A multi-stage fractional processing and utilization technology for medium- and low-temperature coal tar

Abstract

This invention belongs to the field of coal tar technology and relates to a multi-stage fractional processing and utilization process for medium- and low-temperature coal tar, comprising the following steps: 1) Medium- and low-temperature coal tar is distilled under atmospheric pressure to separate light coal tar and heavy coal tar; 2) Crude naphthalene, crude anthracene, crude fluorene, and residual light oil components are separated from the light coal tar by distillation; then, refined naphthalene, refined fluorene, refined anthracene, phenol, cresol, xylenol, and diesel oil are obtained respectively; 3) Heavy coal tar and diesel oil are co-carbonized and thermally polymerized to obtain refined pitch and coking oil. The refined pitch is processed using a three-stage variable-speed heating and pressure process to obtain semi-coke; then, it is calcined and cooled to obtain needle-shaped coke powder, and the coking oil is returned to produce diesel oil. This invention provides a multi-stage fractional processing and utilization process for medium- and low-temperature coal tar, which greatly improves and enhances product performance, fully utilizes raw materials, avoids environmental pollution, and enables industrial application.

Description

Technical Field

[0001] This invention belongs to the field of coal tar technology and relates to a multi-stage fractional processing and utilization process for medium- and low-temperature coal tar. Background Technology

[0002] Low-temperature coal tar is a valuable resource, and with increasing production capacity, the need for its large-scale utilization is becoming increasingly urgent. In production, processes should be tailored to the composition and characteristics of low-temperature coal tar to achieve graded conversion and utilization, ensuring rational resource use. Under suitable process conditions, combining the extraction of phenolic compounds with hydrogenation to produce fuel oil, fully leveraging its compositional advantages, and finding appropriate utilization pathways for other byproducts to maximize their utilization is a reasonable approach. The separation and extraction of numerous valuable compounds should also be a direction for the processing and utilization of low-temperature coal tar, and research should be accelerated.

[0003] Patent CN110396427B authorizes a processing technology for full-fraction coal tar. This process first fractionates the full-fraction coal tar to obtain various grades of coal tar; then, the heavy coal tar is hydrogenated and separated to obtain light and heavy products; the light products are further separated, and the gas and liquid are collected; the light coal tar and gas are hydrogenated, and the hydrogenation product is collected; the heavy products are fractionated, and wax oil is collected; the medium coal tar, liquid, hydrogenation product, and wax oil are hydrogenated, and the hydrogenation product is collected. Patent CN110746996A discloses a method for the comprehensive utilization of pulverized coal through graded processing. The method involves subjecting dried pulverized coal to a low-temperature pyrolysis reaction to produce upgraded coke powder and high-temperature oil and gas. The high-temperature oil and gas are then cooled and separated to obtain crude coal gas, fine coke powder with a particle size of <200μm, pyrolysis water, and coal tar. Finally, the crude coal gas, fine coke powder, pyrolysis water, and coal tar are further processed to produce high-value-added products, thus realizing the graded utilization and clean and efficient conversion of pulverized coal.

[0004] The above methods all propose a fractional utilization approach for coal tar, involving a series of steps such as fractionation and hydrogenation to obtain the product, thus realizing the processing and reuse of coal tar. However, the following problems exist:

[0005] (1) Existing technologies fail to clearly express the final product and downstream products, and the separated and recovered products contain many impurities and have poor product performance. Specifically, the light coal tar and light products are over-cracked, resulting in low added value of polycyclic aromatic hydrocarbons; the mesophase pitch generation process exhibits a self-accelerating effect, and the over-reaction produces a large amount of heavy components and semi-coke insolubles; (2) The utilization of medium and low temperature coal tar raw materials is insufficient. For example, the heavy coal tar in the existing process is difficult to reuse. Directly abandoning it not only wastes resources but also pollutes the environment; (3) The existing utilization methods have a large production load, high energy consumption, and large investment in the distillation process, which is not convenient for industrial application. Summary of the Invention

[0006] To address the technical problems of poor product performance and insufficient utilization in the existing technologies, this invention provides a multi-stage fractional processing and utilization process for medium- and low-temperature coal tar, which greatly improves product performance, fully utilizes raw materials, avoids environmental pollution, and enables industrial application.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A multi-stage fractional processing and utilization technology for medium- and low-temperature coal tar includes the following steps:

[0009] 1) Atmospheric pressure cut fraction

[0010] Low-temperature coal tar is distilled under normal pressure to separate light coal tar and heavy coal tar; the light coal tar is the fraction below 360°C, and the heavy coal tar is the fraction above 360°C.

[0011] 2) Separation and purification of light coal tar

[0012] 2.1) Crude naphthalene, crude anthracene, crude fluorene, and residual light oil components are separated from the light coal tar obtained in step 1) by distillation; corresponding refined naphthalene, refined fluorene, and refined anthracene products are obtained from the crude naphthalene, crude anthracene, and crude fluorene components.

[0013] 2.2) The residual light oil components from step 2.1) are further separated by distillation to obtain phenol, cresol, xylenol and light oil mother liquor, respectively;

[0014] 2.3) Diesel fuel is obtained from light oil mother liquor through hydrocatalytic oxidation;

[0015] 3) Coking from heavy coal tar

[0016] 3.1) Under N2 atmosphere, the heavy coal tar from step 1) and the diesel oil from step 2.3) are co-carbonized at a mass ratio of 1 to 10:1, thermally polymerized and separated to obtain refined pitch and coking oil; the coking oil is returned to step 2.3) and mixed with light oil mother liquor to produce diesel oil;

[0017] 3.2) Under N2 atmosphere, the refined asphalt from step 3.1) is processed using a three-stage variable speed heating and pressure process to obtain semi-coke;

[0018] 3.3) Under a N2 atmosphere, the semi-coke from step 3.2) is calcined and cooled to obtain needle-shaped coke powder.

[0019] Further specifying that in step 2.1), the distillation temperature of the crude naphthalene component is 210℃~230℃, the distillation temperature of the crude fluorene component is 230℃~300℃, and the distillation temperature of the crude anthracene component is 300℃~360℃.

