A method for preparing needle coke by compound modification of medium and low temperature coal tar pitch

Abstract

The present invention provides a method for preparing needle coke by composite modification of medium and low temperature coal tar pitch, belonging to the technical field of coal chemical industry, which includes 1) fractionation cutting to obtain medium and low temperature coal tar pitch; 2) successively carrying out hydrofining treatment, selective extraction treatment and chain extension treatment on the medium and low temperature coal tar pitch to obtain modified pitch; 3) adding a nucleating crystallization agent to the modified pitch for a first-stage variable temperature thermal polymerization reaction, and then adding a metal-organic framework material for a second-stage variable temperature thermal polymerization reaction to prepare semicoke; 4) calcining the semicoke under the protection of a protective gas atmosphere to form needle coke. The needle coke product prepared by the method of the present invention has a high OTI index, high crystallinity, good crystal structure and excellent electrochemical performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal chemical industry, and particularly relates to a method for preparing needle coke by composite modification of medium and low temperature coal tar pitch. Background Art

[0002] Needle coke is a high-quality carbon material with the advantages of low ash content, low thermal expansion, high electrical conductivity and high anisotropy, and is widely used in many fields such as high-power / ultra-high-power graphite electrodes, anode materials for lithium batteries, and special graphite materials. Medium and low temperature coal tar pitch is rich in 3-5 ring aromatic compounds, has a suitable molecular weight, and extremely low quinoline insoluble matter, and is a high-quality raw material for the preparation of coal-based needle coke. In the production process of needle coke, the development of the mesophase is related to the overall carbonization reaction activity, and the carbonization reaction activity depends on the molecular composition of the carbonization raw material. The process of forming the mesophase from the liquid phase generally includes three basic processes, namely the formation (nucleation), growth and coalescence of mesophase spheres. In these processes, the viscosity of the system plays an important role. The content of heteroatoms and asphaltenes in medium and low temperature coal tar pitch is relatively high. Heteroatom compounds will increase the reaction activity of the system, accelerate the polymerization of macromolecular substances, and cause the viscosity of the system to increase too fast, and finally it is easy to form a mesophase pitch with an inlaid optical structure. The lower the minimum viscosity of the carbonization system and the wider the temperature range for maintaining the minimum viscosity, the more conducive it is to the formation of a mesophase with a large-size optical texture structure. In addition, more alkyl structures can improve the fluidity of the carbonization system, effectively reduce the viscosity of the system, promote the orderly arrangement of aromatic molecular layers, and thus improve the performance of needle coke. Therefore, it is particularly important to modify the raw material composition.

[0003] The patent application with the publication number CN113528175A discloses a method for preparing needle coke raw material pitch by a one-step solvent method using coal tar. After desalting and dehydrating the coal tar, heavy oil is obtained by vacuum distillation, which is fully mixed with an aromatic hydrocarbon extractant. After separation, a soluble phase is obtained, and the aromatic hydrocarbon extractant is recovered by vacuum distillation to obtain polycyclic aromatic hydrocarbon oil. The polycyclic aromatic hydrocarbon oil is gas stripped with an inert gas to obtain the raw material pitch for needle coke. The patent with the publication number CN109135789B discloses that heavy components are obtained by distilling medium and low temperature coal tar. A mixed solvent is obtained by mixing a polar solvent, a non-polar solvent, a polar solvent and a non-polar solvent in a certain mass ratio. The heavy components of medium and low temperature coal tar are fed into a reaction kettle, heated to 60-200 °C and stirred evenly, then the mixed solvent is added into the reaction kettle, stirred at 50-200 °C for 1-10 h and then left standing for 1-20 h to remove highly reactive substances. The obtained clarified liquid is analyzed to obtain needle coke raw material pitch, and the needle coke raw material pitch is obtained by coking and calcination processes to obtain needle coke. The patent application with the publication number CN114806620A discloses a pretreatment process for the raw materials for preparing coal-based needle coke: (1) raw material mixing; (2) primary sedimentation; (3) secondary sedimentation; (4) heavy phase distillation; (5) light phase distillation; (6) solvent recycling. By the principle of solvent extraction and sedimentation, two different solvents are mixed to form a mixed solvent, and two extraction and sedimentation separations are carried out, and finally the solvent is recovered by distillation. On the one hand, the yield of refined pitch of the intermediate product is improved, and on the other hand, the quinoline insoluble content can be effectively removed, the content of quinoline insoluble in coal tar pitch is reduced, and finally the purpose of improving the yield of needle coke and reducing the production cost of needle coke is achieved.

[0004] The above-mentioned patents or patent applications all process coal tar pitch by physical separation methods based on the principle of similar solubility. However, the problem with this treatment method is that it is difficult to remove highly reactive substances in coal tar pitch by physical separation methods, and it is easy to form an intercalated structure, resulting in a low OTI value of the finally obtained needle coke and defects in the crystal configuration, which affects the product quality of needle coke. Summary of the Invention

[0005] Aiming at the problem in the above-mentioned prior art that it is difficult to remove highly reactive substances in coal tar pitch by physical separation methods, resulting in a low OTI value of the finally obtained needle coke and defects in the crystal configuration, which affects the product quality of needle coke, the present invention proposes a method for preparing needle coke by compound modification of medium and low temperature coal tar pitch.

[0006] By modifying the asphalt raw material, the present invention makes the composition in the asphalt reasonable, the molecular weight distribution suitable, effectively reduces the content of highly reactive substances and heteroatoms, makes it rich in hydrogenated aromatic hydrocarbons to provide more transferable hydrogen sources, has more alkyl structures, effectively reduces the system viscosity, promotes the orderly arrangement of aromatic molecular lamellae, is conducive to the formation of a mesophase with fine fibrous shape, and makes the prepared needle coke product have a high OTI index, high crystallinity, good crystal structure and excellent electrochemical performance. The specific technical solution is as follows:

[0007] A method for preparing needle coke by compound modification of medium and low temperature coal tar asphalt, comprising the following steps:

[0008] 1) Fraction cutting to obtain medium and low temperature coal tar asphalt;

[0009] 2) Successively carry out hydrofining treatment, selective extraction treatment and chain extension treatment on the medium and low temperature coal tar asphalt to obtain modified asphalt;

[0010] 3) Add a nucleating crystallization agent to the modified asphalt for one-stage variable temperature thermal polymerization reaction, and then add a metal-organic framework material for two-stage variable temperature thermal polymerization reaction to obtain semicoke;

[0011] 4) Under the protection of a protective gas atmosphere, calcine the semicoke to form needle coke.

[0012] Further defined, the specific process of the hydrofining treatment in the step 2) is as follows:

[0013] Mix the medium and low temperature coal tar asphalt and a diluent in a mass ratio of 0.5~2:1, and carry out catalytic hydrotreating under the conditions of a temperature of 300°C to 360°C, a hydrogenation pressure of 8MPa to 12Mpa, a hydrogen-oil volume ratio of 600:1 to 1200:1 and a volume space velocity of 0.5h -1 ~1.5h -1 to obtain hydrofined oil;

[0014] Carry out true boiling point cutting on the obtained hydrofined oil to obtain hydrofined asphalt in the distillation range of 350°C to 500°C.

[0015] Further defined, the specific process of the selective extraction treatment in the step 2) is as follows:

[0016] Mix the hydrofined asphalt and a selective extractant in a mass ratio of 1~6:1, stir at a temperature of 80°C to 120°C for 40min to 80min, stand for 20min to 60min for stratification, take the upper layer liquid to obtain an organic extract, and recover the selective extractant by vacuum distillation to obtain hydrogenated asphalt rich in hydrogenated aromatic hydrocarbons.

