WO2006088322A1

WO2006088322A1 - Carbon nanotubes mass fabrication system and mass fabrication method

Info

Publication number: WO2006088322A1
Application number: PCT/KR2006/000541
Authority: WO
Inventors: Yong Hoon Park
Original assignee: Cnt Co., Ltd
Priority date: 2005-02-17
Filing date: 2006-02-17
Publication date: 2006-08-24
Also published as: KR20060091993A; KR100649744B1

Abstract

Disclosed herein is a mass production system and method of synthesized carbon nanotubes. The system is configured to completely open the reaction chamber to an outside during synthesis of the carbon nanotubes in the reaction chamber while allowing a specific gas to occupy a predetermined region within the reaction chamber, thereby blocking introduction of external air into the reaction chamber which is opened to external air. The system comprises a reaction chamber having at least one opening opened to external air, and at least one different-specific gravity gas occupying region filled with a different specific gravity gas having a different specific gravity from that of the external air to block the external air from being introduced into the reaction chamber through the opening, a carbon nanotube synthesizing unit positioned in the different- specific gravity gas occupying region to synthesize carbon nanotubes by the medium of a catalyst introduced thereto through the opening, a conveying unit to convey the catalyst to the carbon nanotube synthesizing unit through the opening, and a gas supply unit to supply the different specific gravity gas and a carbon source gas used for synthesizing the carbon nanotubes to the different-specific gravity gas occupying region and the carbon nanotube synthesizing unit, respectively.

Description

CARBON NANOTUBES MASS FABRICATION SYSTEM AND MASS FABRICATION METHOD

Technical Field

[1] The present invention relates to a mass production system for synthesized carbon nanotubes, and a mass production method thereof using the same. More particularly, the present invention relates to a mass production system for synthesized carbon nanotubes using a vapor synthesis method, and a mass production method thereof using the same. Background Art

[2] The present invention relates to a mass production system for synthesized carbon nanotubes, and a mass production method thereof using the same. More particularly, the present invention relates to a mass production system for synthesized carbon nanotubes using a vapor synthesis method, and a mass production method thereof using the same.

[3] The carbon nanotubes are composed of graphite sheets wound in a cylindrical shape, and can be classified into single-wall carbon nanotubes, double-wall carbon nanotubes, and multi-wall carbon nanotubes according to the number of graphite sheets.

[4] Carbon nanotubes are anticipated to be useful in a wide variety of applications, for example, electronic information industry, energy industry, high performance composite materials, ultra-fine nano components, etc., in view of their light weight, excellent electrical and mechanical properties, chemical stability, and easy surface reaction. Accordingly, it is necessary to provide a method for synthesizing highly pure carbon nanotubes at low costs in mass production.

[5] Currently, representative methods for synthesizing the carbon nanotubes include an arc-discharge method, a laser deposition method, a chemical vapor deposition method, and a vapor synthesis method. For the arc-discharge method or the laser deposition method, since amorphous materials are generated along with the carbon nanotubes when synthesizing the carbon nanotubes, it is necessary to perform a thermal or chemical refinement process in order to obtain highly pure carbon nanotubes, and it is difficult to accomplish economical mass production. For the chemical vapor deposition method, although it is possible to synthesize highly pure carbon nanotubes by aligning them on a substrate, it is also difficult to accomplish their mass production.

[6] Meanwhile, the vapor synthesis method has been spotlighted as a method for synthesizing the carbon nanotubes at low costs. However, although various vapor synthesis methods have been developed, there is a problem in that the carbon nanotubes synthesized by the conventional vapor synthesis methods comprises a high quantity of amorphous carbon particles, making it difficult to refine the carbon nanotubes. Specifically, the vapor synthesis methods are considered inappropriate for mass production of, especially, the single-wall or double-wall carbon nanotubes in terms of their significantly low yield, and high quantity of amorphous carbon particles contained in the synthesized carbon nanotubes.

[7] In addition, the mass production system of the carbon nanotubes employing the vapor synthesis process is a batch type system in which the carbon nanotubes are synthesized by repeating a series of steps of inputting a metal catalyst into a reaction chamber, heating the reaction chamber for a predetermined period of time, and then cooling the reaction chamber for every batch. However, such a mass production system has problems in terms of high manufacturing costs and significantly low productivity due to repetition of the individual steps as described above for every batch, and of low uniformity of the carbon nanotubes due to difficulty of obtaining the same process conditions for every batch. Disclosure of Invention Technical Problem

[8] Carbon nanotubes are anticipated to be useful in a wide variety of applications, for example, electronic information industry, energy industry, high performance composite materials, ultra-fine nano components, etc., in view of their light weight, excellent electrical and mechanical properties, chemical stability, and easy surface reaction. Accordingly, it is necessary to provide a method for synthesizing highly pure carbon nanotubes in a large quantity at low costs. Technical Solution

[9] The present invention has been made to solve the above problems, and it is an object of the present invention to provide a mass production system and method for synthesizing carbon nanotubes via a vapor synthesis process in an open-type reaction chamber.

[10] The present invention relates to a mass production system for synthesized carbon nanotubes, configured to completely open the reaction chamber to an outside while the carbon nanotubes are being synthesized in the reaction chamber, and to block introduction of external air into the reaction chamber via difference in gravities of gases, and a mass production method thereof.

[11] According to the present invention, it is possible to perform a continuous process of continuously inputting a catalyst from the outside into the reaction chamber while allowing the carbon nanotubes synthesized within the reaction chamber to be con- tinuously discharged to the outside, thereby enabling mass production of the carbon nanotubes.

[12] In addition, according to the present invention, the carbon nanotubes having various properties can be synthesized in a large amount by controlling conveying speed of catalyst, reaction temperature, particle size of metal catalyst, injection amount of carbon source gas, and injection amount of hydrogen.

[13] Mass production of high quality carbon nanotubes is possible by continuous process of reduction of catalyst, systhesis of carbon nanotubes and cooling carbon nanotubes.

[14] In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a mass production system for synthesized carbon nanotubes, comprising: a reaction chamber having at least one opening opened to external air, and at least one different-specific gravity gas occupying region filled with a different specific gravity gas having a different specific gravity from that of the external air to block the external air from being introduced into the reaction chamber through the opening; a carbon nanotube synthesizing unit positioned in the different- specific gravity gas occupying region to synthesize the carbon nanotubes by the medium of a catalyst introduced thereto through the opening; a conveying unit to convey the catalyst to the carbon nanotube synthesizing unit through the opening; and gas supply unit to supply the different specific gravity gas and a carbon source gas used for synthesizing the carbon nanotubes to the different-specific gravity gas occupying region and the carbon nanotube synthesizing unit, respectively.