[0020] Further specifying, in step 2.1), the refined naphthalene product, refined fluorene product, and refined anthracene product are obtained through the following methods:

[0021] 2.1.1) The crude naphthalene component is successively subjected to solvent absorption, cold precipitation separation, and melt crystallization to obtain the refined naphthalene product;

[0022] 2.1.2) The crude fluorene component was subjected to recrystallization using xylene as a solvent to obtain the refined fluorene product;

[0023] 2.1.3) The crude anthracene component was processed using distillation-membrane technology to obtain refined anthracene products;

[0024] Further specified, in step 2.1.1), the solvent absorption uses benzene as the solvent, the circulation rate of benzene is 2 kg / h, and the absorption temperature is 70℃; the melt crystallization is to obtain refined naphthalene by static melt crystallization of the crude naphthalene component after cold precipitation separation, from room temperature to the final crystallization temperature of 75℃~80℃, and holding for 30 min; cooling to room temperature at a rate of 0.05℃ / min.

[0025] Further specifying that in step 2.1.2), after recrystallization, the crude fluorene component is further separated using an acidic solution system to obtain refined fluorene.

[0026] Further specifying that in step 2.1.3), under normal pressure and at a temperature of 60℃~180℃, the crude anthracene component is passed through a zeolite molecular sieve membrane separator to obtain refined anthracene, and the pore size of the zeolite molecular sieve is 5.0A~7.0A.

[0027] Further specifying, in step 2.3), the conditions for hydrogenation catalysis are: catalyst NiMoP / γ-Al2O3, temperature 300℃~360℃, pressure 10MPa~15MPa, hydrogen-to-oil volume ratio 800~1300:1, and liquid hourly space velocity 0.3~0.6h. -1 The catalyst has a Ni loading of 1 wt% to 6 wt% and a MoP loading of 10 wt% to 12 wt%.

[0028] Further specifying, in step 3.1), the conditions for thermal polymerization modification are: under a pressure of 1.5MPa to 3MPa, the temperature is increased to 300℃ to 340℃ at a rate of 3℃ / min, and the reaction is carried out at a constant temperature for 2h to 4h.

[0029] Further specifying, in step 3.2), the conditions for the three-stage variable-speed heating and pressure-switching process are as follows: First, the temperature is increased to 380℃ to 400℃ at a pressure of 1.5MPa to 3MPa and a rate of 1℃ / min to 3℃ / min; second, the temperature is increased to 420℃ to 450℃ at a pressure of 1.5MPa to 2MPa and a rate of 0.5℃ / min to 1℃ / min, and the temperature is kept constant for 6h to 10h; finally, the temperature is increased to 480℃ to 520℃ at a pressure of 0.5MPa to 1MPa and a rate of 0.3℃ / min to 0.5℃ / min, and the temperature is kept constant for 6h to 10h.

[0030] Further specifying, in step 3.3), the calcination conditions are as follows: first, under a pressure of 0.01 MPa to 0.03 MPa, the temperature is increased to 500℃ to 800℃ at a rate of 3℃ / min to 5℃ / min, and the reaction is maintained at this temperature for 2h to 4h; then, under a pressure of 0.01 MPa to 0.03 MPa, the temperature is increased to 1400℃ to 1600℃ at a rate of 1℃ / min to 3℃ / min, and the reaction is maintained at this temperature for 2h to 4h; in step 3.3), the average resistivity of the needle-shaped coke powder is at least 416 μΩ·m, and the compacted density of the needle-shaped coke powder is 0.96 g / cm³. 3 ~1.23g / cm 3 .

[0031] The beneficial effects of this invention are:

[0032] 1. The medium- and low-temperature coal tar grading and processing technology provided by this invention first fractionates the medium- and low-temperature coal tar to obtain light coal tar and heavy coal tar; then, the light coal tar undergoes multiple distillations to obtain crude naphthalene, crude fluorene, and crude anthracene components, etc. Finally, these crude products are processed by melt crystallization, recrystallization, and membrane technology to obtain corresponding refined naphthalene, refined fluorene, and refined anthracene products, thereby effectively avoiding excessive cracking of light coal tar and light products, thus obtaining high-value-added polycyclic aromatic hydrocarbon light products.

[0033] 2. The low-temperature coal tar grading and processing technology provided by this invention involves hydrogenating and catalytically processing the light oil mother liquor produced from the separation and purification of light coal tar to obtain diesel oil. Then, the diesel oil is co-carbonized with heavy coal tar to obtain needle coke. This invention uses the difficult-to-use heavy coal tar to prepare needle coke without polluting the environment. The obtained diesel oil can also be used as a co-carbonizing agent. At the same time, it can reduce the viscosity of the system, which helps to avoid the self-accelerating effect of the mesophase pitch formation process, prevents excessive reaction and the generation of a large amount of heavy components and semi-coke insolubles, adjusts and improves the composition of the mixed raw materials, improves the structure of the prepared needle coke, increases the length and content of fine fibers, and improves the directionality and order.

[0034] 3. The medium- and low-temperature coal tar graded and graded processing technology adopted in this invention achieves graded and graded recycling of components and by-products at each stage, converting almost all medium- and low-temperature coal tar into collected products with no loss of raw materials; it reduces the production load of the distillation process, saves equipment investment, and reduces the consumption of water, electricity and raw materials; equipment costs and energy costs.

[0035] 4. In the process of hydrogenating light oil to produce diesel after removing N and S, the present invention uses NiMoP / γ-Al2O3 catalyst, in which the Ni loading is 1wt% to 6wt% and the total Mo and P loading is 10wt% to 12wt%. The catalyst has good activity and can better remove N and S. Attached Figure Description

[0036] Figure 1 This is a polarized light microstructure image of the needle-shaped coke powder in Example 3;

[0037] Figure 2 Here is a scanning electron microscope image of the needle-shaped coke powder from Example 3;

[0038] Figure 3 The image shows the polarized light microstructure of needle-shaped coke powder in Comparative Example 2.

[0039] Figure 4 This is a scanning electron microscope image of needle-shaped coke powder, which is shown in Comparative Example 2. Detailed Implementation

[0040] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0041] The medium- and low-temperature coal tar multi-stage processing and utilization process provided by this invention includes the following steps:

[0042] 1) Atmospheric pressure cut fraction

[0043] Low-temperature coal tar is distilled under normal pressure to separate light coal tar and heavy coal tar. Light coal tar is the fraction below 360℃, and heavy coal tar is the fraction above 360℃.

[0044] 2) Separation and purification of light coal tar

[0045] 2.1) The crude naphthalene component, crude anthracene component, crude fluorene component and residual light oil component are separated from the light coal tar in step 1) by distillation.

