Method for purifying carbon nanotube

Abstract

The present invention relates to a method for purifying carbon nanotubes, the method comprising, in the purification of unpurified carbon nanotubes containing 50-95 wt% of metal oxides as impurities, the steps of: injecting the unpurified carbon nanotubes into a purification furnace, primarily heating same under an inert gas atmosphere, and supplying an organic chlorine compound to the purification furnace and causing a reaction, thereby chlorinating the metal oxides so as to produce metal chlorides; and secondarily heating the carbon nanotubes containing the metal chlorides to a temperature higher than the primary heating temperature in the purification furnace so as to vaporize the metal chlorides, and obtaining purified carbon nanotubes.

Description

Method for purifying carbon nanotubes

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0139827 filed on October 14, 2024, and all contents disclosed in the document of said Korean patent application are incorporated herein as part of this specification.

[0003] Technology field

[0004] The present disclosure relates to a method for purifying carbon nanotubes, and more specifically, to a purification method capable of obtaining high-purity carbon nanotubes in high yield from unrefined carbon nanotubes containing a high content of metal oxides as impurities.

[0005] Carbon nanotubes (CNTs) are currently expected to have various applications in modern industrial fields based on their excellent properties, such as mechanical strength, chemical stability, thermal conductivity, and electrical conductivity.

[0006] Meanwhile, when manufacturing carbon nanotubes (CNTs) of a specific grade, metal oxides such as aluminum oxide (Al2O3) and magnesium oxide (MgO) are used as catalyst supports. However, since the boiling point of metal oxides is about 200°C or higher than the reaction temperature during carbon nanotube manufacturing, a large amount of metal oxides remains as impurities in the manufactured carbon nanotubes. Impurities of metal components, such as metal oxides, cause problems such as lowering the conductivity of carbon nanotubes or accelerating the decomposition of organic solvents. In particular, carbon nanotubes synthesized with low purity contain more than 50% by weight of metal oxides, so it is necessary to remove them.

[0007] Accordingly, conventionally, to remove metal component impurities contained in low-purity carbon nanotubes, methods are used such as applying a high vacuum at an ultra-high temperature above the boiling point of the metal oxide to vaporize the impurities, using a heated strong acid, such as nitric acid or hydrochloric acid, to dissolve the metal component impurities into a liquid state, or reacting the metal oxide with a halogen-containing gas to convert it into a metal halide and then vaporizing it to remove it.

[0008] However, when purifying CNTs containing a large amount of impurities of metal components, such as aluminum-based oxides or magnesium-based oxides used as catalyst supports, the oxygen generated as the metal oxides and halogens are substituted reacts with the CNTs and causes combustion, which leads to a rapid decrease in the yield of the CNTs. In particular, when metal oxides are present in excess relative to the CNTs in the sample prior to purification, there is a problem in that all the CNTs are lost due to the large amount of oxygen generated during the purification process.

[0009] Accordingly, there is a need to develop a process capable of purifying low-purity, unrefined carbon nanotubes containing large amounts of metal oxides as impurities to high purity and high yield.

[0010] The problem to be solved in this disclosure is to provide a CNT purification method that can increase the yield and purity of purified carbon nanotubes by minimizing the consumption of carbon nanotubes during the purification of unpurified carbon nanotubes containing a high content of metal oxides as impurities, in order to solve the problem mentioned in the background technology above.

[0011] However, the problems that this disclosure aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by a person skilled in the art from the description below.

[0012] According to one embodiment of the present disclosure for solving the above problem, a method for purifying carbon nanotubes comprising 50% to 95% by weight of metal oxide as impurities is provided, comprising the steps of: introducing the unpurified carbon nanotubes into a purification furnace and heating them first under an inert gas atmosphere, and supplying an organic chlorine compound represented by the following chemical formula 1 to the purification furnace to react them, thereby chlorinating the metal oxides to produce a metal chloride; and heating the carbon nanotubes containing the metal chloride in the purification furnace to a temperature higher than the first heating temperature to vaporize the metal chlorides and obtaining purified carbon nanotubes.

[0013] [Chemical Formula 1]

[0014] C x H y Cl z A w O v

[0015] In the above chemical formula 1, x and z are each independently integers greater than 0, x / z is 0.5 or greater, y is an integer from 0 to 8, A is a halogen element selected from fluorine, bromine and iodine, and w and v are each independently integers from 0 to 1.

[0016] According to the method for purifying carbon nanotubes of the present disclosure, metal oxides, which are impurities, are removed to increase the purity of CNTs while minimizing CNT loss, thereby increasing the CNT yield.

