Hydrocracking method for catalyzing diesel oil

Abstract

The invention discloses a hydrocracking method of catalytic diesel oil, which comprises the following steps: (1) mixing a catalytic diesel oil raw material with hydrogen, then feeding into a hydrofining reaction zone, and carrying out contact reaction with a hydrofining catalyst bed layer to obtain hydrofined generated oil; (2) the hydrofined oil obtained in the step (1) enters a hydrocracking reaction zone, and sequentially passes through a first hydrocracking catalyst bed layer and a second hydrocracking catalyst bed layer for a hydrocracking reaction; the first hydrocracking catalyst bed layer is filled with a hydrocracking catalyst I, and the hydrocracking catalyst I contains a modified Y-type molecular sieve; the second hydrocracking catalyst bed layer is filled with a hydrocracking catalyst II, and the hydrocracking catalyst II contains a ZSM-5 type molecular sieve; the light aromatic hydrocarbon (BTX) in the hydrocracking product obtained by the method is good in selectivity and high in yield, and the value maximization utilization of the inferior catalytic diesel oil raw material can be realized.

Description

Technical Field

[0001] The invention belongs to the technical field of petrochemical industry, and in particular relates to a method for catalytic diesel hydrocracking. Background Art

[0002] Catalytic diesel accounts for approximately 30% by weight of my country's diesel pool, with an annual production of over 40 million tons. However, the content of polycyclic aromatic hydrocarbons in catalytic diesel is very high, with the content of two-ring and higher polycyclic aromatic hydrocarbons generally exceeding 50% by weight. This results in poor complete combustion performance, high density, and low cetane number, which has become a limiting factor in product quality upgrades for refining and chemical companies. It is worth noting that catalytic diesel is rich in aromatics, of which the content of polycyclic aromatic hydrocarbons can be as high as 50% by weight. Efficiently converting catalytic diesel into heavy naphtha rich in light aromatics can not only solve the processing problems of catalytic diesel, but also expand the resource base of aromatic raw materials and alleviate the tense situation of insufficient aromatic production capacity.

[0003] CN112322348A discloses a method and system for producing heavy naphtha rich in light aromatics from heavy aromatics. This invention involves hydrotreating a catalytic diesel stream to remove impurities, followed by a hydrocracking reaction. After the reaction, fractions are separated, including light hydrocarbons, heavy naphtha rich in light aromatics, and heavy tail oil. The hydrocracking catalyst comprises, by weight: a2) 5-80 parts of a solid acid zeolite; b2) 0.05-8 parts of a Group VIII metal; c2) 3-25 parts of a Group VIB metal oxide; d2) 0.1-2 parts of a Group VIB metal sulfide; and e2) 20-95 parts of a first binder. However, this method suffers from poor selectivity for light aromatics (BTX) and low yield. Summary of the Invention

[0004] In response to the shortcomings of the prior art, the present invention provides a method for hydrocracking catalytic diesel. The method produces a hydrocracking product with good selectivity and high yield of light aromatics (BTX), thereby maximizing the value of low-quality catalytic diesel feedstock.

[0005] A method for hydrocracking catalytic diesel, comprising the following steps:

[0006] (1) The catalytic diesel feedstock is mixed with hydrogen and enters the hydrotreating reaction zone, where it contacts and reacts with the hydrotreating catalyst bed to obtain hydrotreating product oil;

[0007] (2) The hydrorefined product oil obtained in step (1) enters the hydrocracking reaction zone and passes through the first hydrocracking catalyst bed and the second hydrocracking catalyst bed in sequence to undergo a hydrocracking reaction; the first hydrocracking catalyst bed is loaded with hydrocracking catalyst I, which contains a modified Y-type molecular sieve; the second hydrocracking catalyst bed is loaded with hydrocracking catalyst II, which contains a ZSM-5 molecular sieve;

[0008] (3) the reaction effluent obtained from the hydrocracking reaction in step (2) is subjected to gas-liquid separation and fractionation to obtain gas, a BTX-rich naphtha fraction, and a diesel fraction;

[0009] Wherein, in the hydrocracking reaction zone, the total pore volume of the hydrocracking catalyst I containing the modified Y molecular sieve is higher than that of the hydrocracking catalyst II containing the ZSM-5 molecular sieve, preferably 0.1 cm higher. 3 / g~0.3cm 3 / g; the total pyridine infrared acid content increases, preferably 0.56mmol / g to 0.80mmol / g higher; the proportion of pyridine infrared acid content with a desorption temperature greater than 350°C to the total pyridine infrared acid content decreases, preferably 2% to 10% lower.

[0010] In the method of the present invention, the catalytic diesel raw material in step (1) contains: 8wt.%-18wt.% of paraffins, 5wt.%-16wt.% of cycloalkanes, and 70wt.%-85wt.% of aromatics.

[0011] In the method of the present invention, the catalytic diesel feedstock described in step (1) is mixed with hydrogen and then enters the hydrorefining reaction zone to react with the hydrorefining catalyst bed. The reaction effluent passes through a high-pressure separator and a low-pressure separator in sequence to remove gaseous impurities such as hydrogen sulfide and ammonia to obtain hydrorefined product oil.

[0012] In the method of the present invention, the hydrorefining catalyst loaded into the hydrorefining catalyst bed in step (1) can be any type of commercial catalyst in the prior art, or can be prepared according to common knowledge in the art as needed, as long as the purpose of catalytic diesel hydrorefining in step (1) can be achieved. Specifically, in the present invention, the hydrorefining catalyst is one or more of the commercial brands FF-36, FF-46, and FF-66 hydrorefining catalysts developed by Sinopec (Dalian) Petrochemical Research Institute Co., Ltd.

[0013] In the method of the present invention, a protective agent may be loaded on the upper portion of the hydrorefining catalyst bed in step (1); the protective agent may be selected from various existing commercial catalysts, such as any one of the FZC and FBN series protective agents developed by Sinopec (Dalian) Petrochemical Research Institute Co., Ltd.; or the protective agent may be prepared according to common knowledge in the art as needed.

[0014] In the method of the present invention, the nitrogen content of the hydrorefined oil obtained in step (1) is 10 ppm to 100 ppm, preferably 40 ppm to 60 ppm; the sulfur content is less than 300 ppm, preferably less than 100 ppm; and the aromatics retention rate of the hydrorefined oil is >90 wt.%, preferably >92 wt.%.

