Sulfur aqueous-phase oxidation

Lind, J. A., and A. L. Lazrus, Aqueous Phase Oxidation of Sulfur IV by Some Organic Peroxides, EOS Trans., 64, 670 (1983). 

Another link between halogen and sulfur chemistry is the formation of S(VI) within particles. Aerosol particles grow, among other processes, by uptake of SO2 in cloud droplets where it is oxidized to sulfate. The most important aqueous phase oxidants for S(IV) are often thought to be H2O2 and O3 (e.g., Seinfeld and Pandis, 1998) with O3 being important only for pH > 6. Some authors state that oxidation by O3 is the dominant process for the formation of non-sea-salt sulfate in sea salt particles... 

Other evidence for low Archean atmospheric oxygen concentrations come from studies of mass-independent sulfur isotope fractionation. Photochemical oxidation of volcanic sulfur species, in contrast with aqueous-phase oxidation and dissolution that characterizes the modem sulfur cycle, may have been the major source of sulfate to seawater in the Archean (Farquhar et al., 2002 Farquhar et al., 2000). Distinct shifts in and in sulfide and sulfate from... 

Calvert (2 ) has pointed out that gas-phase reactions of SO2 with ozone (O3), hydroxyl radical (OH ), and hydroperoxyl radical (HOp ) are too slow to account for the aforementioned rates of sulfate production. Consequently, the catalytic autoxidation of SO2 in deliquescent haze aerosol and hydrometeors has been proposed as a viable non-photolytic pathway for the rapid formation of sulfuric acid in humid atmospheres (30-35). In addition, hydrogen peroxide and ozone have been given serious consideration as important aqueous-phase oxidants of dissolved SO2 as discussed by Martin (35). Oxidation by H2O2 seems to be most favorable under low pH conditions (pH < 4) because of a rapid rate of reaction anc[ a negative pH-dependence that favors the facile conversion of HSO3 to sulfate. 

The Sulfolin process is an aqueous phase oxidative H2S removal process closely related to the Stretford technology. It was developed by Linde AG for gas streams having a relatively low hydrogen sulfide concentration. The first conunercial application of the Sulfolin process was in 1985 at the Sasol II sulfur recovery plant in Secunda, South Africa. The unit consisted of one train designed for 171,000 scfm (275,000 Nm /hr) of feed gas and 110 metric TPD of sulfur production (Heisel and Marold, 1987). 

The target was treated with sodium hydroxide solution, iodide carrier added, and the target dissolved with 30% hydrogen peroxide. After evaporation of the solution to near dryness, the iodine was converted to ICl by treatment with hydrochloric acid and sodium chlorate, and the monochloride extracted into butyl acetate. The iodine was back-extracted into water with sulfurous acid and the iodide in the aqueous phase oxidized to the elemental state by acidified sodium nitrite. It was then extracted into toluene. Following back-extraction of the iodine with aqueous sulfurous acid, La(0H)2 and Fe(OH)0 scavenges were carried... 

The anhydride can be made by the Hquid-phase oxidation of acenaphthene [83-32-9] with chromic acid in aqueous sulfuric acid or acetic acid (93). A postoxidation of the cmde oxidation product with hydrogen peroxide or an alkaU hypochlorite is advantageous (94). An alternative Hquid-phase oxidation process involves the reaction of acenaphthene, molten or in alkanoic acid solvent, with oxygen or acid at ca 70—200°C in the presence of Mn resinate or stearate or Co or Mn salts and a bromide. Addition of an aHphatic anhydride accelerates the oxidation (95). 

After epoxidation, propylene oxide, excess propylene, and propane are distilled overhead. Propane is purged from the process propylene is recycled to the epoxidation reactor. The bottoms Hquid is treated with a base, such as sodium hydroxide, to neutralize the acids. Acids in this stream cause dehydration of the 1-phenylethanol to styrene. The styrene readily polymerizes under these conditions (177—179). Neutralization, along with water washing, allows phase separation such that the salts and molybdenum catalyst remain in the aqueous phase (179). Dissolved organics in the aqueous phase ate further recovered by treatment with sulfuric acid and phase separation. The organic phase is then distilled to recover 1-phenylethanol overhead. The heavy bottoms are burned for fuel (180,181). 

Snia Viscosa. Catalytic air oxidation of toluene gives benzoic acid (qv) in ca 90% yield. The benzoic acid is hydrogenated over a palladium catalyst to cyclohexanecarboxyhc acid [98-89-5]. This is converted directiy to cmde caprolactam by nitrosation with nitrosylsulfuric acid, which is produced by conventional absorption of NO in oleum. Normally, the reaction mass is neutralized with ammonia to form 4 kg ammonium sulfate per kilogram of caprolactam (16). In a no-sulfate version of the process, the reaction mass is diluted with water and is extracted with an alkylphenol solvent. The aqueous phase is decomposed by thermal means for recovery of sulfur dioxide, which is recycled (17). The basic process chemistry is as follows ... 

