A method for producing needle coke by a two-stage extraction process

Abstract

The present application belongs to the technical field of coal chemical industry, and relates to a method for preparing needle coke by adopting a two-stage extraction process, comprising the following steps: 1) cutting the washing oil of a 230-300 DEG C fraction section and the coal tar pitch component of a >350 DEG C fraction section of a medium-low temperature coal tar by a conventional pressure reduction cutting; 2) obtaining hydrogenated tail oil by hydrogenating the medium-low temperature coal tar; and then cutting to obtain fraction oil of 230-350 DEG C; 3) two-stage extraction refining, compounding the product after the first-stage extraction of the coal tar pitch component with the fraction oil, and then performing the second-stage extraction by using the washing oil to obtain refined pitch, and cutting to obtain a >300 DEG C fraction section; and 4) thermal nucleation of the >300 DEG C fraction section and a naphthalene-based interfacial dispersant, and then performing a two-stage temperature and pressure process, calcining and cooling to obtain needle coke. By the two-stage extraction and compounding, the present application can fully remove heteroatoms and improve the efficiency of the refined pitch; and the large-basin mesophase pitch with high anisotropy content is obtained, and the needle coke with high fiber structure content is prepared.

Description

Technical Field

[0001] This invention belongs to the field of coal chemical technology and relates to a method for preparing needle coke using a two-stage extraction process. Background Technology

[0002] Needle coke possesses characteristics such as low coefficient of thermal expansion, low average resistivity, and easy graphitization, making it suitable for use as a raw material in the production of high-power and ultra-high-power graphite electrodes, as well as in high-end carbon materials fields such as the preparation of advanced carbon products. The main raw materials for needle coke production are coal-based and petroleum-based, with coal-based needle coke being more suitable for energy storage. Low- and medium-temperature coal tar pitch raw materials contain unfavorable factors that hinder the growth of the mesophase. Common unfavorable factors include high heteroatom content (S, N, O), asphaltenes, quinoline insolubles (QI), and metallic impurities. The presence of these unfavorable factors results in a low content of anisotropic structures in the mesophase, thus affecting the quality of the needle coke product. Therefore, pretreatment of the raw materials is necessary to continuously optimize their performance and prepare high-quality mesophase pitch, thereby obtaining needle coke with a high fibrous structure content. Raw material pretreatment is the most critical and challenging step in the needle coke production process; the quality of the raw materials directly determines the performance of the finished needle coke product.

[0003] Low-temperature coal tar pitch has a high heteroatom content, and heat-sensitive components are difficult to remove. Therefore, reducing the heteroatom content and removing heat-sensitive components are urgent problems to be solved in raw material pretreatment. Patent CN112552959A describes a method of removing sulfur, nitrogen, and other heteroatoms from feedstock oil containing a hydrogenation catalyst through slurry-bed hydrogenation to obtain a hydrogenated product. Non-ideal components are then removed from the hydrogenated product to obtain a feedstock for needle coke production. Patent CN109135789B discloses a method of using a mixture of polar and non-polar solvents as an extractant to extract low-temperature coal tar, removing highly reactive substances to obtain feedstock pitch. The feedstock pitch is then processed through coking and calcination to produce needle coke. Patent CN103789028B describes a method of filtering catalytic oil slurry and then subjecting it to mild hydrogenation treatment. The hydrogenated oil is then subjected to vacuum distillation, and the resulting hydrogenated light distillate is mixed with the remaining hydrogenated oil as a feedstock for needle coke production. Patent CN114806620A utilizes the principle of solvent extraction and sedimentation, mixing two different solvents to form a mixed solvent, and then performing two extraction and sedimentation separations to obtain raw materials for needle coke production. Patent CN107694552B discloses a method using aromatic hydrocarbons and alkanes in an aromatic-to-alkane mass ratio of 1:1 to 5:1 as extractants to remove quinoline-insoluble matter from medium- and low-temperature coal tar. This is then combined with hydrogenation treatment, thermal polymerization, and calcination processes under the action of a non-metallic homogeneous mild hydrogenation catalyst to produce needle coke. Patent CN113604241B discloses a method sequentially employing an organic mixed solvent extraction process, an ionic liquid extraction process, and a component modification process to obtain refined asphalt from cut asphalt. The refined asphalt is then thermally polymerized in a magnetic field to obtain semi-coke, which is subsequently used to produce needle coke.

[0004] The aforementioned patents can all produce needle coke, but there are still many problems: such as the inability to fully remove heteroatoms, resulting in low refining efficiency; poor orientation of the intermediate phase and insufficient structural stability are not conducive to producing high-quality needle coke. Summary of the Invention

[0005] To address the existing technical problems of insufficient removal of heteroatoms and poor orientation of the mesophase, this invention provides a method for preparing needle coke using a two-stage extraction process. Through two-stage extraction and compounding, heteroatoms can be fully removed, improving the efficiency of refined asphalt; large-area mesophase asphalt with high anisotropy content is obtained, and needle coke with high fibrous structure content is produced.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing needle coke using a two-stage extraction process includes the following steps:

[0008] 1) Atmospheric and vacuum cutting

[0009] Medium- and low-temperature coal tar is divided into a 230℃~300℃ fraction and a ≥350℃ fraction by atmospheric and vacuum distillation; the 230℃~300℃ fraction is denoted as wash oil, and the ≥350℃ fraction is denoted as coal tar pitch component;

[0010] 2) Preparation of hydrotreated tail oil

[0011] Medium- and low-temperature coal tar is hydrotreated to obtain hydrotreated tail oil; then, distillate oil at 230–350°C is obtained from the hydrotreated tail oil.

[0012] 3) Two-stage extraction and refining

[0013] 3.1) The coal tar pitch component obtained in step 1) is subjected to primary extraction to obtain medium-low temperature refined coal tar pitch; the mass ratio of coal tar pitch component to primary extractant is 1:3.

[0014] 3.2) The medium-low temperature coal tar refined pitch obtained in step 3.1) is mixed with the distillate oil at 230-350℃ in step 2) at a mass ratio of 9:1 to obtain the compound material;

[0015] 3.3) Using the wash oil obtained in step 1) as the secondary extractant, the compound material obtained in step 3.2) is subjected to secondary extraction to obtain refined asphalt; the mass ratio of compound material to secondary extractant is 1:2;

[0016] 3.4) The refined asphalt is fractionated to obtain light component solutions of the >300℃ fraction and the <300℃ fraction; the light component solution of the <300℃ fraction is subjected to reverse extraction to recover the wash oil.

