 206 15. Coal and Coal as Chemical Feedstock 210 16. Pulp and Paper Industry 231 17. Sugar and Alcohol Industry 262 18. Soap and Detergent 276 19. Petroleum Refining 289 20. Petrochemical Industry 349 21. Polymer, Elastomer and Synthetic Fiber 422 22. Agrochemicals 475 23. Dyestuff Industry 484 24. Paint, Varnish and Lacquers 497

xiv Chemical Process Technology

25. 26. 27. 28.

Pharmaceutical Industry Corrosion and Material of Construction in Chemical Industries Energy Management in Chemical Industry Environment, Health and Safety in Chemical Process Industry

Appendices Appendix 1: Quantities and SI Unit Appendix 2: Physical and Chemical Characteristics of Major Inorganic and Organic Chemicals Appendix 3: Major Petroleum, Petrochemical, Fertilizer and Chemical Industries in India Appendix 4: Major Manufacturing Associations Appendix 5: Cost of Various Crude Oils and Petroleum Products Index

504 514 536 550 577 582 597 622 626 629

Abbreviations ACGIH

American Congress of Governmental Industrial Hygienists

ADU

Atmospheric Distillation Unit

AIHA

American Industrial Hygiene Association

ANGM

Association of Natural Gasoline Manufacturers

API

American Petroleum Institute

Aq.

Aqueous

ARCO

Atlantic Richfield Co

ASTM

American Society for Testing and Materials

Atm.

Atmospheric Pressure

BMCI

Bureau of Mines Correlation Index

BP

British Petroleum; Boiling Point

BRPL

Bongaigaon Refinery and Petrochemicals Limited

BTX

Benzene, Toluene, Xylene

CCR

Continuous Catalyst Regeneration

CCRU

Continuous Catalytic Reforming Unit

CEL

Shell Corrected Energy and Loss Index

CF

Combustion Factor

CFC

Continuous Film Contractor

CFR

Compagnie Fransaus Deraffinage

CLO

Clarified Light Oil

CNG

Compressed Natural Gas

Co.

Corporation

Conc.

Concentration

CPCL

Chennai Petroleum Corporation Limited

CPW

Chlorinated Paraffins Wax

CR

Catalytic Reforming

CSD

Critical Solvent Dewaxing

DAO

Deasphalted Oil

DCC

Deep Catalytic Cracking

DEA

Diethanol Amine

xvi Chemical Process Technology DEG

Diethylene Glycol

DGA

Diglycol Amine

Dil.

Dilute

DIPE

Di-isopropyl Ether

DMF

Dimethyl Formamide

DMSO

Dimethyl Sulfoxide

EIA

Environmental Impact Assessment

EII

Energy Intensity Index

EOR

Enhance Oil Recovery

EPA

Environmental Protection Agency

EPDM

Ethylene Propylene Diene Rubber

ETBA

Ethyl Tertiary Butyl Alcohol

FCC

Fluid Catalytic Cracking

FEP

Fluorinated Ethylene Propylene

FO

Fuel Oil

FP

Freezing Point

FTT

Furnace Transfer Temperature

GAIL

Gas Authority of India Limited

GTL

Gas to Liquids

GIS

Geographic Information System

GPS

Global Positioning System

IPA

Isopropyl Alcohol

GTBA

Gasoline Grade Tertiary Butyl Alcohol

HAZOP

Hazard Operability Study

HCO

Heavy Cycle Oil

H: HC

Hydrogen to Hydrocarbon Ratio

HSD

High Speed Diesel Oil

HTSD

High Temperature Simulated Distillation

IBP

Initial Boiling Point

ICI

Imperial Chemical Industries

IFP

Institut Français du Pétrole

LAB

Linear Alkyl Benzene

LCO

Light Cycle Oil

LD50

Lethal Dose

LDO

Light Diesel Oil

LEL

Lower Explosive Limit

LFL

Lower Flammability Limit

LHSV

Liquid Hourly Space Velocity

LNG

Liquefied Natural Gas Liquid

LPG

Liquefied Petroleum Gas

Abbreviations xvii Ltd.

Limited

LWD

Logging While-Drilling Technologies

MAT

Micro Activity Test

MBK

Methyl Butyl Ketone

MCP

Molecular Collision Parameter

MDD

Maximum Drilling Depth

MDDW

Mobil Distillate Dewaxing

MDEA

Methyldiethanol Amine

MEA

Monoethanol Amine

MEK

Methyl Ethyl Ketone

MHC

Mild Hydro Cracking

MLTD

Mobil Low Temperature Disproportionation

MOGD

Mobil Olefin to Gasoline and Distillate

MON

Motor Octane Number

MP

Melting Point

MSCC

Milli Second Catalytic Crackings

MTBE

Methyl Tertiary Butyl Ether

MVPI

Mobil Vapor Phase Isomerization

MWD

Measurement While Drilling

NA

Naphthenic Acid

NAC

Naphthenic Acid Corrosion

N+2A

Naphthene + Two Times Aromatic Content

NGHS

Natural Gas Hydrates

NIOSH

National Institute for Occupational Safety and Health Services

NMP

N-Methyl Pyrrolidone

NRCC

Non-regenerative Catalytic Cracking

OH&S

Occupational Health and Safety

OISD

Oil Industry Safety Directorate

ONGC

Oil and Natural Gas Corporation

OSA

Oil Spill Authority

OSHA

Occupational Safety and Health Administration

OSMA

Oil Spill Management Authority

OSW

Österreichische Stickstoff Werke

PDM

Positive Displacement Motor

PRMC

Project Review and Monitoring Committee for Oil Spill Management

PSA

Pressure Swing Adsorption

QRA

Quantified Risk Assessment

RFBD

Residue Fluidized Bed Cracking

RFCC

Residue Fluid Catalytic Cracking

RFG

Reformulated Gasoline

xviii Chemical Process Technology (R+M)/2

(RON+MON)/2

RON

Research Octane Number

RVP

Reid Vapor Pressure

SAC

Solid Acid Alkylation Catalyst

SOP

Super Oil Cracking

SCC

Stress Corrosion Cracking

SEC

Specific Energy Consumption

SHE

Safety, Health and Environmental Management

SYDC

Selective Yield Delayed Coking

TAA

Tertiary Amyl Alcohol

TAEE

Tertiary Amyl Ethyl Ether

TAN

Total Acid Number

TAME

Tertiary Amyl Methyl Ether

TBA

Tertiary Butyl Alcohol

TBP

True Boiling Point

TEA

Triethanol Amine

TEG

Tri Ethylene Glycol

TEL

Tetra Ethyl Lead

TFE

Tetrafluoroethylene

THEME

Tertiary Hexyl Methyl Ether

THD

Thermal Hydro Dealkylation

Tm

Melting Point Temperature

TPR

Throughput Ratio

TSA

Temperature Swing Adsorption

UCC

Union Carbide Co

UDEX

Universal Dow Extraction

UEL

Upper Explosive Limit

UOP

Universal Oil Product

VDS

Vortex Disengager Strippers

VGC

Viscosity Gravity Correlation

VGO

Vacuum Gas Oil

VI

Viscosity Index

VLI

Vapour Lock Index

VSS

Vortex Separation System

WABT

Weighted Average Bed Temperature

WAIT

Weighted Average Inlet Temperature

WHSV

Weight Hourly Space Velocity

ZMS

High Silica/Alumina Ratio Zeolite

1

Chemical Process Industries 1.1 INTRODUCTION

Chemical industry is one of the oldest industries and plays an important role in the social, cultural and economic growth of a nation in providing basic needs of humankind— food, shelter and clothing that have become an indispensable part of our life. It is knowledge intensive as well as capital intensive industry. It is an integral constituent of the growing Indian Industry (Annual Report 2016–17, Ministry of chemical and fertilizer, Government of India). Figure 1.1 illustrates the role of chemical industry in daily life. It is one of the most diversified of all industrial sectors covering thousands of products. Chemical industry includes basic chemicals and its product, petrochemicals, fertilizers, paints and varnishes, gases, soap and detergent, perfumes, pharma­ceuticals and covers thousands of products, which are finding use in our daily life from industrial to household goods. Structure of organic chemical industry is shown in Table 1.1. Various products are finding use in various fields like packaging to agriculture, automobiles to telecommunication, construction to home appliances, health care to personal care, explosive, pesticides to fertilizer, textile to tire cord, chemicals to pharmaceuticals (Table 1.2). Indian chemical industry plays an important role in the overall development of Indian economy and contributes significantly in the GDP growth of the country. It comprises large scale, medium scale and small scale units.

Fig. 1.1: Role of chemical industry (Sources: Mall, 2007, 2013, 2017) 1

2

Chemical Process Technology Table 1.1: Structure of chemical industry

Inorganic chemical industry Industrial gases: Syn. gases, hydrogen Nitro­genous industries: Ammonia, urea, nitric acid

Phosphatic and potassium industries: Rock phosphate, phosphoric acid, phos­ phatic fertilizers,

Marine chemicals: Salt, bromine iodine, sodium salts

Electrothermal industries: Calcium carbide

Chloralkali industries, soda ash, bleaching powder, Sulfur and sulfuric acid poly aluminum chloride Ceramic industries: Cement, refractory and glass

Nuclear industries

Metallurgical industry; ferrous and nonferrous metals Organic chemical industry Coal and coal chemicals

Petroleum and petrochemicals

Pulp and paper

Polymers, elastomers, synthetic rubbers

Soap and detergent

Agrichemicals

Sugar and alcohol

Pesticides

Explosives

Dyes and intermediates

Surface coating industries: Paints, varnishes and Pharmaceutical industries lacquers Table 1.2: Major products of chemical industries and their area of application Group of product

Areas

Plastics and polymers

Agricultural water management, packaging, automobiles, telecommunications, health and hygiene, education

Synthetic rubber

Transportation industry, textile, Industrial equipment lining

Synthetic fiber

Non-woven and woven fiber in automobile, hosiery, textile

Soap and synthetic detergents

Health and hygiene domestic as well as industrial

Industrial chemicals

Drugs and pharmaceuticals, pesticides, explosives, surface loading, dyes, lube additives, adhesive oil field, antioxidants, chemicals, metal extraction, printing ink, paints

Sugar and alcohol

Food, alcoholic breverages, chemical feed stock, ethoxylate, biofuel

Pulp and paper

Writing and printing paper, culture paper, news printing paper, tissue paper, packaging paper

Fertilizer

Agriculture, Chemical industry (ammonia and urea)

Agrochemicals

Pesticides

Mineral acids and organic acid

Chemical industry—organic and inorganic

Sources: Mall, 2007, 2013, 2017.

The chemical industry is a key contributor to the world economy and produces more than 8000 products. Chemical industry is very important to the economic growth and wealth of a country and the world as a whole. Production/consumption of chemicals in the world rapidly accelerated from $1.45 trillion in 2003 to $4.1 trillion in 2013

Chemical Process Industries

3

with the rapid accelerated global GDP which increased from $39 trillion to 77 trillion (Ganesan, 2017). According to Word Trade Statics Review 2016 the global exports in chemicals is around $1750 billion (Ganesan, 2017). Chemical industry is a vital part of agricultural and industrial development in India and has key linkages with several other down­stream industries such as automotive, consumer durables, engineering and food processing (Chemical Engineering World, 2004). Organic chemicals are one of the important sectors of the Indian chemical industry, which provide a vital development role by providing petroleum products, chemical feedstock, basic chemicals, intermediates, and important products like polymer, synthetic fiber, synthetic rubber, paints, varnish, pesticides and explosives, dyes, specialty chemicals. Major feed stocks for chemical industries are petroleum feed stock like naphtha, natural gas, kerosene, etc. coal, biomass, oils and fats, sulfur, salt, limestone, rock phosphate, etc. 1.2 CHEMICAL INDUSTRY AND TECHNOLOGICAL DEVELOPMENT

Chemical process industry has evolved considerably over the last century largely in response to changing societal requirements and changing raw material availability and environmental issues. Some of the major technological developments in chemical industry are (Mall 2017): • Leblanc process to Solvay and modified Solvay process • Lead chamber to contact process (single absorption) and double contact double absorption (DCAA) • Diaphragm process to mercury and mercury to membrane • Wet to dry cement process • Coal chemicals to alcohol-based chemicals to petroleum-based chemicals and vice versa • Acetylene-based chemicals to alcohol and petrochemical • Claus to super claus process • Wood-based paper to agro-based and waste paper-based • Pulping to bio-pulping • Stone ground wood pulping to refiner mechanical pulping (RMP), thermomechanical pulping (TMP) • Chlorine to oxygen bleaching and enzymatic bleaching • Sulfur to pyrite-based sulfuric acid plant • Conventional aluminum and iron-based catalyst to zeolite-based catalyst • Coal-based fertilizer to natural gas and naphtha-based fertilizers • Coal- and alcohol-based chemicals to petroleum-based chemicals • Thermal cracking to catalytic cracking • FCC to deep catalytic cracking for olefin and hydrocracking for processing heavier crude • Naphtha reforming to isomerization • Acid catalyst to solid acid catalyst in alkylation process • Naphtha steam cracking to gas cracking • Conventional petroleum fuel to biofuel • Coal as fuel to coal as chemical • Coal gasification to petrocoke and biomass gasification

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Chemical Process Technology

• Chemical pesticide to biopesticide • Chemical fertilizer to biofertilizer • Soap to detergent, liquid soap, non-biodegradable detergent to biodegradable detergent • Natural gas to coal bed methane, shale gas, gas hydrate • Dimethyl terephthalate (DMT) to purified terephthalic acid (PTA) • Conventional caprolactam to ammonium sulfate free caprolactam • Natural fiber to synthetic fiber • Natural rubber to synthetic rubber • Petroleum refinery to natural gas refinery and biorefinery • Petroleum refinery to petrochemical refinery • Conventional gasification to underground gasification • Conventional drilling to horizontal drilling and hydrofracturing • Gas to liquid and methanol to olefin technology • Coal to methanol and olefin • Conventional desulfurization to ultradesulfurization processes and biodesulfurization • Polymer to biopolymer • Conventional Ziegler–Natta catalyst to metallocene catalyst 1.3 STRUCTURE OF CHEMICAL INDUSTRY

Chemical industry can be broadly divided into inorganic and organic chemical industry. Structure of chemical Industry is given in Table 1.1. Revolutionary innovations in chemical process industries are given in Table 1.3. Table 1.3: Revolutionary innovations in chemical process industries Year

Revolutionary innovations

1914

Dubba cracking process

1935

First catalytic process

1938

High octane gasoline First fluid catalytic cracking process

1949

First reformer, PlatformingTM Process

1953

Synthetic zeolites

1957

Biodegradable detergents

1958

Technologies for lead removal from gasoline

1950–60

Steam cracking of naphtha

1960s

Automotive catalytic converter

1970s

ParexTM Process

1971

CCR platforming commercialization

1978

Etherification of isobutylene

1990

OlexTM process

1990

Olex propane dehydrogenation process

1994

Detal solid bed detergent alkylation Contd...

Chemical Process Industries

5

Table 1.3: Revolutionary innovations in chemical process industries (Contd...) Year

Revolutionary innovations

2000 onward developments

Coal to chemicals, coal to methanol, DME, coal to natural gas Coal liquefaction and coal based syn oil, gasification of coal and petrcoke GTL technology, Shale gas by horizontal drilling Low CAT proess, oxygen enriched sulfur recovery Oxidative coupling of methane to olefin

2000 onward older technologies revived

Biofuel, lingo biomass hydrolysis an fermentation Algae biofuel GTL technologies Nano particles for energy and environmental management Application of nano catalyst Resid FCC technology for maximum distillate yield CO2 capture technology LC fining KBR Technology for Phenol BenzOUT technology Biobased Chemicals Electrolysis of water Single step process for hydrogen—CNG Production from natural gas Developing feed stock in Naphtha-based hydrogen generation units

2010 onwards

Synthetic fuel, dimethyl ether, gas to liquid technologies for gasoline, diesel, methanol to gasoline (MTG), syn gas to gasoline (STG plus) Advances in depolymerization of nylons First indigenous Indalin technology for upgradation of low value streams to Petrochemicals First indigenous diesel hydrotreating technology in India Addition of Bharat 6 norms Digitalization of chemical industry and adoption of industry 4.0

1.4 GLOBAL AND INDIAN CHEMICAL INDUSTRIES

The chemical industry is one of the world largest sectors of economy and has impact on many other industries. There has been continuous development in chemical industry with age. Technology commercialization with age of chemical industry is given in Figure 1.2. The global chemical industries consists of a very diverse range of product and global market size. As per Hindu Business Line (2017), global chemical industry is estimated at $4.3 and is expected to grow in future. Global chemical industry is expected to grow at a CGR of 3.9% from 2015 to 2030. Faster big row will be seen in Asia rather than Europe and USA (Chemical News April 2018, p.18). Global chemical production especially petrochemical-based organic chemical based and fertilizer industry is likely to show significant growth with evolution of shale gas, and utilization of more and more natural gas. Global market for cosmetic and toiletry ingredient to reach $24.5 billion

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Chemical Process Technology

Fig. 1.2: Technology commercialization of chemical industry with age. Source: Vora BV. International conference organized by Chemtech during CHEMTECH World Expo 2011.

in 2018 from $18 billion in 2011 and $19.6 billion in 2013 (Chemical Industry Digest December 2012, p.30). Evolution of the Indian chemical industry and technological commercialization with age of industry and age of product is given in Figure 1.3. Revolutionary innovations in chemical process industries are given in Table 1.3. Indian chemical industry is an important constituent of the Indian economy. As per the Hindu Business Line (March 24, 2017), the Indian chemical industry is expected to grow to $226 billion by 2020. In terms of volume it is 12th largest in the world and 3rd largest in Asia. According to ICC president, Indian chemical industry ranked 7th globally and likely to move 5th position by 2025. Indian chemical industry will be reaching a size of $370 billion by 2025. The specialty chemicals industry has the potential to be a $150 billion market by 2025. High demand supply gap for petrochemical would be by 2025 (Chemical News, April 2018, p.12). Currently, per capita consumption of products of chemical industry in India is about 1/10th of the world average. Over the

Fig. 1.3: Evolution of the Indian chemical industry and technological commercialization with age of industry and age of product

Chemical Process Industries

7

last decade, the Indian chemical industry has evolved from being a basic chemical producer to becoming and innovative industry. India is the fourth largest producer of agrochemicals. Evolution of the Indian chemical industry and technological driving force for development of chemical industry is given in Table 1.4. With investments in R&D, the industry is registering significant growth in the knowledge sector comprising of specialty chemicals, fine chemicals, and pharmaceuticals with higher annual growth rate. The chemical industry R&D spends would need to go up from current levels of less than 0.5% to reach closer to global benchmarks of 4% of sales. Industry is expected to grow much more in future due to high end demand based on increasing per capita consumption and population growth, improved export competiveness and resultant growth impact. Indian chemical industry can achieve accelerated growth phase with a strategic roadmap. Some of the critical issue now Indian chemical industries are facing are availability of feedstock, rising cost of raw material including energy and ease of doing business, availability of indigenous technology, poor infrastructure, small capacity plants, etc. The total production of organic chemicals during 2008–09 works out to 1.25 million with value of 0.9717 billion. The size of the petrochemicals segment was estimated as 13.96 billion. Total size of dyestuff industry is estimated as $4 billion. There are 50 organized industries and over 900 small-scale industries. India has 8.5–9% global market share. The India pharmaceutical industry is the fourth largest volume terms and 15th largest market in value terms. The market will reach $30 billion by 2020. The size of the agrochemicals industry estimated at over $1 billion. Consumption of various chemical ingredients for cosmetic and toiletry is increasing due to increased population. Global market for cosmetic and toiletry ingredients is increasing. As a result, the annual consumption of chemical fertilizers has increased in nutrient terms (N, P, K) has increased from 0.7 lakh tons in 1951–52 to 277.39 lakh tons in 2011– 12). Per hectare consumption of fertilizer which was less than 1 kg in 1951–52 has risen to a level of 141.30 in 2011–12 (Ministry of Chemicals and Fertilizer Annual Report, 2012–13). Segments of the Indian chemical industry are given in Table 1.5. Details of major chemical production and growth are shown in Table 1.6. Product-wise production of major chemicals is given in Table 1.7. Value output of different product groups in the chemical and chemical products is given Table 1.8. As per the European Chemical Council, world chemicals (excluding pharmaceuticals) sales in 2012 are valued at 3127 billion. India ranks 10th in world chemical market with chemical 61.1 Euro billon in 2012. As per UN Comrade Data base for 2014, India ranks 14th in the world exports of chemicals (excluding pharmaceutical products) and ranks 8th in the world imports of chemicals (excluding pharmaceutical products). India’s export of chemicals (excluding pharmaceuticals) was $29.76 billion in 2014. Chemical industry is one of the world’s largest industry and has significant influence on many other industries. Total global chemical shipments are worth 5 billion dollars. Global chemical industries consists of a very diverse range of products. Global market size was estimated at 3.9 trillion US dollars and is expected to grow at 3–4% per annum over the next five years to reach 4.7 trillion US dollars (Source: Global Investors Summit (March 7–8, 2016) Gurugram, India’s chemical market to grow $139 billion in FY 2014 to $214 billion by FY2019. With market size of $139 billion the industry accounts for 3.3%

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Chemical Process Technology

of global market (Table 1.9). Globally India ranks 3rd in terms of volume and 14th in terms of value (Source: Global Investors Summit, March 7–8, 2016, Gurugram). India is the second largest producer of cement in the world. As per the Annual Report of 2017, Ministry of Chemicals and Fertilizer Industry, Department of Chemicals and Petrochemicals, National accounts statistics 2016 chemical and chemical products sector accounted for 2.33 of the GVA in 2014–15 compared to 2.34 5 in 2013–14. The size of the Indian chemical Industry in terms of value of output in the year 2014–15 was 8,33,046 crores. Table 1.4: Driving force for Indian chemical industry Surface area

3.287 million km2

Population

1.2 billion

Coastline

6,000 km

Port traffic

Over 350 million TPA

Road length

Over 3 million km

Railways

100,000 Track km (Largest in Asia, 2nd in the World)

Growth of population 1951

36 crore to present 130 crore

Growth in vehicle population

More than fivefolds

India’s passager vehicle production projections

In 2010—2.6 million vehicles By 2015—5.1 million vehicles By 2020—9.7 million vehicles

Contribution of GDP: Agriculture: 25%, Industry: 24% Services: 51% Table 1.5: Segments of the Indian chemical industry Basic chemicals (49.05%): Market value: US$32.78 • Inorganic chemicals (Caustic chlorine, soda ash, sodium bicarbonate, carbon black, titanium oxide, sulfuric acid, hydrochloric acid, etc.) • Organic chemicals (acetic acid, acetic anhydride, acetone, phenol, methanol, formaldehyde, nitrobenzene, malice anhydride, aniline, chloromethane, acetaldehyde, ethanol amines, ethyl acetate, etc. • Petrochemicals (Olefins, aromatics-benzene, toluene, xylene, fiber intermediates MEG, PTA, acrylonitrile, propylene, caprolactam, adipic acid, hexamethylenediamine, phthalic anhydride, methanol, LAB, polymers, synthetic fiber, etc.) • Fertilizers (Nitrogenous and phosphatic) • Other industrial chemicals Specialty chemicals (24.69%): Market value: US$16.50 • Paints and varnishes, Textile chemicals, Dyestuffs and intermediates, Catalysts, Plastic additives, Adhesive sealants, Industrial gases Knowledge chemicals (26.6%): Market value: US$17.55 • Pharmaceuticals • Biotechnology • Agrochemicals Source: Lokhapare, 2011.

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9

Table 1.6: Production of major chemicals and petrochemicals, production 1000 tons Group

Production/Growth rate Production

Alkali chemicals

Growth (%) Production

Inorganic chemicals

Growth (%) Production

Organic chemicals

Growth (%) Production

Pesticides technical

Growth (%) Production

Dyes and pigments

Growth (%)

Total major chemicals

Production Growth (%) Production

Synthetic fiber

Growth (%) Production

Polymers

Growth (%) Production

Elastomers

Growth (%)

Synthetic detergents intermediates

Production Growth (%) Production

Performance plastics

Growth (%)

Total basic major petrochemicals Total major chemicals and petrochemicals

Production Growth (%) Production Growth (%)

2011–12

2015–16

6478

6802

3.3

1002

–1.9

1064

6.1

1640

1589

5.8

1884

–1.9

156

188

8.5

217

0.6

241

304

–1.6

382

6.6

9396

9884

3.2

2.3

3105

2362

–0.6

36071

12.2

6211

8839

17.4

100400

17.0

100

242

–4.7

351

40.8

623

566

–2.4

687

–5.1

969

1700

–0.7

1589

6.9 14900

8.6 20404

8043

2.7

881

11008

2018–19

16269

10.8 24783

6.0

27858

7.3

Source: Annual Report 2015–16, 2016–17, 2019–2020 Government of India Ministry of Chemicals and Fertilizer, Dept. of Chemicals and Petrochemicals. Table1.7: Product-wise production of major chemicals Major chemical products

Production 2014–15 in 1000 MT

2018–19 8043

Alkali chemicals Caustic soda

2439.5

Liquid chlorine

1717.97 2462.00

Total alkali chemicals

6619.47 Contd...

10

Chemical Process Technology Table1.7: Product-wise production of major chemicals (Contd...)

Major chemical products

Production 2014–15 in 1000 MT

2018–19 1064

Inorganic chemicals Aluminum chloride, calcium carbide, carbon black, Potassium chlorate, Titanium oxide, Red phosphorous, Hydrogen peroxide, Calcium carbonate

921.60

Organic chemicals (Acetic acid, Acetic anhydride, Acetone, Phenol, Methanol, Formaldehyde, Nitro­ benzene, Maleic anhydride, Pentaerythritol, Aniline, Chloromethanes, Isobutylene, MEK, ONCB, PNCB, Acetaldehyde, Ethanol amines, Ethyl acetate, Nitro­ toluene)

1619.11

1884

Pesticides and Insecticides

186.63

217

Dyes and Pigment

285.23

382

Synthetic fibers (Acrylic, Polyester, Nylon, Polypropylene, Fiber

3527

3601

Polymers (Polyethylene, Polypropylene, Polystyrene, Polyvinyl chloride)

6523

10040

94

351

Synthetic rubber (Styrene butadiene rubber, Poly­ butadiene rubber, Ethyl propylene dimmers, Ethyl vinyl acetate, Nitrile rubber)

687

Synthetic detergent intermediates LAB

475

Ethylene oxide

164

Performance plastics (ABS resin, Polymethylmethaacrylate (PMMA), Styrene acrylonitrile (SAN), Nylon

766

Fiber intermediates (Acrylonitrile, Caprolactam, Dime­ thyl terephthalate, Monoethylene glycol, Purified terephthalic acid)

4877

Olefins (Ethylene, Propylene, Butadiene)

6276

Aromatics (Benzene, Toluene, Mixed xylene, Orthoxylene, Paraxylene)

4638

Other petro-based chemicals (Butanol, C4 raffinate, diethylene glycol, Diacetone alcohol, 2-ethyl hexanol, methyl methacrylate, Phthalic anhydride, Propylene oxide, Propylene glycol, polyvinyl acetate resin, vinyl acetate monomer)

1962

Total basic major petrochemicals

14905

16269

Total basic major chemicals and petrochemicals

24788

27858

1589

Source: Annual Report 2015–16, 2019–20, Government of India, Ministry of Chemicals and Fertilizer, Department of Chemicals and Petrochemicals.

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Table 1.8: Global and Indian chemical Industry Global industry revenue

US $3.9 trillion

Industry revenue in India

US $144 billion

Estimated revenue in India 2020

US $300 billion

Total production of Indian chemical 19,308 × 1000 tons industry (Fy 2014) Contribution to India’s GDP 2013

2.5%

CAGR of Revenue in India 2013

13% (Chemicals)

Direct and Indirect Employment 1 million (Fy 2012) Indian chemical industry

• Eighth largest producer in India, third largest in Asia • Fourth largest of agrochemicals • 16% of word production of dye stuff and dye intermediates

Source: Global Investors Summit, Gurugram, March 7–8, 2016. Table 1.9: Market size Breakdown of Indian Chemical industry (Market size in $139 billion) Agrochemicals (Pesticides, fertilizers)

20%

Bulk chemicals (Organic and inorganic chemicals)

39%

Biotechnology

4

Pharma

17

Specialty chemicals

20

1.5 CHANGING SCENARIO IN CHEMICAL PROCESS INDUSTRY

There has been continuous change in capacity and size of the plant in chemical industry due to development of process technology, equipment and requirement of products. Changing scenario in chemical industry is given in Table 1.10. Table 1.10: Changing scenarios in chemical process industry Sector

Capacity Past

Present and future

Petroleum refinery

0.4 million tons

34 million tons

Naphtha cracker

20,000 tons/year

>8 lakh tons

Ammonia plant

>500 TPD

>1500 TPD

Urea

300 TPD

>1500 TPD

Sulfuric acid

0.018 million tons/year

0.7 million tons/year

Caustic chlorine

10 TPD

>100 TPD

Cement

0.06–-0.07 million tons

>3 million tons

1.6 CHEMICAL FEEDSTOCKS

With increasing demand of raw material there has been continuous search for new and alternative feedstocks past, present and future, for chemical industry is given in Table 1.11 and in Figure 1.4 (Mall, 2016).

12

Chemical Process Technology Table 1.11: Chemical feedstocks: Past, present and future

Past

Present and future

Coal, Salt, Biomass, Natural • Gaseous: Natural gas, Condensate, Refinery gases, Coal bed rubber, Cotton Methane, Gas hydrate, Shale gas • Liquids: Naphtha, Solvent extracts, Middle distillates • Solids: Coal, Coke, Wax, Residues • Biomass: Agriculture residue, Algae • Sea Chemicals: Salt, Bromine, Iodine, Titanium, Zirconium, etc. More 64 elements

Fig. 1.4: Past, present, and future of chemical feedstocks

1.7 CHARACTERISTICS OF THE INDIAN CHEMICAL INDUSTRY

Characteristics of Indian chemical industry is given below (Lokhapare, 2011): • High domestic demand potential as the Indian markets develops and per capita consumption levels increases • High degree of fragmentation and small scale of operations • Limited emphasis on exports due to domestic market focus • Low-cost competitiveness as compared to other countries due to the high cost of feed stocks and power • Low focus on R&D despite initiatives to innovate processes to synthesis products effectively. 1.7.1 INDIAN CHEMICAL INDUSTRY WEAKNESSES

Although Indian chemical industry has made consistent growth during last six decades, however, compare to global level there is lot of scope for further development. Some of the weaknesses are • Sizes of older units well below global levels • High-cost structures • Higher cost of raw materials • Long gestation periods • Integration and infrastructure inadequacies • Process development, low R&D investment • Mindset.

Chemical Process Industries

13

Diversification, globalization, emerging technologies, etc. has affected the practice of Engineering. Major issues are: 1. Raw material cost reduction, waste minimization and waste utilization and conservation of natural resources 2. Capital investment reduction 3. Energy use reduction and alternate sources of energy 4. Increased process flexibility and inventory reduction 5. Ever greater emphasis on process safety 6. Increase attention to quality 7. Better environmental performance 8. Advance personalized learning and innovative idea 9. Discontinuing certain low value-added products/inefficient technologies 10. Provide access to clean water 11. Better health and safety management strategies. 1.7.2 TYPICAL ISSUES FOR CHEMICAL INDUSTRIES

Due to various technological and engineering developments, chemical industry has been able to reduce the cost of production. Changes in technology and raw materials have shifted regularly and frequently toward lower costs and more competitive­ness, better conversion efficiency, high productivity, less energy consumption, and broader spectrum of product grades. However, due to increasing cost of raw materials and stringent environment issues, chemical industry is facing major challenges in future. Typical issues in chemical industry to meet the future challenges are shown in Figure 1.5. Due to various technological and engineering developments, chemical industry has been able to reduce the cost of production. Changes in technology and raw materials have shifted regularly and frequently to technological development in chemical industry (Fig. 1.6).

Fig. 1.5: Typical issues in chemical industry (Source: Invited talk National conference on Innovation and development in Chemical technology IDCT 2014, Feb. 28–March 1, 2014)

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Chemical Process Technology

Fig. 1.6: Technological development in chemical industry

Over the next few years, we can expect major shifts in three areas: Organizational structure, talent management and corporate culture (Joshi, 2019). Digitalization has become part of our life. With effect of industry 4.0 is likely to have impact in areas of production and supply chain (Durani, 2019). Adoption of industry 4.0 will bring significant strategic advantage and boom the chemical process industry (Shenoy, 2019) BIBLIOGRAPHY 1. Annual reports 2010–11, 2013–14, 2015–16, 2016–17, 2019–20, Department of Chemicals and Petrochemicals, Ministry of Chemicals and Fertilizer, Government of India. 2. Banerjee RB, Tuli DK, Mukhopadhya, Kalia A. Lignocellulosics for 2nd generation Bioethanol production. Journal of Petrotech, July–Sep. 2011, p.55. 3. Chemical Engineering World, 2004, p.74. 4. Chemical Industry Digest, December 2012, p.30. 5. Chemical News April 2018, p.18. 6. Duchesne E. Coal to plastic technology Methane to Olefins (MTO) and olefin cracking process (OCP) case study of total’s pilot research to commercialization”, Chemical Industry Digest April, 2011, p.68. 7. Durani AR. How new industry captains view Industry 4.0, Chemical Industry Digest, April 2019, p.28. 8. Dutta I. Hurdles to maintaining output. The Hindu Survey of Indian Industry, 2011, p.157. 9. Dutta NC. Chemical from renewable resources, Chemical Industry Digest, August 2011, p.75. 10. Energy Outlook, 2003. 11. Furimsky E. Gasification in Petroleum refinery of 21st century. Oil and Gas Science Technology Rev, IFP vol 54, 1999. 12. Global Investors Summit, March 7–8, 2016, Gurugram, Haryana, India. 13. Handa SK, Ganesh C. “Feed stock choice in Petrochemicals Industry”, Chemical Industry Digest, August, 2010, p.60. 14. Hefler P. International Fertilizer Association, June 2013. 15. Hindu Business Line, 2017. 16. Joshi R. How new industry captains view Industry 4.0. Chemical industry April 2019 p.28. 17. Journal of the Petrotech Society, January 2007, p.37–38. 18. Kapoor R. Chemical News April 2018, p.12 19. Lo. Simultaneous saccharification and fermentation and co-fermentation of lignocellulosic biomass from ethanol production, Methods Mol Biol, 581, 2009, 263–280. 20. Lokhapare SR. Indian chemical industry–current status. Chemical News July 2010, p.11. 21. Mall ID Invited talk National conference on Innovation and development in Chemical technology Indraprastha university IDCT 2014, Feb 28–March 1 2014.

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22. Mall ID. Petrochemical Process Technology, First edition, Macmillan, New Delhi, India, 2007. Reprint 2015, Second edition 2017, Trinity Press: Laxmi Publication. 23. Mall ID. NTPEL (Nation Programming on Technology Enhanced Learning) Lectures on Organic Chemical Technology, 2013. 24. Mall ID. Workshop on—Advances in Petroleum ands Petrochemicals” April 16, 2016, Organized by Department of Chemical Engg, R&D Centre, University of Petroleum and Energy Studies and IICHE Regional centre, Dehradun. 25. Mark E Reno, Monique Streff, Andrew Hird, Anjan Ray. Conversion of biomass to fuel as an environmental impact reduction opportunity for the pulp and paper industry. In paper International, April–June 2011. 26. Masood R. Role of raw material in petrochemical industry. Chemical Industry News, July 2002. 27. Mukherji D, Reddy BM, Raghvan KV. Advanced catalysis for sustainable development. Chemical Industry Digest May 2015, p.50. 28. Patil A. Methanol from coal: an emerging alternate feedstock, Chemical Industry digest July 2009, p.69. 29. Rappaport H. Plyolefins “Feed stocks and market by Howard Rappaport” CMAI. Plast. IndiaFeb-2009. 30. Shenoy, SR. How new industry captains view Industry 4.0. Chemical industry April 2019 p.28. 31. Singh MP, Tuli DK, Malhotra RK, Kumar A. Ethanol from lignolcellosic biomas: prospects and challenges. J of the Petrotech society, June 2008, p.39. 32. Tuil HD, Reith JH, Zenson EV, Westmann M, Baker RR, Elberson, HW. Lignocellulosic Ethanol a second option. 33. Vora BV. International conference organized by during CHEMTECH World Expo 2011. 34. World Trade Statistic Review, 2016.

Basic Principles of Chemical Processes and Unit Operations in Chemical Industries

2

INTRODUCTION

Chemical processes usually have three interrelated elementary processes, namely transfer of reactants to the reaction zone, chemical reactions involving various unit processes, and separation of the products from the reaction zone using various unit operations. Processes may involve homogeneous or heterogeneous systems. In homogeneous system, reactants are in same phase—liquid, gas or solid; while heterogeneous system has two or more phases—gas–liquid, gas–solid, gas–gas, liquid–liquid, liquid–solid, solid–solid, etc. Reactions may be reversible or irreversible, endothermic or exothermic, catalytic or noncatalytic. Various variables affecting chemical reactions are temperature, pressure, composition; catalyst activity, selectivity and stability; the rate of heat and mass transfer. The reaction may be carried out in batch, semi-batch or continuous mode. Reactors may be batch, plug flow or continuous stirred tank reactor (CSTR) type. It may be isothermal or adiabatic. Catalytic reactors may be packed bed, moving bed or fluidized bed. Along with knowledge of various unit processes and unit operation, following information are very important for the development of a process and its commerciali­ zation (Austin, 1984): • Material and energy balance, raw material and energy consumption per ton of product, energy changes. • Batch versus continuous process flow diagram. • Chemical process selection: design and operation, pilot plant data, equipment required, material of construction. • Chemical process control and instrumentation. • Chemical process economics: competing processes, material and energy cost, labor, overall cost of production. • Market evaluation: purity of product and uniformity of product for further processing. • Plant Location. • Environment, health, safety and hazard issues. • Construction, erection and commissioning. • Management for productivity and creativity: training of plant personals and motivation at all levels. • Research, development and patient. • Process intensification. 16

Basic Principles of Chemical Processes and Unit Operations in Chemical Industries

17

In order to improve the productivity and for making the process cost-effective and improving overall economy, compact, safe, energy efficient and environmentally sustainable plant, process intensification has become very important and industry is looking beyond the traditional chemical engineering. Teaching the priciple of chemical engineering to produce the ultimate product—the well rounded chemical engineer—is one of the most innovative and continually evolving challenges (Ziemlewski, J CEP February 2009, p.6). Chemical engineering always incorporats the new developments in biotechnology and nanotechnology. Safety, health and environment, productivity through conservation of raw material, better energy mangment through incorporating various developments, and incorporating software computational and and modeling capabilities have become imporatant theme of chemical engineering curricuum. Now chemical engieering environment has become global and mutidisciplinary and demands both technical competencies and soft skills. Five essential soft skills that an engineer needs are teamwork, leadership, communication, cultural diversity organisational development and performance (Ziemlewski, 2009). Today ‘s world is full of challenges and the enire world is witnessing turmoil due to growing energy crisis, food shortage, absence of clean water and rapant acts of terror growing world population. Chemical engineeing is boundary less (Yadav, 2009). The chemical engineering is uniquely placed to solve many of the buisiness, economic and social challenges of 21st century (Liveris, 2007). In the follwing text some basic concepts of chemical engineeing is discussed. 2.1 HEAT TRANSFER

Heat transfer (or heat) is thermal energy in transit due to a spatial temperature difference. There are three modes of heat transfer, i.e. conduction, convection and radiation. 1. Conduction Conduction is the transfer of energy from the more energetic particles of a substance to the adjacent less energetic ones as a result of interactions between the particles. (Area) (Temperature difference) Fourier’s Law: Rate of heat conduction ∝ Thickness or Qcond = – KA DT (K= W/mK) Dx 2. Convection Convection is the mode of energy transfer between a solid surface and the adjacent liquid or gas that is in motion, and it involves the combined effects of conduction and fluid motion. Convection is called forced convection if the fluid is forced to flow over the surface by external means such as a fan, pump, or the wind. In contrast, convection is called natural (or free) convection if the fluid motion is caused by buoyancy forces that are induced by density differences due to the variation of temperature in the fluid. Newton’s law of cooling: Qconv = hAs (Ts–T) (h = W/m2K) 3. Radiation Radiation is the energy emitted by matter in the form of electromagnetic waves (or photons) as a result of the changes in the electronic configurations of the atoms or molecules. A blackbody is defined as a perfect emitter and absorber of radiation.

