Desorptive diffusion of benzene in H-ZSM-5 under catalytic conditions using dynamic sorption/desorption technique

Abstract

A dynamic sorption/desorption technique using a gas chromatograph for obtaining precise desorption kinetic data on zeolites in the short initial period of desorption (even in the first few seconds of desorption) at temperatures at which catalytic reactions occur has been described. The application of this method for studying desorptive diffusion of benzene (in presence of helium) in H-ZSM-5 (Si/Al = 22.0) zeolite at the temperatures at which catalytic processes occur has made it possible to estimate the diffusion coefficients from the desorption data using the simple √ t - law. This is not possible by any known gravimetric or volumetric method. The diffusion of benzene in the zeolite at 523-673 K is highly concentration dependent; it increases almost exponentially with the initial sorbate loading, even at lower intracrystalline sorbate concentrations. It is also highly temperature dependent; the activation energy for the diffusion was determined to be 64.4 kJ . mol^-1.