Method for producing carbon dioxide-based carbon nanotubes by continuous process
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- KOREA CARBON INDUSTRY PROMOTION AGENCY
- Filing Date
- 2025-11-26
- Publication Date
- 2026-06-11
Smart Images
Figure KR2025019744_11062026_PF_FP_ABST
Abstract
Description
Method for manufacturing carbon dioxide-based carbon nanotubes by a continuous process
[0001] The present invention relates to the field of carbon material manufacturing technology, and more specifically, to a continuous process-based method for manufacturing carbon nanotubes (CNTs) that can continuously synthesize carbon nanotubes in a single reaction space or a continuous reaction environment using carbon dioxide (CO2) as a carbon source.
[0002] The present invention enables the CO₂ reduction reaction and the CNT growth reaction to be performed continuously within the same reaction system or interconnected reaction systems, thereby improving reaction efficiency and simplifying the entire process flow from carbon precursor generation to CNT growth and CNT recovery, while simultaneously providing a technical basis for the stable production of high-purity and high-crystallinity CNTs.
[0003] Furthermore, the present invention relates to an eco-friendly material manufacturing technology that can be utilized in the fields of carbon utilization and carbon reduction technologies (CCU / CCUS) by converting CO2 into high-value-added nanocarbon materials.
[0004]
[0005] Carbon dioxide (CO2) is a major greenhouse gas emitted in large quantities during industrial processes and energy production; consequently, there is a continuously growing need for Carbon Capture and Utilization (CCU) technology that aims to convert it into high-value-added materials, moving beyond the simple stages of capture and storage. In particular, the chemical conversion of carbon dioxide is recognized as a key strategy for achieving carbon neutrality, and active research is being conducted on its conversion into various substances, such as carbon precursors, fuels, and chemical materials.
[0006] However, existing CO ₂Conversion studies have primarily focused on the production of low-dimensional compounds such as methanol, carbon monoxide, and synthesis gas, and research on the direct conversion to high-value structured carbon materials, particularly high-dimensional nanomaterials such as carbon nanotubes (CNT), is extremely limited due to technical complexity and the difficulty of reaction control.
[0007] Generally, the mainstream method for CNT synthesis has involved utilizing hydrocarbon gases as carbon sources and growing CNTs through the decomposition and rearrangement reactions of catalytic metals. While a certain level of technological foundation has already been accumulated for this process, directly utilizing CO₂ as a carbon source requires significant energy input during the reduction and decomposition processes due to CO₂'s high thermodynamic stability. Furthermore, various process factors such as reaction rate, precursor formation, and catalyst activation interact in a complex manner, resulting in reaction behavior that is entirely different from conventional hydrocarbon-based CVD processes.
[0008] In addition, for the precursor generated from CO2 to come into contact with the CNT growth catalyst and lead to continuous and uniform CNT growth, multiple reaction conditions, such as the temperature gradient inside the reactor, gas flow pattern, catalyst surface state, and precursor concentration, must be precisely controlled.
[0009] Most CO2-based CNT studies reported in the existing literature have remained at the level of laboratory-scale batch experiments, and it is difficult to consider them established as a process technology at a practical level due to issues such as reaction stability, non-uniformity of CNT growth rates, and catalyst deactivation during long-term operation.
[0010] In other words, the process of continuously synthesizing CNTs using CO2 as a starting material is technically challenging and still has many unresolved research issues; furthermore, conventional technology has not provided sufficient solutions in terms of process stability, productivity, and ensuring CNT quality.
[0011] In particular, the technology of integrating the CO₂ reduction step and the CNT growth step into a single flow within a single chamber or continuous reaction environment has rarely been specifically implemented in prior research, and examples of development to a level capable of commercial scale or continuous operation are even rarer.
[0012] Therefore, there is an urgent need for the development of new continuous process-based technologies capable of stably manufacturing high-quality CNTs by increasing CO2 conversion efficiency and implementing a continuous and integrated process for carbon precursor formation and CNT growth stages.
[0013] Meanwhile, the present invention includes research results carried out with partial support from the Korea Carbon Industry Promotion Agency as follows.
[0014] - Assignment No.-A230101002
[0015] - Project Management (Specialized) Agency Name: Korea Carbon Industry Promotion Agency
[0016] - Research Project Name: Reinvestment Project for Core Technology Development and Research Infrastructure Construction
[0017] - Research Project Title: High-Purity, High-Crystallinity Single-Walled Carbon Nanotubes via CO2 Resource Utilization
[0018] High-speed conversion technology and application development of (SWCNT)
[0019] - Project Implementing Agency Name - Korea Carbon Industry Promotion Agency
[0020] - Research Period: 2023.09.01~2025.12.3
[0021] In addition, the present invention includes research results carried out with partial support from the following government-supported research project.
[0022] - Project ID: 2410000416
[0023] - Project Number: RS-2023-00257573
[0024] - Ministry Name (Central Administrative Agency): Ministry of Trade, Industry and Energy
[0025] - Project Management (Specialized) Agency: Korea Institute of Industrial Technology Planning and Evaluation (KEIT)
[0026] - Research Project Name: Development of Manufacturing Technology for High-Performance Carbon Nanocomposite Fibers
[0027] - Research Project Title: Development of Mass Production Technology for High-Purity Double-Walled Carbon Nanotubes (DWCNT) with High Crystallinity and High Aspect Ratio
[0028] - Project Implementing Agency: JO
[0029] - Research Period: April 1, 2023 – December 31, 2027
[0030]
[0031] The present invention aims to solve the problem of being difficult to directly apply carbon dioxide to the CNT manufacturing process due to its high thermodynamic stability, and to provide a technology that enables the stable implementation of the reaction converting CO₂ into a carbon precursor and the CNT growth reaction within a single continuous reaction stream.
[0032] Furthermore, the present invention aims to provide a manufacturing method capable of maintaining uniform physical properties, such as the number of walls, diameter, and crystallinity of CNTs, by stabilizing the composition of the precursor generated during the CO₂ reduction step and precisely controlling the temperature distribution and gas flow inside the reactor.
