A pitch-based carbon fiber and a method for producing the same

Abstract

The present application provides a pitch-based activated carbon fiber comprising a sheath-core structure; the core layer of the sheath-core structure is anisotropic carbon; the sheath layer of the sheath-core structure is isotropic carbon; between the core layer and the sheath layer, there is a mixed transition layer which is transitioned from anisotropic carbon to isotropic carbon along the direction from the core layer to the sheath layer; and the surface of the sheath layer is covered with nano-scale pores. The present application also provides a preparation method of the pitch-based activated carbon fiber.

Description

Technical Field

[0001] This invention relates to the field of materials and their preparation technology, and in particular to a high-strength pitch-based activated carbon fiber and its preparation method. Background Technology

[0002] Activated carbon fiber, as a third-generation activated carbon material, exhibits adsorption performance far superior to traditional powdered and granular activated carbon, and also possesses better mechanical properties and processing advantages. It is currently widely used in gas purification, solvent recovery, water treatment, and toxic gas filtration. However, due to the surface porosity of activated carbon fibers, their strength is generally low, especially when the specific surface area exceeds 500 m² / g. 2 After / g, its tensile strength decreases to only 30-200MPa.

[0003] To address the issue of low strength in activated carbon fibers, the existing solutions are as follows:

[0004] Activated carbon fibers are prepared using polyacrylonitrile-based carbon fibers. Polyacrylonitrile-based carbon fibers have high strength and are generally used to prepare high-strength activated carbon fibers. However, the activation of polyacrylonitrile-based carbon fibers is difficult to control and has a high overall cost. Furthermore, when the specific surface area of ​​polyacrylonitrile-based carbon fibers exceeds 1000 m², the activation process becomes more complex. 2 When the strength is reduced to a certain value, its strength properties will also decrease significantly.

[0005] Benefiting from the aromatic heterocyclic conjugation effect of polyimide, patent CN201210334784.2 uses polyimide fiber as raw material, and obtains activated carbon fiber with good strength through carbonization and activation. However, polyimide fiber has a high cost and is not suitable for large-scale industrialization.

[0006] Activated carbon fibers are prepared using viscose-based activated carbon fibers. Viscose-based activated carbon fibers are easy to activate and inexpensive, and have long been commonly used in the preparation of activated carbon fibers. However, because using them as raw materials requires the use of catalysts for catalytic curing, the production process is highly polluting and is becoming increasingly obsolete.

[0007] Patent CN201710834671.1 discloses a method for preparing activated carbon fibers using mesophase pitch (anisotropic pitch). The fibers have relatively high strength, but the anisotropic carbon is difficult to activate, and the high modulus makes the fibers brittle and easy to break.

[0008] In view of this, a new technical solution is needed to solve the above-mentioned technical problems. Summary of the Invention

[0009] The first objective of this invention is to provide a carbon fiber with high specific surface area and high tensile strength.

[0010] The second objective of this invention is to provide a method for preparing carbon fibers with high specific surface area and high tensile strength.

[0011] To achieve the above objectives, the present invention employs the following technical means:

[0012] A pitch-based carbon fiber, comprising a core-sheath structure; the core layer of the core-sheath structure is anisotropic carbon; the sheath layer of the core-sheath structure is isotropic carbon; between the core layer and the sheath layer is a mixed transition layer that transitions from anisotropic carbon to isotropic carbon along the direction from the core layer to the sheath layer; the surface of the sheath layer is covered with nanoscale pores.

[0013] Preferably, the diameter of the pitch-based carbon fiber is 5-18 μm.

[0014] Preferably, the thickness of the skin layer is 0.002-0.05 μm.

[0015] Preferably, the thickness of the hybrid transition layer is 0.3-2.5 μm.

[0016] Preferably, the diameter of the core layer is 4-16 μm.

[0017] Preferably, the depth of the micropores is less than or equal to 0.05 μm.

