A method for preparing needle coke for graphite electrodes with high aspect ratio

Abstract

This invention discloses a process for producing needle coke with a high aspect ratio, belonging to the technical field of raw materials for graphite electrodes. The preparation method is characterized by: subjecting refined aromatic oil to delayed coking; after the coking reaction is completed, naturally cooling to room temperature and then directly removing the coke to obtain needle coke; the coking reaction is divided into three stages: the mesophase reaction stage, the directional coking stage, and the drying and solidification stage. The beneficial effects of this invention are: this invention creatively discovers a method for delayed coking of refined aromatic oil, allowing the mesophase to fully merge and develop; in the directional coking stage, the mesophase reaction enters the middle and late stages, ensuring the continued progress of the mesophase reaction while providing upward shear force to the coking system. Before the system viscosity begins to rise sharply, the upward shear force increases the aspect ratio of the coke.

Description

Technical Field

[0001] This invention belongs to the technical field of raw materials for graphite electrodes, and more specifically relates to a process for producing needle coke with a high aspect ratio. Background Technology

[0002] Graphite electrodes are the core conductive material in electric arc furnace steelmaking, and their quality directly determines the smelting efficiency and energy consumption level. With the development of large-scale electric furnaces and ultra-high power steelmaking technology, electrodes need to withstand greater current density, more severe thermal shock and mechanical impact, thus placing higher demands on their quality.

[0003] Needle char readily forms a highly oriented layered structure after graphitization, making it an irreplaceable raw material for producing ultra-high power graphite electrodes. Its coefficient of thermal expansion (CTE), powder resistivity, particle strength, and aspect ratio are strongly correlated with the electrical conductivity, thermal conductivity, and thermal shock resistance of graphite electrodes.

[0004] Most of the published patents and literature currently available focus on improving the conductivity and thermal shock resistance of graphite electrodes by enhancing the coefficient of thermal expansion (CTE), powder resistivity, and particle strength of needle coke. However, there is little research on improving the conductivity and thermal shock resistance of electrodes by increasing the aspect ratio of needle coke.

[0005] However, in the extrusion molding process of the graphite electrode production line, the aspect ratio of the needle coke has a crucial effect on its axial parallelism. The higher the aspect ratio, the better the axial parallelism, that is, the higher the aspect ratio of the needle coke, the better its anisotropy is.

[0006] Therefore, improving the aspect ratio of needle-shaped focal lengths is an important research direction for improving the electrical conductivity and thermal shock resistance of graphite electrodes. Summary of the Invention

[0007] This paper presents a method for preparing high aspect ratio needle coke for graphite electrodes. First, a high-range aromatic oil with a suitable amount of cycloalkane structure is prepared through vacuum cutting, hydrodesulfurization, and raw material blending. Then, using this oil as a raw material, a mesophase reaction, directional coking, and drying and solidification reaction are carried out to finally obtain a needle coke with high aspect ratio for graphite electrodes. The above method can significantly improve the aspect ratio of needle coke for graphite electrodes. Observation of different products using scanning electron microscopy revealed a significant improvement in morphology. After sampling and processing the improved products into 0.4-0.5 mm particles, statistical analysis under professional testing equipment showed that the aspect ratio of the samples was 0.583, and the resistivity of the product electrodes could reach 5.22 μΩ·m.

