A kind of carbon nanotube purification device and purification method

Abstract

A carbon nanotube purification device and purification method, comprising a microwave plasma generator, a purification device, a feeding system, a collecting system and an exhaust system; the microwave plasma generator is used to transport microwave plasma into the purification device, and its structure comprises a microwave generator, a waveguide, a mixer and a microwave plasma head; the microwave generator is connected to the waveguide and transmits microwaves through the waveguide, the mixer is arranged on the waveguide and is used to adjust the microwave reflection power, and the microwave plasma head is connected to the waveguide and is used to introduce microwaves into the purification device; the feeding system is connected to the purification device, the collecting system is connected to the discharge port of the purification device, and the exhaust system is connected to the purification device; the purification device is in a negative pressure state; the scheme of the application can avoid the use of a large amount of strong acid, reduce waste acid and wastewater pollution, has low energy consumption, and can effectively remove carbon-coated metal catalyst particles.

Description

Technical Field

[0001] The present application relates to the technical field of carbon nanotube purification, and in particular to a carbon nanotube (CNT) purification device and purification method. Background Art

[0002] Carbon nanotubes (CNTs), as a new type of one-dimensional nanomaterial, are widely used in new energy, transparent display, anti-static, semiconductors, engineering plastics and other fields due to their excellent electrical conductivity, thermal conductivity, temperature resistance, chemical resistance and mechanical properties.

[0003] At present, carbon nanotubes prepared by traditional methods such as floating catalytic method and arc method are often accompanied by a considerable amount of impurities, such as amorphous carbon, catalyst particles and crystalline carbon nanoparticles. The presence of these impurities affects the performance of the carbon nanotubes themselves and hinders their application in specific fields (such as conductive slurry for lithium-ion batteries). Therefore, people pay more and more attention to the purification research of carbon nanotubes.

[0004] There are two main types of traditional carbon nanotube purification methods. One method is acid washing purification, which is to use strong acids such as hydrochloric acid and nitric acid to dissolve the residual metal catalyst, and then separate it by filtration, centrifugation, etc., such as patent CN102398901B. The disadvantages of this method are: 1) It is difficult to completely remove the metal catalyst with a thicker carbon layer; 2) A large amount of waste acid and wastewater is generated. Another method is high-temperature purification, that is, heating the carbon nanotubes (above 2800°C) under vacuum conditions, and the catalyst metal is gasified and separated from the carbon nanotubes. This method can obtain carbon nanotubes with higher purity, but it also has the disadvantages of high energy consumption and damage to the structure of the carbon nanotubes.

[0005] In the patent application document with publication number CN104401963A, chlorine is used to oxidize metal catalyst particles at a certain temperature to generate metal chloride. The boiling point of chloride is much lower than that of metal element and its oxidation boiling point, so the metal chloride can be gasified and separated from carbon nanotubes at a lower temperature. Compared with high-temperature gasification of metal catalysts, this method greatly reduces energy consumption, but the amount of chlorine used is large, and the strong oxidizing and toxicity of this amount of chlorine also bring high difficulty to the design and operation of the purification device; in addition, this scheme needs to use a resistance furnace to heat at least 400 degrees in the purification process, which greatly increases energy consumption. The patent application document with publication number CN112028056A improves the traditional heating purification method and uses a microwave heating method to purify carbon nanotubes through a chlorine purification method. This purification method utilizes the penetrating, selectivity and instantaneous heating characteristics of microwaves to reduce the damage to the carbon nanotube structure during the purification process. However, this method still purifies carbon nanotubes by indirect heating, and microwaves are only used as a heat source, while metal catalysts or carbon nanotube conductors have a shielding effect on microwaves. Therefore, there are certain limitations.

[0006] Therefore, it is urgent to develop an efficient and low-cost carbon nanotube purification device and purification method to facilitate the subsequent application of carbon nanotubes. Summary of the invention

[0007] In view of the above-mentioned deficiencies in the prior art, the present application provides a carbon nanotube purification device which avoids the use of a large amount of strong acid, reduces waste acid and wastewater pollution, has low energy consumption, and can effectively remove carbon-coated metal catalyst particles.

[0008] In order to solve the above technical problems, the technical solution adopted in the present application is: a carbon nanotube purification device, which includes a microwave plasma generating device, a purification device, a feeding system, a collecting system and an exhaust system; the microwave plasma generating device is used to transport microwave plasma into the purification device, and its structure includes a microwave generator, a waveguide, a mixer and a microwave plasma head, the microwave generator is connected to the waveguide and transmits microwaves through the waveguide, the mixer is arranged on the waveguide to adjust the microwave reflection power, the microwave plasma head is connected to the waveguide and is used to introduce microwaves into the purification device; the feeding system is connected to the purification device, the collecting system is connected to the discharge port of the purification device, and the exhaust system is connected to the purification device; the purification device is in a negative pressure state.

[0009] By adopting the above structure, the present application uses microwave plasma to purify carbon nanotubes for the first time. By continuously conveying the carbon nanotube powder to the microwave lining area in the closed device through the feeding system under negative pressure conditions, the carbon nanotube powder forms a vortex in the purification device under the action of the airflow, and is directly and fully contacted with the microwave plasma. The impurity metal catalyst particles therein form gaseous products under the action of microwave plasma, oxidizing environment and negative pressure, which are discharged by the exhaust system and separated from the carbon nanotubes, thereby achieving the purpose of purifying the carbon nanotubes; this scheme avoids the use of strong acid and will not cause waste acid and wastewater pollution to the product; in addition, compared with the traditional high-temperature purification method, this scheme uses microwave plasma to directly contact the raw material, thereby realizing microscopic ultra-high energy in-situ gasification of the metal catalyst, and the energy required is lower; in addition, compared with the traditional reactive gas (such as chlorine) method, the scheme of the present application greatly reduces the dosage, and can effectively remove impurities such as carbon-coated metal catalyst particles and amorphous carbon, greatly reducing the production cost, and is suitable for large-scale industrial production.

[0010] Furthermore, the microwave plasma head includes an excitation gas inlet pipeline, a water-cooling connecting pipe and a quartz torch glass tube, the water-cooling connecting pipe is coated on the outer wall of the quartz torch glass tube, the excitation gas inlet pipeline is connected to the quartz torch glass tube, and the waveguide is in contact with the quartz torch glass tube; with the above structure, the quartz torch glass tube is used as a container for forming and containing microwave plasma, microwaves can be transported through the waveguide, and then penetrate the tube wall of the quartz glass tube to form microwave plasma, and then fully contact with the carbon nanotubes transported by the feeding system to achieve purification, thereby increasing the contact area between the carbon nanotubes and the microwave plasma and increasing the purification efficiency.

[0011] Furthermore, the outer diameter of the quartz torch glass tube is Φ20-100mm, the wall thickness is 3-8mm, and the length is 200-500mm; the microwave ionizes the carrier gas in the quartz tube to form microwave plasma, which moves downward under the action of the airflow. The diameter of the quartz tube determines the energy density of the microwave plasma. The smaller the diameter, the greater the energy density and the higher the local temperature. Since the quartz tube has a temperature resistance of only 1150°C, the service life of the quartz tube can be extended by controlling the size of the quartz tube; at the same time, the carbon nanotube powder enters from the entrance on one side of the quartz tube. If the diameter is too large, the wall of the quartz tube cannot restrain the shape of the microwave plasma, resulting in an uneven microwave field; therefore, the use of the quartz tube of the above-mentioned specifications of the present application can effectively solve the above-mentioned technical problems, form a uniform microwave field in the tube body, and is conducive to the full purification of the carbon nanotubes.

[0012] Furthermore, the microwave plasma flame generated by the microwave plasma head extends vertically from top to bottom in the quartz torch glass tube, the cooling method is water cooling (that is, water cooling is achieved by circulating water in the water-cooling connecting pipe), and the ignition method is negative pressure excitation; negative pressure ignition can convert microwaves into microwave plasma, thereby increasing the contact area between the raw material and the microwave plasma and improving the purification efficiency.

