Method for chemical degradation and recycling of retired wind turbine blade epoxy composites

Abstract

The application discloses a kind of chemical degradation recycling methods of decommissioned fan blade epoxy composite, belong to new energy solid waste resource utilization and thermosetting composite chemical recycling technical field.Method includes the following steps: first, after cutting or crushing, decommissioned fan blade, acetic acid and zinc chloride are mixed, and selective degradation reaction is carried out;Then, the selective degradation product is subjected to solid-liquid separation;Then, the solid-phase fiber is washed, dried, to obtain recycled glass fiber;Finally, solvent recovery, oligomer separation and zinc chloride regeneration are carried out on the liquid product, and the chemical degradation recycling is completed.The application realizes the selective degradation of decommissioned fan blade epoxy resin under mild conditions through the synergistic effect of acetic acid and zinc chloride, while maintaining the mechanical properties of glass fiber and recycling the resin-derived oligomer with reusability.The method has important significance for the high-value, low-carbon and closed-loop recycling of decommissioned fan blades.

Description

Technical Field

[0001] This invention relates to the field of resource utilization of new energy solid waste and chemical recycling of thermosetting composite materials, specifically to a chemical degradation and recycling method for epoxy composite materials of retired wind turbine blades. Background Technology

[0002] As a crucial component of renewable energy, wind power has experienced rapid growth in installed capacity in recent years. With early-service wind turbines reaching the end of their service life, retired turbine blades are increasingly becoming a large quantity of difficult-to-dispose-of composite solid waste. Most existing commercially retired wind turbine blades are composed of glass fiber reinforced amine-cured epoxy resin composites. The glass fibers impart high mechanical strength to the blades, while the epoxy resin matrix binds the fiber bundles together through a highly cross-linked thermosetting network. Because this type of epoxy resin network is non-meltable, non-remodelable, and difficult to degrade in natural environments, the high-value recycling of retired wind turbine blades faces significant challenges.

[0003] Currently, the main methods for processing retired wind turbine blades include mechanical crushing, heat treatment, and chemical recycling. Mechanical crushing typically involves cutting, crushing, or grinding the blades into short fibers, particles, or powder. The resulting products are often used as fillers in building materials or low-end composite materials. While this method is simple, it cannot effectively maintain the continuity and mechanical properties of the glass fibers, nor can it recover the chemical value of the resin phase, representing a typical case of downgrading. Heat treatment methods include pyrolysis, incineration, or high-temperature pyrolysis, which can remove the resin matrix and release inorganic fibers, but usually require temperatures of 400–700 °C or even higher. During high-temperature treatment, glass fibers are prone to surface etching, diameter reduction, increased defects, and strength decay, leading to a significant decrease in their reuse value. Simultaneously, the resin phase is often decomposed into complex gases, tar, or low-value small-molecule products at high temperatures, resulting in high energy consumption, significant pollution control pressure, and insufficient utilization of resin resources.

[0004] Chemical recycling methods can break down and degrade the network of thermosetting resins under relatively mild conditions using solvents, catalysts, or reaction media, thereby separating the fiber and resin components. However, existing chemical recycling methods still have several shortcomings: First, some systems rely on precious metal catalysts, strong oxidants, or supercritical conditions, resulting in high process costs and equipment requirements; second, some systems involve high reaction temperatures and long reaction times, which can easily lead to excessive cracking of the resin skeleton and the generation of complex phenolic small molecules; third, although some systems can remove resin, they cannot effectively control the breaking sequence of CN crosslinking bonds and COC ether bonds in amine-cured epoxy resins, making it difficult to simultaneously maintain the high strength of glass fibers and achieve high-value recovery of the resin phase; fourth, the recycling pathways for reaction solvents and catalysts are not clearly defined, limiting their engineering scale-up and closed-loop applications.

[0005] Therefore, developing a method that can selectively degrade epoxy resin in retired wind turbine blades under relatively mild conditions while maintaining the mechanical properties of glass fibers and recovering resin-derived oligomers with reuse value is of great significance for the high-value, low-carbon, and closed-loop recycling of retired wind turbine blades. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a chemical degradation and recycling method for epoxy composite materials of decommissioned wind turbine blades. This method solves the problems of high process costs and equipment requirements, easy generation of complex phenolic small molecules, difficulty in simultaneously maintaining the high strength of glass fibers and high-value recovery of the resin phase, and limitations in engineering scale-up applications of existing recycling methods.

[0007] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: In a first aspect, the present invention provides a method for the chemical degradation and recycling of epoxy composite materials for decommissioned wind turbine blades, comprising the following steps: S1, Selective Degradation: The cut or crushed retired wind turbine blades, acetic acid, and zinc chloride are mixed and subjected to a selective degradation reaction to obtain selective degradation products. S2, Solid-liquid separation: The selective degradation products obtained from S1 were subjected to solid-liquid separation to obtain solid-phase products and liquid-phase products; S3, Fiber Recycling: The solid fiber obtained from S2 was washed and dried to obtain recycled glass fiber. S4. Liquid phase product recovery: The liquid product obtained from S2 was subjected to solvent recovery, oligomer separation, and zinc chloride regeneration to complete the chemical degradation and recycling of epoxy composite materials for decommissioned wind turbine blades.

