Method for synthesizing carbon nanotubes

Abstract

The present invention relates to a method for synthesizing carbon nanotubes using a nanoparticle catalyst produced by vaporizing a catalyst raw material using plasma and then condensing it. When using the production method of the present invention, the synthesized carbon nanotubes have high crystallinity and can be easily mass-synthesized.

Description

[Technical Field]

[0001] This invention relates to a method for producing carbon nanotubes that can efficiently produce high-quality carbon nanotubes in a short time by using a nanoparticle catalyst manufactured using plasma and a CVD reactor. [Background technology]

[0002] Carbon nanotubes are nanostructures in which graphene, with a single layer of carbon atoms, is rolled into a cylindrical shape. They are classified into single-walled and multi-walled carbon nanotubes depending on the number of layers of the surrounding shell. Generally, carbon nanotubes refer to those with a diameter of a few nanometers to tens of nanometers and a length that is tens to thousands of times longer than their diameter. Depending on the chiral index (a value representing the diameter and curling angle of the tube as an integer in (n, m)), they can be metallic or semiconducting. Single-walled carbon nanotubes often align in a "bundle" shape, with multiple nanotubes bundled together by van der Waals forces. Multi-walled carbon nanotubes, on the other hand, are composed of multiple shells, with each layer having a different diameter and chiral index. Multi-walled carbon nanotubes also have defects (sp) in their crystal structure. 3 It has many carbon atoms (such as vacancies) and is characterized by weak mechanical properties.

[0003] Carbon nanotubes exhibit properties such as higher electrical and thermal conductivity and superior strength compared to conventional materials, making them useful in various fields such as energy, nanotechnology, optics, and materials engineering. For example, carbon nanotubes have high elasticity of several thousand GPa and high strength of several tens of GPa mechanically.

[0004] In terms of applications, carbon nanotubes can be used as a new electrode material, specifically as a conductive material for the positive and negative electrodes of lithium-ion batteries. Due to their superior strength, conductivity, and low density, carbon nanotubes can improve battery life and capacity during charging and discharging compared to conventional carbon black conductive materials. In particular, single-walled carbon nanotubes demonstrate a clear improvement in battery life when applied to silicon negative electrodes, even though their usage is only about one-tenth that of multi-walled carbon nanotubes.

[0005] Various studies are underway regarding manufacturing methods for the industrial use of carbon nanotubes. Conventionally, methods for synthesizing carbon nanotubes include arc discharge, laser deposition, and chemical vapor deposition. The arc discharge method is a method for producing carbon nanotubes by inducing an arc discharge between carbon rods in an argon or hydrogen atmosphere at a pressure lower than atmospheric pressure. For example, using a Ni·Y catalyst, it is possible to produce single-walled carbon nanotubes that are highly pure, highly crystalline, and have a uniform diameter. While the arc discharge method has the advantage of producing high-quality carbon nanotubes with few defects, it has the disadvantage that amorphous carbon is simultaneously produced, making it unsuitable for large-scale synthesis.

[0006] Laser deposition is a method for producing carbon nanotubes by irradiating a carbon target mixed with a metal catalyst such as nickel or cobalt with strong pulsed light, such as a laser, in a high-temperature atmosphere of over 900°C. Laser deposition has the advantage of being able to produce high-purity carbon nanotubes and allowing for some adjustment of the nanotube diameter by changing the conditions of the irradiated pulsed light. However, it also has the disadvantage of not being suitable for mass production when considering the competitiveness of production scale.

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

[0008] Therefore, there is a need for research into novel manufacturing methods that can solve the problems of the conventional carbon nanotube synthesis methods described above, and that enable the economical and consistent mass synthesis of high-quality carbon nanotubes. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] US8048396B2 [Patent Document 2] KR10-2012-0112918A [Overview of the project] [Problems that the invention aims to solve]

[0010] The object of the present invention is to provide a novel physicochemical manufacturing method for synthesizing high-quality carbon nanotubes with excellent purity and crystallinity. [Means for solving the problem]

[0011] To solve the above problems, the present invention provides a method for producing carbon nanotubes.

