CN110642243B - Carbon nano tube purified by rotary binary secondary gas phase method and purification method - Google Patents
Carbon nano tube purified by rotary binary secondary gas phase method and purification method Download PDFInfo
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Abstract
The invention belongs to the technical field of carbon nanotube purification, and particularly relates to a carbon nanotube purified by a rotary binary gas-phase method and a purification method. The present invention converts the catalyst metal remaining in the carbon nanotube into metal oxide in a single time under the conditions of oxygen enrichment and certain temperature, and utilizes the strong oxidizing property of hydrogen chloride gas in a two-time mode to firstly react the metal catalyst remaining in the carbon nanotube under the heating condition to generate chloride and water, and then utilizes the characteristic that the gasification temperature of the metal chloride is far lower than that of the metal and the oxide thereof to gasify the metal chloride and separate the metal chloride from the carbon nanotube by heating, thereby achieving the purpose of purifying the carbon nanotube. The method is simple, the productivity is easy to amplify, the pollution is small, the engineering is easy, the purification effect is good, and the method is suitable for removing various residual metals in various carbon nano tubes. The carbon nano tube has high purity, wherein the content of single metal impurities is less than 20 ppm.
Description
Technical Field
The invention belongs to the technical field of carbon nanotube purification, and particularly relates to a carbon nanotube purified by a rotary binary gas-phase method and a purification method.
Background
The carbon nano tube is a novel material which is attractive to the world, has an ultra-large specific surface area, light weight, but ultra-strong mechanical strength, excellent conductivity and good physical and chemical stability, and has wide application prospects in the fields of lithium ion battery conductive agents, catalyst carriers, drug carriers, reinforced blending materials, electronic devices and the like.
Carbon nanotubes have been produced by Chemical Vapor Deposition (CVD) at low cost in large quantities. However, the catalyst metal (mainly Fe-based, Ni-based, Co-based, and the like) used in the CVD method remains in the carbon nanotube and is often coated on the end portion of the carbon nanotube. This has severely hindered the application of carbon nanotubes in some industries where the requirements for metal impurities are high, such as in lithium ion battery conductive agents and precision electronic devices. The existing carbon nanotube purification methods mainly comprise three types: one is an acid cleaning purification method, which mainly uses hydrochloric acid and other strong acids to dissolve residual metal catalyst, and then filters and separates, the method can only purify carbon nano tubes to a certain extent, and is difficult to completely remove the metal catalyst with thicker carbon layer coating, and simultaneously, the method can generate a large amount of waste acid and waste water to cause environmental pollution; the second method is to adopt a high-temperature heat treatment purification method, heat-treat the carbon nano-tube at a temperature of more than 2800 ℃ to gasify the residual metal catalyst, thereby achieving the purpose of purifying the carbon nano-tube, the carbon nano-tube obtained by the method has high purity but high energy consumption, and simultaneously, the excessive treatment temperature causes the carbon atoms in the carbon nano-tube to be rearranged, causing some unpredictable property changes; the third method is to utilize the strong oxidizing property of chlorine, firstly the residual metal catalyst in the carbon nano tube reacts to generate chloride under the normal temperature or the heating condition, then the gasification temperature of the metal chloride is far lower than the gasification temperature of the metal and the oxide thereof, and the chloride is gasified and separated from the carbon nano tube by heating, thereby achieving the purpose of purifying the carbon nano tube, and the method has two difficulties in engineering application: firstly, chlorine is extremely toxic, brings great safety risk to use, so the procedure for handling and using chlorine is complicated, and simultaneously, the requirement on use quality is high, so that a high threshold is invisibly set for the use of the technology, and the popularization and the use of the technology are not facilitated; secondly, chlorine has strong corrosive oxidizability at high temperature, and almost all metals cannot be used, which greatly hinders the engineering popularization and application of the technology.
Disclosure of Invention
The invention provides a method for purifying carbon nanotubes by a rotary binary secondary gas phase method, which is simple in operation, low in energy consumption, small in pollution and easy to engineer, and the carbon nanotubes obtained by purification by the method, aiming at the problems of high energy consumption and serious pollution of the traditional strong acid washing and high-temperature gasification and carbon nanotube purification by chlorine.
