Vegetable Oil Transesterification in Supercritical Conditions Using Co-solvent Carbon Dioxide over Solid Catalysts: A Screening Study

Abstract

The transesterification reaction employing supercritical methanol and carbon dioxide used as a co-solvent in the presence of several heterogeneous solid acid catalysts was investigated. The solid acid catalysts were prepared by impregnation methods, with appropriate precursors over magnesium aluminum silicate (cordierite). The catalysts tested were CeO2, WO3, ZnO, ZrO2, ZrO2–SO42–, mixed oxides (50–50%, w/w) WO3– ZrO2, CeO2–ZrO2, ZnO–La2O3, and Al2O3. Reaction tests were conducted at 200 °C and 20 MPa under the condition of 25:1 methanol/oil ratio at a space velocity of 4 min with a fixed-bed continuous flow reactor containing ca. 5 g of catalyst. The best catalytic performance was obtained over ZrO2–SO42– with a yield toward fatty acid methyl esters (FAMEs) of 98%. This value is better to that obtained over the commercial catalyst Nafion SAC-13 (94%). The direct correlation between the conversion and catalyst total acidity was non-existent, but a positive effect of strong acid sites is evidenced.