Cellulosic biomass

Although most ethanol is now produced from corn, research has been done on producing this type of alcohol fuel from cellulosic biomass products including energy crops, forest and agricultural residues, and MSW, which would provide much cheaper feedstocks. The process of chemically converting these cellulosic biomass feedstocks is more involved and until this process can be simplified the price of ethanol will remain high. 

Several different plant layouts for ligno-cellulosic biomass conversion to ethanol are known using enzymatic hydrolysis ... 

Also, a Spanish company (Abengoa Bioenergy) has developed a process for the conversion of ligno-cellulosic biomass to ethanol based on SSF. A demonstration plant on the basis of wheat and barley straw has been operating in Salamanca since 2006, with an annual production capacity of five million litres of ethanol (Abengoa, 2006). 

New catalytic approaches for the pretreatment and hydrolysis of (ligno)cellulose biomass to fermentable sugars... 

Currently, cellulosic biomass use is very hmited due to the expensive pretreatment required for breaking the crystalline stractnre of cellnlose. Bioethanol is already an established commodity due to its ongoing non-fuel uses in beverages, and in the manufactnre of pharmaceuticals and cosmetics. In facf ethanol is the oldest synthetic organic chemical used by mankind. Table 3.3 shows ethanol production in different continents (Demirbas, 2008b). 

Over the past two decades, considerable interest has been directed toward the conversion of cellulosic biomass (such materials as wood wastes, bagasse, and straw) into useful products, notably fuels. Several procedures, including fermentation, gasification, liquefaction, and pyrolysis, have been commercially applied to carbohydrates with various degrees of success. In order to use the polysaccharides present in lignocel-lulosic materials as a substrate in fermentation processes, pretreatments are necessary, such as with steam (under slightly acid conditions) or... 

Traditionally, com is dry-milled and suspended in boiling water to free the carbohydrate-rich starch compound from the nonstarch, cellulose biomass. The starch and cellulose components at this stage carry through the process. The non-convertible cellulose biomass is later separated. The milled com-water slurry, called mash, is boiled for about 1 hour. Enzymes such as a-amylase can be added to the process to help prevent gellation of starch. 

Steeping and wet-milling processes are also utilized to separate soluble compounds from com. One process involves removal of soluble starch and protein from com by steeping com in a warm sulfurous acid solution for about one to two days. The undissolved com solids are then coarsely wet-milled and processed to collect the oil-containing germ for com oil production. Also, for more enzyme-resistant cellulose biomass, sulfuric acid or hydrochloric acid can be used to digest the cellulose polysaccharide into fermentable molecules. 

Lynd, LR et al., Fuel Ethanol from Cellulosic Biomass, Science, 251(4999), 1318-1323 (1991)... 

While this reaction is substantially exothermic (6), it provides an intriguing approach to the production of fuels from renewable resources, as the required acids (including acetic acid, butyric acid, and a variety of other simple aliphatic carboxylic acids) can be produced in abundant yields by the enzymatic fermentation of simple sugars which are, in turn, available from the microbiological hydrolysis of cellulosic biomass materials ( ] ) These considerations have led us to suggest the concept of a "tandem" photoelectrolysis system, in which a solar photoelectrolysis device for the production of fuels via the photo-Kolbe reaction might derive its acid-rich aqueous feedstock from a biomass conversion plant for the hydrolysis and fermentation of crop wastes or other cellulosic materials (4). 

Ethanol production from ligno-cellulosic biomass... 

Production of Ethanol from Cellulosic Biomass Hydrolysates Using Genetically Engineered Saccharomyces Yeast Capable of Cofermenting Glucose and Xylose... 

Lignocellulosic, often termed cellulosic, biomass is the most abundant renewable resource on Earth, and large-scale production of organic fuels and chemicals from this low-cost sustainable resource would provide unparalleled environmental, economical, and strategic benefits (2-5). 

Saccharification of cellulosic biomass by dilute acid has a much longer history than the enzymatic process. The initial acid-catalyzed wood saccharification was in operation in Germany as early as the 1940s (1). In recent... 

Sedlak, M. and Ho,N.W.Y. (2004). Production of Ethanol From Cellulosic Biomass Hydrolysates Using Genetically Engineered Saccharomyces Yeast Capable of Cofermenting Glucose and Xylose. Appl. Biochem. Biotechnol., 113-116, 403-416. 

Figure 15.9 Block diagram for bioethanol from ligno-cellulosic biomass [27], CBP = consolidated biprocessing, CF = cofermetation, SSF = simultaneous saccharification and fermentation, SSCF = simultaneous saccharification and cofermentation. Components C = cellolose,...

Wyman, C., Potential synergies and challenges in refining cellulosic biomass to fuels, chemical, and power, Biotechnol. Prog., 19, 254-262, 2003... 

Freer, S. N., Skory, C. D., and Bothast, R. J. 1998. Production of fuel alcohol from cellulosic biomass. In Pandalai, S. G. (Ed.), Recent Research Developments in Microbiology (pp. 201-210), Trivandrum Research Signpost. 

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