[0008] Furthermore, in S1, the length of a single piece of the decommissioned wind turbine blade after cutting or crushing is 2 / 3 to 3 / 4 of the diameter of the bottom surface of the reactor for selective degradation reaction, and the volume of the reaction solution for selective degradation reaction accounts for 1 / 2 to 2 / 3 of the total volume of the reactor.

[0009] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: This invention cuts or crushes retired wind turbine blades, giving the material a size suitable for reactor loading and liquid phase wetting. This process does not pulverize the material into fine powder, but rather retains a block or sheet-like structure of a certain size, thereby reducing the damage to the glass fiber length and fiber bundle integrity caused by mechanical crushing, providing a foundation for subsequent recycling of high-strength glass fibers. By controlling the matching relationship between the material size and the reactor size, this invention ensures that the retired wind turbine blade material is fully submerged in the reaction liquid, while also reserving a safe gas phase space for changes in acetic acid vapor pressure during the heating reaction, avoiding situations where excessively large materials lead to localized unwetting or excessively small materials result in increased mechanical damage to the fibers.

[0010] Furthermore, the epoxy composite material for the decommissioned wind turbine blades is a glass fiber reinforced amine-cured bisphenol A type epoxy resin composite material.

[0011] Furthermore, the mass-to-volume ratio of the cut or crushed decommissioned wind turbine blades and acetic acid in S1 is 1 g: 10~20 mL; the mass concentration of zinc chloride in acetic acid is 10 wt%~20 wt%.

[0012] The beneficial effects of adopting the above-mentioned further technical solution are as follows: By precisely controlling the amounts of acetic acid and zinc chloride, the selective degradation reaction is controlled within the selective degradation window, prioritizing the breaking of CN crosslinking bonds over COC ether bonds, thereby obtaining resin-derived oligomers that retain the bisphenol A type epoxy aromatic skeleton and inhibiting the formation of monocyclic phenolic small molecules and excessive pyrolysis products. Under this selective degradation condition, the resin network mainly undergoes crosslinking node breakage rather than deep destruction of the aromatic skeleton. The resulting liquid-phase product is mainly composed of resin-derived oligomers that retain the bisphenol A type epoxy aromatic skeleton, and can be used as epoxy resin, composite resin phase, toughening component, or intermediate for remanufacturing resins.

[0013] When the zinc chloride concentration is too low, there are insufficient Lewis acid active sites in the system, making it difficult to effectively promote the cleavage of the resin crosslinking network, and the reaction mainly stops at the acetic acid swelling stage. When the zinc chloride concentration is too high, although it can promote resin degradation, it may increase the subsequent salt recovery load and may exacerbate the further decomposition of resin-derived oligomers. Therefore, controlling the zinc chloride concentration within the above range is beneficial to balancing resin removal efficiency, oligomer retention, and catalyst recycling.

[0014] When the amount of acetic acid is too small, the material cannot be completely submerged, the resin network does not swell sufficiently, and zinc chloride cannot effectively penetrate the interior of the composite material. When the amount of acetic acid is too large, it will increase the energy consumption of subsequent solvent distillation and recovery, and also increase the amount of zinc chloride used. Therefore, controlling the amount of acetic acid within the above range is beneficial to achieving a balance between sufficient wetting, effective swelling, and a low recovery load.

[0015] Furthermore, the selective degradation reaction in S1 is carried out at a temperature of 170-180 °C for 2-4 h.

[0016] The beneficial effects of adopting the above-mentioned further technical solution are as follows: The present invention selectively degrades epoxy resin by adding acetic acid and zinc chloride, so that acetic acid swells the epoxy resin crosslinking network and promotes zinc chloride to enter the interior of the crosslinking network. Zinc chloride, as a Lewis acid, preferentially activates the CN crosslinking bonds in the amine-cured epoxy resin, thereby degrading the resin network into soluble resin-derived oligomers.

[0017] In this step, acetic acid acts not only as a reaction solvent but also as a resin network swelling agent. Acetic acid can penetrate the cross-linked network of the amine-cured epoxy resin, causing the dense resin structure to swell and relax, forming internal diffusion channels that facilitate the migration of zinc chloride. After entering the resin network, zinc chloride acts as a Lewis acid, interacting with the nitrogen-containing cross-linking sites in the amine-cured epoxy resin, preferentially weakening and activating CN cross-linking bonds, thus transforming the three-dimensional cross-linked resin network into soluble resin-derived oligomers.

[0018] Unlike treatment methods that rely solely on external surface corrosion or high-temperature pyrolysis, this step achieves selective decrosslinking of the resin network from the inside through the synergistic effect of acetic acid swelling, zinc chloride internal diffusion, and selective activation of CN crosslinking bonds. This reduces chemical corrosion and mechanical damage to the glass fiber surface while removing the resin matrix.

