Method and device for preparing high-purity carbon nanotubes

Abstract

The invention provides a preparation method and device of a high-purity carbon nanotube. The carbon nanotube is prepared by utilizing a fluidized bed technology, inert gas and hydrogen are introduced into a long-carbon catalyst obtained in a growth section in a degassing stage for degassing reduction, and the removal rate of carbon impurities on the surface of the catalyst in a purification section can be improved, so that the purity of the carbon nanotube can be improved. The device is simple in structure, the fluidized bed technology is adopted in the growth section, the degassing section and the purification section, the fluidization state of the catalyst in the fluidized bed reactor can be regulated and controlled by controlling the process conditions such as temperature and gas speed, continuous preparation of the carbon nanotubes can be achieved, and the production cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of nanomaterial preparation and chemical engineering equipment, and relates to a preparation method and device of high-purity carbon nanotubes. BACKGROUND

[0002] Carbon nanotubes are a kind of nanomaterials with one-dimensional tubular structure, and have become a hotspot in the field of nanomaterials since being discovered.

[0003] The preparation methods of carbon nanotubes include graphite arc method, laser evaporation method and chemical vapor deposition method. The first two methods have low controllability and complex equipment, and are not suitable for industrialization. Only the chemical vapor deposition method can be used for mass production of carbon nanotubes. At present, the chemical vapor deposition method is used to prepare carbon nanotubes in the industry, a fluidized bed is used as a reactor, a supported catalyst is used, raw material gas containing a carbon source is introduced into the fluidized bed, the carbon source is catalytically cracked on the surface of the catalyst at high temperature and grows into carbon nanotubes through a self-assembly process, as shown in FIG. 1, and a large amount of hydrogen is produced as a byproduct. The grown carbon nanotubes are firmly attached to the surface of the catalyst, which is recorded as a growth stage. Figure 1

[0004] The growth of carbon nanotubes in the fluidized bed using the supported catalyst is usually accompanied by catalyst deactivation, which causes carbon-coated iron and amorphous carbon impurities, thereby affecting the performance of the carbon nanotubes. Therefore, the long-carbon catalyst obtained in the growth stage is usually treated by a purification process to remove carbon impurities, that is, the carbon impurities on the surface of the catalyst are removed by carbon burning in an oxidizing atmosphere to obtain a catalyst containing high-purity carbon nanotubes, that is, a purification product. This stage is recorded as a purification stage. Finally, the catalyst is removed from the purification product to obtain high-purity carbon nanotubes.

[0005] However, in actual preparation, the purity of the obtained carbon nanotubes is still low even after the purification stage, and needs to be further improved. SUMMARY

[0006] In view of the above technical status, the present application aims to improve the purity of carbon nanotubes when preparing carbon nanotubes by using a fluidized bed technology.

[0007] In order to achieve the technical purpose, the present inventors found through a large number of experimental explorations that when preparing carbon nanotubes by using a fluidized bed technology, the long-carbon catalyst obtained in the growth stage is first introduced into an inert gas for degassing treatment to remove unreacted carbon source gas (this stage is recorded as a degassing stage), and then is treated by purification, which is beneficial to improving the purity of the carbon nanotubes. When hydrogen is introduced at the same time in the degassing treatment, the deactivated catalytically active components can be reduced, and the carbon burning efficiency in the purification process is increased, thereby further improving the purity of the carbon nanotubes, and high-purity carbon nanotubes are obtained.

[0008] ​That is, the technical solution of the present invention is: a method for preparing high-purity carbon nanotubes, employing a three-stage fluidized bed technology, comprising the following steps:

[0009] (1) The first fluidized bed reactor is loaded with an activated catalyst and a raw gas containing a carbon source is introduced. The carbon source grows fluidized on the surface of the activated catalyst at 600℃-1000℃ to obtain a catalyst with long carbon (including carbon nanotubes and carbon impurities).

[0010] (2) The long carbon catalyst obtained in step (1) is transported to the second fluidized bed reactor, and inert gas and hydrogen are introduced to carry out degassing treatment to remove the unreacted carbon source gas loaded in the catalyst and obtain the degassed long carbon catalyst.

[0011] (3) The degassed long carbon catalyst obtained in step (2) is transported to the third sulfidation bed reactor and purified under an oxidizing atmosphere to remove carbon impurities on the catalyst surface and obtain a catalyst containing high-purity carbon nanotubes.

[0012] The structure of the carbon nanotubes is not limited, including one or more of single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes.

