A method for preparing isotropic graphite

Abstract

This invention discloses a method for preparing isotropic graphite, relating to the field of isotropic graphite preparation technology, and aims to address the shortcomings of existing isotropic graphite preparation methods. The method involves crushing and shaping raw materials, adding them to a kneader, adding modified coal tar pitch, kneading at a set temperature for a period of time, then introducing nitrogen gas into the kneader chamber and pressurizing it. Once the pressure reaches the desired value, the temperature is increased and kneading continues. After kneading, the temperature is lowered and the pressure is released to obtain a paste block. This paste block is then crushed and added back to the kneader, and modified coal tar pitch is added again. After kneading at a set temperature for a period of time, nitrogen gas is introduced into the kneader chamber and pressurization begins. Once the pressure reaches the desired value, the temperature is increased and kneading continues. After kneading, the temperature is lowered and the pressure is released to obtain a paste block, which is then crushed to obtain fine powder. Subsequent processes produce isotropic graphite. This invention features simple, reasonable, and easy-to-operate steps, producing graphite products with excellent isotropy.

Description

Technical Field

[0001] This invention relates to the field of isotropic graphite preparation technology, specifically to a method for preparing isotropic graphite. Background Technology

[0002] Isotropic graphite is an important emerging industrial raw material in recent years. It is a high-quality special graphite with many outstanding physicochemical properties, such as identical physical properties in all directions, properties independent of size, shape, and sampling direction; dense material structure, resulting in high surface hardness and high mechanical strength; good thermal shock resistance, not easily cracking under rapid heating and cooling conditions; high temperature resistance; and strong oxidation resistance. It has been widely used in machinery, metallurgy, nuclear energy, aluminum electrolysis, chemical industry, aerospace, and biological fields, and has become an indispensable high-performance engineering material in the world's industrial development.

[0003] Graphite production often uses pitch coke or needle coke as raw materials. In particular, when using needle coke as raw material, the surface of needle coke has obvious striped patterns. After being broken, it mostly produces long, needle-shaped fragments that have a fibrous structure under a microscope. If it is not processed, the graphite products produced will have a high degree of anisotropy, which limits its application.

[0004] Currently, existing isotropic graphite production mainly uses raw materials with good isotropy or adopts secondary coking technology;

[0005] The invention patent application with publication number CN105645960A, entitled "Method for preparing isotropic graphite materials by self-sintering of high softening point isotropic pitch", discloses a preparation method using only isotropic pitch as raw material. This method can indeed obtain graphite products with relatively good isotropy. However, this isotropic pitch is highly dependent on the quality of raw materials and the cost is uncontrollable.

[0006] The invention patent with announcement number CN102502603B, entitled "Production Process of Large-Size Fine-Particle Isotropic Isostatic High-Purity Graphite", discloses a method for obtaining finished graphite by crushing, grinding, mixing, rolling, grinding again, pressing, and calcining coke raw materials, crushing into secondary coke, grinding again, mixing again, rolling again, grinding again, pressing again, calcining, impregnating three times, calcining three times, and finally graphitizing. Although this method produces graphite with good isotropy, the process steps are numerous and complex, which greatly increases production costs and time. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing isotropic graphite, so as to solve the problem that existing methods for preparing isotropic graphite need to be improved.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing isotropic graphite, comprising the following specific steps:

[0009] Step S1: Using petroleum or coal tar pitch needle coke as raw material, crush and shape the raw material into particles a;

[0010] Step S2: Add granules a to the kneader, then add modified coal tar pitch. After kneading for a period of time at the set temperature, start introducing nitrogen into the kneader chamber and start pressurizing. After the pressure reaches the required value, heat up and continue kneading. After kneading is completed, cool down and depressurize to obtain paste block b.

[0011] Step S3: Crush the paste block b into granules c;

[0012] Step S4: Add granules c to the kneader, then add modified coal tar pitch. After kneading for a period of time at the set temperature, start introducing nitrogen into the kneader chamber and start pressurizing. After the pressure reaches the required value, heat up and continue kneading. After kneading is completed, cool down and release pressure to obtain paste block d.

[0013] Step S5: The paste block d is crushed to obtain fine powder e;

[0014] Step S6: Fine powder e is processed into isotropic graphite through subsequent processes.

[0015] Preferably, in step S1 above, the D50 of particle a is 1 to 10 mm.