[0019] Furthermore, the solid-liquid separation methods in S2 include filtration, vacuum filtration, pressure filtration, or centrifugation.

[0020] The beneficial effects of adopting the above-mentioned further technical solution are as follows: After selective degradation, the epoxy resin network that originally coated and bonded the glass fibers is transformed into soluble oligomers and enters the liquid phase, while the glass fiber bundles are released from the resin matrix. Through solid-liquid separation, the recycled glass fiber precursor can be separated from the liquid phase system containing oligomers, acetic acid, and zinc chloride, providing conditions for subsequent fiber purification and liquid phase closed-loop recycling.

[0021] Furthermore, in S3, the washing method involves washing with organic detergent and water sequentially; the drying temperature is 100~110 ℃, and the time is 12~24 h.

[0022] Furthermore, acetone is chosen as the organic detergent.

[0023] Preferably, the washing method in S3 is to first wash with acetone 2-3 times, and then wash with deionized water 1-2 times.

[0024] The beneficial effects of adopting the above-mentioned further technical solution are as follows: In this invention, the organic detergent is mainly used to remove resin-derived oligomers, acetic acid, and organic intermediates remaining on the surface of solid fibers; water washing is mainly used to remove zinc chloride and inorganic salt components remaining on the fiber surface. Through sequential washing with organic detergent and water, virtually no observable resin residue and crystalline inorganic salt residue can be found on the surface of the recycled glass fibers, which is beneficial for subsequent recycling and reuse.

[0025] Furthermore, the resin removal rate of the recycled glass fiber obtained in S3 is not less than 98%, and the tensile strength retention rate relative to the original glass fiber is not less than 95%.

[0026] Furthermore, S4 specifically includes the following steps: S401. The liquid product is treated by distillation to obtain recovered acetic acid and concentrated liquid. S402. Add water or an aqueous solvent to the concentrate obtained in S401 to separate the resin-derived oligomers and the aqueous phase. The beneficial effects of adopting the above-mentioned further technical solution are as follows: This invention first recovers acetic acid through a distillation process to obtain a concentrated solution. After the acetic acid is distilled off, the concentrated solution mainly contains resin-derived oligomers, zinc chloride, and a small amount of residual acetic acid. The resin-derived oligomers have a relatively hydrophobic aromatic epoxy skeleton, while zinc chloride readily enters the aqueous phase. Therefore, after adding water or an aqueous solvent to the concentrated solution, the solubility of the resin-derived oligomers decreases, and precipitation or phase separation occurs, while zinc chloride mainly remains in the aqueous phase. This process utilizes the difference in solubility between the oligomers and zinc chloride in the aqueous phase to achieve the separation of organic oligomer products from the inorganic salt catalyst.

[0027] S403 removes the solvent from the aqueous phase obtained from S402 to obtain regenerated zinc chloride.

[0028] Furthermore, the distillation process in S401 includes vacuum distillation or rectification.

[0029] Furthermore, the volume ratio of water or aqueous solvent to concentrate in S402 is 5:1 to 10:1; Furthermore, the methods for removing aqueous solvents in S403 include one or more of vacuum concentration, evaporation crystallization, vacuum drying, and spray drying.

[0030] Preferably, the method for removing the aqueous solvent in S403 includes vacuum drying after vacuum concentration.

[0031] Furthermore, the vacuum drying temperature is 80~120 ℃.

[0032] Furthermore, the resin-derived oligomers in S4 include one or more of the following: DGEBA units, DGEBA dimers to pentamers, nitrogen-containing DGEBA derivative fragments, and acetylated DGEBA derivative fragments.

[0033] Furthermore, the recovery rate of the recycled zinc chloride obtained from S4 is not less than 80%.

[0034] Furthermore, the recycled zinc chloride obtained in S4 is returned to S1 for reuse as zinc chloride in a recycling process.

[0035] In a second aspect, the present invention provides a closed-loop chemical recycling system for epoxy composite materials of decommissioned wind turbine blades based on the above-mentioned chemical degradation and recycling method, comprising a pretreatment unit, a closed selective degradation reaction unit, a solid-liquid separation unit, a fiber washing and drying unit, a solvent recovery unit, an oligomer separation unit, and a zinc chloride regeneration unit connected in sequence.

[0036] Furthermore, the pretreatment unit is used to cut or crush the decommissioned wind turbine blades to be treated; the closed selective degradation reaction unit performs a selective degradation reaction on the cut or crushed decommissioned wind turbine blades in an acetic acid and zinc chloride system; the solid-liquid separation unit is used to separate the selective degradation reaction products into solid and liquid phase products; the fiber washing and drying unit is used to wash and dry the solid phase products to obtain recycled glass fiber; the solvent recovery unit is used to treat the liquid phase products by distillation to recover acetic acid and / or organic detergents; the oligomer separation unit is used to add water or aqueous solvent to the concentrate after distillation to separate the resin oligomer derivatives and the aqueous phase; and the zinc chloride regeneration unit is used to remove solvent from the aqueous phase to obtain regenerated zinc chloride.

