High strength pitch coke and method of its calcination

Abstract

The application discloses high-strength pitch coke and a calcining method thereof. The pitch coke is obtained by using a two-section heat preservation calcining process. In the calcining process, the pitch coke is heated from room temperature to low-temperature section heat preservation, the pitch coke is fully carbonized and volatile components are discharged; then the pitch coke is continuously heated to high-temperature section heat preservation, the pitch coke is subjected to polycondensation reaction and the crystal structure and atomic arrangement of the pitch coke are regularized, and the pitch coke is naturally cooled after the heat preservation, so that the high-strength pitch coke is obtained. The application can improve the particle strength of the pitch coke, so that the performance of the pitch coke as special graphite aggregate is optimized.

Description

Technical Field

[0001] This invention relates to the field of special graphite materials technology, and more specifically, to a high-strength pitch coke and its calcination method. Background Technology

[0002] Specialty graphite, also known as high-strength, high-density, and high-purity graphite, refers to graphite products with high strength, high density, and high purity. Based on its microstructure, it can be further classified into coarse-grained graphite, fine-grained graphite, and ultrafine-grained graphite. Specialty graphite has irreplaceable applications in chemical, nuclear, rare earth smelting, and semiconductor industries. With the rapid development of these industries, the market demand for specialty graphite is accelerating year by year.

[0003] Pitch coke is a type of coke obtained from coal tar pitch through delayed coking and high-temperature calcination. Pitch coke generally has low ash and sulfur content, a dense structure, high particle mechanical strength and wear resistance, and is easily graphitized, making it an ideal aggregate for high-strength specialty graphite. To further improve the performance of graphite products, in addition to optimizing the forming and calcination processes of specialty graphite, improving and enhancing the performance of pitch coke as a raw material is also a feasible method.

[0004] Chinese patents CN118270761B and CN118623634A optimize the calcination process of petroleum coke from the perspectives of raw material preparation, heat utilization, and calcination equipment. Liu Changming et al. published a calcination process for coal-based needle coke, mainly discussing the key points of calcination temperature control when using a rotary kiln to calcine coal-based needle coke. Li Fachuang et al. published the effects of high-temperature heat treatment on the structure and properties of pitch coke, studying the influence of the calcination endpoint temperature of 1000-1450℃ on the properties of pitch coke. The results showed that high temperature is beneficial for the removal of impurities, increasing crystallinity, increasing true density, and reducing resistivity. Fang Ning et al. published the effects of different types of petroleum coke and their calcination degrees on the properties of the calcined coke, studying three types of petroleum coke calcined at 800-1100℃. The results showed that sulfur and volatile matter are mainly discharged before 800℃, and the reactivity and resistivity of the calcined coke decrease with increasing calcination temperature. Cheng Junxia et al. published the evolution law of coke microcrystal structure during the calcination of coal-based needle coke, and studied the crystal structure properties of needle coke obtained with different heating rates and calcination temperatures. The results showed that the slower the heating rate and the higher the calcination temperature, the more conducive it is to the development of graphite microcrystals and the improvement of crystal structure. Sun Xiuhuan published a discussion on the calcination conditions of coal-based needle coke, and found that the thermal expansion coefficient of needle coke can be effectively reduced by the method of "low-temperature calcination-cooling-high-temperature calcination". Most of the above technologies are studies on the calcination of needle coke, which improve the true density, reduce resistivity and reduce the thermal expansion coefficient by controlling process parameters such as calcination temperature and heating rate, thereby improving the performance of graphite electrodes prepared from needle coke. There is less research on the calcination of pitch coke. Special graphite products used in semiconductor, nuclear industry and other fields require pitch coke as aggregate to have mechanical properties in addition to thermal expansion coefficient (generally characterized by the crushing strength of particles). However, the above technologies do not involve methods or research on improving the mechanical properties of coke through calcination. Summary of the Invention

[0005] In view of the deficiencies in the existing technology, the purpose of this invention is to provide a high-strength pitch coke and its calcination method, which optimizes the mechanical properties of the pitch coke and improves its crush resistance by adjusting the calcination temperature regime.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The first aspect of this invention provides a calcination method for high-strength pitch coke, wherein the raw pitch coke is produced by a two-stage heat preservation calcination process.

