(631b) Esterification of Free Fatty Acids with Methanol Over Metaloxides Supported ZrO2 Catalysts
Brown grease recovered from waste water is less expensive lipids and would make biodiesel much more competitive with petroleum-based fuels. About 80±5% of the brown grease is free fatty acids. In order to develop heterogeneous catalysts for brown grease conversion toward biodiesel, various mixed metal-oxides supported ZrO2 catalysts has been prepared via sol-gel method and impregnation method. In order to get the best catalyst composition for brown grease conversion, the performances of 35~70 mesh size of catalysts has been tested at 200°C with the mixture of brown grease, methanol, and tetrahydrofuran in batch reactors. Catalyst particles (size of 0.5~5mm) of three different formulas (ZnO2/ZrO2, ZnO2-Al2O3/ZrO2, and ZnO2-La2O3/ZrO2-La2O3) have been tested in continuous flow reactors with changes on temperatures (170, 180, 190, and 200°C) and retention times. A technical grade of oleic acid was used to continuous flow reactors as a model compound for brown grease. The FAME yields were measured with a GC-MS. Dissolved metal species (especially Zn) were measured with an Inductively Coupled Plasma Spectrometer. The ZnO2/ZrO2 catalyst showed very a high activity (98~99% yield) and durability for 54 days at 180°C with 5:1 ratio of methanol:FFA. Zr specie was very stable in the acidic stream of free fatty acids. However, Zn concentration in the product eluted from the continuous flow reactors were initially high as 807 ppm in the 1st day product, and decreased to below 10 ppm in 50th day product. The Zn dissolution can be prevented by using various metal-oxides combinations. In addition, the catalytic activities of the mixed metal-oxides supported catalysts for esterification and transesterification depended on the metal species and amounts of metals used.