The diffusion of benzene, during its adsorption on HZSM-5 zeolite under various conditions (powder or pellet samples with different lengths, mixture of the zeolite with a binder expressing), was studied by 129Xe NMR of adsorbed xenon. The two differential equations expressing the mass balance of the adsorbate in the macropores and in the micropores were solved by taking into account the boundary conditions of the adsorbate-adsorbent system. The solution gives the adsorbate concentration profiles in both the macropores and the micropores which were used to simulate 129Xe NMR spectra. Comparison of simulated and experimental spectra leads to the intracrystalline diffusion coefficient of benzene (3 x 10-14m2/s). For most of the samples, the time necessary to obtain the adsorption equilibrium was imposed by the intercrystalline diffusion, except with shallow bed or small pellets. The presence of a binder increases the influence of the macropores but an apparent adsorption equilibrium constant must be considered in order to take into account the adsorption of benzene by the binder.

Use of 129 Xe NMR Spectroscopy for the Study of Gaseous Reactant Diffusion in a Fixed Bed of Zeolite: Application to Benzene Diffusion in HZSM-5. P.N'Gokoli-Kekele, M.A.Springuel-Huet, J.L.Bonardet, J.Fraissard: Studies in Surface Science and Catalysis C, 2000, 130, 2939-44