Amine-free Synthesis of Molecular Sieve

As zeolite molecular sieves for industrial applications, considering the production and cost, it is hoped that they can be synthesized with cheap or without organic structure directing agent. For example, for molecular sieves such as EU-1, ZSM-11, ZSM-12, SSZ-28, SSZ-32 and SSZ-35, the SDA/SiO2 molar ratio can be reduced to 0.02~0.05. But whether it is possible to completely use organic structure directing agents, It is a subject worthy of attention and research. As early as the early 1980s, the route of synthesizing ZSM-5 without organic template was successfully applied in industrial production. In the presence of ammonia water, amorphous silicic acid was synthesized ZSM-5 was successfully synthesized from aluminum as raw material. In recent years, new development and exploration of amine-free methods have been carried out. They added molecular sieve seeds or gel-directing agents to the amine-free synthesis system at the same time, thereby inducing or promoting molecular sieve Growth in amine-free system. ECR-1 zeolite was successfully synthesized using Y-type molecular sieve gel director; ZSM-34 zeolite was synthesized using L-type gel director; calcined Beta zeolite seeds were also used in the absence of Beta zeolite with high crystallinity was synthesized under the amine system. Although the product has a low Si/Al ratio, the range of its synthetic Si/Al ratio was further expanded, and its crystallization process was studied in detail. It was found that Beta zeolite seeds did not induce Instead, it acts to provide surface growth. According to statistics, so far, aluminum-rich FAU, MOR, AMA and CHA type molecular sieves and silicon-rich ZSM-5, TUN-7, ECR-1, ZSM-34 , Ferrierite, Beta, RTH and MTW and other molecular sieves can be synthesized in the system without organic structure directing agent. The synthesis of zeolite molecular sieve without amine method can greatly reduce the cost of raw materials, and it has potential advantages in economy and environmental protection, but it also faces some problems or challenge:

①　Although seed crystals are added to the synthesis system, if the product has a higher crystallinity (or yield), the required crystallization time is relatively long, because the crystallinity (or yield) is often shorter if the crystallization time is short. ) is not high enough;

②　Compared with the organic amine (ammonium) synthesis method, the zeolite molecular sieve synthesized by the amine-free method tends to have a narrower Si/Al ratio range, and how to widen the Si/Al ratio range is a challenge;

③　Due to the lack of the help of organic amine (ammonium) structure directing agent, it is often easier to generate heterocrystals

④　Control of grain size. If these problems can be solved, the amine-free production will achieve industrial application. It has been reported that some zeolite amine-free production has entered the commercialization stage.