CN111362253A - Carbon nano tube prepared by catalytic cracking of hydrocarbon by gas-phase damping method, device and method - Google Patents
Carbon nano tube prepared by catalytic cracking of hydrocarbon by gas-phase damping method, device and method Download PDFInfo
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Abstract
The invention relates to the technical field of carbon nanotube preparation, in particular to a carbon nanotube prepared by catalytic cracking of hydrocarbon by using a gas phase damping method, a device and a preparation method thereof. The preparation method comprises the steps of feeding the catalyst, catalytically cracking the hydrocarbon and cooling and collecting. The invention utilizes the gravity of the carbon nano tube catalyst to move from top to bottom, and sets a multi-stage gas phase damping ring in the cracking chamber to damp and control the falling speed of the catalyst, thereby prolonging the floating time of the catalyst in the cracking chamber, realizing the full contact of the catalyst and the carbon source gas, realizing different catalysts and different carbon source gases by adjusting the frequency of an ultrasonic vibration sieve, the mesh number of the sieve, the feeding measurement and the cracking temperature of the catalyst, the number of the gas phase damping rings and other measures, and greatly increasing the application range of the carbon nano tube production.
Description
Technical Field
The invention relates to the technical field of carbon nanotube preparation, in particular to a carbon nanotube prepared by catalytic cracking of hydrocarbon by using a gas phase damping method, a device and a preparation method thereof.
Background
The carbon nano tube is used as a one-dimensional nano material, has light weight, perfect connection of a hexagonal structure and a plurality of abnormal mechanical, electrical and chemical properties. With the research of carbon nanotubes and nanomaterials, the wide application prospect is continuously shown in recent years. Since the carbon nanotube has a hollow structure, it can be used as a micro mold. The metal, oxide and other substances can be filled in the nano-sized conductive wire, so that the finest nano-sized conductive wire and the like can be prepared and used in future molecular electronic devices or nano-electronic devices. It can also be used to make carbon nanotube reinforced plastics, carbon nanotube reinforced ceramic composite material, metal-based composite material, and can also be used to make the finest test tube and the nano-scale capable of weighing single atomic mass.
Carbon nanotubes, also known as buckytubes, are the finest fibers recognized in the world, and are one-dimensional quantum materials with special structures (the radial dimension is nanometer magnitude, the axial dimension is micrometer magnitude, and both ends of the tube are basically sealed). The carbon nanotube mainly comprises a coaxial circular tube with several layers to tens of layers formed by carbon atoms arranged in a hexagon, and can be regarded as formed by curling graphene sheets, so that the carbon nanotube can be divided into the following layers according to the number of the graphene sheets: single-walled Carbon nanotubes (or Single-walled Carbon nanotubes, SWCNTs) and Multi-walled Carbon nanotubes (or Multi-walled Carbon nanotubes, MWCNTs), where the Multi-walled tube is formed at the beginning, the layers are likely to become the trap center to trap various defects, and thus the wall of the Multi-walled tube is usually filled with small hole-like defects. Compared with a multi-wall pipe, the single-wall pipe has the advantages of small diameter distribution range, less defects and higher uniformity. The typical diameter of the single-wall pipe is 0.6-2nm, the innermost layer of the multi-wall pipe can reach 0.4nm, the thickest layer can reach hundreds of nanometers, but the typical pipe diameter is 2-100 nm. Carbon hexagons can be classified according to their different orientations in the axial direction: three types are a sawtooth shape, an armchair shape and a spiral shape. Wherein the helical carbon nanotubes have chirality, while the zigzag and armchair carbon nanotubes have no chirality; the materials have good conductivity, high mechanical property and high specific surface area, and play an important role in the technical field of renewable energy conversion such as electrochemical catalysis and energy storage.
