Gas purification techniques

Regenerative adsorption zeolite

 This material forms a good adsorbents for polar substances (for example: water and water soluble substances). By removing aluminum zeolite become hydrophobic and can absorb apolar substances such as VOC. Hydrophobic zeolite can be produced by synthetic under form of crystallization from 1 µm up to 1 mm in diameter. These crystal are tied up to larger grains to reduce the air capacitance of the bed. Because synthetic zeolites are expensive in comparison with natural zeolites they are generally only applied as hydrophobic zeolite or zeolite catalysts. The principle of adsorption like an active carbon is also
considered to the zeolite as a bed. In contrast to active cabbage zeolite are not used one-off and are not afterwards destroyed after saturation, but zeolite are used for applications with regeneration of the zeolite. This is blamed to the cost of the zeolite. 
Zeolite can be obtained with pore sizes of 0.3 - 3 nm. This pore size is uniform for one type zeolite. Zeolite will adsorb no molecules which are larger than the pore size. Also molecules for which are no affinity will not be adsorbed.

Figure: zeolite adsorption

Zeolite are possible used  with active carbon or polymers where
the polymer or the active carbon works at the higher concentrations
and the zeolite as polishing at the lower concentrations. This can become carried out by making a mixture of adsorbentia several beds after each other or by in one bed.
The advantages of zeolite adsorption are:

• High efficiency of VOC disposal

• Very arranged at low VOC concentrations

• Simple and robust technology

• Arranged for discontinue processes

• Easy maintenance

• Easy to place

The disadvantages are:

• Substance can ensure constipations

• Mixtures of components can ensure a fast disruption

• Risk of fires in the bed (ketones, terpentines)

Zeolite are mainly used in concentration applications.
The more concentrated degas must be further treated by means of
combustion or condensation. These concentrators have been applied in degasses of needle cabins, process emissions from enamel producers.

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