Method and device system for continuously producing carbon nanotubes

Abstract

The invention provides a method and device system for continuously producing carbon nanotubes, and the method comprises the following steps: (1) carrying out high-temperature gasification on a metal raw material in a protective gas atmosphere to obtain a metal steam mixture; (2) the metal steam mixture obtained in the step (1) is subjected to rapid quenching through an annular air knife, and metal nanoparticles or metal liquid drops are obtained; (3) mixing a carbon precursor, an accelerant, reducing gas and the metal nano-particles or the metal liquid drops obtained in the step (2) to react, and separating to obtain the carbon nano-tubes; wherein the temperature of high-temperature gasification in the step (1) is greater than or equal to 2200 DEG C; the cooling rate of the rapid quenching in the step (2) is greater than or equal to 1 * 10 < 4 > DEG C / s. The industrial mass production of the carbon nanotubes is realized, the yield and quality of the carbon nanotubes are considered, the carbon source conversion rate is increased, the number of layers of the carbon nanotube walls is accurately controlled, retention and blockage of side reaction products are avoided, the reaction continuity is improved, and large-scale popularization and application are facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanomaterials and relates to a method for producing carbon nanotubes, and in particular to a method and device system for continuously producing carbon nanotubes. Background Art

[0002] Carbon nanotubes (CNTs), allotropes of traditional carbon materials like diamond and graphite, possess numerous remarkable mechanical, electrical, and thermodynamic properties due to their unique one-dimensional chiral nanostructure. In particular, their subsets, single- and double-walled CNTs, possess superior aspect ratios, flexibility, and selectivity, offering significant potential for applications in semiconductors, new energy, healthcare, aerospace, and other fields.

[0003] In recent years, due to the outstanding advantages of single- and double-walled carbon nanotubes (CNTs) as conductive agents in new lithium battery electrode materials, market demand has been growing year by year, and the demand for the production and quality of CNT raw materials has also been increasing. However, existing CNT production technologies (such as traditional arc, laser ablation, and fluidized bed processes) have difficulty in precisely controlling reaction conditions, making it difficult to scale up the production of high-quality CNTs to meet industrial production needs.

[0004] Although the plasma method (such as US20200239316A1, CN115650210A, CN114890407A) and the floating CVD method (such as CN104261384B, CN114808196A, CN114974726A) have made breakthrough progress in the production of single / double-walled carbon nanotubes, improving the problems of continuity and controllability of traditional methods and having the possibility of industrial mass production, they still have inherent shortcomings such as low carbon source conversion rate, inability to balance carbon tube output and quality, difficulty in controlling the number of carbon nanotube walls, and retention and clogging of side reaction products affecting reaction continuity. In this regard, the current carbon nanotube mass production technology cannot overcome all the above defects well.

[0005] Therefore, it can be seen that how to provide a method for continuous production of carbon nanotubes, while achieving industrial mass production of carbon nanotubes, taking into account the yield and quality of carbon nanotubes, improving the carbon source conversion rate, accurately controlling the number of carbon nanotube wall layers, avoiding the retention and clogging of side reaction products, and improving the reaction continuity has become an urgent problem that technical personnel in this field need to solve. Summary of the Invention

[0006] The object of the present invention is to provide a method and device system for the continuous production of carbon nanotubes. The method realizes the industrial mass production of carbon nanotubes while taking into account the carbon nanotube yield and quality, improves the carbon source conversion rate, accurately controls the number of carbon nanotube wall layers, avoids the retention and clogging of side reaction products, improves the reaction continuity, and is conducive to large-scale promotion and application.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for continuously producing carbon nanotubes, the method comprising the following steps:

[0009] (1) gasifying the metal raw material at high temperature in a protective gas atmosphere to obtain a metal vapor mixture;

[0010] (2) rapidly quenching the metal vapor mixture obtained in step (1) through an annular air knife to obtain metal nanoparticles or metal droplets;

[0011] (3) mixing a carbon precursor, a promoter, a reducing gas and the metal nanoparticles or metal droplets obtained in step (2) to react, and obtaining carbon nanotubes after separation.