[0033] In addition, the present invention aims to provide a manufacturing technology that enables stable continuous production of CNTs and suppresses catalyst deactivation even under long-term operating conditions by clearly distinguishing the reaction roles of the first catalyst and the second catalyst, while allowing the two-step reaction to proceed sequentially and continuously within the same or continuous reaction space.
[0034] Furthermore, another objective of the present invention is to provide a continuous process-based CNT manufacturing method suitable for process scale expansion, which increases CO₂ conversion efficiency and improves reaction stability during the CNT growth stage by appropriately setting the structure and temperature profile of the reactor.
[0035]
[0036] A method for manufacturing carbon nanotubes based on carbon dioxide according to one embodiment of the present invention comprises: a step of supplying CO2 to a reactor having a single space or a substantially continuous reaction space; a first reaction step of converting the CO2 into a carbon precursor at a first temperature by a first catalytic reaction by a first catalyst; and a second reaction step of producing carbon nanotubes by contacting the carbon precursor with a second catalyst at a second temperature in the same reaction space or a continuous space.
[0037] The first catalyst may be a particulate catalyst comprising: 1) a nickel (Ni)-based catalyst; 2) a support comprising MgO, silica (SiO2), or Al2O3 beads having mesopores; and nickel particles loaded on the support; or 3) a particulate catalyst comprising nickel particles loaded on MoS2 / Ni foam.
[0038] The second catalyst may be formed by the conversion of a liquid or gaseous catalyst precursor injected into the reactor.
[0039] The second reaction step above may include a step of additionally supplying CO2 to the reaction zone at a concentration of 1 (±0.05) vol%.
[0040] The first reaction step is carried out by fluidized bed catalytic operation using a first catalyst which is a particulate catalyst, and the second reaction step can be carried out by floating catalytic operation by injecting a catalyst precursor which is in a liquid or gaseous state into the reactor.
[0041] The above reactor may have the area where the first reaction step takes place and the area where the second reaction step takes place physically separated by a filter.
[0042] The above reactor is a single integrated space without separate spatial partitions, and the first reaction step and the second reaction step can be carried out sequentially within the same space by changing the temperature profile within the reactor.
[0043] The above reactor is equipped with a tubular furnace consisting of a single integrated space without separate space partitions and a heating module consisting of a plurality of heating units disposed on the outer wall of the tubular furnace, and the reactor may be divided into a first reaction zone in which carbon dioxide is converted into a carbon precursor and a second reaction zone in which the converted carbon precursor is converted into a carbon nanotube according to a temperature profile including temperature changes according to location in the reactor.
[0044] The present method can control the physical properties of the carbon nanotubes produced by controlling the flow rate of the supplied carbon dioxide per unit time and the temperature profile.
[0045] The above temperature profile can be changed by adjusting the temperature of individual heating units within the heating module.
[0046]
[0047] According to the present invention, since the step of converting carbon dioxide into a carbon precursor and the step of growing carbon nanotubes using the carbon precursor can be carried out continuously within a single reaction stream, losses that may occur during the transfer step between processes can be minimized. Accordingly, the conversion process from CO₂ to CNT is aligned into a single stream, which can contribute to process simplification and improved production efficiency.
[0048] Furthermore, according to the present invention, the CO₂ reduction reaction performed by the first catalyst and the CNT growth reaction performed by the second catalyst are stably separated and linked according to the structure and temperature profile of the reactor, thereby improving the stability of precursor generation and the reproducibility of the CNT growth reaction. Consequently, physical properties such as the diameter, number of walls, and crystallinity of the CNTs are maintained uniformly, and quality changes are suppressed even during continuous reactions for a long time.
[0049] Furthermore, the configuration of supplying an additional small amount of CO₂ in the second reaction step controls carbon species accumulated on the catalyst surface, thereby suppressing catalyst deactivation and enhancing the stability of the CNT growth reaction. This configuration is advantageous in terms of reaction sustainability and maintaining catalyst activity, enabling the long-term production of CNTs in a continuous process environment.
[0050] Meanwhile, when the reactor is configured as a single space, the first and second reaction stages can be naturally partitioned simply by appropriately controlling the temperature profile, allowing for the continuous implementation of a two-stage reaction without the need for a separate structural partitioning device. This contributes to the simplification of the device configuration and improved operational convenience, while also reducing the structural burden during process expansion.
[0051] In addition, since the temperature distribution inside the reactor can be precisely controlled by adjusting the temperature of individual heating units within the heating module, the physical properties of the generated CNTs can be controlled according to process conditions. This offers the advantage of stably manufacturing CNTs with various characteristics depending on the purpose.
[0052] Consequently, the present invention provides a technical basis for the continuous conversion of a stable molecule called carbon dioxide into high-value carbon nanotubes, and can improve the limitations of existing technologies in various aspects, such as process stability, reaction efficiency, catalyst durability, and CNT quality uniformity.
[0053]
[0054] Figure 1 is a conceptual process diagram illustrating the basic reaction flow of the carbon dioxide-based carbon nanotube manufacturing method of the present invention.
[0055] FIG. 2 is a conceptual drawing illustrating an example of a first catalyst that can be used in the present invention.
[0056] FIG. 3 is a schematic diagram conceptually showing a method and structure for manufacturing a nickel-based catalyst according to another embodiment of the present invention.
[0057] FIG. 4 is a conceptual diagram illustrating a reactor for realizing a method for manufacturing carbon dioxide-based carbon nanotubes according to a first embodiment of the present invention.
[0058] FIG. 5 is a conceptual diagram illustrating a reactor for realizing a method for manufacturing carbon dioxide-based carbon nanotubes according to a second embodiment of the present invention.
[0059] FIG. 6 is a graph conceptually showing the temperature profile of a reactor according to the first embodiment of the present invention.
[0060] FIG. 7 is a conceptual diagram illustrating another type of reactor for realizing a method for manufacturing carbon dioxide-based carbon nanotubes according to a second embodiment of the present invention.
