阅读说明：本技术 一种中间相沥青和中间相炭微球的制备方法 (Preparation method of mesophase pitch and mesophase carbon microspheres ) 是由 刘�东 龚鑫 李志浩 崔俊杰 赵燕 于 2021-01-13 设计创作，主要内容包括：本发明涉及一种中间相沥青和中间相炭微球的制备方法,以重质油为原料,经正庚烷萃取分离出不溶物,在脱沥青油中掺杂3wt％～10wt％的有机金属配合物进行浅度催化,并对后续炭微球结构实现了金属插层改性；催化产物经减压拔出>450℃组分的缩聚重产物,添加10～200ug/g的正庚烷不溶物和1wt％～10wt％自由基助剂,经二者协同缩聚得到广域中间相沥青,粉碎过筛,取不同筛分目数的中间相沥青颗粒加至高沸点分散介质中乳化成球,经洗涤干燥后得到中间相炭微球。本发明优势在于采用廉价易得的重质油为原料,采用浅度催化-协同缩聚-乳化三元组合工艺制备中间相炭微球,具有收率高,粒径分布均匀,粒径大小可调可控的优点,此外,还实现了金属插层,片层结构得到优化改善。(The invention relates to a preparation method of mesophase pitch and mesophase carbon microspheres, which takes heavy oil as a raw material, extracts and separates out insoluble substances through n-heptane, dopes organic metal complexes with 3 wt% -10 wt% in deasphalted oil for shallow catalysis, and realizes metal intercalation modification on subsequent carbon microsphere structures; and (3) decompressing and drawing out a polycondensation heavy product with components at the temperature of more than 450 ℃ from the catalytic product, adding 10-200 ug/g of n-heptane insoluble substances and 1-10 wt% of free radical auxiliary agents, performing synergistic polycondensation of the n-heptane insoluble substances and the free radical auxiliary agents to obtain wide-area mesophase pitch, crushing and sieving the wide-area mesophase pitch, adding the mesophase pitch particles with different sieving meshes into a high-boiling point dispersion medium to emulsify the mixture into balls, and washing and drying the balls to obtain the mesophase carbon microspheres. The method has the advantages that cheap and easily-obtained heavy oil is used as a raw material, and the shallow catalysis-cooperative polycondensation-emulsification ternary combination process is adopted to prepare the mesocarbon microbeads, so that the method has the advantages of high yield, uniform particle size distribution, adjustable and controllable particle size, metal intercalation and optimized and improved lamellar structure.)

1. A preparation method of mesophase pitch and mesophase carbon microspheres takes one or more of medium-low temperature coal tar, high temperature coal tar and fractions thereof, heavy oil fractions, vacuum residue oil and FCC slurry oil as raw material oil, and is characterized by comprising the following steps:

(1) extracting raw oil by n-heptane to separate insoluble substances, doping 3-10 wt% of organic metal complex into deasphalted oil, carrying out shallow catalysis under the conditions of reaction temperature of 300-350 ℃, inert gas protection and reaction time of 1-6 h, and reducing pressure to extract a polycondensation heavy product of components with the temperature of more than 450 ℃;

(2) adding 10-200 ug/g of n-heptane insoluble substances and 1-10 wt/% of free radical auxiliary agents into the polycondensation heavy product, and performing synergistic polycondensation on the two substances at the reaction temperature of 400-450 ℃, the reaction pressure of 0.1-6 MPa and the reaction time of 6-10 h to obtain wide-area mesophase pitch;

(3) after cooling to normal temperature, crushing and sieving the wide range mesophase pitch, adding the mesophase pitch particles with different sieving meshes into a high boiling point dispersion medium, wherein the ratio of the mesophase pitch particles to the high boiling point dispersion medium is 1: 10-1: 100(g/ml), emulsifying the mesophase pitch particles into balls under the conditions of reaction temperature of 300-350 ℃, heat preservation for 0.5-2 h and stirring speed of 400-600 r/min, and washing and drying to obtain the mesophase carbon microspheres.

2. The method for preparing mesophase pitch and mesophase carbon microbeads according to claim 1, characterized in that: the organic metal complex in the step (1) comprises one or more of carbonyl iron, cobalt carbonyl, nickel carbonyl, dialkyl (aryl) molybdenum dithiocarbamate, dialkyl molybdenum dithiophosphate, molybdenum naphthenate, cobalt naphthenate, molybdenum isooctanoate, molybdenum hexacarbonyl and copper stearate.

