Method for preparing spinnable mesophase pitch and pitch-based carbon fiber through free radical-induced polycondensation

Abstract

The invention provides a method for preparing spinnable mesophase pitch and pitch-based carbon fibers through free radical-induced polycondensation, and relates to the technical field of deep processing of petroleum. The method comprises the following steps: (1) by taking aromatic hydrocarbon-rich heavy oil as a raw material and selecting a CuO / CeMnO3 composite catalyst, carrying out catalytic oxidation polycondensation to prepare an asphalt precursor; (2) regulating the aromatic hydrocarbon composition of the asphalt precursor through supercritical extraction and removing catalyst particles; and (3) taking the extraction component as a raw material, introducing a free radical initiator, and carrying out free radical-initiated induced polycondensation to obtain the spinnable mesophase pitch. And carrying out melt spinning, pre-oxidation, carbonization and graphitization treatment on the mesophase pitch to obtain the pitch-based carbon fiber. The composition of the raw materials is regulated and controlled through catalytic oxidative polycondensation and supercritical extraction, aromatic molecules are induced to generate a semi-rigid structure through the free radical initiator, the fluidity of the mesophase pitch is improved, and the obtained mesophase pitch is high in mesophase content (gt; 95%), the softening point is low (250-290 DEG C), and the spinnability is good.

Description

Technical Field

[0001] The invention relates to a method for preparing spinnable mesophase pitch and pitch-based carbon fibers by free radical-induced polycondensation, and belongs to the field of petroleum deep processing technology and carbonaceous mesophase material research. Background Art

[0002] Mesophase pitch-based carbon fibers exhibit high modulus, high thermal conductivity, low coefficient of expansion, low density, and good electrical conductivity. They are used in a wide range of applications, including sporting goods, aircraft, aerospace, and the automotive industry. Mesophase pitch, the precursor of mesophase pitch-based carbon fibers, is a nematic liquid crystal compound exhibiting optical anisotropy, formed from a large number of disc-shaped or rod-shaped condensed-ring aromatic hydrocarbon molecules. Mesophase pitch has a molecular weight of 400 to 2000, a density of 1.3 to 1.6 g / cm³, and an H / C atomic ratio between 0.35 and 0.6. It exhibits high coking properties, low melt viscosity, and easy graphitization. Mesophase molecules are composed of aromatic macromolecules with a core diameter of 0.6 to 1.5 nm, connected by methylene bridges or biphenyl bonds. Their molecular weight ranges from 400 to 2000. These planar aromatic macromolecules are highly oriented and contain alkyl side chains and cycloalkane structures, which not only impart crystalline properties to the mesophase molecules but also enhance their solubility and meltability. The molecular structure of the mesophase contains both aromatic planar macromolecules and a certain amount of small molecules. These small molecules interact with the aromatic planar macromolecules through π-π conjugated bonds to achieve orderly stacking and improve the overall solubility of the mesophase asphalt.

[0003] The structural composition characteristics of the raw materials are "inherited" into the mesophase pitch molecules, thereby affecting the spinning performance of the mesophase pitch and the mechanical properties of the resulting carbon fibers. The molecular configuration of polycyclic aromatic hydrocarbons (PAHs) is a key factor in determining their thermal reactivity. Because iniposition-condensed PAHs have more exposed, high-valence active sites, their thermal reactivity is higher than that of periposition-condensed PAHs, which exhibit an "inclusion" molecular configuration. Furthermore, for PAHs with the same condensation mechanism, molecules with side chain substituents are more thermally reactive than those without side chains. According to the theory of liquid-phase carbonization of hydrocarbons, the aromatic nucleus configuration of the carbonized feedstock directly influences the structure of the resulting carbon. Pitch molecules with an iniposition configuration and a regular aromatic nucleus periphery have few or no defects within the large, planar molecules formed after condensation. These molecules, upon entering the mesophase, help reduce the viscosity of the mesophase, facilitating the formation of a widely streamlined mesophase pitch, and ultimately, producing carbon products with high graphite crystallinity.

