Method for recovering waste carbon fibers by catalytic pyrolysis with steam
By using potassium hydroxide and sodium carbonate catalysts in a steam atmosphere for catalytic pyrolysis, the problems of carbon fiber damage and residual carbon removal in traditional pyrolysis methods have been solved, achieving low-temperature and high-efficiency carbon fiber recycling and improving the performance and economic value of recycled fibers.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHANGZHOU UNIV
- Filing Date
- 2026-04-17
- Publication Date
- 2026-06-05
AI Technical Summary
Existing pyrolysis technologies require high-temperature and long-term processing, which leads to severe damage to carbon fibers, incomplete resin decomposition, difficulty in removing residual carbon, and high energy consumption, making it difficult to achieve efficient recycling and reuse of carbon fibers.
Potassium hydroxide and sodium carbonate are used as composite catalysts to carry out catalytic pyrolysis under a steam atmosphere. Water vapor is used to assist in the degradation of the resin matrix, reduce the reaction temperature and time, promote the gasification of residual carbon, and preserve the properties of carbon fibers.
Achieving full decomposition of resin and removal of residual carbon at lower temperatures significantly improves the retention rate of mechanical properties of carbon fibers, reduces energy consumption, and enables efficient recycling and reuse of carbon fibers.
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Figure CN122145871A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of resource recycling technology, and specifically discloses a method for recycling waste carbon fiber by steam catalytic pyrolysis. Background Technology
[0002] Carbon fiber reinforced polymer (CFRP) composites, with their excellent specific strength, specific modulus, corrosion resistance, and designability, have been widely used in key fields such as aerospace, wind turbine blades, and automotive lightweighting. With the rapid development and product iteration of these industries, a large amount of waste CFRP has been generated, either reaching the end of its service life or formed during production. If these high-value waste materials are disposed of through traditional landfill or incineration methods, it will not only result in a huge waste of precious carbon fiber resources but also cause serious environmental pollution and land occupation problems due to the difficulty of natural degradation of thermosetting resins, thus violating the development concepts of green, low-carbon, and circular economy.
[0003] To achieve the recycling of carbon fiber resources, the industry has developed various recycling technologies, mainly including mechanical, chemical, and pyrolysis methods. Mechanical methods obtain short fibers through physical crushing; the process is simple, but the fibers suffer severe damage, shortening in length and significantly degrading in performance, typically only suitable for use as fillers, resulting in low economic value. While chemical methods can decompose resins under relatively mild conditions and obtain fibers with better performance retention, they generally suffer from complex processes, require large amounts of organic solvents, are costly, have stringent equipment requirements (high temperature and pressure), and pose potential environmental risks, making large-scale industrial applications difficult.
[0004] In contrast, pyrolysis is currently the most technologically mature and the only recycling method that has been successfully industrialized. Its core principle is to thermally decompose the resin matrix through high-temperature heating in an inert or specific atmosphere, thereby separating the carbon fibers. This method has comprehensive advantages such as large processing capacity, continuous operation, and the ability to recover resin decomposition products as fuel or chemical raw materials, making it considered the most promising recycling method. However, existing traditional pyrolysis technologies still have significant technical bottlenecks. First, to achieve complete resin decomposition, high reaction temperatures (usually above 500-800℃) are often required. Prolonged high-temperature treatment leads to severe thermal oxidation damage to the carbon fibers, destroying the graphite microcrystalline structure and forming surface defects, resulting in significant losses in key mechanical properties such as tensile strength and modulus of the recycled fibers. Second, after pyrolysis in an inert atmosphere, a large amount of amorphous pyrolysis carbon often remains on the fiber surface. If not removed, this will seriously affect the interfacial bonding performance between the regenerated fibers and the resin. Furthermore, if the subsequent oxidation step to remove residual carbon is not properly controlled, it can easily cause secondary oxidation damage to the fiber itself. In addition, high energy consumption and long cycles also increase the operating costs and environmental burden of the entire recycling process.
[0005] Therefore, developing a novel pyrolysis process that can efficiently degrade resin at relatively low temperatures and in a short time, while effectively removing residual carbon and maximizing the protection of the inherent properties of carbon fibers, has become a key technical problem that urgently needs to be solved in the field of high-value recycling of waste CFRP. Summary of the Invention
[0006] This invention addresses the technical problems of traditional pyrolysis methods, such as high temperature, long processing time, and severe damage to carbon fibers, by proposing a steam catalytic pyrolysis method for recycling waste carbon fibers. This method can degrade the resin matrix at lower temperatures, significantly shorten processing time, reduce energy consumption, and achieve efficient and low-loss recycling of carbon fibers.
