Carbon nanotubes and growth units, methods of growth, continuous methods of preparation and systems

Abstract

The application discloses a kind of carbon nanotube and its growth unit, growth method, continuous preparation method and system.The carbon nanotube continuous preparation system includes carbon nanotube growth unit and product collection unit;Carbon nanotube growth unit includes reaction container, anode, cathode, arc stabilizer solution supply mechanism, the arc starting end of the anode and the arc starting end of cathode are spaced apart and opposite each other, arc stabilizer solution supply mechanism is used to inject arc stabilizer solution into the reaction container, and the arc starting end of the anode and cathode is immersed in the arc stabilizer solution when the carbon nanotube growth unit works.Product collection unit is communicated with the reaction container, for collecting the carbon nanotube generated in the reaction container.The application can realize the controllable continuous preparation of high-performance carbon tube, and the product prepared has the advantages of low aspect ratio, high conductivity, high crystallinity, high purity and the like.

Description

Technical Field

[0001] This invention relates to the field of nanomaterial preparation technology, and in particular to a carbon nanotube and its growth unit, growth method, continuous preparation method and continuous preparation system. Background Technology

[0002] Single-walled carbon nanotubes (SWCNTs) are widely used in silicon anodes for lithium-ion batteries due to their excellent electrical and thermal conductivity, high strength, high flexibility, and high aspect ratio, as well as their ability to form a well-developed network within the material even with low dosage addition. They also play an indispensable role in emerging battery technologies such as dry cell electrode coating processes and solid-state batteries.

[0003] Currently, the main methods for preparing SWCNTs include arc discharge, chemical vapor deposition, and laser ablation. Arc discharge involves the evaporation of both the catalyst and the carbon source, making it difficult to control the particle size and distribution of the prepared catalyst, resulting in numerous purity defects. Many byproducts (such as multi-walled carbon nanotubes, carbon spheres, and metallic impurities) account for up to 30%, requiring complex post-processing. These byproducts are difficult to separate and purify, affecting the purity and uniformity of the product and limiting its application range. Furthermore, traditional arc discharge methods also produce onion-like carbon, C60 and other fullerenes, as well as insoluble metallic impurities (such as tungsten, tantalum, and silicon), further increasing the difficulty of purification.

[0004] To overcome the aforementioned problems, researchers attempted to synthesize SWCNTs using arc discharge technology at low current densities. However, this method could not achieve high volumetric concentrations of nanocatalysts, with yields often below the gram level, resulting in a final yield of only 3-5 g / h, which is insufficient to meet market demands. Furthermore, existing arc methods are mostly intermittent, making them unsuitable for industrial-scale applications. Single / double-walled carbon nanotubes prepared by traditional arc and chemical vapor deposition methods are relatively long, with aspect ratios generally greater than 3000-50000. Industry consensus indicates that high aspect ratios are difficult to disperse, posing significant challenges and costs for subsequent processing. There is an urgent need for easily dispersible single / double-walled carbon nanotubes with high crystallinity, high conductivity, and an aspect ratio below 2000 for practical production. How to achieve continuous preparation of single / double-walled carbon nanotubes with lower aspect ratios while maintaining high crystallinity and high yield is a pressing issue in this field. Summary of the Invention

[0005] The main objective of this invention is to provide a carbon nanotube and its growth unit, growth method, continuous preparation method and continuous preparation system, thereby overcoming the shortcomings of the prior art.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0007] A first aspect of the present invention provides a carbon nanotube growth unit, including a reaction vessel, an anode, and a cathode, wherein the arc-initiating ends of the anode and the cathode are spaced apart and opposite to each other, and further comprising:

[0008] An arc stabilizing agent solution supply mechanism is used to inject an arc stabilizing agent solution into the reaction vessel, and when the carbon nanotube growth unit is working, the arc-starting ends of the anode and cathode are both immersed in the arc stabilizing agent solution.

[0009] In some more specific embodiments, the arc-initiating ends of the anode and the cathode are respectively provided with a first nozzle and a second nozzle. The first nozzle is used at least to output catalyst to the carbon nanotube growth region between the anode and the cathode, and the second nozzle is used at least to output arc-initiating gas or carbon source to the carbon nanotube growth region. Specifically, both the anode and the cathode have hollow tubular structures; the distance between the arc-initiating ends of the anode and the cathode is 10-350 mm; the anode and the cathode are coaxially arranged, and when the carbon nanotube growth unit is working, the distance between the axes of the anode and the cathode and the surface of the arc-stabilizing agent solution is 100-1200 mm; when the carbon nanotube growth unit is working, the diffusion angle of the plasma arc formed between the anode and the cathode is within 15°; the diameter of the anode is 5-600 mm, and the diameter of the cathode is 15-200 mm.

[0010] In some more specific embodiments, the arc stabilizer solution contains 5-30 wt% arc stabilizer, the conductivity of the arc stabilizer solution is 1-30 S / cm, the injection flow rate of the arc stabilizer solution is 15-260 L / min, and the arc stabilizer in the arc stabilizer solution includes one or more of potassium chloride, potassium carbonate, sodium carbonate, barium nitrate, sodium chloride, or calcium-potassium mixed salts.

[0011] In some more specific embodiments, the carbon nanotube growth unit further includes a level gauge for monitoring the level of the arc stabilizing agent solution within the reaction vessel. The arc stabilizing agent solution supply mechanism includes a storage tank and a conveying assembly, the conveying assembly being used to input the arc stabilizing agent solution from the storage tank into the reaction vessel.

[0012] In some more specific embodiments, the bottom of the reaction vessel is equipped with a precipitation filtration assembly, which includes a first valve, a second valve, and a precipitation chamber located between the first valve and the second valve. The first valve, through an opening / closing operation, transports the arc stabilizing agent solution containing precipitate in the reaction vessel to the precipitation chamber. The second valve, through an opening / closing operation, transports the arc stabilizing agent solution containing precipitate in the precipitation chamber to the filtration chamber. The filtration chamber is equipped with a filter screen and a filter pump for collecting the precipitate generated during the growth of carbon nanotubes.

[0013] A second aspect of the present invention provides a method for growing carbon nanotubes, comprising:

[0014] A voltage is applied between the anode and cathode to generate an electric arc, and an arc-initiating gas is introduced into the carbon nanotube growth region between the anode and cathode. At least the arc-initiating ends of the anode and the cathode are immersed in an arc-stabilizing agent solution, thereby forming a spatially compressed plasma arc at least in the carbon nanotube growth region. Then, a catalyst and a carbon source are introduced into the carbon nanotube growth region to grow carbon nanotubes.

[0015] In some more specific schemes, the arc-initiating gas is an inert gas, the input flow rate of the arc-initiating gas is 5-350 L / min, and the arc-initiating gas is argon.

[0016] In some more specific embodiments, the plasma arc has a length of 30-350 mm, a temperature of 5000-50000 K, and an energy density of 102. 5 -10 6 W / cm², the arc velocity of the plasma arc is 300-1000 m / s.

[0017] In some more specific embodiments, the catalyst comprises a metal component and a flocculant, wherein the metal component comprises one or more of iron, cobalt, and nickel, the flocculant is a sulfur-containing compound, and the molar ratio of the metal element in the metal component to the sulfur element in the flocculant is 1:5-80:1.

[0018] In some more specific embodiments, the carbon source includes one or more of methane, ethane, ethylene, acetylene, propylene, propane, ethanol, methanol, or natural gas, and the flow rate of the carbon source is 3-90 m / s.

