Mesophase pitch fiber and preparation method thereof

Abstract

The invention relates to the technical field of pitch-based carbon fibers, in particular to a mesophase pitch fiber and a preparation method thereof. The preparation method comprises the following steps: preparing mesophase pitch, carrying out melt spinning, carrying out pre-oxidation treatment, carbonizing and graphitizing, wherein monofilament fibers obtained by melt spinning are soaked in a hydrogen peroxide solution and then are subjected to pre-oxidation treatment; and the pre-oxidation treatment comprises the following steps: keeping the constant temperature of 75-85 DEG C for 1-5 minutes, and then raising the temperature and continuously heating. By adopting a method of combining hydrogen peroxide infiltration and heating oxidation, hydrogen peroxide plays a role in the mesophase pitch-based fiber, the dual effects of catalysis and oxidation are achieved, the problems of long time consumption and high energy consumption are solved, the oxidation effect is remarkably improved while the cost is effectively saved, and finally the yield of the mesophase pitch fiber can be improved; wide application prospects are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of asphalt-based carbon fibers, and in particular to a mesophase asphalt fiber and a preparation method thereof. Background Art

[0002] Asphalt-based carbon fiber is one of the important engineering carbon fibers and is widely used in aerospace, national defense and military industries. The preparation process of asphalt-based carbon fiber is long and has many influencing factors. Due to the lack of understanding of its preparation process, reaction mechanism and regulation methods, the industrial production of asphalt-based carbon fiber with excellent strength performance still faces many difficulties. Taking the carbon fiber production process as the main line, in-depth discussion and analysis of the current status, methods, mechanisms and regulation of raw material pretreatment, asphalt precursor modulation, melt spinning, pre-oxidation, carbonization and graphitization is an effective strategy to improve the carbon fiber production process.

[0003] Whether the pre-oxidation stage of the asphalt-based carbon fiber production process meets the standards is a prerequisite before the carbonization process. The traditional pre-oxidation stage uses air as an oxidant for temperature control and heating, which is not only time-consuming and energy-intensive, but also accompanied by insufficient oxidation, which causes the monofilament fiber to melt during the carbonization stage, thereby reducing the yield rate of the asphalt-based carbon fiber production process.

[0004] Currently, one of the main research directions is to achieve the pre-oxidation effect by directly using oxidants. However, due to the immaturity of the technology, the selection of oxidants is extremely demanding, resulting in high costs and difficulty in industrial application. Summary of the invention

[0005] In order to solve the above-mentioned problems existing in the prior art, the present invention provides a method for preparing mesophase asphalt fibers, comprising: modulating mesophase asphalt, melt spinning, pre-oxidation treatment, carbonization and graphitization; wherein the monofilament fibers obtained by melt spinning are soaked in a hydrogen peroxide solution and then pre-oxidized; the pre-oxidation treatment step comprises: maintaining a constant temperature at 75-85°C for 1-5 minutes, and then increasing the temperature and continuing heating.

[0006] The principle of traditional pre-oxidation treatment is to form a specific cross-linked structure of the polycyclic aromatic hydrocarbon molecules in the asphalt through a slight oxidation reaction, that is, to generate a certain amount of oxygen-containing functional groups in the fiber structure. These oxygen-containing functional groups can transform the asphalt fiber from thermoplastic to thermosetting, thereby ensuring that the molecular structure of the asphalt fiber is sufficiently stable during the carbonization process, and is not melted, and still maintains a single fiber state.

[0007] The present invention proposes a "permeation catalytic pre-oxidation method" to solve the problems of high energy consumption, long time consumption and low oxidation effect of traditional pre-oxidation treatment. The "permeation catalytic pre-oxidation method" is to select a cheap hydrogen peroxide solution to permeate the monofilament fiber before pre-oxidation. Hydrogen peroxide plays the role of both oxidant and catalyst. In the subsequent heating stage, hydrogen peroxide provides more oxygen (oxygen element) sources, which is convenient for generating more oxygen-containing functional groups in the monofilament fiber structure, and accelerates the transformation of the monofilament fiber from thermoplastic to thermosetting. At the same time, more monofilament fibers can achieve the transformation of thermosetting, which greatly improves the pre-oxidation effect, reduces the probability of fiber melting in the carbonization stage, and greatly improves the yield rate of asphalt-based carbon fiber.

[0008] Since the pre-oxidation reaction includes oxidation reaction, condensation reaction, decomposition reaction, dehydration reaction, etc., the reaction process is numerous, so in order to increase the rate of the pre-oxidation reaction, the use of a suitable catalyst is a major first choice, but at the same time, factors such as the cost of the catalyst and corrosion to the equipment must be considered. The present invention does not add other catalysts, but uses the oxidant in the impregnation stage as a catalyst at the same time, achieving a two-in-one effect.