[0061] FIG. 8 is a conceptual diagram illustrating the operation of a tubular reactor and a temperature profile for realizing a carbon dioxide-based carbon nanotube manufacturing method according to a third embodiment of the present invention.
[0062] Figure 9 is a graph showing a temperature profile different from that of Figure 8.
[0063] FIG. 10 is a conceptual diagram illustrating another type of tubular reactor for realizing a method for manufacturing carbon dioxide-based carbon nanotubes according to a third embodiment of the present invention.
[0064]
[0065] Hereinafter, a method for manufacturing carbon dioxide-based carbon nanotubes according to an embodiment of the present invention will be described in detail with reference to the attached drawings. The following descriptions are exemplary descriptions intended to explain the embodied aspects of the technical concept of the present invention, and the technical concept of the present invention is not limited by the following descriptions. The technical concept of the present invention may be interpreted and limited only by the claims set forth below.
[0066] Figure 1 is a conceptual process diagram illustrating the basic reaction flow of the carbon dioxide-based carbon nanotube manufacturing method of the present invention.
[0067] Referring to FIG. 1, the starting materials used in the present invention are carbon dioxide (CO2) and hydrogen (H2) from the air or separately supplied hydrogen, which are supplied simultaneously to one end of the reactor. Since carbon dioxide is generally a very stable molecule and it is difficult to form carbon nanotubes through direct thermal decomposition, in the method of the present invention, a first reaction step for the reduction and conversion of CO2 is first performed in an area provided with a first catalyst. In the first reaction step, CO2 reacts with H2 to produce a carbon precursor mixture containing methane (CH4). In addition to CH4, this precursor mixture may contain CO or unreacted H₂, etc., depending on the reaction conditions. Meanwhile, the first reaction step is carried out at a temperature of 300 to 400°C, but can be modified in various ways depending on the type of catalyst, the method of operation, etc.
[0068] The above first reaction step is carried out in the presence of a first catalyst.
[0069] FIG. 2 is a conceptual drawing illustrating an example of a first catalyst that can be used in the present invention.
[0070] Referring to FIG. 2, the first catalyst may exist in a form in which a plurality of nickel (Ni) particles are dispersed in the internal pores and on the surface of a mesoporous MgO, silica, or alumina bead structure serving as a catalyst support. A catalyst with this structure has high activity in the CO2 methanation reaction, and because the size and distribution of Ni particles are maintained stably, there is an advantage that deformation and aggregation of the catalyst are suppressed even in a thermal reaction environment for a long time. In the present invention, the first catalyst may be in the form of a particulate catalyst, and the form of the catalyst is not limited to the structure shown in FIG. 2.
[0071] In the present embodiment, the first catalyst may include a nickel (Ni)-based catalyst, and the Ni may be in a loaded form on a support. As the support, MgO, silica (SiO2), Al2O3 beads, or a porous metal frame having mesopores may be used, and the pore structure of the support may facilitate the flow of reaction gas and the exposure of the catalyst's active sites, thereby contributing to the conversion of CO₂ to CH₄.
[0072] FIG. 3 is a schematic diagram conceptually showing a method and structure for manufacturing a nickel-based catalyst according to another embodiment of the present invention.
[0073] Referring to FIG. 3, the first catalyst may be in the form of nickel particles dispersed on a MoS2 / Ni foam structure. FIG. 3 conceptually illustrates the process of forming a catalyst structure including such a MoS2-based porous nickel foam, showing a form in which MoS2 is formed on a porous metal frame and a catalyst layer with nickel particles attached thereto is provided. The catalyst structure has a large reaction surface area and high thermal stability, so it can effectively reduce CO2 in the first reaction step.
[0074] Referring again to FIG. 3, the first catalyst can be manufactured through the steps of: washing a 3D microporous Ni microfoam and coating the washed Ni microfoam with (NH4)2MoS4; synthesizing defective MoS2 on the (NH4)2MoS4-coated Ni microfoam using a CVT method to create a MoS2 / Ni foam structure; and decorating the MoS2 / Ni foam structure with Ni nanoparticles to produce a Ni / MoS2 / Ni heterostructure membrane-based catalyst.
[0075] The carbon precursor generated in the first reaction stage can flow directly into the second reaction stage area within the reactor without a separate transfer process. The second reaction stage is a CNT growth reaction carried out in the presence of a second catalyst, in which carbon nanotubes grow through the thermal decomposition of methane (CH4) among the precursors. The second catalyst can be generated directly in the reaction environment by injecting a liquid or gaseous catalyst precursor into the reactor. For example, catalyst precursors such as metal-organic compounds or metal salt solutions are decomposed and reduced inside the reactor to generate catalyst metal particles, which can act as nucleation sites for CNT growth.
[0076] Meanwhile, the second reaction step can be carried out at a temperature of 1200 to 1400°C, which can be variably controlled depending on the type of catalyst or changes in operation.
[0077] Unlike the first catalyst, the second catalyst can be locally introduced during the initial stage of the reaction or in the section where CNT growth is required, and induces the thermal decomposition of methane inside the reactor to promote the growth of the CNT wall structure. Generally, the thermal decomposition of CH4 requires high temperatures, and the second catalyst can be maintained stably even in such high-temperature environments to induce a continuous CNT growth reaction. Meanwhile, an iron (Fe) or cobalt (Co)-based catalyst may be used as the second catalyst, and the type is not significantly limited.
[0078] Meanwhile, in the method of the present invention, an extremely small amount of CO2 may be additionally supplied to the reaction zone in the second reaction step. This is intended to improve the stability of the CNT growth reaction by controlling the reaction atmosphere and suppressing excessive carbon accumulation on the catalyst surface. For example, by introducing approximately 1 vol% of CO₂, deactivation of the catalyst metal is prevented, and the number of walls, diameter, and crystallinity of the CNTs can be maintained more uniformly. Such introduction of a small amount of CO₂ can serve as an effective reaction control means for ensuring uniformity in CNT quality.