[0012] Specifically, (1) the present invention provides a method for producing carbon nanotubes, comprising the steps of: (1) vaporizing a catalyst raw material using a plasma torch to form a catalyst vapor (S1); (2) transferring the catalyst vapor to a rapid cooling zone by a plasma flow (S2); (3) condensing the catalyst vapor in the rapid cooling zone to produce a nanoparticle catalyst (S3); (4) introducing the produced nanoparticle catalyst and the raw material gas into a CVD reactor (S4); and (5) synthesizing carbon nanotubes in the CVD reactor.

[0013] (2) The present invention provides a method for producing carbon nanotubes as described in (1), characterized in that the nanoparticle catalyst has an average particle size of 100 nm or less.

[0014] (3) The present invention provides a method for producing carbon nanotubes as described in (1) or (2), wherein the plasma torch is an inductively coupled RF thermal plasma torch.

[0015] (4) The present invention provides a method for producing carbon nanotubes according to any one of the above (1) to (3), wherein the catalyst raw material comprises one or more metals selected from the group consisting of Fe, Co, Ni, Pd, Pt, Ru, Cu, Mn, Cr, Mo, V, Mg, Si, Ge, and Eu or a precursor thereof.

[0016] (5) The present invention provides a method for producing carbon nanotubes according to any one of the above (1) to (4), wherein the catalyst raw material further comprises sulfur or a sulfide of one or more metals selected from the group consisting of Fe, Co, Ni, Pd, Pt, Ru, Cu, Mn, Cr, Mo, V, Mg, Si, Ge, and Eu.

[0017] (6) In the present invention, the catalyst raw material is in a liquid or solid state, and there is provided a method for producing carbon nanotubes according to any one of the above (1) to (5).

[0018] (7) In the present invention, the catalyst raw material is in a powdery state with an average particle size of 5 to 100 μm, and there is provided a method for producing carbon nanotubes according to any one of the above (1) to (6).

[0019] (8) In the present invention, the rapid cooling zone includes a first rapid cooling zone and a second rapid cooling zone, and the catalyst vapor flows from the first rapid cooling zone to the second rapid cooling zone, and there is provided a method for producing carbon nanotubes according to any one of the above (1) to (7).

[0020] (9) The present invention provides a method for producing carbon nanotubes according to any one of the above (1) to (8), in which an inert gas is injected into the first rapid cooling zone and the second rapid cooling zone.

[0021] (10) The present invention provides a method for producing carbon nanotubes according to any one of the above (1) to (9), in which hydrogen gas is injected into the second rapid cooling zone.

[0022] (11) In the present invention, the raw material gas includes one or more selected from the group consisting of C1-C10 aliphatic hydrocarbons, C6-20 aromatic hydrocarbons, carbon monoxide, natural gas, C1-6 alcohols, and acetone, and there is provided a method for producing carbon nanotubes according to any one of the above (1) to (10).

[0023] (12) In the present invention, the nanoparticle catalyst produced in the S3 step is in an aerosol state, and there is provided a method for producing carbon nanotubes according to any one of the above (1) to (11).

[0024] (13) The present invention provides a method for producing carbon nanotubes according to any one of the above (1) to (12), characterized in that the S4 step further involves adding sulfur or a sulfur-containing compound as a co-catalyst to the CVD reactor.

[0025] (14) The present invention provides a method for producing carbon nanotubes according to any one of the above (1) to (13), characterized in that the S4 step further involves introducing one or more carrier gases selected from the group consisting of inert gas, hydrogen, and nitrogen into the CVD reactor.

[0026] (15) The present invention provides a method for producing carbon nanotubes according to any one of the above (1) to (14), wherein the temperature of the CVD reactor is 800°C to 1400°C.

[0027] (16) The present invention provides a method for producing carbon nanotubes according to any one of the above (1) to (15), wherein the carbon nanotubes produced are single-walled carbon nanotubes, multi-walled carbon nanotubes, or a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0028] (17) The present invention provides a method for producing carbon nanotubes according to any one of the above (1) to (16), wherein the steps S1 to S5 are carried out in succession. [Effects of the Invention]

[0029] When using the carbon nanotube manufacturing method of the present invention, high-quality carbon nanotubes can be produced in a shorter time compared to conventional carbon nanotube manufacturing methods using supported catalyst technology and fluidized bed reactors.

