Carbon isotope enrichment cycle process based on low-temperature selective oxidation of carbon monoxide

Abstract

The application provides a carbon isotope enrichment circulation process based on low-temperature selective oxidation of carbon monoxide, relates to the technical field of isotope enrichment, and is realized by N enrichment stages in cascade. In each enrichment stage: carbon monoxide is catalytically oxidized at -20-100 DEG C to produce carbon dioxide enriched in heavy carbon isotopes and residual carbon monoxide enriched in light carbon isotopes; the carbon monoxide enriched in light carbon is separated by absorption with lye or an organic amine, and the carbon dioxide enriched in heavy carbon is released by acid or heating; the carbon dioxide enriched in heavy carbon is reduced to carbon monoxide by a reducing substance at 200-600 DEG C, and the conversion rate is greater than or equal to 90%. The carbon monoxide enriched in heavy carbon obtained by reduction in a previous stage is used as raw material for oxidation in a subsequent stage, and the carbon monoxide enriched in light carbon separated in the subsequent stage is returned to the oxidation step in the previous stage to form a countercurrent cascade. The application actively generates a separation effect by low-temperature oxidation and avoids re-mixing of isotopes, thereby realizing efficient and low-energy directional enrichment of carbon isotopes.

Description

Technical Field

[0001] This application relates to the field of isotope enrichment technology, specifically to a carbon isotope enrichment cycle process based on low-temperature selective oxidation of carbon monoxide. Background Technology

[0002] Carbon isotopes (such as) 12 C and 13 C) In scientific research, medical diagnosis (such as...) 13 Carbon isotopes have irreplaceable and important applications in fields such as the C-breath test and semiconductor materials. Currently, methods for enriching carbon isotopes mainly include distillation, laser methods, thermal diffusion, and chemical exchange. However, these methods generally suffer from high energy consumption, complex processes, low separation coefficients, or low production capacity.

[0003] In recent years, a recycling technique combining selective oxidation and chemical reduction to enrich carbon isotopes has emerged. The principle typically involves first utilizing the oxidation of carbon monoxide, achieving initial separation based on differences in reaction kinetics or diffusion mass transfer between different carbon isotopes, and then regenerating the oxidation products enriched with heavy isotopes back to the original reactants through a reduction reaction, thus achieving material recycling. However, this technique has a key drawback: traditional oxidation reactions usually require high temperatures (e.g., exceeding 200°C) to obtain sufficient reaction rates. Under high-temperature conditions… 12 C and 13 Due to thermodynamic equilibrium, isotope exchange can occur rapidly between carbon atoms, significantly weakening or even completely eliminating the isotope separation effect painstakingly achieved in the oxidation process (i.e., "remixing"). This severely offsets the enrichment efficiency of the entire process and limits its potential for industrial application. Furthermore, the reduction step of the oxidation products is often carried out at high temperatures, which may also be another risk factor for isotope remixing. Summary of the Invention

[0004] In view of the above-mentioned defects or deficiencies in the prior art, this application aims to provide a carbon isotope enrichment cycle process based on low-temperature selective oxidation of carbon monoxide, which is implemented based on a selective oxidation-reduction coupled cycle system composed of N cascaded enrichment stages, where N is an integer greater than 1; the process includes the following steps: Within each enrichment level, the following steps are performed sequentially: Oxidation step: Using a catalyst, carbon monoxide is selectively catalytically oxidized at -20~100℃ to produce carbon dioxide enriched with heavy carbon isotopes and residual carbon monoxide enriched with light carbon isotopes. Separation steps: The product from the above steps is subjected to alkaline solution and / or organic amine solution to absorb carbon dioxide, and unreacted carbon monoxide enriched with light carbon isotopes is obtained; the absorbed carbon dioxide is released again by acid or heating treatment to obtain carbon dioxide enriched with heavy carbon isotopes. Reduction step: Under high temperature conditions of 200~600℃, carbon dioxide enriched with heavy carbon isotopes is reduced by at least one reducing substance selected from hydrogen, metal oxide, sulfite, and metal powder to generate carbon monoxide enriched with heavy carbon isotopes; wherein the conversion rate of the reduction process is ≥90%, ensuring the separation effect of carbon isotopes by selective oxidation. Joint execution is performed between the enrichment levels described at each level: Enriched material transfer: The carbon dioxide enriched with heavy carbon isotopes produced in the previous oxidation step is reduced by the reduction step to obtain carbon monoxide enriched with heavy carbon isotopes, which is then fed into the next oxidation step as carbon monoxide raw material. Depleted material recycling: The carbon monoxide enriched with light carbon isotopes produced in the subsequent separation step is returned to the previous oxidation step; The cascade coupling of the oxidation step, the separation step, and the reduction step enables the directional enrichment of carbon isotopes.

[0005] According to the technical solution provided in this application, the reaction temperature of the oxidation step is -20~100℃.

[0006] According to the technical solution provided in this application, the catalyst is selected from at least one of noble metal catalysts, transition metal oxide catalysts, supported noble metal catalysts, and supported transition metal oxide catalysts.

[0007] According to the technical solution provided in this application, the oxidation step achieves the desired effect by controlling the reaction space velocity and catalyst particle size. 13 Preferential oxidation of C.

[0008] According to the technical solution provided in this application, in the oxidation step, the reaction space velocity is controlled at 1000~10000 h⁻¹. -1 Within the specified range, and controlling the catalyst particle size between 20 and 200 mesh; through the synergistic effect of the reaction space velocity and the catalyst particle size, the residence time of the reactants at the active sites of the catalyst and the diffusion mass transfer process are regulated, so as to achieve higher reactivity. 12 C preferentially diffuses away from the reaction site, thereby causing the C-containing 13 Carbon monoxide (C) accumulates at active sites and is preferentially oxidized, resulting in enrichment. 13 C carbon dioxide and enrichment 12 Residual carbon monoxide (C).

[0009] According to the technical solution provided in this application, for the enrichment stages from stage 1 to stage K, a preliminary enrichment zone is configured, and a first parameter combination is adopted, wherein the first parameter combination is a reaction space velocity of 5000~10000 h⁻¹. -1 The catalyst particle size is 40-200 mesh to prioritize the material throughput of the system; for the K+1 to Nth enrichment stages, a fine enrichment zone is configured, employing a second parameter combination where the reaction space velocity is 1000-5000 h⁻¹. -1 The catalyst has a particle size of 20-60 mesh to prioritize improving the single-stage separation accuracy; where K is an integer between 1 and N.

[0010] According to the technical solution provided in this application, before each oxidation step, the following steps are also included: The carbon monoxide feedstock entering this oxidation step is adjusted to a preset physical state, which enables the oxidation step to operate stably within a preset operating window; the preset operating window is the range of operating conditions that can effectively cause catalytic oxidation reaction and avoid thermodynamic remixing of carbon isotopes.

[0011] According to the technical solution provided in this application, before adjusting the carbon monoxide raw material entering this oxidation step to a preset physical state, the method further includes the following steps: The temperature of the carbon monoxide feedstock input in the oxidation step of this stage is monitored in real time, and it is determined whether the temperature is within the preset temperature range corresponding to the preset operation window.

[0012] According to the technical solution provided in this application, adjusting the carbon monoxide raw material entering this oxidation step to a preset physical state includes the following steps: The physical state parameters of the carbon monoxide feedstock are monitored in real time, including the rate of change of temperature over time or the rate of change of pressure over time. Determine whether the physical state parameter exceeds the corresponding preset fluctuation threshold; If the physical state parameter exceeds the preset fluctuation threshold, the temperature and / or pressure of the carbon monoxide raw material are adjusted until the physical state parameter is lower than the corresponding preset fluctuation threshold.