[0017] The effects obtainable from the present disclosure are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art to which the present disclosure belongs from the description below.

[0018] Figure 1 is a graph comparing the impurity removal rate and CNT retention rate during CNT purification by the method according to the examples and comparative examples of the present disclosure.

[0019] Terms and words used in the description and claims of the present invention shall not be interpreted as being limited to their ordinary or dictionary meanings, but shall be interpreted in a meaning and concept consistent with the technical spirit of the present disclosure, based on the principle that the inventor may appropriately define the concept of the terms to best describe his invention.

[0020] In relation to the description of the drawings, similar reference numerals may be used for similar or related components.

[0021] The singular form of the noun corresponding to the item may include one or more of the said item unless the relevant context clearly indicates otherwise.

[0022] In the present disclosure, each of the phrases such as “A or B”, “at least one of A and B”, “at least one of A or B”, “A, B or C”, “at least one of A, B and C”, and “at least one of A, B, or C” may include any one of the items listed together in the corresponding phrase, or all possible combinations thereof.

[0023] The term “and / or” includes a combination of multiple related described components or any of the multiple related described components.

[0024] Terms such as "first," "second," or "first" or "second" may be used simply to distinguish a component from another component and do not limit the components in other aspects (e.g., importance or order).

[0025] Additionally, terms such as 'front,' 'rear,' 'top,' 'bottom,' 'side,' 'left,' 'right,' 'top,' and 'bottom' used in this disclosure are defined based on the drawings, and the shape and location of each component are not limited by these terms.

[0026] Terms such as “include” or “have” are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in this disclosure, and do not preclude the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0027] When it is said that one component is “connected,” “combined,” “supported,” or “in contact” with another component, this includes not only cases where the components are directly connected, combined, supported, or in contact, but also cases where they are indirectly connected, combined, supported, or in contact through a third component.

[0028] When it is said that a component is located “on” another component, this includes not only cases where one component is in contact with the other, but also cases where another component exists between the two components.

[0029] Additionally, terms such as "about," "substantially," etc., as used in this disclosure are used to mean at or near the numerical values ​​where inherent manufacturing and material tolerances are presented in the stated meanings, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosed content where precise or absolute numerical values ​​are mentioned to aid in understanding this disclosure.

[0030] The term “fluid” as used in this disclosure may include one or more components of gas, liquid, and solid.

[0031] As used in this disclosure, “pressure” refers to gauge pressure measured relative to atmospheric pressure.

[0032] A method for purifying carbon nanotubes according to the present disclosure comprises, in the purification of unpurified carbon nanotubes containing 50% to 95% by weight of metal oxide as impurities, (S1) a step of introducing the unpurified carbon nanotubes into a purification furnace and heating them first under an inert gas atmosphere, and supplying an organic chlorine compound to the purification furnace to react them, thereby chlorinating the metal oxides to produce a metal chloride; and (S2) a step of heating the carbon nanotubes containing the metal chloride in the purification furnace to a temperature higher than the first heating temperature to vaporize the metal chlorides and obtain purified carbon nanotubes.

[0033] The unpurified carbon nanotubes according to the present disclosure may be produced by growing carbon nanotubes through the decomposition of a carbon source using a catalyst support, and the metal catalyst supported on the catalyst support may be a material that promotes the growth of carbon nanotubes. The supported catalyst may mainly be alumina or magnesium oxide (MgO) supported with Fe, Co, Ni, Mo, etc.

[0034] The above-mentioned unrefined carbon nanotubes may be carbon nanotubes synthesized with low purity, containing a catalyst support such as a metal oxide used during CNT synthesis as an impurity. The above-mentioned low-purity carbon nanotubes may mean that the content of the metal oxide, which is an impurity, is higher than that of the CNTs. For example, the above-mentioned unrefined carbon nanotubes may contain 50% by weight or more of the metal oxide as an impurity relative to the total weight of the above-mentioned unrefined carbon nanotubes. For example, the content of the metal oxide relative to the total weight of the above-mentioned unrefined carbon nanotubes may be 50% by weight to 95% by weight, 60% by weight to 95% by weight, 70% by weight to 95% by weight, or 80% by weight to 95% by weight.

[0035] The carbon nanotube purification method according to the present disclosure may be an effective method, in particular, for low-purity unrefined carbon nanotubes containing 50 weight percent or more of metal oxides as impurities. In the present disclosure, low-purity carbon nanotubes and / or unrefined carbon nanotubes may refer to carbon nanotubes with a CNT purity of less than 50%, preferably less than 30%, most preferably less than 15%.