[0030] Furthermore, in the conventional method of synthesizing carbon nanotubes in a floating reactor using a catalyst precursor (FCCVD), the generation of catalyst nanoparticles and carbon nanotubes occurs simultaneously, making it difficult to independently control the variables in the carbon nanotube synthesis process. This has the disadvantage of making it difficult to optimize carbon nanotube synthesis. In contrast, the carbon nanotube manufacturing method of the present invention allows for the continuous synthesis of high-quality carbon nanotubes by performing the steps of manufacturing catalyst nanoparticles and synthesizing carbon nanotubes separately in physically separated spaces and sequentially linking the two steps. In particular, in the step of manufacturing catalyst nanoparticles, the particle size and distribution of the catalyst nanoparticles can be effectively controlled using a plasma device, more specifically an inductively coupled RF plasma device. In the subsequent carbon nanotube synthesis step, carbon nanotubes with excellent physical properties can be manufactured by synthesizing them using a CVD reactor. [Brief explanation of the drawing]

[0031] [Figure 1] This image shows a carbon nanotube produced in Example 3 of the present invention, observed using a 100K magnification SEM. [Figure 2] This image shows a carbon nanotube produced in Example 3 of the present invention, observed using a 50K magnification SEM. [Modes for carrying out the invention]

[0032] The present invention will be described in more detail below. The terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0033] Method for manufacturing carbon nanotubes A commonly used method for producing large quantities of carbon nanotubes in industrial applications is the use of a fluidized bed reactor. Specifically, in this method, a support containing a metal catalyst is packed into the fluidized bed reactor, then a raw material gas is introduced, the reactor is heated, and carbon nanotubes are grown on the surface of the catalyst particles. While this type of fluidized bed chemical vapor deposition (FBCVD) has the advantages of being able to produce large quantities of carbon nanotubes and enabling the stable synthesis of carbon nanotubes, it also has the following disadvantages.

[0034] 1) When synthesizing carbon nanotubes using a fluidized bed reactor, there are limitations to improving the quality of the carbon nanotubes. The catalysts used in fluidized bed reactors are manufactured by calcining metal catalyst precursors, but catalysts manufactured in this way have a relatively wide particle size distribution. As a result, the uniformity of the diameter of the carbon nanotubes produced is somewhat poor, making it difficult to obtain uniform carbon nanotube products. Furthermore, due to the characteristics of fluidized bed reactors, the reactor is filled with already synthesized carbon nanotubes, so the growth time for each individual carbon nanotube is not constant. This phenomenon can also worsen the uniformity of the carbon nanotubes ultimately produced. In addition, multi-walled carbon nanotubes synthesized at temperatures below 800°C have the disadvantage of low crystallinity (G / D ratio) at level 1 and weak mechanical properties.

[0035] 2) When synthesizing carbon nanotubes using a fluidized bed reactor, there are limitations to improving the efficiency of the manufacturing process. When using a fluidized bed reactor, it is necessary to pre-fill the internal space of the reactor with beds before starting the reactor, and it is also necessary to obtain the grown carbon nanotubes after the reaction is complete, making it difficult to realize a continuous manufacturing process. In addition, heating time is required for the reactor after the reaction has started, so the time consumed by the actual reaction is small compared to the overall process operation time, and there are limitations to improving the efficiency of the manufacturing process in terms of time.

[0036] Therefore, the present invention aims to propose a manufacturing method that can improve the efficiency of the carbon nanotube manufacturing process in terms of time, while also ensuring the uniformity and high quality of the synthesized carbon nanotubes.

[0037] Specifically, the present invention provides a method for producing carbon nanotubes, comprising the steps of: (S1) vaporizing a catalyst raw material using a plasma torch to form a catalyst vapor; (S2) transferring the catalyst vapor to a rapid cooling zone by a plasma flow; (S3) condensing the catalyst vapor in the rapid cooling zone to produce a nanoparticle catalyst; (S4) introducing the produced nanoparticle catalyst and the raw material gas into a CVD reactor; and (S5) synthesizing carbon nanotubes in the CVD reactor.

[0038] The carbon nanotube manufacturing method of the present invention is a sequential, continuous process and can be broadly divided into a section for manufacturing nanoparticle catalysts (steps S1 to S3) and a section for synthesizing carbon nanotubes (steps S4 and S5). Each step of the present invention will be described separately below.

