Effect of sulfite pretreatment on enzymatic hydrolysis of cotton stalk

In order to improve enzymatic hydrolysis efficiency, sulfite pretreatment (SPORL) of cotton stalk was investigated. Added amount of sodium bisulfite, pH value, temperature and time had great effects on cotton stalk saccharification. Cellulose conversion ratio increased with the addition of sodium bisulfite, and levelled off after 8% sodium bisulfite dose. There was an optimal pH value in sulfite pretreatment of cotton stalk. In this study, cellulose conversion ratio reached maximum at pH value 2.65. Before 170℃, the change of enzymatic hydrolysis was not remarkable. After then, enzymatic hydrolysis increased quickly and cellulose conversion ratio got to 70.10% at 180℃ for 20 min. Prolonging holding time was no longer effective. During sulfite pretreatment, both lignin and pentosan were dissolved from cotton stalk in the meantime, which could help cellulose enzymatic hydrolysis. The dissolution of lignin was more effective on cellulose enzymatic hydrolysis than dissolution of pentosan. This study also indicated that the cotton bast was easier to enzymatically hydrolyze than the whole cotton stalk and the cotton xylem was more difficult than the whole cotton stalk in the same conditions of sulfite pretreatment.