A Review on Glycerol Carbonate Synthesis through Catalytic Carbonylation of Glycerol with CO2

This paper reviews the synthesis methods of glycerol carbonate, such as phosgene method, oxidative carbonylation, transesterification, urea glycerolysis, and direct carbonylation. The latest advances in the synthesis of glycerol carbonate were outlined and their drawbacks were also pointed out. The research advances and issues in the catalytic carbonylation of glycerol with CO2 were discussed and assessed in detail. When the carbonylation of glycerol with CO2 was homogeneously catalyzed by di(n-butyl)tin(IV)oxide and HDBU+I‒ protic ionic liquid catalysts utilizing 13X zeolite and styrene oxide as dehydrating agents, glycerol carbonate yields reached 35% and 79.1%, respectively. In the carbonylation reaction catalyzed by di(n-butyl)tin(IV)oxide catalyst, it was suggested that di(n-butyl)tin(IV)oxide was firstly activated by methanol molecules, glycerol molecules replaced the methoxy groups to be activated, and then CO2 molecules interacted with the activated glycerol molecules to produce glycerol carbonate. While HDBU+I‒ protic ionic liquid catalyzed the carbonylation reaction, HDBU+ and I‒ ions activated glycerol and CO2 molecules, resulting in the formation of glycerol carbonate. When the carbonylation of glycerol with CO2 was heterogeneously catalyzed by ZnO catalyst without using a dehydrating agent and Zn-doped CeO2 nanorod catalyst using 2-cyanopyridine as a dehydrating agent, yields of glycerol carbonate were 8.1% and 80.9%, respectively. The dehydrating agent in situ eliminates water in the carbonylation process, which improves the forward reaction towards glycerol carbonate and increases glycerol carbonate yield. Various catalytic reaction mechanisms were proposed in direct carbonylation of glycerol with CO2 towards glycerol carbonate when solid phase catalysts were utilized, which require further investigation. In direct carbonylation of glycerol with CO2, the key problems are to design effective catalysts for activating stable CO2 molecule and efficient dehydrating agent inert to both glycerol and CO2.