Predicting membrane flux of CH4 and CF4 mixtures in faujasite from molecular simulations

The Fickian transport diffusivities of binary, mixtures of methane and CF4 in the zeolite faujasite were investigated as a function of composition and loading. Using equilibrium molecular dynamics simulations, transport diffu sivities of the mixtures were calculated from linear response theory. At lo g, loadings, the diffusive cross terms are an order of magnitude smaller th an the diffusive main terms, but at higher loadings they are oil the same o rder of magnitude. The main term diffusivities are weak functions of concen tration. The transport diffusivities were fitted as a function of adsorbate concentrations and used in the Fickian flux equations to predict codiffusi on, counterdiffusion, and osmotic diffusion through a perfectly, crystallin e faujasite membrane. The osmotic and counterdiffusion cases show that it i s critical to include both the cross term and main term diffusivities to pr edict the correct behavior The permeances of methane and CF4 through the fa ujasite membrane are reported.