Continuous discharging system for single-walled carbon nanotubes prepared by arc method and preparation method thereof

Abstract

The application discloses a continuous discharging system for preparing single-wall carbon nanotubes by an arc method and a preparation method. The system comprises a growth unit, a purging unit, a vortex unit and a collecting unit. The growth unit is provided with a growth tube cavity, and an arc generator is arranged in the growth tube cavity to form a plasma arc. The purging unit is arranged at a first end and is used for inputting purging gas into the growth tube cavity, and the purging gas surrounds the arc generator. The vortex unit is arranged at a second end and is provided with an air flow arrangement structure and is used for limiting the vortex formed by the floating mixed gas in the vortex unit. The collecting unit is communicated with the vortex unit and is used for collecting the carbon nanotubes. The system provided by the application adopts a bottom discharging mode, avoids the accumulation of products around the plasma arc, overcomes the difficulty that a traditional arc furnace system has the advantage of efficiently preparing single-wall carbon nanotubes with high crystallinity but cannot continuously discharge, and has great commercial value and significance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanometer carbon material preparation, and particularly relates to a continuous discharging system for preparing single-wall carbon nanotubes by an arc method and a preparation method. BACKGROUND

[0002] Carbon is one of the most basic elements in nature, and carbon materials almost have all the properties of substances.

[0003] The structure of carbon nanotubes can be regarded as a hollow cylindrical body curled up by graphene layers, and is named as single-wall (single-layer) carbon nanotubes and multi-wall (multi-layer) carbon nanotubes according to the number of curled layers. The single-wall carbon nanotubes can achieve excellent physical and chemical properties by adding a very small amount, so the preparation of single-wall carbon nanotubes has been a hot spot concerned by all circles.

[0004] Among the many single-wall carbon nanotube preparation methods, the plasma arc method has great potential for large-scale preparation of high-crystallinity single-wall carbon nanotubes, because it can provide very high temperature and ionize high-energy particles to provide higher energy to cross the reaction barrier. However, the current vortex generated by the traditional plasma arc furnace structure causes extremely turbulent airflow, and the generated carbon nanotubes are entangled and stacked, which cannot be effectively discharged in time and causes problems such as blockage, so it cannot be continuously prepared. Therefore, designing a new plasma arc furnace system that can quickly and continuously discharge and is not easy to interrupt is a key way to solve this problem. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application aims to provide a continuous discharging system for preparing single-wall carbon nanotubes by an arc method and a preparation method.

[0006] To achieve the foregoing application purposes, the technical solutions adopted by the present application include:

[0007] In a first aspect, the present application provides a continuous discharging system for preparing single-wall carbon nanotubes by an arc method, which comprises a growth unit, a purging unit, a vortex unit and a collection unit arranged in cooperation.

[0008] The growth unit has a growth cavity, and an arc generator is arranged in the growth cavity to form a plasma arc, which is used to convert a growth medium into carbon nanotubes.

[0009] The purging unit is arranged at a first end of the growth cavity, and is used to input a purging gas into the growth cavity. When the purging gas moves in the growth cavity, it surrounds the arc generator and at least mixes with the carbon nanotubes to form floating mixed gas, which moves towards a second end of the growth cavity.

[0010] The vortex unit is arranged at the second end and has an airflow arrangement structure for limiting the vortex of the floating mixed gas formed at the second end in the vortex unit.

[0011] The collecting unit is in communication with the vortex unit for collecting the carbon nanotubes in the floating mixed gas.

[0012] In a second aspect, the application further provides an arc method for preparing single-walled carbon nanotubes, which comprises:

[0013] The above continuous discharging system is used to inject a growth medium into a growth cavity and input a purge gas into the growth cavity from a self-purging unit, a plasma arc generated by an arc generator acts on the growth medium to form single-walled carbon nanotubes.

[0014] The single-walled carbon nanotubes formed are collected from the collecting unit.

