Residual oil and coal tar combined processing technology method

Abstract

The invention discloses a residual oil and coal tar combined processing technique which comprises the following steps: (1) cutting a coal tar raw material to obtain light coal tar and heavy coal tar; (2) in the presence of hydrogen, mixing the light coal tar and the residual oil raw material obtained in the step (1), mixing with alkali metal, and reacting in an alkali metal treatment reaction zone; (3) carrying out solid-liquid separation on the alkali metal treatment reaction effluent obtained in the step (2) to obtain a liquid-phase material flow; and (4) mixing the liquid-phase material flow obtained in the step (3) and the heavy coal tar obtained in the step (1), feeding the mixture into a catalytic cracking reaction zone, contacting the mixture with a catalytic cracking catalyst for reaction, and separating the reaction effluent to obtain dry gas, liquefied gas, gasoline, light diesel oil and heavy distillate oil. According to the method, coal tar is introduced into an alkali metal treatment reaction system for the first time, the coking reaction can be reduced, the liquid phase yield is increased, and combined processing of residual oil and coal tar is achieved.

Description

Technical Field

[0001] The invention belongs to the field of oil refining and chemical industry, and particularly relates to a combined processing method of residual oil and coal tar. Background Art

[0002] With the decreasing resources of conventional oil, the trend of heavy and inferior crude oil is intensifying. As the heaviest component of crude oil, the proportion of residual oil is increasing. The importance of efficient utilization of heavy oil, especially residual oil, is becoming increasingly prominent. At present, there are two main ways to process residual oil, namely hydrogenation and decarbonization. Among them, the decarbonization process mainly includes thermal cracking, visbreaking and solvent deasphalting. The decarbonization process has high technical maturity, but there are problems such as low liquid yield and serious pollution, which cannot meet the needs of clean production of enterprises. The hydrogenation process mainly includes fixed bed hydrogenation, ebullating bed hydrogenation and moving bed hydrogenation. The hydrogenation process has the advantages of environmental friendliness and high liquid yield, but the reaction conditions are demanding and the investment is large. In recent years, researchers have been committed to developing new methods of residual oil processing. Among them, alkali metal treatment technology has the advantages of low reaction severity, high desulfurization selectivity, energy saving and environmental protection, and has received widespread attention.

[0003] CN114736710A discloses a method for hydrogenating low-quality heavy oil, which comprises the following contents: (1) separating the low-quality heavy oil into light distillate oil and heavy distillate oil through a fractionating tower; (2) subjecting the light distillate oil obtained in the optional step (1) to a hydrogenation reaction to obtain a hydrogenation product oil; (3) contacting the heavy distillate oil obtained in the step (1) with an alkali metal to carry out an alkali metal desulfurization reaction; (4) separating the liquid product obtained after the reaction in the step (3), optionally mixing it with the hydrogenation product oil of the step (2) or with the light distillate oil of the step (1), and separating it through a fractionating tower to obtain naphtha, diesel oil and wax oil.

[0004] CN114437822A discloses a method and system for producing fuel oil and its application, as well as fuel oil and its application, the method comprising: (1) contacting sulfur-containing raw oil with alkali metal for pre-reaction to obtain pre-reaction material, the pre-reaction being carried out under non-hydrogenation conditions; (2) contacting the pre-reaction material with a hydrogen supply agent for hydrogenation reaction; (3) separating the material obtained in step (2) to obtain liquid product fuel oil and a solid mixture. The method of the present invention can convert low-quality and cheap raw oil such as heavy residual oil into fuel oil, with high alkali metal utilization efficiency and safe and reliable process.

[0005] The above patents all involve alkali metal treatment technology, which provides a new technical route for residual oil processing. However, the research is not in-depth enough, and the above technical route is not highly compatible when processing specific oil products, such as high-sulfur raw materials.

