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Molecular Sieves Molecular Sieve is one kind of aluminosilicate. Silicon and aluminum are bo0nded through the "bridge" of axyden to form porous structure, which possess uniform porous channel and capacity of large inner surface area. Besides Si, Al and O, there are metalic cations of low positive charge and relative larger diameter, and chemically combined water molecules. Although these water molecules could be released upon heating, the crystal structure does not changed, resulting in formation of many cavities, where there are abundant micropores of uniform size linked together. The molecules less than channel size could be absorbed in pores, on the contrary, these larger than the channel size will be excluded. Thus molecules of different size can be separated by means of seiving. Therefore this aluminosiliate is named as molecular seive. Mixture of gases or compounds than flow though molecular seive can be separated due to sieving effect. Man-made molecular sieve are white powder, that is undissolved in water and organic solvent, but usually dissolves in strong acid. Adhesive is added to the white power to make extruded sphere and pellet in order to easily handle for the application. Molecular Seive has high thermal stability, larger inner surface area (600-1000 m2/ Kg) although its external surface area is small (1% of total surface area). It possess three dimensional frame network, the pore volume is of 28% - 35% of total volume, so that it is able to adsorb large amount of molecules. Its inner crystal surface is highly polarized resulting in forming high electric field.
Due to its homogenous pore size distribution and high adsorptive selectivity, it is powerful adsorbent, catalyst and catalyst support. Therefore, it is widely used in industries, such as oil refining, petrochemical , chemical, metallic, electronic and military field. Beside, it is used more and more in medicine, light industry, agriculture and environmental protection etc.
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