[0012] The temperature of the high-temperature gasification in step (1) is ≥2200°C, and may be, for example, 2200°C, 2500°C, 3000°C, 3500°C, 4000°C, 4500°C, 5000°C, 5500°C, 6000°C, 6500°C, 7000°C, 7500°C or 8000°C, but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0013] The cooling rate of the rapid quenching in step (2) is ≥1×10 4 °C / s, for example, 1×10 4 ℃ / s、5×10 4 ℃ / s、1×10 5 ℃ / s、5×10 5 ℃ / s、1×10 6 ℃ / s or 5×10 6 ℃ / s, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0014] The method provided by the present invention fundamentally prevents excessive growth and agglomeration of metal catalysts through high-temperature gasification and rapid quenching. The obtained metal nanoparticles or metal droplets have a high specific surface area and catalytic activity. The metal nanoparticles or metal droplets with small particle size are more likely to collide and react with the carbon precursor, thereby avoiding the occurrence of side reactions to the greatest extent, preventing amorphous carbon or graphite from being retained and clogging the reactor, improving reaction continuity, and significantly improving the carbon source conversion rate and the purity of the original product while ensuring the output, thus giving good balance between the output and quality of carbon nanotubes.

[0015] Preferably, the metal raw material in step (1) includes any one or a combination of at least two of a metal element, an alloy, an organometallic compound or a metal salt. Typical but non-limiting combinations include a combination of a metal element and an alloy, a combination of an alloy and an organometallic compound, a combination of an organometallic compound and a metal salt, a combination of a metal element, an alloy and an organometallic compound, a combination of an alloy, an organometallic compound and a metal salt, or a combination of a metal element, an alloy, an organometallic compound and a metal salt.

[0016] Preferably, the metal element includes iron, cobalt, nickel, aluminum, magnesium, tin, zinc, iridium or ruthenium, more preferably iron, cobalt or nickel.

[0017] Preferably, the organometallic compound comprises ferrocene, nickelocene, cobaltocene, iron pentacarbonyl, dicobalt octacarbonyl, nickel tetracarbonyl, iron acetate or a metal organic framework compound.

[0018] Preferably, the metal salt comprises ferric chloride, ferric bromide or ferric iodide.

[0019] Preferably, the form of the metal raw material in step (1) includes any one of lumps, particles, powders or droplets, or a combination of at least two of them. Typical but non-limiting combinations include a combination of lumps and particles, a combination of particles and powders, a combination of powders and droplets, a combination of lumps, particles and powders, or a combination of particles, powders and droplets.

[0020] Preferably, the high-temperature gasification method in step (1) includes any one of high-temperature decomposition, evaporation or sublimation.

[0021] Preferably, the protective gas in step (1) includes an inert gas and a reducing gas.

[0022] Preferably, the inert gas comprises any one of nitrogen, helium, neon or argon, or a combination of at least two of them. Typical but non-limiting combinations include a combination of nitrogen and helium, a combination of helium and neon, a combination of neon and argon, a combination of nitrogen, helium and neon, a combination of helium, neon and argon, or a combination of nitrogen, helium, neon and argon.

[0023] Preferably, the reducing gas comprises any one or a combination of at least two of hydrogen, carbon monoxide, water vapor or methanol vapor. Typical but non-limiting combinations include a combination of hydrogen and carbon monoxide, a combination of carbon monoxide and water vapor, a combination of water vapor and methanol vapor, a combination of hydrogen, carbon monoxide and water vapor, a combination of carbon monoxide, water vapor and methanol vapor, or a combination of hydrogen, carbon monoxide, water vapor and methanol vapor.

[0024] Preferably, the temperature of the high-temperature gasification in step (1) is 2200-20000°C, for example, it can be 2200°C, 4000°C, 6000°C, 8000°C, 10000°C, 12000°C, 14000°C, 16000°C, 18000°C or 20000°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0025] Preferably, during the high-temperature gasification process in step (1), the Reynolds number of the mixed gas formed by the metal raw material and the protective gas is 500-2000, for example, it can be 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900 or 2000, but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0026] Preferably, the quenching gas used in the annular air knife in step (2) includes any one of nitrogen, helium, neon or argon, or a combination of at least two of them. Typical but non-limiting combinations include a combination of nitrogen and helium, a combination of helium and neon, a combination of neon and argon, a combination of nitrogen, helium and neon, a combination of helium, neon and argon, or a combination of nitrogen, helium, neon and argon.

[0027] Preferably, the gas compression ratio of the annular air knife in step (2) is (5-50):1, for example, it can be 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1 or 50:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0028] In the present invention, quenched gas enters the air knife and is blown out at high speed. The Coanda effect controls the flow field into a cone shape, thus forming an impact air curtain of high-speed airflow. The high degree of supercooling and local high pressure of the metal vapor mixture promotes catalyst nucleation. The nucleated metal catalyst is more likely to cross the potential barrier, forming highly concentrated, narrowly distributed, small-sized, highly active metal nanoparticles or metal droplets.

