In a narrow sense, molecular sieves are crystalline silicates or aluminosilicates, which are connected by silicon-oxygen tetrahedron or aluminum-oxygen tetrahedron through oxygen bridges to form molecular sieve size (usually 0.3~2.0 nm) pores and pores. Cavity system, which has the characteristics of sieving molecules. However, with the deepening of molecular sieve synthesis and application research, researchers have discovered aluminophosphate molecular sieves, and the framework elements (silicon or aluminum or phosphorus) of molecular sieves can also be composed of B, Ga, Fe, Cr, Ge, Ti, V , Mn, Co, Zn, Be and Cu are substituted, and the size of the pores and cavities can also reach more than 2 nm. Therefore, molecular sieves can be divided into silicon-aluminum molecular sieves, phosphorus-aluminum molecular sieves and framework heteroatom molecular sieves according to the composition of framework elements. According to the pore size, molecular sieves with a pore size smaller than 2 nm, 2-50 nm and larger than 50 nm are called micropore, mesopore and macropore molecular sieves, respectively. Due to its large pore size, it becomes a good carrier for the reaction of large-sized molecules, but the pore walls of mesoporous materials are amorphous, so their hydrothermal and thermal stability cannot meet the harsh conditions required for petrochemical applications. .
Due to the metal ions with lower electricity price and larger ionic radius and water in the combined state, the water molecules are continuously lost after heating, but the crystal skeleton structure remains unchanged, forming many cavities of the same size, and the cavities have many diameters The same micropores are connected, and these tiny pores have uniform diameters, which can adsorb molecules smaller than the diameter of the pores into the interior of the pores, while repelling the molecules larger than the pores, so that the molecules with different shapes and diameters can be removed. Molecules with different degrees of polarity, molecules with different boiling points, and molecules with different degrees of saturation are separated, that is, they have the function of "sieving" molecules, so they are called molecular sieves. At present, molecular sieves are widely used in metallurgy, chemical industry, electronics, petrochemical industry, natural gas and other industries.
Add: Yunxi District, Yueyang City, Hunan Province, China