Sunday, May 3, 2009
3-66
A comparison of lime and sodium hydroxide pretreatment for delignification and enzymatic hydrolysis of rice straw
Yu-Shen Cheng, Jean VanderGheynst, Yi Zheng, Ruihong Zhang, and Bryan Jenkins. Biological and Agricultural Engineering, University of California, Davis, One Shields Ave., Davis, CA 95616
Fresh-harvested and air-dried rice straw was pretreated either by hydrated lime (Ca(OH)2) or by sodium hydroxide (NaOH) in sealed 250-ml containers. A full factorial experiment including parallel wash-only treatments was designed for both pretreatments to investigate the alkaline loading and pretreatment time for delignification. Alkaline loadings for lime pretreatments were 0, 5% and 10% of biomass, and 0, 2% and 4% of biomass for NaOH pretreatments. Reaction time was set at 1, 2 or 3 hours for both pretreatments. Water-to-dry biomass loading ratio was 10 g /g and 5 g /g for lime pretreatment and sodium hydroxide pretreatment, respectively. Reaction temperature was held constant at 95°C for the lime pretreatment and 55°C for the sodium hydroxide pretreatment. The range of delignification was 13.1 to 27.0% for lime pretreatments, and was 8.6 to 23.1% for NaOH pretreatments. Both alkaline loading and reaction time have a significant positive effect on delignification. Additionally, higher temperature also aids the effect of delignification. Delignification with water alone ranged from 9.9% to 14.5% for pretreatment at 95°C , but there was little effect observed at 55°C . The post pretreatment wash step is not necessary for subsequent enzymatic hydrolysis under the design pretreatment conditions. Cellulase and β-glucosidase were added at a dosage 15 FPU/g glucose and 15 CBU/g glucose for enzymatic hydrolysis of pretreated biomass. Hightest glucose yield was 176.27 mg/g 105°C dried biomass (48.53% hydrolysis yield) in lime pretreated and unwashed biomass, and was 142.26 mg/g 105°C dried biomass (39.17% hydrolysis yield) in NaOH pretreated and unwashed biomass.