Preparation method and application of few-walled carbon nanotube

Abstract

The invention relates to the technical field of carbon nanotubes, and provides a preparation method and application of a few-walled carbon nanotube. A liquid iron source and a carrier are dissolved in an organic solvent, the catalyst solution is obtained, and the liquid iron source comprises carbonyl iron and / or ferrocene; and introducing a catalyst solution, a carrier gas and an optional carbon source into the fluidized bed to grow the carbon nanotube to obtain the few-walled carbon nanotube. The low-walled carbon nanotube has the beneficial effects that in the preparation process of the low-walled carbon nanotube, products obtained by decomposing carbonyl iron and / or ferrocene when meeting heat are uniformly distributed in the carrier, agglomeration of metal catalytic activity is avoided, and the low-walled carbon nanotube is easily formed in the preparation process due to the fact that the particle size of the products obtained by decomposing when meeting heat is relatively small; the fluidized bed process is adopted, so that the few-walled carbon nanotubes are produced in an amplified manner, and the application prospect of the few-walled carbon nanotubes in the aspect of the silicon-carbon negative electrode conductive agent is increased.

Description

Technical Field

[0001] The present application belongs to the technical field of preparing carbon nanotubes, and in particular to a preparation method of oligo-walled carbon nanotubes and applications thereof. Background Art

[0002] Carbon nanotubes have excellent electrical, mechanical and chemical properties. Adding carbon nanotubes to polymer, ceramic or metal matrices can significantly improve the electrical conductivity, thermal conductivity and other physical properties of the main material. As a new type of material, carbon nanotubes are mainly used in the fields of lithium battery materials and conductive plastics, and their uses are constantly being researched and expanded.

[0003] Oligocean-walled carbon nanotubes have gradually attracted widespread attention and become a research hotspot due to their small number of carbon nanotube walls, large aspect ratio, and excellent electrical conductivity. Most of the existing methods for preparing ligean-walled carbon nanotubes use floating catalytic chemical vapor deposition methods, and the main equipment is a fixed bed. There are many influencing factors in the growth process of ligean-walled carbon nanotubes, such as carbon source, catalyst, temperature, pressure, etc., and the growth of ligean-walled carbon nanotubes and the regulation of diameter size can be achieved by adjusting different factors. In particular, the structure of catalyst nanoparticles, including composition, morphology and size distribution, directly affects the diameter distribution of ligean-walled carbon nanotubes. The diameter selective growth of ligean-walled carbon nanotubes is achieved by adjusting the catalyst structure, and certain research results have been achieved. However, the above-mentioned growth regulation is mostly carried out in a fixed bed. Although the purity is high and it is easy to regulate, the growth efficiency is low and large-scale preparation cannot be carried out.

[0004] As we all know, fluidized bed process is an expanded means of preparing carbon nanotubes, but it is difficult to prepare oligo-walled carbon nanotubes using fluidized bed process. First, there is no suitable catalyst to enable it to grow on the surface in the fluidized bed process to obtain oligo-walled carbon nanotubes. In addition, the carbon source, reaction temperature and reaction process are difficult to control. Summary of the invention

[0005] The purpose of the present application is to provide a method for preparing oligo-walled carbon nanotubes and its application, aiming to solve the problem that the preparation of oligo-walled carbon nanotubes by fluidized bed process is difficult, has many side reactions and low product purity.

[0006] In order to achieve the above application purpose, the technical solution adopted in this application is as follows:

[0007] In a first aspect, a method for preparing oligo-walled carbon nanotubes is provided, comprising the following steps:

[0008] Preparing a catalyst solution: dissolving a liquid iron source and a carrier in an organic solvent to obtain the catalyst solution; the liquid iron source includes carbonyl iron and / or ferrocene;

[0009] The catalyst solution, carrier gas and carbon source are introduced into the fluidized bed to grow carbon nanotubes to obtain oligo-walled carbon nanotubes.

[0010] According to some embodiments of the preparation method described in the present application, the carbon nanotube growth includes a catalyst activation stage, an initial reaction, an intermediate reaction, and a late reaction;

[0011] The catalyst activation stage includes introducing the catalyst solution, reducing gas and carrier gas into the fluidized bed to perform catalyst activation treatment and preliminary growth of carbon nanotubes.

[0012] According to some embodiments of the preparation method described in the present application, the temperature for activating the catalyst is 600° C.-650° C.; the duration for activating the catalyst is 2 min-10 min.

[0013] According to some embodiments of the preparation method described in the present application, the reducing gas includes hydrogen.

[0014] According to some embodiments of the preparation method described in the present application, the carrier gas in the catalyst activation stage is selected from inert gases.

[0015] According to some embodiments of the preparation method described in the present application, an activation zone is provided in the fluidized bed, and the catalyst activation stage is carried out in the activation zone.

[0016] According to some embodiments of the preparation method described in the present application, the catalyst activation stage includes providing a partition in the fluidized bed, the partition is movably connected to the top of the fluidized bed, and the partition is located below the feed port of the fluidized bed;

[0017] A catalyst solution and a carrier gas are introduced into the fluidized bed, and a partition is opened to separate the fluidized bed into an upper and a lower part for catalyst activation. After the activation is completed, the partition is closed to carry out an initial reaction.

[0018] According to some embodiments of the preparation method described in the present application, the volume flow rate of the carbon source in the initial reaction is smaller than the volume flow rate of the carbon source in the intermediate reaction.

[0019] According to some embodiments of the preparation method described in the present application, in the initial reaction, the ratio of the flow rate of the carbon source to the flow rate of the carrier gas is 1:(4-20).

[0020] According to some embodiments of the preparation method described in the present application, in the mid-term reaction, the ratio of the flow rate of the carbon source to the flow rate of the carrier gas is 1:(1.2-2).

[0021] According to some embodiments of the preparation method described in the present application, only carrier gas is introduced into the later stage reaction.

[0022] According to some embodiments of the preparation method described in the present application, the carrier is selected from one or more of vermiculite, alumina, and magnesium oxide.

