Carbon nanotube reaction device and preparation method

Abstract

The invention provides a carbon nanotube reaction device and a preparation method. According to the device, the catalyst evaporation system is additionally arranged at the gas inlet end at the bottom of the fluidized bed reactor, and the system introduces a gaseous active substance into a reaction area through carrier gas, so that the gaseous active substance is effectively attached to a fluidized powder carrier, and hydrocarbon gas is further catalytically cracked. According to the reaction device and the preparation method, traditional tedious steps for preparing the powder catalyst are omitted, and in-situ generation of the catalyst is achieved. And the active metal particles gradually aggregate and grow from a molecular or atomic state, so that small-size active metal nanoparticles are easier to form. Meanwhile, collision and agglomeration of active metal particles in a high-temperature environment are effectively avoided due to the barrier effect of the porous carrier in the fluidized bed, and finally, the high-quality few-wall or single-wall carbon nanotubes are successfully prepared.

Description

Technical Field

[0001] The invention relates to the field of carbon nanotube production, in particular to a carbon nanotube reaction device and a preparation method. Background Art

[0002] Carbon nanotubes were first discovered when preparing fullerenes, and have now become one of the hottest research objects in the field of nanotechnology. Its structure is a complete graphene network. Theoretically, it is predicted that its strength is about 100 times that of steel, while its density is only 1 / 6 of that of steel. At the same time, it has excellent flexibility, so it is known as "super fiber". When carbon nanotubes are combined with other materials as reinforcements, the advanced composite materials formed show great application potential in cutting-edge fields such as aviation and aerospace. In addition, carbon nanotubes also have excellent field emission properties such as low emission threshold, high emission current density, and high stability, and are expected to be widely used in high-performance flat-panel displays, nano transistors and other fields. Its unique electrical properties make it possible to manufacture nanoelectronic devices and sensors. Therefore, research on carbon nanotubes has received widespread attention from scientists from all over the world and is one of the hot spots and frontiers of scientific research today. People hope to use the special properties of carbon nanotubes to create new functional materials, devices and systems through control and exploration at the nanoscale.

[0003] With the deepening of research on the engineering application of carbon nanotubes, the production of carbon nanotubes with high purity, large output, uniform tube diameter, few defects, convenient operation and low cost has become the focus of carbon nanotube preparation research. The catalytic chemical vapor deposition method has attracted much attention due to its ability to mass produce and has broad prospects for industrial application. Therefore, it is of great significance to study the catalysts and processes for the preparation of carbon nanotubes by catalytic chemical vapor deposition, to achieve mass production of high-purity, specific structure carbon nanotubes, to maintain catalyst activity, to improve the utilization rate of raw materials and other key technical issues.

[0004] In the existing industrial preparation process, moving bed or fluidized bed process is mostly used to prepare carbon nanotubes in batches. These processes usually require the preparation of powder catalysts in advance, and then the catalysts are put into the reactor to grow carbon nanotubes. The active metal particles loaded on the catalyst are the "seeds" for growing carbon nanotubes, and the diameter of carbon nanotubes mainly depends on the size of these active metal particles. So when preparing powder catalysts, it is necessary to adjust the dispersion of active metals on the carrier and the interaction between active metals and carriers from the aspects of loading amount, active metal type, additive type, carrier type, catalyst preparation method, etc., so as to control the size of active metal nanoparticles.

[0005] Although a variety of catalyst systems with excellent performance have been developed for the preparation of multi-walled carbon nanotubes, there are still great technical difficulties in controlling the size of the catalyst active metal particles when preparing few-walled carbon nanotubes and single-walled carbon nanotubes. Although the catalytic floating method can produce high-quality single-walled carbon nanotubes, the required reaction temperature exceeds 1200 ° C, and the equipment material requirements are strict, which limits its practical application. Therefore, how to efficiently and stably prepare high-quality few-walled and single-walled carbon nanotubes at a lower reaction temperature has become a key issue that needs to be solved urgently. Summary of the invention

