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A modified statistical associating fluid theory (SAFT) with variable range version is presented using the family of m-n Mie potentials. The use of this intermolecular potential for modeling repulsion-dispersion interactions between the monomer segments, together with a new method for optimizing the molecular parameters of the equation of state, is found to give a very accurate description of both vapor-liquid equilibria and compressed liquid bulk properties (volumetric and derivative properties) for long-chain n-alkanes. This new equation improves other SAFT-like equations of state which fail to describe derivative properties such as the isothermal compressibility and the speed of sound in the condensed liquid phase. Emphasis is placed on pointing out that the key for modeling the latter properties is the use of a variable repulsive term in the intermolecular potential. In the case of the n-alkanes series, a clear dependence of the characteristic molecular parameters on increasing chain length is obtained, demonstrating their sound physical meaning and the consistency of the new fitting procedure proposed. This systematic method for optimizing the model parameters includes data on the saturation line as well as densities and speed of sound data in the condensed liquid phase, and the results show undoubtedly that the model performance is enhanced and its range of applicability is now widened, keeping in any case a good balance between the accuracy of the different estimated properties.

A recently derived version of the statistical associating fluid theory (SAFT), denoted as SAFT-VR Mie, which incorporates the Mie potentials within the SAFT-VR framework to model the monomer segment interactions (Lafitte et al. J. Chem. Phys. 2006, 124, 024509), is used for the study of second-order derivative properties and phase equilibria of alcohols and 1-alcohol + n-alkane binary mixtures. For this purpose, a variable repulsive potential is used to induce nonconformal interactions in the reference nonbonded fluid. These features have a significant influence on the chain and association contributions through the contact value of the radial distribution function, and they enhance the SAFT theory performance in the application to associating substances. When dealing with pure alcohols and 1-alcohol + n-alkane binary mixtures, an accurate description of both phase equilibria and second-order derivatives is obtained with a single set of molecular parameters. To explore the predictive ability limit of the model we have particularly focused our attention on secondary derivative properties, which display singularities due to the formation of aggregates. With this approach, we have found that the model is able to reproduce accurately the complex behavior of the isobaric heat capacity of alcohols as, for instance, the maximum versus temperature in the compressed liquid region. Furthermore, in the case of 1-hexanol + n-hexane binary mixtures, the proposed equation is found to capture the association effects on the pressure and temperature dependence of the isobaric thermal expansivity. These two special features, which to our knowledge have never been described by a theoretical model, emphasize both the validity of the changes in the model proposed and the physical meaning of the molecular parameters obtained in this study.

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This paper presents new reference correlations for both the density and viscosity of squalane at high pressure. These correlations are based on critically evaluated experimental data taken from the literature. In the case of the density, the correlation, based on the Tait equation, is valid from 273 to 473 K at pressures to 200 MPa. At 0.1 MPa, it has an average absolute deviation of 0.03%, a bias of −0.01%, and an expanded uncertainty (at the 95% confidence level) of 0.06%. Over the whole range of pressures, the density correlation has an average absolute deviation of 0.05%, a bias of −0.004%, and an expanded uncertainty (at the 95% confidence level) of 0.18%. In the case of the viscosity, two correlations are presented, one a function of density and temperature, based on the Assael-Dymond model, and the other a function of temperature and pressure, based on a modified Vogel-Fulcher-Tammann equation. The former is slightly superior to the latter at high temperatures (above 410 K), whereas the reverse is true at low temperatures, where the viscosity is strongly temperature dependent. In the temperature range from 320 to 473 K at pressures to 200 MPa, the first correlation has an average absolute deviation of 1.41%, a bias of −0.09%, and an expanded uncertainty (at the 95% confidence level) of 3%. Below 320 K, deviations from the present scheme rise to a maximum of 20%. In the temperature range from 278 to 473 K at pressures to 200 MPa, the second viscosity correlation has an average absolute deviation of 1.7%, a bias of −0.04%, and an expanded uncertainty (at the 95% confidence level) of 4.75%.

Pressure-composition diagrams were measured at different temperatures ranging from 293.15 to 353.15 K for different perfluoroalkanes including linear (perfluoro-n-octane), cyclic (perfluorodecalin and perfluoromethylcyclohexane), and aromatic compounds (perfluorobenzene and perfluorotoluene), at pressures up to 100 bar. Measurements were performed using a high-pressure cell with a sapphire window that allows direct observation of the phase transition. The different molecular structures were chosen in order to check the influence of the nature of the solvent on the carbon dioxide solubility. The soft-statistical associating fluid theory (soft-SAFT) equation of state (EoS) was used to describe the phase behavior of the mixtures studied, searching for transferable parameters with predictive capability. Optimized values for the chain length, Lennard-Jones (LJ) diameter, and dispersive energy are provided for the different perfluoroalkanes and for carbon dioxide. The effect of the explicit inclusion of a quadrupole moment on carbon dioxide, perfluorobenzene, and perfluorotoluene was studied by adding a polar term to the original soft-SAFT EoS.