Method for recycling and full-quantitative reuse of products of carbon fibers in thermosetting composite materials by chemical assisted pyrolysis

Abstract

The application discloses a kind of carbon fiber chemical auxiliary pyrolysis recovery in thermosetting composite material and product full quantization recycling method, first retired wind power blade thermosetting composite material is cut and sorted to obtain blade block material, then pretreatment agent is handled, then recovery pretreatment agent, again, blade block material after being handled with pretreatment agent is low-temperature pyrolysis with swelling agent, recycles regenerated carbon fiber, finally recovery swelling agent and resin degradation product.The method not only realizes the efficient thermal separation of carbon fiber and matrix resin, but also efficiently recycles the used citric acid reagent by in-depth study of the chemical properties of the degradation products and the pretreatment agent. The method combines centrifugal separation with vacuum distillation technology to separate the swelling agent and the degraded resin polymer, achieving full quantization recovery of the process solid and liquid products. The recycled reagent is directly used for the next round of material degradation treatment, significantly reducing reagent consumption and processing cost, while reducing environmental pollution risk and achieving recycling closed loop.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment technology, specifically to a method for chemically assisted pyrolysis recovery of carbon fibers in thermosetting composite materials and full-scale reuse of the products. Background Technology

[0002] With the adjustment of the global energy structure and the rapid development of the wind power industry, wind power generation has become an important solution to address climate change. However, the issue of wind turbine blade retirement is becoming increasingly prominent, and its resource recycling has become a significant challenge for the green, low-carbon, and high-quality development of the entire wind power industry chain. With the continuous growth of wind power installed capacity and the expiration of equipment lifespan, the amount of retired wind turbine blades will experience explosive growth after 2025. Wind turbine blades are mainly made of glass fiber reinforced resin matrix composites, but with the continuous increase in blade size, carbon fiber reinforced composites, due to their excellent specific strength and specific stiffness, are being used more and more widely in key load-bearing components. This carbon fiber reinforced thermosetting composite material has a stable chemical structure and is difficult to degrade naturally. Traditional treatment methods such as landfill and incineration not only waste resources and damage carbon fiber materials but also easily cause environmental pollution.

[0003] Currently, the mainstream technologies for recycling decommissioned wind turbine blades include mechanical recycling, thermal recycling, and chemical recycling. Mechanical recycling and pyrolysis recycling technologies have the greatest potential for practical engineering applications. Mechanical recycling uses mechanical equipment to cut or crush the blades into small pieces or granules, which can then be used as filler or building materials. This method is technically simple, but it causes fiber breakage, making it impossible to recover high-quality fibers, and it generates a large amount of dust and noise pollution, making it difficult to achieve long fiber recycling and high-value applications. Thermal recycling is usually carried out at high temperatures (>500℃). Although it can effectively separate fibers and resin, the high energy consumption and high temperature can cause damage to the carbon fiber surface, resulting in a significant decrease in mechanical properties. At the same time, the carbon deposits generated by incomplete pyrolysis require additional oxidation treatment, which may further reduce fiber strength. Although chemical recycling can achieve resin degradation at lower temperatures, traditional chemical methods often rely on strong acids or toxic solvents (such as concentrated sulfuric acid, nitric acid, etc.), which not only increases processing costs but may also cause serious secondary pollution. These problems are particularly serious when applied on a large scale. Furthermore, existing technologies generally neglect the full-scale recycling and utilization of degradation products (such as bisphenol A and oligomers) and chemical treatment solvents, leading to resource waste and increased environmental burden. These traditional processes share a common drawback: the difficulty in balancing efficiency, environmental friendliness, and economics, thus hindering breakthroughs in their industrial application.

[0004] Chinese patent CN117644598A discloses a pyrolysis method in which perforated blades are placed in a sealed cavity, and heating rods or heated molten salt are injected into each hole, followed by degradation under an inert atmosphere and high temperature. This method has a high product recovery rate and good fiber properties, but the high temperature (>500℃) usually leads to high energy consumption, and the surface quality of the carbon fiber is also damaged to some extent. In addition, the incomplete pyrolysis products of the high-temperature resin matrix will generate carbon deposits that adhere to the surface of the recycled carbon fiber. Although carbon deposits can be removed by oxidation, it will reduce the tensile strength and other mechanical properties of the material to some extent. Chinese patent CN115739929A ​​invented a chemical recycling method based on a pyrolysis promoter. This method can obtain glass fibers with clean surfaces and good mechanical properties without further mechanical separation or oxidation post-treatment processes to remove pyrolysis carbon. However, the pyrolysis temperature of this method still exceeds 500℃, and the high temperature will damage the fiber quality to some extent. Furthermore, there is no corresponding disposal method for the reagent waste liquid and resin degradation materials generated during the recycling process, resulting in extremely low waste reuse rate. Existing patents sometimes use chemical reagents such as strong acids or toxic solvents, which not only increase recycling costs but also pose a risk of secondary pollution. Chemical reagent-based fiber recycling methods only consider resin degradation products (DERs) as useless byproducts without fully exploring their potential value in material reuse. Small-molecule oligomers generated after epoxy resin degradation are often discarded, failing to achieve resource recycling. The selection of chemical reagents (such as swelling agents and pretreatment agents) often focuses solely on degradation efficiency, without systematically designing for the reagents' environmental friendliness and recycling potential.