[0036] The above metal oxide may include one selected from the group consisting of MgO, CoO, Co3O4, Li2O, Na2O, K2O, Al2O3, MoO3, Fe2O3, Fe3O4, FeO, and combinations thereof, preferably may include MgO, CoO, Co3O4, Li2O, Na2O, or K2O, and more preferably may be MgO.

[0037] A method for purifying carbon nanotubes according to one embodiment of the present disclosure comprises first heating the unpurified carbon nanotubes under an inert gas atmosphere and supplying an organic chlorine compound represented by the following chemical formula 1 to react, thereby chlorinating the metal oxide to produce a metal chloride (S1).

[0038] [Chemical Formula 1]

[0039] C x H y Cl z A w O v

[0040] In the above chemical formula 1, x and z are each independently integers greater than 0, x / z is 0.5 or greater, and y is an integer from 0 to 8. Specifically, x may be an integer greater than 0 and less than or equal to 5, and z may be an integer greater than 0 and less than or equal to 8. Additionally, A is a halogen element selected from fluorine (F), bromine (Br), and iodine (I), and w and v are each independently integers from 0 to 1.

[0041] Here, by purifying CNTs using an organic chlorine compound with x / z greater than 0.5, that is, a C / Cl ratio greater than 0.5, the carbon atoms of the organic chlorine compound can be consumed in place of the CNTs when the chlorine atoms of the organic chlorine compound react with the metal atoms of the metal oxide.

[0042] Specifically, when a metal chloride is produced by the reaction of the metal oxide and the organic chlorine compound, carbon dioxide (CO2) may be produced by the reaction of the oxygen atoms of the metal oxide and the carbon atoms of the organic chlorine compound, as shown in Reaction Scheme 1 below.

[0043] [Reaction Equation 1]

[0044] Unpurified CNT (CNT + metal oxide) + organic chlorine compound → CNT + metal chloride + CO2(g)

[0045] When the metal oxide and the organic chlorine compound react, oxygen (O2) is generated as the metal oxide is chlorinated. At this time, if the C / Cl ratio of the organic chlorine compound is 0.5 or higher, a sufficient amount of carbon can be provided for the carbon atoms of the chlorine compound to react with the oxygen of the metal oxide and be oxidized in place of the CNTs. Consequently, the CNTs are not consumed by the oxygen, thereby increasing the CNT yield. On the other hand, if the C / Cl ratio is less than 0.5, there is a shortage of carbon atoms relative to the metal oxide undergoing the chlorination reaction, which increases the consumption of CNTs and consequently lowers the CNT yield.

[0046] For example, the organic chlorine compound represented by the above chemical formula 1 is tetrachloroethylene (C2Cl4), 1,1,2,2-tetrachloroethane (C2H2Cl4), 1,1,1,2-tetrachloroethane (C2H2Cl4), 1-chloropropane (C3H7Cl), dichloroacetylene (C2Cl2), hexachloropropene (C3Cl6), tetrachlorocyclopropene (C3Cl4), octachlorocyclobutane (C4Cl8), perchlorobutene (C4Cl8), hexachlorobutadiene (C4Cl6), Tetrachlorobutatriene (C4Cl4), dichlorobutadiyne (C4Cl2), perchlorocyclopentane (C5Cl 10 There may be, but are not limited to, octachlorocyclopentene (C5Cl8), hexachlorocyclopentadiene (C5Cl6), 2-bromo-1-chloropropane (C3H6BrCl), and bromoacetyl chloride (BrCH2COCl).

[0047] Meanwhile, the above-mentioned inert gas may include, for example, nitrogen (N2), helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), or a mixture thereof, and specifically, nitrogen gas may be used. Since such inert gases are chemically very stable and possess the property of not exchanging or sharing electrons, they can play a role in enabling the flow and movement of CNTs through the inflow of gas without reaction with the CNTs.

[0048] According to one embodiment, the temperature of the first heating of the above-mentioned unpurified CNT is determined by considering the decomposition behavior of the organic chlorine compound at different temperatures, and the heating may be performed by increasing the temperature from room temperature (e.g., 15°C to 25°C) to a temperature at which the organic chlorine compound decomposes, for example, 550°C to 800°C, preferably 600°C to 750°C, more preferably 650°C to 700°C.

[0049] At this time, since melting of the metal chloride can inhibit additional chlorination reactions, it may be desirable for the primary heating temperature to be lower than the melting point of the metal chloride. For example, the primary heating temperature may be lower, ranging from -50°C to -20°C, preferably from -45°C to -30°C, and more preferably from -45°C to -35°C, based on the melting point of the metal chloride. Since the chlorination reaction is an exothermic reaction, the temperature rises higher than the set temperature during the reaction; therefore, it is necessary to satisfy the above temperature range during the primary heating to prevent the melting of the metal chloride.

