Device and process for producing ultra-high purity carbon from industrial flue gas co2 by liquid bismuth cathode molten salt electrolysis

Abstract

The application discloses a kind of liquid bismuth cathode molten salt electrolysis industrial flue gas CO2 preparation ultra-high purity carbon equipment and process, belong to industrial waste gas resource utilization and molten salt electrochemistry metallurgy technical field.The equipment includes the industrial flue gas pretreatment dust removal dehydration module, CO2 enrichment pressure regulating gas inlet module, molten salt electrolysis reaction kettle, liquid metal bismuth cathode circulating floating mechanism, inert graphite anode, molten salt constant temperature circulation module and carbon powder automatic collection post-processing module in turn coupling.Process with lithium chloride as electrolyte, with high-purity liquid bismuth or bismuth-based alloy, i.e.Carbon product is automatically floated and separated and is cleaned, dried to obtain ultra-high purity carbon powder under the condition of medium-high temperature and low pressure direct current.The application uses CO2 in industrial waste flue gas as carbon source, raw material cost is extremely low, the purity of obtained carbon powder is high, no metal impurity, electrode passivation in electrolysis process, can long time continuous stable operation.

Description

Technical Field

[0001] This invention relates to the fields of industrial waste gas resource utilization and molten salt electrochemical metallurgy technology, specifically to equipment and process for producing ultra-high purity carbon from industrial flue gas CO2 by molten salt electrolysis with liquid bismuth cathode. Background Technology

[0002] Currently, the fields of carbon dioxide fixation and carbon production, as well as the preparation of high-purity carbon powder, suffer from the following unavoidable technical defects: Traditional high-purity carbon preparation technologies are costly and have low production capacity. Existing 6N-grade ultra-high purity carbon powder mainly relies on processes such as high-temperature graphitization purification, chemical vapor deposition, and ultra-high purity organic precursor pyrolysis. These methods involve expensive equipment investment, extremely high energy consumption, and extremely low production capacity, which cannot meet the needs of large-scale industrial production. Furthermore, the raw material costs are extremely high, making it difficult to use for bulk industrial substrates.

[0003] Conventional CO2 pyrolysis carbon production technologies result in low purity and numerous impurities. Traditional high-temperature thermal pyrolysis and plasma pyrolysis carbon production technologies typically require reaction temperatures above 1400℃, resulting in enormous energy consumption. The resulting carbon powder has high ash content, numerous lattice defects, and a disordered structure, and contains a large amount of amorphous impurities and oxide residues, which completely fails to meet the application requirements of superconducting and low-resistivity resonant carbon substrates.

[0004] Existing molten salt electrolysis technology has fatal flaws. Current molten salt electrolysis carbon production technologies generally use solid metal nickel, iron, or steel-based cathodes. At high temperatures, the metal cathodes undergo carburizing, carbonization, and alloying reactions, and metal impurities continuously precipitate into the carbon powder product. The dense carbon layer covering the electrode surface leads to electrode failure, making continuous production impossible and preventing the production of 6N-grade ultra-high purity carbon free of metal impurities.

[0005] There is a lack of high-value utilization pathways for CO2 from industrial flue gas. Currently, large amounts of CO2 generated from steel mills, chemical plants, heating plants, and various kilns are directly discharged into the atmosphere. Although simple desulfurization and denitrification treatments exist, high-value carbon sequestration technologies are lacking. Existing carbon capture technologies are mainly used for oil displacement or the preparation of low-value-added products such as carbonates, and cannot produce high-value pure carbon substrates. Currently, there is no technology that can achieve continuous, low-cost, and metal-free mass production of 6N-grade ultra-high purity carbon from industrial waste gas under medium- and low-temperature conditions. Summary of the Invention

