Carbon fiber in-situ carbonization method

Abstract

The invention relates to the field of carbon fiber preparation, and discloses a carbon fiber in-situ carbonization method which is characterized in that in the process of realizing PAN fiber pre-oxidation and carbonization in a tubular furnace, the PAN fiber is subjected to in-situ carbonization through the change of a carbonization boundary caused by the movement of a furnace plug; the effective pre-oxidized fibers between the pre-oxidized boundaries in the pre-oxidized process before the furnace plug moves are all located in the carbonization boundary entrainment, so that the phenomenon that the PAN fibers are burnt out in the carbonization process due to the influence of the carbonization process on the non-effective pre-oxidized fibers is avoided, and finally the carbon fibers in a fixed carbonization mode are obtained.

Description

Technical Field

[0001] This invention relates to an in-situ carbonization method for carbon fibers, belonging to the field of carbon fiber preparation. Background Technology

[0002] The industrial production of polyacrylonitrile (PAN) carbon fiber involves multiple high-temperature furnaces in processes such as dynamic pre-oxidation and carbonization of PAN fibers. Small-scale laboratory experiments are often limited by space and hardware investment, making it difficult to adopt the aforementioned industrial production technology approach. To achieve the complete process requirements for carbon fiber preparation using simple equipment, a specially structured tube furnace can be used, with one unit performing multiple carbonization processes to meet laboratory preparation needs. To limit the furnace temperature, plugs are installed at both ends of the tubes, ensuring the required high temperature in the furnace cavity while protecting the components at both ends of the tubes from high-temperature failure. During the in-situ pre-oxidation and carbonization of PAN fibers in a tube furnace, the pre-oxidized fibers often burn out near the plugs, leading to preparation failure.

[0003] To address this, an in-situ carbonization method for carbon fibers is proposed to avoid the burn-out of pre-oxidized fibers during the carbonization process, thereby producing qualified carbon fibers. Summary of the Invention

[0004] The purpose of this invention is to propose an in-situ carbonization method for carbon fibers to avoid the burning off of pre-oxidized fibers during the carbonization process; thereby realizing the in-situ preparation of the entire process of carbon fibers by a single tube furnace.

[0005] A method for in-situ carbonization of carbon fibers includes the following steps:

[0006] S1. Pass the PAN fibers sequentially through furnace end structure A, furnace plug A, furnace cavity, furnace plug B, and furnace end structure B. Apply the tension required by the process at both ends of the PAN fibers and keep the PAN fibers and the furnace body relatively stationary.

[0007] S2. According to the pre-oxidation process instructions, the furnace body is heated according to the required temperature change curve. Air is introduced into the furnace body at the process requirement time. The air is introduced from the furnace end structure A, and sequentially passes through furnace plug A, furnace cavity, and furnace plug B, carrying the waste gas and being discharged from the furnace end structure B to obtain pre-oxidized fiber.

[0008] S3. Move furnace plugs A and B towards the furnace cavity;

[0009] S4. According to the carbonization process instructions, the furnace body is heated according to the required temperature change curve. Protective gas is used to replace the air in the furnace body within the required time. The protective gas passes sequentially through furnace plug A, furnace cavity, and furnace plug B, and is discharged from furnace end structure B to obtain carbon fiber.

[0010] S5. In step 2, the obtained pre-oxidized fiber is a part of the PAN fiber that passes through the furnace body. The pre-oxidized fiber that has completed effective pre-oxidation will produce two boundary lines with other parts: the pre-oxidized near-furnace plug A boundary line and the pre-oxidized near-furnace plug B boundary line.

[0011] S6. In step 4, the carbon fiber obtained is a part of the PAN fiber that passes through the furnace body. The carbon fiber that has been effectively carbonized creates two boundary lines with other parts: the carbonization near the furnace plug A boundary line and the carbonization near the furnace plug B boundary line.

[0012] S7. In step 5, the boundary lines of pre-oxidized furnace plug A, pre-oxidized furnace plug B, carbonized furnace plug A, and carbonized furnace plug B are determined by a combination of factors such as the location and shape of the furnace plugs, furnace temperature, and airflow.

[0013] S8. In step 3, the requirement for moving furnace plug A is to move the boundary line of carbonization near furnace plug A towards furnace plug B, so that the distance between the boundary line of carbonization near furnace plug A and furnace plug B is less than the distance between the boundary line of pre-oxidation near furnace plug A and furnace plug B; the distance between the boundary line of carbonization near furnace plug A and the boundary line of pre-oxidation near furnace plug A is not less than 5% of the furnace cavity length before the movement.

[0014] S9. In step 3, the requirement for moving the furnace plug B is to move the boundary line of the carbonization near furnace plug B towards the furnace plug A, so that the distance between the boundary line of the carbonization near furnace plug B and the furnace plug A is less than the distance between the boundary line of the pre-oxidation near furnace plug B and the furnace plug A; the distance between the boundary line of the carbonization near furnace plug B and the boundary line of the pre-oxidation near furnace plug B is not less than 3% of the furnace cavity length before the movement.

[0015] In steps S10, 8, and 9, the distance between the boundary line of the carbonization near-furnace plug A and the boundary line of the pre-oxidation near-furnace plug A should be greater than the distance between the boundary line of the carbonization near-furnace plug B and the boundary line of the pre-oxidation near-furnace plug B.

