U.S. patent application number 17/632730 was filed with the patent office on 2022-09-01 for carbon nanotube production device and production method.
This patent application is currently assigned to WASEDA UNIVERSITY. The applicant listed for this patent is MEIJO NANO CARBON CO., LTD., WASEDA UNIVERSITY. Invention is credited to Katsuya NAMIKI, Suguru NODA, Toshio OSAWA, Hisashi SUGIME, Zihao ZHANG.
Application Number | 20220274836 17/632730 |
Document ID | / |
Family ID | 1000006387838 |
Filed Date | 2022-09-01 |
United States Patent
Application |
20220274836 |
Kind Code |
A1 |
NODA; Suguru ; et
al. |
September 1, 2022 |
CARBON NANOTUBE PRODUCTION DEVICE AND PRODUCTION METHOD
Abstract
Provided are a carbon nanotube production device and production
method capable of realizing high-temperature heating of a catalyst
raw material in a floating catalyst chemical vapor deposition
(FCCVD) method, and improving the quality and yield of carbon
nanotubes synthesized. A carbon nanotube production device 1
includes a synthesis furnace 2 for synthesizing carbon nanotubes; a
catalyst raw material supplying nozzle 3 for supplying a catalyst
raw material used to synthesize carbon nanotubes to the synthesis
furnace 2; and a nozzle temperature adjusting unit 6 capable of
setting a temperature of an inner portion 4 of the catalyst raw
material supplying nozzle 3 higher than a temperature of a reaction
field 5 of the synthesis furnace 2. By supplying to the synthesis
furnace 2 the catalyst raw material that has been thermally
decomposed after being heated to a temperate at which a catalyst
metal will not yet be condensed, and by having the thermally
decomposed catalyst raw material rapidly cooled to a CVD
temperature at the synthesis furnace 2, microscopic catalyst metal
particles will be generated at a high density in the space of the
reaction field 5 such that carbon nanotubes having a small diameter
can be vapor-grown at a high density.
Inventors: |
NODA; Suguru; (Tokyo,
JP) ; NAMIKI; Katsuya; (Tokyo, JP) ; ZHANG;
Zihao; (Tokyo, JP) ; OSAWA; Toshio; (Tokyo,
JP) ; SUGIME; Hisashi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
WASEDA UNIVERSITY
MEIJO NANO CARBON CO., LTD. |
Tokyo
Aichi |
|
JP
JP |
|
|
Assignee: |
WASEDA UNIVERSITY
Tokyo
JP
MEIJO NANO CARBON CO., LTD.
Aichi
JP
|
Family ID: |
1000006387838 |
Appl. No.: |
17/632730 |
Filed: |
July 27, 2020 |
PCT Filed: |
July 27, 2020 |
PCT NO: |
PCT/JP2020/028754 |
371 Date: |
February 3, 2022 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J 4/008 20130101;
C01B 32/162 20170801; B82Y 40/00 20130101; B01J 2204/002 20130101;
B01J 6/008 20130101; B01J 4/002 20130101 |
International
Class: |
C01B 32/162 20060101
C01B032/162; B01J 6/00 20060101 B01J006/00; B01J 4/00 20060101
B01J004/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 9, 2019 |
JP |
2019-147941 |
Claims
1. A carbon nanotube production device comprising: a synthesis
furnace for synthesizing carbon nanotubes; a catalyst raw material
supplying nozzle for supplying a catalyst raw material used to
synthesize the carbon nanotubes to the synthesis furnace; and a
nozzle temperature adjusting unit capable of setting a temperature
of an inner portion of the catalyst raw material supplying nozzle
higher than a temperature of a reaction field of the synthesis
furnace.
2. The production device according to claim 1, wherein the
temperature of the inner portion of the catalyst raw material
supplying nozzle is a temperature at which the catalyst raw
material thermally decomposes to generate a catalyst metal vapor;
the temperature of the reaction field of the synthesis furnace is a
temperature at which catalyst metal particles are generated, and
CNTs are generated.
3. The carbon nanotube production device according to claim 1,
wherein the nozzle temperature adjusting unit is provided inside
the catalyst raw material supplying nozzle.
4. The carbon nanotube production device according to claim 1,
wherein the nozzle temperature adjusting unit is a heater.
5. The carbon nanotube production device according to claim 4,
wherein the heater is composed of carbon, and is electrically
heated to adjust the temperature of the inner portion of the
catalyst raw material supplying nozzle.
6. The carbon nanotube production device according to claim 1,
wherein there are provided a plurality of the catalyst raw material
supplying nozzles.
7. The carbon nanotube production device according to claim 1,
wherein a carbon raw material flow passage for flowing a carbon raw
material therethrough is provided outside an outer circumferential
portion of the catalyst raw material supplying nozzle.
8. A carbon nanotube production method wherein a catalyst raw
material is heated by setting a temperature of an inner portion of
a catalyst raw material supplying nozzle for supplying the catalyst
raw material used to synthesize carbon nanotubes to a synthesis
furnace higher than a temperature of a reaction field of the
synthesis furnace for synthesizing the carbon nanotubes.
9. The production method according to claim 8, wherein the
temperature of the inner portion of the catalyst raw material
supplying nozzle is a temperature at which the catalyst raw
material thermally decomposes to generate a catalyst metal vapor;
the temperature of the reaction field of the synthesis furnace is a
temperature at which CNTs are generated.
10. The carbon nanotube production method according to claim 8,
wherein the temperature of the inner portion of the catalyst raw
material supplying nozzle is adjusted by a nozzle temperature
adjusting unit provided inside the catalyst raw material supplying
nozzle.
11. The carbon nanotube production device according to claim 2,
wherein the nozzle temperature adjusting unit is provided inside
the catalyst raw material supplying nozzle.
12. The carbon nanotube production device according to claim 2,
wherein the nozzle temperature adjusting unit is a heater.
13. The carbon nanotube production device according to claim 3,
wherein the nozzle temperature adjusting unit is a heater.
14. The carbon nanotube production device according to claim 12,
wherein the heater is composed of carbon, and is electrically
heated to adjust the temperature of the inner portion of the
catalyst raw material supplying nozzle.
15. The carbon nanotube production device according to claim 13,
wherein the heater is composed of carbon, and is electrically
heated to adjust the temperature of the inner portion of the
catalyst raw material supplying nozzle.
16. The carbon nanotube production device according to claim 2,
wherein there are provided a plurality of the catalyst raw material
supplying nozzles.
17. The carbon nanotube production device according to claim 3,
wherein there are provided a plurality of the catalyst raw material
supplying nozzles.
18. The carbon nanotube production device according to claim 4,
wherein there are provided a plurality of the catalyst raw material
supplying nozzles.
19. The carbon nanotube production device according to claim 5,
wherein there are provided a plurality of the catalyst raw material
supplying nozzles.
20. The carbon nanotube production device according to claim 2,
wherein a carbon raw material flow passage for flowing a carbon raw
material therethrough is provided outside an outer circumferential
portion of the catalyst raw material supplying nozzle.
Description
TECHNICAL FIELD
[0001] The present invention relates to a device and method for
producing carbon nanotubes.
BACKGROUND ART
[0002] Conventionally, as one of the methods for synthesizing
carbon nanotubes (also referred to as CNTs hereunder), there is
known a floating catalyst chemical vapor deposition (FCCVD) method
where a carbon raw material gas in which catalyst metal particles
are dispersed in vapor phase is to be supplied to a synthesis
furnace, and CNTs are then grown from the catalyst metal particles
in a floating state. The inventors of the present invention
developed a carbon nanotube production method where a tungsten wire
is wound around an outer circumferential portion of an alumina-made
catalyst raw material suppling nozzle for supplying a catalyst raw
material, and such tungsten wire is then electrically heated to
preheat and rapidly raise the temperature of an organic metal
compound as the catalyst raw material so as to produce carbon
nanotubes. The object of this method is to generate, at a high
density, catalyst metal particles with a small diameter in a space
by decomposing the organic metal compound in a short period of
time, and attempts were also made in this method to improve the
quality of CNTs synthesized and increase the yield thereof (e.g.
