The physical properties of four ionic liquids (ILs), including 1-n-butyl-3-methylimidazolium tetrafluoroborate ([C4C1im]­[BF4]), 1-n-butyl-3-methylimidazolium hexafluorophosphate ([C4C1im]­[PF6]), 1-n-butyl-3-methylimidazolium thiocyanate ([C4C1im]­[SCN]), and 1-n-hexyl-3-methylimidazolium chloride ([C6C1im]­[Cl]), and their mixtures with hydrofluorocarbon (HFC) gases HFC-32 (CH2F2), HFC-125 (CHF2CF3), and HFC-410A, a 50/50 wt % mixture of HFC-32 and HFC-125, were studied using molecular dynamics (MD) simulation. Experiments were conducted to measure the density, self-diffusivity, and shear viscosity of HFC/[C4C1im]­[BF4] system. Extensive analyses were carried out to understand the effect of IL structure on various properties of the HFC/IL mixtures. Density, diffusivity, and viscosity of the pure ILs were calculated and compared with experimental values. The good agreement between computed and experimental results suggests that the applied force fields are reliable. The calculated center of mass (COM) radial distribution functions (RDFs), partial RDFs, spatial distribution functions (SDFs), and coordination numbers (CNs) provide a sense of how the distribution of HFC changes in the liquid mixtures with IL structure. Detailed analysis reveals that selectivity toward HFC-32 and HFC-125 depends on both cation and anion. The molecular insight provided in the current work will help the design of optimal ILs for the separation of azeotropic HFC mixtures.

The thermal conductivities of mixtures of ionic liquids (ILs) and fluorocarbon gases are necessary for the design of a variety of engineering and separation applications. Here, a transient hot-wire technique was used to measure the liquid thermal conductivities of 1-ethyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­amide ([EMIm]­[Tf2N]) and 1-n-hexyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­amide ([HMIm]­[Tf2N]) in vapor–liquid equilibrium with the hydrofluorocarbon gas, 1,1,1,2-tetrafluoroethane (R-134a), at (298.15, 323.15, 348.15) K for [HMIm]­[Tf2N] and (298.15, 348.15, 398.15) K for [EMIm]­[Tf2N] and pressures up to 28 bar. The thermal conductivity of the gas-saturated ionic liquid exhibits a very small and relatively linear decrease with increasing pressure (composition) of R-134a even to relatively high compositions (∼80% mol). Only at very high molar compositions of the gas (∼90+% mol) does the thermal conductivity significantly decrease toward that of the value of pure saturated liquid R-134a. However, no simple mixing rule of the pure component properties could correlate the trends in composition. As some potential applications require higher temperatures, the system of [EMIm]­[Tf2N]/R-134a was measured at 398.15 K. Generally, a longer alkyl-chain length on the cation, such as [HMIm]­[Tf2N], experiences a steeper decrease in thermal conductivity with increasing R-134a composition than with the [EMIm] cation.

The liquid thermal conductivity of the ionic liquid (IL), 1‐hexyl‐3‐methyl‐imidazolium bis(trifluoromethylsulfonyl)amide ([HMIm][Tf2N]), saturated with compressed vapor and supercritical carbon dioxide was measured over three isotherms (298.15, 323.15, and 348.15 K) and pressures up to approximately 20 MPa using a transient hot‐wire technique. Pure [HMIm][Tf2N] thermal conductivity was also measured over a temperature range of 293.15–353.15 K at ambient pressure and with hydrostatic pressure to approximately 20 MPa. Literature vapor–liquid equilibrium data were used to predict the liquid CO2 composition at the conditions investigated. Initially, the liquid thermal conductivity slightly decreased with pressure/composition of CO2 followed by a gradual increase that is mainly attributed to hydrostatic pressure effects. Simple composition‐based mixing rules for mixture properties are not qualitatively nor quantitatively accurate. These data could be used to engineer heat transfer equipment required for a variety of proposed IL applications in CO2 capture, absorption refrigeration, biphasic CO2/IL reaction platforms, etc.