18

Chemical Process Technology

Emissivity of a surface represents the ratio of the radiation emitted by the surface at a given temperature to the radiation emitted by a blackbody at the same temperature. The fraction of irradiation absorbed by the surface is called the absorptivity, the fraction reflected by the surface is called the reflectivity, and the fraction transmitted is called the transmissivity. Stefan–Boltzmann law:

Qemit, max = es AsT4 (e = 1 for black body)

C1 Planck’s law: Ebl (l, T) = 5 l [exp (C2/lT) –1] C1 = 2phc 20 = 3.742 × 108W.mm4/m2

Where, Wien’s displacement law:

C2 = hc0/k = 1.439 × 104 mm.K (lT)max power = 2897.8 mm.K

Critical Radius of Insulation

It is the outer radius of the insulation at which the rate of heat transfer is maximum. It depends on thermal conductivity of the material and outer surface’s heat transfer coefficient. Fins

These are extended surfaces, made of highly conductive materials such as aluminum, commonly used in practice to enhance heat transfer, and they often increase the rate of heat transfer from a surface several folds. Boiling and Condensation

When the temperature of a liquid at a specified pressure is raised to the saturation temperature Tsat at that pressure, boiling occurs. Likewise, when the temperature of a vapor is lowered to Tsat, condensation occurs. Typical boiling curve for water at 1 atm pressure is shown in Figure 2.1.

Fig. 2.1: Boiling curve for water at 1 atm pressure

Basic Principles of Chemical Processes and Unit Operations in Chemical Industries

19

Evaporation occurs at the liquid–vapor interface when the vapor pressure is less than the saturation pressure of the liquid at a given temperature. Boiling, on the other hand, occurs at the solid–liquid interface when a liquid is brought into contact with a surface maintained at a temperature Ts sufficiently above the saturation temperature Tsat of the liquid. Two distinct forms of condensation are observed—film condensation and dropwise condensation. In film condensation, the condensate wets the surface and forms a liquid film on the surface that slides down under the influence of gravity. The thickness of the liquid film increases in the flow direction as more vapors condenses on the film. This is how condensation normally occurs in practice. In dropwise condensation, the condensed vapor forms droplets on the surface instead of a continuous film, and the surface is covered by countless droplets of varying diameters. A heat pipe is a simple device with no moving parts that can transfer large quantities of heat over fairly large distances essentially at a constant temperature without requiring any power input. Heat Exchangers

They are devices that facilitate the exchange of heat between two fluids that are at different temperatures while keeping them from mixing with each other. Logarithmic mean temperature difference (LMTD), which is an equivalent mean temperature difference between the two fluids for the entire heat exchanger. Steam Economy

Steam economy is the ratio between total steam evaporated and steam consumed. 2.2 THERMODYNAMICS

There are three types of systems. Open system which can exchange matter and energy with surroundings, closed system, which can exchange energy but not matter with surroundings, isolated system, which can exchange neither energy nor matter with surroundings. Properties of System Intensive Properties

An intensive property is a bulk property, meaning that it is a physical property of a system that does not depend on the system size or the amount of material in the system. Extensive Properties

An extensive property is additive for subsystems. This means the system could be divided into any number of subsystems, and the extensive property is measured for each subsystem; the value of the property for the system would be the sum of the property for each subsystem. Types of Thermodynamic Processes Isothermal

The process in which no change in temperature occurs is termed to be isothermal process.

20

Chemical Process Technology

Isobaric: The process in which no change in pressure occurs is termed to be isobaric

process.

Isochoric: An isochoric process, also called a constant-volume process, and is volumetric

process, or an isometric process, is a thermodynamic process during which the volume of the closed system undergoing such a process remains constant. Adiabatic

The process in which no transfer of heat takes place is called adiabatic process. Cyclic

A cyclic process is the underlying principle for an engine. If the cycle goes counter clockwise, work is done on the system every cycle. Zeroth Law of Thermodynamics

If two systems are in thermal equilibrium with a third system, they must be in thermal equilibrium with each other. First Law of Thermodynamics

Energy can be changed from one form to another, but it cannot be created or destroyed. The total amount of energy and matter in the universe remains constant, merely changing from one form to another. Second Law of Thermodynamics

The entropy of any isolated system not in thermal equilibrium almost always increases. It states that “in all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state.” This is also commonly referred to as law of entropy. Heat Engines

A device that can produce work at the cost of heat input and rejecting the waste heat to low temperature sink. Refrigerators

The transfer of heat from a low-temperature medium to a high-temperature one requires special devices called refrigerators. The objective of a refrigerator is to maintain the refrigerated space at a low temperature by removing heat from it. Heat Pumps

Transfers heat from a low-temperature medium to a high-temperature one to maintain a heated space at a high temperature. Other Common Terms Frequently Used in Thermodynamics Enthalpy

Heat content of a system at constant pressure is known as enthalpy. It is denoted by H. Heat capacity: Amount of heat required to raise the temperature of system by 1°C. Entropy: Entropy is a measure of the “disorder” of a system. What “disorder” refers to is really the number of different microscopic states a system can be in, given that the system has a particular fixed composition, volume, energy, pressure, and temperature.

Basic Principles of Chemical Processes and Unit Operations in Chemical Industries

21

Gibbs free energy: Gibbs free energy is a measure of the amount of energy available to do

work in an isothermal and isobaric (constant temperature and pressure) thermodynamic system. This is where the term “free” comes from; it refers to the amount of energy in a system that is easily available for usage. Helmholtz free energy: In thermodynamics, the Helmholtz free energy is a thermodynamic potential that measures the “useful” work obtainable from a closed thermodynamic system at a constant temperature and volume. Joule Thomson Effect

The pressure drop in the fluid accompanied by a large drop in temperature is called Joule–Thomson effect. Due to this reason throttling devices (based on this effect) are commonly used in refrigeration and air-conditioning applications. The magnitude of the temperature drop (or, sometimes, the temperature rise) during a throttling process is governed by a property called the Joule–Thomson coefficient. It is isenthalpic process. Fugacity

It is the fictitious pressure term used for real gases so as to retain simple form of equation applicable for ideal gases. Activity Coefficient

An activity coefficient is a factor used in thermodynamics to account for deviations from ideal behavior in a mixture of chemical substances. Degree of Freedom

It gives the number of independent variables that should be specified in order to specify a system completely. 2.3 MASS TRANSFER

The mass transfer operation includes the following techniques: Diffusion

It is a spontaneous mixing process aiming at homogenization of the fluid mixture. Gases and liquids are all associated with mass transfer. Diffusion is caused by a random molecular motion being the consequence of thermally induced agitation of molecules, which finally tends to complete homogenization of the mixture. • Adsorption: It is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. This process differs from absorption, in which a fluid (the adsorbate) is dissolved by or permeates a liquid or solid (the adsorbent), respectively. • Absorption: It is a physical or chemical phenomenon or a process in which atoms, molecules or ions enter some bulk phase—gas, liquid or solid material. • Drying: It is a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid. • Humidification and dehumidification: Humidification is the process of constituting the water-vapor content in a gas. The reverse of the operation is called dehumidification.

22

Chemical Process Technology

Both are important for many industrial operations, such as air conditioning, gas cooling, controlled drying of wet solids, comfort heating, etc. When a gas is brought in contact with a pure liquid in which it is essentially insoluble, interphase mass and heat transfer takes place. • Distillation: The process of separation of two or more liquids on the basis of their boiling points is termed to be distillation. • Liquid–liquid extraction: Liquid–liquid extraction also known as solvent extraction and partitioning, is a method to separate compounds based on their relative solubilities in two different immiscible liquids, usually water and an organic solvent. It is an extraction of a substance from one liquid into another liquid phase. Molecular Diffusion

Molecular diffusion is concerned with the movement of individual molecules through a substance by virtue of their thermal energy. It is governed by Fick’s first law. dCA Fick’s first law: JAB = –  CDAB dz NA CDAB NAC – CA (NA + NB) 2 Diffusion in gases: NA = In NA + NB Z NAC – CA1 (NA + NB) DABPt – – Steady state diffusion of A by nondiffusing B: NAZ = (PA –PA ) – 2 RTzP 1 BM DAB – – Equimolar counter diffusion: NAZ = (PA –PA ) 1 2 RTz Diffusion coefficient Gases: DAB ∝ T 3/2, P–1 Liquid:

DAB ∝ T, m–1, M0.5 B

Film Theory

The film theory postulates that the concentration will follow such that the entire concentration difference (CA – CA ) is attributed to molecular diffusion within an effective 1 2 film of thickness Zf. K ∝ DAB

√

D AB Penetration theory: K=2 pq Surface renewal theory:

K=

√SD

AB

Distillation

Distillation is a unit operation in which the constituents of a liquid mixture are separated using thermal energy on the basis of their relative volatility. Relative volatility (a): This is the ratio of the concentration ratio of any A and B compo­ nents in one phase to that in the other phase and is a measure of the separa­bility.

Basic Principles of Chemical Processes and Unit Operations in Chemical Industries

Raoult’s Law

a=

y*/(1–y*) x/(1–x)

=

23

y* (1–x) x(1–y*)

For an ideal solution, the equilibrium partial pressure p* of a constituent at a fixed temperature equals the product of its vapor pressure P when pure at this temperature and its mole fraction in the liquid. –* pA = pAx

Minimum boiling azeotropes: When the positive deviations from ideality are sufficiently large and the vapor pressures of the two components are not too far apart, the total-pressure curves at constant temperature may rise through a maximum at some concentration. Maximum boiling azeotropes: When the difference in vapor pressures of the compo­ nents is not too great and in addition the negative deviations are large, the curve for total pressure against composition may pass through a minimum. Relative Volatility

For a liquid mixture of two components (called a binary mixture) at a given temperature and pressure, the relative volatility is defined as (yi/xi) a= = Ki/Kj (yj/xj) where: a = the relative volatility of the more volatile component i to the less volatile component j yi = the vapor-liquid equilibrium concentration of component i in the vapor phase xi = the vapor-liquid equilibrium concentration of component i in the liquid phase yj = the vapor-liquid equilibrium concentration of component j in the vapor phase xj = the vapor-liquid equilibrium concentration of component j in the liquid phase (y/x) = K commonly called the K value or vapor-liquid distribution ratio of a component Types of Distillation

• Simple distillation • Steam distillation • Flash distillation • Molecular distillation • Extractive distillation • Azeotropic distillation

Mccabe Thiele method: It is commonly used to calculate number of theoretical trays in a distillation tower. Reflux ratio, R = Ratio of flow returned as reflux to flow of top product Total reflux ratio implies: • No product out • High purity • Maximum reboiler heat and condenser cooling capacity.

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Chemical Process Technology

Minimum reflux ratio implies:

• Infinite no. of trays • Minimum reboiler heat and condenser cooling capacity. Overall Efficiency

It is the ratio of number of theoretical plates and number of actual trays in a column. It pertains to entire column. Murphree Efficiency

Murphree tray efficiency is based on a semi-theoretical model that assumes that the vapor between trays is well-mixed, that the liquid in the downcomers is well-mixed, and that the liquid on the tray is well mixed and is of the same composition as the liquid in the down comer leaving the tray. It pertains to single point on given plate. Absorption

Absorption involves the selective dissolution of one or more components of a gas or vapor into liquid. Stripping involves transfer of a component from liquid phase in which it is dissolved to a gas phase. Henry’s law: It states that the solubility of a gas in liquid is dependent on its partial pressure in the gas phase. p = Hx Extraction Separations involving the contact of two insoluble liquid phases are known as liquidextraction operations. In all such operations, the solution which is to be extracted is called the feed, and the liquid with which the feed is contacted is the solvent. The solvent-rich product of the operation is called the extract, and the residual liquid from which solute has been removed is the raffinate.

Distribution coefficient: The ratio of the concentration of the solute in the extract phase to raffinate phase. K = y*/x Selectivity

The ratio of the ratios, the separation factor or selectivity (b) is analogous to relative volatility of distillation. (weight fraction of C in E)/(weight fraction A in E) y*E b= = (weight fraction of C in R)/(weight fraction A in R) x*R Leaching

Leaching is the preferential solution of one or more constituents of a solid mixture by contact with a liquid solvent. Equipments used: • Bollman extractor • Ratocel extractor • Dorr thickner Humidification

Humidification involves interphase of mass and energy which results when a gas is brought into contact with a pure liquid in which it is essentially soluble.

Basic Principles of Chemical Processes and Unit Operations in Chemical Industries

25

Dehumidification is the removal of moisture from air and is opposite to humidification process. Humidity

The ratio mass of vapor/mass of gas is the absolute humidity (Y’). If the quantities are expressed in moles, the ratio is the molal absolute humidity (Y). yA PA PA Y= = = yB PB 1–pA MApA Y'= MB(1–pA) Psat A Saturated absolute humidity: YS = P – Psat 1 A Dry-bulb temperature: This is the temperature of a vapor-gas mixture as ordinarily determined by immersion of a thermometer in the mixture. Wet-bulb temperature: It is the steady state, nonequilibrium temperature reached by a small mass of liquid immersed under adiabatic conditions in a continuous stream of gas. Dew point: It is the temperature at which a vapor–gas mixture becomes saturated when cooled at constant total pressure out of contact with a liquid. Humid volume (VH) of a vapor–gas mixture is the volume of unit mass of dry gas and its accompanying vapor at the prevailing temperature and pressure. 1 Y' tG + 273 υH = 8315 + MB MA Pt Humid heat (Cs) is the heat required to raise the temperature of unit mass of gas and its accompanying vapor one degree at constant pressure. Cs = CD + Y'CA

(

)(

)

Adiabatic Saturation Temperature: The adiabatic saturation temperature (sometimes

referred to as the thermodynamic wet-bulb temperature) is defined as the temperature obtained by an air-water vapor mixture if it becomes saturated with water vapor in an adiabatic process las tG1 – tas = (Y’as –Y’1) CS1 Drying It refers to the separation of volatile liquids from solid materials by vaporizing the liquid and removing the vapor. Moisture content (wet basis): The moisture content of a solid or solution is usually described in terms of weight percent moisture, and unless otherwise qualified this is ordinarily understood to be expressed on the wet basis, i.e. as (kg moisture/kg wet solid) 100 = [kg moisture/(kg dry solid + kg moisture)] 100 = 100X/(1 + X). Moisture content (dry basis): This is expressed as kg moisture/kg dry solid.

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Chemical Process Technology

Equilibrium moisture X*: This is the moisture content of a substance when at equilibrium with a given partial pressure of the vapor. Bound moisture: This refers to the moisture contained by a substance which exerts an equilibrium vapor pressure less than that of the pure liquid at the same temperature. Unbound moisture: This refers to the moisture contained by a substance which exerts an equilibrium vapor pressure equal to that of the pure liquid at the same temperature. Free moisture: Free moisture is that moisture contained by a substance in excess of the equilibrium moisture: X – X*. Only free moisture can be evaporated, and the freemoisture content of a solid depends upon the vapor concentration in the gas. Constant-rate period: It is called when the drying takes place entirely within the constantrate period, so that X1 and Xf > XC and N = NC. S (X –X ) q= s 1 2 ANc Falling rate: If X1 and X2, are both less than XC, so that drying occurs under conditions of changing N. 2.4 REACTION ENGINEERING

Residence time: Residence time (also known as removal time) is the average amount of time that a particle spends in a particular system. This measurement varies directly with the amount of substance that is present in the system. V t= q Where t is used as the variable for residence time, V is the capacity of the system, and q is the flow for the system. Liquid Hourly Space Velocity (LHSV)

It is a method for relating the reactant liquid flow rate to the reactor volume at a standard temperature. Usually, this temperature ranges from 60°F to 75°F (15.6°C to 23.9°C). The volumetric flow rate is treated as a liquid at these conditions, even though the actual material may be a gas under normal operating conditions LHSV = Reactant liquid flow rate/Reactor volume Weight Hourly Space Velocity (WHSV)

WHSV is defined as the weight of feed flowing per unit weight of the catalyst per hour. Since weight of the catalyst charged in to the reactor is not varied and always same, so any variation in flow of liquid per hour will change the WHSV. Conversion

The conversion XA is the number of moles of A that have reacted per mole of A fed to the system. Yield

It is the amount of product obtained in a chemical reaction. The absolute yield can be given as the weight in grams or in moles (molar yield). The fractional yield, relative yield,

Basic Principles of Chemical Processes and Unit Operations in Chemical Industries

27

or percentage yield, which serves to measure the effectiveness of a synthetic procedure, is calculated by dividing the amount of the obtained product by the theoretical yield (the unit of measure for both must be the same). Continuously Stirred Tank Reactor (CSTR)

As the name suggests, it is perfectly mixed reactor where concentration is same at all the places in the reactor. Plug Flow Reactor

The plug flow reactor (PFR, sometimes called continuous tubular reactor, CTR, or piston flow reactors) is a model used to describe chemical reactions in continuous, flowing systems of cylindrical geometry. Fluid going through a PFR may be modeled as flowing through the reactor as a series of infinitely thin coherent “plugs”, each with a uniform composition, traveling in the axial direction of the reactor, with each plug having a different composition from the ones before and after it. The key assumption is that as a plug flows through a PFR, the fluid is perfectly mixed in the radial direction but not in the axial direction (forward or backward). Moving Bed Reactor

Moving bed reactors are catalytic reactors in which the catalyst moves through the reactor along with the reactants. They are open systems and operate at steady state. Recycle Reactor

If one desire to promote back mixing or intermediate mixing in a system, it is then desirable to use recycle reactor. Volume of fluid returned to the reactor enetrance Recyle ratio (R) = Volume of fluid leaving the system Space Velocity

Space velocity refers to the quotient of the entering volumetric flow rate of the reactants divided by the reactor volume (or the catalyst bed volume) which indicates how many reactor volumes of feed can be treated in a unit time. Conversion

The fracssstional conversion of a reactant is the ratio moles reacted Moles reacted f= Moles fed Selectivity The terms yield and selectivity are used to describe the degree to which a desired reaction predominates over competing side reactions. Moles of desired product formed Yield: Moles that would have been formed if there were no side reactions and the limiting reactant had reacted completely

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Chemical Process Technology



Selectivity:

Moles of desired product formed moles of undesired product formed

Arrhenius Equation

The Arrhenius equation is a simple, but remarkably accurate, formula for the temperature dependence of the reaction rate constant, and therefore, rate of a chemical reaction. The Arrhenius equation gives “the dependence of the rate constant k of chemical reactions on the temperature T (in absolute temperature Kelvin) and activation energy Ea”, as shown below: –E /RT k = Ae a Where A is the pre-exponential factor or simply the prefactor and R is the universal gas constant. First-order Reaction

A first-order reaction depends on the concentration of only one reactant (a unimolecular reaction). Other reactants can be present, but each will be zero-order. The rate law for an elementary reaction that is first order with respect to a reactant A is d[A] r= – = k[A] dt Second-order Reaction A second-order reaction depends on the concentrations of one second-order reactant, or two first-order reactants. For a second order reaction, its reaction rate is given by: d[A] d[A] d[A] – = 2k[A]2 or – = k[A] [B] or – = 2k[B]2 dt dt dt Reversible Reaction

A reversible reaction is a chemical reaction that results in an equilibrium mixture of reactants and products. For a reaction involving two reactants and two products this can be expressed symbolically as aA + bB  cC + dD Autocatalytic Reactions Reactions in which the product formed itself acts a catalyst for the reaction are called autocatalytic reactions. Heterogeneous Reactions

These are the chemical reactions in which the reactants are components of two or more phases. 2.5 FLUID MECHANICS (Fig. 2.2)

Newton’s Law of Viscosity It states that the shear stress between adjacent fluid layers is proportional to the negative value of the velocity gradient between the two layers. du t=m dy

Basic Principles of Chemical Processes and Unit Operations in Chemical Industries

29

Fig. 2.2: Fluid mechanics

Newtonian Fluid A fluid which has a linear relationship between shear stress and velocity gradient, i.e. follows Newton’s law of viscosity. Non-Newtonian Fluid

Fluids which do not follow the linear law and are treated in books on rheology. Dilatants, or shear-thickening, fluid increases resistance with increasing applied stress. Pseudo-plastic, or shear-thinning, fluid decreases resistance with increasing stress. If the thinning effect is very strong, as with the dashed-line curve, the fluid is termed plastic. The limiting case of a plastic substance is one which requires a finite yield stress before it begins to flow. The linear-flow Bingham plastic idealization is shown, but the flow behavior after yield may also be nonlinear. An example of a yielding fluid is toothpaste, which will not flow out of the tube until a finite stress is applied by squeezing. Some fluids require a gradually increasing shear stress to maintain a constant strain rate and are called rheopectic. The opposite case of a fluid which thins out with time and requires decreasing stress is termed thixotropic. Fluid Kinematics

It deals with describing the motion of fluids without necessarily considering the forces and moments that cause the motion. A streamline is a curve that is everywhere tangent to the instantaneous local velocity vector. A path line is the actual path traveled by an individual fluid particle over some time period. Continuity Equation

r1A1V1 = r1A1V1

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Chemical Process Technology

Velocity Potential Function (f f)

In an irrotational region of flow, the velocity vector can be expressed as the gradient of a scalar function called the velocity potential function. Velocity Stream Function (y y)

It is the scalar function of space and time in such a way that its derivative in a given direction is equal to the velocity component of the fluid along perpendicular to that direction. Fluid Dynamics Euler’s Equation

Bernoulli’s Equation



dp

r + gdz + ndn = 0 p n2 +z+ = const. rg 2g

Various Flow Meters Venturimeter

A venturimeter is a device used for measuring the rate of flow of a fluid flowing through a pipe. It mainly consists of: • A short converging part: It is that portion of the venturi where the fluid gets converges. • A Throat: It is the portion that lies in between the converging and diverging part of the venturi. The cross section of the throat is much less than the cross section of the converging and diverging parts. As the fluid enters in the throat, its velocity increases and pressure decreases. • Diverging part: It is the portion of the venturimeter (venturi) where the fluid gets diverges. Orifice Meter

The principle of the orifice meter is identical with that of the venturi meter. The reduction of the cross section of the flowing stream in passing through the orifice increases the velocity head at the expense of the pressure head, and the reduction in pressure between the taps is measured by a manometer. Bernoulli’s equation provides a basis for correlating the increase in velocity head with the decrease in pressure head. Pitot Tube

A pitot tube is a pressure measurement instrument used to measure fluid flow velocity. The pitot tube was invented by the French engineer Henri Pitot in the early 18th century and was modified to its modern form in the mid-19th century by French scientist Henry Darcy. It is widely used to determine the airspeed of an aircraft, water speed of a boat, and to measure liquid, air and gas flow velocities in industrial applications. Mechanical Operations Ritinger’s Law

The work required in crushing is proportional to the new surface created. This is equivalent to the statement that the crushing efficiency is constant and, for a giving machine and material, is independent of the sizes of feed and product. If the sphericities

Basic Principles of Chemical Processes and Unit Operations in Chemical Industries

31

(before size reduction) and (after size reduction) are equal and the machine efficiency is constant, the Rittinger’s law can be written as P ∙ = Kr m

( D– 1 – D– 1 ) x1

x2

∙  is the feed rate to crusher, D is the average particle where P is the power required, m x2 ­– diameter before crushing, Dx1 is the average particle diameter after crushing, and Kr is Rittinger’s coefficient. ­–

Power Law

A Power-law fluid, or the Ostwald–de Waale relationship, is a type of generalized Newtonian fluid for which the shear stress, t, is given by ∂u n t=K ∂y where K is the flow consistency index (SI units Pa∙sn), ∂u/∂y is the shear rate or the velocity gradient perpendicular to the plane of shear (SI unit s–1), and “n” is the flow behavior index (dimensionless). If ‘n’ were less than one, the power law predicts that the effective viscosity would decrease with increasing shear rate indefinitely, requiring a fluid with infinite viscosity at rest and zero viscosity as the shear rate approaches infinity, but a real fluid has both a minimum and a maximum effective viscosity that depend on the physical chemistry at the molecular level. Therefore, the power law is only a good description of fluid behavior across the range of shear rates to which the coefficients were fitted.

(

)

Fluids: Fluid which obeys Newton’s law of viscosity and other are non-Newtonian fluids

(paints, tooth paste, jellies, gels, slurryies, polymer solution). Non-Newtonian fluids may be Bingham fluid, pseudoplastic fluids, dialatant fluids. If fluid flos at Reynolds number P column goes to atmosphere via subcooler, reversing heat exchanger.

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Chemical Process Technology

Medium pressure nitrogen is used in the expansion turbine after passing through cold section of reversing heat exchanger as low pressure nitrogen. Argon separation: Argon having purity of about 97% is separated from the top of the

crude argon column.

3.5 METHANE AND SYNTHESIS GAS DERIVATIVES

Methane and synthesis gas are important petrochemical feedstock for manufacture of large number of chemicals, which are used directly or as intermediates, number of which are finding use in plastic, synthetic fiber, rubber, pharmaceutical and other industries. ‘Synthesis gas’ is commonly used to describe two basic gas mixtures—synthesis gas containing CO and hydrogen, and synthesis gas containing hydrogen and nitrogen for production of ammonia. Petrochemical derivatives based on synthesis gas and carbon monoxide have experienced steady growth due to large scale utilization of methanol and development of carbonylation process for acetic acid and oxo synthesis process for detergents, plasticizers, and alcohols. Synthesis gas and carbon monoxide have experienced steady growth due to large scale utilization of methanol and development of carbonylation process for acetic acid and oxo synthesis process for detergents, plasticizers, and alcohols. Various raw materials for synthesis gas production are natural gas, refinery gases, naphtha, fuel oil/residual heavy hydrocarbons and coal. Although coal was earlier used for production of synthesis gas, it has now been replaced by petroleum fractions and natural gas. Petrocoke is the emerging source for synthesis gas. Coal is getting importance alone or with combination of petroleum. Detail of production of synthesis gas is discussed in Chapter 7. 3.6 HYDROGEN

Hydrogen is the most abundant and lightest element in the universe (Chemical Industry Digest vol. 30, October 2017) and has wide application in chemical process industry, i.e. aviation fuel, rocket fuel, hydrogen bomb. It is also used in the manufacture of ammonia, anline, 1,4 butanediol, caprolactam, 2-ethylhexanol, hexamethylene diamine, hydrogen peroxide, isononyl alcohol, toluene diamine, fuel cell, as fuel. Hydrgen is going to be bridge between renewable energy and fossil fuels. Hydrogen is alternate fuel to meet the energy needs of industry, transport, and residential buildings (Sonde, 2020). Raw Material

Major raw materials for production of hydrogen are water, natural gas, naphtha and coal. Although hydrogen was available since 1671, in 1800, Nicholson and Crustal followed by Ritter succeeded in decomposing water in to hydrogen and oxygen gas (Patwardhan, 2017). This method was stared earlier by nangal fertilizer unit of National Fertilizer. With rising cost of electricity, the electrolysis technology is not being used at industrial scale. Production of hydrogen from electrolysis of water using catalyst is again getting importance.

Industrial Gases

53

Hydrogen Producing Technology

• Thermal • Electrochemical • Biological Hydrogen Separation Processes

• Adsorption • Membrane • Cryogenic Electrolysis of Water

• The splitting of water is accomplished by passing a DC electric current through water. • The electricity enters the water at the cathode, a negatively charged terminal, passes through the water and exists via the anode, the positively charged terminal. • The hydrogen is collected at the cathode and the oxygen is collected at the anode. Electrolysis produces very pure hydrogen for use in the electronics, pharmaceutical and food industries. Photobiological

• This method involves using sunlight, a biological component, catalysts and an engineered system. • Specific organisms, algae and bacteria, produce hydrogen as a byproduct of their metabolic processes. • These organisms generally live in water and therefore are biologically splitting the water into its component elements. • Currently, this technology is still in the research and development stage and the theoretical sunlight conversion efficiencies have been estimated up to 24%. Hydrogen from Steam reforming and Partial oxidation, catalytic reforming, by gasification:

Hydrogen is produced in chemical industries, synthesis gas and hydrogen are produced either by steam reforming of natural gas/naphtha or partial oxidation of Fuel oil, Petro coke. Details of the steam reforming and partial oxidation is given in Chapter 7. Hydrogen produced in different refinery processes; catalytic reforming is one of the major sources. The amount of hydrogen rich gas produced depends on feed composition and process conditions in the reactor section (Polovina, 2014). The purity of gas is around 73–75%. Gas is further purifying to 99.99% by absorption followed by pressure swing adsorption. Hydrogen gas in refinery and petrochemical is used in hydrotreating, hydrocracking, catalytic reforming, and isomerization. In petroleum industry, hydrogen is conventionally produced by steam reforming of naphtha; however, because of availability of large amount of coke from refineries due to use of heavier crude. Integrating the gasification of liquid residue into a refinery balances the hydrogen demand for various processes using hydrogen. Now some of the refineries, petrochemical complexes and fertilizer industry are producing or planned for gasification process for production of synthesis gas and hydrogen. Various process

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Chemical Process Technology

used for gasification are Lurgi Fixed bed technology, Kopper-Totzek and Texaco process (entrained bed) and Winkler process using fluidized bed reactor. Honey well technology used for hydrogen plant at CNPC Guangxi Petrochemical Company in China. This is based on PSA and will produce 99.9% purity of hydrogen and with increased hydrogen recovery (Patwardhan, 2017). Small Hydrogen generation Plants: Many manufacturing processes require hydrogen gas in

small quantities with high purity. Modular hydrogen plant with capacity 300–16,500 m3/ hr from Linde Engg India using large variety of feedstocks like natural gas, methanol, LPG and naphtha (Jell and Mamtani, 2012). Uses of Hydrogen: Hydrogen is a versatile and clean fuel (Sonde, 2020). Hydrogen has

wide application in chemical process industry, aviation fuel, rocket fuel, hydrogen bomb. Hydrogen is the highly reactive and is commonly used as reducing agent. Some of the major uses of hydrogen are as intermediate feedstock in the manufacture of large chemical, in hydrogenation reaction, for hydrogenation of unsaturated fats and oil. Hydrogen has gained importance as fuel and in fuel cell. Hydrogen is used in huge amount for the manufacture of ammonia. Hydrogen is used in refinery and petrochemical industry in various process. However, its use has increased in the refinery due to increasing use of hydrotreatment, hydrocracking, catalytic reforming process, and isomerization. Hydrogen can be used as industrial fuel and for generating electricity using fuel cell or microturbines. Hydrogen fueled mobility is one of the most important emerging options because of its lowest CO2 emitting system (Sonde, 2020). 3.7 ACETYLENE (C2H2)

Significant role in the metal industry for cutting and welding. Acetylene is one of the most versatile chemical which was used as a chemical feedstock for the manufacture of large number of chemicals which are used to manufacture wide range of products including plastic, synthetic rubber, dyestuffs, solvents, pharmaceuticals and carbon black. Acetylene is the only organic building block which can be derived from inorganic raw material—lime, coal, and water. With coming of cracker plant now acetylene as raw material for production of petrochemical has been replaced by ethylene and propylene. Oxyacetylene-blown torch is widely used in welding and cutting metals. It can be produced in small quantity from calcium carbide for many welding works. Acetylene is commonly made by reaction of calcium carbide with water. CaC2 + 2H2O

C2H2 + Ca (OH)2

However, the above process is now replaced with electric arc process or parial combustion of natural gas for large scale production. Acetylene is also made from methane by electric arc furnace where energy requirement is very large. 2CH4

C2H2 + 3H2

Acytelene can be also produced from partial oxidation of natural gas. During cracking of ethane and propane acetylene is also obtained as by product and some of the gas based plants in India is recovering acetylene.

Industrial Gases

55

3.8 CARBON DIOXIDE

Research efforts are going on for sequestration of CO2 and utilize it as useful feedstock. At present, the emissions of CO2 are 24 billion tons, and it will reach 57 billion tons in 2050. Developing CO2 to produce chemicals has good potential (presently only 120 million tons only utilized for production of chemicals) due to relative abundance, renewable nature, low cost and can lower global warming. Conversion of CO2 into various industrial products involves application of an appropriate catalyst system that promotes reaction rates, directs the selectivity path way and minimizes the energy of the reaction. Synthesis of urea, soda ash, as blowing agent, supercritical extraction fluid, as cryogenic fluid, carbonation of soft drinks for recycling of waters from acid mines drainage, as cooling media, making calcium carbonate, fire extinguisher, cyclic carbonates for polycarbonate, electrolytes in lithium ion batteries, green solvent, copolymerization of CO2 and epoxide aliphatic polycarbonate, acetic acid and large number of chemicals from catalytic hydrogenative, photochemical, electrochemical process, photochemical, catalytic nonhydrogenative. Some of the important CO2 derivatives are: • Acetic acid • Synthesis of formic acid , carbamate synthesis • As soft oxidant: selective oxidation of ethyl benzene • Production of synthesis gas from CO2 reforming • Methanol synthesis • Catalytic nonhydrogenative process: Lactone, dimethyl carbonates, salicylic acid, formaldehyde, polycarbonates, cyclic carbonate, ethylbenzene and alkanes. Argon

Argon is produced from air fractionation process where is preset as less than one percent in atmosphere. Measure uses of argon are in steel, stainless steel production, welding shielding gases, in light bulbs, fluorescent tubes, fiber optics and some lasers. Because of its highly unreactive nature like nitrogen it is used a protective blanket to prevent substances from oxidizing. Argon is also commonly use as carrier gas in research and laboratory operation due to its inert nature. Noble (or rare) gases (Helium, neon, krypton, xenon): These gases are present in very small

quantity less than two thousandths of one percent of air. Helium is one of the most abundant elements in the universe. Apart from air where it is present in very small quantity, it occurs on earth in presence of natural gas. Helium is recovered from natural gas also. It is very inert having low boiling point. It is very inert and is used for helium-based shielding gases in welding application. It is also used for medicinal and research purposes in many specialized instruments. The main uses of neon are in lighting, display signals and electronics tubes. Krypton is used in eximer lasers, particulary in surgery. Xeon is used in lighting application. It is also used in the field of medicine. Producer gas and water gas (Blue gas): Producer gas is produced by passing air and steam

through bed of coal or coke. Earlier many plants were using producer gas, however due low heating value and high energy consumption of energy now producer gas is not being used by many of the industry due to high heat value gases.

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Water gas is also called blue gases because color of the flame is blue and has low heating value. Coke oven gas: During process of coke production by coal carbonization, coke oven

gas is produced as by-product which is purified for separation of ammonia. Coke oven gases are largely used as fuel in steel plant. Ammonia and sulfur gases in coke oven gases are used for fertilizer manufacture in the steel plants. BIBLIOGRAPHY 1. http;//www.niir.org/projects/industrial-gases/z,39,0,64/index.html 2. Austin George T. Shreve’s chemical process technology. McGraw-Hill International edition (5th ed.) 1984. 3. Expirit Associates. Uses of industrial gases Gases and intermediates. www.gases 4. Jell A, Mamtani M. Small Hydrogeneration Plants, Chemical Industry Digest, May 2012, p.55. 5. Mathew T, Francis A. LNG markets-A Global Perspective and future outlook. Chemical Industry Digest Annual January 2020, p.56. 6. Patwardhan V. Chemical Industry Digest, July 2017, p.32. 7. Patwardhan V. Chemical Industry Digest, September 2017, p.11. 8. Patwardhan V. Chemical Industry Digest, December 2017 p.29. 9. Sonde RS. Hydrogen: Bridge between reneable energy and fossil Fuels. HFC-Hydrogen fuel cells for stationary and mobility applications. Chemical Industry Digest Annual January 2020. 10. Veena Patwardhan. Chemical Industry Digest vol 30, October 2017. 11. Weiss Mac-michale, Heuric H, Roma D, Walter S. Gasification for hydrogen supply, PTQ 2013 p.91.

4

Chlor-caustic and Soda Ash Industry

4.1 INTRODUCTION

The chlor-alkali industry is a very important part of the world of the chemical industry. India is one of the major players in the chlor-alkali sector. It produces producing three important chemicals namely caustic soda, soda ash and chlorine which find wide application in manufacture of a large number of compounds which have downstream applications in paper, textiles, aluminum, soaps and detergents, PVC, chlorinated organics, pesticides, etc. Large quantities of gaseous, liquid and solid pollutants are generated by the caustic soda industry. The chlor-caustic industry is amongst the top highly polluting industries. Due to increasing public concern and awareness, pressure on chlor-caustic industry for better environmental management is expected to increase in the upcoming years. Elemental chlorine was discovered only in the late 18th century (Patwardhan, 2018). The use of chlorine in many chlorine-based industries is on downtrend. Several environmental protection laws and acts have been enforced in India. Although some of the industries are already in process of phasing out use of chlorine in the processes, e.g. CFCs manufacture and chlorine bleaching, chlorine and its various compounds is finding application in disinfection and sanitation and find application of large number of chemicals which are finding many industrial applications. The chlor-alkali industry witness increased environmental regulatory pressures due to toxicity of mercury, chlorine, hydrochloric acid, etc. The good news, however, is that the industry is alive to the environment concerns. Polluting wastes and effluents like mercury, gases like hydrogen, carbon monoxide, chlorine, etc. are now being regulated to conform to limits as required by environment protection laws. But the industry will have to conform to more stringent regulations in the near future. Out of the chlor-alkali units in India, still some plants are based on mercury cell process, while now lage number of plants have now changed membrane cell process, only one is based on diaphragm cell process. Chlor-alkali is an industrial process widely used to produce chlorine, caustic soda and other chlorine and sodium derived/based products, such as sodium hypochlorite, calcium hypochlorite, bleach liquor, chlorosulfonic acid, chlorine dioxide, hydrogen gas, bleaching powder, polyaluminum chloride, chlorinated paraffins, PVC, chloralkali with its three products caustic soda, soda ash, and chlorine form basis of the end user. For every one ton of chlorine 1.1 ton of caustic soda is produced. This is a major challenge for effective utilization of caustic soda and chlorine (Chemical Digest Annual Jan 2018 p.103). 57

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4.2 PROFILE OF CHLOR-ALKALI INDUSTRY (GUJARAT)

The present global capacity of caustic soda is estimated at 94 million MTPA while India’s capacity is only 3.66 million tons, i.e. mere 3.9% of the world capacity (Chemical Industry Digest Annual Jan 2018). There are 37 manufacturing units of caustic soda and chlorine having installed capacity of about 3.246 million tons caustic soda. Chlorine production is in the ratio of 1:0.89. Today 95% plants are running on membrane cell technology which are energy efficient and environmentally friendly. Rest 5% are based on mercury cell process which will be shifting to membrane cell process. Gujarat is the largest producer. Caustic soda industry is highly energy consuming process and consumes 2.5 MW per metric ton of caustic soda. Demands for alumina, paper, textiles are major drivers for caustic which consumes 60% of total demand of caustic soda. As growth of these industries is growing fast, consumption of caustic soda will be also increased. Installed capacity, production and capacity utilization of caustic soda units are given in Table 4.1. Major consuming sectors of chlorine are vinyl chloride, chlorinated paraffin wax, pulp and paper and chemicals. The production scenario of caustic chlorine in India is given in Tables 4.2 and 4.3. India has more than adequate capacity to meet the domestic demand of both caustic soda and chlorine (Indian Chemical Industry XIIth Five-year plan 2012–17) (Table 4.4). The major raw material for caustic chlorine is salt which is obtained mainly from sea water and India has adequate volumes of this resource. Chlorine which is the main byproduct, demand of which is not well developed in India unlike the global chlorine market. Table 4.1: Capacity, production and capacity utilization of caustic soda units Year

Installed capacity

Production

Capacity utilization (%)

2013–14

3,308.7

2,618.3

79.1

2014–15

3,390.0

2,761.8

81.5

2015–16

3,370

2,871.0

85.2

2016–17

3,661.9

3,022.5

82.5

Source: Chemical Industry Digest Annual Jan. 2018, p.104. Table 4.2: India’s caustic consumption industry wise Industry

Percentage

Textile

13.7

Pulp and paper

11.2

Alumina

10.2

Organics

7.7

Soap and detergent

6.5

Inorganics

6.0

Pesticides

5.2

Pharma

4.2

Others

35.2

Source: Indian Chemical Industry, XIIth Five-year plan 2012–17.

