Polymer-Supported Zn-Containing Imidazolium Salt Ionic Liquids as Sustainable Catalysts for the Cycloaddition of CO2: A Kinetic Study and Response Surface Methodology

Metal-containing ionic liquids (MIL) are highly active homogeneous catalysts for the chemical fixation of CO2 into epoxides yielding five-membered cyclic carbonates. To obtain sustainability, polymer-supported MIL catalysts were designed to overcome their previously reported inherent poor recoverability. Polymer-supported Zn-containing imidazolium salts, PS-(Im)2ZnX2, possessing bifunctional properties were identified as sustainable catalysts for the activation of CO2 under solvent-free conditions. PS-(Im)2ZnX2 showed good catalytic performance and was readily recoverable and reusable in the subsequent reaction cycles for the cycloaddition of CO2 to propylene oxide. Kinetic studies for the cycloaddition of CO2 to propylene carbonate using batch or semibatch systems were performed to calculate the approximate rate constants, which provide an explanation for the different reaction systems. In addition, process optimization using the response surface methodology was performed, and the interactions between the operational variables were identified. The results demonstrate the advantage of the semibatch system, which allows the completion of the reaction in less time than when using the batch system.