Preparation method and system of single-walled carbon nanotube

Abstract

The invention discloses a preparation method and system of a single-walled carbon nanotube. The strong heat absorption effect of decomposition of first carbon source gas is relieved through decomposition of second carbon source gas, energy balance in the reaction process is helped to be maintained, the growth environment of the single-walled carbon nanotube is stabilized, and the pipe diameter distribution dispersion can be narrowed. Meanwhile, the combination of different carbon sources dynamically optimizes the carbon supply, so that the directional decomposition efficiency of the carbon sources is further improved, carbon atoms can controllably participate in nucleation and growth, and the limitations of low nucleation rate and low yield in the traditional preparation process are effectively overcome.

Description

A method and system for preparing single-walled carbon nanotubes Technical Field

[0001] This application belongs to the field of nanomaterial preparation technology, specifically relating to a method and system for preparing single-walled carbon nanotubes. Background Technology

[0002] With the rapid development of nanomaterials science, the demand for single-walled carbon nanotubes (SWCNTs), which have unique one-dimensional structures and excellent physicochemical properties, continues to grow in strategic emerging fields such as flexible electronics, energy storage devices, and high-precision sensing. Promoting the industrialization of single-walled carbon nanotubes has become an important development direction in the field of nanomaterials.

[0003] However, in traditional single-walled carbon nanotube (SHU) fabrication processes, methane, as the mainstream single carbon source, exhibits characteristics of stable molecular structure, strong endothermic properties, and difficulty in decomposition. This makes it difficult to maintain energy balance between carbon source decomposition and SHU growth, disrupting the growth environment of SHU and thus inhibiting the efficiency of directional carbon source decomposition. Consequently, this leads to a decrease in SHU nucleation rate, lower yield, and increased dispersion in product diameter distribution, failing to meet the stringent uniformity requirements of high-precision applications. Summary of the Invention

[0004] This application aims to provide a method and system for preparing single-walled carbon nanotubes. The method mitigates the strong endothermic effect of the first carbon source gas decomposition by decomposing a second carbon source gas, helping to maintain the energy balance of the reaction process, stabilize the growth environment of the single-walled carbon nanotubes, and reduce the dispersion of the tube diameter distribution. Simultaneously, the combination of different carbon sources dynamically optimizes the carbon supply, thereby improving the efficiency of directional carbon source decomposition and enabling carbon atoms to participate in nucleation and growth more controllably, effectively overcoming the limitations of low nucleation rate and low yield in traditional preparation processes.

[0005] To solve the above-mentioned technical problems, this application is implemented as follows: In a first aspect, embodiments of this application propose a method for preparing single-walled carbon nanotubes, the method comprising: preheating a first mixed gas and a second mixed gas respectively, and then introducing them into a fluidized bed reactor at 850℃-950℃ through different inlets, and subjecting them to a cracking reaction under the action of a catalyst to generate the single-walled carbon nanotubes; wherein, the first mixed gas is composed of a first carbon source gas and a protective gas, and the second mixed gas is composed of a second carbon source gas and a protective gas; the first carbon source gas is selected from methane and / or carbon monoxide, and the second carbon source gas is selected from at least one of propylene, propane and ethylene.

[0006] Optionally, the volume ratio of the first carbon source gas to the second carbon source gas is (10-20):1.

[0007] Optionally, in the first mixed gas, the volume percentage of the first carbon source gas is 20%-50%.

[0008] Optionally, in the second mixture, the volume percentage of the second carbon source gas is 5%-30%.

[0009] Optionally, in the single-walled carbon nanotubes, the proportion of products with a particle size of 1.2nm-1.8nm is greater than 90%.

[0010] Optionally, before introducing the first mixed gas and the second mixed gas into the fluidized bed reactor, the method further includes: introducing a high-temperature heat source into the fluidized bed reactor to heat the inside of the fluidized bed reactor to 900℃-950℃, and after heating, introducing a reducing gas into the fluidized bed reactor to reduce the catalyst and obtain a reduced catalyst.

[0011] Optionally, the reducing gas includes hydrogen; the volume ratio of the reducing gas to the first carbon source gas is 1:(1-5).

[0012] Optionally, the purity of the first carbon source gas, the second carbon source gas, and the protective gas is ≥99.99%.

[0013] Secondly, embodiments of this application provide a system for preparing single-walled carbon nanotubes. This system is applicable to the method for preparing single-walled carbon nanotubes described in the first aspect above. The system includes: a gas preheating device and a fluidized bed reactor; the outlet of the gas preheating device is connected to the interior of the fluidized bed reactor; the gas preheating device is used to preheat a first mixed gas and a second mixed gas respectively, and to transport the preheated first mixed gas and the second mixed gas to the fluidized bed reactor; the fluidized bed reactor is used to load a catalyst, and to allow the preheated first mixed gas and the second mixed gas to undergo a cracking reaction at 900℃-950℃ to generate the single-walled carbon nanotubes.