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Table 4.3: Production scenario of caustic and chlorine in India (thousand tons) Year

Installed capacity

Production of caustic soda

Production of chlorine

2006–2007

2,547.8

1,993.1

1,765.9

2007–2008

2,741.8

2,160.3

1,914.0

2008–2009

2,923.0

2,198.8

1,948.1

2009–2010

3,202.4

2,326.0

2,060.6

2010–2011

3,246.3

2,457.6

2,177.4

Source: Indian Chemical Industry, XIIth Five-year plan 2012–17. Table 4.4: Per capita consumption of chlorine Country

Per capita consumption of chlorine in kg

Germany

55

USA

45

Japan

29

France

23

China

13

Brazil

7.80

India

1.85

Major global caustic soda and chlorine players: Dow Chemicals (US), Occidental Chemical

Corporation (USA), Bayers AG (Germany), PPG Industries (US), Tata Chemicals, Ltd., Shin Eisu Chemical Co. (Japan), Formosa Plastics Corp (Taiwan), Solvay Chemicals (Belgium), Ineos Chlor Limited, (UK) FMC, Corp., Shandong Halhua Group (China), Clech SA (Poland). Status of Indian chlor-alkali industry as on 31.03.2013 is given in Table 4.5. Table 4.5: Status of Indian chlor-alkali industry as on 31.03.2013 No. of chlor-alkali units in India—34 Total operating capacity of caustic soda— 31.34 lakh MTPA Expected caustic soda capacity by March 2015— 34.5 lakh MTPA During the year 2012–13 Caustic soda production— 25.4 lakh MTPA Caustic soda demand— 28.1 lakh MTPA Caustic soda capacity utilization— 81% Caustic soda demand CAGR during last five years—4.98% Chlorine production— 22.5 lakh MTPA Chlorine demand— 22.5 lakh MTPA Chlorine demand CAGR during last five years—3.67% India has sufficient caustic soda capacity to meet increasing demand of the country; Due to dumping of cheap caustic soda in India by other countries capacity utilization is low. Source: Gilra, 2013.

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4.3 ISSUES AND CHALLENGES BEFORE CHLOR-CAUSTIC INDUSTRY

Some of the major issues and challenges before chlor-caustic industry are: • Increasing price of energy. • Lack of integrated plants, and downstream chlorine utilization projects. • Poor infrastructure and high transportation costs. • Inadequate opportunity for chlorine utilization; PVC, isocyanides, etc. • Industry not fully developed. • Long distance transportation of chlorine due to non-integrated plants. • Increasing regulatory standards and compliances. • Reducing energy input cost and making operations much more energy efficient process. • Increasing salt prices and transportation costs. • Achieving zero effluent discharge and effective water management. 4.4 SEA WATER

Sea water is rich source of large number of minerals. Six most abundant ions of sea water are chloride, sodium, sulfate, magnesium, potassium, calcium, bromine. The amount of these salts varies. Apart from above constituents sea water contain large number of precious elements. 4.5 COMMON SALT

Common salt is one of the major raw materials for caustic chlorine apart from its use as edible purpose (Table 4.6). Per capita



Consumption of salt

India USA UK Japan

14 kg 180 kg 135 kg 65 kg

Presence of iodine in common salt 10 mg/kg of salt. Prevents endemic goiter (morbid enlargement of thyroid gland). Main sources of salt and their availability • Sea water: Sea salt 90% of total production containing 241,900 km3 of salt • Lake water, Subsoil brine: 9.07% • Rock salt: 0.017% Sea water: Vast coastal line of about 5600 km including states of Maharashtra, Gujarat,

Tamil Nadu, Kerala, Andhra Pradesh, Karnataka, Orissa, West Bengal. Salt lakes: Sambhar lake in Rajasthan, Chilka lake in Odisha.

Subsoil water: Dhrangadhru, Didwanu, Pachbadra, Tuticorin, Kharagodu. Rock salt: Mandi mines in Himachal Pradesh.

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Table 4.6: World salt demand (million metric tons) Item World salt demand

Annual growth (%) 2005

2010

2015

2005–2010

2010–2015

245.0

283.5

327.0

3.0

2.9

North America

65.8

67.4

71.5

0.5

1.2

Western Europe

44.0

44.0

43.1

–

–0.4

Asia/Pacific

88.7

118.0

152.0

5.9

5.2

Central and South America

10.8

12.3

13.6

2.6

2.1

Eastern Europe

24.5

28.0

30.8

2.7

1.9

Africa/Mideast

11.2

13.9

16.1

4.4

2.9

Source: Chemical Industry Digest July 2012, p.30.

4.5.1 Processes for Salt Manufacture

Various methods used for production of salt are: • Solar evaporation (for sea water and lake) • Artificial (open pan evaporation), vacuum evaporation • Mining of rock salt either by dry or saturated brine by injecting water • Freezing of sea water. Solar evaporation of sea water is the major source of salt, although some salt is also manufactured by solar evaporation of lake water which is rich in NaCl content. 4.5.2 Factors Affecting Solar Evaporation

Various factors affecting solar evaporation are temperature of air, pressure, direction and velocity of wind, relative humidity. 4.5.3 Causes Which Influence the Rate of Evaporation of Water from Open Surfaces

Various factors which influence the rate of evaporation from open surfaces are temperature of liquid surface, the quantity of water vapor in the surrounding atmos­ phere, renewal of this atmosphere extent of the surface evaporation. 4.5.4 Design Consideration of Solar Salt Works

Various design consideration for locating solar salt works are proximity to sea, topography of land, quality of soil, safeguard against floods, surface of exposure, initial density of brine. 4.5.5 Sea Chemicals

Sea is rich source of many chemicals apart from salt. Sea contains about 35 parts per 1000 (3.5%) dissolved salt. Some of the important minerals are also present in the sea sand. Composition of sea water varies widely and is influenced by a wide variety of chemical transport. Recovery of minerals from sea water and sand present big challenge. It offers enormous scope for chemical process industries and Chemical engineering which involves a large number of unit processes and unit operations. Around 60 elements are found in sea water. Some of the important minerals present in sea water are given in Table 4.7.

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Chemical Process Technology Table: 4.7 Important minerals found in sea water

Elements

Concentration (ppm)

Elements

Concentration (ppm)

Chlorine

19000

Strontium

8

Sodium

10500

Boron

4.6

Magnesium

1350

Lithium

0.17

Sulfur

885

Iodine

0.06

Calcium

400

Titanium

0.001

Potassium

380

Uranium

0.003

Bromine

65

Source: Seetharaman and Srinivasan, 1978; Gopala Rao, Sitting M, 1997; Cruickshank, 2006.

About 30% of the salt produced throughout world is from sea water. Salt itself is source of large number of chemicals like caustic soda, soda ash, hydrochloric acid magnesium compounds. Apart from salt, bromine and potassium recovery is also very important activity. Presence of large number of important minerals from sea floor is also going to open new opening for chemical engineers. Much of the world magnesium is recovered from sea water. Large quantities of bromine is also recovered from sea water (http://www.britannica.com/E Bcheckedd/topic/531121/sea water). Magnesium ion is the third abundant element present sea water. Magnesium is produced from sea water. After separation of salt by evaporation and crystallization the mother liquor is called britten which is source of many chemicals. Sea water has normally 4.176 mg/L of MgCl2 and 0.076 g/L of MBr2 (Gopala Rao, Sitting, 1997). Magnesium compounds are manufactured from sea water using lime. MgCl2 + Ca(OH)2 MgSO4 + Ca(OH)2 +H2O

Mg(OH)2 +CaCl2 Mg(OH)2 + CaSO4 2H2O

Potassium from sea water is recovered from sea bitterns by fractional crystallization in the form of caranallite (KCl.MgCl2.6H2O) from which potassium can be recovered. Bromine recovery from sea water is by vaporizing of chlorinated water and then by passing SO2. –

Cl2 +2Br

SO2 + Br2 + H2O 2HBr + Cl2

–

2Cl = Br2

2HBR +H2SO2 2HCl + Br2

Oil and gas exploration and drilling in ocean for oil and gas has already find attention of chemical engineers, geologists and geophysists. Gas hydrate is rich source of methane. Gas hydrates which are ice like substance composed of water and natural gas are already getting importance in oil and gas sector. Gas hydrates are present in ocean sediments. One cubic meter of gas hydrates yield about 160 m3 of methane (Cruickshank, 2006) and may be potential source of energy and petrochemicals. Sea water is also providing water through reverse osmosis for drinking purposes and chemical and petroleum, petrochemical industry. Sea/ocean beaches contains many precious minerals like platinum, gold, diamonds, limonite, magnetite, zircon, rutile, columbite, chromite, quartz, etc.

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4.6 COMMON TERMS USED IN ELECTROLYTIC PROCESS Energy consumed: Current flowing × Potential of the cell

Gibbs–Helmholtz Equation

E=–

JDH dE +T nF dt

E = Theoretical decomposition voltage DH = Enthalpy change of reaction for 1 g equivalent of product J = Electrical equivalent of heat T = Absolute temperature ºK F = Faraday’s constant n = Number of equivalent involved NaCl + H2O → NaOH + 12  H2 + 12  Cl2 Na(s) +

1 2

 Cl2(g) → NaCl aq.

DH = 407 kJ

H2(g) +

1 2

 O2(g) → H2O (l)

DH = 286 kJ



1 2

 O2(g) +



Na(s) +

1 2

 H2 (g) → NaOH

DH = 469 kJ

Net DH for overall reaction 407 + 286 – 469 = 224 kJ dE Neglecting T, E = 2.31 V dt Decomposition voltage Voltage efficiency = 60–75% Operating voltage 9650ºC of electricity produce 1 g equivalent product 1 amp h = 3600 Coulomb Theoretical current Current efficiency = 95–97% Actual current Current density = Current per unit area amp/cm2

Energy efficiency = Voltage efficiency × Current efficiency Equivalent produced Decomposition efficiency = 60–75% Equivalent charged

4.7 CHLOR-CAUSTIC PRODUCTION

Various processes used for production of caustic and chlorine are: • Mercury cell process (MRCP) • Diaphragm process (DCP) • Membrane cell process (MBCP) During the manufacture of caustic and chlorine various major steps involved in various processes are: • Brine purification

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Chemical Process Technology

• Electrolysis of brine by diaphragm cell, mercury cell or membrane process • Chlorine processing • Hydrogen processing IS specification of salt for industrial purpose is given in Table 4.8. Table 4.8: IS specification of salt for industrial purpose NaCl

98% maximum

SO4

0.50% maximum

Ca

0.20% maximum

Mg

0.20% maximum

Na2CO3

0.60% maximum

Insoluble

0.50% maximum

4.7.1 Brine Purification

Brine purification is the integral part of various cell processes. However, in case of membrane process additional dechlorination process is added because of sensitivity of chlorine toward membrane. In case of membrane process for brine purification two steps are involved, which consist of primary and secondary treatment of brine solution. Waste brine mud obtained from brine purification has been one of the major sources of mercury cell process (Fig. 4.1). Requirement of treated brine

NaCl 310–315 g/L, SO4 1.5–2.0 g/L, Ca di(ropylsulfide > diisomylsulfide > thiophene Sulfur recovery units characteristics: • Small to medium size sulfur recovery units • From a few tons to a few hundred tons/day • Guwahati refinery, IOCL: 5 TPD • Reliance refinery, Jamnagar: 2025 (3 × 675) TPD • Feed composition varies, linked to refinery operating mode and crude feedstock • High flexibility required, multiple trains • Acid gas always rich (high H2S content) • Ammonia (from sour water stripper) always present, sometimes in relatively high quantities

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Chemical Process Technology

19.16 SULFUR RECOVERY UNIT

Sulfur recovery unit consist of recovery of sulfur from H2S present in acid gas from amine treating/regeneration unit and H2S from sour water stripper section. Hydrogen sulfide content of the feed gas is converted to elemental sulfur. Typical sulfur recovery unit is shown in Figure 19.14. 1. Amine absorption and regeneration: Absorption of H 2S-bearing stream and regeneration of amine. H2S-rich stream from amine regeneration is sent to sulfur recovery unit. 2. Sour water stripping: Sour water is tripped off its sulfur and recycled. H2S is sent to sulfur recovery unit. 3. Amine absorption unit: Various hydrodesufurization processes in the refinery and hydrocracker unit generate large quantity of H2S. H2S-bearing gases from various unit is sent to amine treating unit which uses amine as a solvent for absorbing H2S and subsequently releasing H2S as H2S-rich stream in the amine generator.

Fig. 19.14: Typical sulfur recovery unit

19.16.1 Merox (Mercaptan Oxidation Unit)

Merox process is used in the refinery for controlling the mercaptan sulfur in gases, LPG, naphtha and other petroleum fractions. The Process is used for the chemical treatment of LPG, gasoline and distillates from FCCU, OHCU, etc. to remove mercaptans. Mercaptans are either extracted from the stream or sweetened to acceptable disulfides. For treatment of light feedstocks such as LPG, no sweetening is required as mercaptans are nearly removed by extraction. However, feed containing higher molecular weight mercaptans and may require a combination of Merox extraction and sweetening using catalyst. Catalysts promote the oxidation of mercaptans to disulfide using air as the source of oxygen. Merox treatment can in general be used in following ways (Dziabis, 2003): • To improve lead susceptibility of light gasoline • To improve the response of gasoline stocks to oxidation inhibitors added to prevent gum formation during storage • To improve odor of all stocks • To reduce the mercaptans content to meet product specifications

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• To reduce the sulfur content of LPG and light naphtha products • To reduce sulfur content of coker FCC olefins to save acid consumption in alkylation. Process

Pretreatment (remove H2S and naphthenic acids by dilute alkali solution) Extraction (remove caustic soluble mercaptans) Sweetening (Oxidation of mercaptans to disulfides) RSH + NaOH 4NaSR + O2 + H2O

RSNa + H2O RSSR + NaOH

Posttreatment (remove caustic haze) (Caustic settler, wash water, sand, clay filters) Sulfur Recovery from H2S

Sulfur recovery now has become one of the most critical aspects of sulfur management and affects emission sulfur dioxides significantly in the refinery. There are two sulfur recovery processes are: • Claus process (used earlier) • Super Claus process Conventional Claus process has only 99% sulfur recovery. In order to meet the sulfur emission standards now Claus process has been improved substantially to meet the standards. Modern Claus process is shown in Figure 19.15. New processes are characterized by: • New catalysts • COS and CS2 hydrolysis (increased recovery) • Direct conversion of H2S to sulfur by oxidation (Super Claus Process) • Direct conversion of H2S to sulfur by reduction (Pro Claus Process) • High efficiency burners (NH3, BTEX destruction) • Analyzers based control • Enriched air or oxygen blown thermal reactors. Super Claus Process

The Super Claus process was developed to catalytically recover elemental sulfur from H2S containing Claus tail gas to improve the overall sulfur recovery level. The Super Claus process was commercially demonstrated in 1998, and today now more than 160 units are under license and over 140 are in operation. Super Claus process achieves high sulfur recover levels by suppressing SO2 formation in claus stages and selectively oxidizing H2S in presence of oxygen using proprietary catalyst (Scheel, 2011). A typical Super Claus sulfur recovery unit consist of following sections: • Combustion chamber • Claus reactor • Super Claus reactor • Incinerator • Degassing section

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Chemical Process Technology

Function of Claus Reactors

• Claus reaction at catalytic region 2H2 + SO2

3/xSx + 2H2O + 93 k

(Where x = 6 and 8 mainly) • Hydrolysis of COS and CS2 at tempe­ ratures above 300ºC COS + H2O CO2 + H2S

CS2 + 2H2O

CO2 + 2H2S

Function of Super Claus Reactor H2S + 0.5O2

1/8S8 + H2O + 208 kJ

Super Claus process use selective oxi­da­ tion catalyst minimizes side reactions and increase sulfur recovery. Claus Process Limitations

• Thermodynamically limited conversion: Fig. 19.15: Modified Claus process the ‘air to clean gas’ ratio’s is maintained (Source: Taraphdar, 2011) to produce ratio of exactly 2/1 (optimum ratio) in the burner effluent gases. • Increases H2O content to 30 vol.% decreasing H2S and SO2 concentrations. Formation of non-recoverable S-compounds due to side reactions. The big difference between Super Claus catalyst and Claus catalyst is that the reaction is not equilibrium based. Therefore, the conversion efficiency is much higher than the equilibrium limited Claus reaction. Super Claus is a non-cyclic process that has repeatedly shown simplicity in operation, high online reliability and sulfur guarantees up to 99.3 % (Scheel, 2011). Super Sour Process

Stringent environmental regulations have necessitated higher recovery of H2S from sour water stripper unit design. Super Sour process ensures minimum H2S loss. The process employ additional hot feed flash drum upstream of cold feed surge drum. The H2S rich vapors from hot feed flash drum upstream of cold feed surge drum is routed to a small amine scrubber to absorb liberated H2S. The H2S lean gas containing primarily hydrocarbons is then routed to incinerator of the sulfur recovery unit. The absorbed H2S rich amine is recovered in the amine regenerator and is fed to the sulfur unit for converting it to sulfur (Sharma and Nag 2011). INDE Treat and INDE Sweet Technology (Indian Oil Technologies 2001)

INDE Treat and INDE Sweet Technology is based on the continuous film contactor (CFC) for effective removal of undesirable compounds at lower cost. It can remove H2S from LPG, mercaptans from LPG, naphtha, gasoline and ATF/Kerosene, naphthenic acid from diesel, acid gases from natural gases, fuel gases and can regenerate spent caustic if required. CFC technology which is the heart of process. Salient features of CFC are: • Non-dispersive contacting • Enormous surface

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• High mass transfer efficiency • Based on caustic/amine • Efficient removal of contaminants • No aqueous phase entrainment • Low caustic/amine consumption • Low cost • Can be easily retrofitted in existing mixer settler units. Merichem Fiber Film Contactor Technology

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44. Mukherjee M, Nehlsen J. “Consider catalyst developments for alkylation production”. Hydrocarbon Processing, Sep., 2006, p.85. 45. Mukhulyonov IU, Kuznetsov D, Averbukh A, Tumarkina E.Furme.r “Chemical Technology”. Mir Publishers, Moscow,1974. 46. Nakamura DN. “Product sulfur spec will determine future refining configurations”. Oil & Gas Journal, Oct. 18, 2004. 47. Pathan MA. “Special feature on future of oil & gas sector India”. FIPI Volume 16 issue 1 JanMarch 2017. 48. Prasada TSR. “Catalytic Reforming and recent Indian achievements”. Oncology Vol. 6, No.12, May 1992, p.1. 49. Rajaram Panchapakesan. “Latest development UOP isomerisation catalysts”, National workshops on catalysts in hydrocarbon processing, Nov 25–26, 2005, organised by memorial trust New Delhi -110001. 50. Rajgopal S. “Petroleum refining and petrochemicals”. Refining Challenges and Trends. 6th Summer School on June 6,2012, Organised by New Delhi. 51. Rana MS, Samano V, Ancheyta J, Diaz JAI. “A review of recent advances on process technologies for upgrading of heavy oils and residua”. Fuel, vol. 86, (9), June 2007, 1216–1231. 52. Raseev S. “Hydrocracking in Thermal and Catalytic Processes in Petroleum refining” Marcel Dekker, Inc2003, p.681. 53. Raseev S. “Thermal and catalytic Processes in Petroleum Refining”. Marcel Dekker, Inc: New York, 2003. 54. Ravindranath K, Habubula M. “Hydro carbon condensate Fractionation in oil and gas processing complex”. Chemical Engineering World. Vol 27, No.10, 1992, p.43. 55. Refining processes”. Hydrocarbon Processing. November 1998, p.53. 56. Rispoli G, Sanfilippo D, Amoroson A. “ Advanced hydrocracking technology upgrades extra heavy oil”. Hydrocarbo Processing. December 2009, p.39. 57. Roeseler. “UOP AlkyleneTM process for motor fuel alkylation”. Hand Book of Petroleum Refining Process. 2nd edition, edited by Meyers, RA McGraw Hill Companies, 2004, p.125. 58. Rosini S. Catalysis Today. 2003, 77, 467. 59. Sayles S, Romero S. “ Understanding differences between thermal and Hydrocracker”. Hydrocarbon Processing. September 2011, p.2011. 60. Samanti RK. “Refining challenges and Trends” 6thSummer School on “ Petroleum refining and petrochemicals” June 6, 2012, Organised by New Delhi. 61. Samtani RK. DGM (Exploration & Production) IOC Ltd. 6th June, 2011. 62. Sarkar S, Basak TK. “Heavy oil processing in IOCL Refineries”, Compendium 16th Technology Meet, Feb 17–19, 2011. 63. Sarraf DK. “Special feature on future of oil & gas sector India” FIPI Volume 16 issue 1 Jan–March 2017. 64. Saxena AK. “Catalytic reforming” Advances in Petroleum Refining. Petrotech Summer School, IIPM Gurugram, 5th July 2006. 65. Scheel F. “Innovative approach to sulfur recovery unit emissions Reductions”. Compendium 16th Refinery Technology Meet, Feb 17–19, 2011, organized by Centre of High Technology and Indian Oil Corporation Ltd, Kolkata, West Bengal, India. 66. Sharma MK, Nag A. “Super sour Process” J. of Petrotech. July–September 2011, p.49. 67. Sieli GM. “Vis breaking the next generation”. Foster Wheeler Publication, 1998. 68. Singh S, Vaidya SM. “The benefits from refinery and petrochemical Integration”. Chemical Industry Digest. August 2012, p.67. 69. SM Vaidya of IOCL. Hydrocarbon processing.com., 2017. 70. Speight JG. “The chemistry and technology of Petroleum”. Marccel Decker, Inc, New York, 1999.

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20 Petrochemical Industry 20.1 INTRODUCTION

Petrochemical industries have revolutionized our life and are providing the major basic needs of rapidly growing, expanding and highly technical civilization as a source of fertilizers, synthetic fibers, synthetic rubbers, polymers, intermediates, explosives, agrochemicals, dyes, and paints, etc. Modern petrochemical industry fulfill the requirement of large number of products which are being used in some or other form in daily life and also closely linked with the socioeconomic aspiration of people which includes packaging to agriculture, automobiles to telecommunication, construction to home appliances, health care to personal care, pesticides to fertilizer, textile to tyre cord, chemicals to dyes, pharmaceuticals and explosives (Mall, 2007). Linkage of socioeconomic of petrochemical in our life has been given in Table 20.1. There is hardly any area of our life that is not impacted by petrochemicals. Table 20.1: Petrochemical socioeconomic linkage Group of product

Areas

Plastics and polymers

Agricultural water management, packaging, automobiles, telecommu­ nications, health and hygiene, education, transportation, building.

Synthetic rubber

Transportation industry, chemical, electrical, electronics, adhesives, sealants, coatings.

Synthetic fiber

Textile, transportation, industrial fabrics, geotextiles, nonwoven fabrics.

Synthetic detergents

Health and hygiene.

Industrial chemicals

Drugs and pharmaceuticals, pesticides, explosives, surface coating, dyes and intermediates, lubricating oil additives, adhesives, oil field chemicals, antioxidants, chemicals, metal extraction, printing ink, paints, corrosion inhibitors, solvents, perfumes, food additives.

Fertilizers

Agriculture, polymers.

Source: Mall 2007, 2013, 2015, 2017.

The petrochemical industry is highly technological and capital intensive. Developments in petrochemical technology are taking place very fast. Tremendous resources and efforts are being continuously spent on increasing size of the plant, the yield through continuous upgradation of catalyst, reducing energy consumption and cost reduction through novel process rate, new chemistries or scale up approaches. 349

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350

Due to huge population, the per capita consumption of petrochemicals in India is about 506 kg compared to global weighted average 25 kg and China’s consumption of around 25–30 kg. Oil refining and steam cracking of naphtha and natural gas (ethane and propane) are the common routes of producing petrochemicals. Many Indian refineries are now entering petrochemicals in a big way through green field projects and expansions. Major ethylene complexes in India are given in Table 20.2. Top 10 global ethylene complexes are given in Table 20.3. Global regional capacity breakdown of ethylene capacity is given in Table 20.4. Table 20.2: Major ethylene complexes in India (metric tons) Name of the complex

Location

Capacity

Feedstock

Reliance (formerly IPCL)

Vadodara

1,30,000

Naphtha

Reliance (formerly IPCL)

Nagothane

4,00,000

Gas

Reliance (formerly IPCL)

Gandhar

3,00,000

Gas

Reliance

Hazira

2,50,000

Naphtha/Gas

Haldia petrochemicals

Haldia

5,20,000

Naphtha

GAIL

Auria

4,00,000

Gas

Oswal Agro

Mumbai

23,000

Naphtha

Indian Oil Corporation Limited

Panipat

8,00,000

Naphtha

Sources: Annual Report (2010–11, 2019–20), Department of Chemicals and Petrochemicals (Ministry of Chemicals and Fertilizer, Govt. of India) Table 20.3: Top 10 global ethylene complexes Company

Location

Capacity, tpy

1 Formosa Petrochemical Corp.

Mailiao, Taiwan, China

29,35,000

2 Nova Chemicals Corp.

Joffre, Alta

28,11,792

3 Arabian Petrochemical Co.

Jubai, Saudi Arabia

22,50,000

4 Exxon Mobi Chemical Co.

Baytown, Tex.

21,97,000

5 Chevron Philips Chemical Co.

Sweeny, Tex.

18,65,000

6 Dow Chemical Co.

Terneuzen, Netherlands

18,00,000

7 Ineos Olifins & Polymers

Chocolate Bayou, Tex.

17,52,000

8 Equistar Chemicals LP

Channelview, Tex.

17,50,000

9 Yanbu Petrochemical Co.

Yanbu, Saudi Arabia

17,05,000

Shuaiba, Kuwait

16,50,000

10 Equate Petrochemical Co. Source: Oil and Gas Journal, July 4, 2011.

Table 20.4: Regional capacity breakdown Ethylene capacity, tpy Asia-Pacific

4,26,31,000

Eastern Europe

79,71,000

Middle East, Africa

2,33,57,000 Contd...

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Table 20.4: Regional capacity breakdown (Contd...) Ethylene capacity, tpy North America

3,45,08,000

South America

50,83,500

Western Europe

2,49,04,000

Total Capacity

13,84,54,500

Source: Oil and Gas Journal, July 4. 2011.

The potential possible in India can just be imagined, now with growth in various sectors of economy like automotives, construction, textiles, etc. taking off well (Chemical Industry Digest, August 2010, p.5). Polymers accounts for around 50% of total basic major petrochemicals for the year 2019–20. The production of basic major petrochemicals in 2019–20 was about 8054 thousand metric tons (Annual Report 2019–2020, Department of Chemicals and Petro-Chemical, Ministry of Chemicals and Fertilizer, Government of India). 20.2 STRUCTURE OF PETROCHEMICAL COMPLEXES

The petrochemical complexes involve one or a combination of the following operations (Table 20.5) (Mall, 2007). Table 20.5: List of intermediate chemicals and target products First generation intermediates

Hydrogen, ammonia, methanol, olefins and dienic hydro­ carbons, ethylene, propylene, butadiene, isoprene, etc. Aromatic hydrocarbons, benzene, toluene, xylenes, styrene, etc.

Second generation intermediates

Introduction of various heteroatoms into final molecule including oxygen, nitrogen, chlorine and sulfur by various unit process intermediates

Target product

Plastics, synthetic fiber, fertilizers, solvents, elastomer, drugs, dye stuff, detergent, explosive, pesticides

The manufacture of basic raw materials like syngas, methane, ethylene, propylene, acetylene, butadiene, benzene, toluene, xylene, etc. The basic building processes include partial oxidation, steam reforming, catalytic and thermal cracking, alkylation, dealkylation, hydrogenation, disproportionation, isomerization, etc. The commonly used unit operations are distillation, extractive distillation, azeotropic distillation, crystallization, membrane separation, adsorption, absorption, solvent extraction, etc. Manufacture of intermediate chemicals derived from the above basic chemicals by various unit processes like oxidation, hydrogenation, chlorination, nitration, alkylation, dehydrogenation along with various unit operations like distillation, absorption, extraction, adsorption, etc. Manufacture of target chemicals and polymers that may be used in the manufacture of target products and chemicals to meet the consumer needs. It includes plastics, synthetic fibers, synthetic rubber, detergents, explosives, dyes, intermediates, and pesticides. Product profile of a typical petrochemical complex is given in Figure 20.1.

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Chemical Process Technology

PE: Polyethylene, PP: polypropylene, PVC: polyvinyl chloride, EO: ethylene oxide, MEG: monoethylene glycol, ABR: acrylobutadiene rubber, LAB: Linear alkylbenzene, VCM: vinylchloride monomer

Fig. 20.1: Product profile of typical petrochemical complex

20.3 INDIAN PETROCHEMICAL INDUSTRY

Petrochemicals are backbone of chemical industry. Although the origin of petrochemical industry in world was in 1920, however, 1960s marks the era of petrochemicals in India when Union Carbide set up first ethylene complex with capacity 20,000 TPA in 1963 in Mumbai. It was followed by NOCIL with 60,000 TPA ethylene complexes in 1968 in Thane near Mumbai and PSF plant of Chemical and Fibers India Ltd. (CAFI) at Thane–Belapur Road. Indian Petrochemical Corp. Ltd. (IPCL) set up first integrated petrochemical complex in 1970 in public sector at Vadodara. With the modest beginning in 1960 by setting up of 20,000 tons naphtha cracked by Union Carbide in Mumbai, Indian petrochemical industry has sustained a high and steady rate of growth during last four decades and has entered the world market. The petrochemical industry has been the fastest growing sectors in India and become a major segment of chemical industry, which is growing faster than industries overall and within chemicals. It has posed serious threat to chemical industry based on natural feedstock—biomass and coal. The petrochemical industry is major supplier of chemical inputs to a large and growing number of downstream. Petrochemicals sector in India is growing at 13% and is projected to reach $100 billion by 2020 (Chate, 2016). Projected demand of some of the important petrochemicals in MMTTPA from 2012 to 2020 is: ethylene 38.5, propylene 29.8, butadiene 30, benzene 124, and xylkenes 145. The above rising demands require more production of petrochemicals (Sarin, 2016). Indian oil to invest 1.8 trillion to expand refineries and biuld new business in the next 5–7 years (Singh 2017). Indian oil has 20% market share in the petrochemical business.

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353

In view of growing demand for petrochemicals especially polymers Indian oil has plans to invest about 32000 crore more in petrochemical business. Reliance industries 9RIL0 will add $300 million–$400 million in operating this fiscal by replacing naphtha with ethane which will be imported. Ethane imported in very large ethane carriers and is building pipe line to transport ethane to the petrochemical plants at Dahej and Nagothane where the crackers will run at full capacity using ethane as feedstock as feedstock. It is also planning to to producing 33% of ethylene from Hazira cracker in place of expensive naphtha. RIL uses 2.5 million tons of naphtha as feedstock in petrochemical crackers and by use of ethane, naphtha use as feedstock will be reduce by 500,000 tons. IOC will go for expansion of its Paradip refinery capacity by 5 million tons and also set up a polypropylene plant and MEG production facility (Chemical Industry Digest, September 2017, p.11). GAIL to setup petrochemical industry at its Godavari region of Andhra Pradesh. IG petrochemicals to increase its capacity by 53000 tons per annum. Assam petrochemicals will invest about 1337 crore to set up second unit of methanol 600 TPD and 325TPD formalin (Chemical Industry Digest vol. 30, October 2017). A profile of Indian petrochemical industry is shown in Table 20.6. Table 20.6: Profile of Indian petrochemical industry: Installed capacity and production of major petrochemicals 2015–16 (in thousand tons) Installed capacity

Production

Organic chemicals Acetic acid

177.43

157.91

Acetic anhdride

118.30

92.99

47.14

24.96

Acetone Phenol

76.75

40.42

Methanol

474.30

163.62

Formaldehyde

411.30

252.09

Nitrobenzene

91.8

68.37

Malic anhydride

5.40

3.54

Pentaerythritol

13.72

13.97

Aniline

60.10

39.40

221.10

220.18

Chloromethanes Isobutylene

13.80

7.24

ONCB

30.00

19.26

PNCB

30.0

31.27

MEK

5.0

5.75

Acetaldehyde

189.01

58.96

Ethanol amine

17.60

13.25

545.83

360.40

33.65

14.73

Ethyl acetate Menthol

Contd...

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Chemical Process Technology Table 20.6: Profile of Indian petrochemical industry: Installed capacity and production of major petrochemicals 2015–16 (in thousand tons) (Contd...) Installed capacity

Orthonitrotoluene

Production

16.4

Pesticides 292.00

187.52

452.37

304.06

Dyes and intermediate Fiber intermediate Acrylonitrile

41

2

Caprolactam

120

86

Monoethylene glycol (MEG)

1153

1001

Purified terephthalic acid

3753

3432

Total fiber intermediates

5067

4079

Ethylene

4283

3727

Propylene

4746

4457

Butadiene

433

343

9462

8528

Benzene

1566

1333

Toluene

288898

116

898

269

Building blocks (Olefins)

Total olefins Building blocks (aromatics)

Mixed xylenes o-xylene

420

500

p-xylene

3132

3266

Total aromatics

6304

5484

26

11

292

429

Diethylene glycol (DEG)

85

107

Diacetone alcohol

10

0

593

277

55

44

0

0

Major petrochemicals Butanol C4 raffinate

Ethylene dichloride 2–Ethyl hexanol Epicichlorohydrine Iso-butanol

3

2

Isipropynol

70

71

4

2

Methyl methacrylate Phthalic anhydride

349

306

Propylene oxide (PO)

36

37

Prolpylene glycol

20

14 Contd...

Petrochemical Industry

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Table 20.6: Profile of Indian petrochemical industry: Installed capacity and production of major petrochemicals 2015–16 (in thousand tons) (Contd...) Installed capacity

Production

Polyvinyl acetate resin

17

0

Vinyl acetate monomer

30

0

Vinyl chloride

541

791

Plyol

142

72

PBT

1.0

Synthetic detergent intermediates Linear alkyl benzene

547

377

Ethylene oxide

140

188

128

117

28

21

4

1

Styrene acrylonitrile (SAN)

136

99

PET chips/polyester chips

2199

1453

20

9

Performance plastics ABS resin Nylon 6 and Nylon 6,6 Polymethyl methacrylate (PMMA)

PTFE (Teflon)

Source: Annual Report 2015–16. Department of Chemicals and Petrochemicals, Ministry of Chemicals and Fertilizer, Government of India.

20.3.1 Basic Petrochemicals

C1 group C2 group C3 group C4, C5 group Aromatic

Methane, CO–H2 synthesis, synthesis gas derivatives Ethane, ethylene, ethylene derivatives, acetylene Propane, propylene and propylene derivatives Butadiene, butanes, butenes, pentane, pentene, isoprene, cyclopentadiene Benzene, toluene, xylene, naphthalene, BTX derivatives

20.3.2 Major End Products

Polymer, synthetic fiber, synthetic rubber, synthetic detergent, chemical intermediate, dyes and intermediates chemical intermediates, pesticides. 20.3.3 Basic Building Block Process

Petrochemical manufacturing involves building block processes for the manufacture of building blocks and intermediates. Cracking: Steam cracking, catalytic cracking for olefins pyrolysis gasoline by-product Steam reforming and partial oxidation: Synthesis gas Catalytic reforming: Aromatic production Aromatic conversion processes: Aromatic production Alkylation: Linear alkyl benzene Oxo process: Oxo-alcohols Polymerization process: Polymer, elastomers, and synthetic fiber.

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20.4 PETROCHEMICALS FEEDSTOCK

One of the major issues, which have directed the worldwide growth of petrochemical industry, has been the availability of feedstock, which has led to replacement of the natural resources coal, molasses, fats, etc. Basic feedstock used in petrochemical industry for manufacture of olefins and aromatics are derived either from natural gas or petroleum fractions and includes natural gas (associated or non-associated), condensate, naphtha, kerosene, catalytic cracking and reformer gases, waxes, pyrolysis gasoline. Natural gas and petroleum fractions as petrochemicals feedstock is given in Table 20.7 (Mall, 2007, 2015, 2017). Alternative routes to principal petrochemicals are given in Table 20.8 (Masood, 2002). Some of the alternative feedstock choice for petrochemical industry is: Table 20.7: Natural gas and petroleum fractions as petrochemicals feedstock Petroleum fractions and natural gases

Intermediate processes

Intermediate feedstock

Methane, ethane, propane, butane, BP up to 25ºC

Liquefaction, cracking

LPG, ethylene, propylene, butane, butadiene

Distillation and thermal and catalytic cracking, Vis breaking

C4–C12 hydrocarbon, BP 70–200ºC

Cracking, reforming, alkylation, disproportionation, isomerization

Ethylene, propylene, butane, butadiene, benzene, toluene, xylene

Kerosene

Distillation and secondary conversion processes

C9–C10 hydrocarbon, BP 175–275ºC

Fractionation to obtain C10–C14 range hydrocarbon

Linear nC10–nC14 alkanes

Gas oil

Distillation of crude oil and cracking

C10–C25 hydrocarbons, BP 200–400ºC

Cracking

Ethylene, propylene, butadiene, butylenes

Wax

Dewaxing of lubricating oil

C8–C56 hydrocarbon

Cracking

C6–C20 alkanes

Pyrolysis gasoline

Ethylene cracker

Aromatic, alkenes, dienes, alkanes, cycloalkane

Hydrogenation distillation, extraction, crystallization, adsorption

Aromatics

Natural gases and natural gas condensate

Gas fields and crude oil stabilization

Hydrogen, Cracking, methane, ethane, reforming, propane, pentane, separation aromatics

Ethylene, propylene, LPG, aromatics, etc.

Petroleum coke

Crude oil

Carbon

Carbonelectrode, acetylene, fuel

Source

Composition

Refinery gases

Distillation, catalytic cracking, catalytic reforming

Naphtha

Source: Mall, 2013, 2017.

