A carbon fiber spinning precursor and a method for producing carbon fibers

Abstract

The application discloses a carbon fiber spinning precursor and a production method of carbon fiber. The production method of the carbon fiber spinning precursor comprises the following steps: (1) preparing a first pitch material flow; (2) obtaining a first extraction phase and a first raffinate phase after the first pitch material flow is treated with a first extraction agent; obtaining a first product after the first extraction phase is separated; (3) obtaining a second extraction phase and a second raffinate phase after the first raffinate phase is treated with a second extraction agent; obtaining a second product after the second extraction phase is separated; (4) obtaining a third extraction phase and a third raffinate phase after the second raffinate phase is treated with a third extraction agent; obtaining a third product after the third extraction phase is separated; and mixing the first product, the second product, the third product and the third raffinate phase to obtain the carbon fiber spinning precursor. The application further discloses a method for preparing carbon fiber by using the carbon fiber spinning precursor. The method can continuously produce pitch-based carbon fiber products with high tensile strength.

Description

Technical Field

[0001] This invention belongs to the field of carbon materials technology, and relates to a method for producing carbon fiber, particularly a method for producing high tensile strength pitch-based carbon fiber. Background Technology

[0002] Pitch-based carbon fiber possesses excellent properties such as high modulus, corrosion resistance, high temperature resistance, low coefficient of thermal expansion, lightweight, radiation resistance, anti-reflection, high thermal conductivity, electrical conductivity, and thermal conductivity, making it highly sought after in aerospace, military, and electronics industries. In recent years, my country has made significant progress in the scientific research and industrial production of carbon fiber; however, it still relies heavily on imports in the field of high-performance carbon fiber.

[0003] CN102733008A discloses a method for preparing spinnable mesophase and carbon fibers using coal direct liquefaction residue-based pitchene. The method uses coal direct liquefaction residue-based pitchene as raw material. First, the pitchene is ground, then placed in a high-temperature tubular furnace or high-pressure reactor under inert gas protection. After thermal polycondensation, the mesophase is obtained, which is then melt-spun, pre-oxidized, and carbonized to prepare carbon fibers.

[0004] CN112812802A discloses a continuous process for preparing mesophase asphalt from refined feedstock oil. The process uses one or more of the following as raw materials: aromatic heavy oil, catalytic slurry oil, coal tar, or ethylene tar. The process involves reducing pressure to obtain a heavy distillation fraction at a temperature greater than 300°C, and then sequentially passing the product through an ultrasonic-assisted filtration and deashing coupled enhanced extraction unit, a sedimentation unit, an oil-catalyst separation unit, and an integrated liquid-solid adsorption separation unit. Finally, the product undergoes co-carbonization treatment to obtain mesophase asphalt.

[0005] CN202210404871.4 discloses a method for preparing mesophase asphalt from hydrogenated tail oil. The hydrogenated tail oil is prepolymerized in an autoclave, and light component oils are removed by vacuum distillation to obtain prepolymerized asphalt. Co-carbonized asphalt is added to the prepolymerized asphalt and subjected to high-temperature, high-pressure thermal polymerization to obtain mesophase asphalt. The prepolymerization of the hydrogenated tail oil followed by co-carbonization with the asphalt facilitates hydrogen transfer, effectively controls the molecular composition and ordered structure of the mesophase asphalt, and increases carbon yield.

[0006] CN104946289A discloses a high softening point asphalt, its preparation method, and its application. Using medium-temperature asphalt as raw material, a high softening point asphalt is first prepared by air oxidation. Then, a portion of the light components in the high softening point asphalt is removed by vacuuming to obtain a high softening point asphalt suitable for preparing foamed carbon or spinning asphalt. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the main technical solution of this invention is to provide a carbon fiber spinning precursor and a method for producing carbon fibers. This method can use petroleum-based or coal-based raw materials to formulate and continuously produce pitch-based carbon fiber products. The continuously produced pitch-based carbon fibers have the advantage of high tensile strength and are suitable for preparing carbon / carbon, carbon / ceramic, and carbon / metal composite materials.

