Hydrotreating catalysts are of great interest for researchers in oil refining. Nowadays, bulk NiMoW catalysts attract significant attention due to much higher activity in target hydrotreating reactions. The use of these catalysts as an additional catalyst layer in the main catalyst bed can significantly improve hydrotreating process efficiency, but it is a “know-how” knowledge of the catalyst’s producers. In this work we studied the effects of the order of the bulk and supported catalysts in the bed. The experiments include treating the model feedstocks with DBT or quinoline with the bulk catalyst first and then with the supported catalyst, and vice versa. It was shown that when the bulk catalyst was used first, total HDS and HDN activities of the individual compounds are higher than in the case of the supported catalyst to be first. Hence, using the bulk catalyst first increases total activity of the catalyst bed. In the case of simultaneous presence of sulfur and nitrogen compounds, the greater HDN activity of the bulk catalyst at the first stage facilitates HDS and HDN reactions occurring at the second stage over the supported catalyst. Then, the best catalyst order in bed is the bulk catalyst at the top of the reactor and the supported catalyst at the bottom.

The paper describes in detail the procedure for the preparation of a granular bulk NiMoW catalyst and a supported reference NiMo/Al2O3 catalyst. Mention is made of investigations of the supported and bulk catalysts by various physico-chemical methods (nitrogen adsorption-desorption method, X-ray photoelectron spectroscopy, TPD-NH3, HRTEM and X-ray diffraction analysis). The experiments to estimate catalytic activity and compare rate constant of hydrodesulfurization of dibenzothiophene using both catalysts have been carried out. It is shown that textural properties of the catalysts significantly differ. The supported catalyst has more developed specific surface area and pore volume than the bulk catalyst. TPD-NH3 showed an increased acidity of the supported catalyst in comparison the bulk catalyst. It is shown by the X-ray photoelectron spectroscopy method that in both samples Mo on the surface is present exclusively in the form of Mo4+ ion. However, the bulk catalyst differs from the supported catalyst in that it contains a larger amount of Ni as part of the active NiMo(W)S phase. The catalytic activity tests demonstrated that the bulk catalyst is more active at 240, 250 and 260°C, it is discovered that the rate constant in hydrodesulfurization of dibenzothiophene for the bulk NiMoW catalyst is twice higher at 240ºC than that of the supported NiMo/Al2O3 catalyst.

This paper presents a study on the effect of the Ni-Mo-W precursor calcination (300, 450 and 500 degrees C) on properties of granulated bulk Ni-Mo-W catalysts. The Ni-Mo-W precursor and bulk catalysts were studied by XRD, nitrogen adsorption-desorption method, CHNS analysis, thermal analysis, Raman spectroscopy, UV-Vis DR spectroscopy, HRTEM and XPS. It is shown that the increase in calcination temperature of the precursor to 500 degrees C leads to stepwise decomposition of citric acid, transformation of active metals and re-structurization of the samples. Active metals in sulfide catalysts are present in the bulk mixed or individual sulfides and interact with alumina binder to form "NiMoS-like" sulfide phase. Increased crystallinity of the precursor results in the enlargement of bulk nickel particles, capsulation of Mo and W and their rounding by Ni atoms. Catalysts testing in hydrotreatment of SRVGO demonstrates that the best choice of temperature regimes is 300 degrees C for the precursor.

The present study investigates the effects of heat treatment temperature on the physicochemical properties of bulk granular Ni–Mo–W catalysts. A series of bulk catalysts were synthesized and characterized by X-ray diffraction analysis, low-temperature nitrogen adsorption/desorption, CHNS elemental analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. To evaluate the catalytic activity in hydrodesulfurization and hydrodenitrogenation reactions, the catalyst samples were tested in hydrotreating of vacuum gasoil. It was found that the bulk granular catalysts calcined at 400°C and lower temperatures were mainly X-ray amorphous. In the samples calcined above 400°C, a nickel molybdate phase was predominant. In these samples, the content of an active sulfide phase after sulfidation was lower than that in the samples prepared from X-ray amorphous oxide precursors. The test data showed that the catalyst calcined at 300ºC exhibited the highest activity in the hydrodesulfurization of vacuum gasoil.

