A method for processing high aromatics raw materials in a diesel hydrogenation unit

Abstract

The present invention discloses a method for processing a high-aromatic feedstock in a diesel hydroprocessing unit. The method comprises: (a) feedstock oil and hydrogen enter a diesel hydroprocessing reactor and sequentially pass through a diesel hydrorefining catalyst bed and a dearomatization catalyst bed in the diesel hydroprocessing reactor to undergo a hydrogenation reaction; (b) the reaction stream obtained in step (a) enters a separator for gas-liquid separation; and (c) the liquid obtained in step (b) enters a fractionation system to obtain a diesel product; wherein the catalyst loaded in the dearomatization catalyst bed is a polycyclic aromatic hydrocarbon removal catalyst. The present invention enables existing diesel hydroprocessing units to flexibly adapt to feedstock changes and extend operating cycles, while avoiding equipment modification, reducing investment, and lowering equipment energy consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of oil hydrogenation, and in particular to a method for processing high-aromatic hydrocarbon raw materials in a diesel hydrogenation device. Background Art

[0002] As China's diesel sulfur content requirements become increasingly stringent, the development and use of ultra-low sulfur and low aromatics diesel is a global trend in clean fuel development. China implemented the National VI diesel standard on January 1, 2019. While the sulfur content requirement remains unchanged, the polycyclic aromatic hydrocarbons (PAHs) content has been further reduced to 7%.

[0003] Oil refineries worldwide maximize crude oil utilization through secondary processing. Currently, these secondary processing units primarily include coking, catalytic cracking, hydrogenation, and catalytic reforming. In China, catalytic cracking is the primary processing route for refineries. However, catalytic cracking diesel has high aromatic and nitrogen content, high density, low cetane number, and poor engine ignition performance. In particular, the excessive aromatic content prevents it from meeting the VI diesel standard. The continuous upgrade of diesel product quality places significant pressure on refineries, especially when blending catalytic diesel into diesel hydrotreating units. While achieving ultra-deep desulfurization, the company must also avoid issues such as reduced aromatic removal due to elevated reaction temperatures, which can hinder the long-term operation of diesel hydrotreating units.

[0004] US10162310 discloses a two-phase hydrogenation pretreatment process. The process is that fresh raw oil, circulating oil and hydrogen pass through a hydrogen mixing device, hydrogen is dissolved in the oil, and the oil with dissolved hydrogen enters a smaller reactor to contact the catalyst for hydrogenation reaction to remove impurities in the oil. Part of the post-reaction logistics is circulated to the hydrogen mixing device, and part is discharged from the device as a product. This method uses the raw materials and circulating oil to pre-dissolve the required hydrogen in the oil before entering the reactor, and the circulating hydrogen system can be omitted. When this method is used to treat secondary processed intermediate distillate oil, the impurity removal rate is difficult to meet the standard. Although methods such as steam stripping can be used for removal, due to the high temperature and high pressure system, equipment investment and operating costs will also increase.

[0005] CN111321005A discloses a low-energy, long-cycle hydrogenation process for producing ultra-low-sulfur diesel. The process involves fractionating diesel feedstock to produce a light fraction and a heavy fraction. The heavy fraction is first subjected to a hydrodesulfurization reaction and then mixed with the light fraction in a second hydrodesulfurization zone for a hydrodesulfurization reaction. The second hydrodesulfurization zone's logistics are separated into a gas phase and a liquid phase. The resulting hydrogen-rich gas is recycled directly or after desulfurization. The resulting liquid phase is separated to produce gas, naphtha, and diesel products. This method takes into account the severity of desulfurization of diesel fuel of different fractions, but does not consider the impact of diesel polycyclic aromatic hydrocarbons on product quality, nor the effect of reaction temperature on oil dearomatization during long-cycle diesel production.

[0006] CN110157472A discloses a diesel hydrodesulfurization and denitrification process. This process utilizes a fixed-bed reactor filled with a hydrodesulfurization and denitrification catalyst. The processed feedstock is straight-run diesel, which cannot meet the requirements for processing high-aromatic feedstocks.

[0007] In summary, existing diesel hydrotreating technologies can produce superior diesel products, achieving certain improvements in quality, such as cetane number, sulfur content, aromatics content, and density. However, most feedstocks are subject to limitations, limiting the processing of direct diesel or the blending of small amounts of secondary processed oil. In particular, the blending ratio of catalytic diesel must be low, or complex processing is required to ensure that the diesel product meets the National VI emission standards. Furthermore, existing diesel hydrotreating units and catalysts are affected by the aromatics content when processing low-quality feedstocks, making it difficult to produce qualified diesel products over a long period of time. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for processing high-aromatic feedstocks in a diesel hydrotreating unit, particularly for existing diesel hydrotreating units in existing refining and chemical enterprises that use a trickle bed hydrogenation reaction process. This method enables the existing diesel hydrotreating units to flexibly adapt to changes in feedstocks and extend the operating cycle, while avoiding unit modification, reducing investment, and lowering unit energy consumption.