[0006] At the same time, the efficient conversion of unconventional resources such as coal tar has attracted extensive attention from researchers in recent years. Currently, the technology with the greatest development potential is the technology of hydrogenating coal tar to produce light oil products. CN115216341A discloses a medium-low temperature coal tar processing system and a processing method, the method comprising the following contents: (1) hydrogen first enters a mixed hydrogen dissolving unit of a reactor, and then moves upwards through a liquid fraction hydrogenation unit, a raw material flash unit and a gas fraction hydrogenation unit in sequence; the medium-low temperature coal tar raw material enters the raw material flash unit in the reactor and is flashed into a gas fraction and a liquid fraction; (2) the gas fraction moves upwards into the gas fraction hydrogenation unit for shallow hydrogenation reaction, and the gas phase hydrogenation reaction product is discharged from the top of the reactor and enters the fractionation unit to be separated into a triphenyl raw material and a phenol raw material; the liquid fraction flows downwards into the liquid fraction hydrogenation unit for hydrogenation desulfurization, denitrogenation, aromatic saturation and deacidification reaction, and the liquid phase product of the reaction flows downwards into the mixed hydrogen dissolving unit, and after mixing and contacting with hydrogen, a hydrogen-dissolving stream is obtained, which enters the hydrogenation reforming unit for hydrogenation reforming reaction, and the liquid phase effluent is discharged from the bottom of the reactor. In the method of the invention, since the oxygen content of the coal tar raw material is relatively high, the water generated by hydrogenation can easily cause the catalyst to break, which will lead to a rapid increase in the pressure drop in the reactor and affect the operation cycle of the device. Summary of the invention

[0007] Through in-depth research, the inventors found that alkali metal desulfurization technology has problems such as easy coking and low liquid recovery when processing high-sulfur raw materials. The reasons are as follows: Under high temperature conditions, sulfur-containing compounds in residual oil react with alkali metals to generate intermediate species bonded by alkali metals and organic matter. The above intermediate species are prone to condensation reactions and eventually generate coke; the higher the concentration of the above intermediate products in the reaction system, the faster the rate of condensation coking reaction. Furthermore, the inventors also found in the research process that oxygen-containing compounds (phenol and its derivatives) rich in coal tar are highly polar molecules. In other words, when processing high-sulfur and low-quality residual oil raw materials, coal tar is introduced into the reaction system, and phenol and its derivatives will form a parallel competitive reaction with sulfur-containing compounds, which can adjust the conversion rate of sulfur-containing compounds in the reactor, thereby effectively controlling the concentration of intermediate species in the reaction system and reducing the occurrence of side reactions such as coking.

[0008] In view of the shortcomings of the prior art, the inventors provide a combined processing method of residual oil and coal tar based on the theoretical basis of research. The method introduces coal tar into the alkali metal treatment reaction system for the first time, which can reduce the coking reaction, improve the liquid phase yield, and realize the combined processing of residual oil and coal tar.

[0009] A combined processing method of residual oil and coal tar, the method comprising the following contents: (1) After the coal tar raw material is cut, light coal tar and heavy coal tar are obtained; (2) In the presence of hydrogen, the light coal tar and residual oil obtained in step (1) are mixed, and then mixed with an alkali metal and introduced into an alkali metal treatment reaction zone for reaction; (3) The alkali metal treatment reaction effluent obtained in step (2) is subjected to solid-liquid separation to obtain a liquid phase stream; (4) The liquid phase stream obtained in step (3) and the heavy coal tar obtained in step (1) are mixed and introduced into a catalytic cracking reaction zone to react with a catalytic cracking catalyst. The reaction effluent is separated to obtain dry gas, liquefied gas, gasoline, light diesel and heavy distillate oil.

[0010] In the method of the present invention, the coal tar raw material in step (1) is a coal tar raw material obtained after pretreatment. The pretreatment includes desalting, dehydration and desolidification. There is no special limitation on the methods of desalting, dehydration and desolidification, and any one of the existing desalting, dehydration and desolidification methods in the art can be used. Specifically in the present invention, desalting can be carried out by at least one of electric desalting, gravity sedimentation and chemical demulsification; dehydration can be carried out by at least one of heating sedimentation, filtration, centrifugation and microwave radiation; desolidification can be carried out by at least one of natural sedimentation, centrifugation, filtration and electrostatic separation.

[0011] In the method of the present invention, the cutting point of the coal tar raw material in step (1) is 230-280° C., preferably 240-270° C. Studies have shown that highly polar substances phenol and its derivatives are enriched in fractions below 230° C. The method of the present invention cuts the coal tar raw material according to the above cutting point to obtain light coal tar rich in phenol and its derivatives.

[0012] In the method of the present invention, the oxygen content of the light coal tar in step (1) is 7-20wt%, preferably 10-18wt%.