At present, the macro preparation method of the carbon nano tube mainly comprises a catalytic cracking method, an arc discharge method and a chemical vapor deposition method, wherein the catalytic cracking method is a method for preparing the carbon nano tube by decomposing carbon-containing gas raw materials (such as carbon monoxide, methane, ethylene, propylene, benzene and the like) at the temperature of 600-1000 ℃ under the action of a catalyst. The method is to crack the carbon-containing compound into carbon atoms at a higher temperature, and the carbon atoms are attached to the surface of the catalyst particles under the action of the transition metal-catalyst to form the carbon nano-tubes. The active components of the catalyst used in the catalytic cracking method are mostly transition metals of the eighth group or alloys thereof, and a small amount of Cu, Zn, Mg and the like are added to adjust the energy state of the active metals and change the chemical adsorption and decomposition capacity of the active metals. Catalyst precursors have an effect on the activity of forming elemental metals, and metal oxides, sulfides, carbides, and organometallic compounds have also been used. The arc discharge method is a main method for producing carbon nanotubes, and is characterized by that a graphite electrode is placed in a reaction container filled with helium gas or argon gas, and an electric arc is excited between two electrodes, and at this time the temperature can be up to about 4000 deg.C. Under these conditions, the graphite evaporates, and the products produced are fullerenes (C60), amorphous carbon, and single-or multi-walled carbon nanotubes. The arc discharge method has more defects, and the chemical vapor deposition method just makes up part of the defects of the arc discharge method, and the chemical vapor deposition method is to crack hydrocarbon by using a catalyst, take active metal atoms as catalyst crystal nuclei, and deposit the carbon atoms with the nuclei to generate the carbon nano tube. According to the principle of the chemical vapor deposition method, the more fully the catalyst active component contacts with the carbon source gas, the more carbon atoms generated by the cracking of the carbon-hydrogen bond are deposited and grown on the surface of the active metal, the more carbon nanotubes are grown, and the better the growth morphology is. In engineering production, the chemical deposition method mainly adopts a moving method and a boiling method (also called a fluidized bed method). The moving method uses the material boat as a carrier, the catalyst is put into the material boat to move in the tube furnace of the tube furnace, and the carbon nano tube grows in the condition equipment area; in the production process of the moving method, the catalyst is fixed in the material boat, and completely depends on the carbon source gas to be stacked on the catalyst stacking surface of the material boat and permeate into the contact catalyst, namely, the catalyst is passively contacted with the carbon source gas, so that the defects that the contact between the catalyst and hydrocarbon is insufficient, the growth of the carbon nano tube is influenced and the like exist, the catalyst can only be used for preparing the carbon nano tube with low multiplying power, methane is usually used as a carbon source, and meanwhile, catalyst metals (mainly including Fe series, Ni series, Co series and the like) used by the CVD method are remained in the carbon nano tube and are mostly coated on the end part of the carbon nano tube. In order to overcome the above disadvantages of the moving bed, a boiling method (also called fluidized bed method) has been developed to produce carbon nanotubes, in which nitrogen is used to blow the catalyst into a well-type furnace filled with hydrocarbons, and the carbon source gas is fully contacted with the catalyst active metal to better grow the carbon nanotubes.
However, the boiling method has the defects that the nitrogen pressure is unstable, the growth process is difficult to control and the like, meanwhile, a large amount of nitrogen is flushed into the carbon source gas environment to dilute the carbon source gas, and the carbon source gas needs to be flushed into the carbon source gas in a large excess amount to ensure the growth of the carbon nanotubes. The mobile method and the boiling method have respective special requirements on the preparation of the catalyst, and the catalyst cannot be used universally. Most of the existing carbon nanotube preparation equipment has single function, one equipment can only prepare the carbon nanotubes with the same specification, the equipment is not integrated, certain transportation power needs to be provided after the carbon nanotube catalyst is added, so that the resource is greatly wasted, and the production cost is increased.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a carbon nano tube prepared by catalytic cracking of hydrocarbon by a gas phase damping method, a preparation device and a preparation method, and solves the technical problems that the carbon nano tube preparation method and the carbon nano tube prepared by the device in the prior art have single specification, the same device cannot be adopted, carbon nano tubes with different specifications can be prepared by controlling the adding amount of different raw materials and processes, and the carbon nano tube prepared by the prior art has poor quality.
