CN117623283A - Device and method for preparing single-walled carbon nanotubes by reverse flow floating catalysis - Google Patents
Device and method for preparing single-walled carbon nanotubes by reverse flow floating catalysis Download PDFInfo
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Abstract
A device and a method for preparing single-walled carbon nanotubes by reverse flow floating catalysis are provided, wherein the device comprises a gas-liquid supply device, a floating catalytic cracking device and a product collecting device; the gas-liquid supply device is arranged at the tail end of the floating catalytic cracking device and is communicated with the floating catalytic cracking device so as to be used for supplying reaction materials; the head end of the floating catalytic cracking device is communicated with the product collecting device through a pipeline; the floating catalytic cracking device is internally provided with a reverse airflow device which is positioned close to the discharge end in the floating catalytic cracking device and is used for forming axial or radial airflow. According to the scheme, reverse airflow is introduced into the floating catalytic cracking reaction cavity, so that vortex is formed in a high-temperature area, the contact time of carbon-containing free radicals and a catalyst is greatly increased, and the yield of the single-walled carbon nanotubes is improved.
Description
Technical Field
The application relates to the technical field of single-walled carbon nanotubes, in particular to a device and a method for preparing single-walled carbon nanotubes by reverse flow floating catalysis.
Background
Single-walled carbon nanotubes (SWCNT) are widely used as a novel one-dimensional nanomaterial in the fields of new energy, transparent display, antistatic, semiconductors, engineering plastics, etc., due to their excellent electrical conductivity, thermal conductivity, temperature resistance, chemical resistance, mechanical properties, etc. However, the batch preparation technology of SWCNT has restricted its application in various fields, so how to realize low-cost and large-scale preparation is a problem to be solved.
Currently, there are three main ways to prepare single-walled carbon nanotubes: arc methods, laser ablation methods, and chemical vapor deposition methods. The existing arc method and laser ablation method have low yield and high energy consumption, and are difficult to realize large-scale production. The Floating Catalytic Chemical Vapor Deposition (FCCVD) method is the most batched technical scheme at present because of the continuity of raw material supply and product collection (Synthesis of Carbon Nanotubes by Floating Catalyst Chemical Vapor Deposition and TheirAplication. Adv. Funct. Mater. DOI:10.1002/adfm. 202108541); the approaches to improve SWCNT synthesis yield based on FCCVD methods are mainly: 1. optimizing a formula system; 2. optimizing the reactor; 3. the reaction conditions are optimized. The yield of the carbon nanotubes can be improved to a certain extent by optimizing the C/H/O atomic ratio, adjusting the catalyst and the type and optimizing the process parameters, but the quality and the purity of the carbon nanotubes can be reduced. Optimizing the reactor structure is also a way to improve productivity, but because the reaction condition of the single-wall carbon nano tube is harsh, the temperature field distribution of the furnace body is also changed after the cavity structure is changed, the air flow forms vortex in the cavity, the heat capacity of carrier gas is small, the temperature in the middle and at the tube wall is uneven after the carrier gas is introduced into the cold air flow, and the carbon nano tube is easier to grow along the tube wall, so the yield and purity are lower. Recently, zhang Rufan sets of subject groups proposed a substrate interception guiding strategy to realize ultra-high yield preparation of ultra-long carbon nanotubes, the strategy is to gasify a catalyst solution and then introduce the gasified catalyst solution into the front end of a carbon nanotube growing device, and simultaneously place a high-resistant Wen Pingzheng substrate in the middle of the growing device for segmenting a flow field and intercepting floating short carbon nanotubes, so that a large number of floating short carbon nanotubes are converted into the growth mode of the ultra-long carbon nanotubes, and the catalyst utilization rate is improved (Synthesis of Ultralong Carbon Nanotubes with Ultrahigh Yields, nano Letters,2023,23 (2), 523-532).
Therefore, for the floating catalytic cracking method in the prior art, how to optimize the synthesis method from the perspective of the growth mechanism of the single-walled carbon nanotubes, fully realize the dynamic process of gasification-cracking-carbon melting-precipitation of the organic precursor, improve the utilization efficiency of the catalyst as much as possible, reduce the phenomenon of 'tube wall growth' of the carbon nanotubes in the traditional floating catalytic cracking method, realize 'volume growth', and further improve the yield of the single-walled carbon nanotubes, and is a problem to be solved urgently.
Disclosure of Invention
The present application addresses the above-described deficiencies of the prior art by providing an apparatus for preparing single-walled carbon nanotubes by reverse flow floating catalysis that increases the yield of single-walled carbon nanotubes by introducing a reverse gas flow into a floating catalytic cracking reaction chamber to form a vortex in a high temperature region, resulting in a substantial increase in the contact time of carbon-containing radicals with the catalyst.
In order to solve the technical problems, the technical scheme adopted in the application is as follows: the device comprises a gas-liquid supply device, a floating catalytic cracking device and a product collecting device; the gas-liquid supply device is arranged at the tail end of the floating catalytic cracking device and is communicated with the floating catalytic cracking device so as to be used for supplying reaction materials; the head end of the floating catalytic cracking device is communicated with the product collecting device through a pipeline; the floating catalytic cracking device is internally provided with a reverse airflow device which is positioned close to the discharge end in the floating catalytic cracking device and is used for forming axial or radial airflow.
By adopting the structure, the position, close to the discharge end, of the floating catalytic cracking device is provided with the reverse airflow device for the first time, the airflow which extends axially or radially is formed in the cracking device by introducing the gas through the reverse airflow device, and the airflow can form interaction with the ascending reaction airflow to generate vortex or turbulence, so that the contact time of the carbon-containing free radicals in the floating catalytic cracking device and the catalyst is greatly increased, the utilization rate of the catalyst is improved, and the yield of the single-wall carbon nanotubes is further improved.
Further, the end face of the reverse airflow device, which is close to the side of the gas-liquid supply device, is positioned at the critical position of the heating area and the heat preservation area, which are close to the discharge end, in the floating catalytic cracking device; the critical point is a position, close to the discharge end, of the floating catalytic cracking device, which is lower than the limit temperature of the high temperature region, for example, the limit temperature of the high temperature region is 1400 ℃, and the position lower than 1400 ℃ is a critical point, and the critical point is a heat preservation region from the point; by adopting the structure, vortex or turbulence can be formed at the critical point position, the yield of target products is improved, and the position does not influence the gasification of materials in a low-temperature area.
Further, the reverse airflow device comprises an air duct and an airflow dispersing disc, wherein the airflow dispersing disc is arranged in the floating catalytic cracking device and is communicated with the air duct, and the other end of the air duct extends out of the floating catalytic cracking device and is used for conveying gas; by adopting the structure, the air flow can be conveniently introduced into the air flow dispersing disc, and then is output into the floating catalytic cracking device through the air flow dispersing disc, and the air flow and the reaction air flow interact to form vortex.
Further, the air duct is connected with the axial side wall or one end face of the air flow dispersing disc, and the outer wall of the air duct is tightly attached to the inner wall of the floating catalytic cracking device; by adopting the structure, the area of the air duct exposed to the inner cavity of the floating catalytic cracking device can be reduced as much as possible, thereby preventing the yield loss caused by the adhesion of the product to the air duct.
Furthermore, the air duct is a high temperature resistant inorganic pipe material such as a 310S stainless steel pipe, a corundum pipe, a quartz pipe or a graphite pipe, and the like, and is preferably a 310S stainless steel pipe; by adopting the structure, the air duct can bear the high temperature of the inner cavity of the floating catalytic cracking device, and the air duct is prevented from deforming to influence the gas transportation.
Furthermore, the inner diameter of the air guide pipe is 6-12 mm, and the wall thickness is 0.5-2 mm. The arrangement of the structure can not only enable the effective fixed connection between the air duct and the dispersion disk, but also can convey enough proper amount of gas to meet the formation of vortex at the critical position.
Further, the gas flow dispersing disc is a convection type gas flow dispersing disc (used for forming a gas flow opposite to the axial direction of the reaction gas flow) or a vertical flow type gas flow dispersing disc (forming a radial gas flow and the reaction gas flow are mutually perpendicular); by adopting the structure, the air flows in different directions can be formed in the two modes, and the vortex effect at the critical position of the low-temperature area and the high-temperature area can be realized.
