Effect of sulfidation process on catalytic performance over unsupported Ni-Mo-W hydrotreating catalysts

Oxidic unsupported Ni-Mo-W catalysts were chosen to elucidate the effect of sulfidation conditions on the catalytic performance. The catalysts were sulfided in situ by using dimethyl sulfide as sulfiding agent. The relationships between the time needed for sulfidation and the sulfiding conditions were studied by GC-analysis method. Straight-run gas oil with high sulfur and nitrogen content was used to evaluate the hydrotreating performance. The oxidic catalyst precursors and sulfided catalysts were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). With increasing sulfiding liquid hourly space velocity (LHSV) of the sulfiding agent, the reaction time necessary for the sulfidation decreased, while the activity of the catalyst increased significantly. The higher catalytic activity might be due to the MoS₂/WS₂ slabs with shorter length and higher stacking number, which might contribute to the catalyst with more active sites. Sulfiding at 330 °C took the longest sulfidation time, while the catalytic activity was also the highest after sulfiding at this temperature. Furthermore, within a certain range, the sulfidation pressure had no evident effect on the catalytic behavior or activity. The purpose of this work was to provide a basis for actual production and a reference for further research.     

Genesis of new HDS catalysts through a careful control of the sulfidation of both Co and Mo atoms: Study of their activation under gas phase

Impregnation of oxidic precursor with thioglycolic acid aqueous solution was successfully used to improve the performances of thiophene hydrodesulfurization catalysts. Raman, EXAFS and XPS studies indicate that addition of this chelating agent affects the sulfidation of the supported metals. The higher catalytic performances were attributed to an optimization of the nature and morphology of the active phase obtained by the use of this chelating agent which permits a simultaneous sulfidation of both Co and Mo atoms.     

络合剂对加氢精制催化剂影响的研究进展

络合剂作为一种常用的助剂,由于其能提高加氢催化剂的性能而得到了研究者的重视。本文综述了络合剂对加氢催化剂加氢性能的影响,总结了引入络合剂后催化剂硫化行为方面的研究进展。简要介绍了络合剂的加入对金属浸渍液性质与催化剂加氢活性的影响,及采用共浸渍和分步浸渍引入络合剂时络合剂不同的作用机理。总体来看,络合剂的添加可以延迟助剂Ni(Co)的硫化,降低Mo(W)的硫化温度,进而提高Mo(W)的硫化程度,减弱活性组分与载体的相互作用,增强了活性组分的分散性,最终提高了催化剂的加氢脱硫活性。最后指出对络合剂改性的加氢脱硫催化剂在作用机理、工业催化领域等方面的研究是未来的研究方向。     

Preparation of CoMoS catalysts for hydrodesulfurization using methylacetoacetate as a chelating agent

CoMoS/Al₂O₃ catalyst, which was prepared using Co(MeAA)₂·2H₂O as a new Co precursor, showed activity for hydrodesulfurization (HDS) higher than that of conventional catalysts, which were prepared using Co(NO₃)·6H₂O as a Co precursor and/or by adding ethylene-di-amine-tetra-acetic acid (EDTA) as a chelating agent. Catalyst of a similar activity was also obtained simply by impregnating a conventional CoMo/Al₂O₃ catalyst with an aqueous solution of methylacetoacetate (MeAA) followed by drying and sulfidation. The added MeAA reacted with Co to produce Co(MeAA)₂·2H₂O on the catalyst surface during impregnation step, such that the resulting catalyst became similar to one prepared by direct impregnation with Co(MeAA)₂·2H₂O. The in-situ synthesis of Co(MeAA)₂·2H₂O on the catalyst surface was advantageous over the method of directly adding the Co precursor to the impregnation solution because the former method did not use a basic material, which was required for the synthesis of the Co precursor. Furthermore, MeAA was soluble in water, whereas Co(MeAA)₂·2H₂O had to be dissolved in an organic solvent, e.g., 1,4-dioxane. The Co species in the MeAA-added catalysts were sulfided at temperatures higher than those of conventional catalysts, and consequently the former catalysts contained greater amounts of the HDS-active CoMoS phase than the latter.     

