Device and method for preparing single-walled carbon nanotube by thermal plasma CVD (chemical vapor deposition) method

Abstract

The invention discloses a device and a method for preparing a single-walled carbon nanotube by a thermal plasma CVD (chemical vapor deposition) method, and relates to the technical field of nano carbon material preparation, the device structurally comprises a thermal plasma electric arc furnace, a CVD growth chamber, a cooling chamber and a collecting tank which are sequentially connected in series, the thermal plasma electric arc furnace structurally comprises hollow graphite serving as a cathode, a graphite crucible serving as an anode and a furnace body. The graphite crucible is located on the lower portion of the thermal plasma electric arc furnace, and the hollow graphite is located on the upper portion of the thermal plasma electric arc furnace and above the graphite crucible. According to the device and the method, a two-step continuous growth process is adopted, so that the yield and the quality of the single-walled carbon nanotube are remarkably improved; and meanwhile, the common problems of excessive catalyst, coking short circuit, arc breaking and the like in the process of preparing the single-walled carbon nanotube by a conventional plasma arc method can be effectively avoided through a shallow crucible and a bottom gas inlet mode, so that the continuous stability and the yield of the reaction are greatly improved, and the method is an effective route for large-scale preparation and has important commercial value.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of carbon nanomaterials, and particularly provides a device and a method for preparing single-walled carbon nanotubes by a thermal plasma CVD method. Background Art

[0002] Single-walled carbon nanotubes are tubular nanomaterials formed by curling a single layer of graphene, and have excellent mechanical, electrical and thermal properties, showing great application potential in the fields of electronic devices, energy storage, composite materials, etc. The development of their preparation methods has experienced a process from laboratory exploration to industrial promotion. Currently, the mainstream technologies mainly include arc discharge method, laser ablation method, chemical vapor deposition method (CVD) and its derivative processes. Different methods have their own characteristics in terms of yield, purity, cost and structure controllability. The core challenge of SWCNTs preparation technology lies in how to balance large-scale production and precise structure control. Balancing efficiency and quality is still the key problem in the large-scale preparation and application of single-walled carbon nanotubes. Developing new and efficient preparation equipment and methods is still a hot topic in current research.

[0003] Chinese invention patent CN 201910533219.0 is a method for preparing single-walled carbon nanotubes, which uses a plasma arc to evaporate a catalyst metal to prepare a catalyst, and at the same time introduces a carbon source gas. The high-temperature plasma simultaneously realizes the high-temperature evaporation of the metal to prepare the catalyst and the cracking of the organic carbon source, and directly prepares single-walled carbon nanotubes.

[0004] Chinese invention patent 202210608795.9 utilizes the high-temperature zone formed by an arc confined in a deep graphite crucible to obtain a higher reaction temperature and a longer reaction residence time. At the same time, by using the activation effect of arc plasma, single-walled carbon nanotubes with high crystallinity can be prepared. Summary of the Invention

[0005] However, the biggest drawback of the above methods is the excessive evaporation of the catalyst, and the catalyst particle size cannot be effectively screened. In addition, the problems of catalyst condensation and carbon nanotube product coking formed between the electrodes will cause a short circuit between the cathode and the anode, resulting in arc interruption, and the arc stability will drop sharply, making it difficult to achieve stable and continuous preparation. Therefore, controlling the catalyst evaporation amount and avoiding electrode coking are the core points to ensure the high-quality continuous preparation of the product.

