Pitch-based graphite fiber having an axially penetrating ingrowth hole and method of making the same

Abstract

The application discloses a pitch-based graphite fiber with an axial through-endogenous hole and a preparation method thereof, and belongs to the technical field of porous pitch-based graphite fiber preparation. The preparation method of the pitch-based graphite fiber comprises the following steps: uniformly mixing biomass tar fraction and coal-based pitch raw materials, placing the mixture in a high-pressure reaction kettle, and performing a preliminary polymerization reaction under an inert atmosphere; performing a secondary polymerization reaction by increasing the temperature; and obtaining spinnable pitch, melting and spinning the spinnable pitch in a spinning machine, and then performing infusibilization treatment, carbonization treatment and graphitization treatment. The application utilizes the reaction escape behavior of oxygen atoms in biomass tar, introduces specific biomass tar fraction, mixes specific proportions, and performs twice polymerization reactions, so that the formation of the axial through-micro-nano-pore structure of the pitch fiber is regulated, and the prepared pitch-based graphite fiber has excellent mechanical properties and porous characteristics.

Description

Technical Field

[0001] This invention belongs to the field of porous pitch-based graphite fiber preparation technology, specifically relating to a pitch-based graphite fiber with axially interconnected endogenous pores and its preparation method. Background Technology

[0002] Coal tar pitch, with its high carbon content, strong aromaticity, low price, and easy availability, is a commonly used raw material for preparing high-quality carbon fibers. Porous carbon fibers prepared from coal tar pitch have wide applications in various fields due to their unique structural characteristics, such as high specific surface area, lightweight, good electrical / thermal conductivity, chemical stability, and controllable pore structure. There are several methods for preparing porous carbon fibers, such as: template-assisted synthesis, where carbon precursors are filled into the pores of a template, followed by carbonization and template removal to obtain porous carbon fibers with a template shape; chemical activation, where carbon precursors are mixed with an activator and carbonized and activated at high temperatures to form a porous structure; and the sol-gel method, which obtains porous carbon fibers through gelation, drying, and carbonization. Most of these methods are post-processing methods, requiring a pore-forming process after carbon fiber preparation, and the pore structure is mostly exogenous, making orientation difficult to control.

[0003] Due to the high aromaticity and condensation degree of coal-based pitch, its thermal polymerization reaction is difficult to control. Therefore, it is necessary to modify it to prepare spinnable pitch suitable for spinning. Oxidation or hydrogenation can effectively improve the carbonization properties of pitch, producing high-quality general-purpose or mesophase pitch with suitable softening points and excellent spinnability, thereby obtaining high-performance general-purpose or mesophase pitch-based carbon fibers. However, chemical reaction treatment significantly increases the cost and complexity of pitch preparation. Therefore, it is essential to find a simple, low-cost, and structurally controllable method for pitch modification and porous fiber preparation.

[0004] Biomass tar pitch mainly comes from agricultural waste and forestry lignin, and has advantages such as wide availability and low price. Biomass tar pitch contains abundant aliphatic units and oxygen-containing groups, exhibiting high reactivity during carbonization. In particular, it contains a large number of aliphatic side chain structures, which can effectively improve the viscosity of the system during the reaction process of coal-based pitch. At the same time, the introduction of short side chain structures and oxygen atoms is beneficial to improving the reactivity of raw materials such as coal-based pitch.

[0005] Current technologies related to the utilization of biomass tar include patent CN118479468A, which uses a mixture of biomass tar, pitch, and coal powder for granulation to prepare a coal-based carbon raiser with high fixed carbon content. Patent CN117776180A uses an alkali activator to impregnate biomass tar to prepare supercapacitor electrode materials. Patent CN116272942A uses methods such as loading and grafting to introduce functional sites, completing the modification of biomass tar-derived carbon-based materials. Patent CN114715876A uses melamine as a nitrogen source to construct oxygen-containing functional groups on the surface of pyrolyzed biomass tar-based carbon materials through acid oxidation, and utilizes organic synthesis reaction mechanisms to achieve nitrogen heteroatoms on the carbon material surface. Patent CN114477132A uses co-carbonization of biomass tar and coal pitch to prepare carbon microspheres, and the addition of biomass tar can increase the interlayer spacing of carbon microspheres; however, further research has not been conducted on the spinnability of pitch and the process for preparing pitch fibers. Patent CN114164014A uses a mixture of biomass bitumen and coal tar pitch to refine the bitumen, and then performs co-carbonization treatment to obtain bitumen with a wide-area streamlined structure, but it does not study the spinnability and the formation of pore structure.

[0006] In summary, biomass tar has a certain influence on the properties of asphalt, but the relevant technology for using it as an initiator to prepare porous carbon fibers is still lacking. Summary of the Invention

[0007] This invention provides a novel method for producing porous graphite fibers from coal-based pitch by adding different fractions of biomass tar. On one hand, the abundant alkane structures in the biomass tar fractions are used to adjust the viscosity of the reaction system and optimize the spinnability of the pitch. On the other hand, the active oxygen elements in the biomass tar fractions escape under specific high-temperature conditions to construct pitch-based graphite fibers with a directional porous structure. By controlling the blending ratio and reaction conditions, the reaction progress can be effectively regulated, resulting in modified pitch with uniform quality and excellent spinnability. After melt spinning, non-melting, carbonization, and graphitization treatments, porous carbon fibers and graphite fibers are obtained. These fibers not only retain the structural characteristics of pitch fibers but also possess unique pore structures—axially penetrating nanopores—which have the potential for applications in carbon molecular sieves.

[0008] One of the objectives of this invention is to provide a method for preparing pitch-based graphite fibers with axially penetrating endogenous pores.

[0009] The second objective of this invention is to provide a pitch-based graphite fiber with axially interconnected endogenous pores prepared by the method.

