CN115947976A - A system and method for rapid recovery of carbon fiber composite materials based on in-phase microwave heating - Google Patents

Abstract

The invention discloses a system and method for rapidly recovering carbon fiber composite materials based on in-phase microwave heating. The system includes a first heating device, a second heating device and a conveying device. The first heating device includes a first heating chamber, a first The conveyor and the microwave generator of the same-phase microwave, the first conveyor runs through the first heating cavity, and the microwave generator communicates with the first heating cavity; the second heating device includes a second heating cavity, the second conveyor and an electric The heater, the electric heater is arranged in the second heating cavity, the second conveyor is passed through the second heating cavity, and the second conveyor transports the product heated by the first heating device to the second heating cavity.

Description

A system and method for rapid recovery of carbon fiber composite materials based on in-phase microwave heating

technical field

The invention belongs to the field of recycling carbon fiber composite materials, in particular to a system and method for rapidly recycling carbon fiber composite materials based on in-phase microwave heating.

Background technique

Carbon fiber composite materials use resin as a base material, and carbon fiber and resin are mixed and molded to obtain a lightweight and high-strength composite material. The market value of carbon fiber is high, but these composite materials cannot be decomposed in the natural environment after being discarded, causing a lot of waste and environmental problems. Therefore, the existing carbon fiber composite materials are all seeking to recycle carbon fiber after removing the resin substrate and reuse it.

The existing mainstream methods of recycling carbon fiber from composite materials, such as the European ELG company and the American Carbonconversion company, use electric heating to burn the resin or use chemical solvents to remove the resin substrate and recycle carbon fiber. Combustion of composite materials with electric heating to remove resin substrates requires considerable operating time due to heat transfer limitations and tends to damage carbon fiber properties. Removing the resin base material by chemical method is not only time-consuming, but also produces waste solution, which must be processed later, which will increase the cost of the overall manufacturing process, and will cause environmental pollution if it is not treated and discharged directly.

Furthermore, although microwave heating technology has the advantages of rapid temperature rise, energy saving, and is suitable for high-temperature process applications, it is difficult to control the distribution of microwave energy. There is a local magnetic field strengthening or local magnetic field cancellation, resulting in uneven heating area and poor heating efficiency; at the same time, in the process environment above 600 degrees Celsius, as the heating time increases, the carbon fiber is easy to react with oxygen and cause damage, resulting in The monofilament performance retention rate of recycled fibers is insufficient, resulting in uneven mechanical strength in the subsequent production of recycled carbon fiber composites, which is not enough for subsequent regeneration applications.

Contents of the invention

In order to overcome the deficiencies in the prior art, the present invention provides a system and method for rapidly recovering carbon fiber composite materials based on in-phase microwave heating. The specific technical solutions are as follows:

A recovery system for rapid recovery of carbon fiber composite materials based on in-phase microwave heating, including a first heating device, a second heating device and a conveying device, the first heating device includes a first heating chamber, a first conveyor and an in-phase microwave The microwave generator, the first conveyor runs through the first heating cavity, and the microwave generator communicates with the first heating cavity; the second heating device includes the second heating cavity, the second conveyor and an electric heater, and the electric heater is set In the second heating cavity, the second conveyor is installed in the second heating cavity, and the second conveyor transports the product heated by the first heating device to the second heating cavity.

Further, the microwave generator includes a microwave launcher and a metal guide cover, the microwave launcher and the metal guide cover are fixedly connected by fasteners or flanges, and the metal guide cover is connected to the top of the first heating cavity and communicated with the first heating cavity The microwave emitted by the microwave launcher is guided by the metal guide cover and enters the first heating cavity. The metal guide cover includes a parallel part and an enlarged diameter part. The two ends of the enlarged diameter part are respectively connected to the parallel part and the first heating cavity. , the microwave emitter is arranged on the parallel part, and the width of the enlarged diameter part gradually increases from the end connected with the parallel part to the end connected with the first heating cavity.

All microwave generators are connected to a microwave transmission source, and the microwaves generated by the microwave transmission source are demultiplexed n times by 2×(2 ⁿ -1) wave splitters and then passed through 2×(2 ⁿ⁺¹ -1) equal microwaves The transmission element transmits to 2×(2 ⁿ⁺¹ −1) microwave generators to generate in-phase microwaves, where n is an integer.

，其中A为振幅，k为波导数，x为位移，ω为角频率，t为时间，θ为起始相位角。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 starting phase angle.

Preferably, it also includes an inert gas supply device communicating with the first heating device; a gas burning device communicating with the first heating device and the second heating device.

Further, a catalytic converter is also included, which is connected with the gas combustion device.

In this system, the microwave emitted by a high-power microwave emission source is transmitted to the microwave generator equally through 2×(2 ⁿ -1) wave splitters, so as to realize the initial phase of the microwave transmitted to the heating cavity Angles, times and path lengths are all homogenized, resulting in enhanced and consistently reproducible heating effects within the system. According to the electromagnetism-thermal energy conversion formula, the heating of materials by microwaves is mainly caused by the dielectric loss and conduction loss of the material, and the most important factor affecting the heating efficiency is the value of the internal electric field E of the material.