[0019] A third aspect of the present invention provides a carbon nanotube grown by a carbon nanotube growth method, wherein the carbon nanotube comprises single-walled or double-walled carbon nanotubes, has a G / D ratio exceeding 50, and an electrical conductivity greater than 1.1 × 10⁻⁶. 7 S / m, aspect ratio less than 2000, diameter 0.9-3nm, specific surface area 300-1300 m² 2 / g.

[0020] A fourth aspect of the present invention provides a continuous carbon nanotube preparation system, comprising a carbon nanotube growth unit and a product collection unit; the product collection unit is connected to the reaction vessel and is used to collect the carbon nanotubes generated in the reaction vessel. The product collection unit includes a filtration assembly, a liquid-solid separation assembly, and a collection tank; the filtration assembly is used to extract the arc-stabilizing agent solution containing carbon nanotubes from the upper layer of the reaction vessel, the liquid-solid separation assembly is used to separate the carbon nanotubes in the arc-stabilizing agent solution, and the separated carbon nanotubes are stored in the collection tank; the collection tank is provided with a gas outlet for discharging waste gas.

[0021] A fifth aspect of the present invention provides a method for the continuous preparation of carbon nanotubes, comprising:

[0022] A voltage is applied between the anode and cathode to generate an electric arc, and an arc-initiating gas is introduced into the carbon nanotube growth region between the anode and cathode. At least the arc-initiating ends of the anode and cathode are immersed in an arc-stabilizing agent solution, thereby forming a spatially compressed plasma arc at least within the carbon nanotube growth region. Subsequently, a catalyst and a carbon source are introduced into the carbon nanotube growth region to grow carbon nanotubes. Finally, a product collection unit collects the carbon nanotubes generated in the reaction vessel.

[0023] Compared with the prior art, the advantages of the present invention include at least the following:

[0024] First, the carbon nanotube growth method provided by this invention achieves efficient control of the plasma arc through the arc deflection compression capability of the arc stabilizing agent solution and the conductivity constraint effect of the liquid medium: the arc stabilizing agent solution can effectively compress the plasma arc deflection, limiting its diffusion angle to within 15°, thereby obtaining an ultra-high temperature, high energy density plasma arc; at the same time, the conductivity constraint effect of the liquid medium will compress the arc diameter (reducing it to 1 / 3-1 / 5 of that of traditional gas phase discharge), ultimately resulting in a lower aspect ratio and better dispersibility of the prepared carbon nanotubes.

[0025] Secondly, the continuous preparation method of carbon nanotubes provided by this invention relies on the synergistic effect of arc discharge in the arc stabilizing agent solution and the rapid cooling-compression effect of the liquid to achieve high-yield catalyst and carbon nanotube preparation: the synergistic effect of the rapid cooling effect of the liquid and the arc compression effect can maintain both the ultra-high temperature of the arc (5000-50000K) and the high energy density (10^6 K). 5 -10 7 (W / cm²), and can generate a large number of highly catalytically active nanocatalyst particles through instantaneous cooling, significantly improving the reaction efficiency between the catalyst and the carbon source; this mechanism supports a single-machine yield of 10-200 g / min, a daily output of >20 kg, and can continuously produce kilogram-level high-quality carbon nanotubes.

[0026] Third, the present invention provides a continuous preparation method for carbon nanotubes, which, through optimization of the arc stabilizing agent solution and modular continuous production design, achieves controllable continuous preparation of high-performance carbon nanotubes: by optimizing the formulation of the arc stabilizing agent solution and using modular production processes, the stability and controllability of the electric arc in the liquid can be effectively guaranteed, ultimately producing nanotubes with low aspect ratio (<2000) and high conductivity (>1.1×10⁻⁶). 7 Carbon nanotubes with high S / m, high crystallinity (G / D ratio > 50) and high purity meet the requirements of continuous production. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of a continuous carbon nanotube preparation system provided in an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the plasma arc diffusion angle provided in an embodiment of the present invention;

[0029] Figure 3 This is a scanning electron microscope image of single / double-walled carbon nanotubes provided in Embodiment 1 of the present invention;

[0030] Figure 4 This is the Raman spectrum of single / double-walled carbon nanotubes provided in Example 3 of the present invention;

[0031] Figure 5 This is a transmission electron microscope image of a single-walled carbon nanotube provided in Embodiment 3 of the present invention;

[0032] Figure 6 This is a transmission electron microscope image of the double-walled carbon nanotubes provided in Embodiment 3 of the present invention;

[0033] Figure 7 This is a specific surface area diagram of single / double-walled carbon nanotubes provided in Embodiment 3 of the present invention.

[0034] Figure label:

[0035] 100-Continuous carbon nanotube preparation system; 110-Reaction vessel; 120-Composite anode; 130-Composite cathode; 140-Level gauge; 150-Sedimentation chamber; 151-First valve; 153-Second valve; 155-Filter screen; 157-Filter pump; 159-Filter chamber; 160-Storage tank; 170-Transfer pump; 190-Level controller; 210-Collection tank; 220-Suction filter; 230-Transfer chamber; 240-Gas outlet. Detailed Implementation

[0036] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles.

[0037] Please refer to Figure 1 One embodiment of the present invention provides a continuous carbon nanotube preparation system 100, comprising a carbon nanotube growth unit and a product collection unit. The carbon nanotube growth unit includes a reaction vessel 110, a composite anode 120, a composite cathode 130, a storage tank 160, and a transfer pump 170. The product collection unit includes a collection tank 210, a filter 220, and a transition chamber 230.

[0038] In this embodiment, the reaction vessel 110 is designed with an injection port for the arc stabilizing agent solution at its top for easy addition. A finished product outlet is also provided on the side wall of the reaction vessel 110 for convenient collection of the generated carbon nanotubes. The arc stabilizing agent solution is stored in a storage tank 160, which is connected to the injection port at the top of the reaction vessel 110 via a pipeline. To ensure a stable and continuous delivery of the arc stabilizing agent solution to the reaction vessel 110, a transfer pump 170 is installed on the pipeline. The transfer pump 170 effectively and quantitatively delivers the arc stabilizing agent solution from the storage tank 160 to the reaction vessel 110 to maintain the continuity and stability of the reaction.

[0039] In this embodiment, the arc-initiating ends of the composite anode 120 and composite cathode 130 are immersed in an arc-stabilizing agent solution, spaced apart and facing each other. Under an appropriate voltage, the arc-initiating ends of the composite anode 120 and composite cathode 130 can generate a plasma arc within the interval. The generation of the plasma arc is crucial for the synthesis of carbon nanotubes. Please refer to... Figure 2 To ensure the stability of the plasma arc and control its diffusion angle, an arc-stabilizing agent solution is used to compress the diffusion angle of the plasma arc, ensuring it does not exceed 15°. Specifically, the composite anode 120 and composite cathode 130 are coaxially arranged and both remain parallel to the surface of the arc-stabilizing agent solution. The distance between the axes of the composite anode 120 and composite cathode 130 and the surface of the arc-stabilizing agent solution is 100-1200 mm. Furthermore, the diameter of the composite anode 120 is 5-600 mm, and the diameter of the composite cathode 130 is 15-200 mm. The distance between the arc-initiating ends of the composite anode 120 and composite cathode 130 is 10-350 mm.

