Study On Catalytic Conversion Of Cellulose To Glucose And Methyl Levulinate By Solid Acid Catalysts

Biomass is one of the most valuable and renewable resources in the world,with abundant reserves and wide distribution.The use of biomass as energy instead of traditional coal and oil,not only can achieve the supply of energy,but also can improve current environmental problems caused by direct burning and discarding of biomass waste.Cellulosic biomass can be used to produce platform compounds and chemicals through chemical pathways such as catalytic hydrolysis and alcoholysis,and the platform compounds and chemicals can be applied in chemical,pharmaceutical,food and other industries.During the plentiful pathways,catalytic hydrolysis of cellulose to produce glucose and alcoholysis of glucose to prepare levulinic acid esters are two common research processes.These two processes are typical acid catalysis processes and should be carried in the presence of acidic catalysts.Recently,solid acid catalysts have caused great research interest for the advantages of easy separation and convenient recovery while providing high catalytic activity.In this paper,the structural properties of a novel carbon-based solid acid and the mechanism of.high-selective catalytic conversion of cellulose to glucose were studied.Meanwhile,a supported heteropoly acid solid catalyst was used to catalyze the alcoholysis of glucose.The main findings are as follows:(1)Graphene oxide(GO)was added during the hydrothermal carbonation of microcrystalline cellulose,followed by sulfonation of concentrated sulfuric acid to prepare GO modified carbon-based solid acids(SGOC).The addition of GO can change the morphology of the carbonated carbon materials and the loading of oxygen-containing functional groups on the carbon-based solid acids,and then improve the catalytic activity of the catalysts.With the increase of the GO addition,the carbon materials and the sulfonated solid acid catalysts can transform from micro carbon spheres into crumpling layers;the surface oxygen-containing functional groups and hydrophilcity of the GO induced catalysts also get enhanced.The prepred solid acid with 10 wt%addition of GO(10-SGOC)catalyst has a GO-like sheet structure;rich-OH and-COOH functional groups,and good hydrophilicity.The unique layered structure and rich oxygen-containing functional groups interact,so that the catalyst has the best catalytic activity for cellulose hydrolysis.Under the hydrothermal conditions of 160 ? for 5 h,the conversion of microcrystalline cellulose was 18.85%,and the selectivity of reducing sugar reached 94.22%.10-SGOC also shows high thermal stability and activity stability;the conversion of cellulose keeps above 17.69%and selectivity of reducing sugar after 4 times is still higher than 92.48%.(2)Kaolin supported phosphotungstic acid solid acid catalyst(PW/KAOLIN)was prepared by an impregnation method,kaolin(KAOLIN)was served as carrier and phosphotungstic acid(PW)as active components.The catalytic activity of the catalyst is improved by adjusting the loading of PW during the preparation of the catalyst:when the mass of the PW is too low(10 wt%and 18 wt%),the acid activity center on the catalyst was less and the activity was lower.When the mass is too large(32 wt%and 40 wt%),.PW has poor dispersibility on the surface of the carrier and the pore structure of the carrier is blocked,which reduces the effective active center on the catalyst and reduces the activity.Thus,the 25%PW/KAOLIN catalyst prepared with 25 wt%loading of PW shows the best glucose alcoholysis catalytic activity.When the catalyst was applied to catalyze the alcoholysis of glucose in methanol solvent,the conversion of glucose was 93.77%,and the yield of methyl levulinate was 41.3%at 200 ? for 2 h.