Reaction Kinetics and Mechanisms for Hydrolysis and Transesterification of Triglycerides on Tungstated Zirconia

Hydrolysis and transesterification are two reactions which can occur during the synthesis of biodiesel. An Investigation of the mechanistic pathways in hydrolysis and transesterification were carried out at a relatively high temperature (100–130 °C) and moderate pressures (120–180 psi) with tricaprylin and water for hydrolysis or methanol for transesterification using a tungstated zirconia catalyst in a batch reactor. It was found that upon increasing the concentration of TCp, the reaction rates for both hydrolysis and transesterification increased at all conditions. In contrast, water inhibited the reaction rate of hydrolysis by poisoning the active sites. For transesterification, the apparent reaction order of methanol evolved from positive to negative as the concentration of methanol relative to TCp increased. Using a reaction model discrimination procedure, it was found that hydrolysis on WZ could be successfully described by an Eley–Rideal single site mechanism with adsorbed TCp reacting with bulk phase water. The mechanistic pathway for transesterification also seems to follow a similar mechanism, identical to the one previously proposed for transesterification on a solid acid catalyst (SiO₂-supported Nafion-SAC-13) at lower temperature (60 °C).