Patent Application
20240140803
This disclosure relates to a method and an apparatus for producing carbon nanotube aggregates.
In recent years, nanocarbon materials such as carbon nanotubes (hereinafter, also referred to as “CNTs”) have attracted attention as materials with excellent electrical conductivity, thermal conductivity, and mechanical properties. While it is recognized that the nanocarbon materials can exhibit superior properties, the nanocarbon materials are generally more expensive than other materials due to high production costs.
Therefore, various attempts have been made for the purpose of efficient production of the nanocarbon materials. For example, Patent Literature (PTL) 1 discusses a method for producing nanocarbon, which includes continuously supplying hydrocarbons and catalysts with a screw feeder so that the hydrocarbons and the catalysts are in contact with each other in a counter-current or counter-flow condition. Further, for example, Patent Literature (PTL) 2 discusses a method for producing nanocarbon, which includes stirring and moving catalytic bodies through a reaction tube including a catalytic activity zone, a nanocarbon synthesis zone, and a cooling zone using a conveyance means such as a belt conveyor.
In the production of carbon nanotubes using a source gas such as hydrocarbons and catalysts, improving the contact efficiency between the source gas and the catalysts improves carbon conversion efficiency and reduces the amount of source gas used. In addition, by improving the contact efficiency between the source gas and the catalysts, the amount of excess source gas in exhaust is reduced, and the adhesion of byproducts such as tar derived from the excess source gas to an exhaust pipe is reduced, thus enabling stable production over a long period of time during continuous production.
Here, there is room for improvement with respect to the method for producing a nanocarbon material according to the above-described prior art, in terms of improvement in the contact efficiency between a source gas and catalysts, thereby further enhancing the quality and production efficiency of the obtained nanocarbon material.
It would be helpful to provide a method and an apparatus for producing carbon nanotube aggregates in which the contact efficiency between a source gas and catalysts is improved, thereby enabling the efficient production of the carbon nanotube aggregates with high quality.
The inventors have made a diligent study with the aim of solving the above problem. As a result, the inventors have newly found that in the production of CNT aggregates, in a growth step, forming a substrate layer by stacking substrates with catalysts on surfaces at a lower portion of a furnace and supplying a source gas to the substrate layer from a plurality of gas injection ports arranged at the lower portion of the growth furnace, while mechanically stirring and/or conveying the substrate layer, make it possible to improve the contact efficiency between the source gas and the catalysts, thereby enabling the efficient production of the CNT aggregates with high quality, and have completed the disclosure.
In other words, this disclosure aims to advantageously solve the above problem. A CNT aggregate production method according to this disclosure is a method for producing carbon nanotube aggregates, the method including a growth step of growing the carbon nanotube aggregates on substrates with catalysts on surfaces. In the growth step, a source gas supply step of forming a substrate layer by stacking the substrates at a lower portion of a growth furnace configured to perform the growth step, and supplying a source gas to the substrate layer through a plurality of gas injection ports arranged at the lower portion of the growth furnace, and an in-growth furnace stir and conveyance step of mechanically stirring and/or conveying the substrate layer are performed at least in part in an overlapping manner. According to this production method, the contact efficiency between the source gas and the catalysts is improved, thereby enabling the efficient production of the CNT aggregates with high quality.
The CNT aggregate production method according to this disclosure may include performing, before the growth step, a formation step of creating a reducing gas environment in an environment surrounding the catalysts and heating at least one of the catalysts or a reducing gas.
In the formation step,
The CNT aggregate production method according to the disclosure may include performing the formation step and the growth step with prevention of mixing gas environments in the steps with each other, while continuously conveying the substrates,
In the CNT aggregate production method according to the disclosure, in the in-growth furnace stir and conveyance step, mechanical stir and/or conveyance may be performed by rotation of a blade of a screw, a paddle, or a ribbon, or a combination of several of these.
In the CNT aggregate production method according to the disclosure, the source gas environment in the growth step is preferably an environment of high carbon concentration and preferably contains a catalyst activating material. In the growth step, CNTs are grown in the environment of high carbon concentration containing the catalyst activating material, which allows the CNTs to grow while maintaining catalytic activity for a long time, thereby further improving the quality of the obtained CNT aggregates and the production efficiency of the CNT aggregates.
In the CNT aggregate production method according to the disclosure, the source gas environment preferably contains ethylene and carbon dioxide as the catalyst activating material. By performing the growth step in such an environment, the quality of the obtained CNT aggregates and the production efficiency of the CNT aggregates can be further improved.
In the CNT aggregate production method according to the disclosure, each of the substrates is preferably a particle with an apparent density of 2.0 g/cm3 or more. When the substrates are the particles with an apparent density of 2.0 g/cm3 or more, the obtained CNT aggregates can be made longer.
The “apparent density” of a support refers to a mass per unit volume including voids (closed pores) when the support is a particle with voids inside. The “apparent density of the support” can be measured according to the pycnometer method.
In the CNT aggregate production method according to the disclosure, each of the substrates contains any one or more elements of Al, Si, and Zr. The use of the substrates containing one or more elements of Al, Si, and Zr can further improve the production efficiency of the CNT aggregates.
An apparatus for producing carbon nanotube aggregates according to the disclosure is an apparatus for producing carbon nanotube aggregates by growing the carbon nanotube aggregates on substrates with catalysts on surfaces, the apparatus including a growth unit including a growth furnace configured to form a substrate layer by stacking the substrates at a lower portion, a source gas injector including a plurality of gas injection ports arranged at the lower portion of the growth furnace, a source gas being supplied to the substrate layer through the gas injection ports, and a stir and conveyance unit configured to mechanically stir and/or convey the substrate layer. According to this production apparatus, the contact efficiency between the source gas and the catalysts is improved, thereby enabling the efficient production of the CNT aggregates with high quality.
The apparatus for producing the carbon nanotube aggregates according to this disclosure may be an apparatus configured to perform a formation step and a growth step in a single furnace while switching an atmosphere in the furnace, wherein
According to this production apparatus, the formation step and the growth step can be performed in the batch-type system, and the use of the single furnace brings the advantages of space and cost savings in production facilities. In addition, optimization is easy because wide condition ranges can be set for operating factors of each step.
