A device and method for preparing carbon nanotubes

Abstract

The application provides a preparation device and method of carbon nanotubes. The device structure is a transparent reactor, a light-transmitting wall is arranged in the reactor, the light-transmitting wall divides the reactor into a reaction zone and an illumination zone, and a heater is arranged on the outer wall of the reactor. The preparation method is that under the conditions of applying light and heating, carbon source gas is introduced from one end of the reactor, conversion is carried out on the catalyst, and generated carbon-containing mixed materials and gas are discharged from the other end. Due to the excitation effect of light, the activation temperature of the catalyst can be reduced by 150 DEG C-250 DEG C compared with the existing process, which helps to inhibit high-temperature sintering of the catalyst, so that few-walled (1-3 layers) carbon nanotubes can be prepared at low temperature, and the method has the advantages of low cost and continuous operation.

Description

Technical Field

[0001] This application relates to the field of heterogeneous catalysis and nanomaterial manufacturing technology, and more specifically, to an apparatus and method for preparing carbon nanotubes. Background Technology

[0002] Carbon nanotubes are one-dimensional materials with excellent electrical, thermal, and mechanical properties, and have wide applications in many fields such as composite conductivity enhancement and catalyst supports. The properties of carbon nanotubes are related to their structure; as the wall number decreases, the weight-based conductivity increases significantly.

[0003] Traditional methods for preparing carbon nanotubes include chemical vapor deposition (CVD). During this process, the diameter of few-walled carbon nanotubes is always related to the catalyst grain size. Furthermore, the supercooling precipitation of the carbon source and the maintenance of crystallinity are related to high reaction temperatures. However, based on the Ostward ripening model, the catalyst grain size always increases significantly with increasing temperature, directly affecting the diameter of the carbon nanotubes. Simultaneously, the controllable decomposition of the carbon source affects the precipitation of few-walled nanotubes. Chemically inert carbon sources, due to their low conversion rate, control the carbon precipitation rate and are also related to reducing amorphous carbon and the number of carbon nanotube layers.

[0004] For the reasons mentioned above, the preparation of few-walled carbon nanotubes in high-temperature vapor deposition generally suffers from low yield and high cost, which limits the expansion of its application fields. Summary of the Invention

[0005] To address the aforementioned issues, this application provides a device utilizing photothermal synergistic catalysis. By simultaneously activating the catalyst with light and heat, the temperature range for carbon source decomposition is effectively reduced, making the catalyst grain size more controllable. Furthermore, due to the light absorption effect of carbon materials, the carbon precipitation rate at the carbon-metal interface is promoted, thereby effectively increasing the yield of few-walled carbon nanotubes and reducing preparation costs.

[0006] In a first aspect, this application provides an apparatus for preparing carbon nanotubes, including a reactor;

[0007] The reactor is divided into a reaction zone and a light-illuminating zone, which are separated by a light-transmitting wall.

[0008] The reaction zone is provided with a feed inlet at one end and a discharge outlet at the other end.

[0009] A light source is installed in the illumination area, and the light emitted by the light source reaches the reaction area through the light-transmitting wall.

[0010] A heater is provided on the outside of the reactor, and the heater is wrapped around the circumferential outer wall of the reactor.

[0011] Optionally, the illuminated area is provided with an opening;

[0012] The opening allows the light emitter to enter the illumination zone along the length of the reactor.

[0013] Optionally, the reactor may be composed of any one of quartz, high-temperature glass, and transparent ceramic, and the transparent wall may be composed of quartz glass or fluoride glass.

[0014] Optionally, the thickness of the light-transmitting wall is 1 mm to 20 mm.

[0015] Optionally, the reactor is a cylindrical reactor;

[0016] The light-transparent wall has a ring-shaped structure, and the reaction zone is located between the outer wall of the cylindrical reactor and the outer wall of the light-transparent wall;

[0017] The illuminated area is located in the hollow region enclosed by the inner wall of the light-transmitting wall.

[0018] Secondly, this application provides a method for preparing the carbon nanotubes described in the first aspect, the method being applicable to the apparatus for preparing carbon nanotubes described in the first aspect, the method comprising:

[0019] Step S1: Adjust the illuminance of the light source located in the reactor's illumination zone to 10. 5 LX-10 7 LX;

[0020] Step S2: Turn on the heater to raise the temperature of the reaction zone to 500 ℃-750 ℃;

[0021] Step S3: A carbon source gas and a catalyst with a volume concentration ratio of (90-99)%: (1-10)% are fed into the reaction zone through the feed port. Under the action of light and heat, the carbon source gas is decomposed to generate carbon nanotubes with 1-3 tube wall layers. The carbon-containing mixed material obtained from the reaction is discharged from the reaction zone through the discharge port.