[0009] After the impregnation is completed, the monofilament fiber is heated in an air atmosphere. In the initial stage of heating, the thermal conductivity of the monofilament fiber is far less than that of the asphalt-based carbon fiber, which makes the hydrogen peroxide in the monofilament fiber decompose slowly. At this stage, hydrogen peroxide provides a source of oxygen (oxygen element) to improve the oxidation effect. At the same time, it acts as a catalyst to accelerate the initial stage of the pre-oxidation reaction, thereby greatly reducing the reaction time. When the reaction reaches the later stage, even if the hydrogen peroxide has been completely decomposed, the reaction temperature is high enough (not exceeding the minimum softening point temperature) to provide sufficient energy for the reaction to occur, and the reaction rate remains at the same level.

[0010] In order to prevent excessive decomposition of hydrogen peroxide to produce a large amount of gas and cause excessive fragmentation of the monofilament fiber, it is necessary to allow hydrogen peroxide to release appropriate oxygen into the gaps between the monofilament fibers as much as possible to provide sufficient oxygen for subsequent reactions. The temperature needs to be controlled at 75~85℃ and maintained for 1~5 minutes.

[0011] Preferably, the concentration of the hydrogen peroxide solution is 0.01-0.05 mol / L.

[0012] Preferably, the diameter of the monofilament fiber is 9 μm to 12 μm.

[0013] Preferably, when the diameter of the monofilament fiber is 10 μm to 12 μm, a spraying process is used for the impregnation treatment, and the spraying time is 15 to 20 minutes.

[0014] Preferably, when the diameter of the monofilament fiber is less than 10 μm, an impregnation process is used for the impregnation treatment, and the impregnation time is 8 to 10 minutes.

[0015] The present invention further found that different concentrations of hydrogen peroxide, different impregnation processes and impregnation times affect the gas production when the monofilament fiber is internally heated and decomposed, thereby causing different degrees of monofilament fiber fragmentation. When selecting the concentration of the above hydrogen peroxide solution, combined with the above specific impregnation method and time, both the catalytic effect and the oxidation effect can be taken into account.

[0016] Preferably, the immersion is performed at a temperature below 50°C.

[0017] The penetration effect can be enhanced by increasing the temperature, but the temperature needs to be controlled below 50 degrees Celsius so that the decomposition rate of the hydrogen peroxide solution is less than 50%.

[0018] Preferably, the temperature is kept at 80° C. for 3 minutes, and then the temperature is increased and continued.

[0019] Preferably, the heating rate is 0.4-0.5°C / min, most preferably 0.5°C / min.

[0020] Furthermore, the present invention provides mesophase pitch fibers prepared by the preparation method described in any of the above embodiments.

[0021] Compared with the prior art, the present invention has the following beneficial effects: The present invention adopts a method of combining hydrogen peroxide penetration with heating oxidation, so that hydrogen peroxide can play a dual role of catalysis and oxidation inside the mesophase asphalt-based fiber. The present invention can not only solve the problem of long time and high energy consumption, but also use cheap hydrogen peroxide solution to effectively save costs and significantly improve the oxidation effect, and finally improve the yield rate of mesophase asphalt fibers, and has broad application prospects. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] If no specific techniques or conditions are specified in the examples, all are carried out according to conventional methods or the techniques or conditions described in the literature in the field, or according to the product instructions. If no manufacturer is specified for the reagents and instruments used, all are conventional products that can be purchased through regular channels.

[0024] Example 1

[0025] This embodiment provides a method for preparing mesophase pitch fibers, and the steps are as follows: (1) Preparation of mesophase asphalt: crush the petroleum asphalt, heat and stir it at a heating temperature of 400°C and a stirring rate of 200 r / min; (2) Melt spinning: The prepared mesophase pitch is poured into a high-pressure spiral fluid forming machine with the following specific parameters: the speed is 7000 r / min, the pressure is 30 atmospheres (3039750 Pascals), the temperature is controlled at 350°C, and a laser melt differential injection head is used for spinning to obtain a monofilament fiber; (3) Immersion treatment: The monofilament fiber with a diameter of 9 μm obtained after melt spinning was immersed in a 0.01 mol / L hydrogen peroxide solution for 8 min; (4) Pre-oxidation treatment: The impregnated monofilament fiber is placed in an oxidation furnace for pre-oxidation treatment. The pressure of the oxidation furnace is maintained at room pressure. The oxidation furnace is first kept at a constant temperature of 80°C for 3 minutes, and then continuously heated to 450°C at a heating rate of 0.5°C / min and then closed for a period of time; (5) Carbonization treatment: heating at 1000°C for 5 hours; (6) Graphitization treatment: Heating at 2500 °C for 1 h in nitrogen at normal pressure to finally obtain mesophase asphalt fibers.

[0026] Example 2

[0027] This example provides a method for preparing mesophase pitch fibers, the steps of which are different from those of Example 1 only in that: (3) Impregnation treatment: The monofilament fiber with a diameter of 10 μm obtained after melt spinning is sprayed evenly with 0.01 mol / L hydrogen peroxide solution at room temperature and pressure for 15 minutes.

[0028] Example 3

[0029] This example provides a method for preparing mesophase pitch fibers, the steps of which are different from those of Example 1 only in that: (3) Impregnation treatment: The monofilament fiber with a diameter of 12 μm obtained after melt spinning was sprayed with 0.01 mol / L hydrogen peroxide solution evenly on the surface of the monofilament fiber at room temperature and pressure for 20 minutes.

