Adsorption and Adsorbed Species of SO₂ during Its Oxidative Removal over Pitch-Based Activated Carbon Fibers

Abstract

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.

Preparation of activated carbon fibers from polyvinyl chloride

“…Mochida et al developed a unique process for De-SO x from flue gas, in which ACFs were used to recover aq. H 2 SO 4 continuously [7][8][9][10][11][12][13]. It has also been being paid much attention to by a few of researchers to obtain more information about removal of SO 2 over AC and ACFs to understand deeply it [14][15][16][17][18].…”

Air oxidation effects on microporosity, surface property, and CH4 adsorptivity of pitch-based activated carbon fibers

“…Both the structural specialty and the surface chemistry of ACFs significantly influence their specific/nonspecific adsorption properties, catalytic performance, or their performance as catalytic supports. ACFs with tailored surface chemistry or subsequent surface modification with active species such as metal oxides/hydroxides or noble metals were found to be excellent SO 2 adsorbents under high moisture conditions to form sulfuric acid in the micropores (which can be easily removed from carbon surface by water flushing) [14][15][16][17], adsorbents for supercritical gases such as NO [18,19], CH 4 , etc. [20,21], and efficient catalysts for room-temperature NO reduction [22].…”

Surface chemistry of a viscose-based activated carbon cloth modified by treatment with ammonia and steam

“…The woven and knitted forms allow effective and rapid electrical thermal conditioning. ACFs are more suitable for the recovery of sulfuric acid at room temperature than granular activated carbon because the diffusion of sulfuric acid is much easier in the pores of the fiber [6][7][8][9][10]. However, in the case of ACF modified with ammonia and steam, a part of SO 2 would remain non-desorbable by distilled water extraction at ambient temperature [11].…”