Device and method for preparing carbon nanotube by plasma method and preparation of catalyst

Abstract

The invention provides a device and a method for preparing a carbon nanotube by a plasma method. The device comprises plasma generation equipment and a carbon nanotube growth furnace which are communicated with each other, the plasma generation equipment comprises a first carrier gas inlet, a carrier gas inlet, an evaporation chamber, an evaporation chamber outlet and a first heating module; the first heating module is used for heating the evaporation chamber cavity; the first carrier gas inlet is communicated with the cavity of the evaporation chamber; the loading inlet is communicated with the cavity of the evaporation chamber and is used for conveying a catalyst material into the cavity of the evaporation chamber; the cavity of the evaporation chamber is communicated with the furnace chamber of the carbon nanotube growth furnace through the evaporation chamber outlet; the carbon nanotube growth furnace comprises a second carrier gas inlet, a furnace chamber and a heating module, and the second carrier gas inlet is communicated with the furnace chamber; the heating module is used for heating the furnace chamber. The separation of the catalyst evaporation and the carbon nanotube growth reaction process is realized, the high-quality single-wall and double-wall carbon nanotubes are prepared, and the service life of the device is also prolonged.

Description

Technical Field

[0001] The present application relates to the field of carbon material preparation, and in particular to a device and method for preparing carbon nanotubes and the preparation of a catalyst. Background Art

[0002] Plasma technology uses a high-energy plasma torch to bombard an iron source (such as iron particles or iron powder) with high energy, causing it to evaporate into iron atom vapor. Subsequently, these iron atom vapors collide with each other in a specific reaction environment to form tiny and 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 physical and chemical 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 torches, and high rate of component damage.

[0004] The reasons for the problem are as follows: 1. Poor controllability of catalyst particles: In the process of preparing single-walled carbon nanotubes by plasma method, the controllability of catalyst particles has not been effectively solved. Technical limitations make it difficult to accurately control the size of metal iron catalyst particles in a plasma environment, which in turn affects the quality stability of the prepared single-walled carbon nanotubes and limits the performance and application range of the product. 2. High energy consumption of plasma torches: In order to volatilize iron atoms in catalysts in the state of iron sheets, iron particles or iron powder, plasma torches require high power support when preparing single-walled carbon nanotubes. This not only increases energy consumption and increases production costs, but also, under current technology, the evaporation rate of iron particles in a high-temperature environment is difficult to control, further exacerbating the instability of catalyst particle size. In addition, the energy utilization efficiency of plasma torches is not high, and it fails to fully convert into the energy required to prepare single-walled carbon nanotubes. 3. High temperature causes damage to accessories: The high temperature environment generated by the plasma torch produces severe thermal stress on equipment accessories, causing accessories to be easily damaged, thereby shortening the service life of the equipment. Summary of the invention

[0005] In view of the above problems in the prior art, the present application provides a device for preparing carbon nanotubes by plasma method. The specific technical solution is as follows:

[0006] The present application provides a device for preparing carbon nanotubes by a plasma method, the device comprising a plasma generating device and a carbon nanotube growing furnace which are interconnected; the plasma generating device comprises a first carrier gas inlet, a carrier 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 carrier inlet is connected to the cavity of the evaporation chamber, and is used to transport a 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 growing furnace through the evaporation chamber outlet; the carbon nanotube growing furnace comprises a second carrier gas inlet, a furnace cavity, and a heating module, the second carrier gas inlet is connected to the furnace cavity, and the second carrier gas inlet is used to provide a reaction gas to the furnace cavity; the heating module is used to heat the furnace cavity.

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

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

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

[0010] Preferably, the passage of the carrier inlet is inclined toward a side of the plasma evaporation chamber away from the furnace cavity.

[0011] Preferably, a first angle α is formed between the passage of the carrier inlet and the side wall of the plasma evaporation chamber, and the first angle α is 20-60°.

[0012] Preferably, a second angle β is formed between the channel of the second carrier gas inlet and the side wall of the furnace chamber, and the second angle β is 10-45°.

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

[0014] The output power of the plasma generating device is 20 to 50 kW;

[0015] The first heating temperature is 500-1800° C.;

[0016] The second heating temperature is 900-1300° C.;

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

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

[0019] The delivery speed of the catalyst material is 0.1 to 50 g / min;

[0020] The reaction gas introduced from the second carrier gas inlet includes an inert gas, hydrogen and a hydrocarbon gas.

