On the deactivation of alkali solid catalysts for the synthesis of glycerol carbonate from glycerol and dimethyl carbonate

The deactivation of alkali solid catalysts for the synthesis of glycerol carbonate from glycerol and dimethyl carbonate was investigated. Calcium oxide, calcium hydroxide and calcium methoxide were chosen as the representatives of the alkali solid catalysts. When the catalysts were recycled, the yield of glycerol carbonate decreased dramatically. The alkali solid catalyst was converted to the basic calcium carbonate Ca_x(OH)_y(CO ₃)_z, which was the cause of the decrease of glycerol carbonate yield. It was found that the chemical interactions of the alkali solid catalyst with glycerol and glycerol carbonate led to the formation of the basic calcium carbonate Ca_x(OH)_y(CO₃)_z, for which the mechanism was proposed. Based on the deactivation mechanism, calcium diglyceroxide was adopted as a new catalyst for the transesterification of glycerol and dimethyl carbonate. Compared to calcium oxide, calcium hydroxide and calcium methoxide, calcium diglyceroxide showed excellent reusability for the transesterification of glycerol and dimethyl carbonate. For calcium oxide, calcium methoxide and calcium diglyceroxide, there were dissolution losses of the catalysts in the reaction medium. For calcium hydroxide, the catalyst dissolution loss in the reaction medium was nearly negligible. For calcium diglyceroxide, the dissolution of the catalyst in the reaction medium did not influence the yield of glycerol carbonate significantly.