Green Energy and Technology

Ayhan Demirbas

Biofuels

Securing the Planet’s Future Energy Needs

123

Ayhan Demirbas, Professor of Energy Technology Sila Science and Energy Trabzon Turkey

ISBN 978-1-84882-010-4 e-ISBN 978-1-84882-011-1

DOI 10.1007/978-1-84882-011-1

Green Energy and Technology ISSN 1865-3529

A catalogue record for this book is available from the British Library

Library of Congress Control Number: 2008940429

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v

Preface

Today’s world is facing two critical problems: (1) high fuel prices, and (2) cli-matic changes. Experts suggest that current oil and gas reserves would suffice to last only a few more decades. It is well known that transport is almost totally de-pendent on fossil fuels, particularly petroleum-based fuels such as gasoline, diesel fuel, liquefied petroleum gas, and natural gas. Of special concern are the liquid fuels used in automobiles. Hence, there has been widespread recent interest in learning more about obtaining liquid fuels from non-fossil sources. The combina-tion of rising oil prices, issues of security, climate instability, and pollution, and deepening poverty in rural and agricultural areas, is propelling governments to enact powerful incentives for the use of these fuels, which is in turn sparking in-vestment. In fact, the world is on the verge of an unprecedented increase in the production and use of biofuels for transport. Production of grain-based ethanol and vegetable-oil-based biodiesel is today facing difficulties due to competition with food supply. This book unifies the production of various usable liquid fuels from biomass by using a variety of technologies.

Biofuels appear to be a potential alternative “greener” energy substitute for fos-sil fuels. They are renewable and available throughout the world. Biomass can contribute to sustainable development and globally environmental preservation since it is renewable and carbon neutral.

This book on biofuels attempts to address the needs of energy researchers, chemical engineers, chemical engineering students, energy resources specialists, engineers, agriculturists, crop cultivators, and others interested in a practical tool for pursuing their interests in relation to bioenergy. Each chapter in the book starts with basic/fundamental explanations suitable for general readers and ends with in-depth scientific details suitable for expert readers. General readers will include people interested in learning about solutions for current fuel and environmental crises. Expert readers will include chemists, chemical engineers, fuel engineers, agricultural engineers, farming specialists, biologists, fuel processors, policy mak-ers, environmentalists, environmental engineers, automobile engineers, college

vi Preface

students, research faculties, etc. The book may even be adopted as a text book for college courses that deal with renewable energy and/or sustainability.

The Introduction already comprises one seventh of the book; in these pages emphasis is laid in detail on global energy sources, fossil fuels, and renewables, i.e., biomass, hydro, wind, solar, geothermal, and marine energy sources. The second chapter is entitled “Biomass Feedstocks” and includes main biomass sources, characterization, and valorization. The third chapter is an introduction to biofuels. Furthermore, processing conditions are discussed briefly, as well as al-ternative applications of biorenewable feedstocks in the following chapters. The fourth and fifth chapters on “Liquid and Gaseous Biofuels”, including main liquid biofuels such as bioethanol, biodiesel, biogas, biohydrogen, liquid and gaseous fuels from the Fischer–Tropsch synthesis are addressed in detail. The sixth chapter on “Thermochemical Conversion Processes” covers the utilization of biorenew-ables for engine fuels and chemicals. The seventh and eighth chapters include “Biofuel Economy and Biofuel Policy”.

Trabzon, Turkey, July 2008 Ayhan Demirbas

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Contents

1 Introduction............................................................................................. 1 1.1 Introduction to Energy Sources ..................................................... 1 1.2 Short Supply of Fossil Fuels.......................................................... 4

1.2.1 Petroleum in the World .................................................... 4 1.2.2 Natural Gas as the Fastest Growing Primary Energy

Source in the World ......................................................... 10 1.2.3 Coal as a Fuel and Chemical Feedstock........................... 15

1.3 Introduction to Renewable and Biorenewable Sources ................. 18 1.3.1 Non-combustible Renewable Energy Sources ................. 20 1.3.2 Biorenewable Energy Sources ......................................... 31

References................................................................................................. 43

2 Biomass Feedstocks................................................................................. 45 2.1 Introduction to Biomass Feedstocks.............................................. 45

2.1.1 Definitions........................................................................ 46 2.1.2 Biomass Feedstocks ......................................................... 54

2.2 Biomass Characterization .............................................................. 58 2.2.1 Characterization of Biomass Feedstock and Products ..... 59 2.2.2 Biomass Process Design and Development ..................... 60

2.3 Biomass Fuel Analyses.................................................................. 61 2.3.1 Particle Size and Specific Gravity.................................... 62 2.3.2 Ash Content ..................................................................... 62 2.3.3 Moisture Content ............................................................. 62 2.3.4 Extractive Content............................................................ 62 2.3.5 Element Content............................................................... 63 2.3.6 Structural Constituent Content......................................... 63 2.3.7 The Energy Value of Biomass ......................................... 63

2.4 Biomass Optimization and Valorization........................................ 65 2.4.1 Fuels from Biomass ......................................................... 67 2.4.2 Chemicals from Biomass ................................................. 70

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2.4.3 Char from Biomass .......................................................... 72 2.4.4 Adhesives from Biomass ................................................. 74 2.4.5 Valorization of Wood....................................................... 78

References................................................................................................. 81

3 Biofuels .................................................................................................... 87 3.1 Introduction to Biofuels................................................................. 87

3.1.1 Economic Impact of Biofuels........................................... 90 3.1.2 Environmental Impact of Biofuels ................................... 94

References................................................................................................. 99

4 Biorenewable Liquid Fuels .................................................................... 103 4.1 Introduction to Biorenewable Liquid Fuels ................................... 103

