Carbon nanotube and preparation method thereof

Abstract

The present invention relates to a carbon nanotube satisfying a specific equation, and the carbon nanotube of the present invention has excellent productivity and conductivity.

Description

Technical Field

[0001] Cross-referencing related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2023-0144814, filed with the Korean Intellectual Property Office on October 26, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This invention relates to novel carbon nanotubes with high packing density and excellent powder resistivity, and their preparation method. Background Technology

[0004] Carbon nanomaterials can be classified into fullerenes, carbon nanotubes (CNTs), graphene, graphite nanoplates, etc., according to their shape. Among them, carbon nanotubes are large molecules with nanoscale diameters formed by curling the surface of hexagonal honeycomb graphite, in which one carbon atom is bonded to three other carbon atoms.

[0005] Carbon nanotubes are hollow, making them lightweight, and possess electrical conductivity as good as copper, thermal conductivity as good as diamond, and tensile strength as good as steel. Based on their coiled shape, carbon nanotubes can be classified into single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), and rope-like carbon nanotubes.

[0006] The most representative physical properties of carbon nanotubes are their bulk density and specific surface area. Bulk density is a representative physical property of carbon nanotube productivity, while specific surface area is a physical property related to the number of walls in carbon nanotubes and is related to their performance. Higher bulk density results in higher carbon nanotube productivity, and a higher specific surface area and fewer walls lead to better electrical conductivity. However, even with a high specific surface area, if the bulk density of carbon nanotubes increases to a certain level or higher, the electrical conductivity of the carbon nanotubes decreases due to the appearance of structural singularities.

[0007] In other words, the productivity and performance of carbon nanotubes have a complex correlation, and it is generally difficult to synthesize high-performance carbon nanotubes with high productivity. Therefore, there is a need to investigate a method for synthesizing high-performance carbon nanotubes with particularly excellent conductivity at high productivity. Summary of the Invention

[0008] Technical issues

[0009] The purpose of this invention is to provide a novel carbon nanotube and its preparation method, wherein the carbon nanotube exhibits high productivity and achieves conductivity similar to or better than that of conventional commercial carbon nanotubes.

[0010] Technical solution

[0011] To achieve the above objectives, the present invention provides a novel carbon nanotube and its preparation method.

[0012] (1) Specifically, the present invention provides a carbon nanotube, wherein the carbon nanotube satisfies the following equation 1: [Equation 1] 1.6541 × A + 0.6823 ≤ R ≤ 1.6541 × A + 1.6823 In Equation 1 above, R is the powder resistance of carbon nanotubes (mΩ·cm), and A is ln{(specific surface area of ​​carbon nanotubes (m²·cm)}. 2 / g)×bulk density (kg / m³) 3 )) / Purity (wt%)}.

[0013] (2) In (1) above, the present invention provides a carbon nanotube, wherein the specific surface area of ​​the carbon nanotube is 320 m². 2 / g or less.

[0014] (3) In (1) or (2) above, the present invention provides a carbon nanotube, wherein the packing density of the carbon nanotube is 80 kg / m³. 3 above.

[0015] (4) In any one of (1) to (3) above, the present invention provides a carbon nanotube, wherein the carbon nanotube has a purity of 93% by weight or more.

[0016] (5) In any of (1) to (4) above, the present invention provides a carbon nanotube, wherein R is less than 12 mΩ·cm.

[0017] (6) In any of (1) to (5) above, the present invention provides a carbon nanotube, wherein A is 4.5 to 6.5.

[0018] (7) The present invention provides a method for preparing carbon nanotubes according to any one of (1) to (6) above, the method comprising: S1 reacting a carbon source gas in the presence of a supported catalyst to synthesize carbon nanotubes, wherein cobalt and vanadium are supported on a support in the supported catalyst, and the cobalt content based on the total weight of the supported catalyst is 14% to 30% by weight.

[0019] (8) In (7) above, the present invention provides a method for preparing carbon nanotubes, wherein the molar ratio (V / Co) of vanadium to cobalt in the supported catalyst is 0.05 to 0.25.

[0020] Beneficial effects

[0021] Although the packing density of the carbon nanotubes of the present invention is three times higher than that of conventional commercial carbon nanotubes, the carbon nanotubes exhibit powder resistance at a level equal to or higher than that of conventional commercial carbon nanotubes, making the carbon nanotubes particularly suitable for various fields that require both high productivity and conductivity. Detailed Implementation

[0022] The invention will be described in more detail below.