The apparatus for producing carbon nanotube aggregates according to this disclosure may be an apparatus including:
According to this production apparatus, the formation step and the growth step can be performed in a continuous system, which dramatically improves a production rate. Furthermore, it is easy to optimally design specifications of the apparatus separately for the formation step and the growth step, and continuous step control is possible, so the steps can be easily stabilized compared to the batch-type. As a result, the quality of the obtained CNT aggregates and the production efficiency of the CNT aggregates can be further improved.
In the apparatus for producing the carbon nanotube aggregates according to this disclosure, the stir and conveyance unit may include a screw, a paddle, or a ribbon, or a combination of several of these that is configured to stir and/or convey the substrates by rotation of a blade.
According to the present disclosure, it is possible to provide a method and an apparatus for producing carbon nanotube aggregates in which the contact efficiency between a source gas and catalysts is improved, thereby enabling the efficient production of CNT aggregates with high quality.
In the accompanying drawings:
Embodiments of the disclosure will be hereinafter described in detail with reference to the drawings. According to a method and an apparatus for producing carbon nanotube aggregates of the disclosure, the carbon nanotube aggregates can be produced with high efficiency. In the following description, based on the progression of processes from a formation step, to a growth step, an optional cooling step, and a separation step, previous operations or components of a production apparatus that performs such operations are described as “previous stage” operations or components, and later operations or components are described as “later stage” operations or components.
(Method for Producing Carbon Nanotube Aggregate)
The method for producing the carbon nanotube aggregates according to the disclosure includes the growth step of growing the carbon nanotube aggregates on substrates with catalysts on surfaces. In the growth step,
The form of the method for producing the carbon nanotube aggregates according to the disclosure includes “batch-type” and “continuous-type”.
<Batch-Type Production Method>
In one embodiment, the method for producing the carbon nanotube aggregates according to the disclosure may be a “batch-type” production method. The “batch-type” production method is a production method in which the formation step and the growth step are switched in one unit. Such a “batch-type” production method may be, for example, a method for producing carbon nanotube aggregates includes:
The “batch-type” production method may be performed, for example, using a “batch-type” production apparatus (
<Continuous-Type Production Method>
In another embodiment, the method for producing the carbon nanotube aggregates according to the disclosure may be a “continuous-type” production method. The “continuous-type” production method is a production method in which the formation step and the growth step are performed in separate units. Such a “continuous-type” production method may be, for example, a method that performs the formation step and the growth step while preventing gas environments in each step from mixing with each other, while continuously conveying the substrates, with the use of a CNT production apparatus having the following components:
The “continuous-type” production method may be performed using, for example, a “continuous-type” production apparatus (
<Substrate with Catalyst on Surface>
Substrates that constitute the substrates with the catalysts on the surfaces, which are used in the production method according to the disclosure, can be formed by supporting the catalysts on the substrates.
<<Sub strate>>
The substrate is a member capable of supporting a catalyst for synthesizing a CNT on its surface, and not limited in particular, a member made of any material can be used. In particular, the substrate is preferably made of a ceramic material containing any one or more elements of Al, Si, and Zr. Furthermore, the substrate is preferably made of a metal oxide containing any one or more elements of Al, Si, and Zr, and more preferably made of zirconium dioxide (ZrO2). The shape of the substrate is preferably in the form of a particle having an aspect ratio of less than 5. The “aspect ratio” of the substrate particle can be obtained as the average of values of (a major axis/a width orthogonal to the major axis), which are calculated on a microscope image for a plurality of arbitrarily selected particles. Further, the apparent density of the substrate particle is preferably 2.0 g/cm3 or more, preferably 3.8 g/cm3 or more, more preferably 5.8 g/cm3 or more, and preferably 8.0 g/cm3 or less. When the apparent density of the substrate particles is the above-described lower limit or more, the obtained CNT aggregates can be made longer. When the apparent density of the substrate particles is the above-described upper limit or less, the substrate particles are easy to handle and the production efficiency of the CNT aggregates can be further improved. The particle diameter of the substrate particle is preferably 0.05 mm or more, more preferably 0.3 mm or more, preferably 10 mm or less, more preferably 2 mm or less, and even more preferably 1 mm or less. When the particle diameter of the substrate particles is the above-described lower limit or more, the obtained CNT aggregates can be made longer. When the particle diameter of the substrate particles is the above-described upper limit or less, the production efficiency of the CNT aggregates can be further improved. The “particle diameter” of the substrate particles means the volume-average particle diameter D50. The volume-average particle diameter D50 represents the particle diameter at which a cumulative volume calculated from the smallest diameter in particle size distribution (volume basis) measured by the laser diffraction method for the substrate particles is 50%. A deposit formed by the substrates stacked at the lower portion of the furnace by gravity or the like is referred to as the “substrate layer”.
<<Catalyst>>
The catalyst supported on the substrate is not limited, and examples thereof include catalyst components such as nickel (Ni), iron (Fe), cobalt (Co), and molybdenum (Mo). In particular, the catalyst components preferably contain at least one metal of nickel (Ni), iron (Fe), cobalt (Co), or molybdenum (Mo) from the viewpoint of further increasing the production efficiency of the CNT aggregates.
In addition, as a base to support the catalyst on the substrate, for example, a base layer formed of a material such as aluminum oxide, titanium oxide, titanium nitride, silicon oxide, or the like can optionally be provided.
<<Method for Preparing Substrate with Catalyst on Surface>>
A method for supporting the catalyst on the surface of the substrate is not particularly limited, and any existing method can be adopted. In particular, in the case of using the substrate particles as the substrates, a way of using a rotary drum coating apparatus having a substantially cylindrical rotary drum is preferably adopted. Such a way includes a spraying step of, while stirring the substrate particles by disposing the substrates in a substantially cylindrical rotary drum and rotating the rotary drum with an inclined or horizontal axis as the axis of rotation, spraying a catalyst solution containing the above catalyst component to the stirred substrate particles, and a drying step of flowing a drying gas into the rotary drum to bring the drying gas into contact with the substrate particles to which the catalyst solution is sprayed. At least part of an implementation period of the stirring step overlaps with at least part of an implementation period of the spraying step. In a case in which the catalysts are supported after the base layers are disposed on the surfaces of the substrates, the substrate particles having the base layers on the surfaces can be obtained by, prior to spraying and drying the catalyst solution, performing the same spraying step and the drying step as described above using a solution containing a component that can constitute the base layers and the substrate particles. Thereafter, by subjecting the substrate particles having the base layers on the surfaces to the spraying step and the drying step described above, the substrate particles having the base layers and the catalysts supported in this order on the surfaces can be obtained.