Non-patent document 1).
[0003] Further, the inventors of the present invention proposed a
method where a catalyst metal vapor is to be generated by
decomposing a catalyst raw material with a premixed flame, followed
by generating catalyst metal nanoparticles by mixing the catalyst
metal vapor with a carrier gas and a carbon raw material gas so as
to continuously synthesizing single-walled CNTs (e.g. Patent
document 1).
PRIOR ART DOCUMENTS
Non-Patent Documents
[0004] Non-patent document 1: Namiki et al. "vapor-phase synthesis
of single-walled carbon nanotubes using floating catalyst; and
analysis of reaction field/flow field," The Society of Chemical
Engineers, Japan, lecture abstract of 83rd Annual Meeting (2018),
PE383.
Patent Documents
[0004] [0005] Patent document 1: Japanese Patent No. 6455988
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0006] The problem with the CNT synthesis method disclosed in the
non-patent document 1 is as follows. That is, since heating is
performed from outside the catalyst raw material supplying nozzle
with the tungsten wire, while the temperature of an inner portion
of the alumina-made catalyst raw material supplying nozzle can be
raised to a temperature of the same level as the temperature of a
reaction field of the synthesis furnace, it is difficult to set the
temperature of the inner portion higher than the temperature of the
reaction field, which makes it impossible to heat the catalyst raw
material flowing through the catalyst raw material supplying nozzle
to a sufficiently high temperature. Further, since the alumina-made
catalyst raw material supplying nozzle is to be heated to a high
temperature, there is also a problem that the alumina component of
the catalyst raw material supplying nozzle will mix into the CNTs
synthesized.
[0007] The problem with the CNT synthesis method disclosed in the
patent document 1 is that it is difficult to improve a
productivity, because an excessive amount of oxygen (O.sub.2),
water vapor (H.sub.2O) and carbon dioxide (CO.sub.2) will mix into
a raw material for synthesizing CNTs, and the number of the
catalyst metal nanoparticles by which CNTs do not grow will thus
increase.
Means to Solve the Problems
[0008] The present invention was made in view of these
circumstances, and provides a carbon nanotube production device and
production method capable of improving the quality and yield of
CNTs synthesized by a reaction of catalyst metal particles and a
carbon raw material, where a catalyst raw material is to be
thermally decomposed by raising the temperature of the catalyst raw
material in a catalyst raw material supplying nozzle to a high
temperature, the thermally decomposed catalyst raw material is then
supplied to a synthesis furnace to be rapidly cooled to a chemical
vapor deposition (CVD) temperature as a CNT growth temperature band
so as to generate microscopic catalyst metal particles, and an
agglutination caused by the collision between these microscopic
catalyst metal particles is inhibited.
[0009] The present invention provides a carbon nanotube production
device including:
[0010] a synthesis furnace for synthesizing carbon nanotubes;
[0011] a catalyst raw material supplying nozzle for supplying a
catalyst raw material used to synthesize the carbon nanotubes to
the synthesis furnace; and
[0012] a nozzle temperature adjusting unit capable of setting a
temperature of an inner portion of the catalyst raw material
supplying nozzle higher than a temperature of a reaction field of
the synthesis furnace.
[0013] The production device may be such that the temperature of
the inner portion of the catalyst raw material supplying nozzle is
a temperature at which the catalyst raw material thermally
decomposes to generate a catalyst metal vapor; the temperature of
the reaction field of the synthesis furnace is a temperature at
which catalyst metal particles are generated, and CNTs are
generated.
[0014] In the production device of the present invention, the
nozzle temperature adjusting unit may be provided inside the
catalyst raw material supplying nozzle.
[0015] In the production device of the present invention, the
nozzle temperature adjusting unit may be a heater.
[0016] In the production device of the present invention, the
heater may be composed of carbon, and may be electrically heated to
adjust the temperature of the inner portion of the catalyst raw
material supplying nozzle.
[0017] In the production device of the present invention, there may
be provided a plurality of the catalyst raw material supplying
nozzles.
[0018] In the production device of the present invention, a carbon
raw material flow passage for flowing a carbon raw material
therethrough may be provided outside an outer circumferential
portion of the catalyst raw material supplying nozzle.
[0019] The present invention provides a carbon nanotube production
method wherein a catalyst raw material is heated by setting a
temperature of an inner portion of a catalyst raw material
supplying nozzle for supplying the catalyst raw material used to
synthesize carbon nanotubes to a synthesis furnace higher than a
temperature of a reaction field of the synthesis furnace for
synthesizing the carbon nanotubes.
[0020] In the production method of the present invention, the
temperature of the inner portion of the catalyst raw material
supplying nozzle may be a temperature at which the catalyst raw
material thermally decomposes to generate a catalyst metal vapor;
the temperature of the reaction field of the synthesis furnace may
be a temperature at which CNTs are generated.
[0021] In the production method of the present invention, the
temperature of the inner portion of the catalyst raw material
supplying nozzle may be adjusted by a nozzle temperature adjusting
unit provided inside the catalyst raw material supplying
nozzle.
Effects of the Invention
[0022] The present invention can provide a carbon nanotube
production device and production method capable of improving the
quality and yield of CNTs synthesized, by setting the temperature
of the inner portion of the catalyst raw material supplying nozzle
higher than the temperature of the reaction field of the synthesis
furnace.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a schematic view showing a carbon nanotube
production device of an embodiment of the present invention.
[0024] FIG. 2 is a schematic view partially showing an example of a
configuration of a carbon nanotube production device of a working
example 1 of the present invention.
[0025] FIG. 3 is a schematic view showing a nozzle temperature
adjusting unit of the working example 1 of the present
invention.
[0026] FIG. 4 is a schematic view showing a catalyst raw material
supplying nozzle of a comparative example 1.
[0027] FIG. 5 is a schematic view showing a catalyst raw material
supplying nozzle and a coil for electric heating of a comparative
example 2.
[0028] FIG. 6 is a graph showing a temperature distribution in a
depth direction of an inner portion of the catalyst raw material
supplying nozzle of the working example 1 and the comparative
example 2 of the present invention.
[0029] FIG. 7 is a photograph of CNTs produced in the working
example 1 of the present invention.
[0030] FIG. 8 is a graph showing a CNT productivity and EDS
quantitative analysis results of residues obtained after
thermogravimetry differential thermal analysis in the working
example 1, comparative example 1 and comparative example 2 of the
present invention.
[0031] FIG. 9 is a diagram showing a Raman spectrum of CNTs
produced in the working example 1, comparative example 1 and
comparative example 2 of the present invention.
[0032] FIG. 10 is a set of diagrams showing thermogravimetry
differential thermal analysis results of the CNTs produced in the
working example 1, comparative example 1 and comparative example 2
of the present invention.
[0033] FIG. 11 is a set of images including a SEM image (FIG. 11A)
and TEM image (FIG. 11B) of the CNTs produced in the working
example 1 of the present invention.
[0034] FIG. 12 is a diagram showing a Raman spectrum of CNTs
produced in a working example 2a of the present invention.
[0035] FIG. 13 is a SEM image of the CNTs produced in the working
example 2a of the present invention.
[0036] FIG. 14 is a diagram showing a Raman spectrum of CNTs
produced in a working example 2b of the present invention.
[0037] FIG. 15 is a SEM image of the CNTs produced in the working
example 2b of the present invention.