The purpose of the invention is realized by the following technical scheme:
a method for preparing carbon nano-tubes by catalytically cracking hydrocarbons by a gas phase damping method comprises the following steps:
(1) feeding of the catalyst: blowing the carbon nanotube catalyst to an ultrasonic vibration sieve at the top of the cracking chamber through a catalyst feeding port by using nitrogen, and uniformly throwing the catalyst from the top of the cracking chamber into the cracking chamber by using the ultrasonic vibration sieve according to a certain amount;
the invention uses the ultrasonic vibration sieve to feed the catalyst, the catalyst is scattered from the top of the cracking chamber, and the catalyst falls down by the weight of the catalyst without feeding;
the feeding of the catalyst ultrasonic vibration sieve has the beneficial effects that: not only can realize the quantitative feeding of the catalyst, but also can prevent the blockage of a catalyst screen; by controlling the ultrasonic vibration frequency and the mesh number of the screen, different dosages of different catalysts can be fed;
(2) hydrocarbon catalytic cracking: a heating furnace for heating the cracking chamber is arranged outside the cracking chamber, nitrogen is introduced into the cracking chamber to replace oxygen, after the oxygen content of the system is less than 2%, the heating furnace is heated, carbon source gas is introduced from a carbon source gas inlet at the lower end of the cracking chamber, the carbon nanotube catalyst in the step (1) sequentially enters a first-stage gas-phase damping ring and a second-stage gas-phase damping ring in … Nth-stage gas-phase damping ring, the falling speed of the carbon nanotube catalyst is delayed for N times by the damping of the nitrogen in the gas-phase damping rings, the heating time of the carbon nanotube catalyst in the cracking chamber and the contact time of the carbon nanotube catalyst with the carbon source gas are increased until the carbon source gas fully reacts with the carbon nanotube catalyst in the cracking chamber, carbon hydrogen bonds are cracked, carbon atoms are deposited and grown into carbon nanotubes by taking carbon nanotube catalyst crystal nuclei as nuclei, and the gas after; wherein N is more than or equal to 1 and less than or equal to 100;
(3) and cooling and collecting: and the carbon nano tube generated in the cracking chamber enters the cooling chamber from a discharge hole at the bottom end of the cracking chamber, is cooled and then is discharged from a discharge hole, so that the carbon nano tube is obtained.
Furthermore, the method for preparing the carbon nano tube by catalytically cracking the hydrocarbon by the gas phase damping method can prepare the carbon nano tubes with different specifications by controlling the temperature of different heating furnaces, the number of times of gas phase damping circles, the catalyst feeding amount of the ultrasonic vibration sieve and the carbon source gas flow according to different carbon nano tube catalysts or different carbon source gases.
Further, in the method for preparing the carbon nano tube by catalytically cracking the hydrocarbon by the gas phase damping method, the carbon nano tube catalyst in the step (1) is at least one of a nickel-based catalyst, an iron-based catalyst and a cobalt-based catalyst; the feeding amount of the ultrasonic vibration sieve catalyst is 1-300 g/min, preferably 1-2 g/min, and is determined by ultrasonic frequency and the mesh number of the sieve.
Further, in the method for preparing the carbon nano tube by catalytic cracking of the hydrocarbon through the gas phase damping method, the heating temperature of the heating furnace in the step (2) is 600-800 ℃.
Further, in the method for preparing carbon nanotubes by catalytically cracking hydrocarbons by using the gas phase damping method, in the step (2), the carbon source gas is at least one of methane, propylene or ethylene; the flow rate of the carbon source gas is 1-50 m3Preferably 1 to 3m3/h。
Furthermore, in the method for preparing the carbon nano tube by catalytically cracking the hydrocarbon by the gas-phase damping method, the number of the gas-phase damping circles in the step (2) is 10-80.
Further, in the method for preparing the carbon nano tube by catalytically cracking the hydrocarbon through the gas phase damping method, in the step (2), the carbon source gas is at least one of methane, propylene or ethylene, and the flow rate of the carbon source gas is 1-50 m3/h。
Specifically, carbon nanotubes with different specifications can be prepared by setting the following process parameters:
further, the method for preparing the carbon nano tube by catalytically cracking the hydrocarbon by the gas phase damping method comprises the following steps of preparing a catalyst of the carbon nano tube by a nickel-based catalyst; the number N of gas-phase damping turns is 30 levels; the heating temperature of the heating furnace is 790 ℃, the carbon source gas is methane, and the flow rate of the carbon source gas is 2.5m3And h, the feeding amount of the ultrasonic vibration sieve catalyst is 2g/min, the ultrasonic frequency of the ultrasonic vibration sieve is 18KHZ, the mesh number of the sieve is 100 meshes, and finally the hollow fibrous carbon nano tube with the diameter of 30-50 nm is obtained.
Further, the method for preparing the carbon nano tube by catalytically cracking the hydrocarbon by the gas phase damping method is characterized in that the carbon nano tube catalyst is an iron-based catalyst; the number N of gas-phase damping turns is 12 levels; the heating temperature of the heating furnace is 660 ℃, the carbon source gas is propylene, and the flow rate of the carbon source gas is 1.7m3And h, the feeding amount of the ultrasonic vibration sieve catalyst is 1g/min, the ultrasonic frequency of the ultrasonic vibration sieve is 45KHZ, the mesh number of the sieve is 150 meshes, and finally the hollow fibrous carbon nano tube with the diameter of 10-15 nm is obtained.