[0018] A method for preparing pitch-based carbon fiber includes the following steps:

[0019] Asphalt fibers are obtained by screw melt extrusion, spinning, spinning and winding of raw material A and raw material B; the asphalt fibers are then subjected to oxidation, a first heat treatment at 450-800℃, activation, and a second heat treatment at 1000-1600℃ to obtain the asphalt-based carbon fibers; raw material A is isotropic oxidized asphalt, raw material B is anisotropic asphalt, and the softening temperature of raw material A is lower than that of raw material B, and the temperature difference between the softening temperatures of raw material A and raw material B is less than 5℃.

[0020] Preferably, the isotropic oxidized asphalt has a softening point of 250-280℃, an ash content of less than 80ppm, and an oxygen content of less than 1.5%.

[0021] Preferably, the softening point of the anisotropic asphalt is 250-285℃, and the ash content is less than 30ppm;

[0022] Preferably, the weight ratio of raw material A to raw material B is 5:95-25:75;

[0023] Preferably, the temperature of the screw melt extrusion is 280-320℃.

[0024] Preferably, the spinneret temperature is 260-320°C, the spinning temperature is 280-340°C, and the spinneret temperature is 20-40°C lower than the spinning temperature.

[0025] Preferably, the spinning speed is 0.06-0.15 g / min / H, where H is the number of spinneret holes in the spinneret used for spinning.

[0026] Preferably, the spinning pressure is 0.3-2 MPa, the winding speed is 500-1000 m / min, the oxidation temperature is 180-320℃, the oxidation time is 90-400 min, and the oxidation atmosphere is air.

[0027] Preferably, the activation temperature is 550-1000℃, the activation time is 5-60 min, and the activation atmosphere is water vapor or carbon dioxide.

[0028] Preferably, the spinneret includes guide holes, expansion holes, and micro-holes. The guide holes, expansion holes, and micro-holes are connected in sequence. The guide holes have an inverted funnel-shaped structure with a height of 1-3 mm, an upper diameter of 2-3.5 mm, and a lower diameter of 1.5-3 mm.

[0029] Preferably, the enlarged hole has an inverted flared opening structure, with a height of 2-5mm, an upper diameter of 1.5-3mm, and a lower diameter of 0.15-0.3mm.

[0030] Preferably, the diameter of the micropore is 0.15-0.3 mm, and the aspect ratio of the micropore is 1:1-5:1.

[0031] Compared with existing technologies, the beneficial effects of this invention are as follows:

[0032] 1. The pitch-based carbon fiber provided by this invention has a core-sheath structure, which is easily activated, allowing the specific surface area of ​​the pitch-based carbon fiber to reach 1350 m². 2 / g, its core layer has high strength, which can make the tensile strength of the single filament of pitch-based carbon fiber reach 750MPa.

[0033] 2. The method described in this invention improves the separation of isotropic components in the asphalt fiber formation process and forms a core-shell structure fiber with isotropic asphalt encapsulating an anisotropic asphalt core. After subsequent processing, the resulting isotropic carbon skin has well-developed pores, while the anisotropic carbon core layer has molecular orientation characteristics and high strength. The presence of the mixed transition carbon layer in between makes it difficult for surface defects to diffuse into the fiber interior. While obtaining a high specific surface area, it still retains high strength characteristics, thus improving the strength of activated carbon fibers.

[0034] 3. The use of isotropic pitch in this invention makes it easier to activate the carbon fibers prepared, and the control of the pore structure is simpler. By adjusting the oxidation process, activated carbon fibers with high specific surface area can be obtained without the use of a catalyst.

[0035] 4. The preparation method provided by this invention is simple to implement, has mature technology, and is low in cost. Attached Figure Description

[0036] Figure 1 A micrograph of the pitch-based carbon fiber prepared in Example 1 is shown. Detailed Implementation

[0037] This invention provides a pitch-based carbon fiber comprising a core-sheath structure; wherein the core layer of the core-sheath structure is anisotropic carbon, and the sheath layer is isotropic carbon. Anisotropic carbon has high strength, and as the core layer, it can improve the tensile strength of the pitch-based carbon fiber monofilament. The isotropic carbon sheath layer with nanoscale pores on its surface can increase the specific surface area of ​​the pitch-based carbon fiber. The mixed transition layer is naturally formed during the preparation of the pitch-based carbon fiber; there are no clear boundaries between the core layer, the mixed transition layer, and the sheath layer, and they are tightly bonded together.