3. The method for preparing mesophase pitch and mesophase carbon microbeads according to claim 1, characterized in that: the free radical auxiliary agent in the step (2) comprises one or more of tetrahydronaphthalene, decahydronaphthalene, dihydrophenanthrene and dihydroanthracene, the content of the mesophase of the wide-area mesophase pitch is 80-100%, and the softening point is 200-250 ℃.

4. The method for preparing mesophase pitch and mesophase carbon microbeads according to claim 1, characterized in that: the boiling point of the high-boiling point dispersion medium in the step (3) is more than 350 ℃, and the high-boiling point dispersion medium comprises one or more of alkyl naphthalene conduction oil, benzyl biphenyl conduction oil, dibenzyl methyl high-heat oil, aryl modified methyl silicone oil, phenyl methyl silicone oil and phenyl modified silicone oil.

5. The method for preparing mesophase pitch and mesophase carbon microbeads according to claim 1, characterized in that: the yield of the mesocarbon microbeads obtained in the step (3) is 50% -70%, and the median diameter is 12-62 μm.

6. The method for preparing mesophase pitch and mesophase carbon microbeads according to claim 5, wherein: the added raw material mesophase pitch particles are controlled to be 200-300 meshes, and the carbon microsphere product with the median diameter of 48-62 mu m can be produced; the added raw material mesophase pitch particles are controlled to be 300-400 meshes, and the carbon microsphere product with the median diameter of 38-48 mu m can be produced; the added raw material mesophase pitch particles are controlled to be 400-500 meshes and can be used for producing carbon microsphere products with the median diameter of 29-38 mu m; the added raw material mesophase pitch particles are controlled to be 500-600 meshes, and the carbon microsphere product with the median diameter of 20-29 mu m can be produced; the added raw material mesophase pitch particles are controlled to be larger than 600 meshes, and the carbon microsphere product with the median diameter of 12-20 mu m can be produced.

7. Mesophase pitch and mesophase carbon microbead products produced by the process of any of claims 1-6.

8. The use of mesophase pitch and mesophase carbon microsphere products according to claim 7 in novel carbon materials, wherein the novel carbon materials include isostatic graphite materials, ultra high power electrodes, lithium ion battery negative electrode materials, high density isotropic carbons, high specific surface area activated carbons, packing materials for high performance liquid chromatography columns, catalyst supports.

Technical Field

The invention relates to a preparation method of mesophase pitch and mesophase carbon microspheres, in particular to a method for preparing the mesophase pitch and the mesophase carbon microspheres by using heavy oil as a raw material through a shallow catalysis-synergistic polycondensation-emulsification combined process, belonging to the field of preparation of high-grade novel carbon materials.

Background

Crude oil in the world has a tendency to be heavy, and the yield of thick oil is increasing day by day. The yields of vacuum residue, atmospheric residue, catalytic cracking slurry oil, coal tar, ethylene tar and the like after the crude oil is processed are increased year by year, and the production of the carbon material with high added value provides an effective utilization mode for heavy oil.

Mesophase pitch is a liquid crystal phase compound containing a considerable amount of mesophase, which is formed by a series of reactions such as bond breaking, deoxidation, polycondensation and accumulation of organic compounds such as petroleum heavy oil, coal tar and pure aromatic hydrocarbon compounds at high temperature. Mesophase pitch generally has higher purity and aromaticity, and aromatic macromolecules have optical anisotropy due to specific orientation arrangement, and the mesophase pitch has low preparation cost, high oxidation activity and higher carbon purity and is a high-quality parent for preparing high-performance carbon materials.

The carbon microsphere is a novel carbon material, has the characteristics of good chemical stability, thermal stability, excellent electric conduction, heat conduction and the like, and has wide application prospect. The mesocarbon microbeads have the characteristics of sphericity due to the structure of parallel stacking of lamellar molecules, small sphere diameter and uniform distribution, and become the basic materials of a plurality of novel carbon materials, such as: the catalyst is prepared from isostatic pressing graphite materials, ultrahigh power electrodes, lithium ion battery cathode materials, high-density isotropic carbon, high-specific surface active carbon, a filling material of a high performance liquid chromatography column, a catalyst carrier and the like, and can be widely applied to the fields of mechanical industry, nuclear energy industry, chemical industry, semiconductor industry, new energy, environmental protection and the like.

