Sulfides desulfurization

It was thought that some desulfiding of the catalyst might occur, by a reaction similar to that reported by Ivanovskil for iron sulfide desulfurization catalysts (15) ... 

In the special case of aryl alkyl sulfides, desulfurization may be performed by 5n2 reactions with nucleophiles such as RS , RSe , and sometimes RO or RiR2N-43b.43c,s9 i,2-Eliminations, where the thioaryl group is the leaving group, have also been used. ... 

Catalyst poisoning by sulfur has discouraged development of procedures for cleavage of sulfides. Desulfurization of highly activated allylic methyl sulfides can be effected by addition of lead to the palla-dium(O) catalyst. In the presence of various tertiary amines satisfactory cleavage of several related allyl sulfides has been utilized (equation 12) using a modified Pd/CaCOs catalyst. 

Fig. 4. Staple fiber washing sequence 1, a hot acid wash (2% H2SO4 at 90°C) decomposes and washes out most of the insoluble zinc salts. This wash completes the regeneration of xanthate and removes as much sulfur as possible in the form of recoverable CS2 and H2S 2, an alkaline sodium sulfide desulfurization bath solubilizes sulfurous by-products and converts them into easily removed sulfides 3, a sulfide wash to remove the sulfides created in bath 2 4, a bleach bath (optional) uses very dilute hypochlorite or peroxide to improve fiber whiteness 5, a dilute acid or sour bath removes any remaining traces of metal ions and guarantees that any residual bleaching chemicals are destroyed 6, a controlled-pH freshwater final wash removes the last traces of acid and salt prior to drsdng and 7, a finish bath gives the fiber a soft handle for easy drying and subsequent processing.

The problem of the synthesis of highly substituted olefins from ketones according to this principle was solved by D.H.R. Barton. The ketones are first connected to azines by hydrazine and secondly treated with hydrogen sulfide to yield 1,3,4-thiadiazolidines. In this heterocycle the substituents of the prospective olefin are too far from each other to produce problems. Mild oxidation of the hydrazine nitrogens produces d -l,3,4-thiadiazolines. The decisive step of carbon-carbon bond formation is achieved in a thermal reaction a nitrogen molecule is cleaved off and the biradical formed recombines immediately since its two reactive centers are hold together by the sulfur atom. The thiirane (episulfide) can be finally desulfurized by phosphines or phosphites, and the desired olefin is formed. With very large substituents the 1,3,4-thiadiazolidines do not form with hydrazine. In such cases, however, direct thiadiazoline formation from thiones and diazo compounds is often possible, or a thermal reaction between alkylideneazinophosphoranes and thiones may be successful (D.H.R. Barton, 1972, 1974, 1975). 

Since the original cmde oils contain some sulfur compounds, the resulting products and gasolines also contain sulfur compounds, including hydrogen sulfide, mercaptans, sulfides, disulfides, and thiophenes. The processes used to sweeten, ie, desulfurize, the products depend on the type and amount of the sulfur compounds present and the specifications of the finished gasoline or other stocks. 

Ladle metallurgy, the treatment of Hquid steel in the ladle, is a field in which several new processes, or new combinations of old processes, continue to be developed (19,20). The objectives often include one or more of the following on a given heat more efficient methods for alloy additions and control of final chemistry improved temperature and composition homogenisation inclusion flotation desulfurization and dephosphorization sulfide and oxide shape control and vacuum degassing, especially for hydrogen and carbon monoxide to make interstitial-free (IF) steels. Electric arcs are normally used to raise the temperature of the Hquid metal (ladle arc furnace). 

Sulfur Dioxide Emissions and Control. A substantial part of the sulfur dioxide in the atmosphere is the result of burning sulfur-containing fuel, notably coal, and smelting sulfide ores. Methods for controlling sulfur dioxide emissions have been reviewed (312—314) (see also Air POLLUTION CONTROL PffiTHODS COAL CONVERSION PROCESSES, CLEANING AND DESULFURIZATION EXHAUST CONTROL, INDUSTRIAL SULFURREMOVAL AND RECOVERY). 