[0013] In the method of the present invention, the mass ratio of the light coal tar obtained in step (1) to the residual oil raw material in step (2) is (0.03-0.15):1, preferably (0.05-0.10):1. In the method of the present invention, the addition ratio of light coal tar is relatively low, and has little effect on the viscosity and density of the residual oil raw material; however, since light coal tar is rich in phenol and its derivatives, it forms a parallel competitive reaction with sulfur-containing compounds, which can adjust the conversion rate of sulfur-containing compounds in the reactor, thereby effectively controlling the concentration of intermediate species in the reaction system and reducing the occurrence of side reactions such as coking.

[0014] In the method of the present invention, the residual oil feedstock in step (2) is a residual oil feedstock having a sulfur content greater than 2.5 wt.%, preferably greater than 3.5 wt.%.

[0015] In the method of the present invention, the alkali metal in step (2) is one of the six metal elements in group IA of the periodic table except hydrogen (H), and each of them has an outermost electron belonging to the s orbital. The alkali metal is at least one of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr), preferably at least one of lithium (Li), sodium (Na) and potassium (K).

[0016] In the method of the present invention, the molar ratio of the alkali metal to the sulfur content in the residual oil feedstock in step (2) is (1.5-4.0):1, preferably (2.5-3.5):1.

[0017] In the method of the present invention, the alkali metal treatment reaction zone in step (2) is provided with at least one alkali metal treatment reactor, preferably 2-3 alkali metal treatment reactors, and more preferably 2-3 alkali metal treatment reactors arranged in series.

[0018] In the method of the present invention, the alkali metal treatment reaction zone in step (2) is provided with two alkali metal treatment reactors arranged in series, and the two alkali metal treatment reactors are respectively a first alkali metal treatment reactor and a second alkali metal treatment reactor; the light coal tar and residual oil raw materials obtained in step (1) are mixed, mixed with alkali metal and then enter the first alkali metal treatment reactor for reaction, and the reaction effluent is mixed with alkali metal again and enters the second alkali metal treatment reactor for reaction; the molar ratio of the alkali metal in the first alkali metal treatment reactor to the sulfur content in the residual oil raw material is (0.5-3.0):1, preferably (1.2-2.0):1; the molar ratio of the amount of alkali metal added in the first alkali metal treatment reactor to the amount of alkali metal added in the second alkali metal treatment reactor is 1:(0.2-1.5), preferably 1:(0.5-1.0).

[0019] In the method of the present invention, the alkali metal treatment reaction zone in step (2) is provided with three alkali metal treatment reactors arranged in series, and the outlet material of any alkali metal treatment reactor in the alkali metal treatment reaction zone is mixed with the alkali metal again and then enters the downstream alkali metal treatment reactor arranged in series; the three alkali metal treatment reactors are respectively the first alkali metal treatment reactor, the second alkali metal treatment reactor and the third alkali metal treatment reactor; the molar ratio of the alkali metal in the first alkali metal treatment reactor to the sulfur content in the residual oil feedstock is (0.5-2.0):1, preferably (0.8-1.5):1; the molar ratio of the alkali metal addition amount in the first alkali metal treatment reactor, the alkali metal addition amount in the second alkali metal treatment reactor and the alkali metal addition amount in the third alkali metal treatment reactor is 1:(0.2-1.5):(0.2-1.0), preferably 1:(0.3-0.9):(0.3-0.6).

[0020] In the method of the present invention, the alkali metal treatment reactor provided in the alkali metal treatment reaction zone in step (2) may be any one of the prior art reactors capable of realizing liquid-liquid two-phase mixing; specifically, in the present invention, the alkali metal treatment reactor is a kettle reactor and / or a tubular reactor, preferably a kettle reactor, and more preferably an isothermal continuous kettle reactor.

[0021] In the method of the present invention, the operating conditions of the alkali metal treatment reaction zone in step (2) are: reaction temperature 200-400°C, reaction pressure 2.0-18.0MPa, reaction time or residence time 0.5-2.5h, hydrogen to oil volume ratio 500-2000Nm 3 / m 3 Preferably, the reaction temperature is 320-380°C, the hydrogen partial pressure is 5.0-15.0MPa, the reaction time or residence time is 0.5-1.5h, and the hydrogen-oil volume ratio is 700-1500Nm 3 / m 3 .

