A system for preparing carbon nanofibers via in-situ CO2 conversion

Abstract

The application discloses a system for preparing carbon nanofibers by in-situ conversion of CO2, and relates to the technical field of carbon nanofiber preparation. The system comprises a first fluidized bed reactor and a second fluidized bed reactor which are connected in series through a gas path, a feeding pipe which is connected to the first fluidized bed reactor and communicates with the second fluidized bed reactor is connected to a discharge port of the second fluidized bed reactor, a discharge pipe is connected to the bottom of the first fluidized bed reactor, the discharge pipe is connected to a carbon nanotube storage bin, the carbon nanotube enters a circulating shearing structure, the shearing structure is connected to a melting structure, and carbon nanofibers are formed by spraying through the melting structure. The system realizes efficient and low-cost preparation of carbon nanofibers through the synergistic effect of two-stage fluidized bed reactors and two-stage melting units, has high integration degree, good resource recycling rate, low process cost and low system energy consumption.

Description

Technical Field

[0001] This invention relates to the field of carbon nanofiber preparation technology, and specifically to a system for preparing carbon nanofibers through in-situ CO2 conversion. Background Technology

[0002] Under the carbon neutrality strategy, converting carbon dioxide into high-value-added nanomaterials has become a research hotspot. Chemical vapor deposition (CVD) is currently the mainstream process for preparing carbon nanofibers. This method achieves fiber growth by decomposing carbon-containing gases on the surface of a catalyst under specific conditions. In recent years, with the continuous growth of market demand for nanomaterials, the application scope of carbon nanofibers in aerospace, new energy vehicles, and high-end electronic devices has been expanding, placing higher demands on their yield and quality.

[0003] A typical process for preparing carbon nanofibers from carbon dioxide includes raw material pretreatment, catalytic reaction, product separation, and post-treatment. The raw material pretreatment stage requires precise proportioning and purification of carbon dioxide and hydrogen to ensure that the feed gas entering the reactor meets process requirements. The catalytic reaction is mostly carried out in a fixed-bed or fluidized-bed reactor, with the reaction temperature typically maintained at 500℃~800℃ and the pressure at 0.1MPa~2MPa. The catalyst is mainly transition metals and their alloys. In the product separation stage, multi-stage filtration and centrifugation are required to separate the carbon nanofibers from the catalyst. Finally, high-temperature treatment and surface modification are used to obtain the final product.

[0004] However, existing technologies suffer from the following prominent problems: First, traditional fixed-bed reactors have low mass and heat transfer efficiency and uneven gas distribution, resulting in reaction conversion rates generally below 60%, and severe localized catalyst overheating and deactivation. Second, while fluidized-bed reactors improve mass transfer conditions, they suffer from catalyst wear, low product purity, and catalyst lifespan typically not exceeding 200 hours. Third, existing processes are lengthy, with high energy consumption for material transfer between steps, and a lack of effective heat recovery systems, leading to high production costs. Finally, controlling product morphology is difficult, and the wide range of fiber diameter distributions affects product consistency and application performance. These problems severely restrict the industrial-scale promotion and application of carbon nanofiber preparation technology from carbon dioxide.

[0005] Patent document CN117470086A discloses a method for preparing carbon nanofibers based on in-situ growth of carbon nanotubes. This method constructs a carbon nanotube-carbon nanofiber composite structure through catalyst pyrolysis and carbon source pyrolysis. While this method achieves controllable preparation of carbon nanofibers, the preparation process requires multiple high-temperature treatments, resulting in high energy consumption. Furthermore, the use of traditional hydrocarbon gases as the carbon source fails to realize the resource utilization of carbon dioxide.

[0006] Patent document CN116791237A discloses a method for preparing transition metal telluride composite carbon nanofibers, which uses electrospinning and calcination processes to load transition metal telluride nanoparticles into carbon nanofibers. Although this method achieves a uniform distribution of active sites, the material preparation depends on polymer precursors, and the process is complex, making it difficult to achieve large-scale continuous production.

[0007] Therefore, current carbon nanofiber preparation systems still suffer from problems such as low mass transfer efficiency, short catalyst lifespan, difficulty in controlling product morphology, uneven fiber diameter distribution, complex process flow, high system energy consumption, low hydrogen utilization rate, and serious resource waste. These problems severely restrict the industrialization process of carbon dioxide resource utilization. Summary of the Invention

[0008] Given the current problems of complex processes and high energy consumption in carbon nanofiber preparation systems, the purpose of this invention is to provide a system for preparing carbon nanofibers through in-situ CO2 conversion. This system achieves efficient and low-cost preparation of carbon nanofibers through the synergistic effect of a two-stage fluidized bed reactor and a two-stage melting unit. The system has high integration, good resource recycling rate, simple process flow, and low energy consumption.

