Reactor configuration for producing single-walled carbon nanotubes

Abstract

The present invention provides a reactor configuration for producing single-walled carbon nanotubes, the configuration comprising an injector tube having a wide end and a narrow end, an injector, and an inner tube. The injector includes a first end, a gas circulation means formed in the wall of the injector, a hollow chamber for reaction to occur, and a second end. The first end of the injector is configured to receive the narrow end of the injector tube. The diameter of the inner tube is smaller than the diameter of the second end of the injector, thereby allowing the inner tube to thermally expand into the hollow chamber of the injector. The hollow chamber of the injector is configured to mix a CO stream maintained at a temperature between 850°C and 1200°C with a CO stream with a catalyst maintained at a temperature in the range of 6°C to 100°C to produce single-walled carbon nanotubes.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates generally to the field of single-walled carbon nanotube production, and more particularly to a reactor configuration for producing single-walled carbon nanotubes. [Background technology]

[0002] Carbon atoms can bond together in various ways, resulting in the formation of multiple carbon allotropes with distinct physical properties. Known allotropes include graphite, diamond, fullerenes, nanotubes, and graphene. Of these, carbon nanotubes are considered the ultimate engineering material due to their unique and distinctive electronic, mechanical, and material properties. There are two basic types of carbon nanotubes: single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). The most important distinguishing feature of SWCNTs is that the nanotube wall is composed of only one graphene layer. Therefore, single-walled carbon nanotubes (SWCNTs) can be thought of as graphene sheets seamlessly rolled up to form a hollow cylinder with a nanometer diameter and a micron length. The unique structure of SWCNTs endows them with properties such as, but not limited to, high thermal conductivity, high electrical conductivity, high tensile strength, high modulus, high flexibility, and a low coefficient of thermal expansion. Due to their wide range of desirable properties, SWCNTs have found applications in a variety of domains, including but not limited to composites and reinforced plastics, industrial coatings, tires and rubber technology products, structural materials, materials for electrochemical power supplies, adhesives and lubricants, antistatic plastics, and transparent conductive films and cables.

[0003] Various methods and techniques have been demonstrated and practiced for the synthesis of single-walled carbon nanotubes, including arc discharge, laser ablation, and catalytic chemical vapor deposition.

[0004] To produce SWCNTs, arc discharge deposition involves placing a metal catalyst-coated graphite rod, which acts as the cathode, and pure graphite, which acts as the anode, a few millimeters apart and using a high current to evaporate them to form the carbon product. Arc discharge deposition can synthesize CNTs in large quantities (grams) and lengths exceeding 40 μm. A drawback of this technique is the production of large amounts of impure SWCNTs with structural defects.

[0005] In laser ablation, graphite vaporizes under a powerful laser pulse, forming primarily single-walled carbon nanotubes. Laser ablation produces pure CNTs with good diameter control and few defects. One major drawback is the need for expensive lasers and the low yield per watt, making this method commercially unviable.

[0006] Chemical vapor deposition is the most developed method for the commercial production of SWCNTs and involves the catalytic deposition of carbon after heating a carbon-containing gas at high temperatures. The cobalt-molybdenum catalyzed (CoMoCAT) process and the high-pressure carbon monoxide (HiPCO) process are the most effective chemical vapor deposition methods for producing SWCNTs. The cobalt-molybdenum catalyzed (CoMoCAT) process involves growing carbon nanotubes by catalytic decomposition of carbon monoxide over silica-supported Co-Mo bimetallic catalyst particles at 1223 K and 150 psia. This method is easy to control and produces high-purity SWCNTs. Disadvantages of this method include low yields, making it commercially unviable for industrial applications, and poor batch-to-batch consistency due to batch processing.

[0007] The HiPCO production technology employs a floating catalyst approach, whereby the growth catalyst is formed in situ during the production process. Carbon nanotubes are produced by the disproportionation of carbon monoxide over catalytic iron nanoparticles at 1323 K and 450 psia. This method yields high-purity, small-diameter nanotubes. Drawbacks include high energy consumption and the susceptibility of the quartz tube to breakage under pressure.

[0008] Therefore, there is a need for a technology for producing carbon nanotubes that are small in diameter, highly pure, high in quality, consume little energy, are safe, and can withstand high temperatures and pressures.