[0015] In the method of the present invention, the reaction conditions of the hydrofining reaction zone in step (1) can adopt the reaction conditions of catalytic diesel hydrofining known in the prior art. Specifically in the present invention, the reaction conditions of the hydrofining reaction zone are: reaction pressure 5MPa to 10MPa, preferably 6MPa to 8MPa; reaction temperature 300℃ to 420℃, preferably 330℃ to 400℃; volume space velocity 0.5h -1 ~3.0h -1 , preferably 0.8h -1 ~2.0h -1 ; Hydrogen to oil volume ratio 500-2000, preferably 800-1500.

[0016] In the method of the present invention, the total pore volume of the modified Y-type molecular sieve in step (2) is 0.35 cm 3 / g-0.5cm 3 / g, the total pyridine infrared acid content is 0.5mmol / g-1.0mmol / g, wherein the pyridine infrared acid content with a desorption temperature greater than 350°C accounts for 65%-80% of the total pyridine infrared acid content.

[0017] In the method of the present invention, the modified Y-type molecular sieve SiO2 / Al2O3 (molar ratio) in step (2) is 10-30, preferably 15-20; the specific surface area is 700m 2 / g~900m 2 / g, preferably 750m 2 / g~850m 2 / g.

[0018] In the method of the present invention, in step (2), the content of the modified Y-type molecular sieve is 40 wt.% to 70 wt.% based on the weight of the hydrocracking catalyst I.

[0019] In the method of the present invention, the hydrocracking catalyst I in step (2) further contains a binder, which is alumina; based on the weight of the hydrocracking catalyst I, the binder content is 10 wt.% to 35 wt.%.

[0020] In the method of the present invention, the hydrocracking catalyst I in step (2) contains a hydrogenation-active metal component, which contains at least one Group VIII metal component and at least one Group VIB metal component. Preferably, the Group VIII metal component is cobalt and / or nickel, and the Group VIB metal component is molybdenum and / or tungsten. Based on the weight of the hydrocracking catalyst I, the content of the hydrogenation-active metal component (calculated as metal oxide) is 15 wt.% to 25 wt.%, of which the content of the Group VIII metal (calculated as metal oxide) is 2 wt.% to 8 wt.%, and the content of the Group VIB metal (calculated as metal oxide) is 13 wt.% to 20 wt.%.

[0021] In the method of the present invention, the total pore volume of the ZSM-5 molecular sieve in step (2) is 0.2 cm 3 / g-0.25cm 3 / g; the total pyridine infrared acid content is 0.15mmol / g to 0.40mmol / g, wherein the pyridine infrared acid content with a desorption temperature greater than 350°C accounts for 70% to 85% of the total pyridine infrared acid content.

[0022] In the method of the present invention, the ZSM-5 molecular sieve SiO2 / Al2O3 (molar ratio) in step (2) is 30 to 100, preferably 40 to 60; the specific surface area is 350m 2 / g-450m 2 / g.

[0023] In the method of the present invention, the ZSM-5 molecular sieve described in step (2) can be prepared using commercially available products or according to existing technologies. As a non-limiting preparation method, the synthesis method of the ZSM-5 molecular sieve is as follows: ethyl orthosilicate, aluminum chloride hexahydrate, TPAOH aqueous solution, TPABr, ammonium fluoride and water are mixed in a molar ratio of SiO2:Al2O3:TPAOH:TPABr:NH4F:H2O=1:(0.01-0.05):(0.05-0.1):(0.05-0.1):(0.6-1.0):(150-250) to obtain a mother liquor, and the mother liquor is allowed to stand and crystallize at a temperature of 160-180°C for 12-48 hours. The obtained product is filtered, washed, dried, and calcined, and then subjected to ammonium ion exchange and calcination to obtain the ZSM-5 molecular sieve. The drying and calcination can adopt the operating conditions of the existing technology.

[0024] In the method of the present invention, the hydrocracking catalyst II in step (2) contains a hydrogenation-active metal component; the hydrogenation-active metal component is selected from at least one Group VIII metal component and at least one Group VIB metal component. Preferably, the Group VIII metal component is cobalt and / or nickel, and the Group VIB metal component is molybdenum and / or tungsten. Based on the weight of the hydrocracking catalyst II, the content of the hydrogenation-active metal component (calculated as metal oxide) is 13 wt.% to 25 wt.%, of which the content of the Group VIII metal (calculated as metal oxide) is 2 wt.% to 8 wt.%, and the content of the Group VIB metal (calculated as metal oxide) is 11 wt.% to 20 wt.%.

[0025] In the method of the present invention, the hydrocracking catalyst II in step (2) contains a binder, which is alumina. The binder content is 40 wt.% to 75 wt.% based on the weight of the hydrocracking catalyst II.

[0026] In the method of the present invention, the loading volume ratio of the hydrocracking catalyst I to the hydrocracking catalyst II in step (2) is (3-5):1.

[0027] In the method of the present invention, the reaction conditions of the hydrocracking reaction zone in step (2) are as follows: reaction pressure 5MPa-10MPa, preferably 6MPa-8MPa; reaction temperature 330℃-450℃, preferably 360℃-410℃; volume space velocity 0.5h -1 ~2.0h -1 , preferably 0.8 to 1.5 hours -1 ; Hydrogen to oil volume ratio 500-2000, preferably 800-1500.

[0028] In the method of the present invention, the BTX-rich naphtha fraction in step (3) is a fraction with a temperature below 160° C., and the diesel fraction is a fraction with a temperature above 160° C.

[0029] In the method of the present invention, the sulfur content of the diesel fraction in step (3) is less than 20 ppm, preferably less than 1 ppm; the nitrogen content is less than 10 ppm, preferably less than 1 ppm; and the ratio of the mass content of aromatic hydrocarbons in the diesel fraction to the mass content of aromatic hydrocarbons in the hydrorefined oil obtained in step (1) is (0.9 to 0.95):1.

[0030] In the method of the present invention, part or all of the diesel fraction in step (3) is recycled to the hydrocracking reaction zone. Preferably, the diesel fraction is mixed with the hydrorefined oil obtained in step (1) and then recycled to the hydrocracking reaction zone.

[0031] In the method of the present invention, in step (1) and step (2), the hydrofining reaction zone and the hydrocracking reaction zone can share high-pressure hydrogen and a high-pressure hydrogen circulation system.

