Selective adsorption to benzene-cyclohexane gas-phase mixture over ion exchange Y zeolites

Abstract

The selective adsorption to benzene-cyclohexane gas-phase mixture was performed over several parent zeolites (NaY, NaZSM-5, and NaMOR) and over ion exchanged Y zeolites. NaY showed a greatly higher adsorption selectivity & capacity to benzene than NaZSM-5 and NaMOR, primarily attributed to the high density of surface Na+ sites, the high specific surface area, and the better pore diffusion ability of the former. Moreover, a reasonable Zn2+ ion exchange treatment not only significantly enhanced the adsorption selectivity to benzene but also improved the benzene adsorption capacity of Y zeolite. This may be due to the uneven surface charge on the surface of Zn2+ exchanged Y zeolite, where the electrostatic attraction effect between surface Zn2+ and benzene molecules may powerfully promote the preferential adsorption to benzene which even replaces surface cyclohexane molecules. While the exchanged Y zeolites with Cu2+, Cr3+ or Fe3+ displayed the declined performance for selective adsorption. Especially, severe pore blockage occurred after Cr3+ or Fe3+ exchange. Furthermore, based on the optimization on the aspects of the solution concentration and the exchange time during Zn2+ ion exchange treatment, the selectivity to benzene of 93% & 98% and the benzene adsorption capacity of >3.0 mmol/g were obtained over 0.2-Zn-Y (2 h) and 0.1-Zn-Y (4 h) samples, respectively.