[0015] Based on the above technical solution, compared with the prior art, the application has at least the following beneficial effects:

[0016] The bottom discharging method used by the system avoids the accumulation of products around the plasma arc; the plasma arc is limited in the growth unit to avoid the clogging caused by the fact that the growth zone of the traditional arc furnace system is also the material stacking zone; the top downward purge airflow utilizes the characteristics of direct current to facilitate discharging, quickly carries the products to the bottom, avoids the airflow turbulence caused by the vortex of the traditional arc furnace system, and the problem of product entanglement and difficult discharging; more importantly, the downward airflow in the vortex unit with the arc-shaped airflow arrangement structure at the bottom can form a controlled bottom vortex, which can prevent the phenomenon of reverse movement of part of the products to the growth unit caused by the gas backflow due to the large airflow disturbance and temperature gradient of the upper purge airflow, thereby overcoming the difficulty that the traditional arc furnace system has the advantage of efficiently preparing single-walled carbon nanotubes with high crystallinity but cannot continuously discharge, and has great commercial value and significance.

[0017] In addition, the downward cold purge airflow has a partial cooling effect, improves the temperature gradient around the arc and hinders the further growth of catalyst particles, which is beneficial to the formation of single-walled carbon nanotubes, and the direct current is helpful to the formation of the cap end of the carbon nanotube in fluid mechanics, thereby facilitating the nucleation dynamics of the carbon nanotube.

[0018] The above description is only a summary of the technical solutions of the application, in order to enable those skilled in the art to more clearly understand the technical means of the present application, and can be implemented according to the content of the specification, the following is the preferred embodiment of the application and the detailed description of the drawings as follows. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1The structure of the continuous discharging system for preparing single-wall carbon nanotubes by arc method for some typical embodiments of the present application is shown in the schematic view;

[0020] Figure 2 The scanning electron microscope view of the prepared product for a typical embodiment of the present application is shown in the figure;

[0021] Figure 3 The Raman spectrum view of the prepared product for a typical embodiment of the present application is shown in the figure;

[0022] Figure 4 The scanning electron microscope view of the prepared product for another typical embodiment of the present application is shown in the figure;

[0023] Figure 5 The Raman spectrum view of the prepared product for another typical embodiment of the present application is shown in the figure;

[0024] Figure 6 The scanning electron microscope view of the prepared product for another typical embodiment of the present application is shown in the figure;

[0025] Figure 7 The Raman spectrum view of the prepared product for another typical embodiment of the present application is shown in the figure.

[0026] Marked as: 1, feeding unit; 2, growth unit; 3, purging unit; 4, electrode gun; 5, graphite crucible; 6, graphite base; 7, vortex unit; 8, collection tank; 9, air pump; 10, discharging port; 11, tail gas discharge port; 12, filter screen. DETAILED DESCRIPTION

[0027] In view of the deficiencies in the prior art, the present inventors have made long-term research and a large number of practices, and thus have come up with the technical solution of the present application. The technical solution, the implementation process and principles thereof will be further explained as follows.

[0028] In the following description, a lot of specific details are set forth in order to provide a thorough understanding of the present application, however, the present application can also be implemented in other ways different from those described herein, and thus, the protection scope of the present application is not limited by the specific embodiments disclosed below.

[0029] Moreover, the relationship terms such as "first" and "second" are only used to distinguish one from another of the components or method steps with the same name, and do not necessarily require or imply any such actual relationship or sequence between the components or method steps.

[0030] The embodiment of the present application provides a continuous discharging system for preparing single-wall carbon nanotubes by arc method, which comprises a growth unit, a purging unit, a vortex unit and a collecting unit arranged in sequence; the growth unit is provided with a growth cavity, and an arc generator is arranged in the growth cavity to form a plasma arc, which is used for converting a growth medium into carbon nanotubes; the purging unit is arranged at a first end of the growth cavity, and is used for inputting a purging gas into the growth cavity; when the purging gas moves in the growth cavity, it surrounds the arc generator and at least mixes with the carbon nanotubes to form floating mixed gas which moves towards a second end of the growth cavity; the vortex unit is arranged at the second end and is provided with a gas flow arrangement structure, which is used for limiting a vortex of the floating mixed gas formed at the second end in the vortex unit; and the collecting unit is in communication with the vortex unit and is used for collecting the carbon nanotubes in the floating mixed gas.

[0031] In some embodiments, the arc generator comprises oppositely arranged first and second electrodes, and a material input channel, the first and second electrodes form the plasma arc therebetween, and the material input channel is used for conveying the growth medium into the plasma arc.

[0032] In some embodiments, the material input channel is arranged inside the first and / or second electrode.

[0033] In some embodiments, the first electrode extends into the growth cavity along an axial direction of the growth cavity from the first end, and the second electrode extends into the growth cavity along an axial direction of the growth cavity from the vortex unit and in a direction from the second end to the first end.