[0009] BRIEF DESCRIPTION OF THE DRAWINGS So that the described features of the present invention can be understood in detail, certain embodiments are shown in the accompanying drawings.

[0010] It should be noted, however, that the attached drawings depict only typical embodiments of the invention and are therefore not to be considered as limiting the scope of the invention, which may allow other embodiments that are equally effective. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 shows a schematic diagram of a reactor setup for producing single-walled carbon nanotubes according to one embodiment of the present invention. [Figure 2] 1 is a schematic diagram of an injector for producing single-walled carbon nanotubes according to one embodiment of the present invention. [Figure 3] FIG. 1 shows a schematic diagram of an injector for the production of single-walled carbon nanotubes according to an alternative embodiment of the present invention. [Figure 4] FIG. 1 shows a schematic diagram of an injector for producing single-walled carbon nanotubes according to another embodiment of the present invention. [Figure 5] 1 shows a flow diagram for producing single-walled carbon nanotubes according to one embodiment of the present invention. [Figure 6]1 shows a TGA plot of single-walled carbon nanotubes obtained by a reactor configuration according to one embodiment of the present invention. [Figure 7] 1 shows an SEM image of single-walled carbon nanotubes obtained by a reactor configuration according to one embodiment of the present invention. [Figure 8] 1 shows a Raman spectrum of single-walled carbon nanotubes obtained by a reactor configuration according to one embodiment of the present invention. [Figure 9] 1 shows UV Vis NIR spectra of single-walled carbon nanotubes obtained by a reactor configuration according to one embodiment of the present invention. Summary of the Invention

[0012] One aspect of the present invention provides a reactor configuration for producing single-walled carbon nanotubes. The reactor configuration includes an injector tube having a wide end and a narrow end, a first end configured to receive the narrow end of the injector tube, gas circulation means formed in a wall of the injector, a hollow chamber for a reaction to occur, and a second end, and an inner tube having a diameter smaller than the diameter of the second end of the injector. The difference in diameter between the inner tube and the second end of the injector allows the inner tube to thermally expand into the hollow chamber of the injector. The hollow chamber of the injector is configured to mix a CO stream maintained at a temperature between 850°C and 1200°C with the CO stream over a catalyst maintained at a temperature between 6°C and 100°C to produce single-walled carbon nanotubes by a carbon monoxide disproportionation reaction over the catalyst. DETAILED DESCRIPTION OF THE INVENTION

[0013] The embodiments herein and their various features and advantageous details will be more fully described with reference to the non-limiting embodiments shown in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as not to unnecessarily obscure the embodiments herein. The examples used herein are intended only to facilitate understanding of how to practice the embodiments herein and to enable those skilled in the art to practice the embodiments herein. Therefore, these examples should not be construed as limiting the scope of the embodiments herein.

[0014] FIG. 1 shows a schematic diagram of a reactor configuration for producing single-walled carbon nanotubes according to one embodiment of the present invention. The reactor configuration includes an injector tube 1 having a wide end 1a and a narrow end 1b, an injector 3 having a first end 3a, a gas circulation means formed in the wall of the injector 3, a hollow chamber 3b for the reaction to occur, and a second end 3c, and an inner tube 5. The first end 3a of the injector 3 is configured to receive the narrow end 1b of the injector tube 1. The diameter of the inner tube 5 is smaller than the diameter of the second end 3c of the injector 3. The difference in diameter between the inner tube 5 and the injector 3 allows the inner tube 1 to thermally expand into the hollow chamber 3b of the injector 3. The reactor configuration further includes an outer tube 7, a cylindrical heating element 9 surrounding the outer tube 7, and an insulating jacket 11 covering the cylindrical heating element 11.

