A system for recycling carbon fiber by stepwise molten salt

Abstract

The present invention relates to the technical field of carbon fiber recycling, and particularly to a system for recycling carbon fiber by stepped molten salt. The system includes: a heat treatment unit, which includes a primary reactor and a secondary reactor connected in sequence. A plurality of ultrasonic generators are arranged at the bottoms of both the primary reactor and the secondary reactor. The primary reactor contains a first composite molten salt, and the secondary reactor contains a second composite molten salt. The primary reactor is used for pyrolyzing carbon fiber reinforced resin matrix composites once, and the secondary reactor is used for pyrolyzing the carbon fiber reinforced resin matrix composites after the first pyrolysis a second time. The catalytic property of the first composite molten salt is greater than that of the second composite molten salt, and the melting point of the first composite molten salt is lower than that of the second composite molten salt; a carbon fiber recycling unit, which includes a cleaning area and a drying area connected in sequence. The cleaning area is used for cleaning the carbon fiber obtained by the second pyrolysis, and the drying area is used for drying the cleaned carbon fiber to achieve the recycling of carbon fiber.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon fiber recycling, and particularly relates to a system for recycling carbon fiber by stepped molten salt. Background Art

[0002] As a new material, carbon fiber is widely used in cutting-edge fields such as aerospace and wind power generation due to its excellent characteristics of low density and high strength. With the increasing demand for carbon fiber application scenarios such as aircraft, the input proportion of carbon fiber in application components also shows a significant growth trend. When in application, carbon fiber is often bonded and positioned well with a thermosetting resin as the matrix to make a carbon fiber reinforced resin matrix composite (CFRP). After a large amount of CFRP reaches the end of its service life and is discarded, there is an urgent need to recycle the expensive carbon fiber from it for reuse. The cross-linked thermosetting resin is difficult to efficiently remove from CFRP, making the directional recycling of carbon fiber a problem.

[0003] In related technologies, pyrolysis, as the only technology for early commercial application, has initially achieved large-scale recycling of carbon fiber. However, the above method has problems such as long heat treatment time, low resin degradation rate, and poor retained strength of the recycled carbon fiber.

[0004] Therefore, there is an urgent need for a system for recycling carbon fiber by stepped molten salt to solve the above problems. Summary of the Invention

[0005] One or more embodiments of this specification describe a system for recycling carbon fiber by stepped molten salt, which can solve the problems in related technologies such as long heat treatment time, low resin degradation rate, and poor retained strength of the recycled carbon fiber.

[0006] An embodiment of this specification provides a system for recycling carbon fiber by stepped molten salt, including:

[0007] A heat treatment unit, including a primary reactor and a secondary reactor connected in sequence. A plurality of ultrasonic generators are arranged at the bottoms of the primary reactor and the secondary reactor. The primary reactor contains a first composite molten salt, and the secondary reactor contains a second composite molten salt. The primary reactor is used for primary pyrolysis of the carbon fiber reinforced resin matrix composite, and the secondary reactor is used for secondary pyrolysis of the carbon fiber reinforced resin matrix composite after primary pyrolysis. The catalytic property of the first composite molten salt is greater than that of the second composite molten salt, and the melting point of the first composite molten salt is less than that of the second composite molten salt;

[0008] A carbon fiber recycling unit, including a cleaning area and a drying area connected in sequence. The cleaning area is used for cleaning the carbon fiber obtained by secondary pyrolysis, and the drying area is used for drying the cleaned carbon fiber to achieve the recycling of carbon fiber.

[0009] According to the above embodiments, a target organic solvent is further accommodated in the primary reactor, and the dielectric constant of the target organic solvent is greater than 3.6 C2 / (N·m2).

[0010] According to the above embodiments, it further includes:

[0011] A pretreatment unit, connected to the primary reactor, for sorting carbon fiber reinforced resin matrix composites from raw materials and feeding the sorted carbon fiber reinforced resin matrix composites into the primary reactor;

[0012] And / or,

[0013] A supply unit, including a primary molten salt tank, an organic solvent tank, and a secondary molten salt tank, where the primary molten salt tank is used to supply the first composite molten salt to the primary reactor, the organic solvent tank is used to supply the target organic solvent to the primary reactor, and the secondary molten salt tank is used to supply the first composite molten salt to the secondary reactor.

[0014] According to the above embodiments, the melting point of the first composite molten salt is 120-160°C, the melting point of the second composite molten salt is 350-400°C, and the boiling point of the target organic solvent is 160-200°C.