[0006] In view of the above-mentioned deficiencies and defects in the prior art, the purpose of the present invention is to provide a carbon nanotube reaction device and preparation method. Compared with conventional fluidized bed equipment, the present device adds a catalyst evaporation system at the air inlet end at the bottom of the fluidized bed reactor. The system introduces gaseous active substances into the reaction zone through a carrier gas, so that they are effectively attached to the fluidized powder carrier, thereby catalytically cracking hydrocarbon gases. The reaction device and preparation method not only eliminate the cumbersome steps of traditional preparation of powder catalysts, but also realize the in-situ generation of catalysts. Compared with traditional powder catalysts, active metal particles gradually aggregate and grow from the molecular or atomic state, and are easier to form small-sized active metal nanoparticles. At the same time, the barrier effect of the porous carrier in the fluidized bed effectively avoids the collision and agglomeration of active metal particles in a high temperature environment, and finally successfully prepares high-quality few-walled or single-walled carbon nanotubes.

[0007] To achieve the above purpose, the technical solution provided by the present invention is: In a first aspect, the present invention provides a carbon nanotube reaction device, comprising a fluidized bed main reactor, a gas distributor, a powder carrier storage tank, a gas-solid separator, a product collection tank and a catalyst evaporation chamber. The powder carrier storage tank is connected to the main reactor, the gas distributor is arranged at the lower part of the main reactor, the gas-solid separator is located at the top of the main reactor, the product collection tank is connected to the lower part of the main reactor, a gas inlet is arranged at the bottom of the main reactor, and is connected to the gas outlet of the catalyst evaporation chamber, and a gas inlet is arranged on the side wall of the catalyst evaporation chamber.

[0008] The catalyst evaporation chamber includes a furnace tube and a heating furnace. The metallocene raw material is placed in a quartz boat in the furnace tube. The carrier gas enters from the air inlet end of the furnace tube, carrying the volatilized metallocene, and escapes from the air outlet end of the furnace tube, and finally merges with the gas inlet at the bottom of the fluidized bed main reactor and enters the main reactor together.

[0009] The catalyst evaporation chamber can also be designed as a plasma arc furnace, in which a plasma anode is installed at the bottom and a plasma cathode is configured at the top, and the two are connected by a plasma power supply. Under the protection of inert gas, the plasma working gas is introduced from the cathode of the arc furnace, and a plasma arc is generated after being energized. The arc quickly melts and evaporates the anode metal placed in the graphite crucible. Subsequently, the volatilized metal vapor is carried by the carrier gas of the side wall air inlet, escapes from the air outlet of the plasma arc furnace, and finally converges with the gas inlet at the bottom of the fluidized bed main reactor and flows into the main reactor together.

[0010] The catalyst evaporation chamber is equipped with a catalyst raw material storage tank to ensure timely replenishment of the catalyst raw material to meet the needs of continuous and stable catalytic reaction.

[0011] The metallocene raw material is at least one of ferrocene, cobaltocene and nickelocene.

[0012] The anode metal is at least one of iron, cobalt, nickel, molybdenum and copper.

[0013] In a second aspect, the present invention provides a method for preparing carbon nanotubes, using the above-mentioned reaction device, comprising the following steps:

[0014] Step 1: Introduce inert gas to completely exhaust the air inside the device, then start the power supply to gradually heat the fluidized bed main reactor to the preset reaction temperature. At the same time, the heating furnace of the catalyst evaporation chamber is also started and heated to the preset temperature, or a plasma arc furnace is used to pass plasma working gas into the plasma cathode and start the plasma power supply to generate a stable plasma arc between the plasma cathode and the anode, so that the plasma arc furnace is heated to the set temperature.

[0015] Step 2: Place the powder carrier in the powder carrier storage tank into the main reactor, and adjust the flow rate of nitrogen at the main reactor inlet to make the powder carrier reach a fluidized state. Subsequently, the carrier gas is introduced into the gas inlet of the catalyst evaporation chamber, and hydrogen and hydrocarbon gas are introduced into the gas inlet at the bottom of the main reactor. In the constant temperature zone of the main reactor, the cracked organic carbon source combines with the active metal particles formed by evaporation and adsorbed on the powder carrier to catalyze the growth of carbon nanotubes.

[0016] The temperature of the main reactor in step 1 is set at 600-900°C.

[0017] The temperature of the heating furnace of the catalyst evaporation chamber in step 1 is set to 50-400°C.

[0018] The power of the plasma arc furnace in step 1 is 50-300 kW, and the set temperature is 1000-1600°C.

