CN118343745A - Method and system for preparing single/double-wall carbon nano tube by direct current arc discharge - Google Patents
Method and system for preparing single/double-wall carbon nano tube by direct current arc discharge Download PDFInfo
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Abstract
The invention belongs to the technical field of nano material preparation, and relates to a method and a system for preparing a single/double-wall carbon nano tube by direct current arc discharge. The method has great commercial value for large-scale preparation of high-quality single/double-wall carbon nanotubes by an arc discharge method.
Description
Technical Field
The invention belongs to the technical field of nano material preparation, and particularly relates to a method and a system for preparing a single/double-wall carbon nano tube by direct current arc discharge.
Background
Single-wall carbon nanotubes (SWCNTs) have been found in 1993 to have unique mechanical, electrical, thermal, quantum and other properties due to their unique one-dimensional structure, and the largest application of single-wall carbon nanotubes is currently a high-performance electrode, especially a lithium battery, and can be used as a key material of future high-performance carbon-based semiconductor devices.
In recent decades, due to the progress of plasma chemistry technology, the preparation of single-walled carbon nanotubes by a plasma method is valued by scientific research and industry, and the direct-current plasma has the advantages that high-quality single-walled carbon nanotubes can be prepared in a high-temperature environment, so that a new path is opened up for the industrialized preparation of high-quality SWCNTs.
In the prior art, a direct current arc discharge method is adopted to prepare the carbon nano tube, a discontinuous product condition often occurs, the product cannot be continuously produced under the condition that other parameters are not changed, the product is not produced for a long time, the yield is very unstable, catalyst nano particles for growing single-wall carbon nano tubes are not prepared, the arc light has great influence on the preparation of the catalyst and the growth of the product, the arc is observed to deflect all the time in the experimental process, the catalyst enters from an electric shock gun, the probability that the catalyst encounters the arc is low due to the large deflection amplitude, the catalyst nano particles cannot be continuously prepared, the deflection energy of the arc cannot be effectively utilized, and more reaction space is provided. The entry of the catalyst mixture into the reaction zone together with the striking gas can interfere with the stability of the arc, leading to frequent arc breaks, affecting the continuous growth of the product and the uniformity of the product.
In the experimental process, a large amount of high-temperature gas of the direct-current arc is sprayed to one side of the offset, the furnace burden on the offset side is rapidly melted, and the furnace burden on the opposite side of the offset side is slowly melted, so that the furnace burden is unevenly melted. The advantage of the direct current electric furnace that causes the even melting furnace charge is buried, makes the electrical efficiency reduce, and preparation inefficiency, the skew of electric arc reaches 30 degrees, and current equipment ability only exerts 60%, extravagant electric power energy. Further, the heat load on the offset side furnace wall increases, and the loss of the refractory increases, which causes a series of problems such as damage to the water-cooled panel, and as shown in fig. 4, the deflection angle θ is larger than 45 degrees in one of the cases in the arc deflection furnace. The arc is offset to cut down the advantages of the dc furnace. See ferroalloys, 1999, 03 pages 42-47.
The prior art also utilizes a magnetic field induction device to generate a magnetic field perpendicular to the current direction, and controls the rotating direction of the magnetic field through a rotating mechanism, so that the arc plasma spraying direction is realized, and the semi-automatic single-wall carbon nanotube production is realized, but the equipment investment cost is huge, the constraint on the arc is uncontrollable, and the effect is poor. The arc deflection is caused by the fact that a large current flows through a conductor when the direct current arc furnace works, a strong magnetic field is formed around the conductor, an arc of a current path exists in the magnetic field, and the magnetic field stresses the arc, so that the arc deflection is essential. The arc column is a non-rigid body that deflects due to forces acting on the arc, but the arc will drift away without some deflection-inhibiting force. So far, it has not been possible in reality to completely eliminate the offset with respect to the arc.
Disclosure of Invention
The invention discloses a method and a system for preparing a single/double-wall carbon nano tube by direct current arc discharge, which are used for solving any of the technical problems and other potential problems in the prior art.
The technical scheme adopted by the invention for achieving the purpose is as follows: a method for preparing single/double-wall carbon nano tube by DC arc discharge includes such steps as respectively feeding the arc striking gas, catalyst mixture and arc limiting gas into reaction region by annular multi-channel electrode gun from inside to outside to form gas curtain wall, compressing and restraining non-rigid arc column to raise the temp of core reaction region, and regulating the contact probability and time of catalyst mixture with arc column to obtain the catalyst particles (1-18 nm, preferably 1-12 nm) needed for growing single/double-wall carbon nano tube.
