Predicting transport diffusivities of binary mixtures in zeolites

We test the Maxwell–Stefan formulation for diffusion of multicomponent mixtures in zeolites and show that the mixture transport behaviour can be predicted on the basis of information of the pure component jump diffusivities at zero loading. The interaction between the diffusing, adsorbed, species is taken into account by introduction of interchange coefficients  Dij; these encapsulate the correlations in the molecular jumps. A logarithmic-interpolation formula is suggested for estimating these interchange coefficients from information on the pure component jump diffusivities. To verify the developed Maxwell–Stefan formulation we use published molecular dynamics simulation results for transport diffusivities of CH4 and CF4 in Faujasite at 300 K. The predictions of the Maxwell–Stefan model are in very good agreement with the MD simulation results.