Device and Method for Preparing Single-Walled Carbon Nanotubes by a Two-Step Process

Abstract

The present invention discloses an apparatus and a method for preparing single-walled carbon nanotubes by a two-step process. The apparatus includes a carbon nanotube growth chamber, a product collection module, a catalyst supply module, a carbon source supply module, and an etchant supply module; the carbon source supply module is used to introduce a first gas stream containing a carbon source in a first direction, and the etchant supply module is used to introduce a second gas stream containing an etchant in a second direction, and the first direction and the second direction are opposite to each other so that the gas streams intersect to form a vortex; the catalyst supply module introduces catalyst particles in a third direction, and the third direction points to the vicinity of the position where the vortex is located; the product collection module is arranged above the vortex to collect the formed single-walled carbon tubes. The present invention realizes the controllable preparation of catalyst nanoparticles and the orderly separation of the carbon nanotube growth step, reduces the influence of confounding variables on the reaction, the counter-directional intersection of the gas streams forms a vortex, and the vortex avoids the problem of local deposition and blockage of the tangential laminar flow, thereby avoiding the influence on the quality and continuous growth of carbon nanotubes.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of carbon nanomaterials, and in particular to a device and method for preparing single-walled carbon nanotubes in two steps. Background Art

[0002] Single-walled carbon nanotubes are a type of one-dimensional carbon nanomaterial. Structurally, they can be roughly viewed as tubular nanomaterials formed by curling up a single layer of graphene. They have a huge aspect ratio and excellent electrical, mechanical, and thermal properties. Therefore, they can be widely used in a variety of application scenarios such as enhancing electrical properties, enhancing mechanical properties, and photothermal conversion. They are an indispensable type of cutting-edge material in the process of moving towards high-end manufacturing.

[0003] The main methods for preparing single-walled carbon nanotubes include floating catalyst CVD method (FCCVD method, Nanoscale, 2020, 12, 12263), laser ablation method (Science, 1996, 273: 483), high-pressure carbon monoxide method (The Journal of Physical Chemistry B, 2001, 105: 8297-8301), arc method (Nature, 1991, 354: 56), etc. Each technical route has its own advantages and disadvantages. Taking the FCCVD method as an example, although the purity and crystallinity of the prepared single-walled carbon nanotube products are very high, the hourly production capacity of a device still remains at the gram level, and large-scale mass production cannot be achieved. The current difficulties in the large-scale preparation technology of single-walled carbon nanotubes can be summarized as follows: (1) Efficient preparation of catalysts; (2) Efficient conversion of carbon sources; (3) Integration of reaction equipment.

[0004] Having both high crystallinity and high yield is a huge and comprehensive proposition, and the arc method is currently the only technical route that is expected to achieve mass production of single-walled carbon nanotubes. Its core essence is that the growth rate of the catalyst and the cracking rate of the carbon source have been greatly improved thanks to the ultra-high temperature provided by the arc, but disadvantages also come with it. The ultra-high temperature of the arc (greater than 10,000°C) makes it difficult to control the decomposition of the catalyst precursor and the carbon source precursor, so it is difficult to regulate the purity and crystallinity of the generated single-walled carbon nanotube products.

[0005] Therefore, how to achieve large-scale preparation of high-purity and high-crystallinity single-walled carbon nanotubes is a technical problem that needs to be solved urgently. Summary of the invention

[0006] In view of the shortcomings of the prior art, the object of the present invention is to provide a device and method for preparing single-walled carbon nanotubes in two steps.

[0007] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes:

[0008] In a first aspect, the present invention provides an apparatus for preparing single-walled carbon nanotubes by a two-step method, which comprises: a carbon nanotube growth chamber, a product collection module, a catalyst supply module, a carbon source supply module, and an etchant supply module;

[0009] The product collection module, the catalyst supply module, the carbon source supply module, and the etchant supply module are fixedly arranged on the chamber wall of the carbon nanotube growth chamber and communicate with the internal reaction chamber of the carbon nanotube growth chamber;

[0010] The carbon source supply module is used to introduce a first gas stream containing a carbon source into the reaction chamber in a first direction, and the etchant supply module is used to introduce a second gas stream containing an etchant into the reaction chamber in a second direction. The first direction and the second direction are opposite to each other so that the first gas stream and the second gas stream intersect to form a vortex; the catalyst supply module is used to introduce catalyst particles into the reaction chamber in a third direction, and the third direction points to the vicinity of the position where the vortex is located; the product collection module is arranged above the vortex and is used to collect the single-walled carbon nanotubes formed in the vortex.

