Preparation method of coal pitch-based skeleton carbon based on physical activation

Abstract

The invention relates to the technical field of skeleton carbon materials, and discloses coal pitch-based skeleton carbon based on physical activation and a preparation method thereof.The preparation method comprises the following steps that coal pitch is subjected to light component pre-removal treatment, then ground and mixed with a cross-linking agent mixing system to prepare a cross-linking precursor, then the cross-linking precursor is mixed with an organic solvent compounding system to obtain slurry, and the slurry is subjected to solid-liquid separation to obtain the coal pitch-based skeleton carbon based on physical activation. Carrying out spray drying granulation on the slurry to obtain precursor particles, and carrying out segmented oxidation treatment on the precursor particles in an aerobic atmosphere to obtain oxidized precursor particles; performing carbonization treatment, and finally performing high-temperature physical activation to obtain the coal pitch-based skeleton carbon based on physical activation. According to the preparation method, a stable three-dimensional network structure is constructed through the synergistic effect of means such as light pre-removal, cross-linking and segmented oxidation, melting and bonding during high-temperature pyrolysis of the coal pitch are avoided, it is ensured that skeleton carbon keeps a regular spherical morphology, the graphitization degree is controlled to be 20-25%, and the adsorption and electrochemical performance is improved.

Description

Technical Field

[0001] This invention relates to the field of framework carbon materials technology, and more specifically, to a method for preparing coal tar pitch-based framework carbon based on physical activation. Background Technology

[0002] Porous carbon materials (such as activated carbon and carbon molecular sieves) are widely used in energy storage (supercapacitors, lithium-ion batteries), adsorption separation, and catalyst supports due to their high specific surface area, tunable pore structure, good chemical stability, and electrical conductivity. Physical activation methods (usually using steam or carbon dioxide) are an important method for preparing porous carbon materials, with advantages such as simple process, environmental friendliness, and ease of large-scale production.

[0003] Coal tar pitch, a byproduct of coal coking or coal liquefaction processes, is high in carbon and inexpensive, making it an ideal precursor for preparing porous carbon materials. However, directly using coal tar pitch for physical activation presents the following inherent technical challenges: Melting and Deformation: During the high-temperature pyrolysis process, coal tar pitch undergoes softening, melting, and re-solidification stages, which leads to adhesion between particles and morphological collapse. The particles cannot maintain the preset morphology, resulting in a non-uniform structure and poor mechanical strength in the final product.

[0004] Graphitization tendency: Pitch-based substances are prone to the orderly arrangement of graphite microcrystals at high temperatures, leading to excessive graphitization, which is not conducive to the formation of rich micropores and mesopores, thereby reducing activation efficiency and product adsorption performance.

[0005] Low carbon yield: Coal tar pitch contains a large number of low molecular weight light components, which are easily lost through volatilization in the early stage of pyrolysis. This not only reduces the carbon yield, but also leads to poor pore structure development and uneven pore size distribution.

[0006] Existing technologies often employ chemical activation methods (such as KOH and ZnCl2 activation) to obtain high specific surface areas, but this method corrodes equipment, pollutes the environment, and involves complex post-processing.

[0007] Therefore, providing a method for preparing high-performance framework carbon based on physical activation that can effectively solve the above problems is of great value. Summary of the Invention

[0008] In view of this, the present invention proposes a method for preparing coal tar pitch-based framework carbon based on physical activation, aiming to solve at least one of the problems in the current background art.

[0009] This invention proposes a method for preparing coal tar pitch-based framework carbon based on physical activation, characterized by comprising the following steps: S1. Pre-removal treatment of coal tar pitch is carried out to obtain pre-treated coal tar pitch. S2. Grind the pretreated coal tar pitch and then mix it with the crosslinking agent mixture to prepare the crosslinking precursor; S3. Mix the crosslinking precursor with the organic solvent compound system to obtain a slurry of 22-28 wt%. Then, spray dry and granulate the slurry to obtain precursor particles. S4. Place the precursor particles in an oxygen-rich atmosphere and then perform a segmented oxidation process to obtain oxidized precursor particles. S5. Carbonize the oxidized precursor particles to obtain a pre-carbonized material with a preliminary carbon skeleton structure. S6. The pre-carbonized material with a preliminary carbon skeleton structure is placed in an activation atmosphere for high-temperature physical activation to obtain the coal tar pitch-based skeleton carbon based on physical activation. The crosslinking agent mixture system includes a crosslinking agent and a graphitization promoting medium; the crosslinking agent is 1,2,4,5-cyclohexanetetracarboxylic dianhydride or phenolic resin, the graphitization promoting medium is polyborosiloxane microspheres, and the mass ratio of the crosslinking agent to the graphitization promoting medium is 2.5:1.

[0010] Preferably, the method for preparing the polyborosiloxane microspheres includes the following steps: Phenylacetyltrimethoxysilane and triethyl borate were placed in a mixed solvent of ethanol and water at a molar ratio of 3:1. Then a catalyst was added to obtain a mixed system. The mixed system was subjected to a co-hydrolysis and polycondensation reaction at 60°C for 2 hours to form a transparent sol. A transparent sol was slowly added dropwise to an aqueous solution containing a surfactant, and the sol was allowed to self-assemble and solidify using an emulsion-sol-gel method to form monodisperse polyborosiloxane microspheres. Subsequently, hexamethyldisilazane was used to perform vapor-phase surface hydrophobication treatment on the monodisperse polyborosiloxane microspheres to obtain the final polyborosiloxane microspheres.

[0011] Preferably, the catalyst is 4% by mass of dilute hydrochloric acid, the total molar ratio of the catalyst to phenyltrimethoxysilane and triethyl borate is 0.05:1, the ratio of hexamethyldisilazane to monodisperse polyborosiloxane microspheres is 1:22-24, and the parameters of the gas phase surface hydrophobication treatment are: treatment temperature 82-86℃, treatment time 1.5-2h, and system vacuum degree -0.08~-0.09MPa.