Further, the method for preparing the carbon nano tube by catalytically cracking the hydrocarbon by the gas phase damping method comprises the following steps of preparing a carbon nano tube catalyst by a cobalt-based catalyst; the number N of gas-phase damping turns is 22 levels; the heating temperature of the heating furnace is 630 ℃, the carbon source gas is ethylene, and the flow rate of the carbon source gas is 1.3m3And h, the feeding amount of the ultrasonic vibration sieve catalyst is 1g/min, the ultrasonic frequency of the ultrasonic vibration sieve is 32KHZ, the mesh number of the sieve is 120 meshes, and finally the hollow fibrous carbon nano tube with the diameter of 5-10 nm is obtained.
The invention also provides a carbon nano tube prepared by catalytic cracking of hydrocarbon by the gas-phase damping method.
The invention also provides a device for preparing carbon nano tubes by catalytically cracking hydrocarbons by a gas phase damping method, which is used for implementing the preparation method of the carbon nano tubes or preparing the carbon nano tubes prepared by catalytically cracking the hydrocarbons by the gas phase damping method, and comprises the following steps:
the device comprises a cracking chamber, a cooling chamber and a filter, wherein the cooling chamber is positioned below the cracking chamber and communicated with the cracking chamber;
the heating furnace is arranged outside the cracking chamber and used for heating the cracking chamber;
the side wall of the upper part of the cracking chamber is provided with a catalyst charging port, the top of the filter is provided with an exhaust port, the lower part of the cracking chamber is provided with a carbon source inlet valve port, a nitrogen inlet valve port and a discharge port, and the carbon source inlet valve port and the nitrogen inlet valve port are symmetrically arranged on the side wall of the lower part of the cracking chamber; the nitrogen inlet valve is used for introducing nitrogen before preparing the carbon nano tube and removing air in the device; secondly, an air resistance air source is provided for the gas phase damping ring;
an ultrasonic vibration sieve and one or N circles of gas-phase damping rings are sequentially arranged in the cracking chamber from top to bottom;
the discharge port is positioned at the bottom end of the cracking chamber and communicated with the cooling chamber, the discharge port is connected with the cooling chamber through a pipeline, the side wall of the pipeline is provided with the nitrogen port, and the pipeline between the nitrogen port and the cooling chamber is provided with the discharge valve; the lower end of the cooling chamber is provided with a discharge hole, and the discharge hole is provided with a discharge valve.
Further, when the gas phase damping rings are N rings (wherein N is more than or equal to 10 and less than or equal to 80), the distance between the adjacent gas phase damping rings is gradually increased from top to bottom.
The working principle of the device for preparing the carbon nano tube by catalytically cracking the hydrocarbon by the gas-phase damping method is as follows: opening a nitrogen inlet valve port, introducing nitrogen into the cracking chamber to replace oxygen, wherein the oxygen content of the system is less than 2%; heating the cracking chamber to a set temperature, then opening a carbon source gas inlet valve port, introducing a carbon source gas, and controlling the flow rate of the carbon source gas and the amount of the preheated carbon nanotube catalyst in the feed valve according to requirements; opening a waste gas valve port to adjust the air pressure in the cracking chamber, and ensuring that the pressure difference in the system is about +250 Pa; opening a feeding valve port, and putting the carbon nanotube catalyst into the ultrasonic vibration sieve by nitrogen; starting a power supply of the ultrasonic vibration sieve, and scattering the catalyst from the top of the cracking chamber by the ultrasonic vibration sieve; starting a gas source of the gas-phase damping rings, wherein each stage of gas-phase damping rings form multi-stage gas-phase damping, and the upward and downward moving speed of the catalyst is effectively damped; the carbon-hydrogen bond of the initial carbon source gas is cracked into carbon atoms and hydrogen at a small part at the cracking temperature, the hydrogen reduces metal oxide in the carbon nanotube catalyst into elemental metal, the elemental metal is used as a crystal nucleus to catalyze and crack the carbon-hydrogen bond of more hydrocarbons, the carbon atoms are deposited by taking the elemental metal as the crystal nucleus to generate the carbon nanotube, one part of the hydrogen generated by cracking generates water after reducing the metal oxide in the carbon nanotube catalyst into the elemental metal, the water is discharged from a waste gas port as waste gas, and the other part of the hydrogen is directly discharged. Wherein, the carbon-hydrogen bond in the cracking chamber is cracked into carbon and hydrogen, the carbon atoms are continuously and evenly loaded on the surface of the carbon nano tube catalyst to grow into the carbon nano tube, and the carbon nano tube grows while descending. Meanwhile, a part of the generated hydrogen is used as a carrier gas in the cracking chamber, and a part of the generated hydrogen escapes from the cracking chamber and is collected by a gas collection system. And after the reaction is finished, stopping heating, closing the ultrasonic vibration sieve, the carbon source air inlet valve and the gas source of the gas damping ring, opening the discharge valve, discharging the material out of the cracking chamber, entering the cooling chamber, cooling to room temperature, and taking out the material, so that the carbon nano tubes with different specifications can be obtained according to the setting of different process parameters.