[0006] The purpose of this invention is to provide an equipment and process for producing ultra-high purity carbon from CO2 produced by industrial flue gas from liquid bismuth cathode molten salt electrolysis, in order to solve the defects of existing technologies such as insufficient purity, serious metal pollution, inability to produce continuously, high energy consumption, expensive raw materials, and inability to utilize waste gas at high value.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a liquid bismuth cathode molten salt electrolysis device for producing ultra-high purity carbon from industrial flue gas CO2, comprising an industrial flue gas pretreatment dust removal and dehydration module, a CO2 enrichment and pressure stabilization inlet module, a molten salt electrolysis reactor, a liquid metal cathode circulation floating mechanism, an inert graphite anode, a molten salt constant temperature circulation module, and a carbon powder automatic collection and post-processing module; the molten salt electrolysis reactor contains chloride molten salt, i.e., binary or ternary eutectic chloride salt, as the electrolyte, and liquid metal cathode is placed at the bottom of the reactor. The cathode layer is composed of liquid metal cathodes selected from high-purity bismuth or bismuth-based alloys, including tin-bismuth alloys. The outlet of the industrial flue gas pretreatment dust removal and dehydration module is connected to the inlet of the CO2 enrichment and pressure stabilization inlet module. The outlet of the CO2 enrichment and pressure stabilization inlet module is connected to the molten salt medium layer at the bottom of the molten salt electrolysis reactor via a gas distributor, allowing CO2 gas to be uniformly dispersed in the molten salt in the form of microbubbles, increasing the gas-liquid contact area and improving the dissolution and ionization efficiency of CO2 in the molten salt. The liquid metal... The cathode circulation floating mechanism is located inside the electrolysis reactor and below the molten salt medium layer, forming a clear liquid-liquid interface between the liquid metal layer and the molten salt medium layer, serving as the core working interface for the electrochemical reduction reaction. The inert graphite anode is vertically inserted into the molten salt medium layer from the top of the electrolysis reactor, forming a closed electrolysis circuit with the liquid metal cathode through an external DC power supply. The molten salt constant temperature circulation module is connected to the jacket or internal heat exchanger of the electrolysis reactor through a circulation pipeline, heating and controlling the temperature of the molten salt system in the reactor to ensure that the electrolysis reaction takes place within a stable temperature window. The material collection inlet of the automatic carbon powder collection and post-processing module is located at the upper liquid surface of the molten salt medium layer inside the electrolysis reactor, used to collect carbon products floating to the liquid surface in real time and transport them to the post-processing process. The above modules are coupled in sequence to form a complete continuous production line from flue gas input to carbon powder output. The equipment adopts a medium-high temperature closed electrolysis structure to realize the continuous reduction and precipitation of carbon dioxide from industrial waste gas and the preparation of ultra-high purity solid carbon powder.

[0008] Preferably, the chloride molten salt is a lithium chloride-potassium chloride binary eutectic chloride salt with a molar ratio of LiCl:KCl = 42:58–48:52 and a melting temperature range of 352℃–380℃; or a lithium chloride-sodium chloride-potassium chloride ternary eutectic chloride salt with a molar ratio of LiCl:NaCl:KCl = 45–55:20–30:20–30 and a melting temperature range of 346℃–400℃. Compared to binary molten salts, ternary molten salts have a lower eutectic temperature and a wider operating temperature window, which is beneficial for controlling the electrolysis reaction rate and the morphology and structure of carbon products over a wider temperature range. This system has high conductivity, low viscosity, good fluidity, strong adsorption and dissolution capacity for CO2, and is stable at high temperatures without decomposition.

[0009] Preferably, the liquid metal cathode uses 99.99% high-purity metallic bismuth or a bismuth-based alloy, i.e., a tin-bismuth alloy. It completely liquefies at the operating temperature to form a floating liquid metal interface. The liquid metal has high surface tension, causing carbon to automatically float and desorb after precipitation, resulting in no metal impurities and no electrode passivation, enabling permanent recycling. The mass ratio of tin to bismuth in the tin-bismuth alloy is 10:90 to 90:10, preferably 43:57 to 57:43. The eutectic temperature of the tin-bismuth alloy is as low as 139℃, and it exhibits good fluidity within an operating temperature range of 450℃ to 700℃. Different tin-bismuth alloy ratios have different effects on the morphology of carbon products; bismuth-rich alloys are beneficial for obtaining plate-like carbon, while tin-rich alloys are beneficial for obtaining spherical or rod-shaped carbon.

[0010] Preferably, the liquid metal cathode is made of 99.99% high-purity bismuth or a bismuth-based alloy, i.e., tin-bismuth alloy, which is completely liquefied at the working temperature to form a floating liquid metal interface. The liquid metal has a high surface tension, and after carbon is deposited, it automatically floats and desorbs, without the precipitation of metal impurities or electrode passivation, thus achieving permanent recycling.

[0011] Preferably, the CO2 enrichment and pressure stabilization intake module adopts a low-pressure membrane enrichment device, which enriches the low-concentration CO2 in the flue gas and then introduces it into the electrolysis reactor in a stable constant pressure manner to ensure stable intake gas concentration and continuous stable electrolysis state.

[0012] Preferably, the automatic carbon powder collection and post-processing module includes a high-temperature resistant ceramic material scooping mechanism, a deionized water washing unit, a dilute hydrochloric acid micro-washing unit, a pure water rinsing unit, and a vacuum drying unit. Each unit is connected in sequence to form a continuous post-processing production line, realizing online continuous collection and purification of carbon powder.