[0019] The plasma working gas in step 1 is any one of argon, nitrogen and hydrogen, or a mixture of two or three of them in any mixing ratio.

[0020] The powder carrier in step 2 is any one of g-Al2O3, MgO, CaO, SiO2, TiO2, vermiculite and montmorillonite. These carriers can be pre-treated to become composite dual carriers.

[0021] The carrier gas in step 2 is any one of argon, nitrogen and hydrogen, or a mixture of two or three of them in any mixing ratio.

[0022] The hydrocarbon gas in step 2 is any one of ethylene, propylene, methane and natural gas, or a mixture of two or three of them in any mixing ratio.

[0023] Compared with the prior art, the present invention has the following beneficial effects: The present invention adds a catalyst evaporation chamber to the fluidized bed design, and the size of the active metal particles can be directly regulated by controlling the evaporation amount of the active metal-containing substance, thereby eliminating the traditional step of preparing powder catalysts. The active metal particles in the traditional powder catalyst themselves have a certain grain size. Under high temperature reaction conditions, the grain size tends to continue to increase, resulting in the doping of some multi-walled carbon nanotubes in the few-walled or single-walled carbon nanotubes. The present invention adopts a method of aggregation starting from the molecular or atomic state to form small-sized active metal clusters, effectively reducing the generation of multi-walled carbon nanotubes and improving the quality of the product. In addition, the porous carrier in the fluidized bed plays a barrier role in the reaction, effectively preventing the collision and aggregation of active metal particles at high temperatures, and further ensuring the high purity of the few-walled or single-walled carbon nanotubes. Compared with the traditional catalytic floating method, the active metal clusters of the present invention enter the main reactor and are adsorbed on the porous carrier. By interacting with it, the catalytic activity of the active metal particles is promoted, and the temperature required for the reaction is reduced, thereby improving the energy efficiency of the entire production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the overall structure of the reaction device of the present invention;

[0025] Figure 2 It is a schematic structural diagram of a catalyst evaporation chamber in the form of a heating furnace of the present invention;

[0026] Figure 3 It is a schematic diagram of the structure of the catalyst evaporation chamber in the form of a plasma arc furnace of the present invention.

[0027] In the figure: 1. Catalyst evaporation chamber; 2. Fluidized bed main reactor; 3. Gas distributor; 4. Powder carrier storage tank; 5. Main reactor air inlet; 6. Catalyst evaporation chamber air inlet; 7. Gas-solid separator; 8. Product collection tank; 9. Catalyst evaporation chamber air outlet. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0029] like Figure 1 As shown, a carbon nanotube reaction device comprises: a fluidized bed main reactor 2, a powder carrier storage tank 4, a gas distributor 3, a gas-solid separator 7, a product collection tank 8 and a catalyst evaporation chamber 1.

[0030] Among them, the powder carrier storage tank 4 is connected to the main reactor 2, the gas distributor 3 is arranged at the lower part of the main reactor 2, the gas-solid separator 7 is located at the top of the main reactor 2, the product collection tank 8 is connected to the lower part of the main reactor 2, and the catalyst evaporation chamber 1 is placed at the bottom of the main reactor 2. The side wall of the catalyst evaporation chamber is provided with an air inlet 6 and an air outlet 9, and the air outlet 9 is connected to the air inlet 5 at the bottom of the main reactor.

[0031] Specifically, Figure 2 As shown, the catalyst evaporation chamber 1 includes several core parts, namely, a furnace tube 21, a heating furnace 22, a quartz boat 23 and a metallocene storage tank 24. The metallocene is filled in the quartz boat 23, the heating furnace is heated to a set temperature, and the carrier gas enters the evaporation chamber from the air inlet 6 to carry the metallocene vapor generated by the heating, and finally the metallocene vapor is guided to the desired area through the air outlet 9.

[0032] Specifically, Figure 3 As shown, the catalyst evaporation chamber 1 can also be designed in the form of a plasma arc furnace, which mainly includes: an arc furnace body 31, a plasma arc furnace cathode 32, a graphite crucible 33 and a catalyst raw material storage tank 35. The anode metal is placed in the graphite crucible 33, and the plasma working gas is introduced from the cathode 32 of the arc furnace. After being energized and excited, a plasma arc 34 is formed. The arc 34 quickly melts and evaporates the anode metal in the graphite crucible 33. Subsequently, the generated metal vapor is carried by the carrier gas introduced by the side wall air inlet 6 and escapes from the gas outlet 9 of the plasma arc furnace. The metal vapor eventually converges with the gas inlet at the bottom of the fluidized bed main reactor and flows into the main reactor together to provide the required active metal for the reaction process.