As another method for preparing the substrates with the catalysts on the surfaces, in the case of using the substrate particles as the substrates, for example, there is a way including a step of spraying the catalyst solution while the substrate particles are centrifugally swirled and vertically suspended.
<Reducing Gas>
The reducing gas is a gas that has at least one of the following effects: reduction of the catalysts, promotion of particulation of the catalysts, or enhancement of catalytic activity. As the reducing gas, for example, hydrogen gas, ammonia, water vapor, or a mixture thereof can be applied. As the reducing gas, a mixed gas in which hydrogen gas is mixed with an inactive gas, such as helium gas, argon gas, or nitrogen gas, can also be used. The reducing gas is generally used in the formation step, but may be used in the growth step as appropriate.
<Source Gas>
Examples of the source gas used for synthesis of the CNT aggregates include hydrocarbons such as methane, ethane, ethylene, propane, butane, pentane, hexane, heptane propylene, and acetylene; lower alcohols such as methanol and ethanol; and oxygen-containing compounds with low carbon numbers such as acetone and carbon monoxide. A mixture of several of these can also be used. Moreover, the source gas may also be diluted with an inactive gas as described above.
Here, the source gas preferably contains ethylene. Heating ethylene within a predetermined temperature range (700° C. or more and 900° C. or less) accelerates the decomposition reaction of ethylene, and when the decomposition gas contacts the catalysts, fast growth of the CNTs is possible. However, when a thermal decomposition time is too long, the decomposition reaction of ethylene is too advanced, causing deactivation of the catalysts and deposition of carbon impurities on the CNT aggregates. In the CNT aggregate production method according to the disclosure, the thermal decomposition time is preferably in a range of 0.5 seconds or more and 10 seconds or less, for an ethylene concentration of 0.1 volume % to 40 volume %. When the thermal decomposition time is less than 0.5 seconds, the thermal decomposition of ethylene is insufficient and it is difficult to grow the CNT aggregates with high specific surface area at high speed. When the thermal composition time is more than 10 seconds, the decomposition of ethylene is too fast and too many carbon impurities are generated, causing catalyst deactivation and deterioration in the quality of the CNT aggregates. The thermal decomposition time can be calculated from the following equation:
(Thermal decomposition time)=(Heated channel volume)/{(Source gas flow rate)×(273.15+T)/273.15}
Here, the heated channel volume is the volume of a channel, through which the source gas passes prior to contacting the catalysts, heated to a predetermined temperature T° C. The source gas flow rate is a flow rate at 0° C. and 1 atm.
<Catalyst Activating Material>
A catalyst activating material may be added during the growth step of the CNTs. The addition of the catalyst activating material can further improve the production efficiency and quality of the CNT aggregates. The catalyst activating material used here is generally an oxygen-containing material that does not cause significant damage to the CNTs at a growth temperature. Examples of the catalyst activating material include, as well as water, hydrogen sulfide; oxygen-containing compounds with low carbon numbers, such as oxygen, ozone, nitrogen oxide, carbon monoxide, and carbon dioxide; alcohols, such as ethanol and methanol; ethers, such as tetrahydrofuran; ketones, such as acetone; aldehydes; esters; nitrogen oxide; and mixtures thereof. Among these, water, oxygen, carbon dioxide, carbon monoxide, or tetrahydrofuran is preferable, and carbon dioxide is more preferable. In the growth step, the CNTs are grown in an environment of high carbon concentration containing the catalyst activating material, which allows the CNTs to grow while maintaining catalytic activity for a long time, thereby further improving the quality of the obtained CNT aggregates and the production efficiency of the CNT aggregates. Furthermore, in a case in which the source gas contains ethylene, the presence of the carbon dioxide as the catalyst activating material further improves the quality of the obtained CNT aggregates and the production efficiency of the CNT aggregates. The reason for this is inferred to be as follows. First, in the CNT synthesis reaction, ethylene and carbon dioxide have been found to have relatively low activity as a carbon source and a catalyst activating material, respectively. Therefore, when a gas mixture containing each of the above gases passes through a layer constituted of the substrates with the catalysts on the surfaces, that is, a layer constituted of aggregate of the substrates continuously conveyed by screw rotation, decrease in concentration of each gas due to the CNT synthesis reaction is very slow, and the concentration distribution of each gas within the layer can be made relatively uniform. As a result, growth of the CNTs between the substrates is also made uniform, which enhances production efficiency.
In the case of the carbon dioxide, for example, the amount of the catalyst activating material added in the growth step is 0.5 volume % or more of an atmosphere in the growth step, preferably 4 volume % or more, more preferably 5 volume % or more, and generally 40 volume % or less.
<Environment of High Carbon Concentration>
The environment of high carbon concentration means an atmosphere in which the source gas accounts for 0.1 volume % or more of the atmosphere (hereinafter also referred to as “source gas environment”) in the growth step. The percentage of the source gas in the environment of high carbon concentration can be, for example, 40 volume % or less. Furthermore, the percentage of the source gas in the environment of high carbon concentration is preferably 4 volume % or more, more preferably 5 volume % or more, even more preferably 10 volume % or more, and preferably 30 volume % or less. Here, the inclusion of the catalyst activating material in the source gas environment significantly enhances catalytic activity, so that even in the environment of high carbon concentration, the catalyst does not lose its activity. Thus, the CNT aggregates can be grown for a long time at a significantly increased growth rate.
<Reaction Temperature>
The reaction temperature at which the CNT aggregates are grown is not particularly limited, and can be, for example, 400° C. or more and 1100° C. or less. Furthermore, in a case in which the source gas contains ethylene, the temperature is preferably 700° C. or more and 900° C. or less.
