A P-series fuel is a unique blend of liquefied petroleum gas liquids, ethanol, hydro­carbons, and methyltetrahydrofuran (MeTHF). P-series fuels are blends of ethanol, MeTHF, and pentanes, with butane added for blends that would be used in severe cold-weather conditions to meet cold start requirements. P-series fuels are made pri­marily from biorenewable resources and provide significant emissions benefits over reformulated gasoline. A P-series fuel can be mixed with gasoline in any proportion and used in FFVs. P-series fuels are clear, colorless, 89- to 93-octane liquid blends that are formulated for use in FFVs. Like gasoline, low-vapor-pressure formulations are produced to prevent excessive evaporation during summer and high-vapor-pres­sure formulations are used for easy starting in the winter. P-series fuels are at least 60% nonpetroleum. They also have many environmental benefits. Because a major­ity of the components that make up P-series fuels come from domestically produced renewable resources, this alternative fuel promotes both energy security and envi­ronmental quality. P-series fuels could be 96% derived from domestic resources and could reduce fossil energy use by 49 to 57% and petroleum use by 80% rela­tive to gasoline. Greenhouse gas emissions from the production and use of P-series fuels are substantially better than those from gasoline. Each unit of P-series fuel emits approx. 50% less carbon dioxide, 35% less hydrocarbons, and 15% less car­bon monoxide than gasoline. It also has 40% less ozone-forming potential.

The idea of producing biodiesel from microalgae that accumulate high amounts of oil was a main focus in the NREL project (Sheehan et al. 1998). Many species of algae accumulate large amounts of oils that to a large extent are made up of triacylglycerols consisting of three fatty acids bound to glycerol. The algal oil is converted into biodiesel through a transesteriflcation process. Oil extracted from the algae is mixed with alcohol and an acid or a base to produce the fatty acid methylesters that makes up the biodiesel (Chisti 2007). A number of algae strains with good potential for making biodiesel were identified.

Some microalgae appear to be a suitable group of oleaginous microorganisms for lipid production (Chisti 2007). Microalgae have been suggested as potential candi­dates for fuel production because of a number of advantages including higher pho­tosynthetic efficiency, higher biomass production, and higher growth rate compared to other energy crops (Milne et al. 1990; Dote et al. 1994; Minowa et al. 1995). Moreover, according to the biodiesel standard published by the American Society for Testing Materials (ASTM), biodiesel from microalgal oil is similar in properties to standard biodiesel and is also more stable according to their flash point values. Figure 6.4 shows a biodiesel product obtained from microalgae.

Figure 6.4 Biodiesel product obtained from microalgae

5.1 Introduction

The world has been confronted with an energy crisis due to the depletion of finite fossil fuel resources. The use of fossil fuels as energy is now widely accepted as unsustainable due to depleting resources and also due to the accumulation of green­house gases in the atmosphere.

Biomass provides a number of local environmental gains. Biomass resources in­clude agricultural and forest residues, algae and grasses, animal manure, organic wastes, and biomaterials. Supply of these resources is dominated by traditional biomass used for cooking and heating, especially in rural areas of developing coun­tries. Biomass mainly now represents only 3% of primary energy consumption in industrialized countries. However, much of the rural population in developing coun­tries, which represents about 50% of the world’s population, is reliant on biomass, mainly in the form of wood, for fuel.

Energy forestry crops have a much greater diversity of wildlife and flora than the alternative land use, which is arable or pasture land. In industrialized countries, it is expected that the main biomass processes utilized in the future will be direct com­bustion of residues and wastes for electricity generation, bioethanol and biodiesel as liquid fuels, and combined heat and power production from energy crops. The future of biomass electricity generation lies in biomass-integrated gasification/gas turbine technology, which offers high energy-conversion efficiencies. In the future, biomass will have the potential to provide a cost-effective and sustainable supply of energy, while at the same time aiding countries in meeting their greenhouse-gas-reduction targets. By the year 2050, it is estimated that 90% of the world’s population will live in developing countries.