[0032] In the method of the present invention, the feeds in step (1), step (2), step (3) and step (4) can be heat exchanged with the discharges in step (1), step (2), step (3) and step (4) separately or simultaneously, thereby fully utilizing the heat of the reaction system and reducing energy consumption.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] In the hydrocracking method of catalytic diesel of the present invention, a modified Y-type molecular sieve-based catalyst and a ZSM-5 molecular sieve-based catalyst are loaded in a hydrocracking reaction zone in a graded manner. Compared with the hydrocracking catalyst II containing the ZSM-5 molecular sieve, the total pore volume of the hydrocracking catalyst I containing the modified Y-type molecular sieve is increased, the total pyridine infrared acid content is increased, and the proportion of the pyridine infrared acid content with a desorption temperature greater than 350° C. in the total pyridine infrared acid content is reduced. The graded loading method can enhance the ring-opening activity of polycyclic aromatic hydrocarbons and the side chain scission performance of high-alkyl aromatic hydrocarbons, thereby improving the selectivity and yield of BTX. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below with reference to specific examples. The examples are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the protection scope of the present invention is not limited to the following examples.

[0036] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, were purchased from conventional biochemical reagent stores.

[0037] In the present invention, the acid properties of the molecular sieve are determined by pyridine adsorption infrared spectroscopy; the specific process is: the molecular sieve sample is prepared into a self-supporting wafer (5-6 mg / cm 2 ), placed in an in-situ cell, treated at 400°C under vacuum for 4 hours, then cooled to 50°C, and a spectrum was collected; after adsorbing pyridine for 10 minutes, the sample was heated to 200°C for desorption for 1 hour, cooled to room temperature, and a spectrum was collected to calculate the total infrared acid content of pyridine; then heated to 350°C for desorption for 1 hour, cooled to room temperature, and a spectrum was collected to calculate the infrared acid content of pyridine with a desorption temperature greater than 350°C.

[0038] In the present invention, the specific surface area and pore structure of the molecular sieve are measured by N2 adsorption-desorption characterization.

[0039] In the present invention, the modified Y-type molecular sieve can be prepared by the following method:

[0040] 1) A mixture containing catalytic diesel, a silane coupling agent, and a silicon source is subjected to low-temperature heat treatment to obtain material A;

[0041] 2) uniformly mixing the material A obtained in step 1) with an aluminum source, an alkali source and water to obtain a molecular sieve mother liquor, subjecting the molecular sieve mother liquor to hydrothermal crystallization, and then filtering, washing, drying and calcining to obtain a Y-type molecular sieve;

[0042] 3) The Y-type molecular sieve obtained in step 2) is subjected to ion exchange with an ammonium salt aqueous solution, and then modified with an ammonium fluorosilicate solution, and filtered, washed, dried, and calcined to obtain a modified Y-type molecular sieve.

[0043] Furthermore, in the preparation method of the above-mentioned modified Y-type molecular sieve, the catalytic diesel in step 1) can be a catalytic diesel fraction obtained from a catalytic cracking unit; the catalytic diesel composition is: 8wt.%-18wt.% of paraffins, 5wt.%-16wt.% of cycloalkanes, and 70wt.%-85wt.% of aromatics; preferably, the content of bicyclic aromatics in the catalytic diesel is 40wt.%-58wt.%, and the content of tricyclic aromatics is 5wt.%-18wt.%; further preferably, the content of bicyclic aromatics in the catalytic diesel is 42wt.%-55wt.%, and the content of tricyclic aromatics is 8wt.%-15wt.%.

[0044] Furthermore, in the preparation method of the modified Y-type molecular sieve, the density range of the catalytic diesel in step 1) is 0.85 g / cm 3 -0.98g / cm 3 , preferably 0.90 g / cm 3 -0.97g / cm 3 ; The distillation range is 150℃-380℃, preferably 200℃-370℃.

[0045] Furthermore, in the preparation method of the modified Y-type molecular sieve, the silane coupling agent in step 1) is at least one of methacryloxytrimethoxysilane, 3-glycidyl ether propyltrimethoxysilane and 3-aminopropyltriethoxysilane.

[0046] Furthermore, in the above-mentioned preparation method of modified Y-type molecular sieve, the silicon source in step 1) is ethyl orthosilicate and / or methyl orthosilicate.

[0047] Furthermore, in the preparation method of the modified Y-type molecular sieve, in step 1), the mass ratio of catalytic diesel: silicon source (calculated as SiO2) is (0.05-0.15):1, and the molar ratio of silane coupling agent: silicon source (calculated as SiO2) is (0.1-0.3):1.

[0048] Furthermore, in the above-mentioned preparation method of modified Y-type molecular sieve, the low-temperature heat treatment conditions in step 1) are: temperature 50° C.-90° C., preferably 60° C.-80° C.; reaction time 2 h-6 h.

[0049] Furthermore, in the preparation method of the modified Y-type molecular sieve, the aluminum source in step 2) is at least one of sodium metaaluminate, aluminum isopropoxide, aluminum nitrate, aluminum chloride and aluminum sulfate, preferably sodium metaaluminate; and the alkali source is sodium hydroxide.

[0050] Furthermore, in the preparation method of the modified Y-type molecular sieve, the composition of the molecular sieve mother liquor in step 2) is Na2O:Al2O3:SiO2:H2O (molar ratio) = (4-8):1:(10-18):(200-600), and part or all of the silicon source comes from step (1).

[0051] Furthermore, in the preparation method of the modified Y-type molecular sieve, the operating conditions of the hydrothermal crystallization treatment in step 2) are: temperature 80°C-120°C, preferably 90°C-110°C, time 48h-168h, preferably 72h-120h.

[0052] Furthermore, in the above-mentioned preparation method of modified Y-type molecular sieve, the specific operation process of washing in step 2) is as follows: washing the obtained material with deionized water for 1-6 times until the filtrate is neutral.

[0053] Furthermore, in the preparation method of the modified Y-type molecular sieve, the drying temperature in step 2) is 100-120°C, and the drying time is 12-24 hours; the calcination atmosphere is air, the calcination temperature is 500-600°C, and the calcination time is 2-6 hours.

[0054] Furthermore, in the preparation method of the modified Y-type molecular sieve, the ammonium salt used in the ammonium salt aqueous solution in step 3) is one or more of ammonium chloride, ammonium nitrate, ammonium sulfate, ammonium acetate and ammonium oxalate; the concentration of the ammonium salt aqueous solution is 0.5 mol / L-3 mol / L, preferably 1 mol / L-2 mol / L.

[0055] Furthermore, in the preparation method of the modified Y-type molecular sieve, the solid-liquid ratio of the Y-type molecular sieve to the ammonium salt aqueous solution in step 3) is 1:(5-15) in terms of g:mL, preferably 1:(8-10).

