Applications in Design and Simulation of Sustainable Chemical Processes [1st ed.] 9780444638861

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APPLICATIONS IN DESIGN AND SIMULATION OF SUSTAINABLE CHEMICAL PROCESSES ALEXANDRE C. DIMIAN COSTIN SORIN BILDEA ANTON A. KISS

Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, Netherlands The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States Copyright Ó 2019 Elsevier B.V. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).

Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-444-63876-2

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PREFACE

Man’s yesterday may ne’er be like his morrow; Nought may endure but Mutability. Percy Bysshe Shelley (1792e1822).

Sustainable Process Technology is the major change that chemical process industries will undergo in the next years and over a longer perspective. The strategic goal is an effective transition from fossil resources, coal, oil, and gas to renewable raw materials, mainly based on biomass and recycled waste. The integrated biorefinery becomes the new industrial concept for manufacturing biofuels, biochemicals, consumer products, food products for humans and animals and for supplying energy, at best from local available resources. Biobuilding blocks allow constructing a complete offer of chemical products in a way that is comparable or superior to traditional routes starting from fossil materials. Challenges for research and development of sustainable technologies emerge, but these are also opportunities for innovation. The purpose of this book is coaching and training on how to create conceptual flowsheets for sustainable processes by employing systematic process design methods and powerful simulation tools. Boosting the creativity is the final objective and the added value for the reader. For this reason, the book starts with a section devoted to key features of the Sustainable Process Technology and to Process Systems Engineering approach. Fifteen representative case studies are presented afterward. The goal is to develop original process flowsheets and not to reproduce existing technologies. Accordingly, each case study brings elements of novelty, inviting the reader to deepen or to extend the approach to similar applications. Each project starts from the fundamental knowledge about chemistry, thermodynamics, and reaction kinetics, considering the impact on health, safety, and environment as well. A conceptual flowsheet is developed by applying a systemic methodology (process synthesis). Several alternatives are generated, from which the most suitable one is refined by implementing energy saving, process integration, optimization, and plantwide control.

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Computer simulation is employed intensively for data analysis, investigating the feasibility of alternatives, sizing the equipment, and performing the energy and economic studies. The results are the input of a sustainability analysis that supplies the key process performance in terms of material intensity, energy requirements, emissions and ecological footprint, and capital and operation costs. The results may be compared with flowsheets and performance indices of industrial licensed processes. In most cases, the technical solutions proposed in this book are original being the object of peer-evaluated publications. Chapter 1 Sustainable process technology presents the biorefinery concept and the key building blocks produced from renewable raw materials, as biomass, oil, proteins, and bio-based syngas. The most important are methanol and ethanol, which may be converted to C2 and C3 olefins, which together with the glycerol and butanol derivatives may cover all the products available today from C2eC4 petrochemicals. Other important biobuilding blocks available by the fermentation of sugars, as lactic acid, 3-hydroxipropanol, succinic acid, sorbitol, adipic acid, and furandicarboxylic acid, etc., ensure the emergence of new ecological biochemicals, namely biodegradable polymers. The chapter presents also the challenges for process design and simulation raised by biorefineries. Chapter 2 Process Systems Engineering approach presents the systematic conceptual process synthesis applied in the book. This is based on the seminal Hierarchical Approach upgraded by the authors’ experience. Thus, the ecological issues are introduced early at the Input/Output level. The basic flowsheet architecture is determined at the level of Reactor/Separations/ Recycles. Here other systemic issues may be analyzed, as Energy Integration around the reactors, and Plantwide Control strategy. The development of the separation is driven by a systematic task-oriented methodology. Chapter 3 Methanol focuses on methanol as a major commodity and energy carrier. Today, significant research effort is devoted to the development of technologies for methanol synthesis by syngas and CO2 hydrogenation. The chapter deals with methanol manufacturing from synthesis gas (obtained from methane, biogas, coal, or biomass). A new greener alternative process based on carbon dioxide hydrogenation is also explored. Despite being a mature technology, new developments are still emerging because of new catalysts and to more efficient reactor design. Chapter 4 Olefins by MTO process deals with the conceptual design of energy efficient and cost-effective manufacturing of

PREFACE

olefins from methanol. The innovative solution consists in full recovery of the energy generated by reaction. Mechanical vapor compression is employed for upgrading the temperature/ enthalpy profile of the condensing water/hydrocarbon mixture. The energy released in reactor is used in a combined heat and power cycle. The olefin separation and purification take place in a compact scheme of five columns, integrated with the reaction section for energy saving. Heat pump is implemented for propylene purification. Operation and capital costs are minimised because the process may fully cover the energy needs and employ a minimum number of units. Chapter 5 Propylene by olefin metathesis investigates viable solutions for conversion of low-value by-products to high-value olefins, as the demand for propylene is of increasing interest. The chapter considers the olefin metathesis, a process which uses 2-butene (a by-product from fluid catalytic cracking unit) as feedstock for obtaining more valuable olefins. Several process alternatives are generated and evaluated in a hierarchical approach, with the goal of determining the process flowsheet which returns the highest revenue for a fixed flow rate of raw materials. Chapter 6 Isobutene dimerization deals with a process that yields a high-octane number olefinic gasoline. Two options are presented: Reactor/Separation/Recycle (RSR) and reactive distillation (RD). These are compared in terms of specific energy and catalyst requirements. The RSR appears to be more attractive than the RD process, as it allows both the reactor and the separation units to operate close to their optimal conditions. The RD process operates in the overlapping window of process conditions for reaction and distillation and thus suffers from this inherent trade-off. Chapter 7 Castor oil biorefinery converts this valuable resource in special biodiesel and high-value chemicals. The central building block is the methyl ricinoleate ester produced by transesterification with methanol. The technology makes use of a two-step process based on homogeneous base catalysis, employing agitated multicompartment reactor. Methyl ricinoleate ester is converted by pyrolysis to heptaldehyde, which finds many applications in cosmetics, and u-amino-undecylenic acid, a monomer for high-value polyamides. The process involves complex chemistry and species, for which properties estimation from structure was applied. The flowsheet development uses systematic methods and computer simulation, kinetic modeling of reactors, and thermodynamic assessment of separations. Particular attention is given to saving energy aspects.

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The manufacturing of commodity biodiesel has a synergetic effect with the production of high-value biochemicals. Chapter 8 Bioethanol and biobutanol are bioalcohols produced by the action of microorganisms and enzymes through the fermentation of sugars, starches, or cellulose. A key problem in the production is the energy-intensive downstream processing of the diluted mixture obtained by fermentation. This chapter examines the processes for manufacturing bioethanol and biobutanol, with emphasis on the separation and purification as the final costly steps in the process. The optimization of distillationbased processes is carried out and used as a comparison basis for more advanced separation processes (dividing-wall column and heat pumps assisted distillation). Chapter 9 Biodiesel presents the conceptual design of two manufacturing processes. Specific technology issues are developed regarding feed pretreatment, purification, and separation methods are discussed. The first case study considers biodiesel manufacturing from rapeseed (canola) oil using heterogeneous catalysis and two-step transesterification with intermediate glycerol separation. The simulation uses detailed reaction kinetics in view of fulfilling the product specifications. A towertype reactor and a novel variable-time reactor are compared. The second process deals with biodiesel from used cooking oil using homogeneous alkali catalysis. Alternatives for esterification of free fatty acids with methanol are compared: batch reactor with homogeneous catalysis and reactive absorption using solid catalysts, the last bringing substantial advantages. Moreover, a process-intensification method based on reactive distillation is applied for transesterification. Chapter 10 Dimethyl ether (DME) focuses on the simplest ether, which is a useful precursor to other organic compounds and a green aerosol propellant. Recently DME has been considered as candidate for nonconventional cleaner transportation fuels, namely in Scandinavian countries. This chapter handles conceptual process design issues of a classic reaction/ separation/recycle process based on adiabatic reactor, as well as of several process intensification alternatives, with a focus on a novel catalytic distillation process. The key design parameters are identified and steady state optimization (minimizing the annual costs) is performed in Aspen Plus. A combined process (gas-phase reactor and reactive distillation) is also presented as an option for revamping existing DME processes based on methanol dehydration.

PREFACE

Chapter 11 Fuel additives presents several alternatives for converting glycerol into more valuable products, as glycerol is obtained in large quantities as a by-product from biodiesel production. Thus, etherification with isobutene or tert-butanol leads to glycerol ethers, which can be used as fuel additives. Moreover, reaction with aldehydes and ketones leads to acetals and ketalsdoxygenated compounds which, besides improving the properties of fuels, have applications as surfactants and disinfectants or in cosmetic and pharmaceutical industries. Chapter 12 Styrene deals with conceptual design of a process based on ethylbenzene dehydrogenation in adiabatic type reactors. High-performance catalyst is employed. The technology makes use of superheated steam as inert, requiring a large amount of energy. An innovative solution is proposed that gives a spectacular energy saving. The idea is running the water evaporation for steam generation under vacuum followed by mechanical vapor compression (MVR) for restoring the pressure. This change allows installing a feed-effluent-heat-exchanger (FEHE) in an evaporation/condensation zone that concentrates 57% from energy saving. An efficient network of five FEHE units diminishes the utility consumption by 70% with respect to the base case. The economic analysis demonstrates that the cost of energy required by the reaction section dominates the cost of separations. Despite the investment in compressor, the MVR alternative brings a reduction in total annual cost by 30%. Chapter 13 Acetic acid from methanol develops the conceptual design of a sustainable process using rhodium/iridium catalyst. The emphasis is set on energy efficiency by optimizing the reactor cooling in relation with the separation system. In the homogeneous process the separation section consists of three columns, while the reaction section may cover about 45% from the heat needed in the separation section. If heterogeneous catalyst is employed, the separation is reduced to a sequence of two columns. Moreover, the energy requirements may be reduced by 75% if heat pump is applied to acetic acid purification. The economic analysis allows the estimation of capital and operation costs, as well as the product price for 20% return on investment. The case study also shows how to calculate comprehensive sustainability metrics for process design. Chapter 14 Acrylic acid from glycerol deals with the conceptual design of a sustainable process, since the renewable raw material is available in large amounts and at low cost from biodiesel manufacturing. The chemistry involves two steps: dehydration of glycerol to acrolein and further oxidation of

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acrolein to acrylic acid. Heteropolyacids and zeolites catalysts have good performance, but a regeneration method must be included in the reactor design. The study examines three alternatives: bubbling fluidized bed, circulating turbulent fluidized bed, and circulating fluidized bed. Two alternatives for separating the acrylic acideacetic acidewater mixture are developed, using azeotropic distillation and liquideliquid extraction. The exothermal reaction gives good options for energy saving by heat integration. The capital costs are dominated by reactors. The sustainability analysis indicates that the process is a viable green alternative to the petrochemical methods. Chapter 15 Acrylic esters considers the design, plantwide control, and economic evaluation of several processes for higher acrylates production, using solid catalysts. Three reaction/ separation/recycle (RSR) process alternatives for 2ethylhexylacrylate are considered. Each employs a fixed bed reactor with Amberlyst 70 as catalyst and standard separation equipment. The alternative using distillation as first separation step has better economic indicators due to better use of the raw materials, compared to alternatives where a simple flash or a decanter are used. The reactive distillation (RD) technology allows great reduction of the capital and operating costs. Then, the production of n-butyl acrylate is addressed. In this case, the low relative volatility of acrylic acid and n-butyl acrylate clearly favors RD over conventional RSR processes. Dynamic simulations show that, in all cases, the control structure can achieve large throughput changes and copes well with the contamination with water of both fresh reactants. Chapter 16 Dimethyl carbonate focuses on an eco-friendly versatile chemical that is widely employed as a green solvent, methylation, and carbonylation agent and potentially as a fuel additive. The chapter describes two processes for dimethyl carbonate (DMC) synthesis, which avoid the disadvantages of the traditional methanol phosgenation route. The direct synthesis from methanol and carbon dioxide is an environmentally interesting process. Membrane reactors are suggested as a way of overcoming the equilibrium limitations by continuous removal of water from reaction product. The same raw materials can be also used in a more complex route. Thus, DMC is obtained by the transesterification reaction between propylene carbonate (PC) and methanol, where operation at an excess of PC avoids the costly separation of the methanoleDMC azeotrope. The reaction of the propylene glycol by-product with urea leads to PC

PREFACE

(recycled) and ammonia (converted to urea by reaction with carbon dioxide). Chapter 17 Polyesters explores various configurations of a reactive distillation (RD) process for polyesters production. RD is a great process intensification technique that can drastically enhance the unsaturated polyesters synthesis. Multi-product simulations were used to find the operational parameters and transition time for different grades of polyesters made in the same equipment. The results of the rigorous simulations carried out in Aspen Custom Modeler reveal that the best setup has the reactive stripping section as a packed or trayed bubble column and the reactive rectifying section as a packed column. With respect to the feed policy, the feeding of monoesters to the RD column significantly intensifies the polyester process as compared to an anhydride reactant fed to the column. Furthermore, the product transition time in this configuration is also significantly reduced as compared to the other configurations. We are aware that some errors might still be present, despite all of our efforts in the revision and the valuable support of Elsevier. We are open to any remarks and critical suggestions and therefore grateful in advance for feedback from our readers. The authors acknowledge the contribution to this book of many colleagues and students from the Universities of Amsterdam, Delft, Eindhoven, Twente, and Manchester where the authors have spent a large part from their scientific and teaching activities. We express also our gratitude to the colleagues and students from the University Politehnica of Bucharest, where computer simulation is used for decades to teach Chemical Engineering subjects. The authors express their appreciation to company AspenTech for making available to academia an outstanding simulation technology software. And last but not the least we express our gratitude and love to our families for their continuous support and understanding. Alexandre C. Dimian, Costin S. Bildea, Anton A. Kiss

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1 SUSTAINABLE PROCESS TECHNOLOGY CHAPTER OUTLINE 1.1 Introduction 4 1.2 Sustainable Development 5 1.3 Renewable Versus Fossil Raw Materials 7 1.3.1 Biomass 8 1.4 Biorefinery Concept 11 1.5 Chemicals From Biomass 14 1.5.1 Chemicals From C1 Biobuilding Blocks 15 1.5.2 Chemicals From C2 Biobuilding Blocks 16 1.5.3 Chemicals From C3 Biobuilding Blocks 17 1.5.4 Chemicals From C4 Biobuilding Blocks 18 1.5.5 Chemicals From C5 Biobuilding Blocks 19 1.5.6 Chemicals From C6 Biobuilding Blocks 21 1.5.7 Other Chemical Products Obtained From Biomass 1.6 Biofuels 23 1.6.1 Economic Significance 23 1.6.2 Sustainability Issues 25 1.6.3 Biodiesel 28 1.6.4 Bioethanol 29 1.6.5 Other Biofuels 30 1.7 Biopolymers 31 1.8 Process Design Issues 32 1.8.1 Screening of Alternatives 32 1.8.2 Feedstock Pretreatment 32 1.8.3 Chemical Reactors 34 1.8.4 Separation Processes 34 1.8.5 Process Intensification 35 1.9 Economic Challenges 36 1.10 Conclusions 38 References 39

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Applications in Design and Simulation of Sustainable Chemical Processes. https://doi.org/10.1016/B978-0-444-63876-2.00001-2 Copyright © 2019 Elsevier B.V. All rights reserved.

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1.1 Introduction This introductory chapter presents the perspective of fundamental changes in chemical process industries (CPI) generated by the transition from fossil to renewable raw materials and the requirements of sustainable development. The impact of raw materials on process technology and process design is significant, considering that their weight in the final cost of chemical products is typically from 60% to 80%. Rebuilding the chemical industries on new feedstock bases will accelerate considerably in the next years. The answer to various challenges is promoting the innovation. Using renewable raw materials boots the discovery of new “green” chemistries and catalysts. Sustainable technology requires focusing the process design on the minimization of materials and energy consumptions, the reduction of waste, toxic materials and greenhouse gases (GHG) to protect the health and the environment. Chemistry and chemical engineering should work together to bring innovative solutions, beginning with initial stages of projects. Traditionally, the process design of a new process started when the research on chemistry was (almost) completed. It followed various scale-up stages from laboratory to industrial process, including several demonstration and pilot plants. Computer process simulation radically changed this situation. The power of modeling imbedded in the flowsheeting software allows investigating the influence of numerous factors on the process design, in many cases close to the physical reality. Even when the detailed modeling of some units is not accurate, the simulation can offer a precious global view of the process behavior. The systems approach focuses on the functions of units and their interactions rather on the detailed design (Dimian et al., 2014). On this basis, the management can take decisions regarding the feasibility of the design, the availability of hardware, and the incurred costs and risks. Today, process simulation is the key tool in chemical process design. Starting from a given chemistry and property data, the designer can develop a conceptual flowsheet, determine material and energy balances, evaluate the risks on health, safety and environment, as well as the economic feasibility in terms of operation (OPEX) and capital costs (CAPEX). This is the goal of the present book: teach how to produce realistic flowsheets by using advanced process simulation tools available today to a large population of students and professionals. However, switching from fossil to renewable raw materials will take some time. The development of radically innovative

Chapter 1 SUSTAINABLE PROCESS TECHNOLOGY

processes needs time and substantial financial investments, especially in biotechnology. In the next two decades, the fossil resources will continue to ensure a large part of fuels and base chemicals. The manufacturing of drop-in chemicals from biosources, which can replace partially fossil counterparts, can preserve the ability of using existing plants and processes, as for example, the use of olefins for manufacturing traditional polymers.

1.2 Sustainable Development Following a wide-agreed definition (Brundtland, 1987), “Sustainable development meets the needs of the present without compromising the ability of future generations to meet their own needs.” Note that this definition does not neglect the present because the move to this paradigm must start now. Fig. 1.1 illustrates the sustainable development concept as a balanced state that regards three main domains of human activities: economy, environment, and society. This concept reflects a systemic viewpoint, in which the sustainability state is accomplished only when the three components are simultaneously considered, by including positive and negative interactions. Thus, achieving the eco-efficiency of products in terms of economic and environmental performances is not sufficient without integrating the socio-efficiency, such as

Socioefficiency

Social Responsibility

Economic Efficiency

Sustainable Development Ecoefficiency

Eco-social balance

Environment Protec on

Figure 1.1 Sustainable development as a compromise of three constituent parts: environmental, social responsibility, and economic efficiency.

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jobs creation, decent revenues, etc., and the eco-social balance, such as protecting the life and environment quality. For example, the project for implementing a biorefinery plant should consider as key goals, besides profitability, the opportunity to put more value on local biomass resources and to create new jobs, but without damaging the environment and the landscape. Sustainable development is the paradigm that will drive the progress in CPI for the next decades. In Europe, the SusChem initiative (www.suschem.org) has been launched as a common platform for guiding the future R&D actions, as well as the industrial investments. A roadmap called SPIRE (Sustainable Process Industry through Resources and Energy Efficiency) defines the strategy (up to 2030) of a publiceprivate partnership (www.spire2030.eu). This document prescribes the most promising research activities and innovative technologies for achieving the sustainability goals. Emphasis is put on a gradual switching from fossil to renewable raw materials, by promoting the use of biomass and the valorization of waste, residue streams, and recycled materials. Together with chemical engineering, the chemistry plays a central role in developing innovative processes, in which catalysis and biocatalysis are key drivers for converting the material resources with higher yields and lower energy consumption. The impressive progress in the last years in “green chemistry” is a valuable support for the case studies and projects proposed in this book. Among the publications in this field, we recommend the monographs edited by Cavani et al. (2009) and de Jong and van Ommen (2015). The principles of sustainability analysis were outlined in Chapter 17 of our book (Dimian et al., 2014). These include topics as life cycle assessment (LCA), eco-efficiency analysis, socioefficiency analysis, and metrics for design projects. The reader is also encouraged to refer Chapter 16 of the same book, where a number of computational tools for handling health, safety, and environment topics are described. The increasing interest in the use of renewable raw materials, namely of biomass, for producing fuels and chemicals is reflected by the large number of books and monographs published recently. References can be found further in this chapter. These works address predominantly chemistry and technology aspects, but conceptual process design (the invention of flowsheets) is treated only occasionally. The present book aims to compensate this drawback. Useful case-studies can be found also in a previous book (Dimian and Bildea, 2008).

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1.3 Renewable Versus Fossil Raw Materials In the context of the finite availability of fossil raw materials, namely coal, oil, and natural gas, the use of renewable raw materials, especially of biomass, becomes a crucial issue for the future of CPI. The fossil reserves are concentrated in few places, and as a consequence, they become focal points of geopolitical conflicts. In contrast, the biomass is abundant and more evenly distributed over the planet. For countries having only limited fossil resources, incorporating biomass in the industrial profile can contribute to preserve the energetic independence and bring new opportunities for chemical industry, namely in the field of higher value products. Fig. 1.2 presents the today’s problem of resources. The feedstock for energy and petro-refinery plants is based essentially on the use of fossil reserves, namely coal, oil, and natural gas. These industries deliver useful fuels, chemicals, and energy for ensuring the fundamental needs of the society, e.g., for industry and agriculture, food, transportation, heating, etc. The output of these activities results in the air pollution by GHG, particle matters (PM), toxic gases such as NOx and SO2, as well as in soil and water pollution by waste. Putting in a nutshell, the limited fossil

Figure 1.2 Fossil resources versus renewable raw materials.

