Sulfite Pretreatment For Robust Enzymatic Hydrolysis Of Cotton Stalk

Producing fuel ethanol using cellulose as raw material to substitute fossil energy consumption is an effective method to ease energy shortage and environmental pollution, which is very meaningful to the persistent development of our society. Because the structure of lignocellulose is complex and cellulose is bundled by lignin and hemicellulose, the hydrolysis efficiency of natural cellulose is very low. It is necessary to pretreat the raw material to increase enzyme substrate availability, which can improve the conversion rate of enzymatic hydrolysis. In this paper, sulfite pretreatment effect on cotton stalk was studied by analysising conversion rate of enzymatic hydrolysis, glucose yield, dissolution rate of lignin, dissolution rate of pentosan and retention rate.The influences of sodium bisulfite, sulfuric acid, liquid ratio, temperature and holding time on cotton stalk during sulfite pretreatment were investigated. The optimal conditions of sodium bisulfite pretreatment were the dose of sodium bisulfite8%, sulfuric acid0.92%, liquid ratio1:4, temperature180℃, holding time20min, cellulase10FPU/g, cellobiase3.5CBU/g. Under these conditions, conversion rate of enzymatic hydrolysis is70.10%, glucose yield60.06%, lignin dissolution rate51.58%, pentosan dissolution rate28.83%, pentosan retention rate51.23%, and pretreatment solution pH2.65.Under the optimal conditions reaction course of sulfite pretreatment of cotton stalk was studied. The results showed that conversion rate of enzymatic hydrolysis and glucose yield increased with rising temperature. Before17℃conversion rate of enzymatic hydrolysis and glucose yield increased a little. When temperature was up to180℃for20min, they increased obviously. Prolonging holding time was no longer effective.Enzymatic hydrolysis conversion rate was42.63%and glucose yield was28.13%when5.52%sulfuric acid for pretreating corn stalk was used at conditions of liquid ratio1:4180℃for20min; enzymatic hydrolysis conversion rate was42.63%and glucose yield was28.13%when7%sulfurous acid for pretreating corn stalk was used at conditions of liquid ratio1:4180℃for20min. By comparising the above three methods, dilute sulfuric acid pretreatment has less effect on enzymatic hydrolysis efficiency, liquid produced in sulfurous acid pretreatment has too low pH which means corrosion requirement of the equipment is high, so sulfite pretreatment is a better choice.The effect of different parts of cotton stalk during sulfite pretreatment is different. Enzymatic hydrolysis order from easy to difficult is:cotton stalk bark> twigs> cotton stalk> trunk> cotton stalk core.