Thermal decomposition of vegetable oil was performed to prove the theory of the origin of mineral oil from organic matter [14] as early as 1888. Literature up to 1983 has been reviewed by Schwab et al. [15]. In many cases, inadequate characterization of products formed in pyrol­ysis of vegetable oils was found. Therefore, analytical data obtained by gas chromatography—mass spectrometry (GC-MS) from thermally decomposed soybean oil and high oleic safflower oil in the presence of air or nitrogen were reported [15].

The ASTM standard method for distillation of petroleum products D86-82 has been used for decomposition experiments. Catalytic systems were excluded in this destructive distillation. The actual temperature of the oil in the feeder flask was about 100oC higher than the vapor temper­ature throughout the distillation. Under these conditions, GC-MS analy­sis showed that approximately 75% of the products were made up of alkanes, alkenes, aromatics, and carboxylic acids with carbon numbers ranging from 4 to more than 20 (see Table 8.1).

A comparison of fuel properties is given in Table 8.2. The carbon — hydrogen ratio shows 79% C and 11.88% H for the pyrolyzate of soybean

oil. This indicates considerable amounts of oxygenated compounds in the distillate. Consequently, methylation of these oils has revealed 9.6-12.2% of carboxylic acids ranging from C-3 to over C-18. This is reflected in the higher viscosity compared to diesel.

Mass-spectral fingerprints of the entire pyrolysis product slate from tripalmitin, different vegetable oils, and extracted oils from microalgae confirm that the decomposition of ester bonds in the absence of external catalysts is extensive [16-18]. However, a great variability in primary pyrolysis/vaporization product slates was observed [18].

Thermodynamic calculation in the degradation process shows that the cleavage of C-O bond takes place at 288°C and fatty acids are the main product [19]. The actual pyrolysis temperature should be higher than 400°C to obtain maximum diesel yield [20]. The mechanism of pyrolysis of vegetable oil has been discussed by various authors [9, 15, 19]. Generally, thermal decomposition proceeds through either a free-radical or carbonium ion mechanism. The primary R-COO splits off carbon dioxide. The alkyl radicals (R), upon disproportionation and elimination of ethene, give rise to alkanes and alkenes. The formation of aromatics is facilitated by a Diels-Alder addition of ethene to a conjugated diene formed in the pyrol­ysis reactions. However, the product mix and product quality are influenced by many factors such as feed pretreatment, heating rate, and temperature. As vegetable oils may contain trace elements, catalytic effects cannot be completely excluded from any thermal degradation process [21].

8.1.1 Catalytic cracking (CC)

In 1979, a paper [22] from the petrochemical industry reported for the first time that high-molecular-weight triglycerides such as corn oil (C57H104O6) and castor oil (C57H104O9) were convertible to a high-grade gasoline when passed over H-ZSM-5, a catalyst. The latter is a synthetic, medium-pore, shape-selective acid catalyst. Lipids were fed with a piston displacement pump at a rate of 2 mL/h with flowing hydrogen (300 mL/h) over 2 mL of H-ZSM-5 catalyst (0.77 g, 14-30 mesh) contained in a ver­tical Pyrex reactor at atmospheric pressure and T = 400-450°C. Paraffins, olefins, aromatics, and nonaromatics could be detected in the product mixture. The distribution of hydrocarbons is similar to selective conversion of methanol into hydrocarbon units with up to 10 carbon atoms per molecule. In all cases, a high degree of BTX aromatics (ben­zene, toluene, and xylene) was achieved. The precondition for the catalytic conversion is that the molecule penetrate the cavities of microporous zeolite.

This new catalytic approach has paved the way for a variety of appli­cations. A schematic diagram of experimental arrangements for pyrol­ysis and catalytic conversion is given in Fig. 8.1.

Conversion of different kinds of vegetable oils over medium-pore H- ZSM-5 have been investigated in detail [23-26]. Catalytic cracking of by-products from palm oil mills with a selectivity of 51wt.% toward aro­matic hydrocarbon formation has been reported [27]. To achieve higher yields, this type of work was extended to pyrolysis and zeolite conver­sion of both whole algae and their major components as well as whole seeds and selected vegetable oils [18, 28-31]. Hot vapors from solid organic material (microalgae, seeds, etc.) or vaporized vegetable oils were passed directly over the H-ZSM-5 catalyst. Products of different

algae, seeds, or vegetable oils emerging from the passage showed a uni­form, high-octane, aromatic gasoline product. Obviously, the molecular pattern of products is insensitive to the nature of lipids used. This is in contrast to pyrolysis without a catalyst [18].

