Status and Future Challenges for Non-conventional Energy Sources, Volume 1 9789811645044, 9789811645051

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Clean Energy Production Technologies Series Editors: Neha Srivastava · P. K. Mishra

Sanket J. Joshi Ramkrishna Sen Atul Sharma P. Abdul Salam Editors

Status and Future Challenges for Nonconventional Energy Sources Volume 1

Clean Energy Production Technologies Series Editors Neha Srivastava, Department of Chemical Engineering and Technology, IIT (BHU) Varanasi, Varanasi, Uttar Pradesh, India P. K. Mishra, Department of Chemical Engineering and Technology, IIT (BHU) Varanasi, Varanasi, Uttar Pradesh, India

The consumption of fossil fuels has been continuously increasing around the globe and simultaneously becoming the primary cause of global warming as well as environmental pollution. Due to limited life span of fossil fuels and limited alternate energy options, energy crises is important concern faced by the world. Amidst these complex environmental and economic scenarios, renewable energy alternates such as biodiesel, hydrogen, wind, solar and bioenergy sources, which can produce energy with zero carbon residue are emerging as excellent clean energy source. For maximizing the efficiency and productivity of clean fuels via green & renewable methods, it’s crucial to understand the configuration, sustainability and technoeconomic feasibility of these promising energy alternates. The book series presents a comprehensive coverage combining the domains of exploring clean sources of energy and ensuring its production in an economical as well as ecologically feasible fashion. Series involves renowned experts and academicians as volume-editors and authors, from all the regions of the world. Series brings forth latest research, approaches and perspectives on clean energy production from both developed and developing parts of world under one umbrella. It is curated and developed by authoritative institutions and experts to serves global readership on this theme.

More information about this series at http://www.springer.com/series/16486

Sanket J. Joshi • Ramkrishna Sen • Atul Sharma • P. Abdul Salam Editors

Status and Future Challenges for Non-conventional Energy Sources Volume 1

Editors Sanket J. Joshi Oil & Gas Research Center Sultan Qaboos University Muscat, Oman

Ramkrishna Sen Department of Biotechnology Indian Institute of Technology Kharagpur Kharagpur, West Bengal, India

Atul Sharma Department of Sciences and Humanities Rajiv Gandhi Institute of Petroleum Technology Amethi, Uttar Pradesh, India

P. Abdul Salam Department of Energy, Environment, and Climate Change Asian Institute of Technology Pathumthani, Thailand

ISSN 2662-6861 ISSN 2662-687X (electronic) Clean Energy Production Technologies ISBN 978-981-16-4504-4 ISBN 978-981-16-4505-1 (eBook) https://doi.org/10.1007/978-981-16-4505-1 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Preface

The possibility of a partial or complete replacement of ‘non-renewable’ fossil-based energy sources by renewable resources is an ongoing debate, be it in the developed or developing countries. Some of the main driving forces have been the everincreasing demand (for liquid fuels), difficulties in finding new ‘easy-to-recover’ reserves, alarming situations on greenhouse gas (GHG) emissions, and the matter of ‘energy security’ for all. When we think about the future of sustainable energy resources, shifting our focus away from the use of non-renewables (such as fossil fuels), we comprehend that even though it will be a long process, but definitely achievable, if we have cheap and abundant non-conventional energy sources to fill the gap. Currently, the non-conventional energy sources and renewable energy industry is facing ‘cost v/s applicability challenges’ in reaching masses, and also (poses a doubt) to prove as a sustainable business model, as compared to traditional fossil fuel-based industry. However, costs of such non-conventional low-carbon technologies are rapidly reducing, boosting the global renewable energy capacity, which is quite encouraging. One such example would be solar energy, which showed tremendous growth in recent years—both in terms of efficiency and cost. Even though, such non-conventional energy sources are becoming more affordable, it always faces the criticism that: it can’t meet the demand of providing power to our homes, communities, and industries. This is where fossil fuels may still have an advantage, for many more years to come! This book Status and Future Challenges for Non-Conventional Energy Sources: Volume 1 highlights recent advancements in such an important topic, through contribution from experts demonstrating different applications in ‘day-to-day’ life, both existing and newly emerging non-biological technologies, and thoughtprovoking approaches from different parts of the world, potential future prospects associated with some frontier development in non-conventional energy sources. Initial chapters cover different types of natural energy sources such as Ocean, Tidal, and Wave energy: Science and Challenges; Nuclear energy: Clean fuel; Solar cells: Applications and challenges; Geothermal energy: Exploration, Exploitation, and Production; and Hydrogen Fuel: Clean Energy Production Technologies. v

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Energy storage and applications are covered in chapters on: Photovoltaic modules: Battery storage and grid technology; Application of high temperature thermal energy storage materials for power plants; and Combined Heating and Cooling with Phase Change Material: A Novel Approach. Gas hydrates could be game-changer in coming years and is covered in: Natural Gas Hydrates—Energy Locked in Cages; and Gas Hydrates in Man-made Environments: Applications, Economics, Challenges, and Future Directions. Hydrates-based applications are covered in: Hydrate-based Desalination Technology: A Sustainable Approach; and Subsurface Decarbonisation options as CO2 hydrates with Clean Methane Energy Recovery from Natural Gas Hydrate Reservoirs. Energy recovery as a fuel and chemicals based on hydrothermal liquefaction and catalysis are covered in: Hydrothermal Liquefaction (HTL) of Kraft Lignin (KL) Recovered from Lignocellulosic Biomass: State of the Art; and Catalytic Hydropyrolysis and Hydrodeoxygenation of Biomass and Model Compounds for Fuels and Chemicals. We believe that this book will be able to address potential energy applications and challenges in this particular area. We also hope the chapters of this book will be novel to readers and can be readily adopted as references for newer and further research. Moreover, since this book contains information related to different applications, we assume that international readers, especially students and researchers, will also find this book valuable for reference purposes. Last but not least, the editors are thankful to all the researchers, expert academicians, and leading scientists whose contributions as authors and reviewers have enriched this book. We also express our deep sense of gratitude to our family members, whose kind understanding and unconditional support during the course of such scholarly academic activities. While we strived to make sure that this book is free from any misleading or erroneous information, any such mistakes are completely unintentional, and pardon us. We are also thankful to Springer Nature for giving us this opportunity, and especially the editorial support team members, Ms. Aakanksha Tyagi and Ms. Veena Perumal, for their relentless support throughout the publishing process. We would also like to sincerely thank our Universities, for extending the facilities and encouragement for such activities. We thank them from the core of our heart. Muscat, Oman Kharagpur, West Bengal, India Amethi, Uttar Pradesh, India Pathumthani, Thailand

Sanket J. Joshi Ramkrishna Sen Atul Sharma P. Abdul Salam

Contents

1

Ocean, Tidal and Wave Energy: Science and Challenges . . . . . . . . Srinithya Ravinuthala, Sourav Kumar Das, R. Nithya, and Saprativ P. Das

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2

Nuclear Energy and Conventional Clean Fuel . . . . . . . . . . . . . . . . . Akhilesh Yadav, Ajeet Singh, and A. Shukla

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Solar Cells: Application and Challenges . . . . . . . . . . . . . . . . . . . . . Abhishek Anand, Amritanshu Shukla, and Atul Sharma

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Photovoltaic Modules: Battery Storage and Grid Technology . . . . . A. Anand, K. Kant, A. Shukla, A. Sharma, and P. H. Biwole

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Geothermal energy: Exploration, Exploitation, and Production . . . Abhishek Yadav, Gunjan Kumar Agrahari, and Sudha Agrahari

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Application of High-Temperature Thermal Energy Storage Materials for Power Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Abhishek Anand, Navendu Mishra, Amritanshu Shukla, and Atul Sharma

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Hydrogen Fuel: Clean Energy Production Technologies . . . . . . . . . 133 Pranjal Gogoi, Bijoy Tudu, and Pranjal Saikia

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Natural Gas Hydrates: Energy Locked in Cages . . . . . . . . . . . . . . . 155 Chandan Sahu, Anirbid Sircar, Rajnish Kumar, and Jitendra S. Sangwai

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Gas Hydrates in Man-Made Environments: Applications, Economics, Challenges and Future Directions . . . . . . . . . . . . . . . . . 173 Asheesh Kumar, Hari Prakash Veluswamy, Prashant Jadhawar, Antonin Chapoy, and Zachary Aman

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Hydrate-Based Desalination Technology: A Sustainable Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 Hari Prakash Veluswamy, Asheesh Kumar, Rajnish Kumar, and Prashant Jadhawar

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Subsurface Decarbonization Options as CO2 Hydrates with Clean Methane Energy Recovery from Natural Gas Hydrate Reservoirs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 Prashant Jadhawar

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Combined Heating and Cooling System with Phase Change Material: A Novel Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235 A. Sreekumar and D. Sruthi

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Hydrothermal Liquefaction (HTL) of Kraft Lignin (KL) Recovered from Lignocellulosic Biomass: State of the Art . . . . . . . . . . . . . . . . 267 Marttin Paulraj Gundupalli, Anne Sahithi Somavarapu Thomas, Sathish Paulraj Gundupalli, Debraj Bhattacharyya, and Malinee Sriariyanun

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Catalytic Hydropyrolysis and Hydrodeoxygenation of Biomass and Model Compounds for Fuels and Chemicals . . . . . . . . . . . . . . . 293 Kavimonica Venkatesan and Ravikrishnan Vinu

About the Editors

Sanket J. Joshi is a deputy director, Oil & Gas Research Center, and an application specialist, Oil & Gas Science, at Sultan Qaboos University, Oman. He holds BSc and MSc from Sardar Patel University, India, and a PhD from M. S. University of Baroda, India—all in microbiology. Dr. Joshi has 16 years of academic teaching and research experience and 4 years of industrial R&D experience in India and Oman. His current research interests encompass energy, microbial products, and environmental bioremediation. He serves as an academic editor/associate editor/ guest editor for some of the highly reputed journals and as book series editor for Elsevier INC. Ramkrishna Sen is a professor and the head, Department of Biotechnology, IIT Kharagpur. He is also the chairperson of the School of Bioscience and Central Research Facility. He administered as chairman (GATE-&-JAM), IIT Kharagpur. Prof. Sen worked as manager (R&D-Biotech), Cadila Pharma Ltd. He served as Fulbright Visiting Faculty in Columbia University, New York. His research areas include healthcare, energy, environment, and water. So far, 24 PhD scholars completed their degrees under his supervision. He has about 230 international and national publications and 15 patent applications to his credit. Prof. Sen recently featured in the list of top 2% Indian scientists in the world. Atul Sharma is currently associate professor at Rajiv Gandhi Institute of Petroleum Technology, India. He has worked as a scientific officer in Devi Ahilya University, India; as a research assistant at KIER, South Korea; and as a visiting professor in Kun Shan University, Taiwan, R.O.C. Dr. Sharma completed his M. Phil. and Ph.D. from School of Energy and Environmental Studies, Devi Ahilya University, India. Dr. Sharma published several edited books from the various well-known international publishers; research papers in various international journals and conferences. He is working on the development and applications of PCMs, green buildings, solar water heating systems, solar air heating systems, and solar drying systems.

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About the Editors

P. Abdul Salam is currently serving as professor and chair of Sustainable Energy Transition Program, Department of Energy, Environment and Climate Change, Asian Institute of Technology, Thailand. Prof. Salam has over 25 years of international experience in research, consultancy and capacity building in the areas of bioenergy, waste to energy, renewable energy, energy efficiency, energy storage, smart energy buildings, climate change mitigation, and water-energy-food nexus. He has obtained his bachelor’s degree in mechanical engineering from University of Peradeniya, Sri Lanka; ME and PhD in renewable energy and energy technology, respectively, from AIT. Prof. Salam is a member of American Society of Mechanical Engineers, American Society of Heating, Refrigeration and Air-conditioning Engineers, International Solid Waste Association, and World Bioenergy Association.