[0037] The present invention has the following beneficial effects: 1. This invention achieves selective chemical degradation of epoxy composite materials for decommissioned wind turbine blades through the synergistic effect of acetic acid and zinc chloride. Acetic acid can penetrate the cross-linked network of amine-cured epoxy resin and induce swelling, relaxing the originally dense thermosetting resin network and providing a mass transfer channel for zinc chloride to enter the resin. Zinc chloride, as a Lewis acid, preferentially acts on nitrogen-containing cross-linking nodes, promoting the breaking of CN cross-linking bonds, thereby achieving internal decross-linking of the resin network and the release of glass fibers. This method does not simply completely decompose the resin into low-value small molecules, but rather transforms the resin network into resin-derived oligomers that retain the bisphenol A type epoxy aromatic skeleton within the selective degradation window, improving the rapid utilization value of the resin phase recovery products.

[0038] 2. This invention achieves efficient removal of the resin matrix from the epoxy composite material of decommissioned wind turbine blades under relatively mild conditions of 170-180 °C, avoiding or significantly reducing problems such as reduced glass fiber diameter, increased surface defects, and decreased tensile strength under pyrolysis conditions at 600 °C and above. The recovered glass fibers have a clean surface with virtually no observable resin residue or crystalline inorganic salt residue, maintaining a complete and smooth amorphous glass structure, which is beneficial for the subsequent high-value recycling and reuse of the glass fibers.

[0039] 3. This invention constructs a closed-loop liquid-phase recovery process for acetic acid recovery, resin-derived oligomer separation, and zinc chloride regeneration. Acetic acid is recovered through vacuum distillation or rectification, hydrophobic resin-derived oligomers are recovered through water precipitation or phase separation, and zinc chloride is regenerated through concentration and drying. This allows for the graded recovery and recycling of the reaction solvent, resin phase products, and Lewis acid catalyst. Compared with treatment methods relying on precious metal catalysts, supercritical conditions, or high-temperature pyrolysis, this invention offers milder process conditions, readily available catalysts, and high-value products, demonstrating good potential for engineering scale-up and environmental and economic benefits. Detailed Implementation

[0040] The principles and features of the present invention are described below with reference to embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, specific conditions or manufacturer-recommended conditions should be followed in the embodiments. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0041] Example 1: A chemical degradation and recycling method for epoxy composite materials used in decommissioned wind turbine blades includes the following steps: S1. Preprocessing: The epoxy composite material of the decommissioned wind turbine blades is cut into blocks to obtain the wind turbine blade material to be processed. The length of a single block of the wind turbine blade material to be processed is 2 / 3 of the diameter of the bottom surface of the reactor, and the volume of the entire reaction solution accounts for 1 / 2 of the total volume of the reactor.

[0042] In this step, cutting the epoxy composite material of the decommissioned wind turbine blades into blocks instead of crushing them into fine powder can reduce the damage to the length and integrity of the glass fibers caused by mechanical crushing, which is beneficial for obtaining recycled glass fibers with a high tensile strength retention rate in the future.

[0043] S2, Selective Degradation: Weigh 4.0 g of the wind turbine blade material to be treated and add it to a sealed pressure-resistant reactor. Then add 40 mL of acetic acid and 2.2 g of anhydrous zinc chloride to make the mass concentration of zinc chloride in acetic acid 20 wt%. After sealing the reactor, heat it to 170 ℃ and keep it at that temperature for 4 h under static conditions.

[0044] In this step, acetic acid swells the crosslinked network of the amine-cured epoxy resin, causing the resin network to relax and form internal diffusion channels. After zinc chloride enters the interior of the resin network, it preferentially activates the CN crosslinking bonds as a Lewis acid, causing the epoxy resin network to undergo selective decrosslinking and transform into soluble resin-derived oligomers.

[0045] S3, Solid-liquid separation: After the selective degradation reaction in S2 is completed, the sealed pressure-resistant reactor is cooled to room temperature, the reactor is opened, and the reaction mixture is vacuum filtered to obtain a solid product containing glass fiber and a liquid product containing resin-derived oligomers, acetic acid, and zinc chloride.

[0046] S4, Fiber washing and drying The solid product containing glass fibers obtained in S3 was first washed twice with acetone (20 mL each time), and then washed once with deionized water (20 mL each time). After washing, the product was placed in a forced-air drying oven and dried at 105 °C for 12 h to obtain the recovered glass fibers.

[0047] In this step, acetone washing is mainly used to remove resin-derived oligomers, acetic acid, and organic intermediates remaining on the surface of the solid fiber; deionized water washing is mainly used to remove zinc chloride and inorganic salt components remaining on the fiber surface. After washing and drying, there is virtually no observable resin residue and crystalline inorganic salt residue on the surface of the recovered glass fiber.

