The term fossil refers to an earlier geologic age. Fossil fuels were formed a long time ago and are not renewable. Fossil energy sources are petroleum (crude oil), coal, bitumens, natural gas, oil shales, and tar sands. During the last 200 years, developed countries have shifted their energy consumption toward fossil fuels. 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. In fact, today over 80% of the energy we use comes from three fossil fuels: petroleum, coal, and natural gas. Unfortunately, oil is in danger of becoming scarce.

Another problem with petroleum fuels is 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.

The current global energy mix consists of oil (36%), natural gas (24%), coal (28%), nuclear (6%), and renewable energy such as hydro, wind, and solar (about 7%). Once the energy picture has been established we will explore the effect the projected changes in energy supply may have on the world population. Petroleum is the largest single source of energy consumed by the world’s population, exceeding coal, natural gas, nuclear, hydro, and renewables. While fossil fuels are still being created today by underground heat and pressure, they are being consumed more rapidly than they are being created. Hence, fossil fuels are considered nonrenew­able; that is, they are not replaced as fast as they are consumed. And due to oil’s aforementioned looming scarcity, the future trend is toward using alternative energy sources. Fortunately, the technological advances are making the transition possible (Kirtay 2009).

The word petroleum comes from the Greek word petra, or rock, and Latin word oleum, oil. Oil is a thick, dark brown or greenish liquid found in reservoirs in sedi­mentary rock. Tiny pores in the rock allowed the petroleum to seep in. These “reser­voir rocks” hold the oil like a sponge, confined by other, nonporous layers that form a trap. Petroleum 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 alkane and aromatic compounds. 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.

Table 1.1 shows crude oil production data for various regions (IEA 2007). The Middle East produces 32% of the world’s oil, and, more importantly, it has 64% of the total proven oil reserves in the world. Oil fields follow a size distribution consisting of a very few large fields and many smaller ones. This distribution is illustrated by the fact that 60% of the world’s oil supply is extracted from only 1% of the world’s active oil fields. As one of these very large fields plays out it can require the development of hundreds of small fields to replace its production.

Some definitions will be useful. “Petroleum” and “oil” are used interchange­ably to include crude oil, shale oil, oil sands, and natural gas liquids (NGLs). The word petroleum generally refers to crude oil or the refined products obtained from the processing of crude oil (gasoline, diesel fuel, heating oil, etc.). Crude oil (raw petroleum) is separated into fractions by fractional distillation. The fractions at the top are lower than those at the bottom. The heavy bottom fractions are often cracked into lighter, more useful products. All of the fractions are processed further in other refining units. The main crude oil fractions are shown in Table 1.2.

Crude oil is separated by boiling points into six main grades of hydrocarbons: refinery gas (used for refinery fuel), gasoline (naphthas), kerosene, light oils (diesel oil or diesel fuel) and heavy gas oils (fuel oil), and long residue. This initial sep-

Table 1.1 1973 and 2006 regional shares of crude oil production (%) Region 1973 2006 Middle East 37.0 31.1 OECD 23.6 23.2 Former USSR 15.0 15.2 Africa 10.0 12.1 Latin America 8.6 9.0 Asia excluding China 3.2 4.5 China 1.9 4.7 Non-OECD Europe 0.7 0.2 Total (Millions of tons) 2,867 3,936

Table 1.2 Main crude oil fractions
Component	Boiling range, K	Number of carbon atoms
Natural gas	< 273	C1 to C4
Liquefied petroleum gas	231-273	C3 to C4
Petroleum ether	293-333	C5 to C6
Ligroin (light naphtha)	333-373	C6 to C7
Gasoline	313-478	C5 to C12, and cycloalkanes
Jet fuel	378-538	C8 to C14, and aromatics
Kerosene	423-588	C10 to C16, and aromatics
No. 2 diesel fuel	448-638	C10 to C22, and aromatics
Fuel oils	> 548	C12 to C70, and aromatics
Lubricating oils	> 673	> C20
Asphalt or petroleum coke	Nonvolatile residue	Polycyclic structures

aration is done by distillation. The first step in the refining of crude oil, whether in a simple or a complex refinery, is the separation of the crude oil into fractions (fractionation or distillation). These fractions are mixtures containing hydrocarbon compounds whose boiling points lie within a specified range.

A diesel engine burns fuel oil rather than gasoline and differs from the gasoline engine in that it uses compressed air in the cylinder rather than a spark to ignite the fuel. Diesel or diesel fuel in general is any fuel used in diesel engines. Diesel engines are used mainly in heavy vehicles. The main advantage of the diesel engine is that the level of efficiency is greater than in the Otto cycle engine. This means that a greater part of the energy content of the fuel is used. The efficiency of a diesel engine is at best 45%, compared to 30% for the Otto engine.

