The theoretical modelling of confined fluids, and in particular adsorption, where a fluid is in equilibrium with a porous matrix has lagged behind that of the more common bulk fluid description, possibly due to the complexity of the heterogeneity involved and the lack of a clear link to the molecular-level phenomena.
In order to develop a molecular theory of adsorption, ideally an existing equation of state (EoS) should be used as a reference to represent both the bulk phase properties and the main effects of confinement. A recent proposal [1] presents an extension of the van der Waals EoS to model confined fluids in a cylindrical pore. The model has proved to successful in describing the adsorptions of pure fluids in several solids, and the prediction of the five types of isotherms in the IUPAC classification [2]. However, the parameters for the Travalloni model must be regressed from experimental data limiting the approach to a correlation. Furthermore, there is a divorce between the molecular model employed to describe the theory and the results of molecular simulations employing the same force field.
The present work displays an extension of the former; aiming at the description of complex fluids by using the statistical associating fluid theory (in its SAFT-g-Mie version) [3] which has been successfully used to calculate the phase behaviour of complex fluid systems. Grand Canonical Monte Carlo (GCMC) simulations of fluids based on the potential adsorbed into a cylindrical attractive pore are employed in this work as pseudo-experimental data to provide the benchmark data to interpret the theory in terms of the underlying molecular model.
A unique target of this work is the ability to use the same molecular parameters deployed in the theory to perform molecular simulations, tapping into the efforts in developing force fields for coarse grained models of fluids represented with the Mie potential [4]
[1] L. Travalloni, M. Castier, F. W. Tavares, S. I. Sandler. Chem. Eng. Science 65, 3088 (2010).
[2] S. Brunauer, L. S. Deming, W. E. Deming, E. Teller. J. Am. Chem. Soc. 62, 1723 (1940).
[3] T. Lafitte, A. Apostolakou, C. Avendaño, A. Galindo, C. S. Adjiman, E. A. Müller, G. Jackson. J. Chem. Phys. 139, 154504 (2013).
[4] Å. Ervik, A. Mejía, E. A. Müller,. J. Chem. Inf. Model., 56, 1609−1614 (2016).
