(429b) The Impact of Acid Site Concentration, Crystal Size and Reaction Temperature in the Production of C9+ Aromatics in ZSM-5 Catalyzed Xylene Isomerization

ZSM-5 is widely used as a commercial catalyst for xylene isomerization in the production of para-xylene for the ultimate synthesis of polyethylene terephthalate (PET).  Previous studies have shown that the crystal structure (ZSM-11 vs. ZSM-5 vs. mordenite) is very important in determining the selectivity of the disproportionation products in the zeolite catalyzed isomerization of mixed xylene feeds (i.e., those containing ethylbenzene and mixed xylenes).  In this study, we have examined the effects of ZSM-5 crystal size, crystal acid site concentration, and reaction temperature in the selective production of diethylbenzene and dimethylethylbenzene from a mixture of ethylbenzene (14 wt%) and mixed-xylenes (86 wt%).  As expected from diffusivity calculations, all three parameters have a significant effect on DEB and DMEB selectivity.  Reaction conditions used in he study were: 350 - 390oC, Hydrocarbon WHSV = 2 to 150 hr-1,  Hydrogen / Hydrocarbon ratios of 1-2 and a reaction pressure of 200 psig.  The findings are important in the design of shape selective zeolitic xylene isomerization catalysts.