[0050] For example, the metal oxide can be chlorinated by increasing the temperature through the first heating at a rate of 5°C / min to 50°C / min, more specifically 5°C / min to 40°C / min, and more specifically 5°C / min to 30°C / min, to 550°C to 800°C, more specifically 600°C to 750°C, and more specifically 650°C to 700°C.

[0051] If the heating rate during the first heating step is too slow, there may be a problem with the purification time becoming too long. On the other hand, if the heating rate is too fast, the oxidation temperature may be reached before moisture or oxygen in the CNT sample is completely removed, which may damage the CNT, and also cause thermal shock to the purification furnace (e.g., graphite, quartz, etc.) where the purification process is performed, which may cause problems in terms of equipment maintenance.

[0052] In addition, if the above-mentioned first heating temperature range is satisfied, energy suitable for carrying out the chlorination reaction of the metal oxide can be supplied. Specifically, if the above-mentioned first heating temperature is too low, the reaction rate may be too slow or the reaction may not occur, and if the above-mentioned first heating temperature is too high, due to the rapid decomposition of the organic chloride during the chlorination process of the metal oxide, it is difficult for the carbon of the organic chloride to be transferred to the impurities, which may lead to increased CNT consumption or the metal chloride may melt, hindering further chlorination and reducing the impurity removal rate.

[0053] In one embodiment, the organic chlorine compound may be supplied to the purification furnace in a gaseous or liquid state. For example, if the organic chlorine compound is in a gaseous state, the organic chlorine compound may be supplied to the purification furnace at a flow rate of 0.1 to 10 times, preferably 0.5 to 5 times, the internal volume of the purification furnace per minute. As another example, if the organic chlorine compound is in a liquid state, the organic chlorine compound may be supplied to the purification furnace at a flow rate of 0.0001 to 0.01 times, preferably 0.0005 to 0.005 times, the internal volume of the purification furnace per minute.

[0054] If the supply flow rate of the above organic chlorine compound is too low, the time required to remove impurities from CNTs is prolonged, and impurities may accumulate in the exhaust line, causing pipe blockage; if the supply flow rate of the above organic chlorine compound is too high, the consumption of the organic chlorine compound may increase without improving purification efficiency.

[0055] In addition, the chlorination reaction of the metal oxide can be carried out for 10 to 200 minutes, preferably 15 to 150 minutes, and more preferably 30 to 90 minutes. If the reaction time is too short, impurities are not sufficiently removed, so the purity of the CNT cannot be secured, and if the reaction time is too long, the CNT may be lost, and the residual rate of the CNT may decrease.

[0056] A method for purifying carbon nanotubes according to one embodiment of the present disclosure involves heating carbon nanotubes containing metal chloride to a temperature higher than the first heating temperature to vaporize the metal chloride and obtaining purified carbon nanotubes (S2).

[0057] According to one embodiment, the secondary heating may be performed by raising the temperature from the primary heating temperature to a temperature higher than the melting point of the metal chloride, preferably to a temperature close to the boiling point of the metal chloride. For example, the secondary heating temperature may be around 10°C, around 20°C, or around 30°C based on the boiling point of the metal chloride, but is not limited thereto. If the secondary heating temperature is too high, unnecessary energy consumption may increase, and if the secondary heating temperature is too low, the metal chloride may not be removed.

[0058] For example, the metal chloride can be vaporized and removed by increasing the temperature through the above secondary heating at a rate of 5°C / min to 50°C / min, specifically 5°C / min to 40°C / min, and more specifically 5°C / min to 30°C / min, to a temperature greater than 800°C and less than or equal to 1,500°C, specifically 1,000°C to 1,500°C, and more specifically 1,200°C to 1,500°C.

[0059] In the first heating process, the decomposition of organic chlorinated compounds is delayed by performing a chlorination reaction at a relatively low temperature, allowing carbon atoms to be sufficiently transferred to impurities inside the unpurified CNT, and in the second heating process, metal chlorides can be removed by vaporizing them by performing the chlorination reaction at a relatively high temperature. At this time, the boiling point is lowered as the metal oxide is modified into a metal chloride by the chlorination reaction in the first heating process, and as a result, the metal chlorides can be removed by vaporizing them under relatively mild conditions during the second heating.

