A combined process for producing light white oil and btx extraction feedstock

Abstract

A combined method for producing light white oil and BTX extraction raw material, raw oil enters a hydrocracking unit to perform a hydrocracking reaction, the obtained light distillate oil enters an extraction unit to perform extraction with an extraction solvent, the obtained raffinate oil has a mass fraction of aromatic hydrocarbon less than or equal to 0.5% and a sulfur content less than or equal to 10 mg / kg, and is a light white oil product, and the obtained extracted oil is subjected to reaction in an aromatic hydrocarbon lightening unit to obtain a BTX extraction raw material. The method provided by the application fully utilizes aromatic hydrocarbon resources, produces qualified light white oil products, and simultaneously obtains high-quality BTX extraction raw material, and is low in cost and high in economic efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydrocarbon feedstock processing, and particularly relates to a combined method for producing light white oil and BTX extraction raw material. BACKGROUND

[0002] White oil is a kind of colorless, odorless, chemically stable petroleum product obtained by removing unsaturated hydrocarbons and non-hydrocarbon impurities in lubricating oil fractions through deep refining. According to different uses and refining depths, white oil can be divided into industrial grade, cosmetic grade, food grade and medical grade white oil, etc. Among them, the food grade and medical grade white oil has the deepest refining degree.

[0003] The production process of white oil is mainly the process of removing sulfur, nitrogen, aromatic hydrocarbons and other impurities from base oil. Among them, the hydrogenation method for producing white oil has the advantages of no pollution, high yield, wide raw material sources, complete product varieties, and processable high viscosity white oil, etc., and has been rapidly developed and widely applied. According to the different contents of aromatic hydrocarbons, color, sulfur content and bromine index, the light white oil products are divided into two categories of light white oil (I) and light white oil (II) in SH / T0913-2015 light white oil standard. For light white oil (I) products, the mass fraction of aromatic hydrocarbon content is required to be not more than 0.2% or not more than 0.5%; for light white oil (II) products, the mass fraction of aromatic hydrocarbon content is required to be not more than 0.01 or not more than 0.05%. Due to the strict limitation of aromatic hydrocarbon content in light white oil products, the hydrogenation of aromatic hydrocarbons is difficult to be carried out at high temperature due to the limitation of thermodynamic equilibrium, so a higher pressure is required when using non-noble metal hydrorefining catalyst to produce light white oil. For lubricating oil base oil raw materials with high aromatic hydrocarbon content, two-stage hydrogenation is generally required to obtain light white oil (II) products.

[0004] CN1362486A discloses a method for producing food grade white oil by hydrogenation. Its characteristics are that a layered catalyst system is used in the traditional hydrogenation process for producing white oil: the layered catalyst system is a desulfurizer and a reduced nickel catalyst; the process conditions are: pressure 8.0 MPa-20.0 MPa, reaction temperature 150℃-300℃; volume space velocity 0.1 -1 -1.5h -1 , hydrogen / oil volume ratio 100-1500. The method requires that the aromatic hydrocarbon content in the raw material is not more than 10 mass%, the sulfur content is less than 50 ppm, preferably less than 30 ppm; the nitrogen content is less than 10 ppm, preferably less than 5 ppm.

[0005] CN 110938459 A discloses a method for producing petroleum ether and light white oil from naphtha. In this method, the naphtha is passed through a pre-adsorption device to remove trace colloids, sulfur-containing compounds, nitrogen-containing compounds and other impurities in the naphtha, and then aromatics are separated to obtain non-aromatic components through a simulated moving bed. The non-aromatic components are then subjected to deep dearomatization in a fixed bed for adsorption to obtain light white oil.