[0010] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0011] In a first aspect, the present invention provides a method for preparing pitch-based graphite fibers with axially through endogenous pores, comprising the following steps:

[0012] (1) The biomass tar fraction and coal-based pitch raw material are uniformly mixed and placed in a high-pressure reactor for preliminary polymerization under an inert atmosphere; the biomass tar fraction is a whole fraction or a fraction containing a temperature above 200℃; the blending ratio of the biomass tar fraction is 1-10 wt% of the coal-based pitch raw material; the preliminary polymerization reaction temperature is 180-240℃, the preliminary polymerization reaction pressure is 0.1-5 MPa, and the preliminary polymerization reaction time is 0.5-5 h;

[0013] (2) Further heating is carried out to carry out a secondary polymerization reaction to obtain spinnable asphalt; the secondary polymerization reaction temperature is 390~420℃, and the secondary polymerization reaction time is 1~6h;

[0014] (3) The spinnable pitch obtained in step (2) is melt-spun in a spinning machine to obtain pitch-based fiber raw silk;

[0015] (4) The asphalt-based raw fibers obtained in step (3) are subjected to non-melting treatment;

[0016] (5) Carbonize the asphalt-based fibers after the non-melting treatment in step (4) to obtain asphalt-based carbon fibers.

[0017] (6) The pitch-based carbon fiber obtained in step (5) is graphitized to obtain pitch-based graphite fiber with axially through endogenous pores.

[0018] "Having axially continuous internal pores" means that the pore structure of the fiber obtained by the present invention is a regular through-hole formed from the inside along the fiber axis (axial direction), which is different from the external irregular pore structure formed by conventional activation methods.

[0019] Step (1):

[0020] Using biomass tar fraction as raw material, a precursor is first prepared by copolymerizing it with coal-based pitch with different group composition distributions. The molecular structure, softening point, rheological properties, etc. of the coal-based pitch are adjusted by introducing branched structures and oxygen elements from the biomass tar fraction.

[0021] In step (1), the coal-based pitch raw material is one or more of the following: low-temperature pyrolysis coal pitch, high-temperature coal tar pitch, coal liquefaction pitch, and coal-oil co-processing pitch. The coal-based pitch composition ranges as follows: hexane-soluble (HS) 10–40%, hexane-insoluble toluene-soluble (HI-TS) 30–60%, toluene-insoluble quinoline-soluble (TI-QS) 10–30%, and quinoline-insoluble (QI) 0–5%. Preferably, high-temperature coal tar pitch is used as the raw material, wherein the HS component is 20–25%, the HI-TS component is 50–55%, the TI-QS component is 20–25%, and the QI component is less than 0.05%.

[0022] In step (1), the quinoline insoluble matter (QI) content in the biomass tar is 0–0.03%. The biomass tar distillate is a complete fraction or one or more of the following fractions: 150–200℃, 200–250℃, 250–300℃, 300–350℃, and 350–400℃, and must contain a fraction with a temperature above 200℃. Preferably, the biomass tar distillate contains a fraction with a temperature of 300–350℃ or higher.

[0023] Preferably, in step (1), the blending ratio of biomass tar fraction accounts for 1 to 5 wt% of the coal-based pitch raw material.

[0024] Preferably, the initial polymerization reaction temperature in step (1) is 200-220℃, more preferably 220℃; the initial polymerization reaction pressure is 0.5-1MPa, more preferably 0.6MPa; and the initial polymerization reaction time is 1-3h, more preferably 2h.

[0025] Step (2):

[0026] Preferably, the secondary polymerization reaction temperature in step (2) is 400-410℃, more preferably 400℃; the heating rate is 1-5℃ / min, more preferably 3℃ / min; and the secondary polymerization reaction time is 2-4h, more preferably 3h.

[0027] To ensure the spinnability of the prepared asphalt, an inert gas (nitrogen, argon, or helium) is used to purge the reactor during the reaction at a flow rate of 0.5–5 L / min (preferably 3 L / min).

[0028] Step (3):

[0029] In step (3), the spinnable pitch is heated to a spinning temperature of 300-400°C in a spinning machine at a heating rate of 2-10°C / min. Under an N2 pressure of 0.1-3.0 MPa, it is melt-spun through a circular nozzle with a diameter of 0.10-0.30 mm and an aspect ratio of 1-3. The spinning rate is 500-1000 r / min.

[0030] Preferably, the heating rate is 3℃ / min; preferably, the spinning temperature is 370℃; preferably, the spinning pressure is 0.7MPa; preferably, the spinning nozzle diameter is 0.15mm and the length-to-diameter ratio is 3; preferably, the spinning speed is 700r / min.

[0031] Step (4):

[0032] The non-melting treatment in step (4) includes: heating from room temperature to 150-300°C at a heating rate of 2-8°C / min with an air flow rate of 50-150 mL / min, keeping the air flow rate constant, and then heating to 320-360°C at a heating rate of 0.2-1.0°C / min.

[0033] Preferably, the temperature is increased from room temperature to 150°C at a rate of 5°C / min, and then increased to 340°C at a rate of 0.5°C / min; preferably, the air flow rate during the non-melting process is 50 mL / min.

[0034] Step (5):

[0035] The carbonization process in step (5) includes heating from room temperature to 1000-1500℃ at a heating rate of 2-8℃ / min under an inert gas flow rate of 50-150 mL / min.

[0036] Preferably, nitrogen is used as the inert gas during carbonization; preferably, the inert gas flow rate during carbonization is 50 mL / min; preferably, the heating rate during carbonization is 5 °C / min; preferably, the final carbonization temperature is 1300 °C.

[0037] Step (6):

[0038] The graphitization process in step (6) includes: heating to 2600-3000℃ and holding for 5-60 minutes in an inert gas (argon) environment to perform graphitization.