A method for purifying carbon nano tube by rotary binary gas phase method is carried out by rotary furnace for ensuring that metallic impurities of carbon nano tube catalyst are fully oxidized for one time and metallic oxide of carbon nano tube catalyst is fully reacted with chloridization for two times. The method specifically comprises the following steps:
(1) placing the carbon nano tube in a furnace tube of a rotary furnace, heating to 310-320 ℃, introducing dry compressed air into the furnace tube, ensuring the furnace tube to rotate in the reaction process, oxidizing residual metal catalyst in the carbon nano tube into metal oxide, keeping the temperature for a certain time, and cooling to obtain a primary carbon nano tube;
(2) placing the unary secondary carbon nano tube obtained in the step (1) in a rotary furnace tube again, ensuring that the furnace tube rotates in the reaction process, introducing nitrogen into the furnace tube to replace oxygen in the furnace tube, ensuring that the oxygen content in the furnace tube is lower than 1%, heating the unary secondary carbon nano tube in the furnace tube to 300-1100 ℃, introducing hydrogen chloride gas, and contacting a catalyst metal oxide in the unary secondary carbon nano tube with the hydrogen chloride gas to generate metal chloride and water to obtain a binary secondary carbon nano tube;
(3) and (3) keeping the heating temperature of the furnace tube at 300-1100 ℃, changing the metal chloride into gaseous metal chloride, introducing nitrogen into the furnace tube of the rotary furnace in the step (2), volatilizing the gaseous metal chloride adsorbed by the binary carbon nanotube from the carbon nanotube, removing unreacted redundant hydrogen chloride gas, continuously introducing the nitrogen for a period of time, and cooling to normal temperature to obtain the purified carbon nanotube.
The invention converts the catalyst metal remained in the carbon nano tube into metal oxide by one time under the condition of oxygen enrichment and certain temperature, and utilizes the strong oxidizing property of hydrogen chloride gas to react under the heating condition to generate chloride and water by two times, and then utilizes the characteristic that the gasification temperature of the metal chloride is far lower than that of the metal and the oxide thereof, the metal catalyst and the gasification temperature condition commonly used for preparing the carbon nano tube by the CVD method are shown in table 1, and the chloride is gasified and separated from the carbon nano tube by heating, thereby achieving the purpose of purifying the carbon nano tube.
TABLE 1 CVD Process for preparing carbon nanotubes with commonly used metal catalysts and gasification temperature conditions
Further, in the method for purifying the carbon nano tube by the rotary binary gas phase method, in the step (1), the spiral plate is arranged in the rotary furnace tube to rotate, so that the carbon nano tube is stirred to be fully contacted with dry compressed air, and the aim of completely oxidizing oxides in the carbon nano tube is fulfilled.
Further, in the method for purifying the carbon nanotube by the rotary binary vapor phase method, the carbon nanotube in the step (1) is one or more of a multi-walled carbon nanotube, a single-walled carbon nanotube and a double-walled carbon nanotube.
Further, in the method for purifying the carbon nanotube by the rotary binary gas-phase method, the residual metal catalyst in the step (1) is one or more of Fe-based, Ni-based, Co-based, Al-based, Mg-based, Mo-based and La-based catalysts.
Further, the method for purifying the carbon nano tube by the rotary binary sub-gas phase method has the constant temperature time of 1-3 hours in the step (1), so that the residual metal catalyst in the carbon nano tube is completely oxidized into metal oxide.
Further, in the method for purifying the carbon nano tube by the rotary binary secondary gas phase method, the stirring plate is arranged in the furnace tube of the rotary furnace in the step (2), and when the furnace tube rotates, the stirring plate overturns the primary secondary carbon nano tube to be fully contacted with hydrogen chloride gas, so that the aim of generating metal chloride and water by the complete reaction of the catalyst oxide is fulfilled.