[0017] Further defined, the chain extension process in step 2) is specifically as follows:

[0018] Mix the hydrogenated asphalt rich in hydrogenated aromatic hydrocarbons and the chain extender in a mass ratio of 5-20:1, and under the pressure condition of 1 MPa to 3 MPa, heat up at a heating rate of 1 °C / min to 3 °C / min to a reaction temperature of 350 °C to 400 °C, react for 2 h to 6 h, and obtain the modified asphalt after cooling.

[0019] Further defined, the diluent is one or a mixture of two or more of 300-360 °C fraction oil, coking heavy oil, No. 100 aromatic solvent oil, and No. 150 aromatic solvent oil.

[0020] Further defined, the selective extractant is one or a mixture of two or more of furfural, phenol, dimethyl sulfoxide, N,N-dimethylformamide, N-methylpyrrolidone, and sulfolane.

[0021] Further defined, the chain extender is one or a mixture of two or more of polyacrylic acid, polyethylene glycol, oleic acid, methyl iodide, and ethyl iodide.

[0022] Further defined, step 3) is specifically as follows: Mix the modified asphalt and the nucleating crystallizer in a mass ratio of 10-50:1, and under the condition of a reaction pressure of 0.5 MPa to 1.5 MPa, heat up at a heating rate of 0.5 °C / min to 1.5 °C / min to 400 °C to 430 °C, and keep the temperature constant for 2 to 6 h; Add the metal-organic framework material in a mass ratio of the modified asphalt to the metal-organic framework material of 10-50:1, and under the condition of a reaction pressure of 0.5 MPa to 1.5 MPa, heat up at a heating rate of 0.5 °C / min to 1.5 °C / min to 480 °C to 500 °C, and keep the temperature constant for 8 h to 12 h to obtain semi-coke.

[0023] Further defined, the nucleating crystallizer is one or a mixture of two or more of carbon black, graphite, TiO2, graphene, mica, alumina particles, and mesophase pitch powder.

[0024] Further defined, the metal-organic framework material is one or a mixture of two or more of Ni-MOF, Co-MOF, Mn-MOF, Cu-MOF, and Zn-MOF.

[0025] Further defined, the calcination conditions in step 4) are: Heat up at a heating rate of 2 °C / min to 5 °C / min to 1200 °C to 1500 °C, and keep the temperature for calcination for 6 to 10 h.

[0026] Further defined, the low-temperature coal tar pitch in the step 1) is the pitch in the distillation range of 350°C to 480°C.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. In the method for preparing needle coke by compound modification of low-temperature coal tar pitch in the present invention, after the medium and low-temperature coal tar pitch is subjected to hydrofining treatment, selective extraction treatment and chain extension treatment, the highly reactive substances and heteroatom content in the raw material pitch are reduced. The modified pitch is rich in hydrogenated aromatic hydrocarbons, providing more transferable hydrogen sources, and having a suitable aromatic hydrocarbon composition and alkyl structure. Then, a nucleating crystallization agent and a metal-organic framework material are added. The nucleating crystallization agent can effectively reduce the activation energy required for molecular reaction, enabling the system to accelerate the formation of mesophase spheres at a relatively low temperature and shortening the total duration of needle coke preparation. The metal-organic framework material realizes controllable structural properties at the molecular level through the metal center element. A metal-organic coordination compound is formed by the metal center element and polycyclic aromatic hydrocarbon molecules through coordination bonds, making the carbon surface of the formed semi-coke flatter, with fewer wrinkles and smaller roughness after calcination, promoting the ordered arrangement of aromatic molecular sheets, and being conducive to the formation of mesophase with a large-size optical texture structure. Finally, the needle coke product formed after calcination has a high OTI index, high crystallinity, good crystal structure, and excellent electrochemical performance.

[0029] 2. In this application, the medium and low-temperature coal tar pitch is mixed with a diluent, reducing the concentration of the asphalt component, preventing the asphalt from existing in the form of clusters, preventing the asphalt from flocculating and settling, and improving the stability of the asphalt. In addition, through the catalytic hydrogenation treatment process, the concentration of hydrogen radicals in the asphalt inhibits the rapid condensation of aromatic hydrocarbon radicals in the asphalt, slows down the coking rate, prolongs the service life of the catalyst, and at the same time reduces the highly reactive substances and heteroatom content in the raw material pitch.

[0030] 3. In this application, the hydrofined asphalt is mixed with a selective extractant to obtain a hydrogenated asphalt rich in hydrogenated aromatic hydrocarbons, enabling better release of hydrogen radicals in the subsequent thermal polymerization reaction, thereby effectively inhibiting the rapid thermal polycondensation between aromatic molecules, making the average molecular weight of the asphalt increase relatively smoothly, and being conducive to the formation of a wide-range mesophase.

[0031] 4. In this application, the hydrogenated asphalt rich in hydrogenated aromatic hydrocarbons is mixed with a chain extender to attach alkyl side chains to the raw material polycyclic aromatic hydrocarbon molecules, changing the structural composition of the raw material molecules, thereby adjusting the carbonization reaction rate, changing the content of alkyl substituents in the mesophase molecules, and ultimately achieving the effect of improving the fluidity of mesophase molecules and improving the mesophase performance. Description of the Drawings

[0032] Figure 1 The polarized light picture of the needle coke prepared in Example 3;

[0033] Figure 2 Polarized light picture of the needle coke prepared for Comparative Example 3. Detailed implementation manners

[0034] The technical solution of the present invention will be further explained below in conjunction with the accompanying drawings and embodiments, but the present invention is not limited to the embodiments described below.

[0035] The method for preparing needle coke in this application uses medium and low temperature coal tar pitch as raw material, selects a specific distillation fraction; through hydrofining treatment, selective extraction treatment and chain extension treatment to obtain modified pitch; then the modified pitch is fully mixed with a nucleating crystallization agent and a metal-organic framework material, carbonized to prepare semicoke, and calcined to obtain high-quality needle coke.

[0036] A method for preparing needle coke by compound modification of medium and low temperature coal tar pitch in this application includes the following steps:

[0037] 1) Fraction cutting to obtain medium and low temperature coal tar pitch; the medium and low temperature coal tar pitch is the pitch of the 350°C - 480°C distillation fraction obtained.

[0038] 2) Sequentially perform hydrofining treatment, selective extraction treatment and chain extension treatment on the medium and low temperature coal tar pitch to obtain modified pitch.

[0039] 3) Add a nucleating crystallization agent to the modified pitch for a one-stage variable temperature thermal polymerization reaction, and then add a metal-organic framework material for a two-stage variable temperature thermal polymerization reaction to prepare semicoke.

[0040] 4) Under the protection of a protective gas atmosphere, calcine the semicoke to form needle coke.

[0041] The specific process of the hydrofining treatment in step 2) of this application is as follows:

[0042] Mix the medium and low temperature coal tar pitch and a diluent in a mass ratio of 0.5 - 2:1, and carry out catalytic hydrotreating under the conditions of a temperature of 300°C - 360°C, a hydrogenation pressure of 8MPa - 12Mpa, a hydrogen-oil volume ratio of 600:1 - 1200:1 and a volume space velocity of 0.5h -1 ~1.5h -1 to obtain hydrofined oil.

[0043] Perform true boiling point cutting on the obtained hydrofined oil to obtain hydrofined pitch of the 350°C - 500°C distillation fraction.

[0044] The specific process of the selective extraction treatment in step 2) of this application is as follows:

[0045] Mix the hydrofined asphalt and the selective extractant in a mass ratio of 1 to 6:1, stir for 40 min to 80 min under the condition that the temperature is 80 °C to 120 °C, let it stand for 20 min to 60 min for stratification, take the upper layer liquid to obtain the organic extractant, and recover the selective extractant by vacuum distillation to obtain the hydrogenated asphalt rich in hydrogenated aromatics.

