Hydrogen sulfide direct conversion

Hydrogen sulfide is recovered from natural gas or refinery gases by absorption in a solvent or by regenerative chemical absorption.1819 In either case a concentrated hydrogen sulfide stream is produced that is treated further by the Claus process. A typical Claus plant has a feed stream of at least 45 percent H2S, but with modifications can handle streams containing as little as 5 percent H2S. For gas streams with low concentrations of hydrogen sulfide, direct conversion of the hydrogen sulfide to sulfur is accomplished in the solvent system, for example, the Stretford process or CrystaSulf process. 

Sulfides react faster with hydrogen peroxide and alkyl hydroperoxides than do alkenes. For this reason, transition metal catalysts are rarely necessary, but these reactions are acid catalyzed and first order in both sulfide and peroxide. The acid (HX) can be as weak as alcohol or water but the "effectiveness (of the oxidation) is determined by the pXa of the acid. Sulfides also react faster with peroxides than do ketones (see the Baeyer-Villiger reaction, sec. 3.6). Formation of the sulfone in these reactions is straightforward, but requires more vigorous reaction conditions. It is usually easy to isolate the sulfoxide from oxidation of a sulfide. Direct conversion of a sulfide to a sulfone requires excess peroxide and vigorous reaction conditions (heating, long reaction times, more concentrated peroxide). 

Direct conversion of target compounds (sulfur and nitrogen compounds, hydrogen sulfide, polyaromatics, etc.) to an easily removable or desirable product. 

We therefore needed a ready synthesis of the 1,6-epithio epoxide 119. Normally, for such syntheses, the sulftir atom is introduced at an early stage [64]. However, it appeared to us that a suitable doubly-activated sugar such as 120 should be capable of direct conversion to the 1,6-epithio sugar 121 by treatment with some type of sulfur reagent. Indeed, the o-glucosyl bromide 122 was easily prepared and, upon treatment with either hydrogen sulfide and triethylamine in DMF or benzyltriethylammonium tetrathiomolybdate in chloroform, gave the... 

Many processes have been developed for the removal of hydrogen sulfide from gas streams. They can be classified as liquid absorption, liquid oxidation, dry oxidation, and adsorption. One of these processes is usually included in a coal gasification or liquefaction flowsheet since the coal sulfur is converted to H2S and finally elemental sulfur. The Stretford and Townsend direct HpS to S processes and the Recti sol process followed by a Claus plant are frequently included on coal conversion flowsheets (1 ). Kohl and Riesenfeld (2) present pertinent details for many commercial processes. 

Various oxidants have been used in the oxidation of sulfides such as hydrogen peroxide and a number of different peroxycarboxylic acids (RC03H), the latter being the more powerful oxidising agents. In the oxidation (Scheme 18), step 1 is much faster than step 2, and consequently many sulfoxides can be prepared by this route for instance, benzyl methyl sulfoxide (26) can be obtained from benzyl methyl sulfide (25) (Scheme 19). More powerful oxidants or more vigorous conditions effect the direct conversion of sulfides into the corresponding sulfones thus, (27) and (28) are transformed into (29) and (30), respectively (Scheme 20). 

The combined presence of H,S and C02 in a given effluent usually leads to a joint removal operation. This type of treatment stems from the fact that, among the most economical alternatives available, the liquid absorption of acid constituents is the most widespread, and also because, at the technical level, the type of product to be extracted, apart from its acidic character, has little effect on the behavior of the solvent employed. Hence, although, as a rule, hydrogen sulfide is absorbed faster than C02, the separation of the different acid gases is more or less simultaneous. For reasons of environmental protection, this scheme must also be supplemented by the direct conversion of hydrogen sulfide to sulfur,... 

The conversion can be achieved by reacting the hydrogen sulfide gas directly with air in a burner reactor if the gas can be burnt with a stable flame. 

There are essentially three types of practical processes for removing hydrogen sulhde from gas streams sorption on a solid reversible chemical or physical absorption in a Uquid medium and absorption and oxidation in an oxidizir liquid medium (direct conversion). In the direct converaon processes, not only is hydrogen sulfide removed from the sour gas stream, but it is also converted into elemental sulfur in the same liquid medium. There are two methods by w ich this conversion can be achieved. One is the so-called Wet Qaus process, in which sulfur dioxide is introduced and reacts with the hydrogen sulfide according to the following equation ... 

Direct catalytic oxidation of hydrogen sulfide to elemental sulfur in the presence of gaseous paraffinic hydrocarbons or other gases has been reported by Grekel (1959). Although pilot-plant work indicated good conversions and no effect on the hydrocarbons, the process has so far not been successfully commercialized. 

Introduction. The Beavon Sulfur Removal (BSR) process, as repotted by Beavon and King (1970) and Beavon and Vaell (1971), is capable of reducing the total sulfur content of Claus unit tail gases to less than 250 ppm by volume (calculated as sulfur dioxide) and thus of attaining an overall conversion of more than 99.9% of the hydrogen sulfide fed to the Claus unit. The residual sulfur compounds from the Beavon process consist almost entirely of carbonyl sulfide, with only traces of carbon disulfide and hydrogen sulfide. The effluent gas is practically odorless and can often be vented directly to the atmosphere, obviating the need for incineration and the attendant consumption of fuel. 

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