[0013] According to the technical solution provided in this application, the following steps are also included: Real-time online monitoring of the carbon isotope abundance ratio of output materials at at least one target enrichment level; The carbon isotope abundance ratio is compared with a preset target abundance value to obtain the comparison result; Based on the comparison results, at least one key process parameter of the target enrichment stage or its upstream enrichment stage is dynamically adjusted so that the carbon isotope abundance ratio of the output material approaches the preset target abundance value. The key process parameters include at least one of the reaction temperature of the oxidation step, the reaction space velocity, and the temperature of the reduction step.

[0014] Compared with the prior art, the beneficial effects of this application are as follows: First, it fundamentally avoids isotope remixing in high-temperature stages: The core oxidation step is carried out at a low temperature of -20 to 100°C, fundamentally eliminating the destructive effect of high-temperature thermodynamic equilibrium on isotope separation. Simultaneously, even if the subsequent reduction step requires high temperatures of 200 to 600°C, the object of this step is already separated pure carbon dioxide in different phases; its high-temperature effects will not be transmitted back to the low-temperature oxidation step, thus ensuring that the separation effect achieved by the oxidation step can be effectively maintained and accumulated step-by-step in the cascade.

[0015] II. Directed superposition and enrichment of separation effects were achieved: Through intra-stage coupling of low-temperature catalytic oxidation, product separation, and high-temperature reduction, as well as inter-stage integration of enriched material transport and depleted material recycling, a complete closed-loop cascade system was formed. In the oxidation step, heavy carbon isotopes ( 13 C) The carbon isotopes are preferentially oxidized into the carbon dioxide product, then directionally removed after the separation step, and regenerated into carbon monoxide through a reduction step, serving as the feedstock for the next stage. In this way, heavy carbon isotopes are progressively concentrated in the carbon monoxide product, while light carbon isotopes are progressively enriched in the residual depleted carbon monoxide, achieving efficient and targeted enrichment of isotopes.

[0016] Third, it improves the economy and feasibility of the process: The low-temperature operating conditions of the core oxidation step reduce the high-temperature resistance requirements of the reactor material and reduce energy consumption. At the same time, the introduction of catalytic oxidation ensures a sufficient reaction rate even at low temperatures, making the entire process more energy-efficient, controllable, and easier to scale up industrially.

[0017] IV. Active Utilization and Enhanced Separation Effect: Based on this scheme, the reaction mechanism can be adjusted by controlling the space velocity and catalyst particle size, transforming the low-temperature catalytic oxidation process from passively preventing mixing to actively preferentially oxidizing. 13 C generates a new dynamic separation effect that transcends traditional equilibrium limitations. This effect, in conjunction with the original separation effect, further enhances the single-stage separation factor and the enrichment efficiency of the entire system. Attached Figure Description

[0018] Figure 1A flowchart of the steps of the carbon isotope enrichment and recycling process based on low-temperature selective oxidation of carbon monoxide provided in this application. Detailed Implementation

[0019] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] Example 1 As mentioned in the background section, to address the problems in the prior art, this application proposes a carbon isotope enrichment cycle process based on low-temperature selective oxidation of carbon monoxide, implemented using a selective oxidation-reduction coupled cycle system composed of N cascaded enrichment stages, where N is an integer greater than 1. Figure 1 As shown, the process includes the following steps: S1. Within each enrichment level, execute the following sequentially: S11. Oxidation step: Using a catalyst, carbon monoxide is selectively catalytically oxidized at -20~100℃ to produce carbon dioxide enriched with heavy carbon isotopes and residual carbon monoxide enriched with light carbon isotopes. S12. Separation step: The product of the above step is subjected to alkaline solution and / or organic amine solution to absorb carbon dioxide, and unreacted carbon monoxide enriched with light carbon isotopes is separated; the absorbed carbon dioxide is released again by acid or heating treatment to obtain carbon dioxide enriched with heavy carbon isotopes. S13. Reduction step: Under high temperature conditions of 200~600℃, at least one reducing substance selected from hydrogen, metal oxide, sulfite, and metal powder is used to reduce the carbon dioxide enriched with heavy carbon isotopes to generate carbon monoxide enriched with heavy carbon isotopes; wherein the conversion rate of the reduction process is ≥90%, ensuring the separation effect of carbon isotopes by selective oxidation. S2. Joint execution between the enrichment levels described at each level: S21. Enriched material transfer: The carbon dioxide enriched with heavy carbon isotopes produced in the previous oxidation step is reduced by the reduction step to obtain carbon monoxide enriched with heavy carbon isotopes, which is then fed into the next oxidation step as carbon monoxide raw material. S22, Depleted material recycling: The carbon monoxide enriched with light carbon isotopes produced in the separation step of the next stage is returned to the oxidation step of the previous stage; S3. Through the cascade coupling of the oxidation step, the separation step and the reduction step, the directional enrichment of carbon isotopes is achieved.

[0022] Specifically, the selective redox coupled cyclic system includes: The enrichment stage comprises N cascaded enrichment stages, from stage 1 to stage N, where N is an integer greater than 1. Each enrichment stage includes an oxidation unit, a separation unit, and a reduction unit.

[0023] The oxidation unit is configured to selectively catalytically oxidize carbon monoxide-containing feedstocks at low temperatures ranging from -20°C to 100°C in the presence of a catalyst, producing carbon dioxide enriched with heavy carbon isotopes and residual carbon monoxide enriched with light carbon isotopes. This oxidation unit is the core component for isotope separation, utilizing differences in diffusion mass transfer at low temperatures to produce carbon dioxide enriched with heavy carbon isotopes. 13 Carbon monoxide preferentially oxidizes C, actively producing a separation effect.

[0024] The separation unit is configured to receive the mixed gas from the outlet of the oxidation unit, absorb carbon dioxide using an alkaline solution or an organic amine solution, separate unreacted carbon monoxide enriched with light carbon isotopes, and release carbon dioxide enriched with heavy carbon isotopes from the absorbent through acid treatment or heating. This separation unit completely separates the two streams of materials with different isotopic abundances produced in the oxidation step, providing pure materials for subsequent reduction and cascade cycles.

[0025] The reduction unit is configured to reduce the carbon dioxide enriched with heavy carbon isotopes released by the separation unit under high temperature conditions of 200℃~600℃ using at least one reducing substance selected from hydrogen, metal oxide, sulfite or metal powder, to generate carbon monoxide enriched with heavy carbon isotopes, and the reduction conversion rate is not less than 90%.

[0026] A raw material supply pipeline is configured to supply carbon monoxide-containing raw material gas to the oxidation unit of the enrichment stage in stage 1.

[0027] An enrichment material transfer pipeline is configured to transport carbon monoxide enriched with heavy carbon isotopes, produced by the reduction unit of the Mth enrichment stage, to the oxidation unit of the (M+1)th enrichment stage as a carbon monoxide feedstock, where M is an integer from 1 to N-1. Through this pipeline, 13 C abundance increases progressively.

[0028] A depleted material circulation pipeline is configured to transport unreacted carbon monoxide enriched with light carbon isotopes, discharged from the separation unit of the nth enrichment stage, to the inlet of the oxidation unit of the (n-1)th enrichment stage, where n is an integer from 2 to N. Through this pipeline, 12Materials with higher carbon abundance are returned to the preceding stage in reverse, widening the isotopic abundance difference between the inlet and outlet of the preceding oxidation unit, which is beneficial. 13 C concentration at the product end.

[0029] Specifically, a cascaded enrichment stage refers to multiple separation units connected in series, with the output of the previous stage serving as the input of the next. This cascaded design is an efficient method in the field of isotope enrichment, aiming to amplify the small single-stage separation effect step by step through the continuous action of multiple separation units, ultimately obtaining a high-abundance isotope product. In this system, each enrichment stage is a functional unit, containing three core steps: oxidation, separation, and reduction, which work together to complete a full separation cycle.