[0040] More specifically, the composite anode 120 has a hollow tubular structure with a hollow iron rod at the front end. The arc-starting end of the composite anode 120 is equipped with a first nozzle, which is used at least to supply catalyst to the carbon nanotube growth region between the composite anode 120 and the composite cathode 130 within the reaction vessel 110. Similarly, the composite cathode 130 has a hollow tubular structure with a hollow graphite at the front end, and the arc-starting end of the composite cathode 130 is equipped with a second nozzle. The second nozzle is used at least to supply arc-starting gas or a carbon source to the carbon nanotube growth region. During catalyst injection, the arc-stabilizing agent solution may partially overflow from the composite anode 120. To solve this problem, a certain amount of gas is introduced simultaneously with the injection of the arc-stabilizing agent solution. This effectively prevents the overflow of the arc-stabilizing agent solution. Furthermore, a one-way valve can be added at the front end. The function of this one-way valve is to prevent backflow of gas and liquid. Preferably, the one-way valve can be set in an L-shape. This design ensures that the liquid level of the arc-stabilizing agent solution is always lower than the uppermost end of the L-shaped one-way valve. The above settings can be used individually or in combination as needed to achieve the best results.

[0041] A precipitation filter assembly is installed at the bottom of the reaction vessel 110. Its purpose is to promptly isolate amorphous carbon precipitates generated during carbon nanotube growth, preventing them from affecting the conductivity stability of the arc stabilizer solution. Specifically, the precipitates generated during carbon nanotube growth are mainly composed of amorphous carbon. When this substance mixes into the arc stabilizer solution, it alters the solution's conductivity, leading to conductivity fluctuations and affecting the stability of the reaction system. Therefore, it is necessary to isolate it as early as possible.

[0042] Specifically, the precipitation filtration assembly includes a first valve 151, a second valve 153, and a precipitation chamber 150 located between the two; the reaction vessel 110 is also equipped with a filtration chamber 159, which is provided with a filter screen 155 and a filter pump 157, wherein the filter pump 157 is used to extract the arc stabilizer solution containing precipitates, and the precipitates are collected after being filtered by the filter screen 155.

[0043] The specific operating procedure is as follows: At the beginning of the reaction, the first valve 151 is open and the second valve 153 is closed. At this time, the arc stabilizer solution containing amorphous carbon precipitate in the reaction vessel 110 can flow into the precipitation chamber 150 through the first valve 151. After the reaction has been going on for 1-5 hours, the first valve 151 is closed to block the connection between the reaction vessel 110 and the precipitation chamber 150. At the same time, the second valve 153 is opened to connect the precipitation chamber 150 with the filtration chamber. Then, the filtration pump 157 is started to pump the precipitate-containing solution in the precipitation chamber 150 into the filtration chamber. After the amorphous carbon precipitate is intercepted by the filter screen 155, the precipitate is collected. By repeating the above operation procedure of "opening the first valve - closing the first valve and opening the second valve - starting the filtration pump", the continuous growth of carbon nanotubes and the dynamic isolation of precipitate can be achieved, effectively maintaining the conductivity stability of the arc stabilizer solution.

[0044] A level gauge 140 is installed on the side wall of the reaction vessel 110 to monitor the height of the arc stabilizer solution in the reaction vessel 110 in real time, so as to ensure the stable progress of the reaction process.

[0045] After the carbon nanotubes are prepared and float on the surface of the arc stabilizing agent solution, the finished product outlet on the side wall is connected to the pipe of the collection tank 210. The collection tank 210 is directly connected to the reaction vessel 110, the transition chamber 230 is connected to the collection tank 210, and the filter 220 is connected to the transition chamber 230. Through the action of the filter 220, the upper layer of arc stabilizing agent solution in the reaction vessel 110 is introduced into the collection tank 210. The transition chamber 230 is used to separate the carbon nanotubes in the arc stabilizing agent solution. The separated carbon nanotubes are stored in the collection tank 210, while the remaining arc stabilizing agent solution can be stored in the transition chamber 230 and discharged. The collection tank 210 is provided with a vent 240, which is used to discharge the waste gas generated during the preparation process, avoid excessive pressure in the reaction vessel 110, and ensure preparation safety.

[0046] In this embodiment, the arc stabilizing agent content in the arc stabilizing agent solution is 5-30 wt%, and the conductivity of the arc stabilizing agent solution is 1-30 S / cm. The arc stabilizing agent includes one or more of potassium chloride, potassium carbonate, sodium carbonate, barium nitrate, sodium chloride, or calcium-potassium mixed salts. Potassium-containing compounds such as potassium carbonate serve as the core arc stabilizing agent, utilizing the high ionization properties of potassium to enhance the conductivity of the arc channel and maintain discharge stability. Sodium salts (such as sodium carbonate) and barium salts (such as barium nitrate) reduce arc impedance and increase arc energy density by releasing metal ions. Calcium-potassium mixed salts (such as perovskite-type complexes) enhance the arc compression effect through a synergistic ionization effect, increasing the current density by 2-3 times. Their mechanism of action lies in ionization enhancement: containing... , The compounds preferentially ionize, providing a continuous conductive path for the electric arc and preventing the discharge from being interrupted. However, too many... and Ions can hinder the migration of carbon ions from the anode to the central cathode. This can result in short preparation times, low aspect ratios, and easy dispersion of single / double-walled carbon nanotubes. Arc discharge in an arc-stabilizing agent solution provides a simple and cost-effective method for carbon nanotube synthesis, continuously producing high-quality single / double-walled carbon nanotubes. These nanotubes are easily dispersed in electrochemical power sources, elastomers, composites, plastics, paints, and coatings, thereby reducing processing costs.

[0047] An embodiment of this application also provides a method for the continuous preparation of carbon nanotubes, wherein the method is implemented systematically for the continuous preparation of carbon nanotubes, and the method includes:

[0048] S1) A voltage is applied to the composite anode 120 and the composite cathode 130 to generate an electric arc, and an arc-initiating gas is introduced into the carbon nanotube growth region between the composite anode 120 and the composite cathode 130. At least the arc-initiating ends of the composite anode 120 and the composite cathode 130 are immersed in an arc-stabilizing agent solution, thereby forming a spatially compressed plasma arc at least within the carbon nanotube growth region. Specifically:

[0049] First, the power supply to the composite anode 120 and composite cathode 130 is activated. Then, argon gas is supplied into the reaction vessel 110 through the second nozzle of the composite cathode 130. Next, an arc-stabilizing agent solution is injected into the reaction vessel 110 via a delivery pump 170 until the arc-stabilizing agent solution completely submerges the electrodes of the composite anode 120 and composite cathode 130. Within the carbon nanotube growth region between the composite anode 120 and composite cathode 130, the arc-initiating ends of the composite anode 120 and composite cathode 130 are excited, generating a plasma arc.

[0050] At this point, the arc stabilizing agent solution effectively compresses the plasma arc, ensuring that the diffusion angle of the plasma arc does not exceed 15°, thus obtaining a plasma arc with ultra-high temperature and high energy density. The arc stabilizing agent solution itself has the ability to compress arc deflection, which helps to improve energy density. In the liquid medium space, due to the constraint effect of conductivity, the arc is compressed by the medium pressure, resulting in a significant reduction in its diameter, to 1 / 3 to 1 / 5 of the diameter of traditional gas-phase discharge. This constriction effect is very obvious. However, if the arc deflection angle exceeds 15 degrees, it will increase the discharge path, thereby reducing the energy density. In this case, it is not conducive to the formation of high-quality carbon nanotubes; specifically, the G / D ratio of the carbon nanotubes will be greater than 50, indicating that the quality of the carbon nanotubes is not ideal. In addition, an excessively large deflection angle can easily cause arc interruption, making the experiment unable to be carried out continuously, affecting the uniformity of the product, and leading to inconsistencies in experimental results.