[0046] The chain extension treatment process in step 2) of this application is specifically as follows:

[0047] Mix the hydrogenated asphalt rich in hydrogenated aromatics and the chain extender in a mass ratio of 5 to 20:1, under the pressure condition of 1 MPa to 3 MPa, heat up to 350 °C to 400 °C at a heating rate of 1 °C / min to 3 °C / min, react for 2 h to 6 h, and obtain the modified asphalt after cooling.

[0048] The diluent in this application is one or a mixture of two or more of the 300 - 360 °C fraction oil, coking heavy oil, No. 100 aromatic solvent oil, and No. 150 aromatic solvent oil.

[0049] The selective extractant in this application is one or a mixture of two or more of furfural, phenol, dimethyl sulfoxide, N,N - dimethylformamide, N - methylpyrrolidone, and sulfolane.

[0050] The chain extender in this application is one or a mixture of two or more of polyacrylic acid, polyethylene glycol, oleic acid, iodomethane, and iodoethane.

[0051] Step 3) of this application is specifically as follows: Mix the modified asphalt and the nucleating crystallizer in a mass ratio of 10 to 50:1, under the condition that the reaction pressure is 0.5 MPa to 1.5 MPa, heat up to 400 °C to 430 °C at a heating rate of 0.5 °C / min to 1.5 °C / min, and keep it at a constant temperature for 2 to 6 h; add the metal - organic framework material in a mass ratio of the modified asphalt to the metal - organic framework material of 10 to 50:1, under the condition that the reaction pressure is 0.5 MPa to 1.5 MPa, heat up to 480 °C to 500 °C at a heating rate of 0.5 °C / min to 1.5 °C / min, and keep it at a constant temperature for 8 h to 12 h to prepare semicoke.

[0052] The nucleating crystallizer in this application is one or a mixture of two or more of carbon black, graphite, TiO₂, graphene oxide, mica, alumina particles, and mesophase pitch powder.

[0053] The metal - organic framework material in this application is one or a mixture of two or more of Ni - MOF, Co - MOF, Mn - MOF, Cu - MOF, and Zn - MOF.

[0054] In this application, the calcination conditions in step 4) are as follows: heating up to 1200°C to 1500°C at a heating rate of 2°C / min to 5°C / min, and maintaining the temperature for calcination for 6 to 10 hours.

[0055] Example 1

[0056] In this example, a method for preparing needle coke by composite modification of medium and low temperature coal tar pitch includes the following steps:

[0057] 1) Fraction cutting: Place 3 kg of medium and low temperature coal tar in a distillation kettle, distill out the fraction at 380°C to 450°C to obtain medium and low temperature coal tar pitch;

[0058] 2) Modify the medium and low temperature coal tar pitch to obtain modified pitch:

[0059] Take 500 g of medium and low temperature coal tar pitch for pulverization, fully mix it with 250 g of coking heavy oil, heat it to 300°C, place it on a fixed bed reactor, and carry out catalytic hydrogenation treatment under the conditions of a hydrogenation pressure of 8 MPa, a hydrogen-oil volume ratio of 600:1, and a volume space velocity of 0.5 h -1 to obtain hydrofined oil;

[0060] Place the hydrofined oil on a true boiling point distillation apparatus for true boiling point cutting to obtain hydrofined pitch in the fraction range of 350°C to 500°C;

[0061] Mix 200 g of the hydrofined pitch with 200 g of phenol in a beaker, stir at an oil bath temperature of 80°C and a rotation speed of 400 r / min for 40 min, let it stand for 20 min to separate layers, take the upper layer liquid to obtain an organic extract, recover the selective extractant by vacuum distillation to obtain hydrogenated pitch rich in hydrogenated aromatic hydrocarbons;

[0062] Mix 200 g of the hydrogenated pitch rich in hydrogenated aromatic hydrocarbons with 40 g of methyl iodide, add them to a high-pressure reaction kettle, fill it with nitrogen to a pressure of 1 MPa, close the inlet valve, turn on the heating device, heat it up to a reaction temperature of 350°C at a heating rate of 1°C / min and start timing, after reacting for 2 h, stop heating, and obtain modified pitch after cooling;

[0063] 3) Uniformly mix 40 g of modified pitch with 8 g of carbon black and add them to the reaction kettle. Before thermal polymerization, displace the air in the system with nitrogen. Under the condition of a reaction pressure of 0.5 MPa, heat it up to 430°C at a heating rate of 1°C / min, keep it at a constant temperature for 2 h and then take it out; add 4 g of metal-organic framework material (Cu-MOF), under the condition of a reaction pressure of 0.5 MPa, heat it up from room temperature to 480°C at a heating rate of 1°C / min, keep it at a constant temperature for 8 h, and take it out after cooling to obtain semicoke; the nitrogen in this step can also be replaced by an inert gas;

[0064] 4) placing the semi-coke in a high-temperature tubular furnace, heating the temperature to 1200°C at a heating rate of 3°C / min in a protective atmosphere of protective gas, and calcining the temperature for 6 hours to form needle coke; the protective gas in this step is nitrogen or inert gas.

[0065] Example 2

[0066] The present embodiment provides a method for preparing needle coke by composite modification of medium- and low-temperature coal tar pitch, which comprises the following steps:

[0067] 1) Fraction cutting: 3 kg of medium and low temperature coal tar is placed in a distillation kettle, and the 380-450°C fraction is distilled to obtain medium and low temperature coal tar pitch;

[0068] 2) Modify the medium and low temperature coal tar asphalt to obtain modified asphalt:

[0069] 500 g of medium-low temperature coal tar pitch was crushed, mixed with 250 g of coking heavy oil, heated to 300 °C and placed in a fixed bed reactor. The reactor was heated at a hydrogenation pressure of 9 MPa, a hydrogen-to-oil volume ratio of 800:1 and a volume space velocity of 1 h -1 Catalytic hydrogenation is carried out under the conditions of to obtain hydrorefined oil;

[0070] The hydrorefined oil is placed on a real boiling point distillation apparatus for real boiling point cutting to obtain a hydrorefined asphalt in a 350-500°C fraction;

[0071] 300 g of hydrogenated refined asphalt and 50 g of furfural were placed in a beaker and mixed, and stirred for 50 min at an oil bath temperature of 100° C. and a rotation speed of 600 r / min. After standing for 40 min to separate the layers, the upper layer was taken to obtain an organic extract, and the selective extractant was recovered by vacuum distillation to obtain a hydrogenated asphalt rich in hydrogenated aromatics;

[0072] 200 g of hydrogenated asphalt rich in hydrogenated aromatics and 20 g of methyl iodide were mixed and added into a high-pressure reactor, nitrogen was filled to a pressure of 1.5 MPa, the air inlet valve was closed, the heating device was turned on, the temperature was increased at a heating rate of 1°C / min to a reaction temperature of 350°C, and the timing was started. After reacting for 3 hours, the heating was stopped, and the modified asphalt was obtained after cooling;

[0073] 3) Uniformly mix 60 g of modified asphalt with 2 g of alumina particles and add them to a reaction kettle. Before thermal polymerization, displace the air in the system with nitrogen. Under the condition of a reaction pressure of 0.8 MPa, heat it up to 405 °C at a heating rate of 0.5 °C / min, keep it at a constant temperature for 3 h and then take it out; add 1 g of metal-organic framework material (Zn-MOF), under the condition of a reaction pressure of 0.8 MPa, heat it up from room temperature to 485 °C at a heating rate of 0.5 °C / min, keep it at a constant temperature for 9 h, and take it out after cooling to obtain semicoke; the nitrogen in this step can also be replaced by an inert gas;

[0074] 4) Place the semicoke in a high-temperature tube furnace, under the protection of a protective gas, heat it up to 1300 °C at a heating rate of 2 °C / min, and calcine for 8 h to form needle coke; the protective gas in this step is nitrogen or an inert gas.

