KR20140103689A - Continuous process and apparatus for producing carbon nanotubes - Google Patents

Abstract

The present invention relates to a method for manufacturing carbon nanotubes continuously and an apparatus used therefor. The method for manufacturing carbon nanotubes continuously comprises the steps of a) generating carbon nanotubes by making reactive gas, which includes a carbon source, reducing gas and inert gas, react with a catalyst; b) separating carbon nanotubes and mixed gas, which is a by-product, from the product of the reaction; and c) recirculating part of the gaseous component of the separated mixed gas into step a) and discharging the remainder without separating and refining the gaseous component. The method and the apparatus according to the present invention can increase process efficiency greatly by controlling the accumulation amount of a side reactant to a proper level without separately using a gas separation unit or a separation process for separating a certain component of discharged gas.

Description

Technical Field [0001] The present invention relates to a continuous carbon nanotube production method,

The present invention relates to a continuous carbon nanotube manufacturing method and apparatus, and more particularly, to a continuous carbon nanotube manufacturing process in which an exhaust gas is recycled without an additional separation step to increase the efficiency.

Carbon nanotubes (CNTs) are generally manufactured by arc discharge, laser ablation, chemical vapor deposition, or the like. However, the arc discharge method and the laser evaporation method are difficult to mass-produce, and an excessive production cost of an arc or a cost of purchasing a laser device is a problem.

In addition, in the case of the above-mentioned chemical vapor deposition method, there is a problem that the synthesis rate is very slow and the CNT particles to be synthesized are too small in the case of a method using a gas phase dispersion catalyst. There is a limit to the mass production of CNTs.

A rotary kiln system in which CNTs are injected by injecting a catalyst into a reactor in the form of a rotating drum in accordance with a method for mass production of CNTs, and a rotary kiln system in which a fluidizing medium is heated And a fluidized bed reactor in which a CNT is synthesized in the fluidized bed is disclosed.

In this mass production method of CNTs, a reactive gas containing a carbon-derived hydrocarbon gas, an inert diluent gas and a reducing gas controlling a CNT production reaction at high temperature is introduced into the reactor. In the reactor, the carbon source is converted into CNT, (Specifically, hydrogen gas) is produced as a by-product, technical means for controlling them at a specific mixing ratio are needed.

However, the conventional methods using the rotary kiln system and the fluidized bed reactor, which have been conventionally performed, are limited to a maximum of 80% of the conversion rate of the carbon source, and in particular, there is no selective treatment method of the reducing gas, The raw material cost is increased, and the scale of the plant itself is over designed, so that the unit productivity is limited, and there is a problem that a large amount of carbon dioxide or the like is discharged by the incineration treatment of the waste.

Therefore, the conventional method requires the use of a gas separation unit or a process. However, if the accumulation amount of the side reaction material can be controlled to an appropriate level without a separate gas separation unit or separation process, the process efficiency can be greatly improved.

Accordingly, it is an object of the present invention to provide a method and an apparatus for controlling the accumulation amount of side reaction substances during reaction while recycling the gas discharged from the continuous carbon nanotube manufacturing process without using a gas separation unit or a gas separation process do.

In order to achieve the above object,

a) reacting a reaction gas containing a carbon source, a reducing gas and an inert gas with a catalyst to produce a carbon nanotube;

b) separating the carbon nanotubes and the by-product mixture gas from the reaction product; And

and c) recycling the gas component of the separated mixed gas to the step a) without discharging and purifying the gas component separately, and discharging the remainder.

According to an embodiment of the present invention, the molar ratio of the carbon source to the reducing gas in the step a) is preferably 1: 0.5 to 1:10.

According to the embodiment of the present invention, it is preferable that the flow ratio (circulation ratio) of the mixed gas recirculated in the step c) to the discharged gas is 3: 7 to 5: 5.

According to the embodiment of the present invention, it is preferable that the circulation ratio of the mixed gas in the step c) is adjusted such that the sum of the accumulation amount of the side reaction gas, the accumulation amount of the inert gas and the supplied amount becomes constant.

According to the embodiment of the present invention, it is preferable to further carry out the step of removing the solid material containing the carbon nanotubes before the gas mixture is recycled in the step c).

