One-pot conversion of oil palm empty fruit bunch and mesocarp fiber biomass to levulinic acid and upgrading to ethyl levulinate via indium trichloride-ionic liquids

A variety of bio-based chemicals and biofuels have been produced from residual biomass including 5-hydroxymethylfurfural, levulinic acid and ethyl levulinate. In this study, Bronsted-Lewis acidic ionic liquids, which made up of an eco-friendly indium trichloride and a noncorrosive ionic liquids, 1-methylimidazolium hydrogen sulfate, was developed for a cleaner production of ethyl levulinate from biomass conversions. This coupling catalyst was used for the first time without the corrosive alkyl sulfonic acid functionalised group in the ionic liquids. The conversions involve a sequential depolymerisation and esterification. The depolymerisation was conducted at ionic liquids-to-biomass ratio of 5:1 (w/w), 0.15 mmol indium trichloride, 20% (w/w) water and temperature of 160 degrees C for 5 h, whereas, the esterification was conducted at the temperature of 90 degrees C for 10 h in excess ethanol. The coupling catalyst gave ethyl levulinate yields of 13.1% and 14.7%, with process efficiencies of 44.3% and 55.1%, for oil palm empty fruit bunch and oil palm mesocarp fiber conversions, respectively. The coupling catalyst also exhibited minimal losses of <17% of ethyl levulinate yields for the consecutive three runs in reutilisation tests, signifying its potential recycling ability. The experimental results confirm that the proposed non-corrosive coupling catalyst provides a uniquely suitable catalytic system for the conversion of renewable biomass feedstocks into useful products under mild operating conditions. (C) 2017 Elsevier Ltd. All rights reserved.