1. Regeneration of silica gel after water absorption
After silica gel adsorbs water, it can be removed by thermal desorption. There are many ways of heating, such as electric heating furnace, flue waste heat heating and hot air drying. The temperature of heat removal should be controlled at 120-180℃, and 100-120℃ for blue gel indicator, discolored silica gel and blue silica gel. The maximum temperature of various industrial silica gels during regeneration should not exceed the following limits:
Coarse porous silica gel should not be higher than 600℃.
Fine porous silica gel should not be higher than 200℃.
Blue gel indicator agent (or discolored silica gel) should not be higher than 120℃.
Silica-aluminium gel must not be higher than 350℃.
The water content of regenerated silica gel is generally controlled below 2% and can be reused.
2. Regeneration of organic impurities adsorbed by silica gel
(1) roasting method
For coarse porous silica gel, it can be gradually heated to 500-600 C in a calciner for about 6-8 hours.
The colloidal particles are white or yellowish brown. For fine porous silica gel, the calcination temperature should not exceed 200 C.
(2) rinsing method
Silica gel is absorbed in saturated water vapor, soaked and rinsed in hot water. Waste oil or other organic impurities can be removed by using detergent, and then dried and dehydrated after washing with clean water.
(3) Solvent washing method
According to the kinds of organics adsorbed by silica gel, the organics adsorbed in silica gel are dissolved by appropriate solvents, and then the silica gel is heated to remove the solvents.
3. Problems to be noticed in regeneration of silica gel
(1) When drying and regeneration, attention should be paid to gradually raising the temperature so as not to cause the colloidal particles to burst and reduce the recovery rate.
(2) When the silica gel is roasted and regenerated, excessive temperature will cause the change of pore structure of silica gel, which will obviously reduce its adsorption effect and affect its application value. For blue gel indicator or discolored silica gel, the temperature of desorption and regeneration should not exceed 120 C. Otherwise, the chromogenic effect will be lost due to the gradual oxidation of the chromogenic agent.
(3) The regenerated silica gel should be screened to remove the fine particles in order to make the particles uniform.