[0008] During the calcination process, the raw pitch coke is heated from room temperature to a low-temperature section and held at that temperature. The raw pitch coke is fully carbonized and volatiles are released. Then, the temperature is further increased to a high-temperature section and held at that temperature. The pitch coke undergoes a condensation reaction and its crystal structure and atomic arrangement are regularized. After the holding period, it is naturally cooled to obtain high-strength pitch coke.

[0009] Preferably, the calcination process of the raw pitch coke involves placing the raw pitch coke in a graphite crucible and calcining it under nitrogen protection, with a heating rate of 2–20 °C / min.

[0010] Preferably, the low-temperature section has a heat preservation temperature of 400–700°C and a heat preservation time of 10–120 minutes.

[0011] Preferably, the high-temperature section has a heat preservation temperature of 1000–1300°C and a heat preservation time of 30–90 minutes.

[0012] The second aspect of the present invention provides a high-strength pitch coke prepared by a calcination method as described in the first aspect of the present invention.

[0013] Preferably, the crushing strength coefficient of the 1-2 mm particles of the special graphite aggregate asphalt coke is ≥54%, and the crushing strength coefficient of the 2-4 mm particles is ≥45.5%.

[0014] The present invention has the following advantages:

[0015] This invention employs a two-stage heat preservation calcination method to calcine raw pitch coke. During the low-temperature heat preservation, some volatiles are released, and unreacted heavy molecules undergo further reaction. This avoids the large-scale escape of volatiles at high temperatures, which could create pores or directly form loose foam carbon, thus affecting the strength of the pitch coke. During high-temperature calcination, the pitch coke further undergoes a condensation reaction, and its crystal structure and atomic arrangement gradually become more regular, achieving the required true density, resistivity, and other properties. Therefore, compared to pitch coke calcined by traditional methods, pitch coke calcined according to this invention exhibits a slight change in true density and resistivity, while also showing improved crushing strength of its particles, thereby optimizing the performance of pitch coke as a special graphite aggregate. Detailed Implementation

[0016] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with embodiments.

[0017] This invention discloses a calcination method for high-strength pitch coke. The pitch coke raw coke is calcined using a two-stage heat preservation process. During the calcination process, the pitch coke raw coke is heated from room temperature to a low-temperature stage for heat preservation, during which the pitch coke raw coke is fully carbonized and volatiles are released. Then, the temperature is further increased to a high-temperature stage for heat preservation, during which the pitch coke undergoes pyrolysis and condensation reactions and undergoes regularization of its crystal structure and atomic arrangement, making the carbon atom arrangement more regular and gradually tending towards a graphite structure. After the heat preservation is completed, the coke is naturally cooled to obtain high-strength pitch coke.

[0018] In the above-mentioned two-stage heat preservation calcination process, the calcination temperature curve has two heat preservation sections: the low-temperature section has a heat preservation temperature of 400-700℃ and a heat preservation time of 10-120 minutes. During the low-temperature heat preservation, the pitch coke is further carbonized and some volatiles are released. At the same time, heavy molecules are further polymerized, which avoids the large amount of volatiles escaping at high temperatures, which would create pores or directly form loose foam carbon, thus affecting the strength; the high-temperature section has a heat preservation temperature of 1000-1300℃ and a heat preservation time of 30-90 minutes. In the high-temperature section, the raw pitch coke can undergo further condensation reaction and crystal structure regularization. The performance indicators of the pitch coke after high-temperature calcination can meet the product requirements.