Residue upgradation processes, gasification

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Table 20.8: Alternative routes to principal petrochemicals Chemicals

Petroleum source

Alternate source (Europe, except where stated)

Methane

Natural gas: Coal, as by-product of separation of coke Refinery light gases (demethanizer oven-gases (1920–30) or of coal hydro­ overheads) genation (1930–40)

Ammonia

Methane: Light liquid hydrocarbons From coal via water gas (1910–20)

Methyl alcohol

Methane: Light liquid hydrocarbons From coal via water-gas (1920–30); from methane (from coal) by methane-stream and methane oxygen processes (1930–40)

Ethylene

Pyrolysis of gaseous liquidhydro­ carbons

Dehydration of ethyl alcohol (original route). By-product in fractional distil­ lation of coke-oven gas (1925–35). Hydro­ genation of acetylene (1940–45)

Acetylene

Ethylene

Calcium carbide (original process). Methane from coal by partial combustion and by arc process (1935–45)

Ethylene glycol

Ethylene

From ethylene made as above (1925). In America, from coal via carbon-monoxide and formaldehyde (1935–40)

Ethyl alcohol

Synthetic ethyl alcohol co-product

Fermentation of molasses (original route)

Acetaldehyde

Paraffin gas oxidation Direct oxidation of ethylene

Fermentation of ethyl alcohol, or acetylene from carbide (1900–10)

Acetone

Propylene

Wood distillation (original process). Pyro­­ lysis of acetic acid (1920–30) or by acety­ lene-stream reaction (1930–40)

Glycerol

Propylene

By-product of soap manufacture (original process)

Butadiene

1-and 2-butenes, butane, synthetic Ethyl alcohol (1915); acetaldehyde via ethyl alcohol, by-product of ethylene 1:3-butanediol (1920–30); acety­lene and by pyrolysis of liquid hydrocarbons formaldehyde from coal via 1:4-butanediol (1940–45); from 2:3-butanediol by fermen­ tation (1940–45)

Aromatic hydrocarbons

Aromatic-rich and naphthenic-rich By-products of coal-tar distillation fractions by catalytic reforming and direct extraction or by hydroalkylation

• Naphtha from coal via direct liquefaction or indirect liquefaction by FT process • Plastic waste to naphtha and other hydrocarbons through liquefaction, pyrolysis and separation processes • FT naphtha from biomass • Methanol routes: Synthesis gas from methane, coal and biomass; conversion of synthesis gas to methanol and production of olefin by methanol to olefin technology. • Conversion of methanol to dimethyl ether • Product recovery and separation: Recovery of C4 and C5 stream from FCC and steam cracker

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Chemical Process Technology

• Oxidative coupling of methane • Ethanol from biomass: Direct fermentation of sugar rich biomass, hydrolysis of lingo-cellulosic biomass • Gasification of lingo-cellulosic biomass followed by fermentation or chemical catalysis to ethanol. • Carbon dioxide to liquid fuel by engineered bacteria • Gasification of petrocoke to hydrogen. Demand for natural gas in India is likely to increase in power generation to transport and feedstock for the fertilizer and petrochemical industry which heavily dependent on naphtha as feedstock. Growth of natural gas based fertilizer and petrochemical will be major driver for natural gas consumption in India (Joshi, 2017). Gasification of coal, biomass, petcoke and other refinery residue offers a promising option to convert these low value feedstocks to produce wide range of products from syn gas like fuels, methanol and derivatives like a formaldehyde, acetic acid, ammonia, urea, hydrogen, petcoke-based ethanol, olefins and polymers, etc. CO2 generated in gasification can be separated with various available advanced technologies and can be utilized for enhanced oil recovery, coal bed methane recovery, algae growth and other industrial usage, such as dry ice, beverage, etc. (Chate, et al. 2016). 20.4.1 Evaluation of Feedstocks for Aromatics, Olefins and Surfactant Plants

Aromatics — Naphtha, pyrolysis gasoline, LPG Olefins — Ethane, propane, naphtha, gas oil Surfactant plants — Kerosene for paraffins, benzene • Input cost of feed constituents is a major portion of the variable cost for production in petrochemical plants. • Major feed input naphtha/kerosene from the refinery • Feed quality monitoring and improvement efforts are therefore very important aspects having significant impact on the economics of the operation cost. • The precursors and undesirable constituents in feed including catalyst and adsorbents poisons should be known, analyzed and monitored continuously. 20.4.2 Evaluation of Feedstock for Olefin Production

Olefins playing important role in petrochemical industry by providing raw materials for chemical intermediates like ethylene oxide ethylene glycol, acetaldehyde, vinyl chloride, and poly olefins, etc. Olefin production requires more paraffinic naphtha. Desired components in feed for olefins productions (Dave and Khurana, 1996): • Naphthenes: Naphthene yield olefins of higher carbon number. Butane yield increases appreciable with naphthenic feed. Naphthenes also enhance production of aromatics. • Aromatics: The aromatics feed are highly refractory and they pass through the furnace unreacted. • Sulfur: The sulfur in feed suppresses stream reforming reaction catalyzed by nickel present in radiant coil. Optimum level of sulfur is 1 ppm. • Physical properties: Density, distillation ranges are useful and give a rough assessment of feed quality. • Ethylene: The following components in feed give ethylene in decreasing order: ƒ Ethane, butane to decane, 3- and 2-methyl hexane, 2-methyl pentane/2,2 dimethyl butane, isopentane

Petrochemical Industry

359

• Propylene: The following components in feed give propylene in decreasing order: ƒ Isobutane, n-nutane, n-propane, 3 methyl pentane, 2,3 dimethyl butane, 2 methyl hexane, n-pentane, 3 methyl hexane, isopentane. • Butadiene: The following components of feed give butadiene is decreasing order: ƒ Cyclohexane, methyl cycloentane. Some of the key properties for evaluation of naphtha for olefin production are density, ASTM distillation, TBP, FBP, Saybolt color, sulfur, RVP and paraffin, naphthanes and aromatic contents. Aromatic Plant

Aromatics especially benzene toluene, xylenes (p- and o-xylenes) are important petrochemical feedstocks for manufacture of synthetic fiber, pesticides, explosive, surfactants, synthetic rubber. Aromatics are either processed in refinery. Catalytic reforming are processed separately in petrochemical complex for manufacture of p-xylene required for DMT/PTA plant. Quality of naphtha and impurities present in naphtha are very crucial in quality of aromatics as well as long life of catalyst. Naphtha cut C6–C9 Paraffin, napthenes, aromatics 110–140ºC Dehydrogenation of C8 Napthene yield C8 aromatics. Most desirable component 90% of C8 napthalene in feed get converted to C8 aromatics • C8 Paraffins: Dehydrocyclization of C8 paraffins yield aromatics difficult to 20% C8 paraffins gets converted to C8 aromatics. • C8 Aromatics: Pass as refractory and directly contribute to C8 aromatic production. • C8 Aromatic precursors: It is useful to monitor aromatic precursors = 0.2* C8 P + 0.9 * C8 N + 1.0 C8 A. Some of the key properties of naphtha aromatic production are density, ASTM distillation, IBP, FBP sulfur, nitrogen, chloride, metallic poisons, component analysis for paraffins, naphthenes and aromatics (PNA) (Dave and Khurana, 1996): Surfactants

Linear alkyl benzene is one of important feedstock for production of surfactant whose demand is increasing with increasing population all over the world. LAB requires paraffins for production of olefins of carbon range C10–12 to have more biodegradable detergent. Benzene is required for alkylation of olefin to produce LAB. Feedstocks for paraffins are kerosene feed 150–265ºC cut from refinery containing mainly nC7– nC18 components which is fractionated to remove lighter and heavier fractions. The fractionated cut is hydrotreated for removal of sulfur and nitrogen catalysts which are poisonous to molex adsorbent molecular sieve.

Desirable: LAB requires olefin and benzene. At present trend is for manufacture of biodegradable low molecular weight LAB. Paraffins containing nC10 to nC13 carbon atoms are required in LAB manufacture which is obtained by fractionation of kerosene. nC12 improve the flammability of LAB product (Dave and Khurana 1996). Some of the undesirable components in the feed which are sensitive to molex molecular sieves are contaminants like water, sulfur, nitrogen, oxygen, chlorides, metallic poisons. Key properties of LAB feedstocks are density, ASTM distillation, IBP, FBP, sulfur, bromine index, aromatics, Saybolt color, smoke point, flash point, nitrogen component analysis for nC10–nC13, total normal paraffins.

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20.5. INTEGRATION OF REFINERY WITH PETROCHEMICAL

Refinery and petrochemical integration is considered one of the best ways to improve refinery margin due to high projected demand of primary petrochemicals, with relatively higher margins comparison to refined product (Sarin, 2016). Advances in processing technologies are playing a larger role in integrating refining and petrochemical facilities (Kapur, et al. 2009). In the changing scenario, petroleum refining and petrochemical production integration will be of vital importance for maximizing the use of byproducts and improving the overall economy of a petroleum refinery. A great deal of synergy exists between the refinery, aromatic complexes and steam cracker complex. Off gases from the FCC unit and coker containing ethylene and propylene can be integrated with the cold section of steam cracker. Pyrolysis gasoline is a good source of aromatics which can be integrated with the catalytic reforming process. Propylene from FCC and benzene from aromatics are feedstocks for the production of cumene and phenol (Taraphdar, et al. 2012). A new concept of refinery petrochemical integration (Kapoor, et al. 2007) is: • Low to moderate level of integration: uses 5–10% of crude • High level integration: These complexes convert 10–25% of the crude oil • Petrochemical refinery: These complexes produce a significant amount of petrochemicals as compared to fuels. Petrochemical processes within refinery which will help in integration of refinery and petrochemicals (Handa, 2010): • Propylene recovery from FCC gases • Ethylene from FCC gases • C4 and C5 recovery from FCC • C4S from naphtha cracker and refinery to LPG pool as well as feed to cracker • Aromatic recovery and conversations • Light ends and light naphtha conversion • Residue and coke gasification • Hydrogen production • Butane to maleic anhydride and derivative • Benzene–cumene–phenol–acetone • Benzene–cyclohexane–caprolactum • n-Paraffins extraction from kerosene for LAB • Valorization of refinery streams—LCO, LCGO, HCGO • Recovery of valuable chemicals cyclopentadiene, diclopentadiene, isoprene, propolyene • Isobutylene for alkylation • Use of C7–C8 stream from benzene extortion for separation of p-xylene for PTA • Maximizing the use of natural gas in a refinery-petrochemicals complex offers higher margins and lower carbon emissions. Off gas from FCC and delayed coking units contains a good quantity of ethane, ethylene, propylene and some propane and recovery of these hydrocarbons may be economical in the refinery.

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20.5.1 Indamax FCC

Indmax FCC developed by IOC R&D is a breakthrough in FCC technology for converting heavy feedstocks to propylene and other olefins. The operation is quite flexible to maximize propylene plus ethylene or propylene and gasoline (Sarin, 2016). Indmax is a novel patented technology to produce high yield of LPG, light olefins and high-octane gasoline from various petroleum fractions ranging from hydrotreated VGO to residue and mixture thereof. It can also upgrade olefinic naphtha from coker, Vis breaker or FCC (Chemical Engineering World, February 2011, p.71). 20.5.2 Indalin Process

Indalin is a versatile indigenous technology adding value to upstream and downstream oil industry. Indalin is a catalytic cracking process for upgradation of low value naphtha to very high yield of LPG, containing high olefins such as propylene, ethylene butylenes etc. Surplus kerosene and gas oil range fraction can also be processed along with naphtha. Indalin can integrate a refinery with petrochemicals complex and therefore offers a tremendous opportunity for value addition through upgradation of low value streams to petrochemical feedstock (Bhatacharya, et. al. 2011). 20.5.3 Naphtha and Gas Cracking for Production of Olefins

Olefins are major building blocks for petrochemicals. Because of their reactivity and versatility, olefins especially the light olefins like ethylene, propylene, butenes, butadiene, etc. there has been tremendous growth in the demand of the olefins. Olefins are finding wide application in the manufacture of polymers, chemical intermediates, and synthetic rubber. Ethylene itself is basic building block for large number of petrochemicals and is quoted as king of chemicals. The global ethylene capacity at January 1, 2011, net additions and closings was more than 138 million tons compared with nearly 130 million tons in 2008 (Oil and Gas J. Vol. 129, 2011). The steam cracker remains the fundamental unit and is the heart of any petrochemical complex and mother plant and produces large number of products and byproducts such as olefins–ethylene, propylene, butadiene, butane and butenes, isoprene, etc., and pyrolysis gasoline. The choice of the feedstock for olefin production depends on the availability of raw materials and the range of downstream products. Naphtha has made up about 50–55% of ethylene feedstock sources since 1992. Although basic steam cracking technology remain same for naphtha, gas oil and natural gas, different configurations of steam cracking plant are available from various process licensors (Petrochemical processes, 2003). Naphtha/Gas Cracking

Requirement of steam will depend upon the type of feedstock; the lighter hydrocarbon requires less steam as compared to heavier feedstock. Steam cracking relative cost according to feedstock is given in Table 20.9. Steam requirement in steam cracker is given in Table 20.10 (Wiseman, 1986). Energy requirement pattern for olefin production is given in Table 20.11 (Gupta, 2000). Modern ethylene plants incorporate the following major process steps: cracking, compression and separation of the cracked gas by low temperature fractionation. The nature of the feedstock and the level of pyrolysis severity largely determine the operating conditions in the cracking and quenching section. Various steps involved in

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Table 20.9: Steam cracking relative cost according to feedstock Feedstock

Relative investment cost

Table 20.10: Steam requirement in steam cracking

Ethane

1.00

Feed

Propane

1.15

kg steam/kg of hydrocarbon

Butane

1.20

Ethane

0.2–0.4

Naphtha

1.45

Propane

0.3–0.5

Atmospheric gas oil

1.65

Naphtha

0.4–0.8

Vacuum gas oil

1.84

Gas oil

0.8–1.0



Table 20.11: Energy requirement for olefin production Feedstock

Specific energy consumption Kcal/kg of ethylene

Kcal/kg of olefin

Ethane

310

3,050

Propane

4,100

3,050

Ethane/Propane

3,600

3,300

Naphtha

5,000

3,050

Fig. 20.2: Typical naphtha cracker plant

the pyrolysis of naphtha and separation of the products are discussed below. In case of gas cracking, separation of ethane and propane from natural gas is involved. Flow diagram for pyrolysis of naptha is given in Figure 20.2.

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Quench section: To avoid subsequent reaction the effluent is fixed in their kinetic development by sudden quench first by indirect quench by water to 400–450ºC in transfer line exchanger or quench boiler. This is a large heat exchanger that is a bundle of metal tubes through which the gases pass and around which is circulated water under pressure. The hot water produced is used to generate steam for use in the plant. In the next step the quench is done by heavy product of pyrolysis. Hot section: It consists of convection zone and radiant zone. In the convection zone, hydrocarbon feedstock is preheated and mixed with steam and heated to high temperature. In the convection zone the rapid rise in temperature takes place and pyrolysis reaction takes place. The addition of dilution steam enhances ethylene yield and reduces the coking tendency in the furnace coils. The production of the pyrolysis reaction consists of a wide range of saturated and unsaturated hydrocarbons. Descriptions of Hot Section

Feedstock is pyrolized and the effluent conditioned. The product formed are separated and purified. To avoid subsequent reaction the effluents are fixed in their kinetics development by sudden quench. Indirect Indirect quench by water to 400–500ºC generation of high-pressure steam. II Direct Direct quench by heavy residue by-product of pyrolysis. Primary fractionation column Separation of light products of pyrolysis as top and bottom as pyrolysis product. Compression Compression of light products. Caustic scrubbing and drying Scrubbing with caustic followed by molecular sieve adsorption to remove sulfur compounds, mercaptan, etc. Cold section: After compression, caustic scrubbing and drying the light effluents enter the cold section of the unit which performs the separation of (i) hydrogen to various concentration, (ii) ethylene containing 99.4%, (iii) 95% propylene, (iv) A C4 cut containing 25–50% butadiene, and (v) pyrolysis gasoline which is rich in aromatic hydrocarbons. The complexity of the separation section of a cracker increases markedly as the feed changes from ethane. Convection zone Radiation zone Quench

Descriptions of Cold Section

• Hydrogen separation· • Ethylene separation 99.9%· • Propylene separation· • A C4 cut containing 25–50% butadiene • Complementary fraction of pyrolysis gasoline rich in aromatic hydrocarbons.

Demethanizer

Methane condensed at top around –100ºC, pressure 32 Pa.

Deethanizer

Separation of C2 cut (Ethane and ethylene). Acetylene eliminated by selective hydrogenation. Catalyst: Palladium or Nickel 40–80ºC, 3 kPa.

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Separation of ethylene

Ethylene is fractionated and unreacted ethane recycled.

Depropanizer

C3+ cut from bottom of deethanizer is fractionated. C3 cut from top of depropanizer is selectively hydrogenated to remove methyl acetylene and propadience. Propylene content 95%. Separation in supplementary column for more pure propylene.

Removal of propane from propylene

Separation in supplementary column for more pure propylene.

Debutanizer

Separation of C4 stream from C5+ stream.

Reactions in Steam Cracking

The reactions involved in thermal cracking of hydrocarbons are quite complex and involve many radical steps. The thermal cracking reaction proceeds via a free radical mechanism. Two types of reactions are involved in the thermal cracking: (i) primary cracking reaction where the initial formation of paraffin and olefin takes place and (ii) secondary cracking reaction where light products rich in olefins are formed. The total cracking reactions can be grouped as follows: • Initiation reaction • Propagation reaction • Addition reaction • Isomerization reaction • Termination reaction • Molecular cyclization reaction. Operating Variables of Steam Cracking

The main operating variables in the pyrolysis of hydrocarbon are composition of feedstock, reaction temperature, residence time, hydrocarbon partial pressure, and severity. 20.5.4 Composition of Feedstock

Naphthas are mixture of alkanes, cycloalkanes, and aromatic hydrocarbons depending on the type of oil from which the naphtha was derived. The group properties of these components greatly influence the yield pattern of the pyrolysis products. A full range naphtha boiling range approximately 20–200°C would contain compound, with 4–12 carbon atoms. Short naphtha boiling point range from 100 to 140°C and long chain naphtha boiling point lies around 200–220°C. The steam cracking of the naphtha yields wide variety of products, ranging from hydrogen to highly aromatic heavy liquid fractions. The thermal stability of hydrocarbons increases in the following order: paraffins, naphthenes, aromatics. Yield of ethylene as well as that of propylene is higher if the naphtha feedstock is rich in paraffins. It may be seen that relative production of ethylene decreases as the feedstock becomes heavier. The percentage of pyrolysis gasoline C5–200°C cut increases. Simultaneously, butadiene yield varies slight with feedstock in the treatment of liquid petroleum fractions.

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Furnace Run Length

Furnace run length can be calculated from the equation (Chamber and Potter, 1974): Tmd – Tmc Run length = ; Tmd = Maximum allowable tube skin temperature DTm/day DTm /day= Average rise in tube skin temperature per day Tmc = Maximum metal skin temperature in the clean, uncoked condition For any feedstock the heater section run length depends on the pyrolysis coil selectivity, cracking severity and transfer line exchanger design. Run length varied between 21–60 days for gas-based furnaces and 21–40 days for liquid feed-based furnace (Wysiekierski and Fisher, 1999). Pyrolysis Temperature and Residence Time

The effluent exit temperature is generally considered a significant indicator of the operation of a furnace. As the furnace exit temperature rises, the yield also rises, while the yields of propylene and pyrolyis gasoline (C5–200ºC cut) decrease with respect of ethylene yield, each furnace exit temperature, correspond to an optimum. The highest ethylene yield achieved by operating at high severely, namely, around 850ºC with residence time ranging from 0.2 to 0.4 sec. However, operating at high temperature results in high coke formation. Partial Pressure of Hydrocarbon and Steam to Naphtha Ratio

Pyrolysis reaction producing light olefins are more advanced at lower pressure. Decrease into the partial pressure of hydrocarbons by dilution with steam, reduces the overall rate reaction rate, but also help to enhance the selectivity of pyrolysis substantially in favor of the light olefins desired. Other role of steam during pyrolsis is (i) to increase the temperature of feedstock, (ii) reduction in the quantity of heat to be furnished per linear meter of tube in the reaction section, and (iii) to remove partially coke deposits in furnace tubes. The ethylene yield decreases as the partial pressure of hydrocarbon increases. For economic reason, a value of 0.5–0.64 of steam per ton of naphtha is generally adopted as the upper limit. Severity and Selectivity Concept

Severity is often used to describe the depth of cracking or extent of conversion. The definition of severity varies with the different manufactures and may differ accordingly to the type of hydrocarbon treated. In the case of steam cracking of the ethane and propane, it is convenient to express the severity of the operating conditions in terms of feed conversion. At very high severities, the methane and ethylene yield level off, while those of propylene and C4 cut reach a peak and then decline consequently. The ratio of ethylene and propylene yield increases with severity, which hence favors the formation of ethylene. The relative production of C5+ cut passes through a minimum and at the very high severity tends to increase. Modern ethylene plants are normally designed for near maximum cracking severity because of economic considerations.

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Ethylene Furnace Design

Pyrolysis furnace design during the last three decades made significant development. Prior to 1960, the ethylene pyrolysis furnaces were box type with horizontal radiant tubes. The capacity of these furnaces were small capacity (40 MM lb/y) today standards (250 MM/lb/y). High thermal efficiency furnace design can contribute greatly to minimum overall plant utility costs. Higher efficiency can be achieved by: (i) upgrading of pyrolysis furnace capacity, (ii) increasing cracking severity, (iii) improving ethylene selectivity, (iv) improving thermal efficiency, (v) reducing downtime for decoking, and (vi) reducing maintenance cost. This can be achieved by radiant coil with shorter residence time and lower pressure drop, combustion air preheating and short residence time. Small diameter coils coupled with increased dilution steam, with use of booster compressors to reduce furnace outlet pressure can increase efficiency ethylene selectivity. Radiant coils with a short residence time and low hydrocarbon partial pressure give higher ethylene selectivity. Coke Formation during Pyrolysis and Decoking Measures

Pyrolysis of any hydrocarbon feedstock is always accompanied by coke formation, which deposits on the walls of the tubular reactor. Under typical operating conditions, the coke formation in naphtha pyrolysis is about 0.01 wt.% of the feed (Towfighi et al., 2001). The coke deposits on the walls of reactor reducing the overall heat transfer coefficient and increasing the pressure drop across the reactor. This results in gradual decrease with run time of both the reactor tube metal temperature and the pressure drop across the reactor necessitating periodic shut down. The coke formation inside the tube will depend upon (i) characteristics of feedstock and the coking precursor, (ii) hydrocarbon partial pressure, (iii) thermal condition of coil, and (iv) mass velocity which controls the dynamics of gas film close to the wall. Controlling coking rate permits increasing the severity of the furnace to increase conversion rate, reducing the cycle rate and unloading downstream limiting equipment which increases throughput (Burns, et al. 1991). Frequent decoking operating result in loss of production, affect the coil life and increase fuel and utility costs. Run length between two successive decoking varies according to the installation and the type of feedstock, but can be estimated at a few weeks on the average. In ideal conditions, a furnace operating on naphtha can run for go days without decoking. However, run length is always shorter due to the inevitable fouling of the quench boiler. In practice, run length is as long as 90 days on ethane feedstock, 65 days naphtha and 40 days with gas oil (Chauvel A, Lefebvre G. “Petrochemical Process” Vol. 1, Institute Francais du Petrole Publications Editions Technip, 27 Rue Ginwux, Paris, 1989). Various approaches for coke mitigation are based on reduced coke production in the coils and increased rates of coke removal or removal of coke precursors during pyrolysis (Wysiekierski, et al. 1999). By using improved metallurgy and innovative coating systems, ethylene producers seek to improve unit reliability, increase carburization resistance, extend processing run length, reduce downtime and plant shut downs, increase yields and throughput, extend furnace tube life (Wysiekierski and Fisher, 1999). Mechanical decoking, steam air decoking is the method used for decoking. Mechanical decoking processes take 4–7 times longer than steam air decoking. The principal method of decoking with steam air are spalling and burning. The coke is burnt in the presence of steam and air at temperature from (600–800ºC).

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20.5.5 Trends in Technological Developments of Steam Crackers for Production of Ethylene (Mall, 2017)

From the late 1960s through the 1970s, the petrochemical industry built a generation of new steam crackers with an ethylene capacity of several million tons capacity. Older plant consists of typically 10–17 small furnaces with radiant coils having residence time 0.4–0.6 sec., thermal efficiency below 90%, central waste heat recovery system and nitrogen oxide (NOX) emissions 75–100 ppm. Present day olefin plants have capacity more than 1,000,000 tons per year; ethylene produced with 5–7 modern cracking furnaces using twin-cell designs. Short residence time and radiant coil smaller diameters increase yields. The higher selectivity of modern coils reduces specific energy consumption. The modern olefin plants have better ethylene selectivity and improved health, safety and environment standards by incorporating current emission and safety standards (Feigl and Schmidt, 2007). Major energy improvements by revamp or by replacing the existing furnace sections can be achieved by (Fiegel and Schmidt, 2007): • Increased thermal efficiency • Higher radiant efficiency and less excess air by new burner technology and better instrumentation • Reduced heat losses due to fewer and bigger furnace units or new refractory • Higher yields by new radiant coils, reducing specific energy demand • Higher availability by application of new and highly reliable technology, reducing losses due to unplanned shutdowns. Performance of the steam cracking furnace can be upgraded by: (i) increasing furnace capacity, (ii) increasing cracking severity, (iii) improving ethylene selectivity, (iv) improving thermal efficiency, and (v) reducing downtime for decoking and reducing maintenance. Recovery of Chemicals from FCC and Steam Cracker

With the rising demand of ethylene and propylene, there has been a tremendous growth in the steam cracking of hydrocarbons during the last four decades. Similarly, fluid catalytic cracking (FCC) has developed into a major upgrading process in the petroleum refinery industry for the conversion of heavy fuel oil into more valuable products ranging from light olefins to naphtha and middle distillate. Large amounts of C4 and C5 compounds are produced along with the production of ethylene in steam cracking and gasoline in FCC. C4 and C5 streams are an important source of feedstock for synthetic rubber and many chemicals. With increasing demand of C5 hydrocarbons and oxygenates, upgrading of C4 and C5 streams from steam crackers and catalytic cracker is important to the economic performance of the above processes. It also provides a rich resource of reactive mole­ cules, which forms the backbone of the synthetic rubber industry. The quantity and composition of the C4 and C5 stream depends on the severity of the steam cracker operation and feedstock processed. Product profiles of C4 and C5 hydrocarbons are given in Tables 20.12 and 20.13.

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Chemical Process Technology Table 2012: Product profile of C4 hydrocarbon

C4 chemicals

Products

Butadiene

Styrene butadiene (SB), rubber (emulsiom/solution), SB latex, caprolactam, polybutadiene rubber, nitrile rubber, nitrile lsatex, pyridine vinyl SB rubber, n-octanol, telomers, ABS resin, MBS resin, HMDA, lauryl lactam, cyclooctadiene, tetrahydrofuran, 1,4-butanedol 1-octene

Isobutylene

Butyl rubber, polyisobutylenes, methyl methacylate, isoprene monomer, peroxide intermediate, tertbutyl mercaptan, tertbutyl alcohol, tertbutyl amine, alkylphenol MTBE, polybutyliene, diisobutylene, triisobutylene

1-butene

LLDPE comonomer, n-butyl mercaptan,1-polybutene

Mixed butylene

2-Butanol, methyl ethyl ketone, maleicanhydride, C4 alkylate, C4 polygasoline, 2-propyl heptanol, higher oxoalchols

Butanes

1-butene, maleic anhydride, 1,4 butanediol, tetrahydrofuran, butyrolactone, propylene oxide, tertbutyl alcohol, C4 alkylate

Source: Morgan “C4 industry beyond 2000”. Chemistry and Industry. February 2, 1998 p.90; Mall 2013, 2017.

20.5.6 Product Profile of C5 Hydrocarbon

C5 hydrocarbons are an important source of synthetic rubber, solvents, chemical intermediate, MTBE, plasticizers, TAME, rubber chemicals, herbicides, lube oil additives, and pharmaceuticals. Table 20.13: Product profile of C5 hydrocarbons C5 hydrocarbon Isoprene

Polyisoprene, as the cross-linking agent in butyl rubberAs co-monomer in styrene-isoprene copolymers

Isopentane

Solvent, chlorinated derivative, blowing agent for polystyrene

1-Pentene

Organic synthesis, blending agent for high octane fuel

2-Pentene

Polymerization inhibitor, organic synthesis

Cyclopentene

Organic synthesis, polyolefins, epoxies cross-linking agent

2- Methyl-1butene

Synthetic mark, amyl benzene hydrogen synthetic mark, amyl benzene hydrogen peroxide catalyst, 2,4-diamyl phenol (photographs color complex), pinacolone (crop protection chemicals)

3- Methyl-1butene

Monomer for specialty homo-polymer

Cyclopentadiene

Chlorinated insecticides, chemical intermediate, antiviral agent

Piperylene

Polymers, maleic anhydride, chemical intermediate

Fluid Catalytic Cracking

Fluid catalytic cracking (FCC) converts low value crude oil into a variety of higher value products which include gasoline, diesel, heating oil and valuable gases containing LPG,

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propylene and C4 and C5 gases. Various products from fluid catalytic cracking and their uses are given in Table 20.14. FCC units are versatile and can be operated in three main modes which are aimed at maximizing middle distillate, gasoline, or olefins respectively by means of the adequate combination of various parameters such as catalyst type, catalyst to oil ratio, rise of outlet temperature and recycle of fractionators bottom. FCC is the second largest source of propylene supplied for petrochemical application. • Conventional FCC 4–7% propylene and 1–2% ethylene • High severity FCC:10% propylene • Petro FCCTM (UOP): Ethylene 6%, propylene 20–22%, higher aromatics (18%) in naphtha • Higher C4–8 olefins yield which can be cracked to yield lower olefins by total petrochemicals ATOFINA/UOP olefin cracking process • Although FCC is an important petroleum refining process, however, FCC gases have now become important petrochemical feedstock for production of LPG that can be converted to aromatics and C3, C4, and C5 hydrocarbons, i.e., propylene, butene, isobutene, pentene, etc. Product distribution from FCC depends on: • Reactor temperature • Feed preheat temperature • Catalyst activity • Catalyst circulation rate • Catalyst activity • Recycle rate Table 20.14: Various petroleum products from FCC and their uses Product

Composition and uses

Light gases

Primarily H2, C1 and C2S, ethylene can be recovered

LPG

C3S and C4S containing light olefins suitable for alkylations

Gasoline

C5 + high octane component for gasoline pool or light fuel

Light cycle oil (LCO)

Blend component for diesel or light fuel

Heavy cycle oil (HCO)

Fuel oil or cutter oil

Clarified oil

Carbon black feedstock

Coke

Used in regenerator to provide the reactor heat demand

Propylene Recovery from FCC

FCC gases has important source of propylene from refinery and now FCC units are being operated both in gasoline mode and propylene mode. Propylene from FCC may be as high as 25% with new FCC based propylene technologies. Increased production of olefins from FCC units has been achieved through changes in operations, base cracking catalyst and additive catalysts and in hardware designs (Teng and Xie, 2006). Upgrading OF C4 and C5 Streams

C4 and C5 streams from steam cracker and FCC contain C4 and C5 hydrocarbons, recovery of which has become important steps for improving the overall economy of these

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processes. Some of the important C4 streams from cracker and FCC butadiene (from cracker plant only), butene-1, 2-butane, isobutylene, mixed n-butene, and isobutene. C4 stream of steam cracker contains appreciable amount of butadiene which is being recovered from naphtha cracker plants. Typical composition of C4 stream of naphtha cracker and FCC is given Table 20.15. The distribution product will depend on the feedstock, cracking severity and catalyst in case of FCC. Table 20.15: Typical compositions of C4 fractions Component

FCC

Steam cracking

Isobutane

37.0

2.0

Isobutene

24.0

26.0

1-Butene

15.0

13.6

0.2

36.0

2-Butenes (cis and trans)

11.0

12.0

n-Butane

12.0

9.8

1,3-Butadiene

Others

Balance

Balance

Typical C5 cuts from steam cracking contain C4 (1%), n-pentene (26%), isopentane (24%), n-pentene (4.5%), methyl butenes (12%), cyclopentenes (1.5%), isoprene (13.5%), pentadiene (piperylene) (9.0%), cyclopentadiene (7.5%), C6+ (1%) (Chauvel and Lefebvre, 1989). Cyclopentadiene is easily dimerized to higher boiling dicyclopentadiene and separated from C5 stream by simple distillation. Typical composition of C5 cuts from catalytic cracking may be C4 (2%), n-pentane (5.5%), isopentane (31.5%), n-pentenes (22.5%), methyl butenes (37.5%), C6+ (1%) (Chauvel and Lefebvre, 1989). Naphtha feed gives higher yield of C4 (8–10%) than ethane feed (2–3%). Upgrading of C4 olefins: • Production of chemical intermediates • Butene-1, isobutylene, mixed n-butene • Production of motor fuel component (alkylate, dimate, MTBE) Processing of C4 Cut from Steam Cracker and FCC

There is not much difference in the processing of C4 streams after the recovery of butadiene from the steam cracker and C4 streams from the FCC. Butadiene fromC4 stream of naphtha cracker/gas cracker is first recovered, followed by separation of isobutylene, isobutane, butane, butane-1 and butene-2 from C4 stream/FCC and cracker using various processes like etherification, hydrolysis, cracking, adsorption distillation, etc. C4 cut from steam cracker and FCC is shown in Figure 20.3 (Briggs, et al. 1987; Convers, 1987; Vermilion and Niclaes, 1977; Chauvel and Lefebvre, 1989). Isobutene recovery includes either hydration of the C4 stream and subsequent decomposition or etherification with methanol to yield MTBE, which is cracked to give isobutene. Separation of 1-butene is done by selective hydrogenation followed by adsorption for separation of 1-butene and further processing for separation of isobutene and 2-butene by distillation. Separation of 2-butene involves hydro-isomerization and subsequent distillation for separation of isobutene and 2-butene.

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Fig. 20.3: Separation of C4 hydrocarbons from FCC and steam cracker plants

After separation of butadiene, the C4 streams from cracking and FCC is processed for production of n-butene, 1-butene, 2-butene, and isobutene. 20.5.7 Butadiene

Butadiene is important raw material for production of larger number of synthetic rubber and polymers such as styrene butadiene rubber (SBR), polybutadiene, chloroprene rubber, nitrile rubber, acrylonitrile butadiene styrene plastic. Other fastest growing use is in the manufacture of adiponitrile used in the manufacture of nylon 6, 6. Steam cracker and catalytic dehydrogenation of butenes are the two major sources of butadiene. Butenes can be recovered from C4 stream or produced by dehydrogenation of butanes.

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According to SRI consulting global production and consumption of butadiene in 2009 was approximately 9.2 million tons and 9.3 million tons, respectively. Butadiene is expected to average growth of 4.9 per year from 2009–2014. Styrene–butadiene rubber accounted for more than 33% of global butadiene consumption in 2009 and butadiene rubber for about 25%. Polymerization Grade Butadiene

1,3 Butadiene % min. Butenes ppm max. Methyacetylenes ppm.max. Vinyl acetate ppm, max. C5 dimers ppm max. Carbonyl compounds (as aldehyde) max. Inhibitor (p-tert-butylcatechol) Non-volatile residue ppm.

99.6% 4000 25 200 2000 50 100–200 2000

There are four major routes for production of butadiene: 1. Steam cracking of naphtha 2. Catalytic dehydrogenation of butenes 3. Catalytic dehydrogenation of butanes 4. Dehydrogenation-dehydration of ethanol (molasses route). Butadiene from C4 Stream of Cracker Plant

C4 cut from the steam cracker is first sent for butadiene recovery, which includes selective hydrogenation of acetylenics in presence of palladium catalyst, then separation of buta­ diene extractive distillation process steps involved are (Chavel and Lefebvre, 1989): • Extractive distillation in which acetylenic compound and butadiene are extracted in one or two stages • Recovery of solvent • Super fraction of butadiene stream for removal of acetylenic impurities • Water scrubbing butadiene depleted cut to recover the solvent. • Various solvents used for separation of butadiene are furfural, dimethyl formamide (DMF), n-methyl pyrrolidone (NMP), and dimethyl acetamide. Selective hydrogenation results in overall improvement in the economy with higher butadiene yield. Catalytic Dehydrogenation of Butenes Reaction: Catalytic dehydrogenation of butanes is two-stage process:

1. Catalytic dehydrogenation of butanes to butenes

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2. Catalytic dehydrogenation of butenes to butadiene

20.5.8 Isobutylene

Isobutylene is present in the C4 stream naphtha cracker and FCC. Major application of isobutene is in the manufacture of gasoline blending component, such as MTBE, ETBE, alkylation, polymer gasoline. Polymer grade isobutylene can be made by cracking MTBE or for manufacture of polyisobutylene. Isobutylene is used in manufacture of butyl rubber which is made by copolymerization of isobutylene with small amount of isoprene. Various Routes for Isobutylene

Extraction of C4 cuts from steam cracking/FCC: Isobutylene is separated from C4 cuts from naphtha cracker after extraction of butadiene and from FCC gases after propylene recovery. First isobutylenes are converted to MTBE by etherification and recovered by cracking of MTBE to get polymer grade isobutylene it is also obtained by hydration of isobutylene containing stream and then cracking. Isomerization of butene: Isobutylene can also be produced from butane by isomerisation using zeolite ferrierite (zeolite of medium pore size) (Maulijan, et al. 2001). Dehydrogenation of Isobutene

Butene-1: Butene-1 is co-monomer in the production of low-density polyethylene and high-density polyethylene. Butene-1 can be separated from C4 stream of cracker after extraction of butadiene SHB-CB process: This process selectively hydrogenates the butadiene in the C4 cut by converting it to butane-1 and butane-2. Acetylenes and dienes are likewise hydrogenated. If the process is optimized to produce butane-1, about 60% of butadiene is converted to butane-1. The process is operated in the liquid phase mild temperatures and moderate pressures. Upgrading OF C5 Cuts

The steam cracker C5 stream is a rich resource of olefins and diolefins which can be upgraded to produce elastomers, resins and fine chemical intermediates. In steam crackers during cracking process along with ethylene, propylene, C4 stream, aromatics and pyrolysis gasoline bare also formed. Apart from aromatics, pyrolysis gasoline stream also contains C5 stream (Morgan, 1996). The quantity and composition of the stream depend on the nature of the cracked product and severity of cracker operation C5 stream. Various steps in the recovery of C5 chemicals are (Chauvel and Lefebvre, 1985): • Separation of C5 stream from pyrolysis gasoline by distillation • Separation of cyclopentadiene: In first stage cycolpentadine is dimerized to dicyclopentadiene followed by cracking of dicylopentadiene to cyclopentadiene. • Extractive distillation of cyclopentadiene free C5 stream produce isoprene–piperylene stream. Distillation removes the light acetyelenes.

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Chemical Process Technology

• Separation of isoprene and piperylene extract by distillation. • Absorption at atmospheric pressure in the presence of NMP. • Purification of isoprene rich paraffin. • Periodic regeneration of solvent. Solvents used in extraction of isoprene are acetonitrile, N-methylpyropedone, and dimethylformamide. Oxygenates from Refinery C4 and C5 Stream

Several oxygenated fuel components have figured prominently in refinery reformulated gasoline planning are methyl tertiary butyl ether (MTBE), tertiary amyl methyl ether (TAME) and ethyl tertiary butyl ether (ETBE). All oxygenated fuels reduce hydrocarbons in the automobile exhaust. MTBE was considered one of the most important oxygenates used in the production of lead-free gasoline and was used produced on a large scale throughout the world. There has been because of environmental problem. The oxygenated MTBE and ETBE are produced by the reaction of methanol/ethanol and isobutylene. 20.5.9 Methyl Tertiary Butyl Ether (MTBE)

MTBE is one of the important oxygenates and originally its use started as a substitute of tetraethyl lead. MTBE increases the oxygen content of gasoline results in the reduction of harmful emissions. MTBE which is made by etherification of C4 gases from cracker and FCC is also used for production of polymer grade isobutylene for synthetic rubber. MTBE is produced by the reaction of methanol with isobutylene contained in C4 streams from thermal crackers in the presence of ion exchange resin at 40–90ºC and a pressure of 5–10 kg/cm2g. Catalytic cracking butylenes and field butanes are additional possible source of isobutylene. Convention process and catalytic distillation are the two commercial processes available. Figure 20.4 shows the process flow diagram for MTBE conventional methods.