[0006] The present invention provides the following technical solutions for the above problems:

[0007] On the one hand, the present invention provides a device for preparing single-walled carbon nanotubes by a thermal plasma CVD method. The structure of the device includes a thermal plasma arc furnace, a CVD growth chamber, a cooling chamber and a collection tank connected in series in sequence, wherein:

[0008] The structure of the thermal plasma arc furnace includes a hollow graphite as the cathode, a graphite crucible as the anode, and a furnace body;

[0009] The graphite crucible is located at the lower part of the thermal plasma arc furnace, and the hollow graphite is located above the upper part of the thermal plasma arc furnace and above the graphite crucible;

[0010] The hollow graphite enters the furnace body obliquely at a certain angle with the vertical direction of the graphite crucible, and the inclination angle is 30 - 80°;

[0011] The graphite crucible is a shallow crucible with through holes at the edge, the inner wall of the crucible is arc-shaped, and the depth is 1 - 5 cm.

[0012] Furthermore, the device also includes an air supply port and an air inlet. Among them, the air supply port is located between the thermal plasma arc furnace and the CVD growth chamber; the air inlet is located at the left end of the thermal plasma arc furnace.

[0013] Furthermore, the structure of the collection tank includes a screen, a pulse backwashing port, an exhaust port, and a discharge port. Among them, the pulse backwashing port and the exhaust port are located at the upper end of the collection tank, the screen is located below the pulse backwashing port and the exhaust port, and the discharge port is located at the lower end of the collection tank.

[0014] The collection tank uses a metal screen for filtration and enrichment. Combined with the pulse backwashing port, the product enriched on the screen is blown to the bottom discharge port, and then the finished product is collected, and the excess gaseous substances are discharged from the air outlet.

[0015] The power of the plasma power supply is 100 - 1000 kW, the current is 100 - 10000 A, and the voltage is 10 - 500 V.

[0016] On the other hand, the present invention provides a method for preparing single-walled carbon nanotubes by thermal plasma CVD. The method includes generating an arc between the cathode and the anode of the plasma arc furnace to raise the furnace temperature, then sending the catalyst from the hollow cathode to the position of the graphite crucible, quickly evaporating to form catalyst clusters, and discharging the excess catalyst through the discharge port of the arc furnace; at the same time, the carbon source mixed gas enters the plasma arc furnace through the through holes at the edge of the anode graphite crucible, cracks and combines with the catalyst clusters, enters the CVD growth chamber to grow into single-walled carbon nanotubes, and enters the collection tank under the carrier gas to obtain the final product.

[0017] Furthermore, the method specifically includes the following steps:

[0018] S1) Introduce plasma gas, turn on the plasma power supply, generate a plasma arc between the anode and the cathode, raise the furnace temperature to the specified temperature, and at the same time turn on the heating of the CVD growth chamber to the growth temperature;

[0019] S2) The catalyst is sent to the crucible position through the hollow electrode channels, and is rapidly evaporated to form catalyst clusters. The excess unevaporated catalyst particles are blown by the carrier gas blown out from the air inlet 3 to the discharge port of the electric arc furnace.

[0020] S3) At the same time, after mixing the carbon source gas and the carrier gas, they enter the plasma arc furnace through the through holes on the edge of the graphite crucible, and after high-temperature cracking, they enter the CVD growth chamber together with the catalyst.

[0021] S4) In the CVD growth chamber, the carbon source gas and the carrier gas are further supplemented through the gas supplement port to achieve the full growth of single-walled carbon nanotubes.

[0022] S5) The product is cooled by the cooling section driven by the carrier gas, then enters the collection tank, and the product enriched on the sieve mesh is blown to the discharge port through the pulse back-blow port to collect the final product.

[0023] Furthermore, in the step S1), the plasma gas is any one, two or more of argon, nitrogen, helium, hydrogen, water vapor, and the mixed gas with any mixing ratio, and the flow rate is 10 - 500 L / min;

[0024] The specified temperature of the furnace chamber is 1200 - 2000 °C; the growth temperature of the CVD chamber is 900 - 1400 °C.