[15] Preferably, the opening comprises an inlet through which the catalyst is introduced into the reaction chamber, and an outlet through which the carbon nanotubes synthesized by the carbon nanotube synthesizing unit are discharged to an outside of the reaction chamber, and the conveying unit conveys the catalyst and/or the carbon nanotubes via the opening, the different-specific gravity gas occupying region, the carbon nanotube synthesizing unit, and the outlet.

[16] Preferably, the carbon nanotube synthesizing unit comprises a reaction region defined in the reaction chamber so as to be blocked from the external air by the different specific gravity gas filled in the different-specific gravity gas occupying region; a carbon source gas injector to inject the carbon source gas supplied from the gas supply unit to the reaction region such that the catalyst conveyed to the reaction region by the conveying unit reacts with the carbon source gas to synthesize the carbon nanotubes; and a heating member to heat the reaction region.

[17] Preferably, the reaction region of the carbon nanotube synthesizing unit is defined at a lower portion of at least one region in the different-specific gravity gas occupying region filled with a different specific gravity gas having a lower specific gravity than the carbon source gas, and the carbon nanotube synthesizing unit further comprises a carbon source gas restriction part opened at an upper portion to block the carbon source gas injected to the reaction region from escaping from the reaction region.

[18] Preferably, the different-specific gravity gas occupying region comprises a first different-specific gravity gas occupying region filled with a different specific gravity gas having a lower specific gravity than the carbon source gas; and a second different- specific gravity gas occupying region filled with a different specific gravity gas having a higher specific gravity than that of the carbon source gas, the first different-specific gravity gas occupying region, the reaction region, and the second different-specific gravity gas occupying region being sequentially defined in a gravity direction within the reaction chamber.

[19] The different specific gravity gas comprises at least one of a gas having a lower specific gravity than that of the external air, and a gas having a higher specific gravity than that of the external air in order to block the external air from being introduced into the reaction chamber through the opening depending on a location of the opening on the reaction chamber.

[20] Preferably, the system further comprises a heating member to heat at least one region inside the reaction chamber to reduce the catalyst introduced into the reaction chamber through the opening, and at least one of the different specific gravity gases occupying the different-specific gravity gas occupying regions is hydrogen gas.

[21] Preferably, the carbon source gas injector comprises a plurality of nozzles dispersedly arranged corresponding to a dimension of the reaction region to uniformly inject the carbon source gas into the reaction region.

[22] Preferably, the reaction chamber has at least one discharge pipe formed therein to discharge hydrogen gas to the outside of the reaction chamber in order to accomplish an equilibrium state between pressure of the hydrogen gas occupying the different- specific gravity gas occupying region and pressure of the external air.

[23] Preferably, the mass production system further comprises a cooling unit to cool one region of the reaction chamber near the outlet such that the carbon nanotubes are cooled by the cooling unit.

[24] In accordance with another aspect of the present invention, a mass production method of synthesized carbon nanotubes, comprising the steps of: supplying a catalyst into a reaction chamber having at least one opening opened to external air, through which the catalyst is supplied to the reaction chamber, and at least one different- specific gravity gas occupying region filled with a different specific gravity gas having a different specific gas from that of the external air to block the external air from being introduced into the reaction chamber through the opening; supplying a carbon source gas to the reaction chamber to allow the carbon source gas to react with the catalyst in the reaction region blocked from the external air by the different specific gas, thereby synthesizing the carbon nanotubes; and discharging the synthesized carbon nanotubes to an outside of the reaction chamber through the opening. [25] Preferably, the method further comprises supplying hydrogen gas into the reaction chamber to allow the hydrogen gas to react with the catalyst, thereby reducing the catalyst. [26] Preferably, the method further comprises discharging a portion of the hydrogen gas through a discharge pipe formed in the reaction chamber in order to accomplish an equilibrium state between pressure of the hydrogen gas occupying the different- specific gravity gas occupying region and pressure of the external air.

Advantageous Effects [27] The present invention can be applied to the mass production system for synthesized carbon nanotubes using the vapor synthesis method. In particular, the present invention can be applied to the mass production method of synthesized carbon nanotubes employing the mass production system for synthesized carbon nanotubes, which comprises an open-type reaction chamber.

Brief Description of the Drawings [28] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: [29] Fig. 1 is a schematic cross-sectional view illustrating a mass production system for synthesized carbon nanotubes in accordance with a first embodiment of the present invention; [30] Fig. 2 is a schematic cross-sectional view illustrating a mass production system for synthesized carbon nanotubes in accordance with a second embodiment of the present invention; [31] Fig. 3 is a schematic cross-sectional view illustrating a mass production system for synthesized carbon nanotubes in accordance with a third embodiment of the present invention; and [32] Fig. 4 is a schematic cross-sectional view illustrating a mass production system for synthesized carbon nanotubes in accordance with a fourth embodiment of the present invention.

Best Mode for Carrying Out the Invention [33] Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. [34] Fig. 1 is a schematic cross-sectional view illustrating a mass production system for synthesized carbon nanotubes in accordance with a first embodiment of the present invention. Referring to Fig. 1, the mass production system for synthesized carbon nanotubes according to the first embodiment comprises a reaction chamber 1 having a predetermined space defined therein. The reaction chamber 1 has an inlet 2, and an outlet 3 formed at one side thereof. Both inlet 2 and outlet 3 of the reaction chamber have an open type structure which is opened to atmosphere. The system further comprises a conveying unit 15 which conveys a bucket 10, that is, a catalyst containing member which contains a metal catalyst, from the inlet 2 to the outlet 3 via the interior of the reaction chamber 1.

[35] The reaction chamber 1 has an upright structure. The reaction chamber 1 comprises the inlet 2 opened downwardly at one side, a metal catalyst reduction unit 100 extending upwardly from the inlet 2 of the reaction chamber, a carbon nanotube synthesizing unit 200 connected with the metal catalyst reduction unit 100 and extending downwardly therefrom, a cooling unit 300 connected with the carbon nanotube synthesizing unit 200 at a lower portion of the reaction chamber 1, and the outlet 3 connected with the cooling unit 300 and opened upwardly. The metal catalyst reduction unit 100, the carbon nanotube synthesizing unit 200 and/or the cooling unit 300 are connected with a gas supply unit 50, which supplies carbon source gas, hydrogen gas, argon gas (or other inert gas such as nitrogen gas) and the like into the reaction chamber. The reaction chamber has the structure wherein the inlet 2, the metal catalyst reduction unit 100, the carbon nanotube synthesizing unit 200, the cooling unit 300, and the outlet 3 are sequentially connected with each other.