[0056] Furthermore, in the preparation method of the modified Y-type molecular sieve, the ion exchange temperature in step 3) is 30-120° C., preferably 60-90° C.; the ion exchange time is 1-3 h, preferably 2 h; and the number of ion exchanges is 1-3 times, preferably 2 times.

[0057] Furthermore, in the preparation method of the modified Y-type molecular sieve, the concentration of the ammonium fluorosilicate solution in step 3) is 0.05 mol / L-0.2 mol / L; the solid-liquid ratio of the Y-type molecular sieve to the ammonium fluorosilicate solution is 1:(20-50) in g:mL.

[0058] Furthermore, in the preparation method of the modified Y-type molecular sieve, the modification treatment temperature in step 3) is 60°C-120°C, preferably 80°C-100°C; the modification treatment time is 3h-6h, preferably 4h-5h; and the treatment times are 1-2 times, preferably 1 time.

[0059] Furthermore, in the preparation method of the modified Y-type molecular sieve, the drying temperature in step 3) is 100-120°C, and the drying time is 12-24 hours; the calcination atmosphere is air, the calcination temperature is 500-600°C, and the calcination time is 2-6 hours.

[0060] In the preparation process of the modified Y-type molecular sieve, a mixture containing catalytic diesel, a silane coupling agent, and a silicon source is first subjected to a low-temperature heat treatment. The presence of the silane coupling agent can enhance the compatibility of the catalytic diesel and the molecular sieve mother liquor, making the catalytic diesel more evenly dispersed. The molecular sieve is then prepared using the above-mentioned materials as raw materials, and the molecular imprinting effect is used to make the molecular sieve have a suitable mesopore diameter, which is beneficial to enhancing the confinement effect of the molecular sieve channel for the catalytic diesel molecules. The hydrocracking reaction zone is loaded with catalyst grading. When the hydrocracking catalyst I used contains the modified Y-type molecular sieve obtained by the above-mentioned preparation method, the reaction effect can be improved, and the selectivity and yield of BTX can be further improved.

[0061] The method provided by the present invention will be further described below with reference to the examples, but the present invention is not limited thereto.

[0062] In the Examples and Comparative Examples, the BTX product yield is calculated as follows: BTX mass content in the naphtha fraction × naphtha fraction yield × 100%. The BTX product selectivity relative to fresh feedstock is calculated as follows: BTX yield / fresh feedstock feedstock amount × 100%. The BTX mass content in the naphtha fraction was determined by gas chromatography-mass spectrometry.

[0063] In the Examples and Comparative Examples of the present invention, the calculation formula for the aromatics retention rate of the hydrorefining oil is as follows:

[0064]

[0065] In the examples and comparative examples of the present invention, the hydrorefining catalyst used was FF-66 hydrorefining catalyst developed by Sinopec (Dalian) Petrochemical Research Institute Co., Ltd. The γ-alumina used was DK-4 alumina powder developed by Sinopec (Dalian) Petrochemical Research Institute Co., Ltd.

[0066] The properties of the catalytic diesel raw materials used in the examples and comparative examples of the present invention are shown in Table 1.

[0067] Table 1 Catalytic diesel feedstock properties

[0068]

[0069]

[0070] Example 1

[0071] The preparation process of the hydrocracking catalyst I in this embodiment is as follows:

[0072] 1. Preparation of modified Y-type molecular sieve

[0073] (a) Catalytic diesel 1, a silane coupling agent, and a silicon source were uniformly mixed in a mass ratio of catalytic diesel 1:ethyl orthosilicate (calculated by SiO2 content) of 0.1:1 and a molar ratio of methacryloyloxytrimethoxysilane:ethyl orthosilicate of 0.2:1. The mixture was heat treated at 80°C for 3 h and cooled to room temperature to obtain material A for later use.

[0074] (b) Sodium aluminate, sodium hydroxide, material A and water were mixed according to the molar ratio of Na2O:Al2O3:SiO2:H2O of 5.5:1:15:400, transferred to a polytetrafluoroethylene hydrothermal synthesis reactor, and allowed to stand at 100°C for crystallization for 72 hours. The molecular sieve solid was separated by filtration, washed with deionized water until the washing water was neutral, dried at 100°C for 24 hours, and calcined at 550°C for 3 hours to obtain a Y-type molecular sieve.

[0075] (c) The Y-type molecular sieve obtained in step (b) was mixed with a 1.0 mol / L ammonium nitrate solution at a solid-liquid ratio of 1:10 g:mL, and ammonium ion exchange was performed at 90°C for 2 h.

[0076] (d) The molecular sieve obtained in step (c) was mixed with a 0.1 mol / L ammonium fluorosilicate solution at a solid-liquid ratio of 1:40 g / mL and treated at 90°C for 4 h. The molecular sieve product was separated by filtration, washed with deionized water until the washing water was neutral, dried at 100°C for 24 h, and calcined at 500°C for 3 h to obtain a modified Y-type molecular sieve. The specific surface area of ​​the obtained modified Y-type molecular sieve was 841 m 2 / g, the silicon-aluminum ratio (SiO2 / Al2O3 molar ratio) is 15.2; the total pore volume is 0.43cm 3 / g, the total pyridine infrared acid content is 0.88mmol / g, of which the pyridine infrared acid content with a desorption temperature greater than 350℃ accounts for 68.5% of the total pyridine infrared acid content.

[0077] 2. Preparation of catalyst

[0078] The modified Y-type molecular sieve, γ-alumina, nickel nitrate and MoO3 were mixed in a molecular sieve:γ-alumina:NiO:MoO3 mass ratio of 60:22:3:15. Then, a 15 wt.% nitric acid solution was added to the mixture to prepare a catalyst slurry with a solid content of 50 wt.%, which was then kneaded and extruded into strips. The formed catalyst was dried at a constant temperature of 120°C for 3 h and then calcined at 500°C in an air atmosphere for 3 h to obtain hydrocracking catalyst I, numbered HC-I-1.