[0025] Furthermore, in the step S2), the catalyst is a mixed powder of 50 - 95% metal powder and 5 - 50% promoter, where:

[0026] The metal powder is iron, cobalt or nickel metal or a mixture thereof;

[0027] Or an alloy or mixture of iron, cobalt or nickel and refractory metals, where the refractory metal elements are molybdenum, tungsten, tantalum, niobium, hafnium or zirconium, the weight ratio content of the refractory metal elements is 20 - 60%, and the particle size is 50 - 350 mesh;

[0028] The promoter is any one or a mixture of sulfur powder, selenium powder, iron sulfide, ferrous sulfide, nickel sulfide or cobalt sulfide, and the particle size is 100 - 500 mesh;

[0029] The catalyst feeding rate is 0.1 g / min - 100 g / min.

[0030] Furthermore, in the step S3), the carbon source gas is any one of methane, ethylene, acetylene, propylene or propane; the carrier gas is a mixed gas of an inert gas such as nitrogen, argon or helium and hydrogen, where the volume of the carbon source gas is 10 - 80%; the volume of hydrogen gas is 0 - 35%, and the rest is an inert gas such as nitrogen, argon or helium, and the total flow rate is 10 - 200 L / min.

[0031] Further, in the step S4), the total flow rate of the carbon source gas and the carrier gas further supplemented in the CVD growth chamber is 10 - 200 L / min.

[0032] Further, in the step S5), the aperture of the sieve 10 is 0.5 - 50 mm, the gas for back blowing is nitrogen, argon or helium, and the pulse back blowing frequency is 5 - 300 seconds / time.

[0033] Compared with the prior art, the device and method for preparing single-walled carbon nanotubes by a thermal plasma CVD method of the present invention have the following outstanding beneficial effects:

[0034] The device and method of the present invention adopt a two-step continuous growth process, significantly improving the yield and quality of single-walled carbon nanotubes; at the same time, the shallow crucible and the bottom gas inlet method can effectively avoid common problems such as excessive catalyst, coking short circuit, and arc breakage during the preparation of single-walled carbon nanotubes by the conventional plasma arc method, greatly improving the continuous stability and yield of the reaction, which is an effective route for large-scale preparation and has important commercial value. Description of the Drawings

[0035] Figure 1 is a schematic structural diagram of the preparation device of the present invention;

[0036] Figure 2 is a schematic diagram of the graphite citrus structure of the present invention;

[0037] Figure 3 is a scanning electron microscope image of the prepared carbon nanotube product;

[0038] Figure 4 is a Raman spectrum diagram of the prepared carbon nanotube product. Detailed Embodiments

[0039] The present invention will be further described in detail below with reference to the drawings and embodiments.

[0040] As Figure 1 shown, a device for preparing single-walled carbon nanotubes by a thermal plasma CVD method, the structure of the device includes a thermal plasma arc furnace 4, a CVD growth chamber 7, a cooling chamber 8 and a collection tank 9 connected in series in sequence, wherein:

[0041] The structure of the thermal plasma arc furnace 4 includes a hollow graphite 5 as the cathode, a graphite crucible 2 as the anode and a furnace body;

[0042] The graphite crucible 2 is located at the lower part of the thermal plasma arc furnace 4, and the hollow graphite 5 is located above the graphite crucible 2 at the upper part of the thermal plasma arc furnace 4;

[0043] The hollow graphite 5 obliquely enters the furnace body at a certain angle with the vertical direction of the graphite crucible 2, and the inclination angle is 30 - 80°;

[0044] As Figure 2 shown, the graphite crucible 2 is a shallow crucible with through holes 1 at the edge. The inner wall of the crucible is arc-shaped and the depth is 1 - 5 cm.

[0045] The device further includes an air supplement port 6 and an air inlet 3. Among them, the air supplement port 6 is located between the thermal plasma arc furnace 4 and the CVD growth chamber 7; the air inlet 3 is located at the left end of the thermal plasma arc furnace 4.

[0046] The structure of the collection tank 9 includes a screen 10, a pulse back-blow port 11, an exhaust port 12, and a discharge port 13. Among them, the pulse back-blow port 11 and the exhaust port 12 are located at the upper end of the collection tank 9, the screen 10 is located below the pulse back-blow port 11 and the exhaust port 12, and the discharge port 13 is located at the lower end of the collection tank 9.

