Disproportionation of Toluene and Transalkylation of C_9 Aromatics over Hβ Zeolite

Mordenite and ZSM5 catalysts used for the reaction of toluene disproportionation and C_9 aromatics transalkylation have the following drawback: a lower WHSV (1.2~1.7h-1), a lower content of C_9 aromatics in the feed, and a lower X/B ratio (about 2.5) in the product. In order to improve these performance, disproportionation of toluene and transalkylation of C_9 aromatics over Hβ zeolite were studied. The results indicate that when the surface acidity of Hβ zeolite increases, the conversion of toluene increases gradually and the conversion of C_9 atomatics first increases and then keeps stable. Selectivity of B and X decreases gradually and the concentration of C+__10 aromatics in the product increases with increase of surface acidity. The results show that the isomer concentration of ethyl toluene and trimethylbenzene deviate from the thermodynamic equilibrium distributions while the distribution of xylene isomers agrees with thermodynamic data. Resaction mechanism for toluene and C_9 aromatics convesion over Hβ may be as disproportionation of toluene and trimethylbenzene, dealkylation of ethyl toluene and cumene, transalkylation between toluene and trimethylbenzene, between benzene and trimethylbenzene, between toluene and ethyltoluene, and isomerization of xylene, trimethylbenzene and ethyltoluene. Hβ zeolite has better transalkylation function because of its special 12memberedring pore openings, and as a result, the X/B molar ratio is higher than 4.