[0012] Preferably, the pre-light removal treatment in step S1 specifically involves: taking medium-temperature coal tar pitch with a softening point of 80-120℃, crushing it to ≤5mm, removing light under reduced pressure at -0.08~-0.095MPa and 280-350℃ for 2-4 hours, cooling it, and then pulverizing it through a 100-mesh sieve to obtain the pre-treated coal tar pitch.

[0013] Preferably, the preparation of the crosslinking precursor by mixing with the crosslinking agent mixture in step S2 is specifically as follows: the pretreated coal tar pitch and the crosslinking agent mixture are mixed at a mass ratio of 100:9-10, and then 14-16% of anhydrous ethanol by mass of coal tar pitch is added as a dispersion medium. The mixture is stirred at 68-72℃ and 380-420 r / min for 1.4-1.6 h, and then vacuum dried at 88-92℃ and -0.09 MPa for 5-5.2 h to obtain the crosslinking precursor.

[0014] Preferably, the organic solvent compound system in step S3 is composed of anhydrous ethanol and N,N-dimethylformamide mixed at a volume ratio of 3:1; the spray drying granulation specifically involves adding 0.6-0.9% polyethylene glycol to the slurry and ultrasonically dispersing it for 35-50 minutes, followed by spray drying under conditions of an inlet air temperature of 190-210℃ and an outlet air temperature of 85-95℃ to obtain precursor particles.

[0015] Preferably, the aerobic atmosphere in step S4 is obtained by mixing oxygen and nitrogen at a volume ratio of 1:8-10. The segmented oxidation treatment includes a first stage and a second stage, specifically: the first stage is heated to 180-220℃ at a heating rate of 4℃ / min and held at a constant temperature for 2-2.5h; the second stage is heated to 240-250℃ at a heating rate of 5℃ / min and held at a constant temperature for 3-3.5h. After naturally cooling to room temperature, the oxidized precursor particles are obtained.

[0016] Preferably, the carbonization process in step S5 specifically involves: placing the oxidized precursor particles in a nitrogen atmosphere with a flow rate of 60-90 mL / min, first heating them to 520-540℃ at a heating rate of 5-7℃ / min, holding them at that temperature for 1.4-1.6 h, then heating them to 850-900℃ at a heating rate of 3.5-4.0℃ / min, holding them at that temperature for 2.5-3.0 h, and finally cooling them to room temperature to obtain the pre-carbonized material.

[0017] Preferably, the activation atmosphere in step S6 is a mixture of water vapor, carbon dioxide and nitrogen in a volume ratio of 1:1:4. The high-temperature physical activation specifically involves heating to 1000-1100℃ at a heating rate of 3-4℃ / min, maintaining the temperature for 1.5-2.5h, with a gas flow rate of 120-130mL / min during activation, and then continuing to introduce nitrogen to cool to room temperature after activation to obtain coal tar pitch-based skeletal carbon.

[0018] The present invention also provides a physically activated coal tar pitch-based skeletal carbon, which is prepared by the preparation method described in the above technical solution.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention constructs a stable three-dimensional network structure through the synergistic effects of pre-removal of light components, crosslinking, and segmented oxidation. This avoids melting and bonding during the high-temperature pyrolysis of coal tar pitch, ensuring that the framework carbon maintains a regular spherical morphology. The synergistic effect of the crosslinking agent and the graphitization-promoting medium, along with the segmented oxidation process, controls the degree of graphitization at 20-25%, providing a guarantee for the development of microporous-mesoporous structures and improving adsorption and electrochemical performance.

[0020] This invention removes volatile low-molecular-weight components through light metal removal, and reduces carbon loss through cross-linking and oxidation, increasing the carbon yield to over 48%. The physical activation process leaves no chemical reagent residue, resulting in high product purity. By controlling the activation parameters, products with excellent specific surface area and porosity are obtained, with pore sizes concentrated in the range of 2-40 nm, suitable for various application scenarios. Detailed Implementation

[0021] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0022] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0023] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0024] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0025] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0026] This invention proposes a method for preparing coal tar pitch-based framework carbon based on physical activation, characterized by comprising the following steps: S1. Pre-removal treatment of coal tar pitch is carried out to obtain pre-treated coal tar pitch. S2. Grind the pretreated coal tar pitch and then mix it with the crosslinking agent mixture to prepare the crosslinking precursor; S3. Mix the crosslinking precursor with the organic solvent compound system to obtain a slurry of 22-28 wt%. Then, spray dry and granulate the slurry to obtain precursor particles. S4. Place the precursor particles in an oxygen-rich atmosphere and then perform a segmented oxidation process to obtain oxidized precursor particles. S5. Carbonize the oxidized precursor particles to obtain a pre-carbonized material with a preliminary carbon skeleton structure. S6. The pre-carbonized material with a preliminary carbon skeleton structure is placed in an activation atmosphere for high-temperature physical activation to obtain the coal tar pitch-based skeleton carbon based on physical activation. The crosslinking agent mixture system includes a crosslinking agent and a graphitization promoting medium; the crosslinking agent is 1,2,4,5-cyclohexanetetracarboxylic dianhydride or phenolic resin, the graphitization promoting medium is polyborosiloxane microspheres, and the mass ratio of the crosslinking agent to the graphitization promoting medium is 2.5:1.

[0027] The first step in preparing coal tar pitch-based skeletal carbon based on physical activation in this invention is to pre-remove light elements from coal tar pitch to obtain pre-treated coal tar pitch. The pre-light removal treatment specifically involves taking medium-temperature coal tar pitch with a softening point of 80-120℃, crushing it to ≤5mm, and removing light particles under reduced pressure at -0.08~-0.095MPa and 280-350℃ for 2-4 hours. After cooling, it is pulverized and passed through a 100-mesh sieve to obtain the pre-treated coal tar pitch.

