A method for preparing mesophase pitch-based carbon fiber using coal tar

Abstract

The present invention belongs to the technical field of coal tar fractionation and utilization, and relates to a method for preparing mesophase pitch-based carbon fibers using coal tar pitch, comprising: 1) using medium- and low-temperature coal tar pitch as raw material under a nitrogen atmosphere, alternating polycondensation reactions and hydrogenation reactions to obtain mesophase pitch; 2) purifying the mesophase pitch using pyridine insolubles to obtain spinnable mesophase pitch; 3) dissolving polyacrylonitrile, a composite additive, and the spinnable mesophase pitch in a dimethyl sulfoxide solvent to obtain a spinnable sol; 4) sequentially subjecting the spinnable sol to melt spinning, pre-oxidation, carbonization, and graphitization to obtain mesophase pitch-based carbon fibers. The present invention synthesizes the mesophase pitch through a hydrogenation polycondensation process; then dissolves it with polyacrylonitrile and a composite additive in dimethyl sulfoxide to form a sol; and then sequentially melt spinning, pre-oxidation, carbonization, and graphitization to obtain mesophase pitch-based carbon fibers with a denser cross section, excellent mechanical properties, and high electrical conductivity.

Description

Technical Field

[0001] The invention belongs to the technical field of coal tar fractionation and utilization, and relates to a method for preparing mesophase pitch-based carbon fibers by utilizing coal tar. Background Art

[0002] Mesophase pitch-based carbon fiber (MPCF) is a carbon fiber material prepared with mesophase pitch as raw material. It is considered to be one of the most promising materials due to its excellent thermal conductivity and thermal stability. It has been widely used in aerospace, aviation, sports equipment, high-end consumer products and other fields. The preparation of MPCF mainly includes melt spinning, carbonization and graphitization of mesophase pitch. However, it is difficult to obtain carbon fiber with excellent performance in actual preparation. This is because: First, the performance of mesophase pitch raw materials is inseparable from the good thermal conductivity of carbon fiber, especially the microcrystalline structure and optical structure of mesophase pitch raw materials greatly affect the performance of carbon fiber; secondly, mesophase pitch has the characteristics of strong molecular planarity, high softening point and high viscosity, which cause spinning instability, and the volatilization and escape of small asphalt molecules during melt spinning cause fiber defects, which seriously affect the mechanical properties of the product.

[0003] Patent CN115369520B mixes two raw asphalts in a certain proportion, and obtains an isotropic matrix containing large mesophase balls of spinnable mesophase asphalt through high-temperature polymerization reaction. The asphalt is melt-spun to obtain continuous asphalt fibers, which are further melted and carbonized at high temperature to obtain asphalt-based carbon fibers. Patent CN116446075A uses spinnable mesophase pitch with a mesophase content of ≥98% as raw material, melt-spinning through a spinneret with Y-shaped spinning holes, followed by pre-oxidation, carbonization, and graphitization to produce high-thermal-conductivity mesophase pitch-based carbon fibers with a circular cross-section. Patent CN112812801A uses aromatic-rich oil mixed with biomass as raw material, placing it in an autoclave with a co-carbonizing agent for co-carbonization to produce mesophase pitch, and then sequentially performing melt spinning, pre-oxidation, carbonization, and graphitization to produce mesophase pitch-based carbon fibers. Patent CN110205709A modifies mesophase pitch with phosphorus-doped carbene quantum dots, and then spins it at 280-350°C under a mixed inert atmosphere after stirring. After spinning, pre-oxidation, low-temperature carbonization, and continuous graphitization are performed to produce mesophase pitch-based carbon fibers.

[0004] All of the above methods can produce mesophase asphalt-based carbon fibers, but there are defects such as unstable spinning and unevenness in the preparation process, which results in the final carbon fibers having poor mechanical properties such as tensile strength and tensile modulus, and low thermal conductivity, which cannot meet the requirements of the high-end application market. Summary of the Invention

[0005] Based on the technical problem that the above-mentioned prior art has defects such as unstable and uneven spinning, resulting in poor performance of the final obtained carbon fiber, the present invention provides a method for preparing mesophase pitch-based carbon fiber using coal tar.

[0006] The present invention synthesizes mesophase asphalt with excellent optical properties and compact microcrystalline structure through a hydrogenation polycondensation process; then dissolves it with polyacrylonitrile and composite additives in a dimethyl sulfoxide solvent to form a sol; the obtained sol is sequentially melt-spun, pre-oxidized, carbonized and graphitized to obtain mesophase asphalt-based carbon fibers with denser cross-section, excellent mechanical properties and higher electrical conductivity.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A method for preparing mesophase pitch-based carbon fibers using coal tar pitch comprises the following steps:

[0009] 1) Hydrogenation polycondensation

[0010] Under nitrogen atmosphere, using medium-low temperature coal pitch as raw material, polycondensation reaction and hydrogenation reaction are carried out alternately to obtain mesophase pitch;

[0011] The conditions for the polycondensation reaction are: temperature 430°C to 470°C, polycondensation pressure 1.5MPa to 2.5MPa, and time 1.5h to 2.5h; the conditions for the hydrogenation reaction are: temperature 360°C to 400°C, hydrogenation pressure 6MPa to 10MPa, and time 30min to 60min;

[0012] 2) Mesophase pitch purification

[0013] Purifying the mesophase pitch in step 1) using pyridine insolubles to obtain spinnable mesophase pitch; the mass ratio of the mesophase pitch to the pyridine insolubles is 1:1.5-2.5;

[0014] 3) Preparation of spinnable sol

[0015] Dissolving polyacrylonitrile, the composite additive, and the spinnable mesophase pitch obtained in step 2) in dimethyl sulfoxide (DMSO) solvent to obtain a spinnable sol; calculating the mass fraction of each material according to the mass of the spinnable sol as follows: mesophase pitch 20% to 30%, polyacrylonitrile 2% to 8%, composite additive 0.1% to 0.9%, and the remainder being DMSO solvent;

[0016] 4) Preparation of mesophase pitch-based carbon fibers

[0017] The spinnable sol in step 3) is sequentially subjected to melt spinning, pre-oxidation, carbonization and graphitization to obtain mesophase pitch-based carbon fibers.

