CN115477300B

CN115477300B - Carbon nanotube, fluidized bed preparation process thereof and conductive agent

Info

Publication number: CN115477300B
Application number: CN202210926489.XA
Authority: CN
Inventors: 祝立峰; 邓本兴; 韩斌斌; 李雪松; 车晓东; 黄辉; 王静
Original assignee: Ciwan Kecheng Guangzhou New Material Co ltd
Current assignee: Ciwan Kecheng Guangzhou New Material Co ltd
Priority date: 2022-08-03
Filing date: 2022-08-03
Publication date: 2024-05-07
Anticipated expiration: 2042-08-03
Also published as: CN115477300A

Abstract

The application belongs to the technical field of materials, and particularly relates to a carbon nano tube, a fluidized bed preparation process thereof and a conductive agent. Wherein, the preparation process of the carbon nano tube fluidized bed comprises the following steps: the alkaline precipitant, oxalic acid and metal salt solution flow into the base solution to carry out coprecipitation reaction, and the catalyst is obtained by separation; the volume ratio of hydrogen to inert atmosphere is 1: reducing the catalyst under the condition of (20-40) to obtain a reduced catalyst; and conveying the reduction catalyst into a fluidized bed reactor, introducing a mixed atmosphere containing carbon source gas, water vapor and carrier gas, introducing pulse gas at intervals, carrying out fluidized growth of the carbon nanotubes, and separating to obtain the carbon nanotubes. According to the application, the carbon nano tube powder with thin wall, high length-diameter ratio, large tube diameter, low specific surface and good dispersion performance is obtained by optimizing the process for preparing the carbon nano tube by the fluidized bed.

Description

Carbon nanotube, fluidized bed preparation process thereof and conductive agent

Technical Field

The application belongs to the technical field of materials, and particularly relates to a carbon nano tube, a fluidized bed preparation process thereof and a conductive agent.

Background

The conductive agent is an important raw material for manufacturing the conductive paste, the carbon nano tube has excellent electrical property, the conductive effect of the conductive paste manufactured by using the conductive agent of the carbon nano tube is obviously better than that of the traditional carbon black, the addition amount of the conductive agent of the anode and the cathode of the battery can be reduced, and the conductive agent has obvious advantages in the aspects of improving the energy density and the cycle service life of the battery, and is suitable for being used as an electrode material of a lithium ion battery.

The existing mass production method for preparing the carbon nano tubes on a large scale is a fluidized bed preparation process. The fluidized bed process produces high yields of carbon nanotubes, but due to the long residence time in the reactor, the resulting carbon nanotubes are mostly multi-walled carbon nanotubes that are randomly clustered together, difficult to disperse in the conductive paste, and have poor conductivity.

In order to improve the conductivity of the carbon nanotubes in the conductive paste and form a good conductive path, thin-walled carbon nanotubes having a high aspect ratio are required, while in order to improve the dispersibility of the carbon nanotubes in the conductive paste, a lower specific surface area is required.

Disclosure of Invention

The application aims to provide a carbon nano tube, a fluidized bed preparation process thereof and a conductive agent, and aims to solve the problem that the carbon nano tube prepared by the existing fluidized bed is poor in dispersibility and conductivity to a certain extent.

In order to achieve the purposes of the application, the technical scheme adopted by the application is as follows:

In a first aspect, the present application provides a process for preparing a fluidized bed of carbon nanotubes, comprising the steps of:

The alkaline precipitant, oxalic acid and metal salt solution flow into the base solution to carry out coprecipitation reaction, and the catalyst is obtained by separation;

The volume ratio of hydrogen to inert atmosphere is 1: reducing the catalyst under the condition of (20-40) to obtain a reduced catalyst;

And conveying the reduction catalyst into a fluidized bed reactor, introducing a mixed atmosphere containing carbon source gas, water vapor and carrier gas, introducing pulse gas at intervals, carrying out fluidized growth of the carbon nanotubes, and separating to obtain the carbon nanotubes.

In a second aspect, the present application provides a carbon nanotube produced by the above method.

In a third aspect, the present application provides a conductive agent comprising the above carbon nanotube.