[36] The metal catalyst reduction unit 100 serves to remove oxygen from a metal oxide catalyst introduced into the reaction chamber 1 by reducing the metal oxide catalyst. The metal catalyst reduction unit 100 comprises an upper reaction chamber 110 having a space defined therein, and a first heating member 150 provided on the upper reaction chamber 110. The metal catalyst reduction unit 100 is provided with a hydrogen gas discharge pipe 120 at one side above the inlet 2 of the reaction chamber such that the hydrogen gas discharge pipe 120 is exposed to external air. The upper reaction chamber 110 is closed at an upper side to confine a gas rising within the reaction chamber. The first heating member 150 is a heat generating mechanism to heat the interior of the reaction chamber, and is provided with a temperature sensor (not shown) to maintain the interior of the reaction chamber at a temperature of 600 ~ 1,200 °C. The upper reaction chamber 110 of the metal catalyst reduction unit 100 is occupied with hydrogen gas supplied into the reaction chamber. An occupation region of the upper reaction chamber 110 occupied with hydrogen gas having the lowest specific gravity among several gases in the reaction chamber will be referred to as a hydrogen gas occupation region. The metal oxide catalyst is provided in the form of catalyst carrier which contains the metal oxide catalyst. [37] In the carbon nanotube synthesizing unit 200, the metal catalyst reacts with the carbon source gas, synthesizing the carbon nanotubes. The carbon nanotube synthesizing unit 200 comprises a central reaction chamber 210 having an upright space to allow a gas having a lower specific gravity to rise therein, and a second heating member 250 installed to the central reaction chamber 210. Since the central reaction chamber 210 is provided with a reaction region where the metal catalyst reacts with the carbon source gas, thereby allowing synthesis of the carbon nanotubes, the central reaction chamber 210 has an enough length to allow the metal catalyst to pass therethrough for a sufficient period of time, and has an inner diameter greater than the upper reaction chamber 110 or a lower reaction chamber 310 described below in order to ensure that a sufficient amount of carbon source gas exists therein. The second heating member 250 is also a heat generating mechanism to heat the interior of the reaction chamber, and is provided with another temperature sensor (not shown) to maintain the interior of the reaction chamber at a temperature of 600 ~ 1,200 °C. The central reaction chamber 210 constituting the carbon nanotube synthesizing unit 200 is occupied with the carbon source gas, for example, ethylene gas, having a higher specific gravity than that of hydrogen gas. An occupation region of the central reaction chamber 210 occupied with ethylene gas having the higher specific gravity than hydrogen gas among several gases in the reaction chamber will be referred to as an ethylene gas occupation region. The central reaction chamber 210 has been described as an exemplary structure which allows the gases to ascend or descend according to difference in specific gravities thereof. Thus, it should be noted that the central reaction chamber 210 is not limited to a slope shown in Fig. 1, and may comprise any structure which has a suitable slope formed therein as long as it enables the gases to ascend or descend according to difference in specific gravities thereof.

[38] The cooling unit 300 serves to cool the synthesized carbon nanotubes. The cooling unit 300 comprises a lower reaction chamber 310 connected with the carbon nanotube synthesizing unit 200 and having a closed bottom surface to allow a gas, for example, argon gas, heavier than the carbon source gas to remain thereon, and a cooling member 350 provided to the lower reaction chamber 310. The lower reaction chamber 310 constituting the cooling unit 300 is filled with argon gas which is one of inert gases having heavier specific gravities than that of ethylene gas, and an occupation region of the lower reaction chamber 310 occupied with argon gas will be referred to as an argon gas occupation region. As described above, since the hydrogen gas occupation region of the upper reaction chamber and the argon gas occupation region of the lower reaction chamber 310 are occupied with the gases having different specific gravities within the reaction chamber, both regions will be referred to as different-specific gravity gas occupation parts. [39] In this embodiment, the cooling member 350 is constituted by a water cooling jacket. However, it should be noted that various cooling members 350 may be used as long as they can perform a cooling function. The lower reaction chamber 310 is formed at an inside bottom with a U-shaped discharge pipe 20 which discharges byproducts including water. Since the U-shaped discharge pipe 20 has water pooling in a bent structure of the U shape, the gas cannot escape from the lower reaction chamber 310. The cooling unit 300 decreases the temperature of argon gas so that the specific gravity of argon gas is prevented from being lowered due to thermal expansion.

[40] The gas supply unit 50 comprises a carbon source gas tank, an argon gas or nitrogen gas tank, and a hydrogen gas tank, each of which is connected with the reaction chamber via a gas injection pipe having an opening/closing valve. Each of the tanks comprises a purifier. The purifiers purify a mixture of carbon gas and a mixture of hydrogen gas, and supply highly pure carbon source gas and hydrogen gas. Examples of the carbon source gas include methane, ethane, ethylene, acetylene, propylene, butane, butylenes, butadiene, hexane, heptane, toluene, benzene, xylene, gasoline, propane, liquid propane gas (LPG), liquid natural gas (LNG), naphtha, carbon monoxide, and alcohol-based gas. The inert gas is contained in the lower reaction chamber 310. The present invention may use any one of the inert gases heavier than the carbon source gas without being limited to argon or nitrogen. Among the gases supplied into the reaction chamber through the injection pipe of the gas supply unit 50 connected with the cooling unit 300, the carbon source gas moves upwards, and is positioned in the carbon nanotube synthesizing unit 200, while hydrogen gas moves upwards, passes the carbon nanotube synthesizing unit 200, and is then positioned in the metal catalyst reduction unit 100. Here, since hydrogen gas collides with, and causes the carbon source gas filled in the carbon nanotube synthesizing unit 200 to move while rising and passing through the carbon nanotube synthesizing unit 200, the moving carbon source gas is actively brought into contact with the metal catalyst, thereby enabling more active synthesis of the carbon nanotubes.

