Deep Hydrotreatment Research Articles

Conversion of kraft lignin to hydrocarbons using an integrated molten salt pyrolysis/catalytic hydrotreatment approach

Thermochemical conversion of underutilized lignocellulosic streams such as kraft lignin from the pulp and paper industry has the potential to produce sustainable chemicals and biofuels. We here report a process to continuously convert softwood-based lignoboost lignin to hydrocarbons using a three-step approach: i) liquefaction/dispersion of the lignin in a suitable molten salt, ii) pyrolysis of the liquefied/dispersed lignin in a molten salt mixture (ZnCl2, KCl, and NaCl), to obtain a crude lignin oil and iii) upgrading of the lignin oil using a catalytic hydrotreatment to yield hydrocarbons. Step 1 and 2 were integrated using a twin screw extruder with different heating sections at a scale of 20 g/h lignin input. Besides char, a lignin oil, mainly composed of monomeric phenolics, and propylene were the major products. The highest yield of the latter two products was around 32 wt% (23 wt% crude lignin oil and 9 wt% propylene). The lignin oil was subsequently converted to hydrocarbons using a two-step catalytic hydrotreatment approach (stabilization step using CoMo/Al2O3 catalyst and a further deep hydrotreatment over a NiMo/Al2O3 catalyst). The final liquid product contained less than 0.5 wt% of oxygen and was shown to be rich in (cyclo)alkanes and aromatic hydrocarbons. The carbon yield for the overall conversion of lignin to hydrocarbons was 23 %.

Deep Hydrotreatment of Coal-Derived Liquid by Denitrogenation Pretreatment

Deep Hydrotreatment of Coal-Derived Liquid by Denitrogenation Pretreatment

New Prospects of Waste Involvement in Marine Fuel Oil: Evolution of Composition and Requirements for Fuel with Sulfur Content up to 0.5%

Research was carried out on the possibility of involving oil refining wastes and petrochemical by-products in marine fuel oil. It was shown that the properties of the studied products (VAT distillation residue of butyl alcohols, heavy pyrolysis tar, desalted phenol production tar, waste motor oil mixture) mainly differ from primary and secondary oil refining products used in this fuel with increased toxicity (hazard classes 2 and 3). A clear disadvantage of waste motor oils is an increased content of metals, particularly zinc, calcium and phosphorus, which leads to high ash content. Recommended concentrations for introducing components into marine fuels are given. The influences of the composition and sulfur content on operational properties and quality indexes of VLSFO were also studied. It is shown that the use of products of deep hydrotreatment of vacuum-distillate fractions of oil processing can worsen its protective (anticorrosive) properties and colloidal stability; therefore, a reduction of sulfur content below 0.1% in this fuel is inexpedient without the use of additives. The requirements for VLSFO quality indicators have been developed. Application of VLSFO corresponding to the developed requirements will provide an increase in performance of ship power plants and the stability of VLSFO quality, which will contribute to cost reduction of ship owners when using it.

Novel Route to Produce Hydrocarbons from Woody Biomass Using Molten Salts.

The thermochemical decomposition of woody biomass has been widely identified as a promising route to produce renewable biofuels. More recently, the use of molten salts in combination with pyrolysis has gathered increased interest. The molten salts may act as a solvent, a heat transfer medium, and possibly also a catalyst. In this study, we report experimental studies on a process to convert woody biomass to a liquid hydrocarbon product with a very low oxygen content using molten salt pyrolysis (350–450 °C and atmospheric pressure) followed by subsequent catalytic conversions of the liquids obtained by pyrolysis. Pyrolysis of woody biomass in molten salt (ZnCl2/NaCl/KCl with a molar composition of 60:20:20) resulted in a liquid yield of 46 wt % at a temperature of 450 °C and a molten salt/biomass ratio of 10:1 (mass). The liquids are highly enriched in furfural (13 wt %) and acetic acid (14 wt %). To reduce complexity and experimental issues related to the production of sufficient amounts of pyrolysis oils for further catalytic upgrading, model studies were performed to convert both compounds to hydrocarbons using a three-step catalytic approach, viz., (i) ketonization of acetic acid to acetone, (ii) cross-aldol condensation between acetone and furfural to C8–C13 products, followed by (iii) a two-stage catalytic hydrotreatment of the latter to liquid hydrocarbons. Ketonization of acetic acid to acetone was studied in a continuous setup over a ceria–zirconia-based catalyst at 250 °C. The catalyst showed no signs of deactivation over a period of 230 h while also achieving high selectivity toward acetone. Furfural was shown to have a negative effect on the catalyst performance, and as such, a separation step is required after pyrolysis to obtain an acetic-acid-enriched fraction. The cross-aldol condensation reaction between acetone and furfural was studied in a batch using a commercial Mg/Al hydrotalcite as the catalyst. Furfural was quantitatively converted with over 90% molar selectivity toward condensed products with a carbon number between C8 and C13. The two-stage hydrotreatment of the condensed product consisted of a stabilization step using a Ni-based Picula catalyst and a further deep hydrotreatment over a NiMo catalyst, in both batch setups. The final product with a residual 1.5 wt % O is rich in (cyclo)alkanes and aromatic hydrocarbons. The overall carbon yield for the four-step approach, from pinewood biomass to middle distillates, is 21%, assuming that separation of furfural and acetic acid after the pyrolysis step can be performed without losses.

