A device and method for preparing single-walled carbon nanotubes using direct current pulsed plasma

Abstract

The present invention belongs to the technical field of nanomaterial preparation, and relates to a device and method for preparing single-walled carbon nanotubes using a direct current pulse plasma. The device is configured by arranging a cathode and an anode, and providing a melt below the cathode and the anode as a conductor to conduct the cathode and the anode. By switching the cathode and the anode, a pulsed plasma high-temperature environment synthesis zone with a stable temperature field and airflow field is formed. In the synthesis zone, the introduced catalyst is prepared into nanocatalyst particles, which are then fully catalyzed and cracked with the preheated carbon source mixed gas to obtain high-purity single-walled carbon nanotubes. The device of the present invention can maintain the stable operation of the arc equipment at a high temperature for a long time, while reducing the evaporation of the graphite bottom electrode by the high-temperature arc, maintaining the continuous activity of the catalyst, further improving the utilization rate of the carbon source and the catalyst for the arc energy, and ultimately improving the carbon source conversion efficiency. This is the core key technology for the preparation of high-quality single-walled carbon nanotubes by the high-temperature arc method.

Description

Technical Field

[0001] The invention belongs to the technical field of nano material preparation, and relates to a device and method for preparing single-walled carbon nanotubes by using direct current pulse plasma. Background Art

[0002] Single-walled carbon nanotubes (SWCNTs), as a new type of nanomaterial, have excellent mechanical, thermal and optical properties, as well as huge aspect ratio, high specific surface area and lightweight characteristics. They have potential application prospects in new energy batteries, high-power heat dissipation, energy storage, aerospace, flexible displays and smart devices.

[0003] The traditional arc discharge method, also known as arc ablation, uses graphite as a solid carbon source. The resulting product often contains various impurities, including highly crystalline amorphous carbon, onion carbon, and iron-carbon compounds. While the resulting SWCNTs are highly crystalline, these impurities are difficult to further purify into high-purity SWCNTs, resulting in a relatively low purity product. Production conditions typically involve negative pressure and helium, making continuous production difficult in practice. Furthermore, the process places high demands on equipment, and the high-temperature zone in the reaction zone is relatively small. Consequently, production has struggled to break through the 100-gram daily level, enabling large-scale application.

[0004] In the past decade, due to the advancement of plasma chemistry technology, the plasma vapor deposition method for preparing SWCNTs has attracted much attention from the scientific research community and industry, opening up a new path for the industrial production of high-quality SWCNTs. Chinese invention patent CN113860287B uses a deep graphite crucible to form a high-temperature zone with eddy currents through arc discharge in the reaction zone, allowing the carbon source gas and catalyst to fully react in the high-temperature crucible. Although single-walled carbon nanotubes can be obtained under 100kW power conditions, G / I D The highest yield was 72, and the initial product yield increased by at least 20%, but production still failed to achieve a substantial breakthrough. The plasma arc exerted a significant thermal shock on the deep bottom anode graphite crucible, which easily cracked and made long-term stable operation difficult. Excessively high temperatures in the bottom anode graphite crucible easily dissolved the catalyst, reducing the activity of the subsequently evaporated catalyst and affecting the continuous production of products.

[0005] After further improvement, Chinese invention patent CN13929084B uses a V-shaped reaction unit to make the reaction gas flow around the plasma to form a stable convection gas field, which increases the probability of contact between the raw materials and the plasma, improves the utilization rate of the plasma energy, and can increase the carbon conversion rate by at least 2 times. The single-walled carbon nanotubes have high crystallinity. At a power of 30KW, the product I G / I DThe maximum can reach 35, and the maximum primary product output per hour is 52 grams. Although it has theoretically broken through the daily kilogram-level production, the anode graphite crucible at the bottom of the equipment is difficult to withstand long-term plasma bombardment and is easily corroded.

[0006] The high-temperature environment created by high-power plasma is conducive to the growth of high-quality single-walled carbon nanotubes, but it places stringent demands on the tolerance of the bottom anode graphite crucible and the furnace refractory materials. Under prolonged high-temperature conditions, the arc convection energy not only directly corrodes the graphite crucible, but also evaporates highly crystalline graphite solid carbon, which easily wraps around the formed nanocatalyst at high temperatures, forming a nano-carbon-coated iron structure. This inactivates the nanocatalyst and affects catalytic efficiency, resulting in a gradual decrease in yield over time. Furthermore, the highly crystalline carbon-coated iron is difficult to remove during the subsequent purification process, affecting the purity of the final purified product and limiting its application in the new energy sector.

