Synthesis methods of carbon nanotubes

Abstract

This invention relates to a method for synthesizing carbon nanotubes using a nanoparticle catalyst prepared by vaporizing a catalyst feedstock using plasma and then condensing the vaporized catalyst feedstock. The manufacturing method of this invention can produce carbon nanotubes with high crystallinity and is beneficial for large-scale synthesis.

Description

Technical Field

[0001] This invention relates to a method for manufacturing carbon nanotubes, which can efficiently produce high-quality carbon nanotubes in a short time using a CVD reactor and a nanoparticle catalyst prepared using plasma. Background Technology

[0002] Carbon nanotubes are cylindrical nanostructures composed of a single atom-thick layer of graphene rolled up. They are classified into single-walled carbon nanotubes and multi-walled carbon nanotubes based on the number of shell layers. Generally, carbon nanotubes have diameters ranging from several nm to tens of nm, and lengths that are tens to thousands of times their diameter. Furthermore, based on their chirality index (a value representing the tube's diameter and winding angle as an integer (n, m)), carbon nanotubes can be metallic or semiconductor. Single-walled carbon nanotubes are typically arranged in "bundles," where multiple strands are held together by van der Waals forces. Meanwhile, multi-walled carbon nanotubes consist of multiple shells, each with a different diameter and chirality index. Additionally, multi-walled carbon nanotubes exhibit numerous defects in their crystal structure (sp... 3 C, voids, etc., thus the mechanical properties are relatively weak.

[0003] Compared to traditional materials, carbon nanotubes exhibit high electrical and thermal conductivity, as well as excellent strength, making them effective for various applications such as energy, nanotechnology, optics, and materials engineering. For example, carbon nanotubes possess high elasticity (approximately several thousand GPa) and high mechanical strength (approximately tens of GPa).

[0004] In applications, carbon nanotubes can be used as conductive agents in the positive and negative electrodes of lithium-ion batteries, representing a novel electrode material. Due to their excellent strength, conductivity, and low density, carbon nanotubes can improve battery life and capacity during charge and discharge compared to traditional carbon black conductive agents. In particular, when single-walled carbon nanotubes are used in silicon anodes, even at a dosage only 1 / 10 that of multi-walled carbon nanotubes, they still exhibit a significant improvement in battery life.

[0005] Various studies are also underway regarding manufacturing methods for industrial applications of carbon nanotubes. Traditionally, arc discharge, laser deposition, and chemical vapor deposition are known methods for synthesizing carbon nanotubes. Arc discharge is a method for manufacturing carbon nanotubes by initiating an arc discharge between carbon rods at sub-atmospheric pressure in an argon or hydrogen atmosphere. For example, Ni-Y catalysts can be used to produce single-walled carbon nanotubes with high purity, high crystallinity, and uniform diameter. The advantage of arc discharge is that it can produce high-quality carbon nanotubes with few defects, but the disadvantage is that it also produces amorphous carbon, making it unsuitable for large-scale synthesis.

[0006] Laser deposition is a method for manufacturing carbon nanotubes by emitting intense pulses of light, such as lasers, onto a carbon target mixed with metal catalysts like nickel and cobalt in a high-temperature atmosphere above 900°C. The advantages of laser deposition are that it can produce high-purity carbon nanotubes, and the diameter of the carbon nanotubes can be adjusted to some extent by changing the conditions of the emitted pulses. However, it also has disadvantages, as it is not suitable for large-scale production due to the need for economies of scale.

[0007] Chemical vapor deposition (CVD) is the most commonly used method in industrial applications because it allows for large-scale synthesis. Types of CVD include fluidized bed CVD (FBCVD) and floating catalyst CVD (FCCVD). CVD is a method for producing carbon nanotubes in the gas phase by reacting a catalyst with a reaction gas, including a source gas, a reducing gas, and a carrier gas, at high temperatures. Specifically, the carbon source gas is decomposed by the nanoparticle catalyst, thereby forming solid carbon nanotubes on the surface of the liquid nanoparticle catalyst. As a concrete example, single-walled carbon nanotubes can be synthesized at 500°C to 900°C using a Fe:Mo catalyst supported on silica and methane (CH4) as raw materials. However, large-scale synthesis of single-walled carbon nanotubes using supported catalysts or catalyst precursors is limited in terms of productivity and yield.

[0008] Therefore, there is a need to investigate a new method that can overcome the limitations of existing methods for synthesizing carbon nanotubes and is economical and consistent for large-scale synthesis of high-quality carbon nanotubes.

