Deep HDS Research Articles

Competitive adsorptions between thiophenic compounds over a CoMoS/Al2O3 catalyst under deep HDS of FCC gasoline

The transformation of various model sulfur compounds (2-methylthiophene: 2MT, 3-methylthiophene: 3MT and benzothiophene: BT) representative of sulfur compounds in FCC gasoline was investigated over a CoMoS/Al2O3 catalyst. More specifically, a quantitative reactivity scale was established with BT being more reactive than 3MT and 2MT. In mixture, their reactivity was reduced due to the presence of the other sulfur compound, the scale of reactivity being preserved. BT strongly inhibits the transformation of 2MT. With a single kinetic model based on a Langmuir Hinshelwood formalism, kinetic and adsorption parameters were calculated and the results explained by mutual competitive adsorption between 2MT and BT with a higher adsorption constant for BT compared to that of 2MT.

Refractory Character of 4,6‐Dialkyldibenzothiophenes: Structural and Electronic Instabilities Reign Deep Hydrodesulfurization

AbstractWe studied the most commonly S‐containing compounds present in crude oils, the so‐called 4,6‐dialkyldibenzothiophenes. The alkyl derivatives in this study were methyl, ethyl and isopropyl. Computationally rotating the alkyl substituents, we found differences in their stability. The most stable compound (isopropyl) was transformed into the most instable by changes in its structure. Aromaticity revealed the changes taking place upon structural modifications. The most refractory compound (isopropyl derivative) reduced much more its aromatic character than the methyl derivative. The interaction of these molecules with MoS2 confirmed their instable character upon adsorption. The stability of the refractory molecules and their destabilization prior to be transformed shed light into the key step that reign deep HDS.

Selective direct desulfurization way (DDS) with CoMoS supported over mesostructured titania for the deep hydrodesulfurization of 4,6-dimethydibenzothiophene

Mesostructured titania as support for the CoMoS active phase in deep HDS of 4,6-dimethydibenzothiophene leads to a modification of the main desulfurization way in contrast with the conventional CoMoS/alumina catalyst. Indeed, the dispersion of MoS2 active phase onto mesostructured titania supports leads to catalysts, which favor the direct desulfurization of 4,6-dimethydibenzothiophene. We demonstrate that this unexpected behavior is related to the intrinsic acid properties of the supports, arising from the coexistence of amorphous phase with semi-crystalline anatase. Indeed, these solids present both Lewis and Brönsted acidities, which are conserved after the impregnation of cobalt and molybdenum. The characteristic and the efficiency of the mesoporous titania catalysts have been compared either with conventional Al2O3, used for hydrotreatment, or P25, a commercial TiO2 support used as titania reference.

Effect of organic nitrogen compounds on deep hydrodesulfurization of middle distillate

An effect of organic nitrogen compounds on deep hydrodesulfurization catalyst (CoMo/Al2O3) has been carried out using micro-flow reactor at 5 MPa hydrogen pressure, 1.5 h−1 liquid hours space velocity, and 330 to 380 °C temperature. The experiments were conducted in two steps; at first, prepare nitrogen free Kuwaiti straight run gas oil (SRGO) while in the second step is to test hydrotreating (HDT) catalytic activities using synthetic diesel feed to achieve ultra-low sulfur diesel (ULSD). Hence the role of nitrogen compounds and their effect on HDS activity was studied with nitrogen-free SRGO and spiked (added indole and quinoline), which indicated an apparent tendency of strong inhibition effect by basic nitrogen on deep HDS process.Indeed, inhibition and deep HDS conversion are also dependent on the H2 partial pressure and its dissociative species (i.e., Hδ+ and Hδ−). It is expected that basic nitrogen compounds can easily consume Hδ+ ions during hydrotreating which is assumed to be the rationale behind the stronger inhibition of the hydrogenation function. It was found that quinoline has a more noticeable adverse effect than indole, particularly at a lower temperature. HDS activity results indicated that the adsorbed nitrogen species showed more acceptable behavior at a lower temperature while at high-temperature inhibition effect is not very significant, which could be because of the adsorption nature of nitrogen species.