Prior to the establishment of the US Department of Energy’s (DOE) Aquatic Species Program, very little work had been conducted on biofuel production from lipid-accumulating algae. While the general idea of using algae for energy produc­tion has been around for over 50 years (Meier 1955), the concept of using lipids derived from algal cells to produce liquid fuels arose more recently. The research of liquid fuel produced from microalgae was begun in the mid-1980s in 20 centuries

A. Demirbas, M. Fatih Demirbas, Algae Energy DOI 10.1007/978-1-84996-050-2, © Springer 2010

(Xu et al. 2006). Aquatic biomass may represent a convenient solution because it has a higher growth rate than terrestrial plants. Microalgae have been extensively studied so far, as they can grow in both fresh — and saltwater environments. Algal biomass contains three main components: carbohydrates, proteins, and natural oils. Algae are a promising source of renewable energy.

Microalgae can potentially be employed for the production of biofuels in an eco­nomically effective and environmentally sustainable manner. Microalgae have been investigated for the production of a number of different biofuels including biodiesel, bio-oil, biosyngas, and biohydrogen. The production of these biofuels can be cou­pled with flue gas CO2 mitigation, wastewater treatment, and the production of high — value chemicals. Developments in microalgal cultivation and downstream process­ing are expected to further enhance the cost effectiveness of biofuel from microalgae (Li etal. 2008).

Algae, like corn, soybeans, sugar cane, Jatropha, and other plants, use photosyn­thesis to convert solar energy into chemical energy. They store this energy in the form of oils, carbohydrates, and proteins. The plant oil can be converted into bio­diesel; hence biodiesel is a form of solar energy. The more efficient a particular plant is at converting that solar energy into chemical energy, the better it is from a bio­diesel perspective, and algae are among the most photosynthetically efficient plants on Earth.

Algae for biofuels have been studied for many years for the production of hy­drogen, methane, vegetable oils (for biodiesel), hydrocarbons, and ethanol. Algal hydrogen production has been extensively researched for over three decades, but no mechanism for it has ever been demonstrated.

Algae can be used to produce biofuel, called algae fuel, algal fuel, or even third- generation biofuel. Compared with second-generation biofuels, algal fuels have a higher yield: they can produce 30 to 100 times more energy per hectare compared to terrestrial crops.

The advantages and disadvantages of biofuel production using microalgae are shown in Table 5.1. Among the advantages are that the high growth rate of microal­gae makes it possible to satisfy massive demand on biofuels using limited land re­sources without causing potential biomass deficit, microalgal cultivation consumes less water than land crops, the tolerance of microalgae to high CO2 content in gas streams allows high-efficiency CO2 mitigation, microalgal farming could be poten­tially more cost effective than conventional farming, and nitrous oxide release could be minimized when microalgae are used for biofuel production.

On the other hand, one of the major disadvantages of microalgae for biofuel pro­duction is the low biomass concentration in a microalgal culture due to the limited light penetration, which in combination with the small size of algal cells makes the harvest of algal biomasses relatively costly. The higher capital costs and the rather intensive care required by a microalgal farming facility compared to a conventional agricultural farm is another factor that impedes the commercial implementation of the biofuels-from-microalgae strategy.

The amount of biomass available is limited because plants, on average, capture only about 0.1% of the solar energy reaching the Earth (Pimentel and Pimentel 1996). Temperature, water availability, soil nutrients, and the feeding pressure of herbi­vores all limit biomass production in any given region. Under optimal growing con­ditions, natural and agricultural vegetation produce about 12 million kcal/ha/year (approx. 3 t/ha dry biomass). The productive ecosystems in the world total an es­timated 50 billion ha, excluding the icecaps. Marine ecosystems occupy approx. 36.5 billion ha, while the terrestrial ecosystems occupy approx. 13.5 billion ha.