[0028] This invention uses medium-temperature coal tar pitch as raw material, with a softening point in the range of 80-120℃. This ensures that the raw material has a certain degree of fluidity, facilitating subsequent mixing with the crosslinking agent, while avoiding the problem of insufficient thermal stability caused by an excessively low softening point. The high carbon content of the medium-temperature coal tar pitch provides an ample carbon source for the final skeletal carbon formation. This invention also employs a vacuum distillation process for removing light components. By reducing the system pressure, the boiling point of the low-molecular-weight light components is lowered, allowing for efficient removal at 280-350℃, avoiding premature softening and melting of the coal tar pitch caused by direct high-temperature heating.

[0029] The second step of the preparation method of the present invention is: grinding the pretreated coal tar pitch and then mixing it with a crosslinking agent mixture to prepare a crosslinking precursor; Specifically, the preparation of the crosslinking precursor by mixing with the crosslinking agent mixture system involves grinding pretreated coal tar pitch to obtain particles of 10-50 μm, then mixing them with the crosslinking agent mixture system at a mass ratio of 100:9-10, then adding 14-16% of the coal tar pitch mass of anhydrous ethanol as a dispersion medium, stirring at 68-72℃ and 380-420 r / min for 1.4-1.6 h, and then vacuum drying at 88-92℃ and -0.09 MPa for 5-5.2 h to obtain the crosslinking precursor.

[0030] The crosslinking agent mixture system includes a crosslinking agent and a graphitization promoting medium; the crosslinking agent is 1,2,4,5-cyclohexanetetracarboxylic dianhydride or phenolic resin, and the graphitization promoting medium is polyborosiloxane microspheres, with a mass ratio of crosslinking agent to graphitization promoting medium of 2.5:1. The preferred method for preparing the graphitizing medium polyborosiloxane microspheres includes the following steps: Phenylacetyltrimethoxysilane and triethyl borate were placed in a mixed solvent of ethanol and water at a molar ratio of 3:1. The volume ratio of ethanol to water in the mixed solution was 3:1. Then, a catalyst was added to obtain a mixed system. The mixed system was placed at 60°C for a co-hydrolysis condensation reaction for 2 hours to form a transparent sol. A transparent sol was slowly added dropwise to an aqueous solution containing a surfactant, and the sol was allowed to self-assemble and solidify using an emulsion-sol-gel method to form monodisperse polyborosiloxane microspheres. Subsequently, hexamethyldisilazane was used to perform vapor-phase surface hydrophobication treatment on the monodisperse polyborosiloxane microspheres to obtain the final polyborosiloxane microspheres.

[0031] The catalyst is 4% by mass of dilute hydrochloric acid, the total molar ratio of the catalyst to phenyltrimethoxysilane and triethyl borate is 0.05:1, the ratio of hexamethyldisilazane to monodisperse polyborosiloxane microspheres is 1:22-24, and the parameters of the gas phase surface hydrophobication treatment are: treatment temperature 82-86℃, treatment time 1.5-2h, and system vacuum degree -0.08~-0.09MPa.

[0032] Specifically, the preferred process for obtaining monodisperse polyborosiloxane microspheres is as follows: Sodium dodecyl sulfate, a surfactant, is added to deionized water and stirred to dissolve, resulting in a surfactant aqueous solution with a mass fraction of 0.4%, and the solution temperature is controlled at 30°C. A transparent sol is slowly added dropwise to the surfactant aqueous solution at a rate of 1 mL / min, maintaining a stirring rate of 300 r / min during the addition process. After the addition is complete, stirring continues for 30 min to allow the sol to fully disperse and form an emulsion. The emulsion is then placed in a constant temperature environment at 30°C and allowed to solidify for 4 hours, allowing the sol particles in the emulsion to self-assemble into a stable spherical structure. After solidification, the solid particles are separated by vacuum filtration and washed three times with deionized water, each time using five times the mass of the solid particles, to remove residual surfactant and unreacted raw materials.

[0033] The preferred process for obtaining the final polyborosiloxane microspheres is as follows: The washed monodisperse polyborosiloxane microspheres are placed in a vacuum drying oven and dried at 80℃ and -0.08MPa for 2 hours to remove surface moisture, resulting in dried microsphere particles. The dried microsphere particles are then placed in a sealed reaction vessel, and hexamethyldisilazane is added at a mass ratio of 1:22-24 to the microsphere particles. The reaction vessel is sealed, and a vacuum is applied to -0.08~-0.09MPa. The temperature is then raised to 82-86℃ and held at this temperature for 1.5-2 hours to carry out a hydrophobication reaction. After the reaction, the reaction vessel is allowed to cool naturally to room temperature. The vessel door is opened for ventilation for 30 minutes to remove residual hexamethyldisilazane. The microsphere particles are then dried a second time to obtain the final polyborosiloxane microspheres.

[0034] In this invention, the crosslinking agent 1,2,4,5-cyclohexanetetracarboxylic dianhydride contains four anhydride groups. These anhydride groups are highly reactive and can undergo imidization reactions with active groups such as hydroxyl (-OH) and amino (-NH2) groups in the coal tar pitch molecular structure to form stable covalent crosslinks, thereby connecting the coal tar pitch molecular chains to construct a preliminary three-dimensional network structure. Its cyclic molecular structure exhibits good thermal stability and is not easily decomposed during subsequent high-temperature carbonization and activation processes, effectively supporting the carbon skeleton structure and inhibiting melt deformation.