[0079] The preparation method of the hydrocracking catalyst II in this embodiment is as follows:

[0080] (1) Tetraethyl orthosilicate, aluminum chloride hexahydrate, 25 wt.% TPAOH, TPABr, ammonium fluoride and water were mixed in a molar ratio of SiO2:Al2O3:TPAOH:TPABr:NH4F:H2O=1:0.025:0.06:0.06:0.8:180, and the obtained molecular sieve mother liquor was allowed to stand for crystallization at 170°C for 24 hours. The product was filtered for solid-liquid separation and washed, and then dried at 100°C for 12 hours and calcined at 550°C for 3 hours. It was then mixed with 1 mol / L ammonium nitrate solution at a solid-liquid ratio of 10 g / mL, and ammonium ion exchange was carried out at 80°C for 2 hours. Then, it was calcined at 550°C for 3 hours to obtain ZSM-5 molecular sieve. The obtained ZSM-5 molecular sieve has a specific surface area of ​​390 m 2 / g, silicon-aluminum ratio (SiO2 / Al2O3 molar ratio) is 50; pore volume is 0.23cm 3 / g, the total pyridine infrared acid content is 0.29mmol / g, of which the pyridine infrared acid content with a desorption temperature greater than 350°C accounts for 73% of the total pyridine infrared acid content.

[0081] (2) ZSM-5 molecular sieve, γ-alumina, nickel nitrate and MoO3 were mixed in a molecular sieve:γ-alumina:NiO:WO3 mass ratio of 25:60:2:13, and then a 15 wt.% nitric acid solution was added to the mixture to prepare a catalyst slurry with a solid content of 50 wt.%, which was then kneaded and extruded into strips. The formed catalyst was dried at a constant temperature of 120°C for 3 h and then calcined at 500°C in an air atmosphere for 3 h to obtain a hydrocracking catalyst II, numbered HC-II-1.

[0082] The process of this embodiment is as follows:

[0083] Catalytic diesel 1 and hydrogen are mixed and fed into a hydrotreating reactor. The reaction effluent undergoes high-pressure and low-pressure separation to remove impurities, yielding a hydrorefined product oil with an aromatics retention rate of 94.0 wt%. The product oil then enters a hydrocracking reactor, where it is separated into a gas phase, a naphtha fraction (<160°C), and a diesel fraction (>160°C). The diesel fraction is then mixed with the hydrorefined product oil and recycled back to the hydrocracking reactor. The reaction conditions for the hydrorefining and hydrocracking reaction zones are shown in Table 2, and the properties of the hydrorefined product oil and diesel fraction are shown in Table 3.

[0084] Table 2 Process conditions of hydrofining reaction zone and hydrocracking reaction zone

[0085]

[0086] Table 3 Properties of hydrorefining oil and diesel fractions

[0087]

[0088]

[0089] Product Analysis:

[0090] The yield of BTX product in this example is 19.4 wt.%, and the selectivity relative to fresh raw material is 38.4 wt.%.

[0091] Example 2

[0092] The preparation method of the hydrocracking catalyst I in this embodiment is as follows:

[0093] 1. Preparation of modified Y-type molecular sieve

[0094] (a) Catalytic diesel 2, a silane coupling agent, and a silicon source were uniformly mixed in a ratio of catalytic diesel 2:methyl orthosilicate (calculated by SiO2 content) of 0.05:1 by mass and 3-glycidyl ether propyl trimethoxysilane:methyl orthosilicate of 0.1:1 by mole, and subjected to a low-temperature heat treatment at 60°C for 2 h. The mixture was cooled to 25°C to obtain material A for standby use.

[0095] (b) Aluminum sulfate, sodium hydroxide, material A and water were mixed according to the molar ratio of Na2O:Al2O3:SiO2:H2O of 4:1:12:300, transferred to a polytetrafluoroethylene hydrothermal synthesis reactor, and allowed to stand at 90°C for crystallization for 48 hours. The molecular sieve solid was separated by filtration, washed with deionized water until the washing water was neutral, dried at 100°C for 24 hours, and calcined at 500°C for 2 hours to obtain a Y-type molecular sieve.

[0096] (c) The Y-type molecular sieve obtained in step (b) was mixed with a 1.5 mol / L ammonium sulfate solution at a solid-liquid ratio of 1:10 g / mL, and ammonium ion exchange was performed at 60° C. for 2 h, and the process was repeated once.

[0097] (d) The molecular sieve obtained in step (c) was mixed with a 0.05 mol / L ammonium fluorosilicate solution at a solid-liquid ratio of 1:30 g / mL, treated at 60°C for 3 hours, and the process was repeated once. The obtained molecular sieve product was separated by filtration, washed with deionized water until the washing water was neutral, dried at 100°C for 24 hours, and calcined at 500°C for 3 hours to obtain a modified Y-type molecular sieve. The total pyridine infrared acid content of the modified Y-type molecular sieve was 0.98 mmol / g, of which the pyridine infrared acid content with a desorption temperature greater than 350°C accounted for 70% of the total pyridine infrared acid content; the SiO2 / Al2O3 (molar ratio) was 13.2; and the total pore volume was 0.41 cm 3 / g; specific surface area 792m 2 / g.

[0098] 2. Preparation of catalyst

[0099] The modified Y-type molecular sieve, gamma-alumina, nickel nitrate, and ammonium metatungstate were mixed in a molecular sieve:gamma-alumina:NiO:WO3 mass ratio of 50:35:2:13. A 10 wt.% nitric acid solution was then added to the mixture to form a catalyst slurry with a solid content of 60 wt.%. The mixture was then kneaded and extruded into strands. The resulting catalyst was dried at 120°C for 3 hours and then calcined at 500°C in air for 3 hours to obtain a hydrocracking catalyst designated HC-I-2.

[0100] The preparation method of the hydrocracking catalyst II in this embodiment is as follows:

[0101] (1) Tetraethyl orthosilicate, aluminum chloride hexahydrate, 25 wt.% TPAOH, TPABr, ammonium fluoride and water were mixed in a molar ratio of SiO2:Al2O3:TPAOH:TPABr:NH4F:H2O=1:0.02:0.06:0.06:0.7:160, and the mother liquor was allowed to stand for crystallization at 180°C for 24 hours. The product was filtered for solid-liquid separation and washed, and then dried at 120°C for 12 hours and calcined at 550°C for 5 hours. It was then mixed with a 1.5 mol / L ammonium nitrate solution at a solid-liquid ratio of 10 g / mL, and ammonium ion exchange was carried out at 80°C for 3 hours. It was then calcined at 550°C for 5 hours to obtain a ZSM-5 molecular sieve. The obtained ZSM-5 molecular sieve has a specific surface area of ​​358 m 2 / g, silicon-aluminum ratio (SiO2 / Al2O3 molar ratio) is 60; pore volume is 0.21cm 3 / g, the total pyridine infrared acid content is 0.23mmol / g, of which the pyridine infrared acid content with a desorption temperature greater than 350°C accounts for 77% of the total pyridine infrared acid content.