Effect of urea/metal ratio on the performance of NiMoP/Al2O3 catalyst for diesel deep HDS

Alumina-supported NiMoPOx catalysts have been prepared using urea matrix combustion–decomposition method. The effect of urea/metal ratios on the metal oxide dispersion, the conversion of the metal precursor to oxide and the structure and catalyst performance for diesel HDS has been studied. It is shown that the addition of urea adjusts the metal–support interaction, leading to the easy reduction of the metal oxide over the catalyst surface. It also changes the surface cluster of the oxide and the oxide structure. The addition of urea to metal matrix significantly improves the catalytic diesel HDS performance and increases the catalyst stability. The urea to Ni metal ratio of 2 gives the highest sulfur removal rate in the real diesel HDS process.

Effect of titania grafting on behavior of NiMo hydrodesulfurization catalysts supported on different types of silica

In the present work, a comparison study of the NiMo hydrodesulfurization catalysts supported on different types of silica supports (nanostructured supports of MCM-41 and SBA-15-types and commercial amorphous silica) and the same ones modified by TiO2 grafting was undertaken. The aim of this study was to inquire on the effect of the characteristics of the primary silica supports on the activity and selectivity of the NiMo catalysts modified with titania in deep HDS. Supports and catalysts were characterized by nitrogen physisorption, small-angle and powder XRD, TPR, UV–vis DRS, and HRTEM, and tested in the simultaneous HDS of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). It was found that titania grafting on all silica supports resulted in a slight decrease of BET surface area and total pore volume. However, the characteristic p6mm hexagonal pore arrangement of the used nanostructured silica materials was not affected. Powder X-ray diffraction pointed out a good dispersion of Mo and Ni oxide species in all prepared catalysts. TPR characterization of the NiMo catalysts revealed some increase in the metal-support interaction after titania grafting on the silica surface. Further DRS characterization indicated that the best dispersion of Mo oxide species was obtained on the TiSBA-15 support. Titania addition to the silica supports also produced an increase in the dispersion of the sulfided NiMo phase, which was more marked for SBA-15 and commercial silica supports than for the MCM-41 (HRTEM). In line with the characterization results, titania addition to all silica supports resulted in an increase in the HDS activity of NiMo catalysts. However, this increase was smaller for the MCM-41 support than for the SBA-15 and amorphous silica supports used. The most active NiMo/Ti-SBA-15 catalyst resulted to be significantly more active (∼40%) than the reference NiMo/γ-Al2O3 catalyst in HDS of 4,6-DMDBT.

Recent advances in the science and technology of ultra low sulfur diesel (ULSD) production

Sulfur content of diesel fuel has been cut down to ultra low levels by environmental regulation in many countries with the aim of reducing diesel engine's harmful emissions and improving air quality. As a result, research on the production of ultra low sulfur diesel (ULSD) has gained enormous interest in the scientific community worldwide. The renewed interest in ULSD research is driven by the need, to have a comprehensive understanding of the various factors influencing deep desulfurization of diesel to the ultra low level as well as to find cost-effective ways for ULSD production. This review discusses the recent advancement on ULSD production from both scientific and applied point of view. The key fundamentals and the factors influencing the removal of the least reactive sterically hindered sulfur species from diesel feedstocks are reviewed and discussed in detail. Latest development in deep HDS catalyst and the scientific basis for the improvements in the activity of the new generation HDS catalyst are presented. Advancement in the deep HDS process technologies is reviewed and various options available for revamping and modifying the existing low sulfur diesel HDS units for ULSD production are described highlighting the importance of catalyst selection and hydrogen consumption issues. Special attention has been paid to the progress in the alternative (non-hydrogenation) process concepts and technologies that are being developed for ULSD production.