[0079] As such, in the method of the present invention, the reaction of converting CO2 into a carbon precursor in the first reaction step and growing the precursor into CNTs in the second reaction step can be continuously performed within a single reactor. The structure of the reactor may consist of a plurality of reaction zones in a continuous form, or a single integrated space without separate spatial partitions may be functionally divided into a first reaction zone and a second reaction zone according to temperature changes. Since this reaction structure eliminates the need for transfer lines or movement between separate reaction vessels, process losses can be minimized and the continuity of CNT manufacturing can be ensured.
[0080] The method for manufacturing carbon dioxide-based carbon nanotubes according to the present invention will be explained in detail through various embodiments based on the type of reactor and the reaction operation method.
[0081] [Example]
[0082] Example 1: Hybrid Catalyst Operation
[0083] FIG. 4 is a conceptual diagram illustrating a reactor for realizing a method for manufacturing carbon dioxide-based carbon nanotubes according to a first embodiment of the present invention.
[0084] Figure 4 illustrates a vertical reactor, but the carbon nanotube manufacturing method of the present invention can, of course, be applied to horizontal reactors, etc. The determination of whether to use a horizontal reactor or a vertical reactor can be appropriately made by taking into account the required physical properties (quality) of the carbon nanotubes being manufactured and the detailed elements of the manufacturing process as a whole.
[0085] Referring to FIG. 4, the present invention will be explained more specifically by citing a vertical reactor as an example of a reactor (100) for implementing a method for manufacturing carbon dioxide-based carbon nanotubes according to one embodiment of the present invention.
[0086] In the following reactor, carbon dioxide is converted into carbon nanotubes through a two-stage reactor according to the following reaction equation, and the reactions in the first and second reaction stages are carried out by different catalyst operation methods.
[0087] [Reaction Equation 1]
[0088]
[0089] Referring again to FIG. 4, the reactor (100) is largely divided into a fluidized bed region (FU) that performs a fluidized bed stage and a floating region (FO) that performs a floating stage. Meanwhile, in this embodiment, the fluidized bed region (FU) and the floating region (FO) are spatially separated by a filter (150). The filter (150) contains a water adsorbent component such as calcium sulfate (CaSO₄), as well as a carbon monoxide adsorbent component such as activated carbon or zeolite. Thus, through the filter (150), water (H₂O) contained in the hydrocarbon rising from the fluidized bed region (FU) is absorbed, and other impurity gases such as carbon monoxide (CO) are filtered, allowing a high-purity carbon precursor (hydrocarbon, CH₄) to be supplied to the floating region (FO).
[0090] In this embodiment, an example has been described in which the reaction zone of the reactor (100) is separated by a filter (150). However, in a CNT manufacturing process that does not require relatively high quality and accepts a reduction in yield, a reactor (100) consisting of an integrated space that does not include a separate partition (filter, 150) may be considered. The design of such a reactor (100) can be modified in an appropriate manner, taking into account the purpose of use of the manufactured CNT and the unit cost of the product.
[0091] In the above fluidized bed region (FU), a fluidized bed step employing the fluidized bed method described above is performed. Meanwhile, in the above fluidized bed region (FU), a support means (110) is disposed at a predetermined distance from the bottom of the reactor (100) to support the particulate catalyst (10). Naturally, the support means (110) is made of a porous material such as ceramic to facilitate the smooth passage of carbon dioxide.
[0092] As carbon dioxide (CO2) introduced from the bottom moves upward, a catalytic reaction is initiated while floating the particulate catalyst (10). The fluidized bed stage is a catalytic reaction by the particulate catalyst (10), and the energy supplied to the fluidized bed region (FU) may vary depending on the type or physical properties of the catalyst. When a nickel-based catalyst is used as the particulate catalyst, the hydrocarbon conversion reaction according to the fluidized bed stage takes place at a temperature of approximately 300°C to 400°C.
[0093] Although not illustrated in FIG. 2, a heat source, such as a heater, for supplying energy may be placed around the reactor (100). Furthermore, since the type of reaction differs depending on the fluidized bed region (FU) or floating region (FO), it is natural to place a heat source capable of providing different amounts of energy corresponding to this. Meanwhile, in this embodiment, a heat source has been exemplified as the energy, but the type of energy is not limited thereto, and other energy sources such as electricity, arc, or laser may be utilized.
[0094] The method for manufacturing carbon nanotubes according to the present embodiment is not dependent on the type of catalyst, and various metal catalysts other than Ni-based catalysts can be used, and furthermore, various hybrid catalysts can be used, and there are no other restrictions on the use of novel catalysts developed in the future in the present invention.
[0095] Referring again to FIG. 4, a catalyst injection port (120) is formed in the floating region (FO) of the reactor (100) for injecting or spraying a catalyst precursor (20) at the top.
[0096] In the floating region (FO), the injected catalyst precursor (20) is converted into catalyst particles at high temperature and reacts with hydrocarbon (methane) supplied from below, continuously generating CNTs.
[0097] A catalyst precursor (20) in a gaseous (gaseous) state may be injected through the catalyst injection port (120), but a catalyst precursor (20) in a liquid state at the time of injection may also be injected. During the injection process, the catalyst precursor is converted into a gaseous state the moment it is injected into a high-temperature reactor and participates in the floating stage through a mechanism substantially identical to that of the gaseous catalyst precursor (20).
[0098] In this embodiment, the catalyst precursor (20) comprises an iron (Fe)-based compound, and examples of such catalyst precursor (20) include ferrocene (Fe(C5H5)2) or iron pentacarbonyl (Fe(CO)5)-). However, the carbon nanotube manufacturing method of the present invention is not limited to the type of catalyst in the floating step, and any catalyst precursor (20) that can be employed in the floating method may be used in this method.
[0099] In this embodiment, when the iron-based catalyst precursor (20) is used, the CNT generation reaction takes place in the floating region (FO) at a temperature of 800°C to 1200°C.
[0100] As such, according to the present invention, since CNTs are continuously generated in the floating region (FO), continuous CNT production is possible even when carbon dioxide is used as a starting material.