[0046] In this step, the distillation is multi-stage distillation. The distillation temperature of the crude naphthalene component is 210℃~230℃, the distillation temperature of the crude fluorene component is 230℃~300℃, and the distillation temperature of the crude anthracene component is 300℃~360℃.

[0047] In this step, refined naphthalene, refined fluorene, and refined anthracene products are obtained from the crude naphthalene component, crude anthracene component, and crude fluorene component, respectively.

[0048] 2.1.1) The crude naphthalene component is successively subjected to solvent absorption, cold precipitation separation, and melt crystallization to obtain the refined naphthalene product.

[0049] In this step, the crude naphthalene component is fed into a solvent containing benzene. After cold precipitation and filtration, the crude naphthalene component is subjected to static melt crystallization, with the temperature raised from room temperature to a final crystallization temperature of 75℃~80℃ and held for 30 minutes. The temperature is then lowered to room temperature at a rate of 0.05℃ / min to obtain the refined naphthalene product. Benzene is used as the solvent for absorption, with a circulation rate of 2 kg / h and an absorption temperature of 70℃.

[0050] 2.1.2) The crude fluorene component was subjected to recrystallization with xylene as a solvent to obtain the refined fluorene product.

[0051] In this step, recrystallization is performed 1 to 3 times; preferably, recrystallization is performed 2 times.

[0052] After recrystallization, the crude fluorene component is further separated using an acidic solution system to obtain refined fluorene. For example, the acidic solution system is a hydroperoxide-formic acid system.

[0053] 2.1.3) The crude anthracene component is processed using membrane technology to obtain refined anthracene products.

[0054] In this step, the crude anthracene component enters a zeolite molecular sieve membrane separator, and under normal pressure, a temperature of 60℃~180℃, and a molecular sieve pore size of 5.0~7.0A, refined anthracene product is obtained.

[0055] 2.2) The residual light oil components from step 2.1) are separated by distillation to obtain phenol, cresol, xylenol and light oil mother liquor, respectively.

[0056] In this step, the distillation is multi-stage distillation.

[0057] 2.3) Light oil mother liquor is hydrogenated and catalytically treated to obtain diesel.

[0058] In this step, the conditions for hydrorefining are: catalyst NiMoP / γ-Al2O3, temperature 300℃~360℃, pressure 10MPa~15MPa, hydrogen-to-oil volume ratio 800~1300:1, and liquid hourly space velocity 0.3~0.6h. -1 In the NiMoP / γ-Al2O3 catalyst, the Ni loading is 1wt% to 6wt%, and the MoP loading is 10wt% to 12wt%.

[0059] 3) Coking from heavy coal tar

[0060] 3.1) Under N2 atmosphere, the heavy coal tar from step 1) and the diesel oil from step 2.3) are co-carbonized at a mass ratio of 1 to 10:1. After thermal polymerization and separation, refined pitch and coking oil are obtained. The coking oil is returned to step 2.3) and mixed with light oil mother liquor to produce diesel oil.

[0061] In this step, the conditions for thermal polymerization modification are: under a pressure of 1.5MPa to 3MPa, the temperature is increased to 300℃ to 340℃ at a rate of 3℃ / min, and the reaction is carried out at a constant temperature for 2h to 4h.

[0062] 3.2) Under N2 atmosphere, the refined asphalt obtained is processed into semi-coke using a three-stage variable speed heating and pressure process. The conditions for the three-stage variable speed heating and pressure process in this step are as follows: First, the temperature is increased to 380℃ to 400℃ at a pressure of 1.5MPa to 3MPa and a rate of 1℃ / min to 3℃ / min; second, the temperature is increased to 420℃ to 450℃ at a pressure of 1.5MPa to 2MPa and a rate of 0.5℃ / min to 1℃ / min, and the temperature is maintained for 6h to 10h; finally, the temperature is increased to 480℃ to 520℃ at a pressure of 0.5MPa to 1MPa and a rate of 0.3℃ / min to 0.5℃ / min, and the temperature is maintained for 6h to 10h.

[0063] 3.3) Under a N2 atmosphere, semi-coke is calcined and cooled to obtain needle-shaped coke powder.

[0064] In this step, the calcination conditions are as follows: first, under a pressure of 0.01MPa to 0.03MPa, the temperature is increased to 500℃ to 800℃ at a rate of 3℃ / min to 5℃ / min, and the reaction is kept at a constant temperature for 2h to 4h; then, under a pressure of 0.01MPa to 0.03MPa, the temperature is increased to 1400℃ to 1600℃ at a rate of 1℃ / min to 3℃ / min, and the reaction is kept at a constant temperature for 2h to 4h.

[0065] In this step, the needle-shaped coke powder had the lowest average resistivity of 416 μΩ·m and a compacted density of 0.96 g / cm³. 3 ~1.23g / cm 3 .

[0066] The following specific embodiments clearly and completely describe the multi-stage fractional processing technology and the performance of the resulting products provided by the present invention.

[0067] In the following examples, the raw materials were all selected from low-rank coal from a certain region in northern Shaanxi, my country.

[0068] Example 1

[0069] The medium- and low-temperature coal tar multi-stage processing and utilization process provided in this embodiment includes the following steps.

[0070] 1) Atmospheric pressure cut fraction

[0071] Light coal tar and heavy coal tar are separated from low- and medium-temperature coal tar by atmospheric distillation. The light coal tar is the 360°C fraction, and the heavy coal tar is the fraction above 360°C.

[0072] 2) Separation and purification of light coal tar

[0073] 2.1) Light coal tar is separated into crude naphthalene, crude anthracene and crude fluorene components by secondary distillation, and the residual light oil component produced by distillation is collected for later use.

[0074] Specifically, the first distillation is at atmospheric pressure at a temperature of 320℃, and the second fractionation is at atmospheric pressure, separating crude naphthalene, crude anthracene, and crude fluorene at temperatures of 210℃, 230℃, and 300℃, respectively.

[0075] 2.2) The separated crude naphthalene component is sent to a solvent absorption tower, cooled and precipitated as naphthalene intermediates, filtered, and then melted and crystallized to obtain a high-purity refined naphthalene product.

[0076] The solvent benzene is circulated at a rate of 2 kg / h, and the operating temperature is 70℃. The refined naphthalene product is obtained by static melt crystallization at a final crystallization temperature of 70℃, held for 30 min, and then cooled to room temperature at a rate of 0.05℃ / min.

[0077] 2.3) The crude fluorene fraction obtained from the secondary distillation is then recrystallized twice using xylene as a solvent to obtain refined fluorene.

