Silica Removal from Rice Straw To Improve its Hydrolysis and Ethanol Production

Rice straw has high silica content compared with other lignocelluloses. Presence of silica in the outer layer of rice straw reduces enzymatic hydrolysis and ethanol production yield. In this study, silica removal from rice straw was investigated through various alkali treatments. The results showed that sodium carbonate could effectively remove silica from the straw (>91%). To investigate only the effects of silica removal and eliminate the effect of lignin removal on enzymatic hydrolysis, organosolv followed by sodium carbonate pretreatment was conducted. Organosolv pretreatment removed most of the straw lignin, while silica was not separated. Organosolv pretreatment of rice straw improved the glucose and ethanol yield from 34.4% and 39.3% for the untreated straw to only 52.9% and 51.6%, respectively, whereas further treatment with sodium carbonate increased the yields up to 94.8% and 78.7%. The results indicated that the protecting effect of silica layer was greater than that of lignin in rice straw.