[0102] (2) ZSM-5 molecular sieve, γ-alumina, nickel nitrate and ammonium metatungstate were mixed in a molecular sieve:γ-alumina:NiO:WO3 mass ratio of 30:55:2:13, and then a 15 wt.% nitric acid solution was added to the mixture to prepare a catalyst slurry with a solid content of 50%, which was then kneaded and extruded into strips. The formed catalyst was dried at a constant temperature of 120°C for 3 hours and then calcined at 500°C in an air atmosphere for 3 hours to obtain hydrocracking catalyst II, numbered HC-II-2.

[0103] The process of this embodiment is as follows:

[0104] Catalytic diesel 1 and hydrogen are mixed and fed into a hydrotreating reactor. The reaction effluent undergoes high-pressure and low-pressure separation to remove impurities, yielding a hydrorefined product oil with an aromatics retention rate of 90.5 wt%. The product oil then enters a hydrocracking reactor, where it is separated into a gas phase, a naphtha fraction (<160°C), and a diesel fraction (>160°C). The diesel fraction is then mixed with the hydrorefined product oil and recycled back to the hydrocracking reactor. The reaction conditions for the hydrorefining and hydrocracking reaction zones are shown in Table 4, and the properties of the hydrorefined product oil and diesel fraction are shown in Table 5.

[0105] Table 4 Hydrorefining and hydrocracking process conditions

[0106]

[0107] Table 5 Properties of hydrorefining oil and diesel fractions

[0108] Hydrorefining oil 2 Diesel fraction 2 <![CDATA[Density (20 °C) / g·cm -3 > 0.9180 0.876 Distillation range / ℃ 178-342 181-339 <![CDATA[Sulfur / μg·g -1 > 106 9.8 <![CDATA[Nitrogen / μg·g -1 > 31 0.7 Mass spectrum composition, % Alkanes 15.1 18.1 Total cycloalkanes 12.1 14.4 Total aromatics 72.8 67.5 Among them: one ring 57.0 52.7 Second Ring Road 13.9 14.3 Three Rings 1.9 0.5

[0109] Product Analysis:

[0110] The yield of BTX product in this example is 19.3 wt.%, and the selectivity relative to fresh raw material is 37.8 wt.%.

[0111] Example 3

[0112] The preparation method of hydrocracking catalyst I is the same as that of Example 1, numbered HC-I-3, except that catalytic diesel 3 is used as a template in the synthesis process of modified Y-type molecular sieve. The specific surface area of ​​the obtained modified Y-type molecular sieve is 823m 2 / g, the silicon-aluminum ratio (SiO2 / Al2O3 molar ratio) is 14.8; the total pore volume is 0.42cm 3 / g, the total pyridine infrared acid content is 0.90mmol / g, of which the pyridine infrared acid content with a desorption temperature greater than 350°C accounts for 70% of the total pyridine infrared acid content.

[0113] The preparation method of hydrocracking catalyst II is the same as that of Example 1, numbered HC-II-3.

[0114] The process flow in this embodiment is as follows:

[0115] The process flow of this embodiment includes hydrofining catalytic diesel 1, and removing impurities from the reaction effluent through high-pressure separation and low-pressure separation to obtain a hydrofined product oil. The hydrofined product oil has an aromatics retention rate of 92.5wt%. After treatment in the hydrocracking reaction zone, the product oil is separated into light hydrocarbon gas, a naphtha fraction (<160°C), and a diesel fraction (>160°C). The diesel fraction >160°C is completely recycled to the hydrocracking unit. The reaction conditions of the hydrofining reaction zone and the hydrocracking reaction zone are shown in Table 6, and the properties of the hydrofined product oil and the diesel fraction are shown in Table 7.

[0116] Table 6 Hydrorefining and hydrocracking process conditions

[0117]

[0118] Table 7 Properties of hydrorefining oil and diesel fractions

[0119]

[0120]

[0121] Product Analysis:

[0122] The yield of BTX product in this example is 16.8 wt.%, and the selectivity relative to fresh raw material is 34.4 wt.%.

[0123] Example 4

[0124] In this embodiment, the catalyst is:

[0125] The hydrotreating catalyst is FF-66 type hydrotreating catalyst;

[0126] The preparation method of hydrocracking catalyst I is the same as that of Example 2, numbered HC-I-4, except that catalytic diesel 4 is used as a template in the synthesis process of modified Y-type molecular sieve; the specific surface area of ​​the obtained modified Y-type molecular sieve is 845m 2 / g, the silicon-aluminum ratio (SiO2 / Al2O3 molar ratio) is 15.9; the total pore volume is 0.44cm 3 / g, the total pyridine infrared acid content is 0.86mmol / g, of which the pyridine infrared acid content with a desorption temperature greater than 350℃ accounts for 74% of the total pyridine infrared acid content.

[0127] The preparation method of hydrocracking catalyst II is the same as that of Example 2, numbered HC-II-4.

[0128] The process flow in this embodiment is as follows:

[0129] The process flow of this embodiment includes hydrofining catalytic diesel 1, and removing impurities from the reaction effluent through high-pressure separation and low-pressure separation to obtain a hydrofined product oil. The hydrofined product oil has an aromatics retention rate of 94.7wt%. After treatment in the hydrocracking reaction zone, the product oil is separated into light hydrocarbon gas, a naphtha fraction (<160°C), and a diesel fraction (>160°C). The diesel fraction >160°C is completely recycled to the hydrocracking unit. The reaction conditions of the hydrofining reaction zone and the hydrocracking reaction zone are shown in Table 8, and the properties of the hydrofined product oil and the diesel fraction are shown in Table 9.

[0130] Table 8 Hydrorefining and hydrocracking process conditions

[0131]

[0132] Table 9 Properties of hydrorefining oil and diesel fractions

[0133]

[0134]

[0135] Product Analysis:

[0136] In this example, the yield of BTX product is 18.5 wt.%, and the selectivity relative to fresh raw material is 35.2 wt.%.

[0137] Example 5

[0138] In this embodiment, the catalyst is:

[0139] The hydrotreating catalyst is FF-66 type hydrotreating catalyst;

[0140] The preparation method of hydrocracking catalyst I is the same as that of Example 1, numbered HC-I-5, except that the modified Y-type molecular sieve-1 purchased from Deshijie Chemical Co., Ltd. is used in the HC-I-5 catalyst. The specific surface area of ​​the modified Y-type molecular sieve-1 is 828m 2 / g, the silicon-aluminum ratio (SiO2 / Al2O3 molar ratio) is 14.3; the total pore volume is 0.46cm 3 / g, the total pyridine infrared acid content is 0.92mmol / g, of which the pyridine infrared acid content with a desorption temperature greater than 350℃ accounts for 67.5% of the total pyridine infrared acid content.

