A system and method for rapidly recycling carbon fiber composites based on in-phase microwave heating

Abstract

The application discloses a system and method for rapidly recycling carbon fiber composite materials based on in-phase microwave heating, and the system comprises a first heating device, a second heating device and a conveying device. The first heating device comprises a first heating cavity, a first conveyor and a microwave generator of in-phase microwaves. The first conveyor penetrates through the first heating cavity, and the microwave generator is in communication with the first heating cavity. The second heating device comprises a second heating cavity, a second conveyor and an electric heater. The electric heater is arranged in the second heating cavity, and the second conveyor is arranged in the second heating cavity. The second conveyor conveys the product heated by the first heating device to the second heating cavity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of carbon fiber composite material recycling, and particularly relates to a system and method for rapidly recycling carbon fiber composite materials based on in-phase microwave heating. BACKGROUND

[0002] Carbon fiber composite materials are obtained by mixing carbon fibers with resin as a base material and then molding, and have light weight and high strength. Carbon fibers have high market value, but these composite materials cannot be decomposed in the natural environment after being discarded, causing many waste and environmental problems. Therefore, existing carbon fiber composite materials all pursue recycling of carbon fibers after removing the resin base material for reuse.

[0003] The existing mainstream method for recycling carbon fibers from composite materials, such as the European ELG company and the American Carbon Conversion company, is to use electric heating to burn the resin or use a chemical solvent method to remove the resin base material to recycle carbon fibers. The electric heating method for burning composite materials to remove the resin base material requires a relatively long operation time due to heat transfer limitations, and is prone to damage the performance of carbon fibers. The chemical method for removing the resin base material not only takes time, but also generates waste solutions that must be treated, which increases the overall process cost. If not treated and directly discharged, it will also cause environmental pollution.

[0004] Furthermore, although microwave heating technology has the advantages of rapid heating, energy saving, and suitability for high-temperature process applications, the microwave energy distribution is difficult to control. In the case of ordinary microwave heating, electromagnetic wave signals exist in different phases, and local magnetic fields are strengthened or canceled in different points in the heating area, which in turn causes uneven heating and poor heating efficiency. At the same time, in a process environment above 600 degrees Celsius, as the heating time increases, carbon fibers are prone to react with oxygen, causing damage, resulting in insufficient performance retention rate of recycled fiber filaments, uneven mechanical strength in subsequent recycled carbon fiber composite production, and other problems that are not sufficient for subsequent regeneration applications. SUMMARY

[0005] In order to overcome the deficiencies in the prior art, the present application provides a system and method for rapidly recycling carbon fiber composite materials based on in-phase microwave heating, and the specific technical solutions are as follows:

[0006] The application discloses a recycling system for recycling carbon fiber composite materials based on in-phase microwave heating, which comprises a first heating device, a second heating device and a conveying device.

[0007] Further, the microwave generator comprises a microwave radiator and a metal guide cover, and the microwave radiator and the metal guide cover are fixedly connected through a fastener or a flange; the metal guide cover is connected to the top of the first heating cavity and communicates with the first heating cavity; the microwave emitted by the microwave radiator is guided into the first heating cavity through the metal guide cover; the metal guide cover comprises a parallel portion and a diameter expansion portion; the two ends of the diameter expansion portion are connected to the parallel portion and the first heating cavity respectively; the microwave radiator is arranged on the parallel portion; and the width of the diameter expansion portion gradually increases from one end connected to the parallel portion to the other end connected to the first heating cavity.

[0008] All the microwave generators are connected to a microwave emission source; the microwave generated by the microwave emission source is split n times through 2×(2 n -1) wave splitters and then transmitted to 2×(2 n+1 -1) microwave generators through 2×(2 n+1 -1) microwave transmission elements to generate in-phase microwaves, wherein n is an integer.

[0009] The function equation of the microwave generated by each microwave generator is wherein A is an amplitude, k is a waveguide number, x is a displacement, omega is an angular frequency, t is a time, and theta is a starting phase angle.

[0010] Preferably, the system further comprises an inert gas supply device communicating with the first heating device; and a gas combustion device communicating with the first heating device and the second heating device.

[0011] Further, the system further comprises a catalyst converter connected to the gas combustion device.

[0012] In the system, the microwave emitted by a high-power microwave emission source is split n times through 2×(2 n-1) equal to the microwave generator, the realization of the delivery to the heating cavity microwave start phase angle, time and path length are equalized, and then make the system in the heating effect is enhanced and can be stable reproduction. By electromagnetic - thermal energy conversion formula, microwave heating of materials, mainly by the material dielectric loss (dielectric loss) and current Ohm loss (conduction loss) generated, and the most important influence on the heating efficiency is the material internal electric field E value.