[0013] Furthermore, the purification device is made of double-layer water-cooled stainless steel, ceramic or quartz material; by using the above materials, microwave plasma can be confined in the purification device, reducing the loss of microwave plasma and improving the purification efficiency.

[0014] Furthermore, the inner wall of the purification device made of double-layer water-cooled stainless steel is sprayed with a ceramic coating. With this structure, secondary contamination of the purified carbon nanotube powder by metal can be prevented.

[0015] Furthermore, the inner diameter of the purification device is Φ30-400mm, and the length is 200-1000mm; since the diameter and length of the purification device are related to the power of microwave plasma and the supply speed of carbon nanotube powder, the purpose is to ensure the residence time of carbon nanotube powder in the purification cavity and compress the microwave plasma area as much as possible so that the microwave plasma fills the entire cavity, so that the carbon nanotube powder is in more complete contact with the microwave plasma, the reaction is more thorough, and the degree of impurity removal is high.

[0016] Furthermore, the quartz torch glass tube is embedded in the cavity of the purification device at a distance of 100 to 500 mm, and is sealed and connected to the purification device via a sealing ring; this structure allows the feed to fully contact with the microwave plasma.

[0017] Furthermore, the microwave generator has a power of 10-75kw and a microwave frequency of 915MHZ.

[0018] Furthermore, the waveguide is a metal conduit for transmitting microwaves, which then enter the glass tube of the quartz torch to excite the gas under negative pressure to form microwave plasma.

[0019] Furthermore, the adapter is a three-screw adapter, which can adjust the microwave reflection power by changing the depth of three independent screws (microwave power supply power = microwave reflection power + microwave power in the reactor, the microwave power supply power is constant, and the microwave power in the reactor can be indirectly adjusted by adjusting the microwave reflection power).

[0020] Furthermore, the feeding system includes a screw loss-in-weight metering feeder, a main feeding gas pipeline and a feeder gas pipeline; one end of the main feeding gas pipeline is connected to the quartz torch glass tube, and the main feeding gas pipeline is also connected to a feeder gas pipeline, and the feeder gas pipeline is connected to the outlet of the screw loss-in-weight metering feeder and is used to load carbon nanotubes into the microwave plasma area bound in the quartz torch glass tube; with this structure, the reaction gas is provided through the main feeding gas pipeline, and the raw materials are more smoothly input into the main feeding gas pipeline through the feeder gas pipeline to realize the supply of materials; the purpose of the main feeding gas pipeline is to blow the carbon nanotube powder brought into the main pipeline by the feeder gas pipeline to the quartz torch glass tube to prevent material accumulation.

[0021] Furthermore, the screw loss-in-weight metering feeder can be a single-screw or twin-screw structure, and can be flexibly adjusted as needed.

[0022] Furthermore, the screw loss-in-weight metering feeder is equipped with a weighing metering system and PLC control to improve intelligent operation.

[0023] Furthermore, the microwave plasma bound in the quartz torch glass tube leaves the quartz torch glass tube with the carrier gas and then enters the purification device, where the airflow of the microwave plasma weakens and diverges to form a divergent microwave plasma cloud; the above process can make it easier for the microwave plasma to fill the chamber of the purification device, thereby more fully contacting the raw material and improving the purification effect.

[0024] Furthermore, the main feed gas pipeline and the purification device are sealed by a sealing ring, and a water cooling structure is provided at the sealing ring; the above scheme can prevent gas leakage and can also effectively reduce the temperature and avoid damage to the sealing ring due to high temperature.

[0025] Furthermore, the diameter of the main feed gas pipeline is Φ10-40 mm, and its material is one of quartz, ceramic or stainless steel; it can facilitate the control of gas flow and is resistant to high temperatures.

[0026] Furthermore, when the main feed gas pipeline is made of stainless steel, the inner wall of the pipeline is sprayed with polytetrafluoroethylene or ceramic coating to prevent the reactive gas from corroding the pipeline.

[0027] Furthermore, a first gate valve is provided on the main feed gas pipeline to facilitate effective control of the feeding and closing of the feed pipe to meet the needs of different usage conditions.

[0028] Furthermore, the collection system includes a collecting tank, one end of which is connected to the discharge port of the purification device, and a second gate valve is provided between the two; a third gate valve is provided at the discharge end of the collecting tank, and a vacuum pump is connected to one side of the collecting tank, and the vacuum pump is used for vacuuming; with the above structure, the opening and closing of the two gate valves can be controlled as needed, and the vacuum pump can be used to ensure that the collecting tank is in a negative pressure state, thereby facilitating the unloading of materials, avoiding accumulation or residue, and improving the collection efficiency.

[0029] Furthermore, the collection method of the collection tank is intermittent, that is, the collection tank is first evacuated to negative pressure, the pressure is lower than the pressure in the purification device (as long as it is lower than the pressure in the purification chamber), and after the bottom of the purification device collects part of the purified carbon nanotube powder, the second gate valve is opened to collect the powder into the collection tank, and then the second gate valve is closed and the third gate valve is opened to collect the product; the intermittent method can ensure that the processing time of a batch of materials is consistent, and the processing time is insufficient if the materials are continuously unloaded.

[0030] Furthermore, the collecting tank is made of stainless steel and is sealed to the purification device via a sealing ring; adopting this solution will not cause the product to be adsorbed on the inner wall of the collecting tank, which is more conducive to the complete recovery of the material.

[0031] Furthermore, both the collection tank and the purification device are provided with observation windows; this structure can be used to observe the product status; sensors can also be set to monitor the product status and realize automatic collection.

[0032] Furthermore, the exhaust system includes an exhaust pipe connected to the purification device, an exhaust pump arranged on the exhaust pipe, and a fourth gate valve is also arranged on the exhaust pipe, and the fourth gate valve is located on the pipe between the purification device and the exhaust pump; with the above structure, the exhaust gas generated in the purification device can be timely extracted through the exhaust pump, and a part of the exhaust gas can also be absorbed by the exhaust gas filtering device to improve the emission standard of the exhaust gas; in addition, the function of the exhaust pump is to provide negative pressure for the chamber in the purification device, which is beneficial to the reaction of the reactive gas with the impurities in the carbon nanotube powder, so that the catalyst particles are more fully gasified; in addition, more importantly, the function of the exhaust pump is to provide negative pressure for the microwave plasma generating device in the initial stage to realize negative pressure ignition (negative pressure ignition is an ignition method that can convert microwaves into microwave plasma).

[0033] Furthermore, an exhaust gas filter device is provided on the exhaust pipe between the exhaust pump and the fourth gate valve; an alkaline solution is placed in the exhaust gas filter device, and this structure can be used to neutralize tail gas impurities.

[0034] Furthermore, a filter is provided at the connection between the exhaust pipe and the purification device, the mesh size of the filter is smaller than the particle size of the carbon nanotube powder, and the filter can intercept the product to prevent the purified powder from being discharged with the airflow.

[0035] Furthermore, the present application also provides a method for purifying carbon nanotubes using the above-mentioned microwave plasma purification device for carbon nanotubes, the method comprising:

[0036] (1) Connecting the components of the microwave plasma carbon nanotube purification device according to the connection relationship and ensuring the internal sealing, adding the carbon nanotube powder raw material to be purified into the screw weight loss metering feeder (screw weight loss feeder), and placing an alkaline solution in the exhaust gas filter device;

[0037] (2) Turn on the power of the microwave generator and the cooling water circulation in the water-cooling connecting pipe, close the first gate valve, the second gate valve and the third gate valve, open the exciting gas inlet pipeline, set the gas flow rate, turn on the exhaust pump to exhaust so that negative pressure is achieved in the cavity of the purification device, thereby achieving negative pressure ignition (no need to introduce a fire source, microwaves will automatically form microwave plasma flames under negative pressure);

[0038] (3) After ignition, adjust the excitation gas flow rate in the three-screw regulator and the excitation gas inlet pipe so that the microwave plasma fills the cavity of the purification device;

[0039] (4) Opening the first gate valve on the main feed gas pipeline, and starting the screw weight loss metering feeder, the feeder gas pipeline and the main feed gas pipeline, and adjusting the flow of carbon nanotube powder and each gas in proportion;

[0040] (5) After the purification reaction is completed, the purified carbon nanotube powder in the cavity of the purification device is transferred to a collection tank of the collection device.