[0004] CN110629326B provides a method for preparing mesophase pitch by direct thermal polycondensation using a mixture of coal tar and graphene as raw materials and tetralin, decalin, and tetralin as hydrogen donors. The resulting pitch-based carbon fiber has a resistivity of 0.79 to 2.52 μΩ·m and a thermal conductivity of 500 to 1600 W·m-1 ·K -1 . CN119552674A provides a method for preparing spinnable mesophase pitch and carbon fiber by fractionating coal tar, wherein the coal tar fraction is subjected to non-catalytic polymerization and high-temperature polymerization to obtain matrix pitch, which is then subjected to vacuum distillation, solvent extraction or inert gas purging to obtain spinnable mesophase pitch. CN112877087A provides a method for preparing mesophase pitch by catalytic polycondensation using a mixture of aromatic-rich oil and biomass as a raw material and one or more Lewis acids as a catalyst. The presence of the catalyst promotes the stacking of aromatic macromolecules, thereby forming high-quality mesophase pitch. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of the prior art by providing a method for preparing spinnable mesophase pitch and pitch-based carbon fibers through free radical-induced polycondensation. This method uses heavy aromatic-rich oil as a raw material, first undergoing oxidative polycondensation to prepare a pitch precursor, followed by supercritical fluid extraction to obtain an extract. The extract undergoes low-temperature, long-term free radical-induced polycondensation in the presence of a free radical initiator to produce a mesophase pitch with a mesophase content of >95%, a softening point of 250-290°C, and excellent spinnability. Subsequently, the pitch-based carbon fibers are melt-spun, pre-oxidized, carbonized, and graphitized to produce pitch-based carbon fibers with high tensile modulus, high tensile strength, and high thermal conductivity.

[0006] To achieve the above objectives, a method for preparing spinnable mesophase pitch and pitch-based carbon fibers by free radical-induced polycondensation is provided, using heavy aromatic-rich oil as raw material, and the specific steps are as follows:

[0007] (1) Using aromatic-rich heavy oil as raw material, a CuO / CeMnO3 composite catalyst was selected to carry out catalytic oxidative polycondensation to obtain an asphalt precursor.

[0008] (2) The precursor asphalt obtained in step (1) is subjected to solvent extraction under supercritical conditions to obtain an asphalt precursor extraction component.

[0009] (3) subjecting the extracted components obtained in step (2) to low-temperature, long-term free radical-induced polycondensation under the action of a free radical initiator to obtain an intermediate phase pitch.

[0010] (4): The mesophase pitch obtained in step (3) is sequentially subjected to melt spinning, pre-oxidation, and carbonization / graphitization to obtain pitch-based carbon fibers.

[0011] The aromatics-rich oil in step (1) of the present invention is one or more of catalytic slurry oil, ethylene tar, coal tar, and coal liquefaction pitch.

[0012] The oxidative polycondensation temperature in step (1) of the present invention is 240° C., the reaction time is 4 hours, and the amount of catalyst added is 0.5-2 wt %.

[0013] The solvent in step (2) of the present invention is one or more of isooctane, carbon tetrachloride, ether, cyclohexane, and dichloromethane. The extraction conditions are as follows: the mass ratio of the solvent to the asphalt precursor is 5:1, and the extraction temperature is 190-280°C.

[0014] The free radical initiator described in step (3) of the present invention is one or more of 2,3-dimethyl-2,3-diphenylbutane (DMDPB), p-isopropylbenzene polymer (G33), and divinylbenzene (DVB), and the addition amount of the free radical initiator is 1-5wt% of the raw material mass.

[0015] In step (3) of the present invention, the low-temperature and long-term free radical-induced polycondensation temperature is 350-380° C., and the reaction time is 30-40 hours.

[0016] The softening point of the mesophase pitch prepared in step (3) of the present invention is 250-290° C., the anisotropy content is >95%, the H / C atomic ratio is 0.4-0.6, and the residual carbon value is 80%-85%.

[0017] The carbon fiber prepared in step (4) of the present invention has a tensile modulus of 300-300 GPa, a tensile strength of 1200-1800 MPa, and a density of 1.70-1.85 g·cm -3 , resistivity is 0.78~2.55μΩ·m, thermal conductivity is 600~800W·m -1 ·K -1 .

[0018] Compared with the prior art, the present invention has the following advantages and improvements:

[0019] 1. Aromatic-rich oil has a wide molecular weight distribution. The present invention first forms an asphalt precursor with a certain degree of polymerization through catalytic oxidative polycondensation, and then performs supercritical extraction to obtain extraction components with different molecular weight distributions. The group composition and structure of the raw oil are regulated to achieve synchronous polycondensation during the thermal reaction, thereby suppressing the formation of high-softening-point over-carbonized products and effectively improving the spinnability of the mesophase asphalt.

