Preparation method and application of high-performance spinnable mesophase pitch based on hydrogenation modification and segmented thermal sedimentation process

Abstract

The invention relates to a preparation method and application of high-performance spinnable mesophase pitch based on a hydrogenation modification and segmented thermal sedimentation process, the preparation method comprises the following steps: mixing coal pitch and a hydrogenating agent according to a mass ratio of 1: 3-1: 4, and carrying out high-temperature and high-pressure hydrotreating at 350-450 DEG C to prepare hydrogenated pitch; heating the hydrogenated pitch to 390-420 DEG C in an inert atmosphere, keeping the temperature for 5-8 hours, and naturally cooling to obtain initial mesophase pitch containing an anisotropic phase; grinding the primary mesophase pitch, placing the ground primary mesophase pitch in a graded sedimentation device, preserving heat at 370-400 DEG C for 0.5-3 hours to enrich macromolecular components at the lower part, quickly cooling, and collecting a middle sample to obtain target mesophase pitch suitable for spinning; by accurately controlling the temperature, time and atmosphere, hydrogenation, phase change and graded enrichment of the pitch are realized, and finally the high-quality mesophase pitch for spinning is prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon material preparation, and in particular to a method for preparing high-performance spinnable mesophase pitch based on hydrogenation modification and segmented thermal precipitation technology, and the application of high-performance carbon fibers prepared thereby. Background Art

[0002] As an organic polymer compound with a complex configuration, the condensed aromatic hydrocarbon skeleton of coal tar pitch lays a molecular foundation for the synthesis of mesophase asphalt. In the field of high-end carbon fiber preparation, mesophase asphalt as a key spinning precursor directly determines the performance level of the final product. The current process mainly relies on the heat treatment system to induce the directional arrangement of aromatic ring structures in coal tar pitch and carry out orderly molecular reorganization, thereby producing an mesophase product with a high anisotropic phase content. However, conventional processes often make it difficult to accurately control the distribution of macromolecular components, which may not only cause the attenuation of melt rheological properties, but also cause a wide molecular weight distribution, thereby affecting the spinning continuity and mechanical properties of carbon fiber.

[0003] Mesophase pitch is an aromatic polymer material with liquid crystal properties and an important precursor for the preparation of high-performance carbon fibers. By melt spinning the mesophase pitch and subjecting it to pre-oxidation, carbonization and other treatments, carbon fiber materials with excellent mechanical properties can be obtained, which are widely used in high-end fields such as aerospace, national defense, and sports equipment.

[0004] The directional hydrogenation modification technology based on hydrogenating agents can remove unstable components, thereby providing a better reaction environment for the orderly reorganization of microcrystals. However, if the reaction temperature gradient, constant temperature duration and hydrogenation degree parameters are not accurately controlled, problems such as excessive local cross-linking density or residual by-products are likely to occur, which will ultimately limit the homogenization level of the mesophase asphalt. For mesophase asphalt with high aromaticity and enriched macromolecular components, how to balance good fluidity and high orientation in the subsequent spinning process has always been a difficult problem faced in the preparation of mesophase asphalt with excellent spinnability. Thermal precipitation treatment has been proven to be able to effectively enrich macromolecules at a specific temperature and reduce the interference of small molecules or unfavorable components, thereby significantly improving the anisotropy content of the mesophase asphalt.

[0005] Traditional mesophase asphalt preparation methods mainly include heat treatment, solvent extraction and catalytic cracking. Among them, the heat treatment method is widely used due to its relatively simple process and low cost. However, this method has the following obvious shortcomings: on the one hand, it is difficult to accurately control the distribution of macromolecular components in coal tar pitch with simple heat treatment, resulting in a wide molecular weight distribution and poor uniformity of the obtained mesophase asphalt; on the other hand, the unstable components in coal tar pitch are difficult to effectively remove, which will form bubbles or impurities in the subsequent spinning process, causing problems such as fiber breakage and reduced strength.

[0006] In addition, although domestic and foreign researchers have also tried to modify mesophase pitch through methods such as solvent extraction or hydrotreating, these single treatment methods often have difficulty in taking into account both the high anisotropic content and excellent rheological properties of mesophase pitch. For example, excessive hydrotreating may reduce the aromaticity of the pitch, which is not conducive to the formation of mesophase; while the simple solvent extraction method will lead to problems such as low product yield and complex process flow.

[0007] Therefore, there is an urgent need to develop a new method for preparing mesophase pitch that can effectively regulate the molecular weight distribution, increase the anisotropic content, improve the rheological properties, thereby obtaining high-performance spinnable mesophase pitch and further enhancing the mechanical properties of carbon fiber. Summary of the Invention

[0008] In view of the above problems existing in the prior art, the present invention provides a method for preparing high-performance spinnable mesophase pitch based on hydrogenation modification and fractional thermal sedimentation process. Through the combined process of hydrogenation modification and fractional thermal sedimentation, unstable components in coal tar pitch are effectively removed, and the directional enrichment of macromolecular components is realized, significantly enhancing the homogeneity and uniformity of the spinning raw material, thereby obtaining mesophase pitch more suitable for melt spinning.