[0038] FIG. 16 is a diagram showing a Raman spectrum of CNTs
produced in a working example 2c of the present invention.
[0039] FIG. 17 is a SEM image of the CNTs produced in the working
example 2c of the present invention.
[0040] FIG. 18 is a diagram showing a Raman spectrum of CNTs
produced in a working example 2d of the present invention.
[0041] FIG. 19 is a SEM image of the CNTs produced in the working
example 2d of the present invention.
[0042] FIG. 20 is a diagram showing a Raman spectrum of CNTs
produced in a working example 2e of the present invention.
[0043] FIG. 21 is a SEM image of the CNTs produced in the working
example 2e of the present invention.
[0044] FIG. 22 is a diagram showing a thermogravimetry differential
thermal analysis result of the CNTs produced in the working example
2e of the present invention.
[0045] FIG. 23 is a diagram showing a Raman spectrum of CNTs
produced in a working example 2f of the present invention.
[0046] FIG. 24 is a SEM image of the CNTs produced in the working
example 2f of the present invention.
[0047] FIG. 25 is a diagram showing a thermogravimetry differential
thermal analysis result of the CNTs produced in the working example
2f of the present invention.
[0048] FIG. 26 is a diagram showing a Raman spectrum of CNTs
produced in a working example 2g of the present invention.
[0049] FIG. 27 is a SEM image of the CNTs produced in the working
example 2g of the present invention.
[0050] FIG. 28 is a diagram showing a Raman spectrum of CNTs
produced in a working example 2h of the present invention.
[0051] FIG. 29 is a SEM image of the CNTs produced in the working
example 2h of the present invention.
[0052] FIG. 30 is a diagram showing a thermogravimetry differential
thermal analysis result of the CNTs produced in the working example
2h of the present invention.
[0053] FIG. 31 is a schematic view partially showing an example of
a configuration of a carbon nanotube production device of a working
example 3 of the present invention.
[0054] FIG. 32 is a side cross-sectional view partially showing an
example of the CNT production device of the working example 3 of
the present invention that is configured to have a plurality of
catalyst raw material supplying nozzles.
[0055] FIG. 33 is a top cross-sectional view of the production
device, showing an example of the configuration of the working
example 3 of the present invention that has a plurality of the
catalyst raw material supplying nozzles, where the catalyst raw
material supplying nozzles are integrally formed by boring a
plurality of holes in a heat insulation material.
[0056] FIG. 34 is a top cross-sectional view of the production
device, showing an example of the configuration of the working
example 3 of the present invention that has a plurality of the
catalyst raw material supplying nozzles, where the catalyst raw
material supplying nozzles are separately formed using individual
heat insulation materials.
MODE FOR CARRYING OUT THE INVENTION
[0057] Based on drawings and working examples, described hereunder
is a preferable embodiment of a device and method of the present
invention for producing carbon nanotubes (also referred to as CNTs
hereunder).
1. Carbon Nanotube Production Device
[0058] FIG. 1 is a schematic view showing a carbon nanotube
production device 1 of the present embodiment. This production
device 1 includes a synthesis furnace 2 for synthesizing carbon
nanotubes; a catalyst raw material supplying nozzle 3 for supplying
a catalyst raw material used to synthesize carbon nanotubes to the
synthesis furnace 2; and a nozzle temperature adjusting unit 6
capable of setting a temperature of an inner portion 4 of the
catalyst raw material supplying nozzle 3 higher than a temperature
of a reaction field 5 of the synthesis furnace 2.
[0059] A catalyst raw material supplying portion 11 for supplying
the catalyst raw material and a cocatalyst if necessary is
connected to the catalyst raw material supplying nozzle 3 through a
catalyst raw material supplying tube 14. A carbon raw material
supplying portion 12 for supplying a carbon raw material is
connected to a carbon raw material supplying tube 15. Connected to
an inert gas supplying tube 16 is an inert gas supplying portion 13
for supplying, if necessary, an inert gas such as argon (Ar) used
for purging.
[0060] The synthesis furnace 2 is formed of a cylindrical container
made of, for example, quartz glass, ceramics or stainless steel.
The reaction field 5 of the synthesis furnace 2 is a region where
CNTs grow.
[0061] The catalyst raw material and cocatalyst are to be supplied
from the catalyst raw material supplying portion 11 to the catalyst
raw material supplying nozzle 3 through the catalyst raw material
supplying tube 14, in the form of a vapor after being sublimated,
and using argon (Ar) or the like as a carrier gas. Since the
temperature of the inner portion 4 of the catalyst raw material
supplying nozzle 3 is set in such a manner that heating therein
shall take place at a temperature higher than the temperature of
the reaction field 5 of the synthesis furnace 2, the catalyst raw
material will be subjected to a rapid temperature rise and
thermally decomposed inside the catalyst raw material supplying
nozzle 3. The thermally decomposed catalyst raw material will then
be rapidly cooled to a CVD temperature at the synthesis furnace 2
to form catalyst metal particles; carbon nanotubes will then be
produced by having these catalyst metal particles react with the
carbon raw material.
[0062] In a conventional method, as a result of supplying the
catalyst metal particles to the synthesis furnace 2 at a high
concentration, the catalyst metal particles will immediately
agglutinate in vapor phase, which makes it impossible to obtain
CNTs having a small diameter. In the embodiment of the present
invention, the catalyst raw material is heated to a temperature
(e.g. 1,400.degree. C. or higher as the temperature of the inner
portion 4 of the catalyst raw material supplying nozzle 3) higher
than the temperature of the reaction field 5 of the synthesis
furnace 2 in a short period of time (e.g. 10 msec or shorter),
thereby allowing the catalyst raw material to be supplied to the
synthesis furnace while decomposing the same and inhibiting the
generation of the catalyst metal particles. Next, as a result of
having the decomposed catalyst raw material and the carbon raw
material rapidly mixed together, a catalyst metal vapor will be
cooled to the CVD temperature (e.g. 1,200.degree. C. or lower) as
the temperature of the reaction field 5 of the synthesis furnace 2
such that nuclei of metal particles will be generated, and that
microscopic catalyst metal particles will then be generated at a
high density in the space of the reaction field 5 of the synthesis
furnace 2, thus allowing CNTs with a small diameter to be
vapor-grown at a high density without permitting time for the
catalyst metal particles to agglutinate.
[0063] As the catalyst raw material, there can be used a material
containing, as a catalyst component(s), at least one metal element
selected from iron (Fe), cobalt (Co), nickel (Ni), molybdenum (Mo),
yttrium (Y) and copper (Cu). Among these elements, iron (Fe) is
particularly preferred; ferrocene (Fe(C.sub.5H.sub.5).sub.2) is
particularly preferred as the catalyst raw material.
[0064] Sulfur (S) is preferred as the cocatalyst. As a sulfur
source, there may be used, for example, sulfur, thiophene and
hydrogen sulfide. Sulfur is expected to bring about an effect of
stably forming small catalyst metal particles, and promoting carbon
precipitation from the iron catalyst metal particles. However, the
cocatalyst is not an essential component.
[0065] In the present embodiment, the carbon raw material is to be
supplied from the carbon raw material supplying portion 12 to the
synthesis furnace 2 through the carbon raw material supplying tube
15, as a carbon source gas. Examples of the carbon raw material
include methane (CH.sub.4), acetylene (C.sub.2H.sub.2), ethylene
(C.sub.2H.sub.4), toluene (C.sub.6H.sub.5CH.sub.3) and ethanol
(C.sub.2H.sub.5OH); in the present invention, methane (CH.sub.4)
and ethylene (C.sub.2H.sub.4) are particularly preferred as they
are capable of inhibiting the occurrence of impurities such as tar.
