Transformation of toluene and 1,2,4-trimethylbenzene over ZSM-5 and mordenite catalysts: A comprehensive kinetic model with reversibility

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 orthoxylene 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-Monlsmte)) 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.