Study On Enzymatic Hydrolysis Of Corn Stover For Sugar Production Using Combined Acid Followed By Alkali Pretreatment

With the increasing fossil fuels prices and negative environmental effects caused by CO2emissions from burning fossil fuels, more attention has been paid to increased utilization of lignocellulosic biomass which is a renewable bioresource and mainly composed of cellulose, hemicellulose and lignin. The monosaccharides obtained from the hydrolysis of polysaccharides can be converted to liquid fuels or other high-valued chemicals. In general, it is difficult for enzymes to degrade the cellulose in the biomass without any pretreatment due to the recalcitrance formed by the rigid cellulose and the cross-linked lignin. The removal of hemicellulose and lignin by pretretament increases the pore size of biomass and expose the cellulose surface, leading to improvement of enzyme accessibility to cellulose for the subsequent enzymatic hydrolysisIn order to achieve low process energy consumption, low enzyme loading, high sugar yield, and inner recycle of wastewater, a novel two-stage biomass pretreatment method was investigated in this study. Dilute hydrochloric acid hydrolysis was carried out in the first stage to hydrolyze hemicellulose with attempt to maximize xylose yield. Lime was used in the second stage so as to further alter the lignin structure and swell the internal surface of cellulose. The optimal condition was120℃and40min for diluted hydrochloric acid pretreatment followed by lime pretreatment at60℃for12h with lime loading at0.1g/g of substrate. The glucose and xylose yield was78.0%and97.0%, respectively, with cellulase dosage at5FPU/g of substrate. The total glucose yield increased to85.9%when the cellulase loading was increased to10FPU/g of substrate. This two stage process was effective due to the swelling of the internal surface, an increase in the porosity and a decrease in the degree of polymerization. The sugar yield is high and the enzyme dosage is low with the two-stage pretreated corn stover. The dilute hydrochloric could be regenerated and reused through double acids hydrolysis method, and lime is cheap and easy to recovery.Besides this two-stage pretreatment method, an enzyme recycle method was also investigated in this study to increase the glucose concentration. As the result shows, this enzyme recycle method could increase the glucose concentration effectively, but with the recycle times increased, the glucose yield dropped to a low level for the enzyme inhibition caused by sugar accumulation. At last, the effect on delignification of corn stover with alkaline sulfite was discussed under different conditions.