PORESPHERE™ AL-W enables efficient adsorption at high humidity levels and has an adsorption capacity of 35% as well as the ability to adsorb liquid water. It is a high-purity, narrow-pore silica gel with added alumina, which is specifically used for efficient moisture absorption and resistance to liquid water. The product can also be used under difficult conditions such as high humidity or exposure to moisture. PORESPHERE™ AL-W is often used in gas treatment, in environments with very high humidity, or in environments with a lot of condensation. This product has no color indicator, and the corresponding saturation with moisture must be determined. This silica gel is often used in gas treatment, process air drying, the chemical industry, or energy storage.
1. Microstructure and pore structure
PORESPHERE™ AL-W is a silica gel based on an amorphous, three-dimensional network of silicon dioxide (SiO₂). This silica gel contains an addition of aluminum oxide (Al₂O₃), which changes the chemical composition and surface polarity. In PORESPHERE™ AL-W, Si–O–Al bonds (aluminol groups) form in some places instead of the usual Si–O–Si bridges (silanol groups) found in conventional silica gel. These heteroatomic bonds are more energetically stable and have significantly higher hydrolysis resistance. This results in significantly higher hydrothermal stability. The pore structure leads to a slight shift towards more stable mesopores (2–50 nm), which facilitates the mobility of water.
2. Adsorption behavior
ORESPHERE™ AL-W exhibits characteristic adsorption behavior on polarized surfaces without forming chemical bonds (physisorption rather than chemisorption). The partially negatively and positively charged particles in the silanol and aluminol groups and the resulting dipole character attract highly polar water molecules to the surface. Due to the larger number of mesopores compared to narrow-pore zeolite type A, water can quickly diffuse into the interior of the beads. Although the maximum equilibrium loading is slightly lower, this silica gel is particularly suitable for high humidity or processes that require rapid drying.
Since adsorption is based on physical interactions, it can be easily reversed. PORESPHERE™ AL-W can be completely regenerated by increasing the temperature..
Temperature dependence
As with any other silica gel, the adsorption capacity of PORESPHERE™ AL-W is temperature dependent.
| Temperature / C° | |
| < 20 | Maximum capacity high, adsorption rate lower |
| 20 – 60 | Maximum capacity high, adsorption rate lower |
| > 60 | Equilibrium loading decreases, adsorption rate increases |
3. Regeneration
PORESPHERE™ AL-W can be regenerated at a temperature of 140°C. To do this, the beads should be heated evenly over several hours. Temperatures below 100°C are not sufficient to completely regenerate the dry beads, while temperatures above 180°C can damage the pore structure.
Thermal regeneration of silica gel and vacuum regeneration are possible.
4. Resistance to water
PORESPHERE™ AL-W has been specially developed to remain stable even when in direct contact with liquid water. Conventional materials, on the other hand, lose their functionality when in direct contact with water because the surface is damaged. They swell up and the beads can even break.
