| ZSM-22 is a kind of TON zeolite with one-dimensional pore structure of tenmembered ring.Because of its structural diversity and unique performance,it is widely used in petrochemical industry.Hydrothermal synthesis is the most commonly used method for the preparation of ZSM-22 zeolite.Due to the metastable structure of ZSM-22,it is easy to generate heterocrysts such as ZSM-5 and cristobalite in the preparation process,the crystallization time is longer,and the prepared The crystal size is relatively large,and at the same time,the large amount of mother liquor produced after crystallization will cause environmental pollution and waste of resources.Therefore,it is of great significance for the industrial application of ZSM-22 zeolite to synthesize nano-sized ZSM-22 zeolite quickly,economically and greenly,optimize the synthesis conditions and prevent the formation of heterocrysts.Based on the above background,the main research results of this paper are as follows:(1)ZSM-22 zeolite was synthesized by conventional hydrothermal method,using 1,6-hexanediamine(DAH)as a template agent,adding seed crystals to synthesize ZSM-22 zeolite.At the same time,ultrasonic aging technology was applied to the preparation of ZSM-22 zeolite,and the effects of aging methods,ultrasonic aging time and ultrasonic aging temperature on the synthesis of ZSM-22 zeolite were investigated.The sample ZSM-22 zeolite was analyzed by XRD and SEM.The results showed that ultrasonic aging can not only shorten the crystallization time,but also reduce the crystal size.Ultrasonic 0.5 h at 25 ? can shorten the crystallization time from 48 h to 24 h;extend the ultrasonic time to 1.5h,the crystallization time is further shortened to 20 h,the crystal size is reduced from 0.9 ?m to 0.5 ?m,within the range of 25 ~ 55 ? The higher the ultrasonic aging temperature,the higher the crystallinity of the obtained ZSM-22 molecular sieve.(2)According to Arrhenius formula,the relationship between crystallization temperature and crystallization time of ZSM-22 zeolite was calculated.Based on this relationship,the method of rapid hydrothermal synthesis of ZSM-22 zeolite was studied.At the same time,the influence of synthesis factors such as crystallization mode,crystallization temperature,crystallization time and silicon-aluminum ratio on the product ZSM-22 zeolite was investigated,and the preparation conditions were optimized.The experimental results show that when the raw material Si / Al is 35,under dynamic crystallization conditions(rotation speed is 30 rpm),when the crystallization temperature is increased to 240 ?,crystallization for 2 h can obtain pure crystal nanoscale ZSM-with high crystallinity.22 zeolite,the average grain size of the crystal is 55 nm,and the crystal grains are aggregated to form intercrystalline mesopores,which have a large specific surface area and mesopore volume.Under this experimental condition,the Si / Al range of the pure phase ZSM-22 zeolite can be extended to 35-70.(3)Reduce the amount of template agent in the initial reaction solution,add a certain amount of waste mother liquor generated in the crystallization process of molecular sieve,prepare a series of ZSM-22 zeolite,and realize the reasonable use of mother liquor circulation.The effects of the amount of mother liquor added and the amount of template agent on the synthetic samples were investigated.According to the experimental results,it can be seen that when the amount of mother liquor added is 50 wt%(raw material liquid),the synthesized product is pure phase ZSM-22 zeolite with high crystallinity and template agent.The minimum dosage is n(DAH)/ n(SiO2)= 0.2.After three cycles of crystallization mother liquor,the synthesized ZSM-22 molecular sieve has similar crystallinity and size to the initially synthesized ZSM-22 zeolite. |
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