[0075] Example 3

[0076] In this example, a method for preparing needle coke by compound modification of medium and low temperature coal tar pitch includes the following steps:

[0077] 1) Fraction cutting: Place 3 kg of medium and low temperature coal tar in a distillation kettle, distill out the fraction at 380 - 450 °C to obtain medium and low temperature coal tar pitch;

[0078] 2) Modify the medium and low temperature coal tar pitch to obtain modified asphalt:

[0079] Take 500 g of medium and low temperature coal tar pitch for pulverization, fully mix it with 500 g of fraction oil at 300 - 360 °C, heat it to 360 °C and then place it on a fixed bed reactor. Under the conditions of a hydrogenation pressure of 10 MPa, a hydrogen-oil volume ratio of 1200:1, and a volume space velocity of 1.5 h -1 Perform catalytic hydrogenation treatment to obtain hydrorefined oil;

[0080] Place the hydrorefined oil on a true boiling point distillation apparatus for true boiling point cutting to obtain hydrorefined asphalt in the fraction range of 350 - 500 °C;

[0081] Mix 300 g of hydrorefined asphalt with 300 g of N, N-dimethylformamide in a beaker, stir at an oil bath temperature of 120 °C and a rotation speed of 600 r / min for 80 min, let it stand for 60 min to separate layers, take the upper layer liquid to obtain an organic extract, and recover the selective extractant by vacuum distillation to obtain hydrogenated asphalt rich in hydrogenated aromatics;

[0082] Mix 200 g of hydrogenated asphalt rich in hydrogenated aromatic hydrocarbons with 20 g of polyethylene glycol, then add the mixture into a high-pressure reactor. Fill it with nitrogen until the pressure reaches 3 MPa. Close the intake valve, turn on the heating device, and heat it at a rate of 1 °C / min until the reaction temperature reaches 380 °C and then start timing. After reacting for 6 h, stop heating. After cooling, modified asphalt is obtained;

[0083] 3) Uniformly mix 40 g of modified asphalt with 4 g of graphene oxide and then add the mixture into the reactor. Before thermal polymerization, displace the air in the system with nitrogen. Under the condition of a reaction pressure of 0.8 MPa, heat it at a rate of 0.5 °C / min to 405 °C, keep it at a constant temperature for 3 h and then take it out; Add 1 g of metal-organic framework material (Ni-MOF). Under the condition of a reaction pressure of 0.8 MPa, heat it from room temperature to 485 °C at a rate of 0.5 °C / min, keep it at a constant temperature for 9 h, and take it out after cooling to obtain semicoke; The nitrogen in this step can also be replaced by an inert gas;

[0084] 4) Place the semicoke in a high-temperature tubular furnace. Under the protection of a protective gas, heat it at a rate of 3 °C / min to 1400 °C, and calcine for 6 h to form needle coke; The protective gas in this step is nitrogen or an inert gas.

[0085] Example 4

[0086] A method for preparing needle coke by compound modification of medium and low temperature coal tar pitch in this example includes the following steps:

[0087] 1) Fraction cutting: Place 3 kg of medium and low temperature coal tar in a distillation kettle, distill out the fraction at 380 - 450 °C to obtain medium and low temperature coal tar pitch;

[0088] 2) Modify the medium and low temperature coal tar pitch to obtain modified asphalt:

[0089] Take 500 g of medium and low temperature coal tar pitch, pulverize it, fully mix it with 1000 g of No. 150 aromatic hydrocarbon solvent oil, heat it to 340 °C, then place it on a fixed-bed reactor, and carry out catalytic hydrotreating under the conditions of a hydrogenation pressure of 12 MPa, a hydrogen-oil volume ratio of 1000:1, and a volume space velocity of 1.0 h -1 to obtain hydrofined oil;

[0090] Place the hydrofined oil on a true boiling point distillation apparatus for true boiling point cutting to obtain hydrofined asphalt in the fraction range of 350 - 500 °C;

[0091] Mix 300 g of hydrofined asphalt with 100 g of N,N-dimethylformamide in a beaker. Under the condition that the oil bath temperature is 100 °C and the rotation speed is 800 r / min, stir for 60 min. After standing for 60 min for stratification, take the upper layer liquid to obtain an organic extract. Recover the selective extractant by vacuum distillation to obtain a hydrogenated asphalt rich in hydrogenated aromatics;

[0092] Mix 200 g of the hydrogenated asphalt rich in hydrogenated aromatics with 10 g of polyacrylic acid and then add them into a high-pressure reactor. Fill it with nitrogen until the pressure reaches 2.5 MPa. Close the intake valve, turn on the heating device, and heat it at a heating rate of 3 °C / min until the reaction temperature reaches 360 °C and then start timing. After reacting for 4 h, stop heating. After cooling, obtain the modified asphalt;

[0093] 3) Uniformly mix 40 g of the modified asphalt with 2 g of mesophase pitch powder and then add them into the reactor. Before thermal polymerization, displace the air in the system with nitrogen. Under the condition that the reaction pressure is 1.0 MPa, heat it at a heating rate of 0.8 °C / min to 410 °C, keep it at a constant temperature for 4 h and then take it out; Add 1.2 g of metal-organic framework material (Co-MOF). Under the condition that the reaction pressure is 1.0 MPa, heat it from room temperature to 490 °C at a heating rate of 0.8 °C / min, keep it at a constant temperature for 10 h, and take it out after cooling to obtain semi-coke; The nitrogen in this step can also be replaced by an inert gas;

[0094] 4) Place the semi-coke in a high-temperature tubular furnace. Under the protection atmosphere of the protective gas, heat it at a heating rate of 4 °C / min to 1500 °C, and the calcination time is 8 h to form needle coke; The protective gas in this step is nitrogen or an inert gas.

[0095] Example 5

[0096] A method for preparing needle coke by compound modification of medium and low temperature coal tar pitch in this example includes the following steps:

[0097] 1) Fraction cutting: Place 3 kg of medium and low temperature coal tar in a distillation kettle and distill out the fraction at 380 - 450 °C to obtain medium and low temperature coal tar pitch;

[0098] 2) Modify the medium and low temperature coal tar pitch to obtain modified asphalt:

[0099] Take 500 g of medium and low temperature coal tar pitch, pulverize it, fully mix it with 250 g of No. 100 aromatic solvent oil, heat it to 300 °C and then place it on a fixed bed reactor. Under the conditions of a hydrogenation pressure of 8 MPa, a hydrogen-oil volume ratio of 600:1, and a volume space velocity of 0.5 h -1 to carry out catalytic hydrogenation treatment to obtain hydrogenated refined oil;

[0100] The hydrofined oil was subjected to true boiling point distillation on a true boiling point distillation apparatus to obtain hydrofined asphalt in the distillation range of 350-500 °C;

[0101] 300 g of the hydrofined asphalt and 60 g of dimethyl sulfoxide were placed in a beaker and mixed. Under an oil bath temperature of 120 °C and a stirring speed of 800 r / min, the mixture was stirred for 80 min. After standing for 20 min for stratification, the upper layer liquid was taken to obtain an organic extraction solution. The selective extractant was recovered by vacuum distillation to obtain hydrogenated asphalt rich in hydrogenated aromatics;

