Preparation device and method for single-walled or few-walled carbon nanotubes

Abstract

The present invention discloses a preparation device and method for single-walled and few-walled carbon nanotubes, relating to the technical field of nano-carbon materials. The structure of the device includes a heating system, a feeding system, a gas path system, a cooling system, and an electrical system. Among them, the heating system includes an intermediate frequency induction furnace, an induction coil, and a graphite crucible; the gas path system includes an air inlet; the feeding system includes a second catalyst feeding port and a discharge port; wherein the feeding port is arranged above the graphite crucible, the air inlet is arranged on the side of the intermediate frequency induction furnace, and the discharge port is arranged on the other side. Taking the metal molten pool as the heat source, a steady heat source is provided for catalyst evaporation and the growth of single-walled / few-walled carbon nanotubes. Compared with the plasma method and the arc method, the catalyst evaporation is more uniform and gentle, the utilization rate of the catalyst is improved, and the growth efficiency of single-walled / few-walled carbon nanotubes is significantly improved.

Description

Technical Field

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

[0002] Single-walled carbon nanotubes can be regarded as one-dimensional tubular nano-materials formed by curling single-layer graphite. Their extremely strong carbon-carbon bonds endow them with excellent comprehensive properties, such as high strength, high modulus, high thermal conductivity, and excellent electrical conductivity. They have important applications in the fields of structural composite materials, electrochemical energy storage, catalysis, etc.

[0003] Currently, the main preparation methods for single-walled carbon nanotubes include arc discharge, laser ablation, plasma method, and chemical vapor deposition method, etc. Arc discharge, laser ablation, and plasma method are the earliest studied preparation technologies, but it is difficult to improve both the yield and purity, resulting in their difficulty in industrialization. The chemical vapor deposition method has achieved great success in the field of preparing multi-walled carbon nanotubes and has realized the production of tens of thousands of tons. However, the preparation of single-walled carbon nanotubes by this method still remains at the laboratory stage, and high-efficiency and low-cost preparation technology is still a research hotspot.

[0004] U.S. Patent No. US8551413B2 discloses a method for preparing single-walled carbon nanotubes by using a plasma arc to evaporate a metal catalyst, which is currently the only technical route that can realize the industrialization of single-walled carbon nanotubes. However, due to the extremely high temperature of the plasma arc, it is difficult to control the evaporation rate of the catalyst, and a large amount of metal catalyst cannot be effectively utilized. Further control measures must be adopted to screen and purify to obtain the final practical product, resulting in its still high cost.

[0005] Chinese Patent No. CN202111322714.0 can partially solve the current problems by attempting to isolate the catalyst evaporation chamber and the growth chamber. However, the simple division method will cause the catalyst to aggregate and grow during transportation and become ineffective, and at the same time, it will also reduce the thermal energy utilization rate, resulting in a decrease in yield and an increase in preparation cost.

[0006] Chinese Patent No. CN202210608795.9 further improves on this basis. By setting a rotating solid catalyst electrode to make the plasma arc not concentrate on evaporating one position and regulating the evaporation rate of the catalyst by reducing the catalyst evaporation temperature, not only can the power of the plasma generator for preparing catalyst nanoparticles be effectively reduced, but also the particle size distribution of the prepared catalyst nanoparticles can be optimized, which is beneficial to controlling and optimizing the uniformity of the growth products. However, how to balance quality and efficiency and yield is still a very difficult contradictory problem, and there are still great challenges in continuously batch-producing single-walled carbon nanotubes. Summary of the Invention

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

[0008] On the one hand, the present invention provides the following technical solution:

[0009] A preparation device for single-walled and few-walled carbon nanotubes, the structure of the device includes a heating system, a feeding system, a gas path system, a cooling system, and an electrical system, wherein,

[0010] The heating system includes an intermediate frequency induction furnace, an induction coil, and a graphite crucible;

[0011] The gas path system includes an air inlet;

[0012] The feeding system includes a second catalyst feeding port and a discharging port;

[0013] Among them, the feeding port is arranged above the graphite crucible, the air inlet is arranged on the side of the intermediate frequency induction furnace, and the discharging port is arranged on the other side.

[0014] 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.

[0015] On the other hand, the present invention provides a preparation method for single-walled and few-walled carbon nanotubes. The method uses intermediate frequency induction heating to melt the 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 at the same time atomizes and uniformly sprays the second catalyst and the promoter 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, realizing the preparation of the catalyst and the growth of carbon nanotubes in one step, and the grown products are discharged and collected with the tail gas.