[0014] Optionally, the gas preheating device includes: a first gas outlet pipe and a second gas outlet pipe; the first gas outlet pipe is located below the second gas outlet pipe, and the first gas outlet pipe and the second gas outlet pipe are respectively connected to the interior of the fluidized bed reactor; the first gas outlet pipe is used to deliver preheated first mixed gas to the fluidized bed reactor; the second gas outlet pipe is used to deliver preheated second mixed gas to the fluidized bed reactor.

[0015] Beneficial Technical Effects: In the embodiments of this application, a second carbon source gas is added to the first carbon source gas. The second carbon source gas is a hydrocarbon that is relatively easy to decompose, such as propylene, propane, or ethylene. These carbon source molecules have relatively unstable structures and require less energy to decompose, thus they can be rapidly decomposed in the fluidized bed reactor, replenishing the reaction system with active carbon species. The decomposition of the second carbon source gas can alleviate the strong endothermic effect of the decomposition of the first carbon source gas, such as methane, helping to maintain the energy balance of the reaction process and stabilize the growth environment of single-walled carbon nanotubes. This helps to improve the efficiency of directional decomposition of carbon sources, allowing carbon atoms to participate in nucleation and growth more controllably, overcoming the limitations of low nucleation rate and low yield in traditional preparation processes, and helping to narrow the dispersion of tube diameter distribution. Simultaneously, the embodiments of this application also promote the gradual decomposition and synergistic effect of different carbon sources on the catalyst surface by preheating the first and second mixed gases separately and introducing them into the reactor from different inlets.

[0016] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0017] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments in conjunction with the following drawings, in which: Figure 1 is a flowchart of the preparation method of single-walled carbon nanotubes proposed in the embodiments of this application; Figure 2 is a schematic diagram of the structure of the preparation system of single-walled carbon nanotubes proposed in the embodiments of this application.

[0018] Reference numerals: 1. Gas preheating device; 11. Gas mixer; 12. Gas preheating furnace; 13. First gas outlet pipe; 14. Second gas outlet pipe; 2. Fluidized bed reactor; 21. Gas inlet; 22. Material outlet; 23. Tail gas outlet; 24. Filter; 25. Air distribution plate; 26. Fluidized bed body; 3. Tail gas treatment device; 4. Storage unit; 41. Vacuum machine; 42. Storage tank. Detailed Implementation

[0019] The embodiments of this application will now be described in detail. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0020] The terms "first" and "second" in the specification and claims of this application may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise stated, "multiple" means two or more. Furthermore, "and / or" in the specification and claims indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0021] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0022] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0023] In related technologies, the traditional single-walled carbon nanotube preparation process still has the following problems: the decomposition of methane requires the absorption of a large amount of heat, resulting in an excessively high total endothermic load in the reaction system, which not only increases energy consumption but also makes it difficult to maintain energy balance; the imbalance of energy balance directly leads to an increase in the fluctuation range of reaction temperature (usually exceeding ±20℃), and the instability of temperature will seriously damage the growth environment of single-walled carbon nanotubes. On the one hand, this will inhibit the directional decomposition efficiency of carbon source, resulting in a decrease in the nucleation rate and yield of single-walled carbon nanotubes; on the other hand, it will interfere with the control of tube diameter, resulting in an increase in the dispersion of product tube diameter distribution (the standard deviation often exceeds 0.5nm), which cannot meet the stringent requirements of high-precision application scenarios for the uniformity of single-walled carbon nanotubes.

[0024] The efficient preparation of high-quality single-walled carbon nanotubes is a huge challenge we face today, including optimizing the carbon source system, precisely controlling the reaction temperature, and improving equipment compatibility. Among these, the selection of the carbon source and the control of the energy balance of the reaction system are key to the industrialization of single-walled carbon nanotubes.

[0025] Currently, there are various improved processes for preparing single-walled carbon nanotubes, but these processes generally suffer from high costs, poor compatibility, and difficulty in scaling up. For example, some processes lower the energy barrier for methane decomposition by introducing highly active catalysts, but the catalysts are expensive to prepare and prone to agglomeration, increasing the difficulty of product purification. Other processes maintain stable temperatures by increasing heating power, but this significantly increases equipment energy consumption and operating costs, failing to meet economic requirements. Some studies have explored using ethylene, acetylene, etc., as alternative carbon sources, which reduces the difficulty of decomposition, but have poor compatibility with existing methane production lines, requiring large-scale equipment modifications and leading to a surge in investment costs.

