Comparison of Photo‐Esterification Capability of Bismuth Vanadate with Reduced Graphene Oxide Bismuth Vanadate (RGO/BiVO4) Composite for Biodiesel Production from High Free Fatty Acid Containing Non‐Edible Oil

Biodiesel has gained much more attention as an alternative and renewable energy source due to the continuous exhaustion of petroleum reserves and their inauspicious environmental effects. Non‐edible feedstocks are economically viable for the production of biodiesel but the presence of higher amount of free fatty acids (FFAs) in these oils is a main hurdle for getting good quality biodiesel. This issue can be addressed through esterification prior to transesterification of oil. This work was designed to evaluate soapnut oil as a source for biodiesel production. Moreover, the catalytic activity of two sunlight active photocatalysts; BiVO4 and RGO/BiVO4 was also compared for the esterification of higher FFA content present in soapnut oil. BiVO4 and RGO/BiVO4 were characterized through SEM, XRD and FT‐IR. Experimental results revealed that RGO/BiVO4 exhibited higher catalytic activity as compare to BiVO4 for the esterification of FFA under sunlight irradiation. Different process variables were optimized and maximum conversion of FFA (88 %) was obtained at 3 : 1 methanol to oil ratio, 5 % catalyst dose, 300 rpm stirring speed and 3 h of reaction time. Esterified oil was then transesterified by using MgO‐KOH heterogeneous catalyst and maximum yield (94 %) of soapnut methyl esters (SNMEs) was obtained at 9 : 1 methanol to oil ratio, 3 % catalyst dose, 2 h reaction time, 80 °C temperature and at 300 rpm stirring speed. The physic‐chemical analysis of synthesized biodiesel revealed that it meets ASTM standards. Soapnut crop with 45 % of oil content proved to be useful for the production of biodiesel. Higher amount of free fatty acids (FFAs) present in soapnut oil suggest that it must be first esterified for which composite of reduced graphene oxide with bismuth vanadate (RGO/BiVO4) was found to be an efficient photo‐catalyst with 88 % catalytic efficiency for the esterification of FFAs. Transesterification of esterified oil was carried out by using MgO‐KOH a heterogeneous catalyst. 94 % yield of biodiesel was obtained at optimized conditions. Physicochemical analysis of biodiesel showed that it meets ASTM standards.