The carbon raw material can, for example, be supplied to the
synthesis furnace 2 together with a carrier gas such as argon (Ar)
and hydrogen (H.sub.2).
[0066] In FIG. 1, the carbon raw material flows from top down in
the carbon raw material supplying tube 15 provided at an upper
outer circumferential portion of the synthesis furnace 2, and is
then horizontally supplied to the synthesis furnace 2 from a carbon
raw material flow outlet 19 provided at a side portion of the
synthesis furnace 2. There are no particular restrictions on a
method for supplying the carbon raw material so long as the method
allows the carbon raw material and the decomposed catalyst raw
material supplied from the catalyst raw material supplying nozzle 3
to be mixed in the reaction field 5 of the synthesis furnace 2.
[0067] As a method for supplying the carbon raw material, for
example, a carbon raw material flow passage 17 (see FIG. 31) for
flowing the carbon raw material therethrough may be provided
outside an outer circumferential portion of the catalyst raw
material supplying nozzle 3. The carbon raw material is preheated
utilizing the heat discharged from the nozzle temperature adjusting
unit 6, and then supplied to the synthesis furnace 2 after the rise
in temperature, thereby allowing the reaction field 5 to maintain a
high temperature. Next, the thermally decomposed catalyst raw
material and the preheated carbon raw material can be swiftly mixed
together.
[0068] The CNT production device 1 may also be configured in a
manner where there are provided a plurality of the catalyst raw
material supplying nozzles 3. By employing a plurality of the
catalyst raw material supplying nozzles 3, the CNT production
device 1 can be scaled up to a large device such as those used in a
plant so that productivity can be improved as a mass production
facility. A specific configuration example of the CNT production
device 1 having a plurality of the catalyst raw material supplying
nozzles 3 is described later.
[0069] As the nozzle temperature adjusting unit 6, there may be
employed, for example, a unit for heating the inner portion 4 of
the catalyst raw material supplying nozzle 3 from within the
catalyst raw material supplying nozzle 3. Further, there are no
particular restrictions on the unit as the nozzle temperature
adjusting unit 6 for heating the inner portion 4 of the catalyst
raw material supplying nozzle 3 so long as the temperature of the
inner portion 4 of the catalyst raw material supplying nozzle 3 can
be set to a temperature that is sufficiently higher than the
temperature of the reaction field 5 of the synthesis furnace 2; for
example, the inner portion 4 of the catalyst raw material supplying
nozzle 3 may be heated from outside the catalyst raw material
supplying nozzle 3.
[0070] With regard to the nozzle temperature adjusting unit 6, as a
unit for performing heating from within the catalyst raw material
supplying nozzle 3, the nozzle temperature adjusting unit 6 can be
provided inside the catalyst raw material supplying nozzle 3. In
such case, since the catalyst raw material flowing through the
catalyst raw material supplying nozzle 3 can be directly heated by
the nozzle temperature adjusting unit 6, the catalyst raw material
can be decomposed in a short period of time. Further, the catalyst
raw material supplying nozzle 3 can be prevented from being damaged
by the heat generated from the nozzle temperature adjusting unit
6.
[0071] Meanwhile, as the nozzle temperature adjusting unit 6, if
employing a unit for performing heating from outside the catalyst
raw material supplying nozzle 3, this unit may also be used in
combination with a unit for performing heating from within the
catalyst raw material supplying nozzle 3. In such case, as the unit
for performing heating from within the catalyst raw material
supplying nozzle 3, a ceramic heat transfer rod (see FIG. 2 and
FIG. 3), for example, may be installed inside the catalyst raw
material supplying nozzle 3 such that the heat transfer rod will be
heated by a radiation from within the catalyst raw material
supplying nozzle 3. Since the inner portion 4 of the catalyst raw
material supplying nozzle 3 will be evenly heated both from within
the catalyst raw material supplying nozzle 3 and by the surface of
the heat transfer rod, the catalyst raw material can be thermally
decomposed in a short period of time, and then by cooling such
catalyst raw material to the CVD temperature at the reaction field
5 of the synthesis furnace 2, the catalyst metal particles can be
generated at a high density in the space.
[0072] Further, the nozzle temperature adjusting unit 6 may also be
a heater 7 (see FIG. 31). Preferably, the heater 7 is composed of
carbon, and is electrically heated so as to raise the temperature
of the inner portion 4 of the catalyst raw material supplying
nozzle 3, where the temperature of the inner portion 4 of the
catalyst raw material supplying nozzle 3 is adjusted by changing
the amount of electricity conducted. Since the catalyst raw
material can be directly heated by the heater 7, the temperature of
the catalyst raw material can be raised to a high temperature at
which the catalyst metal will not yet be condensed, and while
reliably inhibiting the generation of the catalyst metal particles
at the nozzle inner portion 4 of the catalyst raw material
supplying nozzle 3, by cooling the catalyst metal vapor to the CVD
temperature at the reaction field 5 of the synthesis furnace 2, the
catalyst metal particles can be generated at a high density in the
space.
[0073] In the case of a metallic heater, there is a problem that
the heater will carbonize or embrittle due to the carbons in a
catalyst raw material such as ferrocene (Fe(C.sub.5H.sub.5).sub.2).
The problems with a ceramic heater are that it is of high
resistance; and that the resistance value of the heater will change
as carbons precipitate on the surface, which makes it difficult to
control the temperature of the heater. A carbon heater will not
embrittle due to carbons even when performing electrical heating,
and a change in the resistance value thereof due to carbon
precipitation is small as well.
[0074] It is preferred that a heat retention unit 8 for controlling
the temperature of the reaction field 5 of the synthesis furnace 2
be provided, for example, outside an outer circumferential portion
of the synthesis furnace 2. The heat retention unit 8 may, for
example, be a heating furnace such as an electric furnace
performing heating by passing an electric current through nichrome
wires, a ceramic heat generating body or the like; or a heat
insulation material provided to cover the outer circumferential
portion of the synthesis furnace 2. The temperature of the reaction
field 5 of the synthesis furnace 2 is preferably retained in a
range of 800 to 1,300.degree. C., more preferably 1,000 to
1,200.degree. C., in order to, for example, suit the growth of
carbon nanotubes. The heat retention unit 8 serves to manage the
temperature of the reaction field 5 of the synthesis furnace 2 so
as to maintain a growth temperature of CNT and achieve a longer
growth time thereof. The inventors of the present invention have
confirmed that high-quality single-walled carbon nanotubes (SWCNT)
can be synthesized by mixing the heated catalyst raw material and
the carbon raw material with the temperature of the heat retention
unit 8 being 1,150 to 1,200.degree. C. In the preset invention, the
temperature of the inner portion 4 of the catalyst raw material
supplying nozzle 3 for supplying the catalyst raw material to the
synthesis furnace 2 may be set higher than the temperature of the
reaction field 5 of the synthesis furnace 2.
[0075] The temperature of the inner portion 4 of the catalyst raw
material supplying nozzle 3 is a temperature at which the catalyst
raw material thermally decomposes; particularly, it may be a
temperature at which the catalyst raw material thermally decomposes
to generate the catalyst metal vapor. The temperature of the
reaction field 5 of the synthesis furnace 2 may be a temperature at
which the catalyst metal particles are generated, and CNTs are
generated.
[0076] Particularly, it is preferred that the temperature of the
inner portion 4 of the catalyst raw material supplying nozzle 3 be
a temperature at which the catalyst metal vapor will not be
condensed. For example, when supplying an argon (Ar) gas containing
0.4 Pa of ferrocene (Fe(C.sub.5H.sub.5).sub.2), if the temperature
of the inner portion 4 of the catalyst raw material supplying
nozzle 3 is about 1,400.degree. C. or higher, a vapor of iron (Fe)
as the catalyst metal can be inhibited from being condensed and
generating iron particles.