[0013] In summary, the present invention also includes a process using the aforementioned equipment comprising the following steps: S1. Collect flue gas from the tail end of industrial boilers or kilns, and pre-treat it through dust removal, dehydration, impurity removal, and drying to obtain a clean carbon dioxide mixture. S2. CO2 gas is continuously supplied to the closed electrolysis reactor at a constant micro-positive pressure through a membrane enrichment and pressure stabilization system. S3. Heat the chloride molten salt, i.e., binary or ternary eutectic chloride salt, until it is completely melted to establish a stable conductive electrolytic dielectric layer; S4. Add high-purity bismuth or bismuth-based alloy, i.e., tin-bismuth alloy, and heat to melt, forming a liquid cathode layer at the bottom of the reactor; S5. Continuous electrolysis is performed at 400℃~520℃ and 2.2V~2.8V low-voltage DC, with a current density of 0.15~0.35A / cm². 2 Carbon dioxide is reduced at the liquid bismuth interface to precipitate solid carbon, which then automatically floats to the surface of the molten salt. S6. Online continuous collection of surface high-purity carbon powder, followed by cleaning, desalination, and vacuum drying to obtain ultra-high purity carbon finished product.

[0014] Preferably, the electrolysis process is a medium-high temperature reaction, and the maximum operating temperature of the electrolysis is 450℃~700℃. Compared with traditional high-temperature cracking carbon production, the energy consumption of the electrolysis is significantly reduced by more than 60%.

[0015] Preferably, the purity of the carbon powder can reach 99.999% to 99.9999%, and the carbon powder is free of metal impurities and oxide residues. The carbon powder is suitable as a substrate for high-precision carbon-based functional resonant materials. By adjusting the cathode material (pure bismuth or tin-bismuth alloys with different ratios), adjusting the molten salt composition (binary or ternary chloride salts), and adjusting the operating temperature (450℃ to 700℃), the morphology and structure of the carbon products can be controlled to obtain carbon materials with different morphologies such as sheet-like, spherical, rod-like, or dendritic structures. For example, using a pure bismuth cathode with a binary LiCl-KCl molten salt at a lower temperature of 450℃ to 500℃ tends to yield sheet-like carbon; using a tin-rich tin-bismuth alloy cathode with a ternary LiCl-NaCl-KCl molten salt at a higher temperature of 600℃ to 700℃ tends to yield spherical or rod-like carbon.

[0016] Preferably, the molten salt system and the liquid bismuth cathode can be recycled and reused for a long time. The process consumes no consumables and produces no waste. The process directly uses the factory's waste flue gas as raw material to achieve high-value closed-loop carbon sequestration of industrial waste gas carbon dioxide and self-sufficient mass production of ultra-high purity carbon.

[0017] Compared with the prior art, the beneficial effects of the present invention are: The raw material cost is extremely low. This invention directly utilizes carbon dioxide from the waste flue gas emitted by the factory as a carbon source, eliminating the need to purchase high-purity carbon dioxide gas. It transforms the originally discharged waste gas into a high-value raw material, with the raw material acquisition cost approaching zero, while simultaneously solving the carbon emission problem for the factory.

[0018] The product has high purity. The liquid metal cathode (pure bismuth or bismuth-based alloy) is completely liquid at the operating temperature, and has the unique advantages of zero carburization, zero metal leaching and zero electrode contamination. The resulting carbon powder is free of metal impurities and oxide residues, and can reach an ultra-high purity level, which can meet the stringent requirements of high-precision carbon-based functional resonant materials and other high-end applications for substrate purity.

[0019] It enables continuous industrial production. This invention fundamentally solves the fatal flaw of traditional solid cathodes, which require frequent shutdowns for cleaning or electrode replacement due to surface carbon passivation. The liquid bismuth interface remains fresh and clean at all times, allowing the equipment to operate continuously and stably year-round. The production capacity can be flexibly scaled up according to demand, truly realizing the industrial continuous mass production of ultra-high purity carbon materials.

[0020] Energy consumption is significantly reduced. This invention employs a medium-low temperature molten salt electrolysis process, with a maximum operating temperature far lower than the extreme high-temperature conditions required by traditional high-temperature thermal pyrolysis and plasma pyrolysis carbon production technologies. This significantly reduces energy consumption during the production process, resulting in outstanding economic benefits for industrial operation.