Development of nanosized catalysts for processing synthesis gas to methanol

Conversion of carbon dioxide into chemical waste-free feedstock (carbonates, cyclocarbonates, synthesis gas) requires the use of a two-stage reaction (conversion of carbon monoxide under pressure, followed by purification of the converted gas from carbon dioxide with hot potash or monoethanolamine and removal of residual carbon oxides by catalytic hydrogenation) of the reaction. The main problem with this transformation is that, for energetic reasons, these reactions are difficult to coordinate with each other. To ensure the compatibility of the processes from a thermodynamic point of view, appropriate nanocatalysts are needed to obtain a useful product in the course of the reactions. The authors carried out field tests of various catalysts, discovered the compatibility of the reaction with two catalysts with the required properties: a copper compound for the first stage of the reaction and a compound of zinc oxide for the second stage, and also demonstrated the feasibility of this reaction using phenylethylene contained in a hydrocarbon compound. The numerous processes that can be used to produce methanol can be divided into three categories: indirect, direct, and biofuel. Indirect conversion is widespread throughout the world. This conversion takes place in a process in which biomass, coal or natural gas is converted to a mixture of hydrogen and carbon monoxide known as synthesis gas. The syngas is converted to methanol using a variety of conversion methods. Research on the development and improvement of nanocatalysts for the chemical processing of carbon dioxide into methanol has been carried out. An algorithm has been developed for modeling the composition, structure, and properties of nanocatalysts, and a number of new compounds have been synthesized that are capable of retaining cations with different oxidation states and sizes in the crystal lattice. Work has been carried out to improve nanocatalysts based on nickel for deep methanol hydrotreating.

Studying the Characteristics of a Waste Industrial Со-Мо/Al2O3 Catalyst for the Deep Hydrotreatment of Diesel Fuel

The physicochemical properties of a waste industrial Со-Мо/Al2O3 catalyst for the deep hydrotreating of diesel fuel are studied. IR spectroscopy, thermogravimetry (TG), differential thermal analysis (DTA), and scanning electron microscopy (SEM) are used to establish that the catalyst surface is uniformly coated with a coke film. This soft coke is mostly a mixture of saturated hydrocarbons with a low degree of branching in their structure. The coke is oxidized at temperatures of 190–375°C (soft coke) and 375–525°C (hard coke); its quantitative removal is achieved by means of oxidative calcination in air for 3 h at 550°C. X-ray diffraction, scanning electron microscopy, low-temperature nitrogen adsorption, and chemical analysis are used to show that the waste catalyst undergoes considerable structural transformation with a 7.7% drop in the Mo content and the accumulation of Fe, Ha, and V impurities. As a result of sintering, its specific surface area and total pore volume are reduced by 31.5 and 28.4%, respectively. The obtained data are needed to develop a scheme for its recycling.

