Esterification of oleic acid to biodiesel using biowaste‐based solid acid catalyst under microwave irradiation

Abstract

AbstractA novel carbon‐based solid catalyst was synthesized from waste biomass of watermelon peel (Citrullus lanatus) by one pot carbonization and functionalization with H2SO4 for biodiesel production. Oleic acid was utilized as a test substrate in this study given that it is a key component for majority of feedstocks used for biodiesel production. Synthesized catalyst was extensively characterized by X‐ray diffraction, Fourier transform infrared, thermogravimetric analysis, X‐ray photoelectron spectroscopy, scanning electron microscopy–EDX and Brunauer–Emmett Teller analysis. The catalyst revealed aromatic structure, hydrophilic OH and COOH groups as well as a high density of SO3H active centres with a total acidity of 3.6 mmol g−1. Using the optimized reaction condition (MeOH: oleic acid molar ratio 20:1, catalyst loading 8 wt.%, temperature 100°C and reaction time of 60 min) under microwave irradiation (50 W, 100 psi) a conversion as high as 94.36 ± 0.3% of oleic acid to biodiesel was reported. Activation energy of the esterification was found to be 38.16 kJ mol−1. Catalyst recovery was probed to over five reaction cycles, with a modest loss in activity (81.73 ± 0.4% conversion in the fifth cycle) resulting from limited active site leaching.