[0009] Existing technical documents

[0010] (Patent Document 1) US 8048396 B2

[0011] (Patent Document 2) KR 10-2012-0112918 A Summary of the Invention

[0012] Technical issues

[0013] One aspect of the present invention provides a novel physicochemical manufacturing method for synthesizing high-quality carbon nanotubes with excellent purity and crystallinity.

[0014] Technical solution

[0015] To overcome the above limitations, the present invention provides a method for preparing carbon nanotubes.

[0016] Specifically, (1) according to one aspect of the present invention, a method for manufacturing carbon nanotubes is provided, the method comprising: a step of gasifying a catalyst raw material using a plasma torch to form a catalyst vapor (S1); a step of transferring the catalyst vapor to a quenching zone by a plasma flow (S2); a step of condensing the catalyst vapor in the quenching zone to prepare a nanoparticle catalyst (S3); a step of introducing the prepared nanoparticle catalyst and a source gas into a CVD reactor respectively (S4); and a step of synthesizing carbon nanotubes in the CVD reactor (S5).

[0017] (2) In the above (1) of the present invention, a method for manufacturing the carbon nanotubes is provided, wherein the average particle size of the nanoparticle catalyst is less than 100 nm.

[0018] (3) In (1) or (2) above, the present invention provides a method for manufacturing the carbon nanotubes, wherein the plasma torch is an inductively coupled RF thermal plasma torch.

[0019] (4) In any of (1) to (3) above, a method for manufacturing the carbon nanotubes is provided, wherein the catalyst raw material comprises at least one metal or a precursor thereof selected from the group consisting of Fe, Co, Ni, Pd, Pt, Ru, Cu, Mn, Cr, Mo, V, Mg, Si, Ge and Eu.

[0020] (5) In any of the above (1) to (4) of the present invention, a method for manufacturing the carbon nanotubes is provided, wherein the catalyst raw material further comprises sulfur or a sulfide of at least one metal selected from the group consisting of Fe, Co, Ni, Pd, Pt, Ru, Cu, Mn, Cr, Mo, V, Mg, Si, Ge and Eu.

[0021] (6) In any of (1) to (5) of the present invention, a method for manufacturing the carbon nanotubes is provided, wherein the catalyst raw material is in liquid or solid form.

[0022] (7) In any of (1) to (6) of the present invention, a method for manufacturing the carbon nanotubes is provided, wherein the catalyst raw material is in powder form with an average particle size of 5 μm to 100 μm.

[0023] (8) In any of (1) to (7) of the present invention, a method for manufacturing the carbon nanotubes is provided, wherein the quenching zone includes a first quenching zone and a second quenching zone, and the catalyst vapor flows from the first quenching zone to the second quenching zone.

[0024] (9) In any of (1) to (8) of the present invention, a method for manufacturing the carbon nanotubes is provided, wherein an inert gas is injected into the first quench zone and the second quench zone.

[0025] (10) In any of (1) to (9) of the present invention, a method for manufacturing the carbon nanotubes is provided, wherein hydrogen is injected into the second quench zone.

[0026] (11) In any of (1) to (10) above, a method for manufacturing the carbon nanotubes is provided, wherein the source gas comprises at least one selected from the group consisting of C1-C10 aliphatic hydrocarbons, C6-C20 aromatic hydrocarbons, carbon monoxide, natural gas, C1-C6 alcohols and acetone.

[0027] (12) In any of (1) to (11) of the present invention, a method for manufacturing the carbon nanotubes is provided, wherein the nanoparticle catalyst prepared in step S3 is in an aerosol state.

[0028] (13) In any of (1) to (12) of the present invention, a method for manufacturing the carbon nanotubes is provided, wherein step S4 is carried out by further introducing sulfur or a sulfur-containing compound as a co-catalyst into the CVD reactor.

[0029] (14) In any of (1) to (13) of the present invention, a method for manufacturing the carbon nanotubes is provided, wherein step S4 is performed by further introducing at least one carrier gas selected from the group consisting of an inert gas, hydrogen and nitrogen into the CVD reactor.

[0030] (15) In any of (1) to (14) above, a method for manufacturing the carbon nanotubes is provided, wherein the temperature of the CVD reactor is from 800°C to 1,400°C.

[0031] (16) In any of (1) to (15) of the present invention, a method for manufacturing the carbon nanotubes is provided, wherein the manufactured carbon nanotubes are single-walled carbon nanotubes, multi-walled carbon nanotubes, or a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0032] (17) In any of (1) to (16) of the present invention, a method for manufacturing the carbon nanotubes is provided, wherein the above steps S1 to S5 are performed continuously.