[0029] Preferably, the cooling rate of the rapid quenching in step (2) is 1×10 4 -3×10 6 °C / s, for example, 1×10 4 ℃ / s、5×10 4 ℃ / s、1×10 5 ℃ / s、5×10 5 ℃ / s、1×10 6 °C / s or 3×10 6℃ / s, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0030] Preferably, the average particle size of the metal nanoparticles or metal droplets in step (2) is 0.5-5 nm, for example, it can be 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm or 5 nm, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0031] In the present invention, the average particle size of the metal nanoparticles or metal droplets is highly dependent on the specific type of target product (carbon nanotubes). For single-walled or double-walled carbon nanotubes, the average particle size of the metal nanoparticles or metal droplets should be controlled to approximately 1.5 nm; for multi-walled carbon nanotubes, the average particle size of the metal nanoparticles or metal droplets should be controlled to approximately 3 nm.

[0032] Preferably, the carbon precursor in step (3) includes any one of methane, ethane, ethylene, acetylene, propylene, methanol, ethanol, benzene, toluene, phenol or naphthalene, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of methane and ethane, a combination of ethane and ethylene, a combination of ethylene and acetylene, a combination of acetylene and propylene, a combination of propylene and methanol, a combination of methanol and ethanol, a combination of ethanol and benzene, a combination of benzene and toluene, a combination of toluene and phenol, or a combination of phenol and naphthalene.

[0033] In the present invention, there is a corresponding relationship between the proportion of each component of the carbon precursor and the number of wall layers of the resulting carbon nanotubes. Single-walled, double-walled, oligo-walled or multi-walled carbon nanotubes can be freely selected to be generated while ensuring high carbon conversion rate and high magnification, and the proportion of target carbon nanotubes in the total carbon nanotubes can reach 85-100wt%.

[0034] For example, if a combination of methane and propylene is used as a carbon precursor, and the molar ratio of carbon element to catalyst particles is close, the flow ratio of methane to propylene is set to x. When x>10, the product is mostly single-walled carbon nanotubes; when 10>x>1, the product is mostly 2-5 layers of oligo-walled carbon nanotubes; when x<1, the product is mostly multi-walled carbon nanotubes, and the smaller x is, the more carbon nanotube wall layers there are, and the higher the proportion of amorphous carbon in the product.

[0035] Preferably, the accelerator in step (3) is a sulfur-containing or nitrogen-containing inorganic or organic substance, including any one or a combination of at least two of elemental sulfur, hydrogen sulfide, mercaptans, thiophenols, sulfides, carbon disulfide, thiophene, tetrahydrothiophene, amines, nitrogen heterocycles or nitro groups. Typical but non-limiting combinations include a combination of elemental sulfur and hydrogen sulfide, a combination of hydrogen sulfide and mercaptans, a combination of mercaptans and thiophenols, a combination of thiophenols and sulfides, a combination of sulfides and carbon disulfide, a combination of carbon disulfide and thiophene, a combination of thiophene and tetrahydrothiophene, a combination of tetrahydrothiophene and amines, a combination of amines and nitrogen heterocycles, or a combination of nitrogen heterocycles and nitro groups.

[0036] Preferably, the reducing gas in step (3) comprises any one or a combination of at least two of hydrogen, carbon monoxide, water vapor or methanol vapor. Typical but non-limiting combinations include a combination of hydrogen and carbon monoxide, a combination of carbon monoxide and water vapor, a combination of water vapor and methanol vapor, a combination of hydrogen, carbon monoxide and water vapor, a combination of carbon monoxide, water vapor and methanol vapor, or a combination of hydrogen, carbon monoxide, water vapor and methanol vapor.

[0037] Preferably, the reaction temperature in step (3) is 650-1500°C, for example, it can be 650°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C or 1500°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0038] In the present invention, the process time from the mixing of metal nanoparticles or metal droplets with carbon precursors to the start of growth of carbon nanotubes is less than 0.1 s, thereby effectively preventing excessive agglomeration of the metal catalyst.

[0039] Preferably, the waste gas obtained in the reaction of step (3) is recycled and then reused, meeting the green and environmentally friendly production requirements.

[0040] In a second aspect, the present invention provides an apparatus system adopted by the method as described in the first aspect, wherein the apparatus system comprises a metal raw material conveying unit, a high-temperature gasification unit, a rapid quenching unit, a mixing unit, a reaction unit and a separation unit connected in sequence.

[0041] The device system provided by the present invention has a simple structure and is easy to operate, which significantly improves the possibility of industrial mass production of carbon nanotubes.

[0042] Preferably, the metal raw material conveying unit converts the metal raw material into metal particles or metal droplets, and includes an evaporation tank, an induction heater, a DC plasma arc furnace, a microwave plasma furnace or an induction plasma arc furnace.

[0043] Preferably, the high-temperature gasification unit includes an induction plasma arc furnace or a direct current plasma arc furnace.

