Metallic monolithic catalysts based on calcium and cerium for the production of biodiesel

The present work reports the preparation, characterization and testing of Ca/Ce oxides as heterogeneous catalysts for the transesterification of sunflower oil with methanol (methanolysis), both in powder and structured forms, to produce biodiesel. A series of Ca-based catalysts in powder form were prepared on four different supports (commercial Al2O3, SiO2 and CeO2, along with in-house prepared CeO2) following different techniques. The best catalyst formulation in terms of activity and stability was a Ca/Ce mixed oxide (20 wt% CaO) catalyst prepared under the metallic citrates decomposition technique. Different suspensions could be formulated using this catalyst for further washcoating Fecralloy® monoliths. The effect of the solvent (water or alcohols) and of the use of additives (polyvinyl alcohol, polyvinylpyrrolidone, and colloidal Al2O3 and CeO2) on the catalytic performance of the catalysts in the transesterification reaction was studied. The best results could be obtained for the structured catalysts prepared using suspensions having isopropanol as solvent medium and 1% of polyvinylpyrrolidone. The monoliths prepared using this formulation yielded the best oil conversions after a second reaction cycle reported so far in the literature concerning the use of structured catalysts for biodiesel production, with oil conversion values of 70% after 6 h of reaction at 60 °C using recovered and thermally regenerated monoliths. The thermal reactivation of the catalysts has been proven to be crucial in order to partially recover the catalyst activity, though significant leaching of the active catalytic layer was found to occur during the first reaction cycle. The results presented here are remarkably superior to the best ones previously reported in the literature concerning the use in a second reaction cycle of structured methanolysis catalysts at atmospheric pressure.