[0048] S5. Liquid phase product recovery: First, the liquid product obtained from S3 was subjected to vacuum distillation to recover acetic acid and obtain a concentrated solution. Then, water was added to the concentrated solution at a volume ratio of 5:1 to precipitate or separate the resin-derived oligomers. Subsequently, the resin-derived oligomers and the aqueous phase were separated by centrifugation. The obtained resin-derived oligomers were then concentrated by nitrogen blowing to obtain resin-derived oligomers that retain the bisphenol A type epoxy aromatic skeleton. Finally, the aqueous phase was concentrated under vacuum, and the concentrated product was vacuum dried at 80 °C to obtain regenerated zinc chloride, thus completing the chemical degradation and recycling of epoxy composite materials for decommissioned wind turbine blades.

[0049] Example 2: A chemical degradation and recycling method for epoxy composite materials used in decommissioned wind turbine blades includes the following steps: S1. Preprocessing: The epoxy composite material of the decommissioned wind turbine blades is cut into blocks to obtain the wind turbine blade material to be processed. The length of a single block of the wind turbine blade material to be processed is 3 / 4 of the diameter of the bottom surface of the reactor, and the volume of the entire reaction solution accounts for 2 / 3 of the total volume of the reactor.

[0050] S2, Selective Degradation: Weigh 4.0 g of the wind turbine blade material to be treated and add it to a sealed pressure-resistant reactor. Then add 50 mL of acetic acid and 4.8 g of anhydrous zinc chloride to make the mass concentration of zinc chloride in acetic acid 15 wt%. After sealing the reactor, heat it to 175 ℃ and keep it at that temperature for 3 h under stirring conditions. The stirring speed is 300 rpm.

[0051] S3, Solid-liquid separation: After the selective degradation reaction in S2 is completed, the sealed pressure-resistant reactor is cooled to below 80 °C, the reactor is opened, and the reaction mixture is filtered to obtain a solid product containing glass fiber and a liquid product containing resin-derived oligomers, acetic acid, and zinc chloride.

[0052] S4, Fiber washing and drying The solid product containing glass fibers obtained in S3 was first washed three times with acetone (20 mL each time), and then washed twice with deionized water (20 mL each time). After washing, the product was placed in a forced-air drying oven and dried at 105 °C for 18 h to obtain the recovered glass fibers.

[0053] S5. Liquid phase product recovery: First, the liquid product obtained from S3 is subjected to vacuum distillation to recover acetic acid and obtain a concentrated solution. Then, water is added to the concentrated solution at a volume ratio of 8:1 to precipitate or separate the resin-derived oligomers. Subsequently, the resin-derived oligomers and the aqueous phase are separated by centrifugation, and the obtained resin-derived oligomers are concentrated by nitrogen blowing. Finally, the aqueous phase is concentrated under vacuum, and the concentrated product is vacuum dried at 100 °C to obtain regenerated zinc chloride, thus completing the chemical degradation and recycling of epoxy composite materials for decommissioned wind turbine blades.

[0054] Example 3: A chemical degradation and recycling method for epoxy composite materials used in decommissioned wind turbine blades includes the following steps: S1. Preprocessing: The epoxy composite material of the decommissioned wind turbine blades is cut into blocks to obtain the wind turbine blade material to be processed. The length of a single block of the wind turbine blade material to be processed is 17 / 24 of the diameter of the bottom surface of the reactor, and the volume of the entire reaction solution accounts for 7 / 12 of the total volume of the reactor.

[0055] S2, Selective Degradation: Weigh 4.0 g of the wind turbine blade material to be treated and add it to a sealed pressure-resistant reactor. Then add 40 mL of acetic acid and 4.0 g of anhydrous zinc chloride to make the mass concentration of zinc chloride in acetic acid 10 wt%. After sealing the reactor, heat it to 180 ℃ and keep it at that temperature for 2 h under stirring conditions. The stirring speed is 600 rpm.

[0056] S3, Solid-liquid separation: After the selective degradation reaction in S2 is completed, the sealed pressure-resistant reactor is cooled to room temperature, the reactor is opened, and the reaction mixture is vacuum filtered to obtain a solid product containing glass fiber and a liquid product containing resin-derived oligomers, acetic acid, and zinc chloride.

[0057] S4, Fiber washing and drying The solid product containing glass fibers obtained in S3 was first washed three times with acetone (20 mL each time), and then washed twice with deionized water (20 mL each time). After washing, the product was placed in a forced-air drying oven and dried at 105 °C for 24 h to obtain the recovered glass fibers.

[0058] S5. Liquid phase product recovery: First, the liquid product obtained from S3 was subjected to vacuum distillation to recover acetic acid and obtain a concentrated solution. Then, water was added to the concentrated solution at a volume ratio of 10:1 to precipitate or separate the resin-derived oligomers. Subsequently, the resin-derived oligomers and the aqueous phase were separated by centrifugation, and the obtained resin-derived oligomers were concentrated by nitrogen blowing. Finally, the aqueous phase was concentrated under vacuum, and the concentrated product was vacuum dried at 120 °C to obtain regenerated zinc chloride, thus completing the chemical degradation and recycling of epoxy composite materials for decommissioned wind turbine blades.

