CN114538418B - Fluidization production process of carbon nano tube - Google Patents
Fluidization production process of carbon nano tube Download PDFInfo
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- CN114538418B CN114538418B CN202111668348.4A CN202111668348A CN114538418B CN 114538418 B CN114538418 B CN 114538418B CN 202111668348 A CN202111668348 A CN 202111668348A CN 114538418 B CN114538418 B CN 114538418B
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Abstract
The invention relates to the technical field of carbon nano material preparation, and particularly discloses a fluidization production process of carbon nano tubes. The carbon nano tube fluidization production process comprises the following steps: introducing a mixed gas containing carbon source gas and shielding gas into a fluidized bed reactor filled with a catalyst, and reacting to generate carbon nanotubes; during the reaction, pulsed gas and/or sound waves are introduced at intervals. The invention breaks up secondary aggregates among the carbon nano tube aggregates of the oligowall array by using pulse gas and/or sound waves at intervals of 2-5 min, and keeps the oligowall tube in a good fluidization growth state in the middle and later stages of growth by using the characteristic of fluidization hysteresis, thereby realizing continuous and stable fluidization growth of the oligowall array carbon nano tube.
Description
Technical Field
The invention relates to the technical field of carbon nano material preparation, in particular to a carbon nano tube fluidization production process.
Background
Along with the development of the lithium ion battery to the high nickel, silicon carbon and high multiplying power, a conductive agent with better conductivity is required to be adopted, so that the lower additive amount and lower internal resistance in the lithium battery are realized. Since the number of the walls of the oligowall array carbon nanotube is only 3 to 6, the oligowall array carbon nanotube has better conductivity than the multiwall carbon nanotube (the number of the walls is more than 10) which is currently applied in large-scale commercialization. But due to the low bulk density of the oligowall array carbon nanotubes (about 0.01g/cm 3 ) Making it difficult to perform continuous batch growth through a fluidized bed.
The current fluidized bed process for growing the carbon nano tube requires that the powder has better flow characteristics, the powder is in a fluidized state in the growth process by controlling the flow of the gas, and the gas is ensured to be fully contacted with a catalytic center in the powder, so that the good growth of the carbon nano tube is realized. However, the density of the carbon nano tube powder of the oligowall array is low (less than or equal to 0.02 g/cm) in the middle and later stages of growth 3 ) And the aggregation interaction formed by the oligowall array is large, so that the aggregation is volatile in the middle and late stages of growthAnd (3) fluidization. After the carbon nano tube is fluidized, on one hand, if raw materials are continuously introduced for growth, the impurity carbon of the obtained product is increased, and the product performance is reduced; on the other hand, the carbon nano tube clusters which are lost to fluidization are easier to adhere to the surface of the reactor, the adhesion force between the carbon nano tube clusters and the reactor is increased by the carbon impurities generated by side reaction, finally, coking carbon is formed on the wall of the reactor, the coked reactor continuously adsorbs new carbon nano tubes for coking, the continuous vicious circle not only leads to the performance reduction of products, but also leads to the continuous reduction of the production capacity of the reactor, the coking layer is required to be cooled and cleaned, and the equipment utilization rate is reduced. Although increasing the gas velocity can reduce the probability of the agglomeration and fluidization of the carbon nanotubes, the gas velocity is too high, and the contact time of the raw materials and the catalyst is shortened, so that the residence time of the carbon source gas in the reaction is necessarily reduced, the conversion rate of the carbon source is reduced, and the production cost is increased.
Disclosure of Invention
In order to solve the problems of low product quality, small batch number of continuously prepared and low production efficiency caused by the volatile fluidization of the carbon nanotubes of the oligowall array in the middle and later stages of growth, the invention adopts pulse gas and/or sound waves to break up secondary agglomerates formed by the carbon nanotube agglomeration in the middle and later stages of reaction, realizes the continuous batch growth of the carbon nanotubes of the oligowall array under lower operation gas velocity, and ensures that the fluctuation range of the powder performance between each batch is within +/-7 percent.
