Device and method for preparing single-wall and few-wall carbon nanotubes

Abstract

The invention discloses a device and a method for preparing single-wall and few-wall carbon nanotubes, and relates to the technical field of nano carbon materials, the device structurally comprises a heating system, a feeding system, a gas path system, a cooling system and an electrical system, the heating system comprises a medium-frequency induction furnace, an induction coil and a graphite crucible; the gas path system comprises a gas inlet; the feeding system comprises a second catalyst feeding hole and a discharging hole; wherein the feeding hole is formed above the graphite crucible, the air inlet is formed in the side surface of the medium-frequency induction furnace, and the discharging hole is formed in the other side of the medium-frequency induction furnace. The metal molten pool is used as a heat source, a steady-state heat source is provided for catalyst evaporation and single-wall / few-wall carbon nanotube growth, compared with a plasma method and an electric arc method, catalyst evaporation is more uniform and mild, the catalyst utilization rate is increased, and the single-wall / few-wall carbon nanotube growth efficiency is remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of nano carbon materials, and specifically provides a device and method for preparing single-walled and few-walled carbon nanotubes. Background Art

[0002] Single-walled carbon nanotubes can be regarded as one-dimensional tubular nanomaterials composed of a single layer of curled graphite. Their super-strong carbon-carbon bonds give them superior comprehensive properties, such as high strength, high modulus, high thermal conductivity and excellent electrical conductivity. They have important applications in structural composite materials, electrochemical energy storage, catalysis and other fields.

[0003] At present, the main methods for preparing single-walled carbon nanotubes include arc discharge, laser ablation, plasma method and chemical vapor deposition method. Arc discharge, laser ablation and plasma method are the earliest preparation technologies studied, but the low yield and purity are difficult to improve, making it difficult to industrialize. Chemical vapor deposition has achieved great success in the field of preparing multi-walled carbon nanotubes and has achieved 10,000-ton-level preparation, but the preparation of single-walled carbon nanotubes by this method is still only in the laboratory stage, and high-efficiency and low-cost preparation technology is still a hot topic of research.

[0004] US invention patent US8551413B2 discloses a method for preparing single-walled carbon nanotubes by evaporating metal catalysts using plasma arc, which is currently the only technical route that can achieve the industrialization of single-walled carbon nanotubes. However, due to the extremely high temperature of the plasma arc, the evaporation rate of the catalyst is difficult to control, and a large amount of metal catalysts cannot be effectively utilized. Further control measures must be adopted to screen and purify the final practical product, resulting in its cost remaining high.

[0005] Chinese invention patent CN202111322714.0 attempts to partially solve the current problem by isolating the catalyst evaporation chamber and the growth chamber, but the simple separation approach will cause the catalyst to aggregate and grow during transportation and become ineffective, while also reducing the thermal energy utilization rate, resulting in a decrease in yield and an increase in preparation cost.

[0006] China's invention patent CN202210608795.9 further improves on this basis. By setting a rotating solid catalyst electrode, the plasma arc does not evaporate in one place, and the catalyst evaporation temperature is reduced to regulate the catalyst evaporation rate. This can not only effectively reduce the power of the plasma generator to prepare catalyst nanoparticles, but also optimize and regulate the particle size distribution of the prepared catalyst nanoparticles, which is conducive to controlling and optimizing the uniformity of the grown products. However, how to balance quality, efficiency and yield is still a very difficult and contradictory problem. How to continuously and batch-produce single-walled carbon nanotubes is still a great challenge. Summary of the invention

[0007] In view of the above problems, the present invention provides a device and method for preparing single-walled and few-walled carbon nanotubes to overcome the deficiencies in the prior art.