[0022] In the method of the present invention, the solid-liquid separation in step (3) can adopt any one of the technologies in the prior art that can achieve solid-liquid separation. Specifically, in the present invention, the solid-liquid separation adopts one or more of cyclone separation, filtration separation, sedimentation separation, centrifugal separation and extraction separation.

[0023] In the method of the present invention, the solid content in the liquid phase stream obtained by solid-liquid separation in step (3) is controlled to be 10-200 ppm, and the acid value is less than 1.0 mgKOH / g; preferably, the solid content is 20-100 ppm, and the acid value is less than 0.5 mgKOH / g.

[0024] In the method of the present invention, the solid-liquid separation in step (3) includes a primary solid-liquid separation and a secondary solid-liquid separation; firstly, the alkali metal treatment reaction effluent obtained in step (2) is subjected to a primary solid-liquid separation to obtain a first liquid phase stream; the solid content of the first liquid phase stream is controlled to be 100-1000 ppm, and the alkali value is 15-30 mgKOH / g, preferably the solid content is 300-800 ppm, and the alkali value is 11-20 mgKOH / g; an acidic additive is added to the first liquid phase stream, and then a secondary solid-liquid separation is performed to obtain a second liquid phase stream, wherein the acidic additive is one or more of formic acid, hydrochloric acid, trichloroacetic acid, sulfuric acid and phosphoric acid solution; the solid content of the second liquid phase stream obtained by the secondary solid-liquid separation is controlled to be 10-200 ppm, preferably 20-100 ppm; and the acid value is less than 1.0 mgKOH / g, preferably less than 0.5 mgKOH / g.

[0025] In the method of the present invention, the catalytic cracking reaction zone in step (4) is provided with at least one catalytic cracking reactor, preferably one catalytic cracking reactor.

[0026] In the method of the present invention, the catalytic cracking catalyst in step (4) can be a catalytic cracking catalyst known in the prior art, or can be prepared according to a method disclosed in the prior art. Specifically, in the present invention, any one of a rare earth Y-type molecular sieve (REY) cracking catalyst, an ultrastable Y-type molecular sieve (USY) cracking catalyst, and a rare earth hydrogen Y (REHY) molecular sieve cracking catalyst can be used.

[0027] In the method of the present invention, the operating conditions of the catalytic cracking reaction zone in step (4) are: reaction temperature 400-700°C, reaction pressure 0.1-0.8MPa, catalyst-to-oil ratio (weight) 2-60; preferred operating conditions are: reaction temperature 460-550°C, reaction pressure 0.1-0.4MPa, catalyst-to-oil ratio (weight) 5-20.

[0028] Compared with the prior art, the method of the present invention has the following advantages: 1. The method of the present invention provides a new combined processing route for residual oil and coal tar with low added value. After the residual oil and coal tar are pre-treated with alkali metal treatment to remove impurities such as sulfur and oxygen, the reaction effluent enters the catalytic cracking reaction zone for reaction to obtain light oil products. This route has low reaction severity and is beneficial to refinery emission reduction and efficiency improvement.

[0029] 2. The method of the present invention introduces coal tar into the residual oil alkali metal treatment reaction system for the first time. Phenol and its derivatives contained in the coal tar will form a parallel competitive reaction with the sulfur-containing compounds, which can adjust the conversion rate of the sulfur-containing compounds in the reactor, thereby effectively controlling the concentration of intermediate species in the reaction system and reducing the occurrence of side reactions such as coking. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Attached Figure 1 The present invention provides a schematic diagram of a combined processing process of residual oil and coal tar.

[0031] Among them, 1 is residual oil raw material; 2 is coal tar raw material; 3 is fractionating tower; 4 is light coal tar; 5 is heavy coal tar; 6 is alkali metal treatment reaction zone; 7 is alkali metal treatment reaction effluent; 8 is primary solid-liquid separator; 9 is first liquid phase flow; 10 is solid phase flow obtained by primary solid-liquid separation; 11 is purification treatment device; 12 is waste gas; 13 is effluent from purification treatment device; 14 is acidic additive; 15 is secondary solid-liquid separator; 16 is second liquid phase flow; 17 is solid phase flow obtained by secondary solid-liquid separation; 18 is catalytic cracking reaction zone; 19 is dry gas; 20 is liquefied gas; 21 is gasoline; 22 is light diesel oil; 23 is heavy cycle oil; 24 is coke; 25 is alkali metal. Implementation

[0032] The method provided by the present invention is described below in conjunction with the accompanying drawings.

