Carbon nanotubes and methods for producing the same

Abstract

The present invention relates to carbon nanotubes that satisfy a specific formula, and the carbon nanotubes of the present invention are simultaneously excellent in productivity and electrical conductivity.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2023-0144814 dated October 26, 2023, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] This invention relates to a novel carbon nanotube having high bulk density and excellent powder resistance, and to a method for producing the same. [Background technology]

[0003] Carbon nanomaterials include fullerenes, carbon nanotubes (CNTs), graphenes, and graphite nanoplates, depending on their shape. Of these, carbon nanotubes are giant molecules in which hexagonal honeycomb-shaped graphite sheets, each consisting of one carbon atom bonded to three different carbon atoms, are rolled up to a nanoscale diameter.

[0004] Carbon nanotubes are hollow and lightweight, possess electrical conductivity comparable to copper, thermal conductivity comparable to diamond, and tensile strength comparable to steel. Depending on their coiled form, they can be classified into single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), and rope carbon nanotubes.

[0005] The most representative physical properties that characterize carbon nanotubes are bulk density and specific surface area. Bulk density is a representative physical property that indicates the productivity of carbon nanotubes, while specific surface area is a physical property related to the number of walls in the carbon nanotube and is related to the performance of the carbon nanotube. A higher bulk density means that the productivity of carbon nanotubes is superior, and a higher specific surface area tends to indicate fewer walls and superior conductivity of the carbon nanotube. However, in the case of specific surface area, even if the value is high, if the bulk density of the carbon nanotube also rises above a certain level, structural anomalies occur in the carbon nanotube, and conductivity decreases.

[0006] In other words, the productivity and performance of carbon nanotubes are intricately correlated, and generally, synthesizing high-performance carbon nanotubes with high productivity is extremely difficult. Therefore, research is needed on methods to synthesize high-performance carbon nanotubes, particularly those with excellent electrical conductivity, with high productivity. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The present invention aims to provide a novel carbon nanotube and a method for producing the carbon nanotube that exhibits high productivity and achieves electrical conductivity comparable to or better than that of conventional commercial carbon nanotubes in terms of performance. [Means for solving the problem]

[0008] To solve the above-mentioned problems, the present invention provides a novel carbon nanotube and a method for producing the carbon nanotube.

[0009] (1) Specifically, the present invention provides a carbon nanotube that satisfies the following formula 1. [Formula 1] 1.6541*A+0.6823≦R≦1.6541*A+1.6823 In the above formula 1, R is the powder resistance (mΩ·cm) of carbon nanotubes, A is ln{(Specific surface area of ​​carbon nanotubes (m²) 2 / g)*bulk density (kg / m³ 3 It is )) / purity (weight %).

[0010] (2) In the present invention, in (1) above, the specific surface area of ​​the carbon nanotube is 320 m 2 We provide carbon nanotubes that are less than / g.

[0011] (3) In the present invention, in (1) or (2) above, the bulk density of the carbon nanotube is 80 kg / m³. 3 The above-mentioned carbon nanotubes are provided.

[0012] (4) The present invention provides a carbon nanotube in which the purity of the carbon nanotube is 93% by weight or more in any one of (1) to (3) above.

[0013] (5) The present invention provides a carbon nanotube in which, in any one of (1) to (4) above, R is 12 mΩ·cm or less.

[0014] (6) The present invention provides a carbon nanotube in any one of (1) to (5) above, wherein A is 4.5 to 6.5.

[0015] (7) The present invention provides a method for producing carbon nanotubes according to any one of (1) to (6) above, comprising the step (S1) of reacting a carbon source gas in the presence of a supported catalyst to synthesize carbon nanotubes, wherein the supported catalyst is a support on which cobalt and vanadium are supported, and the cobalt content based on the total weight of the supported catalyst is 14 to 30% by weight.

