Conversion of recalcitrant cellulose to alkyl levulinates and levulinic acid via oxidation pretreatment combined with alcoholysis over Al2(SO4)3

Abstract

Conversion of cellulose to chemicals is an economic and environmental route for biomass utilization. In this work, efficient conversion of cellulose to alkyl levulinates and levulinic acid was realized by oxidation pretreatment combined with alcoholysis over Al2(SO4)3 catalyst. Proper pre-oxidation conditions including oxidation temperature and time are important. By pre-oxidation, part of hydroxymethyl groups on cellulose was converted to carboxyl groups which provide the Bronsted acid sites near the glycosidic bonds to improve the depolymerization of cellulose to monosaccharide. Al2(SO4)3·18H2O can play both Bronsted and Lewis acid roles in methanol and catalyze the conversion of monosaccharide to alkyl levulinates and levulinic acid. After pre-oxidation at optimized conditions, cellulose can be converted into methyl levulinate and levulinic acid over Al2(SO4)3 in methanol efficiently, and total yield of methyl levulinate and levulinic acid can reach 66.8% at 180 °C for 3 h. Furthermore, the simple and cheap Al2(SO4)3 catalyst is recyclable which is important for the practical application.