Method for preparing anticorrosion coating, oxidation furnace and method for preparing carbon fiber

Abstract

The present application relates to the technical field of carbon fiber production, and discloses a preparation method of an anticorrosion coating, an oxidation furnace and a carbon fiber preparation method.The present application provides a preparation method of an anticorrosion coating, comprising: providing a paste, wherein the main components of the paste include graphite-like carbon nitride and polytetrafluoroethylene with a mass ratio of 1-10:0.6; coating the paste on the surface of a substrate, drying and curing to obtain an anticorrosion coating.The oxidation furnace is provided with the anticorrosion coating provided by the present application on the inner wall.The anticorrosion coating provided on the inner wall of the oxidation furnace can effectively prevent the reaction between HCN, NH3 and other acidic gases generated in the pre-oxidation stage of carbon fiber and the metal substrate of the furnace wall; the coating can also pretreat HCN, NH3 and other acidic gases, so that the pressure of the waste discharge system can be reduced when the gases enter the waste discharge system; the unstable oxide skin generated on the metal substrate of the furnace wall under high temperature can be effectively avoided, the environmental pollution in the furnace can be avoided, and the quality of the carbon fiber product can be improved.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber production technology, and more specifically, to a method for preparing an anti-corrosion coating, an oxidation furnace, and a method for preparing carbon fiber. Background Technology

[0002] In the production of carbon fiber, polyacrylonitrile (PAN) precursor fibers require a prolonged pre-oxidation treatment (approximately 60-120 minutes) in an oxidation furnace at 200-300°C. During this process, the precursor fibers release a corrosive atmosphere containing large amounts of hydrogen cyanide (HCN), ammonia (NH3), carbon monoxide (CO), and various complex organic decomposition products. Simultaneously, the continuous flow of air and the high temperature within the furnace create an extremely strong oxidizing atmosphere. These factors can cause the following problems: 1. The carbon fiber pre-oxidation stage will produce acidic gases such as HCN and NH3. These gases will react with the metal matrix, leading to pitting corrosion, uniform corrosion, and even furnace wall perforation. 2. The emission of acidic gases such as HCN and NH3 will cause environmental pollution; 3. At high temperatures, the metal matrix will generate an unstable oxide scale. Repeated peeling of the oxide scale will accelerate the wear and tear of the matrix and pollute the furnace environment, affecting the quality of carbon fiber products.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing an anti-corrosion coating, an oxidation furnace, and a method for preparing carbon fiber, in order to improve at least one of the problems mentioned in the background art.

[0005] This invention is implemented as follows: In a first aspect, the present invention provides a method for preparing an anti-corrosion coating, comprising: A paste is provided, the main components of which include graphite-like carbon nitride and polytetrafluoroethylene in a mass ratio of 1~10:0.6; The paste is applied to the surface of the substrate, dried, and cured to obtain an anti-corrosion coating.

[0006] In an optional embodiment, the mass ratio of the graphite-like carbon nitride to polytetrafluoroethylene with a weight-average molecular weight of 9000-11000 is 1-5:1.

[0007] In an optional embodiment, the solid content of the paste is 50-80%; Optionally, the paste is composed of graphite-like carbon nitride, polytetrafluoroethylene, and a solvent; Optionally, the solvent is selected from at least one of ethanol and methanol.

[0008] In an optional embodiment, the curing temperature is 300~360℃ and the curing time is 40~120min.

[0009] In an optional embodiment, the method for preparing the graphite-like carbon nitride includes: Melamine was calcined at 530-570℃, with the temperature continuously increased at a rate of 2-5℃ / min, and the initial product was obtained after calcination for 3-5 hours. The initial product was ground into powder and then washed with ethanol and deionized water in sequence. After drying, the finished product, graphite-phase carbon nitride, was obtained.

[0010] In an optional embodiment, the washing process involves 2 to 6 cycles of ethanol and deionized water.

[0011] In an optional implementation, the washing method is centrifugal washing; Optionally, the centrifugal washing speed is 5000~6000 r / min.

[0012] In an optional embodiment, the substrate is the inner wall of an oxidation furnace.

[0013] Secondly, the present invention provides an oxidation furnace, the inner wall of which is provided with an anti-corrosion coating, the anti-corrosion coating being prepared by the preparation method described in any of the foregoing embodiments.

[0014] Thirdly, the present invention provides a method for preparing carbon fiber, the preparation steps of which include: pre-oxidizing polyacrylonitrile precursor fibers in an oxidation furnace, wherein the oxidation furnace is the oxidation furnace described in the foregoing embodiments.