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resources are exhausted irreversibly and inexorably. In 2015, the total world hydrocarbon production was about 7.8 Btoe/y (billions tons oil equivalent/year), from which 4.6 was oil and 3.20 gas, respectively (BP Statistical Review, 2016). The exhaustion of oil and gas resources is the object of a harsh debate via the model of the “peak of reserves.” Recently, the success of the shale gas in the United States fueled this controversy. However, it is quite clear that the fossil reserves will be exhausted in a short historical time. As very precious, the hydrocarbon resources should be preserved for the next generations. Following the above report, the ratio of world’s reserve to production in 2015 was about 50.7 years for oil and 52.8 years for gas. Considering the massive rise of world’s population and the legitimate needs for better life, it is obvious that the development based only on fossil resources is not bearable at medium and longer terms. Instead, another approach should be considered, based on renewable resources and circular economy, which means recycling used products and waste. The biomass is the natural energy carrier from the sun to the terrestrial life. At the origin of fossil resources is still the biomass, which was converted in hydrocarbons by processes that occurred in the deep ground during several geological periods! Modern chemical technology must solve the challenging task of replacing fossil hydrocarbon processing by biomass conversion into similar or new products. The modern technology concept is the biorefinery, which supplies fuels chemicals and energy for satisfying the needs of the society. The implementation of this development model implies the availability of advanced technologies for the minimization of energetic and material resources, as well as for recycling the waste from agriculture, industry, or domestic activities. New green chemistries should be invented, and sustainable process design should be generalized.

1.3.1 Biomass Biomass designates materials derived predominantly from plants, which may be used as feedstock in agriculture or industry. From chemical composition viewpoint, biomass is a mixture of complex organic molecules containing for the most part carbon, hydrogen, and oxygen, with small amounts of nitrogen and sulfur, as well as with traces of other elements including metals. In the most cases, the biomass composition is approximately carbon 47%e53%, hydrogen 5.9%e6.1%, and oxygen 41%e45% (EC sugar platform report, 2015). The presence of a large amount of oxygen in biomass makes a significant difference to fossil hydrocarbons. When used as fuel, biomass is less efficient, but more

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suited for getting higher value chemicals and bioproducts as containing already functional molecular groups. The biomass used as industrial feedstock can be supplied by agriculture, forestry, and aquaculture, as well as resulting from various waste materials. The biomass can be classified as follows: 1. Agricultural feedstock • Sugar crops (sugarcane, sugar beet, cassava) • Starch crops (wheat, maize, potatoes) • Oil crops (rapeseed, soy) 2. Dedicated energy crops • Short rotation coppice (poplar, willow, eucalyptus) • High-yield perennial grass (miscanthus, switchgrass) • Nonedible oil plants (Jatropha, Camelina, sorghum) 3. Lignocellulosic waste material • Forestry wood • Agricultural by-products (straw, corn straw) • Industrial by-products (bagasse, paper pulp) 4. Algal crops from land and sea farming The feedstock origin determines the so-called biofuel generation, as presented in Fig. 1.3. The first-generation (1G) biofuels make use of agricultural resources, and as a consequence, they can enter in antagonism with the food chain (edible feedstock). Thus, 1G bioethanol is produced from starch (corn) and sugar (sugarcane, sugar beet) sources, while 1G biodiesel is manufactured as fatty acid methyl esters (FAME) from vegetable oils, namely rapeseed (canola), soya, and palm. However, the merit of the 1G fuels was opening a new chapter in the chemical technology, by setting the bases of large-scale biofuels and biochemicals based on renewable raw materials. In particular, the

Figure 1.3 Relation between biomass feedstock and generation of fuels.

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bioethanol manufacturing, now a global leading chemical, brought substantial progress in the fermentation technology, including the development of efficient enzymes and reaction systems. The FAME biodiesel technology evolved from simple batch to more sophisticated solid catalyst processes, with the advantage of supplying substantial amounts of glycerol, which for today is an important feedstock for getting higher value chemicals. Thus, the development of cost-efficient technologies for biofuels enables the development of innovative technologies for producing more valuable chemical products. While early biofuels were based on easy extractable sugars and vegetable oils, the second-generation (2G) biofuels take advantage from low-value nonedible biomass as dedicated energy crops grown on nonarable land and waste of lignocellulosic or lipid nature. In addition, there is no connection with the food chain. However, the technology of 2G biofuels is demanding in terms of equipment, enzymes, and chemicals. Further progress in sustainability is expected from the thirdgeneration (3G) biofuels based on very high-yield algal crops. The algae cultures can be fed directly with concentrated CO2 streams resulting from industrial processes, such as from coal power plants and from fermentation of sugars. The research of industrial algal farming is in rapid expansion, and the results are very spectacular. Algae can produce triglycerides similar to those originating from plants, but with a yield higher by an order of magnitude. More recently, algal cultures can produce directly various hydrocarbon molecules, including light olefins. The emergence of 1G biofuels raised strong polemics, mainly because of diverting farmland from the food supply chain and thus increasing the prices, especially in the developing countries (see also the page “food versus fuel” in Wikipedia). It is agreed today that the effect of biofuels on the food chain should be weak, mainly because of the limitation of surfaces allowed for energy crops, in general at few percentage from the total farmland. In the same time, the advent of biofuels incited to substantial improvements in farming technology, both in cultivation and harvesting. Thus, after data of American farmers (NCGA, 2015), the yield of corn rose by 70% between 1980 and 2015, hitting a record of 167.5 bushel/acre or 167.5  25.4/0.4047 ¼ 10,514 kg/ha. The yield of conversion of corn to bioethanol could rise to 2.8 gallon/bushel or 2.8  3.785  1000/25.4 ¼ 417 L/ton. This could increase by 20% by employing highly fermentable starch hybrids. The vegetable cake or distiller’s grains obtained after ethanol fermentation process are employed for feeding livestock, such as cattle, pigs, and poultry, while the corn stover may be used

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for supplying energy in processing and/or as feedstock for a lignocellulosic biorefinery. For a typical yield of 10 tonnes dry biomass per hectare and taking into account an ethanol yield of 300 L/ tonne, it would bring a supplement of 3000 L/ha. Thus, the total bioethanol yield from the whole corn plant could reach more than 8000 L/ha. Note that whole US bioethanol production from corn in 2015 (31 Mtpy) has been obtained by increasing the crop productivity and not the farming surface. In this way, the manufacture of biofuels can contribute to ensure good and stable revenues for farmers. Using only 1.4% of the arable land, Brazil has managed to replace almost 42% of the gasoline with ethanol (www.sugarcane.com). The cultivation of agriculture crops for biofuels is notable in countries having large surfaces for agriculture, such as the United States (corn and wheat), Brazil and India (sugarcane), Malaysia and Indonesia (palm oil), and Argentina (soy). It can be noted that nonedible plants, such as Jatropha and Camelina, can be grown with good yield for producing biodiesel in developing countries, easing the pressure of importing high-price oil. Europe has only limited farmland surfaces for biofuels, typically cultivated with rapeseed and sugar beet, although some extensions could be envisaged in Eastern Europe. In the 2G biofuels, the lignocellulosic feedstock (LCF) consists in energetic crops cultivated on low-value soils, by-products from first processing, as bagasse from sugarcane, straw from wheat, corn stover, as well as municipal or industrial waste. From chemistry viewpoint, LCF contains, in general, three main useful components: cellulose, hemicellulose, and lignin. Table 1.1 gives the relative composition for some representative raw materials.

1.4 Biorefinery Concept There is not only an analogy between the concepts of petro- and biorefinery but also fundamental differences. A classic petrorefinery deals primarily with processing oil and gas feedstock for supplying fuels for transportation and heating, as well as energy (steam and electricity). In a much more efficient production mode, petrochemical complex, the refinery outlet can be converted to petrochemical building blocks, which are primary olefins and aromatics (BTX), by thermochemical energyeintensive processes. These molecules are relatively limited for applications. Furthermore, more reactive compounds are obtained by inserting organic functional groups, for example, alcohols, acids, halogens, amines, etc., by spending considerable amounts of energy, and by

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Table 1.1 Typical Composition of Biomass in Wt%. Biomass

Cellulose (%)

Hemicellulose (%)

Lignin (%)

Softwood Hardwood Wheat straw Corn straw Switchgrass

35e40 45e50 33e40 35e41 30e50

25e30 20e25 20e25 17e28 10e40

27e30 20e25 15e20 10e17 5e20

using sophisticated processes. In this way, a large variety of molecules for various applications are obtained, such as intermediates for chemical synthesis, polymers, rubbers, solvents, etc. As an order of magnitude, 90% from global refinery output is directed to fuels’ market, while only 10% is converted to petrochemical products (World Petroleum Council, 2013). A biorefinery has analogue functions, but this time starting from biomass as feedstock. A biorefinery supplies in the first place fuels, chemicals, and energy, but may also deliver food products for livestock and humans, and a large variety of high valueadded products, such as biopolymers. In viewing of manufacturing chemicals, the biomass processing consists of generating in a first stage specific biobuilding blocks. It should be stressed that these are much more suitable for the organic synthesis than the petrochemical counterparts because most of them incorporate already ready-for-synthesis functional groups. Moreover, the biobuilding blocks are got by biochemical processes taking place near ambient temperatures with relatively low-energy requirements. However, the efficient production of biobuilding blocks requires advanced biotechnologies and enzymes, as well as innovative separation methods. The manufacturing of biofuels was the main incentive for constructing biorefineries, starting with the year 2000. The plants producing biochemicals followed, and now the development is in fast progress. Fig. 1.4 presents the essential features of a biorefinery (Dimian, 2007). In the first step, the biomass is submitted to preprocessing, from which some primary products are directly obtained. For example, pyrolysis oil obtained by treatment at elevated temperature leads to valuable chemicals, such as alcohols, esters, phenols, and complex organic molecules, which otherwise would require

Chapter 1 SUSTAINABLE PROCESS TECHNOLOGY

Figure 1.4 Biorefinery concept.

complicated organic synthesis. After preprocessing, the conditioned biomass is sent to dedicated technology platforms to be converted into desired products. The platforms are determined primarily by the compositional characteristic of the feedstock and the chemistry routes, as well as by the technology used for conversion (thermochemical, biochemical, chemical). Biorefinery is today a central issue for the future of CPI. There are several monographs devoted to this subject, from which we mention Kamm et al. (2006), Dembiras (2010), Aresta et al. (2012, 2015), Waldron (2016). The concept of biorefinery was the object of an international work of systematization hosted by the International Energy Agency (IEA) as Bioenergy Task 42 (de Jong et al., 2012). Several technology platforms have been identified as follows: • Biogas: CH4 from anaerobic digestion. • Syngas: mix of CO and H2 from biomass gasification. • Hydrogen by methane steam reforming, water electrolysis, and fermentation. • C6 sugars: hydrolysis of sucrose, starch, cellulose, and hemicelluloses. • C5 sugars: hydrolysis of hemicellulose. • Lignin: processing of lignocellulosic biomass. • Pyrolysis oil. • Lipids (triglycerides) from oil crops, culture of algae, waste oils and fats. • Organic juice as liquid after pressing wet biomass. • Electricity and heat to be used internally or sold to the grid. The most efficient use of biomass is by an integrated biorefinery complex that consists of coupling the manufacturing of

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Chapter 1 SUSTAINABLE PROCESS TECHNOLOGY

Figure 1.5 A lignocellulosic biorefinery for manufacturing fuels, chemicals, and polymers.

biofuels and biochemicals, analogue to an integrated refinery and petrochemical complex. The goal is getting optimal economic efficiency by the valorization of high-volume low-value biofuels with low-volume high-value biochemicals. Fig. 1.5 shows such an integrated biorefinery based on the processing of LCF biomass. A large variety of products can be obtained, from commodity fuels to valuable resins and biopolymers.

1.5 Chemicals From Biomass Fig. 1.6 presents the main biobuilding blocks together with raw materials and technological platforms, as well as key biochemical products. These are ranged in the order of carbon numbers from C1 to C6. It can be observed that the biobuilding blocks make possible the synthesis of a large variety of basic chemicals and polymers manufactured today from fossil materials. Moreover, they are unique resources for some high-value ecological chemicals, namely biodegradable polymers. However, a major drawback of biobuilding blocks is limited availability of aromatics (BTX). This is a long-term challenge for biotechnology. The next sections will present briefly some important valuable chemicals that can be produced from renewable resources. More information can be found in specialized monographs, as published by Sengupta and Pike (2013) and Clark and Deswarte (2015).

Chapter 1 SUSTAINABLE PROCESS TECHNOLOGY

Figure 1.6 Building blocks for organic synthesis in biorefineries.

1.5.1 Chemicals From C1 Biobuilding Blocks As shown in Fig. 1.7, the synthesis of chemicals starting from C1 biobuilding blocks can be organized around methane and methanol. The main source of methane is the biogas, which can be obtained by anaerobic digestion of municipal solid waste. Methanol is manufactured from syngas, which in turn is obtained from biomass by thermal processing, as well as from biogas by steam reforming. Syngas can be converted further to various hydrocarbon species, including gasoline and diesel fuels, by employing FischereTropsch technologies. State of the art of

Figure 1.7 C1 building blocks starting from syngas.

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Chapter 1 SUSTAINABLE PROCESS TECHNOLOGY

FischereTropsch technologies can be found in the monograph of De Clerk (2011), as well in the part III of the multiauthor book on biomass conversion edited by de Jong and van Ommen (2015). Syngas can recover the carbon practically from every carbonated source, for example, from municipal solid waste (MWS). Another important source in the future will be the lignin, which is obtained as subproduct from lignocellulosic biorefineries and paper mills. However, getting sustainable hydrogen for syngas is challenging, as methane reforming remains the best hydrogen source. Methanol is the most valuable C1 chemical. The book by Olah et al. (2009) presents an overview of the manufacturing processes, both classical and innovative, as well as numerous applications. Methanol can be produced from both fossil (namely coal and methane) and renewable materials, namely from syngas and recently by the hydrogenation of carbon dioxide from industrial exhausts. Chapter 3 deals with the methanol manufacturing by both methods. The conversion of methanol to gasoline is known for about 30 years, but today the most promising is the methanol-to-olefin technology. The conceptual design of a sustainable MTO process is handled in the Chapter 4. Several plants have been commissioned so far in China for ethylene and propylene production.

1.5.2 Chemicals From C2 Biobuilding Blocks The main C2 biobuilding blocks are ethanol and acetic acid (Fig. 1.8). Ethanol can be converted easily to ethylene and further to a variety of intermediates, such as ethylene oxide, ethylene glycol, etc., following the classical petrochemical routes. Bioethylene may be cost-competitive with petro-ethylene when low-cost bioethanol is available, as at presently from Brazilian sugarcane. For other sources, the price would be 1.3e2 higher. Fast progress is expected in the next years when the lignocellulosic biorefineries will arrive to maturity (IRENA, 2013). Moreover, for processes where ethylene is only partially responsible for the raw materials cost, such as vinyl chloride monomer and vinyl acetate monomer, the bioethylene can offer profitable alternative solutions, avoiding the need of an oil refinery environment.

Figure 1.8 C2 biobuilding blocks.

Chapter 1 SUSTAINABLE PROCESS TECHNOLOGY

Acetic acid can be produced by the fermentation of ethanol. Today the most efficient method is by the carbonylation of methanol, which is the object of Chapter 12. Other valuable chemicals can be further obtained, such as acetic acid esters and monomers, including vinyl acetate (Dimian and Bildea, 2008) and methyl methacrylate.

1.5.3 Chemicals From C3 Biobuilding Blocks The most important C3 biobuilding blocks are glycerol, propanediol, acrylic acid, lactic acid, and acetone. Glycerol is available today at low price and in large amounts from biodiesel manufacturing, but it can be produced also by the enzymatic fermentation of glucose. Glycerol can be employed as drop-in feedstock for producing traditional petrochemicals, such as epichlorohydrin and propylene oxide. Fig. 1.9 shows that other valuable chemicals may be obtained from glycerol, such as acrylic acid and methionine by acrolein (Dumesic et al., 2006), propylene glycol by hydrogenation (Dasari et al., 2005), and 1,3-propanediol by microbial conversion. For the last, a process based on corn starch fermentation is commercialized by DuPont for manufacturing Sorona polyester fibers. Acrylic acid can be obtained also by the dehydration of 3-hydroxypropionic acid, which is in turn obtained by the fermentation of starch (de Jong et al., 2012). Chapter 13 develops the conceptual design of an innovative process based on the dehydration of glycerol, while Chapter 15 continues its valorisation as esters. Cl O

OH

OH

HO

Epichlohydrine

1,2 Propanediol

1,3 Propanediol

OH

COOH

O

O

OH

HO

Acrylic Acid

OH

Acroleine

Glycidol

Glycerol O

HO

S OH NH2

Methionine

O t-Bu

O t-Bu

O

O

Glycerol t-butyl Ether

O

t-Bu

OH

HO COR

OH

COR COR

Mono & Di-glycerides Figure 1.9 Chemicals derived from glycerol.

O O O

Glycerol Carbonate

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Chapter 1 SUSTAINABLE PROCESS TECHNOLOGY

OH OH OH

Hydrogenation

O Acrylic Acid

1,2-propanediol Hydrogenation

OH OH Esterification

Dehydration

H O Acetaldehyde

OH OR

O

O Lactates

Lactic Acid Esterification

O Oxidation O 2,3-pentanedione

O

O

OH

O Polylactic O

O

O

Lactide

Pyruvic acid

Figure 1.10 Organic syntheses starting from lactic acid (Corma et al., 2007).

Fig. 1.10 presents routes for chemicals deriving from lactic acid. This can be produced economically by the enzymatic fermentation of glucose. Various chemicals can be obtained from lactic acid, such as acrylic acid, propanediol esters, and the valuable polylactic acid (PLA). Acetone can be produced from biomass by fermentation of starch or sugars via the well-known acetoneebutanoleethanol (ABE) process.

1.5.4 Chemicals From C4 Biobuilding Blocks C4 biobuilding blocks are based on butanols, succinic acid, and hydroxybutyric acid (HBA) (Fig. 1.11). N-butanol was produced early by the fermentation of sugars in the ABE process. This process was not competitive until recently, when technology progress brought it back to the industrial scene, namely in China. Isobutanol emerged HO

O

O

OH

n-Butanol

OH

Succinic Acid O

HO

HO

iso-Butanol

OH

beta-Hydroxibutyric Acid

Figure 1.11 C4 biobuilding blocks.

Chapter 1 SUSTAINABLE PROCESS TECHNOLOGY

recently as a valuable biobuilding block for aviation gasoline and for the replacement of C4 petrochemicals. It can be economically produced by the fermentation of C5 and C6 sugars with special yeasts, as demonstrated by the firm GEVO in the United States (www.gevo.com). Recently, a Dutch consortium started a value chain biorefinery around isobutanol in the Rotterdam harbor area (Posada, 2014). Then, isobutene can be obtained via dehydration. Global Bioenergies in France (www.global-bioenergies.com) is developing a process that converts glucose directly to isobutene and further to isooctane, a key component of gasoline. These breakthrough developments can open large opportunities, namely as drop-in chemicals and fuels. Other possibilities emerge in the field of aromatics, such as p-xylene manufacturing and further to terephthalic acid. Succinic acid is a valuable molecule that can be obtained economically by the bacterial fermentation of sugars. Fig. 1.12 presents important derivatives, such as 1,4-butanediol, tetrahydrofuran (THF), pyrrolidone, gamma butyrolactone, and various esters, including polyesters, such as polybutylene succinate. The hydroxybutyric acid (HBA) is mostly known through its polymer PHBA that can replace successfully polyethylene products, but with biodegradability as remarkable added property. Although an important petrochemical intermediate, the 1,3butadiene may be included in the biobuilding blocks. Butadiene was manufactured from ethanol before the World War II in the ex-Soviet Union (Lebedev, one-step process) and USA (Ostromislensky, two-step process via acetaldehyde), to produce synthetic styrene-butadiene rubber (SBR). The interest for these processes revived recently. New magnesium and zirconium-based catalysts or silicates and zeolites promoted by metals may give selectivity of 70% at high ethanol conversion. The major challenge for profitability is to enhance the catalyst lifetime (Pomalaza et al., 2016).

1.5.5 Chemicals From C5 Biobuilding Blocks C5 biobuilding blocks are furfural, itaconic acid, xylitol, isoprene, glutamic acid, and levulinic acid, as displayed in Fig. 1.13. Furfural can be obtained from hemicellulose via the fermentation of xylose, which is a C5-based sugar. Furfural and its derivatives are important as green solvents. The levulinic acid can be produced by fermentation from hemicellulose (C5 sugars) or from starch (C6 sugars) with release of formaldehyde. Fig. 1.14 shows the synthesis of a number of valuable specialty chemicals from levulinic acid, such as lactones and pyrrolidones.

