Removal of Acidic Impurities from Corn Stover Hydrolysate Liquor by Resin Wafer Based Electrodeionization

Dilute acid (sulfuric acid) pretreatment of lignocellulosic biomass releases monomeric xylose, xylo-oligomers, and acetic acid by degradation of hemicellulose. Acids inhibit both the enzymatic hydrolysis of cellulose to monomeric sugars and downstream fermentation of sugars to biofuels. Removal of acetic acid and sulfuric acid, as well as the nonionic toxic impurities, from the hydrolysate liquor prior to enzymatic hydrolysis may improve biofuel yields. Development of an efficient acid separation technique is essential for enhanced process performance and cost-effective biofuel production. We evaluated the use of an electrically driven membrane separation technique, resin wafer based electrodeionization (RW-EDI), for the removal of ionic impurities (acetic acid and sulfuric acid) from corn stover hydrolysate liquor. RW-EDI provides the capability to control solution pH in situ by voltage adjustment. In situ pH control enables pK_a-selective recovery of acids (or bases). The results indicate that RW-EDI is capable of removing ionic impurities using fewer unit operations and less chemicals and water than the existing process using overliming as a conditioning step to dilute acid pretreatment of corn stover. We report greater than 99 and 95% removal of sulfuric and acetic acids, respectively, from dilute sulfuric acid pretreated corn stover hydrolysate liquor. Sugar retention was greater than 98%. We also report strategies to selectively separate sulfuric acid and acetic acid into two individual acid enriched streams from the hydrolysate liquor by manipulating the operating conditions. These results point toward a deployment strategy with sequential (mineral then organic) acid-removal steps.