[0008] The first aspect of this invention provides a method for producing a carbon fiber spinning precursor, comprising the following steps:

[0009] (1) Under inert atmosphere conditions, the raw material oil enters the first reaction unit to undergo thermal polycondensation reaction, and the first asphalt material stream is obtained after the reaction;

[0010] (2) The first asphalt stream obtained in step (1) enters the primary extraction unit and is treated with the primary extractant to obtain the first extract phase and the first raffinate phase; the first extract phase is separated to obtain the reused primary extractant and the first product.

[0011] (3) The first raffinate obtained in step (2) enters the secondary extraction unit and is treated with the secondary extractant to obtain the second extract phase and the second raffinate; the second extract phase is separated to obtain the reused secondary extractant and the second product.

[0012] (4) The second raffinate obtained in step (3) enters the tertiary extraction unit and is treated with the tertiary extractant to obtain the third extract phase and the third raffinate phase; the third extract phase is separated to obtain the reused tertiary extractant and the third product.

[0013] (5) The first product obtained in step (2), the second product obtained in step (3), the third product obtained in step (4) and the third raffinate phase are mixed to obtain the carbon fiber spinning precursor.

[0014] Furthermore, as a specific implementation, the feedstock oil in step (1) can be a coal-based feedstock and / or a petroleum-based feedstock. More specifically, the coal-based feedstock can be at least one of coal tar pitch, coal liquefaction residue, etc., and the petroleum-based feedstock can be one or a mixture of two or more of ethylene tar, catalytic cracking slurry oil, catalytic cracking residue oil, and thermal cracking residue oil.

[0015] Furthermore, as a specific implementation method, the reaction conditions in step (1) are: temperature 350-500℃, preferably 380-480℃; pressure atmospheric pressure to 5MPa, preferably atmospheric pressure to 2.5MPa; and material residence time in the reactor is 0.1-50h, preferably 0.2-48h.

[0016] Furthermore, as a specific implementation, the inert atmosphere in step (1) can be nitrogen and / or an inert gas; wherein the inert gas is one or more of helium, neon, argon, krypton, and xenon.

[0017] Furthermore, as a specific embodiment, the primary extractant in step (2) can be one or a mixture of two or more of n-heptane, n-hexane, and acetone; preferably n-heptane and / or n-hexane.

[0018] Furthermore, as a specific implementation, the operating temperature of the extraction tower in the primary extraction unit in step (2) is 50 to 160°C, preferably 63 to 155°C.

[0019] Furthermore, as a specific embodiment, the secondary extractant in step (3) is one or more benzene compounds, specifically toluene, benzene, or a mixture of two or more of them, preferably toluene.

[0020] Furthermore, as a specific implementation, the second product obtained in step (3) can be divided into two streams. One stream is directly used as a precursor for carbon fiber spinning, while the other stream can enter the second reaction unit for reaction. The product obtained after the reaction is then processed in a tertiary extraction unit. The operating conditions of the second reaction unit are: temperature of 300–420°C, preferably 320–400°C; pressure of atmospheric pressure to 5 MPa, preferably atmospheric pressure to 2 MPa; and residence time of the material in the reactor of 0.1–50 h, preferably 0.2–35 h.

[0021] Furthermore, as a specific implementation, the operating temperature of the extraction tower in the secondary extraction unit in step (3) is 70 to 170°C, preferably 82 to 165°C.

[0022] Furthermore, as a specific implementation, the tertiary extractant in step (4) is one or more nitrogen-containing heterocyclic compounds; specifically, it can be one or a mixture of two or more of pyridine and quinoline.

[0023] Furthermore, as a specific implementation, the operating temperature of the extraction tower in the three-stage extraction unit in step (4) is 110 to 310°C, preferably 114 to 305°C.

[0024] Furthermore, as a specific embodiment, the weight ratio of the first product obtained in step (2), the second product obtained in step (3), the third product obtained in step (4), and the third raffinate phase in step (5) is 25%–50%: 10%–30%: 15%–40%: 1%–20%, preferably 25.5%–48%: 12%–25%: 16%–38%: 1.1%–18%.

