Phase equilibria, critical behavior and derivative properties of selected n-alkane/n-alkane and n-alkane/1-alkanol mixtures by the crossover soft-SAFT equation of state

We present here results from the crossover soft-SAFT equation of state as applied to selected n-alkane/n-alkane and n-alkane/1-alkanol mixtures. The molecular parameters needed to apply the equation to experimental systems were obtained as a function of the molecular weight of the compounds, from published correlations. The fact that the equation takes into account the long range density and composition fluctuations appearing near the critical point enables it to predict with equal accuracy the behavior of the systems far from and close to the critical region. We have found that, for most of the mixtures investigated here, one size binary interaction parameter, with a fixed value for all systems, is enough to quantitatively predict the rich phase behavior shown by these mixtures, while for the case of very asymmetric mixtures, a second binary parameter, also independent of the thermodynamic conditions, is needed to quantitatively describe experimental data. Crossover soft-SAFT accurately reproduces transitions from type I to type V for the critical behavior of the methane/n-alkane and ethane/n-alkane homologous series. The equation also predicts in a quantitative manner the subcritical and critical behavior of the 1-propanol/n-hexane and ethanol/n-butane binary mixtures. Finally, we report speed of sounds of the mixture methane/n-butane and the heat capacities of the mixture 1-propanol/n-decane, in close agreement with experimental data. Results presented here encourage the development of molecular-based equations of state with a term taking into account the singular behavior in the near critical region, especially if one is searching for quantitative predictions in this region for further applications.