[0060] Meanwhile, after the second heating described above, the reaction may be terminated by additionally supplying an inert gas as needed. At this time, the inert gas may include, for example, nitrogen (N2), helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), or a gas containing a mixture of these components, and specifically, nitrogen gas may be used. In addition, the supply of the inert gas may be performed for 10 to 200 minutes, preferably 15 to 150 minutes, and more preferably 30 to 120 minutes. If the supply time is too short, the metal chloride may not be sufficiently removed, and if the supply time is too long, purification costs may increase due to increased process time and inert gas usage.

[0061] Meanwhile, the impurity removal rate of the purified carbon nanotubes obtained in the method for purifying carbon nanotubes according to the present disclosure may be 50 wt% or more, preferably 60 wt% or more, and more preferably 90 wt% or more, based on the total weight of impurities in the unpurified CNTs. A higher impurity removal rate indicates a higher purity of the purified CNTs. Additionally, the residual rate of the purified carbon nanotubes may be 50 wt% or more, preferably 65 wt% or more, and more preferably 85 wt% or more, based on the total weight of CNTs in the unpurified CNTs. A higher CNT residual rate indicates a higher yield of the purified CNTs.

[0062] Although the purification method of carbon nanotubes according to the present disclosure has been described and illustrated in the drawings above, the description and drawings above describe and illustrate only the essential components for understanding the present disclosure. In addition to the processes and devices described and drawings above, processes and devices not separately described and illustrated may be appropriately applied and utilized to carry out the purification method of carbon nanotubes according to the present disclosure.

[0063] The present disclosure will be explained in more detail below through examples. However, the following examples are intended to explain the present disclosure more specifically, and the scope of the present disclosure is not limited by the following examples.

[0064] [Example]

[0065] Comparative Example 1

[0066] Approximately 10 g of synthetic CNT (i.e., 10% purity) containing 90 wt% magnesium oxide (MgO) as impurities was introduced into a furnace with an internal volume of 2 L, and after purging with nitrogen (N2) for 5 minutes, it was heated to 670°C at a heating rate of 10°C / min. Subsequently, liquid carbon tetrachloride (CCl4) at a rate of 2 mL / min was supplied to the furnace using a gear pump for approximately 30 seconds, followed by a waiting period of 30 minutes. Afterward, the process was terminated after purging with nitrogen (N2) gas for 30 minutes.

[0067] Comparative Example 2

[0068] Approximately 10 g of synthetic CNT (i.e., 10% purity) containing 90 wt% magnesium oxide (MgO) as impurities was introduced into a purification furnace with an internal volume of 2 L, and after purging with nitrogen (N2) for 5 minutes, it was heated to 1,400°C at a heating rate of 10°C / min. Subsequently, liquid carbon tetrachloride (CCl4) at a rate of 2 mL / min was supplied to the purification furnace using a gear pump for approximately 30 seconds, followed by a waiting period of 30 minutes. Afterward, the process was terminated after purging with nitrogen (N2) gas for 30 minutes.

[0069] Comparative Example 3

[0070] Approximately 10 g of synthetic CNT (i.e., 10% purity) containing 90 wt% magnesium oxide (MgO) as impurities was introduced into a purification furnace with an internal volume of 2 L, and after purging with nitrogen (N2) for 5 minutes, it was first heated to 670°C at a heating rate of 10°C / min. Subsequently, 2 mL / min of liquid carbon tetrachloride (CCl4) was supplied to the purification furnace using a gear pump for approximately 30 seconds, and then waited for 30 minutes.

[0071] Afterwards, the process was heated a second time to 1,400℃ at a heating rate of 10℃ / min, and then terminated after purging with nitrogen (N2) gas for 30 minutes.

[0072] Comparative Example 4

[0073] Approximately 10 g of synthetic CNT (i.e., 10% purity) containing 90 wt% magnesium oxide (MgO) as impurities was introduced into a purification furnace with an internal volume of 2 L, and after purging with nitrogen (N2) for 5 minutes, it was heated to 670°C at a heating rate of 10°C / min. Subsequently, liquid tetrachloroethylene (C2Cl4) at a rate of 2 mL / min was supplied to the purification furnace using a gear pump for approximately 30 seconds, followed by a waiting period of 30 minutes. Afterward, the process was terminated after purging with nitrogen (N2) gas for 30 minutes.

[0074] Comparative Example 5

[0075] Approximately 10 g of synthetic CNT (i.e., 10% purity) containing 90 wt% magnesium oxide (MgO) as impurities was introduced into a purification furnace with an internal volume of 2 L, and after purging with nitrogen (N2) for 5 minutes, it was heated to 1,400°C at a heating rate of 10°C / min. Subsequently, liquid tetrachloroethylene (C2Cl4) at a rate of 2 mL / min was supplied to the purification furnace using a gear pump for approximately 30 seconds, followed by a waiting period of 30 minutes. Afterward, the process was terminated after purging with nitrogen (N2) gas for 30 minutes.

