An asphalt-based carbon fiber and its preparation method

Abstract

The present invention discloses a method for preparing pitch-based carbon fibers, and the method comprises the following steps: (1) preparing spinnable pitch using a mixture of pitch and oxygen-containing compounds as raw materials; (2) putting the prepared spinnable pitch into a spinneret barrel for spinning to obtain carbon fiber precursor filaments; (3) performing carbonization treatment and graphitization treatment on the carbon fiber precursor filaments, and cooling the treated material to obtain pitch-based carbon fibers. The method uses pitch as a raw material, adds a certain amount of additives to heat together with the raw materials to prepare spinnable pitch. This spinnable pitch has more oxygen-containing functional groups. After spinning and carbonization treatment, carbon fiber precursor filaments are obtained, which have the advantages of good oxidation effect, simple operation, and low treatment cost.

Description

Technical Field

[0001] The present invention belongs to the field of carbon fiber preparation, and relates to a pitch-based carbon fiber and a preparation method thereof. Specifically, it relates to a pitch-based carbon fiber with stable performance and a preparation method thereof. Background Art

[0002] Pitch-based carbon fiber is an important high-value industrial material prepared from petroleum pitch or coal tar pitch as a precursor. It has the characteristics of high strength and high modulus, high temperature corrosion resistance, and excellent thermoelectric conduction performance. It is widely used in aerospace, national defense industry and daily life, and cannot be replaced due to its incomparable advantages over other materials. Since the precursor pitch is a thermoplastic material, if the pitch fiber is directly carbonized at high temperature, it will melt and soften, resulting in disorientation or decomposition, and even losing the fiber morphology. Therefore, the pitch fiber needs to be pre-oxidized before carbonization to convert it from thermoplastic to thermosetting, so as to maintain the fiber morphology during high-temperature carbonization.

[0003] The pre-oxidation treatment actually undergoes an oxidative polycondensation reaction. Due to the action of oxygen, the pitch molecules condense to form lactones, which are interconnected to form a larger molecular network. This macromolecular network continues to oxidize and condense to form a larger and more stable network system with oxygen-containing groups as connection points, thus avoiding melting or decomposition during subsequent carbonization. The pre-oxidation treatment is a key step in the preparation of carbon fibers and has important research significance. However, in the traditional process, the pre-oxidation process takes a long time and the process is more complex, greatly increasing the preparation cost of carbon fibers.

[0004] Patent CN108221089A discloses a preparation method of pitch-based carbon fiber. The steps of this method are as follows: putting high-softening-point pitch into the spinning nozzle cylinder of the spinning equipment, heating it to the melt spinning temperature under nitrogen protection, and then the spinning equipment extrudes and sprays through the spinneret at a high temperature of 325-335 °C to obtain green fiber; putting the green fiber into a pre-oxidation furnace and keeping it at a constant temperature for pre-carbonization for 3-4 hours at 380-450 °C; after the pre-carbonization is completed, heating it to 950-1020 °C and keeping it at a constant temperature for carbonization for 0.6-0.8 hours; transferring the carbonized fiber into a graphitization furnace at a temperature of 2700-3000 °C for carbonization for 0.7-1.2 hours; continuing to introduce nitrogen for protection and cooling to room temperature to obtain pitch-based carbon fiber. This method still requires pre-oxidation treatment at a relatively high temperature for a long time, with a high cost.

[0005] Patent CN112176458A discloses a method for shortening the pre-oxidation time of carbon fiber. By adding a co-oxidant in the pre-oxidation furnace to enhance the pre-oxidation effect, problems such as fiber skin-core structure, over-oxidation and insufficient oxidation during the pre-oxidation process are solved. However, its oxidant needs to be atomized, and the cost of this method is still high. SUMMARY OF THE INVENTION

[0006] In view of the deficiencies of the prior art, the present invention provides an asphalt-based carbon fiber and a preparation method thereof. The method uses asphalt as a raw material, adds a certain amount of additives and heats them together with the raw material to prepare spinnable asphalt. This spinnable asphalt has more oxygen-containing functional groups. After spinning and carbonization treatment, carbon fiber precursor filaments are obtained, which have the advantages of good oxidation effect, simple operation and low treatment cost.

[0007] A preparation method of an asphalt-based carbon fiber, the method includes the following content:

[0008] (1) Prepare spinnable asphalt using a mixture of asphalt and oxygen-containing compounds as raw materials;

[0009] (2) Put the prepared spinnable asphalt into a spinneret barrel for spinning to obtain carbon fiber precursor filaments;

[0010] (3) Carbonize and graphitize the carbon fiber precursor filaments, and cool the treated material to obtain asphalt-based carbon fiber.