[0026] Based on the problems existing in related technologies, this application proposes a method for preparing single-walled carbon nanotubes. Figure 1 is a flowchart of the method for preparing single-walled carbon nanotubes proposed in this application, which specifically includes: Step S1: preheating the first mixed gas and the second mixed gas respectively; it should be noted that the first mixed gas is composed of a first carbon source gas and a protective gas, and the second mixed gas is composed of a second carbon source gas and a protective gas; the first carbon source gas is selected from methane and / or carbon monoxide, and the second carbon source gas is selected from at least one of propylene, propane and ethylene.

[0027] In some embodiments, the first carbon source gas consists of methane and carbon monoxide; the addition of carbon monoxide can suppress the formation of amorphous carbon, reduce side reaction interference, and thus improve the yield and purity of single-walled carbon nanotubes; the second carbon source gas is preferably propylene; propylene, as a weakly endothermic carbon source, is easily decomposed, providing rapid supplemental heat to the reaction system, synergistically maintaining the energy balance of the growth process, promoting the directional decomposition efficiency of the carbon source, increasing the nucleation rate and narrowing the dispersion of the tube diameter distribution, thereby enhancing the uniformity of single-walled carbon nanotubes to meet the requirements of high-precision applications; the protective gas is nitrogen or argon; in some embodiments, the first carbon source gas The volume ratio of the first carbon source gas to the second carbon source gas is (10-20):1; for example, the volume ratio of the first carbon source gas to the second carbon source gas is 10:1, 12:1, 15:1, 17:1, 20:1; In this embodiment, by controlling the volume ratio of the first carbon source gas to the second carbon source gas within the range of (10-20):1, the first carbon source gas is used as the main carbon source to maintain a stable supply during preparation, while a small amount of easily decomposed second carbon source gas is rapidly decomposed as a weakly endothermic carbon source to supplement the heat of the reaction system, promote the maintenance of energy balance, thereby stabilizing the growth environment of single-walled carbon nanotubes and improving the efficiency of directional decomposition of carbon source.

[0028] In some embodiments, the volume percentage of the first carbon source gas in the first mixed gas is 20%-50%; for example, the volume percentage of the first carbon source gas in the first mixed gas is 20%, 25%, 30%, 35%, 40%, 45%, or 50%. By controlling the volume percentage of the first carbon source gas in the first mixed gas to 20%-50%, the first carbon source gas participates in the reaction at a suitable rate and total amount, which avoids the severe endothermic reaction and growth environment disturbance caused by concentrated decomposition at high concentrations, and also prevents insufficient carbon source supply, thereby maintaining the energy balance and thermodynamic conditions of the reaction system more stably in the dual carbon source system.

[0029] In some embodiments, the volume percentage of the second carbon source gas in the second mixed gas is 5%-30%; for example, the volume percentage of the second carbon source gas in the second mixed gas is 5%, 10%, 15%, 20%, 25%, or 30%. By controlling the volume percentage of the second carbon source gas in the second mixed gas to 5%-30%, this embodiment ensures that weakly endothermic carbon sources such as propylene can be rapidly decomposed at an appropriate concentration, continuously replenishing the reaction system with heat and active carbon species, synergistically stabilizing the growth environment of single-walled carbon nanotubes, and promoting the improvement of the directional decomposition efficiency of carbon sources.

[0030] In some embodiments, before introducing the first mixed gas and the second mixed gas into the fluidized bed reactor, the method further includes: introducing a high-temperature heat source into the fluidized bed reactor to heat the inside of the fluidized bed reactor to 850°C-950°C, and after heating, introducing a reducing gas into the fluidized bed reactor to reduce the catalyst and obtain a reduced catalyst.

[0031] It should be noted that the high-temperature heat source is provided by a high-temperature inert gas, such as nitrogen or argon; the internal heating temperature of the fluidized bed reactor is 850℃, 880℃, 900℃, 910℃, 920℃, 930℃, 940℃, and 950℃; the reduction treatment time is 3-5 minutes.

[0032] In this embodiment, the fluidized bed reactor is preheated to 850℃-950℃ to provide a high-temperature environment for the reaction, meet the temperature required for catalyst reduction, and ensure that the reaction system is in the optimal thermodynamic state when the carbon source is introduced, thereby reducing energy imbalance caused by temperature fluctuations and stabilizing the growth conditions of single-walled carbon nanotubes. The catalyst is reduced by introducing reducing gas, which can improve the activity and selectivity of the catalyst, promote the directional decomposition and efficient utilization of the carbon source on the catalyst surface, and enhance the uniformity and controllability of the nucleation process.

