Study On Aromatization Performance Over Modified HZSM-5 Without Hydrogen

The proportion of fluid catalytic cracking(FCC) gasoline is as high as 80 % in our country. The fraction of olefins in FCC gasoline is around 50 v% which has far exceeded national and international criterion. Olefins content in FCC gasoline can be reduced by promoting FCC technology, etherification, hydrogenation and so on. But these methods can not reduce olefins content to a great extent, or they will lower gasoline octane number. Converting olefins in FCC gasoline into aromatics with more octane number than olefins by aromatization technology without hydrogen flow can greatly reduce olefins content, keep octane number even increase it, while it can save energy, reduce equipment demand and bring down production cost finally.In this thesis, Zn, P and Ga modified HZSM-5 catalysts were prepared by co-impregnation method. The structure, surface area, acid properties and coke deposition of modified catalysts with and without hydrothermal treatment were characterized by x-ray powder diffraction(XRD), nitrogen-adsorption surface area measurement(BET), NH3 temperature-programmed-desorption(NH3-TPD), pyridine FT-IR and thermogravimetry(TG). The results showed that hydrothermal treatment did not destroy HZSM-5 framework structure while it decreased surface area, total acid amount, strong acid sites of ZnPGa/HZSM-5 catalyst and the coke deposition on ZnPGa/HZSM-5 catalyst for n-heptane aromatization.The evaluation result of n-heptane aromatization performance over various catalysts showed that introduction of Zn not only restrained n-heptane cracking but also accelerated its aromatization. The optimal Zn loading amount is 2 wt%. Introduction of the second element P could prevent Zn from flowing away while it restricted production of big molecules during aromatization process and decreased coke deposit on the surface of the catalyst so that aromatization stability was enhanced. The optimal P loading amount is 0.2 wt%. Introduction of the third element Ga not only promoted n-heptane conversion and aromatization but also restrained hydrogenolysis of middle production and increase liquid yield. The optimal Ga...