[0041] Furthermore, the carbon nanotube powder in step (1) is crushed carbon nanotube powder, and the particle size of the powder is 20-400 mesh.

[0042] Furthermore, the carbon nanotube powder in step (1) is synthesized by a floating catalytic cracking method or an arc method, but is not limited thereto.

[0043] Furthermore, the catalyst contained in the carbon nanotube powder in step (1) is one or a mixture of iron-containing catalysts, cobalt-containing catalysts, and nickel-containing catalysts, but is not limited thereto.

[0044] Furthermore, the carbon nanotubes described in step (1) are single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, or a mixture of several thereof.

[0045] Furthermore, the negative pressure ignition in step (2) has a negative pressure in the range of -50 to -10 Bar.

[0046] Furthermore, the excitation gas entering the excitation gas inlet pipe is at least one of argon and helium and a trace amount of at least one of oxygen and water vapor (that is, the excitation gas contains at least one of argon and helium, and also contains at least one of oxygen and water vapor).

[0047] Furthermore, the pressure of the excitation gas input into the excitation gas inlet pipe is 0.4MPa to 0.8MPa, and the flow rate of the gas is in the range of 10L / min to 100L / min.

[0048] Furthermore, the content of oxygen or water vapor in the exciting gas is 0.01% to 0.1% (volume percentage), and the content is adjusted according to the amorphous carbon content in the graphene powder; but if the content is too low, the amorphous carbon in the component will not be completely removed, and if the content is too high, part of the carbon nanotubes will be oxidized and cause quality loss. The above content range can effectively overcome this defect.

[0049] Furthermore, the feeding speed of the screw loss-in-weight metering feeder is 1 g / min to 100 g / min.

[0050] Furthermore, the feeder gas pipeline is used to input a first carrier gas, and the first carrier gas is one of argon and helium or a mixture of the two; its purpose is to blow the carbon nanotubes in the feeder into the main feed gas pipeline to prevent material accumulation.

[0051] Furthermore, the carrier gas flow rate in the gas pipeline of the feeder is 1-15 L / min; if the flow rate is too large, it will cause inaccurate weighing, and if the flow rate is too small, the powder cannot be completely conveyed into the main pipeline, causing material accumulation.

[0052] Furthermore, the main feed gas pipeline is connected to a second carrier gas, and the second carrier gas is composed of an inert carrier gas and a reactive medium.

[0053] Furthermore, the inert carrier gas is one of argon and helium or a mixture of the two; the reactive medium is at least one of gases such as chlorine and hydrogen chloride, or at least one of liquids such as hydrochloric acid and nitric acid.

[0054] Furthermore, the flow rate of the second carrier gas is 10 to 100 L / min.

[0055] Furthermore, the volume ratio of the reactive medium in the total gas (the total gas here refers to the sum of the inert gas and the reactive gas in the main feed gas pipeline) is 1-10%.

[0056] Furthermore, when the reaction medium is a liquid (concentrated hydrochloric acid or concentrated nitric acid), the liquid is heated and vaporized or is bubbled into the main feed gas pipeline by an inert carrier gas.

[0057] Furthermore, the duration of the purification process is 30 to 500 seconds (starting from the start of feeding from the feeder); the purification time is related to factors such as the microwave plasma power, the size of the purification cavity, the purity of the carbon nanotube powder, and the content of the reaction gas. If the purification time is too short, the purification effect is not good. If the purification time is too long, some carbon nanotubes will be consumed, resulting in reduced purification efficiency and increased costs.

[0058] Furthermore, an alkaline solution, such as sodium hydroxide, potassium hydroxide, ammonia water, etc., is placed in the exhaust gas filtering device to neutralize tail gas impurities.

[0059] Furthermore, the morphology of the carbon nanotube powder obtained after the purification does not change, and the metal content therein is 0.02-0.1%, and the amorphous carbon content is less than 5%.

[0060] Compared with the prior art, the method of the present application has the following advantages and beneficial effects:

[0061] 1. The technical solution of the present application is the first to plasmatize the carrier gas and the reaction gas under negative pressure and microwave plasma environment to form high-energy ions, which are in full and direct contact with the carbon nanotube powder, react with the impurity metal catalyst particles and amorphous carbon in the carbon nanotubes, and form low-boiling point compounds (low-boiling point compounds such as ferric chloride, etc., have a boiling point of about 320°C, which is much lower than the boiling point of metal elements of 2750°C, while carbon nanotubes are single crystal materials with a boiling point of more than 4000°C; therefore, they can be effectively separated), and vaporize in a microwave field, and separate from the carbon nanotubes under negative pressure conditions, so as to achieve the purpose of purifying carbon nanotubes; the amorphous carbon is a carbon nanotube in a non-crystalline state, and its oxidation temperature is lower than that of the crystalline carbon nanotubes, and the trace amount of carbon in the excited gas is oxidized. Oxygen or water vapor can preferentially etch non-crystalline amorphous carbon, thereby removing the amorphous carbon in the raw material; therefore, the scheme of the present application not only removes metal catalysts but also removes amorphous carbon, thereby expanding the types of impurities removed; the scheme of the present application adjusts the process parameters and the layout of the device to allow microwave plasma to form a microwave plasma cloud that fills the cavity of the purification device, and by extending the residence time of the carbon nanotube powder in the cavity of the purification device (the present application adopts intermittent purification, which can extend the residence time, the purification time is 30 to 500s), the amount of reaction gas used is greatly reduced, and the catalyst particles and amorphous carbon are efficiently removed in situ (partial removal will still leave a small amount of residue, but it will not affect the subsequent further application of carbon nanotubes).

[0062] 2. The technical solution of the present application utilizes microwave plasma for the first time to purify carbon nanotube powder in situ. The solution can remove amorphous carbon and metal catalysts in one step without the need for complex processes such as air oxidation, acid washing or high-temperature purification. Compared with the prior art, the solution avoids the use of large amounts of strong acid and does not cause waste acid and wastewater pollution to the product. In addition, compared with traditional high-temperature purification methods, the present application utilizes microwave plasma microscopic ultra-high energy to gasify metal catalysts in situ, requiring less energy. Compared with traditional reactive gas methods (such as chlorine), the dosage is greatly reduced, and the carbon-coated metal catalyst particles can be effectively removed, which greatly reduces the production cost and is suitable for large-scale industrial production.

[0063] 3. The present application maintains a slight negative pressure state in the purification device during the purification process. This negative pressure state is conducive to the sufficient contact between the reaction gas and the catalyst to remove the catalyst, and is also conducive to the gasification product being discharged from the cavity with the carrier gas; the method described in the present application can achieve a purification amount of 50 to 1000 g (raw material weight) per batch; the feed system and the purification device of the present application are connected vertically, which can make the carbon nanotubes more fully contact with the microwave plasma.

[0064] 4. Since carbon nanotubes synthesized by floating catalytic cracking or arc method contain a certain amount of impurities such as amorphous carbon and metal catalysts, these impurities will affect the specific use effect of carbon nanotubes in subsequent refined applications; the scheme of the present application is the first to purify the carbon nanotubes by combining microwave plasma and negative pressure for the above impurities; the scheme can effectively remove the above impurities, so that their content is greatly reduced (after purification, the metal content is 0.02-0.1%, and the amorphous carbon content is less than 5%); the present application gasifies the metal catalyst in the microwave field (that is, the original solid state existing in the carbon nanotubes is vaporized in the microwave field); The metal catalyst in the carbon nanotube raw material is converted into a gaseous low-boiling point compound in a microwave field, and this change in morphology in a specific scenario is used to separate it from the carbon nanotubes), and then it is separated from the carbon nanotubes by negative pressure extraction; by adding a trace amount of oxygen or water vapor to the excited gas, the non-crystalline amorphous carbon can be preferentially etched in the microwave plasma field, thereby removing the amorphous carbon in the raw material; therefore, the solution of the present application is a new purification method for the metal catalyst as the main impurity in the prepared carbon nanotubes, which effectively removes the metal catalyst and amorphous carbon and improves the purity of the carbon nanotubes. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 This is a schematic diagram of the structure of an exemplary carbon nanotube purification device of the present application.