[0015] The outer tube 7 has an inlet 17 at one end and an outlet 19 at the opposite end. The inlet 17 houses the injector tube 1, and the outlet 19 houses the inner tube 5. The narrow end 1b of the injector tube 1 is detachably attached to the first end 3a of the injector 3. The detachable attachment to the injector 3 is achieved by either a push-fit or a threaded connection. The injector tube 1 is configured to pass a CO gas stream carrying a catalyst through the injector 3. The CO gas stream carrying the catalyst is maintained at a temperature below the decomposition temperature of the catalyst. The temperature of the CO gas stream carrying the catalyst is maintained below the decomposition temperature of the catalyst by using cooling methods known to those skilled in the art, such as air cooling or water cooling. In one embodiment of the present invention, the cooling is preferably achieved by water cooling using circulating water within the injector tube 1. The catalyst is broadly selected from the group of chemicals such as iron, nickel, cobalt, molybdenum carbonyl, and ferrocene. In one embodiment of the present invention, the catalyst is iron pentacarbonyl. In another embodiment of the present invention, the catalyst is nickel pentacarbonyl. In one embodiment of the present invention, the temperature of the CO gas stream with the catalyst is maintained at a temperature in the range of 6°C to 100°C. The outlet 19 of the outer tube 7 is connected to a CO gas passage for countercurrently flowing the CO gas into the outer tube 7. A cylindrical heating element 9 surrounding the outer tube 7 heats the CO gas flowing countercurrently through the outer tube to a temperature in the range of 850°C to 1200°C. The heated CO gas stream is then injected into the injector 3. The injector 3 is configured to mix the CO gas stream with the catalyst, maintained at a temperature in the range of 6°C to 100°C, with another CO gas stream maintained at a temperature in the range of 850°C to 1200°C. The mixing is performed by a gas circulation means formed in the wall of the injector 3, which includes a central hole 13 for the flow of the CO gas stream with the catalyst and a plurality of circumferentially or annularly arranged holes 15 for the flow of the heated CO gas. The mixed gas stream is injected into the hollow chamber 3b of the injector 3, where a reaction occurs. The hollow chamber 3b serves as a reaction zone for producing single-walled carbon nanotubes. The single-walled carbon nanotubes are produced by the disproportionation reaction of carbon monoxide over a catalyst.The produced single-walled carbon nanotubes are collected by the inner tube 5. The inner tube 5 is a cylindrical tube with a diameter ranging from 6 mm to 20 mm. The length of the inner tube varies from 1000 mm to 2500 mm. The inner tube is made of a metal alloy, including, but not limited to, a nickel / chromium alloy or a nickel / chromium / molybdenum alloy. Because the inner tube 5 and the injector 3 are made of a metal alloy, the metal alloy tends to expand during the reaction at temperatures between 900 °C and 940 °C. The difference in diameter of the inner tube 5 relative to the injector 3 allows the inner tube 5 to expand within the hollow chamber 3b of the injector 3. The use of a metal alloy and the inner tube 5's ability to thermally expand within the hollow chamber 3b of the injector allow the inner tube 5 to be reused for repeated operations.

[0016] The inner tube 5 is configured to receive the single-walled carbon nanotubes produced from the reaction zone of the injector 3. The inner tube 5 is provided with an outlet 21 for continuous removal of the produced single-walled carbon nanotubes.

[0017] FIG. 2 is a schematic diagram of an injector for producing single-walled carbon nanotubes according to one embodiment of the present invention. The injector 3 is detachably attached to the injector tube 1 and configured to receive and mix at least two gas streams at different temperatures. In one embodiment of the present invention, the injector 3 is tubular with an outer diameter ranging from 30 mm to 40 mm and an inner diameter ranging from 10 mm to 30 mm. The length of the injector varies from 30 mm to 100 mm. The injector is made of a metal alloy, including, but not limited to, a nickel / chromium alloy and a nickel / chromium / molybdenum alloy. The injector 3 has a first end 3a, a gas circulation means formed in the wall of the injector, a hollow chamber 3b, and a second end 3c. The first end 3a is closed and has a central hole 13. The central hole 13 is configured to allow a CO gas stream to flow therethrough accompanied by a catalyst, preferably iron pentacarbonyl. The temperature of the CO gas stream accompanied by the catalyst is maintained below the decomposition temperature of the catalyst.