Further, in the method for purifying carbon nanotubes by using a rotary binary vapor phase method, the heating temperature of the primary carbon nanotubes in the furnace tube in the step (2) is related to the type of the carbon nanotubes in the furnace tube and the type of the metal catalyst, and specifically, the heating temperature may be:
when the carbon nanotube is a carbon nanotube synthesized by a La-based catalyst, as can be seen from Table 1, the boiling point of the chloride of La is 1000 ℃, and in order to ensure that nitrogen can completely replace the chloride of La, the carbon nanotube of the first order in the furnace tube is heated to 1100 ℃ in the step (2);
when the carbon nanotube is a multi-walled carbon nanotube synthesized by a Co-based catalyst, as can be seen from Table 1, the boiling point of the Co chloride is 1045 ℃, and in order to ensure that nitrogen can completely replace the Co chloride, the monohydric secondary carbon nanotube in the furnace tube is heated to 1100 ℃ in the step (2);
when the carbon nano-tube is a multi-wall carbon nano-tube synthesized by an Fe-based catalyst, as can be seen from the table 1, the boiling point of the chloride of Fe is 315 ℃, and in order to ensure that nitrogen can completely replace the chloride of Fe, the primary carbon nano-tube in the furnace tube is heated to 400 ℃ in the step (2);
when the carbon nano-tube is a multi-wall carbon nano-tube synthesized by a Ni-based catalyst, as can be seen from the table 1, the boiling point of the chloride of Ni is 987 ℃, and in order to ensure that nitrogen can completely replace the chloride of Ni, the primary carbon nano-tube in the furnace tube is heated to 1000 ℃ in the step (2);
when the carbon nanotubes are multi-walled carbon nanotubes synthesized by a Mo-based catalyst, as can be seen from Table 1, the boiling point of the chloride of Mo is 268 ℃, and in order to ensure that nitrogen can completely replace the chloride of Mo, the monohydric secondary carbon nanotubes in the furnace tube are heated to 300 ℃ in the step (2).
Further, the method for purifying the carbon nanotubes by the rotary binary vapor phase method can further comprise the following steps: introducing preheated hydrogen chloride gas into a rotary furnace, continuously adding the primary carbon nano tube from a feeding port, taking gaseous chloride out of the primary carbon nano tube through nitrogen, cooling, collecting the purified carbon nano tube at a receiving port, filling the carbon nano tube into a sample bag, and sealing.
The invention also provides a carbon nano tube obtained by the method for purifying the carbon nano tube by the rotary binary secondary gas phase method, which is characterized in that under the condition of a rotary working condition, the carbon nano tube is firstly converted into the unary secondary carbon nano tube containing the metal oxide under the condition of an oxygen-enriched heating condition, then hydrogen chloride gas is reacted with the metal oxide in the unary secondary carbon nano tube to generate metal chloride and water, different temperatures are selected for treatment according to the types of the metal catalysts in the carbon nano tube to be removed, the chloride is gasified and replaced by nitrogen, and the metal chloride is separated from the carbon nano tube, so that the aim of purifying the carbon nano tube is fulfilled. In order to ensure the effect and efficiency of the two-time operation, a rotation method is adopted. The method is simple, the productivity is easy to amplify, the pollution is small, the engineering is easy, the purification effect is good, and the method is suitable for removing various residual metals in various carbon nano tubes. The carbon nano tube has high purity, wherein the content of single metal impurities is less than 20 ppm.
The invention relates to a rotary binary secondary gas phase method for purifying carbon nano tubes, which is mainly carried out in a rotary furnace, wherein the rotary furnace approximately comprises: a spiral furnace tube, a stirring plate rotary furnace tube and a collecting tank;
the furnace tube of the stirring plate rotary furnace is obliquely arranged, the inclination angle of the furnace body is 0-45 degrees, the bottom of the furnace tube of the stirring plate rotary furnace is provided with a nitrogen valve and a hydrogen chloride air inlet valve, and the nitrogen valve is mainly used for replacing air in the device and discharging gaseous metal chloride during the purification of the carbon nano tube and removing the unreacted redundant hydrogen chloride gas;
the beneficial effects of 0 ~ 45 adjustable installation of stirring board rotary furnace boiler tube and horizontal slope lie in: when the furnace tube rotates, the downward propulsion of the materials in the furnace tube is accelerated, and the downward propulsion speed of the materials can be adjusted by adjusting the inclination angle; the furnace top of the stirring plate rotary furnace tube is provided with a rotating shaft, the rotating shaft is communicated with the bottom of the spiral furnace tube through a section of connecting tube, and the discharge valve is arranged on the connecting tube; the top of the spiral furnace tube is provided with an exhaust valve and a feed valve, the exhaust valve is used for exhausting air, nitrogen after reaction, metal chloride gas and unreacted hydrogen chloride gas, and the feed valve is used for adding carbon nano tubes;
the stirring plate rotating furnace tube inner wall is uniformly provided with a plurality of stirring plates, the stirring plates are perpendicular to the stirring plate rotating furnace tube inner wall and form an included angle of 0-45 degrees with the axial direction inclination of the stirring plate rotating furnace tube, a certain inclination angle is formed, so that carbon nano tube materials can be conveyed in a way of lifting and scattering spiral pushing materials when the furnace tube rotates, the stirring plates are L-shaped, a concave surface with an included angle of 100-135 degrees is formed on a scooping surface of the stirring plates, and the formed concave surface with the angle of 100-135 degrees can scoop and hold the carbon nano tube materials in the air for a longer time and can react with gas more uniformly and completely when the furnace tube rotates;
the bottom of the rotary furnace is communicated with the collecting tank, and a material collecting valve is arranged at a discharge hole of the collecting tank.
