Modeling of gas transport in a microporous solid using a slice selection procedure: Application to the diffusion of benzene in ZSM5

The analytical solution of the equations of gas diffusion in a heterogeneous zeolite bed is presented. The problem is handled by assuming that the bed consists of a large number of very thin layers of solid, perpendicular to the direction of propagation of the gas. Mass transfer by diffusion in such a material is determined by a system of differential equations with boundary and interface conditions. The results allow us to make the theoretical determination of the time dependence of the concentration profiles and the inter- and intracrystallite diffusion coefficients of a gas in each layer of the bed. A numerical application concerns the diffusion of benzene in a cylindrical bed of ZSM5 displaced vertically and rapidly, step-by-step, inside the NMR probe. Thus, the time dependence of the concentration of gas absorbed at the level of each slice and each crystallite can be obtained. These coupled investigations give a better understanding of the diffusion process in this multilayer material.