[0018] It is further defined that a hydrogen donor is also added to the hydrogenation reaction in step 1), wherein the hydrogen donor is a cycloalkane, and the amount of the hydrogen donor added accounts for 4wt% to 8wt% of the medium and low temperature coal tar pitch.

[0019] It is further defined that the number of alternations in step 1) is at least two.

[0020] It is further defined that the purification process of step 2) is as follows: mixing, stirring, standing, separating, and drying.

[0021] It is further defined that the stirring temperature is 60° C. to 85° C., the stirring time is 0.5 h to 1.5 h, and the standing time is 2 h to 4 h.

[0022] It is further defined that in the step 2), the spinnable mesophase pitch is anisotropic mesophase pitch, the H / C of the spinnable mesophase pitch is 0.87-0.97, the softening point is 240°C-280°C, the crystal interlayer spacing is 0.3773-0.3778, and the optical structure index OTI is 50.64-62.83.

[0023] It is further defined that in step 3), the dissolution temperature is 50° C. to 60° C., and the dissolution time is 12 h to 24 h.

[0024] It is further defined that in step 3), the composite additive is one or more of carbon nanotubes, graphene and transition metal carbide.

[0025] It is further defined that in step 4), the maximum length of the mesophase pitch-based carbon fiber is 1000m, and the diameter is 22.09μm to 27.33μm; the tensile strength of the mesophase pitch-based carbon fiber is up to 5.2GPa, the elastic modulus is up to 345GPa, and the resistivity is down to 0.81μΩ·m.

[0026] The beneficial effects of the present invention are:

[0027] 1. The present invention utilizes coal tar to prepare a method for preparing mesophase pitch-based carbon fibers, which can obtain a mesophase pitch with good optical structure and tight microcrystalline structure by alternating polycondensation and hydrogenation. Then, anisotropic (excluding isotropic) spinnable mesophase pitch, polyacrylonitrile, composite additives and solvent are formed into a spinnable sol, and finally, mesophase-based carbon fibers are obtained by spinning, carbonization and graphitization, which overcomes the problems of unstable and uneven spinning, and the obtained carbon fiber product has a denser cross-section and better mechanical properties.

[0028] 2. Compared with direct thermal polycondensation, in the present invention, hydrogen donor cycloalkanes are polycondensed to produce hydrogen radicals during polycondensation and hydrogenation, and a large number of free radicals are generated in the hydrogen transfer reaction saturated system, which reduces the reaction rate and viscosity of the system; on the other hand, the introduced aromatic hydrocarbons are dehydrogenated and condensed to form more polycyclic aromatic hydrocarbons, providing a richer carbon skeleton structure for the formation of the mesophase, which is beneficial to the rearrangement of the mesophase molecular layer; further through purification, the spinnable mesophase asphalt has an H / C of 0.87-0.97, a softening point of 240-280°C, a crystal layer spacing of 0.3773-0.3778, and an optical structure index OTI of 50.64-62.83. The mesophase asphalt has good microcrystalline structure and optical structure, which is beneficial to improving the performance of carbon fiber.

[0029] 3. In the present invention, the mesophase asphalt molecules have strong planarity, high softening point and high viscosity. The use of spinnable sol spinning can reduce the viscosity, maintain good fluidity and increase the stability of spinning. In addition, adding an appropriate amount of polyacrylonitrile to the spinnable sol system can form stronger hydrogen bond interaction with the mesophase molecules. After carbonization and graphitization, the small-sized particles are stacked more compactly and the fiber cross-section is denser. The carbon fiber obtained thereby has higher mechanical properties.

[0030] 4. The present invention adds composite additives to the spinnable sol system. Among them, carbon nanotubes are one-dimensional conductive materials with a large aspect ratio, which is beneficial to improving the mechanical properties of carbon fibers; graphene and MXene have a two-dimensional network structure, which form a conductive network by overlapping with each other, thereby improving the conductive properties of carbon fibers; when multiple additives are used simultaneously, there is a synergistic effect, and even a very small amount can give carbon fibers excellent conductive properties.

[0031] 5. The mesophase pitch-based carbon fibers prepared by the method of the present invention have a maximum tensile strength of 5.2 GPa, a maximum elastic modulus of 345 GPa, and a minimum resistivity of 0.81 μΩ·m. They have higher mechanical properties and play a significant role in special fields such as aerospace and national defense. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 2 are XRD patterns of the purified spinnable mesophase pitches of Example 4 and Comparative Example 4;

[0033] Figure 2 1 and 2 are Raman spectra of the purified spinnable mesophase pitches of Example 4 and Comparative Example 4. DETAILED DESCRIPTION

[0034] The present invention provides a method for preparing mesophase pitch-based carbon fibers using coal tar pitch, comprising the following steps:

[0035] 1) Hydrogenation polycondensation

[0036] Under nitrogen atmosphere, using medium-low temperature coal pitch as raw material, polycondensation reaction and hydrogenation reaction are carried out alternately to obtain mesophase pitch;

[0037] The number of alternations in this step is at least two.

[0038] Preferably, the alternation times is two, that is, the medium and low temperature coal tar pitch adopts the primary polycondensation reaction, the primary hydrogenation reaction, the secondary polycondensation reaction, and the secondary hydrogenation reaction in sequence.

[0039] The conditions for the polycondensation reaction are: temperature 430°C to 470°C, pressure 1.5MPa to 2.5MPa, and time 1.5h to 2.5h; the conditions for the hydrogenation reaction are: temperature 360°C to 400°C, pressure 6MPa to 10MPa, and time 30min to 60min;

[0040] In this step, a hydrogen donor is also added to the hydrogenation reaction. The hydrogen donor is cycloalkane, and the amount of the hydrogen donor added accounts for 4wt% to 8wt% of the medium and low temperature coal tar pitch.

[0041] 2) Mesophase pitch purification

[0042] The mesophase pitch in step 1) is purified by using pyridine insoluble matter to obtain a spinnable mesophase pitch free of isotropic (isotropic) substances.

[0043] The mass ratio of the mesophase pitch to the pyridine insoluble matter is 1:1.5 to 2.5. In practice, the mass ratio of the mesophase pitch to the pyridine insoluble matter can be 1:1.5, 1:1.8, 1:2, 1:2.2, or 1:2.5.

