Fluid-phase behavior of {1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, [C₆mim][NTf₂], + C₂-C₈ n-alcohol} mixtures: Liquid-liquid equilibrium and excess volumes

In the frame of the IUPAC Project entitled Thermodynamics of ionic liquids, ionic liquid mixtures, and the development of standarized systems, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, [C ₆mim][NTf₂], was selected as the "model" ionic liquid to perform round-robin measurements on a series of ionic liquid properties. In this work, the temperature-composition liquid-liquid equilibria of this ionic liquid with linear alkan-1-ols, C_nH_(2n+1)OH, with n = 4, 5, 6, and 8, were determined at a nominal pressure of 0.1 MPa and up to 50 MPa for n = 4, 5, and 6. Excess molar volumes, V^E, of mixtures of this same ionic liquid with linear alkan-1-ols, C_nH _2n+1OH, with n ranging from 2 to 5, were measured at a nominal pressure of 0.1 MPa. The consistency between the two sets of experimental data (phase diagrams and V^E) was analyzed from a theoretical perspective; we noticed that as the alkyl chain length, n, of the linear alcohol varies both the pressure dependence of the phase diagrams and the critical excess molar volume change sign.