Fig. 20.4: MTBE conventional methods

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20.5.10 Ethyl Tertiary Butyl Ether (ETBE)

ETBE is made by etherification of isobutylene with ethanol similar to MTBE. Isobutylene + Ethanol

ETBE

20.5.11 Tertiary Amyl Methyl Ether (TAME)

TAME is produced by etherification of isoamylenes recovered from C5 stream of FCC and steam crackers. Two reactive components of isoamylenes are 2-methyl butene-1 and 2-Methyl butene-2. Catalytic distillation process is used for the manufacture of TAME. Reactions: Reactions are as follows:

20.6 SYNTHESIS GAS AND ITS DERIVATIVES: HYDROGEN, CO, METHANOL, FORMALDEHYDE, METHANOL TO OLEFIN TECHNOLOGY

Methane and synthesis gas are important petrochemical feedstocks for manufacture of large number of chemicals, which are used directly or as intermediates, many of these products are number of which are finding use in plastic, synthetic fiber, rubber, pharmaceutical and other industries. ‘Synthesis gas’ is commonly used to describe two basic gas mixtures—synthesis gas containing CO, hydrogen and synthesis gas containing hydrogen and nitrogen for the production of ammonia. Major requirements of synthesis gas in world scale petrochemical are given in Table 20.16. Some of the emerging technologies in utilization of synthesis gas and methane for the production of petrochemicals are Fischer–Tropsch synthesis, oxidative coupling of methane with chlorine to yield ethane and ethylene, methanol to olefin technology (MTO). Fischer–Tropsch synthesis is being studied in great detail world over and it is promising to be a future technology for manufacture of olefins from synthesis gas. CO can be separated from synthesis gas either by cryogenic or by pressure swing adsorption, is a promising feedstock for production of variety of products. Product profile of methane, synthesis gas and CO-based building blocks are given in Figure 20.5 (Mall 2007).

376

Chemical Process Technology Table 20.16: Synthesis gas requirements for major world scale petrochemicals

Product

Required H2: CO

Typical world-scale capacity, Syn. gas required, Nm3/hr. TPA

Methanol

2:1

1,60,000–12,75,000

48,000–1,90,000

Acetic acid

0:1

2,75,000–5,45,000

18,000–36,000

Acetic anhydride

0:1

90,000

3500

Oxo alcohol

2:1

1,15,000–2,75,000

12,000–25,000

Phosgene

0:1

4,800–1,60,000

3,500–12,000

Formic acid

0:1

45,000

3,500

Methyl formate

0:1

9,000

600

Propionic acid

0:1

45,000–68,000

2,400–3,500

Methyl methacrylate

1:1

45,000

4,700

1,4-Butandiol

2:1

45,000

4,700

Source: Hydrocarbon Processing, Gunadson and Abrardo, 1999.

Fig. 20.5: Methane, synthesis gas and CO building blocks (Source: Mall, 2017)

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20.6.1 Synthesis Gas

Methane and synthesis gas are important petrochemical feedstocks for the manufacture of a large number of chemicals, which are used directly or as intermediates, a number of which are finding use in plastic, synthetic fiber, rubber, pharmaceutical and other industries. ‘Synthesis gas’ is commonly used to describe two basic gas mixtures— synthesis gas containing CO + hydrogen and synthesis gas containing hydrogen + nitrogen for the production of ammonia. Petrochemical derivatives based on synthesis gas and carbon monoxide have experienced steady growth due to large scale utilization of methanol and development of a carbonylation process for acetic acid and Oxo-synthesis process for detergents, plasticizers, and alcohols. Recent market studies show that there will be a dramatic increase in demand of CO and syngas derivatives. Methanol is the largest consumer of synthesis gas. The reformed gas is to meet certain requirements with regard to its composition. It is characterized by the stoichiometric conversion factor, which differs from case to case. Raw Materials for Synthesis Gas

Various raw materials for synthesis gas production are natural gas, refinery gases, naphtha, fuel oil/residual heavy hydrocarbons and coal. Although coal was earlier used for production of synthesis gas, now it has been replaced by petroleum fractions and natural gas. Petrocoke is the emerging source for synthesis gas. Coal is again getting importance alone or with combination of petroleum coke. Reactions in the manufacture of synthesis gas by steam reforming and partial oxidation are shown in Table 20.17. Various routes for synthesis gas and ammonia and methanol manufacture is shown in Figure 20.6. Table 20.17: Reactions in the manufacture of synthesis gas by steam reforming and partial oxidation Process steps

Reaction

Desulfurization: C H SH + H → H S + C H 2 5 2 2 2 6 1st stage C6H5SH + H2 → H2S + C6H6 C4H4SH + 3H2 → H2S + C4H9

Process condition Al-Co-Mo Al-Ni-Mo Catalyst 350–400ºC

CS2 + 4H2 → 2H2S + CH4 COS + H2 → H2S + CO 2nd stage

CH3SC2H5 + H2 H2S + CH4 + C2H4 H2S + ZnO → ZnS + H2O

Zinc oxide absorbent 200–500ºC

Steam reforming two stages

CnHm + 1/4(4n-m)H2O → 1/8(4n+m) CH4 + 1/8(4n-m)CO2 Nickel catalyst 800ºC Endothermic reaction CH4 + H2O → CO + 3H2

Partial oxidation

CnHm + [(2n+m)/4]O2  nCO + m/2H2O

CO + H2O → CO2 + H2 CnHm + nH2O  nCO + (n+m/2) H2 2CO  C + CO2

CO + H2  C + H2O

Exothermic reaction

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Chemical Process Technology

Fig. 20.6: Various routes for synthesis gas and ammonia and methanol manufacture

Process Technology

Various synthesis gas production technologies are steam methane reforming, naphtha reforming, auto-thermal reforming, oxygen secondary reforming, and partial oxidation of heavy hydrocarbons, petroleum coke and coal. Various steps involved in synthesis gas production through steam reforming are: • Desulfurization of gas • Steam reforming and compression • Separation of CO2 Various available synthesis gas generation schemes are: • Conventional steam reforming • Partial oxidation

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• Combined reforming • Parallel reforming • Gas-heated reforming 20.6.2 Methanol

Methanol was first obtained by Robert Boylein in the year 1661 through rectification of crude wood vinegar over milk of lime and was named adiaphorous spiritus liglorum. The term methyl was introduced in chemistry in 1835. Methanol is one of the largest volume chemicals produced in the world. Methanol consumption can be separated into three end-use categories—chemical feedstock, methyl fuels, and miscellaneous uses. About 71% of the current global consumption of methanol is in the production of formaldehyde, acetic acid, methyl methacrylate, and dimethyl terephthalate. The global methanol industry has experienced very fundamental and structural changes and has settled down considerably. Demand changes in key methanol derivatives may adversely affect future demand in case of methanol. Product profile of methanol is given in Table 20.20. Globally the demand is expected to grow exponentially, not only caused by growing internal market of traditional applications but accelerated by new applications such as directing blending with gasoline, methanol to olefins (e.g. propylene) and dimethyl ether (Chemical Weekly, November 15, 2011). Global demand for methanol will reach 122.6 million tons by 2020. Global methanol demand was 26.6 million tons and 44.9 million tons in 2000 and 2010 respectively (Chemical Industry Digest, July 2012, p.29). Present capacity of methanol in India is 4.65 lakh tons. Product profile of methanol, capacity for methanol, unit-wise production and sales of methanol and methanol consumption pattern and growth are given in Tables 20.18 to 2021. Table 20.18: Product profile of methanol Product

Uses

DMT/ polyethylene terephthalate

Polyester fiber and film, adhesives, wire coating, textile sizing, herbicides

Methyl methacrylate (MMA) Cast sheet, surface coating, molding resins, oil additives MTBE

Oxygenate

Mono methanolamine

Naphthyl-n-methyl carbamate, monoethyl hydrazine, mono­methyla­ mine nitrate

Dimethylamine

Dimethyl acetamide, dimethyl formamide, dimethyl hydrazine, 2,4-dichlorophenoxyacetic salt

Methylacetate

Paint remover

Dimethylaniline

Solvent, flavoring, dyes, fragrance

Acetic acid

Vinyl acetate, acetic anhydride, chloroacetic acid, ethyl acetate, butyl acetate, isopropyl acetate, acetyl chloride, acetanilide

Formaldehyde

Phenolic resins, pentaerythritol, trioxane, 1,4-butanediol, formal­ dehyde, sulfoxylate, tetraoxane, resorcinol resin

Methylhalides

Quaternary amines, methyl cellulose, butyl rubber, trimethanol propene

380

Chemical Process Technology Table 20.19: Capacity for methanol in India

Units

Location

Capacity (Tpa)

Gujarat Narmada Valley Fertilizers Ltd.

Gujarat

2,38,100

51.11

Deepak Fertilizers & Petrochemicals Ltd.

Maharashtra

1,00,000

21.46

Rashtriya Chemicals & Fertilizers Ltd.

Maharashtra

7,2,600

15.58

Assam Petrochemicals Ltd.

Assam

3,3,000

7.11

National Fertilizers Ltd.

Punjab

2,2,110

4.74

4,65,810

100.00

Total

Share (%)

Table 20.20: Unit-wise production and sales of methanol Production sales

Units

Sales

2009–10

2010–11

2009–10

2010–11

1,87,079

2,02,544

1,11,511

1,26,059

Deepak Fertilizers & Petrochemicals Ltd.

65,647

81,888

65,703

81,708

Rashtriya Chemicals & Fertilizers Ltd.

44,103

68,700

19,746

41,264

Assam Petrochemicals Ltd.

33,759

30,000

15,040

15,000

2,669

516

131

44

3,33,257

3,83,648

2,12,131

2,64,075

Gujarat Narmada Valley Fertilizers Ltd.

National Fertilizers Ltd. Total

Table 20.21: Methanol consumption pattern and growth Users

Share (%)

Growth rate (%)

Formaldehyde

48

7

Pharmaceuticals

21

8.5

Oxygenates

9

–

Acetic acid

5

4

Alkyl amines

4

9

Dimethyl sulfate

3

8

Agrochemicals

3

5

Chloromethanes

4

8

3

8

100

6

Solvents/others Total

Source: Chemical Weekly, November 15, p.199, 2011.

Methanol and dimethyl ether are likely to be notified as transport fuel which will help lower fuel costs in India using Israel Technology (Chemical Industry Digest, Annual January 2018; p. 15). Methanol Process Technology

From the early 1800s until 1920s, the distillation of wood to make wood alcohol was the source of Methanol. The most common industrially favored method for the production of

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methanol was first developed by BASF in 1923 in Germany from synthesis gas utilizing high pressure process using zinc-chromic oxide catalyst. However, due to high capital and compression energy costs compounded by poor catalyst activity, high-pressure process was rendered obsolete when ICI in the year 1966 introduced a low-pressure version of the process at 5–10 MPa and 210–270ºC, with a new copper-zinc oxide-based catalyst of high selectivity and stability. Process steps involved in the production of methanol are: • Production of synthesis gas using steam reforming or partial oxidation • Synthesis of methanol • High-pressure process (25–30 MPa) • Medium pressure (10–25 MPa) process • Low-pressure process (5–10 MPa) Figure 20.7 illustrates the production of methanol from steam reforming of natural gas and naphtha. The major reactions take place during methanol synthesis converter can be described by following equilibrium reactions: CO + 2H2 CO2 + 3H2 CO2 + H2

CH3OH CH3OH + H2O CO+H2O

DH298ºK= –90.8 kJ/mol DH298ºK= –49.5 kJ/mol DH300ºK= 41.3 kJ/mol

The first two reactions are exothermic and proceed with reduction in volume. In order to achieve a maximum yield of methanol and a maximum conversion of synthesis gas, the process must be affected at low temperature and high pressure. After cooling to ambient temperature, the synthesis gas is compressed to 5.0–10.0 MPa and is added to the synthesis loop which comprises the following items—circulator, converters, heat exchanger, heat recovery exchanger, cooler, and separator. The catalyst used in methanol synthesis must be very selective toward the methanol reaction, i.e. give a reaction rate for methanol production which is faster than that of competing.



Fig. 20.7: Methanol from steam reforming of natural gas and naphtha

382

Chemical Process Technology

20.6.3 Formaldehyde

Some major intermediates derived from formaldehyde are chelating agents, acetal resins, 1,4-butanediol, polyols, methylene diisocynate. It is also used for the manufacture of wide variety of chemicals, including sealant, herbicides, fertilizers, coating, and pharmaceuticals. Product profile of formaldehyde is given in Table 20.22. Table 20.22: Product profile of formaldehyde Product

Uses

Formaldehyde

Thermosetting resin: Phenol, urea melamine, formaldehyde resins Hexamethylenetetramine, plastic and pharmaceuticals 1,4-Butadiol Methylene diisocyanate Fertilizer, disinfectant, biocide preservative, reducing agent, corrosion inhibitor Polyaceta resin p-Formaldehyde Pentaerythritol (Explosive-PETN), alkyl resins

Formaldehyde is commercially available as aqueous solution with concentration ranging from 30–56 wt.% HCHO. It is also sold in solid form as paraformaldehyde or trioxane. The production of formaldehyde in India has been growing at a fairly constant rate during last 10 years. There are presently about 17 units in India. Installed capacity and production of formaldehyde during 2003–04 were 2.72 lakh tons and 1.89 lakh tons, respectively. Various industrial processes for manufacture of formaldehyde using silver and iron-molybdenum catalyst are given in Table 20.23. Process diagram for manufacture of formaldehyde using silver and iron-molybdenum catalyst is shown in Figures 20.8 and 20.9, respectively. Table 20.23: Industrial processes for manufacture of formaldehyde Catalyst

Process licensor

Silver catalyst processes

Bayer, Chemical Construction, Ciba, DuPont, IG Farben, CdFChemie Process, BASF process, ICI Process

Iron-molybdenum catalyst Degussa Process, Formox Process, Fischer-Adler, Hiag-Lurgi, processes IFP-CdFChimleLumus, Motedisous, Nikka Topsoe, Prolex

20.6.4 Acetic Acid (CH3COOH)

Acetic acid is one of the most widely used organic acids and finds application in the manufacture of wide range of chemicals. Acetic acid is the largest methanol-based chemical in terms of volume. World capacity and consumption pattern of acetic acid is given in Table 20.24. Installed capacity of acetic acid in India is mentioned in Table 20.25. Table 20.26 shows the market share of acetic acid in India by different companies. Product profile of acetic acid is given in Table 20.27.

Petrochemical Industry

Fig. 20.8: Formaldehyde using silver catalyst

Fig. 20.9: Formaldehyde from iron molybdenum catalyst

383

384

Chemical Process Technology Table 20.24: World acetic acid capacity and consumption pattern

Product

Consump­tion 2002 (’000 tons)

Consumption growth (%) 1997– 2002– 2007– 2002 2007 2012

Acetic acid

8,302

3.9

3.4

2.5

Capacity AnnouCapacity change 2002 nced capa-­­ needed by 2012–2002 (’000 tons) city due after announcement by 2012 (’000 tons) (%) (’000 tons) 9,559

994

1,785

19

Source: Chemistry Industry News, March 2004; SRI Consulting, World Petrochemicals Program . Table 20.25: Installed capacities of acetic acid in India Company

Installed capacity (tpa)

Indian Organics Chemicals Ltd.

15,000

Somaiya Chemicals Ltd.

15,000

Somaiya Organics

20,000

Andhra Sugars Ltd.

1,000

Ashok Organic Industries

30,000

EID Parry (I) Ltd.

10,000

Gujarat Narmada Valley Fertilizer Corp. Ltd.

50,000

Kanoria Chemicals & Industries

6,000

Laxmi Organic Ltd.

9,500

Trichy Distilleries

12,000

Vam Organics

1,15,500

Ashok Alcochem Ltd.

5,400

Dhampur Sugar Mills

7,300

Pentokey Ltd.

7,000

Polychem Ltd.

7,500

Trident Alcochem

6,000

Table 20.26: Market share of major acetic acid manufacturer Name of the company

Share (%)

Jubilant Organosys Ltd.

22

Ashok Organics Ltd.

17

IOCL

9

Gujarat Narmada Valley Fertilizer Corp. Ltd.

9

Others

43

Source: www.indiainfoline.com/sect/chor/ch05.html.

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Table 20.27: Product profile of acetic acid Product

Uses

Monochloroacetic acid

CMC manufacture, adhesives, thickeners for drilling muds, food industry, pharmaceuticals, textiles, 2,4-D (insecticides)

Ethyl acetate, n-butyl Coatings, adhesives, inks and cosmetics acetate, isopropyl acetate Vinegar

Food Preservative

Cellulose acetate

Fibers, plastic film

Acetic anhydride

Pharmaceuticals, intermediates, cellulose acetate

Acetanilide

Pharmaceutical, dyes intermediate, Rubber accelerator, Peroxide stabilizers

Peracetic acid

Special oxidants

Terephthalic acid, DMT

Polyester fiber, packaging, photographic films, magnetic tape sectors

Vinyl acetate

Polyvinyl acetate, polyvinyl chloride, paints, adhesives, and coatings

20.6.5 Chloromethanes (Methyl Chloride, Methylene Dichloride, Chloroform, Carbon Tetrachloride)

Chlorinated methanes, which include methyl chloride, methylene dichloride, chloroform and carbon tetrachloride, are important derivatives of methane and find wide application as solvents and as intermediate products. Product profile of chloromethane is given in Table 20.28 (Mall, 2007). Table 20.28: Product profile of chloromethane Product

Uses

Methyl chloride

Refrigerant, butyl rubber, silicones, solvent, tetramethyl lead, intermediates

Methylene dichloride Solvent, intermediates, photographic film, degreasing solvents, aerosol, propellants Chloroform

Chlorodifluoromethane, refrigerants, propellants, pharmaceuticals

Carbon tetrachloride

Dichlorodifluoromethane, trichlorofluoromethane, solvent, fire extinguishers

Process Technology

There are two major routes for the manufacture of chloromethane (Fig. 20.10): • Direct chlorination of methane • Through methanol route

Direct chlorination of methane: Chlorination of methane (natural gas) is carried out at around 400–450ºC during which following reaction takes place: CH4 + Cl2 CH3Cl + HCl Methyl chloride

CH3Cl + Cl2 CH2Cl2 + Cl2 CHCl3 + Cl2

CH2Cl2 + HCl Methylene dichloride CHCl3 + HCl Chloroform CCl4 + HCl

386

Chemical Process Technology

Fig. 20.10: Chloromethane from methane and methanol

20.6.6 Dimethylformamide [HCON(CH3)2]

Dimethylformamide is one of widely used solvents in the manufacture of acrylic fiber. Because of its high dielectric constant, aprotic nature, wide liquid range and low volatility, dissolving power, it is frequently used as solvent. Process Technology

Dimethylformamide is made by following two processes (Fig. 20.11): Two-step processes: Process involves carbonization of methanol to methyl formate using basic catalyst and reaction of methyl formate with dimethylamine. CH3OH + CO + HCOOCH3

(CH3)2NH + HCON(CH3)2 + CH3OH

Dimethylformamide CH2OH + CO

Sodium, 3.5 atm, 110–120ºC Methoxide

HCOOCH3 + (CH3)2NH

HCOOCH3

HCON(CH3)2 + CH3OH

Two-stage process



Direct one-step process from synthesis gas and ammonia

Fig. 20.11: Dimethylformamide production

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20.6.7 Acetylene

It played important role during and after World War II in providing feedstock for large number of organic chemicals when petrochemical industry was not well developed. Acetylene’s highly reactive triple bond provided a ready “handle” for chemists to grab onto for designing process chemistry. Safety issues involved with handling of large volumes of acetylene and its expense are big problem with adoption of acetylene-based processes. The process of acetylene requires much energy and is very expensive. Acetylene is still being used for manufacture of chemicals. Various Routes for Acetylene

Calcium carbide route: This is the oldest method for production of acetylene and still acetylene is produced by this process in small scale as well large scale. Calcium carbide is produced by reacting lime with coke at temperature 2,000–2,100ºC in an electric furnace. Two processes produce acetylene from calcium carbide: Wet process and Dry process. Dry process is preferred as in case of calcium hydroxide, which is produced during the process (is produced in the form of dry calcium hydrate). CaC2 + 2H2O

C2H2 + Ca(OH)2

Acetylene from cracking of hydrocarbons: Cracking of hydrocarbons such as methane, ethane, propane, butane, ethylene, and natural gas can make acetylene. 2CH4

C2H2 + 3H2

C 2H 4

C2H2 + H2

C4H10

C2H2 + C2H4 + 2H2

Product derived from acetylene: Acetylene is extremely reactive hydrocarbon and was initially was used for the manufacture of large number of chemicals which are now being derived from acetylene route. Product profile of acetylene is given in Figures 20.12 and 20.13 (Mall, 2007, Huang et al.). Acetaldehyde:

HC  CH + H2O

 CH + HCN Acrylonitrile: HC 

CH3CHO HC = CH = CH2 = CHCN

Chlorinated solvents: HC  CH + 2Cl2

CH2Cl2CHCl2

CHCl = CCl2 + Cl2

CHCl = CCl2 + HCl

CH2Cl2CCl3

CCl2 = CCl2+ HCl

 CH + CH3COOH Vinyl acetate: HC 

CH2 = CHOOCCH3

Chloreprene:

CH2 = CHOOCCH3

HC  CH + CH3COOH CH2 = CHOOCCH3 + Cl2

CH2 = CClCH = CH2

Vinyl chloride and vinylidene chloride: HC  CH + HCl CH2 = CHCl + Cl2 CH2 ClCHCl2

CH2 = CHCl CH2 ClCHCl2 CH2 = CCl2 + HCl

 CH + HF Vinyl fluoride: HC  CH2=CHF

Fig. 20.12: Reactions in acetylene derived chemicals

388

Chemical Process Technology

Fig. 20.13: Product profile of acetylene

20.7 ETHYLENE DERIVATIVES: ETHYLENE OXIDE, ETHYLENE GLYCOL, ETHYLENE DICHLORIDE AND VINYL CHLORIDE

Ethylene is one of the most versatile petrochemicals and its production has steadily increased over the years. Ethylene is called as king of chemicals and surpasses all organic chemicals in production and in amount sold. Ethylene is the basic building block for petrochemicals. Product profile of ethylene is given in Table 20.29. Because of its ready availability at low cost and high purity and reactivity, ethylene has become one of the important raw materials for large number of petrochemicals and products. Ethylene has replaced the earliest route of production of vinyl chloride, acetaldehyde, vinyl acetate and other chemicals through acetylene route. Installed and production capacity of ethylene and its derivatives is mentioned in Table 20.30. Large tonnage of ethylene is being used for the manufacture of polyethylene, ethylene oxide, ethylene glycol and styrene. World requirement of ethylene is given in Figure 20.14. World

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Table 20.29: Product profile of ethylene Product

Uses

Polyethylene LDPE, LLDPE, HDPE

Films, moldings, pipes, cable covering, netting

Ethylene oxide and ethylene glycol

Antifreeze, polyester, solvents, detergent, textile, ethanol amine

Styrene

Synthetic rubber and polystyrene

Ethyl alcohol

Industrial solvent and chemical intermediates

Acetaldehyde (from ethyl alcohol)

Acetic acid (peracetic acid), acetic anhydride, cellulose acetate, vinyl acetate, pyridine, butyraldehyde (ethyl hexanol)

Olefin

n-Butenes, synthetic detergent, oxo-alcohols, synthetic lubricants

Chlorinated solvents

Trichloroethylene, perchloroethylene

Ethyl chloride

Tetraethyl lead, chemical intermediates

Vinyl acetate

Polyvinyl acetate, polyvinyl alcohol

Vinyl chloride

Polyvinyl chloride (PVC) Table 20.30: Installed capcity and production of important ethylene and ethylene derivatives in India

Product

Installed capacity 2008–09 (thousand metric ton)

Ethylene

2,841

2,515

Ethylene oxide

120

117

Monoethylene glycol

820

738

Acetaldehyde

238

59.2

59

43.42

Acetic anhydride Ethanol amine Ethyl acetate

Production 2009–10 (thousand metric ton)

10

7.0

132.0

103.96

Fig. 20.14: World ethylene supply/demand profile 2008 production=117.3 million metric tons Source: Polyolefins Feedstocks and Market by Howard Rappaport CMAI, Plast., India-February, 2009.

390

Chemical Process Technology

ethylene capacity is shown in Figure 20.15. World ethylene complexes, capacity, and top 10 producers are mentioned in Tables 20.31 to 20.33, respectively. Global ethylene capacity growth is given in Table 20.34.

Fig. 20.15: World Ethylene Capacity (120 Million tons 2008) (Source: Petrochemical Economics: Technology Selection in a Carbon Constrained World: http://www.worldscibooks.com/chemistry/ p702.html Table 20.31: World top ethylene complexes Company

Location

Capacity, TPY

1 Formosa Petrochemical Corp.

Mailiao, Taiwan, China

29,35,000

2 Nova Chemicals Corp.

Joffre, Alta

28,11,792

3 Arabian Petrochemical Co.

Jubai, Saudi Arabia

22,50,000

4 Exxon Mobi Chemical Co.

Baytown, Tex.

21,97,000

5 Chevron Philips Chemical Co.

Sweeny, Tex.

18,65,000

6 Dow Chemical Co.

Terneuzen, Netherlands

18,00,000

7 Ineos Olifins and Polymers

Chocolate Bayou, Tex.

17,52,000

8 Equistar Chemicals LP

Channelview, Tex.

17,50,000

9 Yanbu Petrochemical Co.

Yanbu, Saudi Arabia

17,05,000

Shuaiba, Kuwait

16,50,000

10 Equate Petrochemical Co. Source: Oil and Gas Journal, July 4, 2011.

Table 20.32: Regional capacity breakdown Asia-Pacific Eastern Europe

Ethylene capacity, TPY 4,26,31,000 79,71,000

Middle East, Africa

2,33,57,000

North America

3,45,08,000

South America

50,83,500

Western Europe Total capacity Source: Oil and Gas Journal, July 4, 2011.

2,49,04,000 13,84,54,500

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Table 20.33: Top 10 ethylene producers Capacity, TPY

Company

Sites

Saudi Basic Industries Corp.

15

1,33,92,245

1,02,73,759

Dow Chemical Co.

21

1,30,44,841

1,05,29,421

Exxon Mobil Chemical Co.

19

1,25,15,000

85,50,550

Royal Dutch Shell PLC

13

93,58,385

59,46,693

Sinopec

13

75,75,000

72,75,000

Total AS

11

Of entire complexes With only company partial interests

59,33,000

34,71,750

Chevron Philips Chemicals Co. 8

56,07,000

53,52,000

Lyondell Basell

8

52,00,000

52,00,000

National Petrochemical Co.

7

47,34,000

47,34,000

Ineos

6

46,56,000

42,86,000

Source: Oil and Gas Journal, July 4, 2011. Table 20.34: Global ethylene capacity growth (thousand tons) Major region

2008 Capacity

2013 Capacity

08 to ’13 Delta

Middle East/Africa

19,711

34,461

14,751

Asia Pacific

39,617

56,349

16,732

America

40,421

40,434

12

Europe

30,953

31,293

340

World (Total)

130,702

162,537

31,836

20.7.1 Ethylene Oxide (EO)

Ethylene oxide is one of the important petrochemical intermediate used for the manufacture of large number of products; some of the major uses are in the manufacture monoethylene glycol glycol ethers which is made by reaction of ethylne oxide and alcohols, ethanol amines. Surfactant indutry is one of largest user of EO, both for industrial and house hold applications. Product profile of ethylene oxide is given in Table 20.35. Table 20.35: Product profile of ethylene oxide Product

Uses

Ethanol amines

Detergent, soap solvent, cosmetics, morpholine

Monoethylene glycol

Polyester, staple fiber yarn, pet bottles, film

Diethylene glycol

Coolants, pesticides, rubber compounding, plasticizer, polyurethane, alkyl resin

Triethylene glycol

Natural gas conditioning agent’s plasticizer

Polyethylene glycol

Pharmaceuticals, brake fluid, cosmetics

Non-ionic surfactants, ethoxylates

Textile auxiliaries, binders, dyes, pesticides, pharmaceuticals, cosmetics

Glycol ethers

Brake fluid and protective coating

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Chemical Process Technology

Chlorohydrin Process Cl2 + H2O C2H4 + HOCl CH2OH – CH2Cl + Ca (OH)2

HOCl + HCl CH2OH – CH2Cl CH2 – CH2 + CaCl2 + H2O

Direct Oxidation

   Ag, 260–290ºC

H2C = CH2 + 1/2O2 C2H4O H2C = CH2 + 3O2 2CO2 = 2H2O; DH = –135 k.J/mol C2H4O + 5/2O2 2CO2 + 2H2O H2C = CH2 + 1/2O2 CH3CHO H2C = CH2 + 2O2 HCHO

20.7.2 Mono-, Di-, and Tri-ethylene Glycols (MEG, DEG, TEG)

A major petrochemical and find application in manufacture of polyester and as antifreeze accounts for 70% of ethylene oxide production. Ethylene oxide preheated to 195ºC. EO: H2O ratio 10:1 to maximize MEG production by-products DEG, TEG. Figure 20.16 gives detail manufacturing of MEG, DEG and TEG from ethylene oxide.

Fig. 20.16: MEG, DEG and TEG from ethylene oxide

20.7.3 Vinyl Chloride

Vinyl chloride is one of the important petrochemical feedstocks and finds use in manufacture of polyvinyl chloride the second largest tonnage commercial polymer

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after polyethylene. About 95% of the present vinyl chloride production worldwide is used in polymer production or copolymer application. Another important use of vinyl chloride is in the production of vinylidiene chloride. According to SRI consulting global production and consumption of ethylene dichloride (EDC) in 2009 (which accounted for 95% consumption in vinyl chloride manufacture), was about 33.7 million tons with global capacity of about 73% in 2009. Process Technology

The original process of manufacture of vinyl chloride was by reaction of acetylene derived from calcium carbide with hydrochloric acid in gaseous phase in presence of mercuric chloride catalyst at temperature around 100–180ºC. However, with the availability of ethylene from cracker plant now vinyl chloride is made from ethylene obtained from cracker plant. The process of vinyl chloride manufacture takes place in two stages: • First stage: Ethylene is reacted with chlorine in either liquid or vapor phase in presence of ferric chloride. However, the liquid phase process is more common and the reaction takes place at around 50–90ºC and 3–5 atm pressure. • Second stage: Vinyl chloride is produced by pyrolysis of vaporized ethylene dichloride in a set of tubular furnaces at temperature of about 400–500ºC.

Direct chlorination

CH2 = CH2 + Cl2

ClCH2 – CH2Cl

Ethylene chloride by direct chlorination of ethylene: The original process of manufacture of vinyl chloride by ethylene chlorination and cracking of ethylene dichloride had been replaced by oxychlorination process in which no hydrochloric acid is formed as by-product. Process diagram of vinyl chloride from oxychlorination process is shown in Figure 20.17. The process involves production of ethylene dichloride by exothermic reaction of ethylene, hydrochloric acid and oxygen. Liquid phase: Fixed or fluidized bed reactor is used at 170–180ºC and 15–20 atm pressure in presence of copper chloride. Vapor phase reaction: The temperature and pressure are 200–220ºC and 20–50 atm pressure. Reactions

Vinyl chloride by chlorination:

Initiation: ClCH2 – CH2Cl Propagation:

C l + ClCH2 – CH2Cl



ClCH2 – CHCl

Termination:

• 

• 

• 

ClCH2 – CH2 + Cl • 

ClCH2 – CHCl + HCl •   

CH2 = CHCl + Cl • 

Cl + ClCH2 – CH2

• 

CH2 = CHCl + HCl

The first stage is typical electrophilic addition of a halogen to an alkene. The second stage is a free-radical chain reaction.

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Chemical Process Technology

Fig. 20.17: Vinyl chloride from oxychlorination process

Oxychlorination: The original process of manufacture of vinyl chloride by ethylene chlorination and cracking of ethylene dichloride had been replaced by oxychlorination process in which no hydrochloric acid is formed as by-product. The process involves production of ethylene dichloride by exothermic reaction of ethylene, hydrochloric acid, and oxygen. Liquid phase: at about 170–180ºC in at 15–20 atm pressure in presence of copper chloride in either fixed or fluidized bed reactor. Vapor phase reaction: the temperature and pressure are 200–220ºC and 20–50 atm pressure. • Direct chlorination:

CH2 = CH2 + Cl2

• Oxychlorination:

CH2 = CH2 + 2HCl + ½O2

• Ethylene dichloride pyrolysis:

ClCH2 – CH2Cl

• Overall reaction:

2CH2 = CH2 + Cl2 + ½O2

ClCH2 – CH2Cl ClCH2 – CH2Cl + H2O

CH2 = CHCl + HCl CH2 = CHCl + H2O

20.7.4 Vinyl Acetate

Vinyl acetate is one of the important derivatives of ethylene which is used as intermediate for manufacture of polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, etc.

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Global end use pattern of vinyl acetate is—adhesives (23%), paints and coating (29%), textiles (21%), plastics (17%), paper and board (10%). Consumption pattern of vinyl acetate in India is polyvinyl acetate emulsions and resins (50%), polyvinyl alcohol (25%), ethylene vinyl acetate (10%), others (15%). End use pattern of vinyl acetate in India is—adhesives (35–40%), textiles (30–35%), paints and coating (15–20%), others (10–15%). Uses of vinyl acetate is given in Table 20.36. Process Technology

• The ethylene route has replaced the traditional process of manufacture of vinyl acetate. The production of vinyl acetate through acetylene route, which was developed by Wacker in 1930, involves reaction of acetylene and acetic acid in liquid phase at 60–80ºC and 1–2 atm pressure in presence of mercury salt catalyst. H2C = CH2 + CH3COOH

H3COOCHC = CH2

• Vinyl acetate from ethylene route: Vinyl acetate is made by reaction of ethylene with acetic acid by liquid phase process or by vapor phase process in presence of palladium and cupric chloride catalyst. In the vapor phase process, the following reactions take place: CH2 = CH2 + CH3COOH + PdCl2 Pd + 2CuCl2 2CuCl + 2HCl + H2O2

CH2 = CHCOOCH3 + 2HCl + Pd PdCl2 + 2CuCl 2CuCl2 + 2H2O

Table 20.36: Uses of vinyl acetate

Vinyl acetate

Polyvinyl acetate

Surface coating adhesives, textile resins

Polyvinyl alcohol

Textile size, grease proofing paper, vinyl emul­sifier, thickener, viscosity regulators, adhesives,

Acrylonitrile copolymer

Acrylic fibers

Polyvinyl formate

Water resistant insulation enamel

Ethylene vinyl acetate copolymers Textile and paper coating Vinyl chloride comonomers

VC-VAC, LP records, VC-VAC coating

Polyvinyl butyraldehyde

Safety glass

20.7.5 Ethanol

Apart from its major use as a beverage. it is one of the most versatile chemical and basic building blocks of the organic chemical industry. Ethanol is generally produces by fermentation of molasses. Due to the development of petrochemical industry and availability of ethylene, now ethylene provides another major route of formation of ethanol. However, still molasses were used to produce ethanol in India. In India some of the important chemical are still prepared through ethanol which were earlier prepared through petrochemical route. Two such important complexes are Jubilant Organosys Ltd., Gajraula (Uttar Pradesh) and Indian Glycol Ltd., Kashipur (Uttar Pradesh), where large numbers of ethanol derivatives are manufactured through ethanol route. Various routes for manufacture of ethanol: • Fermentation of molasses • Catalytic hydration of ethylene

396

Chemical Process Technology

• Ethylene esterification and hydrolysis • Gas to bioethanol Fermentation of Molasses

Ethyl alcohol is prepared from molasses by fermentation process utilizing yeast enzymes. Separation of 8–10% alcohol is achieved in a series of distillation columns, as alcohol and water at 95% concentration form azeotropic mixture. Ethanol by Esterification and Hydrolysis

Ethylene and sulfuric acid are reacted at 80ºC and 1.5 MPa to form a mixture of ethyl sulfates, which are then hydrolyzed to ethyl alcohol. Ethylene and sulfuric acid are reacted in absorber from which the mixture of ethylene sulfates thus formed is fed to hydrolyzer from which the crude alcohol and sulfuric acid are fed to stripping section and caustic scrubbing section and finally to a series of two distillation columns for separation of ether and alcohol. C2H4 + H2SO4

C2H5OSO3H

2C2H4 + H2SO4

(C2H5O)2SO2

C2H5OSO3H + (C2H5O)2SO2 + 3H2O 2C2H5OH

3C2H5OH + 2H2SO4

C2H5OC2H5 + H2O

Ethanol by Vapor Phase Hydration of Ethylene

An ethylene rich gas is mixed with water and heated to about 300ºC and passed on to fixed-bed catalytic reactor where catalytic hydration of ethylene takes place. The catalyst used is phosphoric acid deposited on silica gel. The reactor effluents are sent to separator for separation of vapor and liquid. The gases from the separator are cooled and scrubbed with water to recover traces of alcohol. The alcohol water mixture is sent to a series of distillation columns where ether is separated in the light end column and finally 95% by volume ethanol water azeotrope is separated (Fig. 20.18).

Fig. 20.18: Ethanol from catalytic recycle hydration of ethylene

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Gas to Bioethanol

IOCL and Lanaza Techare collaboration are going to have process of have the first off-gas to bioethanol unit. The process uses biocatalyst for fermentation of waste offgases. Ethanol produced from recycling of the refiner’s off-gas to have greenhouse gas emissions saving. It will save about 1 million tons of CO2 per annum to produce 40 million liter per annum of ethanol. The process allows refineries to divert waste gases from the grid, supporting the transition to fully renewable power while recycling the carbon to liquid fuels and petrochemicals (Chemical Industry Digest, August 2017). 20.7.6 Acetaldehyde

Product profile of acetaldehyde is shown in Table 20.37. Table 20.37: Product profile of acetaldehyde Product

Uses

Pyridine, picoline

Solvent, drugs, dyes, agricultural chemicals

Chlor-aldehydes

Insecticides, fungicides, disinfectants

Acetaldol

1,3-butylene glycol (polyesters), urethane coating,humcetant, printing ink, crotonaldehyde, n-butyl alcohol, n-butyric acid anhydride, 2-ethyl hexanol, rubber accelerator, sorbic acid

Paraldehyde

Rubber accelerator, antioxidant dye, stuff

Peracetic acid

Epoxidation reaction, reagent in caprolactam, synthetic glycerols

Pentaerythritol

Alkyl resin, stabilizer, plasticizers, chlorinatedpolyether resin, intumescents

Acetic, anhydride

Acetyl salicylic acid, cellulose acetate, esters

Acetic acid

Cellulose acetate, vinyl acetate, chloroacetic acid, ammonium acetate

Lactic acid

Food and, beverages, lactates, adhesives, leather processing

Various Routes for Acetaldehyde 1. Dehydrogenation of ethanol

2. Oxidation of ethanol

3. Acetylene

4. Ethylene

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Chemical Process Technology

5. Dimethylformamide

20.7.7 Acetone Cumene process

Hydrogenation of propanol

Propylene oxidation

Oxidation of 2-propanol

Oxidation of p-di-isopropyl benzene

Fermentation

20.8 PROPYLENE, PROPYLENE OXIDE, AND ISOPROPANOL 20.8.1 Propylene

Propylene often referred as the crown prince of petrochemicals and is superficially similar to ethylene but there are many differences in both production and uses (Hatch and Matar, 1978). Propylene is used in many of the world’s largest and fastest growing synthetic materials and thermoplastics. The demand of propylene has increased rapidly during the last 20 years and primarily driven by polypropylene demand (Mall, 2007). Product profile of propylene is given in Table 20.38. According to SRI consulting 2010 global production and consumption of propylene in 2009 was both approximately 71 million tons with capacity utilization of 78.5%. Global propylene consumption is forecasted to average growth of around 5.1% per year from 2009 to 2014 and 3.5% per year from 2014 to 2019. Consumption of refinery grade propylene made up 9% of total consumption in 2009, chemical grade 23% and polymer grade 68%. Refinery grade propylene is consumed mainly for production of cumene and isopropyl alcohol. Chemical grade propylene mostly goes into oxo-alcohol, propylene oxide, and acrylonitrile.