[0101] As explained above, the floating step according to the present invention forms catalyst particles within the reactor (100) by directly injecting a catalyst precursor, so a separate support is not used, which reduces the possibility of impurity incorporation, and allows for precise control of the catalyst particle size and distribution, which is highly advantageous for obtaining high-quality CNTs of uniform diameter.
[0102] Meanwhile, by controlling the types of the aforementioned catalyst components or the reaction temperature in the floating region (FO), the quality of the manufactured CNTs, such as crystallinity, can be controlled, and furthermore, it is possible to manufacture CNTs having various wall structures, such as single-wall or double-wall.
[0103]
[0104] Example 2: Single-space reactor
[0105] FIG. 5 is a conceptual diagram illustrating a reactor for realizing a method for manufacturing carbon dioxide-based carbon nanotubes according to a second embodiment of the present invention.
[0106] Referring to FIG. 5, a reactor (200) that enables the first reaction step and the second reaction step to be carried out in one space includes a first catalyst support means (210) and a second catalyst support means (220) that are spaced apart from the bottom at a predetermined distance. A first catalyst (10) that participates in a catalytic reaction for converting carbon dioxide into hydrocarbon is disposed on the first catalyst support means (210), and the first catalyst is a particulate (solid) catalyst.
[0107] Meanwhile, a second catalyst (40) that participates in the thermal decomposition in which hydrocarbons are thermally decomposed and converted into carbon nanotubes is disposed on the second catalyst support means (220). In this embodiment, the second catalyst is also a particulate (solid) catalyst.
[0108] Unlike the above, the reactor (200) may include only one catalyst support means (210, 220), and in this case, the first catalyst (30) and the second catalyst (40) may be arranged by sharing the same catalyst support means (210, 220).
[0109] The spacing between catalyst support means (210, 220) and the distance from the bottom, etc., can be modified considering process efficiency, etc.
[0110] This embodiment describes a case where the catalyst is operated by the so-called "fluidized bed method" in both the first reaction step and the second reaction step.
[0111] As carbon dioxide (CO2) introduced from the bottom of the reactor (200) moves upward, the first catalyst (30) is floated, and a catalytic reaction corresponding to the first reaction step is initiated.
[0112] The above fluidized bed method involves injecting a reaction gas (CO2) from the bottom of a reactor or similar location, causing solid catalyst particles to float and move as if in a fluid, thereby reacting with the reaction gas. Since the particles move actively in this fluidized bed method, the contact area between the reaction gas and the catalyst is expanded, and heat and material are efficiently transferred, enabling the realization of a high reaction yield.
[0113] Meanwhile, the above support means (210, 220) is made of a porous ceramic material or the like to facilitate the smooth movement of gas.
[0114] Since the carbon nanotube manufacturing method according to the present invention involves both reaction steps taking place in a single space, a decrease in reaction efficiency may occur due to the loss of raw materials or the residue of intermediate products. However, despite these drawbacks, the method has the advantage of being fully commercializable, considering the purpose of carbon nanotube production, as the reciprocal benefit of producing carbon dioxide-based carbon nanotubes using simplified reaction equipment is significant.
[0115] Meanwhile, the reactions of the first reaction stage and the second reaction stage can be carried out sequentially in the same reactor (200), and such sequential reactions can be achieved by changing the temperature profile of the reactor.
[0116] FIG. 6 is a graph conceptually showing the temperature profile of a reactor according to the first embodiment of the present invention.
[0117] Referring to FIG. 6, the temperature profile within the reactor (200) includes a temperature range in which a first temperature (T1) corresponding to a first stage reaction is maintained and a temperature range in which a second temperature (T2) corresponding to a second stage reaction is maintained by increasing the temperature.
[0118] Although the temperature profile of the present embodiment has been described as including two isothermal sections, the first temperature (T1) and the second temperature (T2) may have their profiles changed to a certain extent within each step section to control process efficiency or the physical properties of the carbon nanotubes.
[0119] Furthermore, although the temperature profile of one cycle is illustrated in FIG. 6, carbon nanotubes can be produced periodically and continuously in the same reactor by supplying carbon dioxide and repeating the temperature profile once a set of reactions is completed and CNTs are obtained. To this end, the detailed configuration and operation of the reactor may be modified in various ways, or additional configurations may be designed.
[0120] The design of variations in the carbon dioxide supply cycle and temperature profile can be implemented in various ways, and this is also possible within the technical scope of the present invention.
[0121] Detailed information regarding the first catalyst has been provided above, so it will be omitted here.
[0122] The second catalyst, which is the pyrolysis catalyst of the second stage, is a particulate catalyst similar to the first catalyst, and in this embodiment, an iron-based catalyst may be used as the second catalyst. Examples of the iron-based catalyst include a catalyst in which iron (Fe) and molybdenum (Mo) are loaded onto MgO (Fe-Mo / MgO).
[0123] In the foregoing, an example was described in which the first catalyst and the second catalyst are each arranged in a particulate form to participate in the reaction, and this example is one in which both the first catalyst and the second catalyst are operated by a fluidized bed method. Substantially, considering the reaction yield, it is preferable to operate the first catalyst and the second catalyst by a fluidized bed method.
[0124] However, when more precise control of physical properties, such as the crystal structure of carbon nanotubes, is required, or when there is a need to consider the quality of the generated carbon nanotubes more carefully, the operation of the catalyst can be designed in a hybrid manner.
[0125] That is, within the reactor (200), the catalyst operation of the first reaction stage and the second reaction stage can be designed differently as shown in the following reaction equation (1). That is, in the reactor (200), carbon dioxide is converted into carbon nanotubes through a two-stage reactor according to the following reaction equation, and the first and second stage reactions are carried out by different catalyst operation methods. [Reaction Equation 1]
[0126]
[0127] Meanwhile, the "floating method" is a process of injecting a catalyst into a reactor (200) in the form of a gaseous or liquid precursor. The catalyst (second catalyst) is generated directly inside the reactor and floats along the gas flow to participate in the reaction. The reactant (CH4) generated by the first step inside the reactor (200) is decomposed by the second catalyst converted from the catalyst precursor while floating along the gas flow in the high-temperature reactor (200), thereby generating CNTs around the second catalyst. In the floating method, since the catalyst exists in a gaseous state without a separate solid support, it is easy to control the aggregation of catalyst particles and prevent contamination of the catalyst.
