Adsorption Characteristics of Trace Volatile Organic Compounds in Gas Streams onto Activated Carbon Fibers

The adsorption characterstics of activated carbon fibers (ACF) prepared from phenolic precursors were examined. Three ACF with specific surface areas of 900, 1610, and 2420 m²/g were used to determine the adsorption of volatile organic compounds (VOC) over a range of concentrations in air or nitrogen gas streams. Gravimetric adsorption was used both to determine the ACF effective pore volume using several individual VOC saturated in nitrogen or air at atmospheric pressure and to determine adsorption isotherms of n-butane over a large range of concentrations (49.8 ppmv to 99.5 vol %) in nitrogen at atmospheric pressure and 25 °C. The experimental results showed that while for saturated adsorption results, where adsorption increased with increasing ACF specific surface area, at lower concentrations the ACF with the least specific surface area adsorbed more. This low concentration reversal was also observed with acetone (10.3 ppmv) in air and benzene (56.5 ppmv) in nitrogen. We conclude that this isotherm crossover results from the ACF activation process where the micropores are widened (and the specific surface area concomitantly increased) with increasing activation duration and that this crossover is in agreement with predictions of the Dubinin-Radushkevich equation. These results are important for the development and design of materials for low concentration adsorption applications such as maintaining and improving ambient air quality.