Liquefaction, Saccharification, and Fermentation of Ammoniated Corn to Ethanol

Abstract

Treatment of whole corn kernels with anhydrous ammonia gas has been proposed as a way to facilitate the separation of nonfermentable coproducts before fermentation of the starch to ethanol, but the fermentability of ammoniated corn has not been thoroughly investigated. Also, it is intended that the added ammonia nitrogen in ammonia treated corn (similar to 1 g per kg corn) may satisfy the yeast nutritional requirement for free amino nitrogen (FAN). In this study, procedures for ammoniation, liquefaction, saccharification, and fermentation at two scales (12-L and 50-mL) were used to determine the fermentation rate, final ethanol concentration, and ethanol yield from starch in ammoniated or nonammoniated corn. The maximum achievable ethanol concentration at 50 h fermentation time was lower with ammoniated corn than with nonammoniated corn. The extra nitrogen in ammoniated corn satisfied some of the yeast requirements for FAN, thereby reducing the requirement for corn steep liquor. Based upon these results, ammoniation of corn does not appear to have a positive impact on the fermentability of corn to ethanol. Ammoniation may still be cost effective, if the advantages in terms of improved separations outweigh the disadvantages in terms of decreased fermentability.