[0128] FIG. 7 is a conceptual diagram illustrating another type of reactor for realizing a method for manufacturing carbon dioxide-based carbon nanotubes according to a second embodiment of the present invention.
[0129] Referring to FIG. 7, the reactor (300) includes a first catalyst support means (310) and a catalyst precursor injection port (320) into which a catalyst precursor (50) of the second catalyst is injected.
[0130] A first catalyst (30) is pre-arranged in the first catalyst support means (310). In this embodiment, the type of the first catalyst (30) is the same as described above, so further explanation is omitted. The first catalyst (310) is suspended as CO2 is supplied to the reactor (300) and participates in the catalytic reaction, converting CO2 into CH4.
[0131] Meanwhile, in this embodiment, the pyrolysis reaction, which is the second stage, proceeds according to the operation of a floating catalyst. That is, as the reaction of the second reaction stage begins, the hydrocarbon (CH4) present in the reactor (300) due to the first reaction stage reaches the second temperature (T2), and the catalyst precursor of the second catalyst is injected into the reactor (300). The catalyst precursor is immediately converted into the second catalyst at a high temperature, and the carbon source of the pyrolyzed hydrocarbon generates CNTs around the second catalyst.
[0132] A gaseous catalyst precursor (50) may be injected into the catalyst precursor injection port (320), but a liquid catalyst precursor (50) may also be injected. During the injection process, the catalyst precursor is converted into a gaseous state the moment it is injected into a high-temperature reactor, and participates in the reaction according to the second reaction stage through a mechanism substantially identical to that of the gaseous catalyst precursor (50).
[0133] In this embodiment, the catalyst precursor (30) comprises an iron (Fe)-based compound, and examples of such catalyst precursor (30) include ferrocene (Fe(C5H5)2) or iron pentacarbonyl (Fe(CO)5)-). However, the carbon nanotube manufacturing method of the present invention is not limited to the type of catalyst in the floating step, and any catalyst precursor (50) that can be employed in the floating method may be used in this method.
[0134] In this embodiment, when the iron-based catalyst precursor (50) is used, the CNT generation reaction is carried out at a temperature of 700°C to 1200°C in the second step.
[0135] The two-step reaction of this embodiment is carried out by a floating method, and since the catalyst precursor (50) is directly injected and catalyst particles are formed within the reactor (300), a separate support is not used, so the possibility of impurity incorporation is low, and the size and distribution of catalyst particles can be precisely controlled, which is very advantageous for obtaining high-quality CNTs of uniform diameter.
[0136] Meanwhile, by controlling the types of the aforementioned first and second catalysts or the reaction temperature (second temperature, T2) in the second reaction step of the floating method, the quality, such as the crystallinity, of the manufactured CNT can be controlled, and furthermore, it is possible to manufacture CNTs having various wall structures, such as single walls or double walls.
[0137] As such, the present invention enables the production of various carbon dioxide-based carbon nanotubes through a highly simplified process using only an integrated reactor facility consisting of a single space, through the design of various catalyst operation methods and modified temperature profiles.
[0138]
[0139] Example 3: Flow Process
[0140] FIG. 8 is a conceptual diagram illustrating the operation of a tubular reactor and a temperature profile for realizing a method for manufacturing carbon dioxide-based carbon nanotubes according to a third embodiment of the present invention.
[0141] Referring to FIG. 8, a tubular reactor (800) includes a tubular furnace (810) and a heating module (830) formed on the outer wall of the tubular furnace (810). The heating module (830) includes a plurality of heating units (831), and the heating units (831) are designed to allow for individual temperature control.
[0142] Meanwhile, the reactor (800) is divided into a first reaction area at the front of the reactor (800) and a second reaction area at the rear of the reactor (800) according to the temperature profile generated by the heating module (830). The intermediate area is a temperature change section and is excluded from the reaction area.
[0143] Carbon dioxide is continuously supplied to one end (left side of FIG. 7) of the above-mentioned reactor (800), and the flow rate and volume of the supplied carbon dioxide can be controlled. Meanwhile, a first catalyst (60) participating in a catalytic reaction to convert carbon dioxide into hydrocarbon is disposed in the first reaction zone, and a second catalyst (70) is disposed in the second reaction zone to pyrolyze the converted catalyst precursor and convert the pyrolyzed carbon sources into carbon nanotubes. The first catalyst (60) and the second catalyst (60) are each positioned in a particulate (solid) form on the first catalyst support means (821) and the second catalyst support means (822), respectively.
[0144] In this embodiment, the first catalyst support means (821) and the second catalyst support means (822) are designed to be horizontal in the tubular furnace (810), but they may be designed diagonally or vertically to maximize reaction efficiency, and the shape of the support means (821, 822) itself may be modified into various shapes.
[0145] Meanwhile, the first reaction region is a region corresponding to the first temperature (T1) of the temperature profile, and the second reaction region is a region corresponding to the second temperature (T2) of the temperature profile. The first temperature (T1) has a temperature range in which the catalytic reaction of the first catalyst (60) is possible, and the second temperature (T2) has a temperature range in which the carbon nanotube generation reaction of the second catalyst (70) is possible. The first temperature (T1) and the second temperature (T2) can be adjusted in various ways considering the type of catalyst and the physical properties of the carbon nanotube required.
[0146] Meanwhile, the heating units (831) of the heating module (30) must be precisely controlled to realize the temperature profile within the reactor (100). This control can become more precise as the correlation between the temperature profile inside the reactor (800) and the temperature distribution of the heating units (831) becomes stronger as the amount of accumulated data increases.
[0147] Meanwhile, although the present embodiment exemplifies a temperature profile including an isothermal section, the temperature profile can be varied in many ways considering process efficiency or the required properties of carbon nanotubes.