[0025] Furthermore, in one specific embodiment, the average molecular weight of the first product is 150-220, preferably 155-225; the average molecular weight of the second product is 210-240, preferably 215-235; the average molecular weight of the third product is 230-340, preferably 235-335; and the average molecular weight of the third raffinate phase is 330-680, preferably 335-670.

[0026] Furthermore, as a specific implementation, the first product obtained in step (2) can also be partially recycled back to the first reaction unit.

[0027] Furthermore, as a specific implementation, the third product and the third raffinate obtained in step (4) can be used as raw materials for the production of petroleum coke, and the obtained petroleum coke can be used as a negative electrode material in the field of lithium batteries.

[0028] Furthermore, as a specific implementation, the carbon fiber spinning precursor obtained in step (5) has a softening point of 220-370°C, an anisotropic structure content of 90-99.9 wt%, and an ash content of less than 100 ppm.

[0029] A second aspect of the present invention provides a method for producing carbon fiber, comprising the following steps:

[0030] S1: Prepare carbon fiber spinning precursor, wherein the carbon fiber spinning precursor is prepared by the aforementioned production method;

[0031] S2: The carbon fiber spinning precursor enters the melt spinning device for spinning to obtain carbon fiber filament. The carbon fiber filament is then pre-oxidized, carbonized and graphitized to obtain pitch-based carbon fiber products.

[0032] Furthermore, as a specific embodiment, the operating conditions of the melt spinning device are: temperature of 190-360℃, preferably 200-355℃, pressure (gauge pressure) of 0-6MPa, preferably 0.1-5.5MPa, and winding roller speed of 200-1500rad / min, preferably 205-1400rad / min.

[0033] Furthermore, as a specific embodiment, the pre-oxidation operation temperature in step S2 is 160–340°C, preferably 165–335°C, and the heating rate is 0.2–10°C / min, preferably 0.5–8°C / min. The pre-oxidation operation is carried out under an oxygen-containing atmosphere, where the oxygen volume content is 0.1–40%. The oxygen-containing atmosphere can be one or more of air, oxygen, or a mixture of oxygen and an inert atmosphere; the inert atmosphere can be nitrogen and / or an inert gas; wherein the inert gas is one or more of helium, neon, argon, krypton, and xenon.

[0034] Furthermore, as a specific implementation, the carbonization in step S2 is carried out under an inert atmosphere, with a carbonization temperature of 400–1700°C, preferably 410–1650°C; and a carbonization time of 0.2–14 h. Preferably, the carbonization is carried out in two stages: the first stage carbonization temperature is 400–800°C, preferably 410–795°C, and the first stage carbonization time is 0.1–8 h, preferably 0.2–6 h; the second stage carbonization temperature is 800–1700°C, preferably 805–1650°C, and the second stage carbonization time is 0.1–6 h, preferably 0.2–5 h.

[0035] Furthermore, as a specific implementation, the graphitization operation temperature in step S2 is 2000-3000℃, preferably 2100-2950℃, thereby obtaining high-performance carbon fibers.

[0036] A third aspect of the present invention provides a carbon fiber prepared by the above method, wherein the carbon fiber has a tensile strength of 3.5 to 5.5 GPa and a tensile modulus of 200 to 340 GPa.

[0037] Compared with the prior art, the advantages of the carbon fiber spinning precursor and carbon fiber production method of the present invention are mainly reflected in the following aspects:

[0038] During the research process, the applicant discovered a contradiction between the softening point and the amount of macromolecular insoluble matter in carbon fiber spinning precursors. To obtain a high softening point spinning precursor, existing technologies inevitably increase the content of macromolecular insoluble matter, which affects the quality of the carbon fiber product. In this invention, the inventors discovered that by performing multi-stage extraction at the molecular level on the mesophase pitch raw material, the molecular composition and ordered structure of the spinning precursor are improved. In particular, the addition of a second reaction unit allows some of the second product to be reacted in the second reaction unit and then introduced into a tertiary extraction unit for extraction together with the second raffinate phase. This allows for the control of the composition and proportion of the third product, thereby increasing the softening point of the spinning precursor while limiting the amount of insoluble product in the tertiary extraction unit. The obtained components are then blended in a certain proportion and used as a precursor for carbon fiber production. This effectively solves the dilemma of the incompatibility between softening point and macromolecular insoluble matter content, and addresses the problem of increased macromolecular insoluble matter content accompanying high softening point during preparation. It also solves the problem that existing methods cannot finely control the structure and properties of the spinning precursor, thus failing to achieve precise control of fiber properties.