[0039] Nanoparticle catalyst manufacturing section (S1~S3) From the perspective of catalysts used in the synthesis of carbon nanotubes, the present invention produces nanoparticle catalyst particles at high speed using a plasma torch instead of the conventional calcination process, thereby obtaining catalyst particles with a small average particle size and a narrow particle size distribution, and enabling the synthesis of high-quality carbon nanotubes in a short time using the nanoparticle catalyst.

[0040] The plasma is generated using any suitable gas that can be ionized in a high-frequency electromagnetic field, and has sufficient energy to vaporize the catalyst material. By vaporizing the catalyst material through the plasma, sufficient vaporization of the catalyst material can be achieved in a short time. Specifically, the plasma may be a thermal plasma, and therefore, the plasma torch, which is a means for supplying the plasma, may be an inductively coupled RF thermal plasma torch. The RF plasma torch can be used to form an inductive plasma, vaporize the catalyst material injected from the outside using the formed inductive plasma, and then transfer and condense the formed catalyst vapor in a rapid cooling zone to produce nanoparticles. In particular, since the plasma flow formed using an inductively coupled RF thermal plasma torch has sufficiently high energy, the catalyst vapor does not easily condense after vaporization, and condenses through the subsequent transfer process, thereby forming a more uniform nanoparticle catalyst.

[0041] In the process of forming nanoparticles using an inductively coupled RF thermal plasma torch, the cooling rate and vapor velocity are generally key parameters that determine the size of the nanoparticles being formed, and a high cooling rate (approximately 10) 5 ~10 6 Even smaller nanoparticles are formed at lower vapor velocities (K / s).

[0042] Step (S1) to vaporize the catalyst raw material. Step S1 is a step in which the catalyst material is vaporized using a plasma torch. Nanoparticle catalysts can be produced by the process of condensing the catalyst material after vaporization, and since the vaporization step requires high energy, the plasma described above can be used. On the other hand, "vaporization" in this invention means converting a catalyst material in a solid or liquid state into vapor, and does not mean only "vaporization" which changes a liquid into a gas, but also includes other concepts such as "sublimation" which changes a solid into a gas.

[0043] In this step, gases such as argon, hydrogen, and nitrogen, which are generally available as thermal plasma working gases, may be used individually or in combination. In this step, the temperature of the thermal plasma must be extremely high enough to vaporize the catalyst material, and for example, it must reach a maximum temperature of 10,000 K.

[0044] In this step, the catalyst raw material introduced may include one or more metals or their precursors selected from the group consisting of Fe, Co, Ni, Pd, Pt, Ru, Cu, Mn, Cr, Mo, V, Mg, Si, Ge, and Eu, and preferably one or more metals or their precursors selected from the group consisting of Fe, Co, and Ni. The metal components listed above are components that have catalytic activity in the carbon nanotube synthesis reaction, and it is preferable to include the substances listed above in order to efficiently synthesize carbon nanotubes from the nanoparticle catalyst produced in subsequent steps. In particular, catalysts containing at least one metal component from Fe, Co, and Ni have the advantage of being able to synthesize carbon nanotubes in high yield.

[0045] Furthermore, the catalyst raw material may further contain sulfur or one or more metal sulfides selected from the group consisting of Fe, Co, Ni, Pd, Pt, Ru, Cu, Mn, Cr, Mo, V, Mg, Si, Ge, and Eu. When the catalyst raw material contains sulfur or metal sulfides, the activity of the final catalyst can be further enhanced.

[0046] The catalyst material introduced in step S1 may be in liquid or solid form, and preferably in powder form with an average particle size of 1 to 100 μm. When the catalyst material is in the above-described form, it has the advantage of being stable and easy to introduce into the plasma apparatus. On the other hand, when the catalyst material is in powder form, the fluidity of the powder within the apparatus should be good in order to further facilitate its introduction into the plasma apparatus, and for this reason, it is particularly preferable that the average particle size of the powder meets the above-described range. More specifically, the average particle size of the powder may be 1 to 100 μm, more preferably 5 to 50 μm.

[0047] Step (S2) to transfer catalyst vapor to the rapid cooling zone. The catalyst raw material, i.e., catalyst vapor, vaporized through the S1 step described above, is transferred to the rapid cooling zone by convection and diffusion, forming a vapor concentration profile. If the temperature of the catalyst vapor's internal centerline is at least 3000K or higher before entering the rapid cooling zone, catalyst nanoparticles can be effectively generated during the subsequent condensation process.

