Method for recycling waste wind turbine blades under mild conditions

Abstract

The application discloses a method for recycling waste wind turbine blades under mild conditions, comprising the following steps: cutting the waste wind turbine blades into blocks, removing the core material, and retaining the fiber reinforced thermosetting resin composite; placing the block-shaped fiber reinforced thermosetting resin composite in a degradation system to perform a degradation reaction; after the degradation reaction is completed, performing filtration, cleaning, and drying to recover the fibers; adding an alkaline solution to the filtrate to separate the responsive eutectic solvent in the degradation system from the degradation product, separating the upper oily material, and obtaining the degradation product; adding an acidic solution to the lower solution, separating the upper oily solution after the solution is separated, and obtaining the recovered responsive eutectic solvent; collecting the lower solution, drying, and recovering the catalyst in the degradation system; the method has the advantages of mild reaction conditions, high efficiency and environmental protection, simple recovery process, and high product added value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of waste wind turbine blade recycling, and particularly relates to a method for recycling waste wind turbine blades under mild conditions. BACKGROUND

[0002] Wind energy, as one of the most potential renewable energy sources, plays an important role in accelerating global energy transformation. Since 2001, the global cumulative installed capacity of wind power has grown exponentially, reaching 1021 GW by 2023, accounting for more than one-third of the total cumulative installed capacity of renewable energy. The service life of a wind turbine is usually 20-25 years, and when it reaches the designed operating period, it will face retirement. By 2030, there will be more than 30,000 retired wind turbines in China, with about 1 million tons of waste blades. However, so far, there is no complete recycling mode for wind turbine blades, which account for about 20% of the total cost of the machine. As the last link of the wind power industry chain, the recycling of waste wind turbine blades is imperative.

[0003] The wind turbine blades currently widely used in the world are mainly composed of thermosetting resin composites and core materials, with a content of thermosetting resin composites up to 93%. The composite material mainly includes fiber reinforcement and thermosetting resin matrix, the reinforcing fiber is mainly glass fiber and carbon fiber, and the thermosetting resin is mainly epoxy resin. Due to its excellent fatigue resistance and stable physical and chemical properties, recycling and utilization face great challenges. The current treatment methods for retired wind turbine blades mainly include physical recycling, thermal recycling, and chemical recycling. Physical recycling is a method of cutting or crushing into plates, blocks, strips, and particles for recycling according to actual use. Generally, it is crushed into particles for use as filler for building and roadbed materials, which fails to fully utilize the value of blade materials. Thermal recycling is a method of heating the cut wind turbine blades in an oxygen-free or oxygen-deficient environment to make the resin crack into small molecular gaseous or liquid products, separating fibers, metal parts, and coke residues for recycling. The reaction temperature is 450-600℃, the reaction time is long, the energy consumption is high, and harmful gases are generated, polluting the environment. Chemical recycling is a method of using chemical reactions to degrade the resin matrix in the composite material into low molecular substances to separate the fibers. The degradation efficiency of thermosetting resin is high, and the mechanical properties of recycled fibers are good, making it a good method for recycling waste wind turbine blades.

[0004] However, current chemical recycling usually uses strong acids, strong bases and organic solvents as reaction environment, and carries out degradation reaction at 100-190°C under high pressure, which has high requirements for reaction equipment and large recycling cost. The waste liquid after reaction is easy to cause secondary pollution to the environment. At the same time, the low molecular substances degraded from the epoxy resin matrix are difficult to recycle, resulting in a large waste of high-value resources. Therefore, in order to efficiently, environmentally, mildly and low-costly treat waste blades and recycle high-value resources such as fibers and resins, a large-scale, environmentally friendly and low-energy-consumption method for recycling waste wind turbine blades is urgently needed.

[0005] As described above, although some researches have been carried out on degrading thermosetting resin composites and recycling waste wind turbine blades, the following problems are still found in production practice:

[0006] 1. Harsh reaction conditions: As disclosed in patent CN104327303A, supercritical fluid is used to degrade epoxy resin at 300°C and 15MPa, which has relatively harsh reaction conditions, requires a special reaction vessel, has high safety risk and high reaction energy consumption. At the same time, supercritical fluid needs to be added into the reaction kettle at time intervals and periodically under high temperature and high pressure, which is complex to operate and is not conducive to large-scale application in production.