Further, the method specifically comprises the following steps:
S1) placing the catalyst mixture in a feeder, and introducing inert gas for emptying; preheating the arc striking gas and the arc limiting mixed gas;
S2) introducing preheated arc striking gas, starting a direct current pulse power supply, and heating the reaction chamber to a preset temperature to form a high-temperature reaction zone of a stable temperature field and an airflow field;
S3) feeding the preheated arc-limiting mixed gas into the reaction chamber through an annular multi-channel electrode gun at a certain flow rate, and feeding the catalyst mixture into the reaction chamber through a carrier gas through annular multi-channel electrode guns in sequence at a certain flow rate;
S4) forming an air curtain wall by the arc limiting mixed gas positioned in the outermost layer channel, compressing and restraining a non-rigid arc column, so that the temperature of a core reaction zone is further improved, nano catalyst particles are prepared by the catalyst mixture in the core reaction zone, and the prepared nano catalyst particles and carbon source gas in the arc limiting mixed gas can be subjected to full catalytic cracking reaction in a reaction chamber to prepare the high-quality single/double-wall carbon nano tube;
S5) separating and collecting the generated product through an annular scraping plate with a filter screen of a collecting unit, and continuously collecting the product through a transition chamber to obtain an initial product.
Further, the catalyst mixture in S1) is an iron-based compound or mixture containing elemental sulfur or elemental selenium; wherein the molar ratio of iron to sulfur element or selenium element is 5:1-150:1;
wherein, the iron in the catalyst is at least one of pentacarbonyl iron, ferric oxide and ferric chloride.
Wherein the sulfur is thiophene, sulfur powder, dimethyl sulfoxide, ferrous sulfide, ferric sulfate or other sulfur-containing or selenium-containing compounds.
The arc striking gas is inert gas; the preheating temperature of the arc striking gas is 200-900 ℃; the preheating temperature of the arc limiting mixed gas is 200-650 ℃.
The inert gas is one or more of nitrogen, argon and helium.
Further, the flow rate of the arc striking gas in the S2) is 3-30m/S;
The predetermined temperature is 700-3000 ℃.
Further, the flow rate of the arc-limiting mixed gas in the step S3) is 3-90m/S; the carrier gas is an inert gas with a flow rate of 3-50m/s.
The inert gas is one or more of nitrogen, argon and helium.
Further, the arc limiting mixed gas comprises carbon source gas, reducing gas and other gases, and the flow ratio of the carbon source gas, the reducing gas and the other gases is 1: (2-25): (0.01-3).
The carbon source gas is one or more mixed gases of methane, ethane, ethylene, acetylene, propylene, propane, ethanol, methanol or natural gas;
the reducing gas is one or more of hydrogen, carbon monoxide, carbon dioxide, hydrogen sulfide and ammonia.
The other gas is water vapor.
Further, the compression constraint in S4) is that the arc column deflection angle is not greater than 20 degrees.
Further, the height of the arc column is 30-500mm, and the diameter of the arc column is 10-100mm.
Another object of the present invention is to provide a system for implementing the method for preparing single/double-walled carbon nanotubes by dc arc discharge, the system comprising a catalyst preparation unit, a preheating unit, a synthesizing unit, a collecting unit and an electrode unit, wherein the electrode unit is an annular multichannel electrode gun; the annular multichannel electrode gun sequentially comprises an arc striking gas channel, a catalyst mixture channel and an arc limiting mixed gas channel from inside to outside;
The arc striking gas channels are arranged at the center of the annular multi-channel electrode gun, and a plurality of catalyst mixture channels are arranged at the circumference sides of the arc striking gas channels; the arc-limiting mixed gas channel is annular, and a plurality of outer sides of the catalyst mixture channels are arranged.
The annular multichannel electrode gun is positioned at the top of the reaction chamber and is arranged in the center of the reaction chamber, one end of the annular multichannel electrode gun is inserted into the reaction chamber, and the other end of the annular multichannel electrode gun is connected with the arc striking gas injection port, the catalyst mixture injection port and the arc limiting gas mixture injection port;
Further, the arc striking gas channel is a round hole with the diameter of 10-150mm, the diameter of the round hole is D1, the circle center of the catalyst mixture channel is positioned between the diameter of D1 and the diameter of D3, 3-32 round holes with the diameter of D2 are uniformly distributed, the diameter range of D2 is 1-30mm, the inner diameter D3 of the circular arc limiting mixed gas channel is 20-300mm, and the outer diameter D4 is 24-360mm.
The product collecting unit comprises a left group and a right group, an annular scraping plate with a filter screen, a collecting chamber, a transition chamber and a tail gas port, and is used for carrying out gas-solid separation on the generated single/double-wall carbon nano tube and realizing left-right switching and continuous collection; the tail gas outlet is arranged at the upper end of the collecting chamber and discharges tail gas.
The preheating unit comprises a gas preheater and an arc-limiting mixed gas injection port; an arc striking gas injection port; and preheating the arc striking gas, the arc limiting mixed gas and the carrier gas.
The collecting unit is connected with one end of the product synthesizing unit, and the other end of the synthesizing unit is connected with the product collecting unit;
the catalyst mixture is introduced into the synthesis unit through a catalyst mixture channel of the electrode unit, and contacts with arc light to prepare a nano-scale catalyst and grow a product;
Wherein the catalyst preparation unit comprises; a feeder; a catalyst mixture injection port; an arc column;
the arc column is formed by discharging a direct current pulse power supply between the lower end of the multi-channel electrode gun and the graphite crucible. The lifting arm is connected with the upper end of the annular multichannel electrode gun, and the height is automatically adjusted under the rated set power condition to keep the electric arc stable and continuous.
