A method of processing coal tar

Abstract

The application discloses a coal tar processing method, which comprises the following steps: (1) mixing coal tar raw material, alkali metal and hydrogen, and then entering an alkali metal treatment reaction zone to react; (2) separating and treating the reacted material obtained in the step (1); and (3) feeding the oil phase material obtained by the separation and treatment in the step (2) into a hydrocracking reaction zone, and separating reaction effluent to obtain gas, gasoline, diesel oil and tail oil fraction. The method combines alkali metal treatment and hydrocracking process organically, has excellent impurity removal effect, thereby effectively improving the quality of gasoline and diesel oil products and prolonging the operation cycle of the device.

Description

Technical Field

[0001] This invention relates to a coal tar processing method, and more specifically to a method for processing coal tar using a combination of alkali metal treatment and hydrocracking processes. Background Technology

[0002] The comprehensive utilization of coal tar resources is of great significance to the value-added transformation of coal resources and regional economic development in my country. Coal tar is a liquid product with a pungent odor, produced as a byproduct of coal dry distillation and gasification. Based on the dry distillation temperature, it can be classified into low-temperature coal tar, medium-temperature coal tar, and high-temperature coal tar. At room temperature, coal tar is a black or dark brown viscous liquid with a high density and high content of impurities such as metals and sulfur. Furthermore, coal tar has a high oxygen content, especially in medium- and low-temperature coal tar, where the oxygen content can reach as high as 30%. Its oxygen-containing compounds are mainly phenol and its derivatives.

[0003] Patent CN102851066A discloses a two-stage combined process for hydrotreating coal tar, comprising: (a) coal tar feedstock entering a hydrotreating reaction section for hydrotreating reaction; (b) the effluent from the hydrotreating reaction section undergoing gas-liquid separation, with the separated liquid phase entering a fractionating unit for fractionation into gasoline fraction, diesel fraction, and heavy fraction; (c) at least a portion of the heavy fraction obtained in step (b) entering a hydrocracking reaction section for hydrocracking reaction; (d) the effluent from the hydrocracking reaction section entering a hot high-pressure separator for separation into gas and liquid phases, with at least a portion of the liquid phase entering the hydrotreating reaction section of step (a); and (e) the gas phase separated by the hot high-pressure separator in step (d) and the diesel fraction obtained by fractionation in step (b) being mixed and entering a diesel hydrotreating reaction section.

[0004] Patent CN104927916A discloses a method for hydrogenating coal tar, which includes introducing hydrogen gas into coal tar through pores with an average pore size of nanometers to obtain hydrogen-containing coal tar; and feeding the obtained hydrogen-containing coal tar into a tubular reactor and contacting it with a hydrogenation catalyst packed in the tubular reactor under liquid-phase hydrogenation treatment conditions.

[0005] Therefore, it can be seen that the current coal tar processing technologies mainly include the two-stage hydrorefining-hydrocracking process, the reverse-sequence series hydrocracking-hydrorefining process, and the delayed coking-fixed-bed hydrorefining process. These technologies generally have the following problems: First, coal tar has a high oxygen content, and the water generated after hydrogenation can cause catalyst breakage, thus requiring extremely high water resistance of the coal tar hydrogenation catalyst; second, coal tar has a high impurity and metal content, which can easily cause bed blockage, leading to an increase in bed pressure drop and affecting the operation cycle of the unit; third, traditional coal tar hydrogenation processes generally suffer from problems such as high reaction severity and low selectivity of hydrodesulfurization. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a coal tar processing method. This method organically combines alkali metal treatment and hydrocracking processes, resulting in excellent impurity removal, thereby effectively improving the quality of gasoline and diesel products and extending the operating cycle of the equipment.

[0007] A method for processing coal tar, the method comprising the following steps:

[0008] (1) Coal tar raw material, alkali metal and hydrogen are mixed and then enter the alkali metal treatment reaction zone for reaction;

[0009] (2) Separate the reaction material obtained in step (1);

[0010] (3) The oil phase material obtained in step (2) enters the hydrocracking reaction zone, and the reaction effluent is separated to obtain gas, gasoline, diesel and tail oil fraction.