[0017] 4) Coking

[0018] The >300℃ fraction obtained in step 3) and the naphthalene-based interfacial dispersant are placed together in a reactor at a mass ratio of 10 to 15:1 and thermally agglomerated to form nuclei under a N2 atmosphere; a two-stage heating and pressure-switching process is used to obtain semi-coke; finally, needle coke is obtained by calcination and cooling.

[0019] Further specifying that in step 2), the hydrogenation catalyst is Ni-Mo / Zr-ASA, the active component Ni is NiO, and the active component Mo is MoO3; the mass fractions of NiO and MoO3 are 1%-5% and 10%-15%, respectively.

[0020] Further specifying that in step 3.1), the primary extractant is obtained by mixing toluene and n-heptane in a mass ratio of 4:1; the primary extraction process conditions are: extraction temperature 60-80℃, extraction time 1-3h, and sedimentation time 2-4h.

[0021] Further specifying, in step 3.3), the secondary extraction process conditions are: extraction temperature 180-220℃, extraction time 2-4h, and sedimentation time 3-6h.

[0022] Further specifying that in step 3.4), the reverse extraction agent is N-methylpyrrolidone; the reverse extraction process conditions are: oil-to-agent ratio of 1:1, extraction temperature of 200-220℃, extraction time of 2-3h, and sedimentation time of 1-2h.

[0023] Further specifying, in step 4), the process conditions for thermal polymerization are: pressure of 2-4 MPa, heating to 400-420°C at a rate of 1°C / min, and constant temperature reaction for 3-6 hours.

[0024] Further specifying, in step 4), the two-stage heating and pressure-changing process conditions are as follows: First, the pressure is 2.0 MPa, and the temperature is increased to 420-440°C at a rate of 1°C / min, and held at the temperature for 5-8 hours; second, the temperature is increased to 480-520°C at a rate of 0.5°C / min, the pressure is reduced to 0.5 MPa, and held at the temperature for 6-10 hours, and then cooled to room temperature to obtain semi-coke.

[0025] Further specifying, in step 4), the calcination conditions are: the N2 introduction rate is 40–60 mL / min. -1 The pressure is 0.1-0.3 MPa, the temperature is increased to 1450℃ at a rate of 1-2℃ / min, and the reaction is carried out at a constant temperature for 3-6 hours.

[0026] Needle coke prepared by the two-stage extraction process described above.

[0027] Further specified, the needle coke has a volatile matter content ≤0.36%, an ash content ≤0.24%, a moisture content ≤0.15%, an average resistivity of at least 431 μΩ·m, and a tap density of 0.85–0.88 g / cm³. 3 .

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. This invention uses a mixed solution of n-heptane and toluene as a primary extractant to perform primary extraction on the ≥350℃ fraction of medium- and low-temperature coal tar, further reducing the content of heteroatoms such as S, N, and O in the modified extracted pitch; increasing the content of aromatics and cycloalkanes, resulting in refined pitch with optimized composition; coke with low S and N content is less prone to crystal expansion during graphitization, the product is almost crack-free, and the resulting needle coke has small packing porosity, high true density, and low resistivity.

[0030] 2. This invention uses a 230-350℃ distillate oil from hydrotreated tail oil to blend with medium-low temperature coal tar after a single extraction. Since hydrotreated tail oil is a non-polar substance, it can extract aromatics and cycloalkanes from the coal tar, removing some of the colloids, asphaltenes, and heteroatom components such as S, N, and O rich in polar groups. Therefore, the advantages of introducing the 230-350℃ distillate oil from the hydrotreated tail oil are: ① Hydrotreated tail oil contains a certain amount of cycloalkanes and aromatics. Using it as a blending solvent can introduce these cycloalkanes and aromatics into the raw material asphalt, optimizing the raw material properties and resulting in a high-performance modified extractable asphalt; ② Hydrotreated tail oil is a byproduct of crude oil hydrocracking, with a simple process. Utilizing this byproduct to improve the performance of needle coke is energy-saving and environmentally friendly.

[0031] 3. This invention incorporates a naphthalene-based interfacial dispersant during the preparation of mesophase asphalt and employs a low-temperature, high-pressure process for thermal polymerization and nucleation. The addition of the naphthalene-based interfacial dispersant helps reduce system viscosity and improve dispersion. In the early stages of mesophase formation, the dispersant reduces system viscosity, promotes physical rearrangement of the aromatic layers, lowers the surface energy, and allows for sufficient contact and fusion between liquid phases, forming microspheres. In the later stages of mesophase formation, the dispersant adsorbs onto the surface of the microspheres, forming a film that expands the molecular structure of the microspheres, creating a steric hindrance effect, slowing down microsphere aggregation, and maintaining the microspheres in a dispersed state for a prolonged period. This promotes microsphere growth and fusion, resulting in a large-area mesophase asphalt with high anisotropy content. The resulting needle coke has a predominantly fibrous structure, a low coefficient of thermal expansion, good thermal shock resistance to rapid temperature changes, and excellent performance.

[0032] 4. The method for preparing needle coke according to this invention first uses chemical solvent extraction to purify the medium- and low-temperature coal tar pitch components. This effectively reduces the content of S, N, O, and primary QI in the medium- and low-temperature coal tar pitch. The purpose of introducing hydrogenated tail oil is to use the added hydrogen as a reactant to cause desulfurization, denitrification, deoxygenation, demetallization reactions or hydrocarbon saturation reactions in the coal tar, extracting aromatics and cycloalkanes, improving the raw material composition, and removing a certain amount of polar heteroatoms, gums, and asphaltenes, thereby achieving classification, transformation, removal, and separation. Finally, the wash oil obtained from the system itself is used for secondary extraction of the pitch to obtain refined pitch with high aromatic and cycloalkanes content and low heteroatom content, which greatly optimizes the raw material composition. In the process of preparing mesophase pitch, the addition of distillate oil at 230-350℃ after hydrotreated tail oil fractionation effectively reduces the viscosity of the system to obtain mesophase pitch with high anisotropic content, thereby producing needle coke with high fibrous structure content. Attached Figure Description

[0033] Figure 1 Example 1: Polarized light micrograph;

[0034] Figure 2 Electron micrograph of Example 1;

[0035] Figure 3 Comparative Example 1: Polarized light micrograph of the structure;

[0036] Figure 4 Comparative Example 1: Electron Micrograph. Detailed Implementation

[0037] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] The experimental raw materials selected for this invention are all low-rank coal from a certain region in northern Shaanxi, my country.

