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 1,1,1,2tetrafluoroethane (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 +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 non-random two-liquid activity coefficient method, and the Henry's law constants at infinite dilution, solvation energies and infinite dilution activity coefficients are calculated.

Toward the Recycling of Low-GWP Hydrofluorocarbon/Hydrofluoroolefin Refrigerant Mixtures Using Composite Ionic Liquid–Polymer Membranes

“…In a similar way to R32/R1234yf separation, the largest anions with a significant degree of fluorination, such as OTf and Tf 2 N, exhibit lower separation capacity toward the R134a/R1234yf pair, which is consistent with the reported low solubility selectivity in ILs for this pair of gases. 11 Overall, these results suggest that although F-gas permeability through ILs is favored by strong enthalpic interactions (F-gases exhibit large electric dipole moments and H-bonding capability), the HFC/HFO separation selectivity may benefit from unfavorable entropic effects that hinder the solvation of large solutes in low-molar volume ILs, a fact that is in good agreement with available F-gas solubility studies in ILs. 11,16 F-Gas Sorption Behavior in Pebax 1657 CILPMs.…”

“…11 Overall, these results suggest that although F-gas permeability through ILs is favored by strong enthalpic interactions (F-gases exhibit large electric dipole moments and H-bonding capability), the HFC/HFO separation selectivity may benefit from unfavorable entropic effects that hinder the solvation of large solutes in low-molar volume ILs, a fact that is in good agreement with available F-gas solubility studies in ILs. 11,16 F-Gas Sorption Behavior in Pebax 1657 CILPMs. Understanding the effect of pressure on the membrane gas solubility is a critical aspect for designing membrane-based separation processes, particularly regarding the permeation of highly soluble penetrants such as CO 2 , organic vapors, and fluorinated hydrocarbon gases, whose transport properties through rubbery polymers strongly depend on pressure.…”

“…The IL 1-ethyl-3-methylimidazolium thiocyanate, [C 2 mim]­[SCN] (>98%), was purchased from IoLiTec, whereas 1-ethyl-3-methylimidazolium tetrafluoroborate, [C 2 mim]­[BF 4 ] (>98%), 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, [C 2 mim]­[OTf] (>98%), and 1-ethyl-3-methylimidazolium bis­[(trifluoromethyl)­sulfonyl]­imide, [C 2 mim]­[Tf 2 N] (>98%), were purchased from Sigma-Aldrich. The selected ILs are categorized as low-viscosity ILs, which added to their virtually no volatility, and good compatibility with the polymer Pebax 1657 makes them excellent candidates for the fabrication of composite membranes. , Table S2 of the Supporting Information shows general properties of the ILs used in this work.…”

“…The selected ILs are categorized as low-viscosity ILs, which added to their virtually no volatility, and good compatibility with the polymer Pebax 1657 makes them excellent candidates for the fabrication of composite membranes. 11,27 Membrane Preparation. Pure polymer membranes and CILPMs were manufactured by the solvent casting method using butanol as a solvent to avoid risks of hydrolysis of the fluorinated ILs.…”

“…As can be seen, some of these HFC/HFO blends, such as those formed by the system R32/R1234yf, exhibit very low temperature difference between the saturated vapor temperature and the saturated liquid temperature (temperature glide). In addition, other mixtures are azeotropic and behave as a pure fluid, for example, blends of R134a and R1234yf. − Therefore, the separation of these mixtures into their constituents by conventional procedures such as cryogenic distillation is very challenging, if not impossible, in a cost-efficient way. , …”