Ionic Liquid Pretreatment of Rice Straw to Enhance Saccharification and Bioethanol Production

Abstract

In this study, rice straw was pretreated by an ionic liquid, 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]), prior to enzymatic hydrolysis and ethanol production. The pretreatment was carried out at 120 °C for 5 h under atmospheric pressure. Afterward, saccharification was conducted at 45 °C for 72 h using 20 FPU cellulase and 30 IU β-glucosidase per gram of cellulose. Glucose yield was significantly increased from 25.7% for the untreated straw to over 75% for the treated straw. Moreover, the ethanol yield by simultaneous saccharification and fermentation was improved from 35.6% for the untreated straw to 79.7% for the treated straw. SEM images showed more open and accessible structure for the treated straw compared to the untreated one which assisted the penetration of hydrolytic enzymes in the saccharification and fermentation. From FTIR analysis, it was suggested that the crystallinity reduction and conversion of cellulose I to II are the main changes in the straw as a result of the pretreatment.