AIR PURIFICATION THROUGH ACTIVATED CARBON
Technology for industrial air depuration through activated carbon establishes that for the process of solvent concentration it is preferred the use of activated carbon of plant origin, such as the one derived from the carbonization of coconut shells. This choice is linked to the higher ignition temperature of such materials, and related to the type of ash contained.
Among the principal properties of activated carbon of plant origin it is worth mentioning:
- specific surface area of the adsorbing active micropores usually around 1200 m2/g
- total porosity of micropores of 0.4 cm3/g
- extremely extended distribution of active micropores, between 0.4 and 2 nm
Moreover the specific extension of the micropores distribution allows the adsorption of a wide range of solvents and organic components, starting from acetone and methanol (more volatile) to heavy aromatics (less volatile).
Here follows an example: solvents with medium and high volatility, such as acetone and ethyl acetate, present in the air with a concentration of 0.3÷0.6 g/Nm3 at room temperature, are adsorbed into the activated carbon by coconut shells in concentrations of 10 ÷ 15% in weight of dry coal, and during the regeneration in air at 120°C are released at roughly 50 ÷ 60% of the initial level of the adsorbent.
Purchasing cost of activated carbon suitable for solvent concentration processing is 2 ÷ 4 €/kg. This type of carbon requires substitution or external regeneration treatment after 3,000 - 4,000 hours of use.
AIR PURIFICATION THROUGH HYDROPHOBIC ZEOLITE
When talking about hydrophobic zeolites, reference is made to inorganic synthetic adsorbents made of silica, whose crystalline matrix contains an orderly dense net of microchannels and micropores of intersection, whose dimensions, usually between 0.5 ÷ 1.5 nm, are constant as they form part of the orderly structure of the crystals.
A particle of hydrophobic zeolite, in a spheroid or cylinder shape of 1.6 mm, is made of single crystals or crystal aggregates of 1 ÷ 5 μm, bound and assembled by a clayey binder that is shaped in thin filaments and that extends onto the crystal surface like a containment net. Interstice between crystals constitute a continuous phase that wrap the crystals, thus forming macrocavities of 0.2 ÷ 0.5 μm.
Hydrophobic zeolites usually require external regeneration after 5-8 years of use, and purchasing cost is higher than the one for activated carbon.