Study On The Catalysts For Propane Aromatization

Propane dehydro-aromatization under non-oxidative conditions opens a new approach to the direct transformation of propane into chemicals. As reported, Zn/HZSM-5 and Ga/HZSM-5 show good catalytic performance for propane dehydro-aromatization. However, the carbonaceous deposits heavily formed during the reaction and caused the severe deactivation of the catalysts. The target of this dissertation is to study the stability of catalysts and the mechanism of propane aromatization on metal modification catalysts.Firstly, by means of ion-exchanged and impregnation methods, zeolites of different pore structure (A, β ,MCM-22,ZSM-5) and different ratio of silicon to aluminium were modified with metal ions (Fe3+, Ga3+, Zn2+) and nonmetal species. Secondly, nanosized zeolite was synthesized by hydrothermal synthesis and ion-exchanged methods.The results of zeolite characterization indicate that: (1)in acidity, β which process 12-memberbed ring has superior acid size, while the acid size of A type zeolite the least. ZSM-5 which has channels formed by 10-memberbed ring, MCM-22 zeolite, with both 10 and 12 member ring,have more Lewis acid centers and less Bronsted acid centers. After modification, the amount of total acid and strong acid of all zeolites decrease, but the weak acid increase with metal modification and decrease with phosphorus modification. When the silicon/aluminium ratio of ZSM-5 zeolite increasing, the acid size decreased. While the crystal size of ZSM-5 zeolite decreasing, the total acid and weak acid increase. (2) in pore structure, mental ions modification has little influence on the pore structure of zeolite. The crystal size decreasing, the volume and surface of zeolite increased.The catalytic performances of prepared zeolite as catalysts for propane aromatization were investigated on a fixed-bed micro-reactor. Results indicate that textural properties is the key factor affecting the catalysis properties, ZSM-5 which possess channels formed by 10-memberbed ring, realized the highest conversion of propane and the highest selectivity for aromatics products. The HZSM-5 catalyst modified with Zn and Ga improve the conversion of propane and the selectivity to aromatics. The incorporation of modifying elements prompts the dehydrogenation of propane and thereby to form aromatics. The Zri-P/ZSM-5 catalyst possessed higher activity stability. The crystal size of ZSM-5 significantly affects the aromatization of propane. The smaller of the crystal size of ZSM-5 was, the higher of the zeolite catalyzing activity, which contributed to the increase of the number of the adsorption sites located near the pore mouth on the external surface of zeolite. Nanosized crystal ZSM-5 zeolite modified by zinc cation gives higher aromatization activity and preferable...