[0021] Clean, environmentally friendly, and free of secondary pollution. The entire reaction process of this invention takes place in a closed system with no waste gas emissions. The oxygen element in carbon dioxide is stably fixed inside the molten salt in the form of oxides, and no waste liquid or solid waste is generated. The system is highly closed-loop, fully complying with industrial carbon emission reduction and green environmental protection policies, and has good environmental and social benefits. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the system of the present invention; Figure 2 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1 This embodiment represents a standard mass production process (pure bismuth cathode + binary molten salt). For example... Figure 1As shown, the equipment of the present invention includes an industrial flue gas pretreatment dust removal and dehydration module, a CO2 enrichment and pressure stabilization inlet module, a molten salt electrolysis reactor, a liquid metal cathode circulation floating mechanism, an inert graphite anode, a molten salt constant temperature circulation module, and a carbon powder automatic collection and post-processing module, which are coupled in sequence. Specifically, the exhaust pipe of the industrial boiler is connected to the industrial flue gas pretreatment dust removal and dehydration module of the equipment of the present invention. The flue gas first passes through a primary cyclone dust collector to remove coarse dust particles with a particle size greater than 10 μm, then passes through a fine bag filter to remove submicron fine particles, then passes through a condenser to cool to below 40°C to condense and remove water vapor, and finally passes through a molecular sieve desiccant filled in a drying filter tank to adsorb residual moisture, thereby obtaining a clean and dry CO2 mixture. The pretreated clean flue gas is piped into the CO2 enrichment and pressure stabilization inlet module. A two-stage low-pressure membrane enrichment device using a polyimide hollow fiber membrane is employed. Under an operating pressure of 0.3 MPa, the initial CO2 concentration of approximately 12%–15% in the flue gas is enriched to over 85%. Constant pressure and constant flow output are achieved through a pressure stabilizing tank and a precision flow controller, with the outlet pressure stabilized at 0.05–0.08 MPa (slight positive pressure). The enriched CO2 gas is then uniformly dispersed into the molten salt medium layer in the form of microbubbles through a gas distributor (made of porous titanium sintered plate with a pore size of 10–20 μm) extending into the bottom of the electrolysis reactor.

[0025] like Figure 1 As shown, the electrolytic reactor is a fully enclosed, pressure-resistant, and high-temperature-resistant stainless steel tank (with an inner wall lined with a silicon nitride corrosion-resistant coating). An external resistance heating jacket is installed, through which circulating heat transfer oil is circulated. The PID temperature control system of the molten salt constant-temperature circulation module maintains a constant temperature inside the reactor. In this embodiment, the molten salt is a binary LiCl:KCl ratio of 45:55 (molar ratio). A total of 500 kg of mixed chloride salt is added to the electrolytic reactor, and the molten salt constant-temperature circulation module is activated, heating the reactor to 370°C to completely melt it. The molten salt layer height is maintained at 60% of the reactor height, forming a uniformly conductive molten salt medium layer. Subsequently, 600 kg of 99.99% high-purity metallic bismuth is added, and the temperature is raised to 480°C to completely liquefy it. Because the density of liquid bismuth is much greater than that of molten salt (the density of liquid bismuth is approximately 10.0 g / cm³), the molten salt solution is suitable for this process. 3 The density of molten salt is approximately 1.6 g / cm³. 3 The bismuth solution naturally settles to the bottom of the reactor, forming a dense liquid metal cathode layer approximately 8–12 cm thick. A molten salt medium layer floats on top of this layer, creating a clear and smooth liquid-liquid interface. An inert graphite anode (made of high-purity graphite, 99.99% purity, cylindrical in shape, 10 cm in diameter) is vertically inserted through the sealing flange at the top of the reactor, with its lower end immersed in the molten salt medium layer but approximately 3–5 cm above the bismuth solution interface. The positive terminal of an external DC power supply is connected to the graphite anode, and the negative terminal is connected to the bismuth solution conductive electrode led out from the bottom of the reactor, forming a closed electrolysis circuit.

[0026] like Figure 1 and Figure 2 As shown, the continuous production process flow of this embodiment is as follows: A stable 2.5V DC voltage is applied, with the current density controlled at 0.25A / cm². 2 High-purity argon gas is continuously introduced into the vessel as a protective atmosphere and maintained at a slight positive pressure (0.02-0.05 MPa).

[0027] Under the above conditions, CO2 gas is fully adsorbed and ionized by the chloride melt as it floats upward in the molten salt medium layer, generating carbon-oxygen active ions. These active ions migrate to the liquid bismuth interface under the action of an electric field, gain electrons on the surface of the bismuth liquid, and are reduced to solid carbon elemental.

