Biodiesel synthesis using a physical mixture of calcium diglyceroxide and spent FCC catalysts – kinetics and catalyst reusability studies

Biodiesel is a renewable fuel that can be prepared from used cooking oil (UCO). This study experimentally simulates UCO by spiking refined sunflower oil (RSFO) with oleic acid. A parametric and kinetic study for biodiesel synthesis from this simulated feed employing a mixture of calcium diglyceroxide (CaD) and spent fluid catalytic cracking (SFCC) catalyst (CaD + 20% SFCC) has been carried out. The reaction parameters for the maximum methyl ester yield (> 99%) with minimum soap conversion (∼ 10%) are found to be 65 °C, 6:1 methanol to oil molar ratio under preset conditions of 3 wt % catalyst loading, 1 h of reaction, and 200 rpm mixing rate. The activation energy (Ea) values obtained for the single-pot synthesis are consistent with literature values (54.2 ± 4.6 kJ mol−1 for transesterification and 37.8 ± 2.9 kJ mol−1 for esterification). These values prove the synergy of the catalysts on the reaction kinetics. Further, the catalyst performance is analyzed for RSFO spiked with 10 wt % and 20 wt % OA, as well as UCO. The methyl ester yield obtained in all these cases exceeded 99% with minimum soap formation. The catalyst reusability is also checked for UCO conversion to biodiesel.