Chapter 1

Ocean, Tidal and Wave Energy: Science and Challenges Srinithya Ravinuthala, Sourav Kumar Das, R. Nithya, and Saprativ P. Das

Abstract Worldwide viable energy requisite keeps on developing with tidal energy giving a noteworthy wellspring of sustainable energy. The ability to produce power from tidal waves is gigantic. Tidal energy is an illimitable source that has an extra incentive in the future as to other sustainable power sources owing to its greater uniformity. Like other renewable power sources, tidal energy has its difficulties at various levels. More sacrifices are to be seen in local communities dealing with tidal energy and when the project is too big. Despite the undertaking benefits that could be decreasing carbon dioxide release and green innovation, likewise has more ecological effects that can forestall the execution of tidal energy. The major challenges are its effect on marine animals, cost, availability and efficiency. The market for tidal energy is smaller and more local, in places where the grid is weak or non-existent. The World Energy Council and Bloomberg New Energy Finance (BNEF) assessed that power created from sea developments costs eightfold to ninefold the amount of the most noteworthy normal cost for wind energy. The market for flowing vitality appears to be restricted, and it relied upon to remain that route soon. The United

S. Ravinuthala Department of Studies in Biotechnology, University of Mysore, Manasagangothri, Mysuru, Karnataka, India e-mail: [email protected] S. K. Das School of Bio Sciences and Technology, Vellore Institute of Technology, Vellore, Tamil Nadu, India e-mail: [email protected] R. Nithya PG & Research Department of Zoology, Justice Basheer Ahmed Sayeed College for Women, Chennai, Tamil Nadu, India e-mail: [email protected] S. P. Das (*) Department of Chemical Engineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 S. J. Joshi et al. (eds.), Status and Future Challenges for Non-conventional Energy Sources Volume 1, Clean Energy Production Technologies, https://doi.org/10.1007/978-981-16-4505-1_1

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States’ Department of Energy (US-DOE) expenditure of $20 million in financing for wave and tidal energy extends this year. Tidal energy is advantageous for locales that are close to drift and have the situations to make this novel type of energy less expensive. The chapter covers an overview of all the challenges faced by this ideal energy and resolve them to have a clean and renewable form of energy. Keywords Tidal energy · BNEF · Waves · Renewable energy

1.1

Introduction

The expanding populace, rising energy utilization, environmental challenges and high oil consumption are quickening the inquiry for alternative, environmentalfriendly energy sources to petroleum products. Some sustainable wellsprings of energy, like wind and sunlight based, are notable, utilize solid innovation and have also set up business sectors. Other inexhaustible advances that are still being developed prove a guarantee in meeting a segment of future power needs. Numerous legislatures are empowering this hunt by organizing obligatory objectives for diversification of their vitality assets by specific cut-off times and vowing to devote a bigger extent of their vitality utilization to renewables. The general movement of the earth, sun along with the moon in collaboration with the gravitational powers, creates tidal energy. The energy and intensity differences in the tides in an area are the after-effect of the changing places of the moon and sun respective to the earth, the impacts of earth revolution and the nearby state of the ocean bottom and coastlines. Tidal energy can be considered an unlimited, sustainable power source as earth’s tides are brought about by the flowing powers due to gravitational attraction between the moon, sun and earth’s rotational movements. A tidal energy generator utilizes these movements to exploit the energy from the seas. The more alongshore the tide is, either in terms of water-level stature or flowing momentum speeds, the more noteworthy the potential for power generation. However, such energy extraction also causes a constant loss of mechanical energy in the earth–moon framework due to the syphoning of water above normal limitations around coastlines causing disturbances in the seabed. Such mechanical energy loss has made the revolution of the earth slow down; over the past 620 million years, the time of earth rotation around itself has increased from 21.9 to 24 h—between these periods, the earth has lost 17% of its rotational energy. While ocean energy extractions may take extra energy from the framework, further increasing the pace of mechanical energy loss, the impact would be recognizable only over a very broad span of time, subsequently being immaterial (Wang and Wang 2019). Nevertheless, escalating population and dependence on innovation in developed nations might cause energy requirements to rise quicker than the populace, in spite of the work being done, and resources being invested towards rising productivity of energy generation. In the USA, for instance, per capita vitality use dropped all through the 1970s and mid-1980s because of enhancement ineffectiveness, yet has

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expanded from that point forward, and is anticipated to increment in the next 20 years, with more popularity for vitality improve proficiency, while restricting the creation of ozone harming substances, sustainable power sources must be created (Bowman and Gorlov 2019). Energy asset use is one of the utmost significant and quarrelsome issues during these days. Investments in energy proficiency and expanded preservation might be the best approach to handle vitality use. But it appears to be far-fetched that objectives for decreasing carbon discharges can be met through request side administration alone. As numerous as 2 billion individuals overall need power today, and as fast populace development in creating nations proceeds, interest for power will in all likelihood rise (Lund 2007). Sustainable power source research has generally focused around the improvement of solar, wind, geothermal and biomass sources. While these sources are altogether encouraging, the most effective and sustainable energy strategy will be used to exploit a full set-up of sustainable power resources. With this in mind, we foresee that administrations, partnerships, designers and researchers will gradually look to the gigantic measures of energy abundance in the ocean (Elsafty and Saeid 2009) (Uihlein and Magagna 2016). While sea energy improvement fundamentally presents a few challenges, a major part of the framework and information crucial in energy extraction from the sea as of now exists based on the offshore gas and oil industry. Research recommends that overcoming mechanical hurdles of ocean and based energies should be approached in an ‘out-of-box’ way, rather than conventional methods (Khan et al. 2017).

1.2

Ocean Energy

As of now, most sea energy innovations can be considered to be at a beginning phase of advancement up to exhibit stage. Sea wave and flowing momentum energy are the two types of sea energy, which are generally reliable and cutting edge, which will contribute altogether to the energy in future (Uihlein and Magagna 2016). The sea energy industry has gained critical ground lately; however, it is still at the beginning phase, with some serious models that are being tried presently. Existing difficulties include incorporating further improvement of innovation to demonstrate unwavering quality and vigour, to lessen costs and decrease dangers of using such technologies. This is reflected in the momentum of research subjects supported, for example, by the EU with 68% of the assets being coordinated to innovation improvement (Onundo and Mwema 2016). Ocean energy can be extracted by two ways—mechanical and thermal. While rotation of the earth and gravitational pull account for the former, the latter is produced through vertical thermal gradients of the ocean. In this section, the mechanisms of harnessing thermal energy will be discussed in detail, while mechanical energy extraction will be dealt with in the further sections.

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Ocean Thermal Energy Conversion (OTEC) Systems

The sun’s thermal energy causes a temperature rise of the ocean surface, as the depths have lower temperatures, due to lower amount of thermal energy penetrating through. Ocean thermal energy is extracted exploiting this temperature difference. For yield of usable energy, a minimal temperature difference of 20
C (36
F) is required, in depths from the surface lower than 1000 m. Ocean thermal energy conversion (OTEC) yields power from the common warm slope of the sea; the heat from the warm surface water is utilized to make steam that drives a turbine, to recondense the steam; cold water from lower depths is syphoned to the surface. OTEC plants can either be assembled coastal or on seaward drifting platforms (Branker et al. 2011). There are three typical OTEC types of systems used—closed, open and hybrid.

1.2.1.1

Closed-Cycle OTEC

The closed-cycle OTEC planned by D’Arsonval in 1881 was the first type of OTEC to be proposed. This cycle, which works on the principle of the Rankine cycle, uses propane or ammonia, or other fluids with a low-boiling point as working fluid in a closed flow path (Fig. 1.1a). The working fluid is initially pumped into the evaporator, where warm seawater is pumped, and is thermodynamically denoted as the isentropic expansion stage. The fluid is vaporized, by the principle of gas laws— temperature increase is directly proportional to pressure rise; this vapour rotates the turbine, generating electricity. In the next stage, known as the isobaric heat rejection stage, the vapour is condensed to liquid in the condenser, leading to decrease in entropy. There is a temperature increase in the pump due to higher pressure, causing

Fig. 1.1 Schematic representation of (a) closed-system OTEC; (b) open-system OTEC

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an isentropic compression in the pump. Isobaric heat causes working fluid to vaporize, the heat supplied by the boiler. At the outlet of the turbine, the working fluid has a higher vapour pressure than cold seawater found at the depths. This seawater is syphoned to the surface, allowing heat exchange between the working fluids. The working fluid is again liquidized, allowing a new cycle to repeat. Theoretically, Rankine cycles produce nonzero power, as increasing liquid pressure requires less energy than when the same expands as vapour. For this reason, when producing energy in this system, phase changes are required. Closed systems occupy less space than open systems, but could produce same amounts of energy and can be designed based on existing heat exchanger designs (Etemadi et al. 2011).

1.2.1.2

Open-Cycle OTEC

The initial step in open-cycle systems is the flash evaporation of warm surface water, a characteristic feature involving complex heat-mass transfer. Flash evaporation is done at low pressures less than the respective saturation point in the temperature where a very low percentage (approximately 0.5%) of mass of the warm water is transferred to the total heat energy. The resulting steam generated in turn causes rotation of the turbine, therefore generating electricity, similar to how electricity is generated in hydrothermal plants. Cold water in the deeper levels of the sea is transferred to the upper surface and acts as the thermal sink. The cold water condenses the steam, and the condensed steam is released back into the environment (Etemadi et al. 2011). A schematic representation of the open-cycle OTEC is shown in Fig. 1.1b. An advantage of open-cycle OTECs is that during flash vaporization, pure vapour is generated with desalinated water as an ultimate by-product. This water can be utilized for domestic use, as portable water sources or in agrarian uses. The cold seawater vacuumed by OTEC pipes to the surface is supplement-rich and parasitefree. It can be syphoned into coastal lakes, for algal, fish or other commercial marine species culture in a controlled framework (International Renewable Energy Agency (IRENA) 2014; Bahaj 2011).

1.2.1.3

Hybrid OTEC Plants

Hybrid plants, encompassing the advantages of the two frameworks—both closed and open, utilize the closed-cycle design, coupled with a second-stage flash evaporator for water desalination achieving an elevated efficiency (International Renewable Energy Agency (IRENA) 2014). It uses seawater as well as working fluid, most commonly ammonia. As in a closed-cycle, seawater is initially flash-evaporated into steam in a vacuum vessel. Ammonia is also evaporated by heat (thermal energy) exchange with warm water in the same vessel. Then, ammonia is mixed physically with warm seawater as a two-substance and two-phase mixture. The ammonia evaporated is separated from the vapour/water phase, recondensed and introduced

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again into the closed-loop cycle. The water/working fluid vapour turns the turbine to produce electricity, due to the phase change. An advantage of this system is that it does not require heat exchangers.

1.2.2

Ocean Energy Potential

It is assessed that altogether, ~10 TW (10 trillion W or 10 billion kW) of intensity, roughly equivalent to the existing worldwide vitality request (Pelc and Fujita 2002), could be given by OTEC without influencing the warm structure of the sea (Khan et al. 2017). However, with the ebb, flow and OTEC cost of power in the range of around 8 and 24 pennies/kWh (Soerensen and Weinstein 2008), fundamentally higher than petroleum derivative costs, it is impossible that asset will be completely evolved except if it is subsidized. The most prominent OTEC potential is likely for use on the little island creating states (SIDS), which require home-grown power and freshwater. Complete utilization of auxiliary advantages (freshwater, hydroponics, cooling and so on) is essential for financial feasibility. OTEC might not be able to make remarkable influences to overall energy needs, yet could give the critical capacity to a few SIDS. OTEC is feasible only in the tropical oceans, in territories where the warm inclination amidst the surface and profundity of 1000 m is at any rate 221C. The open sea regions with this temperature distinction and reasonable for skimming OTEC plants are all-out around 60 million km in the region. For a shorebased plant, an extra prerequisite is a geography that permits admittance to extremely deep depth water (1 km or more depth). Such conditions only exist at certain tropical islands, coral atolls and a restricted number of mainland sites. In the USA, potential locations are around Hawaii, Puerto Rico and the mainland rack of the Gulf of Mexico.