[0008] The specific technical solution of this invention to solve the above-mentioned technical problems is as follows: This method uses FCC slurry as raw material, and through vacuum cutting, hydrodesulfurization, aromatic extraction, raw material blending, and gradient coking reaction, high aspect ratio needle coke is obtained. The detailed process is as follows: Step 1: The FCC slurry is subjected to vacuum cutting to remove solid impurities, gum asphaltenes, and the lighter fraction of the distillation range, to obtain component 1; Step 2: Hydrogenation treatment is performed on component 1 after depressurization to remove impurities such as sulfur, nitrogen, and oxygen from the raw material, resulting in component 2; Step 3: Select FCC oil slurry for aromatic extraction treatment. The extraction treatment process is furfural extraction process. The preferred conditions are an oil-to-solvent ratio of 1-1.3 and an extraction temperature of 35℃-40℃; to obtain component 3 rich in cycloalkane structure. Step 4: After mixing component 2 obtained in step 2 and component 3 obtained in step 3 in a certain proportion, a refined aromatic oil with appropriate cycloalkane structure and high distillation range is obtained. The specifications are: cycloalkane content 23%-28%, four-component aromatic content 65%-70%, 5% distillation temperature 403℃, and 95% distillation temperature 509℃. Step 5: The refined aromatic oil obtained in Step 4 is subjected to delayed coking. After the coking reaction is completed, it is naturally cooled to room temperature and then the coke is removed directly to obtain needle coke. The delayed coking temperature curve is as follows: 455℃ (constant temperature for 25h) → 455℃ (constant temperature for 20h) → 10℃ / min heating rate → 485℃ (constant temperature for 10h), matched with a gas injection process of 0.5L / min (25h) → 5L / min (30h). The characteristics of delayed coking are: ① The temperature is increased in a uniform gradient; ② The coking reaction is divided into three stages: the mesophase reaction stage, the directional coking stage, and the drying and solidification stage; ③ The temperature of the mesophase reaction stage is consistent with that of the directional coking stage, and is lower than that of the drying and curing stage. The temperature difference between the two stages is ΔT=30℃, and the feeding time is t=55h. ④ The gas injection rate during the directional coking stage is consistent with that during the drying and curing stage, and is higher than that during the mesophase reaction stage. The difference between the gas injection rates during the mesophase reaction stage and the gas injection rates during the mesophase reaction stage is ΔF = 4.5 L / min. The characteristic of the needle coke after decoking is that its aspect ratio is 0.583. The resistivity of the graphite electrode rod made from this needle coke after subsequent processing is 5.22 μΩ·m. The aspect ratio data was detected using the dynamic image analyzer-3000 from Jiangsu Changzhou MiPu Technology Co., Ltd., and the electrode resistivity was detected using the method specified in GB / T 24525-2009.

[0009] The beneficial effects of this invention are: This invention creatively discovers a delayed coking method for refined aromatic oils, which allows for the full fusion and development of the mesophase. During the directional coking stage, the mesophase reaction enters the middle and late stages, ensuring the continuous progress of the mesophase reaction while providing an upward shear force to the coking system. Before the system viscosity begins to rise sharply, the upward shear force improves the orientation degree of the coke, i.e., the aspect ratio. During the drying and solidification stage, the mesophase reaction is basically completed, and further increasing the reaction temperature ensures that the reaction proceeds fully. A creative method of delayed coking using refined aromatic oil was adopted. In particular, when refined aromatic oil with an appropriate proportion of cycloalkane components is used in the mesophase reaction process, an appropriate amount of hydrogen free radicals can be formed in the system, which inhibits the increase in reaction space steric hindrance and the excessively rapid increase in system viscosity caused by excessive binding between aromatic free radicals. The active sites of polycyclic aromatic hydrocarbons continuously bind to form a larger molecular configuration that tends to be planar. As this molecular configuration continues to increase, the mesophase eventually forms a streamlined structure with a high degree of orientation under the action of its own surface tension and the matching shear force, which is characterized by the high aspect ratio of needle coke. Attached Figure Description

[0010] Appendix Figure 1 This is a scanning electron microscope image of the needle-shaped coke produced in Example 1; Appendix Figure 2 This is a scanning electron microscope image of the needle-shaped coke produced in Example 2; Appendix Figure 3 This is a scanning electron microscope image of the needle-shaped coke produced in Example 3; Appendix Figure 4 This is a scanning electron microscope image of the needle-shaped coke produced in Comparative Example 1; Appendix Figure 5 This is a scanning electron microscope image of the needle-shaped coke produced in Comparative Example 2; Appendix Figure 6 This is a scanning electron microscope image of the needle-shaped coke produced in Comparative Example 3; Appendix Figure 7 This is a scanning electron microscope image of the needle-shaped coke produced in Comparative Example 4; Appendix Figure 8 This is a scanning electron microscope image of the needle-shaped coke produced in Comparative Example 5; Appendix Figure 9 This is a scanning electron microscope image of the needle-shaped coke produced in Comparative Example 6; Appendix Figure 10 This is a scanning electron microscope image of the needle-shaped coke produced in Comparative Example 7; Appendix Figure 11 This is a scanning electron microscope image of the needle-shaped coke produced in Comparative Example 8; Appendix Figure 12 This is a scanning electron microscope image of the needle-shaped coke produced in Comparative Example 9. Detailed Implementation