[0005] Therefore, this invention proposes a method for chemically assisted pyrolysis recovery of carbon fibers in thermosetting composite materials and full-scale reuse of the products. Summary of the Invention

[0006] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for chemically assisted pyrolysis recovery of carbon fibers in thermosetting composite materials and full-scale reuse of the products. This method not only achieves efficient separation of fibers and resin matrix, but also, through in-depth research and selection of the chemical properties of degradation products and pretreatment agents, adopts appropriate chemical treatment methods to efficiently recover the citric acid reagent used. Furthermore, by combining centrifugal separation with vacuum distillation technology, the swelling agent and degradation resin polymer are separated, achieving full-scale recovery of solid and liquid phase products in the treatment process.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: A method for chemically assisted pyrolysis recovery of carbon fibers in thermosetting composite materials and full-scale reuse of the products includes the following steps: 1) First, remove the metal parts, PVC foam, balsa wood and structural adhesive from the retired wind turbine blades to obtain the blade block material to be used in this invention. The obtained blade block material is mechanically cut and washed to obtain carbon fiber reinforced resin composite material of appropriate size. 2) Equipped with swelling agents and pretreatment agents; 3) First, immerse the carbon fiber reinforced resin composite material obtained in step 1) into a stainless steel pressure vessel containing the pretreatment agent prepared in step 2) and seal it. Place it in a water bath to allow the material to swell and degrade. After the reaction is complete, wash the filtered carbon fiber reinforced resin composite material with ultrapure water. Place the washed carbon fiber reinforced resin composite material in a vacuum oven to dry it. Filter the filtrate to obtain the pretreatment agent waste liquid. 4) Add calcium chloride to the pretreatment agent waste liquid obtained in step 3) to generate calcium citrate precipitate. After washing and drying the calcium citrate precipitate, dissolve it with dilute hydrochloric acid or dilute sulfuric acid to release citric acid solution and generate calcium chloride. Separate the citric acid solution by centrifugation, evaporate and crystallize to obtain solid citric acid, and then recycle it. 5) Next, the dried carbon fiber reinforced resin composite material from step 3) and the swelling agent prepared in step 2) are transported to the high-pressure reactor through the pipe. Nitrogen gas is introduced and the reaction is carried out without stirring. After the reaction is completed, the material in the high-pressure reactor is transported to a centrifuge. The liquid phase in the material is introduced into a vacuum distillation recovery device through the liquid phase outlet of the centrifuge to achieve centrifugal separation of solid and liquid phases. The solid phase in the material is washed with dichloromethane to remove organic matter on the surface and then placed in an oven to dry, obtaining clean regenerated fiber (rCF). 6) The liquid phase obtained in step 5) is separated by vacuum distillation. The swelling agent in the liquid phase is recovered and reused. The bisphenol A and small molecule oligomers in the DER in the liquid phase are used as raw materials to participate in the preparation of novel epoxy materials. 7) Purify the bisphenol A obtained in step 6), then mix it with epichlorohydrin, and add an appropriate amount of catalyst NaOH to react and obtain regenerated epoxy resin; mix the small molecule oligomer obtained in step 6) with a curing agent and a coupling agent to form a modified prepolymer, which can be used directly as an epoxy resin raw material.

[0008] Furthermore, the carbon fiber reinforced resin composite material obtained in step 1) has a length, width, and height of 10-15cm × 2-3cm × 0.5-1.5cm.

[0009] Furthermore, the swelling agent used in step 2) has a purity of 99.5%, and the swelling agent is selected from one or more of 1,3-propanediol and propylene glycol; The pretreatment agent is a citric acid solution with a concentration of 0.5–2 mol / L, preferably 1–2 mol / L; The mass ratio of the swelling agent to the total mass of the swelling agent and pretreatment agent solution is approximately 25-60 wt%, preferably 45-60 wt%; the mass ratio of the pretreatment agent solution to the total mass of the swelling agent and pretreatment agent solution is approximately 40-75 wt%, preferably 40-55 wt%.

[0010] Furthermore, when the swelling agent is propylene glycol methyl ether, due to its low boiling point, triethylene glycol dimethyl ether is used to prepare a mixed reagent with it, with a mass ratio of propylene glycol methyl ether to triethylene glycol dimethyl ether of 2:1 to 3:1.

[0011] Further, in step 3), the sealed stainless steel pressure vessel is placed in a water bath at room temperature. The temperature is first set to reach 80-100°C from room temperature in 5 minutes, and then continued for 2 hours to end the pretreatment stage. Then, the filtered carbon fiber reinforced resin composite material is washed with ultrapure water, and the washed carbon fiber reinforced resin composite material is placed in a vacuum oven and dried at 100°C for 1 hour.

[0012] Furthermore, in step 4), the centrifugation speed is 3000-5000 rpm and the centrifugation time is 5-10 min.

[0013] Furthermore, in step 5), the pressure in the high-pressure reactor is 0.1 MPa to 3.01 MPa, the reaction temperature is 150°C to 300°C, no stirring is performed, and the reaction time is 1 to 2 hours.

[0014] Furthermore, the pressure of vacuum distillation in step 6) is -0.089 to -0.013 MPa, and the vacuum distillation temperature is 130℃ to 170℃.

[0015] Furthermore, when the swelling agent is 1,3-propanediol, the vacuum distillation temperature is 170°C; when the swelling agent is propylene glycol, the vacuum distillation temperature is 150°C; and when the swelling agent is a mixed solvent of propylene glycol methyl ether and triethylene glycol dimethyl ether, the vacuum distillation temperature is 130°C.