Hydrotreating of Jatropha-derived Bio-oil over Mesoporous Sulfide Catalysts to Produce Drop-in Transportation Fuels

The bio-oil was largely produced by thermal pyrolysis of Jatropha-derived biomass wastes (denoted as Jatropha bio-oil) using a pilot plant with a capacity of 20 kg h-1 at Thailand Institute of Scientific and Technological Research (TISTR), Thailand. Jatropha bio-oil is an unconventional type of bio-oil, which is mostly composed of fatty acids, fatty acid methyl esters, fatty acid amides, and derivatives, and consequently, it contains large amounts of heteroatoms (oxygen ~20 wt.%, nitrogen ~ 5 wt.%, sulfur ~ 1000 ppm.). The heteroatoms, especially nitrogen, are highly poisonous to the metal or sulfide catalysts for upgrading of Jatropha bio-oil. To overcome this technical problem, we reported a stepwise strategy for hydrotreating of 100 wt.% Jatropha bio-oil over mesoporous sulfide catalysts (CoMo/γ-Al2O3 and NiMo/γ-Al2O3) to produce drop-in transport fuels, such as gasoline- and diesel-like fuels. This study is very different from our recent work on co-processing of Jatropha bio-oil (ca. 10 wt.%) with petroleum distillates to produce a hydrotreated oil as a diesel-like fuel. Jatropha bio-oil was pre-treated through a slurry-type high-pressure reactor under severe conditions, resulting in a pre-treated Jatropha bio-oil with relatively low amounts of heteroatoms (oxygen < 20 wt.%, nitrogen < 2 wt.%, sulfur < 500 ppm.). The light and middle distillates of pre-hydrotreated Jatropha bio-oil were then separated by distillation at a temperature below 240 °C, and a temperature of 240–360 °C. Deep hydrotreating of light distillates over sulfide CoMo/γ-Al2O3 catalyst was performed on a batch-type high-pressure reactor at 350 °C and 7 MPa of H2 gas for 5 h. The hydrotreated oil was a gasoline-like fuel, which contained 29.5 vol.% of n-paraffins, 14.4 vol.% of iso-paraffins, 4.5 vol.% of olefins, 21.4 vol.% of naphthene compounds and 29.6 wt.% of aromatic compounds, and little amounts of heteroatoms (nearly no oxygen and sulfur, and less than 50 ppm of nitrogen), corresponding to an octane number of 44, and it would be suitable for blending with petro-gasoline. The hydrotreating of middle distillates over sulfide NiMo/γ-Al2O3 catalyst using the same reaction condition produced a hydrotreating oil with diesel-like composition, low amounts of heteroatoms (no oxygen and less than 50 ppm of sulfur and nitrogen), and a cetane number of 60, which would be suitable for use in drop-in diesel fuel.

NiWS/Al2O3 Diesel Fraction Deep Hydrotreating Catalyst Synthesized Using Mesostructured Aluminum Hydroxide

On the basis of alumina synthesized via addition of mesostructured aluminum hydroxide gel, which is prepared by the hydrolysis of secondary aluminum butoxide in the presence of triblock copolymer Pluronic P123 to the AlOOH commercial powder, and the commercial reference sample, NiWS/Al2O3 catalysts are prepared using H3PW12O40 heteropolyacid and nickel citrate. The physicochemical properties of the supports and catalysts are studied by low-temperature nitrogen adsorption, temperature-programmed desorption of ammonia, and high-resolution transmission electron microscopy. The catalytic properties are investigated in the process of straight-run diesel fraction hydrotreating in a flow unit. It is shown that the use of the synthesized alumina as a catalyst support leads to an increase in the dispersity of nanosized particles of the NiWS active phase. The catalytic activity in targeted reactions also grows appreciably. The causes of these phenomena are discussed.

Identification of sulphur, oxygen and nitrogen species in heavy oils by X-ray photoelectron spectroscopy

The removal of heteroelements issued from petroleum products is an important problematic in the developments of the refining processes, in particular for the refining of the unconventional oils for which it is necessary to better understand and quantify the chemical environments of those heteroelements. The aim of this work was to evaluate how the speciation of sulphur, nitrogen and oxygen in oils with the X-ray photoelectron spectroscopy in the “cold” mode could be the appropriate technique. The characterization of liquids and solids with low melting point, has been possible thanks to the use of the liquid nitrogen cooling system, for which the temperature can reach −135°C on the sample holder in the analysis chamber.The S 2p high resolution spectra recorded for the sulphur organic compounds has allowed establishing a valuable database for sulphur environments where six classes can be distinguished. The methodology developed in this work has been applied to the analysis of a straight run atmospheric residue for which thiol and thiophenic/sulfide environment has been identified. The relative concentration of those two chemical classes has been evaluated. 70% of the whole sulphur is present in thiophenic/sulfide group whereas the rest is thiol chemical class. The analyses performed on hydrotreated effluents highlight larger reactivity of the thiol compounds. But, we are facing a quite high detection limit of the XPS technique estimated at 0.1at.% not permitting the detection of sulphur in the highly desulphurised effluents. This is still a main limitation for deep hydrotreatment applications but this technique can be used to investigate visbreaking, deasphalting or combustion processes where the heteroelement removing is less severe. Developments on the XPS technique have to be continued in order to reduce its detection limit. The whole quantitative analysis must be considered carefully as hydrogen is not detected by XPS. However, the S/C, N/C and O/C atomic ratio of the reference samples are relatively consistent with combustion techniques.