[0011] The specific details in the description of this invention are merely for the purpose of fully understanding the embodiments of the invention. However, those skilled in the art should know that the implementation of the invention is not limited to these details. In addition, well-known structures and functions have not been described or shown in detail to avoid obscuring the key points of the embodiments of the invention. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0012] Specific embodiments of the present invention: To better understand the present invention, specific embodiments are described. It is worth emphasizing that the effects of these embodiments are not substantially different from those of various embodiments within the scope of protection of the present invention, including their respective reagents and reagent content ratios. All of them can achieve the effects described in the present invention and solve the above-mentioned problems. Other combinations are not described here. Example 1: This example provides a multi-gradient coking reaction method, including: using FCC slurry as raw material, preparing a high-range aromatic oil with an appropriate amount of cycloalkane structure through vacuum cutting, hydrodesulfurization, and raw material blending. The indicators are: cycloalkane content 23%, four-component aromatic content 65%-70%, 5% distillation temperature 403℃, and 95% distillation temperature 509℃. Then, using this as raw material, carry out mesophase reaction, directional coking, and drying and solidification reaction to finally obtain needle coke product for graphite electrodes. The specific coking temperature curve, gas injection process, and product parameters are shown in Table 1.

[0013] Example 2: This example provides a multi-gradient coking reaction method, including: using FCC slurry as raw material, preparing a high-range aromatic oil with an appropriate amount of cycloalkane structure through vacuum cutting, hydrodesulfurization, and raw material blending. The indicators are: cycloalkane content 26%, four-component aromatic content 65%-70%, 5% distillation temperature 403℃, and 95% distillation temperature 509℃. Then, using this as raw material, carrying out mesophase reaction, directional coking, and drying and solidification reaction, finally obtaining needle coke product for graphite electrodes. The specific coking temperature curve, gas injection process, and product parameters are shown in Table 1.

[0014] Example 3: This example provides a multi-gradient coking reaction method, including: using FCC slurry as raw material, preparing a high-range aromatic oil with an appropriate amount of cycloalkane structure through vacuum cutting, hydrodesulfurization, and raw material blending. The indicators are: cycloalkane content 28%, four-component aromatic content 65%-70%, 5% distillation temperature 403℃, and 95% distillation temperature 509℃. Then, using this as raw material, carry out mesophase reaction, directional coking, and drying and solidification reaction to finally obtain needle coke product for graphite electrodes. The specific coking temperature curve, gas injection process, and product parameters are shown in Table 1.

[0015] To more intuitively demonstrate the technological advantages of this invention, a comparison is made between the preparation method of the graphite electrode using high aspect ratio needle coke and the equivalent substitution method using the same process.

[0016] Comparative Example 1: The raw material properties and preparation method of this comparative example are the same as those of Example 2. The difference is that the stepwise gas injection process was not used in the preparation process of this comparative example. The gas injection process was 1L / min (55h) to obtain oil-based needle coke for graphite electrodes. The specific raw material properties, production process and product indicators are shown in Table 1.

[0017] Comparative Example 2: The raw material properties and preparation method of this comparative example are the same as those of Example 2. The difference is that the stepwise gas injection process was not used in the preparation process of this comparative example. The gas injection process was 2L / min (55h) to obtain oil-based needle coke for graphite electrodes. The specific raw material properties, production process and product indicators are shown in Table 1.

[0018] Comparative Example 3: The raw material properties and preparation method of this comparative example are the same as those of Example 2. The difference is that the stepwise gas injection process was not used in the preparation process of this comparative example. The gas injection process was 3L / min (55h) to obtain oil-based needle coke for graphite electrodes. The specific raw material properties, production process and product indicators are shown in Table 1.

[0019] Comparative Example 4: The raw material properties and preparation method of this comparative example are the same as those of comparative example 2. The difference is that the coking temperature curve is different in the preparation process of this comparative example. The coking temperature curve is 420 (25h) → 420 (20h) → 450 (10h), which yields oil-based needle coke for graphite electrodes. The specific raw material properties, production process and product indicators are shown in Table 1.

[0020] Comparative Example 5: The raw material properties and preparation method of this comparative example are the same as those of comparative example 2. The difference is that the coking temperature curve is different in the preparation process of this comparative example. The coking temperature curve is 470 (25h) → 470 (20h) → 500 (10h), which yields oil-based needle coke for graphite electrodes. The specific raw material properties, production process and product indicators are shown in Table 1.

[0021] Comparative Example 6: The raw material properties and preparation method of this comparative example are the same as those of Example 2. The difference is that the coking temperature curve is different in the preparation process of this comparative example. The coking temperature curve is 420 (25h) → 420 (20h) → 450 (10h) to obtain oil-based needle coke for graphite electrodes. The specific raw material properties, production process and product indicators are shown in Table 1.

