Inhibition of Aquated Sulfur Dioxide Autoxidation by Aliphatic, Acyclic, Aromatic, and Heterocyclic Volatile Organic Compounds

Abstract

The oxidation of dissolved sulfur dioxide, sulfur(IV), by oxygen proceeds through the involvement of sulfoxy radicals among which sulfate radical anion is the main chain carrier. When organics are present, they inhibit the oxidation of sulfur(IV) via scavenging of SO4− radicals. In contrast to previous studies, which were limited mostly to aliphatic compounds, this paper presents the results of the effect of 13 new volatile organic compounds (VOCs) including aromatic and heterocyclic on uncatalyzed sulfur(IV) autoxidation at pH 8.2 and 25°C. In all cases, the kinetics was first order in the presence and absence of VOCs and experimental rate law was Eq. (1). trueright−d[normalSfalse( IV false)]/normaldt=k obs []normalSfalse( IV false)=ko[]normalSfalse( IV false)/{}1+Bfalse[ Inh false]where −d[S(IV)]/dt is the rate of sulfur(IV) disappearance, kobs is the first‐order rate constant in the presence of inhibitor, ko is the first‐order rate constant in the absence of inhibitor, [S(IV)] is concentration of sulfur(IV) at time, t, and B is an inhibition parameter. VOCs cause inhibition by scavenging sulfate radical anions, which propagate the autoxidation chain. An analysis of B (Eq. (1)) and kinh (Eq. (2)) values for 21 aliphatic, aromatic, acyclic, and heterocyclic organic compounds showed that these to be related by Eq. (3) for a subgroup and Eq. (4) for b subgroup. trueright SO 4−+ VOC 0.33em⟶k inh 0.33em SO 42−+ VOC a subgroup (benzamide, 2,2‐dimethyl‐1‐propanol, 1‐hexanol, methanol, ethanol, 1‐propanol, 2‐ propanol, 1‐butanol, 2‐butanol, ethylene glycol, rebaudioside A) truerightB=()0.87±0.21×10−30.16emk inh b subgroup (o‐toluic acid, m‐toluic acid, p‐toluic acid, 4‐hydroxybenzoic acid, 1‐heptanol, glycerol, sucralose, acesuifame K, glycine, 3‐pentanol) truerightB=()1.2±0.3×10−30.16emk inh

Kinetics of the Oxidation of Hydrogen Sulfide by Atmospheric Oxygen in an Aqueous Medium

“…Our attempt failed to find the rate constants of radicals HO 2 /O 2 with any anthropogenic VOCs studied here and this rules out their inhibitory action as noted by us. This is in contrast to sulfite autoxidation in which the anthropogenic VOCs scavenge the sulfoxy radicals [40,41] and strongly inhibit the oxidation.…”

“…(3) A big difference in two studies is the effect of organic free radical scavengers. Whereas, S(IV) reaction is strongly inhibited due to scavenging of sulfate radical anion, SO 4 - [40,41] , H 2 S oxidation is not affected significantly. The latter observation does not require the invocation of free radicals in the present study.…”

“…This led us to look afresh into the atmospheric chemistry of H 2 S oxidation and to examine the effect of several parameters such as reactant concentrations, pH and importantly the effect of some anthropogenic volatile organic compounds(VOCs) particularly those which are reported to strongly inhibit the oxidation of aqueous SO 2 by oxygen in laboratory water. The oxidation kinetics of aqueous SO 2 and effect of VOCs has been studied by several groups [3,8,[40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] .…”

Efficient Inhibition of S(IV) Oxidation in a Novel Basic Aluminum Sulfate Regenerative Flue Gas Desulfurization Process by Ethylene Glycol: Kinetics and Reaction Mechanism

“…Additionally, the S(IV) antioxidation reaction could be induced by additives, such as volatile organic compounds. 23 In particular, high attention has been paid to various alcohols since 1989, such as methanol, ethanol, propanol, and butanol. 24 Besides, carboxymethyl, glycerol, cellulose, and formaldehyde could decelerate the S(IV) oxidation rate.…”

“…Furthermore, the catalytic S­(IV) oxidization can be significantly quickened by transition metals (e.g., Fe 2+ , Mn 2+ , Co 2+ , and Cu 2+ ) or organic acids (peracetic acid). − To avoid the loss of these traditional catalysts in practice, some novel supported catalysts can be used to promote the sulfite oxidation, such as metal nanoparticles on graphitic C 3 N 4 and cobalt nanoparticles over nonporous TiO 2 , which are recyclable and can effectively accelerate the oxidation rate of MgSO 3 . Additionally, the S­(IV) antioxidation reaction could be induced by additives, such as volatile organic compounds . In particular, high attention has been paid to various alcohols since 1989, such as methanol, ethanol, propanol, and butanol .…”