[0006] CN111378504A discloses a harmless refining method for coal-based white oil. The method comprises first subjecting the crude coal-based white oil to atmospheric distillation and vacuum distillation, followed by catalytic hydrogenation to obtain a hydrogenated product. The hydrogenated product is then subjected to heat exchange and refined under the action of a catalyst. The product after reaction is cooled and separated to recycle the solid waste residue, and the gaseous product is condensed to obtain refined white oil. The catalytic hydrogenation reaction temperature is 350-370°C, the pressure is 15-22 MPa, and the mass space velocity is 0.8 h -1 -2h -1 , hydrogen-to-oil ratio 650-850; hydrorefining reaction temperature 160-260℃, mass space velocity 2.5h -1 -3.0h -1 The product after the refining reaction is subjected to a gasification reaction at a temperature of 1000-1800°C and a pressure of 0.5-4 MPa to obtain a gaseous product and liquid waste residue; the gaseous product is liquefied to obtain refined white oil.

[0007] It can be seen that the production of light white oil by hydrogenation has problems such as high requirements for raw materials, harsh processes, catalysts and operating conditions. Summary of the Invention

[0008] The invention aims to solve the problems in the prior art of producing light white oil by hydrogenation, such as high requirements on raw materials, harsh requirements on production process and catalyst, and narrow distillation range of light white oil products.

[0009] The present invention provides a combined method for producing light white oil and BTX extraction raw materials, comprising:

[0010] (1) The feedstock oil enters a hydrocracking unit and, in the presence of hydrogen, sequentially contacts a hydrotreating catalyst and a hydrocracking catalyst to react, and the reaction effluent is separated to obtain at least a light distillate oil having a distillation range of 120 to 255° C. The feedstock oil is wax oil and / or diesel;

[0011] (2) the light distillate oil obtained in step (1) enters an extraction unit, contacts with an extraction solvent, and obtains raffinate oil and extracted oil after separation, wherein the extraction solvent is an alkyl sulfolane having a boiling point higher than 280° C., the raffinate oil has an aromatic mass fraction of less than or equal to 0.5%, a sulfur content of less than or equal to 10 mg / kg, and the raffinate oil is a light white oil product;

[0012] (3) The extracted oil obtained in step (2) enters the aromatic hydrocarbon lightening unit, contacts with the lightening catalyst in the presence of hydrogen to react, and separates the reaction effluent to obtain a C6-C8 fraction, which is the raw material for BTX extraction.

[0013] In the present invention, the wax oil is selected from one or more of atmospheric wax oil, vacuum wax oil, coker wax oil, and deasphalted oil; the diesel has a final distillation point range of 280-360°C and is selected from one or more of catalytic diesel, coker diesel, and straight-run diesel.

[0014] The present invention has strong adaptability to raw oil. In one embodiment of the present invention, the raw oil is ordinary second-line straight-run diesel with a distillation range of 170 to 280°C.

[0015] In one embodiment of the present invention, the reaction conditions of the hydrocracking unit in step (1) are: hydrogen partial pressure of 10.0 MPa to 18.0 MPa, reaction temperature of 300°C to 450°C, hydrogen to oil volume ratio of 500 to 2000 Nm 3 / m 3 , liquid hourly volumetric space velocity is 0.1h -1 ~3.0h -1 , preferably 0.3h -1 ~1.8h -1 .

[0016] In one embodiment of the present invention, the hydrocracking unit of step (1) comprises one or more fixed-bed hydrogenation reactors. According to the logistics direction, the feedstock oil passes through the hydrorefining catalyst and the hydrocracking catalyst in sequence, and the loading volume ratio of the hydrorefining catalyst to the hydrocracking catalyst is 1:5 to 5:1.

[0017] In one embodiment of the present invention, the hydrotreating catalyst comprises a carrier and a Group VIII metal element with a content of 1 to 10 wt% and / or a Group VIB metal element with a content of 10 to 45 wt% supported on the carrier, calculated as oxide and based on the hydrotreating catalyst, wherein the Group VIII metal element is cobalt and / or nickel, and the Group VIB metal element is molybdenum and / or tungsten, and the carrier is at least one of alumina, silica and alumina-silica.