[0044] In this step, the purification process is as follows: mixing, stirring, standing, separation, and drying.

[0045] Specifically, the mesophase asphalt is mixed with pyridine insoluble matter, stirred at 60°C to 85°C for 0.5 to 1.5 hours, then allowed to stand for 2 to 4 hours, and then the upper solution is taken out, and the solvent and solute in the upper solution are separated by existing methods (such as evaporation concentration, crystallization, distillation, etc.). Finally, the solute after drying is the spinnable mesophase asphalt that does not contain isotropic (anisotropic) substances.

[0046] In this step, after purification, the spinnable mesophase pitch obtained is anisotropic (excluding isotropic) mesophase pitch, the H / C of the spinnable mesophase pitch is 0.87~0.97, the softening point is 240℃~280℃, the crystal layer spacing is 0.3773~0.3778, and the optical structure index OTI is 50.64~62.83.

[0047] 3) Preparation of spinnable sol

[0048] Polyacrylonitrile (PNA), composite additives and the spinnable mesophase pitch of step 2) are dissolved in dimethyl sulfoxide solvent (DMSO) to obtain a spinnable sol.

[0049] In this step, the mass fractions of the various materials are calculated based on the mass of the spinnable sol: mesophase pitch 20%-30%, PNA 2%-8%, composite additives 0.1%-0.9%, and the remainder DMSO. In other words, considering the total mass of the spinnable sol as 1, the mass fractions of the mesophase pitch are 20%-30%, PAN 2%-8%, and composite additives 0.1%-0.9%.

[0050] In this step, the temperature during the dissolution process is 50° C. to 60° C., and the dissolution time is 12 h to 24 h.

[0051] In this step, the composite additive is one or more of carbon nanotubes (CNFs), graphene (GO) and transition metal carbide (Mxene).

[0052] During implementation, the composite additive is any one of carbon nanotubes (CNFs), graphene (GO) and transition metal carbide (Mxene).

[0053] In practice, the composite additive is a mixture of carbon nanotubes (CNFs) and graphene (GO), a mixture of carbon nanotubes (CNFs) and transition metal carbide (MXene), a mixture of graphene (GO) and transition metal carbide (MXene), or a mixture of carbon nanotubes (CNFs), graphene (GO), and transition metal carbide (MXene). When two or more additives are mixed, they can be mixed in any proportion.

[0054] Preferably, the transition metal carbide is (Ti,Nb)2CT x 、Ti3CNT x and Ta4C3T x One or more of .

[0055] 4) Preparation of mesophase pitch-based carbon fibers

[0056] The spinnable sol in step 3) is sequentially subjected to melt spinning, pre-oxidation, carbonization and graphitization to obtain mesophase pitch-based carbon fibers.

[0057] In this step, the melt spinning conditions are: spinning diameter of 100 μm, spinning pressure of 0.05-0.15 MPa, 0.1 mol / L HCl solution as coagulation bath, and temperature of 25-30° C.

[0058] In this step, the pre-oxidation conditions are: oxygen atmosphere, temperature of 240-280° C., and residence time of 1-3 hours.

[0059] In this step, the carbonization / graphitization conditions are as follows: nitrogen atmosphere, rising from room temperature to 500-700°C at 5°C / min, and then rising to 1500-1700°C at 10°C / min. When the temperature reaches the highest, it naturally drops to room temperature to complete the reaction.

[0060] Preferably, the carbonization / graphitization conditions are: nitrogen atmosphere, rising from room temperature to 600° C. at 5° C. / min, then rising to 1600° C. at 10° C. / min, and when the temperature reaches the highest, naturally falling to room temperature to complete the reaction.

[0061] Testing has shown that the mesophase pitch-based carbon fibers produced by this invention have a maximum yarn length of 1000m and a diameter of 22.09μm to 27.33μm. They also exhibit a maximum tensile strength of 5.2GPa, a maximum elastic modulus of 345GPa, and a minimum resistivity of 0.81μΩ·m. These fibers possess excellent mechanical properties and could play a significant role in specialized fields such as aerospace and national defense.

[0062] The preparation method provided by the present invention is described in detail below through the following examples, but they are not intended to limit the scope of protection of the present invention.

[0063] It should be noted that, unless otherwise specified, the operations and equipment used in the examples are conventional operations and equipment in the art, such as mixing, stirring, separation, etc.

[0064] It should be noted that, unless otherwise specified, the reagents and drugs used in the following examples were all commercially purchased and of analytical grade.

[0065] Example 1

[0066] The method for preparing mesophase pitch-based carbon fibers using coal tar pitch provided in this embodiment comprises the following steps:

[0067] 1) Preparation of mesophase asphalt by hydrocondensation

[0068] Using medium-low temperature coal tar pitch as raw material (under nitrogen atmosphere), a polycondensation reaction is first carried out in a high-temperature reactor for 2 hours, and then a hydrogenation reaction is carried out for 30 minutes. The polycondensation and hydrogenation operations are alternately performed twice to obtain the intermediate phase pitch.

[0069] During the polycondensation reaction, the amount of cycloalkanes added accounted for 4wt% of the asphalt mass, the polycondensation temperature was 450°C, and the polycondensation pressure was 2MPa. During the hydrogenation reaction, the temperature was 380°C, and the hydrogenation pressure was 8MPa.

[0070] 2) Purification of mesophase pitch

[0071] The mesophase pitch obtained in step 1) is mixed with the pyridine insoluble matter (mass ratio is 1:2), stirred at 80°C for 1 hour, and allowed to stand for 3 hours. The upper layer solution is then taken out, and the solvent and solute in the upper layer solution are separated by existing methods. The dried solute is the spinnable mesophase pitch that does not contain isotropic substances.

[0072] 3) Preparation of spinnable sol

[0073] Take the spinnable mesophase pitch from step 2), add PAN and CNTs and dissolve them in DMSO solvent. Continue dissolving at 60°C for 24 hours until completely dissolved to obtain spinnable pitch. The mass fraction of each component calculated according to the spinnable pitch is: mesophase pitch 28%, PAN 2%, CNTs 0.1t%, and the rest is DMSO solvent.

