Slurry reactor studies of homogeneous and heterogeneous reactions

Abstract

A dynamic model is derived for simultaneous, homogeneous and heterogeneous, first-order reactions in a slurry reactor. The theory is applied to experimental data for the oxidation (with gaseous oxygen) of aqueous sulfite solutions which is first order in oxygen and zero order in sulfite. The homogeneous reaction is very slow at low pH (2-3) where the sulfur exists as dissolved SO, or HS03-, even when cobalt is added as a homogeneous catalyst. At higher pH (7-8.5), considerable homogeneous reaction occurs with and without cobalt ions. Here the predominant species are SO3' and HS03-. Activated carbon is not a heterogeneous catalyst at pH 7 or 8.5, but is responsible for nearly all the reaction at the low pH values. Analysis of the heterogeneous data indicates that the surface reaction between adsorbed oxygen and SO2 controls the rate rather than adsorption of oxygen.

Oxidation of Sulfur Dioxide in Aqueous Suspensions of Activated Carbon

“…The observed independence of the rates on Cso2(aqj at fairly high concentrations of sulfur dioxide in the gas phase reported by Seabum and Engel (1973), Komiyama and Smith (1975a,b), Pavko et al (1981), Recasens et al (1984), Ahn et al (1985), Amadeo et al (1989), andFu et al (1989) can perhaps be as well explained by the rate model proposed here, where SC>2(aq) is not a reactant at all but competes for the active sites on the catalyst.…”

“…Therefore, reaction mechanisms based on s0s2such as the ones proposed by Fu et al (1989) are not applicable. There is no S0s2present at all.…”

“…There is no S032present at all. Therefore, reaction mechanisms based on SO32-such as the ones proposed by Fu et al (1989) are not applicable. Most of the investigations reported in the literature on the mechanism of the aqueous phase oxidation of sulfur dioxide are related to homogeneous catalytic reactions with catalysts such as Cu2+, Mn2+, Co2+ etc.…”

“…Activated carbon is reported to be an important catalyst for the aqueous phase oxidation (Hartman and Coughlin, 1972;Seaburn and Engel, 1973;Smith, 1975a, 1975b;Brodzinsky et al, 1980;Pavko et al, 1981;Recasens et al, 1984;Ahn et al, 1985;Goto and Kojima, 1985;Amadeo et al, 1989;Fu et al, 1989;Lu et al, 1990). The oxidation produces sulfuric acid which when recovered, being an important industrial chemical, might make the desulfurization process for pollution control even profitable.…”

“…The oxidation produces sulfuric acid which when recovered, being an important industrial chemical, might make the desulfurization process for pollution control even profitable. Activated carbon is reported to be an important catalyst for the aqueous phase oxidation (Hartman and Coughlin, 1972; Seabum and Engel, 1973; Smith, 1975a, 1975b;Brodzinsky et al, 1980;Pavko et al, 1981;Recasens et al, 1984;Ahn et al, 1985;Goto and Kojima, 1985; Amadeo et al, 1989;Fu et al, 1989;Lu et al, 1990). These reports have described rate models by considering that dissolved molecular sulfur dioxide (SO2-(aq)) gets oxidized.…”