Therefore, in-phase microwaves are equivalent to uniformly distributing microwave energy in the object to be heated, so as to produce synergistic heating effect. Traditional electric heating requires 100KW, and conventional microwave heating uses a heating power density of 30KW to reach a heating temperature of 600 degrees Celsius. In-phase microwave heating only needs to provide a heating power of 15KW to reach this heating temperature.

A method for rapidly recycling carbon fiber composites based on in-phase microwave heating, comprising the following steps:

Step 1: Heat the carbon fiber composite material with in-phase microwaves in an environment where the oxygen concentration does not exceed 10%, and the heating temperature is 600-800°C (the heating temperature is the temperature on the surface of the composite material monitored by the temperature monitor), The heating time is 1-60Min, the pressure is -20Pa, and the carbon fiber composite material fragments are 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 the resin;

Step 2: In an environment with an oxygen concentration of 20-25%, the heating temperature is 600±50 ^o C, and 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 , to obtain pure carbon fiber.

The in-phase microwave in the step 1 is generated by connecting all microwave generators to a microwave emission source, and the microwave generated by the microwave emission source is demultiplexed n times by 2 × (2 ⁿ -1) wave splitters It is transmitted to 2×(2 ⁿ⁺¹ -1) microwave generators via 2×(2 ⁿ⁺¹ -1) equal microwave transmission elements to generate in-phase microwaves, where n is an integer.

，其中A为振幅，k为波导数，x为位移，ω为角频率，t为时间，θ为起始相位角。Furthermore, the microwave function equation produced by each microwave generator in the 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 starting phase angle.

Preferably, before step 1, the carbon fiber composite material to be recycled is fragmented. The present invention heats and recycles the carbon fiber composite material in two steps. First, the carbon fiber composite material is heated by in-phase microwaves to thermally disintegrate, and then the second step of heating is performed to burn and remove the remaining resin in the composite material, which can greatly save the cost of removing the resin. Working time, specifically, in the first heating device, an inert gas is used to form a low-oxygen environment, and the carbon fiber composite material is heated with in-phase microwaves, so that the carbon fiber composite material is thermally cracked in a low-oxygen environment, thereby removing the carbon fiber composite material. The 85% to 90% resin contained in the chips, and then the intermediate product from which most of the resin has been removed enters the second heating device in an aerobic environment for combustion, and the remaining 10% to 15% resin is removed by oxidation. By performing rapid thermal disintegration first, and then performing constant temperature combustion oxidation to remove the residual base material in the composite material, the operation time for removing the base material can be greatly saved, and the overheating and oxidation damage of carbon fibers can be avoided, and the volatility produced after thermal cracking Organic compounds and burned carbon and oxygen gas can enter the gas combustion device for combustion, and the exhaust gas after combustion of the gas combustion device will be converted into exhaust gas that is harmless to the environment and human body through a catalytic converter, and then discharged to the atmosphere.

Beneficial effects of the present invention: the present invention uses a two-step heating method to recover carbon fiber composite materials, especially the first step of heating and cracking adopts the same-phase microwave heating method, so that the heating energy distribution is more concentrated and uniform, which is different from the existing conventional methods Compared with phase microwave heating, it has higher energy efficiency: first, low heating power is used to achieve high heating temperature, and energy consumption is reduced. A heating power of 15KW can achieve a heating temperature of 600 degrees Celsius, while using ordinary non-in-phase microwave heating requires a heating power of 30KW to achieve this heating temperature in the same heating area; second, the heating time is shorter, due to the same phase Microwave heating can provide a stable high heating temperature in the heating area, so almost all carbon fiber composite materials in the heating area can complete the resin disintegration in a short time. The carbon fiber composite materials of the same type and weight need 30-60 min, using in-phase microwave heating, it only takes 10-15min, the time is significantly shortened, and the risk of carbon fiber oxidation is greatly reduced. It is precisely because the first step uses low power to achieve high-energy heating, shortens the heating time, and combines the control of oxygen content so that the present invention can maintain and recover carbon fibers with performance retention of more than 90% under processing conditions above 600 degrees Celsius.

In addition, the method can recover pure carbon fibers from carbon fiber composite materials, without producing by-products that cause environmental pollution, reducing the cost of recycling carbon fiber processes as a whole and increasing recycling capacity.

