Influence of monovalent cations ion-exchange on zeolite ZSM-5 in separation of para-xylene from xylene mixture

The adsorption behavior of para-xylene on H/ZSM-5 and also monovalent cations ion-exchanged ZSM-5 zeolite was investigated in liquid phase adsorption and breakthrough system. Nitrogen adsorption, X-ray diffraction, transmission electron microscopy (TEM) and also in situ Fourier transform infrared (FTIR) spectroscopy were also performed to characterize the adsorbents and study the type of adsorbed species and their thermal stabilities. The adsorption experiments were carried out at temperature of 130–170 °C and the pressure between 6 and 8 bar. Ion-exchange process was accomplished using metal cations such as lithium, sodium and potassium. H/ZSM-5 was found more efficient than other ion-exchanged ZSM5 zeolites in separation of para-xylene from its isomers. The isotherms for each isomer of C8 aromatics and the desorbents possess the adsorption characteristics of Langmuir type. The selectivity factor of para-xylene and the saturation adsorption capacities of adsorbates were determined. A selectivity factor of para-xylene/meta-xylene, para-xylene/ortho-xylene and para-xylene/ethylbenzene on H/ZSM-5 adsorbent is determined as 24.987, 16.782 and 6.760, respectively. A series of desorbents matched with adsorbents like benzene, toluene, n-butylbenzene, p-diethylbenzene and p-dichlorobenzene were investigated as well. Influence of Si/Al ratio and the zeolite moisture content on selectivity of para-xylene to other C8 aromatic isomers were also studied.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Binder-free zeolitic adsorbent of ZSM-5 with Si/Al ratio >450 was synthesized. ► Influence of monovalent cations ion-exchange such as Li, Na and K for separation of para-xylene. ► Breakthrough method was used for para-xylene separation. ► Maximum selectivity of p-x/m-x, p-x/o-x and p-x/EB acquired 24.986, 16.782 and 6.760, respectively.