Tuesday, May 3, 2011
Many lignocellulosic feedstocks for ethanol production are being considered for commercial processes. One promising new feedstock is sorghum because of its high yield of biomass per acre, shorter growing season, and relative drought resistance. We investigated ethanol production from pretreated dilute-acid pretreated sorghum and corn stover in bench and pilot scale fermentors. To access the carbohydrates, we used a dilute sulfuric acid pretreatment step to convert hemicellulose to fermentable monomeric sugars which also improves the digestibility of cellulose by enzymes. After pretreatment, the hydrolysate pH was adjusted with ammonium hydroxide and a cellulase cocktail was used for enzymatic hydrolysis of cellulose to fermentable glucose. We fermented the monomeric sugars to ethanol using the glucose-xylose co-fermenting recombinant bacteria, Zymomonas mobilis 8b. In small 0.5-L fermentors, we compared ammonium hydroxide neutralization of the hydrolysate with ammonium hydroxide conditioning at two different solids loadings and measured cellulose-to-glucose and sugar-to-ethanol yields. To investigate the ability to achieve similar results at the pilot scale, the best performing condition at the bench scale was tested in a 1,500-L fermentor. We will provide an analysis of the data, highlighting the potential for sorghum as a feedstock in comparison with corn stover.