[0016] Further, in step 7), the mass ratio of bisphenol A to epichlorohydrin and catalyst NaOH is 1:1.2-1.8:0.1-0.3; the mass ratio of small molecule oligomer to curing agent and coupling agent is 1:0.1-0.2:0.02-0.05; the small molecule oligomer includes bisphenol A type epoxy oligomer and a small amount of phenolic condensate; the curing agent is polyetheramine D230; and the coupling agent is KH-550.

[0017] The mechanism of this invention is as follows: 1) This invention innovatively adds the use of citric acid as a pretreatment agent to the swelling agent. The citric acid used introduces protons H... + The oxygen atom in the CO bond and the nitrogen atom in the CN bond are bonded to H, respectively.+ When the swelling agent is activated, it is protonated, which lowers the bond energy and thus lowers the energy barrier for breaking these chemical bonds. This makes it easier for the swelling agent to penetrate into the resin matrix, accelerates the loosening of the cross-linked network, reduces dependence on high temperature, thereby reducing energy consumption and significantly shortening the swelling time, allowing the material to reach a fully swollen state in a shorter time.

[0018] 2) Due to their three-dimensional cross-linked structure and poor solubility, improper handling of carbon fiber reinforced resin composites can severely impact the environment. This invention proposes an environmentally friendly reagent combination (including a swelling agent and a pretreatment agent) that maintains high degradation efficiency and chemical stability during the degradation process. It pioneers the synergistic use of environmentally friendly pretreatment agent citric acid with low-toxicity swelling agents (such as propanol or propylene glycol methyl ether) to achieve an environmentally friendly treatment process. The reagents used in this invention are not only environmentally friendly but also have a similar Hansen solubility parameter to bisphenol A epoxy resin in wind turbine blades, combining greenness and high efficiency. They can efficiently treat composite materials under mild conditions, not only improving swelling and degradation efficiency but also significantly reducing environmental impact and energy consumption, while simultaneously improving the quality of rCF and DER.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) This invention not only achieves efficient separation of fibers and matrix resin, but also, through in-depth research on the chemical properties of degradation products and pretreatment agents, efficiently recovers the citric acid reagent used by employing chemical treatment methods. Furthermore, it combines centrifugal separation with vacuum distillation to separate the swelling agent and degraded resin polymers, achieving dual recovery of solid and liquid phase products during the treatment process. The bisphenol A and oligomers abundant in DER can be used as raw materials in the preparation of novel epoxy materials, and the recovered reagents can be directly used in the next round of material degradation treatment, significantly reducing reagent consumption and treatment costs, while also reducing environmental pollution risks, improving resource utilization, and achieving a closed-loop recycling system. 2) The chemical swelling recovery method used in this invention improves the quality of recycled carbon fibers through the synergistic pyrolysis of swelling agents and pretreatment agents. The tensile strength retention rate of recycled carbon fibers in the preferred experimental group is over 80% (2208MPa), which is far superior to that of high-temperature pyrolysis fibers (usually <1500MPa). This achieves efficient degradation of the resin matrix at a lower temperature, thereby reducing the damage to recycled carbon fibers caused by high-temperature pyrolysis, and at the same time solving the high pollution problem of traditional chemical methods. 3) The chemical swelling recovery method used in this invention significantly reduces the dependence on high temperature in the traditional pyrolysis recovery process, allowing the fiber recovery process to be carried out at low temperature; 4) This invention utilizes a reagent combination involving pretreatment followed by swelling. The reagent selection is based on Hansen solubility parameters and is achieved through proton H... +Catalyzing the breaking of specific chemical bonds, CO and CN bonds, allows the swelling agent to penetrate more effectively into the resin matrix, accelerates the loosening of the cross-linked network, and significantly shortens the swelling time. 5) This invention uses low-toxicity reagent swelling agents (such as propylene glycol methyl ether) and environmentally friendly pretreatment agent citric acid, which can reduce environmental pollution while maintaining the mildness of the pyrolysis process and the high efficiency of resin degradation. The reagents are also less corrosive and will not damage the equipment. 6) This invention recovers citric acid through a "precipitation-centrifugation" technique, combined with vacuum distillation to separate the swelling agent and DER, achieving full-scale, high-value utilization of solvent, fiber, and resin degradation products. Bisphenol A and oligomers can be resynthesized into epoxy resin, forming a resource closed loop and overcoming the limitations of traditional processes that result in the waste of degradation products. 7) The invention, through the systematic recycling design of DER and reagents, enables DER to be efficiently recycled, successfully realizing the closed-loop utilization of resources. This closed-loop system improves the economy and sustainability of the recycling process and helps promote industrial applications. For example, bisphenol A and small molecule polymers in DER can be used as raw materials for further processing to participate in the preparation of new epoxy materials; the pretreatment agent citric acid is also recovered through chemical reaction and can be recycled, which greatly reduces reagent consumption and processing costs, while reducing the risk of environmental pollution. 8) This invention, through the innovative combination of environmentally friendly pretreatment agents and swelling agents, as well as the recovery of solvents and degradation products, reduces the consumption of chemical reagents required in the recycling process and also reduces environmental treatment costs compared to traditional recycling methods. Furthermore, the recyclability of reagents further reduces the overall recycling cost, resulting in good economic and environmental benefits. Attached Figure Description

[0020] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to the scope described.