The present invention also relates to

1) a reactor in which a reaction gas containing a carbon source, a reducing gas, and an inert gas is reacted with a catalyst to produce carbon nanotubes;

2) a separator for separating the carbon nanotubes and the by-product mixture gas from the reaction product; And

3) a continuous carbon nanotube production apparatus comprising a discharge pipe for discharging a re-circulation pipe for recirculating part of the gas mixture separated from the separator to the reactor without separating and purifying the gas component separately.

According to a preferred embodiment of the present invention, the continuous carbon nanotube production apparatus further includes a control means for controlling a flow rate ratio (circulation ratio) of the gas mixture recirculated through the recirculation pipe and the gas mixture discharged through the discharge pipe do.

Preferably, the control means is a flow control valve provided in each of the recirculation pipe and the discharge pipe.

It is also preferable that the control means is a circulating power source of the mixed gas supplied from the recycling pipe to the reactor.

According to an embodiment of the present invention, it is preferable that the apparatus further comprises means for removing the solid material including the carbon nanotubes before recycling the mixed gas separated from the separator to the reactor through the recirculation pipe.

The continuous carbon nanotube manufacturing process according to the present invention can control the accumulation amount of the side reaction material to an appropriate level without separately using the gas separation unit or the separation process for separating certain components of the exhaust gas, Can be improved.

1 is a process diagram showing an example of a continuous carbon nanotube manufacturing process according to the present invention.
Fig. 2 shows the results of measurement of the side-reaction material accumulation amount in the carbon nanotube manufacturing process according to Example 1. Fig.

Hereinafter, the present invention will be described in detail.

The method for producing continuous carbon nanotubes according to the present invention comprises the steps of: a) reacting a reaction gas containing a carbon source, a reducing gas and an inert gas with a catalyst to produce carbon nanotubes; b) separating the carbon nanotubes and the by-product mixture gas from the reaction product; And c) recycling the gaseous components of the separated gaseous mixture to the step a), without separately separating and purifying the gaseous components of the separated gaseous mixture, and discharging the remainder.

The continuous carbon nanotube production apparatus of the present invention used in the above-described method comprises: 1) a reactor for producing a carbon nanotube by reacting a catalyst with a reaction gas containing a carbon source, a reducing gas and an inert gas; 2) a separator for separating the carbon nanotubes and the by-product mixture gas from the reaction product; And 3) a discharge pipe for discharging the gas component of the mixed gas separated in the separator, without recycling the gas component, and a part of the gas is recirculated to the reactor and the remainder is discharged.

Hereinafter, description will be made with reference to Fig. 1 is a process configuration diagram according to a preferred embodiment of the present invention.

The carbon nanotube reactor 100 may be a chemical vapor deposition reactor, preferably a fluidized bed reactor, a fixed bed reactor or a rotary reactor, more preferably a rotary kiln type reactor rotary kiln type reactor) or a fluidized bed reactor, and most preferably a fluidized bed reactor. In this case, productivity is excellent compared with the volume of the reactor, and mass production of CNT is easy.

The fluidized bed reactor 100 is connected to a reaction gas supply pipe 1 through a carbon source, a reducing gas, an inert gas or the like through a preheater (not shown) And then supplied to the upper part of the reactor at the upper part thereof and contacted with the catalyst injected into the reactor 100 through the catalyst supply pipe at the upper part to produce CNTs.

The reaction gas supply pipe 1 is not particularly limited as long as it can be used in a CNT production apparatus, and may be specifically a gas distributor or the like.

The catalyst is generally a heterogeneous catalyst composed of a composite structure of an active metal and a support which can be used for CNT production, more specifically, a supported catalyst, a coprecipitation catalyst, and the like. When the supported catalyst is used as the preferred catalyst, the bulk density of the catalyst itself is higher than that of the coprecipitation catalyst, and unlike the coprecipitation catalyst, the attrition of less than 10 microns It is possible to reduce the possibility of the occurrence of the fine particles and the mechanical strength of the catalyst itself is also excellent, so that the operation of the reactor can be stabilized. When a coprecipitation catalyst is used as another preferred catalyst form, there is a merit that the production method of the catalyst is simple, the preferable metal salts are low in the cost of the catalyst raw material, and there is a virtual beneficial aspect of the production and the specific surface area is wide and the catalytic activity is high.

