ZnAl-Zr hydrotalcite-like compounds activated at low temperature as solid base catalyst for the transesterification of vegetable oils

Abstract

ZnAl hydrotalcite-like compounds were modified through the incorporation of Zr+4 using molar ratios of Zr/Al(X)=0.0, 0.10 and 0.25. The synthesis of these materials was performed by the co-precipitation method and their physicochemical properties were characterized by XRD, UV-Vis-DRS, N2 physisorption, TGA, and finally, the basic properties were analyzed by titration with benzoic acid and adsorption of methanol analyzed by FT-IR. It was found that 200ºC is the most appropriate activation temperature, since the catalytic activity of ZnAl-Zr(X) materials on the transesterification reaction was enhanced, obtaining FAME yields ranging from 68% to 82%. This high catalytic activity at low activation temperature (200ºC) was attributed to the presence of a mixture of the active phases: hydrotalcite, zincite, and hydrozincite; as well as the formation of Brönsted and Lewis basic sites when the hydrotalcite-type materials are dehydrated. In addition, it was possible to calculate the apparent reaction rate constants by means of a simplified lumped first-order reaction model. The reaction rate constant for the ZnAl-Zr(0.25) catalyst was 12.4 x10-3 L/gcat.min which is 1.5 times greater than that of the catalyst without Zr.