[0016] Furthermore, the method specifically includes the following steps:

[0017] S1) Place the first metal catalyst in the graphite crucible;

[0018] S2) Evacuate the intermediate frequency induction furnace to remove air, then switch to introduce an inert gas, and after the pressure is stable, turn on the power supply to heat, melt the first metal catalyst in the graphite crucible until the furnace temperature rises to the specified temperature of 1000 - 2200 °C to form a molten liquid surface;

[0019] S3) Pass the mixed powder of the second catalyst and the promoter carried by the inert gas into the intermediate frequency induction furnace through the feeding port and atomize and spray it on the molten liquid surface;

[0020] S4) After mixing the carbon source gas and the carrier gas, carry water vapor and enter the intermediate frequency induction furnace through the air inlet to start the reaction;

[0021] S5) The reaction product is discharged from the furnace body through the discharge port, and the single-walled and few-walled carbon nanotube product is collected.

[0022] Furthermore, in the step S1), the first metal catalyst is iron, cobalt, nickel metal or a mixture thereof.

[0023] Furthermore, in the step S1), the first metal catalyst is a mixture of iron, cobalt or nickel or their alloys and refractory metals, where the refractory metal elements are molybdenum, tungsten, tantalum, niobium, hafnium or zirconium, and the weight ratio content of the refractory metal elements is 10 - 80% of the first metal catalyst.

[0024] Furthermore, in the step S3), the second catalyst is any one or a mixture of ferrocene, nickelocene, cobaltocene, iron acetylacetonate, nickel acetylacetonate, cobalt acetylacetonate, carbonyl iron powder.

[0025] Furthermore, the promoter is any one of sulfur, selenium, iron sulfide, iron(II) sulfide, nickel sulfide, cobalt sulfide, and the ratio of the second catalyst to the promoter is 1:1 - 20:1, and the feeding rate is 0.1 g / min - 100 g / min.

[0026] Furthermore, in the step S2), the inert gas is any one of argon, nitrogen, helium or a mixed gas with any mixing ratio.

[0027] Furthermore, in the step S4), the carbon source gas is methane, ethylene, acetylene, propylene or propane;

[0028] The carrier gas is a mixed gas of nitrogen, argon or helium inert gas and hydrogen, where the volume of the carbon source gas is 10 - 80%; the volume of hydrogen gas is 1 - 40%, and the rest is inert gas, and the flow rate is 1 L / min - 500 L / min;

[0029] When the water vapor is prepared, the feeding rate of water is 0.5 - 50 mL / min.

[0030] Compared with the prior art, the preparation device and method of a single-walled and few-walled carbon nanotube of the present invention have the following outstanding beneficial effects:

[0031] (1) Using the metal molten pool as the heat source, it provides a steady 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, improving the catalyst utilization rate and significantly increasing the growth efficiency of single-walled / few-walled carbon nanotubes.

[0032] (2) The induction heating of the first metal catalyst rapidly forms a metal molten pool, avoiding the deficiencies of the conventional plasma method and arc method, such as the disturbance of the furnace gas flow caused by the impact of high-speed plasma, and also avoiding the interference of complex atmosphere components on the stability of the plasma arc, overcoming the problem of easy arc breakage, and greatly improving the reaction stability.

[0033] (3) The temperature of the molten pool of the first metal catalyst is controllable, and the evaporation rate of the catalyst can be precisely controlled. In contrast, the non-steady heat source of the non-plasma arc method cannot control the temperature, greatly improving the controllability of various parameters in the carbon nanotube growth process. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic structural diagram of the preparation device of the present invention;

[0035] Figure 2 is a scanning electron microscope image of the carbon nanotube product of the present invention;

[0036] Figure 3 is a Raman spectrum diagram of the carbon nanotube product of the present invention;

[0037] Figure 4 is a transmission electron microscope image of the carbon nanotube product of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0038] The present invention will be further described in detail below in conjunction with the drawings and embodiments. Example 1

[0039] As Figure 1 shown, a preparation device for single-walled and few-walled carbon nanotubes includes auxiliary equipment such as a feeding system, a gas path system, a cooling system, and an electrical system, specifically including an intermediate 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 intermediate frequency induction furnace 1 and 5 cm above the upper edge of the graphite crucible 3, and the inner diameter of the graphite crucible 3 is 50 cm.