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N

O

R

O

2- Pyrrolidones

OH

HO

NH3, RNH2

O Succinic Acid

NH3, RNH2

-H2O H2 O O g-Butyrolactone

ROH

O O O Succinic Anhydride ROH

2H2

O OH

HO

OR

RO

O Succinate Esters

1,4-Butanediol -H2O

RR1CO

O O

RO

R R1 OH

O Alkylidene Succinates

Tetrahydrofuran

Figure 1.12 Organic synthesis starting from succinic acid (Corma et al., 2007). O O

O

Furfural

O

O

HO

OH

Itaconic Acid

OH O

Levulinic Acid

OH OH HO

O

O

HO

OH

OH OH

Xylitol

NH2

D-glutamic Acid

Figure 1.13 C5 biobuilding blocks.

The manufacture of isoprene and farnesene by the fermentation of sugars is a major recent advancement in biotechnology. Trans-b-farnesene is a 15-carbon molecule, 12 long-chain branched, unsaturated hydrocarbon as shown in Fig. 1.15. It offers unique opportunities for the synthesis of higher value materials, such as solvents, lubricants, aviation fuels, and polymers. The company Amyris (www.amyris.com) is developing industrial processes in cooperation with the company Total.

Chapter 1 SUSTAINABLE PROCESS TECHNOLOGY

O

-H2O

CH3

OH

H2

H3C

Methyl Tetrahydrofuran

O

O

CH3

CH2OH

1,4-Pentanediol

Angelica Lactone -H2O

H2

Oxidation Succinic Acid H3C

Enzymatic

O H 2N

ROH

O ROH

COOH

O

Levulinic Acid

COOH

H3C COOR Levulinic Acid Esters

Reductive amination

5-Amino Levulinic Acid

R O

O

O

CH3

a-Methylene-gvalerolactone

N

CH3

Condensation 5-Methyl-N-alkyl-2pyrrolidone

OH

HO

H3C

COOH

Diphenolic Levulinic Acid

Figure 1.14 Organic synthesis starting from levulinic acid (Corma et al., 2007).

CH2

CH3

CH3

H2C

CH3

Figure 1.15 Structure of trans-b-farnesene.

OH

OH OH

HO

O OH HO

OH

O

OH

Adipic Acid

Sorbitol OH

O

OH OH

HO

O OH

OH

Glucaric Acid

O

OH

HO

O O

Furan Di-Carboxylic Acid (FDCA)

Figure 1.16 C6 biobuilding blocks.

1.5.6 Chemicals From C6 Biobuilding Blocks Fig. 1.16 presents biobuilding blocks in C6 chemistry: sorbitol, adipic acid, glucaric acid, itaconic acid, and 2,5-furandicarboxylic acid (FDCA).

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OHC

O

CHO

HO O

OH

DFF

CHO

OHC HO

OH O

OH O

O HMF

HO

O

FFA

O

O FDCA

O HMFA

Figure 1.17 2,5-Furandicarboxylic acid chemistry.

Sorbitol can be obtained by the reduction of glucose that converts the aldehyde group to a hydroxyl group. Further derivatives of interest are isosorbide, lactic acid, and branched polysaccharides. Isosorbide, a diol molecule, resulting by sorbitol dehydration, can be used in the synthesis of various green polymers, such as polyesters, polycarbonates, or green plasticizers (de Jong et al., 2012). The French company Roquette is the worldwide leader. The adipic acid is widely used for manufacturing biosourced polyesters, as PBAT (polybutylene adipate terephthalate). FDCA recently received a particular attention because it can replace successfully the terephthalic acid in classical polyethylene terephthalate (PET) applications. Particularly interesting is the polyethylene furanoate (PEF) polymer, which is biodegradable. In addition, PEF exhibits a higher barrier for oxygen, carbon dioxide and water vapor than PET and therefore it is suitable for manufacturing packaging objects, such as bottles, films and food trays. Fig. 1.17 present a synthesis route from 5-hydroxymethyl furfural (HMF) in turn obtained from fructose by catalytic dehydration. It follows the oxidation of HMF to 2,5-diformyl-furan (DFF) and to 5-hydroxymethyl 2-furancarboxylic acid (HMFA), both oxidized to 5 formyl 2-furancarboxylic acid (FFA) and finally to 2,5-furandicarboxylic acid (FDCA). The Dutch company Avantium developed the competitive costs technology YXY (de Jong et al., 2012).

1.5.7 Other Chemical Products Obtained From Biomass Derivatives of fatty acids find numerous applications, namely in polymer manufacturing. A noteworthy example is the production of Rilsan polymer, a high-value and versatile 6e11 polyamide obtained from castor oil. This is a triglyceride based on ricinoleic

Chapter 1 SUSTAINABLE PROCESS TECHNOLOGY

acid, which is an unsaturated omega-9 fatty acid with the formula 12-hydroxy-9-cis-octadecenoic acid. Glycerol and heptanal are valuable by-products, the latter being used in fragrance formulations. Other route can lead to 6e10 polyamide based on sebacic acid and hexamethylenediamine. Chapter 7 develops a case-study of a bio-refinery based on castor oil. Other interesting applications find the fatty acid dimmers as long carbon diols and diamines. These can be used in the synthesis of specialty polymers, such as polyesters, polycarbonates, and polyurethanes (de Jong et al., 2012).

1.6 Biofuels 1.6.1 Economic Significance The manufacturing of biofuels is the main direction of biomass valorization today. In 2015, the global biofuels production reached about 35 billion gallons (133 billion liters), from which about two-third was bioethanol (BP report, 2016). About twothirds came from the United States and Brazil, mostly from corn and sugarcane, respectively. The global production of biofuels is expected to increase steadily in the next years to a range of 257 to 500 billion litres per year in 2030 (IRENA report, 2016). The projected demand depends on assumptions about policies, biofuel availability and cost. The efficiency of a biofuel technology can be measured over the wheel-to-wheel life cycle, as total renewable energy produced per unit of fossil energy consumed (RER ratio). In 2009, the best technologies for corn ethanol showed RER values up to 5 by processes employing combined heat and power, while for sugarcane RER was more than 9 with mechanized harvesting (Chum et al., 2014). The theoretical yield in fuel of a biomass feedstock may be calculated from its composition. For ethanol by sucrose fermentation this is 617 L/t, but in more realistic conditions it would be about 530 L/t. For corn grains, the theoretical yield is 469 L/dry ton, for corn stover and bagasse 424 L/dry ton, for forest waste 310 L/dry ton. Comprehensive information about biofuels and raw materials may be found on the website of Raugaskas (2019). As illustrated, Table 1.2 presents typical data regarding the performance of several energy crops. Feedstock producing 1G fuels offer good yields, namely sugar beet in Europe and sugarcane in Brazil. Corn ethanol is profitable in the conditions of high-yield and large-scale agriculture, such as in the Midwestern United States. Sweet sorghum is a valuable energy crop suitable for

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Table 1.2 Typical Yield of Crops for the First- and Second-Generation Biofuels. Crops

RM t/ha

Fuel t/t

Fuel t/ha

Observations

Sugar and starch energyebased crops: 1G ethanol

Cane sugara

10.4

0.398

4.3

Corn grainsb Beet sugarc Sorghum sugard

9.4 11.2 6e8

0.348 0.45 0.380

3.27 5.04 2.3e3.1

Y ¼ 5430 L/ha ¼ 574 gal/acre; 1 gal ¼ 3.785 L; 1 ha ¼ 2.47 acres 150 bu/acre; 2.8 gal-EtOH/bu; 1 bushel ¼ 25.38 kg 70 tonne-beet/ha; 160 kg-sugar/ton beet 3000e4000 L/ha; 2e3 crops/year; draught resistant

Vegetable oils: 1G biodiesel

Rapeseed (canola)e Soybean grainse Palm oil e Camelina seedsf,g Jatropha seedsc

3.5

0.35

1.22

40% oil content

2.9 4.0 1.9 3.5

0.194 0.95 0.375 0.344

0.57 3.8 0.72 1.2

44 bu/acre; 1.5 gal/bu; 1 bu/acre ¼ 0.0673 ton/ha 4 t/ha oil in Indonesia 1700 lb/acre; 35%e38% seed oil content Resistant to high degree of aridity

2.6e4.6 4.2e8.4 3.0e9.0

360 L/dry ton 265 L/dry ton 380 L/dry ton

1.6e3.5

300 L/dry ton

Energy crops ethanol: 2G ethanol

Poplar dry bmi Switchgrass dryi Miscanthus dry bmh

9e16 20e40 10e30

0.283 0.21 0.300

Lignocellulosic ethanol: 2G ethanol

Corn stoverj a

7e15

0.235

www.sugarcane.org Brazilian Sugarcane Industry Association May 2015, data 2014. b www.ncga.com US National Corn Growers Association, data 2014. c Various web sources. d www.sweet-project.eu Energy sorghum, an alternative energy crop, 2014. e www.en/wikipedia.com Biodiesel page. f www.cropwatch.unl.edu University of Nebraska, Lincoln, USA. g www.susoils.com Sustainable Oils Global Clean Energy, CaeUSA. h Cheng, P., Peng, L., Chapter 6 in Biological Conversion of Biomass, RSC EE Series, 2014. i Ragauskas, A., Biomass to biofuels primer, at University of Tennessee, www.biorefinery.utk.edu. j www.dupont.com Cellulosic ethanol plant Nevada, Iowa.

Chapter 1 SUSTAINABLE PROCESS TECHNOLOGY

low-value draught land. Rapeseed biodiesel (canola) is mainly used in Europe, while Jatropha in hot climate conditions and low-value land in Africa and Asia. New high-yield energy crops emerged in the last years suited for 2G ethanol, such as poplar, willow, switchgrass, and miscanthus. Corn stover and bagasse are already feedstock for the first commercial lignocellulosic ethanol plants. Very high yields are expected for 3G biofuels from algae, but the biotechnology is only at its beginning.

1.6.2 Sustainability Issues The sustainability of biofuels is a debatable point. Among the assessment criteria, critical issues are GHG impact, food security, indirect land use change (ILUC), soil and air pollution, socioeconomic development, and energy independence. Regarding the second aspect, there is no clear evidence that the biofuel market threatens the food supply chain. For example, in Europe, the crops for biofuels, mostly biodiesel, use only 1% of the agricultural land (REN21 report, 2015). The energetic independence is also a key factor for promoting biofuels, namely for developing countries. Reducing GHG with respect to fossil fuels is considered by most analysts as the key factor for sustainability of biofuels. The GHG assessment follows at present well-to-wheel LCA procedures. The model usually includes emissions from ILUC, farming, transportation, and various stages of the production process (Azapagic and Stichnote, 2011). Credits should be considered for the GHG savings because of producing energy and valuable co-products, such as cattle food or chemicals. The deforestation in view of new plantations without sustainability guarantee should have severe consequences on GHG performance. The most ambitious sustainability targets are applied in Europe following the Renewable Energy Directive (RED) (EC,EBTE, 2015). The GHG reduction in 2015 for biofuels was set at 35% with respect to the reference value of 83.8 g of CO2eq/MJ, which should increase to 50% in 2017 and 60% in 2018. In the United States, the EPA-RFS2 regulation sets the GHG reduction target at 20% for conventional renewable fuels and at 50% for advanced renewable fuels (EPA, 2014). The GHG reduction indices of biofuels are not unique. They depend largely not only on the implemented computation methodology but also on factors specific to each country and to technology adopted at a given stage, for example, energy from coal or from renewable sources.

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Fig. 1.18 presents a comparison of carbon intensity g-CO2/MJ for some typical biofuels, compiled from the European legislation (EU, RED 5, 2009). The data disregard the ILUC effects. The LCA analysis pinpoints the contributions of the key GHG sources: cultivation, transport, and processing. The GHG reduction effect can be obtained by reference to 83.8 g/MJ, a mean value for a standard fossil fuel. Some remarks are useful: • The GHG reduction for biodiesel varies between 30% and 90%. The upper level is attributed to waste and nonedible oils and the middle level to efficient vegetable crops, such as rapeseed in Europe, while the lower level refers to some vegetable oils issued from less sustainable farming. Biodiesel from palm and soybean oil should raise questions about sustainability; modern farming practices should be used, such as methane capture for palm oil. • For bioethanol, the GHG reduction varies between 20% and 90%. The lower limit corresponds to wheat ethanol (similarly for corn), the middle level to sugar beats, and the upper limit to sugarcane and LCF. • Improving the technology at each step, either in farming or in processing, raises the overall sustainability. For example, the heterogeneous catalysis may divide by 2 the investment and operating costs by FAME biodiesel. Similar effect could have energy integration methods, as cogeneration of heat and power. Today, among biofuels, ethanol has the fastest development. Table 1.3 presents the case of lignocellulosic ethanol, as 2G advanced fuel versus US corn and imported Brazilian sugarcane ethanol. Comprehensive GHG from well-to-wheels were

Figure 1.18 The carbon intensity of some biofuels over the life cycle of well to wheels (RED, 2009).

Chapter 1 SUSTAINABLE PROCESS TECHNOLOGY

Table 1.3 GHG Reduction of Bioethanol From Lignocellulosic Biomass Versus Corn and Sugarcane Fuel. Feedstock/LCA g-CO2/MJ

Corn

Sugarcane

Corn Stover

Switchggrass

Miscanthus

Fertilizer N2O Farming Production Transport and distribution Combustion Land usage change Total 1 Credits Total 2 Greenhouse gases reduction %

10 17 4 31 4 1 9 76 14 62 34

5 4 5 3 11 1 16 45 0 45 52

6 0 3 10 3 1 1 22 17 5 95

4 7 2 11 3 1 1 29 17 12 87

3 3 2 11 2 1 12 10 17 7 107

evaluated in term of g-CO2 eq/MJ by using the software GREET from the US Argonne National Laboratory (Wang et al., 2012). The LCA stages are recovery, fertilizer production, N2O from fertilizer, farming, production, transport, and distribution, combustion, and land usage change (LUC). Larger positive LUC numbers signify potential soil degradation attributed in this study to corn and sugarcane. Low LUC numbers indicates no harm, while negative values show carbon sequestration of CO2 from air and stored in the soil, such as for miscanthus. The analysis also considers credits for co-products as livestock food from corn or electricity generated from lignocellulosic waste. Finally, the GHG reduction percentage is obtained by reference to a conventional gasoline with carbon intensity of 94 g-CO2/MJ. Note that this value originates from combustion (74), refining (11), and transport (3). It can be concluded that the GHG reduction for corn, sugarcane, corn stover, switchgrass, and miscanthus are 34%, 52%, 95%, 87%, and 107%, respectively. Higher value than 100% can be explained by a sequestration effect on the carbon in the soil. Note that modern no-till farming methods may bring this improvement too. The bioethanol shows clearly a significant advantage in terms of sustainability, with the perspective of becoming the major renewable fuel for the next decades.

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1.6.3 Biodiesel Today, two types of diesel-compatible biofuels are available commercially: FAME and hydroprocessed esters and fatty acids (HEFA). 1. FAME biodiesel results by the transesterification with methanol of long-chain alkyl triglycerides (TAG), mostly in the range C16eC18. At present, the feedstock comes for the most part from dedicated energy crops and in less extent from animal fats and lipid waste. It is hoped that in the next future, the algae cultures will supply large TAG amounts by ocean farming. The stoichiometric material balance shows that 1 ton of oil plus 100 kg methanol gives 1 ton FAME plus 100 kg glycerol by-product. The feedstock for biodiesel consists typically of energy crops, such as rapeseed in Europe, soybean in South America, and palm oil in Southeast Asia. Nonedible plant crops can be employed at industrial scale, such as Camelina or Jatropha in India and some African countries. Note that the reaction with ethanol gives difficult glycerol separation. The transesterification reaction takes place in the presence of base catalyst, homogeneous (K or Na methanoate) or heterogeneous (metal oxides mixtures). Older processes are of batch-type with homogeneous catalysis working at 55e60 C. The scale-up from laboratory is easy, but the process itself is not very efficient. Heterogeneous catalyst brings the advantage of continuous water-free process, low investment, and reduced energy. Pure glycerol becomes available at low price, with very positive impact on profitability. This technology is implemented at large scale in France and worldwide as ESTERFIP process (Bourney at al., 2005). The solid catalyst technology can be adapted for small and intermediate scale, and even for mobile plants, by implementing an innovative reactor technology (Dimian and Rothenberg, 2016). The FAME technology is still viable for producing fuels to be used in blends with fossil diesel, such as heating oil or for other purposes. Chapter 9 develops the conceptual design of two advanced processes: biodiesel from rapeseed oil using heterogeneous catalyst and from waste cooking oils using reactive distillation based methods. 2. HEFA biodiesel results by the hydrodeoxygenation of lipid feedstock followed by fluid catalytic cracking (FCC). In this way, all triglycerides and FFA present in the feedstock are converted to long-chain alkane molecules similar to fossil diesel,

Chapter 1 SUSTAINABLE PROCESS TECHNOLOGY

delivering a fuel fully compatible with petro-refinery specifications. The glycerol is converted to propane. The process was invented by the Finnish company Neste Oy. Initially, the NesteBTL process was developed for using waste oils and fats. For this reason, this type of product was called green diesel, claiming a 2G-type biofuel. However, the processing requires a refinery environment, namely cheap hydrogen and FCC plant, and is profitable at large capacity, typically over 300 ktpy. Moreover, collecting, storing, and transporting substantial amounts of fat waste raise considerable constraints. The feedstock for HEFA plants is shipped mainly from overseas palm oil plantations to harbor refineries in Europe and Asia. Therefore, the green label may raise questions.

1.6.4 Bioethanol Manufacturing 1G bioethanol from corn or sugarcane is today well-established. As discussed before, the challenge is the development of competitive technologies for producing sustainable 2G bioethanol from LCF. There are numerous demonstration units, but the first commercial-scale plants just emerged in 2013. General information can be found in a recent handbook (Amarasekara, 2014). Detailed information can be found in a case study performed by the US NREL agency (2011). The first step is the mechanical treatment for size reduction of biomass. It follows the pretreatment and separation phases in which the biomass is transformed in soluble sugars submitted to fermentation. The economic success of the technology depends largely of these steps (Kurian et al., 2013). The outlet biomass stream is diverted to (1) C5 xylose stream derived from hemicellulose sent to fermentation and (2) cellulose/lignin stream submitted to enzymatic hydrolysis to supply C6 glucose and further to fermentation. A specialized section deals with the production of enzymes. The enzymatic hydrolysis and fermentation processes can be accomplished using different strategies: separate hydrolysis and fermentation, simultaneous saccharification and fermentation, and direct microbial conversion. The fermentation process is slow and takes place at rigorously controlled temperature, pH, and substrate concentration. Continuous, batch, and mixed arrangements can be used. A modern technique is fed-batch (semibatch) reactor in which nutritional environment is maintained approximately constant by adding controlled amounts of hydrolyzate and enzymes. The reactor design is a determinant factor in technology. Compared to petrochemistry, the fermentation reactors are

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huge from 103 to 104 m3. The mixing patterns at various locations, as well as the temperature and concentration control, are more demanding. The availability of appropriate enzymes to handle a specific feedstock is another prominent issue. At present time, there is no all-purpose enzyme system. The enzymes are rather specialized for handling a typical feedstock, such as wheat straws, corn stover, bagasse, switchgrass, etc. 2G bioethanol plants are already on stream, and some technical performances are known. The first world’s plant opened in 2013 by Beta Renewables in Crescentino, Italy (www. betarenewables.com) has a capacity of 60,000 tons/year with local collected feedstock from energy crops and agricultural waste. It handles 270,000 tons biomass per year. The investment was of 150 million Euros. The process is energetically neutral. The first 2G ethanol plant in the United States was inaugurated in 2014 by the Spanish company Abengoa in Hugoton, Kansas (www. biofuelsdigest.com). It has a capacity of 80,000 ton/year with a biomass consumption of 1000 ton/day of agricultural waste collected on an area of 75 km radius. The plant is energetically self-sufficient, but it can even export electricity. In 2015, DuPont announced the opening of a $225 millions plant of 100,000 ton/ year plant in Nevada, Iowa (www.dupont.com). The feedstock is corn stover collected from about 47,500 ha at a rate of 375,000 ton/year dry biomass, resulting in a productivity of 3.75 tone biomass/tone ethanol. In this way, 600 L/ha can be added to the ethanol obtained from corn grains, an increase of productivity of 30%, rising the total yield to over 4 ton ethanol/ ha (see Table 1.2). After a learning period the technology of cellulosic ethanol should ramp up starting with 2020. Thus, the production in Europe should increase from 31 million litres in 2017 to 2.75 billion litres in 2030, even 3.8 billion litres in the more ambitious scenario. Production costs are projected to be 745-965 EUR/ tonne in 2030 vs. 945-1,010 EUR/tonne in 2017 (E4tech report, 2017).

