Adsorbent: The material upon whose surface the adsorption takes
place is called an adsorbent. Mostly activated carbon is used as an adsorbent
Adsorbents are used usually in the form of spherical pellets,
rods, moldings, or monoliths with hydrodynamic diameters
between 0.5 and 10 mm.
They must have high abrasion resistance, high thermal stability
and small pore diameters, which results in higher exposed
surface area and hence high surface capacity for adsorption.
The adsorbents must also have a distinct pore structure which
enables fast transport of the gaseous vapors.
Most industrial adsorbents fall into one of three classes:
Oxygen-containing compounds are typically hydrophilic and
polar, including materials such as silica gel and zeolites.
Carbon-based compounds are typically hydrophobic and nonpolar,
including materials such as activated carbon and graphite.
Polymer-based compounds are polar or non-polar functional
groups in a porous polymer matrix.
Activated carbon is used for adsorption of organic substances and
non-polar adsorbates and it is also usually used for waste gas (and waste
water) treatment. It is the most widely used adsorbent since most of its
chemical (eg. surface groups) and physical properties (eg. pore size
distribution and surface area) can be tuned according to what is needed. Its
usefulness also derives from its large micropore (and sometimes mesopore)
volume and the resulting high surface area.