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Molecular sieve production process


Molecular sieve is mainly used in gas refining and purification, petrochemical, refrigeration, car, glass construction, medicine, paint and coating, packaging and other fields. In a narrow sense, it is mainly crystalline silicate or aluminosilicate. It is composed of silicon oxide tetrahedron or aluminum oxide tetrahedron connected by oxygen bridge bond to form a pore and cavity system with large and small molecular size, and then has the characteristics of screening molecules. Jiangxi Xintao Technology Co., Ltd. today revealed the production methods of molecular sieve. The production methods of molecular sieve mainly include hydrothermal composition, hydrothermal conversion and ion exchange.


The first is hydrothermal composition method, which is used to produce products with high purity and to form molecular sieves that do not exist in nature. Mix silicon containing compounds (water molecular sieve glass, silica sol, etc.), aluminum containing compounds (hydrated aluminum oxide, aluminum salt, etc.), alkali (sodium hydroxide, potassium hydroxide, etc.) and water in proper proportion, heat them in a autoclave for a certain time, that is, separate molecular sieve crystals. The composition process can be expressed by the following formula:


In the industrial production process, Na molecular sieves are generally formed first, such as 13X and 10X molecular sieves (see figure). Adding some additives in the process of hydrothermal composition can change the structure of the final product, for example, adding quaternary ammonium salt can obtain ZSM-5 molecular sieve.


The second is hydrothermal conversion method, which can convert solid aluminosilicate salt water into molecular sieve in the presence of excess alkali. The materials used are kaolin, bentonite, diatomite, etc., and can also be composed of silicon aluminum gel particles. The cost of this method is low, but the product purity is lower than that of hydrothermal composition method.


The third is the ion exchange method, which generally converts the Na molecular sieve into the molecular sieve containing the desired cations in the aqueous solution. The general formula is as follows: Z - indicates the anion skeleton, and Me+indicates the cations to be exchanged, such as NH 嬃, Ca2+, Mg2+, Zn2+, etc. The materials are generally hollow glass molecular sieve chlorides, sulfates, and nitrates. Cations with different properties in the solution exchange to molecular sieves with different degrees of difficulty, which is called the selection order of cations by zeolite molecular sieves. For example, the selection order of 13X molecular sieves is Ag+, Cu2+, H+, Ba2+, Au3+, Th4+, Sr2+, Hg2+, Cd2+, Zn2+, Ni2+, Ca2+, Co2+, NH , K+, Au2+, Na+, Mg2+, Li+.


The following parameters are commonly used to show the exchange results: exchange degree, that is, the percentage of the amount of Na+exchanged in molecular sieve Cathay; AC capacity, which is the milligram equivalent of AC cation in every 100g molecular sieve; AC power, indicating the mass percentage of cations in solution exchanged to molecular sieve. In order to prepare suitable molecular sieve catalyst, it is sometimes necessary to distribute the products obtained by AC with other components, which may be other catalytic active components, cocatalysts, diluents or adhesives. The allocated materials can be activated after molding. The above is the summary of molecular sieve production. The actual operation needs to constantly summarize experience in the process of practice.