A process for the production of ethylene cracking feedstock by hydrocracking

Abstract

The application discloses a method for producing ethylene cracking raw material by hydrocracking. The method is a one-stage series hydrocracking process, which comprises the following steps: a hydrocracking reactor is fed with a hydrocracking feedstock in an upward feeding mode, a material P is introduced into the hydrocracking reactor between a hydrocracking catalyst bed and a post-hydrorefining catalyst bed, the product obtained from the hydrocracking reactor is first subjected to air cooling, the material P in the product is taken out of the reaction system by water phase through the method of water injection in the air cooling device, the oil phase after air cooling is separated and fractionated to obtain light naphtha, heavy naphtha, aviation kerosene, diesel oil and tail oil fraction, and the tail oil fraction is used as the raw material for producing ethylene by steam cracking; the material P is one or more of C23-C35 phenols, aromatic alcohols, aromatic aldehydes, aromatic ketones and aromatic esters. The method can improve the quality of the tail oil product under the condition of producing the tail oil in the hydrocracking device, so as to prolong the operation cycle of the ethylene cracking furnace.

Description

Technical Field

[0001] This invention relates to the field of hydrocracking technology, and more specifically to a method for producing ethylene cracking feedstock by hydrocracking. Background Technology

[0002] In recent years, the demand for refined oil products has undergone significant changes, with a gradual decline in demand for diesel and gasoline, while the demand for chemical feedstocks has grown rapidly. The hydrocracking process can produce tail oil components that can be used as feedstock for ethylene production via steam cracking. The quality of the tail oil components used as ethylene cracking feedstock determines the degree of coking in the steam cracking unit's cracking furnace. Higher-quality hydrocracking tail oil components can reduce coking tendency in the steam cracking furnace, increase the yield of terpenes, and extend the unit's service life.

[0003] CN116064100A discloses a hydrocracking method for producing chemical feedstocks. The method includes: feedstock oil sequentially passing through a hydrorefining reactor and a hydrocracking reactor; then, the middle distillate oil obtained from the fractionation unit and a small amount of refined effluent enter the upper reaction zone of a partitioned hydrocracking reactor for reaction; the upper reaction effluent is mixed with the remaining refined effluent and then enters the lower reaction zone, which can be used to produce heavy naphtha and tail oil fractions. However, this method does not load a post-refining catalyst into the hydrocracking reactor, resulting in problems such as excessive bromine index in the heavy naphtha and issues with improving the quality of the tail oil product.

[0004] CN101684415B discloses a low-cost, high-volume hydrocracking method for producing chemical feedstocks. The method includes: mixing feedstock oil with hydrogen and then introducing it into a first reaction zone containing a hydrorefining reactor and a hydrocracking reactor; the reaction products are fractionated to obtain naphtha, middle distillate oil, and tail oil fractions. The middle distillate oil is then introduced into a second reaction zone for hydrocracking under low pressure, achieving complete conversion of the middle distillate into chemical feedstocks. This method involves secondary hydrocracking of the middle distillate oil to convert it into naphtha components, which is difficult to achieve at relatively low hydrogen partial pressures; furthermore, this method does not include a post-hydrorefining catalyst and does not consider issues such as excessive bromine index in heavy naphtha and the improvement of tail oil product quality. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for producing ethylene cracking feedstock via hydrocracking. This method improves the quality of tail oil (used as ethylene cracking feedstock) produced by a hydrocracking unit, thereby extending the operating cycle of the ethylene cracking furnace.

[0006] This invention provides a method for producing ethylene cracking feedstock through hydrocracking, employing a single-stage tandem hydrocracking process, comprising the following steps:

[0007] The hydrorefined stream from the wax oil feedstock is fed into the hydrocracking reactor via a top-feed method. Material P is introduced into the hydrocracking reactor between the hydrocracking catalyst bed and the post-hydrorefining catalyst bed. The product obtained from the hydrocracking reactor is first air-cooled, and water is injected into the air-cooling device to carry material P out of the reaction system by the aqueous phase. The air-cooled oil phase is then separated and fractionated to obtain light naphtha, heavy naphtha, jet fuel, diesel oil, and tail oil fractions. The tail oil fraction is used as feedstock for steam cracking to produce ethylene. Material P is one or more of the following C23-C35 compounds: phenols, aromatic alcohols, aromatic aldehydes, aromatic ketones, and aromatic esters.