<Formation Step>
The formation step is a step of creating the reducing gas environment in the environment surrounding the catalysts supported by the substrates, and heating at least one of the catalysts or the reducing gas. The formation step is performed before the growth step described below. The formation step may be performed by implementing, at least in part in an overlapping manner,
In the formation step, the reducing gas can be supplied in any way into the inside space of the furnace of the formation unit, but it is preferable that, while substrate layer is formed by stacking the substrates at the lower portion of the formation furnace, the reducing gas is supplied to the substrate layer through the plurality of gas injection ports arranged at the lower portion of the formation furnace, in terms of improving the contact efficiency between the reducing gas and the substrates. At this time, it is preferable that the substrate layer is mechanically stirred and/or conveyed to further improve the contact efficiency between the reducing gas and the substrates. Reduction in the amount of reducing gas used and reduction in the duration of the formation step can be thereby expected, thus further improving the quality of the CNT aggregates and the production efficiency of the CNT aggregates.
The temperature of the catalyst-bearing supports or the reducing gas atmosphere in the formation step is preferably 400° C. or more and 1100° C. or less. The duration of the formation step can be 3 minutes or more and 120 minutes or less.
<Growth Step>
The growth step is a step of growing the CNT aggregates by creating the source gas environment in the environment surrounding the catalysts, which has become suitable for the production of the CNT aggregates by the above-described formation step, and heating at least one of the catalysts or the source gas.
The growth step is performed by implementing, at least in part in an overlapping manner,
In this case, there may be a time when only the source gas supply step is performed, there may be a time when only the stir and conveyance step is performed, or the source gas supply step and the stir and conveyance step may all overlap. Considering the uniformity of the supplied gas, it is preferable that the source gas supply step at least overlaps with the stir and conveyance step, and it is more preferable that the source gas supply step and the stir and conveyance step all overlap. The mechanical stir and/or conveyance in the stir and conveyance step may be performed by rotation of a blade of a screw, a paddle, or a ribbon, or a combination of several of these.
In the growth step, in the inside space of the furnace of the growth unit, while the substrate layer is formed by stacking the substrates at the lower portion of the growth furnace, the source gas is supplied to the substrate layer through the plurality of gas injection ports arranged at the lower portion of the growth furnace. By supplying the source gas in this manner, the source gas is supplied from under the substrate layer, so the contact efficiency between the source gas and the substrates is improved. Furthermore, since the substrate layer is mechanically stirred and/or conveyed, the contact efficiency between the source gas and substrates is further improved. Reduction in the amount of source gas used and reduction in the duration of the growth step can be thereby expected, thus further improving the quality of the CNT aggregates and the production efficiency of the CNT aggregates.
The total area of the gas injection ports is preferably designed so that a pressure loss generated when the gas passes through the injection ports is 1/10th or more, more preferably 3/10th or more, and even more preferably 1 times or more a pressure loss generated when the gas passes through the substrate layer formed at the lower portion of the growth furnace. This makes a gas flow rate injected from each injection port uniform and stabilized, and the quality of the produced CNT aggregates and the production efficiency of the CNT aggregates can be further improved.
The shape of the gas injection ports can be various shapes such as circular, elliptical, rectangular, or slit. From the viewpoint of processability, circular or slit shapes are preferable, and in the case of using the substrate particles as the substrates, slit shapes are preferable.
A supply rate of the source gas is preferably set so that the reciprocal of average time for the gas to pass through the substrate layer formed at the lower portion of the growth furnace is approximately the same or greater than a CNT synthesis reaction rate coefficient per volume of the substrate layer. Thereby, a CNT synthesis process becomes a reaction rate-limiting process, and optimum growth time can be almost the same when a reactor vessel is scaled up.
<Cooling Step>
Optionally, the cooling step can be performed after the growth step. In the cooling step, the CNT aggregates obtained in the growth step, the catalysts, and the substrates are cooled to an inactive gas atmosphere. Since the CNT aggregates, the catalysts, and the substrates after the growth step are in a high temperature condition, the CNT aggregates, the catalysts, and the substrates after the growth step tend to be oxidized when disposed in an oxygen-containing environment. Therefore, in an inactive gas environment, the aligned CNT aggregates, the catalysts, and the substrates are preferably cooled to 400° C. or less, more preferably 200° C. or less.
<Separation and Recovery Step>
In the separation and recovery step, the carbon nanotube aggregates are separated from the substrates, and the substrates and the carbon nanotube aggregates are separately recovered. A recovery method is not particularly limited, and any known method can be adopted. In particular, a separation and recovery method (see, for example, WO 2019/188979) that uses an external force and a fluid flow (for example, an air vortex formed by a centrifugal force and an air flow as a drag force of the centrifugal force), as a drag force of the external force, is preferably adopted.
<Reuse Step>
In the reuse step, carbon on the recovered substrates is oxidized and removed to make the substrates reusable. A method of oxidation removal is not particularly limited, and includes, for example, heating the substrates while circulating air. By implementing such a reuse step, cost of the substrates can be reduced.
<Attribute of CNT Aggregates>
The specific surface area of the CNT aggregates obtained by the production method according to the disclosure is a value measured by the Brunauer, Emmett, and Teller method from an adsorption/desorption isotherm of liquid nitrogen at 77 K measured for the CNTs that have not been subjected to opening treatment. For example, the specific surface area of the CNT aggregates can be measured using a BET specific surface area measuring apparatus compliant with JIS Z8830. The specific surface area of the CNTs obtained in the disclosure is not particularly limited, but is preferably 600 m2/g or more, preferably 800 m2/g or more, preferably 2600 m2/g or less, and more preferably 1400 m2/g or less, for example. Furthermore, for the CNT aggregates that have been subjected to the opening treatment, the specific surface area is preferably 1300 m2/g or more.