[0007] To achieve the above objectives, the present invention adopts the following technical solution:
[0008] This invention uses waste carbon fiber as raw material and potassium hydroxide and sodium carbonate as composite catalysts to carry out catalytic pyrolysis under a steam atmosphere. Specifically, it includes the following steps:
[0009] S1. The carbon fiber to be degraded is washed with deionized water, dried at 105°C for 8 hours, and then placed in the reaction apparatus.
[0010] In step S1, the waste carbon fiber is polyacrylonitrile-based carbon fiber or pitch-based carbon fiber, with a carbon fiber mass fraction of 60%; the waste carbon fiber forms include chopped fibers, continuous fibers, or carbon fiber fabrics; the resin matrix contained in the carbon fiber is a thermosetting resin, including epoxy resin, unsaturated polyester resin, or vinyl resin, with a resin matrix mass fraction of approximately 40%.
[0011] The carbon fiber to be degraded is cut to a size of 3cm*3cm*2mm and weighs 1g; a tube furnace is selected as the reaction device.
[0012] S2. Add the composite catalyst into the reaction device according to the preset ratio; introduce steam at a flow rate of 50 ml / min, raise the furnace temperature from room temperature to 200-400℃ at a rate of 10℃ / min and keep it at that temperature for 20-40 min.
[0013] In step S2, the composite catalyst uses potassium hydroxide and sodium carbonate in a mass ratio of 1:(0.25-1); the mass ratio of the composite catalyst to carbon fiber is 1.25-2:1.
[0014] S3. After the reaction is complete, wait for the tube furnace to cool to room temperature, take out the product, ultrasonically wash it with deionized water, and dry it to obtain the recovered carbon fiber.
[0015] The present invention has the following beneficial effects:
[0016] (1) The KOH / Na2CO3 composite catalyst used in this invention can effectively catalyze the breaking of chemical bonds in the resin matrix and promote its deep pyrolysis at a lower temperature. This not only significantly reduces the reaction activation energy and shortens the pyrolysis time, but also acts simultaneously on the residual carbon generated during the pyrolysis process, promoting its further gasification or conversion, thereby achieving full removal of the resin matrix and deep cleaning of the fiber surface, solving the problem that residual carbon is difficult to remove in traditional pyrolysis and affects fiber reuse.
[0017] (2) Because the reaction temperature is significantly lower than that of traditional pyrolysis, the oxidation and thermal damage to the carbon fiber structure caused by high temperature are greatly reduced. This invention can ensure that the mechanical properties of recycled carbon fibers are retained at a stable rate of over 95%, which is much higher than many traditional pyrolysis processes, greatly improving the reuse value of recycled fibers and enabling them to be reused in fields with high performance requirements.
[0018] (3) Steam is introduced as the reaction medium, and water gas reaction (C+H2O→CO+H2) and hydroxyl steam reforming reaction (C+H2O→CO+H2) occur under the combined catalysis of KOH / Na2CO3. n H m +nH2O→nCO+(n+m / 2)H2), this function is that the solid coke and high molecular weight liquid tar generated in the early stage of pyrolysis are gasified in situ and converted into clean gases such as H2 and a small amount of CO2. In principle, it eliminates the path of carbon deposition on the fiber surface, so that the surface of the recovered carbon fiber is almost free of residual carbon and no secondary high temperature oxidation treatment is required, thereby maximizing the preservation of the tensile strength of the fiber monofilament. Attached Figure Description
[0019] For ease of explanation, the present invention will be described in detail below with reference to specific embodiments and accompanying drawings.
[0020] Figure 1 The graphs show the weight loss rate and resin degradation rate of carbon fibers prepared in Examples 1-8(a) and Comparative Examples 1-3(b) of this invention.
[0021] Figure 2 SEM images of carbon fibers prepared in Comparative Examples 1(a), 2(b), 3(c), and 6(d) of this invention.
[0022] Figure 3 Thermogravimetric analysis (TGA) diagrams of carbon fibers prepared in Comparative Examples 3 (a, b) and Examples 6 (c, d) of this invention.
[0023] Figure 4 This is a process flow diagram for preparing recycled carbon fiber in Example 6 of the present invention. Detailed Implementation
[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. The carbon fiber in the selected waste carbon fiber composite material is Toray T700, with a single filament tensile strength of 4.90 GPa. It is a PAN-based fiber, in continuous fiber form, and has a mass fraction of 60%. The resin matrix is 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester (TDE-85, approximately 65%), and the curing agent is diaminodiphenyl sulfone (DDS, approximately 35%).