[0007] Both of the above technical solutions utilize a single-electrode DC arc furnace with a bottom anode. This arc generation method, where the lower electrode discharges between the bottom anode and the bottom electrode, results in the bottom anode effect. This exposes the furnace bottom to prolonged high temperatures, which can damage the furnace bottom and dissolve the graphite crucible. Even with proactive management and technical measures, single-electrode DC arc furnaces with bottom anodes still require frequent replacement of the bottom electrode. This is time-consuming and labor-intensive, not only reducing production capacity but also shortening the equipment's operating life and lifespan. Consequently, the difficulty of continuous operation of arc equipment during the single-walled carbon nanotube production process poses significant challenges to industrial production. Summary of the Invention

[0008] The present invention discloses a device and method for preparing single-walled carbon nanotubes using direct current plasma, so as to solve any of the above and other potential problems in the prior art.

[0009] In order to solve the problems existing in the prior art, the technical solution adopted by the present invention is: a device for preparing single-walled carbon nanotubes using direct current pulse plasma, which symmetrically arranges the cathode and anode of the direct current pulse plasma inside a product synthesis unit, and arranges a melt as a conductor below the cathode and anode to connect the cathode and anode. By regularly switching the cathode and anode, a pulse plasma high-temperature environment synthesis zone with a stable temperature field and airflow field is formed in the product synthesis unit. The introduced catalyst is prepared into nanocatalyst particles, which undergo a catalytic reaction with the cracked carbon source gas in the pulse plasma high-temperature environment to prepare highly crystalline single-walled carbon nanotubes.

[0010] Furthermore, the device comprises: a catalyst and co-catalyst introduction unit for introducing the catalyst and co-catalyst via a carrier gas;

[0011] Product synthesis unit, used to form a pulsed plasma high-temperature environment synthesis zone with stable temperature and airflow fields to generate highly crystalline single-walled carbon nanotubes;

[0012] A product collection unit, used for gas-solid separation and collection of generated single-walled carbon nanotubes;

[0013] Wherein, the catalyst and co-catalyst introduction unit and the product collection unit are both arranged on the top of the product synthesis unit.

[0014] The catalyst and co-catalyst introduction unit is connected to the DC pulse plasma of the product synthesis unit, and the product collection unit is connected to the product collection unit through a discharge pipe.

[0015] Furthermore, the product synthesis unit includes a reaction chamber, a preheater, a carbon source mixed gas injection port, a hollow cathode, a hollow anode, a hollow graphite electrode rod, a melt, a graphite crucible, a switching unit, a graphite crucible and a power supply;

[0016] The hollow cathode and the hollow anode are arranged at the top of the reaction chamber and are arranged on both sides of the center line of the reaction chamber in an axisymmetric manner. One end of the hollow cathode and the hollow anode are located inside the reaction chamber, and the ends are provided with the hollow graphite electrode rods. The other end is located outside the reaction chamber and is connected to the carbon source mixed gas injection port and the catalyst and co-catalyst introduction unit respectively.

[0017] The preheater is arranged at the carbon source mixed gas injection port;

[0018] The power supply is connected to the cathode and anode hollow electrodes via a switching unit;

[0019] The melt is arranged inside the reaction chamber and is located in a graphite crucible vertically below the graphite electrode rod.

[0020] Furthermore, the outer diameter d1 of the hollow cathode and the hollow anode are both 20-200 mm, and the inner diameter d2 are both 10-100 mm; the pole center distance D of the hollow cathode and the hollow anode is 60-350 mm;

[0021] The outer diameter and inner diameter of the hollow graphite electrode rod are not greater than the outer diameter and inner diameter of the hollow cathode and the hollow anode, and the length of the hollow graphite rod is not less than 200 mm.

[0022] Furthermore, the melt is a refractory metal; the refractory metal is an iron-containing compound or mixture; and the bottom shape of the melt is circular or notched.

[0023] Furthermore, the catalyst and co-catalyst introduction unit is a feeder.

[0024] Another object of the present invention is to provide a method for preparing single-walled carbon nanotubes using the above-mentioned device, the method specifically comprising the following steps:

[0025] S1) The catalyst and the co-catalyst are mixed in proportion and placed in a feeder, and the carbon source mixed gas is preheated, while an inert gas is introduced into the reaction chamber for evacuation;

[0026] S2) starting a power supply, setting a power supply pulse frequency, and conducting the cathode and anode hollow electrodes through the melt to form a pulsed plasma that heats the reaction chamber to a predetermined temperature. Simultaneously, the cathode and anode are changed once every 5-40 minutes by a switching unit to form a pulsed plasma high-temperature environment synthesis zone with a stable temperature field and airflow field;

[0027] S3) feeding the preheated carbon source mixed gas into the reaction chamber at a certain flow rate, and simultaneously feeding the catalyst and the co-catalyst into the reaction chamber via a certain flow rate of carrier gas, where they are evaporated in the pulse plasma high temperature synthesis zone to form catalyst particles with a particle size of 0.5-10 nanometers, which then undergo a catalytic reaction with the cracked carbon source gas in the pulse plasma high temperature environment to generate products;

[0028] S4) The generated product enters the product collection unit along with the gas through the discharge pipe to obtain highly crystalline single-walled carbon nanotubes.