[0011] In the method of the present invention, in step (1), the asphalt may be petroleum-based or coal-based asphalt. The petroleum-based asphalt includes one or more of residue oil, petroleum asphalt, catalytic slurry, ethylene tar, etc. The coal-based asphalt is one or more of coal tar, coal pitch, liquefied residue, etc. In the asphalt, the aromatic hydrocarbon content is greater than 50 wt%, the resin content does not exceed 10 wt%, and the asphaltene content does not exceed 8 wt%.

[0012] In the method of the present invention, the physical and chemical properties of the oxygen-containing compound in step (1) are as follows: the mass fraction of oxygen element is 20 - 50%, the melting point is 100 - 440 °C, and all have a certain plasticizing effect.

[0013] In the method of the present invention, the oxygen-containing compound in step (1) is one or more of terephthalic acid, polyethylene terephthalate, dimethyl terephthalate.

[0014] In the method of the present invention, the process of preparing spinnable asphalt in step (1) is as follows: mix asphalt and solid particles of oxygen-containing compounds evenly, and conduct co-heat treatment. The heat treatment temperature is 380 - 480 °C.

[0015] In the method of the present invention, the mass content of oxygen element in the spinnable asphalt in step (1) is 4 - 17%, preferably 10 - 15%.

[0016] In the method of the present invention, the process of spinning in step (2) by putting into a spinning nozzle cylinder is as follows: Place the prepared spinnable pitch into the spinning nozzle cylinder, heat it to 220 - 350 °C under the protection of an inert gas atmosphere, keep the temperature constant for 3 - 12 h, and carry out spinning at a pressure of 20 - 300 KPa and a rotation speed of 30 - 150 rad / in to obtain carbon fiber precursor filaments.

[0017] In the method of the present invention, the carbonization treatment process in step (3) is as follows: Place the carbon fiber precursor filaments into a carbonization furnace and carry out heat treatment under the protection of an inert gas atmosphere.

[0018] In the method of the present invention, the carbonization treatment in step (3) is at least divided into two stages. In the first stage, under the protection of an inert gas atmosphere, heat at a rate of 2 - 8 °C / in to 210 - 230 °C, and keep the temperature constant for 0.2 - 2 hours; in the second stage, the carbonization treatment temperature is 800 - 1400 °C, the heating rate is 4 - 12 °C / in, and the residence time is 0.8 - 4 h.

[0019] In the method of the present invention, the graphitization treatment temperature in step (3) is 2400 - 3200 °C, the heating rate is 5 - 16 °C / in, and the residence time is 0.8 - 4 h.

[0020] An asphalt-based carbon fiber prepared by the above method, the tensile strength of the asphalt-based carbon fiber is 0.9 - 2.6 Gpa, and the tensile modulus is 110 - 270 GPa.

[0021] Compared with the prior art, the preparation method of an asphalt-based carbon fiber of the present invention has the following beneficial effects:

[0022] The present invention uses asphalt as a raw material, co-heats it with a certain amount of additives to prepare spinnable pitch with more oxygen-containing functional groups, spins the spinnable pitch, directly carbonizes and graphitizes the carbon fiber precursor filaments to obtain asphalt-based carbon fiber; this preparation method is simple in operation, has a high yield, omits the pre-oxidation step, simplifies the process flow, greatly reduces costs, has good controllability, and at the same time, the prepared carbon fiber has a certain strength, the tensile strength can reach 1.2 - 2.1 Gpa, and the tensile modulus can reach 205 - 395 GPa. Specific Embodiments

[0023] The functions and effects of the method of the present invention will be further illustrated by the following examples and comparative examples. However, the following examples do not limit the method of the present invention. In the context of the present invention, unless otherwise specified, % are all mass percentages. In the examples and comparisons of the present invention, catalytic oil slurry is used as the raw material, and the properties of the catalytic oil slurry are shown in Table 1.

[0024] Table 1

[0025] Sample Name Saturates Aromatics Resins Asphaltenes Catalytic Slurry Oil 22 wt% 70 wt% 4 wt% 3 wt%

[0026] Example 1

[0027] First, catalytic slurry and terephthalic acid are uniformly mixed at a mass ratio of 10:1. Under the protection of an inert gas atmosphere, it is heated to 420 °C and kept at a constant temperature for 12 h to obtain spinnable pitch A. The oxygen mass fraction of spinnable pitch A reaches 4%. Put spinnable pitch A into the spinneret barrel of the spinning equipment, heat it to the melt spinning temperature under the protection of nitrogen, and then the spinning equipment extrudes and spins through the spinneret at a high temperature of 320 °C to obtain carbon fiber precursor filaments; place the carbon fiber precursor filaments in a carbonization furnace, while introducing an inert gas, the temperature in the carbonization furnace is raised to 210 °C at a rate of 2 °C / min, kept at a constant temperature for 2 h, then raised to 1150 °C at a rate of 4 °C / min, and kept at a constant temperature for 4 h. Transfer the carbonized fibers to a graphitization furnace, and under the protection of an inert gas, raise the temperature to 2650 °C at a rate of 15 °C / min, keep the temperature for 1.6 h, continue to introduce an inert gas and cool to room temperature to obtain the prepared pitch-based carbon fiber with a tensile strength of 1.4 GPa and a tensile modulus of 205 GPa.

