Vapor-liquid equilibria and diffusion coefficients of difluoromethane, 1,1,1,2-tetrafluoroethane, and 2,3,3,3-tetrafluoropropene in low-viscosity ionic liquids

Abstract

The phase-down of hydrofluorocarbons (HFCs) established by the Kigali Amendment to the Montreal Protocol is leading to the formulation and commercialization of new refrigerant blends containing hydrofluoroolefins (HFOs), such as 2,3,3,3-tetrafluoropropene (R1234yf), and HFCs with moderate global warming potential, namely, difluoromethane (R32) and 1,1,1,2-tetrafluoroethane (R134a). Moreover, the recycling of refrigerants is attracting attention as a means to reduce the amount of new HFCs produced and their release to the environment. To that end, the use of ionic liquids has been proposed as entrainers to separate refrigerants with close-boiling points or azeotropic blends. Thus, the vapor?liquid equilibria and diffusion coefficients of the refrigerant?ionic liquid pairs formed by R32 + [C2mim][BF4], R134a + [C2mim][BF4], R134a+ [C2mim][OTf], R1234yf + [C2mim][OTf], and R1234yf + [C2mim][Tf2N] are studied using an isochoric saturation method at temperatures ranging from 283.15 to 323.15 K and pressures up to 0.9 MPa. In addition, the solubility behavior is successfully modeled using the nonrandom two-liquid activity-coefficient method, and the Henry?s law constants at infinite dilution, solvation energies, and infinite dilution activity coefficients are calculated.