[0029] Furthermore, the weight ratio of the catalyst to the catalyst promoter in S1) is 5:1-150:1; the preheating temperature of the carbon source mixed gas is 200-660°C;

[0030] The predetermined temperature in S2) is 700-2300° C.; the power pulse frequency is 15-90 kHz;

[0031] The carrier gas velocity in S3) is not less than 4 m / s, and the carbon source mixed gas velocity is 3.5-600 m / s.

[0032] Furthermore, the catalyst in S1) is at least one of ferrocene, nickelocene, iron pentacarbonyl, iron, cobalt, and nickel;

[0033] The co-catalyst is thiophene, dimethyl sulfoxide, carbon disulfide, sulfur powder, ferrous sulfide, ferrous sulfate, tungsten sulfide, molybdenum sulfide or other sulfur-containing compounds;

[0034] The melt is at least one of tungsten, tantalum, rhenium, molybdenum, yttrium, lanthanum, dysprosium compounds or mixtures containing iron;

[0035] The carbon source mixed gas in S3) includes: a carbon source gas, a carrier gas, a reducing gas, and other gases, wherein the flow ratio of the carbon source gas, the carrier gas, the reducing gas, and the other gases is 1:(2-25):(0.1-25):(0.01-3). The carbon source gas is at least one of ethylene, methane, propylene, propane, natural gas, and liquefied petroleum gas; the carrier gas is at least one of the inert gases argon, nitrogen, and helium; the reducing gas is hydrogen; and the other gases are at least one of water vapor, carbon dioxide, carbon monoxide, and ammonia.

[0036] A single-walled carbon nanotube is prepared by the above method.

[0037] The beneficial effects of the present invention are as follows: By adopting the above-mentioned technical solution, the device of the present invention can maintain stable operation of the arc equipment at high temperatures for a long time, while reducing evaporation of the graphite bottom electrode by the high-temperature arc, maintaining the sustained activity of the catalyst, and further improving the utilization of the arc energy by the carbon source and catalyst. Ultimately, the improved carbon source conversion efficiency is the core key technology for the preparation of high-quality single-walled carbon nanotubes by the high-temperature arc method. This is particularly important for achieving both high yields and high-quality, high-purity single-walled carbon nanotubes.

[0038] 1. By symmetrically setting the cathode and anode, and setting a melt below the cathode and anode as a conductor to connect the cathode and anode, this dual-electrode method allows energy to be concentrated at the upper end, converting it into more plasma areas. The dual electrodes reduce the dissolution of solid carbon in the low-anode graphite crucible by high-temperature plasma bombardment, which can maintain the continuous preparation of subsequent catalysts. At the same time, it can significantly reduce the bottom anode effect compared to a single electrode. The catalyst prepared in the synthesis area has a particle size of preferably 1-5nm. The carbon source mixed gas can be preheated at both electrodes and then injected into the hollow electrode to increase the contact area and time with the plasma, effectively improving the utilization rate of the carbon source by 28%. The yield of the prepared single-walled carbon nanotube primary product is not less than 1.5kg / h, and the average Raman characterization I G / I D Not less than 55.

[0039] 2. Without stopping the machine, switching the cathode and anode creates a pulsed plasma high-temperature synthesis zone with a stable temperature and airflow field. This compensates for the significant temperature difference in the reaction chamber caused by the two-fold difference in arc temperature between the cathode and anode, facilitating sustained and stable product growth. This extends the life of the furnace lining material and further prolongs the equipment's reaction time, ultimately achieving the goal of producing large quantities of single-walled carbon nanotubes over a long period of time. The method can produce a primary product yield of up to 4.5 kg / h, and the equipment can operate continuously for over 10 days without stopping.

[0040] 3. The use of a round or notched shape containing the melt at the bottom can not only reduce stress concentration, but also alleviate erosion and damage to the graphite crucible, thereby extending its service life.

[0041] 4. The preheated carbon source mixed gas and the prepared catalyst nanoparticles are more evenly combined, while reducing the equipment load and maintaining the relative uniformity of the temperature field in the reaction chamber. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The present invention is a schematic structural diagram of a device for preparing single-walled carbon nanotubes using direct current pulse plasma.