(Apparatus for Producing Carbon Nanotube Aggregates)
The apparatus for producing the carbon nanotube aggregates of the disclosure is an apparatus for producing the carbon nanotube aggregates by growing the carbon nanotube aggregates on the substrates with the catalysts on the surfaces. The apparatus for production the carbon nanotube aggregates of the disclosure includes the growth unit. The growth unit has the following components:
The form of the apparatus for producing the carbon nanotube aggregates according to the disclosure includes “batch-type” and “continuous-type”.
<Batch-Type Production Apparatus>
In one embodiment, the apparatus for producing the carbon nanotube aggregates according to the disclosure may be a “batch-type” production apparatus. The “batch-type” production apparatus is a production apparatus used for the “batch-type” production method described above, in which the formation unit and the growth unit are the same unit. An example of such a “batch-type” production apparatus is illustrated in
<<Formation/Growth Unit>>
The formation/growth unit 100a is a unit that switches and realizes the formation step and the growth step in the single unit, and is constituted of a set of devices to switch and realize the formation step and the growth step. The formation/growth unit 100a has:
Components that the formation/growth unit 100a may have include:
Normally, however, the formation/growth unit 100a does not have a furnace end opening 109, or the furnace end opening 109 is closed.
—Heating Device—
The heating device 101 is a device that heats at least one of the catalysts or the reducing gas in the formation step, and heats at least one of the catalysts or the source gas in the growth step. The heating device 101 may be the same heating device or different heating devices for the formation step and the growth step. The heating device 101 is not particularly limited, and can be implemented by, for example, a resistance heater, an infrared heater, an electromagnetic induction heater, or the like. The heating device 101 can heat the inside of the system so that the temperature in the formation/growth furnace 102 is 400° C. or more and 1100° C. or less in the formation step, and 600° C. or more and 1000° C. or less in the growth step.
—Formation/Growth Furnace—
The formation/growth furnace 102 is a furnace that combines a furnace (formation furnace) that holds the reducing gas in the formation step and a furnace (growth furnace) that holds the source gas environment in the growth step.
—Gas Injection Ports—
The gas injection ports 103 are gas injection ports through which a gas is injected into the formation/growth furnace 102. The “gas” refers to the “reducing gas” in the formation step, and the “source gas” in the growth step. Since the source gas is injected from the bottom of the formation/growth furnace 102, the gas injection ports 103 for the source gas are located at the lower portion of the formation/growth furnace 102 so that the source gas can be injected from the bottom of the formation/growth furnace 102. The gas injection ports 103 for the reducing gas are preferably located at the lower portion of the formation/growth furnace 102 so that the reducing gas can be injected from the bottom of the formation/growth furnace 102. The gas injection ports 103 for the reducing gas and the source gas may be the same gas injection ports or different gas injection ports. In order to improve injection efficiency, the plurality of gas injection ports 103 is preferably arranged. By arranging the gas injection ports 103 at the lower portion of the formation/growth furnace 102, the source gas is supplied from under the substrate layer (a deposit formed by substrates 107 stacked at a lower portion of the furnace by gravity and the like), and the contact efficiency between the source gas and the catalysts is improved, thereby enabling to efficiently produce the CNT aggregates with high quality.
The total area of the gas injection ports is preferably designed so that a pressure loss generated when the gas passes through the injection ports is 1/10th to 1 times or more a pressure loss generated when the gas passes through the substrate layer formed at the lower portion in a bottom surface of the formation furnace. This makes a gas flow rate injected from each injection port uniform and stabilized, and the quality of the produced CNT aggregates and the production efficiency of the CNT aggregates can be further improved.
—Reducing Gas/Source Gas Inlet—
The reducing gas/source gas inlet 104 is a gas inlet that is connected to the gas injection ports 103 and that supplies the reducing gas and/or the source gas. When the gas injection ports 103 for the reducing gas and for the source gas are the same gas injection ports, the reducing gas/source gas inlet 104 is preferably a single gas inlet. When the gas injection ports 103 for the reducing gas and for the source gas are different gas injection ports, the reducing gas/source gas inlet 104 is constituted of a gas inlet for the reducing gas and a gas inlet for the source gas that are connected to the gas injection ports 103 for the reducing gas and the gas injection ports 103 for the source gas, respectively.
—Exhaust Port—
The exhaust port 105 is an exhaust port that discharges gases (e.g., unreacted reducing gas, source gas) in the furnace out of the system. The formation/growth unit 100a preferably includes at least one exhaust port 105, and may include a plurality of exhaust ports.
—Stir and Conveyance Unit—
The stir and conveyance unit 106 is a unit that stirs and/or conveys the substrates 107. The stir and conveyance unit 106 has the function of at least stirring the substrate layer. The stir and conveyance unit 106 may also have the function of conveying the substrates 107 from outside the formation/growth furnace 102 into the formation/growth furnace 102, and/or conveying the substrates 107 from inside the formation/growth furnace 102 out of the formation/growth furnace 102. The stir and conveyance unit 106 preferably includes a screw, a paddle, or a ribbon, or a combination of several of these, which stirs and/or conveys the substrates by rotation of a blade. For example, as illustrated in
—Substrate Holder—
The substrate holder 108 is a container that is disposed in the formation/growth furnace 102 and that contains the substrates 107 in the form of the substrate layer. When the formation/growth unit 100a has the substrate holder 108, the gas injection ports 103 are disposed at a lower portion of the substrate holder 108. The substrate layer may be stirred in the substrate holder 108 by the stir and conveyance unit 106.
<<Other Units>>
The batch-type production apparatus 100 may further include other units. The other units include a substrate introduction unit (e.g., a hopper, an inlet purge device, a front chamber), a cooling unit, and an outlet unit (e.g., an outlet purge device).
<<Operations of Batch-Type Production Apparatus>>
As operations of the batch-type production apparatus 100 in the production of the carbon nanotube aggregates, the formation step and the growth step are performed by switching an atmosphere in the single furnace (formation/growth furnace). In the formation step, the reducing gas is supplied from the gas injection ports to the substrate layer, whereby the reduced gas environment is created in the environment surrounding the catalysts and at least one of the catalysts or the reducing gas is heated. In the growth step, the source gas is supplied to the substrate layer from the plurality of gas injection ports arranged at the lower portion of the formation/growth furnace, and thereby the inside of the furnace is switched to a source gas atmosphere.