Furthermore, the diameter of the convection type airflow dispersing disc is 1/2-2/3 of the inner diameter of the inner cavity of the floating catalytic cracking device, and the placing position is arranged at the critical position of the heating zone (high temperature zone) and the heat preservation zone and is arranged in the middle; the axial length of the convection type dispersion plate is 12-50mm; by adopting the structure, the formation of vortex airflow with enough area can be ensured, and the vortex airflow is positioned at the critical position of a high-temperature area and a heat preservation area, so that the effect of prolonging the contact time of carbon-containing free radicals and a catalyst can be realized, and the convection airflow dispersing disc with the size has a certain gap with the inside of the floating catalytic cracking device, can not form blockage on reaction materials, and ensures that the reaction materials continuously run towards the next flow; the axial length of the carbon nanotube is set to avoid depositing carbon nanotube product in the heat insulating area and prevent deposited product from obstructing the product to be discharged along with carrier gas.
In a further step, the vertical flow type airflow dispersing disc is of a hollow cylinder shape, and the outer diameter of the vertical flow type airflow dispersing disc of the hollow cylinder shape is equal to the inner diameter of the inner cavity of the floating catalytic cracking device; the wall thickness of the hollow cylindrical vertical flow type airflow dispersing disc is 10-20 mm, the inner wall is a microporous titanium plate, a microporous stainless steel plate, a microporous nickel plate, a microporous corundum plate or a microporous graphite plate, and the microporous direction of the hollow cylindrical vertical flow type airflow dispersing disc extends along the radial direction; with this structure, it is possible to achieve inward blowing in the radial direction of the gas flow, and to form a vortex by mixing collision with the rising process gas, and then to travel upward together.
Further, the convection type air flow dispersing plate is formed by integrally formed high-temperature resistant alumina ceramic, one axial end or a side wall of the convection type air flow dispersing plate is connected with an air duct, the other axial end is an air outlet end face, and a micropore structure is arranged on the air outlet end face, and the air outlet end face is close to the air-liquid supply device side; by adopting the structure, the device can adapt to the high temperature of the inner cavity of the floating catalytic cracking device, and meanwhile, the introduced air flow is dispersed and sprayed out through the arrangement of the micropore structure, and the direction of the introduced air flow is opposite to that of the process air flow, so that larger-area contact is formed between the introduced air flow and the rising materials, and the contact time of the carbon-containing free radicals and the catalyst is prolonged.
Further, the axial extension length of the vertical flow type airflow dispersing disc is 50-100 mm, and the vertical flow type airflow dispersing disc is arranged at the critical position of the heating zone and the heat preservation zone at the upper part of the inner cavity of the floating catalytic cracking device; by adopting the structure, the length of the vertical flow type airflow dispersing disc can cover the length range of the critical position of the heating area and the heat preservation area, so that a sufficient vortex effect is realized, and the yield of a target product is increased.
Furthermore, the convection type airflow dispersing disc can also be formed by sealing a stainless steel cavity and a microporous metal plate through a sealing piece, one axial end or a side wall of the convection type airflow dispersing disc is connected with an air duct, and the other axial end surface is an air outlet end surface and is formed by one of a microporous titanium plate, a microporous stainless steel plate, a microporous nickel plate, a microporous corundum plate or a microporous graphite plate; the structure is convenient to detach so as to replace the micro-pore plate.
Further, each pore diameter of the micropores (micropores for forming axial and radial airflows on the airflow dispersing disc) is 5-30 um, and the porosity is 50% -90%; by adopting the structure, uniform reverse vortex gas can be formed so as to absorb larger-area contact with the ascending reaction gas flow, thereby prolonging the contact time of the carbon-containing free radicals and the catalyst.
Further, the gas-liquid supply device comprises a gas pipeline, a stainless steel capillary liquid pipeline and a sealing flange plate; the gas pipeline and the stainless steel capillary liquid pipeline are connected with the flange in a sealing way, and the sealing flange is connected with the feeding end of the floating catalytic cracking device through a high-temperature sealing ring; by adopting the structure, the gas-liquid material can be effectively conveyed, the sealing effect with the outside is realized, and the sufficient reaction of the material in the furnace tube of the floating catalytic cracking device is ensured.
Further, the gas pipeline surrounds and wraps the periphery of the stainless steel capillary liquid pipeline, the outlet end of the stainless steel capillary liquid pipeline extends out of the outlet end of the gas pipeline along the axial direction, and the distance between the outlet ends of the gas pipeline and the stainless steel capillary liquid pipeline is 5-20 mm; by adopting the structure, the liquid material conveyed from the stainless steel capillary liquid pipeline is higher than the gas position from the gas pipeline, so that the gas is convenient to drive the liquid to move upwards together; and the structure of the gas pipeline surrounding type coating capillary liquid pipeline is adopted, because if the gas pipeline and the capillary liquid pipeline are independently arranged, the liquid coming out of the capillary pipe is likely to be unable to fully ascend, and the liquid can be fully brought to a high temperature region by the carrier gas of the gas pipeline to realize reaction by surrounding coating and setting a specific outlet drop, thereby improving the reaction efficiency.
Furthermore, the inner diameter of the stainless steel capillary liquid pipeline is 0.3-1.5 mm; the tail end (the upper part is close to the outlet end) of the gas pipeline is provided with a gas distributor, and the outlet ends of the gas pipeline and the stainless steel capillary are both positioned in the gas distributor and are in sealing connection with the gas distributor (sealing at the joint indicated by sealing, and a logistics outlet on the gas distributor is normally used); the purpose and effect of the gas distributor are that the reaction materials can be enabled to run upwards in a more dispersed mode, and the inner diameter area of the furnace tube is distributed as much as possible, so that the sufficient heating and mixing are obtained, and the reaction is more thorough.
Further, the gas distributor is arranged in the floating catalytic cracking device, and the temperature in the gas distributor is controlled to be 300-500 ℃; the temperature here is the temperature in the gas distributor, which is set so that the material in the gas distributor is more evenly mixed by gasification and then blown into the reaction zone, so that the reaction is more complete.
Further, the gas distributor consists of a porous nickel net, a copper net, a titanium net or microporous ceramic; the structure can enable the logistics to be dispersed more uniformly and the reaction to be more complete.
Further, the floating catalytic cracking device comprises a heating furnace body and a built-in furnace tube (the heating furnace body is coated on the periphery of the furnace tube), the heating furnace body consists of a silicon molybdenum rod or silicon carbon rod heating element and a polycrystalline alumina fiber heat insulation material, the heating temperature of the heating furnace body is 1100-1400 ℃, and the heating area length is 300-1000 mm; the furnace tube of the floating catalytic cracking device consists of a corundum tube or a silicon carbide tube, and the diameter of the furnace tube is 60-500 mm, and the length of the furnace tube is 1000-3000 mm; by adopting the structure, a low-position region close to two ends and a high-temperature region positioned in the middle are formed in the axial length of the furnace tube, the high-temperature region is externally covered with the heating furnace body so as to realize high temperature, and the two ends can realize the low-temperature region compared with the high-temperature region through heat preservation and temperature control; the gas flow dispersing disc is arranged in a critical area of a high-temperature area and a low-temperature area at the upper part of the furnace tube, the area can enable materials conveyed from a gas-liquid supply device below to fully react, the reaction is not interfered, and a final single-wall carbon nano tube is not formed in the critical area, but a vortex is formed at the critical area, so that (the tail end of the high-temperature area breaks up the process gas flow randomly to form continuous and stable turbulence); the method is essentially different from the reported floating catalytic method, the catalyst and the carbon-containing free radical are contacted more fully in a high-temperature area, the defect that the carbon nano tube grows along the tube wall in the traditional floating catalytic cracking method is overcome, the utilization rate of the catalyst and the conversion rate of a carbon source are greatly improved, and the volume growth is easier to realize.