[0043] Figure 2 The present invention Figure 1 Schematic diagram of the dual electrodes, slot-type melt arrangement and discharge port top view.

[0044] Figure 3 The present invention Figure 1 A partial cross-sectional view of a hollow graphite electrode.

[0045] Figure 4 This is a scanning electron microscope image of the single-walled carbon nanotubes prepared in Example 3 of the present invention.

[0046] Figure 5 This is a thermogravimetric characterization diagram of single-walled carbon nanotubes prepared using the device of the present invention in Example 4 of the present invention.

[0047] Figure 6 This is the Raman spectrum of the single-walled carbon nanotubes prepared in Example 3 of the present invention.

[0048] Figure 7 This is a transmission electron microscope image of the single-walled carbon nanotubes prepared in Example 3 of the present invention.

[0049] In the picture:

[0050] 211. Feeder; 221. Reaction chamber; 222. Preheater; 223. Carbon source mixed gas injection port; 224. Hollow cathode and hollow anode; 225. Hollow graphite electrode rod; 226. Melt; 227. Graphite crucible; 228. Discharge pipe; 229. Switching unit; 230. Power supply; 331. Collection device. DETAILED DESCRIPTION

[0051] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0052] like Figure 1As shown, the present invention discloses a device for preparing single-walled carbon nanotubes using a direct current pulsed plasma. The device comprises symmetrically arranged cathodes and anodes, and a melt 226 is provided below the cathodes and anodes as a conductor. By switching the cathodes and anodes, a pulsed plasma high-temperature environment synthesis zone with a stable temperature field and airflow field is formed. In the synthesis zone, an introduced catalyst is prepared into catalyst particles with a particle size of 0.5-10 nanometers, and fully catalytically cracks the catalyst particles with the preheated carbon source mixed gas to produce high-purity single-walled carbon nanotubes.

[0053] The catalyst and co-catalyst introduction unit is used to introduce the catalyst and co-catalyst into the product synthesis unit through a carrier gas;

[0054] The product synthesis unit is used to prepare the catalyst and the co-catalyst into nano-catalyst particles, and simultaneously preheat the carbon source mixed gas and fully catalyze the cracking reaction under the pulse plasma high temperature environment to generate highly crystalline single-walled carbon nanotubes;

[0055] The product collection unit is used to perform gas-solid separation and collect the generated single-walled carbon nanotubes;

[0056] The collecting unit is connected to the synthesis unit and the collecting device 331 via the discharge pipe 228;

[0057] wherein the catalyst and co-catalyst introduction unit is connected to one end of the product synthesis unit, and the other end of the product synthesis unit is connected to the product collection unit;

[0058] A carbon source mixed gas injection port 223 is provided at the end of one end of the product synthesis unit connected to the catalyst and co-catalyst introduction unit.

[0059] The product synthesis unit includes a reaction chamber 221, a preheater 222, a carbon source mixed gas injection port 223, a hollow cathode and a hollow anode 224, a hollow graphite electrode rod 225, a melt 226, a graphite crucible 227, a discharge pipe 228, a switching unit 229 and a power supply 230;

[0060] The cathode and anode are located at the top of the reaction chamber and are arranged on both sides of the center line of the reaction chamber 221 in an axisymmetric manner.

[0061] One end of the cathode and anode is inserted into the interior of the reaction chamber 221, and a hollow graphite electrode rod 225 is provided at the end. Figure 3 Partial cross-sectional view shown.

[0062] The other ends are connected to the carbon source mixed gas injection port 223 and the discharge port of the feeder 211;

[0063] The melt 226 is disposed at the bottom of the reaction chamber 221 and is located in a graphite crucible vertically below the graphite electrode rod;

[0064] The power source 230 is connected to both the hollow cathode and the hollow anode 224 via a switching unit 229 .

[0065] like Figure 2 As shown, the outer diameter d1 of the hollow cathode and the hollow anode 224 is 20-200 mm, and the inner diameter d2 is 10-100 mm; the pole center distance D of the hollow cathode and the hollow anode 224 is 60-350 mm;

[0066] The outer diameter and inner diameter of the hollow graphite electrode rod 225 are not greater than the outer diameter and inner diameter of the hollow cathode and hollow anode 224 , and the length of the hollow graphite rod 225 is not less than 200 mm.

[0067] The melt 226 is a refractory metal, which is a compound or mixture containing iron. The bottom melt has a circular or notch shape.

[0068] The catalyst and co-catalyst introduction unit is a feeder 211 .