[0013] The catalyst is not limited and includes a catalytically active material supported on a metal oxide. The metal oxide is not limited and includes MgO, Al2O3, or a metal oxide formed by Mg and Al in any ratio. The catalytically active material is a group VIII element, such as one or more of Fe, Co, and Ni.

[0014] The inert gas is not limited, and includes one or more of N2 (nitrogen), Ar (argon), and He (helium).

[0015] The carbon source is not limited and includes one or more of the following: carbon monoxide (CO), alkane gases with 1-4 carbon atoms in the molecule, olefin gases with 2-4 carbon atoms in the molecule, acetylene, natural gas, liquefied petroleum gas, benzene, methanol, and ethanol.

[0016] The oxidizing gas includes one or more of O2 (oxygen), air, H2O, and CO2.

[0017] In step (1), the activated catalyst refers to the catalyst after activation treatment. Preferably, the activation treatment method is as follows: heating the first fluidized bed reactor to 600℃-1000℃, adding the carbon nanotube catalyst at this temperature, and then activating it by introducing hydrogen and an inert gas. Preferably, the volumetric flow rate ratio of hydrogen to inert gas is (0.2-2):(0.5-5). Preferably, the space velocity during the activation process is 1-10000 h⁻¹. -1 (Hour-1 The gas velocity of the mixed gas is 0.01 m / s to 10 m / s. Preferably, the activation time is 5 to 30 minutes.

[0018] In step (1), the flow rate ratio of the introduced carbon source to the inert gas is (0.5-2):(0.5-5). Preferably, the space velocity during the carbon nanotube growth process is 1 h⁻¹. -1 -10000h -1 Preferably, the gas velocity of the mixture of carbon source and inert gas is 0.01 m / s to 5 m / s. Preferably, the carbon nanotube growth time is 5 minutes to 120 minutes.

[0019] In step (2), preferably, the flow rate ratio of the introduced hydrogen gas to the inert gas is (0.2-2):(0.5-5).

[0020] In step (2), preferably, the space velocity during the degassing process is 1 h⁻¹. -1 -10000h -1 .

[0021] In step (2), preferably, the gas velocity of the mixture of hydrogen and inert gas is 0.01 m / s to -3 m / s.

[0022] In step (2), preferably, the catalyst in the degassing section exchanges heat with hydrogen and inert gas, and the degassing time is 15 min-60 min, so that the catalyst temperature is controlled at 200℃-350℃.

[0023] In step (3), preferably, the purification temperature is controlled between 300℃ and 600℃. Preferably, the space velocity of the oxidizing gas is 1 h⁻¹. -1 -10000h -1 The gas flow rate is 0.01 m / s to 3 m / s. Preferably, the oxidation purification time is 30 min to 120 min.

[0024] The carbon nanotubes obtained in step (3) adhere to the catalyst surface. Preferably, the catalyst is then removed. The method for removing the catalyst is not limited; generally, non-oxidizing acids and bases are used for liquid-phase purification, followed by filtration and drying to obtain pure carbon nanotubes with the catalyst removed. The non-oxidizing acids include, but are not limited to, one or more of hydrochloric acid, dilute sulfuric acid, phosphoric acid, and acetic acid. The non-oxidizing acids include, but are not limited to, one or two of sodium hydroxide and potassium hydroxide.

[0025] There are various methods for characterizing carbon nanotubes, commonly including Raman spectroscopy, BET (specific surface area measurement), TGA (thermogravimetric analysis), and SEM (scanning electron microscopy). Raman spectroscopy characterizes the GD ratio (the ratio of the G peak to the D peak) of carbon nanotubes. A higher GD ratio indicates a higher degree of graphitization and fewer defects in the carbon nanotubes. It can also indirectly verify that the carbon nanotube content is higher than that of heterogeneous carbon. Different types of carbon nanotubes have different specific surface areas; for example, single-walled carbon nanotubes have a theoretical specific surface area as high as 1300 m². 2 The specific surface area of ​​carbon nanotubes is approximately 1 g, so its purity can be indicated by BET (Biological Emission Spectrometry). Additionally, SEM (Sequencing Electron Microscopy) can be used to observe the microstructure of carbon nanotubes, providing a clear visual indication of the amount of impurities present.