[0028] Because liquid bismuth has extremely high surface tension (approximately 380–400 mN / m), carbon is difficult to wet and adhere to the bismuth surface. It then detaches from the bismuth interface in the form of fine particles and floats upward with the help of convective heat transfer from the molten salt and the buoyancy of bubbles. It passes through the molten salt medium layer and finally reaches the surface of the molten salt, forming a loose carbon powder floating layer at the liquid surface.

[0029] The high-temperature resistant ceramic scraping mechanism of the automatic carbon powder collection and post-processing module (using silicon nitride scrapers, mounted on a horizontal rotating chain above the liquid surface) continuously scrapes off the surface floating carbon at a frequency of once every 5 minutes. The scraped coarse carbon powder falls into the collection hopper and is then sent to the post-processing system through a closed screw conveyor.

[0030] Combination Figure 2 As shown, the coarse carbon powder first enters the deionized water cleaning unit, where it is washed in a stirred tank with 60°C deionized water at a solid-liquid ratio of 1:10 for 30 minutes to remove most of the molten salt adhering to the surface. Then it enters the dilute hydrochloric acid micro-washing unit, where it is washed with 0.5mol / L dilute hydrochloric acid at room temperature for 15 minutes to remove trace amounts of residual chloride salts. Subsequently, it enters the pure water rinsing unit, where it is repeatedly rinsed three times with high-purity deionized water until the pH of the washing solution is neutral. Finally, it enters the vacuum drying unit, where it is dried for 4 hours at 120°C and a vacuum degree of -0.095MPa.

[0031] The carbon powder obtained after the above treatment was analyzed by inductively coupled plasma mass spectrometry (ICP-MS) and found to have a total metal impurity content of less than 5 ppm. High-frequency infrared carbon-sulfur analyzer showed a stable carbon purity of 99.9998% (5.8N grade). The product was an ultrafine, uniform, high-purity carbon powder with an average particle size D50 of 0.8–1.2 μm. Scanning electron microscopy (SEM) revealed a flake-like morphology, with no metal impurities or oxidation defects, meeting the raw material requirements for high-precision carbon-based functional materials. In this embodiment, continuous operation for 168 hours resulted in an average carbon production of 0.85 kg per hour. The equipment operated stably without electrode passivation.

[0032] This embodiment demonstrates that the standard mass production process of this invention (such as...) is adopted. Figure 1 , Figure 2 As shown, 5.8N grade ultra-high purity carbon powder can be stably obtained under medium-high temperature conditions of 480℃. The equipment can operate continuously for a long time without electrode failure, which verifies the feasibility and stability of the technical route of the present invention and provides reliable benchmark process parameters for industrial promotion and application.

[0033] Example 2 This embodiment describes a high-purity, refined process using a tin-bismuth alloy cathode and ternary molten salt. For example... Figure 1 As shown, the cathode material is a tin-bismuth alloy (Sn:Bi = 43:57, mass ratio), and the molten salt system is a ternary LiCl:NaCl:KCl = 50:25:25 (molar ratio). A total of 500 kg of the ternary mixed chloride salt is added to the electrolytic reactor and heated to 380°C by the molten salt constant-temperature circulation module until completely melted. Then, 600 kg of the tin-bismuth alloy is added, and the temperature is raised to 420°C to completely liquefy it and spread it at the bottom. Figure 2 As shown, this embodiment aims to achieve high integrity and extreme purity of the carbon lattice by introducing a tin-bismuth alloy cathode and a ternary molten salt system, and by reducing the electrolysis temperature and current density, while obtaining a morphological structure different from that of plate-like carbon. Specifically, the electrolysis temperature is set in a low-temperature fine-tuning range of 420℃, the applied voltage is stably controlled at a low voltage of 2.35V, and the current density is finely adjusted to 0.18A / cm². 2 The CO2 gas source, after undergoing the same pretreatment and membrane enrichment process as in Example 1, was introduced into the gas distributor at the bottom of the electrolytic reactor at a slightly lower inlet flow rate (0.8 L / min). Under the mild electrolysis conditions of low temperature and low current density, the dissolution and diffusion rate of CO2 in the molten salt and the interfacial charge transfer rate were appropriately reduced, and the reduction and precipitation rate of carbon atoms at the interface of the tin-bismuth alloy was significantly slowed down. This allowed sufficient time for carbon atoms to undergo surface diffusion and lattice arrangement during the precipitation process, resulting in high-quality carbon products with more complete crystal structures and very few lattice defects. Since the tin component in the tin-bismuth alloy has an inducing effect on carbon precipitation, the carbon products tend to form a spherical morphology. The frequency of automatic carbon powder collection was adjusted to once every 8 minutes to extend the flotation time of carbon powder in the molten salt, allowing for further grain growth and perfection. The post-treatment process was the same as in Example 1, but the deionized water washing temperature was increased to 70°C and the dilute hydrochloric acid concentration was reduced to 0.3 mol / L to further reduce the risk of impurity introduction. After the above-mentioned fine processing, the finished product was analyzed by glow discharge mass spectrometry (GD-MS) with a total elemental scan. The total content of metal impurities was less than 0.8 ppm, and the carbon purity reached 99.9999% (6N grade). The product is highly crystalline ultrapure carbon. The scanning electron microscope (SEM) showed a uniform spherical morphology with clear lattice fringes and extremely low defect density. It is specially designed for use as a substrate in high-end three-dimensional cage carbon hydrogen storage resonant plates.