[0102] 200 g of the hydrogenated asphalt rich in hydrogenated aromatics and 80 g of polyacrylic acid were mixed and then added to a high-pressure reactor. Nitrogen was filled to a pressure of 2 MPa, the inlet valve was closed, the heating device was turned on, and the temperature was raised at a heating rate of 2 °C / min until the reaction temperature reached 400 °C and then timing started. After reacting for 5 h, the heating was stopped. After cooling, modified asphalt was obtained;

[0103] 3) 40 g of the modified asphalt and 4 g of TiO2 were uniformly mixed and then added to the reactor. Before thermal polymerization, the air in the system was displaced with nitrogen. Under a reaction pressure of 1.2 MPa, the temperature was raised at a heating rate of 1.0 °C / min to 415 °C and kept at a constant temperature for 5 h and then taken out; 2 g of metal-organic framework material (Mn-MOF) was added. Under a reaction pressure of 1.2 MPa, the temperature was raised from room temperature to 495 °C at a heating rate of 1.0 °C / min and kept at a constant temperature for 11 h. After cooling, it was taken out to obtain semicoke; The nitrogen in this step can also be replaced by an inert gas;

[0104] 4) The semicoke was placed in a high-temperature tube furnace. Under the protection atmosphere of a protective gas, the temperature was raised at a heating rate of 2 °C / min to 1200 °C and calcined for 6 h to form needle coke; The protective gas in this step is nitrogen or an inert gas.

[0105] Example 6

[0106] A method for preparing needle coke by composite modification of medium and low temperature coal tar pitch in this example includes the following steps:

[0107] 1) Fraction cutting: 3 kg of medium and low temperature coal tar was placed in a rectification kettle, and the fraction in the range of 380-450 °C was distilled out to obtain medium and low temperature coal tar pitch;

[0108] 2) Modifying the medium and low temperature coal tar pitch to obtain modified asphalt:

[0109] 500 g of medium and low temperature coal tar pitch was taken and pulverized, and fully mixed with 1000 g of fraction oil in the range of 300-360 °C. After heating to a temperature of 300 °C, it was placed on a fixed bed reactor. Under a hydrogenation pressure of 12 MPa, a hydrogen-oil volume ratio of 1200:1, and a volume space velocity of 1.5 h-1 Perform catalytic hydrotreating under the following conditions to obtain hydrorefined oil;

[0110] Place the hydrorefined oil on a true boiling point distillation apparatus for true boiling point cutting to obtain hydrorefined asphalt in the distillation fraction range of 350 - 500 °C;

[0111] Mix 300 g of hydrorefined asphalt with 120 g of sulfolane in a beaker. Stir at an oil bath temperature of 120 °C and a rotation speed of 800 r / min for 80 min. After standing for 60 min for stratification, take the upper layer liquid to obtain an organic extract. Recover the selective extractant by vacuum distillation to obtain hydrogenated asphalt rich in hydrogenated aromatics;

[0112] Mix 200 g of hydrogenated asphalt rich in hydrogenated aromatics with 10 g of methyl iodide and add them to a high-pressure reactor. Fill with nitrogen to a pressure of 3 MPa, close the inlet valve, turn on the heating device, and start timing after heating to a reaction temperature of 350 °C at a heating rate of 3 °C / min. After reacting for 5 h, stop heating and obtain modified asphalt after cooling;

[0113] 3) Uniformly mix 400 g of modified asphalt with 8 g of graphene oxide and add them to a reactor. Replace the air in the system with nitrogen before thermal polymerization. Under the condition of a reaction pressure of 1.5 MPa, heat to 420 °C at a heating rate of 1.5 °C / min, keep the temperature constant for 6 h and then take it out; Add 3 g of metal-organic framework material (Ni-MOF), under the condition of a reaction pressure of 1.5 MPa, heat from room temperature to 500 °C at a heating rate of 1.5 °C / min, keep the temperature constant for 12 h, and take it out after cooling to obtain semicoke; The nitrogen in this step can also be replaced by an inert gas;

[0114] 4) Place the semicoke in a high-temperature tubular furnace, under the protection atmosphere of a protective gas, heat to 1500 °C at a heating rate of 5 °C / min, and calcine for 10 h to form needle coke; The protective gas in this step is nitrogen or an inert gas.

[0115] It should be noted that the diluent in the above Examples 1 - 6 can also be a mixture formed by two or more components of 300 - 360 °C fraction oil, coking heavy oil, No. 100 aromatic solvent oil, and No. 150 aromatic solvent oil.

[0116] It should be noted that the selective extractant in the above Examples 1 - 6 can also be a mixture formed by two or more components of furfural, phenol, dimethyl sulfoxide, N,N-dimethylformamide, N-methylpyrrolidone, and sulfolane.

[0117] It should be noted that the chain extender in the above-mentioned Examples 1 to 6 may also be a mixture of two or more components selected from polyacrylic acid, polyethylene glycol, oleic acid, methyl iodide and ethyl iodide.

[0118] It should be noted that the nucleating crystallization agent in the above-mentioned Examples 1 to 6 can also be a mixture of two or more components of carbon black, graphite, TiO2, graphene oxide, mica, alumina particles and mesophase asphalt powder.

[0119] In order to verify the technical effect of the present invention, several groups of comparative examples are made to verify the effect, as follows:

[0120] Comparative Example 1

[0121] This comparative example provides a method for preparing needle coke by composite modification of medium- and low-temperature coal tar pitch, which comprises the following steps:

[0122] 1) 3 kg of medium and low temperature coal tar is placed in a distillation kettle, and a fraction of 380-450°C is distilled to obtain medium and low temperature coal tar pitch;

[0123] 2) Modify the medium and low temperature coal tar asphalt to obtain modified asphalt:

[0124] 500 g of medium-low temperature coal tar pitch was crushed, mixed with 250 g of 300-360 °C distillate oil, heated to 300 °C and placed in a fixed bed reactor. The reactor was heated at a hydrogenation pressure of 10 MPa, a hydrogen-to-oil volume ratio of 1200:1 and a volume space velocity of 1.5 h -1 Catalytic hydrogenation is carried out under the conditions of to obtain hydrorefined oil;

[0125] The hydrorefined oil is placed on a real boiling point distillation apparatus for real boiling point cutting to obtain a hydrorefined asphalt in a 350-500°C fraction;

[0126] 200 g of hydrorefined asphalt and 200 g of polyethylene glycol were placed in a high-pressure reactor, filled with nitrogen to 1.5 MPa, the air inlet valve was closed, the heating device was turned on, and the temperature was raised to 380°C at a heating rate of 1°C / min, and the timing was started. After reacting for 2 hours, the heating was stopped, and the modified asphalt was obtained after cooling;

[0127] 3) Uniformly mix 40 g of modified asphalt with 8 g of graphene oxide, then add them into a reaction kettle. Before thermal polymerization, displace the air in the system with nitrogen. Under the condition of a reaction pressure of 0.5 MPa, heat it up to 390 °C at a heating rate of 1.8 °C / min, keep it at a constant temperature for 2 h and then take it out; add 4 g of metal-organic framework material (Cu-MOF), under the condition of a reaction pressure of 0.5 MPa, heat it up from room temperature to 480 °C at a heating rate of 1.8 °C / min, keep it at a constant temperature for 8 h, and take it out after cooling to obtain semi-coke; the nitrogen in this step can also be replaced by an inert gas;

[0128] 4) Place the semi-coke in a high-temperature tube furnace, under the protection of a protective gas, heat it up to 1400 °C at a heating rate of 3 °C / min, and calcine for 6 h to form needle coke; the protective gas in this step is nitrogen or an inert gas.

[0129] There is no selective extraction process in this comparative example.