[0074] 4) Preparation of mesophase pitch-based carbon fibers

[0075] The spinnable sol obtained in step 3) is sequentially subjected to melt spinning, pre-oxidation, carbonization and graphitization to obtain mesophase pitch-based carbon fibers.

[0076] In this step, the melt spinning conditions are as follows: spinning diameter of 100 μm, spinning pressure of 0.1 MPa, 0.1 mol / L HCl solution as coagulation bath, and temperature of 25° C.

[0077] In this step, the pre-oxidation conditions are: oxygen atmosphere, temperature of 260° C., and residence time of 2 h.

[0078] In this step, the carbonization / graphitization conditions are as follows: in a nitrogen atmosphere, the temperature is raised from room temperature to 600° C. at 5° C. / min, then raised to 1600° C. at 10° C. / min, and then naturally cooled to room temperature to complete the reaction.

[0079] Example 2

[0080] The method for preparing mesophase pitch-based carbon fibers using coal tar pitch provided in this embodiment comprises the following steps:

[0081] 1) Preparation of mesophase asphalt by hydrocondensation

[0082] Using medium-low temperature coal tar as raw material (nitrogen atmosphere), first conduct polycondensation reaction in a high-temperature reactor for 2 hours, then hydrogenate for 45 minutes. The polycondensation and hydrogenation operations are alternately performed twice to obtain the intermediate phase asphalt.

[0083] During the polycondensation process, the amount of cycloalkane added was 6 wt %, the polycondensation temperature was 450° C., and the polycondensation pressure was 2 MPa; during the hydrogenation reaction, the temperature was 380° C. and the hydrogenation pressure was 8 MPa.

[0084] 2) Purification of mesophase pitch

[0085] The mesophase pitch obtained in step 1) is mixed with the pyridine insoluble matter (mass ratio is 1:2), stirred at 80°C for 1 hour, and allowed to stand for 3 hours. The upper layer solution is then taken out, and the solvent and solute in the upper layer solution are separated by existing methods. The dried solute is the spinnable mesophase pitch that does not contain isotropic substances.

[0086] 3) Preparation of spinnable sol

[0087] The spinnable mesophase pitch of step 2) is added with PAN and CNTs and dissolved in DMSO solvent. The mixture is dissolved at 60°C for 24 hours until completely dissolved to obtain spinnable pitch. The mass fraction of each component is calculated as follows: mesophase pitch 25%, PAN 5%, CNTs 0.1t%, and the rest is DMSO solvent.

[0088] 4) Preparation of mesophase pitch-based carbon fibers

[0089] The spinnable sol obtained in step 3) is sequentially subjected to melt spinning, pre-oxidation, carbonization and graphitization to obtain mesophase pitch-based carbon fibers.

[0090] In this step, the melt spinning conditions are: spinning diameter of 100 μm, spinning pressure of 0.1 MPa, 0.1 mol / L HCl solution as coagulation bath, and temperature of 30° C.

[0091] In this step, the pre-oxidation conditions are: oxygen atmosphere, temperature of 260° C., and residence time of 2 h.

[0092] In this step, the carbonization / graphitization conditions are as follows: in a nitrogen atmosphere, the temperature is raised from room temperature to 600° C. at 5° C. / min, then raised to 1600° C. at 10° C. / min, and then naturally cooled to room temperature to complete the reaction.

[0093] Example 3

[0094] The method for preparing mesophase pitch-based carbon fibers using coal tar pitch provided in this embodiment comprises the following steps:

[0095] 1) Preparation of mesophase by hydrogenation polycondensation

[0096] Using medium-low temperature coal tar pitch as raw material (nitrogen atmosphere), first conduct polycondensation reaction in a high-temperature reactor for 2 hours, then hydrogenate for 45 minutes, and alternately perform polycondensation and hydrogenation operations twice to obtain intermediate phase pitch.

[0097] During the polycondensation process, the amount of cycloalkane added was 8 wt %, the polycondensation temperature was 450° C., and the polycondensation pressure was 2 MPa; during the hydrogenation reaction, the temperature was 380° C. and the hydrogenation pressure was 8 MPa.

[0098] 2) Purification of mesophase pitch

[0099] The mesophase pitch obtained in step 1) is mixed with the pyridine insoluble matter (mass ratio is 1:2), stirred at 80°C for 1 hour, and allowed to stand for 3 hours. The upper layer solution is then taken out, and the solvent and solute in the upper layer solution are separated by existing methods. The dried solute is the spinnable mesophase pitch that does not contain isotropic substances.

[0100] 3) Preparation of spinnable sol

[0101] Take the spinnable mesophase pitch of step 2), add PAN, GO, and Mxene and dissolve them in DMSO solvent. Continue dissolving at 60°C for 24 hours until completely dissolved to obtain spinnable pitch. The mass fraction of each component calculated according to the spinnable pitch is: mesophase pitch 22%, PAN 8%, GO 0.2t%, Mxene 0.2wt%, and the rest is DMSO solvent.

[0102] 4) Preparation of mesophase pitch-based carbon fibers

[0103] The spinnable sol obtained in step 3) is sequentially subjected to melt spinning, pre-oxidation, carbonization and graphitization to obtain mesophase pitch-based carbon fibers.

[0104] In this step, the melt spinning conditions are: spinning diameter of 100 μm, spinning pressure of 0.1 MPa, 0.1 mol / L HCl solution as coagulation bath, and temperature of 30° C.

[0105] In this step, the pre-oxidation conditions are: oxygen atmosphere, temperature of 260° C., and residence time of 2 h.

[0106] In this step, the carbonization / graphitization conditions are as follows: in a nitrogen atmosphere, the temperature is raised from room temperature to 600° C. at 5° C. / min, then raised to 1600° C. at 10° C. / min, and then naturally cooled to room temperature to complete the reaction.

[0107] Example 4

[0108] The method for preparing mesophase pitch-based carbon fibers using coal tar pitch provided in this embodiment comprises the following steps:

[0109] 1) Preparation of mesophase by hydrogenation polycondensation

[0110] Using medium-low temperature coal tar as raw material (nitrogen atmosphere), first conduct polycondensation reaction in a high-temperature reactor for 2 hours, then hydrogenate for 45 minutes. The polycondensation and hydrogenation operations are alternately performed twice to obtain the intermediate phase asphalt.