The invention has the beneficial effects that:
1. the preparation method comprises the steps of feeding the carbon nanotube catalyst in a cracking chamber by using an ultrasonic vibration sieve, moving the ultrasonic vibration sieve up and down by depending on the self gravity of the catalyst, contacting the ultrasonic vibration sieve with a carbon source gas in the cracking chamber to crack carbon-hydrogen bonds of the carbon source gas, depositing and growing carbon atoms by taking catalyst active metal as crystal nucleus, and finally preparing the hollow fibrous carbon nanotube; the feeding of the ultrasonic vibration sieve can realize the quantitative supply of the catalyst;
2. the method disclosed by the invention has the advantages that the multistage gas-phase damping rings are arranged in the cracking chamber to damp and control the falling speed of the catalyst, the floating time of the catalyst in the cracking chamber is prolonged, the catalyst is fully contacted with the carbon source gas, the carbon source gas can be fully decomposed to prepare the carbon nano tube, the carbon nano tube is fully utilized, the material reaction is complete, and the obtained carbon nano tube has good impurity appearance, uniform particle size, high purity and less impurities;
3. the method disclosed by the invention has the advantages that the reaction device is integrated, the structure is simple, different catalysts and different carbon source gases are prepared by adjusting the frequency of the ultrasonic vibration sieve, the mesh number of the sieve, the feeding metering and cracking temperature of the catalysts, the number of gas-phase damping rings and other measures, one device is universal, the application range of carbon nanotube production is greatly enlarged, and the possibility of preparing carbon nanotubes of different specifications by the same device is provided.
Drawings
FIG. 1 is an electron microscope scanning image of a large-diameter carbon nanotube prepared by using methane as a carbon source in example 1 of the present invention;
FIG. 2 is an electron microscope scanning image of a small-diameter carbon nanotube prepared by using propylene as a carbon source in example 2 of the present invention;
FIG. 3 is an electron microscope scanning image of a small-diameter carbon nanotube prepared by using ethylene as a carbon source in example 3 of the present invention;
FIG. 4 is a schematic structural diagram of an apparatus for preparing carbon nanotubes by catalytically cracking hydrocarbons by a gas phase damping method;
in the figure, 1-a filter, 2-a cooling chamber, 3-a heating furnace, 4-an ultrasonic vibration sieve, 5-a gas phase damping ring, 6-an exhaust port, 7-a catalyst feeding port, 8-a carbon source inlet valve port, 9-a nitrogen inlet valve port, 10-a nitrogen port, 11-a discharge valve, 12-a discharge valve, 13-a discharge port, 14-a discharge port and 15-a cracking chamber.
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
As shown in fig. 4, an apparatus for preparing carbon nanotubes by catalytically cracking hydrocarbons by a gas phase damping method comprises a cracking chamber 15, a cooling chamber 2 disposed below the cracking chamber 15 and communicated therewith, and a filter 1 disposed above the cracking chamber 15 and communicated therewith;
a heating furnace 3 disposed outside the cracking chamber 15 for heating the cracking chamber 15;
the side wall of the upper part of the cracking chamber 15 is provided with a catalyst feeding port 7, the top of the filter 1 is provided with an exhaust gas port 6, the lower part of the cracking chamber 15 is provided with a carbon source inlet valve port 8, a nitrogen inlet valve port 9 and a discharge port 14, and the carbon source inlet valve port 8 and the nitrogen inlet valve port 9 are symmetrically arranged on the side wall of the lower part of the cracking chamber 15;
an ultrasonic vibration sieve 4 and one or N circles of gas-phase damping rings 5 are sequentially arranged in the cracking chamber 15 from top to bottom; wherein N is more than or equal to 1 and less than or equal to 100;
the discharge port 14 is positioned at the bottom end of the cracking chamber 15 and communicated with the cooling chamber 2, the discharge port 14 is connected with the cooling chamber 2 through a pipeline, the side wall of the pipeline is provided with the nitrogen port 10, and the pipeline between the nitrogen port 10 and the cooling chamber 2 is provided with the discharge valve 11; the lower end of the cooling chamber 2 is provided with a discharge opening 13, and the discharge opening 13 is provided with a discharge valve 12.