[0033] Beneficial effects

[0034] When using the carbon nanotube manufacturing method of the present invention, high-quality carbon nanotubes can be manufactured in a shorter time compared with conventional carbon nanotube manufacturing methods using supported catalyst technology and fluidized bed reactors.

[0035] Furthermore, a drawback of the conventional method for synthesizing carbon nanotubes in a floating reactor using catalyst precursors (FCCVD) is that, since catalyst nanoparticles and carbon nanotubes are generated simultaneously, it is difficult to independently control variables during the carbon nanotube synthesis process, thus hindering optimization of carbon nanotube synthesis. On the other hand, the carbon nanotube manufacturing method of the present invention can continuously synthesize high-quality carbon nanotubes by performing the steps of preparing catalytic nanoparticles and synthesizing carbon nanotubes separately in physically different spaces, and sequentially connecting and performing these two steps. Specifically, in the step of preparing catalyst nanoparticles, a plasma device, more specifically an inductively coupled RF plasma device, is used to effectively control the particle size and distribution of the catalyst nanoparticles. Then, in the step of synthesizing carbon nanotubes, a CVD reactor is used to synthesize carbon nanotubes, thereby producing carbon nanotubes with excellent physical properties. Attached Figure Description

[0036] Figure 1 The carbon nanotubes manufactured in Example 3 of the present invention were obtained by observing SEM images at 100K magnification.

[0037] Figure 2 The carbon nanotubes manufactured in Example 3 of the present invention were obtained by observing SEM images at 50K magnification. Detailed Implementation

[0038] The invention will be described in more detail below.

[0039] It will be understood that the words or terms used in the specification and claims should not be interpreted as having the meaning defined in a common dictionary, and it will also be understood that, based on the principle that the inventors may appropriately define the meaning of words or terms to best interpret the invention, the words or terms should be interpreted as having a meaning consistent with their meaning in the context of the related technology and the technical idea of ​​the invention.

[0040] Methods for manufacturing carbon nanotubes

[0041] Fluidized bed reactors are a commonly used method in industrial applications for manufacturing large quantities of carbon nanotubes. Specifically, in this method, carbon nanotubes are manufactured by filling a fluidized bed reactor with a support containing a metal catalyst, injecting a source gas into the reactor, and heating the reactor to grow carbon nanotubes on the surface of the catalyst particles. The advantages of this fluidized bed chemical vapor deposition (FBCVD) method are that it can not only produce large quantities of carbon nanotubes but also stabilize them stably; however, it has the following disadvantages.

[0042] 1) When synthesizing carbon nanotubes using a fluidized bed reactor, there are limitations to improving the quality of the carbon nanotubes. The catalyst used in the fluidized bed reactor is prepared by sintering a metal catalyst precursor. Because the catalyst prepared by this method has a wide particle size distribution, the uniformity of the diameter of the carbon nanotubes prepared using this catalyst is slightly deteriorated, making it difficult to obtain a uniform carbon nanotube product. Furthermore, due to the characteristics of the fluidized bed reactor, the synthesized carbon nanotubes are filled into the reactor for use, so the growth time of each carbon nanotube may not be constant. This phenomenon may also deteriorate the uniformity of the final manufactured carbon nanotubes. In addition, multi-walled carbon nanotubes synthesized below 800°C have a low crystallinity (G / D ratio) of 1, resulting in weak mechanical properties.

[0043] 2) When using a fluidized bed reactor to synthesize carbon nanotubes, there are limitations to improving the efficiency of the production process. When using a fluidized bed reactor, the internal space of the reactor needs to be filled with a bed before operation, and the grown carbon nanotubes need to be obtained even after the reaction is complete, making continuous manufacturing difficult. Furthermore, since time is required to heat the reactor even after the reaction begins, the actual reaction time is relatively short compared to the total process runtime, thus limiting improvements in production process efficiency in terms of time.

[0044] Therefore, this invention proposes a method for manufacturing carbon nanotubes that can improve the efficiency of the carbon nanotube production process in terms of time and ensure the uniformity and high quality of the synthesized carbon nanotubes.

[0045] Specifically, the present invention provides a method for manufacturing carbon nanotubes, the method comprising: a step of gasifying a catalyst raw material using a plasma torch to form a catalyst vapor (S1); a step of transferring the catalyst vapor to a quenching zone via a plasma flow (S2); a step of condensing the catalyst vapor in the quenching zone to prepare a nanoparticle catalyst (S3); a step of introducing the prepared nanoparticle catalyst and the source gas into a CVD reactor respectively (S4); and a step of synthesizing carbon nanotubes in the CVD reactor (S5).

