Biofuels: Securing the Planet's Future Energy Needs (Green Energy and Technology)

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 © 2009 Springer-Verlag London Limited Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms of licences issued by the Copyright Licensing Agency. Enquiries concerning reproduction outside those terms should be sent to the publishers. The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant laws and regulations and therefore free for general use. The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. Cover design: WMXDesign, Heidelberg, Germany Printed on acid-free paper 9 8 7 6 5 4 3 2 1 springer.com

Preface

Today’s world is facing two critical problems: (1) high fuel prices, and (2) climatic 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 dependent 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 combination 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 investment. 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 fossil 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 indepth 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 makers, environmentalists, environmental engineers, automobile engineers, college

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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 alternative 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 biorenewables for engine fuels and chemicals. The seventh and eighth chapters include “Biofuel Economy and Biofuel Policy”. Trabzon, Turkey, July 2008

Ayhan Demirbas

Contents

1

2

Introduction............................................................................................. 1.1 Introduction to Energy Sources ..................................................... 1.2 Short Supply of Fossil Fuels.......................................................... 1.2.1 Petroleum in the World .................................................... 1.2.2 Natural Gas as the Fastest Growing Primary Energy Source in the World ......................................................... 1.2.3 Coal as a Fuel and Chemical Feedstock........................... 1.3 Introduction to Renewable and Biorenewable Sources ................. 1.3.1 Non-combustible Renewable Energy Sources ................. 1.3.2 Biorenewable Energy Sources ......................................... References.................................................................................................

1 1 4 4 10 15 18 20 31 43

Biomass Feedstocks................................................................................. 2.1 Introduction to Biomass Feedstocks.............................................. 2.1.1 Definitions........................................................................ 2.1.2 Biomass Feedstocks ......................................................... 2.2 Biomass Characterization .............................................................. 2.2.1 Characterization of Biomass Feedstock and Products ..... 2.2.2 Biomass Process Design and Development ..................... 2.3 Biomass Fuel Analyses.................................................................. 2.3.1 Particle Size and Specific Gravity.................................... 2.3.2 Ash Content ..................................................................... 2.3.3 Moisture Content ............................................................. 2.3.4 Extractive Content............................................................ 2.3.5 Element Content............................................................... 2.3.6 Structural Constituent Content......................................... 2.3.7 The Energy Value of Biomass ......................................... 2.4 Biomass Optimization and Valorization........................................ 2.4.1 Fuels from Biomass ......................................................... 2.4.2 Chemicals from Biomass .................................................

45 45 46 54 58 59 60 61 62 62 62 62 63 63 63 65 67 70 vii

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2.4.3 Char from Biomass .......................................................... 2.4.4 Adhesives from Biomass ................................................. 2.4.5 Valorization of Wood....................................................... References.................................................................................................

72 74 78 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 .................................................................... 4.1 Introduction to Biorenewable Liquid Fuels ................................... 4.1.1 Evaluation of Gasoline-Alcohol Mixtures as Motor Fuel Alternatives............................................... 4.1.2 Evaluation of Vegetable Oils and Diesel Fuel Mixtures as Motor Fuel Alternatives............................................... 4.2 Bioalcohols.................................................................................... 4.2.1 Alternate Fuels to Gasoline.............................................. 4.3 Bioethanol ..................................................................................... 4.3.1 Synthetic Ethanol Production Processes .......................... 4.3.2 Production of Ethanol from Biomass ............................... 4.3.3 Sugars from Biomass by Hydrolysis................................ 4.3.4 Bioethanol Production by Fermentation of Carbohydrates .............................................................. 4.3.5 Bioethanol Feedstocks ..................................................... 4.3.6 Fuel Properties of Ethanol................................................ 4.4 Biomethanol .................................................................................. 4.5 Vegetable Oils ............................................................................... 4.5.1 Alternatives to Diesel Fuel............................................... 4.5.2 Vegetable Oil Resources.................................................. 4.5.3 The Use of Vegetable Oils as Diesel Fuel........................ 4.5.4 New Biorenewable Fuels from Vegetable Oils................ 4.5.5 Properties of Triglycerides............................................... 4.5.6 Triglyceride Economy...................................................... 4.6 Biodiesel........................................................................................ 4.6.1 The History of Biodiesel .................................................. 4.6.2 Definitions of Biodiesel ................................................... 4.6.3 Biodiesel from Triglycerides via Transesterification ....... 4.6.4 Recovery of Glycerol ....................................................... 4.6.5 Reaction Mechanism of Transesterification..................... 4.6.6 Current Biodiesel Production Technologies .................... 4.6.7 Biodiesel Production Processes........................................ 4.6.8 Basic Plant Equipment Used in Biodiesel Production ..... 4.6.9 Fuel Properties of Biodiesels ...........................................