[0018] The second end 3c is open and proximate the inner tube 5. The hollow chamber 3b serves as a reaction zone for producing single-walled carbon nanotubes. The injector 3 further includes a plurality of holes 15 disposed either circumferentially or on an annular surface of the second end 3c. The holes 15 are configured to channel a CO gas stream, maintained at a temperature between 850°C and 1200°C, into the hollow chamber 3b of the injector 3. In one embodiment of the present invention, the holes 15 are disposed on the annular surface of the second end 3c of the injector, axially extending along the length of the injector 3 and turning at a 90° angle proximal to the first end 3a to join the flow path of the central hole 13. In another embodiment of the invention, multiple holes 15 are disposed on the annular surface of the injector at the second end 3c, axially extending along the length of the injector 3 and turning at a 45° angle proximal to the first end 3a to merge with the flow path of the central hole 13, improving mixing of the cold and hot CO gas streams. In yet another embodiment of the invention, multiple holes 15 are disposed circumferentially on the injector surface toward the first end 3a (FIG. 3a). Multiple holes 15 are disposed radially and merge with the flow path of the central hole 13. In an alternative embodiment of the invention, multiple holes 15 are disposed circumferentially on the injector surface toward the first end 3a. Multiple holes 15 are disposed tangentially and merge with the flow path of the central hole 13 (FIG. 3b). The hollow chamber 3b functions as a reaction zone, in which a CO gas stream accompanied by a catalyst coming from the central hole 13, maintained at a temperature below the decomposition temperature of the catalyst, mixes with a hot CO gas stream coming from the multiple holes 15, and produces single-walled carbon nanotubes by a disproportionation reaction of carbon monoxide over the catalyst.

[0019] In an alternative embodiment of the present invention, the injector 3 is provided in two parts (FIG. 4a). The first end 3a of the injector is separated from the hollow chamber 3b, and the first end 3a is connected to the hollow chamber 3b via a threaded or push-fit connection. The first end 3a of the injector is connected to the injector tube 1, and water or air cooling is used to maintain the CO flow with the catalyst at a temperature below the decomposition temperature of the catalyst, so that the injector is cooler at this first end, which controls the expansion of the injector diameter during thermal expansion and helps maintain the clearance. In another embodiment of the present invention, the injector 3 is provided in three parts (FIG. 4b). The first end 3a of the injector is provided in two parts: a first part (I) and a second part (II). The first part (I) and the second part (II) are connected via a threaded or push-fit connection. The first part (I) is connected to the injector tube 1 and the second part (II) is removably attached to the hollow chamber 3b via a threaded or push-fit connection. The first part (I) and the second part (II) are made of two different metals or alloys to control diametric expansion due to temperature differences.

[0020] FIG. 5 shows a flow diagram for producing single-walled carbon nanotubes according to one embodiment of the present invention. Single-walled carbon nanotubes are produced by reacting CO gas, maintained at a temperature between 850°C and 1200°C, with a catalyst-bearing CO gas stream in the hollow chamber 3b of the injector. To form high-purity single carbon nanotubes with uniform diameters, a high reaction temperature of 900°C to 1000°C, preferably 950°C, is required. The catalyst temperature is maintained between 6°C and 100°C, below the catalyst's decomposition temperature. The pressure in the reactor configuration is maintained between 10 bar and 50 bar. The pressure of the CO gas stream from the injector 3 through the multiple holes 15 is maintained between 20 bar and 30 bar, while the pressure of the catalyst-bearing CO gas stream is maintained between 15 bar and 60 bar. A higher pressure is applied to ensure continuous forward flow. The pressure in the reactor configuration and the lines carrying the catalyst-bearing CO gas and CO gas streams is maintained by a compressor and a series of forward and backward pressure regulators. From the compressor, a high-pressure CO gas line (L1) at 40-60 bar is split into two lines, L2 (15-60 bar) and L3 (20-30 bar), via a forward pressure regulator. Line L3, carrying CO gas maintained at 20-30 bar, enters the reactor through outlet 19 of outer tube 7 and is heated to a temperature of 950 °C by a cylindrical heating element. The heated CO gas stream from outer tube 7 enters injector 3 through multiple holes 15. Line L2, carrying CO gas maintained at 15-60 bar, enters the vaporizer, where catalytic iron pentacarbonyl is produced and combined with CO to form a catalytic CO gas stream. The catalytic CO gas stream enters the reactor configuration through injector tube 1 and enters injector 3 through central hole 13. In injector 3, the hot CO gas stream mixes with the catalytic iron pentacarbonyl CO stream. In the hollow chamber 3b of the injector, iron pentacarbonyl and CO are atomized at a high temperature of 950°C to 1000°C and a pressure of 20 bar to 30 bar. The atomized metal atoms nucleate to form nanoparticles, on which nanotubes grow.Carbon nanotubes are synthesized by the reverse Boudouard reaction in the presence of catalytic iron clusters formed by the decomposition of iron carbonyl.