The catalyst is a specific example the catalytically active metal precursor _{Co (NO 3) 2 -6H 2} O, (NH 4) 6Mo 7 O 24 -4H 2 O, Fe (NO 3) 2 -6H 2 O or (Ni (NO ₃ ) ₂ -6H ₂ O) were dissolved in distilled water and then dissolved in Al ₂ O ₃ , SiO ₂ Or by wet impregnation of a support such as MgO or the like.

The catalyst may be a catalyst prepared by treating a catalytically active metal precursor with a support such as Al (OH) ₃ , Mg (NO ₃ ) ₂ or colloidal silica together with ultrasonic waves.

In addition, the catalyst may be prepared by a sol-gel method using a chelating agent such as citric acid to facilitate dissolution of a catalytically active metal precursor in water, or by coprecipitating a catalytically active metal precursor dissolved in water lt; RTI ID = 0.0 > coprecipitation. < / RTI >

The inert gas may be nitrogen (N ₂ ), argon (Ar), or the like.

The operation mode of the fluidized bed reactor 100 forms a fluidized bed in the reactor. The reaction occurs when the catalyst contacts the reaction gas in the fluidized bed. As the reaction proceeds, the CNTs grow on the active metal of the catalyst, the bulk density may be lowered to the outside of the reactor. The bulk density may be 0.01 to 0.3 g / cm < ³ >, and preferably 0.03 to 0.1 g / cm < ^{3 &} gt ;.

The flow rate of the fluidized bed formed in the fluidized bed reactor 100 is preferably from 0.03 to 30 cm / s, more preferably from 0.1 to 25 cm / s.

The minimum fluidization velocity of the fluidized bed in the fluidized bed reactor 100 is preferably 0.03 to 15 cm / s, more preferably 1 to 10 cm / s.

The rotary kiln reactor and the fluidized bed reactor may include a catalyst supply pipe to which a catalyst is supplied; A reaction gas supply pipe 1 to which a carbon source, a reducing gas and an inert gas are supplied, and a product transport pipe 2 to which a mixed gas containing the generated carbon nanotubes and a reaction by-product gas are discharged can be connected.

The molar ratio of the carbon source to the reducing gas is preferably 1: 0.5 to 1:10. 1 to 1: 5, more preferably 1: 0.9 to 1: 6, and most preferably 1: 1 to 1: 5. Within this range, the rate of CNT formation is controlled to suppress the formation of amorphous carbon, There is an effect of increasing production.

Examples of the carbon source include a carbon-containing gas which can be decomposed in a heated state, and specific examples thereof include aliphatic alkanes, aliphatic alkenes, aliphatic alkynes, and aromatic compounds. More specific examples thereof include methane, ethane, ethylene, acetylene, But are not limited to, acetone, carbon monoxide, propane, butane, benzene, cyclohexane, propylene, butene, isobutene, toluene, xylene, cumene, ethylbenzene, naphthalene, phenanthrene, anthracene, acetylene, formaldehyde and acetaldehyde, , Ethane, carbon monoxide, acetylene, ethylene, propylene, propane, butane, and a mixture of liquefied petroleum gas (LPG).

The product discharged through the transfer pipe 2 is cooled through the heat exchanger or the condenser 200 and then supplied to the separator 300. The separator 300 is not particularly limited when it is a means, apparatus, or device for separating the CNT and the mixed gas as a by-product, but it may be a cyclone.

The CNT separated from the separator 300 is sent to the recoverer 400 through the pipe 4 and the mixed gas 5 as a byproduct is sent to the recycle pipe 7 and the discharge pipe 6 through the flow control valves 20 and 30 ; ratio control 2-way valve). The present invention is characterized in that the mixed gas transferred through the recycle piping is controlled only in the recirculation rate without any process for separating or purifying a specific gas component. By appropriately adjusting only the recirculation rate, it is possible to further convert 3 to 4 mol% of the feed ethylene into CNT while controlling the total amount of the side reaction gas, the inert gas accumulation amount and the feed amount to be constant.

