AN OVERVIEW OF NEW APPROACHES FOR REMOVING SULFUR FROM REFINERY SYSTEMS

1. AN OVERVIEW OF NEW APPROACHES FOR REMOVING SULFUR FROM REFINERY SYSTEMS

2. INTRODUCTION Due to depleting supplies of quality petroleum crudes, refineries world-wide are increasingly being forced to use inferior quality heavy oils (HO) for producing clean transportation fuels. Unfortunately, the low grades HO are considerably more difficult to process and can significantly reduce the efficiency of clean fuels production. From the viewpoint of continual efficient supply of clean fuels, it is therefore critical to improve key HO processes such as sulphur and nitrogen removal. Overall,new and more effective approaches and continuing catalysis and processing research are needed for producing affordableultra-clean (ultra-low-sulfur and low-aromatics) transportation fuels and non-road fuels, because meeting the new governmentsulfur regulations in 2006�2010 (15 ppm sulfur in highway diesel fuels by 2006 and non-road diesel fuels by 2010; 30 ppmsulfur in gasoline by 2006) is only a milestone. Desulfurization research should also take into consideration of the fuel-cellfuel processing needs, which will have a more stringent requirement on desulfurization (e.g., <1 ppm sulfur) than IC engines.The society at large is stepping on the road to zero sulfur fuel, so researchers should begin with the end in mind and try to develop long term solutions.Overall,new and more effective approaches and continuing catalysis and processing research are needed for producing affordableultra-clean (ultra-low-sulfur and low-aromatics) transportation fuels and non-road fuels, because meeting the new governmentsulfur regulations in 2006�2010 (15 ppm sulfur in highway diesel fuels by 2006 and non-road diesel fuels by 2010; 30 ppmsulfur in gasoline by 2006) is only a milestone. Desulfurization research should also take into consideration of the fuel-cellfuel processing needs, which will have a more stringent requirement on desulfurization (e.g., <1 ppm sulfur) than IC engines.The society at large is stepping on the road to zero sulfur fuel, so researchers should begin with the end in mind and try to develop long term solutions.

6. Market share of main catalysts technology divisionsin percentage in terms of sales value

7. Hydrodenitrogenation (HDN) occurs simultaneously with hydrodesulfurization HDS), hydrodeoxygenation (HDO), hydrogenation (HYD) and hydrodemetallization (HDM) during hydroprocessing. Effects of these reactions upon each other are rather complex. The extent of the mutual effects depends on the origin of feed, type of catalyst, and operating conditions. The HDN has been the focus of attention because nitrogen removal is required to attain the level of sulfur (S) required by fuel specifications. If not removed, nitrogen (N)-compounds would inhibit HDS and other reactions because of their preferential adsorption on catalytic sites.

8. Hydrotreating: A process used in the oil industry to remove objectionable elements such as nitrogen sulfur, oxygen and metals from petroleum distillates by reacting them with H2 over a catalyst. Hydrodenitrogenation (HDN): is the removal of nitrogen from nitrogen containing feeds in the form of NH3. The resulting products are hydrogenated . Hydrodesulfurisation (HDS): is the removal of sulfur from sulfur containing feeds in the form of H2S. The resulting products are hydrogenated . Hydrodeoxygenation (HDO) and hydrodemetalization are the removal of oxygen and metals from the feed.

10. HDS Prevention of poisoning of the metal catalysts by sulfur Control of pollution by SO2 produced in the combustion of gasoline Removal of the unpleasant odour of lube oil caused by the presence of sulfur HDN Nitrogen containing compounds severely reduce the activity of cracking, hydrogenation, isomerisation, reforming and HDS catalysts High nitrogen concentrations are detrimental to product quality To meet the NOx emission restrictions. If present, N-compounds affect the stability of fuels.

14. When organo sulfur compounds are decomposed, gaseous or solid sulfur products are formed and the hydrocarbon part is recovered and remains in the refinery streams. Conventional HDS Sulfur compounds are separated from refinery stream without decomposition Organo sulfur compounds are separated from the streams and simultaneously decomposed in a single reactor unit rather than in a series of reaction and separation vessels 1. The processes can be categorized by the fate of the organosulfur compounds during desulfurization, the role of hydrogen, or the nature of the process used (chemical and/or physical). whether the sulfur compounds are decomposed, separated from refinery stream without decomposition, 2. When organosulfur compounds are decomposed, gaseous or solid sulfur products are formed and the hydrocarbon part is recovered and 1. The processes can be categorized by the fate of the organosulfur compounds during desulfurization, the role of hydrogen, or the nature of the process used (chemical 1. The processes can be categorized by the fate of the organosulfur compounds during desulfurization, the role of hydrogen, or the nature of the process used (chemical and/or physical). whether the sulfur compounds are decomposed, separated from refinery stream without decomposition, 2. When organosulfur compounds are decomposed, gaseous or solid sulfur products are formed and the hydrocarbon part is recovered and 1. The processes can be categorized by the fate of the organosulfur compounds during desulfurization, the role of hydrogen, or the nature of the process used (chemical

17. Sulfided CoMo/Al2O3 and NiMo/Al2O3 catalysts Their performance in terms of desulfurization level, activity and selectivity depends on 1. The properties of the specific catalyst used (active species concentration, Support properties, synthesis route), 2. The reaction conditions (sulfiding protocol, temperature, partial pressure of hydrogen and H2S), nature and concentration of the sulfur compounds present in the feed stream, and reactor and process design.

