Asphalt-based graphite fiber with axial through endogenous hole and preparation method of asphalt-based graphite fiber

Abstract

The invention discloses an asphalt-based graphite fiber with axial through endogenous pores and a preparation method of the asphalt-based graphite fiber, and belongs to the technical field of porous asphalt graphite fibers.The preparation method of the asphalt-based graphite fiber comprises the steps that biomass tar fraction and coal-series asphalt raw materials are evenly mixed and placed in a high-pressure reaction kettle; carrying out a preliminary polymerization reaction in an inert atmosphere; raising the temperature and carrying out secondary polymerization reaction; carrying out melt spinning on the obtained spinnable asphalt in a spinning machine, and then carrying out non-melting treatment, carbonization treatment and graphitization treatment. According to the invention, the reaction escape behavior of oxygen atoms in biomass tar is utilized, and under the conditions of introduction of a specific biomass tar fraction, specific mixing proportion and two polymerization reactions, the formation of an axial through micro-nano pore structure of the asphalt fiber is regulated and controlled, so that the prepared asphalt graphite fiber not only has excellent mechanical properties, but also has a porous characteristic.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of porous pitch-based graphite fibers, and particularly relates to a pitch-based graphite fiber with axially through internal pores and a preparation method thereof. Background Art

[0002] Coal-tar pitch has the advantages of high carbon content, strong aromaticity, low price and easy availability, and is a commonly used raw material for preparing high-quality carbon fibers. Porous carbon fibers prepared from coal tar pitch have wide applications in multiple fields due to their unique structural characteristics, such as high specific surface area, light weight, good electrical / thermal conductivity, chemical stability and adjustable pore structure. There are various preparation methods for porous carbon fibers. For example: the template-assisted synthesis method, where a carbon precursor is filled into the pores of a template, and then a process of carbonization and removal of the template is carried out to finally obtain porous carbon fibers with the shape of the template; the chemical activation method, where a carbon precursor is mixed with an activator and carbonization and activation reactions are carried out at high temperature to form a porous structure; the sol-gel method, where porous carbon fibers are obtained through steps such as gelation, drying and carbonization. The above methods are mostly post-treatment methods, which require a pore-forming process after the carbon fiber is prepared, and the pore structure is mostly external pores, and the orientation is difficult to control.

[0003] Due to the too high aromaticity and condensation degree of coal-tar pitch, its thermal polymerization reaction is not easy to control. Therefore, it is necessary to carry out modification treatment on it to prepare a spinnable pitch suitable for spinning. By methods such as oxidation or hydrogenation, the carbonization properties of pitch can be effectively improved, and high-quality general-purpose pitch or mesophase pitch with suitable softening point and excellent spinnability can be prepared, and then high-performance general-purpose or mesophase pitch-based carbon fibers can be obtained. However, the chemical reaction treatment significantly increases the preparation cost and process complexity of pitch. Therefore, it is very necessary to find a pitch modification and porous fiber preparation method with simple process, low cost and controllable structure.

[0004] Biomass tar pitch mainly comes from agricultural waste and forestry lignin, and has the advantages of wide source and low price. Biomass tar pitch contains rich aliphatic units and oxygen-containing groups, and has high reactivity during the carbonization process. Especially, it contains more aliphatic side chain structures, which can effectively improve the system viscosity during the reaction process of coal-tar pitch; at the same time, the introduction of short side chain structures and their oxygen atoms is beneficial to improving the reactivity of raw materials such as coal-tar pitch.

[0005] Currently, technologies related to the utilization of biomass tar, such as Patent CN118479468A, use biomass tar to mix and granulate with asphalt and pulverized coal to prepare a coal-based carburizer with a high fixed carbon content. Patent CN117776180A uses an alkali activator to impregnate biomass tar to prepare a supercapacitor electrode material. Patent CN116272942A uses methods such as loading and grafting to introduce functional sites to complete 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 realizes the doping of heteroatoms on the surface of carbon materials using the mechanism of organic synthesis reactions. Patent CN114477132A uses the co-carbonization of biomass tar and coal tar pitch to realize the preparation of carbon microspheres, and the addition of biomass tar can expand the interlayer spacing of carbon microspheres. However, the spinnability of pitch and the process for preparing pitch fibers have not been further studied. Patent CN114164014A uses the mixed refining of biomass pitch and coal tar pitch to obtain refined pitch, and co-carbonization treatment can obtain pitch with a wide-range streamline structure, but the spinnability and the formation of pore structure have not been studied.

