ADSORPTION OF SULFUR-DIOXIDE BY ACTIVE-CARBON TREATED BY NITRIC-ACID - II - EFFECT OF PREHEATING ON THE ADSORPTION PROPERTIES

The adsorption and desorption of sulfur dioxide by active carbon, trea ted by nitric acid and followed by heating at 200-1000 degrees C, were studied. The HNO3 treated carbon has a higher adsorption capacity for sulfur dioxide, than the untreated carbon, in spite of its lesser bas icity. This may be the result of interaction of the SO2 with the oxyge nated surface groups of acidic character. Water promotes the adsorptio n of SO2. Heating results in a decrease of the carbon acidity because of decomposition of the surface oxygenated structures. It also leads t o an increase of basicity resulting from the formation of basic sites. These changes of the carbon acid-base properties are particularly pro nounced for the HNO3 treated carbon due to higher concentration of the surface oxygenated groups. The increased basicity promotes adsorption of SO2 and inhibits desorption by an acid-base mechanism different fr om the mechanism of adsorption on the carbon, which has not been prehe ated. (C) 1997 Elsevier Science Ltd.