Preparation of Vegetable Oil as Biodiesel Feedstock Via Re-Esterification: A Suitable Catalyst

A suitable heterogeneous catalyst for reducing 20 wt.% of free fatty acid (FFA) that is contained in vegetable oil to less than 3 wt.% through re-esterification was investigated. There were two groups of heterogeneous catalyst used to reduce FFA: 1) zinc compound: Zn, ZnCl2, ZnO and ZnSO4·7H2O, and 2) stannum compound: SnCl4·5H2O and SnCl2·2H2O. The reaction was operated at 150°C under ambient pressure, stirred at 600 rpm. with spent retention time of approximately 180 min. Final FFA in re-esterification of products, which were cleaned up with centrifuging and hot wet washing, was monitored. The results after centrifuge indicated that only two catalysts (Zn and ZnO) were capable of promoting the reaction and achieving the requirement. Moreover, final FFA in re-esterification of products, which were cleaned up with hot wet washing, was also monitored. It was found that no significant differences existed in the two purification techniques except for the heterogeneous Zn catalyst in re-esterification product. The results showed that thin layer chromatography with a flame ionization detector (TLC/FID) could not detect all of the compositions in the pre-treatment product using Zn as a catalyst. Therefore, ZnO was the most suitable catalyst for effectively reducing FFA via a re-esterification process.