[0130] Comparative Example 2

[0131] A method for preparing needle coke by compound modification of medium and low temperature coal tar pitch in this comparative example includes the following steps:

[0132] 1) Fraction cutting: Place 3 kg of medium and low temperature coal tar in a distillation kettle, distill out the fraction at 380 - 450 °C to obtain medium and low temperature coal tar pitch;

[0133] 2) Modify the medium and low temperature coal tar pitch to obtain modified asphalt:

[0134] Mix 300 g of hydrofined asphalt with 50 g of dimethyl sulfoxide in a beaker, stir at an oil bath temperature of 80 °C and a rotation speed of 400 r / min for 50 min, let it stand for 40 min to separate layers, then take the upper layer liquid to obtain an organic extraction solution, and recover the selective extractant by vacuum distillation to obtain hydrogenated asphalt rich in hydrogenated aromatics;

[0135] Mix 200 g of hydrogenated asphalt rich in hydrogenated aromatics with 20 g of iodoethane and then add them into a high-pressure reaction kettle, fill it with nitrogen to a pressure of 1.5 MPa, close the inlet valve, turn on the heating device, heat it up to a reaction temperature of 400 °C at a heating rate of 3 °C / min and then start timing, after reacting for 3 h, stop heating, and obtain modified asphalt after cooling;

[0136] 3) Uniformly mix 60 g of modified asphalt and 2 g of graphite, then add them into a reaction kettle. Before thermal polymerization, displace the air in the system with nitrogen. Under the condition of a reaction pressure of 1.5 MPa, increase the temperature at a rate of 2 °C / min to 430 °C, keep it at a constant temperature for 6 h and then take it out; add 5 g of metal-organic framework material (Mn-MOF), under the condition of a reaction pressure of 1.5 MPa, increase the temperature from room temperature to 485 °C at a rate of 2 °C / min, keep it at a constant temperature for 9 h, and take it out after cooling to obtain semicoke; the nitrogen in this step can also be replaced by an inert gas;

[0137] 4) Place the semicoke in a high-temperature tubular furnace, under the protection of a protective gas, increase the temperature at a rate of 3 °C / min to 1300 °C, and the calcination time is 7 h to form needle coke; the protective gas in this step is nitrogen or an inert gas.

[0138] There is no hydrofining process in this comparative example.

[0139] Comparative Example 3

[0140] A method for preparing needle coke by compound modification of medium and low temperature coal tar pitch in this comparative example includes the following steps:

[0141] 1) Fraction cutting: Place 3 kg of medium and low temperature coal tar in a distillation kettle, distill out the fraction at 380 - 450 °C to obtain medium and low temperature coal tar pitch;

[0142] 2) Uniformly mix 500 g of medium and low temperature coal tar pitch and 500 g of mica, then add them into a reaction kettle. Before thermal polymerization, displace the air in the system with nitrogen. Under the condition of a reaction pressure of 0.8 MPa, increase the temperature at a rate of 0.5 °C / min to 405 °C, keep it at a constant temperature for 3 h and then take it out; add 1 g of metal-organic framework material (Ni-MOF), under the condition of a reaction pressure of 0.8 MPa, increase the temperature from room temperature to 485 °C at a rate of 0.5 °C / min, keep it at a constant temperature for 9 h, and take it out after cooling to obtain semicoke; the nitrogen in this step can also be replaced by an inert gas;

[0143] 3) Place the semicoke in a high-temperature tubular furnace, increase the temperature to 1200 °C at a rate of 3 °C / min under N2 atmosphere, and the calcination time is 6 h to form needle coke.

[0144] There is no asphalt compound modification process in this comparative example.

[0145] Comparative Example 4

[0146] A method for preparing needle coke by compound modification of medium and low temperature coal tar pitch in this comparative example includes the following steps:

[0147] 1) Fraction cutting: Place 3 kg of medium and low temperature coal tar in a distillation kettle, distill the fraction at 380 - 450 °C to obtain medium and low temperature coal tar pitch;

[0148] 2) Modify the medium and low temperature coal tar pitch to obtain modified pitch:

[0149] Take 500 g of medium and low temperature coal tar pitch, pulverize it, fully mix it with 1000 g of coking heavy oil, heat it to 320 °C, then place it on a fixed bed reactor, and carry out catalytic hydrotreating under the conditions of a hydrogenation pressure of 9 MPa, a hydrogen-oil volume ratio of 800:1, and a volume space velocity of 1.0 h -1 to obtain hydrofined oil;

[0150] Place the hydrofined oil on a true boiling point distillation apparatus for true boiling point cutting to obtain hydrofined pitch in the fraction range of 350 - 500 °C;

[0151] Mix 300 g of the hydrofined pitch with 100 g of furfural in a beaker, stir at an oil bath temperature of 90 °C and a rotation speed of 500 r / min for 60 min, let it stand for 40 min to separate layers, then take the upper layer liquid to obtain an organic extract, recover the selective extractant by vacuum distillation to obtain hydrogenated pitch rich in hydrogenated aromatics;

[0152] 3) Uniformly mix 200 g of the hydrogenated pitch rich in hydrogenated aromatics with 10 g of graphene oxide, then add it to a reaction kettle. Before thermal polymerization, displace the air in the system with nitrogen. Under the condition of a reaction pressure of 1.0 MPa, heat it at a heating rate of 1 °C / min to 430 °C, keep it at a constant temperature for 4 h and then take it out; add 3 g of metal-organic framework material (Co-MOF), under the condition of a reaction pressure of 2.0 MPa, heat it from room temperature to 490 °C at a heating rate of 1 °C / min, keep it at a constant temperature for 10 h, and take it out after cooling to obtain semicoke; the nitrogen in this step can also be replaced by an inert gas;

[0153] 4) Place the semicoke in a high-temperature tubular furnace, under the protection of a protective gas, heat it at a heating rate of 4 °C / min to 1400 °C, and the calcination time is 8 h to form needle coke; the protective gas in this step is nitrogen or an inert gas.

[0154] There is no chain extension treatment process in this comparative example.

[0155] Comparative Example 5

[0156] A method for preparing needle coke by compound modification of medium and low temperature coal tar pitch in this comparative example includes the following steps:

[0157] 1) Fraction cutting: Place 3 kg of medium and low temperature coal tar in a distillation kettle, distill the fraction at 380 - 450 °C to obtain medium and low temperature coal tar pitch;

[0158] 2) Modify the medium and low temperature coal tar pitch to obtain modified pitch:

[0159] Take 500 g of medium and low temperature coal tar pitch, pulverize it, fully mix it with 250 g of No. 150 aromatic solvent oil, heat it to 360 °C, place it on a fixed bed reactor, and carry out catalytic hydrotreating under the conditions of a hydrogenation pressure of 8 MPa, a hydrogen-oil volume ratio of 600:1, and a volume space velocity of 0.5 h -1 to obtain hydrofined oil;

[0160] Place the hydrofined oil on a true boiling point distillation apparatus for true boiling point cutting to obtain hydrofined pitch in the distillation range of 350 - 500 °C;

[0161] Mix 300 g of the hydrofined pitch with 60 g of sulfolane in a beaker, stir at an oil bath temperature of 80 °C and a rotation speed of 500 r / min for 40 min, let it stand for 60 min to separate layers, take the upper layer liquid to obtain an organic extract, recover the selective extractant by vacuum distillation to obtain hydrogenated pitch rich in hydrogenated aromatics;

[0162] Mix 200 g of the hydrogenated pitch rich in hydrogenated aromatics with 80 g of oleic acid, add them to a high-pressure reactor, fill it with nitrogen to a pressure of 1.5 MPa, close the inlet valve, turn on the heating device, heat it at a heating rate of 3 °C / min to a reaction temperature of 370 °C and start timing, after reacting for 5 h, stop heating, and obtain modified pitch after cooling;

[0163] 3) Add 40 g of modified pitch to the reaction kettle, displace the air in the system with nitrogen before thermal polymerization, under the condition of a reaction pressure of 0.5 MPa, heat it at a heating rate of 1 °C / min to 500 °C, keep it at a constant temperature for 12 h and then take it out, and obtain semicoke after cooling; the nitrogen in this step can also be replaced by an inert gas;

[0164] 4) Place the semicoke in a high-temperature tubular furnace, under the protection of a protective gas, heat it at a heating rate of 1 °C / min to 1300 °C, and calcine for 6 h to form needle coke; the protective gas in this step is nitrogen or an inert gas.