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

[0022] Preferably, the plasma anode of the plasma generating device is arranged in the cavity of the evaporation chamber, and the plasma anode is provided with a bearing cavity, and the bearing cavity is used for placing the catalyst material.

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

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

[0025] S11: providing a metal salt solution and a porous oxide carrier material;

[0026] S12: mixing the metal salt solution with the porous oxide support material, and heating the mixture to obtain a solid substance;

[0027] S13: crushing and calcining the solid material to obtain a catalyst precursor;

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

[0029] Preferably, the reduction treatment comprises using a mixture of hydrogen and nitrogen 、 Or the catalyst precursor is reduced by hydrogen gas.

[0030] Preferably, the metal salt comprises any one or a combination of at least two of nitrate, hydrochloride, acetate or sulfate of iron, cobalt or nickel;

[0031] The porous oxide support material includes γ-Al 2 O 3 ,MgO,CaO,SiO 2 、TiO 2 , hydrotalcite, magnesium aluminate spinel (MgAl 2 O 4 ), any one of vermiculite, montmorillonite or molecular sieve, or a combination of at least two of them.

[0032] The present application also provides a method for using the device for preparing carbon nanotubes by a plasma method, comprising the following steps:

[0033] S21: forming an inert atmosphere environment in the plasma generation device and / or the carbon nanotube growth furnace;

[0034] S22: Generate a plasma arc in the cavity of the evaporation chamber based on the plasma generating device, heat the cavity of the evaporation chamber based on the plasma arc, and heat the furnace cavity based on the heating module; and introduce an inert gas into the cavity of the evaporation chamber from a first carrier gas inlet, transport a catalyst material into the cavity of the evaporation chamber from a carrier inlet, and introduce the reaction gas into the furnace cavity from a second carrier gas inlet;

[0035] During the preparation process, the plasma arc in the evaporation chamber melts the metal substance in the catalyst material and generates metal vapor. The inert gas transports the metal vapor to the furnace chamber so that the reaction gas contacts the metal vapor for catalytic growth to obtain carbon nanotubes.

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

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

[0038] 1. The present application separates the two processes of catalyst evaporation and carbon nanotube growth reaction by setting up interconnected plasma generation equipment and carbon nanotube growth furnace, so that the two reactions can be regulated independently, reducing reaction energy consumption and improving energy utilization;

[0039] 2. The separate arrangement of the plasma generation device and the carbon nanotube growth furnace avoids the direct growth of single-walled and double-walled carbon nanotubes in the plasma generation device, thereby eliminating the interference of the growing single-walled and double-walled carbon nanotubes on the plasma torch, significantly improving the stability of the arc, and providing a strong guarantee for the continuous and stable growth of single-walled and double-walled carbon nanotubes;

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

[0041] 4. By pre-loading the active metal-containing compound onto the porous oxide carrier and subjecting it to low-temperature calcination and reduction treatment, the proportion of the active metal on the carrier is more controllable, and the active metal particles are stabilized at the nanometer level, which not only reduces the power demand of the plasma arc, but also enables the evaporation of metal atoms at a lower temperature;

[0042] 5. By lowering the first heating temperature, the evaporation rate of metal atoms is also slowed down accordingly, which effectively avoids the violent collision of metal particles caused by too fast evaporation rate, thereby forming oversized metal particles. This improvement provides strong support for the preparation of high-quality single-walled and double-walled carbon nanotubes. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present application or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0044] Figure 1 : A schematic diagram of the structure of a device for preparing carbon nanotubes by a plasma method provided in an embodiment of the present application;

[0045] Figure 2 This is a transmission electron microscope photograph of the catalyst prepared in Catalyst Material Preparation Example 2 of the present invention;

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

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

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

[0049] Figure 6 is a Raman spectrum of the single-walled carbon nanotubes prepared in Example 2 of the present invention;

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

[0051] Figure 8 This is a scanning electron microscope photograph of the single-walled carbon nanotube prepared in Comparative Example 2 of the present invention;