[0038] In some specific embodiments of the present invention, the diameter of the pitch-based carbon fiber is 5-18 μm, preferably 10-16 μm. The smaller the diameter of the pitch-based carbon fiber, the more demanding the preparation process and parameters, resulting in higher preparation costs, and the strength of the pitch-based carbon fiber will also decrease as its diameter decreases; conversely, if the diameter of the pitch-based carbon fiber is too high, its strength will also decrease, and its specific surface area will also decrease accordingly.

[0039] Specifically, the thickness of the skin layer is 0.002-0.05 μm. The thinner the skin layer, the higher the specific surface area of ​​the pitch-based carbon fiber. When the thickness of the skin layer is greater than 0.05 μm, the depth of the micropores on its surface decreases, and the specific surface area of ​​the pitch-based carbon fiber tends to decrease.

[0040] Specifically, the thickness of the mixed transition layer is 0.3-2.5 μm, preferably 0.3-1.5 μm. A thickness less than 0.3 μm may prevent the formation of a skin layer on the surface of the pitch-based carbon fiber during preparation, while a thickness exceeding 1.5 μm will lead to a decrease in the strength of the pitch-based carbon fiber.

[0041] Specifically, the diameter of the core layer is 4-16 μm, preferably 6-14 μm. When the diameter of the core layer is less than 4 μm, the strength of the pitch-based carbon fiber will decrease. When the diameter of the core layer is greater than 16 μm, the strength of the pitch-based carbon fiber will also decrease, and the specific surface area will decrease accordingly.

[0042] Specifically, the depth of the micropores is less than or equal to 0.05 μm. If the depth of the micropores is too large, it will damage the structure of the core layer, thereby reducing the strength of the pitch-based carbon fiber.

[0043] This invention also provides a method for preparing the aforementioned pitch-based carbon fiber, comprising the following steps: raw material A and raw material B are melt-extruded by a screw extruder, spun, spun, and wound to obtain pitch fiber; the pitch fiber is then subjected to oxidation, a first heat treatment at 450-800℃, activation, and a second heat treatment at 1000-1600℃ to obtain the pitch-based carbon fiber; raw material A is isotropic oxidized pitch, and raw material B is anisotropic pitch; furthermore, the softening temperature of raw material A is lower than that of raw material B, and the temperature difference between the softening temperatures of raw material A and raw material B is less than 5℃. After raw material A and raw material B are melt-mixed in a twin-screw extruder, a relatively uniform melt can be obtained. The melt passes through a material dispersion chamber filled with metal sand to further homogenize the temperature of the melt. Since the viscosity of pitch is greatly affected by temperature, when the melt is spun through a spinneret, the low-viscosity isotropic pitch easily disperses to the pore walls within the micropores, while the high-viscosity anisotropic pitch easily aggregates at the center of the micropores, thereby obtaining pitch fiber with a core-sheath structure.

[0044] Specifically, the softening point of the isotropic oxidized pitch is 250-280℃, the ash content is less than 80ppm, and the oxygen content is less than 1.5%. The softening point of conventional isotropic spinning pitch is 250-280℃. If the softening temperature is too low, the residual carbon in the pitch will be low, leading to a low carbon fiber yield and consequently affecting the strength of the prepared carbon fibers. Conversely, if the softening temperature is too high, the production process will require more sophisticated equipment, thus increasing production costs. The ash content of the isotropic oxidized pitch should not exceed 100ppm, otherwise it will affect the strength of the carbon fibers. Furthermore, the lower the ash content of the isotropic oxidized pitch, the higher the strength of the prepared carbon fibers. The oxygen content of the isotropic oxidized pitch should be less than 1.5% to prevent the softening point from being too high.