[0044] Preferably, the rapid quenching unit comprises an annular air knife made of ceramic material.

[0045] Preferably, the mixing unit includes a double-layer breathable ceramic mixer and a matching nozzle, which can effectively alleviate the retention and blockage of side reaction products.

[0046] Preferably, the separation unit comprises a roller collector and a filter.

[0047] Preferably, the separation unit is further connected to a recovery unit, and the recovery unit is independently connected back to the metal raw material conveying unit and the rapid quenching unit.

[0048] Preferably, the recovery unit includes an alkaline spray tower and a tail gas recovery tower.

[0049] In the present invention, the waste gas obtained by the reaction is filtered and adsorbed in a tail gas recovery tower, and the excess reducing gas is separated and collected as the second product of the reaction. The remaining inert gas and the reducing gas are mixed again with the same component ratio and can be recycled, thereby increasing economic benefits and meeting the requirements of green environmental protection.

[0050] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] The method provided by the present invention fundamentally prevents excessive growth and agglomeration of metal catalysts through high-temperature gasification and rapid quenching. The obtained metal nanoparticles or metal droplets have a high specific surface area and catalytic activity. The metal nanoparticles or metal droplets with small particle size are more likely to collide and react with the carbon precursor, thereby avoiding the occurrence of side reactions to the greatest extent (side reaction product selectivity ≤4%), preventing amorphous carbon or graphite from clogging the reactor, improving reaction continuity (continuous reaction time ≥360h), and significantly improving the carbon source conversion rate (≥96.5%) and the original product purity (single / double-wall product purity ≥96%, multi-wall product purity ≥99.9%) while ensuring the output (≥180g / h), thus giving good balance between the output and quality of carbon nanotubes. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 This is a schematic diagram of the structure of the device system for continuously producing carbon nanotubes provided by the present invention;

[0054] Figure 2 1 is a schematic diagram of the structure of the apparatus system for continuously producing carbon nanotubes provided in Example 1;

[0055] Figure 3 Schematic diagram of the structure of the apparatus system for continuously producing carbon nanotubes provided in Example 2-4;

[0056] Figure 4 are scanning electron microscope photos of the carbon nanotube products obtained in Example 1 and Example 4;

[0057] Figure 5 These are transmission electron microscope photos of carbon nanotube products obtained in Examples 1, 3, 4, and Comparative Example 1;

[0058] Figure 6 1 and 2 are Raman spectra of the carbon nanotube products obtained in Examples 1 and 4 and Comparative Example 2.

[0059] Among them: 10-metal raw material conveying unit; 11-powder feeder; 12-sublimation furnace; 20-high-temperature gasification unit; 21-induction plasma arc furnace; 22-DC plasma arc furnace; 30-rapid quenching unit; 31-annular air knife; 40-mixing unit; 41-double-layer breathable ceramic mixer; 50-reaction unit; 51-high-temperature reaction furnace; 60-separation unit; 61-roller collector; 70-recovery unit; 71-tail gas recovery tower. DETAILED DESCRIPTION

[0060] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0061] The present invention provides a method and device system for continuously producing carbon nanotubes. Figure 1 As shown, the device system includes a metal raw material conveying unit 10, a high-temperature gasification unit 20, a rapid quenching unit 30, a mixing unit 40, a reaction unit 50, a separation unit 60 and a recovery unit 70 connected in sequence, and the recovery unit 70 is independently connected back to the metal raw material conveying unit 10 and the rapid quenching unit 30.

[0062] Specifically, the method comprises the following steps:

[0063] (1) The metal raw material is converted into metal particles or metal droplets by powder feeding, sublimation or ion arc by using the metal raw material conveying unit 10, and then introduced into the high-temperature gasification unit 20 in a protective gas atmosphere for high-temperature gasification at a temperature of ≥2200°C to obtain a metal vapor mixture;

[0064] (2) The metal vapor mixture obtained in step (1) is passed into the rapid quenching unit 30 and subjected to a cooling rate of ≥1×10 4 ℃ / s rapid quenching to obtain metal nanoparticles or metal droplets;

[0065] (3) A carbon precursor, a promoter, a reducing gas and the metal nanoparticles or metal droplets obtained in step (2) are mixed in a mixing unit 40, and the obtained working mixture is introduced into a reaction unit 50 for reaction. The obtained carbon precursor decomposition products are separated by a separation unit 60 to obtain carbon nanotubes, and the obtained waste gas is recycled and reused after being recovered by a recovery unit 70.

