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

A 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 degrees 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.