Readily available, biocompatible sodium citrate catalyst for efficient glycerol carbonate production through transesterification of glycerol and ethylene carbonate

Abstract

As a by-product in the biodiesel industry, surplus glycerol (Gly) has attracted considerable concern. The transesterification of Gly is one of the most promising reaction pathways to convert Gly to a value-added chemical such as glycerol carbonate (GC). Currently, development of catalysts for the transesterification with high activity is underway. Herein, a readily available biocompatible sodium citrate (Na3-citrate) catalyst was applied for efficient production of GC through transesterification of Gly and ethylene carbonate (EC). The effects of reaction parameters such as reaction time, EC to Gly molar ratio, reaction temperature, and catalyst loading on the reaction were investigated. Under optimal conditions, 0.01 wt% of Na3-citrate showed high catalytic activities with a Gly conversion of > 99 %, a GC yield of > 99 %, and a high turnover frequency of 16,925 gGC⋅g−1Cat⋅h−1. Furthermore, the reaction kinetic model for transesterification was established, and the activation energy of the Na3-citrate catalyzed transesterification was calculated as 51.3 kJ·mol−1. In addition, density functional theory calculations were used to unveil mechanism of the Na3-citrate catalyzed transesterification. It revealed that citrate anion of Na3-citrate could activate hydroxy of Gly via strong hydrogen bond interaction, thereby efficiently promoting transesterification by reducing energy barrier of rate-determining step.