where an equilibrium mixture of 23% para-, 51% meta-, and 26% ortho- xylene is produced. An
oxide-modified ZSM-5 catalyst is commonly used to improve the selectivity towards paraxylene.
Further methods for improving the selectivity of para-xylene include operating at higher
temperatures (1022 – 1112°F) which promotes catalyst coking. As the catalyst becomes coked,
active sites on the catalyst are blocked leaving a smaller amount of sites for para-xylene to
become isomerized. Although the selectivity to para-xylene is improved, a decrease in the
available active sites on the catalyst causes a decrease in the overall conversion of toluene. This
indicates a clear trade-off between para-xylene selectivity and toluene conversion.