[0013]

[0014] Therefore, the same phase microwave corresponds to the uniform distribution of microwave energy in the heated object, so as to produce a synergistic heating effect. The traditional electric heating requires 100KW, and the conventional microwave heating adopts a heating power density of 30KW to reach a heating temperature of 600 degrees Celsius. The same phase microwave heating only needs to provide a heating power of 15KW to reach the heating temperature.

[0015] A method for rapidly recycling carbon fiber composite materials based on same phase microwave heating, comprising the following steps:

[0016] Step 1: heating the carbon fiber composite material in an environment with an oxygen concentration of not more than 10% by same phase microwave, the heating temperature is 600-800℃ (the heating temperature is the temperature of the surface of the composite material monitored by a temperature monitor), the heating time is 1-60Min, and the pressure is -20Pa, so that the carbon fiber composite material is pyrolyzed to obtain an intermediate product that removes 85-90% of the resin in the carbon fiber material, and the intermediate product contains carbon fiber and 10-15% of resin;

[0017] Step 2: heating the product obtained in step 1 in an environment with an oxygen concentration of 20-25% at a heating temperature of 600±50 o C, the heating time is 1-60Min, to burn the product obtained in step 1, and remove the resin contained in the product obtained in step 1, so as to obtain pure carbon fiber.

[0018] The same phase microwave in step 1 is generated by connecting all microwave generators to a microwave emission source, and the microwave generated by the microwave emission source is divided n times by 2×(2 n -1) wave dividers and then transmitted to 2×(2 n+1 -1) microwave generators through 2×(2 n+1 -1) microwave transmission members, to generate same phase microwave, wherein n is an integer.

[0019] Further, the microwave function equation generated by each microwave generator in step 1 is where A is the amplitude, k is the waveguide number, x is the displacement, ω is the angular frequency, t is the time, and θ is the initial phase angle.

[0020] Preferably, the carbon fiber composite material to be recycled is subjected to fragmentation treatment before step 1. The present application recycles carbon fiber composite material in two steps, first heating the carbon fiber composite material by in-phase microwave to heat disintegration and then performing the second step of heating to burn and remove the remaining resin in the composite material, which can greatly save the operation time of removing the resin. Specifically, in the first heating device, the carbon fiber composite material is heated by in-phase microwave in a low-oxygen environment formed by inert gas, so that the carbon fiber composite material produces thermal cracking in the low-oxygen environment, thereby removing 85% to 90% of the resin contained in the carbon fiber composite material fragments. Then, the intermediate product with most of the resin removed enters the second heating device in an oxygen environment for combustion to remove the remaining 10% to 15% of the resin in an oxidizing manner. By first performing rapid thermal disintegration and then performing constant-temperature combustion to remove the residual matrix in the composite material, the operation time of removing the matrix can be greatly saved, and the carbon fiber is prevented from being overheated and oxidized to be damaged. Moreover, the volatile organic compounds generated after thermal cracking and the carbon oxygen gas after combustion can enter the gas combustion device for further combustion, and the exhaust gas after combustion of the gas combustion device is converted into harmless exhaust gas to the environment and human body by a catalyst converter, and then discharged to the atmosphere.

[0021] The present application has the following beneficial effects: The present application recycles carbon fiber composite material by two-step heating, especially using in-phase microwave heating in the first step of heating and cracking, which makes the heating energy distribution more concentrated and uniform, and has higher energy efficiency compared with the conventional non-in-phase microwave heating: first, low heating power is used to achieve high heating temperature, and energy consumption is reduced. The present application uses in-phase microwave heating, so that the microwaves in the heating area can be superimposed to generate a higher heating temperature. Therefore, a heating temperature of 600 degrees Celsius can be achieved by using a heating power of 15 KW, while the same heating temperature in the same heating area can be achieved by using a heating power of 30 KW by using ordinary non-in-phase microwave heating. Second, the heating time is shorter. Since in-phase microwave heating can provide a stable high heating temperature in the heating area, almost all carbon fiber composite materials in the heating area can complete resin disintegration in a short time. For the same type and weight of carbon fiber composite material, ordinary microwave heating requires 30-60 min, while in-phase microwave heating only requires 10-15 min, which significantly shortens the time and greatly reduces the risk of oxidation of carbon fiber. It is also because the first step uses low power to achieve high energy heating while shortening the heating time, combined with the control of oxygen content, that the present application can maintain the performance of the recycled carbon fiber at more than 90% under the processing conditions of more than 600 degrees Celsius.