[0006] In summary, biomass tar has a certain influence on the properties of pitch, but the related technology for preparing porous carbon fibers as an initiator is still blank. Summary of the Invention

[0007] The present invention provides a new method for producing porous graphite fibers from pitch-based carbon fibers by adding different fractions of biomass tar to coal-based pitch. On the one hand, the rich alkane structure in the biomass tar fraction is used to adjust the viscosity of the reaction system and optimize the spinnability of pitch. On the other hand, the active oxygen element in the biomass tar fraction escapes in a specific high-temperature environment to construct pitch-based graphite fibers with a porous structure arranged in an oriented manner. By controlling the blending ratio and reaction conditions, the reaction progress can be effectively adjusted to obtain modified pitch with uniform quality and excellent spinnability. After melt spinning, stabilization, carbonization, and graphitization treatments, porous carbon fibers and graphite fibers are obtained. These not only retain the structural characteristics of pitch fibers but also have special pores, which are nano-pores axially penetrating the fibers. This structure has the potential for application as a carbon molecular sieve.

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

[0009] Another objective of the present invention is to provide pitch-based graphite fibers with axially through internal pores prepared by this preparation method.

[0010] In order to achieve the above objectives of the present invention, the following technical solutions are specifically adopted:

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

[0012] (1) Uniformly mix a biomass tar fraction and a coal-tar pitch raw material and place them in a high-pressure reactor for a preliminary polymerization reaction under an inert atmosphere; the biomass tar fraction is a full fraction or a fraction containing components above 200 °C; the blending ratio of the biomass tar fraction accounts for 1-10 wt% of the coal-tar pitch raw material; the temperature of the preliminary polymerization reaction is 180-240 °C, the pressure of the preliminary polymerization reaction is 0.1-5 MPa, and the time of the preliminary polymerization reaction is 0.5-5 h;

[0013] (2) Further increase the temperature for a secondary polymerization reaction to obtain spinnable pitch; the temperature of the secondary polymerization reaction is 390-420 °C, and the time of the secondary polymerization reaction is 1-6 h;

[0014] (3) Melt-spin the spinnable pitch obtained in step (2) in a spinning machine to obtain green pitch-based fibers;

[0015] (4) Subject the green pitch-based fibers obtained in step (3) to infusibilization treatment;

[0016] (5) Carbonize the pitch-based fibers after the infusibilization treatment in step (4) to obtain pitch-based carbon fibers;

[0017] (6) Graphitize the pitch-based carbon fibers obtained in step (5) to obtain pitch-based graphite fibers having axially penetrating internal pores.

[0018] "Having axially penetrating internal pores" means that the pore structure of the fibers obtained in the present invention is a regular through-pore structure formed internally 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 the biomass tar fraction as a raw material, first copolymerize with coal-tar pitches having different group composition distributions to prepare a precursor, and regulate the molecular structure, softening point, rheological properties, etc. of the coal-tar pitch by introducing branched-chain structures and oxygen elements in the biomass tar fraction.

[0021] In step (1), the coal-based asphalt raw material is one or more of low-temperature coal pyrolysis asphalt, high-temperature coal tar asphalt, coal liquefaction asphalt, and co-processing asphalt of coal and kerosene. The composition range of the coal-based asphalt is 10-40% of n-hexane soluble matter (HS), 30-60% of n-hexane insoluble-toluene soluble matter (HI-TS), 10-30% of toluene insoluble-quinoline soluble matter (TI-QS), and 0-5% of quinoline insoluble matter (QI). Preferably, high-temperature coal tar asphalt is used as the raw material, in which 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 content of quinoline insoluble matter (QI) in the biomass tar is 0-0.03%. The biomass tar fraction is the whole fraction or one or more of the fractions of 150-200 °C, 200-250 °C, 250-300 °C, 300-350 °C, and 350-400 °C, and it needs to contain fractions above 200 °C. Preferably, the biomass tar fraction contains fractions at 300-350 °C and above.

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

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

[0025] Step (2):

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

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

[0028] Step (3):

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

[0030] Preferably, the heating rate is 3 °C / min; preferably, the spinning temperature is 370 °C; preferably, the spinning pressure is 0.7 MPa; preferably, the diameter of the spinning nozzle is 0.15 mm, and the aspect ratio is 3; preferably, the spinning rate is 700 r / min.

[0031] Step (4):

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

[0033] Preferably, heat from room temperature to 150 °C at a heating rate of 5 °C / min, and then heat to 340 °C at a heating rate of 0.5 °C / min; preferably, the air flow rate during the stabilization treatment is 50 mL / min.

[0034] Step (5):

[0035] The carbonization treatment in step (5) includes: heating from room temperature to 1000 - 1500 °C at a heating rate of 2 - 8 °C / 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 treatment in step (6) includes: heating to 2600 - 3000 °C in an inert gas (argon) environment and holding for 5 - 60 min for graphitization treatment.

[0039] Preferably, the graphitization temperature is 2800 °C; preferably, the holding time of the graphitization temperature is 10 min.