[0035] The phenolic hydroxyl groups (-OH) and hydroxymethyl groups (-CH2OH) in the phenolic resin molecules of the crosslinking agent can undergo condensation reactions with the active groups (hydroxyl and amino groups) in the coal tar pitch molecular structure to form stable methylene bridge (-CH2-) covalent bonds, which connect the dispersed coal tar pitch molecular chains to each other and construct a continuous three-dimensional network structure. At the same time, the benzene ring structure in the phenolic resin molecular chain can undergo π-π stacking with the aromatic rings of coal tar pitch, further enhancing the compactness of the crosslinking network and inhibiting the melt flow and particle adhesion during the high-temperature pyrolysis of coal tar pitch. Phenolic resin has excellent thermal stability and is not easily decomposed during staged oxidation (180-250℃) and carbonization (850-900℃). Its rigid structure after curing can serve as a skeleton support point to prevent the carbon skeleton from collapsing at high temperatures and ensure that the precursor particles remain regular spherical. During the high-temperature carbonization stage, phenolic resin is pyrolyzed into highly disordered amorphous carbon (carbon yield ≥60%), which not only replenishes the carbon source, but also disrupts the ordered arrangement of coal tar pitch graphite microcrystals due to the disordered structure of amorphous carbon, thus synergistically inhibiting excessive graphitization.

[0036] The graphitization-promoting medium, polyborosiloxane microspheres, are nanoscale particles with high specific surface area and excellent thermal stability. As physical crosslinking points, they fill the three-dimensional network structure formed by the crosslinking agent, further increasing the crosslinking density and strengthening the stability of the framework structure. After hydrophobic treatment, their surface exhibits good compatibility with coal tar pitch and the crosslinking agent, allowing for uniform dispersion in the system and avoiding uneven crosslinking caused by local aggregation. Simultaneously, the presence of boron and silicon elements forms stable oxides at high temperatures, further inhibiting the graphitization process.

[0037] Furthermore, the present invention uses anhydrous ethanol as a dispersion medium, which has good solubility for pretreated coal tar pitch and crosslinking agent, and good dispersibility for graphitization promotion medium, so that the three can be fully mixed, avoiding crosslinking agent agglomeration and ensuring uniform crosslinking reaction.

[0038] The third step of the preparation method of the present invention is: mixing the crosslinking precursor with an organic solvent compound system to obtain a slurry of 22-28 wt%, and then spray drying and granulating the slurry to obtain precursor particles; Specifically, the organic solvent compound system is composed of anhydrous ethanol and N,N-dimethylformamide mixed at a volume ratio of 3:1; the preferred method for spray drying granulation is to add 0.6-0.9% polyethylene glycol to the slurry and ultrasonically disperse it for 35-50 minutes, followed by spray drying under conditions of an inlet air temperature of 190-210℃ and an outlet air temperature of 85-95℃ to obtain precursor particles.

[0039] Anhydrous ethanol exhibits excellent solubility for the coal tar pitch component in the crosslinking precursor, enabling rapid dispersion of the coal tar pitch crosslinking product. N,N-Dimethylformamide (DMF), a polar organic solvent, demonstrates superior solubility for the residual portion of the crosslinking agent 1,2,4,5-cyclohexanetetracarboxylic dianhydride, while also enhancing the dispersion stability of the graphitization-promoting medium and preventing its agglomeration in the slurry. The two are combined in a 3:1 volume ratio to achieve synergistic optimization of dissolution and dispersion, ensuring a uniform and stable slurry system while controlling the slurry viscosity within a reasonable range to meet the atomization requirements of spray drying.

[0040] This invention uses a spray drying granulation method to obtain spherical precursor particles with uniform particle size. The spherical morphology is beneficial to the uniform contact and penetration of gas in subsequent processes, and improves the uniformity of carbonization and activation.

[0041] The fourth step of the preparation method of the present invention is: placing the precursor particles in an oxygen-rich atmosphere and then performing a segmented oxidation treatment to obtain oxidized precursor particles. Preferably, the aerobic atmosphere in step 4 is obtained by mixing oxygen and nitrogen at a volume ratio of 1:8-10. The segmented oxidation treatment includes a first stage and a second stage, specifically: in the first stage, the temperature is increased to 180-220℃ at a heating rate of 4℃ / min and held at a constant temperature for 2-2.5h; in the second stage, the temperature is increased to 240-250℃ at a heating rate of 5℃ / min and held at a constant temperature for 3-3.5h. After naturally cooling to room temperature, the oxidized precursor particles are obtained.

[0042] In the oxygen-enriched atmosphere of this invention, oxygen acts as an oxidation medium, reacting with carbon-hydrogen bonds and carbon-carbon double bonds on the surface and inside of the precursor particles to introduce oxygen-containing functional groups such as hydroxyl (-OH), carboxyl (-COOH), and carbonyl (C=O). Nitrogen acts as a diluent gas, controlling the oxygen volume fraction at 9-11%, which avoids excessive oxidation (particle combustion, structural damage) caused by excessive oxygen concentration, while ensuring that the oxidation reaction proceeds gently and uniformly.

[0043] Furthermore, the oxidation process of this invention is carried out in stages. The first stage is a mild oxidation stage, at which a thin oxide film is first formed on the surface of the precursor particles, introducing a small number of oxygen-containing functional groups, laying the foundation for subsequent deep oxidation, while avoiding stress concentration and cracking inside the particles caused by rapid heating. The second stage is a deep oxidation stage, at which the oxidation reaction penetrates into the particles, introducing a large number of oxygen-containing functional groups, and simultaneously undergoing an oxidative cross-linking reaction, further strengthening the three-dimensional network structure.

[0044] The present invention also sets a reasonable heating rate to ensure that the oxidation reaction proceeds uniformly and avoids uneven oxidation caused by excessively high local temperatures.

[0045] The present invention introduces oxygen-containing functional groups through oxidation treatment to further enhance the stability of the carbon skeleton. At the same time, these functional groups will decompose to generate a small amount of gas during the subsequent carbonization process, forming micropores, which provide more sites for gas etching during the activation process.

[0046] The fifth step of the preparation method of the present invention is: to carbonize the oxidized precursor particles to obtain a pre-carbonized material with a preliminary carbon skeleton structure; In this invention, the carbonization process in step 5 specifically involves: placing the oxidized precursor particles in a nitrogen atmosphere with a flow rate of 60-90 mL / min, first heating them to 520-540°C at a heating rate of 5-7°C / min, holding them at that temperature for 1.4-1.6 h, then heating them to 850-900°C at a heating rate of 3.5-4.0°C / min, holding them at that temperature for 2.5-3.0 h, and finally cooling them to room temperature to obtain the pre-carbonized material.

