Molecular sieves are porous alumino silicate solids with precise and uniform pore size. Examples of molecular include Zeolites, activated carbon, porous glass and clay. Zeolites are a special class of molecular sieves which are highly crystalline alumino silicates of group-IA and group-IIA elements like sodium, potassium, magnesium and calcium. Molecular sieves are used as adsorbents and adsorb molecules smaller than their pore size and exclude the larger molecules. Different types of molecular sieves are available in the market in various forms such as powder and beads. A few examples of various types of molecular sieves are Type-3A, Type-4A, Type-5A and Type-13X. Molecular sieves have many industrial applications which include:
Molecular sieves can be reused after regeneration of the used sieves. They can be regenerated by heating and purging with carrier gas or heating from 100°C to 250°C under high vacuum to remove the absorbates. Small quantities of molecular sieves may be dried in the absence of a purge gas by oven heating followed by slow cooling in a closed system, such as a desiccator.