Tuesday, April 20, 2010
11-64

Evaluation of a whole slurry process for producing ethanol from dilute-acid pretreated corn stover

Edward W. Jennings, Andrew C. Lowell, Darren J. Peterson, Nancy S. Dowe, and Daniel J. Schell. National Bioenergy Center, National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401

A variety of process options are available for converting lignocellulosic biomass to ethanol. One common option involves separating the hemicellulosic liquor from dilute-acid-pretreated biomass slurries, conditioning the liquor and then recombining the liquor with the solids and performing either simultaneous saccharification and fermentation or separate enzymatic hydrolysis and fermentation. Alternatively, the liquid and solid stream could be processed separately and combined in the beer column. The purpose of this study was to explore the performance and economics of a “whole slurry” process in which the solid-liquid separation step is eliminated. Glucose released during enzymatic hydrolysis of the cellulosic solids in a dilute-acid-pretreated corn stover slurry, along with hemicellulosic sugars produced during pretreatment, was fermented to ethanol using a glucose-xylose fermenting Zymomonas mobilis. The slurry was neutralized with ammonium hydroxide to pH 4.8 prior to enzymatic hydrolysis or conditioned, the latter process removes inhibitors and improves hydrolysate fermentability. During the conditioning process, the pH of the pretreated slurry was raised to 8.5 with ammonium hydroxide, held at room temperature for 30 min, and then lowered to 4.8 with sulfuric acid prior to enzymatic hydrolysis. The impact of varying the total solids loading on glucose yields from enzymatic hydrolysis and on sugar-to-ethanol yields during fermentation will be presented as well as the relative economic impact of varying solids loading on ethanol production cost.