[0077] By having the thermally decomposed catalyst raw material
join the carbon raw material without generating the catalyst metal
particles, and by generating the microscopic catalyst metal
particles at a high density in the space of the reaction field 5 of
the synthesis furnace 2 to then immediately start synthesizing
CNTs, CNTs with a small diameter can be vapor-grown at a high
density, high purity, high quality and high yield.
2. Method for Producing Carbon Nanotubes
[0078] In a method of the present embodiment for producing carbon
nanotubes, as described above, the catalyst raw material is to be
heated and decomposed by setting the temperature of the inner
portion 4 of the catalyst raw material supplying nozzle 3 for
supplying the catalyst raw material used to synthesize carbon
nanotubes to the synthesis furnace 2 higher than the temperature of
the reaction field 5 of the synthesis furnace 2 for synthesizing
carbon nanotubes. By supplying the thermally decomposed catalyst
raw material to the synthesis furnace 2 and then rapidly cooling it
to the CVD temperature, carbon nanotubes can be produced without
having the catalyst particles agglutinate together.
[0079] As one example of the unit for setting the temperature of
the inner portion 4 of the catalyst raw material supplying nozzle 3
to a high temperature, as described above, the temperature of the
inner portion 4 of the catalyst raw material supplying nozzle 3 can
be adjusted by the nozzle temperature adjusting unit 6 provided
inside the catalyst raw material supplying nozzle 3.
[0080] Here, the synthesis furnace 2 in FIG. 1 is formed into a
vertical shape elongated in a vertical direction of the drawing;
the synthesis furnace 2 may also be formed into a transverse shape
elongated in a left and right direction of the drawing. Further, in
this drawing, as the vertical synthesis furnace 2, the catalyst raw
material and the carbon raw material are to be supplied from top
down in the drawing. However, one or both of the catalyst raw
material and the carbon raw material may be supplied from bottom up
in the drawing, or from the transverse direction of the drawing.
This also applies when the synthesis furnace 2 is of a transverse
shape.
[0081] According to the CNT production device 1 and production
method of the present embodiment, single-walled carbon nanotubes
(SWCNT) and/or multi-walled carbon nanotubes (MWCNT) can be
produced at a high density, high purity, high quality and high
yield.
Working Examples
[0082] All the documents mentioned in this specification shall be
incorporated thereinto in their entirety by citation. A working
example described below is to exemplify the embodiment of the
present invention, and shall not be interpreted as limiting the
scope of the present invention.
[0083] Evaluations were conducted in working and comparative
examples by performing laser micro-Raman spectroscopic analysis,
thermogravimetry differential thermal analysis (TG-DTA) and EDS
quantitative analysis, using the following methods.
<Laser Micro-Raman Spectroscopic Analysis>
[0084] The crystallizability of CNTs can, for example, be analyzed
via laser micro-Raman spectroscopic analysis. In laser micro-Raman
spectroscopic analysis, a peak observed near 1,590 cm.sup.-1 is
called G-band, and is derived from the in-plane stretching
vibrations of carbon atoms composing a six-membered ring structure.
Further, a peak observed near 1,350 cm.sup.-1 is called D-band, and
is likely to be observed when the six-membered ring structure is
defective. A relative crystallizability of CNTs can be evaluated by
a peak intensity ratio I.sub.G/I.sub.D (G/D ratio) of G-band to
D-band. It can be said that the higher the G/D ratio is, the higher
the crystallizability of CNTs is. A peak observed near 200
cm.sup.-1 is unique to single-walled carbon nanotubes (SWCNT)
called RBM (Radial Breathing Mode) which is a mode where vibrations
occur in the diametrical direction of the tubes. In this working
example, a CNT bulk sample was placed in a laser micro-Raman
spectrometer (model number: HR-800 by HORIBA, Ltd.), and a laser
wavelength of 488 nm was used to perform laser micro-Raman
spectroscopic analysis.
<Thermogravimetry Differential Thermal Analysis>
[0085] In a thermogravimetry differential thermal analysis (TG-DTA)
for analyzing a carbon material, the temperature of the material is
to be raised to about 1,000.degree. C. at about 5.degree. C./min so
as to then analyze a peak temperature of burning and a residue
thereof, thereby making it possible to evaluate the constituent
elements and quality of the carbon material. For example, a product
in FCCVD is a mixture of: a metal contained in the catalyst raw
material, such as iron (Fe); CNTs; amorphous carbon (a-C); and
graphitic carbon (g-C). By raising the temperature of the carbon
material under the above condition, if, for example, a metal such
as iron (Fe) is contained therein, an increase in mass owing to the
oxidation of such metal will be observed. Normally, a-C burns at
about 350 to 450.degree. C.; CNTs and g-C start to burn at about
400.degree. C., and completely burns out at about 700.degree. C. In
this working example, a thermal analysis device (model number:
TG8120 by Rigaku Corporation) was used to perform thermogravimetry
differential thermal analysis under air flow and at a temperature
rise rate of 5.degree. C./min.
<EDS (Energy Dispersive X-Ray Spectroscopy) Quantitative
Analysis>
[0086] Since a residue obtained after conducting thermogravimetry
differential thermal analysis is an oxidized metal(s), they were
subjected to EDS quantitative analysis to calculate an element
ratio between carbon (C), iron (Fe) and aluminum (Al). In this
working example, quantitative analysis of the residue was conducted
using a scanning electron microscope (SEM) (model number: S-4800 by
Hitachi High-Tech Corporation) and an energy dispersive X-ray
analysis (EDX) device (model number: EDAX Genesis by AMETEK.
Inc.).
Working Example 1
[0087] When Heated Both from Outside with Coil and from Inside with
Heat Transfer Rod (Ethylene Raw Material)
[0088] FIG. 2 and FIG. 3 are schematic views partially showing an
example of a configuration of a CNT production device 1 of a
working example 1 of the present invention.
[0089] As shown in FIG. 2, the catalyst raw material supplying
nozzle 3 is connected to the catalyst raw material supplying
portion 11 for supplying the catalyst raw material and, if
necessary, the cocatalyst through the catalyst raw material
supplying tube 14. The carbon raw material supplying tube 15 is
connected to the carbon raw material supplying portion 12 for
supplying the carbon raw material. The inert gas supplying tube 16
is connected to the inert gas supplying portion 13 for supplying,
if necessary, an inert gas such as argon (Ar) used for purging.
[0090] As shown in FIG. 2 and FIG. 3, as the nozzle temperature
adjusting unit 6 of the working example 1, a coil 21 is provided
outside the outer circumferential portion of the catalyst raw
material supplying nozzle 3, and a heat transfer rod 22 is provided
inside the catalyst raw material supplying nozzle 3. There are no
particular restrictions on the position and length of the coil 21.
With such configuration, the inner portion 4 can be heated from
outside the catalyst raw material supplying nozzle 3 by energizing
the coil 21, and also from within the catalyst raw material
supplying nozzle 3 by the heat transfer rod 22 that has been heated
by the radiation from within the catalyst raw material supplying
nozzle 3, thereby allowing the temperature of the inner portion 4
of the catalyst raw material supplying nozzle 3 to be easily set
high. The temperature of the inner portion 4 of the catalyst raw
material supplying nozzle 3 was adjusted by the amount of
electricity conducted to the coil 21.
[0091] Particularly, the temperature of the inner portion 4 of the
catalyst raw material supplying nozzle 3 was set higher than the
temperature of the reaction field 5 of the synthesis furnace 2.
