Apparatus and method for preparing carbon nanotubes by plasma method and preparation of catalyst

Abstract

The application provides a device and a method for preparing carbon nanotubes by a plasma method. The device comprises a plasma generating device and a carbon nanotube growth furnace which are in communication with each other. The plasma generating device comprises a first carrier gas inlet, a carrier inlet, an evaporation chamber, an evaporation chamber outlet and a first heating module. The first heating module is used for heating the cavity of the evaporation chamber. The first carrier gas inlet is in communication with the cavity of the evaporation chamber. The carrier inlet is in communication with the cavity of the evaporation chamber and is used for conveying catalyst materials into the cavity of the evaporation chamber. The cavity of the evaporation chamber is in communication with the furnace cavity of the carbon nanotube growth furnace through the evaporation chamber outlet. The carbon nanotube growth furnace comprises a second carrier gas inlet, a furnace cavity and a heating module. The second carrier gas inlet is in communication with the furnace cavity. The heating module is used for heating the furnace cavity. The separation of the catalyst evaporation and the carbon nanotube growth reaction process is realized, high-quality single-walled and double-walled carbon nanotubes are prepared, and the service life of the device is prolonged.

Description

Technical Field

[0001] This application relates to the field of carbon material preparation, specifically to an apparatus and method for preparing carbon nanotubes and the preparation of a catalyst. Background Technology

[0002] Plasma technology uses a high-energy plasma torch to bombard an iron source (such as iron particles or powder), causing it to evaporate into iron atom vapor. These iron atom vapors then collide with each other in a specific reaction environment, forming tiny, uniform catalyst particles. These highly active catalyst particles provide an ideal "soil" for the growth of single-walled carbon nanotubes. When these catalyst particles come into contact with a carbon source (such as methane), the carbon atoms undergo a series of complex physicochemical changes on the catalyst surface, ultimately generating high-quality single-walled carbon nanotubes.

[0003] However, the plasma method for preparing single and double-walled carbon nanotubes has problems such as poor controllability of catalyst particles, high energy consumption of plasma torch, and high damage rate of accessories.

[0004] The reasons for the problems are as follows: 1. Poor controllability of catalyst particles: In the process of preparing single-walled carbon nanotubes using plasma methods, the controllability of catalyst particles has not yet been effectively solved. Technological limitations make it difficult to precisely control the size of metallic iron catalyst particles in a plasma environment, thus affecting the quality stability of the prepared single-walled carbon nanotubes and limiting the product's performance and application range. 2. High energy consumption of the plasma torch: In order to volatilize iron atoms in the catalyst in the form of iron flakes, iron particles, or iron powder, the plasma torch requires high power support during the preparation of single-walled carbon nanotubes. This not only increases energy consumption and production costs, but also, under current technology, the evaporation rate of iron particles is difficult to control at high temperatures, further exacerbating the instability of catalyst particle size. In addition, the energy utilization efficiency of the plasma torch is not high, failing to fully convert it into the energy required for the preparation of single-walled carbon nanotubes. 3. High temperature leads to component damage: The high-temperature environment generated by the plasma torch generates severe thermal stress on equipment components, making them prone to damage and thus shortening the service life of the equipment. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this application provides an apparatus for preparing carbon nanotubes using a plasma method. The specific technical solution is as follows:

[0006] This application provides an apparatus for preparing carbon nanotubes using a plasma method. The apparatus includes a plasma generation device and a carbon nanotube growth furnace that are interconnected. The plasma generation device includes a first carrier gas inlet, a material inlet, an evaporation chamber, and an evaporation chamber outlet. The first carrier gas inlet is connected to the cavity of the evaporation chamber and is used to introduce an inert gas into the cavity of the evaporation chamber. The material inlet is connected to the cavity of the evaporation chamber and is used to deliver catalyst material into the cavity of the evaporation chamber. The cavity of the evaporation chamber is connected to the furnace cavity of the carbon nanotube growth furnace through the evaporation chamber outlet. The carbon nanotube growth furnace includes a second carrier gas inlet, a furnace cavity, and a heating module. The second carrier gas inlet is connected to the furnace cavity and is used to provide reaction gas to the furnace cavity. The heating module is used to heat the furnace cavity.

[0007] Preferably, the plasma generation device generates a plasma arc to provide a first heating temperature for the cavity of the evaporation chamber; the heating module is disposed on the outside of the furnace cavity (10) to provide a second heating temperature for the catalytic growth of carbon nanotubes.

[0008] Preferably, the inner diameter of the evaporation chamber is larger than the inner diameter of the furnace cavity.

[0009] Preferably, the inner diameter of the evaporation chamber minus the inner diameter of the furnace cavity is 100-200 mm.

[0010] Preferably, the channel of the material inlet is inclined toward the side of the plasma evaporation chamber opposite to the furnace cavity.

[0011] Preferably, the channel of the material inlet has a first included angle α with the side wall of the plasma evaporation chamber, and the first included angle α is 20 to 60°.

[0012] Preferably, the channel of the second carrier gas inlet has a second included angle β with the side wall of the furnace cavity, and the second included angle β is 10 to 45°.

[0013] Preferably, the device satisfies at least one of the following characteristics:

[0014] The output power of the plasma generation device is 20-50kW;

[0015] The first heating temperature is 500–1800℃;

[0016] The second heating temperature is 900–1300℃;

[0017] The inert gas introduced through the first carrier gas inlet is any one or both of argon and nitrogen.