[0009] The present invention provides a method for processing a high-aromatic hydrocarbon feedstock in a diesel hydrotreating unit, comprising:

[0010] (a) The crude oil and hydrogen enter the diesel hydrogenation reactor and sequentially pass through the diesel hydrorefining catalyst bed and dearomatization catalyst bed in the diesel hydrogenation reactor to undergo hydrogenation reaction;

[0011] (b) the reaction stream obtained in step (a) enters a separator for gas-liquid separation;

[0012] (c) the liquid obtained in step (b) enters a fractionation system to obtain a diesel product;

[0013] The catalyst loaded in the dearomatization catalyst bed is a polycyclic aromatic hydrocarbon removal catalyst, the polycyclic aromatic hydrocarbon removal catalyst uses alumina as a carrier, and a molecular sieve and an active component are loaded on the carrier, the active components are Group VIB metal sulfide and Group VIII metal sulfide; the molar ratio of the Group VIII metal sulfide species on the Group VIB metal sulfide wafer to the total amount of the Group VIII metal sulfide is 60%-100%; the molecular sieve is loaded on the outer surface of the catalyst.

[0014] Furthermore, based on the total weight of the polycyclic aromatic hydrocarbon removal catalyst, the molecular sieve accounts for 1wt%-15wt%, preferably 1.5wt%-10wt%, and more preferably 2wt%-8wt%; the VIB group metal sulfide, calculated as sulfide, accounts for 10wt%-35wt%, preferably 15wt%-30wt%, and the Group VIII metal sulfide, calculated as sulfide, accounts for 2wt%-10wt%, preferably 4wt%-8wt%.

[0015] Furthermore, when the polycyclic aromatic hydrocarbon removal catalyst is analyzed by CO-FTIR, the molar ratio of the Group VIII metal-Group VIB metal-S phase to the Group VIII metal (i.e., the molar ratio of the Group VIII metal sulfide species on the Group VIB metal sulfide wafer to the total amount of the Group VIII metal sulfide) is 60%-100%, preferably 65%-90%, more preferably 70%-90%, and most preferably 80%-90%.

[0016] Furthermore, the molecular sieve is at least one selected from Y-type molecular sieve, ZSM-5 molecular sieve, β-type molecular sieve and MCM-41 molecular sieve, preferably Y-type molecular sieve.

[0017] Furthermore, the molecular sieve loaded on the outer surface of the catalyst is loaded on a VIB group metal sulfide, and / or loaded on a VIII group metal sulfide, and / or loaded on alumina.

[0018] Furthermore, the Group VIB metal sulfide is molybdenum sulfide and / or tungsten sulfide, and the Group VIII metal sulfide is nickel sulfide and / or cobalt sulfide.

[0019] Furthermore, the preparation method of the polycyclic aromatic hydrocarbon removal catalyst comprises the following steps:

[0020] (1) impregnating an alumina support with an impregnation solution containing a Group VIB metal salt, followed by drying and sulfurization to obtain a catalyst precursor A;

[0021] (2) impregnating the catalyst precursor of step (1) with an impregnation solution containing a Group VIII metal salt and an organic additive, drying in an inert atmosphere, and then sulfiding to obtain a catalyst precursor B;

[0022] (3) The catalyst precursor B and the molecular sieve precursor of step (2) are subjected to hydrothermal treatment, and then filtered, washed, dried and calcined in an inert atmosphere to obtain a polycyclic aromatic hydrocarbon removal catalyst.

[0023] Furthermore, the impregnation solution containing a Group VIB metal in step (1) is a phosphate or ammonium salt solution of a Group VIB metal, the preparation method of which is well known to those skilled in the art, and is prepared by equal volume impregnation or supersaturated impregnation. The Group VIB metal is preferably Mo and / or W.

[0024] Furthermore, the drying conditions of step (1) are: drying temperature 90-200° C., and drying time 3-6 hours.

[0025] Furthermore, the vulcanization treatment in step (1) is dry vulcanization or wet vulcanization. The dry vulcanizing agent is hydrogen sulfide, and the wet vulcanizing agent is one or two of carbon disulfide, dimethyl disulfide, methyl sulfide, and n-butyl sulfide; the vulcanization pressure is 3.2-6.4 MPa, the vulcanization temperature is 250-400° C., and the vulcanization time is 4-12 hours.

[0026] Furthermore, the impregnation solution containing a Group VIII metal salt in step (2) is at least one of a nitrate, acetate or sulfate solution of a Group VIII metal, and an equal volume impregnation method can be adopted. The Group VIII metal is Ni and / or Co.

[0027] Furthermore, the organic auxiliary agent in step (2) is at least one of alcohols or organic acids containing hydroxyl groups and / or carboxyl groups, wherein the number of carbon atoms is 3-10. Specifically, it is at least one selected from ethylene glycol, glycerol, butanediol, pentanediol, acetic acid, citric acid, malonic acid, succinic acid and glutaric acid.