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

[0053] Figure numerals: 1-plasma generating device, 2-plasma cathode, 3-plasma anode, 4-metal gasket, 5-catalyst material, 6-first carrier gas inlet, 7-carrier inlet, 8-evaporation chamber outlet, 9-second carrier gas inlet, 10-furnace chamber, 11-carbon nanotube growth furnace. DETAILED DESCRIPTION

[0054] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0055] For the following defined terms, these definitions shall apply unless a different definition is given in the claims or elsewhere in this specification. All numerical values, whether or not explicitly indicated, are defined herein as modified by the term "about". The term "about" generally refers to a numerical range that a person of ordinary skill in the art considers to be equivalent to the stated values ​​to produce substantially the same properties, functions, results, etc. A numerical range indicated by a lower value and a higher value is defined to include all numerical values ​​included in the numerical range and all subranges included in the numerical range.

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

[0057] The following is an introduction to a plasma method for preparing carbon nanotubes provided in an embodiment of the present application. Figure 1 , Figure 1 The figure is a schematic diagram of the structure of a device for preparing carbon nanotubes by a plasma method. It can be understood that the structure of the device for preparing carbon nanotubes by a plasma method in the figure is only a technical solution of a specific embodiment of the present application, and the device for preparing carbon nanotubes by a plasma method of the present application may include fewer or more structural features, and is not limited to the device structure described in the figure.

[0058] A device for preparing carbon nanotubes by plasma method comprises a plasma generating device 1 and a carbon nanotube growing furnace 11 which are interconnected, and separates the two processes of plasma generation and carbon nanotube growth. 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 cavity of the evaporation chamber is connected to the furnace chamber 10 of the carbon nanotube growing furnace 11 through the evaporation chamber outlet 8; the first carrier gas inlet 6 is connected to the cavity of the evaporation chamber, and 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. The inert gas can form an inert atmosphere environment in the device on the one hand, and can also be used to transport the plasma generated in the evaporation chamber to the carbon nanotube growing furnace 11 on the other hand. The carrier inlet 7 is connected to the cavity of the evaporation chamber, and is used to transport catalyst materials into the cavity of the evaporation chamber. The carbon nanotube growth furnace 11 comprises a second carrier gas inlet 9 , a furnace chamber 10 and a heating module. The heating module is used to heat the furnace chamber. The second carrier gas inlet 9 is connected to the furnace chamber 10 , and the second carrier gas inlet 9 is used to provide reaction gas to the furnace chamber 10 .

[0059] The present application separates the plasma evaporation reaction from the carbon nanotube growth reaction, thereby avoiding the direct growth of single- and double-walled carbon nanotubes in the evaporation chamber, thereby eliminating the interference of the growing single- and double-walled carbon nanotubes on the plasma torch, significantly improving the stability of the arc, and providing a strong guarantee for the continuous and stable growth of single- and double-walled carbon nanotubes.

[0060] Specifically, the apparatus is provided with a carbon nanotube growth furnace 11 above the plasma generation device 1, and the plasma generation device 1 is used to provide a first heating temperature of the cavity of the evaporation chamber; the heating module is provided outside the furnace cavity 10, and is used to provide a second heating temperature for the catalytic growth of the carbon nanotubes. The temperature settings of the plasma generation device 1 and the carbon nanotube growth furnace 11 are independent of each other, further providing conditions for separating the two processes of plasma generation and carbon nanotube growth, so that the plasma generation device 1 does not need to be heated to the reaction temperature of the carbon nanotubes, effectively reducing the overall energy consumption and improving the energy utilization efficiency.

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

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

[0063] In some embodiments, the passage of the carrier inlet 7 is inclined toward the side of the plasma evaporation chamber away from the furnace chamber 10, and the catalyst material is transported into the evaporation chamber cavity through the carrier inlet 7 at a speed of 0.1 to 50 g / min, and the catalyst material is uniformly transported to the surface of the plasma anode; further, there is a first angle α between the passage of the carrier inlet 7 and the side wall of the plasma evaporation chamber, and the first angle α is 20 to 60°, specifically, the first angle α is 20, 30, 40, 50, 60°. In some embodiments, the plasma anode of the plasma generating device is arranged in the evaporation chamber cavity, and the plasma anode is provided with a bearing cavity for placing the catalyst material, and a metal gasket 4 can also be placed at the bottom of the bearing cavity.