[41] The conveying unit 15 serves to convey the catalyst containing member from the inlet 2 to the outlet 3 of the reaction chamber, and is configured to circulate within the reaction chamber. The conveying unit 15 can control a conveying speed of the catalyst containing member via motor control or the like so that a reduction time of the metal oxide catalyst and a synthesis time of the carbon nanotubes can be freely controlled. The catalyst containing member according to the embodiment is a bucket to supply the metal catalyst required for synthesis of the carbon nanotubes via a vapor synthesizing method to the reaction chamber. The bucket is hingably connected at an upper end with a conveyer system. Accordingly, the bucket is maintained in an upright state at any locations by hinge coupling so that the metal catalyst contained in catalyst containing member is not poured out of the catalyst containing member. The catalyst containing member is not limited to the bucket, and can be realized in various forms appropriate for conveying the metal catalyst. The catalyst containing member may be made of various materials, such as metal, quartz, graphite, and the like. The catalyst containing member may have an aperture formed at a bottom surface thereof to enable active reaction of the metal catalyst with the carbon source gas.

[42] In each drawing, dotted lines dividing respective regions in upper and lower directions schematically indicate regions occupied by different gases.

[43] Although the mass production system of this embodiment has been described as employing the bucket as for the catalyst containing member which contains the metal catalyst, the present invention is not limited to this structure. For example, the mass production system of the invention may employ various members, such as a boat or a tray, which can contain the metal catalyst. In this case, it is possible to select a suitable conveying system according to the kinds of catalyst containing member. This is apparent to the skilled in the art, and thus detailed description will be omitted hereinafter.

[44] A method for synthesizing carbon nanotubes using the system of the synthesized carbon nanotubes according to the first embodiment will be described as follows.

[45] The metal catalyst reduction unit 100 and the carbon nanotube synthesizing unit

200 of the reaction chamber 1 are heated to a desired temperature, for example, to a temperature of 600 ~ 1,200 °C by the first heating member 110 and the second heating member 210 (Step 1).

[46] Then, an inert gas, for example, argon gas or nitrogen gas, is supplied into the reaction chamber through an inert gas injection pipe connected with the upper reaction chamber 110 (Step 2). Specifically, when argon gas is supplied into the reaction chamber through the gas injection pipe connected with the upper reaction chamber 110, argon gas having a higher specific gravity than external air causes air existing in the interior of the reaction chamber to be discharged to the outside of the reaction chamber via the inlet 2 and the outlet 3 while moving to a left or right side of the upper reaction chamber 110. In this manner, air or oxygen is completely discharged from the reaction chamber 1, so that an inert gas atmosphere is formed in the reaction chamber 1.

[47] Next, hydrogen gas and carbon source gas are supplied to the reaction chamber 1 via the gas supply unit 50 (Step 3).

[48] Then, a metal oxide catalyst, or the bucket 10 receiving a catalyst bearing material which comprises the metal oxide catalyst is supplied from the outside into the reaction chamber through the inlet 2 (Step 4). The bucket 10 is conveyed by the conveying unit 15. [49] The catalyst bearing material may have a powder shape, and comprise magnesium oxide (MgO), alumina (Al O ), zeolite, silica or the like. As a method for bearing the metal oxide catalyst into nano-size pores of the catalyst bearing material, a sol-gel method, a precipitation method or an impregnation method may be used.

[50] The metal oxide catalyst of the bucket 10 conveyed into the reaction chamber is reduced to a metal catalyst by the metal catalyst reduction unit 100 (Step 5). For example, if the metal oxide catalyst is an iron oxide, the iron oxide reacts with hydrogen gas, and is converted into pure iron and water. Such a metal oxide catalyst includes Co, Ni, Mo or alloys thereof as well as iron.

[51] After passing through the metal catalyst reduction unit 100, the metal catalyst of the bucket 10 is conveyed to the carbon nanotube synthesizing unit 200. The metal catalyst reacts with a carbon source gas in the carbon nanotube synthesizing unit 200, synthesizing carbon nanotubes (Step 6).

[52] Of course, when synthesizing the carbon nanotubes, it is possible to regulate growth speed, diameter, crystallinity of carbon nanotubes by controlling an injection amount of the carbon source gas, and the temperature of the carbon nanotube synthesizing unit 200.

[53] In particular, the metal catalyst particles are born and secured to the nano-sized pores of the powdery catalyst bearing material so that the metal catalyst particles are suppressed from moving even at high temperatures required for synthesizing the carbon nanotubes, thereby enabling synthesis of carbon nanotubes having a uniform diameter. In addition, since the carbon nanotubes are synthesized with the metal catalyst particles, having a size of several nano meters, born and secured to the nano- sized pores of the powdery matrix, the synthesized carbon nanotubes are highly pure without amorphous carbon clusters formed therein.

[54] The bucket 10 carrying the synthesized carbon nanotubes is conveyed to the cooling unit 300, and is forcibly cooled to room temperature by the cooling member 350 (Step 7). Alternatively, the carbon nanotubes may be discharged to the outside of the reaction chamber, and then cooled at the outside without performing such a cooling process.

[55] After being cooled, the synthesized carbon nanotubes are discharged to the outside of the reaction chamber through the outlet 3 (Step 8). After the carbon nanotubes are taken from the bucket 10, the bucket 10 with a new metal catalyst received therein is conveyed into the reaction chamber via the inlet 2. In this manner, since synthesis of the carbon nanotubes is continuously repeated via reaction between a metal catalyst newly carried by the bucket and the carbon source gas while the bucket is conveyed into and from the reaction chamber, it is possible to produce the synthesis carbon nanotubes in a great quantity. Operation to withdraw the synthesized carbon nanotubes from the bucket, and then input a new metal catalyst thereto can be performed by typical automation equipment known in the art.

[56] As such, since the mass production system for synthesized carbon nanotubes according to the preferred embodiment comprises the metal catalyst reduction unit 100, the carbon nanotube synthesizing unit 200 and the cooling unit 300 successively arranged, and has the open structure opened to the external air, it is possible to synthesize the carbon nanotubes continuously. In other words, the present invention accomplishes synthesis of the carbon nanotubes via a continuous process which enables continuous input of the metal catalyst into the reaction chamber and continuous discharge of the synthesized carbon nanotubes from the reaction chamber to the outside.