[0008] In this invention, a series hydrocracking process is employed, comprising a hydrorefining reactor and a hydrocracking reactor connected in series. The hydrorefining reactor is loaded with a hydrorefining catalyst. In the hydrocracking reactor, a hydrocracking catalyst bed and a post-hydrorefining catalyst bed are sequentially loaded along the liquid phase stream direction. Specifically, the hydrocracking catalyst bed contains a hydrocracking catalyst, and the post-hydrorefining catalyst bed contains a post-hydrorefining catalyst.

[0009] In the method of this invention, wax oil raw material and hydrogen enter a hydrorefining reactor, where they come into contact with a hydrorefining catalyst to carry out a hydrorefining reaction, thereby obtaining a hydrorefined stream.

[0010] In the method of this invention, both the hydrorefining reactor and the hydrocracking reactor are fixed-bed reactors.

[0011] In the method of this invention, the hydrorefining reactor adopts a conventional top-feed, bottom-discharge method. In the hydrocracking reactor, the hydrorefined stream and hydrogen gas adopt a top-feed, bottom-discharge method.

[0012] In the method of this invention, the initial boiling point of the wax oil feedstock is generally 200℃~350℃, and the dry point is generally 485℃~600℃, preferably 490℃~590℃; the nitrogen content is below 2500μg / g, generally 500μg / g~2000μg / g; the sulfur content is not strictly limited, and the content of other impurities only needs to meet conventional requirements. The wax oil feedstock can be at least one of various straight-run or secondary-processed wax oils obtained from processing naphthenic crude oil, intermediate-based crude oil, or paraffinic crude oil, preferably straight-run wax oil components or deasphalted oils from primary-processed paraffinic crude oil, which can be selected from at least one of various vacuum gas oil (VGO) and deasphalted oil (DAO) obtained from processing paraffinic crude oil, such as Daqing VGO, DAO, Changqing VGO, DAO, Shengli VGO, DAO, or several of them. The hydrogen gas is a feedstock with a commonly used industrial impurity content that meets the requirements.

[0013] In the method of this invention, the operating conditions of the hydrorefining reactor are as follows: the reaction temperature is 300℃~420℃, preferably 310℃~390℃; the reactor inlet pressure is 6MPa~20MPa, preferably 8MPa~18MPa; and the volume hourly space velocity is 0.5h⁻¹. -1 ~3.0h -1 0.6h is preferred -1 ~2.5h -1 The hydrogen-to-oil volume ratio at the reactor inlet is 400–1200, preferably 500–1100.

[0014] In the method of this invention, the hydrorefining catalyst and the post-hydrorefining catalyst can be conventional hydrocracking pretreatment catalysts, or the desired catalyst can be prepared according to common knowledge in the art. Conventional hydrocracking pretreatment catalysts include a support and a hydrogenation metal. Based on the weight of the catalyst, they typically include a Group VIB metal component from the periodic table, such as tungsten and / or molybdenum, with a mass content of 10%–35% (based on oxides), preferably 15%–30%, and a Group VIII metal, such as nickel and / or cobalt, with a mass content of 1%–7% (based on oxides), preferably 1.5%–6%. The support is an inorganic refractory oxide, generally selected from at least one of alumina, amorphous silica-alumina, silica, titanium dioxide, etc. The preferred metal for the hydrorefining catalyst is a Mo-Ni combination with a specific surface area ≥160 m². 2 / g, pore volume ≥0.3mL / g. The preferred metal catalyst for post-hydrogenation refining is a Mo-Co combination with a specific surface area ≥160m². 2 / g, pore volume ≥0.3mL / g. The conventional hydrocracking pretreatment catalyst can be any of the existing commercial catalysts, such as the 3936, 3996, FF-12, FF-16, FF-26, FF-36, FF-46, and FF-66 catalysts developed by the Fushun Petrochemical Research Institute (FRIPP). The refining reaction is a process of removing impurities such as desulfurization, denitrification, and aromatic saturation. The hydrorefining catalyst and the post-hydrorefining catalyst can be the same or different.

