Method and system for preparing single-walled / double-walled carbon nanotubes by direct current arc discharge

Abstract

This invention belongs to the field of nanomaterial preparation technology, and relates to a method and system for preparing single / double-walled carbon nanotubes using DC arc discharge. The method involves introducing an arc-initiating gas, a catalyst mixture, and an arc-limiting mixture into the reaction zone through a multi-channel electrode gun. The arc-limiting mixture in the outermost channel forms a gas curtain, compressing and confining the non-rigid arc column, thereby increasing the temperature of the core reaction zone. Simultaneously, the contact probability and time between the catalyst mixture and the arc column are adjusted to obtain catalyst particles of 1-18 nanometers required for the growth of single / double-walled carbon nanotubes, resulting in the continuous and stable preparation of highly crystalline single / double-walled carbon nanotubes. This method has significant commercial value for the large-scale preparation of high-quality single / double-walled carbon nanotubes using arc discharge.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation technology, and particularly relates to a method and system for preparing single / double-walled carbon nanotubes by direct current arc discharge. Background Technology

[0002] Since its discovery in 1993, single-walled carbon nanotubes (SWCNTs) have possessed unique mechanical, electrical, thermal, and quantum properties due to their unique one-dimensional structure. Currently, the biggest application of SWCNTs is in high-performance electrodes, especially lithium batteries. They also have great potential as a key material for future high-performance carbon-based semiconductor devices.

[0003] In the past decade, due to the advancement of plasma chemistry technology, the plasma method for preparing single-walled carbon nanotubes has received much attention from the scientific research community and industry. The advantage of DC plasma is that it can prepare high-quality single-walled carbon nanotubes in a high-temperature environment, opening up a new path for the industrial preparation of high-quality SWCNTs.

[0004] In existing technologies using DC arc discharge to prepare carbon nanotubes, discontinuous product production is frequently observed. Even with unchanged parameters, product production is not continuous, sometimes abruptly interrupted and prolonged periods without product output, resulting in highly unstable yields. This is generally considered to be due to the failure to produce catalyst nanoparticles capable of growing single-walled carbon nanotubes. The arc light significantly impacts catalyst preparation and product growth. During experiments, the arc was observed to be constantly deflected. Since the catalyst enters from the electric arc gun, the large deflection amplitude reduces the probability of the catalyst encountering the arc, leading to inconsistent catalyst nanoparticle production. Furthermore, the deflection energy of the arc cannot be effectively utilized to provide more reaction space. The introduction of the catalyst mixture and arc-initiating gas into the reaction zone interferes with arc stability, causing frequent arc interruptions and affecting the continuous and uniform growth of the product.

[0005] During the experiment, a large amount of high-temperature gas from the DC arc was sprayed towards the offset side. The charge on the offset side melted rapidly, while the charge on the opposite side melted more slowly, resulting in uneven melting of the charge. This negated the advantage of uniform melting in a DC furnace, reducing electrical efficiency and production efficiency. With the arc offset reaching 30 degrees, the existing equipment only operated at 60% capacity, wasting electrical energy. Furthermore, the increased heat load on the furnace wall on the offset side led to increased refractory material wear and a series of problems, such as damage to the water-cooled wall panels. Figure 4 As shown, this is one scenario within an electric arc deflection furnace, where the deflection angle θ is greater than 45 degrees. The arc deflection diminishes the advantages of a direct current electric furnace. See *Ferroalloys*, 1999, Issue 03, pp. 42-47.

[0006] Existing technologies utilize magnetic field induction devices to generate a magnetic field perpendicular to the current direction, and control the direction of magnetic field rotation through a rotating mechanism to achieve the direction of arc plasma jetting, thus enabling semi-automatic production of single-walled carbon nanotubes. However, the equipment investment is enormous, and the restraint of the arc is uncontrollable, resulting in poor performance. The reason for this is that arc deflection occurs because a large current flows through the conductor of a DC arc furnace during operation, creating a strong magnetic field around it. Within this magnetic field, an arc with a current path exists, and the magnetic field exerts force on the arc; this is the essence of arc deflection. The deflection is caused by the force acting on the arc, but the arc column is a non-rigid body; without some kind of suppressive force to inhibit deflection, the arc will drift away. To date, completely eliminating arc deflection in reality is impossible. Summary of the Invention

[0007] This invention discloses a method and system for preparing single / double-walled carbon nanotubes by DC arc discharge, in order to solve any of the above-mentioned technical problems and other potential problems in the prior art.

[0008] To achieve the above objectives, the technical solution adopted by this invention is: a method for preparing single / double-walled carbon nanotubes by DC arc discharge. In this method, an arc-initiating gas, a catalyst mixture, and an arc-limiting mixture are introduced into the reaction zone through a ring-shaped multi-channel electrode gun from the inside out. The arc-limiting mixture in the outermost channel forms a gas curtain wall, which compresses and constrains the non-rigid arc column, thereby increasing the temperature of the core reaction zone. At the same time, the contact probability and time between the catalyst mixture and the arc column are adjusted to obtain catalyst particles of 1-18 nm required for the growth of single / double-walled carbon nanotubes. The preferred catalyst particles are 1-12 nm, thereby continuously and stably preparing highly crystalline single / double-walled carbon nanotubes.

