A Review of the Use of Ionic Liquids for Separation of Hydrofluorocarbon Mixtures

Hydrofluorocarbon (HFC) refrigerants can significantly contribute to global warming and climate change, with some refrigerants being thousands of times more potent than carbon dioxide. HFCs replaced chlorofluorocarbons (CFCs) as refrigerants, as CFCs were lined to the depletion of the Earth’s ozone layer. HFCs are now being phased out in favor of hydrofluoroolefins (HFOs), which have greatly reduced global warming potentials. Many HFCs are sold commercially as azeotropic mixtures that provide the necessary application properties as well as ensure leaked refrigerant maintains composition. However, azeotropes are difficult to separate using distillation and recycle the components. Ionic liquids (ILs) are being studied as potential entrainers for use in an extractive distillation process to separate azeotropic HFC mixtures. Separated refrigerants can then be recycled into HFO mixtures or repurposed into fluorinated feedstocks for other processes. ILs are commonly referred to as salts that have a melting point below 100°C, composed of an organic cation and an organic/inorganic anion. ILs are promising materials for separation due to their high tunability and low volatility. The NSF has sponsored research that has led to the design of specific ILs for the separation of HFC mixtures. Developing this new separation technology requires extensive data on the interactions between various HFC and IL combinations. This poster will review the extensive research done on IL/HFC systems for separation. Key areas of work include physical property measurements, experimental techniques, interaction simulations, and modeling of various system combinations. In these areas, studied IL/HFC systems will be identified. The direction of future work will also be discussed, and an overview will be given on the ongoing design of an extractive distillation process.