[0011] Furthermore, in step (1) of the method of the present invention, the coal tar raw material is pretreated before entering the alkali metal treatment reaction zone. The pretreatment process includes dehydration and removal of mechanical impurities. The pretreated coal tar raw material has a water content of 0.5wt%-3.0wt%, preferably 1.0wt%-2.5wt%; a solid content of 0.05wt%-0.35wt%, preferably 0.10wt%-0.20wt%; an oxygen content of 2.0-20.0wt%, preferably 5.0-10.0wt%.; and a phenolic compound content of 10.0-35.0wt%, preferably 15.0-25.0wt%.

[0012] Furthermore, in step (1) of the method of the present invention, the alkali metal is one or more of lithium, sodium, and potassium, preferably sodium; the mass ratio of the alkali metal to the coal tar raw material is (2.0-20.0):100, preferably (8.0-15.0):100.

[0013] Furthermore, in step (1) of the method of the present invention, an auxiliary agent is introduced, which is an alkali metal hydride; the alkali metal hydride includes at least one of lithium hydride, sodium hydride and potassium hydride, preferably sodium hydride; the mass ratio of the alkali metal to the auxiliary agent is 1:(0.1-0.8), preferably 1:(0.2-0.5).

[0014] Furthermore, in step (1) of the method of the present invention, the auxiliary agent is mixed with the solvent and then mixed with coal tar raw material and hydrogen before entering the alkali metal treatment reaction zone for reaction; the solvent is at least one of dimethyl sulfoxide, N,N-dimethylformamide, diethyl ether and benzene, preferably benzene; the mass ratio of the auxiliary agent to the solvent is 1:(2-20), preferably 1:(5-10). The mixing temperature is 100-400℃, and the mixing time is 0.2-2.0h, preferably the mixing temperature is 200-300℃, and the mixing time is 0.3-1.0h.

[0015] Furthermore, in step (1) of the method of the present invention, the coal tar feedstock and alkali metal are mixed and reacted in the presence of hydrogen. The reaction includes deoxygenation, desulfurization, denitrification, demetallization, and thermal cracking. The deoxygenation reaction is the reaction of alkali metal with oxygen-containing compounds in the coal tar feedstock to produce alkali metal alkoxy compounds. The oxygen-containing compounds are mainly phenolic compounds, and also include carboxylic acid compounds and alcohol compounds. The alkali metal alkoxy compounds are mainly alkali metal organic phenol salts such as sodium phenolate, sodium cresol, sodium xylenol, and potassium phenolate. The operating conditions of the alkali metal treatment reaction zone are: reaction temperature 200-400℃, hydrogen partial pressure 0.5-18.0MPa, reaction time or residence time 0.1-5.0h, and hydrogen-to-oil volume ratio 100-1000Nm. 3 / m 3 The preferred operating conditions are: reaction temperature 280-365℃, hydrogen partial pressure 2.0-12.0 MPa, reaction time or residence time 0.5-2.5 h, and hydrogen-to-oil volume ratio 350-750 Nm³. 3 / m 3 .

[0016] Furthermore, in step (1) of the method of the present invention, the alkali metal treatment reaction zone includes at least two alkali metal treatment reactors; after the coal tar raw material, alkali metal and hydrogen are mixed, they enter the first alkali metal treatment reactor for a primary reaction; after the primary reaction, the material is mixed again with alkali metal and hydrogen and then enters the second alkali metal treatment reactor for a secondary reaction.

[0017] Furthermore, in step (1) of the method of the present invention, the content of alkali metal alkoxy compounds in the material after the first reaction is controlled to be 0.5wt%-15.0wt%, preferably 1.0wt%-5.0wt%; and the solid content is 0.10wt%-0.50wt%, preferably 0.20wt%-0.35wt%.

[0018] Furthermore, in step (1) of the method of the present invention, in the first alkali metal treatment reactor, the mass ratio of alkali metal to coal tar raw material is (2.0-10.0):100, preferably (3.0-5.0):100; the mass ratio of alkali metal introduced in the first alkali metal treatment reactor and the second alkali metal treatment reactor is (10-60):100, preferably (20-50):100.

