Synthesis Of Monodisperse ZSM-5 Zeolites By Seed-directed Method In The Absence Of Organic Template

ZSM-5 zeolite, known as an extreme significance of zeolite molecular sieve, has been applied to be sorbents and catalysts, and used as fine chemical production, petrochemical production,gas and liquid separation due to its distinct shape-selective property, moderate acidity, thermal stability, channel structure. Till now, the synthesis of ZSM-5 currently needs organic amines or inorganic amine as the template agents. Organic amines usually have strong templating effect, however, they are costly and poisonous. Inorganic amine is cheap, but its templating effect is relatively weaker and has severely environment problem. Synthesis of ZSM-5 without template usually suffers from poor crystallinity, non-uniform crystal sizes, lower purity, etc. It is believed that the addition of seed has the possibility to transform the shortcomings evidently.Therefore, the hydrothermal synthesis of ZSM-5 without template but with a small amount of seed was investigated in this paper. The synthesis of ZSM-5 zeolite without template but with a small amount of seed induced has been investigated systematically aiming to synthesize ZSM-5 zeolite with different crystal size and different ratio of Si/Al. The influences on synthesis and crystal size of the synthesis conditions was investigated,too. The main findings are as follows:(1) Firstly, different particle sizes of seed (60nm and 200nm) crystal was prepared by adjusting process parameters. Then, the species and the ratio of the synthesis ingredients are investigated to find the optimal synthesis condition. Then using hydrothermal synthesis method to study and optimize the synthesis condition. The results show that the kinds of silicon source and aluminum source have significant effect on the grain morphology and particle size distribution. Using silica sol and sodium aluminate as silicon source and aluminum source can synthesis ZSM-5 zeolite with the well grain morphology and decent particle size distribution. Higher temperature, lower amount of water, silicon source adding to aluminum source are favorable to the formation of monodisperse crystallites. Si/Al ratio is in the range of 30 to 100. Particle size decreased as the seed amount increased. ZSM-5 zeolite can be synthesized with the well grain morphology and decent particle size distribution by regulating the seed amount in the range of 0.011wt% to 0.332wt%. Particle size is in the range of 2.2?m to 300nm.(2) Using two-step temperature process; Firstly the nucleation stage at lower temperature to accelerate the dissolution of the seed to tiny units followed by the crystallization stage at higher temperature so as to synthesize ZSM-5 zeolite with different crystal size rapidly. The samples can be synthesized in 8 hours. The crystallization temperature and time have no obvious influence on the crystal size, while lower temperature and longer time of pre crystallization are favorable to the formation of small crystallites to some extent. This method can greatly reduce the energy consumption.(3) Characterizations carried out with SiO2/AlO3of 40,60,80,100 sample from scale-up synthesis (in 500mL autoclave) reveal that,zeolite possess well grain morphology,decent particle size distribution and good diffusivity Particle size is in the range of 500nm to 2?m. The characterizations show that ZSM-5 zeolite without template synthesized in the presence of seeds through simple industrial accounting has a promising prospect in industrial production.