The invention relates to a method for purifying carbon nano tubes by a rotary binary secondary gas phase method, which comprises the steps of carrying out secondary treatment on residual metal impurities of a carbon nano tube catalyst, rotating a furnace tube in a primary mode under a condition of enrichment, arranging a rotary vane in the furnace tube, stirring the carbon nano tube in the furnace tube by the rotary vane to enable the carbon nano tube to be fully contacted with oxygen, enabling the metal of the carbon nano tube impurity catalyst to be fully contacted with the oxygen for reaction, completely converting the metal impurities into metal oxides, finally utilizing the strong oxidizing property of hydrogen chloride to place the metal oxides in the rotary furnace tube, arranging a stirring plate in the furnace tube, throwing the primary carbon nano tube in the furnace tube by the stirring plate to enable the primary carbon nano tube to be fully contacted with hydrogen chloride gas, enabling the metal oxides of the primary carbon nano tube impurity catalyst to be fully contacted with the hydrogen chloride for reaction and converted into metal chloride and water, discharging the water in a gaseous, the purpose of purifying metal impurities is achieved. The toxicity of the hydrogen chloride gas is lower than that of the chlorine gas, the safety risk is low, the national management and control are low, the use threshold is low, meanwhile, the oxidative corrosivity of the hydrogen chloride gas is lower than that of the chlorine gas, and the engineering is easy to realize. Some metals may be used for engineering applications of the present invention after a particular surface treatment (e.g., nitriding or carburizing).
Drawings
FIG. 1 is a view of a rotary kiln apparatus according to the present invention;
in FIG. 1, 1-spiral furnace tube, 2-stirring plate rotary furnace tube, 3-collecting tank, 4-rotary shaft, 5-exhaust valve, 6-discharge valve, 7-feed valve, 8-receiving valve, 9-stirring plate, 10-nitrogen valve, 11-hydrogen chloride intake valve;
FIG. 2 is a developed view showing the distribution of the stirring plates in the furnace tube 2 of the stirring plate rotary furnace;
FIG. 3 is a view showing the structure of a paddle;
FIG. 4 is an electron microscope image of a carbon nanotube of example 1;
FIG. 5 is an electron micrograph of a binary carbon nanotube of example 1A;
FIG. 6 is an electron microscope image of a carbon nanotube of example 2;
FIG. 7 is an electron micrograph of a binary carbon nanotube of example 2A;
FIG. 8 is an electron micrograph of a carbon nanotube of example 3;
FIG. 9 is an electron micrograph of binary carbon nanotubes of example 3A.
Detailed Description
The present invention will be described in further detail with reference to specific embodiments, but it should not be construed that the scope of the present invention is limited to the following examples. Various substitutions and alterations can be made by those skilled in the art and by conventional means without departing from the spirit of the method of the invention described above.
Example 1
The apparatus for purifying carbon nanotubes of this embodiment is shown in fig. 1, 2 and 3.