[57] Since the carbon source gas, hydrogen gas, and argon gas supplied to the reaction chamber through the gas injection pipes have different specific gravities, hydrogen gas having the lowest specific gravity is filled in the upper reaction chamber 110 of the metal catalyst reduction unit 100, ethylene gas having a higher specific gravity than hydrogen gas is filled in the central reaction chamber 210 of the carbon nanotube synthesizing unit 200, and argon gas having the highest specific gravity is filled in the lower reaction chamber 310 which is the lowest part of the reaction chamber. During this process, since some gas injection pipes of the gas supply unit 50 are connected with a lower portion of the central reaction chamber 210, ethylene gas and hydrogen gas rise, but argon gas sinks among the gases supplied into the reaction chamber. That is, hydrogen gas rises to the upper reaction chamber 110 after passing through the central reaction chamber 210, and ethylene gas rises to the central reaction chamber 210, causing the gases having been already positioned in the central reaction chamber 210 to flow. Due to the flow, ethylene gas acting as the carbon source gas is actively brought into contact with the metal catalyst, allowing effective synthesis of the carbon nanotubes. In particular, since ethylene gas has the specific gravity higher than hydrogen gas but lower than argon gas, ethylene gas remains in the central reaction chamber 210. In addition, when both upper and lower ends of the central reaction chamber 210 have a bottleneck shape, the central reaction chamber 210 functions to collect and maintain ethylene gas more easily.

[58] Hydrogen gas having a high temperature is collected in the metal catalyst reduction unit 100 above the inlet 2. Since the high temperature hydrogen gas has a lower specific gravity than that of the external air, the air is always located under hydrogen gas, which prevents the external air from permeating into the reaction chamber 1. Specifically, assuming that the interior of the reaction chamber 1 remains at a temperature of about 900 °C, and the exterior of the reaction chamber 1 has a temperature of about 20 °C. Since 1 mole hydrogen gas (22.41) has a weight of 2 g at the standard state (0 °C = 274 K, 1 atm), hydrogen gas has a volume increased four times according to Charles'law within the reaction chamber having the temperature of about 900 °C (1174 K), therefore 1 mole hydrogen gas (22.41) has a weight of about 0.5 g therein. Meanwhile, since 1 mole air (22.4 1) has a weight of 28.9 g at the standard state, 1 mole hydrogen gas (22.4 1) has a weight of about 27 g at room temperature (20 °C). In other words, since the air has the specific gravity about 54 times that of hydrogen gas at the inlet of the reaction chamber where the air is brought into contact with hydrogen gas, air is always located under hydrogen gas due to difference in specific gravity, and cannot permeate through hydrogen gas into the reaction chamber 1.

[59] In addition, since argon gas having a molecular weight of 39.948 positioned under the outlet 3 of the reaction chamber is cooled by the cooling unit 300 and remains at room temperature, 1 mole argon gas (22.41) has a weight of about 35 g. As such, since the external air has the specific gravity lower than that of argon gas, the air is always located above argon gas, and cannot permeate through argon gas into the reaction chamber 1.

[60] A predetermined amount of hydrogen gas introduced into the reaction chamber is discharged to the outside of the reaction chamber through the hydrogen gas discharge pipe 120 of the upper reaction chamber 110. This is for the purpose of securely preventing the external air from permeating into the reaction chamber by providing an equilibrium state between pressures of hydrogen gas and the external air at a region where hydrogen gas in the inlet 2 of the reaction chamber is brought into contact with the external air. In other words, this structure is configured to obtain equilibrium between hydrogen gas and the external air at the inlet of the reaction chamber by allowing the predetermined amount of hydrogen gas to be discharged through the separate the hydrogen gas discharge pipe 120 in order to allow an increase in pressure of hydrogen gas by an excessive amount of hydrogen gas injected into the reaction chamber through the gas injection pipe while preventing hydrogen gas from being discharged to the outside through the inlet 2 due to the increase in pressure of hydrogen gas. That is, although the predetermined amount of hydrogen gas reacts with the metal oxide catalyst upon reduction of the metal oxide catalyst, the pressure of hydrogen gas remains at a predetermined value or more within the reaction chamber by injecting hydrogen gas more than a reacted amount of hydrogen gas into the reaction chamber.

[61] Here, since the predetermined amount of hydrogen gas is discharged to the outside through the hydrogen gas discharge pipe 120, there occurs flow of hydrogen gas from the upper reaction chamber 110 of the metal catalyst reduction unit 100 to the hydrogen gas discharge pipe 120, which is directed towards the inlet 2 of the reaction chamber, thereby securely preventing introduction of the external air through the inlet 2 into the reaction chamber.

[62] According to the present invention, the mass production system of the synthesized carbon nanotubes allows various gases having different specific gravities to occupy specified regions of the reaction chamber so that external air cannot infiltrated into the reaction chamber even with the open structure of the system in which the reaction chamber is completely open.

[63] If external air flows into the reaction chamber, oxygen contained in the air causes an oxidation reaction with the carbon source gas in an instant, thereby failing to synthesize the carbon nanotubes, and reacts with hydrogen gas, possibly causing explosion. Thus, it is necessary for the reaction chamber to have no oxygen therein.

[64] For a conventional batch type mass production system of carbon nanotubes, which employs the vapor synthesizing method, the carbon nanotubes are synthesized after filling the reaction chamber with an inert gas to discharge oxygen and the air to the outside from the reaction chamber with the interior thereof completely blocked from the outside in order to form an oxygen-free interior of the reaction chamber.

[65] For the conventional system as described above, it is necessary to repeat the steps of removing oxygen from the reaction chamber, heating the reaction chamber to synthesize the carbon nanotubes, cooling the reaction chamber, and withdrawing the synthesized carbon nanotubes at every process of synthesizing the carbon nanotubes, which requires an excessive preparation time for synthesis of the carbon nanotubes. As such, with the conventional mass production system for synthesized carbon nanotubes, there is a limit in an increase of productivity due to excessive time for preparation and release in comparison with time for actually synthesizing the carbon nanotubes.

[66] On the contrary, for the mass production system for synthesized carbon nanotubes according to the present invention, reaction atmosphere required for synthesis of the carbon nanotubes is achieved and maintained only with preparation for synthesis of the carbon nanotubes at an initial stage. Accordingly, with the mass production system for synthesized carbon nanotubes according to the invention, the carbon nanotubes can be continuously synthesized without being stopped even for an instant once the system is operated.

[67] Such continuous synthesis of the carbon nanotubes can be achieved by the system of the present invention since the metal catalyst is continuously fed into the reaction chamber which is completely opened. That is, even at a moment when the metal catalyst is fed from the exterior into the reaction chamber, the carbon nanotubes are synthesized continuously in the carbon nanotube synthesizing unit 200.