[0030] The oxidation step is a process of selectively oxidizing carbon monoxide under low-temperature conditions and in the presence of a catalyst. Its technical principle lies in the fact that... 13 Carbon monoxide containing C and 12 The diffusion mass transfer rate of carbon monoxide varies at the active sites of the catalyst. 12 Carbon monoxide diffuses more quickly due to its lighter mass and preferentially leaves the reaction site. 13 Carbon monoxide (C) accumulates on the surface of the active sites and is preferentially oxidized to carbon dioxide, thereby enriching heavy carbon isotopes at the oxidation product end. Low-temperature operation avoids isotope redismixing caused by thermodynamic equilibrium in traditional high-temperature oxidation.

[0031] The separation step employs a chemical absorption method to separate carbon dioxide from unreacted carbon monoxide in the oxidation products. An alkaline solution, such as an aqueous sodium hydroxide solution, or an organic amine solution, such as an aqueous ethanolamine solution, reacts chemically with the carbon dioxide to absorb it, while the carbon monoxide is not absorbed and is directly discharged. The absorbent is then treated with acid or regenerated by heating to release pure carbon dioxide. This step achieves complete separation of two materials with different isotopic abundances.

[0032] The reduction step will separate the enriched product. 13 Carbon dioxide is converted into carbon monoxide through a chemical reduction reaction, allowing it to continue participating in the cycle as a feedstock for the next stage of oxidation. When hydrogen is used, a reverse water-gas shift reaction occurs; when metal powders such as zinc powder are used, direct reduction occurs. This high conversion rate ensures that the isotope separation effect is not lost during the material transformation process.

[0033] The enrichment material transfer and depletion material circulation define the material flow direction of a cascade system. The enriched material is the enriched product from the reduction step. 13 Carbon monoxide (C) is transferred stepwise, with its abundance increasing each time it is removed from the separation process. Depleted material refers to the enriched material discharged from the separation step. 12Carbon monoxide (C) flows backward in stages, decreasing in abundance. This counter-current cascade is a classic fluid dynamics arrangement for achieving efficient enrichment. Implementation requires directional material transport through pumps, compressors, pipelines, and valve systems.

[0034] Furthermore, this process is based on a selective redox coupled cycle system consisting of N cascaded enrichment stages, where N is an integer greater than 1. Each enrichment stage is a functional unit capable of independently completing one full redox cycle. Multiple enrichment stages are connected in series, with the output material of the previous stage directly serving as the input for the next stage. This process amplifies the minute single-stage isotope separation effect step by step, ultimately yielding a high-abundance carbon isotope product.

[0035] Within each enrichment stage, oxidation, separation, and reduction steps are performed sequentially. The oxidation step is the core of isotope separation, and its specific operation is as follows: A feed gas containing carbon monoxide is mixed with an oxidant in a specific ratio and then introduced into a fixed-bed oxidation reactor packed with a catalyst. The feed gas can be pure carbon monoxide or a mixture containing carbon monoxide, such as a carbon monoxide-nitrogen mixture with a volume fraction of 5%. The oxidant can be air or pure oxygen, and the stoichiometric ratio of oxygen to carbon monoxide is usually controlled slightly higher than the required ratio to ensure complete oxidation. The reactor temperature is maintained at a set value between -20°C and 100°C using an external constant temperature bath and a precision temperature control system. Under the action of the catalyst, carbon monoxide undergoes a selective oxidation reaction with oxygen to produce carbon dioxide. Due to the synergistic effect of the low-temperature environment and the catalyst diffusion effect, the carbon monoxide content decreases significantly. 13 Carbon monoxide molecules are preferentially oxidized, and the resulting carbon dioxide... 13 The carbon abundance was significantly higher than that of the feedstock, while the residual unreacted carbon monoxide... 12 The abundance of carbon increases accordingly, thereby achieving the directional enrichment of heavy carbon isotopes at the product end.

[0036] The outlet gas from the oxidation step is a mixture of carbon dioxide and unreacted carbon monoxide, which is introduced into the separation step. The separation step employs chemical absorption: the mixed gas enters the absorption tower and comes into countercurrent contact with an alkaline solution or an organic amine solution. The alkaline solution can be an aqueous sodium hydroxide solution, and the organic amine solution can be an aqueous ethanolamine solution. Carbon dioxide reacts chemically with the absorbent to form carbonates or carbamates and is thus removed. Carbon monoxide does not participate in the reaction and is discharged from the top of the absorption tower, which constitutes enrichment. 12 Carbon monoxide depletion at C. The absorbent saturated solution enters a regeneration tower, where carbon dioxide is released again by adding a strong acid such as dilute sulfuric acid or by heating. After condensation and drying, a high-purity enriched product is obtained. 13 C. Carbon dioxide. This separation step completely separates the two materials with different isotopic abundances, avoiding cross-contamination during subsequent high-temperature operations.

[0037] The reduction step was carried out at high temperatures ranging from 200°C to 600°C. The enrichment obtained from the separation step was then... 13 Carbon dioxide (C) is mixed with at least one reducing agent and introduced into a reduction reactor. The reducing agent is selected from hydrogen, metal oxides, sulfites, or metal powder. When hydrogen is used as the reducing agent, a reverse water-gas shift reaction occurs in the presence of a nickel-based catalyst to produce carbon monoxide and water. When sulfites, such as sodium sulfite, are used as the reducing agent, carbon dioxide is reduced to carbon monoxide, with sulfate as a byproduct. The key indicator for the reduction step is that the carbon dioxide conversion rate must be no less than 90% to ensure that the isotope separation effect produced in the oxidation step is not lost due to the large amount of unreacted carbon dioxide. Enrichment of reduction products is also performed. 13 After being cooled and purified, carbon monoxide (C) is used as the raw material for the next enrichment stage in its oxidation step.

[0038] Interstage material transfer is achieved through enrichment material transfer and depletion material recycling. Enrichment material transfer refers to the transfer of enriched material produced in the previous oxidation step. 13 Carbon dioxide is converted into enriched form after separation and reduction. 13 Carbon monoxide (C) is introduced into the inlet of the next oxidation step through an interstage pipe, so that... 13 C abundance increases progressively. Depleted material recycling refers to the enriched material discharged from the subsequent separation step. 12 Carbon monoxide (C) is returned to the inlet of the previous oxidation step via a circulation pipeline, where it mixes with the fresh feedstock and participates in oxidation again. This is equivalent to introducing carbon monoxide into the previous stage. 12 Materials with higher carbon abundance widen the isotopic abundance difference between raw materials and products, which is more conducive to... 13 C is concentrated at the product end during the oxidation step.

[0039] To verify the above process effect, an oxidation step experiment was conducted in a fixed-bed reactor using a platinum alumina catalyst containing 1% platinum by mass. The feed gas was a mixture of carbon monoxide and nitrogen with a volume fraction of 5%, with an equal volume of oxygen added to the carbon monoxide. 13 The natural abundance of carbon dioxide (C) was 1.13%. The reaction was carried out at different temperatures with varying space velocities. The exit gases were separated and the carbon dioxide and residual carbon monoxide were determined using isotope mass spectrometry. 13 C abundance, the results are shown in Table 1.

[0040] Table 1. Isotopic distribution of oxidation reactions at different temperatures

[0041] Note: Separation factor α is the concentration of CO2 in CO2. 13 C abundance and residual CO 13 The ratio of C abundance, raw materials 13The carbon abundance was 1.13%. It should be noted that, to compare the abundance differences achieved by the catalyst at different temperatures with similar concentrations, the space velocity operating conditions at different temperatures were adjusted to ensure similar carbon monoxide conversion rates, thus obtaining product gases with similar concentrations at different temperatures. The abundance separation effect is shown in Table 1. The higher the temperature, the lower the catalyst separation effect. This also explains why the operating space velocity was changed when analyzing the differences in isotope distribution during oxidation reactions at different temperatures. It should be noted that the separation effect of this invention may be contributed by both diffusion kinetics and thermodynamic equilibrium isotope effects at low temperatures. Regardless of the specific mechanism, those skilled in the art can reproduce the separation effect based on the operating conditions disclosed in this application.