[0034] This embodiment demonstrates that by employing a tin-bismuth alloy cathode and a ternary molten salt system, the electrolysis temperature can be reduced to 420°C and the current density to 0.18 A / cm². 2 Refined process control (such as) Figure 1 , Figure 2 As shown, this invention can achieve stable preparation of carbon products with 6N-level ultra-high purity, and at the same time obtain carbon materials with spherical morphology. This fully demonstrates the flexibility of this invention in carbon product morphology control and the irreplaceable technical advantages of the liquid metal cathode system in the field of ultra-pure carbon preparation, providing a reliable technical solution for the production of ultra-high purity carbon materials for high-end application scenarios.

[0035] Example 3 This embodiment describes a large-scale, industrial-scale, extensive production process using a tin-bismuth alloy cathode and ternary molten salt. For example... Figure 1 As shown, the cathode material is a tin-bismuth alloy (Sn:Bi = 57:43, mass ratio), and the molten salt system is a ternary LiCl:NaCl:KCl = 45:30:25 (molar ratio). The effective volume of the electrolytic reactor is increased to three times that of Example 1 (1500 kg of ternary molten salt and 1800 kg of tin-bismuth alloy). The working temperature inside the reactor is raised to 650°C by the molten salt constant temperature circulation module, a DC voltage of 2.7V is applied, and the current density is increased to 0.32 A / cm². 2 The corresponding total electrolysis current increased significantly, and the CO2 processing capacity and carbon precipitation per unit time increased substantially. The CO2 enrichment and pressure stabilization gas inlet module continuously supplies gas to the reactor at a high flow rate of 3.5 L / min, significantly enhancing the bubble density and molten salt convection intensity within the reactor, and simultaneously increasing the carbon product formation rate and flotation rate. At higher temperatures, the catalytic effect of the tin component in the tin-bismuth alloy on carbon precipitation is enhanced, and the carbon products tend to form rod-shaped or dendritic morphologies. The high-temperature resistant ceramic material scooping mechanism of the automatic carbon powder collection and processing module was adjusted to scoop material once every 2 minutes, and the scraper rotation speed was increased from 0.5 r / min in Example 1 to 1.2 r / min to ensure timely collection of floating carbon on the liquid surface and prevent accumulation. Figure 2As shown, in the post-processing steps, the deionized water cleaning unit uses a two-stage series cleaning tank to achieve continuous countercurrent washing; the dilute hydrochloric acid micro-washing unit uses online pH monitoring for automatic acid replenishment; the pure water rinsing unit is equipped with a three-stage countercurrent rinsing; and the vacuum drying unit uses a double-cone rotary vacuum dryer, increasing the single batch processing capacity to 50 kg. Each unit is connected by an airtight rotary valve and a sealed vibrating conveyor, achieving continuous operation from material collection to finished product. Testing showed that the carbon powder produced in this embodiment has a stable purity of 99.9995% (5.7N grade), slightly lower than that of Examples 1 and 2, but still meeting the needs of most industrial high-purity carbon applications. Scanning electron microscopy (SEM) revealed that the carbon products exhibited a mixed morphology of rod-like and dendritic structures. This embodiment can produce up to 45 kg of carbon per day (24 hours), an increase of over 120% compared to the daily output of 20.4 kg in Example 1, with further reduced energy consumption per unit product. It is suitable for large-scale industrial mass production scenarios and can meet the continuous supply needs of large-scale powder metallurgy high-purity carbon raw material production lines.

[0036] This embodiment demonstrates that at a relatively high temperature of 650℃ and a high current density (0.32A / cm²), 2 Under these conditions, using a tin-bismuth alloy cathode and a ternary molten salt system, the process of this invention can still stably produce 5.7N grade high-purity carbon (such as...). Figure 1 , Figure 2 As shown in the figure, the daily production capacity can reach 45kg, which is more than 120% higher than the standard process. It can also obtain carbon materials with mixed morphologies of rod-shaped and dendritic, which verifies that the present invention has excellent capacity scaling and morphology control capabilities while maintaining high purity. It provides a practical and feasible process path for large-scale continuous industrial production, and fully demonstrates the process flexibility and wide industrial applicability of the present invention under different capacity requirements.

