A Two-Dimensional Model for Equilibrium Partitioning of a Fluid Mixture through a Microporous Semipermeable Crystalline Membrane. A Monte Carlo Study

Abstract

We have considered a simple two-dimensional model for a system consisting of a two-component mixture of hard discs on one side of a microporous slit-like semipermeable membrane and one-component fluid of discs on the other side. The particles of a slit-like membrane are fixed according to either (11) or (10) crystal symmetry. The distance between these particles is chosen such that only one fluid component can permeate the membrane. Osmotic equilibrium in the system is then established. The entire system is confined, for technical convenience, to a wide slit-like pore with the membrane in the center. The walls of the wide pore are distanced from the external surfaces of the membrane to provide the bulk region where the density profiles appear to be constant. Monte Carlo canonical simulation results are presented for the density distributions of the fluid particles in the entire wide pore. We have observed that partitioning of the smaller particles essentially depends on the concentration of the larger particles on one side of the membrane. The osmotic pressure is calculated from the contact values of the density profiles on the walls of a wide pore using the contact theorem. The pressure also has been obtained via Boublik's equation of state for a mixture of hard discs using the bulk densities of species obtained from simulations. The values for the partition coefficients on the osmotic pressure are discussed. Copyright 1998 Academic Press.