[0023] According to some embodiments of the preparation method described in the present application, the organic solvent is selected from one or more of benzene, glycerol, isopropanol, and low molecular weight polyethylene glycol.

[0024] According to some embodiments of the preparation method described in the present application, the carbonyl iron is pentacarbonyl iron.

[0025] According to some embodiments of the preparation method described in the present application, the mass ratio of the liquid iron source, the carrier and the organic solvent is 1:(5-10):(20-50).

[0026] According to some embodiments of the preparation method described in the present application, the carbon source is selected from one or more of CO, ethanol, methanol, methane, acetylene, and propylene.

[0027] According to some embodiments of the preparation method described in the present application, the initial reaction includes introducing a carrier gas and the carbon source into the fluidized bed to grow carbon nanotubes.

[0028] According to some embodiments of the preparation method described in the present application, the carrier gas of the initial reaction is an inert gas.

[0029] According to some embodiments of the preparation method described in the present application, the flow rate of the inert gas in the initial reaction is 450L / min-550L / min; the flow rate of the carbon source is 20L / min-100L / min.

[0030] According to some embodiments of the preparation method described in the present application, the reaction temperature of the initial reaction is 640° C.-680° C., and the reaction time is 30s-300s.

[0031] According to some embodiments of the preparation method described in the present application, the intermediate reaction introduces a carrier gas and the carbon source into the fluidized bed to grow carbon nanotubes.

[0032] According to some embodiments of the preparation method described in the present application, the carrier gas of the intermediate reaction is an inert gas.

[0033] According to some embodiments of the preparation method described in the present application, the flow rate of the inert gas in the mid-term reaction is 450L / min-550L / min, and the flow rate of the carbon source is 300L / min-400L / min.

[0034] According to some embodiments of the preparation method described in the present application, the reaction temperature of the mid-term reaction is 650°C-700°C, and the reaction time is 15min-35min.

[0035] According to some embodiments of the preparation method described in the present application, the carrier gas of the later reaction is an inert gas.

[0036] According to some embodiments of the preparation method described in the present application, the flow rate of the carrier gas in the later reaction is 580L / min-620L / min.

[0037] According to some embodiments of the preparation method described in the present application, the reaction temperature of the later reaction is 600° C.-650° C., and the reaction time is 1 min-5 min.

[0038] The second aspect of the present application provides an oligo-walled carbon nanotube, which is obtained by the preparation method described in the first aspect of the present application.

[0039] According to some embodiments of the oligo-walled carbon nanotubes described in the present application, the number of walls of the oligo-walled carbon nanotubes is less than 6.

[0040] According to some embodiments of the preparation method described in the present application, the powder resistivity of the oligo-walled carbon nanotubes is less than 8 mΩ·cm.

[0041] According to some embodiments of the preparation method described in this application, the specific surface area of ​​the oligo-walled carbon nanotubes is greater than 500 m 2 / g.

[0042] In a third aspect of the present application, there is provided an application of the oligo-walled carbon nanotubes obtained by the preparation method described in the first aspect of the present application or the oligo-walled carbon nanotubes described in the second aspect of the present application in a silicon-carbon negative electrode conductive agent.

[0043] The beneficial effects of the present invention are:

[0044] 1. During the preparation process of the oligo-walled carbon nanotubes described in the present application, the products obtained by thermal decomposition of carbonyl iron and / or ferrocene are evenly distributed in the carrier, thereby avoiding the agglomeration of metal catalytic activity. Since the particle size of the products obtained by thermal decomposition is relatively small, oligo-walled carbon nanotubes are easily formed during the preparation process, thereby realizing continuous large-scale production of oligo-walled carbon nanotubes.

[0045] 2. The present application adopts a fluidized bed process to scale up the production of oligo-walled carbon nanotubes, increasing their application prospects in silicon-carbon negative electrode conductive agents. DETAILED DESCRIPTION

[0046] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0047] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0048] In this application, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple, respectively.

[0049] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0050] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0051] The weight of the relevant components mentioned in the embodiment description of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the embodiment description of the present application, it is within the scope disclosed in the embodiment description of the present application. Specifically, the mass described in the embodiment description of the present application can be a mass unit known in the chemical industry such as μg, mg, g, kg, etc.

[0052] In a first aspect of the present application, a method for preparing oligo-walled carbon nanotubes is provided, comprising the following steps:

[0053] Prepare a catalyst solution: dissolve a liquid iron source and a carrier in an organic solvent to obtain the catalyst solution; the liquid iron source includes carbonyl iron and / or ferrocene, and the stirring rate when the carbonyl iron and / or ferrocene and the carrier are dissolved in the organic solvent can be 1500 rpm, the stirring time can be 30 minutes, and the catalyst solution is formed by stirring and emulsification;

[0054] A catalyst solution, a carrier gas and a carbon source are introduced into the fluidized bed to grow carbon nanotubes to obtain oligo-walled carbon nanotubes.

[0055] The key to the formation of oligo-walled carbon nanotubes is to obtain small nano-catalysts with high activity during the pyrolysis process. Therefore, the active catalytic substance needs to be evenly distributed in the carrier and not agglomerated. In the preparation process of the present application, the products obtained by thermal decomposition of carbonyl iron and / or ferrocene are evenly distributed in the carrier, avoiding the agglomeration of metal catalytic activity. Since the particle size of the products obtained by thermal decomposition is relatively small, oligo-walled carbon nanotubes are easily formed during the preparation process. As a preferred solution, the carbonyl iron is pentacarbonyl iron. That is, the present application provides a suitable catalyst to make the oligo-walled carbon nanotubes suitable for fluidized bed process preparation, thereby increasing its production efficiency.

[0056] In some embodiments, the growth of carbon nanotubes includes a catalyst activation stage, an initial reaction, an intermediate reaction, and a late reaction; the catalyst activation stage includes passing the catalyst solution, the reducing gas, and the carrier gas into the fluidized bed for catalyst activation treatment and initial growth of carbon nanotubes. In the catalyst activation stage, the products obtained by thermal decomposition of carbonyl iron and / or ferrocene are evenly distributed on the surface and inside of the carrier, and the active catalytic substances are evenly distributed in the carrier without agglomeration, which is conducive to the generation of oligo-walled carbon nanotubes.