[0078] The crude fluorene fraction was recrystallized twice with xylene, and then the refined fluorene product was separated using a hydrogen peroxide-formic acid system.

[0079] 2.4) The crude anthracene component is fed into a membrane separator equipped with a zeolite molecular sieve. Under normal pressure, temperature of 60℃ and molecular sieve pore size of 5.0A, high-purity refined anthracene product is obtained.

[0080] 2.5) Separation and purification of phenolic oil

[0081] After distillation in step 2.1), the remaining light oil fraction contains a large amount of phenolic substances. Further distillation is carried out to obtain a mixed solution containing phenol, cresol, and xylenol. After further distillation, the individual monomers obtained are phenol, cresol, and xylenol products, which can be widely used in industries such as polymer materials, fragrances, pharmaceuticals, pesticides, and preservatives. At the same time, the purification and separation of phenolic oil also yields light oil mother liquor.

[0082] 2.6) Hydrogenation to produce diesel fuel

[0083] The light oil mother liquor from step 2.5) was hydrotreated to remove S and N, and then refined to obtain diesel oil. A NiMoP / γ-Al₂O₃ catalyst was first added, followed by the introduction of hydrogen gas. The reaction was carried out at 300℃, 10 MPa, a hydrogen-to-oil volume ratio of 800:1, and a liquid hourly space velocity of 0.3 h⁻¹. -1 .

[0084] The catalyst NiMoP / γ-Al2O3 in this embodiment belongs to the NiMo series catalysts and is used as a hydrogenation catalyst, with Mo / γ-Al2O3 as the support. In the NiMoP / γ-Al2O3 catalyst, the active component is Ni, and the promoter components are a mixture of Mo and P. The Ni loading of the active component is 6 wt%, and the total loading of the promoter component MoP is 12 wt%.

[0085] 3) Coking from heavy components, followed by hydrogenation of coking oil to produce diesel.

[0086] 3.1) In a reactor under N2 atmosphere, the heavy coal tar from step 1) and the diesel oil from step 2.6) are co-carbonized at a mass ratio of 9:1, and then subjected to low-temperature high-pressure thermal polymerization reforming and separation to obtain refined asphalt and coking oil. The refined asphalt is sent to the next process, and the coking oil is returned to step 2.6) to be mixed with light oil mother liquor to produce diesel oil. The thermal polymerization reforming conditions are: at a pressure of 1.5 MPa, the temperature is increased to 300°C at a rate of 3°C / min, and the reaction is kept at a constant temperature for 2 hours.

[0087] 3.2) Under a N2 atmosphere, the obtained refined asphalt was placed in a reactor and a three-stage variable-speed heating and pressure-switching process was used to obtain semi-coke. The three-stage variable-speed heating and pressure-switching process conditions were as follows: First, the reactor pressure was increased to 380℃ at a rate of 1.5 MPa and 1℃ / min; then, the pressure was increased to 420℃ at a rate of 1.5 MPa and 1℃ / min, and the reaction was kept at a constant temperature for 6 hours; finally, the pressure was increased to 480℃ at a rate of 0.5 MPa and 0.3℃ / min, and the reaction was kept at a constant temperature for 6 hours.

[0088] 3.3) Under a N2 atmosphere, semi-coke was calcined at high temperature and then cooled to obtain needle coke. The calcination conditions were as follows: first, the temperature was increased to 500℃ at a rate of 3℃ / min under a pressure of 0.01MPa, and the reaction was kept at a constant temperature for 2 hours; then, the temperature was increased to 1400℃ at a rate of 1℃ / min under a pressure of 0.01MPa, and the reaction was kept at a constant temperature for 2 hours.

[0089] Example 2

[0090] The medium- and low-temperature coal tar multi-stage processing and utilization process provided in this embodiment includes the following steps.

[0091] 1) Atmospheric pressure cut fraction

[0092] Light coal tar and heavy coal tar are separated from medium- and low-temperature coal tar by atmospheric distillation.

[0093] 2) Separation and purification of light coal tar

[0094] 2.1) Light coal tar is separated into crude naphthalene, crude anthracene and crude fluorene by secondary distillation, and the remaining light oil components are collected for later use;

[0095] Specifically, in step 1), the first fractionation is performed at atmospheric pressure and the temperature is 340℃. The second fractionation is performed at atmospheric pressure, separating crude naphthalene, crude anthracene, and crude fluorene components at temperatures of 220℃, 280℃, and 340℃, respectively. Meanwhile, residual light oil components are also collected during the rectification process.

[0096] 2.2) The separated crude naphthalene component is fed into a solvent absorption tower containing benzene. The circulation rate of the solvent benzene is 2 kg / h, and the operating temperature is 70℃. The naphthalene intermediate is cooled and filtered. The filtered crude naphthalene component is then subjected to static melt crystallization at a final crystallization temperature of 70℃ for 30 min, and then cooled to room temperature at a rate of 0.05℃ / min to obtain a high-purity refined naphthalene product.

[0097] 2.3) The crude fluorene component was separated into refined fluorene product by recrystallization twice using xylene as solvent and an acidic system (hydrogen peroxide-formic acid system).

[0098] 2.4) The crude anthracene component is fed into a zeolite molecular sieve membrane separator. Under normal pressure, temperature of 60-180℃ and molecular pore size of 5.0-7.0 Å, high-purity refined anthracene product is obtained using membrane technology.

[0099] 2.5) Separation and purification of phenolic oil

[0100] After distillation in step 2.1), the remaining light oil fraction contains a large amount of phenolic substances. Further distillation is carried out to obtain a mixed solution containing phenol, cresol, and xylenol. After further distillation, the individual monomers obtained are phenol, cresol, and xylenol products, which can be widely used in industries such as polymer materials, fragrances, pharmaceuticals, pesticides, and preservatives. At the same time, the purification and separation of phenolic oil also yields light oil mother liquor.

[0101] 2.6) Hydrogenation to produce diesel fuel

[0102] The light oil mother liquor from step 2.5) is hydrotreated to remove S and N to prepare diesel products.

[0103] Before introducing hydrogen, a NiMoP / γ-Al2O3 catalyst, belonging to the NiMo series, is added as the hydrogenation catalyst, with Mo / γ-Al2O3 as the support. In the NiMoP / γ-Al2O3 catalyst, the Ni loading is 1 wt% and the MoP loading is 10 wt%. Specifically, the hydrogenation conditions are 340℃, a reaction pressure of 13 MPa, a hydrogen-to-oil volume ratio of 1200:1, and a liquid hourly space velocity of 0.5 h⁻¹. -1 .