18. Hydrotreating model catalyst systems are synthesized by impregnating and spin-coating Mo and Co precursor compounds onto flat discs with an oxidic layer as support, a process much like real catalyst preparation. Subsequent sulfidation results in the formation of CoMoS or MoS2 particles

20. Co is present in threedifferent phases. (i) The active CoMoS nanoparticles. (ii) A thermodynamically stable  cobalt sulfide, Co9S8. (iii) Co dissolved in the Al2O3 support.Only the CoMoS particles are catalytically active

22. CoMoS clusters are described as being essentially MoS2-like, but with additional Co atoms embedded into the MoS2 lattice at the perimeter of the cluster. It is proposed that Co atoms located at edge positions create new and more active sites. The promoting role of Co is, however, still extensively discussed, and the exact location of Co has not been identified. A prerequisite for a thorough elucidation of this seems to be a better understanding of the morphology and atomic-scale structure of CoMoS clusters.

23. The ternary CoMoS phase is non-stoichiometric and thus has no thermodynamically stable counterpart. It has, however, been established both experimentally and theoretically that the CoMoS phase can be formed independently of any support, and it should thus be possible to form CoMoS clusters and study them independently. In the literature it is suggested that the number of sulfur vacancies is the main factor controlling the catalytic activity. This is mainly based on a number of studies dealing with trends in the hydrodesulfurization of transition-metal sulfides (TMS)

24. The intercalation model The pseudo-intercalation or decoration model The remote control or contact synergy model The so-called �CoMoS� model, in which Co atoms decorate the edges of MoS2-slabs. This model was first proposed by Ratnasamy and Sivanskar.

26. CVD technique is used to deposit CO using CoCO3 NO on MoS2CVD technique is used to deposit CO using CoCO3 NO on MoS2

28. H2 and S rich oil are trickled thro catalyst bedH2 and S rich oil are trickled thro catalyst bed

31. What is deep desulphurization of the fuels ? More and more of the least reactive sulfur compounds must be converted to H2S. Why is deep desulphurization ? DBT and/or DBT derivatives that are known to be the most refractory S-containing compounds show reactivities 50-fold lower as compared to others. The concentration of the most refractory sulphur compounds in straight-run diesel oil and light cycle oil approaches 3000 and 5000 ppm, respectively.

32. How to approach deep desulfurization? The modification of the physicochemical properties of the supports is one of the still preferred modes of increasing catalytic activity. The synthesis of mesoporous molecular sieves with high surface area and relatively ordered pore structure offers new possibilities of using these materials as modifiers of the porous support structure. Deep desulfurization of refinery streams becomes possible when the severity of the HDS process conditions is increased. Instead of applying more severe conditions, perhaps HDS catalysts with improved activity and selectivity can be synthesized.

33. Ideal hydrotreating catalysts should be able to remove sulfur, nitrogen and, in specific cases, metal atoms from the refinery streams. At the same time they must also improve other fuel specifications, such as octane/cetane number or aromatics content, which are essential for high fuel quality and meeting environmental legislation standards. The use of novel mesoporous supports for catalysts may help larger molecules to have access to the pores thereby enhancing the activity and minimizing the S & N content

37. One way of reducing the steric hindrance of the methyl groups is to shift these groups from 4,6 to 3,7 or to 2,8 positions through an isomerization reaction The complete removal of one or both methyl groups through a dealkylation reaction offers another possibility. The scission of the single C-C bond in the thiophenic ring (isomerization, dealkyalation, and C-C bond scission reactions) as non-hydrogenative routes for desulfurization. This can take place by the following 2 ways. 1.The saturation of one of the phenyl rings depends primarily on the hydrogenation 2. By incorporating a suitable metal such as Ni, W, Pt, Pd, Ru, etc., and/or by providing a suitable support.

40. Conventionally used industrial hydrotreating catalyst Co (Ni)-Mo /?-Al2O3 Additives to ?-Al2O3 Silica, Carbon Mixed Oxides Clays, Zeolites like Y and USY Mesoporous Material MCM-41, HMS, mesoporous Alumina and SBA-15 large pores and bimodal structure consisting of micro and mesopores Low surface area support, Diffusional limitation of large sized moleculesLow surface area support, Diffusional limitation of large sized molecules

41. The strength of the interaction with the support controls the dispersion, reducibility, acidity and catalytic activity. The support mesoporosity is important for better dispersion of sulfide layer. Support design increase significantly the HDS, HYD and HDN functionalities of hydrotreating catalysts. The nature of the support affects sulfidation of the active species, leading to better-promoted active sites and dispersion of the catalysts.

