Microwave-assisted transesterification of glycerol with dimethyl carbonate over sodium silicate catalyst in the sealed reaction system

Abstract

Microwave-assisted transesterification of glycerol to glycerol carbonate (GC) using calcined sodium silicate (Na2SiO3) as a catalyst in the sealed reaction system was studied in this work. Effects of the parameters, including the molar ratio of dimethyl carbonate (DMC) to glycerol, the reaction temperature, the amount of the catalyst, the reaction time and, especially, the microwave-assisted reaction modes on glycerol conversion and GC yield were carefully investigated. It was found that the microwave-assisted reaction modes, namely, the temperature constant mode (TCM) and the power constant mode (PCM), greatly influenced the reaction. When the reaction was conducted in TCM, with the catalyst amount of 5 wt%, reaction temperature of 95 °C, DMC-to-glycerol molar ratio of 4:1, and reaction time of 15 min, the glycerol conversion and the GC yield reached 96.7% and 94.3%, respectively. Similar glycerol conversion and GC yield were also obtained under the condition of the catalyst amount of 1 wt%, DMC-to-glycerol molar ratio of 4:1, microwave irradiation input power of 175 W and reaction time of 50 s in PCM. The reaction in PCM showed much more advantages in reducing the amount of the catalyst and shortening the reaction time than that in TCM. Meanwhile, the transesterification of glycerol with DMC in PCM catalyzed by Na2SiO3 exhibited much higher reaction rate than that catalyzed by CaO. Moreover, in terms of the reaction in PCM, energy consumption could be reduced with the increase of the irradiation power. The investigation on the reusability of the Na2SiO3 catalyst in PCM showed that this catalyst could be reused in five reaction cycles without significant deactivation.