Specifically, the invention relates to the following technical scheme:
a fluidized production process of carbon nanotubes, comprising the following steps: introducing a mixed gas containing carbon source gas and shielding gas into a fluidized bed reactor filled with a catalyst, and reacting to generate carbon nanotubes; during the reaction, pulse gas and/or sound waves are/is intermittently introduced; the interval time of the pulse gas and/or the sound wave is 2-5 min.
The invention can break up secondary agglomerates formed by carbon nano tube agglomeration by introducing pulse gas and/or sound wave into the reaction system at intervals, so that the carbon nano tube and the catalyst are kept in a fluidized state, and the fluidized state is avoided, thereby realizing continuous fluidized production of the carbon nano tube.
According to the invention, pulse gas and/or sound waves are introduced to break up secondary agglomerates of carbon nano tube agglomerates, the interval time is controlled to be 2-5 min, if the interval is less than 2min, the residence time of carbon source gas in a main reaction section of the fluidized bed reactor is too short, the conversion rate is reduced, and the yield of single batch of products is also reduced; if the interval time is more than 5min, secondary agglomerates with strong interaction among carbon nano tube agglomerates are difficult to break up by pulse gas and/or sound waves, and defluidization still occurs. The secondary aggregation formed by the interaction between the carbon nano tube aggregates can be scattered through gas pulse or sonic wave in proper interval time, because the interaction force between the carbon nano tube aggregates is smaller in proper time interval, the flow characteristic of powder can be enhanced by increasing air flow or applying sonic wave, the formed secondary aggregation can be spontaneously disintegrated, and the better flow characteristic can be maintained in a short time due to the 'fluidization hysteresis' phenomenon of the carbon nano tube, so that the possibility of secondary aggregation of the carbon nano tube aggregates is obviously reduced, and the carbon nano tube can keep in a good fluidization growth state.
In some examples of the invention, the pulsed gas and/or sonic waves are introduced at intervals 20 minutes after the reaction occurs. After the cracking reaction occurs for 20min, the carbon nano tube is in the middle and later stages of growth, the phenomenon of carbon nano tube aggregation easily occurs in the middle and later stages, and at the moment, pulse gas and/or sound waves are introduced to break up secondary aggregates formed by the carbon nano tube aggregation.
In some examples of the invention, each pulse of gas and/or sound is provided for a duration of 5s to 20s.
In some examples of the invention, the gas velocity of the mixture is between 0.03m/s and 0.15 m/s. By adopting the production process provided by the invention, continuous batch growth of the carbon nano tube can be realized under a lower operation gas speed.
In some examples of the present invention, the pulse gas is introduced by: and increasing the flow of the shielding gas on the basis of the mixed gas. After the pulse gas is introduced, the gas speed of the mixed gas is more than or equal to 0.2m/s, preferably 0.2m/s to 0.30m/s.
In some examples of the invention, the acoustic waves include ultrasonic waves.
In some examples of the invention, when sound waves are intermittently introduced, the sound wave intensity is more than or equal to 100dB, preferably 100-500 dB.
In some examples of the invention, the mixture further comprises hydrogen. In the mixed gas, the volume ratio of the carbon source gas to the shielding gas to the hydrogen is 1:0.5 to 2:0.00001 to 0.00005.
In some examples of the invention, the various gas flows in the mixture are: the carbon source gas is 500-800L/min, the shielding gas is 500-800L/min, and the hydrogen is 5-50 mL/min. Preferably, the carbon source gas is 600L/min-700L/min, the shielding gas is 600L/min-700L/min, and the hydrogen gas is 10 mL/min-20 mL/min.
In some examples of the present invention, when the pulse gas is introduced, a shielding gas with a flow rate of 2000L/min to 6000L/min, preferably 2500L/min to 5000L/min, may be additionally introduced on the basis of the mixed gas.