[0023] It should be understood that the terms or words used in this specification and claims should not be construed as having the meanings defined in common dictionaries, but should be construed as having meanings and concepts consistent with the technical spirit of the invention, based on the inventor's ability to appropriately define the concepts of the terms to best explain the principles of the invention.

[0024] The term "carbon nanotube" as used in this invention refers to a secondary structure in which carbon nanotube units are assembled, either wholly or partially, into a bundle shape, and the carbon nanotube units are cylindrical graphite sheets with nanometer-sized diameters and an sp2 bond structure. In this case, depending on the angle and structure of the graphite sheets being rolled up, conductive or semiconductor properties can be exhibited. Based on the number of bonds forming the walls, carbon nanotube units can be classified as single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs), with thinner walls resulting in lower electrical resistance.

[0025] The carbon nanotubes of the present invention may include one or more of single-walled carbon nanotube units, double-walled carbon nanotube units, and multi-walled carbon nanotube units.

[0026] carbon nanotubes

[0027] This invention provides a carbon nanotube, which satisfies the following equation 1: [Equation 1] 1.6541 × A + 0.6823 ≤ R ≤ 1.6541 × A + 1.6823 In Equation 1 above, R is the powder resistance of carbon nanotubes (mΩ·cm), and A is ln{(specific surface area of ​​carbon nanotubes (m²·cm)}. 2 / g)×bulk density (kg / m³) 3 )) / Purity (wt%)}.

[0028] The inventors of this invention have studied a method that can improve the productivity of carbon nanotubes while maintaining the performance of carbon nanotubes at the same level. The results show that if the powder resistance, purity, specific surface area and bulk density of carbon nanotubes satisfy Equation 1 above, the productivity and conductivity of carbon nanotubes can be maintained at an excellent level, thus completing this invention.

[0029] More specifically, if the preparation conditions of the catalyst used to prepare 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, or the calcination temperature—the physical properties of the carbon nanotubes prepared by the corresponding catalyst also change. Therefore, by changing the preparation conditions of the catalyst, various carbon nanotubes with different physical properties can be synthesized. Furthermore, as a result of confirming the correlation between the productivity and conductivity of various synthesized carbon nanotubes in various ways, it has been confirmed that carbon nanotubes prepared under specific conditions satisfy Equation 1 above, and thus exhibit excellent productivity and conductivity.

[0030] More specifically, Equation 1 above implies a correlation between the powder resistivity of carbon nanotubes and their purity, specific surface area, and packing density. Equation 1 is derived from data on carbon nanotubes synthesized using catalysts prepared under various conditions, and unlike the usual trade-off between productivity and conductivity of carbon nanotubes, it demonstrates that carbon nanotubes prepared under specific conditions satisfy Equation 1, thus exhibiting excellent productivity and conductivity.

[0031] In Equation 1 above, the values ​​of A and R are values ​​with different units from each other, but in this invention, the unit of each value is ignored, and it is assumed that each value is dimensionless. However, since each value can vary depending on the units of each of the variables of carbon nanotube powder resistance, purity, specific surface area, and bulk density, the units of each variable are fixed when applying Equation 1 as follows.

[0032] Powder resistivity (R) of carbon nanotubes, unit: mΩ·cm

[0033] Carbon nanotube purity unit: weight %

[0034] The unit for the specific surface area of ​​carbon nanotubes is (m²). 2 / g)

[0035] The bulk density of carbon nanotubes is measured in kg / m³. 3

[0036] Meanwhile, in the carbon nanotubes provided by this invention, the specific surface area of ​​the carbon nanotubes can be 320 m². 2 / g or less, preferably 320m 2 / g or less, 310m2 Below / g, or 300m 2 / g or less, and preferably 250m 2 / g or more, 260m 2 / g or more, 270m 2 / g or more, or 280m 2 / g or more. As mentioned above, specific surface area is a factor that directly affects the performance of carbon nanotubes, and the specific surface area of ​​the carbon nanotubes of the present invention is within the above-mentioned range, thus exhibiting excellent conductivity. Furthermore, the specific surface area can be measured using the BET method, and more specifically, it can be calculated by obtaining the amount of nitrogen adsorbed at liquid nitrogen temperature (77K) using the BELSORP-mini II from BEL Japan Co., Ltd.