[0015] According to the above embodiments, the first composite molten salt includes at least one of alkali salts, chloride salts, and nitrate salts; and / or,

[0016] The target organic solvent includes at least one of alcohols, amines, and alkanolamines; and / or,

[0017] The second composite molten salt includes at least one of carbonate salts and sulfate salts.

[0018] According to the above embodiments, it further includes two clamps that can move horizontally and vertically, and the two clamps are used to hold both ends of the carbon fiber reinforced resin matrix composite;

[0019] By using the clamps to hold the carbon fiber reinforced resin matrix composite, the carbon fiber reinforced resin matrix composite is successively driven by the clamps to be immersed in the molten first composite molten salt and the second composite molten salt, and the carbon fiber obtained by secondary pyrolysis is driven to move to the cleaning area and the drying area in sequence.

[0020] According to the above embodiments, the clamping portion of the clamp for holding the end of the carbon fiber reinforced resin matrix composite can rotate around the axis of the carbon fiber reinforced resin matrix composite.

[0021] According to the above embodiments, the carbon fiber recovery unit further includes a shearing zone, the drying zone is connected to the shearing zone, and the shearing zone is configured to shear the dried carbon fiber located between the two fixtures to achieve the recovery of carbon fiber; and / or,

[0022] The cleaning zone includes a water cleaning zone and an organic solvent cleaning zone connected in sequence. The organic solvent cleaning zone is connected to the drying zone. The water cleaning zone is configured to perform water cleaning on the carbon fiber obtained by secondary pyrolysis, and the organic solvent cleaning zone is configured to perform organic solvent cleaning on the carbon fiber after water cleaning.

[0023] According to the above embodiments, it further includes:

[0024] A pyrolysis product recovery unit, including a gas-liquid condensation separator and a fractionator connected in sequence. The gas-liquid condensation separator is configured to separate the volatile components precipitated from the first-stage reactor and the second-stage reactor to obtain pyrolysis oil and pyrolysis gas, and the fractionator is configured to fractionate and purify the pyrolysis oil obtained by the gas-liquid condensation separator to achieve the recovery of pyrolysis products.

[0025] According to the above embodiments, it further includes:

[0026] A waste heat utilization unit, including a gas burner and a tail gas processor connected in sequence. The gas burner is connected to the gas-liquid condensation separator. The gas burner is configured to burn the pyrolysis gas obtained by the gas-liquid condensation separator and output the heat generated by the combustion to the outer walls of the first-stage reactor and the second-stage reactor, and the tail gas processor is configured to perform tail gas treatment on the gas generated by the gas burner.

[0027] According to the system for recovering carbon fiber by cascade molten salt provided in the embodiments of the present specification, by setting a first-stage reactor and a second-stage reactor to form a cascade molten salt for recovering carbon fiber, and a plurality of ultrasonic generators are arranged at the bottoms of the first-stage reactor and the second-stage reactor, so that the heat treatment time can be shortened and the resin degradation rate can be improved; meanwhile, by setting a carbon fiber recovery unit, the recovery of carbon fiber can be realized. Moreover, since the catalytic property of the first composite molten salt is greater than that of the second composite molten salt, and the melting point of the first composite molten salt is less than that of the second composite molten salt, the retention strength of the recovered carbon fiber can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following

[0029] The accompanying drawings in the description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

[0030] Figure 1 Shows a schematic structural diagram of a stepped molten salt carbon fiber recovery system according to an embodiment;

[0031] Figure 2 Shows a schematic structural diagram of a stepped molten salt carbon fiber recovery system according to another embodiment;

[0032] Figure 3 Shows a schematic diagram before and after a fixture clamps a carbon fiber reinforced resin matrix composite according to an embodiment.

[0033] Reference numerals:

[0034] 5 1 - Heat treatment unit;

[0035] 11 - Primary reactor;

[0036] 12 - Secondary reactor;

[0037] 13 - Ultrasonic generator;

[0038] 2 - Carbon fiber recovery unit;

[0039] 0 21 - Water cleaning area;

[0040] 22 - Organic solvent cleaning area;

[0041] 23 - Drying area;

[0042] 24 - Shearing area;

[0043] 3 - Pretreatment unit;

[0044] 5 4 - Supply unit;

[0045] 41 - Primary molten salt tank;

[0046] 42 - Organic solvent tank;

[0047] 43 - Secondary molten salt tank;

[0048] 5 - Fixture;

[0049] 51 - Clamping part;

[0050] 6 - Pyrolysis product recovery unit;

[0051] 61 - Gas - liquid condensation separator;

[0052] 62 - Fractionator;

[0053] 7 - Waste heat utilization unit;

[0054] 71 - Gas burner;

[0055] 72 - Tail gas processor. Detailed implementation manners

[0056] The solutions provided in this specification will be described below with reference to the accompanying drawings.