[0019] Furthermore, in step (1) of the method of the present invention, the operating conditions of the first alkali metal treatment reactor are: reaction temperature 200-350℃, hydrogen partial pressure 0.5-15.0MPa, reaction time or residence time 0.1-5.0h, and hydrogen-to-oil volume ratio 100-1000Nm³. 3 / m 3 The preferred operating conditions are: reaction temperature 280-350℃, hydrogen partial pressure 2.0-10.0 MPa, reaction time or residence time 0.5-2.0 h, and hydrogen-to-oil volume ratio 350-750 Nm³. 3 / m 3 .

[0020] Furthermore, in step (1) of the method of the present invention, compared with the first alkali metal treatment reactor, the second alkali metal treatment reactor has a reaction temperature 10-50℃ higher, a hydrogen partial pressure 1.0-5.0MPa higher, a reaction time or residence time 0.2-1.0h longer, and a hydrogen-to-oil volume ratio 100-500Nm higher. 3 / m 3 The preferred operating conditions are: a reaction temperature 10-30℃ higher, a hydrogen partial pressure 1.0-3.0 MPa higher, a reaction time or residence time 0.2-0.5 h longer, and a hydrogen-to-oil volume ratio 200-350 Nm. 3 / m 3 .

[0021] Furthermore, in step (2) of the method of the present invention, the separation process can employ any one or more existing separation devices, such as vacuum filters, pressure filters, filter centrifuges, sedimentation centrifuges, and membrane filters.

[0022] Furthermore, in step (2) of the method of the present invention, the solid content in the liquid phase material obtained by separation treatment is controlled to be 10-200ppm and the acid value is less than 1.0mgKOH / g; preferably, the solid content is 20-100ppm and the acid value is less than 0.5mgKOH / g.

[0023] Furthermore, in step (2) of the method of the present invention, the separation treatment includes a primary separation treatment and a secondary separation treatment; firstly, the reaction material obtained in step (1) is subjected to a primary separation treatment to obtain oil phase material A; the solid content of oil phase material A is controlled to be 100-1000ppm, the alkalinity is 15-30mgKOH / g, preferably the solid content is 300-800ppm, and the alkalinity is 11-20mgKOH / g; an acidic additive is added to oil phase material A, and then a secondary separation treatment is performed to obtain oil phase material B, wherein the acidic additive includes one or more of formic acid, hydrochloric acid, trichloroacetic acid, sulfuric acid and phosphoric acid solution; the solid content of oil phase material B obtained after the secondary separation treatment is controlled to be 10-200ppm, preferably 20-100ppm; the acid value is less than 1.0mgKOH / g, preferably less than 0.5mgKOH / g.

[0024] Furthermore, in step (3) of the method of the present invention, the hydrocracking unit may be one or more sets, and each set of hydrocracking unit shall include at least one reactor; the hydrocracking reactor may be a conventional reactor in the art, such as a fixed bed reactor and / or a fluidized bed reactor, preferably a fixed bed reactor.

[0025] Furthermore, in step (3) of the method of the present invention, the hydrocracking reactor is filled with at least one hydrocracking catalyst; the hydrocracking catalyst includes a support and an active metal component, the support includes amorphous silica-alumina and / or molecular sieves, the molecular sieves being Y-type and / or β-type molecular sieves; the active metal component is one or more elements from Group VI, Group VII, or Group VIII, preferably one or more from molybdenum, tungsten, cobalt, or nickel. Based on the weight of the catalyst, the content of the active metal component, calculated as metal oxides, is 5-40 wt.%.

[0026] Furthermore, in step (3) of the method of the present invention, the cutting point of the hydrocracked gasoline and diesel is generally 160-220℃, and the cutting point of the diesel and tail oil is generally 340-360℃.

[0027] Furthermore, in step (3) of the method of the present invention, the operating conditions of the hydrocracking unit are generally as follows: reaction temperature 330-450℃, reaction pressure 8.0-20.0MPa, and space velocity 0.1-1.0h. -1 Hydrogen-to-oil volume ratio 100-2500 Nm 3 / m 3 The preferred reaction conditions are: reaction temperature 350℃-430℃, reaction pressure 10.0-18.0MPa, and space velocity 0.2-0.6h. -1 Hydrogen-to-oil volume ratio 500-1500 Nm 3 / m 3 .