[0051] In this implementation scheme, the plasma arc length is 30-350 mm, the plasma arc temperature is 5000-50000 K, and the plasma arc energy density is 10. 5 -10 6 The plasma arc flame velocity is 300-1000 m / s, with a flow rate of 5-350 L / min. To achieve specific power, current and voltage are typically adjusted. In practice, the desired effect is usually achieved through the synergistic effect of mechanical compression, thermal compression, and electromagnetic compression. Mechanical compression is the foundation and prerequisite of the entire process, providing initial constraints for subsequent compression. However, the compression effect of mechanical compression is relatively limited. Therefore, the combined effect of cooling medium and current magnetic field is relied upon to enhance the compression effect. Specifically, thermal compression further reduces the effective conductive area of ​​the arc, thereby significantly increasing the energy density. Electromagnetic compression, under high current conditions, further enhances the arc's contraction effect through electromagnetic force. These three compression methods work together to ultimately transform an ordinary electric arc into a plasma arc with high temperature and high energy density characteristics. The principle of thermal compression can be explained as follows: by introducing a cooling medium, such as gas or water, a low-temperature gas film is formed near the inner wall of the nozzle. The presence of this gas film significantly reduces the ionization level at the periphery of the arc, thereby forcing the current to concentrate in the high-temperature center of the arc. This concentration effect causes the arc to contract further, thus increasing the energy density. Through this multi-layered compression and synergistic effect, efficient control and utilization of the arc are ultimately achieved.

[0052] Under the same power conditions, the longer the arc length, the greater the energy density and the higher the arc temperature, and the higher the G / D ratio of the corresponding product. However, if the arc length is the same, a 15° deflection is more likely to affect the effective arc stroke than a 5° deflection, resulting in a decrease in energy density and temperature. Under the same deflection angle, the longer the arc length, the longer the arc stroke, and the more significant the impact on temperature, temperature range, and energy density, making it more difficult to form products with a G / D ratio greater than 50.

[0053] Introducing argon gas can prevent some of the arc-stabilizing agent solution from entering the reaction vessel 110. Furthermore, introducing argon gas also aims to reduce the difficulty of arc initiation, ensure smooth discharge startup, suppress interference, maintain discharge uniformity, and optimize the growth environment of carbon nanotubes. Specifically, in a gaseous medium, the presence of high-ionization-energy components such as oxygen and nitrogen makes arc initiation difficult or delayed. In the initial stage of arc discharge, the gas between electrodes needs to be ionized to form a conductive channel, i.e., arc initiation. Argon, as an inert gas, has a low ionization energy and is more easily ionized to form plasma under a high-voltage electric field, thereby lowering the voltage threshold required for arc initiation. Moreover, in a liquid arc environment, although the arc-stabilizing agent solution can constrain the arc morphology, the gaseous region between electrodes, such as the through-hole of the composite cathode 130, still requires the protection of an inert gas. Argon gas can effectively remove active components such as oxygen and water vapor from the gaseous region, preventing oxygen ionization from reacting with the electrode material, leading to uneven electrode surface corrosion, and causing arc position shifts or intensity fluctuations. Simultaneously, to prevent hydrogen and oxygen free radicals generated from water vapor decomposition from participating in carbon source reactions and generating oxygen-containing compounds or amorphous carbon, thereby reducing product purity, argon gas filling the gas phase region can maintain the stability of the arc discharge, ensuring the plasma arc's diffusion angle (A≤15°), temperature (5000-50000 K), and energy density (10 K). 5 -10 6 The W / cm² ratio meets the growth requirements for single / double-walled carbon nanotubes.

[0054] S2) Subsequently, a catalyst and a carbon source are introduced into the carbon nanotube growth region to grow carbon nanotubes. Specifically, a catalyst is delivered into the reaction vessel 110 through the first nozzle of the composite anode 120, and a carbon source is delivered into the reaction vessel 110 through the second nozzle of the composite cathode 130 to grow carbon nanotubes.

[0055] In this embodiment, the catalyst comprises a metal component and a flocculant. The metal component can be one or a combination of iron, cobalt, and nickel. The flocculant is a sulfur-containing compound, which inhibits the excessive growth of catalyst particles, thereby controlling the diameter and mass of carbon nanotubes. In this embodiment, the molar ratio of the metal element in the metal component to the sulfur element in the flocculant is 1:5-80:1 to ensure the activity and selectivity of the catalyst, thereby improving the yield and quality of carbon nanotubes.

[0056] In this embodiment, the carbon source includes one or more combinations of methane, ethane, ethylene, acetylene, propylene, propane, ethanol, methanol, or natural gas. These carbon sources are activated by a catalyst inside the reaction vessel 110, generating carbon nanotubes through a chemical reaction. To ensure the growth rate and quality of the carbon nanotubes, the flow rate of the carbon source is controlled at 3-90 m / s, effectively preventing overgrowth or defects in the carbon nanotubes.

[0057] The catalyst is introduced into the plasma arc through a composite anode 120 to form a high concentration of highly efficient catalyst nanoparticles. These nanoparticles exhibit extremely high activity in the high-temperature environment of the plasma arc, effectively promoting the growth of single-walled or double-walled carbon nanotubes.

[0058] S3) Finally, the product collection unit collects the carbon nanotubes generated in the reaction vessel 110.

[0059] In this embodiment, the generated carbon nanotubes gradually float to the surface of the arc stabilizing agent solution. Subsequently, by controlling the level gauge 140, the product floating on the solution surface flows into the collection tank 210 along with the arc stabilizing agent solution.

[0060] To achieve continuous reaction and stable collection of carbon nanotubes, this scheme sets graded liquid level thresholds and combines them with a dynamic liquid level control mechanism. The specific technical solution is as follows:

[0061] First, based on the reaction requirement that the axes of the anode and cathode must maintain an effective distance of 100-1200mm from the surface of the arc stabilizer solution, the following key liquid level parameters are defined: minimum liquid level H1: 250mm from the axis of the anode and cathode; maximum liquid level H2: 1050mm from the axis of the anode and cathode; standard working liquid level H3: range of 250-1050mm.

[0062] The current liquid level H0 of the arc stabilizer solution in the reaction vessel 110 is collected in real time by the level gauge 140, and the graded control logic is triggered based on the relative relationship between H0 and H1, H2, and H3.

[0063] When H0 < H1 is detected, the level gauge 140 sends a low level signal to the level controller 190. The level controller 190 immediately starts the transfer pump 170 to replenish the arc stabilizer solution from the storage tank 160 to the reaction vessel 110 until the liquid level rises back to the standard working level H3 range. This operation ensures that the distance between the electrode and the liquid surface is restored to the effective reaction range, avoiding reaction interruption due to insufficient solution.

[0064] If H0 is within the standard working liquid level H3 range (250mm≤H0≤1050mm), the liquid level gauge 140 determines that the current liquid level meets the reaction requirements, does not send a signal to the liquid level controller 190, maintains a stable state of "no replenishment, no extraction", maintains the optimal reaction conditions between the electrode and the liquid surface, and ensures the continuous growth of carbon nanotubes.

[0065] When H0 > H2 is detected, the level gauge 140 sends a high level signal to the level controller 190. The level controller 190 then activates the filter 220 to extract the upper layer of the arc stabilizer solution containing carbon nanotubes from the reaction vessel (simultaneously collecting the carbon nanotubes) until the liquid level drops back to the standard working level H3. This avoids the risk of solution overflow and ensures the continuous collection of carbon nanotubes through filtration, thus maintaining the dynamic balance of the reaction system.