[0039] Example 1

[0040] This embodiment provides a method for preparing needle coke using a two-stage extraction process, comprising the following steps.

[0041] 1) Atmospheric and vacuum cutting

[0042] Medium- and low-temperature coal tar is divided into a ≤230℃ fraction and a ≥350℃ fraction by atmospheric and vacuum distillation; the ≤230℃ fraction is denoted as wash oil, and the ≥350℃ fraction is denoted as coal tar pitch component.

[0043] 2) Preparation of hydrotreated tail oil

[0044] The entire fraction of medium- and low-temperature coal tar is hydrotreated to obtain hydrotreated tail oil. This tail oil is then further fractionated to obtain distillate oils at 230–350°C. This step uses a Ni-Mo / Zr-ASA hydrotreating catalyst, with Ni as the active component (NiO) and Mo as the active component (MoO3); the mass fractions of NiO and MoO3 are 1% and 10%, respectively.

[0045] 3) Two-stage extraction and refining of asphalt

[0046] 3.1) Primary extraction and refining

[0047] The coal tar pitch component obtained in step 1) at ≥350℃ was subjected to extraction using a toluene and n-heptane mixed solution as the primary extractant, with a toluene-n-heptane mixture at a mass ratio of 4:1. The mass ratio of the coal tar pitch component to the primary extractant was 1:3. Specifically, the extraction temperature was 60℃, the extraction time was 1 hour, and the settling time was 2 hours.

[0048] 3.2) Compound Mixture

[0049] The medium-low temperature coal tar refined pitch obtained from the first extraction in step 3.1) is mixed with the 230℃ distillate oil obtained in step 2) to obtain a compound material with a mass ratio of 9:1.

[0050] 3.3) Secondary extraction and refining

[0051] The compound obtained in step 3.2) is subjected to secondary extraction to obtain refined asphalt of mixed oil. The wash oil obtained in step 1) is used as the secondary extractant. The mass ratio of the compound to the secondary extractant is 1:2. Specifically, the extraction temperature is 180°C, the extraction time is 2 hours, and the settling time is 3 hours.

[0052] 3.4) The refined asphalt from the mixed oil can then be fractionated, with the components in the >300℃ fraction used as feedstock for needle coke preparation. The light component solution in the <300℃ fraction is reserved for later use.

[0053] Back-extraction of the light component solution remaining in the <300℃ fraction after extraction yields a large amount of wash oil. N-methylpyrrolidone is used as the back-extraction agent.

[0054] Specifically, the oil-to-extractant ratio is 1:1 (the mass ratio of the light component solution in the <300℃ fraction to the back-extractant is 1:1), the extraction temperature is 200℃, the extraction time is 2h, and the settling time is 1h.

[0055] 4) Coking

[0056] Inside the reactor, the refined asphalt fraction (i.e., the >300℃ fraction) of the mixed oil from step 3.4) and the naphthalene-based interfacial dispersant are placed together in the reactor at a mass ratio of 10:1. Thermal polymerization is carried out under N2 atmosphere using a low-temperature and high-pressure process, and semi-coke is prepared using a two-stage low-speed temperature and pressure change process. Under N2 atmosphere, the semi-coke obtained above is calcined at high temperature and naturally cooled to obtain needle coke.

[0057] Specifically, the low-temperature high-pressure process conditions are as follows: pressure is 2 MPa, under N2 atmosphere, temperature is increased to 400℃ at 0.5℃ / min, and the reaction is carried out at a constant temperature for 3 hours.

[0058] Two-stage low-speed heating and pressure transformation process: Under N2 atmosphere, pressure 2MPa, temperature is increased to 420℃ at a rate of 0.5℃ / min and held at the temperature for 5h; temperature is increased to 480℃ at a rate of 0.5℃ / min, pressure is reduced to 0.5MPa and held at the temperature for 6h, and then cooled to room temperature to obtain semi-coke.

[0059] The calcination conditions were: N2 rate of 40 mL / min. -1 The pressure was 0.1 MPa, the temperature was increased to 1450℃ at a rate of 1℃ / min, and the reaction was carried out at a constant temperature for 3 hours.

[0060] 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.

[0061] Example 2

[0062] This embodiment provides a method for preparing needle coke using a two-stage extraction process, including the following steps:

[0063] 1) Atmospheric and vacuum cutting

[0064] According to the different fractions of medium and low temperature coal tar, the ≤240℃ fraction is used to obtain wash oil and the ≥350℃ fraction is used to obtain coal tar pitch components.

[0065] 2) Preparation of hydrotreated tail oil

[0066] The entire fraction of medium- and low-temperature coal tar is hydrotreated to obtain hydrotreated tail oil. This tail oil is then fractionated to obtain a 240℃ distillate. This step uses a Ni-Mo / Zr-ASA hydrotreating catalyst, with Ni as the active component (NiO) and Mo as the active component (MoO3); the mass fractions of NiO and MoO3 are 2% and 11%, respectively.

[0067] 3) Two-stage extraction and refining of asphalt

[0068] 3.1) Primary extraction and refining

[0069] The coal tar pitch fraction obtained in step 1) at ≥350℃ was subjected to extraction using a toluene and n-heptane mixed solution as the primary extractant, with a toluene-n-heptane mixture at a mass ratio of 4:1. The mass ratio of the coal tar pitch fraction to the primary extractant was 1:3. Specifically, the extraction temperature was 65℃, the extraction time was 1.5 h, and the settling time was 2.5 h.

[0070] 3.2) Compound Mixture

[0071] The medium-low temperature coal tar refined pitch obtained after one extraction in step 3.1) is mixed with the 240℃ distillate oil obtained in step 2) to obtain a compound material with a mass ratio of 9:1.

