|TAKAMIZAWA, KAZUHIRO - Gifu University
|Anderson, William - Bill
|SINGH, HARI - Fort Valley State University
Submitted to: Industrial Crops and Uses
Publication Type: Book / Chapter
Publication Acceptance Date: 2/1/2010
Publication Date: 9/2/2010
Citation: Takamizawa, K., Anderson, W.F., Singh, H.P. 2010. Ethanol from lignocellulosic crops. In: Singh, B.P., editor. Industrial Crops and Uses. CABI. Wallingford, UK: p. 104-139.
Interpretive Summary: not required
Technical Abstract: Wood, grasses, and most of the plant litter represent the major part of the biomass in nature and are collectively called lignocellulose. Regardless of the source, lignocellulosic materials are mainly composed of cellulose, hemicellulose, and lignin. Over 150 billion tonne of organic substances are photosynthesized annually which consist of above three major constituents with an average proportion of 4:3:3. Various estimates conclude that there are 2.5-4 ×1011 tonne of cellulose and 2-3 ×1011 tonne of lignin on the earth, representing 40% and 30% of organic matter carbon, respectively, with other polysaccharides comprising 26%. Because cellulose, hemicellulose and lignin are closely associated in plants, isolating these compounds to a pure state is virtually impossible. They also are not uniformly distributed in the plant cell wall; the S2-layer of the secondary wall has the highest percentage of cellulose, and the middle lamella has the highest percentage of lignin, but all three compounds are present in every cell wall layer. Their distribution in the different parts of the plant is also not uniform. Gramineous plants have more variation than woody plants. In addition, some grasses contain considerable amounts of pectin in the middle lamella, whereas wood contains only small quantities of extractives, inorganic compounds, and pectin. Based on weight percentage, cellulose and hemicelluloses are higher in hardwoods compared to softwoods and wheat straw, while softwoods have higher lignin content. Historically, ligonocellulosic biomass is used in direct combustion to produce heat or anaerobically to produce charcoal. However, biomass can be converted into a number of other forms of energy. Conversion to electricity can be accomplished by burning or co-firing with coal at power plants. Recently emphasis has also focused on biomass as a feedstock for the production of biofuels for transportation or synthesis of industrial chemicals. There are two primary avenues for conversion of lignocellulosic materials. Biochemical conversion uses enzymes from living organisms to degrade plant cell wall components, except for lignin, to sugars that can then be fermented to alcohols. This is similar to the means that microbes from ruminant animals use to degrade and supply nutrients to the host from forage grasses and legumes. Thermochemical conversion encompasses an array of methods that combines varying levels of heat and pressure to convert biomass to bio-oils, syngas, or biochemicals. These products can then in turn be processed to fuels such as ethanol. Residues from thermochemical processes are char and ash.