[0066] Figure 2 This is a schematic diagram of the structure of another exemplary carbon nanotube purification device of the present application.

[0067] Figure 3 This is the TGA curve before purification of Example 1 of the present application.

[0068] Figure 4 This is the TGA curve after purification of Example 1 of the present application.

[0069] As shown in the attached drawings: 1. Microwave plasma generating device, 101. Microwave generator, 102. Waveguide, 103. Blender, 104. Microwave plasma head, 105. Excitation gas inlet pipeline, 106. Water-cooling connecting pipe, 107. Quartz torch glass tube, 108. Microwave plasma area, 2. Purification device, 3. Feeding system, 301. Screw weight loss metering feeder, 302. Main feeding gas pipeline, 303. Feeder gas pipeline, 304. First gate valve, 4. Collection system, 401. Collection tank, 402. Second gate valve, 403. Third gate valve, 404. Vacuum pump, 5. Exhaust system, 501. Exhaust pipeline, 502. Exhaust pump, 503. Fourth gate valve, 504. Exhaust gas filtering device, 505. Filter, 6. Sealing ring, 7. Observation window. DETAILED DESCRIPTION

[0070] The following will combine the embodiments and drawings to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only preferred embodiments, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application;

[0071] It should also be noted that when a component is referred to as being "fixed to" another component, it may be directly on the other component or there may be another intermediate component, fixed through the intermediate component. When a component is considered to be "connected" to another component, it may be directly connected to the other component or there may be another intermediate component at the same time. When a component is considered to be "set on" another component, it may be directly set on the other component or there may be another intermediate component at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by technicians in the technical field of this application. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0072] The microwave generator, waveguide and three-screw adapter of the present application can all be commercially available products, and all components in the device of the present application can be obtained through market channels unless otherwise specified. The sealing ring of the present application can also be a commercially available high-temperature resistant sealing ring to improve its sealing effect and extend its service life.

[0073] The following is described by specific embodiments and the following devices:

[0074] As attached Figure 1-2 As shown, a carbon nanotube purification device of the present application includes a microwave plasma generating device 1, a purification device 2, a feeding system 3, a collecting system 4 and an exhaust system 5; the microwave plasma generating device 1 is used to transmit microwaves to the purification device to form microwave plasma, and its structure includes a microwave generator 101, a waveguide 102, a mixer 103 and a microwave plasma head 104, the microwave generator 101 is connected to the waveguide 102 and transmits microwaves through the waveguide 102, the mixer 103 is arranged on the waveguide 102 and is used to adjust the microwave reflection power, and the microwave plasma head 104 is connected to the waveguide 102 and is used to introduce microwaves into the purification device 2; the feeding system 3 is connected to the purification device 2 (specifically, the feeding system is connected to the connection and overlap between the purification device and the plasma generating device; the purification device of the present application is a cylindrical hollow tube structure, which is vertically arranged to facilitate the generation and dispersion of microwave plasma and can fully contact with the raw materials; the feeding direction of the feeding system can be perpendicular to the extension direction of the microwave plasma), the collecting system 3 is connected to the discharge port of the purification device 2 (specifically, the discharge port is arranged at the lower end of the purification device to facilitate the downward movement and transportation of materials), and the exhaust system 5 is connected to the purification device 2; the purification device 2 is in a negative pressure state.

[0075] By adopting the above structure, the present application uses microwave plasma to purify carbon nanotubes for the first time. By continuously conveying the carbon nanotube powder to the microwave lining area through the feeding system under negative pressure conditions, the carbon nanotube powder forms a vortex in the purification device under the action of the airflow, and is directly and fully contacted with the microwave plasma. The impure metal catalyst particles therein form gaseous products under the action of microwave plasma, oxidizing environment and negative pressure, which are discharged from the exhaust system and separated from the carbon nanotubes, thereby achieving the purpose of purifying the carbon nanotubes; this scheme avoids the use of strong acid and will not cause waste acid and wastewater pollution to the product; in addition, compared with the traditional high-temperature purification method, this scheme uses microwave plasma to directly contact the raw material, thereby realizing microscopic ultra-high energy in-situ gasification of the metal catalyst, and the energy required is lower; compared with the traditional reactive gas (such as chlorine) method, the dosage is greatly reduced, and at the same time, the carbon-coated metal catalyst particles and impurities such as amorphous carbon can be effectively removed, which greatly reduces the production cost and is suitable for large-scale industrial production.

[0076] As attached Figure 1-2 As shown, the microwave plasma head 104 described in the present application includes an excitation gas inlet pipeline 105, a water-cooling connecting pipe 106 and a quartz torch glass tube 107, wherein the water-cooling connecting pipe 106 is coated on the outer wall of the quartz torch glass tube 107, the excitation gas inlet pipeline 105 is connected to the quartz torch glass tube 107, and the waveguide 102 is in contact with the quartz torch glass tube 107; specifically, the excitation gas inlet pipeline 105 is arranged on the axial upper end surface of the quartz torch glass tube and is connected to the inside, for excitation The water-cooled connecting pipe 106 is coated on the outer peripheral wall of one end of the quartz torch glass tube 107 close to the exciting gas inlet pipeline 105, close to the negative pressure ignition position, and convenient for cooling; with the above structure, the quartz torch glass tube is used as a container for forming and containing microwave plasma, and microwaves can be transported through the waveguide and then penetrate the tube wall of the quartz glass tube to form microwave plasma, and then fully contact with the carbon nanotubes transported by the feeding system to achieve purification, thereby increasing the contact area between the carbon nanotubes and the microwave plasma and increasing the purification efficiency; Figure 1-2 The quartz torch glass tube and the purification device are presented in a partially cutaway manner so that the inside can be visible, so as to facilitate a more intuitive understanding of the technical solution of the present application.

[0077] As an example, the quartz torch glass tube (quartz tube) described in the present application has an outer diameter of Φ20-100 mm, a wall thickness of 3-8 mm, and a length of 200-500 mm; microwaves ionize the carrier gas in the quartz tube to form microwave plasma, which moves downward under the action of the airflow. The diameter of the quartz tube determines the energy density of the microwave plasma. The smaller the diameter, the greater the energy density and the higher the local temperature. Since the quartz tube has a temperature resistance of only 1150°C, the service life of the quartz tube can be extended by controlling the size of the quartz tube; at the same time, the carbon nanotube powder enters from the entrance on one side of the quartz tube. If the diameter is too large, the wall of the quartz tube cannot restrain the shape of the microwave plasma, resulting in an uneven microwave field; therefore, the use of the quartz tube of the above-mentioned specifications of the present application can effectively solve the above-mentioned technical problems, form a uniform microwave field in the tube body, and is conducive to the full purification of the carbon nanotubes.

[0078] Specifically, as attached Figure 1-2 As shown, the microwave plasma flame generated by the microwave plasma head 104 described in the present application extends vertically from top to bottom in the quartz torch glass tube 107, the cooling method is water cooling (that is, water cooling is achieved by circulating water in the water-cooling connecting pipe), and the ignition method is negative pressure excitation; negative pressure ignition can convert microwaves into microwave plasma, thereby increasing the contact area between the raw material and the microwave plasma and improving the purification efficiency.

[0079] As an example, see Figure 2As shown, the purification device 2 described in the present application is made of double-layer water-cooled stainless steel, ceramic or quartz material; that is, it has an interlayer, and a water cooling cycle can be set in the interlayer for cooling; by using the above-mentioned materials, the microwave plasma can be confined in the purification device, the loss of microwave plasma can be reduced, and the purification efficiency can be improved; when the purification device is made of double-layer water-cooled stainless steel, its inner wall is sprayed with a ceramic coating. By using this structure, the secondary contamination of the purified carbon nanotube powder by metal (stainless steel material) can be prevented.