[0039] Instruction manual illustrations

[0040] Figure 1 This is a schematic diagram of the production process of the carbon fiber spinning precursor and carbon fiber of the present invention.

[0041] Figure 2 A schematic diagram of the carbon fiber production process for Comparative Example 1. Detailed Implementation

[0042] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the following embodiments do not constitute a limitation of the present invention.

[0043] like Figure 1 The present invention provides a method for producing a carbon fiber spinning precursor. The specific workflow is as follows: raw material oil 1 enters a heating furnace 2 for heating; the heated raw material oil 3 enters a first reaction unit 4 for thermal polycondensation under an inert atmosphere, resulting in a first pitch stream 5. The first pitch stream 5 enters a primary extraction unit, which includes a primary extraction tower 7 and a primary fractionation tower 10. The first pitch stream 5 is treated with a primary extractant 11 to obtain a first extract phase 9 and a first raffinate phase 8. The first extract phase 9 enters the primary fractionation tower 10 for separation to obtain a reused primary extractant 11 and a first product 6. The first product 6 can be divided into two streams: one stream, first product 13, is used as a carbon fiber spinning precursor; when the first product is in excess, the other stream, first product 12, can be returned to the first reaction unit for further processing. The first raffinate phase 8 is fed into a secondary extraction unit, which includes a secondary extraction tower 14 and a secondary fractionation tower 17. After contact treatment with the secondary extractant 18, a second extract phase 16 and a second raffinate phase 15 are obtained. The second extract phase 16 is fed into the secondary fractionation tower 17 for separation to obtain the reused secondary extractant 18 and a second product. The second product can be divided into two paths. One path, the second product 20, can be directly used as a precursor for carbon fiber spinning. The other path, the second product 19, can be fed into the second reaction unit 21 for reaction. The product 22 obtained after the reaction is fed into the tertiary extraction tower 23 in the tertiary extraction unit for processing. The obtained second raffinate phase 15 enters the tertiary extraction unit, which includes a tertiary extraction tower 23 and a tertiary fractionation tower 26. After contact treatment with the tertiary extractant 27, the third extract phase 25 and the third raffinate phase 24 are obtained. The third extract phase 25 enters the tertiary fractionation tower 26 for separation, yielding the recycled tertiary extractant 27 and the third product 28. The mixture of the first product 13, the second product 20, the third product 28, and the third raffinate phase 24 is used as the carbon fiber spinning precursor 29. Further, the carbon fiber spinning precursor 29 enters the mixing device 30 for uniform mixing, and then enters the melt spinning device 31 for spinning to obtain carbon fiber precursor 32. The carbon fiber precursor 32 is pre-oxidized, carbonized, and graphitized to obtain pitch-based carbon fiber product 33.

[0044] In this paper, tensile strength and tensile modulus were determined according to the method of GB / T 31290-2014.

[0045] In this paper, the softening point was determined using the method of GB / T 4507-2014.

[0046] In this paper, the average molecular weight was determined using the VPO molecular weight determination method.

[0047] The properties of the raw materials used in this paper are shown in Table 1.