[0057] Figure 1 The structural schematic diagram of the system for step - by - step molten salt recovery of carbon fiber according to an embodiment is shown. As Figure 1 shown, the system for step - by - step molten salt recovery of carbon fiber includes a heat treatment unit 1 and a carbon fiber recovery unit 2, where:

[0058] The heat treatment unit 1 includes a primary reactor 11 and a secondary reactor 12 connected in sequence. A plurality of ultrasonic generators 13 are provided at the bottoms of both the primary reactor 11 and the secondary reactor 12. The primary reactor 11 contains a first composite molten salt, and the secondary reactor 12 contains a second composite molten salt. The primary reactor 11 is used for the primary pyrolysis of the carbon fiber reinforced resin - based composite material, and the secondary reactor 12 is used for the secondary pyrolysis of the carbon fiber reinforced resin - based composite material after the primary pyrolysis. The catalytic property of the first composite molten salt is greater than that of the second composite molten salt, and the melting point of the first composite molten salt is less than that of the second composite molten salt;

[0059] The carbon fiber recovery unit 2 includes a cleaning area and a drying area 23 connected in sequence. The cleaning area is used for cleaning the carbon fiber obtained by the secondary pyrolysis, and the drying area 23 is used for drying the cleaned carbon fiber to achieve the recovery of the carbon fiber.

[0060] In this embodiment, by setting the primary reactor 11 and the secondary reactor 12 to form a step - by - step molten salt for carbon fiber recovery, and a plurality of ultrasonic generators 13 are provided at the bottoms of both the primary reactor 11 and the secondary reactor 12, so that the heat treatment time can be shortened and the resin degradation rate can be improved; at the same time, by setting the carbon fiber recovery unit 2, the recovery of the carbon fiber can be realized. Moreover, since the catalytic property of the first composite molten salt is greater than that of the second composite molten salt, and the melting point of the first composite molten salt is less than that of the second composite molten salt, the retention strength of the recovered carbon fiber can be improved.

[0061] It can be understood that in the embodiments of this specification, the catalytic property of the composite molten salt is based on the resin decomposition rate and the degree of damage to the carbon fiber structure. The former is referenced by the removal rate of the resin, and the latter is referenced by the single - filament tensile strength of the carbon fiber, which will not be elaborated here.

[0062] In some embodiments, an inert atmosphere needs to be maintained in the primary reactor 11 and the secondary reactor 12 to avoid the oxidation of carbon fibers under high temperature conditions (such as 100 - 400 °C). Among them, the inert atmosphere can be nitrogen, argon, etc., which are not limited in the embodiments of this specification.

[0063] In an embodiment of this specification, the primary reactor 11 also contains a target organic solvent, and the dielectric constant of the target organic solvent is greater than 3.6 C² / N·m².

[0064] In this embodiment, in order to further remove the resin in the primary reactor 11, an organic solvent with a dielectric constant greater than 3.6 C² / N·m² can be added to the primary reactor 11.

[0065] In some embodiments, the target organic solvent includes at least one of alcohols, amines, and alkanolamines. For example, it can be butanediol, ethylene glycol, ethanolamine, aniline, etc., which are not specifically limited in the embodiments of this specification.

[0066] In an embodiment of this specification, the melting point of the first composite molten salt is 120 - 160 °C, the melting point of the second composite molten salt is 350 - 400 °C, and the boiling point of the target organic solvent is 160 - 200 °C.

[0067] In this embodiment, in order to ensure that the resin can be removed more thoroughly and the retention strength of the recovered carbon fibers can be ensured, it is necessary to make the first composite molten salt have strong catalytic activity and a low melting point, the target organic solvent have strong polarity and good solubility, and the second composite molten salt have weak catalytic activity and a high melting point. Therefore, it is necessary to ensure that the target organic solvent can remain in a liquid form after being mixed with the first composite molten salt, that is, the boiling point of the target organic solvent is greater than the melting point of the first composite molten salt.

