Enzymatic Hydrolysis Of Lignocellulose Pretreated With Green Liquor

Under the circumstance of the contradiction between the shortage of fossil fuel and theincreasing demand for energy, bioconvertion of lignocellulose to biofuel ethanol was a verymeaningful in the sustaining development of our society and economy. Key technologies inethanol production from lignocellulose including pretreatment, cellulase production, enzymatichydrolysis of cellulose and hemicellulose were investigated.The results of pulp analysis, cellulase activity and enzymatic hydrolysis yield of differentgreen liquid pretreated lignocellulose indicated that higher weight loss, lower glycan recovery,and lower level of delignification were observed, when more severe condition was applied inpretreatment. Rice straw showed the greatest weight loss of the three kinds of lignocellulose,followed by corn stover and wheat straw. Optimum cellulase production was in a more gentlestate of pretreatment conditions, especially in a low total alkali charge. When wheat straw,pretreated by cooking temperature140℃, total alkali charge4%and sulfidity0, was taken asthe carbon source for callulase production, optimum cellulase activity (Filter paper activity,FPA) of3.2FPU/mL were achieved. Enzymatic hydrolysis yield was improved with theincrease of pretreatment conditions; the extent of impact on enzymatic hydrolysis yield was inturn total alkali charge, sulfidity, and cooking temperature. In comprehensive consideration,optimum raw material was wheat straw for green liquid pretreatment; the suitable condition ofpretreatment was cooking temperature150℃, total alkali charge (Na2O, on oven dry material)8%, and sulfidity40%.By optimizing the substrate loading, enzyme dosage, enzymatic system and the addition ofTween-80, it was suggested that enzymatic hydrolysis yield could be improved significantly.When substrate concentration was10%, and commercial cellulase15FPU/g cellulose,β-glucosidase9IU/g cellulose, xylanase30IU/g cellulose, Tween-800.05g/g cellulose wereadded into hydrolysis broth simultaneously, after72hours enzymatic hydrolysis, glucose yieldand xylose yield reached82.5%and77.8%, respectively, which were2.6times and1.6timesof that before optimization. In another case, when commercial cellulase20FPU/g cellulose,β-glucosidase12IU/g cellulose, xylanase20IU/g cellulose, Tween-800.075g/g cellulose wereadded into hydrolysis broth simultaneously, glucose yield and xylose yield reached86.8%and81.5%, respectively, which were2.4times and1.6times of that before optimization. If theresidues, that were not washed, continued to be hydrolyzed for24hours, total glucose yield andxylose yield could reach90.2%and82.7%, respectively under a loading of15FPU/gcellulose, and93.6%and87.9%, respectively under a loading of20FPU/g cellulose. Thus, itcould be seen that enzymatic hydrolysis efficiency and proceeding could be enhanced significantly by the removal of hydrolysate.The differences of protein and enzymatic hydrolysis yield of wheat straw pretreated bygreen liquor with several different sources of cellulase were evaluated．It could be found thatcellulase produced in this laboratory showed a better performance than commercial cellulase onenzymatic hydrolysis efficiency. The highest glucose yield and xylose yield was cellulaseproduced from wheat straw pretreated by green liquor. It was suggested that the compositionand structure of cellulase system produced in this laboratory was more reasonable, cellulaseinduced by substrate had a better collaboration. The addition of β-glucosidase, xylanase andTween-80into the cellulase produced in this laboratory was also performed; the effect onenzymatic hydrolysis was investigated. Glucose yield and xylose yield reached90.4%and94.1%, respectively, after72hours enzymatic hydrolysis, which were1.6times and1.2timesof that before optimization. The improvement of enzymatic hydrolysis yield of wheat strawpretreated by green liquor was the comprehensive results of various factors, which could notonly fix our sights on the dosage of enzyme, but also the rational composition of cellulasesystem.