[0018] In one embodiment of the present invention, the hydrocracking catalyst comprises a carrier and a Group VIII metal element and / or a Group VIB metal element supported on the carrier, wherein the carrier is composed of alumina and a molecular sieve, the molecular sieve is a Y-type molecular sieve and / or a β-type molecular sieve, the Group VIII metal element is cobalt and / or nickel, and the Group VIB metal element is molybdenum and / or tungsten;

[0019] Based on the entire hydrocracking catalyst, the hydrocracking catalyst composition, calculated as oxides, is as follows: 30 to 72 weight percent alumina, 1 to 30 weight percent molecular sieve, 15 to 35 weight percent Group VIB metal, and 2 to 8 weight percent Group VIII metal.

[0020] In the present invention, the feedstock is subjected to a hydrocracking reaction in a hydrocracking unit, and the reaction effluent is subjected to gas-liquid separation to obtain a gas phase stream and a liquid phase stream. In one embodiment of the present invention, the obtained liquid phase stream is fractionated to obtain a light naphtha fraction, a heavy naphtha fraction, a light distillate oil and a tail oil, wherein the cut point between the light naphtha fraction and the heavy naphtha fraction is 80-90°C, the cut point between the heavy naphtha fraction and the light distillate oil is 120-205°C, the distillation range of the light distillate oil is 120-255°C, and the tail oil is a fraction above the boiling point of the light distillate oil.

[0021] In one embodiment of the present invention, the tail oil obtained from the hydrocracking unit can be cut into different fractions according to the application or product requirements.

[0022] In the present invention, the light fraction oil obtained in the hydrocracking unit is sent to an extraction unit, where it is contacted with an extraction solvent in an extraction tower for extraction to obtain extracted oil and raffinate oil. The extraction solvent used in the present invention is an alkyl sulfolane having a boiling point greater than 280°C. In a preferred embodiment, the extraction solvent is 3-methylsulfolane and / or 2,4-dimethylsulfolane. Based on the characteristics of the light fraction oil, the present invention optimizes the extraction solvent, which can effectively extract aromatic substances from the light fraction oil, improve the extraction efficiency, and obtain raffinate oil with a lower aromatic content, which is a light white oil product.

[0023] In one embodiment of the present invention, the extraction solvent contains 0.5% to 3.0% by mass of water.

[0024] In one embodiment of the present invention, the light fraction oil enters the extraction tower from the lower part, contacts with the extraction solvent in reverse direction for extraction, and obtains the raffinate oil at the top of the tower and the extracted oil rich in the extraction solvent at the bottom of the tower.

[0025] In one embodiment of the present invention, the temperature of the extraction solvent entering the extraction tower is 60° C. to 180° C., preferably 90° C. to 140° C.; the pressure of the extraction tower is 0.2 MPa to 0.8 MPa absolute pressure; and the mass ratio of the extraction solvent to the extraction feed (light distillate oil) is 3:1 to 7:1.

[0026] In one embodiment of the present invention, the raffinate oil is fed into a water washing tower for water washing, and the raffinate oil washing water obtained enters the lower part of the solvent recovery tower after heat exchange.

[0027] In one embodiment of the present invention, the extracted oil enters the solvent recovery tower, part of the overhead stream of the solvent recovery tower is refluxed to the solvent recovery tower, and the remaining part is sent to the aromatics lightening unit.

[0028] In one embodiment of the present invention, the extracted oil rich in extraction solvent enters a solvent recovery tower. A portion of the overhead stream from the solvent recovery tower is refluxed to the solvent recovery tower, while the remaining portion, as the extracted oil, is sent to the aromatics lightening unit. The water separated from the overhead stream of the solvent recovery tower is used as wash water and enters the upper portion of the water scrubber. The bottoms stream from the solvent recovery tower is the recovered solvent, which is circulated to the extraction tower.

[0029] The mass ratio of washing water to raffinate oil is 0.1-0.5, preferably 0.1-0.3, the pressure at the top of the washing tower is 0.4MPa-0.7MPa absolute pressure, and the washing temperature is 30℃-50℃;

[0030] The number of theoretical plates of the solvent recovery tower is 5 to 30, the reflux ratio is 0.3 to 1.0, the top pressure is 0.05 MPa to 0.15 MPa absolute pressure, and the bottom temperature is 150° C. to 200° C.

