The Study Of Ethanol Biorefinery Process From Corn Stover By Magnesium Bisulfite Pretreatment

This thesis focused on establishing a magnesium bisulfite pretreatment process to pretreat raw corn stover. The key parameters in the lignocellulosic ethanol biorefinery process were discussed in this study, such as, enzyme degradation of lignocellulose, physical and chemical properties of pretreated materials, cellulose saccharification process and fermentation process. According to those studies, a kind of clean and efficient magnesium bisulfite pretreatment technology had been set up.Magnesium bisulfite pretreatment was effective for removing the components of lignin and hemicellulose, while less damage to cellulose component and chemical structure of corn stover. Pretreated by magnesium bisulfite pretreatment at the conditions of 5.27 %(w/v) magnesium bisulfite, magnesium sulfite/sulfurous acid ratio at 1:4(w/v) and pretreated at 170 oC for 60 min, the removal rate of lignin and hemicellulose were 89.09% and 80.28%, respectively. With a enzymatic hydrolysis at condition of 3%(w/v) cellulose concentration, dosages of commercial enzyme were 15 FPU/g cellulose Cellulast 1.5L and 30 IU/g cellulose Novozyme 188 and placed on thermostat shaker set at 50 oC, 150 rpm for 48 h, 90.44% enzymatic hydrolysis yield was obtained. Adding PEG would slightly decrease lignin removal, but helped to improve the enzymatic hydrolysis yield. When PEG 6000 content was 0.08 g/g cellulose, enzymatic hydrolysis yield of pretreated corn stover improved up to 9.07%.Establish high substrate concentration enzymatic hydrolysis process base on using magnesium bisulfite pretreated corn stover as substrate. Under the conditions of 20 FPU/g cellulose Cellulast 1.5L and 40 IU/g cellulose Novozyme 188, mechanical agitation, at 50 oC, with fed-batch substrate process to digest pretreated corn stover at 30% substrate concentration. After 96 h, 160.84 g/L glucose, 31.78 g/L cellobiose and 24.30 g/L xylose were obtained in enzymatic hydrolysate, and the enzymatic hydrolysis yield was 72.83%. In addition, a transglycosylation of β-glucosidase in high substrate concentration enzymatic hydrolysis process was discovered and proved.A mass balance of corn stover biorefinery was performed to evaluate the magnesium bisulfite pretreatment process. In low substrate concentration enzymatic hydrolysis process, 167.2 g ethanol was acquired from 1000 g oven dry raw corn stover, correspond to product 1 kg ethanol require 5.98 kg oven dry raw corn stover. In high substrate concentration enzymatic hydrolysis process, 111.6 g ethanol with concentration of 62.08 g/L was acquired from 1000 g oven dry raw corn stover, correspond to product 1 kg ethanol require 8.96 kg oven dry raw corn stover and a large number cellobiose(yeast could not use) exist in enzymatic hydrolysate.