[0033] In some embodiments, the reducing gas includes hydrogen; the volume ratio of the reducing gas to the first carbon source gas is 1:(1-5); for example, the volume ratio of the reducing gas to the first carbon source gas is 1:1, 1:2, 1:3, 1:4, or 1:5.

[0034] In this embodiment, the reducing effect of hydrogen effectively activates the catalyst surface, enhancing its activity and selectivity, thereby increasing the efficiency of directional adsorption and decomposition of carbon sources on the catalyst. The ratio of reducing gas to the first carbon source gas ensures coordination between the reduction process and subsequent pyrolysis reactions, effectively removing catalyst oxides to stabilize the growth environment while avoiding excessive hydrogen interference with carbon source pyrolysis, thus promoting uniform nucleation and growth of carbon nanotubes.

[0035] In some embodiments, the purity of the first carbon source gas, the second carbon source gas, and the protective gas is ≥99.99%.

[0036] In the embodiments of this application, the purity of the first carbon source gas, the second carbon source gas, and the protective gas is not less than 99.99%, which can reduce the interference of impurity gases on the reaction system. High-purity gases can effectively prevent impurity poisoning and deactivation on the catalyst surface, maintain its high activity and selectivity, and thus ensure the efficiency of directional decomposition of carbon source on catalyst.

[0037] Step S2: The preheated first and second mixed gases are introduced into an 850℃-950℃ fluidized bed reactor through different inlets, and undergo a cracking reaction under the action of a catalyst to generate the single-walled carbon nanotubes. It should be noted that two air inlets are provided on the fluidized bed reactor to allow the first and second mixed gases to be introduced into the reactor separately. In some embodiments, the air inlet for the second mixed gas is located above the air inlet for the first mixed gas in the axial direction, forming a gradient and sequential gas supply reaction environment, allowing the first carbon source gas (methane and / or carbon monoxide) to preferentially contact the catalyst from below and initiate the reaction. The initial pyrolysis occurs; the second carbon source gas is introduced from above. Due to its higher position, it requires a longer diffusion path and residence time in the reactor to reach the catalyst bed, thus slowing down its decomposition rate and preventing premature and rapid decomposition of weakly endothermic carbon sources such as propylene. This allows the heat release of the second carbon source gas and the supply of activated carbon to better match the strongly endothermic decomposition process of the first carbon source gas (such as methane) below. This staged and spatial carbon source supply method synergistically maintains the energy balance of the reaction system, helps stabilize the growth environment of single-walled carbon nanotubes, improves the directional decomposition efficiency of carbon sources, and effectively suppresses the dispersion of tube diameter distribution caused by local energy fluctuations.

[0038] In some embodiments, the growth of single-walled carbon nanotubes needs to be completed in 5-10 minutes.

[0039] In some embodiments, the proportion of products with a particle size of 1.2 nm to 1.8 nm in the single-walled carbon nanotubes is greater than 90%.

[0040] In some embodiments, over 90% of the single-walled carbon nanotubes in the product have particle sizes of 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, 1.6 nm, 1.7 nm, and 1.8 nm. The proportion of single-walled carbon nanotubes with particle sizes of 1.2 nm to 1.8 nm demonstrates that the preparation method provided in this application overcomes the problem of discrete tube diameter distribution caused by energy imbalance and unstable growth environment in traditional processes. This application employs a dual carbon source system, combining the proportional control of carbon source gas, high-purity gas supply, and a gradient gas inlet method to ensure the high efficiency of directional carbon source decomposition and the high controllability of the growth process. This allows the nucleation and growth processes to proceed under stable energy balance, thereby producing highly uniform single-walled carbon nanotubes that can meet the stringent requirements of high-precision applications for the uniformity of nanomaterial size and structure.

[0041] In summary, the method for preparing single-walled carbon nanotubes provided in this application uses a mixed carbon source of "first carbon source gas (methane and / or carbon monoxide + second carbon source gas (propylene, etc.)". The second carbon source gas, with its weak endothermic and easily decomposed properties, replaces part of the first carbon source gas, which is strongly endothermic and difficult to decompose, thereby reducing the system's energy consumption and temperature fluctuation risk from the inherent characteristics of the carbon source. In the embodiments of this application, under reaction conditions of 850℃-950℃ and normal pressure, the total endothermic load of the system can be reduced by 20%-40%, keeping temperature fluctuations within ±10℃. This preparation method can increase the yield of single-walled carbon nanotubes by 15%-30%, reduce the standard deviation of the tube diameter distribution to within 0.5nm, and the raw materials and processes used are compatible with industrial production lines.

