Prediction of VOC adsorption performance for estimation of service life of activated carbon based filter media for indoor air purification

The importance of adsorptive purification of the gas phase in HVAC-systems has constantly increased over the last few years, because people spend a large part of the day indoors. During this time they can be exposed to a variety of harmful gaseous contaminants, e.g. volatile organic compounds (VOC), which negatively influence health. Adsorptive HVAC-filters can help to reduce the concentration levels of noxious gases. For the comparison of HVAC-filter media the standard ISO 10121-1 determines test procedures. In ISO 10121 toluene is suggested as representative test substance for VOC at concentrations of 9 or 90 ppm in conditioned air (23 degrees C, 50% RH). The test concentrations in the standard tests are clearly higher than VOC concentrations in real buildings in order to limit testing times and to avoid being dependent on highly sensitive measurement technology. In this study, a methodology was investigated that forecasts breakthrough curves of toluene at concentrations down to 0.09 ppm predicted from measurement data at normatively proposed higher concentrations. The results can be used to estimate the service life of adsorptive filter media. The prediction is based on the isotherm equations of Langmuir, Freundlich or Dubinin-Radushkevich and the Wheeler-Jonas equation. The methodology was validated using three commercially available activated carbon based filter media. Good agreement between prediction and experimental data was achieved for s-shaped and moderate agreement for convex breakthrough curves. For the prediction of the equilibrium, the Freundlich and Dubinin-Radushkevich equation have proven to be accurate.