[0148] Figure 9 is a graph illustrating a temperature profile different from that of Figure 8.
[0149] As such, the temperature range corresponding to the first reaction zone and the second reaction zone may include rising or falling sections rather than isothermal sections, and as a large amount of data is accumulated in the future, more diverse forms of temperature profiles may be generated, such as including curved sections in the temperature profile, and ultimately, the correlation between the temperature profile and the physical properties or process efficiency of the carbon nanotube can be determined more precisely. As the temperature profile becomes more complex in this way, the precision of the heating module (830) control becomes more important.
[0150] Referring again to FIG. 9, the flow rate per unit time of carbon dioxide supplied to one end of the reactor (800), i.e., the flow rate, is also closely related to the physical properties or process efficiency of the carbon nanotubes produced, just like the temperature profile. Therefore, controlling the flow rate of the carbon dioxide will act as an important process variable, and accumulating various data regarding this is also essential.
[0151] The method for manufacturing carbon dioxide-based carbon nanotubes according to the present invention is a flow-type process in which carbon dioxide is supplied at one end and carbon nanotubes are simultaneously generated at the other end. That is, the present invention can provide an automated method for manufacturing carbon nanotubes in which carbon nanotubes are generated in real time simultaneously with the supply of carbon dioxide.
[0152] As shown in Fig. 9, carbon dioxide supplied to one end is converted into hydrocarbon (CH4) in the first reaction zone, and the converted hydrocarbon (CH4) flows into the second reaction zone due to the partial pressure of the continuously supplied carbon dioxide, and CNTs are generated in the second reaction zone in real time during the flow process.
[0153] As carbon dioxide (CO2) introduced from the left side of the above-mentioned reactor (800) moves to the right side, it floats the first catalyst (60), and a catalytic reaction corresponding to the first reaction step described above is initiated.
[0154] In catalyst operation, this fluidized bed method involves injecting a reaction gas (CO2) at one end of the reactor so that solid catalyst particles float and move like a fluid, thereby reacting with the reaction gas. Since the particles move actively in this fluidized bed method, the contact area between the reaction gas and the catalyst is expanded, and heat and material are efficiently transferred, enabling the realization of a high reaction yield.
[0155] Meanwhile, the above support means (821, 822) is made of a porous ceramic material, etc.
[0156] In this embodiment, a horizontal reactor (800) was described, but it is obvious that a vertical reactor having the same operating principle and structure is also possible.
[0157] As the first catalyst (60) which is the above particulate catalyst, a nickel-based catalyst for converting carbon dioxide into methane may be used.
[0158] When the first catalyst (60) is a nickel-based catalyst, the temperature of the first reaction region, i.e., the first temperature (T1) on the temperature profile, has a range of about 300°C to 400°C, and as described above, the first temperature (T1) may be isothermal but may be variable depending on the location.
[0159] Meanwhile, the second catalyst (70) is a pyrolysis catalyst, and the second catalyst (70) is a particulate catalyst like the first catalyst, and in this embodiment, an iron-based catalyst may be used as the second catalyst. Examples of the iron-based catalyst include a catalyst (Fe-Mo / MgO) in which iron (Fe) and molybdenum (Mo) are loaded onto MgO.
[0160] When the second catalyst (70) is an iron-based catalyst, the temperature of the second reaction region, i.e., the second temperature (T2), is controlled to have a range of 700°C to 1200°C.
[0161] In the above description, an example has been described in which the first catalyst (60) and the second catalyst (70) are each arranged in a particulate form to participate in the reaction, and this example is one in which both the first catalyst (60) and the second catalyst (70) are operated by a fluidized bed method. Substantially, considering the reaction yield, it is preferable to operate the first catalyst (60) and the second catalyst (70) by a fluidized bed method.
[0162] However, when more precise control of physical properties, such as the crystal structure of carbon nanotubes, is required, or when there is a need to consider the quality of the generated carbon nanotubes more carefully, the operation of the catalyst can be designed in a hybrid manner.
[0163] FIG. 10 is a conceptual diagram illustrating another type of tubular reactor for realizing a method for manufacturing carbon dioxide-based carbon nanotubes according to a third embodiment of the present invention.
[0164] According to the present embodiment, the catalyst operation of the first reaction zone and the second reaction zone within the reactor (900) can be designed differently from each other as in the aforementioned reaction equation (1).
[0165] That is, in the reactor (900), carbon dioxide is converted into carbon nanotubes through a two-stage reaction according to the above reaction equation (1), and the first and second stage reactions are carried out by different catalyst operation methods. In addition, the method according to the present invention is characterized in that the first and second stage reactions are carried out simultaneously.
[0166] Meanwhile, the "floating method" is a process of injecting a catalyst into a reactor (900) in the form of a gaseous or liquid precursor. The catalyst (second catalyst) is generated directly inside the reactor and floats along the gas flow to participate in the reaction. The reactant (CH4) generated by the first step inside the reactor (900) is decomposed by the second catalyst converted from the catalyst precursor (80) while floating along the gas flow in the high-temperature reactor (900), thereby generating CNTs around the second catalyst. In the floating method, since the catalyst exists in a gaseous state without a separate solid support, it is easy to control the aggregation of catalyst particles and prevent contamination of the catalyst.
[0167] Referring again to FIG. 10, the reactor (900) includes a tubular furnace (910) and a heating module (930) comprising a plurality of heating units (931). In addition, the reactor includes a first catalyst support means (921) in a first reaction zone and a catalyst precursor injection port (940) into which a catalyst precursor (80) of a second catalyst is injected into a region (upper) of the tubular furnace (910) corresponding to the second reaction zone.
[0168] In this embodiment, the catalyst precursor (80) is described as being injected from the upper catalyst precursor injection port (940), but the installation location or number of catalyst precursor injection ports (9240) are not particularly limited.