[0022] In addition, the method can recover pure carbon fibers from carbon fiber composites, does not produce by-products that cause environmental pollution, and overall reduces the cost of recycling carbon fiber processes and improves recycling capacity. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a schematic diagram of embodiment 2 of the composite carbon fiber recycling system of the present application;

[0024] Figure 2 is another schematic diagram of embodiment 2 of the composite carbon fiber recycling system of the present application;

[0025] Figure 3 is a schematic diagram of the first heating device of embodiment 2 of the present application;

[0026] Figure 4 is a side view of the first heating device of embodiment 2 of the present application;

[0027] Figure 5 is a schematic diagram of the microwave in-phase field formed by the composite recycling method of the present application;

[0028] Figure 6 is a schematic diagram of the microwave in-phase field in the first heating device of embodiment 2 of the present application;

[0029] Figure 7 is a graph of the relationship between heating temperature and time for the first heating device in the four cases in Table 1 at the same power;

[0030] Figure 8 (8A, 8B, 8C, 8D) are energy density schematic diagrams of the heating temperature generated by the first heating device in the four cases in Table 1 at the same power and the same time;

[0031] Figure 9 is a schematic diagram of the second heating device of embodiment 2 of the composite carbon fiber recycling system of the present application;

[0032] Figure 10 is a state change diagram (1) of the composite carbon fiber composite material in each step of the composite recycling method of the present application;

[0033] Figure 11 is a state change diagram (2) of the composite carbon fiber composite material in each step of the composite recycling method of the present application;

[0034] Figure 12 is a state change schematic diagram of the composite carbon fiber composite material in each step of the composite recycling method of the present application;

[0035] Figure 13is the electron microscope contrast chart of carbon fiber epoxy resin composite material before and after the same phase microwave heating;

[0036] Figure 14 is the heating efficiency comparison chart of the present application and ordinary microwave heating

[0037] Wherein 10 is a crushing device; 11 is a feeding hopper; 12 is a conveyor belt; 20 is a first heating device; 21 is a first heating cavity; 22 is a first conveyor; 23 is a microwave generator; 231 is a microwave emitting element; 232 is a metal guide cover; 2321 is a parallel part of the metal guide cover; 2322 is an expanding part of the metal guide cover; 24 is a machine body; 25 is a feeding hopper; 26 is a first exhaust guide; 30 is a second heating device; 31 is a second heating cavity; 32 is a second conveyor; 34 is a machine body; 35 is a feeding hopper; 36 is a turnover mechanism; 37 is a second exhaust guide; 40 is an inert gas supply device; 50 is a gas combustion device; 60 is a catalyst converter; 100 is a carbon fiber composite material recycling system. DETAILED DESCRIPTION

[0038] Example 1

[0039] A system for rapidly recycling carbon fiber composite material based on same phase microwave heating, comprising a first heating device, a second heating device and a conveying device, the first heating device comprising a first heating cavity, a first conveyor and a microwave generator of same phase microwave, the first conveyor penetrating through the first heating cavity, and the microwave generator being in communication with the first heating cavity; the second heating device comprising a second heating cavity, a second conveyor and an electric heater, the electric heater being arranged in the second heating cavity, and the second conveyor being arranged in the second heating cavity, and the second conveyor conveying the product heated by the first heating device to the second heating cavity. There is also an inert gas supply device in communication with the first heating device; a gas combustion device in communication with the first heating device and the second heating device. There is also a catalyst converter connected with the gas combustion device.

[0040] The microwave generator comprises a microwave emitting element and a metal guide cover, the microwave emitting element and the metal guide cover are fixedly connected by a fastener or a flange, the metal guide cover is composed of a parallel part and an expanding part, the parallel part is arranged at the inner top of the first heating cavity, and the expanding part is in communication with the first heating cavity. All the microwave generators are connected to a microwave emitting source, the microwave generated by the microwave emitting source is divided by 2×(2 n -1) wave dividers for n times, and then transmitted to 2×(2 n+1 -1) microwave generators through 2×(2 n+1 -1) equal microwave transmission elements, to generate same phase microwave, wherein n is an integer.

[0041] The microwave function equation generated by each microwave generator is , where A is the amplitude, k is the waveguide number, x is the displacement, ω is the angular frequency, t is the time, and θ is the initial phase angle.

[0042] Example 2

[0043] like Figure 1 and Figure 2 As shown, a system for rapidly recovering carbon fiber composite materials based on in-phase microwave heating is used to recover carbon fibers in carbon fiber composite materials, which are composed of carbon fibers and resin. The carbon fiber composite material recovery system 100 of this embodiment includes: a crushing device 10, a first heating device 20, and a second heating device 30.

