Biodiesel Production from Waste Cooking Oil Using Two Dimensional Photocatalysts: Optimization of Process, Mechanism and Kinetics Study

Biodiesel fuel is an alternative to diesel fuel. Burning biodiesel results in less pollution because its source is vegetable or animal fat. In this study, waste cooking oil (WCO) was used as raw material in the production of biodiesel. The content of free fatty acids (FFAs) in the studied WCO was 4.09%. Production of biodiesel from waste cooking oil was performed by a two-step method. In the first step, under visible irradiation, Cr (x%)-TiO2 photocatalytic esterification of methanol with FFAs in WCO was studied. In the second step, NaOH catalyzed the transesterification of triglycerides with methanol. It was observed that in the presence of TiO2, the efficiency rose by  compared with the case without photocatalysts. The order of photo-esterification reaction by Cr-TiO2 was equal to 1. The activation energy required for the Cr-TiO2 photocatalyst to photo-esterification WCO was 31.36 kJ/mol, confirming the realization of the reaction in mild conditions. Concerning the production of H+, CH3OO· and R-COOH on the photocatalyst surface, we proposed a possible reaction mechanism for the esterification process. The mechanism of the transesterification reaction, OH- was considered as the active species. According to the obtained results, the generated biodiesel density was 0.89 g.cm-3. The pour point and the cloud point for biodiesel are obtained as -5 and 0, respectively. The viscosity of 4.1 mm2.s-1 biodiesel from waste oil was measured, which corresponded to the standard range. The acid value of the biodiesel sample obtained from the waste oil is 0.38 mg KOH g-1.