[0022] Comparative Example 7: The raw material properties and preparation method of this comparative example are the same as those of Example 2. The difference is that the coking temperature curve is different in the preparation process of this comparative example. The coking temperature curve is 470 (25h) → 470 (20h) → 500 (10h) to obtain oil-based needle coke for graphite electrodes. The specific raw material properties, production process and product indicators are shown in Table 1.

[0023] Comparative Example 8: The preparation method is the same as in Example 2, except that the refined aromatic oil used in this comparative example has a different cycloalkanes content. The cycloalkanes content is 12%, and the four-component aromatic content is 65%-70%, resulting in oil-based needle coke for graphite electrodes. The specific raw material properties, production process, and product indicators are shown in Table 1.

[0024] Comparative Example 9: The preparation method is the same as in Example 2, except that the refined aromatic oil used in this comparative example has a different cycloalkanes content. The cycloalkanes content is 32%, and the four-component aromatic content is 65%-70%, resulting in oil-based needle coke for graphite electrodes. The specific raw material properties, production process, and product indicators are shown in Table 1.

[0025] The aspect ratios of the above embodiments and comparative examples were detected using a dynamic image analyzer-3000 from Jiangsu Changzhou MiPu Technology Co., Ltd., and the electrode resistivity was detected using the method specified in GB / T 24525-2009. The detection data are as follows:

[0026] Analysis of the data in Table 1 shows that: (1) In Example 1, the aspect ratio of the product was 0.503, and the resistivity of the corresponding electrode rod was 5.65 μΩ·m. The reason is that the refined aromatic oil with a suitable proportion of cycloalkane components, during the coking process, the coking temperature curve corresponding to Example 1 is: 455℃ (constant temperature for 25h) → 455℃ (constant temperature for 20h) → 10℃ / min heating → 485℃ (constant temperature for 10h), matched with the gas injection process: 0.5L / min (25h) → 5L / min (30h), which can provide a lower temperature in the mesophase reaction stage, so that the mesophase can fully merge and develop, and at the same time, the lower The gas injection rate will not cause unnecessary disturbance to the development process. During the directional coking stage, the mesophase reaction enters the middle and late stages. This process provides a lower temperature while increasing the gas injection rate. While ensuring the mesophase reaction continues, it provides an upward shear force to the coking system. Before the system viscosity begins to rise sharply, the upward shear force improves the orientation degree of the coke, i.e., the aspect ratio. During the drying and curing stage, the mesophase reaction is basically completed. Further increasing the reaction temperature allows the reaction to proceed fully and increases the degree of crosslinking between carbon layers. To maintain sufficient shear force and sufficient escape of volatiles in the system, the gas injection rate remains unchanged.

[0027] Its microstructure was observed using a scanning electron microscope, such as... Figure 1 As shown, under the 500μm standard, the product has a good internal streamline structure and the material has a long strip shape with a length-to-width ratio of 0.503, corresponding to an electrode rod resistivity of 5.65μΩ·m.

[0028] (2) In Example 2, the aspect ratio of the product was 0.583, and the resistivity of the corresponding electrode rod was 5.22 μΩ·m; The reason is that when refined aromatic oil with a suitable proportion of cycloalkane components undergoes the mesophase reaction process, the coking temperature curve corresponding to Example 2 is 455℃ (constant temperature for 25h) → 455℃ (constant temperature for 20h) → 10℃ / min heating → 485℃ (constant temperature for 10h), matched with the gas injection process: 0.5L / min (25h) → 5L / min (30h). This can provide a lower temperature in the mesophase reaction stage, allowing the mesophase to fully merge and develop. At the same time, the lower gas injection volume will not cause unnecessary disturbance to the development process. In the directional coking stage, the mesophase reaction enters the middle and late stages. This process provides a lower temperature while increasing the gas injection volume. While ensuring the mesophase reaction continues, it provides an upward shear force to the coking system. Before the system viscosity begins to rise sharply, the upward shear force improves the orientation degree of the coke, i.e., the aspect ratio. In the drying and curing stage, the mesophase reaction is basically completed. Further increasing the reaction temperature allows the reaction to proceed fully, increasing the degree of crosslinking between carbon layers. In order to maintain sufficient shear force and sufficient escape of volatiles in the system, the gas injection volume remains unchanged.