According to the preparation process of the carbon nano tube fluidized bed, oxalic acid is added during preparation of the catalyst, the oxalic acid is weak in acidity, can be complexed with an alkaline precipitant and metal salt, the coprecipitation reaction process is well controlled, the precipitation of the generated catalyst is quickened, the particle size of the precipitate is reduced, and the catalyst with small particle size is ensured to be prepared. Is beneficial to regulating and controlling the structure and the pipe diameter of the carbon nano-tube which grows subsequently, thereby improving the electrochemical performance of the carbon nano-tube. The volume ratio of hydrogen to inert atmosphere is 1: and (20-40) under the condition of reducing the catalyst to activate the metal in the catalyst and improve the catalytic activity, and under the condition of low hydrogen content, reducing the catalyst to effectively reduce catalyst agglomeration, so that the catalyst activity and the agglomeration are balanced, and the growth efficiency of the thin-walled carbon nanotube is improved. And then, conveying the reduction catalyst into a fluidized bed reactor, and introducing a mixed atmosphere containing carbon source gas, water vapor and carrier gas, wherein the carbon source gas provides a carbon source for the growth of the carbon nanotubes, the water vapor reacts with more active carbon at high temperature, amorphous carbon is removed or the generation efficiency of the multi-wall carbon nanotubes is inhibited, and the generation content of the single-wall or thin-wall carbon nanotubes is improved. In addition, pulse gas is introduced into the carbon nano tube at intervals in the fluidization growth process, so that material agglomeration in the fluidized bed can be effectively avoided, the material is uniformly dispersed in the fluidized bed, the generation of multi-wall carbon nano tubes caused by agglomeration is prevented, and the purity of the thin-wall carbon nano tube is improved. According to the application, the carbon nano tube powder with thin wall, high length-diameter ratio, large tube diameter, low specific surface and good dispersion performance is obtained by optimizing the process for preparing the carbon nano tube by the fluidized bed.

The carbon nano tube provided by the second aspect of the application is thin-walled, high in length-diameter ratio, large in tube diameter, low in specific surface, good in dispersion performance and excellent in conductivity, and is prepared by the method. The application prospect of the carbon nano tube in the conductive agent is improved.

In the technical field, the thin-walled carbon nanotube specifically refers to a carbon nanotube mixture with a wall number of 1-4.

The conductive agent provided by the third aspect of the application comprises the carbon nano tube, and the carbon nano tube has the advantages of thin wall, high length-diameter ratio, large tube diameter, low specific surface, good dispersion performance, low resistivity, excellent conductivity and good mechanical property, and ensures the dispersion stability of the conductive agent and the conductivity of the conductive agent by using the conductive agent as the conductive agent.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments or the description of the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic flow chart of a fluidized bed preparation process for carbon nanotubes according to an embodiment of the present application;

FIG. 2 is a transmission electron microscope image of the carbon nanotubes according to embodiment 1 of the present application;

fig. 3 is a microscopic morphology diagram of the conductive paste made of the carbon nanotubes according to embodiment 1 of the present application.

Detailed Description

In order to make the technical problems, technical schemes and beneficial effects to be solved more clear, the application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application.

In the present application, the term "and/or" describes an association relationship of an association object, which means that three relationships may exist, for example, a and/or B may mean: a alone, a and B together, and B alone. Wherein A, B may be singular or plural. The character "/" generally indicates that the context-dependent object is an "or" relationship.

In the present application, "at least one" means one or more, and "a plurality" means two or more. "at least one of" or the like means any combination of these items, including any combination of single item(s) or plural items(s). For example, "at least one (individual) of a, b, or c," or "at least one (individual) of a, b, and c" may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, c may be single or multiple, respectively.

It should be understood that, in various embodiments of the present application, the sequence number of each process described above does not mean that the execution sequence of some or all of the steps may be executed in parallel or executed sequentially, and the execution sequence of each process should be determined by its functions and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

The terminology used in the embodiments of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

The weights of the relevant components mentioned in the embodiments of the present application may refer not only to the specific contents of the respective components but also to the proportional relationship between the weights of the respective components, and thus, it is within the scope of the disclosure of the embodiments of the present application as long as the contents of the relevant components are scaled up or down according to the embodiments of the present application. Specifically, the mass in the embodiments of the present application may be a mass unit known in the chemical industry such as mu g, mg, g, kg.

The terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated for distinguishing between objects such as substances from each other. For example, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX, without departing from the scope of embodiments of the application. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature.

As shown in fig. 1, a first aspect of the embodiment of the present application provides a process for preparing a fluidized bed of carbon nanotubes, which includes the following steps:

S10, enabling an alkaline precipitant, oxalic acid and a metal salt solution to flow into a base solution, performing coprecipitation reaction, and separating to obtain a catalyst;

S20, the volume ratio of hydrogen to inert atmosphere is 1: reducing the catalyst under the conditions of (20-40) to obtain a reduced catalyst;

S30, conveying the reduction catalyst into a fluidized bed reactor, introducing a mixed atmosphere containing carbon source gas, water vapor and carrier gas, introducing pulse gas at intervals, carrying out fluidized growth of the carbon nanotubes, and separating to obtain the carbon nanotubes.