[0009] This invention is achieved through the following technical solution:

[0010] This application provides a system for preparing carbon nanofibers through in-situ CO2 conversion, comprising a first fluidized bed reactor and a second fluidized bed reactor connected in series via gas paths. CO2 is catalytically hydrogenated to generate mixed olefins, which are then fed into the first fluidized bed reactor to prepare carbon nanotubes. A feed pipe connected to the first fluidized bed reactor is connected to the outlet of the second fluidized bed reactor. A discharge pipe is connected to the bottom of the first fluidized bed reactor, and the discharge pipe is connected to a carbon nanotube storage chamber. The carbon nanotube storage chamber is connected to a shearing structure, which is connected to a melting structure. Carbon nanofibers are formed by spraying through the melting structure.

[0011] Furthermore, the shearing structure includes a first shearer connected to the carbon nanotube storage chamber, the first shearer being connected to an ejector, the ejector being connected to a second shearer, and the second shearer being connected to the molten structure.

[0012] Furthermore, the second shear includes a rotary shear, and a shear material return pipe is connected between the second shear and the jet injector.

[0013] Furthermore, the melting structure includes a primary melter and a secondary melter connected in series. Both the primary and secondary melters are connected to a heat source replenishment structure. A material transport pipeline connecting the shearing structure and the melting structure is connected to a heating structure for the substance to be melted. The heating structure for the substance to be melted is a molten salt heating system.

[0014] Furthermore, the heat source supplementation structure includes hot air ducts connected to the primary melter and the secondary melter. The hot air ducts are connected to fans, and air heating structures are connected to the hot air ducts. The air heating structure is a molten salt heating system. The temperature of the primary melter and the secondary melter can be controlled by adjusting the fan speed to regulate the hot air flow rate. When the temperature of the melting zone deviates from the set value, the fan speed can be adjusted.

[0015] Furthermore, both the first and second fluidized bed reactors are connected to a product separation structure at the top; the outlet pipe of the product separation structure is connected to the catalyst inlet of the second fluidized bed reactor, and a first injector is connected to the outlet pipe; the first injector is connected to a power pipe, a power pump is connected to the power pipe, and the power pipe is connected to the carbon source inlet pipe of the first fluidized bed reactor; a hydrogen inlet pipe is connected to the bottom of the first fluidized bed reactor.

[0016] The product separation structure is a cyclone separator.

[0017] Furthermore, both the first fluidized bed reactor and the second fluidized bed reactor are equipped with a fixed reactor, and the fixed reactor is equipped with a porous gas distribution plate and a flow guide baffle connected to the top of the fixed reactor.

[0018] Furthermore, the outlet end of the product separation structure on the second fluidized bed reactor is connected to an exhaust pipe, which is connected to a catalyst recovery device and a hydrogen recovery device.

[0019] Furthermore, the catalyst recovery device includes a cyclone separator, the top outlet of which is connected to a hydrogen recovery device, and the bottom of which is connected to a catalyst reuse pipeline. The catalyst reuse pipeline is connected to two catalyst reuse branch pipes, which are respectively connected to the first fluidized bed reactor and the second fluidized bed reactor, via a tee connector.

[0020] Furthermore, the hydrogen recovery device includes a second injector connected to a membrane separation unit, which is connected to a pressure swing adsorption (PSA) system. The top of the PSA system is connected to a first hydrogen recycling pipe that is connected to the hydrogen inlet pipe of the first fluidized bed reactor. The bottom of the PSA system and the membrane separation unit is connected to a second hydrogen recycling pipe that is connected to the hydrogen inlet pipe of the second fluidized bed reactor.

[0021] The pressure swing adsorption system is connected to a hydrogen supply pipe at the top. Both the first and second fluidized bed reactors are equipped with heating structures. These heating structures can utilize a molten salt heating system to achieve selective growth of carbon nanotubes by controlling the reaction temperature (500℃~800℃), catalyst concentration, and gas flow rate. The molten salt heating system maintains the reactor's internal temperature at the optimal reaction temperature.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] (1) By connecting a molten structure at the back end of a two-stage fluidized bed reactor, the present invention integrates the carbon dioxide conversion and fiber preparation process, solving the technical problem of separation of reaction and molding processes and complex process in traditional processes. It realizes the direct conversion and continuous molding of carbon nanofibers, with a simple process flow, significantly reduced energy consumption, stable product performance, and is suitable for various working conditions from normal pressure to medium pressure, providing a new technical path for the resource utilization of carbon dioxide.

[0024] (2) The melting structure of the present invention consists of two-stage melters connected in series, so that the carbonaceous product completes basic melting and homogenization in the first stage melter, and then enters the second stage melter for fine conditioning and spinning. Both melters are equipped with a spinning system, which realizes continuous and stable molding of carbon nanofibers, and at the same time can obtain carbon nanofiber products with ideal morphology and consistency.

[0025] (3) The molten structure of the present invention achieves precise control of the microstructure of carbon nanofiber products through the synergistic effect of hot air, thereby improving the quality of the prepared carbon nanofiber products.