[0037] The above three embodiments (such as Figure 1 , Figure 2 (As shown) It covers the full range of application needs from refined high-end preparation to large-scale industrial production. The cathode materials include pure bismuth and tin-bismuth alloys with different ratios (Sn:Bi=43:57 and 57:43). The molten salt systems include binary LiCl-KCl and ternary LiCl-NaCl-KCl. The process parameters span a temperature range of 420℃ to 650℃ and an A / cm² depth of 0.18 to 0.32. 2The current density range and the inlet flow rate range are 0.8–3.5 L / min. The product purity of all three embodiments reached 5.7N or higher, with the fine process achieving a maximum purity of 6N. The carbon product morphologies were plate-like (Example 1), spherical (Example 2), and rod-like / dendritic (Example 3), respectively, fully demonstrating that the technical solution of this invention can maintain excellent product quality within a wide process window, while also possessing the ability to flexibly control the carbon product morphology. In each embodiment, the liquid metal layer does not need to be replaced after the electrolysis reaction; only static precipitation is required to restore the pure interface, allowing it to be directly used for the next batch of production. The molten salt system has stable composition, and the molar ratio fluctuation of each component between batches is no more than ±0.5%, allowing for long-term repeated use. The maximum operating temperature of the entire electrolysis reaction in each embodiment does not exceed 700℃. Compared with traditional high-temperature pyrolysis carbon production technology above 1400℃, the measured power consumption per unit mass of product is reduced by 60%–75%. The entire process directly utilizes the factory's waste flue gas as raw material, eliminating the need to purchase CO2 gas sources. The reaction process is a closed loop with no waste gas emissions. Oxygen is fixed inside the molten salt in the form of oxides, resulting in no waste liquid or solid waste. It fully complies with industrial carbon emission reduction and carbon sequestration environmental protection policies, achieving an organic unity of environmental and economic benefits.

[0038] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A liquid bismuth cathode molten salt electrolysis equipment for producing ultra-high purity carbon from industrial flue gas CO2, comprising an industrial flue gas pretreatment dust removal and dehydration module, a CO2 enrichment and pressure stabilization inlet module, a molten salt electrolysis reactor, a liquid metal cathode circulation floating mechanism, an inert graphite anode, a molten salt constant temperature circulation module, and an automatic carbon powder collection and post-processing module, characterized in that, The molten salt electrolysis reactor contains molten chloride salt, i.e., binary or ternary eutectic chloride salt, as the electrolyte. A liquid metal cathode layer is set at the bottom of the reactor. The liquid metal cathode is selected from high-purity bismuth or bismuth-based alloys, including tin-bismuth alloys. The outlet of the industrial flue gas pretreatment dust removal and dehydration module is connected to the inlet of the CO2 enrichment and pressure stabilization inlet module. The outlet of the CO2 enrichment and pressure stabilization inlet module is connected to the molten salt medium layer at the bottom of the molten salt electrolysis reactor through a gas distributor. The liquid metal cathode circulation floating mechanism is set inside the electrolysis reactor and located below the molten salt medium layer. The inert graphite anode is vertically inserted into the molten salt medium layer from the top of the electrolysis reactor. The molten salt constant temperature circulation module is connected to the jacket or internal heat exchanger of the electrolysis reactor through a circulation pipeline. The material collection inlet of the carbon powder automatic collection and post-processing module is set at the upper liquid surface of the molten salt medium layer inside the electrolysis reactor. The equipment adopts a medium-high temperature closed electrolysis structure to realize the continuous reduction and precipitation of carbon dioxide in industrial waste gas and the preparation of ultra-high purity solid carbon powder.

2. The equipment for producing ultra-high purity carbon from industrial flue gas CO2 by liquid bismuth cathode molten salt electrolysis according to claim 1, characterized in that: The chloride molten salt is a lithium chloride-potassium chloride binary eutectic chloride salt with a molar ratio of LiCl:KCl = 42:58 to 48:52 and a melting temperature range of 352℃ to 380℃; or a lithium chloride-sodium chloride-potassium chloride ternary eutectic chloride salt with a molar ratio of LiCl:NaCl:KCl = 45 to 55:20 to 30:20 to 30 and a melting temperature range of 346℃ to 400℃.

