Molecular sieve is one kind of aluminosilicate. Silicon and aluminum are bonded though the "bridge" of oxygen to form porous structure, which possesses uniform porous channel and cavity of large inner surface area. Besides Si, Al and O, there are metallic cations of low positive charge and relative large 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 uniform cavities, where there are abundant micropores of uniform size linked together. The molecules less than channel size could be adsorbed in the pores, on the contrary, these larger than the channel size will be excluded. Thus molecules of different size can be separated by means of sieving. Therefore this aluminosilicate is named as molecular sieve. Mixture of gases or compounds that flow through molecular sieve can be separated due to sieving effect.