Synthesis Of New Hierarchical ZSM-5 Zeolite By Dry-gel Method

This paper was mainly divided into two parts. On one hand, in view of the situation that macro-mesoporous composite materials had good transfer performance but poor acidity, we selected a dual-templating method to synthesize ordered macro-mesoporous silica-alumina composite by one step in acid solution, using PMMA and P123 as macroporous template and mesoporous template respectively. The content of PMMA, P123 and silica alumina ratio were evaluated in order to get the optimum synthesis condition. The DBT hydrodesulfurization was adopted to evaluate the catalytic activity of macro-mesoporous SiO2 and macro-mesoporous silica-aluminum composite. The research had shown that it could affect the final morphology of the material that changing the dosage of PMMA and P123, and there was an optimum adding amount. The change of silica-alumina ratio could only influence the surface and pore volume of the material slightly, which would not change the main morphology of material. Catalytic reaction results indicated that Al-doping macro-mesoporous composite oxides had more superior catalytic properties. The desulfurization rate could reach 79.5% at 300℃ which was 27% higher than the pure silicon material. Through testing the acid of the materials, the Al-doping macro-mesoporous composite oxides had a strong acid value which leaded to the higher catalytic activity. At the same time it also proved that Al had scattered in the material very well.On the other hand, it was well-known that the ZSM-5 zeolite has high activity but poor transfer performance. To cope with it, we used the macro-mesoporous silica-aluminum composite obtained in the first part as raw materials which had not been calcined. First, the macro-mesoporous silica-aluminum composite was carbonized under anaerobic conditions at 900℃, and then it crystallized using dry-gel method. Finally we could get a new hierarchical ZSM-5 zeolite which would have a macro-meso-microporous struction. The Crystallization time and temperature were evaluated in order to get the optimum synthesis conditions. The results of catalytic performance evaluation showed that the crystallinity of materials would increase with the extension of the crystallization time, but the ordered structure would be damaged. Similarly, the change of crystallization temperature could also produce a similar effect. The results of catalytic performance evaluation showed, compared with commercial ZSM-5, the hierarchical ZSM-5 synthesized in the laboratory improved catalytic performance in FCC for heavy oil conversion due to its macropores and mesopores structure, especially the diesel yield.