Gas Phase Filters

Gas phase filters are a comparatively newer concept in the air filtering field. Gas phase filters are used for removing gases and associated odors, which is produced by the gases emitted from building materials, cooking gas, perfume, paints etc. However, they aren't capable of removing air particulates and allergens. All other filters, like mechanical filters, electronic filters, hybrid filters mostly emphasize on removing particulates from the air and they aren't intended towards removing the gases and odors.

They can also protect against other gases, like those emitted by chemicals (e.g. nitric oxide, formaldehyde, hydrogen sulfide, etc.), manufactured goods (e.g. cleaning solutions, carpet glue, etc.) or even gas emitted by organic compounds.

Working of Gas Phase Filters
The gas phase filters are fitted with a chemical filter, which is designed to remove pollutant gases and from the air. They work on two principles, one is physical adsorption and other is absorption or chemisorption. These processes help to remove certain solvent vapors, odors, and low concentrations of gases and vapors in indoor air.

• Physical Adsorption (Physisorption): Physical adsorption is a type of adsorption in which the adsorbate (here gases and odors) adheres to a surface through weak intermolecular interactions. It is completely a physical process. The surfaces here are solid adsorbents, like activated charcoal, silica gel, activated alumina, zeolites, porous clay minerals, molecular sieves, etc. They are useful adsorbents because of their large internal surface area, stability, and low cost.
  
  
• Chemical Adsorption (Chemisorption): Chemisorption is a chemical process in which the adsorbent attracts gas molecules onto its surface. It involves electron transfer and a bond is formed between the adsorbing surface and the adsorbed molecule. Once the contaminant gaseous molecules are chemically binded, they cannot escape back into the air stream. Chemisorption is irreversible because the individual components are consumed and new product is formed. It is usually slower than physical adsorption because of the complexity of the process.

Adsorbent Types
Various types of adsorbent materials are used in gas phase filters to adsorb the harmful gases from air.

• Activated Carbon: It is widely used as the adsorbent material in the gas filters. It has large surface areas and varied pore sizes.
  
  
• Silica Gel & Alumina: They have lower surface area but they act as a good base for impregnations. They are good specially for polar compounds.
  
  
• Zeolite (Natural and Man-made): Zeolites have uniform pore sizes for special agents, organic solvents and low MW-halides.
  
  
• ASZM-TEDA Carbon: They are activated carbon impregnated with copper, zinc,silver, molybdenum, etc.