Next, the temperature of the catalyst raw material supplied from
the catalyst raw material supplying portion 11 through the catalyst
raw material supplying tube 14 and flowing through the catalyst raw
material supplying nozzle 3, was raised to a high temperature in a
short contact time. Due to the heat transfer rod 22, in the inner
portion 4 of the catalyst raw material supplying nozzle 3, since a
region where the catalyst raw material would decompose was evenly
heated, the catalyst raw material was able to be decomposed in a
short contact time.
[0092] The catalyst raw material supplying nozzle 3 and the heat
transfer rod 22 were made of alumina (Al.sub.2O.sub.3); an inner
diameter of the catalyst raw material supplying nozzle 3 was set to
4 mm, and a diameter of the heat transfer rod was set to 2 mm. The
coil 21 provided outside the outer circumferential portion of the
catalyst raw material supplying nozzle 3 was made of tungsten
(W).
[0093] A numerical symbol "23" denotes a heat insulation material
for keeping the inner portion 4 of the catalyst raw material
supplying nozzle 3 at a high temperature.
[0094] FIG. 4 shows a catalyst raw material supplying nozzle 3 used
in a CNT production device of a comparative example 1. There was
used a catalyst raw material supplying nozzle 3 identical to that
used in the present working example; there were not employed the
heat transfer rod 22 and the coil 21 provided outside the outer
circumferential portion of the catalyst raw material supplying
nozzle 3, and the catalyst raw material was supplied to the
reaction field 5 of the synthesis furnace 2 without being heated.
The rest of the configurations were identical to those of the
working example 1.
[0095] FIG. 5 shows a CNT production device of a comparative
example 2 that includes the catalyst raw material supplying nozzle
3 and the coil 21 provided outside the outer circumferential
portion of the catalyst raw material supplying nozzle 3. Using a
catalyst raw material supplying nozzle 3 and coil 21 that are
identical to those used in the present working example, and without
installing the heat transfer rod 22, the coil 21 was electrically
heated such that the inner portion 4 of the catalyst raw material
supplying nozzle 3 was heated only via the heating unit provided
outside the catalyst raw material supplying nozzle 3. The rest of
the configurations were similar to those of the working example
1.
[0096] FIG. 6 is a graph showing a change in temperature in a depth
direction of the inner portion 4 when flowing a total of 2 SLM of a
gas through the catalyst raw material supplying nozzle 3. In the
working example 1, the temperature was measured using a
thermocouple (not shown) provided in the center of the catalyst raw
material supplying nozzle 3. In the comparative example 2, a
temperature in a central portion of the catalyst raw material
supplying nozzle 3 was calculated via fluid analysis using a
general-purpose numerical value fluid analyzing software (ANSYS
Fluent). The set temperature of the heat retention unit 8 (Furnace)
was 1,150.degree. C. In the comparative example 2, although the
temperature rose toward a flow outlet of the catalyst raw material
supplying nozzle 3, the temperature only rose to a temperature
lower than 1,150.degree. C. In contrast, in the working example 1,
the temperature reached 1,150.degree. C. at 50 to 55 mm of the
catalyst raw material supplying nozzle 3 in a depth direction
thereof where the coil is already gradually wound therearound, and
a temperature of the inner portion 4 of the catalyst raw material
supplying nozzle 3 from such location to the flow outlet became
higher than the set temperature (1,150.degree. C.) of the heat
retention unit 8. A maximum value of the temperature of the inner
portion 4 was about 1,400.degree. C. In the working example 1, the
gas of the flow rate of 2 SLM passes through a gap of a
cross-sectional area of 0.0942 cm.sup.2 between the catalyst raw
material supplying nozzle 3 having the inner diameter of 4 mm and
the heat transfer rod having the diameter of 2 mm. The flow rate of
the gas was 33.3 cm.sup.3/s at 0.degree. C., and became 204
cm.sup.3/s when heated to 1,400.degree. C. The gas passed through
the gap of the cross-sectional area of 0.0942 cm.sup.2 at 2,170
cm/s on average, and a time spent in passing by 2 cm of the heated
portion of the catalyst raw material supplying nozzle 3 was 0.9 ms
on average. The temperature of the reaction field 5 of the
synthesis furnace 2 was either at the same level of or lower than
the set temperature (1,150.degree. C.) of the heat retention unit
8.
[0097] In each of the working example 1, comparative example 1 and
comparative example 2, there were used an identical catalyst raw
material, an identical carbon raw material, an identical gaseous
species of the purge gas and carrier gas, an identical gas flow
rate, an identical gas temperature and an identical set temperature
of the heat retention unit 8.
[0098] By passing 0.5 SLM of an argon (Ar) gas through ferrocene
(Fe(C.sub.5H.sub.5).sub.2) as a catalyst raw material that had been
heated to 80.degree. C., a ferrocene vapor-containing argon gas was
supplied to the catalyst raw material supplying tube 14 from the
catalyst raw material supplying portion 11. Further, by passing 1.0
SLM of an argon (Ar) gas through sulfur (S) as a cocatalyst that
had been heated to 108.degree. C., a sulfur vapor-containing argon
gas was supplied to the catalyst raw material supplying tube 14
from the catalyst raw material supplying portion 11. Moreover, an
argon (Ar) gas as a carrier gas was supplied to the catalyst raw
material supplying tube 14 at 120.degree. C. and 0.5 SLM. An argon
(Ar) gas was supplied from the inert gas supplying portion 13 to
the inert gas supplying tube 16 at 1.0 SLM. Ethylene
(C.sub.2H.sub.4) as the carbon raw material was supplied from the
carbon raw material supplying portion 12 to the carbon raw material
supplying tube 15 at 0.05 SLM. In addition, a hydrogen (H.sub.2)
gas was supplied to the carbon raw material supplying tube 15 at
0.5 SLM, and an argon (Ar) gas as a carrier gas was supplied to the
carbon raw material supplying tube 15 at 1.5 SLM. As the heat
retention unit 8, an electric furnace was provided outside the
outer circumferential portion of the synthesis furnace 2, and the
temperature of the electric furnace was set to 1,150.degree. C.
[0099] As shown in a photograph of FIG. 7, in the working example
1, CNTs were produced as an aggregate 31. The length of the
aggregate taken out from the reaction tube was about 10 cm. Various
evaluations of the CNTs produced in the working example 1,
comparative example 1 and comparative example 2 are collectively
shown in Table 1. Described hereunder are details of each
evaluation result.
TABLE-US-00001 TABLE 1 Carbon CNT Productivity purity
I.sub.G/I.sub.D diameter .sigma. [mg/min] [wt %] [--] [nm] [nm]
Comparative 2.80 80.6 11 2.22 .+-.0.90 example 1 (.sigma. = 3.3)
Comparative 3.81 71.7 55 1.69 .+-.0.63 example 2 (.sigma. = 5.1)
Working 5.73 84.9 57 1.55 .+-.0.43 example 1 (.sigma. = 3.1)
<EDS Quantitative Analysis Result (Productivity and Carbon
Purity)>
[0100] The results of a productivity and the element ratios are
shown in FIG. 8. The productivity was calculated as a yield per
unit time based on the yield of CNTs and a synthesis time. The
productivity in the working example 1 was 5.73 mg/min which was
higher than 2.80 mg/min in the comparative example 1 and 3.81
mg/min in the comparative example 2.
[0101] EDS quantitative analysis was performed on a residue
obtained after performing a later-described thermogravimetry
differential thermal analysis (TG-DTA). As for a ratio of the
carbon (C) derived from CNTs to the iron (Fe) derived from
ferrocene (Fe(C.sub.5H.sub.5).sub.2) as the catalyst raw material
and the aluminum (Al) derived from alumina (Al.sub.2O.sub.3) of the
catalyst raw material supplying nozzle 3, the ratio in the working
example 1 was 84.9 wt % which was higher than 80.6 wt % in the
comparative example 1 and 71.7 wt % in the comparative example
2.