[0018] The flow rate of the inert gas is 1 L / min to 300 L / min;

[0019] The conveying rate of the catalyst material is 0.1–50 g / min;

[0020] The reaction gases introduced through the second carrier gas inlet include inert gases, hydrogen, and hydrocarbon gases.

[0021] Preferably, the hydrocarbon gas includes at least one of ethylene, propylene, methane, or natural gas.

[0022] Preferably, the plasma anode of the plasma generation device is disposed within the evaporation chamber, and the plasma anode is provided with a support cavity for placing the catalyst material.

[0023] Preferably, in the plasma electrode of the plasma generating device, the plasma anode is made of one or both of graphite and copper, and the plasma cathode is made of any one of graphite, lanthanum-tungsten alloy, or tungsten.

[0024] This application also provides a method for preparing a catalyst material, the method comprising the following steps:

[0025] S11: Provides metal salt solutions and porous oxide support materials;

[0026] S12: A solid substance is obtained by mixing a metal salt solution with a porous oxide carrier material and then heating it.

[0027] S13: The solid material is crushed and calcined to obtain the catalyst precursor;

[0028] S14: Reduce the catalyst precursor to obtain the catalyst material.

[0029] Preferably, the reduction process includes passing a mixture of hydrogen and nitrogen gas. 、 Alternatively, hydrogen gas can be used to reduce the catalyst precursor.

[0030] Preferably, the metal salt includes any one or a combination of at least two of the nitrates, hydrochlorides, acetates or sulfates of iron, cobalt or nickel;

[0031] The porous oxide support material includes any one or a combination of at least two of the following: γ-Al2O3, MgO, CaO, SiO2, TiO2, hydrotalcite, magnesium aluminum spinel (MgAl2O4), vermiculite, montmorillonite, or molecular sieve.

[0032] This application also provides a method of using the aforementioned apparatus for preparing carbon nanotubes by plasma method, comprising the following steps:

[0033] S21: An inert atmosphere environment is formed in the plasma generation equipment and / or carbon nanotube growth furnace;

[0034] S22: Based on the plasma generation device, a plasma arc is generated in the evaporation chamber cavity, the evaporation chamber cavity is heated based on the plasma arc, and the furnace cavity is heated based on the heating module; and, inert gas is introduced into the evaporation chamber cavity from the first carrier gas inlet, catalyst material is transported into the evaporation chamber cavity from the material inlet, and the reaction gas is introduced into the furnace cavity from the second carrier gas inlet.

[0035] During the preparation process, the plasma arc in the evaporation chamber melts the metal material in the catalyst material and generates metal vapor. The inert gas transports the metal vapor to the furnace chamber so that the reaction gas comes into contact with the metal vapor to carry out catalytic growth and obtain carbon nanotubes.

[0036] Preferably, the catalyst material is prepared by a method for preparing a catalyst material as described in this application.

[0037] Based on the above technical solution, this application has the following beneficial effects:

[0038] 1. This application achieves the separation of the two processes of catalyst evaporation and carbon nanotube growth reaction by setting up an interconnected plasma generation device and a carbon nanotube growth furnace, so that the two reactions can be independently adjusted, reducing reaction energy consumption and improving energy utilization.

[0039] 2. By separating the plasma generation equipment and the carbon nanotube growth furnace, the direct growth of single and double-walled carbon nanotubes in the plasma generation equipment is avoided, thereby eliminating the interference of single and double-walled carbon nanotubes on the plasma torch during growth, significantly improving the stability of the electric arc, and providing a strong guarantee for continuous and stable growth of single and double-walled carbon nanotubes.

[0040] 3. By adjusting the conveying speed of the catalyst material, this application can control the concentration of metal vapor in the evaporation chamber per unit time, thereby effectively regulating the size of the active metal particles;

[0041] 4. By preloading compounds containing active metals onto porous oxide supports and subjecting them to low-temperature calcination and reduction treatment, the proportion of active metals on the support becomes more controllable, and the active metal particles are stabilized at the nanoscale. This not only reduces the power requirements of the plasma arc but also enables the evaporation of metal atoms at lower temperatures.

[0042] 5. By lowering the initial heating temperature, the evaporation rate of metal atoms is correspondingly slowed down, effectively avoiding violent collisions of metal particles caused by excessively rapid evaporation, thus preventing the formation of excessively large metal particles. This improvement provides strong support for the preparation of high-quality single- and double-walled carbon nanotubes. Attached Figure Description

[0043] To more clearly illustrate the technical solutions and advantages in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This application provides a schematic diagram of the structure of an apparatus for preparing carbon nanotubes using a plasma method.

[0045] Figure 2 A transmission electron microscope image of the catalyst prepared in Example 2 of the catalyst material preparation of the present invention;

[0046] Figure 3 This is a scanning electron microscope image of the single-walled carbon nanotubes prepared in Example 1 of the present invention;

[0047] Figure 4 This is a scanning electron microscope image of the single-walled carbon nanotubes prepared in Example 2 of the present invention;

[0048] Figure 5 This is a transmission electron microscope image of the single-walled carbon nanotubes prepared in Example 2 of the present invention;

[0049] Figure 6 The image shows the Raman spectrum of the single-walled carbon nanotubes prepared in Example 2 of this invention.