[0026] (4) This invention realizes the stepwise catalytic conversion of mixed carbon sources through a two-stage fluidized bed reactor, and achieves efficient utilization of raw materials by using interstage separation and circulation units. It realizes the direct conversion of mixed carbon sources to carbon nanotubes, improves the conversion rate of mixed carbon sources, and also improves the quality of products. The process is simple, energy consumption is significantly reduced, and product performance is stable. This system is suitable for various working conditions from negative pressure to medium pressure, and provides a new technical path for the resource utilization of mixed carbon sources.

[0027] (5) In this invention, the first and second fluidized bed reactors connected in series can achieve continuous feeding. The first fluidized bed reactor achieves catalytic activation of the mixed carbon source to obtain carbon nanotubes and some intermediate products. The formed intermediate products enter the second fluidized bed reactor to continue the reaction and generate carbon nanotubes. The reaction is completed through continuous feeding and discharging. The gas-solid separation is achieved through the interstage separation structure, and the separated catalyst is returned to the reaction system for reuse.

[0028] (6) The fluidized bed reactor of the present invention is equipped with a porous gas distribution plate to ensure that the reaction gas is uniformly distributed in the bed. At the same time, the staggered flow guide plates inside the reactor can effectively prolong the gas-solid phase contact time and improve the raw material conversion efficiency. Meanwhile, the flow guide baffles enhance the airflow disturbance, enabling the reactants to diffuse rapidly to the catalyst active sites. This strong turbulent environment ensures high mass transfer efficiency, allowing the carbon source gas to be rapidly cracked and deposited, thereby achieving high-speed growth of carbon nanotubes.

[0029] (7) The hydrogen recovery device connected in this invention can perform membrane separation and pressure swing adsorption separation on unreacted gas and then return it to the fluidized bed reactor for reuse, thereby improving the utilization rate of raw materials. Through the synergistic effect of dual reactors in series and raw material recycling, the product quality and production efficiency are significantly improved. It has the advantages of high conversion rate and good product consistency. Compared with the traditional single reactor, the process investment cost of this reactor is reduced by more than 40% and the energy consumption is reduced by more than 35% when it is applied, providing a reliable technical approach for the high-value utilization of mixed carbon sources.

[0030] (8) The ejector in this invention is the core power structure. It uses a high-pressure power gas source to generate a vacuum effect, providing stable gas flow power for the entire reaction system. The ejector ensures that the reactants form a stable sulfidation state in the fluidized bed reactor by precisely controlling the gas flow rate and pressure parameters, while realizing the efficient recycling of unreacted gas.

[0031] (9) The system in this invention is stable, energy-efficient, safe and reliable. It can process mixed carbon source raw materials of different concentrations. The system has wide raw material adaptability and high operational flexibility. It is suitable for various process conditions such as negative pressure, normal pressure, pressurization or vacuum. The preparation system is flexible in regulation and has high production efficiency.

[0032] (10) The present invention achieves fully enclosed material transportation through a complete pipeline network, which effectively prevents pollution and improves the purity of the product. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the structure of a system for preparing carbon nanofibers by in-situ conversion of CO2 according to the present invention;

[0035] Figure 2 This is a schematic diagram of the structure of a stationary reactor;

[0036] Figure 3 A cross-sectional view of the gas distribution column at the top of the fixed reactor;

[0037] Figure 4 This is a top view of a stationary reactor.

[0038] Figure label:

[0039] 01-Hydrogen inlet pipe, 02-Heating structure, 03-First fluidized bed reactor, 04-Porous gas distribution plate, 05-Fixed reactor, 06-Baffle plate, 07-First cyclone separator, 08-First hydrogen recovery pipe, 09-Catalyst recovery pipe, 10-Second cyclone separator, 11-Hydrogen replenishment pipe, 12-Pressure swing adsorption system, 13-Secondary membrane separation unit, 14-First-stage membrane separation unit, 15-Second hydrogen recovery pipe, 16-Second injection 17-Second fluidized bed reactor, 18-First ejector, 19-Power pump, 20-Power pipe, 21-Carbon source inlet pipe, 22-Feed pipe, 23-Carbon nanotube storage bin, 24-First shearer, 25-Ejector, 26-Shear material return pipe, 27-Second shearer, 28-First stage melter, 29-Second stage melter, 30-Material return pipe, 31-Fan, 32-Hot air pipe, 33-Carbon dioxide reaction chamber, 34-Gas distribution column. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. The illustrative embodiments and descriptions of this invention are only used to explain this invention and are not intended to limit this invention.

[0041] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known materials or methods have not been specifically described in order to avoid obscuring the invention.

[0042] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases "an embodiment," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described herein, as well as the features of those different embodiments or examples.

