Phase behavior of dipolar associating fluids from the SAFT-VR+D equation of state

Abstract

The statistical associating fluid theory for potentials of variable range plus dipole (SAFT-VR+D) is extended to study associating dipolar fluids. In the SAFT-VR+D approach dipolar interactions are taken into account through the use of the generalized mean spherical approximation to describe a reference fluid of dipolar square-well segments. This enables the effect of the dipolar interactions on the thermodynamics and structure of fluids to be explicitly described. Predictions for the thermodynamic properties and phase behavior of dipolar associating square-well monomers with one, two, and four association sites are considered and compared with new isothermal-isobaric and Gibbs ensemble Monte Carlo simulation data. The results show that the SAFT-VR+D equation provides a good description of the phase behavior of dipolar associating fluids. Additionally we have applied the new theoretical approach to study the vapor pressure and saturated liquid density of water.

Predicting the thermodynamic properties and dielectric behavior of electrolyte solutions using the SAFT‐VR+DE equation of state

“…The AAD over the whole phase diagram is 1.49% for the vapor pressures and 2.43% for the saturated liquid densities using the SAFT‐VR+D equation of state. We note that the %AADs are comparable to those obtained in our previous work (%AADP 0.92 and %AAD ρ 2.87), in which a dipole moment of 1.8 D was used, while giving us a more accurate description of the saturated liquid densities that are essential for liquid phase characterization. As expected, and can be seen from Figure , SAFT‐VR+D overpredicts the critical region of the phase diagram and does not capture the experimentally observed density maximum of water at lower temperature as a temperature‐dependent segment diameter is not used …”

“…Water molecules are modeled as SW dispersive hard spheres with a dipole moment embedded in the center of the sphere and four short‐range attractive SW sites to describe association interactions that mimic hydrogen bonding, as in earlier work . Although it is well known that the value of the water dipole moment varies significantly from the gas to the liquid phase and the gas‐phase dipole moment for water is well characterized, the liquid phase moment is not as well defined.…”

Relative Permittivity of Stockmayer-Type Model Fluids from MD Simulations and COFFEE

“…The aforementioned drawbacks and issues can be alleviated by using “nonprimitive” SAFT-type models. , Here, the relative permittivity is obtained directly from the molecular dipole moments. However, still to date, few nonprimitive models exist, most notably the EOS developed in McCabe’s group − and the efforts by the group of Groß − to develop a perturbation theory based on model mixtures for dipolar hard spheres and hard sphere ions. The results of these theories are quite impressive; however, it is, for example, unclear how to handle the question of finding parameters for models that have both an H-bonding term and an explicit dipolar term, since both are highly linked. , …”

Relative Permittivity of Dipolar Model Fluids from Molecular Simulation and from the Co-Oriented Fluid Functional Equation for Electrostatic Interactions

“…A notable exception is the EOS developed in McCabe's group. In a series of articles [14][15][16][17][18] from that group, an equation of state is combined with results from integral equation theory to couple dipole interactions and electric permittivity. The integral equation theory results are based on an empirical modification of the dipolar mean spherical approximation (dMSA) by Wertheim 19 .…”