[0020] 2. The spinnable mesophase pitch provided by the present invention uses aromatic-rich oil as raw material. The aromatic-rich oil is one or more of catalytic slurry oil, coal tar, ethylene tar, and coal liquefaction pitch. The raw material source is wide, the cost is low, and the product has high added value.

[0021] 3. The present invention innovatively introduces a free radical initiator to induce polycondensation to prepare mesophase asphalt, so that the asphalt precursor extraction components can fully undergo thermal cracking and thermal polycondensation reactions to generate mesophase globules with a certain mesophase content, providing sufficient conditions for the subsequent formation of large-scale mesophase asphalt; in addition, the free radical initiator can retain the methylene structure in the mesophase molecules to generate a semi-rigid mesophase structure, which helps to improve the viscosity of the mesophase asphalt and promote the stacking of planar aromatic sheets, thereby forming a spinnable mesophase asphalt with high order and suitable softening point. In addition, the mesophase asphalt molecules with a semi-rigid structure are more easily oriented under the influence of shear force during the melt spinning process, which helps to reduce internal defects in the fiber and improve the mechanical properties of carbon fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a polarized photo of the mesophase pitch prepared in the present invention.

[0023] Figure 2 SEM image of the mesophase pitch-based carbon fiber prepared by the present invention DETAILED DESCRIPTION

[0024] The following examples further illustrate the method for preparing spinnable mesophase pitch and pitch-based carbon fibers provided by the present invention through free radical-induced polycondensation.

[0025] Implementation Example 1:

[0026] A pitch precursor was prepared using catalytic oil slurry as the raw material, with a CuO / CeMnO3 addition of 0.5%, an air flow rate of 10 mL / min, an oxidation temperature of 240°C, and an oxidation time of 4 hours. Supercritical fluid extraction (SCLE) of the pitch precursor using carbon tetrachloride as the extraction solvent was performed at an extraction temperature of 235°C and a solvent-to-pitch precursor mass ratio of 5:1 to obtain a pitch precursor extract. This extract was then subjected to a low-temperature, long-term, free-radical-induced polycondensation with 2 wt% 2,3-dimethyl-2,3-diphenylbutane (DMDPB) at 350°C for 38 hours to obtain a mesophase pitch. The mesophase pitch exhibited a softening point of 285°C, an anisotropy content of 95%, an H / C atomic ratio of 0.50, and a carbon residue of 85%. The resulting mesophase pitch was melt-spun at 335°C to produce pre-fibers. The pre-fibers were then pre-oxidized, carbonized, and graphitized to yield pitch-based carbon fibers. The tensile modulus of carbon fiber is 325GPa, the tensile strength is 1850MPa, and the density is 1.76g·cm -3 , the resistivity is 1.92μΩ·m, and the thermal conductivity is 800W·m -1 ·K -1 .

[0027] Implementation Example 2:

[0028] A pitch precursor was prepared using ethylene tar as the raw material, with a CuO / CeMnO3 addition of 1wt%, an air flow rate of 15mL / min, an oxidation temperature of 240°C, and an oxidation time of 4h. Ethyl ether was used as the extraction solvent, and supercritical extraction of the pitch precursor was performed at an extraction temperature of 190°C and a mass ratio of 5:1 between the extraction solvent and the pitch precursor to obtain a pitch precursor extract. The pitch precursor extract was then subjected to a low-temperature, long-term, free-radical-induced polycondensation with 3wt% of a p-isopropylbenzene polymer (G33) at a reaction temperature of 360°C for 35h to obtain a mesophase pitch. The mesophase pitch exhibited a softening point of 280°C, an anisotropy content of 92%, an H / C atomic ratio of 0.52, and a carbon residue of 80%. The resulting mesophase pitch was melt-spun at 330°C to produce a precursor fiber. The precursor was then pre-oxidized, carbonized, and graphitized to produce pitch-based carbon fibers. The tensile modulus of carbon fiber is 320GPa, the tensile strength is 1800MPa, and the density is 1.70g·cm -3 , the resistivity is 1.82μΩ·m, and the thermal conductivity is 700W·m -1 ·K -1 .