[0019] In the above calcination process, the calcination process of raw pitch coke can be carried out by placing the raw pitch coke in a graphite crucible or other equipment or device capable of calcination, and calcining it under the protection of nitrogen or inert atmosphere. The heating rate of the calcination process is 2 to 20 °C / min.

[0020] In the aforementioned calcination process, the low-temperature zone is designed to allow incompletely reacted components within the raw coke to further react and to allow volatile components to escape prematurely. The reaction for preparing raw pitch coke is a typical liquid-phase carbonization process, where polycyclic aromatic hydrocarbons undergo pyrolysis, polymerization, and carbonization reactions within a temperature range of 350–600°C. Industrial production of pitch coke utilizes a delayed coking process. The characteristics of delayed coking result in the production of raw coke that may contain insufficiently reacted pitch components and a small amount of coking heavy oil components. These components, when calcined at high temperatures, may violently escape or form foamed carbon, potentially degrading the performance of the pitch coke. In industrial production, the coke tower temperature is generally around 450°C (usually not exceeding 500°C). Therefore, the calcination process of this invention selects a lower limit of 400°C for the low-temperature zone and an upper limit of 700°C to prevent volatile components from directly carbonizing into loose, foamed carbon that cannot be discharged. In industrial production, the coking time is generally 24 hours. The low-temperature section in the above-mentioned calcination process is only used to compensate for the incomplete reaction during delayed coking and to remove residual oil components. Considering that the coking reaction rate and the rate of volatile matter discharge both increase significantly with increasing temperature, the holding time is selected to be 10 to 120 minutes.

[0021] The high-temperature setting in the above calcination process is designed to ensure that the volatile matter, true density, and other important indicators of the calcined coke meet the product requirements for pitch coke. At temperatures above 700℃, the macromolecules of raw pitch coke undergo further pyrolysis, dehydrogenation, and polymerization reactions, accompanied by atomic rearrangement, with the carbon atom arrangement gradually tending towards a regular graphite lamellar structure. When the temperature exceeds 1000℃, the volatile components are almost completely released or carbonized, and the pyrolysis and dehydrogenation reactions are also almost complete. At this point, the volatile matter content decreases to below 0.5%, and the true density increases to 1.98 g / cm³. 3The above conditions meet the relevant standards for pitch coke products. Considering the differences in the characteristics of different types of raw pitch coke, and to ensure that the product indicators are qualified, the temperature range of the high-temperature section in the above calcination process is selected as 1000-1300℃, and the holding time is 30-90 minutes.

[0022] The crushing strength coefficient of the 1-2 mm high-strength pitch coke prepared above is ≥54%, and the crushing strength coefficient of the 2-4 mm high-strength pitch coke is ≥45.5%.

[0023] Example 1

[0024] This embodiment provides a calcination method for high-strength pitch coke, as detailed below:

[0025] One kilogram of raw pitch coke (raw coke 1) was placed in a graphite crucible and calcined under nitrogen protection. The calcination temperature curve was as follows: heating rate 10℃ / min, holding temperature of 550℃ for 1 hour in the low-temperature section, holding temperature of 1150℃ for 1 hour in the high-temperature section, and natural cooling to 200℃ after the holding period to obtain high-strength calcined pitch coke. The coke sample was then taken out of the furnace for subsequent testing.

[0026] As shown in Table 1, the high-strength asphalt coke prepared in this embodiment has a crushing strength coefficient of 55.40% for 1-2 mm particles, a crushing strength coefficient of 46.30% for 2-4 mm particles, and a true density of 1.97 g / cm³. 3 .

[0027] The test method for particle strength coefficient of asphalt coke is as follows: (1) Sieve the coke sample to be tested through a sieve for 10 min to obtain a sample with a particle size of 1-2 mm or 2-4 mm; (2) Accurately weigh 50.00 g of the sample to be tested; (3) Carefully place the sample into the mold (inner diameter Φ40 mm, height 120 mm), place it in the center of the upper and lower pressure heads of the universal testing machine, and turn on the testing machine. (4) Turn on the testing machine and test according to the following parameters: loading rate 10 mm / min, loading to 4800 kgf and holding for 90 s; return to release pressure. (5) Pour out all the samples in the mold and sieve again for 10 min according to the sample preparation method; (6) Accurately weigh the sample that meets the particle size requirements, accurate to 0.01 g; (7) Calculate the result: particle crushing strength coefficient = mass of the sample that meets the particle size requirements after crushing / mass of the sample that meets the particle size requirements before crushing * 100%.