Development of new NiMo/γ-alumina catalysts doped with noble metals for deep HDS

In the present work, with the aim of searching for new, highly effective catalysts for deep HDS, conventional NiMo/γ-Al 2O 3 catalysts were modified by the incorporation of small amounts (1 wt.%) of noble metals (NM = Pt, Pd, Ru) in order to increase their hydrogenation ability. Prepared catalysts were characterized in oxide state by N 2 physisorption, XRD, UV–vis DRS, temperature-programmed reduction and SEM-EDX, and in sulfided state by HRTEM. The catalysts were tested in the 4,6-dimethyldibenzothiophene (4,6-DMDBT) hydrodesulfurization. Results from the catalytic activity tests showed that the nature of the noble metal influences the catalytic performance of trimetallic NMNiMo catalysts supported on alumina. In general, doping of the conventional NiMo/γ-Al 2O 3 catalyst by all noble metals used resulted in an enhancement of the HYD route of 4,6-DMDBT hydrodesulfurization, especially in the case of the Ru-modified sample. However, if Pt and Pd-containing ternary catalysts showed activity 10–20% higher than the reference conventional NiMo/γ-Al 2O 3 sample, Ru addition had a negative effect on the overall catalytic activity. The activity of PdNiMo and PtNiMo/γ-Al 2O 3 catalytic formulations seems to be close to the sum of the activities obtained over NM/γ-Al 2O 3 and NiMo/γ-Al 2O 3 counterparts. This means that there is no synergetic effect between noble metals and conventional NiMo/alumina catalysts.

Deep HDS of Diesel Fuel: Inhibiting Effect of Nitrogen Compounds on the Transformation of the Refractory 4,6-Dimethyldibenzothiophene Over a NiMoP/Al2O3 Catalyst

The effect of nitrogen-containing compounds (acridine and 1,4-dimethylcarbazole: 14DMCARB) on the hydrodesulfurization of 4,6-dimethyldibenzothiophene (46DMDBT) was studied on a sulfided NiMoP/Al2O3 catalyst in a fixed bed microreactor (340 °C, 40 bar). Both nitrogen-containing compounds inhibited the hydrodesulfurization of 46DMDBT. However, the effect of acridine (a basic compound) and mainly its hydrogenated product (presumably 1,2,3,4,5,6,7,8-octahydroacridine: OHA1) was much more significant than the effect of 14DMCARB (a non-basic compound). In the presence of acridine, the so-called direct desulfurization pathway (DDS) of the HDS of 46DMDBT was less affected than the hydrogenation pathway (HYD) and was even slightly promoted when the partial pressure of acridine increased (after a strong initial inhibition). This was ascribed to a cocatalytic contribution of the nitrogen-containing compound to the C–S bond cleavage. 14DMCARB had the same inhibiting effect on both pathways (DDS and HYD). We also demonstrated that acridine inhibited the transformation of 14DMCARB and can explain why carbazoles are generally the main nitrogen impurities present in gasole after hydrotreatment.

Comparison and performance of different sulphided Ti-loaded mesostructured silica-supported CoMo catalysts in deep HDS

Ti-loaded mesostructured silica materials (HMS, MCM-41 and SBA-15), with Si/Ti atomic ratio of 40, were used for the preparation of supported CoMo catalysts. The catalysts were tested in the reaction of HDS of 4,6-DMDBT carried out in a continuous-flow microreactor in the liquid-phase. The samples were characterized by DRS UV-Vis, XPS, Micro-Raman spectroscopy, SBET, XRD, TPR, FT-IR of adsorbed NO and pyridine. The type of mesostructured material has an important effect on the dispersion of both Mo and Co species. The highest catalytic performance in the HDS of 4,6-DMDBT was observed for the catalysts prepared on the Ti-HMS material. The superior performance of this sample was related to the following factors: (i) larger specific area value, (ii) higher acidity, (iii) higher dispersion of the Co and Mo species, and (iv) the lower reduction temperature of the supported species. Traditional reaction pathways for the HDS of 4,6-DMDBT were observed on the conventional CoMo/γ-Al2O3 and CoMo/Ti-SBA-15 samples, while the CoMo/Ti-MCM-41 and CoMo/Ti-HMS samples show some dealkylation of the alkyl groups in the 4,6-DMDBT molecule (producing DBT). Additionally, the CoMo/Ti-HMS sample recorded the isomerization of the one alkyl group in the 4,6-DMDBT molecule. The differences observed in the reaction pathways via the HDS of 4,6-DMDBT are related to the acidity of the samples.