[0011] In a second aspect, the present invention further provides a method for preparing single-walled carbon nanotubes by a two-step method, which comprises:

[0012] Introducing a first gas stream containing a carbon source into the reaction chamber in a first direction, introducing a second gas stream containing an etchant into the reaction chamber in a second direction, and introducing catalyst particles into the reaction chamber in a third direction. The first direction and the second direction are opposite to each other so that the first gas stream and the second gas stream intersect to form a vortex, and the third direction points to the vicinity of the position where the vortex is located;

[0013] Collecting, above the vortex, the single-walled carbon nanotubes formed in the vortex and driven by the flow field of the vortex.

[0014] Based on the above technical solutions, compared with the prior art, the beneficial effects of the present invention at least include:

[0015] In the preparation apparatus and method provided by the present invention, the catalyst, the carbon source, and the etchant are introduced into the reaction chamber through different channels, avoiding the mutual interference phenomenon that occurs among the three in the early stage of the traditional preparation method, especially avoiding the mutual interference between the carbon source and the catalyst, providing a controllable and stable formation process of catalyst particles, realizing the controllable preparation of catalyst nanoparticles and the orderly separation of the carbon nanotube growth step, and reducing the influence of confounding variables on the reaction; in addition, a vortex is formed by the counter-directional intersection of the carbon source gas stream and the etchant gas stream, and the vortex avoids the problem of local siltation and blockage of the tangential laminar flow, thus avoiding the influence on the quality and continuous growth of carbon nanotubes, and finally realizing the mass preparation of high-purity and high-crystallinity single-walled carbon nanotubes.

[0016] The above description is only an overview of the technical solution of the present invention. In order to enable those skilled in the art to more clearly understand the technical means of the present application and implement it in accordance with the content of the specification, the following will describe the preferred embodiments of the present invention in conjunction with the detailed drawings as follows. Description of the Drawings

[0017] Figure 1 Schematic structural diagram of the device for preparing single-walled carbon nanotubes by a two-step method provided for a typical embodiment of the present invention;

[0018] Figure 2 Scanning electron microscope photograph of the product obtained in a typical embodiment of the present invention;

[0019] Figure 3 Transmission electron microscope photograph of the product obtained in a typical embodiment of the present invention;

[0020] Figure 4 Raman spectrum test chart of the product obtained in a typical embodiment of the present invention;

[0021] Figure 5 Thermogravimetric test chart of the product obtained in a typical comparative case of the present invention;

[0022] Figure 6 Thermogravimetric test chart of the product obtained in a typical comparative case of the present invention;

[0023] Figure 7 Raman spectrum test chart of the product obtained in a typical comparative case of the present invention;

[0024] Figure 8 Raman spectrum test chart of the product obtained in a typical comparative case of the present invention;

[0025] Figure 9 Thermogravimetric test chart of the product obtained in a typical comparative case of the present invention.

[0026] Description of the reference numerals: 1. Inductive plasma unit; 2. Catalyst growth unit; 3. Carbon source supply module; 4. Etchant supply module; 5. Carbon nanotube growth chamber; 6. Material outlet channel; 7. Product collection module. Detailed Embodiments

[0027] In view of the deficiencies in the prior art, the inventors of this case have proposed the technical solution of the present invention through long-term research and a large number of practices. The following will further explain the technical solution, its implementation process, principle, etc.

[0028] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be practiced in other ways than those described herein, and thus, the scope of protection of the present invention is not limited by the specific embodiments disclosed below.

[0029] Moreover, relative terms such as "first" and "second" are only used to distinguish one component or method step with the same name from another, and do not necessarily require or imply any actual relationship or order between these components or method steps.

[0030] An embodiment of the present invention provides a device for preparing single-walled carbon nanotubes by a two-step method, which includes: a carbon nanotube growth chamber, a product collection module, a catalyst supply module, a carbon source supply module, and an etchant supply module; the product collection module, the catalyst supply module, the carbon source supply module, and the etchant supply module are fixedly arranged on the cavity wall of the carbon nanotube growth chamber and communicate with the internal reaction chamber of the carbon nanotube growth chamber; the carbon source supply module is used to introduce a first gas stream containing a carbon source into the reaction chamber in a first direction, the etchant supply module is used to introduce a second gas stream containing an etchant into the reaction chamber in a second direction, and the first direction and the second direction are opposite to make the first gas stream and the second gas stream meet to form a vortex; the catalyst supply module is used to introduce catalyst particles into the reaction chamber in a third direction, and the third direction points to the vicinity of the position where the vortex is located; the product collection module is arranged above the vortex and is used to collect the single-walled carbon nanotubes formed in the vortex.

[0031] The present invention adopts a two-step method. The first step is to use an inductively coupled plasma torch as a high-temperature source to form catalyst particles. For example, a catalyst precursor and an inhibitor are rapidly evaporated, cracked, and formed into extremely fine nanoparticles at the high temperature of the plasma. The second step is to introduce a carbon source and an etchant into another cavity so that they meet the catalyst particles, complete the growth of carbon nanotubes, and are rapidly discharged along with the vortex gas stream.