[0042] Meanwhile, the embodiments of this application also design differentiated pretreatment schemes for different carbon source characteristics to ensure that the carbon source mixing ratio is reasonable (e.g., the volume ratio of the second carbon source gas to the first carbon source gas is 1:(10-20), and the volume ratio of the first carbon source gas to the first mixed gas is 20%-50%) and the gas temperature is stable, laying the foundation for the efficient decomposition of the carbon source in the future and avoiding the waste of carbon source and abnormal reaction caused by uneven gas mixing or insufficient temperature.

[0043] Secondly, this application provides a system for preparing single-walled carbon nanotubes. The system is applicable to the method for preparing single-walled carbon nanotubes. Figure 2 is a schematic diagram of the structure of the single-walled carbon nanotube preparation system proposed in this application, specifically including: a gas preheating device 1 and a fluidized bed reactor 2; the outlet of the gas preheating device 1 is connected to the interior of the fluidized bed reactor 2; the gas preheating device 1 is used to preheat a first mixed gas and a second mixed gas respectively, and to transport the preheated first mixed gas and the second mixed gas to the fluidized bed reactor 2; the fluidized bed reactor 2 is used to load a catalyst, and to allow the preheated first mixed gas and the second mixed gas to undergo a cracking reaction at 850℃-950℃ to generate the single-walled carbon nanotubes.

[0044] It should be noted that the gas preheating device 1 includes a gas mixer 11 and a gas preheating furnace 12. When the gas preheating device 1 is running, the gas mixer 11 uniformly mixes the first carbon source gas and the protective gas, and the second carbon source gas and the protective gas, respectively. The resulting first mixed gas and second mixed gas then enter the gas preheating furnace 12, where they are heated and then transported to the fluidized bed reactor 2 through different pipelines. In some embodiments, the gas preheating furnace 12 is an electrically heated preheating furnace. In some embodiments, the gas preheating device 1 preheats the first mixed gas to 350℃-400℃ and the second mixed gas to 300℃-350℃. In some embodiments, the fluidized bed reactor 2 includes an air inlet 21, an air distribution plate 25, a filter 24, a discharge port 22, and a fluidized bed body 26. The air inlet 21 is connected to the gas preheating device... The outlet of fluidized bed reactor 2 is connected to a pipe, and the inlet 21 is used to introduce a first mixed gas, a second mixed gas, etc. into the fluidized bed reactor 2. In some embodiments, the air distribution plate 25 is located axially on the fluidized bed reactor 2 near the air inlet 21. The air distribution plate 25 is used to uniformly introduce gas into the fluidized bed body 26 from the bottom. In some embodiments, the air distribution plate 25 is a sintered plate. In some embodiments, the diameter of the fluidized bed body 26 in the radial direction is 45mm-60mm. The fluidized bed body 26 is used for carbon source pyrolysis to produce single-walled carbon nanotubes. In some embodiments, the filter 24 is located on the fluidized bed reactor 2 near the outlet. The filter 24 is used to filter the exhaust gas discharged from the outlet of the fluidized bed body 26. In some embodiments, the discharge port 22 is used to discharge the reaction products in the fluidized bed body 26. The reaction products are single-walled carbon nanotubes.

[0045] The preparation system provided in this application provides hardware support for solving the problems of energy imbalance, temperature fluctuation, yield, and pipe diameter control caused by the strong endothermic and difficult decomposition of methane in traditional processes by integrating an independently controllable gas preheating device 1 and a high-temperature fluidized bed reactor 2. By preheating the first and second mixed gases separately, the system facilitates control over the initial energy state of different carbon sources entering the reactor. It fully utilizes the differences in characteristics between carbon sources such as methane and propylene, ensuring that the easily decomposed second carbon source gas carries sufficient energy beforehand. This allows for rapid decomposition and heat replenishment upon entering the reaction zone, synergistically stabilizing the thermodynamic environment required for the decomposition of the first carbon source gas and maintaining energy balance and temperature stability throughout the entire growth process.

[0046] Fluidized bed reactor technology, as an important method for the synthesis of single-walled carbon nanotubes, has the advantages of uniform reaction interface and easy continuous production. This application's embodiment, based on a fluidized bed reactor, combines a gas preheating device to form a system structure of preheating before reaction. Combined with the inherent excellent heat and mass transfer characteristics of fluidized beds, this system can match the growth requirements of single-walled carbon nanotubes, achieving efficient carbon source decomposition and product collection, and solving the problem of insufficient gas preheating in traditional fluidized beds. This improves the low carbon source decomposition efficiency, stabilizes gas pressure fluctuations, and prevents disruption of the reaction atmosphere. This system structure simplifies the entire preparation process, makes it easier to scale up, and supports the large-scale, efficient, economical, and reliable production of high-performance single-walled carbon nanotubes, meeting the stringent requirements of high-precision applications and promoting large-scale application.