[0104] 3) Recombinant coking

[0105] 3.1) In the reactor, the heavy coal tar after distillation in step 1) and the diesel oil obtained in step 2.6) are co-carbonized at a mass ratio of 9:1, and then subjected to low-temperature and high-pressure thermal polymerization reforming under N2 atmosphere to separate refined asphalt and coking oil.

[0106] Specifically, the low-temperature, high-pressure thermal polymerization reforming conditions are as follows: at a pressure of 2 MPa, the temperature is increased to 320°C at a rate of 3°C / min, and the reaction is maintained at this temperature for 3 hours. The coking oil is then returned to step 2.6) for recycling and hydrogenation to produce diesel products.

[0107] 3.2) Under a N2 atmosphere, the refined asphalt obtained was placed in a reactor and semi-coke was obtained using a three-stage variable-speed heating and pressure-switching process. The three-stage variable-speed heating and pressure-switching process conditions were as follows: First, the reactor pressure was increased to 390℃ at a rate of 2℃ / min; then, the pressure was increased to 430℃ at a rate of 0.5℃ / min and the reaction was kept at a constant temperature for 8 hours; finally, the pressure was increased to 500℃ at a rate of 0.5℃ / min and the reaction was kept at a constant temperature for 8 hours.

[0108] 3.3) Under a N2 atmosphere, semi-coke is calcined at high temperature and cooled to obtain needle coke.

[0109] The calcination conditions are as follows: first, under a pressure of 0.02 MPa, the temperature is increased to 600℃ at a rate of 4℃ / min, and the reaction is kept at a constant temperature for 3 hours; then, under a pressure of 0.02 MPa, the temperature is increased to 1500℃ at a rate of 2℃ / min, and the reaction is kept at a constant temperature for 3 hours.

[0110] Example 3

[0111] The medium- and low-temperature coal tar multi-stage processing and utilization process provided in this embodiment includes the following steps.

[0112] 1) Atmospheric pressure cut fraction

[0113] Light coal tar and heavy coal tar are separated from medium- and low-temperature coal tar by atmospheric distillation.

[0114] 2) Light coal coke separation and purification

[0115] 2.1) Light coal tar is separated into crude naphthalene, crude anthracene and crude fluorene components by secondary distillation, and the remaining light oil components are collected for later use.

[0116] Specifically, in step 1), the first fractionation is at atmospheric pressure and the temperature is 330℃. The second fractionation is at atmospheric pressure, separating crude naphthalene, crude anthracene and crude fluorene components at temperatures of 230℃, 300℃ and 360℃, respectively.

[0117] 2.2) The crude naphthalene component is fed into a solvent absorption tower containing benzene, with a benzene circulation rate of 2 kg / h and an operating temperature of 70°C. The filtered crude naphthalene component is then subjected to static melt crystallization at a final crystallization temperature of 70°C for 30 min. Finally, the temperature is reduced to room temperature at a cooling rate of 0.05°C / min to obtain a high-purity refined naphthalene product.

[0118] 2.3) The crude fluorene component was subjected to two recrystallizations using xylene as a solvent, followed by separation using an acidic system (hydrogen peroxide-formic acid system) to obtain the refined fluorene product.

[0119] 2.4) The crude anthracene component is fed into a separator of zeolite molecular sieve membrane. Under normal pressure, temperature of 180℃ and molecular sieve pore size of 5.0~7.0A, refined anthracene product is obtained from the crude anthracene component.

[0120] 2.5) Separation and purification of phenolic oil

[0121] After distillation in step 2.1), the remaining light oil fraction contains a large amount of phenolic substances. Further distillation is carried out to obtain a mixed solution containing phenol, cresol, and xylenol. After further distillation, the individual monomers obtained are phenol, cresol, and xylenol products, which can be widely used in industries such as polymer materials, fragrances, pharmaceuticals, pesticides, and preservatives. At the same time, the purification and separation of phenolic oil also yields light oil mother liquor.

[0122] 2.6) Hydrogenation to produce diesel fuel

[0123] The light oil mother liquor from step 2.5) is hydrotreated to remove S and N to obtain diesel product.

[0124] Before introducing hydrogen, a NiMoP / γ-Al2O3 catalyst, belonging to the NiMo series, is added as the hydrogenation catalyst, with Mo / γ-Al2O3 as the support. The NiMoP / γ-Al2O3 catalyst has a Ni loading of 2 wt% and 12 wt%. The hydrogenation conditions are: temperature 360℃, reaction pressure 15 MPa, hydrogen-to-oil volume ratio 1300:1, and liquid hourly space velocity (LHSV) 0.6 h⁻¹. -1 .

[0125] 3) Recombinant coking process,

[0126] 3.1) In a reactor, the heavy coal tar obtained from distillation in step 1) and the diesel oil obtained from step 2.6) are co-carbonized at a mass ratio of 9:1. The mixture undergoes low-temperature, high-pressure thermal polymerization reforming under a N2 atmosphere, followed by condensation and separation to obtain refined asphalt and coking oil. The coking oil is returned to step 2.6) for hydrotreating to remove N and S before producing diesel oil. The thermal polymerization reforming conditions are: a pressure of 2 MPa, a temperature increase of 3 °C / min to 340 °C, and a constant temperature reaction for 4 hours.

[0127] 3.2) Under a N2 atmosphere, the refined asphalt obtained was placed in a reactor and semi-coke was obtained using a three-stage variable-speed heating and pressure-switching process. The three-stage variable-speed heating and pressure-switching process conditions were as follows: First, the reactor pressure was increased to 400℃ at a rate of 3℃ / min; then, the pressure was increased to 450℃ at a rate of 1℃ / min and the reaction was kept at a constant temperature for 9 hours; finally, the pressure was increased to 520℃ at a rate of 0.4℃ / min and the reaction was kept at a constant temperature for 8 hours.

[0128] 3.3) Under a N2 atmosphere, semi-coke was calcined at high temperature and then cooled to obtain needle coke. The calcination conditions were as follows: first, the temperature was increased to 800℃ at a rate of 5℃ / min under a pressure of 0.03MPa and the reaction was kept at a constant temperature for 4 hours; then, the temperature was increased to 1550℃ at a rate of 2℃ / min under a pressure of 0.02MPa and the reaction was kept at a constant temperature for 3 hours.

