Fuel properties of palm-oil biodiesel produced using a coal-fly-ash-supported alkaline catalyst derived from sodium methoxide

Abstract

Coal fly ash is an abundant industrial waste generated by coal-fired power plants and has potential as a low-cost catalyst support due to its porous structure and high silica and alumina content. In this study, coal fly ash was used as a support for sodium methoxide to prepare a fly-ash-supported heterogeneous alkaline catalyst for biodiesel production. Palm oil was transesterified with methanol under different methanol-to-oil molar ratios and catalyst concentrations, and the fuel properties of the resulting biodiesel were compared with those produced using a conventional homogeneous alkaline catalyst. The prepared catalyst was characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM) to evaluate the incorporation of sodium-containing alkaline species onto the coal fly ash support. The results showed that the methanol-to-oil molar ratio and catalyst concentration strongly affected fatty acid methyl ester formation and biodiesel quality. Within the experimental conditions investigated, the highest fatty acid methyl ester content (96.54%) was obtained at a methanol-to-oil molar ratio of 6:1 and a heterogeneous catalyst concentration of 3.1 wt%. Under this condition, the produced biodiesel also exhibited improved fuel properties, including lower moisture content, acid value, specific gravity, and kinematic viscosity, as well as a higher heating value. These findings indicate that coal fly ash can serve as a potential low-cost support for sodium-containing alkaline catalysts for biodiesel production. However, further studies are required to quantify sodium leaching and clarify the chemical nature and long-term stability of the active species.