[0043] In this application, unless otherwise stated, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "middle," "vertical," "horizontal," "lateral," and "longitudinal," etc., generally refer to the directions shown in the drawings or describe the relative positional relationships of the components in a vertical, perpendicular, or gravitational direction. They are used only to describe the relative positional relationships between the components or constituent parts and do not specifically limit the specific installation orientation of each component or constituent part. "Inner" and "outer" generally refer to the interior or exterior of the cavity relative to the chamber or the radial interior or exterior relative to the center of a circle. The above directional terms are defined for ease of understanding of the present invention and therefore do not constitute a limitation on the scope of protection of the present invention.

[0044] Furthermore, in addition to indicating location or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in some cases to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0045] Furthermore, the terms "installation," "setup," "equipped with," "connection," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral structure; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0046] Furthermore, the structures, proportions, sizes, etc., drawn in the accompanying drawings of this application are only used to complement the content disclosed in the specification for those skilled in the art to understand and read, and are not intended to limit the conditions under which this application can be implemented. Therefore, they have no substantial technical significance. Any modification to the structure, change in the proportional relationship, or adjustment of the size, without affecting the effects and purposes that this application can produce, should still fall within the scope of the technical content disclosed in this application.

[0047] Example

[0048] like Figure 1 As shown, this embodiment provides a system for preparing carbon nanofibers through in-situ CO2 conversion, including a first fluidized bed reactor 03 and a second fluidized bed reactor 17 connected in series via gas paths. CO2 is catalytically hydrogenated to generate mixed olefins, which are then fed into the first fluidized bed reactor 03 to prepare carbon nanotubes. A feed pipe 22 connected to the first fluidized bed reactor 03 is connected to the outlet of the second fluidized bed reactor 17. An outlet pipe is connected to the bottom of the first fluidized bed reactor 03, which in turn connects to a carbon nanotube storage chamber 23. The carbon nanotube storage chamber 23 is connected to a shearing structure, which in turn connects to a melting structure. Carbon nanofibers are formed by spraying through the melting structure. Multiple feed pipes can be connected to the carbon nanotube storage chamber 23 to replenish the carbon nanotube material within it.

[0049] Specifically, the shearing structure includes a first shearer 24 connected to the carbon nanotube storage chamber 23, a jet injector 25 connected to the first shearer 24, a second shearer 27 connected to the jet injector 25, and a molten structure connected to the second shearer 27. The second shearer 27 is a rotary shearer, and a shearing material return pipe 26 connects the second shearer 27 and the jet injector 25. The jet injector 25 is a high-speed jet injector 25.

[0050] Specifically, the melting structure includes a primary melter 28 and a secondary melter 29 connected in series. Both the primary melter 28 and the secondary melter 29 are connected to a heat source supplementation structure. A material transport pipe connecting the shear structure and the melting structure is connected to a heating structure 02 for the substance to be melted. The heating structure 02 for the substance to be melted is a molten salt heating system. The heat source supplementation structure includes a hot air duct 32 connected to the primary melter 28 and the secondary melter 29. A fan 31 is connected to the hot air duct 32, and an air heating structure 02 is connected to the hot air duct 32. The air heating structure 02 is also a molten salt heating system.

[0051] The molten structure consists of two series-connected melters. The carbonaceous product undergoes basic melting and homogenization in the first melter 28, followed by fine conditioning and spinning in the second melter 29. Both melters are equipped with spinnerets, enabling continuous and stable formation of carbon nanofibers and yielding carbon nanofiber products with ideal morphology and consistency. Through the synergistic effect of hot air, the molten structure achieves precise control over the microstructure of the carbon nanofiber product, improving the quality of the prepared carbon nanofiber product.

[0052] Specifically, both the first fluidized bed reactor 03 and the second fluidized bed reactor 17 are connected to a product separation structure at their tops. The outlet pipe of the product separation structure is connected to the catalyst inlet of the second fluidized bed reactor 17, and a first injector 18 is connected to the outlet pipe. The first injector 18 is connected to a power pipe 20, and a power pump 19 is connected to the power pipe 20. The power pipe 20 is connected to the carbon source inlet pipe 21 of the first fluidized bed reactor 03. A hydrogen inlet pipe 01 is connected to the bottom of the first fluidized bed reactor 03. The product separation structure is a cyclone separator.

[0053] Specifically, a fixed reactor 05 is installed in both the first fluidized bed reactor 03 and the second fluidized bed reactor 17. A porous gas distribution plate 04 is installed in the fixed reactor 05, and a flow guide baffle 06 is connected to the top of the fixed reactor 05.

[0054] Among them, such as Figures 2-4 As shown, the fixed reactor 05 includes a carbon dioxide reaction chamber 33, a porous gas distribution plate 04 is disposed on the top of the carbon dioxide reaction chamber, and multiple gas distribution columns 34 are connected to the porous gas distribution plate 04.

