Transalkylation of Toluene with 1,2,4-Trimethylbenzene over Large Pore Zeolites

Using industrially relevant operating parameters, the transalkylation of 1,2,4-trimethylbenzene (TMB) with toluene was studied. The effect of acidity and structure, increased reaction pressure, and very low levels of Pt impregnation have been investigated over both H-form and Pt-loaded zeolites: Beta, MOR, and Y. A fixed bed reactor was used at WHSV of 5 h–1, 400 °C, and a 50:50 wt % toluene:TMB ratio with the order of activity after 50 h TOS of Y > Beta ≫ MOR at 1 bar. At elevated pressure (10 bar), all catalysts showed better performance with significant improvement in MOR as pore blockage reduced and the order of activity was Beta > MOR > Y. Incorporation of Pt (0.08 wt %) further improved the activity of all catalysts with the highest conversion after 50 h TOS over Beta (62 wt %) where Beta and MOR yielded similar levels of xylenes (40 wt %). All catalysts were further optimized for activity while maintaining the desired stability and highest xylenes yield

Effect of hydrogenative regeneration on the activity of beta and Pt-Beta zeolites during the transalkylation of toluene with 1,2,4-trimethylbenzene

Catalyst deactivation remains a main challenge in the transalkylation process. To develop a cost-effective catalyst, improving the regeneration characteristics of Beta and Pt-Beta catalysts was investigated. Both Beta and Pt-Beta catalysts were studied in transalkylation in the presence of hydrogen. The regeneration process was carried out using hydrogen for four cycles of operation (30 h on stream per cycle). A Pt-Beta catalyst with enhanced regeneration and activity characteristic relative to the parent materials is presented, and found to be stable, with the activity fully restored by regeneration with hydrogen at 500 °C. The activity of the parent Beta dropped gradually after each cycle suggesting that the hydrogen alone at 500 °C was insufficient in removing the coke formed during the reaction. The drop in activity was attributed to the disappearance of Brønsted acid sites over the spent Beta catalyst due to the growth of coke molecules trapped in the zeolite micropores leading to the formation of highly polyaromatic molecules blocking those active sites. This limitation can be effectively overcome by platinum addition which enhanced the removal of coke during the regeneration via hydrocracking