[0165] In this comparative example, no nucleating crystallization agent and metal-organic framework material are added during the thermal polymerization reaction process.

[0166] Comparative Example 6

[0167] A method for preparing needle coke by compound modification of medium and low temperature coal tar pitch in this comparative example includes the following steps:

[0168] 1) Fraction cutting: Place 3 kg of medium and low temperature coal tar in a distillation kettle, distill the fraction at 380 - 450 °C to obtain medium and low temperature coal tar pitch;

[0169] 2) Modify the medium and low temperature coal tar pitch to obtain modified pitch:

[0170] Take 500 g of medium and low temperature coal tar pitch, pulverize it, mix it thoroughly with 1000 g of coking heavy oil, heat it to 420 °C, then place it on a fixed bed reactor, and carry out catalytic hydrotreating under the conditions of a hydrogenation pressure of 6 MPa, a hydrogen-oil volume ratio of 1200:1, and a liquid hourly space velocity of 1.5 h -1 to obtain hydrofined oil;

[0171] Carry out true boiling point cutting on the hydrofined oil using a true boiling point distillation apparatus to obtain hydrofined pitch in the 350 - 500 °C distillation range;

[0172] Mix 300 g of the hydrofined pitch with 120 g of phenol in a beaker, stir at an oil bath temperature of 150 °C and a rotation speed of 800 r / min for 40 min, let it stand for 60 min to separate layers, then take the upper layer liquid to obtain an organic extract, recover the selective extractant by vacuum distillation to obtain hydrogenated pitch rich in hydrogenated aromatics;

[0173] Mix 200 g of the hydrogenated pitch rich in hydrogenated aromatics with 10 g of polyethylene glycol, add them to a high-pressure reactor, fill it with nitrogen to a pressure of 3 MPa, close the inlet valve, turn on the heating device, heat it at a heating rate of 3 °C / min to a reaction temperature of 320 °C and start timing, after reacting for 6 h, stop heating, and obtain modified pitch after cooling;

[0174] 3) Uniformly mix 400 g of modified pitch with 8 g of carbon black and add them to a reaction kettle. Before thermal polymerization, displace the air in the system with nitrogen. Under the condition of a reaction pressure of 2 MPa, heat it at a heating rate of 2 °C / min to 430 °C, keep it at a constant temperature for 2 h and then take it out; add 2 g of metal-organic framework material (Ni-MOF), under the condition of a reaction pressure of 2 MPa, heat it from room temperature to 510 °C at a heating rate of 2 °C / min, keep it at a constant temperature for 9 h, and take it out after cooling to obtain semicoke; the nitrogen in this step can also be replaced by an inert gas;

[0175] 4) Place the semicoke in a high-temperature tubular furnace, under the protection of a protective gas, heat it at a heating rate of 5 °C / min to 1000 °C, and the calcination time is 4 h to form needle coke; the protective gas in this step is nitrogen or an inert gas.

[0176] In this comparative example, the conditions in the thermal polymerization reaction process are not within a reasonable range.

[0177] The performance of the prepared needle coke was tested, and the results are shown in Table 1 and Table 2.

[0178] Table 1 shows the ash content and physical properties of the needle coke products prepared in Examples 1 to 6, and Table 2 shows the ash content and physical properties of the needle coke products prepared in Comparative Examples 1 to 6.

[0179] Table 1: Ash content and physical properties of the needle coke products prepared in Examples 1 to 6:

[0180] Test performance items Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 OTI value 69 74 81 76 70 72 <![CDATA[CTE, 10 -6 / ℃]]> 1.43 1.38 1.25 1.30 1.35 1.46 Initial discharge specific capacity / (mA·h) / g 327.1 324.5 346.8 330.1 316.6 320.9

[0181] Table 2: Ash content and physical properties of the needle coke products prepared in Comparative Examples 1 to 6

[0182] Test performance items Comparative example 1 Comparative example 2 Comparative example 3 Comparative example 4 Comparative example 5 Comparative example 6 <![CDATA[OTI, g / cm -3 > 61 58 52 60 46 49 <![CDATA[CTE, 10 -6 / ℃]]> 1.78 1.69 1.59 1.51 1.40 1.44 Initial discharge specific capacity / (mA·h) / g 311.2 309.6 297.8 319.6 316.7 301.4

[0183] In the above Tables 1 and 2, OTI refers to the bulk density, and CTE refers to the coefficient of thermal expansion.

[0184] The physical property test method is as follows: the coefficient of thermal expansion (CTE) is measured according to GB / T 3074.4-2016 "Determination Method of Coefficient of Thermal Expansion (CTE) of Graphite Electrodes", and the initial discharge specific capacity is measured according to GB / T 24533-2019 "Graphite Anode Materials for Lithium-Ion Batteries".

[0185] Comparing Table 1 and Table 2, it can be seen that for the needle coke obtained by the preparation method of this application, its coefficient of thermal expansion is less than 1.50×10 -6 / °C, and the lowest is 1.25×10 -6 / °C. It has a small coefficient of thermal expansion and good performance; the OTI value is high, the initial discharge specific capacity is greater than 340.0 (mA·h) / g, and the highest is 346.8 (mA·h) / g, showing excellent electrochemical performance.

[0186] After the medium and low temperature coal tar pitch in Example 3 is modified, the content of highly reactive substances and heteroatoms in the raw pitch is effectively reduced, and it is rich in hydrogenated aromatics which can provide more transferable hydrogen sources, and has a suitable aromatic composition and alkyl structure. When the pitch cracks at high temperature to generate free radicals, the hydrogenated aromatics can release active hydrogen free radicals during the thermal polymerization process. When the free radicals are stabilized by hydrogen transfer and form low molecular weight substances, the carbonization system can maintain a relatively low viscosity, thereby forming needle coke with good optical texture. In addition, the increase in the alkyl structure in the pitch molecules can reduce the internal force within the molecules, making the molecular arrangement relatively loose, which can improve the fluidity of the carbonization system, effectively reduce the system viscosity, promote the orderly arrangement of aromatic molecular layers, and is conducive to the formation of needle coke with high crystallinity, good crystal structure and excellent performance. During the thermal polymerization process, the nucleating and crystallizing agent can reduce the activation energy required for molecular reactions, enabling the system to generate mesophase macromolecules at a relatively low temperature. Moreover, as an attachment body, it can significantly accelerate the formation of mesophase spheres, shorten the total preparation time of needle coke, and improve the OTI value of needle coke. In the thermal reaction curing stage, metal-organic framework materials are introduced to form metal-organic coordination compounds similar to those formed by metal central elements and polycyclic aromatic hydrocarbon molecules through coordination bonds. After calcination, the carbon surface of the semi-coke is flatter, with fewer wrinkles and smaller roughness, the order degree of carbon atom arrangement is high, the resistivity of the product is small, the thermal expansion coefficient is low, and the electrochemical performance is excellent.