[0059] Example 4: A chemical degradation and recycling method for epoxy composite materials used in decommissioned wind turbine blades includes the following steps: S1. Preprocessing: The epoxy composite material of the decommissioned wind turbine blades is cut into blocks to obtain the wind turbine blade material to be processed. The length of a single block of the wind turbine blade material to be processed is 17 / 24 of the diameter of the bottom surface of the reactor, and the volume of the entire reaction solution accounts for 7 / 12 of the total volume of the reactor.

[0060] S2, Selective Degradation: Weigh 4.0 g of the wind turbine blade material to be treated and add it to a sealed pressure-resistant reactor. Then add 40 mL of acetic acid and 4.0 g of anhydrous zinc chloride to make the mass concentration of zinc chloride in acetic acid 10 wt%. After sealing the reactor, heat it to 180 ℃ and keep it at that temperature for 2 h under stirring conditions. The stirring speed is 600 rpm.

[0061] S3, Solid-liquid separation: After the selective degradation reaction in S2 is completed, the sealed pressure-resistant reactor is cooled to room temperature, the reactor is opened, and the reaction mixture is vacuum filtered to obtain a solid product containing glass fiber and a liquid product containing resin-derived oligomers, acetic acid, and zinc chloride.

[0062] S4, Fiber washing and drying The solid product containing glass fibers obtained in S3 was first washed three times with acetone (20 mL each time), and then washed twice with deionized water (20 mL each time). After washing, the product was placed in a forced-air drying oven and dried at 105 °C for 24 h to obtain the recovered glass fibers.

[0063] S5. Liquid phase product recovery: S501, Acetic acid recycling: The liquid product obtained in S3 was transferred to a vacuum distillation apparatus and heated for distillation under reduced pressure. The distilled acetic acid was collected after condensation, yielding recovered acetic acid and a concentrated solution. The recovered acetic acid can be recycled as a reaction solvent in the selective degradation step.

[0064] S502, Oligomer Separation: Deionized water was added to the concentrate obtained in S501 at a water-to-concentrate volume ratio of 10:1. After stirring for 20 min, the mixture was allowed to stand and separate into layers. Because the resin-derived oligomers have a relatively hydrophobic aromatic epoxy backbone, they precipitate, separate, or undergo phase separation upon the addition of water; zinc chloride mainly enters the aqueous phase. Subsequently, the resin-derived oligomers and the aqueous phase were separated by centrifugation, and the resulting resin-derived oligomers were concentrated by nitrogen blowing.

[0065] S503, zinc chloride regeneration and recycling: The aqueous phase obtained in S502 was concentrated under reduced pressure and then dried under vacuum at 100 °C to obtain solid regenerated zinc chloride. The obtained regenerated zinc chloride was returned to the selective degradation step in S2 for recycling.

[0066] Example 5: A method for chemically degrading and recycling epoxy composite materials for decommissioned wind turbine blades is disclosed in this embodiment. The method uses the recovered acetic acid and recycled zinc chloride obtained in Example 4 as raw materials to chemically degrade and recycle the epoxy composite materials for decommissioned wind turbine blades. The specific steps include: S1. Preprocessing: The epoxy composite material of the decommissioned wind turbine blades is cut into blocks to obtain the wind turbine blade material to be processed. The length of a single block of the wind turbine blade material to be processed is 17 / 24 of the diameter of the bottom surface of the reactor, and the volume of the entire reaction solution accounts for 7 / 12 of the total volume of the reactor.

[0067] S2, Selective Degradation: Weigh 4.0 g of the wind turbine blade material to be treated and add it to a closed pressure-resistant reactor. Then add 40 mL of recovered acetic acid and 4.0 g of regenerated zinc chloride to make the mass concentration of regenerated zinc chloride in acetic acid 10 wt%. After sealing the reactor, heat it to 180 ℃ and hold it for 2 h under stirring conditions at a stirring speed of 600 rpm.

[0068] S3, Solid-liquid separation: After the selective degradation reaction in S2 is completed, the sealed pressure-resistant reactor is cooled to room temperature, the reactor is opened, and the reaction mixture is vacuum filtered to obtain a solid product containing glass fiber and a liquid product containing resin-derived oligomers, acetic acid, and zinc chloride.

[0069] S4, Fiber washing and drying The solid product containing glass fibers obtained in S3 was first washed three times with acetone (20 mL each time), and then washed twice with deionized water (20 mL each time). After washing, the product was placed in a forced-air drying oven and dried at 105 °C for 24 h to obtain the recovered glass fibers.

[0070] S5. Liquid phase product recovery: First, the liquid product obtained from S3 was subjected to vacuum distillation to recover acetic acid and obtain a concentrated solution. Then, water was added to the concentrated solution at a volume ratio of 10:1 to precipitate or separate the resin-derived oligomers. Subsequently, the resin-derived oligomers and the aqueous phase were separated by centrifugation, and the obtained resin-derived oligomers were concentrated by nitrogen blowing. Finally, the aqueous phase was concentrated under vacuum, and the concentrated product was vacuum dried at 120 °C to obtain regenerated zinc chloride, thus completing the chemical degradation and recycling of epoxy composite materials for decommissioned wind turbine blades.