[0057] In some embodiments, the temperature of the catalyst activation stage is 600° C.-650° C., such as 600° C., 610° C., 620° C., 630° C., 640° C., 650° C.; the duration of the catalyst activation stage is 2 min-10 min, such as 2 min, 3 min, 4 min, 5 min, 8 min, 10 min. Within this temperature range, carbonyl iron and / or ferrocene can be thermally decomposed and reduced to obtain catalyst active components.

[0058] In some embodiments, the reducing gas includes hydrogen; in some embodiments, the carrier gas in the catalyst activation stage is selected from an inert gas. Hydrogen can reduce iron oxide to iron and prevent oxidation reaction. The ratio of the flow rate of hydrogen to the flow rate of the carrier gas is (3-5):1, for example 3:1, 4:1, 5:1.

[0059] In some embodiments, an activation zone is provided in the fluidized bed, and the catalyst activation stage is carried out in the activation zone. The activation zone can be a partition provided in the fluidized bed, the partition is movably connected to the top of the fluidized bed, and the partition is located below the feed port of the fluidized bed.

[0060] Catalyst solution and carrier gas are introduced into the fluidized bed, and the partition is opened to divide the fluidized bed into upper and lower parts. An activation area is formed in the upper part to activate the catalyst. After the activation is completed, the partition is closed to carry out the initial reaction. The partition and the fluidized bed can be connected in a hinged manner. A fixing device for fixing the partition is provided on the partition. The fixing device can be a fixing rod. One end of the fixing rod is connected to the partition, and the other end is movably connected to the fluidized bed. When the partition needs to be used, the partition can be opened and fixed with the fixing rod. The partition can be retracted by retracting the fixing rod. In some embodiments, the position of the partition is set at one-third to one-fifth of the height of the fluidized bed.

[0061] After the catalyst activation stage is completed, the partition is closed to carry out the initial reaction. The partition plays a role in providing reaction time, which can improve the controllability of the entire fluidized bed reaction and further ensure that the nano iron particles are evenly distributed in the carrier.

[0062] In some embodiments, the volume flow rate of the carbon source in the initial reaction is less than the volume flow rate of the carbon source in the mid-term reaction. In some embodiments, in the initial reaction, the ratio of the flow rate of the carbon source to the flow rate of the carrier gas is 1: (4-20), such as 1: 4, 1: 6, 1: 9, 1: 10, 1: 13, 1: 16, 1: 18, 1: 20; in some embodiments, in the mid-term reaction, the ratio of the flow rate of the carbon source to the flow rate of the carrier gas is 1: (1.2-2), such as 1: 1.2, 1: 1.3, 1: 1.7, 1: 2; in the late reaction, only the carrier gas is introduced.

[0063] The nanotube growth process of the present application is carried out in three stages. The proportion of carbon source is low in the initial stage of the reaction, so that the carbon source is decomposed to grow oligo-walled carbon nanotubes on the surface of the metal catalyst. At the same time, the structure of the carrier also reduces the chance of metal particles agglomerating. The proportion of carbon source is increased in the middle stage to continue to grow oligo-walled carbon nanotubes, forming a competitive advantage and reducing the generation of side reaction multi-walled carbon nanotubes and impurity carbon. Finally, the carbon source is stopped to reduce the probability of carbon nanotubes agglomerating into multi-walled carbon nanotubes in the later stage of the reaction.

[0064] In some embodiments, the carrier is selected from one or more of vermiculite, alumina, and magnesium oxide; for example, expanded vermiculite, porous alumina, etc. In order to meet the needs of expanding production of fluidized beds, the selection of the carrier is very important. It requires good porosity to facilitate the loading of metal active ingredients and can be used in the fluidization process to form a better fluidized state. The selection of the above-mentioned carrier can meet the needs of expanding production of fluidized beds.

[0065] In some embodiments, the organic solvent is selected from one or more of benzene, glycerol, isopropanol, and low molecular weight polyethylene glycol; as a preferred embodiment, the number average molecular weight of polyethylene glycol is 200-400; the solvent selected in the present application is easy to evaporate and can serve as a carbon source in the early stage of the reaction.

[0066] In some embodiments, the mass ratio of the liquid iron source, the carrier and the organic solvent is 1: (5-10): (20-50); for example, 1:5:20, 1:5:30, 1:5:35, 1:5:40, 1:5:45, 1:5:50, 1:8:20, 1:8:30, 1:8:35, 1:8:40, 1:8:45, 1:8:50, 1:9:20, 1:9:30, 1:9:35, 1:9:40, 1:9:45, 1:9:50, 1:10:20, 1:10:30, 1:10:35, 1:10:40, 1:10:45, 1:10:50. By selecting the above dosage ratio, a well-dispersed and uniform catalyst solution can be obtained.

[0067] In some embodiments, the carbon source is selected from one or more of CO, ethanol, methanol, methane, acetylene, and propylene. The reaction rate can be easily controlled by selecting the carbon source.

[0068] In some embodiments, the carrier gas and the carbon source are introduced into the fluidized bed for the initial reaction to grow carbon nanotubes. In some embodiments, the carbon source of the initial reaction can be a mixture of the organic solvent in the catalyst and an additional carbon source, for example, the carbon source can be ethanol and methanol, or a mixture of the organic solvent in the catalyst and ethanol and / or methanol, and the mass ratio of the organic solvent in the catalyst to ethanol or methanol can be adjusted to (8-15):1, for example 8:1, 12:1, 13:1, 15:1, etc.

[0069] In some embodiments, the carrier gas of the initial reaction is an inert gas; the inert gas can be selected from neon, argon, nitrogen, etc.