[0072] 3.3) Secondary extraction and refining

[0073] The compound obtained in step 3.2) is subjected to secondary extraction to obtain refined asphalt of mixed oil. The wash oil obtained in step 1) is used as the secondary extractant. The mass ratio of the compound to the secondary extractant is 1:2.

[0074] Specifically, the extraction temperature was 185℃, the extraction time was 2.5h, and the sedimentation time was 3.5h.

[0075] 3.4) The refined asphalt from the mixed oil can then be fractionated, with the components in the >300℃ fraction used as feedstock for needle coke preparation. The light component solution in the <300℃ fraction is reserved for later use.

[0076] Back-extraction of the light component solution in the <300℃ fraction remaining after extraction in step 3.3) yields a large amount of wash oil. N-methylpyrrolidone is used as the back-extraction agent. Specifically, the oil-to-agent ratio is 1:1 (the mass ratio of the light component solution in the <300℃ fraction to the back-extraction agent is 1:1), the extraction temperature is 205℃, the extraction time is 2 hours, and the settling time is 1 hour.

[0077] 4) Coking

[0078] Inside the reactor, the refined asphalt fraction (i.e., the >300℃ fraction) of the mixed oil from step 3.4) is placed together with a naphthalene-based interfacial dispersant at a mass ratio of 12:1. Thermal polymerization is carried out under a low-temperature, high-pressure process in an N2 atmosphere, and semi-coke is prepared using a two-stage low-speed temperature-pressure change process. Under an N2 atmosphere, the semi-coke obtained above is calcined at high temperature and then naturally cooled to obtain needle coke.

[0079] Specifically, the low-temperature and high-pressure process conditions are as follows: pressure is 2.5 MPa, under N2 atmosphere, temperature is increased to 400℃ at 0.5℃ / min, and the reaction is carried out at a constant temperature for 4 hours.

[0080] Two-stage low-speed heating and pressure transformation process: Under N2 atmosphere, pressure 2MPa, temperature is increased to 420℃ at a rate of 0.5℃ / min and held at the temperature for 6h; temperature is increased to 480℃ at a rate of 0.5℃ / min, pressure is reduced to 0.5MPa and held at the temperature for 6h, and then cooled to room temperature to obtain semi-coke.

[0081] The calcination conditions were: N2 rate of 45 mL / min. -1 The pressure was 0.2 MPa, the temperature was increased to 1450℃ at a rate of 1.5℃ / min, and the reaction was carried out at a constant temperature for 4 hours.

[0082] 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.

[0083] Example 3

[0084] This embodiment provides a method for preparing needle coke using a two-stage extraction process, including the following steps:

[0085] 1) Atmospheric and vacuum cutting

[0086] According to the different fractions of medium and low temperature coal tar, the ≤250℃ fraction is used to obtain wash oil and the ≥350℃ fraction is used to obtain coal tar pitch components.

[0087] 2) Preparation of hydrotreated tail oil

[0088] The entire fraction of medium- and low-temperature coal tar is hydrotreated to obtain hydrotreated tail oil. This tail oil is then fractionated to obtain a 240°C distillate. This step uses a Ni-Mo / Zr-ASA hydrotreating catalyst, with Ni as the active component (NiO) and Mo as the active component (MoO3); the mass fractions of NiO and MoO3 are 3% and 12%, respectively.

[0089] 3) Two-stage extraction and refining of asphalt

[0090] 3.1) Primary extraction and refining

[0091] The coal tar pitch component obtained in step 1) at ≥350℃ was subjected to extraction using a toluene and n-heptane mixed solution as the primary extractant, with a toluene-n-heptane mixing ratio of 4:1 by mass. The mass ratio of the coal tar pitch component to the primary extractant was 1:3. Specifically, the extraction temperature was 70℃, the extraction time was 2 hours, and the settling time was 3 hours.

[0092] 3.2) Compound Mixture

[0093] The medium-low temperature coal tar refined pitch obtained from the first extraction in step 3.1) is mixed with the 240℃ distillate oil obtained in step 2) to obtain a compound material with a mass ratio of 9:1.

[0094] 3.3) Secondary extraction and refining

[0095] The compound obtained in step 3.2) is subjected to secondary extraction to obtain refined asphalt of mixed oil. The wash oil obtained in step 1) is used as the secondary extractant. The mass ratio of compound to secondary extractant is 1:2. Specifically, the extraction temperature is 190℃, the extraction time is 3 hours, and the settling time is 4 hours.

[0096] 3.4) The refined asphalt from the mixed oil can then be fractionated, with the components in the >300℃ fraction used as feedstock for needle coke preparation. The light component solution in the <300℃ fraction is reserved for later use.

[0097] Back-extraction of the light component solution in the <300℃ fraction remaining after extraction yields a large amount of wash oil. N-methylpyrrolidone is used as the back-extraction agent. Specifically, the oil-to-agent ratio is 1:1 (the mass ratio of the light component solution in the <300℃ fraction to the back-extraction agent is 1:1), the extraction temperature is 210℃, the extraction time is 2.5 h, and the settling time is 1.5 h.

[0098] 4) Coking

[0099] Inside the reactor, the refined asphalt fraction (i.e., the >300℃ fraction) of the mixed oil from step 3.4) and the naphthalene-based interfacial dispersant are placed together in the reactor at a mass ratio of 15:1. Thermal polymerization is carried out under a low-temperature and high-pressure process in a N2 atmosphere, and semi-coke is prepared using a two-stage low-speed temperature and pressure change process. Under a N2 atmosphere, the semi-coke obtained above is calcined at high temperature and naturally cooled to obtain needle coke.

[0100] Specifically, the low-temperature and high-pressure process conditions are as follows: pressure is 3 MPa, under N2 atmosphere, temperature is increased to 4100℃ at 1℃ / min, and the reaction is carried out at a constant temperature for 5 hours.

[0101] Two-stage low-speed heating and pressure transformation process: Under N2 atmosphere, pressure 2MPa, heating to 430℃ at a rate of 1℃ / min, and holding at that temperature for 7h; heating to 490℃ at a rate of 0.5℃ / min, reducing the pressure to 0.5MPa, holding at that temperature for 7h, and cooling to room temperature to obtain semi-coke.