[0015] In the method of this invention, the operating conditions of the hydrocracking catalyst bed in the hydrocracking reactor are as follows: reaction temperature is 380℃~415℃, preferably 382℃~398℃; reactor inlet pressure is 10MPa~15MPa, preferably 11MPa~13MPa; volume hourly space velocity is 0.5h. -1 ~5.0h -1 0.6h is preferred -1 ~3.0h -1 The hydrogen-to-oil volume ratio at the reactor inlet is 400–2000, preferably 500–1100. Generally, during the later stages of operation, the hydrocracking reaction temperature is 390℃–405℃.

[0016] In the method of this invention, the operating conditions of the hydrorefining catalyst bed after the hydrocracking reactor are as follows: the reaction temperature is 360℃~435℃, preferably 375℃~430℃; the volume hourly space velocity of the hydrocracking bed products is 10h⁻¹. -1 ~25h -1 12h preferred -1 ~20h -1 The hydrogen-to-oil volume ratio is 400–2000, preferably 500–1100, and the reactor inlet pressure is 6 MPa–20 MPa, preferably 8 MPa–18 MPa. Generally, the reaction temperature of the post-hydrogenation refining catalyst bed is 390℃–430℃ during the later stages of operation.

[0017] In the method of this invention, the hydrocracking catalyst is a conventional hydrocracking catalyst used for producing ethylene cracking feedstock, generally a medium-oil type hydrocracking catalyst. The hydrocracking catalyst includes a cracking component and a hydrogenation component, and may also include a binder. The cracking component typically includes at least one amorphous silica-alumina and / or molecular sieves, such as Y-type, β-type, or USY molecular sieves, and the binder is typically alumina and / or silica. The hydrogenation component is selected from at least one metal, metal oxide, or metal sulfide from Group VIB, Group VIIB, or Group VIII, with the hydrogenation metal more preferably being one or more of iron, chromium, molybdenum, tungsten, cobalt, and nickel. Based on the weight of the catalyst, the hydrogenation component, calculated as oxides, has a content of 29%–35%, preferably 29%–33%, the molecular sieve content is 19%–26%, preferably 20%–25%, and the remainder is amorphous silica-alumina and / or binder components. Conventional hydrocracking catalysts can be selected from various existing commercial catalysts, such as the 3963, FC-50, and FC-50A catalysts developed by FRIPP. Specific hydrocracking catalysts can also be prepared according to the general knowledge in this field.

[0018] In the method of this invention, the material P is one or more of phenols, aromatic alcohols, aromatic aldehydes, aromatic ketones, and aromatic esters of C23-C35, and is further selected from one or more of tetra-tert-butylbiphenol, 3,3',5,5'-tetraisopropylbiphenyl-4,4-diol, guavadialdehyde, 2,2,2-triphenylacetophenone, and biphenyl-4,4'-dimethylbis(oxy-2,1-ethylenedimethyl)diisobutylenoate.

[0019] In the method of the present invention, preferably, relative to the post-hydrorefining catalyst, the volume hourly space velocity of the material P accounts for 28% to 72% of the total volume hourly space velocity of the hydrocracking bed products and the material P, more preferably 30% to 60%, for example, but not limited to 30%, 32%, 35%, 40%, 50%, 55%, 60%, etc., and any value within the range formed by any two of these values.

[0020] The inventors discovered that the main reason for the poor quality of the tail oil produced by hydrocracking units as feedstock for ethylene cracking is that components such as polycyclic aromatic hydrocarbons (PAHs) and PAHs containing partially saturated rings undergo dehydrogenation reactions in the post-refining catalyst reaction zone, generating PAHs and other components with higher unsaturation. These components rapidly coke in the ethylene cracking furnace, thus shortening the furnace's operating cycle and affecting the yield of terene products. Effectively retaining PAHs and PAHs containing partially saturated rings would be highly beneficial for extending the operating cycle of the ethylene cracking unit and improving the yield of terene products. Further research by the inventors revealed that material P will react at a relatively low space velocity (1.5–2.5 h⁻¹). -1 The hydrodeoxygenation reaction is carried out at relatively low temperatures (300–330 °C), but post-hydrogenation purification at high space velocities (2.8–18.0 h⁻¹) is necessary. -1 Deoxygenation reactions are difficult to occur under high-temperature (360℃~435℃) reaction environments. Therefore, introducing material P before post-hydrorefining in the hydrocracking reactor can inhibit the dehydrogenation reaction of polycyclic aromatic hydrocarbons (PAHs) and PAHs containing partially saturated rings in the post-refining process. This helps to efficiently retain PAHs and PAHs containing partially saturated rings. At the same time, material P is highly soluble in water, so material P can be effectively removed before product fractionation. This not only does not affect the yield and product composition of the hydrocracking tail oil, but also ensures that the operating cycle of the subsequent ethylene cracking unit is extended and the yield of triene products is improved.