[0028] Furthermore, the inert atmosphere in step (2) is one or more of N2 and an inert gas; the drying temperature in step (2) is 20-90°C, and the drying time is 4-16 hours.

[0029] Furthermore, the vulcanization treatment in step (2) is dry vulcanization or wet vulcanization. The dry vulcanizing agent is hydrogen sulfide, and the wet vulcanizing agent is one or two of carbon disulfide, dimethyl disulfide, methyl sulfide, and n-butyl sulfide; the vulcanization pressure is 3.2-6.4 MPa, the vulcanization temperature is 250-400° C., and the vulcanization time is 4-12 hours.

[0030] Furthermore, the molecular sieve precursor in step (3) is a gel formed by mixing a silicon source and / or an aluminum source, a precipitant, a template, and water. The preparation method is well known to those skilled in the art, and the molecular sieve precursor is formed by a precipitation method or a sol-gel method. The silicon source is selected from one or more of sodium silicate, ethyl orthosilicate, silica sol, and chromatographic silica gel; the aluminum source is selected from one or more of sodium metaaluminate, aluminum hydroxide, and pseudo-boehmite; the precipitant is selected from at least one of sodium hydroxide, ammonia water, and potassium hydroxide; and the template is selected from one or more of hexadecyltrimethylammonium bromide, ethylenediamine, n-butylamine, tetrapropylammonium bromide, ethanol, tetraethylammonium hydroxide, tetraethylammonium bromide, triethylamine, di-n-propylamine, diisopropylamine, and methylcellulose.

[0031] Furthermore, the hydrothermal treatment conditions in step (3) are as follows: temperature of 90-200°C, preferably 130-200°C, pressure of 0.1-2.0 MPa, pH of 7.5-9.0, and time of 5-48 hours. After the hydrothermal treatment, the molecular sieve precursor is crystallized into a molecular sieve and loaded on the outer surface of the catalyst.

[0032] Furthermore, the inert atmosphere in step (3) is one or more of N2 and an inert gas; the drying temperature in step (3) is 20-90°C, and the drying time is 4-16 hours; the roasting temperature is 300-500°C, and the roasting time is 2-5 hours.

[0033] Furthermore, in step (3), after the hydrothermal treatment, an ammonium ion exchange process is required, and the ammonium ion exchange can be performed using conventional methods in the art. For example, an ammonium salt aqueous solution is used for ammonium ion exchange, and the ammonium salt can be one or more of ammonium chloride, ammonium nitrate, ammonium sulfate, ammonium acetate, etc. The concentration of the ammonium salt aqueous solution is 0.05-3.0 mol / L, the exchange temperature is 55° C.-90° C., the single exchange time is 1-15 h, and the number of exchanges is 1-6 times.

[0034] Furthermore, in step (a), the initial boiling point of the feedstock oil is 100°C-300°C, preferably 120°C-200°C, and the final boiling point is 350°C-400°C. Based on the mass of the feedstock oil, the total mass content of aromatics in the feedstock oil is 30%-60% by weight, and the mass content of two-ring or higher aromatics is 15%-40% by weight, preferably 20%-35% by weight. The feedstock oil is mainly straight-run diesel, and also includes one or more secondary processed oils with high polycyclic aromatic hydrocarbons, such as coker diesel, catalytic diesel, aromatics extraction unit raffinate, coal liquefaction diesel, coal tar diesel, and shale oil diesel fraction.

[0035] Furthermore, in step (a), the hydrogen may be recycled hydrogen and fresh hydrogen. The feedstock oil may first pass through a heat exchanger, and then be mixed with the recycled hydrogen and fresh hydrogen heated by a heating furnace before entering the diesel hydrogenation reactor.

[0036] Furthermore, in step (a), the diesel hydrorefining catalyst is generally supported on a refractory porous oxide, such as aluminum oxide, silicon oxide, titanium oxide, or a composite oxide or mixed oxide support of several elements. A non-acidic or weakly acidic material is generally used as the support, and the hydrogenation active component of the diesel hydrorefining catalyst is a W-Ni, Mo-Ni, or W-Mo-Ni combination. Based on the weight of the diesel hydrorefining catalyst, the content of the hydrogenation active component as an oxide is generally 16 wt%-45 wt%, preferably 19 wt%-46 wt%. The nickel oxide content is preferably 1.5 wt%-10 wt%, more preferably 2 wt%-5 wt%. The diesel hydrorefining catalyst can be a suitable commercial catalyst selected according to the needs of the process flow, or can be prepared according to existing methods, or can be a regenerated catalyst obtained by regenerating a deactivated catalyst. For example, FHUDS-8 produced by the Fushun Branch of Sinopec Catalyst Company can be used.

[0037] Furthermore, in step (a), the volume ratio of the diesel hydrorefining catalyst to the polycyclic aromatic hydrocarbon removal catalyst loaded in the diesel hydrotreating reactor is 9:1-1:1, preferably 5:1-2:1.