[0032] Generally, the prior art often adopts a one-step method. For example, some prior art also proposes technical solutions for preparing single-walled carbon nanotubes by using plasma to form catalyst particles. However, in these prior arts, the formation of catalyst particles and the growth of carbon nanotubes are often completed in the same spatial region. The inventor finds that this is not conducive to the control of microscopic variables and cannot achieve the purpose of mass preparation with high purity and high crystallinity.

[0033] In terms of the preparation principle of carbon nanotubes, the sequence is as follows: (1) First, catalyst particles with appropriate sizes are formed; (2) Secondly, the catalyst particles come into contact with the carbon source, and then the growth of carbon nanotubes occurs. It can be seen that, regardless of the method, its core should conform to the above principle. However, the difficulty in the preparation of single-walled carbon nanotubes currently lies precisely in how to control the uniform preparation of catalyst particles and under what conditions they come into contact with the carbon source.

[0034] Therefore, from the perspective of controlling variables, the disadvantage of the one-step method is that there are too many variables in the same spatial region, making it difficult to achieve the preparation of high-quality single-walled carbon nanotubes. The advantage of the two-step method of the present invention is that the preparation of the catalyst and the growth of carbon nanotubes are separated, making it easier to regulate the variables and thus achieve the preparation of high-quality carbon nanotubes. The differences in the effects of different growth modes are mainly reflected in the regulation of nano-catalyst particles. It is worth noting that nano-scale catalyst particles are the core key to the preparation of high-quality single-walled carbon nanotubes.

[0035] Thanks to the two-step design, the present invention can regulate a series of parameters in the first step and preferentially and controllably adjust the size distribution and components of the catalyst particles, which can be learned from the size distribution of the catalyst. The one-step method concentrates the preparation of the catalyst, the cracking of the carbon source, and the growth of carbon nanotubes in a single chamber. The processes such as the formation of catalyst particles and the decomposition of the carbon source interfere with each other, and the size distribution of the catalyst particles will show a disordered state. The variable parameters involved far exceed those of the present invention, and it is very difficult to repeat and scale up during pilot or mass production tests.

[0036] In addition, the preparation processes proposed in many existing technologies introduce the etchant unidirectionally and in the same direction (i.e., the flow direction of the etchant is the same as that of the carbon source or the two converge in the same direction). At the microscopic level, there are also obvious differences from the present invention, specifically reflected in: (1) The counter-directional introduction of the carbon source gas flow and the etchant gas flow can reduce the pre-contact and pre-reaction of the etchant with the reactants and avoid interfering with the decomposition process of the carbon source; (2) In terms of the step where the etchant takes effect, it occurs after the carbon source contacts and reacts with the catalyst. Therefore, from the perspective of controlling variables, introducing the etchant in a counter-directional and separated form is conducive to maintaining the activity of the catalyst particles; (3) The counter-flow gas contact is more likely to form eddy currents, which are very important for improving the quality and preparation continuity of carbon nanotubes. The existing unidirectional tangential gas flow in the furnace body will have a weak gas flow region, which is not conducive to the formation of eddy currents, resulting in local accumulation and blockage of carbon nanotubes, ultimately affecting the quality and continuous discharging of carbon nanotubes. Therefore, the counter-directional design is also one of the core designs of the present invention.

[0037] Regarding some specific structural features related to the airflow field, in some embodiments, the carbon source supply module is disposed on one side of the carbon nanotube growth chamber, the etchant supply module is disposed on the opposite side of the carbon nanotube growth chamber, and both the first direction and the second direction are horizontally arranged and both point to the center of the eddy current.

[0038] In some embodiments, the carbon nanotube growth chamber is further provided with a heating unit for adjusting the temperature in the reaction chamber. Directly below the product collection module, a vertically upward flow field is formed under the thermal influence of the eddy current.

[0039] In the above solution, the horizontally opposed arrangement is relatively important for forming a stable and centered eddy current. Under the action of the horizontally opposed airflow and heat, the central flow field of the eddy current will point to the product collection module, which is helpful for improving the product quality and preparation efficiency.

[0040] In addition, regarding the supply of the catalyst, in some embodiments, the catalyst supply module includes a cooperatively arranged inductively coupled plasma unit, a catalyst precursor delivery unit, and a catalyst growth unit. The inductively coupled plasma unit is used to form a plasma torch. The catalyst precursor delivery unit is used to deliver a catalyst precursor and a polymerization inhibitor to the plasma torch. The catalyst growth unit is used to form catalyst particles from the catalyst precursor and the polymerization inhibitor under the action of the plasma torch. The catalyst particles enter the reaction chamber under the drive of a third airflow.

