More about Zeolites (Molecular Sieves)

Molecular sieves are desiccants with some differing properties to those of silica gel. With the appearance of small opaque pinkish beads, molecular sieves are synthetically produced, highly porous crystalline metalalumino silicates. They have many internal cavities that are linked by window openings of precise diameters. It is these diameters (measured in Ångstroms) that classify molecular sieves - 3Å, 4Å, 5Å, and 10Å (also known as 13X). Adsorption occurs only for molecules with smaller diameters than these cavity openings. Larger molecules will be excluded from adsorption. Preferentially adsorbed are molecules of greater polarity. This makes molecular sieves ideal for adsorption of water from air, as water molecules are both polar and very small. Molecular sieves will adsorb water molecules from liquids down to very low levels - often just 1 part per million1. Zeolites display some attractive properties as desiccants for use in the protection of MSDs, such as;

High rate of adsorption at low relative humidity

Wide temperature range of adsorption (They perform more effectively as moisture absorbs at higher temperatures (greater than 25°C) than silica gel does.)

They adsorb water vapour more rapidly than silica gel.
They will reduce water vapour to much lower levels than silica gel, making their use essential when a very dry product or atmosphere is required

Ability to retain physical shape and size even when saturated

Low dust generating properties
Zero toxicity
Chemically inert
Excellent ability to regenerate

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