[0016] Preferably, in step S2 above, the mass ratio of particle a to modified coal tar pitch is 1:0.1 to 0.35, the set mixing temperature is 160 to 240°C, after mixing for 30 to 80 minutes, the required pressure for nitrogen gas pressurization is 0.05 to 1 MPa, the temperature for further mixing is raised to 350 to 500°C, and the mixing time is continued for 10 to 40 minutes.

[0017] Preferably, in step S3 above, the D50 of particle c is 0.5 to 2.0 mm.

[0018] Preferably, in step S4 above, the mass ratio of particle c to modified coal tar pitch is 1:0.04 to 0.25, the set mixing temperature is 160 to 240°C, after mixing for 20 to 60 minutes, the required pressure for nitrogen gas pressurization is 0.2 to 2 MPa, the temperature for further mixing is raised to 350 to 500°C, and the mixing time is continued for 10 to 30 minutes.

[0019] Preferably, the kneading pressure in step S2 is less than the kneading pressure in step S4; the modified coal tar pitch used in both kneading processes is the same, with a softening point of 75–140°C.

[0020] Preferably, in step S5 above, the D50 of the fine powder e is 10-200 μm.

[0021] Preferably, the particle size of particle a is greater than the particle size of particle c, which is greater than the particle size of fine powder e.

[0022] Preferably, the above crushing processes all employ a pin crusher.

[0023] Preferably, the subsequent processes in step S6 include molding, baking, impregnation, secondary baking, and graphitization.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1. The preparation method of this isotropic graphite is simple, reasonable and easy to operate. The raw material powder is crushed, ground and shaped in three stages. The particle size after crushing gradually decreases and its anisotropy is gradually eliminated.

[0026] 2. The preparation method of this isotropic graphite uses a nitrogen-protected pressurized kneading and rapid heating technology to convert the binder asphalt into a semi-coke precursor at 350-500℃, retaining most of its plasticity. This not only helps to reduce the total amount of asphalt used and further improve isotropy, but also reduces production costs and improves the morphology of the powder to eliminate its anisotropy.

[0027] 3. The preparation method of this isotropic graphite involves mixing and kneading for a period of time, followed by nitrogen protection and pressurization. This can improve the density of the paste, prevent the paste from being oxidized due to excessive temperature, eliminate internal pores in the paste, and improve the bulk density of the subsequent molded green body and the mechanical strength of the finished product.

[0028] 4. This method for preparing isotropic graphite is applicable to the preparation of isotropic graphite with ultrafine, fine, and medium-coarse structures, and has a wide range of applications. Compared with the secondary coking technology in industrial production, it reduces the molding and calcination processes, lowers production costs and cycle time, and has better isotropy. Detailed Implementation

[0029] A method for preparing isotropic graphite includes the following specific steps:

[0030] First crushing: Using petroleum or coal tar pitch needle coke as raw material, the raw material is crushed and shaped into particles a, the particle size of which can be referenced, D50 should be 1~10mm;

[0031] First mixing: Add particle a to the mixer, then add modified coal tar pitch. The mass ratio of particle a to modified coal tar pitch should be 1:0.1 to 0.35. After mixing for a period of time at the set temperature, start to introduce nitrogen into the mixing chamber and start pressurizing. After the pressure reaches the required value, heat up and continue mixing. After mixing is completed, cool down and release the pressure to obtain paste block b.

[0032] Second crushing: Crush the paste block b into particles c. The particle size of particles c after crushing should generally be smaller than that of particles a. The D50 of particles c can be referenced as 0.5 to 2.0 mm.

[0033] Second mixing: Add granules c to the kneader, then add modified coal tar pitch. The mass ratio of granules c to modified coal tar pitch should be 1:0.04 to 0.25. After kneading for a period of time at the set temperature, start to introduce nitrogen into the kneader chamber and start pressurizing. Generally, the pressurization pressure should be greater than the pressurization pressure in the first mixing. After the pressure reaches the required value, heat up and continue kneading. After the kneading is completed, cool down and release the pressure to obtain paste block d.

[0034] Third crushing: The paste block d is crushed to obtain fine powder e. The particle size of fine powder e after crushing should generally be smaller than that of particle c. The D50 of fine powder e can be referenced as 10-200μm.