[0047] The collection tank 9 uses a metal screen 10 for filtration and enrichment. Combined with the pulse back-blow port 11, the product enriched on the screen 10 is blown down to the bottom discharge port 13, and then the finished product is collected, and the excess gaseous substances are discharged from the air outlet 12.

[0048] Example 1

[0049] Adopt the device for preparing single-walled carbon nanotubes by thermal plasma CVD method as Figure 1 shown. This device is composed of a thermal plasma arc furnace, a CVD growth chamber, a cooling chamber and a collection tank in series. Among them, the thermal plasma arc furnace is composed of a hollow graphite cathode, a graphite crucible anode, a furnace body and an auxiliary system; among them, the hollow graphite cathode and the graphite crucible anode enter the furnace body obliquely at a certain angle, and the inclination angle is 60°; the graphite crucible anode is a shallow crucible with through holes at the edge (as Figure 2 ), the inner wall of the crucible is arc-shaped, and the depth is 2 cm; the power of the plasma power supply is 150 kW, the current is 1000 A, and the voltage is 150 V.

[0050] The preparation process of single-walled carbon nanotubes:

[0051] S1) Introduce the plasma gas argon with a flow rate of 50 L / min, turn on the plasma power supply, generate a plasma arc between the anode and the cathode, raise the furnace temperature to 1500 °C, and at the same time turn on the heating of the CVD growth chamber to raise the temperature to the growth temperature of 1200 °C;

[0052] S2) Send the catalyst (Fe80%-FeS20% mixed powder, particle size 200 mesh) to the crucible position through the hollow electrode channel, with a powder feeding rate of 5 g / min, and quickly evaporate to form catalyst clusters. The excess unevaporated catalyst particles are blown to the discharge port of the arc furnace;

[0053] S3) After mixing the carbon source gas and the carrier gas simultaneously, they enter the plasma arc furnace through the outer edge channels of the graphite crucible. After high-temperature pyrolysis, they enter the CVD growth chamber together with the catalyst. The volume fractions of methane, hydrogen, and argon in the mixed gas are 20%, 40%, and the rest is argon, respectively, and the flow rate is 50 L / min.

[0054] S4) Further supplement the carbon source gas and the carrier gas in the CVD growth chamber to achieve the full growth of single-walled carbon nanotubes. The volume fractions of methane, hydrogen, and argon in the supplemented carbon source mixed gas are 40%, 20%, and the rest is argon, respectively, and the flow rate is 50 L / min.

[0055] S5) The product is cooled in the cooling section driven by the carrier gas and then enters the collection tank. The product enriched on the 2-mm aperture filter screen is blown off to the discharge port by nitrogen pulse backwashing (backwashing frequency: 15 seconds / time), and the final product is collected.

[0056] The reaction can proceed stably. After 72 hours of reaction, the product is collected and weighed. The yield of single-walled carbon nanotubes can reach ~1250 g / h. The product is calcined in a muffle furnace at 900 °C for 2 hours and then weighed for the ash content. The purity of the product is calculated to be 86.3%. The morphology of the product is observed by a scanning electron microscope as Figure 4 shown. The crystallinity is evaluated by the intensity ratio of the G peak and the D peak in the Raman spectrum, as Figure 3 shown, and the G / D ratio is ~68.4.

[0057] Example 2

[0058] Using the device for preparing single-walled carbon nanotubes by the thermal plasma CVD method as Figure 1 shown, this equipment consists of a thermal plasma arc furnace, a CVD growth chamber, a cooling chamber, and a collection tank connected in series. The thermal plasma arc furnace consists of a hollow graphite cathode, a graphite crucible anode, a furnace body, and an auxiliary system. The hollow graphite cathode and the graphite crucible anode enter the furnace body obliquely at a certain angle, and the inclination angle is 30°. The graphite crucible anode is a shallow crucible with through holes on the edge (as Figure 2 )), the inner wall of the crucible is arc-shaped, and the depth is 2 cm. The power of the plasma power supply is 300 kW, the current is 1500 A, and the voltage is 200 V.