[0111] During the polycondensation process, the amount of cycloalkane added was 6 wt %, the polycondensation temperature was 450° C., and the polycondensation pressure was 2 MPa; during the hydrogenation reaction, the temperature was 380° C. and the hydrogenation pressure was 8 MPa.

[0112] 2) Purification of mesophase pitch

[0113] The mesophase pitch obtained in step 1) is mixed with the pyridine insoluble matter (mass ratio is 1:2), stirred at 80°C for 1 hour, and allowed to stand for 3 hours. The upper layer solution is then taken out, and the solvent and solute in the upper layer solution are separated by existing methods. The dried solute is the spinnable mesophase pitch that does not contain isotropic substances.

[0114] 3) Preparation of spinnable sol

[0115] Take the spinnable mesophase pitch of step 2), add PAN, CNTs, GO and Mxene and dissolve them in DMSO solvent, and continue to dissolve them at 60°C for 24 hours until they are completely dissolved to obtain spinnable pitch. The mass fraction of each component calculated according to the spinnable pitch is: mesophase pitch 28%, PAN 2%; CNTs, GO and Mxene are all 0.2t%, and the rest is DMSO solvent.

[0116] 4) Preparation of mesophase pitch-based carbon fibers

[0117] The spinnable sol obtained in step 3) is sequentially subjected to melt spinning, pre-oxidation, carbonization and graphitization to obtain mesophase pitch-based carbon fibers.

[0118] In this step, the melt spinning conditions are as follows: spinning diameter of 100 μm, spinning pressure of 0.1 MPa, 0.1 mol / L HCl solution as coagulation bath, and temperature of 25° C.

[0119] In this step, the pre-oxidation conditions are: oxygen atmosphere, temperature of 260° C., and residence time of 2 h.

[0120] In this step, the carbonization / graphitization conditions are as follows: in a nitrogen atmosphere, the temperature is raised from room temperature to 600° C. at 5° C. / min, then raised to 1600° C. at 10° C. / min, and then naturally cooled to room temperature to complete the reaction.

[0121] Example 5

[0122] The method for preparing mesophase pitch-based carbon fibers using coal tar pitch provided in this embodiment comprises the following steps:

[0123] 1) Preparation of mesophase asphalt by hydrocondensation

[0124] Using medium-low temperature coal tar as raw material (nitrogen atmosphere), a condensation reaction is first carried out in a high-temperature reactor for 2 hours, and then a hydrogenation reaction is carried out for 60 minutes. The condensation and hydrogenation operations are alternately performed twice to obtain the intermediate phase asphalt.

[0125] During the polycondensation process, the amount of cycloalkane added was 4 wt %, the polycondensation temperature was 450° C., and the polycondensation pressure was 2 MPa; during the hydrogenation reaction, the temperature was 380° C. and the hydrogenation pressure was 8 MPa.

[0126] 2) Purification of mesophase pitch

[0127] The mesophase pitch obtained in step 1) is mixed with the pyridine insoluble matter (mass ratio is 1:2), stirred at 80°C for 1 hour, and allowed to stand for 3 hours. The upper layer solution is then taken out, and the solvent and solute in the upper layer solution are separated by existing methods. The dried solute is the spinnable mesophase pitch that does not contain isotropic substances.

[0128] 3) Preparation of spinnable sol

[0129] The spinnable mesophase pitch of step 2) is added with 5 wt% polyacrylonitrile (PAN) and 0.3 wt% carbon nanotubes (CNTs) and dissolved in dimethyl sulfoxide (DMSO) solvent. The mixture is dissolved at 60°C for 24 hours until completely dissolved. The volume ratio of the solvent to the mixture (polyacrylonitrile and carbon nanotubes) is 1:1 to obtain a spinnable sol.

[0130] Take the spinnable mesophase pitch from step 2), add PAN and CNTs and dissolve them in DMSO solvent. Continue dissolving at 60°C for 24 hours until completely dissolved to obtain spinnable pitch. The mass fraction of each component calculated according to the spinnable pitch is: mesophase pitch 25%, PAN 5%, CNTs 0.1t%, and the rest is DMSO solvent.

[0131] 4) Preparation of mesophase pitch-based carbon fibers

[0132] The spinnable sol obtained in step 3) is sequentially subjected to melt spinning, pre-oxidation, carbonization and graphitization to obtain mesophase pitch-based carbon fibers.

[0133] In this step, the melt spinning conditions are: spinning diameter of 100 μm, spinning pressure of 0.1 MPa, 0.1 mol / L HCl solution as coagulation bath, and temperature of 30° C.

[0134] In this step, the pre-oxidation conditions are: oxygen atmosphere, temperature of 260° C., and residence time of 2 h.

[0135] In this step, the carbonization / graphitization conditions are as follows: in a nitrogen atmosphere, the temperature is raised from room temperature to 600° C. at 5° C. / min, then raised to 1600° C. at 10° C. / min, and then naturally cooled to room temperature to complete the reaction.

[0136] Furthermore, the superiority of the performance of the mesophase pitch-based carbon fiber prepared by the method of the present invention is verified through the following comparative examples and performance tests.

[0137] Comparative Example 1

[0138] Different from Example 1, this comparative example only uses polycondensation reaction when preparing the mesophase asphalt.

[0139] The method for preparing mesophase pitch-based carbon fibers using coal tar pitch provided in this comparative example comprises the following steps:

[0140] 1) Preparation of mesophase asphalt by direct polycondensation

[0141] Using medium and low temperature coal tar as raw material (nitrogen atmosphere), the condensation reaction was carried out in a high temperature reactor for 2 hours (temperature 450℃, pressure 2MPa). After changing the temperature and pressure, the reaction was continued in the high temperature reactor for 45 minutes (temperature 380℃, pressure 8MPa). After two condensation reactions, the intermediate phase asphalt was obtained.

[0142] 2) Purification of mesophase pitch

[0143] The mesophase pitch obtained in step 1) is mixed with the pyridine insoluble matter (mass ratio is 1:2), stirred at 80°C for 1 hour, and allowed to stand for 3 hours. The upper layer solution is then taken out and the solvent and the solute are separated. The dried solute is the spinnable mesophase pitch free of isotropic substances.