[0015] The present invention has the following beneficial effects: Cured polytetrafluoroethylene (PTFE) materials are heat-resistant and do not easily age even at temperatures well above 300°C. Oxidation furnaces for carbon fiber production operate at temperatures between 200 and 300°C, allowing PTFE-cured materials to have a long service life within these furnaces. Graphite-like carbon nitride (g-C3N4) exhibits high-temperature and corrosion resistance. Its semiconductor structure's core mechanism lies in its unique layered π-conjugated structure and suitable narrow bandgap of approximately 2.7 eV. Upon absorbing visible light, electrons in the valence band of g-C3N4 are excited and transition to the conduction band, forming electron-hole pairs. Due to the material's layered structure, charge carriers are encouraged to suppress charge recombination, and the separated carriers migrate to the surface to participate in the reaction: electrons in the conduction band have strong reducing power, directly reducing oxygen to generate superoxide radicals and other reactive species; holes in the valence band can directly oxidize pollutants or react with water to generate hydroxyl radicals. These active substances work together to achieve highly efficient degradation of organic pollutants. This mechanism gives g-C3N4 a significant advantage in solar-driven advanced oxidation processes. The coating, composed of PTFE and g-C3N4, imparts corrosion resistance to the interior of the oxidation furnace. It effectively blocks the reaction between acidic gases such as HCN and NH3 generated during the carbon fiber pre-oxidation stage and the furnace wall metal substrate, effectively preventing pitting corrosion, uniform corrosion, and even furnace wall perforation. In addition, the coating can pre-treat acidic gases such as HCN and NH3 before they enter the waste discharge system, reducing the pressure on the system. Finally, applying this coating to the inner wall of the oxidation furnace effectively prevents the formation of unstable oxide scale on the furnace wall metal substrate at high temperatures, avoiding environmental pollution inside the furnace and improving the quality of carbon fiber products. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 The experimental results for Example 1 are shown in the figure. Figure 2 The figure shows the experimental results of Experiment Example 2. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0019] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0020] This invention provides a method for preparing an anti-corrosion coating, comprising: A paste is provided, the main components of which include graphitic carbon nitride in a mass ratio of 1 to 10:0.6 and polytetrafluoroethylene with a weight average molecular weight of 9,000 to 11,000; The paste is applied to the surface of the substrate, dried, and cured to obtain an anti-corrosion coating.

[0021] Cured polytetrafluoroethylene (PTFE) materials are heat-resistant and do not easily age even at temperatures well above 300°C. Oxidation furnaces for carbon fiber production operate at temperatures between 200 and 300°C, allowing PTFE-cured materials to have a long service life within these furnaces. Graphite-like carbon nitride (g-C3N4) also exhibits high-temperature and corrosion resistance. Its semiconductor structure's core mechanism lies in its unique layered π-conjugated structure and suitable narrow band gap of approximately 2.7 eV. Upon absorbing visible light, electrons in the valence band of g-C3N4 are excited and transition to the conduction band, forming electron-hole pairs. Due to the material's layered structure, charge carriers are encouraged to suppress charge recombination, and the separated carriers migrate to the surface to participate in the reaction: electrons in the conduction band have strong reducing power, directly reducing oxygen to generate superoxide radicals and other reactive species; holes in the valence band can directly oxidize pollutants or react with water to generate hydroxyl radicals. These active substances work together to achieve highly efficient degradation of organic pollutants. This mechanism enables g-C3N4 to demonstrate significant advantages in the field of solar-driven advanced oxidation. The coating, composed of PTFE and g-C3N4, imparts corrosion resistance to the interior of the oxidation furnace, effectively preventing the reaction of acidic gases such as HCN and NH3 generated during the carbon fiber pre-oxidation stage with the furnace wall metal substrate, thus effectively avoiding pitting corrosion, uniform corrosion, and even furnace wall perforation. Furthermore, this coating can pre-treat acidic gases such as HCN and NH3 before they enter the waste discharge system, reducing the pressure on the system. Finally, applying this coating to the inner wall of the oxidation furnace effectively prevents the formation of unstable oxide scale on the furnace wall metal substrate at high temperatures, avoiding environmental pollution within the furnace and improving the quality of carbon fiber products.

[0022] It should be noted that the ratio of polytetrafluoroethylene (PTFE) to graphite-like carbon nitride should be within the range required by this invention. For example, if the PTFE content is too high, it will completely coat the graphite-like carbon nitride, leaving little or no exposed graphite-like carbon nitride, resulting in fewer reactive sites and thus a poorer removal effect on acidic gases. If the content is too low, the adhesion of the coating to the substrate will decrease, which will reduce its service life.

[0023] Specifically, the preparation method includes: S1. Preparation of g-C3N4 Melamine is calcined at 530–570°C (e.g., 530°C, 550°C, or 570°C), with the temperature continuously increased at a rate of 2–5°C / min (e.g., 2°C / min, 3°C / min, or 5°C / min) for 3–5 hours (e.g., 3 hours, 4 hours, or 5 hours) to obtain the initial product. This calcination method produces g-C3N4 with relatively higher purity, and multiple studies have shown that this calcination method has been applied.