[0022] Step S4: When the carbon-containing mixed material covers the light-transmitting wall, stop the supply of the carbon source gas and the catalyst, and introduce air into the reaction zone through the feed inlet to oxidize and remove the carbon-containing mixed material on the light-transmitting wall;

[0023] Step S5: Repeat steps S3-S4 until all pyrolysis reactions are completed. The carbon-containing mixed material is ground to remove the catalyst, and the carbon nanotubes are obtained.

[0024] The carbon source gas includes organic compounds with 1-20 carbon atoms;

[0025] The catalyst is composed of a catalytic metal and a support. The catalytic metal includes at least one of iron, cobalt, nickel, chromium, silver, gold, platinum, copper, zinc, palladium, molybdenum, tungsten, manganese, and titanium. The support includes at least one of magnesium oxide, silicon oxide, aluminum oxide, hydrotalcite, and molecular sieve.

[0026] Optionally, in step S1, the illuminance of the light source is adjusted to 2 × 10⁻⁶. 6 LX-8×10 6 LX.

[0027] Optionally, the total content of sulfur, nitrogen, phosphorus, arsenic and halogen elements in the organic matter is 0 ppm-20 ppm;

[0028] The carbon source gas includes any one of hydrocarbons and alcohols with 5-8 carbon atoms, polycyclic aromatic hydrocarbons with 15-20 carbon atoms, hydrocarbons with diesel boiling range, methane, cyclohexane, and hydrocarbons and ketones with diesel boiling range.

[0029] The oxygen content of the carbon source gas is less than 30%.

[0030] Optionally, the crystallite size of the catalytic metal is 0.5 nm-1.5 nm, and the mass fraction of the catalytic metal in the catalyst is 0.1%-10%.

[0031] Thirdly, this application provides a carbon nanotube obtained by the preparation method of the carbon nanotube described in the second aspect above.

[0032] In summary, this application includes at least one of the following beneficial technical effects:

[0033] 1. This application provides a device for preparing carbon nanotubes. By setting up a photoilluminator, a photothermal synergistic catalytic system is formed in the reactor, which makes it easier to provide a light source and a heat source at the same time when using the device, thereby promoting the reaction.

[0034] 2. The carbon nanotube preparation method provided in this application effectively reduces the catalyst activation temperature by 150 ℃-250 ℃. The increase in catalyst activity and the decrease in activation temperature broaden the types of carbon sources that can grow low-walled nanotubes by 60%-65%, reduce the cost of carbon sources by 30%-60%, and hinder the growth of catalyst particle size after the temperature is lowered, thereby increasing the retention of small crystallites of the catalyst by 50%-65%. Based on the above method, the content of low-walled carbon nanotubes in the final product can be increased by 30%-35%. Moreover, in step S5, the carbon nanotubes are separated from the catalyst in time through grinding, and the catalyst structure is not destroyed. The separated catalyst can still be recycled multiple times, thereby reducing the preparation cost by 80%-95%. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application 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.

[0036] Figure 1 A structural diagram of a carbon nanotube fabrication apparatus according to an embodiment of this application is shown;

[0037] Figure 2 A structural diagram of another carbon nanotube fabrication apparatus proposed in an embodiment of this application is shown;

[0038] Figure 3 A flowchart of the preparation method of carbon nanotubes proposed in the application embodiments is shown.

[0039] Explanation of reference numerals in the attached figures:

[0040] 1. Reactor;

[0041] 11. Reaction zone; 111. Feed inlet; 112. Discharge outlet;

[0042] 12. Illuminated area; 121. Light source; 122. Opening;

[0043] 13. Translucent wall;

[0044] 14. Heater. Detailed Implementation

[0045] 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, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0046] In the accompanying drawings, the size of constituent elements, the thickness of layers, or areas may sometimes be exaggerated for clarity. Therefore, any implementation of this disclosure is not necessarily limited to the dimensions shown in the drawings, and the shapes and sizes of the components in the drawings do not reflect true proportions. Furthermore, the drawings schematically illustrate ideal examples, and any implementation of this disclosure is not limited to the shapes or values ​​shown in the drawings.

[0047] In related technologies, the traditional chemical vapor deposition method for preparing carbon nanotubes mainly suffers from the following problems, specifically including:

[0048] 1. In the process of preparing carbon nanotubes by chemical vapor deposition, the catalyst grains serve as the "seeds" for carbon nanotube growth, and their size directly affects the diameter of the carbon nanotubes. According to the Ostward ripening model, as the reaction temperature increases, the solubility difference between catalyst grains increases, leading to the dissolution of small grains and their re-precipitation on large grains, thereby increasing the average size of the catalyst grains. In other words, a high reaction temperature helps the carbon source molecules to undergo supercooling and orderly arrangement on the catalyst surface, but excessively high temperatures can also lead to a significant increase in the size of the catalyst grains, thus affecting the diameter and morphology of the carbon nanotubes.

[0049] 2. The chemically inert carbon source used has a low conversion rate and a slow cracking rate. Although this helps to control the carbon precipitation rate and allow carbon atoms or carbon fragments to be deposited on the catalyst grains in an orderly manner to form few-walled carbon nanotubes, it also results in a low yield of the few-walled carbon nanotubes generated by the conversion.