In some examples of the present invention, the present invention is not particularly limited to the parameters of the reaction temperature, catalyst type, catalyst loading, etc., and these parameters may be determined according to the production methods commonly used in the art and reasonably adjusted according to actual needs. As an example, the temperature of the reaction is 600 ℃ to 800 ℃; the catalyst takes at least one of Fe, co, ni, mo, mn as an active ingredient and takes an oxide of at least one element of Al, mg, si, la as a carrier; the ratio of the loading capacity of the catalyst to the flow rate of the carbon source gas is 1kg: 500L/min-800L/min.
In some examples of the invention, the shielding gas is introduced into the fluidized bed reactor prior to introducing the mixture of the carbon source gas and the shielding gas into the fluidized bed reactor containing the catalyst, so that the oxygen content in the fluidized bed reactor is reduced to less than 0.5%, and then the catalyst is added.
In some examples of the invention, the reaction is carried out continuously in batches, each batch having a reaction time of from 30 minutes to 100 minutes, preferably from 50 minutes to 60 minutes. After each batch of reaction reaches the required time, stopping introducing carbon source gas, and blowing the materials in the fluidized bed reactor into a feed bin to cool the materials under the protection atmosphere.
In some examples of the invention, the batch is greater than or equal to 100, preferably greater than or equal to 150.
In some examples of the invention, the specific surface area of the carbon nanotubes produced in each batch is equal to or greater than 520m 2 /g, preferably 550m 2 /g～600m 2 /g。
In some examples of the invention, the yield of carbon nanotubes produced per batch does not exceed 10% of the average.
In some examples of the invention, the yield of carbon nanotubes produced per batch is greater than or equal to 20kg/kg catalyst, preferably greater than or equal to 22kg/kg catalyst.
In some examples of the present invention, the utilization rate of the carbon source in the carbon nanotube fluidization production process of the present invention is not less than 60%.
In some examples of the invention, the carbon nanotubes are oligowall array carbon nanotubes. The carbon nano tube of the oligowall array is a carbon nano tube with the wall number of 3-6.
Compared with the prior art, the invention has the following beneficial effects:
because the carbon nano-tube of the oligowall array grows to a certain extent, the bulk density is low (less than or equal to 0.02 g/cm) 3 ) The interaction among the carbon nano tube clusters is increased, secondary agglomeration is easy to occur among the clusters, and fluidisation loss is caused, so that on one hand, the quality fluctuation of products is large, the reactor is coked, and on the other hand, equipment is frequently stopped and cleaned. The invention breaks up secondary aggregates among the carbon nano tube aggregates of the oligowall array by using pulse air flow or ultrasonic waves at intervals of 2-5 min, and keeps the oligowall tube in a good fluidization growth state in the middle and later stages of growth by using the characteristic of fluidization hysteresis, thereby realizing continuous and stable fluidization growth of the oligowall array carbon nano tube.
Drawings
Fig. 1 is SEM images of the oligowall array carbon nanotubes of example 1 at different magnifications.
Detailed Description
The invention provides a fluidization production process of carbon nanotubes, which comprises the steps of controlling the gas speed to ensure that the gas speed of a main reaction section is between 0.03m/s and 0.15m/s after the carbon nanotubes grow for 20min, introducing pulse gas and/or sound waves at intervals of 2min to 5min, and continuously dispersing secondary agglomerates of carbon nanotube clusters for 5s to 20s. When pulse gas is introduced, the gas speed of the main reaction section needs to reach 0.2 m/s-0.30 m/s; when the sound wave is introduced, the sound wave intensity is more than or equal to 100dB.
The technical scheme of the invention is further described below with reference to specific examples. The starting materials used in the examples below, unless otherwise specified, are all commercially available from conventional sources; the processes used, unless otherwise specified, are all conventional in the art.
Example 1
Step 1: setting the temperature of the reactor to 650 ℃, introducing inert gas to reduce the oxygen content in the reactor to below 0.5%, and adding 1000g of FeCoNiAlMg catalyst;
step 2: introducing nitrogen (700L/min), ethylene (700L/min) and hydrogen (20 mL/min), wherein the gas speed of the main reaction section is 0.06m/s. After 20min of ethylene, nitrogen was additionally introduced at a flow rate of 2800L/min for about 5s at 2min intervals. After ethylene was introduced for 50min, the ethylene was turned off, the material was blown into the silo and cooled under nitrogen.