[0029] Implementation Example 3:

[0030] A pitch precursor was prepared using coal liquefaction pitch as raw material, using a CuO / CeMnO3 addition of 1.5 wt% at an air flow rate of 20 mL / min, an oxidation temperature of 240°C, and an oxidation time of 4 hours. Supercritical fluid extraction (SCFE) of the pitch precursor using dichloromethane as the extraction solvent was performed at 240°C with a solvent-to-pitch precursor mass ratio of 5:1 to obtain a pitch precursor extract. This extract was then subjected to a low-temperature, long-term, free-radical-induced polycondensation with 2.5 wt% divinylbenzene (DVB) at 370°C for 30 hours to obtain a mesophase pitch. The mesophase pitch exhibited a softening point of 276°C, an anisotropy content of 90%, an H / C atomic ratio of 0.54, and a carbon residue of 75%. The resulting mesophase pitch was melt-spun at 326°C to produce pre-fibers. The pre-fibers were then pre-oxidized, carbonized, and graphitized to yield pitch-based carbon fibers. The tensile modulus of carbon fiber is 300 GPa, the tensile strength is 1700 MPa, and the density is 1.62 g·cm -3 , the resistivity is 1.74μΩ·m, and the thermal conductivity is 650W·m -1 ·K -1 .

Claims

1. A method for preparing spinnable mesophase pitch and pitch-based carbon fibers by free radical-induced polycondensation, using heavy aromatic-rich oil as raw material, characterized in that: The specific steps include: (1) Using aromatic-rich heavy oil as raw material, a CuO / CeMnO3 composite catalyst was selected to carry out catalytic oxidative polycondensation to obtain an asphalt precursor. (2) The asphalt precursor obtained in step (1) is subjected to supercritical solvent extraction to obtain an asphalt precursor extraction component. (3) subjecting the extracted components obtained in step (2) to low-temperature, long-term free radical-induced polycondensation under the action of a free radical initiator to obtain a spinnable mesophase pitch. (4): The mesophase pitch obtained in step (3) is sequentially subjected to melt spinning, pre-oxidation, and carbonization / graphitization to obtain pitch-based carbon fibers.

2. The method for preparing spinnable mesophase pitch and pitch-based carbon fibers by free radical-induced polycondensation according to claim 1, characterized in that: The aromatics-rich oil in step (1) is one or more of catalytic slurry oil, ethylene tar, coal tar, and coal liquefaction pitch.

3. The method for preparing spinnable mesophase pitch and pitch-based carbon fibers by free radical-induced polycondensation according to claim 1, characterized in that: The oxidative polycondensation temperature in step (1) is 240° C., the oxidation time is 4 hours, and the amount of catalyst added is 0.5-2 wt %.

4. The method for preparing spinnable mesophase pitch and pitch-based carbon fibers by free radical-induced polycondensation according to claim 1, characterized in that: The solvent in step (2) is one or more of isooctane, carbon tetrachloride, ether, cyclohexane, and dichloromethane. The extraction conditions are as follows: the mass ratio of the solvent to the asphalt precursor is 5:1, and the extraction temperature is 190-280°C.

5. The method for preparing spinnable mesophase pitch and pitch-based carbon fibers by free radical-induced polycondensation according to claim 1, characterized in that: The free radical initiator described in step (3) is one or more of 2,3-dimethyl-2,3-diphenylbutane (DMDPB), p-isopropylbenzene polymer (G33), and divinylbenzene (DVB), and the amount of the free radical initiator added is 1-5wt% of the raw material mass.

6. The method for preparing spinnable mesophase pitch and pitch-based carbon fibers by free radical-induced polycondensation according to claim 1, characterized in that: In step (3), the low-temperature and long-term free radical initiation and induced polycondensation temperature is 350-380° C., and the reaction time is 30-40 h.

7. The method for preparing spinnable mesophase pitch and pitch-based carbon fibers by free radical-induced polycondensation according to claim 1, characterized in that: The softening point of the mesophase pitch prepared in step (3) is 250-290° C., the anisotropy content is >95%, the H / C atomic ratio is 0.4-0.6, and the residual carbon value is 80%-85%.

8. The method for preparing spinnable mesophase pitch and pitch-based carbon fibers by free radical-induced polycondensation according to claim 1, characterized in that: The carbon fiber prepared in step (4) has a tensile modulus of 300-300 GPa, a tensile strength of 1200-1800 MPa, and a density of 1.70-1.85 g·cm -3 , resistivity is 0.78~2.55μΩ·m, thermal conductivity is 600~800W·m -1 ·K -1 .

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