The patent CN1308113A adopts a method of mixing and heating medium temperature asphalt with Quinoline Insoluble (QI) less than 10 percent and secondary petroleum heavy oil with Quinoline Insoluble (QI) less than 0.5 percent, and adopts an extraction method to carry out extraction and filtration, the yield of the method is generally 10-30 percent, and the yield of the obtained mesocarbon microbead product with the diameter of 15 mu m is 13.8 percent. The patents CN1382624 and CN1278513A respectively use aromatic heavy oil or asphalt, and medium temperature asphalt, and use nitrates of iron, cobalt, and nickel as catalysts, and adjust the particle size, particle size distribution, and surface state of the mesocarbon microbeads by changing the variety, dosage, and mixing ratio of the catalysts. In patent CN1116386C, a mesophase coal tar pitch raw material and secondary petroleum heavy oil are used as raw materials, and after thermal polycondensation, a mesophase carbon microsphere product is obtained by adopting a separation method of an extraction method. Patent CN103268941A discloses a method for preparing mesophase pitch microspheres based on emulsification and suspension, which comprises adding absolute ethanol, ultrasonic dispersing, centrifuging, collecting supernatant, separating mesophase pitch particles, adding petroleum ether in proper amount, ultrasonic dispersing, mixing with high temperature resistant silicone oil, stirring, heating, centrifuging, and repeatedly cleaning with organic solvent. The prior method only carries out one-time thermal polycondensation reaction or direct catalytic polycondensation process, and the obtained mesophase pitch and the mesophase carbon microspheres have low yield and uneven particle size distribution.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, improves the preparation process of mesophase pitch and mesophase carbon microspheres, prepares high-quality wide-area mesophase pitch by using heavy oil as a raw material through the processes of shallow catalysis, synergistic polycondensation and emulsification, prepares high-quality mesophase carbon microspheres by using the high-quality wide-area mesophase pitch as a raw material, and optimizes the production process.

The purpose of the invention is realized by adopting the following technical scheme:

a preparation method of mesophase pitch and mesophase carbon microspheres, which takes one or more of medium-low temperature coal tar, high temperature coal tar and fractions thereof, heavy oil fractions, vacuum residue oil and FCC slurry oil as raw material oil, and pretreats the raw material by doping organic metal, specifically comprises the following steps:

(1) extracting raw oil by n-heptane to separate insoluble substances, doping 3-10 wt% of organic metal complex into deasphalted oil, carrying out shallow catalysis at the reaction temperature of 300-350 ℃ under the protection of inert gas for 1-6 h, and reducing pressure to extract a polycondensation heavy product with the temperature of more than 450 ℃; (2) adding an n-heptane insoluble substance and a free radical auxiliary agent into the polycondensation heavy product, and performing synergistic polycondensation on the n-heptane insoluble substance and the free radical auxiliary agent under the conditions of reaction temperature of 400-450 ℃, reaction pressure of 0.1-6 MPa and reaction time of 6-10 h to obtain wide-area mesophase pitch; (3) after cooling to normal temperature, crushing and sieving the mesophase pitch, adding the mesophase pitch particles with different sieving meshes into a high-boiling-point dispersion medium, wherein the proportion of the mesophase pitch particles to the high-boiling-point dispersion medium is 1: 10-1: 100(g/ml), emulsifying the mesophase pitch particles into balls under the conditions of reaction temperature of 300-350 ℃, heat preservation for 0.5-2 h and stirring speed of 400-600 r/min, and washing and drying to obtain the mesophase carbon microspheres.

In the step (1), the organic metal complex is one or more of carbonyl iron, cobalt carbonyl, nickel carbonyl, dialkyl (aryl) molybdenum dithiocarbamate, dialkyl molybdenum dithiophosphate, molybdenum naphthenate, cobalt naphthenate, molybdenum isooctanoate, molybdenum hexacarbonyl and copper stearate.

The free radical auxiliary agent in the step (2) comprises one or more of tetrahydronaphthalene, decahydronaphthalene, dihydrophenanthrene and dihydroanthracene, the addition amount is 1 wt% -10 wt% of the polycondensation weight product, the addition amount of the n-heptane insoluble substance is 10-200 ug/g, the mesophase content of the obtained wide-area mesophase pitch is 80-100%, and the softening point is 200-250 ℃.