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Table 20.38: Product profile of propylene Product

Uses

Miscellaneous chemicals

1 butanol, 2-ethyl hexanol, allyl chloride, epichlorohydrin

Polymer

Polypropylene, polyacrylamide, nylon 66, acrylic sheets

Propylene oxide

Polyether-polyols, glycol ethers, isopropyl amines, propylene carbamate, surfactants

Propylene glycol

Unsaturated polyester resins, food additives, cellophane, paints and coating, plasticizers, functional fluids, antifreeze, tobacco treatment

Acrylonitrile

Acrylic fiber, acrylic acid, acrylates, methyl methacrylates, adiponitrile

Isopropanol

Acetone, cosmetics, solvents, pharmaceuticals, isopropyl acetate

Polyols

Polyurethane and polyester

Sources of Propylene

Propylene is a by-product of steam crackers and varying number of olefins is produced from steam crackers depending on the type of feedstock. Other sources of propylene may be recovery of propylene from FCC light ends, propane dehydrogenation, metathesis. Some of the major processes for production of propylene is given in Table 20.39. Typical composition of FCC gas stream is given in Table 20.40. Table 20.39: Propylene production technologies Technology

Process

Licensor

Olefin Conversion Technology

This process involves production of propylene from ABB Lumus Global ethylene and 2-butenes in a fixed bed metathesis reactor containing proprietary catalyst, which promotes reaction of ethylene and 2-butene to form propylene and simultaneously isomerizes 1-butene to 2-butene.

Superflex Process

The process uses a fluidized bed catalytic reactor Kellogg Brown & system using proprietary catalyst which converts Root, Inc. low value feedstock to predominantly propylene and ethylene products. Low value light hydrocarbon streams from ethylene plant and refineries can be used, e.g. C4 and C5 olefin rich stream from ethylene plants, FCC naphtha, C4 stream, thermally cracked naphtha from Vis breakers or cokers.

Propylur Process

This process produces propylene beside ethylene Lurgi Oel Gas from low value rich feeds ranging from C4–C8 from Chemie GmbH ethylene plant and refineries in a fixed bed reactor using proprietary catalyst. The process offers high selectivity towards propylene.

UOP Oleflex Process This process produces polymer grade propylene UOP LLC from propane and the process consists of a reactor, catalyst regeneration section and product separation and fractionation section. The process uses platinum catalyst (DeH-12 catalyst). Contd...

400

Chemical Process Technology Table 20.39: Propylene production technologies (Contd...)

Technology

Process

Licensor

UOP/Hydro MTO Process

This process converts crude methanol (produced UOP LLC and from synthesis gas using natural gas) to ethylene and Hydro Norway propylene and can be operated either a maximum ethylene or a maximum propylene production mode using MTO-100 silicoaluminophosphate synthetic molecular sieve-based catalyst. The process utilizes fluidized bed reactor and regenerator.

Methanol to Propylene (MTP) Technology

This process produces propylene through methanol Lurgi Oel Gas route using natural gas. In this process, propylene Chemie GmbH is produced in two steps: First methanol is converted to dimethyl ether in reactor followed by reaction of methanol/DME in second reactor. Methanol can be produced from methane from conventional method.

C4 Hydrogenation and Meta-4 Process

This process involves production of polymer grade Axens, Axens NA propylene plus an isobutylene rich stream or MTBE by upgrading low value C4 stream pyrolysis C4 cuts or butene rich cut. The process steps involve— butadiene and C4 acetylenes selective hydrogenation and butadiene hydroisomerization, isobutylene removal or MTBE production and metathesis step for conversion of butene and ethylene to propylene. The two main equilibrium reactions taking place are metathesis and isomerization.

Olefin Ultra™

A new ultra-high activity ZSM-5 additive that provides the highest activity has been developed by Davision catalysts.

KBR’s Maxofin-3 technology

KBR’s Maxofin process is based on fluidized bed Kellogg Brown & cracking of gas oils and residue feeds using ZSM Root, Inc. catalyst and proprietary MAXOFIN-3 catalyst additive. The process gives 15% or higher propylene yield from gas oil.

Sources: Pujaodo and Vora, 1990; Badoni, et al. 1996; Meyers, 1986; Dunn, et al. 1992; Venner and Kantorowicz, 2001; Petrochemical Processes 2003; Zinger, 2003; Nee, 2003; Dharia, et al. 2004, Eng. et al. 2004. Table 20.40: Typical composition of FCC gas stream Products

Yield weight (%)

Dry gas (including ethylene)

12.7

Propane

6.5

Propylene

21.0

Butene

35.8

Source: Badoni, et al. 1996

Catalytic Dehydrogenation

Catalytic dehydrogenation of light paraffins is of increasing importance because of the growing demand of olefins such as propylene and isobutene (Reasco and Haller, 1994)

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and n-butenes. Propane dehydrogenation accounts for 2% of the total world propylene production. Some of the commercial processes available for dehydrogenation of propane and n-butane are (Badoni, et al. 1996): • Oleflex (UOP) • Catofin (ABB Lumus) • FBD-4 (Snamprogetti SPA) • Star (Phillips Petroleum Company) Catalytic dehydrogenation takes place at high temperature (650ºC) using platinum based or chromium-alumina or Fe, Cr/Al2O3 as catalyst. Reactor effluent treatment for the separation of hydrogen, propylene, and propane is not simple and total investment is high. These production units can be installed only in areas where field propane is available at low costs. Methanol to Propylene

This process produces propylene from natural gas via methanol by converting methanol to dimethyl ether in adiabatic reactor using high activity, high selectivity catalyst. The methanol, water, DME stream is then feed to series of MTP reactor where steam is added. The product stream is first processed for removal of traces of water, CO2 and DME, followed by further processing for yielding polymer grade propylene. 20.8.2 Propylene Oxide, Propylene Glycol, and Polyols

Propylene oxide, propylene glycols, and polyols are important derivatives of propylene. Propylene oxide is used for the manufacture of propylene glycol and polyols. Major consumption of propylene oxide is manufacture of polyurethane and polyester resins. Propylene glycol find major application in the manufacture of unsaturated polyester resins, food additives, pharmaceuticals and personal care, tobacco humectants, cellophane, paints and coatings. Polyols major use is in the manufacture of polyurethane. Propylene Oxide

Processes for making propylene oxide: There are two major processes for the manufacture of propylene oxide: Propylene chlorohydrin process and propylene oxidation process using peroxides. Propylene Chlorohydrin Route: The chlorohydrination process consists of formation of propylene chlorohydrin by the reaction between hypochlorous acid and propylene. The propylene chlorohydrin is epoxidized to propylene oxide by a 10% solution of milk of lime or NaOH. Various steps involved are: • Propylene hypochlorination: Propylene is reacted with aqueous chlorine resulting in the formation of propylene chlorohydrins. Unreacted propylene is recycled. • Neutralization: Neutralization of propylene chlorohydrins containing hydrochloric acid which is formed during the process. • Dehydrochlorination: Reaction of propylene chlorohydrin with milk of lime or caustic soda to produce propylene oxide • Purification: Distillation of crude propylene oxide for separation heavy ends

402

Chemical Process Technology

Reactions: Cl2 + H2O

HOCl + HCl

By-products formed during the reaction are 1,2-dichloropropane and chlorinated di-isopropyl ether. Some of the disadvantages and major economic drawbacks of the process which led to the wide acceptability of epoxidation processes are use of costly chlorine, production of weak calcium chloride byproduct, and corrosion problem due to chlorine handling.

Oxidation route using peroxide compounds: In this process, propylene and peracetic acid (in ethyl acetate) which is produced by oxidation of acetaldehyde are reacted in a series of three specially designed reactors at 50–80ºC and 90–120 MPa pressure. The reaction products are fed to the stripper where a mixture of propylene and propylene oxide are obtained as top product while mixture of ethyl acetate and acetic acid is obtained as bottom product. Both mixtures are fed to two separated columns where separation of propylene oxide, ethyl acetate, acetic acid, and heavy end takes place. Reaction: Peroxide from acetaldehyde

Oxidation of propylene

Propylene Glycol

Propylene glycol is made by hydrolysis of propylene oxide. The process steps involve are:

Reaction section: Hydrolysis of propylene oxide resulting in formation of mono­pro­ pylene glycols (MPG). Small amount of dipropylene glycol (DPG) and tripropylene glycol (TPG) are also formed. Concentration section: Concentration of glycol solution in multiple effect evaporator. Distillation section: Separation of MPG, DIPG and TPG separated from MPG column. n series of distillation column where MPG is separated in first column. Polyols

Polyols are made by polymerization of propylene oxide/ethylene oxide using a pro­ prietary catalyzed chain starter. The process consists of:

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• Raw material preparation: Preparation of chain starter and addition in reactor along with EO/PO • Reaction: Polymerization using catalyzed chain extender • Purification: Purification of raw polyol by neutralization. Isopropanol

Ever since its first commercial introduction in 1920 as one of the first petrochemicals, isopropyl alcohol has found wide use as a solvent and raw material for other chemical products like acetone, isopropyl acetate, glycerol, isopropyl and disopropyl amines, corrosion inhibitor di-isoprpopyl ammonium nitrate, floatation agent isopropyl xanthate, isopropyl myristates, etc. (Akiyama, 1974).

Process technology Two major processes for isopropanol manufacture are: • Esterification of propylene by sulfuric acid and hydrolysis CH3 – CH = CH2 + H2SO4 (CH3)2CH – O – SO3H + H2O

(CH3)2CH – O – SO3H CH3 – CH(OH)CH3 + H2SO4

• Direct catalytic hydration of propylene (vapor phase, liquid phase and mixed phase) CH3 – CH = CH2 + H2O

CH3 – CHOH – CH3 DH298ºK = – 51 kJ/mol

Although originally isopropyl alcohol was made by esterification of propylene and hydrolysis, problems of corrosion and a high heat requirement has led to the use of direct hydration process. Direct hydration of propylene: In liquid phase hydration of propylene (Tokuyama Process) silico tungstate is used. The catalytic hydration process takes at 250–27ºC at 200 atm pressure. Propylene conversion has been reported around 60–70%. Butanols (N-butanol and Iso-butanol)

Various routes for making butanol are: • Acetaldehyde route • Hydroformylation of propylene • Oxidation of butane

Condensation of acetaldehyde: The process involves aldolization, dehydration, hydrogenation

Hydroformylation of propylene: Butanol is manufactured from hydrogenation of n-butyraldehyde and iso-butyraldehyde mixture obtained by hydroformylation reaction of propylene and synthesis gas. Hydrogenation takes place at temperature

404

Chemical Process Technology

150–200ºC and 5–10 MPa pressure using copper or nickel catalyst. The butanols from the hydrogenation reactor go to a series of distillation columns for separation of light effluents and n-butanol and iso-butanol. About 88% of n-butanol and 12% iso-butanol are obtained.

Butadiene (CH2= CH – CH = CH2)

Butadiene is one of the major petrochemicals with a wide range of uses as feedstock for production of a variety of synthetic rubbers and polymer resins, the bulk of which are related to styrene butadiene rubber (SBR), nitrile rubber, chloroprene rubber, polybutadiene rubber, and acrylonitrile butadiene styrene (ABS) resin. Another major use of butadiene is in the manufacture of adiponitrile which is a raw material for the production of nylon 66. Global demand growth for butadiene is set to accelerate. Butadiene based synthetic rubbers are mainly used in the automotive industry. It is also widely used for manufacturing of engineering resins. There are four major routes for production of butadiene: • Steam cracking of naphtha • Catalytic dehydrogenation of butenes • Catalytic dehydrogenation of butanes • Dehydrogenation-dehydration of ethanol (molasses route). 2-Ethyl Hexanol

Major use of 2-ethyl hexanol is in the manufacture of di-2-ethylhexylphthalate which is used as plasticizer for vinyl resins. Other application is in synthetic lubricants, antioxidants and antifoams. 2-Ethyl hexanol is made either by the oxo-synthesis or from acetaldehyde route by condensation and hydrogenation. 2-Ethyl hexanol is also used in the manufacture of ethyl hexa acrylate. Ethyl hexaacylateprodices soft and tacky film with excellent low temperature flexibilities. Ethylhexanol also find application cable coating compositions, nitrocellulose lacquers, as softener in nitrile rubber compounds, in plastic compounds for water proof agents (Nandini Chemical Journal, July 1998, p.21, Mall 2007).

Propylene route: In first step 4n-butyraldehyde is produced along with 1-isobutyral­ dehyde. 4n-butyraldehyde is further hydrogenated to 2-ethylhexanol

Propylene Carbonate (C3H6CO3)

Propylene carbonate is prepared by reaction of propylene oxide and carbon dioxide in presence of ion-exchange resins (Mall, 2007).

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Uses: Propylene carbonate is used as special solvent. It is used in solvent extraction, plasticizers, organic synthesis, natural gas purification, and fiber spinning solvent. Acrylic Acid

Acrylic acid is a versatile chemical which find application in the manufacture of glacial acrylic acid and acrylic esters (acrylates and methaacrylates), polyacrylic acid which is used in manufacture of superabsorbent polymers, flocculants, detergents, paper chemicals and resin. SAP is used for water retention in infants’ diaper, adult in continence products and feminehygine products (Nandini Chemical Journal, July, 1999). Various acrylic esters are methyl acylate, ethyl acrylate, butyl acylate, 2-ethyl hexyl acrylate.

Process technology: Various routes for making acrylic acid are: • Acetylene route • Ethylene oxide Route • Ethylene Route • Chlorination of propianic acid • Propylene route • Formaldehyde and acetic acid route Amongst the above process propylene oxidation through acrolein is commonly used.

Propylene route: In this route, acrolein is made in first stage by oxidation of propylene in presence of mixed catalysts (prepared from oxides of bismuth, potassium, cobalt, and iron, nickel, tin, tellurium, tungsten, etc.). In the second stage, acrolein is oxidized to acrylic acid in the presence of mixed oxides of molybdenum and vanadium at 250–280ºC in the presence of steam. CH2 = CH – CH3 + O2 CH2 = CH – CHO Acrolein

20.9 AROMATIC PRODUCTION

Aromatic hydrocarbons especially benzene, toluene, xylene, ethyl benzene is major feedstock for a large number of intermediates which are used in the production of synthetic fibers, resins, synthetic rubber, explosives, pesticides, detergent, dyes, intermediates, etc. Styrene, linear alkyl benzene and cumene are the major consumer of benzene. Benzene also finds application in the manufacture of a large number of aromatic intermediates and pesticides. As per CMAI, demand for benzene is forecast to grow at an average annual rate of 2.8% per year through 2020 resulting in nearly 57 million tons of demand by 2020. Originally, the aromatics were produced from coal tar distillation, which is the by-product of destructive distillation (carbonization). Major application of toluene is as solvent. Other uses are in the manufacture of benzoic acid, chloro derivatives, nitrotoluenes, toluene sulfonic acid, toluene sulfonamide, benzaldehyde, etc. Xylenes are another important aromatic. Various sources of aromatics are mentioned in Table 20.41.

406

Chemical Process Technology Table 20.41: Various sources of aromatics

Processes

Description

Coal carbonization (Coke oven plant)

From coke oven plant during carbonization, light oil is obtained as by product which contains about 2–8 kg, 0.5–2 kg, 0.1–0.5 kg of benzene, toluene and xylene respectively per tonne of coal.

Steam cracking of hydrocarbons

Steam cracking of naphtha and light hydrocarbon like ethane and propane produce liquid product (pyrolysis gasoline) rich in aromatics containing about 65% aromatics about 50% of which is benzene. About 30–35% of benzene produced worldwide is from pyrolysis gasoline.

Catalytic reforming

Catalytic reforming is a major conversion process, which converts low octane naphtha to high-octane gasoline and produce aromatics rich in BTX. Major reactions involved are dehydrogenation of naphthalenes to aromatics, isomerisation of paraffins and naphthenes, dehydrocyclisation of paraffins to aromatics, and hydrocracking of paraffins.

BP-UOP cyclar process

In this process, BTX is produced by dearomatization of propane and butane. The process consists of reaction system, continuous regeneration of catalyst, and product recovery. Catalyst is a proprietary zeolite incorporated with a non noble metal promoter.

Dearomatization of naphtha

Process consists of extraction of aromatics from high aromatic naphtha feed without prior reforming. The process is useful for naphtha having high aromatics.

Hydrodealkylation and disproportionation

Hydrodealkylation: It involves production of benzene by dealkylation of toluene either by catalytic or thermal process. Catalytic process: Hydeal, Deltol Thermal process: HAD (ARCO), THDC Gulf Oil Disproportionation: It involves conversion of toluene into benzene and xylenes. This process consists of conversion of C8 stream into valuable o- and p-xylene having isomerisation and isomer separation stage.

Mitsubishi’s forming process

This process uses metallosilicate zeolite catalyst to promote dehydrogenation of paraffins followed by oligomerization and dehydrocyclization of paraffins followed by oligomerization.

KTI pyroforming

This process uses a shape selective catalyst to convert C 2 and C3 paraffins to aromatics.

Cheveron’s aromax process

It is similar to conventional catalytic reforming processes and L-type zeolite catalyst.

Isomerization and isomer process

This process consists of conversion of C8 stream into valuable o- and p-xylene having isomerisation and isomer separation stage.

Mitsubishi’s forming Process

This process uses a metallosilicate zeolite catalyst to promote dehydrogenation of paraffins followed by oligomerization and dehydrocyclization of paraffins followed by oligomerization.

KTI pyroforming

This process uses a shape selective catalyst to convert C 2 and C3 paraffins to aromatics.

Cheveron’s aromax process

It is similar to conventional catalytic reforming processes and L-type zeolite catalyst.

Source: Mall, 2007.

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Amongst the xylenes, about 80% of the production is of p-xylene. Finds application in the manufacture of terephthalicacid/DMT.O-Xylene used in the manufacture of phthalic anhydride and m-xylene for isohthalic acid. Typical yield of benzene, toluene, xylene in kg per ton of coal carbonized is about 2.8, 0.5–2, and 0.1–0.5 respectively (Wiseman, 1986). 20.9.1 Catalytic Reforming

Catalytic reforming is a key conversion process in a petroleum and petrochemical industry. The catalytic reforming gives flexibility to meet gasoline octane number requirement. It can also make aromatics of high market value. Catalytic reforming is a refining process that uses selected operating conditions and selected catalysts to convert. Basic objective of catalytic reforming is: • To produce high octave blending stock for motor fuel • To produce high value aromatic hydro carbon such as BTX 20.9.2 Process Description

A typical catalytic reforming process includes following three sections: • Naphtha hydrotreating • Catalytic reforming • Catalyst circulation and regeneration Basic steps in catalytic reforming involve feed preparation, temperature control, reaction in reformer and product recovery. Various types of catalytic reformer are— semi-regeneration, non-regeneration cyclic moving bed. Two types of reformer reactors are in use—radial flow and axial flow. Details of this has been covered in Chapter 19. 20.9.3 Reactions in Catalytic Reforming Process

Number of reactions takes place in catalytic reforming. Dehydrogenation is one of the major reactions. Some of the major reactions are: Dehydrogenation

Methyl Cyclohexane

MCP

Isomerization

n-Hexane

Toluene + H2 Benzene + H2 Neohexane

Dehydrocyclization of paraffins, i-paraffins to aromatics n-heptance

Hydrocracking

Toluene + H2

BTX from Petroleum

20.9.4 Major Units of Aromatic Complex

• Heavy Naphtha pretreatment unit • Catalytic reforming (Platformer unit, CCR unit continuous catalyst regenerator) • Recovery plus • Pressure swing adsorption (PSA) • BTX separation • Xylene fractionation unit for separation of o-xylene from m- and p-xylene • p-xylene andm-xylene separation by crystallization, adsorption.

408

Chemical Process Technology

20.9.5 Process Steps in Aromatic Production

Figure 20.19 gives the details description of aromatics complex. The various steps involved in aromatic production are given below: • First step in making BTX is to distill off a suitable fraction rich in natphthenes which serves as precursors for aromatics. • Catalytic reforming or a team cracking to produce an aromatic gasoline. • Preliminary treatment of this cut: fractionation and/or selective hydrogenations essentially pyrolysis gasoline • Solvent extraction to eliminate non-aromatic from aromatics • Distillation to produce pure benzene and toluene and in cased reformates used alone or blended art a pyrolysis gasoline, the following additional treatment • Distillation aromatic C8 to yield by super fractionation ethyl benzene and o-xylene, after passage through a separation column in a light cut and a heavy cut (splitter) • Production of p-xylene at low temperature with a mother liquor by product rich in m-xylene • Isomerization/delakylation/disporoportionation of m-xylene to p-xylene Separation of Aromatics

Fig. 20.19: Aromatics complex (Source: Mall, 2007; Courtesy: Macmillan India.)

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As nonaromatics and some of the aromatics have close boiling points, various methods used for their separation are: • Liquid–Liquid Extraction (DEG, TEG, tetramethylene Sath NMP-EG, Monoethyle methylforma- midamorphine, DMF) • Distillation, extractive or azeotropic distillation. • Adsorption • Crystallization Process Variables

Various process variables in the catalytic reforming for the production of aromatics are • Feed quality and N + 2A • Temperatures • Space velocity • Hydrocarbon hydrogen ration • Presence of impurities Effect of Feed Quality on Aromatic Yield

• Naphthenes dehydrogenate very fast and give rise to aromatics. Therefore, N + 2A is taken as index of reforming. Higher the N + 2A, better is quality to produce high aromatics. N = Naphthenes %    A = Aromatics % • Lighter fraction has a poor naphthene and aromatic content are, therefore, poor feed for reforming. Low IBP feed results in lower aromatics and H2 yield • Heavy fractions have high naphthene and aromatic hydrocarbon content. Therefore, good reforming feed but tendency of coke formation is high General recommended feed ranges for production 1. Benzene = 60–90ºC fraction 2. Toluene = 90–110ºC fraction 3. Xylenes = 110–140ºC fraction 4. Octane blending stock = 90–140ºC fraction p-Xylene

The p-xylene plant consists of five units are: 1. Pretreatment unit: This unit is used for reducing sulfur content to 5 ppm (max.) by dehydro-desulfurization which takes place at 330–370ºC and 24 kg/cm2 pressure in presence of cobalt molybdenum catalyst. 2. Reformer unit: To get maximum amount of C8 aromatics by reforming process (Process similar to described earlier). 3. Fractionation unit: For separation of o-, m-, and p-xylenes from combined C8 reformate and isomerisate from isomerisation unit (after clay treatment). 4. Parex unit: This unit is for the separation of p-xylene by selective adsorption using molecular sieve followed by desorption. Other method for separation of p-xylene is by crystallisation process.

Isomerization: Isomerization of C8 stream from Parex unit rich in m- and o-xylene and ethyl benzene to p-xylene, which is sent to fractionation unit for separation of high component. The bottom of the column is recycled for further recovery of xylenes.

410

Chemical Process Technology

Aromatic Conversion Processes

Because of higher demand of benzene and p-xylene in comparison to toluene and m-xylene, various processes are commercially available for conversion of toluene and m-xylene to more value added products like benzene and p-xylene. Processes are also available for conversion of paraffins into aromatics. Some of the major aromatic conversion processes and paraffin aromatization processes are given in Tables 20.42 and 20.43. Table 20.42: Aromatic conversion processes Aromatic conversion process

Process details

Isomerization

Isomerizatin of meta-xylenes to para- and orthoxylenes

Transalkylation and disproportion

Transalkylation and disproportionation of C7 and C9

Toluene disproportionation

Toluene disproportionation to xylenes and benzene

Selective toluene disproportionation

Selective conversion of toluene to paraxylene by dispropor­ tionation

Xyelene isomerizations

Maximization of p-xylene, ethyl benzene (EB) conversion and EB dealkylation process

Aromataziation

Conversion of light hydrocarbons to benzene, toluene and xylenes

Table 20.43: Paraffin aromatization processes Process

Licensor

Cycler

UOP-BP

Aroforming

IFP-Sheddon Technology Management

M-2 Forming

Mobil

Z-Forming

Research Association

Cyclar Process

Cyclar process inexpensive and plentiful LPG requires minimal feed pretreatment and product purification requirements and simplicity in operation. Reaction involved in the cycler process is shown in Figure 20.20. Process flow diagram of UOP-BP cycler process for LPG aromatization is shown is Figure 20.21.

Feed: Propane, butane, pentanes or mixture. Liquid product: Largely BTX essentially free from C6–C9 paraffinic and naphthalenes. Preparation of benzene toluene and xylene charges very little with the composition of feed. Aromatic yield: 63.6% of feed for propane 67.5% of feed for butane →  Very high H2 yield of 5.5–6% for feed → H2 purity of about 95%.

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Fig. 20.20: Reactions involved in cyclar process (Source: Hydrocarbonprocessing (Gosling, et al. 1991)

Fig. 20.21: UOP-BP cyclar process for LPG aromatization (Source: Hydrocarbonprocessing (Gosling, et al. 1991)

20.10 AROMATICS PRODUCT PROFILE, ETHYL BENZENE AND STYRENE, CUMENE AND PHENOL, BISPHENOL, ANILINE

Aromatics are backbone of organic chemical industries. Aromatic hydrocarbons especially benzene, toluene, xylene (BTX), and ethyl benzene are major feedstock for large number of intermediates which are used in the production of synthetic fibers, resins, synthetic rubber, explosives, pesticides, detergent, dyes, intermediates, etc. Styrene, linear alkyl benzene, and cumene are the major consumer of benzene. Product profile of aromatics is shown in Figure 20.22.

412

Chemical Process Technology

Fig. 20.22: Product profile of aromatics

20.10.1 Ethyly Benzene and Styrene

Ethyl benzene and styrene are two important aromatics. Ethyl benzene is mainly used for making styrene. Styrene which finds application in synthetic rubber and polymer industry for the manufacture of SBR and polystyrene, ABS plastic. Major route for styrene manufacture is dehydrogenation of ethyl benzene which is manufactured by alkylation of benzene. Styrene plant consists of two major units. The process involves: • Production of ethylene either from molasses route or by naphtha/natural gas cracking • Production of ethyl benzene by alkylation of benzene • Dehydrogenation of ethyl benzene to styrene

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Ethyl Benzene

Ethyl benzene is made by alkylation of benzene with ethylene. Ethylene can be produced from either from molasses route or naphtha/gas cracker. The convention alkylation catalysts are metal chlorides (BF3, AlCl3, etc.) and mineral acids (HF, H2SO4). However, with development of zeolite, now the benzene alkylation I is done by using ZSM-5 catalysts using vapor-phase process (Mobil-badger Process) and liquid phase alkylation using MCM-22 zeolite proprietary catalyst-based catalyst.

Vapor phase alkylation of benzene: The process consists of vapor phase alkylation of benzene with ethylene using zeolite catalyst in a fixed bed catalytic distillation technology. Alkylation and distillation take place in the alkylator. Unreacted ethylene, and benzene vapor are condensed and fed to the finishing reactor where the remaining alkylation is completed in the presence of a catalyst. The product stream goes to fractionating columns where ethyl benzene is separated from the higher ethylated benzene and heavy ends. Higher ethylated alkyl benzene is sent to the trans-alkylator where its trans-alkylated to produce additional ethyl benzene (Petrochemical Processes 2003” Hydrocarbon processing March 1999, p.10). Liquid phase alkylation of benzene with ethylene using MCM-22 catalyst: In this process, alkylation of ethylene takes place in a liquid filled alkylator reactor containing multiple fixed beds of MOBIL MCM-22 catalyst. During alkylation, ethyl benzene and small quantity of polyethylbenzene are formed which is converted to ethyl benzene using trans-alkylation catalyst. The product streams from alkylator and trans-alkylator are sent to various fractionating columns for separation of product ethyl benzene, polyethylbenzene, benzene, gases and heavy ends. Styrene

C6H6 + C2H4

C6H5CH2CH3

Styrene is one of the most important monomers for the production of polymers, resins and rubber. The biggest consumer of styrene monomer is polystyrene, other major derivatives are expanded polystyrene, styrene butadiene (SB) latex, SB rubber, styrene block co-polymers (e.g. ABS, MBS, SBS) (SNOW: an innovative technology for styrene synthesis, hydrocarbon Asia, 2007, p.42). Styrene is made by catalytic dehydrogenation of ethyl benzene. C6H5CH2CH3

C6H5CH = CH2 + H2

Styrene can be also directly recovering from raw pyrolysis gasoline derived from cracking of naphtha, gas oils Using GT styrene process.

Lumus/UOP EB one process: Styrene is made by catalytic dehydrogenation of ethylbenzene in the presence of steam. In Lumus/UOP EB one process involves first alkylation of benzene with ethylene followed by dehydrogenation of EB to form styrene. The benzene and recycled benzene are preheated the liquid phase reactor containing zeolite catalyst. The polyethylbenzene formed during alkylation is fed to another reactor for transalkylating with benzene. Transalkylation reaction is isothermal and reversible in distillation section. The reactor effluent from both reactions is sent to the distillation section for separating ethyl benzene from polyethylbenzene. C6H6 + C2H4

C6H5CH2CH3

C6H5CH2CH3 + C6H6

2C6H5CH5CH3

C6H5CH5CH3 + C6H6

C6H5CH2CH3

414

Chemical Process Technology

Ethyl benzene and recycled ethyl benzene are then dehydrogenated to styrene in the presence of steam at high temperature (550–680ºC) under vacuum in a multistage reactor. C6H5CH2CH3 H2 + ½O2

C6H5CH = CH2 + H2 H2O

During dehydrogenation stages, air or oxygen is introduced to partly oxidize the hydrogen to reheat the process gas and to remove the equilibrium constrain for dehydrogenation reaction (HC, 1999). Reactor effluents are cooled to recover waste heat and condensed, uncondensed gases are used as fuel. The condensed product containing styrene is sent to distillation columns for separating styrene monomer, unconverted ethyl benzene is recycled. Toluene is formed during the process which is recovered. C6H5CHCH2 + H2 C6H5CHCH2

C6H5CH3 C6H5CH3 + C

GT styrene process: Styrene can be also directly recovered from raw pyrolysis gasoline derived from cracking of naphtha, gas oils Using GT styrene process. Raw pyrolysis gasoline is fractionated into a heart cut C8 stream from which styrene is separated by extractive distillation. Innovative SNOW technology: The snow technology has been jointly developed by Snamprogetti and Dow represents a technological and economical breakthrough in styrene production and uses benzene and ethane as raw material which is dehydrogenated in the same reaction for EB dehydrogenation. SNOW reactor is rise type (SNOW: An innovative technology for styrene synthesis, Hydrocarbon Asia, 2007, p.42). 20.10.2 Phthalic Anhydride

Phthalic anhydride first became commercially important during the nineteenth century as an intermediate for dyestuff industry. However, now phthalic anhydride is largely used for the manufacture of plasticizers, alkyd resins, and unsaturated polyester resins where about 95% of the phthalic anhydride production is consumed. With an aggregate installed capacity of 267,200-tpa across India, major PAN producers include IG Petrochemicals Ltd and Thirumalai Chemicals Ltd. Consumption pattern of PAN is shown in Figure 20.23. List of the phthalic anhydride manufacturers in India is given in Table 20.44.

Fig. 20.23: Consumption pattern of PAN (Source: Dutta, P. Phthalicanhydride: A Technocommercial Profile Part I: Indian Scenario, Chemical Weekly, Jan 1, 2008 p.209.)

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Table 20.44: Phthalic anhydride manufacturers in India Company

Location

I.G. Petrochemicals Ltd.

Taloja, Maharashtra

120,000

Thirumalai Chemicals Ltd.

Ranipet, Tamil Nadu

100,000

Asian Paints Ltd.

Ankleshwar, Gujarat

25,200

Mysore Petrochemicals Ltd.

Raichur, Karnataka

12,000

SI Group Ltd.

Thane, Maharashtra

10,000

Total

Installed capacity (TPA)

267,200

Source: Dutta, P.” Phathalicanhydride: A Techno-commercial Profile Part I: Indian Scenario, Chemical Weekly Jan1, 2008 p.209.

The basic raw material for the manufacture of phthalic anhydride is naphthalene and o-xylene. Phthalic anhydride was manufactured from naphthalene. With the availability of large amount of o-xylene as a byproduct during p-xylene production, now phthalic anhydride is made from o-xylene. Both vapor phase and liquid phase oxidation of o-xylene are available. Phthalic anhydride is produced by oxidation of naphthalene in the gas phase using vanadium pentoxide catalyst supported on silica or silicon carbide promoted with various other metal oxides, e.g. titanium oxide (wire) in either a fixed bed multiple reactors or fluidized bed reactor.

Production of phthalic anhydride from o-xylene is similar to naphthalene route. Catalytic oxidation of o-xylene is done either in fixed bed catalytic reactor having multi tube or fluidized bed reactor in the presence of vanadium pentoxide and titanium oxide catalyst.

20.10.3 Cumene

Cumene is made by alkylkating benzene with propylene using zeolite catalyst. Following three major processes are available

416

Chemical Process Technology

1. Catalytic distillation technology: The process uses a specially formulated zeolite alkylation catalyst in a proprietary catalytic distillation (CD) process and a transalkylator reactor using zeolite catalyst. In CD column combines both reaction and fractionation takes place. 2. Liquid phase q-max process: In this process, cumene is produced by liquid phase alkylation of benzene with propylene in presence of zeolite catalyst. 3. Cumene by Mobil Badger process: The process produces cumene from benzene and any grade of propylene using a new generation of zeolite catalysts from Exxon m Mobil. The process includes a fixed bed alkylation reactor and a fixed bed transalkylation reactor and distillation section. 20.10.4 Phenol

According to SRI consulting report 2010 global production and consumption of phenol were both around 8.0 million tons with global capacity utilization of 77%. Phenol consumption is expected to average growth of 5.1% per year from 2009 to 2014 and around 2.5% from 2014–19. Phenol is consumed mainly for production of bis-phenol A and phenolic resins which accounted for 42% and 28%, respectively of total phenol consumption in 2009. Various routes for phenol: • Phenol from cumene • Phenol from benzoic acid • Phenol from chlorobenzene • Benzene sulfonation. With the availability of propylene now phenol is made by cumene route with added advantage of acetone as by product. 20.10.5 Aniline

The process of aniline manufacture involves two stages: Companies which produce aniline is given in Table 20.45. Table 20.45: Company-wise production of aniline Company

Years

Production

Sales quantity

Sales value

Gujarat Narmada Valley Fertilizers Ltd. 2008–09

27,077

27,090

1,865

2009–10

33,848

33,825

2,167

2010–11

39,896

–

–

2009–10

5,538

5,231

309

2010–11

1,833

1,826

135

Hindustan Organic Chemicals Ltd.

Source: Chemical Weekly January 24, p.198, 2012.

Nitrobenzene Route

• Nitration of benzene with nitric acid • Hydrogenation of nitrobenzene to aniline

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Ammonolysis of chlorobenzene

Ammonolysis of phenol

20.10.6 Benzoic Acid (C6H5COOH)

Benzoic acid is the simplest member of the aromatic carboxylic acid. Benzoic acid, which is used in the manufacture of caprolactam, phenol, terephthalic acid and used as mordant, is manufactured by liquid phase catalytic oxidation of toluene in presence of cobalt acetate at 165ºC and 11.2 atm pressure. Major processing steps in the manufacture of benzoic acid consist of: • Catalytic liquid phase air oxidation of toluene • Stripping of unreacted toluene and light end precursors from the benzoic acid for recycle • Distillation to recover benzoic acid as a pure overhead product

418

Chemical Process Technology

20.10.7 Bisphenol

Bisphenol is an important building block and its measure use is in the manufacture of polycarbonate plastic and epoxy resins. Other uses include in flame retardants, unsaturated polyester resin and polyacrylate, polyetherimide and polysulfone resin (Chemical Weekly, 2008). India and Global Demand of Bisphenol (Chemical Business, 2012)

• Demand of bisphenol in India during 2010–11 was 30,000 tons per annum • Global installed capacity: around 5.2 million tons • Global demand around 4.2 million tons • Global growth rate in demand 5–6% • Polycarbonate resins are the largest and fast-growing BPA market, consuming 60% of the global production. Process Technology

Various process technologies available for manufacture of bisphenol are: • Condensation of phenol with acetone • Condensation of phenol with alkenyl phenol • Condensation of phenol with ethylene and acetylenes • Condensation of phenol with alkyl benzene. Bisphenol from Phenol and Acetone

Bisphenol is synthesized by a condensation reaction between phenol and acetone using proprietary cation exchange resin-base catalyst (4PET) in a packed bed reactor. The catalyst has higher acetone conversion, higher BPA selectivity and longer life. Reactor effluents are process in series of distillation column for separation of product bisphenol, unreacted acetone, water, phenol. Phenol and acetone are recycled. Bisphenol is purified by crystallization where bisphenol crystals are separated from the impurities. Although the impurities are removed with mother liquor, however, two stage crystallization can lower the impurities captured in the crystal. Bisphenol is sent to prilling tower to get final bisphenol in the form of spherical prill. BIBLIOGRAPHY 1. 2-Ethyl hexanol-Indian and global scenario. Nandini Chemical Journal, July 1998, p.21, Mall 2007 2. “Acrylic acid-investment opportunity”, Nandini Chemical Journal July 1999, p.10. 3. Chte V, Singal S, Koppel P, Ravikumar R. “ Syngas fro gasification as an alternate feedstocks for chemicals, Petrochemicals and Power’ Chemical Industry Digest, February 2016, p.70. 4. “Energy Conservation Process Industry”, Energy Conservation Department, Engineers India Ltd., New Delhi, 1992. 5. “Petrochemical Processes 2003” Hydrocarbon Processing, 2003. 6. Akiyama S. “Direct hydration of C3H6 yields Isopropyl alcohol”, Chemical Engineering, July 9, 1973. 7. Austin GT. “Industrially significant organic chemicals part 6” Chemical engineering, May 27, 1974. 8. Badoni RP, Kumar Y, Uma Shanker, Prasada Rao TSR. Chemical Engineering World, Vol. 31, 12, December 1996, p. 105.