4.1.1 Evaluation of Gasoline-Alcohol Mixtures as Motor Fuel Alternatives............................................... 104

4.1.2 Evaluation of Vegetable Oils and Diesel Fuel Mixtures as Motor Fuel Alternatives............................................... 105

4.2 Bioalcohols .................................................................................... 105 4.2.1 Alternate Fuels to Gasoline.............................................. 106

4.3 Bioethanol ..................................................................................... 108 4.3.1 Synthetic Ethanol Production Processes .......................... 108 4.3.2 Production of Ethanol from Biomass ............................... 109 4.3.3 Sugars from Biomass by Hydrolysis................................ 111 4.3.4 Bioethanol Production by Fermentation

of Carbohydrates .............................................................. 115 4.3.5 Bioethanol Feedstocks ..................................................... 119 4.3.6 Fuel Properties of Ethanol................................................ 120

4.4 Biomethanol .................................................................................. 122 4.5 Vegetable Oils ............................................................................... 126

4.5.1 Alternatives to Diesel Fuel............................................... 131 4.5.2 Vegetable Oil Resources.................................................. 133 4.5.3 The Use of Vegetable Oils as Diesel Fuel........................ 137 4.5.4 New Biorenewable Fuels from Vegetable Oils ................ 143 4.5.5 Properties of Triglycerides............................................... 153 4.5.6 Triglyceride Economy...................................................... 156

4.6 Biodiesel........................................................................................ 156 4.6.1 The History of Biodiesel .................................................. 158 4.6.2 Definitions of Biodiesel ................................................... 160 4.6.3 Biodiesel from Triglycerides via Transesterification....... 162 4.6.4 Recovery of Glycerol ....................................................... 171 4.6.5 Reaction Mechanism of Transesterification..................... 173 4.6.6 Current Biodiesel Production Technologies .................... 176 4.6.7 Biodiesel Production Processes........................................ 180 4.6.8 Basic Plant Equipment Used in Biodiesel Production ..... 185 4.6.9 Fuel Properties of Biodiesels ........................................... 186

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4.6.10 Advantages of Biodiesels................................................. 193 4.6.11 Disadvantages of Biodiesel as Motor Fuel....................... 198 4.6.12 Engine Performance Tests................................................ 199

4.7 Bio-oils from Biorenewables......................................................... 211 4.8 Other Alternate Liquid Fuels ......................................................... 217

4.8.1 Glycerol-Based Fuel Oxygenates for Biodiesel and Diesel Fuel Blends .................................................... 217

4.8.2 P-series Fuels ................................................................... 220 4.8.3 Dimethyl Ether (DME) .................................................... 221 4.8.4 Fischer–Tropsch (FT) Liquid Fuel from Biomass ........... 221 4.8.5 Other Bio-oxygenated Liquid Fuels................................. 222

References................................................................................................. 223

5 Biorenewable Gaseous Fuels .................................................................. 231 5.1 Introduction to Biorenewable Gaseous Fuels ................................ 231 5.2 Biogas............................................................................................ 232

5.2.1 Aerobic Conversion Processes......................................... 233 5.2.2 Anaerobic Conversion Processes ..................................... 233 5.2.3 Biogas Processing ............................................................ 236 5.2.4 Reactor Technology for Anaerobic Digestion.................. 242

5.3 Landfill Gas................................................................................... 245 5.4 Crude Gases from Pyrolysis and Gasification of Biomass ............ 248 5.5 Biohydrogen from Biorenewable Feedstocks................................ 249

5.5.1 Hydrogen from Biorenewable Feedstocks via Thermochemical Conversion Processes ..................... 250

5.5.2 Biohydrogen from Biorenewable Feedstocks .................. 254 5.6 Gaseous Fuels from Fischer–Tropsch Synthesis of Biomass ........ 255 References................................................................................................. 257

6 Thermochemical Conversion Processes ................................................ 261 6.1 Introduction to Thermochemical Conversion Processes................ 261 6.2 Thermal Decomposition Mechanisms of Biorenewables .............. 264 6.3 Hydrothermal Liquefaction of Biorenewable Feedstocks ............. 266

6.3.1 The Role of Water During the HTL Process.................... 270 6.3.2 HTU Applications ............................................................ 270

6.4 Direct Combustion of Biomass...................................................... 271 6.4.1 Combustion Efficiency .................................................... 273

6.5 Direct Liquefaction........................................................................ 275 6.6 Pyrolysis Processes........................................................................ 277

6.6.1 Reaction Mechanism of Pyrolysis.................................... 281 6.7 Gasification Research and Development....................................... 283

6.7.1 Biomass Gasification ....................................................... 285 6.7.2 Biomass Gasification Systems ......................................... 287 6.7.3 Electricity from Cogenerative Biomass Firing

Power Plants..................................................................... 293

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6.7.4 Fischer–Tropsch Synthesis (FTS) .................................... 296 6.7.5 Supercritical Steam Gasification...................................... 299

References................................................................................................. 302

7 Biofuel Economy ..................................................................................... 305 7.1 Introduction to Biofuel Economy .................................................. 305 7.2 Biofuel Economy........................................................................... 307

7.2.1 Estimation of Biofuel Prices ............................................ 309 7.2.2 Biodiesel Economy .......................................................... 309 7.2.3 Bioethanol Economy........................................................ 313 7.2.4 Biorenewable Energy Costs

and Biohydrogen Economy.............................................. 315 References................................................................................................. 316

8 Biofuel Policy........................................................................................... 319 8.1 Introduction to Biofuel Policy ....................................................... 319 8.2 Biofuel Policy................................................................................ 320

8.2.1 Biodiesel Policy ............................................................... 321 8.3 Global Biofuel Projections ............................................................ 325 References................................................................................................. 328

Index ................................................................................................................. 331