Because phenols are weak acids, they can be freed from neutral impurities by dissolution in aqueous N sodium hydroxide and extraction with a solvent such as diethyl ether, or by steam distillation to remove the non-acidic material. The phenol is recovered by acidification of the aqueous phase with 2N sulfuric acid, and either extracted with ether or steam distilled. In the second case the phenol is extracted from the steam distillate after saturating it with sodium chloride (salting out). A solvent is necessary when large quantities of liquid phenols are purified. The phenol is fractionated by distillation under reduced pressure, preferably in an atmosphere of nitrogen to minimise oxidation. Solid phenols can be crystallised from toluene, petroleum ether or a mixture of these solvents, and can be sublimed under vacuum. Purification can also be effected by fractional crystallisation or zone refining. For further purification of phenols via their acetyl or benzoyl derivatives (vide supra). 

There are well over 100 gaseous and aqueous phase reactions that can lead to acid formation and more than fifty oxidizing agents and catalysts may be involved. However, in the simplest terms sulfur in fuels is oxidized to SO2, and SO2 in the atmosphere is further oxidized and hydrolyzed to sulfuric acid. Most nitric acid is formed by the fixation of atmospheric nitrogen gas (N2) to NO. (NO and NO2) during high temperature combustion, followed by further oxidation and hydrolysis that produces nitric acid in the atmosphere. These materials can be dry-... 

A biosorption method for the separation of sulfur compounds from fossil fuels, by using a sulfur-biosorption agent and followed by the oxidation of the biosorbed complex. The oxidation is carried out in an aqueous phase containing an effective amount of oxygen and, optionally a biocatalyst, in which case an incubating stage is incorporated for the reaction to take place. 

Oxidation of these model sulfur compounds was studied without solvent to investigate the chemical structure of the products using S K-edge XANES. A solvent free tri-phase (organic/ H202aq./catalyst) was used under the described conditions. Figure 1 shows the XANES spectra from the organic and aqueous phases as well as reference materials. The thiophene oxidized to thiophene-sesquioxide [3a,4,7,7a-tetrahydro-4,7-epithiobenzo[b]-thiophene 1,1.8-trioxide ] first.. The sesquioxide solid precipitated from the solvent free reaction mixture and was identified by NMR, IR and C,H,S elemental analytical. The sesquioxide oxidized to sulfate. 2-MT and 2,5 DMT also oxidized to... 

The crude tetrachloride mixture of zirconium and hafnium is dissolved in ammonium thiocyanate solution. The solution is extracted with methyl isobutyl ketone (MIBK). MIBK is passed countercurrent to aqueous mixture of tetrachloride in the extraction column. Halhium is preferentially extracted into MIBK leaving zirconium in the aqueous phase. Simultaneously, zirconium tetrachloride oxidizes to zirconyl chloride, ZrOCb. When sulfuric acid is added to aqueous solution of zirconyl chloride, the chloride precipitates as a basic zirconium sulfate. On treatment with ammonia solution the basic sulfate is converted into zirconium hydroxide, Zr(OH)4. Zirconium hydroxide is washed, dried, and calcined to form zirconium oxide, Zr02. 

As discussed in Chapters 7, 8, and 9, there are a number of free radical species whose reactions in the aqueous phase drive the chemistry of clouds and fogs. These include OH, HOz, NO-, halogen radicals such as Cl2, sulfur oxide radicals, and R02. Generation of these radicals in the liquid phase for use in kinetic... 

FIGURE 7.14 Model-estimated increase in S(IV) oxidation in the aqueous phase of sea salt particles due to the uptake and reactions of NO,. O, taken as 40 ppb, NO, as 0.1 ppb, and H202 as 0.05 ppb. The Y-axis is the calculated ratio of oxidized sulfur, S(VI), formed in droplets when NO, chemistry is included to that when it is not (adapted from Rudich et al., 1998). 

Other species that can initiate this sulfur oxidation chemistry are N03 (discussed in Chapter 7.D.1) and ClJ. The latter radical anion is formed in sea salt particles when atomic chlorine is generated and reacts with chloride ion. In addition, Vogt et al. (1996) have proposed that oxidation of SO2- by HOC1 and HOBr in sea salt particles may be quite important. Table 8.13 summarizes the aqueous-phase chlorine chemistry that occurs in sea salt particles and Table 8.14 the oxidation of S(IV) by reactive chlorine and bromine species in solution. 

While the emphasis has been on oxidation of DMS and other reduced sulfur compounds in the gas phase, there is some indication that oxidation in the aqueous phase in clouds and fogs should also be considered. For example, Lee and Zhou (1994) have shown that DMS reacts with 03 in aqueous solutions quite rapidly, with a rate constant at 288 K of 4 X 108 L mol-1 s-1. They estimate that at 30 ppb 03, a level found globally, the lifetime for in-cloud oxidation of DMS is about 3 days, of the same order of magnitude as that for the gas-phase oxidation by OH (see Table 8.17). Given the moderately high solubility of not only DMS but other sulfur compounds as well (see Henry s law constants in Table 8.1), this is clearly an area that warrants further research. 

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