[0009] To solve the above technical problems, the present invention adopts the following technical solutions: A method for preparing high-performance spinnable mesophase pitch based on hydrogenation modification and fractional thermal sedimentation process, the method comprising the following steps: (1) Mix coal tar pitch with a specific hydrogenating agent in a mass ratio of 1:3 to 1:4, and carry out high-temperature and high-pressure hydrotreating in an inert atmosphere within the temperature range of 350 °C to 450 °C to obtain hydrogenated pitch; (2) Heat the hydrogenated pitch obtained in step (1) to 390 °C to 420 °C at a heating rate of 5 °C / min to 10 °C / min in an inert atmosphere, and keep it at this temperature for 5 h to 8 h. After natural cooling to room temperature, obtain preliminary mesophase pitch with a certain anisotropic phase content; (3) Grind the preliminary mesophase pitch obtained in step (2) and place it in a fractional sedimentation device, keep it at a temperature range of 370 °C to 400 °C for 0.5 h to 3 h under the protection of an inert atmosphere, fractionally enrich the molecular components, so that the macromolecular components are enriched in the lower part, and then quickly cool to room temperature and collect the middle sample to obtain the target mesophase pitch suitable for spinning.

[0010] Preferably, the specific hydrogenating agent in step (1) is selected from tetralin, tetrahydroquinoline, naphthyltetrahydro compounds, polycyclic aromatic hydrocarbon hydrides and their mixtures. These hydrogenating agents have good hydrogen transfer ability, can effectively stabilize free radicals in coal tar pitch, prevent excessive cross-linking, and at the same time promote the orderly arrangement of aromatic structures.

[0011] Furthermore, the high-temperature and high-pressure hydrotreating in step (1) is carried out under the conditions of a reaction pressure of 3 MPa to 10 MPa and a heat preservation time of 2 h to 6 h. By precisely controlling the reaction pressure and the heat preservation time, an appropriate degree of hydrogenation modification effect can be obtained, which can not only effectively remove unstable components but also not reduce the aromaticity of the pitch.

[0012] In one embodiment of the present invention, the inert atmosphere in step (2) is nitrogen, argon or helium, and the gas flow rate is 50 ml / min to 200 ml / min. The selection of the inert atmosphere and the control of the flow rate are of great significance for preventing the oxidation of the mesophase pitch.

[0013] Particularly, the fractional sedimentation device in step (3) is a three-stage vertical reactor with a temperature gradient control function. The reactor is provided with an upper region, a middle region and a lower region from top to bottom, and the temperature of each region can be independently controlled. This specially designed fractional sedimentation device can form a temperature gradient during the thermal sedimentation process, promoting the directional migration and enrichment of components with different molecular weights.

[0014] More preferably, in the three-stage vertical reactor, the temperature gradient is such that the temperature of the upper region is 5°C to 15°C lower than that of the middle region, and the temperature of the lower region is 5°C to 15°C higher than that of the middle region. The temperature of the middle region is 370°C to 400°C, and heat preservation is carried out within this temperature range for 0.5 h to 3 h. This temperature gradient design can ensure the downward enrichment of macromolecular components while avoiding the decrease in molecular mobility caused by too low a temperature.

[0015] In addition, the middle sample in step (3) refers to the sample within a range of 5 mm to 20 mm away from the boundaries of the upper region and the lower region in the middle region of the fractional sedimentation device. The middle sample has both an appropriate molecular weight distribution and a high anisotropic phase content, and is an ideal choice for preparing high-performance spinnable mesophase pitch.

[0016] To ensure the purity of the reaction environment, steps (1) to (3) are all carried out under an inert atmosphere with an oxygen content of less than 50 ppm. This helps prevent the oxidation of the mesophase pitch at high temperatures and maintain its excellent rheological properties and anisotropic phase structure.

[0017] The high-performance spinnable mesophase pitch prepared by the preparation method of the present invention has a softening point of 275°C to 330°C, a mesophase content of more than 95%, a toluene-insoluble content of more than 80% and a quinoline-insoluble content of more than 18%, and presents a wide-area streamline optical texture.

[0018] The present invention also provides the application of the high-performance spinnable mesophase pitch in the preparation of carbon fibers, including the following steps: a. melt spinning the mesophase pitch at 340° C. to 375° C. to obtain prefibers; b. pre-oxidizing the prefiber obtained in step a in an air atmosphere at a temperature ranging from 200° C. to 300° C. for a pre-oxidation time of 0.5 h to 2 h; c. The pre-oxidized fiber obtained in step b is heated to 1000°C to 2000°C at a heating rate of 5°C / min to 15°C / min under an inert atmosphere and kept at this temperature for 0.5 h to 2 h for carbonization treatment to obtain high-performance mesophase asphalt-based carbon fiber.

[0019] Compared with the prior art, the present invention has the following significant technical effects: 1. Through the combined process of hydrogenation modification and segmented thermal precipitation, the unstable components in coal tar pitch are effectively removed, the directional enrichment of macromolecular components is achieved, and the uniformity and homogeneity of spinning raw materials are significantly enhanced, thereby obtaining a mesophase pitch that is more suitable for melt spinning. The mesophase pitch prepared by this method has a softening point of 275°C to 330°C, a mesophase content of more than 95%, a large-area streamlined optical texture, a toluene insoluble content of more than 80%, and a quinoline insoluble content of more than 18%. These characteristics make it have ideal spinning performance.