[0080] As an example, the inner diameter of the purification device 2 described in the present application is Φ30~400mm, and the length is 200~1000mm; since the diameter and length of the purification device are related to the power of microwave plasma and the supply speed of carbon nanotube powder, the purpose is to ensure the residence time of carbon nanotube powder in the purification cavity, and compress the microwave plasma area as much as possible so that the microwave plasma fills the entire cavity, so that the carbon nanotube powder is more fully in contact with the microwave plasma, the reaction is more thorough, and the degree of impurity removal is high.

[0081] As attached Figure 1-2 As shown, the quartz torch glass tube 107 described in the present application is embedded in the cavity of the purification device 2, the embedding distance is 100 to 500 mm, and is sealed and connected to the purification device 2 through a sealing ring 6; the sealing ring here can adopt a water-cooled sealing ring for timely and effective cooling, and this structure can make the feed fully contact with the microwave plasma; in the present application, a metal cover or other materials capable of shielding microwaves can be set at the position where the outer wall of the quartz torch glass tube is not covered by the purification device, that is, a material that prevents microwaves from being lost from the quartz tube, thereby improving the efficiency of converting microwaves into microwave plasma and improving the purification performance.

[0082] As an example, the microwave generator 101 described in the present application has a power of 10-75 kW and a microwave frequency of 915 MHZ.

[0083] As an example, the waveguide 102 described in the present application is a metal conduit. With this structure, microwaves can be effectively transmitted into the quartz torch glass tube and the loss of microwaves can be reduced. Then, the gas can be excited under negative pressure conditions to form microwave plasma.

[0084] As an example, the adapter 103 described in the present application is a three-screw adapter, which can adjust the microwave reflection power by changing the depth of three independent screws (microwave power supply power = microwave reflection power + microwave power in the reactor, the microwave power supply power is constant, and the microwave power in the reactor can be indirectly adjusted by adjusting the microwave reflection power).

[0085] As attached Figure 1-2As shown, the feeding system 3 described in the present application includes a screw loss-in-weight metering feeder 301, a main feeding gas pipeline 302 and a feeder gas pipeline 303; one end of the main feeding gas pipeline 302 is connected to the quartz torch glass tube 107, and the main feeding gas pipeline 302 is also connected to the feeder gas pipeline 303, and the feeder gas pipeline 303 is connected to the outlet of the screw loss-in-weight metering feeder 301, and is used to load the carbon nanotubes into the microwave plasma area 108 bound in the quartz torch glass tube 107; with this structure, the reaction gas is provided through the main feeding gas pipeline, and the raw materials are more smoothly input into the main feeding gas pipeline through the feeder gas pipeline, so as to realize the supply of materials; the purpose of the main feeding gas pipeline is to blow the carbon nanotube powder brought into the main pipeline by the feeder gas pipeline to the quartz torch glass tube to prevent material accumulation.

[0086] As an example, the screw loss-in-weight metering feeder 101 described in this application can be a single screw or a twin screw structure, which can be flexibly adjusted as needed; for commercially available feeding devices, the corresponding model is selected according to the specific feeding conditions of each batch. More specifically, the screw loss-in-weight metering feeder is equipped with a weighing and metering system and PLC control to improve intelligent operation. For commercially available products, the screw loss-in-weight metering feeder equipped with the above-mentioned weighing and metering system and PLC control can be used in this application.

[0087] As attached Figure 1-2 As shown, the microwave plasma trapped in the quartz torch glass tube 107 described in the present application leaves the quartz torch glass tube 107 with the carrier gas, and then enters the purification device 2, where the airflow of the microwave plasma weakens and diverges (the tube diameter of the purification device becomes larger), forming a divergent microwave plasma cloud; the above process can make it easier for the microwave plasma to fill the chamber of the purification device 2, thereby more fully contacting the raw material and improving the purification effect.

[0088] As attached Figure 1-2 As shown, the main feed gas pipeline 302 described in the present application is sealed with the purification device 2 by a sealing ring 6, and a water cooling structure is provided at the sealing ring 3 (specifically, cooling can be achieved by building a cooling water circulation pipe inside the sealing ring, etc.); the above scheme can avoid gas leakage, and can also effectively reduce the temperature and avoid damage to the sealing ring due to high temperature.

[0089] As an example, the diameter of the main feed gas pipeline 302 described in the present application is Φ10-40 mm, and its material is one of quartz, ceramic or stainless steel; it can facilitate the control of gas flow and is resistant to high temperatures.

[0090] As an example, when the main feed gas pipeline 302 is made of stainless steel, the inner wall of the pipeline is sprayed with polytetrafluoroethylene or ceramic coating to prevent the reactive gas from corroding the pipeline.

[0091] As attached Figure 1-2 As shown, the main feed gas pipeline 302 described in the present application is provided with a first gate valve 304 to control the opening and closing of the pipeline, so as to facilitate the effective control of the feeding and closing of the feed pipe to meet the needs of different usage conditions.

[0092] As attached Figure 1-2 As shown, the collection system 4 described in the present application includes a collecting tank 401, one end of the collecting tank 401 is connected to the discharge port of the purification device 2, and a second gate valve 402 is also arranged between the two, that is, it is arranged on the pipeline connecting the two and is used to control the opening and closing of the pipeline; a third gate valve 403 is arranged at the discharge end of the collecting tank 401, and a vacuum pump 404 is connected to one side of the collecting tank 401, and the vacuum pump 404 is used for vacuuming; specifically, the collecting tank is located at the lower end outlet position of the purification device, and a pipeline is arranged on the side wall of the collecting tank to connect with the vacuum pump. By adopting the above structure, the opening and closing of the two gate valves can be controlled as needed, and the vacuum pump can be used to evacuate the inside of the collecting tank to ensure that the inside of the collecting tank is in a negative pressure state, thereby facilitating the unloading of materials, avoiding accumulation or residue, and improving the collection efficiency.

[0093] As an example, the collection method of the collection tank 401 described in the present application is intermittent, that is, the collection tank is first evacuated to negative pressure, the pressure is lower than the pressure in the purification device (as long as it is lower than the pressure in the purification chamber), and when the bottom of the purification device collects part of the purified carbon nanotube powder, the second gate valve is opened to collect the powder into the collection tank, and then the second gate valve is closed and the third gate valve is opened to collect the product; the intermittent method can ensure that the processing time of a batch of materials is consistent. If the materials are unloaded continuously, the processing time will be insufficient.

[0094] As an example, the collecting tank 401 described in the present application is made of stainless steel and is sealed to the purification device 2 via a sealing ring 6; adopting this solution will not cause the product to be adsorbed on the inner wall of the collecting tank, which is more conducive to the complete recovery of the material.

[0095] As attached Figure 2 As shown, the collection tank 401 described in the present application and the purification device 2 described are both provided with an observation window 7, that is, a transparent observation window, through which the internal situation can be seen; this structure can be used to observe the product situation; a sensor can also be set to monitor the product status to achieve automatic collection; the sealing ring material, observation window material, etc. of the present application can be a high-temperature resistant material, that is, a high-temperature resistant material that will not cause material damage in the negative pressure plasma reaction field of the present application can be suitable for the present application.

[0096] As attached Figure 1-2 As shown, the exhaust system 5 described in the present application includes an exhaust pipe 501 connected to the purification device 2, an exhaust pump 502 arranged on the exhaust pipe 501, and a fourth gate valve 503 is also arranged on the exhaust pipe 501, and the fourth gate valve 503 is located on the pipe between the purification device 2 and the exhaust pump 502; with the above structure, the exhaust gas generated in the purification device can be timely extracted through the exhaust pump, and a part of the exhaust gas can also be absorbed by the exhaust gas filtering device to improve the emission standard of the exhaust gas; in addition, the function of the exhaust pump is to provide negative pressure for the chamber in the purification device, which is beneficial to the reaction of the reactive gas with the impurities in the carbon nanotube powder, so that the catalyst particles are more fully gasified; in addition, more importantly, the function of the exhaust pump is to provide negative pressure for the microwave plasma generating device in the initial stage to realize negative pressure ignition (negative pressure ignition is an ignition method that can convert microwaves into microwave plasma).