Because of the nature of the fluidized bed reactor, the linear velocity of the reaction gas is one of the important reaction parameters. Since methane and other hydrocarbons produced by the side reactions have little reactivity, the amount of inert gas (nitrogen, for example) It is possible to keep the linear velocity constant by decreasing the amount by the same amount as the sum of the gas and the accumulated inert gas. That is, the accumulated amount of inert gas and the inert gas? When the sum of the accumulated amount becomes larger than the inert gas supply decrease amount, the linear velocity increases. According to a preferred embodiment of the present invention, the amount of the inert gas supplied can be reduced to about 30 to 50%.

The mixed gas transferred through the recycle line 7 is passed through a means 500 for removing carbon nanotubes or other solid by-products from the separator 300 before being fed to the reactor. It is preferably a filter.

The mixed gas discharged through the discharge pipe 6 can be discharged through a filtration means 600 such as a wet scrubber as in a conventional process.

The filter 500 recovers the CNT particles remaining in the mixed gas separated by the separator 300 and the scrubber 600 separates the harmful substances such as halides present in the mixed gas separated by the separator 300 Can be removed.

The mixed gas 8 having passed through the filter 500 is introduced into the reaction gas supply pipe 1 by a circulating power source, preferably the blower 50, and then supplied to the reactor 100. It is also possible to control the flow rate (circulation ratio) of the mixed gas supplied to the recycle pipe 7 and the discharge pipe 6 by adjusting the power / RPM of the blower.

The circulation ratio controlled by the flow control valves 20 and 30 or the blower 50 is such that the flow ratio of the recirculated mixture gas 7 and the exhaust gas mixture 6 is 3: 7 to 5: 5, Or less.

The circulation ratio can be changed according to the composition of the gas discharged from the reactor 100. For example, if the amount of reducing gas (eg, hydrogen) in the exhaust gas is twice that of the reducing gas supplied, the circulating ratio can be adjusted to be about 5: 5.

The present invention utilizes a simple device such as a circulating power source (50) or a gas flow control valve (20, 30) to re-use a part of the exhaust gas to the reactor so as to reuse the unreacted hydrogen, hydrogen and inert gas, Not only can the amount of gas supplied to the reactor be reduced, but also 3 to 4% of the supplied ethylene can be further converted into CNTs.

Therefore, the present invention is advantageous in that it can improve the process efficiency and reduce the exhaust gas without expensive facilities for separating and purifying specific components in the mixed gas.

 1 has been described with reference to FIG. 1, it is to be understood that FIG. 1 depicts only the apparatus necessary to illustrate the present invention and that other conventional apparatuses, such as pumps, additional valves, piping, Is omitted.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention. Such variations and modifications are intended to be within the scope of the appended claims.

Example  One

≪ Preparation of CNT catalyst >

A flask A in which 37.039 g of Co (NO ₃ ) ₂ -6H ₂ O was dissolved in 200 ml of an aqueous solution and a flask B prepared by dissolving 32.30 g of (NH ₄ ) 6 Mo ₇ O ₂₄ -4 H ₂ O in 200 ml of an aqueous solution were prepared The flasks A and B were added sequentially or together to a flask C containing 50 g of Al ₂ O ₃ (D50 = 76 microns, pore volume: 0.64 cm ³ / g, surface area: 237 m ² / g, manufactured by Saint Gobain) The catalyst precursor was supported on Al ₂ O ₃ sufficiently by stirring for 60 minutes or longer and then filtered under reduced pressure using a 10 micron filter paper or a 4 × glass filter to carry the catalytically active metal precursor The filter cake was separated and washed with distilled water. The recovered filter cake was dried in an oven at 120 캜 for 24 hours. The dried catalyst was calcined at 600 ° C for 3 hours to prepare a CNT catalyst.

<CNT Manufacturing>

5 g of the CNT catalyst was charged on top of a dispersion plate (bubble cap or sieve) of a vertical type fluidized bed reactor having a diameter of 55 mm and a height of 1 m and a reaction gas (C ₂ H ₄ : H ₂ : N ₂ = 1: 1: 1) was injected into the reactor at a rate of 3,000 ml / min through a reaction gas supply pipe connected to the lower portion of the reactor, and CNT was synthesized at 800 ° C. for 1 hour.