The high-boiling point dispersion medium in the step (3) is one or more of alkyl naphthalene conduction oil, benzyl biphenyl conduction oil, dibenzyl methyl high-thermal oil, aryl modified methyl silicone oil, phenyl methyl silicone oil and phenyl modified silicone oil.

The yield of the intermediate phase carbon microspheres prepared in the step (3) is 50-70%, and the added raw material intermediate phase asphalt particles are controlled to be 200-300 meshes, so that the intermediate phase carbon microspheres with the median diameter of 48-62 mu m can be produced; the added raw material mesophase pitch particles are controlled to be 300-400 meshes, and the mesophase pitch particles can be used for producing mesophase carbon microsphere products with the median diameter of 38-48 mu m; the added raw material mesophase pitch particles are controlled to be 400-500 meshes and can be used for producing mesophase carbon microsphere products with the median diameter of 29-38 mu m; the added raw material mesophase pitch particles are controlled to be 500-600 meshes, and the mesophase pitch particles can be used for producing mesophase carbon microsphere products with the median diameter of 20-29 mu m; the added raw material mesophase pitch particles are controlled to be larger than 600 meshes, and the mesophase pitch particles can be used for producing mesophase carbon microsphere products with the median diameter of 12-29 mu m. After the graphite is graphitized at 2800 ℃, the graphitization degree of the microsphere is more than or equal to 92 percent.

The invention also provides the mesophase pitch and the mesophase carbon microsphere product prepared by the method and application of the mesophase pitch and the mesophase carbon microsphere product in novel carbon materials, wherein the novel carbon materials comprise an isostatic pressing graphite material, an ultrahigh power electrode, a lithium ion battery cathode material, high-density isotropic carbon, high-specific surface active carbon, a filling material of a high performance liquid chromatography column and a catalyst carrier.

The invention adopts a three-component combination process of shallow catalysis, synergistic polycondensation and emulsification to prepare the mesophase carbon microspheres, and the main reasons are that the composition of heavy oil raw materials is complex, the thermal polycondensation reaction activity of composition molecules is not uniform, and the phenomenon that the particle size distribution of mesophase spheres is too wide and fused and serious can occur if the heavy oil raw materials are directly thermally polymerized. Therefore, firstly, the heptane insoluble substance with higher reaction activity is separated by solvent extraction, then the organic metal complex is added for preliminary induced polycondensation, the organic metal complex has oleophilic groups and can be uniformly dispersed in the heavy oil component, the organic metal complex can dissociate out metal atoms with high activity in the pyrolysis process, and the thermal polycondensation reaction of aromatic hydrocarbon molecules in the raw oil is accelerated under the catalysis of the metal atoms, so that the aromaticity and the reaction activity of an intermediate product are increased; then adding a free radical assistant and heptane insoluble substances for carrying out cooperative polycondensation, wherein the free radical assistant can release a large amount of transfer hydrogen radicals through thermal cracking at high temperature, the hydrogen radicals can participate in the reaction of the system, so that the concentration of the condensed ring radicals in the reaction system is reduced, the excessive polycondensation is inhibited, mesophase molecules with uniform molecular weight distribution are generated, meanwhile, part of condensed ring structures of the asphalt are converted into main ring structures, the fluidity of the mesophase asphalt in a molten state is increased, the softening point of the mesophase asphalt can be reduced to a certain extent, a small amount of heptane insoluble substances can be used as a nucleation promoter, the mesophase nucleation time can be shortened, and under the synergistic action of the two, the mesophase asphalt in a wide area can be rapidly formed in a short time, and the yield of the mesophase asphalt is improved. Then under the emulsification and dispersion action of a high-boiling point dispersion medium, the mesophase pitch particles can be emulsified to form the mesophase carbon microspheres with uniform particle size distribution. The method realizes high value-added utilization of inferior heavy oil, and prepares the mesocarbon microbeads with high yield and uniform particle size. In addition, the metal complex catalyst added into the carbon microsphere is not required to be removed, and the metal lattices inserted into the carbon microsphere can not only realize the subsequent catalytic graphitization of the mesocarbon microsphere and improve the graphitization degree of the mesocarbon microsphere, but also increase the conductivity of the carbon microsphere, thereby being beneficial to preparing the high-performance negative electrode material for the lithium ion battery.