1.3

Tidal Energy

Tides are the intermittent movement of the waters of the ocean due to the between alluring powers between the divine bodies. They are significant stretch waves that travel through the seas as a result of the attractional forces of the moon and sun. The moon is the fundamental tide-producing body. Because of its greater distance from the earth, the sun’s impact is just 46% of the moon’s, though the sun is almost 400 times the size of the moon. (Bowman and Gorlov 2019). Tide, ebb and flow are inter-related but not equivalents. Both ebb and flow define movements of tides. In general terms, a tide that moves away from the coast is known as ebb. Similarly, tide movement towards the coast is known as flood. Tidal energy is boundless and can be considered as a sustainable power source. While many of the conventional different sources of energy are causatives of negative changes in the atmosphere, utilizing tidal energy as power sources does

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not lead to such consequences in the atmosphere (Myhr et al. 2014). The majority of the current innovation utilized for vitality conversion is from the wind power industry. Scientists have predicted that the UK can deliver over 20% of its electrical needs from its flowing assets. It is likewise a reality that the examinations did so far in predicting the vitality that can be removed from tides have just centred around the over significant period accessibility of the vitality. In any case, it is likewise crucial to indicate the impacts of abusing the sustainable power hotspots for vitality extraction. There needs to be a comprehension among the designers concerning when and where to stop the vitality extraction so that there is least or no unsettling influence caused to the ordinary regular marvel (Liu et al. 2011). Flowing stream generators draw vitality from ebbs and flows, which have a similar working as wind turbines. The higher density of water, multiple times more the density of air, implies that a single generator can generate higher power densities, even at low flowing stream speeds, as contrasted to need of higher wind speeds for the same. In other words, water tidal forces of almost one-tenth of the speed of wind give a similar capacity to a similar size of the turbine framework (Garrett and Cummins 2004).

1.3.1

Tidal Energy Extraction

Various techniques have been proposed by creators for the extraction of flowing vitality. In any case, the fundamental standard behind the techniques stays the same; there are two essential strategies to extract tidal energy (Bryden and Couch 2006; Bryden and Couch 2007). (a) Estuaries into which large amounts of seawater streams causing high flowing extent, caught behind floods, and turbines are pivoted by using the potential vitality of the put-away water. (b) Active vitality of moving water utilized to separate vitality as done in the rule of extraction of wind energy. The two techniques that are referenced above have been proposed and followed, each having their own advantages and drawbacks. It might likewise be sensible to utilize syphoning techniques for floods to acquire better proficiency and to coordinate power requests better. The gadgets that are utilized in the tidal energy generation are different in many parameters such as size, shape and determinations. Depending on the mechanisms, these devices have been classified into three types as follows: 1. Flowing floods that store flowing stream and produce power through release. 2. Flowing wall that blocks a section and concentrates vitality in either of the two bearings of flowing stream. 3. Flowing current gadgets that are fixed or secured inside a flowing stream.

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Turbines

Most flowing turbine makers utilize a traditional air gap generator. These types of generators are used commonly in hydropower stations and wind turbines. Inside an air gap generator, the stator–rotor hole inside the generator is filled with air. In tidal turbines, the air gap generator must be encased in a water-tight nacelle. The internal nacelle space is disconnected by seawater utilizing a high-pressure turning seal on the pivoting shaft of the turbine. Fixing the nacelle secures against the consumption and electrical breakdown of basic parts, like the generator curls and magnets (Wani et al. 2020). Turbine configuration is a significant component as it decides a significant number of the activity limitations including stream rate, head change and range, start–stop recurrence and whether two-way (reversible) usage is conceivable (Blunden and Bahaj 2006).

1.3.2.1

Bulb Turbine

Bulb turbines are the most frequently utilized turbine plan for flowing stations in the light of their high proficiency (most extreme effectiveness surpassing 90%) for low head, their moderately little volume and cost-effectiveness, and being reversible, generating energy during both the flood and ebb tides. The name originated from the bulb-formed upstream packaging, which contains the generator. The bulb turbine along with the generator is put together in the centre of the waterway along with the flat hub. A conspicuous issue with tidal station bulb turbines is the requirement of turbine support to be lifted off the water (Fig. 1.2). An example of the La Rance Tidal Station unit is considered—to accomplish higher productivity in flood stage generation, a changed variant of bulb turbine presenting a second arrangement of guide vanes was proposed. A hypothetical test found an improvement of flood stage effectiveness from 69.64% to 80.12%; a moderately low drop was observed in the forward bearing from 84.03% to 80.12% while including the additional guide vanes. The modified turbine was additionally tried at Wanapum Dam where a higher sheer was shown, as a result, destructive to fish, which possibly presents a more prominent environmental hazard. Luo et al. have additionally presented an enhancement system for low-head bidirectional Fig. 1.2 Schematic representation of bulb turbine

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turbine bulb turbine sprinter to alter the bulb turbine plan under given working conditions. The enhancement strategies acquainted are said with improving the displayed turbine proficiency by 5.5% (ebb), 2.9% (flood) for a four-bladed turbine and 4.3% and 4.5%, respectively, for a three-bladed turbine. In expansion, a mathematical technique to anticipate precisely the model pressure-driven execution was suggested with the upstream store displaying for low-head bulb turbine activity (Myers and Bahaj 2009).

1.3.2.2

Edge Turbine

The edge turbine consists of the engine rotor joined to an external ring of the turbine sprinter. The engine stator inside the rim turbine is further joined with the generator rotor; external ring of the turbine sprinter and the generator stator are attached inside the foundation. The advantages include the better performance of the turbine under continuous changing top of the flow station, cost-effectiveness, simple to install along with low maintenance. Hypothetically, it has more noteworthy idleness (in this manner better solidness). However, a drawback is that it can only work on the ebb tide. The biggest edge turbine unit among tidal stations till date is in the Annapolis flowing station in Canada. This turbine has an estimated output of 17.8 MW with a measurement of 8.2 m, effectiveness of 89.1% and activity productivity 87.3%. The generator consists of 144 posts connected to the external surface of the sprinter and the stator of measurement 13 m lowered in the solid. An air cooler is also attached for cooling. The unit is generally made of carbon steel and incompletely tempered steel, utilizing cathodic deposits to maintain a strategic distance from erosion. It is additionally detailed that the edge turbine in Annapolis is fatal to hundreds of thousands of fish, and studies are now being conducted upon the framework of the station with respect to the fish decline (Rice and Baker 1992).

1.3.3

Energy Calculation

Different generator designs have varying levels of efficiencies; these variances cause the varying power outputs (Morris et al. 2016). The power output of these kinetic systems can be expressed as follows: P ¼ Cp  0.5  ρ  A  V3. where Cp ¼ the coefficient of performance. P ¼ the power generated (in watts). ρ ¼ the density of the water (seawater is 1025 kg/m3). A ¼ the swept area (in m2). V3 ¼ the velocity of the flow cubed (i.e. V * V * V).

10

1.3.4

S. Ravinuthala et al.

Tidal Power Utilization

Tidal stations are typically introduced close to coastlines where the flowing reach is adequate and economically sustainable; the energy produced is relative to the tidal energy squared. In Europe, the potential tidal energy asset is assessed to surpass 12 GW of introduced limit. Ideal areas with large amounts of energy harvesting potential are found around the British Islands coasts and Ireland, France and the Channel Islands, around Aegean and the Straits of Messina in Italy and Sicily. An additional 90 GW is estimated extractable along the north–west shore of Russia and 20 GW at the channel of Mezen Stream in the White Sea. In Asia, China holds a hypothetical capability of 13.9 GW randomly circulated flowing force about 7 GW round the Estuary of Yangtze River in Zhejiang and Jiangsu Province; the West Coast of India is assessed to conceivably create 8 GW of flowing force. Some other different areas with high flowing levels around the globe comprise the west shore of Malaysia and the Philippines, the west bank of Australia, and the east and west shorelines of Canada. Even though the worldwide hold of flowing force is colossal, as of now, only a meagre amount has been exploited for power generation (Wang and Wang 2019).

1.4

Wave Energy

Waves are created when the winds produced by differential heating of the surface of the earth through thermal energy blow over the surface of the sea. The amplitude of energy in the waves depends upon the wind characteristics like wind speed, duration and distance covered (fetch) (Koca et al. 2013). Wave energy has been discussed, trialled and developing over centuries, dating way back to 1799. However, only in the 1970s during the oil setback after Stephen Salter published a noteworthy article on wave energy, they have gained interest as power source (Salter 1974). Devices that convert energy in waves into electricity are defined as wave energy converters (WECs), and the amount of energy produced from the kinetic movement of waves is considered in kilowatts per metre of wave front (kW/m). WECs can be divided into different classes according to various parameters. They can be divided into three primary classes depending on their location (Fig. 1.3)—onshore (with water depths of up to 800
C) and short residence time in the presence of oxidizing environment to produce high yield of syngas (85%). The predominant gases produced include CO, CO2, H2 and CH4 (Dickerson and Soria 2013). Liquid fraction called ‘bio-oil’ can be increased by processing the biomass at moderate temperatures (400–600
C) at short vapour residence time (< 2 s) and at a high heating rate (Perkins et al. 2018). These reaction conditions in fast pyrolysis (FP) influence the

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C

C

C

C

C

Fig. 14.4 Different modes of pyrolysis and the typical product yields. Data taken from Bridgwater (2003, 2012), Perkins et al. (2018) and Panwar et al. (2012)

release of volatiles from biomass and also prevent the secondary cracking of evolved vapours. High yield of bio-oil (~75 wt.%) is achieved as a result (Bridgwater 2003). Carbonization or slow pyrolysis takes place around 450
C with a residence time of the order of minutes at low heating rates. It results in ~35% yield of char, ~35% gases and ~ 30% liquid. Intermediate pyrolysis is carried out at 500
C, with a residence time of 10–30 s producing 50% yield of liquid fraction. Among all the aforementioned variants of pyrolysis, fast pyrolysis is a potential route for the high production of liquid product, bio-oil.

14.1.2.2

Influence of Feedstock Factors

There are several factors related to the feedstock that affects the thermochemical conversion processes like pyrolysis. Firstly, the proportion of cellulose, hemicellulose and lignin in biomass is a key parameter that determines the composition of the products. Typically, the composition of cellulose, hemicellulose and lignin in lignocellulosic biomass varies in the range of 40–50 wt.%, 15–20 wt.% and 25–35 wt.%, respectively (Saidi et al. 2014). However, this proportion is strongly dependent on the type of biomass (Wang et al. 2017). From Table 14.1 (Wang et al. 2017; Huber et al. 2006; Demirbaş 2005; Nolte and Shanks 2017; Zheng et al. 2014; Di Blasi et al. 2010; Qu et al. 2011; Brosse et al. 2012), it can be observed that

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Table 14.1 Biochemical composition of various biomass types Feedstocks Rice husk Corn Stover Switchgrass Sugarcane Eucalyptus Sweet sorghum Spruce wood Oak

Cellulose 37.0 36 40-45 22 48 35

Hemicellulose 23.43 23 31-35 15 18 18

Lignin 24.77 17 6-12 11 29 17

Extractives 3.19 6 0 43 2 23

Ash 17.27 10 5-6 9 1 5

References Wang et al. (2017) Huber et al. (2006) Huber et al. (2006) Huber et al. (2006) Huber et al. (2006) Huber et al. (2006)

43

29.4

27.6

1.7

0.6

Demirbaş (2005)

40.7

22.8

33.3

–

0.4

Corn cob Pine Straw Poplar Beech Fir Rice straw Miscanthus

36.26 46.36 37.00 49 45 45 37 50.34

33.31 21.38 26.84 24 33 21 16.5 24.83

13.51 27.29 15.23 20 20 30 13.6 12.02

8.10 2.67 6.89 5.9 2 2.6 13.1 2.67

3.04 0.60 13.01 1 0.2 0.5 19.8 –

Nolte and Shanks (2017) Zheng et al. (2014) Zheng et al. (2014) Zheng et al. (2014) Di Blasi et al. (2010) Di Blasi et al. (2010) Di Blasi et al. (2010) Qu et al. (2011) Brosse et al. (2012)

woody biomass contains the major components in high proportions, while agricultural and herbaceous wastes contain significant fraction of extractives and ash. Notably, woody feedstocks are rich in cellulose content (Rabemanolontsoa and Saka 2013). The other factors that play a vital role in thermochemical conversion process include moisture, ash and biomass particle size (Perkins et al. 2018). Moisture content in biomass influences the behaviour of pyrolysis and also the physicochemical properties of pyrolysis oil. Further, the major drawbacks of biomass feedstock with high moisture content include high energy requirement to heat the feedstock to the pyrolysis temperature at a low heating rate. Hence, efficient processing of the feedstock using pyrolysis technique requires low moisture content (< 10 wt. %) in the biomass. Lignocellulosic biomass with high lignin content (i.e. woody biomass) is mostly preferred for the production of aromatic hydrocarbons in different processes (Yildiz et al. 2016). Additionally, biomass with low ash content could be considered because accumulation of ash usually leads to catalyst/enzyme poisoning. Yildiz et al. (2015) observed significant impact of biomass ash on the product yields, especially the liquid yield, in catalytic fast pyrolysis (CFP) of pinewood. Moreover, a change in the activity of the catalyst was observed due to the blocking of active sites or pores inside the catalyst. Besides, the inorganic ash plays a key role in secondary pyrolysis reactions by influencing the reactivity of pyrolysis char. Consequently, it tends to decrease the liquid yield by increasing the formation of char and gas. This could be attributed to the acceleration of dehydration and charring reactions during primary and secondary pyrolysis in the presence of inorganic

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materials. Feedstock size is one of the important factors that determine the yield and quality of products. Heat transfer is uniform in smaller particles, whereas larger particles suffer from poor heat transfer leading to low average particle temperature, which subsequently results in low liquid yield. Hence, there is a limitation to the particle size of the biomass being fed to the reactor. Accordingly, finely ground biomass with improved surface area is required for effective heating and better mass transfer rates (Demirbaş 2005). All these influential factors necessitate the implementation of biomass pre-treatment steps such as drying and grinding prior to processing. In case of high ash containing feedstocks, an additional leaching step (using acidic solution) may be considered before drying (Nolte and Shanks 2017).