[0045] Specifically, the softening point of the anisotropic asphalt is 250-285℃, and the ash content is less than 30ppm. If the softening temperature is too low, the residual carbon in the asphalt will be low, leading to a low carbon fiber yield and consequently affecting the strength of the prepared carbon fibers. Conversely, if the softening temperature is too high, the production process requires more sophisticated equipment, thus increasing production costs. The ash content of the isotropic oxidized asphalt must not exceed 50ppm, otherwise it will affect the strength of the carbon fibers. Furthermore, the lower the ash content of the isotropic oxidized asphalt, the higher the strength of the prepared carbon fibers.

[0046] Specifically, the weight ratio of raw material A to raw material B is 5:95-25:75. If the specific gravity of raw material A is too low, the core-sheath structure cannot be prepared; if the specific gravity of raw material A is too high, the strength of the prepared carbon fiber will be reduced.

[0047] Specifically, the temperature of the screw melt extrusion is 280-320℃. The viscosity of the molten asphalt extruded at this temperature is 50-10 Pa·s, which makes it easier to achieve uniform mixing of raw material A and raw material B.

[0048] Specifically, the spinneret temperature is 260-320℃, the spinning temperature is 280-340℃, and the spinneret temperature is 20-40℃ lower than the spinning temperature. The spinneret temperature is the setting temperature of the pitch fiber. If the spinneret temperature is too high, the pitch fiber will stick to the surface of the spinneret; if the spinneret temperature is too low, the spinning pressure will increase. When the spinning temperature is 280-340℃, the corresponding pitch viscosity is 10-2.5 Pa·s, which facilitates the flow of isotropic pitch to the micropore walls.

[0049] Specifically, the spinning speed is 0.06-0.15 g / min / H, where H is the number of spinneret orifices. The spinning speed must correspond to the spinning pressure and the diameter of the spinneret orifices.

[0050] Specifically, the spinning pressure is 0.3-2 MPa, and the take-up speed is 500-1000 m / min. Excessive spinning pressure can cause decomposition gases generated by material decomposition to dissolve in the material, ultimately leading to fiber defects; insufficient spinning pressure is detrimental to stable spinning. Excessive take-up speed places high demands on the take-up equipment, and excessively high rotation speeds are also detrimental to equipment dynamic balance, ultimately resulting in unstable take-up; insufficient take-up speed reduces efficiency.

[0051] Specifically, the oxidation temperature is 180-320℃, the oxidation time is 90-400 minutes, and the oxidation atmosphere is air. Too high an oxidation temperature can easily lead to fiber melting or over-oxidation, while too low an oxidation temperature can prevent the fibers from achieving "curing and shaping," and also result in excessively long oxidation times, increasing manufacturing costs. Curing and shaping are achieved when the oxygen content of the non-melting fibers obtained after oxidation is 11-18%.

[0052] Preferably, the second heat treatment (low-temperature carbonization) is performed at a temperature of 450-800℃, in a nitrogen atmosphere, for a time of 5-30 minutes. Excessively high low-temperature carbonization temperatures can lead to the styling of the fiber carbon structure, increasing the difficulty of activation; conversely, excessively low low-temperature carbonization temperatures allow water vapor or carbon dioxide to easily etch the fibers, resulting in low fiber strength.

[0053] Specifically, the activation temperature is 550-1000℃, the activation time is 5-60 minutes, and the activation atmosphere is water vapor or carbon dioxide. If the activation temperature is too high, the requirements for the equipment are too demanding; an activation temperature exceeding 1100℃ will significantly reduce the equipment's lifespan. If the activation temperature is too low, water vapor or carbon dioxide will not easily etch the material, resulting in a low specific surface area.

[0054] Specifically, the second heat treatment (high-temperature carbonization) is performed at a temperature of 1000-1600℃ for 1-30 minutes to obtain high-temperature activated carbon fibers with a diameter of 10-16μm. If the high-temperature carbonization temperature is too high, the micropores generated during activation will collapse, resulting in a decrease in specific surface area; if the high-temperature carbonization temperature is too low, activation cannot be completed.