[0009] Furthermore, the method specifically includes the following steps:

[0010] S1) Place the catalyst mixture in a feeder, introduce inert gas for venting, and preheat the arc-initiating gas and the arc-limiting mixed gas;

[0011] S2) Introduce the preheated arc-igniting gas, start the DC pulse power supply, and heat the reaction chamber to the predetermined temperature to form a high-temperature reaction zone with a stable temperature field and airflow field;

[0012] S3) The preheated arc-limiting mixed gas is then fed into the reaction chamber through the annular multi-channel electrode gun at a certain flow rate. The catalyst mixture is then fed into the reaction chamber through the carrier gas at a certain flow rate via the annular multi-channel electrode gun.

[0013] S4) The arc-limiting mixed gas located in the outermost channel forms a gas curtain wall, which compresses and confines the non-rigid electric arc column, further increasing the temperature of the core reaction zone. This enables the catalyst mixture to prepare nano-catalyst particles in the core reaction zone. The prepared nano-catalyst particles and the carbon source gas in the arc-limiting mixed gas can fully catalyze the cracking reaction in the reaction chamber, thus preparing high-quality single / double-walled carbon nanotubes.

[0014] The product generated in S5) is separated and collected by an annular scraper with a filter screen in the collection unit, and the initial product is obtained by continuous collection through the transition chamber.

[0015] Furthermore, the catalyst mixture in S1) is an iron-based compound or mixture containing sulfur or selenium; wherein the molar ratio of iron to sulfur or selenium is 5:1-150:1.

[0016] The iron in the catalyst is at least one of iron pentacarbonyl, iron, iron oxide, and iron chloride.

[0017] The sulfur in question is thiophene, sulfur powder, dimethyl sulfoxide, ferrous sulfide, ferric sulfate, or other compounds containing sulfur or selenium.

[0018] The arc-initiating gas is an inert gas; the preheating temperature of the arc-initiating gas is 200-900℃; the preheating temperature of the arc-limiting mixed gas is 200-650℃.

[0019] The inert gas is one or more of nitrogen, argon, and helium.

[0020] Furthermore, the flow rate of the arc-initiating gas in S2) is 3-30 m / s;

[0021] The predetermined temperature is 700-3000℃.

[0022] Furthermore, the flow velocity of the arc-limiting mixture in S3) is 3-90 m / s; the carrier gas is an inert gas with a flow velocity of 3-50 m / s.

[0023] The inert gas is one or more of nitrogen, argon, and helium.

[0024] Furthermore, the arc-limiting mixed gas includes a carbon source gas, a reducing gas, and other gases, with a flow rate ratio of 1:(2-25):(0.01-3).

[0025] The carbon source gas is one or more of the following: methane, ethane, ethylene, acetylene, propylene, propane, ethanol, methanol, or natural gas.

[0026] The reducing gas is one or more of hydrogen, carbon monoxide, carbon dioxide, hydrogen sulfide, and ammonia.

[0027] The other gas mentioned is water vapor.

[0028] Furthermore, in S4), the compression constraint is that the deflection angle of the electric arc column is no greater than 20 degrees.

[0029] Furthermore, the height of the electric arc column is 30-500mm, and the diameter of the arc column is 10-100mm.

[0030] Another object of the present invention is to provide a system for realizing the above-described method for preparing single / double-walled carbon nanotubes by DC arc discharge. The system includes a catalyst preparation unit, a preheating unit, a synthesis unit, a collection unit, and an electrode unit. The electrode unit is a ring-shaped multi-channel electrode gun. The ring-shaped multi-channel electrode gun includes, from the inside out, an arc-initiating gas channel, a catalyst mixture channel, and an arc-limiting mixed gas channel.

[0031] The arc-initiating gas channel is located at the center of the annular multi-channel electrode gun, and several catalyst mixture channels are located on the circumference of the arc-initiating gas channel; the arc-limiting gas channel is annular, and several catalyst mixture channels are located on the outer side.

[0032] The annular multi-channel electrode gun is located at the top of the reaction chamber and is positioned at the center of the reaction chamber. One end of the annular multi-channel electrode gun is inserted into the interior of the reaction chamber, and the other end is connected to the arc-initiating gas injection port, the catalyst mixture injection port, and the arc-limiting mixture injection port.

[0033] Furthermore, the arc-initiating gas channel is a circular hole with a diameter of 10-150 mm, and the diameter of the circular hole is D1. The catalyst mixture channel has 3-32 circular holes with a diameter of D2 evenly distributed between the diameters D1 and D3, and the diameter of D2 ranges from 1-30 mm. The inner diameter D3 of the annular arc-limiting mixing gas channel is 20-300 mm, and the outer diameter D4 is 24-360 mm.

[0034] The product collection unit comprises two sets, left and right, annular scrapers with filters, a collection chamber, a transition chamber, and an exhaust port, used for gas-solid separation of the generated single / double-walled carbon nanotubes and can switch between left and right sides for continuous collection; the exhaust port is located at the upper end of the collection chamber to discharge exhaust gas.

