Synthesis of highly effective [Emim]IM applied in one-step CO2 conversion to dimethyl carbonate

Abstract

Ionic liquid 1-ethyl-3-methylimidazolium ([Emim]IM) with high thermal stability and strong basicity was successfully synthesized. Using [Emim]IM as catalyst, dimethyl carbonate (DMC) was directly synthesized from epoxy propane (PO), CO2, and methanol under mild reaction conditions. A continuous two-stage DMC synthesis process was developed. The cycloaddition of CO2 and PO was first conducted to produce propylene carbonate (PC), and then methanol was introduced into the system to synthesize DMC. During the cycloaddition process, 97.40% PO conversion and 97.40% PC yield were achieved with TON of 99.49. In the subsequent transesterification stage, DMC yield attained 83.63% with selectivity higher than 99% and TON of 70.15. [Emim]IM was reused for seven times without obvious deactivation, exhibiting good stability. The effects of reaction temperature, reaction time, the initial pressure of CO2, and catalyst weight on cycloaddition and transesterification reactions were systematically investigated. The kinetic study showed that the activation energies (Ea) of cycloaddition and transesterification reactions were 28.02 and 38.53 KJ·mol−1, respectively, much lower than those of catalysts reported in the literatures. In addition, [Emim]IM displayed superior catalytic activity for the cycloaddition of CO2 with various epoxy compounds.