[68] Although the interior of the reaction chamber is completely opened with respect to external air, a specified gas of a predetermined region in the reaction chamber serves to completely block introduction of the external air into the reaction chamber. That is, gases having different specific gravities occupy specified regions within the reaction chamber, respectively, so that each gas blocks other gases from permeating into its specified region inside the reaction chamber, thereby preventing the external air from permeating into the reaction chamber. Since the gas occupying the specified region of the reaction chamber is in an equilibrium state in pressure with the external air, the external air is prevented from permeating into the reaction chamber.

[69] Fig. 2 is a schematic cross-sectional view illustrating a mass production system for synthesized carbon nanotubes according to a second embodiment of the present invention. As shown in Fig. 2, the mass production system of the second embodiment comprises a reaction chamber 1 having a heating member and a passage 4 with an inner space defined therein to communicate with an outside of the reaction chamber, and a conveying unit 15 to convey a metal catalyst into the reaction chamber 1 through the passage 4.

[70] The reaction chamber 1 of the mass production system according to this embodiment has the passage 4 open downwardly, and a carbon nanotube synthesizing unit 200 formed above the passage 4 inside the reaction chamber.

[71] The reaction chamber is provided with a gas supply unit 50, which comprises gas tanks and gas injection pipes, each connecting an associated gas tank with the reaction chamber and having an opening/closing valve, to supply carbon source gas, hydrogen gas, and an inert gas into the reaction chamber, respectively.

[72] The carbon nanotube synthesizing unit 200 comprises a shower head 230 connected with a carbon source gas tank at an upper portion of the reaction chamber 1 and having plural injection nozzles arranged to allow uniform injection of a carbon source gas, a carbon source gas restriction part 280 positioned below the shower head 230 and opened at an upper portion, such as a box without an upper surface, to collect the carbon source gas, and a heating member 250 installed to the reaction chamber.

[73] The carbon source gas restriction part 280 has a box structure which is surrounded by a wall having a predetermined height, and opened only at an upper portion thereof. The shower head 230 is positioned deeper from an upper end of the wall of the carbon source gas restriction part 280. With this structure, after being injected from the shower head 230, the carbon source gas remains inside the carbon source gas restriction part 280. A portion of the carbon source gas overflowing from the carbon source gas restriction part 280 exists mainly at a lower space within the reaction chamber.

[74] The shower head has an enough area to cover most area of the opened upper portion of the carbon source gas restriction part. Of course, the carbon nanotube synthesizing unit has a space for allowing entrance of a catalyst containing member into the carbon source gas restriction part, and a space for allowing exit of the catalyst containing member from the carbon source gas restriction part between the shower head and the carbon source gas restriction part. Accordingly, the shower head very efficiently prevents hydrogen having a lighter weight than the carbon source gas from entering the carbon source gas restriction part while allowing entrance and exit of the catalyst containing member into and from the carbon source gas restriction part, thereby maintaining high synthesizing yield of the carbon nanotubes.

[75] The carbon source gas restriction part 280 has a leeway space defined at an upper portion to allow a bucket, that is, the catalyst containing member, to enter through the upper portion at one side and to leave through the upper portion at the other side. As a result, the carbon source gas positioned in the carbon source gas restriction part reacts with the metal catalyst in a reaction region formed below hydrogen gas occupying the leeway space above the carbon source gas restriction part.

[76] The carbon source gas restriction part 280 is formed with a discharge pipe 285 through which water, a residual carbon source gas, and other by-products can be discharged. If the carbon source gas is excessively supplied into the reaction chamber, a portion of the carbon source gas is discharged to the outside through the discharge pipe 285. The carbon source gas restriction part 280 serves to collect the carbon source gas heavier than hydrogen gas, and is not limited to the box structure. Alternatively, the carbon source gas restriction part 280 has various structures, which have an opened upper portion, a closed periphery, and the bottom surface.

[77] The heating member attached to the reaction chamber heats the whole interior of the reaction chamber. Thus, when the bucket 10 is conveyed into the reaction chamber through the passage 4, a metal oxide catalyst in the bucket 10 is reduced via reaction with hydrogen gas injected through the gas injection pipe and filled in the reaction chamber before the bucket 10 reaches the carbon source gas restriction part 280, so that oxygen is removed from the reaction chamber. Accordingly, the reaction chamber itself filled with hydrogen gas serves as the metal catalyst reduction unit which reduces the metal catalyst.

[78] Additionally, the reaction chamber is formed with a separate reduction inducing guide surface contacting one side of the carbon source gas restriction part in order to ensure reduction of the metal catalyst. The reduction inducing guide surface has a sufficient length in a lateral direction, and enables the metal oxide catalyst of the catalyst containing member to be reduced while moving for a sufficient time along an upper space of the reaction chamber. Although the present embodiment is described as comprising the separate reduction inducing guide surface, the present invention is not limited to this structure. Alternatively, the conveying unit is disposed to have a suitable conveyance path such that the catalyst containing member moves a sufficiently long distance along the upper portion of the reaction chamber before reaching the carbon source gas restriction part, allowing the metal oxide catalyst to be reduced for a sufficient time.

[79] The passage 4 extends a predetermined distance downwardly from the reaction chamber. The reaction chamber further comprises a cooling unit 300 which is formed around the passage 4, and comprises a cooling member 250 to cool the carbon nanotubes when the carbon nanotubes are discharge from the reaction chamber to the outside after being synthesized therein.

[80] A hydrogen gas discharge pipe 120 is formed at one side of the passage 4. If hydrogen gas is excessively supplied from the gas supply unit 50, the pressure of hydrogen gas continues to increase. Thus, it is necessary to discharge a predetermined amount of hydrogen gas to the outside of the reaction chamber in order to maintain equilibrium between the pressures of hydrogen gas and external air at a region where hydrogen gas of the passage 4 contacts the external air. To this end, hydrogen gas is discharged through the hydrogen gas discharge pipe 120 instead of the passage 4. The reason that the hydrogen gas discharge pipe 120 is formed at a lower portion of the reaction chamber is that, when hydrogen gas rises to an upper portion of the reaction chamber at a high temperature condition in the reaction chamber, hydrogen gas is prevented from being immediately discharged to the outside, but is sufficiently filled in the reaction chamber, thereby sufficiently increasing the pressure of hydrogen gas within the reaction chamber.

[81] Since the external air outside the reaction chamber has the specific gravity higher than that of hydrogen gas, it remains below hydrogen gas. In this regard, since the passage 4 is open downwardly, the external air having the higher specific gravity is prevented from permeating into the reaction chamber filled with hydrogen gas. Furthermore, since the equilibrium state between the pressures of hydrogen gas and the external air is maintained at the region where hydrogen gas of the passage 4 contacts the external air, the external air is prevented from permeating into the reaction chamber.