[0021] Further research by the inventors revealed that the content of C25-C32 polycyclic cycloalkanes and polycyclic aromatic hydrocarbons in the hydrocracking catalyst bed products changes before and after passing through the post-hydrorefining catalyst bed. When the retention rate of C25-C32 polycyclic cycloalkanes and polycyclic aromatic hydrocarbons is lower than 75% due to dehydrogenation reaction with the post-hydrorefining catalyst, it significantly affects the quality of the tail oil. Therefore, feedstock P is added to inhibit the dehydrogenation reaction of C25-C32 polycyclic cycloalkanes and polycyclic aromatic hydrocarbons. However, since there is a chemical reaction equilibrium between feedstock P, hydrocracking bed products, and post-hydrorefining catalyst, the dehydrogenation reaction of C25-C32 polycyclic cycloalkanes and polycyclic aromatic hydrocarbons cannot be completely prevented. It is preferable to control a certain retention rate.

[0022] In the method of this invention, preferably, after the hydrocracking bed product stream passes through the post-hydrorefining catalyst, the retention rate of C25-C32 polycyclic cycloalkanes and polycyclic aromatic hydrocarbons is above 75 wt%, more preferably 78 wt% to 92 wt%. Wherein, the retention rate of C25-C32 polycyclic cycloalkanes and polycyclic aromatic hydrocarbons = (concentration of C25-C32 polycyclic cycloalkanes and polycyclic aromatic hydrocarbons in the post-refined product / concentration of C25-C32 polycyclic cycloalkanes and polycyclic aromatic hydrocarbons in the hydrocracking bed product stream) * 100%.

[0023] Hydrocracking units typically involve a separation process (generally including hot high-performance fraction, hot low-performance fraction, cold high-performance fraction, and cold low-performance fraction) before fractionation of the hydrocracking products. This process separates the gaseous components from the products, improving the efficiency of the fractionation process and reducing energy consumption. Specifically, a water injection process occurs after the hot high-performance fraction and before air cooling. This is to prevent the precipitation of ammonium salts during the cooling process, which could clog pipelines and equipment. Since the material P in the method of this invention is highly soluble in water, it can be carried out of the reaction system by the aqueous phase.

[0024] In the method of the present invention, an air cooling device is set up before the fractionation of the obtained product. The air cooling device is injected with water so that the material P in the product is carried out of the reaction system by the aqueous phase. The amount of water injected is 2 to 30 times the mass flow rate of material P, preferably 3 to 9 times the mass flow rate of material P.

[0025] In the method of this invention, the subsequent product separation, fractionation process and various qualified products are all conventional technical contents familiar to those skilled in the art, and will not be described in detail here.

[0026] In the method of this invention, the final boiling point of light naphtha is 50-68℃, preferably 55-62℃; the initial boiling point of heavy naphtha is 55-75℃, preferably 60-68℃, and the final boiling point is 120-190℃, preferably 145-180℃; the initial boiling point of jet fuel is 160-200℃, preferably 170-185℃, and the final boiling point is 200-230℃, preferably 205-215℃; the initial boiling point of diesel fuel is 205-270℃, preferably 210-265℃, and the final boiling point is 300-360℃, preferably 310-350℃; and the initial boiling point of tail oil (raw material for ethylene production by steam cracking) is 310-390℃, preferably 325-365℃.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] (1) The catalysts used in the hydrocracking unit in the method of the present invention are all conventional catalysts, and there is no need to develop new catalysts;

[0029] (2) In the method of the present invention, the tail oil quality problem is specifically improved by introducing material P, without causing changes in product distribution and other product properties;

[0030] (3) In the method of the present invention, material P is soluble in water and can be discharged from the system with the demineralized water during the separation of hydrocracking products. It will not enter the fractionation system, so that the tail oil will not have any impurities. The process is energy-saving and efficient.