[0026] The present invention also provides an apparatus for preparing high-purity carbon nanotubes, comprising a first fluidized bed reactor, a second fluidized bed reactor and a third fluidized bed reactor;

[0027] The first fluidized bed reactor is provided with a first feed inlet, a first discharge outlet, a first gas inlet, and a first gas outlet;

[0028] The second fluidized bed reactor is equipped with a second feed inlet, a second discharge outlet, a second gas inlet, and a second gas outlet;

[0029] The third fluidized bed reactor is equipped with a third feed inlet, a third discharge outlet, a third gas inlet, and a third gas outlet;

[0030] The first feed inlet is connected to the first silo via a feed valve, the first discharge outlet is connected to the second feed inlet via a first discharge valve, the second discharge outlet is connected to the third feed inlet via a second discharge valve, and the third discharge outlet is connected to the second silo via a third discharge valve.

[0031] Preferably, the first gas inlet is located at the bottom of the first fluidized bed reactor, and the first gas outlet is located at the top of the first fluidized bed reactor.

[0032] Preferably, the second gas inlet is located at the bottom of the second fluidized bed reactor, and the second gas outlet is located at the top of the second fluidized bed reactor.

[0033] Preferably, the third gas inlet is located at the bottom of the third fluidized bed reactor, and the third gas outlet is located at the top of the third fluidized bed reactor.

[0034] Preferably, the first gas outlet is provided with a first filter element, and the gas in the first fluidized bed reactor is output from the first gas outlet after passing through the first filter element.

[0035] Preferably, the second gas outlet is equipped with a second filter element, and the gas in the second fluidized bed reactor is output from the second gas outlet after passing through the second filter element.

[0036] Preferably, the third gas outlet is equipped with a third filter element, and the gas in the third fluidized bed reactor is output from the third gas outlet after passing through the third filter element.

[0037] Preferably, the first discharge port is connected to the second inlet port through a first riser pipe.

[0038] Preferably, the second discharge port is connected to the third inlet port through the second riser pipe.

[0039] Preferably, the third discharge port is connected to the second hopper via a third lifting pipe.

[0040] Preferably, the gas output from the first gas outlet can be recycled and reused.

[0041] Preferably, the gas output from the second gas outlet in the degassing section includes unreacted carbon source gas. Since the degassing section completes heat exchange, the output gas contains heat. Therefore, it is preferred to reuse the gas as raw material for the growth section to maximize energy utilization.

[0042] Preferably, the gas output from the third gas outlet can be recycled and reused.

[0043] The production of high-purity carbon nanotubes using the apparatus of the present invention includes the following steps:

[0044] (1) Catalyst activation

[0045] The first silo contains the catalyst. The feed valve is opened to deliver the catalyst to the first fluidized bed reactor. Hydrogen and inert gas are introduced through the first gas inlet to activate the catalyst at 600℃-1000℃. After activation, the hydrogen input is stopped.

[0046] (2) Carbon nanotube growth

[0047] Carbon source gas is introduced through the first gas inlet, and carbon nanotubes are grown at 600℃-1000℃; after growth is completed, the carbon source gas input is stopped.

[0048] (3) Material transfer and degassing

[0049] Open the first discharge valve to deliver the long carbon catalyst to the second fluidized bed reactor, and introduce inert gas and hydrogen through the second gas inlet for degassing; after degassing is completed, stop the hydrogen input;

[0050] (4) Gas phase purification

[0051] Open the second discharge valve to transport the degassed long-carbon catalyst to the third fluidized bed reactor, and introduce inert gas and oxidizing gas through the third gas inlet for purification treatment; after the purification treatment is completed, stop the oxidizing gas input;

[0052] (5) Material transfer output

[0053] Open the third discharge valve to deliver the purified catalyst to the second silo, and obtain a catalyst containing high-purity carbon nanotubes.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] (1) In the preparation of carbon nanotubes using fluidized bed technology, the catalyst with long carbon obtained in the growth section is first degassed by passing an inert gas to remove the unreacted carbon source gas loaded in the catalyst. At the same time, hydrogen is passed in and the deactivated catalyst surface is reduced by hydrogen at a certain temperature, thereby increasing the efficiency of carbon burning in the purification oxidation process. This results in carbon nanotubes with high GD ratio, high specific surface area and low impurities, which greatly improves the purity of carbon nanotubes.

[0056] (2) The high-purity carbon nanotube preparation device provided by the present invention realizes that the growth section, degassing section and purification section all adopt fluidized bed technology. It can control the fluidization state of the catalyst in the fluidized bed reactor by controlling process conditions such as temperature and gas velocity, and can realize the continuous preparation of carbon nanotubes, thereby reducing production costs. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of the catalytic cracking and growth of carbon nanotubes from a carbon source on the catalyst surface.

