Sulphur compounds purification

Toluene free from sulphur compounds may be purchased. Commercial toluene may contain methyl thiophenes (thiotolenes), b.p. 112-113 °C, which cannot be removed by distillation. It may be purified with concentrated sulphuric acid in a similar manner to the purification of benzene, but care must be taken that the... 

A number of oxygen and sulphur compounds are sufficiently powerful electron-pair donors to form borine adducts by reaction with diborane. Of these the unstable solid dimethyl ether borine, Me20+.BH3, used in the purification of diborane, is well known. 

A hydrogen partial pressure increase, which is favorable for sulphur compounds conversion is limited due to mechanical constraints of maximum total pressure of existing hydrotreating reactor. However, a substantial increase of hydrogen partial pressure could be obtained by purification of make up hydrogen or recycled hydrogen. 

It will be recalled that before and after most reaction stages, separation steps are necessary. Also certain processes have no reaction stages and are just a scries of physical unit operations, for example, milk processing or natural gas treatment. The raw material may need purifying and with regard to the Case Studies (CS) the following are important examples for CSl, filtration of molten sulphur and drying of the combustion air for CS2, removal of sulphurous compounds from the feed to the primary reformers for CS.3, air purification is often important and for CS4, water and silt, which are produced simultaneously with the oil and gas, are removed from the hydrocarbons as soon as possible. 

Separation of sulphur compounds from gases has been described widely in literature, cf., e.g., [7-19]. A series of papers is specifically dedicated to the removal of H2S. For this particular purpose, several methods were recommended, e.g., physical gas washing , including absorption/extraction by means of organic solvents, e.g., amines, neutralization of acidic components, oxidation, chemical drying, purification by means of membranes and adsorption by carbonaceous sorbent materials. 

Although a variety of purification techniques has been developed [81] complete elimination of impurities from NVK prepared from coal-tar seems to be impossible. NVK from coal-tar contains substantial amounts of sulphur compounds as well as a variety of condensed aromatic impurities like anthracene. For... 

The nitrosophenol is precipitated from the cooled aqueous solution by acidification with dilute sulphuric acid and is extracted with ether in a separating funnel. After brief drying over calcium chloride the brownish-green solution is concentrated on the water bath. The sparingly soluble compound crystallises from the ether on cooling. Melting point 120°-130° (decomp.). Complete purification of nitrosophenol is difficult. 

Another method of preparation is as follows 1 33 parts of fluorescein are dissolved in 5 parts of ether and treated with 25 parts of selenium chloride in the same solvent. A yellowish-red precipitate separates, and after long stirring at the ordinary temperature the ether is distilled off. The residue is stirred with water, the mixture filtered and the residue now dissolved in sodium hydroxide. After further filtration the filtrate is treated with hydrochloric acid, which precipitates seleno-fluorescei n. Further purification is effected by solution in alkali and reprecipitation. A reddish-brown powder is obtained, soluble with fluorescence in alcohol, but insoluble in water. In concentrated sulphuric acid it dissolves to give an orange solution. Its alkali salts are very soluble in wrater, giving red solutions. This process may also be applied to phthalins, which are obtained by the reduction of phthaleins and their halogen derivatives. If the selenium chloride is replaced by the oxychloride similar products are obtained.2 In place of the phthalins specified in the patents quoted, their O-acetyl compounds or O-acetyl compounds of the phthaleins may be used in indifferent solvents. The products are different from those obtained by the action of selenium on fluoresceins in aqueous alkali solutions.3... 

This reaction is not so common as the second and third. Thus, e.g., formic aldehyde and most of the aromatic aldehydes behave differently toward ammonia. Whenever this reaction does take place it can also be used with advantage for the purification of the aldehyde, as in case of acetaldehyde by allowing the well-crystallised double compound to separate out, on treating it with dilute sulphuric add, the free aldehyde is obtained. 

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