Technical article

Classification of molecular sieve desiccant


Molecular sieve is a kind of aluminosilicate microporous crystal, which has the characteristics of uniform pore size and extremely high specific surface area, good thermal stability, strong adsorption performance, large internal surface area and high strength. Due to their different uses, molecular sieves are divided into 3A, 4A, 5A, 13X, 13X APG molecular sieves, insulating glass molecular sieves, activated molecular sieve powder, carbon molecular sieves, etc.
Selective adsorption according to the size and shape of the molecule, that is, only those molecules smaller than the pore size of the molecular sieve are adsorbed. For small polar molecules and the higher the degree of unsaturation, the stronger the selective adsorption.
With strong water absorption, even at higher temperature, higher air velocity and lower water content, there is still a fairly high water absorption capacity.
The following are the classification of several common molecular sieves (granular):

Types Bulk density (kgs/m3) Static H2O adsorption (%) Wear ratio
Main application
Molecular sieve 3A 680~720 >21 <0.25 For drying of petroleum cracked gas and olefins
Molecular sieve 4A 680~720 >21.5 <0.2 For natural gas drying and alkane separation
Molecular sieve 5A 680~720 >22 <0.2 Air drying and purification, natural gas dehydration and desulfurization, petroleum gas desulfurization and pressure swing adsorption for oxygen production and hydrogen production
Molecular sieve 10X 500~600 >26 <0.2 High-efficiency adsorbents for drying, desulfurization, decarbonization and aromatics separation of gases and liquids
Molecular sieve 13X >640 >27 <0.2 Drying, desulfurization and purification of LPG and natural gas
Molecular sieve 13X HP >620 >30 <0.3 Pressure swing adsorption oxygen generator (PSA oxygen generator)
Lithium molecular sieve 600~670 >30 <1 Low pressure adsorption vacuum desorption oxygen production equipment (VPSA oxygen production)
Carbon molecular sieve 660~700 / / Pressure swing adsorption nitrogen generator (PSA nitrogen generator)
Insulation glass
Molecular sieve
720~760 >20 <0.3 Insulating glass plays the role of adsorbing water vapor
Common desiccants on the market are divided into physical drying and chemical drying. The following are the most widely used adsorbents in industry:
1st type of adsorbent: Molecular sieve
Usually in the petrochemical industry, molecular sieves are often used as desiccants and adsorbents, which are divided into spherical and strip shapes, and are mostly used to absorb moisture in the air and absorb trace moisture in liquids to achieve the purpose of drying. Compared with other adsorbents, this adsorbent has the higher price, but the water adsorption is also the highest.
2nd type of adsorbent: Silica gel
Silica gel, as mentioned above, is divided into indicator silica gel and non-color-changing silica gel, which can be divided into water resistant silica alumina gel WS type and non-waterresistant silica gel H type according to whether the bead is broken or not when meet water. How to judge whether the silica gel is out of use? Generally, the water content can be observed. The higher the water content, the greater the degree of discoloration, which also tells us that the water absorption of the silica gel has reached saturation, and the silica gel needs to be regenerated. It is also often divided into small packages of desiccant and placed in the finished product. The price of fine pored white silica gel is medium, and the price of high grade silica aluminum gel is higher.
3rd type of adsorbent: Activated alumina
Activated alumina has excellent adsorption properties for water, and is often used in industrial drying. Many adsorption dryers commonly use KA401 activated alumina from OIM Chemicals as adsorbents in compressed adsorption dryers. The price of activated alumina is the lowest, and it is also a widely used adsorbent. It is also useful to work matched with molecular sieve 4A and activated alumina. Due to the higher compressive strength of activated alumina, it is usually placed at the bottom of the tank to protect our molecular sieve 4A, thereby reducing the pulverization of molecular sieve and improving the use of adsorption dryers life.
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Tracy Chen
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