[0050] Based on the above problems, this application provides an apparatus and method for preparing carbon nanotubes that can reduce the temperature of the carbon source pyrolysis, make the particle size of the catalyst more controllable, thereby making the diameter of the generated carbon nanotubes more controllable, while accelerating the pyrolysis reaction and improving the yield of low-walled carbon nanotubes.

[0051] See Figure 1 , Figure 1 An apparatus for preparing carbon nanotubes according to an embodiment of this application is shown, specifically including reactor 1;

[0052] The reactor 1 is divided into a reaction zone 11 and a light-illuminating zone 12, which are separated by a light-transmitting wall 13.

[0053] The reaction zone 11 is provided with a feed inlet 111 at one end and a discharge outlet 112 at the other end;

[0054] A light source 121 is provided in the illumination area 12, and the light emitted by the light source 121 passes through the light-transmitting wall 13 to reach the reaction area 11.

[0055] A heater 14 is provided on the outside of the reactor 1, and the heater 14 is wrapped around the circumferential outer wall of the reactor 1.

[0056] In the apparatus provided in this application embodiment, by setting up a photoilluminator 121, a photothermal synergistic catalytic system is formed inside the reactor 1, which can improve the preparation efficiency when preparing carbon nanotubes. In particular, the yield of few-walled carbon nanotubes is greatly improved, meeting the industry's urgent need for high-performance few-walled carbon nanotubes.

[0057] This application reduces energy consumption and raw material waste, improves resource utilization, and lowers the preparation cost of carbon nanotubes by optimizing the internal structure of the device and applying a photothermal synergistic catalytic mechanism, making the production of carbon nanotubes more economical and efficient.

[0058] In some embodiments, the inlet 111 of the reaction zone 11 is located at the bottom and the outlet 112 is located at the top. In application, the reactants enter the reaction zone 11 from bottom to top through the inlet 111, and the resulting product is discharged from the outlet 112 at the top.

[0059] In some embodiments, the heater 14 may be an electric heater (system), a shell-and-tube external heating reactor, a shell-and-tube internal heating reactor, etc. The type of heater 14 is not specifically limited in the embodiments of this application.

[0060] See Figure 2 , Figure 2 This application illustrates another apparatus for preparing carbon nanotubes, wherein the inlet 111 of the reaction zone 11 is located at the top, and the outlet 112 is located at the bottom. In application, the reactants enter the reaction zone 11 from top to bottom through the inlet 111, and the resulting product is discharged from the outlet 112 at the bottom.

[0061] In some embodiments, the illumination area 12 is provided with an opening 122;

[0062] The opening 122 allows the light emitter 121 to enter the illumination zone 12 along the length of the reactor 1.

[0063] In practical implementation, the opening 122 facilitates the installation and removal of the light source 121. When the light provided by the light source 121 is insufficient, a new light source 121 can be replaced, improving the ease of use of the device. The methods for fixing the light source 121 in the illumination area 12 include, but are not limited to: bolt fixing, bracket fixing, hanging fixing, adsorption fixing, etc.

[0064] In some embodiments, the reactor 1 is composed of any one of quartz, high-temperature glass and transparent ceramic, and the light-transmitting wall 13 is composed of quartz glass or fluoride glass.

[0065] In the process of preparing carbon nanotubes, the material of reactor 1 needs to meet the requirements of high temperature resistance, high pressure resistance, and chemical corrosion resistance, as well as high light transmittance, so that more of the light emitted by the illuminator 121 can pass through the light-transmitting wall 13 to reach the reaction zone 11. It also facilitates the observation of the reaction process inside the reaction zone 11 from outside the reactor 1. The above-mentioned materials all have these functions and can be well applied to the device provided in the embodiments of this application.

[0066] In some embodiments, the thickness of the light-transmitting wall 13 is 1 mm to 20 mm.

[0067] Since the apparatus provided in this application is used to prepare carbon nanotubes, the reaction process is at a high temperature and is corrosive. Therefore, it is necessary to reasonably set the thickness of the light-transmitting wall 13 to ensure both high light transmittance and resistance to high temperature and corrosion, so that the reaction process can proceed stably.

[0068] In specific implementation, the thickness of the light-transmitting wall 13 is 5 mm-15 mm.

[0069] In some embodiments, the reactor 1 is a cylindrical reactor;

[0070] The light-transparent wall 13 has a ring structure, and the reaction zone 11 is located between the outer wall of the cylindrical reactor and the outer wall of the light-transparent wall 13;

[0071] The illuminated area 12 is located in the hollow area enclosed by the inner wall of the light-transmitting wall 13.

[0072] By setting up a cylindrical reactor, the reaction zone 11 can be evenly distributed around the light-illuminated zone 12. Combined with the annular structure of the light-transmitting wall 13, light can be evenly irradiated into the reaction zone 11, forming a synergistic catalytic effect with the heat generated by the heater 14.