14.1.3 Typical Composition of Bio-Oil Bio-oil is a complex mixture of organic compounds including carboxylic acids, alcohols, aldehydes, esters, ketones, furan derivatives and phenols. The composition of chemical functionalities in bio-oil correlates strongly with the amount of cellulose, hemicellulose and lignin in biomass. Consequently, the proportion of these major components depends on the type of biomass feedstock as mentioned in the earlier section. A prior understanding of the feedstock characteristics and its pyrolysis behaviour is necessary to interpret the composition of bio-oil. There are significant differences in the decomposition profiles of major components. Cellulose and hemicellulose decompose in the temperature range of 315–400
C and 220–315
C, respectively. The decomposition of lignin is difficult due to its structural complexity and occurs in a wide temperature range of 160–900
C (Liu et al. 2014). In a study by Yang et al. (2007), it was reported that cellulose pyrolysis is endothermic with a peak at ~355
C, while pyrolysis of hemicellulose and lignin are exothermic in the temperature range of 150–500
C with peaks at 275 and 365
C, respectively. However, an opposite behaviour was observed at high temperatures (>500
C). The predominant gases evolved during pyrolysis (CO, CO2, CH4 and H2) can also be correlated with the biochemical composition of biomass. CO2 evolution is due to the cracking and reforming reactions of C¼O and COOH groups present in the hemicellulose fraction. CO yield is reported to be higher from cellulose fraction of biomass due to carbonylation reaction of C-O-C and C¼O groups. Release of H2 and CH4 gases is attributed to the cracking of methoxy groups in the lignin. The thermal stabilities of the three components follow the trend: lignin > cellulose > hemicellulose (Zheng et al. 2014). Owing to this, lignin contributes largely to the char formation compared to cellulose and hemicellulose. These differences in the pyrolysis behaviour of the three components can be ascribed to their inherent chemical structure, which consequently affects the yield of products and selectivity of organic compounds in the bio-oil. Typical pyrolysis products evolved from the biochemical components of lignocellulosic biomass are depicted in Fig. 14.5. Thermal decomposition of cellulose results initially in the formation of anhydrosugars such as levoglucosan,

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Fig. 14.5 Key products from pyrolysis of cellulose, hemicellulose and lignin, and the typical transformations involved

1,4:3,6-dianhydro-β-D-glucopyranose and 1,6-anhydro-β-D-glucofuranose by the cleavage of β-1,4-glycosidic linkages, which subsequently undergoes ring opening and dehydration reactions to produce low molecular weight oxygenates and furan derivatives. Likewise, hemicellulose degrades to form water, methanol, formic acid, acetic acid, propionic acid, hydroxyl-1-propanone, hydroxyl-1-butanone, 2-methyl furan and 2-furfuraldehyde. The pyrolysates from lignin include guaiacol, methyl guaiacol, ethyl guaiacol, propyl guaiacol, vinyl guaiacol, eugenol, homovanillic acid, syringol, phenol, cresol, ethyl phenol, dimethyl phenol, catechol, methyl catechol and dimethoxy toluene. This occurs by depolymerization of lignin into monolignols (viz. coumaryl, coniferyl and sinapyl alcohols) followed by deformylation, alkylation, retro-aldol and hydrodeoxygenation (HDO) reactions to yield various simple phenolic compounds (Ojha et al. 2017; Patwardhan et al. 2011). The formation of char and non-condensable gases as a result of dehydration, decarbonylation and decarboxylation reactions is also an important step in pyrolysis. The reaction pathways of cellulose, hemicellulose and lignin pyrolysis are discussed in several works (Qu et al. 2011; Liu et al. 2014; Ansari et al. 2019; Chen et al. 2019; Kanaujia et al. 2014). Aromatic and coke yields are reported to be higher from biomass species with high content of holocellulose (cellulose and hemicellulose) and lignin, respectively. Zheng et al. (2014) showed that in CFP of straw and pine over

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Table 14.2 Bio-oil composition from various lignocellulosic biomass via pyrolysis Bio-oil composition Phenols Furans Acids, esters Alcohols Aldehydes, ketones, sugars Hydrocarbons PAHs Heavy Unidentified Total yield of organics Reference a

Pinewood (wt.%) 15.42 3.3 2.49 1.75 14.14

Corncoba

Miscanthusa

LIGNOCELa

Sprucea

38.61 – 5.96 4.14 25.42

11.39 4.17 13.3 12.04 10.73

20.97 9.31 5.6 11.45 12.57

18.9 3.9 4.6 4.9 29.9

– – – 10.16 47.9

7.83 – – 18.04 33.9

10.5 1.75 17.73 18.39 22.51

12.43 2.68 13.87 11.12 19.05

0.7 0.4 9.9 27 17.6

Amutio et al. (2012)

Zhang et al. (2009)

Antonakou et al. (2006)

Antonakou et al. (2006)

Adam et al. (2006)

Based on wt.% of organic fraction

ZSM-5 catalyst, high carbon yields of aromatics (28 mol%) and coke (56.4 mol%), respectively, were obtained. The bio-oil obtained from pinewood pyrolysis is reported to contain levoglucosan, hydroxyacetaldehyde, acetic acid, propanoic acid, furfural, 2-cyclopenten-1-one, 1,2-benzenediol, 4-methyl-1,2-benzenediol, 3-methyl-1,2cyclopentanedione, furanone, vinyl guaiacol, guaiacol and cresol (Yildiz et al. 2013; Thangalazhy-Gopakumar et al. 2011a). Similarly, the major compounds observed in bio-oil from spruce wood include furfural, phenol, 2-cresol, guaiacol, 4-methyl guaiacol, 4-ethyl guaiacol, 4-vinyl guaiacol, isoeugenol, propanal, hydroxyacetaldehyde, acetic acid, furanone, benzofuran and 5-hydroxymethyl-furfural (Adam et al. 2005). Acetic acid, methyl pyruvate, furfural, hydroxy cyclopentenone, furanone, methyl pyrimidinone, guaiacol, 1,2-benzenediol, 4-methyl guaiacol, vinyl guaiacol, vanillin and levoglucosan were the major compounds reported from pinecone pyrolysis at 600
C (Jeong et al. 2019). Bio-oil from red oak is majorly composed of formaldehyde, glycolaldehyde, methyl glyoxal, acetal, acetic acid, levoglucosan and cellobiose (Nolte and Shanks 2017). Table 14.2 presents the yield (wt.%) of key functional groups in bio-oil from various biomass feedstocks. A study by Thangalazhy-Gopakumar et al. (2011a) clearly outlined the difference in pyrolysates obtained from grassy crop such as switchgrass and woody biomass such as pinewood. Switchgrass pyrolysis resulted in significant production of syringol compounds, while no syringol derivatives were observed from pinewood pyrolysis. This is mainly due to the existence of sinapyl moieties in the lignin structure of grassy crops. To summarize, bio-oil obtained from various woody biomass and agricultural residues are rich in organo-oxygen compounds that impart various undesirable properties.

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14.1.4 Properties of Bio-Oil Fast pyrolysis bio-oil appears dark brown in colour with a smoky odour and exists in two phases (organic and aqueous). The type of biomass feedstock and mode of pyrolysis determine the appearance of bio-oil. The direct usage of bio-oil is undesirable due to various detrimental properties like high oxygen content, high water content, high viscosity, high acidity (Oasmaa et al. 2010), presence of ash and immiscibility with petroleum-derived fuels (Perkins et al. 2018). These innate properties impart low heating value to bio-oil making it incompatible with conventional fuels. Various properties of bio-oil are compared with conventional fuels in Table 14.3. The foremost issue with bio-oil as compared to petroleum-derived fuels is the significant presence of oxygen (~35–40% depending on the feedstock) in the form of various organic functionalities. Such a high oxygen content leads to low energy density of bio-oil as compared to conventional crude/fuel oil. Another notable issue is the existence of high amount of moisture (15–30%) in bio-oil, which is due to inherent moisture in the feedstock and water release by dehydration reactions during pyrolysis. High water content also contributes to low heating value and flame temperature of the bio-oil (Zhang et al. 2007). Existence of aqueous phase in bio-oil alleviates its miscibility with fossil fuels. On the contrary, water content improves fluidity by reducing viscosity, which would be beneficial during atomization and combustion of bio-oil in the engine. Generally, pyrolysis oil is highly viscous (35–1000 cP at 40
C) and tends to increase with storage time. Loss of volatile compounds could also be partly responsible for the increase in viscosity. This poses a negative impact on storage and pumping efficiency. As bio-oil is a condensate produced from biomass, it does not exist in thermodynamic equilibrium at storage temperatures. This in turn drives the chemical composition of bio-oil towards thermodynamic equilibrium during storage. This slow transformation of various organic compounds present in bio-oil is called Table 14.3 Comparison of bio-oil properties with conventional fuels (Czernik and Bridgwater 2004; Perkins et al. 2018) Physicochemical properties Moisture (%) pH Viscosity (cP) (at 50
C and 25% H2O) Density (kg/L) HHV (MJ/kg) Elemental analysis (wt.%) C H O N

Bio-oil 15–30 2.5 40–100

Crude oil 0.1 – 180

Gasoline

0.37–0.44

1.05–1.25 16–19

0.86–0.94 40

0.737 44

54–58 5.5–7.0 35–40 0–0.2

85 11 1 0.3

84.9 14.8 – 0.08

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‘aging’. The characteristics of bio-oil are closely related to its composition (Xiu and Shahbazi 2012). Aldehydes undergo various secondary reactions like formation of oligomers and resins in the process of aging. Furthermore, organic acids combine with alcohols to form esters by the elimination of water. These secondary reactions during storage impart instability to bio-oil. Bio-oil is highly acidic with a low pH of 2–3 owing to the presence of carboxylic acids like acetic and formic acid. This makes bio-oil highly corrosive and poses serious effects on the construction materials of transport vessels, storage vessels and existing refinery infrastructure. Finally, the high ash content causes serious erosion, corrosion and kicking problems in engines. Specifically, alkali metals like sodium, potassium, vanadium and calcium are responsible for corrosion and deposition (Bridgwater 2003). However, the ash content in bio-oil has a strong dependence on the type of biomass feedstock selected. As the above-mentioned problems limit the direct utilization of bio-oil, it is mandatory to address these issues prior to putting the bio-oil to commercial use.