Sustainable production of biomass will limit supply. The total biomass produced is approx. 77 billion t or approx. 12.6 t/person/year (Pimentel 2001). Globally, suit­able abandoned cropland and pastureland amounts to approx. 1.5 million square miles. Realistically, energy crops raised on this land could be expected to yield about 27 exajoules (EJ) of energy each year (1EJ = 1018 J). This is a huge amount of energy, equivalent to 172 million barrels of oil. In 2003 the EU biomass pro­duction was about 69 Mtoe, covering about 4% of EU energy needs; the production potential is estimated to increase to 186 to 189Mtoe in 2010, to 215 to 239Mtoe in 2020, and up to 243 to 316 Mtoe in 2030 (EEA 2005). One analysis carried out by the UN Conference on Environment and Development (UNCED) estimates that biomass could potentially supply about half of the present world primary energy consumption by the year 2050 (Ramage and Scurlock 1996).

Global biomass production on the Earth’s land surface is equal to 4,560 EJ (the gross primary production), of which half is lost by autotrophic respiration and de­composition, leaving 2,280 EJ (net primary production or NPP) (Smeets et al. 2007). The availability of the NPP for use in food and energy production is restricted by many factors, e. g., logistics, economics, or legal restraints. Without intervention this NPP is in balance with natural decomposition. There are three types of biomass energy sources: dedicated bioenergy crops, agricultural and forestry residues and waste, and forest growth. The bioenergy potential in a region is limited by vari­ous factors, such as the demand for food, industrial round wood, traditional wood fuel, and the need to maintain existing forests for the protection of biodiversity. The global potential of bioenergy production from agricultural and forestry residues and wastes was calculated to be 76 to 96EJ/year by the year 2050. The potential of bioenergy production from surplus forest growth was calculated to be 74 EJ/yr by 2050 (Smeets et al. 2007).

Biomass resources can be divided into six categories: energy crops on surplus cropland, energy crops on degraded land, agricultural residues, forest residues, an­imal manure, and organic wastes. The range of the global potential of primary biomass (in about 50 years) is very broadly quantified at 33 to 1,135EJ/year (Hoog — wijk et al. 2003).

Plant height, main stem diameter, stems, leaves, leaf length, leaflet width and length, and leaflets are important traits that are used to estimate herbage yield (Ates and Tekeli 2005). Trait characterization is part of sustainable crop systems. The im­provement of crops for tolerance to various forms of abiotic stress and for utilization in semiarid regions can be achieved by using trait analyses in multiple environments. This involves analyzing crop phenotypes for stress physiology and agronomic traits (e. g., high yield, grain quality) in different locations under different growth environ­ments.

There is a need to accelerate breeding applications to improve quality traits in crops that contribute to food security, health, and agricultural sustainability. The complex genetics and quality traits of many crops are difficult to manipulate by conventional breeding. There is a lack of useful variability for key quality traits and stress tolerance in cultivars and adapted germplasm.

In the microbial fermentation of biomass, different waste materials can be used as substrates. A new and unique process has been developed where substrates such as carbohydrates are fermented by a consortium of bacteria; they produce hydro­gen and carbon dioxide. Highly concentrated organic waste water is one of the most abundantly available biomasses that can be exploited for microbial conver­sion into hydrogen (Nath and Das 2003). Municipal solid wastes and digested sewage sludge have the potential to produce large amounts of hydrogen by sup­pressing the production of methane through the introduction of low-voltage elec­tricity into the sludge. The substrate from the acidogenesis of fruit and vegetable market wastes gives higher hydrogen evolution rates (about threefold) compared to synthetic medium. A mixed culture of photosynthetic anaerobic bacteria provides a method of utilization of a variety of resources for biohydrogen production (Miyake et al. 1990).

Hydrogen produced by photosynthetic organisms is one of a range of popular scenarios for renewable energy. Hydrogen can be produced by algae under specific conditions. Three different ways to produce hydrogen have been proposed: direct and indirect photolysis and ATP-driven hydrogen production. Direct photolysis is possible when the resulting hydrogen and oxygen are continuously flushed away.