The method specifically comprises the following steps:
140 g of nickel-based catalyst (SiO as carrier) with the loading of 6 percent is taken2Nickel oxide is nickel oxide), and is put into the ultrasonic vibration sieve 4 through a catalyst feeding port 7; opening a catalyst feed opening 7, opening a nitrogen gas inlet valve port 9 and a waste gas port 6, introducing oxygen in a nitrogen gas replacement device, after the oxygen content of a system is less than 2%, closing the nitrogen gas inlet valve port 9, the catalyst feed opening 7 and the waste gas port 6, heating to 790 ℃ through a heating furnace 3, starting an ultrasonic vibration sieve, controlling the catalyst feed opening 7 according to the amount of 2g/min, then opening a carbon source inlet valve port 8, introducing methane, and controlling the flow of methane to be 2.5m3Opening a nitrogen inlet valve port 9 to provide a nitrogen source for the gas-phase damping rings, operating 30 groups of gas-phase damping rings, opening an exhaust gas adjusting port 6 to ensure that the pressure difference in the system is about +250Pa, and the reaction time is about 2.5 hours; in the initial stage, a small part of carbon-hydrogen bonds of methane gas are cracked into carbon atoms and hydrogen at 790 ℃, the hydrogen reduces nickel oxide in a catalyst into elemental metal nickel, the elemental metal nickel is used as a crystal nucleus to catalyze and crack more carbon-hydrogen bonds of hydrocarbons, the carbon atoms are deposited by taking the nickel as the crystal nucleus to generate a carbon nano tube, and part of the hydrogen generated by cracking is used for generating water after reducing the nickel oxide into the elemental nickel and is discharged as waste gas; another part of the hydrogen is discharged through the off-gas port 6. The carbon-hydrogen bond in the cracking chamber is cracked into carbon and hydrogen, carbon atoms are continuously and uniformly loaded on the surface of the nickel-based catalyst to grow into the carbon nano tube, meanwhile, part of generated hydrogen is used as carrier gas in the cracking chamber, and part of generated hydrogen escapes from the cracking chamber and is collected by the gas collecting system.
And after the reaction is finished, stopping heating the heating furnace, closing a carbon source air inlet valve port 8, opening a nitrogen gas port 10, introducing waste gas in a nitrogen gas replacement system, cooling, after nitrogen gas replacement for 30 minutes, closing the nitrogen gas port 10, opening a discharge valve 11, allowing the material to enter a cooling chamber 2, cooling to room temperature, and taking out the material to obtain the hollow fibrous carbon nanotube, wherein the carbon nanotube has a good shape, relatively uniform diameter and mainly distributed between 30 nm and 50 nm.
Example 2
A device for preparing carbon nano-tubes by catalytic cracking of hydrocarbons by a gas phase damping method is the same as that in example 1.
The method specifically comprises the following steps:
taking 70 g of iron-based catalyst (SiO as carrier) with the loading of 6 percent2Iron oxide is ferric oxide), and is put into the ultrasonic vibration sieve 4 through a catalyst feeding port 7; opening a catalyst feed inlet 7, opening a nitrogen gas inlet valve port 9 and a waste gas port 6, introducing oxygen in a nitrogen gas replacement device, after the oxygen content of a system is less than 2%, closing the nitrogen gas inlet valve port 9, the catalyst feed inlet 7 and the waste gas port 6, heating to 660 ℃ through a heating furnace 3, opening an ultrasonic vibration sieve, controlling the catalyst feed inlet 7 according to the amount of 1g/min, then opening a carbon source inlet valve port 8, introducing propylene, and controlling the flow of the propylene to be 1.7m3Opening a nitrogen inlet valve port 9 to provide a nitrogen source for the gas-phase damping rings, working 12 groups of gas-phase damping rings, opening an exhaust gas adjusting port 6 to ensure that the pressure difference in the system is about +250Pa, and the reaction time is about 1 hour; the carbon-hydrogen bond of the propylene gas is cracked into carbon atoms and hydrogen in a small part at 660 ℃ in the initial stage, the hydrogen reduces iron oxide in the catalyst into elemental metal iron, the elemental metal iron is used as a crystal nucleus to catalyze and crack the carbon-hydrogen bond of more hydrocarbons, the carbon atoms are deposited by taking the iron as the crystal nucleus to generate a carbon nano tube, and part of the hydrogen generated by cracking generates water after reducing the iron oxide into the elemental iron and is discharged as waste gas; another part of the hydrogen is discharged through the off-gas port 6. The carbon-hydrogen bond in the cracking chamber is cracked into carbon and hydrogen, carbon atoms are continuously and uniformly loaded on the surface of the iron-based catalyst to grow into the carbon nano tube, meanwhile, part of generated hydrogen is used as carrier gas in the cracking chamber, and part of generated hydrogen escapes from the cracking chamber and is collected by the gas collecting system.