[0069] The switching unit is a large relay or dual power supply used for currents below 630A.

[0070] Another object of the present invention is to provide a method for preparing single-walled carbon nanotubes using the above-mentioned device, which method specifically comprises the following steps:

[0071] S1) The catalyst and the co-catalyst are mixed in proportion and placed in a feeder 211, and an inert gas is introduced to evacuate the mixture; and the carbon source gas mixture is preheated;

[0072] S2) starting the power supply 230, setting the power supply pulse frequency, and heating the reaction chamber 221 to a predetermined temperature. At the same time, the cathode and anode are changed every 5-40 minutes to form a pulsed plasma high temperature environment synthesis zone with a stable temperature field and air flow field;

[0073] S3) feeding the preheated carbon source mixed gas into the reaction chamber at a certain flow rate, and simultaneously feeding the catalyst and the co-catalyst into the reaction chamber via a certain flow rate of carrier gas, where they are evaporated in the pulse plasma high temperature synthesis zone to form catalyst particles with a particle size of 0.5-10 nanometers, which then undergo a catalytic reaction with the cracked carbon source gas in the pulse plasma high temperature environment to generate products;

[0074] S4) The generated product enters the collection unit 331 along with the gas through the discharge pipe 228 to obtain the final product.

[0075] The weight ratio of the catalyst to the catalyst promoter in S1) is 5:1-150:1; the preheating temperature of the carbon source mixed gas is 200-660°C.

[0076] The predetermined temperature in S2) is 700-2300° C.; the power pulse frequency is 15-90 kHz;

[0077] The flow ratio of the carbon source gas, carrier gas, reducing gas and other gases in the carbon source mixed gas in S3) is 1:(2-25):(0.1-25):(0.01-3).

[0078] The flow rate of the catalyst and co-catalyst carrier gas is not less than 4 m / s, and the flow rate of the carbon source mixed gas is usually 3.5-600 m / s.

[0079] The catalyst in S1) is at least one of ferrocene, nickelocene, iron pentacarbonyl, iron, cobalt, and nickel;

[0080] The co-catalyst is thiophene, dimethyl sulfoxide, carbon disulfide, sulfur powder, ferrous sulfide, ferrous sulfate, tungsten sulfide, molybdenum sulfide or other sulfur-containing compounds.

[0081] The melt is at least one of tungsten, tantalum, rhenium, molybdenum, yttrium, lanthanum, dysprosium compounds or mixtures containing iron.

[0082] The carbon source mixed gas includes: carbon source gas, carrier gas, reducing gas and other gases, wherein the carbon source gas is: at least one of ethylene, methane, propylene, propane, natural gas, and liquefied petroleum gas; the carrier gas is at least one of the inert gases argon, nitrogen, and helium; the reducing gas is hydrogen; and the other gases are at least one of water vapor, carbon dioxide, carbon monoxide, and ammonia.

[0083] Example 1:

[0084] The catalyst, ferrocene, and the co-catalyst, sulfur powder, were mixed in a 90:1 weight ratio and placed in a feeder. The mixture was then purged with inert gas. The flow ratio of the carbon source gas, carrier gas, reducing gas, and other gases in the carbon source mixture was 1:20:20:1. The carbon source gas was methane, the carrier gas was inert argon, the reducing gas was hydrogen, and the other gases were water vapor. The carbon source mixture was preheated to 300°C. The catalyst and co-catalyst were then fed into the reaction chamber at a carrier gas flow rate of 16 m / s, and the carbon source mixture was delivered at a flow rate of 90 m / s through the hollow cathode and hollow anode.

[0085] Start the power supply, the pulse frequency is 30kHz, the double electrodes in the reaction chamber discharge through the iron-containing tungsten compound or mixture melt to form a high temperature and heat it to a predetermined temperature of 1200℃, and the bottom melt is in the shape of a notch. Figure 2As shown. The cathode and anode are changed every 30 minutes to form a pulsed plasma high-temperature environment synthesis zone with a stable temperature field and air flow field. The catalyst, co-catalyst and preheated carbon source mixed gas are sent into the reaction chamber through the hollow cathode and anode electrodes. The outer diameter d1 of the hollow cathode and anode electrodes is 100mm, and the inner diameter d2 is 30mm; the pole center distance D of the hollow cathode and anode electrodes is 180mm; the outer diameter and inner diameter of the hollow graphite electrode rod are 80mm and 30mm respectively, and the length is 350mm. Its partial cross-sectional view is shown as follows. Figure 3 shown.

