Summary: Enhancing P-xylene selectivity during m-xylene transformation using mildly pre-
coked ZSM-5 catalyst
Department of Chemical Engineering, King Fahd University of Petroleum &
Minerals, Dhahran 31261, Saudi Arabia.
In the present work, the transformation of m-xylene was studied over fresh and pre-coked H-
ZSM-5 catalyst in a riser simulator over the temperature range of 350-500o
were observed in both the activity and product selectivity pattern for the two forms of the catalyst.
While, the fresh catalyst generally gave higher m-xylene conversion, the pre-coked catalyst produced
higher Isomerization/Disproportionation (I/D) and Para/ Ortho xylene (P/O) ratios .For both forms of
the catalyst, m-xylene conversion was found to increase with both reaction temperature and reaction
time (0-15 s). A maximum conversion of 30.8% was achieved at 500o
C for a reaction time of 15 s
using the fresh catalyst. The corresponding value for the pre-coked catalyst was 24.6%. P/O and I/D
ratios as high as 2.5 and 10 respectively were observed with the pre-coked catalyst. It was also
observed that the P/O and I/D ratios decreased with increasing temperature for both catalyst and that
the difference between these ratios for the two catalysts is more pronounced between 400 and 450o