What is the difference between 3A, 4A and 5A molecular sieves? How to choose the most suitable one?

1. Chemical formulas of 3A, 4A and 5A molecular sieves

3A molecular formula:

0.4K2O 0.6Na2O Al2O3 2SiO2 4.5H2O (SiO2·Al2O3≈2)

4A molecular formula:

Na2O Al2O3 2SiO2 4.5H2O (SiO2·Al2O3≈2)

5A molecular formula:

0.7CaO 0.3Na2O Al2O3 2SiO2 4.5H2O (SiO2·Al2O3≈2)

2. Pore size of 3A, 4A and 5A molecular sieves

The working principle of molecular sieves is mainly related to the pore size of molecular sieves, which are 0.3nm/0.4nm/0.5nm respectively. They can adsorb gas molecules whose molecular diameter is smaller than the pore size. The larger the pore size, the greater the adsorption capacity. The adsorption is selective according to the size and shape of the molecules, that is, only those molecules smaller than the pore size of the molecular sieve are adsorbed. It has selective adsorption properties. The greater the polarity and the higher the degree of unsaturation, the stronger its selective adsorption properties. Has strong water absorption. Even at higher temperatures, larger airspeeds and lower water contents, there is still a fairly high water absorption capacity.

Different pore sizes filter and separate different things.

To put it simply, 3a molecular sieve can only adsorb molecules below 0.3nm. For 4a molecular sieve, the adsorbed molecules must also be smaller than 0.4nm. The same is true for 5a molecular sieve. When used as a desiccant, a molecular sieve can absorb at least 21% of its own weight in moisture.

3. Application of 3A, 4A and 5A molecular sieves

3A molecular sieve is mainly used for drying petroleum cracked gas, olefins, refinery gas and oil field gas, as well as desiccant in chemical, pharmaceutical, insulating glass and other industries.

Mainly used for liquid (such as ethanol) drying, insulating glass air drying, refrigerant drying, etc.

4A molecular sieve is mainly used for deep drying of air, natural gas, alkanes, refrigerants and other gases and liquids; preparation and purification of argon; static drying of pharmaceutical packaging, electronic components and perishable substances; as a dehydrator in paints, fuels and coatings agent.

5A molecular sieve is mainly used for the separation of normal and isoparaffins, deep drying and purification of gases and liquids, separation of oxygen and nitrogen, and desulfurization of oil and petroleum gas. It can be used as an adsorbent in dewaxing technology using steam as a desorbent.

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