[0068] In an embodiment of this specification, the first composite molten salt includes at least one of alkali salts, chlorides, and nitrates.

[0069] In some embodiments, the alkali salt can be sodium hydroxide, potassium hydroxide, etc., the chloride can be sodium chloride, potassium chloride, etc., the nitrate can be sodium nitrate, potassium nitrate, etc., which are not specifically limited in the embodiments of this specification. At the same time, the specific ratio of each molten salt is not specifically limited either, as long as the above characteristics (i.e., melting point, boiling point, catalytic activity, polarity, solubility, etc.) are satisfied.

[0070] In an embodiment of this specification, the second composite molten salt includes at least one of carbonates and sulfates.

[0071] In some embodiments, the carbonate may be sodium carbonate, potassium carbonate, etc., and the sulfate may be sodium sulfate, potassium sulfate, etc. The embodiments of the present specification do not specifically limit their types. At the same time, the specific ratio of each molten salt is not specifically limited as long as the above characteristics (i.e., melting point, boiling point, catalytic property, polarity, solubility, etc.) are satisfied.

[0072] Figure 2 FIG. shows a schematic structural diagram of a system for recycling carbon fiber by cascade molten salt according to another embodiment. As Figure 2 shown, in an embodiment of the present specification, the above system further includes a pretreatment unit 3. The pretreatment unit 3 is connected to the first-stage reactor 11. The pretreatment unit 3 is used to separate the carbon fiber reinforced resin matrix composite material from the raw materials and send the separated carbon fiber reinforced resin matrix composite material into the first-stage reactor 11.

[0073] In this embodiment, generally speaking, the carbon fiber reinforced resin matrix composite material is mostly a specific component (such as a fan blade). Therefore, through machine vision, the pretreatment unit 3 can separate the carbon fiber reinforced resin matrix composite material from the raw materials to remove the easily distinguishable mixed components that do not belong to CFRP, and can send the separated carbon fiber reinforced resin matrix composite material into the first-stage reactor 11 through a conveyor belt (not shown in the figure). Here, the embodiments of the present specification do not elaborate on the specific machine vision algorithm of the pretreatment unit 3.

[0074] Please continue to refer to Figure 2 , in an embodiment of the present specification, the above system further includes a supply unit 4. The supply unit 4 includes a first-stage molten salt tank 41, an organic solvent tank 42, and a second-stage molten salt tank 43. The first-stage molten salt tank 41 is used to supply the first composite molten salt to the first-stage reactor 11, the organic solvent tank 42 is used to supply the target organic solvent to the first-stage reactor 11, and the second-stage molten salt tank 43 is used to supply the first composite molten salt to the second-stage reactor 12.

[0075] In this embodiment, in order to facilitate the supply of the first composite molten salt to the first-stage reactor 11, the supply of the target organic solvent to the first-stage reactor 11, and the supply of the first composite molten salt to the second-stage reactor 12, the first composite molten salt with preset components and a preset ratio can be stored in the first-stage molten salt tank 41 in advance, the target organic solvent with preset components and a preset ratio can be stored in the organic solvent tank 42, and the second composite molten salt with preset components and a preset ratio can be stored in the second-stage molten salt tank 43.

[0076] In an embodiment of the present specification, the cleaning area includes a water cleaning area 21 and an organic solvent cleaning area 22 connected in sequence. The organic solvent cleaning area 22 is connected to the drying area 23. The water cleaning area 21 is used to perform water cleaning on the carbon fibers obtained by secondary pyrolysis, and the organic solvent cleaning area 22 is used to perform organic solvent cleaning on the carbon fibers after water cleaning.

[0077] In this embodiment, first, the water cleaning area 21 is used to perform water cleaning on the carbon fibers obtained by secondary pyrolysis. This is beneficial for washing away the molten salt and large-particle-size resin residues on the surface of the carbon fibers. Then, the organic solvent cleaning area 22 is used to perform organic solvent cleaning on the carbon fibers after water cleaning. This can dissolve the liquid-phase macromolecular organic substances adhered to the surface of the carbon fibers, so as to completely dissolve and wash away the resin on the surface of the carbon fibers to obtain the desired carbon fibers. Among them, the organic solvent can be acetone, which is not limited in the embodiments of the present specification.