[0029] Its microstructure was observed using a scanning electron microscope, such as... Figure 2 As shown, under the 500μm standard, the product has a good internal streamline structure and the material has a long strip shape with a length-to-width ratio of 0.583, corresponding to an electrode rod resistivity of 5.22μΩ·m.

[0030] (3) In Example 3, the aspect ratio of the product was 0.524, and the resistivity of the corresponding electrode rod was 5.51 μΩ·m. The reason is that when the refined aromatic oil with a suitable proportion of cycloalkane components undergoes the mesophase reaction process, the coking temperature curve corresponding to Example 3 is 455℃ (constant temperature for 25h) → 455℃ (constant temperature for 20h) → 10℃ / min heating → 485℃ (constant temperature for 10h), which matches the gas injection process: 0.5L / min (25h) → 5L / min (30h). This can provide a lower temperature in the mesophase reaction stage, allowing the mesophase to fully merge and develop. A lower gas injection rate will not cause unnecessary disturbance to the development process. During the directional coking stage, the mesophase reaction enters the middle and late stages. This process provides a lower temperature while increasing the gas injection rate. While ensuring the mesophase reaction continues, it provides an upward shear force to the coking system. Before the system viscosity begins to rise sharply, the upward shear force improves the orientation degree of the coke, i.e., the aspect ratio. During the drying and curing stage, the mesophase reaction is basically completed. Further increasing the reaction temperature allows the reaction to proceed fully and increases the degree of crosslinking between carbon layers. To maintain sufficient shear force and sufficient escape of volatiles in the system, the gas injection rate remains unchanged.

[0031] Its microstructure was observed using a scanning electron microscope, such as... Figure 3 As shown, under the 500μm standard, the internal structure of the product has a good streamline shape, the material has a long strip shape, the aspect ratio is 0.524, and the corresponding electrode rod resistivity is 5.51μΩ·m. Compared with Example 2, the aspect ratio is lower, and the corresponding electrode rod resistivity is slightly higher, but the overall level is better.

[0032] (4) The aspect ratio of the product obtained in Comparative Example 1 is 0.386, and the resistivity of the corresponding electrode rod is 6.39 μΩ·m; The reason is that when refined aromatic oil with a suitable proportion of cycloalkane components undergoes the mesophase reaction process, the coking temperature curve corresponding to Comparative Example 1 is consistent with that of Example 2: 455℃ (25h constant temperature) → 455℃ (20h constant temperature) → 10℃ / min heating → 485℃ (10h constant temperature), matched with a gas injection process of 1L / min (55h). Although a lower temperature is provided in the mesophase reaction stage and the mesophase develops relatively well, in the directional coking stage, the mesophase reaction enters the middle and late stages. Compared with the process of Example 2, this process does not significantly increase the gas injection volume and does not provide upward shear force, resulting in insufficient orientation of the mesophase. Ultimately, the aspect ratio is low, and the resistivity of the corresponding electrode rod of the product is high.

[0033] Its microstructure was observed using a scanning electron microscope, such as... Figure 4 As shown, under the 500μm standard, the product structure has poor streamline and the material does not have a good elongated shape. The aspect ratio is 0.386, and the corresponding electrode rod resistivity is 6.39μΩ·m.

[0034] (5) The aspect ratio of the product obtained in Comparative Example 2 is 0.425, and the resistivity of the corresponding electrode rod is 6.13 μΩ·m; The reason is that when refined aromatic oil with a suitable proportion of cycloalkane components undergoes the mesophase reaction process, the coking temperature curve corresponding to Comparative Example 2 is consistent with that of Example 1: 455℃ (25h constant temperature) → 455℃ (20h constant temperature) → 10℃ / min heating → 485℃ (10h constant temperature), matched with a gas injection process of 2L / min (55h). Although a lower temperature is provided in the mesophase reaction stage, the mesophase development is relatively good. However, in the directional coking stage, the mesophase reaction enters the middle and late stages. Compared with the process of Example 2, this process does not significantly increase the gas injection volume and does not provide upward shear force, resulting in insufficient orientation of the mesophase. As a result, the aspect ratio is lower and the resistivity of the corresponding electrode rod of the product is higher. However, compared with Comparative Example 1, the gas injection volume is increased throughout the process, and the aspect ratio and resistivity of the product electrode rod are better than those of Comparative Example 1.

[0035] Its microstructure was observed using a scanning electron microscope, such as... Figure 5 As shown, under the 500μm standard, the product structure has poor streamline and the material does not have a good elongated shape. The aspect ratio is 0.425, and the corresponding electrode rod resistivity is 6.13μΩ·m.