100g of an iron-based catalyst (SiO as a carrier)2) The synthesized multi-walled carbon nanotubes (marked as example 1) are filled into a spiral furnace tube 1 through a feed valve 7, a discharge valve 6 is closed, an exhaust valve 5 is opened, then the temperature is increased to 315 ℃, the furnace tube is rotated, dry compressed air is introduced for 0.5 hour, the compressed air is changed into nitrogen, the air atmosphere in the tube is replaced, when the oxygen content is lower than 1%, the exhaust valve 5 and the feed valve 7 are closed, the temperature is increased to 400 ℃, the discharge valve 6 is opened, a stirring plate rotating furnace tube 2 is rotated, the unary carbon nanotubes in the spiral furnace tube 1 are filled into the stirring plate rotating furnace tube 2, and a hydrogen chloride gas inlet valve 11 is opened to introduce hydrogen chloride gas for reaction for 0.5 hour. After the reaction is finished, stopping introducing the hydrogen chloride, rotating the furnace tube, opening the nitrogen valve 10, introducing the nitrogen, keeping the temperature constant at 400 ℃ for 10 minutes, stopping heating, continuing introducing the nitrogen, rotating the furnace tube, opening the material receiving valve 8 when the temperature is lower than 40 ℃, taking out the carbon nano tubes, filling the carbon nano tubes into a sample bag, and sealing the sample bag (marked as example 1A). The tail gas in the whole process is absorbed by sodium hydroxide aqueous solution.
In example 1, the electron microscope image is shown in fig. 4, and in example 1A, the electron microscope image is shown in fig. 5, and fig. 4 and fig. 5, it can be seen that the carbon nanotubes have completely consistent morphology after the catalyst metal impurities are oxidized for the first time and the catalyst metal oxides of the carbon nanotubes are purified for the second time, which indicates that the carbon nanotubes are not damaged or affected after the hydrogen chloride is purified.
Example 2
The apparatus for purifying carbon nanotubes of this embodiment is shown in fig. 1, 2 and 3.
80g of nickel-based catalyst (SiO as carrier)2) The multi-walled carbon nanotube (labeled as example 2) synthesized by (Ni) is filled into a furnace tube 1 of a rotary spiral furnace through a feed valve 7, a discharge valve 6 is closed, an exhaust valve 5 is opened, then the temperature is raised to 315 ℃, the furnace tube is rotated, and after dry compressed air is introduced for 0.5 hour, the compressed air is changed into nitrogenReplacing the air atmosphere in the tube, closing the exhaust valve 5 and the feed valve 7 when the oxygen content is lower than 1%, raising the temperature to 1000 ℃, opening the discharge valve 6, rotating the stirring plate rotary furnace tube 2, loading the primary carbon nanotubes in the spiral furnace tube 1 into the stirring plate rotary furnace tube 2, opening the hydrogen chloride inlet valve 11, and introducing hydrogen chloride gas for reaction for 0.5 h. After the reaction is finished, stopping introducing the hydrogen chloride, rotating the furnace tube, opening the nitrogen valve 10, introducing the nitrogen, keeping the temperature constant at 1000 ℃ for 10 minutes, stopping heating, continuing introducing the nitrogen and rotating the furnace tube, opening the material receiving valve 8 when the temperature is lower than 40 ℃, taking out the carbon nano tubes, filling the carbon nano tubes into a sample bag, and sealing the sample bag (marked as example 2A). The tail gas in the whole process is absorbed by sodium hydroxide aqueous solution.
In example 2, the electron microscope image is shown in fig. 6, and the electron microscope image in example 2A is shown in fig. 7, and fig. 6 and 7 show that the carbon nanotubes have completely consistent morphology after the catalyst metal impurities are oxidized for the first time and the catalyst metal oxides of the carbon nanotubes are purified for the second time, which indicates that the carbon nanotubes are not damaged or affected after the hydrogen chloride is purified.
Example 3
The apparatus for purifying carbon nanotubes of this embodiment is shown in fig. 1, 2 and 3.
12g of a cobalt-based catalyst (SiO as support)2) The synthesized multi-walled carbon nanotubes (marked as example 3) are filled into a spiral furnace tube 1 of a rotary furnace through a feed valve 7, a discharge valve 6 is closed, an exhaust valve 5 is opened, then the temperature is increased to 315 ℃, the tube is rotated, dry compressed air is introduced for 0.5 hour, the compressed air is changed into nitrogen, the air atmosphere in the tube is replaced, when the oxygen content is lower than 1%, the exhaust valve 5 and the feed valve 7 are closed, the temperature is increased to 1100 ℃, the discharge valve 6 is opened, a rotary stirring plate rotary furnace tube 2 is rotated, the unary carbon nanotubes in the spiral furnace tube 1 are filled into a stirring plate rotary furnace tube 2, and a hydrogen chloride gas inlet valve 11 is opened to introduce hydrogen chloride gas for reaction for 0.5 hour. After the reaction is finished, stopping introducing the hydrogen chloride, rotating the furnace tube, opening the nitrogen valve 10, introducing the nitrogen, keeping the temperature constant at 1100 ℃ for 10 minutes, stopping heating, continuing introducing the nitrogen, rotating the furnace tube, opening the material receiving valve 8 when the temperature is lower than 40 ℃, taking out the carbon nano tubes, filling the carbon nano tubes into a sample bag, and sealing the sample bag (marked as example 3A). The whole processThe tail gas in the process is absorbed by sodium hydroxide aqueous solution.