[0044] The crushing device 10 is used to receive carbon fiber composite materials and crush them into carbon fiber composite material fragments. The crushing device 10 can be an existing crusher, such as a single-shaft crusher, twin-shaft crusher, jaw crusher, cone crusher, double-roll crusher, etc. After the carbon fiber composite material enters the crushing device 10 from the feed hopper 11, it is cut, crushed, hammered, or impacted by the cutters or other crushing mechanisms of the crushing device 10 to form carbon fiber composite material fragments. The carbon fiber composite material fragments are discharged from the bottom of the crushing device 10 and then conveyed to the feed inlet of the first heating device 20 via the conveyor belt 12. In this embodiment, the crushing device 10 has a processing capacity of 12.5 kg of carbon fiber composite material per hour, and the size of the crushed carbon fiber composite material fragments is 3-10 cm.

[0045] like Figures 3-4 As shown, the first heating device 20 creates an environment where the oxygen concentration is maintained below 10% and receives carbon fiber composite material fragments, heating the carbon fiber composite material fragments in a low-oxygen environment at a heating temperature of 600°C. o C to 800 oC, to cause pyrolysis of the carbon fiber composite material pieces. The first heating device 20 of this embodiment includes a first heating cavity 21, a first conveyor 22, and a plurality of microwave generators 23. The first heating device 20 also includes a machine body 24 and a feeding hopper 25. The first heating cavity 21 and the first conveyor 22 are disposed on the machine body 24, and the first conveyor 22 passes through the first heating cavity 21. The feeding hopper 25 is disposed above the first conveyor 22. The carbon fiber composite material pieces are conveyed from the crushing device 10 to the feeding hopper 25, and then fall from the feeding hopper 25 to the first conveyor 22. The first conveyor 22 conveys the carbon fiber composite material pieces through the first heating cavity 21. The heated carbon fiber composite material pieces are discharged from the first conveyor 22. The first conveyor 22 of this embodiment is a key plate conveyor belt. The plurality of microwave generators 23 are disposed on the top of the first heating cavity 21. The microwave generators 23 generate microwaves and irradiate the microwaves into the first heating cavity 21. The microwaves act on the carbon fiber composite material pieces conveyed by the first conveyor 22 through the first heating cavity 21, so that the temperature of the carbon fiber composite material pieces is increased. A fluffy intermediate product is generated through the heating process. The time for the first conveyor 22 to convey the carbon fiber composite material pieces through the first heating cavity 21 is 10 minutes. Through the first heating cavity 21, 85-90 wt% of the resin contained in the carbon fiber composite material is decomposed, and a fluffy intermediate product is formed. The residual resin content is 10-15 wt% of the carbon fiber composite material when the material is fed.

[0046] The system 100 for rapidly recycling carbon fiber composite material of this embodiment also includes an inert gas supply device 40. The inert gas supply device 40 is connected to the first heating device 20 and provides inert gas to the first heating device 20 to form a low-oxygen environment, so as to prevent the composite material from being excessively combusted and oxidized and the carbon fiber from being damaged. The inert gas supply device 40 of this embodiment is a nitrogen gas supply device. The inert gas of this embodiment is nitrogen gas. The nitrogen gas is introduced into the first heating cavity 21, so that the first heating cavity 21 is kept at a micro-negative pressure (-20 Pa) to prevent volatile organic compounds from being discharged and polluting the environment. In addition, the nitrogen gas is flushed into the first heating cavity 21 to form a low-oxygen concentration environment, so as to provide the condition for the carbon fiber composite material pieces to be pyrolyzed. The nitrogen gas surrounds the carbon fiber composite material pieces, so as to prevent the carbon fiber composite material pieces from contacting oxygen and being combusted and oxidized.

[0047] The first heating device 20 of this embodiment uses in-phase microwaves to rapidly heat the carbon fiber composite material pieces. Figure 5The first heating device 20 includes four microwave generators 23, which indicates that the microwave generated by the microwave emission source O of the present embodiment is subjected to power distribution twice. In another embodiment, the microwave generated by the microwave emission source O can also not be subjected to power distribution and only one microwave generator 23 is provided, i.e. N=0. N wherein N is a natural number, N representing the number of times of power distribution, Figure 2 The first heating device 20 shown includes four microwave generators 23, which indicates that the microwave generated by the microwave emission source O of the present embodiment is subjected to power distribution twice. In another embodiment, the microwave generated by the microwave emission source O can also not be subjected to power distribution and only one microwave generator 23 is provided, i.e. N=0.