[0058] Figure 2 This is a schematic diagram of the apparatus for preparing carbon nanotubes in Embodiment 1 of the present invention.

[0059] Figure 3 This is a process flow diagram of carbon nanotube preparation in Examples 2, 3, and 4 of the present invention.

[0060] Figure 4 The images show a comparison of SEM images of carbon nanotubes obtained after removing the catalyst from the catalysts containing high-purity carbon nanotubes obtained in Example 4 and Comparative Example 4.

[0061] Figure 2 The attached diagrams are labeled as follows: 1. First silo; 2. First fluidized bed reactor; 3. Second fluidized bed reactor; 4. Third fluidized bed reactor; 5. Second silo; 6. Feed valve.

[0062] First feed inlet 11, first discharge outlet 12, first gas inlet 13, first gas outlet 14, first air inlet valve 15, first air outlet valve 16, first discharge valve 17, first filter element 18, first elevator 19;

[0063] Second feed inlet 21, second discharge outlet 22, second gas inlet 23, second gas outlet 24, second air inlet valve 25, second air outlet valve 26, second discharge valve 27, second filter element 28, second elevator 29;

[0064] Third feed inlet 31, third discharge outlet 32, third gas inlet 33, third gas outlet 34, third air inlet valve 35, third air outlet valve 36, third discharge valve 37, third filter element 38, third elevator 39. Detailed Implementation

[0065] The present invention will be further described in detail below with reference to the embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention. Non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above description of the present invention are still within the protection scope of the present invention.

[0066] Example 1:

[0067] Devices for preparing carbon nanotubes, such as Figure 2 As shown, it includes a first silo 1, a first fluidized bed reactor 2, a second fluidized bed reactor 3, a third fluidized bed reactor 4, and a second silo 5.

[0068] The first fluidized bed reactor 2 is provided with a first feed inlet 11, a first discharge outlet 12, a first gas inlet 13, and a first gas outlet 14. The first feed inlet 11 is connected to the first hopper 1 through a feed valve 6. External gas is connected to the first gas inlet 13 through a first inlet valve 15. A first filter element 18 is installed inside the first fluidized bed reactor 1 near the first gas inlet 13; the first gas outlet 14 is connected to a first outlet valve 16 outside the first fluidized bed reactor. A first discharge valve 17 and a first elevator 19 are sequentially installed between the first discharge outlet 12 and the second feed inlet 21.

[0069] The second fluidized bed reactor 3 is equipped with a second feed inlet 21, a second discharge outlet 22, a second gas inlet 23, and a second gas outlet 24. External gas is connected to the second gas inlet 23 via a second inlet valve 25. A second filter element 28 is installed inside the second fluidized bed reactor 3 near the second gas inlet 23. The second gas outlet 24 is connected to a second outlet valve 26 outside the second fluidized bed reactor. A second discharge valve 27 and a second elevator 29 are sequentially installed between the second discharge outlet 22 and the third feed inlet 31.

[0070] The third fluidized bed reactor 4 is equipped with a third feed inlet 31, a third discharge outlet 32, a third gas inlet 33, and a third gas outlet 34. External gas is connected to the third gas inlet 33 via a third inlet valve 35. A third filter element 38 is installed inside the third fluidized bed reactor near the third gas inlet 33; the third gas outlet 34 is connected to a third outlet valve 36 outside the third fluidized bed reactor. A third discharge valve 37 and a third elevator 39 are sequentially installed between the third discharge outlet 32 ​​and the second hopper 5.

[0071] The preparation of carbon nanotubes using the apparatus in Example 1 includes the following steps:

[0072] (1) Catalyst activation

[0073] The catalyst is contained in the first silo 1. The feed valve 6 is opened, and the catalyst is fed into the first fluidized bed reactor 2 through the first feed port 11. The first gas inlet valve 15 is opened, and hydrogen and inert gas are introduced through the first gas inlet 13 to activate the catalyst at high temperature. After activation is complete, the hydrogen supply is stopped.

[0074] (2) Carbon nanotube growth

[0075] Raw material gas containing carbon source is introduced through the first gas inlet 13, and carbon nanotubes are grown at high temperature; after growth is completed, the input of carbon source is stopped.

[0076] (3) Material transfer and degassing

[0077] Open the first discharge valve 17 and introduce nitrogen into the first elevator 19 to transport the activated catalyst to the first fluidized bed reactor 2; open the second inlet valve 25 and introduce inert gas and hydrogen through the second gas inlet 23 for degassing; after degassing is completed, stop the input of hydrogen.