Among the known synthesis procedures and reagents for unsupported Ni–Mo–W catalysts, there is no consensus about optimal preparation conditions of their precursors. In the present work, Ni–Mo–W precursors were prepared via three preparation techniques—hydrothermal synthesis, precipitation method and spray drying—after the synthesis of complex compounds in solution. Ni–Mo–W precursors were studied by the XRD analysis, SEM methods, Raman and UV-vis spectroscopies and XPS measurements and used for the hydrotreatment of straight-run gasoil. Precursors prepared by hydrothermal synthesis contain particles with stacked plate shapes, while other methods provide spherical particles. The formation of different amounts of individual molybdates, tungstates or mixed phases such as W1−xMoxO3 possibly doped by Ni was detected. The precipitation technique results in the formation of spheres, with W located at the center and is unavailable for catalysis. The catalytic activity increased when all active metals are available for the feedstock, and a more mixed phase containing Ni, Mo and W is formed. This mixed phase is realized when the synthesis of the Ni–Mo–W precursors is carried out in solution followed by spray drying. The resulting catalyst has 1.2–4 times higher activity than catalysts prepared by other methods.

This review considers and systematizes the results of studying the deactivation of hydrotreatment catalysts currently available in the scientific and technical literature. The effect the composition of the feedstock and the conditions of hydrotreatment have on the coking of catalysts is shown. The reasons for the morphological changes of the active component and the possibility of reducing this type of catalyst deactivation during commercial operation are considered. The effect of a pressure drop on the run time, the action of catalyst poisons, and the ways, in which they enters the hydrotreatment distillates is shown. This information could be useful and interesting to chemical engineers studying catalytic systems, and to workers of oil refining industry.

The results of studies on deactivation of hydrotreating catalysts reported in scientific and technical literature are considered and systematized in the review. The effect exerted by the feedstock composition and hydrotreatment conditions on the catalyst coking is revealed. The factorsleading to changes in the morphology of active component and the possibilities to weaken this type of catalyst deactivation during commercial operation are considered. The effect of a pressure drop over the catalyst bed on the run time as well as the action of catalytic poisons and the ways of their penetration into hydrotreatment distillates are shown. This review can be interesting and useful to chemical engineers involved in the study of catalytic systems and to oil industry specialists.

Hydrotreating is one of the largest processes used in a refinery to improve the quality of oil products. The great demand of the present is to develop more active catalysts which could improve the energy efficiency of the process when it is necessary for heavier feedstock to be processed. Unsupported catalysts could solve this problem, because they contain the greatest amount of sulfide active sites, which significantly increase catalysts’ activity. Unfortunately, most of the information on the preparation and properties of unsupported catalysts is devoted to powder systems, while industrial plants require granular catalysts. Therefore, the present work describes a method for the preparation of granular Ni—Mo—W unsupported hydrotreating catalysts and studies the influence of the Ni/Mo/W atomic ratio on their properties. Catalysts have been prepared by plasticizing Ni—Mo—W precursor with aluminum hydroxide followed by granulation and drying stages. Ni—Mo—W precursor and granular catalysts were studied by X-ray diffraction (XRD), nitrogen adsorption–desorption method, high-resolution transmission electron microscopy (HRTEM), and thermal analysis. Granular catalysts were sulfided through a liquid-phase sulfidation procedure and tested in hydrotreating of straight-run vacuum gasoil. It was shown that the Ni/Mo/W atomic ratio influenced the formation and composition of active compounds and had almost no influence on the textural properties of catalysts. The best hydrodesulfurization (HDS) activity was obtained for the catalyst with Ni/Mo/W ratio—1/0.15/0.85, while hydrodenitrogenation (HDN) activity of the catalysts is very similar.

A NiMoP/Al2O3 catalyst deactivated at the industrial plant was subjected to oxidative regeneration and reactivation with water and an aqueous solution of citric acid. The catalyst was studied at all stages by XRD, UV–vis, Raman spectroscopy, FTIR spectroscopy, XPS and HRTEM methods. The catalyst samples after oxidative regeneration, treatment with water and rejuvenation with citric acid were tested in hydrotreatment of the model feedstock and straight-run gasoil. It was established that the regenerated catalyst contained phosphorus strongly bound to the support and soluble or insoluble Ni and Mo compounds. The catalyst after water treatment contained only insoluble Ni and Mo compounds and a phosphate monolayer, while treatment with citric acid resulted in the formation of citrate complex compounds. Ni and Mo compounds in the sulfide form, which were obtained from insoluble components, showed high activity in the target hydrotreating reactions.

