Direct methanol fuel cells are similar to the PEMFC as they also use a polymer membrane as the electrolyte. However, it produces power by direct conversion of liquid methanol to hydrogen ions on the anode side of the fuel cell. In the DMFC, the anode catalyst draws hydrogen directly from the liquid methanol, thus eliminating the need for a fuel reformer. All the DMFC components (anode, cathode, membrane, and catalysts) are the same as those of a PEMFC. A DMFC system is shown in Fig. 9.6. Methanol diluted to a specified concentration is fed to the fuel cell stack. During operation, the concentration of the methanol solution exiting the stack is reduced. Therefore, pure methanol is added in the feed cycle to restore the original concentration of the solution. A gas—liquid separa­tor is used to remove carbon dioxide from the solution loop, and a com­pressor feeds air to the DMFC stack. Water and heat are recovered by passing the outlet air through a condenser. A portion of the recov­ered water is returned to the fuel circulation loop. The stack temper­ature is maintained by removing the excess heat from the fuel circulation loop using a heat exchanger. The DMFC can attain high efficiencies of 40% with a Nafion-117 membrane at 60oC, with current

density in the range of 100-120 mA/cm2. Studies have shown that DMFC efficiency decreases with increasing methanol concentration. Therefore, operating a fuel cell to maintain the maximum efficiency needs close con­trol of methanol concentration and temperature. An online concentra­tion sensor is used in the feedback loop for this purpose. Some of the advantages of this system, relative to the hydrogen systems, are that the liquid feed (methanol) helps in attaining the uniform stack tem­perature and maintenance of membrane humidity; it is also easy to refill since the fuel (methanol) is in liquid form.

As compared to the PEMFC, the DMFC has a very sluggish electro­chemical reaction (significant activation over voltage) at the anode. It therefore requires a high surface area of 50:50% Pt-Ru (a more expen­sive bimetal) alloy as the anode catalyst to overcome the sluggish reac­tion and an increase in catalyst loading of more than 10 times that for the PEMFC. Even then, the output voltage on the load is only 0.2-0.4 V with an efficiency of about 40% at operating temperatures between 60°C and 90°C. This is relatively low, and therefore, the DMFC is attractive only for tiny to small-sized applications (cellular phones, laptops, etc.) [17]. Another potential application for the DMFC is in transport vehi­cles; as it operates on liquid fuels, it would greatly simplify the onboard system as well as the infrastructure needed to supply fuel to passenger cars and commercial fleets and can create a large potential market for commercialization of fuel cell technology in vehicle applications.

The continuous use of the world’s crude oil reserve and a corresponding escalation in its price together with the limited coal reserves have stimu­lated the hunt for renewable sources of energy. The main sources of renew­able energy are biomass, biogas, methanol, ethanol, and biodiesel; solar active (photovoltaic), solar passive (preheating of water), wind, mini hydel, and mini tidal are important sources which produce less pollution and pro­tect the environment.

Much attention has been given to biomass and its modifications as a substitute for fossil fuels in the Western world. Among the modifications are biogas, alcohol, biodiesel, and manure. Presently, electrical power is attractive in many respects and the search is on for renewable and nonfinite resources to produce and supplement electrical energy.

The first chapter discusses energy and its biological sources. If bio­fuel is one of the expected solutions, we must know where is the begin­ning of the crisis and its solution. This chapter reviews the background story along with an optimistic outlook for a safe energy resource on our green earth. The second chapter discusses energy from photosynthetic plants and their inherent recycling nature, as well as the environmen­tal benefits involved. These sources of energy are the solution for energy management. The third chapter discusses bioethanol, which is now one of the main actors in the fuel market. Its market grew from less than a billion liters in 1975 to more than 39 billion liters in 2006, and is expected to reach 100 billion liters in 2015. The chapter discusses the variety of raw materials, such as sugars, starch, and lignocellulosic substances, that produces bioethanol and also covers some of the market issues. To extend the use of biodiesel, the main concern is the economic viability of producing biodiesel. Edible oils are too valuable for human feeding to run automobiles. So, the emphasis must be on low-cost oils, i. e., nonedible oils, animal fats, and used frying oils. There are many nonedible feed­stock crops growing in underdeveloped and developing countries; biodiesel programs here would give multiple social and economic benefits.

