Influence of alkaline catalyst addition on compressed liquid hot water pretreatment of rice straw

Abstract

Liquid hot water (LHW) pretreatment of cellulosic feedstock improves its enzymatic digestibility by removing hemicellulose/lignin, thus making the remaining cellulose more accessible to cellulases. In this study, alkaline-catalyzed (NaOH) LHW pretreatment of rice straw was explored. Various NaOH concentrations (0.25–1.0%) were tested for removal of hemicellulose and lignin as well as enzymatic hydrolysis of the pretreated material at 140–160°C for 5–20min. It was found that glucose recovery from enzymatic hydrolysis was markedly higher for rice straw pretreated by LHW in the presence of NaOH compared with LHW pretreatment in the absence of NaOH. Alkaline catalysis of LHW pretreatment also increased removal of hemicellulose and lignin from solid residue and increased the pentose yield in the liquid phase. Under optimum LHW condition of 140°C for 10min in the presence of 0.25% NaOH, a maximum glucose yield of 71.8% was obtained from the enzymatic hydrolysis of pretreated rice straw; combined with hydrolyzed glucose in the liquid, this represents a maximum glucose recovery of 74.6% from rice straw. The results thus demonstrate the usefulness of NaOH catalyst for LHW pretreatment of rice straw for increasing sugar recovery and reducing energy requirement.