[0086] Catalyst particles with a particle size of 1-5 nanometers are obtained in the pulsed plasma high-temperature environment synthesis zone. The nanocatalyst particles and the carbon source mixed gas fully catalyze the cracking reaction to prepare single-walled carbon nanotubes. The generated product enters the collection unit with the gas through the discharge pipe to obtain the final product.

[0087] like Figure 1 The figure shows the device structure diagram of the embodiment 1 of the present invention. Figure 2 A top view of the double electrode and slot type melt arrangement and discharge port. Figure 3 The present invention Figure 1 Partial cross-sectional view of the hollow graphite electrode. Table 2 shows the average I of the primary product obtained in Example 1. G / I D The ratio is 56, the product TG residue is 37.6%, the initial product output is 1.6 kg / h, and the equipment can operate continuously for 98 hours, nearly 5 days.

[0088] The device and method of the present invention can facilitate the continuous and effective production of single-walled carbon nanotubes over a long period of time, and have similar effects to other similar reactors, thus having a certain degree of versatility.

[0089] With regard to the nanostructures obtained using the described methods and devices, they relate to many of the most promising directions in materials science, nanotechnology, plasma physics, applied chemistry and others.

[0090] The Raman spectroscopy, thermogravimetric characterization method, scanning electron microscopy and energy dispersive X-ray spectroscopy characterization method, transmission electron microscopy characterization method, and ultraviolet-visible-near-infrared absorption spectroscopy characterization method standards for high-quality single-walled carbon nanotube samples are shown in GB / T 32871-2016, GB / T 24490-2009, GB / T 32869-2016, GB / T 30534-2014, and GB_T39114-2020. The test scheme is described in Table 1.

[0091] Table 1 Test plan

[0092]

[0093] Example 2

[0094] The device and process method used in Example 1 differ in that the catalyst is iron, the catalyst promoter is ferrous sulfide, and the weight ratio of the catalyst to the catalyst promoter, sulfur powder, is 10:1. The carbon source mixture is preheated to 400°C; the flow rate ratio of the carbon source gas, carrier gas, reducing gas, and other gases in the carbon source mixture is 1:25:20:2. The flow rate of the catalyst and catalyst promoter is 20 m / s, and the flow rate of the carbon source mixture is 6 m / s. The pulse frequency is 60 kHz. The melt is a tantalum mixture containing iron, and the bottom melt is circular. The melt in each reaction chamber is heated to a predetermined temperature of 1330°C by discharge. The cathode and anode are replaced every 20 minutes. The outer diameter d1 of the hollow cathode and anode electrodes is 160 mm, and the inner diameter d2 is 60 mm. The center-to-center distance D between the hollow cathode and anode electrodes is 350 mm. The outer and inner diameters of the hollow graphite electrode rods are 120 mm and 60 mm, respectively, and the length is 450 mm. The generated product enters the collection unit along with the gas through the discharge pipe to obtain the final product.

[0095] From Table 2, we can see that the average I of the primary product obtained in Example 1 G / I D The ratio is 58, the product TG residue is 35.3%, the initial product output is 4.5 kg / h, and the equipment operates continuously for more than 7 days.

[0096] Example 3

[0097] The difference between the device and process method of Example 2 is that the catalyst is iron, the catalyst promoter is ferrous sulfide, and the weight ratio of the catalyst and the catalyst promoter sulfur powder is 12:1. The carbon source mixture is preheated to 460°C; the flow ratio of the carbon source gas, carrier gas, reducing gas and other gases in the carbon source mixture is 1:25:25:2.5. The amount of carbon source is 2 cubic meters per hour. The melt in the reaction chamber discharges to form a high temperature and is heated to a predetermined temperature of 1530°C. The cathode and anode are changed every 10 minutes. The outer diameter d1 of the hollow cathode and anode electrodes is 180mm; the pole center distance D of the hollow cathode and anode electrodes is 300mm; and the length of the hollow graphite electrode rod is 650mm. The generated product enters the collection unit with the gas through the discharge pipe to obtain the final product.

[0098] Figure 6 The Raman spectrum of the sample prepared in Example 3 was obtained at 180 cm -1 It has obvious and sharp RBM characteristic absorption peak, that is, the product contains single-walled carbon nanotubes. Under the condition of excitation wavelength of 532nm, the product I G / I DThe ratio is 72, that is, the prepared product is a high-quality single-walled carbon nanotube. From Table 2, we know that the TG residue of the initial product is 17.8%, the carbon content is close to 82.2%, and the purity of the initial product is high. Table 2 shows that the output is 3.5kg / h, and the carbon content of the initial product is close to 2.8kg. The utilization rate of the carbon source is calculated to be 28%. Figure 4 Scanning electron microscopy can further verify that the sample of Example 3 has fewer surface impurities, which is consistent with the TG residue characterization results. Figure 7 Transmission electron microscopy (TEM) characterization of the product prepared in Example 3 further confirmed the presence of single-walled carbon nanotubes. The image shows numerous single-walled carbon nanotube bundles. High-resolution TEM analysis revealed a relatively uniform particle size distribution of the catalyst, with the catalyst particles used for growth being approximately 3 nm in size. The equipment was operational for 267 hours, exceeding 10 days.