[0070] In some embodiments, the flow rate of the inert gas in the initial reaction is 450 L / min-550 L / min, for example 450 L / min, 480 L / min, 490 L / min, 520 L / min, 550 L / min; the flow rate of the carbon source is 20 L / min-100 L / min, for example 20 L / min, 30 L / min, 45 L / min, 73 L / min, 100 L / min.

[0071] In some embodiments, the reaction temperature of the initial reaction is 640°C-680°C, for example 640°C, 650°C, 660°C, 670°C, 680°C; the reaction time is 30s-300s, for example 30s, 70s, 90s, 105s, 130s, 180s, 210s, 300s.

[0072] In some embodiments, during the mid-stage reaction, a carrier gas and a carbon source are introduced into the fluidized bed to grow carbon nanotubes; the carbon source can be selected from one or more of CO, methane, acetylene and propylene. Selecting this carbon source can increase the yield and facilitate scale-up production.

[0073] In some embodiments, the carrier gas of the intermediate reaction is an inert gas, which can be selected from argon, neon, and nitrogen.

[0074] In some embodiments, the flow rate of the inert gas in the mid-term reaction is 450 L / min-550 L / min, for example 450 L / min, 480 L / min, 490 L / min, 520 L / min, 550 L / min; the flow rate of the carbon source is 300 L / min-400 L / min, for example 300 L / min, 315 L / min, 361 L / min, 379 L / min, 400 L / min.

[0075] In some embodiments, the reaction temperature of the intermediate reaction is 650° C.-700° C., such as 650° C., 660° C., 670° C., 680° C., 690° C., 700° C., and the reaction time is 15 min-35 min, such as 15 min, 20 min, 27 min, 30 min, 35 min. Within this temperature range, the oligo-walled carbon nanotubes can be better grown.

[0076] In some embodiments, the carrier gas of the later reaction is an inert gas; the inert gas can be selected from argon, neon, and nitrogen. The flow rate of the carrier gas in the later reaction is 580L / min-620L / min, such as 580L / min, 590L / min, 600L / min, and 620L / min; the reaction temperature of the later reaction is 600°C-650°C, such as 600°C, 610°C, 620°C, 630°C, 640°C, and 650°C, and the reaction time is 1min-5min, such as 1min, 2min, 3min, and 5min. Within this temperature range, the growth of oligo-walled carbon nanotubes can be promoted better.

[0077] The second aspect of the present invention provides an oligo-walled carbon nanotube, which is obtained by the preparation method described in the first aspect of the present invention.

[0078] The number of walls of the oligo-walled carbon nanotubes is less than 6, such as 5, 4, 3, 2, 1; the powder resistivity of the oligo-walled carbon nanotubes is less than 8 mΩ·cm, such as 7 mΩ·cm, 6 mΩ·cm, 5 mΩ·cm, 4 mΩ·cm, 3 mΩ·cm, 2 mΩ·cm, 1 mΩ·cm; the specific surface area of ​​the oligo-walled carbon nanotubes is greater than 500 m 2 / g, for example 520m 2 / g, 580m 2 / g、600m 2 / g, 680m 2 / g, 730m 2 / g, 760m 2 / g, 850m2 / g、900m 2 / g, 930m 2 / g、1000m 2 / g; in some embodiments, D50 of the oligo-walled carbon nanotubes is ≤10nm, for example, 10nm, 9nm, 8nm, 7nm, 6nm, 5nm, 4nm, 2nm, 1nm, etc.; D90 of the oligo-walled carbon nanotubes is ≤20nm, for example, 20nm, 18nm, 16nm, 14nm, 12nm, 10nm, 8nm, 7nm, 5nm, etc.

[0079] The third aspect of the present application provides an application of the oligo-walled carbon nanotubes obtained by the preparation method of the first aspect of the present application or the oligo-walled carbon nanotubes described in the second aspect of the present application in silicon-carbon negative electrode conductive agents.

[0080] Since the present application adopts the fluidized bed process to scale up the production of oligo-walled carbon nanotubes, its application prospects in silicon-carbon negative electrode conductive agents are increased. Specific embodiments

[0082] Example 1

[0083] Preparation of catalyst solution:

[0084] (1) dissolving ferrocene in a certain amount of benzene solution to form a saturated ferrocene benzene solution, and adding an appropriate amount of polyethylene glycol with a number average molecular weight of 200, wherein the mass of the polyethylene glycol is 10% of the mass of the benzene solution;

[0085] (2) adding expanded vermiculite to the mixed solution obtained in step 1) so that the mass ratio of ferrocene to expanded vermiculite is 1:6, mixing and shaking thoroughly (stirring rate 1500 rpm, 30 min), emulsifying and standing until the ferrocene solution fully penetrates into the expanded vermiculite, to obtain a catalyst solution;

[0086] Fluidized bed preparation: A partition is movably connected to the top of the fluidized bed, and the partition is located below the feeding port of the fluidized bed. Specifically, the partition is located at one-fifth of the height of the fluidized bed, which can separate the fluidized bed into an upper fluidized bed and a lower fluidized bed;

[0087] (3) The partition is opened to separate the fluidized bed into an upper fluidized bed and a lower fluidized bed, and the above catalyst solution, hydrogen and nitrogen (the volume ratio of hydrogen and nitrogen is 3:1) are injected at a rate of 75 L / h, and the total gas flow of hydrogen and nitrogen is 100 L / min. The partition is closed after 5 minutes. During these 5 minutes, the ferrocene in the catalyst solution is thermally decomposed at a temperature of 620°C and the product is evenly distributed in the carrier, so that the catalyst is activated. In this operation, the catalytic active components are not agglomerated together, and the small particle size makes it easy to form oligo-walled carbon nanotubes.

[0088] (4) Close the partition, and continue to input inert gas and carbon source (CO), and control the gas flow rate of the carbon source (CO) in the initial reaction to 25 L / min and 500 L / min of inert gas, the reaction temperature to 640 ° C, the reaction time to 30 s, and then adjust the gas flow rate to 300 L / min of carbon source (CO) and 500 L / min of inert gas (argon) to continue the reaction at a temperature of 700 ° C for 20 min, then immediately interrupt the carbon source, increase the inert gas flow rate to 600 L / min, and terminate the reaction at a temperature of 600 ° C for 2 min.