[0035] The preheating unit includes a gas preheater, an arc-limiting mixture injection port, and an arc-igniting gas injection port; it preheats the arc-igniting gas, the arc-limiting mixture, and the carrier gas.

[0036] The collection unit is connected to one end of the product synthesis unit, and the other end of the synthesis unit is connected to the product collection unit.

[0037] The catalyst mixture is introduced into the synthesis unit through the catalyst mixture channel of the electrode unit, and is brought into contact with the electric arc to prepare nanoscale catalysts and grow products.

[0038] The catalyst preparation unit includes: a feeder; a catalyst mixture injection port; and an electric arc column.

[0039] The electric arc column is formed between the lower end of the annular multi-channel electrode gun and the graphite crucible by discharge through a DC pulse power supply. The lifting arm is connected to the upper end of the annular multi-channel electrode gun, and under rated power conditions, it automatically adjusts its height to maintain a stable and unbroken arc.

[0040] The product synthesis unit includes a reaction chamber; a bottom anode graphite crucible; a lifting arm and a DC pulse power supply; the synthesis unit prepares catalyst nanoparticles by fully contacting the input catalyst mixture and the electric arc column, and the catalyst nanoparticles are catalytically cracked in the reaction chamber by encountering the preheated arc-limiting mixed gas in the arc-limiting channel under high temperature environment to generate highly crystalline single / double-walled carbon nanotubes.

[0041] The single / double-walled carbon nanotubes produced products with an average G / D ratio exceeding 170 and a yield of up to 0.23 kg / h.

[0042] The beneficial effects of this invention are as follows: By adopting the above technical solution, this invention introduces the arc-initiating gas, catalyst mixture, and arc-limiting gas into the reaction zone through a multi-channel electrode gun and a multi-channel graphite electrode, avoiding interference from the catalyst mixture on the deflection and stability of the arc column. The arc-limiting gas forms a gas curtain that is difficult to ionize in the outermost channel, constraining the non-rigid arc column and ensuring the necessary contact between the catalyst mixture and the arc column. This allows for the continuous preparation of more highly catalytically active 1-18 nanometer catalysts that meet with the carbon source in the preheated arc-limiting gas for a full pyrolysis reaction. The multi-channel design ensures the preparation of more catalyst particles, which meet with the carbon source in the preheated arc-limiting gas for a full pyrolysis reaction, improving the utilization rate of the carbon source in the conversion to single / double-walled carbon nanotubes and increasing the yield by up to 0.23 kg / h.

[0043] The outermost arc-limiting gas can confine the arc to a certain extent, suppressing the arc deflection amplitude and keeping the arc deflection angle within 20 degrees. This concentrates the arc light in a relatively narrow region, resulting in an arc column with higher temperature and energy density. Increasing the temperature of the core reaction zone is beneficial for preparing highly crystalline single / double-walled carbon nanotubes, with an average G / D ratio of the product exceeding 170. (See...) Figure 7 As shown.

[0044] This can alleviate the problem of excessive arc deflection leading to low energy efficiency, while also preventing overheating damage to the furnace wall caused by arc deflection and the situation where the bottom anode burns through the furnace bottom. Figure 4 As shown, this is one scenario inside an arc deflection furnace, where the arc deflection angle θ exceeds 45 degrees. Preheating the arc-initiating gas and the arc-limiting mixture before introducing them into the reaction chamber significantly improves arc stability and simultaneously reduces the DC power supply load. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the device for preparing single / double-walled carbon nanotubes by DC arc discharge according to the present invention.

[0046] Figure 2 As described in this invention Figure 1 One type of front view of a medium-ring multi-channel electrode gun.

[0047] Figure 3 As described in this invention Figure 1 One of the partial cross-sectional views of the central ring multi-channel electrode gun.

[0048] Figure 4 One of the conditions inside an electric arc deflection furnace.

[0049] Figure 5 This is a scanning electron microscope image of the single / double-walled carbon nanotubes prepared in Example 3 of the present invention.

[0050] Figure 6 Thermogravimetric characterization diagram of single / double-walled carbon nanotubes prepared using the apparatus of the present invention in Example 4 of the present invention.

[0051] Figure 7 The image shows the Raman spectrum of the single / double-walled carbon nanotubes prepared in Example 5 of this invention.

[0052] Figure 8 This is a transmission electron microscope (TEM) image of the single-walled carbon nanotubes prepared in Example 5 of the present invention.

[0053] Figure 9 This is a transmission electron microscope (TEM) image of the double-walled carbon nanotubes prepared in Example 5 of the present invention.

[0054] Figure 10 Transmission electron microscopy (TEM) image of the single / double-walled carbon nanotubes prepared in Example 1 of this invention.

[0055] Figure 11 This is a specific surface area diagram of the single / double-walled carbon nanotubes prepared in Example 5 of the present invention.