According to the preparation process of the carbon nanotube fluidized bed, oxalic acid is added during preparation of the catalyst, the oxalic acid is weak in acidity, can be complexed with an alkaline precipitant and metal salt, the coprecipitation reaction process is well controlled, the precipitation of the generated catalyst is quickened, the particle size of the precipitate is reduced, and the catalyst with small particle size is ensured to be prepared. Is beneficial to regulating and controlling the structure and the pipe diameter of the carbon nano-tube which grows subsequently, thereby improving the electrochemical performance of the carbon nano-tube. The volume ratio of hydrogen to inert atmosphere is 1: and (20-40) under the condition of reducing the catalyst to activate the metal in the catalyst and improve the catalytic activity, and under the condition of low hydrogen content, reducing the catalyst to effectively reduce catalyst agglomeration, so that the catalyst activity and the agglomeration are balanced, and the growth efficiency of the thin-walled carbon nanotube is improved. And then, conveying the reduction catalyst into a fluidized bed reactor, and introducing a mixed atmosphere containing carbon source gas, water vapor and carrier gas, wherein the carbon source gas provides a carbon source for the growth of the carbon nanotubes, the water vapor reacts with more active carbon at high temperature, amorphous carbon is removed or the generation efficiency of the multi-wall carbon nanotubes is inhibited, and the generation content of the single-wall or thin-wall carbon nanotubes is improved. In addition, pulse gas is introduced into the carbon nano tube at intervals in the fluidization growth process, so that material agglomeration in the fluidized bed can be effectively avoided, the material is uniformly dispersed in the fluidized bed, the generation of multi-wall carbon nano tubes caused by agglomeration is prevented, and the purity of the thin-wall carbon nano tube is improved. According to the embodiment of the application, the carbon nano tube powder with thin wall, high length-diameter ratio, large tube diameter, low specific surface and good dispersion performance is obtained by optimizing the process for preparing the carbon nano tube by the fluidized bed.

In some embodiments, in step S10, the co-precipitation reaction is performed by flowing the alkaline precipitant, oxalic acid and metal salt solution into the base solution. In some specific embodiments, after preparing the metal salt into the metal salt solution, under the stirring state, the alkaline precipitant, oxalic acid and the metal salt solution flow into the base solution to perform coprecipitation reaction, filter and separate the generated catalyst precipitate, and then the catalyst precipitate is put into an oven to be dried overnight, wherein the drying temperature is preferably 150-200 ℃, and the dried catalyst is further ground, so that the catalyst particle size is refined and homogenized, and the catalyst fine powder is obtained.

In some embodiments, the molar ratio of alkaline precipitant, oxalic acid and metal salt is (1.05 to 1.2): (1.05-1.2): 1. the oxalic acid added in the embodiment of the application can be complexed with the alkaline precipitant and the metal salt, so that the reaction process is well controlled, and the particle size of precipitated particles separated out in the coprecipitation process is reduced. The molar dosage of the alkaline precipitant and oxalic acid is slightly higher than that of the metal salt, which is favorable for regulating and controlling the particle size of the catalyst, so that the prepared catalyst has small particle size and high uniformity, and is favorable for regulating and controlling the pipe diameter and structure of the grown carbon nano-tube subsequently.

In some embodiments, the conditions of the coprecipitation reaction include: reacting for 2-3 hours at 60-70 ℃ to enable the metal salt in the reaction system to fully react with the alkaline precipitant and oxalic acid to form metal catalyst sediment.

In some embodiments, the alkaline precipitant comprises at least one of ammonium carbonate, ammonium bicarbonate, urea, aqueous ammonia; these basic precipitants are each capable of combining with metal ions in the metal salt solution to produce a metal catalyst precipitate.

In some embodiments, the metal salt includes iron, cobalt, nickel, and magnesium salts; wherein, ferric salt and cobalt salt provide main catalyst active ingredient for the catalyst, nickel salt provides secondary catalyst active ingredient for the catalyst, can assist iron cobalt metal catalyst, provide catalytic activity, magnesium salt is used as the carrier of the catalyst, provides the adhesion carrier for the growth of the catalyst. Specifically, metallic elements in iron salt, cobalt salt and nickel salt in the metal salt form alloy catalyst active particles of Fe-Co-Ni, and the alloy catalyst active particles are attached to the surfaces of magnesium metal salt particles.