[0047] The carbonization process of this invention is carried out in stages. The first stage is a low-temperature carbonization stage, which mainly removes small amounts of residual organic solvents and small molecule compounds (such as CO, CO2, H2O, etc.) generated by the decomposition of oxygen-containing functional groups from the particles. The heating rate is slightly faster in this stage to improve the removal efficiency. The second stage is a high-temperature carbonization stage. At this temperature, the aromatic compounds in the coal tar pitch undergo deep aromatization and cyclization reactions to form a stable carbon skeleton structure. The heating rate is slightly slower in this stage to avoid stress concentration and cracking of the carbon skeleton structure caused by rapid heating. The low-temperature carbonization is held at a constant temperature for 1.4-1.6 hours to ensure sufficient removal of volatiles; the high-temperature carbonization is held at a constant temperature for 2.5-3.0 hours to ensure that the aromatization reaction proceeds fully and forms a carbon skeleton with a stable structure and suitable crystallinity, which ensures mechanical strength and avoids excessive graphitization.

[0048] This invention utilizes carbonization to transform oxidized precursors into pre-carbonized materials with a preliminary carbon skeleton structure, further increasing carbon content and significantly enhancing mechanical strength. The segmented carbonization process effectively removes residual volatiles, preventing pore defects within the carbon skeleton and controlling the degree of graphitization, laying the foundation for the formation of rich microporous-mesoporous structures during subsequent activation. Nitrogen atmosphere protection ensures the stability of the carbonization process, avoids material oxidation loss, and further improves carbon yield.

[0049] The sixth step of the preparation method of the present invention is: placing the pre-carbonized material with a preliminary carbon skeleton structure under an activation atmosphere for high-temperature physical activation to obtain the coal tar pitch-based skeleton carbon based on physical activation; Preferably, the activation atmosphere in step six is ​​a mixture of water vapor, carbon dioxide and nitrogen in a volume ratio of 1:1:4. The high-temperature physical activation specifically involves heating to 1000-1100℃ at a heating rate of 3-4℃ / min, maintaining the temperature for 1.5-2.5 hours, with a gas flow rate of 120-130mL / min during activation, and then continuing to introduce nitrogen to cool to room temperature after activation to obtain coal tar pitch-based skeletal carbon.

[0050] This invention uses a mixture of water vapor, carbon dioxide, and nitrogen to create an activation atmosphere, and specifically limits the volume ratio of these gases. This ensures that the activation medium of water vapor and carbon dioxide can guarantee sufficient etching intensity to form a well-developed pore structure, while avoiding structural damage caused by excessive etching. The volume ratio of water vapor to carbon dioxide can achieve the synergistic development of micropores and mesopores, meeting the pore structure requirements of different application scenarios.

[0051] The present invention also imposes special limits on activation temperature and heating rate to ensure uniform heating of pre-carbonized material, avoid uneven etching caused by excessive local temperature, and allow sufficient time for activation medium to penetrate into carbon skeleton to achieve uniform etching and form a well-developed porous structure, while avoiding over-etching caused by excessive activation time.

[0052] The present invention also provides a physically activated coal tar pitch-based skeletal carbon, which is prepared by the preparation method described in the above technical solution.

[0053] Example 1 (1) Raw material preparation Medium-temperature coal tar pitch: softening point 100℃, crushed to a particle size not exceeding 5mm; Crosslinking agent: 1,2,4,5-cyclohexanetetracarboxylic dianhydride (purity ≥98%). Graphitization promoting medium: Polyborosiloxane microspheres (self-made, particle size 50-200 nm, specific surface area 80-120 m²) 2 / g); Crosslinking agent mixture system: crosslinking agent to graphitization medium mass ratio 2.5:1; Dispersion medium: Anhydrous ethanol (analytical grade); Organic solvent compounding system: Anhydrous ethanol and N,N-dimethylformamide (both analytical grade) are mixed at a volume ratio of 3:1; Dispersant: Polyethylene glycol (molecular weight 2000, analytical grade); Industrial gases: oxygen, nitrogen, water vapor, carbon dioxide (all with a purity ≥ 99.9%). Raw materials for preparing polyborosiloxane microspheres: phenyltrimethoxysilane (purity ≥98%), triethyl borate (purity ≥97%), 4% dilute hydrochloric acid (analytical grade hydrochloric acid diluted), sodium dodecyl sulfate (surfactant, analytical grade), hexamethyldisilazane (purity ≥98%), anhydrous ethanol (analytical grade), and deionized water.

[0054] (2) Preparation of polyborosiloxane microspheres Phenylacetyltrimethoxysilane and triethyl borate were added to a mixed solvent of ethanol and water at a molar ratio of 3:1 (ethanol to water volume ratio of 3:1). The mixture was stirred until the raw materials were completely dissolved to form an initial mixture. 4% dilute hydrochloric acid was added dropwise to the initial mixture at a rate of 2 mL / min as a catalyst. The total molar ratio of the catalyst to phenyltrimethoxysilane and triethyl borate was 0.05:1. The mixture was stirred at 200 rpm for 15 minutes to obtain a homogeneous mixture. The mixture was then transferred to a constant-temperature water bath at 60°C and a stirring rate of 200 rpm for 2 hours to form a transparent sol with a viscosity of 80-100 mPa·s.

[0055] Prepare a 0.4% sodium dodecyl sulfate aqueous solution and maintain the solution temperature at 30°C. Slowly add the transparent sol dropwise to the aqueous solution at a rate of 1 mL / min, while maintaining a stirring speed of 300 rpm. After the addition is complete, continue stirring for 30 minutes to form a homogeneous emulsion. Place the emulsion in a constant temperature environment of 30°C and allow it to solidify for 4 hours. Then, separate the solid particles by vacuum filtration and wash them three times with deionized water, each time using five times the mass of the solid particles, to remove residual impurities.