[0034] In some embodiments, the first electrode comprises a cathode electrode gun, the second electrode comprises a graphite base and a graphite crucible, a bottom end of the graphite base is fixed on an end face of the vortex unit, a top end of the graphite base is in abutment with the graphite crucible, the graphite crucible faces the cathode electrode gun, and a height of the graphite base is more than 5 times of a height of the graphite crucible.

[0035] In some embodiments, the purging unit comprises a purging gas input channel for inputting the purging gas, the purging gas input channel is arranged at the first end and forms a rotationally symmetric gas output structure with the first electrode as a symmetric axis.

[0036] In some embodiments, the gas flow arrangement structure comprises a curved cavity and an extension cavity arranged in sequence along a direction from the first end to the second end, an inlet of the curved cavity is connected with an outlet of the growth cavity, and an outlet of the curved cavity is connected with an inlet of the extension cavity.

[0037] The extension tube cavity is coaxial with the growth tube cavity and the inner diameter of the extension tube cavity is larger than that of the growth tube cavity, at the joint of the curved tube cavity and the growth tube cavity, the inner cavity walls of the curved tube cavity and the growth tube cavity form an edge, and the center of curvature of the curved tube cavity is located inside the vortex unit.

[0038] As to the specific size features, in some embodiments, the ratio of the inner diameter of the growth tube cavity to the inner diameter of the extension tube cavity is 1:1.2-1.5, in specific embodiments, the value is specifically 1:1.37; the radius of curvature of the curved tube cavity is adaptively set, mainly to satisfy that the edge is an acute edge with an included angle less than 90° to prevent the gas flow from having an upward movement trend, and to satisfy that the joint between the curved tube cavity and the extension tube cavity is a relatively smooth transition.

[0039] In some embodiments, the bottom end surface of the growth tube cavity is closed, the outlet of the growth tube cavity is arranged on the side wall of the growth tube cavity close to the bottom end surface; the inlet of the collection unit is connected with the outlet of the growth tube cavity.

[0040] In some embodiments, the collection unit comprises a collection tank, a filter screen and a gas suction pump, the side wall of one end of the collection tank is provided with an inlet communicated with the outlet of the growth tube cavity, the side wall opposite to the inlet is provided with a discharge outlet, the other end of the collection tank is provided with a tail gas discharge outlet, the filter screen is arranged in the collection tank for blocking the product and allowing the gas to pass through, and the gas suction pump is arranged on the side wall of the collection tank for forming a pressure difference between the growth tube cavity and the collection tank.

[0041] The second aspect of the embodiment of the present application further provides an electric arc method for preparing single-walled carbon nanotubes, which comprises the following steps:

[0042] The above-mentioned continuous discharging system is used to inject a growth medium into the growth tube cavity and input a purge gas into the growth tube cavity from the purge unit, a plasma arc generated by the electric arc generator acts on the growth medium to form single-walled carbon nanotubes.

[0043] The single-walled carbon nanotubes formed are collected from the collection unit.

[0044] Referring to Figure 1As shown, the embodiment of the present application exemplarily provides a continuous discharge system and process method for preparing single-walled carbon nanotubes by arc method, which comprises a feeding unit 1, a growth unit 2, a purging unit 3, a vortex unit 7 and a collecting unit. The feeding unit 1 is used for sending catalyst into a plasma arc area by carrier gas. The carrier gas can be argon or helium, but is not limited to them. The growth unit 2 has a growth tube cavity, and a device for generating plasma arc in the cavity is used for generating plasma arc to provide reaction conditions for carbon nanotube growth of catalyst and mixed gas. The purging unit 3 is used for quickly vertically taking the generated carbon nanotube product into the bottom to achieve partial cooling effect, improve the temperature gradient around the plasma arc and reduce the further growth of catalyst particles, which is beneficial to the formation of single-walled carbon nanotubes, and also helps the nucleation kinetics of the cap end of the carbon nanotube. The vortex unit 7 is used for preventing the phenomenon of excessive purging gas flow and temperature gradient from causing the upward movement of part of the product to the upper growth unit 2 by using the characteristics of vortex formed in the arc area by the downward airflow. The collecting unit is used for storing the carbon nanotube product and realizing discharge collection.