[0144] 3) Preparation of spinnable sol

[0145] The spinnable mesophase pitch prepared in step 2) was dissolved in dimethyl sulfoxide (DMSO) solvent with 2 wt% PAN, 0.1% CNTs, 0.1 wt% GO, and 0.1 wt% MXene. The mixture was dissolved at 60°C for 24 h until completely dissolved. The volume ratio of the solvent to the mixture was 1:1 to obtain a spinnable sol.

[0146] Take the spinnable mesophase pitch of step 2), add PAN, CNTs, GO, and Mxene and dissolve them in DMSO solvent. Continue dissolving at 60°C for 24 hours until completely dissolved to obtain a spinnable pitch. The mass fraction of each component in the spinnable pitch is: mesophase pitch 28%, PAN 2%, CNTs 0.1%, GO 0.1%, Mxene 0.1%, and the rest is DMSO solvent.

[0147] 4) Sol spinning and carbonization

[0148] The spinnable sol obtained in step 3) is sequentially subjected to melt spinning, pre-oxidation, carbonization and graphitization to obtain mesophase pitch-based carbon fibers.

[0149] Comparative Example 2

[0150] Different from Example 2, in this comparative example, no polyacrylonitrile was added when preparing the spinnable sol.

[0151] The method for preparing mesophase pitch-based carbon fibers using coal tar pitch provided in this comparative example comprises the following steps:

[0152] 1) Preparation of mesophase by hydrogenation polycondensation

[0153] Using medium- and low-temperature coal tar pitch as the raw material (under a nitrogen atmosphere), a polycondensation reaction was performed in a high-temperature reactor for 2 hours, followed by hydrogenation for 45 minutes. This polycondensation and hydrogenation process was repeated twice to produce mesophase pitch. The cycloalkanes added during the polycondensation process were 6 wt%. The hydrogenation temperature and pressure were 380°C, 8 MPa, and the polycondensation temperature and pressure were 450°C, 2 MPa.

[0154] 2) Purification of mesophase pitch

[0155] The mesophase pitch obtained in step 1) is mixed with the pyridine insoluble matter (mass ratio is 1:2), stirred at 80°C for 1 hour, and allowed to stand for 3 hours. The upper layer solution is then taken out and the solvent and the solute are separated. The dried solute is the spinnable mesophase pitch free of isotropic substances.

[0156] 3) Preparation of spinnable sol

[0157] The spinnable mesophase pitch prepared in step 2) was dissolved in dimethyl sulfoxide solvent with 0.1% CNTs, 0.1wt% GO, and 0.1wt% MXene. The mixture was dissolved at 60°C for 24 hours until completely dissolved. The volume ratio of the solvent to the mixture (CNTs, GO, and MXene) was 1:1 to obtain a spinnable sol.

[0158] Take the spinnable mesophase pitch of step 2), add CNTs, GO, and Mxene and dissolve them in DMSO solvent. Continue dissolving at 60°C for 24 hours until they are completely dissolved to obtain a spinnable pitch. The mass fractions of the components in the spinnable pitch are: mesophase pitch 30%, CNTs 0.1%, GO 0.1wt%, Mxene 0.1wt%, and the rest is DMSO solvent.

[0159] 4) Sol spinning and carbonization

[0160] The spinnable sol obtained in step 3) is sequentially subjected to melt spinning, pre-oxidation, carbonization and graphitization to obtain mesophase pitch-based carbon fibers.

[0161] Comparative Example 3

[0162] Different from Example 3, no composite additive was added when preparing the spinnable sol in this comparative example.

[0163] The method for preparing mesophase pitch-based carbon fibers using coal tar pitch provided in this comparative example comprises the following steps:

[0164] 1) Preparation of mesophase asphalt by hydrocondensation

[0165] Using medium- and low-temperature coal tar pitch as the raw material (under a nitrogen atmosphere), a polycondensation reaction was performed in a high-temperature reactor for 2 hours, followed by hydrogenation for 45 minutes. This polycondensation and hydrogenation process was repeated twice to produce mesophase pitch. The cycloalkanes added during the polycondensation process were 8 wt%. The hydrogenation temperature and pressure were 380°C, 8 MPa, and the polycondensation temperature and pressure were 450°C, 2 MPa.

[0166] 2) Purification of mesophase pitch

[0167] The mesophase pitch obtained in step 1) is mixed with the pyridine insoluble matter (mass ratio is 1:2), stirred at 80°C for 1 hour, and allowed to stand for 3 hours. The upper layer solution is then taken out and the solvent and the solute are separated. The dried solute is the spinnable mesophase pitch free of isotropic substances.

[0168] 3) Preparation of spinnable sol

[0169] Take the spinnable mesophase pitch in step 2), add PAN and dissolve it in DMSO solvent, and continue dissolving at 60°C for 24 hours until it is completely dissolved to obtain a spinnable pitch. The mass fractions of the components in the spinnable pitch are: mesophase pitch 26%, PAN 4%, and the rest is DMSO solvent.

[0170] 4) Sol spinning and carbonization

[0171] The spinnable sol obtained in step 3) is sequentially subjected to melt spinning, pre-oxidation, carbonization and graphitization to obtain mesophase pitch-based carbon fibers.

[0172] Comparative Example 4

[0173] Different from Example 4, this comparative example directly adopts polycondensation when preparing mesophase pitch; and then, when preparing carbon fiber, no polyacrylonitrile and composite additives are added, and the purified spinnable mesophase pitch is directly spun, carbonized and graphitized to prepare carbon fiber.

[0174] The method for preparing mesophase pitch-based carbon fibers using coal tar pitch provided in this comparative example comprises the following steps:

[0175] 1) Preparation of mesophase asphalt by direct polycondensation

[0176] Using medium- and low-temperature coal tar as raw material (nitrogen atmosphere), the polycondensation reaction was carried out in a high-temperature reactor for 2 hours (temperature 450°C, pressure 2MPa). After changing the temperature and pressure, the reaction was continued in the high-temperature reactor for 45 minutes (temperature 380°C, pressure 8MPa). After alternating the operation twice, the intermediate phase asphalt was obtained.