[0141] The hydrocracking catalyst II is the catalyst numbered HC-II-1 prepared in Example 1. The ZSM-5 molecular sieve contained in HC-II-1 has a pore volume of 0.23 cm 3 / g, the total pyridine infrared acid content is 0.29mmol / g, of which the pyridine infrared acid content with a desorption temperature greater than 350°C accounts for 73% of the total pyridine infrared acid content.

[0142] The remaining conditions are the same as in Example 1.

[0143] Product Analysis:

[0144] In this comparative example, the BTX product yield was 16.4 wt.%, and the selectivity to fresh raw material was 32.5 wt.%.

[0145] Example 6

[0146] In this embodiment, the catalyst is:

[0147] The hydrotreating catalyst is FF-66 type hydrotreating catalyst;

[0148] The preparation method of hydrocracking catalyst I is the same as that of Example 1, numbered HC-I-6, except that the modified Y-type molecular sieve-2 purchased from Desje Chemical Co., Ltd. is used in the HC-I-6 catalyst. The specific surface area of ​​the modified Y-type molecular sieve-2 is 805m 2 / g, the silicon-aluminum ratio (SiO2 / Al2O3 molar ratio) is 16.3; the total pore volume is 0.43cm 3 / g, the total pyridine infrared acid content is 0.83mmol / g, of which the pyridine infrared acid content with a desorption temperature greater than 350℃ accounts for 66.8% of the total pyridine infrared acid content.

[0149] The preparation method of hydrocracking catalyst II is the same as that of Example 1, numbered HC-II-6, except that ZSM-5 molecular sieve purchased from Desje Chemical Co., Ltd. is used in HC-II-6 catalyst, wherein the specific surface area of ​​ZSM-5 molecular sieve is 409m 2 / g, silicon-aluminum ratio (SiO2 / Al2O3 molar ratio) is 61; pore volume is 0.18cm 3 / g, the total pyridine infrared acid content is 0.24mmol / g, of which the pyridine infrared acid content with a desorption temperature greater than 350°C accounts for 72% of the total pyridine infrared acid content.

[0150] The remaining conditions are the same as in Example 1.

[0151] Product Analysis:

[0152] In this comparative example, the BTX product yield was 15.9 wt.%, and the selectivity relative to fresh raw material was 31.6 wt.%.

[0153] Comparative Example 1

[0154] The catalyst in this comparative example:

[0155] The hydrotreating catalyst is FF-66 type hydrotreating catalyst;

[0156] The hydrocracking reaction zone is filled with two hydrocracking catalysts, HC-I-4 and HC-II-1. The total pore volume of the modified Y-type molecular sieve contained in HC-I-4 is 0.44 cm 3 / g, the total pyridine infrared acid content is 0.86mmol / g, of which the pyridine infrared acid content with a desorption temperature greater than 350℃ accounts for 74% of the total pyridine infrared acid content; the pore volume of the ZSM-5 molecular sieve contained in HC-II-1 is 0.23cm 3 / g, and the total pyridine infrared acid content was 0.29mmol / g, of which the pyridine infrared acid content with a desorption temperature greater than 350°C accounted for 73% of the total pyridine infrared acid content. Compared with the ZSM-5 molecular sieve, the modified Y-type molecular sieve has a higher proportion of pyridine infrared acid content with a desorption temperature greater than 350°C.

[0157] The remaining conditions are the same as in Example 1.

[0158] Product analysis: In this comparative example, the BTX product yield was 13.2 wt.%, and the relative fresh raw material selectivity was 31.1 wt.%.

[0159] Comparative Example 2

[0160] The catalyst in this comparative example:

[0161] The hydrotreating catalyst is FF-66 type hydrotreating catalyst;

[0162] The hydrocracking reaction zone is filled with two hydrocracking catalysts, HC-C-1 and HC-II-1 respectively. The preparation method of the hydrocracking catalyst HC-C-1 is the same as that in Example 1, except that the modified Y molecular sieve-3 purchased from Desje Chemical Co., Ltd. is used; the specific surface area of ​​the modified Y molecular sieve-3 is 817m 2 / g, the silicon-aluminum ratio (SiO2 / Al2O3 molar ratio) is 16.6; the total pore volume is 0.42cm 3 / g, the total pyridine infrared acid content is 0.82mmol / g, of which the pyridine infrared acid content with a desorption temperature greater than 350℃ accounts for 72% of the total pyridine infrared acid content. The pore volume of the ZSM-5 molecular sieve contained in HC-II-1 is 0.23cm 3 / g, the total pyridine infrared acid content is 0.29mmol / g, of which the pyridine infrared acid content with a desorption temperature greater than 350°C accounts for 73% of the total pyridine infrared acid content.

[0163] Compared with ZSM-5 molecular sieve, the total pyridine infrared acid content of the modified Y molecular sieve only increases by 0.53mmol / g, and the proportion of pyridine infrared acid content with desorption temperature greater than 350℃ to the total pyridine infrared acid content only decreases by 1%.

[0164] The remaining conditions are the same as in Example 1.

[0165] Product analysis: In this comparative example, the BTX product yield was 12.8 wt.%, and the relative fresh raw material selectivity was 30.7 wt.%.

Claims

1. A method for hydrocracking of catalytic diesel, characterized in that: The method comprises the following steps: (1) The catalytic diesel feedstock is mixed with hydrogen and enters the hydrotreating reaction zone, where it contacts and reacts with the hydrotreating catalyst bed to obtain hydrotreating product oil; (2) The hydrorefined product oil obtained in step (1) enters the hydrocracking reaction zone and passes through the first hydrocracking catalyst bed and the second hydrocracking catalyst bed in sequence to undergo a hydrocracking reaction; the first hydrocracking catalyst bed is loaded with hydrocracking catalyst I, which contains a modified Y-type molecular sieve; the second hydrocracking catalyst bed is loaded with hydrocracking catalyst II, which contains a ZSM-5 type molecular sieve; (3) The reaction effluent obtained from the hydrocracking reaction in step (2) is subjected to gas-liquid separation and fractionation to obtain gas, a BTX-rich naphtha fraction, and a diesel fraction; Wherein, in the hydrocracking reaction zone, the total pore volume of the hydrocracking catalyst I containing the modified Y molecular sieve is higher than that of the hydrocracking catalyst II containing the ZSM-5 molecular sieve, preferably 0.1 cm higher. 3 / g~0.3cm 3 / g; the total pyridine infrared acid content increases, preferably 0.56mmol / g~0.80mmol / g higher; the proportion of pyridine infrared acid content with a desorption temperature greater than 350°C to the total pyridine infrared acid content decreases, preferably 2%~10% lower.