[0040] In a specific embodiment, a preparation method of pitch graphite fiber with axially through - hole includes the following steps:

[0041] (1) Uniformly mix the biomass tar fraction with the coal - based pitch raw material in a certain proportion and place it in a high - pressure reaction kettle. The excess air in the reaction kettle is purged with N2 for 10 - 20 min to be emptied. The reaction temperature is 180 - 240 °C, and the pressure in the reaction kettle is ensured to be within the range of 0.1 - 5 MPa. When the reaction pressure is insufficient, additional inert gas is supplemented. The reaction time is 0.5 - 5 h to complete the preliminary polymerization of the coal - based pitch and the biomass tar.

[0042] (2) Heat it at a heating rate of 1 - 5 °C / min to 350 - 430 °C and react the copolymer product obtained in (1) for 1 - 6 h to prepare the spinnable pitch. During this period, purge it with an inert gas at a flow rate of 0.5 - 5 L / min.

[0043] (3) Heat the pitch obtained in step (2) in a spinning machine at a heating rate of 2 - 5 °C / min to 300 - 400 °C, and under an N2 pressure of 0.1 - 3.0 MPa, conduct melt spinning through a circular nozzle with a diameter of 0.10 - 0.30 mm and a length - diameter ratio of 3, and the spinning rate is 500 - 1000 r / min.

[0044] (4) After the reaction is completed, heat the pitch - based fiber obtained in step (3) from room temperature to 150 - 300 °C at a heating rate of 2 - 8 °C / min under an air flow rate of 50 - 150 mL / min, then keep the air flow rate unchanged, and heat it to 320 - 360 °C at a heating rate of 0.2 - 1 °C / min for infusibilization treatment.

[0045] (5) After the reaction is completed, heat the infusibilized pitch - based fiber obtained in step (4) from room temperature to 1000 - 1500 °C at a heating rate of 2 - 8 °C / min under an inert gas flow rate of 50 - 150 mL / min for carbonization treatment.

[0046] (6) After the reaction is completed, heat the pitch - based carbon fiber obtained in step (5) to 2600 - 3000 °C in an argon environment and hold it for 5 - 60 min for graphitization treatment.

[0047] In the second aspect, the present invention provides a pitch - based graphite fiber with axially - through internal pores obtained by the above - mentioned preparation method.

[0048] The present invention provides a new method for preparing spinnable pitch by using coal-based pitch as a raw material, adding biomass tar fractions for blending and modification, and performing two-step polymerization reactions, and then obtaining highly oriented axially continuous endoporous graphite fibers through spinning and heat treatment. First, the coal-based pitch undergoes a copolymerization reaction with biomass tar fractions at a relatively low temperature to obtain a modified pitch precursor, and then the pitch precursor is polymerized again at a high temperature to prepare spinnable pitch. Adding biomass tar fractions can regulate the composition, molecular structure, and molecular weight of coal-based pitch, make up for the defects of low content of aliphatic hydrocarbon structures and too high degree of condensation in coal-based pitch, and at the same time introduce oxygen atoms into the structure. Through high-temperature carbonization, a deoxidation diffusion reaction occurs to form a highly oriented axially continuous micro-nano pore structure inside the fiber. On the one hand, the aliphatic hydrocarbons in biomass tar can regulate the spinnability of coal-based synthetic pitch; on the other hand, the abundant oxygen elements in biomass tar react and escape under specific conditions to form a rich axially continuous micro-nano pore structure inside the fiber. The carbon fibers prepared from the modified pitch not only have good mechanical properties but also have a special regular micro-nano pore structure, similar to the characteristics of molecular sieves, and have good application prospects.

[0049] Advantages:

[0050] 1. The present invention uses coal-based pitch as a raw material and regulates the spinnability of pitch by adding biomass tar fractions, achieving an improvement in spinnability.

[0051] 2. In the method of the present invention, by utilizing the reaction and escape behavior of oxygen atoms in biomass tar, under the conditions of introducing specific biomass tar fractions, blending a specific ratio, and two polymerization reactions, the formation of an axially continuous micro-nano pore structure in the pitch fiber is regulated, so that the prepared pitch graphite fiber not only has excellent mechanical properties but also has a porous characteristic.

[0052] 3. The pore structure in the present invention is special, being continuous pores axially penetrating the fiber body and nano-scale pores, enabling the material to have the application potential of carbon molecular sieves and mechanical properties such as high strength and high modulus that cannot be compared with other carbon materials.

[0053] The present invention has been described in detail above, but the above embodiments are essentially illustrative and are not intended to limit the present invention. In addition, the present invention is not restricted by any theory described in the foregoing prior art or the invention content or the following embodiments. Description of the Drawings

[0054] Figure 1 It is an electron micrograph of the pitch-based graphite fiber prepared in Example 1 of the present invention;

[0055] Figure 2 It is an electron micrograph of the pitch-based graphite fiber prepared in Example 2 of the present invention;

[0056] Figure 3 SEM cross-sectional image of the pitch-based graphite fiber prepared in Example 3 of the present invention;

[0057] Figure 4 SEM image of the pore structure of the activated fiber prepared in Comparative Example 6 of the present invention. Detailed implementation manners

[0058] The present invention will be further described below in conjunction with 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 claimed by the present invention.

