Seed-induced Synthesis Of ZSM-5 Zeolite Without Any Organic Template System

ZSM-5 zeolite has been widely used in various catalysis fields in petrochemical industry because of its abundant three-dimensional cross pores,controllable acidity,good hydrothermal stability and pore shape selectivity.However,most of the ZSM-5 zeolite are synthesized under the organic template system,which will bring about the problems of high raw material cost,high energy consumption and serious environmental pollution,which does not conform to the research concept of green chemistry.Therefore,it has important academic significance and practical value to study the synthesis of ZSM-5 molecular sieve without organic template system.In this paper,the synthesis of ZSM-5 zeolite with different morphologies was studied using seed induction strategy under the system without organic template.The main research contents are as follows:1)Using self-made nano-pure Silicalite-1 zeolite as seed crystals,ZSM-5 nano-aggregates were induced to synthesize.The effects of the silicon-to-aluminum ratio,the amount of Na₂O,the amount of water and the amount of seed crystal added in the feed on the synthesis of ZSM-5 zeolite were studied.The results show that under a certain amount of seed induction,ZSM-5 zeolite with a wide range of silicon-to-aluminum ratios（Si O₂/Al₂O₃=30～120）can be synthesized.and nano aggregates can be prepared when the silicon to aluminum ratio is 30 and 50;the increase in the amount of Na₂O helps to reduce the particle size of the aggregates,and the particle morphology tends to be spherical;the increase in the amount of synthetic liquid water significantly reduces the yield of the molecular sieve,and is accompanied by an increase in the particle size of the aggregates;the molecular sieve with high yield can be prepared with a lower amount of seed crystals（<3%）.An increase in the amount of seed crystals can reduce the size of the primary nanoparticles and further affect the particle size of the entire agglomerate;the increase in the amount of synthetic liquid water significantly reduces the yield of the zeolites,and aggregates size increases.2)Using self-made small-grain ZSM-5 zeolite as seed crystals,the monodisperse ZSM-5molecular sieve was synthesized.The effects of seed crystals with different morphologies,amount of seed crystals added,crystallization temperature,synthesis solution concentration and different aluminum sources on ZSM-5 zeolite and the growth process of‘benzene ring’crystal grains were studied.The results show that the size of the seed crystal has a certain effect on the size of the induced ZSM-5 crystal grains,and there is no obvious difference in the pore structure of the induced samples of different sizes and the morphology of the seed crystal is very similar to the target product;during the growth of benzene ring-shaped grains,it was found that benzene ring-shaped particles began to appear in about 4 hours,and crystallized completely in about 20 hours;the addition of seed crystals increases,the particle size of the product decreases from 2μm to 700 nm,and the dispersibility becomes worse;the crystallization temperature was reduced from 170°C to 150°C,and the crystallization time was extended from 24h to 48h.The product obtained maintains the crystal grain c-axis length（1μm）unchanged,and the b-axis length is reduced from 260nm to 120nm;at the same p H,the concentration of the synthetic solution has a greater impact on the morphology of the target product.As the gel concentration decreases,the crystal grain size of the product decreases;under the same p H environment,using sodium metaaluminate and aluminum sulfate as the aluminum source can synthesize benzene ring-shaped grains with no significant difference,using aluminum nitrate as the aluminum source tends to synthesize elongated grains,and using aluminum hydroxide as the aluminum source Tend to synthesize ring-shaped benzene grains with a smaller size.3)The optimized nano-aggregates and monodisperse‘benzene ring’crystal grains were synthesized by 20 times magnification,and the results are as follows:for the synthesis of monodisperse crystal grains,under static crystallization in a large kettle,products with no significant difference in crystallinity,morphology,pore structure and thermal stability can be produced in a small kettle,however,under the conditions of dynamic crystallization in a large kettle,the synthesized product is not uniform enough;for the synthesis of nano-aggregate,under dynamic crystallization in a large kettle,uniform nano-aggregate products can be synthesized,with regular overall appearance and slightly low crystallinity,reaching the level of small-scale synthesis as a whole.