[0007] 2. Low catalyst activity: Transition metal salts can be used as reaction catalysts to degrade epoxy resin-based composites and maintain high fiber recovery rate, but the ratio of catalyst to degradation material is high, and the recycling method is not reported. Therefore, the cost of catalyst is high, and it may cause secondary pollution.

[0008] 3. Incomplete recovery of degradation products: As shown in patents CN114456439B and CN113621171B, current researches mainly focus on recycling glass fibers, carbon fibers and other composite reinforcing materials, and less on recycling epoxy resin degradation products. In actual production, the economic value of resin degradation products is much higher than that of glass fibers. Therefore, ignoring the recycling of epoxy resin degradation products will waste a large amount of high-value resources, thereby reducing the degradation and recycling efficiency and reducing the production enthusiasm. SUMMARY

[0009] In view of the problems existing in the prior art, the present application provides a method for recycling waste wind turbine blades under mild conditions, which has the advantages of mild reaction conditions, high efficiency, environmental protection, simple recycling process and high added value of products.

[0010] The technical solution of the present application is as follows:

[0011] In the first aspect of the present application, a method for recycling waste wind turbine blades under mild conditions is provided, comprising the following steps:

[0012] Step one, cutting the waste wind turbine blade into blocks, removing the core material, and retaining the fiber reinforced thermosetting resin composite;

[0013] Step two, placing the blocky fiber reinforced thermosetting resin composite in a degradation system for degradation reaction, the degradation system uses a eutectic solvent as a degradation solvent, and a metal salt as a catalyst;

[0014] Step three, after the degradation reaction is completed, filtering, washing, and drying are performed to recover the fibers;

[0015] Step four, adding an alkaline solution to the filtrate to separate the eutectic solvent in the degradation system from the degradation products, separating the upper oily material to obtain the degradation products;

[0016] Step five, adding an acidic solution to the lower solution, and after the solution is separated, separating the upper oily solution to obtain the recovered eutectic solvent;

[0017] Step six, collecting the lower solution, drying, and recovering the catalyst in the degradation system.

[0018] The one or more technical solutions of the present application have the following beneficial effects:

[0019] (1) The method for recycling waste wind turbine blades under mild conditions provided by the present application uses RDES as a degradation solvent, which has strong reactivity, is widely available, low in cost, environmentally friendly, easy to synthesize, stable in physical and chemical properties, and can be reused. The physical and chemical properties of RDES can be designed according to different combinations of hydrogen bond donors and hydrogen bond acceptors. Chemical reactions in this solution can significantly reduce the activation energy of molecules, allowing them to react under mild conditions such as normal pressure, lower temperature, and shorter time. This simplifies the recycling process, reduces operating costs, avoids production risks, and helps to promote the industrial application of degradation methods.

[0020] (2) The method for recycling waste wind turbine blades under mild conditions provided by the present application uses a metal salt as a catalyst and RDES as a reaction environment, which can effectively improve the catalytic activity of metal cations in the reaction, thereby significantly reducing the amount of catalyst used. In the subsequent RDES conversion process, the catalyst can be effectively recovered, greatly reducing the cost of the catalyst.

[0021] (3) The method for recycling waste wind turbine blades under mild conditions provided by the present application uses the addition of an alkaline solution or an acidic solution to convert the eutectic solvent into a hydrophilic or hydrophobic phase, allowing the recovery of the degradation products and the eutectic solvent. When an alkaline solution is added, the eutectic solvent is converted into a hydrophilic phase, and the degradation products are obtained by separating the oil phase. When an acidic solution is added, the eutectic solvent is converted into a hydrophobic phase, and the responsive eutectic solvent is recovered by separating the oil phase.