Upgrading of crude tall oil to fuels and chemicals has been studied at atmospheric pressure and in the temperature range of 370—440oC, in a fixed-bed microreactor containing H-ZSM-5 [32]. The oil was co-fed with diluents such as tetralin, methanol, and steam. High oil conversions, in the range of 80-90 wt.%, were obtained using tetralin and methanol as diluents. Conversions under steam were reduced to 36-70 wt.%. The maximum concentration of gasoline-range aromatic hydrocarbons was 52-57 wt.% with tetralin and steam, but only 39% with methanol. The amount of gas product in most runs was 1-4 wt.% [32].

Gasification, an exothermic reaction, yields mostly producer gas, a mixture of carbon monoxide, hydrogen, and methane at temperatures

above 1000oC, mostly in the absence of air. The starting materials may be any kind of organic matter, preferably waste materials like cotton and jute sticks, corn cobs, bagasse, and many other plant and vegetation products. In India, annually 16 million tons of rice husk, 160 million tons of paddy straw, 2 million tons of jute sticks, and 2.2 million tons of groundnut shells are available as agricultural by-products.

The gas can be directly used as fuel or used to drive irrigation pump sets. Several designs are available.

Pyrolysis, a thermochemical conversion, also performed in absence of air at a temperature of 500-6000C, yields gaseous components, hydro­carbons, carbon monoxide, hydrogen, methane, butane, some liquids, tars, and a little coke, all of which have very high energy content. Starting materials are similar to those mentioned under gasification. The vegetable matter in the municipal refuse (as much as 50%) is also good feed for pyrolysis. Very optimistic economic analysis for the pyrolytic process has been put forward by investigators, and a properly designed plant, say capable of handling 250 tons of organic refuse per day, will be fully paid off at the end of 5 years. There are 20 domestic or family-size models suggested by organizations. As per the available information, large-scale use of either gasifier or pyrolyser has not been noticed so far. But for the municipalities, the responsibility of quick dis­posal of the refuse and the environmental issues will prompt installa­tion of such plants in the near future. One such flowchart of a model plant is given in Fig. 1.12.

A great number of bacteria are able to produce ethanol, although many of them generate multiple end products in addition to ethanol. Zymomonas mobilis is an unusual Gram-negative bacterium that has several appealing properties as a fermenting microorganism for ethanol production. It has a homoethanol fermentation pathway and tolerates up to 120 g/L ethanol. Its ethanol yield is comparable with S. cerevisiae, while it has much higher specific ethanol productivity (2.5 X) than the yeast. However, the tolerance of Z. mobilis to ethanol is lower than that of S. cerevisiae, since some strains of S. cerevisiae can produce ethanol to give concentrations as high as 18% of the fermentation broth. The tol­erance of Z. mobilis to inhibitors and low pH is also low. Similarly,

S. cerevisiae and Z. mobilis cannot utilize pentoses [14, 57]. Several genetic modifications have been performed for utilization of arabinose and xylose by Z. mobilis. However, S. cerevisiae has been more welcomed for industrial application, probably because of the industrial problems that may arise in working with bacteria. Separation of S. cerevisiae from fermentation media is much easier than separation of Z. mobilis, which is an important characteristic for reuse of the microorganisms in ethanol production processes.

Using genetically engineered bacteria for ethanol production is also applied in many studies. Ingram et al. [58] have reviewed metabolic engineering of bacteria for ethanol production. Recombinant Escherichia coli is a valuable bacterial resource for ethanol production. Construction of E. coli strains to selectively produce ethanol was one of the first suc­cessful applications of metabolic engineering. E. coli has several advan­tages as a biocatalyst for ethanol production, including the ability to ferment a wide spectrum of sugars, no requirements for complex growth factors, and prior industrial use (e. g., for production of recombinant protein). The major disadvantages associated with using E. coli cultures are a narrow and neutral pH growth range (6.0—8.0), less hardy cultures compared to yeast, and public perceptions regarding the danger of E. coli strains. Lack of data on the use of residual E. coli cell mass as an ingre­dient in animal feed is also an obstacle to its application [8].

Recently, the Japanese Research Institute of Innovative Technology for the Earth (RITE) developed a microorganism for ethanol production. The RITE strain is an engineered strain of Corynebacterium glutamicum that converts both pentose and hexose sugars into alcohol. The central metabolic pathway of C. glutamicum was engineered to produce ethanol. A recombinant strain that expressed the Z. mobilis gene coding for pyru­vate decarboxylase and alcohol dehydrogenase was constructed [59]. RITE and Honda jointly developed a technology for production of ethanol production from lignocellulosic materials using the strain. It is claimed that application of this strain by using engineering technology from Honda enables a significant increase in alcohol conversion efficiency, in comparison to conventional cellulosic—bioethanol production processes.

Besides nonedible oils, there are some edible oils from plants that yield a relatively lower-cost source to produce biodiesel compared to biodiesel from rapeseed oil or soybean oil.