And after the reaction is finished, stopping heating the heating furnace, closing a carbon source air inlet valve port 8, opening a nitrogen gas port 10, introducing waste gas in a nitrogen gas replacement system, cooling, after nitrogen gas replacement for 30 minutes, closing the nitrogen gas port 10, opening a discharge valve 11, allowing the material to enter a cooling chamber 2, cooling to room temperature, and taking out the material to obtain the hollow fibrous carbon nanotube, wherein the carbon nanotube has a good shape, relatively uniform diameter and mainly distributed between 10nm and 15nm as shown in figure 2.
Example 3
A device for preparing carbon nano-tubes by catalytic cracking of hydrocarbons by a gas phase damping method is the same as that in example 1.
The method specifically comprises the following steps:
taking 70 g of cobalt-based catalyst (SiO as carrier) with the loading of 6 percent2Cobalt oxide is cobalt oxide), and the cobalt oxide is put into the ultrasonic vibration sieve 4 through a catalyst feeding port 7; opening a catalyst feed opening 7, opening a nitrogen gas inlet valve port 9 and a waste gas port 6, introducing oxygen in a nitrogen gas replacement device, after the oxygen content of a system is less than 2%, closing the nitrogen gas inlet valve port 9, the catalyst feed opening 7 and the waste gas port 6, heating to 630 ℃ through a heating furnace 3, opening an ultrasonic vibration sieve, controlling the catalyst feed opening 7 according to the amount of 1g/min, then opening a carbon source inlet valve port 8, introducing ethylene, controlling the flow of the ethylene by 1.3m3Opening a nitrogen inlet valve port 9 to provide a nitrogen source for the gas-phase damping rings, operating 22 groups of gas-phase damping rings, opening an exhaust gas adjusting port 6 to ensure that the pressure difference in the system is about +250Pa, and the reaction time is about 1 hour; the carbon-hydrogen bond of the ethylene gas is cracked into carbon atoms and hydrogen in a small part at the temperature of 630 ℃ in the initial stage, the hydrogen reduces the cobalt oxide in the catalyst into simple substance metal cobalt, the simple substance metal cobalt is used as a crystal nucleus to catalyze and crack the carbon-hydrogen bond of more hydrocarbons, the carbon atoms are deposited by using the cobalt as the crystal nucleus to generate a carbon nano tube, and part of the hydrogen generated by cracking generates water after reducing the cobalt oxide into the simple substance cobalt and is discharged as waste gas; another part of the hydrogen is discharged through the off-gas port 6. The carbon-hydrogen bond in the cracking chamber is cracked into carbon and hydrogen, carbon atoms are continuously and uniformly loaded on the surface of the cobalt-based catalyst to grow into the carbon nano tube, meanwhile, part of generated hydrogen is used as carrier gas in the cracking chamber, and part of generated hydrogen escapes from the cracking chamber and is collected by the gas collecting system.
And after the reaction is finished, stopping heating the heating furnace, closing a carbon source air inlet valve port 8, opening a nitrogen gas port 10, introducing waste gas in a nitrogen gas replacement system, cooling, after nitrogen gas replacement for 30 minutes, closing the nitrogen gas port 10, opening a discharge valve 11, allowing the material to enter a cooling chamber 2, cooling to room temperature, and taking out the material to obtain the hollow fibrous carbon nanotube, wherein the carbon nanotube has a good shape, relatively uniform diameter and mainly distributed between 5nm and 10nm as shown in figure 3.