[0050] Figure 7 This is a scanning electron microscope image of the single-walled carbon nanotubes prepared in Example 3 of the present invention;

[0051] Figure 8 A scanning electron microscope image of the single-walled carbon nanotubes prepared in Comparative Example 2 of this invention;

[0052] Figure 9 This is a transmission electron microscope image of the single-walled carbon nanotubes prepared in Comparative Example 2 of the present invention.

[0053] Reference numerals: 1-Plasma generation equipment, 2-Plasma cathode, 3-Plasma anode, 4-Metal gasket, 5-Catalyst material, 6-First carrier gas inlet, 7-Material inlet, 8-Evaporation chamber outlet, 9-Second carrier gas inlet, 10-Furnace cavity, 11-Carbon nanotube growth furnace. Detailed Implementation

[0054] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0055] For the terms defined below, unless a different definition is given elsewhere in the claims or this specification, these definitions shall apply. All numerical values, whether explicitly indicated or not, are defined herein as being modified by the term "about." The term "about" generally refers to a range of numerical values ​​that a person skilled in the art would consider equivalent to the stated values ​​to produce substantially the same properties, functions, results, etc. A range of numerical values ​​indicated by a low value and a high value is defined as including all numerical values ​​included within that range and all subranges included within that range.

[0056] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0057] The following describes an apparatus for preparing carbon nanotubes using a plasma method, as provided in an embodiment of this application. Please refer to [link / reference]. Figure 1 , Figure 1 This is a schematic diagram of an apparatus for preparing carbon nanotubes using a plasma method. It is understood that the apparatus structure shown in the figure is merely one specific embodiment of this application, and the apparatus for preparing carbon nanotubes using a plasma method may include fewer or more structural features, and is not limited to the structure described in the figure.

[0058] An apparatus for preparing carbon nanotubes using a plasma method includes a plasma generation device 1 and a carbon nanotube growth furnace 11 connected to each other, separating the plasma generation and carbon nanotube growth processes. The plasma generation device 1 includes a first carrier gas inlet 6, a material inlet 7, an evaporation chamber, and an evaporation chamber outlet 8. The cavity of the evaporation chamber is connected to the furnace cavity 10 of the carbon nanotube growth furnace 11 via the evaporation chamber outlet 8. The first carrier gas inlet 6, connected to the cavity of the evaporation chamber, is used to introduce an inert gas into the cavity of the evaporation chamber. Specifically, the inert gas can be any one or both of argon and nitrogen. This inert gas serves two purposes: firstly, it creates an inert atmosphere within the apparatus; secondly, it can be used to transport the plasma generated in the evaporation chamber to the carbon nanotube growth furnace 11. The material inlet 7, connected to the cavity of the evaporation chamber, is used to deliver catalyst material into the cavity of the evaporation chamber. The carbon nanotube growth furnace 11 includes a second carrier gas inlet 9, a furnace cavity 10, and a heating module. The heating module is used to heat the furnace cavity. The second carrier gas inlet 9 is connected to the furnace cavity 10 and is used to provide reaction gas to the furnace cavity 10.

[0059] This application separates the plasma evaporation reaction from the carbon nanotube growth reaction, avoiding the direct growth of single and double-walled carbon nanotubes in the evaporation chamber. This eliminates the interference of single and double-walled carbon nanotubes on the plasma torch during growth, significantly improves the stability of the electric arc, and provides a strong guarantee for continuous and stable growth of single and double-walled carbon nanotubes.

[0060] Specifically, the device includes a carbon nanotube growth furnace 11 positioned above the plasma generation device 1. The plasma generation device 1 provides a first heating temperature for the evaporation chamber. A heating module is located outside the furnace chamber 10 and provides a second heating temperature for the catalytic growth of carbon nanotubes. This allows the temperature settings of the plasma generation device 1 and the carbon nanotube growth furnace 11 to be independent, further separating the plasma generation and carbon nanotube growth processes. This eliminates the need for the plasma generation device 1 to be heated to the reaction temperature of the carbon nanotubes, effectively reducing overall energy consumption and improving energy efficiency.

[0061] In some embodiments, the plasma generating device 1 has an output power of 20 to 50 kW, the plasma arc temperature can reach 5000 to 10000°C, the first heating temperature of the evaporation chamber after heating can reach 500 to 1800°C, and the second heating temperature of the carbon nanotube growth furnace 11 is 900 to 1300°C.

[0062] Specifically, the output power of the plasma generating device 1 is 20, 30, 40, or 50 kW, and the first heating temperature inside the cavity of the plasma generating device 1 can be 500, 600, 700, 800, 900, 1000, 1300, 1500, or 1800 °C; the second heating temperature of the carbon nanotube growth furnace 11 can be 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, or 1300 °C.

[0063] In some embodiments, the channel of the loading inlet 7 is inclined toward the side of the plasma evaporation chamber away from the furnace cavity 10. The catalyst material is transported into the evaporation chamber through the loading inlet 7 at a rate of 0.1–50 g / min, uniformly conveying the catalyst material to the surface of the plasma anode. Further, the channel of the loading inlet 7 has a first included angle α with the side wall of the plasma evaporation chamber, the first included angle α being 20–60°, specifically 20, 30, 40, 50, or 60°. In some embodiments, the plasma anode of the plasma generation device is disposed in the evaporation chamber, and the plasma anode has a supporting cavity for placing the catalyst material. A metal gasket 4 may also be placed at the bottom of the supporting cavity.