103 103 104 105 105 106 108 108 109 111 115 119 120 122 126 131 133 137 143 153 156 156 158 160 162 171 173 176 180 185 186

Contents

4.6.10 Advantages of Biodiesels................................................. 4.6.11 Disadvantages of Biodiesel as Motor Fuel....................... 4.6.12 Engine Performance Tests................................................ 4.7 Bio-oils from Biorenewables......................................................... 4.8 Other Alternate Liquid Fuels......................................................... 4.8.1 Glycerol-Based Fuel Oxygenates for Biodiesel and Diesel Fuel Blends .................................................... 4.8.2 P-series Fuels ................................................................... 4.8.3 Dimethyl Ether (DME) .................................................... 4.8.4 Fischer–Tropsch (FT) Liquid Fuel from Biomass ........... 4.8.5 Other Bio-oxygenated Liquid Fuels................................. References................................................................................................. 5

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193 198 199 211 217 217 220 221 221 222 223

Biorenewable Gaseous Fuels.................................................................. 5.1 Introduction to Biorenewable Gaseous Fuels ................................ 5.2 Biogas............................................................................................ 5.2.1 Aerobic Conversion Processes......................................... 5.2.2 Anaerobic Conversion Processes ..................................... 5.2.3 Biogas Processing ............................................................ 5.2.4 Reactor Technology for Anaerobic Digestion.................. 5.3 Landfill Gas................................................................................... 5.4 Crude Gases from Pyrolysis and Gasification of Biomass ............ 5.5 Biohydrogen from Biorenewable Feedstocks................................ 5.5.1 Hydrogen from Biorenewable Feedstocks via Thermochemical Conversion Processes ..................... 5.5.2 Biohydrogen from Biorenewable Feedstocks .................. 5.6 Gaseous Fuels from Fischer–Tropsch Synthesis of Biomass ........ References.................................................................................................

231 231 232 233 233 236 242 245 248 249

Thermochemical Conversion Processes ................................................ 6.1 Introduction to Thermochemical Conversion Processes................ 6.2 Thermal Decomposition Mechanisms of Biorenewables .............. 6.3 Hydrothermal Liquefaction of Biorenewable Feedstocks ............. 6.3.1 The Role of Water During the HTL Process.................... 6.3.2 HTU Applications ............................................................ 6.4 Direct Combustion of Biomass...................................................... 6.4.1 Combustion Efficiency .................................................... 6.5 Direct Liquefaction........................................................................ 6.6 Pyrolysis Processes........................................................................ 6.6.1 Reaction Mechanism of Pyrolysis.................................... 6.7 Gasification Research and Development....................................... 6.7.1 Biomass Gasification ....................................................... 6.7.2 Biomass Gasification Systems ......................................... 6.7.3 Electricity from Cogenerative Biomass Firing Power Plants.....................................................................

261 261 264 266 270 270 271 273 275 277 281 283 285 287

250 254 255 257

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6.7.4 Fischer–Tropsch Synthesis (FTS) .................................... 296 6.7.5 Supercritical Steam Gasification...................................... 299 References................................................................................................. 302 7

8

Biofuel Economy ..................................................................................... 7.1 Introduction to Biofuel Economy .................................................. 7.2 Biofuel Economy........................................................................... 7.2.1 Estimation of Biofuel Prices ............................................ 7.2.2 Biodiesel Economy .......................................................... 7.2.3 Bioethanol Economy........................................................ 7.2.4 Biorenewable Energy Costs and Biohydrogen Economy.............................................. References.................................................................................................

305 305 307 309 309 313

Biofuel Policy........................................................................................... 8.1 Introduction to Biofuel Policy ....................................................... 8.2 Biofuel Policy................................................................................ 8.2.1 Biodiesel Policy ............................................................... 8.3 Global Biofuel Projections ............................................................ References.................................................................................................