Step 3: continuous batch growth is carried out according to the steps 1 and 2, and the yield and the specific surface area of each batch are counted (static multipoint BET method) until the yield of the carbon nano tubes in a single batch is reduced by more than 10 percent of the average value or the specific surface area of the powder is reduced to 520m 2 And/g or less.
The test results are shown in Table 1.
Meanwhile, SEM images of the obtained product are shown in FIG. 1, and FIG. 1 shows that the obtained product has a nanotube array structure, and the number of walls is 3-6, which indicates that the oligowall array carbon nanotubes are successfully obtained.
Example 2
Step 1: setting the temperature of the reactor to 650 ℃, introducing inert gas to reduce the oxygen content in the reactor to below 0.5%, and adding 1000g of FeCoNiAlMg catalyst;
step 2: introducing nitrogen (700L/min), ethylene (700L/min) and hydrogen (20 mL/min), wherein the gas speed of the main reaction section is 0.06m/s. After 20min of ethylene, nitrogen was additionally introduced at a flow rate of 4600L/min for about 15s at 5min intervals. After ethylene was introduced for 50min, the ethylene was turned off, the material was blown into the silo and cooled under nitrogen.
Step 3: continuous batch growth is carried out according to the steps 1 and 2, and the yield and the specific surface area of each batch are counted (static multipoint BET method) until the yield of the carbon nano tubes in a single batch is reduced by more than 10 percent of the average value or the specific surface area of the powder is reduced to 520m 2 And/g or less.
The test results are shown in Table 1.
Example 3
Step 1: setting the temperature of the reactor to 650 ℃, introducing inert gas to reduce the oxygen content in the reactor to below 0.5%, and adding 1000g of FeCoNiAlMg catalyst;
step 2: introducing nitrogen (700L/min), ethylene (700L/min) and hydrogen (20 mL/min), wherein the gas speed of the main reaction section is 0.06m/s. After ethylene was fed for 20min, sound waves were fed at 3min intervals with an intensity of 150dB for about 10s. After ethylene was introduced for 50min, the ethylene was turned off, the material was blown into the silo and cooled under nitrogen.
Step 3: continuous batch growth is carried out according to the steps 1 and 2, and the yield and the specific surface area of each batch are counted (static multipoint BET method) until the yield of the carbon nano tubes in a single batch is reduced by more than 10 percent of the average value or the specific surface area of the powder is reduced to 520m 2 And/g or less.
The test results are shown in Table 1.
Comparative example 1
The difference between this comparative example and example 1 is that: the interval time of the pulse gas is reduced to below 2min, specifically 1.5min.
Step 1: setting the temperature of the reactor to 650 ℃, introducing inert gas to reduce the oxygen content in the reactor to below 0.5%, and adding 1000g of FeCoNiAlMg catalyst;
step 2: introducing nitrogen (700L/min), ethylene (700L/min) and hydrogen (20 mL/min), wherein the gas speed of the main reaction section is 0.06m/s. After 20min of ethylene, additional nitrogen was introduced at a flow rate of 2800L/min for about 5s at 1.5min intervals. After ethylene was introduced for 50min, the ethylene was turned off, the material was blown into the silo and cooled under nitrogen.
Step 3: continuous batch growth is carried out according to the steps 1 and 2, and the yield and the specific surface area of each batch are counted (static multipoint BET method) until the yield of the carbon nano tubes in a single batch is reduced by more than 10 percent of the average value or the specific surface area of the powder is reduced to 520m 2 And/g or less.
The test results are shown in Table 1.
Comparative example 2
The difference between this comparative example and example 1 is that: the interval time of the pulse gas is increased to more than 5min, specifically 6min.