[0041] In some embodiments, the catalyst supply module is disposed on the top of the carbon nanotube growth chamber and is biased towards the carbon source supply module side, and the third direction forms an angle less than 90° with the first direction.

[0042] Regarding the collection of products, in some embodiments, the product collection module includes a material outlet channel and a product collection module disposed at the top end of the chamber wall of the carbon nanotube growth chamber. The single-walled carbon nanotubes formed in the eddy current enter the material outlet channel under the drive of the flow field. The product collection module collects the single-walled carbon nanotubes and discharges the tail gas.

[0043] As some typical examples of the above technical solutions, in the actual process, the device may include three chambers: a catalyst formation chamber, a carbon nanotube growth chamber, and a product collection chamber. Among them, the catalyst formation chamber includes an inductively coupled plasma unit, a catalyst precursor delivery unit, and a catalyst growth unit; the carbon nanotube growth chamber includes an opposed airflow channel for forming an eddy current, an electric heating unit, a carbon source supply module, an etchant supply module, and a material outlet channel; the product collection chamber includes a gas-solid separation device and a tail gas treatment device.

[0044] The second aspect of the embodiments of the present invention also provides a method for preparing single-walled carbon nanotubes by a two-step process, which includes the following steps:

[0045] Introduce a first gas stream containing a carbon source into the reaction chamber in a first direction, introduce a second gas stream containing an etchant into the reaction chamber in a second direction, and introduce catalyst particles into the reaction chamber in a third direction. The first direction and the second direction are opposite to each other so that the first gas stream and the second gas stream intersect to form a vortex, and the third direction points to the vicinity of the position where the vortex is located;

[0046] Collect single-walled carbon nanotubes formed in the vortex and driven by the flow field of the vortex above the vortex.

[0047] As some typical examples, the specific process flow of the above method is as follows: The first step is to use an inductively coupled plasma torch flame as a high-temperature heat source. The catalyst precursor and the polymerization inhibitor are rapidly evaporated, cracked, and formed into extremely fine nanoparticles at high temperature. The formed nanoparticles enter the growth chamber under the action of the gas stream. The second step is to introduce a carbon source and an etchant into the growth chamber, control the reaction temperature, complete the cracking of the carbon source on the surface of the catalyst nanoparticles and the growth of carbon nanotubes, and enter the collection device upward along with the gas stream outlet, finally realizing the batch preparation of high-quality single-walled carbon nanotubes.

[0048] For a more detailed device and process, reference can be made to Figure 1 As shown, the figure shows a device for preparing single-walled carbon nanotubes by a two-step process. The device includes an inductively coupled plasma unit 1, a catalyst growth unit 2, a carbon source supply module 3, an etchant supply module 4, a carbon nanotube growth chamber 5, a material outlet channel 6, and a product collection unit 7.

[0049] The catalyst precursor and the polymerization inhibitor precursor enter the catalyst growth unit 2 through the inductively coupled plasma unit 1. Under the action of high temperature and the polymerization inhibitor, the catalyst precursor is evaporated, cracked, and re-nucleated into nanoparticles with a size less than 10 nm, and enters the carbon nanotube growth chamber 5 along with the carrier gas. Then, the carbon source enters the carbon nanotube growth chamber 5 along with the carrier gas through the carbon source supply module 3, and the etchant enters the carbon nanotube growth chamber 5 along with the carrier gas through the etchant supply module 4 to form a vortex, and the cracking, carburization, carbon precipitation, and carbon tube growth of the carbon source are completed on the surface of the catalyst nanoparticles. Then, the product enters the material outlet channel 6 upward along the vortex outlet direction and finally enters the product collection unit 7.

[0050] And the process steps in actual operation are, for example:

[0051] a. Exclude the air in the reaction system, continuously introduce an inert gas, adjust the input power of the inductively coupled plasma torch and start it, and at the same time set the temperature of the carbon tube growth chamber and start it to make the catalyst formation chamber and the carbon tube growth chamber reach the required reaction temperature;

[0052] b. A mixture of a catalyst precursor and a polymerization inhibitor is introduced at the inlet of the inductively coupled plasma torch, so that the catalyst precursor is completely evaporated and further grows to the nanoscale. The nanoparticles enter the carbon nanotube growth chamber under the action of an inert gas flow.

[0053] c. A mixed gas flow of a carbon source and a carrier gas is quantitatively introduced on one side of the carbon nanotube growth chamber, and a mixed gas flow of an etchant and a carrier gas is quantitatively introduced on the other side, forming a vortex in the second chamber. After the vortex contacts the catalyst particles, the carbon source is cracked on the surface of the catalyst particles and the carbon nanotubes grow.