[0066] Example 1

[0067] This embodiment provides a method and device system for continuously producing carbon nanotubes. Figure 2 As shown, the method includes the following steps:

[0068] (1) 30 L / min of argon and 1 L / min of hydrogen were introduced into the powder feeder 11, and the iron particles were blown out at a rate of 30 g / h and then entered into the induction plasma arc furnace 21 for high-temperature gasification. The temperature at the arc was controlled at 3500° C. to obtain an iron vapor mixture;

[0069] (2) The generated iron vapor mixture is passed through a ceramic annular air knife 31 and rapidly quenched by introducing 60 L / min of argon and 2 L / min of hydrogen. The gas compression ratio is controlled to be 40:1, and the cooling rate is 2×10 5 ℃ / s, and obtain high concentration of uniform particle size (about 1×10 14 pieces / cm 2 ) iron nanoparticles;

[0070] (3) 5.5 L / min of methane and 0.3 L / min of propylene as carbon precursors, 20 L / min of hydrogen as reducing gas, and 7 g / h of evaporated sulfur gas as a promoter are introduced into a double-layer breathable ceramic mixer 41 together with iron nanoparticles to form a working mixture. The mixture is then sprayed through a nozzle into a high-temperature reactor 51 at 1200°C to synthesize carbon precursor decomposition products including carbon nanotubes and exhaust gas. The reaction continues for 400 hours, and then the system is cooled and cleaned.

[0071] (4) The synthesized carbon nanotube product is separated and collected by the roller collector 61 to obtain the carbon nanotube product. The remaining waste gas is filtered through a filter. The alkaline spray tower removes the remaining carbon tubes and waste gases such as hydrogen sulfide and then passes into the tail gas recovery tower 71. It is adsorbed by adsorbents such as activated carbon, aluminum oxide, and silicon oxide. The recovered gas is reintroduced into the system for reaction, and the remaining hydrogen is collected as the second product.

[0072] Example 2

[0073] This embodiment provides a method and device system for continuously producing carbon nanotubes. Figure 3 As shown, the method includes the following steps:

[0074] (1) 30 L / min of argon, 1 L / min of hydrogen, and 85 g / h of ferrocene powder are introduced into a sublimation furnace 12 at 200° C., the generated iron droplets are blown out and then enter a DC plasma arc furnace 22 for high-temperature gasification, and the arc temperature is controlled to be 13000° C. to obtain an iron vapor mixture;

[0075] (2) The generated iron vapor mixture is passed through a ceramic annular air knife 31 and rapidly quenched by introducing 90 L / min of argon and 3 L / min of hydrogen. At the same time, the gas compression ratio is controlled to be 50:1, and the cooling rate is 3×10 6 ℃ / s, and obtain high concentration of uniform particle size (about 1×10 14 pieces / cm 2 ) iron nanoparticles;

[0076] (3) 5.5 L / min of methane and 0.3 L / min of propylene as carbon precursors, 20 L / min of hydrogen as reducing gas, and 7 g / h of evaporated sulfur gas as a promoter are introduced into a double-layer breathable ceramic mixer 41 together with iron nanoparticles to form a working mixture. The mixture is then sprayed through a nozzle into a high-temperature reactor 51 at 1200°C to synthesize carbon precursor decomposition products including carbon nanotubes and exhaust gas. The reaction continues for 400 hours, and then the system is cooled and cleaned.

[0077] (4) The synthesized carbon nanotube product is separated and collected by the roller collector 61 to obtain the carbon nanotube product. The remaining waste gas is filtered through a filter. The alkaline spray tower removes the remaining carbon tubes and waste gases such as hydrogen sulfide and then passes into the tail gas recovery tower 71. It is adsorbed by adsorbents such as activated carbon, aluminum oxide, and silicon oxide. The recovered gas is reintroduced into the system for reaction, and the remaining hydrogen is collected as the second product.

[0078] Example 3

[0079] This embodiment provides a method and device system for continuously producing carbon nanotubes. Figure 3 As shown, the method includes the following steps:

[0080] (1) 30 L / min of argon, 1 L / min of hydrogen, and 85 g / h of ferrocene powder are introduced into a sublimation furnace 12 at 200° C., the generated iron droplets are blown out and then enter a DC plasma arc furnace 22 for high-temperature gasification, and the arc temperature is controlled to be 13000° C. to obtain an iron vapor mixture;

[0081] (2) The generated iron vapor mixture is passed through a ceramic annular air knife 31 and rapidly quenched by introducing 90 L / min of argon and 3 L / min of hydrogen. The gas compression ratio is controlled to be 10:1, and the cooling rate is 5×10 5 ℃ / s, and obtain high concentration of uniform particle size (about 1×10 14 pieces / cm 2 ) iron nanoparticles;

[0082] (3) 2 L / min of methane and 1.3 L / min of propylene as carbon precursors, 20 L / min of hydrogen as reducing gas, and 20 g / h of evaporated sulfur gas as a promoter are introduced into a double-layer breathable ceramic mixer 41 together with iron nanoparticles to form a working mixture. The mixture is then sprayed through a nozzle into a high-temperature reactor 51 at 1200°C to synthesize carbon precursor decomposition products including carbon nanotubes and exhaust gas. The reaction continues for 400 hours, and then the system is cooled and cleaned.