[0020] 2. The mesophase pitch obtained by the method of the present invention exhibits excellent stability during the spinning process, moderate melt viscosity, significantly reduced fiber breakage rate, and significantly reduced number of fiber surface defects, and can maintain a high spinning efficiency in large-scale continuous production.

[0021] 3. The cross section of the carbon fiber prepared by the method of the present invention has a distinct radial structure, defects such as holes and cracks are significantly reduced, and the uniformity and mechanical properties of the fiber are significantly improved. The final tensile strength of the carbon fiber can reach 1600 to 2400 MPa, and the modulus can reach 160 to 300 GPa. These performance indicators have approached or reached the international advanced level.

[0022] 4. The method of the present invention is easy to operate, has a reasonable process flow, low energy consumption, is suitable for industrial production, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 This is a schematic diagram of a three-stage vertical reactor used in the present invention.

[0025] Figure 2 It is the polarized light image of the mesophase pitch prepared in Example 1 of the present invention.

[0026] Figure 3 It is the SEM image of the carbon fiber prepared in Example 6 of the present invention. Detailed implementation manners

[0027] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0028] The present invention will be further described below through specific embodiments. The present invention provides a method for preparing a high-performance spinnable mesophase pitch based on hydrogenation modification and thermal sedimentation process. By subjecting coal tar pitch to hydrogenation modification and fractional thermal sedimentation treatment, unstable components are effectively removed, directional enrichment of macromolecular components is achieved, and the anisotropic phase content and rheological properties of the mesophase pitch are significantly improved, thereby preparing a high-performance spinnable mesophase pitch.

[0029] In the present invention, first, the coal tar pitch is subjected to hydrotreating. Coal tar pitch is a high-molecular mixture with a complex chemical structure, mainly composed of polycyclic aromatic hydrocarbons and their derivatives. Through hydrotreating, free radicals in the coal tar pitch can be stabilized, crosslinking reactions can be reduced, and at the same time, unstable groups such as oxygen-containing and sulfur-containing groups can be removed, creating favorable conditions for the subsequent formation of mesophase. During the hydrotreating process, parameters such as the selection and dosage of the hydrogenating agent, reaction temperature and pressure have an important impact on the modification effect. The present invention preferably uses compounds with good hydrogen transfer ability such as tetralin and tetrahydroquinoline as the hydrogenating agent, mixes them in a mass ratio of 1:3 to 1:4 with the coal tar pitch, and performs high-temperature and high-pressure treatment under the conditions of 350 °C to 450 °C and 3 MPa to 10 MPa, and the heat preservation time is 2 h to 6 h.

[0030] Secondly, the hydrogenated modified pitch is placed under an inert atmosphere for heat treatment to form a preliminary mesophase structure. In this stage, aromatic molecules in the hydrogenated pitch undergo dehydrogenation condensation reactions under high temperature to form anisotropic phases with liquid crystal properties. In the present invention, the heat treatment process is heated to 390 °C to 420 °C at a heating rate of 5 °C / min to 10 °C / min and held at this temperature for 5 h to 8 h. Such relatively mild heat treatment conditions are conducive to the orderly arrangement of aromatic molecules and reduce the formation of bubbles and impurities.

[0031] Finally, the preliminarily formed mesophase pitch is subjected to fractional thermal sedimentation treatment to achieve the directional enrichment of molecular components. Thermal sedimentation is a method of component separation under the action of gravity based on the density and fluidity differences caused by molecular weight differences. In this invention, a specially designed three-stage vertical reactor is used for thermal sedimentation treatment. By controlling the temperature gradient in different regions, the macromolecular components are promoted to enrich downward, and the medium and small molecular components migrate upward. The fractional thermal sedimentation process is carried out in the temperature range of 370 °C to 400 °C, and the heat preservation time is 0.5 h to 3 h. After the heat preservation is completed, it is quickly cooled to room temperature, and the middle part sample is collected as the target product. The middle part sample has both a suitable molecular weight distribution and a high anisotropic phase content, and is an ideal choice for preparing high-performance spinnable mesophase pitch.

[0032] Example 1 The preparation method of high-performance spinnable mesophase pitch based on hydrogenation modification and fractional thermal sedimentation process in this example includes the following steps: (1) Coal tar pitch and tetralin (analytical pure, Aladdin Reagent Co., Ltd.) are fully mixed according to a mass ratio of 1:3 and added into a high-temperature and high-pressure reactor with an internal volume of 1 L. After sealing the reactor, it is first purged with nitrogen 3 times to remove the air in the reactor, and then heated to 420 °C at a heating rate of 5 °C / min under a nitrogen atmosphere. The reaction pressure is 5 MPa, and the heat preservation time is 4 h. After the reaction is completed, it is cooled to room temperature to obtain hydrogenated pitch.

