Predicting the adsorption of n-perfluorohexane in BAM-P109 standard activated carbon by molecular simulation using SAFT-γ Mie coarse-grained force fields

Abstract

This work is framed within the Eighth Industrial Fluid Properties Simulation Challenge, with the aim of assessing the capability of molecular simulation methods and force fields to accurately predict adsorption in porous media for systems of relevant practical interest. The current challenge focuses on predicting adsorption isotherms of n-perfluorohexane in the certified reference material BAM-P109 standard activated carbon. A temperature of T ¼ 273 K and pressures of p=p 0 ¼ 0:1, 0.3, and 0.6 relative to the bulk saturation pressure p 0 (as predicted by the model) are the conditions selected in this challenge. In our methodology we use coarse-grained intermolecular models and a top-down technique where an accurate equation of state is used to link the experimental macroscopic properties of a fluid to the force-field parameters. The stateof-the-art version of the statistical associating fluid theory (SAFT) for potentials of variable range as reformulated in the Mie group contribution incarnation (SAFT-Mie) is employed here. The parameters of the SAFT-Mie force field are estimated directly from the vapour pressure and saturated liquid density data of the pure fluids using the equation of state, and further validated by molecular dynamic simulations. The coarse-grained intermolecular potential models are then used to obtain the adsorption isotherm kernels for argon, carbon dioxide, and n-perfluorohexane in graphite slit pores of various widths using Grand Canonical Monte Carlo simulations. A unique and fluid-independent pore size distribution curve with total micropore volume of 0.5802 cm 3 /g is proposed for the BAM-P109. The pore size distribution is obtained by applying a non-linear regression procedure over the adsorption integral equation to minimise the quadratic error between the available experimental adsorption isotherms for argon and carbon dioxide and

Surrogate Models for Studying the Wettability of Nanoscale Natural Rough Surfaces Using Molecular Dynamics

“…This connection facilitates the direct estimation of effective force field parameters by fitting the resulting equation of state to a wide a range of thermophysical properties without the need to perform extensive simulations. To date, the SAFT force field has been used successfully in the prediction of the behavior of crude oils in bulk [81,82] and confined reservoirs [83], high pressure oil/water interfacial tensions [84], adsorption [85], and the wetting behavior of surfactant solutions on surfaces [56,86], amongst others.…”

SAFT-γ force field for the simulation of molecular fluids: 8. Hetero-segmented coarse-grained models of perfluoroalkylalkanes assessed with new vapour–liquid interfacial tension data

“…In addition to the higher resolution (atomistic and united-atom) force fields mentioned earlier, CG models have also been developed for n-alkanes [60][61][62][63] and for perfluoro-n-alkanes [64,65]; we are not, however, aware of an integrated CG model which can deal quantitatively with the subtleties of having the two chemical moieties fused on the PFAA molecule. For this purpose, the SAFT-γ Mie force fields developed in our current study are assessed by comparing the simulated and experimental surface tension data of PFAAs which are not used to parameterize the model; the comparison thus serves as a validation of the molecular models.…”

A multiscale method for simulating fluid interfaces covered with large molecules such as asphaltenes

“…However, if one recognizes the conformal nature of the underlying Mie potential, one can formulate the equation of state in terms of a corresponding-states model and can express the properties of any nonassociating fluid in terms of a finite set of defining properties: a critical temperature, the acentric factor and a well-defined density. This approach [45] greatly simplifies the parameter estimation without detriment to the robustness of the methodology, as exemplified by the predictions of adsorption [46], transport and interfacial properties [41] which are not part of the original fit, and the description of complex molecules such as surfactants [47,48], resins and asphaltenes [49]. This approach is used to construct the force field parameters used in this work.…”