[0028] Coal tar feedstock has a high oxygen content, mostly in the form of phenol and its derivatives. Traditional hydrogenation processes generate large amounts of water from the hydrogenation of oxygen-containing compounds, placing extremely high demands on the water resistance of the catalyst. The method of this invention utilizes alkali metal treatment technology to upgrade coal tar feedstock. This technology does not require a catalyst; instead, it directly uses alkali metals as reactants to remove oxygen-containing compounds from the coal tar feedstock. It can also efficiently remove sulfur and heavy metal impurities such as iron and calcium from the coal tar feedstock, thereby providing high-quality feedstock for downstream hydrocracking units and extending the unit's operating cycle.

[0029] Furthermore, the inventors discovered during their research that the reaction between molten alkali metals and liquid coal tar is a two-phase reaction, and the mass transfer rate between the two phases is a key factor affecting the reaction rate. However, molten alkali metals have high surface tension and are prone to self-aggregation, which is detrimental to mass transfer between the liquid and liquid phases. This invention proposes introducing alkali metal hydrides (auxiliaries) into the alkali metal treatment reaction system. These auxiliaries have high surface tension, which can improve the spreading ability of molten alkali metals on their surface, thereby significantly accelerating the reaction rate and improving the reaction effect. In addition, alkali metal hydrides can react alone with phenolic compounds to achieve deoxidation; moreover, adding alkali metal hydrides to the reaction system does not cause any side effects, and they can be electrolytically recovered together with the desulfurization reaction product, alkali metal sulfides.

[0030] Furthermore, the alkali metal treatment process includes two stages: a primary reaction and a secondary reaction. The intermediate products generated in the primary reaction are a two-phase solid-liquid mixture, consisting of a solid-phase alkali metal sulfide and a liquid-phase alkali metal alkoxy compound. The solid-phase alkali metal sulfide acts as a dispersion medium, promoting the dispersion of alkali metals in the coal tar feedstock; the liquid-phase alkali metal alkoxy compound acts as a surfactant, further achieving efficient dispersion of alkali metals and improving their utilization rate and reaction effect.

[0031] Compared with the prior art, the advantages of the method of the present invention are as follows:

[0032] 1. The method of this invention combines alkali metal treatment and hydrocracking technologies for the processing of coal tar feedstock. The alkali metal treatment technology serves as a pretreatment step to upgrade the coal tar feedstock. This technology does not require a catalyst; instead, it directly utilizes alkali metals as reactants to remove oxygen-containing compounds from the coal tar feedstock. Furthermore, it can efficiently remove sulfur and heavy metal impurities such as iron and calcium from the coal tar feedstock, thereby providing high-quality feedstock for downstream hydrocracking units and extending the unit's operating cycle.

[0033] 2. The mass transfer rate between liquid and liquid phases is a key factor affecting the reaction rate between molten alkali metals and liquid coal tar. This invention proposes introducing alkali metal hydrides (auxiliaries) into the alkali metal treatment reaction system. These auxiliaries have high surface tension, which improves the spreading ability of molten alkali metals on their surface, thereby significantly accelerating the reaction rate and enhancing the reaction effect. Furthermore, alkali metal hydrides can react alone with phenolic compounds to achieve deoxidation; moreover, adding alkali metal hydrides to the reaction system does not cause any side effects, and they are electrolytically recovered together with the desulfurization reaction product, alkali metal sulfides.

[0034] 3. In the method of this invention, the alkali metal treatment process includes two processes: a primary reaction and a secondary reaction. The intermediate product generated in the primary reaction is a solid-liquid two-phase mixture, including a solid-phase alkali metal sulfide and a liquid-phase alkali metal alkoxy compound. The solid-phase alkali metal sulfide can serve as a dispersion medium to promote the dispersion of alkali metals in coal tar feedstock; the liquid-phase alkali metal alkoxy compound can act as a surfactant to further achieve efficient dispersion of alkali metals, thereby improving the utilization rate of alkali metals and the reaction effect. Attached Figure Description

[0035] Appendix Figure 1 This is a schematic diagram of a coal tar processing method provided by the present invention.