[0031] (4) The method of the present invention has strong applicability and can improve the quality of tail oil for any hydrocracking catalyst and process conditions. The adjustment method is flexible. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the process of the present invention;

[0033] The annotations in the attached figures are explained as follows:

[0034] 1-Feedstock oil and hydrogen, 2-Hydrorefining reactor, 3-Hydrorefining product, 4-Hydrocracking reactor, 5-Hydrocracking catalyst bed, 6-Post-hydrorefining catalyst bed, 7-Feed P, 8-Hydrocracking product, 9-Water, 10-Air cooler, 11-Cooled feedstock, 12-Cold high-efficiency fractionator, 13-Cold high-efficiency gas phase component, 14-Acidic water, 15-Cold high-efficiency oil phase component, 16-Cold low-efficiency fractionator, 17-Cold low-efficiency gas phase component, 18-Cold low-efficiency oil phase component, 19-Fractioning system, 20-Naphtha, 21-Jet fuel, 22-Diesel, 23-Tail oil. Detailed Implementation

[0035] The method of the present invention will be described in more detail below with reference to specific embodiments and comparative examples.

[0036] The hydrocracking method for improving the quality of hydrocracking tail oil provided by this invention, such as... Figure 1 As shown, it includes:

[0037] Feedstock oil and hydrogen 1 are sequentially passed through hydrorefining reactor 2 and hydrocracking reactor 4 (equipped with hydrocracking catalyst bed 5 and post-hydrorefining catalyst bed 6). Material P7 is introduced between the hydrocracking catalyst bed 5 and the post-hydrorefining catalyst bed 6. The product from the hydrocracking bed and material P7 are passed together through the post-hydrorefining catalyst bed 6 to obtain hydrocracking product 8. Hydrocracking product 8 is mixed with water 9 and then cooled in air cooler 10. The cooled material 11 enters cold high-efficiency separator 12 for separation to obtain cold high-efficiency gas phase component 13, cold high-efficiency oil phase component 15, and acidic water 14. The acidic water 14 contains material P7 dissolved in the water. The cold high-grade oil phase component 15 enters the cold low-grade separator 16 for separation, resulting in the cold low-grade gas phase component 17 and the cold low-grade oil phase component 18. The cold low-grade oil phase component 18 enters the fractionation system 19 for separation, resulting in naphtha 20, jet fuel 21, diesel fuel 22, and tail oil 23.

[0038] In the embodiments and comparative examples of the present invention, the distillation range of light naphtha is the fraction below 62°C, the distillation range of heavy naphtha is 62 to 178°C, the distillation range of jet fuel is 178 to 213°C, the distillation range of diesel is 213 to 335°C, and the tail oil (the feedstock for ethylene production by steam cracking) is the fraction above 335°C.

[0039] The properties of the feedstock used in the following examples and comparative examples are shown in Table 1, and the main properties of the catalysts used in the examples and comparative examples are shown in Table 2.

[0040] Table 1 Main Properties of Crude Oil

[0041] project crude oil type Straight-run wax oil <![CDATA[Density, g / cm 3 > 0.8996 Distillation range, °C 305～495 S, wt% 0.94 N, μg / g 953

[0042] Table 2 Main properties of the catalyst

[0043]

[0044]

[0045] Example 1

[0046] Adopting such Figure 1 This is a series process flow. Hydrorefining catalyst A is used, hydrocracking catalyst B is used, and post-hydrorefining catalyst A is used again. Feedstock P uses tetra-tert-butylbiphenol, controlling the tail oil yield to approximately 38%, and sampling and analyzing the properties of the tail oil products.

[0047] Example 2

[0048] Adopting such Figure 1 This is a series process flow. Hydrorefining catalyst A is used, hydrocracking catalyst B is used, and post-hydrorefining catalyst C is used. Feed P consists of 3,3',5,5'-tetraisopropylbiphenyl-4,4-diol, guavadialdehyde, and 2,2,2-triphenylacetophenone (where the mass ratio of 3,3',5,5'-tetraisopropylbiphenyl-4,4-diol, guavadialdehyde, and 2,2,2-triphenylacetophenone is 0.5:2.1:1.3). The tail oil yield is controlled at approximately 38%, and the properties of the tail oil product are sampled and analyzed.