[0064] Correspondingly, the flow rate of the inert gas into the first carrier gas inlet 6 is 1L / min to 300L / min, and the flow rate can be set according to different stages. When it is necessary to evacuate the air inside the device, the flow rate of the inert gas is 100 to 300L / min, and the time of passing is 30-60min, until the oxygen concentration of the tail gas is less than 10ppm; when the plasma generating device starts to work, the flow rate of the inert gas of the first carrier gas inlet 6 is 30 to 70L / min; when melting and evaporating the catalyst material, the flow rate of the inert gas of the first carrier gas inlet 6 is 10 to 30L / min, specifically, it can be 10L / min. Since the plasma arc can quickly 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 of the first carrier gas inlet 6, escapes from the outlet 8 of the evaporation chamber, and smoothly flows into the furnace chamber 10 of the carbon nanotube growth furnace, providing a catalyst for the catalytic cracking reaction of the active metal clusters in the furnace chamber.

[0065] In some embodiments, the inner diameter of the evaporation chamber cavity is larger than the inner diameter of the furnace chamber 10, and the inner diameter is reduced at the connection between the plasma generating device 1 and the carbon nanotube growth furnace 11, which is more convenient for the metal vapor to escape when the metal vapor leaves the evaporation chamber, and also prevents the reaction gas from flowing back to the evaporation chamber. Specifically, the inner diameter of the evaporation chamber is 300nm, and the inner diameter of the furnace chamber 10 is 100-200nm.

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

[0067] In order to stabilize the active metal particles at the nanometer level, the present application provides a method for preparing a catalyst material, comprising the following steps:

[0068] S11: providing a metal salt solution and a porous oxide carrier material;

[0069] S12: mixing the metal salt solution with the porous oxide support material, and heating the mixture to obtain a solid substance;

[0070] S13: crushing and calcining the solid material to obtain a catalyst precursor;

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

[0072] The metal salt includes any one of nitrate, hydrochloride, acetate or sulfate of iron, cobalt or nickel, or a combination of at least two thereof;

[0073] The porous oxide support material includes γ-Al 2 O 3 ,MgO,CaO,SiO 2 、TiO 2 , hydrotalcite, magnesium aluminate spinel (MgAl 2 O 4 ), any one of vermiculite, montmorillonite or molecular sieve or a combination of at least two thereof;

[0074] The reduction process involves the use of a mixture of hydrogen and nitrogen 、 Or the catalyst precursor is reduced by hydrogen gas. That is, the catalyst precursor is reduced in an atmosphere of a mixture of hydrogen and nitrogen or in an atmosphere of hydrogen gas to obtain nano-scale active metal particles supported on an oxide carrier, namely the catalyst material.

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

[0076] Nanoscale active metal particles not only reduce the power demand of the evaporation chamber for the plasma torch, but also achieve the evaporation of metal atoms at a lower temperature. Due to the reduction in evaporation temperature, the evaporation rate of metal atoms is also slowed down accordingly, effectively avoiding the violent collision of metal particles caused by too fast evaporation speed, and then forming oversized metal particles, which provides strong support for the preparation of high-quality single and double-walled carbon nanotubes. In addition, due to the presence of porous oxide carriers, metal particles will not melt during the melting process, thereby extending the service life of the catalyst material. In addition, by adjusting the proportion of active components on the carrier and the powder feeding speed of the catalyst material, the present application realizes the control of the concentration of active metal particles per unit time in the evaporation chamber cavity.

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

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

[0079] S22: Generate a plasma arc in the evaporation chamber cavity based on the plasma generating device 1, heat the evaporation chamber cavity based on the plasma arc, and heat the furnace cavity 10 based on the heating module; and introduce an inert gas into the cavity of the evaporation chamber from the first carrier gas inlet 6, transport a catalyst material into the cavity of the evaporation chamber from the carrier inlet 7, and introduce a reaction gas into the furnace cavity 10 from the second carrier gas inlet 9;

[0080] Specifically, a working gas, such as an inert gas such as argon or nitrogen, is introduced from the plasma cathode at a flow rate of 1 L / min to 300 L / min. The working gas is introduced from the hollow structure inside the plasma cathode 2, and after being energized, a strong plasma arc is generated.

[0081] During the preparation process, the plasma arc in the evaporation chamber melts the metal substance 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 contacts the metal vapor for catalytic growth to obtain carbon nanotubes.