[0022] Please refer to Figure 1 A method for chemically assisted pyrolysis recovery of carbon fibers in thermosetting composite materials and full-scale reuse of the products includes the following steps: 1) First, remove the metal parts, PVC foam, balsa wood and structural adhesive from the retired wind turbine blades to obtain the blade block material to be used in this invention. The obtained blade block material is then mechanically cut to obtain carbon fiber reinforced resin composite material of appropriate size. The blade block material obtained in step 1) is made of carbon fiber reinforced resin composite material; the suitable length, width and height dimensions are 10-15cm × 2-3cm × 0.5-1.5cm.

[0023] 2) Equipped with swelling agents and pretreatment agents; The swelling agent used in step 2) has a purity of 99.5%, and the swelling agent is selected from one or more of 1,3-propanediol and propylene glycol; when the swelling agent is propylene glycol methyl ether, due to its low boiling point, triethylene glycol dimethyl ether is used to prepare a mixed reagent with it, and the mass ratio of propylene glycol methyl ether to triethylene glycol dimethyl ether is 2:1 to 3:1.

[0024] The pretreatment agent is a citric acid solution with a concentration of 0.5–2 mol / L (i.e., 8.05–32.2 wt%), preferably 1–2 mol / L; The mass ratio of the swelling agent to the total mass of the swelling agent and pretreatment agent solution is approximately 25-60 wt%, preferably 45-60 wt%; the mass ratio of the pretreatment agent solution to the total mass of the swelling agent and pretreatment agent solution is approximately 40-75 wt%, preferably 40-55 wt%.

[0025] In the embodiments of the present invention, it was found that when the concentration of the pretreatment agent was less than 8.05 wt%, the pretreatment agent did not significantly promote the swelling and degradation of the leaf blocks; however, when the content of the pretreatment agent in the solution was greater than 32.2 wt%, the promoting effect of the pretreatment agent on the pyrolysis of the leaves remained almost unchanged or even decreased with the increase of its concentration, and excessive pretreatment agent would increase the cost of leaf recycling.

[0026] 3) First, immerse the carbon fiber reinforced resin composite material obtained in step 1) into a stainless steel pressure vessel containing the pretreatment agent prepared in step 2) and seal it. Place it in a water bath to allow the material to swell and degrade. After the reaction is complete, wash the filtered carbon fiber reinforced resin composite material with ultrapure water. Place the washed carbon fiber reinforced resin composite material in a vacuum oven to dry it. Filter the filtrate to obtain the pretreatment agent waste liquid. In step 3), the sealed stainless steel pressure vessel is placed in a water bath at room temperature. The temperature is first set to reach 80-100℃ from room temperature in 5 minutes, and then continued for 2 hours to end the pretreatment stage. Then, the filtered blade material is washed with ultrapure water and placed in a vacuum oven to dry at 100℃ for 1 hour.

[0027] Experiments have shown that water bath heating at a certain temperature promotes the subsequent swelling and degradation reaction of the material and shortens the pyrolysis time. This treatment can increase the thermal motion of reagent molecules and enhance the activity of molecular chain segments in the resin matrix, allowing the swelling reagent to penetrate into the cross-linked network of the epoxy resin matrix more quickly.

[0028] 4) Add calcium chloride to the pretreatment agent waste liquid obtained in step 3) to generate calcium citrate precipitate. After washing and drying the calcium citrate precipitate, dissolve it with dilute hydrochloric acid or dilute sulfuric acid to release citric acid solution and generate calcium chloride. Separate the citric acid solution by centrifugation, evaporate and crystallize to obtain solid citric acid, and then recycle it. First, filter paper is used to filter out the impurities generated during pretreatment. Then, calcium chloride is added to the citric acid waste liquid to obtain insoluble calcium citrate (Ca3(C6H5O7)2). The chemically generated liquid is poured out to separate the calcium citrate precipitate. The precipitate is washed with ultrapure water to remove impurities and placed in an oven to dry for 1 hour.

[0029] After drying, dilute hydrochloric acid or dilute sulfuric acid is added to dissolve calcium citrate, releasing citric acid solution and generating calcium chloride. The solution containing citric acid and calcium chloride is transferred to a centrifuge tube, which is then placed in a centrifuge. The centrifugation speed (3000-5000 rpm) and time (5-10 minutes) are adjusted. After centrifugation, the calcium chloride and citric acid solutions in the solution separate. Calcium chloride precipitates at the bottom of the centrifuge tube, while the citric acid solution remains on top. The upper layer (citric acid solution) is extracted from the centrifuge tube using a pipette or tube. The upper liquid is then heated to evaporate the water, promoting the crystallization of citric acid, ultimately yielding solid citric acid for recycling. Citric acid in solution reacts chemically with calcium chloride to form insoluble calcium citrate (Ca3(C6H5O7)2), as shown in the following equation: The chemical reaction of dissolving calcium citrate with dilute hydrochloric acid or dilute sulfuric acid to release citric acid solution and generate calcium chloride is as follows: 5) Next, the dried carbon fiber reinforced resin composite material from step 3) and the swelling agent prepared in step 2) are transported to the high-pressure reactor through the pipe. Nitrogen gas is introduced and the reaction is carried out without stirring. After the reaction is completed, the material in the high-pressure reactor is transported to a centrifuge. The liquid phase in the material is introduced into a vacuum distillation recovery device through the liquid phase outlet of the centrifuge to achieve centrifugal separation of solid and liquid phases. The solid phase in the material is washed with dichloromethane to remove organic matter on the surface and then placed in an oven to dry, obtaining clean rCF. The specific process is as follows: Next, the dried blade material and the prepared swelling agent are transported to the high-pressure reactor through a pipe. Nitrogen is selected as the atmosphere. A gas cylinder is connected to the gas inlet of the reactor via a pressure reducing valve and a pipe. Nitrogen is slowly introduced into the reactor to purge air from the reactor. The gas flow rate is set to 200 ml / min. The high-pressure reactor is pressurized from 0.1 MPa to 3.01 MPa, and the temperature is increased to the specified temperature at a rate of 10 °C / min. The reaction temperature is 150 °C to 300 °C without stirring, and this temperature is maintained for 1 to 2 hours.

