(222s) Predicting the Phase Behavior of Fluorinated Complex Systems Using the GC-SAFT-VR Equation of State

Predicting the Phase Behavior of Fluorinated Complex Systems Using the GC-SAFT-VR Equation of State

Jessica D. Haley¹, M. Carolina dos Ramos¹ and Clare McCabe^1,2

¹Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN

²Department of Chemistry, Vanderbilt University, Nashville, TN

Fluorinated molecules such as fluoroalkanes, perfluoroalkanes (PFA), perfluroalkylalkanes (PFAA), and fluorinated ethers possess interesting physical properties that lead to their use in a wide range of applications, for example as catalysts, solvents, and pharmaceuticals.  However, while there is an abundance of thermophysical data for alkanes, only limited studies have been performed that report the thermodynamic properties of the corresponding fluorinated species. With only limited data available, predictive approaches are needed to accurately and reliably determine the physical properties of these molecules. The statistical associating fluid theory (SAFT) [1] is a commonly used molecular-based equation of state that has been successfully applied to study a wide range of fluid systems.  In recent work, the GC-SAFT-VR equation was developed, which combines the SAFT equation for potentials of variable range (VR) [2] with a group contribution (GC) approach [3] that allows for the description of hetero-segmented chains. The equation has been shown to provide an excellent description of the phase behavior of pure associating and non-associating fluids and their mixtures, with a minimal reliance on fitting the model parameters to experimental data [3-5]. Parameters for key functional groups (such as CH₃, CH₂, CH, CH₂=CH, C=O, C₆H₅, ether and ester, OH, NH₂, CH=O, COOH) were obtained by fitting to experimental vapor pressure and saturated liquid density data for selected low molecular weight fluids and then used to predict the phase behavior of pure non-associating fluids and their mixtures without adjusting the group parameters to binary mixture data.  Here we report parameters for the CF₃,CF₂, CF, CH₂F, CHF₂, and CHF functional groups and their cross interactions.  Comparing the theoretical predictions with experimental data for pure perfluoroalkanes and PFAAs as well as mixtures of alkanes, perfluoroalkanes, fluorinated ethers and PFAAs test the transferability of the fluorinated parameters. The GC-SAFT-VR approach is found to accurately predict the phase behavior of the systems studied without adjusting the group parameters to binary mixture data.

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[2] Gil-Villegas, A.; Galindo, A.; Whitehead, P. J.; Mills, S. J.; Jackson, G. and Burgess, A. N. Journal Of Chemical Physics, 106, 4168-4186. (1997).

[3] Y. Peng, K. D. Goff, M. C. dos Ramos, C. McCabe, Fluid Phase Equilibria 277(2), 131- 144 (2009).

[4] Y. Peng, K. D. Goff, M. C. dos Ramos and C. McCabe, Industrial & Engineering Chemistry Research, 49 (3), 1378-1394 (2010).

[5] M. C. dos Ramos, J. D. Haley, J. R. Westwood, and C. McCabe, Fluid Phase Equilibria, 306, 97-111 (2011).