Universal and low energy-demanding platform to produce propylene carbonate from CO2 using hydrophilic ionic liquids

Abstract

Ionic liquids (ILs) have been extensively proposed as efficient catalysts to promote CO2 cycloaddition reaction to epoxides for producing cyclic carbonates. Recently, liquid-liquid extraction with water as an enhancer approach to regenerate ILs and to purify the product was proposed, since it reduces energy consumption and enhances the neat catalytic activity of the IL due to hydroxyl groups of water. In this work, a comprehensive sample of homogeneous IL catalysts proposed in the literature is experimentally evaluated both in the catalytic step and in its separation by liquid-liquid extraction with water, to demonstrate the universality of the proposed reaction-separation proposal for hydrophilic ILs. Then the complete processes for CO2 conversion to propylene carbonate were modelled using Aspen Plus to compare the catalyst/product separation efficiency and the specific energy consumption using liquid-liquid extraction and distillation-based platforms. The energy consumption is significantly lower using liquid-liquid platform (1.1–1.3 kWh/kgPC) than distillation one (2.4–3.1 kWh/kgPC). It is concluded that hydrophilic ionic liquids, as those formed by [EtOHmim] cation and halide anions, are promising catalysts since they allow: (i) reducing the process energy consumption due to their high catalytic activity and (ii) full catalyst recovering, even at high catalyst loadings, by improving the water extractive properties for IL separation from PC.