Hydrodesulphurization reaction

Sites at the surface of non-metallic catalysts have also been investigated. The adsorption of H2 by Co304 has been studied by diffraction and has been referred to earlier.12 The adsorption of H2 by Mo and W sulphides however, has been the subject of a number of inelastic scattering investigations which have gone a long way to clarify the sites at which adsorption occurs, and probably the sites from which H2 is transferred in hydrodesulphurization reactions. 

It is now generally accepted that in hds catalysts MoSj (or WSj) is the active component and that Co (or Ni) is a promoter that increases the number but does not change the nature of the active sites. However, Massoth points out that, although bulk Co-Mo sulphides are active in hds it is not conclusively proved that bulk sulphides are the active ingredients for hydrodesulphurization reactions for the mildly sulphided catalysts employed in industry . In certain industrial applications representing more severe sulphiding conditions, some bulk sulphides may be present but it is not certain that aU the Mo has been converted to sulphide. 

Apart from hydrodesulphurization, reactions causing transformation or destruction of the thiophen ring are rather rare. Three interesting examples have been reported. In the first, photolysis of 3-cyanothiophen (22) in furan affords the adduct (23) as the major product. 2-Cyanothiophen behaves in a similar way, and an analysis of permutation patterns has indicated that there is a mechanism involving first the 2,5-bridged compound (24) followed by a walk of the sulphur atom. Anils (25) are converted into pyrroles (26) by triethyl phosphite a similar ring-opening by intramolecular insertion of nitrene has also been shown to occur with o-nitrophenyl-di-(2-thienyl)methanes. ... 

The objective of the present work is to classify the catalytic performances of unsupported transition metal sulphides (TMS) for these different reactions dehydrogenation of a sulphur containing molecule without sulphur elimination, hydrodesulphurization and hydrogenation. 

The catalysts were tested in the dehydrogenation of tetrahydrothiophene (DHN of THT), the hydrodesulphurization of thiophene (HDS of thiophene) and the hydrogenation of biphenyl (HN of BP). The reactions were carried out in the vapor phase using dynamic flow microreactors equipped with an automatic online analysis. Reaction conditions are given in Table 1. 

Beuther, H., and B. K. Schmid, "Reaction Mechanisms and Rates in Residue Hydrodesulphurization " Proc. 6th World Petroleum Congress, Section III, 1964, p. 297. 

Sulphide Catalysts Characterization and Reactions Including Hydrodesulphurization... 

Pd-based catalyst studies have focused on the influence of S-containing gases on reactions including thiophene hydrodesulphurization and methane oxidation. It appears that not only does the presence of sulfiir-containing gases decreases the effectiveness of the Pd-based catalysts studied, but the formation of Pd-sulfldes does as well [136, 137]. Eeuerriegel and coworkers demonstrated complete Pd-catalyst deactivation for the oxidation of methane with as low as 5.4 ppm of HaS present and as little as 0.08 ML of S completely poisoning the surface [137], while Vazquez and co-workers witnessed a 60% decrease in thiophene conversion for a sulfided catalyst as compared to a sulfide-free Pd catalyst [136]. 

Thiophens may also be obtained from aldehydes in like manner. The kinetics and mechanism of these sulphurization reactions, and especially of the industrially important reverse reactions (hydrodesulphurization), have been examined in some detail thiols may be intermediates. 

In case of a relatively low concentration of the liquid reactant, for example, in the rear part of the reactor or in processes like hydrodesulphurization of fuels (with a typical feed concentration of organic sulfur between 100 and 1000 ppm), the effective rate is limited by the concentration of the liquid reactant. The rate is determined by the interplay of the chemical reaction and the diffusion of the liquid reactant to and within the catalyst Depending on the type of reaction, an increase in pressure may not help to improve the reaction rate, as demonstrated here for the hydrogenation of 1-octene. Then a hquid recycle would probably decrease the rate Although the liquid-solid mass transfer coefficient is increased, this effect is more than compensated by the decrease of the liquid reactant concentration. 

Catal3dic hydrodesulphurization is based on the reaction of organic sulfur compounds with hydrogen as catalysts. During reactions, the organic sulfur compounds are first converted to the inorganic sulfur compounds such as H2S, and then removed by the absorption of zinc oxide. The reactions involved are summarized as follows. 

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