[0021]

number

[0022] The produced single-walled carbon nanotubes, by-product CO2, and unreacted gases exit the reactor through outlet 21 of inner tube 5 and pass through various filters. A nanotube filter removes and collects the nanotubes, and a carbon dioxide filter removes the CO2. Unreacted CO2 gas passes through a backpressure regulator, maintained at 16 bar to 25 bar, and is returned to the compressor. The produced single-walled carbon nanotubes have diameters ranging from 0.8 nm to 1.2 nm and lengths ranging from 700 nm to 1000 nm.

[0023] Characterization: Characterization of the single-walled carbon nanotubes is performed using scanning electron microscopy (SEM), Raman spectroscopy, and thermogravimetric analysis (TGA).

[0024] Figure 6 shows a TGA plot of single-walled carbon nanotubes obtained using a reactor according to one embodiment of the present invention. TGA is used to verify the purity of the SWCNTs. The thermogram of the as-prepared material shows multiple peaks corresponding to various temperatures of SWCNT decomposition, catalyst particle oxidation, and carbonaceous aggregate decomposition. TGA analysis of graphite, fullerene, and nanotube samples indicates that as the C-C bonds within the nanotubes become stronger, fewer dangling bonds are available for oxidation, improving oxidation resistance. It is well known that graphite and fullerenes oxidize at their maximum rates at 650°C and 420°C, respectively. Active sites for oxidation are found in defects in the tube structure, such as open ends, dislocations, and missing carbon atoms. The first step in the initiation of the oxidation reaction is the presence of pentagons at both ends of the tube, which are sites of tension. The initial weight gain in the thermogram of pure nanotubes is less than 1% and is not significant, as it can be attributed to the addition of oxygen atoms. As oxidation progresses, weight decreases due to the loss of carbon as CO and CO2. The TGA plot shows that the material contains approximately 85% carbon and approximately 15% residue (non-carbon impurities). No significant weight loss is observed between 100°C and 200°C, indicating very little or no moisture in the material.

[0025] 7 shows an SEM image of single-walled carbon nanotubes obtained by a reactor according to one embodiment of the present invention. The SEM image shows the nanotubes magnified up to 200,000 times to visualize the nanotube bundles. The SEM image shows clean tubes and fibrous carbon nanotubes with very little amorphous carbon.

[0026] 8 shows the Raman spectrum of single-walled carbon nanotubes obtained by a reactor according to one embodiment of the present invention. This figure shows the Raman spectrum of single-walled carbon nanotubes at an excitation wavelength of 514 nm. The Raman spectrum includes a peak at 200 cm -1There is a low frequency peak around 1340 cm, which corresponds to the radial breathing mode (RBM) of SWCNTs, which is distinct from graphite. This RBM characteristic, measured in frequency, is inversely proportional to the radius (r) of the nanotube. The D band in the spectrum, which indicates structural defects or disorder, is located at 1340 cm. -1 This corresponds to the peak seen around 1550cm -1 ~1600cm -1 The peak seen at lies in the G band of the spectrum, indicating the presence of graphene sheets in the sample and that the sample is graphitized. This G band is divided into the G+ and G- bands. The G- curves have different shapes for metallic and semiconducting SWCNTs. The G+ signal indicates vibrational confinement by the tube circumference, a property that is independent of the tube radius and depends on the atomic motion within the graphene plane. The line known as the G' band or 2D band, considering that it originates from the second harmonic of the D band, appears at 2650 cm. -1 Near the sample, indicating long-range order. All sp 2 The C=C bond stretching that occurs in carbon systems corresponds to the G band in the as-prepared Raman spectrum. The G-band appears to be split by the curvature of the tube. The resulting nanotubes have a G / D ratio of 25.