[0040] The preparation process is as follows:

[0041] S1) Place 60% Fe - 40% Mo alloy of the first metal catalyst in the graphite crucible 3;

[0042] S2) Evacuate the intermediate frequency induction furnace 1 to remove air, then switch to inert gas Ar. After the pressure is stable, turn on the power supply for heating 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;

[0043] S3) Feed the mixed powder of ferrocene and sulfur powder = 10:1 carried by inert gas into the intermediate frequency induction furnace 1 through the feed port 6, and atomize and spray it on the molten liquid surface at a feed rate of 2 g / min;

[0044] S4) Form a mixed gas of carbon source gas and carrier gas, where methane is 60%; hydrogen is 20%, and argon is 20%, with a flow rate of 50 L / min. Carry water vapor and enter the intermediate frequency induction furnace 1 through the inlet port 5. The feed rate of water during the preparation of water vapor is 5 mL / min, and the reaction starts;

[0045] S5) Discharge the reaction product from the discharge port of the furnace body, and collect to obtain the single-walled and few-walled carbon nanotube product.

[0046] The reaction can proceed continuously and stably. After 6 hours of reaction, collect the product, weigh it, and calculate that the yield of single-walled carbon nanotubes can reach 810 g / h. Calcinate it in a muffle furnace at 900 °C for 2 hours, weigh the ash, and calculate that the purity of the product is 83.8%.

[0047] The morphology of the product is observed by a scanning electron microscope as Figure 2 shown;

[0048] Use the ratio of the peak intensities of the G peak and D peak in Raman spectroscopy to evaluate its crystallinity, as Figure 3 shown, G / D ratio ~ 52.5.

[0049] Further observe the tube diameter and the number of tube walls through a transmission electron microscope. The product is mainly composed of single-layer and double-layer, and there are also some triple-walled carbon nanotubes, as Figure 4 shown. Example 2

[0050] In this example, the inlet port 5 is 1 cm above the upper edge of the graphite crucible 3, and the inner diameter of the graphite crucible 3 is 10 cm.

[0051] Preparation process:

[0052] S1) Place 60% Co - 40% Mo alloy of the first metal catalyst in the graphite crucible;

[0053] S2) Evacuate the intermediate frequency induction furnace 1 to remove air, then switch to inert gas Ar. After the pressure is stable, turn on the power supply to heat, and melt the first metal catalyst in the graphite crucible 3 to form a flat molten pool until the furnace temperature rises to 1000 °C;

[0054] S3) Feed the mixed powder of cobalt acetylacetonate and selenium powder = 1:1 carried by inert gas into the intermediate frequency induction furnace 1 through the feed port, and atomize and spray it on the molten liquid surface at a feed rate of 0.1 g / min;

[0055] S4) A mixed gas is formed by the carbon source gas and the carrier gas, where ethylene is 10%; hydrogen is 40%, argon is 50%, the flow rate is 1 L / min, and it carries water vapor and enters the intermediate frequency induction furnace 1 through the inlet 5. The feeding rate of water during the preparation of water vapor is 0.5 mL / min, and the reaction starts;

[0056] S5) The reaction product is discharged from the furnace body through the discharge port 8, and the single-walled / few-walled carbon nanotube product is collected.

[0057] The reaction can proceed continuously and stably. After 6 hours of reaction, the product is collected, weighed, and the single-walled carbon nanotube yield can reach 25 g / h. The product is calcined in a muffle furnace at 900 °C for 2 hours, the ash is weighed, and the product purity is calculated to be 75.2%. Example 3

[0058] In this example, the inlet 5 is 10 cm above the upper edge of the graphite crucible, and the inner diameter of the graphite crucible 3 is 200 cm.

[0059] Preparation process:

[0060] S1) Place the first metal catalyst Fe in the graphite crucible 3;

[0061] S2) Evacuate the intermediate frequency induction furnace 1 to remove air, then switch to the inert gas Ar. After the pressure is stable, turn on the power supply to heat, melt the first metal catalyst in the graphite crucible 1 to form a flat molten pool until the furnace temperature rises to 2200 °C;

[0062] S3) The mixed powder of cobalt acetylacetonate: sulfur powder = 20:1 carried by the inert gas enters the intermediate frequency induction furnace 1 through the feed port 6, and is atomized and sprayed on the molten surface, with a feeding rate of 100 g / min;

[0063] S4) A mixed gas is formed by the carbon source gas and the carrier gas, where propylene is 80%; hydrogen is 10%, argon is 10%, the flow rate is 500 L / min, and it carries water vapor and enters the intermediate frequency induction furnace 1 through the inlet 5. The feeding rate of water during the preparation of water vapor is 50 mL / min, and the reaction starts;

[0064] S5) The reaction product is discharged from the furnace body through the discharge port 8, and the single-walled / few-walled carbon nanotube product is collected.