In some embodiments, the molar ratio of iron salt, cobalt salt, nickel salt, and magnesium salt is 1: (0.8-1.2): (0.5-0.7): (3-4). Wherein the magnesium salt mainly provides a carrier for the catalyst, so that the molar content of the magnesium salt is relatively high, the ferric salt and the cobalt salt provide main catalytic active components for the catalyst, and the nickel salt provides auxiliary active components for the catalyst, so that the molar ratio of main catalytic active metals is higher than that of auxiliary catalytic active metals. The catalyst prepared from the iron salt, the cobalt salt, the nickel salt and the magnesium salt in the proportion has better catalytic activity, small particle size and high uniformity.

In some embodiments, the form of the metal salt includes at least one of a nitrate, chloride, sulfate. In some embodiments, the iron salt comprises at least one of ferric nitrate, ferric chloride, ferric sulfate; the cobalt salt comprises at least one of cobalt nitrate, cobalt chloride and cobalt sulfate; the magnesium salt comprises at least one of magnesium nitrate, magnesium chloride and magnesium sulfate.

In some embodiments, the catalyst has a particle size of 10 to 15nm; the catalyst prepared by the embodiment of the application has small particle size and high uniformity, and the particle size of the catalyst not only controls the carbon free radical directly required by the growth of the carbon nano tube, but also controls the structure of the carbon nano tube by directly serving as a template. The most visual embodiment of the catalyst particle size to determine the carbon nanotube structure is to influence the diameter of the obtained carbon nanotubes. The catalyst with the grain diameter of 10-15 nm ensures that the grown carbon nano tube has a relatively uniform tube diameter, and improves the purity of the carbon nano tube.

In some embodiments, the base fluid is selected from water. Specifically, the alkaline precipitant, oxalic acid and metal salt solution are flowed into base solution water to carry out coprecipitation reaction, filtered and separated, and then the mixture is put into an oven for overnight drying, so as to obtain the catalyst.

In some embodiments, in the step S20, the step of performing the reduction treatment on the catalyst includes: at the temperature of 300-400 ℃, the volume ratio of hydrogen to inert atmosphere is 1: and (20-40) reducing for 60-100 min. The catalyst is pre-reduced and activated in a high-temperature hydrogen atmosphere. The metal oxide in the catalyst is reduced to active metal by utilizing the strong reducibility of hydrogen, but the transition metal element is easy to generate sintering agglomeration phenomenon by hydrogen reduction, so that the activity of the catalyst is reduced, the yield is reduced, and the pipe diameter consistency of the produced carbon nano-tube is also deteriorated. Therefore, the balance of catalyst activation and agglomeration is regulated and controlled by controlling the hydrogen ratio in the reaction atmosphere, so that the thin-walled carbon nanotubes with different wall numbers can be prepared. In some embodiments, the inert atmosphere comprises nitrogen, argon, helium, and the like.

In some embodiments, in the step S30, the reduction catalyst is transported to the fluidized bed reactor by using inert atmospheres such as nitrogen, helium, argon, etc., a mixed atmosphere containing carbon source gas, water vapor and carrier gas is introduced, and pulse gas is introduced at intervals to perform fluidized growth of the carbon nanotubes, and the carbon nanotubes are separated to obtain the carbon nanotubes.

In some embodiments, the volume ratio of carbon source gas, water vapor, and carrier gas in the mixed atmosphere is (1 to 1.4): (0.01-0.03): 1. In this case, when the carbon-containing raw material gas is decomposed into carbon products by catalysis, the trace amount of water can prevent amorphous carbon or multi-walled carbon nanotubes from being generated, and the purity of the thin-walled carbon nanotubes can be improved. In particular, water vapor will react with the more reactive C and can be used to remove impurities and amorphous carbon. Therefore, the outer carbon tube part of the multi-wall carbon nano tube can be removed by reaction with water vapor, and compared with the single-wall carbon nano tube, the multi-wall carbon nano tube is easier to react with the water vapor, so that the content of the single-wall carbon nano tube is improved to a certain extent. However, the addition amount is very small, which would otherwise affect the cracking growth of carbon sources into carbon nanotubes.

