Sulfur dioxide oxidation effects

Yamamoto, K., M. Seki, and K. Kawazoe. Effect of sulfuric acid accumulation on the rate of sulfur dioxide oxidation on activated carbon surface. Nippon Kaguku Kaiski 7 1268-2179, 1973. (in Japanese, summary in English)... 

Stockwell, W. R., The Effect of Gas-Phase Chemistry on Aqueous-Phase Sulfur Dioxide Oxidation Rates, J. Atmos. Chem., 19, 317-329 (1994). 

Several other reports have also shown the importance of effective catalyst wetting on the performance of a bench-scale trickle-bed reactor. Hartman and Coughlin37 concluded that for sulfur dioxide oxidation in qojjntercurrejQt trickle-bed reactor packed with carbon particles, the catalyst was not completely wet at low liquid flow rates (of the order of 5 x 10 4 cm s-1). Sedricks and Kenney86 found that, during catalytic hydrogenation of crotonaldehyde in a cocurrent trickle-bed reactor, liquid seeped. into dry palladium-on-alumina... 

The reverse-flow chemical reactor (RFR) has been shown to be a potentially effective technique for many industrial chemical processes, including oxidation of volatile organic compounds such as propane, propylene, and carbon monoxide removal of nitrogen oxides sulfur dioxide oxidation or reduction production of synthesis gas methanol formation and ethylbenzene dehydration into styrene. An excellent introductory article in the topic is given by Eigenberger and Nieken on the effect of the kinetic reaction parameters, reactor size, and operating parameters on RFR performance. A detailed review that summarizes the applications and theory of RFR operation is given by Matros and Bunimovich. 

Gorman, D. N., "The Effect of Organic Acids on the Sulfur Dioxide Oxidation," B.S. Thesis, University of Virginia... 

Nikolov, I., I. Vitanova, V. Najdenov, T. Milusheva, and T. Vitanov (1997). Effect of pyrolysis temperature of the catal54ic activity of active carbon -I- cobalt phthalocya-nines in sulfur dioxide oxidation by oxygen. J. Appl. Electrochem. 27, 77-82. 

Lewis et al. (1949) have discussed the three theories of browning presented by Stadtman (1948). They consider the theory that sulfur dioxide is effective because of preferential oxidation to be overruled by the fact that the sulfur dioxide was more effective under their anaerobic experimental conditions than when oxygen was present. Likewise, the theory that sulfur dioxide bleaches dark compounds during their forma-... 

Conventional industrial processes operate continuously and at steady state. Steady-state operation, however, is sometimes less economical, particularly in cases where considerable energy effects are encountered. For example, classical sulfur dioxide oxidation processes involve a large reactor-heat exchanger system to force conversion of the reactant to an acceptable level. By non-steady-state operation, the reactor volume can be considerably diminished. Unconventional operation modes are much more sensitive than conventional steady-state modeling. Very advanced dynamic modeling concepts are thus needed. 

At the tail end following flue gas desulfurization. Dust problems and sulfur dioxide oxidation were avoided but the gas had to be reheated for the catalytic NOX reduction to be effective. 

Hydrochloric acid reacts with sulfur only in the presence of iron to form hydrogen sulfide. Sulfur dioxide forms when sulfur is heated with concentrated sulfuric acid at 200°C. Dilute nitric acid up to 40% concentration has Htde effect, but sulfur is oxidized by concentrated nitric acid in the presence of bromine with a strongly exothermic reaction (19). 

A derivative of the Claus process is the Recycle Selectox process, developed by Parsons and Unocal and Hcensed through UOP. Once-Thm Selectox is suitable for very lean acid gas streams (1—5 mol % hydrogen sulfide), which cannot be effectively processed in a Claus unit. As shown in Figure 9, the process is similar to a standard Claus plant, except that the thermal combustor and waste heat boiler have been replaced with a catalytic reactor. The Selectox catalyst promotes the selective oxidation of hydrogen sulfide to sulfur dioxide, ie, hydrocarbons in the feed are not oxidized. These plants typically employ two Claus catalytic stages downstream of the Selectox reactor, to achieve an overall sulfur recovery of 90—95%. 

Metals and alloys, the principal industrial metalhc catalysts, are found in periodic group TII, which are transition elements with almost-completed 3d, 4d, and 5d electronic orbits. According to theory, electrons from adsorbed molecules can fill the vacancies in the incomplete shells and thus make a chemical bond. What happens subsequently depends on the operating conditions. Platinum, palladium, and nickel form both hydrides and oxides they are effective in hydrogenation (vegetable oils) and oxidation (ammonia or sulfur dioxide). Alloys do not always have catalytic properties intermediate between those of the component metals, since the surface condition may be different from the bulk and catalysis is a function of the surface condition. Addition of some rhenium to Pt/AlgO permits the use of lower temperatures and slows the deactivation rate. The mechanism of catalysis by alloys is still controversial in many instances. 

Health effects attributed to sulfur oxides are likely due to exposure to sulfur dioxide, sulfate aerosols, and sulfur dioxide adsorbed onto particulate matter. Alone, sulfur dioxide will dissolve in the watery fluids of the upper respiratory system and be absorbed into the bloodstream. Sulfur dioxide reacts with other substances in the atmosphere to form sulfate aerosols. Since most sulfate aerosols are part of PMj 5, they may have an important role in the health impacts associated with fine particulates. However, sulfate aerosols can be transported long distances through the atmosphere before deposition actually occurs. Average sulfate aerosol concentrations are about 40% of average fine particulate levels in regions where fuels with high sulfur content are commonly used. Sulfur dioxide adsorbed on particles can be carried deep into the pulmonary system. Therefore, reducing concentrations of particulate matter may also reduce the health impacts of sulfur dioxide. Acid aerosols affect respiratory and sensory functions. 

The deleterious effect of sulfur dioxide and sulfites in domestic water is increased corrosivity owing to the lowered pH. However, oxidation of sulfite to sulfate in aqueous solutions uses dissolved oxygen, and lliis may retard corrosion. While llte oxichition of sulfite and sulfiirous acid to sulfate and sulfuric acid in the atmosphere is an environmental concern, this reaction is too... 

From the results of other authors should be mentioned the observation of a similar effect, e.g. in the oxidation of olefins on nickel oxide (118), where the retardation of the reaction of 1-butene by cis-2-butene was greater than the effect of 1-butene on the reaction of m-2-butene the ratio of the adsorption coefficients Kcia h/Kwas 1.45. In a study on hydrogenation over C03O4 it was reported (109) that the reactivities of ethylene and propylene were nearly the same (1.17 in favor of propylene), when measured separately, whereas the ratio of adsorption coefficients was 8.4 in favor of ethylene. This led in the competitive arrangement to preferential hydrogenation of ethylene. A similar phenomenon occurs in the catalytic reduction of nitric oxide and sulfur dioxide by carbon monoxide (120a). 

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