[0059] The preparation process of single-walled carbon nanotubes:

[0060] S1) Introduce the plasma gas argon with a flow rate of 100 L / min, turn on the plasma power supply to generate a plasma arc between the anode and the cathode, raise the furnace temperature to 1700 °C, and at the same time turn on the heating of the CVD growth chamber to raise the temperature to the growth temperature of 1100 °C.

[0061] S2) Send the catalyst (Fe 72%-Mo 18%-S 10% mixed powder, particle size 200 mesh) to the crucible position through the hollow electrode channel at a powder feeding rate of 10 g / min, and quickly evaporate to form catalyst clusters. The excess unevaporated catalyst particles are blown to the discharge port of the electric arc furnace;

[0062] S3) At the same time, after mixing the carbon source gas and the carrier gas, they enter the plasma arc furnace through the channel along the outer edge of the graphite crucible, and after high-temperature cracking, they enter the CVD growth chamber together with the catalyst. Among them, the volume fraction in the mixed gas is 20% ethylene, 40% hydrogen, and the rest is argon, and the flow rate is 80 L / min;

[0063] S4) Further supplement the carbon source gas and the carrier gas in the CVD growth chamber to achieve the full growth of single-walled carbon nanotubes. Among them, the volume fraction in the supplemented carbon source mixed gas is 40% ethylene, 20% hydrogen, and the rest is argon, and the flow rate is 100 L / min;

[0064] S5) The product is cooled in the cooling section driven by the carrier gas and then enters the collection tank. The product enriched on the 2-mm pore size filter screen is blown to the discharge port by nitrogen pulse back blowing (back blowing frequency 15 seconds / time), and the final product is collected.

[0065] The reaction can proceed continuously and stably. After 72 hours of reaction, the product is collected and weighed. The yield of single-walled carbon nanotubes can reach ~1750 g / h. The ash is weighed after calcination in a muffle furnace at 900 °C for 2 hours, and the product purity is calculated to be 87.5%. The morphology of the product is observed by scanning electron microscope as Figure 4 shown, and the crystallinity is evaluated by the peak intensity ratio of the G peak and the D peak in the Raman spectrum, as Figure 3 shown, and the G / D ratio is ~65.4.

[0066] Example 3

[0067] Use the device for preparing single-walled carbon nanotubes by thermal plasma CVD method as Figure 1 shown. The device consists of a thermal plasma arc furnace, a CVD growth chamber, a cooling chamber and a collection tank connected in series. Among them, the thermal plasma arc furnace consists of a hollow graphite cathode, a graphite crucible anode, a furnace body and an auxiliary system; among them, the hollow graphite cathode and the graphite crucible anode enter the furnace body obliquely at a certain angle, and the inclination angle is 60°; the graphite crucible anode is a shallow crucible with through holes at the edge (such as Figure 2 ), the crucible has an arc-shaped inner wall, and the depth is 2 cm; the power of the plasma power supply is 150 kW, the current is 1000 A, and the voltage is 150 V.