[0033] (2) Weigh 80 g of the above hydrogenated pitch, grind it to below 200 meshes, and put it into a tube furnace. Under nitrogen protection (oxygen content < 30 ppm, gas flow rate is 100 ml / min), it is heated to 410 °C at a heating rate of 5 °C / min and kept for 5 h. After the experiment is completed, it is naturally cooled to room temperature, and the sample is taken out to obtain a preliminary mesophase pitch with a certain anisotropic phase content.

[0034] (3) Take 50 g of the above preliminary mesophase pitch, grind it and place it in Figure 1In the shown three-stage vertical reactor, the filling amounts in each region are approximately equal. Nitrogen (flow rate: 80 ml / min) is introduced into the reactor. After removing the air, the reactor is heated to the predetermined temperatures: 365 °C in the upper region, 370 °C in the middle region, and 380 °C in the lower region, and kept at these temperatures for 1 h. After the reaction ends, it is quickly cooled to room temperature with cooling water, and samples more than 10 mm away from the upper and lower boundaries in the middle region are collected to obtain the target mesophase pitch. The sample in the light component aggregation area is located in the upper part of the three-stage vertical reactor and contains un-deposited or incompletely reacted mesophase pitch components, with a low mesophase content; the target sample collection area is located in the area between the two dotted lines, that is, in the middle part of the three-stage vertical reactor, which can not only ensure a relatively low softening point of the pitch but also ensure a relatively high mesophase content; while the sample in the heavy component deposition area is located in the area below the bottom dotted line, that is, in the lower part of the three-stage vertical reactor, and is mainly composed of mesophase pitch aggregated by gravitational sedimentation and during the reaction process.

[0035] (4) Performance tests are carried out on the obtained target mesophase pitch. The results show that: the softening point is 275 °C, the mesophase content is 95%, the toluene-insoluble content is 82.5%, the quinoline-insoluble content is 19.2%, and it presents a large-area streamline optical texture, as Figure 2 shown.

[0036] (5) The above-mentioned target mesophase pitch is melt-spun at 350 °C, then pre-oxidized in an air atmosphere at 250 °C for 1 h, and then heated to 1500 °C at a heating rate of 10 °C / min under nitrogen protection and kept at this temperature for 1 h for carbonization treatment to obtain carbon fibers. The test results show that the tensile strength of the carbon fiber is 1850 MPa and the modulus is 180 GPa.

[0037] Example 2 This example is a method for preparing high-performance spinnable mesophase pitch based on hydrogenation modification and segmented thermal sedimentation process, including the following steps: (1) Coal tar pitch and tetralin are fully mixed according to a mass ratio of 1:3 and added into a high-temperature and high-pressure reactor with an internal volume of 1 L. After sealing the reactor, it is first purged with nitrogen 3 times to remove the air in the reactor, and then heated to 420 °C at a heating rate of 5 °C / min under a nitrogen atmosphere, with a reaction pressure of 5 MPa, and kept at this temperature for 4 h. After the reaction ends, it is cooled to room temperature to obtain hydrogenated pitch.

[0038] (2) Weigh 80 g of the above hydrogenated asphalt, grind it to less than 200 mesh, and put it into a tube furnace. Under nitrogen protection (oxygen content <30ppm, gas flow rate of 100ml / min), heat it to 410°C at a heating rate of 5°C / min and keep it warm for 5 h. After the experiment, cool it naturally to room temperature, take out the sample, and obtain a preliminary mesophase asphalt with a certain anisotropic phase content.

[0039] (3) Take 50g of the above preliminary mesophase asphalt, grind it and place it in a three-stage vertical reactor. Introduce nitrogen (flow rate is 80 ml / min) into the reactor, exclude air, and heat the reactor to the predetermined temperature: 370°C in the upper area, 380°C in the middle area, and 390°C in the lower area, and keep it warm for 1 hour. After the reaction is completed, cool it down to room temperature quickly with cooling water, collect samples in the middle area that are more than 10 mm away from the upper and lower boundaries, and obtain the target mesophase asphalt.

[0040] (4) The performance of the target mesophase asphalt was tested. The results showed that the softening point was 305°C, the mesophase content was 98%, the toluene insoluble content was 83.7%, the quinoline insoluble content was 20.1%, and it exhibited a large-area streamlined optical texture.

[0041] (5) The target mesophase pitch was melt-spun at 360°C, then pre-oxidized at 250°C in an air atmosphere for 1 h, and then heated to 1500°C at a heating rate of 10°C / min under nitrogen protection and kept at that temperature for 1 h for carbonization treatment to obtain carbon fiber. The test results show that the tensile strength of the carbon fiber is 2020 MPa and the modulus is 210 GPa.

[0042] Example 3 The method for preparing high-performance spinnable mesophase pitch based on hydrogenation modification and segmented thermal precipitation process in this embodiment comprises the following steps: (1) Coal tar pitch and tetralin were fully mixed in a mass ratio of 1:3 and added to a high-temperature and high-pressure reactor with an internal volume of 1 L. After sealing the reactor, the air in the reactor was removed by replacing it with nitrogen three times. Then, the temperature was raised to 420°C at a heating rate of 5°C / min under a nitrogen atmosphere. The reaction pressure was 5 MPa and the temperature was kept for 4 h. After the reaction was completed, the mixture was cooled to room temperature to obtain hydrogenated asphalt.

