A molecular sieve is a material with pores of uniform size. These pore diameters are similar in size to small molecules, and thus large molecules cannot enter or be adsorbed, while smaller molecules can. As a mixture of molecules migrate through the stationary bed of porous, semi-solid substance referred to as a sieve (or matrix), the components of highest molecular weight (which are unable to pass into the molecular pores) leave the bed first, followed by successively smaller molecules. ,Usually, molecular sieves are used as desiccants (some examples include activated charcoal and silica gel).
Molecular Sieve 5A:
• Chemical formula: 0.7CaO•0.30Na2O•Al2O3•2.0SiO2 •4.5H2O
• Silica-alumina ratio: SiO2/ Al2O3≈2
5Å molecular sieves are often utilized in the petroleum industry, especially for the purification of gas streams and in the chemistry laboratory for separating compounds and drying reaction starting materials. They contain tiny pores of a precise and uniform size, and are mainly used as an adsorbent for gases and liquids.
5Å molecular sieves are used to dry natural gas, along with performing desulfurization and decarbonation of the gas. They can also be used to separate mixtures of oxygen, nitrogen and hydrogen, and oil-wax n-hydrocarbons from branched and polycyclic hydrocarbons.