Molecular Sieve

Why is molecular sieve the best desiccant that money can buy? Molecular sieve, also known as synthetic alumina silicate is a unique adsorbent in that it has a very unique pore structure. This product has been developed so that differentiation in actual pore openings can be as small as one angstrom (1 angstrom = 1/1000 of a human hair). It is by far the best choice in terms of desiccant for those companies looking to maintain the lowest possible relative humidity (RH).

Why is Molecular Sieve the best desiccant?

Molecular sieves retain their ability to adsorb water vapor molecules over a much wider spectrum of temperatures as compared to other desiccant media and also have a much higher equilibrium capacity for water vapor under very low RH conditions. Molecular sieves contain a uniform network of crystalline pores and empty adsorption cavities, which give it an internal adsorptive surface area of 700-800gm² (½ the total volume of the crystals). Due to its uniform structure, molecular sieves will not release any trapped water vapor back into the environment or package as readily as silica gel or clay as temperatures rise.

Unlike indicating silica gel which will turn from blue to pink as it becomes saturated with water vapor, indicating molecular sieve turns from blue to beige. The following is a helpful list of molecules that the various types of molecular sieves will adsorb:

3A: NH₃, H₂0, (not C₂H₆), good for drying polar liquids
4A: H₂0, Co2, SO₂, H₂S, C₂H₄, C₂H₆, C₃H₆, EtOH. Will not adsorb C₃H₈ and higher hydrocarbons. Good for drying nonpolar liquids and gases
5A: Adsorbs normal (linear) hydrocarbons to n-C₄H₁₀, alcohols to C₄H₉OH, mercaptans to C₄H₉SH. Will not adsorb isocompounds or rings greater than C₄
13X (pore size 10A): Adsorbs di-n-butylamine (not tri-n-butylamine. Useful for drying HMPA