Morphology and Atomic-Scale Structure of MoS2 Nanoclusters Synthesized with Different Sulfiding Agents

We use scanning tunneling microscopy to investigate the morphology and atomic-scale edge structure of MoS₂ nanoclusters synthesized on a gold single crystal as a model system for hydrodesulfurization catalysts using three different sulfur sources for sulfiding. Crystalline and triangularly shaped MoS₂ nanoclusters are predominantly produced from sulfiding with H₂S, dimethyl disulfide (DMDS) and dimethyl sulfide (DMS), but the detailed dispersion, stacking and distribution of active edge sites is sensitive to the selection of the sulfiding agent. The main effect of varying the sulfiding agent seems to be related to the variation in the reactivity of the sulfur, i.e. changes in the sulfur chemical potential. H₂S and DMDS both yield fully sulfided edge structures, but lower sulfur content is obtained on the edges of MoS₂ sulfided with DMS reflected by Mo-edges terminated by sulfur monomers. The present model studies demonstrate that MoS₂ morphology and hereby also the dispersion, type and amounts of active edge sites can be manipulated by control of sulfiding conditions and choice of sulfiding agent. The findings are in line with previous reports on activity variations on technical catalysts which have undergone different sulfidation procedures.     

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 (T₉₅) 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 T₉₅ 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.     

A comparative study on the effect of promoter content of hydrodesulfurization catalysts at different evaluation scales

CoMo and NiMo supported Al₂O₃ catalysts have been investigated for hydrotreating of model molecule as well as industrial feedstock. Activity studies were carried out for thiophene and SRGO hydrodesulfurization (HDS) in an atmospheric pressure and batch reactor respectively. These activities on sulfided catalysts were evaluated as a function of promoter content [M/(M + Mo) = 0.30, 0.34, 0.39; M = Co or Ni] using fixed (ca. 8 wt.%) molybdenum content. The promoted catalysts were characterized by textural properties, XRD, and temperature programmed reduction (TPR). TPR spectra of the Co and Ni promoter catalysts showed that Ni promotes the easy reduction of Mo species compared with Co. With the variation of promoter content NiMo catalyst was found to be superior to CoMo catalyst for gas oil HDS, while at low-promoter content the opposite trend was observed for HDS of thiophene. The behavior was attributed to the several reaction mechanisms involved for gas oil HDS. A nice relationship was obtained for hydrodesulfurized gas oil refractive index (RI) and aromatic content, which corresponds to the Ni hydrogenation property.     

Realistic Surface Science Models of Hydrodesulfurization Catalysts on Planar Thin-Film Supports: The Role of Chelating Agents in the Preparation of CoW/SiO2 catalysts

Realistic surface science models of supported molybdenum- and tungsten-based hydro-treating catalysts have been made by impregnating planar thin films of silica and alumina with aqueous solutions of the normally utilized precursor salts of active elements. These models have enabled detailed studies of catalyst preparation and hydrodesulfurization kinetics. Optimization of the catalysts is possible by applying appropriate chelating agents for the promoting elements cobalt and nickel. These complexes work by stabilizing the promoting element such that during sulfidation MoS₂ and WS₂ structures form before the promoters are released so that these have a higher chance to end up at the edges of MoS₂ and WS₂ instead of forming the less active Co₉S₈ and Ni₂S₃ phases. The extent to which sulfidation of the promoter cobalt is delayed correlates with the activity of the catalyst for thiophene hydrodesulfurization.     

Decomposition of dimethyldisulfide on various W–Ni catalysts

The decomposition of dimethyldisulfide (DMDS) was studied on WNi/Al₂O₃, WNi/Beta + Y, WNi/Beta, and WNi/Y catalysts. DMDS was rapidly converted to methanethiol. The methanthiol was subsequently transformed to methane, H₂S, and dimethylsulfide (DMS). On WNi/Al₂O₃, methanthiol and dimethylsulfide were slowly consumed to sulfide catalyst. On the zeolite containing catalysts, the methanthiol and dimethylsulfide (DMS) were completely and rapidly consumed for sulfidation. Considerable amounts of C4–C5 alkanes were formed during the transformation of dimethylsulfide (DMS) on the zeolite containing catalysts. The formation of the alkanes was closely related to the synergic effect between the metal–sulfur interaction and the acidity of catalysts. The quantity of alkanes changed directly proportionally with the reaction pressure.     

Development of iron oxide sorbents for Hg removal from coal derived fuel gas: Sulfidation characteristics of iron oxide sorbents and activity for COS formation during Hg removal