[0042] As shown in Table 1, under all test conditions ranging from 20°C to 100°C, the carbon dioxide generated... 13 The abundance of carbon (C) was significantly higher than that of residual carbon monoxide, and the separation factor was greater than 1.06, even reaching 1.359 at 20 degrees Celsius, far exceeding the industrially acceptable threshold of 1.01. This fully demonstrates that the oxidation step has a significant active separation capability, which can directionally enrich heavy carbon isotopes into carbon dioxide.

[0043] With the oxidation temperature fixed at 40 degrees Celsius on the same apparatus, the operating space velocity was varied, and the results shown in Table 2 were obtained.

[0044] Table 2. Isotopic distribution of oxidation reaction at different space velocities at 40°C

[0045] Table 2 shows that under constant temperature conditions of 40 degrees Celsius, as the space velocity gradually increases from 1000 hV / h to 10000 hV / h, the single-pass conversion rate of carbon monoxide increases from approximately 10% to approximately 90%, but the separation factor remains almost constant at around 1.201. This indicates that... 13 The selectivity of C preferential oxidation remains highly stable over a wide space velocity range. The separation effect is mainly controlled by diffusion mass transfer rather than thermodynamic equilibrium. Therefore, the oxidation step can be flexibly matched to different throughput requirements without sacrificing separation accuracy.

[0046] Based on the cascaded coupling of the above steps, the entire process achieves directional enrichment of carbon isotopes. Its technical principle lies in combining the kinetic separation effect of low-temperature selective oxidation, the thoroughness of chemical absorption separation, and the high-conversion material regeneration capability of chemical reduction, and utilizing counter-current cascading to achieve... 13 C is concentrated step by step at the product end. 12 C is diluted stepwise at the waste end, which fundamentally avoids isotope remixing caused by high-temperature oxidation. At the same time, the oxidation step itself contributes additional separation gain, significantly improving the overall enrichment efficiency.

[0047] In a preferred embodiment, the reaction temperature of the oxidation step is -20 to 100°C.

[0048] Specifically, this temperature range was determined through systematic experimental screening, ensuring that the catalyst has sufficient carbon monoxide oxidation activity while maximally suppressing the thermodynamic remixing of carbon isotopes.

[0049] In practice, the oxidation reactor is a jacketed fixed-bed reactor, filled with a catalyst bed. A cooling or heating medium, such as an aqueous ethylene glycol solution, is circulated through the jacket, with its temperature controlled by a thermostatic circulator. When operation below zero degrees Celsius is required, the inlet pipeline must be insulated and heated to prevent trace amounts of moisture in the gas from freezing and clogging the pipeline. The reactor temperature is monitored in real-time by a thermocouple inserted at the center of the catalyst bed. The output of the thermostatic circulator is adjusted by a PID controller to keep temperature fluctuations within ±1 degree Celsius. When the reaction releases a large amount of heat, causing the bed temperature to rise, the circulation medium flow rate can be appropriately increased or the medium temperature decreased to stabilize operation.

[0050] Table 1 clearly shows the effect of temperature on the separation effect. At 20 degrees Celsius, the separation factor is as high as 1.359. As the temperature rises to 100 degrees Celsius, the separation factor gradually decreases to 1.061, but is still significantly greater than 1. This data indicates that below 100 degrees Celsius, 13 The tendency for carbon dioxide to preferentially oxidize to enrich heavier carbons remains constant, and the separation effect is more significant at lower temperatures. Even at temperatures close to -20 degrees Celsius, the reaction can still proceed as long as a suitable low-temperature, highly active catalyst is selected, and based on the theory of isotope effects, the separation factor has the potential to be further increased.

[0051] The technical principle behind strictly limiting the oxidation temperature below 100 degrees Celsius is to avoid thermodynamic remixing of isotopes. Carbon isotopes can gradually reach equilibrium through oxygen exchange reactions between carbon monoxide and carbon dioxide, and the rate of this equilibrium process increases exponentially with increasing temperature. In high-temperature oxidation environments above 200 degrees Celsius, although a certain tendency for separation may occur in the initial stages of the reaction due to kinetic isotope effects, the high temperature promotes... 12 C and 13 The rapid exchange of carbon between molecules causes the isotopic composition of carbon dioxide and residual carbon monoxide to approach thermodynamic equilibrium, significantly reducing or even eliminating the separation effect. However, when the temperature is controlled below 100 degrees Celsius, especially below 50 degrees Celsius, the exchange reaction rate is extremely slow, negligible on an industrial residence time scale, thus minimizing the effects of the oxidation step. 13The separation result formed by preferential oxidation of C is completely preserved and solidified into two materials with different abundances through the separation step.

[0052] Furthermore, cryogenic operation offers significant engineering and economic advantages. The reactor body can be made of ordinary stainless steel instead of expensive high-temperature alloys, reducing manufacturing and installation costs. Since carbon monoxide oxidation is an exothermic reaction, the heat generated at low temperatures is more easily carried away by the cooling medium, minimizing the risk of catalyst burnout due to overheating, thus enhancing safety. Simultaneously, the reduced temperature difference between the oxidation step and the upstream separation operation near room temperature, along with the high-temperature downstream reduction step, significantly lowers the load on intermediate heat exchangers, resulting in more efficient thermal integration throughout the process and a substantial decrease in operating energy consumption. These factors collectively ensure high efficiency, low energy consumption, and long-term stable operation across the entire temperature range.

[0053] In a preferred embodiment, the catalyst is selected from at least one of noble metal catalysts, transition metal oxide catalysts, supported noble metal catalysts, and supported transition metal oxide catalysts.

[0054] Specifically, noble metal catalysts refer to catalytic materials with noble metal elements such as platinum, palladium, rhodium, ruthenium, and gold as active components. Pure noble metals such as platinum black and platinum mesh can be used directly, but due to their high cost and low utilization rate, they are mostly made into supported catalysts in industry. Transition metal oxide catalysts refer to catalysts with oxides of transition metals such as cobalt, manganese, copper, iron, and chromium as the main active components, such as cobalt tetroxide, copper oxide, and mixtures of copper and manganese oxides. Supported catalysts are prepared by highly dispersing the active components on the surface of a porous support. The support material can be gamma alumina, titanium dioxide, silica, activated carbon, or molecular sieves. The active component can be a noble metal or a transition metal oxide. After loading the active component, the specific surface area of ​​the catalyst increases several times, the number of active sites increases, and the low-temperature activity is significantly improved. At the same time, the porous structure of the support provides the possibility of regulating the diffusion behavior of reactant molecules, which helps to amplify the reaction. 12 C and 13 The difference in diffusion rate of C promotes 13 Enrichment and preferential reaction of C on the surface of active sites.

[0055] For the specific preparation and selection of catalysts, conventional impregnation methods can be used. Taking the preparation of platinum alumina catalysts as an example, gamma alumina support is immersed in an aqueous solution of chloroplatinic acid, stirred and impregnated at a certain temperature, then removed, dried, and calcined for decomposition. Finally, it is reduced and activated in a hydrogen atmosphere to obtain a platinum alumina catalyst with highly dispersed platinum metal particles. The catalyst is usually in the shape of columnar or spherical particles, and the target particle size range is obtained by sieving through a standard sieve before being packed into a fixed-bed reactor. During packing, it is necessary to ensure that the bed is uniform and dense, avoid bridging and channeling phenomena, and ensure uniform gas flow distribution.

[0056] The data shown in Tables 1 and 2 were obtained using a platinum alumina catalyst. Table 1 shows that using this catalyst, a high separation factor of 1.359 can be obtained at 20°C, and it remains at 1.061 at 100°C, demonstrating that the supported noble metal catalyst can stably exert its catalytic effect within a wide temperature range and achieve [the desired separation factor]. 13 C is preferentially oxidized. Table 2 shows that at 40°C, even with a tenfold change in space velocity, the separation factor remains consistently around 1.201, demonstrating the catalyst's excellent diffusion selectivity control and stable separation performance under different operating conditions. Besides platinum alumina, experiments using palladium-on-carbon catalysts or copper-manganese hogallat catalysts under similar conditions also yielded the same results for carbon dioxide. 13 The results showed that the abundance of C was higher than that of residual carbon monoxide, and the separation factor was greater than 1.05, indicating that the catalyst types listed in this embodiment are universal.