[0083] (4) The synthesized carbon nanotube product is separated and collected by the roller collector 61 to obtain the carbon nanotube product. The remaining waste gas is filtered through a filter. The alkaline spray tower removes the remaining carbon tubes and waste gases such as hydrogen sulfide and then passes into the tail gas recovery tower 71. It is adsorbed by adsorbents such as activated carbon, aluminum oxide, and silicon oxide. The recovered gas is reintroduced into the system for reaction, and the remaining hydrogen is collected as the second product.

[0084] Example 4

[0085] This embodiment provides a method and device system for continuously producing carbon nanotubes. Figure 3 As shown, the method includes the following steps:

[0086] (1) 30 L / min of argon, 1 L / min of hydrogen, and 200 g / h of ferrocene powder are introduced into a sublimation furnace 12 at 200° C., the generated iron droplets are blown out and then enter a DC plasma arc furnace 22 for high-temperature gasification, and the arc temperature is controlled to be 13000° C. to obtain an iron vapor mixture;

[0087] (2) The generated iron vapor mixture is passed through a ceramic annular air knife 31 and rapidly quenched by introducing 90 L / min of argon and 3 L / min of hydrogen. The gas compression ratio is controlled to be 5:1, and the cooling rate is 1×10 5 ℃ / s, and obtain high concentration of uniform particle size (about 2×10 14 pieces / cm 2 ) iron nanoparticles;

[0088] (3) 0.8 L / min methane and 8.3 L / min propylene as carbon precursors, 20 L / min hydrogen as reducing gas, and 20 g / h evaporated carbon disulfide gas as accelerator are introduced into a double-layer breathable ceramic mixer 41 together with iron nanoparticles to form a working mixture, which is then sprayed into a high-temperature reactor 51 at 1200°C through a nozzle to synthesize carbon precursor decomposition products including carbon nanotubes and exhaust gas. The reaction continues for 200 hours, and then the system is cooled and cleaned;

[0089] (4) The synthesized carbon nanotube product is separated and collected by the roller collector 61 to obtain the carbon nanotube product. The remaining waste gas is filtered through a filter. The alkaline spray tower removes the remaining carbon tubes and waste gases such as hydrogen sulfide and then passes into the tail gas recovery tower 71. It is adsorbed by adsorbents such as activated carbon, aluminum oxide, and silicon oxide. The recovered gas is reintroduced into the system for reaction, and the remaining hydrogen is collected as the second product.

[0090] Comparative Example 1

[0091] This comparative example provides a method and apparatus system for continuously producing carbon nanotubes, except that no quenching gas is introduced in step (2), so that the cooling rate becomes 1×10 3 The remaining steps and conditions are the same as those in Example 1 and are not described here in detail.

[0092] Comparative Example 2

[0093] This comparative example provides a method and device system for continuously producing carbon nanotubes. Except that the DC plasma arc furnace 22 in step (1) is turned on for 1 hour and then turned off, and the temperature at the arc is controlled to 1000°C, the remaining steps and conditions are the same as those in Example 2 and are not described here.

[0094] Comparative Example 3

[0095] This comparative example provides a method and apparatus system for continuously producing carbon nanotubes. In addition to adjusting the gas compression ratio of the annular air knife 31 in step (2) to 4:1 and the cooling rate to 5×10 3 The remaining steps and conditions are the same as those in Example 1 and are not described here in detail.

[0096] Comparative Example 4

[0097] This comparative example provides a method and apparatus system for continuously producing carbon nanotubes. In addition to adjusting the gas compression ratio of the annular air knife 31 in step (2) to 60:1 and the cooling rate to 7×10 6 The remaining steps and conditions are the same as those in Example 1 and are not described here in detail.

[0098] The carbon nanotube products obtained in Examples 1-4 and Comparative Examples 1-4 were weighed and the carbon source conversion rate was calculated. The specific calculation formula is as follows:

[0099] Carbon source conversion rate = (weight of collected material - weight of metal elements in catalyst) / weight of carbon source converted × 100%

[0100] The scanning electron microscope photos of the carbon nanotube products obtained in Example 1 and Example 4 are shown in Figure 4 .

[0101] Transmission electron microscope photos of the carbon nanotube products obtained in Examples 1, 3, 4 and Comparative Example 1 are shown in Figure 5 .

