The Adaptation Exploration Of Corn Stover Pretreatment Process And Cellulosic Hydrolysis Sugars For Ethanol Fermentation

This study was focus on the enzymatic and fermentation properties of corn straw residues after pretreatment. The diluted acid pretreatment, steam explosion, acid-base pretreatment and two-step acid hydrolysis pretreatment were researched to determine the optimum pretreatment process. The three components (cellulose, hemicelluloses and lignin) of corn straw before and after pretreatment were tested to determine the pretreatment effects. The study researched on the xylose and glucose utilization efficiency by Pichia stipitis CICC and determined the optimum fermentation process by optimizing the dissolved oxygen, inoculation concentration and carbon and nitrogen ratio. Steam explorsion hydrolysate of xylose was used to domesticate P. stipitis, after acclimation, xylose to ethanol fermentation rate increased to 85%.Compared the sulfuric acid combined sodium hydroxide pretreatment, two-steps acid pretreatment and acid or base steam explorsion pretreatment of corn straw for ethanol production, the results showed the cellulose content can reach to 41-43% after steam explorsion pretreatment of 0.3% sulfuric acid soaked straw, meanwhile, the conversion of cellulose to ethanol was 79.7% of theoretical value, which can reach to 72.6% by base soaked straw. Compared acid and base combined pretreatment process, the steam explosion can consume small energy; reduce the experimental procedure, less sewage, and low acid-base dosage strengths for optimal condition.This study researched on optimizing fermentation conditions of xylose to ethanol by P. stipitis and the ethanol yield by fermentation the mixed different ratio of glucose and xylose. Also, P. stipitis and Saccharomyces cerevisiae were mixed to ferment the mixed sugars for ethanol production, the results showed that S. cerevisiae were graw faster and xylose was used slowly by P. stipitis. And P. stipitis can reach the highly ethanol concentration by 22g/L and 78% yield, which can grow at 40g/L ethanol concentration and optimized xylose to ethanol conversion rate can reach to 80% of the theoretical value at the initial xylose concentration of 40g/L.Using xylose mother liquor and acid pretreatment of corn straw hydrolysate for ethanol fermentation, both of which contained the similar glucose, xylose, arabinose proportion, and the result showed that ethanol concentration can reach to 19g/L, sugar alcohol conversion rate of 55.6%, the overall conversion efficiency is not high. We need to further improve the efficiency of fermentation of xylose mother liquor and straw pretreatment liquid.The single factor and orthogonal experiments determined the optimum fermentation experiment conditions were 12.5% solids, presaccharification time for 4h and added 2.5% enzyme dosage and 0.3% corn steep liquor,2% v/v yeast inoculum and fermented at 34 ?. In this final fermentation conditions 48h fermentation of cellulosic ethanol conversion rate of more than 80% ethanol concentration of 29.6g/L.P. stipitis was domesticated for adapting the inhibitor environment of steam explosion hydrolyzate. Meanwhile, the optimum fermentation conditions of steam explosion hydrolysate by P. stipitis were optimized: inoculation 12.5%,250mL conical bottled liquid volume 100mL, rocker swing oscillation frequency of 90 times/min, tampons sealing, fermentation at 30 ?, and the highest ethanol concentration was 10g/L, xylose to ethanol conversion rate of 85%.