[0089] The oligo-walled carbon nanotubes prepared in Example 1 have a D50≤10nm, a D90≤20nm, a wall number of <6, a powder resistivity of <8mΩ·cm, and a specific surface area of ​​>500m 2 / g.

[0090] Example 2

[0091] Preparation of catalyst solution:

[0092] (1) dissolving iron pentacarbonyl in glycerol solvent to prepare the iron pentacarbonyl substance concentration to be 0.5 mol / L, adding an appropriate amount of polyethylene glycol with a number average molecular weight of 200, the mass of the polyethylene glycol being 5% of the total mass of the solution;

[0093] (2) Add expanded vermiculite to the mixed solution obtained in step 1) so that the mass ratio of pentacarbonyl iron to expanded vermiculite is 1:6, mix and shake thoroughly (stirring rate 1500 rpm, 30 min), emulsify and let stand until pentacarbonyl iron fully penetrates into the expanded vermiculite, to obtain a catalyst solution.

[0094] Fluidized bed preparation: A partition is movably connected to the top of the fluidized bed, and the partition is located below the feeding port of the fluidized bed. Specifically, the partition is located at one-fifth of the height of the fluidized bed, which can separate the fluidized bed into an upper fluidized bed and a lower fluidized bed;

[0095] (3) The partition is opened to separate the fluidized bed into an upper fluidized bed and a lower fluidized bed, and the above catalyst solution, hydrogen and nitrogen (the volume ratio of hydrogen and nitrogen is 3:1) are injected at a rate of 75 L / h, and the total gas flow of hydrogen and nitrogen is 100 L / min. The partition is closed after 5 minutes. During these 5 minutes, the pentacarbonyl iron in the catalyst solution is thermally decomposed at a temperature of 600°C and the product is evenly distributed in the carrier, so that the catalyst is activated. In this operation, the catalytic active components are not agglomerated together, and the small particle size makes it easy to form oligo-walled carbon nanotubes.

[0096] (4) While closing the partition, continue to input inert gas and carbon source (CO), and control the gas flow rate of the initial reaction to 25 L / min of carbon source (CO) and 500 L / min of inert gas, the reaction temperature to 680°C, and the reaction time to 30S. Then adjust the gas flow rate to 300 L / min of carbon source (CO) and 500 L / min of inert gas (argon) to continue the reaction at a temperature of 650°C for 20 min, then immediately interrupt the carbon source gas, increase the inert gas flow rate to 600 L / min, and terminate the reaction at a temperature of 600°C for 2 min.

[0097] The oligo-walled carbon nanotubes prepared in Example 2 have a D50≤10nm, a D90≤20nm, a wall number of <6, a powder resistivity of <8mΩ·cm, and a specific surface area of ​​>500m 2 / g.

[0098] Example 3

[0099] Preparation of catalyst solution:

[0100] (1) dissolving iron pentacarbonyl in glycerol solvent to prepare the iron pentacarbonyl substance concentration to be 0.5 mol / L, adding an appropriate amount of polyethylene glycol with a number average molecular weight of 200, the mass of the polyethylene glycol being 5% of the total mass of the solution;

[0101] (2) Add expanded vermiculite to the mixed solution obtained in step 1) so that the mass ratio of pentacarbonyl iron to expanded vermiculite is 1:6, mix and shake thoroughly (stirring rate 1500 rpm, 30 min), emulsify and let stand until pentacarbonyl iron fully penetrates into the expanded vermiculite, to obtain a catalyst solution.

[0102] Fluidized bed preparation: A partition is movably connected to the top of the fluidized bed, and the partition is located below the feeding port of the fluidized bed. Specifically, the partition is located at one-fifth of the height of the fluidized bed, which can separate the fluidized bed into an upper fluidized bed and a lower fluidized bed;

[0103] (3) The partition is opened to separate the fluidized bed into an upper fluidized bed and a lower fluidized bed, and the above catalyst solution, hydrogen and nitrogen (the volume ratio of hydrogen and nitrogen is 3:1) are injected at a rate of 75 L / h, and the total gas flow of hydrogen and nitrogen is 100 L / min. The partition is closed after 5 minutes. During these 5 minutes, the pentacarbonyl iron in the catalyst solution is thermally decomposed at a temperature of 650°C and the product is evenly distributed in the carrier, so that the catalyst is activated. In this operation, the catalytic active components are not agglomerated together, and the small particle size makes it easy to form oligo-walled carbon nanotubes.

[0104] (4) Close the partition and continue to inject inert gas and carbon source (CO) into the fluidized bed reactor. Control the initial reaction carbon source (CO) gas flow rate to 25 L / min and 500 L / min of inert gas, reaction temperature to 680 ° C, reaction time to 30 s, then adjust the gas flow rate to 300 L / min of carbon source (CO) and 500 L / min of inert gas (argon) to continue the reaction for 20 min, then immediately interrupt the carbon source gas, increase the inert gas flow rate to 600 L / min, and terminate the reaction at a temperature of 650 ° C for 2 min.

[0105] The oligo-walled carbon nanotubes prepared in Example 3 have a D50≤10nm, a D90≤20nm, a wall number of <6, a powder resistivity of <8mΩ·cm, and a specific surface area of ​​>500m 2 / g.