[0045] The growth unit 2 can specifically include a cathode electrode gun 4, an anode graphite crucible 5 and a graphite base 6. The center of the graphite crucible 5 coincides with the center of the arc furnace growth unit 2, the electrode gun 4 is suspended above the anode graphite crucible 5 by 5-30 cm, and the height of the graphite base 6 is more than 5 times the height of the graphite crucible 5, which supports the graphite crucible 5 and provides current for the graphite crucible 5.

[0046] The purging unit 3 is composed of at least 4 center-symmetrically distributed gas inlets. The gas inlets are equal-diameter cylinders and are connected to the upper end of the growth unit 2, the gas in the gas inlets is inert gas, and the gas flow is 0.5-3 times the gas flow of the electrode gun 4 (i.e. the gas flow of the growth medium), and the inert gas includes argon or helium.

[0047] The upper end of the vortex unit 7 is an arc-shaped wall, and the upper end is connected to the lower end of the straight-cylinder growth unit 2.

[0048] The collecting unit includes a collecting tank 8, a filter screen 12, a tail gas discharge port 11, a discharge port 10 and a gas suction pump 9. The left end of the collecting tank 8 is connected to the bottom of the right end of the vortex unit 7 through a pipe, the filter screen 12 is located in the upper part of the collecting tank 8, the tail gas discharge port 11 is located at the rightmost upper end of the collecting tank 8, the discharge port 10 is located at the center of the lowermost end of the collecting tank 8, and the gas suction pump 9 is located at the upper end of the collecting tank 8 close to the connection end of the collecting pipe and the vortex unit 7. The right end of the feeding unit 1 is connected to the left end of the growth unit 2.

[0049] As to the specific process, the mixed gas is generally hydrogen, carbon source and inert gas. The carbon source is methane, ethylene, propylene or acetylene, and the inert gas is argon or helium. Further, the mixed gas enters from the channel in the electrode gun 4. Further, the hydrogen, carbon source and inert gas in the mixed gas can be 3-6L / min, 6-10L / min and 20-40L / min, respectively.

[0050] The electrode gun 4 is a plasma electrode gun 4, and the power of the plasma electrode gun 4 is greater than 10kW.

[0051] Using the above system and method, the single-walled carbon nanotubes prepared by the continuous discharge system of the arc method have the following Raman characteristics: G / I D The I -1 / I -1 is greater than 50, and the continuous discharge is not blocked.

[0052] The technical solutions of the present application are further described in detail below by several embodiments in conjunction with the drawings. However, the selected embodiments are only used to illustrate the present application, and do not limit the scope of the present application.

[0053] Embodiment 1

[0054] Using the continuous discharge system for preparing single-walled carbon nanotubes by arc method as shown in Figure 1 , first, the argon gas is introduced into the growth unit from the electrode gun at a gas flow rate of 20L / min to perform evacuation, then the power of the plasma arc furnace is set to 20kW, the arc discharge is formed to form plasma at a distance of 5cm between the electrode gun and the graphite crucible, then when the temperature rises to 2200℃, the catalyst is introduced from the feeding port, the hydrogen, methane and argon are introduced from the electrode gun at a gas flow rate of 4L / min, 8L / min and 20L / min respectively to generate the product; at the same time, the argon gas is introduced from the four gas inlets of the purging unit at a gas flow rate of 16L / min to carry the generated product to the bottom, and then flow into the collection tank, so that the continuous preparation can be realized. As shown in Figure 2 , it is a scanning electron microscope image of the product prepared in embodiment 1 of the present application, Figure 3 , it is a Raman spectrum of the product prepared in embodiment 1 of the present application, and from the spectrum, the RBM characteristic peak unique to single-walled carbon nanotubes can be seen in the range of 100-300cm -1 , and the D and G peak values corresponding to 1350cm -1 and 1590cm -1 nearby in the spectrum can be calculated as I G / I D equal to 51, indicating that the product has high crystallinity.

