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The adsorption of 5A molecular sieve can be divided into physical adsorption and chemical adsorption, with physical adsorption mainly occurring in the process of removing liquid and gas phase impurities. The porous structure of 5A provides a large surface area, making it easy to absorb and collect impurities. Like magnets, all molecules have mutual attraction. Therefore, a large number of molecules on the 5A pore wall will produce strong gravity, attracting impurities from the medium into the pore. It should be pointed out that the molecules of these adsorbed impurities have a diameter smaller than the pore size of 5A molecular sieve, and the impurities are adsorbed into the pore. This is why different molecular sieves with varying pore sizes are manufactured by constantly changing raw materials and activation conditions, making them suitable for various impurity absorption applications.
Natural gas drying, desulfurization and decarbonization.
Nitrogen-oxygen separation, nitrogen-hydrogen separation, oxygen-nitrogen-hydrogen preparation.
Petroleum dewaxing, separation of n-paraffins, branched alkanes, and cyclic hydrocarbons.
Molecular sieves are classified according to the size of the molecules they can adsorb. 3A molecular sieve can adsorb molecules with a critical diameter less than 3.5, while 5A can adsorb molecules with a critical diameter less than 5. The micropores are about 5.5A, which can adsorb molecules smaller than the pore size in the micropores and separate them from other molecules. In addition to physical adsorption, chemical reactions usually occur on the surface of 5A, which not only contains aluminum but also a small amount of chemical bonds. Oxygen and hydrogen act as functional groups, such as carboxyl, hydroxyl, phenol, lactone, anthracene, ether, etc. These surfaces contain ground oxides or complexes that can react chemically with absorbing substances and bind to the surface of molecular sieve 5A.
5A molecular sieve is a calcium-type silicoaluminophosphate with a pore size of 5A, a bulk density of 700-800 kg/m3, a specific surface area of 750-800 m2/g, a porosity of 47%, a mechanical strength of over 95%, and a water adsorption of about 21.5% and a carbon dioxide adsorption of 1.5%.
13X molecular sieve is a sodium-type silicoaluminophosphate with a pore size of 10A, a volume density of 600-700 kg/m3, a specific surface area of 800-1000 m2/g, a porosity of 50%, a mechanical strength of over 90%, a water absorption of about 28.5%, and a carbon dioxide adsorption of 2.5%. Compared with the two adsorbents, the adsorption performance of 13X molecular sieve is better than that of 5A molecular sieve. However, the mechanical strength and wear resistance of 13X molecular sieve are slightly poorer, and the manufacturing process is more complicated, so the price is relatively high.
The working pressure of the small oxygen generator molecular sieve purifier is high, at atmospheric pressure of 1.5-2.5 MPa, and a starting pressure of 5.0 MPa, with a working cycle of 3-6 months. The carbon dioxide content in the processed air after passing through the molecular sieve purifier is less than 5×10-6. Therefore, molecular sieve 5A has been commonly used for medium-pressure molecular sieve purifiers in the past. Nowadays, 13X molecular sieve is also used as an adsorbent for medium-pressure purifiers to extend the working cycle of oxygen generators. Due to the low working pressure, the dynamic adsorption capacity of zeolite molecular sieve for water and carbon dioxide decreases, and all low-pressure molecular sieve purifiers use 13X molecular sieve to reduce the amount of molecular sieve used.
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