[0082] The specific embodiments of the present application are introduced below in conjunction with the above-mentioned technical scheme. The following examples describe the technical scheme of the present application in more detail, and these examples are only used for illustrative purposes, because it is obvious to those skilled in the art that various modifications and changes are made within the scope of the disclosure of the present application. The reagents used in the examples can be obtained commercially or synthesized according to conventional methods, and can be used directly without further treatment, and the instruments and devices used in the examples can be obtained commercially.

[0083] Catalyst material preparation example 1

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

[0085] S12: 10g γ-Al 2 O 3 The powder was added to the solution, stirred at room temperature for 2 h, and then gradually heated to 60° C. and stirred continuously until the water was completely evaporated to obtain a solid substance;

[0086] S13: crushing the obtained solid material, and calcining it in a nitrogen atmosphere at 300° C. for 1 h to obtain a catalyst precursor;

[0087] S14: The catalyst precursor is reduced by a mixture of 15 vol % hydrogen and 85 vol % nitrogen to obtain a catalyst supported on γ-Al 2 O 3 Nano-sized Fe particles on the carrier, i.e. Fe / γ-Al 2 O 3 Catalyst (catalyst material 1).

[0088] In the above preparation, the Fe catalytically active particles are 2 O 3 The loading on the support was 30 wt%.

[0089] Catalyst material preparation example 2

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

[0091] S12: adding 10 g of MgO powder to the solution, stirring at room temperature for 2 h, gradually heating to 90° C., and continuing stirring until the water is completely evaporated to obtain a solid substance;

[0092] S13: crushing the obtained solid material, and calcining it in a nitrogen atmosphere at 300° C. for 1 h to obtain a catalyst precursor;

[0093] S14: The catalyst precursor is reduced by a mixture of 10 vol % hydrogen and 90 vol % nitrogen to obtain nano-sized Fe particles supported on a MgO carrier, namely, a Fe / MgO catalyst (catalyst material 2).

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

[0095] Catalyst material preparation example 3

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

[0097] S12: 10 g MgAl 2 O 4 The powder was added to the solution, stirred at room temperature for 2 h, and then gradually heated to 80° C. and stirred continuously until the water was completely evaporated to obtain a solid substance;

[0098] S13: crushing the obtained solid material, and calcining it in a nitrogen atmosphere at 400° C. for 0.5 h to obtain a catalyst precursor;

[0099] S14: The catalyst precursor is reduced by a mixture of 20 vol % hydrogen and 80 vol % nitrogen to obtain a catalyst supported on MgAl 2 O 4 Nanoscale Co particles on the support, i.e. Co / MgAl 2 O 4 Catalyst (catalyst material 3).

[0100] In the above preparation, the Co catalytically active particles were 2 O 4 The loading on the support was 20 wt%.

[0101] Catalyst material preparation example 4

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

[0103] S12: 10g SiO 2 The powder was added to the solution, stirred at room temperature for 2 h, and then gradually heated to 60° C. and stirred continuously until the water was completely evaporated to obtain a solid substance;

[0104] S13: crushing the obtained solid material, and calcining it in a nitrogen atmosphere at 350° C. for 2 h to obtain a catalyst precursor;

[0105] S14: The catalyst precursor is reduced by a mixture of 30 vol % hydrogen and 70 vol % nitrogen to obtain a catalyst supported on SiO 2 Nano-sized Ni particles on the carrier, i.e. Ni / SiO 2 Catalyst (catalyst material 4).

[0106] In the above preparation, Ni catalytically active particles are 2 The loading on the support was 30 wt%.

[0107] Catalyst material comparative example 1

[0108] According to patent CN116947025A, 70g iron powder, 10g calcium carbonate and 20g ferrous sulfide were used as raw materials to prepare Fe / CaCO 3 / FeS catalyst (catalyst material 5)

[0109] This embodiment also provides a method for preparing carbon nanotubes, which is based on the use of the device for preparing carbon nanotubes by plasma method of this application to prepare single-walled and double-walled carbon nanotubes. The embodiment is as follows:

[0110] Example 1

[0111] S21: introducing argon gas from the first carrier gas inlet 6 to exhaust the air in the device, so as to form an inert atmosphere environment in the plasma generating device 1 and the carbon nanotube growth furnace 11;

