The Effects of Steam Treatment, Impregnation with P, Mg and Ion Exchange on Diffusion in HZSM-5 Zeolite

Abstract

The effects of steam treatment, impregnation with P, Mg and monovalent cation exchange on the diffusion properties of HZSM-5 zeolite have been investigated by the measurement of adsorption kinetics. The diffusion behaviors of cyclohexane, benzene and p-xylene in HZSK-5 are different. The order of diffusion coefficients D is benzene ≥ p-xylene > cyclohexane The D value for cyclohexane is approximately invariable with the amount adsorbed, whereas the D values for benzene and p-xylene are increased with increasing amount adsorbed. The steam treatment results in the increases of the D values for cyclohexane, benzene and p-xylene in HZSM-5, while the diffusion activation energy E and pre-exponential factor De are both decreased. The more severe the steam treatment is, the stronger this effect is. The impregnation with P, Mg and monovalent cation exchange may also lead to the decrease of E and D. for cyclohexane. It has been shown that the polarity interaction between diffusing species and surface of HZSM-5 plays an important role in the diffusion process. The explanation of experimental data was given.