Application of Quaternary Ammonium-Based Deep Eutectic Solvents as Catalysts for the Glycerolysis of Free Fatty Acids

Abstract

Nonedible waste sourced lipids such as fatty acid distillates, brown grease, and animal tallow, among many others, are excellent alternatives for expanding the feedstock inventory for biodiesel synthesis. A quaternary ammonium-based deep eutectic solvents (DESs) was used as a catalyst in the glycerolysis of free fatty acids (FFAs) in this study. Reaction optimization was carried out with oleic acid as the model molecule, followed by an in-depth examination of the reaction mechanism. Optimum conditions such as 130 °C and 10 wt % catalyst dosage with 10 min of reaction time gave an equilibrium conversion of 94%. The catalyst was found to remain in the glycerol phase allowing its reuse. Palm fatty acid distillate, brown grease, and crude glycerol were utilized for testing the novel DES at optimum conditions. FFA conversion was found to be 94% for both palm fatty acid distillate and brown grease. In the case of crude glycerol, FFA conversion decreased proportionally to the impurity level. Water was responsible for restricting equilibrium conversion and decreasing catalyst recyclability, necessitating further research into effective removal during the reaction. Aggressive nitrogen purging to remove water during the reaction pushed the reaction toward near-completion in 60 min. The catalyst reusability study showed a drop in equilibrium conversion to 62.5% at the end of the 5th cycle, even when water was removed.