Ethanol is a liquid fuel and is blended with gasoline in various compositions (e.g., “E85” is 85% ethanol and 15% gasoline by volume). Most ethanol produced in the U.S. is derived from the fermentation of corn. Ethanol can also be produced from cellulosic feedstocks such as switchgrass or corn stover (a residue from corn crops). Biochemical conversion of cellulosic feedstocks has a pretreatement step that breaks cellulose into simpler sugars that can be easily fermented. Thermochemical conversion converts cellulosic feedstock into syngas (a mixture of carbon monoxide and hydrogen) that is then converted to ethanol.
LCA: Ethanol from Biomass
This is a life cycle environmental and cost analysis of ethanol using starch and cellulosic feedstocks. It provides a life cycle comparison of three tiers of technology, three types of biomass feedstocks, and two fuel-blending compositions for a total of 18 distinct pathways. When ethanol is blended with gasoline at an 85/15 ratio between ethanol and gasoline, the life cycle greenhouse gas (GHG) emissions are highly variable due to different feedstock types and ethanol production technologies. The biochemical chemical conversion of cellulosic feedstocks to ethanol has the lowest GHG emissions in this analysis, because of the energy recovered at the ethanol plant.
Authors: Tim Skone, James Littlefield, Gurbakhash Bhander, Tom Davis, Robert Eckard, John Haslbeck, Maura Nippert, Robert Wallace, Joe Marriott, PhD
Date: August, 2011
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