[0065] The reaction can proceed continuously and stably. After 6 hours of reaction, the product is collected, weighed, and the single-walled carbon nanotube yield can reach 3460 g / h. The product is calcined in a muffle furnace at 900 °C for 2 hours, the ash is weighed, and the product purity is calculated to be 80.5%. Example 4

[0066] In this example, the inlet 5 is 5 cm above the upper edge of the graphite crucible 3, and the inner diameter of the graphite crucible 3 is 50 cm.

[0067] Preparation process:

[0068] S1) Place the first metal catalyst, 60% Ni - 40% Ta alloy, in the graphite crucible 3;

[0069] S2) Evacuate the intermediate frequency induction furnace 1 to remove air, then switch to the inert gas Ar. After the pressure stabilizes, turn on the power supply to heat, melt the first metal catalyst in the graphite crucible 3 to form a flat molten pool until the furnace temperature rises to 1500 °C;

[0070] S3) Feed the mixed powder of iron acetylacetonate: iron sulfide = 10:1 carried by the inert gas into the intermediate frequency induction furnace 1 through the feed port 6, and atomize and spray it on the molten surface at a feed rate of 2 g / min;

[0071] S4) Form a mixed gas of carbon source gas and carrier gas, where methane is 40%; hydrogen is 40%, and argon is 20%, with a flow rate of 50 L / min. Carry water vapor into the intermediate frequency induction furnace through the inlet port 5. The feed rate of water during the preparation of water vapor is 5 mL / min, and start the reaction;

[0072] S5) The reaction product is discharged from the furnace body through the discharge port 8, and the single - wall / few - wall carbon nanotube product is collected.

[0073] The reaction can proceed continuously and stably. After 6 hours of reaction and completion, the product is collected and weighed. The yield of single - wall carbon nanotubes can reach 760 g / h. The product is calcined in a muffle furnace at 900 °C for 2 hours, weighed for ash content, and the product purity is calculated to be 82.3%. Example 5

[0074] In this example, the inlet port 5 is 5 cm above the upper edge of the graphite crucible 3, and the inner diameter of the graphite crucible 3 is 50 cm.

[0075] Preparation process:

[0076] S1) Place the first metal catalyst, Co, in the graphite crucible 3;

[0077] S2) Evacuate the intermediate frequency induction furnace to remove air, then switch to the inert gas Ar. After the pressure stabilizes, turn on the power supply to heat, melt the first metal catalyst in the graphite crucible to form a flat molten pool until the furnace temperature rises to 2000 °C;

[0078] S3) Feed the mixed powder of nickel acetylacetonate: nickel sulfide = 10:1 carried by the inert gas into the intermediate frequency induction furnace 1 through the feed port 6, and atomize and spray it on the molten surface at a feed rate of 2 g / min;

[0079] S4) A mixed gas is formed by the carbon source gas and the carrier gas, in which propane is 40%, hydrogen is 40%, and argon is 20%, with a flow rate of 100 L / min. It carries water vapor and enters the intermediate frequency induction furnace through the inlet 5. The feeding rate of water during the preparation of water vapor is 10 mL / min, and the reaction starts;

[0080] S5) The reaction products are discharged from the furnace body through the outlet 8, and the single-wall / few-wall carbon nanotube products are collected.

[0081] The reaction can proceed continuously and stably. After 6 hours of reaction, the products are collected and weighed. The yield of single-wall carbon nanotubes can reach ~1450 g / h. The products are calcined in a muffle furnace at 900 °C for 2 hours, and the ash is weighed. The purity of the products is calculated to be 81.6%.

[0082] Comparative Example 1

[0083] This comparative example has the same equipment parameters and experimental parameters as Example 1. The difference is that the comparative example uses a plasma arc as the heat source for the reaction, and the carbon source mixed gas, the second catalyst, and the arc gas all enter the arc furnace through the hollow graphite electrode. Due to the discontinuous reaction, only a 2-hour experiment can be carried out. The products are collected and the yield is calculated to be ~240 g / h. The purity of the products is obtained by thermal analysis as 41.5%.