[0073] The cylindrical reactor has a compact structure and high space utilization. The reaction zone 11 and the illumination zone 12 are separated by the light-transmitting wall 13, which not only ensures the uniformity of light illumination, but also makes full use of the internal space of the reactor 1, making the entire preparation process more efficient and energy-saving.

[0074] See Figure 3 , Figure 3 The present application illustrates a method for preparing carbon nanotubes according to an embodiment, the specific operations of which include:

[0075] S1: Adjust the illuminance of the light source located in the reactor's illumination zone to 10. 5 LX-10 7 LX;

[0076] S2: Turn on the heater to raise the temperature of the reaction zone to 500 ℃-750 ℃;

[0077] S3: A carbon source gas and a catalyst with a volume concentration ratio of (90-99)%: (1-10)% are fed into the reaction zone through the feed port. Under the action of light and heat, the carbon source gas is decomposed to generate carbon nanotubes with 1-3 tube wall layers. The carbon-containing mixed material obtained from the reaction is discharged from the reaction zone through the discharge port.

[0078] S4: When the carbon-containing mixed material covers the light-transmitting wall, stop the supply of the carbon source gas and the catalyst, and introduce air into the reaction zone through the feed inlet to oxidize and remove the carbon-containing mixed material on the light-transmitting wall;

[0079] S5: Repeat steps S3-S4 until all pyrolysis reactions are completed. The carbon-containing mixed material is ground to remove the catalyst and obtain the carbon nanotubes.

[0080] The carbon source gas includes organic compounds with 1-20 carbon atoms;

[0081] The catalyst is composed of a catalytic metal and a support. The catalytic metal includes at least one of iron, cobalt, nickel, chromium, silver, gold, platinum, copper, zinc, palladium, molybdenum, tungsten, manganese, and titanium. The support includes at least one of magnesium oxide, silicon oxide, aluminum oxide, hydrotalcite, and molecular sieve.

[0082] The carbon nanotube preparation method provided in this application, by precisely adjusting the illuminance of the illuminator and the temperature of the reaction zone, and optimizing the ratio of carbon source gas and catalyst, effectively reduces the temperature of the cracked carbon source, thereby limiting the growth of catalyst particles and allowing small-diameter catalysts to remain for a longer time. This facilitates the efficient preparation of carbon nanotubes with 1-3 wall layers, solving the problems of low yield and high cost of carbon nanotubes in traditional preparation methods. This application employs a photothermal synergistic catalysis approach, combined with the light absorption effect of the carbon source, to accelerate the carbon precipitation rate at the carbon-metal interface, thereby reducing the formation of amorphous carbon and making the number of carbon nanotube layers more controllable, thus enabling the precise production of more carbon nanotubes with 1-3 wall layers.

[0083] The method provided in this application fully utilizes light and heat energy during the preparation process, reducing energy consumption. The method has clear steps, is simple to operate, and is easy to implement for industrial production.

[0084] In step S4, due to the rapid reaction rate in the reaction zone, a large amount of carbon-containing mixed material is generated. Some of this carbon-containing mixed material will cover the light-transmitting wall, affecting the illumination effect. Therefore, it is necessary to stop the introduction of carbon source gas and catalyst, and introduce air into the reaction zone to oxidize and remove the carbon-containing mixed material on the light-transmitting wall, in order to maintain a stable illumination effect and allow the reaction to proceed smoothly.

[0085] In some embodiments, the temperature of the reaction zone affects the cracking of the carbon source gas and the formation of carbon nanotubes. Controlling the temperature between 500 ℃ and 750 ℃ ​​ensures high catalyst activity, inhibits excessive growth of carbon nanotubes, allows for more complete cracking of the carbon source gas, and accelerates the formation of carbon nanotubes.

[0086] Preferably, the temperature of the reaction zone is raised to 550 ℃-700 ℃.

[0087] In some embodiments, the volume concentration ratio of carbon source gas to catalyst is (95-98)%:(2-5)%. By limiting the ratio of carbon source gas to catalyst, it is more conducive to the formation of carbon nanotubes with stable structural morphology.

[0088] In some embodiments, the residence time of the catalyst in the reaction zone is 1-6 minutes.

[0089] In some embodiments, in step S1, the illuminance of the light source is adjusted to 2 × 10⁻⁶. 6 LX-8×10 6 LX. Illuminance has a significant impact on the effect of photothermal synergistic catalysis; suitable illuminance helps to improve catalyst activity and accelerate carbon source decomposition.

[0090] In some embodiments, the total content of sulfur, nitrogen, phosphorus, arsenic and halogen elements in the organic matter is 0 ppm-20 ppm;

[0091] The carbon source gas includes any one of hydrocarbons and alcohols with 5-8 carbon atoms, polycyclic aromatic hydrocarbons with 15-20 carbon atoms, hydrocarbons with diesel boiling range, methane, cyclohexane, and hydrocarbons and ketones with diesel boiling range.