[0078] (4) Gas phase purification

[0079] Open the second discharge valve 27, and nitrogen gas is introduced into the second elevator 29. Under the action of the second elevator 29, the degassed catalyst is transported from the second discharge port 22 to the third fluidized bed reactor 2. Open the third inlet valve 25, and oxidizing gas is introduced through the third gas inlet 33 for purification treatment. After the purification treatment is completed, the input of oxidizing gas is stopped.

[0080] (5) Material transfer output

[0081] Open the third discharge valve 37, and nitrogen gas is introduced into the third elevator 39. Under the action of the third elevator 29, the purified catalyst is transported from the third discharge port 32 to the second silo 5 to obtain a catalyst containing high-purity carbon nanotubes.

[0082] Example 2:

[0083] Carbon nanotubes were prepared using the apparatus described in Example 1, and the process flow is as follows: Figure 3 As shown, it includes the following steps:

[0084] (1) Catalyst activation

[0085] The first fluidized bed reactor was heated to 750°C. At this temperature, the multi-walled carbon nanotube catalyst from the first silo was transported to the first fluidized bed reactor. The catalyst density was 210 kg / m³. 3 The mass is 1.2 kg; a mixture of hydrogen and nitrogen is introduced through the first gas inlet, with a volume flow ratio of hydrogen:nitrogen = 1:4, and the space velocity during the activation process is 525 h⁻¹. -1 The gas velocity of the mixed gas was 0.024 m / s, and the activation time was 15 minutes.

[0086] (2) Carbon nanotube growth

[0087] After activation, a mixture of propylene and nitrogen is introduced through the first gas inlet, with the volumetric flow rate ratio of the mixture controlled at propylene:nitrogen = 1:0.8, and the space velocity during carbon nanotube growth is 525 h⁻¹. -1 The gas velocity of the mixed gas was 0.024 m / s, the carbon nanotube growth time was 60 minutes, and then the carbon source propylene was stopped.

[0088] (3) Material transfer and degassing

[0089] Open the first discharge valve to transfer the long-carbon catalyst in the first fluidized bed reactor to the second fluidized bed reactor;

[0090] In the second fluidized bed reactor, hydrogen and nitrogen are introduced through the second gas inlet at a volumetric flow rate ratio of hydrogen:nitrogen = 1:4, and the space velocity during the degassing process is 420 h⁻¹. -1 The gas velocity of the mixed gas is 0.0127 m / s, the degassing time is 20 min, then the hydrogen supply is stopped, the second outlet valve is opened, and the tail gas in the second fluidized bed reactor is filtered by the second filter element and discharged to the first gas inlet through the second gas outlet. That is, the tail gas of the degassing section is reused as the raw material gas of the growth section.

[0091] (4) Gas phase purification

[0092] Open the second discharge valve to transfer the degassed catalyst from the second fluidized bed reactor to the third fluidized bed reactor. Air and nitrogen are introduced into the third fluidized bed reactor for carbonization and impurity removal. The volumetric flow rate ratio of air to nitrogen is 1:2, the O2 concentration is 7%, the carbonization temperature is controlled at 520℃-540℃, and the space velocity of the mixed gas is 700 h⁻¹. -1 The air velocity was 0.0212 m / s, the oxidation and purification time was 50 min, and then the air supply was stopped.

[0093] (5) Material transfer output

[0094] Open the third discharge valve to transfer the purified catalyst from the third fluidized bed reactor to the second silo to obtain a catalyst containing high-purity carbon nanotubes.

[0095] Comparative Example 2:

[0096] This embodiment is a comparative embodiment of Embodiment 2.

[0097] In this embodiment, the preparation method of carbon nanotubes is basically the same as that in Example 1. The difference is that in the material transfer and degassing in step (3), only nitrogen gas is introduced into the second gas inlet, and hydrogen gas is not introduced.

[0098] Example 3:

[0099] The preparation of carbon nanotubes using the apparatus in Example 1 includes the following steps:

[0100] (1) Catalyst activation

[0101] The first fluidized bed reactor was heated to 820℃, and at this temperature, the double-walled carbon nanotube catalyst in the first silo was transported to the first fluidized bed reactor. The catalyst density was 190 kg / m³. 3 The mass is 1.0 kg; a mixture of hydrogen and nitrogen is introduced through the first gas inlet, with a volume flow ratio of hydrogen:nitrogen = 1:2, and the space velocity during the activation process is 570 h⁻¹. -17 (Hour -1 The gas velocity of the mixed gas was 0.024 m / s, and the activation time was 20 minutes.

