Transformation of Toluene and 1,2,4-Trimethylbenzene over ZSM-5 and Mordenite Catalysts: A Comprehensive Kinetic Model with Reversibility

Abstract

The catalytic transformations of toluene, 1,2,4-trimethylbenzene (TMB), and an equimolar mixture of the two compounds were investigated over H-mordenite and H-ZSM-5 catalysts. A series of experiments were conducted in a riser simulator over a temperature range of 300−400 °C and reaction times of 5−20 s. The influence of reaction conditions on variation of 1,2,4-TMB conversion, toluene conversion, para- to ortho-xylene ratio, xylenes to TMB isomers ratio, 1,3,5-TMB to 1,2,3-TMB ratio, and xylenes to benzene ratio were discussed. The study also includes the development of comprehensive kinetic models for isomerization, disproportionation, and transalkylation reactions of 1,2,4-TMB and toluene. The models account for reversibility of the isomerization reaction based on values of temperature dependent thermodynamic equilibrium constants. Catalysts deactivation was modeled using an activity decay function based on time-on-stream (TOS). The developed models gave a good match with experimental data based on a statistically significant estimate of the kinetic parameters in the models. For the 1,2,4-TMB reaction and transalkylation of 1,2,4-TMB with toluene, the apparent activation energy over H-ZSM-5 was higher than that over H-mordenite (i.e., E app,(H-ZSM-5) > E app,(H-Mordenite)) while the reverse order was observed for the toluene reaction over the two catalysts. A simple correlation that gives accurate representation of the temperature dependency of thermodynamic equilibrium compositions of TMB isomers was also reported.

Xylene Isomerization in the Liquid Phase Using Large‐Pore Zeolites

“…Xylene isomerization, disproportionation, and dealkylation are catalyzed by Brønsted acid sites [6][7][8]. Disproportionation needs higher concentrations of acid sites [9] and the strength of these sites follows the trend: isomerization < dealkylation < disproportionation [10,11]. The acidity of zeolites is determined by their Si/Al ratio, with the total number of acid sites decreasing with increasing Si/Al ratio due to the lower amount of Al [2,5,12,13].…”

Chemical Imaging of the Binder‐Dependent Coke Formation in Zeolite‐Based Catalyst Bodies During the Transalkylation of Aromatics

“…[13][14][15] However, it was found that medium-pore zeolites, like ZSM-5, have a higher selectivity towards p-xylene. Firstly, the pores need to be large enough for the diffusion of the bulky TMB species.…”

“…Previous studies have shown that 12-membered rings have a higher catalytic activity than 10-membered rings due to their enhanced diffusion capacity. [13][14][15] However, it was found that medium-pore zeolites, like ZSM-5, have a higher selectivity towards p-xylene. [16,17] Secondly, the reaction pathway taking place depends on the acid site strength.…”

A Novel Approach for Prediction of Industrial Catalyst Deactivation Using Soft Sensor Modeling

“…One of these processes with high potential of deactivation is the disproportonation (DP) of toluene and/or transalkilation (TA) of C 9 aromatics and toluene to C 8 aromatics over zeolites in fixed-bed reactors. DP and TA involve solid-acid catalytic processes which occur over medium-pore zeolites, such as ZSM-5, and large-pore zeolites, such as mordenite, Beta, and Y [1][2][3][4]. For H-mordenite, the temperature is a dominant factor that determines the activity and coking tendency, as the undesired reaction, due to its one-dimensional channel system [5].…”

“…In these models, however, many simplified conditions have been assumed. Most of these models have been conducted at the laboratory scale under certain conditions with applying no dynamic data [1][2][3][4][5][6][7]12]. Additionally, online investigation of the industrial reactors' parameters (e.g., catalyst deactivation, conversion, product…”