Synthesis of glycerol carbonate from glycerol and dimethyl carbonate catalyzed by calcined silicates

Several anhydrous silicates were prepared by calcination at 400 degrees C and utilized as solid base catalyst for synthesizing glycerol carbonate (GC) by transesterification of glycerol with dimethyl carbonate (DMC). Among them, calcined sodium silicate showed the best catalytic activity with glycerol conversion of 97.7%. Then, a series of sodium silicates calcined at different temperatures were characterized using TGA, Hammett indicator method, BET, XRD, FT-IR and FESEM. Effect of calcination temperature on their catalytic ability was carefully investigated, followed by a reaction optimization study. The basicity of sodium silicates calcined at different temperatures highly depended on calcination temperature; their catalytic ability was affected by their total basicity rather than by their BET surface area; and the increased amount of strong basic sites resulted in the formation of by-product which decreased the GC yield and GC selectivity. Sodium silicate calcined at 200 degrees C (Na2SiO3-200), which had the intermediate total basicity and relative low amount of strong basic sites, incurred the highest GC yield. The highest catalytic performance of Na2SiO3-200 was achieved under the condition that the 4:1 molar ratio of DMC to glycerol was reacted at 75 degrees C for 2.5 h. This catalyst could be reused five times without noticeable drop in catalytic activity.