Visible light active photocatalysts have attracted a lot of interest due to their simple chemical workup and recyclability. In this study, the role of Strontium Titanate/graphitic Carbon Nitride composite (SrTiO3/g‐C3N4) was investigated for the pretreatment of waste frying oil (WFO) to reduce high free fatty acids (FFAs) for biodiesel production. SrTiO3/g‐C3N4 photo‐catalyst was synthesized through the facile refluxing method and its activity was also compared with simple graphitic carbon nitride (g‐C3N4). Experimental results revealed that SrTiO3/g‐C3N4 possesses higher efficiency as compared to g‐C3N4. Photo‐catalyst was characterized through SEM‐EDX, XRD and FT‐IR. Maximum conversion of FFAs (85 %) was achieved at 1 % catalyst dose, 800 rpm stirring speed, 3 : 1 methanol to oil ratio, and 4 hours of reaction time. Esterified WFO was converted to waste frying oil methyl esters (WFOME) by using CaO‐KOH heterogeneous catalyst. The maximum yield of WFOME was obtained at 1.25 % catalyst dose, 65 °C, 600 rpm, 2 h of reaction time, and 12 : 1 methanol to oil ratio. Physicochemical analysis of WFOME revealed that it is in accord with ASTM standards.

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; BiVO 4 and RGO/BiVO 4 was also compared for the esterification of higher FFA content present in soapnut oil. BiVO 4 and RGO/BiVO 4 were characterized through SEM, XRD and FT-IR. Experimental results revealed that RGO/BiVO 4 exhibited higher catalytic activity as compare to BiVO 4 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.

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