[0129] Comparative Example 1

[0130] The difference from Example 2 lies in the different process of separating and purifying light coal tar.

[0131] 1) Atmospheric pressure cut fraction

[0132] Light coal tar and heavy coal tar are separated from medium- and low-temperature coal tar by atmospheric distillation.

[0133] 2) Separation and purification of light coal tar

[0134] 2.1) Light coal tar is separated into crude naphthalene, crude anthracene and crude fluorene components by secondary distillation, and the remaining light oil components are collected for later use;

[0135] Specifically, the first fractionation was performed at atmospheric pressure and the temperature was 340℃. The second fractionation was performed at atmospheric pressure, separating crude naphthalene, crude anthracene, and crude fluorene components at temperatures of 220℃, 280℃, and 340℃, respectively.

[0136] 2) Separation and purification of light coal tar (comparison of purification processes)

[0137] 2.1) The separated crude naphthalene is sent to a solvent absorption tower, cooled and filtered to precipitate naphthalene intermediates, and a high-purity refined naphthalene product is obtained.

[0138] 2.2) The crude fluorene fraction can be recrystallized using toluene as a solvent to obtain the refined fluorene product;

[0139] 2.3) The crude anthracene fraction is distilled to obtain refined anthracene products.

[0140] 2.4) Separation and purification of phenolic oil

[0141] After distillation in step 2.1), the remaining light oil components collected for later use contain a large amount of phenolic substances. Further distillation separation yields a mixed solution containing phenol, cresol, and xylenol, as well as light oil mother liquor.

[0142] 2.6) Hydrogenation to produce diesel fuel

[0143] The light oil mother liquor from step 2.5) is subjected to hydrotreating to remove S and N. Before introducing hydrogen, a NiMoP / γ-Al2O3 catalyst is added. This catalyst belongs to the NiMo series and is used as the hydrotreating catalyst, with Mo / γ-Al2O3 as the support.

[0144] Specifically, the reaction was conducted at 340℃, a reaction pressure of 13 MPa, a hydrogen-to-oil volume ratio of 1200:1, and a liquid hourly space velocity of 0.5 h⁻¹. -1 .

[0145] 3) Recombinant coking

[0146] 3.1) Under N2 atmosphere, in a reactor, the heavy coal tar after distillation in step 1) and the diesel oil obtained in step 2.6) are co-carbonized at a mass ratio of 9:1. The low-temperature high-pressure thermal polymerization reforming yields refined asphalt, which is separated by a condenser to obtain coking oil. The coking oil is returned to step 2.6) for hydrogenation to produce diesel oil. The low-temperature high-pressure thermal polymerization reforming conditions are: at a pressure of 2 MPa, the temperature is increased to 320°C at a rate of 3°C / min, and the reaction is carried out at a constant temperature for 3 hours.

[0147] 3.2) Under a N2 atmosphere, the refined asphalt obtained was placed in a reactor and semi-coke was obtained using a three-stage variable-speed heating and pressure-switching process. The three-stage variable-speed heating and pressure-switching process conditions were as follows: First, the reactor pressure was increased to 390℃ at a rate of 2℃ / min; then, the pressure was increased to 430℃ at a rate of 0.5℃ / min and the reaction was kept at a constant temperature for 8 hours; finally, the pressure was increased to 500℃ at a rate of 0.5℃ / min and the reaction was kept at a constant temperature for 8 hours.

[0148] 3.3) Under a N2 atmosphere, semi-coke was calcined at high temperature and then cooled to obtain needle coke. The calcination conditions were as follows: first, the temperature was increased to 600℃ at a rate of 4℃ / min under a pressure of 0.02MPa, and the reaction was kept at a constant temperature for 3h; then, the temperature was increased to 1500℃ at a rate of 2℃ / min under a pressure of 0.02MPa, and the reaction was kept at a constant temperature for 3h.

[0149] Comparative Example 2

[0150] The difference from Example 3 is that no diesel fuel was added for carbonization in the needle coke production from heavy coal tar.

[0151] 1) Atmospheric pressure cut fraction

[0152] Light coal tar and heavy coal tar are separated from medium- and low-temperature coal tar by atmospheric distillation.

[0153] 2) Light coal coke separation and purification

[0154] 2.1) Light coal tar is separated into crude naphthalene, crude anthracene and crude fluorene components by secondary distillation, and the remaining light oil components are collected for later use.

[0155] Specifically, in step 1), the first fractionation is at atmospheric pressure and the temperature is 330℃. The second fractionation is at atmospheric pressure, separating crude naphthalene, crude anthracene and crude fluorene components at temperatures of 230℃, 300℃ and 360℃, respectively.

[0156] 2.2) The crude naphthalene component is fed into a solvent absorption tower containing benzene, with a benzene circulation rate of 2 kg / h and an operating temperature of 70°C. The filtered crude naphthalene component is then subjected to static melt crystallization at a final crystallization temperature of 70°C for 30 min. Finally, the temperature is reduced to room temperature at a cooling rate of 0.05°C / min to obtain a high-purity refined naphthalene product.

[0157] 2.3) The crude fluorene component was subjected to two recrystallizations using xylene as a solvent, followed by separation using an acidic system (hydrogen peroxide-formic acid system) to obtain the refined fluorene product.

[0158] 2.4) The crude anthracene component is fed into a separator of zeolite molecular sieve membrane. Under normal pressure, temperature of 180℃ and molecular sieve pore size of 5.0~7.0A, refined anthracene product is obtained from the crude anthracene component.

[0159] 2.5) Separation and purification of phenolic oil

[0160] After distillation in step 2.1), the remaining light oil fraction contains a large amount of phenolic substances. Further distillation is carried out to obtain a mixed solution containing phenol, cresol, and xylenol. After further distillation, the individual monomers obtained are phenol, cresol, and xylenol products, which can be widely used in industries such as polymer materials, fragrances, pharmaceuticals, pesticides, and preservatives. At the same time, the purification and separation of phenolic oil also yields light oil mother liquor.

[0161] 3) Coking from heavy coal tar

[0162] 3.1) In a reactor, the heavy coal tar after distillation in step 1) is carbonized, and then subjected to low-temperature, high-pressure thermal polymerization reforming under N2 atmosphere, followed by condensation and separation to obtain refined pitch and coking oil. The thermal polymerization reforming conditions are: at a pressure of 2 MPa, the temperature is increased to 340°C at a rate of 3°C / min, and the reaction is carried out at a constant temperature for 4 hours.

