Preparation of ethyl levulinate from wheat straw catalysed by sulfonate ionic liquid

Abstract

Wheat straw, a typical lignocellulosic biomass, is difficult to be liquefied because of its complex structure, which limits its further conversion to valuable products. Ionic liquid can dissolve the cellulose, which can destroy the connection of biomass components. Ionic liquids, [BMIM][HSO4], [BMIM][Cl], and [HSO3-BMIM][HSO4], were used in the liquefaction of wheat straw to produce ethyl levulinate (EL) in a one-pot reaction under mild conditions in ethanol, which served as both solvent and reactant. The highest conversion rate, 85.50%, was obtained following reaction at 200 °C for 60 min using the acidic ionic liquid 1-methyl-3-(4-sulfobutyl) imidazole bisulphate as the catalyst. Under optimal conditions, ethyl levulinate was obtained with a yield of 16.23% and its content in the liquid products was 28.11%. Without the acidic ionic liquid catalyst, the conversion rate of wheat straw and the yield of ethyl levulinate were only 22.33% and 6.23%, respectively. Of the catalysts evaluated, [HSO3-BMIM][HSO4] was the most effective, and its recovery rate was 64.71%. This study provides a theoretical basis for the development and utilisation of low-corrosion and environment-friendly catalysts for liquefaction processes for the preparation of high-grade chemicals.