[0056] In the picture:

[0057] Reaction chamber 221; Gas preheater 222; Arc-limiting mixed gas injection port 223; Annular multi-channel electrode gun 224; Arc column 227; Bottom anode graphite crucible 228; Feeder 229; Arc-igniting gas injection port 230; Catalyst mixture injection port 231; Lifting arm 233; DC pulse power supply 235; Collection chamber 331; Annular scraper with filter screen 333; Transition chamber 335; Tail gas port 337; Unmelted melt 431; Cathode 432; Arc jet 433; Local overheated zone on furnace inner wall 434; Bottom anode 435; Arc-igniting gas channel 511; Catalyst mixture channel 512; Arc-limiting mixed gas channel 513. Detailed Implementation

[0058] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. The present invention provides a method for preparing single / double-walled carbon nanotubes using DC arc discharge. In this method, an arc-initiating gas, a catalyst mixture, and an arc-limiting mixture are introduced into the reaction zone through a ring-shaped multi-channel electrode gun 224 from the inside out. The arc-limiting mixture in the outermost channel forms a gas curtain, compressing and constraining the non-rigid arc column, thereby increasing the temperature of the core reaction zone. Simultaneously, the contact probability and time between the catalyst mixture and the arc column are adjusted to obtain 1-18 nm catalyst particles required for the growth of single / double-walled carbon nanotubes, thus continuously and stably preparing highly crystalline single / double-walled carbon nanotubes.

[0059] The method specifically includes the following steps:

[0060] S1) The catalyst mixture is placed in the feeder 229 and vented with inert gas; and the arc-initiating gas and the arc-limiting mixed gas are preheated.

[0061] S2) Introduce the preheated arc-igniting gas, start the DC pulse power supply 235, and heat the reaction chamber 221 to the predetermined temperature to form a high-temperature reaction zone with a stable temperature field and airflow field.

[0062] S3) The preheated arc-limiting mixed gas is then fed into the reaction chamber 221 through the annular multi-channel electrode gun 224 at a certain flow rate. The catalyst mixture is then fed into the reaction chamber sequentially through the annular multi-channel electrode gun via the carrier gas at a certain flow rate.

[0063] S4) The arc-limiting mixed gas located in the outermost channel forms a gas curtain wall, which compresses and confines the non-rigid electric arc column, further increasing the temperature of the core reaction zone. This enables the catalyst mixture to prepare nano-catalyst particles in the core reaction zone. The prepared nano-catalyst particles and the carbon source gas in the arc-limiting mixed gas can fully catalyze the cracking reaction in the reaction chamber, thus preparing high-quality single / double-walled carbon nanotubes.

[0064] The product generated in S5) is separated and collected by an annular scraper with a filter screen in the collection unit, and the initial product is obtained by continuous collection through the transition chamber.

[0065] The catalyst mixture in S1) is an iron-based compound or mixture containing sulfur or selenium; wherein the molar ratio of iron to sulfur or selenium is 5:1-150:1.

[0066] The iron in the catalyst is at least one of iron pentacarbonyl, iron, iron oxide, and iron chloride.

[0067] The sulfur in question is thiophene, sulfur powder, dimethyl sulfoxide, ferrous sulfide, ferric sulfate, or other compounds containing sulfur or selenium.

[0068] The arc-initiating gas is an inert gas; the preheating temperature of the arc-initiating gas is 200-900℃; the preheating temperature of the arc-limiting mixed gas is 200-650℃.

[0069] The inert gas is one or more of nitrogen, argon, and helium.

[0070] The flow rate of the arc-initiating gas in S2) is 3-30 m / s; the predetermined temperature is 700-3000℃.

[0071] The flow velocity of the arc-limiting mixture in S3) is 3-90 m / s; the carrier gas is an inert gas with a flow velocity of 3-50 m / s. The inert gas is one or more of nitrogen, argon, and helium.

[0072] The arc-limiting mixed gas includes a carbon source gas, a reducing gas, and other gases, with a flow ratio of 1:(2-25):(0.01-3).

[0073] The carbon source gas is one or more of the following: methane, ethane, ethylene, acetylene, propylene, propane, ethanol, methanol, or natural gas.

[0074] The reducing gas is one or more of hydrogen, carbon monoxide, carbon dioxide, hydrogen sulfide, and ammonia. The other gas is water vapor.

[0075] In S4), the compression constraint is that the deflection angle of the electric arc column is no greater than 20 degrees.

[0076] The height of the electric arc column is 30-500mm, and the diameter of the arc column is 10-100mm.

[0077] like Figure 1As shown, a system for preparing single / double-walled carbon nanotubes by DC arc discharge as described above is provided. The system includes a catalyst preparation unit, a preheating unit, a synthesis unit, a collection unit, and an electrode unit. The electrode unit is a ring-shaped multi-channel electrode gun 224. The ring-shaped multi-channel electrode gun includes, from the inside out, an arc-initiating gas channel 511, a catalyst mixture channel 512, and an arc-limiting mixed gas channel 513.

[0078] The arc-initiating gas channel 511 is located at the center of the annular multi-channel electrode gun 224, and a plurality of catalyst mixture channels 512 are located on the circumference of the arc-initiating gas channel 511; the arc-limiting gas channel 513 is annular and is located on the outer side of the plurality of catalyst mixture channels 512, for reference. Figure 2 and Figure 3 As shown.