Further, the product collecting device comprises a collecting tank, a back blowing cavity, a microporous filter plate and an air extracting device; the back blowing cavity is communicated with a discharge pipeline of the floating catalytic cracking device, the microporous filter plate is positioned above the discharge pipeline, and an air outlet of the air extracting device is positioned above the microporous filter plate; the collecting tank is positioned below the back blowing cavity; by adopting the connection mode, the air extraction device and the air outlet can be used for extracting air, so that the air flow drives the product to be attached to the bottom surface of the microporous filter plate, and the collection of the product is realized; when excessive products are attached to the bottom surface of the microporous filter plate, the products can be blown towards the microporous filter plate reversely through the outlet gas, so that the products can be discharged into the collecting tank.
Furthermore, the microporous filter plate can be a microporous titanium plate, a microporous copper plate and the like made of metal materials, or a sand core filter plate made of ceramic materials.
The application also provides a method for preparing the single-walled carbon nanotube by using the device for preparing the single-walled carbon nanotube by reverse flow floating catalysis, which specifically comprises the following steps:
(1) Connecting a gas-liquid pipeline, and installing a reverse airflow device at a set position (a critical position of a high-temperature region and a heat preservation region) in a furnace tube of the floating catalytic cracking device;
(2) Introducing process gas for evacuation, and setting a process temperature according to process requirements;
(3) Preserving heat for 25-40min after the set temperature is reached;
(4) Starting a gas-liquid supply device, feeding according to the set gas flow speed and the set liquid supply speed, setting the gas flow of a reverse gas flow device, and starting to synthesize the single-walled carbon nanotubes;
(5) The product was collected into a product collection device.
Further, the gas flow of the reverse gas flow device is 50% -120% of the gas flow of the gas-liquid supply device; the catalyst in the high temperature area is not fully contacted with the carbon-containing free radical due to the excessively low flow rate of the reverse airflow, and the result is not much different from the traditional floating catalytic cracking; the excessively high reverse airflow rate can cause excessively high airflow speed in a high-temperature region, short carbon nanotube growth time and reduced yield.
Further, the process gas or the gas in the gas flow dispersing plate is one or a mixture of more of nitrogen, argon, helium and hydrogen, preferably argon.
Further, the process temperature in the step (2) is as follows: the high temperature cavity is 1100-1500 ℃.
Further, the liquid supply in the step (4) is an organic liquid precursor, which may be a formulation reported in literature and known patents for synthesizing single-walled carbon nanotubes, and generally includes a carbon source, a catalyst, an accelerator, an etchant, and the like. The carbon source is liquid carbon source such as ethanol, methanol, toluene, xylene, tetrahydrofuran, benzene, n-hexane, cyclohexane, etc., or gaseous carbon source such as methane, acetylene, etc.; the catalyst is generally ferrocene, nickel-cyclopentadienyl, cobalt-cyclopentadienyl, ferric trichloride, carbonyl iron, ferric lactate and the like (the solid catalyst can be placed at a specific position in the furnace tube in advance, and if the solid catalyst is gas, the solid catalyst is conveyed into the furnace tube through a gas pipeline); the accelerator is typically a sulfur-containing compound such as thiophene.
Furthermore, the gas and liquid flow rates of the gas and liquid supply device are consistent with the technological parameters reported in the literature and known patents for synthesizing the single-walled carbon nanotubes, and the parameters are different under the influence of the formula and the diameter of the furnace tube.
Compared with the prior art, the application has the following advantages and beneficial effects:
(1) According to the technical scheme, the air flow dispersing disc is introduced into the floating catalytic cracking device for the first time, and the position of the air flow dispersing disc is critical, so that vortex (turbulence) disturbance is formed in the critical area of the high-temperature area and the heat-preserving area, and the contact efficiency of the catalyst and the carbon-containing free radicals is improved; when the airflow dispersing disc is completely placed in a high-temperature area, the generated turbulence destroys the carbon source and the cracking environment of the catalyst, and has negative influence on the carbon source and the cracking environment of the catalyst, so that the catalyst is oversized and the activity is reduced; when the airflow dispersing disc is completely arranged in a heat preservation area behind a high temperature area, a carbon source completes a cracking-melting process under the action of a catalyst, a carbon nano tube product is formed by supersaturation precipitation in the heat preservation area (a low temperature area), the effect of reverse airflow on improving the synthesis yield of single-wall carbon nano tubes is not obvious, network-shaped carbon nano tube fibers are blocked at the heat preservation area, and the collection is inconvenient; therefore, the reverse airflow device is arranged at the tail end of the high-temperature area (namely, the critical position of the high-temperature area and the heat preservation area), is opposite to or perpendicular to the direction of the process airflow (the airflow conveyed by the gas-liquid supply device), and the process airflow is scattered randomly at the tail end of the high-temperature area to form continuous and stable turbulence.
(2) The reverse airflow does not interfere the action of the process gas in the low temperature area, the gasification of the catalyst and the carbon source is not affected, and meanwhile, the airflow speed of the reaction cavity at the rear end of the high temperature area is increased by introducing the reverse airflow (after the airflow of the airflow dispersing disc is mixed with the process airflow, the airflow of the airflow dispersing disc and the process airflow are simultaneously discharged from the vertical airflow dispersing disc or from a gap between the convection airflow dispersing disc and the inner wall of the furnace tube, and the gas quantity at the moment is the sum of two gas quantities, so that the gas quantity is increased, the area of the discharged gas is reduced, and the gas flow rate is increased), so that the carbon nano tubes are not easy to lap into a reticular fiber structure and can not block the pipe orifice, thereby facilitating the collection of single-wall carbon nano tube powder and realizing mass preparation.
(3) Compared with the traditional floating catalytic cracking method, the single-walled carbon nanotube has the advantages that the yield of the single-walled carbon nanotube is improved by 3-5 times, the conversion rate of carbon sources is 3-7%, the analysis purity of TGA is 60-85%, and the analysis purity of Raman I is improved D /I G The diameter of the single-wall carbon nano tube is about 1.8nm and is 0.1-0.4.
Drawings
Fig. 1 is a schematic structural diagram of a reverse flow floating catalytic cracking device according to an embodiment of the present application.
Fig. 2 is a schematic structural diagram of a reverse flow floating catalytic cracking device according to another embodiment of the present application.
Fig. 3 is a schematic structural view of a convection type air flow distribution plate of the present application.
Fig. 4 is a schematic structural view of a vertical flow type airflow dispersing plate.
Fig. 5 is a schematic structural view of the gas-liquid supply device of the present application.
Fig. 6 is a schematic structural view of the reverse airflow device of the present application.
Fig. 7 is a schematic structural diagram (vertical flow) of a reverse flow floating catalytic cracking device according to a third embodiment of the present application.
Fig. 8 is a schematic structural diagram of a vertical flow type reverse airflow device according to the present application.
FIG. 9 is a photograph of a carbon nanotube product according to a preferred embodiment of the present application.
Fig. 10 is a Raman spectrum of single-walled carbon nanotubes in a preferred embodiment of the present application.
As shown in the accompanying drawings: as shown in the accompanying drawings: 1-a gas-liquid supply device; 11-gas piping; 12-stainless steel capillary liquid tubing; 13-sealing the flange plate; 14-a gas distributor; 15-perforated plates of gas distributors; 2-a floating catalytic cracking unit; 21-heating the furnace body; 22-furnace tube; 23-a heating element; 3-a product collection device; 31-a collection tank; 32-a product blowback chamber; 33-microporous filter plates; 34-outlet (vent); 4-a reverse airflow device; 41-an airway; 42-an air flow dispersion plate; 43-outlet end face.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments and the accompanying drawings, and it is obvious that the described embodiments are only preferred embodiments, not all embodiments. All other embodiments, based on the embodiments herein, which a person of ordinary skill in the art would obtain without undue effort, are within the scope of protection of the present application;
furthermore, it is to be noted that: when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. When an element is referred to as being "disposed on" another element, it can be directly on the other element or intervening elements may also be present. The terms "vertical," "horizontal," "left," "right," and the like are used herein for illustrative purposes only. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.
