Removal of Acetic Acid From Hydrolysate Using a Membrane Extractor/Reactor

Production of bioethanol from lignocellulosic biomass requires pretreatment of the biomass to hydrolyze hemicellulose, separate lignin and reduce cellulose crystallinity. During the pretreatment by dilute acid hydrolysis, acetic acid is generated in concentrations of up to several grams per liter. Before the subsequent enzymatic hydrolysis, acetic acid needs to be removed from the hydrolysate since it can dramatically reduce the efficiency of fermentation by inhibiting enzyme activity. Currently, detoxification is done by lime treatment of the hydrolysate, but it consumes significant quantities of calcium hydroxide and does also not produce any valuable products. Therefore, we propose to remove the acetic acid with an alternative process whereby acetic acid is extracted into 1-octanol in a membrane extractor and reacted with 1-octanol in situ on the membrane or in a separate reactor yielding 1-octyl acetate. Acetic acid concentration in hydrolysate will be reduced from 12.5 g/L to < 1 g/L. The extracted acid will be esterified with 1-octanol and the ester will be removed periodically from the organic phase. Thus, the membrane extractor/reactor removes the acetic acid and produces a valuable product in an environmentally friendly process.