RECENT TRENDS IN THE CLEANING OF DIESEL FUELS VIA DESULFURIZATION PROCESSES

ABSTRACTThis paper is a selective review of new approaches and emerging technologies for ultra-clean (ultra-low sulfur) diesel fuels. The issues of diesel deep desulfurization are becoming more serious because some crude oils are higher in sulfur contents, while the regulated sulfur limits are becoming lower and lower. Deep reduction of diesel sulfur (from 500 to < 15 ppmw sulfur) is dictated largely by 4,6-dimethyldibenzothiophene, which represents the least reactive sulfur compound that have substitutions on both 4- and 6- positions. The deep HDS problem of diesel streams is exacerbated by the inhibiting effects of co-existing polyaromatics and nitrogen compounds in the feed as well as, H2S in the product. New and more effective approaches and continuing catalysis and processing researches are needed for producing affordable ultra-clean diesel fuels, in order to meet the new government sulfur regulations in 2006-2010. Desulfurization research should also take into consideration the fuel-cell fuel processing needs, which will have stringent requirement on desulfurization.

Highly active deep HDS catalysts prepared using Mo and W heteropolyacids supported on SBA-15

A series of Mo (W) catalysts promoted by Ni and supported on pure siliceous SBA-15 was prepared using Keggin-type heteropolyacids (H3PMo12O40 or H3PW12O40) as active phase precursors. These catalysts were compared with corresponding NiMo(W)/SBA-15 catalysts prepared from the traditional precursors (ammonium heptamolybdate, ammonium metatungstate). Prepared catalysts were characterized by N2 physisorption, small- and wide-angle XRD, UV–vis DRS, FT-IR, TPR, 31P MAS NMR, HRTEM and evaluated in hydrodesulfurization of 4,6-dimethyldibenzothiophene (4,6-DMDBT). It was found that both Mo and W catalysts prepared from heteropolyacids showed better performance in deep HDS of 4,6-DMDBT than the counterparts prepared from traditionally used Mo (W) ammonium salts. The possible reasons of this phenomenon are discussed.

Hydrodesulfurization of 4,6-dimethyldibenzothiophene over Co(Ni)MoS 2 catalysts supported on alumina: Effect of gallium as an additive

The effect of gallium over CoMo/Al 2O 3 and NiMo/Al 2O 3 catalysts was investigated in the hydrodesulfurization of 4,6-dimethyldibenzothiophene. The γ-Al 2O 3 support was modified, before the catalyst preparation, by impregnation with an aqueous solution of Ga(NO 3) 3·8H 2O and calcined at 450 °C. The catalytic results were correlated to the catalysts physicochemical properties which were obtained by different characterization techniques such as X-ray diffraction, X-ray Photoelectron Spectroscopy, Transmission Electron Microscopy and Diffuse Reflectance Spectroscopy. A change of the promoter (Co 2+ or Ni 2+) interaction with the support is induced by the affinity of gallium (at low loadings) for the tetrahedral sites of alumina, leading to an increase in the octahedral species of Ni or Co. This improves the decoration of the MoS 2 slabs. Gallium also modifies the interaction of MoS 2 with the support, decreasing the numbers of Mo–O–Al anchors and increasing the stacking of the MoS 2 slabs. These modifications improve the activity of the NiMo and CoMo catalysts in the deep HDS of 4,6-DMDBT.

Ti-modified alumina supports prepared by sol–gel method used for deep HDS catalysts

The typical physico-chemical properties and their hydrodesulfurization activities of NiMo/TiO 2-Al 2O 3 series catalysts with different TiO 2 loadings were studied. The catalysts were evaluated with a blend of two kinds of commercially available diesels in a micro-reactor unit. Many techniques including N 2-adsorption, UV–vis DRS, XRD, FT-Raman, TPR, pyridine FT-IR and DRIFT were used to characterize the surface and structural properties of TiO 2-Al 2O 3 binary oxide supports and the NiMo/TiO 2-Al 2O 3 catalysts. The samples prepared by sol–gel method possessed large specific surface areas, pore volumes and large average pore sizes that were suitable for the high dispersion of nickel and molybdenum active components. UV–vis DRS, XRD and FT-Raman results indicated that the presence of anatase TiO 2 species facilitated the formation of coordinatively unsaturated sites (CUS) or sulfur vacancies, and also promoted high dispersion of Mo active phase on the catalyst surfaces. DRIFT spectra of NO adsorbed on the pure MoS 2 and the catalysts with TiO 2 loadings of 15 and 30% showed that NiMo/TiO 2-Al 2O 3 catalysts possessed more CUS than that of pure MoS 2. HDS efficiencies and the above characterization results confirmed that the incorporation of TiO 2 into Al 2O 3 could adjust the interaction between support and active metals, enhanced the reducibility of molybdenum and thus resulted in the high activity of HDS reaction.

