Self-Diffusion Studies of Binary Mixtures in NaX Zeolites Using Pulsed Field Gradient NMR and a Maxwell−Stefan Model

Intracrystalline self-diffusion coefficients were measured by pulsed field gradient (PFG) NMR for single components and binary mixtures of CF(4) and various hydrocarbons in large-crystal NaX zeolites. A short-time diffusion model was used to obtain the unrestricted intracrystalline self-diffusivities by extrapolating to zero diffusion time, when no molecules can leave the crystal during the measurement. The results were used to test a theoretical model from Skoulidas, Sholl, and Krishna for predicting diffusion coefficients of mixtures in zeolites from single-component data. The predicted binary self-diffusivities are consistent with those directly measured in PFG NMR mixture experiments, thus providing an experimental validation of the model.