4.3.1 Cardoon oil

Crop description. Cynara cardunculus L.—commonly known as car­doon, Spanish artichoke, artichoke thistle, cardone, dardoni, or cardo— belongs to the family Asteracea (see Fig. 4.14). Artichokes originated in the Mediterranean region and climates, becoming an important weed of the Pampas in Argentina, and in Australia, and California because of its adaptation to dry climate. Its fatty acid composition mainly includes palmitic acid (19.3%), stearic acid (6.1%), oleic acid (39%), and linoleic acid (30%) [123].

Main uses. The leaf stalks are eaten as a vegetable. The leaves contain cynarin, which improves gall bladder and liver functions, increases bile flow, and lowers cholesterol. The down from the seed heads is used as rennet.

Encinar et al. transesterified C. cardunculus oil using methanol and several catalysts (sodium hydroxide, potassium hydroxide, and sodium methoxide) to produce biodiesel. Best properties were achieved by using 15% methanol and 1% sodium methoxide as catalyst, at 60°C temperature [124].

The reaction can also be accomplished by using an ethanol-oil molar ratio of 12:1 and 1% sodium hydroxide, at 75°C [125]. C. cardunculus methyl esters also provide a significant reduction in particulate emis­sions, mainly due to reduced soot and sulfate formation [126].

Ethanol is the most appropriate fuel for India to replace petrol, and the utmost of efforts have been made to increase alcohol production in the country. India is in an extremely happy position in this regard as it is the world’s largest producer of sugarcane, a major source of alcohol. India topped the world in sugar production with 181 Mton (in 1978), followed by Brazil (130 Mton) and Cuba (67 Mton).

Alcohol is derived not directly from sugarcane but molasses-sugar­cane by-products. All starch-rich plants like maize, tapioca, and potato can be used to produce alcohol; cellulosic waste materials can also be used. Production of ethanol from biomass involves fermentation and distillation of crops. India has a vast potential to produce ethanol, and only 2.5% of the country’s irrigated land is used to produce sugarcane. This can be raised to a much higher level without adversely affecting the production of food-bearing crops.

At present, Brazil is the only country that produces fuel alcohol on a large scale from agricultural products (mainly sugarcane). Other coun­tries, especially those with an substantial agricultural surpluses, such as the United States and Canada, are also bound to enter into this field of so-called energy forming. The area of land required is substantial. A medium-sized car with an annual run of 15,000 km needs 2000 L of ethanol. To produce this amount, the crop areas required are given in Table 7.2. To provide enough sugar beet alcohol to fuel 20 million cars in Germany requires half the area of the entire country.

Sugarcane. The present method adopted to obtain alcohol for energy purposes requires three stages: (1) extracting the juice from sugarcane, (2) fermentation of the juice, and (3) distillation into 90-95% alcohol.

Molasses. The black residue remaining after the sugar is extracted from sugarcane is called molasses. It contains mostly invert sugars and some sucrose. This sucrose also undergoes hydrolysis to produce invert sugar by a catalytic action of acids in molasses.

C12H22O11 + H2O ^ C6H12O11 (D-Glucose) + C6H12O6 (D-Fructose)

This mixture product is not crystallizable. Yeast organisms in the pres­ence of oxygen oxidize sugars into CO2 and H2O and convert sucrose mostly into ethyl alcohol.

C6H12O6 ^ 2C2H5OH + 2CO2

Process adopted. Molasses is mixed with water so that the concentra­tion of sugar in it is 10-18% (optimum is 12%). If the concentration is high, more alcohol may be produced and may kill the yeast. Then, a selected strain of yeast is added (it should not contain any wild yeast). For some nutrient substances like ammonium and phosphates, the pH value is kept between 4 and 5, which favors the growth of yeast organ­isms. H2SO4 is used for lowering pH. The temperature of the mixture is kept at 15-25°C. The fermentation takes place as follows:

1. First, the yeast cells multiply at an optimum temperature (30°C).

2. Rapid fermentation takes place at the boiling temperature, and oxygen is given off. The optimum temperature (50°C) is maintained, and the process is continued for 20-30 h.

3. The fermentation rate is reduced, and alcohol is produced slowly. Total time for fermentation is 36-48 h, depending upon the temper­ature and sugar content. Last, the formed ethanol is distilled.

Starch. In this process, starchy materials are first converted into fer­mentable sugars. This is done by enzymatic conversion (by means of malt process) or by acid hydrolysis.

Starch ^ C12H22O11 (Maltose) + C6H12O6 (Dextrose)

Malt process. Malt is prepared by germination of barley grains to pro­duce required enzymes. The grain is ground and steam cooked at 100-150oC to break the cell wall of starch. For every 25 kg of grain, 100 L of water is added. Then the formed mass is cooled to 60-700C and taken to large vessels where malt is added within 2 h and 60-70% of the stock is converted into maltose. Converted mash is cooled to a fermenting temperature of 20-250C. pH is adjusted and fermentation is affected, producing ethanol.