[0102] The calcination conditions were: N2 rate of 50 mL / min. -1 The pressure was 0.2 MPa, the temperature was increased to 1450℃ at a rate of 1.5℃ / min, and the reaction was carried out at a constant temperature for 5 hours.

[0103] 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.

[0104] Example 4

[0105] This embodiment provides a method for preparing needle coke using a two-stage extraction process, including the following steps:

[0106] 1) Atmospheric and vacuum cutting

[0107] According to the different fractions of medium and low temperature coal tar, the ≤300℃ fraction is separated to obtain wash oil and the ≥350℃ fraction is separated to obtain coal tar pitch components;

[0108] 2) Preparation of hydrotreated tail oil

[0109] The entire fraction of medium- and low-temperature coal tar is hydrotreated to obtain hydrotreated tail oil. This tail oil is then fractionated to obtain a 240°C distillate. This step uses a Ni-Mo / Zr-ASA hydrotreating catalyst, with Ni as the active component (NiO) and Mo as the active component (MoO3); the mass fractions of NiO and MoO3 are 5% and 15%, respectively.

[0110] 3) Two-stage extraction and refining of asphalt

[0111] 3.1) Primary extraction and refining

[0112] The coal tar pitch fraction obtained in step 1) at ≥350℃ was subjected to extraction using a toluene and n-heptane mixed solution as the primary extractant, with a toluene-n-heptane mixture at a mass ratio of 4:1. The mass ratio of the coal tar pitch fraction to the primary extractant was 1:3. Specifically, the extraction temperature was 80℃, the extraction time was 2 hours, and the settling time was 3 hours.

[0113] 3.2) Compound Mixture

[0114] The medium-low temperature coal tar refined pitch obtained from the first extraction in step 3.1) is mixed with the 240℃ distillate oil obtained in step 2) to obtain a compound material with a mass ratio of 9:1.

[0115] 3.3) Secondary extraction and refining

[0116] The compound obtained in step 3.2) is subjected to secondary extraction to obtain refined asphalt of mixed oil. The wash oil obtained in step 1) is used as the secondary extractant, and the mass ratio of the compound to the secondary extractant is 1:2. Specifically, the extraction temperature is 220℃, the extraction time is 3 hours, and the settling time is 2 hours.

[0117] 3.4) The refined asphalt from the mixed oil is then fractionated, with the components in the >300℃ fraction used as feedstock for needle coke preparation. The light component solution in the <300℃ fraction is reserved for later use.

[0118] Back-extraction of the light component solution remaining in the <300℃ fraction after extraction yields a large amount of wash oil. N-methylpyrrolidone is used as the back-extraction agent.

[0119] Specifically, the oil-to-solvent ratio was 1:1 (the mass ratio of the light component solution in the <300℃ fraction to the back-extraction agent was 1:1), the extraction temperature was 220℃, the extraction time was 3h, and the settling time was 2h.

[0120] 4) Coking

[0121] Inside the reactor, the refined asphalt fraction (i.e., the >300℃ fraction) of the mixed oil from step 3.4) and the naphthalene-based interfacial dispersant are placed together in the reactor at a mass ratio of 10:1. Thermal polymerization is carried out under N2 atmosphere using a low-temperature and high-pressure process, and semi-coke is prepared using a two-stage low-speed temperature and pressure change process. Under N2 atmosphere, the semi-coke obtained above is calcined at high temperature and naturally cooled to obtain needle coke.

[0122] Specifically, the low-temperature and high-pressure process conditions are as follows: pressure is 3 MPa, under N2 atmosphere, temperature is increased to 420℃ at 1℃ / min, and the reaction is carried out at a constant temperature for 5 hours.

[0123] Two-stage low-speed heating and pressure transformation process: Under N2 atmosphere, pressure 2MPa, heating to 440℃ at a rate of 1℃ / min, and holding at that temperature for 7h; heating to 520℃ at a rate of 0.5℃ / min, reducing the pressure to 0.5MPa, holding at that temperature for 8h, and cooling to room temperature to obtain semi-coke.

[0124] The calcination conditions were: N2 rate of 55 mL / min. -1 The pressure was 0.2 MPa, the temperature was increased to 1450℃ at a rate of 1℃ / min, and the reaction was carried out at a constant temperature for 5 hours.

[0125] 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.

[0126] Comparative Example 1

[0127] The difference between this comparative example and Example 1 is that: the medium-low temperature coal tar was directly mixed with the hydrogenated tail oil and then a naphthalene-based interfacial dispersant was introduced before the preparation of needle coke. Heptane and toluene were not used as the first-stage extractants to remove heteroatoms from the medium-low temperature coal tar.

[0128] The same atmospheric and vacuum distillation fraction cutting, two-stage low-rate heating and pressure-switching process conditions, and calcination process as in Example 1 are used. The specific preparation process is as follows:

[0129] 1) Atmospheric and vacuum cutting

[0130] According to the different fractions of medium and low temperature coal tar, the ≤230℃ fraction was separated to obtain wash oil and the ≥350℃ fraction was separated to obtain coal tar pitch components;

[0131] 2) Preparation of hydrotreated tail oil

[0132] The entire fraction of medium- and low-temperature coal tar is hydrotreated to obtain hydrotreated tail oil. This tail oil is then fractionated to obtain a 230°C distillate. This step uses a Ni-Mo / Zr-ASA hydrotreating catalyst, with Ni as the active component (NiO) and Mo as the active component (MoO3). The mass fractions of NiO and MoO3 are 1% and 10%, respectively.

[0133] 3) Compound Mixture

[0134] The medium- and low-temperature coal tar refined pitch and the hydrogenated tail oil obtained by fractionation of 2) to obtain a 230℃ distillate oil were blended together with a blending mass ratio of 9:1.

[0135] 4) Extraction and refining

[0136] The blended oil obtained from step 3) was extracted to obtain refined asphalt from the blended oil. The wash oil obtained from step 1) was used as the extractant. The mass ratio of refined asphalt from the blended oil to the extractant was 1:2.

[0137] Specifically, the extraction temperature was 180℃, the extraction time was 2 hours, and the sedimentation time was 3 hours.

