Optimization of wheat and corn straw pretreating process with subcritical water and investigation on bioethanol production

【Objective】The research optimized the subcritical water pretreatment conditions for wheat and corn straw,and then the enzymolysis and fermentation of residuals from the pretreatment with optimal conditions were investigated.【Method】Subcritical water was employed for wheat and corn straw pretreatment and the pretreatment temperature and time were optimized by Central Composite Design for the highest total reducing sugar content in water-soluble materials,and the enzymolysis and fermentation of the residuals after pretreatment under the optimal conditions were investigated.【Result】The optimal subcritical water pretreatment temperature and time for wheat straw were 194℃and 0min and those for corn straw were 190℃and 0min,respectively.With the optimal conditions,the contents of lignin,cellulose and hemicellulose for pretreated wheat straw decreased by 44.9%,4.9% and 74.7%,respectively;while those for pretreated corn straw decreased by 34.2%,7.2% and 69.5%,respectively.Enzymolysis and fermentation rates of wheat straw were better than that of corn straw.The enzymolysis rate for pretreated wheat straw was 35%,which was 5times more than the untreated materials(6.9%);while the enzymolysis rate for pretreated corn straw was 28.8%,which was 3times more than untreated materials(9%).The final ethanol concentrations from residuals of wheat and corn straw fermented at 35 ℃ with mass fraction of 11% were 12.8and 10.4g/L,respectively.【Conclusion】Subcritical water pretreatment was effective to remove hemicelluloses and lignins while reserved more than 90% celluloses for wheat and corn straw,simultaneously enhanced their enzymolysis and fermentation.