3. The equipment for producing ultra-high purity carbon from industrial flue gas CO2 by liquid bismuth cathode molten salt electrolysis according to claim 1, characterized in that: The liquid metal cathode uses 99.99% high-purity bismuth or a bismuth-based alloy, namely a tin-bismuth alloy, which is completely liquefied at the operating temperature to form a floating liquid metal interface. After carbon products are precipitated, they automatically float and separate, with no metal impurities precipitated and no electrode passivation. The mass ratio of tin to bismuth in the tin-bismuth alloy is 10:90 to 90:

10.

4. The equipment for producing ultra-high purity carbon from industrial flue gas CO2 by liquid bismuth cathode molten salt electrolysis according to claim 1, characterized in that: The inert graphite anode is made of high-temperature resistant, high-purity graphite material, which does not participate in the reaction, does not corrode, and does not shed impurities.

5. The equipment for producing ultra-high purity carbon from industrial flue gas CO2 by liquid bismuth cathode molten salt electrolysis according to claim 1, characterized in that: The CO2 enrichment and pressure stabilization intake module uses a low-pressure membrane enrichment device to enrich low-concentration CO2 in flue gas and then introduce it into the electrolysis reactor in a stable constant pressure manner to ensure stable intake gas concentration.

6. The equipment for producing ultra-high purity carbon from industrial flue gas CO2 by liquid bismuth cathode molten salt electrolysis according to claim 1, characterized in that: The automatic carbon powder collection and post-processing module includes a high-temperature resistant ceramic material scooping mechanism, a deionized water washing unit, a dilute hydrochloric acid micro-washing unit, a pure water rinsing unit, and a vacuum drying unit. These units are connected in sequence to form a continuous post-processing production line.

7. A process for producing ultra-high purity carbon from industrial flue gas CO2 by electrolysis using liquid bismuth cathode molten salt electrolysis with the equipment described in any one of claims 1 to 6, characterized in that... Includes the following steps: S1. Collect flue gas from the tail end of industrial boilers or kilns, and pre-treat it through dust removal, dehydration, impurity removal, and drying to obtain a clean carbon dioxide mixture. S2. CO2 gas is continuously supplied to the closed electrolysis reactor at a constant micro-positive pressure through a membrane enrichment and pressure stabilization system. S3. Heat the chloride molten salt, i.e., binary or ternary eutectic chloride salt, until it is completely melted to establish a stable conductive electrolytic dielectric layer; S4. Add high-purity bismuth or bismuth-based alloy, i.e., tin-bismuth alloy, and heat to melt, forming a liquid cathode layer at the bottom of the reactor; S5. Continuous electrolysis is performed at 400℃~520℃ and 2.2V~2.8V low-voltage DC, with a current density of 0.15~0.35A / cm². 2 Carbon dioxide is reduced at the liquid bismuth interface to precipitate solid carbon, which then automatically floats to the surface of the molten salt. S6. Online continuous collection of surface high-purity carbon powder, followed by cleaning, desalination, and vacuum drying to obtain ultra-high purity carbon finished product.

8. The equipment for producing ultra-high purity carbon from industrial flue gas CO2 by liquid bismuth cathode molten salt electrolysis according to claim 1, characterized in that: The entire electrolysis process is a medium-to-high temperature reaction, with the highest operating temperature of the electrolysis being 450℃~700℃. Compared with traditional high-temperature pyrolysis carbon production, the energy consumption of the electrolysis is significantly reduced by more than 60%.

9. The equipment for producing ultra-high purity carbon from industrial flue gas CO2 by liquid bismuth cathode molten salt electrolysis according to claim 1, characterized in that: The purity of the carbon powder can reach 99.999% to 99.9999%. The carbon powder is free of metal impurities and oxide residues. The carbon powder is suitable as a substrate for high-precision carbon-based functional resonant materials. By adjusting the cathode material (pure bismuth or tin-bismuth alloy with different ratios), adjusting the composition of the molten salt (binary chloride salt or ternary chloride salt), and adjusting the working temperature (450℃ to 700℃), the morphology and structure of the carbon products can be controlled to obtain carbon materials with different morphologies such as flakes, spheres, rods, or dendrites.

10. The equipment for producing ultra-high purity carbon from industrial flue gas CO2 by liquid bismuth cathode molten salt electrolysis according to claim 1, characterized in that: The molten salt system and the liquid bismuth cathode can be recycled and reused for a long time. The process consumes no consumables and produces no waste. The process directly uses the factory's waste flue gas as raw material to achieve high-value closed-loop carbon sequestration of industrial waste gas carbon dioxide and self-sufficient mass production of ultra-high purity carbon.

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