Dynamic adsorption on activated carbons of SO2 traces in air: I. Adsorption capacities

Sulphur dioxide is an atmospheric pollutant which, among numerous others, has to be eliminated by habitacle filters. Breakthrough curves of low concentration SO2 streams through beds of activated carbons have been obtained. Two carbons were studied, an activated PAN fiber (CF) and a granulated activated carbon (CN) under SO2 concentrations lower than 100 ppm. Carbon CN used ‘as received’ is able to trap SO2 in air at concentrations as low as 2.5 ppm. At this concentration, the adsorption of SO2 is essentially irreversible. The fraction of reversibly adsorbed SO2 rapidly increases when SO2 content in air increases from 2.5 to 100 ppm. As expected, the amounts of SO2 adsorbed per gram of carbon are much smaller than in the case of high SO2 contents in air (>1000 ppm). The presence of water in carbon micropores enhances both reversible and irreversible adsorption of SO2. The reversibly adsorbed part is physisorbed while the irreversibly adsorbed part results in oxidation of SO2 at the carbon surface. This oxidation was evidenced by TPD from carbon samples after adsorption. The mechanism of SO2 adsorption is discussed in relation to the mechanisms proposed in literature for high SO2 contents (>1000 ppm).