Description of drawings

Fig. 1 is the schematic diagram of embodiment 2 of composite material carbon fiber recycling system of the present invention;

Fig. 2 is another schematic diagram of embodiment 2 of the composite material carbon fiber recycling system of the present invention;

Fig. 3 is the schematic diagram of the first heating device of embodiment 2 of the present invention;

Fig. 4 is a side view of the first heating device of Embodiment 2 of the present invention;

Fig. 5 is the schematic diagram that the microwave in-phase field of composite material recycling method of the present invention forms;

Fig. 6 is a schematic diagram of the microwave in-phase field in the first heating device according to Embodiment 2 of the present invention;

Fig. 7 is the graph of the relation between the heating temperature and the time that the first heating device of 4 kinds of situations in table 1 produces under the same power;

Figure 8 (8A, 8B, 8C, 8D) is a schematic diagram of the energy density of the heating temperature generated by the first heating device in the four situations in Table 1 under the same power and the same time;

Fig. 9 is the schematic diagram of the second heating device of embodiment 2 of the composite material carbon fiber recovery system of the present invention;

Fig. 10 is the state change diagram (1) of the composite material carbon fiber composite material of each step in the composite material recycling method of the present invention;

Fig. 11 is the state change diagram (2) of the composite material carbon fiber composite material of each step in the composite material recycling method of the present invention;

Fig. 12 is the schematic diagram of the state change of the composite material carbon fiber composite material in each step in the composite material recycling method of the present invention;

Figure 13 is an electron microscope comparison diagram of carbon fiber epoxy resin composite materials before and after in-phase microwave heating;

Fig. 14 is the contrast figure of the heating efficiency of the present invention and common microwave heating

10-crushing device; 11-feed hopper; 12-conveyor belt; 20-first heating device; 21-first heating chamber; 22-first conveyor; 23-microwave generator; 231-microwave launcher ; 232-metal guide cover; 2321-parallel part of metal guide cover; 2322-expanding part of metal guide cover; 24-machine body; 25-feed hopper; 26-first exhaust guide; Heating device; 31-second heating chamber; 32-second conveyor; 34-machine body; 35-feed hopper; 36-turning mechanism; 37-second exhaust guide; 40-inert gas supply device; 50-gas combustion device; 60-catalytic converter; 100-carbon fiber composite recycling system.

Detailed ways

Example 1

A system for rapidly recovering carbon fiber composite materials based on in-phase microwave heating, including a first heating device, a second heating device, and a conveying device, the first heating device including a first heating cavity, a first conveyor, and a microwave in-phase microwave generator, the first conveyor runs through the first heating cavity, and the microwave generator communicates with the first heating cavity; the second heating device includes a second heating cavity, a second conveyor and an electric heater, and the electric heater is arranged on In the second heating cavity, the second conveyor is passed through the second heating cavity, and the second conveyor transports 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. Also included is a catalytic converter connected to the gas combustion unit.

The microwave generator includes a microwave launcher and a metal guide cover, the microwave launcher and the metal guide cover are fixedly connected by fasteners or flanges, the metal guide cover is composed of a parallel part and an enlarged neck, and the parallel part is arranged in the first heating chamber The inner top of the body, and the expanded neck communicates with the first heating cavity. All microwave generators are connected to a microwave transmission source, and the microwaves generated by the microwave transmission source are demultiplexed n times by 2×(2 ⁿ -1) wave splitters and then passed through 2×(2 ⁿ⁺¹ -1) equal microwaves The transmission element transmits to 2×(2 ⁿ⁺¹ −1) microwave generators to generate in-phase microwaves, where n is an integer.

，其中A为振幅，k为波导数，x为位移，ω为角频率，t为时间，θ为起始相位角。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 starting phase angle.

Example 2

As shown in Figures 1 and 2, a system based on in-phase microwave heating for rapid recovery of carbon fiber composites is used to recover carbon fibers in carbon fiber composites, which are made of carbon fibers and resins. The carbon fiber composite recovery system 100 of this embodiment includes: a crushing device 10 , a first heating device 20 and a second heating device 30 .

The crushing device 10 is used to receive the carbon fiber composite material and crush the carbon fiber composite material into carbon fiber composite material fragments. The crushing device 10 can be an existing crusher, such as a single-shaft crusher, a double-shaft crusher, a jaw crusher, a cone crusher, a roller crusher, etc., and the carbon fiber composite material enters the crushing device from the feed hopper 11 After 10, cutting, rolling, beating or impacting through the cutter or other crushing mechanism of the crushing device 10 will form carbon fiber composite material fragments, and the carbon fiber composite material fragments will be discharged from the bottom of the crushing device 10 and transported to the second stage via the conveyor belt 12. A feed to the heating device 20 . The processing capacity of the crushing device 10 in this embodiment is to crush 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.