319 319 320 321 325 328

315 316

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

Chapter 1

Introduction

1.1 Introduction to Energy Sources Energy plays a vital role in our everyday lives. Energy is one of the vital inputs to the socio-economic development of any country. There are different ways in which the abundance of energy around us can be stored, converted, and amplified for our use. Energy production has always been a concern for researchers as well as policy makers. Energy sources can be classified into three groups: fossil, renewable, and nuclear (fissile). Fossil fuels were formed in an earlier geological period and are not renewable. The fossil energy sources include petroleum, coal, bitumens, natural gas, oil shales, and tar sands. Today fuels and chemicals are predominately derived from unsustainable mineral resources, petroleum, and coal, which leads to environmental pollution, greenhouse gas emissions, and problems with energy security. The renewable energy sources include biomass, hydro, wind, solar (both thermal and photovoltaic), geothermal, and marine energy sources. The main fissile energy sources are uranium and thorium (Demirbas, 2008). The energy reserves of the world are shown in Table 1.1 (Demirbas, 2006). The world is presently being confronted with the twin crises of fossil fuel depletion and environmental degradation. To overcome these problems, recently renewable energy has been receiving increasing attention due to its environmental benefits and the fact that it is derived from renewable sources such as virgin or cooked vegetable oils (both edible and non-edible). The world’s over-demand of Table 1.1 Energy reserves of the world Deuterium 7.5 × 10

9

Uranium 1.2 × 10 15

5

Coal

Shale oil

Crude oil

Natural gas Tar sands

320.0

79.0

37.0

19.6

6.1

11

Each unit = 1×10 MJ = 1.67×10 bbl crude oil Source: Demirbas, 2006a A. Demirbas, Biofuels, © Springer 2009

1

2

1 Introduction

energy, the oil crisis, and the continuous increase in oil prices have led countries to investigate new and renewable fuel alternatives. Hence, energy sources, like sun, wind, geothermal, hydraulic, nuclear, hydrogen, and biomass have been taken into consideration (Karaosmanoglu and Aksoy, 1988). Fissile materials are those that are defined to be materials that are fissionable by neutrons with zero kinetic energy. In nuclear engineering, a fissile material is one that is capable of sustaining a chain reaction of nuclear fission. Nuclear power reactors are mainly fueled with uranium, the heaviest element occurring in nature in more than trace quantities. The principal fissile materials are uranium-235, plutonium-239, and uranium-233. Petroleum is the largest single source of energy consumed by the world’s population; exceeding coal, natural gas, nuclear and renewables, as shown in Table 1.2 for the year 2005. In fact today, over 80% of the energy we use comes from three fossil fuels: petroleum, coal, and natural gas. While fossil fuels are still being created today by underground heat and pressure, they are being consumed much more rapidly than they are created. Hence, fossil fuels are considered to be nonrenewable; that is, they are not replaced as fast as they are consumed. Unfortunately, petroleum oil is in danger of becoming short in supply. Hence, the future trend is towards using alternate energy sources. Fortunately, technological developments are making the transition possible. About 98% of carbon emissions result from fossil fuel combustion. Reducing the use of fossil fuels would considerably reduce the amount of carbon dioxide and other pollutants produced. This can be achieved by either using less energy altogether or by replacing fossil fuel by renewable fuels. Hence, current efforts focus on advancing technologies that emit less carbon (e.g., high efficiency combustion) or no carbon such as nuclear, hydrogen, solar, wind, geothermal, or on using energy more efficiently and on developing sequestering carbon dioxide emitted during fossil fuel combustion. Another problem with petroleum fuels are their uneven distribution in the world; for example, the Middle East has 63% of the global reserves and is the dominant supplier of petroleum. This energy system is unsustainable because of equity issues as well as environmental, economic, and geopolitical concerns that have far reaching implications. Interestingly, the renewable energy resources are more evenly Table 1.2 Energy consumption in the world (2005) Energy source