[0057] These catalysts achieve 13 The technical principle of preferential oxidation of carbon lies in the fact that their surfaces can adsorb and activate carbon monoxide and oxygen under low-temperature conditions. The adsorption of carbon monoxide on noble metal surfaces is typically non-dissociative adsorption. 12 Carbon monoxide (C) is lighter and has a higher diffusion coefficient, making it easier for it to desorb and escape from the micropores of the catalyst. 13 Carbon monoxide (C) tends to remain near the active sites, thus being preferentially oxidized. Transition metal oxides participate in the reaction through lattice oxygen or surface-adsorbed oxygen, exhibiting similar diffusion-controlled selectivity. Regardless of the specific catalyst used, as long as it belongs to the type defined in this embodiment, diffusion differences can be utilized to achieve oxidation under low-temperature conditions. 13 The preferential oxidation of C provides a stable and reliable basis for single-stage separation in this process, which can then be used to obtain high-abundance carbon isotope products through cascade scale-up.

[0058] In a preferred embodiment, the oxidation step achieves control over the reaction space velocity and catalyst particle size. 13 Preferential oxidation of C.

[0059] Specifically, reaction space velocity, or gas volume space velocity, is usually represented by the symbol GHSV. It is defined as the volumetric flow rate of gaseous reactants passing through a unit volume of catalyst bed per unit time, expressed in hours. The formula is: GHSV = total gas volumetric flow rate divided by the catalyst packing volume. For example, if the catalyst packing volume is 0.5 liters and the target space velocity is set to 4000 GHSV, then the required total gas flow rate is 0.5 liters multiplied by 4000 GHSV, which equals 2000 liters per hour, or approximately 33.3 liters per minute. It is important to note that gas volumetric flow rate usually refers to the volume under standard conditions or at a specified temperature and pressure; in actual operation, it should be uniformly converted to the same standard. Space velocity directly determines the average residence time of reactant molecules in the catalyst bed. The formula for residence time is: residence time = catalyst bed void volume divided by gas volumetric flow rate. The void volume can be obtained by multiplying the catalyst packing volume by the bed porosity; the porosity of a fixed bed is generally between 0.3 and 0.5. The higher the airspeed, the shorter the dwell time, and vice versa.

[0060] Catalyst particle size refers to the diameter of catalyst particles, usually expressed in mesh count. Mesh count is defined as the number of sieve openings per inch of screen length. The conversion between mesh count and particle size is: particle size (micrometers) is approximately equal to 15000 divided by mesh count. For example, 40 mesh corresponds to a particle size of approximately 375 micrometers, 100 mesh corresponds to a particle size of approximately 150 micrometers, and 200 mesh corresponds to a particle size of approximately 75 micrometers. The choice of catalyst particle size directly determines the length of the diffusion path of reactant molecules within the micropores of the catalyst particles, i.e., the magnitude of internal diffusion resistance. Larger particles result in longer internal diffusion paths and longer residence times of molecules within the pores. 12 C and 13 The more significant the cumulative amplification effect of minute differences in the diffusion coefficient of C molecules, the more pronounced the effect.

[0061] In practice, the catalyst type is first determined based on process requirements, followed by particle size screening. Purchased finished catalysts or laboratory-made catalysts are sieved using standard sieves. For example, to obtain a catalyst with a particle size of 40 to 60 mesh, the catalyst is poured into a 40-mesh upper sieve and a 60-mesh lower sieve, covered, and vibrated on a vibrating sieve machine for 10 to 15 minutes. The particles retained between the two sieves are the catalyst within the target particle size range. After sieving, the required loading amount is weighed, and its bulk volume is recorded, or measured directly with a graduated cylinder. The catalyst is uniformly loaded into the isothermal section of the fixed-bed reactor. During loading, the outer wall of the reactor is gently tapped to ensure a dense and uniform bed, avoiding bridging or channeling. After loading, the actual height of the catalyst bed is measured and multiplied by the cross-sectional area of ​​the reactor to obtain the loading volume V_cat.

[0062] The determination of space velocity requires comprehensive consideration of both the target conversion rate and the separation effect. According to the experimental data in Table 2, under conditions of 40 degrees Celsius and a catalyst mesh of 40 to 60 mesh, a stable separation factor greater than 1.20 can be obtained within a space velocity range of 1000 to 10000 kilometres per hour. If a certain enrichment stage aims to achieve a single-pass conversion rate of approximately 50%, a space velocity of approximately 5000 kilometres per hour can be selected with reference to Table 2. When calculating the total gas flow rate, multiply the target space velocity value by the packing volume V_cat. For example, if V_cat is 0.2 liters and the target space velocity is 5000 kilometres per hour, then the total flow rate should be set to 0.2 multiplied by 5000, which equals 1000 liters per hour. This total flow rate consists of two parts: carbon monoxide feed gas and oxidant. If the feed gas is a 5% carbon monoxide-nitrogen mixture, the oxidant is air, the stoichiometric ratio of carbon monoxide to oxygen is 2:1, and a 20% oxygen excess coefficient is allowed to ensure complete reaction, then the flow rates of the carbon monoxide mixture and air can be calculated separately based on material balance, and set and adjusted separately by two mass flow controllers. During operation, the outlet concentrations of carbon monoxide and carbon dioxide are monitored by an online gas chromatograph or infrared gas analyzer, the actual conversion rate is calculated, and compared with the target conversion rate. If the deviation is too large, the space velocity can be finely adjusted for correction. Through the above steps, the space velocity and particle size can be accurately controlled in a coordinated manner.

[0063] In a preferred embodiment, during the oxidation step, the reaction space velocity is controlled to be between 1000 and 10000 h⁻¹. -1 Within the specified range, and controlling the catalyst particle size between 20 and 200 mesh; through the synergistic effect of the reaction space velocity and the catalyst particle size, the residence time of the reactants at the active sites of the catalyst and the diffusion mass transfer process are regulated, so as to achieve higher reactivity. 12 C preferentially diffuses away from the reaction site, thereby causing the C-containing 13 Carbon monoxide (C) accumulates at active sites and is preferentially oxidized, resulting in enrichment. 13 C carbon dioxide and enrichment 12 Residual carbon monoxide (C).

[0064] Specifically, the determination of the space velocity range of 1000 to 10000 space velocities per hour is based on an optimized range verified by a large number of experiments. As shown in the experimental data in Table 2 above, at 40 degrees Celsius, with a catalyst of 40 to 60 mesh, and raw materials... 13At a carbon abundance of 1.13%, the separation factor α remains stable at around 1.201 across the entire space velocity range from 1000 h⁻¹ to 10000 h⁻¹. Below 1000 h⁻¹, although the conversion rate approaches complete, the excessively long residence time may cause the reaction to approach thermodynamic equilibrium, weakening the separation effect controlled by kinetic diffusion, and resulting in an uneconomical catalyst throughput per unit area. Above 10000 h⁻¹, the residence time is too short, leading to extremely low conversion rates. If the space velocity significantly exceeds 10000 h⁻¹, the single-pass conversion rate may drop below 5%, requiring large-scale material recycling. This drastically increases the energy consumption for downstream separation and recycling compression, rendering the process unfeasible for industrial applications. The catalyst particle size range of 20 to 200 mesh covers the particle size range commonly used in industrial fixed-bed reactors. 20 mesh corresponds to approximately 840 micrometers, and 200 mesh corresponds to approximately 74 micrometers. Particle sizes larger than 20 mesh, i.e., excessively coarse particles, result in excessive internal diffusion resistance leading to a low effective reaction rate, and excessively high bed porosity, causing gas channeling and uneven distribution. If the particle size is less than 200 mesh, that is, the particles are too fine, the pressure drop of the catalyst bed will increase sharply, the airflow will require a higher inlet pressure, the pressurization energy consumption will increase significantly, and the fine particles will be easily lost under the scouring of the airflow, so an additional fine filtration device is required.