[0030] 6) The liquid phase obtained in step 5) is separated by vacuum distillation. The swelling agent in the liquid phase is recovered and reused. The bisphenol A and small molecule oligomers in the DER in the liquid phase are used as raw materials to participate in the preparation of novel epoxy materials. DER and the swelling agent are recovered and disposed of. The distillation apparatus consists of a beaker containing the reaction product connected to a condenser, an Erlenmeyer flask, etc., and performs vacuum distillation at a pressure of -0.089 to -0.013 MPa. The temperature of the vacuum distillation is 130℃ to 170℃, depending on the selected swelling agent (1,3-propanediol, processing temperature 170℃; propylene glycol, processing temperature 150℃; a mixture of propylene glycol methyl ether and triethylene glycol dimethyl ether, processing temperature 130℃). The reagent evaporates, and the evaporated reagent vapor is cooled by the condenser, reliquefied, and collected in the Erlenmeyer flask to obtain the recovered reagent. After distillation, the mixture is cooled to room temperature, and the residue remaining in the beaker is the DER.

[0031] 7) Purify the bisphenol A obtained in step 6), then mix it with epichlorohydrin, and add an appropriate amount of catalyst NaOH to react and obtain regenerated epoxy resin; mix the small molecule oligomer obtained in step 6) with a curing agent and a coupling agent to form a modified prepolymer, which can be used directly as an epoxy resin raw material.

[0032] In step 7), the mass ratio of bisphenol A to epichlorohydrin and catalyst NaOH is 1:1.2-1.8:0.1-0.3; the mass ratio of small molecule oligomer to curing agent and coupling agent is 1:0.1-0.2:0.02-0.05; the small molecule oligomer includes bisphenol A type epoxy oligomer and a small amount of phenolic condensate; the curing agent is polyetheramine D230; and the coupling agent is KH-550. Example 1

[0033] Decommissioned wind turbine blades were cut to suitable dimensions (10.2cm x 3cm x 1.5cm, weighing 7.453g) and immersed in a pre-prepared citric acid solution with a concentration of 16.1wt% (24.02g citric acid and 125g water). The blades were then placed in a water bath at 80℃ for 2 hours. Citric acid was recovered using a chemical reagent method and recycled. After immersion, the blade pieces were removed, washed with ultrapure water, and placed in an oven at 100℃ for 1 hour. Next, propylene glycol methyl ether and triethylene glycol dimethyl ether were mixed at a ratio of 3:1 to prepare 64.61g of swelling agent. The dried blade pieces and swelling agent were placed in a high-pressure reactor under nitrogen atmosphere. The reactor was purged to remove air at a nitrogen flow rate of 200ml / min. The heating rate was set at 10℃ / min to reach the specified temperature of 200℃. The pressure was 0.42MPa, and the heating time was 2 hours. The solid and liquid phases were separated by centrifugation. The solid phase rCF was washed with dichloromethane and dried in an oven to obtain clean rCF. The liquid phase, i.e., DER, and the swelling agent waste liquid were subjected to vacuum distillation at a pressure of -0.013 MPa and a temperature of 130°C. After the process, DER and the recovered swelling agent were obtained, which can be recycled.

[0034] Under these conditions, the recovered rCF passed the tensile test, with an average tensile strength of 2208.52 MPa. The calculated resin degradation rate of the block material was 92.29%. After the experiment, citric acid and the swelling agent were recovered and recycled, with a citric acid recovery rate of 65.62% and a swelling agent recovery rate of 80.91%.

[0035] Bisphenol A purified from DER was mixed with epichlorohydrin at a mass ratio of 1:5, and an appropriate amount of NaOH catalyst was added. The mixture was reacted at 70°C for 5 hours. After washing with water and solvent removal, regenerated epoxy resin was obtained. The separated small molecule oligomers were mixed with 12wt% polyetheramine D230 curing agent and 3wt% silane coupling agent KH-550 and pre-reacted at 100°C for 1 hour to form a modified prepolymer. This prepolymer can be used directly as a raw material for epoxy resin. Example 2

[0036] Decommissioned wind turbine blades were cut to suitable dimensions, approximately 11.7cm × 2.2cm × 1.5cm, weighing 6.452g. They were then immersed in a pre-prepared citric acid solution with a concentration of 16.1wt% (24.02g citric acid and 125g water). The solution was placed in a water bath at 80℃ for 2 hours, and the citric acid was recovered and recycled using a chemical reagent method. After immersion, the blade pieces were removed, rinsed with ultrapure water, and placed in an oven at 100℃ for 1 hour. Next, 72.55g of propylene glycol, a swelling agent, was prepared. The dried blade pieces and the swelling agent were placed in a high-pressure reactor under a nitrogen atmosphere. The reactor was purged to remove air at a nitrogen flow rate of 200ml / min. The heating rate was set at 10℃ / min to reach the specified temperature of 220℃, with a pressure of 0.25MPa, and the heating time was 2 hours. The solid and liquid phases were separated by centrifugation. The solid phase rCF was washed with dichloromethane and dried in an oven to obtain clean rCF. The liquid phase, i.e., DER, and the swelling agent waste liquid were subjected to vacuum distillation at a pressure of -0.084 MPa and a temperature of 150°C. After the process, DER and the recovered swelling agent were obtained, which can be recycled.