[0031] In one embodiment of the present invention, the light white oil product obtained in step (2) has an aromatics mass fraction of less than or equal to 0.2% and a sulfur content of less than or equal to 10 mg / kg. The light white oil product obtained in the present invention meets the requirements of light white oil (I) products in the SH / T 0913-2015 standard.

[0032] In the present invention, the extracted oil obtained in step (2) is sent to an aromatics lightening unit to carry out an aromatics lightening reaction.

[0033] In one embodiment of the present invention, the reaction conditions of the aromatic hydrocarbon lightening unit are as follows: reaction temperature is 350℃~450℃, reaction pressure is 0.5~3.5MPa, volume space velocity is 1h -1 ~5h -1 , the hydrogen-to-oil volume ratio is 500-1200.

[0034] In one embodiment of the present invention, the lightweighting catalyst is a catalyst containing ZSM-5 zeolite, alumina and a Class VIII noble metal, and the catalyst has the following composition based on the carrier: 30% to 70% by mass of ZSM-5 zeolite and 30% to 70% by mass of γ- or η-Al2O3 as the carrier, loaded with (1) 0.1% to 0.5% by mass of Re, 0.1% to 0.5% by mass of Sn and 0.05% to 0.3% by mass of Pt, or (2) 0.1% to 0.5% by mass of Re, 0.1% to 0.5% by mass of Sn and 0.2% to 0.8% by mass of Pd.

[0035] In one embodiment of the present invention, the aromatic lightening reaction product is separated to obtain a BTX-rich C6-C8 fraction, which is fed into a BTX extraction unit as a high-quality BTX extraction feedstock, and a single BTX product is obtained after extraction and separation.

[0036] Features of the present invention:

[0037] (1) The method provided by the present invention can produce qualified light white oil products and obtain high-quality BTX extraction raw materials at the same time, with high economic efficiency.

[0038] (2) The preferred extraction solvent of the present invention has good aromatic selectivity, is easy to recover, and has low operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of one embodiment of the combined method for producing light white oil and BTX extraction raw material provided by the present invention. DETAILED DESCRIPTION

[0040] The present invention will be further described below with reference to the accompanying drawings, but the present invention is not limited thereto.

[0041] Figure 1 FIG. 1 is a schematic diagram of one embodiment of the combined method for producing light white oil and BTX extraction raw materials provided by the present invention. Figure 1As shown, in the hydrocracking unit, the feedstock oil is mixed with the hydrogen-rich gas from pipeline 2 via pipeline 1, and then enters the hydrorefining reactor 101 to contact with the hydrorefining catalyst for reaction. The resulting hydrorefining reaction effluent enters the hydrocracking reactor 102 via pipeline 3 to contact with the hydrocracking catalyst for reaction. The effluent from the hydrocracking reactor enters the separator 103 via pipeline 4 for gas-liquid separation. The resulting gas phase enters the compressor 104 via pipeline 6 for pressurization and is mixed with supplementary hydrogen as hydrogen-rich gas. The resulting oil phase enters the fractionating tower 105 via pipeline 5 for fractionation to obtain a light naphtha fraction, a heavy naphtha fraction, a light distillate oil and tail oil, which are extracted through pipelines 7, 8, 9 and 10 respectively. Light distillate oil enters the lower portion of extraction tower 106 of the extraction unit via pipeline 9, while lean solvent (recovery solvent) enters the upper portion of extraction tower 106 via pipeline 12. The two enter countercurrent contact for extraction. Extracted oil (rich solvent) enriched in extraction solvent, obtained at the bottom of extraction tower 106, enters the middle portion of recovery tower 107 via pipeline 13. Extracted oil obtained at the top of recovery tower 107 is condensed via pipeline 14 and then enters reflux tank 11. After water separation, a portion of the extracted oil is returned to recovery tower 107 via pipeline 15, while the remainder enters aromatics lightening unit 109 via pipeline 16. Water separated from the reflux tank water drum is used as wash water and enters the upper portion of water scrubber 108 via pipeline 17. The lean solvent obtained at the bottom of recovery tower 107 is heat exchanged and returned to the upper portion of extraction tower 106 via pipeline 12. The raffinate oil obtained at the top of extraction tower 106 enters the lower portion of water scrubber 108 via pipeline 18. After water scrubbing, the raffinate oil is obtained as a light white oil product and discharged from the device via pipeline 19. The washed water at the bottom of water scrubber 108 undergoes heat exchange and then enters the lower portion of recovery tower 107 via pipeline 20. The extracted oil from pipeline 16 enters aromatics lightening unit 109 for aromatics lightening reaction. The BTX extraction feed obtained by separation of the reaction products is delivered to the BTX extraction unit via pipeline 21.

