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'''Molecular sieves''' are a type of material with very small holes of precise and uniform size. These holes are small enough to block large molecules, while allowing small molecules to pass. Although the term also encompasses [[silica gel]] and activated charcoal, this article will focus on the classic zeolite spherical beads.

==Properties==
===Physical===
Molecular sieves are generally white spheres, though they also come in the form of cylinders, of various sizes, though the most common type has a diameter or 2-3 mm. They are made of various materials, such as zeolite, or clays. The size of the sieves is measured in Angstroms (Å). They will absorb water and other fluids from various liquids or air. This process is reversible.

===Chemical===
Molecular sieves have no reactivity towards common solvents, but they will react with corrosive chemicals such as a acids.

==Availability==
Molecular sieves are sold by many chemical suppliers, as well as many industrial products sellers. Ebay is a good place to start.

Sometimes they can also be found inside the [http://www.sorbentsystems.com/desiccants_caps.html caps] of certain medical drug tubes.

A low grade form of molecular sieves can be acquired from [http://commercialrefrigeration.danfoss.com/assets/0/114/137/138/17179871081/17179873145/60a301d9-2c9f-4b21-87c1-a900d7b2bd9a.jpg fridge filter driers]. These beads require desorption in order to remove the water content, as well as washing them with an organic solvent to remove any traces of oil that tends to contaminate the drying column. If the driers come from an old fridge, they may contain freons, and purifying the sieves becomes complicated, as freons are toxic.

==Projects==
*Dry solvents
*Purify gas streams
*Reactor catalyst

==Handling==
===Safety===
Molecular sieves pose little toxicity as they're made of zeolite, which are also found in nature. If they have adsorbed any toxic gasses, such as freons, they may pose health problems.

===Storage===
In sealed bottles, just like any desiccant: away from any moisture or volatile compounds.

===Disposal===
They can be regenerated by heating them in a stream of fluid. Do not heat them too high, or they will crack.

==References==
<references/>
===Relevant Sciencemadness threades===
*[http://www.sciencemadness.org/talk/viewthread.php?tid=5958 molecular sieves]
*[http://www.sciencemadness.org/talk/viewthread.php?tid=13114 What molecular sieve sizes do I need for methanol, ethanol and diethyl ether?]
*[http://www.sciencemadness.org/talk/viewthread.php?tid=33458 Drying with molecular seives - how fast?]

[[Category:Lab equipment]]
[[Category:Desiccants]]