[0027] 9 shows the UV Vis NIR spectrum of single-walled carbon nanotubes obtained by a reactor according to one embodiment of the present invention. The UV Vis NIR spectrum shows a chirality shift in favor of smaller diameter single-walled carbon nanotubes.

[0028] The present invention provides a manufacturing technology for producing carbon nanotubes that are small in diameter, high in purity, high in quality, low in energy consumption, safe, and can withstand high temperatures and pressures. The configuration of the present invention can be used in the HiPCO process.

[0029] The foregoing description of specific embodiments fully reveals the general nature of the embodiments herein, such that, by applying current knowledge, such specific embodiments can be readily modified and / or adapted to various uses without departing from the general concept; therefore, such adaptations and modifications should, and are intended to, be understood within the meaning and range of equivalents of the disclosed embodiments. It should be understood that the phraseology or terminology used herein is for the purpose of description and not of limitation. Thus, while the embodiments herein have been described as preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modifications within the spirit and scope of the embodiments described herein.

Claims

1. 1. A reactor configuration for producing single-walled carbon nanotubes, comprising: an injector tube (1) having a wide end (1a) and a narrow end (1b); an injector (3) having a first end (3a) configured to receive the narrow end (1b) of the injector tube (1), gas circulation means formed in the wall of the injector, a hollow chamber (3b) for the reaction to occur, and a second end (3c); an inner tube (5) having a diameter smaller than the diameter of the second end (3c) of the injector.

2. 2. The arrangement of claim 1, further comprising an outer tube (7), a cylindrical heating element (9) surrounding said outer tube (7), and an insulating jacket (11) covering said cylindrical heating element (9).

3. 2. The arrangement of claim 1, wherein the gas circulation means formed in the wall of the injector allows circulation of at least two gas streams of different temperatures, one of the at least two gas streams being a CO gas stream with a catalyst and the other gas stream being a CO gas stream.

4. 2. The arrangement of claim 1, wherein the injector tube (1) is configured to inject the CO gas stream accompanied by the catalyst, preferably iron pentacarbonyl, and the CO stream accompanied by the catalyst is maintained at a temperature below the decomposition temperature of the catalyst, and the temperature of the CO stream accompanied by the catalyst is maintained at a temperature in the range of 6°C to 100°C.

5. 2. The arrangement of claim 1, wherein the outer tube (7) is configured for countercurrent flow of CO gas, forming the CO gas stream maintained at a temperature in the range of 850°C to 1200°C.

6. 2. The arrangement of claim 1, wherein the gas circulation means formed in the wall of the injector includes a central hole (13) for flowing the CO gas stream with the catalyst and a plurality of circumferentially or annularly arranged holes (15) for flowing the CO gas stream.

7. 2. The arrangement of claim 1, wherein the hollow chamber of the injector is configured to mix the CO stream maintained at a temperature between 850°C and 1200°C with the CO stream with the catalyst maintained at a temperature in the range of 6°C to 100°C, and produce single-walled carbon nanotubes by disproportionation of carbon monoxide over the catalyst.

8. 2. The arrangement according to claim 1, wherein the outer tube (7) has an inlet (17) at one end for receiving the injector tube (1) and an outlet (19) at the opposite end for receiving the inner tube (5).

9. 2. The arrangement of claim 1, wherein the difference in diameter between the inner tube (5) and the second end (3c) of the injector allows the inner tube (5) to thermally expand into the hollow chamber (3b) of the injector.

10. The arrangement of claim 1 , wherein the arrangement allows the inner tube to be reused for repeated operations.

11. The arrangement of claim 1 , wherein the outer tube has a diameter in the range of 30 mm to 40 mm.

12. The arrangement of claim 1 , wherein the inner tube has a diameter in the range of 6 mm to 20 mm.

13. 2. The composition of claim 1, wherein the diameter of the single-walled carbon nanotubes is in the range of 0.8 nm to 1.2 nm.

14. 2. The arrangement of claim 1, wherein the inner tube has an outlet (21) for continuous removal of the produced single-walled carbon nanotubes.

15. 2. The arrangement according to claim 1, wherein the outer tube 1 and the inner tube 3 are made of a nickel / chromium alloy or a nickel / chromium / molybdenum alloy.

16. The arrangement of claim 1 , wherein the injector is made of copper, stainless steel, or a combination thereof.

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