[0016] (8) The present invention provides the method for producing carbon nanotubes according to (7) above, wherein the molar ratio of vanadium to cobalt (V / Co) in the supported catalyst is 0.05 to 0.25. Effects of the Invention

[0017] Although the bulk density of the carbon nanotubes of the present invention is at least three times higher than that of conventional commercially available carbon nanotubes, the powder resistance thereof is at a level equal to or higher than that of conventional commercially available carbon nanotubes. Therefore, the carbon nanotubes of the present invention are particularly suitable for use in various fields where both high productivity and conductivity are required at the same time. Mode for Carrying Out the Invention

[0018] Hereinafter, the present invention will be described in more detail.

[0019] Terms and words used in the present specification and claims shall not be construed as being limited to their ordinary or dictionary meanings. In accordance with the principle that inventors can appropriately define the concept of terms in order to describe their invention in the best way, said terms and words shall be interpreted with meanings and concepts that conform to the technical idea of the present invention.

[0020] In this invention, the term "carbon nanotube" refers to a secondary structure formed by the assembly of carbon nanotube units, either entirely or partially, in a bundled form. The carbon nanotube unit consists of a graphite sheet with a nanoscale diameter and a cylindrical shape, and has an sp2 bond structure. Depending on the angle and structure in which the graphite sheet is wound, it can exhibit conductive or semiconductor properties. The carbon nanotube unit is classified into single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs) according to the number of bonds forming the wall, with lower resistance occurring as the wall thickness decreases.

[0021] The carbon nanotubes of the present invention may include one or more single-walled, double-walled, and multi-walled carbon nanotube units.

[0022] carbon nanotubes The present invention provides carbon nanotubes that satisfy the following formula 1.

[0023] [Formula 1] 1.6541*A+0.6823≦R≦1.6541*A+1.6823

[0024] In the above formula 1, R is the powder resistance (mΩ·cm) of carbon nanotubes, A is ln{(Specific surface area of ​​carbon nanotubes (m²) 2 / g)*bulk density (kg / m³ 3 It is )) / purity (weight %).

[0025] The inventors of this invention diligently researched methods to maintain the performance level of carbon nanotubes and increase their productivity. As a result, they discovered that when the powder resistance, purity, specific surface area, and bulk density of carbon nanotubes satisfy the above formula 1, the productivity and electrical conductivity of carbon nanotubes can all be maintained at excellent levels, thus completing the present invention.

[0026] More specifically, when the manufacturing conditions of the catalyst used to produce carbon nanotubes are changed—specifically, the content of the active ingredient, the ratio of the main catalyst component to the co-catalyst component, the content of organic acids in the precursor solution, and the calcination temperature—the physical properties of the carbon nanotubes produced from the catalyst also change. Therefore, by changing the manufacturing conditions of the catalyst, various carbon nanotubes with different physical properties can be synthesized. Furthermore, by examining the correlation between the productivity and electrical conductivity of the various synthesized carbon nanotubes using various methods, it was confirmed that carbon nanotubes produced under specific conditions satisfy Equation 1 above, exhibiting both excellent productivity and electrical conductivity.

[0027] More specifically, Equation 1 means that there is a correlation between the powder resistance of carbon nanotubes and their purity, specific surface area, and bulk density. Equation 1 is derived from data on carbon nanotubes synthesized using catalysts produced under various conditions. Generally, there is a trade-off relationship between the productivity and electrical conductivity of carbon nanotubes, but unlike that, carbon nanotubes produced under specific conditions can be found to have excellent productivity and electrical conductivity by satisfying Equation 1.

[0028] In the above formula 1, the A value and the R value are values ​​with different units from each other, but in this invention, the units of each value are ignored and each value is assumed to be a dimensionless number. However, since each value may differ depending on the units of the variables of each value, namely the powder resistance, purity, specific surface area, and bulk density of carbon nanotubes, the units of each variable are fixed as follows when applying the above formula 1.

