Desulphurisation

Reported plant applications of a.c. impedance and electrochemical noise are rare, but include stainless steels in terephthalic acid (TA) plant oxidation liquors , nuclear fuel reprocessing , and fluegas desulphurisation (FGD) scrubber systems . 

The mechanism for the synthesis of 3-aminopyrroles by ring transformation-desulphurisation of substituted 2-methylisothiazolium salts was investigated and evidence for the intermediacy of 3-aIkylideneaminothioacrylamides (30) and 27f-l,3-thiazines (31) obtained <96JCS(P1)2239>. 

Oldfield, C. Wood, N. T. Gilbert, S. C., et al., Desulphurisation of Benzothiophene and Dibenzothiophene by Actinomycete Organisms Belonging to the Genus Rhodococcus, and... 

Kenakkala, T. and Valimaki, E., Desulphurisation in Coal Combustion Systems, Institution of Chemical Engineers, Rugby, England, 1989, 113. 

Sulphuric acid is the largest volume chemical in the world with an annual production of about 180 mill, t/year which is used primarily for phosphate fertilizers, petroleum alkylation, copper ore leaching and in smaller quantities for a number of other purposes (pulp and paper, other acids, aluminium, titanium dioxide, plastics, synthetic fibres, dyestuffs, sulphonation etc.). The major sulphur sources for sulphuric acid production are sulphur recovered from hydrocarbon processing in the refineries and from desulphurisation of natural gas, SO2 from metallurgical smelter operations, spent alkylation acid, and to a minor extent mined elemental sulphur and pyrites. A simplified flow sheet of a modem double-absorption plant for sulphuric acid production from sulphur is shown in Fig. 1. 

In the preparation of 1,5-disubstituted biguanides by this method, alcoholic ammonia at 100° in a closed vessel is used (755). Thiourea is an effective desulphurising agent (755). 

Under the influence of desulphurising agents, guanidines and thioureas combine to form biguanides (XIX), albeit in low yields (722, 575). In their re-examination of this reaction. Curd, Rose et al. (24, 57, 754) synthesised 1,5-disubstituted biguanides however, the yields did not... 

Aryldithiobiurets 371), on reaction with ammonia and a desulphurising agent, are reported to 5deld c3 noguanidines 681). 

The data for the carbon, hydrogen, sulphur and specific surface area for all four catalysts are summarised in Table VI. Only the sulphur contents of the Mo-containing catalysts showed any dependence on repeat contact. The sulphur content increased with contact number, reflecting gr al sulphidation of the metal content. For the ZriW catalyst, the sulphur content reached a relatively constant value after the first contact, the value corresponding to sulphidation of the Zn content only, suggesting that the level of H2S produced by desulphurisation was inadequate to cause sulfidation of the metal content... 

This paper presents an examination of the overall question of fossil fuel desulphurisation as it currently exists including solid, liquid and gas phase hydrocarbon fuels and technologies for their desulphurisation, in situ, in refining, during combustion and post combustion (see Figure 3). 

While the sulphur values associated with gas, oil and bitumens are either in the form of H2S or organosulphur compounds coals can have significant inorganic sulphur values. This introduces the possibility of desulphurisation by chemical methods different from that required for removal of organic sulphur values. Nonetheless, the desulphurisation problems associated... 

Recent work ( ) with model organosulphur compounds has shown that at temperatures above 350 C and pressures in excess of 100 atm (1500 psig), the hydrolytic desulphurisation reaction occurs readily with thioethers, mercaptans and other non-thio-phenic types of organosulphur compounds. Thiophene itself is more resistant to this type of reaction but desulphurisation is significant in the 450 - 500 C range. More complex fused ring sulphur containing aromatic structures, can, however, be more reactive. 

Desulphurisation of hydrocarbon fuels has traditionally been carried out primarily as part of the refining and upgrading process. Accordingly by far the most advanced and best understood chemistry and technology is to be found in this area. Prior to the advent of major concern for environmental impact of fossil fuel combustion products relatively little was done to desulphurise hydrocarbon fuels (principally coal) prior to combustion and past effects of large scale consumption of high sulphur coals can still be seen in major industrialised areas around the world. 

The first major attempt at precombustion desulphurisation was in the coal gas industry and a number of efficient and effective techniques for removal of H2S, COS, CS2, mercaptans and other volatile sulphur containing products of the gasification process were developed. Many of these techniques found application in the subsequent development of sour natural gas processing where large volumes of hydrogen sulphide had to be removed from the hydrocarbon component. 

Sulphur content of crude oils has always been regarded as a discounting factor and as environmental restrictions on sulphur emissions have been tightened, the need to desulphurise refinery... 

This trend to heavier and higher sulphur content feedstocks is likely to continue. As noted earlier, the heavy oils and bitumens of both Canada and Venezuela, are rich in sulphur and will undoubtedly be desulphurised in ever increasing amounts as supplies of the lighter, lower sulphur content feedstocks dwindle. 

Techniques similar to that discussed earlier for the desulphurisation of coal have been used. Treatment of sulphur containing coke with lime can yield calcium sulphide which can be converted back to lime with generation of H2S by hydrolysis. 

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