[0037] Furthermore, the packing density of the carbon nanotubes of the present invention can be 80 kg / m³. 3 The above is preferably 80kg / m 3 Above, 85kg / m 3 Above, 90kg / m 3 Above, 95kg / m 3 Above, and 120kg / m 3 Below, 115kg / m 3 Below, 110kg / m 3 Below, 105kg / m 3 The following describes the packing density, a factor that reflects the productivity of carbon nanotubes. The carbon nanotubes of the present invention have a packing density within the aforementioned range, thus exhibiting excellent productivity. The packing density of the carbon nanotubes of the present invention is higher than that of conventional commercial carbon nanotubes, and compared to conventional commercial carbon nanotubes, the carbon nanotubes of the present invention can be prepared in sufficiently large quantities even with a small amount of catalyst. Furthermore, the packing density can be calculated by measuring the weight of the carbon nanotubes contained in a 25 ml SUS measuring cup by free fall and dividing the measured weight by the volume of the container.

[0038] Furthermore, the purity of the carbon nanotubes of the present invention can be 93% by weight or more, and is 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. Purity refers to the content of carbon nanotubes remaining after removing impurities from the carbon nanotubes, and can be calculated using the following equation: Purity = (Carbon nanotubes produced - Catalyst added) / Carbon nanotubes produced × 100% Similar to the packing density of carbon nanotubes mentioned above, purity is also an index that can reflect the productivity of carbon nanotubes, and it can be confirmed that even with the above purity values, the carbon nanotubes of the present invention exhibit high productivity.

[0039] Furthermore, the powder resistance R of the carbon nanotubes of the present invention can be 12 mΩ·cm or less, 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 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 nanotubes of the present invention have high productivity and low powder resistance, and therefore can have excellent conductivity. Meanwhile, when the compressed density is measured using the MCP-PD51 device of Nittoseiko Analytech Co., Ltd. at 1 g / cc, the powder resistance can be the resistance based on pressure.

[0040] Furthermore, in the carbon nanotubes of the present invention, the A value calculated from the above specific surface area, bulk density and purity can be 4.5 to 6.5, preferably 5 to 6.

[0041] Preparation methods of carbon nanotubes

[0042] This invention provides a method for synthesizing carbon nanotubes that satisfies Formula 1 above.

[0043] More specifically, the present invention provides a method for preparing carbon nanotubes, the method comprising: S1 reacting a carbon source gas in the presence of a supported catalyst to synthesize carbon nanotubes, wherein cobalt and vanadium are supported on a support in the supported catalyst, and the cobalt content based on the total weight of the supported catalyst is 14% to 30% by weight.

[0044] The carbon nanotubes of the present invention can be prepared only using a catalyst prepared under specific conditions. The catalyst used in the preparation of the carbon nanotubes of the present invention requires conditions of supported cobalt and vanadium, with the cobalt content being 14% to 30% by weight of the total weight of the catalyst.

[0045] In supported catalysts, if the cobalt content is less than or greater than the above range, the powder resistance of the carbon nanotubes obtained from the catalyst may increase, and in some cases, its specific surface area may also increase, which may reduce the electrical conductivity of the carbon nanotubes.

[0046] Meanwhile, in supported catalysts, the molar ratio of vanadium to cobalt (V / Co) can be between 0.05 and 0.25. If the molar ratio is low, resulting in the catalyst containing no vanadium or only a very small amount of vanadium, the powder resistivity of the carbon nanotubes prepared from the corresponding catalyst may increase significantly. Conversely, if the molar ratio is high, the packing density of the carbon nanotubes may decrease significantly, which could reduce productivity.

[0047] Meanwhile, the supported catalyst can be prepared by immersing a support in an aqueous precursor solution in which cobalt and vanadium precursors are dissolved, followed by drying and calcination. In this method, the properties of the catalyst can vary depending on the amount of polycarboxylic acid contained in the aqueous precursor solution. In the case of the supported catalyst of the present invention, the molar ratio of polycarboxylic acid to vanadium (polycarboxylic acid / V) is preferably 0.3 to 1.0, and catalysts prepared within this range can be used to prepare carbon nanotubes with low powder resistivity. Citric acid can also be used as the polycarboxylic acid.

[0048] In addition, porous metal oxides can be used as supports for supported catalysts, and more specifically, one or more selected from hydrotalcite, alumina (Al2O3), magnesium peroxide (MgO2), magnesium oxide (MgO) and boehmite can be used.

[0049] Furthermore, in the carbon nanotube preparation method of the present invention, the carbon source gas is a carbon-containing gas that can decompose at high temperature to form carbon nanotubes. Specific examples may include various carbon-containing compounds, such as aliphatic alkanes, aliphatic alkenes, aliphatic alkynes, aromatic compounds, etc. 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, acetaldehyde, etc., can be used.

[0050] Furthermore, in the method for preparing carbon nanotubes of the present invention, the reaction of the carbon source gas can be carried out by heating the carbon source gas in the presence of a supported catalyst, and the heating temperature can be 600 to 800°C. In addition, the reactor in which the reaction takes place can be a chemical vapor deposition reactor, a fixed-bed reactor, or a fluidized-bed reactor.