[0106] Example 4

[0107] Preparation of catalyst solution:

[0108] (1) dissolving ferrocene in a certain amount of benzene solution to form a saturated ferrocene benzene solution, and adding an appropriate amount of polyethylene glycol with a number average molecular weight of 200, wherein the mass of the polyethylene glycol is 10% of the mass of the benzene solution;

[0109] (2) adding expanded vermiculite to the mixed solution obtained in step 1) so that the mass ratio of ferrocene to expanded vermiculite is 1:6, mixing and shaking thoroughly (stirring rate 1500 rpm, 30 min), emulsifying and standing until the ferrocene solution fully penetrates into the expanded vermiculite, to obtain a catalyst solution;

[0110] Fluidized bed preparation: A partition is movably connected to the top of the fluidized bed, and the partition is located below the feeding port of the fluidized bed. Specifically, the partition is located at one-fifth of the height of the fluidized bed, which can separate the fluidized bed into an upper fluidized bed and a lower fluidized bed;

[0111] (3) The partition is opened to separate the fluidized bed into an upper fluidized bed and a lower fluidized bed, and the above catalyst solution, hydrogen and nitrogen (the volume ratio of hydrogen and nitrogen is 3:1) are injected at a rate of 75 L / h, and the total gas flow of hydrogen and nitrogen is 100 L / min. The partition is closed after 5 minutes. During these 5 minutes, the ferrocene in the catalyst solution is thermally decomposed at a temperature of 620°C and the product is evenly distributed in the carrier, so that the catalyst is activated. In this operation, the catalytic active components are not agglomerated together, and the small particle size makes it easy to form oligo-walled carbon nanotubes.

[0112] (4) Close the partition, and continue to input inert gas and carbon source (CO), and control the gas flow rate of the carbon source (CO) in the initial reaction to 50 L / min and 500 L / min of inert gas, the reaction temperature to 640 ° C, the reaction time to 30S, and then adjust the gas flow rate of the carbon source (CO) to 350 L / min and the inert gas (argon) to 500 L / min and continue to react at a temperature of 700 ° C for 20 min, then immediately interrupt the carbon source, increase the inert gas flow rate to 600 L / min, and terminate the reaction at a temperature of 600 ° C for 2 min.

[0113] The oligo-walled carbon nanotubes prepared in Example 1 have a D50≤10nm, a D90≤20nm, a wall number of <6, a powder resistivity of <8mΩ·cm, and a specific surface area of ​​>500m 2 / g.

[0114] Example 5

[0115] Preparation of catalyst solution:

[0116] (1) dissolving ferrocene in a certain amount of benzene solution to form a saturated ferrocene benzene solution, and adding an appropriate amount of polyethylene glycol with a number average molecular weight of 200, wherein the mass of the polyethylene glycol is 10% of the mass of the benzene solution;

[0117] (2) adding expanded vermiculite to the mixed solution obtained in step 1) so that the mass ratio of ferrocene to expanded vermiculite is 1:6, mixing and shaking thoroughly (stirring rate 1500 rpm, 30 min), emulsifying and standing until the ferrocene solution fully penetrates into the expanded vermiculite, to obtain a catalyst solution;

[0118] Fluidized bed preparation: A partition is movably connected to the top of the fluidized bed, and the partition is located below the feeding port of the fluidized bed. Specifically, the partition is located at one-fifth of the height of the fluidized bed, which can separate the fluidized bed into an upper fluidized bed and a lower fluidized bed;

[0119] (3) The partition is opened to separate the fluidized bed into an upper fluidized bed and a lower fluidized bed, and the above catalyst solution, hydrogen and nitrogen (the volume ratio of hydrogen and nitrogen is 3:1) are injected at a rate of 75 L / h, and the total gas flow of hydrogen and nitrogen is 100 L / min. The partition is closed after 5 minutes. During these 5 minutes, the ferrocene in the catalyst solution is thermally decomposed at a temperature of 620°C and the product is evenly distributed in the carrier, so that the catalyst is activated. In this operation, the catalytic active components are not agglomerated together, and the small particle size makes it easy to form oligo-walled carbon nanotubes.

[0120] (4) Close the partition, and continue to input inert gas and carbon source (CO), and control the gas flow rate of the carbon source (CO) in the initial reaction to 100 L / min and 500 L / min of inert gas, the reaction temperature to 640 ° C, the reaction time to 30S, and then adjust the gas flow rate to 400 L / min of carbon source (CO) and 500 L / min of inert gas (argon) to continue the reaction at a temperature of 700 ° C for 20 min, then immediately interrupt the carbon source, increase the inert gas flow rate to 600 L / min, and terminate the reaction at a temperature of 600 ° C for 2 min.

[0121] The oligo-walled carbon nanotubes prepared in Example 1 have a D50≤10nm, a D90≤20nm, a wall number of <6, a powder resistivity of <8mΩ·cm, and a specific surface area of ​​>500m 2 / g.

[0122] Comparative Example 1

[0123] The difference between Comparative Example 1 and Example 1 is that in the fluidized bed preparation process, an iron-based catalyst is used instead of the catalyst solution, and the remaining operating steps are the same as those of Example 1.

[0124] Preparation of the iron-based catalyst in Comparative Example 1: Dissolve iron nitrate, cobalt nitrate and nickel nitrate in water at a molar ratio of Fe, Co and Ni of 1:1:0.6 to form a nitrate solution of nickel, cobalt and iron;

[0125] According to the molar ratio of urea, citric acid and nitrate solution of nickel, cobalt and iron being 1.05:1.05:1, urea, citric acid and nitrate solution of nickel, cobalt and iron are added to water in parallel and mixed evenly, heated to 200°C, stirred and reacted for 2h to prepare a catalyst precursor. The prepared catalyst precursor is placed in a muffle furnace, calcined at 500°C for 2h, and sieved through a 80-100 mesh screen after cooling to obtain an iron-based agent.

[0126] The carbon nanotubes prepared in Comparative Example 1 are mainly multi-walled entangled carbon nanotubes, and the content of oligo-walled carbon nanotubes is less than 10%.

