A molecular sieve concept

Molecular sieve, as the name suggests, is a porous material with the ability to sieve molecules. Its basic structure consists of silica-aluminate crystals with regular and uniform pores and cavities. The size of these pores and cavities is comparable to the size of some molecules, so it can selectively adsorb molecules to achieve molecular level screening effect.

Second, the main source of molecular sieve composition and chemical formula

Molecular sieves are mainly derived from natural minerals or synthetic. Nature molecular sieve, such as zeolite, is a water-bearing aluminum silicate mineral, formed after billions of years of geological changes. Artificially synthesized molecular sieves are more diverse and are mainly synthesized on a laboratory or industrial scale by simulating the conditions under which nature's zeolites are generated.

Chemically, molecular sieves can be expressed as a variety of types, among which the MFI-type molecular sieves are very common, and their chemical formula can be expressed as Na12[(AlO2)12(SiO2)12]-xH2O, where Na is the cation, AlO2 and SiO2 are the tetrahedral structural units, and x is the amount of crystalline water. In addition to the MFI type, there are many types of molecular sieves such as A-type, X-type, Y-type, etc., and their chemical formulas vary according to their composition and structure.

Third, the use of molecular sieve and applicable places

Because of its special pore structure and adsorption performance, molecular sieve is widely used in various fields:

Petrochemical industry: In the field of petrochemical industry, molecular sieves are mainly used in catalytic cracking, catalytic reforming, isomerization and other reactions to improve the quality and yield of petroleum products.

Gas separation and purification: molecular sieve can be used for gas separation and purification due to its difference in adsorption capacity for different gases, such as separating oxygen and nitrogen from air, or removing impurities from industrial gases.

Drying and adsorption: molecular sieve has strong moisture adsorption ability and can be used as desiccant for drying gas and dehydrating liquid. At the same time, it can also adsorb organic substances, heavy metal ions and other pollutants for waste water treatment and environmental protection.

Refrigeration and air-conditioning: In refrigeration and air-conditioning systems, molecular sieve can remove water from refrigerants, prevent system icing and corrosion, and ensure the normal operation of the system.

Other fields: molecular sieves are also widely used in many fields such as environmental protection, medicine, food, agriculture, etc., such as for air purification, drug purification, preparation of food additives and so on.

Fourth, the type of molecular sieve on the market

There are many types of molecular sieves on the market, the following is a list of several common types:

1. Silicon aluminum molecular sieve:

·X type molecular sieves: with medium silica-aluminum ratio, suitable for adsorption and drying applications.

·Y type molecular sieves: with high silica to aluminum ratio, mainly used in catalytic cracking and reforming.

·USY type molecular sieves: super-stable Y-type, specially treated to improve thermal stability.

2.Aluminum phosphate molecular sieve:

·AIPO-5: with three-dimensional pore structure, suitable for catalysis and macromolecule adsorption.

·AIPO-11: Layered structure, good acidity, commonly used in esterification reaction.

3.Titanium-silicon molecular sieve:

·TS-1: titanium-containing silica-aluminum molecular sieves, high catalytic oxidation performance, commonly used in olefin epoxidation.

4.Carbon molecular sieve:

· activated carbon: high specific surface area, widely used in gas separation and liquid decolorization.

· carbon nanotubes: one-dimensional nanostructure, high conductivity and adsorption properties.

5.Other molecular sieves:

· Zeolite molecular sieves: such as MFI, AEL, etc., with special pore structure and catalytic activity.

· Metal-organic framework materials (MOFs): new porous materials with high specific surface area and tunability.

V. Conclusion

As a kind of porous material, molecular sieve plays an important role in many fields. With the progress of science and technology and in-depth research, the types and properties of molecular sieves will continue to be optimized and improved, bringing more convenience to human production and life.