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Synthesis, Characterization And Catalytic Cracking Performance Of MWW Type Zeolites

Posted on:2002-03-12Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z Q LiuFull Text:PDF
GTID:1101360062975605Subject:Chemical processes
Abstract/Summary:PDF Full Text Request
MWW type zeolites, such as MCM-22, with both 10 and 12 member nng pore openings, high thermal/hydrothermal stability and excellent performance in several catalytic reactions, are promising new catalytic materials. Up to now, the synthesis of zeolites with MWW topology is costly, the study of zeolite crystallization has contradictory results, their application in FCC is not systematacially investigated, and zeolites with MWW topology containing other metals, such as Zn, Ni, W et al., have not yet been reported. Based on the reasons mentioned above, the synthesis, crystallization mechanism and the catalytic cracking performance of these zeolites have been studied. The main results are as follows.1.Highly efficient static crystallization method for zeolites with MWW topology has been developed. The method reduces the template/silica ratio and water/silica ratio to 0.09 and 12 respectively. It is found that the utilization of silica gel with high surface area and high activity as silica resource, is the key for the highly efficient static synthesis of zeolites with MWW topology, while the aging procedure during the preparation of gel does not show significant influence on the synthesis. The investigation indicates that the Si02/A1203 ratios (SAR) of the gel system ranging from 18 to 80 used for synthesis can produce zeolites with MWW topology, which may be further trans-crystallized into MIFf at high SAR, such as 50, and into MOR at low SAR, such as 20.2.Crystallization temperature and SAR are the most important factors for the synthesis of MWW zeolites. In the same reaction gel, MCM-22(p) is produced at low crystallization temperature, MCM-49 at high crystallization temperature; at the same crystallization temperature, MCM-49 is produced at low SAR, MCM-22(p) at high SAIR. The crystal with unit cell c-parameter between MCM-22(p) and MCM-49 was also synthesized. We propose that the structures of interlayer oxygen bridges, Sil-O 1-All, are easier to form than Sil-Ol-Sil structures, which may be ascribed to the fact that the bond length of Al-O is longer than that of Si0.Zeolite MCM-49 with higher SAR than that presented in the literature was synthesized based on the above finding. It is aslo found that the higher basicity of gel is favorable to produce MCM-49, but the concentration of Na~ and of the template show little effect on the formation of MCM-49. The results we have obtained could explain some of the contradictory results reported in the literature.3.Zeolites with MWW topology containing metals, such as, Zn, Ni, W et al., are synthesized under highly efficient static condition, and ITQ2 is also produced.4.Zeolites with MWW topology are characterized by XRD, SEMI, TG, MAS N7M1R and UY-Raman. The results show that the structures of MCM-22(p), MCM-49(Zn-MCM-49) and MCM-22 have fine difference, and their unit cell c-parameter decreases in sequence.5.The crystallization process of zeolites with MIV./W topology is characterized by XRF, XRD, SEMI, JR and MAS NMIR. It is demonstrated that the crystallization of the zeolites under highly efficient static condition follows liquid phase ion transportation mechanism. during the crystallization process, aluminium source, template and partial dissolved silica source nucleate first in liquid, then the crystal grow up quickly. The unit cell c-parameter decreases during the crystallization process, that is, the structures of interlayer oxygen bridges, T1-01-T1, are formed gradually. Interlayer oxygen bridges of the zeolite is easier to form when zinc is introduced into the reaction gel, which maybe due to zinc incorporating into the Ti position of the zeolite.6.The performance of MCM-22, ZSM-5 and Beta used as FCC additives, with 8wt% and i4wt% of additive in the total amount of catalyst, is investigated. The experimental data show that the MCM-22 additive yields more gasoline, diesel and coke, less gases comparing with ZSM-5, and less gasoline and diesel, more coke and gases comparing with Beta. The hydrogen transfer activity of MCM-22 is highe...
Keywords/Search Tags:Zeolite, MWW, Synthesis, Crystallization mechanism, Catalytic cracking, Additive
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