[0102] (2) Carbon nanotube growth

[0103] After activation, a mixture of ethane and argon is introduced through the first gas inlet, with the volumetric flow rate ratio of the mixture controlled at ethane:argon = 1:1. The space velocity during carbon nanotube growth is 570 h⁻¹. -1 The gas velocity of the mixed gas was 0.024 m / s, the carbon nanotube growth time was 30 minutes, and then the carbon source propylene was stopped.

[0104] (3) Material transfer and degassing

[0105] Open the first discharge valve to transfer the long-carbonized catalyst from the first fluidized bed reactor to the second fluidized bed reactor;

[0106] In the second fluidized bed reactor, hydrogen and nitrogen are introduced through the second gas inlet at a volumetric flow rate ratio of hydrogen:nitrogen = 1:2, and the space velocity during the degassing process is 475 h⁻¹. -1The gas velocity of the mixed gas is 0.0133 m / s, the degassing time is 20 min, then the hydrogen supply is stopped, the second outlet valve is opened, and the tail gas in the second fluidized bed reactor is filtered by the second filter element and discharged to the first gas inlet through the second gas outlet. That is, the tail gas of the degassing section is reused as the raw material gas of the growth section.

[0107] (4) Gas phase purification

[0108] Open the second discharge valve to transfer the degassed catalyst from the second fluidized bed reactor to the third fluidized bed reactor. Air, nitrogen, and water are introduced into the third fluidized bed reactor for carbonization and impurity removal. The volumetric flow rate ratio of air, nitrogen, and water is 1:2:0.2, the O2 concentration is 6.56%, the carbonization temperature is controlled at 500℃-520℃, and the space velocity of the mixed gas is 760 h⁻¹. -1 The air velocity was 0.0213 m / s, the oxidation and purification time was 45 min, and then the air supply was stopped.

[0109] (5) Material transfer output

[0110] Open the third discharge valve to transfer the purified catalyst from the third fluidized bed reactor to the second silo to obtain a catalyst containing high-purity carbon nanotubes.

[0111] Comparative Example 3:

[0112] This embodiment is a comparative embodiment of embodiment 3.

[0113] In this embodiment, the preparation method of carbon nanotubes is basically the same as that in Example 2. The difference is that in the material transfer and degassing in step (3), only nitrogen gas is introduced into the second gas inlet, and hydrogen gas is not introduced.

[0114] Example 4:

[0115] The preparation of carbon nanotubes using the apparatus in Example 1 includes the following steps:

[0116] (1) Catalyst activation

[0117] The first fluidized bed reactor was heated to 950°C. At this temperature, the single-walled carbon nanotube catalyst from the first silo was transported to the first fluidized bed reactor. The catalyst density was 180 kg / m³. 3 The mass is 0.8 kg; a mixture of hydrogen and argon is introduced through the first gas inlet, with a volumetric flow rate ratio of hydrogen:argon = 2:1, and the space velocity during the activation process is 630 h⁻¹. -17 (Hour -1 The gas velocity of the mixed gas was 0.022 m / s, and the activation time was 20 minutes.

[0118] (2) Carbon nanotube growth

[0119] After activation, a mixture of methane and argon is introduced through the first gas inlet, with the volumetric flow rate ratio of the mixture controlled at methane:argon = 0.5:1. The space velocity during carbon nanotube growth is 630 h⁻¹. -1 The gas velocity of the mixed gas was 0.022 m / s, the carbon nanotube growth time was 20 minutes, and then the methane supply was stopped.

[0120] (3) Material transfer and degassing

[0121] Open the first discharge valve to transfer the long-carbonized catalyst from the first fluidized bed reactor to the second fluidized bed reactor;

[0122] In the second fluidized bed reactor, hydrogen and nitrogen are introduced through the second gas inlet at a volumetric flow rate ratio of hydrogen:nitrogen = 2:1, and the space velocity during the degassing process is 585 h⁻¹. -1 The gas velocity of the mixed gas is 0.0138 m / s, the degassing time is 20 min, then the hydrogen supply is stopped, the second outlet valve is opened, and the tail gas in the second fluidized bed reactor is filtered by the second filter element and discharged to the first gas inlet through the second gas outlet. That is, the tail gas of the degassing section is reused as the raw material gas of the growth section.