[0097] As attached Figure 1-2 As shown, a filter screen 505 is provided at the connection between the exhaust pipe 501 described in the present application and the purification device 2. The mesh size of the filter screen 505 is smaller than the particle size of the carbon nanotube powder. The filter screen can intercept the product and prevent the purified powder from being discharged with the airflow.

[0098] As an example, an exhaust gas filter device 504 is also provided on the exhaust pipe 501 described in the present application between the exhaust pump 502 and the fourth gate valve 503; an alkaline solution is placed in the exhaust gas filter device 504, and this structure can be used to neutralize tail gas impurities.

[0099] In the example of this application, the microwave generator is set to have a rated power of 25kW and a frequency of 915HZ, and the power can be adjusted by a three-screw adjuster; the inner diameter of the quartz torch head glass tube (i.e., a glass tube made of quartz material) is 50mm, the wall thickness is 5mm, and the length is 300mm; the inner diameter of the purification device is 300mm, the height (length) is 500mm, and the length of the quartz tube embedded in the purification device is 150mm.

[0100] The carbon nanotube powder raw material used in the present application is a raw material prepared by a floating catalytic cracking method, wherein the amorphous carbon content in the carbon nanotubes prepared by the floating catalytic cracking method is 12.2%, and the content of the metal catalyst is 20%; the particle size of the carbon nanotube fibers prepared by this method after crushing can pass through a 60-80 mesh sieve.

[0101] Example 1

[0102] 1) Add 1000 g of carbon nanotube powder into a screw weight-loss metering feeder, and place 20 L of 10 M sodium hydroxide solution in an exhaust gas filter;

[0103] 2) Turn on the microwave power supply and circulating cooling water, close the first gate valve on the main feed gas pipeline and the second and third gate valves on the collecting device, open the valve of the exciting gas inlet pipeline to introduce argon gas, the gas pressure is 0.6Mpa, the flow rate is 10L / min, turn on the exhaust pump to exhaust, so that the pressure in the cavity of the purification device is maintained at -10bar, and perform negative pressure ignition.

[0104] 3) After ignition, adjust the three-screw dispenser to adjust the microwave output power to 20kw, adjust the argon flow rate to 50L / min, and the oxygen flow rate to 25mL / min, so that the microwave plasma fills the purification cavity;

[0105] 4) Open the plug valve on the main feed gas pipeline, start the screw weightlessness metering feeder, the feeder gas pipeline to feed carrier gas, and the main feed gas pipeline to feed carrier gas, set the powder feeding speed to 50g / min, and set the argon gas inlet carrier gas flow rate of the feeder gas pipeline to 10L / min, the argon gas flow rate of the main feed gas pipeline to 30L / min, and the chlorine gas flow rate to 450mL / min; 5) Control the air pressure in the purification process of the purification device by the exhaust pump to maintain at -15 to -10bar, and the purification time is 300s;

[0106] 6) After the purification is completed, the feeding is stopped, the gate valve on the collection tank is opened, and the carbon nanotube powder in the cavity of the purification device is transferred to the cavity of the collection tank by using the pressure difference.

[0107] In this embodiment, the mass percentage content of metal (metal catalyst) in the purified carbon nanotubes is 0.03%, and the mass percentage content of amorphous carbon is 3.53%.

[0108] like Figure 3-4 As shown, they are unpurified single-walled carbon nanotube powder ( Figure 3 ) and carbon nanotube powder purified by microwave plasma ( Figure 4 ), with mass percentage as the ordinate, indicating mass reduction; and temperature as the abscissa; they describe how the weight of the sample changes with temperature or time under a specific program, that is, the ratio of the weight of the sample under current conditions to the initial weight; from the figure, it can be seen that the initial decomposition temperature of the single-walled carbon nanotube powder is about 400°C (the determination of the initial decomposition temperature can be achieved by finding the intersection of the horizontal tangent before the TG step and the tangent at the inflection point of the curve), and the terminal decomposition temperature is about 860°C; the thermal weight loss before 400°C is mainly caused by moisture and amorphous carbon impurities in the powder, and the decomposition temperature of amorphous carbon is between 300 and 400°C; after 860°C, the catalyst metal iron of the powder is oxidized to form iron oxide, and the residual mass increases with increasing temperature.

[0109] Example 2

[0110] 1) Add 1000g of carbon nanotube powder into a screw weight-loss metering feeder, and place 20L of 10M sodium hydroxide solution in an exhaust gas filter;

[0111] 2) Turn on the microwave power supply and circulating cooling water, close the first gate valve on the main feed gas pipeline and the second and third gate valves on the collecting device, open the valve of the exciting gas inlet pipeline to introduce argon gas, the gas pressure is 0.6Mpa, the flow rate is 10L / min, turn on the exhaust pump to exhaust, so that the pressure in the purification chamber is maintained at -10bar, and perform negative pressure ignition.

[0112] 3) After ignition, adjust the three-screw dispenser to adjust the microwave output power to 20kw, adjust the argon flow rate to 50L / min, and the oxygen flow rate to 50mL / min, so that the microwave plasma fills the purification cavity;

[0113] 4) Open the plug valve on the main feed gas pipeline, start the screw weightlessness metering feeder, the feeder gas pipeline to feed carrier gas, and the main feed gas pipeline to feed carrier gas, set the powder feeding speed to 200g / h, and set the argon gas inlet carrier gas flow rate of the feeder gas pipeline to 10L / min, the argon gas flow rate of the main feed gas pipeline to 30L / min, and the chlorine gas flow rate to 600mL / min; 5) Control the air pressure of the purification process to be maintained at -15 to -10bar by the exhaust pump, and the purification time is 500s;

[0114] 6) After the purification is completed, the feeding is stopped, the plug valve on the collection chamber is opened, and the carbon nanotube powder in the purification chamber is transferred to the collection chamber by using the pressure difference.

[0115] After purification, the metal content of this embodiment is 0.02%, and the amorphous carbon content is 2.18%.

[0116] Example 3

[0117] 1) Add 1000g of carbon nanotube powder into a screw weight-loss metering feeder, and place 20L of 10M sodium hydroxide solution in an exhaust gas filter;

[0118] 2) Turn on the microwave power supply and circulating cooling water, close the gate valve on the main feed pipeline (main feed gas pipeline) and the gate valve on the collection device, open the valve of the excitation gas pipeline (excitation gas inlet pipeline) to introduce argon gas, with a pressure of 0.6Mpa and a flow rate of 10L / min, turn on the exhaust pump to exhaust, so that the pressure in the cavity of the purification device is maintained at -10bar, and perform negative pressure ignition. 3) After ignition, adjust the three-screw dispenser to adjust the microwave output power to 20kw, adjust the argon flow rate to 50L / min, and the oxygen flow rate to 10mL / min, so that the microwave plasma fills the cavity of the purification device;

[0119] 4) Open the main feed pipeline valve, and start the weightless metering feeder, feeder inlet carrier gas, and main pipeline inlet carrier gas, set the powder supply rate to 200g / h, and set the feeder (feeder gas pipeline) argon inlet carrier gas flow rate to 10L / min, the main pipeline (main feed gas pipeline) argon gas flow rate to 30L / min, and the chlorine gas flow rate to 300mL / min;

[0120] 5) The gas pressure of the purification device during the purification process is maintained at -15 to -10 bar by controlling the exhaust pump, and the purification time is 100 seconds;

[0121] 6) After the purification is completed, the feeding is stopped, the plug valve on the collection chamber is opened, and the carbon nanotube powder in the purification chamber is transferred to the collection chamber by using the pressure difference.

[0122] After purification, the metal content of this embodiment is 0.05%, and the amorphous carbon content is 4.95%.

[0123] Example 4

[0124] 1) Add 1000 g of carbon nanotube powder into a screw weight-loss metering feeder, and place 20 L of 10 M sodium hydroxide solution in an exhaust gas filter;

[0125] 2) Turn on the microwave power supply and circulating cooling water, close the main feed pipeline gate valve and the gate valve on the collecting device, open the exciting gas pipeline valve to introduce argon gas, the gas pressure is 0.6Mpa, the flow rate is 10L / min, turn on the exhaust pump to exhaust, so that the pressure in the purification chamber is maintained at -10bar, and perform negative pressure ignition.

