Application of a renormalization-group treatment to the statistical associating fluid theory for potentials of variable range (SAFT-VR)

Forte, Esther; Llovell, Fèlix; Vega, Lourdes F.; Trusler, J. P. Martin; Galindo, Amparo

doi:10.1063/1.3570614

Cited by 44 publications

(53 citation statements)

References 109 publications

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“…It is therefore not surprising to find a small overshoot in the critical temperature for strong associating fluids such as water. A proper renormalisation-group treatment would have to be employed in this regard (e.g., as implemented in a number of studies within the SAFT formalism [175][176][177][178]), but this is beyond the scope of our current work.…”

Section: Watermentioning

confidence: 99%

The A in SAFT: developing the contribution of association to the Helmholtz free energy within a Wertheim TPT1 treatment of generic Mie fluids

et al. 2015

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(2015) The A in SAFT: developing the contribution of association to the Helmholtz free energy within a Wertheim TPT1 treatment of generic Mie fluids, Molecular Physics, 113:9-10, 948-984, DOI: 10.1080/00268976.2015 An accurate representation of molecular association is a vital ingredient of advanced equations of state (EOSs), providing a description of thermodynamic properties of complex fluids where hydrogen bonding plays an important role. The combination of the first-order thermodynamic perturbation theory (TPT1) of Wertheim for associating systems with an accurate description of the structural and thermodynamic properties of the monomer fluid forms the basis of the statistical associating fluid theory (SAFT) family of EOSs. The contribution of association to the free energy in SAFT and related EOSs is very sensitive to the nature of intermolecular potential used to describe the monomers and, crucially, to the accuracy of the representation of the thermodynamic and structural properties. Here we develop an accurate description of the association contribution for use within the recently developed SAFT-VR Mie framework for chain molecules formed from segments interacting through a Mie potential [T. Lafitte, A. Apostolakou, C. Avendaño, A, Galindo, C. S. Adjiman, E. A. Müller, and G. Jackson, J. Chem. Phys. 139, 154504 (2013)]. As the Mie interaction represents a soft-core potential model, a method similar to that adopted for the Lennard-Jones potential [E. A. Müller and K. E. Gubbins, Ind. Eng. Chem. Res. 34, 3662 (1995)] is employed to describe the association contribution to the Helmholtz free energy. The radial distribution function (RDF) of the Mie fluid (which is required for the evaluation of the integral at the heart of the association term) is determined for a broad range of thermodynamic conditions (temperatures and densities) using the reference hyper-netted chain (RHNC) integral-equation theory. The numerical data for the association kernel of Mie fluids with different association geometries are then correlated for a range of thermodynamic states to obtain a general expression for the association contribution which can be applied for varying values of the Mie repulsive exponent. The resulting SAFT-VR Mie EOS allows for a much improved description of the vapour-liquid equilibria and single-phase properties of associating fluids such as water, methanol, ammonia, hydrogen sulphide, and their mixtures. A comparison is also made between the theoretical predictions of the degree of association for water and the extent of hydrogen bonding obtained from molecular simulations of the SPC/E and TIP4P/2005 atomistic models.

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Section: Watermentioning

confidence: 99%

The A in SAFT: developing the contribution of association to the Helmholtz free energy within a Wertheim TPT1 treatment of generic Mie fluids

et al. 2015

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“…Especially noteworthy is the greatly reduced “overshoot” of the critical point; previously, such good performance simultaneously for both the subcritical and near‐critical regions using an analytical EOS had been possible only with the incorporation of a cross‐over treatment, such as those of Refs. .…”

Section: Discussionmentioning

confidence: 99%

Developing intermolecular‐potential models for use with the SAFT‐VRMie equation of state

et al. 2015

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A major advance in the statistical associating fluid theory (SAFT) for potentials of variable range (SAFT-VR) has recently been made with the incorporation of the Mie (generalized Lennard-Jones [LJ]) interaction between the segments comprising the molecules in the fluid (Lafitte et al. J. Chem. Phys. 2013;139:154504). The Mie potential offers greater versatility in allowing one to describe the softness/hardness of the repulsive interactions and the range of the attractions, which govern fine details of the fluid-phase equilibria and thermodynamic derivative properties of the system. In our current work, the SAFT-VR Mie equation of state is employed to develop models for a number of prototypical fluids, including some of direct relevance to the oil and gas industry: methane, carbon dioxide and other light gases, alkanes, alkyl benzenes, and perfluorinated compounds. A complication with the use of more-generic force fields such as the Mie potential is the additional number of parameters that have to be considered to specify the interactions between the model molecules, leading to a degree of degeneracy in the parameter space. A formal methodology to isolate intermolecular-potential models and assess the adequacy of the description of the thermodynamic properties in terms of the complex parameter space is developed. Fluid-phase equilibrium properties (the vapor pressure and saturated-liquid density) are chosen as the target properties in the refinement of the force fields; the predictive capability for other properties such as the enthalpy of vaporization, single-phase density, speed of sound, isobaric heat capacity, and Joule-Thomson coefficient, is appraised. It is found that an overall improvement of the representations of the thermophysical properties of the fluids is obtained using the more-generic Mie form of interaction; in all but the simplest of fluids, one finds that the LJ interaction is not the most appropriate.

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“…146 This does not mean that the resulting intermolecular potential will lead to a poor estimate of the critical point by simulation, as we will show later in the paper. We obtain the following optimal molecular parameters for our single-site SAFT-γ Mie force field for CO 2 : σ = 3.741…”

Section: B Coarse-graining Co 2 As a Single-site Modelmentioning

confidence: 97%

SAFT-γ Force Field for the Simulation of Molecular Fluids. 1. A Single-Site Coarse Grained Model of Carbon Dioxide

et al. 2011

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An application of the "top-down" concept for the development of accurate coarse-grained intermolecular potentials of complex fluids is presented. With the more common "bottomup" procedure, coarse-grained models are constructed from a suitable simplification of a fulldetailed atomistic representation, and minor adjustments to the intermolecular parameters are made by comparison with limited experimental data where necessary. By contrast in the top-down approach, a molecular-based equation of state is used to obtain an effective coarsegrained intermolecular potential that reproduces the macroscopic experimental thermophysical properties over a wide range of conditions. These coarse-grained intermolecular potentials can then be used in a conventional molecular simulation to obtain properties (such as structure or dynamics) that are not directly accessible from the equation of state or at extreme conditions where the theory is expected to fail. In order to demonstrate our procedure, a coarse-

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Application of a renormalization-group treatment to the statistical associating fluid theory for potentials of variable range (SAFT-VR)

Cited by 44 publications

References 109 publications

The A in SAFT: developing the contribution of association to the Helmholtz free energy within a Wertheim TPT1 treatment of generic Mie fluids

The A in SAFT: developing the contribution of association to the Helmholtz free energy within a Wertheim TPT1 treatment of generic Mie fluids

Developing intermolecular‐potential models for use with the SAFT‐VRMie equation of state

SAFT-γ Force Field for the Simulation of Molecular Fluids. 1. A Single-Site Coarse Grained Model of Carbon Dioxide

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