ZSM35 Molecular Sieve Preparation

- Feb 08, 2021-

Molecular sieves are the most important family of inorganic microporous crystalline materials, with a regular pore structure crystal structure (X-ray diffraction spectrum can be used to determine its characteristic structure). According to the statistics of the International Molecular Sieve Society (IZA) in 2009, the total number of molecular sieves has reached more than 190.

     Aluminosilicate molecular sieve is a microporous crystal material with strict three-dimensional lattice structure formed by connecting Si04 tetrahedron and A104 tetrahedron through a common oxygen atom. Due to the peculiar pore structure characteristics of zeolite molecular sieve, its regular structure and The uniform pore system of a certain size results in the shape-selective properties of reactants, intermediate states and product molecules, and the properties of molecular sieves such as acidity and structure are also easy to adjust, making zeolite molecular sieves used as catalytic materials, gas separation and Adsorbents, ion exchangers, etc. are widely used in oil and natural gas processing, fine chemicals, environmental protection, and nuclear waste treatment. The synthesis of zeolite molecular sieves is therefore of great significance, and the development of new synthetic methods of molecular sieves has always been the focus of scientific research personnel.

The ZSM-35 molecular sieve has a vertically intersecting two-dimensional channel system, in which the size of the 10-membered ring channel parallel to the surface is 0.54nmX0.42nm, and the size of the eight-membered ring channel parallel to the surface is 0.48nmX0. 35nm. ZSM-35 molecular sieve can be widely used in hydrocarbon conversion processes, such as isomerization, polymerization, aromatization and cracking, etc., and has good application prospects. Studies have shown that ZSM-35 molecular sieve has good catalytic activity in the reaction of normal C4 and C5 olefin skeletal isomerization to isomerized olefins, the latter being the important additives of unleaded gasoline, methyl tert-butyl ether and tert-amyl methyl The raw material of base ether, in fact, ZSM-35 molecular sieve is the best catalyst for olefin skeletal isomerization found so far.

It is precisely based on the good olefin isomerization performance that has been continuously studied for the synthesis of ZSM-35 molecular sieve. For example, USP3992466, USP4016245, USP4088739, USP41017195, USP4251499 and other documents adopt a synthesis method that does not use organic templates, but the shortcomings of the template-free method are high reaction temperature, long reaction time, and relatively narrow synthesis interval. ZSM-35 molecular sieve The silicon and aluminum are relatively low. In order to obtain a ZSM-35 molecular sieve product with high silicon-to-aluminum ratio and high crystallinity, the preferred synthesis scheme is to introduce organic amine templates, such as pyridine, cyclohexylamine, pyrrolidine, ethylenediamine, tetramethylammonium hydroxide, etc. Documents such as USP4000248, USP4795263, CNOl 123880. I, CN200410077908. 9, USP4205053, USP4578259, EP501577 and other documents, as well as synthetic methods using non-amine organics such as tetrahydrofuran.

However, the use of organic templates not only increases the synthesis cost, but also the traditional hydrothermal synthesis method will produce a large amount of wastewater containing high-concentration organic templates during the washing process of molecular sieves, which not only increases the cost of environmental treatment, but also because of expensive organic templates. Can not recycle and cause huge waste of resources.

ZSM35 Molecular Sieve manufacturers directly select cyclohexylamine as the synthesis medium of ZSM-35 molecular sieve. In the presence of a small amount of water, using cyclohexylamine's template-directing effect and solvent effect, it can synthesize a high silicon-to-aluminum ratio and good crystallinity. ZSM-35 molecular sieve, this method combines the advantages of hydrothermal synthesis and solvothermal synthesis, but overcomes the shortcomings of the hydrothermal method that produces a large amount of waste water containing high-concentration organic template. The whole synthesis process does not produce waste water, and it also Overcoming the solvothermal solvent and organic template separation process, the obtained cyclohexylamine mother liquor can be directly reused without any separation treatment, and the molecular sieve does not need to be washed. After vacuum drying, the original ZSM-35 molecular sieve powder can be obtained. At the same time, the cyclohexylamine attached to the molecular sieve is further recovered, which greatly simplifies the production process of the ZSM-35 molecular sieve, and is a new green and environmentally friendly molecular sieve synthesis process.