[0056] The washed solid particles were placed in a vacuum drying oven and dried at 80℃ and -0.08MPa for 2 hours to obtain dried monodisperse polyborosiloxane microspheres. The microspheres were then placed in a sealed reactor, and hexamethyldisilazane was added at a mass ratio of 1:23 (hexamethyldisilazane to microspheres). After sealing, the reactor was evacuated to -0.085MPa, heated to 84℃, and held at this temperature for 1.8 hours for hydrophobication treatment. After the reaction, the mixture was allowed to cool naturally to room temperature, ventilated for 30 minutes to remove residual modifier, and then dried again at 80℃ and -0.08MPa for 1 hour to obtain the final polyborosiloxane microspheres.

[0057] (3) Preparation of carbon framework based on coal tar pitch The crushed medium-temperature coal tar pitch was placed in a vacuum distillation apparatus and subjected to vacuum removal for 3 hours at a vacuum degree of -0.09 MPa and a temperature of 320℃. After cooling, it was crushed and passed through a 100-mesh sieve to obtain pretreated coal tar pitch. The pretreated coal tar pitch is placed in a grinding equipment and ground into particles with a particle size of 10-50μm for later use. The ground coal tar pitch and crosslinking agent mixture was mixed at a mass ratio of 100:9.5, and 15% anhydrous ethanol by mass of coal tar pitch was added. The mixture was stirred at 70℃ and 400 r / min for 1.5 h, and then vacuum dried at 90℃ and -0.09 MPa for 5 h to obtain the crosslinking precursor. The crosslinking precursor was mixed with an organic solvent compound system to prepare a 25wt% slurry. 0.7% polyethylene glycol was added to the slurry and ultrasonically dispersed for 40 min. Then, it was spray-dried at an inlet air temperature of 200℃ and an outlet air temperature of 90℃ to obtain spherical precursor particles of 80-150μm. The precursor particles were placed in an aerobic atmosphere, which was a mixture of oxygen and nitrogen in a volume ratio of 1:9. The temperature was first increased to 200℃ at 4℃ / min and held at that temperature for 2.2h. Then the temperature was increased to 245℃ at 5℃ / min and held at that temperature for 3.2h. The particles were then naturally cooled to room temperature to obtain the oxidized particles. The oxidized particles were placed in an atmosphere with a nitrogen flow rate of 75 mL / min, and the temperature was first increased to 530℃ at 6℃ / min and held at that temperature for 1.5 h. Then the temperature was increased to 880℃ at 3.8℃ / min and held at that temperature for 2.8 h. The particles were then cooled to room temperature to obtain the pre-carbonized material. The pre-carbonized material was placed in an activation atmosphere consisting of water vapor, carbon dioxide, and nitrogen in a volume ratio of 1:1:4. The temperature was increased to 1050℃ at 3.5℃ / min and activated at a constant temperature for 2 hours. The total gas flow rate during the activation process was 125mL / min. After activation, nitrogen was continuously introduced to cool the material to room temperature, thus obtaining coal tar pitch-based skeletal carbon.

[0058] Example 2 (1) Raw material preparation Medium-temperature coal tar pitch: softening point 80℃, crushed to a particle size not exceeding 5mm; Crosslinking agent: 1,2,4,5-cyclohexanetetracarboxylic dianhydride (purity ≥98%). Graphitization promoting medium: Polyborosiloxane microspheres (self-made, particle size 50-200nm, specific surface area 80-120m² / g); Crosslinking agent mixture system: crosslinking agent to graphitization medium mass ratio 2.5:1; Dispersion medium: Anhydrous ethanol (analytical grade); Organic solvent compounding system: Anhydrous ethanol and N,N-dimethylformamide (both analytical grade) are mixed at a volume ratio of 3:1; Dispersant: Polyethylene glycol (molecular weight 3000, analytical grade); Industrial gases: oxygen, nitrogen, water vapor, carbon dioxide (all with a purity ≥ 99.9%). Raw materials for preparing polyborosiloxane microspheres: phenyltrimethoxysilane (purity ≥98%), triethyl borate (purity ≥97%), 4% dilute hydrochloric acid (analytical grade hydrochloric acid diluted), sodium dodecyl sulfate (surfactant, analytical grade), hexamethyldisilazane (purity ≥98%), anhydrous ethanol (analytical grade), and deionized water.

[0059] (2) Preparation of polyborosiloxane microspheres Phenylacetyltrimethoxysilane and triethyl borate were added to a mixed solvent of ethanol and water (volume ratio 3:1) at a molar ratio of 3:1 and stirred to dissolve, forming an initial mixture. 4% dilute hydrochloric acid was added dropwise to the initial mixture at a rate of 2 mL / min, with the total molar ratio of catalyst to the two raw materials being 0.05:1. Stirring was maintained at 200 rpm during the addition, and a homogeneous mixture was obtained after 15 min of stirring. The mixture was then placed in a 60°C constant temperature water bath and stirred at 200 rpm for 2 hours to form a transparent sol.

[0060] Prepare a 0.4% sodium dodecyl sulfate aqueous solution at 30℃. Add the transparent sol dropwise at a rate of 1 mL / min and stir at 300 r / min for 30 min to form an emulsion. After standing and solidifying for 4 hours, separate the solid particles by vacuum filtration and wash with deionized water 3 times (each time the amount of water is 5 times the mass of the particles).

[0061] The washed particles were dried at 80℃ and -0.08MPa for 2 hours, then placed in a sealed reactor. A modifier was added at a mass ratio of hexamethyldisilazane to particles of 1:22. The reactor was then evacuated to -0.08MPa and heated to 82℃ for 1.5 hours for hydrophobication treatment. After cooling and ventilation, the particles were dried a second time at 80℃ and -0.08MPa for 1 hour to obtain polyborosiloxane microspheres.

