Thermodynamics insights into the gas-phase synthesis of glycolide from methyl glycolate

Abstract

Gas-phase synthesis of glycolide (GL) from methyl glycolate (MG) is of great significance for producing biodegradable polyglycolic acid. Here, we report a detailed thermodynamics study for the gas-phase synthesis of GL from MG, which involves complex reaction pathways, by utilizing the Gibbs free energy minimization method. The results indicate that the decompositions of MG and GL and the polymerization of MG are thermodynamically favorable as compared with the target pathway, i.e., the cyclization of MG. Effects of the reaction conditions including temperature, pressure and feed composition on the formation of GL and linear polymers have also been addressed, which demonstrate that the higher temperature and lower pressure can effectively inhibit the formation of linear methyl ester dimer and improve the selectivity to GL. In addition, the higher N₂/MG ratio is beneficial for the formation of GL in the process promoted by catalysts. These thermodynamics results indicate that the process promoted by catalysts would benefit from the kinetics control by high-performance catalysts and the operation at high temperature, low pressure and high N₂/MG ratio to enhance the yield of targeted GL. The insights demonstrated here from thermodynamics are valuable for guiding the design of catalysts and/or optimization of reaction conditions for the gas-phase synthesis of GL from MG.