Photosynthetic water splitting are coupled, results in the simultaneous production of hydrogen and oxygen. This results in major safety risk and costs to separate the hydrogen and oxygen. Major factors affecting the cost of hydrogen production by microalgae are the cost of the huge photobioreactor and the cost of hydrogen storage facilities that guarantee continuous hydrogen supply both during the night or during cloudy periods of the day.

Anaerobic hydrogen production proceeds photofermentatively as well as without the presence of light. Anaerobic bacteria use organic substances as the sole source of electrons and energy, converting them into hydrogen.

Glucose + 2H2O ! 2Acetate + 2CO2 + 4H2 Glucose! Butyrate + 2CO2 + 2H2

The reactions involved in hydrogen production (Equations 5.4 and 5.5) are rapid, and these processes do not require solar radiation, making them useful for treating large quantities of wastewater by using a large fermentor.

Since they cannot utilize light energy, the decomposition of organic substrates is incomplete. Further decomposition of acetic acid is not possible under anaero­bic conditions. Nevertheless, these reactions are still suitable for the initial steps of wastewater treatment and hydrogen production followed by further waste treatment stages.

A new fermentation process that converts valueless organic waste streams into hydrogen-rich gas has been developed by Van Ginkel et al. (2001). The process em­ploys mixed microbial cultures readily available in nature, such as compost, anaer­obic digester sludge, soil, etc., to convert organic wastes into hydrogen-rich gas. The biodegradation efficiencies of the pollutants were examined by changing the hydraulic retention time (HRT) as a main operating variable. An enriched culture of hydrogen-producing bacteria such as Clostridia was obtained by heat treatment, pH control, and HRT control of the treatment system. The biohydrogen fermentation technology could enhance the economic viability of many processes utilizing hy­drogen as a fuel source or as raw material. Figure 5.9 shows the basic components of an anaerobic digestion system.

Anaerobic fermentative microorganisms, cyanobacteria, and algae are suitable in the biological production of hydrogen via hydrogenase due to reversible hydro- genases (Adams 1990). Cyanobacteria and algae can carry out the photoevolution of hydrogen catalyzed by hydrogenases. The reactions are similar to electrolysis involving splitting of water into oxygen and hydrogen (Gaffron 1940).

Biological hydrogen can be generated from plants by biophotolysis of water using microalgae (green algae and cyanobacteria), fermentation of organic com­pounds, and photodecomposition of organic compounds by photosynthetic bacte­ria. To produce hydrogen by fermentation of biomass, a continuous process using a nonsterile substrate with a readily available mixed microflora is needed (Hussy et al. 2005). A successful biological conversion of biomass into hydrogen depends strongly on the processing of raw materials to produce feedstock, which can be fer­mented by the microorganisms.

Hydrogen-producing bacteria (Clostridia) were found to have growth rates about 5 to 10 times higher than that of methane-producing bacteria (Van Ginkel et al. 2001). In a continuous-flow bioreactor system, hydrogen production showed a de­clining trend in the later stages of reactor operation. Based on these findings, it is hypothesized that Clostridia may have gone through a phenomenon known as "de­generation” in which they lose their ability to produce hydrogen. Therefore, inocu­lating fresh mixed cultures may be a feasible way to maintain sustainable hydrogen production. Based on this hypothesis, a two-stage anaerobic reactor has been pro­posed. The first-stage reactor is designed as a hydrogen-producing reactor, whereas the second-stage reactor will be employed to cultivate fresh seed culture to perpetu­ally supply to the first one.

This book examines the production of algae culture and usage of algal biomass conversion products. In this book, the modern biomass-based transportation fuels biodiesel, bio-oil, biomethane, biohydrogen, and high-value-added products from algae are briefly reviewed. The most significant distinguishing characteristic of algal oil is its yield and, hence, its biodiesel yield. According to some estimates, the yield (per acre) of oil from algae is over 200 times the yield from the best-performing plant/vegetable oils. The lipid and fatty acid contents of microalgae vary in accor­dance with culture conditions. The availability of algae and the advantages of algal oil for biodiesel production have been investigated.