[0064] Accordingly, the flow rate of inert gas entering the first carrier gas inlet 6 is 1 L / min to 300 L / min. This flow rate can be set according to different stages. When it is necessary to purge the air inside the device, the flow rate of inert gas is 100 to 300 L / min, and the duration of introduction is 30 to 60 min, until the oxygen concentration of the tail gas is less than 10 ppm. When the plasma generation equipment starts to work, the flow rate of inert gas at the first carrier gas inlet 6 is 30 to 70 L / min. When melting and evaporating the catalyst material, the flow rate of inert gas at the first carrier gas inlet 6 is 10 to 30 L / min, specifically, it can be 10 L / min. Since the plasma arc can rapidly melt and evaporate the active metal particles on the surface of the catalyst material 5, the volatilized metal vapor is then carried by the carrier gas at the first carrier gas inlet 6 and escapes from the outlet 8 of the evaporation chamber, smoothly flowing into the furnace cavity 10 of the carbon nanotube growth furnace, providing a catalyst for the catalytic cracking reaction of the active metal clusters in the furnace cavity.

[0065] In some embodiments, the inner diameter of the evaporation chamber is larger than the inner diameter of the furnace cavity 10. A design with a narrowing inner diameter is adopted at the connection between the plasma generation device 1 and the carbon nanotube growth furnace 11. This facilitates the escape of metal vapor as it leaves the evaporation chamber and also prevents the backflow of reactive gases into the evaporation chamber. Specifically, the inner diameter of the evaporation chamber is 300 nm, and the inner diameter of the furnace cavity 10 is 100–200 nm.

[0066] In some embodiments, the channel of the second carrier gas inlet 9 has a second included angle β with the side wall of the furnace cavity 10. The second included angle β is 10° to 45°, specifically 10°, 20°, 30°, 40°, and 45°. The included angle is set so that the reactant gas enters the furnace cavity 10 with a certain airflow direction to prevent the reactant gas from entering the evaporation chamber. In some embodiments, the reactant gas includes an inert gas, hydrogen, and a hydrocarbon gas. The hydrocarbon gas includes at least one of ethylene, propylene, methane, or natural gas. In addition, a small amount of additives, such as hydrogen sulfide or thiophene, may also be introduced.

[0067] To stabilize active metal particles at the nanoscale, this application provides a method for preparing a catalyst material, comprising the following steps:

[0068] S11: Provides metal salt solutions and porous oxide support materials;

[0069] S12: A solid substance is obtained by mixing a metal salt solution with a porous oxide carrier material and then heating it.

[0070] S13: The solid material is crushed and calcined to obtain the catalyst precursor;

[0071] S14: Reduce the catalyst precursor to obtain the catalyst material.

[0072] Metal salts include any one or a combination of at least two of the nitrates, hydrochlorides, acetates or sulfates of iron, cobalt or nickel;

[0073] The porous oxide support material includes any one or a combination of at least two of the following: γ-Al2O3, MgO, CaO, SiO2, TiO2, hydrotalcite, magnesium aluminum spinel (MgAl2O4), vermiculite, montmorillonite, or molecular sieve.

[0074] The reduction process includes passing a mixture of hydrogen and nitrogen gases. 、 Alternatively, the catalyst precursor may be reduced using hydrogen gas. Specifically, the catalyst precursor is reduced in an atmosphere of a mixture of hydrogen and nitrogen, or in an atmosphere of hydrogen gas, to obtain nanoscale active metal particles supported on an oxide carrier, which is the catalyst material.

[0075] Specifically, at least one of iron, cobalt, or nickel salts is dissolved in an appropriate amount of deionized water to form a metal salt solution with a concentration of 0.3–0.5 g / mL. The metal salt solution is mixed and stirred with a porous oxide support material, and the temperature is gradually raised to 60–90°C while continuing to stir until the water evaporates, yielding a solid substance. The solid substance is then pulverized and calcined in a nitrogen atmosphere at 150–400°C for 0.5–2 h to obtain a catalyst precursor. Finally, the catalyst precursor is reduced with hydrogen or a mixture of hydrogen and nitrogen for 0.5–5 h to obtain the catalyst material. The catalyst material comprises nanoscale active metal particles supported on an oxide support, and the loading of the active component on the porous oxide support is 1–50 wt%, preferably 5–30 wt%.

[0076] Nanoscale active metal particles not only reduce the power requirements of the plasma torch in the evaporation chamber but also enable the evaporation of metal atoms at lower temperatures. Due to the lower evaporation temperature, the evaporation rate of metal atoms is correspondingly slowed down, effectively avoiding violent collisions of metal particles caused by excessively rapid evaporation, thus preventing the formation of excessively large metal particles. This provides strong support for the preparation of high-quality single- and double-walled carbon nanotubes. Furthermore, the presence of a porous oxide support prevents metal particles from merging during melting, thereby extending the lifespan of the catalyst material. Additionally, by adjusting the proportion of the active component on the support and the feed rate of the catalyst material, this application achieves control over the concentration of active metal particles per unit time within the evaporation chamber.

[0077] Accordingly, this application also provides a method for using an apparatus for preparing carbon nanotubes by plasma method, comprising the following steps:

[0078] S21: An inert atmosphere environment is formed in the plasma generation device 1 and / or the carbon nanotube growth furnace 11; specifically, the inert gas can be introduced from the first carrier gas inlet 6 and / or the anion hollow structure, or introduced into the device of this application in other ways.