[0112] S22: 50L / min of inert gas argon is introduced from the first carrier gas inlet 6, the working gas argon is introduced into the plasma cathode, the power of the plasma generating device is started, the power of the plasma generating device is set to 40kW, the temperature in the cavity of the evaporation chamber of the plasma generating device 1 is increased to 900°C, and a plasma arc is generated in the cavity of the evaporation chamber of the plasma generating device 1; the heating module is started to gradually increase the temperature of the furnace chamber 10 of the carbon nanotube growth furnace to 1250°C; then, the catalyst material 1 is transported from the carrier gas inlet 7 to the cavity of the evaporation chamber at a powder feeding speed of 2.7g / min, and the catalyst material 1 is transported to the surface of the plasma anode. At this time, the argon gas flow rate of the first carrier gas inlet 6 is 10L / min, and the plasma arc in the cavity of the evaporation chamber melts the metal substance in the catalyst material 1 and generates metal vapor, and the argon gas transports the metal vapor to the furnace cavity 10. At this time, 30 L / min of argon, 5 L / min of hydrogen and 20 L / min of methane are introduced into the furnace chamber 10 from the second carrier gas inlet 9. In the furnace chamber 10, methane combines with active metal particles formed by evaporation and collision in the metal vapor to generate carbon nanotube products 1 in the catalytic reaction.

[0113] Example 2

[0114] S21: introducing argon gas from the first carrier gas inlet 6 to exhaust the air in the device, so as to form an inert atmosphere environment in the plasma generating device 1 and the carbon nanotube growth furnace 11;

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

[0116] Example 3

[0117] S21: introducing argon gas from the first carrier gas inlet 6 to exhaust the air in the device, so as to form an inert atmosphere environment in the plasma generating device 1 and the carbon nanotube growth furnace 11;

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

[0119] Example 4

[0120] S21: introducing argon gas from the first carrier gas inlet 6 to exhaust the air in the device, so as to form an inert atmosphere environment in the plasma generating device 1 and the carbon nanotube growth furnace 11;

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

[0122] Comparative Example 1

[0123] S21: introducing argon gas from the first carrier gas inlet 6 to exhaust the air in the device, so as to form an inert atmosphere environment in the plasma generating device 1 and the carbon nanotube growth furnace 11;

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

[0125] Comparative Example 2

[0126] S21: introducing argon gas from the first carrier gas inlet 6 to exhaust the air in the device, so as to form an inert atmosphere environment in the plasma generating device 1 and the carbon nanotube growth furnace 11;

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

[0128] The data results are as follows:

[0129] Table 1

[0130]

[0131]

[0132] It can be clearly seen from the data in Table 1 that the nanoscale active metal particle catalyst material loaded on the surface of the carrier (Preparation Example 1 to Preparation Example 4) can more easily control the particle size of the catalyst particles for preparing single-walled carbon nanotubes than the catalyst material 5 prepared by the mechanical mixing method. Figure 5 and Fig. 9 It can be found that in the single-walled carbon nanotubes prepared using the catalyst material of the preparation example of the present 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 nanometers, and the agglomeration phenomenon of the single-walled carbon nanotubes is more serious.

[0133] The use of nano-scale metal particles can significantly reduce the power requirement of the plasma torch. For example, in Comparative Example 1, when using micron-level catalyst material 5, a power of 50kW is required to start evaporating iron atoms, and the effect is not ideal; and when the power is increased to 100kW, a large amount of iron atoms can be evaporated to obtain more carbon products. In contrast, the nano-scale metal particle catalyst of the present application can achieve effective evaporation at a lower power due to its smaller particle size, thereby reducing energy consumption and extending the service life of the electrode. In addition, since nano-scale metal particles are easier to evaporate, the metal atoms fed into the evaporation chamber can be more fully utilized, mainly participating in the catalytic hydrocarbon conversion reaction, rather than wasting the active components of the catalyst due to the melting phenomenon.

[0134] The difference in carbon purity can reflect the uniformity of the catalyst particles. When the catalyst particles are more uniform, it is easier to obtain small-sized nanoparticles, and it is easier to prepare single-walled and double-walled carbon nanotubes; on the contrary, if the catalyst particle size becomes larger, a carbon-encapsulated metal structure will be formed, causing the carbon purity to decrease.

