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American Chemical Society, Journal of Physical Chemistry B (Soft Condensed Matter and Biophysical Chemistry), 17(117), p. 5195-5205, 2013

DOI: 10.1021/jp401754r

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Transport Properties of Mixtures by the Soft-SAFT + Free-Volume Theory: Application to Mixtures ofn-Alkanes and Hydrofluorocarbons

Journal article published in 2013 by F. Llovell ORCID, R. M. Marcos, L. F. Vega
This paper is available in a repository.
This paper is available in a repository.

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Abstract

In a previous paper [Llovell et al., J. Phys. Chem. B (submitted)], the Free Volume Theory (FVT) was coupled with the soft-SAFT equation of state for the first time to extend the capabilities of the equation to the calculation of transport properties. The equation was tested with molecular simulations and applied to the family of n-alkanes. The capability of the soft-SAFT + FVT treatment is extended here to other chemical families and mixtures. The compositional rules of Wilke [Wilke, C. R. J. Chem. Phys. 1950, 18, 517-519] are used for the diluted term of the viscosity, while the dense term is evaluated using very simple mixing rules to calculate the viscosity parameters. The theory is then used to predict the vapor-liquid equilibrium and the viscosity of mixtures of non-associating and associating compounds. The approach is applied to determine the viscosity of a selected group of hydrofluorocarbons, in a similar manner as previously done for n-alkanes. The soft-SAFT molecular parameters are taken from a previous work, fitted to vapor-liquid equilibria experimental data. The application of FVT requires 3 additional parameters related to the viscosity of the pure fluid. Using a transferable approach, the α parameter is taken from the equivalent n-alkane, while the remaining two parameters B and Lv are fitted to viscosity data of the pure fluid at several isobars. The effect of these parameters is then investigated and compared to those obtained for n-alkanes, in order to better understand their effect on the calculations. Once the pure fluids are well characterized, the vapor-liquid equilibrium and the viscosity of non-associating and associating mixtures, including n-alkane + n-alkane, hydrofluorocarbon + hydrofluorocarbon and n-alkane + hydrofluorocarbon mixtures are calculated. One or two binary parameters are used to account for deviations in the vapor-liquid equilibrium diagram for non-ideal mixtures; these parameters are used in a transferable manner to predict the viscosity of the mixtures. Very good agreement with available experimental data is found in all cases, with an Absolute Average Deviation ranging between 1% and 5.5%, even when the system presents azeotropy, reinforcing the robustness of the approach.