[0022] (4) The method for recycling waste wind turbine blades under mild conditions provided by the application can realize comprehensive recovery of degradation products, can recover solvents, catalysts, fibers and resin degradation products in the system, and thus greatly improves the economic benefits of recycling. The solvents and catalysts in the degradation system can be recycled and reused through a simple process; the recycled fibers have good mechanical properties; the degradation products of thermosetting resins have molecular weights of 440-580 and 855-981, and can be synthesized into adhesives for reuse. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A flowchart of the method for recycling waste wind turbine blades under mild conditions of the application is shown in the figure.

[0024] Figure 2 A front and back comparison schematic diagram of RDES degradation of waste wind turbine blades is shown in the figure.

[0025] Figure 3 A front and back comparison schematic diagram of waste wind turbine blade degradation is shown in the figure. DETAILED DESCRIPTION

[0026] The application will be further described below in combination with the drawings and examples.

[0027] In a typical embodiment of the application, a method for recycling waste wind turbine blades under mild conditions is provided, which comprises the following steps:

[0028] Step 1: cutting the waste wind turbine blades into blocks, removing the core material and retaining the fiber-reinforced thermosetting resin composite material;

[0029] Step 2: placing the block-shaped fiber-reinforced thermosetting resin composite material in a degradation system for degradation reaction;

[0030] Step 3: after the degradation reaction is completed, filtering, washing and drying are performed to recover the fibers;

[0031] Step 4: adding an alkaline solution to the filtrate to separate the responsive deep eutectic solvent in the degradation system from the degradation products, separating the upper oily material to obtain the degradation products;

[0032] Step 5: adding an acidic solution to the lower solution, separating the upper oily solution after the solution is separated to obtain the recycled responsive deep eutectic solvent;

[0033] Step 6: collecting the lower solution, drying and recovering the catalyst in the degradation system.

[0034] The responsive deep eutectic solvent (RDES) as a fan blade degradation solvent can degrade the thermosetting resin under mild conditions of normal pressure, lower temperature and shorter time, simplify the recycling process, reduce operating costs, avoid production risks, and help promote the industrial application of degradation methods. The metal salt as a catalyst is added to the solvent to promote the breaking of chemical bonds of epoxy resin-based composites, accelerate the degradation reaction, and maintain a high fiber recovery rate.

[0035] In some embodiments of the present application, the fibers in the fiber-reinforced thermosetting resin composite in step one include glass fibers, carbon fibers and glass-carbon hybrid fibers, and the thermosetting resin is an amine-cured epoxy resin.

[0036] In some embodiments of the present application, the deep eutectic solvent is a responsive deep eutectic solvent formed by hydrogen bonding.

[0037] In some embodiments of the present application, the hydrogen bond donor and acceptor are at least two of choline chloride, menthol, octanol, diethanolamine, thymol, hexanoic acid, octanoic acid, decanoic acid, nonanoic acid, lauric acid and salicylic acid. Those skilled in the art can select at least two substances for mixing as needed, and mix at least two substances in a certain proportion as needed to obtain a responsive hydrophobic deep eutectic solvent.

[0038] In some embodiments of the present application, the metal salt catalyst is a salt formed by zinc, iron, nickel, copper, aluminum, ruthenium or cobalt metal ions and halogen ions, organic acid radicals or thymol ligands; in order to ensure the efficiency and rate of the degradation reaction under the premise of controlling the cost, the dosage of the metal salt catalyst is 5-20wt% of the responsive deep eutectic solvent.

[0039] In some embodiments of the present application, the reaction pressure of the degradation reaction in step two is normal pressure, and the reaction time is 0.5-48h. In order to ensure sufficient degradation reaction and lower energy consumption cost, the reaction temperature is selected to be 80-200℃.

[0040] In some embodiments of the present application, the basic solution in step four is an alkali metal hydroxide or amino compound solution with a concentration of 3mol / L or above. By adding a basic solution, the deep eutectic solvent becomes a hydrophilic phase, and by separating the oil phase, the degradation products are recovered.

[0041] In some embodiments of the present application, the amount of the basic solution added is 20-60wt% of the responsive deep eutectic solvent.

