Effects of disordered porous media on the vapour-liquid phase equilibrium in ionic fluids: application of the association concept

We study the vapour-liquid phase diagram of a model ionic fluid, the so-called restricted primitive model, confined in a disordered porous medium formed by the matrix of hard sphere (HS) or overlapping hard sphere (OHS) particles. Our theoretical approach is based on a combination of the scaled-particle theory and the associative mean-spherical approximation incorporating the concept of ion association. It is shown that the HS and OHS matrices have a similar effect on the phase diagrams of an ionic fluid: the critical temperature T-c and the critical density pc lower with a decrease of the matrix porosity and the coexistence region gets narrower. However, quantitatively both Tc and pc are higher in the case of OHS matrix than in the HS matrix. It is also observed that the presence of disordered porous media leads to a decrease of the degree of dissociation in comparison with the bulk case. (C) 2016 Elsevier B.V. All rights reserved.