[0076] Example 1

[0077] Approximately 10 g of synthetic CNT (i.e., 10% purity) containing 90 wt% magnesium oxide (MgO) as impurities was introduced into a purification furnace with an internal volume of 2 L, and after purging with nitrogen (N2) gas for 5 minutes, it was first heated to 550°C at a heating rate of 10°C / min. Subsequently, liquid tetrachloroethylene (C2Cl4) at a rate of 2 mL / min was supplied to the purification furnace using a gear pump for approximately 30 seconds, and then waited for 30 minutes.

[0078] Afterwards, the above purification furnace was heated a second time to 1,400°C at a heating rate of 10°C / min, and the process was terminated after purging with nitrogen (N2) gas for 30 minutes.

[0079] Example 2

[0080] Approximately 10 g of synthetic CNT (i.e., purity 10%) containing 90 wt% magnesium oxide (MgO) as impurities was introduced into a purification furnace with an internal volume of 2 L, and after purging with nitrogen (N2) gas for 5 minutes, it was heated to 670°C at a heating rate of 10°C / min. Subsequently, 2 mL / min of liquid tetrachloroethylene (C2Cl4) was supplied to the purification furnace using a gear pump for approximately 30 seconds, and then waited for 30 minutes.

[0081] Afterwards, the process was heated a second time to 1,400℃ at a heating rate of 10℃ / min, and then terminated after purging with nitrogen (N2) gas for 30 minutes.

[0082] Example 3

[0083] Approximately 10 g of synthetic CNT (i.e., 10% purity) containing 90 wt% magnesium oxide (MgO) as impurities was introduced into a purification furnace with an internal volume of 2 L, and after purging with nitrogen (N2) gas for 5 minutes, it was first heated to 800°C at a heating rate of 10°C / min. Subsequently, liquid tetrachloroethylene (C2Cl4) at a rate of 2 mL / min was supplied to the purification furnace using a gear pump for approximately 30 seconds, and then waited for 30 minutes.

[0084] Afterwards, the process was heated a second time to 1,400℃ at a heating rate of 10℃ / min, and then terminated after purging with nitrogen (N2) gas for 30 minutes.

[0085] Comparative Example 6

[0086] Approximately 10 g of synthetic CNT (i.e., purity 10%) containing 90 wt% magnesium oxide (MgO) as impurities was introduced into a purification furnace with an internal volume of 2 L, and after purging with nitrogen (N2) for 5 minutes, it was heated to 670°C at a heating rate of 10°C / min. Subsequently, 2 mL / min of liquid 1,1,2,2-tetrachloroethane (C2H2Cl4) was supplied to the purification furnace using a gear pump for approximately 30 seconds, followed by a 30-minute waiting period. Afterward, the process was terminated after purging with nitrogen (N2) gas for 30 minutes.

[0087] Comparative Example 7

[0088] Approximately 10 g of synthetic CNT (i.e., purity 10%) containing 90 wt% magnesium oxide (MgO) as impurities was introduced into a purification furnace with an internal volume of 2 L, and after purging with nitrogen (N2) for 5 minutes, it was heated to 1,400°C at a heating rate of 10°C / min. Subsequently, liquid 1,1,2,2-tetrachloroethane (C2H2Cl4) was supplied to the purification furnace at a rate of 2 mL / min using a gear pump for approximately 30 seconds, followed by a waiting period of 30 minutes. Afterward, the process was terminated after purging with nitrogen (N2) gas for 30 minutes.

[0089] Example 4

[0090] Approximately 10 g of synthetic CNT (i.e., 10% purity) containing 90 wt% magnesium oxide (MgO) as impurities was introduced into a purification furnace with an internal volume of 2 L, and after purging with nitrogen (N2) gas for 5 minutes, it was heated to 550°C at a heating rate of 10°C / min. Subsequently, liquid 1,1,2,2-tetrachloroethane (C2H2Cl4) was supplied to the purification furnace at a rate of 2 mL / min using a gear pump for approximately 30 seconds, and then waited for 30 minutes.

[0091] Afterwards, the process was heated a second time to 1,400℃ at a heating rate of 10℃ / min, and then terminated after purging with nitrogen (N2) gas for 30 minutes.