[0048] Specifically, when the catalyst vapor is transferred to a rapid cooling zone by a plasma flow, it can be mixed with other components (e.g., co-catalysts) by convection and diffusion within the reactor during the transfer process, and the uniformity of the catalyst vapor can be ensured. As a result, the composition of the nanoparticle catalyst produced is uniform, its particle size distribution is obtained in a log-normal form, and its distribution can be narrowed.

[0049] In contrast, if the aforementioned transfer step is omitted, some of the catalyst raw material powder that did not completely vaporize during the vaporization and condensation process may be mixed with nanoparticles, making it difficult to achieve more effective condensation of the catalyst vapor. As a result, the particle size distribution of the nanoparticle catalyst obtained thereafter is in a bimodal form, and its distribution can be broadened.

[0050] In this step, the transfer of the catalyst vapor to the rapid cooling zone means that, following step S1, the catalyst vapor is transferred to the rapid cooling zone by a plasma flow within the reactor. The reactor may be made of a high-temperature refractory material such as graphite. On the other hand, the time for which the catalyst vapor is transferred may vary depending on the amount of catalyst raw material introduced and the size of the thermal plasma device, but it must be a time sufficient to obtain sufficient uniformity. If the above time is too short or too long, the uniformity of the formed nanoparticles may decrease. For example, the residence time of the catalyst vapor in the reactor may be 1 millisecond (ms) to 10 seconds, and more specifically, 10 milliseconds to 1 second. When the residence time in the reactor is within the above range, the uniformity of the produced nanoparticle catalyst can be further increased.

[0051] Condensation step (S3) The catalyst vapor transferred in the previous step can be condensed in a rapid cooling zone to produce nanoparticle-like catalysts. In particular, if the cooling rate is fast, it is possible to produce nanoparticles with a relatively short solid particle growth time, a narrow particle size distribution, and a small average particle size.

[0052] The condensation step may be carried out using a quenching gas, and a skilled technician may select a suitable gas from among those known to be used for quenching and apply it to the present invention, for example, an inert gas or nitrogen gas may be used as the quenching gas. When quenching is performed using a quenching gas, a condensation phenomenon occurs at the interface between the plasma flow transporting the catalyst vapor and the quenching gas, thereby producing nanoparticle-like catalyst at the interface. On the other hand, the nanoparticles formed at the interface can be transported together with the flow of quenching gas, and so the nanoparticles are in an aerosol state mixed with the quenching gas, and can then be introduced into a CVD reactor.

[0053] In this step, the average particle size of the catalyst produced can be controlled by controlling the flow rate of the cooling gas. For example, by increasing the flow rate of the cooling gas to speed up the cooling process, smaller nanoparticle catalysts can be produced.

[0054] On the other hand, in this step, the rapid cooling zone in which rapid cooling takes place includes a first rapid cooling zone and a second rapid cooling zone, and the catalyst vapor may flow from the first rapid cooling zone to the second rapid cooling zone. Furthermore, a rapid cooling gas may be injected into the first and second rapid cooling zones, and hydrogen gas may be further injected into the second rapid cooling zone along with the rapid cooling gas. When the rapid cooling process is carried out in two distinct regions in this way, and hydrogen gas is further injected into the second rapid cooling zone in which condensation finally takes place, there is a technical advantage in terms of controlling the size of the nanoparticle catalyst.

[0055] The nanoparticle catalyst obtained in this step after the previous steps may have an average particle size of 100 nm or less, and preferably an average particle size of 20 nm or less. As described above, when the catalyst is produced through the steps described above, it is possible to produce a nanoparticle catalyst with a small average particle size and a narrow particle size distribution, and specifically, a nanoparticle catalyst that satisfies the above conditions can be produced. On the other hand, the average particle size can be measured by the BET analysis method. Specifically, the average particle size can be calculated by the following formula.

[0056] Average particle size=6 / (BET specific surface area*density) In the above formula, the unit of the BET specific surface area is m 2 The BET specific surface area is expressed as / g, and a device such as the BELSORP-max manufactured by BEL Japan Inc. can be used to measure the BET specific surface area.