[0092] The oxygen content of the carbon source gas is less than 30%.

[0093] By setting the content of sulfur, nitrogen, phosphorus, arsenic, and halogen elements in the organic matter to be low, the purity of the final carbon nanotubes can be improved. Reducing the content of impurities also helps to minimize interference factors during the carbon nanotube growth process, making the decomposition of the carbon source gas on the catalyst surface more controllable and more conducive to the formation of few-walled carbon nanotubes with 1-3 wall layers. In particular, impurities such as sulfur and nitrogen readily react with the catalyst; reducing their content allows the catalyst to maintain high stability and activity, thereby extending its lifespan, enabling its recycling, and reducing production costs.

[0094] In specific implementation, preferably, the oxygen content of the carbon source gas is less than 20%. More preferably, the oxygen content of the carbon source gas is less than 5%.

[0095] In some embodiments, the crystallite size of the catalytic metal is 0.5 nm to 1.5 nm, and the mass fraction of the catalytic metal in the catalyst is 0.1% to 10%.

[0096] By controlling the crystallite size of the catalytic metal to 0.5 nm–1.5 nm, the catalyst particles maintain uniform size during the pyrolysis reaction. Smaller particle sizes of the catalyst are more conducive to guiding the carbon source gas to undergo efficient and controllable pyrolysis on its surface, thereby generating more low-wall carbon nanotubes with 1–3 wall layers.

[0097] Since the catalyst is composed of a catalytic metal and a support, and the mass fraction of the catalytic metal in the catalyst is in the range of 0.1%-10%, it can ensure that the catalyst has sufficient active sites, while avoiding excessive metal particles that could lead to catalyst agglomeration or deactivation.

[0098] Preferably, the crystal size of the catalytic metal is 0.6 nm-1.3 nm.

[0099] The mass fraction of catalytic metal in the catalyst is 1%-8%.

[0100] This application provides a carbon nanotube obtained by the above-described method. In this carbon nanotube, carbon nanotubes with 1-3 wall layers account for 85%-96% of the total number of carbon nanotubes.

[0101] The method described in this application significantly improves the yield of carbon nanotubes with 1-3 wall layers by designing the preparation apparatus and optimizing the reaction conditions. The high proportion of few-walled carbon nanotubes obtained makes the prepared carbon nanotube material applicable in a wider range of fields. For example, in the biomedical field, few-walled carbon nanotubes have attracted much attention due to their excellent biocompatibility and cell penetration; in the sensor field, the high sensitivity and rapid response characteristics of few-walled carbon nanotubes make them ideal sensing materials, and so on.

[0102] Example

[0103] Examples 1-4 below all employ Figure 1 The carbon nanotube preparation apparatus shown is used specifically as follows:

[0104] Example 1

[0105] Step 1: Place the light source along the opening in the illuminated area of ​​the reactor and adjust its illuminance to 1×10⁻⁶. 5 LX;

[0106] Step 2: Activate the outermost electric heating system (heater) of the reactor to raise the temperature in the reaction zone and the light-illuminated zone to 700 ℃-750 ℃;

[0107] Step 3: The carbon source gas (which is an organic compound with 1-3 carbon atoms, oxygen content less than 5%, and free of sulfur, nitrogen, phosphorus, arsenic, halogens, etc.) and the catalyst (metal-supported catalyst, wherein the metal is 1% iron + 2% molybdenum, and the crystal size is 0.5 nm-0.6 nm; the support is magnesium aluminum hydrotalcite) are introduced into the reaction zone through the bottom feed port. Under the action of light and heat, the carbon source gas is decomposed on the catalyst to generate low-walled carbon nanotubes. The volume concentration of the catalyst in the carbon source gas is controlled at 3%, and the residence time of the catalyst in the reaction zone is controlled at 3 minutes. The carbon-containing mixed material obtained from the reaction is discharged from the reaction zone through the top discharge port.

[0108] Step 4: When the light-transmitting wall of the reaction zone is covered by carbon-containing mixed material, resulting in insufficient light, stop the supply of carbon source gas and catalyst, and introduce air from the feed inlet to oxidize and remove the carbon-containing mixed material on the light-transmitting wall at 550 ℃.

[0109] Step 5: Repeat the above steps to make the process continuous until all pyrolysis reactions are completed. The carbon-containing mixed material is ground to remove the catalyst and obtain carbon nanotubes. These carbon nanotubes are used as products. The proportion of low-wall (1-3 layers) carbon nanotubes in the product is 92%. The catalyst continues to participate in the next cycle.