[0177] 2) Purification of mesophase pitch

[0178] The mesophase pitch obtained in step 1) is mixed with the pyridine insoluble matter (mass ratio is 1:2), stirred at 80°C for 1 hour, and allowed to stand for 3 hours. The upper layer solution is then taken out and the solvent and the solute are separated. The dried solute is the spinnable mesophase pitch free of isotropic substances.

[0179] 3) Mesophase spinning and carbonization

[0180] The spinnable mesophase pitch obtained in step 2) is sequentially subjected to melt spinning, pre-oxidation, carbonization and graphitization to obtain mesophase pitch-based carbon fibers.

[0181] Comparative Example 5

[0182] Different from Example 5, in this comparative example, the mesophase pitch was prepared directly by polycondensation; and no composite additive was added when the spinnable sol was prepared.

[0183] The method for preparing mesophase pitch-based carbon fibers using coal tar pitch provided in this comparative example comprises the following steps:

[0184] 1) Direct polycondensation to prepare mesophase

[0185] Using medium- and low-temperature coal tar as raw material (nitrogen atmosphere), the polycondensation reaction was carried out in a high-temperature reactor for 2 hours (temperature 450°C, pressure 2MPa). After changing the temperature and pressure, the reaction was continued in the high-temperature reactor for 45 minutes (temperature 380°C, pressure 8MPa). After alternating the operation twice, the intermediate phase asphalt was obtained.

[0186] 2) Purification of mesophase pitch

[0187] The mesophase pitch obtained in step 1) is mixed with the pyridine insoluble matter (mass ratio is 1:2), stirred at 80°C for 1 hour, and allowed to stand for 3 hours. The upper layer solution is then taken out and the solvent and the solute are separated. The dried solute is the spinnable mesophase pitch free of isotropic substances.

[0188] 3) Preparation of spinnable sol

[0189] The spinnable mesophase pitch prepared in step 2) was dissolved in dimethyl sulfoxide (DMSO) solvent with 5 wt% PAN and dissolved at 60° C. for 24 h until completely dissolved, wherein the volume ratio of the solvent to the mixture was 1:1, to obtain a spinnable sol.

[0190] Take the spinnable mesophase pitch in step 2), add PAN and dissolve it in DMSO solvent, and continue dissolving at 60°C for 24 hours until it is completely dissolved to obtain a spinnable pitch. The mass fractions of the components in the spinnable pitch are: mesophase pitch 25%, PAN 5%, and the rest is DMSO solvent.

[0191] 4) Sol spinning and carbonization

[0192] The spinnable sol obtained in step 3) is sequentially subjected to melt spinning, pre-oxidation, carbonization and graphitization to obtain mesophase pitch-based carbon fibers.

[0193] Comparative Example 6

[0194] Different from Example 4, the mesophase pitch prepared by hydrogenation and polycondensation in this comparative example was not purified and was directly used for spinning.

[0195] The method for preparing mesophase pitch-based carbon fibers using coal tar pitch provided in this comparative example comprises the following steps:

[0196] 1) Preparation of mesophase by hydrogenation polycondensation

[0197] Using medium-low temperature coal tar as raw material (nitrogen atmosphere), first conduct polycondensation reaction in a high-temperature reactor for 2 hours, then hydrogenate for 45 minutes. The polycondensation and hydrogenation operations are alternately performed twice to obtain the intermediate phase asphalt.

[0198] During the polycondensation process, the amount of cycloalkane added was 6 wt %, the polycondensation temperature was 450° C., and the polycondensation pressure was 2 MPa; during the hydrogenation reaction, the temperature was 380° C. and the hydrogenation pressure was 8 MPa.

[0199] 2) Preparation of spinnable sol

[0200] Take the mesophase pitch of step 1), add PAN, CNTs, GO and Mxene and dissolve them in DMSO solvent, and continue dissolving at 60°C for 24 hours until completely dissolved to obtain a spinnable pitch. The mass fractions of the components in the spinnable pitch are: mesophase pitch 28%, PAN 2%; CNTs, GO and Mxene are all 0.2%, and the rest is DMSO solvent.

[0201] 3) Preparation of mesophase pitch-based carbon fibers

[0202] The spinnable sol obtained in step 2) is sequentially subjected to melt spinning, pre-oxidation, carbonization and graphitization to obtain mesophase pitch-based carbon fibers.

[0203] The spinnable mesophase pitch prepared in the above examples and comparative examples and the mesophase pitch-based carbon fibers finally prepared were subjected to performance tests.

[0204] Verification 1 OTI of mesophase pitch

[0205] The purified spinnable mesophase pitches of Examples 1 to 5, the purified spinnable mesophase pitches of Comparative Examples 1 to 5, and the mesophase pitches prepared in step 1) of Comparative Example 6 were used. The OTI index of the mesophase pitches was measured according to YB / T077-2017 "Determination of Optical Structure of Coke". The results are shown in Table 1.

[0206] It can be seen from the data in Table 1 that the optical structure index (OTI) of the mesophase pitch can be improved through polycondensation, hydrogenation and purification, and the optical structure index (OTI) of the mesophase pitch prepared in Example 4 is the highest at 62.83.

[0207] Verification 2

[0208] The spinnable mesophase pitch purified in Example 4 and Comparative Example 4 was taken and its crystal structure was determined by using a D8 ADVANCE X-ray diffractometer (XRD) and a HORIBA LabRAM HR Raman spectrometer, respectively. Figure 1 and Figure 2 shown.

[0209] from Figure 1 The XRD patterns and Figure 2 It can be seen from the Raman spectrum that the spinnable mesophase pitch prepared in Example 4 has an excellent crystal structure; at the same time, according to the spectrum, it is calculated using conventional methods that the crystal layer spacing of the mesophase pitch is 0.3773-0.3778.

[0210] Verification 3

[0211] The spinnable mesophase pitch purified in Examples 1 to 5 was taken and its softening point was measured using a Leica DM4P polarizing microscope, and its H / C ratio was measured using a multi EA 5100 elemental analyzer.

[0212] The results show that the spinnable mesophase pitch prepared by the present invention has an H / C ratio of 0.87 to 0.97 and a softening point of 240° C. to 280° C.