[0126] 3) After ignition, adjust the three-screw dispenser to adjust the microwave output power to 10kw, adjust the argon flow rate to 20L / min, and the oxygen flow rate to 5mL / min, so that the microwave plasma fills the purification cavity;

[0127] 4) Open the main feed pipeline valve, and start the weightless metering feeder, feeder inlet gas carrier, and main pipeline inlet gas carrier, set the powder supply rate to 50g / h, and set the feeder argon inlet gas flow rate to 5L / min, the main pipeline argon gas flow rate to 15L / min, and the chlorine gas flow rate to 90mL / min;

[0128] 5) The air pressure during the purification process is controlled by an exhaust pump and maintained at -15 to -10 bar, and the purification time is 300 seconds;

[0129] 6) After the purification is completed, the feeding is stopped, the plug valve on the collection chamber is opened, and the carbon nanotube powder in the purification chamber is transferred to the collection chamber by using the pressure difference.

[0130] After purification, the metal content of this embodiment is 0.04%, and the amorphous carbon content is 4.31%.

[0131] Example 5

[0132] 1) Add 1000 g of carbon nanotube powder into a screw weight-loss metering feeder, and place 20 L of 10 M sodium hydroxide solution in an exhaust gas filter;

[0133] 2) Turn on the microwave power supply and circulating cooling water, close the main feed pipeline gate valve and the gate valve on the collecting device, open the exciting gas pipeline valve to introduce argon gas, the gas pressure is 0.6Mpa, the flow rate is 10L / min, turn on the exhaust pump to exhaust, so that the pressure in the purification chamber is maintained at -10bar, and perform negative pressure ignition.

[0134] 3) After ignition, adjust the three-screw dispenser to adjust the microwave output power to 10 kW, the argon flow rate to 20 L / min, and the water vapor flow rate to 5 mL / min, so that the microwave plasma fills the purification cavity;

[0135] 4) Open the main feed pipeline valve, and start the weightless metering feeder, feeder inlet gas carrier, and main pipeline inlet gas carrier, set the powder supply rate to 50g / h, and set the feeder argon inlet gas flow rate to 5L / min, the main pipeline argon gas flow rate to 15L / min, and the hydrogen chloride flow rate to 90mL / min;

[0136] 5) The air pressure during the purification process is controlled by an exhaust pump and maintained at -15 to -10 bar, and the purification time is 300 seconds;

[0137] 6) After the purification is completed, the feeding is stopped, the plug valve on the collection chamber is opened, and the carbon nanotube powder in the purification chamber is transferred to the collection chamber by using the pressure difference.

[0138] After purification, the metal content of this embodiment is 0.05%, and the amorphous carbon content is 4.69%.

[0139] Comparative Example 1

[0140] The same as Example 1, except that the oxygen flow rate in step 3) is set to 0, and the purification result shows that the amorphous carbon content is 10.7%;

[0141] Comparative Example 2

[0142] The same as Example 1, except that the oxygen flow rate in step 3) is set to 100 mL / min. The purification results show that the weight of the collected powder is reduced by about 20% compared with Example 1;

[0143] Comparative Example 3

[0144] The same as Example 1, except that the chlorine gas flow rate in step 4) is set to 0. The purification results show that the content of the metal catalyst in the collected product is 3.9%;

[0145] Comparative Example 4

[0146] The same as Example 1, except that the chlorine flow rate in step 4) was set to 1.5 L / min. The purification results showed that the metal catalyst content in the collected product was 0.01%, but the equipment pipeline was corroded;

[0147] Comparative Example 5

[0148] The same as Example 1, except that in step 5), the purification process is at normal pressure (i.e., the purification is carried out under normal pressure conditions inside the equipment rather than under negative pressure). The purification results show that the metal catalyst content in the collected product is 9.8%;

[0149] Comparative Example 6

[0150] The same as Example 1, except that in step 5), the purification time is 20 seconds, and the metal catalyst content in the collected product is 1.9%;

[0151] Comparative Example 7

[0152] The same as Example 1, except that in step 5), the purification time is 1000s, and the metal catalyst content in the collected product is 0.02%, but the powder weight is reduced by about 5% compared with Example 1;

[0153] Through the above examples and comparative examples, the results are analyzed: from Examples 1 to 5, it can be seen that under the same conditions, within a certain range, as the oxygen content in the system increases, the amorphous carbon content decreases; as the reactive gas chlorine content increases, the metal catalyst content in the powder decreases. However, when there is no oxidizing gas oxygen in the system (Comparative Example 1), the amorphous carbon in the system increases significantly to 10.7%, and when the oxygen content in the system is too high (Comparative Example 2), the mass of the collected powder product decreases significantly, which indicates that in a large amount of oxygen environment, some carbon nanotubes are oxidized and lost in microwave plasma; the type of reactive gas also has a certain influence on the purification effect of the catalyst. From Example 5, it can be seen that the effect of hydrogen chloride is slightly worse than that of chlorine. When there is no reactive gas chlorine in the system (Comparative Example 3), the metal catalyst content in the product increases significantly, but it is still significantly reduced compared with the metal catalyst content in the initial state. This is because the local high temperature of microwave plasma makes it easier to gasify the catalyst free on the surface of the carbon nanotube, and the metal catalyst wrapped in the carbon layer needs to be effectively removed in an oxidizing atmosphere; when the reactive gas chlorine content in the system is too high (Comparative Example 4), the metal catalyst content is further reduced, but excessive chlorine corrodes the purification cavity agent seal, which is not conducive to large-scale production. The results of Comparative Example 5 show that maintaining a slight negative pressure during the purification process is helpful for the purification effect, because the catalyst particle gasification temperature is lower under negative pressure conditions. Comparative Examples 6 and Comparative Examples 7 show that the purification time also has a certain effect on the purification effect. When the purification time is too short, the purification effect is not good; if the purification time is too long, high-energy microwave plasma will destroy the carbon nanotube structure, resulting in a decrease in product yield.

[0154] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the principles and spirit of the present application are included in the protection scope of the present application.

Claims

1. A carbon nanotube purification device, characterized in that: The device comprises a microwave plasma generating device (1), a purification device (2), a feeding system (3), a collecting system (4) and an exhaust system (5); the microwave plasma generating device (1) is used to transport microwave plasma into the purification device (2), and its structure comprises a microwave generator (101), a waveguide (102), a mixer (103) and a microwave plasma head (104); the microwave generator (101) is connected to the waveguide (102) and transmits microwaves through the waveguide (102); The mixer (103) is arranged on the waveguide (102) for adjusting the microwave reflection power; the microwave plasma head (104) is connected to the waveguide (102) and is used to introduce microwaves into the purification device (2); the feeding system (3) is connected to the purification device (2); the collecting system (4) is connected to the discharge port of the purification device (2); the exhaust system (5) is connected to the purification device (2); the purification device (2) is in a negative pressure state; The microwave plasma head (104) comprises an excitation gas inlet pipeline (105), a water-cooling connecting pipe (106) and a quartz torch glass tube (107); the water-cooling connecting pipe (106) is coated on the outer wall of the quartz torch glass tube (107), the excitation gas inlet pipeline (105) is connected to the quartz torch glass tube (107), and the waveguide (102) is in contact with the quartz torch glass tube (107).

2. The carbon nanotube purification device according to claim 1, characterized in that: The outer diameter of the quartz torch glass tube (107) is Φ20-100 mm, the wall thickness is 3-8 mm, and the length is 200-500 mm.

3. The carbon nanotube purification device according to claim 1, characterized in that: The microwave plasma flame generated by the microwave plasma head (104) extends vertically from top to bottom in the quartz torch glass tube (107), the cooling method is water cooling, and the ignition method is negative pressure excitation.

4. The carbon nanotube purification device according to claim 1, characterized in that: The purification device (2) is made of double-layer water-cooled stainless steel, ceramic or quartz material.

5. The carbon nanotube purification device according to claim 4, characterized in that: The inner wall of the purification device (2) made of double-layer water-cooled stainless steel is sprayed with a ceramic coating.