Wherein the product synthesis unit comprises a reaction chamber; a bottom anode graphite crucible; lifting arm and DC pulse power supply; the synthesis unit fully contacts an input catalyst mixture with an arc column to prepare catalyst nano particles, and the catalyst nano particles are subjected to catalytic cracking reaction in a high-temperature environment by using a preheated arc-limiting mixed gas in an arc-limiting channel in a reaction chamber to generate high-crystallinity single/double-wall carbon nanotubes;
the average G/D ratio of the product of the single/double-wall carbon nano tube can be up to 170, and the yield can reach 0.23kg/h.
The beneficial effects of the invention are as follows: by adopting the technical scheme, the arc striking gas, the catalyst mixture and the arc limiting gas are respectively fed into the reaction zone through the multi-channel electrode gun and the multi-channel graphite electrode, so that the interference of the catalyst mixture on deflection and stability of the arc column is avoided, the arc limiting gas mixture forms a gas curtain wall which is difficult to ionize in the outermost channel, the non-rigid arc column is restrained and ensured to be in necessary contact with the catalyst mixture, more high-catalytic activity 1-18 nano catalysts can be continuously prepared and the carbon sources in the preheating arc limiting gas meet, the full cracking reaction is realized, the multi-channel design is ensured to prepare more catalyst particles, the full cracking reaction is realized with the meeting carbon sources in the preheating arc limiting gas, the utilization rate of converting the carbon sources into single/double-wall carbon nanotubes is improved, the utilization rate of converting the carbon sources into high-quality single/double-wall carbon nanotubes is improved, and the yield can be increased by 0.23kg/h.
The arc limiting gas at the outermost layer can limit the arc to a certain extent, inhibit the deflection amplitude of the arc, keep the deflection angle of the arc within 20 ℃, concentrate the arc to a relatively narrow area, obtain an arc column with higher temperature and energy density, and improve the temperature of a core reaction area so as to be beneficial to preparing the single/double-wall carbon nano tube with high crystallinity, wherein the average G/D ratio of the product is higher than 170, as shown in figure 7.
The problems of excessive arc deflection, low energy efficiency, overheating damage to the hearth wall due to arc deflection measurement and the condition that the bottom anode burns through the hearth can be alleviated, and as shown in fig. 4, the arc deflection angle theta exceeds 45 degrees in one of the conditions in the arc deflection furnace. Preheating the arc striking gas and the arc limiting gas mixture and introducing the mixture into the reaction chamber greatly helps to ensure the stability of the arc, and simultaneously reduces the load of a direct current power supply.
Drawings
Fig. 1 is a schematic structural diagram of an apparatus for preparing single/double-walled carbon nanotubes by dc arc discharge according to the present invention.
Fig. 2 is a front view of one of the annular multi-channel electrode guns of fig. 1 according to the present invention.
Fig. 3 is a partial cross-sectional view of the annular multi-channel electrode gun of fig. 1 in accordance with the present invention.
Fig. 4 one of the conditions in an arc deflection furnace.
FIG. 5 is a scanning electron microscope image of a single/double wall carbon nanotube prepared in example 3 of the present invention.
FIG. 6 is a thermogravimetric characterization of single/double walled carbon nanotubes prepared using the apparatus of the present invention in example 4 of the present invention.
FIG. 7 is a Raman spectrum of the single/double walled carbon nanotube prepared in example 5 of the present invention.
Fig. 8 is a transmission electron microscope image of a single-walled carbon nanotube prepared in example 5 of the present invention.
Fig. 9 is a transmission electron microscope image of the double-walled carbon nanotube prepared in example 5 of the present invention.
Fig. 10 is a transmission electron microscope image of the single/double wall carbon nanotubes prepared in example 1 of the present invention.
FIG. 11 is a graph showing the specific surface area of the single/double wall carbon nanotubes prepared in example 5 of the present invention.
In the figure:
a reaction chamber 221; a gas preheater 222; an arc-limiting mixture injection port 223; an annular multichannel electrode gun 224; arc column 227; a bottom anode graphite crucible 228; a feeder 229; an arc striking gas injection port 230; a catalyst mixture injection port 231; a lifting arm 233; a dc pulsed power supply 235; a collection chamber 331; an annular scraper 333 with a filter screen; a transition chamber 335; and a tail gas port 337. An undissolved melt 431; a cathode 432; arc spraying 433; a furnace inner wall local superheat zone 434; a bottom anode 435. An arc striking gas passage 511; catalyst mixture channels 512; an arc limiting mixed gas passage 513.
Detailed Description
The technical scheme of the invention is further described below with reference to the accompanying drawings and specific embodiments. The invention relates to a method for preparing a single/double-wall carbon nano tube by direct current arc discharge, which comprises the steps of respectively feeding arc striking gas, catalyst mixture and arc limiting mixed gas into a reaction zone through an annular multi-channel electrode gun 224 from inside to outside, forming a gas curtain wall by the arc limiting mixed gas positioned on an outermost channel, compressing and restraining a non-rigid arc column, improving the temperature of a core reaction zone, simultaneously adjusting the contact probability and time of the catalyst mixture and the arc column, obtaining catalyst particles of 1-18 nanometers required by the growth of the single/double-wall carbon nano tube, and continuously and stably preparing the single/double-wall carbon nano tube with high crystallization.