[0092] Example 5

[0093] Approximately 10 g of synthetic CNT (i.e., purity 10%) containing 90 wt% magnesium oxide (MgO) as impurities was introduced into a purification furnace with an internal volume of 2 L, and after purging with nitrogen (N2) gas for 5 minutes, it was heated to 670°C at a heating rate of 10°C / min. Subsequently, liquid 1,1,2,2-tetrachloroethane (C2H2Cl4) was supplied to the purification furnace at a rate of 2 mL / min using a gear pump for approximately 30 seconds, and then waited for 30 minutes.

[0094] Afterwards, the process was heated a second time to 1,400℃ at a heating rate of 10℃ / min, and then terminated after purging with nitrogen (N2) gas for 30 minutes.

[0095] Example 6

[0096] Approximately 10 g of synthetic CNT (i.e., 10% purity) containing 90 wt% magnesium oxide (MgO) as impurities was introduced into a purification furnace with an internal volume of 2 L, and after purging with nitrogen (N2) gas for 5 minutes, it was first heated to 800°C at a heating rate of 10°C / min. Subsequently, liquid 1,1,2,2-tetrachloroethane (C2H2Cl4) was supplied to the purification furnace at a rate of 2 mL / min using a gear pump for approximately 30 seconds, and then waited for 30 minutes.

[0097] Afterwards, the process was heated a second time to 1,400℃ at a heating rate of 10℃ / min, and then terminated after purging with nitrogen (N2) gas for 30 minutes.

[0098] [Experimental Example]

[0099] Table 1 below describes the purification process conditions and the impurity removal rate (%) and CNT retention rate (%) of the purified CNTs in the above examples and comparative examples, and the results are shown in Figure 1.

[0100] Here, the impurity removal rate and CNT retention rate were calculated using the following method.

[0101] Equation (1): Impurity removal rate (%) = (Mass of impurities removed after purification / Mass of impurities before purification) * 100

[0102] Equation (2): CNT Residual Rate (%) = (Mass of CNT after purification / Mass of CNT before purification) * 100

[0103] Specifically, the upper limit of the impurity removal rate according to the above formula (1) and the CNT retention rate according to the above formula (2) is 100% each. For example, a higher impurity removal rate means that more impurities are removed, resulting in higher CNT purity, and a higher CNT retention rate means that less CNT is consumed during the purification process, resulting in a higher CNT yield.

[0104] Organic Chloride Compound Heating Temperature (°C) Impurity Removal Rate (%) CNT Residual Rate (%) Type C / Cl Ratio 1st 2nd Comparative Example 1 CCl 40.25 670 27.28 4.2 Comparative Example 2 CCl 40.25 1,400 94.5 5.6 Comparative Example 3 CCl 40.25 670 1,400 93.3 20.7 Comparative Example 4 C2Cl 40.5 670 28.0 8 9.0 Comparative Example 5 C2Cl 40.5 1,400 94.0 26.3 Example 1 C2Cl 40.5 550 1,400 56.6 90.9 Example 2 C2Cl 40.5 670 1,400 92.5 8 7.0 Example 3 C2Cl 40.5 800 1,400 69.1 6 9.8 Comparative Example 6C2H2Cl4 0.567023.888.4 Comparative Example 7C2H2Cl4 0.51,40095.829.2 Example 4C2H2Cl4 0.55501,40058.496.4 Example 5C2H2Cl4 0.56701,40091.189.3 Example 6C2H2Cl4 0.58001,40068.271.7 CCl4: Carbon tetrachloride C2Cl4: Tetrachloroethylene C2H2Cl4: 1,1,2,2-tetrachloroethane

[0105] Referring to Table 1 and Figure 1 above, it was confirmed that Examples 1 to 6, which underwent a two-step heating process using an organic chlorine compound satisfying a C / Cl ratio of 0.5 or higher, satisfied all conditions of impurity removal rate and CNT retention rate of 50% or higher.

[0106] More specifically, Examples 1 to 3 used tetrachloroethylene as the organic chlorine compound, and Examples 4 to 6 used 1,1,2,2-tetrachloroethane as the organic chlorine compound; in Examples 1 to 3 and Examples 4 to 6, the CNT purification process was performed by varying only the primary heating temperature. Referring to this, it was confirmed that when the primary heating was performed at 670°C, which is a temperature lower than the melting point (approx. 714°C) of magnesium chloride (MgCl2) produced by the chlorination reaction of metal oxides during the primary heating process and closest to the melting point of said MgCl2, the impurity removal rate was 91.1% or higher and the CNT retention rate was 87% or higher, indicating that both the purity and yield of the CNTs were excellent.