[0038] Furthermore, in step (a), the diesel hydrogenation reactor is a trickle bed reactor. The diesel hydrogenation reactor can be two or more reactors used in series. The conditions for the hydrogenation reaction in the diesel hydrogenation reactor are as follows: hydrogen partial pressure of 2.0MPa-20.0MPa, preferably 5.5MPa-12.0MPa, reaction temperature of 260℃-450℃, preferably 330℃-430℃; volume space velocity of 0.1h -1 -6.0h -1 , preferably 0.5h -1 -3h -1 ; The volume ratio of hydrogen to oil is 100:1-2000:1, preferably 300:1-1000:1.

[0039] Furthermore, in step (b), the separator can be a conventional gas-liquid separator in the diesel hydrogenation field. Preferably, the reaction stream obtained in step (a) is sequentially separated by a cold high-pressure separation and a cold low-pressure separation. The gas separated by the separator is subjected to gas desulfurization and then mixed with fresh hydrogen and feedstock oil. The gas desulfurization can be carried out using conventional desulfurization methods in the hydrogenation field.

[0040] Furthermore, in step (c), the fractionation system may be a conventional fractionation system in the field of diesel hydrogenation.

[0041] The method for processing high aromatics raw materials in a diesel hydrotreating unit of the present invention has the following beneficial effects:

[0042] 1. The present invention fully utilizes existing diesel hydrotreating units and employs a trickle bed reactor, eliminating the need for process modifications. This effectively addresses the problem of reduced polycyclic aromatic hydrocarbon removal rates at the end of the processing process due to high aromatic content, particularly polycyclic aromatic hydrocarbons (PAHs). After the hydrogenation reaction, the present invention effectively addresses the problem of excessively high PAH content at the end of the long-term operation of diesel hydrotreating units, ensuring their long-term operation.

[0043] 2. Molecular sieves are added to the catalyst for removing polycyclic aromatic hydrocarbons of the present invention, and the molecular sieves are loaded on the outer surface of the catalyst instead of being mixed with the carrier. On the one hand, this is beneficial to increasing the contact surface between the molecular sieve and the active metal, and at the same time, it is beneficial to load the molecular sieve onto the active site of the active metal, giving full play to the ability of the molecular sieve to provide H protons, and improving the hydrogenation activity of the catalyst; on the other hand, the hydrogenation saturation and ring-opening and chain-breaking activity of polycyclic aromatic hydrocarbons can be accurately controlled by controlling the type and content of the molecular sieve, and the catalyst has high flexibility; thirdly, the utilization rate of the molecular sieve is increased, thereby reducing the amount of molecular sieve used and reducing the cost of the catalyst.

[0044] In addition, the present invention first performs a sulfidation treatment on the Group VIB metal and then impregnates the Group VIII metal. On the one hand, the Group VIB metal that is difficult to sulfidize can be sulfided, thereby improving the sulfidation degree of the Group VIB metal. On the other hand, the subsequent impregnation of the Group VIII metal is conducive to loading the Group VIII metal on the edges and corners of the wafer of the Group VIB metal sulfide, thereby improving the hydrogenation active sites of the catalyst. On the other hand, direct sulfidation after impregnation with the Group VIB metal solution or impregnation with the Group VIII metal solution and drying is performed without a roasting process, thereby preventing the interaction between the metal oxide and the support, which is conducive to improving the metal sulfidation degree.

[0045] 3. The polycyclic aromatic hydrocarbons of the present invention react in a hydrogenation reactor, which is reversible and highly exothermic and will be subject to thermodynamic limitations. Under the same pressure, the hydrodearomatization reaction should increase kinetically with the increase of reaction temperature, but it is also limited by thermodynamic equilibrium. When the reaction temperature reaches a certain level, it is not suitable for the dearomatization reaction. Since the catalyst will inevitably be deactivated with long-term operation, it is necessary to increase the reaction temperature to compensate for the loss of hydrodesulfurization activity, but the hydrodearomatization reaction will inevitably be limited. The ring-opening reaction that occurs under moderate acidity converts most of the polycyclic aromatic hydrocarbons into monocyclic aromatic hydrocarbons, avoiding the thermodynamic equilibrium limitation of hydrodearomatization. Combined with a partial removal of polycyclic aromatic hydrocarbons catalyst, its hydrogenation performance at low temperature can be fully utilized to ensure the liquid recovery of the device; and its acidity can be stimulated after the reaction temperature is increased at the end of the operation, which is more conducive to moderate ring opening, reducing the thermodynamic limitation of the hydrodearomatization reaction, and can effectively extend the operation cycle of the device. The polycyclic aromatic hydrocarbon removal catalyst of the present invention still has high polycyclic aromatic hydrocarbon hydrogenation activity after long-term operation. With the cooperation of the overall process, polycyclic aromatic hydrocarbons in the diesel feedstock are selectively hydrogenated and removed, thereby obtaining high-quality diesel products.