The method specifically comprises the following steps:
S1) placing the catalyst mixture in a feeder 229, and introducing inert gas for emptying; preheating the arc striking gas and the arc limiting mixed gas;
S2) introducing preheated arc striking gas, starting a direct current pulse power supply 235, and heating the reaction chamber 221 to a preset temperature at high temperature to form a high-temperature reaction zone of a stable temperature field and an airflow field;
S3) feeding the preheated arc-limiting mixed gas into the reaction chamber 221 through the annular multi-channel electrode gun 224 at a certain flow rate, and feeding the catalyst mixture into the reaction chamber through the carrier gas through the annular multi-channel electrode gun in sequence at a certain flow rate;
S4) forming an air curtain wall by the arc limiting mixed gas positioned in the outermost layer channel, compressing and restraining a non-rigid arc column, so that the temperature of a core reaction zone is further improved, nano catalyst particles are prepared by the catalyst mixture in the core reaction zone, and the prepared nano catalyst particles and carbon source gas in the arc limiting mixed gas can be subjected to full catalytic cracking reaction in a reaction chamber to prepare the high-quality single/double-wall carbon nano tube;
S5) separating and collecting the generated product through an annular scraping plate with a filter screen of a collecting unit, and continuously collecting the product through a transition chamber to obtain an initial product.
The catalyst mixture in the S1) is an iron compound or a mixture containing sulfur element or selenium element; wherein the molar ratio of iron to sulfur element or selenium element is 5:1-150:1;
wherein, the iron in the catalyst is at least one of pentacarbonyl iron, ferric oxide and ferric chloride.
Wherein the sulfur is thiophene, sulfur powder, dimethyl sulfoxide, ferrous sulfide, ferric sulfate or other sulfur-containing or selenium-containing compounds.
The arc striking gas is inert gas; the preheating temperature of the arc striking gas is 200-900 ℃; the preheating temperature of the arc limiting mixed gas is 200-650 ℃.
The inert gas is one or more of nitrogen, argon and helium.
The flow speed of the arc striking gas in the S2) is 3-30m/S; the predetermined temperature is 700-3000 ℃.
The flow speed of the arc limiting mixed gas in the step S3) is 3-90m/S; the carrier gas is an inert gas with a flow rate of 3-50m/s. The inert gas is one or more of nitrogen, argon and helium.
The arc limiting mixed gas comprises carbon source gas, reducing gas and other gases, and the flow ratio of the carbon source gas, the reducing gas and the other gases is 1: (2-25): (0.01-3).
The carbon source gas is one or more mixed gases of methane, ethane, ethylene, acetylene, propylene, propane, ethanol, methanol or natural gas;
The reducing gas is one or more of hydrogen, carbon monoxide, carbon dioxide, hydrogen sulfide and ammonia. The other gas is water vapor.
The compression constraint in the step S4) is that the deflection angle of the arc column is not more than 20 degrees.
The height of the arc column is 30-500mm, and the diameter of the arc column is 10-100mm.
As shown in fig. 1, a system for implementing the method for preparing single/double-walled carbon nanotubes by dc arc discharge includes a catalyst preparation unit, a preheating unit, a synthesizing unit, a collecting unit, and an electrode unit, wherein the electrode unit is an annular multi-channel electrode gun 224; the annular multi-channel electrode gun sequentially comprises an arc striking gas channel 511, a catalyst mixture channel 512 and an arc limiting mixed gas channel 513 from inside to outside;
The arc striking gas passage 511 is provided at the center of the annular multi-passage electrode gun 224, and a plurality of the catalyst mixture passages 512 are provided at the circumferential side of the arc striking gas passage 511; the arc-limiting mixed gas passage 513 is formed in a circular ring shape, and a plurality of outer sides of the catalyst mixture passage 512 are provided, as shown with reference to fig. 2 and 3.
The annular multi-channel electrode gun 224 is located at the top of the reaction chamber and is disposed in the center of the reaction chamber 221, one end of the annular multi-channel electrode gun 224 is inserted into the reaction chamber 221, and the other end is connected with the arc striking gas injection port, the catalyst mixture injection port and the arc limiting gas mixture injection port, as shown in fig. 1;
The arc striking gas channel 511 is a round hole with a diameter of 10-150mm, the center of the catalyst mixture channel 512 is located between the diameter D1 and the diameter D3, 3-32 round holes with a diameter of D2 are uniformly distributed, the diameter D2 ranges from 1mm to 30mm, the inner diameter D3 of the circular arc limiting mixed gas channel is 20-300mm, and the outer diameter D4 is 24-360mm, and the arc limiting mixed gas channel is shown by referring to FIG. 3.
The product collecting unit comprises a left group and a right group, an annular scraping plate 333 with a filter screen, a collecting chamber 331, a transition chamber 335 and a tail gas port 337, and is used for carrying out gas-solid separation on the generated single/double-wall carbon nano tube and realizing left-right switching and continuous collection; the tail gas outlet is arranged at the upper end of the collecting chamber and discharges tail gas.