[0054] d. Driven by the upward vortex gas flow, the generated carbon nanotube products enter the collection system.

[0055] Regarding the specific details in the above method, in some embodiments, the carbon source includes any one or a combination of two or more of methanol, ethanol, toluene, acetone, ethylene, propylene, methane, ethane, carbon monoxide, but is not limited thereto.

[0056] In some embodiments, the carrier gas of the first gas flow and / or the second gas flow includes any one or a combination of two or more of argon, helium, and nitrogen, but is not limited thereto.

[0057] In some embodiments, the etchant includes any one or a combination of two or more of water, hydrogen, and carbon dioxide, but is not limited thereto.

[0058] In some embodiments, the volume ratio of the carbon source to the carrier gas in the first gas flow is 1:0 to 100, and the volume ratio of the etchant to the carrier gas in the second gas flow is 1:0 to 100.

[0059] In some embodiments, the flow rate ratio of the first gas flow and the second gas flow ranges from 0.01 - 1:1. The flow rate ratio of the first gas flow and the second gas flow has a certain influence on the formation of the vortex. Generally, the ratio between the two is about 0.5 - 1:1, but even in the range of 0.01:1, the effect of forming a vortex can be achieved.

[0060] In some embodiments, the catalyst particles are formed from a catalyst precursor and a polymerization inhibitor under the action of an inductively coupled plasma torch, and the temperature of the inductively coupled plasma torch is 3000 - 30000 °C.

[0061] In some embodiments, the temperature in the reaction chamber is 800 - 1500 °C;

[0062] In some embodiments, the catalyst precursor includes any one or a combination of two or more of ferrocene, ferrous chloride, ferric chloride, ferric sulfate, iron, iron oxide, cobalt, cobalt chloride, cobalt sulfate, nickel, nickel chloride, and nickel sulfate; the polymerization inhibitor includes any one or a combination of two or more of thiophene, dimethyl sulfoxide, thiourea, sulfur, sodium sulfate, sodium sulfide, and iron sulfide, but is not limited thereto.

[0063] In some embodiments, the polymerization inhibitor includes any one or a combination of two or more of thiophene, dimethyl sulfoxide, thiourea, sulfur, sodium sulfate, sodium sulfide, and iron sulfide, but is not limited thereto.

[0064] In some embodiments, the molar ratio of the catalyst precursor to the polymerization inhibitor is 1:0.001 - 5.

[0065] In some embodiments, the product purity of the single-walled carbon nanotubes prepared by the method can reach 70 - 85%, the G / D ratio is greater than 30, the yield can reach 1 - 10 kg / day, continuous batch processing can be achieved, and it has important commercial application value.

[0066] It should be noted that the above specific technical details are some exemplary details for the implementation of the preparation of single-walled carbon nanotubes in the present invention, which mainly serve as a reference for those skilled in the art. It does not mean that the scope that can be implemented based on the core idea of the present invention is limited thereto. Devices designed based on the key concept of the present invention or methods adopted belong to the feasible scope, and the specific reaction materials and conditions therein can refer to the precedents of single-walled carbon nanotube growth mentioned in many existing technologies or develop new reaction raw materials and conditions by oneself.

[0067] The above technical solution provides ultra-high energy for the preparation of the nanocatalyst by the inductively coupled plasma arc method, greatly improving the decomposition efficiency of the catalyst precursor; by using the two-step process to separate the preparation process of the catalyst nanoparticles from the carbon nanotube growth process, the controllable preparation of the catalyst nanoparticles and the orderly separation of the carbon nanotube growth steps are realized, reducing the influence of confounding variables on the reaction; by designing and optimizing the reaction chamber and the gas flow rate, the residence time of the catalyst and the cracking efficiency of the carbon source are effectively controlled; by introducing a vortex in the carbon nanotube growth chamber, the flow field outlet direction of the vortex is uniform, enabling the carbon nanotube products to be discharged from the reaction chamber in a timely manner and realizing long-term continuous preparation.

[0068] The technical solution of the present invention will be further described in detail below through several examples in combination with the accompanying drawings. However, the selected examples are only used to illustrate the present invention and do not limit the scope of the present invention.

[0069] Example 1

[0070] This example exemplifies a process for preparing single-walled carbon nanotubes by a two-step method, which includes:

[0071] Step 1: Evacuate the air in the reaction system through a vacuum pump and fill it with helium. Start the induction plasma device to strike an arc, and at the same time, turn on the electric heating device of the carbon nanotube growth chamber, and set the temperature to 1200 °C.

[0072] Step 2: After reaching the set temperature, ferrocene (20 g / min) and thiophene (5 g / min) are introduced at the inlet of the induction plasma unit. Ferrocene and thiophene are completely evaporated and cracked, and then further grow to the nanoscale. The nanoparticles enter the carbon nanotube growth chamber under the action of an inert gas flow.