[0046] The method for manufacturing carbon nanotubes of the present invention can be mainly divided into a part for preparing nanoparticle catalysts (steps S1 to S3) and a part for synthesizing carbon nanotubes (steps S4 and S5). The steps of the present invention will be described below.

[0047] Parts for preparing nanoparticle catalysts (S1 to S3)

[0048] Regarding catalysts used for the synthesis of carbon nanotubes, this invention enables the high-speed preparation of catalyst particles in nanoparticle form using a plasma torch, replacing the existing sintering process for catalyst preparation. This results in catalyst particles with small average particle size and narrow particle size distribution, and allows for the synthesis of high-quality carbon nanotubes in a short time using nanoparticle catalysts.

[0049] Plasma is generated using any suitable gas ionized in a high-frequency electromagnetic field, possessing sufficient energy to vaporize the catalyst feedstock. Furthermore, the catalyst feedstock can be fully vaporized in a short time via plasma. Specifically, the plasma can be thermal plasma; therefore, the plasma torch used to supply the plasma can be an inductively coupled RF thermal plasma torch. The RF plasma torch can be used to generate nanoparticles by forming an inductively coupled plasma, using the formed inductively coupled plasma to vaporize externally injected catalyst feedstock, and then transferring the formed catalyst vapor to a quenching zone and condensing the transferred catalyst vapor. In particular, because the plasma flow formed using an inductively coupled RF thermal plasma torch has sufficiently high energy, the catalyst vapor does not easily condense immediately after vaporization; instead, it condenses through the subsequent transfer process, thus forming more uniform nanoparticle catalysts.

[0050] In the process of forming nanoparticles using an inductively coupled RF thermal plasma torch, the cooling rate and vaporization rate are key parameters determining the nanoparticle size. At high cooling rates (approximately 10⁻⁶), the vaporization rate is crucial. 5 K / s to 10 6 Nanoparticles with small size are formed at low vapor rates (K / s) and low vapor rates.

[0051] Step S1: Gasification of the catalyst feedstock

[0052] Step S1 described above involves vaporizing the catalyst feedstock using a plasma torch. Nanoparticle catalysts can be prepared through the processes of vaporizing and condensing the catalyst feedstock. The vaporization step requires high energy, hence the use of the aforementioned plasma. Furthermore, the term "vaporization" as used herein refers to the conversion of a solid or liquid catalyst feedstock into vapor, and encompasses not only the conversion of liquid to gas but also other concepts including "sublimation," which converts a solid to a gas.

[0053] In this step, gases commonly used as working gases for thermal plasma, such as argon, hydrogen, or nitrogen, can be used alone or in combination. The temperature of the thermal plasma in this step should be extremely high, sufficient to vaporize the catalyst feedstock, for example, up to 10,000 K.

[0054] The catalyst feedstock introduced in this step may contain at least one metal or its precursor selected from the group consisting of Fe, Co, Ni, Pd, Pt, Ru, Cu, Mn, Cr, Mo, V, Mg, Si, Ge, and Eu, and preferably may contain at least one metal or its precursor selected from the group consisting of Fe, Co, and Ni. The listed metal components are catalytically active in the carbon nanotube synthesis reaction, and the materials listed are preferred, thereby enabling the efficient synthesis of carbon nanotubes from the nanoparticle catalyst prepared in subsequent steps. In particular, catalysts containing at least one metal component selected from Fe, Co, and Ni have the advantage of synthesizing carbon nanotubes in high yields.

[0055] In addition, the catalyst feedstock may also contain sulfur or a sulfide of at least one metal selected from the group consisting of Fe, Co, Ni, Pd, Pt, Ru, Cu, Mn, Cr, Mo, V, Mg, Si, Ge, and Eu. The presence of sulfur or metal sulfides in the catalyst feedstock can further enhance the activity of the final catalyst.

[0056] The catalyst raw material introduced in step S1 above can be in liquid or solid form, preferably in powder form with an average particle size of 1 μm to 100 μm. When the catalyst raw material is in the above form, it has the advantages of excellent stability and ease of introduction into the plasma device. Simultaneously, when the catalyst raw material is in powder form, the powder should have good flowability in the device, making it easier to introduce into the plasma device. Therefore, it is particularly preferred that the average particle size of the powder meets the above range. More specifically, the average particle size of the powder can be 1 μm to 100 μm, more preferably 5 μm to 50 μm.