[0043] (2) Weigh 80 g of the above hydrogenated asphalt, grind it to less than 200 mesh, and put it into a tubular furnace. Under nitrogen protection (oxygen content <30 ppm, gas flow rate of 100 ml / min), heat it to 410°C at a heating rate of 5°C / min and keep it warm for 5 h. After the experiment, cool it naturally to room temperature, take out the sample, and obtain a preliminary mesophase asphalt with a certain anisotropic phase content.

[0044] (3) Take 50 g of the above preliminary mesophase asphalt, grind it and place it in a three-stage vertical reactor. Introduce nitrogen (flow rate is 80 ml / min) into the reactor, exclude air, and heat the reactor to the predetermined temperature: 380°C in the upper area, 390°C in the middle area, and 400°C in the lower area, and keep it warm for 1 hour. After the reaction is completed, cool it down to room temperature quickly with cooling water, collect samples in the middle area that are more than 10 mm away from the upper and lower boundaries, and obtain the target mesophase asphalt.

[0045] (4) The performance of the target mesophase asphalt was tested. The results showed that the softening point was 325°C, the mesophase content was 98%, the toluene insoluble content was 85.2%, the quinoline insoluble content was 21.5%, and it exhibited a large-area streamlined optical texture.

[0046] (5) The target mesophase pitch was melt-spun at 375°C, then pre-oxidized at 260°C in an air atmosphere for 1 h, and then heated to 1600°C at a heating rate of 10°C / min under nitrogen protection and kept at that temperature for 1 h for carbonization treatment to obtain carbon fiber. The test results show that the tensile strength of the carbon fiber is 2200 MPa and the modulus is 230 GPa.

[0047] Example 4 The method for preparing high-performance spinnable mesophase pitch based on hydrogenation modification and segmented thermal precipitation process in this embodiment comprises the following steps: (1) Coal tar pitch and tetrahydroquinoline (analytical grade, Aladdin Reagent Company) were fully mixed in a mass ratio of 1:4 and added to a high-temperature and high-pressure reactor with an internal volume of 1 L. After sealing the reactor, the air in the reactor was removed by replacing it with nitrogen three times, and then the temperature was raised to 420°C at a heating rate of 5°C / min under a nitrogen atmosphere. The reaction pressure was 6 MPa and the temperature was kept for 4 h. After the reaction was completed, it was cooled to room temperature to obtain hydrogenated asphalt.

[0048] (2) Weigh 80g of the above hydrogenated asphalt, grind it to less than 200 mesh, and put it into a tubular furnace. Under nitrogen protection (oxygen content <30 ppm, gas flow rate of 100 ml / min), heat it to 410℃ at a heating rate of 5℃ / min and keep it warm for 5 hours. After the experiment, cool it naturally to room temperature, take out the sample, and obtain a preliminary mesophase asphalt with a certain anisotropic phase content.

[0049] (3) Take 50 g of the above preliminary mesophase asphalt, grind it and place it in a three-stage vertical reactor. Introduce nitrogen (flow rate is 80 ml / min) into the reactor, exclude air, and heat the reactor to the predetermined temperature: 365°C in the upper area, 370°C in the middle area, and 380°C in the lower area, and keep it warm for 1 hour. After the reaction is completed, cool it down to room temperature quickly with cooling water, collect samples in the middle area that are more than 10 mm away from the upper and lower boundaries, and obtain the target mesophase asphalt.

[0050] (4) The performance of the target mesophase asphalt was tested. The results showed that the softening point was 283°C, the mesophase content was 98%, the toluene insoluble content was 84.3%, the quinoline insoluble content was 20.5%, and it exhibited a large-area streamlined optical texture.

[0051] (5) The target mesophase pitch was melt-spun at 340°C, then pre-oxidized at 240°C in an air atmosphere for 1 h, and then heated to 1500°C at a heating rate of 10°C / min under nitrogen protection and kept at that temperature for 1 h for carbonization treatment to obtain carbon fiber. The test results show that the tensile strength of the carbon fiber is 2110 MPa and the modulus is 200 GPa.

[0052] Example 5 The method for preparing high-performance spinnable mesophase pitch based on hydrogenation modification and segmented thermal precipitation process in this embodiment comprises the following steps: (1) Coal tar pitch and a mixture of tetrahydronaphthalene (a mixture of tetrahydronaphthalene and dihydronaphthalene in a mass ratio of 1:1) were fully mixed in a mass ratio of 1:4 and added to a high-temperature and high-pressure reactor with an internal volume of 1L. After the reactor was sealed, it was replaced with nitrogen three times to remove the air in the reactor. Then, the temperature was increased to 420℃ at a heating rate of 5℃ / min in a nitrogen atmosphere, the reaction pressure was 7 MPa, and the temperature was kept for 4 hours. After the reaction was completed, it was cooled to room temperature to obtain hydrogenated asphalt.

