Enzymolysis And Fermentation Of Pretreated Corn Stover Pretreatments To Product Bioethanol

Corn stalk mainly consists of cellulose, hemicellulose and lignin. As one of the important raw materials for fuel ethanol production, corn stalk is a renewable source with rich amount. In order to improve the conversion of corn stalk to ethanol, this study explored the influence of three pretreatment methods: ethanol amine, sodium bisulfite and ethanol amine combined with sodium bisulfite. The different proportions of cellulase and xylanase were tested to explore the optimal enzymatic hydrolysis efficiency. The fermentations were carried out under the optimal pretreatment method or under the optimal enzyme proportion, respectively. The fermentations results were compared to find out a better way of converting corn stalk to ethanol.The results showed that the two-step pretreatment combined ethanol amine with sodium bisulfite was the best. The pretreatment conditions were as followed: the corn stalk was treated with 5% ethanol amine 90 min at 121 ℃, and then with 8% sodium bisulfite 120 min at 121 ℃. After pretreatment, the contents of cellulose and xylan were 51% and 29.6%, respectively. The contents of cellulose and xylan in corn stalk increased by 58.04% and 37.87% respectively, compared with the corn stalk without pretreatment. The lignin content was 11.59% after pretreatment, which decreased 57.53%.After the two-step pretreatment, different enzyme ratio of cellulase and xylanase were tested and the enzymatic hydrolysis efficiency was analized. The optimal condition was Cellulast1.5L 3.17 mg, 1.5 L, Novozym 188 1.63 mg, Xylanase 1.2 mg per gram substrate. The concentration of glucose reached 10.2 g/L and xylose reached 4.79 g/L after 72 h hydrolyzation under this optimal condition. The cellulose conversion rate was 90.09% and the xylan conversion rate was 70.98%. The reducing sugar and total digestion efficiency is 14.99 g/L and 82.95%, respectively. Compared with the corn stalk without pretreatment, the hydrolysis efficiency increased nearly 4.7 times.After the enzymatic hydrolysis, the corn stalk was fermented by Saccharomyces cerevisiae 1445. The highest ethanol concentration reached 4.27 g/L for 4 h. The sugar-alcohol conversion rate reached 82.08% of the theoretical value and the ethanol yield was 73.95%. Compared to the corn stalk without pretreatment, ethanol yield increased 3.4 times.