[0016] The beneficial effects of this invention are that, in the process of PAN fiber pre-oxidation and carbonization in a tube furnace, the change in the carbonization boundary line caused by the movement of the furnace plug ensures that all the effective pre-oxidized fibers between the pre-oxidation boundary lines during the pre-oxidation process before the furnace plug moves are located in the carbonization boundary line entrainment, thus avoiding the carbonization process from affecting the non-effective pre-oxidized fibers and causing the PAN fibers to burn out during the carbonization process; the influence of airflow factors is fully considered, so that the yield of the final carbon fiber is maximized by the fixed carbonization method. Attached Figure Description

[0017] Figure 1 This is a three-dimensional structural schematic diagram of an in-situ carbonization method for carbon fibers according to the present invention.

[0018] The diagram is marked as follows: 1. Furnace end structure A; 2. Furnace end structure B; 3. Furnace plug A; 4. Furnace plug B; 5. Boundary line of pre-oxidation near furnace plug A; 6. Boundary line of pre-oxidation near furnace plug B; 7. Boundary line of carbonization near furnace plug A; 8. Boundary line of carbonization near furnace plug B. Detailed Implementation

[0019] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. One example is as follows:

[0020] S1. Pass the PAN fiber sequentially through furnace end structure A(1), furnace plug A(3), furnace cavity, furnace plug B(4), and furnace end structure B(2). Apply tension at the corresponding carbonization stage at both ends of the PAN fiber and keep the PAN fiber and the furnace body relatively stationary.

[0021] S2. The pre-oxidation process is divided into three stages of gradient heating. The furnace body is heated according to the required temperature change curve. Air is introduced into the furnace body at the required time of the three stages of gradient heating. The air is introduced from the furnace end structure A (1) and passes through the furnace plug A (3), furnace cavity, and furnace plug B (4) in sequence. The exhaust gas is carried out from the furnace end structure B (2) to obtain pre-oxidized fiber.

[0022] S3. Move the furnace plugs A (3) and B (4) towards the furnace cavity to ensure that the distance between the boundary line (7) of the carbonization near furnace plug A and the boundary line (5) of the pre-oxidation near furnace plug A is 5% of the length of the furnace cavity before the move, and the distance between the boundary line (8) of the carbonization near furnace plug B and the boundary line (6) of the pre-oxidation near furnace plug B is 3% of the length of the furnace cavity before the move.

[0023] S4. The carbonization process is divided into two stages of gradient heating. The furnace body is heated according to the required temperature change curve. During the required time of the two-stage gradient heating, the air in the furnace body is replaced by protective gas. The protective gas passes through the furnace plug A (3), the furnace cavity, and the furnace plug B (4) in sequence, and is discharged from the furnace end structure B (2) to obtain carbon fiber.

Claims

1. A method for in-situ carbonization of carbon fibers, characterized in that, include: S1. Pass the PAN fibers sequentially through furnace end structure A, furnace plug A, furnace cavity, furnace plug B, and furnace end structure B. Apply the tension required by the process at both ends of the PAN fibers and keep the PAN fibers and the furnace body relatively stationary. S2. According to the pre-oxidation process instructions, the furnace body is heated according to the required temperature change curve. Air is introduced into the furnace body at the process requirement time. The air is introduced from the furnace end structure A, and sequentially passes through furnace plug A, furnace cavity, and furnace plug B, carrying the waste gas and being discharged from the furnace end structure B to obtain pre-oxidized fiber. S3. Move furnace plugs A and B towards the furnace cavity; S4. According to the carbonization process instructions, the furnace body is heated according to the required temperature change curve. Protective gas is used to replace the air in the furnace body within the required time. The protective gas passes sequentially through furnace plug A, furnace cavity, and furnace plug B, and is discharged from furnace end structure B to obtain carbon fiber. S5. In step 2, the obtained pre-oxidized fiber is a part of the PAN fiber that passes through the furnace body. The pre-oxidized fiber that has completed effective pre-oxidation will produce two boundary lines with other parts: the pre-oxidized near-furnace plug A boundary line and the pre-oxidized near-furnace plug B boundary line. S6. In step 4, the carbon fiber obtained is a part of the PAN fiber that passes through the furnace body. The carbon fiber that has been effectively carbonized creates two boundary lines with other parts: the carbonization near the furnace plug A boundary line and the carbonization near the furnace plug B boundary line. S7. In step 5, the boundary lines of pre-oxidized furnace plug A, pre-oxidized furnace plug B, carbonized furnace plug A, and carbonized furnace plug B are determined by a combination of factors such as the location and shape of the furnace plugs, furnace temperature, and airflow. S8. In step 3, the requirement for moving furnace plug A is to move the boundary line of carbonization near furnace plug A towards furnace plug B, so that the distance between the boundary line of carbonization near furnace plug A and furnace plug B is less than the distance between the boundary line of pre-oxidation near furnace plug A and furnace plug B; the distance between the boundary line of carbonization near furnace plug A and the boundary line of pre-oxidation near furnace plug A is not less than 5% of the furnace cavity length before the movement. S9. In step 3, the requirement for moving the furnace plug B is to move the boundary line of the carbonization near furnace plug B towards the furnace plug A, so that the distance between the boundary line of the carbonization near furnace plug B and the furnace plug A is less than the distance between the boundary line of the pre-oxidation near furnace plug B and the furnace plug A; the distance between the boundary line of the carbonization near furnace plug B and the boundary line of the pre-oxidation near furnace plug B is not less than 3% of the furnace cavity length before the movement. In steps S10, 8, and 9, the distance between the boundary line of the carbonization near-furnace plug A and the boundary line of the pre-oxidation near-furnace plug A should be greater than the distance between the boundary line of the carbonization near-furnace plug B and the boundary line of the pre-oxidation near-furnace plug B.

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