Biodiesel production from waste vegetable oils in deep eutectic solvent catalysis and investigation of reaction kinetics

Biodiesel is considered an alternative fuel to petroleum diesel. However, the high costs of raw materials and catalysts restrict large-scale industrial applications of biodiesel. The use of waste cooking oils used in biodiesel production would both reduce the production cost and reduce the environmental damage of waste cooking oils. In this study, biodiesel synthesis was carried out from waste cooking oil using deep eutectic solvent (DES) as acid catalyst by microwave heating method. DES was synthesized from tetraethyl ammonium bromide and p-toluene sulfonic acid and its structure was characterized using 1H-NMR spectroscopy. Biodiesel synthesis from waste cooking oil was carried out by microwave method and tested parameters were temperature, time, methanol-oil molar ratio, and catalyst amount. In accordance with the tested parameters, the best biodiesel conversion was obtained as 96.6% under the following reaction conditions: 150°C reaction temperature, 2 hours reaction time, 28:1 methanol/oil molar ratio, and 10% (wt) catalyst. In addition, biodiesel synthesis was carried out using the conventional heating method under these determined conditions and compared with the microwave method. The results showed that the microwave method can perform biodiesel synthesis in a shorter time than the conventional heating method. Finally, the reaction kinetics were examined and the reaction followed pseudo-first-order kinetics, with an activation energy (Ea) of 51.24 kJ/mol and a pre-exponential factor (A) of 6.1×104 min−1.