[0073] Step 3: Input a mixture of propylene (40 L / min) and helium (200 L / min) through the carbon source supply module, and input a mixture of hydrogen (40 L / min) and helium (200 L / min) through the etchant supply module to form a vortex in the carbon nanotube growth chamber. With the introduction of the carbon source, under the action of the catalyst, black carbon tube products are instantly generated.

[0074] Step 4: Subsequently, the product enters the product collector through the material outlet, and the gas is discharged after passing through the tail gas treatment device.

[0075] After the reaction is completed, an appropriate amount of sample is taken for characterization. The microscopic morphology, size, crystallinity, and carbon content of the single-walled carbon nanotubes are measured by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and thermogravimetry respectively. For the specific characterization methods, refer to GB / T 32869-2016, GB / T 30534-2014, GB / T 32871-2016, and GB / T 24490-2009.

[0076] The characterization results are as Figures 2-5 shown. The thermogravimetric characterization results show that the as-prepared single-walled carbon nanotube primary product has a carbon content of ~78 wt%. In the Raman spectrum ( Figure 4 ), sharp graphite peaks (G band), extremely small disorder peaks (D band), and highly obvious radial breathing mode characteristic peaks (RBM) can be shown at the wavelength ranges of 1570 cm -1 , 1350 cm -1 , and 0 - 200 cm -1 respectively. The G / D ratio is 52.2, indicating a high crystallinity of the carbon tubes. In the high-resolution transmission electron microscopy characterization results ( Figure 3 ), the size of the catalyst particles can be seen to be 3 - 5 nm.

[0077] Comparative Example 1

[0078] This comparative example is generally the same as Example 1, and the main difference is that:

[0079] Turn off the etchant supply module. A mixture of hydrogen (40 L / min) and helium (200 L / mm) is mixed with the original carbon source gas flow (propylene (40 L / min) and helium (200 L / min)) and injected into the reaction chamber together through the channels of the original carbon source supply module.

[0080] All other reaction conditions and reaction materials are the same as those in Example 1.

[0081] In this comparative example, since the etchant and the carbon source are introduced in a co-current and confluent manner, the etchant can act at the initial stage of the carbon source cracking reaction, interfering with the formation process of carbon nanotubes. Moreover, this co-directional gas flow is difficult to form a vortex, resulting in stagnation in some corners of the reaction chamber. The stagnant substances diffuse everywhere, which also affects the formation process of carbon nanotubes. And the stagnant substances themselves are also a kind of impurity. Therefore, the obtained products cannot be discharged in time, blocking the reaction chamber in large quantities, thus leading to the inability to carry out continuous production.

[0082] Comparative Example 2

[0083] This comparative example is generally the same as Example 1, and the main difference lies in:

[0084] The inductively coupled plasma coil of the catalyst supply module is arranged outside the pipeline of the carbon source supply module, and the catalyst, inhibitor and the corresponding inert gas are mixed with the carbon source gas flow and then passed through this inductively coupled plasma coil and then introduced into the reaction chamber.

[0085] All other reaction conditions and reaction materials are the same as those in Example 1.

[0086] In this comparative example, since the formation process of catalyst particles is mixed with the carbon source too early, the growth of catalyst particles is interfered, and the number of influencing variables increases sharply, making it difficult to control stably. Therefore, the G / D ratio and purity of the obtained products are significantly lower. The results are as Figure 6 、 Figure 7 shown. The G / D ratio is only about 10, and the TG residue reaches 112%, far from meeting the industrialization requirements.

[0087] Comparative Example 3

[0088] This comparative example is generally the same as Example 1, and the main difference lies in:

[0089] The catalyst supply module is arranged on one side closer to the etchant supply module and still points it near the position where the vortex is formed (i.e., below the material outlet).

[0090] All other reaction conditions and reaction materials are the same as those in Example 1.

[0091] In this comparative example, since the catalyst particles encounter the etchant first and then the carbon source, the action of the etchant does not occur after the contact reaction between the carbon source and the catalyst particles. Therefore, both the G / D ratio and the purity of the obtained product decrease, as Figure 8 、 Figure 9 shown, but the product can still be discharged continuously.

[0092] Example 2

[0093] An apparatus and method for preparing single-walled carbon nanotubes by a two-step method, comprising:

[0094] Step 1: Evacuate the air in the reaction system through a vacuum pump and fill it with argon. Start the induction plasma device to strike an arc, and at the same time turn on the electric heating device of the carbon nanotube growth chamber, and set the temperature to 1500 °C.