As shown in Figures 3-4, the first heating device 20 forms an environment in which the oxygen concentration is kept below 10% and receives the fragments of carbon fiber composite materials, and heats the fragments of carbon fiber composite materials in a low-oxygen environment at a heating temperature of 600 ^o C To 800 ^o C, the fragments of carbon fiber composites are thermally cracked. 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 feed hopper 25, the first heating cavity 21 and the first conveyor 22 are arranged on the machine body 24, and the first conveyor 22 passes through the first heating cavity 21 , the feed hopper 25 is arranged above the first conveyor 22, and after the carbon fiber composite material fragments are conveyed from the crushing device 10 to the feed hopper 25, the feed hopper 25 falls to the first conveyor 22, and the first conveyor 22 conveys The carbon fiber composite fragments pass through the first heating cavity 21 . The heated carbon fiber composite material fragments are discharged from the first conveyor 22 . The first conveyor 22 in this embodiment is a key-plate conveyor belt. A plurality of microwave generators 23 are arranged on the top of the first heating chamber 21, and the microwave generators 23 generate microwaves and irradiate them into the first heating chamber 21, and the microwaves act on the microwaves transported by the first conveyor 22 through the first heating chamber. 21 of the carbon fiber composite material fragment, the temperature of the carbon fiber composite material fragment is increased, and a fluffy intermediate product is produced through overheating. The time for the first conveyor 22 to transport the carbon fiber composite material fragments through the first heating chamber 21 is 10 minutes. After passing through the first heating chamber 21, 85%-90wt% of the resin contained in the carbon fiber composite material can be decomposed to form a fluffy intermediate product, wherein the residual resin content is 10%-15wt% of the carbon fiber composite material at the time of feeding.

The system 100 for quickly recovering carbon fiber composite materials in 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 hypoxic environment , prevent excessive combustion and oxidation of composite materials, and destroy carbon fibers. The inert gas supply device 40 of the present embodiment is a nitrogen gas supply device, the inert gas of the present embodiment is nitrogen gas, and the nitrogen gas is introduced into the first heating chamber 21 to keep the first heating chamber 21 at a slight negative pressure (-20Pa) to avoid Volatile organic compounds leak and pollute the environment. In addition, nitrogen gas is injected into the first heating chamber 21 to form an environment with a low oxygen concentration, thereby providing conditions for thermal disintegration of the carbon fiber composite fragments. Nitrogen surrounds the carbon fiber composite material fragments, which can prevent the carbon fiber composite material fragments from contacting with oxygen and avoid carbon fiber combustion and oxidation.

The first heating device 20 of this embodiment uses in-phase microwaves to rapidly heat the carbon fiber composite material fragments. FIG. 5 is a schematic diagram of the microwave in-phase field formation of the carbon fiber composite material recovery device of this embodiment. The first heating device 20 includes a plurality of microwave generators 23, all microwave generators 23 are connected to a microwave emission source O, after the microwave MW generated by the microwave emission source O is distributed through the first wave splitter D1, one of the microwave MW The first microwave transmission part MT1 is transmitted to the second wave splitter D2 and another microwave MW is transmitted by the second microwave transmission part MT2 to the third wave splitter D3, and then the second wave splitter D2 is distributed and transmitted to the first wave splitter. The sub-microwave transmission part MST1 and the second microwave transmission part MST2, on the other hand, the third wave splitter D3 distributes the transmission between the third microwave transmission part MST3 and the fourth microwave transmission part MST4, and finally the sub-microwave transmission parts The transmission elements are respectively transmitted to the corresponding microwave generators 23 . In this way, when the microwave MW is transmitted through the microwave transmission elements, they have the same phase angle with each other, and when the microwave MW is transmitted through the microwave transmission elements, they also have the same phase angle with each other. Finally, the microwave generator 23 emits The microwaves all have the same phase angle, and the formation of the same phase field of microwaves will not cause the phase delay phenomenon like the existing microwave generators using multiple microwave emission sources O, especially when the microwave MW is in the The phase angles of the microwave transmission elements and the secondary microwave transmission elements are not the same when they transmit. The microwave emission source O generates microwaves with a frequency of 915MHz, which has a lower frequency than the traditional microwave emission source O that generates microwaves with a frequency of 2.45GHz. The material penetration depth is increased, and the thermal efficiency of electromagnetic energy conversion is increased by 50%. The number of frequency microwave generators 23 is 2 ^N , where N is a natural number, and N represents the number of times for power distribution. The first heating device 20 shown in Figure 2 includes four microwave generators 23, which represent the microwave emission of the present embodiment. The microwave generated by source O undergoes two power distributions. In another embodiment, the microwaves generated by the microwave emission source O may also be provided with only one microwave generator 23 without power distribution, that is, N=0.

Each microwave generator 23 includes a microwave launcher 231 and a metal guide cover 232. The metal guide cover 232 is connected to the top of the first heating cavity 21 and communicated with the first heating cavity 21. The microwave emitted by the microwave launcher 231 passes through the metal The guide cover 232 is guided to enter the first heating cavity 21 . The metal guide cover 232 includes a parallel portion 2321 and an enlarged diameter portion 2322. The two ends of the enlarged diameter portion 2322 are connected to the parallel portion 2321 and the first heating cavity 21 respectively. The width of 2322 gradually increases from the end connected to the parallel portion 2321 to the end connected to the first heating cavity 21 , thus forming a tapered enlarged shape. As shown in FIG. 6 , the microwaves emitted by the microwave emitting element 231 form an in-phase field effect area F1 of the microwave in-phase field S in the expanded diameter portion 2322 .

