Sorbent impregnated filters

Galameau, E., Hamer, T., Shoeib, M., Kozma, M. and Lane, D. (2006) A preliminary investigation of sorbent-impregnated filters (SIFs) as an alternative to polyurethane foam (PUF) for sampling gas-phase semivolatile organic compounds in air. Atmospheric Environment, 40, 5734-40. 

Sorbent filters remove gas-phase air contaminants using either physical adsorption or chemical sorption. Physical adsorption results from the electrostatic interaction between a molecule of gas or vapor and a surface (NIOSH, 2003), and chemical sorption results from the reaction between a molecule of gas or vapor and a solid sorbent or reactive agents impregnated in the sorbent material. A variety of sorbents are available for different applications, and they vary in their abilities to remove different chemicals. 

Sorbent filters have several limitations. First, a sorbent filter could preferentially remove some chemicals in a mixture and allow other contaminants to pass through. Second, most sorbents do not perform as well under high humidity (for example, silica gel adsorbs water in preference to hydrocarbons, so that the adsorption of hydrocarbons is essentially blocked by water vapor). Third, adsorbent impregnation could lose reactivity over time, but determining when and to what extent this occurs is difficult. Fourth, sorbent filters are bulky, heavy, and expensive compared to particulate filters. Consequently, while particulate filtration is extremely common in buildings of all types and required by codes and standards, gas-phase filtration is uncommon in most buildings. 

Under extreme filtration conditions (temperature >150°C), impregnated charcoals suffer from an increasing desorption of radioiodine. For such severe conditions other iodine filter materials have been developed such as silver-containing inorganic sorbents which exhibit a very low desorption of iodine even under extreme conditions, since the adsorbed iodine is bound as the very stable chemical compound Agl. However, such conditions are far more severe than those to be expected in design basis accidents there is no need, therefore, to replace the impregnated charcoals by these expensive materials. 

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