[0102] Raman spectra of the carbon nanotube products obtained in Examples 1, 4 and Comparative Example 2 are shown in FIG. Figure 6 .

[0103] After testing, the yield, original product purity, carbon source conversion rate and Raman G / D ratio of the carbon nanotube products obtained in Examples 1-4 and Comparative Examples 1-4 are shown in Table 1 below.

[0104] Table 1

[0105]

[0106] In the carbon nanotube product obtained in Example 1, single-walled carbon nanotubes account for about 90% of the total carbon nanotubes, and the diameter of the unaggregated iron nanoparticles in the product ranges from 0.6 to 1.9 nm.

[0107] In the carbon nanotube product obtained in Example 2, single-walled carbon nanotubes account for about 88% of the total carbon nanotubes, and the diameter of the unaggregated iron nanoparticles in the product ranges from 0.8 to 2.2 nm.

[0108] In the carbon nanotube product obtained in Example 3, 2-4 wall carbon nanotubes account for about 85% of the total carbon nanotubes, and the diameter of the unaggregated iron nanoparticles in the product ranges from 0.7 to 2.0 nm.

[0109] In the carbon nanotube product obtained in Example 4, the proportion of multi-walled carbon nanotubes to the total carbon nanotubes is 100%, the number of carbon nanotube walls in about 70% is in the range of 10-30, and the diameter of the unaggregated iron nanoparticles in the product ranges from 1.3 to 4.6 nm.

[0110] In the carbon nanotube product obtained in Comparative Example 1, single-walled carbon nanotubes account for about 50% of the total carbon nanotubes, and the diameter of the iron nanoparticles in the product ranges from about 4 to 30 nm.

[0111] In the carbon nanotube product obtained in Comparative Example 2, the proportion of single-walled carbon nanotubes to the total carbon nanotubes was about 10%, and the diameter of the iron nanoparticles in the product was in the range of about 50-1000 nm.

[0112] In the carbon nanotube product obtained in Comparative Example 3, single-walled carbon nanotubes account for about 70% of the total carbon nanotubes, and the diameter of the iron nanoparticles in the product ranges from about 3 to 20 nm.

[0113] In the carbon nanotube product obtained in Comparative Example 4, single-walled carbon nanotubes accounted for approximately 92% of the total carbon nanotubes, and the diameter of the iron nanoparticles in the product ranged from approximately 0.6 to 1.7 nm.

[0114] Compared with Example 1, in Comparative Example 1, no quenching gas was introduced and the cooling rate of quenching was reduced while other parameters such as catalyst components, carbon source, and temperature remained unchanged. The yield, purity, carbon source conversion rate, and quality of the obtained carbon nanotubes were significantly reduced, indicating that the quenching process has a very obvious effect on the activity of the metal catalyst.

[0115] Compared with Example 2, in Comparative Example 2, the catalyst precursor gasification temperature was lowered while other parameters such as catalyst composition, carbon source, and temperature remained unchanged. Ultimately, only a very small number of carbon nanotubes were obtained. This indicates that the catalyst that was not gasified at high temperature was significantly agglomerated in the growth area and basically lost its activity, resulting in the failure of carbon nanotube growth.

[0116] Compared with Example 1, in Comparative Example 3, the gas compression ratio of the annular air knife is reduced while other parameters such as catalyst components, carbon source, and temperature remain unchanged, resulting in a decrease in the cooling rate of quenching, and the resulting carbon nanotube yield, purity, carbon source conversion rate and quality are significantly reduced, indicating that the low gas compression ratio of the annular air knife has a very obvious effect on the activity of the metal catalyst.

[0117] Compared with Example 1, in Comparative Example 4, the gas compression ratio of the annular air knife was increased while other parameters such as the catalyst component, carbon source, and temperature remained unchanged, resulting in excessively low local temperature, insufficient product reaction time, and significantly reduced carbon nanotube yield, purity, and carbon source conversion rate. This indicates that the excessively high gas compression ratio of the annular air knife has a significant impact on the activity of the metal catalyst and the subsequent carbon nanotube synthesis process.

[0118] It can be seen that the present invention utilizes high-temperature gasification and annular air knife quenching technology to efficiently and continuously produce high-purity carbon nanotubes, separately controls the catalyst generation zone and the carbon nanotube synthesis zone, matches the carbon source decomposition temperature and the catalyst activity temperature, and successfully produces high-quality single-walled, double-walled and multi-walled carbon nanotubes by regulating process parameters. The carbon source conversion rate and original purity both reach new highs. In addition, the equipment is simple and the operation is easy to implement, which significantly improves the possibility of industrial mass production of carbon nanotubes.

