The influence of porosity and polarity on the adsorption of volatile organic chemicals by activated carbons

Full text of publication follows: The dynamic adsorption properties of activated carbons containing a variety of pore size distributions surface polarities have been studied. The aim of the study was to identify the optimum carbon porosity and polarity for adsorption of volatile organic chemicals from humid air streams. Carbons were prepared using a combination of templating [1] and controlled rate activation [2] techniques. Variations in the activating agent and conditions also enabled different levels of surface polarity to be incorporated. In this way, highly meso-porous and highly microporous carbons were prepared, with a range of mixed micro/meso-porous carbons also being studied in order to assess the effects of pore size and pore size distribution on the dynamic adsorption properties. The carbons were characterised using static nitrogen and water adsorption isotherms. Carbons (ca. 100 mg) were packed into 0.45 mm diameter tubes and tested in a flowing air stream against several volatile hydrocarbons. Breakthrough was analysed using gas chromatography or mass spectrometry. Testing was carried out in dry (RH≤10%) or humid (RH80%) air streams in order to assess the impact of pre-adsorbed water vapour on the performance of each of the carbons. Total uptakes from dynamic testing have been shown to correlate with adsorption isotherm data for the hydrocarbons, measured using a Hiden Isochema Intelligent Gravimetric Analyser (IGA). The data have been used to assess the ease with which pre-adsorbed water can be displaced, thereby enabling the effect of carbon porosity on filtration under realistic conditions to be studied. [1] Han, S.J., Kim, M., Hyeon, T.; 'Direct fabrication of meso-porous carbons using in-situ polymerized silica gel networks as a template'; Carbon, 41, 2003, 1525-1532; [2] Dawson, E.A., Parkes, G.M.B., Barnes, P.A., Chinn, M.J.; 'an investigation of the porosity of carbons prepared by constant rate activation in air'; Carbon, 41, 2003, 571-578. (authors)