A GROUP CONTRIBUTION MODEL FOR LIQUIDS AND THEIR MIXTURES WITH EXPERIMENTAL DETERMINATION OF INFINITE DILUTION ACTIVITY COEFFICIENTS.

A gas-liquid partition chromatograph (GLPC) has been constructed for the accurate determination of K values and activity coefficients at infinite dilution. There are several salient features of this apparatus which are improvements over previously reported models. Vaporization of the stationary phase in the GLPC column is suppressed by operating at elevated pressures, minimizing pressure drop across the GLPC column, and presaturating the carrier gas. Data are reported for a number of n-alkanal, alkanoate, alkane, and alkanone solutes in the solvents n-hexadecane, n-octane, 4-methyl-2-pentanone at temperatures from 55(DEGREES)C to 150(DEGREES)C. A structural group contribution model is used for the correlation of the thermodynamic properties of dense polar and nonpolar liquids and their solutions. Calculations are done for molar volume, energy of vaporization, activity coefficients, excess enthalpy, and liquid-liquid equilibria. The model is based on the cell theory in which the repulsive forces between the molecules are expressed as a modified cell partition function based on the Carnahan-Starling equation of hard spheres. The attractive forces are represented by group interactions. Previous to this work parameters have been determined for the methyl, methylene, hydroxyl, and carbonyl groups. This allows predictions to be made for n-alkanes, n-alkanols, n-alkanones, and their mixtures. The parameters for the methine, quaternary carbon, and nitrile groups are given in this work. Calculations are done for branched alkanes, alkanols, alkanones, and normal alkanenitriles.