A Demonstration of the Consistency of Maize Stover Pretreatment by Soaking in Aqueous Ammonia from Bench to Pilot-Scale

Abstract

Soaking in aqueous ammonia (SAA) is a means of pretreating biomass at moderate temperatures and ammonia concentrations (15% w/w). To establish process consistency and scalability, sieved maize stover was pretreated at 50-ml, 300-ml, and 100-l scales. Each scale was carried out through different methods. Sealed reactor tubes were used for 50-ml pretreatment. Fabric dyeing apparatus was used for the 300-ml pretreatment and a commercial Littleford DVT reactor was used for 100-l pretreatment. For each scale, biomass washing and solid-liquid separations were scaled appropriately. Washed pretreated solids were analyzed for composition and recovery of dry biomass and carbohydrates calculated. Nearly 100% of the glucan content was recovered in pretreated solids at all three scales, indicating the viability of SAA pretreatment. Pretreated solids (15% w/w) were hydrolyzed in a 1-l twin Sigma blade mixer using Cellic CTec2 (15 FPU.g-glucan−1) followed by fermentation in shake flasks. Hydrolytic yields ranged 65–70% across scale treatments. In comparison, fermentative yields averaged 95% across scale treatments, indicating saccharification to be a rate-limiting step in effective bioconversion of lignocellulose.