[0055] The porous gas distribution plate 04 ensures uniform distribution of reactant gases within the bed. Meanwhile, the staggered baffles inside the reactor effectively extend the gas-solid contact time, improving feed conversion efficiency. Simultaneously, the baffle 06 enhances airflow turbulence, allowing reactants to rapidly diffuse to the catalyst's active sites. This highly turbulent environment ensures high mass transfer efficiency, enabling rapid cracking and deposition of the carbon source gas, thus achieving high-speed carbon nanotube growth. Furthermore, the surface of the baffle 06 forms a synergistic interaction surface with the reactor's inner wall, increasing the reaction interface area, enhancing the system's mass and heat transfer efficiency, and significantly improving energy utilization efficiency.

[0056] Specifically, the outlet end of the first cyclone separator 07 on the second fluidized bed reactor 17 is connected to an exhaust pipe, which is connected to a catalyst recovery device and a hydrogen recovery device.

[0057] The catalyst recovery device includes a second cyclone separator 10. The top outlet of the second cyclone separator 10 is connected to a hydrogen recovery device, and the bottom is connected to a catalyst reuse pipe 09. The catalyst reuse pipe 09 is connected to two catalyst reuse branch pipes that are respectively connected to the first fluidized bed reactor 03 and the second fluidized bed reactor 17 via a tee connector.

[0058] The hydrogen recovery device includes a second injector 16, which is connected to a membrane separation unit. The membrane separation unit is connected to a pressure swing adsorption (PSA) system 12. The top of the PSA system 12 is connected to a first hydrogen recycling pipe 08, which is connected to the hydrogen inlet pipe 01 of the first fluidized bed reactor 03. The bottom of the PSA system 12 and the membrane separation unit is connected to a second hydrogen recycling pipe 15, which is connected to the hydrogen inlet pipe 01 of the second fluidized bed reactor 17.

[0059] The membrane separation unit consists of a primary membrane separation unit 14 and a secondary membrane separation unit 13, forming a two-stage membrane separation structure. It can recover and purify more than 95% of the hydrogen in the reaction tail gas and return it to the reaction system for recycling.

[0060] By connecting a hydrogen recovery unit, unreacted gases can be separated by membrane separation and pressure swing adsorption and then returned to the fluidized bed reactor for reuse, improving the utilization rate of raw materials. Through the synergistic effect of dual reactors in series and raw material recycling, product quality and production efficiency are significantly improved. It has the advantages of high conversion rate and good product consistency. Compared with traditional single reactors, the process investment cost of this reactor is reduced by more than 40% and energy consumption is reduced by more than 35%, providing a reliable technical approach for the high-value utilization of mixed carbon sources.

[0061] The ejector is the core power structure. It uses a high-pressure power gas source to generate a vacuum effect, providing stable gas flow power for the entire reaction system. The ejector ensures that the reactants form a stable sulfidation state in the fluidized bed reactor by precisely controlling the gas flow rate and pressure parameters, while realizing the efficient recycling of unreacted gases.

[0062] Specifically, a hydrogen supply pipe 11 is connected to the top of the pressure swing adsorption system 12. The purpose of connecting the hydrogen supply pipe to the top of the pressure swing adsorption system 12 is that when the hydrogen in the pressure swing adsorption system 12 cannot meet the hydrogen requirements of the second fluidized bed reactor 17, hydrogen can be added from the outside to the pressure swing adsorption system 12 to meet the reaction requirements of the second fluidized bed reactor 17.

[0063] Specifically, both the first fluidized bed reactor 03 and the second fluidized bed reactor 17 are connected to a heating structure 02. This heating structure 02 is a molten salt heating system, which controls the reaction temperature in the first fluidized bed reactor and the second fluidized bed reactor 17, so that carbon nanotubes are prepared within a suitable temperature range, thereby improving product quality.

