Reaction Kinetics and Mechanism for the Synthesis of Glycerol Carbonate from Glycerol and Urea Using ZnSO4 as a Catalyst

Abstract

A series of Zn salts were used as catalysts for the reaction of glycerol and urea to produce glycerol carbonate and it was found that ZnSO4 showed the highest catalytic activity. Furthermore, the effects of reaction parameters on the glycerol conversion and glycerol carbonate yield were studied in detail. The results indicated that the glycerol conversion and glycerol carbonate yield were increased with the reaction temperature, reaction time, and catalyst amount while the optimal reaction conditions were 140 °C, 240 min, catalyst amount of 5 wt% (based on the glycerol weight), and urea-to-glycerol molar ratio of 1.1:1. During the reaction, the ZnSO4 catalyst is transformed into Zn(NH3)2SO4 at the initial stage of the reaction and then further transformed into Zn(C3H6O3). Zn(C3H6O3) and (NH4)2SO4 may be the true active species for the activation of urea and glycerol, respectively. The reaction mechanism is proposed in this article. Based on the experimental results, a reaction kinetics model considering the change in volume of the reaction system was also established, and the model parameters were obtained by fitting the experimental data. The statistical results showed that the established kinetics model is accurate.