The preheating unit comprises a gas preheater 222 and an arc-limiting mixed gas injection port 223; an arc striking gas injection port 230; and preheating the arc striking gas, the arc limiting mixed gas and the carrier gas.
The collecting unit is connected with one end of the product synthesizing unit, and the other end of the synthesizing unit is connected with the product collecting unit;
Wherein the catalyst mixture is introduced into the synthesis unit through the catalyst mixture channel 512 of the electrode unit, and contacts with arc light to perform nano-scale catalyst preparation and product growth; the catalyst preparation unit includes; a feeder 229; a catalyst mixture injection port 231; arc column 227;
The arc column 227 is formed by discharging a direct current pulse power supply 235 between the lower end of the annular multichannel electrode gun 224 and the bottom anode graphite crucible 228. The lifting arm 233 is connected with the upper end of the annular multi-channel electrode gun 224, and is capable of automatically adjusting the height to keep the electric arc stable and continuous under the rated power setting condition.
Wherein the product synthesis unit comprises a reaction chamber 221; a bottom anode graphite crucible 228; a lift arm 233 and a dc pulse power supply 235; the synthesis unit fully contacts the input catalyst mixture with the arc column to prepare catalyst nano particles, and the catalyst nano particles are subjected to catalytic cracking reaction in a high-temperature environment in the reaction chamber 221 by the preheated arc-limiting mixed gas in the arc-limiting channel to generate the high-crystallinity single/double-wall carbon nano tube;
the average G/D ratio of the product of the single/double-wall carbon nano tube can be up to 170, and the yield can reach 0.23kg/h.
For single/double walled carbon nanotubes obtained using the methods described herein, there is a great deal of interest in the fields of materials science, nanotechnology, new energy sources, application chemistry, etc.
The unique properties of single/double walled carbon nanotubes improve the properties of materials used in their field. For example, rubber articles based on various rubbers, silicones, and thermoplastic elastomers of single/double walled carbon nanotubes offer technical advantages. By increasing the strength and elastic properties of the rubber formulation, the use of single/double walled carbon nanotubes in tires can greatly increase the key properties of wear resistance, fuel efficiency, adhesion properties, etc., which improvements are achieved at very low concentrations of nanotubes, which allows the core production technology to be preserved. The single/double-wall carbon nano tube used in the lithium ion battery can obviously improve the storage density and the charging cycle number of the battery and prolong the service life of the battery.
The high-quality single-walled carbon nanotube sample is characterized by Raman spectroscopy, thermogravimetric characterization, scanning electron microscopy and energy dispersion X-ray spectrum characterization, transmission electron microscopy characterization and ultraviolet-visible near-infrared absorption spectroscopy, and the test schemes are described in the following table 1.
Table 1 test protocol
| Technical specification of | Unit (B) | Evaluation method |
| Carbon tube content | wt％ | TEM，EDX，TGA |
| Number of carbon nanotube walls | / | TEM，EDX，TGA |
| Diameter of carbon nanotube | nm | Raman，TEM，NIR-Vis |
| I G/ID ratio | / | Raman |
| Specific surface area | m2/g | BET |
Example 1
The arc striking gas, the catalyst mixture and the arc limiting mixed gas respectively enter the reaction zone through an annular multi-channel electrode gun from inside to outside, the arc limiting mixed gas positioned in the outermost channel forms a gas curtain wall, the non-rigid arc column is compressed and restrained, the temperature of the core reaction zone is improved, and meanwhile, the contact probability and time of the catalyst mixture and the arc column are regulated, so that the catalyst particles of 1-18 nanometers required by the growth of the single/double-wall carbon nano tube are obtained. The catalyst nano particles are prepared by fully contacting an input catalyst mixture with an arc column, and the arc-limiting mixed gas preheated in an arc-limiting channel in a reaction chamber is subjected to catalytic cracking reaction in a high-temperature environment to generate the high-crystallinity single/double-wall carbon nano tube, wherein the specific method comprises the following steps of:
S1) placing pentacarbonyl iron and thiophene with the iron-sulfur ratio of 5:1 in a catalyst mixture in a feeder, and introducing inert gas for emptying; argon which is an arc striking gas with the flow rate of 13m/s is preheated to 350 ℃, and the arc limiting mixed gas is preheated to 450 ℃, wherein carbon source gas in the arc limiting mixed gas is methane and ethylene, reducing gas is hydrogen, other gas is water vapor, and the flow ratio of the three is 1:8:0.05.
S2) introducing preheated arc striking gas, starting a direct current pulse power supply, forming an arc column between the lower end of the annular multichannel electrode gun and the graphite crucible, and automatically adjusting the height under the rated power condition to keep the arc stable and continuous. The reaction chamber is heated to 930 ℃ at high temperature to form a stable high-temperature reaction zone of the temperature field and the airflow field.
S3) feeding the preheated arc-limiting mixed gas into a reaction chamber through an annular multi-channel electrode gun at a flow speed of 26m/S, wherein the annular multi-channel electrode gun sequentially comprises an arc-striking gas channel, a catalyst mixture channel and an arc-limiting mixed gas channel from inside to outside; the diameter D1 of the arc striking gas channel is a round hole with the diameter of 12mm, the circle center of the catalyst mixture channel is positioned between the diameter D1 and the diameter D3, 4 round holes with the diameter D2 are uniformly distributed, the diameter range of D2 is 3mm, the inner diameter D3 of the circular arc limiting mixed gas channel is 22mm, the outer diameter D4 is 30mm, and the arc striking gas channel is shown by referring to FIG. 3. And then the catalyst mixture is fed into the reaction chamber through an argon carrier gas with a flow rate of 12m/s in turn of an annular multichannel electrode gun.