[0047] In some embodiments, the gas preheating device 1 includes: a first gas outlet pipe 13 and a second gas outlet pipe 14; the first gas outlet pipe 13 is located below the second gas outlet pipe 14, and the first gas outlet pipe 13 and the second gas outlet pipe 14 are respectively connected to the interior of the fluidized bed reactor 2; the first gas outlet pipe 13 is used to deliver preheated first mixed gas to the fluidized bed reactor 2; the second gas outlet pipe 14 is used to deliver preheated second mixed gas to the fluidized bed reactor 2.

[0048] It should be noted that both the first outlet pipe 13 and the second outlet pipe 14 must meet the requirements for stable gas delivery and avoid gas pressure fluctuations exceeding ±5 kPa. In some embodiments, the second outlet pipe 14 and the first outlet pipe 13 are arranged vertically along the axial direction and are independently connected to the internal reaction zone of the fluidized bed reactor 2. In some embodiments, the inner diameter of the first outlet pipe 13 is 6 mm, which is suitable for delivering preheated first mixed gas to the lower middle part of the fluidized bed reactor 2. In some embodiments, the inner diameter of the second outlet pipe 14 is 6 mm, which is used to deliver preheated second mixed gas to the upper middle part of the fluidized bed reactor 2. In some embodiments, the air inlet 21 includes a first air inlet and a second air inlet, and the first air inlet is connected to the first outlet pipe 13, and the second air inlet is connected to the second outlet pipe 14. Axially, the first air inlet is located below the second air inlet. In this embodiment, this vertically separated pipe layout realizes the fixed-point and zoned introduction of the first mixed gas and the second mixed gas at different axial heights in the reactor.

[0049] This embodiment of the application sets up a first gas outlet pipe 13 and a second gas outlet pipe 14. The first gas outlet pipe 13, located below, transports the first carbon source gas to the main area of ​​the catalyst bed in the reactor, while the second gas outlet pipe 14, located above, allows the second carbon source gas to start its reaction path from the upper space of the reactor. This arrangement not only achieves a gradual supply of carbon source in space, but also uses the axial distance to delay the contact time between the second carbon source gas and the catalyst. This allows the heat generated by its decomposition and the active carbon species to more smoothly and accurately compensate for the energy consumption caused by the strong endothermic decomposition of the first carbon source gas below. As a result, a more stable energy gradient and temperature field are established in the axial direction of the reactor, effectively solving the problems of energy imbalance and drastic temperature fluctuations in traditional processes.

[0050] In some embodiments, the system further includes a temperature control unit and a gas control unit; wherein the gas control unit is connected to the gas preheating device 1 via a pipeline, and the gas control unit can adjust the gas feed rate; the temperature control unit is connected to the fluidized bed reactor 2 and is used to dynamically adjust the reactor temperature so that the temperature inside the fluidized bed reactor 2 is stabilized at 850℃-950℃, and the temperature fluctuation is ≤±5℃.

[0051] This embodiment of the application, by setting up a gas path control unit and a temperature control unit in the system, can adjust the feed rate of the dual carbon source gases, so that the easily decomposed second carbon source gas can be supplemented with heat and active carbon species as needed, alleviate the strong endothermic effect during the decomposition of the first carbon source gas, and maintain the dynamic energy balance of the reaction system. At the same time, the temperature control unit dynamically adjusts and ensures that the temperature in the fluidized bed reactor 2 is stable at 900℃-950℃ with fluctuations ≤±5℃, providing a highly constant thermal environment for the growth of single-walled carbon nanotubes, and avoiding the damage of temperature fluctuations to the carbon source decomposition efficiency, nucleation process, and tube diameter consistency.

[0052] In some embodiments, the system further includes an exhaust gas treatment device 3; the exhaust gas treatment device 3 is connected to the exhaust gas outlet 23 of the fluidized bed reactor 2 via a pipeline; the exhaust gas treatment device 3 is used to treat the exhaust gas discharged from the outlet, reduce the exhaust gas emitted into the environment, and reduce pollution to the environment.

[0053] In some embodiments, the system further includes a storage unit 4 for collecting reaction products; in some embodiments, the storage unit 4 includes a vacuum pump 41 and a storage tank 42; wherein, the vacuum pump 41 is connected to the fluidized bed reactor 2, and the outlet 22 of the fluidized bed reactor 2 is connected to the inlet of the storage tank 42; in specific implementation, the vacuum pump 41 is used to evacuate the inside of the fluidized bed reactor 2, so that the prepared single-walled carbon nanotubes enter the storage tank 42 through the outlet 22 for storage.

