Integration of Autohydrolysis and Organosolv Delignification for Efficient Acetone, Butanol, and Ethanol Production and Lignin Recovery

A two-stage pretreatment, i.e., autohydrolysis and organosolv delignification, was used prior to enzymatic hydrolysis and fermentation by Clostridium acetobutylicum for the improvement of acetone, butanol, and ethanol (ABE) production from rice straw, pine, and elm. Through the autohydrolysis, a liquid, "autohydrolysate", containing 2-7 g/L sugar and 13-27 g/L oligomer, and a pretreated solid were obtained. The solid was subjected to organosolv delignification leading to 490-600 g of pretreated lignocelluloses (70%-74% cellulose) and 100-140 g lignin from each kilogram of lignocelluloses. The pretreated lignocelluloses were hydrolyzed to "cellulosic hydrolysates" and fermented to 6-10 g/L ABE. Through this process, 70-123 g of ABE was produced from each kilogram of lignocelluloses. "Overall hydrolysates" with further sugar concentrations of 16-50 g/L were obtained by hydrolysis of pretreated solid in the autohydrolysate. The yield of ABE production was progressed to 133 g ABE/kg elm by fermenting its overall hydrolysate.