[0048] Each microwave generator 23 includes a microwave emission element 231 and a metal cover 232, the metal cover 232 being connected to the top of the first heating cavity 21 and being in communication with the first heating cavity 21, the microwave emitted by the microwave emission element 231 being guided into the first heating cavity 21 via the metal cover 232. The metal cover 232 includes a parallel portion 2321 and an expanding portion 2322, the two ends of the expanding portion 2322 being respectively connected to the parallel portion 2321 and the first heating cavity 21, the microwave emission element 231 being arranged on the parallel portion 2321, the width of the expanding portion 2322 gradually increasing from the end connected to the parallel portion 2321 to the end connected to the first heating cavity 21, thus forming a tapered expanding shape. As shown in the figure, Figure 6As shown, the microwave emitted from the microwave emitter 231 forms a microwave in-phase field S in the in-phase field effect region Fl of the diameter-expanding portion 2322.

[0049] The wave function equation of the electromagnetic wave is as follows, to illustrate the relationship of the final electromagnetic field sum of different intensities and directions when the multiple microwave generators 23 of the first heating device 20 act in the form of in-phase, cancellation phase and indefinite phase.

[0050] Wherein, A is the amplitude, k is the waveguide number, x is the displacement, ω is the angular frequency, t is the time, and θ is the initial phase angle.

[0051] When the power is turned on, high voltage acts on multiple magnetrons, which will emit electromagnetic wave signals with different initial phase angles from the microwave emission source O according to different time differences. After the respective signals are transmitted into the cavity interior space through the power distribution assembly (such as a waveguide), the final electromagnetic field sum of different intensities and directions is caused to each point in the cavity interior space according to the path and time difference of the signals.

[0052] As shown in Table I and Figure 7 The relationship of heating temperature and heating time of the four cases of the multiple microwave generators 23 of the first heating device 20 under the same power, in-phase or different phase microwave heating. Referring to Figure 1 Each case has four microwave generators 23 arranged sequentially and equidistantly on the top of the first heating cavity 21. Each microwave generator 23 of the first case is in-phase with a phase angle θ = 0°, and each microwave generator 23 of the second case is in-phase with a phase angle θ = 75°. Compared with the third case and the fourth case, the resulting composite wave after superposition of the waveforms has a larger amplitude, thereby increasing the microwave intensity and generating a higher heating temperature under in-phase microwave heating in the same heating time.

[0053] When each microwave generator of the third case is heated with a cancellation phase, the waveforms after superposition cancel each other due to the opposite phase angle θ, and only have a lower heating temperature in the same heating time.

[0054] When each microwave generator 23 of the fourth case is heated with an indefinite phase, because each has a different phase angle, the resulting composite wave after superposition of the waveforms is not cancelled as in the third case, and the amplitude of the resulting composite wave is not as large as in the first case and the second case. Therefore, the heating temperature generated by the first heating device of the fourth case in the same heating time is between the first case (or the second case) and the third case.

[0055] Table I

[0056] First scenario (in phase) Second scenario (in phase) Third scenario (opposite phase) Fourth scenario (undefined phase) First microwave generator θ = 0° θ = 75° θ = 0° θ = 75° Second microwave generator θ = 0° θ = 75° θ = 180° θ = 245° Third microwave generator θ = 0° θ = 75° θ = 0° θ = 105° Fourth microwave generator θ = 0° θ = 75° θ = 180° θ = 25° Phase angle difference 0° 0° 180° 30°~225°

[0057] Figure 8 In the figures, 8A, 8B, 8C and 8D are the energy density diagrams of the heating temperature generated by the first heating device of each case in Table 1 at the same power and the same time. In this embodiment, the microwave generators 23 can be arranged at the top of the first heating cavity 21, and the microwave generators 23 can be divided into the first microwave generator 23', the second microwave generator 23'', the third microwave generator 23''', and the fourth microwave generator 23'''. When the first conveyor 22 conveys the carbon fiber composite material pieces through the first heating cavity 21, the microwave generators 23 can heat the corresponding heating range. Different colors in the color card represent different energy densities of heating temperature. In the color card, the red color (black in the figure) represents the highest temperature, and the blue color (gray in the figure) at the other end of the red color represents the lowest temperature. Figure 8 A (corresponding to the first case in Table 1) and Figure 8 B (corresponding to the second case in Table 1) show that under the same heating time, the red area under the microwave heating with the same phase angle is the most. And Figure 8 D (corresponding to the fourth case in Table 1) shows that under the same heating time, the red area is significantly reduced, but there are still a few red areas. And Figure 8 C (corresponding to the third case in Table 1) shows that under the same heating time, there is almost no red area, and yellow, green or blue areas (light gray area) with lower temperature are mainly shown. Combined with Figures 7-8 and Table 1, it is not difficult to find that the first heating device 20 has better heating efficiency under the microwave heating with the same phase than the cancellation phase or the indefinite phase when heating the carbon fiber composite material pieces in the low oxygen environment.

