Reduced organic sulphur compounds

Hydrogen sulphide This is produced by the putrefaction of organic sulphur compounds or by the action of sulphate-reducing bacteria in anaerobic conditions (e.g. in polluted river estuaries). It is fairly rapidly oxidised to SOj and concentrations are considerably lower than those of (Table 2.6). Nevertheless it is responsible for the tarnishing of copper and silver at normal atmospheric concentrations. 

A difficult condenser-tube corrosion problem arises from the use of polluted cooling waters from harbours and estuaries that may be severely contaminated. All condenser-tube materials are liable to suffer corrosion in these circumstances, and the choice of materials is made difficult by the fact that different orders of merit apply at different locations and even at the same location at different times. The state of the water when the tubes first enter service may well determine whether or not a satisfactory fife will be obtained". The most corrosive waters are those containing free hydrogen sulphide produced by the action of sulphate-reducing bacteria. Waters may also be rendered abnormally corrosive by the presence of small amounts of organic sulphur compounds produced by bacterial action, as shown by Rogers". 

Sulfinol process A regenerative process used to remove or reduce the level of hydrogen sulphide, carbon dioxide, carbonyl sulphide, and other organic sulphur compounds such as mercaptans from natural gas. It involves gas absorption with solvents in which the gas is contacted countercurrently in an absorption column with the solvent The scrubbing process uses di-isopropanolamine dissolved in a mixture of sulfolane (C H SO ) and water. Regenerated solvent is introduced at the top of the absorber The solvent in which... 

Sulphur cannot be utilised by the body. It is absorbed in the form of SOf ions by a number of micro-organisms and is reduced to sulphur compounds. The main sources of sulphur are meat, fish, eggs, liver, cereals, dairy foods, nuts and leguminous plants. Sulphur is present in the body in the form of variotis organic compoimds, hormones, coenzyme A, keratin etc. It is present in the living cells as essential amino acids, pol eptides and sulphur iron proteins. 

T. roseopersicina is a phototrophic purple sulphur bacterium the strain marked BBS has been isolated from the cold water of the North Sea. Its anaerobic photosynthesis uses reduced sulphur compounds (sulphide, thiosulfide, or elementary sulphur), but it can also grow on organic compounds (sugar, acetate) in the dark. The bacterium contains a nitrogenase enzyme complex, thus it is capable of fixing atmospheric N2, a process accompanied by H2 production [Vignais et al., 1995],... 

The application of 33S NMR spectroscopy to the qualitative characterization of sulphur compounds in coals and petroleum has been another subject of a certain interest.99-10 The presence of organic and inorganic sulphur derivatives in variable amounts in fuels has serious economic and environmental consequences. Coals and crude oils can be treated chemically to reduce sulphur content, and it is of fundamental importance to develop an analytical method to rapidly and accurately analyse sulphur before and after the desulphurization process. 

Organic sulphur- and nitrogen-compounds in motor fuels are a source for acid rain and harmful to the environment. Moreover, they are poisonous to the auto exhaust catalysts. To meet new developments in EU regulations on the S-concentration, a commonly applied one-step hydrodesulfurization (HDS), using conventional catalysts, e.g. C0-M0/7-AI2O3, is insufficient. A second HDS step, viz. a deep HDS step, can be more economical to reduce the S-content to the currently allowed European level of 350 ppm. This level will be reduced further to 50 ppm in 2005 [1]. In the first HDS step, often the heavy organic sulfur-containing polyaromatics survived, such as dibenzothiophene (DBT) and (4-, and/or 6-) alkylated DBTs [2,3]. They are the most refractory. In crude oils, there are also aromatic N-compounds, which suppress the performance of the HDS catalysts. Hence, a model feed for representative HDS-activity measurements should contain characteristic S- and N- compounds for practical relevance. 

Sulphur is found widely in nature. Inorganic sulphates can be reduced via sulphide to be incorporated into amino acids. Some micro-organisms can use hydrogen sulphide as a source of sulphur, organo-sulphur compounds may also provide microbial sulphur. 

The sulphur compounds found in fuels vary. In the case of natural gas, the only sulphur compounds may be the odorants that have been added by the utility company for safely reasons. With petroleum fractions, the compounds may be highly aromatic in nature. Gasoline currently contains some 300 to 400 ppm of sulphur as organic compounds. In the drive to reduce emissions from vehicles, regulations are being introduced to limit the sulphur in gasoline and diesel fuels. For example in the United States, the proposed limit is 30 to 80 ppm for the year 2004. As levels are reduced, the methods used to remove or desulphurise such fuels may need to be adapted. 

The Sulphur Cycle.— Unlike phosphorus, sulphur appears in both oxidised and reduced forms in the history of life. Completely oxidised as sulphate, it enters the plant from the soil, and is converted into partially reduced organic compounds containing the thiol group —SH or the disulphide linkage —S—S—. From these, the completely reduced form, HjS, is derived by bacterial degradation either in the soil or in the alimentary tract of the animal. Hydrogen sulphide is attacked by the sulphur-oxidising bacteria, with the ultimate formation of sulphate, which is available for plant absorption. 

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