[0024] The initial product was ground into powder and then washed sequentially with ethanol and deionized water. After drying, the finished product, graphite-phase carbon nitride, was obtained. The surface of the calcined initial product contained impurities such as organic matter and salt ions. These impurities were effectively removed by using ethanol and deionized water, thus obtaining high-purity g-C3N4.

[0025] Optionally, to ensure that impurities are removed more thoroughly, the washing process may be repeated with ethanol and deionized water 2 to 6 times (e.g., 2, 4, or 6 times).

[0026] Optionally, to ensure that impurities are removed more thoroughly, centrifugal washing is used. Preferably, the centrifugal washing speed is 5000~6000 r / min (e.g., 5000 r / min, 5500 r / min or 6000 r / min).

[0027] S2, Preparation of paste A paste with a solid content of 50-80% (e.g., 50%, 60%, 65%, 70%, or 80%) is prepared by uniformly mixing g-C3N4, a PTFE-containing dispersion, and a solvent, wherein the mass ratio of g-C3N4 to PTFE is 1-10:0.6 (e.g., 1:0.6, 2:0.6, 5:0.6, or 10:0.6). When the solid content of the paste is within the above range, it exhibits optimal viscosity, ensuring better adhesion of the paste to the inner wall of the oxidation furnace.

[0028] Preferably, the mass ratio of g-C3N4 to PTFE is 1 to 5:0.6 (e.g., 1:0.6, 3:0.6 or 5:0.6), and more preferably 2:0.6.

[0029] Optionally, the solvent is selected from at least one of alcohols such as ethanol and methanol, which are volatile and stable.

[0030] S3, Forming a coating The paste is applied to the surface of the substrate, dried, and cured to obtain an anti-corrosion coating.

[0031] Optionally, the drying temperature is 80~120℃ (e.g., 80℃, 100℃ or 120℃) and the time is 60~120min (e.g., 60 min, 80 min, 100 min or 120 min).

[0032] Optionally, the curing temperature is 320–360°C (e.g., 320°C, 340°C, or 360°C), and the time is 40–120 min (e.g., 40 min, 60 min, 80 min, 100 min, or 120 min). At this temperature, the particles or molecular chain segments are physically fused, crystallized, or form a dense structure using high temperature. This is a physical change, rather than a thermosetting crosslinking chemical reaction like that of thermosetting resins, thus obtaining a coating with high-temperature resistance.

[0033] Preferably, the substrate is the inner wall of an oxidation furnace.

[0034] This invention also provides an oxidation furnace, the inner wall of which is provided with an anti-corrosion coating, the anti-corrosion coating being prepared by the method provided by this invention.

[0035] This invention also provides a method for preparing carbon fiber, the preparation steps of which include: pre-oxidizing polyacrylonitrile precursor fibers in an oxidation furnace, wherein the oxidation furnace is the oxidation furnace provided in this invention.

[0036] Because this preparation method uses the oxidation furnace provided in the embodiments of the present invention to pre-oxidize the polyacrylonitrile-based precursor fibers, the furnace wall is not easily corroded and the materials inside the furnace are not easily contaminated, so it is foreseeable that the carbon fibers produced will be of good quality.

[0037] Example 1 (1) Using thermal polymerization, powdered melamine was placed in a ceramic boat, the ceramic boat was wrapped with tin foil to prevent the material from volatilizing, and then placed in a muffle furnace and calcined at 550°C. During the calcination process, the temperature was continuously increased at a heating rate of 4°C / min for 4 hours. After the calcination was completed, the sample was cooled to room temperature.

[0038] After cooling, the material was ground into powder, and the resulting particles were washed sequentially by centrifugation with ethanol and deionized water. Finally, it was dried at 105°C to obtain g-C3N4.

[0039] (2) g-C3N4 powder catalyst, dispersion containing 60%wt PTFE (Dongguan Xingwang Plastic Raw Materials Co., Ltd., Daikin d210, where the weight average molecular weight of PTFE is 10000), and ethanol were mixed uniformly in a mass ratio of 2:1:1 to obtain a paste-like mixture with a solid content of 65%.

[0040] (3) Apply the paste mixture to the inner wall of the oxidation furnace, dry it at 120°C for 1 hour, and then raise the temperature to 340°C to cure for 60 minutes, forming a corrosion-resistant coating with a thickness of 2 cm on the inner wall of the oxidation furnace.

[0041] Example 2 This embodiment is basically the same as Example 1, except that the mass ratio of g-C3N4 to the dispersion containing 60%wt PTFE is 1:1, that is, the mass ratio of g-C3N4 to PTFE is 1:0.6.