1-8, a device for preparing single-walled carbon nanotubes by reverse flow floating catalysis comprises a gas-liquid supply device 1, a floating catalytic cracking device 2 and a product collecting device 3; the gas-liquid supply device 1 is arranged at the tail end of the floating catalytic cracking device 2 (the lower end is shown in the vertical structure of fig. 1, the left end is shown in the horizontal structure of fig. 2) and is communicated with the floating catalytic cracking device 2 for supplying reaction materials; the head end (the upper end when the vertical structure is shown in fig. 1 and the right side when the horizontal structure is shown in fig. 2) of the floating catalytic cracking device 2 is communicated with the product collecting device 3 through a pipeline; the floating catalytic cracking device 2 is also internally provided with a reverse airflow device 4, the reverse airflow device 4 is positioned near the discharge end (near the upper end when the vertical structure is shown in fig. 1, and near the right end when the horizontal structure is shown in fig. 2) in the floating catalytic cracking device 2, and the reverse airflow device 4 is used for forming an axial or radial airflow (namely, the reverse airflow device can jet out airflow, and the airflow is in axial opposite direction or reverse direction or vertical contact with the reactant airflow in the direction of the gas-liquid supply device, so that turbulence or vortex is formed); more preferably, the reverse airflow device 4 is disposed at a critical position between a heating zone and a heat preservation zone near a discharge end in the floating catalytic cracking device, specifically, an end face of the reverse airflow device 4 near the side of the gas-liquid supply device 1 is disposed at a critical position between a heating zone and a heat preservation zone near an upper part in the floating catalytic cracking device 2, the critical position is a critical point between a high temperature zone and a heat preservation zone in the floating catalytic cracking device, for example, a point with a limit temperature of 1400 ℃ in the high temperature zone is a critical point, and a point with a limit temperature lower than 1400 ℃ is a heat preservation zone from the critical point; the critical point location may also be referred to as the back end location of the high temperature zone.
By adopting the structure, the application sets up reverse air flow device in the floating catalytic cracking device for the first time, thereby the gas is let in through this reverse air flow device and forms the vortex in the heat preservation district (low temperature zone) of floating catalytic cracking device and the critical department in high temperature zone for the contact time of carbonaceous free radical in the floating catalytic cracking device and catalyst increases by a wide margin, thereby improves the utilization ratio of catalyst, and then improves the productivity of single-walled carbon nanotube.
As shown in fig. 1-4 and 7-8, the reverse airflow device 4 in the present application includes an air duct 41 and an airflow dispersion plate 42, where the airflow dispersion plate 42 is disposed in the floating catalytic cracking device 2 and is in communication with the air duct 41, and the other end (the end not connected to the airflow dispersion plate) of the air duct 41 extends out of the floating catalytic cracking device 2 and is used for conveying air; by adopting the structure, the air flow can be conveniently introduced into the air flow dispersing disc through the air duct, then is output into the floating catalytic cracking device through the air flow dispersing disc, and interacts with the air flow of the air-liquid supply device to form continuous and stable vortex, so that the catalyst and the carbon-containing free radicals are contacted more fully in a high-temperature area, the defect that the carbon nano tube grows along the tube wall in the traditional floating catalytic cracking method is overcome, the utilization rate of the catalyst and the conversion rate of the carbon source are greatly improved, and the volume growth is easier to realize.
As shown in fig. 1-4 and 7-8, the air duct 41 is connected with an axial side wall or an axial end face of the air flow dispersing plate 42, and the outer wall of the air duct 41 is tightly attached to the inner wall of the floating catalytic cracking device; by adopting the structure, the area of the air duct exposed to the inner cavity of the floating catalytic cracking device can be reduced as much as possible, thereby preventing the yield loss caused by the adhesion of the product to the air duct.
By way of example, the air duct 41 described in the present application is made of a high temperature resistant inorganic material such as 310S stainless steel tube, corundum tube, quartz tube or graphite tube, and preferably 310S stainless steel tube; by adopting the structure, the air duct can bear the high temperature of the inner cavity of the floating catalytic cracking device, and the air duct is prevented from deforming to influence the gas transportation.
By way of example, the inner diameter of the airway 41 described herein is 6 to 12mm and the wall thickness is 0.5 to 2mm. The arrangement of the structure can not only enable the effective fixed connection between the air duct and the dispersion plate, but also can convey enough proper amount of gas to meet the formation of vortex in a high temperature area.
As shown in fig. 2, 4 and 8, the flow distribution plate 42 described herein is a counter-flow distribution plate (shown in fig. 2), or a vertical flow distribution plate (shown in fig. 4, 8); both air flow dispersing discs are of cylindrical structures; the body of the convection type air flow dispersing disc is a cavity, the end face close to the air-liquid supply device is an end face with uniformly distributed micropores, the air flow of the air duct is introduced into the cavity and then is sprayed out from the micropores on the end face of the micropores, and the air flow provided by the air-liquid supply device are exactly aligned to each other to form stable vortex or turbulent flow; the vertical flow type air flow dispersing disc is characterized in that the body of the dispersing disc is of a hollow cylindrical structure and is communicated up and down, double-side tube walls of an interlayer are arranged on the tube walls close to the inner side, a plurality of uniformly distributed micropores are radially arranged on the tube walls close to the inner side, an air duct introduces air flow into the interlayer and then radially ejects the air flow from the micropores, the air flow is exactly perpendicular to the air flow provided by the air-liquid supply device, and two air flows interact to form turbulence; by adopting the structure, the air flows in different directions can be formed in the two modes, and the vortex effect at the critical position of the low-temperature area and the high-temperature area can be realized.
As an example, the diameter of the convection type air flow dispersing disc 42 is 1/2-2/3 of the inner diameter of the inner cavity of the floating catalytic cracking device 2, and the placement position (the critical position between the heating zone (high temperature zone) and the heat preservation zone) specifically means that the end face of the convection type air flow dispersing disc, which is close to the air-liquid supply device, is arranged at the critical position), and is arranged centrally (i.e. the air flow dispersing disc is cylindrical, the outer edge of the air flow dispersing disc is equidistant from the inner wall of the floating catalytic cracking device, i.e. the air flow dispersing disc and the air flow dispersing disc are coaxially arranged); the axial length of the convection type dispersion plate is 12-50mm; by adopting the structure, the formation of vortex airflow with enough area can be ensured, and the vortex airflow is positioned at the critical position of a high-temperature area and a heat preservation area, so that the effect of prolonging the contact time of carbon-containing free radicals and a catalyst can be realized, and the convection airflow dispersing disc with the size has a certain gap with the inside of the floating catalytic cracking device, can not form blockage on reaction materials, and ensures that the reaction materials continuously run towards the next flow; the axial length of the carbon nano tube can be set to avoid depositing carbon nano tube products in the heat preservation area, and prevent the deposited products from obstructing the discharge of the products along with carrier gas.
7-8, the vertical flow type airflow dispersing plate 42 is a hollow cylinder, and the outer diameter of the vertical flow type airflow dispersing plate is equal to the inner diameter of the inner cavity of the floating catalytic cracking device (namely, the inner diameter and the outer diameter of the vertical flow type airflow dispersing plate are mutually matched, and the airflow runs from a hollow cavity which is vertically communicated with the vertical flow type airflow dispersing plate); the wall thickness of the hollow cylinder type vertical flow type airflow dispersing disc is 10-20 mm (the difference between the circumferential outermost side and the inner side), the inner wall is provided with an air outlet end face 43, and the air outlet end face can be specifically a microporous titanium plate, a microporous stainless steel plate, a microporous nickel plate, a microporous corundum plate, a microporous graphite plate or the like, and the microporous direction of the air outlet end face extends along the radial direction; with this structure, it is possible to achieve inward blowing in the radial direction of the gas flow, and to form a vortex by mixing collision with the rising process gas, and then to travel upward together.
