Phase equilibria of imidazolium ionic liquids and the refrigerant gas, 1,1,1,2-tetrafluoroethane (R-134a)

A number of applications with ionic liquids (ILs) and hydrofluorocarbon gases have recently been proposed. Detailed phase equilibria and modeling are needed for their further development. In this work, vapor-liquid equilibrium, vapor-liquid-liquid equilibrium. and mixture critical points of imidazolium ionic liquids with the hydrofluorocarbon refrigerant gas, 1,1,1,2-tetrafluoroethane (R-134a) was measured at temperatures of 25 degrees C, 50 degrees C, 75 degrees C and pressure up to 143 bar. The ionic liquids include 1-hexyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide ([HMlm][Tf2N])), 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMlm][PF6]), and 1-hexyl-3-methyl-imidazolium tetrafluoroborate ([HMlm][BF4]). The effects of the anion and cation on the solubility were investigated with the anion having greatest impact. [HMlm][Tf2N] demonstrated the highest solubility of R-134a. The volume expansion and molar volume were also measured for the ILs and R-134a. The Peng-Robinson Equation of State with van der Waals 2-parameter mixing rule with estimated IL critical points were employed to model and correlate the experimental data. The models predict the vapor-liquid equilibrium and vapor-liquid-liquid equilibrium pressure very well. However, the mixture critical points predictions are consistently lower than experimental values. (C) 2009 Elsevier B.V. All rights reserved.