[0064] Working principle: When preparing carbon nanofibers using this system, a mixed carbon source is introduced into the first fluidized bed reactor 03 through the carbon source inlet pipe 21 connected to the first fluidized bed reactor 03, and hydrogen is introduced into the first fluidized bed reactor 03 through the hydrogen inlet pipe 01 connected to the first fluidized bed reactor 03. Simultaneously, a catalyst is introduced into the first fluidized bed reactor 03 through the catalyst inlet. Both the mixed carbon source and hydrogen entering the first fluidized bed reactor 03 are first heated by a molten salt heating system connected to the carbon source inlet pipe 21 and the hydrogen inlet pipe 01 before entering the mixed carbon source in the first fluidized bed reactor 03. The feed gas is first uniformly distributed through a porous gas distribution plate 04 to form a stable fluidized state. Simultaneously, it is heated and temperature-controlled by a molten salt heating system connected to a fixed reactor 05. After the feed gas fully reacts in the fixed reactor 05, carbon nanotubes and some intermediate products are generated. After separation by a cyclone separator connected to the top of the first fluidized bed reactor 03, the carbon nanotubes fall downwards through a channel formed between the guide baffle 06 and the wall of the first fluidized bed reactor 03, and are then discharged from the outlet at the bottom of the first fluidized bed reactor 03. The resulting intermediate products or remaining gas enter the second fluidized bed reactor 17 through an inlet pipe. Before entering the second fluidized bed reactor 17, the gas enters the first ejector 18. The first ejector 18 utilizes a high-pressure power gas source to generate a vacuum effect, providing stable gas flow power for the entire reaction system. Simultaneously, through precise control of gas flow rate and pressure parameters, it ensures that the reactants form a stable sulfidation state within the fluidized bed reactor.The intermediate products or residual gas generated in the first fluidized bed reactor 03 are introduced into the second fluidized bed reactor 17 through the first injector 18 for further catalytic reaction. Simultaneously, a mixed carbon source is introduced into the second fluidized bed reactor 17 through the carbon source inlet pipe 21. The hydrogen required in the second fluidized bed reactor 17 comes from the hydrogen recovery system. After the feed gas fully reacts in the second fluidized bed reactor 17, carbon nanotubes are formed, and some intermediate products or residual hydrogen may also be formed. The generated carbon nanotubes can be directly discharged from the bottom outlet of the second fluidized bed reactor 17, or a feed pipe can be connected to the outlet of the second fluidized bed reactor 17 to introduce the carbon nanotubes generated in the second fluidized bed reactor 17 into the first fluidized bed reactor 03, and then discharged together from the bottom outlet of the first fluidized bed reactor 03. The carbon nanotubes are then transported through the feed pipe 22. The material is transported to the carbon nanotube storage chamber 23. When carbon nanofibers need to be prepared, the carbon nanotubes in the storage chamber are first transported to the first shear 24 for primary dispersion, and then enter the high-speed jet injector 25. After being dispersed again in the high-speed jet injector 25, the material enters the second shear 27 (rotary shear) for deep processing. Some of the material returns to the high-speed jet injector 25 through the shear material return pipe 26 for further processing. The homogenized material enters the first-stage melter 28 and the second-stage melter 29 in sequence. The material is first plasticized in the first-stage melter 28, and then enters the second-stage melter 29. With the assistance of hot air, the material is deeply melted. The melted material is directly sprayed through the pipe to form carbon nanofibers, and then enters the pressing device to complete the final shaping before the carbon nanofiber product is output.

[0065] If there is any material that is not completely melted during the carbon nanofiber spraying process, it can be passed through the material return pipe 30 into the primary melter 28 and the secondary melter 29 for remelting.

[0066] In addition, the residual gas after reaction in the second fluidized bed reactor 17 is separated by a cyclone separator and enters the second cyclone separator 10. The second cyclone separator 10 separates the hydrogen and catalyst. The separated hydrogen is then fed into a hydrogen recovery device. The hydrogen first enters the second injector 16, and then enters the primary membrane separation unit 14 and the secondary membrane separation unit 13 for separation and purification, achieving efficient hydrogen recovery. The hydrogen after being processed by the membrane separation unit enters the pressure swing adsorption system 12. When hydrogen needs to be introduced into the second fluidized bed reactor 17, the hydrogen separated in the pressure swing adsorption system 12 can be used, achieving efficient resource utilization. The separated catalyst is then reintroduced into the first fluidized bed reactor 03 and the second fluidized bed reactor 17 for use.

[0067] This invention's carbon nanofiber preparation system integrates carbon dioxide conversion and fiber preparation processes by connecting a melting structure at the rear end of a two-stage fluidized bed reactor. This solves the technical challenges of traditional processes involving the separation of reaction and molding steps and complex processes, enabling direct conversion and continuous molding of carbon nanofibers. The process is simple, energy consumption is significantly reduced, product performance is stable, and it is suitable for various working conditions from atmospheric to medium pressure, providing a new technical path for the resource utilization of carbon dioxide. Compared to traditional stepwise preparation systems, the product fiber diameter uniformity is improved by approximately 40%, tensile strength is increased by approximately 35%, and production energy consumption is reduced by approximately 45%. The high-speed jet injector 25 effectively improves the material dispersion uniformity through a strong turbulent flow field; two sets of shears perform secondary shearing treatment on the carbon nanotubes, further enhancing the nanoscale dispersion effect of the material; the secondary melt strengthening unit optimizes the plasticization process of the material through stepped temperature control; and the direct spraying of the molten carbon nanotubes enables continuous preparation of carbon nanofibers. This integrated design not only significantly improves production efficiency but also significantly reduces energy and raw material consumption.