[0078] In an embodiment of the present specification, the above system further includes a pyrolysis product recovery unit 6. The pyrolysis product recovery unit 6 includes a gas-liquid condensation separator 61 and a fractionator 62 connected in sequence. The gas-liquid condensation separator 61 is used to separate the volatile components (specifically generated above the molten salt liquid surface, that is, gas-liquid components) precipitated from the first-stage reactor 11 and the second-stage reactor 12 to obtain pyrolysis oil and pyrolysis gas. The fractionator 62 is used to fractionate and purify the pyrolysis oil obtained by the gas-liquid condensation separator 61 to realize the recovery of pyrolysis products.

[0079] In this embodiment, by setting the gas-liquid condensation separator 61 and the fractionator 62, the collection of pyrolysis products such as pyrolysis gas and pyrolysis oil can be completed.

[0080] In an embodiment of the present specification, the above system further includes a waste heat utilization unit 7. The waste heat utilization unit 7 includes a gas burner 71 and a tail gas processor 72 connected in sequence. The gas burner 71 is connected to the gas-liquid condensation separator 61. The gas burner 71 is used to burn the pyrolysis gas obtained by the gas-liquid condensation separator 61 and output the heat generated by the combustion to the outer walls of the first-stage reactor 11 and the second-stage reactor 12. The tail gas processor 72 is used to perform tail gas treatment on the gas generated by the gas burner 71.

[0081] In this embodiment, by setting the gas burner 71, it is beneficial to burn the pyrolysis gas obtained by the gas-liquid condensation separator 61 and output the heat generated by the combustion to the outer walls of the first-stage reactor 11 and the second-stage reactor 12, so as to realize the waste heat utilization of the volatile components.

[0082] Figure 3 The schematic diagrams before and after the fixture clamps the carbon fiber reinforced resin matrix composite according to an embodiment are shown. Please refer to Figure 2 and Figure 3, in an embodiment of the present specification, the above system further includes two clamps 5 that can move horizontally and vertically. The two clamps 5 are used to clamp both ends of the carbon fiber reinforced resin matrix composite material;

[0083] By using the clamps 5 to clamp the carbon fiber reinforced resin matrix composite material, the carbon fiber reinforced resin matrix composite material is successively driven by the clamps 5 to be immersed in the molten first composite molten salt and second composite molten salt, and the carbon fiber obtained by secondary pyrolysis is driven to move to the cleaning area and the drying area 23 in sequence.

[0084] In this embodiment, by setting the clamps 5, it is beneficial to improve the rate of carbon fiber recovery, and compared with the method of using tweezers to pick up in the related art, the final desired carbon fiber product can be obtained more conveniently.

[0085] It can be understood that the clamps 5 can be connected to a motor (not shown in the figure), and the motor can drive the clamps 5 to lift and move horizontally. Here, the embodiments of the present specification will not elaborate. At the same time, the clamps 5 can be any structure capable of clamping the carbon fiber reinforced resin matrix composite material, and the embodiments of the present specification will not elaborate and limit here.

[0086] In some embodiments, the clamps 5 can be made of Hastelloy. Hastelloy is a kind of nickel-based alloy, which is currently mainly divided into three series: B, C, and G. It is mainly used in strong corrosive medium occasions where ferritic Cr-Ni or Cr-Ni-Mo stainless steels, non-metallic materials, etc. cannot be used. Of course, the clamps 5 can also be made of other corrosion-resistant alloys, and the embodiments of the present specification will not limit here.

[0087] In an embodiment of the present specification, the clamping portion 51 of the clamps 5 for clamping the end of the carbon fiber reinforced resin matrix composite material can rotate around the axis of the carbon fiber reinforced resin matrix composite material.

[0088] In this embodiment, by setting the clamping portion 51 that can rotate around the axis of the carbon fiber reinforced resin matrix composite material, not only can the height of the carbon fiber reinforced resin matrix composite material be adjusted to better immerse it below the liquid level of the molten salt, but also during the subsequent cleaning and drying processes, the carbon fiber can be rotated to accelerate the cleaning and drying processes, improving the efficiency of obtaining the final desired carbon fiber.

[0089] It can be understood that the clamping portion 51 is also provided with a rotating motor (not shown in the figure), and the embodiments of the present specification will not elaborate here.

[0090] In an embodiment of the present specification, the carbon fiber recovery unit 2 further includes a shearing area 24. The drying area 23 is connected to the shearing area 24, and the shearing area 24 is used to shear the carbon fiber that is dried and located between the two clamps 5 to achieve the recovery of the carbon fiber.