[0055] The present invention will be further described below with reference to embodiments.

[0056] In this embodiment of the invention, the spinning die used in the spinning and spun yarn steps includes an upper material dispersion chamber and a spinneret. The material dispersion chamber is filled with metal sand or filter media. A 200-3000 mesh filter screen is provided on the upper part of the spinneret, and the spinneret has 100-1000 holes. The metal sand or filter media can uniformly regulate the material temperature. The filter screen on the upper part of the spinneret is mainly used to filter impurities that may be introduced into the material, and it can also uniformly regulate the material pressure. The spinneret also has guide holes, expansion holes, and micropores. The guide holes, expansion holes, and micropores are connected in sequence. The guide holes have an inverted funnel-shaped structure with a height of 1-3 mm, an upper diameter of 2-3.5 mm, and a lower diameter of 1.5-3 mm. The expansion holes have an inverted funnel-shaped structure with a height of 2-5 mm, an upper diameter of 1.5-3 mm, and a lower diameter of 0.15-0.3 mm. The micropores have a diameter of 0.15-0.3 mm and a length-to-diameter ratio of 1:1-5:1.

[0057] Example 1

[0058] The material dispersion chamber of the spinning die is filled with 80-mesh metal sand; a 2000-mesh filter screen is installed on the upper part of the spinneret, and the spinneret has 500 holes. Its dedicated spinneret has guide holes with an inverted funnel-shaped structure, 1mm high, 3.5mm upper diameter, and 3mm lower diameter; enlarged holes also have an inverted funnel-shaped structure, 3mm high, 3mm upper diameter, and 0.2mm lower diameter; micro-orifice diameter is 0.2mm; and the micro-orifice length-to-diameter ratio is 3:1.

[0059] Ethylene tar-based isotropic oxidized pitch with a softening point of 257℃, ash content of 50ppm, and oxygen content of 1.2% was selected as raw material A; anisotropic pitch with a softening point of 260℃ and ash content of 30ppm was selected as raw material B. Raw materials A and B were mixed evenly at a mass ratio of 10:90, and then added to a twin-screw extruder heated to 290℃ to melt and mix evenly, obtaining molten pitch. The molten pitch was extruded using the twin-screw extruder and conveyed to a metering pump. The metering pump delivered the molten pitch to the spinning die at a rate of 0.1g / min / 500, while simultaneously controlling the spinning die pressure at 1.2MPa. The spinning die was heated to 300℃, and the spinneret surface was heated to 270℃ before the molten pitch was spun into fibers. After spinning, the fibers are taken in at a speed of 600 m / min to obtain pitch fibers with a diameter of 14 μm. The pitch fibers are then heated from 180 to 280 °C at a rate of 1 °C / min and held at that temperature for 180 min for air oxidation treatment to obtain infusible fibers with an oxygen content of 13%. The infusible fibers are then heat-treated at 600 °C for 15 min in a nitrogen atmosphere to obtain low-temperature carbonized fibers. The low-temperature carbonized fibers are then activated at 890 °C for 15 min in a water vapor atmosphere to obtain low-temperature activated carbon fibers. Finally, the low-temperature activated carbon fibers are heat-treated at 1000 °C for 2 min in a nitrogen atmosphere to obtain the pitch-based carbon fibers.

[0060] The pitch-based carbon fiber has a diameter of 12 μm and consists of a 0.03 μm thick isotropic porous carbon outer layer, a 0.5 μm thick mixed transition carbon layer, and an 11 μm diameter anisotropic carbon core layer. The surface of the isotropic porous carbon outer layer is covered with nanoscale pores with a depth of <0.03 μm. The specific surface area of ​​the activated carbon fiber is 1350 m². 2 / g, the tensile strength of a single filament is 530MPa.

