Desiccants

Desiccants

Desiccants

The adsorbents used industrially have a very large inner surface compared to the outer surface. The inner surface is composed of submicron, micro, meso and macropores and can occupy a few 100 m2 / g. For adsorption to be economical, the adsorbent must meet some criteria. Thus, among other things, a high useful capacity and a high selectivity for certain adsorptive 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.
  • Steric effect: only adsorptive molecules that are smaller than the pore diameter of the adsorbent can penetrate into the adsorbent.
  • Kinetic effect: one component is adsorbed faster than another component.

In addition, in the selection of adsorbents a favorable desorption behavior and a good regenerability must be considered. Other important criteria are, for example, a high abrasion resistance as well as a good sorption stability. As a result of different processing methods, a variety of technical adsorbents with a wide variety of properties can be produced. For the gas phase adsorption of humidity, silica gel and molecular sieve have prevailed due to their hydrophilic properties. The following table summarizes the physical data of these two water-absorbent 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

 

 

Further information on silica gel can be found on our homepage as well as in our blog. More documents can be found here. More detailed information on molecular sieves can also be found on our homepage or in our blog. You can find more documents about the molecular sieves at this link.