[0042] In some embodiments of the application, the acid solution in step five is one of perchloric acid, hydroiodic acid, hydrobromic acid, hydrochloric acid, sulfuric acid and nitric acid with a concentration of 1 mol / L or more. The addition of the acid solution changes the responsive deep eutectic solvent into a hydrophobic phase. The oil phase is separated to realize the recovery of the responsive deep eutectic solvent. The amount of the acid solution added is determined according to the actual need, and the amount of the acid solution added is determined according to the actual need.

[0043] The waste fan blades used in the following examples were from Guyuan County, Zhangjiakou City, Hebei Province. They were further cut into 1.4*1.9*0.4 cm (2.0±0.05 g) block-shaped blades, and the core material (including PVC, balsa wood, etc.) was removed, leaving the fiber-reinforced thermosetting resin composite.

[0044] Preferably, the following examples only demonstrate that the catalyst is zinc chloride, and the doping amount is 20 wt% of the responsive deep eutectic solvent (RDES).

[0045] Example 1

[0046] Caprylic acid and lauric acid were stirred at 60°C until a colorless transparent liquid was obtained. No crystals were precipitated after standing for 24 hours. The RDES was prepared and ready for use. The RDES, ZnCl2 and block-shaped blades were mixed at a ratio of m(RDES):m(ZnCl2):m(block-shaped blades) = 5:1:1 and placed in an oil bath at 150°C with 200 rpm / min heating. After 5 hours, the degradation rate of the resin was up to 57.42%.

[0047] After the reaction was completed, the fibers were filtered, washed with excess ethanol, and dried at 100°C for 2 hours to obtain clean fibers. A small amount of 5M NaOH solution was added to the filtrate, mixed uniformly, and then left to stand. The liquid was separated into two phases. The upper liquid was collected as the degradation product, and the lower layer was the hydrophilic RDES and the catalyst. A small amount of excess 12M HCl solution was added to the lower layer solution, and the hydrophilic RDES was converted into a hydrophobic phase. After the solution was separated, the upper RDES was recovered. The lower layer solution was collected and dried to obtain the recovered catalyst.

[0048] Example 2

[0049] Nonanoic acid and thymol were stirred at 60°C until a colorless transparent liquid was obtained. No crystals were precipitated after standing for 24 hours. The RDES was prepared and ready for use. The RDES, ZnCl2 and block-shaped blades were mixed at a ratio of m(RDES):m(ZnCl2):m(block-shaped blades) = 5:1:1 and placed in an oil bath at 150°C with 200 rpm / min heating. After 5 hours, the degradation rate of the resin was up to 68.61%. The subsequent recovery steps were consistent with Example 1.

[0050] Example 3

[0051] The tributyl phosphate and lauric acid were stirred at 60°C to a colorless transparent liquid, no crystals precipitated after 24h, RDES preparation was completed, ready for use; RDES, ZnCl2, block blade were mixed with m(RDES):m(ZnCl2):m(block blade)=5:1:1, and placed in an oil bath pot at 150°C, heated at 200rpm / min, after 5h the degradation rate of the resin can reach up to 30.06%. The subsequent recovery steps are consistent with example 1.

[0052] Example 4

[0053] The octanoic acid, nonanoic acid and decanoic acid were stirred at 60°C to a colorless transparent liquid, no crystals precipitated after 24h, RDES preparation was completed, ready for use; RDES, ZnCl2, block blade were mixed with m(RDES):m(ZnCl2):m(block blade)=5:1:1, and placed in an oil bath pot at 150°C, heated at 200rpm / min, after 5h the degradation rate of the resin can reach up to 32.86%. The subsequent recovery steps are consistent with example 1.

[0054] Example 5

[0055] The decanoic acid, menthol and thymol were stirred at 60°C to a colorless transparent liquid, no crystals precipitated after 24h, RDES preparation was completed, ready for use; RDES, ZnCl2, block blade were mixed with m(RDES):m(ZnCl2):m(block blade)=5:1:1, and placed in an oil bath pot at 150°C, heated at 200rpm / min, after 5h the degradation rate of the resin can reach up to 62.45%.