The wave function equation of the electromagnetic wave is as follows, which is used to explain that when the multiple microwave generators 23 of the first heating device 20 act in the form of the same phase, the offset phase and the indeterminate phase, the sum of the electromagnetic fields with different intensities and directions is finally caused. relation.

其中，A为振幅，k为波导数，x为位移，ω为角频率，t为时间，θ为起始相位角。

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.

When the power is turned on, the high voltage acts on the plurality of magnetrons, and electromagnetic wave signals with different initial phase angles are excited from the microwave emission source O according to different time differences. After individual signals are transmitted into the inner space of the cavity through power distribution components (such as waveguides), the path and time passed by the signals are different, resulting in the sum of electromagnetic fields with different intensities and directions on each point in the space in the cavity.

As shown in Table 1 and FIG. 7, it is the relationship between heating temperature and heating time for microwave heating with the same phase or different phases for the multiple microwave generators 23 of the first heating device 20 under the same power. Referring to Fig. 1, each situation has four microwave generators 23 arranged in sequence and equidistantly on the top of the first heating cavity 21, and each microwave generator 23 of the first kind of situation is in the phase angle θ= 0° and each microwave generator 23 of the second case have the phase angle θ=75° of the same phase, compared with the third case and the fourth case, in the same heating time, microwaves with the same phase Under heating, the synthetic wave produced by superposition of waveforms has a larger amplitude, which in turn increases the intensity of the microwave, resulting in a higher heating temperature.

In the third case, when each microwave generator heats with microwaves at a phase angle that cancels the phase, the waveforms cancel each other out after being superimposed due to the opposite phase angle θ. In the same heating time, it only has a lower heating temperature. .

In the fourth case, when each microwave generator 23 heats microwaves with phase angles of indeterminate phases, because they each have phase angles of different phases, the synthesized waves after the waveforms are superimposed do not cancel each other as in the third case, and produce The amplitude of the synthetic wave is not as large as the first case and the second case, so the heating temperature produced by the first heating device in the fourth case is lower than that of the first case (or the same heating time) in the same heating time. between the second case) and the third form.

Table I

The first case (same phase) The second case (same phase) The third case (offset phase) The fourth case (indeterminate aspect) 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°

In FIG. 8 , 8A, 8B, 8C and 8D are schematic diagrams of the energy density of the heating temperature generated by the first heating device in each case in Table 1 under the same power and the same time. In this embodiment, the microwave generators 23 can be respectively arranged on the top of the first heating cavity 21, and the microwave generators 23 can be further divided into a first microwave generator 23' and a second microwave generator 23'' , the third microwave generator 23''' and the fourth microwave generator 23'''', and when the first conveyor 22 transports the carbon fiber composite material pieces through the first heating cavity 21, the microwave generators 23 It can be heated in the corresponding heating range, and the different colors of the color cards in the figure represent the energy density of different heating temperatures, and the red in the color card (the figure shows dark areas such as black) The energy density of the heating temperature shown is the highest temperature, while the energy density of the heating temperature shown by the blue at the opposite end of the red (the figure shows off-white) is the lowest temperature. As shown in Figure 8A (corresponding to the first situation in Table 1) and Figure 8B (corresponding to the second situation in Table 1), in the same heating time, under microwave heating with the same phase angle The red area is the most. As shown in FIG. 8D (corresponding to the fourth situation in Table 1), in the same heating time, the displayed red areas are significantly reduced, but there are still a few red areas. As shown in Figure 8C (corresponding to the third situation in Table 1), in the same heating time, there is almost no red area, but the lower temperature yellow, green or blue area (light-colored area such as off-white) is the host. Combining Figures 7-8 and Table 1, it is not difficult to find that when the first heating device 20 heats the carbon fiber composite material fragments with microwaves in the same phase in a low-oxygen environment, it has better performance when compared with offset phase or indeterminate phase microwave heating. heating efficiency.

As shown in Figure 9, the second heating device 30 forms an aerobic environment, which has the oxygen content as in the atmosphere, and the second heating device 30 receives the intermediate product and uses electric heating to externally heat the intermediate product to achieve combustion of the substrate. The cracking temperature is oxidized and removed 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 feed hopper 35, the second heating cavity 31 and the second conveyor 32 are arranged on the machine body 34, and the feed hopper 35 is arranged above the second conveyor 32 , the intermediate product falls from the feed hopper 35 to the second conveyor 32 . The electric heater is arranged in the second heating cavity 31, the second conveyor 32 is penetrated in the second heating cavity 31, the intermediate product is carried by the second conveyor 32 and transported into the second heating cavity 31, and the electric heater is outside The finished intermediate product in the first heating chamber 21 is heated. The intermediate product is externally heated to 600 ^o C ± 50 ^o C by an electric heater, so that the remaining small amount of resin substrate contained in the intermediate product is oxidized to generate carbon dioxide gas and ash. After the resin is removed from the intermediate product, purified carbon fibers are obtained, and the carbon fibers are continuously transported by the second conveyor 32 and dropped into the transport carrier from the other end.