[0187] In Comparative Example 3, no modification treatment is carried out, resulting in the presence of more heteroatoms. During the thermal polymerization process, the heteroatoms form too many active centers, the system viscosity increases, which hinders the growth, coalescence and transformation into anisotropic structures of the spheres, and an intercalated structure is generated. After hydrorefining, the oil product contains a large amount of alkanes, cycloalkanes and a small amount of polycyclic aromatic hydrocarbons. Without selective extraction, in the initial stage of the reaction, dehydrogenation reactions occur at the highly active reaction sites of cycloalkane molecules, and alkane molecules undergo cracking reactions, thereby generating a large number of active free radicals and small molecules in the early stage of the reaction, which is not conducive to the formation of mesophase. Without adding a nucleating agent, the time for mesophase formation is prolonged and the OTI value is small.

[0188] For the needle coke prepared in Example 3 and Comparative Example 3, a polarized light microscope was used to observe its internal structure. The instrument used was a ZEISS Axio scope A1 polarized light microscope, see Figure 1 and Figure 2 . Among them, Figure 1 is the polarized light picture of the needle coke prepared in Example 3; Figure 2 is the polarized light picture of the needle coke prepared in Comparative Example 3; Figure 1The optical structure of medium needle coke is mainly a fine fiber structure, and the OTI value is the highest at 81. The asphalt in Example 3 can effectively reduce the heteroatom content in the raw asphalt after modification, and is rich in hydrogenated aromatics to provide more transferable hydrogen sources, suitable aromatic composition and alkyl structure. The highly reactive components contained in the carbonization system produce macromolecular free radicals. The more transferable hydrogen content, the lower the spin concentration. The free radical fragments induced by heat will be annihilated by transferable hydrogen and stabilized into small molecular weight substances. Small molecular substances can maintain a lower viscosity at a higher temperature, thereby developing an intermediate phase and obtaining coke with a larger optical texture. After adding the nucleating agent, the activation energy required for the molecular reaction is effectively reduced, so that the system can generate intermediate phase macromolecules at a relatively low temperature, and the planar aromatic macromolecules are arranged more orderly and have more stacked layers. Figure 2 Although there is a certain domain structure in the structure, the overall structure is still a mosaic structure with an OTI value of 52. This is mainly because the raw materials of Comparative Example 3 have not been reasonably formulated and contain a certain amount of highly reactive substances and heteroatoms. The highly reactive substances and heteroatoms increase the dipole moment of the aromatic compounds, significantly increase the viscosity of the system, and disrupt the parallel stacking of the sheet molecules due to the interaction between adjacent molecules. In addition, due to the small number of hydrogen radicals generated, a large number of condensation reactions will occur at the same time, causing the viscosity of the reaction intermediates to increase rapidly, resulting in the difficulty of the obtained large-sized aromatic molecules to fully rearrange under the action of π-π bonds, and ultimately only forming needle coke with a mosaic structure.

[0189] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make various equivalent modifications or substitutions within the technical scope described in the present invention, which should all be included in the protection scope of the present invention.

Claims

1. A method for preparing needle coke by compound modification of medium and low temperature coal tar pitch, characterized in that, It includes the following steps: 1) Fractionation to obtain medium and low temperature coal tar pitch; 2) Successively carry out hydrofining treatment, selective extraction treatment and chain extension treatment on the medium and low temperature coal tar pitch to obtain modified pitch; 3) Add a nucleating crystallization agent to the modified pitch for a first-stage variable temperature thermal polymerization reaction, and then add a metal-organic framework material for a second-stage variable temperature thermal polymerization reaction to prepare semicoke; 4) Under the protection of a protective gas atmosphere, calcine the semicoke to form needle coke.

2. The method for preparing needle coke by composite modification of medium and low temperature coal tar pitch according to claim 1, characterized in that, The specific process of the hydrofining treatment in step 2) is as follows: Mix medium and low temperature coal tar pitch with a diluent in a mass ratio of 0.5~2:

1. Under the conditions of a temperature of 300°C to 360°C, a hydrogenation pressure of 8 MPa to 12 MPa, a hydrogen-oil volume ratio of 600:1 to 1200:1, and a volumetric space velocity of 0.5 h -1 ~1.5 h -1 , carry out catalytic hydrogenation treatment to obtain hydrorefined oil; Perform true boiling point distillation on the obtained hydrofined oil to obtain hydrofined pitch in the distillation range of 350°C to 500°C.

3. The method for preparing needle coke by compound modification of medium and low temperature coal tar pitch according to claim 2, characterized in that, The specific process of the selective extraction treatment in step 2) is as follows: Mix the hydrofined pitch and the selective extractant in a mass ratio of 1 to 6:1, stir for 40 min to 80 min at a temperature of 80°C to 120°C, stand for 20 min to 60 min, after stratification, take the upper layer liquid to obtain an organic extract, and recover the selective extractant by vacuum distillation to obtain hydrogenated pitch rich in hydrogenated aromatics.

4. The method for preparing needle coke by medium and low temperature coal tar pitch composite modification according to claim 3, characterized in that, The specific process of the chain extension treatment in step 2) is as follows: Mix the hydrogenated pitch rich in hydrogenated aromatics and the chain extender in a mass ratio of 5 to 20:1, under a pressure condition of 1 MPa to 3 MPa, heat up to 350°C to 400°C at a heating rate of 1°C / min to 3°C / min, react for 2 h to 6 h, and cool to obtain modified pitch.

5. The method for preparing needle coke by complex modification of medium and low temperature coal tar pitch according to claim 2, characterized in that, The diluent is one or a mixture of two or more of 300 - 360°C fraction oil, coking heavy oil, No. 100 aromatic solvent oil and No. 150 aromatic solvent oil.

6. The method for preparing needle coke by medium and low temperature coal tar pitch composite modification according to claim 3, characterized in that, The selective extractant is one or a mixture of two or more of furfural, phenol, dimethyl sulfoxide, N,N-dimethylformamide, N-methylpyrrolidone and sulfolane.

7. The method for preparing needle coke by compound modification of medium and low temperature coal tar pitch according to claim 4, characterized in that, The chain extender is one or a mixture of two or more of polyacrylic acid, polyethylene glycol, oleic acid, methyl iodide and ethyl iodide.

8. The method for preparing needle coke by composite modification of medium and low temperature coal tar pitch according to claim 1 or 4, characterized in that, Step 3) is specifically as follows: Mix the modified pitch and the nucleating crystallization agent in a mass ratio of 10 to 50:1, under a reaction pressure of 0.5 MPa to 1.5 MPa, heat up to 400°C to 430°C at a heating rate of 0.5°C / min to 1.5°C / min, and keep the temperature constant for 2 to 6 h; add the metal-organic framework material in a mass ratio of 10 to 50:1 of the modified pitch to the metal-organic framework material, under a reaction pressure of 0.5 MPa to 1.5 MPa, heat up to 480°C to 500°C at a heating rate of 0.5°C / min to 1.5°C / min, and keep the temperature constant for 8 h to 12 h to prepare semicoke.

9. The method for preparing needle coke by composite modification of medium and low temperature coal tar pitch as claimed in claim 8, wherein, The nucleating crystallization agent is one or a mixture of two or more of carbon black, graphite, TiO2, graphene oxide, mica, alumina particles and mesophase pitch powder; the metal-organic framework material is one or a mixture of two or more of Ni-MOF, Co-MOF, Mn-MOF, Cu-MOF, Zn-MOF.

10. The method for preparing needle coke by complex modification of medium and low temperature coal tar pitch as claimed in claim 8, characterized in that, The calcination conditions in step 4) are as follows: heating up to 1200°C to 1500°C at a heating rate of 2°C / min to 5°C / min, and maintaining the temperature for calcination for 6 to 10 hours.

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