Benzothiophenes hydrodesulfurization

A cationic molybdenum sulfide cluster [Mo3S4(H20)9] " with incomplete cubane-type structure and a cationic nickel-molybdenum mixed sulfide cluster [Mo3NiS4Cl(H20)9p " with complete cubane-type structure were introduced into zeolites NaY, HUSY and KL by ion exchange. Stoichiometry of the ion exchange was well established by elemental analyses. The UV-visible spectra and EXAFS analysis data exhibited that the structure of the molybdenum cluster remained virtually intact after ion exchange. MoNi/NaY catalyst prepared using the molybdenum-nickel sulfide cluster was found to be active and selective for benzothiophene hydrodesulfurization. 

The cube [Mo3NiS4(El20)1o]4+ has been incorporated into zeolites by an ion exchange procedure, which lead to catalysts for benzothiophene hydrodesulfurization as well as highly selective catalysis for the formation of C2 species from CO and El2.327,328... 

Although desulfurization is a process, which has been in use in the oil industry for many years, renewed research has recently been started, aimed at improving the efficiency of the process. Envii onmental pressure and legislation to further reduce Sulfur levels in the various fuels has forced process development to place an increased emphasis on hydrodesulfurization (HDS). For a clear comprehension of the process kinetics involved in HDS, a detailed analyses of all the organosulfur compounds clarifying the desulfurization chemistry is a prerequisite. The reactivities of the Sulfur-containing structures present in middle distillates decrease sharply in the sequence thiols sulfides thiophenes benzothiophenes dibenzothio-phenes (32). However, in addition, within the various families the reactivities of the Substituted species are different. 

Thiophenes continue to play a major role in commercial applications as well as basic research. In addition to its aromatic properties that make it a useful replacement for benzene in small molecule syntheses, thiophene is a key element in superconductors, photochemical switches and polymers. The presence of sulfur-containing components (especially thiophene and benzothiophene) in crude petroleum requires development of new catalysts to promote their removal (hydrodesulfurization, HDS) at refineries. Interspersed with these commercial applications, basic research on thiophene has continued to study its role in electrocyclic reactions, newer routes for its formation and substitution and new derivatives of therapeutic potential. New reports of selenophenes and tellurophenes continue to be modest in number. 

Hydrodesulfurization of Benzothiophene Catalyzed by Molybdenum Sulfide Cluster Encapsulated into Zeolites... 

Thiophene is the typical model compound, which has been extensively studied for typifying gasoline HDS. Although, some results are not completely understood, a reaction network has been proposed by Van Parijs and Froment, to explain their own results, which were obtained in a comprehensive set of conditions. In this network, thiophene is hydrodesulfurized to give a mixture of -butenes, followed by further hydrogenation to butane. On the considered reaction conditions, tetrahydrothiophene and butadiene were not observed [43], The consistency between the functional forms of the rate equations for the HDS of benzothiophene and thiophene, based on the dissociative adsorption of hydrogen, were identical [43,44], suggesting equivalent mechanisms. 

Whitehurst, Isoda, and Mochida write about catalytic hydrodesulfurization of fossil fuels, one of the important applications of catalysis for environmental protection. They focus on the relatively unreactive substituted di-benzothiophenes, the most difficult to convert organosulfur compounds, which now must be removed if fuels are to meet the stringent emerging standards for sulfur content. On the basis of an in-depth examination of the reaction networks, kinetics, and mechanisms of hydrodesulfurization of these compounds, the authors draw conclusions that are important for catalyst and process design. 

J-Bonded metal complexes, hydrodesulfurization models with benzothiophene, 1, 769 with dibenzothiophene, 1, 769 Bonding studies energetics, 1, 285 overview, 1, 573—603 ring size effects, 1, 396 strength, 1, 609... 

Thus, it has become possible to define certain general trends that occur in the hydrodesulfurization of petroleum feedstocks. One of the more noticeable facets of the hydrodesulfurization process is that the rate of reaction declines markedly with the molecular weight of the feedstock (Figure 4-6) (Scott and Bridge, 1971). For example, examination of the thiophene portion of a (narrowboiling) feedstock and the resulting desulfurized product provides excellent evidence that benzothiophenes are removed in preference to the dibenzothiophenes and other condensed thiophenes. The sulfur compounds in heavy oils and residua are presumed to react (preferentially) in a similar manner. 

It is also generally accepted that the simpler sulfur compounds (e.g., thiols, R-SH, and sulfides, R-S-R1) are (unless steric influences offer resistance to the hydrodesulfurization) easier to remove from petroleum feedstocks than the more complex cyclic sulfur compounds such as the benzothiophenes). It should be noted here that, because of the nature of the reaction, steric influences would be anticipated to play a lesser role in the hydrocracking process. 

P-07 - Hydrodesulfurization of benzothiophene over noble metals supported on mesoporous silica MCM-41... 

Thiophenic compounds are naturally present in crude oil. Although hydrodesulfurization targets them and converts toward hydrocarbon and hydrogen sulfide [7] still significant quantities are present after this treatment. The reactivities of the 1- to 3-ring compounds decreases in the order thiophenes > benzothiophenes > dibenzothiophenes. In gasoline benzothiophenes are present, in jet fuel - benzothiophenes and dibenzothiophenes whereas in diesel fuel dibenzothiophenes and 4, 6-dimethyldibenzothiophene (4,6-DMDBT) are found. The latter is considered as the most refractory suffur compound towards HDS. The most common refractory sulfur compounds in liquid fuels are presented in Fig. 4. 

FIGURE 6 Hydrodesulfurization (HDS) mechanisms for thiophene, benzothiophene, and dibenzothiophene in the presence of layered MS2 catalyst. 

In recent years, kinetic studies have concentrated on the HDS of dibenzothio-phene (DBT) derivatives as these species are by orders of magnitude less reactive than sulfur species such as thioles, sulfides, and thiophene, or benzothiophene (Figure 5.1.22). The reaction network of hydrodesulfurization is illustrated in Scheme 6.8.2 for the example of HDS of DBT on CoMo. 

Kilanowski, D.R., Teeuwen, H., de Beer, V.H.J., Gates, B.C., Schuit, G.C.A., and Kwart, H. (1978) Hydrodesulfurization of thiophene, benzothiophene, dibenzothiophene, and related compounds catalyzed by sulfided CoO-Mo03-y-Al20j low-pressure reactivity studies./. Catal., 55,129. 

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