The second heating device 30 also includes a turning mechanism 36 , which is disposed in the second heating cavity 31 and above the second conveyor 32 to turn the intermediate product. The turning mechanism 36 of this embodiment includes a plurality of rotatable blades. When the second conveyor 32 carries the intermediate product and moves through the second heating cavity 31, the turning mechanism 36 can turn the intermediate product to increase the contact area of the intermediate product with oxygen. , to increase the rate of intermediate product combustion.

Furthermore, the first heating device 20 further includes at least one first exhaust guide 26, which communicates with the first heating cavity 21, and the volatile organic compounds generated after the pyrolysis of the carbon fiber composite fragments are passed through the first row. The air guide 26 exits the first heating cavity 21 . The first exhaust guide 26 in this embodiment is an exhaust pipe.

The second heating device 30 further includes at least one second exhaust guide 37, which is communicated with the second heating cavity 31, and the gas (carbon dioxide) generated after the combustion of the intermediate product is discharged into the second exhaust guide 37 through the second exhaust guide 37. The cavity 31 is heated. The second exhaust guide 37 in this embodiment is an exhaust pipe.

The system 100 for quickly recovering carbon fiber composite materials in this embodiment further includes a gas combustion device 50, the gas combustion device 50 is 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 for combustion through the first exhaust guide 26 and the second exhaust guide 37 . The gas of volatile organic compounds generated by the first heating device 20 and the carbon dioxide and carbon monoxide generated by the second heating device 30 are discharged by the first exhaust guide 26 and the second exhaust guide 37 respectively. The gas is introduced into the gas combustion device 50 for combustion, and the volatile organic compounds are combusted to form oxides. The combustion temperature of the gas combustion device 50 can reach 850 ^o C, and the residence time of volatile organic compounds in the gas combustion device 50 is greater than 2 seconds.

The system 100 for quickly recovering carbon fiber composite materials in this embodiment further includes a catalytic converter 60 connected to the gas combustion device 50, and the exhaust gas generated by the gas combustion device after burning volatile organic compounds is converted into exhaustable gas by the catalytic converter 60 discharged into the atmosphere. The combustion of volatile organic compounds may produce hydrocarbons HC, carbon monoxide CO or nitrogen oxides NOx, etc. The catalytic converter 60 can further oxidize hydrocarbons HC and carbon monoxide CO to form carbon dioxide (CO ₂ ) and water (H ₂ O) , nitrogen oxides NOx can be reduced to N ₂ and O ₂ through the catalytic converter 60 . The exhaust gas is converted into a gas harmless to the environment and human body through the catalytic converter 60, and then discharged to the atmosphere.

Example 3

A method for quickly recovering carbon fiber composite materials, in step S1, the carbon fiber composite materials of the composite materials are crushed to form carbon fiber composite material fragments, and the carbon fiber composite materials of the composite materials are crushed into carbon fiber composite material fragments by a crushing device 10 . Then go to step S2.

In step S2, the carbon fiber composite fragments are heated with microwaves in a hypoxic environment, and the microwaves generated by the microwave generator 23 of the first heating device 20 act on the carbon fiber composite fragments to thermally disintegrate the carbon fiber composite fragments to obtain an intermediate product. Step S2 may include the step of providing an inert gas to form a hypoxic environment, and the inert gas in this embodiment may be nitrogen. Then go to step S3.

In step S3, the intermediate product is heated by the electric heater of the second heating device 30 in an aerobic environment, the base material of the intermediate product is oxidized and burned, and the base material contained in the intermediate product is removed to obtain pure carbon fiber.

As shown in Figure 10-12, it can be seen from the figure that in the crushing process of step S1, the carbon fiber composite material W of the composite material is crushed into carbon fiber composite material fragments W1, and the carbon fiber composite material fragments W1 contain the base material B And carbon fiber CF. In step S2, after the carbon fiber composite material fragment W1 is heated with microwaves in a hypoxic environment, the base material B of the intermediate product is significantly reduced, and the base material B of the intermediate product is 10%~ of the base material content of the carbon fiber composite material fragment W1. 15%. As shown in Fig. 11 and Fig. 12, in step S3, the base material of the intermediate product is oxidized and burnt out, and finally pure carbon fibers are obtained.

Example 4

A method based on in-phase microwave heating to quickly recycle carbon fiber epoxy resin composites, comprising the following steps:

Step 1, the carbon fiber epoxy-based composite material is crushed by a crushing device to form 10-50mm carbon fiber epoxy-based composite material fragments. Under a low-oxygen environment with an oxygen concentration of 8%, use the first heating device 20 to crush the carbon fiber epoxy-based composite material. In-phase microwave heating, the heating temperature is 650°C, the heating time is 10Min, and the pressure is -20Pa, so that the carbon fiber composite material fragments 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, which may be nitrogen. After this step, the electron microscope schematic diagram of the change of the composite material is shown in Figure 13. It can be clearly seen that carbon fibers with less resin residue are obtained.