Acid hydrolysis. This process involves treatment with concentrated sulfuric or hydrochloric acid at pH 2-3 and 10-20 kg pressure in an auto­clave to make sugar and then conversion of sugar to alcohol by yeast.

Cellulose material.

Wood. Cellulose from wood is hydrolyzed into simple sugars by using diluted acid at a high temperature or concentrated acid at a low tem­perature. Similarly, cellulosic agricultural waste and straws can be used in place of wood.

Sulfite waste liquor from paper manufacture. Waste liquor contains 2-3.5% of sugar, out of which 65% is fermentable into alcohol. Before fermen­tation, all acids in the liquor are removed by adding calcium. Then fer­mentation is carried out by special yeasts. Generally, 1% of liquor is converted into alcohol.

Hydrocarbon gases.

Hydration of ethylene. Conversion of ethylene to ethyl alcohol can be carried out with high yield by first treating ethylene with H2SO4, forming ethyl hydrogen sulphate and diethyl sulfate, as given by the following reactions:

C2H5HSO4 — (C2H5)2SO4 2C2H4 + H2SO4 — (C2H5)2SO4

These products, ethyl sulfuric acid and diethyl sulfate, when treated with water give ethanol as per the following reactions:

C2H5HSO4 + H2O — C2H5OH + H2SO4
(C2H5)2SO4 + 2H2O — 2C2H5OH + H2SO4

Direct hydration. Ethanol is also formed as per the following chemical reaction:

C2H4 + H2O — C2H5OH

This type of conversion is very small as the reaction is exothermic; it is not a suitable method for mass production. The corn is first ground, then mixed with water and enzymes, and cooked at 150oC to convert starch to sugar. The mixture is then cooled and sent to fermentation tanks, where yeast is added and the sugar is allowed to ferment into ethanol. After 60 h in the tanks, the mixture is sent to distillation columns, where ethanol is evaporated out, condensed, and mixed with unleaded gaso­line to form gasohol, which contains 90% gasoline and 10% ethanol.

Tapioca materials. Tapioca is available in plenty in Asia, the United States, central Europe, and Africa. Its production can be increased through modern cultivation techniques. The process consists of con­verting the tapioca flour into fermentation sugars with enzymes prior to fermentation with yeast. Modern technology uses a-amyl glycosidase, one of two enzymes required in the process, and then saccharification of the material into alcohol by using yeast.

Anhydrous alcohol from vegetable wastes. The Philippines has embarked on an “alcogas program” to produce its own anhydrous alcohol from local vegetable wastes for blending with petrol. The program is cur­rently based on sugarcane juice and molasses, but it plans to diversify by using other raw materials. In the basic process, cellulose conversion begins with the pretreatment of the raw materials, which may include coffee hulls, rice straw, grass—even sawmill wastes. Enzymes then take over by converting the feedstock into a sugary liquid that is fermented and finally distilled into anhydrous alcohol. After distillation, waste residues can be evaporated into syrup to feed animals, while uncon­verted cellulose is used as the primary fuel for the plant. If the Philippines could engineer a breakthrough in this area, its agricultural and forestry wastes could supply energy equivalent to 9720 mL of oil annually. In the years to come, this new energy source could make a sig­nificant economic impact on a country that depends on imports of crude oil for 95% of its energy.

Manioc. As oil prices continue to rise, more and more work is being done on alternatives. Manioc is one such staple crop in many tropical lands. Brazil has planned to use manioc in its ethanol production plants, aiming to make 35,000 bbl a day from 400 X 103 ha of manioc plantation. Conversion of manioc to ethanol is somewhat more complex than is the case with sugarcane. The raw material has to be turned into sugar by fer­mentation. This first step requires the use of enzymes. Danish Co. has developed the necessary heat-resistant enzymes in a pilot plant in Brazil.

Manioc does not grow in higher temperature zones; so scientists have turned to other plants, and there is work being done in Sweden that is in an advanced stage. They have developed fast-growing poplars and wil­lows. Their yield is 30 ton/ha, which is equal to 12 tons of fuel oil.

It is estimated that 1000 X 103 ha planted with such trees can pro­vide 10% of Sweden’s electricity. Also in Sweden, work has been carried out on the common reed, and the estimated yield is 10 ton/(yr • ha), which is equal to 4.5 tons of oil. Sweden has plans to have 100 X 103 ha of reeds. Brazil’s program of ethanol from sugarcane and manioc may employ 200 X 103 people and save $1600 million each year in foreign exchange.

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.