[0058] As Figure 9The second heating device 30 forms an oxygen environment, such as the oxygen content in the atmosphere, and receives the intermediate product and externally heats the intermediate product by electric heating to reach the combustion pyrolysis temperature of the substrate to be oxidized and removed, and to obtain pure carbon fibers. The second heating device 30 includes a second heating cavity 31, a second conveyor 32, and an electric heater. The second heating device 30 includes a machine body 34, and a feeding hopper 35. The second heating cavity 31 and the second conveyor 32 are arranged in the machine body 34, and the feeding hopper 35 is arranged above the second conveyor 32, and the intermediate product falls from the feeding hopper 35 to the second conveyor 32. The electric heater is arranged in the second heating cavity 31, and the second conveyor 32 passes through the second heating cavity 31, and the intermediate product is carried and conveyed by the second conveyor 32 into the second heating cavity 31, and the electric heater externally heats the intermediate product completed by the first heating cavity 21. The intermediate product is externally heated by the electric heater to 600 o C+50 o C, to oxidize the remaining small amount of resin substrate contained in the intermediate product, to generate carbon dioxide gas and ash. After the resin in the intermediate product is removed, pure carbon fibers are obtained, and the carbon fibers are continuously conveyed by the second conveyor 32 and fall into the transport carrier from the other end.

[0059] The second heating device 30 further includes a turnover mechanism 36 arranged in the second heating cavity 31 and above the second conveyor 32 to turn over the intermediate product. The turnover mechanism 36 of the present embodiment includes a plurality of rotatable blades, which can turn over the intermediate product when the second conveyor 32 moves through the second heating cavity 31, increasing the contact area between the intermediate product and oxygen, and increasing the combustion rate of the intermediate product.

[0060] Further, the first heating device 20 further includes at least one first exhaust guide 26 connected to the first heating cavity 21, and the volatile organic compounds generated after the pyrolysis of the carbon fiber composite material are discharged from the first heating cavity 21 through the first exhaust guide 26. The first exhaust guide 26 of the present embodiment is an exhaust pipe.

[0061] The second heating device 30 further includes at least one second exhaust guide 37 connected to the second heating cavity 31, and the gas (carbon dioxide) generated after the combustion of the intermediate product is discharged from the second heating cavity 31 through the second exhaust guide 37. The second exhaust guide 37 of the present embodiment is an exhaust pipe.

[0062] The system 100 for rapidly recycling carbon fiber composite material of the present embodiment further comprises a gas combustion device 50 connected to the first heating device 20 and the second heating device 30, and the gas combustion device 50 is connected to the first exhaust guide 26 and the second exhaust guide 37. The gas generated by the first heating device 20 and the second heating device 30 is introduced into the gas combustion device 50 through the first exhaust guide 26 and the second exhaust guide 37 for combustion. The volatile organic compound gas generated by the first heating device 20 and the carbon dioxide and carbon monoxide generated by the second heating device 30 in some cases are introduced into the gas combustion device 50 through the first exhaust guide 26 and the second exhaust guide 37 for combustion, respectively, to burn the volatile organic compound to generate oxides. The temperature of the gas combustion device 50 can reach 850 o C, and the volatile organic compound stays in the gas combustion device 50 for more than 2 seconds.

[0063] The system 100 for rapidly recycling carbon fiber composite material of the present embodiment further comprises a catalyst converter 60 connected to the gas combustion device 50. The exhaust gas generated after the volatile organic compound is combusted by the gas combustion device is converted into exhaust gas that can be discharged into the atmosphere by the catalyst converter 60. After the volatile organic compound is combusted, hydrocarbons HC, carbon monoxide CO, or nitrogen oxides NOx may

[0064] Embodiment 3

[0065] A method for rapidly recycling carbon fiber composite material, in step S1, carbon fiber composite material of a composite material is crushed to form carbon fiber composite material pieces, and the carbon fiber composite material of the composite material is crushed into carbon fiber composite material pieces by the crushing device 10. Then step S2 is entered.

[0066] In step S2, the carbon fiber composite material pieces are heated by microwaves in a low-oxygen environment, and the microwaves generated by the microwave generating element 23 of the first heating device 20 act on the carbon fiber composite material pieces to cause thermal disintegration of the carbon fiber composite material pieces to obtain an intermediate product. Step S2 can include a step of providing an inert gas to form a low-oxygen environment, and the inert gas of the present embodiment can be nitrogen. Then step S3 is entered.

[0067] In step S3, the intermediate product is heated by the electric heater of the second heating device 30 in an aerobic environment, and the matrix of the intermediate product is oxidized and burned to remove the matrix contained in the intermediate product to obtain pure carbon fiber.