[0054] To enable those skilled in the art to better understand this application, the following embodiments will be used to provide a detailed description of the preparation method and system for single-walled carbon nanotubes provided in this application.

[0055] Example 1 uses the single-walled carbon nanotube preparation system shown in Figure 2, specifically including the following steps: (1) 20g of Co-based hydrotalcite catalyst is placed in a fluidized bed reactor with an inner diameter of 50mm, and then high-temperature argon gas is introduced into the fluidized bed reactor. The operating pressure is 0.18MPa and the target temperature is 900℃; (2) When the temperature of the fluidized bed reactor stabilizes at 900℃, 0.485L / min of hydrogen gas is introduced to reduce the catalyst for 5min; (3) After the reduction treatment, a first mixed gas (methane accounting for 20%) consisting of methane and argon gas preheated to 350℃ by a gas preheating device at 4L / min and a second mixed gas consisting of propylene and argon gas preheated at 0.8L / min are introduced into the fluidized bed reactor respectively. Gas (propylene accounts for 10%), in which the volume ratio of propylene to methane is 1:10. Under the action of high temperature and catalyst, methane and propylene are cracked in the fluidized bed reactor to produce single-walled carbon nanotubes. The growth time is 10 min. During the growth process, the temperature in the fluidized bed reactor is stable at 945℃-955℃, with fluctuations ≤±5℃. (4) The particle size distribution of the single-walled carbon nanotubes obtained by the reaction is mainly 1.2-2.2nm (accounting for 92% of the product). The carbon content of the crude single-walled carbon nanotubes is ≥18%, the impurity carbon content is <3%, the carbon utilization rate is ≥30%, and the g / d ratio is ≥70. The overall energy consumption is reduced by 30% compared with the traditional electric heating device.

[0056] Example 2 uses the single-walled carbon nanotube preparation system shown in Figure 2, specifically including the following steps: (1) 20g of Co-based hydrotalcite catalyst is placed in a fluidized bed reactor with an inner diameter of 50mm, and then high-temperature argon gas is introduced into the fluidized bed reactor. The operating pressure is 0.18MPa and the target temperature is 850℃; (2) When the temperature of the fluidized bed reactor stabilizes at 850℃, 0.485L / min of hydrogen gas is introduced to reduce the catalyst for 5min; (3) After the reduction treatment, 4L / min of a first mixed gas composed of methane, carbon monoxide and argon gas preheated to 350℃ by a gas preheating device (methane accounts for 20% and carbon monoxide accounts for 5%) and 0.8L / min of propylene and argon gas are introduced into the fluidized bed reactor respectively. The second mixed gas (propylene accounts for 5%), in which the volume ratio of propylene to methane is 1:20, under the action of high temperature and catalyst, methane and propylene are cracked in the fluidized bed reactor to produce single-walled carbon nanotubes. The growth time is 10 min. During the growth process, the temperature in the fluidized bed reactor is stable at 945℃-955℃, with fluctuations ≤±5℃; (4) The particle size distribution of the single-walled carbon nanotubes obtained by the reaction is mainly 1.2-1.8nm (accounting for 94% of the product). The carbon content of the crude single-walled carbon nanotubes is ≥16%, the impurity carbon content is <3%, the carbon utilization rate is ≥30%, and the g / d ratio is ≥70; the overall energy consumption is reduced by 30% compared with the traditional electric heating device.

[0057] Example 3 uses the single-walled carbon nanotube preparation system shown in Figure 2, specifically including the following steps: (1) 20g of Co-based hydrotalcite catalyst is placed in a fluidized bed reactor with an inner diameter of 50mm, and then high-temperature argon gas is introduced into the fluidized bed reactor. The operating pressure is 0.18MPa and the target temperature is 900℃; (2) When the temperature of the fluidized bed reactor stabilizes at 900℃, 0.485L / min of hydrogen gas is introduced to reduce the catalyst for 5min; (3) After the reduction treatment, 4L / min of a first mixed gas composed of methane, carbon monoxide and argon gas preheated to 350℃ by a gas preheating device (methane accounts for 25% and carbon monoxide accounts for 5%) and 1L / min of ethylene and argon gas are introduced into the fluidized bed reactor respectively. The second mixed gas (ethylene accounts for 10%), in which the volume ratio of ethylene to methane is 1:10, under the action of high temperature and catalyst, methane and single-walled carbon nanotubes are produced by cracking in the fluidized bed reactor. The growth time is 10 min. During the growth process, the temperature in the fluidized bed reactor is stable at 945℃-955℃, with fluctuations ≤±5℃; (4) The particle size distribution of the single-walled carbon nanotubes obtained by the reaction is mainly 1.2-1.8nm (accounting for 93% of the product). The carbon content of the crude single-walled carbon nanotubes is ≥20%, the impurity carbon content is <3%, the carbon utilization rate is ≥35%, and the g / d ratio is ≥70; the overall energy consumption is reduced by 30% compared with the traditional electric heating device.