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

[0060] Source of raw materials:

[0061] Coal-tar pitch comes from high-temperature coal-tar pitch in a coking plant or liquefied pitch from a direct coal liquefaction plant;

[0062] Biomass tar comes from a biomass pyrolysis process and uses one or several of the whole fraction or fractions extracted using a temperature gradient: 150 - 200 °C fraction, 200 - 250 °C fraction, 250 - 300 °C fraction, 300 - 350 °C fraction, 350 - 400 °C fraction.

[0063] Example 1

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

[0065] (2) Raise the temperature to 400 °C at a rate of 3 °C / min to allow the copolymerization product obtained in (1) to react for 3 h to prepare the pitch. During this period, purge with N2 at a flow rate of 3 L / min.

[0066] (3) Raise the temperature of the pitch obtained in step (2) to 370 °C at a rate of 3 °C / min in a spinning machine. Under a N2 pressure of 0.7 MPa, perform melt spinning through a circular nozzle with a diameter of 0.15 mm and a length-to-diameter ratio of 3, and the spinning rate is 700 r / min.

[0067] (4) After the reaction, the pitch-based fibers obtained in step (3) were heated from room temperature to 150 °C at a heating rate of 5 °C / min with an air flow rate of 50 mL / min, and then the air flow rate was kept unchanged, and the temperature was raised to 340 °C at a heating rate of 0.5 °C / min for stabilization treatment.

[0068] (5) After the reaction, the stabilized pitch-based fibers obtained in step (4) were heated from room temperature to 1300 °C at a heating rate of 5 °C / min with an N2 flow rate of 50 mL / min for carbonization treatment.

[0069] (6) After the reaction, the pitch-based carbon fibers obtained in step (5) were heated to 2800 °C in an argon environment and kept for 10 min for graphitization treatment to obtain pitch-based graphite fibers.

[0070] The C / H atomic ratio of the pitch prepared by adding 1 wt.% of the 300 - 350 °C fraction of biomass tar to high-temperature coal tar pitch is 2.20. The contents of C, H, N, S, and O elements of this pitch measured by an elemental analyzer are 94.05 wt.%, 3.56 wt.%, 0.82 wt.%, 0.36 wt.%, and 1.21 wt.%, respectively. The softening point of the pitch obtained by this method measured by a thermomechanical analyzer is 267.5 °C. As Figure 1 shown, using a scanning electron microscope to observe the interfacial structure of the prepared carbon fibers and graphite fibers, it was found that after high-temperature carbonization and graphitization of the fibers, nano-scale pore structures appeared in the fiber cross-section, which were axial through-holes. At the same time, the carbonized fibers had a tensile strength of 1.06 GPa (GB / T 31290-2022), and the graphitized fibers had 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 group composition of the high-temperature coal tar pitch is 23.44% n-hexane soluble matter (HS), 51.88% n-hexane insoluble-toluene soluble matter (HI-TS), 24.67% toluene insoluble-quinoline soluble matter (TI-QS), and 0.01% quinoline insoluble matter (QI). Add 0.05 kg of the 250 - 300 °C fraction of biomass tar (QI content 0.01%) and 0.10 kg of the 300 - 350 °C fraction of biomass tar (QI content 0.01%) to the high-pressure reactor. After purging with N2 for 20 min, react at 220 °C under a pressure of 0.6 MPa for 2 h to complete the copolymerization of biomass tar and coal tar pitch.

[0073] (2) Raise the temperature at a rate of 3 °C / min to 400 °C, and let the copolymer product obtained in (1) react for 3 h to prepare pitch. During this period, purge with N2 at a flow rate of 3 L / min.

[0074] (3) Raise the temperature of the pitch obtained in step (2) in a spinning machine at a rate of 3 °C / min to 370 °C, and carry out melt spinning through a circular nozzle with a diameter of 0.15 mm and a length-to-diameter ratio of 3 under a N2 pressure of 0.7 MPa. The spinning rate is 700 r / min.

[0075] (4) After the reaction is completed, heat the pitch-based fiber obtained in step (3) from room temperature to 150 °C at a rate of 5 °C / min under an air flow rate of 50 mL / min, then keep the air flow rate unchanged, and raise the temperature to 340 °C at a rate of 0.5 °C / min for stabilization treatment.

[0076] (5) After the reaction is completed, heat the stabilized pitch-based fiber obtained in step (4) from room temperature to 1300 °C at a rate of 5 °C / min under a N2 flow rate of 50 mL / min for carbonization treatment.