14.1.5 Applications of Bio-Oil Bio-oil finds widespread applications and can be employed as a viable substitute to conventional fuels. It can be potentially utilized in furnaces, boilers, turbines, diesel engines and Stirling engines (Bridgwater and Peacocke 2000; Bridgwater 2003; Czernik and Bridgwater 2004). Bio-oil can be employed for heat and power generation in furnaces and boilers, which are not fuel-specific. Though bio-oil is immiscible with conventional fuel, diesel engines can be fed with bio-oil after emulsification process using surfactants. However, the cost of surfactants and energy intensity involved are the two main disadvantages of emulsification technique for commercial use. As mentioned earlier, bio-oil is chemically complex with a variety of organic compounds, which could be plausibly used as an alternative renewable source for the production of chemicals including methanol, acetic acid, levoglucosan, guaiacol and other phenols. Consequently, these chemical precursors are used in the manufacture of surfactants, food flavourings, fertilizers, agrochemicals, biodegradable polymers and pharmaceuticals (Xiu and Shahbazi 2012; Bridgwater 2003). Nevertheless, fractionation of a specific chemical from the complex mixture requires energy-intensive extraction, distillation and other unit operations, which are not economical. Besides these applications of bio-oil in various sectors, the most important utilization is in the transportation sector. Currently, the bio-oil obtained from biomass cannot be utilized directly in engines and requires upgradation via deoxygenation to improve its quality. Overall, bio-oil finds application in heat and power generation, production of chemical precursors and fuels. However, improving the quality of bio-oil to the standards of conventional fuels like fuel oil or transportation grade fuels via various upgrading strategies is mandatory. Figure 14.6 depicts the H/C and O/C ratios of various lignocellulosic biomass feedstocks, biomass components and bio-oil in a Van Krevelen plot. It emphasizes

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Fig. 14.6 Van Krevelen plot

the importance of bio-oil upgrading via hydrodeoxygenation (HDO) to meet the standards of conventional fuels.

14.1.6 Catalytic Fast Pyrolysis (CFP) Catalytic fast pyrolysis (CFP) is a promising technique to overcome the undesirable properties of biomass-derived oil as it involves deoxygenation of bio-oil using catalysts. The quality of bio-oil can be enhanced greatly in terms of low oxygen content, non-corrosiveness, miscibility with petroleum fuels, better heating value, lower viscosity and higher thermal stability. Deoxygenation occurs via decarbonylation (CO), decarboxylation (CO2) and dehydration (H2O) pathways. Decarbonylation removes one oxygen atom per carbon atom, whereas the removal of oxygen in the form of CO2 rejects two oxygen atoms per carbon atom. On the contrary, hydrodeoxygenation (HDO) process involves removal of oxygen via H2O in the presence of hydrogen and heterogeneous catalyst (Huber et al. 2006). HDO does not contribute to carbon loss, which reduces the yield of hydrocarbons as noticed in the other two routes. Hence, the most preferred route of oxygen removal

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Fig. 14.7 Key reaction steps involved in catalytic fast pyrolysis of biomass (adapted from Yildiz et al. 2016)

is through H2O as it improves the energy density and stability of the oil (Nolte and Shanks 2017). Generally, in catalytic fast hydropyrolysis, there is a noticeable increase in the production of light gases such as CO, CO2 and H2O due to the aforementioned deoxygenation reactions. Several other reactions such as cracking, hydrogenation, oligomerization, aromatization, cyclization and alkylation also occur during catalytic deoxygenation process as depicted in Fig. 14.7. There are certain influential factors that need to be thoroughly studied in order to successfully commercialize the CFP process to produce refinery-ready blendstocks. Firstly, it is vital to understand the effect of various operating conditions such as reactive gas ambience, operating pressure, pyrolysis temperature, heating rate and vapour residence time on the yield of products and selectivity to organic compounds in the bio-oil. Secondly, investigation of the deoxygenation chemistry of biomassderived oxygenates over various catalysts provides theoretical insights for the rational design of efficient catalysts for CFP. Bio-oil can be upgraded to the standards of transportation fuel by two main routes: (1) HDO using suitable catalysts and (2) zeolite cracking. The outcome of catalytic upgrading is evaluated based on the degree of deoxygenation achieved and bio-oil yield. Degree of deoxygenation describes the quality of bio-oil, while yield refers to the amount of upgraded liquid generated per unit mass of biomass feedstock. Thereupon, a combination of optimum reaction conditions and appropriate deoxygenation catalyst helps in achieving the desired quality of the upgraded product (Sharifzadeh et al. 2019). However, the objective of complete deoxygenation faces several technical setbacks in process optimization and proper catalyst selection due to the complexity of bio-oil, which are discussed in the following sections.

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Effect of Operating Conditions

Reactive Gas Ambience There are two strategies to upgrade the pyrolysis vapours, which is a mixture of chemically unstable oxygenated compounds. The first one involves condensation of pyrolysis vapours and subsequent ex-situ treatment of bio-oil over catalyst in a secondary unit. However, upgradation of condensed fast pyrolysis oil is difficult and expensive, as it requires high hydrogen addition at relatively higher pressures with low space velocities (Marker et al. 2014). To overcome this, a direct one-step process called catalytic fast hydropyrolysis (CFHP) is developed, which involves pyrolysis of biomass in the presence of a deoxygenation catalyst using hydrogen as reactive gas. Here, the organic vapours evolved during pyrolysis are eventually hydrogenated in the presence of hydrogen, which serves as a potential source of radicals. As a consequence, the formation of unsaturated hydrocarbons is inhibited, thus improving the quality of bio-oil (Balagurumurthy and Bhaskar 2014). A notable improvement in the stability and composition of bio-oil is also observed. In addition, hydrogen ambience hampers the extent of polymerization reaction, which results in the suppression of char (Liu et al. 2014). Coke formation on catalysts is also minimized in the presence of hydrogen (Balagurumurthy and Bhaskar 2014). More importantly, exothermic catalytic hydropyrolysis reaction sustains the endothermic pyrolysis reaction, thus alleviating the need of a solid heat carrier recirculation (Marker et al. 2012). Higher the hydrogen content in the fuel product, better is its quality. However, it is very important to estimate the consumption of hydrogen during hydropyrolysis. This was investigated by Venderbosch et al. (2010) for bio-oil upgrading over Ru/C catalyst in a fixed bed reactor. Hydrogen consumption is reported to depend on two important factors, viz. desired degree of deoxygenation and the nature of organic molecule to be deoxygenated. Hydrogen consumption is a function of deoxygenation degree, and it increases with higher degree of deoxygenation. Furthermore, highly reactive oxygenates like ketones could be easily deoxygenated with low hydrogen consumption. However, oxygen bound to stable compounds like furan derivatives requires initial saturation that exceeds the stoichiometric hydrogen consumption at higher degree of deoxygenation (Furimsky 2000). Grange et al. (1996) studied the reactivity of various oxygenated compounds over Co-MoS2/ Al2O3 catalyst and found that ketone deoxygenation is easier with low hydrogen consumption as compared to deoxygenation of dibenzofuran. With increase in degree of deoxygenation, the yield of oil obviously decreases due to increased formation of non-condensable gases owing to dehydration, decarbonylation and decarboxylation reactions (Mortensen et al. 2011). The composition of bio-oil obtained from hydropyrolysis is different from that formed in inert atmosphere. Thangalazhy-Gopakumar et al. (2011b) observed a significant reduction in the yield of oxygenated compounds with high molecular weight in non-catalytic hydropyrolysis of pinewood chips. Nevertheless, the carbon

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yield of compounds was higher in helium (22 wt.%) compared to hydrogen (6 wt.%) atmosphere. It was speculated that hydrogen ambience leads to the formation of undetectable low molecular weight compounds. On the contrary, Nguyen et al. (2016b) observed no evident difference in the properties and chemical composition of bio-oil obtained from catalytic pyrolysis of white pine over Na2CO3/Al2O3 using Ar and 35% H2/Ar as reactant gas. This signifies minimal effect of hydrogen at atmospheric pressure. Although hydrogen at atmospheric pressure in the presence of catalyst alters the bio-oil composition to a certain extent, the overall quality of the pyrolysates obtained from CFHP is not evidently different from that obtained from CFP at atmospheric pressure. This compels the operation of catalytic hydropyrolysis at higher pressures.

Hydrogen Pressure and Pyrolysis Temperature High pressure of hydrogen ensures higher solubility of hydrogen in the oil, which increases the availability of hydrogen for performing HDO reactions in the presence of a catalyst. Several studies investigating the influence of hydrogen pressure and temperature on CFHP of biomass are discussed below. Dayton et al. (2013) observed an increase in liquid yield from 41.7 wt.% at 3.4 bar to 49.5% at 10.3 bar along with low char formation at high pressures in non-catalytic hydropyrolysis of loblolly pine chips at 400
C. However, in the absence of catalyst, deoxygenation of liquid product was not profound even at high pressures. In the presence of a hydroprocessing catalyst, the organic fraction of bio-oil contained much lower oxygen content and high aromatics. Effect of pressure was investigated in another study by Putun et al. (1994), where increase in hydrogen pressure in cellulose hydropyrolysis led to lower char and higher hydrocarbon gas yield. Balagurumurthy et al. (2014) observed an increase in the yield of bio-oil obtained from hydropyrolysis of cotton residue from 1 to 20 bar. The bio-oil yield further decreased when pressure was further increased to 40 bar at all temperatures (300, 350, 400 and 450
C). Likewise, at all pressures of 1, 20 and 40 bar, there was an increase in the yield of bio-oil with increase in temperature until 400
C. At 450
C, the yield of bio-oil decreased slightly due to secondary reactions resulting in the increased yield of gases. Hence, 20 bar and 400
C was observed to the optimum condition for hydropyrolysis of cotton residue. Similarly, Stummann et al. (2018) subjected beech wood to catalytic hydropyrolysis in a fluid bed reactor over sulphided CoMo/ MgAl2O4 catalyst followed by ex-situ HDO over NiMo/Al2O3 catalyst in a fixed bed reactor. The effects of fluid bed temperature (365–511
C) and total pressure (16–36 bar) on product yields were studied. It was reported that increasing fluid bed temperature and total pressure increased the gas yield and aqueous yield, respectively. Increase in aqueous yield was due to oxygen removal via HDO at higher hydrogen partial pressures. Increase in char yield was also noticed with increasing pressure. The feasibility of producing fungible drop-in biofuels from biomass and waste feedstocks has been demonstrated by an integrated hydropyrolysis and

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Fig. 14.8 Comparison of product distribution from non-catalytic and catalytic hydropyrolysis of pine sawdust at different H2 partial pressures and temperatures (modified and redrawn from Venkatesan et al. 2020)

hydroconversion (IH2®) process developed by Gas Technology Institute (GTI) (Marker et al. 2012; Marker et al. 2014). It is a two-stage process involving hydropyrolysis in the first reactor with fluidized catalyst bed operating at ~350–450
C and 14–35 bar, and a secondary hydroconversion unit with fixed catalyst bed at ~350–450
C. In the first reactor, devolatilization of biomass and hydrodeoxygenation of pyrolysis vapours occur simultaneously producing hydrocarbon mixture, C1-C3 gases, H2O, COx and char. Deoxygenation of hydropyrolysis vapours takes place in the second-stage hydroconversion unit. Interestingly, this process is self-sustainable in producing the required hydrogen from steam reforming of light gases (C1–C3). In one of our recent works (Venkatesan et al. 2020), pyrolysate composition from hydropyrolysis of pine sawdust at different H2 partial pressures (1,5,10 and 20 bar) and temperatures (400, 500 and 600
C) revealed prominent decrease in the production of oxygen-containing organics with increase in pressure as depicted in Fig. 14.8. The selectivity to aromatic hydrocarbons, PAHs and aliphatic hydrocarbons at 20 bar and 500
C was 18.3%, 15.5% and 35%, respectively, owing to the HDO of oxygen-containing compounds via dehydration, decarbonylation and decarboxylation pathways at higher pressures. Particularly, increase in reaction pressure led to

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an increase in the aliphatic-to-aromatic ratio. A comparison of the pyrolysate composition at 20 bar and different temperatures reveals a notable increase in the production of phenolic derivatives in the following order: 9.4% (400
C) < 11.5% (500
C) < 30% (600
C). Likewise, the selectivity to aromatic hydrocarbons followed the trend: 5.0% (400
C) < 18.3% (500
C) < 26.3% (600
C), substantiating the increase in aromatic hydrocarbons with increase in pyrolysis temperature. This can be ascribed to increased rate of cracking reactions at high temperatures. Furthermore, upgradation of pyrolysates evolved from hydropyrolysis at 20 bar and 500
C over proprietary HDO catalyst supplied by Shell Technologies, maintained at 500
C, resulted in complete deoxygenation of pyrolysates with ~98% hydrocarbons as depicted in Fig. 14.8. A trade-off between biomass conversion and secondary decomposition needs to be achieved with regard to pyrolysis temperature. At higher temperatures (> 600
C), secondary decomposition dominates, which increases the gas yield at the cost of char and liquid oil yields. It is well established that liquid yield is maximized in the temperature range of 450–550
C. Temperatures beyond this range lead to more gases and less char formation. In a work by Xiao and Yang (2013), liquid yield obtained from rice straw pyrolysis was maximum at 500
C. Moreover, increasing the temperature promoted the yield of gases. The product composition of cellulose, lignin and hemicellulose pyrolysis at different operating temperatures (200–550
C) was investigated by Ansari et al. (2019). By increasing the operating temperature, the primary products derived from cellulose and xylan such as anhydrosugars, furans and pyrans were converted to other furans, light oxygenates and light gases through various reactions such as ring opening, fragmentation, retro-Diels–Alder, decarbonylation and dehydration. Thangalazhy-Gopakumar et al. (2011a) observed an increase in concentration of phenols and toluene with increase in pyrolysis temperature (450–750
C) during the pyrolysis of pinewood and switchgrass. Other reaction parameters such as heating rate and vapour residence time also play a vital role in catalytic hydropyrolysis process. Low vapour residence time and high heating rate are recommended to obtain maximum yield of bio-oil through pyrolysis. Low residence time prevents the occurrence of secondary reactions, which leads to the formation of light gases. Fast heating rates promote the fragmentation of biomass quickly and enhance the yield of volatiles. Hence, for CFHP, a combination of high hydrogen partial pressure at moderate pyrolysis temperature, high heating rate and short residence time is preferred for better yield of liquid product (Thangalazhy-Gopakumar et al. 2011a).