The fourth chapter discusses different plant sources used for production of biodiesel, properties of biodiesel, and processing of vegetable oils as biodiesel, and compares engine performance with different biodiesels.

Biodiesel is the methyl or other alkyl esters of vegetable oils, animal fats, or used cooking oils. Biodiesel also contains minor components such as free fatty acids and acylglycerols. Important fuel properties of biodiesel that are determined by the nature of its major and minor com­ponents include ignition quality and exhaust emissions, cold flow, oxida­tive stability, viscosity, and lubricity. The fifth chapter discusses how the major and minor components of biodiesel influence the mentioned properties.

Different techniques of biodiesel preparation and resulting engine performance are discussed in detail in Chap. 6. The seventh chapter dis­cusses ethanol and methanol as fuel in the internal combustion engine and emphasizes their advantages (such as a higher octane number) over gasoline. Cracking of lipids turns polar esters into nonpolar hydro­carbons. This is accompanied by a fundamental change in physical and chemical properties. Products formed give rise to new applications in the fuel sector and for chemical commodities, e. g., detergents. The eighth chapter explores routes to provide these alternative hydrocarbons from lipids. It concentrates on substrates (seeds, vegetable oils, animal fat) and conversion pathways as well as analytical tools.

The ninth chapter discusses the fuel cell, an electrochemical device and nonpolluting alternative energy source that converts the chemical energy of a fuel (hydrogen, natural gas, methanol, gasoline, etc.) and an oxidant (air or oxygen) into electricity with water and heat as by-products.

The book is organized in a manner to cater to the needs of students, researchers, managerial organizations, and readers at large. We welcome the reader’s opinions, suggestions, and added information, which will improve future editions and help readers in the future. Readers’ bene­fits will be the best reward for the authors.

Ahindra Nag, Ph. D.

Biomass can be converted into different types of products, including:

1. Electrical/heat energy

2. Transport fuel

3. Chemical feedstock

Woody and herbaceous species are the ones used most often by biomass researchers and industry. Several parameters are important in the biomass conversion process. The principal considerations in terms of the material type are moisture content, calorific value, fixed carbon and volatile pro­portion, ash/residue content, alkali metal content, and cellulose-lignin ratio. In a wet-biomass conversion process, the moisture content and cellulose-lignin ratio is of prime concern, while in a dry-biomass conver­sion process, it is the alkali metal content and cellulose-lignin ratio. The Laticiferous plant species of Apocyanaceae, Asclepiadaceae, Convolvulaceae, and Euphorbiaceae have been analyzed for use as renewable energy sources. Analysis of oil and hydrocarbon contents of 15 different plant species tested has revealed that Carissa carandas L., Ceropegia juncea Roxb., Hemidesmus indicus R. Br., and Sarcostemma brunourianum W. A. are the most suitable species [16]. In another study, five different plant species Plumeria alba, C. procera, Euphorbia nerifolia, Nerium indicum, and Mimusops elengi have been evaluated as potential renewable energy sources. Whole plants and plant parts (leaf, stem, and bark) have been ana­lyzed for oil, polyphenol, hydrocarbons, crude protein, a-cellulose, lignin, ash, and mineral content. The barks of these plants were identified to have greater hydrocarbon content than the leaves. Based on the dry-biomass yields, hydrocarbon content, and other properties, these plant species most suitable for renewable energy sources have been identified [17]. In a study conducted on 51 plant species in Tennessee, in the United States, an exam­ination of the oil, polyphenol, hydrocarbon, protein, and ash content reveals that Lapsana communis yields the maximum oil (6.1% dry, ash-free plant sample basis). Chrysopsis graminifolia, Solidago erecta, and Verbesina alternifolia have been identified as rubber-producing species with 0.4-0.7% hydrocarbon [18].