[0036] Among them, 1-alkali metal treatment reactor, 2-primary separation unit, 3-purification treatment unit, 4-secondary separation unit, 5-hydrocracking reactor, 6-alkali metal, 7-hydrogen, 8-coal tar feedstock, 9-alkali metal treatment reaction product, 10-solid phase product obtained from primary separation treatment, 11-oil phase material A, 12-gas, 13-liquid phase product obtained from purification treatment, 14-acidic additive, 15-oil phase material B, 16-solid phase product obtained from secondary separation treatment, 17-gas, 18-hydrocracking gasoline, 19-hydrocracking diesel, 20-hydrocracking tail oil. Implementation

[0037] The method provided by the present invention will now be described with reference to the accompanying drawings.

[0038] Coal tar feedstock from pipeline 8 is mixed with hydrogen from pipeline 7 and alkali metal from pipeline 6 and then enters alkali metal treatment reactor 1 for reaction. The alkali metal treatment reaction product enters primary separation unit 2 via pipeline 9 for separation. The solid phase product is extracted via pipeline 10, and oil phase material A enters purification treatment unit 3 via pipeline 11, where it reacts with acidic additives from pipeline 14 to obtain gaseous products such as hydrogen and hydrogen sulfide, as well as liquid products. The gaseous products such as hydrogen and hydrogen sulfide are extracted via pipeline 12. The liquid product enters secondary separation unit 4 via pipeline 13 for separation to obtain oil phase material B and solid products. The solid product is extracted via pipeline 16. Oil phase material B enters hydrocracking unit 5 via pipeline 15 for cracking reaction, and then is separated into gaseous, gasoline, diesel, and tail oil fractions by fractionation equipment, which are extracted via pipelines 17, 18, 19, and 20, respectively.

[0039] The following embodiments will further illustrate the method provided by the present invention, but do not limit the present invention.

[0040] The alkali metal treatment experiments in the examples were conducted on a pilot-scale alkali metal treatment device designed in the laboratory. The reactor used was a batch reactor with a stirring rate of 600 r / min. The separation treatment included primary separation treatment and secondary separation treatment. First, the reaction material obtained in step (1) was subjected to primary separation treatment to obtain oil phase material A. An acidic additive was added to oil phase material A, and then secondary separation treatment was performed to obtain oil phase material B. The acidic additive used was a mixture of formic acid and acetic acid, with a mass ratio of formic acid to acetic acid of 2:1. The hydrorefining and hydrocracking experiments in the examples and comparative examples were conducted on a fixed-bed hydrotreating unit. The hydrorefining catalyst used was 3936 hydrorefining catalyst, and the hydrocracking catalyst was the commercial brand FC-32 hydrocracking catalyst. Both catalysts were developed by the Fushun Petrochemical Research Institute of Sinopec.

[0041] Example 1

[0042] (1) Coal tar raw material, sodium alkali metal and hydrogen are mixed and then fed into the alkali metal treatment reactor for reaction;

[0043] (2) The materials after the reaction in step (1) are separated;

[0044] (3) The oil phase material obtained from the separation process in step (2) enters the hydrocracking reaction zone, and the reaction effluent is separated to obtain gas, gasoline, diesel and tail oil fractions. The cut-off point for hydrocracking gasoline and diesel is 160℃, and the cut-off point for diesel and tail oil is 340℃.

[0045] Example 2

[0046] The process flow in this embodiment is the same as in embodiment 1.

[0047] Example 3

[0048] The process flow of this embodiment is the same as that of embodiment 1. The difference is that sodium hydrosulfide (auxiliary agent) is introduced in step (1). Sodium hydrosulfide is mixed with benzene and then mixed with coal tar raw material, alkali metal sodium and hydrogen before entering the alkali metal treatment reaction zone for reaction. The mass ratio of sodium hydrosulfide to benzene is 1:5. The mixing temperature is 300℃ and the mixing time is 0.5h.

[0049] Example 4

[0050] The process flow in this embodiment is the same as in embodiment 3.