[0084] The summary of the experimental results of the examples is shown in Table 1.

[0085] Table 1

[0086] Example Inner diameter of crucible (cm) First metal catalyst Second catalyst Intake air volume L / min Yield 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 Iron 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%

[0087] The above-described embodiments are only relatively preferred specific embodiments of the present invention. Any ordinary 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 preparation method of single-wall and few-wall carbon nanotubes, characterized in that, The method uses medium-frequency induction heating to melt a first metal catalyst to form a high-temperature molten pool. First metal catalyst particles are obtained by evaporation from the surface of the molten liquid. At the same time, a second catalyst and a promoter 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, realizing catalyst preparation and carbon nanotube growth in one step. The grown products are discharged and collected with the tail gas; The method specifically includes the following steps: S1) Place the first metal catalyst in a graphite crucible; S2) Evacuate the medium-frequency induction furnace to remove air, and then switch to introduce an inert gas. After the pressure stabilizes, turn on the power supply to heat and melt the first metal catalyst in the graphite crucible until the furnace temperature rises to the specified temperature of 1000 - 2200 °C to form a molten liquid surface; S3) Pass the mixed powder of the second catalyst and the promoter carried by the inert gas into the medium-frequency induction furnace through the feed port and atomize and spray it on the molten liquid surface; S4) After mixing the carbon source gas with the carrier gas, carry water vapor and enter the medium-frequency induction furnace through the inlet to start the reaction; S5) The reaction products are discharged from the furnace body through the discharge port, and single-walled and few-walled carbon nanotube products are collected; In the S1), the first metal catalyst is iron, cobalt, nickel metal or a mixture thereof; or, in the S1), the first metal catalyst is a mixture of iron, cobalt or nickel or their alloy and a refractory metal, where the refractory metal element is molybdenum, tungsten, tantalum, niobium, hafnium or zirconium, and the weight ratio content of the refractory metal element is 10 - 80% of the first metal catalyst; In the S3), the second catalyst is any one or a mixture of ferrocene, nickelocene, cobaltocene, iron acetylacetonate, nickel acetylacetonate, cobalt acetylacetonate, carbonyl iron powder; 2. A method for preparing single-walled and few-walled carbon nanotubes according to claim 1, characterized in that The promoter is any one of sulfur, selenium, iron sulfide, ferrous sulfide, nickel sulfide, cobalt sulfide, and the ratio of the second catalyst to the promoter is 1:1 to 20:1, and the feeding rate is 0.1 g / min - 100 g / min.

3. A method for preparing single-walled and few-walled carbon nanotubes according to claim 1, characterized in that The inert gas in the S2 is any one of argon, nitrogen, helium or a mixed gas with any mixing ratio; 4. A method for preparing single-walled and few-walled carbon nanotubes according to claim 1, characterized in that The carbon source gas in the S4 is methane, ethylene, acetylene, propylene or propane; The carrier gas is a mixed gas of an inert gas such as nitrogen, argon or helium and hydrogen, where the volume of the carbon source gas is 10 - 80%; the volume of hydrogen gas is 1 - 40%, and the rest is an inert gas, and the sum of the carbon source gas, hydrogen gas and inert gas is 100%, and the flow rate is 1 L / min - 500 L / min; The feeding rate of water for preparing the water vapor is 0.5 - 50 mL / min.

5. An apparatus for preparing single-walled few-walled carbon nanotubes for implementing the method according to any one of claims 1-4, characterized in that, The structure of the device includes a heating system, a feeding system, a gas path system, a cooling system, and an electrical system, where The heating system includes a medium-frequency induction furnace (1), an induction coil (2), and a graphite crucible (3); The gas path system includes an air inlet (5); The feeding system includes a second catalyst feeding port (6) and a discharging port (8); Among them, the second catalyst feeding port (6) is arranged above the graphite crucible (3), the air inlet (5) is arranged on the side of the intermediate frequency induction furnace (1), and the discharging port (8) is arranged on the other side.

6. The preparation device of a single-walled and few-walled carbon nanotube according to claim 5, characterized in that, The inner diameter of the graphite crucible (3) is 10 - 200 cm, and the air inlet (5) is 1 - 10 cm higher than the upper edge of the graphite crucible.

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