Compared with the prior art, the invention has the beneficial effects that:

(1) the raw materials related by the invention have rich sources, low cost and high degree of freedom; reasonable design, precise production process, high raw material treatment depth, low requirement on equipment and easy realization of industrialization.

(2) By adopting the process, the shallow catalysis and the synergistic induction polycondensation are organically combined, the high-quality raw material with uniform molecular weight can be used for preparing the mesophase pitch (high mesophase content, lower softening point and low viscosity) with excellent properties through the polycondensation reaction, and the mesophase pitch can be used as the high-quality raw material for preparing the mesophase carbon microspheres by an emulsification method.

(3) The invention screens the mesophase pitch, correlates the particle sizes of the mesophase pitch particles with different particle sizes to form the mesophase carbon microspheres, and the mesophase carbon microspheres prepared by the emulsification method have better sphericity and narrower size distribution and are adjustable and controllable.

(4) The invention does not need to remove the metal complex catalyst added into the small balls, realizes metal intercalation, and the inserted metal lattices are beneficial to the subsequent high-temperature carbonization and graphitization of the mesocarbon microbeads, and also can increase the conductivity of the small balls, thus being beneficial to preparing the high-performance negative electrode material for the lithium ion battery.

Detailed Description

The preparation methods of mesophase pitch and mesophase carbon microbeads provided by the present invention are further described below with reference to examples.

Example 1

Subjecting the heavy oil fraction of medium-low temperature coal tar to an N-heptane solvent extraction separation device to obtain N-heptane insoluble substances, evaporating the solvent from the solvent extract oil to dryness, collecting 300g, doping 15g of molybdenum isooctanoate, mixing thoroughly, adding into a high pressure reaction kettle, reacting at 330 deg.C under N₂Carrying out shallow catalysis for 5h under the protection of atmosphere, and pulling out the catalyst through a pressure reducing device>Heavy polycondensation products of components at 450 ℃; adding 10mg of n-heptane insoluble substances and 6g of radical assistant tetrahydronaphthalene into the polycondensation heavy product, fully mixing, adding 200g of the mixture into a high-pressure reaction kettle, reacting at the reaction temperature of 420 ℃, the reaction pressure of 4MPa and the reaction time of 8 hours, and performing synergistic polycondensation on the two to obtain wide-area mesophase pitch with the content of 94.7% and the softening point of 246 ℃; cooling the mesophase pitch to normal temperature, crushing the mesophase pitch, sieving the mesophase pitch by a sample sieve, taking 200-300 meshes of mesophase pitch particles, emulsifying the mesophase pitch particles into balls under the conditions that the reaction temperature is 350 ℃, the heat preservation is 1.5h and the stirring speed is 500r/min, washing and drying to obtain the mesophase carbon microspheres, wherein the yield of the obtained mesophase carbon microspheres is 58%, and d₅₀And 54 μm. After graphitizing at 2800 ℃, the graphitization degree of the microsphere is 92%.

Example 2

The high-temperature coal tar heavy oil fraction is subjected to an N-heptane solvent extraction separation device to obtain N-heptane insoluble substances, 300g of solvent extract oil is obtained after the solvent is evaporated to dryness, 6g of carbonyl iron is doped into the solvent extract oil, the mixture is fully mixed and then added into a high-pressure reaction kettle, and the reaction temperature is 350 ℃ and N is₂Carrying out shallow catalysis for 6h under the protection of atmosphere, and pulling out the catalyst through a pressure reducing device>Heavy polycondensation products of components at 450 ℃; adding 10mg of N-heptane insoluble substances and 2g of decalin as a free radical assistant into the polycondensation heavy product, fully mixing, adding 200g of the mixture into a high-pressure reaction kettle, and reacting at the temperature of 450 ℃ under the condition of N₂Reacting for 8 hours under the protection of atmosphere, and obtaining wide-area mesophase asphalt with the content of 97.7 percent and the softening point of 247 ℃ through the synergistic polycondensation of the two; cooling the mesophase pitch to normal temperature, pulverizing the mesophase pitch, sieving with a sample sieve, and collecting>600 mesh mesophase pitch particles, mesophase pitch particlesThe ratio of the intermediate phase pitch particles to the alkyl naphthalene heat conducting oil is 1:10(g/ml), the intermediate phase pitch particles are emulsified into balls under the conditions that the reaction temperature is 350 ℃, the temperature is kept for 2 hours, and the stirring speed is 600r/min, the intermediate phase carbon microspheres are obtained after washing and drying, the yield of the obtained intermediate phase carbon microspheres is 59 percent, and d is₅₀And 15 μm. After graphitizing at 2800 ℃, the graphitization degree of the microsphere is 93 percent.