[0028] Example 2

[0029] This embodiment provides a calcination method for high-strength pitch coke, as detailed below:

[0030] One kilogram of raw pitch coke (raw coke 2) was placed in a graphite crucible and calcined under nitrogen protection. The calcination temperature curve was as follows: heating rate 10℃ / min, holding temperature of 500℃ in the low-temperature section for 0.5h, holding temperature of 1150℃ in the high-temperature section for 1h, and then naturally cooled to 200℃ after the holding period to obtain high-strength pitch coke. The coke sample was then taken out of the furnace for subsequent testing.

[0031] As shown in Table 1, the high-strength asphalt coke prepared in this embodiment has a crushing strength coefficient of 54.70% for 1-2 mm particles, a crushing strength coefficient of 45.64% for 2-4 mm particles, and a true density of 2.00 g / cm³. 3 .

[0032] Example 3

[0033] This embodiment provides a calcination method for high-strength pitch coke, as detailed below:

[0034] One kilogram of raw pitch coke (raw coke 2) was placed in a graphite crucible and calcined under nitrogen protection. The calcination temperature curve was as follows: heating rate 10℃ / min, holding temperature of 550℃ in the low-temperature section for 0.5h, holding temperature of 1150℃ in the high-temperature section for 1h, and then naturally cooled to 200℃ after the holding period to obtain high-strength pitch coke. The coke sample was then taken out of the furnace for subsequent testing.

[0035] As shown in Table 1, the high-strength pitch coke prepared in this embodiment has a crushing strength coefficient of 55.12% for 1-2 mm particles, a crushing strength coefficient of 46.22% for 2-4 mm particles, and a true density of 2.00 g / cm³. 3 .

[0036] Example 4

[0037] This embodiment provides a calcination method for high-strength pitch coke, as detailed below:

[0038] One kilogram of raw pitch coke (raw coke 2) was placed in a graphite crucible and calcined under nitrogen protection. The calcination temperature curve was as follows: heating rate 10℃ / min, holding temperature of 480℃ in the low-temperature section for 0.5h, holding temperature of 1150℃ in the high-temperature section for 1h, and then naturally cooled to 200℃ after the holding period to obtain high-strength pitch coke. The coke sample was then taken out of the furnace for subsequent testing.

[0039] As shown in Table 1, the high-strength pitch coke prepared in this embodiment has a crushing strength coefficient of 54.70% for 1-2 mm particles, a crushing strength coefficient of 46.08% for 2-4 mm particles, and a true density of 2.01 g / cm³. 3 .

[0040] Example 5

[0041] This embodiment provides a calcination method for high-strength pitch coke, as detailed below:

[0042] One kilogram of raw pitch coke (raw coke 3) was placed in a graphite crucible and calcined under nitrogen protection. The calcination temperature curve was as follows: heating rate 10℃ / min, holding temperature of 700℃ for 2 hours in the low-temperature section, holding temperature of 1200℃ for 1 hour in the high-temperature section, and natural cooling to 200℃ after the holding period to obtain high-strength pitch coke. The coke sample was then taken out of the furnace for subsequent testing.

[0043] As shown in Table 1, the high-strength pitch coke prepared in this embodiment has a crushing strength coefficient of 56.30% for 1-2 mm particles, a crushing strength coefficient of 49.92% for 2-4 mm particles, and a true density of 2.04 g / cm³. 3 .