[0077] (6) After the reaction is completed, raise the temperature of the pitch-based carbon fiber obtained in step (5) to 2800 °C in an argon environment and keep it for 10 min for graphitization treatment to obtain pitch-based graphite fiber.

[0078] The C / H atomic ratio of the pitch prepared by adding 3 wt.% biomass tar fraction to high-temperature coal tar pitch is 2.26. The contents of C, H, N, S, and O elements of this pitch measured by an elemental analyzer are 93.97 wt.%, 3.47 wt.%, 0.95 wt.%, 0.35 wt.%, and 1.26 wt.%, respectively. The softening point of the pitch obtained by this method measured by a thermomechanical analyzer is 273.4 °C. As Figure 2 shown, by using a scanning electron microscope to observe the interfacial structure of the prepared carbon fiber and graphite fiber, it is found that after the fiber undergoes high-temperature carbonization and graphitization, there are many nano-scale pore structures on the fiber cross-section, which are axial through-holes. At the same time, the carbonized fiber has a tensile strength of 1.25 GPa (GB / T 31290-2022), and the graphitized fiber has a tensile strength of 2.06 GPa (GB / T 31290-2022).

[0079] Example 3

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

[0081] (2) Raise the temperature to 400 °C at a heating rate of 3 °C / min to allow the copolymer product obtained in (1) to react for 3 h for asphalt preparation. During this period, purge with N2 at a flow rate of 3 L / min.

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

[0083] (4) After the reaction, heat the pitch-based fiber obtained in step (3) from room temperature to 150 °C at a heating rate of 5 °C / min under an air flow rate of 50 mL / min, and then keep the air flow rate unchanged. Raise the temperature to 340 °C at a heating rate of 0.5 °C / min for stabilization treatment.

[0084] (5) After the reaction, heat the stabilized pitch-based fiber obtained in step (4) from room temperature to 1300 °C at a heating rate of 5 °C / min under a N2 flow rate of 50 mL / min for carbonization treatment.

[0085] (6) After the reaction, raise the temperature of the pitch-based carbon fiber obtained in step (5) to 2800 °C in an argon environment and hold for 10 min for graphitization treatment to obtain pitch-based graphite fiber.

[0086] The C / H atomic ratio of the asphalt prepared by adding 5 wt.% of biomass tar fraction to high-temperature coal tar pitch is 2.27. The contents of C, H, N, S, and O elements of this asphalt measured by an elemental analyzer are 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 by a thermomechanical analyzer is 283.9 °C. As Figure 3As shown in the figure, using a scanning electron microscope to observe the interfacial structure of the prepared carbon fibers and graphite fibers, it is found that after the fibers are subjected to high-temperature carbonization and graphitization, more nano-scale pore structures appear on the fiber cross-section, which are axial through-holes. At the same time, the carbonized fibers have a tensile strength of 1.01 GPa (GB / T 31290-2022), and the graphitized fibers have a tensile strength of 1.86 GPa (GB / T 31290-2022).

[0087] Example 4

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

[0089] (2) Raise the temperature to 400 °C at a rate of 3 °C / min to allow the copolymerization product obtained in (1) to react for 3 h to prepare the pitch. During this period, purge with N2 at a flow rate of 3 L / min.

[0090] (3) Raise the pitch obtained in step (2) to 370 °C at a rate of 3 °C / min in a spinning machine. Under a N2 pressure of 0.7 MPa, conduct melt spinning through a circular nozzle with a diameter of 0.15 mm and a length-diameter ratio of 3, and the spinning rate is 700 r / min.

[0091] (4) After the reaction is completed, heat the pitch-based fibers obtained in step (3) from room temperature to 150 °C at a rate of 5 °C / min under an air flow rate of 50 mL / min and then keep the air flow rate unchanged. Raise the temperature to 340 °C at a rate of 0.5 °C / min for infusibilization treatment.

[0092] (5) After the reaction is completed, heat the infusibilized pitch-based fibers obtained in step (4) from room temperature to 1300 °C at a rate of 5 °C / min under a N2 flow rate of 50 mL / min for carbonization treatment.

[0093] (6) After the reaction is completed, raise the temperature of the pitch-based carbon fibers obtained in step (5) to 2800 °C in an argon environment and hold for 10 min for graphitization treatment to obtain pitch-based graphite fibers.

[0094] Add 5 wt.% biomass tar fraction to high-temperature coal tar pitch, and the C / H atomic ratio of the pitch prepared by secondary polymerization is 2.36. The contents of C, H, N, S, and O elements of this pitch measured by an elemental analyzer are 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 is measured by a thermomechanical analyzer to be 281.7 °C. Using a scanning electron microscope to observe the interfacial structure of the prepared carbon fiber and graphite fiber, it is found that after the fiber is carbonized and graphitized at high temperature, a certain nano-level pore structure appears in the fiber cross-section, which is an axially through hole. At the same time, the carbonized fiber has a tensile strength of 1.08 GPa (GB / T 31290-2022), and the graphitized fiber has a tensile strength of 1.94 GPa (GB / T 31290-2022).