[0079] S22: Based on the plasma generation device 1, a plasma arc is generated in the evaporation chamber cavity, the evaporation chamber cavity is heated based on the plasma arc, and the furnace cavity 10 is heated based on the heating module; and, inert gas is introduced into the evaporation chamber cavity from the first carrier gas inlet 6, catalyst material is transported into the evaporation chamber cavity from the material inlet 7, and reaction gas is introduced into the furnace cavity 10 from the second carrier gas inlet 9.

[0080] Specifically, a working gas, such as argon or nitrogen, is introduced into the plasma cathode at a flow rate of 1 L / min to 300 L / min. The working gas is introduced through the hollow structure inside the plasma cathode 2 and, after being excited by electricity, generates a strong plasma arc.

[0081] During the preparation process, the plasma arc in the evaporation chamber melts the metal material in the catalyst material and generates metal vapor. The inert gas transports the metal vapor to the furnace chamber 10 so that the reaction gas comes into contact with the metal vapor to carry out catalytic growth and obtain carbon nanotubes.

[0082] The following describes specific embodiments of this application in conjunction with the above-described technical solutions. The following embodiments describe the technical solutions of this application in more detail. These embodiments are for illustrative purposes only, as various modifications and variations within the scope of the disclosure of this application will be apparent to those skilled in the art. The reagents used in the embodiments are commercially available or synthesized using conventional methods and can be used directly without further processing. Similarly, the instruments and apparatus used in the embodiments are commercially available.

[0083] Catalyst material preparation example 1

[0084] S11: Dissolve 21.6g of ferric nitrate in 43mL of deionized water to form a ferric nitrate solution with a concentration of 0.5g / mL;

[0085] S12: Add 10g of γ-Al2O3 powder to the solution, stir at room temperature for 2h, gradually raise the temperature to 60℃, and continue stirring until the water is completely evaporated to obtain a solid substance;

[0086] S13: The obtained solid material is crushed and calcined in a nitrogen atmosphere at 300°C for 1 hour to obtain the catalyst precursor;

[0087] S14: The catalyst precursor is reduced by a mixture of 15 vol 1% hydrogen and 85 vol 1% nitrogen to obtain nanoscale Fe particles supported on a γ-Al2O3 support, namely Fe / γ-Al2O3 catalyst (catalyst material 1).

[0088] In the above preparation, the loading of Fe catalytic active particles on the γ-Al2O3 support was 30 wt%.

[0089] Catalyst material preparation example 2

[0090] S11: Dissolve 7.2g of ferric nitrate in 24mL of deionized water to form a ferric nitrate solution with a concentration of 0.3g / mL;

[0091] S12: Add 10g of MgO powder to the solution, stir at room temperature for 2 hours, then gradually raise the temperature to 90°C and continue stirring until the water is completely evaporated to obtain a solid substance;

[0092] S13: The obtained solid material is crushed and calcined in a nitrogen atmosphere at 300°C for 1 hour to obtain the catalyst precursor;

[0093] S14: The catalyst precursor is reduced by a mixture of 10 vol 1% hydrogen and 90 vol 1% nitrogen to obtain nanoscale Fe particles supported on MgO, i.e., Fe / MgO catalyst (catalyst material 2).

[0094] In the above preparation, the loading of Fe catalytically active particles on the MgO support was 10 wt%. (Reference) Figure 2 As shown, the gray substance is the MgO carrier, while the black particles circled in red are Fe particles, and the size of these Fe particles reaches the nanoscale.

[0095] Catalyst material preparation example 3

[0096] S11: Dissolve 9.9g of cobalt nitrate in 33mL of deionized water to form a cobalt nitrate solution with a concentration of 0.3g / mL;

[0097] S12: Add 10g of MgAl2O4 powder to the solution, stir at room temperature for 2 hours, gradually raise the temperature to 80°C, and continue stirring until the water is completely evaporated to obtain a solid substance;

[0098] S13: The obtained solid material is crushed and calcined in a nitrogen atmosphere at 400℃ for 0.5h to obtain the catalyst precursor;

[0099] S14: The catalyst precursor is reduced by a mixture of 20 vol 1% hydrogen and 80 vol 1% nitrogen to obtain nano-sized Co particles supported on a MgAl2O4 support, namely the Co / MgAl2O4 catalyst (catalyst material 3).

[0100] In the above preparation, the loading of Co catalytic active particles on the MgAl2O4 support was 20 wt%.

[0101] Catalyst material preparation example 4

[0102] S11: Dissolve 14.8g of nickel nitrate in 33mL of deionized water to form a nickel nitrate solution with a concentration of 0.3g / mL;

[0103] S12: Add 10g of SiO2 powder to the solution, stir at room temperature for 2 hours, gradually raise the temperature to 60°C, and continue stirring until the water is completely evaporated to obtain a solid substance;

[0104] S13: The obtained solid material is crushed and calcined in a nitrogen atmosphere at 350°C for 2 hours to obtain the catalyst precursor;

[0105] S14: The catalyst precursor is reduced by a mixture of 30 vol 1% hydrogen and 70 vol 1% nitrogen to obtain nano-sized Ni particles supported on a SiO2 support, namely Ni / SiO2 catalyst (catalyst material 4).

[0106] In the above preparation, the loading of Ni catalytic active particles on the SiO2 support was 30 wt%.

[0107] Catalyst Material Comparative Example 1

[0108] According to patent CN116947025A, an Fe / CaCO3 / FeS catalyst (catalyst material 5) was prepared using 70 grams of iron powder, 10 grams of calcium carbonate, and 20 grams of ferrous sulfide as raw materials.