[0036] (6) The aspect ratio of the product obtained in Comparative Example 3 was 0.392, and the resistivity of the corresponding electrode rod was 6.31 μΩ·m; The reason is that when the refined aromatic oil with a suitable proportion of cycloalkane components undergoes the mesophase reaction process, the coking temperature curve corresponding to Comparative Example 3 is consistent with that of Example 2: 455℃ (constant temperature for 25h) → 455℃ (constant temperature for 20h) → 10℃ / min heating → 485℃ (constant temperature for 10h), matched with a gas injection process of 3L / min (55h). Compared with the process of Example 2, this process has an excessively large gas injection volume. Although it provides a lower temperature in the mesophase reaction stage, the mesophase development is greatly disturbed by the gas injection, and it fails to fully merge and develop. As a result, the mesophase does not have sufficient orientation within the same curing cycle, and the final aspect ratio is lower, resulting in a higher resistivity of the corresponding electrode rod of the product.

[0037] Its microstructure was observed using a scanning electron microscope, such as... Figure 6As shown, under the 500μm standard, the internal structure of the product has poor streamline and the material does not have a good elongated shape. The aspect ratio is 0.392, and the corresponding electrode rod resistivity is 6.31μΩ·m.

[0038] (7) The aspect ratio of the product obtained in Comparative Example 4 is 0.411, and the resistivity of the corresponding electrode rod is 6.19 μΩ·m; The reason is that when refined aromatic oil with a suitable proportion of cycloalkane components undergoes the mesophase reaction process, the coking temperature curve corresponding to Comparative Example 4 is: 420℃ (constant temperature for 25h) → 420℃ (constant temperature for 20h) → 10℃ / min heating → 450℃ (constant temperature for 10h), matched with the gas injection process: 2L / min (55h). This gas injection process is consistent with the gas injection process of Comparative Example 2, but the coking temperature curve provides a lower temperature than that of Comparative Example 2, resulting in a lower overall heat supply during the coking process, an excessively slow reaction, insufficient reaction, and failure to form a broad mesophase. However, the solidification rate of the system does not decrease within the limited feeding time, ultimately resulting in the product not forming a broad streamlined microstructure, having a low aspect ratio, and a high resistivity of the corresponding electrode rod.

[0039] Its microstructure was observed using a scanning electron microscope, such as... Figure 7 As shown, when observed under the 500μm standard, the internal structure of the product has poor streamline and the material does not have a good elongated shape. The measured aspect ratio of 0.411 corresponds to an electrode rod resistivity of 6.19μΩ·m.

[0040] (8) The aspect ratio of the product obtained in Comparative Example 5 was 0.407, and the resistivity of the corresponding electrode rod was 6.02 μΩ·m; The reason is that when refined aromatic oil with a suitable proportion of cycloalkane components undergoes the mesophase reaction process, the coking temperature curve corresponding to Comparative Example 5 is: 470℃ (constant temperature for 25h) → 470℃ (constant temperature for 20h) → 10℃ / min heating → 500℃ (constant temperature for 10h), matched with the gas injection process: 2L / min (55h). This gas injection process is consistent with the gas injection process of Comparative Example 2, but the coking temperature curve provides a higher temperature than that of Comparative Example 2. Under this condition, the initial temperature of the coking reaction is too high, which leads to an excessively fast reaction rate of the mesophase, ultimately causing the viscosity of the system to rise too quickly. Some mesophase regions have not fully fused before solidifying into coke, and the final product cannot form a wide-area streamlined microstructure, with a low aspect ratio and a high resistivity of the corresponding electrode rod.

[0041] Its microstructure was observed using a scanning electron microscope, such as... Figure 8 As shown, when observed under the 500μm standard, the internal structure of the product has poor streamline and the material does not have a good elongated shape. The measured aspect ratio of 0.407 corresponds to an electrode rod resistivity of 6.02μΩ·m.

[0042] (9) The aspect ratio of the product obtained in Comparative Example 6 was 0.376, and the resistivity of the corresponding electrode rod was 6.67 μΩ·m; The reason is that when refined aromatic oil with a suitable proportion of cycloalkane components undergoes the mesophase reaction process, the coking temperature curve corresponding to Comparative Example 6 is: 420℃ (constant temperature for 25h) → 420℃ (constant temperature for 20h) → 10℃ / min heating → 450℃ (constant temperature for 10h), matched with the gas injection process: 0.5L / min (25h) → 5L / min (30h). This gas injection process is consistent with the gas injection process of Example 2, but the coking temperature curve provides a lower temperature than that of Example 2, resulting in a lower overall heat supply during the coking process, an excessively slow reaction, and the failure to form a broad mesophase. However, the solidification rate of the system did not decrease within the limited feeding time, ultimately resulting in the product not forming a broad streamlined microstructure, having a low aspect ratio, and a high resistivity of the corresponding electrode rod.

