High-Pressure Densities of 2,2,2-Trifluoroethanol plus Ionic Liquid Mixtures Useful for Possible Applications in Absorption Cycles

2,2,2-Trifluoroethanol (TFE) + ionic liquids constitute new possible refrigerant/absorbent pairs in refrigeration and heat absorption systems. In this work, volumetric data were measured on these systems in order to estimate their potential as alternatives to the commonly used fluids. Original high-pressure (up to 40 MPa) density data of mixtures 2,2,2-trifluoroethanol (TFE) + 1-methyl-3-ethylimidazolium tetrafluoroborate, [EMIm][BF4], or 1-methyl-3-butylimidazolium bis-(trifluoromethanesulfonyl)imide, [BMIm][NTf2], have been measured in the temperature ranges 293.15-333.15 K and 283.15-333.15 K, respectively. Mixtures with {BMIm][NTf2] present higher densities and thus are more adequate for refrigeration systems. Excess molar volumes, V-m(E), and derived properties (isothermal compressibility, kappa(T), and thermal expansion, alpha(P)) were calculated from experimental density data fitted to the Tait equation. alpha(P) and kappa(T) of the pure ionic liquids are smaller than those of the pure alcohol. Mixtures present derived properties similar to those of pure ionic liquids even at equimolar composition. From a technological aspect, these properties, being equivalent for both ionic liquids and most of their mixtures with TFE, will not be a criterion to select an absorbent-refrigerant pair. The excess molar volumes of the considered mixtures are small in absolute value and so can be considered as negligible when designing an absorption cycle. Finally, the PC-SAFT model was used to calculate the compressed densities. Acceptable results were obtained with trends as a function of temperature and pressure corresponding to what was experimentally observed. Using this model and a limited number of experimental data, the vapor pressures of the mixtures could be estimated with a reasonable precision.