2.4 Products

Several processes similar to petroleum refining are involved in the con­version of biomass into different products. Biorefineries convert biomass into different products in different stages. The different stages involved in the conversion of biomass to products are depicted in Fig. 2.11.

There has been a tremendous increase in biobased products such as ethanol, high-fructose syrups, citric acid, monosodium glutamate, lysine, enzymes, and specialty chemicals worldwide. It is estimated that in 2000-2006 in United States alone, there will be an increase in the use of liquid fuels, organic chemicals, and biopolymers from the current level of ~2%, 10%, and 90% each to 10%, 25%, and 95%, respec­tively [19].

Fermented broth or “mash” typically contains 2-12% ethanol. Further­more, it contains a number of other materials that can be classified into microbial biomass, fusel oil, volatile components, and stillage. Fusel oil is a mixture of primary methylbutanols and methylpropanols formed from a-ketoacids and derived from or leading to amino acids. Depending on the resources used, important components of fusel oil can be isoamylal- cohol, n-propylalcohol, sec-butylalcohol, isobutylalcohol, n-butlyalcohol, active amylalcohol, and n-amylalcohol. The amount of fusel oil in mash depends on the pH of the fermentor. Fusel oil is used in solvents for paints, polymers, varnishes, and essential oils. Acetaldehyde and trace amounts of other aldehydes and volatile esters are usually produced from grains and molasses. Typically, 1 L of acetaldehyde and 1-5 L of fusel oil are produced per 1000 L of ethanol [9, 47].

Stillage consists of the nonvolatile fraction of materials remaining after alcohol distillation. Its composition depends greatly on the type of feedstock used for fermentation. Stillage generally contains solids, resid­ual sugars, residual ethanol, waxes, fats, fibers, and mineral salts. The solids may be originated from feedstock proteins and spent microbial cells [9].

Crop description. Shorea robusta Gaertn. f.—commonly known as sal, shal, saragi, sakhu, sakher, shaal, ral, gugal, mara, sagua, salwa, sakwa, kandar, and kung—is a large tree belonging to the family Dipterocar — paceae (see Fig. 4.23). The tree is native to southern Asia, ranging south of the Himalayas, from Myanmar in the east to India, Bangladesh, and Nepal. It grows in dry tropical forests, in a well-drained, moist, sandy loam soil. This tree can attain heights up to 35 m. The seeds of sal are an important source of edible oil. The seed contains around 20% of oil [183, 184].

Main uses. Although sal is a highly valued timber species, it is also used for house construction, and as poles, agriculture implements, fuelwood, fencing, leaves for cups and plates, and compost [185]. The oil is used for lighting and cooking purposes, and as a substitute for

Figure 4.23 Shorea robusta Gaertn. f. (Photo courtesy of Dr. Mike Kuhns [http: / / extension. usu. edu/forestry/ UtahForests/TreeID/Assets/ Images/sal-1.3.jpg].)

cocoa butter in the manufacture of chocolates. It is suitable for soap making after blending with other softer oils. The oil cakes that remain after oil extraction contain 10-12% protein and about 50% starch, and are used as cattle and poultry feed. However, the oil cake contains 5-14% tannin; consequently, not more than 20% is concentrated for cattle without detrimental effects. As the protein remains completely undigested, the oil cake yields energy only. Sal resin is burned as incense in Hindu ceremonies. It is also used for varnishes, for hard­ening softer waxes for use in the manufacture of shoe polishes, and as cementing material for plywood, asbestos sheets, and so forth. The resin is used in an indigenous system of medicine as an astringent and detergent [184]. No references about its use as a biodiesel source have been found so far.

Methanol-fueled vehicles emit less CO2 and other polluting gases com­pared to gasoline-fueled vehicles. Therefore, methanol use maintains good air quality. For a higher compression ratio compared to gasoline, a higher level of NOx can be achieved. But low flame temperature and latent heat of vaporization tend to decrease NOx emissions. The over­all effect is a lower level of NOx emissions.