[0095] Example 5

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

[0097] (2) Raise the temperature to 400 °C at a heating rate of 3 °C / min to react the copolymer product obtained in (1) for 3 h to prepare the pitch. During this period, purge with N2 at a flow rate of 3 L / min.

[0098] (3) Raise the temperature of the pitch obtained in step (2) to 370 °C at a heating rate of 3 °C / min in a spinning machine, and carry out melt spinning through a circular nozzle with a diameter of 0.15 mm and a length-diameter ratio of 3 under a N2 pressure of 0.7 MPa, with a spinning rate of 700 r / min.

[0099] (4) After the reaction is completed, heat the pitch-based fiber obtained in step (3) from room temperature to 150 °C at a heating rate of 5 °C / min under an air flow rate of 50 mL / min, and then keep the air flow rate unchanged and raise the temperature to 340 °C at a heating rate of 0.5 °C / min for infusibilization treatment.

[0100] (5) After the reaction is completed, the infusibilized pitch-based fibers obtained in step (4) are carbonized by heating from room temperature to 1300 °C at a heating rate of 5 °C / min under a N₂ flow rate of 50 mL / min.

[0101] (6) After the reaction is completed, the pitch-based carbon fibers obtained in step (5) are graphitized by heating to 2800 °C in an argon environment and holding for 10 min to obtain pitch-based graphite fibers.

[0102] 5 wt.% of biomass tar fraction is added to high-temperature coal tar pitch, and the C / H atomic ratio of the pitch prepared by secondary polymerization is 2.09. The contents of C, H, N, S, and O elements of this pitch measured by an elemental analyzer are 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 is measured to be 290.2 °C by a thermomechanical analyzer. Using a scanning electron microscope to observe the interfacial structure of the prepared carbon fibers and graphite fibers, it is found that after the fibers are subjected to high-temperature carbonization and graphitization, a certain amount of nano-scale pore structures appear in the fiber cross-section, which are axial through-holes. At the same time, the carbonized fibers have a tensile strength of 1.00 GPa (GB / T 31290-2022), and the graphitized fibers have 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 group composition of the high-temperature coal tar pitch is 22.48% of n-hexane soluble matter (HS), 54.56% of n-hexane insoluble-toluene soluble matter (HI-TS), 22.95% of toluene insoluble-quinoline soluble matter (TI-QS), and 0.01% of quinoline insoluble matter (QI). Add 0.10 kg of biomass tar fraction at 250-300 °C (QI content 0), 0.10 kg of biomass tar fraction at 300-350 °C (QI content 0.01%), and 0.05 kg of biomass tar fraction at 350-400 °C (QI content 0.01%) to the high-pressure reactor. After purging with N₂ for 20 min, react at 220 °C under a pressure of 0.6 MPa for 2 h to complete the copolymerization of biomass tar and coal tar pitch.

[0105] (2) Raise the temperature to 420 °C at a heating rate of 3 °C / min, and let the copolymerization product obtained in (1) react for 3 h to prepare pitch. During this period, purge with N₂ at a flow rate of 3 L / min.

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

[0107] (4) After the reaction ended, the pitch-based fibers obtained in step (3) were heated from room temperature to 150 °C at a heating rate of 5 °C / min under an air flow rate of 50 mL / min, and then the air flow rate remained unchanged. The fibers were further heated to 340 °C at a heating rate of 0.5 °C / min for infusibilization treatment.

[0108] (5) After the reaction ended, the infusibilized pitch-based fibers obtained in step (4) were heated from room temperature to 1300 °C at a heating rate of 5 °C / min under a N2 flow rate of 50 mL / min for carbonization treatment.

[0109] (6) After the reaction ended, the pitch-based carbon fibers obtained in step (5) were heated to 2800 °C in an argon environment and held for 10 min for graphitization treatment to obtain pitch-based graphite fibers.

[0110] 5 wt.% of biomass tar fraction was added to high-temperature coal tar pitch, and the C / H atomic ratio of the pitch prepared by secondary polymerization was 2.31. The contents of C, H, N, S, and O elements of this pitch were measured by an elemental analyzer to be 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 measured by a thermomechanical analyzer to be 287.5 °C. Using a scanning electron microscope to observe the interfacial structure of the prepared carbon fibers and graphite fibers, it was found that after the fibers were subjected to high-temperature carbonization and graphitization, nanoscale pore structures appeared in the fiber cross-section, which were axial through-holes. At the same time, the carbonized fibers had a tensile strength of 1.11 GPa (GB / T 31290-2022), and the graphitized fibers had a tensile strength of 1.96 GPa (GB / T 31290-2022).

