摘要
用真空微量Cahn电天平法研究了中孔分子筛SAPO-11及HZSM-5分子筛样品上的二甲苯扩散性能,探讨了影响烷基化反应产物对位选择性的各种因素,并测定了样品上的二甲苯异构化反应性能。结果表明对-二甲苯选择性不仅与烷基化反应的扩散/反应动力学有关,还与产物在分子筛表面的二次异构化反应性能有关。中孔分子筛的对位选择性主要决定于酸性的强弱。未改性的SAPO-11分子筛正是由于它的特殊的中等孔径、一维直孔道结构和中等强酸性的协同效应而有较高的对位选择性。
The diffusivitics of Xylene in medium pore SAPO-11 and HZSM-5 samples were studied gravimetrieally wilh a Cahn 2000 electric microbalance. The factors affecting p-Xylene selectivity in the alkylation of toluene with methanol were discussed. The catalytic properties for x lene isomerization were also investigated. The model of diffusion/reaction kinetics for selective alkylation on medium pore molecular sieve has been used to explain our experimental results. The p-xylene selectivity was mainly controlled by the diffusion of alkylation products and isomerization of xylene on the surface strong acid sites. For medium pore molecular sieves, the para-selectivity mainly depended on their acidic properties. The higher selectivity for p-xylene of the unmodified SAPO-11 resulted from its medium pore and medium acidic strcngth.
基金
国家自然科学基金
