Continuous Conversion of Carbon Dioxide to Propylene Carbonate with Supported Ionic Liquids

We present the use of silica-supported ionic liquids as catalysts for the continuous production of propylene carbonate from propylene oxide using supercritical carbon dioxide as solvent and reagent. Considerable differences in the catalytic activity of ionic liquids in homogeneous catalysis in batch mode and in continuous-flow using supported species processes were found, suggesting that a synergistic effect between ionic liquid and silica support material takes place. While supported ionic liquids prepared via physisorption of [C2mim]Br showed the highest catalytic activity, studies on long-term stability showed a rapid loss in yield due to the formation of undesired polypropylene carbonate that agglomerated in the ionic liquid layer. Improved long-term stability was found for ionic liquids covalently bound to the silica support materials, suggesting that a compromise between activity and stability is the best solution for the continuous production of propylene carbonate.