Step 1: setting the temperature of the reactor to 650 ℃, introducing inert gas to reduce the oxygen content in the reactor to below 0.5%, and adding 1000g of FeCoNiAlMg catalyst;
step 2: introducing nitrogen (700L/min), ethylene (700L/min) and hydrogen (20 mL/min), wherein the gas speed of the main reaction section is 0.06m/s. After 20min of ethylene, additional nitrogen was introduced at a flow rate of 4400L/min for about 15s at 6min intervals. After ethylene was introduced for 50min, the ethylene was turned off, the material was blown into the silo and cooled in a nitrogen atmosphere.
Step 3: continuous batch growth is carried out according to the steps 1 and 2, and the yield and the specific surface area of each batch are counted (static multipoint BET method) until the yield of the carbon nano tubes in a single batch is reduced by more than 10 percent of the average value or the specific surface area of the powder is reduced to 520m 2 And/g or less.
The test results are shown in Table 1.
TABLE 1 continuous batch fluidization growth of carbon nanotubes
As is clear from Table 1, in examples 1 to 3, by adding pulse air intake or sound wave at the middle and late stages of growth, 150 or more batches of continuous growth oligowall tubes were realized, the average utilization rate of carbon sources was not less than 60%, and the fluctuation of the yield and specific surface area of each batch was within 7%. In comparative example 1, the interval between the pulse gas introduction was approximately 200 batches of continuous growth, but the yield per batch was 17% or more lower, and the carbon source conversion rate was only 49.6%. In comparative example 2, the interval of the pulse gas is too long, the secondary agglomerates of carbon tube agglomerates are difficult to break up by increasing the gas flow, the fluidization state in the middle and later stages of growth is deteriorated, the number of continuous batches of stable fluidization growth is drastically reduced, and the yield and performance fluctuation of the continuous batches are increased.
The result shows that the secondary agglomerates of the carbon tube agglomerates are scattered by adopting the pulse airflow or sound wave method, the fluidization state of the carbon nanotubes of the oligowall array in the middle and later stages of growth can be effectively improved, and more than 150 batches of continuous stable fluidization growth can be realized.
The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above examples, and any other changes, modifications, substitutions, combinations, and simplifications that do not depart from the spirit and principle of the present invention should be made in the equivalent manner, and the embodiments are included in the protection scope of the present invention.
Claims (6)
1. A fluidization production process of carbon nanotubes is characterized in that: the method comprises the following steps: introducing a mixed gas containing carbon source gas and shielding gas into a fluidized bed reactor filled with a catalyst, and reacting to generate carbon nanotubes;
the reaction is continuously carried out in batches, and the reaction time of each batch is 30-100 min;
during the reaction, pulse gas and/or sound waves are/is intermittently introduced; the interval time of the pulse gas and/or the sound wave is 2-5 min; the pulse gas and/or the sound wave are/is introduced at intervals after the reaction occurs for 20 min; the duration time of each time of introducing pulse gas and/or sound wave is 5 s-20 s; when the pulse gas is introduced, the protective gas with the flow of 2000L/min-6000L/min is additionally introduced on the basis of the mixed gas; when the sound waves are introduced at intervals, the intensity of the sound waves is more than or equal to 100dB.
2. The fluidized production process of carbon nanotubes according to claim 1, wherein: the gas velocity of the mixed gas is between 0.03m/s and 0.15 m/s.
3. The carbon nanotube fluidization production process according to claim 2, wherein: the pulse gas is introduced in the following way: and increasing the flow of the shielding gas on the basis of the mixed gas.
4. The fluidized production process of carbon nanotubes according to claim 3, wherein: after pulse gas is introduced, the gas speed of the mixed gas is more than or equal to 0.2m/s.
5. The fluidized production process of carbon nanotubes according to claim 1, wherein: the batch is more than or equal to 100.
6. The fluidized production process for carbon nanotubes according to any one of claims 1 to 5, characterized in that: the carbon nanotubes are carbon nanotubes with the wall number of 3-6.
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