[0065] In practical implementation, for space velocity control, a high-precision mass flow controller needs to be installed on the main inlet pipe of the oxidation reactor. Its control accuracy is typically ±1% of full scale. The mass flow controller should be calibrated using a soap film flow meter or a standard flow meter before installation. The control system operates according to the following logic: First, the target space velocity value GHSV_set is set. Based on the loading volume V_cat, the target total flow rate F_total is calculated, which equals GHSV_set multiplied by V_cat. Then, based on the target composition of the feed gas and the stoichiometric relationship, the flow rate setpoint F_i for each gas is determined. For example, the carbon monoxide mixture flow rate F_CO_mix and the air flow rate F_air must satisfy the following: the molar ratio of the carbon monoxide flow rate obtained by multiplying F_CO_mix by its carbon monoxide concentration to the oxygen flow rate obtained by multiplying F_air by the oxygen concentration in the air is 1:0.6, i.e., 20% oxygen excess. The control system sends the calculated flow rate setpoints for each gas to the corresponding mass flow controller, which automatically adjusts the opening of the built-in valve until the flow rate stabilizes. To control catalyst particle size, after catalyst preparation or procurement, rigorous sieving is performed using standard test sieves and a vibrating sieve machine. The sieving process employs a two-stage method: the upper sieve aperture corresponds to the upper limit of particle size, and the lower sieve aperture corresponds to the lower limit. Particles retained between the two sieves are collected after sieving. After sieving, samples are taken and the particle size distribution is verified using a laser particle size analyzer or microscopy to ensure D... 50 The particle size should be near the center of the target range, and the span should not be too large.

[0066] The synergistic effect is reflected in the matching and selection of parameters. When coarser catalyst particles, such as 60 to 80 mesh, are used, the internal diffusion path is longer. 12 C and 13 The difference in diffusion rate of C is fully amplified, resulting in strong selectivity for diffusion control. A moderate space velocity, such as 3000 to 5000 mph, should be used to ensure the conversion rate is not too low. When using finer catalyst particles, such as 100 to 200 mesh, the internal diffusion resistance is lower, and the reaction is closer to surface reaction control. Selectivity may decrease slightly, but the reaction rate is faster. In this case, a higher space velocity, such as 6000 to 10000 mph, can be used to leverage the high throughput advantage. Table 1 further illustrates the interaction between temperature, space velocity, and particle size. At 20°C, a space velocity of 2000 mph, and using a 40 to 60 mesh catalyst, the separation factor is as high as 1.359. As the temperature rises to 100°C, the separation factor decreases to 1.061, but remains greater than 1. This indicates that within the space velocity and particle size range defined in this embodiment, the separation effect can be further optimized by selecting a suitable operating temperature. In engineering practice, a separation factor response surface diagram with space velocity, particle size and temperature as variables can be established through pilot-scale experiments. Then, during actual operation, the operating points can be adjusted online or offline according to the product purity requirements so that the whole system always operates within its optimal operating window.

[0067] In a preferred embodiment, the enrichment stages from level 1 to level K are configured as preliminary enrichment regions, employing a first parameter combination where the reaction space velocity is 5000 to 10000 h⁻¹. -1 The catalyst particle size is 40-200 mesh to prioritize ensuring the system's material throughput. For the K+1 to Nth enrichment stages, a fine enrichment zone is configured, employing a second parameter combination where the reaction space velocity is 1000-5000 h⁻¹. -1 The catalyst has a particle size of 20 to 60 mesh to prioritize improving the single-stage separation accuracy; where K is an integer between 1 and N.

[0068] Specifically, determining the K value requires material balance and economic evaluation of the cascade system. It is assumed that the total number of stages N has been determined using cascade theory based on the raw material abundance C0, the target product abundance CN, and the expected average single-stage separation factor α. The function of the initial enrichment zone is to rapidly concentrate the low-abundance material, which constitutes the majority of the raw material volume, to a medium abundance. Typically, when the material flow rate drops to about one-third to one-quarter of the initial feed flow rate due to diversion and concentration, and the abundance has reached 50% to 70% of the target value, the system can be moved to the fine enrichment zone. The K value can be determined according to the following steps: First, set the first-stage feed flow rate F0 and abundance C0, and set the target conversion rate X1 and separation factor α for each primary stage. Second, calculate the feed flow rate and abundance for the Mth stage based on material conservation, decreasing the flow rate and increasing the abundance at each stage. Third, when the flow rate drops below one-third of F0, the stage is tentatively designated as K. The fourth step is to verify whether switching to the enrichment region parameters from this level can push the abundance to the target value within the remaining NK levels. If insufficient, the K value is shifted forward; if too generous, the K value is shifted backward. After several trials and optimizations, the final value of K can be determined.

[0069] The first parameter combination operation in the initial enrichment zone is implemented as follows: The catalyst particle size is selected to be relatively fine, within the range of 40 to 200 mesh, for example, 60 to 100 mesh, to reduce internal diffusion resistance and ensure the reaction rate at high throughput. The catalyst loading amount is determined based on the processing throughput. Due to the large feed flow rate and the relatively large size of the primary reactor, a multi-tube fixed bed configuration can be used in parallel to reduce bed pressure drop. The space velocity is set to 6000 to 8000 rpm. For example, if the catalyst loading volume of an enrichment stage is 2 liters and the target space velocity is 7000 rpm, the total gas flow rate is 14000 liters per hour. The flow rates of each feed component are calculated separately and input into the mass flow controller. The focus of operation in this zone is to maintain stable high throughput; the conversion rate can be appropriately relaxed to 40% to 50%, with the key being to maximize the total amount of feed processed per unit time. During system operation, the conversion rate and abundance of the effluent are monitored online. Taking the data in Table 2 as an example, if the same catalyst as in Table 2 is used, the single-pass conversion rate is approximately 80% and the separation factor is 1.201 under a space velocity of 8000 h⁻¹. In actual operation, if the conversion rate is lower than 40% due to excessive throughput, the space velocity should be appropriately reduced; if the conversion rate is much higher than 50% and the separation factor does not decrease significantly, the space velocity can be further increased to fully exploit the equipment's potential.

[0070] The second parameter combination operation in the enrichment zone is implemented as follows. The catalyst particle size is selected to be relatively coarse, within the range of 20 to 60 mesh, for example, 30 to 50 mesh, to maximize the selectivity of diffusion control and improve separation accuracy. Since the material flow rate in the enrichment zone has been significantly reduced, the reactor size can be correspondingly reduced. Higher temperature control accuracy is required, necessitating the use of a more precise thermostatic bath. The space velocity is set to 2000 to 4000 kilometres per hour. For example, if the catalyst loading volume of a certain stage is 0.1 liters, the target space velocity is 2500 kilometres per hour, and the total gas flow rate is 250 kilometres per hour. At low space velocities, the residence time is prolonged. 13 C has a greater chance of being enriched and oxidized at active sites, and the separation factor can be maintained at a high level. Referring to the data in Table 2, at a space velocity of 2000 h⁻¹, the separation factor is 1.202, and the conversion rate is approximately 20%. If the conversion rate is too low, resulting in insufficient yield of effective product, the space velocity can be appropriately increased, but only if the separation factor does not fall below the preset threshold. Each exit of the enrichment zone is equipped with an online isotope mass spectrometer or laser spectrometer to measure product abundance in real time.

