Basics on the Regeneration of Silica Gel
Structure and function of silica gel
Silica gels have an amorphous microstructure and thus a wide pore radius distribution. Due to their polarity, silica gels belong to the hydrophilic adsorbents, which is also shown in their affinity to dipole molecules like e. g. water.
As the of water adsorption of silica gel is a physisorption, the water is not bound on the surface by strong van der Waals forces. Remaining chemically unchanged, the adsorbed water can easily be released.
Colour change of silica gel
The used indicators are pH-based indicators that belong to the organic dyes. They are characterized as weak acids or bases whereas each acid has a different colour than the corresponding base. Related to silica gel, this means that the pH-value is increasing with increasing water content and consequently the colour changes from orange to dark brown and black. This process is reversible. Changing the pH-value will restore the original colour.
Ageing by regeneration
If colourless silica gel with narrow pores is regenerated for trial at 150 °C, the equilibrium load is reduced by about 20 % and the half-life diffusion coefficient by 32 % after 100 cycles whereas the dry weight increases by 2 %.It is interesting that after about 100 cycles a limit value for the reduction of the equilibrium load and the apparent diffusion coefficient is reached, which does not significantly drop for up to 500 cycles. In short: The thermal treatment does not significantly affect the pore structure anymore after 100 cycles.
Proper use of desiccant
The humidity in your desiccator can be reduced most rapidly if you spread it on a big surface. The provided desiccant tray is best suitable for it. Please make sure that the desiccant surface is not higher than one centimeter. If you have to increase the desiccant quantity for your experiment, please take another tray.
Up to 16 g humidity can be absorbed by the SICCO desiccant within 24 hours.