[0095] Step 2: After reaching the set temperature, feed cobalt powder (20 g / min), iron powder (20 g / min), and thiourea (5 g / min) at the inlet of the induction plasma unit. The cobalt powder, iron powder, and thiourea are completely evaporated and cracked, and then further grow to the nanoscale. The nanoparticles enter the carbon tube growth chamber under the action of an inert gas stream.

[0096] Step 3: Input a mixture of methane (50 L / min) and argon (400 L / min) through the carbon source supply module, and input a mixture of water (10 L / min) and helium (500 L / min) through the etchant supply module to form a vortex in the carbon nanotube growth chamber. With the introduction of the carbon source, black carbon tube products are instantly generated under the action of the catalyst.

[0097] Step 4: Subsequently, the product enters the product collector through the material outlet, and the gas is discharged after passing through the tail gas treatment device.

[0098] The obtained product is similar to that of Example 1, having the characteristics of high purity and high crystallinity, and also having excellent stability during continuous batch preparation.

[0099] Example 3

[0100] An apparatus and method for preparing single-walled carbon nanotubes by a two-step method, comprising:

[0101] Step 1: Evacuate the air in the reaction system through a vacuum pump and fill it with nitrogen. Start the induction plasma device to strike an arc, and at the same time turn on the electric heating device of the carbon nanotube growth chamber, and set the temperature to 1000 °C.

[0102] Step 2: After reaching the set temperature, nickel powder (10 g / min), ferrocene (30 g / min), and thiourea (10 g / min) are introduced at the entrance of the inductively coupled plasma unit. The nickel powder, ferrocene, and thiourea are completely evaporated and cracked, and then further grow to the nanoscale. The nanoparticles enter the carbon nanotube growth chamber under the action of an inert gas flow.

[0103] Step 3: A mixture of ethanol (0.1 L / min) and nitrogen (300 L / min) is input through the carbon source supply module, and a mixture of hydrogen (20 L / min), water (0.05 L / min), and nitrogen (400 L / min) is input through the etchant supply module to form a vortex in the carbon nanotube growth chamber. With the introduction of the carbon source, black carbon nanotube products are instantaneously generated under the action of the catalyst.

[0104] Step 4: Subsequently, the product enters the product collector through the material outlet, and the gas is discharged after passing through the tail gas treatment device.

[0105] The obtained product is similar to that of Example 1, having the characteristics of high purity and high crystallinity, and also having excellent stability during continuous batch preparation.

[0106] Example 4

[0107] An apparatus and method for preparing single-walled carbon nanotubes by a two-step method, comprising:

[0108] Step 1: The air in the reaction system is evacuated by a vacuum pump and filled with argon. The inductively coupled plasma device is started to strike an arc, and at the same time, the electric heating device of the carbon nanotube growth chamber is turned on, and the temperature is set to 1400 °C.

[0109] Step 2: After reaching the set temperature, iron oxide (20 g / min) and thiophene (10 g / min) are introduced at the entrance of the inductively coupled plasma unit. The iron oxide and thiophene are completely evaporated and cracked, and then further grow to the nanoscale. The nanoparticles enter the carbon nanotube growth chamber under the action of an inert gas flow.

[0110] Step 3: A mixture of methane (40 L / min) and argon (200 L / min) is input through the carbon source supply module, and a mixture of hydrogen (40 L / min), water (0.01 L / min), and argon (200 L / min) is input through the etchant supply module to form a vortex in the carbon nanotube growth chamber. With the introduction of the carbon source, black carbon nanotube products are instantaneously generated under the action of the catalyst.

[0111] Step 4: Subsequently, the product enters the product collector through the material outlet, and the gas is discharged after passing through the tail gas treatment device.

[0112] The obtained product is similar to that of Example 1, with the characteristics of high purity and high crystallinity, and also has excellent stability during continuous batch preparation.

[0113] Based on the above examples and comparative examples, it can be clearly seen that the preparation device and method provided by the present invention avoid the mutual interference phenomenon that occurs among the catalyst, carbon source, and etchant in the early stage of the reaction by introducing them into the reaction chamber through different channels. In particular, the mutual interference between the carbon source and the catalyst is avoided, providing a controllable and stable formation process of catalyst particles, realizing the orderly separation of the controllable preparation of catalyst nanoparticles and the growth step of carbon nanotubes, and reducing the influence of confounding variables on the reaction. In addition, a vortex is formed by the counter-directional intersection of the carbon source gas flow and the etchant gas flow, which avoids the problem of local deposition and blockage of the tangential laminar flow, thus avoiding the influence on the quality and continuous growth of carbon nanotubes, and finally realizing the large-scale preparation of single-walled carbon nanotubes with high purity and high crystallinity.