[0066] Through the closed-loop control logic of "low liquid level replenishment - normal liquid level maintenance - high liquid level filtration", the liquid level of the arc stabilizer solution in the reaction vessel 110 can be dynamically maintained, so that the electrode and the liquid surface are always in an effective reaction distance, and finally the continuous growth and efficient collection of carbon nanotubes can be achieved.

[0067] During the collection process, a continuous liquid-solid separation operation is performed using a filter 220 to ensure that carbon nanotubes can be effectively separated from the solution. Simultaneously, the generated waste gas is discharged through an outlet 240, thus efficiently obtaining pure carbon nanotubes.

[0068] The carbon nanotubes obtained in this application include single-walled or double-walled carbon nanotubes with a G / D ratio exceeding 50 and an electrical conductivity greater than 1.1 × 10⁻⁶. 7 S / m, aspect ratio less than 2000, diameter 0.9-3nm, specific surface area 300-1300 m² 2 / g. The single / double-walled carbon nanotubes prepared by this method not only have high crystallinity, high electrical conductivity, and low aspect ratio, but are also easily dispersed in electrochemical power sources, elastomers, composite materials, plastics, paints, and coatings. They can be widely used in new energy batteries and high-end composite materials, and have significant commercial value and broad application prospects. They can also meet the needs of continuous production.

[0069] In this application, the axial growth of carbon nanotubes in a liquid environment is limited by thermal-fluid coupling, specifically achieved through the following mechanism:

[0070] First, the high heat capacity and thermal conductivity of the liquid medium induce rapid cooling in the arc region, forming a steep axial temperature gradient (high temperature at the arc center, low temperature at the periphery). This inhibits the prolonged deposition of carbon sources (such as decomposed carbon atoms) at the tube ends, thus shortening the tube length. Simultaneously, the shear stress generated by the liquid flow (convection induced by arc heat or external forced flow) acts on the surface of the growing carbon nanotubes, both interfering with the axial directional deposition of carbon atoms and promoting radial (diameteral) growth, while also damaging the fragile ends of the newly formed carbon nanotubes and preventing their continued extension. Furthermore, the liquid environment, through cooling and flow, reduces the mobility of active sites in the dispersed metal catalysts (such as iron and cobalt), limiting the nucleation and short-range growth of carbon nanotubes to a limited area on the catalyst surface, rather than continuous axial extension. Finally, the "microscale turbulence" formed by heat-fluid coupling, combined with the catalyst interface, leads to an unstable carbon nanotube growth environment, preferentially forming short and thick structures (length-to-diameter ratio <2000).

[0071] Finally, the prepared carbon nanotubes, due to their light density and hydrophobicity, will slowly float on the surface of the arc stabilizer solution, while denser impurities will slowly settle in the precipitation filter chamber 150 below. Through this natural physical separation process, the product and impurities can be initially separated, thereby simplifying subsequent purification steps and improving the efficiency of the entire preparation process and the purity of the product.

[0072] In the process of preparing carbon nanotubes by liquid arc method, the distance L1 between the arc-initiating end of composite anode 120 and the arc-initiating end of composite cathode 130 significantly affects the growth characteristics of carbon nanotubes through three core pathways: electrical, thermodynamic, and hydrodynamic. The specific mechanisms are as follows:

[0073] First, the electrical path is directly related to arc stability: as L1 increases, the liquid dielectric resistance rises, requiring a higher arc voltage to maintain the discharge, which can easily lead to arc fluctuations or even breakage (for example, when the vacuum arc spacing increases from 100mm to 200mm, the voltage rises significantly and the morphology becomes unstable); while a smaller L1 can enhance the liquid's constraint on the arc, allowing the dielectric pressure to compress the arc diameter to 1 / 3-1 / 5 of that of traditional gas-phase discharge, thereby increasing the current density to 10. 7 On the order of A / m², high current density generates temperatures of thousands of K, promoting efficient cracking of carbon sources.

[0074] In the thermodynamic control of carbon nanotube fabrication via liquid arc method, the liquid medium plays a crucial role through a dual mechanism: on the one hand, the liquid medium achieves a sharp drop in temperature gradient (greater than 10°C) in the arc region through vaporization endothermic reaction. 4The K / s of the liquid medium creates an instantaneous quenching effect on high-temperature synthesized nanomaterials (such as catalyst particles and carbon nanotubes), thereby inhibiting excessive grain growth and maintaining their nanoscale characteristics. On the other hand, although the liquid medium reduces the core temperature of the electric arc by about 15%-20%, it increases the local energy density by 3-5 times through the compression effect, ultimately forming a gradient temperature field, which provides suitable thermodynamic conditions for different reaction stages.

[0075] Secondly, thermodynamic and hydrodynamic pathways synergistically regulate the morphology of carbon nanotubes: Under small L1, the arc energy is more concentrated, but the high thermal conductivity of the liquid will form a steep axial temperature gradient, which restricts the long-distance diffusion and deposition of carbon atoms and inhibits the axial extension of carbon nanotubes; at the same time, the violent convection of the liquid induced by the arc generates turbulent shear force, which mechanically damages the fragile ends of the newly formed carbon nanotubes, promoting radial thickening rather than axial growth of carbon nanotubes; in addition, the spatial limitation of the narrow discharge region further constrains the growth morphology of carbon nanotubes (e.g., by setting the composite electrode coaxially, the aspect ratio of carbon nanotubes can be reduced to less than 2000).

[0076] In summary, the electrode spacing achieves effective control over carbon nanotube growth characteristics through the synergistic effect of three mechanisms: the electrical path (reduced spacing → reduced resistance → increased current density), the thermodynamic path (reduced spacing → increased energy density → increased temperature gradient → axial growth inhibition), and the fluid path (reduced spacing → increased turbulent shear force → radial growth of carbon nanotubes dominates).

[0077] In summary, under the spatial confinement effect of the liquid medium, the electric arc is compressed by the medium pressure, resulting in a significant reduction in its diameter, to about 1 / 3 to 1 / 5 of the diameter of a traditional gas-phase discharge. This compression effect allows for a substantial increase in local current density, reaching up to 10-1. 7 The flow rate is on the order of A / m². Due to the enhanced discharge stability, the liquid phase resistance characteristics enable the arc to automatically adjust its channel impedance, thereby achieving more precise control. Through precise control of the liquid's compressible structure, the liquid phase environment can effectively restrict the axial growth of carbon nanotubes by utilizing thermal-fluid coupling, enabling the preparation of double-walled carbon nanotubes with low aspect ratios (less than 2000) and high crystallinity.

[0078] The arc-stabilizing agent solution not only possesses a certain degree of conductivity, which can stabilize the electric arc, but also has a strong cooling capacity, significantly exceeding that of deionized water, but lower than that of liquid nitrogen. However, arc discharge in liquid nitrogen is unstable due to its electrical insulation properties. The superior cooling capacity of the arc-stabilizing agent solution is beneficial to the synthesis of single / double-walled carbon nanotubes during arc discharge, and the solution flow during arc discharge also hinders the further growth of single / double-walled carbon nanotubes, thus forming high-quality single / double-walled carbon nanotubes with low aspect ratios. In traditional preparation techniques, such as arc discharge and chemical vapor deposition, the produced single-walled or double-walled carbon nanotubes typically have high aspect ratios, generally between 3000 and 50000. However, the carbon nanotubes obtained in this application have an aspect ratio of less than 2000, which greatly improves the dispersibility of the carbon nanotubes. When the aspect ratio is low, carbon nanotubes can be more uniformly dispersed in various matrix materials, such as electrochemical power sources, elastomers, and composite materials. This helps reduce the aggregation of carbon nanotubes, allowing them to fully exert their excellent physicochemical properties, reduce the cost of material processing, and improve production efficiency.