Step 2. In an environment where the oxygen concentration is 20%, the intermediate product is heated with the electric heater of the second heating device 30. The heating temperature is 550° C., and the heating time is 30 min. material, remove the resin contained in the intermediate product, and obtain pure carbon fiber, and the recovery rate of carbon fiber is over 95%.

In this example, if ordinary microwave heating is used to crack the carbon fiber epoxy resin composite material (in this example, the epoxy resin accounts for 50% by weight of the carbon fiber composite material), the microwave heating efficiency comparison between the two is shown in Figure 14 . Since the resin is cracked during the microwave heating process, the weight of the composite material is reduced, leaving carbon fiber and a small amount of resin, so this comparison chart is based on the same weight of carbon fiber epoxy resin composite material, under the same heating time (5min, 10min , 15min, 20min, 25min, 30Min, 35min), weighed and compared the intermediate products under the two heating methods, and found that under the same phase microwave heating, the weight of the intermediate product decreased faster, and it only took about 10min to complete the cracking of the resin ; while ordinary microwave heating, the weight loss of the intermediate product is relatively slow, and it takes at least 30 minutes to complete the cracking of the resin.

Example 5

A method based on in-phase microwave heating to quickly recycle carbon fiber epoxy resin composites, comprising the following steps:

Step 1, the carbon fiber epoxy-based composite material is crushed by a crushing device to form 10-50mm carbon fiber epoxy-based composite material fragments. Under a low-oxygen environment with an oxygen concentration of 5%, use the first heating device 20 to In-phase microwave heating, the heating temperature is 800°C, the heating time is 3Min, and the pressure is -20Pa, so that the carbon fiber composite material fragments 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, which may be nitrogen.

Step 2. In an environment where the oxygen concentration is 20%, the intermediate product is heated with the electric heater of the second heating device 30. The heating temperature is 550° C., and the heating time is 30 min. material, remove the resin contained in the intermediate product, and obtain pure carbon fiber.

Example 6

A kind of method based on in-phase microwave heating quick recovery carbon fiber vinyl composite material, comprises the following steps:

Step 1. Break the carbon fiber vinyl resin composite material through a crushing device to form 10-50mm carbon fiber composite material fragments. Under a low oxygen environment with an oxygen concentration of 5%, use the first heating device 20 to heat it with microwaves in the same phase , the heating temperature is 700°C, the heating time is 20Min, and the pressure is -20Pa, so that the carbon fiber composite material fragments 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 filled with inert A gas is formed, the inert gas may be nitrogen.

Step 2. In an environment where the oxygen concentration is 20%, the intermediate product is heated with the electric heater of the second heating device 30. The heating temperature is 600° C., and the heating time is 20 min. material, remove the resin contained in the intermediate product, and obtain pure carbon fiber.

Example 7

A kind of method based on in-phase microwave heating quick recovery carbon fiber polyimide resin composite material, comprises the following steps:

Step 1. The carbon fiber polyimide resin composite material is crushed by a crushing device to form 10-50mm carbon fiber composite material fragments. In a low-oxygen environment with an oxygen concentration of 5%, use the first heating device 20 to phase it Microwave heating, the heating temperature is 750°C, the heating time is 20Min, and the pressure is -20Pa, so that the carbon fiber composite material fragments are pyrolyzed to obtain an intermediate product that removes 85-90% of the resin in the carbon fiber composite material; into the formation of inert gas, the inert gas can be nitrogen.

Step 2. In an environment where the oxygen concentration is 20%, the intermediate product is heated with the electric heater of the second heating device 30. The heating temperature is 650° C., and the heating time is 20 min. material, remove the resin contained in the intermediate product, and obtain pure carbon fiber.

Example 8

A kind of method based on in-phase microwave heating quick recovery carbon fiber phenolic resin composite material, comprises the following steps:

Step 1. The carbon fiber phenolic resin composite material is crushed by a crushing device to form 10-50mm carbon fiber composite material fragments. Under a low-oxygen environment with an oxygen concentration of 5%, use the first heating device 20 to heat it with microwaves in the same phase. The heating temperature is 800°C, the heating time is 60Min, and the pressure is -20Pa, so that the carbon fiber composite material fragments 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 filled with inert gas Formed, the inert gas may be nitrogen.

Step 2. In an environment where the oxygen concentration is 20%, the intermediate product is heated with the electric heater of the second heating device 30. The heating temperature is 650° C., and the heating time is 30 min. material, remove the resin contained in the intermediate product, and obtain pure carbon fiber.