[0068] Furthermore, in the preparation of carbon nanotubes, a two-stage fluidized bed reactor was used to achieve the stepwise catalytic conversion of mixed carbon sources. The interstage separation and recycling units enabled efficient utilization of raw materials, achieving direct conversion from mixed carbon sources to carbon nanotubes. This improved the conversion rate of mixed carbon sources and also enhanced product quality. The process is simple, energy consumption is significantly reduced, and product performance is stable. This system is suitable for various operating conditions, from negative pressure to medium pressure, providing a new technical path for the resource utilization of mixed carbon sources. In addition, the first fluidized bed reactor 03 and the second fluidized bed reactor 17, connected in series, allow for continuous feeding. The first fluidized bed reactor 03 catalytically activates the mixed carbon source to obtain carbon nanotubes and some intermediate products. The resulting intermediate products enter the second fluidized bed reactor 17 to continue the reaction and generate carbon nanotubes. Continuous feeding and discharging ensure complete reaction. The interstage separation structure achieves efficient gas-solid separation, and the separated catalyst is returned to the reaction system for reuse. Moreover, the system is stable, energy-efficient, safe, and reliable. It can handle mixed carbon source raw materials of different concentrations, has wide raw material adaptability, and high operational flexibility, making it suitable for various industrial conditions. Compared to traditional single-reactor carbon source conversion processes, this reaction system achieves directional pyrolysis and efficient conversion of different carbon source raw materials, improving the yield of carbon nanotubes. The system boasts strong raw material adaptability, a short process flow, and energy consumption that is 25-35% lower than traditional reaction beds. Furthermore, the product exhibits uniform structure and stable quality, making it suitable for large-scale conversion of various mixed carbon source raw materials. The system achieves fully enclosed material transport through a sophisticated pipeline network, effectively preventing contamination and improving product purity.

[0069] Experimental Example 1

[0070] The system of this invention converts captured carbon dioxide into carbon nanofibers. The primary fluidized bed reactor has a diameter of 200 mm and a height of 800 mm, while the secondary fluidized bed reactor has a diameter of 120 mm and a height of 400 mm. The fluidized beds are filled with an iron-based catalyst with particle diameters of 5 μm. The temperature in the primary reaction zone is 650°C, the temperature in the secondary reaction zone is 750°C, and the reaction pressure is 0.5 MPa. The CO2 volume fraction in the feed gas is 20%, and the H2 / CO2 molar ratio is 5:1. The temperature of the secondary melting unit is 1350°C, and the drawing rate is 120 m / min. The resulting carbon nanofibers have a diameter of 150 nm, a tensile strength of 1.2 GPa, and a CO2 conversion rate of 62%.

[0071] Experiment Example 2

[0072] The system of this invention converts captured carbon dioxide into carbon nanofibers. The primary fluidized bed reactor has a diameter of 280 mm and a height of 850 mm, while the secondary fluidized bed reactor has a diameter of 150 mm and a height of 420 mm. The fluidized beds are filled with a cobalt-molybdenum composite catalyst with particle diameters of 12 μm. The temperature in the primary reaction zone is 680°C, the temperature in the secondary reaction zone is 780°C, and the reaction pressure is 0.8 MPa. The CO2 volume fraction in the feed gas is 25%, and the H2 / CO2 molar ratio is 2.5:1. The temperature of the secondary melting unit is 1400°C, and the drawing rate is 150 m / min. The resulting carbon nanofibers have a diameter of 80 nm, a tensile strength of 4.1 GPa, and a CO2 conversion rate of 68%. The overall energy consumption of the system is reduced by 35% compared to traditional processes.

[0073] Experimental Example 3

[0074] The system of this invention converts captured carbon dioxide into carbon nanofibers. The primary fluidized bed reactor has a diameter of 350 mm and a height of 1200 mm, while the secondary fluidized bed reactor has a diameter of 200 mm and a height of 600 mm. A nickel-based catalyst is used. The temperature in the primary reaction zone is 700℃, and the temperature in the secondary reaction zone is 800℃, with a reaction pressure of 1.0 MPa. The CO2 volume fraction in the feed gas is 35%, and the H2 / CO2 molar ratio is 3:1. The temperature of the secondary melting unit is 1450℃, and the drawing rate is 100 m / min. The resulting carbon nanofibers have a diameter of 200 nm, a tensile strength of 2.8 GPa, and a CO2 conversion rate of 85%. The system equipment investment is reduced by 40% compared to traditional separate-unit devices.

[0075] Compared to traditional separate reactive spinning systems, this integrated system achieves continuous control of the catalytic reaction and fiber formation through the synergistic coupling of a fluidized bed reactor and a secondary melting unit. This enhances the thermal integration and mass transfer efficiency of the process, improving the structural regularity and mechanical properties of carbon nanofibers. The integrated system offers high operational flexibility and low energy consumption, reducing investment and energy consumption by 20-50% compared to traditional separate fixed-bed spinning devices. Furthermore, it has broad raw material adaptability and can handle different concentrations of captured carbon dioxide.

[0076] As can be seen from the above experimental examples, the system in this invention achieves directional pyrolysis and efficient conversion of different carbon source materials, thereby improving the yield of carbon nanotubes. This system exhibits strong raw material adaptability, a short process flow, and lower energy consumption compared to traditional reaction beds. Furthermore, the product has a uniform structure and stable quality, making it suitable for the large-scale conversion of various mixed carbon source materials.