[0042] The present invention will be further described below with reference to the examples, but the present invention is not limited thereto.

[0043] The commercial grades of the hydrorefining catalysts used in the examples and comparative examples are RN-410 and RS-2100, and the commercial grades of the hydrocracking catalysts are RHC-210 and RHC-220, all of which are produced by the Changling Catalyst Plant of Sinopec Catalyst Company.

[0044] The raw materials used in the examples and comparative examples are shown in Table 1, wherein raw material A is catalytic diesel, raw material B is straight-run conventional second-line diesel, and raw material C is straight-run wax oil.

[0045] In the present invention, the relevant calculation formulas in the embodiments and comparative examples are as follows:

[0046]

[0047] Example 1

[0048] This embodiment uses feedstock oil B, according to Figure 1 The process is as follows:

[0049] (1) The crude oil enters the hydrocracking unit and, in the presence of hydrogen, sequentially contacts with a hydrotreating catalyst and a hydrocracking catalyst to react, and the reaction effluent is separated to obtain a light naphtha fraction, a heavy naphtha fraction, a light distillate oil, and a tail oil.

[0050] (2) The light fraction oil obtained in step (1) enters the extraction unit and contacts with the extraction solvent in countercurrent. After separation, raffinate oil and extracted oil rich in extraction solvent are obtained. The raffinate oil enters the water washing tower for water washing. The raffinate oil after water washing is a light white oil product. The water obtained after washing the raffinate oil enters the lower part of the solvent recovery tower after heat exchange. The extracted oil rich in extraction solvent enters the solvent recovery tower. The overhead stream of the solvent recovery tower is partially refluxed to the solvent recovery tower, and the remaining part is the extracted oil sent to the aromatics lightening unit. The water obtained by separating the overhead stream of the solvent recovery tower enters the upper part of the water washing tower as washing water. The bottom stream of the solvent recovery tower is the recovered solvent, which is circulated to the extraction tower.

[0051] (3) The extracted oil obtained in step (2) enters the aromatic hydrocarbon lightening unit, contacts with the lightening catalyst in the presence of hydrogen to react, and separates the reaction effluent to obtain a C6-C8 fraction, which is the raw material for BTX extraction.

[0052] The grades or compositions of the hydrotreating catalyst, hydrocracking catalyst, and lightening catalyst are shown in Table 2. The operating conditions of the hydrotreating reactor, hydrocracking reactor, lightening reactor, and extraction unit towers are shown in Table 3. 3-Methylsulfolane was used as the extraction solvent, and the mass fraction of water in the extraction solvent was 0.9%. The properties of the hydrocracking unit products are shown in Table 4, the properties of the raffinate oil (light white oil product) are shown in Table 5, and the properties of the extracted oil and the lightening products obtained by the extracted oil lightening reaction are shown in Table 5.

[0053] Example 2

[0054] This embodiment uses a mixture of raw material A (mass fraction 30%) and raw material C (mass fraction 70%). Figure 1 process for processing.

[0055] The grades or compositions of the hydrotreating catalyst, hydrocracking catalyst, and lightening catalyst are shown in Table 2. The operating conditions of the hydrotreating reactor, hydrocracking reactor, lightening reactor, and extraction unit towers are shown in Table 3. The extraction solvent used was 2,4-dimethylsulfolane, and the mass fraction of water in the extraction solvent was 0.9%. The properties of the hydrocracking unit products are shown in Table 4, the properties of the raffinate oil (light white oil product) are shown in Table 5, and the properties of the extracted oil and the lightening products obtained by the extracted oil lightening reaction are shown in Table 5.

