CN106276846B - A kind of system and method for preparing CNT - Google Patents

Abstract

The invention belongs to the technical field of carbon nanotube preparation, and in particular relates to a system and method for preparing carbon nanotubes. The system is a Jiugongge flame reactor, the main structure of the reactor is symmetrical, and the cross-sectional shape is Jiugongge; the central flame channel is located in the central grid, and four identical and centrally symmetrical peripheral flame channels are located in the four corners. ; Between every two adjacent peripheral flame channels, there are four identical and centrally symmetrical preparation reaction channels arranged. The flame reactor provided by the invention can continuously prepare carbon nanotubes, and has the advantages of low cost, high output, simple equipment and operation method.

Description

A system and method for preparing carbon nanotubes

technical field

The invention belongs to the technical field of carbon nanotube preparation, and in particular relates to a system and method for preparing carbon nanotubes.

Background technique

Carbon nanotubes are known as the "King of Nano" and exhibit many amazing properties, such as its strength modulus is almost the same as that of diamond, and it has excellent flexibility; it can transport current without resistance at room temperature; it can construct nanoelectronics devices etc. Therefore, more and more scholars begin to study it, and carbon nanotubes have become one of the most popular research topics in the world. Carbon nanotubes have a typical tubular hollow structure, and the tube wall is composed of hexagonal carbon rings formed by combining carbon atoms of graphite-like crystals. The radial size of carbon nanotubes is small, and the diameter of the tubes is generally around several nanometers to tens of nanometers, but the length of the tubes can reach the order of microns, with a very large aspect ratio. Therefore, carbon nanotubes are considered to be a A typical one-dimensional nanomaterial.

Over the years, the preparation technology of carbon nanotubes has been concerned by scientists at home and abroad. At present, there are four main methods for the preparation of carbon nanotubes: arc discharge method, laser evaporation method, chemical vapor deposition method and flame method. Among them, the research work of the first three methods has been carried out more and has been relatively mature so far, but these methods are subject to greater constraints in terms of cost, equipment, and operation. Although the existing flame method for preparing carbon nanotubes achieves the goals of lower cost and convenient operation, most of them have low output, low utilization rate of carbon source, and simple equipment, which does not meet the conditions for mass continuous production. .

Therefore, it is necessary to find a more effective method for preparing carbon nanotubes, so that the preparation process of carbon nanotubes is continuous, batch, controllable, low in cost, simple in equipment, and convenient in operation.

Contents of the invention

The invention provides a system and method for preparing carbon nanotubes, the specific technical scheme is as follows:

A system for preparing carbon nanotubes, the system is a Jiugongge flame reactor, the main structure of the reactor is symmetrical, and the cross-sectional shape is Jiugongge; the central flame channel is located in the central grid, and the four complete The same and centrally symmetrical peripheral flame channels; between every two adjacent peripheral flame channels, four completely identical and centrally symmetrical preparation reaction channels are arranged.

Preferably, the upper outlets of the central flame channel and the peripheral flame channel are located at 5% to 50% of the height of the preparation reaction channel, and the relative height between the flame channel and the preparation reaction channel can be adjusted as required.

Preferably, a fin is installed on each of the four corners of the top of the reactor.

The method for preparing carbon nanotubes by using the above-mentioned system: fuel gas and air are input from the lower end of the central flame passage and four peripheral flame passages, and are ignited at the upper outlet to form a vertically upward central flame and peripheral flame, thereby for The preparation of carbon nanotubes provides the required heat energy; the reaction gas is input from the lower ends of the four preparation reaction channels, and the incompletely reacted residual carbon source gas and other flammable reaction gases are ignited at the upper outlet; Under the action of heating, the carbon source gas in the reaction gas undergoes a chemical reaction in the preparation reaction channel. First, a large number of carbon atoms are decomposed, and then after a series of complicated processes, the carbon atoms are precipitated and graphitized on the surface of the active catalyst particles, and then Nucleation and growth of carbon nanotubes; the process of decomposing a large amount of carbon atoms from the carbon source gas is carried out in the lower part of the preparation reaction channel, and the process of combining carbon atoms into carbon nanotubes is carried out in the upper part of the preparation reaction channel.

Preferably, the fuel gas is acetylene with concentrated flame and high calorific value.

Preferably, the reaction gas is CO, H ₂ and He, wherein CO is the carbon source gas, and H ₂ is a flammable reaction gas.

Preferably, a non-contact thermometer is used to measure the temperature of the carbon atom dissociation reaction zone and the carbon nanotube preparation reaction zone.

Preferably, the non-contact thermometer is a thermocouple.

Preferably, a gas mass flow controller is used to measure and control the mass flow of the gas, and the mass flow of the gas is observed and recorded through a matching digital display instrument.

Preferably, for the prepared carbon nanotubes, the sampling method is: sampling from the vicinity of the upper outlet of the preparation reaction channel by the sampling substrate, or taking a sample by protruding the sampling probe into the interior of the preparation reaction channel.

