Insights into adsorption of chlorobenzene in high silica MFI and FAU zeolites gained from chromatographic and diffractometric techniques

Abstract

In this work, the capability of two commercial high silica zeolites (HSZs), namely ZSM-5 and Y, for the removal of chlorobenzene (CB) from water was investigated by combining chromatographic and diffractometric techniques. The adsorption isotherms and kinetics of CB on ZSM-5 and Y zeolites were determined from batch tests. The adsorption kinetics were very fast; the time to reach equilibrium was less than 10 min. The equilibrium data of CB on the two HSZs showed dissimilarities that are particularly evident in the adsorption data concerning the low concentration range, where Y zeolite is characterized by low adsorption. On the contrary, at higher solution concentrations the adsorption capacity of Y is higher than that of ZSM-5. The crystalline structures of Y and ZSM-5 saturated with CB were investigated by X-ray diffraction (XRD) techniques. Rietveld refinement analyses of XRD data allowed for quantitative probing of the structural modifications of both zeolites after CB adsorption and provided insight into the preferred zeolite adsorption sites in both microporous materials. The refined framework–extraframework bond distances confirm that interactions between the selected organic contaminant and hydrophobic zeolites are mediated via co-adsorbed H2 O. The occurrence of H2 O–CB–framework oxygen oligomers explains variations in both the unit cell parameters and the shape of the channels, clearly confirming that water plays a very relevant role in controlling the diffusion and adsorption processes in hydrophobic zeolites.