[0057] The step of transferring the catalyst vapor to the quench zone (S2)

[0058] The catalyst feedstock, i.e., the catalyst vapor, which has been vaporized in step S1, is transferred to the quench zone by convection and diffusion to form a vapor concentration distribution. When the temperature of the catalyst vapor at its internal centerline is at least 3,000 K before entering the quench zone, catalyst nanoparticles can be effectively generated during the subsequent condensation process.

[0059] Specifically, when the catalyst vapor is transferred to the quench zone via plasma flow, the catalyst vapor can be mixed with other components (e.g., co-catalyst) during the transfer process due to convection and diffusion in the reactor. This ensures the uniformity of the catalyst vapor, so that the composition of the final nanoparticle catalyst can be uniform and its particle size distribution can be obtained in a log-normal form, thus the distribution can be narrow.

[0060] On the other hand, when no transfer step is performed, some catalyst feedstock powder that has not been completely vaporized during the gasification and condensation process may be mixed with nanoparticles, and it is difficult to effectively condense the catalyst vapor. Therefore, the particle size distribution of the nanoparticle catalyst obtained subsequently may be bimodal and the distribution may be relatively wide.

[0061] In this step, transferring the catalyst vapor to the quench zone refers to transferring the catalyst vapor to the quench zone along the plasma flow within the reactor after step S1 described above. The reactor can be made of a high-temperature refractory material such as graphite. The time for transferring the catalyst vapor can vary depending on the amount of catalyst feedstock introduced or the size of the thermal plasma device, but it should be a time sufficient for achieving adequate homogeneity. If the time is too short or too long, the homogeneity of the formed nanoparticles may deteriorate. For example, the residence time of the catalyst vapor in the reactor can be from 1 millisecond (ms) to 10 seconds, more specifically from 10 ms to 1 second. When the residence time in the reactor is within the above range, the homogeneity of the prepared nanoparticle catalyst can be higher.

[0062] Condensation step (S3)

[0063] Nanoparticle catalysts can be prepared by condensing the catalyst vapor transferred in the previous step in a quenching zone. In particular, if the cooling rate is fast, the growth time of the solid particles is relatively short, thus enabling the preparation of nanoparticles with narrow particle size distribution and small average particle size.

[0064] The condensation step can be carried out using a quenching gas. Those skilled in the art can select a suitable gas from known quenching gases and apply the selected gas to the present invention; for example, an inert gas or nitrogen can be used as the quenching gas. When quenching is performed using a quenching gas, condensation can occur at the interface between the plasma flow carrying catalyst vapor and the quenching gas, thus allowing the preparation of a catalyst in nanoparticle form at the interface. Simultaneously, the nanoparticles formed at the interface can be transferred along with the flow of the quenching gas; therefore, the nanoparticles can then be introduced into the CVD reactor in an aerosol state mixed with the quenching gas.

[0065] The average particle size of the prepared catalyst can be controlled by adjusting the flow rate of the cooling gas in this step. For example, by increasing the cooling rate through increasing the flow rate of the cooling gas, catalysts with small-sized nanoparticles can be prepared.

[0066] Simultaneously, in this step, the quenching zone can include a first quenching zone and a second quenching zone, and catalyst vapor can flow from the first quenching zone to the second quenching zone. Additionally, quenching gas can be injected into both the first and second quenching zones, and hydrogen can be further injected into the second quenching zone along with the quenching gas. Performing the quenching process in two distinct regions and additionally injecting hydrogen into the second quenching zone where condensation ultimately occurs offers advantages in controlling the size of the nanoparticle catalyst.

[0067] The nanoparticle catalyst obtained in this step through the preceding steps can have an average particle size of less than 100 nm, and preferably less than 20 nm. As described above, when preparing the catalyst through the above steps, nanoparticle catalysts with small average particle size and narrow particle size distribution can be prepared; specifically, nanoparticle catalysts that meet the above conditions can be prepared. Meanwhile, the average particle size can be determined by BET analysis. Specifically, the average particle size can be calculated using the following formula.

[0068] Average particle size = 6 / (BET specific surface area × density)

[0069] In the above formula, the unit of BET specific surface area is m². 2 / g, the BET specific surface area can be measured using devices such as BELSORP-max from BEL Japan Inc.

[0070] Parts of the carbon nanotube synthesis (S4 and S5)

[0071] Carbon nanotubes can be synthesized using the nanoparticle catalyst prepared in the previous catalyst particle preparation section, and carbon nanotubes can be prepared by introducing the specially prepared nanoparticle catalyst and the source gas into the CVD reactor (S4) and synthesizing carbon nanotubes in the CVD reactor (S5).