[0111] Comparative Example 1

[0112] Same as Example 3, except that no biomass tar was added in step (1), that is, the high-temperature coal tar pitch was directly subjected to step (3) and subsequent steps.

[0113] The prepared pitch has a C / H atomic ratio of 2.57. The contents of C, H, N, S, and O elements in this pitch measured by an elemental analyzer are 94.94 wt.%, 3.08 wt.%, 0.87 wt.%, 0.21 wt.%, and 0.90 wt.% respectively. The softening point of the pitch obtained by this method measured by a thermomechanical analyzer is 298.2 °C. After the fibers are carbonized and graphitized at high temperature, another form of fibers (without pores), mesophase pitch fibers, are formed, and no nano-scale pore structure is found in the fiber cross-section. At the same time, the carbonized fibers have a tensile strength of 1.31 GPa (GB / T 31290-2022), and the graphitized fibers have a tensile strength of 1.98 GPa (GB / T 31290-2022).

[0114] Comparative Example 2

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

[0116] Weigh 5 kg of high-temperature coal tar pitch and place it in a high-pressure reactor. Add 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%) into the high-pressure reactor. The prepared pitch has a C / H atomic ratio of 1.93. The contents of C, H, N, S, and O elements in this pitch measured by an elemental analyzer are 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 measured by a thermomechanical analyzer is 293.1 °C. Using a scanning electron microscope to observe the interfacial structure of the prepared carbon fibers and graphite fibers, it is found that after the fibers are carbonized and graphitized at high temperature, no nano-scale pore structure is found in the fiber cross-section, and there are relatively large defects in the fiber structure. At the same time, the carbonized fibers have a tensile strength of 0.61 GPa (GB / T 31290-2022), and the graphitized fibers have a tensile strength of 0.69 GPa (GB / T 31290-2022).

[0117] Comparative Example 3

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

[0119] The C / H atomic ratio of the asphalt prepared by adding 0.25kg of biomass tar 200-250℃ fraction to high-temperature coal tar pitch is 2.23. The contents of C, H, N, S, and O in the asphalt measured by an elemental analyzer are 93.28wt.%, 3.48wt.%, 0.92wt.%, 0.46wt.%, and 1.86wt.%, respectively. The softening point of the asphalt obtained by this method measured by a thermomechanical analyzer is 266.2℃. After the fiber is carbonized and graphitized at high temperature, a small amount of nanoscale pore structure is found in the fiber cross section, indicating that the biomass tar 200-250℃ fraction has a weak effect on the formation of pores. At the same time, the fiber has a tensile strength of 0.62GPa after carbonization (GB / T31290-2022) and a tensile strength of 1.29GPa after graphitization (GB / T 31290-2022).

[0120] Comparative Example 4

[0121] The process is the same as Example 3, except that the copolymerization of coal tar pitch and biomass tar fraction by reacting at 220° C. and 0.6 MPa for 2 h in step (1) is omitted.

[0122] The C / H atomic ratio of the asphalt prepared by adding 0.10kg of biomass tar 250-300℃ fraction, 0.10kg of biomass tar 300-350℃ fraction, and 0.05kg of biomass tar 350-400℃ fraction to high-temperature coal tar pitch and directly heating to 400℃ is 2.29. The contents of C, H, N, S, and O elements in the asphalt measured by an element analyzer are 93.88wt.%, 3.42wt.%, 0.92wt.%, 0.43wt.%, and 1.35wt.%, respectively. The softening point of the asphalt obtained by this method is 275.1℃ measured by a thermomechanical analyzer. After the fiber is carbonized and graphitized at high temperature, the pore structure content in the fiber cross section is less or some pores are not through, indicating that only one-step polymerization reaction is not conducive to the formation of axial through-hole structure. At the same time, the fiber has a tensile strength of 0.58 GPa after carbonization (GB / T 31290-2022), and has a tensile strength of 1.14 GPa after graphitization (GB / T31290-2022), indicating that the second-step polymerization temperature has a significant effect on the formation of the pore structure and the mechanical properties of asphalt.

[0123] Comparative Example 5

[0124] The asphalt was prepared in the same manner as in Example 3, except that the temperature was raised to 380°C at a rate of 3°C / min in step (2), and the copolymer product obtained in (1) was reacted for 6 hours.