The upper outlets of the central flame channel and the peripheral flame channel are located at 5% to 50% of the height of the preparation reaction channel, and the relative height between the flame channel and the preparation reaction channel can be adjusted as required. This structure naturally separates the dissociation process of carbon atoms from the generation process of carbon nanotubes, which is conducive to the control of preparation conditions, and the sampling method becomes simple and flexible.

Each preparation reaction channel is heated by the central flame and the peripheral flame at the same time, which makes the heating effect of the flame more obvious, and the gas in the preparation reaction channel is heated more uniformly, which is conducive to increasing the heating temperature and eliminating temperature deviation.

The four preparation reaction channels are identical and center-symmetrical, the heating method and heating conditions are exactly the same, and there is no difference in the composition and flow rate of the gas in each channel, that is, the physical and chemical conditions in the four preparation reaction channels are exactly the same, ensuring the preparation. There is no big difference in shape and quality of carbon nanotubes. In this way, it is only necessary to take samples from these four preparation reaction channels at the same time, and by comparing the shape and quality of the four groups of samples, the contingency of the experimental results can be eliminated, and the credibility and persuasiveness of the experiment can be enhanced; In addition, it also saves the waiting time for sampling in repeated experiments, and greatly improves the efficiency.

Since the peripheral flame channel is in the atmospheric environment, when the required flame temperature is not particularly high, there is no need to input air into it, only need to fix or change the flow rate of the input fuel gas to maintain the combustion of the peripheral flame or adjust the temperature of the peripheral flame . Although the central flame passage is surrounded by the preparation reaction passage, its top is still completely open, and there is enough air to maintain the combustion of the central flame. To adjust the temperature of the central flame, an appropriate amount of air can be input to the central flame passage. Air.

The peripheral flame channel and the preparation reaction channel are not fixed together, and the relative height between them can be changed at will, which is beneficial to control and adjust the dissociation temperature of carbon atoms and the formation temperature of carbon nanotubes. Controlling the dissociation reaction of carbon atoms and the formation reaction of carbon nanotubes separately can control the formation process of carbon nanotubes better and faster, and at the same time facilitates the analysis and discussion of the experimental results.

At the same time, the upper outlets of the central flame channel and the peripheral flame channel are located at 5% to 50% of the height of the preparation reaction channel, and the relative height between them can be adjusted according to needs, which is beneficial to control the dissociation reaction of carbon atoms respectively zone and the temperature of the carbon nanotube generation reaction zone.

In the present invention, the reaction gases in the preparation reaction channel are CO, H ₂ and He. CO provides a carbon source, which can prevent the catalyst surface from being covered by amorphous carbon by competing for active sites, and breaks up large iron particles to generate more active surfaces. _H2 hydrogenates CO to precipitate carbon, and promotes the adsorption of dissociated carbon by iron particles, which is beneficial to the growth of carbon nanotubes and maintains the activity of the catalyst. He mainly plays the role of local dilution and cooling, and the helium carrying the mist catalyst into the reactor also affects the supply speed of the catalyst. In addition, H ₂ and He also have the effect of purging and purifying the surface of carbon nanotubes, and can also effectively maintain the activity of the catalyst.

In particular embodiments, other carbon sources may be substituted for CO.

A fin is installed on the four corners of the top of the Jiugongge reactor. On the one hand, they can cause the CO ₂ gas produced by the peripheral flame to flow around, so as to merge with the CO ₂ gas produced by the central flame. , so that a large amount of CO ₂ gas surrounds the top of the preparation reaction channel, hindering the entry of oxygen, thereby forming a relatively anoxic environment, reducing the flame temperature at the top of the preparation reaction channel, preventing the prepared carbon nanotubes from being burned, and helping to improve carbon nanotubes. The output of the tube; on the other hand, it promotes the return of the peripheral flame to enhance combustion, improve the utilization rate of fuel gas, and save fuel.

In the present invention, both the carbon atom dissociation reaction zone and the carbon nanotube preparation reaction zone require relatively high temperatures, which cannot be measured by a general thermometer. At the same time, considering the factors of measurement accuracy, high-precision thermocouples and other non-contact thermometers are selected to measure the temperature.

The flame reactor provided by the invention can continuously prepare carbon nanotubes, and has the advantages of low cost, high output, simple equipment and operation method.

Description of drawings

Fig. 1 is the top view of Jiugongge type reactor;

Fig. 2 is the 3D schematic diagram (lateral top view) of Jiugongge type reactor;

Fig. 3 is the 3D schematic diagram (side looking up) of Jiugong grid type reactor;

Symbols in the figure: 1-peripheral flame channel, 2-central flame channel, 3-preparation reaction channel, 4-fin, 5-jiugongge flame reactor, 6-reaction gas input, 7-flame fuel input.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Figure 1 shows a nine-square flame reactor for preparing carbon nanotubes. The main structure of the reactor is symmetrical, and the cross-sectional shape is a nine-square grid; the central flame channel is located in the central grid, and four identical flame channels are located at the four corners. and a centrally symmetrical peripheral flame channel; between every two adjacent peripheral flame channels, four completely identical and centrally symmetrical preparation reaction channels are arranged.

