Search

Calcium-containing perovskites CaTiO3, CaMnO3, CaZrO3 and Ca2Fe2O5 were synthesized by calcination of mechanochemically treated stoichiometric mixtures of CaCO3 and either TiO2, MnO2, ZrO2 or Fe2O3 powders. X-ray diffraction analysis revealed a pure single perovskite phase for all four samples after calcination. This study proved that the pure perovskite phase exhibited low or no catalytic activity at 60 °C for the methanolysis of sunflower oil. However, at 165 °C FAME yield of more than 90% was reached after 2 h using CaTiO3, CaMnO3 and CaZrO3 as catalyst. Contrary to inactive pure perovskites at 60 °C, the CaTiO3 and Ca2Fe2O5 samples containing a very small amount of “free” CaO also showed methanolysis activity at 60 °C. This fact can be used to explain some contradictory statements reported in literature related to the perovskites as catalyst for biodiesel synthesis at mild temperatures.

A heterogeneous cerium-manganese oxide catalyst was synthesized by a co-precipitation method, characterized and tested in soybean oil transesterification with methanol under subcritical condition for methanol. Conversion of triglycerides after 40 min of transesterification in a batch process was over 99% with a fatty acid methyl ester (FAME) yield of 91.6% when 3 wt.% of catalyst based on oil, and 18:1 methanol/oil molar ratio were applied. The same amount of catalyst was used in 12 cycles of transesterification with catalyst regeneration performed only after the 7th cycle. The catalyst exhibited good tolerance toward soybean oil containing below 1.5 wt.% of water or 4 wt.% of free fatty acids. The mechanisms of Ce/Mn catalytic activity and its deactivation were discussed according to the characterization of the fresh and used catalyst according to results of different analytical methods: the Hammett titration, BET surface area, scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), FTIR, X-ray diffraction (XRD), ICP-MS and TG-DSC. It was assumed that deactivation of catalyst was mainly a consequence of manganese solubility in methanol and glycerol.