Claims (10)
1. A method for preparing carbon nano tubes by catalytically cracking hydrocarbon through a gas phase damping method is characterized by comprising the following steps:
(1) feeding of the catalyst: blowing the carbon nanotube catalyst to an ultrasonic vibration sieve at the top of the cracking chamber from a catalyst feeding port by using nitrogen, and uniformly throwing the catalyst from the top of the cracking chamber into the cracking chamber by using the ultrasonic vibration sieve according to a certain amount;
(2) hydrocarbon catalytic cracking: a heating furnace for heating the cracking chamber is arranged outside the cracking chamber, nitrogen is introduced into the cracking chamber to replace oxygen, after the oxygen content of the system is less than 2%, the heating furnace is heated, carbon source gas is introduced from a carbon source gas inlet at the lower end of the cracking chamber, the carbon nanotube catalyst in the step (1) sequentially enters a first-stage gas-phase damping ring and a second-stage gas-phase damping ring in … Nth-stage gas-phase damping ring, the falling speed of the carbon nanotube catalyst is delayed for N times by the damping of the nitrogen in the gas-phase damping rings, the heating time of the carbon nanotube catalyst in the cracking chamber and the contact time of the carbon source gas are increased until the carbon source gas fully reacts with the carbon nanotube catalyst in the cracking chamber, carbon hydrogen bonds are cracked, and carbon atoms are deposited and; wherein N is more than or equal to 1 and less than or equal to 100;
(3) and cooling and collecting: and the carbon nano tube generated in the cracking chamber enters the cooling chamber from a discharge hole at the bottom end of the cracking chamber, is cooled and then is discharged from a discharge hole, so that the carbon nano tube is obtained.
2. The method of claim 1, wherein the carbon nanotubes of different specifications can be prepared by controlling the temperature of the heating furnace, the number of damping cycles of the gas phase, the feeding amount of the catalyst of the ultrasonic vibration sieve and the flow rate of the carbon source gas according to different carbon nanotube catalysts or different carbon source gases.
3. The method for preparing carbon nanotubes by catalytic cracking of hydrocarbons through gas phase damping according to claim 1 or 2, wherein the carbon nanotube catalyst in step (1) is at least one of a nickel-based catalyst, an iron-based catalyst and a cobalt-based catalyst; the feeding amount of the ultrasonic vibration sieve catalyst is 1-300 g/min, preferably 1-2 g/min, and is determined by ultrasonic frequency and the mesh number of the sieve.
4. The method for preparing carbon nanotubes by catalytic cracking of hydrocarbons through gas phase damping method according to claim 1 or 2, wherein the heating temperature of the heating furnace in the step (2) is 600-800 ℃.
5. The method for preparing carbon nanotubes by catalytic cracking of hydrocarbons through gas phase damping method according to claim 1 or 2, wherein the carbon source gas in step (2) is at least one of methane, propylene or ethylene; the flow rate of the carbon source gas is 1-50 m3Preferably 1 to 3m3/h。
6. The method for preparing carbon nanotubes by catalytic cracking of hydrocarbons through gas phase damping method according to claim 1 or 2, wherein the number of times of gas phase damping in step (2) is 10-80.
7. The method for preparing carbon nanotubes by catalytic cracking of hydrocarbons through a gas phase damping method according to any one of claims 1 to 6, wherein the carbon nanotube catalyst is a nickel-based catalyst; the number N of gas-phase damping turns is 30 levels; the heating temperature of the heating furnace is 790 ℃, the carbon source gas is methane, and the flow rate of the carbon source gas is 2.5m3The feeding amount of the ultrasonic vibration sieve catalyst is 2g/min, and the final product with the diameter of 30-50 nm is obtainedHollow fiber-like carbon nanotubes.
8. The method for preparing carbon nanotubes by catalytic cracking of hydrocarbons through a gas phase damping method according to any one of claims 1 to 6, wherein the carbon nanotube catalyst is an iron-based catalyst; the number N of gas-phase damping turns is 12 levels; the heating temperature of the heating furnace is 660 ℃, the carbon source gas is propylene, and the flow rate of the carbon source gas is 1.7m3And h, feeding the catalyst into the ultrasonic vibration sieve at a feeding amount of 1g/min, and finally obtaining the hollow fibrous carbon nano tube with the diameter of 10-15 nm.
9. The method for preparing carbon nanotubes by catalytic cracking of hydrocarbons through a gas phase damping method according to any one of claims 1 to 6, wherein the carbon nanotube catalyst is a cobalt-based catalyst; the number N of gas-phase damping turns is 22 levels; the heating temperature of the heating furnace is 630 ℃, the carbon source gas is ethylene, and the flow rate of the carbon source gas is 1.3m3And h, feeding the catalyst into the ultrasonic vibration sieve at a feeding amount of 1g/min, and finally obtaining the hollow fibrous carbon nano tube with the diameter of 5-10 nm.
10. A carbon nanotube prepared by catalytic cracking of hydrocarbon by a gas phase damping method, which is characterized by being prepared by the preparation method of any one of claims 1 to 9.
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