Cerium-manganese oxide as catalyst for transesterification of soybean oil with subcritical methanol

Abstract

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.