Billions of years ago the Earth’s atmosphere was filled with CO2. Thus there was no life on Earth. Life on Earth started with Cyanobacteria and algae. These hum­ble photosynthetic organisms sucked out the atmospheric CO2 and started releasing oxygen. As a result, the levels of CO2 started decreasing to such an extent that life evolved on Earth. Once again these smallest of organisms are poised to save us from the threat of global warming.

In the context of climatic changes and soaring prices for a barrel of petroleum, biofuels are now being presented as a renewable energy alternative. Presently, re­search is being done on microscopic algae, or microalgae, which are particularly rich in oils and whose yield per hectare is considerably higher than that of sun­flower or rapeseed. Algae will become the most important biofuel source in the near future. Microalgae appear to be the only source of renewable biodiesel that is capa­ble of meeting the global demand for transport fuels. Microalgae are theoretically a very promising source of biodiesel.

Algae are the fastest-growing plants in the world. Industrial reactors for algal culture are open ponds, photobioreactors, and closed systems. Algae are very im­portant as a biomass source and will some day be competitive as a source for bio­fuel. Different species of algae may be better suited for different types of fuel. Algae can be grown almost anywhere, even on sewage or salt water, and does not require fertile land or food crops, and processing requires less energy than the algae pro­vides. Algae can be a replacement for oil-based fuels, one that is more effective
and has no disadvantages. Algae are among the fastest-growing plants in the world, and about 50% of their weight is oil. This lipid oil can be used to make biodiesel for cars, trucks, and airplanes. Microalgae have much faster growth rates than ter­restrial crops. the per unit area yield of oil from algae is estimated to be between 20,000 and 80,000 L per acre per year; this is 7 to 31 times greater than the next best crop, palm oil. Most current research on oil extraction is focused on microalgae to produce biodiesel from algal oil. Algal oil is processed into biodiesel as easily as oil derived from land-based crops. Algae biomass can play an important role in solving the problem of food or biofuels in the near future.

Microalgae contain oils, or lipids, that can be converted into biodiesel. The idea of using microalgae to produce fuel is not new, but it has received renewed attention recently in the search for sustainable energy. Biodiesel is typically produced from plant oils, but there are widely voiced concerns about the sustainability of this prac­tice. Biodiesel produced from microalgae is being investigated as an alternative to using conventional crops such as rapeseed; microalgae typically produce more oil, consume less space, and could be grown on land unsuitable for agriculture.

Using microalgae as a source of biofuels could mean that enormous cultures of algae are grown for commercial production, which would require large quantities of fertilizers. While microalgae are estimated to be capable of producing 10 to 20 times more biodiesel than rapeseed, they need 55 to 111 times more nitrogen fertilizer — 8 to 16 tons/ha/year.

This book on algae energy attempts to address the needs of energy researchers, chemical engineers, chemical engineering students, energy resource specialists, en­gineers, agriculturists, crop cultivators, and others interested in practical tools for pursuing their interests in relation to bioenergy. Each chapter in the book starts with basic explanations suitable for general readers and ends with in-depth scientific de­tails suitable for expert readers. General readers include people interested in learn­ing about solutions to current fuel and environmental crises. Expert readers include chemists, chemical engineers, fuel engineers, agricultural engineers, farming spe­cialists, biologists, fuel processors, policymakers, environmentalists, environmental engineers, automobile engineers, college students, research faculty, etc. The book may even be adopted as a textbook for college courses that deal with renewable energy or sustainability.