[0079] The standards for Raman spectroscopy, thermogravimetric characterization, scanning electron microscopy and energy-dispersive X-ray spectroscopy, transmission electron microscopy, ultraviolet-visible-near-infrared absorption spectroscopy, and gas absorption spectroscopy for determining the specific surface area of ​​solids for single-walled carbon nanotube samples are as described in GB / T 32871-2016, ISO / TS 11308:2011 (E) Nanotechnology, ISO / TS 10798:2011 (E) Nanotechnology, ISO / TS 10797:2012 (E) Nanotechnology, GB / T 39114-2020, and ISO / TS9277:2010 (E), and refer to Table 1 for the test schemes described in these standards.

[0080] Table 1 Test Plan

[0081] ;

[0082] The following experimental data will provide a detailed explanation.

[0083] Example 1

[0084] The continuous preparation method of carbon nanotubes provided in this embodiment is based on Figure 1 The carbon nanotube continuous preparation system shown is implemented.

[0085] In this continuous carbon nanotube preparation system, the composite anode 120 is made of 316L stainless steel and pure iron, and the composite cathode 130 is made of 316L stainless steel and graphite. The diameter of the anode is 600 mm, the diameter of the cathode is 200 mm, the distance between their arc-starting ends is 250 mm, the arc-stabilizing agent solution is potassium chloride with a concentration of 30 wt%, and the conductivity of the arc-stabilizing agent solution is 30 S / cm.

[0086] The continuous preparation method for carbon nanotubes specifically includes the following steps:

[0087] S1) Start the power supply, introduce argon gas (the arc-igniting gas) through the composite cathode 130 with the central hole, and control the arc length to 350 mm, the arc temperature to 6000 K, and the energy density to 1.2 × 10⁻⁶. 5 W / cm 2 The plasma arc flame velocity is 300 m / s. Then, through the level gauge 140, the pump 170 slowly injects the arc stabilizing agent solution from the arc stabilizing agent storage tank 160 into the reactor 110 at a flow rate of 100 L / min until the distance between the electrode axis and the liquid surface is 1200 mm, thereby forming a spatially compressed plasma arc between the composite cathode 130 and the composite anode 120. The diffusion angle of the plasma arc formed between the anode and cathode is within 14°.

[0088] S2) Then, the catalyst mixture is injected from the composite anode 120, and a carbon source gas at a certain flow rate is injected from the composite cathode 130 to start product generation. The catalyst mixture is composed of iron powder and thiophene, with a molar ratio of metal element in the metal component to sulfur element in the anti-condensation agent of 2:1, and the carbon source gas is methane with a flow rate of 80 m / s.

[0089] S3) The product slowly floats to the surface of the arc stabilizer, and then the floating product is allowed to flow into the collection tank 210 along with the arc stabilizer liquid by controlling the liquid level gauge 140. The liquid and solid are continuously separated by the filter 220, the waste gas is discharged through the gas outlet 240, and the initial product is continuously collected through the transition chamber 230.

[0090] The final product obtained in this embodiment is single / double-walled carbon nanotubes, with a yield of 20.3 kg / d and an electrical conductivity of 1.15 × 10⁻⁶. 7 s / m, diameter 1.8-3.0 nm, aspect ratio 1950, specific surface area 357 m² 2 / g, while its Raman spectrum (excitation wavelength: 532 nm) is at 1570 cm⁻¹. -1 1350 cm -1 and 200cm -1The amplitude shows a sharp graphite peak (G band), an unusually small disorder peak (D band), and a highly pronounced radial breathing pattern (RBM) characteristic peak, indicating the presence of single-walled / double-walled carbon nanotubes in the product. The ratio of the G band peak intensity to the D band peak intensity (G / D ratio) is 52, indicating high crystallinity. Please refer to [reference needed]. Figure 3 Scanning electron microscopy characterization of the single / double-walled carbon nanotubes prepared in Example 1 showed that the initial product had relatively few impurities and good product uniformity.

[0091] Example 2

[0092] The continuous preparation method of carbon nanotubes provided in this embodiment is based on Figure 1 The carbon nanotube continuous preparation system shown is implemented.

[0093] In this continuous carbon nanotube preparation system, the composite anode 120 is made of 304 stainless steel and pure iron, and the composite cathode 130 is made of 304 stainless steel and graphite. The specific dimensions are: the diameter of the composite anode is 5 mm, the diameter of the composite cathode is 15 mm, the distance between the arc-starting ends of the two is 10 mm, and the specific composition of the arc stabilizing agent solution is potassium carbonate with a concentration of 5 wt% and a conductivity of 5 S / cm.

[0094] The continuous preparation method for carbon nanotubes specifically includes the following steps:

[0095] S1) Start the power supply, introduce argon gas (the arc-igniting gas) through the composite cathode 130 with the central hole, and control the arc length to be 30 mm, the arc temperature to be 35000 K, and the energy density to be 1.0 × 10⁻⁶. 6 W / cm 2 The plasma arc flame velocity is 1000 m / s. Then, through the level gauge 140, the transfer pump 170 slowly injects the arc stabilizing agent solution from the arc stabilizing agent storage tank 160 into the reactor 110 at a flow rate of 90 L / min until the distance between the electrode axis and the liquid surface is 100 mm, thereby forming a spatially compressed plasma arc between the composite cathode 130 and the composite anode 120. The diffusion angle of the plasma arc formed between the anode and cathode is within 12°.

[0096] S2) Then, the catalyst mixture is injected from the composite anode 120, and a carbon source gas at a certain flow rate is injected from the composite cathode 130 to begin product generation. The catalyst mixture specifically consists of cobalt powder and sulfur powder, with a molar ratio of metal element in the metal component to sulfur element in the anti-condensing agent of 10:1. The molar ratio of metal element in the metal component to sulfur element in the anti-condensing agent is 60:1. The carbon source gas is ethylene, with a flow rate of 3 m / s.

[0097] S3) The product slowly floats to the surface of the arc stabilizer, and then the floating product is allowed to flow into the collection tank 210 along with the arc stabilizer liquid by controlling the liquid level gauge 140. The liquid and solid are continuously separated by the filter 220, the waste gas is discharged through the gas outlet 240, and the initial product is continuously collected through the transition chamber 230.

[0098] The final product obtained in this embodiment is single / double-walled carbon nanotubes, with a yield of 23.5 kg / d and an electrical conductivity of 2.23 × 10⁻⁶. 7 s / m, diameter 1.5-2.3nm, aspect ratio 1823, specific surface area 551 m² 2 The ratio of peak intensity in the G band to peak intensity in the D band (G / D ratio) is 58, indicating that it has a high degree of crystallinity.

[0099] Example 3

[0100] The continuous preparation method of carbon nanotubes provided in this embodiment is based on Figure 1 The carbon nanotube continuous preparation system shown is implemented.

[0101] In this continuous carbon nanotube preparation system, the composite anode 120 is made of 310s material, and the composite cathode 130 is made of 310s and isostatic graphite. The diameter of the composite anode is 400 mm, the diameter of the composite cathode is 120 mm, and the distance between their arc-starting ends is 60 mm. The arc-stabilizing agent solution is a mixture of potassium chloride and sodium chloride with a concentration of 18 wt% and a conductivity of 23 S / cm.