45. The special features of SiMCM-41 (Conventional) Mild acidity High surface area Medium uniform pore size

51. SBA-15 possesses abnormal hydrothermal stability The large hexagonal pores (40-100A�) and bimodal structure consisting of micro and mesopores. The high surface area can be exploited for achieving good dispersion of catalytically active transition metal oxides.

52. The large pores of these materials may help larger molecules to have access to the pores thereby enhancing the activity and minimizing the S & N content. Diffusion of large molecules like 4,6-DMDBT will be slow in Alumina supported catalyst and the reaction is diffusion controlled. With these new and novel supports like nano spherical MCM-41 and AlSBA-15 the process are made non diffusional. HDS takes place through two routes. One by HYDS and the other by DDS. Sterically hindered compounds can be desulfurised by hydrogenation using new and novel supported catalysts.

53. The interaction of Ni and Mo species with the support becomes stronger with Al loading into the SBA-15. Both framework and extraframework Al3+ species participate in the interaction with the deposited Mo species acting as anchoring sites for Mo. In line with this, the dispersion of oxidic and sulfided Mo species increases leading to an increase in the catalytic activity of NiMo catalysts. NiMo catalysts supported on Al-containing SBA-15 materials with Si/Al molar ratio between 30 and 10 show high activity in HDS of 4,6-dimethyldibenzothiophene. This can be attributed to both good dispersion of Ni and Mo active phases and to the bifunctional character of these catalysts, namely, to the participation of Bronsted acid sites of the support in the catalytic transformations of 4,6-DMDBT prior to its desulfurization

57. SBA-15 and Al-SBA-15 supported > g-Al2O3 supported  co-Mo catalysts SBA-15 = Al-SBA-15 supported catalysts for HDS  For Hydrogenation reaction Al-SBA-15 is a better support for Mo, CoMo and NiMo than SBA-15. It appears high molybdenum dispersion on isolated Al sites in Al-SBA-15 and consequent increase of anion vacancies at the edge sites of Mo as a function ofSi/Al ratio appears to be responsible for the outstanding activities of SBA-15 and Al-SBA-15 supported catalysts.

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61. Schematic representation of tungstenin the surface and wall of WO3-SBA-15:(A) low tungsten content and (B) high tungsten content. Ordered SBA-15 silica containing tungsten oxides and tungsten carbides have been directly synthesized, and their structures have been investigated in detail. All the WO3-SBA-15 andWxCSBA- 15 samples have an ordered mesoporous structure in which tungsten is dispersed within SBA-15 in three different types of sites, R-W inside SBA-15 channels, �-W embedded in the intrachannel surfaces of SBA-15, and �-W inside the framework Figure 12. Schematic representation of carburization pathway from WO3-SBA-15 to WxC-SBA-15: (A) low tungsten content and (B) high tungsten content. Synthesis and Structure of Ordered SBA-15 Mesoporous Silica J. Phys. Chem. C, Vol. 111, No. 42, 2007 15183 of SBA-15. The different chemical environments of R-W, �-W, and �-W lead to their having different influences on the mesoporous structure of SBA-15.Ordered SBA-15 silica containing tungsten oxides and tungsten carbides have been directly synthesized, and their structures have been investigated in detail. All the WO3-SBA-15 andWxCSBA- 15 samples have an ordered mesoporous structure in which tungsten is dispersed within SBA-15 in three different types of sites, R-W inside SBA-15 channels, �-W embedded in the intrachannel surfaces of SBA-15, and �-W inside the framework Figure 12. Schematic representation of carburization pathway from WO3-SBA-15 to WxC-SBA-15: (A) low tungsten content and (B) high tungsten content. Synthesis and Structure of Ordered SBA-15 Mesoporous Silica J. Phys. Chem. C, Vol. 111, No. 42, 2007 15183 of SBA-15. The different chemical environments of R-W, �-W, and �-W lead to their having different influences on the mesoporous structure of SBA-15.

62. Combinatorial catalysis is understood as a methodology by which a large number of solid materials are prepared and tested in parallel using automated techniques.Combinatorial catalysis is understood as a methodology by which a large number of solid materials are prepared and tested in parallel using automated techniques.

63. Hydrotreating efficiency can also be increased by employing advanced reactor design such as multiple bed systems within one reactor, new internals in the catalytic reactor or new types of catalysts and catalyst support (e.g. structured catalysts). The best results are usually achieved by a combination of the latter two approaches, namely, using an appropriate catalyst with improved activity in a reactor of advanced design.