[0123] (4) Gas phase purification

[0124] Open the second discharge valve to transfer the degassed catalyst from the second fluidized bed reactor to the third fluidized bed reactor. Air, nitrogen, and carbon dioxide are introduced into the third fluidized bed reactor for carbonization and impurity removal. The volumetric flow rate ratio of air, nitrogen, and carbon dioxide is 1:2:0.1, the O2 concentration is 6.77%, the carbonization temperature is controlled at 500-510℃, and the space velocity of the mixed gas is 720 h⁻¹. -1 The air velocity was 0.017 m / s, the oxidation and purification time was 70 min, and then the air supply was stopped.

[0125] (5) Material transfer output

[0126] Open the third discharge valve to transfer the purified catalyst from the third fluidized bed reactor to the second silo to obtain a catalyst containing high-purity carbon nanotubes.

[0127] Comparative Example 4:

[0128] This embodiment is a comparative embodiment of embodiment 4.

[0129] In this embodiment, the preparation method of carbon nanotubes is basically the same as that in Example 4. The difference is that in the material transfer and degassing in step (3), only nitrogen gas is introduced into the second gas inlet, and hydrogen gas is not introduced.

[0130] The catalysts containing high-purity carbon nanotubes obtained in Examples 2-4 and Comparative Examples 2-4 were subjected to catalyst removal by using hydrochloric acid and sodium hydroxide for liquid-phase purification. Finally, after filtration and drying, pure carbon nanotubes with catalyst removed were obtained.

[0131] The carbon nanotubes obtained were characterized by Raman and BET methods, and the results are shown in Table 1 below:

[0132] Table 1: Test results of performance parameters for the examples and comparative examples.

[0133]

[0134]

[0135] Table 1 shows that after carbon nanotubes are grown in the growth section, they are first degassed and then purified. In the degassed section, both inert gas and hydrogen are introduced, compared to the degassed section where only inert gas is introduced:

[0136] (1) The GD ratio and specific surface area of ​​the carbon nanotubes obtained were significantly increased, indicating that the impurities in the carbon nanotubes were significantly reduced and the purity of the carbon nanotubes increased significantly.

[0137] (2) SEM images of the obtained carbon nanotubes show that, in addition to inert gas, hydrogen gas was introduced into the degassing section, resulting in a significant reduction in impurities in the obtained carbon nanotubes. For example, a comparison image of Example 4 and Comparative Example 4 is shown below. Figure 4 As shown, (a) is a SEM image of the carbon nanotubes obtained in Example 4, and (b) is a SEM image of the carbon nanotubes obtained in Comparative Example 4. It can be seen that compared with Comparative Example (4) in which only inert gas is introduced in the degassing section, the carbon nanotubes obtained in Example 4 in which not only inert gas but also hydrogen gas is introduced in the degassing section have significantly reduced impurities.

[0138] Since the residence time of the growth section and the degassing section is generally not matched with that of the purification section, the residence time of the catalyst in the purification section is usually 2-3 times the sum of the residence times of the growth section and the degassing section. In this embodiment, the size of the second fluidized bed reactor and the third fluidized bed reactor is designed to be 1.5-2 times that of the first fluidized bed reactor in order to meet the requirements of continuous production.

[0139] The above embodiments provide a detailed description of the technical solution of the present invention. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-purity carbon nanotubes, characterized in that: The three-stage fluidized bed technology includes the following steps: (1) The first fluidized bed reactor is loaded with an activated catalyst and a raw gas containing a carbon source is introduced. The carbon source grows fluidized on the surface of the activated catalyst at 600℃-1000℃ to obtain a long carbon catalyst. (2) The long carbon catalyst obtained in step (1) is transported to the second fluidized bed reactor and degassed by introducing inert gas and hydrogen to remove the unreacted carbon source gas loaded in the catalyst and obtain the degassed long carbon catalyst. (3) The degassed long carbon catalyst obtained in step (2) is transported to the third sulfide bed reactor and purified under an oxidizing atmosphere to remove carbon impurities on the catalyst surface and obtain a catalyst containing high-purity carbon nanotubes.

2. The preparation method according to claim 1, characterized in that: The carbon nanotube structure includes one or more of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes. Preferably, the carbon source is one or more of the following: carbon monoxide, alkane gas with 1-4 carbon atoms in the molecule, olefin gas with 2-4 carbon atoms in the molecule, acetylene, natural gas, liquefied petroleum gas, benzene, methanol, and ethanol.

3. The preparation method according to claim 1, characterized in that: In step (2), the flow rate ratio of the introduced hydrogen gas to the inert gas is (0.2-2):(0.5-5); Preferably, in step (2), the catalyst temperature is controlled at 200℃-350℃.