[0055] Embodiment 2

[0056] Adopting such Figure 1 The illustrated continuous discharge system for preparing single-walled carbon nanotubes using the electric arc method first purges the growth unit with argon gas at a flow rate of 20 L / min from the electrode gun. Then, the power supply of the plasma arc furnace is set to 20 kW, and an arc discharge is initiated at a distance of 7 cm from the graphite crucible to form plasma. Next, when the temperature reaches 2400℃, a catalyst is introduced through the feed inlet, and hydrogen, methane, and argon are introduced through the electrode gun at flow rates of 6 L / min, 8 L / min, and 20 L / min, respectively, to generate the product. Simultaneously, argon gas is introduced through the four inlets of the purging unit at a flow rate of 18 L / min to carry the generated product to the bottom, where it flows into the collection tank, enabling continuous production. Figure 4 The image shown is a scanning electron microscope image of the product prepared in Example 1 of this invention. Figure 5 The image shows the Raman spectrum of the product prepared in Example 1 of this invention. The horizontal axis of the spectrum is 100-300 cm⁻¹. -1 The spectrum shows characteristic RBM peaks unique to single-walled carbon nanotubes, with the peak at 1350 cm⁻¹. -1 and 1590 cm -1 I can be calculated from the corresponding D and G peak values ​​in the vicinity. G / I D A value of 59 indicates that the product has high crystallinity.

[0057] Example 3

[0058] Adopting such Figure 1 The illustrated continuous discharge system for preparing single-walled carbon nanotubes using the electric arc method first purges the growth unit with argon gas at a flow rate of 20 L / min from the electrode gun. Then, the power of the plasma arc furnace is set to 15 kW, and an arc discharge is initiated at a distance of 7 cm from the graphite crucible to form plasma. Next, when the temperature reaches 2200℃, a catalyst is introduced through the feed inlet, and hydrogen, methane, and argon are introduced through the electrode gun at flow rates of 4 L / min, 10 L / min, and 25 L / min, respectively, to generate the product. Simultaneously, argon gas is introduced through the four inlets of the purging unit at a flow rate of 20 L / min to carry the generated product to the bottom, where it flows into the collection tank, enabling continuous production. Figure 6 The image shown is a scanning electron microscope image of the product prepared in Example 1 of this invention. Figure 7 The image shows the Raman spectrum of the product prepared in Example 1 of this invention. The horizontal axis of the spectrum is 100-300 cm⁻¹. -1 The spectrum shows characteristic RBM peaks unique to single-walled carbon nanotubes, with the peak at 1350 cm⁻¹. -1 and 1590 cm -1I can be calculated from the corresponding D and G peak values ​​in the vicinity. G / I D A value of 52 indicates that the product has high crystallinity.

[0059] Example 4

[0060] Adopting such Figure 1 The illustrated continuous feed system for preparing single-walled carbon nanotubes using the electric arc method first purges the growth unit with argon gas at a flow rate of 20 L / min through the electrode gun. Then, the power supply of the plasma arc furnace is set to 25 kW, and an arc discharge is initiated at a distance of 5 cm from the graphite crucible to form plasma. Next, when the temperature reaches 2400 °C, the catalyst is introduced through the feed inlet, and hydrogen, methane, and argon are introduced through the electrode gun at flow rates of 6 L / min, 8 L / min, and 25 L / min, respectively, to generate the product. Simultaneously, argon gas is introduced through the four inlets of the purging unit at a flow rate of 20 L / min to carry the generated product to the bottom, where it flows into the collection tank, enabling continuous production. The calculated Raman spectroscopy results for the product are shown. G / I D A value of 55 indicates that the product has high crystallinity.

[0061] Comparative Example 1

[0062] This comparative example is largely the same as Example 1, with the main difference being:

[0063] Instead of using a vortex unit, the bottom sidewall of the growth unit is directly connected laterally to the collection tank.

[0064] Because there is no eddy current unit to regulate the process, the product at the bottom will return to the plasma region, affecting continuous preparation and significantly shortening the time for continuous and stable operation of the equipment.

[0065] Comparative Example 2

[0066] This comparative example is largely the same as Example 1, with the main difference being:

[0067] The curved surface segment of the vortex element is modified into a flat, frustum-shaped cone, connecting pipe segments of different diameters at the top and bottom.

[0068] Because the cross-sectional shape has been changed to a non-curved surface, the eddy current rectification effect is also lost, and the product backflow phenomenon will occur, resulting in the loss of long-term continuous preparation capability.