[0099] The device and process of Example 3 differ in that the catalyst is iron pentacarbonyl and the catalyst promoter is thiophene. They are mixed in a weight ratio of 125:6 and placed in a feeder. The carbon source gases are ethylene and propylene, the carrier gas is inert argon, the reducing gas is hydrogen, and the other gases are water vapor and carbon monoxide.

[0100] The melt in the reaction chamber is heated to a predetermined temperature of 1680°C by discharge. The pulse frequency is 90 kHz, and the cathode and anode are replaced every 15 minutes. The distance D between the hollow cathode and anode electrodes is 350 mm. The generated product is transported along with the gas through a discharge pipe to a collection unit to obtain the final product.

[0101] From Table 2, it can be seen that the average I of the products obtained in Example 4 G / I D The ratio is 68, the output is 2.8kg / h, and the equipment operation time is 245h, which is more than 10 days.

[0102] Example 5

[0103] The difference between the device and process method of Example 4 is that the mixture is placed in a feeder after being mixed in a weight ratio of 125:3, and the flow ratio of the carbon source gas, carrier gas, reducing gas and other gases in the carbon source mixture is 1:10:25:3, wherein the carbon source gas is methane and propylene, the carrier gas is the inert gas argon and helium, the reducing gas is hydrogen, and the other gases are at least one of water vapor and ammonia; the preheating temperature is 560°C. The melt is a dysprosium mixture containing iron. Each pair of reaction chamber melt discharges to form a high temperature and is heated to a predetermined temperature of 1800°C.

[0104] From Table 2, it can be seen that the average I of the products obtained in Example 5 G / I DThe ratio is 78, the product TG residue is 37.8%, the output is 1.8 kg / h, and the equipment operation time is 257 hours, which is more than 10 days.

[0105] Table 2 Comparison of product performance in the examples

[0106]

[0107] The above describes in detail the apparatus and method for preparing single-walled carbon nanotubes using a direct current pulsed plasma, as provided in the embodiments of this application. The description of the above embodiments is intended only to facilitate understanding of the method and core concept of this application. Furthermore, those skilled in the art will appreciate that variations in the specific implementation and scope of application may occur based on the concepts of this application. Therefore, this specification should not be construed as limiting this application.

[0108] For example, certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that hardware manufacturers may use different nouns to refer to the same component. This specification and claims do not use differences in names as a way to distinguish components, but use differences in the functions of components as the criteria for distinction. For example, "including" and "comprising" mentioned throughout the specification and claims are open-ended terms, so they should be interpreted as "including / including but not limited to". "Approximately" means that within an acceptable error range, those skilled in the art can solve the technical problems within a certain error range and basically achieve the technical effects. The subsequent description in the specification is a preferred embodiment of the present application, but the description is for the purpose of illustrating the general principles of the present application, and is not used to limit the scope of the present application. The scope of protection of the present application shall be as defined in the attached claims.

[0109] It should also be noted that the terms "include," "comprises," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a product or system comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such product or system. In the absence of further limitations, an element defined by the phrase "comprises a..." does not exclude the presence of other identical elements in the product or system comprising the element.

[0110] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0111] The above description shows and describes several preferred embodiments of the present application. However, as previously mentioned, it should be understood that the present application is not limited to the form disclosed herein and should not be construed as excluding other embodiments. Instead, the present application can be used in various other combinations, modifications, and environments and can be modified within the scope of the application concept described herein through the above teachings or technology or knowledge in the relevant field. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present application should be protected by the claims appended hereto.