As an example, the convection type air flow dispersing plate 42 is formed by integrally forming high temperature resistant alumina ceramic, one axial end or side wall (shown in fig. 3) of the convection type air flow dispersing plate is connected with an air duct 41, the other axial end is an air outlet end face 43, and the air outlet end face 43 is arranged in a micropore structure, and is close to the air-liquid supply device side; by adopting the structure, the device can adapt to the high temperature of the inner cavity of the floating catalytic cracking device, and meanwhile, the introduced air flow is dispersed and sprayed out through the arrangement of the micropore structure, and the direction of the introduced air flow is opposite to that of the process air flow, so that larger-area contact is formed between the introduced air flow and the ascending material air flow, and the contact time of the carbon-containing free radicals and the catalyst is prolonged.
As an example, the axial extension length of the vertical flow type airflow dispersing disc is 50-100 mm, and the vertical flow type airflow dispersing disc is arranged at the critical position of the heating area and the heat preservation area at the upper part of the inner cavity of the floating catalytic cracking device (namely, the end face of the vertical flow type airflow dispersing disc, which is close to the side of the gas-liquid supply device, is positioned at the critical position, so that turbulent airflow is formed at the critical position); by adopting the structure, the length of the vertical flow type airflow dispersing disc can cover the length range of the critical position of the heating area and the heat preservation area, so that a sufficient vortex effect is realized, and the yield of a target product is increased.
As an example, the convection type air flow dispersing disc 42 described in the application may also be formed by a stainless steel cavity (i.e. a cylinder with an opening at one end, the opening end and the microporous metal plate are sealed by a sealing member), and the microporous metal plate is sealed by a sealing member, one axial end or a side wall of the stainless steel cavity is connected with an air duct 41 (the air duct is connected to the sealing end at the opposite axial end of the microporous metal plate and is communicated with the interior of the stainless steel cavity, and air flow is introduced and sprayed out from micropores of the microporous metal plate and contacts with the process air flow reversely to form turbulence), and the other end is an air outlet end face 43, which is formed by one of a microporous titanium plate, a microporous stainless steel plate, a microporous nickel plate, a microporous corundum plate or a microporous graphite plate; the structure is convenient to detach so as to replace the micro-pore plate.
By way of example, the micropores described herein have individual pore diameters of 5 to 30um and porosities of 50% to 90% (i.e., the distribution of the micropores on their opposite inner walls or end faces); by adopting the structure, uniform reverse vortex gas can be formed so as to contact the ascending materials in a larger area, thereby prolonging the contact time of the carbon-containing free radicals and the catalyst.
As shown in fig. 1-2, 5 and 7, the gas-liquid supply device 1 described in the present application includes a gas pipe 11, a stainless steel capillary liquid pipe 12 and a sealing flange 13; the gas pipeline 11, the stainless steel capillary liquid pipeline 12 and the flange 13 are connected in a sealing way, and the sealing flange 13 is connected with a furnace tube 22 of the floating catalytic cracking device 2 through a high-temperature sealing ring; by adopting the structure, the gas-liquid material can be effectively conveyed, the sealing effect with the outside is realized, and the sufficient reaction of the material in the furnace tube of the floating catalytic cracking device is ensured.
As shown in fig. 1-2, 5 and 7, the gas pipe 11 is wrapped around the periphery of the stainless steel capillary liquid pipe 12, the upper outlet of the stainless steel capillary liquid pipe 12 extends out of the upper outlet of the gas pipe 11 along the axial direction, and the outlet distance between the two is 5-20 mm (i.e. the upper port of the stainless steel capillary liquid pipe and the upper port of the gas pipe are both extended in the furnace tube, and the upper port of the stainless steel capillary liquid pipe extends out of the upper port of the gas pipe body, and a drop is formed between the two); the side wall of the gas pipeline extends to form an air inlet branch pipe, and gas enters the gas pipeline from the lateral branch pipe and is sealed between the lower end face of the gas pipeline and the capillary tube; by adopting the structure, the liquid material conveyed from the stainless steel capillary liquid pipeline is higher than the gas position from the gas pipeline, so that the gas is convenient to drive the liquid to move upwards together; and the structure of the gas pipeline surrounding type coating capillary liquid pipeline is adopted, because if the gas pipeline and the capillary liquid pipeline are independently arranged, the liquid coming out of the capillary pipe is likely to be unable to fully ascend, and the liquid can be fully brought to a high temperature region by the carrier gas of the gas pipeline to realize reaction by surrounding coating and setting a specific outlet drop, thereby improving the reaction efficiency.
By way of example, the stainless steel capillary liquid tube 12 described herein has an inner diameter of 0.3 to 1.5mm; the tail end (the upper part is close to the outlet end) of the gas pipeline 11 is provided with a gas distributor 14, and the outlet ends of the gas pipeline 11 and the stainless steel capillary pipeline 12 are positioned in the gas distributor 14 and are in sealing connection with the gas distributor 14 (only through micropore discharge of the gas distributor); the purpose and effect of the gas distributor are that the reaction materials can be enabled to run upwards in a more dispersed mode, and the inner diameter area of the furnace tube is distributed as much as possible, so that the sufficient heating and mixing are obtained, and the reaction is more thorough.
As an example, the gas distributor 14 is disposed in the furnace tube 22 for catalytic cracking, and the temperature in the gas distributor 14 is controlled between 300 ℃ and 500 ℃; the temperature here is the temperature in the gas distributor, which is set so that the material in the gas distributor is more evenly mixed by gasification and then blown into the reaction zone, so that the reaction is more complete. By way of example, the gas distributor 14 described herein is comprised of a porous nickel mesh, copper mesh, titanium mesh, or microporous ceramic; the structure can make the dispersion more uniform and the reaction more sufficient.
As an example, the floating catalytic cracking device 2 described in the application includes a heating furnace body 21 and a built-in furnace tube 22, wherein the heating furnace body 21 is composed of heating elements 23 (heating units are used for heating the furnace body) such as silicon molybdenum rods or silicon carbon rods and polycrystalline alumina fiber insulation materials, the heating temperature of the heating furnace body 21 is 1100-1400 ℃, and the length of a heating zone is 300-1000 mm (the heating furnace body is coated on the outer side of the furnace tube and is arranged along the axial direction of the furnace tube in a central way and is coated with a furnace tube with partial length); the furnace tube 22 of the floating catalytic cracking device 2 is made of corundum tubes or silicon carbide tubes, and the like, and the diameter (inner diameter) of the furnace tube 22 is 60-500 mm, and the length is 1000-3000 mm; by adopting the structure, a low-position region (or a heat preservation region) close to two ends and a high-temperature region or a heating region which is positioned in the middle are formed in the axial length of the furnace tube, the high-temperature region is externally covered with a heating furnace body so as to realize a high-temperature heating function, the two ends are not covered by the heating furnace body, and the low-temperature region or the heat preservation region which is compared with the high-temperature region can be realized through heat preservation measures and temperature control measures; the gas flow dispersing disc is arranged in a critical area of a high-temperature area and a heat-preserving area (low-temperature area) at the upper part of the furnace tube, the area can enable materials conveyed from a gas-liquid supply device below to fully react, the reaction is not disturbed, a final single-wall carbon nano tube is not formed in the critical area, and a continuous stable turbulence or vortex is formed by randomly dispersing a gas flow output by a process gas flow through the gas flow dispersing disc at the tail end of the high-temperature area; therefore, the scheme of the method is essentially different from the reported floating catalytic method, the method enables the catalyst and the carbon-containing free radicals to be in contact in a high-temperature area more fully, the defect that the carbon nano tube grows along the tube wall in the traditional floating catalytic cracking method is overcome, the utilization rate of the catalyst and the conversion rate of the carbon source are greatly improved, and the volume growth is easier to realize.
As shown in fig. 1-2 and 7, the product collecting device 3 described in the present application includes a collecting tank 31, a blowback chamber 32, a microporous filter plate 33, and an air extracting device (only need to omit a device for conventionally implementing air flow extraction, such as an air extracting pump); the back blowing cavity 32 is communicated with a discharge pipeline of the floating catalytic cracking device 2, the microporous filter plate 33 is positioned above the discharge pipeline, and an air outlet (air outlet) 34 of the air extracting device is positioned above the microporous filter plate 33; the collecting tank 21 is positioned below the back blowing cavity 32; a narrowed channel is arranged between the collecting tank and the back blowing cavity, so that materials are prevented from being back-pumped out of the collecting tank; by adopting the connection mode, the air extraction device and the air outlet can be used for extracting air, so that the air flow drives the product to be attached to the bottom surface of the microporous filter plate, and the collection of the product is realized; when excessive products are attached to the bottom surface of the microporous filter plate, the products can be blown towards the microporous filter plate reversely through the outlet gas, so that the products can be discharged into the collecting tank.
