Adsorption of SO₂ on Bituminous Coal Char and Activated Carbon Fiber

Abstract

The SO 2 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 SO 2 adsorption, whereas adsorption of SO 2 on the series of ACFs was inversely proportional to N 2 BET surface area. Higher surface area ACFs had wider pores and adsorbed less SO 2; thus, pore size distribution is thought to play a significant role in SO 2 adsorption for these materials. Oxidation with HNO 3 and/or H 2 SO 4, followed by heat treatment at 700−925 °C to remove carbon−oxygen complexes, resulted in increased SO 2 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 SO 2 adsorption. The use of nitrogen-containing functional groups on ACFs of proper pore size shows promise for further increasing SO 2 adsorption capacities. Knowledge of the relationship among the number of free sites, pore size, and surface chemistry on corresponding SO 2 adsorption should lead to the development of more efficient adsorbents prepared from either coal or ACFs.