[0079] The annular multi-channel electrode gun 224 is located at the top of the reaction chamber 221 and is positioned at the center of the reaction chamber 221. One end of the annular multi-channel electrode gun 224 is inserted into the interior of the reaction chamber 221, and the other end is connected to the arc-initiating gas injection port, the catalyst mixture injection port, and the arc-limiting mixture injection port. (Refer to...) Figure 1 As shown;

[0080] The arc-initiating gas channel 511 is a circular hole with a diameter of 10-150 mm. The catalyst mixture channel 512 has its center located between diameters D1 and D3, and is evenly distributed with 3-32 circular holes of diameter D2, ranging from 1-30 mm. The inner diameter D3 of the annular arc-limiting mixing gas channel is 20-300 mm, and the outer diameter D4 is 24-360 mm. (Reference) Figure 3 As shown.

[0081] The product collection unit comprises two sets, left and right, with a filter-equipped annular scraper 333, a collection chamber 331, a transition chamber 335, and an exhaust port 337. It is used for gas-solid separation of the generated single / double-walled carbon nanotubes and can switch between left and right sides for continuous collection. The exhaust port is located at the upper end of the collection chamber to discharge exhaust gas.

[0082] The preheating unit includes a gas preheater 222, an arc-limiting mixture injection port 223, and an arc-ignition gas injection port 230; it preheats the arc-ignition gas, the arc-limiting mixture, and the carrier gas.

[0083] The collection unit is connected to one end of the product synthesis unit, and the other end of the synthesis unit is connected to the product collection unit.

[0084] The catalyst mixture is introduced into the synthesis unit through the catalyst mixture channel 512 of the electrode unit, and is in contact with the electric arc to prepare nanoscale catalysts and grow products. The catalyst preparation unit includes: a feeder 229; a catalyst mixture injection port 231; and an electric arc column 227.

[0085] The electric arc column 227 is formed between the lower end of the annular multi-channel electrode gun 224 and the bottom anode graphite crucible 228, through discharge by a DC pulse power supply 235. The lifting arm 233 is connected to the upper end of the annular multi-channel electrode gun 224, and automatically adjusts its height to maintain a stable and unbroken arc under rated power conditions.

[0086] The product synthesis unit includes a reaction chamber 221; a bottom anode graphite crucible 228; a lifting arm 233; and a DC pulse power supply 235. The synthesis unit prepares catalyst nanoparticles by fully contacting the input catalyst mixture with the electric arc column. In the reaction chamber 221, the preheated arc-limiting mixed gas in the arc-limiting channel catalyzes the cracking reaction at high temperature to generate highly crystalline single / double-walled carbon nanotubes.

[0087] The single / double-walled carbon nanotubes produced products with an average G / D ratio exceeding 170 and a yield of up to 0.23 kg / h.

[0088] Single / double-walled carbon nanotubes obtained using the methods described in this paper have attracted much attention in many promising fields such as materials science, nanotechnology, new energy, and applied chemistry.

[0089] The unique properties of single / double-walled carbon nanotubes (SNTs) enhance the performance of materials used in their respective fields. For example, rubber products made from various rubbers, silicones, and thermoplastic elastomers based on SNTs offer technological advantages. In tires, the use of SNTs in tires can significantly improve key properties such as abrasion resistance, fuel efficiency, and adhesion by enhancing the strength and elasticity of rubber formulations. These improvements are achieved at very low nanotube concentrations, allowing for the retention of core production technologies. In lithium-ion batteries, the use of SNTs can significantly improve storage density and charge cycle life, extending battery life.

[0090] For the Raman spectroscopy, thermogravimetric characterization, scanning electron microscopy and energy-dispersive X-ray spectroscopy, transmission electron microscopy and ultraviolet-visible-near-infrared absorption spectroscopy characterization methods for high-quality single-walled carbon nanotube samples, please refer to GB / T 32871-2016, GB / T 24490-2009, GB / T 32869-2016, GB / T 30534-2014 and GB / T39114-2020 standards. The test schemes described are as shown in Table 1.

[0091] Table 1 Test Plan

[0092] Technical Specifications unit Evaluation methods Carbon nanotube content wt% TEM, EDX, TGA carbon nanotube wall number / TEM, EDX, TGA carbon nanotube diameter nm Raman, TEM, NIR-Vis <![CDATA[I G / I D ratio]]> / Raman Specific surface area <![CDATA[m 2 / g]]> BET

[0093] Example 1

[0094] The ignition gas, catalyst mixture, and arc-limiting gas mixture are introduced into the reaction zone through a ring-shaped multi-channel electrode gun from the inside out. The arc-limiting gas mixture in the outermost channel forms a gas curtain, compressing and confining the non-rigid arc column, increasing the temperature of the core reaction zone. Simultaneously, the contact probability and time between the catalyst mixture and the arc column are adjusted to obtain 1-18 nm catalyst particles required for the growth of single / double-walled carbon nanotubes. Catalyst nanoparticles are prepared by ensuring sufficient contact between the input catalyst mixture and the arc column. These nanoparticles then undergo a catalytic cracking reaction in the reaction chamber under high-temperature conditions with preheated arc-limiting gas in the arc-limiting channel, generating highly crystalline single / double-walled carbon nanotubes. The specific steps are as follows:

[0095] S1) Place the iron-sulfur ratio of pentacarbonyl iron and thiophene in the catalyst mixture (5:1 ratio) into a feeder and purge with inert gas; preheat the arc-initiating gas argon at a flow rate of 13 m / s to 350°C and preheat the arc-limiting mixed gas to 450°C. The arc-limiting mixed gas contains methane and ethylene as carbon sources, hydrogen as a reducing gas, and water vapor as another gas. The flow ratio of the three gases is 1:8:0.05.

[0096] S2) Introduce preheated arc-igniting gas and start the DC pulse power supply to form an electric arc column between the lower end of the annular multi-channel electrode gun and the graphite crucible. Under rated power conditions, the height is automatically adjusted to maintain a stable and uninterrupted arc. The reaction chamber is heated to 930°C to form a high-temperature reaction zone with a stable temperature and airflow field.

[0097] S3) The preheated arc-limiting mixed gas is then fed into the reaction chamber through an annular multi-channel electrode gun at a flow rate of 26 m / s. The annular multi-channel electrode gun, from the inside out, includes an arc-initiating gas channel, a catalyst mixture channel, and an arc-limiting mixed gas channel. The arc-initiating gas channel has a diameter D1 of 12 mm. The catalyst mixture channel has four evenly distributed holes with a diameter D2 of 3 mm, centered between diameters D1 and D3. The annular arc-limiting mixed gas channel has an inner diameter D3 of 22 mm and an outer diameter D4 of 30 mm. (Reference) Figure 3 As shown. The catalyst mixture is then fed into the reaction chamber sequentially via an annular multi-channel electrode gun using argon carrier gas at a flow rate of 12 m / s.

[0098] S4) The arc-limiting mixed gas located in the outermost channel forms an air curtain wall to compress and constrain the non-rigid electric arc column, wherein the electric arc column has a height of 50mm and a diameter of 20mm.

[0099] S5) The product collection unit includes two sets of left and right ring scrapers with filters for separation and collection, used for gas-solid separation of generated single / double-walled carbon nanotubes, so as to continuously collect and obtain the initial product.

[0100] As shown in Table 2, the product obtained in Example 1, under the condition of excitation wavelength of 532nm, has an average G / D ratio of 171, a TG residue of 67.6%, an arc column deflection angle of no more than 20 degrees, and the iron content in the initial product is still too high. The yield is 0.23kg / h, which can achieve the preparation of kilogram-level products per day. Figure 10 The image shown is a transmission electron microscope (TEM) image of the single / double-walled carbon nanotubes prepared in Example 1 of this invention. The image shows a bundle of single / double-walled carbon nanotubes agglomerated together. High-resolution transmission electron microscopy characterization shows that the prepared catalyst particles have a very uniform size distribution. According to statistics, the size of the catalyst particles used for growth is about 1-12 nm.

[0101] Example 2

[0102] The difference between the apparatus and system in Example 1 is that the catalyst mixture contains iron oxide and sulfur powder with an iron-to-sulfur ratio of 10:1; the arc-initiating gas is argon with a flow rate of 18 m / s; the preheating temperature is 550°C; and the arc-limiting mixed gas is preheated to 480°C. The arc-limiting mixed gas contains propylene as the carbon source gas and hydrogen and hydrogen sulfide as the reducing gases, with a flow ratio of 1:10:0.8. The reaction chamber is heated to 1230°C. The preheated arc-limiting mixed gas is fed into the reaction chamber through a ring-shaped multi-channel electrode gun at a flow rate of 28 m / s. The arc-initiating gas channel has a diameter D1 of 18 mm. The catalyst mixture channel has eight evenly distributed circular holes with a diameter D2 of 4 mm, centered between diameters D1 and D3. The inner diameter D3 of the annular arc-limiting mixed gas channel is 30 mm, and the outer diameter D4 is 35 mm. The catalyst mixture is sequentially fed into the reaction chamber via an annular multi-channel electrode gun using argon carrier gas at a flow rate of 18 m / s. The arc column has a height of 80 mm and a diameter of 25 mm.

[0103] As shown in Table 2, the average G / D ratio of the product obtained in Example 1 is 198, the residual TG of the product is 45.3%, the product contains a relatively large amount of iron catalyst, the arc column deflection angle is no more than 17 degrees, and the yield is 0.37 kg / h.

[0104] Example 3

[0105] The difference between the apparatus and system used in Example 2 is that the catalyst mixture contains iron oxide and dimethyl sulfoxide with an iron-to-sulfur ratio of 18:1; the arc-initiating gas, argon, flows at a rate of 23 m / s and is preheated to 650°C; the arc-limiting mixed gas is preheated to 556°C, wherein the carbon source gas in the arc-limiting mixed gas is propane-ethanol, the reducing gases are hydrogen and ammonia, and the other gas is water vapor, with a flow ratio of 1:15:1. The reaction chamber is heated to 1350°C.