[0071] Comparative Example 1: A high-temperature pyrolysis treatment method for epoxy composite materials used in decommissioned wind turbine blades includes the following steps: Weigh 4.0 g of epoxy composite material from the same source and size as in Example 3, and place it in a tube furnace. Heat the material to 600 °C at a rate of 10 °C / min under a nitrogen atmosphere, and hold at 600 °C for 10 min to allow the resin matrix to pyrolyze. After pyrolysis, allow it to cool naturally to room temperature, and collect the pyrolyzed glass fibers.

[0072] Comparative Example 2: A chemical degradation and recycling method for epoxy composite materials of retired wind turbine blades is disclosed. The processing method of this comparative example is the same as that of Example 3, except that anhydrous zinc chloride in S2 is replaced with aluminum chloride, while the other steps remain unchanged. The final product is recycled glass fiber, recycled acetic acid and recycled aluminum salt.

[0073] Comparative Example 3: A chemical degradation and recycling method for epoxy composite materials of retired wind turbine blades. The processing method of this comparative example is the same as S1~S3 in Example 3, except that anhydrous zinc chloride in S2 is replaced with ferric chloride, and the other steps remain unchanged, and finally recycled glass fiber is obtained.

[0074] Comparative Example 4: A chemical degradation and recycling method for epoxy composite materials of decommissioned wind turbine blades is disclosed. In this comparative example, the recovered acetic acid and recovered aluminum salt obtained from Comparative Example 2 are used as raw materials to chemically degrade the epoxy composite materials of decommissioned wind turbine blades. The processing method of this comparative example is the same as S1 to S3 in Example 3, except that the acetic acid in S2 is replaced with the recovered acetic acid obtained from Comparative Example 2, and the anhydrous zinc chloride is replaced with the recovered aluminum salt obtained from Comparative Example 2. The remaining steps remain unchanged, and finally, recycled glass fiber is obtained.

[0075] Experimental example: The surface condition, resin removal rate, tensile strength retention rate relative to the original glass fiber, and recovery rate of regenerated zinc chloride of the recovered glass fibers obtained in Examples 1-5 and Comparative Examples 1-4 were characterized, and the experimental results are shown in Table 1.

[0076] Table 1. Results of Recycling Performance Characterization

[0077] Experimental results show that after treatment according to the embodiments of the present invention, the surface of the recovered glass fibers is clean, with virtually no observable resin residue or crystalline inorganic salt residue. The resin removal rate of the recovered glass fibers is no less than 98%, the tensile strength retention rate of the recovered glass fibers relative to the original glass fibers is no less than 95%, and the recovery rate of regenerated zinc chloride is no less than 80%, demonstrating the superiority of the method of the present invention in the chemical degradation and recycling of epoxy composite materials for decommissioned wind turbine blades. In Example 5, using the recovered acetic acid and regenerated zinc chloride obtained in Example 4 as raw materials for cyclic degradation, the effective removal of the resin matrix in the epoxy composite material of decommissioned wind turbine blades can still be achieved. The resin removal rate of the recovered glass fibers is no less than 98%, and the tensile strength retention rate is no less than 95%. These results indicate that the method of the present invention can achieve graded recovery of acetic acid, zinc chloride, and resin-derived oligomers, and has the potential for closed-loop recycling.

[0078] Comparative Example 1 used a high-temperature pyrolysis method. Although the glass fiber obtained after high-temperature pyrolysis could remove the resin matrix, the fiber bundles were more prone to breakage and embrittlement, the surface defects of the glass fiber increased, the average diameter decreased, and the tensile strength retention rate was significantly lower than that of the recycled glass fiber obtained in the embodiments of the present invention. Compared with Comparative Example 1, Examples 1-5 of the present invention used an acetic acid and zinc chloride system for selective chemical degradation at 170-180 °C, which can achieve resin matrix removal under milder conditions, while significantly reducing the strength attenuation of glass fiber caused by high-temperature treatment, and can obtain resin-derived oligomers that retain the bisphenol A type epoxy aromatic backbone.

[0079] Compared with Comparative Examples 2 and 3, although the aluminum chloride and ferric chloride used in Comparative Examples 2 and 3 are also Lewis acids of metal chlorides, they cannot achieve sufficient selective decrosslinking of the resin network and efficient release of glass fibers in the glass fiber reinforced epoxy composite material system of retired wind turbine blades, as can the zinc chloride of this invention. In particular, ferric chloride has a weak selective decrosslinking ability on the crosslinking network of amine-cured epoxy resin, and the resin removal rate is only 32%.

