Adsorption of SO₂ on bituminous coal char and activated carbon fiber

The SO₂ adsorption behaviors of activated carbons produced from Illinois coal and of commercially prepared activated carbon fibers (ACFs) were compared. There was no relation between surface area of coal-based carbons and SO₂ adsorption, whereas adsorption of SO₂ on the series of ACFs was inversely proportional to N₂ BET surface area. Higher surface area ACFs had wider pores and adsorbed less SO₂; thus, pore size distribution is thought to play a significant role in SO₂ adsorption for these materials. Oxidation with HNO₃ and/or H₂SO₄, followed by heat treatment at 700−925°C to remove carbon−oxygen complexes, resulted in increased SO₂ adsorption for both coal chars and ACFs. This behavior was explained by an increase in the available number of free sites, previously occupied by oxygen and now available for SO₂ adsorption. The use of nitrogen-containing functional groups on ACFs of proper pore size shows promise for further increasing SO₂ adsorption capacities. Knowledge of the relationship among the number of free sites, pore size, and surface chemistry on corresponding SO₂ adsorption should lead to the development of more efficient adsorbents prepared from either coal or ACFs.