The reaction is carried out in a continuous reaction with a flow rate ratio of circulation / discharge = 4/6 (unreacted carbon source C ₂ H ₄ , inert gas N ₂ , reducing gas H ₂ ) mixed with the CNT product via cyclone Molar ratio) was recycled to the reaction gas feed line through the recycle line to produce CNT. At this time, the gas components at the rear stage of the reactor were 72% of hydrogen, 20% of nitrogen, 6% of methane, 1% of ethylene and 1% of ethane in terms of volume.

Existing method
Feed gas Recirculation system Feed gas Recirculating gas Inert gas One 0.42 0.58 Reducing gas One 0 One Carbon source One One 0

When the recycle ratio was 4/6, only 42% of the inert gas (nitrogen) was supplied to the feed gas and no reducing gas (hydrogen) was supplied.

Fig. 2 shows the result of measuring the accumulation amount of side reaction materials. The amount of recycled hydrogen was adjusted to the same amount as the amount to be fed. After 45 hours' reaction, the CNTs collected in the CNT recoverer showed a yield of 950% by weight based on the amount of the catalyst.

CNT yield = [(collected CNT weight - charged catalyst weight) / charged catalyst weight] × 100

The ethane selectivity [ethane / ethylene] was 4 mol% and the ethane stock was also 4 mol%, and the amount of CNT conversion in ethane was 3-4 mol% based on ethylene supplied. Therefore, it was confirmed that about 3 to 4 mol% of the ethylene supplied was further converted to CNT.

1. 10. Reaction gas feed pipe
2. 3. Reaction product transfer tube
4. CNT transfer tube
5. Mixed gas transfer pipe
6. Mixed gas vent tube
7. 8. 9. Mixed gas circulation tube
20. 30. Ratio control 2-way valve
40. Flowmeter
50. Circulation power source
100. Reactor
200. Capacitors
300. Separator (cyclone)
400. CNT withdrawal machine
500. Filter
600. Wet Scrubber

Claims (10)

a) reacting a reaction gas containing a carbon source, a reducing gas and an inert gas with a catalyst to produce a carbon nanotube;
b) separating the carbon nanotubes and the by-product mixture gas from the reaction product; And
c) recycling the gaseous components of the separated gaseous mixture to the step a), without separately separating and purifying the gaseous components of the separated gaseous mixture;
Wherein the carbon nanotube is a carbon nanotube.
The method according to claim 1,
Wherein the molar ratio of the carbon source to the reducing gas in the step a) is 1: 0.5 to 1:10.
The method according to claim 1,
Wherein the flow ratio (circulation ratio) of the mixed gas recirculated in the step c) to the discharged gas is 3: 7 to 5: 5.
The method according to claim 1,
Wherein the circulating ratio of the mixed gas in the step c) is adjusted so that the sum of the accumulation amount of the auxiliary reaction gas, the accumulation amount of the inert gas, and the supplied amount becomes constant.
The method according to claim 1,
And removing the solid material including carbon nanotubes before recycling the mixed gas in the step c).
1) a reactor in which a reaction gas containing a carbon source, a reducing gas, and an inert gas is reacted with a catalyst to produce carbon nanotubes;
2) a separator for separating the carbon nanotubes and the by-product mixture gas from the reaction product; And
3) a continuous carbon nanotube production apparatus, comprising: a discharge pipe for discharging a gas component of the mixed gas separated by the separator, and a part of the gas is recycled to the reactor and the remainder is discharged.
The method according to claim 6,
Wherein the continuous carbon nanotube production apparatus further comprises control means for controlling a flow rate ratio (circulation ratio) of the gas mixture recirculated through the recirculation piping and the gas mixture discharged through the discharge piping. Tube manufacturing apparatus.
8. The method of claim 7,
Wherein the control means is a flow control valve provided in the recycle pipe and the discharge pipe, respectively.
8. The method of claim 7,
Wherein the control means is a circulating power source of the mixed gas supplied from the recycling pipe to the reactor.
The method according to claim 6,
Further comprising means for removing the solid material including the carbon nanotubes before recycling the mixed gas separated from the separator to the reactor through the recirculation pipe.

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