[0072] Steps for introducing the nanoparticle catalyst and the source gas (S4)

[0073] To synthesize carbon nanotubes, a step should be performed whereby a nanoparticle catalyst prepared using a plasma device and a source gas are introduced into a CVD reactor. The catalyst is the same as described above, and the source gas, used to form carbon nanotubes on the catalyst surface, should be a carbon-containing gas.

[0074] The source gas can be a carbon-containing gas capable of decomposing at high temperatures to form carbon nanotubes. Specific examples include various carbon-containing compounds such as aliphatic alkanes, aliphatic alkenes, aliphatic alkynes, and aromatic compounds. More specifically, it can include at least one selected from the group consisting of C1-C10 aliphatic hydrocarbons, C6-C20 aromatic hydrocarbons, carbon monoxide, natural gas, C1-C6 alcohols, and acetone. Even more specifically, it can use compounds such as methane, ethane, ethylene, acetylene, methylacetylene, vinylacetylene, propane, butane, pentane, hexane, propylene, carbon monoxide, natural gas, butadiene, benzene, toluene, cyclopentadiene, cyclohexane, ethanol, methanol, propanol, or acetone. For economic and efficiency reasons, methane is particularly preferred.

[0075] In this invention, carbon nanotubes are synthesized via a CVD reactor, which can be physically separated from a plasma device capable of performing the aforementioned steps S1 to S3. The CVD reactor is suitable for reactions involving a mixture of nanoparticle catalyst and source gas introduced in an aerosol state, and allows carbon nanotubes to be grown on a surface while the nanoparticle catalyst is floating. The CVD reactor can be a chemical vapor deposition (CVD) reactor, a catalytic chemical vapor deposition (CCVD) reactor, or a floating catalyst chemical vapor deposition (FCCVD) reactor.

[0076] Meanwhile, in the carbon nanotube manufacturing method of the present invention, the nanoparticle catalyst and the source gas can be introduced separately into the CVD reactor. When the nanoparticle catalyst and the source gas are premixed and introduced into the CVD reactor, the equipment for premixing the two components should be located between the plasma device and the CVD reactor. Therefore, a potential limitation is that the process not only becomes complicated, but the catalyst also becomes deactivated due to coking, making it difficult to synthesize carbon nanotubes. On the other hand, when the nanoparticle catalyst and the source gas are introduced separately into the CVD reactor, not only can the input control variables of various components be easily controlled, but the crystallinity of the finally manufactured carbon nanotubes can also be improved.

[0077] In this step, in addition to the nanoparticle catalyst and reaction source gas as described above, a co-catalyst can be further introduced into the CVD reactor. The co-catalyst can enhance catalytic activity to improve the production yield of carbon nanotubes, and can be sulfur or sulfur-containing compounds, more specifically, at least one selected from the group consisting of thiophene, alkylthiophene, benzothiophene, hydrogen sulfide, and carbon disulfide.

[0078] The amount of co-catalyst added can vary depending on the type and amount of source gas introduced into the CVD reactor, the amount of catalyst, etc., but for example, the weight ratio of catalyst to co-catalyst can be from 1:1 to 100:1. When the amount of co-catalyst added is too large, it may poison the catalyst itself, while when the amount is too small, the effect of the co-catalyst may be insignificant.

[0079] Carbon nanotube synthesis step (S5)

[0080] Carbon nanotubes can be synthesized simultaneously with the decomposition of the source gas on the surface of the aerosol-state nanoparticle catalyst introduced into the CVD reactor in a previous step. Specifically, carbon nanotubes can be synthesized by heating the CVD reactor. The heated CVD reactor can have a temperature of 800°C to 1,400°C. At these temperatures, the reaction source gas decomposes, and carbon nanotubes form on the surface of the liquid catalyst particles. When the temperature of the CVD reactor is below this temperature, the reaction source gas may not decompose sufficiently, while when the temperature of the CVD reactor is above this temperature, the synthesis yield of carbon nanotubes may decrease significantly.

[0081] In this step, carbon nanotubes are synthesized by growing them on the surface of liquid catalyst particles, and the final carbon nanotube product may also contain the catalyst particles. Furthermore, the carbon nanotubes obtained in this step can be single-walled carbon nanotubes, multi-walled carbon nanotubes, or a mixture of single-walled and multi-walled carbon nanotubes. Additionally, the carbon nanotubes can be obtained in powder form.

