Auswahl der wissenschaftlichen Literatur zum Thema „Dibenzothiophene HDS“

ABSTRACT Dibenzothiophene (DBT), and in particular substituted DBTs, are resistant to hydrodesulfurization (HDS) and can persist in fuels even after aggressive HDS treatment. Treatment by Rhodococcussp. strain ECRD-1 of a middle distillate oil whose sulfur content was virtually all substituted DBTs produced extensive desulfurization and a sulfur level of 56 ppm.

Les raffineurs doivent faire face au renforcement des exigences environnementales relatives à la teneur en soufre des carburants ainsi qu'à l'utilisation de pétrole brut plus lourd pour la production de carburants à l'aide de procédés catalytiques d'hydrotraitement. Une des approches pour améliorer l'activité catalytique est le développement de sulfures trimétalliques NiMoW. Sur des catalyseurs supportés sur alumine, l'utilisation de précurseurs mixtes, les hétéropolyacides (HPA) de Keggin H4SiMo1W11O40 et H4SiMo3W9O40, s'est avérée plus favorable à la formation d'une phase MoWS mixte hautement active que le mélange de deux précurseurs monométalliques H4SiMo12O40 et H4SiW12O40. Dans cette étude, un nouveau protocole pour la synthèse de précurseurs mixtes H4SiMonW12-nO40 avec n = 6 et 9 a été développé. Ces nouveaux composés ont été caractérisés par spectroscopie IR et Raman, ainsi que par DRX sur monocristal. Des catalyseurs d'hydrotraitement massiques et supportés ont été synthétisés à partir de cette série d’HPA. Concernant les catalyseurs non promus supportés sur alumine, l'influence du rapport atomique Mo/(Mo+W) sur la composition de la phase active a été étudié ainsi que son effet sur l'activité catalytique dans des réactions d'hydrotraitement de composés modèles (hydrodésulfuration du dibenzothiophène et hydrogénation du naphtalène). Il a été observé par HAADF que pour un rapport atomique Mo/(Mo+W) égal à 0,25 et 0,5, la structure de la phase active après sulfuration en phase gaz est une structure core-shell. Une augmentation de la teneur en molybdène jusqu'à un ratio Mo/(Mo+W) de 0,75 conduit à une structure désordonnée de la phase active, correspondant à une diminution de l'activité catalytique. En revanche, pour les catalyseurs obtenus à partir d'un mélange des HPA monométalliques, la phase active s’est avérée principalement constituée de cristallites monométalliques MoS et WS, quel que soit le rapport atomique Mo/(Mo+W), avec une activité inférieure à celle des catalyseurs préparés à partir de HPA mixtes.L'influence du rapport atomique Mo/(Mo+W) pour les systèmes promus au nickel, après sulfuration en phase liquide afin de se rapprocher au maximum des conditions industrielles, a également été étudiée. L'introduction de Ni n'empêche pas la formation de la phase active mixte MoWS, ce qui a été confirmé par HAADF et EXAFS. De plus, l’effet d’inhibition dû à la présence de composés azotés dans la charge à hydrotraiter a été analysé. Il a été observé que les catalyseurs NiMoW/Al2O3 riches en tungstène sont plus résistants à la présence des composés azotés et que le choix de la composition du catalyseur doit être adapté selon la composition de la charge traitée.La dissolution par acide du support alumine a permis d'obtenir à partir d'échantillons sulfurés MonW12-n/Al2O3 des catalyseurs massiques MoWS avec une concentration en phase active supérieure à 90%. Des analyses par ToF-SIMS et EXAFS ont montré que la phase MoWS2 mixte est présente à la fois dans les catalyseurs synthétisés à partir des HPA mixtes et dans les échantillons obtenus à partir du mélange de deux HPA. Cependant, la concentration en sulfures mixtes dans le premier cas est beaucoup plus élevée, du fait que des cristallites mixtes étaient déjà présentes dans le solide supporté, alors que dans le cas du mélange des deux HPA, une phase mixte se forme à la suite du frittage des particules lors de la re-sulfuration. La concentration élevée en sulfures mixtes a permis d’obtenir une activité plus élevée des catalyseurs dans des réactions modèles.Enfin, le remplacement de l'alumine par une silice mésostructurée a permis d'augmenter l'activité des catalyseurs MoW non promus. Cependant, les valeurs similaires du degré de sulfuration, de la dispersion ainsi que des résultats des tests catalytiques entre les catalyseurs obtenus à partir des deux types de précurseurs semblent indiquer que la formation de phase mixte MoWS ne se produit pas sur ce type de support