In some embodiments, the carbon source gas comprises at least one of propylene, ethylene, hexane, acetylene, methane, butane, carbon monoxide, benzene, ethanol. At least one carbon source gas of acetylene, ethylene, hexane, methane, propylene, butane, carbon monoxide, benzene and ethanol adopted by the embodiment of the application can be rapidly and stably cracked into carbon atoms at the temperature of 600-700 ℃, thereby providing a material foundation for rapid, efficient and stable growth of the subsequent carbon nanotubes. The carbon source gas is preferably propylene, and the reaction is easy to control.

In some embodiments, the carrier gas comprises at least one of nitrogen, argon, helium; these carrier gases have good stability.

In some embodiments, the flow rate of the mixed atmosphere is between 1000 and 1400L/min, which is advantageous for uniform and stable growth of carbon nanotubes in the fluidized reactor.

In some embodiments, the fluidized growth is carried out at a temperature of 600to 700 ℃ for a time of 40 to 60 minutes, which is advantageous in promoting the cracking of the carbon source and in catalyzing the growth of the carbon nanotubes.

In some embodiments, the pulsed gas comprises at least one of nitrogen, argon, helium.

In some embodiments, the flow rate of the pulsed gas is 50 to 100L/min. In some embodiments, the pulse gas is introduced for a period of 2 to 5 minutes. The pulse gas is introduced at intervals in the fluidized growth process of the carbon nano tube, and the pulse gas is mainly used for scattering and agglomerating at the dense positions of materials, so that the materials are scattered, and the generation of the multi-wall carbon nano tube caused by agglomeration is prevented. The separation time and the flow velocity do not prevent the fluidization growth of the carbon nano tube in the fluidized bed reactor, can effectively prevent the agglomeration phenomenon of the carbon nano tube and improve the purity of the thin-walled carbon nano tube. In some embodiments, the pulsed gas is introduced at the fluidized material collection site of the fluidized bed reactor, e.g., a gas distributor disposed at the material collection site inside the fluidized bed reactor is involved in the fluidized growth process of the carbon nanotubes.

In some embodiments, after the fluidized growth is finished, stopping introducing the carbon source gas and the water vapor, controlling the flow rate of the inert atmosphere in the fluidized bed reactor to be 0.5-1.0 m/s, separating the generated carbon nanotubes from the carrier, and cooling to obtain the carbon nanotubes.

In some embodiments, the carbon nanotube fluidized bed preparation process comprises the steps of:

S11, the molar ratio is (1.05-1.2): (1.05-1.2): 1, oxalic acid and metal salt solution are flowed into base solution water, coprecipitation reaction is carried out for 2 to 3 hours under the temperature of 60 to 70 ℃, and the catalyst is obtained by separation; wherein, the metal salt comprises the following components in mole ratio of 1: (0.8-1.2): (0.5-0.7): iron, cobalt, nickel and magnesium salts of (3-4); the alkaline precipitant comprises at least one of ammonium carbonate, ammonium bicarbonate, urea and ammonia water; the particle size of the catalyst is 10-15 nm;

s21, at the temperature of 300-400 ℃, the volume ratio of hydrogen to inert atmosphere is 1: under the condition of (20-40), reducing the catalyst for 60-100 min to obtain a reduced catalyst;

S31, conveying the reduction catalyst into a fluidized bed reactor, and introducing the reduction catalyst into the fluidized bed reactor at a flow rate of 1000-1400L/min with a volume ratio of (1-1.4): (0.01-0.03), wherein the mixed atmosphere of carbon source gas, water vapor and carrier gas is formed by introducing at least one pulse gas of nitrogen, argon and helium at the flow rate of 50-100L/min for 2-5 min at intervals, and carrying out fluidization growth of carbon nano tubes, and separating to obtain the carbon nano tubes; wherein the carbon source gas comprises at least one of propylene, ethylene, hexane, acetylene, methane, butane, carbon monoxide, benzene and ethanol; the carrier gas includes at least one of nitrogen, argon, helium.

In a second aspect, the present application provides a carbon nanotube, which is manufactured by the above method.

The carbon nanotube provided by the second aspect of the embodiment of the application is thin-walled, high in length-diameter ratio, large in pipe diameter, low in specific surface, good in dispersion performance and excellent in conductivity, and is prepared by the method. The application prospect of the carbon nano tube in the conductive agent is improved.

In some embodiments, the carbon nanotubes comprise a mixture of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes, wherein the mass percent of the single-walled carbon nanotubes is 10 to 20wt%. The single-wall carbon nano tube has more excellent conductive performance and mechanical performance, and the carbon nano tube in the embodiment of the application comprises 10-20wt% of the single-wall carbon nano tube, so that the conductive performance and mechanical performance of the whole carbon nano tube can be effectively improved.

