The Phase Behavior Effect On the Kinetics of Transesterification Reactions for Biodiesel Production

The kinetics of transesterification reactions catalyzed by potassium-based compounds for biodiesel production using the model triglyceride compound triolein have been investigated. The influence of the methanol to triolein molar ratio, catalyst concentration, and temperature were studied. Depending on the value of the methanol to triolein molar ratio, the volume ratio of the two species can be less than, equal to, or greater than 1. When the volume ratio is less than 1, there exists a greater volume of triolein than methanol. When mixed, small droplets of methanol form inside the triolein phase. On the other hand, when the volume ratio is greater than 1, small droplets of triolein form inside the methanol. Since the catalyst is more soluble in the polar methanol phase, the triolein must transfer to the methanol phase for reaction to occur. A volume ratio equal to 1 corresponds to a molar ratio of approximately 24, well within the experimental range studied for biodiesel production. The effectiveness of a kinetic model incorporating first, the transport of triolein into the methanol phase and second, the subsequent transesterification reaction between the triolein and methanol, was evaluated. Kinetic rate constants and activation energies were also experimentally determined. The use of the model triglyceride compound greatly facilitates quantitative analysis, which was carried out using reversed-phase HPLC as opposed to the more commonly used gas chromatographic methods.