Esterification of Levulinic Acid to Ethyl Levulinate Using Liquefied Oil Palm Frond-Based Carbon Cryogel Catalyst

Oil palm biomass, which is abundantly available in Malaysia, has many types of applications in various industries. In this study, oil palm frond (OPF) was liquefied with 1-butyl-3-methylimidazole hydrogen sulfate ([BMIM][HSO4]) ionic liquid (IL) at optimum conditions. The liquefied OPF-ionic liquid (LOPF-IL) was mixed with furfural at a ratio of 0.8 (w/w), water-to-feedstock ratio of 0.125 (w/w), and sulfuric acid loading of 0.5 mL at 100 °C for 1 h to form a gel. Carbon cryogel liquefied oil palm frond (CCOPF) was prepared using a freeze-dryer followed by calcination. CCOPF was further characterized using N2 sorption, NH3-TPD, TGA, XRD, FTIR, and FESEM to determine its physical and chemical properties. The thermally stable CCOPF exhibited a large total surface area (578 m2/g) and high total acidity (17.6 mmol/g). Next, CCOPF was tested for levulinic acid catalytic esterification by varying the parameters including ethanol-to-levulinic acid molar ratio, catalyst loading, and reaction time at 78 °C. At the optimum conditions, the conversion of levulinic acid and ethyl levulinate yield was 70.9 and 71.7 mol%, respectively. CCOPF was reusable up to five runs with no significant conversion drop. Accordingly, CCOPF is conferred as a potential biomass-derived acid catalyst for ethyl levulinate production.