[0091] In this embodiment, after drying, the carbon fiber located between the two jigs 5 can be sheared using scissors to achieve the recycling of carbon fiber.

[0092] The above solution will be introduced below in combination with a specific embodiment (recovering carbon fiber from waste wind turbine blades).

[0093] After the full-process recycling of 20 kg of waste wind turbine blades by the above system, approximately 8 kg of carbon fiber is obtained. The tensile strength retention rate of the carbon fiber monofilament is about 95%, and the total time consumed in the whole cycle is about 1 h. The specific process can be seen in the following steps:

[0094] 1) Heat and raise the temperature of a total of 200 kg of pre-mixed NaNO3-KNO3-NaNO2 (7-53-40 wt%) to 150 °C in the first-stage reactor 11, and heat and raise the temperature of a total of 200 kg of pre-mixed K2CO3-Li2CO3-Na2CO3 (34.5-32.1-33.4 wt%) to 400 °C in the second-stage reactor 12. Both the first-stage reactor 11 and the second-stage reactor 12 are insulated for 1 h to fully melt the eutectic salt, and then 20 kg of ethanolamine is added to the first-stage reactor 11;

[0095] 2) After the waste wind turbine is simply disassembled, the pretreatment unit 3 is used to remove the remaining components other than the blades;

[0096] 3) Fix the waste wind turbine blade with the jig 5 and immerse it below the molten salt level in the first-stage reactor 11. Open the multiple ultrasonic generators 13 on the side and bottom of the first-stage reactor 11 and keep it warm for 10 min;

[0097] 4) The jig 5 takes out the waste wind turbine blade and immerses it below the molten salt level in the second-stage reactor 12. Open the multiple ultrasonic generators 13 on the side and bottom of the second-stage reactor 12 and keep it warm for 10 min;

[0098] 5) The jig 5 takes out the waste wind turbine blade and immerses it in the water cleaning area 21 for 5 min;

[0099] 6) The jig 5 takes out the waste wind turbine blade and immerses it in the organic solvent cleaning area 22 for 5 min;

[0100] 7) The jig 5 takes out the carbon fiber and dries it in the drying area 23 to remove moisture;

[0101] 8) The jig 5 takes out the carbon fiber and removes both ends of the material in the shearing area 24 to obtain clean carbon fiber, thus realizing the recycling of carbon fiber.

[0102] Note: The volatile matter evolved during the pyrolysis process is separated into pyrolysis oil and pyrolysis gas by the gas-liquid condenser 61. Among them, the pyrolysis oil is fractionated and collected by the multi-stage fractionator 62, and the pyrolysis gas generates heat through the gas burner 71 to supply heat to the first reactor 11 and the second reactor 12 for molten salt insulation, enabling the recovery of the next batch of waste. The tail gas is treated by the tail gas processor 72.

[0103] It should be noted that in this document, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such process, method, article or device.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this specification, and are not intended to limit them; although the above specification has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of this specification.

Claims

1. A system for recycling carbon fiber by stepwise molten salt, characterized in that, Including: A heat treatment unit (1), including a primary reactor (11) and a secondary reactor (12) connected in sequence. A plurality of ultrasonic generators (13) are provided at the bottoms of both the primary reactor (11) and the secondary reactor (12). A first composite molten salt is contained in the primary reactor (11), and a second composite molten salt is contained in the secondary reactor (12). The primary reactor (11) is used for pyrolyzing the carbon fiber reinforced resin matrix composite material once, and the secondary reactor (12) is used for pyrolyzing the carbon fiber reinforced resin matrix composite material after the first pyrolysis twice. The catalytic property of the first composite molten salt is greater than that of the second composite molten salt, and the melting point of the first composite molten salt is less than that of the second composite molten salt. The catalytic property of the composite molten salt is indexed by the resin decomposition rate and the degree of damage to the carbon fiber structure. The resin decomposition rate is referenced by the removal rate of the resin, and the degree of damage to the carbon fiber structure is referenced by the tensile strength of a single carbon fiber filament. A carbon fiber recovery unit (2), including a cleaning area and a drying area (23) connected in sequence. The cleaning area is used for cleaning the carbon fiber obtained by the secondary pyrolysis, and the drying area (23) is used for drying the cleaned carbon fiber to achieve the recovery of the carbon fiber. It also includes two clamps (5) that can move horizontally and vertically. The two clamps (5) are used for clamping both ends of the carbon fiber reinforced resin matrix composite material. By using the clamps (5) to clamp the carbon fiber reinforced resin matrix composite material, the carbon fiber reinforced resin matrix composite material is successively driven by the clamps (5) to be immersed in the molten first composite molten salt and the second composite molten salt, and the carbon fiber obtained by the secondary pyrolysis is successively driven to move to the cleaning area and the drying area (23). The clamping part (51) of the clamp (5) for clamping the end of the carbon fiber reinforced resin matrix composite material can rotate around the axis of the carbon fiber reinforced resin matrix composite material. It can not only adjust the height of the carbon fiber reinforced resin matrix composite material to better immerse it below the molten salt liquid level, but also accelerate the cleaning and drying processes by rotating the carbon fiber during the subsequent cleaning and drying processes, improving the efficiency of obtaining the finally desired carbon fiber.