Diesel fuel is produced by distilling raw oil extracted from bedrock. Diesel is a fossil fuel. Diesel fuel consists of hydrocarbons with between 9 and 27 carbon atoms in a chain as well as a smaller amount of sulfur, nitrogen, oxygen, and metal compounds. It is a general property of hydrocarbons that the auto-ignition temper­ature is higher for more volatile hydrocarbons. The hydrocarbons present in diesel fuels include alkanes, naphthenes, olefins, and aromatics. In addition, other sub­stances are added to improve the characteristics of diesel fuel. Its boiling point is between 445 and 640 K. A good diesel fuel is characterized by low sulfur and aro­matic content, good ignition quality, the right cold weather properties, and a low content of pollutants, as well as the right density, viscosity, and boiling point.

Diesel fuel comes in several different grades, depending upon its intended use. Like gasoline, diesel fuel is not a single substance but a mixture of various petroleum-derived components, including paraffins, isoparaffins, napthenes, olefins, and aromatic hydrocarbons, each with their own physical and chemical properties.

Unlike spark-ignition engines, the power and economy of diesel engines are comparatively insensitive to fuel volatility. There is some indirect impact in that less volatile fuels have higher heating values (HHVs). Conversely, fuels with higher front-end volatility tend to improve starting and warm-up performance and reduce smoke. Ideal fuel volatility requirements will vary based on engine size and de­sign, speed and load conditions, and atmospheric conditions. As an example, more volatile fuels may provide better performance for fluctuating loads and speeds such as those experienced by trucks and buses.

The viscosity of diesel fuel is an important property that impacts the performance of fuel injection systems. Some injection pumps can experience excessive wear and power loss due to injector or pump leakage if viscosity is too low. If fuel viscosity is too high, it may cause too much pump resistance and filter damage and adversely affect fuel spray patterns. High fuel viscosity can cause an injector spray pattern with poor fuel dispersion.

Gasoline is a petroleum-derived liquid mixture, primarily used as fuel in internal combustion engines, specifically in spark-ignition engines. In the Otto cycle engine a mixture of gasoline and air is compressed and then ignited by a spark plug.

The important characteristics of gasoline are density, vapor pressure, distillation range, octane number, and chemical composition. To be attractive, a motor gasoline must have (a) the desired volatility, (b) antiknock resistance (related to octane rat­ing), (c) good fuel economy, (d) minimal deposition on engine component surfaces, and (e) complete combustion and low pollutant emissions.

The density of gasoline is 0.71 to 0.77 kg/L. Gasoline is more volatile than diesel oil, Jet-A, or kerosene, not only because of its base constituents but because of the additives that are put into it. The final control of volatility is often achieved by blending with butane. The desired volatility depends on the ambient temperature: in hotter climates, gasoline components of higher molecular weight, and thus lower volatility, are used. In cold climates, too little volatility results in cars failing to start. In hot climates, excessive volatility results in what is known as “vapor lock,” where combustion fails to occur because the liquid fuel has changed into a gaseous fuel in the fuel lines, rendering the fuel pump ineffective and starving the engine of fuel.

An important characteristic of gasoline is its octane number or octane rating, which is a measure of how resistant gasoline is to the abnormal combustion phe­nomenon known as predetonation (also known as knocking, pinging, spark knock, and other names). Octane number is measured relative to a mixture of 2,2,4-tri- methylpentane and n-heptane. Octane number is a measure of the gasoline quality for the prevention of early ignition, which leads to cylinder knocks. Higher octane numbers are preferred in internal combustion engines. For gasoline production, aro­matics, naphthenes, and isoalkanes are highly desirable, whereas olefins and n-par — affins are less desirable.

The typical composition of gasoline hydrocarbons (% volume) is as follows: 4 to 8% alkanes, 2 to 5% alkenes, 25 to 40% isoalkanes, 3 to 7% cycloalkanes, to 4% cycloalkenes, and 20 to 50% total aromatics (0.5 to 2.5% benzene). Ad-

Table 1.3 Physical and chemical properties of gasoline Property Information Color Colorless to pale brown or pink Average molecular weight 108 Density, kg/L 0.7-0.8 Flash point, K 227.2 Explosive limits in air 1.3-6.0% Flammability limits 1.4-7.4% Autoignition, K 553-759 Boiling point, K Initially 312 After 10% distillate 333 After 50% distillate 383 After 90% distillate 443 Final boiling point 477 Solubility Water at 293 K Insoluble Absolute ethanol Soluble Diethyl ether Soluble Chloroform Soluble Benzene Soluble

ditives and blending agents are added to the hydrocarbon mixture to improve the performance and stability of gasoline. These compounds include antiknock agents, antioxidants, metal deactivators, lead scavengers, antirust agents, anti-icing agents, upper-cylinder lubricants, detergents, and dyes. The physical and chemical proper­ties of gasoline are given in Table 1.3. Table 1.4 shows the major components of gasoline.

Worldwide coal production is roughly equal to gas production and only second to that of oil. Coal is produced in deep mines (hard coal) and in surface mines (lignite). Coal has played a key role as a primary source of organic chemicals as well as a primary energy source. Coal may become more important both as an energy source and as the source of carbon-based materials, especially aromatic chemicals, in the 21st century (Schobert and Song 2002).