14.1.6.2

Effect of HDO Catalysts

Noble Metals Several noble catalysts investigated for the HDO of bio-oil are discussed in this section. Addition of a metal to the support improves the overall catalytic performance due to synergistic effects. Sun et al. (2016) demonstrated better activity of Fe/

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ZSM-5 than ZSM-5 catalyst for the conversion of oxygenates to monoaromatic hydrocarbons. In a work by Fisk et al. (2009), Pt/Al2O3 catalyst exhibited better activity for decreasing the oxygen content to 2.8 wt.% from an initial value of 41.4 wt.% in synthetic bio-oil. Hydropyrolysis of lignin conducted at 17.2 bar and 650
C over Pd/HZSM-5 catalyst with catalyst-to-lignin mass ratio of 20:1 resulted in the production of 44% aromatic hydrocarbons, which was more than that using HZSM-5. This could be attributed to the acceleration of deoxygenation reactions by Pd metal on HZSM-5 (Jan et al. 2015). Moreover, the formation of char by bimolecular polymerization of aryl radicals was inhibited in the presence of hydrogen atoms facilitated by Pd metal. Zhu et al. (2011) investigated the role of bifunctional Pt/H-beta catalyst on HDO of anisole at 400
C and atmospheric pressure. In general, H-beta catalyses the transalkylation reaction, while Pt catalyses demethylation, hydrodeoxygenation and hydrogenation reactions. However, Pt metal loaded onto H-beta is hypothesized to exhibit bifunctionality by accelerating both transalkylation and HDO reactions resulting in the formation of benzene, toluene and xylene. In addition, this catalyst reduced the rate of deactivation and coke deposition. In another work (Cheng et al. 2012), addition of Ga to ZSM-5 catalyst is shown to increase the rate of formation of aromatic hydrocarbons from furan. This was substantiated by the promotion of decarbonylation and olefin aromatization reactions by Ga, while oligomerization and cracking were catalysed by ZSM-5. Amorphous silica–alumina (ASA) loaded with alkali or alkaline earth metals (Na, K, Cs, Mg and Ca) was investigated for deoxygenation of bio-oil obtained from Canadian pinewood pyrolysed at 450
C (Zabeti et al. 2012). K/ASA and Na/ASA were observed to promote deoxygenation via decarboxylation, while Cs/ASA was active in promoting the decarbonylation pathway. This resulted in the reduction of oxygen content to 29.5%, 30.6% and 35.1% using Na/ASA, K/ASA and Cs/ASA, respectively, from an initial oxygen content of 40.6% in Canadian pinewood. Effective deoxygenation using Na/ASA and K/ASA catalysts was reflected in an increase in the heating value of the upgraded oil. In another study by Zabeti et al. (2016), the oxygen content reduced significantly after catalytic pyrolysis over Cs/ASA. The heating value of upgraded oil obtained from cellulose, hemicellulose and lignin was high, and they were 34.2, 34.4 and 39.7 MJ kg1, respectively. Thangalazhy-Gopakumar et al. (2012) showed that there is no effect of hydrogen pressure on bio-oil compounds evolved from pinewood pyrolysis in the presence of H+ZSM-5 catalyst in the pressure range of 6.9-27.6 bar. However, the aromatic yield increased on impregnation of metal (Ni, Co, Mo and Pt) into ZSM-5 due to the possibility of hydrogenation reactions on metal sites prior to aromatization.

Non-noble Metal Catalysts Apart from noble metal catalysts, transition metal carbides are also reported to be active in the HDO of oxygenates derived from biomass. They are known to catalyse hydrogenolysis, hydrogenation, isomerization and dehydration reactions owing to

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their metallic and acidic characteristics (Sullivan et al. 2016). However, the presence of oxygen on the carbide surface impedes the metallic function and promotes acidic character resulting in selective cleavage of C-O bond. Therefore, sequential hydrogenation reactions are not promoted by the metal carbide catalysts and this distinguishes them from noble metal catalysts. Molybdenum and tungsten carbides are some of the widely studied transition metal carbides for HDO of biomass-derived oxygenates. In one of our previous works (Venkatesan et al. 2018), W2C/γ-Al2O3 was tested for HDO of oxygenates obtained from pinewood hydropyrolysis at 500
C in an analytical Pyroprobe® reactor. It proved to be an efficient deoxygenation catalyst with 82% selectivity to aromatic hydrocarbons like benzene, toluene, xylene and ethyl benzene. Hollak et al. (2013) compared the activity of tungsten and molybdenum carbide catalysts in HDO of oleic acid. The difference in hydrogenation activity of carbide catalysts was demonstrated by the formation of olefinic and paraffinic compounds with tungsten and molybdenum catalysts, respectively. The effect of support on deoxygenation of pyrolysis vapours from commercial wood biomass (Lignocel HBS 150-500) originating from beech wood was evaluated by Stefanidis et al. (2011) using FCC, ZSM-5, MgO, NiO, alumina, zirconia, titania and silica–alumina catalysts. Among all the catalysts, better performance, in terms of high organic liquid yield, reduced oxygen content and high aromatic hydrocarbons, was exhibited by zirconia, titania and ZSM-5 catalysts. This can be attributed to low coke formation and a balanced promotion of deoxygenation via CO, CO2 and H2O. Investigation of some novel catalysts also exhibited promising activity in bio-oil HDO. Nguyen et al. (2013) produced bio-oil from Canadian white pine chips with oxygen content of 12.3 wt.% and HHV of 37 MJ kg1 using 20 wt.% Na2CO3/γ-Al2O3. Moreover, the acidity of thermal bio-oil with TAN of 119 was significantly reduced to 3.8 after upgrading over the catalyst. Emergence of new sodium phase due to the interaction between sodium and alumina in the catalyst was reported to be responsible for high activity. Importantly, the catalytic bio-oil was comparable to fuel oil with a heating value of 40 MJ kg1 and 1% oxygen content. Furthermore, upgradation of pinewood pyrolysis vapours over dual catalyst bed of Na2CO3/γ-Al2O3 and Pt/γ-Al2O3 in the presence of 35% H2/Ar gas produced bio-oil with a heating value of 43 MJ Kg1 and 5.6 wt% oxygen content (Nguyen et al. 2016b). The possibility of replacing hydrogen with n-butane as the reactive gas for biomass hydropyrolysis was also tested in this work. Interestingly, n-butane exhibited equivalent effect as hydrogen in the bio-oil composition and its properties, proving its viability as an economical hydrogen source.

Zeolite Cracking Zeolites are crystalline microporous aluminosilicate materials that are widely used as catalysts in the industry for crude oil refining and production of fine and speciality chemicals. Zeolites are well known for their high surface area and acidity. Further, the strength of acid sites can be controlled by tuning the SiO2/Al2O3 (Si/Al) ratio required for various applications (Huber et al. 2006). High Si/Al ratio portrays low

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acidity with low deoxygenation activity. Zeolite cracking usually occurs at high temperatures (300–600
C) involving a number of reactions such as dehydration, cracking, polymerization, aromatization and deoxygenation (Saidi et al. 2014). Zeolite cracking reactions alleviates the need for reactive hydrogen ambience, and hence, the reaction can be carried out at atmospheric pressure, which also reduces the operating cost. Zeolites have been conventionally used for fluid catalytic cracking (FCC) in order to reduce the chain length of hydrocarbons. Zeolite cracking yields alkenes and aromatic hydrocarbons in the product mixture due to β-scission reactions. This is the main advantage of zeolite cracking reactions over HDO process if aromatics, the key ingredient for octane number improvement, are desired. However, the disadvantages with zeolite cracking include high coke formation, poor hydrocarbon yield and catalyst deactivation. Several zeolites have been investigated for CFP of biomass including ZSM-5, HY, H-Beta, MCM-41, MCM-22 and SAPO 34. The importance of framework structure, pore size and acidity of zeolites in deoxygenation of pyrolysis vapours to form aromatic hydrocarbons is widely investigated (Mihalcik et al. 2011; Engtrakul et al. 2016). CFP of glucose using ZSM-5 produced highest yield of aromatic hydrocarbons as compared to other catalysts such as silicalite, β-zeolite, silica– alumina and Y-zeolite (Carlson et al. 2008). Although silicalite exhibits similar pore structure as that of ZSM-5, the use of silicalite yields low aromatics and more coke due to the absence of Brønsted acid sites (Zheng et al. 2017). Silica–alumina also has Brønsted acid sites, but due to its amorphous nature, it is less active. This implies the importance of both pore structure and acidity of zeolites for deoxygenation. The effect of Si/Al ratio of microporous HY catalysts was investigated by Jeong et al. (2019) for catalytic pyrolysis of pinecone. The highly acidic HY (30) produced more aromatic hydrocarbons compared to HY (60). Importantly, low biomass-to-catalyst ratio produced more monoaromatic hydrocarbons. Deoxygenation reactions are promoted through carbonium ion mechanism by the acidic sites in HZSM-5 catalyst, which also catalyses other reactions such as cracking, oligomerization, cyclization, aromatization and alkylation (Vitolo et al. 2001). Mihalcik et al. (2011) examined the capability of H-ferrierite (20), H-mordenite (20), HZSM-5 (23) and H-beta (25) to deoxygenate the pyrolytic vapours from various lignocellulosic biomass feeds. Among all the catalysts, H-beta yielded high coke due to premature deactivation and HZSM-5 produced high amount of aromatic hydrocarbons. With all the catalysts, an increase in the yield of non-condensable gases and decrease in the yield of bio-oil compared to non-catalytic pyrolysis were observed. This can be attributed to the promotion of deoxygenation reaction via H2O liberation at low catalyst bed temperatures, and via CO and CO2 release at high catalyst bed temperatures. These results are also consistent with catalytic pyrolysis of rice husk over ZSM-5 catalyst conducted by Williams and Nugranad (2000) in a fluidized bed reactor. Deactivation of zeolite occurs by coke deposition on the surface of the catalyst or at the pores of zeolite. Polycondensation of biomass vapours, hydrogen transfer and carbonium ion chemistry are the dominant mechanisms for coke formation. The olefins get converted to polyaromatic hydrocarbons via oligomerization–condensation reactions, which eventually led to coke formation

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Table 14.4 Product yields from CFP of biomass over ZSM-5 catalysts Catalyst ZSM-5

Feed Pinewood

ZSM-5

Pinewood

HZSM5(24)

Corncob

ZSM-5

Rice husk

HZSM5(23)

Oak Corn cob Corn Stover Switchgrass Lignocel HBS 150-500 (beech wood)

ZSM-5 (61) ZSM-5 (90) ZSM-5 (138) ZSM-5 (80) ZSM-5 (25) ZSM-5 (80)

Cornstalk

Reaction conditions Pyrolysis: 500
C WHSV:1 h-1 Pyrolysis: 550
C Cat:Bed: 450
C Cat:Bio- 5:1 Pyrolysis: 550
C Cat:Bio- 5:1 Fluidized gas flow rate: 3.4 L min-1 Pyrolysis: 550
C Cat. Bed: 450
C Pyrolysis: 550
C

Pyrolysis: 500
C Biomass: 1.5 g Catalyst: 0.7 g Residence time: 0.031 s

Pyrolysis: 550
C Heating rate: 500
C min1 Gas flow rate: 400 cm3 min-1

Liquid (wt.%) 43

Gas

Char

O

References

30

22

17.8

Yildiz et al. (2015)

50.1

23.9

15.7

–

Yildiz et al. (2013)

39.3

26.0

20.1

14.7

Zhang et al. (2009)

31.9

26.6

30.3

12.5

Williams and Nugranad (2000)

59.6 48.5 31.4 51.7 53.5

26.5 28.1 40.4 19.4 20.1

13.9 23.4 28.2 28.9 26.4

–

Mihalcik et al. (2011)

34.7

Stefanidis et al. (2011)

52.5

19.8

27.7

36.8

48.5

25.8

25.7

30.9

34.3

31.3

31.4

4.2

43.9

30.1

25.9

14.21

43

32

25

20.2

Iliopoulou et al. (2012) Stephanidis et al. (2011) Uzun and Sarioǧlu (2009)

WHSV—weight hourly space velocity, Cat:bio—catalyst:biomass mass ratio

(Zheng et al. 2017; Gayubo et al. 2004). Few other salient results on the use of ZSM-5 catalysts for CFP of biomass are shown in Table 14.4. Due to the high susceptibility of microporous zeolites to coke formation, a drive towards mesoporous materials has attracted the attention of researchers recently. MCM-41 is one of the mesoporous materials with larger pore size (1.4–10 nm), high surface area and better accessibility to active sites than conventional zeolites.