2. The system for recycling carbon fiber by stepwise molten salt according to claim 1, wherein The first-stage reactor (11) also contains a target organic solvent, and the dielectric constant of the target organic solvent is greater than 3.6 C 2 / (N·M 2 ).

3. The system for recycling carbon fiber by stepwise molten salt according to claim 2, wherein It also includes: A pretreatment unit (3), connected to the primary reactor (11). The pretreatment unit (3) is used for sorting the carbon fiber reinforced resin matrix composite material from the raw materials and feeding the sorted carbon fiber reinforced resin matrix composite material into the primary reactor (11). And / or, A supply unit (4), including a primary molten salt tank (41), an organic solvent tank (42), and a secondary molten salt tank (43). The primary molten salt tank (41) is used for supplying the first composite molten salt to the primary reactor (11), the organic solvent tank (42) is used for supplying the target organic solvent to the primary reactor (11), and the secondary molten salt tank (43) is used for supplying the first composite molten salt to the secondary reactor (12).

4. The system for recycling carbon fiber by stepwise molten salt according to claim 2, characterized in that, The melting point of the first composite molten salt is 120 to 160 °C, the melting point of the second composite molten salt is 350 to 400 °C, and the boiling point of the target organic solvent is 160 to 200 °C.

5. The system for recycling carbon fiber by stepwise molten salt according to claim 4, wherein The first composite molten salt includes at least one of alkali salts, chloride salts, and nitrate salts; and / or, The target organic solvent includes at least one of alcohols, amines, and alkanolamines; and / or, The second composite molten salt includes at least one of carbonate salts and sulfate salts.

6. The system for recovering carbon fiber by stepwise molten salt according to claim 1, wherein, The carbon fiber recovery unit (2) further includes a shearing zone (24). The drying zone (23) is connected to the shearing zone (24). The shearing zone (24) is used to shear the carbon fiber that has been dried and is located between the two jigs (5) to achieve the recovery of the carbon fiber; and / or, The cleaning zone includes a water cleaning zone (21) and an organic solvent cleaning zone (22) connected in sequence. The organic solvent cleaning zone (22) is connected to the drying zone (23). The water cleaning zone (21) is used to perform water cleaning on the carbon fiber obtained by secondary pyrolysis, and the organic solvent cleaning zone (22) is used to perform organic solvent cleaning on the carbon fiber after water cleaning.

7. The system for recovering carbon fiber by stepwise molten salt according to any one of claims 1-6, characterized in that, It further includes: A pyrolysis product recovery unit (6), including a gas-liquid condensation separator (61) and a fractionator (62) connected in sequence. The gas-liquid condensation separator (61) is used to separate the volatile components precipitated from the first-stage reactor (11) and the second-stage reactor (12) to obtain pyrolysis oil and pyrolysis gas. The fractionator (62) is used to fractionate and purify the pyrolysis oil obtained by the gas-liquid condensation separator (61) to achieve the recovery of pyrolysis products.

8. The system for recycling carbon fiber by stepwise molten salt according to claim 7, characterized in that, It further includes: A waste heat utilization unit (7), including a gas burner (71) and a tail gas processor (72) connected in sequence. The gas burner (71) is connected to the gas-liquid condensation separator (61). The gas burner (71) is used to burn the pyrolysis gas obtained by the gas-liquid condensation separator (61) and output the heat generated by the combustion to the outer walls of the first-stage reactor (11) and the second-stage reactor (12). The tail gas processor (72) is used to perform tail gas treatment on the gas generated by the gas burner (71).

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