Deep desulfurization of full range and low boiling diesel streams from Kuwait Lower Fars heavy crude

Information on feed quality and, in particular, various types of sulfur compounds present in the diesel (gas oil) fractions produced form different crudes and their HDS reactivities under different operating conditions are of a great value for the optimization and economics of the deep HDS process. This paper deals with deep desulfurization of gas oils obtained from a new heavy Kuwaiti crude, namely, Lower Fars (LF) which will be processed in the future at Kuwaiti refineries. Comparative studies were carried out to examine the extent of deep HDS, and the quality of diesel product using two gas oil feeds with different boiling ranges. The results revealed that the full range diesel feed stream produced from the LF crude was very difficult to desulfurize due to its low quality caused by high aromatics content (low feed saturation) together with the presence of high concentrations of organic nitrogen compounds and sterically hindered alkyl DBTs. The low-boiling range gas oil showed better desulfurization compared with the full range gas oil, however, deep desulfurization to 50 ppm sulfur was not achieved even at a temperature as high as 380 °C for both feeds. The desulfurized diesel product from the low-boiling gas-oil feed was better in quality with respect to the S, N and PNA contents and cetane index than the full-range gas-oil feed.

Ultra-deep desulfurization of coker and straight-run gas oils: Effect of lowering feedstock 95% boiling point

Production of diesel fuels with ultra-low-sulfur levels by deep desulfurization of gas oil feeds has received considerable importance in the petroleum refineries in recent years. The type of the gas oil feed and its distillation temperature play a key role in the deep desulfurization process. In the present research project, the effect of lowering the 95% distillation temperature ( T 95) of two gas oil feeds, namely, straight-run gas oil (SRGO) and coker gas oil (CGO), on deep desulfurization to ultra-low-sulfur levels was investigated. The results showed that for both types of feeds a higher degree of desulfurization was achieved with reduction of T 95 from > 360 °C to < 340 °C. The refractory alkyl dibenzothiophenes boiling above 320 °C were present in very low concentrations in the low-boiling cuts and deep HDS to ultra-low-sulfur levels (< 50 ppm) was achieved at low severity operating conditions. Among the two feeds, the CGO that contained high nitrogen content, high concentrations of sterically hindered alkyl DBTs and high aromatics content (low feed saturation) was more difficult to desulfurize than SRGO.

Development of Highly Active Co-Mo Catalysts with Phosphorus and Citric Acid for Ultra-deep Desulfurization of Diesel Fractions (Part 1) Preparation and Performance of Catalysts

HY-Al2O3-supported Co-Mo catalysts were prepared with citric acid and phosphorus for the hydrodesulfurization of diesel fractions. The HDS activity was measured with straight-run light gas oil feedstocks under actual hydrotreating conditions. CoMoP/HY-Al2O3 catalyst had three times higher HDS activity compared with the conventional CoMoP/Al2O3 catalyst. The long-term stability test of ultra-deep HDS of the developed catalyst was carried out in a pilot plant under conditions maintaining 10 ppm sulfur content in the product. This catalyst enables deep HDS of diesel fuel and shows no significant deactivation. Commercial operation with the developed catalyst has successfully demonstrated high performance. The developed catalyst has super high activity, which enables <10 ppm sulfur content in products in a commercial hydrotreater designed to produce 500 ppm sulfur diesel fuels. The reaction kinetics of the HDS over the developed catalyst in the diesel hydrotreater fit 1.2-order kinetics. The apparent activation energy calculated from the Arrhenius plots is 100 kJ/mol.