[0061] Example 2

[0062] The material dispersion chamber of the spinning die head is filled with 80-mesh steel balls; a 1000-mesh filter screen is installed on the upper part of the spinneret, and the spinneret has 1000 holes. Its special spinneret has a guide hole with an inverted flared shape, 1mm high, 3.5mm upper diameter, and 3mm lower diameter. The expansion hole also has an inverted flared shape, 5mm high, 3mm upper diameter, and 0.3mm lower diameter. The micro-hole diameter is 0.3mm, and the micro-hole length-to-diameter ratio is 5:1.

[0063] Ethylene tar-based isotropic oxidized pitch with a softening point of 270℃, ash content of 80ppm, and oxygen content of 0.8% was selected as raw material A; anisotropic pitch with a softening point of 275℃ and ash content of 10ppm was selected as raw material B. Raw materials A and B were mixed evenly at a mass ratio of 20:80, and then added to a twin-screw extruder heated to 295℃ to melt and mix evenly, obtaining molten pitch. The molten pitch was extruded using the twin-screw extruder and conveyed to a metering pump. The metering pump delivered the molten pitch to the spinning die at a rate of 0.2g / min / 1000, while simultaneously controlling the spinning die pressure at 0.9MPa. The spinning die was heated to 310℃, and the spinneret surface was heated to 285℃ before the molten pitch was spun into fibers. After spinning, the fibers are taken in at a speed of 500 m / min to obtain pitch fibers with a diameter of 16 μm. The pitch fibers are then heated from 180 °C to 280 °C at a rate of 0.5 °C / min and held at that temperature for 200 min for air oxidation treatment to obtain infusible fibers with an oxygen content of 13%. The infusible fibers are then heat-treated at 500 °C for 30 min in a nitrogen atmosphere to obtain low-temperature carbonized fibers. The low-temperature carbonized fibers are then activated at 800 °C for 20 min in a water vapor atmosphere to obtain low-temperature activated carbon fibers. Finally, the low-temperature activated carbon fibers are heat-treated at 1000 °C for 5 min in a nitrogen atmosphere to obtain the pitch-based carbon fibers.

[0064] The pitch-based carbon fiber has a diameter of 14 μm and consists of a 0.03 μm thick isotropic porous carbon outer layer, a 0.4 μm thick mixed transition carbon layer, and a 12.2 μm diameter anisotropic carbon core layer. The surface of the isotropic porous carbon outer layer is covered with nanoscale pores with a depth of <0.03 μm. The specific surface area of ​​the activated carbon fiber is 1050 m². 2 / g, with a single filament tensile strength of 670MPa.

[0065] Example 3

[0066] The material dispersion chamber of the spinning die head is filled with 60-mesh steel balls; a 1000-mesh filter screen is installed on the upper part of the spinneret, and the spinneret has 1000 holes. Its special spinneret has a guide hole with an inverted flared shape, 1mm high, 3.5mm upper diameter, and 3mm lower diameter. The expansion hole also has an inverted flared shape, 5mm high, 3mm upper diameter, and 0.3mm lower diameter. The micro-hole diameter is 0.3mm, and the micro-hole length-to-diameter ratio is 5:1.

[0067] Isotropic oxidized pitch with a softening point of 270℃, ash content of 50ppm, and oxygen content of 1.3% was selected as raw material A; anisotropic pitch with a softening point of 274℃ and ash content of 10ppm was selected as raw material B. Raw materials A and B were mixed evenly at a mass ratio of 15:85, and then added to a twin-screw extruder heated to 300℃ to melt and mix evenly, obtaining molten pitch. The molten pitch was extruded using the twin-screw extruder and conveyed to a metering pump. The metering pump delivered the molten pitch to the spinning die at a rate of 0.09 g / min / 1000, while simultaneously controlling the spinning die pressure to 2 MPa. The spinning die was heated to 325℃, and the spinneret surface was heated to 290℃ before the molten pitch was spun into fibers. After spinning, the fibers are taken in at a speed of 800 m / min to obtain pitch fibers with a diameter of 13 μm. The pitch fibers are then heated from 180°C to 280°C at a rate of 1°C / min and held at that temperature for 120 min for air oxidation treatment to obtain infusible fibers with an oxygen content of 11%. The infusible fibers are then heat-treated at 700°C for 10 min in a nitrogen atmosphere to obtain low-temperature carbonized fibers. The low-temperature carbonized fibers are then activated at 900°C for 5 min in a water vapor atmosphere to obtain low-temperature activated carbon fibers. Finally, the low-temperature activated carbon fibers are heat-treated at 1400°C for 5 min in a nitrogen atmosphere to obtain the pitch-based carbon fibers.