[0071] Implementation of interstage connection and switching. An interstage buffer and adjustment device needs to be installed between the last stage (stage K) of the preliminary enrichment zone and the first stage (stage K+1) of the fine enrichment zone. Enrichment at the outlet of the stage K reduction unit. 13 Before entering the K+1 stage oxidation unit, carbon monoxide's physical state has been adjusted to a preset window by the pretreatment unit. Regarding parameter switching, since stages K and K+1 use different combinations of space velocity and particle size, the flow rate and pressure of the material entering stage K+1 must match the design requirements of the enrichment zone. If the flow rate of the material at the K-stage outlet is greater than the required flow rate of stage K+1, a bypass must be installed on the intermediate buffer tank to store or divert the excess for other uses; if the flow rate is insufficient, it must be supplemented from the storage tank or the internal circulation must be activated. This zoned gradient configuration, while ensuring the throughput of the upstream stage, provides an optimal reaction environment for the downstream stage, resulting in significantly better economic efficiency than operating the entire system with a single parameter.

[0072] In a preferred embodiment, prior to each oxidation step, the following step is further included: The carbon monoxide feedstock entering this oxidation step is adjusted to a preset physical state, which enables the oxidation step to operate stably within a preset operating window; the preset operating window is the range of operating conditions that can effectively cause catalytic oxidation reaction and avoid thermodynamic remixing of carbon isotopes.

[0073] Specifically, the carbon monoxide feedstock typically comes from two sources: one is the high-temperature enriched carbon monoxide produced in the previous reduction unit. 13 Carbon monoxide (C) can be found at temperatures between 300 and 500 degrees Celsius; another location is the ambient-temperature enrichment from the subsequent stage separation unit's recycled material. 12Carbon monoxide (C) has a temperature of approximately 30 to 50 degrees Celsius. Since these two materials have different temperatures and pressures, they must be mixed and regulated before proceeding to the oxidation step.

[0074] The preset operating window is determined based on the overall requirements of the selected catalyst and process. Taking platinum alumina catalyst as an example, its ignition temperature is typically around -10 degrees Celsius, so the lower limit of the temperature can be set to 0 degrees Celsius to ensure a self-sustaining reaction; the upper limit of the temperature is set to 100 degrees Celsius to avoid thermodynamic remixing of isotopes. For the operating pressure window, considering that the fixed-bed pressure drop is typically controlled between 0.01 and 0.05 MPa, and the pipeline and absorber resistance that the downstream separation unit needs to overcome, the oxidation reactor inlet pressure window can be set to 0.10 to 0.20 MPa. The flow rate window corresponds to the allowable fluctuation range of the target space velocity and is typically set to ±10%. The upper and lower limits of the above parameters constitute the preset operating window for this stage.

[0075] In the specific implementation of pretreatment regulation, a physical state regulation unit needs to be installed before the inlet of the oxidation reactor. This unit consists of a heat exchanger, a buffer pressure tank, measuring instruments, and actuators. The heat exchanger is a shell-and-tube or plate heat exchanger, with refrigerant flowing through the shell side to cool the high-temperature material. The volume of the buffer pressure tank is designed according to the flow rate and the required pressure stabilization time, typically taking the volume corresponding to a residence time of 1 to 3 minutes based on the feed volumetric flow rate. A pressure transmitter and pressure regulating valve are installed on the tank. The specific operation of temperature regulation is as follows: high-temperature carbon monoxide from the reduction unit first enters the shell side of the heat exchanger, while the refrigerant flows in the tube side. The refrigerant flow rate is controlled by a regulating valve using PID control based on the material temperature at the heat exchanger outlet. The temperature setpoint is usually the midpoint of the oxidation operating window temperature range, such as 50 degrees Celsius. At ambient temperature, the circulating gas directly enters the buffer tank and mixes with the cooled material inside. A sheathed platinum resistance thermometer is installed on the tank outlet pipeline to measure the temperature T_mix of the mixed gas in real time and transmit the data to the PLC or DCS. The control system compares T_mix with the set temperature T_set. If T_mix is ​​higher than T_set, the opening of the refrigerant valve on the heat exchanger is increased or the refrigerant temperature is decreased; if T_mix is ​​lower than T_set, the refrigerant flow rate is reduced or electric heat tracing is activated. The pressure regulation is as follows: the pressure transmitter on the tank top measures P_mix in real time and transmits the data to the control system. P_mix is ​​compared with the pressure setpoint P_set. If P_mix is ​​higher than P_set, the vent valve on the tank top is slightly opened to release a small amount of gas to the flare or recovery system; if P_mix is ​​lower than P_set, the supply pressure is increased by adjusting the back pressure valve at the outlet of the upstream reduction unit or the circulating gas booster pump. After both temperature and pressure stabilize at the set values, the mixed gas enters the oxidation reactor through the flow regulating valve. Flow measurement uses a vortex or thermal gas mass flow meter, and the flow signal is linked to the mass flow controller to achieve precise closed-loop flow regulation.

[0076] Through the complete measurement and closed-loop control circuit described above, it is ensured that the feedstock entering the oxidation step is always within the preset operating window in terms of temperature, pressure, and flow rate, providing stable and reproducible feed conditions for the low-temperature catalytic oxidation reaction, thereby ensuring the stability of the single-stage separation factor and the long-term reliable operation of the entire cascade system.

[0077] In a preferred embodiment, before adjusting the carbon monoxide feedstock to a preset physical state before entering this oxidation step, the method further includes the following steps: The temperature of the carbon monoxide feedstock input in the oxidation step of this stage is monitored in real time, and it is determined whether the temperature is within the preset temperature range corresponding to the preset operation window.

[0078] In practical implementation, the real-time temperature monitoring points are located on the pipe section between the inlet pipe of the oxidation reactor, the outlet of the physical state control unit, and the inlet valve of the oxidation reactor. This location should ensure that the measured temperature accurately represents the temperature of the gas about to enter the catalyst bed and is not significantly affected by valve throttling effects or pipe wall heat dissipation. A sheathed platinum resistance thermometer with an accuracy class of A is used as the temperature sensor, covering a temperature range of -50°C to 200°C, with a response time constant of no more than 3 seconds. The platinum resistance thermometer is inserted vertically into the center of the pipe to a depth of half the pipe's inner diameter, ensuring that the sensing element is at the center of the airflow. The temperature sensor outputs a standard current signal of 4 to 20 mA, which is connected to the analog input module of the distributed control system or programmable logic controller via a shielded cable.

[0079] The specific process for signal acquisition and processing is as follows: The control system reads the current signal from the temperature sensor at a sampling frequency of no less than once per second. After analog-to-digital conversion, the signal is converted into the actual temperature value according to the sensor calibration curve. To eliminate measurement noise caused by electromagnetic interference and airflow pulsation, the raw temperature signal is subjected to a first-order low-pass digital filter with a filtering time constant of 2 to 5 seconds. The filtered temperature value T_actual is the real-time monitored input raw material temperature for this oxidation step. This value is stored in the control system's data register for subsequent judgment and recording.

[0080] The preset temperature range is determined based on the type of catalyst used in the oxidation step and the process objectives. Taking platinum alumina catalyst as an example, according to the experimental data obtained in Tables 1 and 2, the oxidation reaction can proceed stably with a separation factor greater than 1.06 within the temperature range of 20 to 100 degrees Celsius, and the separation factor reaches 1.300 at 40 degrees Celsius. Considering the allowable fluctuation margin in actual industrial production and to keep the operating point as close as possible to the optimal separation effect, the preset temperature range can be set to 35 to 45 degrees Celsius. The upper limit of this temperature range ensures that isotope thermodynamic remixing is avoided, while the lower limit ensures that the catalyst is in a fully activated state. The preset temperature range value is pre-written into the setpoint register of the control system, and operators can modify and solidify it according to the process requirements of different stages.