In some embodiments, the average length of the carbon nanotubes is not less than 150 μm, the average tube diameter is 5-10 nm, the average specific surface area is 200-260 m ²/g, and the powder resistivity is 10-15 mΩ cm. The carbon nano tube provided by the embodiment of the application has the advantages of long average length, larger tube diameter, lower specific area, improved dispersion performance, lower resistivity and good conductivity.

In a third aspect, an embodiment of the present application provides a conductive agent, where the conductive agent includes the carbon nanotube.

The conductive agent provided by the third aspect of the embodiment of the application comprises the carbon nano tube, and the carbon nano tube has the advantages of thin wall, high length-diameter ratio, large tube diameter, low specific surface, good dispersion performance, low resistivity, excellent conductivity and good mechanical property, and can be used as the conductive agent, so that the dispersion stability of the conductive agent is ensured, and the conductivity of the conductive agent is ensured.

In order that the above implementation details and operation of the present application may be clearly understood by those skilled in the art, and that the carbon nanotubes and the fluidized bed preparation process thereof and the advanced performance of the conductive agent according to the embodiments of the present application are remarkably embodied, the above technical solutions are exemplified by the following examples.

Example 1

The fluidized bed preparation process of the carbon nano tube comprises the following steps:

1. Preparation of the catalyst

Preparing a metal salt solution from hydrated ferric nitrate, hydrated cobalt nitrate, hydrated nickel nitrate and hydrated magnesium nitrate in a molar ratio of Fe: co: ni: mg=1: 1:0.6:3.5. in the stirred state, the molar ratio was 1.05:1.05:1, ammonia water, oxalic acid and metal salt solution are added into base liquid water in parallel flow, and react for 2 hours under the condition of 60 ℃; filtering, drying overnight in a drying oven at 150 ℃, and further grinding into fine powder to obtain the catalyst with the particle size of 10-15 nanometers.

2. Catalyst reduction

The volume ratio of the mixture to the flow rate of 20L/min is 1:30, and reducing the catalyst for 60min at the temperature of 400 ℃ to obtain the reduction catalyst.

3. Preparation of carbon nanotubes

The reduction catalyst was continuously fed into the fluidized-bed reactor with nitrogen at a gas velocity ratio of 1.2: nitrogen, water vapor and propylene were introduced at a ratio of 0.02:1, with a total flow rate of 1200L/min. Reacting at 660 ℃ for 40min; in the reaction process, nitrogen pulse gas is introduced at intervals of 100L/min at intervals of 5 min; after the reaction is finished, the gas is changed into pure nitrogen, the gas speed in the fluidized bed is controlled to be 0.5-1.0m/s, so that the generated carbon nano tube is separated from the inert carrier particles, and the carbon nano tube is obtained after natural cooling.

Example 2

1. Preparation of the catalyst

Preparing a metal salt solution from hydrated ferric sulfate, hydrated cobalt sulfate, hydrated nickel sulfate and hydrated magnesium sulfate in a molar ratio of Fe: co: ni: mg=1: 1:0.5:3.0. in the stirred state, the molar ratio was 1.1:1.2:1, ammonia water, oxalic acid and metal salt solution are added into base liquid water in parallel flow, and react for 3 hours at the temperature of 70 ℃; filtering, drying overnight in a drying oven at 200 ℃, and further grinding into fine powder to obtain the catalyst with the particle size of 10-15 nanometers.

2. Catalyst reduction

The volume ratio of the mixture to the flow rate of 20L/min is 1:35, and reducing the catalyst for 60min at the temperature of 350 ℃ to obtain the reduction catalyst.

3. Preparation of carbon nanotubes

The reduction catalyst was continuously fed into the fluidized-bed reactor with nitrogen at a gas velocity ratio of 1.1: nitrogen, water vapor and propylene were introduced at a ratio of 0.02:1, with a total flow rate of 1200L/min. Reacting at 680 ℃ for 40min; in the reaction process, nitrogen pulse gas is introduced at intervals of 100L/min at intervals of 4 min; after the reaction is finished, the gas is changed into pure nitrogen, the gas speed in the fluidized bed is controlled to be 0.5-1.0m/s, so that the generated carbon nano tube is separated from the inert carrier particles, and the carbon nano tube is obtained after natural cooling.