The feasibility of the reactivation of CoMo/Al2O3 hydrotreating catalysts poisoned by Si compounds has been studied. CoMo/AAl(2)O(3) catalysts poisoned with 3, 4 and 5 wt.% of silicon were obtained during hydrotreating of diesel fraction contaminated with decamethylcyclopentasiloxane. Catalysts poisoned by different amount of silicon were regenerated by oxidative treatment and subsequently reactivated using citric acid solution. The catalysts were studied by nitrogen adsorption-desorption method, CHNS analysis, UV-vis, thermal analysis, SEM, HRTEM, XPS. It was shown that the hydrodesulfurization activity of regenerated catalysts decreased with increasing silicon content. According to UV-vis results, the increase in Si content on the spent catalyst leads to the formation of CoOx oxides after oxidative regeneration. Probably, cobalt oxides do not promote MoS2 slabs during sulfidation, convert to inactive Co species and decrease hydrodesulfurization activity. After reactivation procedure, there was the increase in active component particles dispersion, while catalytic activity in hydrodesulfurization of dibenzothiophene and hydrodenitrogenation of quinoline increased. It was established that hydrodesulfurization and hydrodenitrogenation activities of CoMo/Al2O3 catalyst with less than 3 wt.% of Si could be completely restored by reactivation.

Commercial NiMoP/Al2O3 catalyst was reactivated by a solution of citric acid and orthophosphoric acid after a commercial operation and oxidative regeneration. Catalysts were described with using of many different methods, such as N-2 adsorption, UV-vis DRS, FTIR, Raman, XPS spectroscopy, and HRTEM. Catalytic properties were measured in hydrotreating of dibenzothiophene and SRGO using a fixed bed high-pressure flow reactor. Reactivation with citric and orthophosphoric acids resulted in the significantly recovery of HDS activities. The maximal recovery of activity was overseen for the catalyst treated with a solution of orthophosphoric acid in the concentration corresponded to the ratio P/Ni = 0.2.

Hydrocracking of vacuum gas oil has been studied over NiMo/zeolite-Al2O3 catalysts. Three different zeolites have been used for catalysts preparation: zeolites Beta (BEA) and Y (FAU) having small crystal size and zeolite Y modified by recrystallization (RFAU). HRTEM, low-temperature N-2 adsorption, FTIR of adsorbed CO and TPD-NH3 showed that zeolites had different crystal sizes, mesopore volume, strength and concentration of acid sites. Sulfide active component particles have been revealed to be similar in all catalysts by HRTEM and XPS. NiMo/ BEA catalyst having zeolite with the smallest average particle size and the highest concentration of Bronsted acid sites (BAS) demonstrated the highest hydrocracking activity. Selectivity to middle distillates decreased in the following order: NiMo/FAU > NiMo/RFAU > NiMo/BEA. This effect is accounted for by optimal zeolite acidity and improved availability of the acid sites for bulky molecules of the heavy feedstock.

Data on the processing of secondary middle distillates are surveyed. Modern processes and technologies for the refining of secondary distillates to produce motor fuel components that meet the requirements of modern standards have been considered. Problems arising in relation to hydrofining of secondary feedstock with a high unsaturates and aromatics content are touched on.

Commercial liquid-phase-sulfided type II CoMo/Al2O3 catalyst was reactivated after commercial operation and oxidative regeneration. For this purpose, the use of citric acid (CA) that reactivates a regenerated CoMo/Al2O3 catalyst was studied. The study of the reactivated catalyst was carried out by means of UV-DRS, FTIR, Raman spectroscopy, XRD, XPS, and HTREM. The catalytic activity was estimated in the HDS of straight-run gasoil (SRGO). It was shown that the treatment of the catalyst with CA leads to the formation of a Co–Mo complex compound and significantly reduces the proportion of β-CoMoO4 and MoO3 in the catalyst. Eventually, this leads to the formation of CoMoS phase type II in a higher proportion enhancing the HDS catalytic properties.

Effect of various chelating components, multibasic carboxylic acids and glycols, used to prepare hydrotreating catalysts on the activity regeneration of calcined hydrotreating catalysts was studied. Reactivated catalyst samples were tested in a model reaction of hydrodesulfurization of dibenzothiophene. It was shown that the treatment of calcined catalysts with the chelating components leads to an increase in the catalytic activity. The best catalytic characteristics are observed for the catalyst reactivated with a solution containing citric acid and triethylene glycol.

The results from industrial tests of technology developed earlier for the reactivation of CoMo/Al 2 O 3 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.

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.