[0213] It can be seen from the above experiments that the spinnable mesophase asphalt prepared by the present invention has an excellent optical structure and a tight crystal structure. This is because compared with direct condensation, the process of hydrogenation and polycondensation adopted by the present invention can maintain a higher concentration of cycloalkyl structure in the system during the asphalt carbonization process, thereby making the system have a lower viscosity, which is conducive to the formation of a mesophase asphalt with a uniform structure, thereby generating an mesophase asphalt with high H / C, low softening point, and excellent optical / microcrystalline structure.

[0214] Verification 4

[0215] The physical properties of the carbon fibers prepared in Examples 1-5 and Comparative Examples 1-6 were measured.

[0216] The test method is as follows: The physical properties of carbon fiber, including length, diameter, elastic modulus, and tensile strength, are measured according to GB / T 31290-2022, "Determination of tensile properties of carbon fiber monofilaments." The resistivity is measured according to GB / T 24525-2009, "Determination of resistivity of carbon materials."

[0217] The test results show that the maximum carbon fiber yarn length exceeds 1000m, with a diameter ranging from 22.09 to 27.33μm. The elastic modulus, tensile strength, and resistivity results are shown in Table 1.

[0218] Table 1 Physical properties of spinnable mesophase pitch prepared in Examples 1 to 5 and Comparative Examples 1 to 6

[0219]

[0220] From the performance indicators of the mesophase pitch-based carbon fibers, it can be seen that the tensile strength and elastic modulus of Examples 1 to 5 are higher than those of the comparative example, while the resistivity is lower than that of the comparative example. The highest tensile strength is 5.2 GPa, the highest elastic modulus is 345 GPa, and the lowest resistivity is 0.81 μΩ·m. This is because the mesophase pitch molecules prepared in the comparative example have strong planarity, a high softening point, and high viscosity, which are not conducive to spinning. The mesophase pitch prepared in the present application, which has undergone hydrogenation and polycondensation and purification, has a high H / C, a low softening point, and an optical / microcrystalline structure. The spinnable sol prepared in this way can reduce viscosity, maintain good fluidity, and increase spinning stability. In addition, adding an appropriate amount of polyacrylonitrile to the spinnable sol system can form stronger hydrogen bond interactions with the mesophase molecules. After carbonization, the small-sized particles are more compactly stacked and the fiber cross-section is denser. The carbon fibers obtained thereby have higher mechanical properties. At the same time, in this embodiment, the spinnable sol system is added with a carbon nanotube additive having a large aspect ratio, which improves the mechanical properties of the carbon fiber. The spinnable sol system is added with graphene and Mxene additives having a two-dimensional network structure, which overlap with each other to form a conductive network, thereby improving the conductive properties of the carbon fiber. The synergistic effect when the three additives are used at the same time can give the carbon fiber excellent conductive properties even at a very small addition amount.

[0221] The above content is part of the implementation method of the technical solution of the present invention and is a further detailed explanation of the technical solution of the present invention. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or replacements made without departing from the concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing mesophase pitch-based carbon fibers using coal tar pitch, characterized in that: The following steps are involved: 1) Hydrogenation polycondensation Under nitrogen atmosphere, using medium-low temperature coal pitch as raw material, polycondensation reaction and hydrogenation reaction are carried out alternately to obtain mesophase pitch; The conditions for the polycondensation reaction are: temperature 430°C to 470°C, polycondensation pressure 1.5MPa to 2.5MPa, and time 1.5h to 2.5h; the conditions for the hydrogenation reaction are: temperature 360°C to 400°C, hydrogenation pressure 6MPa to 10MPa, and time 30min to 60min; 2) Mesophase pitch purification Purifying the mesophase pitch in step 1) using pyridine insolubles to obtain spinnable mesophase pitch; the mass ratio of the mesophase pitch to the pyridine insolubles is 1:1.5-2.5; 3) Preparation of spinnable sol Dissolving polyacrylonitrile, the composite additive, and the spinnable mesophase pitch prepared in step 2) in dimethyl sulfoxide (DMSO) solvent to obtain a spinnable sol; calculating the mass fractions of the respective materials based on the mass of the spinnable sol as follows: mesophase pitch 20%-30%, polyacrylonitrile 2%-8%, composite additive 0.1%-0.9%, and the remainder being DMSO solvent; 4) Preparation of mesophase pitch-based carbon fibers The spinnable sol of step 3) is sequentially subjected to melt spinning, pre-oxidation, carbonization and graphitization to obtain mesophase pitch-based carbon fibers; In the step 3), the composite additive is one or more of carbon nanotubes, graphene and transition metal carbide.

2. The method for preparing mesophase pitch-based carbon fiber using coal tar pitch according to claim 1, characterized in that: In the hydrogenation reaction of step 1), a hydrogen donor is further added, wherein the hydrogen donor is a cycloalkane, and the amount of the hydrogen donor added accounts for 4wt% to 8wt% of the medium and low temperature coal tar pitch.

3. The method for preparing mesophase pitch-based carbon fiber using coal tar pitch according to claim 2, characterized in that: The number of alternations in step 1) is at least two.

4. The method for preparing mesophase pitch-based carbon fiber using coal tar pitch according to claim 1, characterized in that: The purification process of step 2) is as follows: mixing, stirring, standing, separating, and drying.

5. The method for preparing mesophase pitch-based carbon fiber using coal tar pitch according to claim 4, characterized in that: The stirring temperature is 60° C. to 85° C., the stirring time is 0.5 h to 1.5 h, and the standing time is 2 h to 4 h.

6. The method for preparing mesophase pitch-based carbon fiber using coal tar pitch according to claim 1, characterized in that: In the step 2), the spinnable mesophase pitch is anisotropic mesophase pitch, and the H / C ratio of the spinnable mesophase pitch is 0.87-0.97, the softening point is 240° C.-280° C., the crystal interlayer spacing is 0.3773-0.3778, and the optical structure index (OTI) is 50.64-62.

83.

7. The method for preparing mesophase pitch-based carbon fiber using coal tar pitch according to claim 1, characterized in that: In the step 3), the dissolution temperature is 50° C. to 60° C., and the dissolution time is 12 h to 24 h.

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