Sulfur compounds oxidations

Nickel Aluminum, aluminum(III) chloride, ethylene, 1,4-dioxan, hydrogen, methanol, nonmetals, oxidants, sulfur compounds... 

Desulfurization using purified enzymes Investigations into enzymatic desulfurization as an alternative to microbial desulfurization has revealed several enzymes capable of the initial oxidation of sulfur. A study reported use of laccase with azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a mediator for oxidation of DBT [181]. The rate of this reaction was compared to hydrogen peroxide-based phosphotungstic acid-catalyzed oxidation and the latter was found to be about two orders of magnitude higher. The authors also oxidized diesel oil sulfur to no detectable levels via extraction of the oxidized sulfur compounds from diesel. In Table 9, the enzymes used in oxidation of DBT to DBTO are reported. 

More specifically, the invention involves the use of Thiobacillus denitrificans under anaerobic conditions to oxidize sulfur compounds such as hydrogen sulfide to sulfate. The process may be carried out in various ways such as in a batch or a continuous bioreactor system using a suspended or an immobilized biocatalyst. The method is particularly applicable to treating natural gas containing hydrogen sulfide and producing a biomass byproduct. 

In ODS, sulfur compounds present in fuels are oxidized to more polar sulfones / sulfoxides to facilitate their removal by solvent extraction or adsorption. Various oxidation systems have been reported in the literature for this transformation. Among these oxidants like hydrogen peroxide (H2O2) and carboxylic acid as catalyst3"5. For the chemical industry, it becomes more and more important to develop cleaner technologies. Solvent extraction processes are used to separate sulfones / sulfoxides from oxidized fuels. These processes required suitable and selective solvents for separation of oxidized sulfur compounds from petroleum feedstocks. 

As discussed in Chapter 2 and in more detail in Chapter 11, a variety of organic sulfur compounds in addition to inorganics such as H2S and COS are emitted by biological sources. In the troposphere, they may ultimately be oxidized to S02 and H2S04. However, the chemistry of these compounds tends to be complex, and a variety of partially oxidized sulfur compounds is formed first. 

Hydrogen peroxide used over a wide pH range has been employed to oxidize sulfur compounds. The scope of the oxidation using hydrogen peroxide includes coupling of thiols to disulfides355 and thiols coupled with amines,356 which are used to produce industrially important compounds. For example, sulfenamides are accelerators for rubber vulcanization (Figure 3.91).357... 

With the exception of L. ferroxidans, the same microorganisms can also oxidize sulfur compounds. 

The evolution of photosynthetic oxidation of sulfur compounds permitted the development of the full microbial sulfur cycle in sulfureta. In this cycle, some bacteria and archaea reduce oxidized sulfur compounds, pumping them downward in the microbial mat, while other bacteria reoxidize them photosynthetically. The development of this cycle, coupled with the use of stored sulfur as a redox bank balance that could be exploited either way the redox budget swung during tidal and diurnal cycles, would have greatly expanded the thermodynamic power of the biosphere. 

Although DMS is only moderately soluble in rainwater, there has been some interest in the oxidation in the liquid phase, where modeling suggests that the multiphase reactions can be important. Ozone seems to be the most important oxidant, where there is a predicted lifetime for DMS of a few days in clouds. The oxidation reactions offer the potential for these heterogeneous processes to yield more soluble oxidized sulfur compounds such as DMSO and DMSO2 (Betterton, 1992 Campolongo e/u/., 1999). 

Corrosion of concrete by bacteria that oxidize sulfur compounds into sulfuric acid was reported by Parker (1945, 1947) and has been examined more recently by Fjerdingstad (1969). The lowest pH is tolerated by Thiobacillus concretivorus Parker (pH 2.75 + 0.42) and T. thiooxidans Waksman and Joffe (pH 2.35 0.32). Within 100 days of incubation in a T. thiooxidans culture, 60% of a 3.6 g block of concrete were dissolved. Bacterial destructive activity has also been established on buildings and monuments (Krum-... 

It is possible that parts of the dissimilatory pathway shown in Fig. 6.2.2 are induced in microorganisms not normally associated with dissimilatory reduction, in the presence of high concentrations of oxidized sulfur compounds. The particular case of Clostridium pasteurianum (McCready et al. 1975) is considered later (see p. 328). 

The ODS of hydrocarbon fuels consists of the conversion of sulfur compounds in the fuels by oxidation to element sulfur, sulfur oxides, sulfoxides, and/or sulfones followed by adsorption or abstraction separation of the oxidized sulfur compounds from the hydrocarbon fuels. The potential advantages for ODS are (a) the process does not need to use H2 gas (b) ODS takes place at relatively mild operating conditions in comparison with HDS or even at ambient conditions and (c) ODS is able to remove some refractory sulfur compounds, such as 4,6-DMDBT, that are difficult to be removed by HDS or selective adsorption. 

Recently, Ma et al.238 explored a novel ODS method of liquid hydrocarbon fuels, which combines a catalytic oxidation step of the sulfur compounds using molecular oxygen followed by an adsorption step to remove oxidized sulfur compounds in the treated fuel using an AC. The ODS of an MJF and a real JP-8 jet fuel was conducted in a batch system at ambient conditions. They found that the oxidation using... 

We know rather well the concentration of oxidized sulfur compounds (S02 and SOJ") over industralized North America and Europe as well as over the Atlantic Ocean. However, our knowledge of the concentration of reduced sulfur is much poorer because of analytical problems. 

Others such as pig liver microsomal FAD-containing monooxygenase have to be isolated from tissue with very low yields141 or like hydrocarbon monooxygenase from Pseudomonas oleovorans 12 131 require several protein components and cofactors, substantially limiting the use of these enzymes for the production of oxidized sulfur compounds. 

Reaction characteristics Heat removal 560 kJ mol Catalyst separation Heat removal ca 280 kJ mol Separation of large amounts of solids Separation of (soluble) oxidized sulfur compounds... 

Continued reaction, which is irreversible, forms oxidized sulfur compounds. After regeneration, the resin is occasionally treated with a rejuvenating solution (e.g., alkaline NaHS) to reverse reaction (6). 

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