[0037] Under these conditions, the recovered rCF passed the tensile test, with an average tensile strength of 2071.57 MPa. The calculated resin degradation rate of the block was 95.68%. After the experiment, citric acid and the swelling agent were recovered and recycled, with a citric acid recovery rate of 71.04% and a swelling agent recovery rate of 84.24%.

[0038] Bisphenol A purified from DER was mixed with epichlorohydrin at a mass ratio of 1:6, and an appropriate amount of NaOH catalyst was added. The mixture was reacted at 65°C for 5 hours. After washing with water and solvent removal, regenerated epoxy resin was obtained. The separated small molecule oligomers were mixed with 12wt% polyetheramine D230 curing agent and 3wt% silane coupling agent KH-550 and pre-reacted at 100°C for 1 hour to form a modified prepolymer. This prepolymer can be used directly as an epoxy resin raw material. Example 3

[0039] Decommissioned wind turbine blades were cut to suitable dimensions, approximately 12.4cm × 2.6cm × 1.4cm, weighing 6.836g. They were then immersed in a prepared pretreatment solution containing 16.1wt% citric acid (24.02g citric acid and 125g water). The solution was placed in a water bath at 80℃ for 2 hours, and the citric acid was recovered and recycled using a chemical reagent method. After immersion, the blade pieces were removed, rinsed with ultrapure water, and placed in an oven at 100℃ for 1 hour. Next, 73.71g of a swelling agent, 1,3-propanediol, was prepared. The dried blade pieces and the swelling agent were placed in a high-pressure reactor under a nitrogen atmosphere. The reactor was purged to remove air at a flow rate of 200ml / min. The heating rate was set at 10℃ / min to reach a specified temperature of 220℃, with a pressure of 0.12MPa, and the heating time was 2 hours. The solid and liquid phases were separated by centrifugation. The solid phase rCF was washed with dichloromethane and dried in an oven to obtain clean rCF. The liquid phase, i.e., DER, and the swelling agent waste liquid were subjected to vacuum distillation at a pressure of -0.089 MPa and a temperature of 170°C. After the process, DER and the recovered swelling agent were obtained, which can be recycled.

[0040] Under these conditions, the recovered rCF passed the tensile test, with an average tensile strength of 1852.64 MPa. The calculated resin degradation rate of the block was 96.05%. After the experiment, citric acid and the swelling agent were recovered and recycled, with a citric acid recovery rate of 73.62% and a swelling agent recovery rate of 82.53%.

[0041] Bisphenol A purified from DER was mixed with epichlorohydrin at a mass ratio of 1:6, and an appropriate amount of NaOH catalyst was added. The mixture was reacted at 65°C for 5 hours. After washing with water and solvent removal, regenerated epoxy resin was obtained. The separated small molecule oligomers were mixed with 12wt% polyetheramine D230 curing agent and 3wt% silane coupling agent KH-550 and pre-reacted at 100°C for 1 hour to form a modified prepolymer. This prepolymer can be used directly as a raw material for epoxy resin. Example 4

[0042] Decommissioned wind turbine blades were cut to suitable dimensions, approximately 13cm × 3cm × 1.5cm, weighing 9.231g. They were then immersed in a prepared pretreatment solution containing 19.7wt% citric acid (36.02g citric acid and 125g water). The solution was placed in a water bath at 90℃ for 2 hours, and the citric acid was recovered and recycled using a chemical reagent method. After immersion, the blade pieces were removed, rinsed with ultrapure water, and placed in an oven at 100℃ for 1 hour. Next, 161.02g of the swelling agent 1,3-propanediol was prepared. The dried blade pieces and the swelling agent were placed in a high-pressure reactor under a nitrogen atmosphere. The reactor was purged to remove air at a nitrogen flow rate of 200ml / min. The heating rate was set at 10℃ / min to reach a specified temperature of 220℃, with a pressure of 0.12MPa, and the heating time was 2 hours. The solid and liquid phases were separated by centrifugation. The solid phase rCF was washed with dichloromethane and dried in an oven to obtain clean rCF. The liquid phase, i.e., DER, and the swelling agent waste liquid were subjected to vacuum distillation at a pressure of -0.089 MPa and a temperature of 170°C. After the process, DER and the recovered swelling agent were obtained, which can be recycled.

[0043] Under these conditions, the recovered rCF passed the tensile test, with an average tensile strength of 1767.08 MPa. The calculated resin degradation rate of the block was 97.37%. After the experiment, citric acid and the swelling agent were recovered and recycled, with a citric acid recovery rate of 70.39% and a swelling agent recovery rate of 84.94%.