[0029] Powder resistance (R) of carbon nanotubes, unit: mΩ·cm Purity of carbon nanotubes, unit: wt% Specific surface area of carbon nanotubes, unit: m 2 / g Bulk density of carbon nanotubes, unit: kg / m 3

[0030] On the other hand, in the carbon nanotubes provided by the present invention, the specific surface area of the carbon nanotubes is 320 m 2 / g or less, preferably 320 m 2 / g or less, 310 m 2 / g or less, or 300 m 2 / g or less, and preferably 250 m 2 / g or more, 260 m 2 / g or more, 270 m 2 / g or more, or 280 m 2 / g or more. As described above, the specific surface area is a factor that directly affects the performance of carbon nanotubes, and the carbon nanotubes of the present invention can exhibit excellent electrical conductivity by having a specific surface area within the above range. Meanwhile, the specific surface area may be measured by the BET method, and more specifically, may be calculated by determining the nitrogen gas adsorption amount under liquid nitrogen temperature (77 K) using BELSORP-mini II manufactured by BEL Japan.

[0031] Furthermore, the bulk density of the carbon nanotubes of the present invention is 80 kg / m 3 or more, preferably 80 kg / m 3 or more, 85 kg / m 3 or more, 90 kg / m 3 or more, or 95 kg / m 3 or more, and 120 kg / m 3 or less, 115 kg / m 3 or less, 110 kg / m 3 or less, or 105 kg / m 3The following may also apply. The bulk density is a factor that can indicate the productivity of carbon nanotubes, and the carbon nanotubes of the present invention may have excellent productivity by having a bulk density within the above range. The bulk density value of the carbon nanotubes of the present invention is higher than that of conventional commercial carbon nanotubes, and the carbon nanotubes of the present invention can be produced in sufficiently large quantities even with the use of less catalyst compared to conventional commercial carbon nanotubes. On the other hand, the bulk density can be calculated by measuring the weight of the carbon nanotubes that have entered the container by free fall using a 25 ml SUS measuring cup, and dividing the measured weight by the volume of the container.

[0032] Furthermore, the carbon nanotubes of the present invention may have a purity of 93% by weight or more, and particularly preferably 93.5% by weight or more, 94% by weight or more, 94.5% by weight or more, or 95% by weight or more. The purity refers to the content of carbon nanotubes remaining after impurities have been removed from the carbon nanotubes, and can be calculated by the following formula.

[0033] Purity = (Amount of carbon nanotubes obtained - Amount of catalyst added) / Amount of carbon nanotubes obtained * 100%

[0034] The aforementioned severity, like the bulk density of carbon nanotubes described above, is an indicator that can show the productivity of carbon nanotubes, and the purity value also confirms that the carbon nanotubes of the present invention exhibit high productivity.

[0035] Furthermore, the powder resistance R of the carbon nanotube of the present invention may be 12 mΩ·cm or less, and is particularly preferably 12 mΩ·cm or less, 11.5 MΩ·cm or less, 11.3 mΩ·cm or less, or 11 mΩ·cm or less, and may also be 10 MΩ·cm or more, 10.2 mΩ·cm or more, 10.4 mΩ·cm or more, or 10.5 mΩ·cm or more. As described above, the carbon nanotube of the present invention may have high productivity, low powder resistance, and excellent electrical conductivity. On the other hand, the powder resistance may be measured using the MCP-PD51 equipment manufactured by Nittoseiko Analytech, Inc., when the compressed density is 1 g / cc and the resistance is measured under pressure.

[0036] Furthermore, in the carbon nanotube of the present invention, the A value calculated from the aforementioned specific surface area, bulk density, and purity may be 4.5 to 6.5, and preferably 5 to 6.

[0037] Method for manufacturing carbon nanotubes The present invention provides a method for synthesizing carbon nanotubes that satisfy the aforementioned formula 1.