% of total

Petroleum Natural gas Coal Nuclear energy power Renewable energy

40 23 23 08 06

Source: Demirbas, 2008

1.1 Introduction to Energy Sources

3

distributed than fossil or nuclear resources. Also the energy flows from renewable resources are more than three orders of magnitude higher than current global energy need. Today’s energy system is unsustainable because of equity issues as well as environmental, economic, and geopolitical concerns that will have implications far into the future. Hence, sustainable renewable energy sources such as biomass, hydro, wind, solar (both thermal and photovoltaic), geothermal, and marine energy sources will play an important role in the world’s future energy supply. For example, it is estimated that by year 2040 approximately half of the global energy supply will come from renewables, and the electricity generation from renewables will be more than 80% of the total global electricity production. Table 1.3 shows the estimated global renewable energy scenario by 2040. In recent years, recovery of the liquid transportation biofuels from biorenewable feedstocks has become a promising method for the future. The biggest difference between biorenewable and petroleum feedstocks is the oxygen content. Biorenewables have oxygen levels ranging from 10–44%, while petroleum has essentially none; making the chemical properties of biorenewables very different from petroleum. For example, biorenewable products are often more polar and some easily entrain water and can therefore be acidic. According to the International Energy Agency (IEA), scenarios developed for the USA and the EU indicate that near-term targets of up to 6% displacement of petroleum fuels with renewable biofuels appear feasible using conventional biofuels, given available cropland. A 5% displacement of gasoline in the EU requires about 5% of the available cropland to produce ethanol while in the USA 8% is required. A 5% displacement of diesel requires 13% of cropland in the USA, and 15% in the EU (IEA, 2004). Table 1.3 Estimated Global renewable energy scenario by 2040

Total consumption (million tons oil equivalent) Biomass Large hydro Geothermal Small hydro Wind Solar thermal Photovoltaic Solar thermal electricity Marine (tidal/wave/ocean) Total renewable energy sources Renewable energy sources contribution (%) Source: Demirbas, 2008

2001

2010

2020

2030

2040

10,038

10,549

11,425

12,352

13,310

01,080 00,022.7 00,043.2 00,009.5 00,004.7 00,004.1 00,000.2 00,000.1 00,000.05 01,365.5 00,013.6

01,313 00,266 00,086 00,019 00,044 00,015 00,002 00,000.4 00,000.1 01,745.5 00,016.6

01,791 00,309 00,186 00,049 00,266 00,066 00,024 00,003 00,000.4 02,694.4 00,023.6

02,483 00,341 00,333 00,106 00,542 00,244 00,221 00,016 00,003 04,289 00,034.7

03,271 00,358 00,493 00,189 00,688 00,480 00,784 00,068 00,020 06,351 00,047.7

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1 Introduction

1.2 Short Supply of Fossil Fuels Our modern way of life is intimately dependent upon fossil fuels, specifically hydrocarbons including petroleum, coal, and natural gas. For example, the plastic in keyboards and computers comes from crude oil or natural gas feedstocks. One of our most important sources of energy today is fossil fuels. Fossil fuels are found deposited in rock formations. Fossils are non-renewable and relatively rare resources. More importantly, the major energy demand is fulfilled by fossil fuels. Today, oil and natural gas are important drivers of the world economy. Oil and natural gas are also found in beds of sedimentary rock. Fossil fuels or mineral fuels are fossil source fuels, that is, hydrocarbons found within the top layer of the Earth’s crust. It is generally accepted that they formed from the fossilized remains of dead plants and animals by exposure to heat and pressure in the Earth’s crust over hundreds of millions of years.

1.2.1 Petroleum in the World Petroleum (derived from the Greek petra – rock and elaion – oil or Latin oleum – oil) or crude oil, sometimes colloquially called black gold or “Texas tea”, is a thick, dark brown or greenish liquid. It is used to describe a broad range of hydrocarbons that are found as gases, liquids, or solids beneath the surface of the Earth. The two most common forms are natural gas and crude oil. Petroleum consists of a complex mixture of various hydrocarbons, largely of the alkane and aromatic compounds, but may vary much in appearance and composition. The physical properties of petroleum vary greatly. The color ranges from pale yellow through red and brown to black or greenish, while by reflected light it is, in the majority of cases, of a green hue. Petroleum is a fossil fuel because it was formed from the remains of tiny sea plants and animals that died millions of years ago, and sank to the bottom of the oceans. This organic mixture was subjected to enormous hydraulic pressure and geothermal heat. Over time, the mixture changed, breaking down into compounds made of hydrocarbons by reduction reactions. This resulted in the formation of oil-saturated rocks. The oil rises and is trapped under non-porous rocks that are sealed with salt or clay layers. According to well accepted biogenic theory, crude oil, like coal and natural gas, is the product of compression and heating of ancient vegetation and animal remains over geological time scales. According to this theory, an organic matter is formed from the decayed remains of prehistoric marine animals and terrestrial plants. Over many centuries this organic matter, mixed with mud, is buried under thick sedimentary layers. The resulting high pressure and heat causes the remains to transform, first into a waxy material known as kerogen, and then into liquid and gaseous hydrocarbons by process of catagenesis. The fluids then migrate through adjacent rock layers until they become trapped underground in porous rocks

