Abstract
The catalytic transformation of C 8 aromatic hydrocarbons (present in a naphtha reformate) over H-ZSM-5, NiH-ZSM-5, PtH-ZSM-5, and PtNiH-ZSM-5 are reported. The influence of the SiO 2 Al 2O 3 ratio in the zeolite, the temperature of calcination and the reaction parameters of temperature, contact time, pressure, and space velocity have been investigated. The incorporation of nickel and platinum enhances the efficiency of the catalysts in producing para-xylene (by isomerization of the meta isomer and hydroisomerization of ethylbenzene). Simultaneously, these metals suppress the disproportionation and loss of xylenes to toluene and trimethylbenzenes. To elucidate the acidity of the active sites involved in the various reactions of the xylene isomerization process, selective poisoning with NH 3 was carried out. From the results it is concluded that relatively strong acid sites are needed for the disproportionation of xylenes and ethylbenzene, whereas relatively weak acid sites are sufficient for xylene isomerization. By selective suppression of the strong acid sites responsible for xylene disproportionation, it is feasible to enhance the net para-xylene production.
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