Referring to
<<Materials of Apparatus Parts to be Exposed to Reducing Gas or Source Gas>>
Some parts of the formation/growth unit 100a and the stir and conveyance unit 106 are exposed to the reducing gas or the source gas. Materials constituting each of these components include materials capable of withstanding high temperature, for example, quartz, heat-resistant ceramics, heat-resistant alloys, and the like, and the heat-resistant alloys are preferable from the viewpoint of accuracy and flexibility of processing, and cost. The heat-resistant alloys include heat-resistant steel, stainless steel, nickel-based alloys, and the like. Those having Fe as a main component and another alloy content of 50% or less are generally referred to as the heat-resistant steel. Steel containing Fe as a main component and having another alloy content of 50% or less and Cr of approximately 12% or more is generally referred to as the stainless steel. The nickel-based alloys include alloys obtained by adding Mo, Cr, Fe, and the like to Ni. Specifically, SUS310, Inconel 600, Inconel 601, Inconel 625, Incoloy 800, MC Alloy, Haynes 230 Alloy, and the like are preferable in terms of heat resistance, mechanical strength, chemical stability, low cost, and the like.
When inner walls of the furnace and/or parts used in the furnace are made of metal, it is preferable that heat-resistant alloys are used as the materials and that surfaces are molten-aluminum plated or polished so as to have an arithmetic average roughness of Ra≤2 μm.
<Continuous Production Apparatus>
In another embodiment, the production apparatus of the carbon nanotube aggregates according to the disclosure may be the “continuous-type” production apparatus. The “continuous-type” production apparatus is a production apparatus used in the above-described “continuous-type” production method in which the formation unit and the growth unit are separate units. An example of such a “continuous-type” production apparatus is illustrated in
Components that a continuous-type production apparatus 200 may have include, for example, the following in the order of conveying substrates 212:
<<Inlet Purge Device>>
The inlet purge device 201 is constituted of a set of devices to prevent outside air from entering the inside of a furnace through a substrate inlet. The inlet purge device 201 has the function of replacing an environment surrounding the substrates conveyed into the CNT aggregate production apparatus 200 with a purge gas. There are, for example, a furnace or a chamber for holding the purge gas, an injector for injecting the purge gas, and the like. An inactive gas is preferable as the purge gas, especially nitrogen is preferable in terms of safety, cost, and purgeability. A small amount of hydrogen may be contained for the purpose of improving catalytic activity. When the substrate inlet is always open, the purge gas injector is preferably implemented as a gas curtain device that is constituted of an air blowing device configured to inject the purge gas in a shower-like manner from above and below, to prevent the outside air from entering the CNT aggregate production apparatus 200 through the inlet. In an aspect illustrated in
<<Formation Unit>>
The formation unit 202 includes a set of devices for realizing the formation step. The formation unit 202 has the function of creating the reducing gas environment in the environment surrounding the catalysts and heating at least one of the catalysts or the reducing gas. The formation unit 202 may include, for example, the formation furnace 202a for holding the reducing gas, the reducing gas injector 202b for injecting the reducing gas, the heating device 202c for heating at least one of the catalysts or the reducing gas, the exhaust device 202d for discharging the gas in the furnace out of the system, and the like. The heating device 202c is not particularly limited, and may be implemented by, for example, a resistance heater, an infrared heater, an electromagnetic induction heater, or the like. The heating device 202c can heat the inside of the system so that the temperature in the formation furnace is 400° C. or more and 1100° C. or less. Furthermore, the exhaust device 202d is a component, which includes a reducing gas exhaust port disposed on a side surface of a furnace body of the formation furnace 202a, for exhausting the reducing gas in the furnace. The formation unit 202 preferably includes at least one reducing gas exhaust port, and may have more than one.
<<Growth Unit>>
The growth unit 204 includes a set of devices for realizing the growth step. The growth unit 204 has the function of creating the source gas environment in the environment surrounding the catalysts, which have become suitable for the production of the CNT aggregates by the formation step, and heating at least one of the catalysts or the source gas to grow the CNT aggregates. Specifically, the growth unit 204 may include the growth furnace 204a for holding the source gas environment, the source gas injector 204b for injecting the source gas, the heating device 204c for heating at least one of the catalysts or the source gas, the exhaust device 204d for discharging the gas in the furnace out of the system, and the like. The heating device 204c is not particularly limited, and may be implemented by, for example, a resistance heater, an infrared heater, an electromagnetic induction heater, or the like. Although not illustrated, the growth unit 204 preferably includes a catalyst activating material adding device. The exhaust device 204d is a component for exhausting the source gas in the furnace out of the system, including a source gas exhaust port disposed on a side surface of a furnace body of the growth furnace 204a. The growth unit 204 preferably includes at least one source gas exhaust port, and may have more than one.
<<Catalyst Activating Material Adding Device>>
The catalyst activating material adding device is constituted of a set of devices for adding a catalyst activating material into the source gas or directly adding the catalyst activating material to the environment surrounding the catalysts in a space in the growth furnace. The catalyst activating material adding device is not particularly limited in order to supply the catalyst activating material, but may include, for example, a supply system capable of performing supply by a bubbler, supply by vaporizing a solution containing a catalyst activating agent, supply by gas as it is, and supply by liquefying and vaporizing a solid catalyst activating agent. Examples of such a supply system may include vaporizers, mixers, agitators, dilutors, sprayers, pumps, compressors, and the like. Furthermore, a measurement device for catalyst activating material concentration may be installed in a supply pipe or the like for the catalyst activating material. By feedback control using this output value, the catalyst activating material can be stably supplied with little change over time.
<<Stir and Conveyance Unit>>
The (first and second) stir and conveyance units 207 and 208 are units for stirring and/or conveying the substrates 212. The stir and conveyance units may each include a screw, a paddle, or a ribbon, or a combination of several of these, which stirs and/or conveys the substrates by rotation of a blade. For example, as illustrated in
The first stir and conveyance unit 207 and the second stir and conveyance unit 208 may be arranged not in parallel but at an angle. Such an angle may be, for example, 10° or less.