[0044] Comparative Example 1

[0045] One kilogram of raw pitch coke (raw coke 1) was placed in a graphite crucible and calcined under nitrogen protection. The calcination temperature curve was as follows: heating rate 10℃ / min, directly heating from room temperature to the high-temperature section, holding temperature 1150℃, holding time 1h, and then naturally cooling to 200℃ after the holding time. The coke sample was then removed from the furnace for subsequent testing. According to Table 1, the crushing strength coefficient of the 1-2 mm particles of the obtained calcined pitch coke was 51.08%, the crushing strength coefficient of the 2-4 mm particles was 45.32%, and the true density was 2.00 g / cm³. 3 .

[0046] Comparative Example 2

[0047] One kilogram of raw pitch coke (raw coke 2) was placed in a graphite crucible and calcined under nitrogen protection. The calcination temperature curve was as follows: heating rate 10℃ / min, directly heating from room temperature to the high-temperature section, holding temperature 1150℃, holding time 1h, and then naturally cooling to 200℃ after holding. The furnace was then opened and the coke sample was taken out for subsequent testing. According to Table 1, the crushing strength coefficient of the 1-2 mm particles of the obtained calcined pitch coke was 51.36%, the crushing strength coefficient of the 2-4 mm particles was 46.14%, and the true density was 2.01 g / cm³. 3 .

[0048] Comparative Example 3

[0049] One kilogram of raw pitch coke (raw coke 3) was placed in a graphite crucible and calcined under nitrogen protection. The calcination temperature curve was as follows: heating rate 10℃ / min, directly heating from room temperature to the high-temperature section, holding temperature 1200℃, holding time 1h, and then naturally cooling to 200℃ after the holding time. The furnace was then opened and the coke sample was taken out for subsequent testing. According to Table 1, the crushing strength coefficient of the 1-2 mm particles of the obtained calcined pitch coke was 55.66%, the crushing strength coefficient of the 2-4 mm particles was 48.22%, and the true density was 2.03 g / cm³. 3 .

[0050] Table 1

[0051]

[0052] As shown in Table 1, for the same raw coke samples, the true density of the high-strength pitch coke prepared in the embodiments of the present invention is not significantly different from that of the pitch coke prepared in comparative examples 1 to 3. In terms of strength, for the same raw coke samples, the high-strength pitch coke prepared in the embodiments of the present invention has a significant improvement in the strength of 1-2 mm particles compared with the pitch coke prepared in the comparative examples, and the strength of 2-4 mm particles is also basically slightly improved.

[0053] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A method for calcining high-strength pitch coke, characterized in that: The raw asphalt coke is produced using a two-stage heat preservation calcination process. During the calcination process, the raw pitch coke is heated from room temperature to a low-temperature section and held at that temperature. The raw pitch coke is fully carbonized and volatiles are released. Then, the temperature is further increased to a high-temperature section and held at that temperature. The pitch coke undergoes a condensation reaction and its crystal structure and atomic arrangement are regularized. After the holding period, it is naturally cooled to obtain high-strength pitch coke.

2. The calcination method for high-strength pitch coke according to claim 1, characterized in that: The calcination process of the raw pitch coke involves placing the raw pitch coke in a graphite crucible and calcining it under nitrogen or an inert atmosphere. The heating rate during the calcination process is 2–20 °C / min.

3. The calcination method for high-strength pitch coke according to claim 1, characterized in that: The low-temperature section has a heat preservation temperature of 400–700℃ and a heat preservation time of 10–120 minutes.

4. The calcination method for high-strength pitch coke according to claim 1, characterized in that: The high-temperature section has a heat preservation temperature of 1000-1300℃ and a heat preservation time of 30-90 minutes.

5. A high-strength pitch coke prepared by a calcination method according to claims 1 to 4.

6. The high-strength pitch coke according to claim 5, characterized in that: The crushing strength coefficient of the 1-2 mm particles of the high-strength pitch coke is ≥54%, and the crushing strength coefficient of the 2-4 mm particles is ≥45.5%.

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