Reactivation of an industrial batch of CoMo/Al2O3 catalyst for the deep hydrotreatment of oil fractions

The results from industrial tests of technology developed earlier for the reactivation of CoMo/Al2O3 catalyst for the deep hydrotreating of diesel fuel, including the oxidative regeneration of the catalyst with subsequent treatment using organic complexing agents, are presented. Samples of the catalyst, fresh and at different stages of its reactivation, are investigated using a set of analytical and physicochemical methods. The chemical composition, textural characteristics, mechanical strength, structure of the active sulfide component (TEM, XPS) are determined. Catalytic tests are performed that include lifetime tests (360 h) in the hydrotreatment of a straight-run diesel fraction. The restoration of the physicochemical and catalytic properties is observed for a sample subjected to oxidative regeneration with subsequent treatment using organic complexing agents. An industrial batch of deep hydrotreatment catalyst reactivated by this technology is loaded into an L-24-6 industrial plant facility and ensures stable purification of straight-run diesel fuel containing up to 10% of light catalytic cracking gas oil to a residual sulfur content of less than 10 ppm. Comparison of the obtained results and data on the industrial operation of fresh catalysts shows that the technology developed by the Institute of Catalysis and PAO Gazprom Neft ensures almost complete restoration of the properties of the deactivated catalysts.

Development of New Russian Catalysts for Deep Hydroconversion of Vacuum Gasoil

New Russian catalysts for deep hydrotreatment and hydrocracking of vacuum gasoil (VGO) were developed at the Boreskov Institute of catalysis in cooperation with the Institute for Hydrocarbon Processing and Topchiev Institute of Petrochemical Synthesis. The work was supported by the JSC Gazpromneft-Omsk Refinery under the Complex Project «Creation of the technology for the production of import-substituting catalysts for deep hydroconversion of vacuum gasoil» in the framework of the Federal Targeted Program “Research and Development in Priority Areas of the Scientific and Technological Complex of Russia for 2014–2020”. The high efficiency of the catalysts was experimentally proved. Preliminary works on implementation of the developed technologies for the production of the VGO hydrotreatment and hydrocracking catalysts including production of the catalyst components (amorphous aluminosilicates, zeolites) are in progress now.

Reactivation of the Industrial CoMo/Al2O3 Catalyst for Deep Hydrotreatment of Oil Fractions

Industrial testing of the developed technology for reactivation of the CoMo/Al 2 O 3 catalysts for deep hydrotreatment of diesel fuel was the oxidative regeneration of the catalyst followed by the treatment with organic complexing agents. A series of analytic and physicochemical techniques were used for studying samples of the catalyst, both fresh and at different stages of the reactivation. The chemical composition, textural parameters, mechanical strength and the structure of the active sulfide component were determined (TEM, XPS). Catalytic and life (360 h) tests were conducted using hydrotreatment of the straight-run diesel fraction. The physicochemical and catalytic properties of the sample were demonstrated to restore after the said treatments. The reactivated industrial catalyst for the deep hydrotreatment was loaded to an industrial reactor L-24-6 and demonstrated the stable operation in purifying the straight-run diesel fuel (containing up to 10 % of light catcracking gasoil) to provide no more than 10 ppm of the residual sulfur. The results obtained were compared to the performance of fresh industrial catalysts to show that the developed technology ensures practically complete restoration of properties of the deactivation catalysts.