[0053] (2) Weigh 80 g of the above hydrogenated asphalt, grind it to less than 200 mesh, and put it into a tubular furnace. Under nitrogen protection (oxygen content <30 ppm, gas flow rate of 100 ml / min), heat it to 410℃ at a heating rate of 5℃ / min and keep it warm for 5 h. After the experiment, cool it naturally to room temperature, take out the sample, and obtain a preliminary mesophase asphalt with a certain anisotropic phase content.

[0054] (3) Take 50 g of the above-mentioned preliminary mesophase pitch, grind it and place it in a three-stage vertical reactor. Introduce nitrogen (flow rate: 80 ml / min) into the reactor. After removing the air, heat the reactor to the predetermined temperature: the upper region is 370 °C, the middle region is 380 °C, and the lower region is 390 °C, and keep it warm for 1 h. After the reaction is completed, quickly cool it to room temperature with cooling water, and collect the samples more than 10 mm away from the upper and lower boundaries in the middle region to obtain the target mesophase pitch.

[0055] (4) Conduct performance tests on the obtained target mesophase pitch. The results show that: the softening point is 290 °C, the mesophase content is 100%, the toluene-insoluble content is 86.5%, the quinoline-insoluble content is 22.3%, and it presents a wide-field streamline optical texture.

[0056] (5) Melt-spin the above-mentioned target mesophase pitch at 350 °C, then pre-oxidize it in an air atmosphere at 250 °C for 1 h, and then heat it to 1700 °C at a heating rate of 10 °C / min under nitrogen protection and keep it warm for 1 h for carbonization treatment to obtain carbon fibers. The test results show that the tensile strength of the carbon fiber is 2400 MPa and the modulus is 260 GPa.

[0057] Example 6 The preparation method of high-performance spinnable mesophase pitch based on hydrogenation modification and segmented thermal sedimentation process in this example includes the following steps: (1) Thoroughly mix coal tar pitch and a polycyclic aromatic hydrocarbon hydride mixture (a mixture composed of anthracene hydride and phenanthrene hydride in a mass ratio of 1:1) in a mass ratio of 1:4, and add it to a high-temperature and high-pressure reactor with an internal volume of 1 L. After sealing the reactor, displace it with nitrogen 3 times to remove the air in the reactor, and then heat it to 420 °C at a heating rate of 5 °C / min under a nitrogen atmosphere, with a reaction pressure of 8 MPa, and keep it warm for 4 h. After the reaction is completed, cool it to room temperature to obtain hydrogenated pitch.

[0058] (2) Weigh 80 g of the above-mentioned hydrogenated pitch, grind it to less than 200 mesh, and put it into a tubular furnace. Under nitrogen protection (oxygen content < 30 ppm, gas flow rate: 100 ml / min), heat it to 410 °C at a heating rate of 5 °C / min and keep it warm for 5 h. After the experiment is completed, naturally cool it to room temperature, take out the sample, and obtain a preliminary mesophase pitch with a certain anisotropic phase content.

[0059] (3) Take 50 g of the above-mentioned preliminary mesophase pitch, grind it and place it in a three-stage vertical reactor. Introduce nitrogen into the reactor (flow rate: 80 ml / min). After removing air, heat the reactor to the predetermined temperature: 370 °C in the upper region, 380 °C in the middle region, and 390 °C in the lower region, and keep it warm for 1 h. After the reaction is completed, quickly cool it to room temperature with cooling water, and collect samples more than 10 mm away from the upper and lower boundaries in the middle region to obtain the target mesophase pitch.

[0060] (4) Perform performance tests on the obtained target mesophase pitch. The results show that the softening point is 320 °C, the mesophase content is 100%, the toluene-insoluble content is 87.2%, the quinoline-insoluble content is 23.1%, and it exhibits a large-area streamline optical texture.

[0061] (5) Melt-spin the above-mentioned target mesophase pitch at 370 °C, then pre-oxidize it in an air atmosphere at 270 °C for 1 h, and then heat it to 1800 °C at a heating rate of 10 °C / min under nitrogen protection and keep it warm for 1 h for carbonization treatment to obtain carbon fibers. The scanning electron microscope photos are as Figure 3 shown. The test results show that the tensile strength of the carbon fiber is 2120 MPa and the modulus is 220 GPa.

[0062] Comparative Example 1 Prepare mesophase pitch by the traditional heat treatment method: directly add coal tar pitch into a tubular furnace, and heat it to 410 °C at a heating rate of 5 °C / min under nitrogen protection and keep it warm for 5 h. After the experiment is completed, cool it to room temperature naturally and take out the sample. The test results show that the softening point is 290 °C, the mesophase content is 85%, the toluene-insoluble content is 75.3%, and the quinoline-insoluble content is 15.6%. Use this mesophase pitch for melt spinning according to the method described in Example 1, and after pre-oxidation and carbonization treatment under the same conditions, the obtained carbon fiber has a tensile strength of 1200 MPa and a modulus of 150 GPa.

[0063] Comparative Example 2 On the basis of Example 1, prepare mesophase pitch only by the method of hydrogenation modification: fully mix coal tar pitch and tetralin in a mass ratio of 1:3, treat it at high temperature and high pressure (420 °C, 5 MPa) for 4 h, and then cool it to room temperature to obtain hydrogenated pitch. Then heat the hydrogenated pitch to 410 °C at a heating rate of 5 °C / min under nitrogen protection and keep it warm for 5 h to obtain mesophase pitch.

