Application of the GC-Saft-Vr Equation to Predict Fluid Phase Behavior

Joel R. Westwood, M. Carolina Dos Ramos, and Clare McCabe. Department of Chemical and Biomolecular Engineering, Vanderbilt University, Box 6525 Station B, Nashville, TN 37235

SAFT-VR is a widely used molecular-based equation of state that has been successfully applied to study a wide range of fluid systems.  It provides a framework in which the effects of molecular shape and interactions on the thermodynamics and phase behavior of fluids can be separated and quantified.  In the original SAFT-VR approach, molecules were modeled as chains composed of identical segments [1].  Hence the heterogeneity of molecules was described implicitly through effective parameters.  In a recent work, the GC-SAFT-VR [2] approach was developed to account explicitly for the effects of molecular structure and composition. This approach provides an excellent description of phase behavior of pure non-associating fluids and mixtures, where the parameters for different key functional groups (CH3, CH2, CH, CH2=CH, C=O, C6H5, CH3O and CH2O esters groups) were obtained. In this work, we apply the CG-SAFT-VR approach to study the phase behavior of associating systems such as alcohols, amines, aldehydes, and acids, and their mixtures. New functional groups (OH, NH2, CH=O, COOH) are defined and their molecular parameters are characterized by fitting to experimental vapor pressure and saturated liquid density data for selected small molecules of different chemical families. Transferability of the parameters is tested by comparing the theoretical predictions with experimental data for pure fluids and binary mixtures not included in the fitting process.

1.    Gil-Villegas, A., et al., Statistical associating fluid theory for chain molecules with attractive potentials of variable range. Journal Of Chemical Physics, 1997. 106, 4168-4186.

2. Peng, Y.; Goff, K. D.; dos Ramos, M. C.; McCabe, C. Submitted to Fluid Phase Equilibria 2008