[0008] On one hand, the present invention provides the following technical solutions: A device for preparing single-walled and few-walled carbon nanotubes, the structure of the device includes a heating system, a feeding system, a gas circuit system, a cooling system, and an electrical system, wherein: The heating system includes a medium frequency induction furnace, an induction coil, and a graphite crucible; The gas circuit system includes an air inlet; The feeding system comprises a second catalyst feeding port and a discharging port; The feed port is arranged above the graphite crucible, the air inlet is arranged on the side of the medium frequency induction furnace, and the discharge port is arranged on the other side.

[0009] Furthermore, the inner diameter of the graphite crucible is 10-200 cm, and the air inlet is 1-10 cm higher than the upper edge of the graphite crucible.

[0010] On the other hand, the present invention provides a method for preparing single-walled and few-walled carbon nanotubes. The method utilizes medium-frequency induction heating to melt a first metal catalyst to form a high-temperature molten pool, and obtains first metal catalyst particles by evaporation on the surface of the molten liquid. At the same time, a second catalyst and a co-catalyst are atomized and evenly sprayed on the molten liquid surface, and a carbon source gas is introduced. The heat radiated by the high-temperature molten pool provides a heat source for the cracking of the second catalyst and the carbon source gas, thereby achieving catalyst preparation and carbon nanotube growth in one step, and the growth product is discharged and collected with the tail gas.

[0011] Furthermore, the method specifically comprises the following steps: S1) placing a first metal catalyst in a graphite crucible; S2) evacuate the medium frequency induction furnace to remove air, then switch to introduce inert gas, and turn on the power supply to heat after the pressure stabilizes, so as to melt the first metal catalyst in the graphite crucible until the furnace temperature rises to a specified temperature of 1000-2200°C, forming a molten liquid surface; S3) introducing a mixed powder of the second catalyst and the promoter carried by the inert gas into the medium frequency induction furnace from the feed port, and atomizing and spraying the mixed powder onto the molten liquid surface; S4) After the carbon source gas is mixed with the carrier gas, it carries water vapor into the medium frequency induction furnace from the air inlet to start the reaction; S5) The reaction product is discharged from the furnace through the discharge port, and the single-walled and few-walled carbon nanotube products are obtained by collection.

[0012] Furthermore, the first metal catalyst in S1) is iron, cobalt, nickel or a mixture thereof.

[0013] Furthermore, the first metal catalyst in S1) is a mixture of iron, cobalt or nickel or their alloys and refractory metals, wherein the refractory metal element is molybdenum, tungsten, tantalum, niobium, hafnium or zirconium, and the weight ratio of the refractory metal element is 10-80% of the first metal catalyst. Furthermore, the second catalyst in S3) is any one of ferrocene, nickelocene, cobaltocene, ferric acetylacetonate, nickel acetylacetonate, cobalt acetylacetonate, carbonyl iron powder or a mixture thereof.

[0014] Furthermore, the co-catalyst is any one of sulfur, selenium, iron sulfide, ferrous sulfide, nickel sulfide, and cobalt sulfide, wherein the ratio of the second catalyst to the co-catalyst is 1:1~20:1, and the feed rate is 0.1 g / min-100 g / min.

[0015] Furthermore, the inert gas (S2) is any one of argon, nitrogen, and helium, or a mixture of any proportion.

[0016] Furthermore, the carbon source gas in S4) is methane, ethylene, acetylene, propylene or propane; The carrier gas is a mixture of nitrogen, argon or helium inert gas and hydrogen, wherein the volume of the carbon source gas is 10-80%; the volume of hydrogen is 1-40%, and the rest is inert gas, with a flow rate of 1 L / min-500 L / min; The water feed rate during the water vapor preparation is 0.5-50 mL / min.

[0017] Compared with the prior art, the device and method for preparing single-walled and few-walled carbon nanotubes of the present invention have the following outstanding beneficial effects: (1) The molten metal pool is used as the heat source, which provides a steady-state heat source for catalyst evaporation and single-walled / few-walled carbon nanotube growth. Compared with the plasma method and the arc method, the catalyst evaporation is more uniform and gentle, which improves the catalyst utilization rate and significantly improves the growth efficiency of single-walled / few-walled carbon nanotubes.

