Infinite dilution activity coefficients, specific retention volumes and solvation thermodynamics of hydrocarbons in C 78H 158 branched alkane solvent

Abstract

Kováts's retention indices were determined for 60 hydrocarbons by capillary gas–liquid chromatography at temperatures from 373.15 to 433.15 K using fused silica open tubular column coated with 19,24-dioctadecyldotetracontane (C 78H 158) as stationary phase. Gas–liquid equilibrium parameters (specific retention volumes, standard Gibbs energy differences and limiting activity coefficients) were calculated for isoalkanes, cycloalkanes, alkenes, alkynes, aromatics on the basis of absolute retention data of n-alkanes determined by GLC using packed column with the same stationary phase. It was concluded that molecular shape and size have an important effect on limiting activity coefficient values. The standard Gibbs free energy differences of solute transfer were correlated by a Kirchhoff-type temperature function and the thermodynamic parameters of the solvation (partial molar standard enthalpy and entropy differences at reference temperature T * = 403.15 K, furthermore heat capacity differences) were determined. The predictive ability of various entropic models was investigated on the new experimental data of saturated hydrocarbons and it is shown that the modified UNIFAC-FV model, Kannan-FV, represents satisfactorily the presented experimental limiting activity coefficient data of alkanes in size-asymmetric solutions.