Trabzon, TURKEY (September 2009)

Introduction

1.1 Introduction

Energy is defined as the ability to do work. However, there is no concept of force that includes all definitions of force. For example, the forces that form light en­ergy, heat (thermal) energy, mechanical energy, electrical energy, magnetic energy, etc. are different. There are many forms of energy, but they all fall into one of two categories: kinetic and potential. Electrical, radiant, thermal, motion, and sound en­ergies are kinetic; chemical, stored mechanical, nuclear, and gravitational energies are types of potential energy. It can exist in the form of motion. This is known as kinetic energy. The motion can relate to different things. If the motion is of a large object, the kinetic energy is said to be mechanical. If moving objects are electrically charged, they are said to form an electric current. If moving objects are individual molecules, there are two possibilities. If their motion is organized into waves, then their kinetic energy is associated with sound. If their motion is completely disor­ganized, then their kinetic energy is associated with what we call heat or thermal energy. Another form of kinetic energy is light (and other forms of electromagnetic radiation, like radio waves and microwaves). Other forms of energy do not have the form of motion, but they can cause an increase in motion at a later time. Water at the top of a dam can spill over the dam. A battery can produce an electric current when it is connected to a circuit. Fuels can be burned to produce heat. All of these are examples of potential energy.

The world is presently confronted with twin crises of fossil fuel depletion and environmental degradation. To overcome these problems, renewable energy has re­cently been receiving increased 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 nonedible). The world’s excessive demand for energy, the oil crisis, and the continuous increase in oil prices have led countries to investigate new and renewable fuel alternatives. Hence, energy sources such as solar, wind, geothermal, hydro, nuclear, hydrogen, and biomass have been considered.

A. Demirbas, M. Fatih Demirbas, Algae Energy DOI 10.1007/978-1-84996-050-2, © Springer 2010

3.1 Introduction

Today’s energy system is unsustainable because of equity issues as well as environ­mental, economic, and geopolitical concerns that have implications far into the fu­ture. Bioenergy is one of the most important components to mitigate greenhouse gas emissions and substitute for fossil fuels (Goldemberg 2000; Dincer 2008). Renew­able energy is one of the most efficient ways to achieve sustainable development.

Plants use photosynthesis to convert solar energy into chemical energy. It is stored in the form of oils, carbohydrates, proteins, etc. This plant energy can be con­verted to biofuels. Hence biofuels are primarily a form of solar energy. For biofuels to succeed at replacing large quantities of petroleum fuel, the feedstock availability needs to be as high as possible.

In the context of climatic changes and of soaring prices for a barrel of petroleum, biofuels are now being presented as a renewable energy alternative. Presently, re­search is being done on microscopic algae, or microalgae, which are particularly rich in oils and whose yield per hectare is considerably higher than that of sunflower or rapeseed.

In recent years, recovery of liquid transportation biofuels from biorenewable feedstocks has became a promising method. The biggest difference between biore­newable and petroleum feedstocks is oxygen content. Biorenewables have oxygen levels of 10 to 44% while petroleumhas essentially none, making the chemical prop­erties of biorenewables very different from those of petroleum (Demirbas 2008; Balat 2009). For example, biorenewable products are often more polar and some easily entrain water and can therefore be acidic.

There are two global transportation fuels — gasoline and diesel fuel. The main transportation fuels that can be obtained from biomass using different processes are sugar ethanol, cellulosic ethanol, grain ethanol, biodiesel, pyrolysis liquids, green diesel, green gasoline, butanol, methanol, syngas liquids, biohydrogen, algae diesel, algae jet fuel, and hydrocarbons. Renewable liquid biofuels for transportation have recently attracted considerable attention in different countries around the world be-

A. Demirbas, M. Fatih Demirbas, Algae Energy DOI 10.

solid waste. On the other hand, “traditional biomass” is produced in an unsustain­able way and is used as a noncommercial source — usually with very low efficiencies for cooking in many countries.

A biorefinery is an integrated plant producing multiple value-added products from a range of renewable feedstocks. This innovative approach responds to chang­ing markets for traditional forest products as well as new products such as energy, chemicals, and materials. The range of feedstocks, processes, and potential products is large; each combination of feedstock, process, and product is characterized by its own unique combination of technical and economic opportunities, emerging tech­nologies, and barriers. Figure 3.2 shows an overview of conversion routes of plant biomass feedstocks to biofuels.