[0018] (2) The first metal catalyst is heated by induction to quickly form a molten metal pool, which avoids the problem of high-speed plasma impact causing turbulent air flow in the furnace in conventional plasma and arc methods. It also avoids the interference of complex atmosphere components on the stability of the plasma arc, overcomes the problem of easy arc breaking, and greatly improves the reaction stability.

[0019] (3) The temperature of the first metal catalyst melt pool is controllable, which can accurately control the evaporation rate of the catalyst, while the non-steady-state heat source of the non-plasma arc method cannot control the temperature, which greatly improves the controllability of various parameters in the carbon nanotube growth process. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1This is a schematic diagram of the structure of the preparation device of the present invention; Figure 2 This is a scanning electron microscope image of the carbon nanotube product of the present invention; Figure 3 This is a Raman spectrum of the carbon nanotube product of the present invention; Figure 4 This is a transmission electron microscope image of the carbon nanotube product of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Example 1

[0022] like Figure 1 As shown, a preparation device for single-walled and few-walled carbon nanotubes includes auxiliary equipment such as a feeding system, a gas circuit system, a cooling system, and an electrical system, and specifically includes a medium-frequency induction furnace 1, an induction coil 2, a graphite crucible 3, an air inlet 5, a feeding port 6, and a discharging port 8. The feeding port 6 is arranged above the graphite crucible 3, the air inlet 5 is arranged on the side of the medium-frequency induction furnace 1 and is 5 cm higher than the upper edge of the graphite crucible 3, and the inner diameter of the graphite crucible 3 is 50 cm.

[0023] The preparation process is as follows: S1) placing a first metal catalyst 60% Fe-40% Mo alloy in a graphite crucible 3; S2) evacuate the medium frequency induction furnace 1 to remove air, then switch to inert gas Ar, and turn on the power supply for heating after the pressure stabilizes to melt the first metal catalyst in the graphite crucible 3 to form a flat molten pool until the furnace temperature rises to 1700°C; S3) a mixed powder of ferrocene and sulfur powder in a ratio of 10:1 carried by an inert gas is fed into the medium frequency induction furnace 1 through the feed port 6 and atomized and sprayed onto the molten liquid surface at a feed rate of 2 g / min; S4) The carbon source gas and the carrier gas form a mixed gas, wherein methane is 60%, hydrogen is 20%, and argon is 20%, and the flow rate is 50 L / min. The mixed gas carries water vapor and enters the medium frequency induction furnace 1 from the gas inlet 5. When the water vapor is prepared, the water feed rate is 5 mL / min, and the reaction starts; S5) The reaction product is discharged from the furnace through the discharge port, and the single-walled and few-walled carbon nanotube products are obtained by collection.

[0024] The reaction can be carried out stably and sustainably. After 6 hours of reaction, the product was collected and weighed, and the single-walled carbon nanotube yield was calculated to be 810 g / h. The ash content was weighed after calcination at 900°C in a muffle furnace for 2 hours, and the purity of the product was calculated to be 83.8%.

[0025] The morphology of the product was observed by scanning electron microscopy. Figure 2 As shown; The crystallinity was evaluated by the peak intensity ratio of G peak and D peak in Raman spectrum, such as Figure 3 As shown, the G / D ratio is ~52.5.

[0026] Further observation of the tube diameter and the number of tube walls by transmission electron microscopy showed that the products were mainly single-layer and double-layer carbon nanotubes, with some three-layer carbon nanotubes, such as Figure 4 shown. Example 2

[0027] In this embodiment, the air inlet 5 is 1 cm higher than the upper edge of the graphite crucible 3, and the inner diameter of the graphite crucible 3 is 10 cm.

