Molecular Sieves are crystalline zeolites that have been activated for adsorption by removing their water of hydration. During this dehydration, highly porous adsorbents are formed that have strong affinity for water and certain other gases and liquids.
The pores of any particular type of Molecular Sieve are precisely uniform in size and of molecular dimensions. Depending on the size of these pores, molecules may be readily adsorbed , slowly adsorbed or completely excluded.
Molecular Sieves have been used in many commercial and industrial systems for drying and purifying liquids and gases. Also, these adsorbents have made possible the development of large scale separation processes used to recover normal paraffins from branched chain and cyclic hydrocarbons.
Molecular Sieves can be used in the following types of adsorption systems:
Multiple-Bed Adsorption. This method can be used for the majority of commercial large scale fluid purification operations. Conventional fixed bed, heat regenerated adsorption systems are generally utilized. A typical dual-bed installation places one bed on-stream purifying the fluid while the other is being heated, purged and cooled.
Single-Bed Adsorption. When interrupted product flow can be tolerated, it is sometimes convenient to use a single adsorption bed. When the adsorption capacity of the bed is reached, it can be regenerated for further use or discarded, depending on process economics.
Static Adsorption. When formed into wafers or other shapes, Molecular Sieves can be used as static desiccants in closed gas or liquid systems.
The basic types of Molecular Sieves are the 3A, 4A, 5A and 13X sieves. Each of these are available in the form of beads of 4 x 8 (2 mm) and 8 x 12 (4 mm) mesh sizes.