Table 1.4 Major components of gasoline Component Composition, % by weight n-alkanes C5 3.0 C6 11.6 C7 1.2 C9 0.7 C10-C13 0.8 Total n-alkanes 17.3 Branched alkanes C4 2.2 C5 15.1 C6 8.0 C7 1.9 C8 1.8 C9 2.1 C10-C13 1.0 Total branched alkanes 32.0 Cycloalkanes C6 3.0 C7 1.4 C8 0.6 Total cycloalkanes 5.0 Olefins C6 1.8 Total olefins 1.8 Aromatics Benzene 3.2 Toluene 4.8 Xylenes 6.6 Ethylbenzene 1.4 C3-benzenes 4.2 C4-benzenes 7.6 Others 2.7 Total aromatics 30.5

The first known and oldest fossil fuel is coal. Coal has played a key role as a pri­mary energy source as well as a primary source of organic chemicals. It is a com­plex, heterogeneous combustible material made up of portions that are either useful (carbon and hydrogen) or useless (diluents such as moisture, ash, and oxygen or con­taminants such as sulfur and heavy metals). Coal can be defined as a sedimentary rock that burns. It was formed by the decomposition of plant matter and is a com­plex substance that can be found in many forms. Coal is divided into four classes: anthracite, bituminous, subbituminous, and lignite. Elemental analysis gives em­pirical formulas such as C137H97O9NS for bituminous coal and C240H90O4NS for high-grade anthracite.

Coal accounts for 26% of the world’s primary energy consumption and 37% of the energy consumed worldwide for electricity generation. For coal to remain com­petitive with other sources of energy in the industrialized countries of the world, continuing technological improvements in all aspects of coal extraction are nec­essary. Nearly all the different forms of coal are used in one way or another. For instance, peat has been used for burning in furnaces, lignite is used in power sta­tions and home (residential) stoves, whereas bituminous coal is used extensively for the generation of electricity.

Coal is formed from plant remains that have been compacted, hardened, chemi­cally altered, and metamorphosed underground by heat and pressure over millions of years. When plants die in a low-oxygen swamp environment, instead of decay­ing by bacteria and oxidation, their organic matter is preserved. Over time, heat and pressure remove the water and transform the matter into coal. The first step in coal formation yields peat, compressed plant matter that still contains leaves and twigs. The second step is the formation of brown coal or lignite. Lignite has already lost most of the original moisture, oxygen, and nitrogen. It is widely used as a heating fuel but is of little chemical interest. The third stage, bituminous coal, is also widely utilized as a fuel for heating. Bituminous is the most abundant form of coal and is the source of coke for smelting, coal tar, and many forms of chemically modified fuels. Table 1.5 shows the world’s recoverable coal reserves (IEA 2007).

The role of natural gas (NG) in the world’s energy supply is growing rapidly. NG is the fastest growing primary energy source in the world. The reserves and resources of conventional NG are comparable in size to those of conventional oil, but global gas consumption is still considerably lower than that of oil. Proven gas reserves are not evenly distributed around the globe: 41% are in the Middle East and 27% in Russia. A peak in conventional gas production may occur between 2020 and 2050. NG accounts today for 25% of world primary energy production (Jean — Baptiste and Ducroux 2003). Because it is cleaner fuel than oil or coal and not as controversial as nuclear power, gas is expected to be the fuel of choice for many countries in the future. Increasing demand for NG is expected in all sectors of the world, as resource availability, rate of depletion, and environmental considerations all favor its use. World NG reserves by country are given in Table 1.6.

Table 1.5 World’s recoverable coal reserves Country Bituminous including anthracite Subbituminous Lignite United States 115,891 101,021 33,082 China 62,200 33,700 18,600 India 82,396 — 2,000 South Africa 49,520 — — Kazakhstan 31,100 — 3,000 Brazil — 11,929 — Colombia 6,267 381 — Canada 3,471 871 2,236 Indonesia 790 1,430 3,150 Botswana 4,300 — — Uzbekistan 1,000 — 3,000 Turkey 278 761 2,650 Pakistan — 2,265 — Thailand — — 1,268 Chile 31 1,150 — Mexico 860 300 51 Peru 960 — 100 Kyrgyzstan — — 812 Japan 773 — — Korea 300 300 — (Dem. People’s Rep.) Zimbabwe 502 Venezuela 479 — — Philippines — 232 100 Mozambique 212 — — Swaziland 208 — — Tanzania 200 — — Others 449 379 27

Table 1.6 World natural gas reserves by country
Country	Percent of world total
Russian Federation	33.0
Iran	15.8
Qatr	5.8
United Arab Emirates	4.1
Saudi Arabia	4.0
United States	3.3
Venezuela	2.8
Algeria	2.5
Nigeria	2.4
Iraq	2.1
Turkmenistan	2.0
Top 20 countries	89.0
Rest of world	11.0