Summary: Xylenes Reactions and Diffusions in ZSM-5 Zeolite based Catalyst
Department of Chemical Engineering
King Fahd University of Petroleum & Minerals
Dhahran 31261, Saudi Arabia.
Xylenes transformations have been investigated over ZSM-5 zeolite in a riser simulator
that mimics closely the operation of commercial fluidized-bed reactors. P-xylene was
found to be more reactive than the other isomers followed by o-xylene and m-xylene was
found to be least reactive. The order of reactivity is consistent with the order of diffusivity.
At low temperature (400°C), isomerization and disproportionation yields for all xylenes
were found equal at constant conversion. However, as reaction temperature increases to
500°C, m-xylene reaction will be more selective to disproportionation than other xylene
isomers. The effectiveness factor for all xylene isomers reactions was found based on two
different diffusivities used from the literature. Generally m-xylene effectiveness factor was
estimated to be less than 0.1 indicating to a high diffusion obstacle inside ZSM-5 zeolite.
While o-xylene was found to have effectiveness factor in a range of 0.35-0.45, p-xylene
effectiveness factor was found to be close to unity indicating no diffusion limitation.
Keywords: Xylene transformation, Kinetic modeling, fluidized-bed reactor, ZSM-5, isomerization,
disproportionation, effectiveness factor, Thiele modulus.