[0051] Example 5

[0052] Sodium hydrosulfide (an additive) and benzene (a solvent) are mixed to obtain a mixture stream, with a sodium hydrosulfide to benzene mass ratio of 1:5; the mixing temperature is 300℃, and the mixing time is 0.5 h. The mixture stream is then mixed with coal tar feedstock, sodium alkali metal, and hydrogen before entering the first alkali metal treatment reactor for a primary reaction. After the primary reaction, the feed stream is mixed again with sodium alkali metal, the mixture stream, and hydrogen before entering the second alkali metal treatment reactor for a secondary reaction. The feed stream obtained from the secondary reaction undergoes solid-liquid separation. The remaining process is the same as in Example 1.

[0053] Analysis showed that the alkali metal alkoxy compound content in the feed stream after one reaction was 4.3 wt%, and the solid content was 0.32 wt%.

[0054] Example 6

[0055] The process flow in this embodiment is the same as in Example 5. Analysis showed that the alkali metal alkoxy compound content in the feed stream after one reaction was 1.8 wt%, and the solid content was 0.27 wt%.

[0056] The raw material used in the examples and comparative examples was medium- and low-temperature coal tar, the properties of which are shown in Table 1. The operating conditions of the alkali metal processing unit and the hydrocracking unit are shown in Table 2, and the product properties are shown in Table 3.

[0057] Table 1 Properties of Coal Tar Raw Materials

[0058]

[0059] Table 2 Operating conditions of alkali metal processing unit and hydrocracking unit

[0060]

[0061] Table 3 Product Properties

[0062]

[0063] Comparative Example 1

[0064] The coal tar feedstock first enters the hydrorefining reaction zone for reaction, and the resulting effluent enters the hydrocracking reaction zone for hydrocracking. After separation, it yields gas, gasoline, diesel, and tail oil. The operating conditions and reaction results are shown in Table 4.

[0065] Table 4. Operating conditions and reaction results of Comparative Example 1

[0066]

Claims

1. A method for processing coal tar, the method comprising the following steps: (1) Coal tar raw material, alkali metal and hydrogen are mixed and then enter the alkali metal treatment reaction zone for reaction; (2) Separate the reaction material obtained in step (1); (3) The oil phase material obtained from the separation process in step (2) enters the hydrocracking reaction zone, and the reaction effluent is separated to obtain gas, gasoline, diesel and tail oil fraction; In step (1), the alkali metal treatment reaction zone includes at least two alkali metal treatment reactors; coal tar raw material, alkali metal and hydrogen are mixed and then enter the first alkali metal treatment reactor for a primary reaction; the material after the primary reaction is mixed with alkali metal and hydrogen again and then enters the second alkali metal treatment reactor for a secondary reaction; In step (1), the content of alkali metal alkoxy compounds in the material after the first reaction is controlled to be 0.5wt%-15.0wt%; the solid content is 0.10wt%-0.50wt%. In step (1), the alkali metal is one or more of lithium, sodium, and potassium; In step (1), an auxiliary agent is also introduced, which is an alkali metal hydride; the alkali metal hydride includes at least one of lithium hydride, sodium hydride and potassium hydride; the mass ratio of the alkali metal to the auxiliary agent is 1:(0.1-0.8). In step (1), the mass ratio of alkali metal to coal tar raw material in the first alkali metal treatment reactor is (2.0-10.0):100; the mass ratio of alkali metal introduced into the first alkali metal treatment reactor and the second alkali metal treatment reactor is (10-60):

100. In step (1), the operating conditions of the first alkali metal treatment reactor are: reaction temperature 200-350℃, hydrogen partial pressure 0.5-15.0MPa, reaction time 0.1-5.0h, and hydrogen-to-oil volume ratio 100-1000Nm³. 3 / m 3 ; In step (1), compared with the first alkali metal treatment reactor, the second alkali metal treatment reactor has a reaction temperature 10-50℃ higher, a hydrogen partial pressure 1.0-5.0MPa higher, a reaction time 0.2-1.0h longer, and a hydrogen-to-oil volume ratio 100-500Nm higher. 3 / m 3 .