[0030] Example 4

[0031] This example provides a method for preparing mesophase pitch fibers, the steps of which are different from those of Example 1 only in that: (4) Pre-oxidation treatment: The impregnated monofilament fiber is placed in an oxidation furnace for pre-oxidation treatment. The pressure of the oxidation furnace is maintained at room pressure. First, the oxidation furnace is kept at a constant temperature of 75°C for 3 minutes, and then the temperature is continuously heated to 450°C at a heating rate of 0.5°C / min. After a period of time, the oxidation furnace is turned off.

[0032] Example 5

[0033] This example provides a method for preparing mesophase pitch fibers, the steps of which are different from those of Example 1 only in that: (4) Pre-oxidation treatment: The impregnated monofilament fiber is placed in an oxidation furnace for pre-oxidation treatment. The pressure of the oxidation furnace is maintained at room pressure. First, the oxidation furnace is kept at a constant temperature of 85°C for 3 minutes, and then the temperature is continuously heated to 450°C at a heating rate of 0.5°C / min. After a period of time, the oxidation furnace is turned off.

[0034] Example 6

[0035] This example provides a method for preparing mesophase pitch fibers, the steps of which are different from those of Example 1 only in that: (3) Immersion treatment: The single fiber with a diameter of 9 μm obtained after melt spinning was immersed in a 0.01 mol / L hydrogen peroxide solution for 15 min.

[0036] Example 7

[0037] This example provides a method for preparing mesophase pitch fibers, the steps of which differ from those of Example 2 only in that: (3) Impregnation treatment: The monofilament fiber with a diameter of 10 μm obtained after melt spinning is sprayed evenly with 0.01 mol / L hydrogen peroxide solution at room temperature and pressure for 25 minutes.

[0038] Comparative Example 1

[0039] This comparative example adopts the traditional preparation method to prepare the mesophase pitch fiber, and the steps are only different from those in Example 1 in that the impregnation treatment is omitted, and the constant temperature maintenance at 80° C. for 3 minutes is omitted in the pre-oxidation treatment.

[0040] Comparative Example 2

[0041] This comparative example adopts the traditional preparation method to prepare the mesophase pitch fiber, and the steps are only different from those in Example 2 in that the impregnation treatment is omitted, and the constant temperature maintenance at 80° C. for 3 minutes is omitted in the pre-oxidation treatment.

[0042] Comparative Example 3

[0043] This comparative example adopts the conventional preparation method to prepare the mesophase pitch fiber, and the steps are only different from those in Example 3 in that the impregnation treatment is omitted, and the constant temperature maintenance at 80° C. for 3 minutes is omitted in the pre-oxidation treatment.

[0044] Test example

[0045] The properties of the mesophase pitch fibers prepared in the above examples and comparative examples were tested.

[0046] The test method for the pre-oxidation effect (yield rate) is as follows: Since monofilament fibers with poor pre-oxidation effect will melt during the carbonization stage, the yield rate is statistically calculated after a batch of the same number of monofilament fibers are carbonized in different embodiments. The prepared intermediate phase asphalt-based carbon fibers are further tested for tensile strength, elastic modulus, thermal conductivity and other properties under the same test conditions, and the test results are shown in Table 1. The comparison of reaction time is as follows: In the comparative example, the duration of pre-oxidation is 15 hours, and the shortened time of pre-oxidation treatment in different embodiments compared with the comparative example is shown in Table 1.

[0047] Table 1

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing mesophase pitch fiber, comprising: The method comprises the steps of modulating intermediate phase pitch, melt spinning, pre-oxidation treatment, carbonization and graphitization, wherein the monofilament fibers obtained by melt spinning are soaked in a hydrogen peroxide solution and then pre-oxidized; the pre-oxidation treatment comprises the steps of maintaining a constant temperature at 75-85°C for 1-5 minutes, and then increasing the temperature and continuously heating.

2. The preparation method according to claim 1, characterized in that: The concentration of the hydrogen peroxide solution is 0.01-0.05 mol / L.

3. The preparation method according to claim 1, characterized in that: The diameter of the monofilament fiber is 9 μm to 12 μm.

4. The preparation method according to claim 3, characterized in that: When the diameter of the monofilament fiber is 10μm~12μm, the spraying process is used for impregnation treatment, and the spraying time is 15~20min.

5. The preparation method according to claim 3, characterized in that: When the diameter of the monofilament fiber is less than 10 μm, an impregnation process is used for impregnation treatment, and the impregnation time is 8 to 10 minutes.

6. The preparation method according to claim 5, characterized in that: The immersion is performed at 50°C or below.

7. The preparation method according to claim 1, characterized in that: The temperature was kept at 80°C for 3 min, and then the temperature was increased and continued to heat.

8. The preparation method according to claim 1, characterized in that: The heating rate is 0.4-0.5°C / min.

9. The preparation method according to claim 1, characterized in that: The heating is continued to above 450°C.

10. A mesophase pitch fiber, characterized in that: It is prepared by the preparation method described in any one of claims 1 to 9.

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