[0138] 5) The refined asphalt from the mixed oil is then fractionated, with the components in the >300℃ fraction used as feedstock for needle coke preparation. The light component solution in the <300℃ fraction is reserved for later use.

[0139] Back-extraction of the light component solution in the fraction below 300℃ remaining after extraction yields a large amount of wash oil. N-methylpyrrolidone is used as the back-extraction agent. The oil-to-agent ratio is 1:1, the extraction temperature is 200℃, the extraction time is 2 hours, and the settling time is 1 hour.

[0140] 6) Coking

[0141] Inside the reactor, the fraction of refined asphalt cut from the mixed oil in step 4) (i.e., the fraction >300℃) and the naphthalene-based interfacial dispersant are placed together in the reactor. Thermal polymerization is carried out under N2 atmosphere using a low-temperature and high-pressure process. Semi-coke is prepared using a two-stage low-speed temperature and pressure change process. Under N2 atmosphere, the semi-coke obtained above is calcined at high temperature and naturally cooled to obtain needle coke.

[0142] Specifically, the low-temperature and high-pressure process conditions are as follows: pressure is 2 MPa, under N2 atmosphere, temperature is increased to 400℃ at 0.5℃ / min, and the reaction is carried out at a constant temperature for 3 hours.

[0143] Two-stage low-speed heating and pressure transformation process: Under N2 atmosphere, pressure 2MPa, temperature is increased to 420℃ at a rate of 0.5℃ / min and held at the temperature for 5h; temperature is increased to 480℃ at a rate of 0.5℃ / min, pressure is reduced to 0.5MPa and held at the temperature for 6h, and then cooled to room temperature to obtain semi-coke.

[0144] The calcination conditions were: N2 rate of 40 mL / min. -1 The pressure was 0.1 MPa, the temperature was increased to 1450℃ at a rate of 1℃ / min, and the reaction was carried out at a constant temperature for 3 hours.

[0145] Comparative Example 2

[0146] The difference between this comparative example and Example 2 is that no hydrogenated tail oil was introduced for component optimization in medium- and low-temperature coal tar.

[0147] The process is the same as in Example 2, involving atmospheric and vacuum distillation, high-pressure low-temperature process, two-stage low-speed heating and pressure-switching process, and calcination. The specific preparation process is as follows:

[0148] 1) Atmospheric and vacuum cutting

[0149] According to the different fractions of medium and low temperature coal tar, the ≤240℃ fraction is used to obtain wash oil and the ≥350℃ fraction is used to obtain coal tar pitch components;

[0150] 2) Extraction and refining

[0151] The coal tar pitch component from the ≥350℃ fraction obtained in step 1) was extracted to obtain medium- and low-temperature refined coal tar pitch. A mixed solution of toluene and n-heptane was used as the extractant, with a mass ratio of toluene to n-heptane of 4:1. The mass ratio of the coal tar pitch component from the ≥350℃ fraction to the extractant was 1:3. Specifically, the extraction temperature was 65℃, the extraction time was 1.5 h, and the settling time was 2.5 h.

[0152] 3) Coking

[0153] Inside the reactor, the medium-low temperature coal tar refined pitch obtained in step 2) and the naphthalene-based interfacial dispersant are placed together in the reactor and thermally agglomerated under a low temperature and high pressure process in a N2 atmosphere. Semi-coke is prepared by a two-stage low-speed heating and pressure-switching process. Under a N2 atmosphere, the semi-coke obtained above is calcined at high temperature and naturally cooled to obtain needle coke.

[0154] Specifically, the low-temperature and high-pressure process conditions are as follows: pressure is 2.5 MPa, under N2 atmosphere, temperature is increased to 400℃ at 0.5℃ / min, and the reaction is carried out at a constant temperature for 4 hours.

[0155] Two-stage low-speed heating and pressure transformation process: Under N2 atmosphere, pressure 2MPa, temperature is increased to 420℃ at a rate of 0.5℃ / min and held at the temperature for 6h; temperature is increased to 480℃ at a rate of 0.5℃ / min, pressure is reduced to 0.5MPa and held at the temperature for 6h, and then cooled to room temperature to obtain semi-coke.

[0156] The calcination conditions were: N2 rate of 45 mL / min. -1 The pressure was 0.2 MPa, the temperature was increased to 1450℃ at a rate of 1.5℃ / min, and the reaction was carried out at a constant temperature for 4 hours.

[0157] 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.

[0158] Comparative Example 3

[0159] The difference between this comparative example and Example 3 is that only a solvent is used to extract and refine the raw material asphalt; and no naphthalene-based interfacial dispersant is added during the preparation of the mesophase asphalt.

[0160] The specific preparation process is as follows:

[0161] 1) Atmospheric and vacuum cutting

[0162] According to the different fractions of medium and low temperature coal tar, the ≤250℃ fraction is separated to obtain wash oil and the ≥350℃ fraction is separated to obtain coal tar pitch components;

[0163] 2) Preparation of hydrotreated tail oil

[0164] The entire fraction of medium- and low-temperature coal tar is hydrotreated to obtain hydrotreated tail oil. This tail oil is then fractionated to obtain a 240°C distillate. This step uses a Ni-Mo / Zr-ASA hydrotreating catalyst, with Ni as the active component (NiO) and Mo as the active component (MoO3). The mass fractions of NiO and MoO3 are 3% and 12%, respectively.

[0165] 3) Primary extraction and refining

[0166] The coal tar pitch fraction obtained from step 1) at ≥350℃ was subjected to extraction using a toluene and n-heptane mixed solution as the primary extractant, with a toluene-n-heptane mixture at a mass ratio of 4:1. The mass ratio of the coal tar pitch fraction at ≥350℃ to the primary extractant was 1:3. Specifically, the extraction temperature was 70℃, the extraction time was 2 hours, and the settling time was 3 hours.

[0167] 4) Compound Mixture

[0168] The medium-low temperature coal tar refined pitch obtained from the first extraction in step 3) is mixed with the 240℃ distillate oil obtained in step 2) to obtain a compound material with a mass ratio of 9:1.

