Viscosity and self-diffusivity of ionic liquids with compressed hydrofluorocarbons: 1-Hexyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide and 1,1,1,2-tetrafluoroethane

Abstract

The viscosity and self-diffusivity of mixtures of the ionic liquid, 1-hexyl-3methylimidazolium bis(trifluoromethylsulfonyl)amide ([HMIm][Tf 2 N]), and the compressed gas, 1,1,1,2-tetrafluoroethane (R-134a), were measured at three different temperatures (298.15 K, 323.15 K, 343.15 K) and pressures to 21 bar. The high-pressure vapor-liquid equilibrium (VLE) of the ionic liquids with R-134a was measured to calculate the composition of the liquid phase at the various pressures encountered in the viscosity and diffusivity measurements. The viscosity of the ionic liquid decreases significantly with increased composition of R-134a at VLE. The "excess" viscosity demonstrates positive values that are believed to represent relatively strong intermolecular forces of the polar R-134a and [HMIm][Tf 2 N]. The self-diffusivity of mixtures of [HMIm][Tf 2 N] and liquefied R-134a (298.15 K and 6.7 bar) was measured and increases significantly with increases in the composition of R-134a. The selfdiffusivity of [HMIm][Tf 2 N] in vapor-liquid equilibrium with compressed R-134a gas was measured and indicates similar increases in diffusivity with composition of R-134a. The diffusivity demonstrates close Stokes-Einstein behavior using the measured mixture viscosity data and ambient pressure self-diffusivity.

Viscosity of 1-Alkyl-1-methylpyrrolidinium Bis(trifluoromethylsulfonyl)imide Ionic Liquids Saturated with Compressed CO2

“…It is most striking for [C 6 C 1 Pyr]­[NTf 2 ], which has 2.5-fold improvement in diffusivity (with a 56% reduction in viscosity) with increasing CO 2 pressure from 0.1 to 2 MPa (3 to 41 mol % CO 2 composition) at 298.15 K. At 318.15 K and similar increasing CO 2 pressures, the diffusivity enhancement of [C 3 C 1 Pyr]­[NTf 2 ]/CO 2 was about 37%, while for [C 6 C 1 Pyr]­[NTf 2 ]/CO 2 a 65% improvement in the diffusivity was found. Similar qualitative trends in diffusivity with gas solubility and viscosity were observed by Ahosseini et al for the system of 1,1,1,2-tetrafluoroethane in the IL 1-hexyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­amide ([C 6 C 1 Im]­[NTf 2 ]), albeit with self-diffusivity of the gas and IL …”

“…25,54−56 However, the viscosities of all of these ionic liquids become ), albeit with self-diffusivity of the gas and IL. 57 These diffusivity data may be analyzed with the current mixture viscosity data starting from the Stokes−Einstein theory:…”

Phase equilibrium and diffusivities of hydrofluorocarbons in a synthetic polyol ester lubricant

“…For instance, Shiflett and Yokozeki reported diffusivity coefficients in the range of 10 −10 to 10 −11 m 2 /s for HFC refrigerants (R‐134a, R‐32, R‐23, R‐125, R‐143a, and R‐152a) in 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([bmim][PF 6 ]) and 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([bmim][BF 4 ]) over a temperature range of 283.15–348.15 K 12 . Ahosseini et al measured the self‐diffusivity of R‐134a in the ionic liquid [HMIm][Tf 2 N] and values on the order of 10 −10 m 2 /s for liquid compositions of less than 80% mole of R‐134a were obtained 34 …”

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

“…We and other groups have begun measuring the viscosity and diffusivity in IL/gas systems. 55,56 Mixture heat transport properties of IL systems are very scarce in the literature. Such properties would be necessary for optimal design and sizing of engineering components utilizing IL/gas mixtures such as heat exchangers, reboilers, etc.…”

“…84,85 We have also reported data on the viscosity and self-diffusivity of pure ILs as well as ILs saturated with compressed gases, such as R-134a, at varying pressures and temperatures. 55,86,87 This study reports the liquid thermal conductivity values of biphasic systems of…”