[0039] Preferably, the graphitization temperature is 2800℃; preferably, the graphitization temperature is maintained for 10 minutes.

[0040] In one specific embodiment, a method for preparing pitch graphite fibers with axially through-holes includes the following steps:

[0041] (1) The biomass tar fraction is mixed with coal-based pitch raw material in a certain proportion and placed in a high-pressure reactor. Excess air in the reactor is purged with N2 for 10-20 minutes. The reaction temperature is 180-240℃ and the pressure in the reactor is kept within the range of 0.1-5MPa. If the reaction pressure is insufficient, additional inert gas is added. The reaction time is 0.5-5h to complete the initial polymerization of coal-based pitch and biomass tar.

[0042] (2) The temperature is increased to 350–430°C at a rate of 1–5°C / min, and the copolymer obtained in (1) is reacted for 1–6 h to prepare spinnable pitch. During this period, inert gas is used for purging at a flow rate of 0.5–5 L / min.

[0043] (3) The asphalt obtained in step (2) is heated to 300-400°C in a spinning machine at a heating rate of 2-5°C / min. Under N2 pressure of 0.1-3.0MPa, it is melt-spun through a circular nozzle with a diameter of 0.10-0.30mm and an aspect ratio of 3. The spinning rate is 500-1000r / min.

[0044] (4) After the reaction is completed, the asphalt-based fiber obtained in step (3) is heated from room temperature to 150 to 300°C at an air flow rate of 2 to 8°C / min and the air flow rate is kept constant. Then, the temperature is raised to 320 to 360°C at a heating rate of 0.2 to 1°C / min for non-melting treatment.

[0045] (5) After the reaction is completed, the asphalt-based fibers obtained in step (4) after non-melting treatment are heated from room temperature to 1000-1500℃ at a heating rate of 2-8℃ / min under an inert gas flow rate of 50-150mL / min.

[0046] (6) After the reaction is complete, the pitch-based carbon fiber obtained in step (5) is heated to 2600-3000℃ in an argon atmosphere and kept for 5-60 minutes for graphitization treatment.

[0047] Secondly, the present invention provides a pitch-based graphite fiber with axially through endogenous pores obtained by the above preparation method.

[0048] This invention provides a novel method for preparing spinnable pitch through a two-step polymerization reaction using coal-based pitch as raw material, adding biomass tar fraction for blending and modification, and then obtaining highly oriented, axially interconnected, endoporous graphite fibers through spinning and heat treatment. First, coal-based pitch is copolymerized with biomass tar fraction at a lower temperature to obtain a modified pitch precursor. Then, the pitch precursor is subjected to a second polymerization at high temperature to prepare spinnable pitch. The addition of biomass tar fraction regulates the composition, molecular structure, and molecular weight of the coal-based pitch, compensating for the low content of aliphatic hydrocarbons and excessive condensation in coal-based pitch. Simultaneously, oxygen atoms are introduced into the structure, and a deoxygenation diffusion reaction occurs during high-temperature carbonization, forming a highly oriented, axially interconnected micro / nanoporous structure within the fiber. On one hand, the aliphatic hydrocarbons in biomass tar can adjust the spinnability of the synthesized coal-based pitch; on the other hand, the abundant oxygen in biomass tar reacts and escapes under specific conditions, forming a rich axially interconnected micro / nanoporous structure within the fiber. Carbon fibers prepared from modified pitch not only have good mechanical properties, but also have a special regular micro-nano pore structure, exhibiting characteristics similar to molecular sieves, and have good application prospects.

[0049] Beneficial effects:

[0050] 1. This invention uses coal-based pitch as raw material and improves the spinnability of pitch by adding biomass tar fraction.

[0051] 2. In the method of the present invention, the reaction and escape behavior of oxygen atoms in biomass tar is utilized. Under the conditions of introducing specific biomass tar fractions, blending in a specific ratio and two polymerization reactions, the formation of axially interconnected micro-nano pore structures of pitch fibers is controlled, so that the prepared pitch graphite fibers have both excellent mechanical properties and porous characteristics.

[0052] 3. The pore structure in this invention is special, consisting of continuous pores that axially penetrate the fiber body and are nanoscale pores. This gives the material the application potential of carbon molecular sieves and provides mechanical properties such as high strength and high modulus that are unmatched by other carbon materials.

[0053] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments. Attached Figure Description

[0054] Figure 1 Electron micrograph of the pitch-based graphite fibers prepared in Example 1 of this invention;

[0055] Figure 2 This is an electron microscope image of the pitch-based graphite fibers prepared in Example 2 of the present invention;

[0056] Figure 3 This is a cross-sectional scanning electron microscope image of the pitch-based graphite fibers prepared in Example 3 of the present invention;

[0057] Figure 4 This is an electron microscope image of the pore structure of the activated fiber prepared in Comparative Example 6 of this invention. Detailed Implementation

[0058] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0059] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0060] Raw material source:

[0061] Coal-based pitch comes from high-temperature coal tar pitch from coking plants or liquefied pitch from direct coal liquefaction plants.

[0062] Biomass tar comes from biomass pyrolysis processes, using one or more fractions extracted using the whole fraction or temperature gradients, namely the 150–200℃ fraction, the 200–250℃ fraction, the 250–300℃ fraction, the 300–350℃ fraction, and the 350–400℃ fraction.

[0063] Example 1

[0064] (1) Weigh 5 kg of high-temperature coal tar pitch and place it in a high-pressure reactor. The high-temperature coal tar pitch has the following composition: hexane soluble (HS) 24.24%, hexane insoluble-toluene soluble (HI-TS) 52.33%, toluene insoluble-quinoline soluble (TI-QS) 23.41%, and quinoline insoluble (QI) 0.02%. Add 0.05 kg of biomass tar 300-350℃ fraction (QI content is 0.01%) to the high-pressure reactor. After purging with N2 for 20 min, react at 220℃ and 0.6 MPa pressure for 2 h to complete the copolymerization of biomass tar and coal tar pitch.