Refiners have to face the strengthening of environmental requirements for the sulfur content in fuels together the use of heavier crude oil for producing market fuels using hydrotreatment catalytic processes. One of the approaches to improve catalytic activity is the development of bulk and supported ternary NiMoW sulfide catalysts following the recent introduction of industrial mixed bulk NiMoW catalysts NEBULA and Celestia. Previously, for supported alumina catalysts, the use of mixed precursors, H4SiMo1W11O40 and H4SiMo3W9O40 Keggin heteropyacids, has shown a better positive effect on the formation of a highly active mixed MoWS phase than the use of two corresponding monometallic H4SiMo12O40 and H4SiMo12O40 precursors. In this study, a new protocol for the synthesis of mixed Keggin-type H4SiMonW12-nO40 precursors with n = 6 and 9 has been developed. The new compounds were characterized by IR and Raman spectroscopy, as well as single-crystal XRD. Bulk and supported hydrotreating catalysts based on the whole series of H4SiMonW12-nO40 HPAs were synthesized. The influence of the atomic Mo/(Mo+W) ratio on the composition and structure of the active phase and its effect on the catalytic activity of unpromoted alumina supported catalysts in model hydrotreating reactions (hydrodesulfurization of dibenzothiophene and hydrogenation of naphthalene) were studied in detail. It was found that for an atomic Mo/(Mo+W) ratio equal to 0.25 and 0.5, the structure of the active phase under gas-phase sulfidation conditions is a core-shell structure, according to HAADF. A further increase in the molybdenum content up to 0.75 leads to disordering of the active phase structure, which has a negative effect on the catalytic activity. In contrast, for the catalysts obtained from a mixture of monometallic H4SiMo12O40 and H4SiMo12O40 HPAs, the active phase consisted mainly of monometallic MoS2 and WS2 crystallites, regardless of the atomic Mo/(Mo+W) ratio, as a result of which the catalysts showed lower activity compared to the samples prepared from mixed HPAs.The study of the influence of atomic Mo/(Mo+W) ratio for Ni-promoted systems, under the liquid-phase sulfidation in order to be as close as possible to industrial conditions, is also reported. It was shown that the introduction of Ni does not prevent the formation of a mixed MoWS active phase, which was confirmed by HAADF and EXAFS. Moreover, testing in the presence of a nitrogen-containing component made it possible to further study the inhibition on catalytic reactions. It was found that tungsten-rich NiMoW/Al2O3 catalysts are more resistant to the action of nitrogen-containing compounds indicating that the choice of the catalyst composition should be adapted to the composition of the processed feedstock.The use of acid (HF) etching of the alumina support made it possible to obtain from sulfided MonW12-n/Al2O3 samples bulk MoWS catalysts with an active phase concentration of more than 90%. ToF-SIMS and EXAFS showed that the mixed MoWS2 phase is present both in the catalysts synthesized from the mixed HPAs and in the samples obtained from the mixture of two HPAs. However, the concentration of mixed sulfides in the first case is much higher, due to the fact that mixed crystallites have already been formed, whereas in the case of a mixture of two HPAs, a mixed phase is formed as a result of the sintering of particles during re-sulfidation. The high concentration of mixed sulfides made it possible to provide a higher activity of catalysts in model reactions.Replacing alumina with mesostructured silica made it possible to increase the activity of unpromoted MoW catalysts. At the same time, similar values of the degree of sulfidation and dispersion, as well as the results of catalytic tests, seem to indicate that the formation of mixed MoWS2 phase does not occur on this type of supports, which requires additional research to be confirmed

Kinetic models were developed to account for the partial contributions of intermediates in complex parallel–consecutive reactions. The models allow precise estimation of the apparent rate constants of all steps in such a reaction network. The hydrodesulfurization (HDS) of dibenzothiophene (DBT) over CoMo-based alumina and carbon catalysts, and over an unsupported molybdenum sulfide catalyst, were investigated in a batch reactor and used to represent this type of reaction. The HDS reactions proceeded through two parallel–consecutive reaction pathways, i.e., direct desulfurization (DDS) and hydrogenation (HYD), in which two main intermediates, namely biphenyl and partially hydrogenated DBT, were involved. Different selectivities in terms of yield fraction (percentage ratio of HYD/DDS) were observed for these catalysts. The results are discussed in the context of proposed HDS reaction networks. Use of these models enables more accurate assessment of differences among the performances of different catalysts.