[0033] The coal tar raw material 2 enters the fractionation tower 3 and is cut to obtain light coal tar 4 and heavy coal tar 4. The light coal tar 4 is mixed with the residual oil raw material 1, and then mixed with the alkali metal 25 and enters the alkali metal treatment reaction zone 6 for reaction; the alkali metal treatment reaction effluent 7 enters the primary solid-liquid separator 8 for treatment to obtain the first liquid phase stream 9 and the solid phase stream 10; the first liquid phase stream 9 enters the purification treatment device 11, and is mixed with the acidic additive 14 for reaction, and the effluent enters the secondary solid-liquid separator 15 for treatment to obtain the second liquid phase stream 16 and the solid phase stream 17. The second liquid phase stream 16 and the heavy coal tar 4 are mixed and enter the catalytic cracking reaction zone 18, and are contacted with the catalytic cracking catalyst for reaction. The reaction effluent is separated to obtain dry gas 19, liquefied gas 20, gasoline 21, light diesel 22, heavy cycle oil 23 and coke 24.

[0034] The following examples will further illustrate the method provided by the present invention, but are not intended to limit the present invention.

[0035] Unless explicitly stated otherwise, throughout the specification and claims, the term “comprise” or variations such as “include” or “comprising”, etc., will be understood to include the stated elements or components but not to exclude other elements or components.

[0036] In this document, for the convenience of description, spatial relative terms such as "below", "below", "down", "above", "above", "upper", etc. may be used to describe the relationship between one element or feature and another element or feature in the accompanying drawings. It should be understood that the spatial relative terms are intended to include different directions of objects in use or operation in addition to the directions drawn in the drawings. For example, if the object in the figure is turned over, the elements described as being "below" or "below" other elements or features will be oriented "above" the elements or features. Therefore, the exemplary term "below" can include both below and above directions. Objects may also have other orientations (rotated 90 degrees or other orientations) and the spatial relative terms used in this document should be interpreted accordingly.

[0037] In this document, the terms "first", "second", etc. are used to distinguish two different elements or parts, and are not used to limit a specific position or relative relationship. In other words, in some embodiments, the terms "first", "second", etc. can also be interchangeable.

[0038]

[0043] All numerical values ​​for parameters (eg, amounts or conditions) herein are to be understood as being modified in all instances by the term "about", whether or not "about" actually appears before the numerical value.

[0039] The alkali metal treatment test in the embodiment and comparative example was carried out on an alkali metal treatment device designed independently in the laboratory. The alkali metal treatment reactor used was a kettle reactor with a stirring rate of 800r / min. The specific operation process of solid-liquid separation is as follows: the reaction effluent is subjected to a solid-liquid separation to obtain a first liquid phase stream; formic acid is added to the first oil phase material, and then a second solid-liquid separation is performed to obtain a second liquid phase stream.

[0040] The catalytic cracking tests in the examples and comparative examples were conducted on a catalytic cracking unit. The catalytic cracking unit was equipped with a reactor. The catalyst used was the LC-7 catalyst produced by Lanzhou Petrochemical Catalyst Plant.

[0041] The properties of the residual oil raw materials and coal tar raw materials used in the examples and comparative examples are shown in Table 1.

[0042] Table 1 Properties of residual oil and coal tar raw materials

[0043] Example 1 use Figure 1 The process flow is shown.

[0044] (1) After the coal tar raw material is cut, light coal tar and heavy coal tar are obtained; the cutting point is 240°C; the oxygen content of the light coal tar is 11.7wt%; (2) In the presence of hydrogen, the light coal tar and residual oil raw materials obtained in step (1) are mixed at a mass ratio of 0.05:1, and then mixed with sodium and introduced into an alkali metal treatment reaction zone for reaction; only one reactor is provided in the alkali metal treatment reaction zone; (3) The alkali metal treatment reaction effluent obtained in step (2) is subjected to solid-liquid separation to obtain a liquid phase stream; (4) The liquid phase stream obtained in step (3) and the heavy coal tar obtained in step (1) are mixed and introduced into a catalytic cracking reaction zone to react with a catalytic cracking catalyst. The reaction effluent is separated to obtain dry gas, liquefied gas, gasoline, light diesel and heavy distillate oil.