[0028] Preparation process: S1) placing a first metal catalyst 60% Co-40% Mo alloy in a graphite crucible; S2) evacuate the medium frequency induction furnace 1 to remove air, then switch to inert gas Ar, and turn on the power supply for heating after the pressure stabilizes to melt the first metal catalyst in the graphite crucible 3 to form a flat molten pool until the furnace temperature rises to 1000°C; S3) a mixed powder of cobalt acetylacetonate and selenium powder in a ratio of 1:1 carried by an inert gas is fed into the medium frequency induction furnace 1 through a feed port and atomized and sprayed onto the molten liquid surface at a feed rate of 0.1 g / min; S4) The carbon source gas and the carrier gas form a mixed gas, wherein ethylene is 10%, hydrogen is 40%, and argon is 50%, and the flow rate is 1 L / min. The mixed gas carries water vapor and enters the medium frequency induction furnace 1 from the gas inlet 5. When the water vapor is prepared, the water feed rate is 0.5 mL / min, and the reaction starts; S5) The reaction product is discharged from the furnace through the discharge port 8, and the single-walled / few-walled carbon nanotube product is obtained by collection.

[0029] The reaction can be carried out stably and sustainably. After 6 hours of reaction, the product was collected and weighed, and the single-walled carbon nanotube yield was calculated to be 25 g / h. The ash content was weighed after calcination at 900°C in a muffle furnace for 2 hours, and the purity of the product was calculated to be 75.2%. Example 3

[0030] In this embodiment, the air inlet 5 is 10 cm higher than the upper edge of the graphite crucible, and the inner diameter of the graphite crucible 3 is 200 cm.

[0031] Preparation process: S1) placing a first metal catalyst Fe in a graphite crucible 3; S2) evacuate the medium frequency induction furnace 1 to remove air, then switch to inert gas Ar, turn on the power supply for heating after the pressure stabilizes, melt the first metal catalyst in the graphite crucible 1 to form a flat molten pool, until the furnace temperature rises to 2200°C; S3) a mixed powder of cobalt acetylacetonate and sulfur powder (20:1) carried by an inert gas enters the medium frequency induction furnace 1 through the feed port 6 and is atomized and sprayed on the molten liquid surface at a feed rate of 100 g / min; S4) The carbon source gas and the carrier gas form a mixed gas, wherein propylene is 80%, hydrogen is 10%, and argon is 10%, and the flow rate is 500 L / min, and water vapor is carried into the medium frequency induction furnace 1 from the air inlet 5. When the water vapor is prepared, the water feed rate is 50 mL / min, and the reaction starts; S5) The reaction product is discharged from the furnace through the discharge port 8, and the single-walled / few-walled carbon nanotube product is obtained by collection.

[0032] The reaction can be carried out stably and sustainably. After 6 hours of reaction, the product was collected and weighed, and the single-walled carbon nanotube yield was calculated to be 3460 g / h. The ash content was weighed after calcination at 900 °C in a muffle furnace for 2 hours, and the purity of the product was calculated to be 80.5%. Example 4

[0033] In this embodiment, the air inlet 5 is 5 cm higher than the upper edge of the graphite crucible 3, and the inner diameter of the graphite crucible 3 is 50 cm.

[0034] Preparation process: S1) placing a first metal catalyst 60% Ni-40% Ta alloy in a graphite crucible 3; S2) evacuate the medium frequency induction furnace 1 to remove air, then switch to inert gas Ar, turn on the power supply for heating after the pressure stabilizes, melt the first metal catalyst in the graphite crucible 3 to form a flat molten pool, until the furnace temperature rises to 1500°C; S3) a mixed powder of ferrous acetylacetonate and ferrous sulfide in a ratio of 10:1 carried by an inert gas is fed into the medium frequency induction furnace 1 through the feed port 6 and atomized and sprayed onto the molten liquid surface at a feed rate of 2 g / min; S4) The carbon source gas and the carrier gas form a mixed gas, wherein methane is 40%, hydrogen is 40%, and argon is 20%, and the flow rate is 50 L / min. The water vapor is carried into the medium frequency induction furnace from the gas inlet 5. When the water vapor is prepared, the water feed rate is 5 mL / min, and the reaction starts; S5) The reaction product is discharged from the furnace through the discharge port 8, and the single-walled / few-walled carbon nanotube product is obtained by collection.