Conceptual design of a reactive distillation process for ultra-low sulfur diesel production

Abstract Based on a thermodynamic analysis in terms of reaction-separation feasibility, a conceptual design of a reactive distillation column for ultra-low sulfur diesel production has been developed. The thermodynamic analysis considers the computation of reactive and non-reactive residue curve maps for a mixture that models the sulfured diesel fuel. The visualization of the reactive residue curves is posed in terms of elements. From the reactive residue curve maps, it is found that there is a high temperature region where the vaporization of hydrogen sulfide favors the elimination of the heavier organo-sulfur compounds. Considering the differences in volatility and reactivity of the organo-sulfur compounds and the phase behavior through the residue curve maps, a conceptual reactive distillation column design was developed. The reactive distillation column considers two reactive zones: In reactive zone I, located above the hydrocarbon feed stream, thiophene and benzothiophene are preferentially eliminated. In reactive zone II, located below the feed stream, dibenzothiophene and 4,6-dimethyl-dibenzothiophene (4,6-DMDBT) are mostly consumed. To validate the conceptual design, rigorous steady state simulations were performed. The design goal was stated to produce 4000 bbl/day of ultra-low sulfur diesel with a 99% conversion of 4,6-DMDBT. It is shown that reactive distillation may be considered a viable technological alternative for deep HDS of diesel.

Contrast activities of four alumina and alumina–silica-supported nickel–molybdenum sulfide catalysts for deep desulfurization of gas oils

Four NiMoS catalysts on conventional alumina (NMA-1), acidified alumina (NMA-2), and on two alumina–silica mixtures of different preparation procedures with 70% (NMASA1-70) and 50% (NMASA2-50) silica supports were prepared. In HDS and HDN of straight run gas oil (SRGO) and its desulfurized oil (HSRGO), their selective activities toward above reactions were compared since the best combination of two catalysts in two-layer bed was expected to achieve deep HDS of SRGO rather easily. NMA-1 removed reactive sulfur species effectively and refractory sulfur species moderately but failed to remove nitrogen species in SRGO. The catalyst was not effective to remove refractory sulfur species in HSRGO to achieve the total sulfur level of less than 10 ppm S in the second layer. NiMoS on acidified alumina (NMA-2) and NMASA1-70 removed nitrogen species very effectively but sulfur species in SRGO were not so efficiently removed. Both catalysts were very active for HSRGO to attain 10 ppm sulfur level. Rapid HDN in SRGO over the catalysts appears to retard HDS of SRGO, leaving even reactive sulfur species unreacted. Among the catalysts, NiMoASA2-50 was very active for all reactions to achieve less than 10 ppm from SRGO via two stages. The rapid HDN over the particular catalyst allowed the effective HDS after the rapid completion of HDN. Such contrast activities of four catalysts are compared as regards their surface area, acidity and NiMoS location on the support particles. NiMo on alumina or on the border of acidified alumina and silica of right content is most activated for HDN as well as HDS. Acidity appears essential for HDN. Larger surface area of the particular alumina–silica support is certainly favorable for both HDS and HDN. The larger content of silica in NMASA1-70 may not be favorable for high dispersion of NiMoS to show higher activity for HDS while HDN progresses.

The role of titania in supported Mo, CoMo, NiMo, and NiW hydrodesulfurization catalysts: analysis of past and new evidences

Previous results and new evidence on the role of titania in supported hydrodesulfurization catalysts are analyzed in order to construct a rational explanation for the different findings in Ti-containing HDS catalysts. Some of the important findings follow. The preparation method of Al–Ti oxide supports is important to catalytic activity. It is not the total amount of Ti but the Ti oxide surface structures that is relevant. TiO 2 is an electronic promoter in HDS catalysts. Ti 3+ species formed under HDS reaction conditions act as electron donors. These electrons can be easily transferred, through the conduction band of the support, and be injected to the Mo 3d conduction band. This causes a weakening of the Mo S bonds and helps the creation of more CUS. The addition of TiO 2 to the surface of alumina eliminates the most reactive surface hydroxyl groups and avoids the formation of tetrahedral Mo oxide species, causing an increase of well-sulfided active phase and hence in catalytic activity. This effect, although significant, is less important than the electronic promotion of Mo by Ti. TiO 2-containing catalysts are well suited for deep HDS because they facilitate the formation of a greater number of CUS in MoS 2 (or WS 2), favoring the hydrogenation–hydrodesulfurization route of transformation of 4,6-DMDBT.