[0048] Table 1 Properties of Raw Materials

[0049] Property Indicators raw material Density, g / cm3 1.0816 Ash content, wt% 0.013 C, wt% 90.85 H, wt% 8.23 S, wt% 0.52 N, ppm 1998 H / C atomic ratio 1.09 Four components, wt% Saturated fraction 13.85 Aromatic components 81.04 gelatinous 4.23 Asphalt 0.88

[0050] Example 1

[0051] use Figure 1 The production process shown involves two streams of the second product. One stream, second product 20, is directly used as a precursor for carbon fiber spinning, while the other stream, second product 19, enters the second reaction unit 21 for reaction. The resulting product 22 is then processed in the third-stage extraction tower 23 of the third-stage extraction unit. The properties of the raw materials are shown in Table 1. The primary extractant is n-heptane, the secondary extractant is toluene, and the tertiary extractant is quinoline. Under the operating conditions shown in Table 2, the first product, second product, third product, and third raffinate phase are obtained. 48% of the first product (average molecular weight 203), 25 wt% of the second product (average molecular weight 231), 20 wt% of the third product (average molecular weight 328), and 7 wt% of the third raffinate phase (average molecular weight 592) are mixed to obtain the spinning precursor. This precursor is then melt-spun at 320℃, 3 MPa, and 600 rad / min to obtain carbon fiber filaments. Pre-oxidation was carried out in air at a temperature of 280℃ and a heating rate of 1℃ / min; then, carbonization was carried out at a low temperature of 600℃ for 0.2h in a nitrogen atmosphere, followed by high-temperature carbonization at 1400℃ for 0.5h, and finally graphitization at 2800℃ to obtain carbon fiber products with a tensile strength of 5.5GPa and a tensile modulus of 340GPa.

[0052] Table 2 Basic Operating Conditions

[0053] Temperature (°C) Pressure (MPa) Time (h) First reaction unit 420 2 10 Second reaction unit 360 1 8 Primary extraction tower 80 Atmospheric pressure continuous Secondary extraction tower 150 Atmospheric pressure continuous Three-stage extraction tower 230 Atmospheric pressure continuous

[0054] Example 2

[0055] use Figure 1The production process shown differs in that a second reaction unit is not set up, and the second product is not divided into two streams; the second product is directly used as the carbon fiber spinning precursor. The raw material properties are shown in Table 1. The primary extractant is n-heptane, the secondary extractant is toluene, and the tertiary extractant is quinoline. Under the operating conditions shown in Table 3, the first product, second product, third product, and third raffinate phase are obtained, respectively. 48 wt% of the first product (average molecular weight 203), 25 wt% of the second product (average molecular weight 231), and 20 wt% of the third product (average molecular weight 235) are mixed with 7 wt% of the third raffinate phase (average molecular weight 662) to obtain the spinning precursor. This precursor is then melt-spun at 290℃, 3 MPa, and 600 rad / min to obtain carbon fiber filaments. Pre-oxidation was carried out in air at a temperature of 280℃ and a heating rate of 1℃ / min; then, carbonization was carried out at a low temperature of 600℃ for 0.2h in a nitrogen atmosphere, followed by high-temperature carbonization at 1400℃ for 0.5h, and finally graphitization at 2800℃ to obtain carbon fiber products with a tensile strength of 1.3GPa and a tensile modulus of 120GPa.

[0056] Table 3 Basic Operating Conditions

[0057] Temperature (°C) Pressure (MPa) Time (h) First reaction unit 420 2 10 Primary extraction tower 80 Atmospheric pressure continuous Secondary extraction tower 150 Atmospheric pressure continuous Three-stage extraction tower 230 Atmospheric pressure continuous

[0058] Example 3

[0059] use Figure 1 The production process shown involves two streams of the second product. One stream, second product 20, is directly used as a precursor for carbon fiber spinning, while the other stream, second product 19, enters the second reaction unit 21 for reaction. The resulting product 22 is then processed in the tertiary extraction tower 23 of the tertiary extraction unit. The primary extractant is n-heptane, the secondary extractant is toluene, and the tertiary extractant is quinoline. Under the operating conditions shown in Table 4, the first product, second product, third product, and third raffinate phase are obtained. A spinning precursor is obtained by mixing 30 wt% of the first product (average molecular weight 175), 25 wt% of the second product (average molecular weight 215), and 25 wt% of the third product (average molecular weight 255) with 10 wt% of the third raffinate phase (average molecular weight 468). This precursor is then melt-spun at 300°C, 3 MPa, and 600 rad / min to obtain carbon fiber filaments. Pre-oxidation was carried out in air at a temperature of 280℃ and a heating rate of 1℃ / min; then, carbonization was carried out at a low temperature of 600℃ for 0.2h in a nitrogen atmosphere, followed by high-temperature carbonization at 1400℃ for 0.5h, and finally graphitization at 2800℃ to obtain carbon fiber products with a tensile strength of 3.2GPa and a tensile modulus of 190GPa.

