Comparative study of triglyceride transesterification in the presence of catalytic amounts of sodium, magnesium, and calcium methoxides

An array of metal methoxides, homogeneous Mg(OCH 3) 2, solid MgO x (OCH 3) 2−2 x , Ca(OCH 3) 2, has been studied in a model reaction for biodiesel production. Peculiarities of each catalyst are elucidated. ▪ A solution of Mg(OCH 3) 2 in methanol, in-house prepared solid MgO x (OCH 3) 2−2 x , and commercial Ca(OCH 3) 2 were tested at 60 °C in transesterification of tributyrin with methanol—a model reaction for biodiesel production. The homogeneous magnesium methoxide acts fast at the beginning of the reaction but quickly forms a suspension/precipitate mixture of much lower catalytic activity. The precipitate was found to be a complex composition including glycerol and butyric acid derivatives. The reaction over solid MgO x (OCH 3) 2−2 x is catalytic but sluggish with deactivation taking place in ca. 4 h. Analysis of the used catalyst revealed surface butyric acid as the most likely species responsible for the catalyst deactivation. In the presence of Ca(OCH 3) 2, the yields of the products reach final values in about 4 h. The reaction starts as a heterogeneous process, however, interaction of Ca(OCH 3) 2 with reaction products such as glycerol gives rise to catalytically active homogeneous species. Formed in a side reaction calcium butyric acid derivatives contribute to Ca(OCH 3) 2 dissolution but do not deactivate the surface of the catalyst.