[0110] Example 2

[0111] Step 1: Place the light source along the opening in the illuminated area of ​​the reactor and adjust its illuminance to 2×10⁻⁶. 6 LX;

[0112] Step 2: Activate the outermost electric heating system of the reactor to raise the temperature in the reaction zone and the light-irradiated zone to 700℃-750℃;

[0113] Step 3: The carbon source gas (which is a hydrocarbon and alcohol with 5-8 carbon atoms, containing less than 20% oxygen and free of sulfur, nitrogen, phosphorus, arsenic, halogens, etc.) and the catalyst (a metal-supported catalyst, wherein the metal is 2% nickel + 3% copper, with a crystal size of 0.5 nm-0.9 nm; the support is a molecular sieve) are introduced into the reaction zone through the bottom feed port. Under the action of light and heat, the carbon source gas is decomposed on the catalyst to generate low-walled carbon nanotubes. The volume concentration of the catalyst in the carbon source gas is controlled at 10%, and the residence time of the catalyst in the reaction zone is controlled at 3 minutes. The carbon-containing mixed material obtained from the reaction is discharged from the reaction zone through the top discharge port.

[0114] Step 4: When the light-transmitting wall of the reaction zone is covered by carbon-containing mixed material, resulting in insufficient light, stop the supply of carbon source gas and catalyst, and introduce air from the feed inlet to oxidize and remove the carbon-containing mixed material on the light-transmitting wall at 650 °C.

[0115] Step 5: Repeat the above steps to make the process continuous until all pyrolysis reactions are completed. The carbon-containing mixed material is ground to remove the catalyst and obtain carbon nanotubes. These carbon nanotubes are used as products. The proportion of low-wall (1-3 layers) carbon nanotubes in the product is 85%. The catalyst continues to participate in the next cycle.

[0116] Example 3

[0117] Step 1: Place the light source along the opening in the illuminated area of ​​the reactor and adjust its illuminance to 8 × 10⁻⁶. 6 LX;

[0118] Step 2: Activate the outermost electric heating system of the reactor to raise the temperature in the reaction zone and the light-irradiated zone to 750°C;

[0119] Step 3: The carbon source gas (methane) and the catalyst (metal-supported catalyst, wherein the metal is 1% palladium + 4% copper + 5% zinc, and the crystal size is 0.8 nm-1.5 nm; the support is 70% alumina + 20% silicon oxide) are introduced into the reaction zone through the bottom feed port. Under the action of light and heat, the carbon source gas is decomposed on the catalyst to generate low-walled carbon nanotubes. The volume concentration of the catalyst in the carbon source gas is controlled at 1%-5%, and the residence time of the catalyst in the reaction zone is controlled at 6 minutes. The carbon-containing mixed material obtained from the reaction is discharged from the reaction zone through the top discharge port.

[0120] Step 4: When the light-transmitting wall of the reaction zone is covered by carbon-containing mixed material, resulting in insufficient light, stop the supply of carbon source gas and catalyst, and introduce air from the feed inlet to oxidize and remove the carbon-containing mixed material on the light-transmitting wall at 700 ℃.

[0121] Step 5: Repeat the above steps to make the process continuous until all pyrolysis reactions are completed. The carbon-containing mixed material is ground to remove the catalyst and obtain carbon nanotubes. These carbon nanotubes are used as products. The proportion of carbon nanotubes with few walls (1-2 layers) in the product is 96%. The catalyst continues to participate in the next cycle.

[0122] Example 4

[0123] Step 1: Place the light source along the opening in the illuminated area of ​​the reactor and adjust its illuminance to 4×10⁻⁶. 6 LX;

[0124] Step 2: Activate the outermost electric heating system of the reactor to raise the temperature in the reaction zone and the light-irradiated zone to 680℃-710℃;

[0125] Step 3: The carbon source gas (the total content of elements such as hydrocarbons, ketones, ethers, sulfur, nitrogen, phosphorus, arsenic, and halogens with a boiling range of diesel fuel, is 10 ppm) and the catalyst (a metal-supported catalyst, in which the metal is 0.05% gold + 0.05% silver with a crystal size of 0.5 nm-1.25 nm; the support is 90% alumina + 9.9% molecular sieve) are introduced into the reaction zone through the bottom feed port. Under the action of light and heat, the carbon source gas is decomposed on the catalyst to generate low-walled carbon nanotubes. The volume concentration of the catalyst in the carbon source gas is controlled at 2%, and the residence time of the catalyst in the reaction zone is controlled at 2.5 minutes. The carbon-containing mixed material obtained from the reaction is discharged from the reaction zone through the top discharge port.

[0126] Step 4: When the light-transmitting wall of the reaction zone is covered by carbon-containing mixed material, resulting in insufficient light, stop the supply of carbon source gas and catalyst, and introduce air from the feed inlet to oxidize and remove the carbon-containing mixed material on the light-transmitting wall at 500 ℃.

[0127] Step 5: Repeat the above steps to make the process continuous until all pyrolysis reactions are completed. The carbon-containing mixed material is ground to remove the catalyst and obtain carbon nanotubes. These carbon nanotubes are used as the product. The proportion of carbon nanotubes with few walls (1-2 layers) in the product is 96%. The catalyst continues to participate in the next cycle.