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

[0136] The above description has fully disclosed the specific implementation methods of the present application. It should be pointed out that any changes made by technicians familiar with the field to the specific implementation methods of the present application do not deviate from the scope of the claims of the present application. Accordingly, the scope of the claims of the present application is not limited to the above specific implementation methods.

Claims

1. A device for preparing carbon nanotubes by plasma method, characterized in that: The device comprises a plasma generating device (1) and a carbon nanotube growing furnace (11) which are interconnected; The plasma generating device (1) comprises a first carrier gas inlet (6), a carrier material inlet (7), an evaporation chamber, and an evaporation chamber outlet (8); The first carrier gas inlet (6) 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 carrier inlet (7) is connected to the cavity of the evaporation chamber and is used to transport the catalyst material into the cavity of the evaporation chamber; The cavity of the evaporation chamber is connected to the furnace chamber (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 chamber (10) and a heating module, wherein the second carrier gas inlet (9) is connected to the furnace chamber (10), and the second carrier gas inlet (9) is used to provide reaction gas to the furnace chamber (10); The heating module is used for heating the furnace cavity (10).

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

3. The device for preparing carbon nanotubes by plasma method according to claim 1, characterized in that: The inner diameter of the evaporation chamber cavity is greater than the inner diameter of the furnace cavity (10).

4. The device for preparing carbon nanotubes by plasma method according to claim 1, characterized in that: The passage of the carrier inlet (7) is inclined toward a side of the plasma evaporation chamber that is away from the furnace cavity (10).

5. The device for preparing carbon nanotubes by plasma method according to claim 1, characterized in that: A first angle α is formed between the channel of the carrier inlet (7) and the side wall of the plasma evaporation chamber, and the first angle α is 20-60°.

6. The device for preparing carbon nanotubes by plasma method according to claim 1, characterized in that: A second angle β is formed between the channel of the second carrier gas inlet (9) and the side wall of the furnace chamber (10), and the second angle β is 10-45°.

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

8. The device for preparing carbon nanotubes by plasma method according to claim 7, characterized in that: The hydrocarbon gas includes at least one of ethylene, propylene, methane or natural gas.

9. A method for preparing a catalyst material, characterized in that: The preparation method of the catalyst material comprises the following steps: S11: providing a metal salt solution and a porous oxide carrier material; S12: mixing the metal salt solution with the porous oxide support material, and heating the mixture to obtain a solid substance; S13: crushing and calcining the solid material to obtain a catalyst precursor; S14: reducing the catalyst precursor to obtain the catalyst material.

10. The method for preparing a catalyst according to claim 9, characterized in that: The reduction treatment includes using a mixture of hydrogen and nitrogen 、 Or the catalyst precursor is reduced by hydrogen gas.

11. The method for preparing a catalyst according to claim 9, characterized in that: The metal salt includes any one or a combination of at least two of nitrate, hydrochloride, acetate or sulfate of iron, cobalt or nickel; The porous oxide carrier material includes any one of γ-Al2O3, MgO, CaO, SiO2, TiO2, hydrotalcite, magnesium aluminum spinel (MgAl2O4), vermiculite, montmorillonite or molecular sieve, or a combination of at least two thereof.

12. The device for preparing carbon nanotubes by plasma method according to any one of claims 1 to 8, characterized in that: The method for using the device comprises the following steps: S21: forming an inert atmosphere environment in the plasma generating device (1) and / or the carbon nanotube growing furnace (11); S22: Based on the plasma generating device (1), a plasma arc is generated in the cavity of the evaporation chamber, the cavity of the evaporation chamber is heated based on the plasma arc, and the furnace cavity (10) is heated based on the heating module; and an inert gas is introduced into the cavity of the evaporation chamber from the first carrier gas inlet (6), a catalyst material is transported into the cavity of the evaporation chamber from the carrier inlet (7), and the reaction gas is introduced into the furnace cavity (10) from the second carrier gas inlet (9); During the preparation process, the plasma arc in the evaporation chamber melts the metal substance in the catalyst material and generates metal vapor, and the inert gas transports the metal vapor to the furnace chamber (10), so that the reaction gas contacts the metal vapor for catalytic growth, thereby obtaining carbon nanotubes.

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