Competitive transesterification of soybean oil with mixed methanol/ethanol over heterogeneous catalysts.

Methylesters and ethylesters of fatty acids were synthesized using homogeneous CH(3)ONa and CH(3)CH(2)ONa, anion exchanged resin, and CaO-La(2)O(3) catalysts. Methanol, ethanol, and methanol/ethanol mixtures were used as the alcohol feed for transesterification of soybean oil. With a homogeneous catalyst (CH(3)ONa) there was essentially no difference in conversion rates between methanolysis and ethanolysis in batch reactions. However, with a heterogeneous resin and CaO-La(2)O(3) catalysts, significant differences in the conversion rates between the methanolysis and ethanolysis were observed. The formation rate of methylesters over a CaO-La(2)O(3) catalyst was higher than that of ethylesters, which may be attributable to a steric hindrance effect. Conversely, with a heterogeneous resin catalyst, the conversion rate of ethylester was higher than that of methylesters which may be attributable to the surface hydrophobicity of the anion exchanged resin. When the transesterification of soybean oil was carried out with an equimolar methanol/ethanol mixture, the yield ratio of methylester to ethylester formed within the first 30 min was 2.6 for the homogeneous catalyst (0.3% CH(3)ONa), and 3.4 for the heterogeneous CaO-La(2)O(3)catalyst. These differences in selectivity are likely due to both the higher reactivity of methoxide and to a steric hindrance effect of ethoxide on the catalyst surface. In addition, the transformation of methylester to ethylester was observed when a methanol/ethanol mixture was used.