Inorganic sulfur, forms

The selectivity toward sulfur compound structure was differently induced for the CB1 culture, than that of the CB2 culture. In the first case DBT was used as the sole sulfur substrate, while in the second case, biphenyl sulfide was employed. One might deduce then, the application of the CB1 strain for oil and CB2 strain for coal and heavy oils. Plasmid characterization and strain catalytic evaluation results indicated that oxidation of DBT by CB 1 is not plasmid mediated and that inorganic sulfur forms cannot be oxidized by CB 1. 

It is generally accepted that there are several forms of mineral sulfur, other than sulfate and pyritic, present in coals. Mossbauer studies of inorganic sulfur forms in coal have shown the presence of pyrrhotite (FeS) (2), and the presence of other sulfides such as sphalerite (ZnS), and chalcopyrite (CuFeS2) have been reported by other workers (3). Several investigators have reported as much as 1% sphalerite in some northwestern Illinois coals (4-6). The presence of elemental sulfur has also been reported (7-9V The failure to account for these mineral sulfur forms results in high values for organic sulfur using the ASTM method. 

Aspiras, R. B., D. R. Keeney, and G. Chesters. 1972. Determination of reduced inorganic sulfur forms as suphide by zinc-hydrochloric acid distillation. Anal. Lett. 5 425-432. 

When the data for initial materials are compared with that for the substrates after the system had been operating from October 23, 1987 to January 16, 1988, interesting changes have apparently occurred. In all sampling locations in all thr cells, there is a change from organic to inorganic sulfur forms. In Cell A, there is a major increase in the amount of total sulfur. 

Nonmeta.ls, Sulfur reacts with fluorine to yield the remarkably stable sulfur hexafluoride, SF. Operating conditions must be controlled because a mixture of the lower fluorides such as disulfur difluoride [13709-35-8] 2 2 disulfur decafluoride [5714-22-7] 2 10 sulfur tetrafluoride [7783-60-0] SF4, may also be formed. When this reaction is carried out between 310 and 340°C, SF is primarily obtained and essentially no SF and only trace amounts of lower fluorides. Below 300°C, and preferably at ca 275°C, SF is the primary product. At 450—500°C, a mixture comprising ca 50% SF and the lower sulfur fluorides is formed (see Fluorine compounds, inorganic-sulfur). 

Sulfur forms several series of haUdes with all of the halogens except iodine. The fluorides include the commercially important sulfur hexafluoride [2551-62-4] (see Fluorine compounds, inorganic). 

The simplest NHIP is rubredoxin, in which the single iron atom is coordinated (Fig. 25.9a) to 4 S atoms belonging to cysteine residues in the protein chain. It differs from the other Fe-S proteins in having no labile sulfur (i.e. inorganic sulfur which can be liberated as H2S by treatment with mineral acid sulfur atoms of this type are not part of the protein, but form bridges between Fe atoms.)... 

Sulfur in crude oils is mainly present in the form of organosulfur compounds. Hydrogen sulfide is the only important inorganic sulfur compound found in crude oil. Its presence, however, is harmful because of its corrosive nature. Organosulfur compounds may generally be classified as acidic and non-acidic. Acidic sulfur compounds are the thiols (mercap-tans). Thiophene, sulfides, and disulfides are examples of non-acidic sulfur compounds found in crude fractions. Extensive research has been carried out to identify some sulfur compounds in a narrow light petroleum fraction.Examples of some sulfur compounds from the two types are ... 

The products of incomplete combustion may be associated with particulate matter before their discharge into the atmosphere, and these may ultimately enter the aquatic and terrestrial environments in the form of precipitation and dry deposition. It is therefore essential to ensure total destruction of the contaminants, generally by raising the temperature. The spectrum of compounds that have been examined is quite extensive, and several of them are produced by reactions between hydrocarbons and inorganic sulfur or nitrogen constituents of air. Some illustrative examples involving other types of reaction include the following ... 