[0045] Example 2 The process flow is the same as that of Example 1.

[0046] Example 3 The process flow is the same as in Example 1. The difference is: (1) The cutting point is 270°C; the oxygen content of light coal tar is 10.2wt%; (2) The mass ratio of light coal tar and residual oil raw materials is 0.10:1; three reactors are set in the alkali metal treatment reaction zone.

[0047] Example 4 The process flow is the same as that of Example 3.

[0048] Example 5 The process flow is the same as in Example 1. The difference is: (1) The cutting point is 255°C; the oxygen content of light coal tar is 11.1wt%; (2) Two reactors are set up in the alkali metal treatment reaction zone.

[0049] Example 6 The process flow is the same as that of Example 5.

[0050] Comparative Example 1 The process flow is the same as in Example 1. The difference is: No light coal tar is introduced; in the presence of hydrogen, the residual oil raw material is mixed with sodium and enters the alkali metal treatment reaction zone for reaction; only one reactor is set in the alkali metal treatment reaction zone. The alkali metal treatment and catalytic cracking reaction conditions are the same as in Example 1.

[0051] Comparative Example 2 The process flow is the same as in Example 1. The difference is: (1) After the coal tar raw material is cut, light coal tar and heavy coal tar are obtained; the cutting point is 240°C; the light coal tar is dephenolized by an alkali washing method, and the specific operation process is as follows: an equal volume of 15wt% sodium hydroxide solution is added to the light coal tar, stirred at 80°C for 30 minutes, and then separated by liquid-liquid separation. The above process is repeated three times to obtain dephenolized light coal tar; the oxygen content of the dephenolized light coal tar is 0.4wt%; (2) In the presence of hydrogen, the dephenolized light coal tar and residual oil obtained in step (1) are mixed at a mass ratio of 0.05:1, mixed with sodium and introduced into an alkali metal treatment reaction zone for reaction; only one reactor is provided in the alkali metal treatment reaction zone. The alkali metal treatment and catalytic cracking reaction conditions are the same as those in Example 1.

[0052] Tables 2 and 3 are the reaction conditions of Examples 1-4 and Examples 5-6, respectively; Table 4 is the liquid phase flow yield of the alkali metal treatment device; Table 5 is the properties of the catalytic cracking products. It can be seen that the liquid phase flow yield of the embodiment is significantly higher than that of the comparative example, and the product properties are also better than those of the comparative example, proving that the introduction of coal tar into the alkali metal treatment reaction system can reduce the coking reaction, increase the liquid phase yield, and realize the efficient combined processing of residual oil and coal tar.

[0053] Table 2 Reaction conditions of Examples 1-4

[0054] Table 3 Reaction conditions of Examples 5-6

[0055] Table 4 Liquid phase flow yield of alkali metal treatment unit

[0056] Table 5 Properties of catalytic cracking products

Claims

1. A combined processing method of residual oil and coal tar, characterized in that: The method includes the following contents: (1) After the coal tar raw material is cut, light coal tar and heavy coal tar are obtained; (2) In the presence of hydrogen, the light coal tar and residual oil obtained in step (1) are mixed, and then mixed with an alkali metal and introduced into an alkali metal treatment reaction zone for reaction; (3) The alkali metal treatment reaction effluent obtained in step (2) is subjected to solid-liquid separation to obtain a liquid phase stream; (4) The liquid phase stream obtained in step (3) and the heavy coal tar obtained in step (1) are mixed and introduced into a catalytic cracking reaction zone to react with a catalytic cracking catalyst. The reaction effluent is separated to obtain dry gas, liquefied gas, gasoline, light diesel and heavy distillate oil.

2. The method according to claim 1, characterized in that: The cutting point of the coal tar raw material is 230-280°C, preferably 240-270°C.

3. The method according to claim 1, characterized in that: In step (2), the mass ratio of the light coal tar and residual oil obtained in step (1) is (0.03-0.15):1, preferably (0.05-0.10):

1.

4. The method according to claim 1, characterized in that: The residual oil feedstock in step (2) is a residual oil feedstock having a sulfur content greater than 2.5 wt.%, preferably greater than 3.5 wt.%.

5. The method according to claim 1, characterized in that: The alkali metal in step (2) is at least one of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr), preferably at least one of lithium (Li), sodium (Na) and potassium (K).