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9. Bhatacharya D, Brijesh Kumar, Raj Gopal S. “Indian: A versatile indigenous process Technology”, J of Petrotech July–Sep 2011, p.56. 10. Briggs BA, Simpson SO, Lemerk CA, Ward DJ. “Fluid catalytic cracker as a source of petrochemical olefins”, Chemical Age of India, Volume 38, No. 1, 1987, p. 21. 11. Burns KG, Ciarella DJ, Rowe CT, Sigmon JL. “Chemicals increase ethylene plant efficiency”, Hydrocarbon Processing, January 1991, p.83. 12. Chambers LE, Potter WS. “Design ethylene furnace part I, Maximum ethylene”, Hydrocarbon Processing, January 1974, p.121. 13. Chauvel A, Lefebvre G. “Petrochemical Processes”, 1989, Volume I, Edition Technip, Paris. 14. Chauvel A, Lefebvre G. “Sources of olefinic and aromatic hydrocarbons’, Petrochemical Processes, 1985, Volume I, edition Technip, p.129. 15. Chauvel A, Lefebvre G. “Sources of Olefinic and aromatic hydrocarbons”, Petrochemical Processes, 1985, Volume I, edition Technip, p.129. 16. Chauvel A, Lefebvre G. “Treatment of olefinic C4 and C5 cuts”, in Petrochemical Processes, Synthesis-Gas derivatives and major hydrocarbons, Editions Technip Paris 1985, p.195. 17. Chemical Business, Annual Report 2010–11 Dept of Chemicals & Petrochemicals (Ministry of Chemicals & Fertiliser), Govt. of India, April 2ii, p.22. 18. Chemical Business, January 2012, p.12. 19. Chemical Industry Digest, August 2010, p.5. 20. Chemical Industry Digest, July 2012, p.29. 21. Chemical Industry Digest Vol. 30, October 2017. 22. Chemical Industry Digest AuguVolume 30, August 2017, p.13. 23. Chemical Industry Digest September Volume 30,2017, p.11. 24. Chemical Industry Digest Annual January 2018, p.15. 25. Chemical Engineering World February 2011, p.71. 26. Chemical Weekly, December 27, p.198, 2011. 27. Chemical Weekly, January 1,2008, p.209. 28. Chemical Weekly, January 24, 2012, p.198. 29. Chemical Weekly, June 10, 2008, p.187. 30. Chemical Weekly, November 15, p.199, 2011. 31. Chemistry Industry News, March 2004 SRI consulting, World Petrochemicals Program 32. Convers A. “Make chemicals from C4 olefinic fractions”, Chemical Age of India, 33. Dave RR, Khurana ML. “Evaluation of Feedstocks for aromatics, olefins and surfactant Plants”, Proceeding of National workshop in crude oil evaluation, edited by Nagpal, JM, Tata Mcgraw Hill Publishing Company Limited, New Delhi. 34. Desai DM. “New technologies for Petrochemical’s part-1”, Chemical Business, Sept.–Oct. 4, 25, 1991. 35. Dharia D, Letzsch W, Kim H, McCue, Chapin L. “Increase light olefins production”, Hydrocarbon Processing, April 2004, p.61. 36. Dutta P. “Phathalic anhydride: A Techno-commercial Profile Part I: Indian Scenario. 37. Eng C, Tallman MJ, Oriss R, Miller R. “Economic routes to propylene”, Hydrocarbon Asia, July/ August 2004, p.36. 38. Feigl J, Schmidt G. “Consider furnace replacement for existing olefin units”, Hydrocarbon Processing, June 2007, p.45. 39. Ganapati M. “Aromatic technologies state of the art”, Chemical Weekly, 8 Dec. 1992, p.129. 40. Gosling CD, Wilcher FP, Sullivan L, Mountiford RA. “Process LPG to BTX products”, Hydrocarbon Processing, December 1991, p.69. 41. Gunardson HH, Abrardo JM. “Produce CO rich synthesis gas”, Hydrocarbon Processing, Volume 66, No. 4, 1998, p.87.

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42. Gupta AK. Invited lecture, AICTE Staff development programme on Hydrocarbon Engineering, IIT Roorkee, 3–22 January, 2000. 43. Gupta AK. Invited lecture, QIP short term course on Advances in Hydrocarbon Engineering, IIT Roorkee, 23 June-4 July, 2003. 44. Gupta AK. Invited lecture, QIP short term course on Advances of Petrochemicals, organized QIP Center, Indian institute of Technology, Roorkee (India), 21 June-5 July, 1994. 45. Handa SK. “Feedstock choice in petrochemicals industry” Chemical Industry Digest, August 2010, p.60. 46. Howard Rappaport “Plyolefins Feedstocks & Market” CMAI. PlastIndia-Feb-2009. 47. http://www.worldscibooks.com/chemistry/p702.html 48. Huang Sun-Yi, Lipp DW, Farinto RS. “Acetylene derived chemicals” in KirmOthomer encyclopedia of Chemical technology, Fifth edition volume 1 Wiley-Interscience, p.227. 49. Hydrocarbon Processing, March 1999, p.10. 50. Joshi P. “Special feature on future of oil & gas sector India” FIPI Volume 16 issue 1 Jan–March 2017. 51. Kappor S, Vaidyanatht RA, Menegaz D. “Why integrate refineries and petrochemical plants” Hydrocarbon processing February, 2009, p.29. 52. Little DM. “Catalytic Reforming”, 1985, Penn Well Books, Tulsa, Oklahoma. 53. Mall ID. NPTEL lecture Organic Chemical technology 2013. 54. Mall ID. “Petrochemical process technology”, First edition, New Delhi, Macmillan India 2007. 55. Mall ID. “Petrochemical Process Technology”, Re (print 2015, Second edition., Laxmi Publication 2016 New Delhi. 56. Masood R. “Role of raw materials in petrochemical industry”, Chemical Industry News, July 2002, p.13. 57. Meyers RA. ‘Handbook of Petroleum Refining processes’, McGraw Hill, 1986. 58. Morgan M. “C5 hydrocarbons and derivatives new opportunity”, Chemistry and Industry 2 September, 1996, p.646. 59. Moulijan JA, Makkee M, Diepen AV. “Chemica Process Technology”, John Wiley & Sons, 2001. 60. Nee RD. “The evolution role of fluid catalytic cracking in the petrochemicals market”, Hydrocarbon Processing, March/April 2003, p.26. 61. Oil and Gas Journal, Vol 109, issue 27, April 7,2011. 62. Petrochemical Economics - Technology Selection in a Carbon Constrained World. 63. Petrochemical Overview, SRI Consulting Chemistry Industry News, March 2004. 64. Petrochemical Processes, 2003. Hydrocarbon Processing March 2003. 65. Pujaodo PR, Vora PV. “Make C3–C4 olefins selectively”, Hydrocarbon Processing, vol.69, no.3, March 1990, p.65. 66. Sarin AK. “Refinery and Petrochemical integration” Chemical Industry digest Feb 2016, P.49. 67. Singh S. Chemical Industry Digest September 2017, p.13. 68. SNOW: An innovative technology for styrene synthesis, hydrocarbon Asia, 2007, p.42. 69. Styrene market and Asian demand to drive global benzene markets, Chemical Weekly, November 22,2011, p.205. 70. Taraphdar T, Yadav P, Prasad MK. “Natural gas fuels the integration of refining and petro­ chemicals”, PTQ quarterly, Q3, 2012, p.39. 71. Teng J, Xie Z. “OCC process for propylene production”, Hydrocarbon Asia May/June 2006, p.26. 72. Towfighi J, Sadramdi M, Niuei A. “Simulation of furnace length”, Petrochemical Technology, Quarterly Autumn, 2001, p.137. 73. Venner RM, Kantorowicz SI, “Metathesis: refinery and ethylene plant applications”, Petroleum Technology QuarterlySummer, 2001, p.141.

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74. Vermilion WL, Niclaes HJ. “Petrochemicals from the FCC unit”, Hydrocarbon Processing, September 1977, p.193. 75. Wiseman P. “Petrochemicals”, 1986, Ellis Horwood Ltd, Chichester, p.33. 76. Wiseman P. “Petrochemicals”, 1986, Ellis Horwood Ltd, Chichester, p.33. 77. www.indiainfoline.com/sect/chor/ch05.html 78. Wysiekierski AG, Fisher G, Schillmoller CM. “Control coking for olefins plant”, Hydrocarbon Processing, January 1999, p.97.

Polymer, Elastomer and Synthetic Fiber

21

21.1 INTRODUCTION

Use of plastics, synthetic rubber and fibers has taken enormous importance in our daily life in various forms. Increasing population increasing cost of cotton has increased the use of synthetic fiber in textile industry. Use of various synthetic fibers like polyester and nylons have also increased in automobile sectors. Although polymers were accidentally synthesized, however as more and more applications were later discovered, polymers have penetrated into all fields of application and in volume of around 205 million tons per annum including standard polymers, engineering resins, elastomers, duromers, fibers and textiles, dispersions. Polyolefins (LDPE, LLDPE, HDPE, and polypropylene) are by far the largest group of thermoplastic polymers (CMAI, 2003). Polypropylene resins along with polyester resins (PET) are one of the fastest-growing categories of commodity thermoplastic resins in the world. The United States and China now represent more than 15% and 22%, respectively of world polypropylene consumption. Amongst the plastics, thermoplastic market represents approximately 10% of global chemical industry. World polymer demand in 2010 was 280 million tons. Types of polymer and its global demand are shown in Figure 21.1. Typical consumption of plastic by industry and as polymer is shown in Figure 21.2. PET resins in packaging industry has revolutionized our life especially in the forms of PET bottles for water and soft drinks.

Fig. 21.1: World total polymer demand in 2010 approx: 280 million tons (Courtesy: CAMI Consulting, 2010)

Plastics have become one of the important commodities giving big challenge to steel and stainless steel which is shown in Table 21.1. Plastics can be readily, efficiently and continuously converted to various useful products like packaging films, tubes and pipes, 422

Polymer, Elastomer and Synthetic Fiber

423

tanks, cables, fibers, molded bottles, extruded sheets, polymer composites (Trivedi, 2017). Volume wise its production is more than steel comparative production (MMTA).

Fig. 21.2: Plastic consumption, according to industry and polymer (Source: Ways to get rid of the plastic, Chemical News, October 2011, p.21.) Table 21.1: Comparative production of steels and polymers Materials

MMTA

Specific gravity range

Steel

1800

7.5–8.0

Stailess steel

450

7.8–8.0

Polymers

380

0.95–1.5

Plastic materials are lighter than metals and due to this plastic products are uses is almost 7–8 times in volumes as compared to steel. Plastics can be reinforced with talk or calcium carbonate or glass fibers or carbon fibers and other fillers and additives. Plastics may be foamed to lower density (Trivedi, 2017). Some of the recycled or discarded plastics may be recycled or may be re-polymerized. Per capita consumption of plastic in India is low 9.7 kg as against 100 kg or more in advance countries. The plastic industry in India is growing at 8.1% every year. Estimate indicates that production is growing from 14 million tons per year to 30 million tons per year in 2030 (Chemical News, April 2018) Polyolefins represent the largest segment of the global thermoplastics business at approximately 88 million tons (about 62% of the total market in 2002). Major success factors for polyolefins are: easy accessible, reasonable raw materials (oil and natural gas based), low production cost by modern energy saving and non polluting processes, resources saving products, environmentally harmless products, energetically exploitable products after usage, broad product portfolio, and tailor made products. Various types of polymer and their uses are illustrated in Figure 21.3. Global consumption of polyethylene in 2009 was approximately 64 million metric tons. Global capacity utilization was 80% in 2009, down from 82% in 2008. Polyvinyl Chloride (PVC) is the second largest commodity thermoplastic in the world, after

424

Chemical Process Technology

the polyethylenes. According to global production and consumption of polyvinyl chloride (PVC) in 2010 was approx. 34 million metric tons. Average global utilization of polyethylene rates are expected remain under 80% during the next five years, gradually increasing to the high-80s by 2019. World polyethylene per capita consumption is targeted to grow from 9.0–11.0 kg from 2001 to 2006. High density PE (HDPE) accounted for around 45% of global polyethylene consumption in 2009, followed by linear low density PE (LLDPE) and low density PE (LDPE). Figure 21.4 shows the percent uses of plastic in different fields. Due to non-biodegradable nature of the plastics, now biodegradable plastic or bioplastics are also getting importance. However, increased cost is major deterrent in its use on large scale.

Fig. 21.3: Various types of polymer and their application (Source: Mall, 2007)

Global demand for polymers is estimated to increase at 5% per annum to reach 227 MMT by 2015. Polymer demand in India is expected to grow at 13–14% per year and will account for 9% of global polymer demand by 2015. The total polymer demand in India by 2015 is estimated to be around 22 MMT. Table 21.2 gives the detail of India share in global polymer demand. Table 21.2: India’s share in the global polymer demand by 2015 2004

2015

India

4%

9%

Rest of world

96%

91%

Source: Dept of Chemicals & Petrochemicals, Govt. of India, IMACS Analysis.

Polymer, Elastomer and Synthetic Fiber

425

Fig. 21.4: Uses of plastics in different fields (Source: Envis, Volume 5, Issue 2, April–Jun 2007, p.15.)

21.2 PLASTIC INDUSTRY IN INDIA

• Consumption—4.8 million tons/annum • Over 96% (4.6 million tons) is accounted for commodity plastics • Per capita consumption, 4.8 kg as against world average 20 kg • Projected demand in 2010–11 was 8.5 million tons (growth rate @15%) • Raw material prices are influenced by international demand and supply of crude oil. Reliance polymers is one of the largest producers of polymers in the world with a combined capacity of 4.4 million metric tons per annum across their brands Repol PP (Polypropylene), Reliance PE (polyethylene) and rayon (PVC) and finding application in diverse sectors packaging, agricultural, infrastructure, automobile, health care and lifestyle resulting in better products. Reliance is also major producer of PET resins (Table 21.3). Table 21.3: Installed capacity and production of performance plastics 2015–16 (in thousand tons) Performance plastics ABS resin Nylon 6 and nylon 6,6 Polymethyl methacrylate (PMMA) Styrene acrylonitrile (SAN) PET chips/polyester chips PTFE (Teflon)

Installed capacity

Production

128

117

28

21

4

1

136

99

2,199

1,453

20

9

426

Chemical Process Technology

21.2.1 Classification of Polymer

Natural and synthetic polymers could be classified in several other ways, viz., organic and inorganic; on the basis of physical properties as plastomers (plastics), elastomers (elastic), and fibrous (fiber); on the basis of response to temperature as thermoplastics and thermosets. Various ways of classification of polymer is given in Figure 21.5 (Mall, 2007). Polymers or resins are generally classified in two broad categories: thermoplastic and thermosetting. Repeated heating and cooling does not alter the chemical nature of thermoplastic while thermosets are permanent setting resin and once solidified these materials may not be reshaped or formed by applying heat. Thermoset plastic are stronger than thermoplastic (Mall, 2007). Thermoplastics

Thermoplastics are organic chain polymers that usually become soft when heated and can be molded under pressure. Thermoplastic resin are linear or branched chain polymers with little or no cross linking (Hatch and Mater, 1979). Various thermoplastic resins are polyethylene, polypropylene, PVC, polyvinyl acetate, polymethyl methacrylate, polycarbonates, and polystyrene (Table 21.4). Thermosetting Plastics

Thermosetting plastics are a network of long chain molecules that are cross-linked which gives the polymer a three-dimensional infusible structure. They polymerize irreversibly under heat or pressure to form hard, rigid mass. Various thermoset resins are phenol-, urea-, melamine-formaldehydes, polyurethane, alkyd resins, epoxy resins, etc. Various thermoset resins are given in Table 21.5. Table 21.4: Major thermoplastic polymers Name

Abbreviation Family

Formula

Melting temp.

Density

Low density polyethylene

LDPE

Polyolefin

110 (Tm) 0.910

High density polyethylene

HDPE

Polyolefin

120 (Tm) 0.950

Polypropylene

PP

Polyolefin

175 (Tm) 0.902

Polyvinyl chloride PVC

Vinyl

100 (Tg)

1.35

Polyvinyl acetate

PVA

Vinyl

Polystyrene

PS

Styrenic

100 (Tg)

1.05

Contd...

Polymer, Elastomer and Synthetic Fiber

427

Table 21.4: Major thermoplastic polymers (Contd...) Name

Abbreviation Family

Acrylonitrile butadiene styrene

ABS

Styrenic

Acrylonitrile styrene

SAN

Styrenic

Polymethylmethacrylate

Formula

Melting temp.

Density

—

—

—

—

—

—

Acrylic

Polyhexamethylenediamide

Nylon 66

Polyamide

265 (Tm) 1.14

Polycaprolactum

Nylon 6

Polyamide

225 (Tm) 1.14

Polyethyleneterephthalate

PET

Polyester

270 (Tm)

Polybutyleneterephthalate

PBT

Polyester

250 (Tm) 1.3

Polycarbonates

PC

Polyester

190 (Tg)

Polyethers

181 (Tm)

Polyacetals

1.2

Source: Hatch and Matar, 1979. Table 21.5: Various thermoset resins S. no.

Name

Family

1.

Polyurethane

Ester-amide

2.

Alkyd resins

Polyester

3.

Unsaturated polyesters

Polyester

4.

Epoxy resins

Polyether

Formula

Contd...

428

Chemical Process Technology Table 21.5: Various thermoset resins (Contd...)

S. no.

Name

Family

Formula

5.

Phenol formaldehyde

Phenolic

6.

Urea formaldehyde

Urea

7.

Melamine formaldehyde

Melamine

Source: Hatch and Matar, 1980.

21.3 ELASTOMER

Rubber can be broadly classified as natural rubber and synthetic rubber. Natural rubber is a product of the tree Heveabrasiliensis while synthetic rubber is elastomer derived from petrochemical feedstock product. Table 21.6 shows the general and special purpose rubber. Table 21.6: General purpose and special purpose rubber General purpose

Special purpose

• Styrene butadiene rubber (SBR) • Styrene butadiene • Emulsion/solution • Polybutadiene (BR) • Polyisoprene (PS) • Ethylene propylene (EP) and ethylene propylene diene (EPDM) • Butyl rubber (BR) • Ethylene vinyl acetate (EVA)

• Polychloroprene (CR) • Styrene isoprene rubber (SIR) • Acrylonitrile butadiene (NBR) • Silicone rubbers • Acrylic rubber • Polyester urethanes • Polyether urethane elastomer • Epichlorohydrin • Polyisobutylene • Polydialkyl siloxane (Silicon rubber) • Vinyl pyridine butadiene rubber (PBR) • Hypalon • Polysulfide rubber • Fluorocarbon rubber

21.4 SYNTHETIC FIBER

Synthetic fiber industry is playing an important role in providing one of the basic needs of mankind. Synthetic fiber may be broadly classified as woven and non-woven fiber.

Fig. 21.5: Classification of polymer

Polymer, Elastomer and Synthetic Fiber

429

430

Chemical Process Technology

With development of petrochemical industry there has been significant growth in the synthetic fiber industry due to availability of raw materials. Some of the important petrochemical-based synthetic fibers are nylon 6, nylon 6,6, acrylic fiber, polyester, polypropylene fiber, polyurethane fiber, etc. Cellulosic-based synthetic fiber especially viscose rayon has been providing synthetic fiber before arrival of the petrochemicalbased fiber. Some of the important cellulose-based fibers are viscose rayon, acetate rayon, cuprammonium rayon, etc. • First manmade fiber—naturally occurring polymers from cellulose and protein— Viscose rayon first manufactured in 1886 in England • First true synthetic in 1935—Nylon by DuPont • Nylon was followed by acrylic and mod acrylic fiber based on acrylonitrile in 1950. • Polyester fiber in 1953 in India • Viscose rayon in India started in 1950 • Acetate rayon in 1954 in India. Installed capacity and production of synthetic rubber, polyester yarn/fiberfil, and fiber intermediates in 2015–16 are given in Tables 21.7 to 21.9. World consumption of non-woven man-made fiber is mentioned in Table 21.10. Table 21.7: Installed capacity and production of synthetic rubber 2015–16 (in thousand tons) Synthetic rubber

Installed capacity

Production

Styrene butadiene rubber (SBR)

271

379.13

Polybutadiene rubber (PB)

114

114

25

0

Nitrile rubber (NBR) Ethyl vinyl acetate (EVA) Total synthetic rubber

15

2

425

495.13

Source: Annual Report 2016–17, Department of Chemicals and Petrochemicals, Ministry of Chemicals and Fertilizers, Government of India. Table 21.8: Installed capacity and production of polyester yarn/fiberfil 2015–16 (in thousand tons) Synthetic fibers

Installed capacity

Production

Polyester filament yarn

2,820

2,179

Polyester staple fiber

1,170

1,040

Polyester staple fiberfil

69

51

Polyester industrial yarn

22

15

Rayon grade pulp: Harihar Polyfiber, Gwalior Rayon, Travancore Rayon, Baroda Rayon, Andhra Rayon, Shri Ram Rayon, Kesoram Rayon, South India Viscose Rayon. Caprolactam: Gujarat State Fertilizer and Chemicals (Vadodara), Fertilizer and Chemicals (Travancore). DMT/purified terephthalic acid (PTA): Bombay Dying, BRPL, Reliance (Patal Ganga, Hazira, Vadodara), IOC (Panipat). p-Xylene: BRPCL, Reliance (Patal Ganga, Hazira, Vadodara, Jamnagar), Indian Oil Corporation projected consumption of fiber in India.

Polymer, Elastomer and Synthetic Fiber

431

Table 21.9: Installed capacity and production of fiber intermediates 2015–16 (in thousand tons) Fiber intermediate

Installed capacity

Production

Acrylonitrile

41

2

Caprolactam

120

86

Monoethylene glycol (MEG)

1,153

1,001

Purified terephthalic acid

3,753

3,432

Total fiber intermedites

5,067

4,079

Source: Annual Report 2016–17, Department of Chemicals and Petrochemicals, Ministry of Chemicals and Fertilizers Government of India. Table 21.10: World consumption of nonwoven man-made fibers (% of total) Man-made fibers Polyester

1998

2000

24

Polyamides Acrylic fibers

1.5

2005

2007

22.5

23.0

1.5

1.5

23 1.5

1.5

2.0

3.0

3.0

62.0

63.0

62.7

62.7

Viscose rayon

8.0

8.0

7.0

7.0

Other synthetic fibers

3.0

3.0

2.8

2.8

Total consumption, million tons

2.4

3.3

2.5

4.0

Polypropylene fibers

Details of man-made fiber is shown in Figure 21.6.

Fig. 21.6: Man-made fiber and raw material (Source: Mall 2017, NPTEL 2013).

432

Chemical Process Technology

Terms Used in Synthetic Fiber Industry

• Denier: It is the measure of coarseness of a yarn and is defined as the weight in grams of a length 9000 meters of a yarn or filament. • Tex and Millitex: Tex is the defined as the weight in grams of 1000 meters. • Tenacity: The tenacity or strength of rayon is expressed as grams per denier. If a load of 250 g will just break at a denier yarn, the tenacity is said to be 2.5 g per denier. • Elongation at break: Elongation is an important property of a yarn. If a length of 100 cm of a yarn can be stretched 112 cm before it breaks, it is said to have elongation at break of 12%. • Moisture regain: Regain of a fiber is the percentage of moisture calculated on oven dry basis. • Staple: The chopped fiber is called staple. • Filament yarn: Reeled filaments yarn • Elasticity: The elasticity of a fiber is its ability to recover from strain. 21.4.1 Overview of Indian Man-made Textile Industry

• Second largest producer of cellulosic fiber/yarn • Fifth largest producer of synthetic fibers/yarns. • Production of synthetic fibers nearly 10 lakh MT (2009–10) • Production of synthetic yarn about 15 lakh MT (2009–10). Indian: Fiber Demand

• Currently All fiber demand is arround 80 lakh MT • Cotton 43 lakh MT and polyester around 30 lakh MT • All fiber demand to grow nearly 130 lakh MT by 2020 @5% CAGR • PFY has grown at around 10% CAGR in last decade and is likely to sustain similar growth rates. Indian: Textile Growth Drivers

• Higher disposable income and changing lifestyle • Increasing fashion awareness even in tier B and C cities • New emerging segment of non-apparel application • Increasing urban households and working women population • Rapid spread of organized retail sector • Rise in exports to traditional and new markets • Favorable government policies like TUFS, SITP (textile parks). Emerging scenario of man-made fiber is given in Table 21.11. Table 21.12 gives the details of demands of man-made fiber in India. Brief details of various synthetic fiber producing units in India is given in Table 21.13. Table 21.14 gives the details of rising demand of polyester. Per capita consumption of cotton and man-made fiber are mentioned in Table 21.15.

Polymer, Elastomer and Synthetic Fiber

433

Table 21.11: Emerging scenario of synthetic fiber Year

2010

2020

Cotton

33%

29%

Polyester

48%

55%

Others

19%

16%

Source: Rakesh Mehra. Emerging trends in Man-Made Textiles, the Synthetic & Rayon Textiles Export Promotion Council (SRTEPC), 5th Texcon Asian Textile Conference. Table 21.12: Man-made fiber demand in India KT

2000

Polyester

2005

2010

2015

2020

CAGR CAGR 2010/2000 2020/2010

1,381

1,672

2,844

4,591

5,513

7%

Nylon

86

117

111

118

107

3%

0%

Viscose

284

271

309

334

293

1%

–1%

Acrylic

111

110

96

121

110

–1%

1%

Polypropylene

7%

42

54

64

80

76

4%

2%

Total MMF

1,904

2,224

3,424

5,244

6,099

6%

6%

All fibers

4,948

5,735

7,826

10,871

12,984

5%

5%

Source: PCI. Table 21.13: Various synthetic fiber-producing units in India Sl. no.

Name and location of industrial unit

Product

1

JK Synthetics, Rajasthan

NFY, PFY, NTC, PSF, ASF

2

Garware Nylon, Pune

NFY, PFY

3

Nirlon Synthetic Fibers and Chemicals

NFY, PFY, NTC

4

Modipon, Modi Nagar, Uttar Pradesh

NFY, PFY

5

Century Enka, Pune

NFY, PFY

6

Baroda Rayon Corporation

NFY, PFY, VFY, NTC

7

Shree Synthetics, Madhya Pradesh

NFY, PFY

8

Stretch Fibers

NFY

9

Petrofils Cooperative

PFY

10

Chemicals and Fibers, Thane

PSF

11

Ahmedabad Manufacturing and Calico Printing Company

PSF

12

Swadeshi Polytex, Uttar Pradesh

PSF

13

Indian Organic Chemicals, Manali, Tamil Nadu

PSF

14

Bongaigaon Refinery and Petrochemicals

PSF

15

Reliance Industries (formally Indian Petrochemicals Corporation, Koyali, Baroda, Gujarat)

ASF

16

Neomar Ltd.

PPSF

17

Shriram Fibers, Manali, Tamil Nadu

NTC Contd...

434

Chemical Process Technology Table 21.13: Various synthetic fiber-producing units in India (Contd...)

Sl. no.

Name and location of industrial unit

Product

18

National Rayon Corporation, Kalyan,

NTC, VTC, VFY

19

Travancore Rayon, Rayanopuram, Kerala

VFY

20

Century Rayon, Kalyan,

VFY, VTC

21

JK Rayon, Uttar Pradesh

VFY

22

Kesoram Rayon, Triveni, West

VFY

23

South Indian Vescose, Tamil Nadu

VFY, VSF, PNSF

24

Indian Rayon Corporation, Veraval

VFY

25

Sirsilk Ltd, Kaghaznagar, Andhra Pradesh

AFY, ATSF

26

Rayon, Nagda, Madhya Pradesh

VSF

27

Rayon, Mavoor, Kerala

VSF

28

Shriram Rayon, Rajasthan

VTC

29

Harihar Poly Fibers, Harihar, Karnataka

PNSF

Source: Technical EIA Guidance Manual Project Sponsored by the Ministry of Environment and Forests. Table 21.14: Rising demand: Domination of polyester kg per capital

Year

Market share (%)

Cotton

Polyester

1960

3.3

0.0

67

1970

3.3

0.5

55

1980

3.2

1.2

48

1990

3.5

1.6

47

2000

3.3

3.2

37

2010

3.6

5.2

33

Table 21.15: Per capita consumption of cotton and man-made fiber Year

Cotton, kg per capita

Man-made fiber, kg per capita

2005

1.85

2.4

2010

1.65

2.75

2015

1.51

3.3

2020

1.52

3.6

21.5 RAW MATERIALS

Plastic, elastomers and synthetic fiber production needs extremely pure raw materials and chemicals. The most important chemicals are monomers, catalysts, and solvents. Various raw materials for polymers, elastomers and synthetic fiber are given below: • Ethylene, propylene, vinyl chloride, vinylpyridine styrene, isocyanate, phthalic anhydride

Polymer, Elastomer and Synthetic Fiber

435

ƒ Butadiene, isoprene, styrene, chloroprene, ethyl vinyl estate ƒ Vinyl esters, vinyl ethers, acrylic and methacrylic esters, vinyl ethers ƒ Dimethylformamide for dry spining ƒ Adipic acid, hexamethylenediamine, benzene, ammonia, caprolactam ƒ p-xylene, dimethyterephalate, terephthalic acid, ethylene glycol ƒ Formaldehyde, phenol, urea, melamine

• Phenol, phosgene, bisphenol A ƒ Maleic anhydride ƒ Cellulosoe, NaOH, acetic acid , carbon disulfide acetic anhydride, etc. • Catalysts which are used to speed up or initiate the polymerization reaction. Common catalysts include Zieger catalysts (titanium chloride and aluminum alkyl compounds), chromium-containing compounds, and organic peroxides. • Various solvents are sometimes used to dissolve or dilute the monomer or reactants. The use of solvents facilitates polymer transport through the plant, increases heat dissipation in the reactor, and promotes uniform mixing in the reactor. 21.6 POLYMERS 21.6.1 Polyolefins

Polyolefinsis family of polymers derived from a particular group of base materials known as olefins, are the world’s fastest growing polymer family. Polyolefins such as polyethylene (PE) and polypropylene (PP) are commodity plastics found in applications varying from house hold items such as grocery bags, containers, carpets, toys and applications, to high tech products such as engineering plastics, industrial pipes, automotive parts, medical appliances and even prosthetic implants (Kapur, et al, 2008). Ethylene and propylene are monomers for polyethylene and polypropylene respectively. Global polyolefin market is likely to be 200 million tons by the year 2020. In India, the domestic polymer industry (like global industry) is dominated by polyolefins (polyethylene, polypropylene) (Shashi Kant and Kapur, 2011). Market coverage of polyethylene, polypropylene is given in Table 21.16. Polystyrene is another important polyolefin and find wide application in manufacture of all sorts of packaging material. Styrene copolymerized with acrylonitrile resulting in SAN polymer is characterized with high tensile strength than polystyrene. Another important styrene copolymer is acrylonitrile butadiene styrene (ABS) plastic that finds use in engineering plastic and is characterized with special mechanical properties. Table 21.16: Polyethylene/polypropylene market coverage Polymer types

Grade

Market coverage

HDPE

Film grade

Blown film with paper like quality, suitable for counter bags, carrier bags and wrapping films

Pipe grade

Pipes PE-80/100 class, drinking water and gas pipes, waste pipes and sewer pipes their fitting, etc.

Large BM grade

Universal container grade, vol. approx. 1,500 L; heating oil storage tanks, transport containers

Small BM grade

Disinfectant bottles, up to 2 L, tubes for the cosmetics, containers from few mL up to 10 L. Contd...

436

Chemical Process Technology Table 21.16: Polyethylene/polypropylene market coverage (Contd...)

Polymer types

LLDPE

PP

Grade

Market coverage

Raffia grade

Stretched films and tapes for production of high strength knitted and woven sacks/bags/nets, etc.

Injection molding

For transport and stacking crates, particularly bottle crates

Films

Garment bags, grocery sacks, liner, blends, trash bags, cast like film diapers, etc.

Roto molding

Large industrial parts used indoors, large industrial/ agri­cultural tanks, shipping drums, toys, etc.

Injection molding

House wares, crates, master batches, pails, food container, etc.

Homo polymer

Injection molding (battery cases, crates, furniture, house ware, luggage, sports/toys), blow molding, sheets, Tape/Raffia, FIBC,TQPP/BOPP films (food packaging, bottle labels, etc.), extrusion coatings, etc.

Random copolymer

Thin walled injection molding, low heat seal and high transparency films, Blow molding, packaging parts, automotive parts, etc.

Impact copolymer

Automotive parts (bumper, exterior trims, instrument panels, interior trims), appliances, house wares, rigid packaging, thermoforming, etc.

Source: Kapur, et al. 2008, Journal of the Petrotech Society, Mall 2006, Mall 2013.

Catalyst for Polyolefin

There are four major families of catalysts used for olefin polymerization are given below. The main driver for change in polyolefin catalysts is requirement of improved resin performance. Characteristics of catalyst is given in Table 21.17. Ziegler Natta catalysts are spherical, high activity with low fines, thus leading to operational advantages and reduced cost. Metallocene catalyst afford greater control over molecular weight, molecular weight distribution, short-chain branching (SCB) and SCB distribution (Jensen, et al. 2008). • Ziegler Natta catalyst • Phillips (chrome) • Metallocene • Late transition metal catalyst. Table 21.17: Characteristics of polyolefin catalyst Type

State

Typical examples

Ziegler/

Heterogeneous

Ziegler–Natta

Heterogeneous

TiCl3, TiCl4/MgCl2

Phillips (chrome)

Heterogeneous

CrO3/SiO2

Metallocene

Homogeneous

Cp2ZrCl2

Heterogeneous Late transition metalbased Homogeneous Source: Kapur, et al. 2008.

VCl4, VPCl3

Cp2ZrCl2/MgCl2 Ni, Pd, Co, Fe, with diimine, and other ligands

Polymer, Elastomer and Synthetic Fiber

437

21.6.2 Polyethylene

Polyethylene is one of the most widely used thermoplastic and its ever increasing demand is due to availability of monomer ethylene from naphtha and gas cracker plant. First polyethylene plant in India was based on ethylene from molasses. Some of the other driving force for fast growth and use of polyethylene are ease of processing the polymer, its relative low cost, resistance to chemicals and its flexibility (Hatch and Matar, 1979). A wide variety of polyethylene varying density and characteristics for wide range of application is available. • Low density polyethylene (Branched) produced by high pressure • LDPE 0.910–925 MP 105–110ºC Crystallinity 60–70% • Medium density MDPE 0.920–940 • High density HDPE 0.941–0.959 MP 125–130ºC • Crystallinity 75–90% • Very few side chains. Produced by low pressure • Linear high density to ultra high density homopolymers • Linear low density polyethylene (LLDPE) 0.916–0.940 alpha-olefin as comonomer density 70.941 • High molecular weight – High density PE (HMW-HDPE)

Molecular mass: 200,000–500,000 Advantage: Low cost, excellent dielectric properties, moisture resistance, very good

chemical resistance, available in food grade, processed by all thermoplastic molding. Process Technology for Polyethylene

Several processes have been commercialized for the manufacture of polyethylene with varying densities. Various processes for manufacture of polyethylene are given in Table 21.18. Table 21.18: Various polyethylene processes Process

Licensor

Process

Product

Innovene process

BP Chemicals

Polymerization in fluidized bed reac­ LDPE, HDPE tor using Ziegler Natta catalyst or chromium catalyst Temperature 75–110ºC

Broster process

Borealis A/S

Uses gas phase low pressure reactor. Ziegler Natta catalyst Comonomer hydrogen Prepolymerization in slurry loop reac­t or and fluidized bed reactor. Temperature 75–100ºC

Bimodal and unimodel LLDPE, MDPE

Contd...

438

Chemical Process Technology Table 21.18: Various polyethylene processes (Contd...)

Process

Licensor

High pressure free radicals process

Exxon Chemicals Polymerization occurs in autoclave LLDPE Co reactors or tubular reactor

Process

Product

Speriline gas phase process

Montell Technology Co

Phillips Co, LPE process

Phillip Petroleum Polymerization takes place in an iso­ Lineal Co. butene slurry using very high activity polyethylene proprietary catalyst in loop reactor.

Polymerization in gas phase reac­tor LLDPE, using Ziglernatta catalyst HDPE

UNIPOL PE process Union carbide Corp

Low pressure polymerization in flui­ LLDPE to dized bed reactor at 25 kg/cm2 and HDPE 100ºC

Sclairtech process

Polyethylene is produced by solution HDPE, polymerization using ethylene gas and MDPE, cyclohexane as solvent. Comonomer: LLDPE butene or octane or both; Catalyst: Ziegle Natta catalyst

DuPont

Source: Hydrocarbon processing. Petrochemical Process, 2003.

UNIPOL Process

The process produces low density polyethylene and high density polyethylene using low pressure in gas phase. Wide range of polyethylene is produced using proprietary solid and slurry catalyst. The process produces wide range of polyethylene in a gas phase, fluidized bed reactor using proprietary solid and slurry catalyst. Gaseous ethylene, comonomer and catalyst are fed to fluidized bed reactor containing a fluidized bed of growing polymer particles operating at 25 kg/cm2 and 100ºC. Polymer density is easily controlled from 0.915 to 0.97 g/cm. Process flow diagram for polyethylene manufacture is given in Figure 21.7.

Fig. 21.7: Fluidized-bed gas phase: PE process

Polymer, Elastomer and Synthetic Fiber

439

DuPont Sclairtech Process

A broad range of polyethylene with density varying from 0.919 to 0.9605 g/cm2 with varying melt index can be made by this process. The process can be divided into three major areas • Reaction area • Recycle/recovery area • Extrusion and finishing • Dowtherm vaporizer. The process involves solution polymerization of gaseous ethylene using cyclohexane solvent and comonomer butene or octane comonomer (incase of low density polymers). Zigler catalyst is used to polymerize ethylene using cycloheaxane as solvent. A chain terminator is used to control the molecular weight at the reactor outlet a catalyst deactivator is added to terminate the reaction. The polymer is depressurized to flash off solvent, unreacted ethylene and comonomer from the molten polyethyelene which are separated and recovered using distillation. The polymer after stripping the residual solvents fed to main extruder and resulting polymer pellets are dried and send to blender for homogenizing and finally conveyed to storage silo. In the process, Dowtherm is added as heating media. Process flow diagram for the manufacture of polyethylene by Sclairtech process is given in Figure 21.8. 21.6.3 Polypropylene

Polypropylene is a low density semi-crystalline stereo-regular polymer which exists in three forms—isotactic, syndiotactic, and atactic. Polypropylene was discovered in March 1954 by Professor Giulio Natta demand of polypropylene is growing at a much faster rate due to its strong demand. Per capita consumption of polypropylene is given in Figure 21.9. Process Technology for Polypropylene

Polypropylene polymerization process have undergone a number of revolutionary changes since the production of crystalline polypropylene were commercialized in 1957

Fig. 21.8: LLDPE process by Sclairtech process

440

Chemical Process Technology

Fig. 21.9: Per capita consumption of polypropylene (Source: Shah, A. Indian propylene markets (India Petrochem 2009).

by Motecatini in Italy and Hercules in U.S. Commercial polypropylene processes based on low pressure processes using Ziegler–Natta catalyst that produces a product with an isotactic content of 90% or more. Various processes for polypropylene manufacturing are given in Table 21.19.Typical polypropylene processes are given in Figures 21.10 and 20.11. UNIPOL process: The process produces homopolymer, random copolymer and impact

copolymer polypropylene. Polymerization takes place in a fluidized bed reactor using Table 21.19: Polypropylene manufacturing process Process and licensor Summary of process

Product

Borstar Polypropyene process Licensor Borealis A/S

Produced by bulk polymerization in loop reactor followed by final gas phase a fluidized bed reactor (temp. 80–90ºC and 25–35 bar)

A versatile process and through the choice of reactor combinations, homopolymer, random copolymers, heterophasic copolymers and a very high rubber content heterophasic copolymers can be produced

Spheripol Process Montell Technology

Homopolymer and random copo­ lymer polymerization takes place in liquid propylene in a loop reactor. Heterophasic impact copoly­m eri­z ation is done by adding a gas phase reactor.

Process produces propylene based polymers including homopolymer PP, random and heterophasic impact and specialty impact copolymers

Novolen Process Krupp Uhde GmbH

Polymerization is conducted in Polypropylene homopolymer, ran­ one or two gas phase reactors dom copolymer and impact copo­lymer connected in series. including metallocene PP

Union carbide gas phase UNIPOL PP process

A wide range of polypropylene is Homopolymer, random polymer and made in a gas phase, fluidized bed impact copolymer polypropylene reactor using proprietary catalyst.

Sperizone Process Technology owner: Basellpolyolefins

Sperizone process is new proprietary gaseous technology based on a multi-zone circulating concept reactor.

A broad range of propylene based polymer can be produced including mono- and bimodal (medium/wide, very wide MWD)

Source: Petrochemical Processes 2003, Hydrocarbon Processing, March 2003.