Here, in the embodiment illustrated in
Further, by connecting and arranging the formation unit 202 and the growth unit 204 in series by the connection portion 254, as separate components vertically spaced as in the aspect illustrated in
<<Gas Mixture Prevention Device>>
The gas mixture prevention device 203 is installed in the connection portion 254 that spatially connects the formation unit 202 and the growth unit 204 to each other. The gas mixture prevention device 203 is constituted of a set of devices for realizing the function of preventing the gases from being mixed into the furnace spaces of the formation unit 202 and the growth unit 204. The gas mixture prevention device 203 is not particularly limited, and can be implemented by a gate valve device or rotary valve device that can mechanically block the spatial connection of each unit at times other than during the transfer of the substrates from unit to unit, a gas curtain device constituted of an air blowing device configured to inject the purge gas, an exhaust device that exhausts the gases present inside the connection portion 254, inside the formation unit 202 in the vicinity of the connection portion 254, and inside the growth unit 204 in the vicinity of the connection portion 254 out of the system, or the like. In particular, it is preferable that the gas mixture prevention device 203 has the exhaust device 203b that sucks at least one of the reducing gas flowing in from the formation unit 202 or the source gas flowing in from the growth unit 204, and exhausts the reducing gas or the source gas out of the CNT aggregate production apparatus 200. Furthermore, it is preferable that the gas mixture prevention device 203 has, in addition to the exhaust device 203b, the purge gas injector 203a that injects the purge gas (sealing gas) along an opening surface of the connection portion 254, and the exhaust device 203b sucks the purge gas and exhausts the purge gas out of the production apparatus. According to the CNT aggregate production apparatus 200 having such a configuration, the reduction of the catalysts in the formation step is less likely to be inhibited, and the quality of the obtained CNT aggregates and the production efficiency of the CNT aggregates can be further improved. In addition, the screw conveyors, which are the stir and conveyance units 207 and 208, rectify the flows of gases in the furnace space into flows along the screw blades 207a and 208a, thereby suppressing diffusion of the gases by suction and/or injection by the gas mixture prevention device 203 and further improving a gas mixture prevention effect. These can also be used in combination with the gate valve device and/or the rotary valve device.
<<Cooling Unit>>
The cooling unit 206 is constituted of a set of devices required to cool the substrates on which the CNT aggregates have grown. The cooling unit 206 has the function of preventing oxidation and cooling the CNT aggregates, the catalysts, and the substrates after the growth step in the growth unit 204. The cooling unit 206 illustrated in
<<Connection Portions>>
As described above, the front chamber 252, the formation furnace 202a, the growth furnace 204a, and the cooling vessel 206a are spatially connected to each other by the connection portions 253, 254, and 210. In other words, the connection portions 253, 254, and 210 are a set of devices for spatially connecting the furnace space of each unit and preventing the substrates 212 from being exposed to the outside air when the substrates 212 are conveyed from unit to unit. The connection portions 253, 254, and 210 include, for example, furnaces, chambers, or the like that can block the environment surrounding the substrates from the outside air and allow the substrates 212 to pass from unit to unit. For example, the material of the connection portions 253, 254, and 210 may be Inconel 601.
In the embodiment illustrated in
Here, as illustrated in
<<Outlet Purge Device>>
The outlet purge device 205 is constituted of a set of devices for preventing the outside air from entering the furnace through a substrate outlet. The outlet purge device 205 has the function of creating a purge gas environment in the environment surrounding the substrates 212. Specifically, the outlet purge device 205 may be implemented by a furnace or a chamber for holding the purge gas environment, an injector for injecting the purge gas, and the like. The purge gas is preferably an inactive gas, and especially nitrogen is preferable in terms of safety, cost, and purgeability. When the substrate outlet is always open, a gas curtain device that injects the purge gas in a shower-like manner from above and below is preferably provided as the purge gas injector, to prevent the outside air from entering through the apparatus outlet.
<<Injectors for Reducing Gas, Source Gas, and Catalyst Activating Material>>
As the reducing gas injector 202b, the source gas injector 204b, and an injector for the catalyst activating material, a plurality of injection ports is provided. For example, a plurality of nozzles is provided from walls of the formation furnace and/or the growth furnace toward the center of the screw. A single or plurality of injection ports may be provided at a tip of each nozzle. Alternatively, the tip of the nozzle may be pinned out and a plurality of injection ports may be provided on a side surface and/or a tip of each pin. In such a case, the screw blade needs to have notches to avoid interference with the pins.
When a plurality of injection ports is provided as the reducing gas injector 202b in this manner, the reducing gas can be spread uniformly on the substrates, and the catalysts can be reduced efficiently. As a result, the uniformity of the CNT aggregates grown on the substrates can be improved and the consumption of the reducing gas can be reduced.
When a plurality of injection ports is provided as the source gas injector 204b in this manner, the source gas can be spread uniformly on the substrates, and the source gas can be consumed efficiently. As a result, the uniformity of the aligned CNT aggregates grown on the substrates can be improved and the consumption of the source gas can be reduced.
When a plurality of injection ports is provided as an injector for the catalyst activating material in this manner, the catalyst activating material can be spread uniformly on the substrates. This increases catalytic activity and extends the life of the catalysts, thus allowing the growth of aligned CNTs to continue for a long time. The same is true when the catalyst activating material is added to the source gas and a shower head is used as the injector.
<<Materials of Apparatus Parts to be Exposed to Reducing Gas or Source Gas>>
Some parts of the formation unit 202, the growth unit 204, the stir and conveyance units 207 and 208, the gas mixture prevention device 203, and the connection portions 253, 254, and 210 are exposed to the reducing gas or the source gas. Materials constituting each of these components include materials capable of withstanding high temperature, for example, quartz, heat-resistant ceramics, heat-resistant alloys, and the like, and the heat-resistant alloys are preferable from the viewpoint of accuracy and flexibility of processing, and cost. The heat-resistant alloys include heat-resistant steel, stainless steel, nickel-based alloys, and the like. Those having Fe as a main component and another alloy content of 50% or less are generally referred to as the heat-resistant steel. Steel containing Fe as a main component and having another alloy content of 50% or less and Cr of approximately 12% or more is generally referred to as the stainless steel. The nickel-based alloys include alloys obtained by adding Mo, Cr, Fe, and the like to Ni. Specifically, SUS310, Inconel 600, Inconel 601, Inconel 625, Incoloy 800, MC Alloy, Haynes 230 Alloy, and the like are preferable in terms of heat resistance, mechanical strength, chemical stability, low cost, and the like.