[0046] 4. By adopting the method provided by the present invention, the existing diesel hydrotreating unit is fully utilized. By adjusting the catalyst grading, the hydrotreating catalyst and the polycyclic aromatic hydrocarbon removal catalyst with an appropriate amount of molecular sieve are combined to achieve long-term removal of high-aromatic feedstock oil, making the diesel hydrotreating unit raw material adaptable.

[0047] 5. The method provided by the present invention adjusts the catalyst grading system without making any adjustments to the entire device, thereby reducing the modification cost of the device. At the same time, the method does not change much from the original operating steps and is more suitable for operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 is a schematic diagram of the process used in Examples 4-6 of the present invention;

[0049] Among them, the main figures are marked as follows: 1-raw oil, 2-new hydrogen, 3-circulating hydrogen, 4-diesel hydrogenation reactor, 6-cold high-pressure separator, 9-circulating hydrogen compressor, 11-cold low-pressure separator, 13-distillation system. DETAILED DESCRIPTION

[0050] The following non-limiting examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0051] The conventional diesel hydrorefining process used in the embodiments and comparative examples of the present invention uses a trickle bed reactor.

[0052] The method disclosed in the present invention is described in more detail below with reference to the accompanying drawings and specific embodiments. Figure 1Some equipment is omitted, such as oil pumps, valves, heating furnaces, etc.

[0053] like Figure 1 As shown, the raw oil 1 is mixed with new hydrogen 2 and circulating hydrogen 3, and enters the reactor from the top of the diesel hydrogenation reactor 4. The materials are successively contacted with the diesel hydrorefining catalyst and the polycyclic aromatic hydrocarbon removal catalyst to react, and the reaction products flow out from the bottom of the reactor; through pipeline 5, they enter the cold high-pressure separator 6 for gas-liquid separation, and the gas phase goes upward through the circulating hydrogen pipeline 7 to enter the circulating hydrogen desulfurization system and the circulating hydrogen compressor 9, and is mixed with the new hydrogen and raw oil materials through pipeline 10; the liquid phase enters the cold low-pressure separator 11 through pipeline 8, and then enters the fractionation system 13 through pipeline 12.

[0054] The present invention will be further described below in conjunction with preferred embodiments. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0055] The diesel hydrotreating catalyst used in the examples and comparative examples of the present invention was developed by Fushun Petrochemical Research Institute, specifically FHUDS-8 produced by Fushun Branch of Sinopec Catalyst Company. FHUDS-8 catalyst uses alumina as a carrier and Mo-Ni as an active component.

[0056] The composition of the catalyst provided by the present invention is characterized by combining inductively coupled plasma (ICP) and XPS spectroscopy. First, the total content of Group VIB metals and the total content of Group VIII metals in the catalyst are characterized by ICP, and then the content of metal elements of different valence states in the catalyst is quantitatively characterized by XPS spectrometer.

[0057] The present invention uses CO-FTIR (carbon monoxide in situ infrared analysis) to analyze the content of Group VIII metal oxides on Group VIB metal oxide wafers. The CO-FTIR measurement conditions include: after the catalyst is ground, it is pressed into a Φ13mm self-supporting sheet and placed on the in-situ cell sample holder. It is sulfurized with 3.0% H2S at 320°C for 3 hours, then cooled to room temperature in an H2S atmosphere, and then vacuumed to 300°C for purification for 2 hours. CO adsorption is performed under liquid nitrogen lowering conditions. A small amount of CO gas is introduced into the in-situ cell, and after adsorption equilibrium for 30 minutes, it is desorbed to 10 -4 Pa. Collect infrared spectra before and after CO adsorption, and the difference between the two is the infrared spectrum result of CO adsorption on the catalyst. The experiment uses Nicolet 6700 Fourier transform infrared spectrometer with 32 scans and a resolution of 4cm -1 , 4000-650cm -1 Measurement, detector is MCT / A.

[0058] Example 1

[0059] (1) The ammonium heptamolybdate solution was impregnated into an alumina support, and then dried at 100°C for 3 hours. The support was then sulfided using hydrogen containing 1.5% H2S at a temperature of 330°C, a pressure of 3.2 MPa, and a time of 4 hours. The support was then cooled to room temperature in a N2 atmosphere to obtain a catalyst precursor A.

[0060] (2) The nickel nitrate and ethylene glycol solution were impregnated into the catalyst precursor A prepared in step (1), and then dried at 90°C in a nitrogen atmosphere for 4 hours, and then subjected to a sulfurization treatment at a sulfurization temperature of 300°C, a sulfurization pressure of 3.2 MPa, and a sulfurization time of 4 hours, and then cooled to room temperature in a N2 atmosphere to obtain a catalyst precursor B.

