Transalkylation of 1,2,4-trimethylbenzene with toluene over large pore zeolites: Role of pore structure and acidity

Effects of pore structure and acidity over Beta and Y zeolites with a range of Brønsted and Lewis acid sites on their catalytic behaviour in the transalkylation reaction were investigated. The tests were conducted for a time-on-stream (TOS) of 50 h in a fixed-bed reactor at 400 °C, 10 bar, H₂/HC = 4, and WHSV=5 h⁻¹ with a 50:50 wt. % toluene:124-TMB mixture as feedstock. While initial (TOS ≤3 h) TMBs conversion was similar, wide differences were evident as the effects of partial deactivation became apparent with TOS. Zeolite Beta (Si/Al = 12.5) exhibited highest conversion and xylenes yield. As the Si/Al ratio of zeolite Beta is increased, the performance dropped whereas an opposite trend was observed for Y zeolites underscoring the importance of optimum level of dealumination depending on the zeolite structure. Isomerization of 124-TMB was observed over Beta which was not sustained by Y. The existence of separate active sites for TMB isomerization and its transalkylation with toluene in Beta is suggested.