Example 3

1. Preparation of the catalyst

Preparing ferric chloride hydrate, cobalt chloride hydrate, nickel chloride hydrate and magnesium chloride hydrate into a metal salt solution, wherein the molar ratio of the ferric chloride hydrate, the cobalt chloride hydrate, the nickel chloride hydrate and the magnesium chloride hydrate is Fe: co: ni: mg=1: 1:0.4:3.2. in the stirred state, the molar ratio was 1.1:1.1:1, ammonia water, oxalic acid and metal salt solution are added into base liquid water in parallel flow, and react for 3 hours under the condition of 65 ℃; filtering, drying overnight in a drying oven at 180 ℃, and further grinding into fine powder to obtain the catalyst with the particle size of 10-15 nanometers.

2. Catalyst reduction

The volume ratio of the mixture to the flow rate of 20L/min is 1:40, and reducing the catalyst for 90min at the temperature of 350 ℃ to obtain the reduction catalyst.

3. Preparation of carbon nanotubes

Comparative example 1

1. Preparation of the catalyst

Preparing a metal salt solution from hydrated ferric nitrate, hydrated cobalt nitrate, hydrated nickel nitrate and hydrated magnesium nitrate in a molar ratio of Fe: co: ni: mg=1: 1:0.4:3.2. in the stirred state, the molar ratio was 1.1:1.1:1, ammonia water, oxalic acid and metal salt solution are added into base liquid water in parallel flow, and react for 3 hours under the condition of 65 ℃; filtering, drying overnight in a drying oven at 180 ℃, and further grinding into fine powder to obtain the catalyst with the particle size of 10-15 nanometers.

2. Catalyst reduction

The volume ratio of the mixture to the flow rate of 80L/min is 1:1 and reducing the catalyst for 30min at the temperature of 350 ℃ to obtain the reduction catalyst.

3. Preparation of carbon nanotubes

Comparative example 2

1. Preparation of the catalyst

2. Catalyst reduction

3. Preparation of carbon nanotubes

The reduction catalyst was continuously fed into the fluidized-bed reactor with nitrogen at a gas velocity ratio of 1.2:1 is introduced with nitrogen and propylene, and the total flow rate is 1200L/min. Reacting at 660 ℃ for 40min; in the reaction process, nitrogen pulse gas is introduced at intervals of 100L/min at intervals of 5min; after the reaction is finished, the gas is changed into pure nitrogen, the gas speed in the fluidized bed is controlled to be 0.5-1.0m/s, so that the generated carbon nano tube is separated from the inert carrier particles, and the carbon nano tube is obtained after natural cooling.

Comparative example 3

1. Preparation of the catalyst

2. Catalyst reduction

3. Preparation of carbon nanotubes

The reduction catalyst was continuously fed into the fluidized-bed reactor with nitrogen at a gas velocity ratio of 1.2: nitrogen, water vapor and propylene were introduced at a ratio of 0.02:1, with a total flow rate of 1200L/min. Reacting at 660 ℃ for 40min; after the reaction is finished, the gas is changed into pure nitrogen, the gas speed in the fluidized bed is controlled to be 0.5-1.0m/s, so that the generated carbon nano tube is separated from the inert carrier particles, and the carbon nano tube is obtained after natural cooling.

Further, to verify the advancement of the embodiments of the present application, the following performance tests were performed:

1. The carbon nanotube powder prepared in examples 1-3 was subjected to structural characterization, and the length and the tube diameter thereof were characterized by electron microscopy and scanning electron microscopy, wherein a transmission electron microscopy image of the carbon nanotube prepared in example 1 is shown in fig. 2.

2. The specific surface area (m ²/g) of the carbon nanotubes was characterized by physical adsorption-desorption of N ₂ using a specific surface and pore size analyzer (model 3H-2000PS4, bei Shide instruments and technologies (beijing).

3. And testing the powder resistivity of the carbon nano tube by using a semiconductor powder resistivity tester.

4. Preparing the carbon nanotubes prepared in examples 1 to 3 and comparative examples 1 to 3 into conductive paste according to a conventional method in the art, wherein the addition amount of CNT is 0.6%; the control group adopts commercially available kaempferia technology LB1G3-54NMP series conductive paste, wherein the graphene content is 5.00+/-0.15%. The conductivity of the conductive paste is tested, and the testing method comprises the following steps: and adjusting the gap of the scraper to 400 micrometers, coating the prepared carbon nanotube conductive paste on a carbon fiber paper substrate, drying at 80 ℃, and testing the sheet resistance under the pressure of 2 MPa. The control group was tested in the same manner. Wherein, the micro morphology pattern of the conductive paste prepared by the carbon nano tube of example 1 coated on the substrate after drying is shown in fig. 3.

