Biodiesel can be made from any oil/lipid source; the major components of these sources are triacylglycerol molecules. In general, biodiesel feedstocks can be cate­gorized into three groups: pure vegetable oils, animal fats, and waste cooking oils.

Biodiesel from Pure Vegetable Oil

The first group is pure oils derived from various crops and plants such as soybean, canola (rapeseed), corn, cottonseed, flax, sunflower, peanut, and palm. These are the most widely used feedstocks by commer­cial biodiesel producers. The oil composition from vege­table crops is pure; this cuts down on preprocessing steps and makes for a more consistent quality of bio­diesel product. However, there is an obvious disadvan­tage for vegetable oils as biodiesel feedstocks: wide scale production of crops for biodiesel feedstocks can cause an increase in worldwide food and commodity prices. Such a "food vs fuels" debate has reached national atten­tion when using vegetable oils for biodiesel production. Alternative feedstocks usually arise out of necessity from regions of the world where the above materials are not locally available or as part of a concerted attempt to reduce reliance on imported petroleum.

JATROPHA CURCAS (JATROPHA)

The nonedible oil from Jatropha curcas (Jatropha) has recently attracted extensive attention as a feedstock for biodiesel production in India and other climatically par­allel regions of the world (Kumartiwari et al., 2007; Kalbande et al., 2008). The Jatropha tree is a perennial shrub belonging to the Euphorbiaceae family whose seeds contain up to 30 wt% oil. This plant can be found in tropical and subtropical regions such as Africa, Indian subcontinent, Central America, and other countries of Asia. Since Jatropha oil contains a relatively elevated percentage of saturated fatty acids (Table 1.4), the corre­sponding methyl esters display relatively poor low

temperature operability, as evidenced by pour point (PP) value of 2 °C (Kumartiwari et al., 2007).

Vijai K. Gupta1’*, Ravichandra Potumarthi2, Anthonia O’Donovan,
Christian P. Kubicek3, Gauri Dutt Sharma4, Maria G. Tuohy 1’*

1Molecular Glycobiotechnology Group, Department of Biochemistry, School of Natural Sciences, National
University of Ireland Galway, Galway, Ireland, ^Department of Chemical Engineering, Monash University,
Clayton, Victoria, Australia, ^Research Area Biotechnology and Microbiology, Institute of Chemical Engineering,
TU Wien, Gumpendorferstrasse Wien, Austria, 4Bilaspur University, Bilaspur, Chattisgarh, India
*Corresponding author email: vijai. gupta@nuigalway. ie, maria. tuohy@nuigalway. ie

OUTLINE

Introduction 23

Current Bioenergy Practices 25

Main Biofuel Technologies and Current Processes 26

Technological Routes for Bioenergy Production 28

Biomass Pretreatment 28

Hydrolysis 29

Fermentation 29

Combined Pretreatment, Hydrolysis and Fermentation Strategies 29

Advanced Biomass-to-Biofuels Development Platform 30

INTRODUCTION

Fossil fuels such as petrol, diesel or crude oil, are nonrenewable sources of fuel and are not natural resources in many countries making these nations depen­dent on fossil fuel-rich countries at enormous expense. The rising cost and simultaneous depletion of fossil fuels, in addition to political instability in key countries, means the competitiveness of biomass-derived energy has increased considerably. Additionally bioenergy sources, including biofuels, pose a reduced threat to the environment because they are biodegradable and
nontoxic; biofuel spillages present far less risk than fossil fuel spillages (Hahn-Hagerdal et al., 2006).

Bioenergy is a term broadly used to describe gaseous, liquid or solid energy products that, for the most part, are derived from biological raw materials (biomass). In the 1990s bioethanol was a promising technological option to reduce transportation sector greenhouse gas (GHG) emissions (Lynd, 1996); most of this ethanol was derived from so-called first-generation, starch — and sucrose-rich feedstocks. Bioethanol is readily made from starchy seeds, tubers, or roots of plants such as maize (Zea mays), barley (Hordeum vulgare),

Bioenergy Research: Advances and Applications

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wheat (Triticum aestivum), rice (Oryza sativa), potato (Solanum tuberosum), sweet potato (Ipomea batatas), cassava (Manihot esculenta), Jerusalem artichoke (Helian — thus tuberosus), etc. and from the sugar-rich stems and roots of sugarcane (Saccharum officinarum), sweet sorghum (Sorghum vulgare), and sugar beet (Beta vulga­ris). Indeed, the basic technology for making ethanol from such crops is centuries old (Lemus and Parrish,

