Study On The Enzymatic Hydrolysis And Fermentation To Ethanol With Corn Stalk

With the continuous development of society and shortage of other non-renewable resources, straw biomass to manufacture fuel ethanol has attracted of people. Due to the dense structure of straw, depolymerization can achieve efficient conversion of straw. The paper adopts the compound enzyme method, NMMO two-step hydrolysis method of depolymerization to corn straw, study on inhibitors from preatment of corn straw for efficient conversion of straw resources is a very important practical value. The results were given as follows:(1) After acid and compound enzyme hydrolysis of corn straw, the surface structure of straw was loose, and the whole layer was stratified, and the structure of cell wall of straw fiber was destroyed. The change of crystallinity of cellulose shows that the acid hydrolysis destroys the amorphous region of cellulose, and the enzymatic hydrolysis mainly destroys the crystalline region of cellulose, which makes most of the cellulose into soluble sugar. The yields of glucose, xylose, and enzyme hydrolysis were 67.83%,3.25%, and 73.65%, respectively, when the pretreated corn straw was hydrolyzed using pectinase, β-glucosidase, and cellulase were 45U/mL, 30U/mL and 60U/mL for a period of 48 h. Compared with cellulose and P-glucosidase hydrolysis, the yields of glucose, xylose and enzymatic hydrolysis with compound enzymes increased to 21.82%, 2.52% and 21.67%; compared with single cellulose enzymatic hydrolysis, the yields of glucose, xylose and enzymatic hydrolysis with compound enzymes increased to 65.04%,20.82%, and 65.06%. The yields of ethanol with compound enzymes increased to 72.50% in the step by step fermentation for 5 days.(2) The sugar yield and ethanol yield be used as an indexes to study on the effects of depolymerization inhibitors from 1-7 acid pretreatment of corn straw on ethanol fermentation by alcohol yeast. The tested inhibitors had a no significant effect on ethanol fermentations when they were added separately at a concentration according to analysis result from hydrolysate of corn stalk. However, when they were added as a mixture, the inhibitory effects become obvious. The highest inhibition effect on fermentation was found in 5% sulfuric acid hydrolysate. There was a delay on ethanol productivity with furfural (≥3.0 g/L), acetic acid (≥3.0 g/L), ferulic acid (≥5.0 g/L). But complete inhibition was observed at 5.0g/L furfural, 10.Og/L acetic acid,7.0g/L ferulic acid, and 7.0g/L p-coumaric acid, respectively.The inhibitory rate decreased in the order:furfural >acetic acid>ferulic acid>p-coumaric acid>HMF. Fed-batch with acid-pretreated RCS produced the higher amount of ethanol yield as compared with disposable feeding.(3) With N-methylmorpholine-N-oxide (NMMO) coupling acid depolymerization corn stalk, it can effectively reduce the cellulose crystallinity and improves glucose yield. When dealing with 3% acid +NMM07h depolymerization, The maximum yields of glucose and xylose were 48.37% and 28.64%, respectively, The maximum enzymatic hydrolysis yield was 65.05%. The corresponding ethanol yield increased from 18.82% to 48.43%.(4) N-methylmorpholine-N-oxide (NMMO) combined with alkali two-step depolymerization of corn straw can be effective transfer of hemicellulose and lignin. Hemicellulose removal was improved by increasing the pretreatment time from 1 to 7 h. Hemicellulose content was decreased from 29.13% for untreated CS to 8.94%. The maximum enzymatic hydrolysis yield of 98.03% was in 1% alkali+ NMMO 7 h treated. The yield for corresponding ethanol yield was 64.64% while untreated corn stalk was only 18.8% samples. Xylose yield obtained from untreated CS was only 11.14%, while this value was 93.77%o Moreover, The NMMO coupling of corn straw alkali depolymerization effect than coupling acid was better.