[0102] The continuous preparation method for carbon nanotubes specifically includes the following steps:

[0103] S1) Start the power supply, introduce argon gas (the arc-igniting gas) through the composite cathode 130 with its central hole, and control the arc length at 135 mm, the arc temperature at 27000 K, and the energy density at 1.6 × 10⁻⁶. 6 W / cm 2 The plasma arc flame velocity is 50 m / s. Then, through the level gauge 140, the transfer pump 170 slowly injects the arc stabilizing agent solution from the arc stabilizing agent storage tank 160 into the reactor 110 at a flow rate of 46 L / min until the distance between the electrode axis and the liquid surface is 280 mm, thereby forming a spatially compressed plasma arc between the composite cathode 130 and the composite anode 120. The diffusion angle of the plasma arc formed between the anode and cathode is within 8°.

[0104] S2) Then, the catalyst mixture is injected from the composite anode 120, and a carbon source gas at a certain flow rate is injected from the composite cathode 130 to begin product generation. The catalyst mixture is composed of pure iron powder and hydrogen sulfide, with a molar ratio of metal element in the metal component to sulfur element in the anti-condensation agent of 20:1. The carbon source gas is methane, with a flow rate of 68 m / s.

[0105] S3) The product slowly floats to the surface of the arc stabilizer, and then the floating product is allowed to flow into the collection tank 210 along with the arc stabilizer liquid by controlling the liquid level gauge 140. The liquid and solid are continuously separated by the filter 220, the waste gas is discharged through the gas outlet 240, and the initial product is continuously collected through the transition chamber 230.

[0106] This embodiment ultimately yields single / double-walled carbon nanotubes. Please refer to [link / reference needed]. Figure 4 The Raman spectrum of the sample prepared in Example 3 (excitation wavelength: 532 nm) was found to be at 150 cm⁻¹. -1 The product exhibits distinct and sharp RBM characteristic absorption peaks, indicating that it is a high-quality single / double-walled carbon nanotube. The concentrated RBM characteristic peaks and a G / D ratio of 147 suggest high crystallinity. With a yield of 26.2 kg / d, it can achieve a daily production of 20 kg of initial product, possessing an annual production capacity of tons, paving the way for its industrialization. The electrical conductivity is 4.53 × 10⁻⁶. 7 s / m, please refer to Figure 5 The product prepared in Example 3 contains single-walled carbon nanotubes with a diameter of 1.15 nm. Please refer to [link / reference needed]. Figure 6 The product prepared in Example 5 contained double-walled carbon nanotubes with a diameter of 2.1 nm. Figure 7 It can be seen that the specific surface area of ​​single / double-walled carbon nanotubes is relatively large, at 1268.74 m². 2 / g.

[0107] Comparative Example 1

[0108] The continuous carbon nanotube preparation system and method provided in this comparative example are basically the same as those in Example 1, except that an arc-stabilizing agent solution was not injected into the reaction vessel during carbon nanotube growth. The yield of single / double-walled carbon nanotubes was 1.77 kg / d, with a diameter of 1.0-2.8 nm and an aspect ratio of 32850, significantly longer than those in Example 1, and the specific surface area decreased to 316 m². 2 / g, the ratio of G-band peak intensity to D-band peak intensity (G / D ratio) is 32, and the crystallinity also deteriorates. Compared with Example 1, the phase conductivity decreases significantly by 3.1×10 6 s / m.

[0109] Comparative Example 2

[0110] The continuous carbon nanotube preparation system and method provided in this comparative example are basically the same as those in Example 2, except that: during the growth of carbon nanotubes, the distance between the axes of the cathode and anode and the surface of the arc-stabilizing agent solution is 500 mm, the yield of single / double-walled carbon nanotubes is 21.5 kg / d, and the conductivity is 2.12 × 10⁻⁶. 7 s / m, diameter 1.2-2.6nm, aspect ratio 1617, specific surface area 780 m² 2 / g, G / D ratio is 51.

[0111] Comparative Example 3

[0112] The continuous carbon nanotube preparation system and method provided in this comparative example are basically the same as those in Example 1, except that: during the growth of carbon nanotubes, the arc flow rate of the plasma arc is 600 m / s, the yield of single / double-walled carbon nanotubes is 21.7 kg / d, and the electrical conductivity is 1.19 × 10⁻⁶. 7 s / m, diameter 0.9-2.7nm, aspect ratio 1489, specific surface area 913m² 2 / g, G / D ratio is 57.

[0113] Comparative Example 4

[0114] The continuous carbon nanotube preparation system and method provided in this comparative example are basically the same as those in Example 3, except that: when the concentration of the arc stabilizing agent solution is too high (40wt%) during carbon nanotube growth, the arc is severely confined, the energy density is very high, and the arc is short. This causes some of the product to be damaged by high temperature, making it difficult to form highly conductive, high-quality single / double-walled carbon nanotubes. The yield is 3.8 kg / d, and the conductivity is 5.31 × 10⁻⁶. 6 s / m, diameter 1.4-2.8nm, aspect ratio 5326, specific surface area 913 m² 2 / g, G / D ratio is 17.

[0115] Comparative Example 5

[0116] The continuous carbon nanotube preparation system and method provided in this comparative example are basically the same as those in Example 3, except that: when the concentration of the arc stabilizer solution is too low (2wt%), it is difficult to control the arc confinement angle within 15°, and the plasma energy density will drop sharply, failing to provide sufficient energy for growth. This makes it difficult to generate high-quality, high-yield, and highly conductive single / double-walled carbon nanotubes, with a yield of 2.2 kg / d and an electrical conductivity of 2.11 × 10⁻⁶. 6 s / m, diameter 1.8-5.3nm, aspect ratio 2856, specific surface area 438 m² 2 / g, G / D ratio is 13.

[0117] Comparative Example 6

[0118] The continuous carbon nanotube preparation system and method provided in this comparative example are basically the same as those in Example 3, except that the arc length of the plasma arc during carbon nanotube growth is 400 mm. A longer arc length not only lowers the arc temperature but also reduces the arc energy density. The resulting single / double-walled carbon nanotubes will have poor conductivity and quality, and the tube diameter will be uncontrollable. The yield is 1.1 kg / d, and the conductivity is 3.15 × 10⁻⁶. 6 s / m, diameter 0.9-5.6nm, aspect ratio 4589, specific surface area 325 m² 2 / g, G / D ratio is 23.

[0119] Comparative Example 7

[0120] The continuous carbon nanotube preparation system and method provided in this comparative example are basically the same as those in Example 3, except that the arc length of the plasma arc is 20 mm during carbon nanotube growth, which increases the energy density of the arc and allows for the formation of high-quality carbon nanotubes, but at the cost of reduced yield. The yield of single / double-walled carbon nanotubes is 0.3 kg / d, and the conductivity is 1.19 × 10⁻⁶. 7 s / m, diameter 0.6-1.6nm, aspect ratio 860, specific surface area 487 m² 2 / g, G / D ratio is 176.

[0121] Table 2 Product Indicators in Examples

[0122] ;

[0123] As can be seen from Table 2 above, Example 3 is the optimal solution, which achieves the highest level of crystallinity while having a relatively low aspect ratio of carbon nanotubes. More importantly, it also achieves the highest yield.

