Tag Archive | activated carbon

Removing gas pollutants; let’s talk Tech!

Three main technologies are used to remove gaseous pollutants. They have different operating principles, energy requirements, potential side effects and efficiencies. Below is a basic description of these technologies.

Photo catalytic oxidation (PCO)

How does it work?

PCO technology uses ultraviolet light (UV) on a catalytic surface (often titanium oxide TiO2). It triggers the formation of  highly reactive species (hydroxyl radicals, ions, ozone,etc. ), which enable VOCs to be decomposed into CO2 and water.

Are there potential side effects?

UVPCO generates ozone, which is harmful in itself (increasing the risk of respiratory diseases) and may also react with other organic compounds to form harmful by-products such as formaldehyde. Alcohols can also create poisoning of the catalyst and cause incomplete oxidation leading to production of aldehydes or unwanted species.

Sorbents

How does it work?

Solid sorbents are materials with large internal surface, enabling electrostatic interaction between the gas molecules and a surface. Some examples include activated charcoal, silica gel, activated alumina, lithium chloride, zeolites to porous clay minerals. Gaseous pollutants removed by physical sorbents include ozone, nitrogen dioxide or VOCs (except low molecular weight carbon compounds such as formaldehyde and ammonia).

For chemisorption gas filters, the working principle is similar but in addition, a bond-forming chemical reaction between the adsorbed gas pollutant molecule and the adsorbing surface occurs, involving electron transfer. One common chemisorbent is potassium permanganate, an active oxidating reagent. It  can convert formaldehyde into water and carbon dioxide. The efficiency of the sorbent, measured via the rate of adsorption, decreases with the amount of pollutants captured. Similarly to mechanical air filters, sorbents require energy to pull the air through.

Are there potential side effects?

Carbon filters have high biocompatibility and microorganisms may multiply on filters.

Plasma cluster ions 

How does it work?

One type of ion generator is called cluster generators or plasma generator (the term DBD or Dielectric Barrier Discharge may also be used). It uses AC discharges to produce clouds of positive and negative ions successively. Electrons are separated from oxygen molecules and the electrons are combined with the oxygen molecules to produce oxygen cations and anions. The oxygen anions react with water in the air and produce reactive species, which then agglomerate and form ion clusters. Ion clusters can damage the surface of airborne microbial and oxidize gaseous volatile organic compounds and PM.

Are there potential side effects?

Ion generators may generate ozone and undesired by-products.  Plasma systems tend to be very popular and displace UVPCO systems although they use a lot more energy.

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