GeeJay Chemicals have been UK manufacturers of desiccant silica gel sachets since 1984.
Silica gel adsorbs moisture from an enclosed space to help prevent moisture damage to items in transit or store.
Standard sachet sizes (in grams) are : 1/2, 1, 3, 5, 10, 25, 50, 100, 250, 500, 1,000 and 2,500.
They are available filled with non-indicating (white) or self-indicating (mostly orange to green but also orange to colourless and blue to pink) silica gels.
Custom made packing, shapes and weights of sachet are made to order.
These include sachets with hanging tapes,
sachets to Def Stan 81-68/4 or MIL-D-3464E
and sachets in bandoliers or individually overwrapped in foils or polybags.
Bulk packs of silica gel also available in sizes 500g, 1kg, 3kg, 4kg, 10kg, 12.5kg, 25kg and 150kg.
Bulk packs are foils / tubs / tins or drums of silica gel that is used loose rather than in sachets.
Applications will include breather units, desiccators even flower drying or food uses (icing and pastry craft).
Molecular sieves are crystalline, highly porous aluminosilicates.
Their crystal structure is a three dimensional pore system with identical pores of precisely defined diameters. These characteristics give the molecular sieve desiccant some unique properties not found in other conventional desiccants:
Highest moisture capacity at low relative humidity (<30% RH).
Fastest rate of moisture pick up.
Capability to selectively adsorb water (and/or other molecules).
Best desiccant at high temperatures
Their unique internal structure acts like a sponge in terms of porosity and internal surface. As the adsorption occurs on this internal surface, the component must physically pass though the molecular sieve pore openings to be adsorbed. As the size of these pore openings are all the same, the molecules are 'sieved' out on passing through, hence the name, molecular sieve.
There are a number of defined pore sizes commercially available.
These are normally designated by the molecular sieve pore size i.e. 3A, 4A, 5A and 10A (this last type is also known as 13X). A is an Angstrom or 0.1 nanometers.
Note the pore size in desiccant silica gel ranges from 5A to 100A.
The properties of molecular sieves make them very useful in many applications but they do have some drawbacks when compared to silica gel:
Total adsorption only about 20% w/w compared with 40% w/w with silica gel
Not easy to regenerate – require high temperatures, high pressure or dry, hot gas streams
Not available in self-indicating forms
Examples of the applications of the differing molecular sieve grades are :
Grade 3Å. Dries unsaturated gases and organic liquids (e.g methanol).
Used to remove water from cleaning fluids in ultrasonic baths.
Grade 4Å. Is a general dryer of liquids and natural gases. Also an excellent adsorber of carbon dioxide.
Grade 10Å (13X). Is used in air prepurification (due to its high water and carbon dioxide adsorption capacity)
and also adsorbs sulphur compounds ('sweetens'). It will remove decomposition products following
the quenching of arcing in electrical products.