2. The method according to claim 1, wherein: The catalytic diesel raw material in step (1) contains: 8wt.%-18wt.% of paraffins, 5wt.%-16wt.% of cycloalkanes, and 70wt.%-85wt.% of aromatics.

3. The method according to claim 1, wherein: The hydrotreating catalyst in step (1) is one or more of the hydrotreating catalysts with the trade names FF-36, FF-46 and FF-66 developed by Sinopec (Dalian) Petrochemical Research Institute Co., Ltd.

4. The method according to claim 1, wherein: The upper portion of the hydrorefining catalyst bed in step (1) is filled with a protective agent; the protective agent is selected from any one of the FZC and FBN series protective agents developed by Sinopec (Dalian) Petrochemical Research Institute Co., Ltd.

5. The method according to claim 1, wherein: The nitrogen content of the hydrorefined oil obtained in step (1) is 10 ppm to 100 ppm, preferably 40 ppm to 60 ppm; the sulfur content is less than 300 ppm, preferably less than 100 ppm; and the aromatics retention rate of the hydrorefined oil is >90 wt.%, preferably >92 wt.%.

6. The method according to claim 1, wherein: The reaction conditions of the hydrofining reaction zone in step (1) are as follows: reaction pressure 5MPa~10MPa, preferably 6MPa~8MPa; reaction temperature 300℃~420℃, preferably 330℃~400℃; volume space velocity 0.5h -1 ~3.0h -1 , preferably 0.8h -1 ~2.0h -1 ; Hydrogen to oil volume ratio 500~2000, preferably 800~1500.

7. The method according to claim 1, wherein: The total pore volume of the modified Y-type molecular sieve described in step (2) is 0.35 cm 3 / g-0.5cm 3 / g, the total pyridine infrared acid content is 0.5mmol / g~1.0mmol / g, of which the pyridine infrared acid content with desorption temperature greater than 350℃ accounts for 65%~80% of the total pyridine infrared acid content.

8. The method according to claim 1, wherein: The modified Y-type molecular sieve SiO2 / Al2O3 (molar ratio) in step (2) is 10-30, preferably 15-20; the specific surface area is 700m 2 / g~900m 2 / g, preferably 750m 2 / g~850m 2 / g.

9. The method according to claim 1, wherein: In step (2), based on the weight of the hydrocracking catalyst I, the content of the modified Y-type molecular sieve is 40 wt.% to 70 wt.%.

10. The method according to claim 1, wherein: The hydrocracking catalyst I in step (2) contains a binder, which is alumina; based on the weight of the hydrocracking catalyst I, the binder content is 10 wt.% to 35 wt.%.

11. The method according to claim 1, wherein: The hydrocracking catalyst I in step (2) contains a hydrogenation-active metal component, wherein the hydrogenation-active metal component contains at least one Group VIII metal component and at least one Group VIB metal component. Preferably, the Group VIII metal component is cobalt and / or nickel, and the Group VIB metal component is molybdenum and / or tungsten. Based on the weight of the hydrocracking catalyst I, the content of the hydrogenation-active metal component (calculated as metal oxide) is 15 wt.% to 25 wt.%, wherein the content of the Group VIII metal (calculated as metal oxide) is 2 wt.% to 8 wt.%, and the content of the Group VIB metal (calculated as metal oxide) is 13 wt.% to 20 wt.%.

12. The method according to claim 1, wherein: The total pore volume of the ZSM-5 molecular sieve described in step (2) is 0.2 cm 3 / g-0.25cm 3 / g; the total pyridine infrared acid content is 0.15mmol / g~0.40mmol / g, of which the pyridine infrared acid content with a desorption temperature greater than 350℃ accounts for 70%~85% of the total pyridine infrared acid content.

13. The method according to claim 1, wherein: The ZSM-5 molecular sieve SiO2 / Al2O3 (molar ratio) in step (2) is 30-100, preferably 40-60; the specific surface area is 350m 2 / g-450m 2 / g.

14. The method according to claim 1, wherein: The synthesis method of the ZSM-5 molecular sieve in step (2) is as follows: ethyl orthosilicate, aluminum chloride hexahydrate, TPAOH aqueous solution, TPABr, ammonium fluoride and water are mixed in a molar ratio of SiO2:Al2O3:TPAOH:TPABr:NH4F:H2O=1:(0.01~0.05):(0.05~0.1):(0.05~0.1):(0.6~1.0):(150~250) to obtain a mother liquor, and the mother liquor is allowed to stand and crystallize at a temperature of 160°C-180°C for 12h-48h. The obtained product is filtered, washed, dried, calcined, and then subjected to ammonium ion exchange and calcination to obtain the ZSM-5 molecular sieve.

15. The method according to claim 1, wherein: The loading volume ratio of the hydrocracking catalyst I and the hydrocracking catalyst II in step (2) is (3-5):

1.

16. The method according to claim 1, wherein: The reaction conditions of the hydrocracking reaction zone in step (2) are as follows: reaction pressure 5MPa~10MPa, preferably 6MPa~8MPa; reaction temperature 330℃~450℃, preferably 360℃~410℃; volume space velocity 0.5h -1 ~2.0h -1 , preferably 0.8~1.5h -1 ; Hydrogen to oil volume ratio 500~2000, preferably 800~1500.

17. The method according to claim 1, wherein: The BTX-rich naphtha fraction in step (3) is a fraction <160°C, and the diesel fraction is a fraction >160°C.

18. The method according to claim 1, wherein: The sulfur content of the diesel fraction in step (3) is less than 20 ppm, preferably less than 1 ppm; the nitrogen content is less than 10 ppm, preferably less than 1 ppm; and the ratio of the mass content of aromatic hydrocarbons in the diesel fraction to the mass content of aromatic hydrocarbons in the hydrorefined oil obtained in step (1) is (0.9-0.95):

1.

19. The method according to claim 1, wherein: Part or all of the diesel fraction in step (3) is recycled to the hydrocracking reaction zone. Preferably, the diesel fraction is mixed with the hydrorefined oil obtained in step (1) and then recycled to the hydrocracking reaction zone.

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