[0044] Bisphenol A purified from DER was mixed with epichlorohydrin at a mass ratio of 1:6, and an appropriate amount of NaOH catalyst was added. The mixture was reacted at 65°C for 5 hours. After washing with water and solvent removal, regenerated epoxy resin was obtained. The separated small molecule oligomers were mixed with 12wt% polyetheramine D230 curing agent and 3wt% silane coupling agent KH-550 and pre-reacted at 100°C for 1 hour to form a modified prepolymer. This prepolymer can be used directly as an epoxy resin raw material. Example 5

[0045] Decommissioned wind turbine blades were cut to suitable dimensions, approximately 12.6cm × 2.8cm × 1.5cm, weighing 8.572g. They were then immersed in a pre-prepared citric acid solution with a concentration of 19.7wt% (36.02g citric acid and 125g water). The solution was placed in a water bath at 100℃ for 2 hours, and the citric acid was recovered and recycled using a chemical reagent method. After immersion, the blade pieces were removed, rinsed with ultrapure water, and placed in an oven at 100℃ for 1 hour. Next, 184.3g of a swelling agent, 1,3-propanediol, was prepared. The dried blade pieces and the swelling agent were placed in a high-pressure reactor under a nitrogen atmosphere. The reactor was purged to remove air at a nitrogen flow rate of 200ml / min. The heating rate was set at 10℃ / min to reach a specified temperature of 260℃, with a pressure of 0.27MPa, and the heating time was 2 hours. The solid and liquid phases were separated by centrifugation. The solid phase rCF was washed with dichloromethane and dried in an oven to obtain clean rCF. The liquid phase, i.e., DER, and the swelling agent waste liquid were subjected to vacuum distillation at a pressure of -0.089 MPa and a temperature of 170°C. After the process, DER and the recovered swelling agent were obtained, which can be recycled.

[0046] Under these conditions, the recovered rCF passed the tensile test, with an average tensile strength of 1582.69 MPa. The calculated resin degradation rate of the block material was 98.45%. After the experiment, citric acid and the swelling agent were recovered and recycled, with a citric acid recovery rate of 72.62% and a swelling agent recovery rate of 81.58%.

[0047] Bisphenol A purified from DER was mixed with epichlorohydrin at a mass ratio of 1:5, and an appropriate amount of NaOH catalyst was added. The mixture was reacted at 70°C for 5 hours. After washing with water and solvent removal, regenerated epoxy resin was obtained. The separated small molecule oligomers were mixed with 12wt% polyetheramine D230 curing agent and 3wt% silane coupling agent KH-550 and pre-reacted at 100°C for 1 hour to form a modified prepolymer. This prepolymer can be used directly as an epoxy resin raw material. Example 6

[0048] Decommissioned wind turbine blades were cut to suitable dimensions, approximately 11cm × 2.2cm × 1.5cm, weighing 6.126g. They were then immersed in a prepared pretreatment solution containing 19.7wt% citric acid (36.02g citric acid and 125g water). The solution was placed in a water bath at 100℃ for 2 hours, and the citric acid was recovered and recycled using a chemical reagent method. After immersion, the blade pieces were removed, rinsed with ultrapure water, and placed in an oven at 100℃ for 1 hour. Next, 241.53g of a swelling agent, 1,3-propanediol, was prepared. The dried blade pieces and the swelling agent were placed in a high-pressure reactor under a nitrogen atmosphere. The reactor was purged to remove air at a flow rate of 200ml / min. The heating rate was set at 10℃ / min to reach a specified temperature of 300℃, with a pressure of 0.39MPa, and the heating time was 2 hours. The solid and liquid phases were separated by centrifugation. The solid phase rCF was washed with dichloromethane and dried in an oven to obtain clean rCF. The liquid phase, i.e., DER, and the swelling agent waste liquid were subjected to vacuum distillation at a pressure of -0.089 MPa and a temperature of 170°C. After the process, DER and the recovered swelling agent were obtained, which can be recycled.

[0049] Under these conditions, the recovered rCF passed the tensile test, with an average tensile strength of 1465.74 MPa. The calculated resin degradation rate of the block material was 99.12%. After the experiment, citric acid and the swelling agent were recovered and recycled, with a citric acid recovery rate of 75.30% and a swelling agent recovery rate of 79.68%.

[0050] Bisphenol A purified from DER was mixed with epichlorohydrin at a mass ratio of 1:5, and an appropriate amount of NaOH catalyst was added. The mixture was reacted at 70°C for 5 hours. After washing with water and solvent removal, regenerated epoxy resin was obtained. The separated small molecule oligomers were mixed with 12wt% polyetheramine D230 curing agent and 3wt% silane coupling agent KH-550 and pre-reacted at 100°C for 1 hour to form a modified prepolymer. This prepolymer can be used directly as an epoxy resin raw material.

[0051] As shown in Examples 1-6, the environmentally friendly recycling of fiber composite materials for retired wind turbine blades was successfully achieved. At the same time, the solvent waste liquid was efficiently recycled, and new epoxy resin materials were prepared using DER, achieving full-scale high-value utilization.

