Silica gel Orange – Green

Silica gels are the most commonly used desiccants and consist of 99% silicon dioxide (SiO2). For the ventilation of hydraulic units, gearboxes, storage tanks, transformers, etc., the silica gel orange-green is the most suitable desiccant due to its high water absorption capacity of up to approx. 40% of the dry mass, easy regeneration in the oven, harmless handling and good high-contrast color indicator.

With a granule size of 2-5 mm spheres, the pressure build-up is very low as well as the gap volume is optimal to ensure a very good contact of the water molecules to the silica gel surface. Thus, with a properly designed adsorber, dew points as low as -40°C can be achieved.

The regeneration temperature of silica gel orange-green is 120°C.

Depending on the selection of the color indicator in the silica gel, the drying efficiency and the maintenance interval of an adsorber can be influenced. A selection can be made from very strong drying and a short maintenance interval to weaker air drying and a long maintenance interval.

Other silica gels

Silica gel Orange – Colorless
Silica gel White

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Chemical properties

Chemical name: Amorphous silicon dioxide
Composition: SiO2
CAS number: 112926-00-8

Narrow-pore
Appearance and shapeRound, solid balls
Grain size3 – 5 mm
Bulk density0,75 – 0,85 kg/l
Pore volume0,35 – 0,45 ml/g
Breaking strength> 200 N
Specific surface600 – 800 m²/g
Silicon dioxide (SiO2)99%
Trace elements1%
Water adsorption capacity> 370 ml/kg

Equilibrium loading

The combination of narrow-pore silica gel and water corresponds to a convex isotherm type. The isotherm exhibits a steep slope. The monomolecular occupancy of the silica gel is completed at about 30%, after which multilayer occupancy of the adsorbent surface and capillary condensation take place. At an adsorption capacity of about 35% it takes a plateau and increases only slightly.

Adsorption isotherms of narrow-pore and wide-pore silica gels

Isotherms of narrow-pore silica gel at 20°C, 40°C, 60°C

Color indicators

Silica gel is dyed with an indicator to visually indicate the loading of water vapor. The metal salt cooper chlorid is used. When water is adsorbed on the surface of the silica gel, the granules changes the color.

Color change of silica gel Orange-Green

0%

5%

10%

15%

20%

40%

Regeneration

In practice, the most common regeneration method is temperature increase. When desorbing water vapor from silica gel, the temperature must be above 100°C. For silica gels without a color indicator, a regeneration temperature between 150°C and 175°C is recommended. However, color indicators would be damaged at these temperatures. For silica gels with color indicator, a regeneration temperature of 121°C to a maximum of 140°C is therefore recommended.

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