[0060] Table 4 Basic Operating Conditions

[0061] Temperature (°C) Pressure (MPa) Time (h) First reaction unit 440 1 20 Second reaction unit 380 2 6 Primary extraction tower 80 Atmospheric pressure continuous Secondary extraction tower 150 Atmospheric pressure continuous Three-stage extraction tower 230 Atmospheric pressure continuous

[0062] Example 4

[0063] use Figure 1 The production process shown involves two streams of the second product. One stream, second product 20, is directly used as a precursor for carbon fiber spinning, while the other stream, second product 19, enters the second reaction unit 21 for reaction. The resulting product 22 is then processed in the tertiary extraction tower 23 of the tertiary extraction unit. The primary extractant is n-hexane, the secondary extractant is benzene, and the tertiary extractant is pyridine. Under the operating conditions shown in Table 5, the first product, second product, third product, and third raffinate phase are obtained. A spinning precursor is obtained by mixing 25 wt% of the first product (average molecular weight 220), 15 wt% of the second product (average molecular weight 235), 40 wt% of the third product (average molecular weight 335), and 20 wt% of the third raffinate phase (average molecular weight 668). This precursor is then melt-spun at 360°C, 3 MPa, and 600 rad / min to obtain carbon fiber filaments. Pre-oxidation was carried out in air at a temperature of 340℃ and a heating rate of 1℃ / min; then, carbonization was carried out at a low temperature of 600℃ for 0.2h in a nitrogen atmosphere, followed by high-temperature carbonization at 1400℃ for 0.5h, and finally graphitization at 2800℃ to obtain carbon fiber products with a tensile strength of 2.3GPa and a tensile modulus of 160GPa.

[0064] Table 5 Basic Operating Conditions

[0065] Temperature (°C) Pressure (MPa) Time (h) First reaction unit 480 1 42 Second reaction unit 320 2 20 Primary extraction tower 135 Atmospheric pressure continuous Secondary extraction tower 140 Atmospheric pressure continuous Three-stage extraction tower 280 Atmospheric pressure continuous

[0066] Comparative Example 1

[0067] use Figure 2 The production process shown involves the following steps: Raw material oil 1 is heated in furnace 2, and the heated raw material oil 3 enters the first reaction unit 4 for thermal polycondensation under an inert atmosphere, yielding carbon fiber spinning precursor 5. Further, the carbon fiber spinning precursor 5 is mixed evenly in a mixing device 6 and then spun in a melt spinning device 7 to obtain carbon fiber filament 8. The carbon fiber filament 8 undergoes pre-oxidation, carbonization, and graphitization treatments to obtain carbon fiber 9. The operating conditions are: reaction tower temperature 460℃, pressure 1MPa, residence time 10h; and the spinning precursor is melt-spun at 320℃, 3MPa, and 600rad / min to obtain carbon fiber filament. Pre-oxidation was carried out in air at a temperature of 280℃ and a heating rate of 1℃ / min; then, carbonization was carried out at a low temperature of 600℃ for 0.2h in a nitrogen atmosphere, followed by high-temperature carbonization at 1400℃ for 0.5h, and finally graphitization at 2800℃ to obtain carbon fiber products with a tensile strength of 0.3GPa and a tensile modulus of 60GPa.

[0068] Comparative Example 2

[0069] use Figure 1 The production process shown is the same as in Example 1, yielding a first product, a second product, a third product, and a third raffinate phase. 20% of the first product (average molecular weight 203), 8 wt% of the second product (average molecular weight 231), 12 wt% of the third product (average molecular weight 328), and 60 wt% of the third raffinate phase (average molecular weight 592) are mixed to obtain a spinning precursor. This precursor is then melt-spun at 360°C, 3 MPa, and 600 rad / min to obtain carbon fiber filaments. Pre-oxidation is performed in air at 240°C with a heating rate of 1°C / min. After low-temperature carbonization at 600°C for 0.2 h in a nitrogen atmosphere, followed by high-temperature carbonization at 1400°C for 0.5 h, and then graphitization at 2800°C, a carbon fiber product is obtained with a tensile strength of 0.4 GPa and a tensile modulus of 100 GPa.

