Modeling Xylene Reactions over ZSM-5 Zeolite in a Riser Simulator:  1,3- versus 1,2-Methyl Shift

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 is based on a triangular reaction path which assumes a direct interconversion between o- and p-xylene isomers (1,3-methyl shift), and a second scheme assumes the reactions 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 that of the 1,2-methyl shifts only. In addition, the riser simulator and the modeling procedures employed have shown to be very effective in investigating xylene isomerization kinetics.

Enhancing p -xylene selectivity during m -xylene transformation using mildly pre-coked ZSM-5 catalyst

“…The decrease of I/D with temperature indicates that disproportionation reaction is more sensitive to temperature than isomerization. This observation is in line with the fact that disproportionation requires a higher energy of activation as compared to isomerization reaction [31][32][33]. conversion, this ratio decreases from 7.5 to 1.8 by increasing the temperature from 400 to 500°C.…”

Xylene Isomerization in the Liquid Phase Using Large‐Pore Zeolites

“…Following this mechanism, the reaction scheme comprises interconversion between OX and MX and between MX and PX; this scheme is often called the linear scheme. However, a triangular scheme including direct conversion between OX and PX is also used to account for the faster diffusion of PX inside the pores [18,39]. Both schemes are presented in Fig.…”

Catalytic transformation of C7–C9 methyl benzenes over USY-based FCC zeolite catalyst

“…Higher conversion was observed with p-xylene reactant as compared to m-and o-xylene. Furthermore, a comprehensive kinetic model for xylenes isomerization and disproportionation has been reported by Iliyas and Al-Khattaf [17] and Al-Khattaf et al [18]. This kinetic modeling is based on the triangular reaction scheme and time-on-stream (T-O-S) deactivation function.…”