[0109] This embodiment also provides a method for preparing carbon nanotubes, using the plasma method for preparing carbon nanotubes as described in this application to prepare single- and double-walled carbon nanotubes. The embodiments are as follows:

[0110] Example 1

[0111] S21: Argon gas is introduced through the first carrier gas inlet 6 to exhaust the air in the device, so as to form an inert atmosphere environment in the plasma generation equipment 1 and the carbon nanotube growth furnace 11.

[0112] S22: Inert argon gas at a flow rate of 50 L / min is introduced through the first carrier gas inlet 6 to introduce the working argon gas into the plasma cathode. The power supply of the plasma generation device is started, and the power of the plasma generation device is set to 40 kW. The temperature inside the evaporation chamber of the plasma generation device 1 is raised to 900°C, and a plasma arc is generated in the evaporation chamber of the plasma generation device 1. The heating module is started to gradually raise the temperature of the furnace cavity 10 of the carbon nanotube growth furnace to 1250°C. Then, the catalyst material 1 is fed into the evaporation chamber from the material inlet 7 at a powder feeding rate of 2.7 g / min. The catalyst material 1 is transported to the surface of the plasma anode. At this time, the argon flow rate at the first carrier gas inlet 6 is 10 L / min. The plasma arc in the evaporation chamber melts the metal material in the catalyst material 1 and generates metal vapor. The argon gas transports the metal vapor to the furnace cavity 10. At this time, argon gas at a rate of 30 L / min, hydrogen gas at a rate of 5 L / min, and methane gas at a rate of 20 L / min are introduced into the furnace chamber 10 through the second carrier gas inlet 9. Inside the furnace chamber 10, the methane combines with the active metal particles formed by evaporation and collision in the metal vapor, and generates carbon nanotube product 1 in the catalytic reaction.

[0113] Example 2

[0114] S21: Argon gas is introduced through the first carrier gas inlet 6 to exhaust the air in the device, so as to form an inert atmosphere environment in the plasma generation equipment 1 and the carbon nanotube growth furnace 11.

[0115] S22: Inert argon gas at a flow rate of 30 L / min is introduced through the first carrier gas inlet 6 to introduce the working argon gas into the plasma cathode. The power supply of the plasma generation device is started and the power of the plasma generation device is set to 20 kW. The plasma generation device 1 generates a plasma arc in the evaporation chamber cavity, raising the temperature of the evaporation chamber cavity of the plasma generation device 1 to 700°C. The heating module is started to gradually raise the temperature of the furnace cavity 10 of the carbon nanotube growth furnace to 1200°C. Then, the catalyst material 2 is fed into the evaporation chamber cavity from the material inlet 7 at a powder feeding rate of 5 g / min. The catalyst material 2 is then transported to the surface of the plasma anode. At this time, the argon flow rate of the first carrier gas inlet 6 is 10 L / min. The plasma arc in the evaporation chamber cavity melts the metal material in the catalyst material 2 and generates metal vapor. The argon gas transports the metal vapor to the furnace cavity 10. At this time, argon gas at a rate of 30 L / min, hydrogen gas at a rate of 5 L / min, and methane gas at a rate of 10 L / min are introduced into the furnace chamber 10 through the second carrier gas inlet 9. Inside the furnace chamber 10, the methane combines with the active metal particles formed by evaporation and collision in the metal vapor, and generates carbon nanotube product 2 in the catalytic reaction.

[0116] Example 3

[0117] S21: Argon gas is introduced through the first carrier gas inlet 6 to exhaust the air in the device, so as to form an inert atmosphere environment in the plasma generation equipment 1 and the carbon nanotube growth furnace 11.

[0118] S22: Inert argon gas at a flow rate of 60 L / min is introduced through the first carrier gas inlet 6 to introduce the working argon gas into the plasma cathode. The power supply of the plasma generation device is started and the power of the plasma generation device is set to 30 kW. The plasma generation device 1 generates a plasma arc in the evaporation chamber cavity, raising the temperature of the evaporation chamber cavity of the plasma generation device 1 to 800°C. The heating module is started to gradually raise the temperature of the furnace cavity 10 of the carbon nanotube growth furnace to 1150°C. Then, the catalyst material 3 is fed into the evaporation chamber cavity from the material inlet 7 at a powder feeding rate of 6 g / min. The catalyst material 3 is then transported to the surface of the plasma anode. At this time, the argon flow rate of the first carrier gas inlet 6 is 10 L / min. The plasma arc in the evaporation chamber cavity melts the metal material in the catalyst material 3 and generates metal vapor. The argon gas transports the metal vapor to the furnace cavity 10. At this time, argon gas at a rate of 70 L / min, hydrogen gas at a rate of 10 L / min, and methane gas at a rate of 23 L / min are introduced into the furnace chamber 10 through the second carrier gas inlet 9. Inside the furnace chamber 10, the methane combines with the active metal particles formed by evaporation and collision in the metal vapor, and generates carbon nanotube product 3 in the catalytic reaction.

[0119] Example 4

[0120] S21: Argon gas is introduced through the first carrier gas inlet 6 to exhaust the air in the device, so as to form an inert atmosphere environment in the plasma generation equipment 1 and the carbon nanotube growth furnace 11.

