THE PREPARATION AND PROPERTIES OF SOME CHLORINATED ACTIVATED CARBONS .2. FURTHER OBSERVATIONS

The adsorptive properties of chlorinated coal or nutshell carbons depend on the chlorination temperature. Chlorination at about 180-degrees-C, followed by extraction with water or methanol, yields carbons that have similar adsorption properties and are relatively hydrophobic compared to the controls. Under these conditions, stable surface carbon-chlorine complexes are formed, and the function of extraction is solely to displace strongly physically adsorbed chlorine. At lower chlorination temperatures, the hydrophobicity of the carbon surface is dependent on the chemical used for the extraction step; compared to the controls, the carbon surface is relatively hydrophilic after extraction with water and relatively hydrophobic after extraction with methanol. It is probable that at chlorination temperatures below about 180-degrees-C, weak carbon-chlorine complexes form, which chemically react during extraction. Chlorination at low temperatures may therefore offer a way of introducing different functional groups onto carbon surfaces. Unlike the controls, none of the treated carbons degrade (age) during storage in high humidity air. The suitability of carbons chlorinated at about 180-degrees-C for vapour filtration in situations where ageing effects degrade adsorption performance is confirmed from break-through measurements using chloropicrin, toluene, and carbon tetrachloride. Such carbons also afford some resistance to oxidation with the pollutant NO2.