[0128] Examples 5-7 below all employ Figure 2 The carbon nanotube preparation apparatus shown is used specifically as follows:

[0129] Example 5

[0130] Step 1: Place the light source along the opening in the illuminated area of ​​the reactor and adjust its illuminance to 6 × 10⁻⁶. 6 LX;

[0131] Step 2: Activate the outermost electric heating system of the reactor to raise the temperature in the reaction zone and the light-irradiated zone to 550℃-650℃;

[0132] Step 3: The carbon source gas (a polycyclic aromatic hydrocarbon with 15-20 carbon atoms) and the catalyst (a metal-supported catalyst, wherein the metal is 6.6% cobalt + 1.4% tungsten, with a crystal size of 0.5 nm-0.7 nm; the support is 50% hydrotalcite + 42% molecular sieve) are introduced into the reaction zone through the top feed port. Under the action of light and heat, the carbon source gas is decomposed on the catalyst to generate low-walled carbon nanotubes. The volume concentration of the catalyst in the carbon source gas is controlled at 2.5%, and the residence time of the catalyst in the reaction zone is controlled at 3 minutes. The carbon-containing mixed material obtained from the reaction is discharged from the reaction zone through the bottom outlet.

[0133] Step 4: When the light-transmitting wall of the reaction zone is covered by carbon-containing mixed material, resulting in insufficient light, stop the supply of carbon source gas and catalyst, and introduce air from the feed inlet to oxidize and remove the carbon-containing mixed material on the light-transmitting wall at 600 ℃.

[0134] Step 5: Repeat the above steps to make the process continuous until all pyrolysis reactions are completed. The carbon-containing mixed material is ground to remove the catalyst and obtain carbon nanotubes. These carbon nanotubes are used as products. The proportion of carbon nanotubes with few walls (1-2 layers) in the product is 94%. The catalyst continues to participate in the next cycle.

[0135] Example 6

[0136] Step 1: Place the light source along the opening in the illuminated area of ​​the reactor and adjust its illuminance to 1×10⁻⁶. 7 LX;

[0137] Step 2: Activate the outermost electric heating system of the reactor to raise the temperature in the reaction zone and the light-irradiated zone to 650℃-710℃;

[0138] Step 3: The carbon source gas (the total content of elements such as hydrocarbons, sulfur, nitrogen, phosphorus, arsenic, and halogens with a boiling range of diesel oil is 20 ppm) and the catalyst (metal-supported catalyst, in which the metal is 5% nickel + 5% tungsten, and the crystal grains are 1.0 nm-1.3 nm; the support is 90% magnesium oxide) are introduced into the reaction zone through the top feed port. Under the action of light and heat, the carbon source gas is decomposed on the catalyst to generate low-walled carbon nanotubes. The volume concentration of the catalyst in the carbon source gas is controlled at 1%, and the residence time of the catalyst in the reaction zone is controlled at 1-6 minutes. The carbon-containing mixed material obtained from the reaction is discharged from the reaction zone through the bottom discharge port.

[0139] Step 4: When the light-transmitting wall of the reaction zone is covered by carbon-containing mixed material, resulting in insufficient light, stop the supply of carbon source gas and catalyst, and introduce air from the feed inlet to oxidize and remove the carbon-containing mixed material on the light-transmitting wall at 500 ℃.

[0140] Step 5: Repeat the above steps to make the process continuous until all pyrolysis reactions are completed. The carbon-containing mixed material is ground to remove the catalyst and obtain carbon nanotubes. These carbon nanotubes are used as products. The proportion of low-wall (1-3 layers) carbon nanotubes in the products is 85%-96%. The catalyst continues to participate in the next cycle.

[0141] Example 7

[0142] Step 1: Place the light source along the opening in the illuminated area of ​​the reactor and adjust its illuminance to 7×10⁻⁶. 6 LX;

[0143] Step 2: Activate the outermost electric heating system of the reactor to raise the temperature in the reaction zone and the light-irradiated zone to 750°C;

[0144] Step 3: The carbon source gas (cyclohexane) and the catalyst (metal-supported catalyst, wherein the metal is 0.1% platinum + 0.9% titanium, with a crystal size of 0.5 nm-0.8 nm; the support is 60% alumina + 39% magnesium oxide) are introduced into the reaction zone through the top feed port. Under the action of light and heat, the carbon source gas is decomposed on the catalyst to generate low-walled carbon nanotubes. The volume concentration of the catalyst in the carbon source gas is controlled at 4%-5%, and the residence time of the catalyst in the reaction zone is controlled at 4 minutes. The carbon-containing mixed material obtained from the reaction is discharged from the reaction zone through the bottom outlet.

[0145] Step 4: When the light-transmitting wall of the reaction zone is covered by carbon-containing mixed material, resulting in insufficient light, stop the supply of carbon source gas and catalyst, and introduce air from the feed inlet to oxidize and remove the carbon-containing mixed material on the light-transmitting wall at 650 °C.