[0065] (2) The temperature was increased to 400℃ at a rate of 3℃ / min, and the copolymer obtained in (1) was reacted for 3h to prepare asphalt. During this period, N2 was used for purging at a flow rate of 3L / min.

[0066] (3) The asphalt obtained in step (2) is heated to 370°C in a spinning machine at a heating rate of 3°C / min. Under a N2 pressure of 0.7MPa, it is melt-spun through a circular nozzle with a diameter of 0.15mm and an aspect ratio of 3, and the spinning rate is 700r / min.

[0067] (4) After the reaction is completed, the asphalt-based fiber obtained in step (3) is heated from room temperature to 150°C at a heating rate of 5°C / min with an air flow of 50 mL / min. Then, the air flow is kept constant and the temperature is raised to 340°C at a heating rate of 0.5°C / min for non-melting treatment.

[0068] (5) After the reaction is completed, the non-melting treated pitch-based fibers obtained in step (4) are heated from room temperature to 1300℃ at a N2 flow rate of 50mL / min and a heating rate of 5℃ / min for carbonization treatment.

[0069] (6) After the reaction is completed, the pitch-based carbon fiber obtained in step (5) is heated to 2800℃ in an argon atmosphere and held for 10 minutes to obtain pitch-based graphite fiber.

[0070] The asphalt prepared by adding 1 wt.% of biomass tar fraction at 300–350℃ to high-temperature coal tar pitch has a C / H atomic ratio of 2.20. Elemental analysis revealed that the contents of C, H, N, S, and O in this asphalt were 94.05 wt.%, 3.56 wt.%, 0.82 wt.%, 0.36 wt.%, and 1.21 wt.%, respectively. The softening point of the asphalt obtained by this method, measured using a thermomechanical analyzer, was 267.5℃. Figure 1 As shown, scanning electron microscopy (SEM) observation of the interface structure of the prepared carbon fibers and graphite fibers revealed that after high-temperature carbonization and graphitization, nanoscale porous structures with axially interconnected pores appeared in the fiber cross-section. Furthermore, the carbonized fibers exhibited a tensile strength of 1.06 GPa (GB / T 31290-2022), while the graphitized fibers exhibited a tensile strength of 1.92 GPa (GB / T 31290-2022).

[0071] Example 2

[0072] (1) Weigh 5 kg of high-temperature coal tar pitch and place it in a high-pressure reactor. The high-temperature coal tar pitch has the following composition: hexane soluble (HS) 23.44%, hexane insoluble-toluene soluble (HI-TS) 51.88%, toluene insoluble-quinoline soluble (TI-QS) 24.67%, and quinoline insoluble (QI) 0.01%. Add 0.05 kg of biomass tar 250-300℃ fraction (QI content 0.01%) and 0.10 kg of biomass tar 300-350℃ fraction (QI content 0.01%) to the high-pressure reactor. After purging with N2 for 20 min, react at 220℃ and 0.6 MPa pressure for 2 h to complete the copolymerization of biomass tar and coal tar pitch.

[0073] (2) The temperature was increased to 400℃ at a rate of 3℃ / min, and the copolymer obtained in (1) was reacted for 3h to prepare asphalt. During this period, N2 was used for purging at a flow rate of 3L / min.

[0074] (3) The asphalt obtained in step (2) is heated to 370°C in a spinning machine at a heating rate of 3°C / min. Under a N2 pressure of 0.7MPa, it is melt-spun through a circular nozzle with a diameter of 0.15mm and an aspect ratio of 3, and the spinning rate is 700r / min.

[0075] (4) After the reaction is completed, the asphalt-based fiber obtained in step (3) is heated from room temperature to 150°C at a heating rate of 5°C / min with an air flow of 50 mL / min. Then, the air flow is kept constant and the temperature is raised to 340°C at a heating rate of 0.5°C / min for non-melting treatment.

[0076] (5) After the reaction is completed, the non-melting treated pitch-based fibers obtained in step (4) are heated from room temperature to 1300℃ at a N2 flow rate of 50mL / min and a heating rate of 5℃ / min for carbonization treatment.

[0077] (6) After the reaction is completed, the pitch-based carbon fiber obtained in step (5) is heated to 2800℃ in an argon atmosphere and held for 10 minutes to obtain pitch-based graphite fiber.

[0078] The asphalt prepared by adding 3 wt.% biomass tar fraction to high-temperature coal tar pitch has a C / H atomic ratio of 2.26. Elemental analysis revealed that the contents of C, H, N, S, and O in this asphalt were 93.97 wt.%, 3.47 wt.%, 0.95 wt.%, 0.35 wt.%, and 1.26 wt.%, respectively. The softening point of the asphalt obtained by this method, measured using a thermomechanical analyzer, was 273.4℃. Figure 2 As shown, scanning electron microscopy (SEM) observation of the interface structure of the prepared carbon fibers and graphite fibers revealed that after high-temperature carbonization and graphitization, the fiber cross-section exhibited numerous nanoscale pore structures, which were axially interconnected. Furthermore, the carbonized fibers possessed a tensile strength of 1.25 GPa (GB / T 31290-2022), while the graphitized fibers exhibited a tensile strength of 2.06 GPa (GB / T31290-2022).