1.6.5 Other Biofuels Biobutanol can be used as biofuel, similarly to ethanol. The advantages are more energy density (20% higher than ethanol), reduced oxygen content (lower NOx), and volatility close to gasoline (better ignition). The feedstock is as for ethanol, including starch and lignocellulosic materials, but the fermentation process makes use of different yeasts. Ethanol plants can be easily retrofitted to butanol plants. It is expected that butanol fuel will know

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a rapid growth in the next years. Chapter 8 develops the manufacturing of bioalcohols (bioethanol and biobutanol) by the fermentation of sugars, starches, or cellulose; employing process intensification for improving the efficiency. Dimethyl ether (DME) is an alternative fuel with good potential, as substitute for LPG and in mixtures with both gasoline and diesel. The combustion gives very low emissions as CO, NOx, and PM. As available from waste materials, DME is considered as a 2G fuel. The manufacturing of DME is handled in Chapter 10.

1.7 Biopolymers Biopolymers are materials made totally or partially from renewable raw materials. They may be biodegradable/compostable and recyclable. The manufacturing of high-value bioplastics is a central issue of a chemical industry based on biomass. Three categories of biopolymers can be identified: • Drop-in biopolymers, identical with petrochemical counterparts, being obtained from the same monomer. Examples include bio-PE (ethylene from bioethanol), bio-PP (propylene from biomass). • Fully biobased biopolymers, such as PLA, polyhydroxyalkanoates (PHAs), poly-FDCA, PBAT (poly-butylene-adipateterephthalate), PBS (poly-butylene-succinate), PA 11 (C11 polyamide), thermostatic starch, cellulose fibers, etc. • Partially biobased biopolymers, in which a substantial amount (over 30%) comes from biosources. Examples include bio-PET in which the glycol monomer has a biomass origin, some polyamides, bio-VCM with ethylene from ethanol, bio-VAM, with ethylene or/and acetic acid from biomass. Following a report of the European Plastics agency, the global production of biopolymers was of about 2.054 million tonnes in 2017 and is forecasted to 2.440 million tonnes in 2022. In 2017 the share of global production was is 56% Asia, 18% Europe, 16 % North-America and 10% South-America, from which about 43% biodegradable (www.eu.europa-bioplastics). The development of the drop-in biopolymers depends in a decisive extent on the profitability of the biomonomer. For bioethylene, this condition is fulfilled today only with ethanol from sugarcane in Brazil, but it should be met with the 2G ethanol in the next future. The use of ethylene from biomass should be also profitable in situations where the availability from a refinery complex is neither economical nor possible, but the other co-raw materials should have low price, as mentioned above.

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Fully biopolymers, such as PLA, PHA, PBAT and PBS, will have a fast development in the next years because the ecological advantages can overpass the argument of price only.

1.8 Process Design Issues Process design of biorefineries is a recent activity in the engineering bureaus. Some design and sizing methods are taken over from the classical technology, namely from petrochemical industry, while others are developed as new applications appear. Some relevant issues for conceptual design are discussed below.

1.8.1 Screening of Alternatives Mathematical programming is a powerful technique for screening alternatives, selecting the best ones, and performing preoptimization (Grossmann, 1999). For example, we may cite the work of Martin and Grossmann (2014) regarding the optimal production of i-butene and ethanol from switchgrass by integrating the alternatives in a superstructure. These consider two technologies for the pretreatment (dilute acid and ammonia), enzymatic hydrolysis to glucose and xylose, pressure swing adsorption for i-butene recovery, and using lignin for steam generation. The problem is formulated as MINLP optimization, where the objective function is the production cost. The most promising process involves dilute acid pretreatment and membrane purification of i-butene. The decision of producing i-butene alone or with ethanol depends on the prices for bioethanol and biomass. Manufacturing only i-butene is less sensitive to the feedstock price. Higher ethanol price favors the simultaneous manufacturing of both products. In another valuable paper (Giulani et al., 2016), the optimization of a lignocellulosic biorefinery has been performed for producing levulinic acid, succinic acid, and ethanol by including in analysis several alternatives for the reactions, separations, and heat integration.

1.8.2 Feedstock Pretreatment Feedstock pretreatment determines the products’ profile and the biochemical technology. Let us consider the case of an LCF biorefinery. As lignocellulosic biomass is only low digestible in its natural form, often less than 20%, the primary purpose of pretreatment is to break down the structure of the biomass such as

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to make free and separate the main components, namely cellulose, hemicellulose, and lignin, and further to allow an efficient enzymatic hydrolysis to C6 and C5 sugars. There are chemical barriers, such as the heterogeneous composition and the recalcitrant nature of the cellulosic part of the biomass, the presence of acetyl groups, and physical barriers, such as crystallinity, surface area, and degree of polymerization (Kim, 2013). There are several pretreatment methods, each one with advantages and disadvantages. These are described in detail in numerous monographs, such in Yang et al. (2013), Lin and Luque (2014), De Jong and van Ommen (2015), and Waldron (2016). The most representatives are briefly commented: 1. Alkali pretreatment with sodium hydroxide, lime, or ammonia: An efficient method in this category is AFEX (ammonia fiber expansion). After treatment in mild conditions (70e90 C, 15e20 bar), the ammonia can be easily recovered and recycled. The result is that the biomass preserves most of the C5 and C6 sugars resulting in higher yields in fermentation products. The disadvantage is the high solid content to be carried out in processing. 2. Acid pretreatment: Mostly, liquid water under pressure (130e220 C) with diluted sulfuric acid makeup is used. Nearly complete hydrolysis of hemicellulose and partially of cellulose occurs. Degradation species, as furfural, must be removed before enzymatic hydrolysis. 3. Autohydrolysis: The key advantage is the absence of costly and polluting chemicals. The disadvantage is the limited selectivity, as well as the formation of secondary toxic species. a. Liquid hot water: The treatment takes place at 130e220 C (6e14 bar) with almost complete hydrolysis of hemicellulose and 30%e40% delignification. b. Steam explosion: This is the most commonly used method. The operation conditions are temperatures from 160 to 270 C, with 70%e90% hemicellulose solubilization and 20%e40% delignification. 4. Supercritical water: This recent method delivers with highyield separate streams of xylose, glucose, and lignin byproducts. 5. Solvents: Mixtures of water with THF, alcohols, dedicated solvents, such as organosolv, as well as sulfuric acid solutions, have been proposed for commercialization by different companies. 6. Ionic liquids: These new solvents from renewable chemicals aim to separate with high-yield lignin and hemicellulose.

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1.8.3 Chemical Reactors The selection and design of the biochemical reactor is a central issue in biomass processing, namely for the enzymatic hydrolysis and fermentation. The topic is treated in general purpose books, as in a recent edition of Coulson and Richardson’s handbook (2017), or in monographs, such as by Katoh et al. (2015). Characteristic for bioreactors is the very large size of units, typically from hundreds up to thousands of m3. These operate in general as batch or feed-batch vessels, in which the nutrients are rigorously added to match the complex biochemical pathways. The mixing pattern is a key design element being intimately linked with the complex kinetics of the biochemical process and the makeup policy of substrates. The scale-up from lab or demo plant to the industrial implementation is complicated. That is why computational fluid dynamics (CFD) can bring valuable insights and be used as a powerful investigation analysis and design tool. A tutorial about CFD-aided bioreactor design can be found in the work of Vial and Stiriba (2013). Innovative reactor design can be applied based on the use of heterogeneous catalysis, porous catalyst, or immobilized enzymes, coupled with membrane technology.

1.8.4 Separation Processes The arrival of biomass as a major bioresource for sustainable technologies raises challenges and opportunities for separation processes. This topic is presented in a recent paper by Kiss et al. (2016). With specific features for biorefineries, one may cite the following: • The output from bioreactors consists of complex mixtures of highly functionalized organic molecules with significant differences in chemical structure, molecular size, and physical properties. Accordingly, the use of affinity-based methods, as well as membrane-based separations, increases. • The mixtures resulting from preprocessing and fermentation are often diluted water solutions. For this reason, the concentration of solutions in view of further processing is energyintensive. • The separation of biomolecules is sensitive to temperature, typically over 150 C. Vacuum distillation may be applied together with low temperature separations, such as liquid extraction, crystallization, membrane-based techniques, etc.

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• Large feed variability of mixtures resulting from the large variability of biomass may greatly affect the performance of the separation and purification processes. This key issue has to be considered in the selection and sequencing of the separation methods, as some configurations may be more flexible than others. • Detoxification after pretreatment is necessary for removing toxins that may hinder the fermentation process. Effective methods include ion-exchange, adsorption, extraction, or precipitation. These separation challenges are particularly encountered in the front end of the biorefineries. Once the streams upgraded to well-defined and thermally stable platform molecules, the conventional methods, such as distillation, may be effectively applied. Among suitable separation methods for biorefineries, one may cite the following: 1. Phase-change separations: distillation, crystallization, and filtration. 2. Affinity-based separations: liquideliquid extraction, solide liquid extraction, absorption, adsorption, simulated moving bed. 3. Size/charge separations: ion-exchange, membrane separations (microfiltration, ultrafiltration, nanofiltration), electrodialysis. The selection of these methods in a frame of a systematic approach will be discussed in Chapter 2.

1.8.5 Process Intensification Process intensification (PI) has significantly improved many industrial processes. By applying the PI principles, various processing advances can be attained such as higher energy efficiency, lower raw material usage, prevention of waste generation (improved product quality), and safer process, as demonstrated in several industrial applications. PI methods contribute to reduce the capital and operation costs by combining reaction and separation in a single unit or as a compact flowsheet of few units. The applications of reactive separations regard mostly the reactions constrained by chemical equilibrium. By taking advantage of phase equilibrium, the reaction can be shift to completion, while the product may be separated to high purity. Typically, reaction selectivity is improved, and significant energy saving is obtained. The following reactive separation methods are of interest for sustainable process technology: • Reactive distillation (RD) combines reaction with distillation in a single column. The challenge is finding compatible operating

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conditions (pressure and temperature) for both reaction and vaporeliquid separation. For this reason, this operation makes use of catalyst, preferably solid. Among specific biorefinery applications, one may cite the wide class of esterification of acids with alcohols, including biodiesel manufacturing (Omota et al., 2003; Kiss et al., 2006). • Reaction and membrane separations include (bio)reactorsmembrane, bioreactor-membrane pervaporation/distillation. Applications have been developed for water removal by esterification reactions, butanol production, and biodiesel manufacturing (Kiss, 2014). • Reactive extraction (RE) makes use of solvent extraction to shift chemical equilibrium and separate the target product. • Extractive fermentation is specific for biorefineries, for example, the extraction of butanol from the fermentation broth. Membrane-assisted solvent extraction can also be used for recovery and separation of organic acids, biofuels, and other chemicals (Ramaswamy et al., 2013).

1.9 Economic Challenges The market of biofuels, biochemicals, and biopolymers is in full expansion. There are good reasons to believe that the growth will accelerate in the next decades, as the use of renewable materials is pushed strongly by the needs of sustainable development. Table 1.4 presents a view of the situation of the biobased chemicals at the end of 2014 and highlights future trends. Bioethanol dominates largely (73.1 Mtpa), followed by n-butanol (via ABE process), acetic acid, and lactic acid. Xylitol, sorbitol, and furfural derived from sugars also show significant markets, without petrochemical alternatives. Succinic acid shows a fast development. Small biomarkets are those in R&D phase, such as HPA, HMF, isobutene, isoprene, acrylic acid, and adipic acid. The prices of new products, such as FDCA, derivatives of levulinic acid, and farnesene, are relatively high, but these should drop rapidly. Different studies estimate that the market of biochemicals will continue a sustained development, particularly in Europe, at a compound annual growth rate (CAGR) of 8 to 10% namely for the platform chemicals, polymers and adhesives (EU/JRC, 2019).

Table 1.4 Market for BioBased Chemicals and Total Product Markets. Product

Acetic acid Ethylene Ethylene glycol Ethanol 3-HPA Acetone Acrylic acid Lactic acid Propanediol 1,4-Butanediol Isobutanol n-butanol Isobutene Succinic acid Furfural Isoprene Itaconic acid Levulinic acid Xylitol Furandicarboxylic acid 5-Hydroxymethylfurfural Adipic acid Sorbitol p-Xylene Farnesene Algal lipids polyhydroxyalkanoates

BioBased Market

Total Market (bio D fossil)

Price ($/t)

Volume (ktpa)

Sales (m$/y)

% of Total Market

Price ($/t)

Volume (ktpa)

Sales (m$/y)

617 1300e2000 1300e1500 815 1100 1400 2688 1450 1760 >3000 121 1890 >>1850 2940 1000e1450 >2000 1900 6500 3900 NA (high) >2655 2150 650 1415 5581 >>1000 6500

1357 200 425 71,310 0.04 174 0.3 472 128 3.0 105 590 0.01 38 300e700 0.02 41 3.0 160 0.045 0.02 0.001 164 1.5 12 122 17

837 260e400 553e638 58,141 0.04 244 0.9 684 225 9 181 1115 0.02 111 300e1015 0.04 79 20 624 w10 0.05 0.002 107 2.1 68 >122 111

10% 0.2% 1.5% 93% 100% 3.2% 0.01% 100% 100% 0.1% 21% 20% 0.00006% 49% 100% 0.002% 100% 100% 100% 100% 20% 0.00003% 100% 0.004% 100% 100% 100%

617 1100e1600 900e1100 823 1100 1400 2469 1450 1760 1800e3200 1721 1250e1550 1850 2500 1000e1450 2000 1900 6500 3900 NA (high) 2655 1850e2300 650 1350e1450 5581 >>1000 6500

13,570 127,000 28,000 76,677 0.04 5500 5210 472 128 2500 500 3000 15,000 76 300e700 850 41.4 3.0 160 0.045 0.1 3019 164 35,925 12.2 122 17

8373 1,40,000e203,000 25,200e30,800 63,141 0.04 7700 12,863 684 225 4500e8000 860 3750e4650 27,750 191 300e1015 1700 79 20 624 w10 0.27 5600e6900 107 48,500e52,100 68 >122 111

After European Union, (2015). European Biofuels Technology Platform (EBTP), Factsheets. Available at: http://www.biofuelstp.eu.

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1.10 Conclusions Sustainable technologies backed by the growing use of renewable raw materials, namely the biomass, will mark the development of CPI in the coming decades. Biorefinery is the new technological environment, which besides biofuels is designed to supply a diversity of bioproducts, such as chemicals, polymers, human and animal food products, as well as thermal and electrical energy. Projections estimate that around 2030 the share of biomass-based chemicals and fuels should be 25%e30%. This tendency could accelerate because of the awareness raised by the global climate change and the preservation of biodiversity, the biomass being a key factor in ensuring a sustainable development. The manufacturing of biofuels supports the development of biorefineries. Bioethanol is today one of the world’s top chemicals. The first large-scale plants for manufacturing 2G bioethanol are on stream. At longer term, biodiesel remains an important sustainable energy source, namely in the perspective of new renewable sources, such as algae crops. New alternative fuels are emerging, based on biogas, DME, and butanol. The use of biofuels is compatible with the strategic goal to a neutral carbon economy. The manufacturing of biochemicals from biomass takes profit from specific building blocks. These are molecules containing already more complex reactive groups, in contrast with the petrochemical starting blocks. The most interesting today are methanol for getting hydrocarbon and olefins and ethanol for bioethylene, glycerol, lactic acid, n- and isobutanol, succinic acid, and levulinic acid. The production of a new generation of polymers is a remarkable feature of the technologies based on biomass. Competitivecost biodegradable polymers are now available to replace non-degradable fossil-based plastics, namely polyethylene, in packaging applications. Petrochemical polyesters can be replaced in packaging and beverage bottles by polymers based on FDCA. On the other hand, olefin from biomass, such as ethylene, propylene, isobutene, and isoprene, can be used as drop-in feedstock in the existing manufacturing processes. The technologies based on renewable raw materials promote the sustainable development and counteract the use of highly polluting marginal fossil resources, such as tar sand oil, deep water, or shale gas oils. Over a long perspective, a balanced mix of biomass and environmentally conscious exploited fossil resources should ensure the feedstock basis for supplying fuels and chemicals.

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New processes have to be invented, mainly based on biotechnologies. Suitable chemical reactors and separation methods have to be developed. Conceptual process design, supported by systematic systemic methods and computer simulation tools, should boost the development of alternative solutions starting from the fundamental information got in laboratory and pilot plants. The applications proposed in this book aims to bring an useful contribution in this direction, by helping students and professionals, both chemists and chemical engineers, to be more efficient in their effort to innovation.

References Amarasekara, A.A., 2014. Handbook of cellulosic ethanol. Wiley-Scrivner. Aresta, M., Dibenedetto, A., Dumeignil, F. (Eds.), 2012. Biorefinery, From Biomass to Chemicals and Fuels. De Gruyter, Berlin. Aresta, M., Dibenedetto, A., Dumeignil, F. (Eds.), 2015. Biorefineries. An Introduction. De Gruyter, Berlin. Azapagic, A., Stichnote, H., 2011. Life Cycle Sustainability Assessment of Biofuels. Handbook of Biofuels Production. Woodhead Publ, UK. Bourney, L., Casanave, D., Delfort, B., Hillion, G., Chodorge, J.A., 2005. New heterogeneous process for biodiesel production. Catalysis Today 106, 109e114. BP Statistical Review of World Energy, 2016. Available at: www.bp.com. Brundtland Commission, 1987. Report of the World Commission on Environment and Development (United Nations). Cavani, F., Centi, G., Perathoner, S., Trifiro, F., 2009. Sustainable Industrial Chemistry. Wiley-VCH, Weinheim. Chum, H.L., Warner, E., Seabra, & J., Macedo, I., 2014. A comparison of commercial ethanol from Brazilian sugarcane and US corn. Biofuels, Bioproducts and Biorefining 8 (2), 205e210. Clark, J., Deswerte, F. (Eds.), 2015. Introduction to Chemicals From Biomass. Wiley, Hoboken, NJ. Corma, A., Iborra, S., Velty, A., 2007. Chemical routes for the transformation of biomass into chemicals. Chemical Reviews 107, 2411e2502. Coulson and Richardson’s Chemical Engineering, 2017. Chemical and Biochemical Reactors and Reaction Engineering, fourth ed., Volume 3A. Butterworth-Heinemann. Dasari, M.A., Kiatsimkul, P.P., Sutterlin, W.R., Suppes, G.J., 2005. Low-pressure hydrogenolysis of glycerol to propylene glycol. Applied Catalysis: A General 281 (1e2), 225e231. De Clerk, A., 2011. FischereTropsch Refining. Wiley-VCH, Weinheim. De Jong, W., van Ommen, R. (Eds.), 2015. Biomass as Sustainable Energy Source for the Future. AIChE-Wiley, USA, Hoboken, NJ. De Jong, E., Higson, A., Walsh, P., Wellish, M., 2012. Bio-based chemicals: valueadded products from biorefineries. International Energy Agency Report Bioenergy Task 42. Denbiras, A., 2010. Biorefineries for Upgrading Biomass Facilities. Springer Verlag, Berlin.

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Dimian, A.C., 2007. Renewable raw materials: chance and challenge for Computer-Aided Process Engineering. In: Proceedings 17th European Symposium on Computer Aided Process Engineering. Elsevier, Amsterdam, pp. 309e318. Dimian, A.C., Bildea, C.S., 2008. Chemical Process Design Case Studies. WileyVCH, Weinheim. Dimian, A.C., Rothenerg, G., 2016. An effective modular process for biodiesel manufacturing using heterogeneous catalysis. Catalysis Science and Technology 6, 6097e6104. Dimian, A.C., Bildea, S., Kiss, A.A., 2014. Integrated Design and Simulation of Chemical Processes In: Computer-Aided Chemical Engineering, second ed., vol. 35. Elsevier, Amsterdam. Dumesic, J.A., et al., 2006. Glycerol as source for fuels and chemicals. Angewandte Chemie International Edition 45 (24), 3982e3985. EPA (Environmental Protection Agency) USA, 2014. Final Renewable Fuels Standards for 2014 to 2017. https://www.epa.gov. European Commission, 2015. E4tech, RE-CORD and WUR. From the Sugar Platform to Biofuels and Biochemicals final report. Contract No. ENER/C2/ 423-2012/SI2.673791, 2015. European Union, 2009. Renewable Energy Directive RED 5/2009, Annex V, Rules for Calculating the Greenhouse Gas Impact of Biofuels, Bioliquids and Their Fossil Fuel Comparators. European Union, 2017. E4tech. Ramp up of lignocellulosic ethanol in Europe to 2030. Report 2017, Available at: www.e4tech.com. European Union, 2015. European Biofuels Technology Platform (EBTP), Factsheets. Available at: http://www.biofuelstp.eu. European Union, April 2019. Joint Research Centre, Insights into the European market for bio-based chemicals. Giuliano, A., Cerulli, R., Poletto, M., Raiconi, G., Barletta, D., 2016. Process pathways optimization for a lignocellulosic biorefinery producing levulinic acid, succinic acid and ethanol. Industrial and Engineering Chemistry Research 55 (40), 10699e10717. GREET® (Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation Model), Fuel/vehicle Life Cycle Model, Jan 02, 2018. National Argonne Laboratory, USA. Grossmann, I.E., Caballero, J., Yeomans, H., 1999. Mathematical programming approaches to the synthesis of chemical process systems. Korean Journal of Chemical Engineering 16, 407e426. International Renewable Agency (IRENA), 2013. Production of Bio-Ethylene. Technology Brief I13. IEA-ETSAP. International Renewable Agency (IRENA), 2016. Innovation Outlook Advanced Liquid Biofuels. Download from: www.irena.org/publications. Kamm, B., Gruber, P.R., Kamm, M. (Eds.), 2006. Biorefinery. Industrial Processes and Products. Wiley-VCH, Weinheim. Katoh, S., Horiuchi, J., Yoshida, F., 2015. Biochemical Engineering. Wiley-VCH, Weinheim. Kim, T.H., 2013. Pretreatment of lignocellulosic biomass. In: Yang, S.-T., et al. (Eds.), Bioprocessing Technologies in Biorefineries. AIChE-Wiley, New York. Kiss, A.A., Omota, F., Dimian, A.C., Rothenberg, G., 2006. The heterogeneous advantage: biodiesel by reactive distillation. Topics in Catalysis 40, 141e146. Kiss, A.A., 2014. Process Intensification Technologies for Biodiesel Production e Reactive Separation Processes. Springer Verlag, Berlin.