[0035] The reaction can be carried out stably and sustainably. After 6 hours of reaction, the product was collected and weighed, and the single-walled carbon nanotube yield was calculated to be 760 g / h. The ash content was weighed after calcination at 900°C in a muffle furnace for 2 hours, and the purity of the product was calculated to be 82.3%. Example 5

[0036] In this embodiment, the air inlet 5 is 5 cm higher than the upper edge of the graphite crucible 3, and the inner diameter of the graphite crucible 3 is 50 cm.

[0037] Preparation process: S1) placing a first metal catalyst Co in a graphite crucible 3; S2) evacuate the medium frequency induction furnace to remove air, then switch to inert gas Ar, and turn on the power supply for heating after the pressure stabilizes to melt the first metal catalyst in the graphite crucible to form a flat molten pool until the furnace temperature rises to 2000 °C; S3) A mixed powder of nickel acetylacetonate and nickel sulfide in a ratio of 10:1 carried by an inert gas is fed into the medium frequency induction furnace 1 through the feed port 6 and atomized and sprayed onto the molten liquid surface at a feed rate of 2 g / min; S4) The carbon source gas and the carrier gas form a mixed gas, of which propane is 40%, hydrogen is 40%, and argon is 20%, with a flow rate of 100 L / min. The water vapor is carried into the medium frequency induction furnace from the gas inlet 5. When the water vapor is prepared, the water feed rate is 10 mL / min, and the reaction starts; S5) The reaction product is discharged from the furnace through the discharge port 8, and the single-walled / few-walled carbon nanotube product is obtained by collection.

[0038] The reaction can be carried out stably and sustainably. After 6 hours of reaction, the product was collected and weighed, and the single-walled carbon nanotube yield was calculated to be ~1450 g / h. The ash content was weighed after calcination at 900°C in a muffle furnace for 2 hours, and the product purity was calculated to be 81.6%.

[0039] Comparative Example 1 The equipment parameters and experimental parameters of this comparative example are the same as those of Example 1, except that the comparative example uses plasma arc as the heat source reaction, and the carbon source mixed gas, the second catalyst and the arc gas all enter the arc furnace from the hollow graphite electrode. Due to the discontinuous reaction, the experiment can only be carried out for 2 hours, and the product is collected to calculate the yield of ~240g / h, and the product purity obtained by thermal analysis is 41.5%.

[0040] The experimental results of the embodiments are summarized in Table 1.

[0041] Table 1 Example Crucible inner diameter (cm) First metal catalyst Second catalyst Air intake L / min Productivity g / h purity Example 1 50 Fe60%-Mo40% Ferrocene 50 810 83.8% Example 2 10 60%Co-40%Mo Cobalt acetylacetonate 1 25 75.2% Example 3 200 Fe Cobalt acetylacetonate 500 3460 80.5% Example 4 50 60%Ni-40%Ta Ferric acetylacetonate 50 760 82.3% Example 5 50 Co Nickel acetylacetonate 100 1450 81.6% Comparative Example 1 50 Fe60%-Mo40% Ferrocene 50 240 41.5% The embodiments described above are only preferred specific implementations of the present invention. Common changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A device for preparing single-walled and few-walled carbon nanotubes, characterized in that: The structure of the device includes a heating system, a feeding system, a gas circuit system, a cooling system, and an electrical system, wherein: The heating system comprises a medium frequency induction furnace (1), an induction coil (2), and a graphite crucible (3); The gas circuit system comprises an air inlet (5); The feeding system comprises a second catalyst feeding port (6) and a discharge port (8); The feed port (6) is arranged above the graphite crucible (3), the air inlet (5) is arranged on the side of the medium frequency induction furnace (1), and the discharge port (8) is arranged on the other side.

