Molecular sieve is a kind of aluminosilicate compound with cubic lattice. It is mainly composed of silicon and aluminum connected by oxygen bridges to form an empty framework structure. In the structure, there are many pores with uniform pore size and cavities with neat arrangement and large internal surface area. In addition, it also contains metal ions with lower electricity prices and larger ion radius and water in a combined state. Because water molecules are continuously lost after heating, but the structure of the crystal skeleton remains unchanged, many cavities of the same size are formed, and the cavities are connected by many pores with the same diameter. These tiny pores are of uniform diameter and can be compared to the pores. Molecules with small diameters are adsorbed into the inside of the pores, and molecules larger than the pores are excluded. Therefore, molecules with different shapes and diameters, molecules with different polarities, molecules with different boiling points, and molecules with different saturation levels can be separated. It has the function of "sieving" molecules, so it is called molecular sieve.
Molecular sieve models commonly used in the gas industry:
Type A: Potassium A (3A), Sodium A (4A), Calcium A (5A)
Type X: Calcium X (10X), Sodium X (13X)
Type Y: Sodium Y, Calcium Y
Molecular sieve has strong moisture absorption capacity and is used for gas purification treatment. Avoid direct exposure to the air during storage. Molecular sieves that have been stored for a long time and have absorbed moisture should be regenerated before use. Molecular sieve should avoid oil and liquid water, and should avoid contact with oil and liquid water when using it.
The general formula of its chemical composition is: [M2(Ⅰ)M(Ⅱ)]O.Al2O3.nSiO2.mH2O where M2(Ⅰ) and M(Ⅱ) are monovalent and divalent metal ions, mostly sodium and Calcium and n are called the silicon-to-aluminum ratio of zeolite. Silicon mainly comes from sodium silicate and silica gel, while aluminum comes from sodium aluminate and Al(OH)3. They are colloids made by reacting with aqueous sodium hydroxide. After drying, it becomes zeolite, generally n=2~10, m=0~9.
3A molecular sieve
3A molecular sieve refers to potassium A-type aluminosilicate. 3A molecular sieve can adsorb molecules with a critical diameter not greater than 3A. It is often used in industry to dry unsaturated hydrocarbon gases (such as ethylene, propylene, butadiene, etc.). The drying of liquids (such as ethanol, etc.) is the preferred desiccant necessary for the deep drying, refining and polymerization of gas and liquid phases in the petroleum and chemical industries.
Application:
Refrigerant drying
Pyrolysis gas drying
Natural gas drying
Dehydration of gas or air in hollow glass
Dehydration of methanol, ethanol and other polar compounds
Dehydration of unsaturated hydrocarbons (such as ethylene, propylene, butadiene).
4A molecular sieve
4A molecular sieve refers to sodium A type aluminosilicate. 4A molecular sieve can adsorb molecules with a critical diameter not greater than 4A. It can adsorb water, methanol, hydrogen sulfide, carbon dioxide, sulfur dioxide, ethylene, propylene, etc., where it can be adsorbed on 3A molecular sieve All molecules can be adsorbed to 4A type.
Application:
Drying of refrigerant and air in valve
Remove carbon dioxide, ammonia, methanol from the gas stream
Dry and purify hydrocarbons, such as natural gas, LPG, air, inert gas and atmosphere
Electronic components, medicines, food, etc. are dried.
5A molecular sieve
5A molecular sieve refers to calcium A type aluminosilicate. 5A molecular sieves can adsorb molecules with a critical diameter not greater than 5A. Any molecule that can be adsorbed on 3A and 4A molecular sieves can be adsorbed on 5A. It can be separated from branched chain hydrocarbons and cyclic hydrocarbons through selective adsorption process. At present, it is used in large-scale normal isoparaffin separation process in industry.
Application:
Separation of normal isoparaffins in petrochemical industry
Purification of hydrogen and oxygen by pressure swing adsorption process
Drying and purification of petroleum, natural gas and other industrial gases, removing impurities such as water, carbon dioxide and sulfur from the gas stream.
13X molecular sieve
13X molecular sieve is an alkali metal aluminosilicate. The 13X molecular sieve in the form of sodium salt has an effective pore size of 10 angstroms and adsorbs molecules not greater than 10 angstroms. It can be used for catalyst carrier, water and carbon dioxide co-adsorption, water and hydrogen sulfide gas co-adsorption, and is mainly used for drying in medicine and air compression systems.
Application:
Remove hydrogen sulfide and mercaptans from hydrocarbons and natural gas;
Remove carbon dioxide and water from air (air pre-purification) and other gases;
Separate oxygen from the air, protect the catalyst, and remove oxides from hydrocarbons.