[0058] In summary, the embodiments of this application employ a mixed carbon source of a first carbon source gas and a second carbon source gas. The weakly endothermic and easily decomposed characteristics of the second carbon source gas replace part of the strongly endothermic and difficult-to-decompose first carbon source gas, thereby reducing the system's energy consumption and temperature fluctuation risks from the inherent characteristics of the carbon source. Furthermore, differentiated pretreatment schemes are designed for different carbon source characteristics to ensure accurate carbon source mixing ratios and stable gas temperatures, laying the foundation for efficient subsequent carbon source decomposition and avoiding carbon source waste and reaction abnormalities caused by uneven gas mixing or insufficient temperature. The system structure for preparing single-walled carbon nanotubes in the embodiments of this application is simple, without complex and precision components, and is compatible with existing methane-based single-walled carbon nanotube production lines, requiring no large-scale modifications, resulting in low system investment costs and minimal difficulty in process scale-up.

[0059] Other configurations of the embodiments of this application, such as ... and ..., and operations, are known to those skilled in the art and will not be described in detail here.

[0060] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0061] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing single-walled carbon nanotubes, characterized in that, The method includes: preheating a first mixed gas and a second mixed gas respectively, and then introducing them into a fluidized bed reactor at 850℃-950℃ through different inlets, where a cracking reaction occurs under the action of a catalyst to generate the single-walled carbon nanotubes; wherein, the first mixed gas consists of a first carbon source gas and a protective gas, and the second mixed gas consists of a second carbon source gas and a protective gas; the first carbon source gas is selected from methane and / or carbon monoxide, and the second carbon source gas is selected from at least one of propylene, propane and ethylene.

2. The method for preparing single-walled carbon nanotubes according to claim 1, characterized in that, The volume ratio of the first carbon source gas to the second carbon source gas is (10-20):

1.

3. The method for preparing single-walled carbon nanotubes according to claim 1, characterized in that, In the first mixed gas, the volume percentage of the first carbon source gas is 20%-50%.

4. The method for preparing single-walled carbon nanotubes according to claim 1, characterized in that, In the second mixture, the volume percentage of the second carbon source gas is 5%-30%.

5. The method for preparing single-walled carbon nanotubes according to claim 1, characterized in that, In the single-walled carbon nanotubes, the proportion of products with a particle size of 1.2nm-1.8nm is greater than 90%.

6. The method for preparing single-walled carbon nanotubes according to claim 1, characterized in that, Before introducing the first mixed gas and the second mixed gas into the fluidized bed reactor, the method further includes: introducing a high-temperature heat source into the fluidized bed reactor to heat the inside of the fluidized bed reactor to 900℃-950℃, and after heating, introducing a reducing gas into the fluidized bed reactor to reduce the catalyst and obtain the reduced catalyst.

7. The method for preparing single-walled carbon nanotubes according to claim 6, characterized in that, The reducing gas includes hydrogen; the volume ratio of the reducing gas to the first carbon source gas is 1:(1-5).

8. The method for preparing single-walled carbon nanotubes according to claim 1, characterized in that, The purity of the first carbon source gas, the second carbon source gas, and the protective gas is ≥99.99%.

9. A system for preparing single-walled carbon nanotubes, characterized in that, The system is applicable to the preparation method of single-walled carbon nanotubes according to any one of claims 1-7. The system includes: a gas preheating device and a fluidized bed reactor; the gas preheating device is connected to the interior of the fluidized bed reactor; the gas preheating device is used to preheat a first mixed gas and a second mixed gas respectively, and to transport the preheated first mixed gas and the second mixed gas to the fluidized bed reactor; the fluidized bed reactor is used to load a catalyst, and to allow the preheated first mixed gas and the second mixed gas to undergo a cracking reaction at 850℃-950℃ to generate the single-walled carbon nanotubes.

10. The preparation system for single-walled carbon nanotubes according to claim 9, characterized in that, The gas preheating device includes: a first gas outlet pipe and a second gas outlet pipe; the first gas outlet pipe is located below the second gas outlet pipe, and the first gas outlet pipe and the second gas outlet pipe are respectively connected to the interior of the fluidized bed reactor; the first gas outlet pipe is used to deliver preheated first mixed gas to the fluidized bed reactor; the second gas outlet pipe is used to deliver preheated second mixed gas to the fluidized bed reactor.

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