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

•Native rice straw was pretreated with NaOH-catalyzed under liquid hot water.•Pretreatment increased the solubilization of hemicellulose in the liquid fraction.•Addition of alkaline catalyst increased sugar recovery from enzymatic hydrolysis.•The maximum pentose yield of 79.4% was achieved in the presence of catalyst.•Effects of promoter to structure changes of biomass were observed.

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 5–20 min. 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 10 min 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.

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