[0056] Example 3

[0057] This example uses raw oil C, and the process flow shown in Figure 1 is used for processing. Figure 1

[0058] The brand or composition of the hydrofining catalyst, the hydrocracking catalyst, and the lightening catalyst are shown in Table 2, and the operating conditions of the hydrofining reactor, the hydrocracking reactor, the lightening reactor, and the extraction unit are shown in Table 3. The extraction solvent is 3-methylsulfolane, and the mass fraction of water in the extraction solvent is 1.5%. The properties of the hydrocracking unit product are shown in Table 4, the properties of the raffinate oil (light white oil product) are shown in Table 5, and the properties of the extracted oil and the lightened product obtained by lightening the extracted oil are shown in Table 5.

[0059] Comparative Example 1

[0060] The same raw oil and process flow as in Example 1 are used, and the same hydrofining catalyst, hydrocracking catalyst, and hydrocracking reaction conditions are used, except that 3-methylsulfolane with a mass fraction of water of 1% is selected as the extraction solvent. The specific extraction operating conditions are shown in Table 6, and the properties of the extracted oil and the raffinate oil are shown in Table 7.

[0061] As can be seen from Table 7, the content of aromatic hydrocarbons in the raffinate oil of this comparative example is as high as 1.5% by mass, which cannot meet the quality requirements of the light white oil product.

[0062] Table 1

[0063]

[0064]

[0065] Table 2

[0066]

[0067]

[0068] Table 3

[0069]

[0070]

[0071] Table 4

[0072]

[0073] Table 5

[0074]

[0075] ​

[0076] Table 6

[0077] Item Comparative Example 1 Extraction column Theoretical plate number 12 Solvent / Feed mass ratio 15 Water content in solvent, mass % 1.0 Tower top pressure (absolute), MPa 0.6 Solvent inlet temperature, °C 120 Feed inlet temperature, °C 40 Tower bottom temperature, °C 83 Recovery column Theoretical plate number 20 Tower top pressure (absolute), MPa 0.04 Tower bottom temperature, °C 176 Reflux ratio (mass) 0.6 Water washing column Theoretical plate number 4 Tower top pressure (absolute), MPa 0.8 Water washing water / raffinate oil mass ratio 0.5 Water washing temperature, °C 40

[0078] Table 7

[0079] Item Comparative Example 1 Extracted oil Aromatic content, mass % 53.0 Raffinate oil Aromatic content, mass % 1.5 Yield, mass % 91.6

Claims

1. A combined method for producing light white oil and BTX extraction raw materials, comprising: (1) The feedstock oil enters a hydrocracking unit and, in the presence of hydrogen, sequentially contacts a hydrotreating catalyst and a hydrocracking catalyst to react, and the reaction effluent is separated to obtain at least a light distillate oil having a distillation range of 120 to 255° C. The feedstock oil is wax oil and / or diesel; (2) the light distillate oil obtained in step (1) enters an extraction unit, contacts with an extraction solvent, and obtains raffinate oil and extracted oil after separation, wherein the main solvent of the extraction solvent is 3-methylsulfolane and / or 2,4-dimethylsulfolane, the extraction solvent contains 0.5% to 3.0% by mass of water, the mass fraction of aromatics in the obtained raffinate oil is less than or equal to 0.5%, the sulfur content is less than or equal to 10 mg / kg, and the raffinate oil is a light white oil product; (3) The extracted oil obtained in step (2) enters the aromatic lightening unit, contacts with the lightening catalyst in the presence of hydrogen to react, and separates the reaction effluent to obtain a C6-C8 fraction, which is the raw material for BTX extraction; the reaction conditions of the aromatic lightening unit are: reaction temperature of 350°C to 450°C, reaction pressure of 0.5-3.5 MPa, volume space velocity of 1 h -1 ~5h -1 , hydrogen to oil volume ratio is 500-1200; The lightweighting catalyst is a catalyst containing ZSM-5 zeolite, alumina and a Group VIII noble metal, and has the following composition based on the carrier: 30% to 70% by mass of ZSM-5 zeolite and 30% to 70% by mass of γ- or η-Al2O3 as the carrier, loaded with (1) 0.1% to 0.5% by mass of Re, 0.1% to 0.5% by mass of Sn and 0.05% to 0.3% by mass of Pt, or (2) 0.1% to 0.5% by mass of Re, 0.1% to 0.5% by mass of Sn and 0.2% to 0.8% by mass of Pd.