[0125] 0.10 kg of the 250 - 300 °C fraction of biomass tar, 0.10 kg of the 300 - 350 °C fraction of biomass tar, and 0.05 kg of the 350 - 400 °C fraction of biomass tar were added to high-temperature coal-tar pitch. The secondary polymerization temperature was 380 °C, and the prepared pitch had a C / H atomic ratio of 2.24. The contents of C, H, N, S, and O elements in this pitch were measured by an elemental analyzer to be 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 was measured by a thermomechanical analyzer to be 276.4 °C. After the fibers were carbonized and graphitized at high temperature, irregular pore structures existed in the fiber cross-section, and nodules appeared on the fibers. At the same time, the carbonized fibers had a tensile strength of 0.63 GPa (GB / T 31290 - 2022), and the graphitized fibers had a tensile strength of 1.02 GPa (GB / T 31290 - 2022), indicating that the second polymerization temperature had a significant effect on the formation of fibers and pore structures and the mechanical properties of the pitch.

[0126] Comparative Example 6

[0127] Without adding biomass tar, a conventional steam chemical activation method was used. That is, high-temperature coal-tar pitch was subjected to steps (3) - (5), and then the carbonized fibers were put into an activation furnace. After heating to 800 °C, steam was introduced for activation for 1 h, and then it was naturally cooled to obtain activated fibers.

[0128] The C / H atomic ratio of the pitch was 2.57. The contents of C, H, N, S, and O elements in this pitch were measured by an elemental analyzer to be 94.94 wt.%, 3.08 wt.%, 0.87 wt.%, 0.21 wt.%, and 0.90 wt.% respectively. The softening point of the pitch obtained by this method was measured by a thermomechanical analyzer to be 298.2 °C. After the fibers were activated, a large number of pore structures with different scales and randomly distributed were found on the surface and inside of the fibers, as Figure 4 shown. At the same time, the carbonized fibers lost their tensile strength.

[0129] Through the analysis of the results of the comparative examples, it can be seen that the addition of biomass tar fractions can effectively promote the formation of axially penetrating internal pores in the fibers, and adding an appropriate proportion of biomass tar fractions can realize the regulation of the number of internal pores in the fibers. It should be noted that after adding biomass tar fractions, copolymerization is first carried out at low temperature and then the temperature is raised to high temperature for polymerization, which plays a positive role in the formation of nano-pore structures in the fibers. On the one hand, low-temperature copolymerization can enable the molecules of biomass tar fractions to fully integrate into the asphalt molecules; on the other hand, at an appropriate high temperature, larger molecular structures can be effectively formed, which helps the stacking of molecular structures; at the same time, the axially penetrating micro-nano pore structures have the characteristics of a molecular sieve structure while not affecting the mechanical properties of the carbon fibers, and have good application potential.

[0130] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting it. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: within the scope of the spirit and essence defined by the claims of the present invention, the technical solutions described in the foregoing embodiments can be modified, or some or all of the technical features can be equivalently replaced; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. A preparation method of an asphalt-based graphite fiber with axially through internal pores, characterized in that, It includes the following steps: (1) Uniformly mix the biomass tar fraction and the coal-tar pitch raw material and place them in a high-pressure reactor for a preliminary polymerization reaction under an inert atmosphere; the biomass tar fraction is the whole fraction or the fraction containing 200 °C or higher; the blending ratio of the biomass tar fraction accounts for 1-10 wt% of the coal-tar pitch raw material; the temperature of the preliminary polymerization reaction is 180-240 °C, the pressure of the preliminary polymerization reaction is 0.1-5 MPa, and the time of the preliminary polymerization reaction is 0.5-5 h; (2) Further raise the temperature for a secondary polymerization reaction to obtain spinnable pitch; the temperature of the secondary polymerization reaction is 390-420 °C, and the time of the secondary polymerization reaction is 1-6 h; (3) Perform melt spinning on the spinnable pitch obtained in step (2) in a spinning machine to obtain green pitch-based fibers; (4) Subject the green pitch-based fibers obtained in step (3) to infusibilization treatment; (5) Carbonize the pitch-based fibers after the infusibilization treatment in step (4) to obtain pitch-based carbon fibers; (6) Graphitize the pitch-based carbon fibers obtained in step (5) to obtain pitch-based graphite fibers with axially through internal pores.

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

3. The preparation method according to claim 1, characterized in that, In step (1), the biomass tar fraction contains fractions at 300-350 °C and above, and the content of quinoline insoluble matter is 0-0.03%.

4. The preparation method according to claim 1, wherein In step (1), the temperature of the preliminary polymerization reaction is 200-220 °C, the pressure of the preliminary polymerization reaction is 0.5-1 MPa, and the time of the preliminary polymerization reaction is 1-3 h.

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

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

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

8. The preparation method according to claim 1, wherein In step (5), the carbonization treatment includes: heating from room temperature to 1000-1500 °C at a heating rate of 2-8 °C / min under an inert gas flow rate of 50-150 mL / min.

9. The preparation method according to claim 1, characterized in that, In step (6), the graphitization treatment includes: heating to 2600-3000 °C under an inert gas and holding for 5-60 min.

10. An asphalt-based graphite fiber with axially penetrating internal pores, characterized in that, Prepared by the preparation method according to any one of claims 1-9.

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