[0169] 5) Secondary extraction and refining

[0170] The compounded material (mixed oil) obtained from 4) is subjected to secondary extraction to obtain refined asphalt from the mixed oil. The wash oil obtained from 1) is used as the secondary extractant, and the mass ratio of the compounded material to the secondary extractant is 1:2.

[0171] Specifically, the extraction temperature was 190℃, the extraction time was 3 hours, and the sedimentation time was 4 hours.

[0172] 6) The refined bitumen from the mixed oil is then fractionated to serve as feedstock for needle coke production. The light component solution from the <300℃ fraction is reserved for later use.

[0173] Back-extraction of the light component solution in the fraction below 300℃ remaining after extraction yields a large amount of wash oil. N-methylpyrrolidone is used as the back-extraction agent. Specifically, the oil-to-agent ratio is 1:1, the extraction temperature is 210℃, the extraction time is 2.5 h, and the settling time is 1.5 h.

[0174] 7) Coking

[0175] Inside the reactor, the fraction of refined asphalt cut from the mixed oil in step 6) (i.e. the component of the fraction with a temperature >300℃) is placed inside the reactor and thermally nucleated using a low-temperature and high-pressure process under N2 atmosphere. Semi-coke is prepared using a two-stage low-speed temperature and pressure change process. Under N2 atmosphere, the semi-coke obtained above is calcined at high temperature and naturally cooled to obtain needle coke.

[0176] Specifically, the low-temperature and high-pressure process conditions are as follows: pressure is 3 MPa, under N2 atmosphere, temperature is increased to 410℃ at 1℃ / min, and the reaction is carried out at a constant temperature for 5 hours.

[0177] Two-stage low-speed heating and pressure transformation process: Under N2 atmosphere, pressure 2MPa, heating to 430℃ at a rate of 1℃ / min, and holding at that temperature for 7h; heating to 490℃ at a rate of 0.5℃ / min, reducing the pressure to 0.5MPa, holding at that temperature for 7h, and cooling to room temperature to obtain semi-coke.

[0178] The calcination conditions were: N2 rate of 50 mL / min. -1 The pressure was 0.2 MPa, the temperature was increased to 1450℃ at a rate of 1.5℃ / min, and the reaction was carried out at a constant temperature for 5 hours.

[0179] 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 determined.

[0180] The physical properties were tested using the following methods: ash content was determined according to GB / T 1429-2009 "Determination of Ash Content in Carbon Materials"; powder tap density was determined according to GB / T 21354-2008 "General Method for Determination of Tap Density of Powder Products"; resistivity was determined according to GB / T 24525-2009 "Determination of Resistivity in Carbon Materials"; and the coefficient of thermal expansion was determined according to GB / T 3074.4-2016 "Determination of Coefficient of Thermal Expansion (CTE) of Graphite Electrodes". Specific results are shown in Table 1.

[0181] Table 1. Physical properties of needle coke prepared in Examples 1-4 and comparative examples.

[0182]

[0183] Elemental analysis was performed on Examples 1 and 1 (Comparative Example 1) to determine the content of organic elements (O, N, S). The effect of using a mixed solvent (toluene and n-heptane) as an extractant on the removal of heteroatoms from medium- and low-temperature coal tar was investigated.

[0184] The content of each element in the raw material was determined using a German Elementar Vario MicroCube elemental analyzer.

[0185] Test conditions: CHNS mode, combustion tube temperature 1150℃, using high-temperature combustion for complete decomposition. The O element content was calculated by difference method, and the test results are shown in Table 2.

[0186] Table 2. Organic element (O, N, S) content of Example 1 and Comparative Example 1

[0187] O / ％ N / ％ S / ％ Example 1 7.2 0.83 0.42 Comparative Example 1 5.87 0.76 0.256

[0188] As can be seen from Tables 1 and 2, the needle coke obtained by the preparation method of this embodiment has an ash content ≤0.24% (low ash content), a resistivity less than 600 μΩ·m (low resistivity, with a minimum of 431 μΩ·m), and a coefficient of thermal expansion less than 1.5 × 10⁻⁶. -6 / ℃, minimum is 1.2×10 -6 The temperature is / ℃, and the coefficient of thermal expansion is low. This is because, firstly, a mixed solvent (toluene and n-heptane) is used as the extractant to remove heteroatoms from the medium- and low-temperature coal tar, further reducing the content of heteroatoms such as S, N, and O in the modified extraction pitch, thus deeply optimizing the raw material composition. Coke with low S and N content is less prone to crystal expansion during graphitization, and the product has almost no cracks. The resulting needle coke has small packing porosity, high true density, and low resistivity. Secondly, the hydrogenated tail oil is mixed with the medium- and low-temperature coal tar and then subjected to secondary extraction with wash oil to extract non-polar hydrocarbons from the coal tar, remove some of the colloids, asphaltenes, and a large amount of polar substances such as S, N, and O rich in polar groups from the coal tar, and increase the content of aromatics and cycloalkanes in the pitch. Finally, the introduction of a naphthalene-based interfacial dispersant helps to reduce the viscosity of the system and improve the dispersion ability. In the early stage of mesophase formation, the viscosity of the system is reduced, promoting the physical rearrangement of the aromatic layer, which lowers the surface energy and allows for full contact and fusion between the liquid phases, forming microspheres. In the later stage of mesophase formation, the dispersant is adsorbed onto the surface of the microspheres as a film, which expands the molecular structure of the microspheres, creates a steric hindrance effect, slows down the aggregation rate of the microspheres, and keeps the microspheres in a dispersed state for a long time, which is conducive to the growth and fusion of the microspheres. This results in a large-area mesophase asphalt with high anisotropy content, and the resulting needle coke has a fibrous structure, low coefficient of thermal expansion, and excellent performance.

[0189] Comparing Comparative Example 3 and Example 3, it can be seen that after adding a naphthalene-based interfacial dispersant during the preparation of mesophase pitch, the coefficient of thermal expansion decreased from 1.45 × 10⁻⁶. -6 / ℃ decreased to 1.28×10 -6 The temperature of / ℃ indicates that adding a naphthalene-based interfacial dispersant during the preparation of mesophase pitch can improve the quality of needle coke. Adding a dispersant is beneficial for producing mesophase pitch with high anisotropy content in large watersheds. The resulting needle coke has a predominantly fibrous structure, a low coefficient of thermal expansion, and good thermal shock resistance to rapid temperature changes.