[0079] Example 3

[0080] (1) Weigh 5 kg of high-temperature coal tar pitch and place it in a high-pressure reactor. The high-temperature coal tar pitch has the following composition: hexane soluble (HS) 22.48%, hexane insoluble-toluene soluble (HI-TS) 54.56%, toluene insoluble-quinoline soluble (TI-QS) 22.95%, and quinoline insoluble (QI) 0.01%. Add 0.10 kg of biomass tar 250-300℃ fraction (QI content 0), 0.10 kg of biomass tar 300-350℃ fraction (QI content 0.01%), and 0.05 kg of biomass tar 350-400℃ fraction (QI content 0.01%) to the high-pressure reactor. After purging with N2 for 20 min, react at 220℃ and 0.6 MPa pressure for 2 h to complete the copolymerization of biomass tar and coal tar pitch.

[0081] (2) The temperature was increased to 400℃ at a rate of 3℃ / min, and the copolymer obtained in (1) was reacted for 3h to prepare asphalt. During this period, N2 was used for purging at a flow rate of 3L / min.

[0082] (3) The asphalt obtained in step (2) is heated to 370°C in a spinning machine at a heating rate of 3°C / min. Under a N2 pressure of 0.7MPa, it is melt-spun through a circular nozzle with a diameter of 0.15mm and an aspect ratio of 3, and the spinning rate is 700r / min.

[0083] (4) After the reaction is completed, the asphalt-based fiber obtained in step (3) is heated from room temperature to 150°C at a heating rate of 5°C / min with an air flow of 50 mL / min. Then, the air flow is kept constant and the temperature is raised to 340°C at a heating rate of 0.5°C / min for non-melting treatment.

[0084] (5) After the reaction is completed, the non-melting treated pitch-based fibers obtained in step (4) are heated from room temperature to 1300℃ at a N2 flow rate of 50mL / min and a heating rate of 5℃ / min for carbonization treatment.

[0085] (6) After the reaction is completed, the pitch-based carbon fiber obtained in step (5) is heated to 2800℃ in an argon atmosphere and held for 10 minutes to obtain pitch-based graphite fiber.

[0086] The asphalt prepared by adding 5 wt.% biomass tar fraction to high-temperature coal tar pitch has a C / H atomic ratio of 2.27. Elemental analysis revealed that the contents of C, H, N, S, and O in this asphalt were 94.02 wt.%, 3.45 wt.%, 0.88 wt.%, 0.34 wt.%, and 1.31 wt.%, respectively. The softening point of the asphalt obtained by this method, measured using thermomechanical analysis, was 283.9℃. Figure 3As shown, scanning electron microscopy (SEM) observation of the interface structure of the prepared carbon fibers and graphite fibers revealed that after high-temperature carbonization and graphitization, more nanoscale pore structures, consisting of axially interconnected pores, appeared in the fiber cross-section. Furthermore, the carbonized fibers exhibited a tensile strength of 1.01 GPa (GB / T 31290-2022), while the graphitized fibers exhibited a tensile strength of 1.86 GPa (GB / T31290-2022).

[0087] Example 4

[0088] (1) Weigh 5 kg of high-temperature coal tar pitch and place it in a high-pressure reactor. The high-temperature coal tar pitch has the following composition: hexane soluble (HS) 22.48%, hexane insoluble-toluene soluble (HI-TS) 54.56%, toluene insoluble-quinoline soluble (TI-QS) 22.95%, and quinoline insoluble (QI) 0.01%. Add 0.10 kg of biomass tar 250-300℃ fraction (QI content 0), 0.10 kg of biomass tar 300-350℃ fraction (QI content 0.01%), and 0.05 kg of biomass tar 350-400℃ fraction (QI content 0.01%) to the high-pressure reactor. After purging with N2 for 20 min, react at 180℃ and 0.6 MPa pressure for 2 h to complete the copolymerization of biomass tar and coal tar pitch.

[0089] (2) The temperature was increased to 400℃ at a rate of 3℃ / min, and the copolymer obtained in (1) was reacted for 3h to prepare asphalt. During this period, N2 was used for purging at a flow rate of 3L / min.

[0090] (3) The asphalt obtained in step (2) is heated to 370°C in a spinning machine at a heating rate of 3°C / min. Under a N2 pressure of 0.7MPa, it is melt-spun through a circular nozzle with a diameter of 0.15mm and an aspect ratio of 3, and the spinning rate is 700r / min.

[0091] (4) After the reaction is completed, the asphalt-based fiber obtained in step (3) is heated from room temperature to 150°C at a heating rate of 5°C / min with an air flow of 50 mL / min. Then, the air flow is kept constant and the temperature is raised to 340°C at a heating rate of 0.5°C / min for non-melting treatment.

[0092] (5) After the reaction is completed, the non-melting treated pitch-based fibers obtained in step (4) are heated from room temperature to 1300℃ at a N2 flow rate of 50mL / min and a heating rate of 5℃ / min for carbonization treatment.

[0093] (6) After the reaction is completed, the pitch-based carbon fiber obtained in step (5) is heated to 2800℃ in an argon atmosphere and held for 10 minutes to obtain pitch-based graphite fiber.

[0094] Adding 5 wt.% biomass tar fraction to high-temperature coal tar pitch and then performing secondary polymerization yielded pitch with a C / H atomic ratio of 2.36. Elemental analysis revealed that the contents of C, H, N, S, and O in this pitch were 94.62 wt.%, 3.34 wt.%, 0.62 wt.%, 0.22 wt.%, and 1.20 wt.%, respectively. The softening point of the pitch obtained by this method was 281.7℃. Scanning electron microscopy (SEM) observation of the interface structure of the prepared carbon and graphite fibers revealed that after high-temperature carbonization and graphitization, the fibers exhibited a certain nanoscale porous structure with axially continuous pores in their cross-section. Furthermore, the carbonized fibers possessed a tensile strength of 1.08 GPa (GB / T 31290-2022), and the graphitized fibers possessed a tensile strength of 1.94 GPa (GB / T31290-2022).