4. The preparation method according to claim 1, characterized in that: In step (2), the space velocity during the degassing process is 1 h⁻¹. -1 -10000h -1 ; Preferably, in step (2), the gas velocity of the mixture of hydrogen and inert gas is 0.01 m / s to 3 m / s.

5. The preparation method according to claim 1, characterized in that: The catalyst containing high-purity carbon nanotubes obtained in step (3) is subjected to catalyst removal to obtain pure carbon nanotubes; As a preferred method, the catalyst containing high-purity carbon nanotubes is purified in the liquid phase using non-oxidizing acids and bases, and then filtered and dried to obtain pure carbon nanotubes. Preferably, the non-oxidizing acid includes one or more of hydrochloric acid, dilute sulfuric acid, phosphoric acid, and acetic acid; Preferably, the non-oxidizing alkali includes one or both of sodium hydroxide and potassium hydroxide.

6. An apparatus for implementing the method for preparing high-purity carbon nanotubes according to any one of claims 1 to 5, characterized in that: It includes a first fluidized bed reactor, a second fluidized bed reactor, and a third fluidized bed reactor; The first fluidized bed reactor is provided with a first feed inlet, a first discharge outlet, a first gas inlet, and a first gas outlet; The second fluidized bed reactor is equipped with a second feed inlet, a second discharge outlet, a second gas inlet, and a second gas outlet; The third fluidized bed reactor is equipped with a third feed inlet, a third discharge outlet, a third gas inlet, and a third gas outlet; The first feed inlet is connected to the first silo via a feed valve, the first discharge outlet is connected to the second feed inlet via a first discharge valve, the second discharge outlet is connected to the third feed inlet via a second discharge valve, and the third discharge outlet is connected to the second silo via a third discharge valve.

7. The apparatus as claimed in claim 6, characterized in that: The first gas inlet is located at the bottom of the first fluidized bed reactor, and the first gas outlet is located at the top of the first fluidized bed reactor; Preferably, the second gas inlet is located at the bottom of the second fluidized bed reactor, and the second gas outlet is located at the top of the second fluidized bed reactor; Preferably, the third gas inlet is located at the bottom of the third fluidized bed reactor, and the third gas outlet is located at the top of the third fluidized bed reactor.

8. The apparatus as claimed in claim 6, characterized in that: The first gas outlet is equipped with a first filter element, and the gas in the first fluidized bed reactor is output from the first gas outlet after passing through the first filter element. Preferably, the second gas outlet is provided with a second filter element, and the gas in the second fluidized bed reactor is output from the second gas outlet after passing through the second filter element. Preferably, the third gas outlet is equipped with a third filter element, and the gas in the third fluidized bed reactor is output from the third gas outlet after passing through the third filter element.

9. The apparatus as claimed in claim 6, characterized in that: The first discharge port is connected to the second inlet port through the first lift pipe; Preferably, the second discharge port is connected to the third inlet port through a second riser pipe; Preferably, the third discharge port is connected to the second hopper via a third lifting pipe.

10. The apparatus as claimed in claim 6, characterized in that: The gas output from the second gas outlet is reused as the raw material gas for the growth section; Preferably, the gas output from the first gas outlet is recycled and reused; Preferably, the gas output from the third gas outlet is recycled and reused.

11. A method of using the apparatus according to any one of claims 6 to 10, characterized in that: Includes the following steps: (1) The catalyst is contained in the first silo. The feed valve is opened and the catalyst is transported to the first fluidized bed reactor. Hydrogen and inert gas are introduced through the first gas inlet and the catalyst is activated at 600℃-1000℃. After activation is complete, stop the hydrogen input; (2) Input raw material gas containing carbon source through the first gas inlet and grow carbon nanotubes at 600℃-1000℃; after growth is completed, stop inputting carbon source. (3) Open the first discharge valve to transport the long carbon catalyst to the second fluidized bed reactor, and degas it by introducing inert gas and hydrogen through the second gas inlet; after degassing is completed, stop the hydrogen input; (4) Open the second discharge valve and transport the degassed long carbon catalyst to the third fluidized bed reactor. Inert gas and oxidizing gas are introduced through the third gas inlet for purification treatment. After the purification treatment is completed, the oxidizing gas input is stopped. (5) Open the third discharge valve and transport the purified catalyst to the second silo to obtain a catalyst containing high-purity carbon nanotubes.

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