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Karnjanakom et al. (2017) observed that 1 wt.% Mg-doped Al-MCM-41 catalyst exhibited high activity and selectivity to hydrocarbons (86.2%) in the upgradation of bio-oil obtained from sunflower stalk pyrolysis. In the evaluation of different types of MCM-41 catalysts for catalytic pyrolysis of commercial wood and miscanthus, low Si/Al ratio is reported to exhibit a positive effect on the yield of products and their composition. Metal-loaded MCM-41 showed better performance compared to plain MCM-41 catalyst in terms of stability and phenol production (Antonakou et al. 2006). CFHP primarily produces aromatic hydrocarbons. Although the production of aromatic hydrocarbons by catalytic upgrading enhances the quality of bio-oil in terms of better octane number, the composition of bio-oil can be tuned to alkanes and cycloalkanes by the addition of a secondary hydrotreating unit (Resende 2016). In general, CFHP involves higher yield of water at the expense of organic yield due to extensive dehydration reactions. Moreover, coke formation is responsible for the reduction in the liquid yield. Due to these reasons, the yield of bio-oil in catalytic experiments is always lower than non-catalytic fast pyrolysis at similar temperatures. Generally, metal catalyst is involved in demethylation, hydrogenation and hydrodeoxygenation activity, while acidic support performs dehydration and transalkylation reactions. In addition to proper catalyst selection, considerable attention to reaction parameters such as catalyst bed temperature, vapour residence time, catalyst-to-biomass ratio and mode of catalytic upgradation is also necessary to obtain high yield of liquid and high selectivity to the desired products.

14.1.6.3

Mode of Upgradation: Ex-situ vs In-situ

On the basis of upgradation mode employed for the pyrolytic vapours, catalytic pyrolysis can be classified into in-situ and ex-situ pyrolysis, which are also depicted in Fig. 14.9. In-situ catalytic pyrolysis involves thorough mixing of catalyst and biomass feedstock in required proportion before pyrolysing the mixture. Generally, in this configuration, pyrolysis reaction and catalytic upgradation of pyrolysis vapours occur in a single reactor, whereas, in ex-situ catalytic pyrolysis, pyrolytic vapours are carried through a catalyst bed placed external to the feedstock reactor (Wang et al. 2017). Hence, pyrolysis reaction and catalytic upgradation are carried out in two separate reactors. Intimate contact of biomass particles with catalyst in in-situ pyrolysis facilitates the obstruction of polymerization and charring reactions of the primary pyrolysates. Yildiz et al. (2013) showed that char yield from CFP of pinewood decreased by 2.3 wt. % in in-situ compared to that of ex-situ configuration. Higher conversion of biomass was reported due to high heat carrier-to-biomass ratio. Furthermore, the quality of bio-oil was also considered to be better in in-situ compared to ex-situ mode. However, in-situ configuration requires more catalyst-tobiomass ratio compared to ex-situ upgradation in order to enhance the degree of deoxygenation (Zhou et al. 2016). In a study involving catalytic pyrolysis of pinewood chips over ZSM-5 performed by Thangalazhy-Gopakumar et al. (2011b), two different methods called catalyst mixing and catalyst bed were reported. Catalyst

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Fig. 14.9 In-situ and ex-situ pyrolysis

mixing involves mixing of catalyst and biomass, whereas catalyst bed method involves packing of biomass and catalyst in separate beds in the same reactor. The production of aromatic hydrocarbons was reported to be higher in catalyst mixing mode compared to catalyst bed method. Moreover, in-situ catalytic pyrolysis was concluded to be a better upgradation option as O/C ratio of bio-oil compounds was higher in the catalyst bed method than catalyst mixing method. Thorough mixing of biomass with catalyst in in-situ arrangement provides good surface contact enabling better mass transfer for catalytic cracking reactions, whereas in ex-situ mode, the pyrolytic vapours adsorbed on the catalyst surface undergo cracking reactions resulting in aromatic hydrocarbons. Consequently, this leads to the formation of coke at the pores of catalyst preventing further diffusion of vapours. On the other hand, in-situ catalytic pyrolysis in a single reactor limits the optimization ability for both pyrolysis and catalytic upgradation. Further, catalyst poisoning due to inorganic minerals in biomass and difficulty in the separation of char and catalyst after reaction are other practical problems encountered in in-situ mode (Yildiz et al. 2016). Ex-situ is more advantageous in terms of achieving the optimum operating conditions for pyrolysis and catalytic conversion, as they occur in two independent reactors. Nonetheless, both in-situ catalytic pyrolysis and ex-situ catalytic pyrolysis improve the quality of the pyrolysis vapours with their own advantages at the expense of some drawbacks. Appropriate considerations related to the type of feedstock, operating conditions and required organic compounds in bio-oil should be taken into account while choosing the upgradation mode for

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catalytic pyrolysis. In-situ mode is usually performed in laboratory-scale analytical reactors to screen catalysts. However, pilot scale and commercial upgradation facilities prefer ex-situ mode due to easy recovery of the used catalyst, and the possibility of catalyst regeneration by combustion of coke.

14.1.7 Model Compounds Due to the complexity in the chemical composition of bio-oil obtained from CFHP of biomass, the interpretation of the HDO reaction chemistry and kinetics is quite tedious. To overcome this limitation, several studies have investigated the CFP of representative bio-oil compounds. This also helps in the development of novel hydrodeoxygenation catalysts. The most widely studied bio-oil compounds include furfural, furan, phenol, anisole, guaiacol, cresol and vanillyl alcohol (Saidi et al. 2014; Furimsky 2000; Bu et al. 2012; Ruddy et al. 2014).

14.1.7.1

Furan Derivatives

Furfural is an intermediate commodity chemical used in the synthesis of a wide range of speciality chemicals required for the production of resins, adhesives and flavouring agents. It is a product of dehydration of sugars from holocellulosic fraction of biomass. HDO of furfural is one of the key steps in CFP of lignocellulosic biomass, and this occurs via two main routes as depicted in Fig. 14.10. Pathway 1 involves decarbonylation of furfural to furan, followed by hydrogenation to tetrahydrofuran. Pathway 2 involves hydrogenation of furfural to furfuryl alcohol, which on dehydration forms methyl furan. However, the predominant HDO pathway is dependent on the type of catalyst. In addition to the influence of catalytic activity on the reaction pathways, there are several other factors that influence the selectivity to final product. Shi and Vohs (2015) studied the effect of catalyst alloying on product selectivity and found that the adsorption and reaction of furfural on the

Fig. 14.10 Reaction pathway of furfural HDO (modified and redrawn from He and Wang 2013)

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surface of Pt (111) and Zn-modified Pt (111) are the key steps. It was reported that furfural adsorbs on Pt (111) surface via furan ring and undergoes C-C bond scission and ring opening to produce CO and H2. However, on a Zn-modified Pt (111) surface, it bonds via aldehyde carbonyl group. In this configuration, the C-O bond is weakened and cleaved, resulting in the selective production of methyl furan. Cheng and Huber (2011) studied the effect of temperature on the conversion of furan over HZSM-5 catalysts. Furan was selectively converted to olefins and CO at high temperatures (>650
C) via oligomerization reactions. At low temperature (450
C) and intermediate temperature (450–600
C), the formation of benzofuran via Diels–Alder condensation and aromatic hydrocarbons via alkylation and cyclization reactions was observed.

14.1.7.2

Phenolic Compounds

HDO studies on phenolic compounds have received considerable attention due to their low reactivity in HDO process. Moreover, phenolic compounds are the major pyrolysates from lignin fraction of biomass. The major pathways of lignin-derived phenolic compounds are depicted in Fig. 14.11.

Phenol Phenol is one of the widely investigated lignin-derived compounds with one hydroxyl group attached to the aromatic ring. The two major HDO routes of phenol include hydrogenolysis and hydrogenation. Hydrogenolysis of phenol results in the production of benzene, which can be further hydrogenated to cyclohexane via cyclohexene intermediate. On the other hand, hydrogenation of phenol results in the formation of cyclohexanone and then cyclohexanol (Saidi et al. 2014). Catalytic HDO of lignin model compounds such as phenol, guaiacol and syringol over HZSM-5(50) catalyst at various catalyst bed temperatures (350, 400, 450 and 500
C) was investigated in one of our previous studies as depicted in Fig. 14.12 (Venkatesan et al. 2021). Catalytic HDO experiments were conducted in an analytical pyrolyser (Pyroprobe®5200) coupled with a gas chromatograph/mass spectrometer (GC/MS). In a typical experiment, 0.2  0.01 mg of the model compound was weighed accurately and vaporized at a probe heating rate of 10,000
C s1, and maintained at the set temperature for a hold time of 60 s. The vapours were carried to the pre-heated catalyst bed with catalyst-to-sample ratio of 10:1 wt./wt. The conversion of phenol using HZSM-5 catalyst increased with increase in temperature in the following order: 350
C (11.1%) < 400
C (53.6%) < 450
C (76.0%) < 500
C (98.6%). The major product from phenol conversion was benzene, which was formed by dehydration reaction over the acidic sites. The conversion of phenol varied with the type of zeolite maintained at different bed temperatures. Over HZSM-5 catalyst, there was no evidence of HDO at 350
C. On the other hand, conversion of phenol to benzene, cresol and toluene occurred over HY(60) and

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Fig. 14.11 Reaction chemistry of HDO of lignin-derived compounds. HDO reactions are indicated ), demethylation ( ), dehydroxylation ( ), as (1) demethoxylation ( ) and hydrogenation ( ) transalkylation (

H-Beta(360) catalysts at 350
C as depicted in Fig. 14.13a and b. All the three catalysts ensured almost complete conversion of phenol to benzene with high selectivity at 500
C.