6. The method according to claim 1, characterized in that: In step (2), the molar ratio of the alkali metal to the sulfur content in the residual oil feedstock is (1.5-4.0):1, preferably (2.5-3.5):

1.

7. The method according to claim 1, characterized in that: The alkali metal treatment reaction zone in step (2) is provided with at least one alkali metal treatment reactor, preferably 2-3 alkali metal treatment reactors, and more preferably 2-3 alkali metal treatment reactors arranged in series.

8. The method according to claim 7, characterized in that: In step (2), the alkali metal treatment reaction zone is provided with two alkali metal treatment reactors arranged in series, and the two alkali metal treatment reactors are respectively a first alkali metal treatment reactor and a second alkali metal treatment reactor; the light coal tar and residual oil raw materials obtained in step (1) are mixed, mixed with alkali metal and then enter the first alkali metal treatment reactor for reaction, and the reaction effluent is mixed with alkali metal again and then enters the second alkali metal treatment reactor for reaction.

9. The method according to claim 8, characterized in that: The molar ratio of the alkali metal in the first alkali metal treatment reactor to the sulfur content in the residual oil feedstock is (0.5-3.0):1, preferably (1.2-2.0):1; the molar ratio of the alkali metal addition amount in the first alkali metal treatment reactor to the alkali metal addition amount in the second alkali metal treatment reactor is 1:(0.2-1.5), preferably 1:(0.5-1.0).

10. The method according to claim 7, characterized in that: In step (2), the alkali metal treatment reaction zone is provided with three alkali metal treatment reactors arranged in series, and the outlet material of any alkali metal treatment reactor in the alkali metal treatment reaction zone is mixed with the alkali metal again and then enters the downstream alkali metal treatment reactor arranged in series; the three alkali metal treatment reactors are respectively the first alkali metal treatment reactor, the second alkali metal treatment reactor and the third alkali metal treatment reactor.

11. The method according to claim 10, characterized in that: The molar ratio of the alkali metal in the first alkali metal treatment reactor to the sulfur content in the residual oil feedstock is (0.5-2.0):1, preferably (0.8-1.5):1; the molar ratio of the alkali metal addition amount in the first alkali metal treatment reactor, the alkali metal addition amount in the second alkali metal treatment reactor and the alkali metal addition amount in the third alkali metal treatment reactor is 1:(0.2-1.5):(0.2-1.0), preferably 1:(0.3-0.9):(0.3-0.6).

12. The method according to claim 1, characterized in that: The alkali metal treatment reactor in step (2) is a tank reactor and / or a tubular reactor, preferably a tank reactor, and more preferably an isothermal continuous tank reactor.

13. The method according to claim 1, characterized in that: The operating conditions of the alkali metal treatment reaction zone in step (2) are: reaction temperature 200-400°C, reaction pressure 2.0-18.0 MPa, reaction time or residence time 0.5-2.5 h, hydrogen to oil volume ratio 500-2000 Nm 3 / m 3 Preferably, the reaction temperature is 320-380°C, the hydrogen partial pressure is 5.0-15.0MPa, the reaction time or residence time is 0.5-1.5h, and the hydrogen-oil volume ratio is 700-1500Nm 3 / m 3 .

14. The method according to claim 1, characterized in that: The solid-liquid separation in step (3) is carried out by one or more of cyclone separation, filtration separation, sedimentation separation, centrifugal separation and extraction separation.

15. The method according to claim 1, characterized in that: The catalytic cracking reaction zone in step (4) is provided with at least one catalytic cracking reactor, preferably one catalytic cracking reactor.

16. The method according to claim 1, characterized in that: The catalytic cracking catalyst in step (4) is any one of a rare earth Y-type molecular sieve (REY) cracking catalyst, an ultrastable Y-type molecular sieve (USY) cracking catalyst and a rare earth hydrogen Y (REHY) molecular sieve cracking catalyst.

17. The method according to claim 1, characterized in that: The operating conditions of the catalytic cracking reaction zone in step (4) are: reaction temperature 400-700°C, reaction pressure 0.1-0.8MPa, catalyst-to-oil ratio (weight) 2-60; preferred operating conditions are: reaction temperature 460-550°C, reaction pressure 0.1-0.4MPa, catalyst-to-oil ratio (weight) 5-20.

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