Is Excess Methanol Addition Required To Drive Transesterification of Triglyceride toward Complete Conversion?

To clarify whether excess methanol addition is required to drive the transesterification of triglyceride toward complete conversion, the effect of the molar ratio of methanol to triglyceride on the reaction behavior was studied using not only the conventional homogeneous alkali catalyst but also the novel heterogeneous anion-exchange resin catalyst. For the heterogeneous anion-exchange resin catalyst, the transesterification completely proceeded even at the stoichiometric molar ratio of 3:1 because the saponification, which preferentially proceeded at the lower molar ratio of methanol to cause the catalyst depletion and the product contamination, never occurred. The reaction rate at 3:1 was much higher than that at the molar ratio of 6:1, widely used in the industrial production process of the biodiesel fuel. This was because the homogeneous single phase was formed at 3:1 and the mass-transfer resistance between the methanol/triglyceride phases disappeared.