The Study Of Pretreatment And Enzymatic Hydrolysis Of Ucalyptus Raw Materials

Due to climate change and the gradual depletion of fossil fuel, there is a renewedinterest in bioenergy for sustainable energy production and economic development.Biofuel meets sustainable economic development by reducing carbon dioxideemissions."Second-generation bioethanol", based on lignocellulose biomass, does notcompete with feed and food for feedstock. However, lignocellulosic materials is astructural materials that has natural resistance to enzyme and microbial destruction.Pretreatment of lignocelluloses biomass can change cell wall structure to reduce itsrecalcitrance. In this study, Eucalyptus lignocellulose was pretreated by weak basicitysulfite, liquid hot water and dilute acids. The pretreatment of obtained sample wasconducted for cellulose enzyme hydrolysis. Through determining the total sugarsyield in the prehydrolysate and enzymolysis liquid, the best pretreatmenttechnological conditions were optimized. The results of this study were summarizedas follow:(1) The best pretreatment technological conditions of weak basicity sulfite wereoptimized as follow: sodium sulfite charge12%, sodium hydroxide charge3%,cooking temperature170℃, heating preservation time120min. On the basis of100graw materials,10.89g xylose and39.88g glucose can be recovered after bothpretreatment and enzyme hydrolysis; The raw material, pretreatment sample, andenzyme scraps were investigated by FT-IR,SEM and XRD. The results show that afterpretreatment, some hemicellulose and lignin were hydrolysed, the crystalline degree ofcellulose decreased by14.34%, SEM pictures showed that the alkaline sulfitepretreatment cause the relaxation of carbohydrate of eucalyptus, the breakage of pitmembrane, the increasement of fiber fragments, which are greatly improving theaccessibility of cellulose; From the material balances, we can know that althoughsome materials were loss during pretreatment and enzymatic hydrolysis. The totalglucose recovery in the liquid streams was over92%, the total xylose recovery in theliquid was over70.71%,52.39%acid-insoluble lignin can be reused in the enzymescraps. (2) The best pretreatment technological conditions of liquid hot water wereoptimized as follow: the cooking temperature170℃,1/20(w/v) solid/liquid ratio,heating preservation time20min. On the basis of100g raw materials,13.80g xyloseand29.83g glucose can be recovered after both pretreatment and enzyme hydrolysis;Both the raw material, pretreatment sample, and enzyme scraps were investigated byFT-IR, SEM and XRD. The results show that after pretreatment, most of thehemicellulose were hydrolysed, the crystalline degree of cellulose changed a little,SEM pictures showed that the liquid hot water pretreatment cause the relaxation ofcarbohydrate of eucalyptus, the breakage of pit membrane, the increasement of fiberfragments, which are greatly improving the accessibility of cellulose; From thematerial balances, we can know that the total glucose recovery in the liquid streamswas over70%, the total xylose recovery in the liquid was over90%,91%acid-insoluble lignin can be reused in the enzyme scraps.(3) The best pretreatment technological conditions of dilute acids wereoptimized as follow: the cooking temperature160℃, the sulfuric acid charge0.75%,heating preservation time10min. On the basis of100g raw materials,12.25g xyloseand35.74g glucose can be recovered after both pretreatment and enzyme hydrolysis;Both the raw material, pretreatment sample, and enzyme scraps were investigated byFT-IR, SEM and XRD. The results show that after pretreatment, most of thehemicellulose were hydrolysed, the crystalline degree of cellulose decreased from61.22%to58.34%, SEM pictures showed that dilute acids pretreatment cause therelaxation of carbohydrate of eucalyptus, the breakage of pit membrane, theincreasement of fiber fragments, which are greatly improving the accessibility ofcellulose; From the material balances, we can know that the total glucose recovery inthe liquid streams was over84%, the total xylose recovery in the liquid was over82%,80%acid-insoluble lignin can be reused in the enzyme scraps.