For environmental and economic reasons, the eady practice of roasting zinc sulfide and discharging the sulfur dioxide to the atmosphere gave way to plants where the sulfur dioxide is converted to sulfuric acid. Desulfurization takes place while the ore particles are suspended in hot gases. Called flash-and fluid-bed roasters, these processes are described below. Some plants use combinations of roasters and sintering for desulfurization. 

The primary reactions occurring during hydrotreating are (43) desulfurization of sulfides, polysulftdes, mercaptans, and thiophene as exemplified by... 

Electrophilic attack on the sulfur atom of thiiranes by alkyl halides does not give thiiranium salts but rather products derived from attack of the halide ion on the intermediate cyclic salt (B-81MI50602). Treatment of a s-2,3-dimethylthiirane with methyl iodide yields cis-2-butene by two possible mechanisms (Scheme 31). A stereoselective isomerization of alkenes is accomplished by conversion to a thiirane of opposite stereochemistry followed by desulfurization by methyl iodide (75TL2709). Treatment of thiiranes with alkyl chlorides and bromides gives 2-chloro- or 2-bromo-ethyl sulfides (Scheme 32). Intramolecular alkylation of the sulfur atom of a thiirane may occur if the geometry is favorable the intermediate sulfonium ions are unstable to nucleophilic attack and rearrangement may occur (Scheme 33). 

Effect of HjS, Carbon Oxides, Etc. Hydrogen sulfide in the treat gas has an inhibiting effect on the kinetics of hydrotreating. Being a product of the desulfurization reactions, HjS must diffuse from the catalyst surface into the bulk gas stream. Any HjS present beyond that formed, further slows down the rate of diffusion with a consequent decrease in the amount of desulfurization for a given amount of catalyst. Therefore, additional catalyst would be required. 

The Gassman indole synthesis involves an one-pot process in which hypohalite, a P-carbonyl sulfide derivative 2, and a base are added sequentially to an aniline or a substituted aniline 1 to provide 3-thioalkoxyindoles 3. Raney nickel-mediated desulfurization of 3 then produces the parent indole... 

Tlie thermal reaction of dithiiranes is of particular interest in relation with the dithiirane/thioketone 5-sulfide manifold. Heating 5-oxodithiiranes (4) in solution led to both isomerization to 6,7-dithia-8-oxabicyclo[3.2.1]-octanes 74 and desulfurization to 5-oxothiones 75, the ratio of which was dependent on the reaction conditions employed. The intramolecular [3 + 2] cycloaddition of the thioketone 5-sulfide 76, generated by ring-opening, provides a straightforward explanation for the formation of 74. Meanwhile, 75 is probably formed by a nucleophilic attack on the sulfur atom by another molecule of 4 and/or by elemental sulfur formed during the reaction. 

Although desulfurization is a process, which has been in use in the oil industry for many years, renewed research has recently been started, aimed at improving the efficiency of the process. Envii onmental pressure and legislation to further reduce Sulfur levels in the various fuels has forced process development to place an increased emphasis on hydrodesulfurization (HDS). For a clear comprehension of the process kinetics involved in HDS, a detailed analyses of all the organosulfur compounds clarifying the desulfurization chemistry is a prerequisite. The reactivities of the Sulfur-containing structures present in middle distillates decrease sharply in the sequence thiols sulfides thiophenes benzothiophenes dibenzothio-phenes (32). However, in addition, within the various families the reactivities of the Substituted species are different. 

Schwefel-einschlag, m. sulfur match (for casks) sulfuring (of casks), eisen, n. iron sulfide (usiially ferrous sulfide, Iron(II) sulfide), -entfernung,/. removal of sulfur, desulfurization. -erz, n. sulfur ore. -faden, m. sulfured wick, sulfur match, -farbe, /. sulfur color sulfur dye (of wool) stoved shade. 

Identifying sulfur compounds in crude oils and their products is of little use to a refiner because all sulfur compounds can easily be hydro-desulfurized to hydrogen sulfide and the corresponding hydrocarbon. 

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