[0163] 3.2) Under a N2 atmosphere, the refined asphalt obtained was placed in a reactor and semi-coke was obtained using a three-stage variable-speed heating and pressure-switching process. The three-stage variable-speed heating and pressure-switching process conditions were as follows: First, the reactor pressure was increased to 400℃ at a rate of 3℃ / min; then, the pressure was increased to 450℃ at a rate of 1℃ / min and the reaction was kept at a constant temperature for 9 hours; finally, the pressure was increased to 520℃ at a rate of 0.4℃ / min and the reaction was kept at a constant temperature for 8 hours.

[0164] 3.3) Under a N2 atmosphere, semi-coke was calcined at high temperature and then cooled to obtain needle coke. The calcination conditions were as follows: first, the temperature was increased to 800℃ at a rate of 5℃ / min under a pressure of 0.03MPa and the reaction was kept at a constant temperature for 4 hours; then, the temperature was increased to 1550℃ at a rate of 2℃ / min under a pressure of 0.02MPa and the reaction was kept at a constant temperature for 3 hours.

[0165] The naphthalene, fluorene, and anthracene products collected in the above embodiments and comparative examples were measured, and the corresponding measurement results are shown in Table 1 below.

[0166] Table 1 Purity of Naphthalene, Fluorene, and Anthracene

[0167] Naphthalene purity Fluorine purity Anthracene purity Example 1 97％ 95％ 96％ Example 2 99％ 96％ 98％ Example 3 94％ 92％ 94％ Comparative Example 1 84％ 82％ 80％ Comparative Example 2 92％ 92％ 93％

[0168] As shown in Table 1, the processing technology of the full-fraction coal tar of the present invention yields naphthalene, fluorene and anthracene with high purity, which can effectively process and utilize coal tar.

[0169] A comparison of the data from Comparative Example 1 and Example 2 shows that the purification and processing technology used in this invention has high purity and can better utilize various high-value-added light components.

[0170] The product indicators of diesel collected in Example 1 of this invention were tested, and the corresponding test results are shown in Table 2 below.

[0171] Table 2 Product Specifications of Diesel Fuel of the Present Invention

[0172] project unit Quality Indicators Test methods density <![CDATA[Kg / m 3 (20℃)]]> 750～900 GB / T1884 distillation range ℃ 200～360 GB / T6536 Sulfur content mg / kg ≤11 SH / T0689 Nitrogen content mg / kg ≤18 SH / T0657 Flash point ℃ 44～65 GB / T3536 Pour point ℃ ≤12 GB / T510

[0173] As shown in Table 2, the diesel fuel produced by this invention has low sulfur and nitrogen content and high product indicators. In contrast, the diesel fuel collected in Comparative Example 1 has a sulfur content greater than 12% and a nitrogen content greater than 20%.

[0174] Using existing measurement methods, the volatile matter, ash content, moisture content, average powder resistivity, powder tap density, and coefficient of thermal expansion of the needle coke prepared in this embodiment were measured. The specific results are shown in Table 1.

[0175] Table 3. Physical properties of needle coke prepared in the examples and comparative examples.

[0176]

[0177] The physical property testing methods are as follows: ash content is determined according to GB / T 1429-2009 "Determination of Ash Content in Carbon Materials"; powder tap density is determined according to GB / T 21354-2008 "General Method for Determination of Tap Density of Powder Products"; resistivity is determined according to GB / T24525-2009 "Determination of Resistivity in Carbon Materials"; and coefficient of thermal expansion is determined according to GB / T 3074.4-2016 "Determination of Coefficient of Thermal Expansion (CTE) of Graphite Electrodes".

[0178] As can be seen from Table 3, the needle coke obtained by the preparation method of this embodiment has an ash content of ≤0.24wt%, indicating low ash content; a resistivity of less than 600μΩ·m, with a minimum of 452μΩ·m, also indicating low resistivity; and a coefficient of thermal expansion of less than 1.5×10⁻⁶. -6 / ℃, the lowest being 1.28×10 -6 / ℃, with a low coefficient of thermal expansion.

[0179] A comparison of Comparative Example 2 and Example 3 shows that, during the delayed coking process, the addition of diesel fuel to adjust the medium- and low-temperature coal tar reduces the coefficient of thermal expansion from 1.65 × 10⁻⁶. -6 / ℃ decreased to 1.35×10 -6 The temperature range of / ℃ indicates that the addition of diesel fuel during the co-carbonization process with medium- and low-temperature coal tar better optimizes the composition of the coal tar, ultimately improving the quality of the prepared needle coke. The resulting needle coke has a predominantly fibrous structure, a low coefficient of thermal expansion, and good thermal shock resistance to rapid temperature changes.

[0180] In addition, the structure of the needle coke powders prepared in Example 3 and Comparative Example 2 was tested, and the microstructure of the needle coke was observed using a ZEISSSIGMA scanning electron microscope (SEM). The needle coke needed to be ground into a fine powder (particle size <75 μm). Before testing, the fine needle coke powder was coated with platinum. The obtained polarized light micrographs and SEM images are shown below. Figures 1-4 As shown.

[0181] from Figure 1 Example 3: Polarized light microstructure of needle-shaped coke powder and Figure 2The scanning electron microscope (SEM) image of the needle coke powder obtained in Example 3 shows that the needle coke obtained in Example 3 is mainly composed of fine fibers, with high microstructural order, high total fiber content, and a very obvious and relatively regular lamellar structure, similar to graphite lamellars. This is because in Example 3, diesel oil was added during the delayed coking process to blend the medium- and low-temperature coal tar. There is a good balance and modification relationship between diesel oil and coal tar pitch. Adding an appropriate amount of diesel oil to the coal tar pitch can lower the softening point of the mixed raw materials, adjust the group composition mainly to HS and HI-TS, and contain more aliphatic short-chain aromatic compounds, causing hydrogen transfer reactions between component molecules, providing a suitable environment for the formation of the mesophase and an appropriate amount of gas escape, which is conducive to the formation of high-quality needle coke.

