Adsorption and mass transfer behavior of benzene on hierarchically structured Y by acid-base treatment

A series of hierarchical NaY zeolites with different pore size distribution were synthesized by sequential treatment with ethylenediaminetetraacetic acid and NaOH. The structural properties of the as-synthesized hierarchical NaY zeolites were characterized by X-ray diffraction, N₂ sorption, SEM and TEM. The adsorption and diffusion performances of benzene on NaY and hierarchical NaY zeolites were studied by frequency response (FR) and intelligent gravimetric analyser (IGA). It was found that the structure of NaY zeolite was remained by suitable acid and base treatment, but the connectivity in the pores was finely tailored. Mesoporous was introduced to reduce the molecular diffusion resistance in the pores, while the larger pore size and connectivity in the mesoporous was more beneficial to diffusion and accessibility of activity site. The adsorption of benzene on NaY was found to be the rate-controlling step. While, the limiting steps for the overall mass transfer processes in the hierarchical zeolites are the diffusion process in the length scale of micropore/mesopore and the mass transfer at the micropore-mesopore molecular exchange rather than the intracrystalline diffusion one in the micropores of the zeolite crystals.