Molecular simulation of the vapor-liquid phase behavior of Lennard-Jones mixtures in porous solids

We present vapor-liquid phase coexistence curves for binary fluid mixtures in a disordered porous solid. The porous material is modeled as a collection of randomly dispersed hard spheres. A variant of the Monte Carlo Gibbs ensemble method [J. K. Brennan and W. Dong, J. Chem. Phys. 116, 8948 (2002)] is used to simulate Lennard-Jones fluid mixtures at several porosities: 0.9, 0.95, and 0.975. Effects based on the size and the energetics of the mixture components are studied. Pressure-composition and pressure-density phase diagrams at reduced temperatures of 0.75 and 1.0 are reported. Compared to the bulk fluid behavior, dramatic shifts in the phase envelope were found for even highly porous structures. Both the Lennard-Jones size and energy mixture parameters were found to strongly influence the resulting shape of the phase envelope.