2. The method according to claim 1, characterized in that The wax oil is selected from one or more of atmospheric wax oil, vacuum wax oil, and coker wax oil; the diesel has a final boiling point range of 280-360° C. and is selected from one or more of catalytic diesel, coker diesel, and straight-run diesel.

3. The method according to claim 1, characterized in that The reaction conditions of the hydrocracking unit in step (1) are: hydrogen partial pressure of 10.0 MPa to 18.0 MPa, reaction temperature of 300°C to 450°C, hydrogen to oil volume ratio of 500 to 2000 Nm 3 / m 3 , liquid hourly volumetric space velocity is 0.1h -1 ~3.0h -1 .

4. The method according to claim 3, characterized in that The reaction conditions of the hydrocracking unit in step (1) are: liquid hourly volume space velocity of 0.3h -1 ~1.8h -1 .

5. The method according to claim 1, wherein In the hydrocracking unit of step (1), the loading volume ratio of the hydrorefining catalyst to the hydrocracking catalyst is 1:5 to 5:

1.

6. The method according to claim 1, characterized in that Calculated on the basis of oxides and based on the hydrotreating catalyst, the hydrotreating catalyst contains a carrier and a Group VIII metal element with a content of 1 to 10 weight percent and / or a Group VIB metal element with a content of 10 to 45 weight percent supported on the carrier, wherein the Group VIII metal element is cobalt and / or nickel, and the Group VIB metal element is molybdenum and / or tungsten, and the carrier is at least one of alumina, silica and alumina-silica.

7. The method according to claim 1, characterized in that The hydrocracking catalyst comprises a carrier and a Group VIII metal element and / or a Group VIB metal element supported on the carrier, wherein the carrier is composed of alumina and a molecular sieve, the molecular sieve is a Y-type molecular sieve and / or a β-type molecular sieve, the Group VIII metal element is cobalt and / or nickel, and the Group VIB metal element is molybdenum and / or tungsten; Based on the entire hydrocracking catalyst, the hydrocracking catalyst composition, calculated as oxides, is: 30 wt% to 72 wt% alumina, 1 wt% to 30 wt% molecular sieve, 15 wt% to 35 wt% Group VIB metal, and 2 wt% to 8 wt% Group VIII metal.

8. The method according to claim 1, characterized in that The temperature of the extraction solvent entering the extraction tower is 60° C. to 180° C.; the pressure of the extraction tower is 0.2 MPa to 0.8 MPa absolute pressure; and the mass ratio of the extraction solvent to the extraction feed is 3:1 to 7:

1.

9. The method according to claim 8, characterized in that The temperature of the extraction solvent entering the extraction tower is 90-140°C.

10. The method according to claim 1, characterized in that The raffinate oil enters the water washing tower for water washing, and the water obtained after the raffinate oil washing enters the lower part of the solvent recovery tower after heat exchange. The mass ratio of washing water to raffinate oil is 0.1-0.5, the pressure at the top of the washing tower is 0.4MPa-0.7MPa absolute pressure, and the washing temperature is 30℃-50℃; The number of theoretical plates of the solvent recovery tower is 5 to 30, the reflux ratio is 0.3 to 1.0, the top pressure is 0.05 MPa to 0.15 MPa absolute pressure, and the bottom temperature is 150° C. to 200° C.

11. The method according to claim 1, wherein The mass ratio of washing water to raffinate oil is 0.1 to 0.

3.

12. The method according to claim 1, characterized in that The aromatics mass fraction of the light white oil product obtained in step (2) is less than or equal to 0.2%.

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