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26 - Biofuels from cellulosic biomass via aqueous processing
- from Part 3 - Renewable energy sources
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- By Jian Shi, Center for Environmental Research and Technology, University of California, Riverside, CA, USA, Qing Qing, Center for Environmental Research and Technology, University of California, Riverside, CA, USA Department of Chemical and Environmental Engineering, University of California, Riverside, CA, USA, Taiying Zhang, Center for Environmental Research and Technology, University of California, Riverside, CA, USA, Charles E. Wyman, Center for Environmental Research and Technology, University of California, Riverside, CA, USA Department of Chemical and Environmental Engineering, University of California, Riverside, CA, USA, Todd A. Lloyd, Mascoma Corporation, Lebanon, NH, USA
- Edited by David S. Ginley, National Renewable Energy Laboratory, Colorado, David Cahen, Weizmann Institute of Science, Israel
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- Book:
- Fundamentals of Materials for Energy and Environmental Sustainability
- Published online:
- 05 June 2012
- Print publication:
- 30 November 2011, pp 336-348
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Summary
Focus
Thermochemical aqueous processing of cellulosic biomass requires depolymerization of long chains of carbohydrate molecules into fragments that can be metabolized by micro-organisms or catalytically converted to fuels and chemicals. This chapter focuses on such processes for carbohydrate depolymerization and their integration with subsequent product-formation steps in an effort to produce ethanol and other biofuels.
Synopsis
Cellulosic biofuels, which once were widely used but whose usage dropped sharply upon the introduction of refined petroleum products to the energy supply, can be a cost-effective fuel with applications in vital areas. Current strategies focus on maximizing the efficiency of conversion of cellulosic biomass waste into energy-rich products, especially liquid fuels, such as alcohols and other hydrocarbons. Recent research on the chemical and biological pretreatment of cellulosic feedstock materials shows promise for surpassing thermal processes in catalyzing the breakdown of cellulose and lignin, which is a crucial first step in the production of useful fuels. Chemical pretreatments include autohydrolysis, application of low and high pH (i.e., acids and bases), exposure to ammonia, and treatment with organic solvents and ionic liquids. Each of these methods is effective at breaking cellulose down so that it can be more easily digested enzymatically. These techniques generally offer good yields from a variety of feedstocks and therefore should be broadly applicable. In particular, it is expected that feedstocks will include waste materials such as food-crop residues (e.g., corn stover and sugarcane bagasse) and dedicated energy crops (e.g., switchgrass) that can be grown on otherwise agriculturally poor land. This aspect is particularly important in terms of minimizing the societal and environmental impacts of biofuels technology. For example, use of such feedstocks is intended to eliminate competition with food crops for arable land, which could lead to sharp increases in food prices. It should also help minimize the issue of indirect land-use change (see Chapter 2) that could actually result in increased CO2 emissions.
Cellulosic Ethanol: A Unique Sustainable Liquid Transportation Fuel
- Charles E. Wyman
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- Journal:
- MRS Bulletin / Volume 33 / Issue 4 / April 2008
- Published online by Cambridge University Press:
- 31 January 2011, pp. 381-383
- Print publication:
- April 2008
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- Article
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Although ethanol is now made from the sugars in the starch fraction of corn and other crops and from the sugar in sugarcane, a much greater impact for ethanol in terms of fuel use could be realized if the sugars from more recalcitrant cellulosic biomass could be converted to ethanol. Cellulosic biomass is the structural portion of plants and includes agricultural (e.g., corn stover, which is all of the above-ground portion of the corn plant, excluding the grain) and forestry (e.g., sawdust) residues, major fractions of municipal solid waste (e.g., waste paper and yard waste), and herbaceous (e.g., switchgrass) and woody (e.g., poplar) crops grown as energy resources. Although distinctive in outward appearance, these materials all comprise about 40–50% cellulose and 20–30% hemicellulose, with lesser amounts of lignin and other compounds such as sugars, oils, and minerals. Cellulose is a polymer of glucose sugar molecules that are physically linked together in a crystalline structure to provide structural support for plants. Hemicellulose is also made up of sugars covalently joined together in long chains, but it generally includes fve different sugars: arabinose, galactose, glucose, mannose, and xylose. In addition, hemicellulose is an amorphous, branched material. Lignin is a phenylpropene compound that can be viewed as a low-sulfur, immature coal.