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Fig. 14.12 Comparison of the yields of HDO products from phenol, guaiacol and syringol using HZSM-5 catalyst. ‘Non-catalytic’ corresponds to vaporization of phenol, guaiacol and syringol at 190, 220 and 270
C, respectively (redrawn from Venkatesan et al. (2021))

Cresol Catalytic conversion of cresols (o-cresol, m-cresol, p-cresol) to other valuable chemicals such as toluene, phenol, benzene and methyl cyclohexane can occur through the following pathways. Hydrogenolysis of the methyl group in cresol (pathway 7, Fig. 14.11) leads to the formation of phenol, while consecutive partial hydrogenation, deoxygenation and dehydrogenation yield toluene (pathway 8). Pathway 9 involves hydrogenation of cresol to form methyl cyclohexanol, which on subsequent hydrogenation produces methyl cyclohexane. Methyl cyclohexane can also be formed by hydrogenation of toluene. Importantly, cresol acts as a precursor to coke formation. The orientation of the adsorbed molecule on the active site of the catalyst determines the reaction pathway. Vertical adsorption of cresol on the metal surface results in the formation of toluene. When cresol is adsorbed co-planar to the metal surface, it results in methyl cyclohexane formation via methyl cyclohexanol as intermediate. Further, catalyst acidity plays a dominant role in determining the end product. Zanuttini et al. (2014) studied the effect of acid site

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Fig. 14.13 Comparison of the yields of HDO products from phenol, guaiacol and syringol using (a) HY and (b) H-beta catalysts maintained at different catalyst bed temperatures

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on deoxygenation of m-cresol using Pt catalysts supported on materials with varying acidity (γ-alumina, silica and H-beta zeolites). Zeolites with high density of acid sites were found to be undesirable due to high coke formation. On the other hand, Pt/γ-Al2O3 and Pt/SiO2 performed better than Pt/H-beta. Hence, a high metal-toacid site ratio is reported to be essential for the formation of HDO products, especially toluene, from cresol. Similarly, the importance of acidity and mesoporous structure of Pt-based catalysts such as Pt/γ-Al2O3, Pt/ZSM-5 and Pt loaded on mesoporous ZSM-5 (Pt/MZSM-5) was studied by Wang et al. (2013) using cresol as model compound. Methyl cyclohexane was the main product over Pt/ZSM-5 and Pt/MZSM-5 catalysts. Conversely, methyl cyclohexanol was produced over Pt/γ-Al2O3 due to its weak acidity.

Anisole Deoxygenation of anisole involves various reactions such as demethylation, demethoxylation, hydrogenation and transalkylation. The three major pathways of HDO of anisole include the following: 1. Demethylation, leading to the formation of phenol and methane. 2. Demethoxylation to benzene followed by hydrogenation to form cyclohexane. 3. Transalkylation of anisole resulting in cresol formation, which, on subsequent dehydration, forms toluene. The importance of temperature and pressure on HDO was studied by Gamliel et al. (2018) using anisole as a bio-oil model compound over 4% Ni-ZSM-5 catalyst and found that the yield of alkanes was low at high temperatures indicating hydrogenation to be thermodynamically limited. On the contrary, aromatics were predominant at high temperatures and low pressures.

Guaiacol and Syringol Guaiacol, which contains one hydroxyl and one methoxy group in its chemical structure, represents many other lignin-derived pyrolysates. Conversion of guaiacol is initiated via three routes (Bu et al., 2012): (1) demethoxylation to produce phenol and methanol, (2) dehydration to anisole and (3) demethylation to catechol. Conversion of guaiacol was studied over various bifunctional catalysts consisting of noble metals (Pt, Rh, Pd and Ru) supported on acidic matrices of Al2O3, SiO2-Al2O3 and nitric acid-treated carbon black (Lee et al. 2012). These catalysts exhibited dual role of aromatic ring hydrogenation by metal sites and deoxygenation by acidic supports. Moreover, hydrogenation of the aromatic ring was found to precede deoxygenation reaction resulting in the formation of 2-methoxy cyclohexanol on the metal site, followed by cyclohexane formation on metal-supported acid catalyst. In a study conducted by Hellinger et al. (2015), hydrogenation of aromatic ring in guaiacol was observed to be the first step on Pt-based catalysts.

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In another study by Gutierrez et al. (2009), zirconia-supported noble metal (Rh, Pd, Pt) catalysts are shown to actively promote hydrogenation and HDO of guaiacol at 100
C and 300
C, respectively. Due to a decrease in equilibrium coverage of hydrogen on the catalyst with increase in temperature, the rate of hydrogenation is reduced. Consequently, saturation of aromatic ring is favoured at low temperatures. In another study by Jongerius et al. (2013), carbon nanofibre-supported W2C and Mo2C catalysts were investigated for guaiacol HDO in which Mo2C was more active compared to W2C at 300–375
C and 55 bar hydrogen pressure to form benzene and toluene. Nimmanwudipong et al. (2011) investigated the conversion of guaiacol in a flow reactor at 300
C and 1.4 bar over Pt/γ-Al2O3 catalyst, which resulted in the formation of phenol, catechol and methylcatechol via hydrodeoxygenation, hydrogenolysis and transalkylation reactions, respectively. The HDO selectivity increased with increasing hydrogen partial pressure and decreasing temperature over Pt/γ-Al2O3. It was also reported that hydrogenolysis and hydrogenation reactions are catalysed by Pt, while alumina support promotes transalkylation reaction. Likewise, in gas-phase HDO of guaiacol at ambient pressure, Co-supported Al-MCM-41 catalysed the C-O bond hydrogenolysis to form oxygen-free aromatics. Interestingly, Ni-supported Al-MCM-41 catalysed the hydrogenolysis of C-C bond producing methane in the gas phase. The methyl transfer reactions occurred over the acid sites of Al-MCM-41 (Tran et al. 2016). From the results generated in our group depicted in Figs. 14.12 and 14.13, it can be observed that demethoxylation of the methoxy group attached to the aromatic carbon in guaiacol to form phenol is the most favourable HDO pathway. This is substantiated by the low bond dissociation energy (BDE) of Caryl–OCH3 (102.9 kcal mol1) compared to Caryl–OH (111.8 kcal mol1). With increase in temperature, dehydration and transalkylation reactions become prominent resulting in the formation of anisole and cresol, respectively. Further increase in temperature to 450
C led to hydrogenolysis of the hydroxyl group in cresol resulting in the formation of toluene. Beyond 400
C, complete conversion of guaiacol was observed with HZSM-5. The total yield of major compounds from syringol conversion over HZSM-5 catalyst was in the range of 31.3–76.2 wt.% in the temperature range of 350–500
C (Fig. 14.12). The experimental mass closure of major products at 450 and 500
C was observed to be low, which is 51.1 and 31.3 wt% from syringol conversion, respectively. Importantly, the total liquid yields were found to decrease with increase in temperature, and the liquid yields were low for syringol conversion followed by guaiacol and phenol conversion. This is primarily due to the formation of gases via dehydration and demethoxylation reactions, and also due to coke formation, which is highest from syringol conversion. Figure 14.13a shows an interesting trend of product selectivity using HY catalyst with increase in temperature. With HY, at 350
C, phenol, cresol and guaiacol were the major products from syringol conversion. Further increase in temperature to 450
C resulted in enhanced production of benzene, anisole and toluene. Low yields with HY and H-beta catalyst can be attributed to premature deactivation of these catalysts and high coke formation

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compared to HZSM-5. Notably, in guaiacol and syringol HDO studies, complete deoxygenation of phenol was not achieved due to its high stability.

Vanillyl Alcohol The effect of acid site on the extent of deoxygenation of vanillyl alcohol was studied by Nguyen et al. (2016a) over Na2CO3, Na2CO3/Al2O3 and Al2O3 catalysts. It was observed that the extent of deoxygenation increased with increase in concentration of acid sites. Accordingly, the use of highly acidic γ-Al2O3support resulted in the production of aromatic hydrocarbons like 2-methyl naphthalene, xylene, naphthalene, 2-methylindene and phenanthrene derivatives via deoxygenation of the alkoxy groups.

14.1.7.3

Linear Oxygenates

HDO of linear oxygenates such as carboxylic acids, aldehydes and alcohols is also reported in the literature. HDO of carboxylic acids proceeds via three general routes as stated by He and Wang (2013). The first pathway involves ketonization via C-O bond cleavage to form ketones, followed by hydrogenation to produce alcohols. In a study by Anand et al. (2017), palmitic and myristic acids produced from fast pyrolysis of Schizochytrium limacinum microalgae underwent ketonization reaction to form ketones in the presence of metal oxides. Pathway 2 involves hydrogenolysis of the C-O bond to produce aldehyde, followed by hydrogenation to form alcohols. The alcohols are further converted to alkanes via dehydration and hydrogenation. Alternatively, alcohol can also react with carboxylic acid to form ester. The third route is direct decarboxylation and decarbonylation to form alkanes. Figure 14.14 depicts the pathways involved in the conversion of aldehydes: (1) direct hydrogenolysis of C¼O, (2) hydrogenation of C¼O bond to form alcohols followed hydrogenolysis of C-O to produce alkanes, (3) hydrogenation of C¼O bond to form alcohols, dehydration to produce olefins and subsequently C¼C bond hydrogenation to form alkanes and (4) decarbonylation of C¼O to form CO and alkane. HDO of alcohols is depicted by steps (2) and (3).

Fig. 14.14 HDO of aldehydes and alcohols (He and Wang (2013))

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Peng et al. (2012) studied the gas-phase conversion of 2-propanol over 3 wt.% Pt/Al2O3 in a continuous fixed bed flow reactor and reported the formation of acetone and propene via dehydrogenation and dehydration pathways, respectively. It was concluded that the Lewis acid sites of alumina are responsible for dehydration and Pt sites catalyse the dehydrogenation reaction. The activity of Ni-MoS2/ MgAl2O4 catalyst in HDO of model compounds such as acetic acid, ethylene glycol and cyclohexanol was investigated in a fixed bed reactor at 380–450
C (Dabros et al. 2019). Cyclohexene and cyclohexane were the dominant products from cyclohexanol with 60–80% and 14–30% yields, respectively. Studies using model compounds play an important role in understanding the reactivity pattern and consequently aid in developing suitable catalysts for biomass upgradation. However, the existing studies could not adequately address all the key challenges such as reactivity of individual compounds in the vicinity of other bio-oil compounds. This requires more detailed studies using binary and ternary mixtures of model compounds.

14.1.8 Conclusions and Future Prospects Biomass-derived fuels are potential substitutes for petroleum-based fuels in the near future. Lignocellulosic biomass is one of the most promising, sustainable, carbonrich feedstocks that can plausibly replace the dependence on fossil fuels for production of energy via fast pyrolysis technique. Research on catalytic fast pyrolysis of biomass to produce fuels and chemicals has been carried out extensively for several years. However, the scale-up of the hydropyrolysis unit from bench scale to fullscale production faces several challenges such as feedstock heterogeneity, reliable processing mode, suitable pyrolysis reactor, optimum bio-oil yield, energy efficiency, process heat integration, economic feasibility, successful catalyst performance with low coke formation and regenerability, efficient heat and mass transfer, high pressure operability and availability of economical hydrogen source. One of the key challenges in bio-oil upgradation process is catalyst formulation. An ideal catalyst for bio-oil upgradation should exhibit high deoxygenation activity resulting in the high yield of hydrocarbons with low rate of coking and deactivation. Investigations on the influence of operating parameters and activity of various catalysts including noble metals, non-noble metals, transition metal carbides, amorphous silica–alumina and zeolites in the HDO of bio-oil are reported in this study. Although upgradation of pyrolysates over various catalysts exhibited promising results in HDO, selection of suitable catalyst with high activity and stability is still a challenge. Future works should focus on the design of the catalyst with high stability and tolerance to the varying reaction conditions, high water content and organic acids. Theoretical studies based on quantum chemical ab initio and density functional theory calculations provide valuable insights on reaction chemistry on catalyst active sites and surfaces, and the role of bimetallic catalysts on reaction kinetics. Theoretical studies and experimental studies using model compounds and

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specific catalysts should be conducted in tandem and in synergism. An in-depth combined knowledge of reaction chemistry and kinetics is a pre-requisite for iterative modelling calculations of processing units, which serves as a basis for the conceptualization of reactor design. Moreover, studies on multiscale modelling that consider the integrated effect of feedstock characteristics, operating conditions, reactor modelling and transport phenomena from molecular to reactor level are necessary to develop a robust pyrolysis technology. This would help in real-time process optimization besides minimizing the time, cost and resources involved in experimentation and reactor design. Most of the experimental studies employ model biomass compounds as feedstocks for better understanding of the specific reaction chemistry on the catalyst. However, future works should focus on complicated feedstocks to understand the change in the HDO activity and adaptability of catalyst to various conditions including different biomass feedstocks and wide operating conditions. The insights acquired from the above studies can be very useful to devise better upgradation strategies and optimize them. Accordingly, the acquired knowledge can be translated for implementing catalytic fast hydropyrolysis technique on a larger scale to bridge the existing gap between biofuels and conventional fuels.

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