Improvement of saccharification and ethanol production from rice straw by NMMO and [BMIM][OAc] pretreatments

Rice straw, one of the abundantly available and mainly unused lignocellulosic resources in the world, was successfully pretreated with two cellulose solvents to improve enzymatic hydrolysis and ethanol production. The treatments were conducted with N-methyl morpholine N-oxide (NMMO) and 1-buthyl-3-methylimidazolium acetate ([BMIM][OAc]) at 120 °C for 1, 3, and 5 h with 5% rice straw loading. Then, the treated and untreated straws were subjected to enzymatic hydrolysis at 45 °C for 72 h by 20 FPU cellulase and 30 IU β-glucosidase per each gram of substrate. Hydrolysis results indicated complete conversion of glucan in [BMIM][OAc]-treated straw to glucose and hydrolysis yield of 96% for NMMO-treated samples, while the conversion was only 27.7% for the untreated straw. Ethanol production by simultaneous saccharification and fermentation was carried out at 38 °C for 48 h. The results showed that ethanol production yield was improved from 35.4% for untreated straw to 93.3% and 79.7% after 5 h pretreatment with NMMO and [BMIM][OAc], respectively. The structural analysis reveals that the crystallinity reduction was the main reason of the observed improvements.

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► Rice straw was successfully pretreated with two cellulose solvents.
► Complete hydrolysis of glucan in [BMIM][OAc]-treated straw.
► Improved hydrolysis from 27.7% for the untreated straw to 96% by NMMO treatment.
► Ethanol yield improved from 35% to 93% and 80% by NMMO and [BMIM][OAc] treatments.
► Crystallinity reduction was the main reason of the observed improvements.