DISQUAC characterization of mixtures containing alkynes and alkanes or 1-alkanols. Comparison with ERAS model

Mixtures formed by alkynes and n-alkanes, cycloalkanes or 1-alcohols have been examined in the framework of the DISQUAC group contribution model. The corresponding interaction parameters are reported. These ones follow some simple rules: (a) the quasichemical (QUAC) interchange coefficients for the aliphatic/acetylene contacts are independent of the alkyne; (b) the dispersive (DIS) parameters for such contacts when isomeric non-terminal alkynes are involved are also independent of the alkyne; (c) in 1-alkanols+alkynes mixtures, the QUAC parameters for the hydroxyl/acetylenic contacts do not depend on the mixture compounds. Thermodynamic properties such as vapor–liquid equilibria (VLE), including coordinates of azeotropes or activity coefficients at infinite dilution (γi∞), and excess molar enthalpies (HE) are correctly described by DISQUAC. The model can be applied over a wide range of temperature. 1-Alkanols+1-alkynes, or + 3-hexyne systems have been also characterized in terms of the ERAS model. Calculations were developed neglecting the possible self-association of 1-alkynes. This is reasonable in view of the good results provided by DISQUAC (a purely physical model), and of the very low values of the equilibrium constants obtained from the ERAS model when analyzing 1-alkynes+n-alkanes mixtures. ERAS results on HE are improved by DISQUAC. Both models provide similar results on excess molar Gibb’s energies (GE) of 1-alkanols + 3-hexyne mixtures. Excess molar volumes of solutions containing 1-alkanols and 1-alkynes are represented qualitatively by ERAS. Interactions in the treated solutions are analyzed in terms of the effective dipole moment (μ̄). So, the higher HE of 1-alkynes + n-alkanes mixtures compared to that of non-terminal isomeric alkynes + n-alkanes solutions may be attributed to the higher μ̄ of 1-alkynes. Structural effects are also relevant. In 1-alkanols + 1-alkynes systems, interactions between unlike molecules become weaker with the size increase of the mixture components.