Transesterification of waste cooking oil for biodiesel production using alkaline-modified graphitic carbon nitride heterogeneous catalyst

Developing efficient, stable, cost-effective, and environmentally benign heterogeneous catalysts for transesterification is highly required for sustainable biodiesel production. The present study explores the biodiesel production from waste cooking oil (WCO) using graphitic carbon nitride (g-C3N4) and its alkaline-modified nanocatalyst. The catalysts were characterised by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). From the XRD analysis, crystalline sizes of g-C3N4 and alkaline g-C3N4 were found to be 26 and 29 nm, respectively. Transesterification of WCO was carried out at 60 °C for a reaction time of 2 h using 2 wt.% of g-C3N4 and alkaline g-C3N4. Transesterification reaction catalysed by alkaline-modified g-C3N4 was found with a higher yield of biodiesel (89%) than the biodiesel yield (78%) with transesterification reaction catalysed by g-C3N4. The recyclability of both catalysts was also evaluated by reusing them for up to the 5th cycle. The obtained biodiesel was analyzed by using FTIR and GC-MS. The synthesised biodiesel was found to have significant level of monounsaturated fatty acids and saturated fatty acids, which make it usefuel for use as fuel. Some physicochemical properties of the obtained biodiesel were also calculated and found appropriate as per the American Society for Testing and Materials (ASTM) standards. With high reusability and good catalytic activity, the synthesised alkaline-modified g-C3N4 can be employed as a viable option for biodiesel production from WCO.