[0106] The arc-limiting mixed gas is fed into the reaction chamber through an annular multi-channel electrode gun at a flow rate of 38 m / s. The arc-initiating gas channel has a diameter D1 of 18 mm. The catalyst mixture channel has eight evenly distributed holes of diameter D2, with a diameter range of 4 mm, located between diameters D1 and D3. The inner diameter D3 of the arc-limiting mixed gas channel is 46 mm, and the outer diameter D4 is 50 mm. The catalyst mixture is fed into the reaction chamber sequentially through the annular multi-channel electrode gun using argon carrier gas at a flow rate of 27 m / s. The arc column has a height of 80 mm and a diameter of 25 mm.

[0107] Table 2 shows that the average G / D ratio of the product obtained in Example 1 is 203, indicating highly crystalline single / double-walled carbon nanotubes. The initial product has a TG residue of 31.8%, relatively few impurities in the surface product, an arc column deflection angle of no more than 15 degrees, and a yield of 0.53 kg / h. Figure 5 Scanning electron microscopy characterization of the single / double-walled carbon nanotubes prepared in Example 3 showed that the initial product had relatively few impurities, consistent with the TG characterization of the sample, indicating good product uniformity.

[0108] Example 4

[0109] The difference between the apparatus and system used in Example 3 is that the catalyst mixture contains iron and selenium with an iron-to-sulfur ratio of 38:1; the arc-initiating gas, argon, flows at a velocity of 27 m / s and is preheated to 760°C; the arc-limiting mixed gas is preheated to 610°C, wherein the carbon source gas in the arc-limiting mixed gas is methane, the reducing gas is hydrogen, and the other gas is water vapor, with a flow ratio of 1:15:1. The reaction chamber is heated to 1550°C.

[0110] The arc-limiting mixed gas is fed into the reaction chamber through an annular multi-channel electrode gun at a flow rate of 36 m / s. The arc-initiating gas channel has a diameter D1 of 30 mm. The catalyst mixture channel has nine evenly distributed circular holes with a diameter D2 of 5 mm, centered between diameters D1 and D3. The inner diameter D3 of the annular arc-limiting mixed gas channel is 80 mm, and the outer diameter D4 is 86 mm. The catalyst mixture is fed into the reaction chamber sequentially through the annular multi-channel electrode gun using argon carrier gas at a flow rate of 25 m / s. The arc column has a height of 180 mm and a diameter of 40 mm.

[0111] Table 2 shows that the average G / D ratio of the product obtained in Example 1 is 215, indicating highly crystalline single / double-walled carbon nanotubes. Figure 6 Thermogravimetric analysis of the single / double-walled carbon nanotubes prepared in Example 4 showed that the residual TG content was 33.4%, and the content of synthesized single / double-walled carbon nanotubes in the material was 66.6 wt%. The arc column deflection angle was no more than 13 degrees, and the yield was 0.77 kg / h, which can achieve the preparation of initial products at the level of 7 kg per day.

[0112] Example 5

[0113] The difference between the apparatus and system used in Example 4 is that the iron-sulfur ratio in the catalyst mixture is 45:1; the arc-initiating gas, argon, flows at a rate of 30 m / s and is preheated to 870°C; the arc-limiting mixed gas is preheated to 640°C, wherein the carbon source gas in the arc-limiting mixed gas is methane, the reducing gas is hydrogen, and the other gas is water vapor, with a flow ratio of 1:20:2. The reaction chamber is heated to 1750°C.

[0114] The arc-initiating gas channel has a diameter D1 of 36 mm. The catalyst mixture channel has 16 evenly distributed circular holes with a diameter D2 of 6 mm, centered between diameters D1 and D3. The inner diameter D3 of the annular arc-limiting gas mixing channel is 120 mm, and the outer diameter D4 is 130 mm. The catalyst mixture is sequentially fed into the reaction chamber via an annular multi-channel electrode gun using argon carrier gas at a flow rate of 18 m / s. The arc column has a height of 200 mm and a diameter of 50 mm.

[0115] As shown in Table 2, the arc column deflection angle obtained in Example 1 is no greater than 11 degrees. Figure 7 The Raman spectrum of the sample prepared in Example 3 was found to be at 150 cm⁻¹. -1The product exhibits distinct and sharp RBM characteristic absorption peaks, indicating the presence of single / double-walled carbon nanotubes. The calculated G / D ratio is 178, suggesting that the prepared product is high-quality single / double-walled carbon nanotubes. The three points show obvious RBM characteristic absorption peaks, which are relatively similar and concentrated, indicating a high concentration of carbon nanotube diameters. The product has a TG residue of 17.8%, indicating high initial purity. The yield is 1.33 kg / h, enabling a daily production of 13 kg of initial product and possessing an annual production capacity of tons, paving the way for its industrialization. Figure 8 and Figure 9 There are many bundles formed by the aggregation of single / double-walled carbon nanotubes. Figure 8 The product prepared in Example 5 contains single-walled carbon nanotubes with a diameter of 1.65 nm. Figure 9 The product prepared in Example 5 contained double-walled carbon nanotubes with a diameter of 2.3 nm, further confirming that the sample had low impurity content and good uniformity. Figure 11 It can be seen that single / double-walled carbon nanotubes have a relatively large specific surface area of ​​1269 m². 2 / g.