[0051] The invention will be described in more detail below with reference to embodiments and experimental examples, but the invention is not limited to these embodiments and examples. Embodiments of the invention can be modified into various other forms, and the scope of the invention should not be construed as limited to the embodiments described below. Embodiments of the invention are provided to enable those skilled in the art to describe the invention more fully.

[0052] Catalyst preparation example

[0053] Co(NO3)2·6H2O was used as the cobalt precursor, and NH4VO3 was used as the vanadium precursor. The cobalt and vanadium precursors were dissolved in water, and citric anhydride (CA) was dissolved together using a polycarboxylic acid (as a complexing agent) to prepare an aqueous precursor solution. The catalyst precursor composition was thoroughly stirred and then introduced into a hydrotalcite support. The mixture was then dried in an oven at 190°C for 3 hours, and then calcined at 680°C in atmospheric conditions for 1 hour to complete the catalyst. In the above method, the cobalt content, V / Co molar ratio, and citric acid / V molar ratio of the final catalyst were adjusted in various ways to prepare various types of catalysts. The preparation conditions of the catalysts in each example are summarized in Table 1 below.

[0054] [Table 1]

[0055] CA: Citric anhydride

[0056] Examples and Comparative Examples

[0057] The catalyst used in the above catalyst preparation examples was used to synthesize carbon nanotubes. Specifically, 6.4 g of the prepared catalyst was added to a fluidized bed reactor, and then nitrogen gas was injected into the reactor at 3,000 sccm, raising the internal temperature of the reactor to 690°C by heating. Subsequently, ethylene gas, as the carbon source gas, was injected at 1,000 sccm, thereby continuing the reaction for 120 minutes to synthesize carbon nanotubes. The catalysts used in the examples and comparative examples are summarized in Table 2 below.

[0058] [Table 2]

[0059] Experimental Example 1. Confirmation of whether the prepared carbon nanotubes satisfy Equation 1

[0060] The purity, specific surface area, bulk density, and powder resistivity of the carbon nanotubes prepared in the above examples and comparative examples, as well as five commercially available carbon nanotubes, were determined to confirm whether Equation 1 was satisfied. Each physical property was measured in the following manner.

[0061] 1) Purity = (Produced carbon nanotubes - Added catalyst) / Produced carbon nanotubes × 100%

[0062] 2) Specific surface area: The amount of nitrogen adsorbed at liquid nitrogen temperature (77K) was obtained using BELSORP-mini II from BEL Japan Co., Ltd., and the specific surface area was calculated.

[0063] 3) Bulk density: The bulk density is calculated by measuring the weight of the carbon nanotubes contained in the container by free fall using a 25ml SUS measuring cup and dividing the measured weight by the volume of the container.

[0064] 4) Powder resistance: The resistance was measured using an MCP-PD51 instrument from Nittoseiko Analytech Co., Ltd., based on pressure, when the compressive density was 1 g / cc.

[0065] The measurement results are summarized in Table 3 below.

[0066] [Table 3]

[0067] As shown in Table 3 above, the carbon nanotubes according to the embodiments of the present invention satisfy Equation 1. Meanwhile, the carbon nanotubes according to the comparative examples do not satisfy Equation 1.

[0068] As can be seen from the above results, the carbon nanotubes of the present invention have excellent productivity and conductivity, while in the prior art, productivity and conductivity are known to have a typical trade-off.

Claims

1. A carbon nanotube satisfying the following Equation 1: [Equation 1] 1.6541 x A + 0.6823 ≤ R ≤ 1.6541 x A + 1.6823 where in the above Equation 1, R is a powder resistance (mΩ·cm) of the carbon nanotube, A is In {(specific surface area (m 2 / g) x bulk density (kg / m 3 )) / purity (wt%)}.

2. The carbon nanotube of claim 1, wherein, The specific surface area of the carbon nanotubes is 320 m 2 / g or less.

3. The carbon nanotube of claim 1, wherein, The bulk density of the carbon nanotubes is 80 kg / m 3 The above.

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

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

6. The carbon nanotube of claim 1, wherein, the A is 4.5 to 6.

5.

7. A method for producing the carbon nanotube according to claim 1, the method comprising: (S1) reacting a carbon source gas in the presence of a supported catalyst, thereby synthesizing a carbon nanotube, wherein: in the supported catalyst, cobalt and vanadium are supported on a support; and a cobalt content based on a total weight of the supported catalyst is 14% by weight to 30% by weight.

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

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