Split addition of enzymes in enzymatic hydrolysis at high solids concentration to increase sugar concentration for bioethanol production

One challenge in making bioethanol production economical is to increase total solids in hydrolysis system while maintaining sugar conversion efficiency. Because the removal of excess water from hydrolysate requires enormous amounts of heat, large volume of reaction towers and high capital expenditure (CAPEX) for equipment, a lengthy operating time, and high operating costs. When solids loading in hydrolysis system increased from 5% to 20% with no mixing strategies, final sugar conversion decreased markedly. If cellulase is mixed with pulp at 5% solids and pressed to 20% solids, then 80% of the cellulase retained in the pulp thinned down the pulp mixture in 2 h. This thinning effect enabled additional cellulase, xylanase, and β-glucosidase to be mixed into the slurry. Sugar concentration was significantly improved; from 26 g/L to 121 g/L, while sugar conversion was remained as enzymatic hydrolysis with 5% total solids enzymatic hydrolysis. A US patent has been granted to NCSU for this concept and licenses have been granted to various companies.