[0061] (3) Sodium hydroxide, silica sol, sodium aluminate and ethylenediamine are added to deionized water, wherein the molar ratio of each component is n(SiO2):n(Al2O3):n(Na2O):n(ethylenediamine):n(H2O)=10:1:6:4:180, and stirred to form a uniform sol, i.e., a precursor of Y molecular sieve, and then mixed with the catalyst precursor B prepared in step (2), and then hydrothermally treated for 5 hours at 190°C, 2.0MPa, and pH=8.0; the obtained material is placed in a 0.15mol / L NH4Cl aqueous solution, mixed at a liquid-to-solid volume ratio of 3:1, the exchange temperature is 80°C, the single exchange time is 3h, and the total number of exchanges is 3 times; then filtered, washed with deionized water three times, and dried at 110°C in a nitrogen atmosphere for 4 hours to obtain a polycyclic aromatic hydrocarbon removal catalyst C-1.

[0062] The weight percentages of the components in the polycyclic aromatic hydrocarbon removal catalyst C-1 are: MoS2 is 20%, NiS is 4.0%, Y molecular sieve is 3.5%, and the rest is an alumina carrier; analysis shows that the content of Group VIII metal oxide on the Group VIB metal oxide wafer (Ni-Mo-S content) is 81%.

[0063] Example 2

[0064] (1) The ammonium heptamolybdate solution was impregnated into an alumina support, and then dried at 110°C for 4 hours. The support was then sulfided with hydrogen containing 1.5% H2S at a temperature of 310°C, a pressure of 3.2 MPa, and a time of 4 hours. The support was then cooled to room temperature in a N2 atmosphere to obtain a catalyst precursor A.

[0065] (2) The nickel nitrate and propylene glycol solution was impregnated into the catalyst precursor A prepared in step (1), and then dried at 90°C in a nitrogen atmosphere for 5 h, and then subjected to a sulfurization treatment at a sulfurization temperature of 300°C, a sulfurization pressure of 3.2 MPa, and a sulfurization time of 4 h, and then cooled to room temperature in a N2 atmosphere to obtain a catalyst precursor B.

[0066] (3) Sodium hydroxide, silica sol, sodium aluminate and ethylenediamine are added to deionized water, wherein the molar ratio of each component is n(SiO2):n(Al2O3):n(Na2O):n(n-butylamine):n(H2O)=21:1:6:5:200, and stirred to form a uniform sol, i.e., a precursor of Y molecular sieve, which is then mixed with the catalyst precursor B prepared in step (2), and then hydrothermally treated at 150°C, 1.5MPa, and pH=8.0 for 10h; the obtained material is placed in a 0.15mol / L NH4Cl aqueous solution, mixed at a liquid-to-solid volume ratio of 3:1, the exchange temperature is 80°C, the single exchange time is 3h, and the total number of exchanges is 3 times; then filtered, washed with deionized water three times, and dried at 90°C in a nitrogen atmosphere for 4h to obtain a polycyclic aromatic hydrocarbon removal catalyst C-2.

[0067] The weight percentages of the components in the polycyclic aromatic hydrocarbon removal catalyst C-2 are: MoS2 is 23%, NiS is 4.2%, Y molecular sieve is 4.0%, and the rest is alumina support. Analysis shows that the content of Group VIII metal oxide on the Group VIB metal oxide wafer (Ni-Mo-S content) is 85%.

[0068] Example 3

[0069] (1) The ammonium heptamolybdate solution was impregnated into an alumina carrier, and then dried at 120°C for 3 hours. The carrier was then sulfided with hydrogen containing 1.5% H2S at a temperature of 320°C, a pressure of 3.5 MPa, and a time of 5 hours. The carrier was then cooled to room temperature in a N2 atmosphere to obtain a catalyst precursor A.

[0070] (2) The nickel nitrate and citric acid solution is impregnated into the catalyst precursor A prepared in step (1), and then dried at 110°C in a nitrogen atmosphere for 3 hours, and then subjected to a sulfurization treatment at a sulfurization temperature of 280°C, a sulfurization pressure of 3.0 MPa, and a sulfurization time of 4 hours, and then cooled to room temperature in a N2 atmosphere to obtain a catalyst precursor B.

[0071] (3) Sodium aluminate and sodium hydroxide were dissolved in deionized water, and then tetraethylammonium bromide was added, stirred vigorously, and silica sol was slowly added dropwise. The mixture was aged for 3 hours, wherein the molar ratio of each component was n(SiO2):n(Al2O3):n(Na2O):n(tetraethylammonium bromide):n(H2O)=24:1:7:6:260, to form a precursor of Y molecular sieve, which was then mixed with the catalyst precursor B prepared in step (2), and then hydrothermally treated at 150°C, 2.0MPa, and pH=9.0 for 20 hours; the obtained material was placed in a 0.15mol / L NH4Cl aqueous solution, mixed according to a liquid-to-solid volume ratio of 3:1, the exchange temperature was 80°C, the single exchange time was 3 hours, and the total number of exchanges was 3 times; then filtered, washed with deionized water three times, and dried at 90°C in a nitrogen atmosphere for 4 hours to obtain a polycyclic aromatic hydrocarbon removal catalyst C-3.

[0072] The weight percentages of the components in the polycyclic aromatic hydrocarbon removal catalyst C-3 are: MoS2 is 25%, NiS is 7.0%, Y-type molecular sieve is 5.0%, and the rest is alumina support. Analysis shows that the content of Group VIII metal oxide on the Group VIB metal oxide wafer (Ni-Mo-S content) is 86%.

