Kinetic study of free fatty acid esterification reaction catalyzed by recoverable and reusable hydrochloric acid

The catalytic performance and recoverability of several homogeneous acid catalysts (hydrochloric, sulfuric, and nitric acids) for the esterification of enzyme-hydrolyzed free fatty acid (FFA) and methanol were studied. Although all tested catalysts drove the reaction to a high yield, hydrochloric acid was the only catalyst that could be considerably recovered and reused. The kinetics of the esterification reaction catalyzed by hydrochloric acid was investigated under varying catalyst loading (0.1–1 M), reaction temperature (303–343 K), and methanol/FFA molar ratio (1:1–20:1). In addition, a pseudo-homogeneous kinetic model incorporating the above factors was developed. A good agreement (r2 = 0.98) between the experimental and calculated data was obtained, thus proving the reliability of the model. Furthermore, the reusability of hydrochloric acid in FFA esterification can be predicted by the developed model. The recoverable hydrochloric acid achieved high yields of FFA esterification within five times of reuse.