Prediction of Binary and Ternary Diagrams Using the Statistical Associating Fluid Theory (SAFT) Equation of State

Abstract

A modified statistical associating fluid theory (SAFT) equation of state has been applied to predict the phase equilibria behavior of binary and ternary mixtures. In order to study multicomponent systems, the equation is first applied to pure fluids. The SAFT equation is written in the same spirit as that presented by Huang and Radosz [Ind. Eng. Chem. Res. 1990, 29, 2284−2294], but with two important differences: the reference term is a Lennard−Jones fluid, accounting explicitly for dispersive and repulsive forces, and the equation is extended to heteronuclear chains. The molecular parameters of pure substances are obtained by fitting to the saturated liquid density and by equating the chemical potentials in both phases. Three molecular parameters are needed to obtain the thermodynamic properties of pure substances, namely, the segment size, dispersive energy, and chain length. Two additional parameters are needed to describe the associating molecules, the association energy, and volume. They are obtained by fitting to experimental saturated liquid density and by equating the chemical potentials in both phases over a wide range of temperatures. The molecular parameters are found to scale with the molecular weight for the alkanes. The binary parameters of the mixtures, ξ12 and η12 in the generalized Lorentz−Berthelot combining rules, are fitted to experimental data for the molar fractions on the liquid and vapor sides at a given temperature, in such a way that they do not depend on the composition and/or temperature. These binary parameters are used to predict the behavior of the mixture at different thermodynamic conditions. Ternary mixtures are predicted from the previous parameters without any further adjustment. The agreement between prediction and experimental results is excellent in all cases.

A density functional theory for vapor-liquid interfaces using the PCP-SAFT equation of state

“…A successful theoretical framework for nonspherical and associating fluids, the statistical associating fluid theory ͑SAFT͒ equation of state, has been developed by Chapman et al 7,8 based on Wertheim's thermodynamic perturbation theory of first order ͑TPT1͒. [9][10][11][12] Several modifications were suggested over the years, [13][14][15][16][17] with widespread applications. 18 The TPT1 of Wertheim is formulated in density functional form and has been applied to inhomogeneous associating fluids in several studies.…”

Modeling the vapor–liquid equilibrium and association of nitrogen dioxide/dinitrogen tetroxide and its mixtures with carbon dioxide

“…The approach we have taken here is to use the soft-SAFT equation of state [26,27], as it explicitly builds on the association and the quadrupolar interactions. Therefore, the equation is able to provide insights on the mixture behavior, as for instance, the degree of aggregation of associating molecules in each phase in equilibrium [28].…”

Excess Thermodynamics of Mixtures Involving Xenon and Light Linear Alkanes by Computer Simulation

“…As can be seen, simulation data and SAFT predictions deviate from experimental results in the same qualitative way for the systems xenon + propane and xenon + butane, the SAFT values being closer to the experiment than the simulation data. As a matter of fact, the model behind the SAFT approach, especially after the corrections for the effect of conformational changes upon mixing, 28 and the united atom TraPPE force field are models that are formally very close to each other, leading naturally to results in close agreement.…”