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Kiss, A.A., Lange, J.P., Schuur, B., Brilman, D.W.F., van der Ham, A.G.J., Kersten, S.R.A., 2016. Separation Technology - Making a Difference in Biorefineries. Biomass and Bioenergy. https://doi.org/10.1016/ j.biombioe.2016.05.021. Kurian, J.K., Nair, G.R., Hussain, A., Raghavan, V., 2013. Feedstocks, logistics and pre-treatment processes for sustainable lignocellulosic biorefineries: a comprehensive review. Renewable and Sustainable Energy Reviews 25, 205e219. Lin, C., Luque, R. (Eds.), 2014. Renewable Resources for Biorefineries. RSC Green Chemistry, London. Martin, M., Grosssmann, I.E., 2014. Optimal simultaneous production of i-butene and ethanol from switchgrass. Biomass and Bioenergy 61, 93e103. National Corn Growers Association (NCGA), Sept. 2015. US Corn Update. Available at: www.ncga.com. NREL-USA (National Renewable Energy Laboratory), 2011. Report on Process Design and Economics for Biochemical Conversion of Lignocellulosic Biomass to Ethanol. Olah, A.G., Goeppert, A., Prakash, S., 2009. Beyond Oil and Gas: The Methanol Economy. Wiley-VCH, Weinheim. Omota, F., Dimian, A.C., Bliek, A., 2003. Fatty acid esterification by reactive distillation. Chemical Engineering Science 58, 3159e3174, 3175-3185. Pomalaza, G., Capron, M., Ordomsky, V., Dumeignil, F., 2016. Recent breakthroughs in the conversion of ethanol to butadiene. Catalyst (MDPI) 6, 203. Posada, J.A., Zirkzee, H., van Hellemond, E.W., Lopez-Contreras, A., van Hal, J.W., Straathof, A.J.J., 2014. A Biorefinery in Rotterdam with Isobutanol as Platform? ECN. (Energy Onderzoek Centrum) publications, NL. Ragauskas, A., 2019. Basics of biofuels. University of Tennessee-USA. Available at: www.biorefinery.utk.edu. Ramaswamy, S., Huang, H.-J., Ramarao, B.V. (Eds.), 2013. Separation and Purification Technologies in Biorefineries. Wiley. REN21, 2015. Renewable 2015 Global Status Report. Available at: http://www. ren21.net. Sengupta, D., Pike, R.W., 2013. Chemicals From Biomass: Integrating Bioprocesses into Chemical Production Complexes for Sustainable Development, Green Chemistry and Chemical Engineering. CRC Press, Taylor & Francis, Boca Raton, FL. Talebnia, F., Karakashev, D., Angelidaki, I., 2010. Production of bioethanol from wheat straw: an overview on pretreatment, hydrolysis and fermentation. Bioresource Technology 101, 4744. Vial, C., Stiriba, Y., 2013. Characterisation of bioreactors using CFD. In: Soccol, C.R., Pandey, A., Larroche, C. (Eds.), Fermentation Process Engineering in the Food Industries. CRC Press, Boca Raton, FL. Waldron, K. (Ed.), 2016. Advances in Biorefineries, first ed. Elsevier, Amsterdam. Wang, M., Han, J., Dunn, J.B., Cai, H., Elgowainy, A., 2012. Well-to-wheels energy use and greenhouse gas emissions of ethanol from corn, sugarcane and cellulosic biomass for US use. Environmental Research Letters 7, 459. World Petroleum Council (WPC), 2013. Guide, Petrochemicals and Refining. Available at: www.world_petroleum.com. Yang, S.-T., El-Enshasy, H., Tongchhul, N., 2013. Bioprocessing Technologies in Biorefineries for Sustainable Production of Fuels, Chemicals and Polymers. AIChE-Wiley.

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2 PROCESS SYSTEMS APPROACH IN CONCEPTUAL PROCESS DESIGN CHAPTER OUTLINE 2.1 Process Synthesis by Hierarchical Approach 2.2 Bases of Design 47 2.2.1 Project Definition 47 2.2.2 Plant and Site Data 47 2.2.3 Health, Safety, and Environment Data 48 2.2.4 Economic Data 48

45

2.2.4.1 Products and Raw Materials 48 2.2.4.2 Utilities and Environment 49

2.2.5 Technology Review and Research Papers 49 2.3 Chemistry, Thermodynamics, and Properties 50 2.3.1 Chemistry 50 2.3.1.1 Main Reactions 50 2.3.1.2 Secondary Reactions 50 2.3.1.3 Catalyst 50

2.3.2 Chemical Equilibrium 51 2.3.3 Eco-Performance of Chemical Reactions 2.3.4 Reaction Engineering Data 52 2.3.4.1 Reactor Design 52 2.3.4.2 Kinetics of Reactions

2.3.5 Thermodynamic Analysis

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2.3.5.1 Physical Properties of the Main Components 2.3.5.2 Phase Equilibrium 52 2.3.5.3 Residue Curve Map 53

2.4 Input/Output Analysis 53 2.4.1 Design Decisions 53 2.4.2 Overall Material Balance 55 2.4.3 Health, Safety and Environment Analysis 2.4.4 Economic Potential 57

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Applications in Design and Simulation of Sustainable Chemical Processes. https://doi.org/10.1016/B978-0-444-63876-2.00002-4 Copyright © 2019 Elsevier B.V. All rights reserved.

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2.5 Reactor/Separation/Recycles 60 2.5.1 Material Balance Envelope 60 2.5.1.1 Excess of Reactant

62

2.5.2 Nonlinear Behavior of Recycle Systems 2.5.2.1 2.5.2.2 2.5.2.3 2.5.2.4 2.5.2.5

63

Inventory of Components and Makeup Strategies Snowball Effects 64 Multiple Steady States 65 Minimum Reactor Volume 65 Control of Selectivity 65

2.5.3 Reactor Selection

66

2.5.3.1 Reactors for Homogeneous Systems 66 2.5.3.2 Reactors for Heterogeneous Systems 67

2.5.4 Reactor Design Issues

67

2.5.4.1 Heat Effects 67 2.5.4.2 Equilibrium Limitations 67 2.5.4.3 Heat Integrated Reactors 68

2.6 Separation System 69 2.6.1 Superstructure of Separations 69 2.6.2 Methods for the First Phase Split 70 2.6.3 Methodology for Sequencing of Separations 73 2.6.4 Vapor Recovery and Gas Separation System 76 2.6.4.1 Separation Methods 76 2.6.4.2 Split Sequencing 76

2.6.5 Liquid Separation System

79

2.6.5.1 Separation Methods 80 2.6.5.2 Split Sequencing 81

2.7 Distillation 83 2.7.1 Separation of Zeotropic Mixtures

83

2.7.1.1 Sequence of Separations 83 2.7.1.2 Complex Distillation Columns 84 2.7.1.3 Sequence Optimization 85

2.7.2 Azeotropic Distillation

86

2.7.2.1 Homogeneous Azeotropic Distillation 86 2.7.2.2 Heterogeneous Azeotropic Distillation 88

2.7.3 Enhanced Distillation

89

2.7.3.1 Pressure Swing Distillation 2.7.3.2 Extractive Distillation 90

89

2.7.4 Hybrid Separations 91 2.8 Optimization of the Material Balance 2.9 Energy Integration 92 2.10 Health, Safety, and Environment 93 2.11 Process Control System 93 2.12 Process Intensification 94 2.13 Process Simulation Issues 94 References 96

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2.1 Process Synthesis by Hierarchical Approach Conceptual design or preliminary design is a compulsory step for assessing the feasibility of a process design project. Main objectives can be formulated as following: • Find the optimal flowsheet architecture with respect to efficiency of raw materials, energy use, safe operation, and minimal impact on the environment. • Set feasible and close-to-optimum tasks for selecting and sizing the equipment. • Evaluate the effect of interactions between units through recycles of mass and energy. • Solve the key issues in preserving health, safety, and environment (HSE). • Study the plantwide strategy for controlling the mass and energy balances. The conceptual design focuses on the architectural structure of the process. The detailed design and sizing of the operational units, the implementation of process instrumentation and control, and the connection with the system of utilities remain downstream engineering activities. This chapter presents in a compact form the framework applied throughout the whole book called the Hierarchical Approach. This methodology, founded by the works of J. Douglas (1988), has proved over the years to be simple to apply and effective as results. Here we present the main features of an improved methodology developed in the authors’ book “Integrated Design and Simulation of Chemical Processes” (Dimian et al., 2014). The Hierarchical Approach describes the conceptual design as a top-down sequence of levels consisting of analysis, synthesis, and evaluation steps. Accordingly, the analysis results in formulating design decisions. On this basis, process synthesis generates a collection of alternatives. An evaluation procedure based on economic and technological criteria eliminates the less attractive ones. The goal of the procedure is getting a feasible but closeto-optimum efficient flowsheet. The analysis is empowered by the use of state-of-the-art thermodynamic methods, while the synthesis employs systematic conceptual techniques and heuristics. The evaluation of alternatives is performed by comprehensive computer simulation by the flowsheeting approach, which allows the simulation of complex processes with recycles of mass and energy. Although the Hierarchical Approach is not a mathematical or algorithmic procedure, it allows an efficient

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framing of the optimal design space, where the best solution can be worked out. Embedding the computer simulation at various levels and tasks brings the necessary quantitative tools for analysis and design. Moreover, it allows the designer to keep full control on the design process. The wide-ranging merits of this approach have been proven by numerous applications in various technologies. The hierarchical methodology of conceptual process design presented in Fig. 2.1 is organized as a cascade of levels as follows: Level 0: Bases of Design. Level 1: Chemistry, Thermodynamics, and Physical Properties. Level 2: Input/Output: Material Balance, Economic Potential, HSE Analysis. Level 3: Reactor/Separation/Recycle. Level 4: Separation System. Level 5: Energy Integration. Level 6: Hazop and Sustainability. Level 7: Process Control System. The levels 1 to 4 belong to process synthesis, which decides the architectural design of the process, namely the key unit operations and the interconnections of material and energy streams,

Bases of Design

Chemistry Thermodynamics Properes

Process Synthesis

Input/Output Material Balance Economic Potenal HSE Analysis

Reactor/ Separator/ Recycle

Separaon system

Process Control

Flowsheet

Figure 2.1 Hierarchical methodology of conceptual process design.

Process Integraon

Hazop Sustainability

Alternaves

Energy Integraon

Chapter 2 PROCESS SYSTEMS APPROACH IN CONCEPTUAL PROCESS DESIGN

as well as the key features of material and energy balances. The levels 5 to 7 solve process integration issues needed for operation, such as optimal use of energy, additional resources (water, solvents, hydrogen, etc), safety, hazard, and environmental aspects, as well as plantwide control. In addition, the design and sizing of units is consolidated in view of process optimization. Integrated Process Design handles the combination of both process synthesis and integration steps. It may be observed that bringing modifications at process integration levels might imply structural flowsheet changes, clearly not desirable. For this reason, the hierarchical design approach becomes more efficient by reducing the interactions between synthesis and integration levels. The Input/Output level, where detailed chemistry and preliminary material balance is available, becomes the place for the assessment of preliminary economic feasibility. Here the most relevant issues for HSE protection are considered, such as gaseous emissions, treatment of pollutants and residues, etc. In our approach, the Reactor/Separation/Recycle (RSR) level is fundamental for determining the flowsheet structure. If the reaction kinetics is known, it is also the place for designing the chemical reactor. A more advanced issue is the effect of recycles on the stability and flexibility in operation, with implications on the plantwide control strategy, as feed policy of reactants and control of components’ inventory. At this level, the energy integration around the chemical reactor is analyzed too, namely in the case of highly exothermic reactions.

2.2 Bases of Design 2.2.1 Project Definition The project starts by defining the product(s) to be manufactured, alternative raw materials, quality specifications of products, with particular attention to the purity needed for the main applications. Consider an annual working time of 8000 h. Decide if the process is continuous or batch. Continuous processes are suitable for larger manufacturing rate, such as commodities, while batch processes are applied for specialty products, in general below 10,000 tpy.

2.2.2 Plant and Site Data Location: The economic profitability is greatly favored by the proximity of raw materials, as well as by the availability of transportation facilities. Often the location is chosen close to a harbor

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site. Choosing an industrial complex allows sharing the infrastructure of an integrated site. Climate: Climate conditions are necessary for selecting utilities and for designing the equipment. Data are minimum/maximum temperatures, humidity, salt and dust air content, and meteorological variability. Information about local catastrophic risks, such as earthquake and flooding, has to be evaluated. Storage: The storage for raw materials, products, and intermediates can be significant in the total investment cost, namely when dealing with commodities. Toxic and hazard chemicals should not be stored, but consumed immediately on site by respecting the HSE regulations. Utility system: Chemical plants require large amounts of utilities. The on-site utility production must be included in the economic analysis when this is not available from a site source.

2.2.3 Health, Safety, and Environment Data Material Safety Data Sheet (MSDS) gives precious information regarding the physical properties of components and materials, as well as potential HSE problems. MSDS data can be found by Internet search. The MSDS compilation is compulsory before starting the project because these can lead to important design decisions. Moreover, the problems raised by gaseous emissions, pollutants of soil and water, and waste disposal should be examined in view of the legal frame. The following elements should deserve attention: • Toxicity: Specify the toxicity of the main components and impurities involved in the process. Additional information can be found on the websites of public agencies, such as the US Environmental Protection Agency (EPA) and European Environmental Agency (EEA). • Explosions risks: Identify potentially explosive mixtures developed in chemical reactors and storage facilities. Specify the range of concentration and temperature. • Fire risks: Find information about flash point, autoignition temperature, and flammability limits.

2.2.4 Economic Data 2.2.4.1 Products and Raw Materials The prices of products and raw materials are not only the key elements in design but also the most uncertain. The models for forecasting prices may capture the long-term trend, but fail over short periods. In the case of commodities, it was found

Chapter 2 PROCESS SYSTEMS APPROACH IN CONCEPTUAL PROCESS DESIGN

that the prices of products and raw materials follow parallel trends, and thus the gross margin, representing the difference, is relatively stable. The price of raw materials should include systematically the transportation costs. When manufacturing intermediate chemicals, got often from integrated platforms, the so-called transfer prices are considerably cheaper than shipped from remote locations. In addition, the analysis should examine the relation price versus purity, as well as include the prices for valuable by-products. Another possibility is the backward calculation of the maximum price of raw materials that would ensure target profitability with reference to a desired product price (Dimian et al., 2014). Based on existing or similar processes, one can estimate the contribution of fixed and variable costs by using ratio factors. The method also allows the identification of critical elements where design improvements are desirable. Sources of prices are trade journals or specialized consultants, as ICIS (www.ics.org), where free access of some data is granted for academic purposes.

2.2.4.2 Utilities and Environment Information about the cost of common utilities (fuel, steam, cooling water, electricity, and refrigeration) can be found in the literature (Dimian et al., 2014; Turton et al., 2013; Towler and Sinnott, 2013; Seider et al., 2010). Prices on transactional basis may be notably lower. The costs of emissions and waste disposal are necessary to asses the sustainability indices. The cost of CO2 and other greenhouse gases (GHG) must be included. Methods for estimating the environmental costs are given in Appendix C in the authors’ book (2014).

2.2.5 Technology Review and Research Papers Information about technology can be found in the encyclopedic works, such as Ullmann’s Encyclopedia of Industrial Chemistry and Kirk-Othmer Encyclopedia of Chemical Technology, periodically updated. Other useful information can be found in monographic works on particular subjects. More specific data, such as chemistry, catalysis, thermodynamics, and kinetics, are available in research papers. The usual way is the Internet search on Web of Science (Clarivate Analytics), ScienceDirect (Elsevier) and ACS/AIChE/Wiley network. Patents bring valuable information regarding process feasibility and reaction engineering. Some patents address process design aspects, such as separation techniques and energy saving methods.

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2.3 Chemistry, Thermodynamics, and Properties 2.3.1 Chemistry The knowledge of a chemical reaction network is a crucial aspect in the conceptual process design. Using stoichiometric relations allows the development of a consistent material balance.

2.3.1.1 Main Reactions • Identify the linearly independent chemical reactions. Include intermediate components that can be separated and recycled. Each step indicates the reaction phase, as well as the temperature and pressure range. • List the thermal effect of reactions in standard and operating conditions. Identify high exothermic reactions, as well as temperature-sensitive reactions with large activation energy. • List technological constraints, such as the ratio of reactants at the reactor inlet, pressure and temperature, maximum allowable concentrations, flammability, and explosion limits.

2.3.1.2 Secondary Reactions • List secondary reactions leading to by-products and impurities in the range of temperatures and pressures mentioned above. • Search data about yield or selectivity and its variation with conversion. • Pay special attention to the formation of impurities, not only inside chemical reactors but also in some physical operations, such as distillations, because of long residence time or high temperature in reboiler. • Consider reactions involving impurities entered with raw materials. These can generate other impurities that are difficult to separate. Feed purification is often necessary.

2.3.1.3 Catalyst • List alternative catalysts and note the following properties: chemical composition, geometry, pellet and bulk densities, activity expressed as product rate per mass catalyst, selectivity or yield, operation time, thermal and chemical stability, poisoning impurities, mechanical strength with respect to the attrition and formation of fines, and regeneration methods. • Examine the formation of by-products and impurities specific to the selected catalyst.

Chapter 2 PROCESS SYSTEMS APPROACH IN CONCEPTUAL PROCESS DESIGN

• Check the effect of temperature and impurities on catalyst activity. • Examine the environmental problems raised by catalyst regeneration and disposal, as well as the need for solvents or special chemicals. • Finally, select the most suitable catalyst by taking into account activity, robustness in long operation time, purchasing price, and costs for regeneration and disposal.

2.3.2 Chemical Equilibrium Chemical equilibriumecontrolled reactions take place when the reaction rate is fast enough compared with the residence time. The thermodynamic analysis allows finding the maximum achievable conversion and the reaction mixture composition. It may suggest measures for improving conversion and selectivity. Computer simulation offers a powerful method based on Gibbs free energy minimization with respect to both chemical and phase equilibrium. However, the user should note that the computation is very sensitive with respect to errors in the thermodynamic data. For example, an error of 15% in computing  DG 0 RT in the range [ 4, 4] would give a relative error of 180% in estimating the equilibrium constant.

2.3.3 Eco-Performance of Chemical Reactions Alternative chemistries can be compared in terms of ecological performance by means of the waste E-factor (Sheldon et al., 2007) defined as following: E ¼

mass of waste mass of desired product

In this approach, waste may be everything but the desired product, such as by-products, losses of solvents and auxiliary chemicals, unrecovered catalyst, etc. Water in large amount is not included, as it should be recycled after wastewater treatment. A supplementary Q-factor may account for differences in toxicity and cost of posttreatment. The E-factor is weak for oil refining ( 50

P > 25 15 < P < 25 P < 15 P40 C or aij > 7 aij > 2

Optimize pressure and temperature.

Condensation

Boiling points Relative volatility

Cryogenic distillation

Boiling points Relative volatility

Physical absorption

Solubility

Ki > 4

Chemical Absorption

Reversible process

Molecular sieving

Reactive function as acid or base groups Size/shape

Significant differences

Equilibrium adsorption

Adsorption coefficient

Favorable adsorption

Membrane permeation

Perselectivity

Catalytic oxidation

Chemical family

Catalytic hydrogenation

Chemical family

Chemical treatment

Chemical family

Perselectivity greater than 15 Impurities below 10% of the flammability point Components containing double bond Selective reaction

2. Sharp separation consists of splitting the mixture for high recovery of target components. The sharpness is defined as the ratio of key component concentrations in products. This should be better than 10. Potential techniques are physical absorption, cryogenic distillation, molecular sieving, as well as equilibrium adsorption when the molar fraction of adsorbate is less than 0.1. Chemical absorption may be also applicable when the component concentration is low. 3. Purification deals with the removal of impurities with the goal of achieving very high concentration of the dominant

Large-scale processes. Remove first freezable components. Optimize pressure and temperatureand. Recycle the solvent. Optimize the solvent ratio. Remove first fouling components. Remove first fouling components. Remove first fouling components. Danger of dioxin, not for halogenated organics. Develop selective catalyst. Dry treatment. Recovery of support preferred.

