Transesterification of Waste Cooking Oil Utilizing Heterogeneous K2CO3/Al2O3 and KOH/Al2O3 Catalysts

Abstract

Biodiesel production from waste oil is preferable these days as the amount of fossil fuel available for diesel production is decreasing year by year. In this study, the transesterification of waste cooking oil was performed, producing simple alkyl esters from the chemical reaction of triglycerides and methanol, supported by a heterogeneous catalyst to speed up the reaction. Potassium carbonate (K2CO3) and potassium hydroxide (KOH) catalysts loaded at concentrations of 10% and 30% on an aluminium oxide (Al2O3) support were prepared by the incipient wetness impregnation (IWI) method. The feedstock used was waste cooking oil (WCO) collected from households, with a free fatty acid (FFA) value of 1.05 and a moisture content of less than 0.015%. The catalysts were extensively investigated using Thermogravimetric analysis (TGA), X-Ray Diffraction Spectroscopy (XRD) and Brunauer-Emmett-Teller (BET) analysis, while the ester content of the biodiesel produced was characterised using Gas Chromatography-Mass Spectroscopy (GC-MS). The operating conditions for the transesterification reaction included an oil to methanol ratio of 1:12, catalyst loading of 5 wt%, and reaction temperature of 65oC. It was found that 10 wt% K2CO3/Al2O3 was the best catalyst, yielding 9.86g (98.6%) of biodiesel, with a conversion of 81.92% of ester content that made the total biodiesel yield equal to 8.75g (87.57%). These catalysts showed promising results in converting the triglycerides in waste oil to fatty acid methyl esters (FAME).