[0062] (3) Preparation of carbon framework based on coal tar pitch The crushed medium-temperature coal tar pitch was depressurized and lightened for 2.5 hours under vacuum conditions of -0.085 MPa and 290℃. After cooling, it was crushed and passed through a 100-mesh sieve to obtain pretreated coal tar pitch. Grind the pretreated coal tar pitch into particles with a particle size of 10-50 μm for later use; The ground coal tar pitch and crosslinking agent mixture was mixed at a mass ratio of 100:9, and 14% anhydrous ethanol by mass of coal tar pitch was added. The mixture was stirred at 68℃ and 380 r / min for 1.6 h, and then vacuum dried at 88℃ and -0.09 MPa for 5.2 h to obtain the crosslinking precursor. The crosslinking precursor was mixed with an organic solvent compound system to prepare a 22wt% slurry. 0.6% polyethylene glycol was added and ultrasonically dispersed for 35 min. The slurry was then spray-dried at an inlet air temperature of 190℃ and an outlet air temperature of 85℃ to obtain spherical precursor particles of 50-120μm. The precursor particles were placed in an aerobic atmosphere with an oxygen to nitrogen volume ratio of 1:8. The temperature was first increased to 180℃ at 4℃ / min and held at that temperature for 2.5h. Then the temperature was increased to 240℃ at 5℃ / min and held at that temperature for 3.5h. The mixture was then allowed to cool naturally to room temperature. The oxidized particles were placed in an atmosphere with a nitrogen flow rate of 60 mL / min, and the temperature was first increased to 520℃ at 5℃ / min and kept at a constant temperature for 1.6 h. Then the temperature was increased to 850℃ at 3.5℃ / min and kept at a constant temperature for 3.0 h. The pre-carbonized material was obtained by cooling to room temperature. The pre-carbonized material was placed in an activation atmosphere containing water vapor, carbon dioxide and nitrogen in a volume ratio of 1:1:4, and heated to 1000℃ at a rate of 3℃ / min. The temperature was maintained for 2.5 h. The total gas flow rate during the activation process was 120 mL / min. After cooling, coal tar pitch-based skeletal carbon was obtained.

[0063] Performance testing The coal tar pitch-based skeleton carbon obtained in Examples 1 and 2 was used as the test object, and a control group was set up. The coal tar pitch-based skeleton carbon used in the control group was prepared by the traditional physical activation method without pre-removal of light elements, cross-linking, or segmented oxidation treatment. Other raw materials and carbonization and activation core parameters were the same as in Example 1.

[0064] (1) Graphitization degree test Refer to GB / T 3074.3-2014 "Pitch coke for graphite electrodes - Part 3: Determination of graphitization degree" (X-ray diffraction method) A Bruker D8 Advance X-ray diffractometer was used, with a Cu target and Kα rays, tube voltage of 40 kV, tube current of 40 mA, scanning range of 2θ = 10°-80°, and scanning rate of 5° / min. The degree of graphitization was calculated based on the diffraction angle of the (002) plane, and the test results are shown in Table 1. Table 1. Results of Graphitization Degree Test

[0065] As shown in Table 1, the carbon graphitization degree of the coal tar pitch-based skeleton obtained by this invention is only 20-22%, which is much lower than the 48% of the control group. This indicates that the crosslinking system and the segmented oxidation process can effectively inhibit excessive graphitization and provide a guarantee for the development of pore structure.

[0066] (2) Carbon yield test Referring to HG / T 2022-2018 "Method for Determination of Coking Value of Coal Tar Pitch", and combining the process adjustment calculation method of this invention, the initial coal tar pitch raw material mass and the final product mass were accurately weighed, and the carbon yield was calculated as (product mass / initial raw material mass) × 100%. The average value was taken for three parallel tests, and the test results are shown in Table 2. Table 2 Carbon Yield Test Table

[0067] As shown in Table 2, the carbon yield of the coal tar pitch-based skeleton obtained by this invention is 48-50%, which is significantly higher than that of the control group, verifying the technical effectiveness of pre-removal of low-molecular-weight light components and cross-linking and oxidation to reduce carbon loss. (3) Pore structure test Refer to GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method" and GB / T 21650.3-2011 "Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Intrusion Porosimetry and Gas Adsorption Method - Part 3: Analysis of Micropores by Gas Adsorption Method"; The Micromeritics TriStar II 3020 fully automatic surface area and porosity analyzer was used. The samples were degassed at 120℃ for 4 hours. The specific surface area and porosity were determined by nitrogen adsorption-desorption method. The pore size distribution was calculated by BJH model. The test results are shown in Table 3. Table 3 Test Results of Porous Structure

[0068] As shown in Table 3, the carbon specific surface area and porosity of the coal tar pitch-based skeleton obtained by this invention are much higher than those of the control group, and the pore size distribution is concentrated and uniform.

[0069] (4) Mechanical strength test Referring to GB / T 1938-2009 "Determination of Compressive Strength of Carbon Materials at Room Temperature"; using an Instron 5967 universal testing machine, 100-150μm particles were selected, the loading rate was 0.5mm / min, 10 particles were tested and the average value was taken. The test results are shown in Table 4. Table 4. Results of Mechanical Strength Test

