Sodium carbonate–sodium sulfite pretreatment for improving the enzymatic hydrolysis of rice straw

Abstract

The performance of sodium carbonate–sodium sulfite (Na2CO3–Na2SO3) pretreatment on improving the enzymatic hydrolysis of rice straw was investigated. The results indicated that both Na2CO3 and Na2SO3 pretreatments are effective in improving the enzymatic digestibility of rice straw. A higher ratio of Na2SO3 in pretreatment liquor performed better at softening the rice straw through degradation of hemicellulose, delignification, and lignin sulfonation, while it was conserving more polysaccharides during the pretreatment than Na2CO3. The highest sugar recovery of pretreated rice straw, 74.5%, 82.7%, and 59.5% for total sugar, glucan, and xylan, respectively, was obtained at cellulase loading of 20FPU/g-cellulose after the pretreatment at 140°C, chemical charge of 12%, Na2CO3–Na2SO3 ratio of 0:1 (i.e., only Na2SO3 pretreatment). The corresponding delignification ratio of pretreated solid was 53.4%, and 91.4% of the polysaccharides were conserved. The sugar recovery of only Na2CO3 pretreatment at the ratio of 1:0 was 67.1%, 74.4%, and 53.7% for total sugar, glucan, and xylan, respectively, at 140°C, chemical charge of 12%, and enzyme loading of 20FPU/g-cellulose. Its corresponding delignification ratio was 40.3%, and polysaccharides conservation ratio was 88.9%.