[0049] Example 3

[0050] Adopting such Figure 1 This is a series process flow. Hydrorefining catalyst A is used, hydrocracking catalyst B is used, and post-hydrorefining catalyst C is used. Material P consists of tetra-tert-butylbiphenol, guavadialdehyde, 2,2,2-triphenylacetophenone, and biphenyl-4,4'-dimethylbis(oxy-2,1-ethylenediyl)diisobutylenoate (where the mass ratio of tert-butylbiphenol, guavadialdehyde, 2,2,2-triphenylacetophenone, and biphenyl-4,4'-dimethylbis(oxy-2,1-ethylenediyl)diisobutylenoate is 1.6:3.1:0.7:0.8). The tail oil yield is controlled at approximately 42%, and the properties of the tail oil product are sampled and analyzed.

[0051] Comparative Example 1

[0052] Compared with Example 1, the only difference is that material P is not introduced and water is injected into the air-cooled room in a conventional manner.

[0053] A conventional single-stage series process was adopted. Catalyst A was used for hydrorefining, catalyst B for hydrocracking, and catalyst A was used for post-hydrorefining. The tail oil yield was controlled at approximately 38%, and the properties of the tail oil products were sampled and analyzed.

[0054] Comparative Example 2

[0055] Compared with Example 3, the only difference is that material P is not introduced and water is injected into the air-cooled room in a conventional manner.

[0056] A conventional single-stage series process was adopted. Catalyst A was used for hydrorefining, catalyst B for hydrocracking, and catalyst C for post-hydrorefining. The tail oil yield was controlled at approximately 42%, and the properties of the tail oil products were sampled and analyzed.

[0057] Comparative Example 3

[0058] The difference compared to Example 3 is that the material P is different.

[0059] Adopting such Figure 1 This is a series process flow. Hydrorefining catalyst A is used, hydrocracking catalyst B is used, and post-hydrorefining catalyst C is used. Feedstock P consists of ninhydrin hydrate, 4-methylumbelliferone, rhein, and cinnamyl alcohol (mass ratio of ninhydrin hydrate, 4-methylumbelliferone, rhein, and cinnamyl alcohol is 1.6:3.1:0.7:0.8). The tail oil yield is controlled at approximately 42%, and tail oil product properties are sampled and analyzed.

[0060] The effects of the above embodiments and comparative examples are compared in Table 3.

[0061] Table 3. Reaction conditions and results for each embodiment and comparative example.

[0062]

[0063]

Claims

1. A method for producing ethylene cracking feedstock by hydrocracking, employing a single-stage tandem hydrocracking process, comprising the following steps: The hydrorefined stream from the wax oil feedstock is fed into the hydrocracking reactor via a top-feed method. Material P is introduced into the hydrocracking reactor between the hydrocracking catalyst bed and the post-hydrorefining catalyst bed. The product obtained from the hydrocracking reactor is first air-cooled, and water is injected into the air-cooling device to carry material P out of the reaction system by the aqueous phase. The air-cooled oil phase is then separated and fractionated to obtain light naphtha, heavy naphtha, jet fuel, diesel oil, and tail oil fractions. The tail oil fraction is used as feedstock for steam cracking to produce ethylene. Material P is one or more of the following C23-C35 compounds: phenols, aromatic alcohols, aromatic aldehydes, aromatic ketones, and aromatic esters.

2. The method according to claim 1, characterized in that, A series hydrocracking process includes a hydrorefining reactor and a hydrocracking reactor connected in series. The hydrorefining reactor is filled with a hydrorefining catalyst. In the hydrocracking reactor, a hydrocracking catalyst bed and a post-hydrorefining catalyst bed are sequentially filled along the liquid phase stream direction. The hydrocracking catalyst bed contains a hydrocracking catalyst, and the post-hydrorefining catalyst bed contains a post-hydrorefining catalyst.

3. The method according to claim 2, characterized in that, The wax oil feedstock and hydrogen enter the hydrorefining reactor, where they come into contact with the hydrorefining catalyst to carry out the hydrorefining reaction, yielding the hydrorefined stream.

4. The method according to claim 2, characterized in that, Both the hydrorefining reactor and the hydrocracking reactor are fixed-bed reactors; the hydrorefining reactor adopts a top-feed and bottom-discharge method; in the hydrocracking reactor, the hydrorefining stream and hydrogen gas adopt a top-feed and bottom-discharge method.