[0025] Example 1
[0026] The carbon fibers to be degraded were washed with deionized water, dried at 105℃ for 8 hours, and then cut to dimensions of 3cm*3cm*2mm, weighing 1g, and placed in a tube furnace. Potassium hydroxide and sodium carbonate were spread evenly on the cut carbon fibers at a mass ratio of 1:0.25, with a spreading amount of 0.1g / cm². 2 The product was placed in a tube furnace. Steam was introduced at a flow rate of 50 ml / min, and the furnace temperature was increased from room temperature (25°C) to 300°C at a rate of 10°C / min and held for 20 minutes. After the reaction was complete, the tube furnace was allowed to cool to room temperature. The product was then removed, ultrasonically washed with deionized water, and dried to obtain the recovered carbon fiber.
[0027] According to the ASTM-D3379 standard, the recycled carbon fiber was subjected to a single filament tensile test, and the single filament tensile strength was 3.73 GPa, with a strength retention rate of 3.73 / 4.90 = 76.12%.
[0028] Example 2
[0029] The carbon fibers to be degraded were washed with deionized water, dried at 105℃ for 8 hours, and then cut to dimensions of 3cm*3cm*2mm, weighing 1g. These were then placed in a tube furnace. Potassium hydroxide and sodium carbonate were spread evenly on the cut carbon fibers at a mass ratio of 1:0.25, with a spreading amount of 0.1g / cm². 2 The product was placed in a tube furnace. Steam was introduced at a flow rate of 50 ml / min, and the furnace temperature was increased from room temperature (25°C) to 350°C at a rate of 10°C / min and held for 20 minutes. After the reaction was complete, the tube furnace was allowed to cool to room temperature. The product was then removed, ultrasonically washed with deionized water, and dried to obtain the recovered carbon fiber.
[0030] According to the ASTM-D3379 standard, the recycled carbon fiber was subjected to a single filament tensile test, and the single filament tensile strength was 3.88 GPa, with a strength retention rate of 3.88 / 4.90=79.18%.
[0031] Example 3
[0032] The carbon fibers to be degraded were washed with deionized water, dried at 105℃ for 8 hours, and then cut to dimensions of 3cm*3cm*2mm, weighing 1g. These were then placed in a tube furnace. Potassium hydroxide and sodium carbonate were spread evenly on the cut carbon fibers at a mass ratio of 1:0.25, with a spreading amount of 0.1g / cm². 2 The product was placed in a tube furnace. Steam was introduced at a flow rate of 50 ml / min, and the furnace temperature was increased from room temperature (25°C) to 400°C at a rate of 10°C / min and held for 20 minutes. After the reaction was complete, the tube furnace was allowed to cool to room temperature. The product was then removed, ultrasonically washed with deionized water, and dried to obtain the recovered carbon fiber.
[0033] According to the ASTM-D3379 standard, the recycled carbon fiber was subjected to a single filament tensile test, and the single filament tensile strength was 3.68 GPa, with a strength retention rate of 3.68 / 4.90=75.10%.
[0034] Example 4
[0035] The carbon fibers to be degraded were washed with deionized water, dried at 105℃ for 8 hours, and then cut to dimensions of 3cm*3cm*2mm, weighing 1g. These were then placed in a tube furnace. Potassium hydroxide and sodium carbonate were spread evenly on the cut carbon fibers at a mass ratio of 1:0.25, with a spreading amount of 0.1g / cm². 2 The product was placed in a tube furnace. Steam was introduced at a flow rate of 50 ml / min, and the furnace temperature was increased from room temperature (25°C) to 350°C at a rate of 10°C / min and held for 30 minutes. After the reaction was complete, the tube furnace was allowed to cool to room temperature. The product was then removed, ultrasonically washed with deionized water, and dried to obtain the recovered carbon fiber.
[0036] According to the ASTM-D3379 standard, the recycled carbon fiber was subjected to a single filament tensile test, and the single filament tensile strength was 4.48 GPa, with a strength retention rate of 4.48 / 4.90=91.43%.
[0037] Example 5
[0038] The carbon fibers to be degraded were washed with deionized water, dried at 105℃ for 8 hours, and then cut to dimensions of 3cm*3cm*2mm, weighing 1g. These were then placed in a tube furnace. Potassium hydroxide and sodium carbonate were spread evenly on the cut carbon fibers at a mass ratio of 1:0.25, with a spreading amount of 0.1g / cm². 2 The product was placed in a tube furnace. Steam was introduced at a flow rate of 50 ml / min, and the furnace temperature was increased from room temperature (25°C) to 350°C at a rate of 10°C / min and held for 40 minutes. After the reaction was complete, the tube furnace was allowed to cool to room temperature. The product was then removed, ultrasonically washed with deionized water, and dried to obtain the recovered carbon fiber.