The power-conditioning system is an integral part of a fuel cell system. It converts the dc electric power generated by the fuel cell into regulated dc or ac for consumer use. The electrical characteristics of a fuel cell are very far from that of an ideal electric power source. The dc output voltage of a fuel cell stack varies considerably with the load current (see Fig. 9.15), and it has very little overload capacity. It needs considerable auxiliary power for pumps, blowers, and so forth, and requires consid­erable start-up time due to heating requirements. It is slow to respond to load changes, and its performance degrades considerably with the age of the fuel cell. The various blocks of a fuel cell power-conditioning system are shown in Fig. 9.16.

The dc voltage generated by a fuel cell stack is usually low in magni­tude (<50 V for a 5- to 10-kW system, <350 V for a 300-kW system) and varies widely with the load. A dc—dc converter stage is required to reg­ulate and step up the dc voltage to 400-600 V (typical for 120/240-V ac output). Since the dc—dc converter draws power directly from the fuel cell, it should not introduce any negative current into the fuel cell and must be designed to match the fuel cell ripple current specifications. A dc—ac conversion (inverter) stage is needed for converting the dc to ac power at 50 or 60 Hz (see Fig. 9.17). Switching frequency harmonics are filtered out using a filter connected to the output of the inverter to generate a high-quality sinusoidal ac waveform suitable for the load.

Whether they are green algae (chlorella) or the higher plants, autotrophs in general are gifted in nature to fix carbon dioxide and produce biomass. In ecologic terms, these are producers. The dominant autotroph is pho­totrophic. Photosynthesis has two distinct aspects: the light dependent step, where photolysis of water takes place:

ADP + Pi ——^ ATP

During this reaction, oxygen is set free, Co II is reduced and phosphory­lation of ATP takes place. The photoenergy is chemically utilized twofold.

In the next step, through a very complex enzymic sequence, CO2 is incorporated into the existing metabolite pool and higher carbohydrates are biosynthesized. This step of the reaction finds variation in different species; carbohydrates, proteins, and lipids are biosynthesized. Then, the first part of the reaction makes the autotrophs unique. Light falling on chloroplasts develops an electrical field across the membrane.

In the presence of the pigments in chloroplasts, the light energy is trapped and activates water and lyses it. Ideally, water, if converted into its elemental components, requires (at 25°C) 68.3 kcal/mol (from liquid) or 57.8 kcal/mol (from vapor). Thermal energy is not sufficient to bring this change. During photolysis, the plant pigment augments electron flow, and the electron flow system culminates in the two energy-rich chemical prod­ucts (reduced Co II, ATP, and O2), as already mentioned (see Fig. 1.7).

Lester Packer’s group at the University of California at Berkeley has shown the steps of the pathway with chloroplasts from spinach leaves,

ferredoxin from Spirulina, and hydrogenase of Clostridium pasteuri — anum [3].

2H, O ^ 4H + 4e + O2
4 Ferredoxin+ + 4e~ ^ 4 Ferredoxin
4H+ + 4 Ferredoxin ^ 2H2 + 4 Ferredoxin+

O2 + Glucose ^ Gluconate + H2O2 H2O2 + Ethanol ^ 2H2O + Acetaldehyde The overall reaction is

Glucose + Ethanol ^ Gluconate + Acetaldehyde + H2

Two H2 are produced for each O2 produced (if not consumed by an oxidase-type reaction as shown previously). Dr John Benemann of the same university has also suggested that hydrogen and methane pro­duction is possible by designing a two-stage system separated from each other (see Fig. 1.8).

Dibromothymoquinone blocks the natural electron flow system at plastocyanin level (see Fig. 1.9). Thus, in the presence of an artificial donor or acceptor, the photo systems I and II can be separated at pre — and post-blocking points.

