During use, silica gel gradually loses adsorption capacity as it takes up water vapour or other substances from the media. It can be brought back to full performance through regeneration and reused.
1. Regeneration After Adsorbing Water Vapour
After adsorbing moisture, silica gel can be dried by thermal desorption. There are several heating methods — for example an electrically heated oven, waste heat from a flue, or hot-air drying. The desorption temperature should generally be controlled at 120–180 °C; for blue indicating silica gel, 100–120 °C.
The maximum regeneration temperature for various industrial silica gels should not exceed the following limits:
| Silica Gel Type | Maximum Temperature |
|---|
| Coarse pore silica gel | No higher than 600 °C |
| Narrow pore silica gel | No higher than 200 °C |
| Blue indicating silica gel | No higher than 120 °C |
| Al silica gel | No higher than 350 °C |
After regeneration, moisture content is generally held below 2% and the gel can be put back into service.
2. Regeneration After Adsorbing Organic Impurities
Roasting method: For coarse pore silica gel, heat gradually to 500–600 °C in a roasting furnace for about 6–8 hours until the particles turn white or yellow-brown. For narrow pore silica gel, the roasting temperature must not exceed 200 °C.
Rinsing method: Saturate the gel with water vapour, then soak and rinse in hot water, optionally with detergent, to remove waste oil or other organic impurities, then wash with clean water and dry.
Solvent flushing method: Select a suitable solvent according to the type of organic matter adsorbed, dissolve it out of the silica gel, then heat the gel to remove the solvent.
3. Points to Watch During Regeneration
- Increase temperature gradually when drying to avoid violent drying, which can crack the particles and reduce recovery.
- Over-high roasting temperatures change the pore structure and markedly reduce adsorption performance.
- For blue or colour-indicating silica gel, desorption should not exceed 120 °C, otherwise the indicator oxidises and loses its colour function.
- After regeneration, sieve out fine particles to keep the granule size uniform.