In example 3, the electron microscope image is shown in fig. 8, and the electron microscope image in example 3A is shown in fig. 9, and fig. 8 and 9 show that the carbon nanotubes have completely consistent morphology after the catalyst metal impurities are oxidized for the first time and the catalyst metal oxides of the carbon nanotubes are purified for the second time, which indicates that the carbon nanotubes are not damaged or affected after the hydrogen chloride is purified.
And (3) performance testing:
first, ash content detection
The ash content of the carbon nanotubes obtained in example 1, example 2 and example 3 were tested and compared, respectively: the carbon nanotubes of 4 examples produced in step 8 were weighed with a one-hundred-thousandth electronic balance, placed in a muffle furnace, thermostated at 900 ℃ for 4 hours, cooled and reweighed, and ash results are shown in table 2.
From table 2, it can be derived: the residual impurity of the iron-based catalyst carbon nano tube is 3.1 percent before purification, and after the carbon nano tube is purified by a rotary binary gas phase method, the residual ash content impurity is 0.016 percent, and the purity is 193 times of the original purity; the nickel-based catalyst carbon nanotube has 12% of residual impurities before purification, and has 0.024% of residual ash impurities after purification by a rotary binary gas-phase purification method, wherein the purity of the residual ash impurities is 500 times that of the original impurities; the cobalt-based catalyst carbon nano tube has 2.1 percent of residual impurities before purification, and has 0.0235 percent of residual ash impurities after purification by a rotary binary gas phase method, and the purity of the residual ash impurities is 89 times that of the original carbon nano tube.
Secondly, detecting the metal content in the purified carbon nano tube
Example 1 test: 0.1g of the carbon nanotube (labeled as example 1A) purified in example 1 was weighed and put in a tetrafluoroethylene digestion tank, and 6ml of HNO was added3+2ml HCl +4ml HF, placed in a microwave digestion chamberDigesting, fixing the volume to 50ml, filtering to obtain clear transparent liquid, and performing ICP-OES on-machine test to obtain the liquid with iron content of 11PPm, molybdenum content of 3PPm and total metal content of 14 PPm.
Example 2 detection: weighing 0.1g of the carbon nanotube (marked as example 2A) sample purified in the example 2, adding 6ml of HNO3+2ml of HCl +4ml of HF into a tetrafluoroethylene digestion tank, placing the mixture in a microwave digestion chamber for digestion, metering the volume to 50ml, filtering, obtaining clear transparent liquid, and performing ICP-OES machine test, wherein the nickel content is 17PPm, the lanthanum content is 5PPm, and the total metal content is 22 PPm.
Example 3 detection: 0.1g of the carbon nanotube (labeled as example 3A) purified in example 3 was weighed and put in a tetrafluoroethylene digestion tank, and 6ml of HNO was added3And putting the +2ml HCl +4ml HF into a microwave digestion instrument for digestion, fixing the volume to 50ml, filtering to obtain clear transparent liquid, and performing ICP-OES machine test on the clear transparent liquid, wherein the cobalt content is 15PPm, the magnesium content is 6PPm, and the total metal content is 21 PPm.
In conclusion: the carbon nano tube obtained by the method has high purity, the content of single impurities is lower than 20ppm, and the content of total metals is lower than 25 ppm.
