Desiccants

Desiccants

Desiccants

The technically used adsorbents have a very large inner surface compared to the outer surface. The inner surface consists of submicro-, micro-, meso- and macropores and can take up several 100 m2/g. For adsorption to be economical, the adsorbent must fulfil a number of criteria. Among other things, a high useful capacity and a high selectivity for certain adsorptives are required. The selectivity of adsorbents is based on three effects:

  • Equilibrium effect: one component is more strongly bound to the adsorbent than another because the interaction forces between the adsorbent and the adsorptive molecules are different strong.
  • Steric effect: only adsorptive molecules smaller than the pore diameter of the adsorbent can penetrate the adsorbent.
  • Kinetic effect: one component is adsorbed faster than another component.

In addition, a favourable desorption behaviour and good regenerability must be taken into account when selecting adsorbents. Other important criteria include high abrasion resistance and good sorption stability. As a result of different processing methods, a large number of technical adsorbents with various properties can be produced. Silica gel and molecular sieve have established themselves for the gas phase adsorption of humidity due to their hydrophilic properties.The following table summarises the physical data of these two water-absorbing adsorbents.

Spezification Silica gels Molecular sieves
Bulk density [kg/m³] 300 - 850 400 - 900
True density [kg/m³] 2200 2100 - 2600
Apparent density [kg/m³] 750 - 1250 1100 - 1300
Grain porosity 0,45 - 0,65 0,5 - 0,6
Inner surface [m²/g] 100 - 850 350 - 1100
Mean pore diameter[nm] 2 - 10 0,3 - 0,75
Pore volume [cm³/g] 0,35 - 0,95 0,2 - 0,7
Desorption temperature [°C] 120 - 250 200 - 300

 

 

adsorbentien-glaeser-reihe

 

Further information about silica gels at ...

... Homepage: https://www.giebel-adsorber.de/en/products/adsorbents-silicagel
... Blog: https://blog.giebel-adsorber.de/trockenmittel/
... Documents: https://www.giebel-adsorber.de/en/knowledge/support

 

Further information on molecular sieves can be found at ...

... Homepage: https://www.giebel-adsorber.de/en/products/molecularsieve-adsorbents
... Blog: https://blog.giebel-adsorber.de/molekularsiebe/
... Documents: https://www.giebel-adsorber.de/en/knowledge/support