Optimisation studies on the conversion of oil palm biomass to levulinic acid and ethyl levulinate via indium trichloride-ionic liquids: A response surface methodology approach

This work is a continuation and extension of previously published study on the conversions of oil palm empty fruit bunch and mesocarp fiber biomass to levulinic acid and ethyl levulinate via an eco-friendly indium trichloride-l-methylimidazolium hydrogen sulfate (Tiong et al., 2017). Herein, a response surface methodology based on a central composite design method was used to optimise the operating conditions of the conversions. The conversions consisted of a two-sequential steps, that is, depolymerisation to levulinic acid, followed by esterification to ethyl levulinate. The optimum depolymerisation occurred at 177 degrees C in 4.8 h with 0.15 mmol indium trichloride in ionic liquids-to-biomass ratio of 6.6:1 (w/w) and 22.7% (w/w) of water, whilst esterification was at 105 degrees C in 12.2 h with ethanol to substrate ratio of 7.2:1 (v/v). The maximum levulinic acid yields of 17.7% and 18.4%, and the subsequent ethyl levulinate yields of 18.7% and 20.1% were achieved from the conversions of oil palm empty fruit bunch and mesocarp fiber biomass, respectively. LA and EL efficiencies were > 63% for both biomass conversions. The ionic liquids could be recycled up to three consecutive runs with a minimal loss of < 25% of ethyl levulinate yield. This study highlighted the potential of proposed ionic liquids for biorefinery processing of renewable feedstock in a greener and sustainable approach.