[0127] Comparative Example 2

[0128] Comparative Example 2 uses a floating method to prepare single-walled carbon nanotubes. The specific operation method is as follows:

[0129] 38.69g of pentacarbonyl iron powder was dissolved in 500g of propylene glycol solvent, and the molar concentration of pentacarbonyl iron was configured to be 0.5mol / L. It was stirred at 1500rpm (carbonyl iron is easy to self-ignite in the air) under anaerobic conditions for 30min to emulsify it, and the catalyst precursor solution was obtained; H2: N2: C3H6: carbonyl iron was introduced into the reaction device kept at 850℃ according to the molar ratio of 2.5: 0.75: 1.5: 0.5, that is, the feed rate was: H2 was 1.25L / min, N2 was 0.37L / min, and black powder was collected. Its process can only use fine fixed bed equipment, with low output, which is not conducive to expanding production. For example, the above mass can only produce 20.15g of carbon nanotubes. The output ratio is much lower than the 40-50 times of the fluidized bed, and it is impossible to make a large amount of carbon nanotube powder at one time, only a small batch of carbon nanotubes.

[0130] Comparative Example 3

[0131] Preparation of catalyst solution:

[0132] (1) dissolving iron pentacarbonyl in glycerol solvent to prepare the iron pentacarbonyl substance concentration to be 0.5 mol / L, adding an appropriate amount of polyethylene glycol with a number average molecular weight of 200, the mass of the polyethylene glycol being 5% of the total mass of the solution;

[0133] (2) Add expanded vermiculite to the mixed solution obtained in step 1) so that the mass ratio of pentacarbonyl iron to expanded vermiculite is 1:6, mix and shake thoroughly (stirring rate 1500 rpm, 30 min), emulsify and let stand until pentacarbonyl iron fully penetrates into the expanded vermiculite, to obtain a catalyst solution.

[0134] Fluidized bed preparation: A partition is movably connected to the top of the fluidized bed, and the partition is located below the feeding port of the fluidized bed. Specifically, the partition is located at one-fifth of the height of the fluidized bed, which can separate the fluidized bed into an upper fluidized bed and a lower fluidized bed;

[0135] (4) Open the partition to separate the fluidized bed into an upper fluidized bed and a lower fluidized bed, inject the above catalyst solution, hydrogen and nitrogen (the volume ratio of hydrogen and nitrogen is 3:1) into the fluidized bed reactor at a rate of 75 L / h, and the total gas flow of hydrogen and nitrogen is 100 L / min. Close the partition after 5 minutes. During these 5 minutes, the pentacarbonyl iron in the catalyst solution is thermally decomposed at a temperature of 650°C and the product is evenly distributed in the carrier, so that the catalyst is activated. In this operation, the catalytic active components are not agglomerated together, and the small particle size makes it easy to form oligo-walled carbon nanotubes.

[0136] (4) The partition was closed, and the inert gas and carbon source (CO) were continuously injected into the fluidized bed reactor. The flow rate of the carbon source (CO) gas was controlled to be 300 L / min and 500 L / min of the inert gas. The reaction was continued at a reaction temperature of 680°C for 23 min, and then the reaction was terminated.

[0137] The diameters of the few-walled carbon nanotubes prepared in Comparative Example 3 are D50≤20nm and D90≤50nm. Therefore, there are more multi-walled carbon nanotubes.

[0138] Comparative Example 4

[0139] The difference between Comparative Example 4 and Example 1 is that the flow rate of the carbon source in the initial reaction is equal to the flow rate of the carbon source in the mid-term reaction, and the rest of the operations are the same as in Example 1.

[0140] Specifically:

[0141] Preparation of catalyst solution:

[0142] (1) dissolving ferrocene in a certain amount of benzene solution to form a saturated ferrocene benzene solution, and adding an appropriate amount of polyethylene glycol with a number average molecular weight of 200, wherein the mass of the polyethylene glycol is 10% of the mass of the benzene solution;

[0143] (2) adding expanded vermiculite to the mixed solution obtained in step 1) so that the mass ratio of ferrocene to expanded vermiculite is 1:6, mixing and shaking thoroughly (stirring rate 1500 rpm, 30 min), emulsifying and standing until the ferrocene solution fully penetrates into the expanded vermiculite, to obtain a catalyst solution;

[0144] Fluidized bed preparation: A partition is movably connected to the top of the fluidized bed, and the partition is located below the feeding port of the fluidized bed. Specifically, the partition is located at one-fifth of the height of the fluidized bed, which can separate the fluidized bed into an upper fluidized bed and a lower fluidized bed;

[0145] (3) Open the partition to separate the fluidized bed into an upper fluidized bed and a lower fluidized bed, inject the above catalyst solution, hydrogen and nitrogen (the volume ratio of hydrogen and nitrogen is 3:1) at a rate of 70-80L / h, and the total gas flow of hydrogen and nitrogen is 100L / min. Close the partition after 5 minutes. During these 5 minutes, the ferrocene in the catalyst solution is thermally decomposed at a temperature of 620°C and the product is evenly distributed in the carrier, so that the catalyst is activated. In this operation, the catalytic active components are not agglomerated together, and the small particle size makes it easy to form oligo-walled carbon nanotubes.

[0146] (4) Close the partition, and continue to input inert gas and carbon source (CO), and control the gas flow rate of the carbon source (CO) in the initial reaction to 25 L / min and 500 L / min of inert gas, the reaction temperature to 640 ° C, the reaction time to 30S, and then maintain the gas flow rate of the carbon source (CO) at 20 L / min and the inert gas (argon) at 500 L / min to continue the reaction at a temperature of 700 ° C for 20 min, then immediately interrupt the carbon source, increase the inert gas flow rate to 600 L / min, and terminate the reaction at a temperature of 600 ° C for 2 min.

[0147] Performance study of the oligo-walled carbon nanotubes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 of the present application:

[0148] The measurement results are shown in Table 1:

[0149] Table 1

[0150]

[0151]

[0152] Note: The ratio is the multiple of the weight of the final crude product containing catalyst and carbon nanotubes to the weight of the initial catalyst.

[0153] Powder resistivity refers to the ratio between actual resistance value and theoretical resistance value;

[0154] D50 refers to the particle size corresponding to when the cumulative particle size distribution percentage of the sample reaches 50%.

[0155] D90 refers to the particle size value corresponding to when the cumulative distribution percentage from small to large in the sample particle size distribution reaches 90%.