[0035] Subsequent processes: Fine powder e is processed into isotropic graphite through subsequent processes; subsequent processes may include molding, calcination, graphitization, etc., for example, isostatic pressing followed by a first calcination, impregnation followed by a second calcination, and finally graphitization, or existing processes such as no impregnation, multiple impregnation, and multiple calcination can be used. This invention is mainly aimed at improving crushing and kneading, so all existing subsequent processing methods are applicable.

[0036] In a preferred embodiment, the kneading temperature set in step S2 is 160-240°C. After kneading for 30-80 minutes, the required pressure for nitrogen gas pressurization is 0.05-1 MPa. The temperature for further kneading is raised to 350-500°C, and the kneading time is continued for 10-40 minutes.

[0037] In a preferred embodiment, the kneading temperature set in step S4 is 160-240°C. After kneading for 20-60 minutes, the required pressure for nitrogen gas pressurization is 0.2-2 MPa. The temperature for further kneading is raised to 350-500°C, and the kneading time is continued for 10-30 minutes.

[0038] The same modified coal tar pitch should be used for both mixing processes, with a softening point of 75–140℃.

[0039] The secondary coking technology in the CN102502603B patent mentioned in the background section uses a precast powder to modified asphalt mass ratio of 52-65:35-48, or approximately 1:(0.52-0.93), in both mixing processes. The amount of asphalt used is much higher than that in the method of this invention.

[0040] In addition, all of the above-mentioned crushing operations can be performed using a pin crusher.

[0041] Example 1

[0042] 1) Crushing: Using petroleum needle coke as raw material, the raw material is crushed and shaped into particles a with a D50 of 5mm using a pin crusher;

[0043] 2) Mixing: Add particle a to the mixer, then add modified coal tar pitch with a softening point of 120℃. The mass ratio of particle a to modified coal tar pitch is 1:0.3. The mixing temperature is 220℃. After mixing for 60 minutes, nitrogen gas is introduced into the mixing chamber and pressurization is started. After the pressure reaches 0.5MPa, the mixing temperature is increased to 400℃. After 30 minutes, the temperature is lowered and the pressure is released. After the process is completed, paste block b is obtained.

[0044] 3) Secondary crushing: The paste block b is added to the pin crusher for crushing into particles c with a D50 of 1.0mm;

[0045] 4) Secondary kneading: Add particle c to the kneader, then add modified coal tar pitch with a softening point of 120℃. The mass ratio of particle c to modified coal tar pitch is 1:0.2. The kneading temperature is 220℃. After kneading for 40 minutes, nitrogen gas is introduced into the kneader chamber and pressurization is started at 1MPa. Then the kneader temperature is increased to 500℃. After 10 minutes, the temperature is reduced and the pressure is released. After the process is completed, paste block d is obtained.

[0046] 5) Three-stage crushing and grinding: The paste block d is added to the pin crusher for crushing into fine powder e with D50 of 50μm;

[0047] 6) Subsequent processes: molding, baking, impregnation, secondary baking, graphitization to obtain isotropic graphite.

[0048] Example 2

[0049] 1) Crushing: Using petroleum needle coke as raw material, the raw material is crushed and shaped into particles a with a D50 of 1mm using a pin crusher;

[0050] 2) Mixing: Add particle a to the mixer, then add modified coal tar pitch with a softening point of 75℃. The mass ratio of particle a to modified coal tar pitch is 1:0.2. The mixing temperature is 160℃. After mixing for 30 minutes, nitrogen gas is introduced into the mixing chamber and pressurization is started. After the pressure reaches 1.0 MPa, the mixing temperature is increased to 350℃. After 10 minutes, the temperature is lowered and the pressure is released. After the process is completed, paste block b is obtained.

[0051] 3) Secondary crushing: The paste block b is added to the pin crusher for crushing into particles c with a D50 of 0.5mm;

[0052] 4) Secondary kneading: Add particle c to the kneader, then add modified coal tar pitch with a softening point of 75℃. The mass ratio of particle c to modified coal tar pitch is 1:0.1. The kneading temperature is 220℃. After kneading for 20 minutes, nitrogen gas is introduced into the kneader chamber and pressurization is started at 2.0 MPa. Then the kneader temperature is increased to 400℃. After 30 minutes, the temperature is reduced and the pressure is released. After the process is completed, paste block d is obtained.

[0053] 5) Three-stage crushing and grinding: The paste block d is added to the pin crusher for crushing into fine powder e with D50 of 20μm;

[0054] 6) Subsequent processes: molding, baking, impregnation, secondary baking, graphitization to obtain isotropic graphite.