[0182] from Figure 3 Comparative Example 2: Polarized light microstructure of needle-like coke powder and Figure 4 Comparison of the scanning electron microscope (SEM) images of the needle-shaped coke powder in Comparative Example 2 shows that the needle-shaped coke obtained in Comparative Example 2 is mainly composed of short fibers, with low microstructural order and low total fiber content. It contains some lamellar structures, but these lamellar structures are not regular, and the lamellar thickness varies significantly. This further demonstrates that, compared to Example 3, Comparative Example 2 did not involve adding diesel fuel to the medium- and low-temperature coal tar during the delayed coking process, resulting in more oxygen-containing functional groups and heteroatoms. The oxygen-containing crosslinking during carbonization affected the planarity, leading to poor planar aggregation of the mesophase and a wider needle-like spacing in the mesophase.

[0183] The above embodiments are only some embodiments of the present invention, and not all embodiments. Based on the technical solutions provided by the present invention, any other implementation methods obtained by those skilled in the art through equivalent substitutions or modifications without creative effort should fall within the protection scope of the present invention.

Claims

1. A multi-stage fractional processing and utilization technology for medium- and low-temperature coal tar, characterized in that, Includes the following steps: 1) Atmospheric pressure cut fraction Low-temperature coal tar is distilled under normal pressure to separate light coal tar and heavy coal tar; the light coal tar is the fraction below 360°C, and the heavy coal tar is the fraction above 360°C. 2) Separation and purification of light coal tar 2.1) Crude naphthalene, crude anthracene, crude fluorene, and residual light oil components are separated from the light coal tar in step 1) by distillation; corresponding refined naphthalene, refined fluorene, and refined anthracene products are obtained from the crude naphthalene, crude anthracene, and crude fluorene components, respectively. In step 2.1), the refined naphthalene product, refined fluorene product, and refined anthracene product are obtained through the following methods: 2.1.1) The crude naphthalene component is successively subjected to solvent absorption, cold precipitation separation, and melt crystallization to obtain the refined naphthalene product; 2.1.2) The crude fluorene component was subjected to recrystallization using xylene as a solvent to obtain the refined fluorene product; 2.1.3) The crude anthracene component was processed using distillation-membrane technology to obtain refined anthracene products; In step 2.1.3), under normal pressure and at a temperature of 60℃~180℃, the crude anthracene component is passed through a zeolite molecular sieve membrane separator to obtain refined anthracene, and the pore size of the zeolite molecular sieve is 5.0A~7.0A. 2.2) The residual light oil components from step 2.1) are further separated by distillation to obtain phenol, cresol, xylenol and light oil mother liquor, respectively; 2.3) Diesel fuel is obtained from light oil mother liquor through hydrocatalytic oxidation; 3) Coking from heavy coal tar 3.1) Under N2 atmosphere, the heavy coal tar from step 1) and the diesel oil from step 2.3) are co-carbonized at a mass ratio of 1 to 10:1, thermally polymerized and separated to obtain refined pitch and coking oil; the coking oil is returned to step 2.3) and mixed with light oil mother liquor to produce diesel oil; 3.2) Under N2 atmosphere, the refined asphalt from step 3.1) is processed using a three-stage variable speed heating and pressure process to obtain semi-coke; 3.3) Under a N2 atmosphere, the semi-coke from step 3.2) is calcined and cooled to obtain needle-shaped coke powder; In step 3.1), the conditions for thermal polymerization modification are: under a pressure of 1.5MPa to 3MPa, the temperature is increased to 300℃ to 340℃ at a rate of 3℃ / min, and the reaction is carried out at a constant temperature for 2h to 4h.

2. The multi-stage fractional processing and utilization technology for medium- and low-temperature coal tar according to claim 1, characterized in that, In step 2.1), the distillation temperature of the crude naphthalene component is 210℃~230℃, the distillation temperature of the crude fluorene component is 230℃~300℃, and the distillation temperature of the crude anthracene component is 300℃~360℃.

3. The multi-stage fractional processing and utilization technology for medium- and low-temperature coal tar according to claim 2, characterized in that, In step 2.1.1), the solvent absorption uses benzene as the solvent, with a circulation rate of 2 kg / h and an absorption temperature of 70°C. The melt crystallization involves statically melting the crude naphthalene component after cold precipitation separation, maintaining it at room temperature until the final crystallization temperature reaches 75°C to 80°C for 30 minutes, and then cooling it to room temperature at a rate of 0.05°C / min to obtain refined naphthalene.

4. The multi-stage fractional processing and utilization technology for medium- and low-temperature coal tar according to claim 3, characterized in that, In step 2.1.2), after recrystallization, the crude fluorene component is further separated using an acidic solution system to obtain refined fluorene.

5. The multi-stage fractional processing and utilization technology for medium- and low-temperature coal tar according to claim 1, characterized in that, In step 2.3), the conditions for hydrogenation catalysis are as follows: catalyst NiMoP / γ-Al2O3, temperature 300℃~360℃, pressure 10MPa~15MPa, hydrogen-to-oil volume ratio 800~1300:1, and liquid hourly space velocity 0.3~0.6h. -1 The catalyst has a Ni loading of 1 wt% to 6 wt% and a MoP loading of 10 wt% to 12 wt%.

6. The multi-stage fractional processing and utilization technology for medium- and low-temperature coal tar according to claim 5, characterized in that, In step 3.2), the conditions for the three-stage variable-speed heating and pressure-switching process are as follows: First, the temperature is increased to 380℃ to 400℃ at a pressure of 1.5MPa to 3MPa and a rate of 1℃ / min to 3℃ / min; second, the temperature is increased to 420℃ to 450℃ at a pressure of 1.5MPa to 2MPa and a rate of 0.5℃ / min to 1℃ / min, and the temperature is kept constant for 6h to 10h; finally, the temperature is increased to 480℃ to 520℃ at a pressure of 0.5MPa to 1MPa and a rate of 0.3℃ / min to 0.5℃ / min, and the temperature is kept constant for 6h to 10h.

7. The multi-stage fractional processing and utilization technology for medium- and low-temperature coal tar according to claim 6, characterized in that, In step 3.3), the calcination conditions are as follows: first, under a pressure of 0.01 MPa to 0.03 MPa, the temperature is increased to 500℃ to 800℃ at a rate of 3℃ / min to 5℃ / min, and the reaction is kept at a constant temperature for 2h to 4h; then, under a pressure of 0.01 MPa to 0.03 MPa, the temperature is increased to 1400℃ to 1600℃ at a rate of 1℃ / min to 3℃ / min, and the reaction is kept at a constant temperature for 2h to 4h. In step 3.3), the needle-shaped coke powder has the lowest average resistivity of 416 μΩ·m and the compacted density of 0.96 g / cm³. 3 ~1.23g / cm 3 .

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