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

Abstract

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 (SiO 2 -supported Nafion-SAC-13) at lower temperature (60°C).

The Role of Zirconia Surface on Catalytic Activity of Tungstated Zirconia via Two-Phase Esterification of Acetic Acid and 1-Heptanol

“…As known, acidity of WZ catalyst is a key factor to enhance the catalytic activity for several reactions by generation of active sites [2][3][4][5][6][7][8][9][10][11][12][13]. The catalytic active sites were plausible for high surface acidity form with a monolayer of polytungstated species (WO x ) [3,4,11].…”

“…A heterogeneous catalyst as a tungsten oxide supported on zirconia (WZ) has been tremendously used for alkane isomerization [2][3][4][5], alcohol dehydration [6,7] and recently biodiesel forming reaction [8][9][10][11][12][13]. This is because of their acid properties, stability under reducing and oxidizing conditions and regenerability [14].…”

Silica‐supported morpholine alkaline ionic liquid catalysts for preparation of biodiesel

“…The three ester groups with large molecular weight are replaced by methanol with small molecular weight to produce the fatty acid methyl ester and glycerol with small molecular weight. [ 31,32 ]…”

Recent developments in the production of liquid fuels via catalytic conversion of microalgae: experiments and simulations

“…The simulated results also showed that increasing the initial ethanol concentration increases the initial production rate and yield of fatty acid ethyl ester and lowers the final concentration of free fatty acid. Using a tungstated zirconia catalyst, Ngaosuwan et al 107 investigated the mechanistic pathways for hydrolysis (with water) and transesterification (with methanol) of tricaprylin and found that increasing the concentration of tricaprylin increased the reaction rates for both hydrolysis and transesterification under all conditions. However, water inhibited the reaction rate of hydrolysis by poisoning the active sites.…”