Disproportionation of Chlorous Acid at a Strong Acidity

Abstract

Commercial chlorine dioxide generators are operated in an about 4.5-mol/L sulfuric acid solution. The chlorous acid disproportionation may be an important pathway to generate chlorine dioxide under such a condition. On the basis of the product determination, we found that, in the absence of a chloride ion, chloric acid, hypochlorous acid, and chlorine, rather than chlorine dioxide, are the products from the chlorous acid disproportionation. However, chloride addition to the chlorous acid solution under otherwise the same condition results in the generation of chlorine dioxide. The underlying mechanism of the chloride effect on the chlorous acid disproportionation is discussed.

Kinetics and Mechanism of the Decomposition of Chlorous Acid

“…Although elimination of the pH-dependent path does not increase the average deviation significantly (see Table 2), we have kept this process in the final model, because decreasing the pH increases the rate of decomposition of chlorous acid even in solutions containing 0.5-4.5 M sulfuric acid. 20 The third step (reaction 3) is the reaction of Cl 2 O 3 with chloride to produce hypochlorous acid and Cl 2 O 2 . This route shifts the stoichiometry in the presence of chloride toward higher SR values.…”

“…More recently, the decomposition of chlorous acid has been studied at high acidity 20 (4.5 M sulfuric acid solution), and the effect of chloride ion on chlorine dioxide formation has been discussed. 20,21 Except in the studies of Kieffer and Gordon, 5 only the concentration of chlorine dioxide was followed. Kieffer and Gordon followed the change of concentration of chlorous acid and chlorine dioxide simultaneously, but their mechanistic analysis and proposed rate equation were based on the consumption of chlorous acid only.…”

Identifying the chloroperoxyl radical in acidified sodium chlorite solution

“…xChlorine dioxide-based elemental chlorine-free (ECF) technology has long been the dominant process in the pulp and paper industry to produce bleached chemical pulps [ 1 , 2 ]. Chlorine dioxide is usually generated when sodium chlorate or sodium chlorite in highly acidic conditions is reduced using hydrochloric acid, sulfuric acid, and hydrogen peroxide [ 2 , 3 ].…”

“…It is well known that in an acidic solution of NaClO 2 , ClO 2 is formed by the following reactions [ 2 , 4 , 6 ]: …”

“…Eq (2) is the stoichiometry of the disproportionation of chlorous acid reported by several researchers [ 2 , 4 , 7 – 9 ]. This reaction under acidic conditions forms chlorate ions, chlorine dioxide, and chloride ions.…”