Claus reaction mechanism

Scheme 68 Potential mechanism for the Claus reaction catalyzed by cis-[Pt(SH)2(PPh3)2]...

Choppin GR (2003) Actinide speciation in the environment. Radiochim Acta 91 645-649 Claus P (1998) Selective hydrogenation of a,P-unsaturated aldehydes and other C = O and C = C bonds containing compounds. Top Catal 5 51-62 Colon D, Weber EJ, Anderson JL, Winget P, Suarez LA (2006) Reduction of nitrobenzenes and N-hydroxylanilines by Fe(II) species Elucidation of the reaction mechanism. Environ Sci Technol 40 4449-4454... 

From the temperature coefficient of the rate constant, the activation energy for the Claus reaction over the Chromosorb-A was determined to be 25.0 kcal/mole and for the sodium hydroxide-loaded Chromosorb-A it was about 15 kcal/mole. The apparent change in the slope of the Arrhenius plot might indicate some transition in the controlling mechanism. Over the cobalt-molybdena catalyst, the Claus reaction appeared to be diffusion-controlled with an activation energy of 5.5 kcal/mole (2). 

The mechanism of the Claus reaction is complicated, and the sequence of the surface reaction steps is not fioUy elucidated (361). The primary step is certainly the strong adsorption of SO2 on acid—base pairs with formation of sulfite and bisulfite species (354—356), which later react with gaseous or weakly adsorbed H2S. The strength of the SO2 adsorption depends on the surface basicity, which is influenced by the amount of sodium present (225) however, it must be taken into account that the reactivity of the formed sulfites is lower on more basic surface sites. Thus, the acid—base properties of the catalyst play a key role in this reaction. According to Clark et al. (362), sulfate and thiosulfate species apparently form in addition to the sulfites. It was proposed that sulfate and thiosulfate react to form [HS404] ions, which then react with H2S to form the S3 sulfur polymorph, which is subsequently converted into cychc Se and Sg molecules. 

Various reaction mechanisms have been proposed for the formation of carbonyl sulfide and carbon disulfide and for their subsequent hydrolysis to hydrogen sulfide and carbon dioxide (Paskall and Sames, 1992). The plant data available indicate that carbonyl sulfide is formed primarily from the reaction between elemental sulfur and carbon monoxide, which in turn are derived from hydrogen suUide and carbon oxides present during combustion of the feed gas in the Claus thermal stage. The production of carlxin disulfide in the thermal stage is usually attributed to the presence of hydrocarbons in the feed gas because carbon disulfide is produced commercially by reacting elemental sulfur with saturated hydrocarbons. The... 

Grancher, P., 1978, Advances in Claus technology, Part 1 Studies in reaction mechanics, Hydro. Process., Vol. 57, No. 7, pp. 155-160, Advances in Claus technology. Part 2 Improvements in industrial units operating methods, Hydro. Process., Vol, 57, No. 9, pp. 257-262. 

The heterogeneously catalyzed reaction of starting materials A and B can follow different mechanisms [Claus 1996, Ertl 1990]. The models of Langmuir-Hinshelwood, Eley-Rideal, and Mars-van Krevelen are widely used in practice. 

Claus and Yycudilik have reported the details of the dehydration reaction catalysed by phosphorus pentoxide between DMSO and aryl amines to afford iminosulphuranes in good yield. Lerch and Moffatt have reported that the DMSO-DCC oxidation reaction could be applied to iminosulphurane synthesis simply by the addition of an aryl amine to the reaction mixture rather than the usual alcohol. In both instances the mechanism probably involved displacement from sulphur by the amine of an oxy-leaving group (a pyrophosphate or a urea). The latter workers found that hydrazines could not be used in the place of the aryl amine, probably because of subsequent intramolecular eliminations by the iminosulphuranes. 

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