[0069] Based on the above embodiments, it can be clear that the embodiments of the present application provide a continuous discharge system and method for preparing single-walled carbon nanotubes by arc method, which belongs to the technical field of new materials. The system comprises a feeding unit, a growth unit, a purging unit, a vortex unit and a collecting unit. The catalyst and mixed gas are sent into the arc growth unit by the feeding unit and the electrode gun respectively, carbon nanotube growth is carried out, the top of the growth unit is centrally symmetrically distributed with purging ports, the products are directly brought into the vortex unit, and finally flow into the collecting unit. The present application utilizes fluid mechanics design, not only realizes the continuous and smooth discharge of carbon nanotube products, but also the downward cold purging straight flow gas, which is beneficial to improve the temperature gradient around the arc and inhibit the growth of catalyst particles, thereby being beneficial to the formation of high-quality single-walled carbon nanotubes, overcoming the problem that the traditional arc furnace system has the advantage of efficiently preparing high-crystallinity single-walled carbon nanotubes but cannot continuously discharge, and has great commercial value and significance.

[0070] It should be understood that the above embodiments are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made in accordance with the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A continuous discharge system for electric arc method of single wall carbon nanotube production, characterized by, The growth unit, the purging unit, the vortex unit and the collecting unit are arranged in cooperation; The growth unit has a growth cavity in which an arc generator is arranged for forming a plasma arc for converting a growth medium into carbon nanotubes; The purging unit is arranged at a first end of the growth cavity for inputting a purging gas into the growth cavity, the purging gas moving in the growth cavity and surrounding the arc generator and mixing with the carbon nanotubes at least to form a floating mixed gas moving towards a second end of the growth cavity; The vortex unit is arranged at the second end and has a gas flow arrangement structure for limiting a vortex of the floating mixed gas formed at the second end in the vortex unit, the gas flow arrangement structure including a curved cavity and an extension cavity arranged in sequence along a direction from the first end to the second end, an inlet of the curved cavity being connected with an outlet of the growth cavity, an outlet of the curved cavity being connected with an inlet of the extension cavity, the extension cavity being coaxial with the growth cavity and having an inner diameter larger than that of the growth cavity, at a connection between the curved cavity and the growth cavity, inner cavity walls of the curved cavity and the growth cavity form an edge, and a curvature center of the curved cavity is located inside the vortex unit; The collecting unit is in communication with the vortex unit for collecting the carbon nanotubes in the floating mixed gas.

2. The continuous dischargeable system of claim 1, wherein, The arc generator includes oppositely arranged first and second electrodes and a material input channel, the first and second electrodes forming the plasma arc therebetween, and the material input channel being used for conveying the growth medium into the plasma arc.

3. The continuous dischargeable system of claim 2, wherein, The material input channel is arranged inside the first electrode and / or the second electrode.

4. The continuous dischargeable system according to claim 2 or 3, characterized in that, The first electrode extends into the growth cavity along an axial direction of the growth cavity from the first end, and the second electrode extends into the growth cavity along an axial direction of the growth cavity from the vortex unit and in a direction from the second end to the first end.

5. The continuous dischargeable system of claim 4, wherein, The first electrode includes a cathode electrode gun, the second electrode includes a graphite base and a graphite crucible, a bottom end of the graphite base is fixed on an end face of the vortex unit, a top end of the graphite base is in abutment with the graphite crucible, the graphite crucible faces the cathode electrode gun, and a height of the graphite base is more than 5 times a height of the graphite crucible.

6. The continuous outfeed system of claim 4, wherein, The purging unit includes a purging gas input channel for inputting the purging gas, the purging gas input channel being arranged at the first end and forming a rotationally symmetric gas outlet structure with the first electrode as a symmetric axis.

7. The continuous outfeed system of claim 1, wherein, A bottom end face of the growth cavity is closed, and an outlet of the growth cavity is arranged on a side wall of the growth cavity close to the bottom end face; An inlet of the collecting unit is connected with the outlet of the growth cavity.

8. The continuous outfeed system of claim 1, wherein, The collecting unit comprises a collecting tank, a filter screen and a suction pump. An inlet is formed in the side wall of one end of the collecting tank and communicates with the outlet of the growth tube cavity. An outlet is formed in the side wall opposite to the inlet. A tail gas discharge port is arranged at the other end of the collecting tank. The filter screen is arranged in the collecting tank to block the product and allow the gas to pass through. The suction pump is arranged on the side wall of the collecting tank to form a pressure difference between the growth tube cavity and the collecting tank.

9. An arc method for preparing single-walled carbon nanotubes, characterized by, The method comprises the following steps: The single-walled carbon nanotubes are collected from the collecting unit. The single-walled carbon nanotubes are collected from the collecting unit.

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