[0095] Example 5

[0096] (1) Weigh 5 kg of high-temperature coal tar pitch and place it in a high-pressure reactor. The high-temperature coal tar pitch has the following composition: hexane soluble (HS) 22.48%, hexane insoluble-toluene soluble (HI-TS) 54.56%, toluene insoluble-quinoline soluble (TI-QS) 22.95%, and quinoline insoluble (QI) 0.01%. Add 0.10 kg of biomass tar 250-300℃ fraction (QI content 0), 0.10 kg of biomass tar 300-350℃ fraction (QI content 0.01%), and 0.05 kg of biomass tar 350-400℃ fraction (QI content 0.01%) to the high-pressure reactor. After purging with N2 for 20 min, react at 240℃ and 0.6 MPa pressure for 2 h to complete the copolymerization of biomass tar and coal tar pitch.

[0097] (2) The temperature was increased to 400℃ at a rate of 3℃ / min, and the copolymer obtained in (1) was reacted for 3h to prepare asphalt. During this period, N2 was used for purging at a flow rate of 3L / min.

[0098] (3) The asphalt obtained in step (2) is heated to 370°C in a spinning machine at a heating rate of 3°C / min. Under a N2 pressure of 0.7MPa, it is melt-spun through a circular nozzle with a diameter of 0.15mm and an aspect ratio of 3, and the spinning rate is 700r / min.

[0099] (4) After the reaction is completed, the asphalt-based fiber obtained in step (3) is heated from room temperature to 150°C at a heating rate of 5°C / min with an air flow of 50 mL / min. Then, the air flow is kept constant and the temperature is raised to 340°C at a heating rate of 0.5°C / min for non-melting treatment.

[0100] (5) After the reaction is completed, the non-melting treated pitch-based fibers obtained in step (4) are heated from room temperature to 1300℃ at a N2 flow rate of 50mL / min and a heating rate of 5℃ / min for carbonization treatment.

[0101] (6) After the reaction is completed, the pitch-based carbon fiber obtained in step (5) is heated to 2800℃ in an argon atmosphere and held for 10 minutes to obtain pitch-based graphite fiber.

[0102] Adding 5 wt.% biomass tar fraction to high-temperature coal tar pitch and then performing secondary polymerization yielded pitch with a C / H atomic ratio of 2.09. Elemental analysis revealed that the contents of C, H, N, S, and O in this pitch were 93.50 wt.%, 3.72 wt.%, 0.91 wt.%, 0.51 wt.%, and 1.36 wt.%, respectively. The softening point of the pitch obtained by this method was 290.2℃. Scanning electron microscopy (SEM) observation of the interface structure of the prepared carbon and graphite fibers revealed that after high-temperature carbonization and graphitization, a certain amount of nanoscale pores, consisting of axially interconnected pores, appeared in the fiber cross-section. Furthermore, the carbonized fibers exhibited a tensile strength of 1.00 GPa (GB / T 31290-2022), and the graphitized fibers exhibited a tensile strength of 1.64 GPa (GB / T 31290-2022).

[0103] Example 6

[0104] (1) Weigh 5 kg of high-temperature coal tar pitch and place it in a high-pressure reactor. The high-temperature coal tar pitch has the following composition: hexane soluble (HS) 22.48%, hexane insoluble-toluene soluble (HI-TS) 54.56%, toluene insoluble-quinoline soluble (TI-QS) 22.95%, and quinoline insoluble (QI) 0.01%. Add 0.10 kg of biomass tar 250-300℃ fraction (QI content 0), 0.10 kg of biomass tar 300-350℃ fraction (QI content 0.01%), and 0.05 kg of biomass tar 350-400℃ fraction (QI content 0.01%) to the high-pressure reactor. After purging with N2 for 20 min, react at 220℃ and 0.6 MPa pressure for 2 h to complete the copolymerization of biomass tar and coal tar pitch.

[0105] (2) The temperature was increased to 420°C at a rate of 3°C / min, and the copolymer obtained in (1) was reacted for 3 hours to prepare asphalt. During this period, N2 was used for purging at a flow rate of 3 L / min.

[0106] (3) The asphalt obtained in step (2) is heated to 370°C in a spinning machine at a heating rate of 3°C / min. Under a N2 pressure of 0.7MPa, it is melt-spun through a circular nozzle with a diameter of 0.15mm and an aspect ratio of 3, and the spinning rate is 700r / min.

[0107] (4) After the reaction is completed, the asphalt-based fiber obtained in step (3) is heated from room temperature to 150°C at a heating rate of 5°C / min with an air flow of 50 mL / min. Then, the air flow is kept constant and the temperature is raised to 340°C at a heating rate of 0.5°C / min for non-melting treatment.

[0108] (5) After the reaction is completed, the non-melting treated pitch-based fibers obtained in step (4) are heated from room temperature to 1300℃ at a N2 flow rate of 50mL / min and a heating rate of 5℃ / min for carbonization treatment.

[0109] (6) After the reaction is completed, the pitch-based carbon fiber obtained in step (5) is heated to 2800℃ in an argon atmosphere and held for 10 minutes to obtain pitch-based graphite fiber.

[0110] Adding 5 wt.% biomass tar fraction to high-temperature coal tar pitch and then performing secondary polymerization yielded pitch with a C / H atomic ratio of 2.31. Elemental analysis revealed that the contents of C, H, N, S, and O in this pitch were 94.32 wt.%, 3.40 wt.%, 0.75 wt.%, 0.31 wt.%, and 1.22 wt.%, respectively. The softening point of the pitch obtained by this method was 287.5℃. Scanning electron microscopy (SEM) observation of the interface structure of the prepared carbon and graphite fibers revealed that after high-temperature carbonization and graphitization, nanoscale porous structures with axially continuous pores appeared in the fiber cross-section. Furthermore, the carbonized fibers exhibited a tensile strength of 1.11 GPa (GB / T 31290-2022), and the graphitized fibers exhibited a tensile strength of 1.96 GPa (GB / T31290-2022).