2009) . Currently bioethanol is produced commercially by fermentation of sugars derived from corn, sugar cane and sugar beet. It is expected that, in light of the increase in global population and the "food versus fuel" debate, there will be limits to the supply of these feedstocks for biofuel production in the near future ulti­mately making first-generation biofuels an unsustain­able approach to meet future energy needs (O’Donovan et al., 2013; Groom et al., 2008; Simpson et al., 2008).

Perennial herbaceous energy crops make good feed­stocks because they do not require annual reseeding once established, need fewer energy inputs (such as fer­tilizers and pesticides) than annual cropland, and can be grown on marginal lands (Dien et al., 2005). They also have environmental benefits that include reduced soil erosion, enhanced carbon sequestration, and conserva­tion of wildlife habitats (Lemus and Lai, 2005). The major herbaceous energy crops that have been selected for bioethanol production in the United States are switch grass (Panicum virgatum), Miscanthus (Miscanthus spp. Anderss.), canary grass (Phalaris arundinacea), giant reed (Arundo donax L.), and alfalfa (Medicago sativa L.). They are considered to have energetic, economic, and environmental advantages over food crops for ethanol production. While these dedicated energy crops contain substantial amounts of holocellulose (cellulose and hemicelluloses) in their cell walls, their feedstock quality for livestock makes them less attractive options for fuel ethanol and bioenergy generation (Hill et al., 2006).

It is essential to approach renewable energy (REN) production through the application of complementary technologies. The recent "food versus fuel" debate has motivated the development of technologies to utilize nonfood crops as well as food wastes and agri­processing wastes, in biomass to bioenergy strategies; therefore, lignocellulosic residues and other nonfood plant biomass types are considered attractive alternative feedstocks.

Large efforts are being made worldwide in order to develop technologies that generate clean, sustainable energy sources from nonfood biomass feedstocks that could substitute fossil fuels (Ragauskas et al., 2006; Levin et al., 2006). At present, in the United States, biomass provides about 40 times as much energy as photovoltaics (Banerjee, 2011) and represents 78% of the total REN generated worldwide (International Energy Agency (IEA), 2010). Biofuels are the only viable energy source for the foreseeable future and can provide sustainable development in a manner that will address socioeconomic and environmental concerns (Demirbas, 2005).

Bionergy derived from second-generation feedstocks,

i. e. lignocellulosic materials is now the prime target for commercial biofuel production (O’Donovan et al., 2013; Demain, 2009). Lignocellulosic biomass is an abun­dant, domestic, renewable feedstock source rich in com­plex carbohydrates, which can be converted to liquid transportation fuel and other chemicals by strategies involving carbohydrate degradation and subsequent fermentation. More than 70% of lignocellulosic biomass is made up of the complex biopolymers, cellulose, hemi — cellulose, and lignin. The organization of these struc­tural polymers in the plant cell wall makes such feedstocks highly recalcitrant to bioconversion and diffi­cult to use as a raw material in ethanol production compared with starch (O’Donovan et al., 2013; Abramson et al., 2010; Somerville et al., 2010). However, lignocellulosic biomass in the form of wood and agricul­tural residues is virtually inexhaustible (Sarkar et al., 2012; Zhang et al., 2007; Zhang and Lynd, 2006; Lynd et al., 2002; Kuhad et al., 1997). Agricultural residuals or by-products are annually renewable, abundantly available and account for more than 180 million tons of biomass per year (Kapdan and Kargi, 2006). The most abundant lignocellulose agricultural residues are corncobs, corn stover, wheat, rice, barley straw, sorghum stalks, coconut husks, sugarcane bagasse, switchgrass, pineapple and banana leaves (Demain et al., 2005; Kim and Dale, 2004). Cereal crops, pulse crops and harvest — able palm oil biomass are also being produced in large amounts worldwide annually (Rajaram and Verma, 1990). In addition, wood and paper industries generate huge amounts of residual lignocellulosic biomass. Along with agricultural and forestry wastes and residues, locally available nonfood plant biomass and municipal solid wastes are potential candidates to meet demands for biofuel and bioenergy production, since additional costs for cultivation and harvesting are not involved. It is likely that the diversity of raw materials will support the decentralization of fuel production with geopolitical, economic, and social benefits (Wyman, 2007), thus bringing further socioeconomic benefits.