[0057] Carbon nanotube synthesis section (S4 and S5) Carbon nanotubes can be synthesized using the nanoparticle catalyst produced in the previous catalyst particle production section. Specifically, carbon nanotubes can be produced by the steps of introducing the produced nanoparticle catalyst and the raw material gas into a CVD reactor (S4), and synthesizing the carbon nanotubes in the CVD reactor (S5).

[0058] Step (S4) involves introducing the nanoparticle catalyst and the source gas, respectively. To synthesize carbon nanotubes, the step of introducing a nanoparticle catalyst manufactured using a plasma apparatus and a source gas into a CVD reactor must be performed. The catalyst is as described above, and the source gas is a carbon-containing gas for forming carbon nanotubes on the surface of the catalyst.

[0059] The aforementioned raw material gas is a carbon-containing gas that can decompose 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 may contain one or more selected from the group consisting of C1-C10 aliphatic hydrocarbons, C6-20 aromatic hydrocarbons, carbon monoxide, natural gas, C1-6 alcohols, and acetone. Even more specifically, 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, and acetone can be used. Methane is particularly preferred in terms of economy and efficiency.

[0060] The present invention synthesizes carbon nanotubes via a CVD reactor, and the CVD reactor may be physically separated from the plasma apparatus capable of performing the previous S1-S3 steps. The CVD reactor is suitable for mixing nanoparticle catalysts and raw material gases introduced in an aerosol state and carrying out the reaction, and allows carbon nanotubes to be grown on the surface of the nanoparticle catalyst while it is floating. The CVD reactor may be a chemical vapor deposition (CVD), catalytic chemical vapor deposition (CCVD), or floating catalyst chemical vapor deposition (FCCVD) reactor.

[0061] On the other hand, in the carbon nanotube manufacturing method of the present invention, the nanoparticle catalyst and the raw material gas may be introduced into the CVD reactor separately. If the nanoparticle catalyst and the raw material gas are pre-mixed and introduced into the CVD reactor, equipment for pre-mixing the two components must be provided between the plasma device and the CVD reactor, which not only complicates the process but may also lead to problems such as the catalyst being deactivated by coking, making it difficult to synthesize carbon nanotubes. In contrast, if the nanoparticle catalyst and the raw material gas are introduced into the CVD reactor separately, the input control variables for each component can be easily controlled, and the crystallinity of the final carbon nanotube can also be improved.

[0062] In this step, in addition to the nanoparticle catalyst and reaction feedstock gas described above, a co-catalyst may be further added to the CVD reactor. The co-catalyst can enhance catalytic activity and improve the carbon nanotube production yield, and may be sulfur or a sulfur-containing compound, more specifically, one or more selected from the group consisting of thiophene, alkylthiophene, benzothiophene, hydrogen sulfide, and carbon disulfide.

[0063] The amount of co-catalyst added may vary depending on the type and amount of raw material gas introduced into the CVD reactor, the amount of catalyst, etc. For example, the co-catalyst may be added with a weight ratio of catalyst to co-catalyst of 1:1 to 100:1. If too much co-catalyst is added, it may inactivate (poison) the catalyst itself, and if too little is added, the effect of adding the co-catalyst may be negligible.

[0064] Carbon nanotube synthesis step (S5) Carbon nanotubes can be synthesized by the decomposition of the raw material gas on the surface of the aerosolized nanoparticle catalyst introduced into the CVD reactor in a previous step. Specifically, carbon nanotubes can be synthesized by heating the CVD reactor. The temperature of the heated CVD reactor may be 800°C to 1400°C. At these temperatures, the reaction raw material gas is decomposed and carbon nanotubes can be formed on the surface of the liquid phase catalyst particles. If the temperature of the CVD reactor is lower than this, sufficient decomposition of the reaction raw material gas may not occur, and if the temperature of the CVD reactor is higher than this, the synthesis yield of carbon nanotubes may decrease significantly.

[0065] In this step, carbon nanotubes are grown and synthesized on the surface of liquid-phase catalyst particles, and the final carbon nanotube product may contain catalyst particles. The carbon nanotubes obtained in this step may be single-walled carbon nanotubes, multi-walled carbon nanotubes, or a mixture of single-walled and multi-walled carbon nanotubes. The carbon nanotubes may also be obtained in powder form.

