Adsorption Characteristics
Selective Adsorption of Water and other Polar Substances
The up-take of water or other species in zeolites is called adsorption and functions on the basis of physisorption. The main driving force for adsorption is the highly polar surface within the pores. This unique characteristic distinguishes zeolites from other commercially available adsorbents, enabling an extremely high adsorption capacity for water and other polar components even at very low concentrations.
In addition, the pore size plays a significant role, allowing or prohibiting the entrance of molecules to the pore system.
The adsorption on molecular sieves is therefore dependent on the following physical molecular properties:
- Size and Shape: Molecules larger than the pore opening of the molecular sieve can not be adsorbed, smaller molecules can.
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Molecular Polarity: Molecules with large polarity or polarisability can be adsorbed preferentially under identical conditions
Of note is the high capacity of Grace Davison´s Molecular Sieves even at low water concentration, allowing to dry to very low water contents. The Grace Davison molecular sieve can retain its high capacity at high temperature, which makes it the optimal material if drying needs to be carried out at comparatively high temperatures.
The adsorption process is fully reversible and of purely physical nature. The structure of the zeolite stays intact during the adsorption process (and its later regeneration), and dissolution effects like with other drying agents like calcium compounds can not happen.