[0039] According to the ASTM-D3379 standard, the recycled carbon fiber was subjected to a single filament tensile test, and the single filament tensile strength was 4.18 GPa, with a strength retention rate of 4.18 / 4.90 = 85.31%.
[0040] Example 6
[0041] The carbon fibers to be degraded were washed with deionized water, dried at 105℃ for 8 hours, and then cut to dimensions of 3cm*3cm*2mm, weighing 1g. These were then placed in a tube furnace. Potassium hydroxide and sodium carbonate were spread evenly on the cut carbon fibers at a mass ratio of 1:0.5, with a spreading amount of 0.1g / cm². 2 The product was placed in a tube furnace. Steam was introduced at a flow rate of 50 ml / min, and the furnace temperature was increased from room temperature (25°C) to 350°C at a rate of 10°C / min and held for 30 minutes. After the reaction was complete, the tube furnace was allowed to cool to room temperature. The product was then removed, ultrasonically washed with deionized water, and dried to obtain the recovered carbon fiber.
[0042] According to the ASTM-D3379 standard, the recycled carbon fiber was subjected to a single filament tensile test, and the single filament tensile strength was 4.82 GPa, with a strength retention rate of 4.82 / 4.90 = 98.37%.
[0043] Example 7
[0044] The carbon fibers to be degraded were washed with deionized water, dried at 105℃ for 8 hours, and then cut to dimensions of 3cm*3cm*2mm, weighing 1g. These were then placed in a tube furnace. Potassium hydroxide and sodium carbonate were spread evenly on the cut carbon fibers at a mass ratio of 1:0.75, with a spreading amount of 0.1g / cm². 2 The product was placed in a tube furnace. Steam was introduced at a flow rate of 50 ml / min, and the furnace temperature was increased from room temperature (25°C) to 350°C at a rate of 10°C / min and held for 30 minutes. After the reaction was complete, the tube furnace was allowed to cool to room temperature. The product was then removed, ultrasonically washed with deionized water, and dried to obtain the recovered carbon fiber.
[0045] According to the ASTM-D3379 standard, the recycled carbon fiber was subjected to a single filament tensile test, and the single filament tensile strength was 4.42 GPa, with a strength retention rate of 4.42 / 4.90=90.20%.
[0046] Example 8
[0047] The carbon fibers to be degraded were washed with deionized water, dried at 105℃ for 8 hours, and then cut to dimensions of 3cm*3cm*2mm, weighing 1g. These were then placed in a tube furnace. Potassium hydroxide and sodium carbonate were spread evenly on the cut carbon fibers in a 1:1 mass ratio, with a spreading amount of 0.1g / cm². 2 The product was placed in a tube furnace. Steam was introduced at a flow rate of 50 ml / min, and the furnace temperature was increased from room temperature (25°C) to 350°C at a rate of 10°C / min and held for 30 minutes. After the reaction was complete, the tube furnace was allowed to cool to room temperature. The product was then removed, ultrasonically washed with deionized water, and dried to obtain the recovered carbon fiber.
[0048] According to the ASTM-D3379 standard, the recycled carbon fiber was subjected to a single filament tensile test, and the single filament tensile strength was 4.36 GPa, with a strength retention rate of 4.36 / 4.90=88.98%.
[0049] Comparative Example 1
[0050] The carbon fibers to be degraded were washed with deionized water, dried at 105℃ for 8 hours, and then cut to dimensions of 3cm*3cm*2mm, weighing 1g. These were then placed in a tube furnace. Steam was introduced at a flow rate of 50ml / min, and the furnace temperature was increased from room temperature (25℃) to 350℃ at a rate of 10℃ / min and held for 30 minutes. After the reaction was complete, the tube furnace was allowed to cool to room temperature. The product was then removed, ultrasonically washed with deionized water, and dried to obtain the recovered carbon fibers.
[0051] According to the ASTM-D3379 standard, the recycled carbon fiber was subjected to a single filament tensile test, and the single filament tensile strength was 2.95 GPa, with a strength retention rate of 2.95 / 4.90=60.20%.