[0102] As can be seen from above, it was indicated that the working
example 1 provides a CNT production device and method having a high
productivity, and that CNTs with a high purity can be produced
thereby.
<Laser Micro-Raman Spectroscopic Analysis Result
(Crystallizability)>
[0103] FIG. 9 is a Raman spectrum of the CNTs produced. As a result
of calculating I.sub.G/I.sub.D (G/D ratio), the ratio in the
working example 1 was 57 which was higher than 11 in the
comparative example 1 and 55 in the comparative example 2. There
was also observed the RBM peak occurring near 200 cm.sup.-1. Thus,
in the working example 1, it was indicated that SWCNTs with a high
crystallizability were able to be produced.
<Thermogravimetry Differential Thermal Analysis Result (Catalyst
Utilization Efficiency)>
[0104] An upper graph in FIG. 10 is a graph showing a
thermogravimetric analysis (TG) result of the CNTs produced; a
lower graph in FIG. 10 is a graph showing a differential thermal
analysis result (DTA). Table 2 shows the evaluation results of
thermogravimetry differential thermal analysis. As for the result
of TG, in the working example 1, the mass increased in the
beginning due to the oxidation of iron (Fe) as the catalyst ((1) in
the graph). A peak of mass increase in the working example 1 was
smaller than those in the comparative examples 1 and 2. Burning
started at about 350.degree. C. Based on a peak change in DTA, it
can be concluded that a range of about 350.degree. C. to about
420.degree. C. was where the burning of amorphous carbon (a-C) took
place ((2) in FIG. 10), and that a range of about 420.degree. C. to
about 650.degree. C. was where the burning of CNTs took place ((3)
in the graph). In the working example 1, the amount of the ashes of
the residue was 22 wt % as compared to before burning, which was
smaller than 30 wt % in the comparative example 1 and 43 wt % in
the comparative example 2. Thus, it was indicated that in the
working example 1, the utilization efficiency of the catalyst was
able to be improved.
TABLE-US-00002 TABLE 2 Residue Burnout amount [.degree. C.] a - C
Crystallizability [Wt %] Comparative example 1 500 Many Low 30
Comparative example 2 700 Few High 43 Working example 1 700 Few
High 22
<Observational Result by Scanning Electron Microscope (SEM) and
Transmission Electron Microscope (TEM)>
[0105] FIG. 11 includes a SEM image (FIG. 11A) of the CNTs produced
in the working example 1; and a TEM image thereof (FIG. 11B). As
shown in the SEM image, it was indicated that the number of the
particles was small. That is, it was indicated that the number of
the catalyst metal particles that were not used for synthesizing
CNTs was small, whereas the number of the catalyst metal particles
that were effective in growing the CNTs had increased.
[0106] The TEM image indicates that SWCNT 32 was produced. There,
the diameter of the CNTs and the distribution thereof were observed
by TEM.
[0107] The diameter of the CNTs produced in the working example 1
was 1.55 nm on average which was smaller than 2.22 nm in the
comparative example 1 and 1.69 nm in the comparative example 2. In
this way, it was indicated that in the working example 1, CNTs with
a small diameter were able to be produced by thermally decomposing
the catalyst raw material, mixing the decomposed catalyst metal raw
material with the carbon source gas to then rapidly perform cooling
to the CVD temperature so as to generate the microscopic catalyst
metal particles and immediately generate CNTs.
[0108] A standard deviation .sigma. of the diameter of the CNTs
produced in the working example 1 was 0.43 which was smaller than
0.90 in the comparative example 1 and 0.63 in the comparative
example 2. In this way, it was indicated that by using the heat
transfer rod 22, the temperature distribution in the inner portion
4 of the catalyst raw material supplying nozzle 3 will be even such
that the thermal decomposition of the catalyst raw material shall
spatially evenly take place, and that as a result, the catalyst
metal particles are able to be spatially evenly generated.
Working Example 2
[0109] When Heated Both from Outside with Coil and from Inside with
Heat Transfer Rod (Methane Raw Material)
[0110] Carbon nanotubes were synthesized in a manner such that a
device identical to that used in the working example 1 was used, a
catalyst raw material-containing argon (Ar) gas was passed through
the catalyst raw material supplying tube 14 from the catalyst raw
material supplying portion 11 under a condition identical to that
of the working example 1, and as the carbon source, methane
(CH.sub.4) was used instead of ethylene (C.sub.2H.sub.4). Other
synthesis conditions for working examples 2a to 2h are as shown in
Table 3; experiments were conducted by changing the temperature of
the synthesis furnace 2 in a range of 1,150 to 1,200.degree. C. The
temperature of the inner portion of the catalyst raw material
supplying nozzle is as shown in FIG. 6; and a region having a
temperature higher than that of the synthesis furnace 2 was set to
be about 20 mm.
[0111] FIGS. 12, 14, 16, 18, 20, 23, 26 and 28 are all Raman
spectra of the CNTs produced in the working examples 2a to 2h;
I.sub.G/I.sub.D (G/D ratio) in each working example was calculated.
FIGS. 13, 15, 17, 19, 21, 24, 27 and 29 are all SEM images of the
CNTs produced in the working examples 2a to 2h.
[0112] The evaluation results are shown in Table 3. Under any of
the conditions employed in the working examples 2a to 2h, the G/D
ratio was not lower than 58.8, and the productivity was not lower
than 5.31 mg/min; carbon nanotubes were able to be synthesized at a
quality and quantity higher than those of the comparative examples
1 and 2.
[0113] With regard to the working examples 2e, 2f and 2h,
thermogravimetry differential thermal analysis (TG-DTA) was
performed (FIGS. 22, 25 and 30). As shown in Table 3, the amount of
the ashes of the residue was not larger than 23.1 wt % as compared
to before burning, which was smaller than those in the comparative
examples 1 and 2.
[0114] As for the working example 2h, EDS quantitative analysis was
performed on a residue obtained after performing thermogravimetry
differential thermal analysis (TG-DTA). The ratio of the carbon (C)
derived from CNTs to the iron (Fe) derived from ferrocene
(Fe(C.sub.5H.sub.5).sub.2) as the catalyst raw material and the
aluminum (Al) derived from alumina (Al.sub.2O.sub.3) of the
catalyst raw material supplying nozzle 3 was 92.7 wt % which was
higher than those in the comparative examples 1 and 2.
TABLE-US-00003 TABLE 3 Heat Inert gas retention Catalyst raw
material supplying Carbon raw material unit 8 supplying tube 14
tube 16 supplying portion 12 Residue Working Temperature Fc + Ar S
+ Ar Ar Ar CH.sub.4 H.sub.2 Ar Total I.sub.G/I.sub.D Productivity
amount example (.degree. C.) (SLM) (SLM) (SLM) (SLM) (SLM) (SLM)
(SLM) (SLM) [--] [mg/min] [Wt %] 2a 1150 0.50 1.00 0.50 0.20 0.35
2.00 0.50 5.05 81.6 5.31 -- 2b 1200 0.50 1.00 0.50 0.20 0.35 2.00
0.50 5.05 92.8 6.76 -- 2c 1150 0.50 1.00 0.50 0.20 0.35 1.75 0.70
5.00 73.8 7.81 -- 2d 1200 0.50 1.00 0.50 0.20 0.35 1.75 0.70 5.00
84.4 7.19 -- 2e 1150 0.50 1.00 0.50 0.20 0.35 1.45 1.00 5.00 58.8
8.16 23.1 2f 1200 0.50 1.00 0.50 0.20 0.35 1.45 1.00 5.00 102.1
8.03 6.7 2g 1200 0.50 1.00 0.50 0.20 0.35 1.55 0.90 5.00 84.3 10.5
-- 2h 1200 0.50 1.00 0.50 0.20 0.35 2.05 0.40 5.00 75.7 12.1
10.4
Working Example 3
[0115] When Heated from Inside with Carbon Heater
[0116] FIG. 31 is a schematic view partially showing an example of
a configuration of a CNT production device 1 of a working example 3
of the present invention.