1.2 Short Supply of Fossil Fuels

5

termed reservoirs, forming an oil field, from which the liquid can be removed by drilling and pumping. The reservoirs are at different depths in different parts of the world, but the typical depth is 4–5 km. The thickness of the oil layer is about 150 m and is generally termed the “oil window”. Three important elements of an oil reservoir are: a rich source rock, a migration conduit, and a trap (seal) that forms the reservoir. According to the not well accepted abiogenic theory, the origin of petroleum is natural hydrocarbons. The theory proposes that large amounts of carbon exist naturally on the planet, some in the form of hydrocarbons. Due to it having a lower density than aqueous pore fluids, hydrocarbons migrate upward through deep fracture networks. The first oil wells were drilled in China in the 4th century or earlier. The wells, as deep as 243 meters, were drilled using bits attached to bamboo poles. The oil was burned to produce heat needed in the production of salt from brine evaporation. By the 10th century, extensive bamboo pipelines connected oil wells with salt springs. Ancient Persian tablets indicate the medicinal and lighting uses of petroleum in the upper echelons of their society. In the 8th century, the streets of the newly constructed Baghdad were paved with tar derived from easily accessible petroleum from natural fields in the region. In the 9th century, oil fields were exploited to produce naphtha in Baku, Azerbaijan. These fields were described by the geographer Masudi in the 10th century, and the output increased to hundreds of shiploads in 13th century as described by Marco Polo. The modern history of petroleum began in 1846, with the discovery of the refining of kerosene from coal by Atlantic Canada’s Abraham Pineo Gesner. Poland’s Ignacy Łukasiewicz discovered a means of refining kerosene from the more readily available “rock oil” (“petroleum”) in 1852; and in the following year the first rock oil mine was built in Bobrka, near Krosno in southern Poland. The discovery rapidly spread around the world, and Meerzoeff built the first Russian refinery in the mature oil fields of Baku in 1861, which produced about 90% of the world’s oil. In fact, the battle of Stalingrad was fought over Baku (now the capital of the Azerbaijan Republic). The first commercial oil well in North America was drilled by James Miller Williams in 1858 in Oil Springs, Ontario, Canada. In the following year, Edwin Drake discovered oil near Titusville, Pennsylvania, and pioneered a new method for producing oil from the ground, in which he drilled using piping to prevent borehole collapse, allowing for the drill to penetrate deeper into the ground. Previous methods for collecting oil had been limited. For example, ground collection of oil consisted of gathering it from where it occurred naturally, such as from oil seeps or shallow holes dug into the ground. The methods of digging large shafts into the ground also failed, as collapse from water seepage almost always occurred. The significant advancement that Drake made was to drive a 10 meter iron pipe through the ground into the bedrock below. This allowed Drake to drill inside the pipe, without the hole collapsing from the water seepage. The principle behind this idea is still employed today by many companies for petroleum drilling.

