Thermodynamics of n-octane+hexynes binary mixtures

The vapor pressures of binary mixtures of n-octane+hex-2-yne, or hex-3-yne and of the three pure components were measured by means of a static device at temperatures between 263 and 343 K. Molar excess Gibbs energies GE were calculated for several constant temperatures, taking into account the vapor phase imperfection in terms of the second molar virial coefficients, and were fitted to the Redlich–Kister equation. Calorimetric excess enthalpy HE measurements for n-octane+hex-2-yne, +hex-3-yne, or +hex-1-yne are also reported at 303.15 K. These data, along with previous vapor–liquid equilibrum data for the n-octane+hex-1-yne mixture, are examined on the basis of DISQUAC, an extended quasichemical group-contribution model. In terms of DISQUAC, the mixtures studied were characterized by only one type of contact: aliphatic/alkyne. The interchange coefficients are not available in the literature, and are estimated in this work. The model consistently describes the excess functions GE and HE of the investigated n-octane+alkynes mixtures.