[0073] Example 4

[0074] use Figure 1 The hydrogenation process flow is as follows: diesel hydrorefining catalyst FHUDS-8 and polycyclic aromatic hydrocarbon removal catalyst C-1 prepared in Example 1 are loaded from top to bottom in the reactor. The main process operating conditions are: the total reaction space velocity is 1.3h -1 The reaction pressure was 8.0 MPa, the hydrogen-to-oil volume ratio was 500:1, the operation time was 800 h, the reaction temperature was 345 °C, the operation time was 20,000 h, the reaction temperature was 395 °C, and the reaction results are shown in Table 2.

[0075] Example 5

[0076] use Figure 1 The hydrogenation process flow of Example 4 is different from that of Example 4 in that the catalyst for removing polycyclic aromatic hydrocarbons is the catalyst C-2 prepared in Example 2. The reaction results are shown in Table 2.

[0077] Example 6

[0078] use Figure 1 The hydrogenation process flow of Example 4 is different from that of Example 4 in that the catalyst for removing polycyclic aromatic hydrocarbons is the catalyst C-3 prepared in Example 3. The reaction results are shown in Table 2.

[0079] Comparative Example 1

[0080] use Figure 1The hydrogenation process flow of Example 4 is different from that of Example 4 in that only FHUDS-8 catalyst is used in the catalyst system. The reaction results are shown in Table 2.

[0081] Comparative Example 2

[0082] (1) Y-type molecular sieve is uniformly mixed with alumina powder, nitric acid, and deionized water, wherein the mass ratio of Y-type molecular sieve: alumina powder: nitric acid: deionized water is 6:92:4:60, and then kneaded and extruded into strips, and then dried at 90°C for 6 hours and calcined at 450°C for 3 hours to obtain a modified alumina carrier, wherein the content of Y-type molecular sieve is 4.5%.

[0083] (2) The ammonium heptamolybdate solution was impregnated into the modified alumina support prepared in step (1), followed by drying at 110° C. for 3 hours and calcining at 350° C. for 3 hours to obtain a catalyst precursor.

[0084] (3) The nickel nitrate solution was impregnated into the catalyst precursor prepared in step (2), followed by drying at 90°C for 3 hours, calcining at 250°C for 3 hours, and performing ammonium ion exchange (the method was the same as in Example 1) to obtain catalyst BC-1.

[0085] The weight percentages of the components in catalyst BC-1 are: MoO3 is 22%, nickel oxide is 4.0%, Y molecular sieve is 4.5%, and the rest is aluminum oxide.

[0086] Comparative Example 3

[0087] use Figure 1 The hydrogenation process flow is different from that of Example 4 in that the catalyst for removing polycyclic aromatic hydrocarbons is the catalyst BC-1 prepared in Comparative Example 2. The reaction results are shown in Table 2.

[0088] The raw oils used in the examples of the present invention and the comparative examples are shown in Table 1. The main operating process conditions and gasoline product properties in the examples of the present invention and the comparative examples are shown in Table 2.

[0089] Table 1 Properties of crude oil

[0090] Diesel blend <![CDATA[Density (20 °C), g / cm 3 > 0.8716 Distillation range, ℃ (ASTMD86) Initial distillation point / 10% 136 / 182 50％ / 90％ 285 / 341 95% / dry point (final distillation point) 357 / 365 Sulfur, μg / g 9567 Nitrogen, μg / g 356 Aromatic content, % 45 PAHs content, % 26

[0091] Table 2 Main operating process conditions and diesel product properties at different times

[0092]

[0093] As can be seen from the data results of the Examples and Comparative Examples, the method of the present invention for processing high-aromatic feedstocks in a diesel hydrotreating unit achieves the goal of producing higher-quality products over a longer period of time by grading the catalyst without making any adjustments to the entire unit. The method of the present invention requires minimal or no modification to the original reaction units, thereby reducing the investment cost for the renovation of the unit.