[0038] More specifically, the present invention provides a method for producing carbon nanotubes, comprising the step (S1) of synthesizing carbon nanotubes by reacting a carbon source gas in the presence of a supported catalyst, wherein the supported catalyst is a support on which cobalt and vanadium are supported, and the cobalt content, based on the total weight of the supported catalyst, is 14 to 30% by weight.

[0039] The carbon nanotubes of the present invention can only be produced using a catalyst manufactured under specific conditions. The requirements for the catalyst used in the production of the carbon nanotubes of the present invention are that it is supported with cobalt and vanadium, and that the cobalt content, based on the total weight of the catalyst, is 14 to 30% by weight.

[0040] If the cobalt content in the supported catalyst is lower or higher than described above, the powder resistance of the carbon nanotubes obtained from the catalyst may increase, and in some cases the specific surface area may also increase, potentially reducing the electrical conductivity of the carbon nanotubes.

[0041] On the other hand, in the supported catalyst, the molar ratio of vanadium to cobalt (V / Co) in the supported catalyst may be 0.05 to 0.25. If the molar ratio is low and the catalyst contains no vanadium or only a very small amount, the powder resistance of the carbon nanotubes produced from the catalyst may increase significantly, and if the molar ratio is high, the bulk density of the carbon nanotubes may decrease significantly, potentially reducing productivity.

[0042] On the other hand, the supported catalyst may also be manufactured by immersing a support in an aqueous precursor solution containing a dissolved cobalt precursor and a vanadium precursor, followed by drying and calcination. In this process, the properties of the catalyst may also differ depending on the amount of multicarboxylic acid contained in the aqueous precursor solution. In the case of the supported catalyst of the present invention, the molar ratio of the multicarboxylic acid to vanadium (multicarboxylic acid / V) is preferably 0.3 to 1.0, and carbon nanotubes with lower powder resistance can be produced using a catalyst manufactured within this range. On the other hand, citric acid can be used as the multicarboxylic acid.

[0043] Furthermore, the support for the supported catalyst may be a porous metal oxide, and more specifically, one or more selected from the group consisting of hydrotalcite, alumina (Al2O3), magnesium peroxide (MgO2), magnesium oxide (MgO), and boehmite may be used.

[0044] Furthermore, in the method for producing carbon nanotubes of the present invention, the carbon source gas is a carbon-containing gas that can be decomposed 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, compounds such as methane, ethane, ethylene, acetylene, ethanol, methanol, acetone, carbon monoxide, propane, butane, benzene, cyclohexane, propylene, butene, isobutene, toluene, xylene, cumene, ethylbenzene, naphthalene, phenanthrene, anthracene, acetylene, formaldehyde, and acetaldehyde can be used.

[0045] Furthermore, in the method for producing carbon nanotubes of the present invention, the reaction of the carbon source gas may also involve heating the carbon source gas in the presence of the supported catalyst, and the heating temperature may be 600 to 800°C. In addition, the reactor in which the reaction takes place may be a chemical vapor deposition reactor, a fixed-bed reactor, or a fluidized-bed reactor.

[0046] The present invention will be described in more detail below with reference to examples and experimental examples in order to specifically illustrate it. However, the present invention is not limited to these examples and experimental examples. The examples of the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to give a more complete explanation of the present invention to a person of average skill in the art.

[0047] Examples of catalyst manufacturing Co(NO3)2·6H2O was used as the cobalt precursor, and NH4VO3 as the vanadium precursor. The cobalt and vanadium precursors were dissolved in water, and citrate anhydride (CA), a multicarboxylic acid complexing agent, was dissolved together to prepare an aqueous precursor solution. After thoroughly stirring the catalyst precursor composition, it was added to hydrotalcite, which was used as a support. Subsequently, the catalyst was dried in an oven at 190°C for 3 hours, and then calcined at 680°C in air for 1 hour to complete the catalyst. In the above process, the cobalt content, V / Co molar ratio, and citrate / V molar ratio of the final catalyst were adjusted in various ways to produce various catalysts, and the production conditions for each production example are summarized in Table 1 below.