[0064] The test results show that: the softening point is 280 °C, the mesophase content is 92%, the toluene-insoluble content is 78.5%, and the quinoline-insoluble content is 17.2%. According to the method described in Example 1, this mesophase pitch was used for melt spinning. After pre-oxidation and carbonization treatments under the same conditions, the obtained carbon fiber had a tensile strength of 1500 MPa and a modulus of 170 GPa.

[0065] Comparative Example 3 Based on Example 1, a mesophase pitch was prepared only by the method of segmented thermal sedimentation: The coal tar pitch was directly added into a tubular furnace. Under nitrogen protection, it was heated to 410 °C at a heating rate of 5 °C / min and held for 5 h to obtain a preliminary mesophase pitch. Take 50 g of the above-mentioned preliminary mesophase pitch, grind it and place it in a three-stage vertical reactor as shown in Figure 1 and the filling amounts in each region are roughly equal. Nitrogen (flow rate: 80 ml / min) was introduced into the reactor. After removing the air, the reactor was heated to the predetermined temperature: the upper region was 365 °C, the middle region was 370 °C, and the lower region was 380 °C, and held for 1 h. After the reaction ended, it was quickly cooled to room temperature with cooling water, and samples more than 10 mm above and below the upper and lower boundaries in the middle region were collected to obtain the target mesophase pitch.

[0066] The test results show that: the softening point is 300 °C, the mesophase content is 90%, the toluene-insoluble content is 77.8%, and the quinoline-insoluble content is 16.5%. According to the method described in Example 1, this mesophase pitch was used for melt spinning. After pre-oxidation and carbonization treatments under the same conditions, the obtained carbon fiber had a tensile strength of 1450 MPa and a modulus of 165 GPa.

[0067] Comparative Example 4 Based on Example 1, a mesophase pitch was prepared by the method of hydrogenation modification and thermal sedimentation (without segmented treatment): The coal tar pitch and tetralin were fully mixed at a mass ratio of 1:3, and after being treated at high temperature and high pressure (420 °C, 5 MPa) for 4 h, it was cooled to room temperature to obtain hydrogenated pitch. The hydrogenated pitch was added into a tubular furnace. Under nitrogen protection, it was heated to 410 °C at a heating rate of 5 °C / min and held for 5 h to obtain a preliminary mesophase pitch. Then, this preliminary mesophase pitch was placed in a three-stage vertical reactor for thermal sedimentation treatment (370 °C, 1 h), and the middle sample was collected as the product. The test results show that: the softening point is 280 °C, the mesophase content is 95%, the toluene-insoluble content is 80.1%, and the quinoline-insoluble content is 19.1%. According to the method described in Example 1, this mesophase pitch was used for melt spinning. After pre-oxidation and carbonization treatments under the same conditions, the obtained carbon fiber had a tensile strength of 1550 MPa and a modulus of 175 GPa.

[0068] The comparative analysis of the test results is as follows: 1. Comparison of the properties of mesophase pitch As can be seen from the data in the table, the mesophase pitch prepared in the examples of the present invention has higher mesophase content (95 - 100%), toluene insoluble content (82.5 - 87.2%) and quinoline insoluble content (19.2 - 23.1%). This indicates that the method of the present invention can more effectively promote the orderly arrangement of molecules and the enrichment of macromolecular components. In the comparative examples, the mesophase pitch prepared by only using a single treatment method has significantly lower mesophase content, toluene insoluble content and quinoline insoluble content than those in the examples of the present invention, indicating that the combined process of hydrogenation modification and thermal sedimentation has a significant synergistic effect.

[0069] 2. Comparison of the properties of carbon fibers As can be seen from the data in the table, the carbon fibers prepared in the examples of the present invention have significantly better mechanical properties than those in the comparative examples. The tensile strength of Examples 1 - 6 is between 1850 - 2400 MPa, and the modulus is between 180 - 260 GPa, while the tensile strength of Comparative Examples 1 - 4 is only 1200 - 1550 MPa, and the modulus is 150 - 175 GPa. This significant performance difference is mainly attributed to the fact that the mesophase pitch prepared by the method of the present invention has better molecular composition and structural characteristics, enabling a more perfect carbon layer structure to be formed during the spinning and carbonization processes.

[0070] In addition, from the observation results of the fiber morphology, it can be seen that the cross-section of the carbon fibers prepared in the examples of the present invention presents a regular circular shape and an obvious radial structure, with very few surface defects; while the cross-section of the carbon fibers prepared in the comparative examples presents a flat or irregular shape, with more cracks and holes. This further proves the superiority of the method of the present invention.