Hemicelluloses are heterogeneous polymers of pentoses (e. g., xylose and arabinose), hexoses (e. g., mannose, glucose, and galactose), and sugar acids. Unlike cellulose, hemicelluloses are not chemically homogeneous. Hemicelluloses are relatively easily hydrolyzed by acids to their monomer components consisting of glucose, mannose, galactose, xylose, arabinose, and small amounts of rhamnose, glucuronic acid, methylglucuronic acid, and galacturonic acid. Hardwood hemicelluloses contain mostly xylans, whereas softwood hemicelluloses contain mostly glucomannans. Xylans are the most abundant hemicelluloses. Xylans of many plant materials are heteropolysaccharides with homopolymeric backbone chains of 1,4- linked ^-D-xylopyranose units. Xylans from different sources, such as grasses, cereals, softwood, and hardwood, differ in composition. Besides xylose, xylans may contain arabinose, glucuronic acid or its 4-O-methyl ether, and acetic, ferulic, and p-coumaric acids. The degree of polymer­ization of hardwood xylans (150-200) is higher than that of softwoods (70-130) [14, 15].

1.5.2 Lignin

Lignin is a very complex molecule. It is an aromatic polymer constructed of phenylpropane units linked in a three-dimensional structure. Generally, softwoods contain more lignin than hardwoods. Lignins are divided into two classes, namely, “guaiacyl lignins” and “guaiacyl — syringyl lignins.” Although the principal structural elements in lignin have been largely clarified, many aspects of their chemistry remain unclear. Chemical bonds have been reported between lignin and hemi — cellulose, and even cellulose. Lignins are extremely resistant to chem­ical and enzymatic degradation. Biological degradation can be achieved mainly by fungi, but also by certain actinomycetes [15, 17].

Crop description. Gossypium spp., commonly known as cotton, belongs to the family Malvaceae and is native to the tropical and subtropical regions (see Fig. 4.4). Four separate domesticated species of cotton grown in various parts of the world are G. arboreum L., G. herbaceum L., G. hirsutum L., and G. barbadense L. Cotton shrubs are annual and found in the United States, Australia, Asia, and Egypt. Some have been grown for many years in southern Europe, mainly the Balkans and Spain. It can grow up to 3 m high [61-64].

Main uses. Cotton is a major world fiber crop. Its fiber grows around the seeds of the cotton plant and is used to make textile, which is the most widely used natural-fiber cloth. The seeds yield a valuable oil used for the production of cooking oil or margarine. The fatty acid composi­tion includes mainly palmitic acid (21%), stearic acid (2.4%), oleic acid (19.5%), linoleic acid (54.3%), and myristic acid (0.9%). Cottonseed oil, cake, meal, and hulls for feeding are other uses of the by-products. Whole cottonseed may be used as a feed for mature cattle. Cottonseed meal is an excellent protein supplement for cattle. The limitations on effective utilization of this product in rations for swine and poultry are of minor significance to ruminant animals. Cottonseed meal has a rel­atively low rumen degradability and is therefore a good source of by-pass protein and is especially useful in rations for milking cows [61-64].

Figure 4.4 Gossypium spp. (Photo courtesy of Prof. Jack Bacheler [http:/ /ipm. ncsu. edu/ cotton/InsectCorner/photos/ images/Open_cotton_plant. jpg].)

Kose et al. investigated the transesterification of refined cottonseed oil, using primary and secondary alcohols (oil-alcohol molar ratio 1:4) in the presence of an immobilized enzyme from Candida antarctica (30% enzyme, based on oil weight). The reaction was carried out at 50°C for 7 h, showing that conversion using secondary alcohols was more effective

[65] . Some authors have also proposed the use of lipase with methanol

[66] . Royon et al. used the same catalyst in a t-butanol solvent. Maximum yield was observed after 24 h at 50°C with a reaction mixture contain­ing 32.5% t-butanol, 13.5% methanol, 54% oil, and 0.017 g of enzyme per g of oil [67]. Recent tendencies propose the use of ultrasonically assisted extraction transesterification to increase ester yield [68].