[0082] Steps S1 to S5 described above can be performed continuously. In conventional methods for manufacturing carbon nanotubes using fluidized bed reactors, the fluidized bed reactors operate intermittently. However, in this invention, because the introduction of raw materials and nanoparticle catalysts is continuous, catalyst particles can be obtained continuously, and the CVD reactor can also be operated continuously. Therefore, the entire manufacturing method can also be carried out continuously.

[0083] The carbon nanotubes obtained by the manufacturing method of the present invention can be bundled. A "bundle" of carbon nanotubes refers to a secondary structure in which multiple carbon nanotubes are arranged in parallel or aligned along a certain direction to form a bundle or rope. In particular, the carbon nanotubes obtained by the method of the present invention can be bundled, and therefore can be suitable for use as conductive agents, etc.

[0084] The carbon nanotubes manufactured by the method of the present invention can have a diameter of 1,000 m. 2 Specific surface area below / g and 0.05g / cm² 3 The above-mentioned packing density. Furthermore, the carbon nanotubes manufactured by the method of the present invention can have a maximum crystallinity of 40 or higher (I0). G / ID It has a high crystallinity and excellent crystallinity. Furthermore, it can utilize I measured by Raman spectroscopy. G / I D The value is used to determine the degree of crystallinity.

[0085] The invention will be described in more detail below with reference to embodiments and experimental examples to illustrate the invention, but the invention is not limited to these embodiments and experimental examples. Embodiments of the invention can be modified in many different ways, and the scope of the invention should not be construed as limited to the embodiments described below. Rather, embodiments of the invention will be provided to illustrate the invention in more detail to those skilled in the art.

[0086] Material

[0087] As catalyst raw materials, Fe powder and FeS powder with a particle size of 10μm to 50μm are mixed and used, and the moisture is removed in advance by drying the catalyst raw materials in a vacuum oven before introducing the catalyst material into the feeding section.

[0088] Example 1

[0089] To ignite the plasma under vacuum, Ar (32 lpm) and H2 (1.4 lpm) were injected into a plasma torch containing a sheath gas, and Ar (12 lpm) was injected into the center gas. After ignition, the pressure inside the plasma device was maintained at atmospheric pressure (14.7 psi), and a catalyst feedstock (FeS content of 16 wt%) was supplied to the feed section of the RF thermal plasma device (carrier gas: Ar, flow rate: 5 lpm), thereby vaporizing the catalyst feedstock in the plasma torch. The formed catalyst vapor was transferred to the quench zone via convection and diffusion, and quench gas Ar at 75 lpm and 175 lpm was injected into the first and second quench zones, respectively, to quench and condense the catalyst vapor. Simultaneously, in the second quench zone, H2 gas was injected along with Ar at a flow rate of 30 lpm. The catalyst vapor from both the first and second quench zones condensed to form aerosol-state nanoparticle catalyst, which was then introduced into a CVD reactor preheated to 1,350 °C.

[0090] In addition, methane gas, which serves as the source gas, is separately injected into the CVD reactor at a flow rate of 4 lpm from the nanoparticle catalyst, and the methane gas is preheated to 500°C before injection.

[0091] Nanoparticle catalyst and source gas are introduced into the CVD reactor, and carbon nanotube synthesis begins simultaneously, proceeding for 20 minutes. After this process is complete, gas injection is stopped, and the CVD reactor is cooled to obtain carbon nanotubes.

[0092] Example 2

[0093] Carbon nanotubes were obtained in the same manner as in Example 1, except that a mixture with a FeS content of 20% by weight was used as the catalyst feedstock, the temperature of the CVD reactor was heated to 1,400°C, and methane gas was injected into the CVD reactor at a flow rate of 3 lpm and hydrogen gas was injected into the CVD reactor at a flow rate of 9.5 lpm.

[0094] Example 3

[0095] Carbon nanotubes were obtained in the same manner as in Example 2, except that methane gas was injected into the CVD reactor at a flow rate of 3 lpm and hydrogen gas was injected into the CVD reactor at a flow rate of 50 lpm.

[0096] Comparative Example 1

[0097] Carbon nanotubes were obtained in the same manner as in Example 2, except that 4 lpm of methane gas and 9.5 lpm of hydrogen gas were premixed with the aerosol-state nanoparticle catalyst in a small chamber before being injected into the CVD reactor, and the CVD reactor was heated to 1,300°C.

[0098] The manufacturing conditions for the embodiments and comparative examples are summarized and shown in Table 1 below.