S4) forming an air curtain wall by the arc limiting mixed gas positioned in the outermost layer channel, and compressing and restraining a non-rigid arc column, wherein the height of the arc column is 50mm, and the diameter of the arc column is 20mm.
S5) the product collecting unit comprises a left group and a right group, and the annular scraping plates with the filter screen are used for separating and collecting the generated single/double-wall carbon nano tubes and performing gas-solid separation to realize continuous collection and obtain initial products.
As is clear from Table 2, the product obtained in example 1 has an average G/D ratio of 171 when measured at 532nm excitation wavelength, a TG residue of 67.6%, an arc deflection angle of not more than 20 degrees, a too high iron content of the metal element in the initial product, and a yield of 0.23kg/h, and can be used for daily production in kg. FIG. 10 is a transmission electron microscope image of single/double walled carbon nanotubes prepared in example 1 of the present invention, which is a bundle of agglomerated single/double walled carbon nanotubes, and the particle size distribution of the prepared catalyst is very uniform as shown by the high resolution transmission electron microscope characterization, and the particle size of the catalyst for growth is about 1-12nm.
Example 2
The device and system of the embodiment 1 are adopted, wherein the iron oxide and sulfur powder with the iron-sulfur ratio of 10:1 in the catalyst mixture are characterized in that the flow rate is 18m/s of arc striking gas argon, the preheating temperature is 550 ℃, and the arc limiting mixed gas is preheated to 480 ℃, wherein the carbon source gas in the arc limiting mixed gas is propylene, the reducing gas is hydrogen and hydrogen sulfide, and the flow ratio of the three is 1:10:0.8. the reaction chamber is heated to 1230 ℃ at a high temperature, the preheated arc-limiting mixed gas is fed into the reaction chamber through an annular multi-channel electrode gun at a flow speed of 28m/s, the diameter D1 of the arc-striking gas channel is an 18mm round hole, the circle center of the catalyst mixture channel is positioned between the diameter D1 and the diameter D3, 8 round holes with the diameter D2 are uniformly distributed, the diameter range of the D2 is 4mm, the inner diameter D3 of the annular arc-limiting mixed gas channel is 30mm, and the outer diameter D4 is 35mm. The catalyst mixture was fed into the reaction chamber by argon carrier gas at a flow rate of 18m/s in turn with an annular multichannel electrode gun. The height of the arc column is 80mm, and the diameter of the arc column is 25mm.
As is clear from Table 2, the average G/D ratio of the product obtained in example 1 was 198, the TG residue of the product was 45.3%, the residual iron catalyst in the product was relatively large, the deflection angle of the arc column was not more than 17℃and the yield was 0.37kg/h.
Example 3
The apparatus and system used in example 2 was distinguished by iron oxide and dimethyl sulfoxide in an iron to sulfur ratio of 18:1 in the catalyst mixture; the flow rate is 23m/s of arc striking gas argon, the preheating temperature is 650 ℃, the arc limiting mixed gas is preheated to 556 ℃, wherein carbon source gas in the arc limiting mixed gas is propylene glycol, reducing gas is hydrogen and ammonia, other gases are water vapor, and the flow ratio of the three is 1:15:1. the reaction chamber was heated to 1350 ℃ at high temperature.
The arc limiting mixed gas is fed into the reaction chamber through an annular multi-channel electrode gun at a flow speed of 38m/s, the diameter D1 of the arc striking gas channel is an 18mm round hole, the circle center of the catalyst mixture channel is positioned between the diameter D1 and the diameter D3, 8 round holes with the diameter D2 are uniformly distributed, the diameter range of the D2 is 4mm, the inner diameter D3 of the arc limiting mixed gas channel is 46mm, and the outer diameter D4 of the arc limiting mixed gas channel is 50mm. The catalyst mixture was fed into the reaction chamber by argon carrier gas at a flow rate of 27m/s in turn with an annular multichannel electrode gun. The height of the arc column is 80mm, and the diameter of the arc column is 25mm.
As shown in Table 2, the average G/D ratio of the product obtained in example 1 was 203, which is a highly crystalline single/double wall carbon nanotube, the initial product TG remained at 31.8%, the impurities in the surface product were relatively few, the deflection angle of the arc column was not more than 15 degrees, the yield was 0.53kg/h, and the scanning electron microscope characterization of the single/double wall carbon nanotube prepared in example 3 of FIG. 5 showed that the initial product had relatively few impurities consistent with the TG characterization of the sample, and the uniformity of the product was good.
