Parametric Study of Biodiesel Synthesis from Waste Cooking Oil Using Ca-Rich Mixed Metal Oxides

Biodiesel production from waste cooking oil (WCO) is a key step in sustainable energy production. The use of heterogeneous catalysts in the biodiesel production process offers significant advantages, particularly due to their reusability and low environmental impact. In this study, calcium-containing mixed metal oxide catalysts, derived from Ca-rich hydrotalcite-like structures and prepared at various metal oxide ratios, were evaluated for their catalytic activity in the transesterification of WCO with methanol. Parametric studies were conducted to investigate the effects of alcohol-to-oil ratio, catalyst amount, and reaction time on the performance of the most active catalyst, CaAl hydrotalcite-like. The fatty acid methyl ester (FAME) yield was calculated by using the EN14103 method. The optimal reaction conditions were determined to be 338 K for 5 h, a methanol-to-WCO molar ratio of 6:1, and a 3% catalyst amount. Under these conditions, a FAME yield of 96% was achieved using CaAl hydrotalcite as the catalyst. The reusability of the CaAl hydrotalcite-like catalyst was also assessed in the transesterification of WCO, showing no significant loss of activity after the first four uses. However, further reusability tests revealed that the CaAl hydrotalcite-like catalyst dissolved in the reaction medium over time. Fuel tests on the obtained biodiesel indicated that it met the requirements of the European Biodiesel Standard EN 14214.