The test results are shown in table 1 below:

TABLE 1

From the above test results, the carbon nanotubes prepared by the fluidized bed process of the embodiment of the application have better length, tube diameter and specific surface area, and lower resistivity. And the carbon nano tube is prepared into conductive paste, and the conductive paste is coated on a substrate and dried, so that the formed film layer has lower resistivity and better conductive performance. However, the physical and chemical properties of the carbon nanotubes prepared in comparative example 1 were lower than those of examples 1 to 3 of the present application, because the hydrogen content during the catalyst reduction operation was too high, water vapor was not added during the preparation of carbon nanotubes in comparative example 2, and pulse gas was not added at intervals during the preparation of carbon nanotube catalysts in comparative example 3.

The foregoing description of the preferred embodiments of the application is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the application.

Claims

1. The preparation process of the carbon nano tube fluidized bed is characterized by comprising the following steps of:

The molar ratio is (1.05-1.2): (1.05-1.2): 1, the alkaline precipitant, oxalic acid and metal salt solution flow into a base solution to carry out coprecipitation reaction, so that the oxalic acid, the alkaline precipitant and the metal salt are subjected to complexation precipitation, and the catalyst is obtained through separation; the particle size of the catalyst is 10-15 nm; the alkaline precipitant comprises at least one of ammonium carbonate, ammonium bicarbonate, urea and ammonia water; the metal salt comprises ferric salt, cobalt salt, nickel salt and magnesium salt;

at the temperature of 300-400 ℃, the volume ratio of hydrogen to inert atmosphere is 1: reducing the catalyst under the condition of (20-40) to obtain a reduced catalyst;

2. The fluidized bed preparation process of carbon nanotubes according to claim 1, wherein the form of the metal salt comprises at least one of nitrate, chloride and sulfate;

and/or the base fluid is selected from water.

3. The fluidized bed preparation process of carbon nanotubes according to claim 2, wherein the molar ratio of the iron salt, the cobalt salt, the nickel salt and the magnesium salt is 1: (0.8-1.2): (0.5 to 0.7): (3-4).

4. A process for preparing a fluidized bed of carbon nanotubes according to any one of claims 1 to 3, wherein the step of reducing the catalyst comprises: at the temperature of 300-400 ℃, the volume ratio of hydrogen to inert atmosphere is 1: reducing for 60-100 min under the condition of (20-40);

And/or, the conditions of the coprecipitation reaction include: and reacting for 2-3 hours at the temperature of 60-70 ℃.

5. The process for preparing a fluidized bed of carbon nanotubes according to claim 4, wherein the volume ratio of the carbon source gas, the water vapor and the carrier gas in the mixed atmosphere is (1 to 1.4): (0.01-0.03): 1;

and/or the carbon source gas comprises at least one of propylene, ethylene, hexane, acetylene, methane, butane, carbon monoxide, benzene, ethanol;

And/or the carrier gas comprises at least one of nitrogen, argon and helium;

and/or the flow rate of the mixed atmosphere is 1000-1400L/min.

6. The process for preparing a fluidized bed of carbon nanotubes of claim 5, wherein the pulsed gas comprises at least one of nitrogen, argon, helium;

and/or the flow rate of the pulse gas is 50-100L/min;

And/or the interval introducing time of the pulse gas is 2-5 min;

And/or the pulse gas is introduced at the fluidized material gathering position of the fluidized bed reactor.

7. The process for preparing a fluidized bed of carbon nanotubes according to claim 1 or 6, wherein after the fluidized growth is completed, stopping introducing the carbon source gas and the water vapor, and controlling the flow rate of the inert atmosphere in the fluidized bed reactor to be 0.5-1.0 m/s, so that the generated carbon nanotubes are separated from the carrier to obtain the carbon nanotubes;

and/or the temperature condition of the fluidization growth is 600-700 ℃ and the time is 40-60 min.

8. A carbon nanotube, wherein the carbon nanotube is produced by the fluidized bed preparation process of any one of claims 1 to 7.

9. The carbon nanotube of claim 8, wherein the carbon nanotube comprises 10-20wt% single-walled carbon nanotubes;

And/or the average length of the carbon nano tube is not less than 150 mu m, the average tube diameter is 5-10 nm, the average specific surface area is 200-260 m ²/g, and the powder resistivity is 10-15 mΩ & cm.

10. A conductive agent, wherein the conductive agent comprises the carbon nanotube according to any one of claims 8 to 9.