Adsorption and adsorbed species of SO2 during its oxidative removal over pitch-based activated carbon fibers

Adsorption and adsorbed species of SO 2 in humid air during its oxidative removal were studied over pitch-based activated carbon fibers (ACFs) to clarify the reaction scheme of continuous removal of SO 2 , influence of reaction variables, and origin of activity enhancement by the calcination in inert atmosphere. The temperature-programmed desorption of SO 2 adsorbed species suggests that when both oxygen and water were present, the main species on ACF was hydrated SO 3 (H 2 SO 4 ), which desorbed in the form of SO 2 around 300 °C, and that the presence of both increased the amount of species by oxidizing and hydrating the adsorbed SO 2 , which desorbed around 60 °C without oxidation and 200 °C with oxidation but without hydration. The amount of adsorbed H 2 SO 4 over ACF stayed at the same level after 25 h of reaction by balancing elution and adsorption of H 2 SO 4 to allow the steady removal of SO 2 . More water enhanced the adsorption of SO 2 at the initial stage but reduced the amount of adsorbed H 2 SO 4 at the steady state, eluting out H 2 SO 4 faster than the adsorption of SO 2 to keep more active sites open over ACF at the steady state. Hence, complete removal was achieved. A higher calcination temperature significantly increased the rate and amount of both oxidative and oxidative/hydrating adsorption, explaining the largest activity of ACF calcined at 1100 °C. The amounts of adsorbed SO 2 and evolved CO from OG-20As by calcination at 500-1000 °C are well correlated, indicating that the evolved CO creates an adsorption site on the ACF surface. A similar but different correlation was obtained among ACFs of different surface areas calcined at different temperatures.