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Summary: Modeling Xylene Reactions over ZSM-5 Zeolite in a Riser Simulator: 1,3
versus 1,2-Methyl Shift
S. Al-Khattaf*, N. M. Tukur and A. Al-Amer
Department of Chemical Engineering
King Fahd University of Petroleum & Minerals
Dhahran 31261, Saudi Arabia.
Abstract
Xylene transformation reactions have been investigated over ZSM-5 zeolite in a riser
simulator that mimics closely the operation of commercial fluidized-bed reactors. Two
reaction schemes have been used to model the transformation reactions. The first based on
triangular reaction path which assumes a direct interconversion between o- and p-xylene
isomers (1,3-methyl shift), and a second scheme that assumes the reactions to proceed via
1,2-methyl shift only (o-xylene m-xylene p-xylene). The rate constants and
activation energies are obtained from simplified kinetic models based on the isomerization
of the pure xylene isomers using the "Time on Stream" decay model. The results provide
ample evidence to suggest that direct interconversion between o- and p-xylene isomers (a
1,3-methyl shift) occurs with the same rate as the conversion of m- to o-xylene (a 1,2-
methyl shift) over ZSM-5 zeolite catalyst, and the 1,3-methyl shift reaction path is a better
representation of the xylene isomerization mechanism in ZSM-5 zeolite than the 1,2-
methyl shifts only. In addition, the riser simulator and the modeling procedures employed
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