[0111] Comparative Example 1

[0112] Similar to Example 3, except that biomass tar is no longer added in step (1), that is, high-temperature coal tar pitch is directly used in step (3) and subsequent steps.

[0113] The prepared asphalt had a C / H atomic ratio of 2.57. Elemental analysis revealed that the contents of C, H, N, S, and O in this asphalt were 94.94 wt.%, 3.08 wt.%, 0.87 wt.%, 0.21 wt.%, and 0.90 wt.%, respectively. The softening point of the asphalt obtained by this method was 298.2℃. After high-temperature carbonization and graphitization, the fibers formed another type of fiber (without pores): mesophase asphalt fibers. No nanoscale pore structure was found in the fiber cross-section. Furthermore, the carbonized fibers exhibited a tensile strength of 1.31 GPa (GB / T 31290-2022), and the graphitized fibers exhibited a tensile strength of 1.98 GPa (GB / T31290-2022).

[0114] Comparative Example 2

[0115] Same as in Example 3, except that 15 wt.% of biomass tar fraction is added in step (1).

[0116] Five kilograms of high-temperature coal tar pitch were weighed and placed in a high-pressure reactor. 0.30 kg of biomass tar fraction at 250–300°C (QI content 0%), 0.30 kg of biomass tar fraction at 300–350°C (QI content 0.01%), and 0.15 kg of biomass tar fraction at 350–400°C (QI content 0.01%) were added to the reactor. The prepared pitch had a C / H atomic ratio of 1.93. Elemental analysis revealed that the contents of C, H, N, S, and O in this pitch were 92.11 wt.%, 3.98 wt.%, 0.99 wt.%, 0.63 wt.%, and 2.29 wt.%, respectively. The softening point of the pitch obtained by this method was measured to be 293.1°C using a thermomechanical analyzer. Scanning electron microscopy (SEM) observation of the interfacial structures of the prepared carbon and graphite fibers revealed that after high-temperature carbonization and graphitization, no nanoscale pore structures were found in the fiber cross-section, indicating significant structural defects. Furthermore, the carbonized fibers exhibited a tensile strength of 0.61 GPa (GB / T 31290-2022), while the graphitized fibers exhibited a tensile strength of 0.69 GPa (GB / T 31290-2022).

[0117] Comparative Example 3

[0118] Same as in Example 3, except that 5 wt.% of biomass tar at 200-250°C is added in step (1).

[0119] The asphalt prepared by adding 0.25 kg of biomass tar 200-250℃ fraction to high-temperature coal tar pitch had a C / H atomic ratio of 2.23. Elemental analysis revealed that the contents of C, H, N, S, and O in this asphalt were 93.28 wt.%, 3.48 wt.%, 0.92 wt.%, 0.46 wt.%, and 1.86 wt.%, respectively. The softening point of the asphalt obtained by this method was 266.2℃. After high-temperature carbonization and graphitization, a small number of nanoscale pore structures were found in the fiber cross-section, indicating that the 200-250℃ fraction of biomass tar had a weak promoting effect on pore formation. Furthermore, the carbonized fiber exhibited a tensile strength of 0.62 GPa (GB / T31290-2022), and the graphitized fiber exhibited a tensile strength of 1.29 GPa (GB / T 31290-2022).

[0120] Comparative Example 4

[0121] Similar to Example 3, except that in step (1) the copolymerization of coal tar pitch and biomass tar fractions is not carried out at 220°C and 0.6MPa pressure for 2 hours.

[0122] The asphalt prepared by adding 0.10 kg of biomass tar fraction at 250–300℃, 0.10 kg of biomass tar fraction at 300–350℃, and 0.05 kg of biomass tar fraction at 350–400℃ to high-temperature coal tar pitch and directly heating to 400℃ has a C / H atomic ratio of 2.29. Elemental analysis showed that the contents of C, H, N, S, and O in this asphalt were 93.88 wt.%, 3.42 wt.%, 0.92 wt.%, 0.43 wt.%, and 1.35 wt.%, respectively. The softening point of the asphalt obtained by this method was 275.1℃. After high-temperature carbonization and graphitization, the fiber cross-section showed a low content of pore structure or some pores were not interconnected, indicating that a single-step polymerization reaction is not conducive to the formation of axially interconnected pore structures. Meanwhile, the carbonized fiber exhibits a tensile strength of 0.58 GPa (GB / T 31290-2022), while the graphitized fiber exhibits a tensile strength of 1.14 GPa (GB / T31290-2022), indicating that the polymerization temperature in the second step has a significant impact on the formation of the pore structure and the mechanical properties of the asphalt.

[0123] Comparative Example 5

[0124] Similar to Example 3, except that in step (2), the temperature is increased to 380°C at a rate of 3°C / min, and the copolymer obtained in (1) is reacted for 6 hours to prepare asphalt.

[0125] A pitch prepared by adding 0.10 kg of biomass tar fraction at 250–300℃, 0.10 kg of biomass tar fraction at 300–350℃, and 0.05 kg of biomass tar fraction at 350–400℃ to high-temperature coal tar pitch, with a secondary polymerization temperature of 380℃, has a C / H atomic ratio of 2.24. Elemental analysis revealed that the contents of C, H, N, S, and O in this pitch were 93.22 wt.%, 3.47 wt.%, 0.94 wt.%, 0.41 wt.%, and 1.96 wt.%, respectively. The softening point of the pitch obtained by this method, measured by thermomechanical analysis, was 276.4℃. After high-temperature carbonization and graphitization, the fibers exhibited an irregular porous structure in their cross-section and showed nodules. Meanwhile, the carbonized fiber exhibits a tensile strength of 0.63 GPa (GB / T 31290-2022), while the graphitized fiber exhibits a tensile strength of 1.02 GPa (GB / T 31290-2022), indicating that the polymerization temperature in the second step has a significant impact on the formation of the fiber and pore structure, as well as the mechanical properties of the asphalt.