As an example, the microporous filter plate 33 described in the present application may be a microporous titanium plate, a microporous copper plate, or the like made of metal, or may be a sand core filter plate made of ceramic.
The application also provides a method for preparing the single-walled carbon nanotube by using the device for preparing the single-walled carbon nanotube by reverse flow floating catalysis, which specifically comprises the following steps:
(1) Connecting a gas-liquid pipeline, and installing a reverse airflow device at a set position in a furnace tube of the floating catalytic cracking device;
(2) Introducing process gas for evacuation, and setting a process temperature according to process requirements;
(3) Preserving heat for 25-40min after the set temperature is reached;
(4) Starting a gas-liquid supply device, feeding according to a certain gas flow speed and a certain liquid supply speed, setting the gas flow of a reverse gas flow device, and starting to synthesize the single-walled carbon nanotubes;
(5) And collecting the product into a collecting tank to obtain the target product of the single-walled carbon nanotube.
As an example, the gas flow rate of the reverse gas flow device is 50% -120% of the gas flow rate of the gas-liquid supply device; because if the flow rate of the reverse gas is too low, the contact between the catalyst and the carbon-containing free radicals in the high temperature area is insufficient, and the result is not much different from that of the traditional floating catalytic cracking; if the flow rate of the reverse airflow is too high, the airflow speed in the high temperature area is too high, the growth time of the carbon nano tube is shorter, and the yield is reduced.
As an example, the process gas or the gas in the gas flow dispersing plate described in the present application is one or a mixture of several of nitrogen, argon, helium and hydrogen, preferably argon.
As an example, the process temperature described in step (2) of the present application is: the temperature in the high temperature cavity is 1100-1500 ℃ (namely the temperature range set by the high temperature zone in the furnace tube of the floating catalytic cracking device).
In the present application, the liquid supply in step (4) is an organic liquid precursor, which may be a formulation reported in literature and known patents for synthesizing single-walled carbon nanotubes, and generally includes a carbon source, a catalyst, an accelerator, an etchant, and the like. The carbon source is liquid carbon source such as ethanol, methanol, toluene, xylene, tetrahydrofuran, benzene, n-hexane, cyclohexane, etc., or gaseous carbon source such as methane, acetylene, etc.; the catalyst is generally ferrocene, nickel-cyclopentadienyl, cobalt-cyclopentadienyl, ferric trichloride, carbonyl iron, ferric lactate and the like (the solid catalyst can be placed at a specific position in the furnace tube in advance, and if the solid catalyst is gas, the solid catalyst is conveyed into the furnace tube through a gas pipeline); the accelerator is typically a sulfur-containing compound such as thiophene.
In the application, the gas and liquid flow rates of the gas and liquid supply device are consistent with the technological parameters reported in the literature and known patents for synthesizing the single-walled carbon nanotubes, and the parameters are different under the influence of the formula and the diameter of the furnace tube.
If the catalyst is solid, the catalyst can be firstly placed in the furnace tube, and then the gas material is introduced into the furnace tube through the gas pipeline and the liquid material through the stainless steel capillary liquid pipeline; the main innovation point of the application is the arrangement of the reverse airflow device and the control of the proportion relation between the air inlet speed and the process airflow; the materials for preparing the single-walled carbon nanotubes can be all existing materials.
The single-walled carbon nanotubes were prepared by the following specific examples and the above-described apparatus:
organic precursor formula (mass ratio): methanol/benzene/ferrocene/thiophene = 90/10/2.5/1;
the floating catalytic cracking device is as follows: a silicon molybdenum rod heating furnace, wherein the heating temperature zone is 300mm long; the furnace tube is a 99 corundum tube (temperature resistant 1650 ℃, outer diameter 80mm, inner diameter 70 mm) and length 1 meter (1000 mm); the gas distributor is a porous copper net, the reverse gas flow device is fixed by penetrating from the product outlet end to the edge of the high temperature region (the initial end surface is positioned at the critical position of the high temperature region and the heat preservation region), the inner diameter of a gas guide pipe of the reverse gas flow device is 8mm, the material is 310S, and the gas guide pipe is tightly attached to the inner wall of the heating furnace tube; the air flow dispersing disc of the reverse air flow device in some embodiments is a convection air flow dispersing disc (shown in figures 1-3), the outer diameter of the convection air flow dispersing disc is 40mm, one side of the air outlet is made of a microporous titanium plate, and the aperture is 10um; the air flow dispersing plate of the reverse air flow device of some embodiments is a vertical flow air flow dispersing plate (shown in fig. 4 and 7-8), the length is 60mm, the outer diameter is 68mm, the wall thickness of the cylinder is 10mm (the difference between the integral radial outer wall and the inner wall), the inner diameter of the air guide pipe is 10mm, and the inner wall is provided with a microporous titanium plate and the microporous diameter is 10um.
Raman testing uses a laser confocal raman spectroscopy system, 532nm single mode laser, band range: 531-632nm, wavenumber range: -20-2800cm -1 The intensity ratio of the D peak to the G peak is obtained by comparing the intensity ratio of wave numbers near 1350 and 1580, and the disorder degree and defect concentration of the carbon nano tube are evaluated; and (3) evaluating radial respiration modes (RBM) of the single-walled carbon nanotubes by observing Raman signals between 100 and 300 wave numbers to obtain diameter information.
Example 1
The vertical floating catalytic cracker shown in figure 1 was used, and the reverse flow apparatus shown in figure 3 was used.
Step one: connecting the gas-liquid pipeline, and installing a reverse airflow device at a set position in the furnace tube;
step two: argon is introduced to empty, and the temperature of the heating furnace is set to 1450 ℃;
step three: preserving the heat for 30min after the set temperature is reached;
step four: opening a gas-liquid supply device, setting the liquid inlet speed to be 1.0g/min, and setting the flow of gas, namely argon to be 1.5L/min; setting the argon flow of a reverse airflow device to be 1.0L/min, and starting to synthesize the single-walled carbon nanotubes;
step five: collecting the product into a collection tank;
after the preparation is completed, detection and knowing: the yield of the single-walled carbon nanotubes of this example was 4.1g/h, the conversion of carbon source was 6.83% and the purity of TGA analysis was 84%; FIG. 9 is a photograph showing a specific product of single-walled carbon nanotubes prepared in this example, and Raman spectrum analysis of FIG. 10 shows that Raman I D /I G 0.13, RBM peak position 138cm -1 The diameter of the single-walled carbon nanotubes was found to be about 1.8nm as calculated by d=248/ω.
Example 2
The vertical floating catalytic cracker shown in fig. 7 was used, and the reverse air flow apparatus shown in fig. 4 and 8 was used.
Step one: connecting the gas-liquid pipeline, and installing a reverse airflow device at a set position in the furnace tube;
step two: argon is introduced to empty, and the temperature of the heating furnace is set to 1450 ℃;
step three: preserving the heat for 30min after the set temperature is reached;
step four: opening a gas-liquid supply device, setting the liquid inlet speed to be 1.0g/min and the argon flow to be 1.5L/min; setting the argon flow of a reverse airflow device to be 1.0L/min, and starting to synthesize the single-walled carbon nanotubes;
step five: collecting the product into a collection tank;
the single-walled carbon nanotubes of this example had a yield of 3.7g/h, a carbon source conversion of 6.17%, a TGA analytical purity of 82%, I D /I G 0.15.
Example 3
The horizontal floating catalytic cracker shown in figure 2 was used, and the reverse flow apparatus shown in figure 3 was used.