[0066] The S1 to S5 steps described above may be carried out continuously. In contrast to conventional carbon nanotube manufacturing methods using a fluidized bed reactor, which operate in batch mode, the present invention allows for the continuous input of raw materials and nanoparticle catalysts, thus enabling the continuous production of catalyst particles. Furthermore, the operation of the CVD reactor can also be carried out continuously, allowing the entire manufacturing process to be carried out continuously.

[0067] The carbon nanotubes obtained by the production method of the present invention may be bundled. When the carbon nanotubes are "bundled", it means that a plurality of carbon nanotubes are arranged or aligned in a certain direction to form a secondary structure in the form of a bundle or a rope, and in particular, the carbon nanotubes obtained by the production method of the present invention are suitable for use as a conductive material or the like by bundling.

[0068] The carbon nanotubes produced by the production method of the present invention have a specific surface area of 1000 m 2 / g or less and a bulk density of 0.05 g / cm 3 or more. Also, the carbon nanotubes produced by the production method of the present invention can have a maximum crystallinity (I G / I D value) of 40 or more and excellent crystallinity. On the other hand, the crystallinity can be measured as the value of I G / I D measured by Raman analysis.

[0069] Hereinafter, examples and experimental examples will be given to explain the present invention more specifically, but the present invention is not limited to these examples and experimental examples. The examples according to the present invention may be deformed into various different forms, and the scope of the present invention should not be construed as being limited to the examples described later. The examples of the present invention are provided to explain the present invention more specifically to those having average knowledge in the industry.

[0070] Materials As a catalyst raw material, Fe powder and FeS powder with a particle size of 10 to 50 μm were mixed and used, and the catalyst raw material was dried in a vacuum oven to remove moisture in advance before being fed into a feeder.

[0071] Example 1 To ignite the plasma in a vacuum, Ar (32 lpm) and H2 (1.4 lpm) were injected as sheath gases into the plasma torch, and Ar (12 lpm) was injected as a central gas. After ignition was complete, the pressure inside the plasma apparatus was atmospheric pressure (14.7 psi), and the catalyst material (FeS content 16 wt%) was supplied to the feeder of the RF thermal plasma apparatus (carrier gas: Ar, flow rate: 5 lpm), and the catalyst material was vaporized by the plasma torch. The formed catalyst vapor was transferred to the rapid cooling zone by convection and diffusion, and Ar, the rapid cooling gas, was injected into the first and second rapid cooling zones at a rate of 75 lpm and 175 lpm, respectively, to rapidly cool and condense the catalyst vapor. Meanwhile, H2 gas was injected into the second rapid cooling zone along with Ar at a flow rate of 30 lpm. The catalyst vapor, having passed through both the first and second rapid cooling zones, condensed to form aerosol-state nanoparticle catalysts, which were then introduced into a CVD reactor preheated to 1350°C.

[0072] In addition, separate from the nanoparticle catalyst, methane gas, which is the raw material gas, was injected into the CVD reactor at a flow rate of 4 lpm and passed through a preheating device heated to 500°C before injection.

[0073] The aforementioned nanoparticle catalyst and raw material gas were introduced into the CVD reactor, and the synthesis of carbon nanotubes was started. The synthesis process was carried out for 20 minutes. After the completion of the process, gas injection was stopped, the CVD reactor was cooled, and carbon nanotubes were obtained.

[0074] Example 2 In the above-described Example 1, a catalyst raw material was used that was mixed to have a FeS content of 20% by weight, the CVD reactor was heated to 1400°C, and methane gas was injected into the CVD reactor at a flow rate of 3 lpm and hydrogen gas at a flow rate of 9.5 lpm. The procedure was carried out in the same manner as above, except that the procedure was carried out in the same manner.

[0075] Example 3 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 at a flow rate of 50 lpm.

[0076] Comparative Example 1 In Example 2 described above, carbon nanotubes were obtained by following the same procedure as described above, except that 4 lpm of methane gas and 9.5 lpm of hydrogen gas were pre-mixed with an aerosolized nanoparticle catalyst using a small chamber before being injected into the CVD reactor, and the CVD reactor was heated to a temperature of 1300°C.

[0077] The manufacturing conditions for the above examples and comparative examples are summarized in Table 1 below.

