Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

Ionic liquids (ILs) and carbon dioxide (CO2) systems have unique phase behavior that has been applied to applications in reactions, extractions, materials, etc. Detailed phase equilibria and modeling are highly desired for their further development. In this work, the vapor-liquid equilibrium, vapor-liquid-liquid equilibrium and liquid-liquid equilibrium of n-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ionic liquids with CO2 were measured at temperatures of 298.15 K, 323.15 K, 343.15 K and pressure up to 250 bar. With a constant anion of bis(trifluoromethylsulfonyl)amide, the n-alkyl chain length on the cation was varied from 1-ethyl- 3-methyl-imidazolium ([EMIm][Tf2N]), 1-hexyl-3-methyl-imidazolium ([HMIm][Tf2N]), to 1-decyl-3- methyl-imidazolium ([DMIm][Tf2N]). The effects of the cation on the phase behavior and CO2 solubility were investigated. The longer alkyl chain lengths increase the CO2 solubility. The Peng- Robinson Equation of State with van der Waals 2-parameter mixing rule with estimated IL critical properties were used to model and correlate the experimental data. The models correlate the vapor-liquid equilibrium and liquid-liquid equilibrium very well. However, extrapolation of the model to much higher pressures (greater than 300 bar) can results in the prediction of a mixture critical point which, as of yet, has not been found in the literature.