(603a) Performance Of Alkaline Pretreatment As Affected By Reagent, Mode Of Reaction, And Feedstock Composition

Alkaline pretreatments were applied to hybrid poplar feedstock using aqueous ammonia and NaOH. Two batches of hybrid poplar were used: high lignin (HL) hybrid poplar and low lignin (LL) hybrid poplar. These feedstocks were treated with three different types of alkaline pretreatment processes. Two different modes of operation was used in aqueous ammonia pretreatment: a flow-through process termed as ammonia recycle percolation (ARP), and a batch process named soaking in aqueous ammonia (SAA). Additionally a batch pretreatment using NaOH was investigated. Both reagents were effective in delignifying the biomass and increasing the glucan digestibility. In treatment using ammonia, most of the hemicellulose is retained in solids. NaOH, however, reacts with carbohydrates in biomass during pretreatment causing slight loss in it. Addition of hydrogen peroxide during NaOH treatment was found helpful in increasing the delignification as well as carbohydrate retention in solids. For LL hybrid Poplar, pretreatment by ammonia or NaOH gave above 90% of glucan and xylan digestibilities with use of cellulase/xylanase mixture. For HL hybrid poplar, pretreatment with NaOH gave better results than ammonia. NaOH/H2O2 treated HL hybrid poplar gave nearly quantitative glucan and xylan digestibilities when cellulase/xylanase mixture was applied. The maximum glucan/xylan digestibilities obtained for ammonia treated HL hybrid poplar were 86%/77%. Reaction products in the pretreatment liquids were analyzed to identify the reactions occurring in the liquid during pretreatment. In NaOH treatment, substantial fraction of dissolved hemicellulose reacts with lignin forming a lignin-carbohydrate complex (LCC). In ammonia treatment, partial hydrolysis of hemicellulose occurs. The carbohydrates in the liquid were primarily xylose oligomers.