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:
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.