Step one: connecting the gas-liquid pipeline, and installing a reverse airflow device at a set position in the furnace tube;
step two: argon is introduced to empty, and the temperature of the heating furnace is set to 1450 ℃;
Step three: preserving the heat for 30min after the set temperature is reached;
step four: opening a gas-liquid supply device, setting the liquid inlet speed to be 1.0g/min and the argon flow to be 1.5L/min; setting the argon flow of a reverse airflow device to be 1.0L/min, and starting to synthesize the single-walled carbon nanotubes;
step five: collecting the product into a collection tank;
the single-walled carbon nanotubes of this example had a yield of 3.9g/h, a carbon source conversion of 6.5%, a TGA analytical purity of 83%, I D /I G 0.14.
Example 4
The horizontal floating catalytic cracker shown in figure 2 was used, and the reverse flow apparatus shown in figure 4 was used.
Step one: connecting the gas-liquid pipeline, and installing a reverse airflow device at a set position in the furnace tube;
step two: argon is introduced to empty, and the temperature of the heating furnace is set to 1450 ℃;
step three: preserving the heat for 30min after the set temperature is reached;
step four: opening a gas-liquid supply device, setting the liquid inlet speed to be 1.0g/min and the argon flow to be 1.5L/min; setting the argon flow of a reverse airflow device to be 1.0L/min, and starting to synthesize the single-walled carbon nanotubes;
step five: collecting the product into a collection tank;
the single-walled carbon nanotubes of this example had a yield of 3.6g/h, a carbon source conversion of 6%, a TGA analytical purity of 79%, I D /I G 0.17.
Example 5
The vertical floating catalytic cracker shown in figure 1 was used, and the reverse flow apparatus shown in figure 3 was used.
Step one: connecting the gas-liquid pipeline, and installing a reverse airflow device at a set position in the furnace tube;
step two: argon is introduced to empty, and the temperature of the heating furnace is set to 1450 ℃;
step three: preserving the heat for 30min after the set temperature is reached;
step four: opening a gas-liquid supply device, setting the liquid inlet speed to be 1.0g/min and the argon flow to be 1.5L/min; setting the argon flow of the reverse airflow device to be 0.75L/min, and starting to synthesize the single-walled carbon nanotubes;
step five: collecting the product into a collection tank;
the single-walled carbon nanotubes of this example had a yield of 1.9g/h, a carbon source conversion of 3.17%, a TGA analytical purity of 76%, and a Raman I D /I G 0.31.
Example 6
The vertical floating catalytic cracker shown in figure 1 was used, and the reverse flow apparatus shown in figure 3 was used.
Step one: connecting the gas-liquid pipeline, and installing a reverse airflow device at a set position in the furnace tube;
step two: argon is introduced to empty, and the temperature of the heating furnace is set to 1450 ℃;
step three: preserving the heat for 30min after the set temperature is reached;
step four: opening a gas-liquid supply device, setting the liquid inlet speed to be 1.0g/min and the argon flow to be 1.5L/min; setting the argon flow of a reverse airflow device to be 1.8L/min, and starting to synthesize the single-walled carbon nanotubes;
Step five: collecting the product into a collection tank;
the single-walled carbon nanotubes of this example had a yield of 2.1g/h, a carbon source conversion of 3.5%, a TGA analytical purity of 75%, and a Raman I D /I G 0.39.
Comparative example 1
Comparative example 1 corresponds to example 1 with the difference that no counter current air flow device was installed;
the single-wall carbon nano tube powder prepared in the comparative example has the yield of 0.6g/h, the conversion rate of carbon source of 1 percent, the purity of 70 percent and I D /I G 0.45.
Comparative example 2
Comparative example 2 corresponds to example 1, except that the reversing air flow device was completely installed in the high temperature zone (i.e., the length of the section of furnace tube covered by the highest temperature of the heating rod of the furnace);
the single-walled carbon nanotube powder prepared in this comparative example had a yield of 0.3g/h, a carbon source conversion of 0.5%, a purity of 53% and an ID/IG of 0.78.
Comparative example 3
Comparative example 3 was identical to example 1 except that the argon flow of the reverse flow apparatus was 0.2L/min;
the single-wall carbon nano tube powder prepared in the comparative example has the yield of 0.7g/h, the conversion rate of carbon source of 1.16 percent, the purity of 64 percent and I D /I G 0.51.
Comparative example 4
Comparative example 4 was identical to example 1 except that the argon flow of the reverse flow apparatus was 3L/min;
The single-wall carbon nano tube powder prepared in the comparative example has the yield of 0.9g/h, the conversion rate of carbon source of 1.5 percent, the purity of 68 percent and I D /I G 0.47.
Comparative example 5
Comparative example 5 is identical to example 1 in steps except that the gas flow dispersion plate of the counter-current gas flow device is a counter-current gas flow dispersion plate, and the outer diameter of the dispersion plate is 20mm (which is far smaller than the inner diameter of the furnace tube);
the single-wall carbon nano tube powder prepared in the comparative example has the yield of 1.4g/h, the conversion rate of carbon source of 2.3 percent and the purity of 72 percent, I D /I G 0.41.
Comparative example 6
Comparative example 6 was identical to example 1 except that the gas flow dispersion plate of the counter-current gas flow device was a counter-current gas flow dispersion plate, the pore diameter of the dispersion plate was 1um, and the porosity was 30%;
the single-wall carbon nano tube powder prepared in the comparative example has the yield of 1.7g/h, the conversion rate of carbon source of 2.8 percent, the purity of 74 percent and I D /I G 0.39.
Comparative example 7
Comparative example 7 was identical to example 1 except that the reverse air flow device did not use a microporous dispersion plate and the air duct was directly supplied with air;
the single-wall carbon nano tube powder prepared in the comparative example has the yield of 0.7g/h, the conversion rate of carbon source of 1.16 percent and the purity of 59 percent,I D /I G 0.59.
Results: from the results of examples 1 to 6, it was found that the reverse flow apparatus used was capable of synthesizing single-walled carbon nanotubes with higher yield and purity within the parameters set in the present application. From examples 1 and 2, the results of the convective gas flow dispersion plate were slightly better than those of the vertical gas flow dispersion plate, since the convective catalyst and the carbon-containing radical were mixed more thoroughly, and the productivity was slightly higher. As can be seen from the comparison results of examples 1, 3 and 2 and 4, the reverse airflow device is introduced into the horizontal floating catalytic cracker and the vertical floating catalytic cracker, so that single-walled carbon nanotubes with high yield can be synthesized. Example 5 and example 6, the adjustment of the gas flow in the counter-current flow device, has a significant effect on the yield of single-walled carbon nanotubes. From a combination of the results of comparative examples 3 and 4, it is found that too low a reverse gas flow rate results in insufficient contact of the catalyst with the carbon-containing radicals in the high temperature zone, resulting in a significant reduction in yield; the excessive reverse airflow can cause the too high airflow speed in the high temperature area, the growth time of the carbon nano tube is shorter, and the yield is also reduced.
Comparative example 1 was not using a countercurrent gas flow apparatus, and the yield of single-walled carbon nanotubes was only 0.7g/h, the conversion of carbon source was 1.16%, which was very different from example 1 (yield 4.1g/h, conversion of carbon source was 6.83%). Comparative example 2 the reverse flow apparatus was completely placed in a high temperature zone, the productivity was lowered and the quality of the product was lowered (single-walled carbon nanotube powder yield of 0.3g/h, carbon source conversion of 0.5%, purity of 53%, I) D /I G 0.78) because the countercurrent gas flow device is mainly used for forming turbulence disturbance, so that the contact efficiency of the catalyst and the carbon-containing free radicals is improved, and when the gas flow dispersion disc is completely placed in a high-temperature area, the turbulence destroys a carbon source and the cracking environment of the catalyst, and has negative effects on the carbon source and the cracking environment, so that the catalyst is oversized, the activity is reduced, and the yield is reduced. Comparative examples 5 to 7 change the structure of the reverse air flow device, resulting in excessively high or excessively low reverse air flow speed, which is unfavorable for air flow disturbance in the high temperature region, resulting in a decrease in yield.
The foregoing description of the preferred embodiment of the present invention is provided for the purpose of illustration only, and is not intended to limit the scope of the present invention, as any modification, equivalent replacement, improvement or the like which comes within the spirit and principles of the present invention.
