Gas-phase filtration is used to remove gaseous pollutants from air flows. Unlike particle filters, which capture solid or liquid particles, gas-phase filters must remove individual molecules and vapours from the air. Typical pollutants include hydrogen sulphide, sulphur dioxide, nitrogen oxides, ozone, ammonia and volatile organic compounds (VOCs).
Separation is primarily achieved through adsorption onto highly porous materials with a very large internal surface area. The most commonly used adsorbent is activated carbon. Through chemical impregnation, specific pollutants can be selectively bound or converted. In addition to activated carbon, zeolites, potassium permanganate media and ion-exchange materials are also used.
The performance of a gas-phase filter depends on various factors. These include the pollutant concentration, the air flow rate, the residence time of the air in the filter, the temperature and the relative humidity. As the adsorption capacity is limited, gas-phase filters have a finite service life and must be regularly monitored and replaced.
The ISO 10121 standard is used internationally to evaluate and classify gas-phase filters. It describes test methods for adsorption media and complete filter systems. Furthermore, in corrosion-critical applications, corrosivity measurements in accordance with ANSI/ISA 71.04 are frequently carried out.
Gas-phase filtration is used in numerous sectors today. These include data centres, industrial production facilities, cleanrooms, hospitals, museums, airports and water and wastewater treatment plants. By reducing corrosive and odourous gases, it helps to protect people, buildings, technical installations and sensitive electronic components. At the same time, it helps to minimise operational downtime, reduce maintenance costs and increase the reliability of critical infrastructure.