Mixtures of sulfur and potassium perchlorate, used in pyrotechnic devices, can be exploded by moderate impact. All other inorganic perchlorates form such impact-sensitive mixtures. 

The above mixture is incubated. The water-soluble salt contaminants would transfer from the fossil fuel into the aqueous phase during the procedure. Secondly, the biocatalytic agent would selectively break C—S bonds in the sulfur-bearing molecules to form water-soluble inorganic sulfur molecules. Both of these reactions occur without depleting the fossil fuel of combustible organic molecules and... 

Shell s microbiological desulfurization process is carried out by mixing coal with an aqueous biocatalyst solution [158], The coal considered in this invention concerns bituminous coal containing inorganic sulfur (pyritic).This process seems to be applicable to refinery pet-coke, which contains sulfur in the form of inorganic sulfides. Nowadays, when coke has become one of the major products of heavy oil and bitumens refining, such desulfurization processes might have potential uses. 

A brief historical note on the structure of the iron-sulfur clusters in ferredoxins is relevant. After the first analytical results revealed the presence of (nearly) equimolar iron and acid-labile sulfur, it was clear that the metal center in ferredoxins did not resemble any previously characterized cofactor type. The early proposals for the Fe S center structure were based on a linear chain of iron atoms coordinated by bridging cysteines and inorganic sulfur (Blomstrom et al., 1964 Rabino-witz, 1971). While the later crystallographic analyses of HiPIP, PaFd, and model compounds (Herskovitz et al., 1972) demonstrated the cubane-type structure of the 4Fe 4S cluster, the original proposals have turned out to be somewhat prophetic. Linear chains of sulfide-linked irons are observed in 2Fe 2S ferredoxins and in the high-pH form of aconitase. Cysteines linked to several metal atoms are present in metallothionein. The chemistry of iron-sulfur clusters is rich and varied, and undoubtedly many other surprises await in the future. 

Recently Bogolytsin and co-authors (62) found that the associations of sulfur dioxide and other inorganic sulfur derivatives interact with the aromatic nuclei of lignins, and strongly influence their reaction and redox behavior. This association effect also forms a selective pre-association state in the sulfonation reaction in wood pulping. It is evident that a wide range of similar association effects may be present, but they remain to be detected and studied. 

The third form of inorganic sulfur - the sulfate variety - is realitively unimportant in energy conversion. Fresh coal contains very little sulfate its presence is usually indicative of a weathered (oxidized) feedstock. Additionally, sulfate may be formed to a minor degree from other types of sulfur by moderate heating of the feedstock, by reaction with the bound oxygen in that feed. This effect can even occur under a hydrogen atmosphere. ... 

Cysteine not only is an essential constituent of proteins but also lies on the major route of incorporation of inorganic sulfur into organic compounds.443 Autotrophic organisms carry out the stepwise reduction of sulfate to sulfite and sulfide (H2S). These reduced sulfur compounds are the ones that are incorporated into organic substances. Animals make use of the organic sulfur compounds formed by the autotrophs and have an active oxidative metabolism by which the compounds can be decomposed and the sulfur reoxidized to sulfate. Several aspects of cysteine metabolism are summarized in Fig. 24-25. Some of the chemistry of inorganic sulfur metabolism has been discussed in earlier chapters. Sulfate is reduced to H2S by sulfate-reducing bacteria (Chapter 18). The initial step in assimilative sulfate reduction, used by... 

Sulfur. Undoubtedly, many of the reactions involve or are influenced by the presence of sulfur in the petroleufh-forming stages as they are in the formation of mineral accumulations (118). Indeed this critical stage of the formation of petroleum is profoundly influenced by the redox conditions established by the inorganic sulfur system. 

The biotransformations of sulfur compounds by microorganisms can have large-scale impacts on global chemistry. As an example, sulfate-reducing bacteria have, throughout histoiy, formed major deposits of elemental sulfur and iron sulfides on Earth, and these processes are continuing today (1). Contemporary sulfate-reduction coupled with the oxidation of reduced inorganic sulfur... 

---