[0052] Comparative Example 2
[0053] The carbon fibers to be degraded were washed with deionized water, dried at 105℃ for 8 hours, and then cut to dimensions of 3cm*3cm*2mm, weighing 1g, and placed in a tube furnace. Potassium hydroxide was then spread evenly on the cut carbon fibers at an amount of 0.1g / cm². 2 The product was placed in a tube furnace. Steam was introduced at a flow rate of 50 ml / min, and the furnace temperature was increased from room temperature (25°C) to 350°C at a rate of 10°C / min and held for 30 minutes. After the reaction was complete, the tube furnace was allowed to cool to room temperature. The product was then removed, ultrasonically washed with deionized water, and dried to obtain the recovered carbon fiber.
[0054] According to the ASTM-D3379 standard, the recycled carbon fiber was subjected to a single filament tensile test, and the single filament tensile strength was 3.14 GPa, with a strength retention rate of 3.14 / 4.90=64.08%.
[0055] Comparative Example 3
[0056] The carbon fibers to be degraded were washed with deionized water, dried at 105℃ for 8 hours, and then cut to dimensions of 3cm*3cm*2mm, weighing 1g, and placed in a tube furnace. Sodium carbonate was then evenly spread on the cut carbon fibers at a rate of 0.1g / cm². 2 The product was placed in a tube furnace. Steam was introduced at a flow rate of 50 ml / min, and the furnace temperature was increased from room temperature (25°C) to 350°C at a rate of 10°C / min and held for 30 minutes. After the reaction was complete, the tube furnace was allowed to cool to room temperature. The product was then removed, ultrasonically washed with deionized water, and dried to obtain the recovered carbon fiber.
[0057] According to the ASTM-D3379 standard, the recycled carbon fiber was subjected to a single filament tensile test, and the single filament tensile strength was 3.35 GPa, with a strength retention rate of 3.35 / 4.90=68.37%.
[0058] The mechanical properties of the carbon fibers obtained in the various embodiments and comparative examples of this invention are shown in Table 1.
[0059] Table 1 Mechanical properties of pyrolytic carbon fibers
[0060]
[0061] The carbon fibers obtained in Example 6 and each comparative example were subjected to the same elemental analysis, and the results are shown in Table 2.
[0062] Table 2 Elemental Analysis of Pyrolytic Carbon Fibers
[0063]
Claims
1. A method for recovering waste carbon fiber by steam catalytic pyrolysis, characterized in that, The method uses waste carbon fiber as raw material and potassium hydroxide and sodium carbonate as composite catalysts to carry out catalytic pyrolysis under a steam atmosphere.
2. The method for recovering waste carbon fiber by steam catalytic pyrolysis according to claim 1, characterized in that, The method steps are as follows: S1. The waste carbon fiber to be degraded is washed with deionized water, dried and then placed in a tube furnace. S2. Place the composite catalyst into the tube furnace, introduce steam, raise the furnace temperature from room temperature to the reaction temperature, and maintain the temperature. S3. After the reaction is complete, wait for the tube furnace to cool to room temperature, take out the product, ultrasonically wash it with deionized water, and dry it to obtain the recovered carbon fiber.
3. The method for recovering waste carbon fiber by steam catalytic pyrolysis according to claim 2, characterized in that, In step S1, the waste carbon fiber is polyacrylonitrile-based carbon fiber or pitch-based carbon fiber, and the carbon fiber mass fraction is 60%.
4. The method for recovering waste carbon fiber by steam catalytic pyrolysis according to claim 2, characterized in that, In step S1, the waste carbon fiber forms include chopped fibers, continuous fibers, or carbon fiber fabrics.
5. The method for recovering waste carbon fiber by steam catalytic pyrolysis according to claim 2, characterized in that, In step S1, the resin matrix of the carbon fiber is epoxy resin, unsaturated polyester resin or vinyl resin, and the mass fraction of the resin matrix is 40%.
6. The method for recovering waste carbon fiber by steam catalytic pyrolysis according to claim 2, characterized in that, In step S1, the waste carbon fiber to be degraded is cut into pieces with dimensions of 3cm*3cm*2mm. The carbon fiber is dried at 105℃ for 8 hours.
7. The method for recovering waste carbon fiber by steam catalytic pyrolysis according to claim 2, characterized in that, In step S2, the mass ratio of potassium hydroxide to sodium carbonate in the composite catalyst is 1:0.25-1.
8. The method for recovering waste carbon fiber by steam catalytic pyrolysis according to claim 2, characterized in that, In step S2, the mass ratio of the composite catalyst to the carbon fiber is 1.25-2:1, and the water vapor flow rate is 50 ml / min.
9. The method for recovering waste carbon fiber by steam catalytic pyrolysis according to claim 2, characterized in that, In step S2, the reaction temperature is 200-400℃, the holding time is 20-40 min, and the heating rate is 10℃ / min.