[0068] As Figures 10-12 shown, in the crushing process of step S1, the carbon fiber composite material W is crushed into carbon fiber composite material pieces W1, which contain the base material B and the carbon fiber CF. In step S2, after the carbon fiber composite material pieces W1 are heated by microwaves in a low-oxygen environment, the base material B of the intermediate product is significantly reduced, and the base material B of the intermediate product is 10-15% of the base material content of the carbon fiber composite material pieces W1. Figure 11 、 12 As shown in step S3, the base material of the intermediate product is oxidized and burned out, and finally pure carbon fiber is obtained.

[0069] Example 4

[0070] A method for rapidly recycling carbon fiber epoxy resin composite material based on in-phase microwave heating, comprising the following steps:

[0071] Step one, the carbon fiber epoxy resin composite material is crushed by a crushing device to form carbon fiber epoxy composite material pieces of 10-50 mm. In an oxygen concentration of 8% low-oxygen environment, the first heating device 20 is used to heat the carbon fiber composite material pieces by in-phase microwave heating, the heating temperature is 650℃, the heating time is 10 min, and the pressure is -20 Pa. The carbon fiber composite material pieces are pyrolyzed to obtain an intermediate product that removes 85-90% of the resin in the carbon fiber composite material. The low-oxygen environment can be formed by filling inert gas, and the inert gas can be nitrogen. After this step, the scanning electron microscope (SEM) diagram of the composite material change is shown in FIG. 2B. It can be clearly seen that carbon fibers with less resin residue are obtained. Figure 13

[0072] Step two, in an oxygen concentration of 20% environment, the second heating device 30 is used to heat the intermediate product by an electric heater, the heating temperature is 550℃, and the heating time is 30 min. The base material obtained in step one is burned to remove the resin contained in the intermediate product, and pure carbon fiber is obtained, and the carbon fiber recovery rate is more than 95%.

[0073] In this embodiment, if ordinary microwave heating is used to pyrolyze the carbon fiber epoxy resin composite material (in this embodiment, the weight percentage of epoxy resin in the carbon fiber composite material is 50%), the microwave heating efficiency comparison diagram of the two is shown in FIG. 3B. Figure 14 ​The comparative chart is based on weighing the intermediate products under the two heating methods using the same weight of carbon fiber epoxy resin composite under the same heating time (5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min), and it is found that under the in-phase microwave heating, the weight of the intermediate product decreases faster, and it only takes about 10 min to complete the cracking of the resin; while under the ordinary microwave heating, the weight of the intermediate product decreases relatively slowly, and it takes at least 30 min to complete the cracking of the resin.

[0074] Example 5

[0075] A method for rapidly recycling carbon fiber epoxy resin composite based on in-phase microwave heating, comprising the following steps:

[0076] Step one, the carbon fiber epoxy resin composite is crushed by a crushing device to form carbon fiber epoxy composite blocks of 10-50 mm, and the carbon fiber composite blocks are in-phase microwave heated by the first heating device 20 in a low-oxygen environment with an oxygen concentration of 5%, a heating temperature of 800°C, a heating time of 3 min, and a pressure of -20 Pa, so that the carbon fiber composite blocks are pyrolyzed to obtain an intermediate product removing 85-90% of the resin in the carbon fiber composite; the low-oxygen environment can be formed by filling an inert gas, and the inert gas can be nitrogen.

[0077] Step two, the intermediate product is heated by the electric heater of the second heating device 30 in an environment with an oxygen concentration of 20%, a heating temperature of 550°C, and a heating time of 30 min, so as to burn the substrate on the intermediate product obtained in step one and remove the resin contained in the intermediate product to obtain pure carbon fiber.

[0078] Example 6

[0079] A method for rapidly recycling carbon fiber vinyl composite based on in-phase microwave heating, comprising the following steps:

[0080] Step one, the carbon fiber vinyl resin composite is crushed by a crushing device to form carbon fiber composite blocks of 10-50 mm, and the carbon fiber composite blocks are in-phase microwave heated by the first heating device 20 in a low-oxygen environment with an oxygen concentration of 5%, a heating temperature of 700°C, a heating time of 20 min, and a pressure of -20 Pa, so that the carbon fiber composite blocks are pyrolyzed to obtain an intermediate product removing 85-90% of the resin in the carbon fiber composite; the low-oxygen environment can be formed by filling an inert gas, and the inert gas can be nitrogen.

[0081] Step two, in the environment of oxygen concentration of 20%, the intermediate product is heated by the electric heater of the second heating device 30, the heating temperature is 600℃, the heating time is 20min, the substrate on the intermediate product obtained in step one is burned to remove the resin contained in the intermediate product, and pure carbon fiber is obtained.