Claims (10)
1. A method for purifying carbon nanotubes by a rotary binary secondary gas phase method is characterized by comprising the following steps:
(1) placing the carbon nano tube in a furnace tube of a rotary furnace, heating to 310-320 ℃, introducing dry compressed air into the furnace tube, oxidizing residual metal catalyst in the carbon nano tube into metal oxide, keeping the temperature for a certain time, and cooling to obtain a primary carbon nano tube;
(2) placing the unary secondary carbon nano tube obtained in the step (1) in a rotary furnace tube again, introducing nitrogen into the furnace tube to replace oxygen in the furnace tube to ensure that the oxygen content in the furnace tube is lower than 1%, heating the unary secondary carbon nano tube in the furnace tube to 300-1100 ℃, introducing hydrogen chloride gas, contacting a catalyst metal oxide in the unary secondary carbon nano tube with the hydrogen chloride gas, and reacting to generate metal chloride and water to obtain a binary secondary carbon nano tube;
(3) and (3) keeping the heating temperature of the furnace tube at 300-1100 ℃, changing the metal chloride into gaseous metal chloride, introducing nitrogen into the furnace tube of the rotary furnace in the step (2), volatilizing the gaseous metal chloride adsorbed by the binary carbon nanotube from the carbon nanotube, removing unreacted redundant hydrogen chloride gas, continuously introducing the nitrogen for a period of time, and cooling to normal temperature to obtain the purified carbon nanotube.
2. The method for purifying carbon nanotubes by the rotary binary minor gas phase method as claimed in claim 1, wherein in the step (1), the helical plate is arranged in the tube of the rotary furnace to rotate, so as to stir the carbon nanotubes to fully contact with the dry compressed air, thereby achieving the purpose of completely oxidizing the metal therein.
3. The method for purifying carbon nanotubes by using the rotary binary vapor phase method as claimed in claim 1 or 2, wherein the carbon nanotubes in step (1) are one or more of multi-walled carbon nanotubes, single-walled carbon nanotubes and double-walled carbon nanotubes.
4. The method for purifying carbon nanotubes by using the rotary binary vapor phase method according to claim 1 or 2, wherein the residual metal catalyst in the step (1) is one or more of Fe-based, Ni-based, Co-based, Al-based, Mg-based, Mo-based and La-based catalysts.
5. The method for purifying carbon nanotubes by using the rotational binary sub-vapor phase method as claimed in claim 3, wherein the residual metal catalyst in the step (1) is one or more of Fe-based, Ni-based, Co-based, Al-based, Mg-based, Mo-based and La-based catalysts.
6. The method for purifying carbon nanotubes by the rotary binary vapor phase method according to claim 1 or 2, wherein the constant temperature time in the step (1) is 1-3 h.
7. The method for purifying carbon nanotubes by the rotary binary minor gas phase method according to claim 3, wherein the constant temperature time in the step (1) is 1-3 h.
8. The method of claim 1, wherein the stirring plate is disposed in the tube of the rotary furnace in step (2), and the stirring plate is used to turn the carbon nanotubes of the first order over the hydrogen chloride gas to fully contact with the hydrogen chloride gas during the rotation of the tube, thereby achieving the purpose of generating metal chloride and water through the complete reaction of the catalyst oxide.
9. The method of claim 1, wherein the heating temperature of the monohydric carbon nanotubes in the furnace tube in step (2) is related to the type of carbon nanotubes in the furnace tube and the type of metal catalyst, and specifically comprises:
when the carbon nano tube is synthesized by the La-based catalyst, heating the primary carbon nano tube in the furnace tube to 1100 ℃ in the step (2);
when the carbon nano tube is synthesized by a Co-based catalyst, heating the primary carbon nano tube in the furnace tube to 1100 ℃ in the step (2);
when the carbon nano tube is synthesized by the Fe-based catalyst, heating the primary carbon nano tube in the furnace tube to 400 ℃ in the step (2);
when the carbon nano tube is synthesized by a Ni-based catalyst, heating the primary carbon nano tube in the furnace tube to 1000 ℃ in the step (2);
when the carbon nanotubes are synthesized by a Mo-based catalyst, the carbon nanotubes of one unit in the furnace tube are heated to 300 ℃ in step (2).
10. The method of claim 9, further comprising the steps of: introducing hydrogen chloride gas into the rotary furnace, continuously adding the primary carbon nano tube from the feeding port, taking gaseous chloride out of the primary carbon nano tube through nitrogen, cooling, collecting the purified carbon nano tube at the receiving port, filling the carbon nano tube into a sample bag, and sealing.
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