[0028] Example 2

[0029] First, catalytic slurry and terephthalic acid are uniformly mixed at a mass ratio of 10:2. Under the protection of an inert gas atmosphere, it is heated to 420 °C and kept at a constant temperature for 12 h to obtain spinnable pitch B. The oxygen content of spinnable pitch B reaches 8%. Put spinnable pitch B into the spinneret barrel of the spinning equipment, heat it to the melt spinning temperature under the protection of nitrogen, and then the spinning equipment extrudes and spins through the spinneret at a high temperature of 320 °C to obtain carbon fiber precursor filaments; place the carbon fiber precursor filaments in a carbonization furnace, while introducing an inert gas, the temperature in the carbonization furnace is raised to 210 °C at a rate of 2 °C / min, kept at a constant temperature for 2 h, then raised to 1150 °C at a rate of 4 °C / min, and kept at a constant temperature for 4 h. Transfer the carbonized fibers to a graphitization furnace, and under the protection of an inert gas, raise the temperature to 2650 °C at a rate of 15 °C / min, keep the temperature for 1.6 h, continue to introduce an inert gas and cool to room temperature to obtain pitch-based carbon fiber B. The prepared pitch-based carbon fiber has a tensile strength of 1.6 GPa and a tensile modulus of 265 GPa.

[0030] Example 3

[0031] First, catalytic slurry oil and terephthalic acid are uniformly mixed at a ratio of 10:3, heated to 420 °C under the protection of an inert gas atmosphere, and kept at a constant temperature for 12 h to obtain spinnable pitch C. The oxygen content of spinnable pitch C reaches 11.5%. The spinnable pitch C is placed in the spinneret barrel of the spinning equipment, heated to the melt spinning temperature under the protection of nitrogen, and then the spinning equipment extrudes and spins through the spinneret at a high temperature of 320 °C to obtain carbon fiber precursor filaments; the carbon fiber precursor filaments are placed in a carbonization furnace, and while introducing an inert gas, the temperature in the carbonization furnace is increased to 210 °C at a rate of 2 °C / min, kept at a constant temperature for 2 h, then increased to 1150 °C at a rate of 4 °C / min, and kept at a constant temperature for 4 h. The carbonized fibers are transferred to a graphitization furnace, heated to 2650 °C at a rate of 15 °C / min under the protection of an inert gas, kept at the temperature for 1.6 h, and continue to introduce an inert gas and cooled to room temperature to obtain pitch-based carbon fiber C. The tensile strength of the prepared pitch-based carbon fiber is 1.8 GPa and the tensile modulus is 325 GPa.

[0032] Example 4

[0033] First, catalytic slurry oil and terephthalic acid are uniformly mixed at a ratio of 10:4, heated to 420 °C under the protection of an inert gas atmosphere, and kept at a constant temperature for 12 h to obtain spinnable pitch D. The oxygen content of spinnable pitch D reaches 14.3%. The spinnable pitch D is placed in the spinneret barrel of the spinning equipment, heated to the melt spinning temperature under the protection of nitrogen, and then the spinning equipment extrudes and spins through the spinneret at a high temperature of 320 °C to obtain carbon fiber precursor filaments; the carbon fiber precursor filaments are placed in a carbonization furnace, and while introducing an inert gas, the temperature in the carbonization furnace is increased to 210 °C at a rate of 2 °C / min, kept at a constant temperature for 2 h, then increased to 1150 °C at a rate of 4 °C / min, and kept at a constant temperature for 4 h. The carbonized fibers are transferred to a graphitization furnace, heated to 2650 °C at a rate of 15 °C / min under the protection of an inert gas, kept at the temperature for 1.6 h, and continue to introduce an inert gas and cooled to room temperature to obtain pitch-based carbon fiber D. The tensile strength of the prepared pitch-based carbon fiber is 2.1 GPa and the tensile modulus is 395 GPa.