[0169] A first catalyst (60) is pre-arranged in the first catalyst support means (921). In this embodiment, the type of the first catalyst (60) is the same as described above, so further explanation is omitted. The first catalyst (10) is suspended as CO2 is supplied to the reactor (900) and participates in the catalytic reaction, converting CO2 into CH4.
[0170] Meanwhile, in this embodiment, the pyrolysis reaction in the second reaction zone (second reaction stage) proceeds according to the operation of a floating catalyst. That is, as the second reaction stage reaction is initiated, the hydrocarbon (CH4) present in the reactor (900) due to the first reaction stage reaction moves to the second reaction zone and reaches the second temperature (T2), and as the catalyst precursor (60) of the second catalyst is injected into the reactor (200), the catalyst precursor (80) is immediately converted into the second catalyst at a high temperature, and the carbon source of the pyrolyzed hydrocarbon generates CNTs around the second catalyst.
[0171] A gaseous catalyst precursor (80) may be injected through the catalyst precursor injection port (940), but a liquid catalyst precursor (80) may also be injected. During the injection process, the catalyst precursor is converted into a gaseous state the moment it is injected into a high-temperature reactor, and participates in the second stage reaction through a mechanism substantially identical to that of the gaseous catalyst precursor (80).
[0172] In this embodiment, the catalyst precursor (80) comprises an iron (Fe)-based compound, and examples of such catalyst precursor (80) include ferrocene (Fe(C5H5)2) or iron pentacarbonyl (Fe(CO)5)-). However, the carbon nanotube manufacturing method of the present invention is not limited to the type of catalyst in the floating step, and any catalyst precursor (80) that can be employed in the floating method may be used in this method.
[0173] In this embodiment, when the iron-based catalyst precursor (30) is used, the temperature of the second reaction region (second temperature, T2) has a temperature range of 700°C to 1200°C.
[0174] The second reaction step of the present embodiment is carried out by a floating method, and since the catalyst precursor (80) is directly injected and catalyst particles are formed within the reactor (900), a separate support is not used, so the possibility of impurity incorporation is low, and the size and distribution of catalyst particles can be precisely controlled, which is very advantageous for obtaining high-quality CNTs of uniform diameter.
[0175] Meanwhile, by controlling the types of the aforementioned first and second catalysts or the reaction temperature (second temperature, T2) in the second stage of the floating method, the quality, such as the crystallinity of the manufactured CNTs, can be controlled, and furthermore, it is possible to manufacture CNTs having various wall structures, such as single walls or double walls.
[0176] In addition, by controlling the flow rate and flow rate of carbon dioxide supplied to the reactor (900) and changing the temperature profile of the entire reactor (900), the physical properties of the carbon nanotubes produced can be precisely controlled.
[0177] Thus, through the design of various carbon dioxide supply control, catalyst operation methods, and temperature profile modifications, the present invention can generate carbon nanotubes with various physical properties in real time simultaneously with the supply of carbon dioxide, and furthermore, can continuously produce carbon nanotubes using only a simplified tubular reactor facility.
Claims
1. A method for continuously manufacturing carbon nanotubes by supplying carbon dioxide, wherein A step of supplying CO2 to a reactor having a single space or substantially continuous reaction space; A first reaction step of converting the CO2 into a carbon precursor at a first temperature by a first catalytic reaction using a first catalyst; and A second reaction step comprising contacting the carbon precursor with a second catalyst at a second temperature in the same reaction space or a continuous space to produce carbon nanotubes, Method for manufacturing carbon dioxide-based carbon nanotubes.
2. In Paragraph 1, The first catalyst above is a particulate catalyst, 1) Nickel (Ni)-based catalyst; 2) MgO, silica (SiO2), or Al2O3 beads having mesopore pores as a support; and a catalyst comprising nickel particles loaded onto the support: or 3) A method for manufacturing carbon dioxide-based carbon nanotubes, characterized in that the particulate catalyst comprises a catalyst containing nickel particles loaded on MoS2 / Ni foam.
3. In Paragraph 1, A method for manufacturing carbon dioxide-based carbon nanotubes, characterized in that the second catalyst is formed by the conversion of a liquid or gaseous catalyst precursor injected into the reactor.
4. In Paragraph 1, In the second reaction step above, A method for manufacturing carbon dioxide-based carbon nanotubes, characterized by including the step of additionally supplying CO2 to a reaction zone at a concentration of 1 (±0.05) vol%.
5. In Paragraph 1, The above first reaction step is carried out by fluidized bed catalytic operation using a first catalyst which is a particulate catalyst, and A method for manufacturing carbon dioxide-based carbon nanotubes, characterized in that the second reaction step is carried out by injecting a catalyst precursor in a liquid or gaseous state into the reactor and operating the catalyst in a floating manner.
6. In Paragraph 5, A method for manufacturing carbon dioxide-based carbon nanotubes, characterized in that the reaction furnace is physically partitioned by a filter into an area where the first reaction step is performed and an area where the second reaction step is performed.
7. In Paragraph 1, A method for manufacturing carbon dioxide-based carbon nanotubes, characterized in that the reactor is a single integrated space without separate spatial partitions, and the first reaction step and the second reaction step are sequentially performed within the same space by changing the temperature profile within the reactor.
8. In Paragraph 1, The above reactor comprises a tubular furnace consisting of a single integrated space without separate space partitions and a heating module consisting of a plurality of heating units disposed on the outer wall of the tubular furnace, and A method for manufacturing carbon dioxide-based carbon nanotubes, characterized in that the above-described reactor is divided into a first reaction zone in which carbon dioxide is converted into a carbon precursor and a second reaction zone in which the converted carbon precursor is converted into a carbon nanotube according to a temperature profile including temperature changes according to location in the reactor.
9. In Paragraph 8, A method for manufacturing carbon dioxide-based carbon nanotubes characterized by controlling the physical properties of the carbon nanotubes produced by controlling the flow rate per unit time of the supplied carbon dioxide and the temperature profile.
10. In Paragraph 9, A method for manufacturing carbon dioxide-based carbon nanotubes, characterized in that the above temperature profile is changed by controlling the temperature of individual heating units within the heating module.