Claims

1. A device for preparing single-walled carbon nanotubes using a direct current pulsed plasma, characterized in that: The device comprises: a catalyst and co-catalyst introduction unit, used for introducing the catalyst and co-catalyst via a carrier gas; The product synthesis unit is used to regularly switch the cathode and anode of the pulsed plasma to form a pulsed plasma high-temperature synthesis zone with a stable temperature field and airflow field. The catalyst is prepared into nano-catalyst particles, which react with the cracked carbon source gas in the pulsed plasma high-temperature environment to produce highly crystalline single-walled carbon nanotubes. A product collection unit, used for gas-solid separation and collection of the generated single-walled carbon nanotubes; Wherein, the catalyst and co-catalyst introduction unit and the product collection unit are both arranged on the top of the product synthesis unit. The catalyst and co-catalyst introduction unit is connected to the product synthesis unit, and the product synthesis unit is connected to the product collection unit through a discharge pipe; The product synthesis unit includes a reaction chamber, a preheater, a carbon source mixed gas injection port, a hollow cathode, a hollow anode, a hollow graphite electrode rod, a melt, a switching unit, a graphite crucible and a power supply; The hollow cathode and the hollow anode are arranged at the top of the reaction chamber and are arranged in an axisymmetric manner on both sides of the center line of the reaction chamber. One end of the hollow cathode and the hollow anode are located inside the reaction chamber, and the ends are provided with the hollow graphite electrode rods. The other end is located outside the reaction chamber and is connected to the carbon source mixed gas injection port and the catalyst and co-catalyst introduction unit respectively. The preheater is arranged at the carbon source mixed gas injection port; The power supply is connected to the hollow cathode and the hollow anode via a switching unit, and the switching unit is used to switch the hollow cathode and the hollow anode at regular intervals; The melt is arranged inside the reaction chamber and is located in a graphite crucible vertically below the graphite electrode rod.

2. The device according to claim 1, characterized in that The outer diameter d1 of the hollow cathode and the hollow anode is 20-200 mm, and the inner diameter d2 is 10-100 mm; the pole center distance D of the hollow cathode and the hollow anode is 60-350 mm; The outer diameter and inner diameter of the hollow graphite electrode rod are not larger than the outer diameter and inner diameter of the hollow cathode and the hollow anode, and the length of the hollow graphite electrode rod is not less than 200 mm.

3. The device according to claim 1, characterized in that The melt is a refractory metal; the refractory metal is an iron-containing compound or mixture; and the bottom shape of the melt is circular or notched.

4. The device according to claim 1, characterized in that The catalyst and co-catalyst introduction unit is a feeder.

5. A method for preparing single-walled carbon nanotubes using the apparatus according to any one of claims 1 to 4, characterized in that: The method specifically comprises the following steps: S1) The catalyst and the co-catalyst are mixed in proportion and placed in a feeder, and the carbon source mixed gas is preheated, while an inert gas is introduced into the reaction chamber for evacuation; S2) Start the power supply, set the power supply pulse frequency, conduct the cathode and anode hollow electrodes through the melt, and form a pulsed plasma to heat the reaction chamber to a predetermined temperature. At the same time, the cathode and anode are changed once every 5-40 minutes by the switching unit to form a pulsed plasma high-temperature environment synthesis zone with a stable temperature field and air flow field; S3) The preheated carbon source gas mixture is fed into the reaction chamber at a certain flow rate. Simultaneously, a catalyst and a co-catalyst are fed into the reaction chamber via a carrier gas at a certain flow rate. The catalyst particles are evaporated in the pulsed plasma high temperature synthesis zone to form catalyst particles with a particle size of 0.5-10 nanometers. The catalyst particles then react with the cracked carbon source gas in the pulsed plasma high temperature environment to generate products. S4) The generated product enters the product collection unit along with the gas through the discharge pipe to obtain highly crystalline single-walled carbon nanotubes.

6. The method according to claim 5, characterized in that The weight ratio of the catalyst to the co-catalyst in S1) is 5:1-150:1; the preheating temperature of the carbon source mixed gas is 200-660°C; The predetermined temperature in S2) is 700-2300°C; the power pulse frequency is 15-90 kHz; The carrier gas velocity in S3) is not less than 4 m / s, and the carbon source mixed gas velocity is 3.5-600 m / s.

7. The method according to claim 5, characterized in that The catalyst in S1) is at least one of ferrocene, nickelocene, iron pentacarbonyl, iron, cobalt, and nickel; The co-catalyst is thiophene, dimethyl sulfoxide, carbon disulfide, sulfur powder, ferrous sulfide, ferrous sulfate, tungsten sulfide, molybdenum sulfide or other sulfur-containing compounds.

8. The method according to claim 5, characterized in that The melt in S2) is at least one of tungsten, tantalum, rhenium, molybdenum, yttrium, lanthanum, dysprosium compounds or mixtures containing iron; The carbon source mixed gas in S3) comprises carbon source gas, carrier gas, reducing gas and other gases, and the flow ratio of the carbon source gas, carrier gas, reducing gas and other gases is 1:2-25:0.1-25:0.01-3.

9. A single-walled carbon nanotube, characterized in that: The single-walled carbon nanotubes are prepared by the method according to any one of claims 5 to 8.

Images