The utility model relates to a synthetic hydrated aluminosilicate (zeolite) or natural zeolite with the function of screening molecules. The general chemical formula is (m ′ 2m) O · Al2O3 · xsio2 · yh2o. M ′ and m are monovalent and divalent cations, such as potassium ion, sodium ion, calcium ion, barium ion, etc. In structure, it has many pores with uniform pore size and neatly arranged pores. Molecular sieves with different pore sizes separate molecules of different sizes and shapes. Molecular sieves with different pore sizes were obtained according to the different molecular ratios of silica and alumina. Its models include: 3A (potassium type A), 4a (sodium type A), 5A (calcium type A), 10z (calcium type Z), 13z (sodium type Z), y (sodium type Y), sodium mordenite, etc. It has high adsorption capacity, strong selectivity and high temperature resistance. It is widely used in organic chemical industry and petrochemical industry. It is also an excellent adsorbent for gas dehydration. More and more attention has been paid to waste gas purification.
There is a kind of natural aluminosilicate in nature, which has the functions of molecular screening, adsorption, ion exchange and catalysis. This natural substance is called zeolite, and the synthetic zeolite is also called molecular sieve. The general chemical composition formula of molecular sieve is: (m) 2 / no · Al2O3 · xsio2 · ph2o, M represents metal ions (usually Na in artificial synthesis), n represents the valence of metal ions, X represents the mole number of SiO2, also known as silicon aluminum ratio, and P represents the mole number of water. The most basic structure of molecular sieve skeleton is SiO4 and alo4 tetrahedron, which form three-dimensional network structure crystals through the combination of common oxygen atoms. This combination form forms cavities and pores with molecular level and uniform pore size. Due to different structures and forms, "cage" shaped space holes are divided into α、β、γ、 Hexagonal column, octahedral zeolite and other "cage" structures. The crystal structures of A-type, X-type and Y-type molecular sieves are shown in Fig. 1 and Fig. 2.
Because alo4 tetrahedron has a negative charge, it can combine with sodium plasma and become electrically neutral. In aqueous solution, sodium ions are easily exchanged with other cations. Most molecular sieve catalysts are the exchange of multivalent metal cations or h. molecular sieves can be used as catalysts or supports because of their acidity and selectivity to molecular size. High silica zeolites show high affinity for organic groups. In contrast, low silica zeolites show hydrophilicity due to their Lewis and Bronsted acid properties. Silicon and aluminum atoms form an oxygen ring through oxygen, and the size of the oxygen ring determines the pore size of zeolite. The number of oxygen atoms in each oxygen ring is 4 ~ 12. Generally, there are eight membered rings (0.4 ~ 0.5nm), ten membered rings (0.5 ~ 0.6Nm) and twelve membered rings (0.7 ~ 0.9nm) with molecular sieve function.
Y-type molecular sieve (x = 3.1 ~ 6.0) and mordenite (x = 9 ~ 11) with twelve membered oxygen ring. The former can be used as cracking catalyst and bifunctional catalyst, and the latter can be used as disproportionation catalyst of toluene.
There are ZSM series molecular sieves such as ZSM-5 and ZSM-11.
Octavalent oxygen ring includes A-type molecular sieve (x = 2), T-type molecular sieve and zsm-34. Their pores are so small that only straight chain hydrocarbons can enter the pores. The catalyst with molecular sieve as the catalytic active component or the main active component is called molecular sieve catalyst. Molecular sieves have ion exchange properties, uniform molecular size pores, excellent acid catalytic activity, good thermal and hydrothermal stability. It can be made into a catalyst with high activity and selectivity for many reactions.