Hydrodesulfurization (HDS) is an important technology to produce clean fuels, in which the nickel phosphide catalysts exhibit excellent catalytic performances. In this work, a series of NixP/SBA-15 catalysts with various P/Ni molar ratios were prepared using the mesoporous molecular sieve SBA-15 as the support. The structure and surface properties of the catalysts were characterized by X-ray diffraction (XRD), N2 sorption analysis, transmission electron microscopy (TEM), Fourier transform infrared spectrometry (FTIR), and in situ diffuse reflectance infrared Fourier transfer spectroscopy (DRIFTS). The catalytic performances for the HDS of dibenzothiophene (DBT) were evaluated. The results demonstrated that the NixP/SBA-15 catalysts possessed high specific surface area and the mesoporous structures, which benefited the elimination of the internal diffusion limitation in the HDS reactions. Both Ni2P and Ni12P5 phases showed catalytic activity in HDS reactions while Ni2P was more active. The optimal P/Ni molar ratio was about 0.75. The DBT conversion can reach 95.8% under the reaction condition of pressure at 3.0 MPa, H2:oil=600, WHSV at 26.7 h-1, and temperature at 340oC. In situ DRIFTS spectra indicated that the coordinative unsaturated Nid+ (0<d<1) species on the catalysts surface were the active sites for the HDS of DBT.

Hydrodesulphurization (HDS) is a standard process for removing sulphur compounds in fuel oils in industry. HDS is effective to remove simple aliphatic sulphur compounds while less effective to remove thiophenes, dibenzothiophenes, and their derivatives because of sterically hindered adsorption on catalyst surface. Application of ionic liquids (ILs, a new class of compounds) substituting for traditional volatile organic solvents in extractive desulphurization (EDS) or oxidative desulphurization (ODS), have been being studied intensively in the latest decades, and many very promising results have been obtained, showing a good prospect as complement method to HDS. In this chapter, these fresh research results of EDS and ODS using ILs are summarized along with comprehensive discussions on diversified desulphurization factors along with some potential problems. It can be inferred that ILs are a class of potential ideal solvents to realize clean fuel oil in future although some problems come too.

Atropisomerism has opened new ways for DKR processes by exploiting the interconversion of atropisomeric unstable compounds as a beneficial property. The cleavage of a short bridge that causes configurational instability allows an elegant access to axially chiral biaryl products. Thus, Bringmann has demonstrated that biaryl lactones could be ring opened with chiral nucleophiles according to the principle of DKR. This cleavage can be achieved highly atropo-enantio- or -diastereoselectively by involving a range of chiral metallated nucleophiles including metallated amines, alcohols, C-nucleophiles or hydride transfer reagents; by using uncharged chiral or achiral nucleophiles after Lewis acid activation of the lactone; or by involving a η6-coordination of a transition metal fragment to one of the aromatic rings of the biaryl lactone. Moreover, the last fifteen years have seen novel families of atropisomers based on structures other than biaryls come forward as potential new starting materials for DKRs. Among them, atropisomeric anilides, benzamides and naphthamides have been resolved through DKR. Despite the prevalence and importance of atropisomerism in organic structures, the field of asymmetric catalysis has not yet recorded extensive success in the development of catalysis. Among the best recent results of atropo-enantioselective reactions are aldol reactions of atropisomeric benzamides and naphthamides using L-proline as organocatalyst developed by Walsh; nickel-catalysed cross coupling of dibenzothiophenes with Grignard reagents performed in the presence of chiral phosphines developed by Hayashi; ring-opening of biaryl lactones with methanol catalysed by AgBF4 combined with (R)-BINAP developed by Yamada; and DKR of biaryl atropisomers via peptide-catalysed bromination developed by Miller.