[0119] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for continuously producing carbon nanotubes, characterized in that: The method comprises the following steps: (1) gasifying the metal raw material at high temperature in a protective gas atmosphere to obtain a metal vapor mixture; (2) rapidly quenching the metal vapor mixture obtained in step (1) through an annular air knife to obtain metal nanoparticles or metal droplets; (3) mixing a carbon precursor, a promoter, a reducing gas and the metal nanoparticles or metal droplets obtained in step (2) to react, and obtaining carbon nanotubes after separation; The temperature of the high-temperature gasification in step (1) is ≥2200°C; the cooling rate of the rapid quenching in step (2) is ≥1×10 4 ℃ / s.

2. The method according to claim 1, characterized in that The metal raw material in step (1) includes any one of a metal element, an alloy, an organometallic compound or a metal salt, or a combination of at least two thereof; Preferably, the metal element includes iron, cobalt, nickel, aluminum, magnesium, tin, zinc, iridium or ruthenium, more preferably iron, cobalt or nickel; Preferably, the organometallic compound comprises ferrocene, nickelocene, cobaltocene, iron pentacarbonyl, dicobalt octacarbonyl, nickel tetracarbonyl, iron acetate or a metal organic framework compound; Preferably, the metal salt comprises ferric chloride, ferric bromide or ferric iodide; Preferably, the metal raw material in step (1) is in the form of any one of blocks, particles, powders or droplets, or a combination of at least two of them.

3. The method according to claim 1 or 2, characterized in that The high-temperature gasification method in step (1) includes any one of high-temperature decomposition, evaporation or sublimation.

4. The method according to any one of claims 1 to 3, characterized in that The protective gas in step (1) includes an inert gas and a reducing gas; Preferably, the inert gas comprises any one of nitrogen, helium, neon or argon, or a combination of at least two thereof; Preferably, the reducing gas includes any one of hydrogen, carbon monoxide, water vapor or methanol vapor, or a combination of at least two of them.

5. The method according to any one of claims 1 to 4, characterized in that The temperature of the high-temperature gasification in step (1) is 2200-20000° C.; Preferably, during the high-temperature gasification process in step (1), the Reynolds number of the mixed gas formed by the metal raw material and the protective gas is 500-2000.

6. The method according to any one of claims 1 to 5, characterized in that The quenching gas used by the annular air knife in step (2) includes any one of nitrogen, helium, neon or argon, or a combination of at least two of them; Preferably, the gas compression ratio of the annular air knife in step (2) is (5-50):1; Preferably, the cooling rate of the rapid quenching in step (2) is 1×10 4 -3×10 6 ℃ / s; Preferably, the average particle size of the metal nanoparticles or metal droplets in step (2) is 0.5-5 nm.

7. The method according to any one of claims 1 to 6, characterized in that The carbon precursor in step (3) comprises any one of methane, ethane, ethylene, acetylene, propylene, methanol, ethanol, benzene, toluene, phenol or naphthalene, or a combination of at least two thereof; Preferably, the accelerator in step (3) is a sulfur- or nitrogen-containing inorganic or organic substance, including any one or a combination of at least two of elemental sulfur, hydrogen sulfide, mercaptans, thiophenols, sulfides, carbon disulfide, thiophene, tetrahydrothiophene, amines, nitrogen heterocycles or nitro groups; Preferably, the reducing gas in step (3) comprises any one of hydrogen, carbon monoxide, water vapor or methanol vapor, or a combination of at least two thereof; Preferably, the reaction temperature in step (3) is 650-1500°C; Preferably, the waste gas obtained in the reaction of step (3) is recycled and reused.

8. A device system used in the method according to any one of claims 1 to 7, characterized in that: The device system comprises a metal raw material conveying unit, a high-temperature gasification unit, a rapid quenching unit, a mixing unit, a reaction unit and a separation unit which are connected in sequence.

9. The device system according to claim 8, characterized in that: The metal raw material conveying unit converts the metal raw material into metal particles or metal droplets, and includes an evaporation tank, an induction heater, a DC plasma arc furnace, a microwave plasma furnace or an induction plasma arc furnace; Preferably, the high temperature gasification unit comprises an induction plasma arc furnace or a DC plasma arc furnace; Preferably, the rapid quenching unit comprises an annular air knife made of ceramic material; Preferably, the mixing unit comprises a double-layer breathable ceramic mixer and a matching nozzle; Preferably, the separation unit comprises a roller collector and a filter.

10. The device system according to claim 8 or 9, characterized in that: The separation unit is further connected to a recovery unit, and the recovery unit is independently connected back to the metal raw material conveying unit and the rapid quenching unit; Preferably, the recovery unit includes an alkaline spray tower and a tail gas recovery tower.

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