The aim of this study is to develop a process for the removal of Hg⁰ using H₂S over iron oxides sorbents, which will be located just before the wet desulfurization unit and catalytic COS converter of a coal gasification system. It is necessary to understand the reactions between the iron oxide sorbent and other components of the fuel gas such as H₂S, CO, H₂, H₂O, etc. In this study, the sulfidation behavior and activity for COS formation during Hg⁰ removal from coal derived fuel gas over iron oxides prepared by precipitation and supported iron oxide (1 wt% Fe₂O₃/TiO₂) prepared by conventional impregnation were investigated. The iron oxide samples were dried at 110 °C (designated as Fe₂O₃-110) and calcined at 300 and 550 °C (Fe₂O₃-300 and Fe₂O₃-550). The sulfidation behavior of iron oxide sorbents in coal derived fuel gas was investigated by thermo-gravimetric analysis (TGA). COS formation during Hg⁰ removal over iron oxide sorbents was also investigated using a laboratory-scale fixed-bed reactor. It was seen that the Hg⁰ removal activity of the sorbents increased with the decrease of calcinations temperature of iron oxide and extent of sulfidation of the sorbents also increased with the decrease of calcination temperature. The presence of CO suppressed the weight gain of iron oxide due to sulfidation. COS was formed during the Hg⁰ removal experiments over Fe₂O₃-110. However, in the cases of calcined iron oxides (Fe₂O₃-300, Fe₂O₃-550) and 1 wt% Fe₂O₃/TiO₂, formation of COS was not observed but the Hg⁰ removal activity of 1 wt% Fe₂O₃/TiO₂ was high. Both FeS and FeS₂ were active for Hg⁰ removal in coal derived fuel gas without forming any COS.     

硫化条件对氧化铈高温煤气脱硫剂的影响

氧化铈是一种新型的高温煤气脱硫剂,它的主要优点是再生过程中能产生单质硫。本文采用工业硝酸铈Ce（NO3）3.6H2O为原料制取CeO2,用干混法制备CeO2高温煤气脱硫剂。在固定床反应器中考察不同空速、不同硫化温度以及水气氛对脱硫剂脱硫效率的影响。结果表明：硫化温度800℃,空速1 500 h-1脱硫剂的脱硫效率较高;水气氛的存在,抑制了脱硫剂的还原与硫化,使得脱硫剂的脱硫效率下降。     

Reactivation of an industrial batch of CoMo/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> 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.     

器外再生重整催化剂3932/3933开工技术的首次应用

介绍了重整催化剂3932/3933器外再生后的工业使用情况，包括各个工序操作指标和过程。最终干燥温度为450 ℃，系统中控制的最终氧含量为16%；还原控制升温速率20～30 ℃·h^－1，还原最高温度480 ℃。硫化以二甲基二硫为硫化剂。半再生重整装置的处理能力为300 kt·a^－1。重整催化剂经过干燥、还原和硫化后投入工业应用，汽油产品质量符合设计要求，通过博士实验，腐蚀等级1a，研究法辛烷值为92。重整装置运行平稳。     

Two-step adsorption process for deep desulfurization of diesel oil

An integrated adsorption process for deep desulfurization of diesel fuel was proposed and examined. Conventionally hydrodesulfurized straight run gas oil (HDS-SRGO) having less than 50 ppm sulfur was also adsorptively treated with activated carbon fiber (ACF) to attain the ultra low sulfur gas oil having less than 10 ppm sulfur. The ACF, used in cleaning-up HDS-SRGO, was successively examined in straight run gas oil (SRGO) treatment to enhance its hydrodesulfurization (HDS) reactivity over conventional CoMo catalyst by removing the nitrogen and refractory sulfur species contained in SRGO. Such integrated adsorption–reaction process makes it possible to utilize the maximum adsorption capacity of ACF and achieve ultra deep desulfurization og SRGO. Regeneration of used ACF with a conventional solvent was proved very effective in restoring its adsorption capacity.     

Support effects in the hydrotreatment of model molecules

The support effect on the activity of hydrotreating catalysts using model molecules was analyzed for catalysts supported on TiO₂, SiO₂ and MgO. The results reported in the literature indicate that adequate design of the characteristics of the catalytic support is of great importance in the development of better hydrotreating catalysts. It was shown that by means of an adequate support design it is possible to increase significantly the HDS, HYD and HDN functionalities of hydrotreating catalysts. Semiconducting supports like TiO₂ can improve the HDS and HYD activities by exerting electronic effects on the active phase, helping in this way the formation of sulfur vacancies. Alumina supports modified by SiO₂ can facilitate the sulfidation of the active species, leading to better-promoted type II active sites with increased HDS and HYD catalyst functionalities. The nature of the support affects the sulfidation and dispersion of the catalysts even when chelating agents are used during catalyst preparation.     

