Conversion of Oil Palm Biomass to Ethyl Levulinate via Ionic Liquids

Abstract

Biomass is a potential renewable feedstock that can be used as a replacement for fossil resources. A variety of high end chemicals have been produced from biomass including ethyl levulinate, which is a viable biofuel for diesel engines. In this study, the capability of three types of imidazolium based ionic liquids (ILs) catalysts, i.e., 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]), 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM][HSO₄]) and 1-methylimidazolium hydrogen sulfate ([HMIM][HSO₄]) to convert oil palm empty fruit bunch (OPEFB) and oil palm mesocarp fiber (OPMF) biomass to ethyl levulinate were compared. The procedure entailed a sequential reaction of depolymerisation of biomass at 160 °C for 3 hours, followed by an esterification at 90 °C for 12 h in excess ethanol, with ILs-to-biomass ratio of 5 : 1 by weight and 20 wt% water. It was demonstrated that only the last two acidic [HSO₄]^- counteranion based ILs are able to convert the biomass to ethyl levulinate. Mono-alkylated ILs, [HMIM][HSO₄], consistently gave a higher efficiency than multi-alkylated ILs, [BMIM][HSO₄], for both OPEFB and OPMF biomass conversions, with ethyl levulinate yields of 11.61 % and 13.54 %, and the process efficiencies of 39.26 % and 50.79 %. OPMF appears to be a slightly more efficient feedstock in ethyl levulinate production than OPEFB. This indicates the performance of ILs was dependent upon the character of their cation side chain, seeing that both ILs used have the same acidic [HSO₄]^- counteranion. The experimental results suggested that [HMIM][HSO₄] has the potential to be used in ethyl levulinate production from sustainable biomass feedstocks under mild operating conditions.