Study of CHF₃/CH₂F₂ Adsorption Separation in TIFSIX-2-Cu-i

Hydrofluorocarbons (HFCs) have important applications in different industries; however, they are environmentally unfriendly due to their high global warming potential (GWP). Hence, reclamation of used hydrofluorocarbons via energy-efficient adsorption-based separation will greatly contribute to reducing their impact on the environment. In particular, the separation of azeotropic refrigerants remains challenging, such as typical mixtures of CH₂F₂ (HFC-23) and CHF₃ (HFC-32), due to a lack of adsorptive mechanisms. Metal-organic frameworks (MOFs) can provide a promising solution for the separation of CHF₃-CH₂F₂ mixtures. In this study, the adsorption mechanism of CHF₃-CH₂F₂ mixtures in TIFSIX-2-Cu-i was revealed at the microscopic level by combining static pure-component adsorption experiments, molecular simulations, and density-functional theory (DFT) calculations. The adsorption separation selectivity of CH₂F₂/CHF₃ in TIFSIX-2-Cu-i is 3.17 at 3 bar under 308 K. The existence of similar TiF₆^2- binding sites for CH₂F₂ or CHF₃ was revealed in TIFSIX-2-Cu-i. Interactions between the fluorine atom of the framework and the hydrogen atom of the guest molecule were found to be responsible for determining the high adsorption separation selectivity of CH₂F₂/CHF₃. This exploration is important for the design of highly selective adsorbents for the separation of azeotropic refrigerants.