[0082] Example 7

[0083] A method for rapidly recycling carbon fiber polyimide resin composite based on in-phase microwave heating, comprising the following steps:

[0084] Step one, the carbon fiber polyimide resin composite is crushed by a crushing device to form carbon fiber composite fragments of 10-50mm, and the carbon fiber composite fragments are heated by the first heating device 20 in an in-phase microwave under a low-oxygen environment with an oxygen concentration of 5%, the heating temperature is 750℃, the heating time is 20min, and the pressure is-20Pa, so that the carbon fiber composite fragments are pyrolyzed to obtain an intermediate product in which 85-90% of the resin in the carbon fiber composite is removed; the low-oxygen environment can be formed by filling inert gas, and the inert gas can be nitrogen.

[0085] Step two, in the environment of oxygen concentration of 20%, the intermediate product is heated by the electric heater of the second heating device 30, the heating temperature is 650℃, the heating time is 20min, the substrate on the intermediate product obtained in step one is burned to remove the resin contained in the intermediate product, and pure carbon fiber is obtained.

[0086] Example 8

[0087] A method for rapidly recycling carbon fiber phenolic resin composite based on in-phase microwave heating, comprising the following steps:

[0088] Step one, the carbon fiber phenolic resin composite is crushed by a crushing device to form carbon fiber composite fragments of 10-50mm, and the carbon fiber composite fragments are heated by the first heating device 20 in an in-phase microwave under a low-oxygen environment with an oxygen concentration of 5%, the heating temperature is 800℃, the heating time is 60min, and the pressure is-20Pa, so that the carbon fiber composite fragments are pyrolyzed to obtain an intermediate product in which 85-90% of the resin in the carbon fiber composite is removed; the low-oxygen environment can be formed by filling inert gas, and the inert gas can be nitrogen.

[0089] Step two, in the environment of oxygen concentration of 20%, the intermediate product is heated by the electric heater of the second heating device 30, the heating temperature is 650℃, the heating time is 30min, the substrate on the intermediate product obtained in step one is burned to remove the resin contained in the intermediate product, and pure carbon fiber is obtained.

[0090] The performance test was carried out on the recycled carbon fiber filaments prepared in examples 4-8, since the recycled carbon fiber lacks the surface oil agent of the new carbon fiber, we used T300 grade carbon fiber composite material as the test sample, used long time soaking of acetone, dissolved out the resin to obtain the recycled carbon fiber (T300 grade) which was complete and intact without sizing as the comparison original sample, the GB / T 31290-2014 national standard was used for filament test, the comparison performance results are shown in table two, the strength retention rate of the recycled carbon fiber of the application is >90%, the modulus performance retention rate is >95%.

[0091] Table two

[0092]

[0093] As can be seen from the above, the in-phase microwave heating step of the application, under the condition that the oxygen concentration is 1-10% and the heating temperature is above 600℃, since the in-phase microwave reaction is faster and more uniform, the recycled carbon fiber in this case will avoid being excessively attacked by oxygen or organic matter such as gasified resin, so that the mechanical performance can be maintained better (retaining more than 90% performance).

Claims

1. A system for rapid recovery of carbon fiber composites based on co-phase microwave heating, comprising a first heating device, a second heating device and a conveying device, characterized in that: The first heating device comprises a first heating cavity, a first conveyor and a plurality of microwave generators generating in-phase microwaves, the first conveyor penetrating through the first heating cavity, and the microwave generators being in communication with the first heating cavity; the second heating device comprises a second heating cavity, a second conveyor and an electric heater, the electric heater being arranged in the second heating cavity, and the second conveyor being arranged in the second heating cavity, and the second conveyor conveying the product heated by the first heating device into the second heating cavity; Each microwave generator comprises a microwave radiator and a metal cover, the microwave radiator and the metal cover being fixedly connected by a fastener or a flange, the metal cover being connected to the top of the first heating cavity and being in communication with the first heating cavity, the microwaves emitted by the microwave radiator being guided into the first heating cavity through the metal cover, the metal cover comprising a parallel portion and an expanding portion, two ends of the expanding portion being connected to the parallel portion and the first heating cavity respectively, the microwave radiator being arranged in the parallel portion, and the width of the expanding portion gradually increasing from one end connected to the parallel portion to the other end connected to the first heating cavity; the microwaves emitted by the microwave radiator form a same-phase field effect of the same-phase field of the microwaves in the expanding portion; All microwave generators are connected to a microwave emission source, and the microwave generated by the microwave emission source is transmitted to 2x(2 n -1) microwave generators via 2x(2 n+1 -1) wave splitters and 2x(2 n+1 -1) microwave transmission elements after being split n times, where n is an integer. The first heating device further comprises an inert gas supply device in communication with the first heating device; and a gas combustion device in communication with the first heating device and the second heating device; The first heating device further comprises a catalyst converter connected to the gas combustion device.

Images