Is it possible to regenerate the silica gel?
In industry it is common to regenerate silica gel in special ovens. In domestic use it should be borne in mind that by its nature, despite being completely inert, silica gel is a chemical compound and should not be used in environments where there is promiscuity with food such as domestic ovens. If you want to proceed with the regeneration at home it is therefore advisable not to use domestic ovens and to use a dedicated appliance for this operation.
Better to open the silica gel sachets
The regeneration of the bulk silica gel and clay can be performed in a normal microwave oven. However, it is important to regenerate only the silica gel or clay salts (bentonite) without the casing, that is, without the sachets that contain them, as the different materials that compose them are not suitable for thermal stress. In addition, the sachets in special Tyvek material allow moisture to permeate inside, but prevent any emission to the outside. Consequently, it is impossible to force the emission of water vapor from a sachet with a Tyvek wrap.
A Tyvek sachet placed in a microwave oven tends to swell like a balloon, precisely because the pressure of the water vapor, which cannot permeate outside, causes it to swell.
In the microwave oven the temperature of 90 ° can be exceeded to speed up the regeneration procedure, however it is better to always keep some limitations in mind so as not to exceed. The silica gel and activated clay can be regenerated at a maximum temperature of 120 ° C.
In reality, the dehydrating material has a much higher melting point but it must be borne in mind that at each regenerative cycle the silica gel crystal or the clay granule is subjected to a sort of thermal stress which progressively deteriorates its hygroscopic capacity. A regeneration at a temperature limited to a maximum of 120 ° is certainly slower but at the same time more conservative for the duration of the dehydrating product which can therefore be used for several cycles.
There is no precise and calculated maximum number of cycles in which the silica gel or clay permanently lose their effectiveness and must therefore be disposed of. Obviously, this loss of hygroscopic capacity occurs slowly. As an indication, if the regeneration temperatures are respected, the product can be reused for a few times.
Leaving the sachets overnight on the radiator or exposing them to the summer sun can perhaps be effective with very small sachets (around five grams) but with sachets of higher weights all this is practically useless. The common electric oven can be of some help with small quantities of silica gel, but regenerating the silica gel or bentonite in quantity involves a use of energy (time required for the oven to be used) that far exceeds the advantage of regeneration itself.
A separate discussion is the so-called "indicating silica gel", that is the silica gel with indicator, that is capable of turning color to signal the initial dry state and the exhausted and saturated state of water. "Silica gel with indicator" means brown silica gel and orange silica gel.
For this particular product, it is advisable to limit the oven temperature to no more than 100 ° because in addition to the single crystal it is also necessary to preserve the indicator substance in which the crystal itself is soaked. Therefore, silica gel with indicator can lose its hygroscopic capacity after each regenerative cycle, but at the same time it can discolour. With brown or orange silica gel, regeneration must therefore be carried out precisely and with caution, to preserve both the hygroscopic capacity of the material and the peculiar characteristic of visual indicator of the state of absorption of water in the crystal.
How can I verify that the regeneration has been completed?
With brown or orange silica gel, which contain the visual indicator, the procedure is all too simple: just observe when the crystal regains its original color, i.e. amber yellow for brown silica gel and orange for orange silica gel.
As far as the white silica gel is concerned, the only way is to check the weight.
To provide a clear understanding of the dehydrating capabilities of the various sachets and to understand exactly when they have reached the maximum amount of absorbable water we have prepared the following tables below.
The only way to understand the status of the sachets and check if they are still effective or are now exhausted and to be regenerated is to weigh them individually. Each sachet, based on the weight, is able to absorb a precise amount of water and this affects the total weight of the sachet. The sachet is therefore like an sfist that absorbs water while gaining weight. When the maximum indicative weight per sachet is reached, then it must be regenerated.