Molecular sieves are crystalline metal aluminosilicates having a threedimensional interconnecting network of silica and alumina tetrahedra. Natural water of hydration is removed from this network by heating to produce uniform cavities which selectively adsorb molecules of a specific size.
Type 3A: Will exclude most molecules except water. Type 3A is used for drying natural gas, ethanol and reactive monomers such as olefins etc. Type 3A is usually made by ion-exchanging potassium onto Type 4A in place of sodium.
Type 4A: The sodium form of Type A is widely used as a general purpose drying agent. Under certain conditions it can also be used for removal of carbon dioxide.
Type 5A: This is the calcium-exchanged form of the Type A zeolite. The strong ionic forces of the divalent calcium cation make 5A an excellent choice for removing carbon dioxide, carbon monoxide, hydrogen sulphide and other weakly polar molecules. This product is also effective for the bulk separation of normal and iso-paraffin hydrocarbons.