CoNiMo/Al2O3 catalysts for deep hydrotreatment of vacuum gasoil

Trimetallic Co-Ni-Mo catalysts with different Co and Ni content (Co3Ni0, Co1.8Ni1.2, Co1.5Ni1.5, Co1.2Ni1.8 and Co0Ni3) were studied. Catalysts were characterized by HRTEM, XPS, EXAFS and XANES methods. It was shown that all catalysts contain metals preferentially in the form of sulfide active component with the structure that is similar to Co-Mo-S phase. Co-Mo and Ni-Mo catalysts contain active component in the form of Co-Mo-S and Ni-Mo-S phases respectively. Trimetallic catalysts were shown to contain mixed Ni-Co-Mo-S phases. Catalytic tests showed that the catalyst with 1.8% Co, 1.2% Ni and 10% Mo has the highest activity in hydrotreating of VGO. The highest activity of the catalyst is proposed to be provided by the formation of mixed Ni-Co-Mo-S phase.

Preparation of Nickel Phosphide Hydrodesulfurization Catalysts Assisted by Supercritical Carbon Dioxide

AbstractTo meet the increasing demand for clean fuels, deep hydrotreatment reactions are required, and thereby, improvement of the performance of the catalysts is highly desired. Silica‐supported nickel phosphide (Ni2P) nanoparticles have been reported to be efficient catalysts for hydrodesulfurization (HDS) reactions. We propose herein an innovative preparation method assisted by supercritical carbon dioxide (scCO2) to produce highly active Ni2P nanoparticles combining small size and high reducibility. In addition, scCO2 promotes the formation of the Ni2P phase with respect to the less active Ni12P5 phase. Such phosphide catalysts exhibit high activity for the HDS of 4,6‐dimethyldibenzothiophene, with a rate constant up to one order of magnitude higher than that of non‐supercritical references and close to conventional alumina supported NiMoS catalyst.

A new method for reactivating the supported deep hydrotreatment CoMo/Al2O3 and NiMo/Al2O3 catalysts after oxidative regeneration

A new method for the reactivation of CoMo/Al2O3 and NiMo/Al2O3 catalysts for the deep hydrotreatment of diesel fuel after the oxidative regeneration stage involves impregnating regenerated catalysts with aqueous solutions of such chelating compounds as citric and oxalic acids, ethyleneglycol, and diethyleneglycol with subsequent drying. The activity of reactivated catalysts subjected to such treatment can be higher than for fresh samples. The effect of the nature and amount of introduced chelates on the activity of the IK-GO-1 catalyst in the hydrotreatment of straight-run diesel fuel is studied. Treating an oxidized sample with a solution containing both citric acid and glycol at the optimum molar ratio of total chelate compounds to total metals (0.5–1.0) yields the best results. Regenerated catalysts thus enable the production of ultralow sulfur diesel fuels (10 ppm) at an initial hydrotreatment temperature 10–15°C lower than for catalysts after their oxidative regeneration and 3–4°C lower than for fresh catalysts.

Ultra Deep Hydrotreatment of Iraqi Vacuum Gas Oil Using a Modified Catalyst

A set of hydro treating experiments are carried out on vacuum gas oil in a trickle bed reactor to study the hydrodesulfurization and hydrodenitrogenation based on two model compounds, carbazole (non-basic nitrogen compound) and acridine (basic nitrogen compound), which are added at 0–200 ppm to the tested oil, and dibenzotiophene is used as a sulfur model compound at 3,000 ppm over commercial CoMo/Al2O3 and prepared PtMo/Al2O3. The impregnation method is used to prepare (0.5% Pt) PtMo/Al2O3. The basic sites are found to be very small, and the two catalysts exhibit good metal support interaction. In the absence of nitrogen compounds over the tested catalysts in the trickle bed reactor at temperatures of 523 to 573 K, liquid hourly space velocity 1 to 3 hr−1, and a pressure range of 16 to 20 bar, the results show an increase in conversion from 0.2214 to 0.6748 and 0.2920 to 0.7341 for CoMo and PtMo, respectively, with the increase of temperature, a little positive effect on conversions when pressure increases, and a significant decrease in conversion: 0.6748 to 0.3284 and 0.7341 to 0.3734 for CoMo and PtMo, respectively, when liquid hourly space velocity increases. The results showed a first-order kinetic of Dibenzothiphene (DBT) hydrodesulphurization. The activation energies are 75.399 and 67.983 kJ/mol for hydrodesulphurization of DBT over CoMo and PtMo, respectively.