[0034] Example 5

[0035] First, catalytic oil slurry and terephthalic acid are uniformly mixed in a ratio of 10:5, heated to 420 °C under the protection of an inert gas atmosphere, and kept at a constant temperature for 12 h to obtain spinnable pitch E. The oxygen content of spinnable pitch E reaches 17%. Spinnable pitch E is put into the spinneret barrel of the spinning equipment, heated to the melt spinning temperature under nitrogen protection, and then the spinning equipment extrudes the spinneret at a high temperature of 320 °C to obtain carbon fiber precursor filaments. The carbon fiber precursor filaments are placed in a carbonization furnace, and while introducing an inert gas, the temperature in the carbonization furnace is raised to 210 °C at a rate of 2 °C / min, kept at a constant temperature for 2 h, then raised to 1150 °C at a rate of 4 °C / min, and kept at a constant temperature for 4 h. The carbonized fibers are transferred to a graphitization furnace, heated to 2650 °C at a rate of 15 °C / min under the protection of an inert gas, kept at this temperature for 1.6 h, and continue to introduce an inert gas and cool to room temperature to obtain pitch-based carbon fiber E. The tensile strength of the prepared pitch-based carbon fiber is 1.9 GPa and the tensile modulus is 360 GPa.

[0036] Comparative Example 1

[0037] Using the catalytic oil slurry in the above example as the raw material, the difference in the operating conditions from Example 1 is that pre-oxidation treatment is added and the low-temperature treatment in the carbonization process is reduced. The prepared carbon fiber precursor filaments are placed in a pre-oxidation furnace and heated to 210 °C at a rate of 2 °C / min in an air atmosphere and kept at a constant temperature for 5 h for pre-oxidation treatment. The tensile strength of the obtained pitch-based carbon fiber F is 0.9 GPa and the tensile modulus is 135 GPa. Compared with the product of Example 1, the performance has decreased, and the process takes longer time and has higher cost.

[0038] The above examples are only for illustrating the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the present invention; the technologies not involved in the present invention can be realized through the prior art.

Claims

1. A preparation method of pitch-based carbon fiber, characterized in that: The method includes the following steps: (1) Preparing spinnable pitch using a mixture of pitch and an oxygen-containing compound as raw materials; (2) Placing the prepared spinnable pitch into a spinneret cartridge for spinning to obtain carbon fiber precursor filaments; (3) Directly carbonizing and graphitizing the carbon fiber precursor filaments, and cooling the treated material to obtain pitch-based carbon fibers; The oxygen-containing compound described in step (1) is terephthalic acid; The mass content of oxygen element in the spinnable pitch described in step (1) is 4% - 17%; The process of preparing spinnable pitch in step (1) is as follows: Mixing pitch and solid particles of the oxygen-containing compound evenly, and conducting co-thermal treatment, with the heat treatment temperature being 380 - 480°C; The carbonization treatment in step (3) is at least divided into two stages. In the first stage, under the protection of an inert gas atmosphere, the temperature is raised at a rate of 2 - 8°C / min to 210 - 230°C and kept at a constant temperature for 0.2 - 2 hours. In the second stage, the carbonization treatment temperature is 800 - 1400°C, the heating rate is 4 - 12°C / min, and the residence time is 0.8 - 4 h.

2. The method according to claim 1, wherein: The pitch described in step (1) is petroleum-based or coal-based pitch. The petroleum-based pitch includes one or more of residue oil, petroleum asphalt, catalytic slurry oil, and ethylene tar. The coal-based pitch is one or more of coal tar, coal asphalt, and liquefied residue.

3. The method according to claim 1, characterized in that: The aromatic hydrocarbon content in the pitch described in step (1) is greater than 50 wt%, the resin content does not exceed 10 wt%, and the asphaltene content does not exceed 8 wt%.

4. The method according to claim 1, characterized in that: The mass content of oxygen element in the spinnable pitch described in step (1) is 10 - 15%; 5. The method according to claim 1, wherein: The process of spinning by placing into the spinneret cartridge in step (2) is as follows: Placing the prepared spinnable pitch into the spinneret cartridge, heating it to 220 - 350°C under the protection of an inert gas atmosphere, keeping it at a constant temperature for 3 - 12 h, and spinning at a pressure of 20 - 300 KPa and a rotation speed of 30 - 150 rad / min to obtain carbon fiber precursor filaments.

6. The method according to claim 1, characterized in that: The carbonization treatment process in step (3) is as follows: Placing the carbon fiber precursor filaments into a carbonization furnace and conducting heat treatment under the protection of an inert gas atmosphere.

7. The method according to claim 1, wherein: The graphitization treatment temperature in step (3) is 2400 - 3200°C, the heating rate is 5 - 16°C / min, and the residence time is 0.8 - 4 h.

8. The method according to claim 1, wherein: The tensile strength of the pitch-based carbon fibers is 0.9 - 2.6 GPa, and the tensile modulus is 110 - 270 GPa.