Energy plays a vital role in our everyday lives. A country’s standard of living is con­sidered to be proportional to the energy consumption by the people of that country. Energy is one of the vital inputs to the socioeconomic development of any coun­try. The abundance of energy around us can be stored, converted, and amplified for our use in a variety of ways. Energy production has always been a concern for researchers as well as policymakers.

Global energy sources are classified into two groups, fossil and renewable. Pri­mary energy sources can be divided into nonrenewables and renewables. Nonre­newable energy sources include coal, petroleum, gas, gas hydrate, and fissile mate­rial, while renewable energy sources include biomass, hydro, geothermal, solar, and wind energy. The main fissile energy sources are uranium and thorium.

An energy source can also be classified according to its depletion rate. While biomass energy can be depleted, solar and wind energy are nondepletable. In real­ity the energy availability from nonrenewable sources is limited, and beyond that, the exploration, processing, and use of energy involve considerable impacts on the environment. Fossil fuels have been the prime sources of energy for the purpose of transportation, power generation, and agriculture, as well as in commercial, res­idential, and industrial activity for more than a century. The world’s energy re­quirements are currently satisfied by fossil fuels, which serve as the primary energy source.

Because of the increase in petroleum prices, especially after the oil crisis in 1973 and then the Gulf war in 1991, in addition to the geographically reduced availability of petroleum and more stringent governmental regulations on exhaust emissions, researchers have studied alternative fuels and alternative solutions.

Interestingly, renewable energy resources are more evenly distributed than fossil or nuclear resources. 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.

Developing renewable sources of energy has become necessary due to the limited supply of fossil fuels. Global environmental concerns and decreasing resources of crude oil have prompted demand for alternative fuels. Global climate change is also the major environmental issue of our time. Global warming, the Kyoto Protocol, the emission of greenhouse gases, and the depletion of fossil fuels are the topics of environmental concern worldwide. Due to rapidly increasing energy requirements along with technological development around the world, research and development activities have perforce focused on new and renewable energy.

The major sources of alternative energy are biorenewables, hydro, solar, wind, geothermal, and other forms of energy, each of them having their own advantages and disadvantages, including political, economic, and practical issues. Renewable energy is a promising alternative solution because it is clean and environmentally safe. Sources of renewable energy also produce lower or negligible levels of green­house gases and other pollutants as compared with the fossil energy sources they replace.

Liquid biofuels will be important in the future because they replace petroleum fu­els. The biggest difference between biofuels and petroleum feedstocks is oxygen content. Biofuels are nonpolluting, locally available, accessible, sustainable, and re­liable fuel obtained from renewable sources. Biofuels can be classified based on their production technologies: first-generation biofuels (FGBs), second-generation biofuels (SGBs), third-generation biofuels (TGBs), and fourth-generation biofuels.

The FGBs refer to biofuels made from sugar, starch, vegetable oils, or animal fats using conventional technology. The basic feedstocks for the production of FGBs
are often seeds or grains such as wheat, which yields starch that is fermented into bioethanol, or sunflower seeds, which are pressed to yield vegetable oil that can be used in biodiesel.

SGBs and TGBs are also called advanced biofuels. SGBs are made from nonfood crops, wheat straw, corn, wood, and energy crops using advanced technology. Algae fuel, also called algal oil or a TGB, is a biofuel from algae. Algae are low-input/high- yield (30 times more energy per acre than land) feedstocks to produce biofuels using more advanced technology. On the other hand, an emerging fourth-generation fuel is based on the conversion of vegetable oil and biodiesel into biogasoline using the most advanced technology.

