Assessment of ethanol production options for corn products

The production of ethanol from corn fiber has the potential to increase ethanol yields by a maximum of 0.3 gal/bushel in a wet-milling process. Incremental yields would be 0.13 gal/bushel from hexose, 0.1 from -xylose and 0.07 from -arabinose, at 100% hydrolysis and fermentation efficiency. At 80% efficiency for hexose hydrolysis and fermentation, and 70% for pentose, an incremental yield of 0.22 gallons/bushel of corn is expected. Of this total, 0.1 gal/bushel would be from hexoses, 0.07 from -xylose, and 0.05 from arabinose. A maximum practical incremental yield would probably fall between 0.22 and 0.3 gallons/bushel. These calculations are based on published compositional analyses of cellulose, starch, mono-saccharides, hemicellulose, protein and oil as distributed between the compartmentalized components of the corn kernel and published yield factors for hexose and pentose fermentations. Experimental yield factors for xylose (0.36 g ethanol/g xylose) and arabinose (0.34) fermenting microorganisms are lower than that for glucose (0.45–0.50), and significantly less than the theoretical yield of 0.51 g ethanol/g pentose. Nonetheless, we estimate that a wet-milling facility which currently produces 100 million gallons/year of ethanol from starch could generate an additional $4–8 million of annual income if the fiber components were processed into ethanol. Hence, advances in fiber pretreatment and pentose fermentation are likely to have a major impact on enhancing productivity of corn ethanol plants. An engineering framework for assigning economic consequences of the additional utilization of fiber is presented.