[0077] Finally, it should be noted that the specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention. For those skilled in the art, it is obvious that this application is not limited to the details of the above exemplary embodiments, and that the present application can be implemented in other specific forms without departing from the spirit or basic characteristics of the present application. Furthermore, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe various possible combinations separately. Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of this application is defined by the appended claims rather than the foregoing description, and therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included within this application.

Claims

1. A system for preparing carbon nanofibers via in-situ CO2 conversion, characterized in that, The reactor comprises a first fluidized bed reactor (03) and a second fluidized bed reactor (17) connected in series via gas paths. CO2 is catalytically hydrogenated to generate mixed olefins, which are then fed into the first fluidized bed reactor (03) to prepare carbon nanotubes. The outlet of the second fluidized bed reactor (17) is connected to a feed pipe (22) that communicates with the first fluidized bed reactor (03). The bottom of the first fluidized bed reactor (03) is connected to a discharge pipe, which is connected to a carbon nanotube storage chamber (23). The carbon nanotube storage chamber (23) is connected to a shear structure, which is connected to a melting structure. Carbon nanofibers are formed by spraying through the melting structure.

2. The system for preparing carbon nanofibers via in-situ CO2 conversion according to claim 1, characterized in that, The shearing structure includes a first shearer (24) connected to the carbon nanotube storage chamber (23), the first shearer (24) being connected to an ejector (25), the ejector (25) being connected to a second shearer (27), and the second shearer (27) being connected to the molten structure.

3. The system for preparing carbon nanofibers via in-situ CO2 conversion according to claim 2, characterized in that, The second shear (27) includes a rotary shear, and a shear material return pipe (26) is connected between the second shear (27) and the jet (25).

4. The system for preparing carbon nanofibers via in-situ CO2 conversion according to claim 1, characterized in that, The melting structure includes a primary melter (28) and a secondary melter (29) connected in series. Both the primary melter (28) and the secondary melter (29) are connected to a heat source supplementation structure. The material transfer pipeline connected to the shearing structure and the melting structure is connected to a heating structure (02) for the material to be melted.

5. The system for preparing carbon nanofibers via in-situ CO2 conversion according to claim 4, characterized in that, The heat source supplementation structure includes a hot air pipe (32) connected to the primary melter (28) and the secondary melter (29), the hot air pipe (32) is connected to a fan (31), and an air heating structure (02) is connected to the hot air pipe (32).

6. The system for preparing carbon nanofibers via in-situ CO2 conversion according to claim 1, characterized in that, The top of the first fluidized bed reactor (03) and the second fluidized bed reactor (17) are both connected to a product separation structure; the gas outlet of the product separation structure is connected to the catalyst inlet of the second fluidized bed reactor (17), and a first injector (18) is connected to the gas outlet; the first injector (18) is connected to a power pipe (20), and a power pump (19) is connected to the power pipe (20); the power pipe (20) is connected to the carbon source inlet pipe (21) of the first fluidized bed reactor (03); a hydrogen inlet pipe (01) is connected to the bottom of the first fluidized bed reactor (03).

7. The system for preparing carbon nanofibers via in-situ CO2 conversion according to claim 6, characterized in that, Both the first fluidized bed reactor (03) and the second fluidized bed reactor (17) are equipped with a fixed reactor (05). The fixed reactor (05) is equipped with a porous gas distribution plate (04), and the top of the fixed reactor (05) is connected to a flow guide baffle (06).

8. The system for preparing carbon nanofibers via in-situ CO2 conversion according to claim 6, characterized in that, The product separation structure on the second fluidized bed reactor (17) is connected to an exhaust pipe at its outlet, and the exhaust pipe is connected to a catalyst recovery device and a hydrogen recovery device.

9. The system for preparing carbon nanofibers via in-situ CO2 conversion according to claim 8, characterized in that, The catalyst recovery device includes a cyclone separator. The top outlet of the cyclone separator is connected to a hydrogen recovery device, and the bottom is connected to a catalyst reuse pipeline (09). The catalyst reuse pipeline (09) is connected to two catalyst reuse branch pipes that are respectively connected to the first fluidized bed reactor (03) and the second fluidized bed reactor (17) through a tee connector.

10. A system for preparing carbon nanofibers via in-situ CO2 conversion according to claim 8, characterized in that, The hydrogen recovery device includes a second injector (16), which is connected to a membrane separation unit. The membrane separation unit is connected to a pressure swing adsorption system (12). The top of the pressure swing adsorption system (12) is connected to a first hydrogen recycling pipe (08) that is connected to the hydrogen inlet pipe (01) of the first fluidized bed reactor (03). The bottom of the pressure swing adsorption system (12) and the membrane separation unit is connected to a second hydrogen recycling pipe (15) that is connected to the hydrogen inlet pipe (01) of the second fluidized bed reactor (17).

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