On the formation of cobalt–molybdenum sulfides in silica‐supported hydrotreating model catalysts

Model catalysts, consisting of a conducting substrate with a thin SiO₂ layer on top of which the active catalytic phase is deposited by spincoating impregnation, were applied to study the formation of the active CoMoS phase in HDS catalysts. The catalysts thus prepared showed representative activity in the hydrodesulfurization of thiophene, confirming that these models of HDS catalysts are realistic. Combination of the sulfidation behaviour of Co and Mo studied by XPS and activity measurements shows that the key in the formation of the CoMoS phase is the retardation of the sulfidation of Co. Complexing Co to nitrilotriacetic acid complexes retarded the Co sulfidation, resulting in the most active catalyst. Due to the retardation of Co in these catalysts, the sulfidation of Mo precedes that of Co, thereby creating the ideal conditions for CoMoS formation. In the CoMo catalyst without NTA the sulfidation of Co is also retarded due to a Co–Mo interaction. However, the sulfidation of Mo still lags behind that of Co, resulting in less active phase and a lower activity in thiophene HDS. This revised version was published online in June 2006 with corrections to the Cover Date.     

Removal of sulfur at high temperatures using iron-based sorbents supported on fine coal ash

This paper deals with the simultaneous removal of H₂S and COS in the temperature range of 400-650 °C at 1 bar by using iron-based sorbents. The iron-based sorbents were prepared using iron oxide and cerium oxide with coal fine ash as the support. Simulated coal gas was used in the sulfidation experiments and 5% O₂ in N₂ gas was used for regeneration of sorbents. Both sulfidation and regeneration experiments have been carried out using a fixed-bed quartz reactor. The product gases were analyzed using a GC equipped with a TCD and a FPD. The results demonstrated that both H₂S and COS can be effectively reduced using the iron-based sorbents supported on fine coal ash. XRD analysis shows that Fe_1−xS phase has formed during sulfidation indicating a high sulfur capacity of the sorbent. The mechanism of the removal of COS simultaneously with H₂S is also discussed.     

直馏柴油络合萃取脱硫

分别采用络合剂FeCl3,AlCl3,TiCl4对产自盘锦慧丰的直馏柴油进行络合脱硫,结果表明:AlCl3的脱硫效果最好,络合剂用量为2 g时,脱硫率达到73.9%。通过实验得到在络合脱硫时,直馏柴油中的碱性氮含量减少,说明碱性氮消耗了络合剂,降低了络合剂的脱硫效果。本文采用自制脱氮剂LCH-28对盘锦慧丰直馏柴油进行脱氮,脱氮率达到90.0%。使用络合剂AlCl3对已脱氮的直馏柴油比未脱氮的直馏柴油脱硫率提高约5%~10%。为了取得更好的脱硫效果,采用络合剂AlCl3和三种萃取剂95%乙醇,甲醇,DMF进行复配。结果表明:以40 g柴油为基准,LCH-28的剂油比为1:200,AlCl3用量为2 g,95%乙醇用量为0.25 mL,在反应时间为20 min,反应温度为50℃的工艺条件下,对直馏柴油的脱硫率达到83.4%。     

Silica-Supported Cobalt Catalysts for Fischer–Tropsch Synthesis: Effects of Calcination Temperature and Support Surface Area on Cobalt Silicate Formation

Cobalt silicate formation reduces the activity of the catalyst in Fischer–Tropsch synthesis (FTS). In this article, the effects of calcination temperature and support surface area on the formation of cobalt silicate are explored. FTS catalysts were prepared by incipient wetness impregnation of cobalt nitrate precursor into various silica supports. Deionized water was used as preparation medium. The properties of catalysts were characterized at different stages using FTIR, XRD and BET techniques. FTIR-ATR analysis of the synthesized catalyst samples before and after 48 h reaction identified cobalt species formed during the impregnation/calcination stage and after the reduction/reaction stage. It was found that in the reduction/reaction stage, metal-support interaction (MSI) added to the formation of irreducible cobalt silicate phase. Co/silica catalysts with lower surface area (300 m²/g) exhibited higher C₅₊ selectivity which can be attributed to less MSI and higher reducibility and dispersion. The prepared catalysts with different drying and calcination temperatures were also compared. Catalysts dried and calcined at lower temperatures exhibited higher activity and lower cobalt silicate formation. The catalyst sample calcined at 573 K showed the highest CO conversion and the lowest CH₄ selectivity.     

Novel preparation method of highly active Co/SiO2 catalyst for Fischer-Tropsch synthesis with chelating agents

Co/SiO₂ catalysts were prepared by the incipient wetness method using the aqueous Co nitrate solution modified with various organic acids and/or chelating agents followed by drying and calcination. After H₂ reduction at 773 K, the catalyst prepared with nitrilotriacetic acid (NTA) showed Fischer-Tropsch synthesis (FTS) activity ca. 3 times higher than the catalyst without additives under mild reaction conditions (503 K, 1.1 MPa).