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Category: Applied and Industrial Microbiology
Production of Ethanol from Corn and Sugarcane, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815547/9781555819057_Chap01-1.gif /docserver/preview/fulltext/10.1128/9781555815547/9781555819057_Chap01-2.gifAbstract:
Cornstarch is processed to ethanol by either the dry-grind or wet-milling process. The two processes differ in how the kernel is initially treated to access starch for enzymatic hydrolysis. In addition to the use of sugar in ethanol production, wet-milled starch can also be sold as dried or modified corn starch, or converted enzymatically to dextrins and sweeteners, or fermented to any number of products. Alternate fermentation products include amino acids, vitamins, citric acid, and lactic acid. Some wet mills also produce vitamins, enzymes, pharmaceuticals, nutraceuticals, films, solvents, pigments, polyols, or fibers. Wet-milled corn fiber can also be converted to ethanol. As with corn, ethanol is produced from cane in two primary types of facilities, integrated sugar/ethanol production facilities and autonomous distilleries. Integrated sugar/ethanol production facilities are capable of switching cane processing between sugar and ethanol depending on economic driving forces, whereas autonomous plants are designed to process sugarcane solely for the production of ethanol. As with corn-based ethanol production facilities, sugar plants employ conventional distillation to concentrate ethanol to near-azeotropic (96%) concentrations for subsequent dehydration. Future biorefineries that process the whole corn plant (starch, fiber, and stover) or the whole sugarcane plant (sugars and bagasse) could produce liquid fuel, edible oil or sugars, animal feed, power, and polymers or chemical intermediates. Starch and sugars will continue to play an important role in ethanol production, even as lignocellulosic feedstocks come into production.
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Structure of the corn kernel. Reproduced from Nichols et al., 2006.
Scanning electron micrograph images of native corn starch granules. Bar, 20 μm. (A) Granules visible in a germinating corn kernel; (B) starch has undergone partial hydrolysis by day 7 of germination; (C) untreated purified starch granules; (D) purified granules treated with Aspergillus kawachi alpha-amylase and Aspergillus niger glucoamylase ( Shetty et al., 2005 ). Images courtesy of David Johnston and Peter Cooke, U.S. Department of Agriculture, Agricultural Research Service; and Jay Shetty, Genencor International, Inc.
The glucose-to-ethanol fermentation pathway.
Comparison of the dry-grind and wet-mill processes for production of ethanol. Courtesy of National Corn-to-Ethanol Research Center. Reproduced from Nichols et al., 2006 .
Simplified flow diagram of sugar and ethanol production at an integrated cane-processing facility.
Simplified flow diagram of ethanol production from cane at an autonomous distillery.