A new catalyst for the deep hydrotreatment of vacuum gas oil, a catalytic cracking feedstock

A new CoNiMo/Al2O3 deep vacuum gas oil hydrotreatment catalyst designed for the production of catalytic cracking feedstocks containing 200–500 ppm of sulfur is developed. The method for its preparation includes the following stages: the preparation of a support with specified textural, strength, and granulometric characteristics; the synthesis of bimetallic (Co-Mo and Ni-Mo) complex compounds in solution; and their deposition and drying. The new sample is compared to current domestic and imported industrial analogs according to their physicochemical (texture, morphology, active phase structure) and catalytic characteristics and analyzed. It is shown that the catalyst allows hydrotreatment at temperatures 5–20°C lower and target fraction yields 4–13% higher than all the reference samples. The high activity of the new catalyst is due to the formation of one-layer trimetallic Co(Ni)MoS phase particles at the stage of its sulfidation. The catalyst preparation technique is ready for industrial use (OOO Sintez, Barnaul, 1000 t/yr), and the principal technological regimes of the hydrotreatment of vacuum gas oil on the developed catalyst are determined.

Modern approaches to testing granulated catalysts in the hydrotreatment of oil distillates under laboratory conditions

Problems related to granular catalysts testing in hydrotreatment of petroleum distillates in laboratory are discussed. Requirements for laboratory facilities that ensure high reliability in determining the performance of diesel fraction hydrotreatment in industrial reactors are formulated. It is shown that diluting catalyst pellets with small particles of inert nonporous material (silicon carbide) allows us to obtain reproducible results in small three-phase reactors, minimizing such factors as the incomplete wetting of the catalyst, the wall effect, and the back-mixing of liquids. Laboratory facilities and analysis techniques are described, and results obtained at different laboratories in studying catalysts for the deep hydrotreatment of diesel fractions are compared.

Evaluate Impact of Catalyst Type on Oil Yield and Hydrogen Consumption from Mild Hydrotreating

Bio-oil derived by fast pyrolysis of biomass represents a potentially attractive source of hydrocarbon transportation fuels. Raw bio-oil, however, is unsuitable for application as a fuel due primarily to high organic oxygen content, which imparts a number of undesirable properties including high acidity and low stability. These problems can be overcome by catalytic hydrodeoxygenation; however, removing oxygen to very low levels by hydrotreating carries a strong economic penalty. Mild hydrotreating (where moderate levels of deoxygenation take place) coupled with coprocessing in a petroleum refinery represents an alternative to deep hydrotreating which may improve the economics of manufacture of hydrocarbon transportation fuels from biomass. This study reports on the effect of catalyst type on the quality of bio-oil produced via mild hydrotreating in a semibatch reactor at three severities. Sulfided Ni–Mo/Al2O3, Pd/C(activated), Pd/char, Pt/char, and Ru/char were compared. Speciation of oxygen functional gr...

Deep hydrotreating of different feedstocks over a highly active Al2O3-supported NiMoW sulfide catalyst

The major challenge for deep hydrotreating of diesel fuels is the removal of refractory sulfur-containing compounds and reducing aromatics to meet the stringent environmental regulations. In the present study, the hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodearomatization (HDA) reactions of various real feedstocks over alumina-supported NiMoW catalyst synthesized by impregnation solution-based combustion method have been examined in order to gain insight into the capability of this preparation method to produce deep hydrotreating catalysts. The results show that a single exothermic peak with an ignition temperature of 272°C decomposes the NiMo-urea redox solution deposited on tungsten oxide-modified alumina surface, a subsequent impregnation with NiMo-urea solution produces an increase of the decomposition period of the metal oxide precursor and urea. Furthermore, the addition of Ni and Mo to WOx-modified alumina facilities the NiO–Mo (or W) Ox interaction and promotes MeOx reducibility. On the other hand, feed with lower density and higher end-boiling point (T95) shows lower HDS reactivity and hence more demanding operating conditions (i.e., high hydrogen pressure, high reaction temperature and low liquid contact time) are required to obtain diesel fuel with low aromatics, high cetane index and ultra low-S and -N concentrations. The strong inhibiting effect of N-containing compounds and weak effect of aromatics over the HDS reactivity of real feedstock is reflected on smaller HDS rate constant than HDN rate constant for γ-alumina-supported NiMo, NiMoW and even CoMo sulfide catalysts. The presence of tungsten in the NiMo catalyst selectively enhances the rates of the HDS reactions compared to the HDN reactions, particularly of refractory S compounds.