[0070] As shown in Table 4, the compressive strength of the coal tar pitch-based skeleton carbon obtained by the present invention is more than 1.8 times that of the control group. Based on this, it can be seen that the carbon skeleton structure obtained by the present invention is stable and has excellent mechanical properties.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing coal tar pitch-based framework carbon based on physical activation, characterized in that, Includes the following steps: S1. Pre-removal treatment of coal tar pitch is carried out to obtain pre-treated coal tar pitch. S2. Grind the pretreated coal tar pitch and then mix it with the crosslinking agent mixture to prepare the crosslinking precursor; S3. Mix the crosslinking precursor with the organic solvent compound system to obtain a slurry of 22-28 wt%. Then, spray dry and granulate the slurry to obtain precursor particles. S4. Place the precursor particles in an oxygen-rich atmosphere and then perform a segmented oxidation process to obtain oxidized precursor particles. S5. Carbonize the oxidized precursor particles to obtain a pre-carbonized material with a preliminary carbon skeleton structure. S6. The pre-carbonized material with a preliminary carbon skeleton structure is placed in an activation atmosphere for high-temperature physical activation to obtain the coal tar pitch-based skeleton carbon based on physical activation. The crosslinking agent mixture system includes a crosslinking agent and a graphitization promoting medium; the crosslinking agent is 1,2,4,5-cyclohexanetetracarboxylic dianhydride or phenolic resin, the graphitization promoting medium is polyborosiloxane microspheres, and the mass ratio of the crosslinking agent to the graphitization promoting medium is 2.5:

1.

2. The method for preparing coal tar pitch-based framework carbon based on physical activation according to claim 1, characterized in that, The preparation method of the polyborosiloxane microspheres includes the following steps: Phenylacetyltrimethoxysilane and triethyl borate were placed in a mixed solvent of ethanol and water at a molar ratio of 3:

1. Then a catalyst was added to obtain a mixed system. The mixed system was subjected to a co-hydrolysis and polycondensation reaction at 60°C for 2 hours to form a transparent sol. A transparent sol was slowly added dropwise to an aqueous solution containing a surfactant, and the sol was allowed to self-assemble and solidify using an emulsion-sol-gel method to form monodisperse polyborosiloxane microspheres. Subsequently, hexamethyldisilazane was used to perform vapor-phase surface hydrophobication treatment on the monodisperse polyborosiloxane microspheres to obtain the final polyborosiloxane microspheres.

3. The method for preparing coal tar pitch-based framework carbon based on physical activation according to claim 2, characterized in that, The catalyst is 4% by mass of dilute hydrochloric acid. The total molar ratio of the catalyst to phenyltrimethoxysilane and triethyl borate is 0.05:

1. The ratio of hexamethyldisilazane to monodisperse polyborosiloxane microspheres is 1:22-24. The parameters for the vapor-phase surface hydrophobication treatment are: treatment temperature 82-86℃, treatment time 1.5-2h, and system vacuum degree -0.08~-0.09MPa.

4. The method for preparing coal tar pitch-based framework carbon based on physical activation according to claim 1, characterized in that, The pre-light removal treatment in step S1 is as follows: take medium-temperature coal tar pitch with a softening point of 80-120℃, crush it to ≤5mm, remove light under reduced pressure at -0.08~-0.095MPa and 280-350℃ for 2-4 hours, cool it and then crush it through a 100-mesh sieve to obtain the pre-treated coal tar pitch.

5. The method for preparing coal tar pitch-based framework carbon based on physical activation according to claim 1, characterized in that, The preparation of the crosslinking precursor in step S2 by mixing with the crosslinking agent mixture system is as follows: the pretreated coal tar pitch and the crosslinking agent mixture system are mixed at a mass ratio of 100:9-10, and then 14-16% of anhydrous ethanol by mass of coal tar pitch is added as a dispersion medium. The mixture is stirred at 68-72℃ and 380-420 r / min for 1.4-1.6 h, and then vacuum dried at 88-92℃ and -0.09 MPa for 5-5.2 h to obtain the crosslinking precursor.

6. The method for preparing coal tar pitch-based framework carbon based on physical activation according to claim 1, characterized in that, The organic solvent compound system mentioned in step S3 is composed of anhydrous ethanol and N,N-dimethylformamide mixed at a volume ratio of 3:1; the spray drying granulation specifically involves adding 0.6-0.9% polyethylene glycol to the slurry and ultrasonically dispersing it for 35-50 minutes, followed by spray drying under conditions of an inlet air temperature of 190-210℃ and an outlet air temperature of 85-95℃ to obtain precursor particles.

7. The method for preparing coal tar pitch-based framework carbon based on physical activation according to claim 1, characterized in that, The aerobic atmosphere mentioned in step S4 is obtained by mixing oxygen and nitrogen at a volume ratio of 1:8-10. The segmented oxidation treatment includes a first stage and a second stage, specifically: the first stage is heated to 180-220℃ at a heating rate of 4℃ / min and held at a constant temperature for 2-2.5h; the second stage is heated to 240-250℃ at a heating rate of 5℃ / min and held at a constant temperature for 3-3.5h. After naturally cooling to room temperature, the oxidized precursor particles are obtained.

8. The method for preparing coal tar pitch-based framework carbon based on physical activation according to claim 1, characterized in that, The carbonization process described in step S5 is as follows: the oxidized precursor particles are placed in a nitrogen atmosphere with a flow rate of 60-90 mL / min, heated to 520-540℃ at a heating rate of 5-7℃ / min, and held at that temperature for 1.4-1.6 h. Then, the temperature is increased to 850-900℃ at a heating rate of 3.5-4.0℃ / min and carbonized at that temperature for 2.5-3.0 h. After cooling to room temperature, the pre-carbonized material is obtained.

9. The method for preparing coal tar pitch-based framework carbon based on physical activation according to claim 1, characterized in that, The activation atmosphere in step S6 is a mixture of water vapor, carbon dioxide and nitrogen in a volume ratio of 1:1:

4. The high-temperature physical activation is specifically as follows: the temperature is increased to 1000-1100℃ at a heating rate of 3-4℃ / min, and the temperature is kept constant for 1.5-2.5h. During the activation process, the gas flow rate is 120-130mL / min. After the activation is completed, nitrogen is continuously introduced to cool to room temperature to obtain coal tar pitch-based skeletal carbon.

10. A coal tar pitch-based skeletal carbon based on physical activation, characterized in that, The physically activated coal tar pitch-based skeletal carbon is prepared by the preparation method described in any one of claims 1 to 9.

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