[0043] Its microstructure was observed using a scanning electron microscope, such as... Figure 9 As shown, when observed under the 500μm standard, the internal structure of the product has poor streamline and the material does not have a good elongated shape. The measured aspect ratio of 0.376 corresponds to an electrode rod resistivity of 6.67μΩ·m.

[0044] (10) Comparative Example 7 shows that the aspect ratio of the product is 0.381 and the resistivity of the corresponding electrode rod is 6.45 μΩ·m; The reason is that when refined aromatic oil with a suitable proportion of cycloalkane components undergoes the mesophase reaction process, the coking temperature curve corresponding to Comparative Example 7 is: 470℃ (constant temperature for 25h) → 470℃ (constant temperature for 20h) → 10℃ / min heating → 500℃ (constant temperature for 10h), and the matching gas injection process is: 0.5L / min (25h) → 5L / min (30h). This gas injection process is consistent with the gas injection process of Example 2, but the coking temperature curve provides a higher temperature than that of Example 2. Under this condition, the initial temperature of the coking reaction is too high, which leads to an excessively fast mesophase reaction rate, ultimately causing the viscosity of the system to rise too quickly. Some mesophase regions have not yet fully developed and merged before solidifying into coke. As a result, the final product cannot form a wide-area streamlined microstructure, has a low aspect ratio, and the resistivity of the corresponding electrode rod is too high.

[0045] Its microstructure was observed using a scanning electron microscope, such as... Figure 10 As shown, when observed under the 500μm standard, the internal structure of the product has poor streamline and the material does not have a good elongated shape. The measured aspect ratio of 0.381 corresponds to an electrode rod resistivity of 6.45μΩ·m.

[0046] (11) The aspect ratio of the product obtained in Comparative Example 8 was 0.393, and the resistivity of the corresponding electrode rod was 6.26 μΩ·m; The reason is that the raw material of Comparative Example 8 contains less cycloalkanes, which means less hydrogen-donating components can be provided during coking. This results in a faster rate of viscosity increase in the coking system, which prevents the mesophase from fully merging and developing. Although the process control is good, the resulting product still fails to achieve a high degree of orientation, i.e., a low aspect ratio.

[0047] Its microstructure was observed using a scanning electron microscope, such as... Figure 11 As shown, under the 500μm standard, the internal structure of the product has poor streamline and the material does not have a good elongated shape. The aspect ratio is 0.393, and the corresponding electrode rod resistivity is 6.26μΩ·m.

[0048] (12) The aspect ratio of the product obtained in Comparative Example 9 was 0.388, and the resistivity of the corresponding electrode rod was 6.37 μΩ·m; The reason is that the raw material of Comparative Example 9 contains too much cycloalkane. During the coking process, the excessive cycloalkane component, after the cycloalkane structure breaks, excessively combines with the side chain of the aromatic molecule or the free radical after the methylene structure breaks, making the molecular structure more complex. The steric hindrance of the intermolecular reaction increases, the planar structure deteriorates, and the viscosity of the system increases rapidly. As a result, the product cannot form a high aspect ratio.

[0049] Its microstructure was observed using a scanning electron microscope, such as... Figure 12 As shown, when observed under the 500μm standard, the internal structure of the product has poor streamline and the material does not have a good elongated shape. The aspect ratio is 0.388, and the corresponding electrode rod resistivity is 6.37μΩ·m.