[0078] [Table 1]

[0079] Experimental Example 1. Confirmation of the crystallinity of manufactured carbon nanotubes. Raman spectroscopy was used to determine the I of carbon nanotubes produced in the above examples and comparative examples. G and I D The values ​​were measured, and the average crystallinity and maximum crystallinity were calculated and shown in Table 2 below. The average crystallinity and maximum crystallinity were calculated for multiple locations in the carbon nanotube sample. G / I D After measuring the values, the average and maximum values ​​were taken.

[0080] [Table 2]

[0081] As can be seen from Table 2 above, the carbon nanotubes produced in the examples of the present invention showed high crystallinity with a maximum crystallinity of 40 or higher, while the carbon nanotubes produced in Comparative Example 1 showed a crystallinity value of less than 1. In other words, the crystallinity of the carbon nanotubes produced in Comparative Example 1 is significantly inferior to that of the examples, and this means that high-quality carbon nanotubes can be produced using the carbon nanotube production method of the present invention.

[0082] Experimental Example 2. Confirmation of SEM images of carbon nanotubes produced in the example. The carbon nanotubes produced in Example 3 were observed using SEM imaging. The images were taken at magnifications of 100K and 50K, and the results are shown in Figures 1 and 2.

[0083] As can be seen from Figures 1 and 2, when using the carbon nanotube manufacturing method of the present invention, it was confirmed that multiple thin and flexible carbon nanotubes are manufactured in a bundled form.

Claims

1. Step (S1) involves vaporizing the catalyst raw material using a plasma torch to form a catalyst vapor, Step (S2) of transferring the catalyst vapor to a rapid cooling zone by plasma flow, Step (S3) involves condensing the catalyst vapor in the rapid cooling zone to produce a nanoparticle catalyst, Step (S4) involves introducing the manufactured nanoparticle catalyst and the source gas into the CVD reactor, The step of synthesizing carbon nanotubes in the CVD reactor (S5), Includes, The rapid cooling zone includes a first rapid cooling zone and a second rapid cooling zone. The catalyst vapor flows from the first rapid cooling zone to the second rapid cooling zone. An inert gas is injected into the first and second rapid cooling zones. A method for producing carbon nanotubes, wherein hydrogen gas is injected into the second rapid cooling zone.

2. The method for producing carbon nanotubes according to claim 1, characterized in that the nanoparticle catalyst has an average particle size of 100 nm or less.

3. The method for producing carbon nanotubes according to claim 1, wherein the plasma torch is an inductively coupled RF thermal plasma torch.

4. The method for producing carbon nanotubes according to claim 1, wherein the catalyst raw material comprises one or more metals selected from the group consisting of Fe, Co, Ni, Pd, Pt, Ru, Cu, Mn, Cr, Mo, V, Mg, Si, Ge, and Eu, or a precursor thereof.

5. The method for producing carbon nanotubes according to claim 4, wherein the catalyst raw material further comprises sulfur, or a sulfide of one or more metals 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 for producing carbon nanotubes according to claim 1, wherein the catalyst raw material is in liquid or solid form.

7. The method for producing carbon nanotubes according to claim 6, wherein the catalyst raw material is in the form of a powder with an average particle size of 5 μm to 100 μm.

8. The method for producing carbon nanotubes according to claim 1, wherein the raw material gas comprises one or more selected from the group consisting of C1-C10 aliphatic hydrocarbons, C6-20 aromatic hydrocarbons, carbon monoxide, natural gas, C1-6 alcohols, and acetone.

9. The method for producing carbon nanotubes according to claim 1, wherein the nanoparticle catalyst produced in step S3 is in an aerosol state.

10. The method for producing carbon nanotubes according to claim 1, characterized in that the S4 step further involves adding sulfur or a sulfur-containing compound as a co-catalyst to the CVD reactor.

11. The method for producing carbon nanotubes according to claim 1, characterized in that the S4 step further involves introducing one or more carrier gases selected from the group consisting of inert gas, hydrogen, and nitrogen into a CVD reactor.

12. The method for producing carbon nanotubes according to claim 1, wherein the temperature of the CVD reactor is 800°C to 1400°C.

13. The method for producing carbon nanotubes according to claim 1, wherein the produced carbon nanotubes are single-walled carbon nanotubes, multi-walled carbon nanotubes, or a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes.

14. A method for producing carbon nanotubes according to any one of claims 1 to 13, wherein the steps S1 to S5 are carried out continuously.

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