[0068] Process for preparing single-walled carbon nanotubes:

[0069] S1) Introduce argon, a plasma gas, with a flow rate of 50 L / min. Turn on the plasma power supply to generate a plasma arc between the anode and the cathode, raise the furnace temperature to 1500 °C, and at the same time turn on the heating of the CVD growth chamber to raise the temperature to the growth temperature of 1400 °C;

[0070] S2) Send the catalyst (Co48%-Mo32%-S20% mixed powder, particle size 200 mesh) to the crucible position through the hollow electrode channel at a powder feeding rate of 5 g / min, and quickly evaporate to form catalyst clusters. The excess unevaporated catalyst particles are blown to the discharge port of the electric arc furnace;

[0071] S3) At the same time, after mixing the carbon source gas and the carrier gas, they enter the plasma arc furnace through the outer edge channel of the graphite crucible, and after high-temperature cracking, they enter the CVD growth chamber together with the catalyst. Among them, the volume fraction of propylene in the mixed gas is 20%, hydrogen is 40%, and the rest is argon, with a flow rate of 50 L / min;

[0072] S4) Further supplement the carbon source gas and the carrier gas in the CVD growth chamber to achieve the full growth of single-walled carbon nanotubes. Among them, the volume fraction of propylene in the supplemented carbon source mixed gas is 60%, hydrogen is 10%, and the rest is argon, with a flow rate of 100 L / min;

[0073] S5) The product is cooled in the cooling section driven by the carrier gas, and then enters the collection tank. The product enriched on the 2-mm aperture filter screen is blown off to the discharge port by nitrogen pulse backwashing (backwashing frequency: 15 seconds / time), and the final product is collected.

[0074] The reaction can proceed continuously and stably. After 72 hours of reaction, the product is collected and weighed. The yield of single-walled carbon nanotubes can reach ~1550 g / h. The product is calcined in a muffle furnace at 900 °C for 2 hours, and the ash is weighed. The purity of the product is calculated to be 85.8%. The morphology of the product is observed by a scanning electron microscope as Figure 4 shown, and the crystallinity is evaluated by the intensity ratio of the G peak and the D peak in the Raman spectrum, as Figure 3 shown, and the G / D ratio is ~78.2.

[0075] The above embodiments are only relatively preferred specific embodiments of the present invention. The general changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. An apparatus for preparing single-walled carbon nanotubes by thermal plasma CVD method, characterized in that, The structure of the device includes a thermal plasma arc furnace (4), a CVD growth chamber (7), a cooling chamber (8), and a collection tank (9) connected in series in sequence, where: The structure of the thermal plasma arc furnace (4) includes a hollow graphite (5) serving as the cathode, a graphite crucible (2) serving as the anode, and a furnace body; The graphite crucible (2) is located at the lower part of the thermal plasma arc furnace (4), and the hollow graphite (5) is located above the upper part of the thermal plasma arc furnace (4) and above the graphite crucible (2); The hollow graphite (5) obliquely enters the furnace body at a certain angle with respect to the vertical direction of the graphite crucible (2); The graphite crucible (2) is a shallow crucible with through holes (1) at the edge.

2. The apparatus for preparing single-walled carbon nanotubes by thermal plasma CVD method according to claim 1, wherein, The device further includes a gas supplement port (6) and a gas inlet port (3). Among them, the gas supplement port (6) is located between the thermal plasma arc furnace (4) and the CVD growth chamber (7); the gas inlet port (3) is located at the left end of the thermal plasma arc furnace (4).

3. The apparatus for preparing single-walled carbon nanotubes by thermal plasma CVD according to claim 1 or 2, characterized in that, The structure of the collection tank (9) includes a sieve mesh (10), a pulse backwashing port (11), an exhaust port (12), and a discharge port (13). Among them, the pulse backwashing port (11) and the exhaust port (12) are located at the upper end of the collection tank (9), the sieve mesh (10) is located below the pulse backwashing port (11) and the exhaust port (12), and the discharge port (13) is located at the lower end of the collection tank (9).

4. A method for preparing single-walled carbon nanotubes by thermal plasma CVD according to any one of claims 1-3, characterized in that, The method involves igniting an arc between the cathode and anode of the plasma arc furnace (4) to raise the furnace temperature, then sending the catalyst from the hollow cathode (5) to the position of the graphite crucible (2), quickly evaporating to form catalyst clusters, and discharging the excess catalyst through the arc furnace discharge port (14); at the same time, the carbon source mixed gas enters the plasma arc furnace (4) through the through holes (1) at the edge of the anode graphite crucible (2), combines with the catalyst clusters after cracking, enters the CVD growth chamber (7) to grow into single-walled carbon nanotubes, and enters the collection tank (9) under the carrier gas to obtain the final product.

