Absorption separation of fluorinated refrigerant gases with ionic liquids: Equilibrium, mass transport, and process design

Abstract

• F-gas + IL mixture equilibrium and mass transport properties are reviewed. • Influence of IL molecular structure in F-gas solubility and selectivity is discussed. • Design of absorption, extractive distillation and membrane separations are analyzed. • Extensive database containing 5000+ data is provided. Interest in recovering and reclaiming refrigerant gases is growing as a consequence of increasing concern about the high global warming potential of some hydrofluorocarbons (HFCs). However, advanced separation processes, like extractive distillation, are required to selectively separate azeotropic and close-boiling refrigerant mixtures. In this regard, ionic liquids (ILs) arise as promising entrainers because of their favorable properties, including nonvolatility and good HFC solubility selectivity. The aim of this review is to become a reference text for the research and design of novel separation processes for mixtures of fluorinated gases based on the use of ILs. We include an extensive compilation of publications on equilibrium, mass transport, and absorption and membrane separation related to the use of ILs to selectively separate, not only the most relevant refrigerants employed nowadays, namely, HFCs, hydrofluoroolefins, and hydrochlorofluoroolefins, but also other relevant refrigerant families, such as chlorofluorocarbons, hydrochlorofluorocarbons, and perfluorocarbons. The UC-RAIL database provided as Supplementary Information compiles more than 5000 data points that are comprehensively analyzed in the review focusing on process design. Finally, we provide a set of directions that lead to the recovery of fluorinated refrigerant gases, to shift the refrigeration and air conditioning sector towards a more circular economy.