It can be seen from Figure 2 and Figure 3 that the upper outlets of the central flame channel and the peripheral flame channel are located at 5% to 50% of the height of the preparation reaction channel, and the relative height between the flame channel and the preparation reaction channel can be adjusted according to the needs. Adjustment. And each of the four corners on the top of the reactor is equipped with a fin.

The method for preparing carbon nanotubes using the above-mentioned system: acetylene and air are input from the lower end of the central flame channel and four peripheral flame channels, and are ignited at the upper end outlet to form a vertically upward central flame and peripheral flame; CO, H ₂ and He are input from the lower ends of the four preparation reaction channels, H ₂ and incompletely reacted residual CO are ignited at the outlet of the upper end; under the double heating of the central flame and the peripheral flame, CO undergoes a chemical reaction in the preparation reaction channel, First, a large number of carbon atoms are decomposed, and then after a series of complicated processes, the carbon atoms are precipitated and graphitized on the surface of the active catalyst particles, and then nucleated and grown into carbon nanotubes; the process of decomposing a large amount of carbon atoms from the carbon source gas is in The lower half of the preparation reaction channel is carried out, and the process of combining carbon atoms into carbon nanotubes is carried out in the upper half of the preparation reaction channel.

A non-contact thermometer is used to measure the temperature of the carbon atom dissociation reaction zone and the carbon nanotube preparation reaction zone. The gas mass flow controller is used to measure and control the gas mass flow, and the gas mass flow is observed and recorded through the supporting digital display instrument. For the prepared carbon nanotubes, the sampling method is as follows: sampling from the vicinity of the upper outlet of the preparation reaction channel by the sampling substrate, or protruding the sampling probe into the interior of the preparation reaction channel for sampling.

Claims (9)

1. a system for preparing carbon nanotubes is characterized in that, the system is a nine-square grid flame reactor (5), and the main body structure of the reactor is symmetrical, and the cross-sectional shape is a nine-square grid; what is positioned at the center grid is a central flame passage ( 2), located on the four corners are four identical and centrally symmetrical peripheral flame passages (1); between every two adjacent peripheral flame passages (1), there are four identical and centrally symmetrical The preparation reaction channel (3); the upper end outlets of the central flame channel (2) and the peripheral flame channel (1) are all located at 5% to 50% of the height of the preparation reaction channel (3), and the flame channel and the preparation reaction channel ( 3) The relative height between them can be adjusted as required. 2. A system for preparing carbon nanotubes according to claim 1, characterized in that a piece of fin (4) is respectively installed on the four corners of the top of the reactor. 3. utilize the method for preparing carbon nanotube according to any one of claim 1-2 system, it is characterized in that fuel gas and air are imported from the lower end of central flame passage (2) and four peripheral flame passages (1), in The outlet at the upper end is ignited to form a vertical upward central flame and peripheral flame; The reaction gas is input from the lower ends of the four preparation reaction channels (3), and the incompletely reacted residual carbon source gas and other flammable reaction gases are ignited at the outlet of the upper end; under the double heating of the central flame and the peripheral flame, the reaction gas The carbon source gas undergoes a chemical reaction in the preparation reaction channel (3). First, a large number of carbon atoms are decomposed, and then after a series of complicated processes, the carbon atoms are precipitated and graphitized on the surface of the active catalyst particles, and then nucleate and grow into carbon nanotubes; The process of decomposing a large amount of carbon atoms from the carbon source gas is carried out in the lower part of the preparation reaction channel (3), and the process of combining carbon atoms into carbon nanotubes is carried out in the upper part of the preparation reaction channel (3). 4. The method of claim 3, wherein the fuel gas is acetylene. 5. The method according to claim 3, wherein the reaction gas is CO, H ₂ and He, wherein CO is the carbon source gas, and H ₂ is a flammable reaction gas. 6. The method according to claim 3, characterized in that a non-contact thermometer is used to measure the temperature of the carbon atom dissociation reaction zone and the carbon nanotube preparation reaction zone. 7. The method of claim 6, wherein the non-contact thermometer is a thermocouple. 8. The method according to claim 3, characterized in that a gas mass flow controller is used to measure and control the mass flow of the gas, and the mass flow of the gas is observed and recorded through a supporting digital display instrument. 9. The method according to claim 3, characterized in that, for the prepared carbon nanotubes, the sampling method is: sampling near the upper end outlet of the preparation reaction channel (3) by the sampling substrate, or extending the sampling probe into Internal sampling of the reaction channel (3) is prepared.