Centralized low-severity EA treatment can be integrated with the AFEXTM-based depots to significantly reduce enzyme requirements in the biorefinery

The implementation of large scale biorefineries brings logistic challenges that include moving large amounts of low-density biomass from long distances in a cost-effective way. AFEX pretreatment allows the production of stable and highly dense biomass pellets which are more easily stored and transported long distances from regional depots to large scale biorefineries. Recent advancements in pretreatment technology have introduced Extractive Ammonia (EA) pretreatment, allowing ~ 60% reduction of enzyme loading and the production of more fermentable hydrolysates compared to AFEX. EA pretreatment is effective by converting cellulose I to a more digestible cellulose III, cleaving lignin-carbohydrate crosslinks and selectively extracting lignin from the plant cell wall. Though cellulose III can be formed at low temperatures, higher temperatures are required to break lignin-carbohydrate crosslinks and make lignin more extractible. A major bottleneck for EA pretreatment is the high operating pressure generated at temperatures around 120˚C. To solve this issue, we subjected corn stover to high temperature reactions during AFEX, simulating the depot concept. The AFEX-treated pellets were further EA-treated in a large-scale biorefinery scenario at moderate temperatures and pressures to activate cellulose III and extract lignin. Detailed process mass balances were performed using optimum EA pretreatment conditions at 25˚C (200 psi), 6% glucan loading enzymatic hydrolysis and yeast fermentation. Results were compared to standalone AFEX and EA scenarios, respectively. This study shows that an additional EA pretreatment step after AFEX improves ethanol yields from 0.11 to 0.17 g/g biomass, using 7.5 mg enzyme/g glucan, comparing with a standalone AFEX scenario.