Silica gels are the most common desiccants and consist of 99% silica (SiO2). For use in ventilation dryers for ventilation of hydraulic power units, gears, storage tanks, transformers, etc., the silica gel is orange-green due to the high water absorption capacity of up to approx. 40% of the dry mass, a simple regeneration in the furnace, safe handling, and of the good contrast color indicator, the most suitable drying agent.
With a granule size of 2-5 mm spheres, the pressure build-up is very low and the gap volume optimal to ensure a very good contact of the water molecules to the silica gel surface.
With a properly designed adsorber, dew points of up to -40 ° C are achieved. 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. It can be selected from very strong drying and short maintenance interval to a weaker air drying and a long maintenance interval.
- Hydraulic units
- Storage tanks
- Barrel & IBC
|Product flyer||Safety data sheet||Safety data sheet||Safety data sheet||Customs information|
|Orange - Green||Orange - Colourless||White|
Material and technical data
- Chemical designation: Amorphous silicon dioxide
- Composition: SiO2
- CAS-Number: SiO2 63231-67-4
|Appearance and shape||Round, solid balls||Round, solid balls|
|Grain size||3 - 5 mm||3 - 5 mm|
|Bulk density||0,75 - 0,85 kg/l||0,60 kg/l|
|Pore volume||0,35 - 0,45 ml/g||0,70 ml/g|
|Crushing strength||> 200 N||-|
|Specific surface||600 - 800 m²/g||300 m²/g|
|Silicon dioxide SiO2||99%||99.8%|
|Water adsorption capacity||> 370 ml/kg||> 750 ml/g|
Combining fine-pore silica gel-water corresponds to a convex isotherme type. The isotherme shows a steep rise. The mono molecular occupancy of the silica gel is complete at about 30%, then takes a multi-layered occupation of adsorbent surface and capillary instead. At an adsorption capacity level of about 35% it occupies as a plateau and rises slightly.
Regeneration of silica gels
In practice, the most common method used to regenerate silica gel is to increase the temperature. In the desorption of water vapor from silica gel, the temperature must be above 100°C. Recommended for regeneration are temperatures between 150°C to 175°C. However, bearing in mind that one is damaged in the silica gel applied color indicator at these temperatures. Therefore, a regeneration temperature is specified from 121°C for silica gel with color indicator and should not exceed 140°C.
For visual display of loading with steam silica gel is dyed with an indicator.
Frequently pH indicators are used. In the adsorption of water on the surface of the silica gel, the pH value changes.
This change causes a change in color of the indicator. Further, iron and the heavy metal salts of cobalt (II) chloride are used.
|Color indicator||Color indicator||Hesitation|
|Orange -> Green||pH-indicator||harmless|
|Orange -> Colorless||pH-indicator||critical|
|Blue -> Pink||Heavy metal||critical|
|Orange -> Red||pH-indicator||harmless|
|Blue -> Red||pH-indicator||harmless|