[0099] [Table 1]

[0100]

[0101] Experimental Example 1. Identification of the crystallinity of the manufactured carbon nanotubes

[0102] The I-values ​​of the carbon nanotubes manufactured in the examples and comparative examples were determined using Raman spectroscopy. G and I D The values ​​were determined, and the average and maximum crystallinity were calculated. The results are shown in Table 2 below. The I values ​​were determined at various points on the carbon nanotube samples. G / I D The average and maximum values ​​are then taken to obtain the average crystallinity and maximum crystallinity.

[0103] [Table 2]

[0104] Average crystallinity 29 32 64 0.736 Maximum crystallinity 48 76 99 0.867

[0105] As can be seen from Table 2 above, the carbon nanotubes manufactured in the embodiments of the present invention exhibit a high crystallinity of 40 or more, while the carbon nanotubes manufactured in Comparative Example 1 exhibit a crystallinity value of less than 1. That is, this means that the crystallinity of the carbon nanotubes manufactured in Comparative Example 1 is significantly lower than that of the embodiments, and the carbon nanotube manufacturing method of the present invention can be used to manufacture high-quality carbon nanotubes.

[0106] Experimental Example 2. Confirmation of SEM images of the carbon nanotubes fabricated in the examples

[0107] The carbon nanotubes fabricated in Example 3 were observed using SEM images. The carbon nanotubes were observed at magnifications of 100K and 50K, and the results are shown below. Figure 1 and 2 .

[0108] exist Figure 1 and 2 As can be seen, it can be confirmed that when using the carbon nanotube manufacturing method of the present invention, multiple strands of fine and flexible carbon nanotubes can be manufactured in a bundled form.

Claims

1. A method for manufacturing carbon nanotubes, the method comprising: The step of using a plasma torch to vaporize the catalyst feedstock to form catalyst vapor (S1); Step (S2) of transferring the catalyst vapor to the quenching zone via plasma flow; The step of condensing the catalyst vapor in the quenching zone to prepare nanoparticle catalyst (S3); The step of introducing the prepared nanoparticle catalyst and source gas into the CVD reactor respectively (S4); and In step (S5), carbon nanotubes are synthesized in the CVD reactor. The quenching zone includes a first quenching zone and a second quenching zone, and the catalyst vapor flows from the first quenching zone to the second quenching zone. Hydrogen gas is injected into the second quench zone.

2. The method as described in claim 1, wherein, The average particle size of the nanoparticle catalyst is less than 100 nm.

3. The method of claim 1, wherein, The plasma torch is an inductively coupled RF thermal plasma torch.

4. The method of claim 1, wherein, The catalyst feedstock comprises at least one metal or its precursor selected from the group consisting of Fe, Co, Ni, Pd, Pt, Ru, Cu, Mn, Cr, Mo, V, Mg, Si, Ge and Eu.

5. The method of claim 4, wherein, The catalyst feedstock further comprises sulfur or a sulfide of at least one metal selected from the group consisting of Fe, Co, Ni, Pd, Pt, Ru, Cu, Mn, Cr, Mo, V, Mg, Si, Ge and Eu.

6. The method of claim 1, wherein, The catalyst feedstock can be in liquid or solid form.

7. The method of claim 6, wherein, The catalyst raw material is in powder form with an average particle size of 5 μm to 100 μm.

8. The method of claim 1, wherein, Inert gas is injected into the first quench zone and the second quench zone.

9. The method of claim 1, wherein, The source gas comprises at least one selected from the group consisting of C1-C10 aliphatic hydrocarbons, C6-C20 aromatic hydrocarbons, carbon monoxide, natural gas, C1-C6 alcohols, and acetone.

10. The method of claim 1, wherein, The nanoparticle catalyst prepared in step S3 above is in an aerosol state.

11. The method of claim 1, wherein, Step S4 above is carried out by further introducing sulfur or sulfur-containing compounds as co-catalysts into the CVD reactor.

12. The method of claim 1, wherein, Step S4 above is carried out by further introducing at least one carrier gas selected from the group consisting of inert gas, hydrogen and nitrogen into the CVD reactor.

13. The method of claim 1, wherein, The temperature of the CVD reactor is between 800°C and 1,400°C.

14. The method of claim 1, wherein, The manufactured carbon nanotubes are single-walled carbon nanotubes, multi-walled carbon nanotubes, or a mixture of single-walled and multi-walled carbon nanotubes.

15. The method of claim 1, wherein, Continue performing steps S1 to S5 as described above.

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