[0055] Example 3

[0056] 1) Crushing: Using petroleum needle coke as raw material, the raw material is crushed and shaped into particles a with a D50 of 10mm using a pin crusher;

[0057] 2) Mixing: Add particle a to the mixer, then add modified coal tar pitch with a softening point of 140℃. The mass ratio of particle a to modified coal tar pitch is 1:0.1. The mixing temperature is 240℃. After mixing for 80 minutes, nitrogen gas is introduced into the mixing chamber and pressurization is started. After the pressure reaches 0.05MPa, the mixing temperature is increased to 500℃. After 40 minutes, the temperature is lowered and the pressure is released. After the process is completed, paste block b is obtained.

[0058] 3) Secondary crushing: The paste block b is added to the pin crusher for crushing into particles c with a D50 of 2.0mm;

[0059] 4) Secondary kneading: Add particle c to the kneader, then add modified coal tar pitch with a softening point of 140℃. The mass ratio of particle c to modified coal tar pitch is 1:0.25. The kneading temperature is 240℃. After kneading for 60 minutes, nitrogen gas is introduced into the kneader chamber and pressurization is started at 1MPa. Then the kneader temperature is increased to 350℃. After 20 minutes, the temperature is reduced and the pressure is released. After the process is completed, paste block d is obtained.

[0060] 5) Three-stage crushing and grinding: The paste block d is added to the pin crusher for crushing into fine powder e with D50 of 200μm;

[0061] 6) Subsequent processes: molding, baking, impregnation, secondary baking, graphitization to obtain isotropic graphite.

[0062] Example 4

[0063] 1) Crushing: Using petroleum needle coke as raw material, the raw material is crushed and shaped into particles a with a D50 of 3mm using a pin crusher;

[0064] 2) Mixing: Add particle a to the mixer, then add modified coal tar pitch with a softening point of 90℃. The mass ratio of particle a to modified coal tar pitch is 1:0.1. The mixing temperature is 200℃. After mixing for 80 minutes, nitrogen gas is introduced into the mixing chamber and pressurization is started. After the pressure reaches 0.8MPa, the mixing temperature is increased to 400℃. After 30 minutes, the temperature is lowered and the pressure is released. After the process is completed, paste block b is obtained.

[0065] 3) Secondary crushing: The paste block b is added to the pin crusher for crushing into particles c with a D50 of 1.5mm;

[0066] 4) Secondary kneading: Add particle c to the kneader, then add modified coal tar pitch with a softening point of 90℃. The mass ratio of particle c to modified coal tar pitch is 1:0.05. The kneading temperature is 220℃. After kneading for 50 minutes, nitrogen gas is introduced into the kneader chamber and pressurization is started at 1.5MPa. Then the kneader temperature is increased to 450℃. After 20 minutes, the temperature is reduced and the pressure is released. After the process is completed, paste block d is obtained.

[0067] 5) Three-stage crushing and grinding: The paste block d is added to the pin crusher for crushing into fine powder e with D50 of 100μm;

[0068] 6) Subsequent processes: molding, baking, impregnation, secondary baking, graphitization to obtain isotropic graphite.

[0069] Comparative Example 1

[0070] The particles c from the broken paste block b in step 3) of Example 1 are directly shaped, calcined and graphitized, without secondary mixing and tertiary crushing and grinding. The remaining steps are the same as in Example 1 to obtain the graphite product.

[0071] Comparative Example 2

[0072] In Example 1, steps 2) and 4) are omitted, including the process of mixing for a period of time, passing nitrogen gas, heating, and pressurizing. The remaining steps are the same as in Example 1, and graphite products are obtained.

[0073] Comparative Example 3

[0074] 1) Crushing: Using the same petroleum needle coke as in Example 1 as raw material, the raw material is crushed and shaped into particles a with a D50 of 5mm using a pin crusher;

[0075] 2) Mixing: Add particle a to the mixer, then add modified coal tar pitch with a softening point of 120℃. The mass ratio of particle a to modified coal tar pitch is 1:0.5. The mixing temperature is 220℃. After mixing for 60 minutes, paste block b is obtained.

[0076] 3) Crushing and grinding: The paste block b is added to the pin crusher for crushing into fine powder e with D50 of 50μm;

[0077] The subsequent processes are the same as in Example 1, resulting in a graphite product.