The SGBs include renewable and green diesels. The former involves a technol­ogy that incorporates vegetable oils in the crude-oil-derived diesel production pro­cess to produce a renewable carbon-based diesel with no oxygen content and a very high cetane number, while the latter entails the production of middle distillate by means of Fischer-Tropsch (FT) catalysts, using synthesis gas produced by the gasi­fication of biomass. FT-like catalysts (synthol process) can also produce ethanol and mixed alcohols.

There are some barriers to the development of biofuel production. They are tech­nological, economic, supply, storage, safety, and policy barriers. Reducing these barriers is one of the driving factors in government involvement in biofuel and bio­fuel research and development. Production costs are uncertain and vary with the feedstock available. The production of biofuels from lignocellulosic feedstocks can be achieved through two very different processing routes: biochemical and ther­mochemical. There is no clear candidate for “best technology pathway” between the competing biochemical and thermochemical routes. Technical barriers for enzy­matic hydrolysis include low specific activity of current commercial enzymes, high cost of enzyme production, and lack of understanding of enzyme biochemistry and mechanistic fundamentals.

The major nontechnical barriers are restrictions or prior claims on of land use (food, energy, amenity use, housing, commerce, industry, leisure or designations as areas of natural beauty, special scientific interest, etc.), as well as the environmental and ecological effects of large areas of monoculture. For example, vegetable oils are a renewable and potentially inexhaustible source of energy with energy content close to that of diesel fuel. On the other hand, extensive use of vegetable oils may cause other significant problems such as starvation in developing countries. The vegetable oil fuels were not acceptable because they were more expensive than petroleum fuels.

There are few technical barriers to building biomass-fired facilities at any scale, from domestic to around 50 MW, above which considerations of the availability and cost of providing fuel become significant. In general, however, the capacity and generating efficiency of biomass plants are considerably less than those of modern natural-gas-fired turbine systems. The main nontechnical limitations to investment in larger systems are economic, or in some countries reflect planning conditions and public opinion, where a clear distinction may not be made between modern effective biomass energy plant and older polluting incinerator designs.

The most important biorenewable liquid fuels are bioethanol and biodiesel. Bioethanol is a petrol additive/substitute. Biodiesel is a diesel alternative. Biore­newable fuels are safely and easily biodegradable and so are particularly attractive from an environmental perspective. Biodiesel, a biofuel that can directly replace petroleum-derived diesel without engine modifications, has gained a lot of attention due to its environmental and technological advantages.

Production of motor fuel alternatives from biomass materials is an important application area of biotechnological methods. Table 3.1 shows the potential and available motor fuels. Biorenewable sourced motor fuel alternatives are:

1. Gasoline-alcohol mixtures

2. Alcohol substituting for gasoline

3. Gasoline-vegetable oil mixtures

4. Diesel fuel-vegetable oil mixtures

5. Vegetable oil substituting for diesel fuel.

In gasoline-alcohol mixtures ethanol and methanol are generally used, and in gaso­line engine mixtures containing 20% or less alcohol by volume can be used without altering the construction of the engine. Because of the hygroscopic properties of ethanol and methanol, gasoline-alcohol mixtures are in fact ternary mixtures com­posed of gasoline-alcohol and water. In the evaluation of such mixtures as motor fuel, there is the phase separation problem, which depends on several factors. It is evident in the literature that numerous attempts have been made to overcome this problem (Mislavskaya et al. 1982; Osten and Sell 1983).

In gasoline-methanol mixtures containing 0.1% water i-propanol is added to the environment (medium) in order to decrease the phase separation temperature, and fuels containing different ratios of gasoline-methanol-i-propanol and water are com­posed that have proven to be stable in certain climatic conditions. An increase in the aromatic character of the gasoline, a decrease in the water content of the mix­ture, and an increase in the amount of the additive used results in a decrease in the phase separation temperature of the mixture. In gasoline-ethanol mixtures the ad­ditive used is also i-propanol. In gasoline-alcohol mixtures various additives like i-propanol, n-butanol, i-butanol, and i-amylalcohol are used.

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-

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-

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).

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.