[0048] [Table 1A] [Table 1B]

[0049] Examples and Comparative Examples Carbon nanotubes were synthesized using the catalyst used in the catalyst production example described above. Specifically, 6.4 g of the produced catalyst was packed into a fluidized bed reactor, and then nitrogen gas was injected into the reactor at a rate of 3,000 sccm, heating the internal temperature of the reactor to 690°C. Next, ethylene gas, which is the carbon source gas, was injected at a rate of 1,000 sccm, and the reaction was continued for 120 minutes to synthesize carbon nanotubes. The catalysts used in each example and comparative example are summarized in Table 2 below.

[0050] [Table 2A] [Table 2B]

[0051] Experimental Example 1. Verification of whether the manufactured carbon nanotubes satisfy Equation 1. The purity, specific surface area, bulk density, and powder resistance of the carbon nanotubes produced in the above examples and comparative examples, as well as five types of commercial carbon nanotubes, were measured to confirm whether they satisfied Equation 1. Each physical property was measured by the following method.

[0052] 1) Purity: (Amount of carbon nanotubes obtained - Amount of catalyst added) / Amount of carbon nanotubes obtained * 100% 2) Specific surface area: This was calculated by determining the amount of nitrogen gas adsorbed under liquid nitrogen temperature (77K) using BELSORP-mini II manufactured by BEL Japan. 3) Bulk density: The weight of carbon nanotubes that entered the container by free fall was measured using a 25 ml SUS quantitative cup, and the bulk density was calculated by dividing the measured weight by the volume of the container. 4) Powder resistance: Using the MCP-PD51 equipment manufactured by Nittoseiko Analytech, the resistance under pressure was measured when the compressed density was 1 g / cc.

[0053] The measured results are summarized in Table 3 below. [Table 3A] [Table 3B] [Table 3C]

[0054] As can be seen from Table 3 above, the carbon nanotubes according to the embodiments of the present invention satisfy formula 1. On the other hand, the carbon nanotubes according to the comparative examples do not satisfy formula 1.

[0055] From the results described above, it was confirmed that the carbon nanotubes of the present invention exhibit excellent productivity and electrical conductivity simultaneously, which are known to be in a trade-off relationship with conventional materials.

Claims

1. A carbon nanotube characterized by satisfying the following formula 1. [Formula 1] 1.6541*A+0.6823≦R≦1.6541*A+1.6823 In the above formula 1, R is the powder resistance (mΩ·cm) of carbon nanotubes. A is ln{(Specific surface area of ​​carbon nanotubes (m²) ２ / g) * bulk density (kg / m³) ３ )) / Purity (weight %)}.

2. The specific surface area of ​​the carbon nanotube is 320 m². ２ The carbon nanotube according to claim 1, wherein the amount is less than or equal to / g.

3. The bulk density of the carbon nanotubes is 80 kg / m³. ３ The carbon nanotube described in claim 1 is as described above.

4. The carbon nanotube according to claim 1, wherein the purity of the carbon nanotube is 93% by weight or more.

5. The carbon nanotube according to claim 1, wherein R is 12 mΩ·cm or less.

6. The carbon nanotube according to any one of claims 1 to 5, wherein A is 4.5 to 6.

5.

7. The process includes the step (S1) of synthesizing carbon nanotubes by reacting a carbon source gas in the presence of a supported catalyst, The supported catalyst is one in which cobalt and vanadium are supported on a support. The method for producing carbon nanotubes according to claim 1, wherein the cobalt content, based on the total weight of the supported catalyst, is 14% to 30% by weight.

8. The method for producing carbon nanotubes according to claim 7, wherein the molar ratio of vanadium to cobalt (V / Co) in the supported catalyst is 0.05 to 0.25.

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