5. The method for preparing single-walled carbon nanotubes by thermal plasma CVD according to claim 4, characterized in that, The method specifically includes the following steps: S1) Introduce plasma gas, turn on the plasma power supply to generate a plasma arc between the anode and cathode, raise the furnace temperature to the specified temperature, and at the same time turn on the CVD growth chamber (7) to heat up to the growth temperature; S2) Send the catalyst to the position of the crucible (2) through the channels of the hollow electrode (5), quickly evaporate to form catalyst clusters, and blow the excess unevaporated catalyst particles to the arc furnace discharge port (14) by the carrier gas blown from the gas inlet port (3); S3) At the same time, mix the carbon source gas and the carrier gas and enter the plasma arc furnace (4) through the through holes (1) at the edge of the graphite crucible (2), and enter the CVD growth chamber (7) together with the catalyst after high-temperature cracking; S4) Further supplement the carbon source gas and the carrier gas through the gas supplement port (6) in the CVD growth chamber (7) to achieve the full growth of single-walled carbon nanotubes; S5) The product is cooled by the cooling section (8) under the drive of the carrier gas, enters the collection tank (9), and blows the product enriched on the sieve mesh (10) to the discharge port (13) through the pulse backwashing port (11) to collect the final product.

6. The method for preparing single-walled carbon nanotubes by thermal plasma CVD according to claim 5, characterized in that, The plasma gas in the step S1) is any one, two or more than two kinds of mixed gas of argon, nitrogen, helium, hydrogen, water vapor with any mixing ratio, and the flow rate is 10 - 500 L / min; The specified temperature of the furnace is 1200 - 2000 °C; the growth temperature of the CVD chamber is 900 - 1400 °C.

7. The method for preparing single-walled carbon nanotubes by thermal plasma CVD according to claim 5, wherein The catalyst in the step S2) is a mixed powder of 50 - 95% metal powder and 5 - 50% promoter, where: The metal powder is iron, cobalt or nickel metal or a mixture thereof; Or an alloy or mixture of iron, cobalt or nickel and refractory metals, where the refractory metal element is molybdenum, tungsten, tantalum, niobium, hafnium or zirconium, the weight ratio content of the refractory metal element is 20 - 60%, and the particle size is 50 - 350 mesh; The promoter is any one or a mixture of sulfur powder, selenium powder, iron sulfide, ferrous sulfide, nickel sulfide or cobalt sulfide, and the particle size is 100 - 500 mesh; The catalyst feeding rate is 0.1 g / min - 100 g / min.

8. The method for preparing single-walled carbon nanotubes by thermal plasma CVD according to claim 5, wherein The carbon source gas in the step S3) is any one of methane, ethylene, acetylene, propylene or propane; the carrier gas is a mixed gas of an inert gas such as nitrogen, argon or helium and hydrogen, where the volume of the carbon source gas is 10 - 80%; the volume of hydrogen gas is 0 - 35%, and the rest is an inert gas such as nitrogen, argon or helium, and the total flow rate is 10 - 200 L / min.

9. A method for preparing single-walled carbon nanotubes by thermal plasma CVD according to claim 5, characterized in that, In the step S4), the total flow rate of the further supplemented carbon source gas and carrier gas in the CVD growth chamber (7) is 10 - 200 L / min.

10. A method for preparing single-walled carbon nanotubes by thermal plasma CVD according to claim 5, characterized in that, In the step S5), the aperture of the sieve (10) is 0.5 - 50 mm, the backflush gas is nitrogen, argon or helium, and the pulse backflush frequency is 5 - 300 times / second.

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