[0078] Table 1. Isotropic properties of the examples and comparative products

[0079] Isotropic degree Example 1 1.01 Example 2 1.03 Example 3 1.02 Example 4 1.01 Comparative Example 1 1.09 Comparative Example 2 1.17 Comparative Example 3 1.28

[0080] Isotropy is defined as the ratio of properties in different directions (larger value to smaller value). For example, if the product is a cylinder, isotropy is the ratio of properties along the axis to properties along the diameter. Generally, a ratio less than 1.05 indicates isotropy, and a ratio greater than 1.05 indicates anisotropy. The larger the value, the greater the anisotropy and the worse the isotropy.

[0081] As can be seen from the results in Table 1, the isotropy of the embodiments is below 1.05, achieving isotropy. Comparative Example 3 shows that although the initial and final crushed particle sizes are the same as in Example 1, it was not processed using the method of the present invention, and its graphite product has an isotropy of 1.28, indicating anisotropy. Comparative Example 1 shows that after two crushing and shaping processes and one pressurized kneading and rapid heating treatment, the isotropy decreased from 1.28 to 1.09, demonstrating the effectiveness of the method of the present invention. Comparative Example 2 shows that only three crushing and grinding processes were performed without pressurized kneading and rapid heating treatment, yet its anisotropy was also relatively high, at 1.17.

[0082] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

[0083] Any aspects of this invention not described in detail are well-known to those skilled in the art.

Claims

1. A method for preparing isotropic graphite, characterized in that, The specific steps include the following: Step S1: Using petroleum or coal tar pitch needle coke as raw material, crush and shape the raw material into particles a; Step S2: Add granules a to the kneader, then add modified coal tar pitch. After kneading for a period of time at the set temperature, start to introduce nitrogen into the kneader chamber and start pressurizing. After the pressure reaches the required value, heat up and continue kneading. The temperature of the kneading continues to rise to 350-500℃. After the kneading is completed, cool down and release the pressure to obtain paste block b. Step S3: Crush the paste block b into granules c; Step S4: Add granules c to the kneader, then add modified coal tar pitch. After kneading for a period of time at the set temperature, start to introduce nitrogen into the kneader chamber and start pressurizing. After the pressure reaches the required value, heat up and continue kneading. The temperature of the kneading continues to rise to 350-500℃. After the kneading is completed, cool down and release the pressure to obtain paste block d. Step S5: The paste block d is crushed to obtain fine powder e; Step S6: Fine powder e is processed into isotropic graphite through subsequent processes.

2. The method for preparing isotropic graphite according to claim 1, characterized in that: In step S1, the D50 of particle a is 1-10 mm.

3. The method for preparing isotropic graphite according to claim 1, characterized in that: In step S2, the mass ratio of particle a to modified coal tar pitch is 1:0.1 to 0.35, the set mixing temperature is 160 to 240°C, after mixing for 30 to 80 minutes, the required pressure for nitrogen gas pressurization is 0.05 to 1 MPa, and the mixing time for further heating is 10 to 40 minutes.

4. The method for preparing isotropic graphite according to claim 1, characterized in that: In step S3, the D50 of particle c is 0.5 to 2.0 mm.

5. The method for preparing isotropic graphite according to claim 1, characterized in that: In step S4, the mass ratio of particle c to modified coal tar pitch is 1:0.04 to 0.25, the set mixing temperature is 160 to 240°C, after mixing for 20 to 60 minutes, the required pressure for nitrogen gas pressurization is 0.2 to 2 MPa, and the mixing time is 10 to 30 minutes.

6. The method for preparing isotropic graphite according to claim 1, characterized in that: The kneading pressure in step S2 is less than the kneading pressure in step S4; the modified coal tar pitch used in both kneading processes is the same, with a softening point of 75–140°C.

7. The method for preparing isotropic graphite according to claim 1, characterized in that: In step S5, the D50 of the fine powder e is 10-200µm.

8. A method for preparing isotropic graphite according to any one of claims 1, 2, 4, and 7, characterized in that: Particle size of particle a > particle size of particle c > particle size of fine powder e.

9. The method for preparing isotropic graphite according to claim 1, characterized in that: All crushing operations are performed using a pin crusher.

10. The method for preparing isotropic graphite according to claim 1, characterized in that: The subsequent processes in step S6 include molding, baking, impregnation, secondary baking, and graphitization.