[0190] Furthermore, the needle-shaped cokes prepared in Example 1 and Comparative Example 1 of this invention were subjected to polarizing microscopy and scanning electron microscopy to obtain polarized light microstructure images and scanning electron microscopy images, respectively. See [link to relevant documentation]. Figures 1-4 .

[0191] from Figure 1 and Figure 2 It can be seen that the needle-like coke obtained in Example 1 has a high content of fine fiber structure, a high degree of microstructural order, a large total fiber content, and a distinct and regular lamellar structure. This is because, in Example 1 provided by the present invention, firstly, the raw material asphalt is treated by a combination of two extraction processes, which can deeply optimize the raw material composition, so that the obtained needle-like coke is mainly composed of fibrous structure with small packing porosity, high true density, and low resistivity. Secondly, the naphthalene-based interfacial dispersant added during the thermal agglomeration nucleation process can obtain large-area mesophase asphalt with high anisotropy content, resulting in a high content of fine fiber structure in the obtained needle-like coke and a distinct and regular lamellar structure.

[0192] from Figure 3 and Figure 4 It can be seen that the needle coke obtained in Comparative Example 1 is mainly composed of short fibers, with low microstructural order, low total fiber content, and contains a very small amount of lamellar structure, which is irregular and the product has cracks. This further proves that compared with Example 1, the raw material pitch in Comparative Example 1, which did not undergo primary extraction, has low aromatic and cycloalkanes content and contains a large amount of unfavorable components such as S, N, and O. Coke with high S and N content will undergo crystal expansion during graphitization, causing cracks in the product. The resulting needle coke has a short fiber structure, low total fiber content, irregular lamellar structure, and cracks.

[0193] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent modifications or substitutions made by those skilled in the art within the scope of the technology described in the present invention should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing needle coke using a two-stage extraction process, characterized in that, Includes the following steps: 1) Atmospheric and vacuum cutting Medium- and low-temperature coal tar is divided into a 230℃~300℃ fraction and a ≥350℃ fraction by atmospheric and vacuum distillation; the 230℃~300℃ fraction is denoted as wash oil, and the ≥350℃ fraction is denoted as coal tar pitch component; 2) Preparation of hydrotreated tail oil Medium- and low-temperature coal tar is subjected to hydrotreating to obtain hydrotreated tail oil; then, distillate oil at 230~350℃ is obtained from the hydrotreated tail oil. 3) Two-stage extraction and refining 3.1) The coal tar pitch component obtained in step 1) is subjected to primary extraction to obtain medium-low temperature refined coal tar pitch; the mass ratio of coal tar pitch component to primary extractant is 1:3; the primary extractant is toluene and n-heptane obtained at a mass ratio of 4:1; the primary extraction process conditions are: extraction temperature 60~80℃, extraction time 1~3h, sedimentation time 2~4h; 3.2) The medium-low temperature coal tar refined pitch obtained in step 3.1) is mixed with the distillate oil at 230~350℃ in step 2) at a mass ratio of 9:1 to obtain the compound material; 3.3) Using the wash oil obtained in step 1) as a secondary extractant, the compound material obtained in step 3.2) is subjected to secondary extraction to obtain refined asphalt; the mass ratio of compound material to secondary extractant is 1:2; 3.4) The refined asphalt is fractionated to obtain light component solutions of the >300℃ fraction and the <300℃ fraction; the light component solution of the <300℃ fraction is subjected to reverse extraction to recover the wash oil. 4) Coking Step 3) The >300℃ fraction obtained is placed together with the naphthalene-based interfacial dispersant in a reaction vessel at a mass ratio of 10~15:1 and thermally agglomerates into nuclei under N2 atmosphere; a two-stage heating and pressure-switching process is used to obtain semi-coke; finally, needle coke is obtained by calcination and cooling.

2. The method for preparing needle coke using a two-stage extraction process according to claim 1, characterized in that, In step 2), the hydrogenation catalyst is Ni-Mo / Zr-ASA, with Ni being NiO and Mo being MoO3; the mass fractions of NiO and MoO3 are 1%-5% and 10%-15%, respectively.

3. The method for preparing needle coke using a two-stage extraction process according to claim 1, characterized in that, In step 3.3), the secondary extraction process conditions are: extraction temperature 180~220℃, extraction time 2~4h, and sedimentation time 3~6h.

4. The method for preparing needle coke using a two-stage extraction process according to claim 3, characterized in that, In step 3.4), the reverse extraction agent is N-methylpyrrolidone; the reverse extraction process conditions are: oil-to-agent ratio of 1:1, extraction temperature of 200-220℃, extraction time of 2-3h, and sedimentation time of 1-2h.

5. The method for preparing needle coke using a two-stage extraction process according to claim 4, characterized in that, In step 4), the process conditions for thermal polymerization are: pressure of 2~4MPa, heating to 400~420℃ at a rate of 1℃ / min, and constant temperature reaction for 3~6h.

6. The method for preparing needle coke using a two-stage extraction process according to claim 5, characterized in that, In step 4), the two-stage heating and pressure-changing process conditions are as follows: First, the pressure is 2.0 MPa, and the temperature is increased to 420~440℃ at a rate of 1℃ / min, and held at the temperature for 5~8h; second, the temperature is increased to 480~520℃ at a rate of 0.5℃ / min, the pressure is reduced to 0.5 MPa, and held at the temperature for 6~10h, and then cooled to room temperature to obtain semi-coke.

7. The method for preparing needle coke using a two-stage extraction process according to claim 6, characterized in that, In step 4), the calcination conditions are: the N2 introduction rate is 40~60 mL•min. -1 The pressure is 0.1~0.3MPa, the temperature is increased to 1450℃ at a rate of 1~2℃ / min, and the reaction is kept at a constant temperature for 3~6h.

8. A needle coke prepared by the two-stage extraction process as described in claim 1.

9. The needle-shaped coke according to claim 8, characterized in that, The needle coke has a volatile matter content ≤0.36%, an ash content ≤0.24%, a moisture content ≤0.15%, and an average resistivity as low as 431 μΩ•m. The tap density of the needle coke is 0.85~0.88 g / cm³. 3 .

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