[0107] Meanwhile, Comparative Examples 1 to 3 used organic chlorine compounds with a C / Cl ratio of less than 0.5, and the impurity removal rate or CNT retention rate was reduced to 50% or less. In particular, referring to Comparative Example 3, it was confirmed that even when performing the two-step heating process according to the present disclosure, the CNT retention rate remained low at 20.7% when using organic chlorine compounds with a C / Cl ratio of less than 0.5.

[0108] Comparative Examples 4 to 7 use the same organic chlorine compounds as Examples 1 to 3 or Examples 4 to 6, but perform only a single-step heating process. Specifically, Comparative Examples 4 and 6 performed a single-step heating process at 670°C, which is the same temperature as the first-step heating temperature of Examples 2 and 5, which showed the best effect; however, in this case, the impurity removal rate was significantly reduced to 28% or less. On the other hand, Comparative Examples 5 and 7, which performed a single-step heating process at 1,400°C, which is the same temperature as the second-step heating temperature of Examples 2 and 5, were found to have a CNT residue rate reduced to 29.2% or less.

[0109] Although exemplary embodiments of the present disclosure have been described above, the present disclosure is not limited thereto, and those skilled in the art will understand that various changes and modifications are possible within the scope and concept of the claims set forth below.

Claims

1. In the purification of crude carbon nanotubes containing 50% to 95% by weight of metal oxide as impurities, A step of introducing the above-mentioned unpurified carbon nanotubes into a purification furnace and heating them first under an inert gas atmosphere, and supplying an organic chlorine compound represented by the following chemical formula 1 to the purification furnace to react, thereby chlorinating the metal oxide to produce a metal chloride; and A method for purifying carbon nanotubes, comprising the step of: secondarily heating carbon nanotubes containing metal chloride in the purification furnace to a temperature higher than the first heating temperature to vaporize the metal chloride and obtain purified carbon nanotubes; [Chemical Formula 1] C x H y Cl z A w O v In the above chemical formula 1, x and z are each independently greater than 0 integers, x / z is 0.5 or greater, and y is an integer from 0 to 8, and A is a halogen element selected from fluorine, bromine, and iodine, and w and v are each independently integers from 0 to 1.

2. In Paragraph 1, A method for purifying carbon nanotubes, wherein the above-mentioned organic chlorine compound is selected from tetrachloroethylene, 1,1,2,2-tetrachloroethane, 1,1,1,2-tetrachloroethane, 1-chloropropane, dichloroacetylene, hexachloropropene, tetrachlorocyclopropene, octachlorocyclobutane, perchlorobutene, hexachlorobutadiene, tetrachlorobutatriene, dichlorobutadiene, perchlorocyclopentane, octachlorocyclopentene, hexachlorocyclopentadiene, 2-bromo-1-chloropropane, and bromoacetyl chloride.

3. In Paragraph 1, A method for purifying carbon nanotubes, wherein when a metal chloride is produced by the reaction of the metal oxide and the organic chlorine compound, the oxygen atom of the metal oxide reacts with the carbon atom of the organic chlorine compound to produce carbon dioxide.

4. In Paragraph 1, The above first heating is performed by raising the temperature to between 550℃ and 800℃, and A method for purifying carbon nanotubes, wherein the above secondary heating involves heating by raising the temperature from the above primary heating temperature to a temperature of 800°C or higher and 1,500°C or lower.

5. In Paragraph 4, A method for purifying carbon nanotubes, wherein the above-mentioned first heating temperature is a temperature lower than the melting point of the metal chloride.

6. In Paragraph 1, A method for purifying carbon nanotubes, wherein the above first heating includes heating by increasing the temperature at a rate of 5℃ / min to 50℃ / min.

7. In Paragraph 1, A method for purifying carbon nanotubes, wherein the chlorination reaction of the metal oxide is performed for 10 to 200 minutes.

8. In Paragraph 1, A method for purifying carbon nanotubes, wherein the above secondary heating includes heating by increasing the temperature at a rate of 5℃ / min to 50℃ / min.

9. In Paragraph 1, A method for purifying carbon nanotubes, wherein the supply of the organic chlorine compound is to supply the gaseous organic chlorine compound at a flow rate of 0.1 to 10 times the internal volume of the purification chamber per minute.

10. In Paragraph 1, A method for purifying carbon nanotubes, wherein the supply of the above organic chlorine compound is to supply the liquid organic chlorine compound at a flow rate of 0.0001 to 0.1 times the internal volume of the purification chamber per minute.

11. In Paragraph 1, A method for purifying carbon nanotubes, wherein the metal oxide is selected from the group consisting of MgO, CoO, Co3O4, Li2O, Na2O, K2O, Al2O3, MoO3, Fe2O3, Fe3O4, FeO, and combinations thereof.

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