Hβ沸石上甲苯歧化和C_9芳烃烷基转移反应

Disproportionation of Toluene and Transalkylation of C_9 Aromatics over Hβ Zeolite

:研究了不同表面酸度的 Hβ沸石上甲苯歧化和 C9芳烃烷基转移反应。结果表明 :随 Hβ沸石表面酸度增加 ,甲苯转化率逐渐增大 ,C9芳烃转化率先增大后逐渐下降 ,芳烃总转化率先增大后趋于稳定 ;苯和二甲苯选择性随表面酸度增加而逐渐下降 ,产物中的 C+1 0 芳烃量逐渐增多 ,反应产物中甲乙苯、三甲苯异构体比例偏离热力学平衡值 ,二甲苯异构体比例与热力学平衡值一致。反应产物中二甲苯与苯间的摩尔比均大于 4 ,Hβ沸石具有优异的甲苯或苯与 C9芳烃烷基转移性能。

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.