Claims

1. A method for chemically assisted pyrolysis recovery of carbon fibers in thermosetting composite materials and full-scale reuse of the products, characterized in that... Includes the following steps: 1) First, remove the metal parts, PVC foam, balsa wood and structural adhesive from the retired wind turbine blades to obtain the blade blocks to be used. The obtained blade blocks are then mechanically cut and washed to obtain carbon fiber reinforced resin composite materials of appropriate size. 2) Prepare a swelling agent and a pretreatment agent; the pretreatment agent is a citric acid solution; 3) First, immerse the carbon fiber reinforced resin composite material obtained in step 1) into a stainless steel pressure vessel containing the pretreatment agent prepared in step 2) and seal it. Place it in a water bath to allow the material to swell and degrade. After the reaction is complete, wash the filtered carbon fiber reinforced resin composite material with ultrapure water. Place the washed carbon fiber reinforced resin composite material in a vacuum oven to dry it. Filter the filtrate to obtain the pretreatment agent waste liquid. 4) Add calcium chloride to the pretreatment agent waste liquid obtained in step 3) to generate calcium citrate precipitate. After washing and drying the calcium citrate precipitate, dissolve it with dilute hydrochloric acid or dilute sulfuric acid to release citric acid solution and generate calcium chloride. Separate the citric acid solution by centrifugation, evaporate and crystallize to obtain solid citric acid, and then recycle it. 5) Next, the dried carbon fiber reinforced resin composite material from step 3) and the swelling agent prepared in step 2) are transported to the high-pressure reactor through the pipe. Nitrogen gas is introduced and the reaction is carried out without stirring. After the reaction is completed, the material in the high-pressure reactor is transported to a centrifuge. The liquid phase in the material is introduced into a vacuum distillation recovery device through the liquid phase outlet of the centrifuge to achieve centrifugal separation of solid and liquid phases. The solid phase in the material is washed with dichloromethane to remove organic matter on the surface and then placed in an oven to dry, resulting in clean regenerated fibers. 6) The liquid phase obtained in step 5) is separated by vacuum distillation. The swelling agent in the liquid phase is recovered and reused. The bisphenol A and small molecule oligomers in the resin degradation products in the liquid phase are used as raw materials to participate in the preparation of novel epoxy materials. 7) Purify the bisphenol A obtained in step 6), then mix it with epichlorohydrin, and add an appropriate amount of catalyst NaOH to react and obtain regenerated epoxy resin; mix the small molecule oligomer obtained in step 6) with a curing agent and a coupling agent to form a modified prepolymer, which can be used directly as an epoxy resin raw material.

2. The method for chemically assisted pyrolysis recovery of carbon fibers in thermosetting composite materials and the full-scale reuse of the products according to claim 1, characterized in that... The carbon fiber reinforced resin composite material obtained in step 1) has a length, width and height of 10-15cm × 2-3cm × 0.5-1.5cm.

3. The method for chemically assisted pyrolysis recovery of carbon fibers in thermosetting composite materials and the full-scale reuse of the products according to claim 1, characterized in that... The swelling agent used in step 2) has a purity of 99.5%, and the swelling agent is selected from one or more of 1,3-propanediol and propylene glycol; The pretreatment agent is a citric acid solution with a concentration of 0.5–2 mol / L; The mass ratio of the swelling agent to the total mass of the swelling agent and pretreatment agent solution is 25-60 wt%; the mass ratio of the pretreatment agent solution to the total mass of the swelling agent and pretreatment agent solution is 40-75 wt%.

4. The method for chemically assisted pyrolysis recovery of carbon fibers in thermosetting composite materials and the full-scale reuse of the products according to claim 1, characterized in that... When the swelling agent is a mixture of propylene glycol methyl ether and triethylene glycol dimethyl ether, the mass ratio of propylene glycol methyl ether to triethylene glycol dimethyl ether is 2:1 to 3:

1.

5. The method for chemically assisted pyrolysis recovery of carbon fibers in thermosetting composite materials and the full-scale reuse of the products according to claim 1, characterized in that... In step 3), the sealed stainless steel pressure vessel is placed in a water bath at room temperature. The temperature is first set to reach 80-100℃ from room temperature in 5 minutes, and then continued for 2 hours to complete the pretreatment stage. Then, the filtered carbon fiber reinforced resin composite material is washed with ultrapure water, and the washed carbon fiber reinforced resin composite material is placed in a vacuum oven and dried at 100℃ for 1 hour.

6. The method for chemically assisted pyrolysis recovery of carbon fibers in thermosetting composite materials and the full-scale reuse of the products according to claim 1, characterized in that... In step 4), the centrifugation speed is 3000-5000 rpm and the centrifugation time is 5-10 min.

7. The method for chemically assisted pyrolysis recovery of carbon fibers in thermosetting composite materials and the full-scale reuse of the products according to claim 1, characterized in that... In step 5), the pressure in the high-pressure reactor is 0.1 MPa to 3.01 MPa, the reaction temperature is 150℃ to 300℃, no stirring is performed, and the reaction time is 1 to 2 hours.

8. The method for chemically assisted pyrolysis recovery of carbon fibers in thermosetting composite materials and the full-scale reuse of the products according to claim 1, characterized in that... The pressure of vacuum distillation described in step 6) is -0.089 to -0.013 MPa, and the vacuum distillation temperature is 130℃ to 170℃.

9. The method for chemically assisted pyrolysis recovery of carbon fibers in thermosetting composite materials and the full-scale reuse of the products according to claim 8, characterized in that... When the swelling agent is 1,3-propanediol, the vacuum distillation temperature is 170℃; when the swelling agent is propylene glycol, the vacuum distillation temperature is 150℃; when the swelling agent is a mixed solvent of propylene glycol methyl ether and triethylene glycol dimethyl ether, the vacuum distillation temperature is 130℃.

10. The method for chemically assisted pyrolysis recovery of carbon fibers in thermosetting composite materials and the full-scale reuse of the products according to claim 1, characterized in that... In step 7), the mass ratio of bisphenol A to epichlorohydrin and catalyst NaOH is 1:1.2-1.8:0.1-0.3; the mass ratio of small molecule oligomer to hardener and coupling agent is 1:0.1-0.2:0.02-0.05.

Images