[0126] Comparative Example 6

[0127] Without adding biomass tar, the conventional steam chemical activation method is used, namely high temperature coal tar pitch for steps (3) to (5). Then the carbonized fiber is placed in the activation furnace, heated to 800℃ and activated by steam for 1 hour, and then naturally cooled to obtain activated fiber.

[0128] The asphalt has a C / H atomic ratio of 2.57. Elemental analysis revealed that the contents of C, H, N, S, and O in this asphalt were 94.94 wt.%, 3.08 wt.%, 0.87 wt.%, 0.21 wt.%, and 0.90 wt.%, respectively. The softening point of the asphalt obtained by this method, measured using a thermomechanical analyzer, was 298.2℃. After fiber activation, numerous randomly distributed pore structures of varying sizes were observed on the fiber surface and within the fiber, such as... Figure 4 As shown. Simultaneously, the fiber loses its tensile strength after carbonization.

[0129] Analysis of the results with comparative examples shows that the addition of biomass tar fractions can effectively promote the formation of axially interconnected endogenous pores in the fibers, and the number of pores within the fibers can be controlled by adding an appropriate proportion of biomass tar fractions. Notably, the process of copolymerizing at low temperatures followed by high-temperature polymerization after adding biomass tar fractions plays a positive role in the formation of nanoporous structures in the fibers. On the one hand, low-temperature copolymerization allows biomass tar fraction molecules to fully integrate into the pitch molecules; on the other hand, suitable high temperatures can effectively form larger molecular structures, which is conducive to molecular stacking. Simultaneously, the axially interconnected micro- and nanoporous structures possess molecular sieve-like characteristics without affecting the mechanical properties of the carbon fibers, demonstrating good application potential.

[0130] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and substance defined by the claims of the present invention; and such modifications or substitutions are still within the scope defined by the claims of the present invention.

Claims

1. A method for preparing pitch-based graphite fibers with axially continuous endogenous pores, characterized in that, Includes the following steps: (1) The biomass tar fraction and coal-based pitch raw material are uniformly mixed and placed in a high-pressure reactor for preliminary polymerization under an inert atmosphere; the biomass tar fraction is above 200℃ and contains fractions of 300~350℃; the blending ratio of biomass tar fraction accounts for 1~10wt% of coal-based pitch raw material; the preliminary polymerization reaction temperature is 180~240℃, the preliminary polymerization reaction pressure is 0.1~5MPa, and the preliminary polymerization reaction time is 0.5~5h; (2) Further heating is carried out to carry out a secondary polymerization reaction to obtain spinnable asphalt; the secondary polymerization reaction temperature is 390~420℃, and the secondary polymerization reaction time is 1~6h; (3) The spinnable pitch obtained in step (2) is melt-spun in a spinning machine to obtain pitch-based fiber raw silk; (4) The asphalt-based raw fibers obtained in step (3) are subjected to non-melting treatment; (5) Carbonize the asphalt-based fibers after the non-melting treatment in step (4) to obtain asphalt-based carbon fibers. (6) The pitch-based carbon fiber obtained in step (5) is graphitized to obtain pitch-based graphite fiber with axially through endogenous pores.

2. The preparation method according to claim 1, characterized in that, In step (1), the coal-based pitch raw material is one or more of the following: low-temperature pyrolysis pitch of coal, high-temperature coal tar pitch, coal liquefaction pitch, and coal-oil co-refining pitch. The coal-based pitch composition range is 10-40% hexane-soluble, 30-60% hexane-insoluble toluene-soluble, 10-30% toluene-insoluble to quinoline-soluble, and 0-5% quinoline-insoluble.

3. The preparation method according to claim 1, characterized in that, In step (1), the content of quinoline insoluble matter in the biomass tar fraction is 0~0.03%.

4. The preparation method according to claim 1, characterized in that, In step (1), the initial polymerization reaction temperature is 200~220℃, the initial polymerization reaction pressure is 0.5~1MPa, and the initial polymerization reaction time is 1~3h.

5. The preparation method according to claim 1, characterized in that, In step (2), the secondary polymerization reaction temperature is 400~410℃, the heating rate is 1~5℃ / min, and the secondary polymerization reaction time is 2~4h.

6. The preparation method according to claim 1, characterized in that, In step (3), the spinnable pitch is heated to a spinning temperature of 300-400℃ in a spinning machine at a heating rate of 2-10℃ / min. Under an N2 pressure of 0.1-3.0MPa, it is melt-spun through a circular nozzle with a diameter of 0.10-0.30mm and an aspect ratio of 1-3. The spinning rate is 500-1000r / min.

7. The preparation method according to claim 1, characterized in that, The non-melting treatment in step (4) includes: heating from room temperature to 150-300℃ at a heating rate of 2-8℃ / min with an air flow rate of 50-150mL / min, keeping the air flow rate constant, and then heating to 320-360℃ at a heating rate of 0.2-1.0℃ / min.

8. The preparation method according to claim 1, characterized in that, The carbonization process in step (5) includes heating from room temperature to 1000-1500℃ at a heating rate of 2-8℃ / min under an inert gas flow rate of 50-150 mL / min.

9. The preparation method according to claim 1, characterized in that, The graphitization process in step (6) includes heating to 2600~3000℃ under an inert gas and holding for 5~60 minutes.

10. A pitch-based graphite fiber with axially continuous endogenous pores, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

Images