Molecular sieves are transition metal aluminosilicates with a uniform pore crystalline structure. Molecular sieves operate on the size exclusion principle. Smaller molecules that fit into the pores are adsorbed while larger molecules pass through. Molecular sieves have regular pore openings of 3, 4, 5, or 10 Angstroms. Polarity of the molecules matter because the highly polarized molecules are adsorbed more readily into the pores than non-polar molecules. Molecules are selectively removed in this manner.  Sepcor provides 3A molecular sieves for insulated gas, olefin drying, and polyurethanes.  4A molecular sieves for drying gases, natural gas, and hydrocarbon liquids, 5A molecular sieves for dehydration and removal of CO2, and H2S; Isosiv units, and pressure swing adsorption for hydrogen purification.  13X Zeolites for polar molecules from a variety of hydrocarbon streams and for air prepurification.