7.6 Summary and Final Tasks
This lesson continued from the previous lesson, but went into greater depth with the processing aspects of ethanol production. Starch and cellulose must first be converted into glucose before fermentation into ethanol and CO2. Starch feedstocks include sugarcane in Brazil, sugarbeets in Europe, and corn in the US. In order to process corn, there are five steps: grinding, cooking and liquefaction, saccharification, fermentation, and distillation. Enzymes are needed in saccharification, and yeast is needed in fermentation. Cellulose to glucose requires some additional steps and enzymes in order to break the structure down, but once it gets to the glucose stage, all the processing is the same. Because the water in the ethanol must be removed for use as a fuel, the last steps include distillation and molecular sieve.
Butanol can be produced in a similar way, but acetone and ethanol also accompany butanol processing. Different enzymes are used. While the concentration of butanol is low when converting from feed materials, butanol has some advantages over using ethanol; it mixes better with gasoline and has a higher energy content.
Pryor, Scott; Li, Yebo; Liao, Wei; Hodge, David; “Sugar-based and Starch-based Ethanol,” BEEMS Module B5, USDA Higher Education Challenger Program, 2009-38411-19761, 2009.
Bothast, R.J., Schilcher, M.A., Biotechnological processes for conversion of corn into ethanol, Appl. Microbiol. Biotechnol., 67, 19-25, 2005.
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