[0117] As shown in FIG. 31, the nozzle temperature adjusting unit 6
is provided inside the catalyst raw material supplying nozzle 3.
This configuration allows the temperature of the inner portion 4 of
the catalyst raw material supplying nozzle 3 to be easily set high,
and even higher than the temperature of the reaction field 5 of the
synthesis furnace 2. Further, the temperature of the catalyst raw
material supplied from the catalyst raw material supplying portion
11 through the catalyst raw material supplying tube 14 and flowing
through the catalyst raw material supplying nozzle 3, can be raised
to a high temperature in a short period of time. With this
configuration, since the temperature of the catalyst raw material
supplying nozzle can be maintained lower than that of the nozzle
temperature adjusting unit 6, when the temperature of the nozzle
temperature adjusting unit 6 is set to an especially high
temperature, the catalyst raw material whose temperature has been
raised will be thermally decomposed at a high temperature and in a
short period of time to generate a catalyst metal vapor, and the
catalyst metal vapor thus generated will then be supplied to the
reaction field 5 of the synthesis furnace 2 without being
condensed.
[0118] Further, by installing the nozzle temperature adjusting unit
6 inside the catalyst raw material supplying nozzle 3, a thermal
damage of the catalyst raw material supplying nozzle 3 can be
inhibited as compared to when performing heating from outside by
installing a coil outside the outer circumferential portion of the
catalyst raw material supplying nozzle 3.
[0119] In the present working example, the nozzle temperature
adjusting unit 6 is the heater 7. This heater 7 is composed of
carbon, and is electrically heated so as to then adjust the
temperature of the inner portion 4 of the catalyst raw material
supplying nozzle 3 by changing the amount of electricity conducted.
The catalyst raw material supplying nozzle 3 can be made of a
heat-resistant ceramics material; for example, it may be a cylinder
made of zirconia (ZrO.sub.2). The heater 7 may, for example, be
formed into an inverted U shape with a slit 18 being provided in a
C/C composite (carbon fiber-reinforced carbon composite material)
sheet, and be arranged inside the catalyst raw material supplying
nozzle 3. A Ni-made electrode 9 may, for example, be connected to
the heater 7 so as to electrically conduct the heater 7 through
such electrode 9. Since the heater 7 will heat the catalyst raw
material to a temperature higher than the temperature of the
reaction field 5 of the synthesis furnace 2, the nucleation of the
metal particles from the catalyst raw material can be inhibited
from occurring in the catalyst raw material supplying nozzle 3. The
heated catalyst raw material will then be supplied to the reaction
field 5 of the synthesis furnace 2 as the catalyst metal vapor.
[0120] A numerical symbol "17" denotes the carbon raw material flow
passage that is provided outside the outer circumferential portion
of the catalyst raw material supplying nozzle 3, and allows the
carbon raw material to flow therethrough. The carbon raw material
is supplied from the carbon raw material supplying portion 12 to
the carbon raw material flow passage 17 through the carbon raw
material supplying tube 15. Although the carbon raw material flows
outside the outer circumferential portion of the catalyst raw
material supplying nozzle 3 whose inner portion 4 has been heated
to a temperature higher than the temperature of the reaction field
5 of the synthesis furnace 2, since a heat-insulating catalyst raw
material supplying nozzle 3 is used, the carbon raw material can be
efficiently preheated to the extent that it will not decompose. In
this case, not only there can be prevented the generation of a
by-product(s) or the like causing catalyst inactivation, but the
thermally decomposed catalyst raw material and the carbon raw
material can be rapidly mixed together. If using methane (CH.sub.4)
as the carbon raw material, by adjusting a preheating temperature,
there can also be generated via preheating carbon sources for
promoting the synthesis of CNTs, such as acetylene (C.sub.2H.sub.2)
and ethylene (C.sub.2H.sub.4).
[0121] FIG. 32 is a side cross-sectional view of a CNT production
device 1 configured to have a plurality of the catalyst raw
material supplying nozzles 3, as opposed to the CNT production
device 1 of FIG. 31 that has only one catalyst raw material
supplying nozzle 3. FIG. 33 is a top view corresponding to FIG. 32.
Except for the configuration of employing a plurality of the
catalyst raw material supplying nozzles 3, this production device 1
can be configured in a similar manner as FIG. 31. In FIG. 33, the
plurality of the catalyst raw material supplying nozzles 3 are
formed by boring in a cylindrical heat insulation material a
plurality of holes 41 penetrating such heat insulation material
from the upper surface thereof to the lower surface thereof. The
heater 7 is provided in each of the plurality of holes 41, and the
catalyst raw material supplying tube 14 is connected to the upper
portion of each hole. As a method for forming a plurality of the
catalyst raw material supplying nozzles 3, FIG. 34 shows an example
different from FIG. 33. In FIG. 34, each of the plurality of the
catalyst raw material supplying nozzles 3 is individually made of a
cylindrical heat insulation material. The heater 7 is provided
inside each cylindrical heat insulation material, and the catalyst
raw material supplying tube 14 is connected to the upper portion of
each heat insulation material.
[0122] As shown in the working examples 1 to 3, the carbon nanotube
production method of the present invention can be performed using
the production device(s) shown in FIGS. 1 to 3 and FIGS. 31 to 34,
whereby carbon nanotubes can be produced at a high density, high
purity, high quality and high yield.
[0123] The embodiment and working examples of the present invention
have been described as above; the present invention may be
variously modified before exploitation. For example, sizes such as
the diameter and length of the catalyst raw material supplying
nozzle 3, the width and length of the heater 7 provided inside the
catalyst raw material supplying nozzle 3 and the width of the slit
18, are not limited to those shown in FIG. 31, but may be
appropriately configured. There are also no particular restrictions
on the shape of the heater 7; for example, even if it is to be
formed into an inverted U shape, a production method thereof shall
not be limited to the method described above. Other than electric
heating, induction heating or the like may also be employed for
heating the heater 7.
[0124] Further, the production device may also be a device where
the carbon raw material is to be supplied to the synthesis furnace
2 at a low temperature without being preheated, and then rapidly
heated at the synthesis furnace 2.
[0125] Furthermore, only the working example 3 is described as a
specific configuration employing a plurality of the catalyst raw
material supplying nozzles 3; as is the case with the working
example 3, the working examples 1 and 2 may also have a
configuration employing a plurality of the catalyst raw material
supplying nozzles 3.
DESCRIPTION OF THE SYMBOLS
[0126] 1 Carbon nanotube production device [0127] 2 Synthesis
furnace [0128] 3 Catalyst raw material supplying nozzle [0129] 4
Inner portion [0130] 5 Reaction field [0131] 6 Nozzle temperature
adjusting unit [0132] 7 Heater [0133] 8 Heat retention unit [0134]
9 Electrode [0135] 11 Catalyst raw material supplying portion
[0136] 12 Carbon raw material supplying portion [0137] 13 Inert gas
supplying portion [0138] 14 Catalyst raw material supplying tube
[0139] 15 Carbon raw material supplying tube [0140] 17 Carbon raw
material flow passage [0141] 18 Slit [0142] 19 Carbon raw material
flow outlet [0143] 21 Coil [0144] 22 Heat transfer rod [0145] 23
Heat insulation material [0146] 31 Aggregate of CNTs [0147] 32
Single-walled carbon nanotubes (SWCNT) [0148] 41 Hole
* * * * *