[0156] Dmax refers to: the maximum particle size in the sample particle size distribution diagram.

[0157] It can be seen from Table 1 that the yield of the oligo-walled carbon nanotubes obtained by the preparation method of the present application is high, and the diameter D50, D90, specific surface area and powder resistivity of the obtained oligo-walled carbon nanotubes are better than those of the oligo-walled carbon nanotubes prepared in Comparative Examples 1 to 3.

[0158] In Comparative Example 1, the preparation of oligo-walled carbon nanotubes uses a traditional iron-based catalyst instead of the catalyst described in the present application, and the content of the obtained oligo-walled carbon nanotubes is less than 10%, and the yield is relatively low.

[0159] In Comparative Example 2, the preparation of oligo-walled carbon nanotubes adopts a fixed bed preparation process, which has a relatively low yield and is not conducive to large-scale production.

[0160] In comparative example 3, the preparation of oligo-walled carbon nanotubes was not carried out in stages. The carbon source content was high in the initial stage of the reaction, and carbon nanotubes with larger diameters were easily grown on the surface of the catalyst metal particles. At the same time, they were easily agglomerated together, increasing the probability of carbon nanotubes agglomerating into multi-walled carbon nanotubes.

[0161] In the preparation of oligo-walled carbon nanotubes in Comparative Example 4, the carbon source flow rate in the initial reaction stage is equal to the carbon source flow rate in the later reaction stage. Due to the low carbon source content, the reaction is slow, resulting in a significant decrease in the final carbon tube rate. In addition, due to insufficient growth, the length of the carbon tube decreases, the specific surface area decreases, and the powder resistivity increases.

[0162] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing oligo-walled carbon nanotubes, characterized in that: The following steps are included: Preparing a catalyst solution: dissolving a liquid iron source and a carrier in an organic solvent to obtain the catalyst solution; the liquid iron source includes carbonyl iron and / or ferrocene; The catalyst solution, carrier gas and carbon source are introduced into the fluidized bed to grow carbon nanotubes to obtain oligo-walled carbon nanotubes.

2. The preparation method according to claim 1, characterized in that The carbon nanotube growth includes a catalyst activation stage, an initial reaction, an intermediate reaction and a late reaction; The catalyst activation stage includes introducing the catalyst solution, reducing gas and carrier gas into the fluidized bed to perform catalyst activation treatment and preliminary growth of carbon nanotubes.

3. The preparation method according to claim 2, characterized in that The temperature of the catalyst activation stage is 600°C-650°C; the duration of the catalyst activation stage is 2min-10min; and / or, the reducing gas comprises hydrogen; and / or, the carrier gas in the catalyst activation stage is selected from inert gases; And / or, an activation zone is provided in the fluidized bed, and the catalyst activation stage is carried out in the activation zone.

4. The preparation method according to claim 2, characterized in that The carbon source volume flow rate of the initial reaction is smaller than the carbon source volume flow rate of the mid-term reaction; and / or, in the initial reaction, the ratio of the flow rate of the carbon source to the flow rate of the carrier gas is 1:(4-20); and / or, in the mid-term reaction, the ratio of the flow rate of the carbon source to the flow rate of the carrier gas is 1:(1.2-2); And / or, only carrier gas is introduced into the latter stage reaction.

5. The preparation method according to any one of claims 1 to 4, characterized in that The carrier is selected from one or more of vermiculite, alumina, and magnesium oxide; And / or, the organic solvent is selected from one or more of benzene, glycerol, isopropyl alcohol, and polyethylene glycol; and / or, the carbonyl iron is pentacarbonyl iron; And / or, the mass ratio of the liquid iron source, the carrier and the organic solvent is 1:(5-10):(20-50); And / or, the carbon source is selected from one or more of CO, ethanol, methanol, methane, acetylene, and propylene.

6. The preparation method according to any one of claims 2 to 4, characterized in that The initial reaction includes introducing the carrier gas and the carbon source into the fluidized bed to grow carbon nanotubes; and / or, the carrier gas for the initial reaction is an inert gas; And / or, the flow rate of the inert gas in the initial reaction is 450 L / min-550 L / min, and the flow rate of the carbon source is 20 L / min-100 L / min; And / or, the reaction temperature of the initial reaction is 640° C.-680° C., and the reaction time is 30s-300s.

7. The preparation method according to any one of claims 2 to 4, characterized in that The mid-term reaction includes introducing the carrier gas and the carbon source into the fluidized bed to grow carbon nanotubes; and / or, the carrier gas for the mid-term reaction is an inert gas; and / or, the flow rate of the inert gas in the mid-term reaction is 450 L / min-550 L / min, and the flow rate of the carbon source is 300 L / min-400 L / min; And / or, the reaction temperature of the mid-term reaction is 650° C.-700° C., and the reaction time is 15 min-35 min; and / or, the carrier gas for the later reaction is an inert gas; And / or, the carrier gas flow rate in the later reaction is 580 L / min-620 L / min; And / or, the reaction temperature of the later reaction is 600° C.-650° C., and the reaction time is 1 min-5 min.

8. An oligo-walled carbon nanotube, characterized in that: The oligo-walled carbon nanotubes are obtained by the preparation method according to any one of claims 1 to 7.

9. The oligo-walled carbon nanotube according to claim 8, characterized in that The number of walls of the oligo-walled carbon nanotubes is less than 6; and / or the powder resistivity of the oligo-walled carbon nanotubes is less than 8 mΩ·cm; And / or, the specific surface area of ​​the oligo-walled carbon nanotubes is greater than 500 m 2 / g; And / or, the diameter D50 of the oligo-walled carbon nanotube is ≤10 nm, and the diameter D90 of the oligo-walled carbon nanotube is ≤20 nm.

10. Use of the oligo-walled carbon nanotubes obtained by the preparation method according to any one of claims 1 to 7 or the oligo-walled carbon nanotubes according to any one of claims 8 to 9 as a conductive agent for silicon-carbon negative electrodes.

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