Study On Hydrolysis Of Microcrystalline Cellulose Over Solid Acid Catalysts

As the only renewable organic carbon resource in nature,biomass is considered as one of the best alternatives to fossil energy.Catalytic conversion of cellulose for production of fuels and value-added chemicals has become the hotspot of academic research.As environmentally friendly catalysts,solid acid catalysts have broad application prospects in cellulose hydrolysis.In this study,the catalytic activities of niobic acid,zeolite and heteropoly acid for cellulose hydrolysis are investigated.The catalytic activity of a sulfonated hydrothermal carbon catalyst for ethanolysis of microcrystalline cellulose in supercritical ethanol is examined.The catalytic hydrolysis of microcrystalline cellulose was examined over a niobic acid catalyst(NBO)prepared by alkali fusion method.Cellulose was mainly converted into glucose and 5-hydroxymethylfurfural(HMF).The catalytic activity was significantly affected by the reaction conditions and further acid treatment.The highest HMF yield of 7.0 mol% and a glucose yield of 17.7 mol% at cellulose conversion of 54.2% were achieved at 230 °C for 2 h.The H2SO4-treated(NBS)and H3PO4-treated(NBP)samples showed greatly improved performance due to the introduction of strong acid sites and the increase in specific surface area.NBO exhibited excellent recyclability for the catalytic hydrolysis of cellulose.The catalytic activity of the recovered NBS and NBP samples decreased in the recycle tests,which could be regenerated by calcination and subsequent acid treatment.Zeolite catalysts including H-ZSM-5,SAPO-34 and H-? were examined for cellulose hydrolysis.Cellulose was mainly converted to cellobiose,glucose,fructose,formic acid,levulinic acid and HMF.The catalytic activities were in order of H-ZSM-5 > SAPO-34 > H-?,which was consistent with the order of acid strength in three zeolite catalysts.The reaction temperature had great influence on the catalytic performances of three zeolite catalysts.High temperature promoted the formation of glucose over H-ZSM-5 and the formation of HMF over SAPO-34,while low temperature promoted the formation of glucose over H-?.Keggin type heteropoly acid catalysts including phosphotungstic acid(HPW),silicotungstic acid(HSi W)and molybdophosphoric aicd(HPMo)were investigated for cellulose hydrolysis.Cellulose was mainly converted into glucose,fructose,formic acid and levulinic acid.The catalytic activities of three heteropoly acid catalysts were in order of HPW > HSi W > HPMo,which was consistent with the order of acid strength.Lower reaction temperature,shorter reaction time and more amount of catalyst were favorable for the glucose production and weak acidity conditions were favorable for the formation of levulinic acid.The distribution of products in hydrolysate can be controlled by adjusting the catalyst amounts.The catalytic ethanolysis of microcrystalline cellulose in supercritical ethanol is examined over a sulfonated hydrothermal carbon catalyst(SHTC).SHTC is amorphous carbon containing-OH,-COOH and-SO3 H groups with total acidity of7.15 mmol/g and-SO3 H acidity of 1.72 mmol/g.Complete conversion of microcrystalline cellulose with high yields of ethyl levulinate and ethyl glucoside is obtained over SHTC in supercritical ethanol.The reaction temperature,time and catalyst amount have significant effects on the catalytic performances of SHTC.Appropriate reaction time and less catalyst amount are favorable for the production of ethyl glucoside,while prolonged reaction time and appropriate catalyst amount favor the production of ethyl levulinate.SHTC exhibited excellent selectivity towards ethyl levulinate.The selectivity of ethyl levulinate reached 91.9% under appropriate reaction conditions.SHTC shows good stability in the recycle experiments with slight loss of catalytic activity.