Thermal Conductivity of 1-Alkyl-3-methylimidazolium [Tf₂N] Ionic Liquids and Compressed 1,1,1,2-Tetrafluoroethane (R-134a)

Abstract

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.

Thermal conductivity of the ionic liquid [HMIm][Tf2N] with compressed carbon dioxide

“…The behavior for CO 2 in ILs is quite different than other more polar gases. For instance, we are currently measuring the thermal conductivity of [1‐alkyl‐3‐methyimidazolium][Tf 2 N] ([RMIm][Tf 2 N]) ILs saturated with compressed hydrofluorocarbon refrigerant gases, such as 1,1,1,2‐tetrafluoroethane (R‐134a) 114 . As a Type V system, R‐134a becomes miscible with [RMIm][Tf 2 N] ILs at 298.15 K at its pure component vapor pressure of 0.67 MPa as 298.15 K is below the lower critical endpoint (LCEP).…”

Phase Equilibrium and Transport Properties of the Ionic Liquid 1-Ethyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)amide and Compressed Difluoromethane and Pentafluoroethane

“…A Flucon Fluid Control GmbH thermal conductivity probe employing the transient hot-wire technique is coupled with a high-pressure equilibrium cell to measure the thermal conductivity of the biphasic IL/refrigerant mixtures. A detailed description of the system and the derivation of the governing equation are provided in our previous work, , and an overview is provided here. A transient hot-wire sensor equipped with a platinum wire is used with a high-pressure equilibrium cell that is loaded with an initial amount of IL.…”

“…71−73 However, we are the first group to report the thermal conductivity values of ILs 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide [EMIm][Tf 2 N] and [HMIm][Tf 2 N] saturated with an HFC (R-134a). 74 Here, we report on experimental data and modeling for the vapor−liquid equilibrium (VLE), density, and viscosity of the IL [EMIm][Tf 2 N] saturated with R-32 or R-125 at 298.15 K, 323.15 K, and 348.15 K and pressures to 3.5 MPa. R-32 and R-125 constitute common azeotropic mixture R-410A and are two of the three constituents in the R-407 series of refrigerant blends.…”

Condensable Gases Capture with Ionic Liquids

“…In a recent study, the vapor−liquid equilibria of [EMIM][NTf 2 ] and [HMIM][NTf 2 ] with R-134a at different temperatures and 28 bar were measured using a transient hotwire technique. 322 The thermal conductivity of the pure IL decreases with increasing temperature. Increasing the molar composition of R-134a reduces the thermal conductivity of the mixture in the two systems.…”

“…Understanding the thermophysical properties of pure IL and IL mixtures saturated with fluorinated gases is necessary for the optimal design of various engineering and separation applications. In a recent study, the vapor–liquid equilibria of [EMIM]­[NTf 2 ] and [HMIM]­[NTf 2 ] with R-134a at different temperatures and 28 bar were measured using a transient hot-wire technique . The thermal conductivity of the pure IL decreases with increasing temperature.…”