[82] Although the passage 4 is open downwardly in the mass production system of this embodiment, the external air having the higher specific gravity than that of hydrogen gas having a high temperature in the reaction chamber is always located below hydrogen gas, and thus is prevented from permeating into the reaction chamber 1.

[83] In this embodiment, an argon gas injection pipe is connected with the shower head of the reaction chamber. With this structure, if argon gas is injected at a reaction preparation stage, it pushes down air existing within the reaction chamber, and discharges the air through the passage, so that the interior of the reaction chamber becomes an inert gas atmosphere. Then, the carbon nanotubes are synthesized by supplying hydrogen gas along with the carbon source gas into the reaction chamber to reduce the metal catalyst. Other components and processes of the second embodiment are the same as those of the first embodiment, and thus detailed description thereof will be omitted hereinafter.

[84] Fig. 3 is a schematic cross-sectional view illustrating a mass production system for synthesized carbon nanotubes according to a third embodiment of the invention. As shown in Fig. 3, the mass production system of the third embodiment is the same as that of the second embodiment in that it enables entrance and exit of a bucket 10, that is, the catalyst containing member, through a passage 4. However, the third embodiment is different from the second embodiment, particularly, in that the passage 4 is open upwardly, and is connected with a U-shaped part 300. The mass production system of the third embodiment further comprises a conveying unit 15 which conveys the bucket 10 containing a metal oxide catalyst into a reaction chamber to synthesize carbon nanotubes, and then conveys the bucket to the outside of the reaction chamber.

[85] The U-shaped part 400 is formed downwardly from the passage 4, bent and horizontally extends a predetermined length, and is then connected at an extended end with a carbon nanotube synthesizing unit 200 serving to synthesize the carbon nanotubes.

[86] The U-shaped part 400 constitutes a cooling unit 300 which comprises a cooling member 350 disposed around the U-shaped part 400. Next to the U-shaped part 400, a metal catalyst reduction unit 100, and the carbon nanotube synthesizing unit 200 are formed within the reaction chamber.

[87] The U-shaped part 400 is filled with argon gas injected through an argon gas injection pipe of a gas supply unit 50 up to a predetermined height, while being cooled by the cooling member 350. The cooled argon gas is considerably increased in specific gravity greater than air outside the reaction chamber. Thus, the external air is always located above argon gas having the higher specific gravity at the passage 4 of the reaction chamber, thereby blocking the external air from permeating into the reaction chamber 1. The gas occupying the U-shaped part 400 may be any of inert gases having a higher specific gravity than that of the external air as well as argon gas.

[88] The reaction chamber has a horizontal extension part 105, which is bent from the

U-shaped part 400 and heated by a heating member installed to the outside of the reaction chamber. In the horizontal extension part 105, hydrogen gas injected into the reaction chamber through hydrogen gas injection pipe reacts with a metal oxide catalyst introduced into the horizontal extension part 105 of the reaction chamber by the conveying unit 15 so that oxygen is removed from the metal oxide catalyst. After passing through the horizontal extension part 105, the catalyst containing member is conveyed adjacent to a ceiling surface of a rear reaction chamber 105. Thus, even though there is a little non-reduced metal oxide catalyst, it is reduced by hydrogen gas filled in an upper space of the rear reaction chamber 205, so that the metal oxide catalyst is completely reduced. The horizontal extension part 105 is not limited to the length shown in Fig. 3, and has enough length to allow the metal oxide catalyst to be reduced for a sufficient time.

[89] The rear reaction chamber 205 connected with the horizontal extension part 105 has a space of a predetermined size defined therein, and a shower head 230 installed at an upper portion to uniformly inject a carbon source gas thereto. The rear reaction chamber 205 is provided at the upper portion with a hydrogen gas discharge pipe 207 through which hydrogen, being lighter than the carbon source gas, is discharged to the outside, and at a lower portion with a heating member 250. The metal oxide catalyst in the catalyst containing member conveyed into the rear reaction chamber 150 by the conveying unit 15 reacts with the carbon source gas while passing below the shower head 230, and synthesizes carbon nanotubes. With the synthesized carbon nanotubes contained therein, the catalyst containing member is discharged to the outside of the reaction chamber along the same path by the conveying unit 15.

[90] The rear reaction chamber 205 has a bottom surface deeper than the horizontal extension part 105, and the shower head 230 is set adjacent to the bottom surface of the rear reaction chamber 205. With this structure, the rear reaction chamber 205 allows the carbon source gas to accumulate in a predetermined space on the bottom, which constitutes a reaction region where the metal catalyst reacts with the carbon source gas. Since the metal catalyst passes directly above the bottom of the rear reaction chamber 205, it reacts with the carbon source gas densely accumulated thereon, thereby actively synthesizing the carbon nanotubes. In other words, the bottom of the rear reaction chamber 205 is formed deeper than the horizontal extension part 205 for the purpose of enhancing reaction efficiency by forcing the carbon source gas heavier than hydrogen gas to be accumulated in the lower space of the rear reaction chamber 205 via gravity.

[91] Other components of the third embodiment can be easily understood with reference to the first embodiment, and thus detailed description thereof will be omitted hereinafter.

[92] Fig. 4 is a schematic cross-sectional view illustrating a mass production system for synthesized carbon nanotubes in accordance with a fourth embodiment of the invention. As shown in Fig. 4, the mass production system according to the fourth embodiment is the same as that of the third embodiment except that the mass production system of the fourth embodiment does not comprise the U-shaped part, and has a downwardly open passage.

[93] Since hydrogen gas is filled in the reaction chamber from the passage which is opened downwardly, air outside the reaction chamber cannot be introduced into the reaction chamber. The reason that the external air cannot be introduced into the reaction chamber has been already described in the first and second embodiments, and thus repetitious description will be omitted hereinafter.

[94] The mass production system of the fourth embodiment is different from the third embodiment in that a hydrogen gas discharge pipe 207 is formed upper portion of the passage. With the hydrogen gas discharge pipe 207 formed near the passage, hydrogen gas is prevented from being discharged through the passage.

[95] In the mass production systems according to the above embodiments, if the carbon nanotube synthesizing unit 200 has an extended length, a length for the catalyst containing member to move while being subjected to reaction is increased, and thus a conveying speed of the catalyst containing member can be increased. In other words, for the case where reaction time and temperature inside the reaction chamber is specified for synthesis reaction, if the carbon nanotube synthesizing unit 200 has an extended length, it is possible to increase a speed of inputting the metal catalyst into the reaction chamber, thereby increasing productivity.