[0116] Table 2 Product Indicators in Examples

[0117]

[0118] The above provides a detailed description of a method and system for preparing single / double-walled carbon nanotubes using DC arc discharge, as provided in the embodiments of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the apparatus and its core concepts; furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

[0119] Certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The terms "comprising" and "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising / including but not limited to". "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error. The following descriptions in the specification are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of illustrating the general principles of this application and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0120] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes said element.

[0121] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0122] The foregoing description illustrates and describes several preferred embodiments of this application. However, as previously stated, it should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the application concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be within the protection scope of the appended claims.

Claims

1. A method for preparing single / double-walled carbon nanotubes by direct current arc discharge, characterized in that, The method involves introducing the arc-initiating gas, catalyst mixture, and arc-limiting gas into the reaction zone through a ring-shaped multi-channel electrode gun from the inside out. The arc-limiting gas in the outermost channel forms a gas curtain, compressing and confining the non-rigid arc column, thereby increasing the temperature of the core reaction zone. Simultaneously, the contact probability and time between the catalyst mixture and the arc column are adjusted to obtain 1-18 nm catalyst particles required for the growth of single / double-walled carbon nanotubes, thus continuously and stably producing highly crystalline single / double-walled carbon nanotubes. The method specifically includes the following steps: S1) Place the catalyst mixture in a feeder, introduce inert gas for venting, and preheat the arc-initiating gas and the arc-limiting mixed gas; The catalyst mixture is an iron-based compound or mixture containing sulfur or selenium; wherein the molar ratio of iron to sulfur or selenium is 5:1 to 150:

1. The arc-initiating gas is an inert gas; the preheating temperature of the arc-initiating gas is 200-900℃; the preheating temperature of the arc-limiting mixed gas is 200-650℃. S2) Introduce the preheated arc-igniting gas, start the DC pulse power supply, and heat the reaction chamber to the predetermined temperature to form a high-temperature reaction zone with a stable temperature field and airflow field; The flow rate of the arc-initiating gas is 3-30 m / s; The predetermined temperature is 700-3000℃; S3) The preheated arc-limiting mixed gas is then fed into the reaction chamber through the annular multi-channel electrode gun at a certain flow rate. The catalyst mixture is then fed into the reaction chamber through the carrier gas at a certain flow rate. The flow rate of the arc-limiting mixed gas is 3-90 m / s; the carrier gas is an inert gas with a flow rate of 3-50 m / s. The arc-limiting mixed gas includes a carbon source gas, a reducing gas, and water vapor, with a flow ratio of 1:(2-25):(0.01-3). S4) The arc-limiting mixed gas located in the outermost channel forms a gas curtain wall, which compresses and confines the non-rigid electric arc column, further increasing the temperature of the core reaction zone. This enables the catalyst mixture to prepare nano-catalyst particles in the core reaction zone. The prepared nano-catalyst particles and the carbon source gas in the arc-limiting mixed gas can fully catalyze the cracking reaction in the reaction chamber, thus preparing high-quality single / double-walled carbon nanotubes. The product generated in S5) is separated and collected by an annular scraper with a filter screen in the collection unit, and the initial product is obtained by continuous collection through the transition chamber.

2. The method according to claim 1, characterized in that, In S4), the compression constraint is that the arc column deflection angle is no greater than 20 degrees. The height of the electric arc column is 30-500mm, and the diameter of the electric arc column is 10-100mm.

3. A system for preparing single / double-walled carbon nanotubes by DC arc discharge as described in any one of claims 1-2, the system comprising a catalyst preparation unit, a preheating unit, a synthesis unit, a collection unit, and an electrode unit, characterized in that, The electrode unit is a ring-shaped multi-channel electrode gun; the ring-shaped multi-channel electrode gun includes, from the inside out, an arc-initiating gas channel, a catalyst mixture channel, and an arc-limiting mixed gas channel. The arc-initiating gas channel is located at the center of the annular multi-channel electrode gun, and several catalyst mixture channels are located on the circumference of the arc-initiating gas channel; the arc-limiting gas channel is annular and located on the outside of several catalyst mixture channels.

4. The system according to claim 3, characterized in that, The arc-initiating gas channel is a circular hole with a diameter of 10-150 mm. The catalyst mixture channel has 3-32 circular holes with a diameter of D2 evenly distributed between the diameters D1 and D3. The diameter of D2 ranges from 1-30 mm. The inner diameter D3 of the annular arc-limiting gas mixing channel is 20-300 mm, and the outer diameter D4 is 24-360 mm.

5. A single / double-walled carbon nanotube, characterized in that, The single / double-walled carbon nanotubes are prepared by the method described in any one of claims 1-2, and the average G / D ratio of the product is greater than 170, with a yield of 0.23 kg / h.

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