Example 3

Vacuum residue is extracted by an N-heptane solvent extraction separation device to obtain N-heptane insoluble substances, the solvent extract oil is evaporated to dryness to obtain 300g of solvent, 21g of cobalt naphthenate is doped into the solvent extract oil, the mixture is fully mixed and then added into a high-pressure reaction kettle, and the reaction temperature is 330 ℃, and N is₂Carrying out shallow catalysis under the condition of 5h of reaction time under the atmosphere protection, and pulling out the catalyst through a pressure reducing device>Heavy polycondensation products of components at 450 ℃; adding 20mg of n-heptane insoluble substances and 10g of free radical auxiliary agent dihydrophenanthrene into the polycondensation heavy product, fully mixing, adding 200g of the mixture into a high-pressure reaction kettle, reacting at the reaction temperature of 440 ℃, the reaction pressure of 3MPa and the reaction time of 10 hours, and performing synergistic polycondensation on the two to obtain wide-area mesophase asphalt with the content of 95.89% and the softening point of 250 ℃; after the mesophase pitch is cooled to normal temperature, the mesophase pitch is crushed and sieved by a sample sieve, the proportion of the mesophase pitch particles with 500-600 meshes to the alkyl naphthalene heat transfer oil is 1:10(g/ml), the mesophase pitch particles are emulsified into balls under the conditions of reaction temperature of 350 ℃, heat preservation for 2h and stirring speed of 500r/min, the mesophase pitch particles are washed and dried to obtain the mesophase carbon microspheres, the yield of the obtained mesophase carbon microspheres is 51%, and d₅₀And 26 μm. After graphitizing at 2800 ℃, the graphitization degree of the microsphere is 92%.

Example 4

Subjecting FCC oil slurry to N-heptane solvent extraction separation device to obtain N-heptane insoluble substance, evaporating solvent from solvent extract oil to dryness, collecting 300g, doping 30g of molybdenum dialkyl dithiophosphate, mixing thoroughly, adding into high pressure reactor, reacting at 300 deg.C and N₂Carrying out mild catalysis under the condition of atmosphere protection reaction time of 4h, and pulling out the catalyst through a pressure reducing device>Heavy polycondensation products of components at 450 ℃; adding 30mg of n-heptane insoluble matter and 14g of free radical auxiliary agent dihydroanthracene into the polycondensation productMixing, adding 200g of the mixture into a high-pressure reaction kettle, reacting at the reaction temperature of 450 ℃, the reaction pressure of 5MPa and the reaction time of 6 hours, and performing synergistic polycondensation on the mixture and the high-pressure reaction kettle to obtain wide-area mesophase pitch with the content of 92.58% and the softening point of 244 ℃; after the mesophase pitch is cooled to normal temperature, the mesophase pitch is crushed and sieved by a sample sieve, 300-400 mesh mesophase pitch particles are taken, the ratio of the mesophase pitch particles to alkyl naphthalene conduction oil is 1:10(g/ml), the mesophase pitch particles are emulsified into balls under the conditions that the reaction temperature is 350 ℃, the heat preservation is 1.5h and the stirring speed is 400r/min, and the mesophase carbon microspheres are obtained after washing and drying, wherein the yield of the obtained mesophase carbon microspheres is 62%, and d₅₀Was 42 μm. After graphitizing at 2800 ℃, the graphitization degree of the microsphere is 94%.

Comparative example 1

The other steps were the same as in example 1, except that 15g of molybdenum isooctanoate was not doped; obtaining wide-area mesophase pitch with the content of 92% and the softening point of 276 ℃; the yield of the obtained mesocarbon microbeads is 42 percent, d₅₀And 54 μm. After graphitizing at 2800 ℃, the graphitization degree of the microsphere is 86%.