[96] In the mass production systems of the above embodiments, although the heating member and the cooling member 250 are described as being installed at the outside of the reaction chamber, the present invention is not limited to this structure. Instead, these components can be installed at any suitable locations for heating and cooling.

[97] According to the present invention, the mass production system may comprise one or more different-specific gravity gas occupying parts according to the shape of the reaction chamber. In addition, the different-specific gravity gas occupying parts separated from each other may be occupied with the same gas or different gases.

[98] A mechanism for conveying the catalyst containing member may be not only a conveyor, but also any of various well-known conveying members.

[99] The carbon source gas restriction part 280 in the reaction chamber is provided for the purpose of enhancing efficiency of synthesizing the carbon nanotubes, and serves to accumulate the carbon source gas on a specific location.

[100] Although the embodiment of the invention comprises a separate cooling member to cool the synthesized carbon nanotubes to room temperature, the invention is not limited to this structure, and thus the carbon nanotubes may be cooled at the outside after being discharged from the reaction chamber instead of using the cooling member.

[101] It should be understood that the embodiments and the accompanying drawings have been described for illustrative purposes and the present invention is limited by the following claims. Further, those skilled in the art will appreciate that various modifications, additions and substitutions are allowed without departing from the scope and spirit of the invention as set forth in the accompanying claims. Industrial Applicability The present invention can be used for the mass production system of carbon nanotubes using a vapor synthesis process. In particular, the present invention can be used for the method of synthesizing the carbon nanotubes in a great quantity using the mass production system comprising an open type reaction chamber.

Claims

[1] A mass production system for synthesized carbon nanotubes, comprising: a reaction chamber having at least one opening opened to external air, and at least one different-specific gravity gas occupying region filled with a different specific gravity gas having a different specific gravity from that of the external air to block the external air from being introduced into the reaction chamber through the opening; a carbon nanotube synthesizing unit positioned in the different-specific gravity gas occupying region to synthesize carbon nanotubes by the medium of a catalyst introduced thereto through the opening; a conveying unit to convey the catalyst to the carbon nanotube synthesizing unit through the opening; and a gas supply unit to supply the different specific gravity gas and a carbon source gas used for synthesizing the carbon nanotubes to the different-specific gravity gas occupying region and the carbon nanotube synthesizing unit, respectively.

[2] The system according to claim 1, wherein the opening comprises an inlet through which the catalyst is introduced into the reaction chamber, and an outlet through which the carbon nanotubes synthesized by the carbon nanotube synthesizing unit are discharged to an outside of the reaction chamber, and the conveying unit conveys the catalyst and/or the carbon nanotubes via the opening, the different-specific gravity gas occupying region, the carbon nanotube synthesizing unit, and the outlet.

[3] The system according to claim 1 or 2, wherein the carbon nanotube synthesizing unit comprises: a reaction region defined in the reaction chamber so as to be blocked from the external air by the different specific gravity gas filled in the different-specific gravity gas occupying region; a carbon source gas injector to inject the carbon source gas supplied from the gas supply unit to the reaction region such that the catalyst conveyed to the reaction region by the conveying unit reacts with the carbon source gas to synthesize the carbon nanotubes; and a heating member to heat the reaction region.

[4] The system according to claim 3, wherein the reaction region of the carbon nanotube synthesizing unit is defined at a lower portion of the at least one portion of the different-specific gravity gas occupying region filled with a different specific gravity gas having a lower specific gravity than the carbon source gas, and the carbon nanotube synthesizing unit further comprises a carbon source gas restriction part opened at an upper portion to block the carbon source gas injected to the reaction region from escaping from the reaction region.

[5] The system according to claim 3, wherein the different-specific gravity gas occupying region comprises: a first different-specific gravity gas occupying region filled with a different specific gravity gas having a lower specific gravity than the carbon source gas; and a second different-specific gravity gas occupying region filled with a different specific gravity gas having a higher specific gravity than that of the carbon source gas, the first different-specific gravity gas occupying region, the reaction region, and the second different-specific gravity gas occupying region being sequentially defined in a gravity direction within the reaction chamber.

[6] The system according to any one of claims 1 to 5, wherein the different specific gravity gas comprises: at least one of a gas having a lower specific gravity than that of the external air; and a gas having a higher specific gravity than that of the external air in order to block the external air from being introduced into the reaction chamber through the opening depending on a location of the opening on the reaction chamber.

[7] The system according to any one of claims 1 to 5, further comprising: a heating member to heat at least one region inside the reaction chamber to reduce the catalyst introduced into the reaction chamber through the opening, and wherein at least one of the different specific gravity gases occupying the different-specific gravity gas occupying regions is hydrogen gas.

[8] The system according to claim 3, wherein the carbon source gas injector comprises a plurality of nozzles dispersedly arranged corresponding to a dimension of the reaction region to uniformly inject the carbon source gas into the reaction region.

[9] The system according to claim 7, wherein the reaction chamber has at least one discharge pipe formed therein to discharge hydrogen gas to the outside of the reaction chamber in order to accomplish an equilibrium state between pressure of the hydrogen gas occupying the different-specific gravity gas occupying region and pressure of the external air.

[10] The system according to any one of claims 1 to 5, further comprising: a cooling unit to cool one region of the reaction chamber near the outlet such that the carbon nanotubes are cooled by the cooling unit.

[11] A mass production method of synthesized carbon nanotubes, comprising the steps of: supplying a catalyst into a reaction chamber having at least one opening opened to external air, through which the catalyst is supplied to the reaction chamber, and at least one different-specific gravity gas occupying region filled with a different specific gravity gas having a different specific gas from that of the external air to block the external air from being introduced into the reaction chamber through the opening; supplying a carbon source gas to the reaction chamber to allow the carbon source gas to react with the catalyst in the reaction region blocked from the external air by the different specific gas, thereby synthesizing the carbon nanotubes; and discharging the synthesized carbon nanotubes to an outside of the reaction chamber through the opening.

[12] The method according to claim 11, further comprises: supplying hydrogen gas into the reaction chamber to allow the hydrogen gas to react with the catalyst, thereby reducing the catalyst.

[13] The method according to claim 12, further comprising: discharging a portion of the hydrogen gas through a discharge pipe formed in the reaction chamber in order to accomplish an equilibrium state between pressure of the hydrogen gas occupying the different-specific gravity gas occupying region and pressure of the external air.