[0068] The pitch-based carbon fiber has a diameter of 11.5 μm and consists of a 0.03 μm thick isotropic porous carbon outer layer, a 0.5 μm thick mixed transition carbon layer, and an anisotropic carbon core layer with a diameter of approximately 10.5 μm. The surface of the isotropic porous carbon outer layer is covered with nanoscale pores with a depth of <0.03 μm. The specific surface area of ​​the activated carbon fiber is 850 m² / g. 2 / g, monofilament tensile strength 750MPa.

[0069] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing pitch-based activated carbon fiber, characterized in that: The pitch-based activated carbon fiber includes a core-sheath structure; The core layer of the skin-core structure is anisotropic carbon; The outer layer of the core-skin structure is isotropic carbon; Between the core layer and the skin layer is a mixed transition layer that transitions from anisotropic carbon to isotropic carbon along the direction from the core layer to the skin layer; The surface of the skin layer is covered with nanoscale pores; The preparation method of the pitch-based activated carbon fiber includes the following steps: Asphalt fiber is obtained by screw melt extrusion, spinning, and winding of raw material A and raw material B. The asphalt fiber is obtained by oxidation, a first heat treatment at 450-800℃, activation, and a second heat treatment at 1000-1600℃. The raw material A is ethylene tar-based isotropic oxidized pitch, the raw material B is anisotropic pitch, and the softening temperature of the raw material A is lower than that of the raw material B, the temperature difference between the softening temperatures of the raw material A and the raw material B is less than 5°C; the weight ratio of the raw material A to the raw material B is 5:95-25:

75. The temperature of the screw melt extrusion is 280-320°C, and the viscosity of the molten asphalt extruded at this temperature is 50-10 Pa·s. The temperature of the spinneret is 260-320°C, and the temperature of the spinning is 280-340°C. The temperature of the spinneret is 20-40°C lower than the spinning temperature. The spinneret temperature is the asphalt fiber setting temperature. When the spinning temperature is 280-340°C, the corresponding viscosity of the spun asphalt is 10-2.5 Pa·s.

2. The method for preparing pitch-based activated carbon fiber as described in claim 1, characterized in that: The diameter of the pitch-based activated carbon fiber is 5-18 μm; The thickness of the skin layer is 0.002-0.05 μm; The thickness of the hybrid transition layer is 0.3-2.5 μm; The diameter of the core layer is 4-16 μm.

3. The method for preparing pitch-based activated carbon fiber as described in claim 1, characterized in that: The depth of the nanoscale pores is less than or equal to 0.05 μm.

4. The method for preparing pitch-based activated carbon fiber as described in claim 1, characterized in that, The softening point of raw material A is 250-280℃, the ash content is less than 80ppm, and the oxygen content is less than 1.5%. The softening point of raw material B is 250-285℃, and the ash content is less than 30ppm.

5. The method for preparing pitch-based carbon fiber as described in claim 1, characterized in that: The spinning speed is 0.06-0.15 g / min / H, where H is the number of spinneret holes in the spinneret.

6. The method for preparing pitch-based carbon fiber as described in claim 1, characterized in that: The spinning pressure is 0.3-2 MPa, and the winding speed is 500-1000 m / min.

7. The method for preparing pitch-based carbon fiber as described in claim 1, characterized in that: The oxidation temperature is 180-320℃, the oxidation time is 90-400 min, and the oxidation atmosphere is air.

8. The method for preparing pitch-based carbon fiber as described in claim 1, characterized in that: The activation temperature is 550-1000℃, the activation time is 5-60 min, and the activation atmosphere is water vapor or carbon dioxide.

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