[0056] Example 6

[0057] The menthol and thymol were stirred at 60°C to a colorless transparent liquid, no crystals precipitated after 24h, RDES preparation was completed, ready for use; RDES, ZnCl2, block blade were mixed with m(RDES):m(ZnCl2):m(block blade)=5:1:1, and placed in an oil bath pot at 150°C, heated at 200rpm / min, after 5h the degradation rate of the resin can reach up to 40.00%. The subsequent recovery steps are consistent with example 1.

[0058] From the above examples, it can be seen that when the waste fan blade is degraded, the RDES prepared by the method of the present application has the advantages of Figure 1The shown method degrades, and the degradation rate of the resin can reach more than 50%, which can effectively realize the recycling of the fiber in the waste blade. The waste fan blades before and after degradation are shown in Figure 2 and Figure 3 .

[0059] Although the specific embodiments of the present application are described above with reference to the drawings, they are not a limitation on the scope of protection of the present application. Those skilled in the art should understand that various modifications or changes made by those skilled in the art on the basis of the technical solutions of the present application without creative labor are still within the scope of protection of the present application.

Claims

1. A method for resource-based recycling of waste wind turbine blades under mild conditions, characterized in that, Includes the following steps: Step 1: Cut the discarded wind turbine blades into blocks, remove the core material, and retain the fiber-reinforced thermosetting resin composite material; Step 2: Place the block fiber reinforced thermosetting resin composite material in a degradation system for degradation reaction. The degradation system uses a eutectic solvent as the degradation solvent and a metal salt as the catalyst. Step 3: After the degradation reaction is complete, filter, wash, and dry the fibers to recover them. Step 4: Add an alkaline solution to the filtrate to separate the eutectic solvent and degradation products in the degradation system, separate the upper oily substance, and obtain the degradation products; Step 5: Add an acidic solution to the lower layer solution. After phase separation, separate the upper oily solution to obtain the recovered eutectic solvent. Step 6: Collect the lower layer solution, dry it, and recover the catalyst in the degradation system.

2. The method for resource-based recycling of waste wind turbine blades under mild conditions as described in claim 1, characterized in that, In step one, the fibers in the fiber-reinforced thermosetting resin composite material include glass fibers, carbon fibers, and glass-carbon mixed fibers, and the thermosetting resin is an amine-cured epoxy resin.

3. The method for resource-based recycling of waste wind turbine blades under mild conditions as described in claim 1, characterized in that, The eutectic solvent is a responsive eutectic solvent formed by hydrogen bonding.

4. The method for resource-based recycling of waste wind turbine blades under mild conditions as described in claim 3, characterized in that, The hydrogen bond donor and acceptor are at least two of the following: choline chloride, menthol, octanol, diethanolamine, thymol, hexanoic acid, caprylic acid, decanoic acid, nonanoic acid, lauric acid, and salicylic acid.

5. The method for resource-based recycling of waste wind turbine blades under mild conditions as described in claim 3, characterized in that, Metal salt catalysts are salts formed by zinc, iron, nickel, copper, aluminum, ruthenium or cobalt metal ions with halide ions, organic acid radicals or thymol ligands.

6. The method for resource-based recycling of waste wind turbine blades under mild conditions as described in claim 3, characterized in that, The metal salt catalyst dosage is 5–20 wt% of the responsive eutectic solvent.

7. The method for resource-based recycling of waste wind turbine blades under mild conditions as described in claim 1, characterized in that, The degradation reaction in step two is carried out at atmospheric pressure, at a temperature of 80–200°C, and for a time of 0.5–48 h.

8. The method for resource-based recycling of waste wind turbine blades under mild conditions as described in claim 1, characterized in that, The alkaline solution in step four is an alkali metal hydroxide or amino compound solution with a concentration of 3 mol / L or higher.

9. The method for resource-based recycling of waste wind turbine blades under mild conditions as described in claim 8, characterized in that, The amount of alkaline solution added is 20-60 wt% of the eutectic solvent.

10. The method for resource-based recycling of waste wind turbine blades under mild conditions as described in claim 1, characterized in that, The acidic solution in step five is one of the following: perchloric acid, hydroiodic acid, hydrobromic acid, hydrochloric acid, sulfuric acid, and nitric acid, with a concentration of 1 mol / L or higher.

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