[0146] Step 5: Repeat the above steps to make the process continuous until all pyrolysis reactions are completed. The carbon-containing mixed material is ground to remove the catalyst and obtain carbon nanotubes. These carbon nanotubes are used as products. The proportion of carbon nanotubes with few walls (1-2 layers) in the product is 90%. The catalyst continues to participate in the next cycle.

[0147] In summary, the carbon nanotube preparation apparatus and method provided in this application, by setting up a photoilluminator, utilizes both light and heat to simultaneously activate the catalyst, effectively reducing the catalyst activation temperature by 150℃-250℃. This improves the small crystallite retention of the catalyst by 50%-65% and increases the content of few-walled carbon nanotubes in the product by 30%-35%. Due to the increased catalyst activity and lower activation temperature, the types of carbon sources capable of growing few-walled nanotubes are broadened by 60%-65%, and the cost of carbon sources decreases by 30%-60%. Finally, the carbon nanotubes are separated from the catalyst in a timely manner through grinding technology without damaging the catalyst structure. The separated catalyst can be recycled multiple times, reducing costs by 80%-95%.

[0148] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0149] Although preferred embodiments of the present application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present application.

[0150] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element.

[0151] The above provides a detailed description of the apparatus and method for preparing carbon nanotubes provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for preparing carbon nanotubes, characterized in that, The method includes: S1. Adjust the illuminance of the light source located in the reactor's illumination zone to 10. 5 LX-10 7 lx; S2. Turn on the heater to raise the temperature of the reaction zone to 500 ℃-750 ℃; S3. A carbon source gas and a catalyst with a volume concentration ratio of (90-99)%: (1-10)% are fed into the reaction zone through the feed port. Under the action of light and heat, the carbon source gas is decomposed to generate carbon nanotubes with 1-3 tube wall layers. The carbon-containing mixed material obtained from the reaction is discharged from the reaction zone through the discharge port. S4. When the carbon-containing mixed material covers the light-transmitting wall, stop the introduction of the carbon source gas and the catalyst, and introduce air into the reaction zone through the feed inlet to oxidize and remove the carbon-containing mixed material on the light-transmitting wall; S5. Repeat steps S3-S4 until all pyrolysis reactions are completed. The carbon-containing mixed material is ground to remove the catalyst and obtain the carbon nanotubes. The carbon source gas includes organic compounds with 1-20 carbon atoms; The catalyst is composed of a catalytic metal and a support. The catalytic metal includes at least one of iron, cobalt, nickel, chromium, silver, gold, platinum, copper, zinc, palladium, molybdenum, tungsten, manganese, and titanium. The support includes at least one of magnesium oxide, silicon oxide, aluminum oxide, hydrotalcite, and molecular sieve. The method is carried out in a carbon nanotube preparation apparatus, which includes a reactor; The reactor is a cylindrical reactor; the light-transmitting wall has an annular structure; the reaction zone is located between the outer wall of the cylindrical reactor and the outer wall of the light-transmitting wall; the illumination zone is located in the hollow area enclosed by the inner wall of the light-transmitting wall. The reactor is divided into a reaction zone and a light-illuminating zone, which are separated by a light-transmitting wall. The light-illuminating zone has an opening, which allows the light emitter to enter the light-illuminating zone along the length of the reactor. The reaction zone is provided with a feed inlet at one end and a discharge outlet at the other end. A light source is installed in the illumination area, and the light emitted by the light source reaches the reaction area through the light-transmitting wall. A heater is provided on the outside of the reactor, and the heater is wrapped around the circumferential outer wall of the reactor.

2. The method for preparing carbon nanotubes according to claim 1, characterized in that, The reactor is composed of any one of quartz, high-temperature glass, and transparent ceramic. The transparent wall is made of quartz glass or fluoride glass.

3. The method for preparing carbon nanotubes according to claim 1, characterized in that, The thickness of the light-transmitting wall is 1 mm to 20 mm.

4. The method for preparing carbon nanotubes according to claim 1, characterized in that, In step S1, the illuminance of the light source is adjusted to 2 × 10⁻⁶. 6 lx-8×10 6 lx.

5. The method for preparing carbon nanotubes according to claim 1, characterized in that, The total content of sulfur, nitrogen, phosphorus, arsenic and halogen elements in the organic matter is 0 ppm-20 ppm; The carbon source gas includes at least one of the following substances: hydrocarbons with 5-8 carbon atoms, alcohols with 5-8 carbon atoms, polycyclic aromatic hydrocarbons with 15-20 carbon atoms, hydrocarbons with the boiling range of diesel fuel, methane, and ketones with the boiling range of diesel fuel. The oxygen content of the carbon source gas is less than 30%.

6. The method for preparing carbon nanotubes according to claim 1, characterized in that, The catalytic metal has a grain size of 0.5 nm to 1.5 nm and a mass fraction of 0.1% to 10% in the catalyst.

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