Claims (16)
1. A device for preparing single-walled carbon nanotubes by reverse flow floating catalysis is characterized in that: the device comprises a gas-liquid supply device, a floating catalytic cracking device and a product collecting device; the gas-liquid supply device is arranged at the tail end of the floating catalytic cracking device and is communicated with the floating catalytic cracking device so as to be used for supplying reaction materials; the head end of the floating catalytic cracking device is communicated with the product collecting device through a pipeline; the floating catalytic cracking device is internally provided with a reverse airflow device which is positioned close to the discharge end in the floating catalytic cracking device and is used for forming axial or radial airflow.
2. The apparatus for preparing single-walled carbon nanotubes by reverse flow floating catalysis according to claim 1, wherein: the end face of the reverse airflow device, which is close to the side of the gas-liquid supply device, is positioned at the critical position of the heating area and the heat preservation area, which are close to the discharge end, in the floating catalytic cracking device; the reverse airflow device comprises an air duct and an airflow dispersing disc, the airflow dispersing disc is arranged in the floating catalytic cracking device and is communicated with the air duct, and the other end of the air duct extends out of the floating catalytic cracking device and is used for conveying air; the air duct is connected with the axial side wall or one end face of the air flow dispersing disc, and the outer wall of the air duct is tightly attached to the inner wall of the floating catalytic cracking device.
3. The apparatus for preparing single-walled carbon nanotubes by reverse flow floating catalysis according to claim 2, wherein: the air duct is a 310S stainless steel pipe, a corundum pipe, a quartz pipe or a graphite pipe; the inner diameter of the air guide pipe is 6-12 mm, and the wall thickness is 0.5-2 mm.
4. The apparatus for preparing single-walled carbon nanotubes by reverse flow floating catalysis according to claim 2, wherein: the air flow dispersing plate is a convection type air flow dispersing plate or a vertical flow type air flow dispersing plate.
5. The apparatus for preparing single-walled carbon nanotubes by reverse flow floating catalysis according to claim 4, wherein: the diameter of the convection type airflow dispersing disc is 1/2-2/3 of the inner diameter of the inner cavity of the floating catalytic cracking device, the placing position is arranged at the critical position of the heating area and the heat preservation area and is arranged in the middle, and the axial length of the convection type airflow dispersing disc is 12-50mm; the vertical flow type airflow dispersing disc is hollow cylinder, and the outer diameter of the vertical flow type airflow dispersing disc is equal to the inner diameter of the inner cavity of the floating catalytic cracking device; the wall thickness of the hollow cylinder type vertical flow type airflow dispersing disc is 10-20 mm, the inner wall of the hollow cylinder type vertical flow type airflow dispersing disc is a microporous titanium plate, a microporous stainless steel plate, a microporous nickel plate, a microporous corundum plate or a microporous graphite plate, and the microporous direction of the hollow cylinder type vertical flow type airflow dispersing disc extends along the radial direction.
6. The apparatus for preparing single-walled carbon nanotubes by reverse flow floating catalysis according to claim 5, wherein: the convection type air flow dispersing disc is formed by integrally formed high-temperature-resistant alumina ceramic, one axial end or side wall of the convection type air flow dispersing disc is connected with an air duct, the other axial end is an air outlet end face, and a micropore structure is arranged on the air outlet end face, and the air outlet end face is close to the air-liquid supply device; the axial extension length of the vertical flow type airflow dispersing disc is 50-100 mm, and the vertical flow type airflow dispersing disc is arranged at the critical position of the heating area and the heat preservation area at the upper part of the inner cavity of the floating catalytic cracking device.
7. The apparatus for preparing single-walled carbon nanotubes by reverse flow floating catalysis according to claim 5, wherein: the convection type air flow dispersing disc is formed by sealing a stainless steel cavity and a microporous metal plate through a sealing piece, one axial end or a side wall of the convection type air flow dispersing disc is connected with an air duct, and the other axial end surface is an air outlet end surface and is formed by one of a microporous titanium plate, a microporous stainless steel plate, a microporous nickel plate, a microporous corundum plate or a microporous graphite plate.
8. The apparatus for preparing single-walled carbon nanotubes by reverse flow floating catalysis according to claim 6, wherein: the pore diameter of each micropore is 5-30 um, and the porosity is 50% -90%.
9. The apparatus for preparing single-walled carbon nanotubes by reverse flow floating catalysis according to claim 1, wherein: the gas-liquid supply device comprises a gas pipeline, a stainless steel capillary liquid pipeline and a sealing flange plate; the gas pipeline and the stainless steel capillary liquid pipeline are connected with the flange in a sealing way, and the sealing flange is connected with the feeding end of the floating catalytic cracking device through a high-temperature sealing ring.
10. The apparatus for preparing single-walled carbon nanotubes by reverse flow floating catalysis according to claim 9, wherein: the gas pipeline surrounds the periphery of the stainless steel capillary liquid pipeline, the outlet end of the stainless steel capillary liquid pipeline extends out of the outlet end of the gas pipeline along the axial direction, and the distance between the outlet ends of the gas pipeline and the stainless steel capillary liquid pipeline is 5-20 mm; the inner diameter of the stainless steel capillary liquid pipeline is 0.3-1.5 mm; the outlet end of the gas pipeline is provided with a gas distributor, and the outlet ends of the gas pipeline and the stainless steel capillary are both positioned in the gas distributor and are in sealing connection with the gas distributor.
11. The apparatus for preparing single-walled carbon nanotubes by reverse flow floating catalysis according to claim 10, wherein: the gas distributor is arranged in the floating catalytic cracking device, and the temperature in the gas distributor is controlled to be 300-500 ℃; the gas distributor consists of a porous nickel net, a copper net, a titanium net or microporous ceramic.
12. The apparatus for preparing single-walled carbon nanotubes by reverse flow floating catalysis according to claim 1, wherein: the floating catalytic cracking device comprises a heating furnace body and a built-in furnace tube, wherein the heating furnace body consists of a silicon-molybdenum rod or silicon-carbon rod heating element and a polycrystalline alumina fiber heat-insulating material, the heating temperature of the heating furnace body is 1100-1400 ℃, and the heating area length is 300-1000 mm; the furnace tube consists of a corundum tube or a silicon carbide tube, and has the diameter of 60-500 mm and the length of 1000-3000 mm.
13. The apparatus for preparing single-walled carbon nanotubes by reverse flow floating catalysis according to claim 1, wherein: the product collecting device comprises a collecting tank, a back blowing cavity, a microporous filter plate and an air extracting device; the back blowing cavity is communicated with a discharge pipeline of the floating catalytic cracking device, the microporous filter plate is positioned above the discharge pipeline, and an air outlet of the air extracting device is positioned above the microporous filter plate; the collecting tank is positioned below the back blowing cavity.
14. The apparatus for preparing single-walled carbon nanotubes by reverse flow floating catalysis according to claim 13, wherein: the microporous filter plate is one of a microporous titanium plate and a microporous copper plate which are made of metal materials.
15. A method for preparing single-walled carbon nanotubes according to the apparatus for preparing single-walled carbon nanotubes by reverse flow floating catalysis according to any of claims 1-14, characterized in that: the method specifically comprises the following steps:
(1) Connecting a gas-liquid pipeline, and installing a reverse airflow device at a set position in a furnace tube of the floating catalytic cracking device;
(2) Introducing process gas for evacuation, and setting a process temperature according to process requirements;
(3) Preserving heat for 25-40min after the set temperature is reached;
(4) Starting a gas-liquid supply device, feeding according to the set gas flow speed and the set liquid supply speed, setting the gas flow of a reverse gas flow device, and starting to synthesize the single-walled carbon nanotubes;
(5) The product was collected into a product collection device.
16. The method of making single-walled carbon nanotubes according to claim 15, wherein: the gas flow of the reverse gas flow device is 50% -120% of the gas flow of the gas-liquid supply device; the process gas or the gas in the gas flow dispersing disc is one or a mixture of more of nitrogen, argon, helium and hydrogen; the process temperature in the step (2) is as follows: the temperature in the high-temperature cavity is 1100-1500 ℃.
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