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Apparent molal volumes of a number of n-perfluoroalkanes (PA) and perfluoroalkylalkanes (PFAA) in n-octane have been measured at 298.15 K as a function of composition. The corresponding partial molal volumes at infinite dilution have been obtained by extrapolating the apparent molal volumes to zero composition. The results were interpreted using the hetero-SAFT-VR equation of state. The perfluoroalkylalkanes were modeled as heterosegmented diblock chains, and the cross interactions, both intra-and intermolecular, were characterized using parameters developed in earlier studies of alkane + perfluoroalkane mixtures. Through this strategy, a fully predictive approach has been developed that is able to accurately predict the volumetric behavior of the solutions of perfluoroalkylalkanes studied, without fitting to any experimental data for perfluoroalkylalkanes.

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In this work, the molecular based Variable Range Statistical Associating Fluid Theory (SAFT-VR) has been used to estimate the global phase equilibria diagram of the ternary mixture water + carbon dioxide + methane, over a wide pressure and temperature range. An accurate determination of the phase equilibria of this mixture is relevant in Petrophysics, as, for instance, in enhanced natural gas recovery from low permeability reservoirs (the so-called tight gas reservoirs), or in geology, as it is the basic composition of many geological fluids. A previous study on the phase behavior of the binary mixtures involved is presented, using in a transferable manner the characteristic molecular parameters for the three molecules involved. The ternary mixture presents a very rich and complex phase behavior, with a wide region of the thermodynamic space of phases (at higher pressures) presenting a large gap of ternary liquid-liquid equilibria, that upon descending pressures leads to the transition to a three-phase liquid-liquid-vapor equilibria region, and both regions are separated by a continuous critical end point line. The ability of the theory to describe this complex multicomponent mixture phase transition with a reduced and physically sound set of characteristic parameters must be underlined.

The high-pressure phase diagram and other thermodynamic properties of the water + carbon dioxide binary mixture are examined using the SAFT-VR approach. The carbon dioxide molecule is modeled as two spherical segments tangentially bonded. The water molecule is modeled as a spherical segment with four associating sites to represent the hydrogen bonding. Dispersive interactions are modeled using the square-well intermolecular potential. The polar and quadrupolar interactions present in water and carbon dioxide are treated in an effective way via square-well potentials of variable range. The optimized intermolecular parameters are taken from the works of Galindo and Blas (Fluid Phase Equilib. 2002, 194 − 197, 502; J. Phys. Chem. B 2002, 106, 4503) and Clark et al. (Mol. Phys. 2006, 22 − 24, 3561) for carbon dioxide and water, respectively. The phase diagram of the mixture exhibits a number of interesting features:  type-III phase behavior according to the classification of Scott and Konynenburg, three-phase behavior at low temperatures with its corresponding upper critical end point, a gas−liquid critical line at high temperatures and pressures that continuously changes from gas−liquid to liquid−liquid as the pressure is increased and gas−gas immiscibility of second kind. Only one unlike interaction parameter is fitted to give the best possible representation of the temperature minimum of the gas−liquid critical line of the mixture. This unlike parameter is then used in a transferable manner to study the complete pressure−temperature−composition phase diagram. The phase diagram calculated with SAFT-VR is in excellent agreement with the experimental data taken from the literature in a wide range of thermodynamic conditions. The theory is also able to predict a good qualitative description of the excess molar volume and enthalpy of the mixture as well as the most important features of the Henry's constants at different temperatures.

We extend the SAFT‐VR+DE equation of state to describe 19 aqueous electrolyte solutions with both a fully dissociated and a partially dissociated model. The approach is found to predict thermodynamic properties such as the osmotic coefficient, water activity coefficient, and solution density, across different salt concentrations at room temperature and pressure in good agreement with experiment using only one or two fitted parameters. At higher temperatures and pressures, without any additional fitting, the theory is found to be in qualitative agreement with experimental mean ionic activities and osmotic coefficients. The behavior of the dielectric constant as a function of salt concentration is also reported for the first time using a statistical associating fluid theory (SAFT)‐based equation of state. At high salt concentrations, the stronger electrostatic interactions between the ionic species due to the dielectric decrement, is captured through the inclusion of ion association. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3053–3072, 2015

The high-pressure phase diagram and excess thermodynamic properties of the binary mixture of carbon dioxide and water are examined using the statistical associating fluid theory for potentials of variable range (SAFT-VR). The carbon dioxide molecule is modelled with two tangentially bonded spherical segments, while the water molecule is modelled as spherical with four associating sites to represent the hydrogen bonding. Dispersion interactions are modelled using square-well potentials. The optimised intermolecular parameters are taken from the works of Galindo and Blas [

The recently developed heteronuclear group contribution SAFT-VR equation (GC-SAFT-VR) [ Peng Peng Fluid Phase Equilib.2009227131144] enables the predictive study of the thermodynamic properties of fluids and their mixtures by using a molecular-based model in which the molecules are described by heterosegmented chains in which each type of segment represents a functional group present in the molecule. Given the success of the GC-SAFT-VR approach in predicting the fluid phase equilibria of mixtures without fitting to any mixture data, and the known difficulties in determining equation-of-state parameters for polymers because of the lack of coexistance data, in this work, we extend the GC-SAFT-VR equation to study the phase equilibria of small molecules in polymer systems. The results demonstrate the ability of the GC-SAFT-VR equation of state to predict the vapor−liquid and liquid−liquid equilibria of polymer solutions and accurately capture the effects of polymer molecular weight and molecular topology on phase behavior.