Zeolite With MFI Structure:Economical Synthesis And Morphology Control

Zeolites with MFI topology possess excellent shape-selectivity due to its special pore structure. The diversity of framework atoms makes it good acidic or oxidative catalysts, widely used in fields of petroleum refining and fine chemicals. In this dissertation, colloidal seeds were used for the synthesis of MFI zeolites with controllable morphology and hierarchical porosity, which may be benefit to better understanding of the structure-activity relationship. In order to reduce N-containing wastewater, simplify synthesis procedure and reduce production costs and energy consumption during the synthesis of MFI zeolites, the role of colloidal seeds was studied.Firstly, synthesis of nanocrystalline ZSM-5aggregates with hierarchical porosity was investigated. Colloidal TPA-silicalite-1was firstly prepared using colloidal silica as silica source and TPAOH as template. Using this colloidal TPA-silicalite-1as seeds, nanocrystalline ZSM-5aggregates with hierarchical porosity were synthesized. TPA+/SiO2ratio can be reduced to as low as0.005while the as-prepared ZSM-5aggregates were in size of about2μm, possessing mesopore volume as large as0.2cm3g-1. The influence of seeding amount, batch SiO2/Al2O3ratio and Na2O/SiO2ratio was discussed. By tracking the structure and morphology changes during crystallization, new insight into the formation mechanism of the ZSM-5aggregates was obtained.In general, as-synthesized ZSM-5usually contains Na+for the compensation of the negative charge of the tetrahedral aluminum, which should be transformed to the H-form before being used as acid catalyst. In the second part, we focused on the one-step synthesis of nano-sized NH4-ZSM-5using colloidal silicalite-1as seeds. The influence of SiO2/AlO3ratio, the amount of seeding suspension and ammonia was investigated. Crystal sizes ranging from～200nm to～1μm could be controlled by simply adjusting the amount of seeding suspension. The as-prepared NH4-ZSM-5could be directly transformed to the H-form ZSM-5by a simple calcination. Compared to the conventional method, this process was fast and facile and possessed considerable potential for the large-scaled production.In the third part, the morphological control of the ZSM-5zeolites with high SiO2/Al2O3ratios was studied. Using colloidal silicalite-1as seeds and a small amount of TPABr or TEABr as auxiliary template, we synthesized highly crystallized ZSM-5zeolites with SiO2/Al2O3ratios higher than100. Crystal size of the synthesized ZSM-5could be controlled in the range of tens of nanometers and several micrometers by varying the seeding amount. Colloidal silicalite-1prepared from different silica sources also influenced the crystal sizes.ZSM-5with similar morphology and size but different SiO2/Al2O3ratios was synthesized with above method. The synthesized ZSM-5was transformed to the H-form and mixed with aluminum phosphate matrix to prepare microspheric catalysts via spray drying. The influence of the ZSM-5-containing additive for maximizing propylene in the FCC process was investigated. The yield of propylene and the octane number of the gasoline increased with the addition of ZSM-5additive. Influence of SiO2/AlO3ratio on the propylene yield was stressed, as the zeolite ZSM-5used was similar in morphology and size. With the increase of SiO2/AlO3ratio, the yield of propylene first increased and then decreased.The last part focused on the cost effective synthesis of zeolite TS-1. In this part, colloidal silicalite-1was used as seed for the synthesis of TS-1, largely reducing the amount of expensive template, TPAOH. The influence of feeding sequence, seeding amount, the species and the amount of amines or ammonia was investigated. Epoxidation of1-hexene was used as probe reaction to evaluate the catalytic performance of the synthesized TS-1. Besides, inorganic Ti(SO4)2was used as titanium source instead of organic TBOT, in order to further reduce the synthetic cost.