6. The carbon nanotube purification device according to claim 1, characterized in that: The inner diameter of the purification device (2) is Φ30-400 mm and the length is 200-1000 mm; the quartz torch glass tube (107) is embedded in the cavity of the purification device (2) at a distance of 100-500 mm and is sealed and connected to the purification device (2) through a sealing ring (6).

7. The carbon nanotube purification device according to claim 1, characterized in that: The power of the microwave generator (101) is 10-75kw, and the microwave frequency is 915MHZ; the waveguide (102) is a metal conduit for transmitting microwaves, which then enter the quartz torch glass tube (107) and then excite the gas under negative pressure conditions to form microwave plasma; the mixer (103) is a three-screw mixer.

8. The carbon nanotube purification device according to claim 1, characterized in that: The feeding system (3) comprises a screw weight loss metering feeder (301), a main feeding gas pipeline (302) and a feeder gas pipeline (303); one end of the main feeding gas pipeline (302) is interconnected with the quartz torch glass tube (107), and the main feeding gas pipeline (302) is also connected to the feeder gas pipeline (303), and the feeder gas pipeline (303) is connected to the outlet of the screw weight loss metering feeder (301) and is used to load carbon nanotubes into the microwave plasma region bound in the quartz torch glass tube (107).

9. The carbon nanotube purification device according to claim 8, characterized in that: The screw weight loss metering feeder (301) is a single screw or twin screw structure; the screw weight loss metering feeder (301) is equipped with a weighing metering system and PLC control.

10. The carbon nanotube purification device according to claim 8, characterized in that: The microwave plasma bound in the quartz torch glass tube (107) leaves the quartz torch glass tube (107) along with the carrier gas and then enters the purification device (2), whereupon the airflow of the microwave plasma weakens and diverges, forming a divergent microwave plasma cloud.

11. The carbon nanotube purification device according to claim 8, characterized in that: The main feed gas pipeline (302) and the purification device (2) are sealed by a sealing ring (6), and a water cooling structure is provided at the sealing ring (6).

12. The carbon nanotube purification device according to claim 8, characterized in that: The main feed gas pipeline (302) has a diameter of Φ10-40 mm and is made of quartz, ceramic or stainless steel.

13. The carbon nanotube purification device according to claim 12, characterized in that: When the main feed gas pipeline (302) is made of stainless steel, the inner wall of the pipeline is sprayed with polytetrafluoroethylene or ceramic coating; the main feed gas pipeline (302) is provided with a first gate valve (304).

14. The carbon nanotube purification device according to claim 1, characterized in that: The collecting system (4) comprises a collecting tank (401), one end of which is connected to the discharge port of the purification device (2), and a second gate valve (402) is provided between the two; a third gate valve (403) is provided at the discharge end of the collecting tank (401), and one side of the collecting tank (401) is connected to a vacuum pump (404), and the vacuum pump (404) is used for vacuuming.

15. The carbon nanotube purification device according to claim 14, characterized in that: The collection method of the collection tank (401) is intermittent, that is, the collection tank (401) is first evacuated to a negative pressure, the pressure being lower than the pressure in the purification device (2). After the bottom of the purification device (2) collects part of the purified carbon nanotube powder, the second gate valve (402) is opened to collect the powder into the collection tank (401), and then the second gate valve (402) is closed, and the third gate valve (403) is opened to collect the product.

16. The carbon nanotube purification device according to claim 14, characterized in that: The collecting tank (401) is made of stainless steel and is sealed to the purification device (2) via a sealing ring (6).

17. The carbon nanotube purification device according to claim 14, characterized in that: The collecting tank (401) and the purification device (2) are both provided with an observation window (7).

18. The carbon nanotube purification device according to claim 1, characterized in that: The exhaust system (5) comprises an exhaust pipe (501) connected to the purification device (2), an exhaust pump (502) arranged on the exhaust pipe (501), and a fourth gate valve (503) is also arranged on the exhaust pipe (501). The fourth gate valve (503) is located on the pipe between the purification device (2) and the exhaust pump (502).

19. The carbon nanotube purification device according to claim 18, characterized in that: An exhaust gas filtering device (504) is also provided on the exhaust pipe (501) between the exhaust pump (502) and the fourth gate valve (503), and an alkaline solution is placed in the exhaust gas filtering device (504); a filter screen (505) is provided at the connection between the exhaust pipe (501) and the purification device (2), and the mesh size of the filter screen (505) is smaller than the particle size of the carbon nanotube powder.

20. A method for purifying carbon nanotubes according to the carbon nanotube purification device according to any one of claims 1 to 19, characterized in that: The method includes: (1) Connecting the components of the carbon nanotube purification device according to their connection relationship and ensuring internal sealing; then adding the carbon nanotube powder raw material to be purified into the screw weight loss metering feeder, and placing an alkaline solution in the exhaust gas filtering device; (2) Turn on the power of the microwave generator and the cooling water circulation in the water-cooling connecting pipe, close the first gate valve, the second gate valve and the third gate valve, open the exciting gas inlet pipeline, set the gas flow rate, turn on the exhaust pump to exhaust gas so that negative pressure is achieved in the cavity of the purification device, thereby achieving negative pressure ignition; (3) After ignition, adjust the excitation gas flow rate in the three-screw regulator and the excitation gas inlet pipe so that the microwave plasma fills the cavity of the purification device; (4) opening the first gate valve on the main feed gas pipeline, and starting the screw weight loss metering feeder, the feeder gas pipeline and the main feed gas pipeline, and adjusting the flow of carbon nanotube powder and each gas in proportion to purify; (5) After the purification reaction is completed, the purified carbon nanotube powder in the cavity of the purification device is transferred to a collection tank of the collection device.

21. The method for purifying carbon nanotubes according to claim 20, characterized in that: The carbon nanotube powder described in step (1) is crushed carbon nanotube powder, and the particle size of the powder is 20 to 400 meshes; the carbon nanotube powder described in step (1) is synthesized by a floating catalytic cracking method or an arc method; the catalyst contained in the carbon nanotube powder described in step (1) is one or a mixture of iron-containing catalysts, cobalt-containing catalysts, and nickel-containing catalysts; the carbon nanotubes described in step (1) are one or a mixture of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes; the negative pressure ignition described in step (2) has a negative pressure range of -50 to -10 Bar.

22. The method for purifying carbon nanotubes according to claim 20, characterized in that: The excitation gas entering the excitation gas inlet pipe is at least one of argon and helium and at least one of trace amounts of oxygen and water vapor; the gas pressure of the excitation gas input into the excitation gas inlet pipe is 0.4MPa to 0.8MPa, and the gas flow range is 10L / min to 100L / min.

23. The method for purifying carbon nanotubes according to claim 22, characterized in that: The content of oxygen or water vapor in the exciting gas is 0.01% to 0.1%; the feeding speed of the screw weightlessness metering feeder is 1g / min to 100g / min; the gas pipeline of the feeder is used to input the first carrier gas, and the first carrier gas is one of argon and helium or a mixture of the two; the carrier gas flow rate in the gas pipeline of the feeder is 1 to 15L / min; the main feed gas pipeline is connected to a second carrier gas, and the second carrier gas is composed of an inert carrier gas and a reactive medium.

24. The method for purifying carbon nanotubes according to claim 22, characterized in that: The inert carrier gas is one of argon and helium or a mixture of the two; the reactive medium is at least one of chlorine and hydrogen chloride gas, or at least one of hydrochloric acid and nitric acid in liquid state; the flow rate of the second carrier gas is 10 to 100 L / min; the volume ratio of the reactive medium in the total gas is 1 to 10%.

25. The method for purifying carbon nanotubes according to claim 24, characterized in that: When the reaction medium is liquid, the liquid is heated and vaporized or loaded into the main feed gas pipeline by bubbling an inert carrier gas; the duration of the purification process is 30 to 500 seconds; an alkaline solution of any one of sodium hydroxide, potassium hydroxide and ammonia water is placed in the exhaust gas filtering device; the morphology of the carbon nanotube powder obtained after the purification does not change, and the metal content therein is 0.02 to 0.1%, and the amorphous carbon content is less than 5%.

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