[0114] It should be understood that the above examples are only used to illustrate the technical concept and characteristics of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. It is not intended to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A two-step method for preparing single-walled carbon nanotubes, characterized in that: include: A carbon nanotube growth chamber, a product collection module, a catalyst supply module, a carbon source supply module, and an etchant supply module; The product collection module, catalyst supply module, carbon source supply module and etchant supply module are fixedly mounted on the cavity wall of the carbon nanotube growth chamber and are in communication with the internal reaction chamber of the carbon nanotube growth chamber; The carbon source supply module is used to pass a first gas flow containing a carbon source into the reaction chamber in a first direction, and the etchant supply module is used to pass a second gas flow containing an etchant into the reaction chamber in a second direction, and the first direction and the second direction are opposite to each other so that the first gas flow and the second gas flow converge to form a vortex; the catalyst supply module is used to pass catalyst particles into the reaction chamber in a third direction, and the third direction points to the vicinity of the position of the vortex; the product collection module is arranged above the vortex, and is used to collect single-walled carbon nanotubes formed in the vortex.

2. The device according to claim 1, characterized in that The carbon source supply module is disposed on one side of the carbon nanotube growth chamber, the etchant supply module is disposed on the other side opposite to the carbon nanotube growth chamber, and the first direction and the second direction are both disposed horizontally and both point to the center of the vortex.

3. The device according to claim 2, characterized in that The carbon nanotube growth chamber is also provided with a heating unit for adjusting the temperature in the reaction chamber. Directly below the product collection module, the vortex forms a vertically upward flow field under the influence of heat.

4. The device according to claim 1, characterized in that The catalyst supply module includes an induction plasma unit, a catalyst precursor delivery unit and a catalyst growth unit that are arranged in coordination. The induction plasma unit is used to form a plasma torch. The catalyst precursor delivery unit is used to deliver catalyst precursors and inhibitors to the plasma torch. The catalyst growth unit is used to form catalyst particles from the catalyst precursors and inhibitors under the action of the plasma torch. The catalyst particles enter the reaction chamber driven by a third gas flow.

5. The device according to claim 1 or 4, characterized in that: The catalyst supply module is disposed on the top of the carbon nanotube growth chamber and is biased toward one side of the carbon source supply module. The third direction forms an angle less than 90° with the first direction.

6. The device according to claim 1, characterized in that The product collection module includes a material outlet channel and a product collection module arranged at the top of the cavity wall of the carbon nanotube growth chamber. The single-walled carbon nanotubes formed in the vortex enter the material outlet channel driven by the flow field. The product collection module collects the single-walled carbon nanotubes and discharges the tail gas.

7. A two-step method for preparing single-walled carbon nanotubes, characterized in that: include: A first gas flow containing a carbon source is introduced into a reaction chamber in a first direction, a second gas flow containing an etchant is introduced into the reaction chamber in a second direction, and catalyst particles are introduced into the reaction chamber in a third direction, wherein the first direction and the second direction are opposite to each other so that the first gas flow and the second gas flow meet to form a vortex, and the third direction points to the vicinity of the location of the vortex; The single-walled carbon nanotubes formed in the vortex and carried by the flow field of the vortex are collected above the vortex.

8. The method according to claim 7, characterized in that The carbon source includes any one or a combination of two or more of methanol, ethanol, toluene, acetone, ethylene, propylene, methane, ethane, and carbon monoxide; and / or, the carrier gas of the first gas flow and / or the second gas flow comprises any one of argon, helium, and nitrogen, or a combination of two or more thereof; And / or, the etchant includes any one of water, hydrogen, and carbon dioxide, or a combination of two or more thereof; and / or, the volume ratio of the carbon source to the carrier gas in the first gas flow is 1:0-100, and the volume ratio of the etchant to the carrier gas in the second gas flow is 1:0-100; And / or, the flow ratio of the first airflow to the second airflow is 0.01-1:

1.

9. The method according to claim 7, characterized in that: The catalyst particles are formed by a catalyst precursor and an inhibitor under the action of a plasma torch, and the temperature of the plasma torch is 3000-30000°C; And / or, the temperature in the reaction chamber is 800-1500°C.

10. The method according to claim 9, characterized in that The catalyst precursor includes any one or a combination of two or more of ferrocene, ferrous chloride, ferric chloride, ferric sulfate, iron, ferric oxide, cobalt, cobalt chloride, cobalt sulfate, nickel, nickel chloride, and nickel sulfate; the inhibitor includes any one or a combination of two or more of thiophene, dimethyl sulfoxide, thiourea, sulfur, sodium sulfate, sodium sulfide, and iron sulfide; And / or, the polymerization inhibitor includes any one or a combination of two or more of thiophene, dimethyl sulfoxide, thiourea, sulfur, sodium sulfate, sodium sulfide, and iron sulfide; And / or, the molar ratio of the catalyst precursor to the polymerization inhibitor is 1:0.001-5.

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