5. The method according to claim 1, characterized in that, The initial boiling point of the wax oil raw material is 200℃~350℃, and the dry point is 485℃~600℃, preferably 490℃~590℃; the nitrogen content is below 2500μg / g, preferably 500μg / g~2000μg / g.

6. The method according to claim 1, characterized in that, The operating conditions of the hydrorefining reactor are as follows: reaction temperature 300℃~420℃, preferably 310℃~390℃; reactor inlet pressure 6MPa~20MPa, preferably 8MPa~18MPa; volume hourly space velocity 0.5h⁻¹. -1 ~3.0h -1 0.6h is preferred -1 ~2.5h -1 The hydrogen-to-oil volume ratio at the reactor inlet is 400–1200, preferably 500–1100.

7. The method according to claim 1, characterized in that, The aforementioned hydrorefining catalyst and post-hydrorefining catalyst are hydrocracking pretreatment catalysts; Preferably, the hydrorefining catalyst is a Mo-Ni metal combination with a specific surface area of ​​≥160 m². 2 / g, pore volume ≥ 0.3mL / g; Preferably, the catalyst for post-hydrogenation refining is a Mo-Co metal combination with a specific surface area of ​​≥160 m². 2 / g, pore volume ≥0.3mL / g.

8. The method according to claim 1, characterized in that, The operating conditions of the hydrocracking catalyst bed in the hydrocracking reactor are as follows: reaction temperature 380℃~415℃, preferably 382℃~398℃; reactor inlet pressure 10MPa~15MPa, preferably 11MPa~13MPa; volume hourly space velocity 0.5h⁻¹. -1 ~5.0h -1 0.6h is preferred -1 ~3.0h -1 The hydrogen-to-oil volume ratio at the reactor inlet is 400–2000, preferably 500–1100.

9. The method according to claim 1, characterized in that, The operating conditions for the hydrorefining catalyst bed after the hydrocracking reactor are as follows: reaction temperature 360℃~435℃, preferably 375℃~430℃; volume hourly space velocity of the hydrocracking bed products 10h⁻¹. -1 ~25h -1 12h preferred -1 ~20h -1 The hydrogen-to-oil volume ratio is 400–2000, preferably 500–1100, and the reactor inlet pressure is 6 MPa–20 MPa, preferably 8 MPa–18 MPa.

10. The method according to claim 1, characterized in that, The hydrocracking catalyst comprises a cracking component and a hydrogenation component. The cracking component comprises amorphous silica-alumina and / or molecular sieves, such as at least one of Y-type, β-type or USY molecular sieves. The hydrogenation component is selected from at least one of metals, metal oxides or metal sulfides of Group VIB, Group VIIB or Group VIII. The hydrogenation metal is more preferably one or more of iron, chromium, molybdenum, tungsten, cobalt and nickel. Preferably, based on the weight of the catalyst, the content of the hydrogenation component, calculated as oxide, is 29% to 35%, more preferably 29% to 33%, and the content of molecular sieve is 19% to 26%, more preferably 20% to 25%.

11. The method according to claim 1, characterized in that, The material P is one or more of phenols, aromatic alcohols, aromatic aldehydes, aromatic ketones, and aromatic esters of C23-C35, and is further selected from one or more of tetra-tert-butylbiphenol, 3,3',5,5'-tetraisopropylbiphenyl-4,4-diol, guavadialdehyde, 2,2,2-triphenylacetophenone, and biphenyl-4,4'-dimethylbis(oxy-2,1-ethylenedimethyl)diisobutylenoate.

12. The method according to claim 1, characterized in that, Compared to the post-hydrocracking catalyst, the volume hourly space velocity of the material P accounts for 28% to 72% of the total volume hourly space velocity of the hydrocracking bed products and the material P, and is more preferably 30% to 60%.

13. The method according to claim 1, characterized in that, After the hydrocracking bed product flows through the post-hydrorefining catalyst, the retention rate of C25-C32 polycyclic cycloalkanes and polycyclic aromatic hydrocarbons is above 75 wt%, and more preferably 78 wt% to 92 wt%.

14. The method according to claim 1, characterized in that, An air-cooling device is installed before the fractionation of the obtained product. The air-cooling device is injected with water so that material P in the product is carried out of the reaction system by the aqueous phase. The amount of water injected is 2 to 30 times the mass flow rate of material P, preferably 3 to 9 times the mass flow rate of material P.

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