[0080] The test results of Comparative Example 4 show that after recycling aluminum salts, the degradation effect of the resin matrix further decreased, and there was obvious resin residue in the solid fiber product. Glass fiber release was insufficient, and the resin removal rate was only 30%, far lower than Comparative Example 2, and significantly lower than Examples 1-5 of this invention. The results indicate that although aluminum chloride has a certain resin degradation capacity in its fresh state, it is prone to irreversible degradation or activity decay during the acetic acid / water separation and recovery process, resulting in poor recycling efficiency. Therefore, it is not suitable for constructing the closed-loop recycling process of acetic acid-oligomery-catalyst graded recovery of this invention. In contrast, zinc chloride in the system of this invention can not only promote the selective decrosslinking of the resin network, but also achieve regeneration and recycling through aqueous phase concentration and drying, making it more suitable for the closed-loop chemical degradation and recovery of epoxy composite materials for decommissioned wind turbine blades.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the chemical degradation and recycling of epoxy composite materials for decommissioned wind turbine blades, characterized in that, Includes the following steps: S1, Selective Degradation: The cut or crushed retired wind turbine blades, acetic acid, and zinc chloride are mixed and subjected to a selective degradation reaction to obtain selective degradation products. S2, Solid-liquid separation: The selective degradation products obtained from S1 were subjected to solid-liquid separation to obtain solid-phase products and liquid-phase products; S3, Fiber Recycling: The solid fiber obtained from S2 was washed and dried to obtain recycled glass fiber. S4. Liquid phase product recovery: The liquid product obtained from S2 was subjected to solvent recovery, oligomer separation, and zinc chloride regeneration to complete the chemical degradation and recycling of epoxy composite materials for decommissioned wind turbine blades.

2. The chemical degradation and recycling method for epoxy composite materials of decommissioned wind turbine blades according to claim 1, characterized in that, In S1, the length of a single piece of the decommissioned wind turbine blade after cutting or crushing is 2 / 3 to 3 / 4 of the diameter of the bottom surface of the reactor for selective degradation reaction, and the volume of the reaction solution for selective degradation reaction accounts for 1 / 2 to 2 / 3 of the total volume of the reactor.

3. The chemical degradation and recycling method for epoxy composite materials of decommissioned wind turbine blades according to claim 1, characterized in that, In S1, the mass-to-volume ratio of the cut or crushed decommissioned wind turbine blades to acetic acid is 1 g: 10~20 mL; the mass concentration of zinc chloride in acetic acid is 10 wt%~20 wt%; the selective degradation reaction temperature is 170~180 ℃, and the time is 2~4 h.

4. The chemical degradation and recycling method for epoxy composite materials of decommissioned wind turbine blades according to claim 1, characterized in that, The solid-liquid separation method in S2 includes filtration, vacuum filtration, pressure filtration, or centrifugation.

5. The chemical degradation and recycling method for epoxy composite materials of decommissioned wind turbine blades according to claim 1, characterized in that, The washing method in S3 involves washing with organic detergent and water in sequence; the drying temperature is 100~110 ℃ and the time is 12~24 h.

6. The chemical degradation and recycling method for epoxy composite materials of decommissioned wind turbine blades according to claim 1, characterized in that, S4 specifically includes the following steps: S401. The liquid product is treated by distillation to obtain recovered acetic acid and concentrated liquid. S402. Add water or an aqueous solvent to the concentrate obtained in S401 to separate the resin-derived oligomers and the aqueous phase. S403 removes the solvent from the aqueous phase obtained from S402 to obtain regenerated zinc chloride.

7. The chemical degradation and recycling method for epoxy composite materials of decommissioned wind turbine blades according to claim 6, characterized in that, The distillation process in S401 includes vacuum distillation or rectification. The volume ratio of water or aqueous solvent to concentrate in S402 is 5:1 to 10:

1. The method for removing aqueous solvent in S403 includes one or more of the following: vacuum concentration, evaporation crystallization, vacuum drying, and spray drying.

8. The chemical degradation and recycling method for epoxy composite materials of decommissioned wind turbine blades according to claim 1, characterized in that, The recycled zinc chloride obtained in S4 is returned to S1 for reuse as zinc chloride in a recycling process.

9. A closed-loop chemical recycling system for epoxy composite materials of decommissioned wind turbine blades based on the chemical degradation and recycling method according to any one of claims 1 to 8, characterized in that, It includes a pretreatment unit, a closed selective degradation reaction unit, a solid-liquid separation unit, a fiber washing and drying unit, a solvent recovery unit, an oligomer separation unit, and a zinc chloride regeneration unit connected in sequence.

10. The closed-loop chemical recovery system according to claim 9, characterized in that, The pretreatment unit is used to cut or crush the decommissioned wind turbine blades to be treated; the closed selective degradation reaction unit performs a selective degradation reaction on the cut or crushed decommissioned wind turbine blades in an acetic acid and zinc chloride system; the solid-liquid separation unit is used to separate the selective degradation reaction products into solid products and liquid products. The fiber washing and drying unit is used to wash and dry the solid phase product to obtain recycled glass fiber; the solvent recovery unit is used to process the liquid phase product through a distillation process to recover acetic acid and / or organic detergent; the oligomer separation unit is used to add water or an aqueous solvent to the concentrate after distillation to separate the resin oligomer derivatives and the aqueous phase; the zinc chloride regeneration unit is used to remove solvent from the aqueous phase to obtain regenerated zinc chloride.

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