Performance tests were carried out on the recycled carbon fiber monofilaments prepared in Examples 4-8. Since recycled carbon fibers lack the surface oil agent of new carbon fibers, we used T300 grade carbon fiber composite materials as test samples, soaked in acetone for a long time, and the dissolved resin was intact. 1. Recycled carbon fiber without sizing (T300 grade) is used as the comparison original, and the national standard GB/T 31290-2014 is used for monofilament testing. The comparison performance results are shown in Table 2. The strength retention rate of the recycled carbon fiber of the present invention is >90%, and the modulus Performance retention rate> 95%.

Table II

It can be seen from the above that in the in-phase microwave heating step of the present invention, when the oxygen concentration is 1-10% and the heating temperature is above 600°C, since the in-phase microwave reaction is faster and more uniform, the recovered carbon fibers in this case It will avoid being excessively attacked by organic substances such as oxygen or gasified resin, so that it can maintain good mechanical properties (retain more than 90% of the properties).

Claims (10)

1. A system for rapidly recycling carbon fiber composite materials based on in-phase microwave heating comprises a first heating device, a second heating device and a conveying device, and is characterized in that 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 communicated 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, the second conveyor penetrates through the second heating cavity, and a product heated by the first heating device is conveyed to the second heating cavity by the second conveyor.

2. The in-phase microwave heating-based system for rapidly recycling carbon fiber composite materials according to claim 1, wherein the microwave generator comprises a microwave emitter and a metal guide cover, the microwave emitter 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 communicated with the first heating cavity, microwaves emitted by the microwave emitter are guided by the metal guide cover to enter the first heating cavity, the metal guide cover comprises a parallel portion and an expanding portion, two ends of the expanding portion are respectively connected to the parallel portion and the first heating cavity, the microwave emitter is arranged on the parallel portion, and the width of the expanding portion gradually increases from one end connected with the parallel portion to one end connected with the first heating cavity.

3. The in-phase microwave heating-based system for rapid recovery of carbon fiber composite according to claim 1 or 2, wherein all microwave generators are connected to a microwave emission source, and the microwaves generated by the microwave emission source are transmitted through 2 x (2) ⁿ -1) wave-splitting of the wave-splitter n times and then passing through 2 x (2) ⁿ⁺¹ -1) transmission of equal microwave transmission elements to 2 × (2) ⁿ⁺¹ -1) microwave generators for generating in-phase microwaves, wherein n is an integer.

4. The in-phase microwave heating-based system for rapid recovery of carbon fiber composite material according to claim 3, wherein the function of the microwave generated by each microwave generator is represented by the following equation, where A is amplitude, k is number of waveguides, x is displacement, ω is angular frequency, t is time, and θ is initial phase angle.

5. The in-phase microwave heating-based system for rapidly recycling the carbon fiber composite material as claimed in claim 4, further comprising an inert gas supply device communicated with the first heating device; and the gas combustion device is communicated with the first heating device and the second heating device.

6. The carbon fiber composite recycling system according to claim 5, further comprising a catalytic converter connected to the gas combustion device.

7. A system for rapidly recycling carbon fiber composite materials based on in-phase microwave heating is characterized in that the recycling system of any one of claims 1 to 6 is adopted, and comprises the following steps:

step 1: heating the carbon fiber composite material by same-phase microwave under the environment that the oxygen concentration is not more than 10%, wherein the heating temperature is 600-800 ℃, the heating time is 1-60Min, and the pressure is-20 Pa, so that broken carbon fiber composite material fragments are thermally cracked to obtain an intermediate product for removing 85-90% of resin in the carbon fiber material, and the intermediate product contains carbon fiber and 10-15% of resin;

and 2, step: heating at 600 + -50 deg.C in an environment with oxygen concentration of 20-25% ^o C, heating for 1-60Min, burning the product obtained in the step 1, and removing residual coking resin contained in the product obtained in the step 1 to obtain the pure carbon fiber.

8. The in-phase microwave heating-based method for rapidly recycling carbon fiber composite material according to claim 7, wherein the microwaves in step 1 are in-phase microwaves generated by connecting all microwave generators to a microwave emission source, and the microwaves generated by the microwave emission source pass through 2 x (2) ⁿ -1) wave-splitting by the wave-splitters n times via 2 × (2) ⁿ⁺¹ -1) transmission of equal microwave transmission elements to 2 × (2) ⁿ⁺¹ -1) microwave generators for generating in-phase microwaves, wherein n is an integer.

9. The in-phase microwave heating-based method for rapidly recycling carbon fiber composite material according to claim 7 or 8, wherein the function of the microwave generated by each microwave generator in step 1 is represented by the following equation, wherein A is amplitude, k is waveguide number, x is displacement, ω is angular frequency, t is time, and θ is initial phase angle.

10. The in-phase microwave heating-based method for rapidly recycling carbon fiber composite materials according to claim 7, wherein the carbon fiber composite materials to be recycled are subjected to a fragmentation treatment before the step 1.

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