Example 4
The apparatus and system of example 3 was used with the exception that the iron and selenium were present in the catalyst mixture in an iron to sulfur ratio of 38:1; the flow rate is 27m/s of arc striking gas argon, the preheating temperature is 760 ℃, the arc limiting mixed gas is preheated to 610 ℃, wherein the carbon source gas in the arc limiting mixed gas is methane, the reducing gas is hydrogen, the other gases are water vapor, and the flow ratio of the three is 1:15:1. the reaction chamber is heated to 1550 ℃ at high temperature.
The arc limiting mixed gas is fed into the reaction chamber through an annular multi-channel electrode gun at a flow speed of 36m/s, the diameter D1 of the arc striking gas channel is a round hole with the diameter of 30mm, the circle center of the catalyst mixture channel is positioned between the diameter D1 and the diameter D3, 9 round holes with the diameter D2 are uniformly distributed, the diameter range of D2 is 5mm, the inner diameter D3 of the annular arc limiting mixed gas channel is 80mm, and the outer diameter D4 is 86mm. The catalyst mixture was fed into the reaction chamber by argon carrier gas at a flow rate of 25m/s in turn with an annular multichannel electrode gun. The height of the arc column is 180mm, and the diameter of the arc column is 40mm.
As is clear from Table 2, the average G/D ratio of the product obtained in example 1 was 215, which is a highly crystalline single/double walled carbon nanotube, and the thermal weight of the single/double walled carbon nanotube prepared in example 4 of FIG. 6 was found to be 33.4% by weight of TG remaining, and the content of the single/double walled carbon nanotube synthesized in the synthetic material was 66.6% by weight. The deflection angle of the arc column is not more than 13 degrees, the yield is 0.77kg/h, and the preparation of the primary product with the daily yield of 7kg grade can be realized.
Example 5
The apparatus and system of example 4 was used with the exception that the iron and sulfur were present in the catalyst mixture in an iron to sulfur ratio of 45:1; the flow rate is 30m/s of arc striking gas argon, the preheating temperature is 870 ℃, the arc limiting mixed gas is preheated to 640 ℃, wherein the carbon source gas in the arc limiting mixed gas is methane, the reducing gas is hydrogen, the other gases are water vapor, and the flow ratio of the three is 1:20:2. the reaction chamber is heated to 1750 ℃ at high temperature.
The diameter D1 of the arc striking gas channel is a round hole with the diameter of 36mm, the circle center of the catalyst mixture channel is positioned between the diameter D1 and the diameter D3, 16 round holes with the diameter D2 are uniformly distributed, the diameter range of D2 is 6mm, the inner diameter D3 of the circular arc limiting mixed gas channel is 120mm, and the outer diameter D4 is 130mm. The catalyst mixture was fed into the reaction chamber by argon carrier gas at a flow rate of 18m/s in turn with an annular multichannel electrode gun. The height of the arc column is 200mm, and the diameter of the arc column is 50mm.
As can be seen from Table 2, the deflection angle of the arc column obtained in example 1 is not greater than 11 degrees, and FIG. 7 shows a Raman spectrum of the sample obtained in example 3, wherein the sample has an obvious and sharp RBM characteristic absorption peak at 150cm -1, namely, the product contains single/double-walled carbon nanotubes, the G/D ratio of the product is calculated to be 178, namely, the prepared product is a high-quality single/double-walled carbon nanotube, and the three points have obvious RBM characteristic absorption peaks, the RBM characteristic peaks are relatively similar, the peaks are relatively concentrated, and the diameters of the carbon nanotubes are relatively concentrated. The residual TG of the product is 17.8%, the initial purity is higher, the yield is 1.33kg/h, 13 kg-grade initial products of daily yield can be realized, the preparation capacity of annual yield ton grade is provided, and a road is opened for industrialization of the product. Fig. 8 and 9 show bundles of many single/double walled carbon nanotubes agglomerated, fig. 8 shows that the product prepared in example 5 contains single walled carbon nanotubes with a diameter of 1.65nm, and fig. 9 shows that the product prepared in example 5 contains double walled carbon nanotubes with a diameter of 2.3nm, which further proves that the sample has a lower impurity content and better uniformity. As can be seen from FIG. 11, the specific surface area of the single/double walled carbon nanotubes was 1269m 2/g.
Table 2 product index in examples
The method and the system for preparing the single/double-wall carbon nano tube by direct current arc discharge provided by the embodiment of the application are described in detail. The above description of the embodiments is only for aiding in the understanding of the device of the present application and its core ideas; meanwhile, as those skilled in the art will have variations in the specific embodiments and application scope in accordance with the ideas of the present application, the present description should not be construed as limiting the present application in view of the above.
Certain terms are used throughout the description and claims to refer to particular components. Those of skill in the art will appreciate that a hardware manufacturer may refer to the same component by different names. The description and claims do not take the form of an element differentiated by name, but rather by functionality. As referred to throughout the specification and claims, the terms "comprising," including, "and" includes "are intended to be interpreted as" including/comprising, but not limited to. By "substantially" is meant that within an acceptable error range, a person skilled in the art is able to solve the technical problem within a certain error range, substantially achieving the technical effect. The description hereinafter sets forth a preferred embodiment for practicing the application, but is not intended to limit the scope of the application, as the description is given for the purpose of illustrating the general principles of the application. The scope of the application is defined by the appended claims.
It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a product or system that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such product or system. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a commodity or system comprising such elements.