[0033] Using the carbon nanotube reaction device, the preparation method specifically includes the following steps: Step 1: Inert gas is introduced to completely exhaust the air inside the device, and then the power is started to gradually heat the fluidized bed main reactor 2 to a preset reaction temperature. At the same time, the heating furnace 22 of the catalyst evaporation chamber 1 is also started and heated to a preset temperature, or a plasma arc furnace 31 is used to introduce plasma working gas into the plasma cathode 32, and the plasma power is started to generate a stable plasma arc 34 between the plasma cathode and the anode, so that the plasma arc furnace is heated to a set temperature.

[0034] Step 2: The powder carrier in the powder carrier storage tank 4 is placed into the main reactor 2, and the powder carrier is fluidized by adjusting the flow rate of nitrogen at the main reactor air inlet 5. Subsequently, the carrier gas is introduced into the gas inlet 6 of the catalyst evaporation chamber, and hydrogen and hydrocarbon gas are introduced into the gas inlet 5 at the bottom of the main reactor. In the constant temperature zone of the main reactor, the cracked organic carbon source combines with the active metal particles formed by evaporation and adsorbed on the powder carrier to catalyze the growth of carbon nanotubes.

[0035] The setting temperature of the main reactor in step 1 is 600-900°C.

[0036] The temperature of the heating furnace of the catalyst evaporation chamber in step 1 is set to 50-400°C.

[0037] The power of the plasma arc furnace in step 1 is 50-300 kW, and the set temperature is 1000-1600°C.

[0038] The plasma working gas in step 1 is any one of argon, nitrogen and hydrogen, or a mixture of two or three of them in any mixing ratio.

[0039] The powder carrier in step 2 is any one of g-Al2O3, MgO, CaO, SiO2, TiO2, vermiculite and montmorillonite. These carriers can be pre-treated to become composite dual carriers.

[0040] The carrier gas in step 2 is any one of argon, nitrogen and hydrogen, or a mixture of two or three of them in any mixing ratio.

[0041] The hydrocarbon gas in step 2 is any one of ethylene, propylene, methane and natural gas, or a mixture of two or three of them in any mixing ratio.

[0042] Example 1 (1) Inert gas is introduced to completely exhaust the air inside the device, and then the power is turned on to gradually heat the fluidized bed main reactor to 750°C. At the same time, the heating furnace 22 of the catalyst evaporation chamber is also started and heated to 100°C. The metallocene raw material is ferrocene; (2) The g-Al2O3 powder carrier in the powder carrier storage tank is placed into the main reactor, and the powder carrier is fluidized by adjusting the flow rate of nitrogen at the main reactor inlet. Subsequently, nitrogen is introduced into the gas inlet of the catalyst evaporation chamber, and hydrogen and ethylene are introduced into the gas inlet at the bottom of the main reactor.

[0043] (3) After the reaction is completed, the product is transferred to a product collection tank.

[0044] Example 2 (1) Inert gas is introduced to completely exhaust the air inside the device, and then the power is turned on to gradually heat the fluidized bed main reactor to 680°C. At the same time, in the 50 kW plasma arc furnace 31, argon as a plasma working gas is introduced into the plasma cathode, and the plasma power is turned on to generate a stable plasma arc between the plasma cathode and the anode, so that the temperature of the plasma arc furnace is raised to 1400°C. The anode metal is iron powder.

[0045] (2) The g-Al2O3 powder carrier in the powder carrier storage tank is placed into the main reactor, and the powder carrier is fluidized by adjusting the flow rate of nitrogen at the gas inlet of the main reactor. Subsequently, argon and hydrogen are introduced into the gas inlet of the catalyst evaporation chamber, and hydrogen and propylene are introduced into the gas inlet at the bottom of the main reactor.

[0046] (3) After the reaction is completed, the product is transferred to a product collection tank.