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Table 2.10 Selectors and Methods for Gas Separations. Separation Method

Enrichment

Sharp Separation

Purification

Condensation Cryogenic distillation Physical absorption Chemical scrubbing Molecular sieve adsorption Equilibrium limited adsorption Membranes Catalytic oxidation Catalytic hydrogenation Chemical treatment

Yes Yes Yes No Yes Yes Yes No No No

No Yes Yes Yes Yes Yes Yes No No No

No No No Yes Yes Yes No Yes Yes Yes

component. The initial concentration of impurity in mixture should be lower than 2000 ppm, while the final concentration of impurity in product should be less than 100 ppm. Suitable separation methods are equilibrium adsorption, molar sieve adsorption, chemical absorption, and catalytic conversion. The generation and sequencing of splits can be managed by means of heuristics. It starts by trying sequentially the generic rules presented in Table 2.8. Table 2.11 presents more

Table 2.11 Special Sequencing Heuristics for Gas Separations. 1. 2. 3. 4. 5.

Favor condensation for removing high boilers from noncondensable when cooling water can be used as thermal agent. Favor glycol absorption for large-scale desiccation operations requiring dew point depression of 27 C or less. Favor adsorption for small-scale desiccation operations. This is the cheapest alternative for processing small amounts of gas. Favor adsorption for processes that require essentially complete removal of water vapor. This is capable of achieving dew point depression of more than 44 C. Favor catalytic conversion when impurities may be converted into desired product or when they accumulate in recycles or when they produce other impurities by side reactions.

Chapter 2 PROCESS SYSTEMS APPROACH IN CONCEPTUAL PROCESS DESIGN

specific heuristics for gas separations. The condensation of subcritical components at suitable pressure by water cooling is often employed. Before applying low-temperature separations or membranes, the removal of water by glycol absorption or by adsorption is compulsory. In the case of impurities that accumulate in recycles, a powerful method is chemical conversion by selective catalysis with preconcentration by enrichment. Catalytic conversion is also recommended for handling volatile organic components.

2.6.5 Liquid Separation System Removing light- and heavy-end impurities is compulsory before any other separations. Fig. 2.11 presents some common methods for light-end removal: 1. Series of flashes by reducing the pressure or/and increasing the temperature. 2. Distillation with vapor product. When a partial condenser is used, the flash drum plays the role of a vapor/liquid separator. In the setup known as stabilizer, there is only vapor distillate, while the liquid is returned as reflux. The column has a pasteurization section when a gaseous stream leaves in top, while the purified liquid product is obtained as side stream few stages below. The condenser temperature is determined by the available temperature of the cooling agent. The column pressure should be optimized against losses in useful component. 3. Reboiled stripping: In this case, the vapor needed for stripping is produced internally. This method may replace conveniently steam distillation. Note that the initial mixture should be fed at sufficiently low temperature on the top stage. Partial condenser

Stabiliser DV

DV

Pasteurisation section

Reboiled stripping

DV DV

DL DL

Figure 2.11 Alternative methods for removing light ends.

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The removal of heavy species and impurities can be done by using an adsorption device, such as clay or ion-exchange towers, with the inconvenient that the retention capacity diminishes in time and the adsorbent has to be regenerated by washing with solvent.

2.6.5.1 Separation Methods Characteristic physical properties and corresponding separation methods are presented in Table 2.12. Industrial experience demonstrated that when the distillation is feasible, it should be adopted immediately, particularly for large-scale processes. In a second attempt, other alternative separation methods could be rated against distillation.

Table 2.12 Separation Methods for Liquid Mixtures. Separation Method

Characteristic Property

Observation

Zeotropic distillation Simple and complex columns Pressure swing distillation Stripping L-L extraction Melt crystallization Adsorption Molecular sieves Chromatography Azeotropic distillation extractive distillation L-L extraction CO2 supercritical extraction Membrane permeation Pervaporation Reverse osmosis Ion exchange Electrodialysis

Relative volatility a

Use heuristics for sequencing. Not feasible if a < 1.1. Check thermal stability of components. Recommended for thermal sensitive components. Differences larger than 20 C. Pay attention to adsorbent regeneration.

Vapor pressure variation Boiling point Freezing point Chemical affinity wrt adsorbent

Chemical affinity wrt mass separation agent (MSA)

MSA selection is the main issue. Recycling MSA increases the costs. MSA may affect products purity.

Shape, size, affinity

Emerging technologies for purification of gases and liquids, water treatment. Wastewater applications

Electric charge

Chapter 2 PROCESS SYSTEMS APPROACH IN CONCEPTUAL PROCESS DESIGN

2.6.5.2 Split Sequencing The LSM deals with two selectors: zeotropic and azeotropic mixtures. A second decomposition may take place as function of mixture composition and sensitivity to temperature. The first criterion generates dilute and bulk separations, while the second one leads to temperature-sensitive and temperature-insensitive separations. A separation is diluted when the distillate or the bottom product is less than 5% weight with respect to feed. The distillation (simple, extractive, or azeotropic) might be not the most economical. Other methods, such as liquideliquid extraction, stripping, crystallization, adsorption, or membrane permeation, should be tried. The decision depends on the mixture composition and the nature of components. In bulk separations, the desired product is more than 5% in the initial mixture. Distillation is the most economical method. It is important to note that the split generation follows different patterns for zeotropic and azeotropic mixtures. For the zeotropic mixtures, the problem is not feasibility, because always a suitable column can be found, but the optimal sequencing of splits. The optimality criterion is usually the total cost of separations, in terms of investment and operation. In opposition, when dealing with azeotropic mixtures, the feasibility of separation is not guaranteed. Entrainer selection is the central problem. The number of splits is less important. For example, in the case of a binary mixture, typically minimum two and maximum three columns are employed for separation, with solvent recycle (discussed later in this chapter). In the case of temperature-sensitive separations, appropriate methods are stripping, liquideliquid extraction, adsorption, and crystallization, as well as vacuum distillation. The classification of separation methods suitable for the four mentioned selectors is summarized in Table 2.13. Note that azeotropic distillation, membrane permeation, and melt crystallization are expensive, but inevitable in handling complex mixtures. These methods are valid for biorefineries, but additional techniques may be considered, as discussed in Chapter 1. General heuristics, as shown in Table 2.14, may be used for sequencing the separation of liquid mixtures. More specific rules for zeotropic mixtures will be discussed later in this chapter. Some comments about the above heuristics are useful: 1. Remove troublesome species as early as possible, with the priority of lights. 2. Obtaining high-purity component as top product in the final distillation is the “golden rule.” For recycle streams sent to reactors, the purity should be not necessarily high, but constant. Obviously, harmful impurities for catalyst should be removed.

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Table 2.13 Liquid Separation Manager: Selectors and Separation Methods. Separation Method

Dilute Separations

Bulk Separations

Azeotropic Mixtures

Temperature Sensitive

Simple distillation Complex distillation Stripping Extractive distillation Azeotropic distillation L-L extraction Adsorption Molecular sieves Membrane permeation Melt crystallization

Yes No Yes No No Yes Yes Yes Yes No

Yes Yes Yes Yes No Yes Yes Yes No Yes

Yes No No Yes Yes Yes Yes Yes Yes No

Yesa No Yes No No Yes Yes Yes Yes Yes

a

Vacuum distillation.

Table 2.14 General Heuristics for Separation Sequencing of Liquid Mixtures. 1. 2. 3. 4. 5. 6. 7. 8.

Remove first corrosive, hazardous, fouling, reactive, and any troublesome components. Consider also in the first place the removal of light ends. Deliver high-purity products as top distillate. The same is valid for reactants sent to reactors sensitive to impurities. When separation by distillation is feasible, prefer it in a first attempt. Isolate zeotropic and azeotropic mixtures. Perform difficult zeotropic separations later, but before azeotropic separations. Examine other options, such as extractive distillation, L-L extraction, crystallization, adsorption, or molecular sieves. Examine the separation of azeotropic mixtures last. Remove the components in order of decreasing percentage of the feed. This operation will reduce the cost of the next separation. Favor 50/50 splits.

Chapter 2 PROCESS SYSTEMS APPROACH IN CONCEPTUAL PROCESS DESIGN

3. Distillation remains the most reliable separation technique and the most efficient in a large number of cases. Therefore, it should be tried first, or other methods should be rated against it. 4. The partition in zeotropic and azeotropic submixtures simplifies tremendously the separation. These are coupled by recycles or bridge separations, if some components are distributed. 5. Difficult zeotropic separations should not appear in the middle of a separation sequence, but in the last place before azeotropic separations; low relative volatility demands large number of stages and high reflux. Energy saving is a central issue. Employing other separation methods should be investigated, such as crystallization, adsorption, and molecular sieving. 6. The separation of azeotropic mixtures is complicated. Homogeneous azeotropic distillation is appealing, but finding a suitable entrainer is difficult. The heterogeneous azeotropic distillation gives much better results. Extractive distillation (ED) is a good alternative when high-boiler solvent may be found. Often combining distillation with other separation techniques is recommended. 7. Removing systematically the most plentiful component in intermediate mixtures will reduce considerably the cost of separation, both as investment and energy consumption. This heuristics leads typically to a direct sequence. 8. When the components are evenly distributed, a 50/50 split is recommended because it leads to a drastic reduction of the number of downstream separations.

2.7 Distillation Distillation remains the most employed separation method in process engineering. Hereafter we mention only some fundamental issues.

2.7.1 Separation of Zeotropic Mixtures 2.7.1.1 Sequence of Separations The separation of zeotropic mixtures by distillation is always feasible. The question is the most economic sequence, and in some cases the best operable. Split sequencing can be analyzed on the basis of two fundamental alternatives for separating the

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B

A

A,B,C

B,C

A

A,B,C A,B

C direct sequence

C

B

indirect sequence

Figure 2.12 Direct and indirect sequences for separating a ternary mixture.

ternary mixture ABC, with components ranked by decreasing volatility, as presented in Fig. 2.12. In a first attempt, one considers simple columns with one feed two products. In the direct sequence, the components are taken as overhead product in the order of relative volatilities, firstly A and then B. In the indirect sequence, the components are separated in the inverse order of volatility, firstly the heaviest C as bottoms from the first column followed by the A/B separation in the second column. Direct sequence is the mostly applied. The choice also depends on the mixture composition. Note that supplementary alternatives may be considered when the first split is not sharp, but sloppy, which means that the two products rich in A and C contain variable proportions of B. As important applications of this strategy, one can cite DWC (divided wall column), heat integrated columns, and azeotropic distillation devices. The separation of more than 3 components leads to a combinatorial explosion, for example, 5 alternatives in 3 columns by 4 components and 14 alternatives in 4 columns by 5 components. From practical viewpoint, the sequencing may be guided by heuristics, as given in Table 2.15.

2.7.1.2 Complex Distillation Columns Complex columns are compact and economic devices that can handle multicomponent mixtures of minimum three species. A complex column consists of a main tower surrounded by additional columns, such as prefractionator, side strippers, and side rectifiers. As illustrated, Fig. 2.13 presents five alternatives for separating a ternary mixture ABC: 1. Side-stream rectifier: A and C from main column, B as top product of side rectifier. 2. Side-stream stripper: A and C as before, but B as bottoms of side stripper.

Chapter 2 PROCESS SYSTEMS APPROACH IN CONCEPTUAL PROCESS DESIGN

Table 2.15 Heuristics for Separation Sequencing of Zeotropic Mixture. 1. 2. 3.

Perform difficult separations last, but before separations of azeotropes. Remove first the lightest component one by one as overhead products. Remove components in order of decreasing percentage of the feed. This operation will reduce the cost of the next separation. Favor near 50/50 splits.

4.

A

A

A

A

A

B B

B B B C D1

C D2

C D3

C

C D4

D5

Figure 2.13 Types of complex columns.

3. Prefractionator: Separate AB and BC mixtures in first column by sloppy separation and then take pure components A, B, and C in a side-stream second column. 4. Side-stream low position: Take B as side-stream below the feed. 5. Side-stream high position: Take B as side-stream above the feed. Note that configurations D1, D2, and D3 can be combined in some situations (feed composition and relative volatility of components) in a DWC (Kiss, 2013).

2.7.1.3 Sequence Optimization The optimization of a separation sequence can be done by ranking against operation and capital costs. A practical approach for single columns is minimizing the function NT (RR þ 1), where

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NT is the number of stages and RR the reflux ratio. Near-optimal sequences may be got by minimizing the total vapor rate of key components (Doherty and Malone, 2001). However, when the relative volatility of key components differs considerably, this method might be in large error. A true optimal sequencing can be found by mathematical programming.

2.7.2 Azeotropic Distillation Azeotropic distillation deals with the separation of mixtures involving one or several azeotropes. In the past, this problem was tackled by means of experience and intuition, but today by means of systematic methods based on thermodynamic analysis by RCMs. Accordingly, the reliability of the liquid activity model plays a central role. This topic is complex. We recommend reading Chapter 9 in the authors’ book (2014), as well as specialized monographs, such as Stichlmair and Fair (1999), Doherty and Malone (2001) and Seader et al. (2011). Typically, an azeotropic distillation problem consists of finding a method to separate (break) an azeotrope AB in the components A and B of desired purity by employing an MSA (entrainer or solvent) C. The investigation of this problem can be split into two categories: homogeneous and heterogeneous azeotropic distillation.

2.7.2.1 Homogeneous Azeotropic Distillation The solution of the separation problem can be divided into two categories: (1) Separation in one distillation region. (2) Separation in two distillation regions. In the first case, the whole RCM space may be used. Fig. 2.14 illustrates the principle by means of the azeotrope acetone (1)/ heptane (B) broken with benzene (2). Normal boiling points of pure components are 56.2 and 98.4 C, while the azeotrope with 89.8% A boils at 55.1 C. The entrainer is an intermediate boiler at 80.1 C. The flowsheet consists of two simple columns, in direct or indirect sequence. The indirect sequence has better performance as number of stages and energy consumption (Dimian et al., 2014). In the second case, the separation is constrained by a distillation boundary that connects the AB azeotrope with the entrainer or with its azeotrope. Rules for entrainer selection that can be found in the references are mentioned. The feasibility condition

Chapter 2 PROCESS SYSTEMS APPROACH IN CONCEPTUAL PROCESS DESIGN

Figure 2.14 Separation of an azeotropic mixture in one distillation region.

is that a split must cross the distillation boundary from the concave side, which may happen when this is sufficiently curved. Fig. 2.15 illustrates the principle of separation for the mixture acetone (nbp 56.1 C) and chloroform (nbp 61.2 C) forming a maximum boiling azeotrope (nbp 64.7 C) with 30.1% acetone, by employing as entrainer toluene (nbp 110.9 C). There are two alternatives, two of three columns and one of two columns. The full simulation may be found in the authors’ book (2014). In the presented alternative, the distillation boundary is crossed in the first column C-1 by a sloppy split, resulting in two rich mixtures in acetone and chloroform situated on opposite sides of

d2(A) b3

C

Toluene b3

d3(B)

d1

b1

b1 m’

m1

f1

1

2

3 m1

m1 b1

m’

b2(az)

b3(C) C-1

feed C-3 border

d2 A

d1

b2 f1

max. az.

d3 B

d2 Acetone

b2

C-2 d1

az

d3 Chloroform

Figure 2.15 Separation of an azeotrope in two distillation regions: acetone and chloroform with toluene.

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the boundary. The next splits C-2 and C-3 deliver high-purity acetone and chloroform as top distillate, with recycles of azeotrope and entrainer from bottoms to the first column. The most economical is the alternative of two columns. As conclusion, it should be noted that breaking an azeotrope by homogeneous azeotropic distillation is difficult in practice because finding a suitable entrainer is not easy. An alternative method with many industrial applications is the ED.

2.7.2.2 Heterogeneous Azeotropic Distillation The formation of a heterogeneous azeotrope and employing a liquideliquid phase split can help to overcome the constraint of distillation boundary. The problem now is finding a suitable entrainer. RCM is the preferred tool for analysis and design. The principle is illustrated in Fig. 2.16 by the recovery of highpurity ethanol from a mixture of ethanol and water. Ethanol (nbp 78.4 C) and water (nbp 100 C) gives a low boiler binary azeotrope with 0.96 M fraction ethanol and nbp at 78.2 C. Hydrocarbon entrainers may be used, such as pentane, cyclohexane, and benzene. If benzene is employed, a ternary heterogeneous azeotrope is formed, which is the lowest boiler (nbp 64.1 C) and removes selectively more water. On the basis of the RCM analysis, alternatives with three or even two columns can be developed. Fig. 2.16 depicts an alternative with two columns, in which the initial feed is concentrated close to the azeotrope (point F). The first column is for ethanol recovery, while the second for water removal. The first column receives as reflux the organic phase o1 and recycled stream FR to

E o1 Faz

C-2

C-1

o1

az1 W

Et

III

f1 I Et

az3

y1

az2 F

FR

w1

II

W

Figure 2.16 Separating ethanol from water by heterogeneous azeotropic distillation. Two columns alternative.

Chapter 2 PROCESS SYSTEMS APPROACH IN CONCEPTUAL PROCESS DESIGN

produce the overall feed f1 situated in the distillation region I; note that ethanol and ternary azeotrope are the highest and lowest boilers. The column can be designed to give high-purity ethanol in the bottom of and a top vapor of composition close to the ternary azeotrope y1, which must fall into the heterogeneous region after condensation. This is the feasibility condition for applying this method. Next two-phase separation occurs by liquideliquid split; the organic phase with the composition o1 is recycled to the ethanol column, while the aqueous phase of composition w1 is sent to the water column. In this way, ethanol of high purity may be obtained. Note that the impurity might be benzene or water, depending on the column design.

2.7.3 Enhanced Distillation Enhanced distillation designates special techniques for separating azeotropic mixtures or zeotropic mixtures with very low relative volatility. If an MSA is employed, this has to be recycled.

2.7.3.1 Pressure Swing Distillation Pressure swing distillation (PSD) is suitable when the azeotrope composition is sufficiently sensitive to pressure. Fig. 2.17 illustrates the principle for a minimum azeotrope. By pressure elevation, the azeotropic point shifts to more A component. The flowsheet consists of two columns, operated at lower and higher pressure, respectively. The distillate from the low-pressure (LP) column is sent as feed to the high-pressure (HP) column. Pure components A and B can be got as bottom streams from the LP and HP columns. Practical example is the separation of the tetrahydrofuran/water mixture. Note that the heat integration of columns can bring important energy saving. In the case of a maximum azeotrope, the components separate as top products. Practical examples are formic acid/water or hydrochloric/water

P2

D2

D1

D2 F2

P1

D1

F F

B

F1

P1

F2

P2

F1 A

A

Figure 2.17 Pressure swing distillation.

B

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(maximum azeotropes). The air separation in nitrogen and oxygen by cryogenic distillation is a very important PSD application.

2.7.3.2 Extractive Distillation ED is a widespread method for separating zeotropic mixtures of low relative volatility, as well as azeotropic mixtures. ED is an affinity-based separation that takes advantage of the capacity of an entrainer (solvent) to carry out selectively a component, while increasing the relative volatility of the other components. Typical entrainers include liquid solvents, solid salts, combination of both, or novel ionic liquids. The entrainer must be the highest boiler. The light component separates as top product, while the heavy component leaves out with the solvent in bottoms. For this reason, ED may be regarded also as an extractive absorption. In practice, the ED is carried out in a sequence consisting of two columns, the first for ED and the second for solvent recovery, as shown in Fig. 2.18. The entrainer is fed near the top for zeotropic mixture or a minimum-boiling azeotrope or mixed with the feed for a maximum-boiling azeotrope. There are many industrial applications, namely in petrochemistry, as for separating the C4 fraction with solvents, such as furfural, acetonitrile, NMP, DMF, etc. The separation of acetone/chloroform binary examined before can be solved elegantly by using ED with dimethylsulfoxide (Luyben, 2013). As illustrated by Fig. 2.18, breaking the ethanol/ water azeotrope can be done employing ED with ethylene glycol.

Figure 2.18 Separation of the binary mixture ethanol water by extractive distillation.

Chapter 2 PROCESS SYSTEMS APPROACH IN CONCEPTUAL PROCESS DESIGN

The two columns of a conventional ED sequence can also be conveniently integrated into a DWC (Kiss, 2013).

2.7.4 Hybrid Separations In hybrid separations, distillation is combined with other separation methods, such as L-L extraction, adsorption, crystallization, membranes, or even with chemical reaction. It is mainly employed when simple distillation is unfeasible or is very costly because unfavorable vapor pressure difference or because azeotropes form between the key components. The combination of distillation with L-L extraction is suitable for breaking azeotropes, for example, cyclohexane/benzene by acetone, in turn extracted selectively with water. The combination with molecular sieve adsorption or membrane permeation allows breaking an azeotrope without a contaminating solvent. This is advantageous when separating ultrapure components, such as medical grade ethanol from its azeotrope with water. Fig. 2.19 illustrates another example, when there is no azeotrope, but getting pure component is hindered by high nonideal VLE, such as the separation of acetic acid from water solutions. In this case, the problem is solved by using combined distillation with L-L extraction. A suitable entrainer is in this case diisopropyl ether.