Claims

1. A method for producing a carbon fiber spinning precursor, comprising the following steps: (1) Under inert atmosphere conditions, the raw material oil enters the first reaction unit to undergo thermal polycondensation reaction, and the first asphalt material stream is obtained after the reaction; (2) The first asphalt material obtained in step (1) enters the primary extraction unit and is treated with the primary extractant to obtain the first extract phase and the first raffinate phase; the first extract phase is separated to obtain the reused primary extractant and the first product; the primary extractant is one or a mixture of two or more of n-heptane, n-hexane and acetone. (3) The first raffinate obtained in step (2) enters the secondary extraction unit and is treated with the secondary extractant to obtain the second extract phase and the second raffinate. After the second extract phase is separated, the secondary extractant and the second product are obtained. The secondary extractant is one or more of the benzene series compounds. The second product is divided into two paths, one of which is directly used as a carbon fiber spinning precursor, and the other enters the second reaction unit for reaction. The product obtained after the reaction enters the tertiary extraction unit for treatment. (4) The second raffinate obtained in step (3) enters the tertiary extraction unit and is treated with the tertiary extractant to obtain the third extract phase and the third raffinate phase; the third extract phase is separated to obtain the reused tertiary extractant and the third product; the tertiary extractant is one or more nitrogen-containing heterocyclic compounds. (5) The first product obtained in step (2), the second product obtained in step (3), the third product obtained in step (4) and the third raffinate phase are mixed to obtain a carbon fiber spinning precursor; the weight ratio of the first product obtained in step (2), the second product obtained in step (3), the third product obtained in step (4) and the third raffinate phase is 25%~50%: 10%~30%: 15%~40%: 1%~20%; the average molecular weight of the first product is 150~220, the average molecular weight of the second product is 210~240, the average molecular weight of the third product is 255~340, and the average molecular weight of the third raffinate phase is 330~680.

2. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The feedstock in step (1) is a coal-based feedstock and / or a petroleum-based feedstock. The coal-based feedstock is at least one of coal tar pitch and coal liquefaction residue. The petroleum-based feedstock is one or a mixture of two or more of ethylene tar, catalytic cracking slurry oil, catalytic cracking residue oil, and thermal cracking residue oil.

3. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The reaction conditions in step (1) are: temperature of 350-500℃, pressure of atmospheric pressure to 5MPa, and residence time of the material in the reactor of 0.1-50h.

4. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The reaction conditions in step (1) are: temperature of 380-480℃; pressure of atmospheric pressure to 2.5MPa; and residence time of the material in the reactor of 0.2-48h.

5. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The inert atmosphere in step (1) is nitrogen and / or an inert gas; wherein the inert gas is one or more of helium, neon, argon, krypton, and xenon.

6. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The primary extractant in step (2) is n-heptane and / or n-hexane.

7. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The operating temperature of the extraction tower in the primary extraction unit in step (2) is 50–160 °C.

8. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The operating temperature of the extraction tower in the primary extraction unit in step (2) is 63-155℃.

9. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The secondary extractant in step (3) is one or a mixture of two or more of toluene and benzene.

10. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The secondary extractant in step (3) is toluene.

11. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The operating conditions for the second reaction unit are: temperature 300–420℃, pressure atmospheric pressure to 5 MPa, and material residence time in the reactor 0.1–50 h.

12. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The operating conditions for the second reaction unit are: temperature 320–400℃, pressure atmospheric pressure to 2 MPa, and material residence time in the reactor 0.2–35 h.

13. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The operating temperature of the extraction tower in the secondary extraction unit in step (3) is 70 to 170°C.

14. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The operating temperature of the extraction tower in the secondary extraction unit in step (3) is 82-165℃.

15. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The tertiary extractant in step (4) is one or both of pyridine and quinoline.

16. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The operating temperature of the extraction tower in the three-stage extraction unit in step (4) is 110 to 310°C.

17. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The operating temperature of the extraction tower in the three-stage extraction unit in step (4) is 114–305 °C.

18. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The weight ratio of the first product obtained in step (2), the second product obtained in step (3), the third product obtained in step (4), and the third raffinate phase in step (5) is 25.5%–48%: 12%–25%: 16%–38%: 1.1%–18%.

19. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The average molecular weight of the first product is 155–225, the average molecular weight of the second product is 215–235, the average molecular weight of the third product is 255–335, and the average molecular weight of the third raffinate is 335–670.

20. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The first product obtained in step (2) is partially recycled back to the first reaction unit.

21. The method for producing the carbon fiber spinning precursor according to claim 1, characterized in that: The carbon fiber spinning precursor obtained in step (5) has a softening point of 220-370℃, an anisotropic structure content of 90-99.9wt%, and an ash content of less than 100ppm.

22. A method for producing carbon fiber, comprising the following steps: S1: Prepare carbon fiber spinning precursor, wherein the carbon fiber spinning precursor is prepared by the production method described in any one of claims 1-21; S2: The carbon fiber spinning precursor enters the melt spinning device for spinning to obtain carbon fiber filament. The carbon fiber filament is then pre-oxidized, carbonized and graphitized to obtain pitch-based carbon fiber products.

23. The method for producing carbon fiber according to claim 22, characterized in that: The operating conditions for the melt spinning device are: temperature 190–360℃ and pressure 0–6 MPa.

24. The method for producing carbon fiber according to claim 22, characterized in that: The operating conditions for the melt spinning device are: temperature 200–355℃ and pressure 0.1–5.5 MPa.

25. The method for producing carbon fiber according to claim 22, characterized in that: The pre-oxidation operation temperature in step S2 is 160–340 °C.

26. The method for producing carbon fiber according to claim 22, characterized in that: The pre-oxidation operation temperature in step S2 is 165–335 °C.

27. The method for producing carbon fiber according to claim 22 or 26, characterized in that: The pre-oxidation operation is carried out under an oxygen-containing atmosphere, wherein the oxygen volume content of the oxygen-containing atmosphere is 0.1% to 40%, and the oxygen-containing atmosphere is one or more of the mixture of air, oxygen and an inert atmosphere; the inert atmosphere is nitrogen and / or an inert gas; wherein the inert gas is one or more of helium, neon, argon, krypton and xenon.

28. The method for producing carbon fiber according to claim 22, characterized in that: The carbonization in step S2 is carried out under an inert atmosphere, with a carbonization temperature of 400–1700℃ and a carbonization time of 0.2–14h.

29. The method for producing carbon fiber according to claim 22, characterized in that: The carbonization in step S2 is carried out under an inert atmosphere, with a carbonization temperature of 410–1650 °C and a carbonization time of 0.2–14 h.

30. The method for producing carbon fiber according to claim 22, characterized in that: The carbonization in step S2 is carried out in two stages. The first stage carbonization temperature is 400-800℃ and the first stage carbonization time is 0.1-8h. The second stage carbonization temperature is 800-1700℃ and the second stage carbonization time is 0.1-6h.

31. The method for producing carbon fiber according to claim 22, characterized in that: The carbonization in step S2 is carried out in two stages. The first stage carbonization temperature is 410-795℃ and the first stage carbonization time is 0.2-6h. The second stage carbonization temperature is 805-1650℃ and the second stage carbonization time is 0.2-5h.

32. The method for producing carbon fiber according to claim 22, characterized in that: The graphitization operation temperature in step S2 is 2000–3000℃.

33. The method for producing carbon fiber according to claim 22, characterized in that: The graphitization operation temperature in step S2 is 2100–2950 °C.

34. A carbon fiber obtained by the production method of the carbon fiber according to any one of claims 22-33.

35. The carbon fiber according to claim 34, characterized in that: The tensile strength of carbon fiber is 3.5–5.5 GPa, and the tensile modulus is 200–340 GPa.

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