Claims

1. A method for processing a high aromatics feedstock in a diesel hydrotreating unit, comprising: (a) The crude oil and hydrogen enter the diesel hydrotreating reactor and pass through the diesel hydrorefining catalyst bed and dearomatization catalyst bed in the diesel hydrotreating reactor in sequence to undergo hydrogenation reaction; (b) the reaction stream obtained in step (a) enters a separator for gas-liquid separation; (c) the liquid obtained in step (b) enters a fractionation system to obtain a diesel product; The catalyst loaded in the dearomatization catalyst bed is a polycyclic aromatic hydrocarbon removal catalyst, the polycyclic aromatic hydrocarbon removal catalyst is supported by alumina, and a molecular sieve and an active component are supported on the support, and the active component is a Group VIB metal sulfide and a Group VIII metal sulfide; the molar ratio of the Group VIII metal sulfide species on the Group VIB metal sulfide wafer to the total amount of the Group VIII metal sulfide is 60%-100%; the molecular sieve is supported on the Group VIB metal sulfide, and / or the molecular sieve is supported on the Group VIII metal sulfide, and / or the molecular sieve is supported on the alumina; Based on the total weight of the polycyclic aromatic hydrocarbon removal catalyst, the molecular sieve accounts for 1wt%-15wt%, the Group VIB metal sulfide, calculated as sulfide, accounts for 10wt%-35wt%, and the Group VIII metal sulfide, calculated as sulfide, accounts for 2wt%-10wt%; Based on the mass of the raw oil, the total mass content of aromatic hydrocarbons in the raw oil is 30%-60wt%, and the mass content of aromatic hydrocarbons with two or more rings is 15%-40wt%; The preparation method of the polycyclic aromatic hydrocarbon removal catalyst comprises the following steps: (1) impregnating an alumina support with an impregnation solution containing a Group VIB metal salt, and then drying and sulfurizing to obtain a catalyst precursor A; (2) impregnating the catalyst precursor of step (1) with an impregnation solution containing a Group VIII metal salt and an organic additive, drying the impregnation solution in an inert atmosphere, and then subjecting the impregnation solution to a sulfurization treatment to obtain a catalyst precursor B; (3) The catalyst precursor B and the molecular sieve precursor of step (2) are hydrothermally treated, and then filtered, washed, and dried in an inert atmosphere to obtain a polycyclic aromatic hydrocarbon removal catalyst.

2. The method according to claim 1, characterized in that Based on the total weight of the polycyclic aromatic hydrocarbon removal catalyst, the molecular sieve accounts for 1.5wt%-10wt%, the VIB group metal sulfide accounts for 15wt%-30wt% as sulfide, and the VIII group metal sulfide accounts for 4wt%-8wt% as sulfide.

3. The method according to claim 2, characterized in that Based on the total weight of the polycyclic aromatic hydrocarbon removal catalyst, the molecular sieve accounts for 2wt%-8wt%.

4. The method according to claim 1, wherein The molecular sieve is at least one selected from Y-type molecular sieve, ZSM-5 molecular sieve, β-type molecular sieve and MCM-41 molecular sieve; and / or, The Group VIB metal sulfide is molybdenum sulfide and / or tungsten sulfide, and the Group VIII metal sulfide is nickel sulfide and / or cobalt sulfide.

5. The method according to claim 1, wherein The drying conditions in step (1) are: drying temperature 90-200°C, and drying time 3-6 hours.

6. The method according to claim 1, characterized in that The vulcanization treatment in step (1) or step (2) is dry vulcanization or wet vulcanization; the vulcanization pressure is 3.2-6.4 MPa, the vulcanization temperature is 250-400° C., and the vulcanization time is 4-12 h.

7. The method according to claim 1, characterized in that The organic auxiliary agent in step (2) is an alcohol or an organic acid, wherein the number of carbon atoms is 3-10.

8. The method according to claim 1, characterized in that The hydrothermal treatment conditions in step (3) are: temperature of 90-200°C, pressure of 0.1-2.0 MPa, pH of 7.5-9.0, and time of 5-48 hours.

9. The method according to claim 8, characterized in that The hydrothermal treatment conditions in step (3) are as follows: the temperature is 130-200°C.

10. The method according to claim 1, characterized in that The inert atmosphere in step (3) is N2; the drying temperature in step (3) is 20-90°C, and the drying time is 4-16 hours.

11. The method according to claim 1, wherein In step (a), the initial distillation point of the feedstock oil is 100°C-300°C, and the final distillation point is 350°C-400°C.

12. The method according to claim 11, characterized in that In step (a), the initial boiling point of the feedstock oil is 120° C.-200° C.; and the mass content of two-ring or higher aromatic hydrocarbons in the feedstock oil is 20%-35% by weight based on the mass of the feedstock oil.

13. The method according to claim 1, wherein In step (a), the volume ratio of the diesel hydrorefining catalyst to the polycyclic aromatic hydrocarbon removal catalyst loaded in the diesel hydrotreating reactor is 9:1-1:

1.

14. The method according to claim 13, characterized in that In step (a), the volume ratio of the diesel hydrorefining catalyst to the polycyclic aromatic hydrocarbon removal catalyst loaded in the diesel hydrotreating reactor is 5:1-2:

1.

15. The method according to claim 1, wherein The conditions for the hydrogenation reaction in the diesel hydrogenation reactor are as follows: hydrogen partial pressure of 2.0MPa-20.0MPa, reaction temperature of 260℃-450℃, volume space velocity of 0.1h -1 -6.0h -1 , the volume ratio of hydrogen to oil is 100:1-2000:

1.

16. The method according to claim 15, characterized in that The conditions for the hydrogenation reaction in the diesel hydrogenation reactor are as follows: hydrogen partial pressure of 5.5MPa-12.0MPa, reaction temperature of 330℃-430℃; volume space velocity of 0.5h -1 -3h -1 ; The volume ratio of hydrogen to oil is 300:1-1000:1.

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