Figure 2.19 Combination of L-L extraction and distillation.

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2.8 Optimization of the Material Balance The mass balance envelop is closed by completing the synthesis of reaction and separation systems. The EP after process synthesis becomes EP ¼ EPI=O

fReactor costs=Payback timeg

fCost of recycles and feed conditionningg fCost of separationsg fEnvironmental costsg

fUtilities costsg (2.8)

Put in this way, the approach consists of a complex multivariable optimization task subject to many uncertainties. A practical method is assuming that the chemical reactor and the cost of recycles determine the position of the overall optimum, considering the conversion of the reference reactant as key variable. Lower conversion gives in general better selectivity, but higher costs of recycles. Higher conversion gives more subproducts and impurities, increasing sharply the cost of separations. The optimization of subsections should modify only the absolute value of the Economic Potential, but not affect the flowsheet architecture. Accurate optimization involves cost relations as function of throughput and performance of units. This problem may be tackled by using the capabilities of simulation packages. Examples may be found in Dimian et al. (2014).

2.9 Energy Integration The level 5 from Hierarchical Approach deals with the integration of energy use and helping material resources. This activity involves systematic methods that can regard the following tasks: a. Design of heat exchanger networks by pinch point analysis. b. Energy saving in separations. c. Design of refrigeration systems. d. Waste heat recovery. e. Water minimization and recycling. f. Solvent minimization and recycling. d. Site integration of optimal use of energetic and material utilities. Note that the evolution of design between the levels 4 and 5 can result in supplementary alternatives. However, these should not affect the basic flowsheet structure defined at the Reactor/ Separations/Recycles level. Applying local energy integration

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measures and process intensification (PI) methods can produce an effective design both as hardware and operation costs. Besides energy, the optimal use of other resources is of highest interest. Similar methods based on the pinch principle have been developed for optimal recycling and management of water, hydrogen, and solvents. More appropriate seems the direct optimization based on the allocation of resources. A comprehensive treatment of energy integration problems can be found in the book of Smith (2016), while the optimal management of resources is handled in the monographs of El-Halwagi (2006) and Klemes et al. (2010). A practical approach of the topics a to d mentioned before can be found in Chapters 13 and 14 of the authors’ book (2014).

2.10 Health, Safety, and Environment As the qualitative factors affecting HSE have been identified earlier at I/O analysis, this level implies a quantitative evaluation of these effects on the conceptual design. In the first place, impact factors are collected by using MSDS for components or estimated by computer-aided methods. These properties regard three types on impact factors, on toxicity, safety, and environment. The goal of HSE studies is achieving inherently safer design. The development of these aspects is beyond the purpose of this chapter, but a detailed treatment can be found in Chapter 18 of the authors’ book (2014). The application on acrylonitrile manufacturing covers the key HSE aspects in a conceptual design project.

2.11 Process Control System Integration of design and control starting with the early conceptual stages is a central issue in modern chemical process design. Huge experience has been accumulated over the years in the control of individual unit operations. However, the search of appropriate strategies of controlling the plant as a whole, socalled plantwide control, is relatively of recent date. The need of such approach originates from three reasons: (1) The increase of material and energy recycles in modern plants because of tight integration; (2) the suppression or the limitation of intermediate storage tanks to improve the overall dynamics and/or increase the safety; and (3) the demand in designing flexible plants, with superior dynamics both at lower and higher throughput. The advent of powerful and user-friendly dynamic simulation

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software makes possible to handle the plantwide control strategy directly with nonlinear plant model. Theoretical aspects of plantwide control can be found in the monograph of Luyben et al. (1999), as well in the authors’ books (2003; 2014). Computer-aided applications can be found in the books of Dimian and Bildea (2008) and Luyben (2011).

2.12 Process Intensification PI is defined as a set of innovative principles applied in process and equipment design, which can bring significant benefits in terms of process and chain efficiency, lower capital and operating expenses, higher quality of products, less wastes, and improved process safety. The interest of PI in conceptual design regards two main aspects, equipment and methods. Among PI equipment one may cite the following: • Chemical reactors: spinning disk reactor, static mixer reactor, microreactor, and monolithic reactor. • Equipment for nonreactive systems: rotating packed bed, centrifugal absorber, static mixer, and compact heat exchanger. As PI methods one can mention the following: • Multifunctional reactors: heat-integrated reactor, reactive separation processes (reactive distillation/stripping/absorption/ extraction/crystallization, and membrane reactors), reactive comminution, reactive extrusion, and fuel cells. • Hybrid separations: DWC, membrane distillation, pervaporation, membrane adsorption, and adsorptive distillation. • Alternative energy sources: solar energy, microwave, ultrasound, electric field, and centrifugal field. • Other methods: supercritical fluids, plasma technology, periodic operation. At the level of a conceptual project, these aspects are limited. However, some PI methods can be object of a challenging student project, such as integrated reaction/separation methods or hybrid separations. A detailed treatment of these topics can be found in the Chapter 10 of the authors’ book (2014).

2.13 Process Simulation Issues Modern conceptual design project involves heavily the process simulation. Appropriate training is necessary before rushing to simulator. We strongly recommend reading the three chapters of our book (2014) devoted to process simulation, as well as

Chapter 2 PROCESS SYSTEMS APPROACH IN CONCEPTUAL PROCESS DESIGN

two chapters reviewing the thermodynamic modeling for simulation. The following 10 rules in flowsheeting are useful: 1. Careful analysis of the problem is necessary before rushing to simulator. The analysis has to examine the modeling environment of the simulator. Understanding how the engine of the simulator works is highly recommended for getting reliable results. 2. The most critical aspect in process simulation is the selection of the thermodynamic models. Different thermo models can be used on different parts of the flowsheet or for some units. The accuracy of thermodynamic parameters should always be checked for the key units. Thermodynamic analysis should be employed systematically in simulating separations. 3. Entering feasible specifications requires understanding the concept of degrees of freedom. For good selection of specifications, the user should know, even loosely, the way in which the simulation works. Material balance specifications are the simplest and most robust. 4. Simulating complex processes raises the problem of convergence of recycles. Some specifications perfectly feasible for standalone units might become infeasible when dealing with recycles. Most of the troubles in convergence have as origin inconsistencies in the I/O material balance, for example, when specifying all outputs as absolute flow rates, or because insufficient removal of some components in exit streams. 5. In sequential-modular approach, the calculation sequence plays an important role in getting overall convergence. Transmission of information techniques may be used to untie the nested loops and simplify the calculation sequence. 6. Flowsheet controllers are powerful tools in defining more complex specifications or in achieving desired performances of units. These tools can be also used for simulating the behavior at steady state of process control structures. 7. Analyzing the reasons of nonconvergence is more efficient than increasing the number of iterations. In most cases, the failures originate from incorrect problem statement, unreliable property methods, and conflicting specifications. A failure in steady-state convergence might be an indication about possible troubles with dynamics and control. 8. Stream report is a mirror of the process. However, this is insufficient to evaluate the quality of the simulation. Examining the performance of units individually is compulsory. Profiles of variables help to understand how the unit really works.

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9. Sensitivity analysis and case studies are valuable flowsheet analysis tools. 10. Flowsheet optimization is difficult and should be preceded by careful analysis of the objective function and its sensitivity to different variables.

References Allen, D.T., Shonnard, D.R., 2002. Green Engineering, Environmentally Conscious Design of Chemical Processes. Prentice Hall PTR. Anastas, P.T., Eghbali, N., 2010. Green chemistry. Principles and practice. Chemical Society Reviews 39, 301e312. Barnicki, S.D., Fair, J.R., 1990. Separation system synthesis: a knowledge based approach: 1. Liquid mixture separations. Industrial and Engineering Chemistry Research 29, 431e439. Barnicki, S.D., Fair, J.R., 1992. Separation System Synthesis: a knowledge based approach: 2. Gas/Vapour mixtures. Industrial and Engineering Chemistry Research 31, 1679e1694. Bildea, C.S., Dimian, A.C., 1998. Stability and multiplicity approach to the design of heat-integrated PFR. AIChE Journal 44, 2703e2712. Bildea, C.S., Dimian, A.C., 2003. Fixing flow rates in recycle systems: Luyben’s rule revisited. Industrial and Engineering Chemistry Research 42, 4578e4588. Bildea, C.S., Dimian, A.C., Iedema, P.D., 2000. Nonlinear behaviour of reactorseparator-recycle systems. Computers and Chemical Engineering 24 (Nos. 2e7), 209e217. Dimian, A.C., Bildea, C.S., 2004. Component inventory control. In: Seferlis, Georgiadis (Eds.), Integrating Design and Control. Elsevier, pp. 401e430. CACE series No. 17. Dimian, A.C., Bildea, C.S., 2008. Chemical Process Design: Computer-Aided Case Studies. Wiley-VCH. Dimian, A.C., Bildea, C.S., Kiss, A.A., 2014. Integrated Design and Simulation of Chemical Processes, second ed. Elsevier. CAPE series No. 33. Dimian, A.C., 2003. Integrated Design and Simulation of Chemical Processes, first ed. Elsevier. CAPE series No. 13. Doherty, M., Malone, M., 2001. Synthesis of Distillation Systems. McGraw-Hill. Douglas, J.M., 1988. Conceptual Design of Chemical Processes. McGraw-Hill. El-Halwagi, M., 2006. Process Integration. Academic Press. Kiss, A.A., Bildea, C.S., Dimian, A.C., 2007. Computers and Chemical Engineering 31, 601e611. Kiss, A.A., 2013. Advanced Distillation Technologies: Design, Control and Applications. Wiley. Klemes, I., Friedler, F., Bulatov, I., Varbanov, P., 2010. Sustainability in the Process Industry: Integration and Optimization. McGraw-Hill. Luyben, W.L., Tyreus, B., Luyben, M.L., 1999. Plantwide Process Control. McGraw Hill. Luyben, W.L., 2011. Principles and Case Studies of Simultaneous Design. Wiley. Luyben, W.L., 2013. Comparison of extractive distillation and pressure-swing distillation for acetone/chloroform separation. Computers and Chemical Engineering 50, 1e7. Seader, J.D., Henley, E.J., Roper, D.K., 2011. Separation Process Principles, third ed. Wiley.

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Seider, W., Seader, J.D., Lewin, D.R., Widagdo, S., 2010. Product and Process Design Principles: Synthesis, Analysis and Design, third ed. Wiley. Sheldon, R.A., Arends, I., Hanefeld, U., 2007. Green Chemistry and Catalysis. Wiley. Smith, R., 2016. Chemical Process: Design and Integration, second ed. Wiley. Stichlmair, J.G., Fair, J.R., 1999. Distillation, Principles and Practice. Willey-VCH. Strathmann, H., 2011. Membrane and membrane separation processes. In: Ullmann’s Encyclopaedia of Industrial Chemistry, vol. A16. Wiley. Towler, G., Sinnott, R., 2012. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design, second ed. Elsevier. Turton, R., Bailie, R.C., Whiting, W.B., Shaeiwitz, J.A., Bhattacharyya, D., 2013. Analysis, Synthesis, and Design of Chemical Processes, fourth ed. Prentice Hall.

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3 METHANOL CHAPTER OUTLINE 3.1 Introduction 101 3.2 Renewable Versus Fossil Raw Materials 105 3.2.1 Synthesis From Syngas 105 3.2.2 Synthesis by CO2 Hydrogenation 106 3.3 Chemistry, Thermodynamics, and Kinetics 106 3.3.1 Chemical Reactions Network 106 3.3.2 Chemical Equilibrium 107 3.3.3 Catalysts and Kinetics 108 3.4 Process Technologies 113 3.4.1 Reactor Types 113 3.4.2 Process Technologies 116 3.5 Methanol Production From Syngas 123 3.5.1 General Considerations 123 3.5.2 Process Simulation 124 3.5.3 Reactor Design 125 3.5.4 Design of the Separation Section 127 3.6 Methanol Synthesis by CO2 Hydrogenation 128 3.6.1 Process Design and Simulation 129 3.7 Conclusions 138 Notation 138 Greek Symbol 138 Subscript 138 Abbreviations 139 References 139 Appendix 141

3.1 Introduction Methanol is a viable alternative energy source, offering a convenient solution for the efficient energy storage on a large scale, while playing an important role in economy and sustainability by converting the CO2 waste from industry into a valuable product (Olah et al., 2009). As fundamental sustainable raw material, Applications in Design and Simulation of Sustainable Chemical Processes. https://doi.org/10.1016/B978-0-444-63876-2.00003-6 Copyright © 2019 Elsevier B.V. All rights reserved.

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methanol recovers carbon from every source, including biomass and coal. It is an excellent substitute for natural gas in chemical industry, being used for example in China in large-scale methanol-to-olefin plants for producing olefins from coal. At industrial scale, methanol is produced from synthesis gas (CO/ CO2/H2) using various catalysts based on CuO/ZnO/Al2O3. Complementary to carbon capture and sequestration (CCS), much effort is being put on the development of technologies for methanol production from carbon dioxide. Methanol synthesis began in the 1800s with the isolation of “wood” alcohol from the dry distillation (pyrolysis) of wood. At the beginning of the 20th century, research to convert syngas to liquid fuels and chemicals led to the concurrent discovery of methanol and the FischereTropsch synthesis processes (Fiedler et al., 2005). Methanol is a by-product of FischereTropsch synthesis when alkali metalepromoted catalysts are used. Methanol synthesis is now a well-developed commercial catalytic process with high activity and very high selectivity (>99%). Methanol can be produced from syngas, which is obtained via natural gas steam reforming (no oxygen used), autothermal reforming (oxygen used), or a combination of the two. The syngas is fed to a gasphase catalytic reactor which produces methanol, water, and small amounts of other by-products. The crude methanol contains up to 18% water, ethanol, higher alcohols, ketones, and ethers. Purification is done by distillation in a first unit that removes the volatile compounds and a second unit which removes the water and higher alcohols. Unreacted syngas is recycled back to the methanol reactor resulting in overall conversion efficiency greater than 99%. Fig. 3.1 shows a generic methanol synthesis process flow diagram (Bildea, 2017). The methanol industry is one of the world’s most dynamic and vibrant, producing a basic chemical molecule that is extremely important in the modern life. From the basic chemical building block of paints, solvents, and plastics to innovative applications in energy, transportation fuel, and fuel cells, methanol is a key commodity and an integral part of the global economy (Olah et al., 2009; Ott et al., 2012). Methanol, one of the most versatile compounds developed, is the basis for hundreds of chemicals, and it is second in the world in amount shipped and transported around the globe yearly. As truly global commodity, methanol is a key component, and new applications are paving the way forward to innovation. Methanol is most often converted into formaldehyde, acetic acid, and olefinsdall basic chemical

Chapter 3 METHANOL

Figure 3.1 Simplified diagram of the methanol synthesis process (from natural gas).

building blocks for many common products. There are a large number of products that are developed from these materials; needless to say, methanol is all around us and is a critical component of modern life. Materials such as plastics, synthetic fibers, paints, resins, magnetic film, safety glass laminate, adhesives, solvents, carpeting, insulation, refrigerants, windshield washer fluid, particle board, and pigments and dyes are made from methanol (Fiedler et al., 2005). Besides being transformed into many vital products and commodities, methanol is also used on its own in a number of applications (Bildea, 2017): • Transportation fuel: Methanol is easy to transport, readily available, and has a high-octane rating that allows for superior

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•

•

•

•

vehicle performance compared with gasoline. The use as fuel is driven in large part by the low price of methanol compared with gasoline or ethanol and the very small incremental cost to modify current vehicles to run on blends of methanol fuel. Methanol also produces much less toxic emissions than reformulated gasoline, with less particulate matter and smog forming emissions. Wastewater denitrification: Methanol is also used by municipal and private wastewater treatment facilities to aid in the removal of nitrogen from effluent streams. As wastewater is collected in a treatment facility, it contains high levels of ammonia. Through a bacterial degradation process, ammonia is converted into nitrate. If discharged into the environment, the nutrient-rich nitrate in sewage effluent can have a devastating effect on water ecosystems, creating miles long algae blooms that sap oxygen and sunlight from aquatic life. Methanol, which quickly biodegrades, is a cost-effective way to help revitalize waterways tainted by the effects of nitrates. Fuel cell hydrogen carrier: Methanol is used as a key component in the development of different types of fuel cells, which are quickly expanding to play a larger role in our energy economy. From large-scale fuel cells to power vehicles or providing backup power to remote equipment to portable fuel cells for electronics and personal use, methanol is an ideal hydrogen carrier. With a chemical formula of CH3OH, methanol has more hydrogen atoms in each molecule than any other liquid that is stable in normal conditions. Biodiesel production: In the process of making biodiesel fuel, methanol is used as a key component in (trans-)esterification where methanol is used to convert the triglycerides in different types of oils into useable biodiesel fuel. In this process, methanol reacts with the triglyceride oils contained in vegetable oils, animal fats, or recycled greases, forming fatty acid alkyl esters (biodiesel) and the by-product glycerin. Biodiesel production continues to grow around the globe, with everything from large-scale commercial operations to smaller, backyard blenders mixing this environmentally friendly fuel for everyday use in diesel engines. Electricity generation: Different companies are also exploring the use of methanol to drive turbines to create electricity. There are a number of projects currently underway that are using methanol as the fuel source to create steam to drive turbines, which is an excellent option for areas rich in resources other than traditional electricity sources (Methanol Institute, 2007).

Chapter 3 METHANOL

The methanol industry spans the entire globe, with production sites in Asia, North and South America, Europe, Africa, and the Middle East. Worldwide, over 90 methanol plants have a combined production capacity of about 100 million metric tons (almost 90 billion liters), and each day more than 100,000 tons of methanol is used as a chemical feedstock or as a transportation fuel (225 million liters). Methanol is also a truly global commodity, and each day there is more than 80,000 metric tons of methanol shipped from one continent to another (Markets and Markets Analysis, 2013). The worldwide methanol market is anticipated to see robust growth in the years to come; in 2016, it exceeded 107.7 million tons. However, the methanol markets will likely face oversupply, and as a result, the existing facilities are poised to undergo restructuring. China is set to maintain its leadership in the world methanol market.

3.2 Renewable Versus Fossil Raw Materials Most methanol processes still use natural gas and coal as primary raw materials, but renewable methanol (green methanol) produced from biogas or biomass gasification is also available.

3.2.1 Synthesis From Syngas Methanol is mainly produced from syngas, which can be produced from many different feedstock, such as coal, lignite, natural gas, shale gas, oil, oil refinery residues (vacuum residues or petroleum coke), as well as from renewable resources such as wood, wood and agricultural residues, biogas and waste, and using a variety of different syngas-generating technologies. A more sustainable route to produce methanol would involve using CO2 (from CCS activities) that can be hydrogenated using H2 from electrolysis processes (based on renewable electricity, e.g., solar, wind, geothermal). Various reforming technologies are applicable for the conversion of natural gas, oil-associated gas, and other gaseous feedstock to (methanol) synthesis gas. Although most of the plants worldwide use conventional steam reforming, it is important to consider other proven technologies when the most economical methanol plant concept should be the objective. The syngas composition, characterized by the stoichiometric number (SN), has an important influence on the overall cost.

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SN ¼

xH2 xCO2 xCO þ xCO2

(3.1)

Typical resulting syngas compositions include the following: • Steam reforming by means of CO2 recycle: H2:CO ¼ 4e6 and SN ¼ 2.7e3.0 • Autothermal reforming: H2:CO ¼ 2.7e3.3 and SN ¼ 1.5e1.6 • Lurgi Multi Purpose Gasification (MPG): H2:CO ¼ 1.7e1.8 and SN ¼ 1.5e1.6

3.2.2 Synthesis by CO2 Hydrogenation In addition to CCS, much effort is being put on the development of technologies for methanol production from CO2. Converting carbon dioxide to methanol by hydrogenation is considered to be a great industrial opportunity (Olah et al., 2009). While plenty of CO2 is available from CCS activities, flue gas, or as by-product in various processes (e.g., bioethanol production), the sources of hydrogen are more limited but feature processes such as steam methane reforming, coal gasification, partial oxidation of light oil residues, dry reforming, water electrolysis (using renewable electricity), and sulfureiodine or copper chloride processes (Jadhav et al., 2014). Another major industrial source is the chloralkali process, where H2 is formed as by-product of the salt electrolysis (Kiss et al., 2016). Based on the stoichiometry, 1 ton of chlorine leads to 28 kg hydrogen that can be further converted into 149 kg methanol, using 205 kg CO2.

3.3 Chemistry, Thermodynamics, and Kinetics This section aims to provide more details about the thermochemistry of the methanol process.