[0042] Example 3 This embodiment is basically the same as Embodiment 1, except that the mass ratio of g-C3N4 to the dispersion containing 60%wt PTFE is 5:1, that is, the mass ratio of g-C3N4 to PTFE is 5:0.6.

[0043] Example 4 This embodiment is basically the same as Embodiment 1, except that the mass ratio of g-C3N4 to the dispersion containing 60%wt PTFE is 10:1, that is, the mass ratio of g-C3N4 to PTFE is 10:0.6.

[0044] Experimental Example 1 The NO removal efficiency of the coatings prepared in Examples 1-4 and Comparative Example 1 was tested using the following method: The NO flow rate was adjusted to 39 mL / min, and the compressed air flow rate was adjusted to 0.86 mL / min. The two gases were fed into a high-pressure mixer in a specific ratio and magnetically stirred to form a mixed gas. This mixed gas was then introduced into an oxidation furnace with the aforementioned coating on its inner wall. The NO removal efficiency was recorded after different time periods. Figure 1 middle.

[0045] from Figure 1 It can be seen that the coating containing g-C3N4 has a significant removal effect on NO. The optimal ratio of g-C3N4 to PTFE-containing dispersion is 1–5:1, with 2:1 being the best. If the PTFE ratio is too low, the coating's adhesion decreases, thus reducing removal efficiency. If the PTFE ratio is too high, the PTFE over-encapsulates the g-C3N4, resulting in the loss of many reactive sites and further reducing the removal rate.

[0046] Experiment Example 2 A cyclic experiment was conducted on the coating of Example 1, with each cycle lasting 120 minutes, for a total of 5 cycles. The results were recorded. Figure 2 , Figure 2 The vertical axis represents the ratio of actual concentration to initial concentration; a lower ratio indicates a higher pollutant removal rate. Figure 2As can be seen, the removal efficiency remains stable after 5 cycles, and the coating prepared in this embodiment of the invention has good mechanical strength and cycle stability.

[0047] In summary, the coating prepared by the method provided by this invention, being composed of polytetrafluoroethylene and graphite-like carbon nitride, imparts corrosion resistance to the inner wall of the oxidation furnace. It effectively blocks the reaction of acidic gases such as HCN and NH3 generated during the carbon fiber pre-oxidation stage with the furnace wall metal substrate, effectively preventing pitting corrosion, uniform corrosion, and even furnace wall perforation. Furthermore, the coating can pre-treat acidic gases such as HCN and NH3 before they enter the waste discharge system, reducing the pressure on the system. Finally, applying this coating to the inner wall of the oxidation furnace effectively prevents the formation of unstable oxide scale on the furnace wall metal substrate at high temperatures, avoiding environmental pollution within the furnace and improving the quality of carbon fiber products.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an anti-corrosion coating, characterized in that, include: A paste is provided, the main components of which include graphitic carbon nitride in a mass ratio of 1 to 10:0.6 and polytetrafluoroethylene with a weight average molecular weight of 9,000 to 11,000; The paste is applied to the surface of the substrate, dried, and cured to obtain an anti-corrosion coating.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the graphitic carbon nitride to the polytetrafluoroethylene is 1~5:

1.

3. The preparation method according to claim 1, characterized in that, The solid content of the paste is 50-80%; Optionally, the paste is composed of graphite-like carbon nitride, polytetrafluoroethylene, and a solvent; Optionally, the solvent is selected from at least one of ethanol and methanol.

4. The preparation method according to claim 1, characterized in that, The curing temperature is 300~360℃ and the curing time is 40~120min.

5. The preparation method according to claim 1, characterized in that, The method for preparing the graphite-like carbon nitride includes: Melamine was calcined at 530-570℃, with the temperature continuously increased at a rate of 2-5℃ / min, and the initial product was obtained after calcination for 3-5 hours. The initial product was ground into powder and then washed with ethanol and deionized water in sequence. After drying, the finished product, graphite-phase carbon nitride, was obtained.

6. The preparation method according to claim 5, characterized in that, Wash with ethanol and deionized water 2 to 6 times in sequence.

7. The preparation method according to claim 5, characterized in that, The washing method is centrifugal washing; Optionally, the centrifugal washing speed is 5000~6000 r / min.

8. The preparation method according to claim 1, characterized in that, The substrate is the inner wall of an oxidation furnace.

9. An oxidation furnace, characterized in that, Its inner wall is provided with an anti-corrosion coating, which is prepared by the preparation method described in any one of claims 1 to 8.

10. A method for preparing carbon fiber, characterized in that, The preparation steps include: pre-oxidizing polyacrylonitrile precursor fibers in an oxidation furnace, wherein the oxidation furnace is the oxidation furnace as described in claim 9.

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