The concept of replacing fossil fuels with alternative biobased energy sources and fuels has been markedly enhanced by the realization that plant biomass also has the potential to provide a wide range of feedstock (bio)chemicals that can yield high-value commodity products and offset bioenergy production costs in lignocellulose-based biorefinery approaches (Zhu and Zhuang, 2012; Cherubini, 2010; FitzPatrick et al., 2010; Percival Zhang, 2008; Taylor, 2008; Kamm and Kamm,

2004) . Bioenergy production processes (e. g. anaerobic digestion and thermochemical treatments) can also generate organic wastes that still have significant market potential, for example, as organic fertilizers and bio­chars, which are most important for soil enrichment. The developments in biorefining have underpinned several recent and promising advances in bioenergy (Aden et al., 2002).

Bioethanol, biobutanol and biomethane are prom­ising future bioenergy and biofuel sources. Biomethane is produced most frequently through anaerobic diges­tion, in which biomass is converted by consortia of bacteria via hydrolysis, fermentation, acetogenesis and methanogenesis reaction steps to methane and smaller amount of other gases (Keating et al., 2012; Liew et al., 2012; McHugh et al., 2003; Mata-Alvarez et al., 2000). Liquid fuels that are being produced from biomass are typically of higher quality and burn more cleanly than petroleum-based diesel and jet fuels. Biofuels also reduce the release of volatile organic compounds, as the addition of ethanol to gasoline oxygenates the fuel mixture causing it to burn more completely. Biodiesel is another important biofuel usually produced from oleaginous crops, such as rapeseed, soybean, sunflower, palm and from microalgae through a chemical transes­terification process of their oils with shortchain alcohols, mainly methanol (Antolin et al., 2002). Thus, a shift to biofuels for current fuel needs would reduce energy dependency on oil imports and could boost rural devel­opment, providing farmers and crop producers with an additional source of income.

Another nonedible biomass originated in India is Pongamia pinnata (Karanja), which is a medium-sized de­ciduous plant that grows fast in damp and subtropical environments and matures in 5—7 years to tender fruit that contains two kidney-shaped kernels (Mohibbeazam et al., 2005). The oil content of Karanja kernels ranges be­tween 25 wt% and 40 wt% (Karmee et al., 2005; Mohibbeazam et al., 2005). The primary fatty acid found in Karanja oil is oleic acid (45—70 wt%), followed by palmitic, linoleic, and stearic acids (Karmee et al., 2005; Naik et al., 2008). The low-temperature operability of the parallel methyl esters from karanja is superior to that of jatropha oil methyl esters as a result of the fairly high percentage of oleic acid in karanja oil, as evidenced by cloud point (CP) and PP values of —2 °C and —6 °C, respectively (Srivastava and Verma, 2008).

MADHUCA INDICA (MAHUA)

Madhuca indica, commonly known as "Mahua", is a tropical plant found frequently in the central and north­ern plains and forests of India. It belongs to the family Sapotaceae and grows rapidly up to 20 m in height, pos­sesses evergreen or semievergreen foliage, and is well adapted to dry environments (Ghadge and Raheman, 2006; Kumari et al., 2007). The fruit is nonedible, obtained from the tree in 4—7 years and contains one to two kidney-shaped kernels (Mohibbeazam et al., 2005). The oil content of dried Mahua seeds is about 50 wt%. Mahua oil is characterized by free fatty acid (FFA) con­tent of around 20 wt% and a comparatively high percent­age of saturated fatty acids such as stearic (14.0 wt%) and palmitic (17.8 wt%) acids (Ghadge and Raheman,

2006) . The remaining fatty acids are mostly spread among unsaturated components such as linoleic (17.9 wt%) and oleic (46.3 wt%) acids (Singh and Singh, 1991). The relatively high percentage of saturated fatty acids (35.8 wt%) found in Mahua oil results in relatively poor low-temperature properties of the parallel methyl esters, as evidenced by PP value of 6 °C (Ghadge and Raheman, 2006).