3.3.1 Chemical Reactions Network The pathways for methanol formation from CO2/CO and H2 on a metallic Cu catalyst are given in Kondratenko et al. (2013). The actual chemistry of CO2 hydrogenation involves three main reversible reactions (R1, R2, and R3) leading to methanol and water (Fiedler et al., 2005): R1: CO þ 2H2 $ CH3 OH

DH298K ¼

90:77 kJ=mol

(3.2)

Chapter 3 METHANOL

K equilibrium / [atm-2 ]

1

K1

K3

K2

0.1 0.01 0.001 0.0001 0.00001 0.000001 150

200

250

300

350

Temperature / [C] Figure 3.2 Effect of temperature on the equilibrium constants of the main chemical reactions.

R2: CO2 þ H2 $ CO þ H2 O DH298K ¼ þ41:21 kJ=mol; Reverse WGS reaction R3: CO2 þ 3H2 $ CH3 OH þ H2 O

DH298K ¼

(3.3)

49:16 kJ=mol (3.4)

The CO2 conversion to CO (3.3) is endothermic; hence the temperature increase is favorable to the equilibrium. However, the CO and CO2 conversions to methanol (3.2) and (3.4) are exothermic; hence the temperature increase has a negative impact on equilibrium. These reactions also proceed with a decrease of number of moles. Thus, higher methanol equilibrium yields are obtained at lower temperatures and higher pressures. This effect is clearly illustrated in Fig. 3.2 showing the effect of temperature on the chemical equilibrium (discussed in details in the next section). Note that in a process having all three components (CO2, CO, and H2) in the feed, the composition has to be adjusted such that the SN is equal to 2. A higher value (SN >2) indicates that there is an excess of H2 in the feed gas, while a lower value (SN 55

15e35 15e50 48.8 24 22 19 21 21e25

20 20 12.9

Other

Patent Date

Zr-2-18 Mg

1987 1965 1978 1973 1987

Rare earth oxided5 12 31 17 10

Table 3.1 lists the commercial methanol synthesis catalyst formulations used typically (Methanol Institute, 2007). Synthesis from CO2: Some of the earliest methanol plants operating in the 1920e1930s were commonly using CO2 and hydrogen (generally obtained as by-products of other processes) for methanol production. Efficient catalysts based on metals and their oxides have been recently developed for this reaction (Olah et al., 2009). However, the technology for converting CO2 into methanol is still in the early development stages. Lurgi AG and Sud-Chemie developed a highly selective catalyst, active and stable at 260 C (Goehna and Koenig, 1994). The first pilot plant for the production of methanol (50 kg/h) from CO2 and H2 was built in Japan using a SiO2-modified Cu/ZnO catalyst (Saito, 1998). Mitsui Chemicals (Japan) announced a pilot plant producing methanol from CO2 and H2 with an annual capacity of 100 tonnes/year, where hydrogen is generated by photochemical splitting of water using solar energy (Tremblay, 2008). In Iceland, Carbon Recycling International (carbonrecycling.is/george-olah) had built and operates a plant which produces 5 million liters of methanol per year. The plant recycles 5.5 ktonnes of carbon dioxide per year. The energy is generated from hydro- and geothermal sources. The plant uses electricity to make hydrogen. The CO2 is captured from flue gas released by a geothermal power plant.

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Several review papers have been published during the past decade, covering many topics related to CO2 hydrogenation, such as the following (Kiss et al., 2016): • Liu et al. (2003) reviewed the progress in the catalyst innovation, optimization of the reaction conditions, reaction mechanism, and catalyst performance in CO and CO2 hydrogenation to methanol, highlighting the key issues of catalyst improvement and areas of priority in R&D. • Centi and Perathoner (2009) analyzed the possibilities of converting CO2 to fuels, noting that the requisites for this objective are minimization of the consumption of hydrogen, production of fuels that can be easily stored and transported, and the use of renewable energy sources. Their review included CO2 reverse WGS and hydrogenation to hydrocarbons, alcohols, DME or formic acid, as well as the reaction to synthesis gas; photo- and electrochemical/catalytic conversion; and thermochemical conversion. • Kondratenko et al. (2013) discussed the heterogeneously catalyzed hydrogenation, as well as the photocatalytic and electrocatalytic conversion of CO2 to hydrocarbons or oxygenates, along with the design of electrodes to improve their performance and the recent developments of the application of ionic liquids as electrolytes and of microorganisms as co-catalysts. • Saeidi et al. (2014) focused on hydrocarbon and methanol synthesis as methods to convert CO2 to value-added products. The reaction mechanisms and the effects of catalyst, reactor type, and operating conditions on product efficiency enhancement of each process were reviewed. Also, a brief overview on the reactor types and configurations was provided. • Yan et al. (2014) concentrated on the recent advances in designing efficient catalysts for the hydrogenation of CO2 to fuels, e.g., CO2 hydrogenation to methanol, CO2 conversion to CO via reverse WGS reaction, and production of hydrocarbons through FischereTropsch synthesis. • Jadhav et al. (2014) tackled various aspects on the CO2 hydrogenation reaction system such as thermodynamics, innovations in catalysts, influences of reaction variables, overall catalyst performance, reaction mechanism and kinetics, and recent technological advances. • Ali et al. (2015) made a critical review on innovative catalysts for methanol synthesis, the research progress for their development, and their use in the catalytic process, while providing

Chapter 3 METHANOL

an overview on recent developments in methanol synthesis from syngas, CO2 hydrogenation, and photocatalytic reduction of CO2. The use of various reactors, the influence of preparation method, support, promoter, different types of catalysts used, and their properties and performance during methanol synthesis were also thoroughly reviewed.

3.5 Methanol Production From Syngas 3.5.1 General Considerations Considering that the methanol process is equilibrium-limited and therefore incomplete conversion is achievable in the reactor, the process resembles the classic reactoreseparatorerecycle structure (Bildea et al., 2000; Kiss, 2010; Dimian et al., 2014). Fig. 3.8 shows a generic block diagram of the methanol process. Note that the difference in boiling points of reactants (CO, CO2, H2) and reaction products (methanol, water) is very large. This allows performing the reactants/products split by a simple flash (a single vapor-liquid equilibrium (VLE) stage is enough), achieved after cooling and pressure reduction. Therefore, the recycle requires a costly compressor. Moreover, the feed contains some amounts of methane, an inert species. As separation of methane from the reactor outlet mixture is difficult, a purge is required to avoid accumulation. Thus, the key units, common to all technologies, commonly described are the reaction unit (including the reactor and the eventual heat exchangers for indirect cooling), flash (vapor liquid separation), purge, compressor, and a direct sequence of distillation columns. After the feed conditioning, the reaction takes place in gas phase, followed by the phase separation of products (condensable) from the unconverted (gas) reactants, which are recycled. A small amount is being purged to avoid the accumulation of Purge SN =

y

−y

y

+y

=2

Lights

Methanol

Unreacted COx + H2 Recycle

COx

Reactor H2

200-300°C 50-100 bar

COx + H2 CH3OH + H2O

G-L Flash

Sep 1

Sep 2

Water

Figure 3.8 Block diagram of the methanol process.

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124

Chapter 3 METHANOL

inert species. The purification stage delivers the main product, as well as by-products and impurities (Dimian et al., 2014). Comparing the different design alternatives, the multibed reactor with indirect cooling has the advantage of simple construction but requires several external heat exchangers. The multibed reactor with direct (quench) cooling is cheaper to build because of the smart use of the raw materials stream to cool the reaction mixture, eliminating the use of heat exchangers. However, the conversion per pass is lower, and hence the cost of recycling is higher. The option of a multitubular cooled reactor offers a higher yield (and therefore lower recycling costs), but it is more difficult to build and operate. A rough estimation of the reaction section (including the reactor, heat exchangers, flash drum, and recycle compressor) shows that the three alternatives have similar costs (but with different CapEx and OpEx contributions), the differences being within the accuracy of the estimation relationships. This finding is in-line with the industrial practice, where all reactor types are being currently used. This section will focus on methanol plant built around the multitubular, cooled reactor, the other options being left as an exercise for the reader.

3.5.2 Process Simulation Aspen Plus was used for design and simulation of a 150 ktpy methanol plant. The process takes place at two different pressure levels, higher pressure for methanol synthesis and lower pressure for methanol purification. For the first part, a standard selection for the thermodynamic model is an EOS, for example, Penge Robinson or SRK. For the second part, a liquid activity model is suited, such as Wilson, UNIQUAC, or nonrandom two-liquid (NRTL), but capable of handling supercritical gaseous components, such as CO, CO2, CH4, and H2, by means of Henry coefficients (Dimian et al., 2014). The property methods used were SRK (for the reaction section), and NRTL-RK with CO, CO2, CH4, and H2 declared as Henry components (for the separation section). Note that the composition of the fresh syngas is 21.79% CO, 7.74%CO2, 67.53%H2, and 2.94%CH4 (mole fractions), typical for a natural gas combined reforming plant (Plass et al., 2014). The intrinsic reaction rates provided by Graaf et al. (1990) were used, with effectiveness factors calculated according to Bozga and Muntean (2001). The formation of light by-products was model as methanol dehydration to DME, assuming 98% selectivity. The process flowsheet of the Methanol plant is presented in Fig. 3.9 (Bildea and Bozga, 2017).

Chapter 3 METHANOL

Figure 3.9 Process flow diagram of the methanol process.

3.5.3 Reactor Design A main piece of equipment is the reactor, simulated by the RPLUG model from Aspen Plus. The tubes diameter was fixed to 0.04 m, which ensures a compromise between high values of the specific area (at small diameter) and low-pressure drop (at large diameter). The fluid velocity at reactor inlet was fixed to 0.5 m/s, from which the number of tubes can be calculated. The reactor-inlet and coolant temperatures were both set to 242 C (515 K). The heat transfer coefficient from the reaction mixture to the tube wall was calculated (by a FORTAN block executed before the reactor model) according to the following relationship:   6$dp 0:33 Nu ¼ 2:26$Re0:8 $Pr $exp (3.28) p dt where dp ¼ 4.3 mm and dt ¼ 0.04 are the tube and catalyst particle diameters. Nu, Re, and Pr are the Nusselt, Reynold (with particle diameter as characteristic length), and Prandtl numbers. The resistance to heat transfer of the tube and on the coolant side was neglected. The pressure drop was calculated according to Ergun equation. The reactor was optimized using the total annual cost (TAC) as objective function to be minimized, taking into consideration the CapEx, OpEx, and syngas cost. The cost of the reactor was calculated as CReactor ¼ CR þ CCatalyst

(3.29)

125

126

Chapter 3 METHANOL

CR ¼

M&S $474:7$A0:65 R $ð2:29 þ Fm ðFd þ Fp ÞÞ 280

(3.30)

where M&S is the Marshall and Swift equipment cost index (M&S ¼ 1536.5 in 2012), AR is the area of the reactor tubes (m2), Fm ¼ 1 (carbon steel), Fp ¼ 1 þ 0.0074(P-3.48) þ 0.00023(P-3.48)2, and Fd ¼ 0.8. CCatalyst ¼ ntubes $

p$dt2 $L$rcat $ð1 4

εÞ$Ccat;sp

(3.31)

where Ccat,sp ¼ 4$/kg; rcat ¼ 2000 kg/m3; ε ¼ 0.5. Ccompressor ¼

M&S $664:1$BP 0:82 $Fc 280

(3.32)

with BP (brake power) in kW and Fc ¼ 1.29 (reciprocating, motor). TAC ¼

CAPEX þ OPEX þ CSyngas payback period

(3.33)

The price of the syngas was considered as 30$/thousand cubic meters (TCM) (1000 cubic meters, in normal conditions). The compressing cost was taken as 16.8$/GJ. The objective function to be minimized is the TAC. The decision variables are the number of reactor tubes (NT) and their length (L), the purge fraction (f), and the flow rate of fresh syngas (F0). The importance of including the purge fraction (which must remove the inert present in the feed stream) in the optimization problem should be emphasized: a large purge with low inert concentration implies loss of raw material, while a small purge with high inert concentration is inefficient due to inert recycling. Including the syngas flow rate in the optimization problem is necessary to ensure the required production rate. The minimization is subject to several constrains, namely a production rate P* ¼ 610 kmol/h of methanol (corresponding to about 150 ktpy), a constant superficial velocity of the mixture inside the reactor of 0.5 m/s, and the mass, energy, and momentum balance of the units as implemented by Aspen Plus models. 8 > P ¼ P > > < m fobj ¼ min TAC s.t. u ¼ 0:5; s L;4;F0 ;NT > > > : mass; energy; and momentum balance (3.34)

Chapter 3 METHANOL

Figure 3.10 Optimization of the reaction section.

The configuration of the optimal reactor is 8 m length, 6092 tubes, 0.04 m tube diameter, and 61,243 kg of catalyst. The optimal value of the purge fraction is 0.016. This small value emphasizes the important weight of the raw material in the TAC (the costs associated with recycling the inert methane, which reaches 24%mole in the recycle, are smaller than the costs due to loss of reactants in the purge stream). Fig. 3.10 show results of sensitivity studies performed around the optimal operating point. Catalyst deactivation issues can be considered. Bildea and Bozga (2017) showed that the catalyst activity drops to about 50% after 4 years of operation. The optimal policy (leading to highest profit) is to change the catalyst every 2 years, but this is subject to the catalyst price. Another option is to gradually increase the operating temperature to compensate the deactivating catalyst. Table 3.2 presents the temperature, pressure, flow rates, and composition of the streams from the reaction section (Bildea, 2017).

3.5.4 Design of the Separation Section The first column (COL-1) separates methanol and water from the light components (DME, H2, CO, CO2, and CH4). The column works as a stripper (feed on the first tray, no condenser), the reboiler duty being adjusted such that the recovery of methanol in the bottoms stream is 99.5% (the mole fraction of methanol

127

128

Chapter 3 METHANOL

Table 3.2 Stream Table of the Reaction Section.

Temperature/[ C] Pressure/[bar] Mole flows/[kmol/h]

Syngas

Reactor inlet

Reactor outlet

Flash_Liq

Flash_Vap

Purge

Recycle

850 50 2274.6

241.9 50 15726.9

243.4 49.7 14479.6

25.0 45 808.7

25.0 45 13,671

25.0 45 218.7

37.2 50 13452.2

0.2179 0.6753 0.0774 0.0294 0 0 0 25,801

0.0597 0.6950 0.0315 0.2106 0.0019 0.00016 0.00068 124,831

0.0312 0.6597 0.02487 0.2288 0.04423 0.01002 0.00119 124,830

0.0010 1.04$10 0.0431 0.0175 0.7543 0.1762 0.00786 24,192

0.0330 0.6988 0.0238 0.2413 0.0022 0.0002 0.0008 100,639

0.0330 0.6988 0.0238 0.2413 0.0022 0.0002 0.0008 1610

0.0330 0.6988 0.0238 0.2413 0.0022 0.0002 0.0008 98,683

Mole Fractions

CO H2 CO2 CH4 CH3OH H2O DME Mass flows/[kg/h]

5

in the LIGHTS is about 5%). This ensures that the bottoms stream is free of DME and lighter components. The first distillation column has a diameter of 0.93 m, a height of 7.8 m, 9 theoretical stages (including the reboiler and condenser), with the feed on stage 2. The sizing of the methanol purification column was optimized, with TAC as objective function, reflux ratio, distillate rate, number of trays and feed tray as decision variables, and purity of the top and bottom products as constraints. The optimal column has a diameter of 1.88 m, a height of 32.4 m, 38 theoretical stages (50 real trays, reboiler, and condenser), with the feed on the 28th theoretical tray (39th real tray). The reflux ratio is 0.59 kmol/kmol. The methanol and water products have purities 99.9% (molar fractions).

3.6 Methanol Synthesis by CO2 Hydrogenation This section describes an efficient process for the CO2 conversion to methanol using wet hydrogen (saturated with water), in a catalytic process based on highly active Cu/Zn/Al/Zr fibrous

Chapter 3 METHANOL

catalyst (Kiss et al., 2013, 2016). The issue is that the direct use of water-saturated hydrogen stream has a strong negative impact on the chemical equilibrium. To solve this issue, an efficient new process is proposed that includes a key feature, namely the use of stripper that has a double positive effect, as it removes the CO2 from the methanolewater mixture produced and avoids the presence of CO/CO2 in the products, while also removing the water from the wet hydrogen feed initially saturated with water. The efficiency of the process is thus increased, leading to low consumption figures. The results are provided for a 100 ktpy methanol plant, simulated in Aspen Plus and including experimental data previously reported in literature (An et al., 2009).

3.6.1 Process Design and Simulation The complete process was rigorously simulated in Aspen Plus using the SRK property model, which is most suitable for these components (H2, CO, CO2, H2O, and CH3OH) and conditions (pressure up to 50 bar and temperature up to 250 C). The NRTL model was used complementary to the SRK property model for modeling the distillation section operating at low pressure and in which no hydrogen is present. This is in line with literature recommendations for such systems (Kiss, 2013; Dimian et al., 2014). Note that all the binary interaction parameters related to the property models, SRK and NRTL, are available in the pure components databank of the Aspen Plus process simulator. The amount of catalyst considered in the reactor corresponds to a gas hourly space velocity of GHSV ¼ 5.9 m3/kgcath. Because of the geometrical design of the multitubular reactor, the gas velocity does not exceed 1.5 m/s. The following parameters were varied in the specified range: T ¼ 200e300 C, p ¼ 1e100 bar, reactants ratio R ¼ H2:CO2 ¼ 3e12, and catalyst loadings within the range GHSV ¼ 0.1e105 m3/kgcath. Figs. 3.11 and 3.12 show the main results of the sensitivity analysis, in terms of methanol and CO yield as a function of temperature, pressure, and catalyst loading, at different reactants ratios (Kiss et al., 2016). Because of the kinetic limitations at lower temperatures versus equilibrium limitations at higher temperatures, an optimal operating region exists and this depends on the reactants ratio. The effect of pressure on the MeOH and CO yields is straightforward. The formation of methanol is clearly favored at higher pressures because of the fact that CO2 and CO hydrogenation reactions proceed with a decrease of the total number of moles. Consequently, as more CO is converted to methanol at higher pressures, the CO yield decreases when the pressure is increased.

129

60

P=50 bar

M eOH, P=40b M eOH, P=50b M eOH, P=60b M eOH, P=100b

40

Yield / [%]

Yield / [%]

40

50

CO, R=3 CO, R=6 CO, R=9 CO, R=12

MeOH, R=3 MeOH, R=6 MeOH, R=9 MeOH, R=12

50

30 20

R=3

30 20 10

10 0 200

220

240

260

280

0 200

300

220

240

Temperature / [C]

60

CO, R=3 CO, R=6 CO, R=9 CO, R=12

280

300

30

T=250°C

Yield / [%]

MeOH, R=3 MeOH, R=6 MeOH, R=9 MeOH, R=12

70

260

Temperature / [C]

80

Yield / [%]

CO, P=40b CO, P=50b CO, P=60b CO, P=100b

50 40 30 20

MeOH, R=3:1:0 MeOH, R=3:1:0.1 MeOH, R=3:1:0.25 MeOH, R=3:1:0.5

20

CO, R=3:1:0 CO, R=3:1:0.1 CO, R=3:1:0.25 CO, R=3:1:0.5

P=50 bar 10

10 0 0

20

40

60

80

0 200

100

220

240

Pressure / [bar]

260

280

300

Temperature / [C]

Figure 3.11 Effect of temperature and pressure on the MeOH and CO yield at various reactants ratio (GHSV ¼ 5.9 m3/kgcath). 60 P=50 bar T=200°C

Yield / [%]

50

MeOH, MeOH, MeOH, MeOH,

40

R=3 R=6 R=9 R=12

CO, CO, CO, CO,

R=3 R=6 R=9 R=12

30 20 10 0 0.1

1

10

100

1000

10000 100000

3

GHSV / [m /kgcath] 60

Yield / [%]

50

P=50 bar T=250°C

MeOH, MeOH, MeOH, MeOH,

40

R=3 R=6 R=9 R=12

CO, CO, CO, CO,

R=3 R=6 R=9 R=12

30 20 10 0 0.1

1

10

100

1000

10000 100000

3

GHSV / [m /kgcath]

Figure 3.12 Effect of the catalyst loading on the MeOH and CO yield at various reactants ratios and fixed pressure and temperature (P ¼ 50 bar, T ¼ 200 C, and T ¼ 250 C).

Chapter 3 METHANOL

25 MeOH, T=250°C MeOH, T=200°C MeOH, T=300°C

Yield / [%]

20

CO, T=250°C CO, T=200°C CO, T=300°C

15 10 5 0 R=3:1:0

R=3:1:0.1

R=3:1:0.25

R=3:1:0.5

Methanol yield / [%]

20 15 10 5

30 0

28 0

Temperature / [C]

26 0

24 0

22 0

20 0

0

Water

Figure 3.13 Effect of the water content (R ¼ H2:CO2:H2O) on the yield at various temperatures (GHSV ¼ 5.9 m3/kgcath).

Fig. 3.12 shows that at 200 C, the reaction is kinetically limited, as an increase in catalyst loading leads to an increase in methanol yield (Kiss et al., 2016). Therefore, it makes sense to increase the catalytic activity (or the amount of catalyst) at lower temperatures to improve the yield. However, at higher temperatures (>250 C), the reaction is equilibrium-limited when a sufficient amount of catalyst is used (GHSV