Polymer, Elastomer and Synthetic Fiber

441

Fig. 21.10: Polypropylene process

Fig. 21.11: Polypropylene manufacturing by Unipol process (Sources: Petrochemical processes. Hydrocarbon Processing, March 2003, p.124.) (Courtesy: Hydrocarbon Processing)

slurry (TiCl4 supported on MgCl2 in slurry form in mineral oil. Co-catalyst TEAL, purified propylene and ethylene incase of random PP), purified H2 and selectivity control agent is continuously fed to the reactor. Temperature 35ºC and pressure 33 kg/cm2 are maintained in the reactor. Figure 21.11 illustrates the Unipol process for manufacturing of polypropylene. 21.6.4 Polystyrene

Polystyrene is an important thermoplastic. Polystyrenes because of its ease of fabrication, low specific gravity, thermal stability and low cost, find wide applications in consumer durable goods, electronics, packaging, toys, structural foams, wall tiles, shoe soles, blister packages, lenses, bottle caps, wire and cable sheathing, small jars, vacuum formed refrigerator liners, containers of all kinds, transparent display boxes and automobile interior parts. When styrene is copolymerized with acrylonitrile, the polymer styrene

442

Chemical Process Technology

acrylonitrile (SAN) resin has a higher tensile strength than polystyrene. Acrylonitrile butadiene styrene (ABS) polymer has special mechanical properties and find application as engineering plastics. Styrene is produced by dehydrogenation of ethyl benzene which is made by alkylation of benzene. Ethylbenzene by UOP EB one process is produced by liquid phase alkylation of benzene using proprietary zeolite catalyst which can be regenerated repeatedly thereby avoiding significant catalyst disposal problems associated with other aluminum chloride catalyst. The process offers better product quality, better heat integration, low investment and a more rugged and reliable catalyst system. (http://www.uop.com/ aromatics/3020.html) Lumus/UOP classic SM process: In this process, styrene is made by catalytically dehydrogenating ethylbenzene in presence of steam in multistage reactor system. The reaction is carried out at high temperature under vacuum. The process uses an oxidative reheat technology. Polystyrene is clear transparent resin with a wide range of melting points and good flow properties which make it suitable for injection molding (Hatch and Matar, 1979). Process Technology

The two major processes for the production of polystyrene are NOVA’s Polystyrene Technology and UOP Polystyrene Technology. NOVA’s polystyrene technology: The process produces a complete range of general

purpose (crystal) and impact resistant polystyrene. This is based on bulk continuous polymerization technology. UOP polystyrene technology: This process is based on continuous bulk polymerization to

produce a wide range of general purpose polystyrene, high impact polystyrene and SAN resin. A typical plant includes feed preparation, reactor section, de-volatilization section, monomer recovery section, water removal, product pelletizing and bulk resin handling. 21.7 ELASTOMERS

Elastomers are used in wide variety of industrial, medical and household products and major portion of elastomers consumption goes into tires, next largest product sector is latex goods. There are two major types of elastomers; natural rubber a product of tropical tree Heveabrasiliensis and synthetic rubber- a family of materials derived from petrochemical feed stocks (Chemistry and Industry August 5, 1996, p.574). Major natural rubber producing countries are Thailand, Indonesia, Malaysia, Africa, Latin America, Brazil, Cambodia, Nigeria, Sri Lanka and India. Demand for natural is estimated to be around 10.9 million tons in 2011 out of which around 45% was from Asia. About 92% of natural rubber is produced from Asian countries. The demand for natural rubber globally is projected to grow by 3–4% through 2013 (Chemical Weekly, Jan 17, 2012). Synthetic rubbers have slowly replaced natural rubbers and have undergone various developments for applications in automotives, chemical industry, energy generation, sports, aerospace industry, etc. Styrene butadiene rubber (SBR), polybutadiene, nitrile rubber are some of the important elastomers. 21.7.1 Historical Development Natural and Synthetic Rubber

1525

Elastic ball reported by Mexico tribal people

Polymer, Elastomer and Synthetic Fiber

1735 1820 1832 1845 1902 1910 1914–18 1930 1931 1932 1933 1936 1963 1976 1978

443

First scientific study of rubber by Charles de la Condamine First planting of rubber in India at Travancore Rosburg factory was set up for rubber goods with non–vulcanized rubber RW Thomson invented the pneumatic tire First commercial plantation First large scale commercial production of butadiene rubber Methyl isoprene rubber in Germany Organic polysulfide rubber Neoprene production started First synthetic rubber plant in USSR BUNA-S made in USSR First automatic tire factory (Dunlop) in India First synthetic rubber plant in India First nitrile rubber by Synthetics Chemicals First polybutadiene plant in India by IPCL

Petro-based synthetic rubber 20% in India, 80% in developed countries. Annual growth rate 7%. Natural Rubber

Christopher Columbus voyage to Haiti 1496 Tree: Cau-achu Weeping wood Priestley (1770), Rubber Rub-off 1839 Vulcanizing of rubber 1840 Henry Wickham smuggled 70,000 Herca tree seed to England planted at London. 21.7.2 Synthetic Rubber

With the availability of petrochemical feedstocks, there has been tremendous increase in the production of synthetic rubber. World synthetic rubber market and its production is given in Figures 21.12 and 21.13, respectively. Synthetic rubber may be classified as general purpose rubber, specialty rubbers, thermoplastic rubber or liquid processing rubber (e.g. silicon rubber, liquid polysulfide rubber). Synthetic and natural rubber consumption scenario is given in Table 21.20. Forecast of synthetic rubber and natural rubber consumption in India is given in Table 21.21.

Capacity (2011) by region (15,965 kmta)

Fig. 21.12: World synthetic rubbers market by region

Chemical Process Technology

444

Fig. 21.13: World rubber production (Sources: International Rubber Study Group.) Table 21.20: Synthetic and natural rubber consumption scenario India

2005

2010

Capacity

85

–

233

406

613

(148)

(293)

–

Consumption Oversupply/(shortage)

2015 113

Source: IISRP (2011), TSRC Corporation. Table 21.21: Indian consumption of synthetic rubber (SR) and natural rubber (NR) forecast (Unit: 000’ metric ton) 2010

2011

2012

2013

2014

2015

NR, Tire Sector

661

680

772

783

850

897

950 1,010 1,046 1,093 1,152

NR, Non-tire Sector

283

284

295

308

329

342

358

Sub-total

944

964 1,017 1,091 1,179 1,239 1,308 1,393 1,443 1,507 1,599

SR, Tire Sector

145

143

156

164

166

178

189

210

214

221

248

SR, Non-tire Sector

261

285

342

414

452

513

570

625

636

661

687

Sub-total

406

428

498

578

618

691

759

835

850

882

935

Total of rubber consump­­tion

2016

2017 383

2018 397

2019 414

2020 447

1,350 1,392 1,515 1,669 1,797 1,930 2,067 2,228 2,293 2,389 2,534

Source: IRSG (December), TSRC Corporation 2011.

21.7.3 Styrene Butadiene Rubber

Styrene butadiene rubber (SBR) is the most widely used elastomer in the world.SBR is used for both tire and non-tire application. Styrene butadiene rubber known as Buna-S was first prepared by IG Farben Industry in Germany. There has been significant development in the process technology of styrene butadiene rubber manufacture. Amongst the various processes, emulsion polymerization of SBR is most commonly used. The cold emulsion polymerization process has replaced the hot polymerization process. In India, first SBR manufacture was started by Synthetic and Chemicals, Bareilly in 1963, however; the unit has been closed presently. Although butadiene is recovered from cracker plant, it can be also made from ethanol route. Styrene is made from ethyl benzene by alkylation of benzene with ethylene which can be also recovered from FCC gases.

Polymer, Elastomer and Synthetic Fiber

445

SBR is made by emulsion polymerization at 50ºC. Initiation occurs through reaction of potassium peroxodisulfate with n-dodecyl mercaptan. Chain propagation occurs by the growing chain free radical of mercaptyl attaching either butadiene or styrene. The reaction is terminated at 60–75% of completion. Unreacted butadiene and styrene were recovered. Antioxidant is added followed by coagulation, washing and drying. It is used as elastomer, emulsion and solution. Used in tires and tire-related product, mechanical goods, automotive uses, adhesive, shoe products. SBR is a hard rubber which is used for soles of shoes, tire treads and other places where durability is important. It is a type of copolymer called a block copolymer. Its backbone chain is made of three segments—first polystyrene, second polybutadiene and third polystyrene. Polystyrene is tough hard plastic and this gives SBS its durability (file:/A:\ Poly (styrene-butadiene-styrene).htm). Process flow diagram of SBR manufacture is given in Figure 21.14.

Fig. 21.14: Process flow diagram of SBR manufacture

21.7.4 Polybutadiene

Stream of steam cracker is major source of butadiene. Other routes for butadiene manufacture are: • Catalytic dehydrogenation of butenes • Catalytic dehydrogenation of butane With the availability of butadiene from cracker plant, manufacture of polybutadiene has increased significantly in recent years. Polybutadiene is made by free radical emulsions, alkali methyl solution and transition metal coordination solution processes. Most processes are based on solution process. Large volume use of polybutadiene rubber has been primarily in blend with other polymers. Blend with SBR or natural rubber has improved crack resistance. It is also characterized by better resistance to heat degradation and blowouts, good hysteresis properties, large scale use in tire tread, modification of plastics, conveyor and V-belts, sports goods, foot wear material, 90% in tire industry.

446

Chemical Process Technology

21.7.5 Polyisobutylene (Butyl Rubber)

Polyisobutylene is gas impermeable and because of this property it is used for making ballon. Polyisobutylene is made by polymerization of isobutylene. Isobutylene can be recovered from C4 stream of steam cracker and FCC. Other routes for isobutylene are: dehydrogenation of isobutene, n-butane with small amount of isoprene formed by isomerization in gas phase using platinum catalysts. Butyl rubber is made by slurry polymerization. The polymerization is carried out in slurry of monomer in methyl chloride using an aluminum chloride catalyst at –100 to –90ºC. The rubber is precipitated by adding water and finally washed and dried. Butyl rubber has unique elastomeric qualities, low rate of gas permeability, thermal stability, good ozone and weathering resistance, vibration damping and higher coefficients of friction, chemical and moisture resistance. Used in tubes, tire inner liner due to low permeability of air, automotive mechanical parts, adhesives, and sealant. 21.7.6 Nitrile Rubber

Acrylonitrile butadiene copolymers are commonly known as nitrile rubber. Nitrile rubbers are available in many grades varying in acrylonitrile content. Increase in acrylonitrile improves resistance to fuels and oil, tensile strength and modulus, processing behavior, heat resistance; increases abrasion resistance and hardness, permeability resistance to gas diffusion; decreases low temperature flexibility, resilience and elasticity, plasiticizer compability (Patel, 1991). Abroad range of properties can be obtained from properly compounded nitrile rubber. Nitrile rubber is made by emulsion copolymerization of butadiene and acrylonitrile at 5ºC. The basic steps involved are polymerization, coagulation, washing and drying. A basic polymerization recipe in addition to the monomer contains water, stabilizers, emulsifiers, shortstop catalyst activator and electrolytes. Following polymerization cycle material is transferred to blow down tank in which short stop and antioxidant are added and residual monomers are recovered. Then finally, the latex is concentrated, coagulated, washed, dewatered and finally dried. Nitrile rubber is used in seals; O-rings, gaskets, oil field parts, diaphragm, gloves, belts, wire cable insulation, hosepipes, foot wear shoes products, molded rubber goods. In the polymerization process the monomer is emulsified in water, a free radical generating catalyst is added and the mixture is agitated. After the polymerization the material from the polymerization reactor is transferred to blow tank in which short stop and antioxidant are added and the residual monomers are removed. The latex formed is concentrated and coagulated into fine crumbs by addition of salt and acids. This followed by washing, dewatering and drying. The dried crumbs are compacted (Patel, 1991). Acrylonitrile 18–50%, with increase in acrylonitrile resistance to oil, fuel, abrasion and heat increases, higher tensile strength, hardness, gas impermeability. • Low temperature resistance, resilience, plasticizer compatibility decreases require less sulfur, more accelerators than SBR, highly oil resistant. Application: Fuel hoses, collapsible containers. Nitrile rubber may be reinforced by phenolic resins and PVC. • Resistance to ozone, weathering, better gloss, bright colors, high resistance to abrasion and oil. Process flow diagram of manufacture of nitrile rubber is given Figure 21.15.

Polymer, Elastomer and Synthetic Fiber

447

21.7.7 Polyisoprene

Polyisoprene is one of the most well known natural elastomers derived from the sap of the Heavea tree. However, synthetic polyisoprne is made by polymerization of isoprene. Isoprene is recovered from the C5 fraction of naphtha cracker. Isoprene polymerization is carried out in an inert hydrocarbon solvent (aliphatic solvents). Basic steps in manufacture of polystyrene are—raw material preparation and purification, polymerization, catalyst deactivation and removal, solvent recovery, polymer drying. Polymerization catalysts are either of the coordination (Zeigler) or alkyl lithium types. Coordination catalysts are trialkyl aluminum/titanium tetrachloride. Often polymerization short stops and antioxidants are added. The solvent remaining is stripped off. Polyisoprene has good uncured track, high pure gum tensile strength, high resilience, low hysteresis, good hot tear strength. Tire market is the major consumer of polyisoprene, a substitute of natural rubber in the tread of truck, aircraft and off the road tires, for dipped goods, adhesive, extruded thread.

Fig. 21.15: Process flow diagram of acrylonitrile rubber (nitrile rubber) manufacture

21.7.8 Neoprene (Polychloroprene)

Chloroprene is made either via acetylene route or from butadiene. Butadiene process is commonly used (Nadini Chemical Journal, April 1998, p.21). Acetylene route involves dimerization of acetylene to monovinyl acetylene followed by reaction of monovinyl acetylene with HCl. Chloroprene from butadiene involves three steps: • Chlorination of butadiene: Various steps involved are • Chorination of butadiene- 1,4 dichloro 2-butene and 3,4-dichloro-1-butene • Isomerization of 1,4 dichloro 2-butene to 3,4-dichloro 1-butene • Dehydrochlorination of 3,4-dichloro 1-butene to chloroprene in presence of caustic soda resulting in formation of chloroprene (CH2 = CH – CCL = CH2). Polychloroprene is made by emulsion polymerization process using resin acid soap emulsifier. Polymerization is carried out at 40ºC in presence of sulfur. Uses: Adhesives, transportation industry (automotive: gaskets, V-belts, shock absorber covers, wire jackets, molded seats; aviation: wire cable, gaskets, seats, etc. rail brake hose, track mountings).

448

Chemical Process Technology

21.7.9 Chlorobutyl Rubber

Chlorobutyl rubber is made from isobutylene and 1–3% isoprene. Introducing a continuous stream of chlorine gas in a hexane solution of butyl, which is prepared by low temperature copolymerization of isobutylene, and isoprene in methyl chloride gives chlorobutyl. Chlorobutyl rubber possesses greater vulcanization flexibility and tubeless tires, tire side wall components, heat resistant truck inner tubes, hose pipes, gaskets, conveyor belts, adhesive, sealants, tire curing bays, tank lining, etc. 21.7.10 Silicone Rubber (Polysiloxanes)

Silicone elastomer is made by ring opening reaction caused by action of alkali on monomer acyclic siloxane characterized by exceptional mechanical and electrical performance under extreme temperature condition. Used in aerospace, appliances, electrical industry, construction industry, automotive industry, gaskets sealings, spark plug boots, hose, rubber rolls. 21.7.11 Fluorosilicone Rubber

Fluorosilicone rubber (FSR) is characterized by excellent low temperature flexibility, very good heat resistance, excellent aging characteristics. However, it has poor resistance to aromatic hydrocarbon and common polar solvent. 21.7.12 Polyurethane Rubber

Polyurethane is made by reacting polyisocyanates and polyhydroxyl groups using curing agents. Good abrasion resistance, oil and solvent resistance, oxygen ozone, temperature. Finds wide application in solid tires for industrial trucks, seals and boots, calendar sheet, potting and sealing of electronic components, general engineering mechanical goods, shoe heels and soles, elastic threads, insulation, mattresses, vibration damping. 21.7.13 Ethylene/Propylene Number

Ethylene/propylene number (EPDM) is made by polymerization of ethylene, propylene, diene using Ziegler–Natter type catalyst in combination of transition metal halides and metal alkyls. Polymerization is carried out in a series of two or three vessels. Adding polar material (e.g. water) stops polymerization. Unpolymerized monomers are recovered and rubber is separated from the solvent by steam flocculation. Rubber floc or crumbs are dewatered and dried. EPDM has outstanding resistance to heat, ozone oxidation, weathering, and aging due to the saturated backbone, low brittle point and glass transition temperature, low density and maintain acceptable properties at higher filler loading. EPDM are non-tacking, used in single ply roofing, wire and cable installations and automotive parts. 21.7.14 Ethylene Vinyl Acetate Rubber

Ethylene vinyl acetate rubber (EVA) has excellent resistance to heat, ozone and sunlight, moderate resistance to oil and gasoline. It has poor resistance to aromatic and oxygenated solvents, fair process ability. 21.7.15 Hypalon

Hypalon are chlorosulfonated polyethylene and are made by free radical catalyzed reaction of chlorinated and SO with polyethylene.

Polymer, Elastomer and Synthetic Fiber

449

Hypalon is characterized by ozone resistance, light stability, heat resistance, weather ability, resistance to deterioration by corrosive chemicals and weather ability, resistance to deterioration by corrosive chemicals and good oil resistance, flame resistance, toughness. It finds applications in automotive eat liner coatings, spark plug boots, primary and ignition wire, tarpaulins, hose, conveyor belt, coated fabric. 21.7.16 Spandex

Spandex is a polyurethane elastomer which has both urea and urethane linkage and has hard and soft blocks in its repeat structure. 21.7.17 Polysulfide Rubber

Polysulfide rubber has outstanding resistance to oil, gasoline and solvents, good resistance to weather, ozone and sunlight, impermeability to gases and vapor. It has poor resistance to abrasion, tear, cut growth and low tensile strength. 21.8 SYNTHETIC FIBER

Nylon 6 and nylon 6,6 are low important polyamides and find application in woven and non-woven industries. Nylon 6 and nylon 6,6 are commonly used in textile, hosiery and tire card industry. Polyester and acrylic fibers are other important synthetic fibers. Apart from this polypropylene and polyurethane fibers also find application. 21.8.1 Nylon 6, Nylon 6,6, Cyclohexane, Caprolactam, Adipic Acid and Hexamethylene Diamine

Caprolactam is monomer for nylon 6 while monomers for nylon 6,6 is nylon salt which are made from adipic acid and hexamethylene diamine. Nylons are exceptionally strong, elastic, abrasion resistant, lustrous, easy to wash, resistant to oil and many chemicals, low in moisture absorbency (http://www.fibersource.com/f-tutor/nylon. htm). Characteristics of nylon 6 and nylon 6,6 are given in Table 21.22. Nylon fiber finds application in apparel, home furnishings, tire cord, hose, conveyer and seat belts, parachutes, racket strings, ropes tents thread, monofilament, fishing net, dental floss. Nylon 6,6 is preferred for tire cord because of high melting point. Melt spinning process is used for producing fiber stable and yarn. Nylon 6 is the first synthetic fiber introduced in India starting with a modest volume of 175 tons in 1962. Installed capacity and production of nylon filament yarn and nylon industrial yarn is 36000 and 70000 tons and 33000, 86000 tons in 2010–11, respectively in India. Cyclohexane

Cyclohexane is an important chemical intermediate derived from benzene. It is used for the manufacture of adipic acid and hexamethylene diamine for nylon 6,6 and caprolactam for nylon 6. Ninety percent of the cyclohexane is used in the manufacture of nylon fiber and nylon molding resin and remaining 10% of cyclohexane ends up as solvents or plasticizers. Cyclohexane is made by catalytic hydrogenation of benzene in liquid phase or vapor phase. Process flow diagram of manufacturing process is shown in Figure 21.16. UOP hydrogenation process uses liquid phase hydrogenation of benzene at 200–300ºC in presence of platinum based catalyst promoted by lithium salt at 3 MPa pressure. In the IFP process cyclohexane is produced by liquid phase hydrogenation of benzene at 160–200ºC and 4 MPa using Raney nickel catalyst.

450

Chemical Process Technology

Fig. 21.16: Cyclohexane from benzene Table 21.22: Characteristics of nylon 6 and nylon 6,6 Name of the syn­­thetic fiber

Monomer

Basic chemicals

Properties of the synthetic fiber

Characteristics

Density Moisture Melting regain point

Nylon 6 O

Phenol, 1.14 cyclohexane, toluene

4.5

213– 221ºC

Resistant to weak acids, decomposed by strong mineral acid, swelling is low. Very good biological resistance, good resistance to heat. Good adhesion to rubber. Tenacity 4.3–8.3 g/denier, elongation at breaks 18–45%.

Phenol, cyclohexane, butadiene, furfural

4.0–4.5

230ºC

Resistant to weak acid, decomposed by strong mineral acid. Chemically, it is extremely stable. Good biological resistance. Tenacity 8.0 g/ denier, elon­ga­tions at break 16–20%.

HN Caprolactam

Nylon 6,6 Adipic acid HOOC – (CH2)4 – COOH

Hexamethylene diamine H2N – (CH2)6 – NH2

1.14

Caprolactam

• Caprolactam is the principal raw material for nylon 6, a versatile material used as fibers, industrial yarns and floor covering as well as for engineering plastics/films. • Nylon 6 was first made in 1899 by heating 6-aminohexanoic acid but commercially feasible synthesis from caprolactam was first discovered in 1935 by Paul Shalack. • Global caprolactam production and demand scenario is given in Table 21.23.

Polymer, Elastomer and Synthetic Fiber

451

Table 21.23: Global caprolactam production and demand scenario Caprolactam production (’000 tons)

Caprolactam demand (’000 tons)

Fibers

Resins

Fibers

Resins

1990

2,463

499

–

–

2010

2,559

1,845

2,463 (56%)

1,941 (44%)

Year

Manufacturing caprolactam: Process of manufacturing caprolactam involves three basic steps: • Manufacture of cyclohexanone • Manufacture of hydroxylamine sulfate • Manufacture of caprolactam Manufacture of cylohexanone: In subsequent stages cyclohexane is oxidized cobalt salt

as catalyst in multicompartment reactor at a temperature of 158–160ºC and 10 atm pressure where the liquid flows in series from one chamber to another using. The product stream is treated with sodium hydroxide to neutralize acids, saponify esters and to decompose peroxides. Sodium salts which are immiscible with the main product stream are separated in a gravity settler. Organic phase containing cyclohexane, cyclohexanol, cyclohexanone are fed to series of three distillation columns where these are separated. Cyclohexane is separated as top product from the last column. Cyclohexanol separated in the last column as bottom product is dehydrogenated to cyclohexanone in presence of zinc carbonate and calcium carbonate catalyst at 400ºC. The unconverted cyclohexanol and cyclohexanone after removal of light ends recycled to third distillation column for recovery of cyclohexanone. Manufacture of hydroxylamine sulfate: Production of hydroxylamine sulfate involves

production of ammonium carbonate by absorption of CO2 in 24% aqueous ammonium solution. Production of nitrous oxide from mixture of NO and NO2, which is produced by oxidation of ammonia in presence of platinum catalyst at 85ºC. Absorption of nitrous gases from the ammonia combustion in ammonium carbonate to yield ammonium nitrite. Manufacture of caprolactam: Manufacture of caprolactam involves production of

cyclohexanone oxime by reacting cyclohexanone with hydroxylamine sulfate in a multicompartment reactor. During this process ammonium sulfate is formed as byproduct. Caprolactam and aqueous ammonium sulfate are sent to a series of extractors where toluene is used as a solvent. Various routes of caprolactam is shown in Figure 21.17 (Nair and Lal, 1969; Taverna and Chiti, 1970; Vaidya and Gupta, 1986; Chavel and Lefebvre, 1989, Mall, 2007). Ammonium sulfate collected from the extractor bottom is purified, crystallized, centrifuged and dried. Caprolactam solution is concentrated in multiple effect evaporators and finally purified. Flow diagram for the manufacture of caprolactam is given in Figure 21.18 (Mall, 2007). Adipic Acid

• Adipic acid is the basic raw material for the manufacture of nylon 6,6. • World overall demand for adipic acid is growing by 3.6% during 2000–2010. • Adipic acid is manufactured from number of starting raw materials like phenol, cyclohexane, tetrahydrofuran, etc. Various routes for adipic acid manufacture

452

Chemical Process Technology

1. Original process: Phenol

Cyclohexanol

Cyclohexanone

Cyclohexanone oxime

Caprolactam

2. Allied chemical phenol process: Phenol

Cyclohexanone

Cyclohexanone oxime

Caprolactam

3. Cyclohexane process via cyclohexanone: Cyclohexane

Cyclohexanol

Cyclohexanone

Cyclohexanone oxime

Caprolactam

4. Toyo rayon photonitrozation: Cyclohexane

Cyclohexanone oxime

Caprolactam

5. SNIA Viscosa toluene process: Toluene

Benzoic acid

Cyclohexane carboxylic acid

Caprolactam

6. Union carbide process via caprolactam: Cyclohexane

Cyclohexanol

Cyclohexanone

Caprolactone

Caprolactam

7. DuPont process via nitrocyclohexane: Cyclohexane

Nitrocyclohexane

Cyclohexanone oxime

Caprolactam

8. Techni-chem process:

Cyclohexane Cyclohexanol Cyclohexanone Nitrocyclohexanone Caprolactam Aminocaproic acid Nitrocaproic acid

Fig. 21.17: Various routes for caprolactam

Fig. 21.18: Manufacture of caprolactam

Various routes of adipic acid manufacturing is shown in Figure 21.19 (Vaidya and Gupta, 1986; Chavel and Lefebvre, 1989; Saxena, 2000; Mall, 2007).

Polymer, Elastomer and Synthetic Fiber

453

Fig. 21.19: Various routes for manufacture of adipic acid

Process: Cyclohexane is oxidized by air to form cyclohexanol and cyclohexanone in presence of cobalt naphthenate catalyst at temperature of 145–150ºC. The cyclohexanol and cyclohexanone mixture is oxidized to adipic acid in presence of nitric acid using ammonium metavanadate and copper scrap at 60–80ºC. The adipic acid formed is crystallized, centrifuged and finally dried with hot air. Hexamethylene diamine is another intermediate for the manufacture of nylon 6,6. Hexamethylene diamine is manufactured by catalytic hydrogenation of adiponitrile in presence of catalyst either by high pressure process (60–65 MPa) or low pressure process (3 MPa). Catalyst in low pressure is nickel whereas in case of high pressure process it is cobalt and copper. Process flow diagram for the manufacture of hexamethylene diamine is given in Figure 21.20. NC(CH2)4CN + 2H2

HN = CH(CH2)4CH = NH

Fig. 21.20: Process flow diagram for hexamethylene diamine

Nylon 6

Nylon 6 is produced from polymerization of caprolactam. Process steps involved in production of nylon 6 involves the following steps: • Caprolactam melting and addition of additives • Polymerization: Batch/continuous and chips production • Chips washing and drying • Spinning of nylon • Recovery section.

454

Chemical Process Technology

Caprolactam is polymerized to nylon 6 polymer by ring opening polymerization at 240–270ºC in presence of water, which opens the ring structure of the caprolactam to give aminocaproic acid. Reacting SO2 with ammonium nitrite and ammonium carbonate which results in production of hydroxylamine disulfonate finally hydrolysis of hydroxylamine disulfonate at 95ºC to yield hydroxylamine sulfate and ammonium sulfate as by-product. Process flow diagram for nylon 6 manufacturing is shown in Figure 21.21.

Fig. 21.21: Manufacture of nylon 6

Nylon 6,6

Nylon 6,6 is produced by polymerization of adipic acid and hexamethylene diamine. Manufacturing process flow diagram for nylon 6,6 is shown in Figure 21.22. • Production of nylon salt (hexamethylene diammonium adipate) by reaction of adipic acid and hexamethylene diamine • Concentration of nylon salt • Polymerization of nylon salt in a jacketed vessel equipped with internal coils and heated by dowtherm • Cooling and chips production • Spinning of nylon 6,6 chips • Recovery section

Fig. 21.22: Process of nylon 6,6 manufacture

21.8.2 Dimethyl terephthalate (DMT) and Terephathalic Acid (TPA), Polyester, PET Resin, PBT Resin

Global polyester production in all forms is currently around 56 million tons and may cross 100 million in the next decade. Higher capacity addition is estimated in polyester filament and chips segment compared to staple fibers in the next 2–3 years. Indian textile industry has the potential to grow to US$ 220 billion by 2020 from current size of around 80 billion. Besides, the lower per capita consumption of around 5 kg as against global average of 11 kg indicates huge potential for expansion of fiber (Udeshi, 2012). Table 21.24 gives the details of fiber per capita consumption.

Polymer, Elastomer and Synthetic Fiber

455

Table 21.24: Per capita fiber consumption Kg/per capita

2000

2011

North America

35

Latin America

7

35 8

West Europe

22

24

East Europe

6

12

Africa/Middle-East

3

4

China

10

20

India

4

5

Source: PCI Udeshi, 2012.

Indian polyester production is likely to grow at a CAGR of 10–11% as against global average of 7% and is expected to reach 10 million tons by 2020. In India, the polyester filament and resin markets are witnessing higher growth prospects. Reliance is taking significant expansions across the polyester chain (Udeshi, 2012). Characteristics of polyester fibers are shown in Table 21.25. Terephthalic acid (TPA) and dimethyl terephthalate (DMT) are major building blocks for manufacture of polyethylene terephthalate (polyester) fibers and resins. The increase in the PET demand in the major market fibers, film and rigid packaging has been the primary drivers for the DMT/PTA market. Table 21.25: Characteristics of polyester fiber Name of the synthetic fiber Polyester

Monomer Dimethyl terephthalate and purified terephthalic acid (PTA)

Properties of the synthetic fiber Basic chemicals Density Moisture Melting regain point p-Xylene, 1.38 methanol, ethylene glycol

0.4–0.5

250ºC, Sticking point = 240ºC

Characteristics Disintegrate in conc. H2SO4, resistant to alkali, disintegrate in boiling strong alkalies. Biological resistance is good, resis­ tance to weak acid and alkali is good. Ironing temperature 135ºC. Tenacity 4.0–7.0 g/denier, elongations at break 18–22%.

Paraxylene (P-Xylene)

PX is produced from the heart cut naphtha feed range 114–140ºC. p-Xylene plant consists of five units: Pretreatment unit, reformer unit, fractionation unit, parex or crystallization unit, and isomerization unit. Details of the p-xylene process is given Chapter 20. Dimetyl Terephthalate (DMT)

Global production and consumption of DMT in 2009 was almost 2.0 million tons with capacity utilization of 84.4. p-xylene and recycle p-toluic esters (PTE) are oxidized with air at 140–150ºC at 6 kg/cm2 in presence of catalyst cobalt or manganese salts to form p-toluic acid and TPA, monomethyl terephthalate (MMT). The final oxidation product

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Chemical Process Technology

goes to the esterification column. In the esterification column the oxidation product is esterified with methanol. Esterification takes place at 240–250ºC and 25 kg/cm2. p-Toluic acid is esterified to p-toluic ester while TPA and MMT form DMT. Consumption of Terephthalic Acid or Purified Terephthalic Acid

Some of the advantages of TPA over DMT are as follows (Paranjbe and Mathur, 1987): • Per unit of polyester produced about 15% less TPA is required. • Bulk density of TPA is 1.0 ton/m3 as compared to DMT (0.5 ton/m3). Thus transpor­ tation costs and storage requirements for TPA are significantly lower. • TPA requires a lesser feed mole ratio of glycol to PTA of around 1.2 against 1.6 for DMT. • DMT is fed to the transesterification process in molten form while TPA cannot be melted. • Esterification reaction of TPA does not require any catalyst whereas the transes­ terification of DMT has to be catalyzed. • With TPA it is simpler to maintain a constant degree of esterification. In case of DMT, transesterification step is very sensitive to the quality of raw material, change in mole ratio, etc. • With TPA process, water is the byproduct whereas with DMT process methanol is the byproduct. Therefore, more process hazards in handling methanol. • With the TPA process, it is easier to reclaim polymer. • Product from TPA is better with respect to thermal and hydrolytic stability. • Product cost in case of TPA is lesser due to reduced raw material requirement, reduced transport and handling cost. There are two major steps: 1. Catalytic oxidation of PX to make crude terephthalic acid (CTA): This involves oxidation, crystallization, solvent recovery, filtering, drying, etc. 2. Purification of CTA to make TPA: It involves hydrogenation, crystallization (AMCO process), centrifuging, drying, conveying, storage, bagging, etc. or by leaching and sublimation (Mobil process) TPA Manufacturing Process Technology

AMCO process: Manufacture of terephthalic acid by AMCO process consists of two steps—oxidation of p-xylene to crude terephthalic acid and purification of crude terephthalic acid by crystallization. 1. Crude terephthalic acid: • Oxidation section • Crystallization section • Separation and drying section • Off-gases recovery section • Solvent recovery section • Catalyst recovery section. 2. Pure terephthalic acid: • Feed preparation section • Reactor section • Crystallization section • Separation and drying section • PTA storage and warehouse.

Polymer, Elastomer and Synthetic Fiber

457

Oxidation of p-Xylene: p-Xylene is oxidized with air at 20 atm pressure and 200–210ºC

temperature in presence of catalyst cobalt acetate, manganese acetate and hydrobromic acid as promoter. Reactions involved in manufacturing process is shown in Figure 21.23. Figure 21.24 illustrates the process technology for PTA.

Fig. 21.23: Reaction involved in PTA manufacturing from p-xylene (Source: Singh, 2011).

Fig. 21.24: Process technology for purified terephthalic acid

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Chemical Process Technology

Mobil process: In Mobil process, p-xylene is oxidized in presence of cobalt based catalyst without using any promoter. The reaction takes place in acetic acid medium at around 130ºC. Methyl ethyl ketone is used as activator. After cooling, washing and centrifuging, crude TPA is sent to purification section. Detail of manufacturing process of TPA is shown in Figure 21.25.

Fig. 21.25: Manufacturing process of TPA (Source: Ichikawa and Takeuchi, 1972.)

Here the purification of crude TPA takes place in two steps. The crude TPA is slurried with acetic acid and charged to leaching stage. During leaching impurities like p-carboxybenzaldehyde and cobalt catalyst are removed from the crude TPA. Crude TPA (about 99.5% pure) is further purified by sublimation. Crude TPA from leaching operation is dispersed in steam; hydrogen and catalyst are added to the dispersed TPA, which is then passed through heated furnace. The purified TPA vapors after separating impurities are condensed.

Polymer, Elastomer and Synthetic Fiber

459

Polyethylene Terephthlate (Polyester)

There are two routes for making polyester: DMT route or PTA route. However, with availability of the pure terephthalic acid and because of its advantages over dimethyl terephthalate, now polyester through esterification route is more commonly used.

Raw material: Terephthalic acid (TPA), ethylene glycol, dimethyl terephthalate Dacron





Terylene

DMT

TPA

Ethylene glycol

Process unit: Typical polyester plant consist of the following unit: • P-xylene • DMT unit/PTA unit • Ethylene glycol • Polyester manufacture • Transesterification (in case of DMT)/esterification (in case of PTA) • Polymerization • Spinning • Cutting and bailing. Polyethylene terephthalate (PET) from DMT: PET from DMT is made by transesterification route by reaction of dimethyl terephthalate with ethylene glycol followed by polycondensation. Polyester through transesterification route was more common earlier due to non-availability of purified terephthalic acid. During transesterification, methanol obtained as by product. Figure 21.26 describes the manufacturing process of polyester from DMT.

Fig. 21.26: Polyester from dimethyl terephthalate (DMT)

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Chemical Process Technology

Polyester from DMT routes

Polyethylene terephthalate (PET) from TPA (PTA): PET from TPA is made by esterification route by reaction of purified terephthalic acid (PTA) with ethylene glycol followed by polycondensation. Figure 21.27 describes the manufacturing process of polyester from PTA. Polyester from PTA routes

1. Polycondensation: Temperature 270–280ºC, short polycondensation time, high vacuum for proper degree of polycondensation. Thermal decomposition increases with high melt temperature and higher degree of polycondensation. Thermal instability of polyester melt influence the fiber. Decomposition lowers the viscosity of polyester melt. • Catalyst: Antimony trioxide • Flasher, prepolymerizer, finisher • Vacuum at last stage: 2 mm Hg, 285ºC. 2. Spinning: Spinning of polyester is done by melt spinning. Molten polymer passed through spinnerate. The extruded filaments from the spinnerates are quenched and cooled by air. The quenched filaments are passed to winding unit through finish applicator. The spun yarn is passed to draw twisting and draw texturing unit. Polyethylene Terephthalate (Pet) and Polybutene Terephthalate (PBT) Resin

Polyethylene terephthalate (PET) and polybutene terephthalate (PBT) are two important saturated thermoplastics. PET apart from its major use as synthetic fiber finds application in photographic film, videotape, computer and magnetic tapes, beverage bottles, etc. Demand for PET packaging resin continues to grow strong and attracting new entrants into market. PET packaging industry growth rates are driven by continued strong demand for bottle water, the expansion of niche carbonated soft drink markets and new packaging applications for PET.

Polymer, Elastomer and Synthetic Fiber

461

Fig. 21.27: Polyester from purified terephthalic acid

As the use of PET in packaging matures in established segments like carbonated soft drinks and bottled water, the world PET resin market is expected to be around 17 million tons by 2010. PET packaging resin has come of age and is now a globally traded commodity with inter regional world trade amounting to around 15% of global consumption (Chemical News and Intelligence, www.conionline.com). The IntegRex™PET processsis the world’s first integrated PET process specially designed for packaging resin. Compared to conventional PTA and PET processes, IntegRex™technology stands out for fewer process steps, is simpler, more reliable and

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Chemical Process Technology

more cost efficient. Polybutylene terephthalate which was introduced in 1962 and was made available around 1971 is made by condensing terephthalic acid or dimethyl ester with 1,4-butanediol. Polybutene terephthalate is polymerized in two stages. In first stage bis-hydroxy butyl terephthalate (Bis-HBT) is formed through trans-esterification of DMT with 1,4-butanediol. In second stage, Bis-HBT is polycondensed into PBT with elimination of 1,4-butanediol. The reaction involved is:

PBT finds use as engineering material due its dimensional stability, particularly in water and its resistance to hydrocarbon oils without showing stress cracking, high mechanical strength and excellent electrical properties, lower water absorption. Blends of PET and PBT are used in glass fibers reinforced grade. PBT find application in pipe, pump hosing, impeller bearing brushing, gear wheels, and electrical parts such as connector and fuse cases, automotive parts and toothbrush bristles. Because of thermoplastic nature both PET and PBT may be injection or extrusion molded. 21.8.3 Acrylonitrile, Acrylic Fiber, Modified Acrylic Fiber, Polyurethane

Acrylic fibers are third largest class of synthetic fiber after polyester and nylons. Commercial acrylic fiber was developed by DuPont in US as Orlon while modified acrylic fiber was developed by Union carbide as Dynel. In acrylic fiber monomer is acrylonitrile while in case of modified acrylic fiber acrylonitrile is copolymerized with vinylidiene chloride vinyl chloride. The halogenated monomers impart flame resistance and are suitable for home furnishing, protective coatings, sleepwear, and hospital blankets. Characteristics of acrylic fiber and modified acrylic fiber are mentioned in Table 21.26. Table 21.26: Characteristics of acrylic fiber Name of the Monomer synthetic fiber Acrylic fiber

Basic chemicals

Acrylonitrile Propylene, ammonia

Properties of the synthetic fiber

Characteristics

Density

Moisture Melting regain point

1.17

1.5–2.5

Sticking point = 235ºC

Silk like luster, good resistance to weathering, alkalies and acids, high bulking, tensile strength 2–3 g/denier. Elongations at break 16–21%

Modified Acryloniacrylics trile, vinyl chloride, vinylidene chloride

Propylene, ammonia, ethylene

–

1.5–2.5

Sticking point = 235ºC

Good resistance to weathe­ ring, alkalies and acids, high bulking, good resis­ tance to combustion

Polypro­pylene

Propylene

0.85– 0.94