When inner walls of the furnace and/or parts used in the furnace are made of metal, it is preferable that materials are heat-resistant alloys and surfaces are molten-aluminum plated or polished so as to have an arithmetic average roughness of Ra≤2 μm.
The method and the apparatus for producing the carbon nanotube (CNT) aggregates according to the disclosure will be described in detail with specific examples below, but the disclosure is not limited to these examples.
Zirconia (zirconium dioxide) beads (ZrO2, volume-average particle diameter D50: 650 μm) as the substrates were placed in a rotary drum coating apparatus. While the zirconia beads were stirred (20 rpm), a solution containing aluminum was sprayed (a spray volume 3 g/minute, spray time of 940 seconds, spray pressure of 10 MPa) with a spray gun, and was dried by supplying compressed air (300 L/minute) into the rotary drum to form aluminum-containing coating films on the zirconia beads. Next, the zirconia beads with the aluminum-containing coating films were sintered at 480° C. for 45 minutes to produce primary catalyst particles with aluminum oxide layers. Furthermore, while the primary catalyst particles were placed in another rotary drum coating apparatus and stirred (20 rpm), an iron catalyst solution was sprayed (a spray volume 2 g/minute, spray time of 280 seconds, spray pressure of 5 MPa) with a spray gun, and was dried by supplying compressed air (300 L/minute) into the rotary drum to form iron-containing coating films on the primary catalyst particles. Next, the primary catalyst particles with the iron-containing coating films were sintered at 220° C. for 20 minutes to produce the substrates with iron oxide layers.
The substrates having the catalysts on surfaces, which were prepared in this manner, were stacked in the substrate holder of the production apparatus. While respective process gases were injected from the plurality of gas injection ports arranged on a bottom surface of the substrate holder, the substrates were subjected to the formation step, the growth step, and the cooling step in this order to produce CNT aggregates.
The conditions of each step were set as follows.
CNTs synthesized on the substrates were separated and recovered using a forced vortex classifier (rotation speed: 1600 rpm, air flow rate: 2.5 Nm3/minute). The average recovery rate of the CNT aggregates was approximately 98%.
The characteristics of the CNT aggregates produced according to this example were, as typical values, tap bulk density: 0.006 g/cm3, average CNT length: 200 μm, BET-specific surface area: 900 m2/g, average outer diameter: 4.0 nm, carbon purity: 99%, CNT yield: 6 mg/g-beads, and carbon conversion efficiency: 56%.
It has been demonstrated that the apparatus according to the disclosure can produce the long CNT aggregates with high specific surface area with high carbon conversion efficiency.
The catalyst-bearing supports prepared as in Example 1 were fed into the feeder hopper of the production apparatus. The catalyst-bearing supports were subjected to the formation step, the growth step, and the cooling step in this order, while being stirred and conveyed with the screw conveyors, to produce CNT aggregates.
Each condition of the inlet purge section, the formation unit, the gas mixture prevention means, the growth unit, the output purge section, and the cooling unit of the production apparatus was set as follows.
CNTs synthesized on the substrates were separated and recovered using a forced vortex classifier (rotation speed: 1600 rpm, air flow rate: 2.5 Nm 3/minute). The average recovery rate of the CNT aggregates was approximately 98%.
The characteristics of the CNT aggregates produced according to this example were, as typical values, tap bulk density: 0.006 g/cm3, average CNT length: 200 μm, BET-specific surface area: 800 m2/g, average outer diameter: 4.0 nm, carbon purity: 99%, CNT yield: 6 mg/g-beads, and carbon conversion efficiency: 15%. The results of the continuous production are depicted in Table 1.
Sampling was performed every hour. Comparing the first and 300th sampling, no phenomenon of decrease in production volume and deterioration in the quality of the CNT aggregates could be observed.
It has been demonstrated that the apparatus according to the disclosure can continuously produce the long CNT aggregates with high specific surface area with high efficiency, without causing decrease in production volume or deterioration in quality during continuous production.
3 kg of the catalyst-bearing supports used to produce the CNT aggregates in Example 2 were recovered and oxidized in a rotary kiln furnace (air atmosphere, temperature: 800° C., processing time: 30 minutes) to remove carbon adhered to the surfaces of the catalyst-bearing supports in a reuse step. The catalyst-bearing supports after the reuse step were subjected to each step in the same manner as in Example 2 to produce CNT aggregates.
As compared to Example 2, the characteristics of the CNT aggregates produced according to this example were similar, except that the yield was reduced to 4.7 mg/g-beads by approximately 80%.
It has been demonstrated that the production method according to the disclosure can produce the long CNT aggregates with high specific surface area by reusing the catalyst-bearing supports.
Using the same catalyst substrate particles and production apparatus as in Example 1, CNT aggregates were attempted to be produced under the same conditions as in Example 1, except that the reduction/source gases in the formation/growth steps were introduced through the furnace end opening 109, instead of being injected through the plurality of gas injection ports arranged on the bottom surface of the substrate holder, and the paddle mixer was not rotated.
As a result, the CNT aggregates grew only in the vicinity of a top surface of the substrate layer, and no CNT aggregates grew inside the substrate layer, thus resulting in decrease to an average CNT yield for the entire substrate layer: 1 mg/g-beads and to a carbon conversion efficiency: approximately 2.5%.
This indicates that in the production of the CNT aggregates, it is required to inject the source gas from under the substrate layer and to mechanically stir the substrate layer at least in an overlapping manner, in order to improve the production efficiency and the carbon conversion efficiency.
According to the disclosure, the contact efficiency between the source gas and the catalysts is improved, thereby enabling efficient production of the CNT aggregates with high quality.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-038581 | Mar 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/005724 | 2/14/2022 | WO |