[0050] In summary: This invention creatively discovers a delayed coking method for refined aromatic oils, which allows for the full fusion and development of the mesophase. During the directional coking stage, the mesophase reaction enters the middle and late stages, ensuring the continuous progress of the mesophase reaction while providing an upward shear force to the coking system. Before the system viscosity begins to rise sharply, the upward shear force improves the orientation degree of the coke, i.e., the aspect ratio. During the drying and solidification stage, the mesophase reaction is basically completed, and further increasing the reaction temperature ensures that the reaction proceeds fully. A creative method for delayed coking using refined aromatic oil was employed. In particular, when refined aromatic oil with an appropriate proportion of cycloalkane components was used in the mesophase reaction process, a suitable amount of hydrogen free radicals were formed in the system. These free radicals "temporarily bind" to the short aliphatic side chain structures of polycyclic aromatic hydrocarbons in the feedstock after bond breaking, thereby inhibiting the increase in steric hindrance and the excessively rapid increase in system viscosity caused by excessive binding between aromatic free radicals. During the continuous mesophase reaction, this "temporary binding" was further broken, and the active sites of polycyclic aromatic hydrocarbons continued to bind to form a larger, planar molecular configuration. As this molecular configuration continued to increase, the mesophase, under the action of its own surface tension and the aforementioned matching shear force, eventually formed a streamlined structure with a high degree of orientation, exhibiting the high aspect ratio characteristics of needle coke.

Claims

1. A method for preparing needle coke for graphite electrodes with high aspect ratio, characterized in that... The preparation method is as follows: the refined aromatic oil is subjected to delayed coking treatment. After the coking reaction is completed, it is naturally cooled to room temperature and then the coke is removed directly to obtain needle coke. The coking reaction is divided into three stages: the mesophase reaction stage, the directional coking stage, and the drying and solidification stage. The temperature of the mesophase reaction stage is consistent with that of the directional coking stage, and is lower than that of the drying and curing stage. The temperature difference between the mesophase reaction stage and the drying and curing stage is ΔT=30℃, and the feeding time is t=55h. The gas injection rate during the directional coking stage is consistent with that during the drying and curing stage, and is higher than that during the mesophase reaction stage. The difference between the gas injection rates during the mesophase reaction stage and the mesophase reaction stage is ΔF = 4.5 L / min.

2. The method for preparing needle coke for graphite electrodes with high aspect ratio according to claim 1, characterized in that... The intermediate phase reaction stage maintains the same temperature as the directional coking stage, but is lower than the drying and curing stage temperature. The temperature difference between the intermediate phase reaction stage and the drying and curing stage is ΔT=30℃, and the feeding time is t=55h. The delayed coking temperature curve is as follows: 455℃ constant temperature for 25h → 455℃ constant temperature for 20h → 10℃ / min heating → 485℃ constant temperature for 10h.

3. The method for preparing needle coke for graphite electrodes with high aspect ratio according to claim 1, characterized in that... The gas injection rate during the directional coking stage is consistent with that during the drying and curing stage, and is higher than that during the mesophase reaction stage. The difference between the gas injection rate during the mesophase reaction stage and that during the mesophase reaction stage is ΔF = 4.5 L / min. The gas injection process is as follows: 0.5 L / min for 25 h → 5 L / min for 30 h.

4. The method for preparing needle coke for graphite electrodes with high aspect ratio according to any one of claims 1-3, characterized in that... The refined aromatic oil contains 23%-28% cycloalkanes, 65%-70% of the four aromatic components, and has a 5% distillation temperature of 403℃ and a 95% distillation temperature of 509℃.

5. The method for preparing needle coke for graphite electrodes with high aspect ratio according to claim 4, characterized in that... The method for preparing the refined aromatic oil: Step 1: The FCC slurry is subjected to vacuum cutting to remove solid impurities, gum asphaltenes, and the lighter fraction of the distillation range, to obtain component 1; Step 2: Hydrogenation treatment is performed on component 1 after depressurization to remove impurities such as sulfur, nitrogen, and oxygen from the raw material, resulting in component 2; Step 3: Select FCC oil slurry for aromatic extraction treatment. The extraction treatment process is furfural extraction process. The preferred conditions are an oil-to-solvent ratio of 1-1.3 and an extraction temperature of 35℃-40℃; to obtain component 3 rich in cycloalkane structure. Step 4: Mix component 2 obtained in step 2 with component 3 obtained in step 3 until homogeneous to obtain refined aromatic oil.

6. The method for preparing needle coke for graphite electrodes with high aspect ratio according to claim 4, characterized in that... The needle coke has an aspect ratio of 0.503-0.583 and is used to manufacture graphite electrode rods.

7. The method for preparing needle coke for graphite electrodes with high aspect ratio according to claim 5, characterized in that... The needle coke has an aspect ratio of 0.503-0.583 and is used to manufacture graphite electrode rods.

8. The method for preparing needle coke for graphite electrodes with high aspect ratio according to claim 6 or 7, characterized in that... The resistivity of the graphite electrode rod is 5.22-5.65 μΩ·m.

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