[0121] S22: Inert argon gas at a flow rate of 70 L / min is introduced through the first carrier gas inlet 6, and working argon gas is introduced into the plasma cathode. The power supply of the plasma generation device is started and the power of the plasma generation device is set to 50 kW. The plasma generation device 1 generates a plasma arc in the evaporation chamber cavity, raising the temperature of the evaporation chamber cavity of the plasma generation device 1 to 1000°C. The heating module is started, and the furnace cavity 10 of the carbon nanotube growth furnace is gradually heated to 1300°C. Then, the catalyst material 4 is fed into the evaporation chamber cavity from the material inlet 7 at a powder feeding rate of 3 g / min. The catalyst material 4 is then transported to the surface of the plasma anode. At this time, the argon flow rate of the first carrier gas inlet 6 is 10 L / min. The plasma arc in the evaporation chamber cavity melts the metal material in the catalyst material 4 and generates metal vapor. The argon gas transports the metal vapor to the furnace cavity 10. At this time, argon gas at a rate of 30 L / min, hydrogen gas at a rate of 5 L / min, and methane gas at a rate of 20 L / min are introduced into the furnace chamber 10 through the second carrier gas inlet 9. Inside the furnace chamber 10, the methane combines with the active metal particles formed by evaporation and collision in the metal vapor, and generates carbon nanotube product 4 in the catalytic reaction.

[0122] Comparative Example 1

[0123] S21: Argon gas is introduced through the first carrier gas inlet 6 to exhaust the air in the device, so as to form an inert atmosphere environment in the plasma generation equipment 1 and the carbon nanotube growth furnace 11.

[0124] S22: Inert argon gas at a flow rate of 50 L / min is introduced through the first carrier gas inlet 6 to introduce the working argon gas into the plasma cathode. The power supply of the plasma generation device is started and the power of the plasma generation device is set to 50 kW. The plasma generation device 1 generates a plasma arc in the evaporation chamber cavity, raising the temperature of the evaporation chamber cavity of the plasma generation device 1 to 1000°C. The heating module is started to gradually raise the temperature of the furnace cavity 10 of the carbon nanotube growth furnace to 1250°C. Then, the catalyst material 5 is fed into the evaporation chamber cavity from the material inlet 7 at a powder feeding rate of 2.7 g / min. The catalyst material 5 is then transported to the surface of the plasma anode. At this time, the argon gas flow rate at the first carrier gas inlet 6 is 10 L / min. The plasma arc in the evaporation chamber cavity melts the metal material in the catalyst material 5 and generates metal vapor. The argon gas transports the metal vapor to the furnace cavity 10. At this time, argon gas at a rate of 30 L / min, hydrogen gas at a rate of 5 L / min, and methane gas at a rate of 20 L / min are introduced into the furnace chamber 10 through the second carrier gas inlet 9. Inside the furnace chamber 10, the methane combines with the active metal particles formed by evaporation and collision in the metal vapor, and generates carbon nanotube product 5 in the catalytic reaction.

[0125] Comparative Example 2

[0126] S21: Argon gas is introduced through the first carrier gas inlet 6 to exhaust the air in the device, so as to form an inert atmosphere environment in the plasma generation equipment 1 and the carbon nanotube growth furnace 11.

[0127] S22: Inert argon gas at a flow rate of 50 L / min is introduced through the first carrier gas inlet 6 to introduce the working argon gas into the plasma cathode. The power supply of the plasma generation device is started and the power of the plasma generation device is set to 100 kW. The plasma generation device 1 generates a plasma arc in the evaporation chamber cavity, raising the temperature of the evaporation chamber cavity of the plasma generation device 1 to 1500°C. The heating module is started to gradually raise the temperature of the furnace cavity 10 of the carbon nanotube growth furnace to 1250°C. Then, the catalyst material 5 is fed into the evaporation chamber cavity from the material inlet 7 at a powder feeding rate of 2.7 g / min. The catalyst material 5 is then transported to the surface of the plasma anode. At this time, the argon gas flow rate at the first carrier gas inlet 6 is 10 L / min. The plasma arc in the evaporation chamber cavity melts the metal material in the catalyst material 5 and generates metal vapor. The argon gas transports the metal vapor to the furnace cavity 10. At this time, argon gas at a rate of 30 L / min, hydrogen gas at a rate of 5 L / min, and methane at a rate of 20 L / min are introduced into the furnace chamber 10 through the second carrier gas inlet 9. Inside the furnace chamber 10, the methane combines with the active metal particles formed by evaporation and collision in the metal vapor, and generates carbon nanotube product 6 in the catalytic reaction.

[0128] The data results are as follows:

[0129] Table 1

[0130]

[0131]

[0132] As can be clearly seen from the data in Table 1, the catalyst materials using nanoscale active metal particles supported on the surface of the support (Preparation Examples 1 to 4) allow for easier control of the particle size of the catalyst particles used to prepare single-walled carbon nanotubes compared to the catalyst material 5 prepared by mechanical mixing. (Comparison with attached...) Figure 5 and Figure 9 It can be observed that in the single-walled carbon nanotubes prepared using the catalyst material of the preparation example of this application, the catalyst particle size is generally less than 5 nm, while in the single-walled carbon nanotubes prepared using the catalyst material of Comparative Example 1, some catalyst particles have a size exceeding 10 nm, and the aggregation phenomenon of single-walled carbon nanotubes is more serious.

