ASSESSMENT OF ETHANOL-PRODUCTION OPTIONS FOR CORN PRODUCTS

The production of ethanol from corn fiber has the potential to increas e ethanol yields by a maximum of 0.3 gal/bushel in a wet-milling proce ss. Incremental yields would be 0.13 gal/bushel from hexose, 0.1 from D-xylose and 0.07 from L-arabinose, at 100% hydrolysis and fermentatio n efficiency. At 80% efficiency for hexose hydrolysis and fermentation and 70% for pentose, an incremental yield of 0.22 gallons/bushel of c orn is expected Of this total, 0.1 gal/bushel would be from hexoses, 0 .07 from D-xylose, and 0.05 from L-arabinose. A maximum practical incr emental yield would probably fall between 0.22 and 0.3 gallons/bushel. bushel. These calculations are based on published compositional analy ses of cellulose, starch, mono-sac charides, hemicellulose, protein an d oil as distributed between the compartmentalized components of the c orn kernel and published yield factors for hexose and pentose fermenta tions. Experimental yield factors for xylose (0.36 g ethanol/g xylose) and arabinose (0.34) fermenting microorganisms are lower than that fo r glucose (0.45-0.50), and significantly less than the theoretical yie ld of 0.51 g ethanol/g pentose. Nonetheless, we estimate that a wet-mi lling facility which currently produces 100 million gallons/year of et hanol from starch could generate an additional $4-8 million of annual income if the fiber components were processed into ethanol. Hence, adv ances in fiber pretreatment and pentose fermentation are likely to hav e a major impact on enhancing productivity of corn ethanol plants. An engineering framework for assigning economic consequences of the addit ional utilization of fiber is presented. Copyright (C) 1997 Elsevier S cience Ltd.