2. The method according to claim 1, characterized in that: In step (1), the coal tar raw material is pretreated before entering the alkali metal treatment reaction zone. The pretreated coal tar raw material has a water content of 0.5wt%-3.0wt%, a solid content of 0.05wt%-0.35wt%, an oxygen content of 2.0-20.0wt%, and a phenolic compound content of 10.0-35.0wt%.

3. The method according to claim 2, characterized in that: In step (1), the coal tar raw material is pretreated before entering the alkali metal treatment reaction zone. The pretreated coal tar raw material has a water content of 1.0wt%-2.5wt%, a solid content of 0.10wt%-0.20wt%, an oxygen content of 5.0-10.0wt.%, and a phenolic compound content of 15.0-25.0wt.

4. The method according to claim 1, characterized in that: In step (1), the alkali metal is sodium.

5. The method according to claim 1, characterized in that: In step (1), the mass ratio of the alkali metal to the coal tar raw material is (8.0-15.0):

100.

6. The method according to claim 1, characterized in that: In step (1), the alkali metal hydrosulfide is sodium hydrosulfide; the mass ratio of the alkali metal to the auxiliary agent is 1:(0.2-0.5).

7. The method according to claim 1, characterized in that: In step (1), the additive is mixed with the solvent and then mixed with coal tar raw material and hydrogen before entering the alkali metal treatment reaction zone for reaction; the solvent is at least one of dimethyl sulfoxide, N,N-dimethylformamide, diethyl ether and benzene; the mass ratio of the additive to the solvent is 1:(2-20); the mixing temperature is 100-400℃ and the mixing time is 0.2-2.0h.

8. The method according to claim 7, characterized in that: In step (1), the solvent is benzene; the mass ratio of the additive to the solvent is 1:(5-10); the mixing temperature is 200-300℃ and the mixing time is 0.3-1.0h.

9. The method according to claim 1, characterized in that: In step (1), the content of alkali metal alkoxy compounds in the material after the first reaction is controlled to be 1.0wt%-5.0wt%; and the solid content is 0.20wt%-0.35wt%.

10. The method according to claim 1, characterized in that: In step (1), the mass ratio of alkali metal to coal tar raw material in the first alkali metal treatment reactor is (3.0-5.0):100; the mass ratio of alkali metal introduced in the first alkali metal treatment reactor to that in the second alkali metal treatment reactor is (20-50):

100.

11. The method according to claim 1, characterized in that: In step (1), the operating conditions of the first alkali metal treatment reactor are: reaction temperature 280-350℃, hydrogen partial pressure 2.0-10.0MPa, reaction time 0.5-2.0h, and hydrogen-to-oil volume ratio 350-750Nm. 3 / m 3 .

12. The method according to claim 1, characterized in that: In step (1), compared with the first alkali metal treatment reactor, the second alkali metal treatment reactor has a reaction temperature 10-30℃ higher, a hydrogen partial pressure 1.0-3.0 MPa higher, a reaction time 0.2-0.5 h longer, and a hydrogen-to-oil volume ratio 200-350 Nm higher. 3 / m 3 .

13. The method according to claim 1, characterized in that: In step (2), the equipment used for the separation process is one or more of the following: vacuum filter, pressure filter, filter centrifuge, sedimentation centrifuge and membrane filter.

14. The method according to claim 1, characterized in that: In step (3), at least one hydrocracking catalyst is packed in the hydrocracking reaction zone; the hydrocracking catalyst includes a support and an active metal component, wherein the active metal component is one or more of molybdenum, tungsten, cobalt or nickel; based on the weight of the catalyst, the content of the active metal component as metal oxide is 5-40 wt.%.

15. The method according to claim 1, characterized in that: In step (3), the operating conditions of the hydrocracking reaction zone are: reaction temperature 330-450℃, reaction pressure 8.0-20.0MPa, and space velocity 0.1-1.0h. -1 Hydrogen-to-oil volume ratio 100-2500 Nm 3 / m 3 .

16. The method according to claim 15, characterized in that: In step (3), the operating conditions of the hydrocracking reaction zone are: reaction temperature 350℃-430℃, reaction pressure 10.0-18.0MPa, and space velocity 0.2-0.6h. -1 Hydrogen-to-oil volume ratio 500-1500 Nm 3 / m 3 .

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