[0124] In comparison, Comparative Example 2 and Example 2 exhibited essentially similar characteristics overall, but there were still subtle differences between them: during the growth of carbon nanotubes, the distance between the axes of the cathode and anode of Comparative Example 2 and the surface of the arc stabilizer solution was set to 500 mm. This parameter adjustment made Example 2 perform better in terms of crystallinity and yield, with higher crystallinity and more considerable yield.

[0125] Similarly, Comparative Example 3 is consistent with Example 1 in most respects, but the key difference is that the plasma arc flow rate used in Comparative Example 3 was set to 600 m / s during carbon nanotube growth. The comparison reveals that Comparative Example 3 shows improvements in both crystallinity and yield, exhibiting higher crystallinity and higher yield. Comparative Example 1, however, has a relatively low average G / D ratio, reflecting lower crystallinity and a lower yield, failing to achieve the desired effect. Further analysis of the data from Comparative Examples 4, 5, and 6 reveals that the average G / D ratios of these three examples are also low, indicating that the crystallinity is at a low level, failing to achieve the expected crystallization effect. Although Comparative Example 7 has a high G / D ratio, its yield is poor, resulting in low production and limiting its practical application value.

[0126] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for growing carbon nanotubes, characterized in that, include: A voltage is applied between the anode and the cathode to generate an electric arc, and an arc-initiating gas is introduced into the carbon nanotube growth region between the anode and the cathode. At least the arc-initiating ends of the anode and the cathode are immersed in an arc-stabilizing agent solution, thereby forming a spatially compressed plasma arc at least in the carbon nanotube growth region. Then, a catalyst and a carbon source are introduced into the carbon nanotube growth region to grow carbon nanotubes. The ignition gas is an inert gas with an input flow rate of 5-350 L / min, the plasma arc length is 30-350 mm, the plasma arc temperature is 5000-50000 K, and the plasma arc energy density is 102 K. 5 -10 6 The plasma arc has a flow rate of 300-1000 m / s (W / cm²); the distance between the arc-starting ends of the anode and cathode is 10-350 mm; the distance between the axes of the anode and cathode and the surface of the arc-stabilizing agent solution is 100-1200 mm; the arc-stabilizing agent solution compresses the plasma arc to ensure that the diffusion angle of the plasma arc does not exceed 15°; the arc-stabilizing agent content in the arc-stabilizing agent solution is 5-30 wt%, and the conductivity of the arc-stabilizing agent solution is 1-30 S / cm; the arc-stabilizing agent includes one or more of potassium chloride, potassium carbonate, sodium carbonate, barium nitrate, sodium chloride, or calcium-potassium mixed salts. The catalyst comprises a metal component and a flocculant. The metal component comprises one or more of iron, cobalt, and nickel. The flocculant is a sulfur-containing compound. The molar ratio of the metal element in the metal component to the sulfur element in the flocculant is 1:5-80:

1. The carbon source comprises one or more of methane, ethane, ethylene, acetylene, propylene, propane, ethanol, methanol, or natural gas. The flow rate of the carbon source is 3-90 m / s.

2. The carbon nanotube growth method according to claim 1, characterized in that: The arc-igniting gas includes argon.

3. A carbon nanotube growth unit for implementing the carbon nanotube growth method according to any one of claims 1-2, comprising a reaction vessel, an anode, and a cathode, wherein the arc-initiating ends of the anode and the arc-initiating ends of the cathode are spaced apart and opposite to each other, characterized in that, Also includes: An arc stabilizing agent solution supply mechanism is used to inject an arc stabilizing agent solution into the reaction vessel, and when the carbon nanotube growth unit is working, the arc-starting ends of the anode and cathode are both immersed in the arc stabilizing agent solution.

4. The carbon nanotube growth unit according to claim 3, characterized in that, The anode and the cathode are respectively provided with a first nozzle and a second nozzle. The first nozzle is used to output catalyst to the carbon nanotube growth region between the anode and the cathode, and the second nozzle is used to output arc-starting gas or carbon source to the carbon nanotube growth region.

5. The carbon nanotube growth unit according to claim 3, characterized in that, Both the anode and cathode have hollow tubular structures; And / or, the distance between the arc-starting end of the anode and the arc-starting end of the cathode is 10-350 mm; And / or, the anode and cathode are coaxially arranged, and when the carbon nanotube growth unit is working, the distance between the axis of the anode and cathode and the surface of the arc stabilizer solution is 100-1200 mm; And / or, when the carbon nanotube growth unit is operating, the diffusion angle of the plasma arc formed between the anode and the cathode is within 15°; And / or, the diameter of the anode is 5-600 mm, and the diameter of the cathode is 15-200 mm.

6. The carbon nanotube growth unit according to claim 3, characterized in that, The injection flow rate of the arc stabilizing agent solution is 15-260 L / min.

7. The carbon nanotube growth unit according to claim 3, characterized in that, The carbon nanotube growth unit also includes a level gauge for monitoring the level of the arc stabilizer solution in the reaction vessel.

8. The carbon nanotube growth unit according to claim 3, characterized in that, The arc stabilizer solution supply mechanism includes a storage tank and a conveying assembly, the conveying assembly being used to input the arc stabilizer solution in the storage tank into the reaction vessel.

9. The carbon nanotube growth unit according to claim 3, characterized in that, The bottom of the reaction vessel is equipped with a precipitation filtration assembly, which includes a first valve, a second valve, and a precipitation chamber located between the first valve and the second valve. The first valve, through an opening / closing operation, transports the arc stabilizing agent solution containing precipitate in the reaction vessel to the precipitation chamber. The second valve, through an opening / closing operation, transports the arc stabilizing agent solution containing precipitate in the precipitation chamber to the filtration chamber. The filtration chamber is equipped with a filter screen and a filter pump for collecting the precipitate generated during the growth of carbon nanotubes.

10. A continuous carbon nanotube preparation system, characterized in that, The invention includes a carbon nanotube growth unit and a product collection unit as described in any one of claims 3-9; the product collection unit is connected to the reaction vessel and is used to collect the carbon nanotubes generated in the reaction vessel. The product collection unit includes a filtration assembly, a liquid-solid separation assembly, and a collection tank; the reaction vessel is connected to the collection tank, and the collection tank, the liquid-solid separation assembly, and the filtration assembly are connected in sequence; the filtration assembly is used to extract the arc stabilizing agent solution containing carbon nanotubes from the upper layer of the reaction vessel and input it into the collection tank; the liquid-solid separation assembly is used to filter the carbon nanotubes in the arc stabilizing agent solution and store the filtered carbon nanotubes in the collection tank; the arc stabilizing agent solution flows into the liquid-solid separation assembly; the collection tank is provided with a gas outlet for discharging waste gas.

11. A method for continuous preparation of carbon nanotubes, characterized in that, The continuous carbon nanotube preparation method is implemented based on the continuous carbon nanotube preparation system of claim 10, and the continuous carbon nanotube preparation method includes: Carbon nanotubes are synthesized within a carbon nanotube growth unit, and a reaction mixture containing carbon nanotubes is output. The carbon nanotubes in the reaction mixture are separated and collected using a product collection unit.

12. A carbon nanotube, characterized in that, Formed by the carbon nanotube growth method according to any one of claims 1-2 The carbon nanotubes include single-walled or double-walled carbon nanotubes with a G / D ratio exceeding 50 and an electrical conductivity greater than 1.1 × 10⁻⁶. 7 S / m, aspect ratio less than 2000, diameter 0.9-3nm, specific surface area 300-1300 m² 2 / g.

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