Infinite dilution partition coefficients of benzene, toluene, chlorobenzene and naphthalene in the ionic liquid, 1-butyl-3-methyl-imidazolium hexafluorophosphate ([bmim][PF6])-CO2 system were measured with a chromatographic technique. Partition coefficients for each solute increased with increasing pressure and had the trend of at a given temperature. At pressures above 12 MPa, became one order in magnitude smaller than that of the other components, which is attributed to the [pi]-[pi] interactions between naphthalene and the imidazolium group of the ionic liquid. The Sanchez-Lacombe equation of state was found to provide adequate correlation of the data and their temperature and pressure trends.

Abstract: Activity coefficients at infinite dilution ³i have been measured for 17 polar solutes (linear and branched C1 to C5 alcohols, acetonitrile, acetone, 1,4-dioxane, tetrahydrofuran, ethyl acetate, and chloromethanes) in the ionic liquid 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM][CF3SO3]) by the gasliquid chromatographic method with the ionic liquid as the stationary phase. The measurements were carried out in the temperature range of (303.15 to 363.15) K. The partial molar excess enthalpies at infinite dilution HiE, of the solutes in the ionic liquid were also derived from the temperature dependence of the ³i values.

Abstract: We take advantage of the recent advances in statistical mechanics on mixtures to examine a century-old problem in solution thermodynamics, specifically for the popular activity coefficient model, with regard to the absence of a standard state for the non-condensable gases in the mixture. This defect is traced back to the excess Gibbs free energy formalism where insistence on a pure liquid-state reference fluid is incorporated. By examining the molecularly derived counterparts, we propose a new division of the component chemical potential along the line of the molecular theory. A new definition of a reference fugacity and that of a molecular-inspired activity coefficients are formulated to cure this defect. We employ the Ornstein-Zernike equations to actually evaluate the molecular activity coefficients for a mixture of methane and n-pentane. The system temperature is 444 K. Thus, methane is the suprecritical component and does not fit into the classical activity coefficient model. We demonstrate that the molecular activity coefficients of methane and n-pentane can be evaluated and do not suffer nonexistence. Furthermore, these values are used to determine the dew point and bubble point of the mixture. The results compare favorably with the experimental data of Sage and Lacey.

Infinite dilution activity coefficient is an important thermodynamic property, which is widely used in evaluating the intermolecular interaction and screening potential solvents for the separation of a fluid mixture by extraction, distillation or selective absorption. In this paper, UNIFAC model and a new group segmentation method are used to correlate infinite dilution activity coefficients based on the experimental data. Among the groups considered in this work, 1,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide ([MMIM][BTI]) and 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]) are treated as the main groups. A number of infinite dilution activity coefficients of some molecular solutes are well correlated based on the method proposed, which include alkanes, alkenes, aromatics, alcohols, ketones and water in six ionic liquids (ILs), viz. 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides with alkyl being methyl, ethyl, butyl, hexyl, octyl ([MMIM][BTI], [EMIM][BTI], [BMIM][BTI], [HMIM][BTI], [OMIM][BTI]), and [MMIM][DMP] in the temperature range of 303.15-373.15 K. It is found that the overall accuracy is within 9% in terms of root-mean-square deviation (RMSD); and the overall RMSD is less than 4.2% when the resulting parameters from obtained UNIFAC model are used to predict the vapor pressure of binary mixtures containing IL at varying composition and temperature. The results manifest the applicability of the UNIFAC model and the rationality of the group interaction parameters.