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1 Introduction

Drake’s well was 23 meters deep, which is very shallow compared to today’s well depth of 1000–4000 meters. Although technology has improved the odds since Edwin Drake’s days, petroleum exploration today is still a gamble. For example, only about 33 in every 100 exploratory wells have oil, and the remaining 67 come up “dry”. For about 10 years Pennsylvania was the one great oil producer of the world, but since 1870 the industry has spread all over the globe. From the time of the completion of the first flowing well on the Baku field, Russia has ranked second on the list of producing countries, whilst Galicia and Romania became prominent in 1878 and 1880, respectively. Sumatra, Java, Burma, and Borneo, where active development began in 1883, 1886, 1890, and 1896, bid fair to rank before long among the chief sources of the oil supplies of the world. Before the 1850s, Americans often used whale oil to light their homes and businesses. Drake refined the oil from his well into kerosene for lighting, which was used till the discovery of light bulbs. Gasoline and other products made during refining were simply discarded due to lack of use. In 1892, the “horseless carriage” solved this problem since it required gasoline. By 1920 there were nine million motor vehicles in USA and many gas stations to supply gasoline. 1.2.1.1

Properties of Petroleum, Crude Oil Refining, and World Petroleum Reserves

Crude oil is a complex mixture that is between 50% and 95% hydrocarbon by weight. The first step in refining crude oil involves separating the oil into different hydrocarbon fractions by distillation. An oil refinery cleans and separates the crude oil into various fuels and byproducts, including gasoline, diesel fuel, heating oil, and jet fuel. Main crude oil fractions are listed in Table 1.4. Since various components boil at different temperatures, refineries use a heating process called distillation to separate the components. For example, gasoline has a lower boiling point than kerosene, allowing the two to be separated by heating to different temperatures. Another important job of the refineries is to remove contaminants from Table 1.4 Main crude oil fractions Fraction

Boiling range (K)

Number of carbon atoms

Natural gas Petroleum ether Ligroin (light naphtha) Gasoline Jet fuel Kerosene No. 2 diesel fuel Fuel oils Lubricating oils Asphalt or petroleum coke

548 >673 Non-volatile residue

C1 to C4 C5 to C6 C6 to C7 C5 to C12, and cycloalkanes C8 to C14, and aromatics C10 to C16, and aromatics C10 to C20, and aromatics C12 to C70, and aromatics >C20 Polycyclic structures

1.2 Short Supply of Fossil Fuels

7

the oil. For example, sulfur from gasoline or diesel to reduce air pollution from automobile exhausts. After processing at the refinery, gasoline and other liquid products are usually shipped out through pipelines, which are the safest and cheapest way to move large quantities of petroleum across land. An important non-fuel use of petroleum is to produce chemical raw materials. The two main classes of petrochemical raw materials are olefins (including ethylene and propylene) and aromatics (including benzene and xylene isomers), both of which are produced in large quantities. A very important aspect of petrochemicals is their extremely large scale. The olefins are produced by chemical cracking by using steam or catalysts, and the aromatics are produced by catalytic reforming. These two basic building blocks serve as feedstock to produce a wide range of chemicals and materials including monomers, solvents, and adhesives. From the monomers, polymers or oligomers are produced for use as plastics, resins, fibers, elastomers, certain lubricants, and gels. The oil industry classifies “crude” according to its production location (e.g., “West Texas Intermediate, WTI” or “Brent”), relative density (API gravity), viscosity (“light”, “intermediate”, or “heavy”), and sulfur content (“sweet” for low sulfur, and “sour” for high sulfur). Additional classification is due to conventional and non-conventional oil as shown in Table 1.5. Oil shale is a sedimentary rock that contains the solid hydrocarbon wax kerogen in tightly packed limy mud and clay. The kerogen may be decomposed at elevated temperatures (723 K), resulting in an oil suitable for refinery processing (Dorf, 1977). The oil shale layer is not hot enough to complete the oil generation. For the final step the kerogen must be heated up to 775 K and molecularly combine with additional hydrogen to complete the oil formation. This final process must be performed in the refinery and needs huge amounts of energy that otherwise have been provided by the geological environment during oil formation (Demirbas, 2000). The kerogen is still in the source rock and can not accumulate in oil fields. Typically, the ratio of kerogen to waste material is very low, making the mining of oil shales unattractive. Hence, due to a combination of environmental and economic concerns, it is very unlikely that oil shale mining will ever be performed at large scale, though in some places it has been utilized in small quantities. However, the shale oil reserves in the world are greater than those of crude oil or natural gas, as shown in Table 1.1.

Table 1.5 Classification of oils Class

Viscosity of oil (measured in °API)

Light crude Medium oil Heavy oil Deep sea oil above 500 meters water depth Extra heavy oil below (including tar sands) Oil shale Bitumen from tar sands

>31.1 022.3–31.1