[0133] Using nanoscale metal particles can significantly reduce the power requirements of plasma torches. For example, in Comparative Example 1, when using micron-sized catalyst material 5, 50 kW of power was required to begin evaporating iron atoms, and the effect was not ideal; while when the power was increased to 100 kW, a large amount of iron atoms were evaporated to obtain a significant amount of carbon products. In contrast, the nanoscale metal particle catalyst of this application, due to its smaller particle size, can achieve effective evaporation at lower power, thereby reducing energy consumption and extending the lifespan of the electrode. Furthermore, because nanoscale metal particles are easier to evaporate, the metal atoms fed into the evaporation chamber can be more fully utilized, mainly participating in the catalytic conversion reaction of hydrocarbons, rather than being wasted due to melting and coalescence.

[0134] Differences in calcined carbon purity reflect the uniformity of catalyst particles. The more uniform the catalyst particles, the easier it is to obtain small-sized nanoparticles, and thus the easier it is to prepare single- and double-walled carbon nanotubes. Conversely, if the catalyst particle size increases, a carbon-encapsulated metal structure will form, resulting in a decrease in calcined carbon purity.

[0135] In the prior art, using nickel as a catalyst is not conducive to the growth of single-walled carbon nanotubes. However, using the apparatus of this application, in Example 4, not only were single-walled carbon nanotubes prepared, but also a carbon purity of 78.8% was achieved.

[0136] The foregoing description has fully disclosed the specific embodiments of this application. It should be noted that any modifications made by those skilled in the art to the specific embodiments of this application do not depart from the scope of the claims. Accordingly, the scope of the claims of this application is not limited to the foregoing specific embodiments.

Claims

1. An apparatus for preparing carbon nanotubes using a plasma method, characterized in that, The device comprises a plasma generating device (1) and a carbon nanotube growth furnace (11) arranged above the plasma generating device (1); The plasma generating device (1) comprises a first carrier gas inlet (6), a carrier inlet (7), an evaporation chamber, and an evaporation chamber outlet (8); The first carrier gas inlet (6) is in communication with the cavity of the evaporation chamber and is used for introducing inert gas into the cavity of the evaporation chamber; The carrier inlet (7) is in communication with the cavity of the evaporation chamber and is used for conveying catalyst material into the cavity of the evaporation chamber; The cavity of the evaporation chamber is in communication with the furnace cavity (10) of the carbon nanotube growth furnace (11) through the evaporation chamber outlet (8); The carbon nanotube growth furnace (11) comprises a second carrier gas inlet (9), a furnace cavity (10), and a heating module, the second carrier gas inlet (9) is in communication with the furnace cavity (10), and the second carrier gas inlet (9) is used for providing reaction gas for the furnace cavity (10); The heating module is used for heating the furnace cavity (10); The inner diameter of the evaporation chamber cavity is greater than the inner diameter of the furnace cavity (10); The channel of the second carrier gas inlet (9) and the sidewall of the furnace cavity (10) have a second included angle β, and the second included angle β is 10-45°.

2. The apparatus for preparing carbon nanotubes by plasma method according to claim 1, wherein The plasma arc generated by the plasma generating device (1) is used for providing a first heating temperature of the cavity of the evaporation chamber; the heating module is arranged outside the furnace cavity (10) and is used for providing a second heating temperature for the catalytic growth of carbon nanotubes.

3. The apparatus for preparing carbon nanotubes by plasma method according to claim 1, wherein The channel of the carrier inlet (7) is inclined toward the side of the plasma evaporation chamber away from the furnace cavity (10).

4. The apparatus for preparing carbon nanotubes by a plasma method according to claim 1, wherein The channel of the carrier inlet (7) and the sidewall of the plasma evaporation chamber have a first included angle α, and the first included angle α is 20-60°.

5. The apparatus for preparing carbon nanotubes by plasma method according to any one of claims 1 to 4, characterized in that, The device satisfies at least one of the following characteristics: The output power of the plasma generating device (1) is 20-50 kW; The first heating temperature is 500-1800℃; The second heating temperature is 900-1300℃; The inert gas introduced from the first carrier gas inlet (6) is any one or both of argon and nitrogen; The flow rate of the inert gas is 1 L / min-300 L / min; The conveying speed of the catalyst material is 0.1-50 g / min; The reaction gas introduced from the second carrier gas inlet (9) comprises inert gas, hydrogen, and hydrocarbon gas.

6. The apparatus for preparing carbon nanotubes by a plasma method according to claim 5, wherein The hydrocarbon gas comprises at least one of ethylene, propylene, methane, or natural gas.

7. The apparatus for preparing carbon nanotubes by plasma method according to any one of claims 1 to 6, wherein The method for using the device comprises the following steps: S21: forming an inert gas atmosphere in the plasma generating device (1) and / or the carbon nanotube growth furnace (11). S22: generating a plasma arc in the evaporation chamber cavity based on the plasma generating device (1), heating the evaporation chamber cavity based on the plasma arc, and heating the furnace cavity (10) based on the heating module; and, introducing an inert gas into the evaporation chamber cavity from the first carrier gas inlet (6), delivering the catalyst material into the evaporation chamber cavity from the carrier inlet (7), and introducing the reaction gas into the furnace cavity (10) from the second carrier gas inlet (9); In the preparation process, the plasma arc in the evaporation chamber cavity melts the metal substance in the catalyst material and generates metal vapor, the inert gas delivers the metal vapor into the furnace cavity (10) to make the reaction gas contact with the metal vapor for catalytic growth, and carbon nanotubes are obtained.

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