[0047] The above is a detailed introduction to a carbon nanotube reaction device and preparation method provided in the embodiments of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application; at the same time, for those skilled in the art, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as limiting the present application.

Claims

1. A carbon nanotube reaction device, characterized in that: A catalyst evaporation system is added at the air inlet end at the bottom of the fluidized bed reactor. The reaction device includes a fluidized bed main reactor, a gas distributor, a powder carrier storage tank, a gas-solid separator, a product collection tank and a catalyst evaporation chamber.

2. A carbon nanotube reaction device according to claim 1, characterized in that: The powder carrier storage tank is connected to the main reactor, the gas distributor is arranged at the lower part of the main reactor, the gas-solid separator is located at the top of the main reactor, the product collection tank is connected to the lower part of the main reactor, a gas inlet is provided at the bottom of the main reactor, and is connected to the gas outlet of the catalyst evaporation chamber, and a gas inlet is provided on the side wall of the catalyst evaporation chamber.

3. The carbon nanotube reaction device according to claim 1, characterized in that: The catalyst evaporation chamber includes a furnace tube and a heating furnace. The metallocene raw material is placed in a quartz boat in the furnace tube. The carrier gas enters from the air inlet end of the furnace tube, carrying the volatilized metallocene, and escapes from the air outlet end of the furnace tube, and finally merges with the gas inlet at the bottom of the fluidized bed main reactor and enters the main reactor together.

4. The carbon nanotube reaction device according to claim 1, characterized in that: The catalyst evaporation chamber can also be designed as a plasma arc furnace, in which a plasma anode is installed at the bottom and a plasma cathode is provided at the top, and the two are connected by a plasma power supply. Under the protection of an inert gas, a plasma working gas is introduced from the cathode of the arc furnace, and a plasma arc is generated after being energized. The arc rapidly melts and evaporates the anode metal placed in the graphite crucible. Subsequently, the volatilized metal vapor is carried by the carrier gas from the side wall air inlet, escapes from the air outlet of the plasma arc furnace, and finally converges with the gas inlet at the bottom of the fluidized bed main reactor and flows into the main reactor together; The catalyst evaporation chamber is equipped with a catalyst raw material storage tank to ensure timely replenishment of the catalyst raw material to meet the needs of continuous and stable catalytic reaction; The metallocene raw material is at least one of ferrocene, cobaltocene and nickelocene; The anode metal is at least one of iron, cobalt, nickel, molybdenum and copper.

5. A method for preparing carbon nanotubes using the reaction device according to claim 1, characterized in that: The steps include: Step 1: Introduce inert gas to completely exhaust the air inside the device, then start the power supply to gradually heat the fluidized bed main reactor to the preset reaction temperature. At the same time, the heating furnace of the catalyst evaporation chamber is also started and heated to the preset temperature, or a plasma arc furnace is used to pass plasma working gas into the plasma cathode and start the plasma power supply to generate a stable plasma arc between the plasma cathode and the anode, so that the plasma arc furnace is heated to the set temperature; The setting temperature of the main reactor is 600-900°C; The heating furnace temperature of the catalyst evaporation chamber is set to 50-400°C; The power of the plasma arc furnace is 50-300 kW, and the set temperature is 1000-1600 °C; The plasma working gas is any one of argon, nitrogen and hydrogen, or a mixture of two or three of them in any mixing ratio; Step 2: Place the powder carrier in the powder carrier storage tank into the main reactor, and adjust the flow rate of nitrogen at the air inlet of the main reactor to make the powder carrier reach a fluidized state. Subsequently, introduce the carrier gas into the gas inlet of the catalyst evaporation chamber, and introduce hydrogen and hydrocarbon gas into the gas inlet at the bottom of the main reactor. In the constant temperature zone of the main reactor, the cracked organic carbon source combines with the active metal particles formed by evaporation and adsorbed on the powder carrier to catalyze the growth of carbon nanotubes; The powder carrier is any one of g-Al2O3, MgO, CaO, SiO2, TiO2, vermiculite and montmorillonite. These carriers can be pre-treated to become composite dual carriers; The carrier gas is any one of argon, nitrogen and hydrogen, or a mixture of two or three of them in any mixing ratio; The hydrocarbon gas is any one of ethylene, propylene, methane and natural gas, or a mixture of two or three of them in any mixing ratio.

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