2. The device for preparing single-walled and few-walled carbon nanotubes according to claim 1, characterized in that: The inner diameter of the graphite crucible 3 is 10-200 cm, and the air inlet (6) is 1-10 cm higher than the upper edge of the graphite crucible.

3. A method for preparing single-walled and few-walled carbon nanotubes, characterized in that: The method utilizes medium frequency induction heating to melt a first metal catalyst to form a high-temperature molten pool, obtains first metal catalyst particles by evaporation on the surface of the molten liquid, and simultaneously atomizes a second catalyst and a co-catalyst and sprays them uniformly on the molten liquid surface, and introduces a carbon source gas. The heat radiated by the high-temperature molten pool provides a heat source for the cracking of the second catalyst and the carbon source gas, thereby achieving catalyst preparation and carbon nanotube growth in one step, and the growth products are discharged and collected with the tail gas.

4. The method for preparing single-walled and few-walled carbon nanotubes according to claim 3, characterized in that: The method specifically comprises the following steps: S1) placing a first metal catalyst in a graphite crucible (3); S2) evacuating the medium frequency induction furnace (1) to remove air, then switching on the inert gas, and turning on the power supply for heating after the pressure is stabilized to melt the first metal catalyst in the graphite crucible (3) until the furnace temperature rises to a specified temperature of 1000-2200° C., forming a molten liquid surface; S3) introducing a mixed powder of the second catalyst and the promoter carried by the inert gas into the medium frequency induction furnace (1) from the feed port (6), and atomizing and spraying the mixed powder onto the molten liquid surface; S4) After the carbon source gas is mixed with the carrier gas, it carries water vapor into the medium frequency induction furnace from the air inlet to start the reaction; S5) The reaction product is discharged from the furnace through the discharge port, and the single-walled and few-walled carbon nanotube products are obtained by collection.

5. The method for preparing single-walled and few-walled carbon nanotubes according to claim 3, characterized in that: The first metal catalyst in S1) is iron, cobalt, nickel or a mixture thereof.

6. The method for preparing single-walled and few-walled carbon nanotubes according to claim 3, characterized in that: The first metal catalyst in S1) is a mixture of iron, cobalt or nickel or their alloys and refractory metals, wherein the refractory metal element is molybdenum, tungsten, tantalum, niobium, hafnium or zirconium, and the weight ratio of the refractory metal element is 10-80% of the first metal catalyst.

7. The method for preparing single-walled and few-walled carbon nanotubes according to claim 5 or 6, characterized in that: The second catalyst in S3) is any one of ferrocene, nickelocene, cobaltocene, ferric acetylacetonate, nickel acetylacetonate, cobalt acetylacetonate, carbonyl iron powder or a mixture thereof.

8. The method for preparing single-walled and few-walled carbon nanotubes according to claim 7, characterized in that: The co-catalyst is any one of sulfur, selenium, iron sulfide, ferrous sulfide, nickel sulfide, and cobalt sulfide, wherein the ratio of the second catalyst to the co-catalyst is 1:1-20:1, and the feed rate is 0.1 g / min-100 g / min.

9. The method for preparing single-walled and few-walled carbon nanotubes according to claim 3, characterized in that: The inert gas (S2) is any one of argon, nitrogen, and helium, or a mixture of any proportion.

10. The method for preparing single-walled and few-walled carbon nanotubes according to claim 1, characterized in that: The carbon source gas in S4) is methane, ethylene, acetylene, propylene or propane; The carrier gas is a mixture of nitrogen, argon or helium inert gas and hydrogen, wherein the volume of the carbon source gas is 10-80%; the volume of hydrogen is 1-40%, and the rest is inert gas, with a flow rate of 1 L / min-500 L / min; The water feed rate during the water vapor preparation is 0.5-50 mL / min.

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