[0071] The present invention combines hydrogenation modification and thermal sedimentation treatment. First, unstable groups in coal tar pitch can be removed under high temperature and high pressure conditions during the hydrogenation process, enabling the pitch to obtain a purer aromatic skeleton and suitable rheological properties. Subsequently, by moderately controlling the thermal sedimentation temperature and holding time, macromolecular components are fractionally enriched and overly small molecules or impurities are excluded, thereby significantly reducing the generation of micropores and defects while maintaining high aromaticity and good spinnability. This combined process can improve the controllability and stability of the raw materials, taking into account the optimization of the molecular weight distribution and the orderliness of the molecular structure. It not only effectively improves the filament formation rate and continuity of mesophase pitch during the melt spinning process, but also enables the final carbon fibers to exhibit higher strength and modulus, and reduces the generation of surface cracks and holes, providing more superior comprehensive properties for carbon fibers in high-end application fields.

[0072] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-performance spinnable mesophase pitch based on hydrogenation modification and segmented thermal sedimentation process, characterized in that, It includes the following steps: (1) Mix coal tar pitch with a specific hydrogenating agent and conduct high-temperature and high-pressure hydrotreating in an inert atmosphere to obtain hydrogenated pitch; (2) Heat-treat the hydrogenated pitch obtained in step (1) in an inert atmosphere, and after natural cooling to room temperature, obtain a preliminary mesophase pitch with a certain anisotropic phase content; (3) Grind the preliminary mesophase pitch obtained in step (2) and place it in a fractional sedimentation device. Conduct fractional thermal sedimentation treatment under the protection of an inert atmosphere to fractionally enrich the molecular components, so that the macromolecular components are enriched in the lower part. Subsequently, quickly cool to room temperature and collect the middle sample to obtain a target mesophase pitch suitable for spinning.

2. The method for preparing a high-performance spinnable mesophase pitch based on a hydrogenation modification and a segmented thermal sedimentation process according to claim 1, characterized in that: In step (1), the specific hydrogenating agent is selected from tetralin, tetrahydroquinoline, naphthyl tetrahydro compounds, polycyclic aromatic hydrocarbon hydrides and their mixtures, and the mass ratio of coal tar pitch to the specific hydrogenating agent is 1:3 to 1:

4.

3. The method for preparing a high-performance spinnable mesophase pitch based on a hydrogenation modification and a segmented thermal sedimentation process according to claim 1, wherein: In step (1), the high-temperature and high-pressure hydrotreating is carried out at a reaction temperature of 350 °C to 450 °C, a reaction pressure of 3 MPa to 10 MPa, and a heat preservation time of 2 h to 6 h.

4. The method for preparing high-performance spinnable mesophase pitch based on hydrogenation modification and segmented thermal sedimentation process according to claim 1, characterized in that: In step (2), the inert atmosphere is nitrogen, argon or helium, the gas flow rate is 50 ml / min to 200 ml / min, the heat treatment temperature is 390 °C to 420 °C, the heating rate is 5 °C / min to 10 °C / min, and the heat preservation time is 5 h to 8 h.

5. The method for preparing high-performance spinnable mesophase pitch based on hydrogenation modification and segmented thermal sedimentation process according to claim 1, characterized in that: In step (3), the fractional sedimentation device is a three-section vertical reaction kettle with a temperature gradient control function. The reaction kettle is provided with an upper region, a middle region and a lower region from top to bottom, and the temperature of each region can be independently controlled.

6. The preparation method of high-performance spinnable mesophase pitch based on hydrogenation modification and thermal sedimentation process according to claim 5, characterized in that: In step (3), in the fractional thermal sedimentation treatment, the temperature gradient in the three-section vertical reaction kettle is that the temperature of the upper region is 5 °C to 15 °C lower than that of the middle region, the temperature of the lower region is 5 °C to 15 °C higher than that of the middle region, and the temperature of the middle region is 370 °C to 400 °C, and heat preservation is carried out for 0.5 h to 3 h within this temperature range.

7. The preparation method of high-performance spinnable mesophase pitch based on hydrogenation modification and segmented thermal sedimentation process according to claim 5, characterized in that: The middle sample in step (3) refers to the sample within a range of 5 mm to 20 mm away from the boundaries of the upper region and the lower region in the middle region of the fractional sedimentation device.

8. The method for preparing a high-performance spinnable mesophase pitch based on a hydrogenation modification and a segmented thermal sedimentation process according to claim 1, wherein: Steps (1) to (3) are all carried out in an inert atmosphere with an oxygen content lower than 50 ppm.

9. The high-performance spinnable mesophase pitch prepared by the preparation method according to any one of claims 1-8, characterized in that: The mesophase pitch has a softening point of 275 °C to 330 °C, a mesophase content greater than 95%, a toluene-insoluble content greater than 80% and a quinoline-insoluble content greater than 18%, presenting a large-area streamline optical texture.

10. Use of the high-performance spinnable mesophase pitch according to claim 9 in the preparation of carbon fibers, characterized in that It includes the following steps: a. Melt-spin the mesophase pitch in step at 340 °C to 375 °C to obtain pre-fibers; b. Pre-oxidize the pre-fibers obtained in step a in an air atmosphere within a temperature range of 200 °C to 300 °C, and the pre-oxidation time is 0.5 h to 2 h; c Heat the pre-oxidized fibers obtained in step b to 1000 °C to 2000 °C at a heating rate of 5 °C / min to 15 °C / min under an inert atmosphere and hold for 0.5 h to 2 h for carbonization treatment to obtain high-performance mesophase pitch-based carbon fibers.

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