Sulfur reduction processes

Discuss the main peculiarities of sulfur biogeochemical evolution. Present the isotopic record of the sulfur reduction process and its role in evolution of the sulfur cycle. 

Sulfur reduction processes are sensitive to both amount and structure of the sulfur compounds being removed. Tests that can provide information about both of these factors are becoming increasingly important, and analytical tests that provide information about other constituents of interest (e.g., nitrogen, organometallic constituents) are also valuable and being used for characterization. 

The Wellman-Lord process can be a significant factor in helping domestic power plants to meet the air pollution abatement requirements of the Clean Air Act of 1970. To show its applicability to the utilities industry, Davy Powergas Inc. is building a demonstration installation at the Dean H. Mitchell Station of Northern Indiana Public Service Co. in Gary, Ind. When completed, it will consist of a Wellman—Lord sulfur dioxide recovery unit connected to an Allied Chemical Co. sulfur dioxide-to-sulfur reduction process to produce elemental sulfur. Davy Powergas guarantees emissions of 200 ppm by volume or less of sulfur dioxide at this facility. 

The gangue content of DRI is typically comprised of oxides such as Si02, AI2O2, CaO, MgO, Ti02, K2O, Na20, MnO, etc, and is dictated by the chemistry of the iron ore used. The phosphoms in DRI is normally in the form of P2 5- Sulfur content in the DRI depends on the sulfur level in the ore and reductant, and the amount of sulfur released or absorbed by the DRI during the reduction process. 

The reduction ia tetraethyl lead for gasoline production is expected to iacrease the demand for petroleum alkylate both ia the U.S. and abroad. Alkylate producers have a choice of either a hydrofluoric acid or sulfuric acid process. Both processes are widely used. However, concerns over the safety or potential regulation of hydrofluoric acid seem likely to convince more refiners to use the sulfuric acid process for future alkylate capacity. 

Various improvements in the sulfur dioxide reduction processes have been commercialized, including the Canadian International Paper Process (1946) and the Kesting, Persson, and Holst processes. A variation combining both chloride and sulfur dioxide reductant processes was developed and patented by KemaNord AB (47). 

Chlorine dioxide produced from the methanol reductant processes contains carbon dioxide and small amounts of formic acid. For this reason, sulfur dioxide and chloride-based chlorine dioxide processes are stih used for sodium chlorite production. This problem has been addressed by recycling a portion of the vapor from methanol-based generators so that formic acid further reacts to carbon dioxide ... 

Improvements to the methanol reductant processes may be found in the patent Hterature. These include methods of operation to reduce acidity in the crystallisation 2one of the generator to promote crystallisation of sodium sulfate and to reduce sulfuric acid consumption (48). Other improvements sought are the elimination of formic acid and chlorine impurities from the chlorine dioxide, as weU as methods of recovering acid and sodium hydroxide, or acid and neutral sodium sulfate from the soHd sodium sesquisulfate salt waste stream (48—52). 

Conventional coal cleaning processes can remove about 50% of pyritic sulfur and 30% of total sulfur. For northern Appalachian region coals it has been shown that a greater sulfur reduction can be achieved by applying physical coal cleaning to finer size coals (Table 3) (8). 

Developments in the metallurgy of copper or its alloys were mentioned in 1556 in De MetalBca where the process of copper ore was described by Agricola (see also Copper alloys). About that time, smelting operations commenced at Mansfield, Germany, and at the Swansea smelter in Wales. Both smelters employed successive oxidations and reductions to eliminate iron and sulfur. The process used in the Swansea smelter is similar to modern techniques. 

General 1. Use cokeless iron- and steel-making processes, such as the direct reduction process, to eliminate the need to manufacture coke. 2. Use beneficiation (preferably at the coal mine) and blending processes that improve the quality of coal feed to produce coke of desired quality and reduce emissions of sulfur oxides and other pollutants. 

The induced co-deposition concept has been successfully exemplified in the formation of metal selenides and tellurides (sulfur has a different behavior) by a chalcogen ion diffusion-limited process, carried out typically in acidic aqueous solutions of oxochalcogenide species containing quadrivalent selenium or tellurium and metal salts with the metal normally in its highest valence state. This is rather the earliest and most studied method for electrodeposition of compound semiconductors [1]. For MX deposition, a simple (4H-2)e reduction process may be considered to describe the overall reaction at the cathode, as for example in... 

Biodesulfurization (BDS) is the excision (liberation or removal) of sulfur from organosul-fur compounds, including sulfur-bearing heterocycles, as a result of the selective cleavage of carbon-sulfur bonds in those compounds by the action of a biocatalyst. Biocatalysts capable of selective sulfur removal, without significant conversion of other components in the fuel are desirable. BDS can either be an oxidative or a reductive process, resulting in conversion of sulfur to sulfate in an oxidative process and conversion to hydrogen sulfide in a reductive process. However, the reductive processes have been rare and mostly remained elusive to development due to lack of reproducibility of the results. Moderate reaction conditions are employed, in both processes, such as ambient temperature (about 30°C) and pressure. 

The most noteworthy multistage element cycles in which bacteria play important roles are the nitrogen and sulfur redox cycles. The fixation of nitrogen is a reductive process that provides organisms with nitrogen in a form usable for the synthesis of amino acids, nucleic acids, and other cell constituents. In essence, the overall conversion to the key intermediate, ammonia, can be represented as ... 

The dissimilarity found between the homogeneous and heterogeneous reduction processes can be attributed to a specific interaction of the sulfur-containing groups with the material of the electrode. 

Characteristics often ascribed to MVT deposits include temperatures generally <200°C and deposition from externally derived fluids, possibly basinal brines. Sulfur isotope valnes from MVT deposits suggest two major sulfide reservoirs, one between -5 and +15%c and one greater than +20%c (Seal 2006). Both sulfide reservoirs can be related, however, to a common sea water sulfate source that has undergone different sulfur fractionation processes. Reduction of sulfate occurs either bacterially or by abiotic thermochemical reduction. High 5 S-values should reflect minimal fractionations associated with thermochemical reduction of sea water sulfate (Jones et al. 1996). 

From the viewpoint of inorganic chemistry, the reaction of potassium nitrate with sulfur and charcoal can be described as an oxidation-reduction reaction in which electron transfer between reacting species involves a loss or gain of electrons resulting in an oxidation or reduction process respectively. 

Hahn. Reasoning from the observation that proteins and other substances which contain sulfhydryl groups produce hydrogen sulfide on addition of sulfur, Heffter denied that a biochemical reduction process took place at all. As a generalization this negation seems definitely unjustified (see pp. 93 and 95). 

Chromium metal is produced hy thermal reduction of chromium(III) oxide, Cr203 by aluminum, silicon or carbon. The starting material in all these thermal reduction processes are Cr203 which is obtained from the natural ore chromite after the removal of iron oxide and other impurities. In the aluminum reduction process, the oxide is mixed with A1 powder and ignited in a refractory-lined vessel. The heat of reaction is sufficient to sustain the reaction at the required high temperature. Chromium obtained is about 98% pure, containing traces of carbon, sulfur and nitrogen. 

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