It should be understood that the term "and/or" as used herein is merely one relationship describing the association of the associated objects, meaning that there may be three relationships, e.g., a and/or B, may represent: a exists alone, A and B exist together, and B exists alone. In addition, the character "/" herein generally indicates that the front and rear associated objects are an "or" relationship.
While the foregoing description illustrates and describes the preferred embodiments of the present application, it is to be understood that the application is not limited to the forms disclosed herein, but is not to be construed as limited to other embodiments, and is capable of numerous other combinations, modifications and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein, either as a result of the foregoing teachings or as a result of the knowledge or technology of the relevant art. And that modifications and variations which do not depart from the spirit and scope of the application are intended to be within the scope of the appended claims.
Claims (10)
1. A method for preparing a single/double-wall carbon nano tube by direct current arc discharge is characterized in that arc striking gas, a catalyst mixture and arc limiting mixed gas respectively enter a reaction zone through an annular multi-channel electrode gun from inside to outside, the arc limiting mixed gas positioned in an outermost channel forms a gas curtain wall, a non-rigid arc column is compressed and restrained, the temperature of a core reaction zone is increased, meanwhile, the contact probability and time of the catalyst mixture and the arc column are regulated, 1-18 nm catalyst particles required for preparing the single/double-wall carbon nano tube are obtained, and the single/double-wall carbon nano tube with high crystallization is continuously and stably prepared.
2. The method according to claim 1, characterized in that it comprises in particular the following steps:
S1) placing the catalyst mixture in a feeder, and introducing inert gas for emptying; preheating the arc striking gas and the arc limiting mixed gas;
S2) introducing preheated arc striking gas, starting a direct current pulse power supply, and heating the reaction chamber to a preset temperature to form a high-temperature reaction zone of a stable temperature field and an airflow field;
S3) feeding the preheated arc-limiting mixed gas into the reaction chamber through an annular multi-channel electrode gun at a certain flow rate, and feeding the catalyst mixture into the reaction chamber through a carrier gas through annular multi-channel electrode guns in sequence at a certain flow rate;
S4) forming an air curtain wall by the arc limiting mixed gas positioned in the outermost layer channel, compressing and restraining a non-rigid arc column, so that the temperature of a core reaction zone is further improved, nano catalyst particles are prepared by the catalyst mixture in the core reaction zone, and the prepared nano catalyst particles and carbon source gas in the arc limiting mixed gas can be subjected to full catalytic cracking reaction in a reaction chamber to prepare the high-quality single/double-wall carbon nano tube;
S5) separating and collecting the generated product through an annular scraping plate with a filter screen of a collecting unit, and continuously collecting the product through a transition chamber to obtain an initial product.
3. The method according to claim 2, wherein the catalyst mixture in S1) is an iron-based compound or mixture containing elemental sulfur or elemental selenium; wherein the molar ratio of iron to sulfur element or selenium element is 5:1-150:1;
The arc striking gas is inert gas; the preheating temperature of the arc striking gas is 200-900 ℃; the preheating temperature of the arc limiting mixed gas is 200-650 ℃.
4. The method according to claim 2, wherein the flow rate of the striking gas in S2) is 3-30m/S;
The predetermined temperature is 700-3000 ℃.
5. The method according to claim 2, wherein the flow rate of the arc-limiting gas mixture in S3) is 3-90m/S; the carrier gas is an inert gas with a flow rate of 3-50m/s.
6. A method according to claim 3, wherein the arc limiting gas mixture comprises a carbon source gas, a reducing gas and other gases, and the flow ratio between the three is 1: (2-25): (0.01-3).
7. The method of claim 2, wherein the compression constraint in S4) is that the arc column deflection angle is no greater than 20 degrees;
the height of the arc column is 30-500mm, and the diameter of the arc column is 10-100mm.
8. A system of the method for preparing single/double walled carbon nanotubes by direct current arc discharge according to any of claims 1 to 7, comprising a catalyst preparation unit, a preheating unit, a synthesis unit, a collection unit and an electrode unit, wherein the electrode unit is a ring-shaped multichannel electrode gun; the annular multichannel electrode gun sequentially comprises an arc striking gas channel, a catalyst mixture channel and an arc limiting mixed gas channel from inside to outside;
The arc striking gas channels are arranged at the center of the annular multi-channel electrode gun, and a plurality of catalyst mixture channels are arranged at the circumference sides of the arc striking gas channels; the arc-limiting mixed gas channel is annular, and a plurality of outer sides of the catalyst mixture channels are arranged.
9. The system of claim 8, wherein the arc striking gas channel is a round hole with the diameter of 10-150mm, the center of the catalyst mixture channel is positioned between the diameter of D1 and the diameter of D3, 3-32 round holes with the diameter of D2 are uniformly distributed, the diameter of D2 is 1-30mm, the inner diameter D3 of the circular ring-shaped arc limiting mixed gas channel is 20-300mm, and the outer diameter D4 is 24-360mm.
10. A single/double walled carbon nanotube, wherein the single/double walled carbon nanotube is prepared by the method of any of claims 2-9, and the average G/D ratio of the product is greater than 170, and the yield is 0.23kg/h.
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