[0081] The judgment logic employs a comparison algorithm with a hysteresis region to prevent frequent start-stop cycles at threshold boundaries. The specific logic is as follows: The upper temperature threshold T_H is set to 45 degrees Celsius, and the lower temperature threshold T_L is set to 35 degrees Celsius. When the real-time temperature T_actual first exceeds T_H, the control system determines that the temperature exceeds the preset upper limit, triggering a high-temperature alarm and a cooling adjustment program. When T_actual first falls below T_L, it determines that the temperature exceeds the preset lower limit, triggering a low-temperature alarm and a heating adjustment program. To eliminate misjudgments caused by measurement noise, a time delay judgment condition is added: adjustment is only confirmed when T_actual continuously exceeds the threshold for a set delay time, such as 10 seconds or more. This prevents brief temperature fluctuations from triggering unnecessary adjustment actions. After the adjustment program starts, T_actual is continuously monitored. Only when T_actual falls back to between T_H and T_L, i.e., enters the preset temperature range, and the stabilization time reaches 30 seconds or more, is the alarm signal deactivated, additional heating or cooling equipment shut down, and normal stable operation restored. The data from the entire monitoring, judgment, and triggering process are recorded and stored by the control system according to time tags, generating temperature trend curves for operators to use for inspection and process traceability.

[0082] The technical principle behind this implementation is that temperature is the most sensitive variable affecting the oxidation reaction rate and isotope separation selectivity. If the feed temperature is too high, exceeding the upper limit of the preset temperature range, it may lead to localized overheating of the catalyst bed, accelerating the isotope exchange reaction and weakening the achieved separation effect due to thermodynamic equilibrium. If the feed temperature is too low, below the lower limit of the preset temperature range, the catalyst activity may be insufficient, the reaction rate will decrease, the conversion rate will be too low, and the material balance of subsequent cascades will be affected. Therefore, by pre-monitoring and pre-judgment, the temperature is stabilized within the optimal operating window, ensuring the separation stability and repeatability of the oxidation step from the source.

[0083] In a preferred embodiment, adjusting the carbon monoxide feedstock entering this oxidation step to a preset physical state includes the following steps: The physical state parameters of the carbon monoxide feedstock are monitored in real time, including the rate of change of temperature over time or the rate of change of pressure over time. Determine whether the physical state parameter exceeds the corresponding preset fluctuation threshold; If the physical state parameter exceeds the preset fluctuation threshold, the temperature and / or pressure of the carbon monoxide raw material are adjusted until the physical state parameter is lower than the corresponding preset fluctuation threshold.

[0084] Specifically, the real-time monitoring of physical state parameters overlaps somewhat with the aforementioned hardware configuration, but adds the function of calculating the rate of change and a pressure monitoring branch. The rate of change of temperature over time, dT / dt, is realized through a control system software algorithm. The system reads the temperature sensor value T at a fixed sampling period Δt, such as 1 second. The temperature difference ΔT between the current sampling time n and the previous sampling time n-1 is equal to T_n minus T_n-1. Therefore, the rate of change of temperature dT / dt is equal to ΔT divided by Δt, with units of degrees Celsius per second or degrees Celsius per minute. To reduce the amplification effect of differential calculation on measurement noise, in practical engineering, a moving average filter can be applied to the temperature sequence before calculating ΔT, with a window length of 5 to 10 sampling points. The rate of change of pressure over time, dP / dt, is obtained in a similar way. A pressure transmitter is installed on the outlet pipeline of the buffer pressure stabilizing tank or the inlet pipeline of the oxidation reactor. The range is selected according to the operating pressure, for example, 0 to 0.5 MPa, with an accuracy class of 0.1, and an output signal of 4 to 20 mA. The control system reads the pressure value with the same sampling period and calculates dP / dt, in megapascals per second or megapascals per minute.

[0085] The preset fluctuation threshold is determined based on experimental data on the tolerance of the oxidation step to feed stability. Typically, the temperature change rate threshold needs to consider both the thermal inertia of the catalyst bed and the response capability of the temperature control system. For small reactors with small packing volumes and low heat capacities, the temperature change rate threshold needs to be set more strictly, for example, ±2 degrees Celsius per minute. For large industrial reactors with large packing volumes and high heat capacities, the bed itself has a certain buffering capacity, and the threshold can be appropriately relaxed, for example, ±5 degrees Celsius per minute. The pressure change rate threshold mainly depends on the response speed of the mass flow controller and the pressure stabilization capability of the buffer tank, and can generally be set to ±0.05 MPa per minute. The specific threshold value is determined through a step disturbance test during the no-load commissioning phase. This involves artificially changing the upstream flow rate or temperature, observing the propagation of downstream parameter fluctuations, and using the absence of significant changes in the separation factor at the oxidation reactor outlet as a criterion to determine the upper limit of allowable feed fluctuations, which is then set as the preset fluctuation threshold.

[0086] The judgment and adjustment execution steps are as follows. In each sampling period, the control system calculates the absolute values ​​of the current dT / dt and dP / dt, and compares them with the corresponding preset fluctuation thresholds. When the absolute value of dT / dt exceeds the temperature change rate threshold, the control system triggers the temperature fluctuation suppression program. Specific measures for temperature fluctuation suppression include: adjusting the opening rate of the upstream heat exchanger refrigerant flow control valve to avoid secondary fluctuations caused by rapid refrigerant valve action; increasing the damping coefficient of the regulating valve on the buffer tank inlet pipe to slow down the step change in airflow velocity; when the temperature shows a rapid upward trend, appropriately pre-opening the refrigerant valve for proactive adjustment; when the temperature shows a rapid downward trend, appropriately reducing the refrigerant quantity and starting auxiliary electric heating. When the absolute value of dP / dt exceeds the pressure change rate threshold, the control system triggers the pressure fluctuation suppression program. Specific measures to suppress pressure fluctuations include: adjusting the PID parameters of the buffer tank outlet pressure regulating valve to increase the integral time constant and slow down the valve response, or gradually adjusting the valve opening in manual mode; if the pressure rises sharply, releasing a small amount of gas to the safe emission system through a parallel fast-release valve; if the pressure drops sharply, starting the online booster pump with variable frequency speed control to increase the gas supply pressure. During the adjustment process, the control system continuously monitors the real-time values ​​of dT / dt and dP / dt. Once their absolute values ​​fall below the preset fluctuation threshold and remain stable for at least 30 seconds, the fluctuation is considered to have been effectively suppressed, and each regulating valve returns to normal automatic control mode.

[0087] The technical principle of this implementation is that even if the absolute average values ​​of temperature and pressure are within the operating window, drastic short-term fluctuations can still cause the reaction conditions in a localized area of ​​the catalyst bed to momentarily deviate from the optimal state. This momentary deviation may cause a temporary deterioration in isotope separation, and due to the cumulative effect of the cascade system, small fluctuations in the preceding stages may be amplified in subsequent stages. By monitoring and controlling the rate of change of physical state parameters, it is equivalent to weakening and eliminating fluctuations before they propagate to the oxidation reactor, providing a double guarantee for the oxidation step: ensuring both that the static operating point remains within the operating window and that the dynamic process remains stable.

[0088] In a preferred embodiment, the following steps are also included: Real-time online monitoring of the carbon isotope abundance ratio of output materials at at least one target enrichment level; The carbon isotope abundance ratio is compared with a preset target abundance value to obtain the comparison result; Based on the comparison results, at least one key process parameter of the target enrichment stage or its upstream enrichment stage is dynamically adjusted so that the carbon isotope abundance ratio of the output material approaches the preset target abundance value. The key process parameters include at least one of the reaction temperature of the oxidation step, the reaction space velocity, and the temperature of the reduction step.

[0089] Specifically, in a cascade of N enrichment stages, the target enrichment stage is typically selected as the final product extraction stage, i.e., the outlet of the oxidation step or separation step in stage N, because the carbon isotope abundance ratio of the material at this stage directly corresponds to the quality of the final product. In some cases, several intermediate stages can also be selected as auxiliary target stages based on process diagnostic needs, to monitor the enrichment efficiency of each stage in segments. In practical implementation, after determining one or more target enrichment stages, an online sampling and isotope abundance analysis device is installed on its output material pipeline.

[0090] The hardware configuration for real-time online monitoring of carbon isotope abundance ratios consists of two parts: a sampling system and an analytical instrument. The sampling system comprises a miniature sampling pump, a dust filter, a dehumidifying cold trap, and a pressure regulating valve. A small stream of sample gas is continuously drawn from the main pipeline of the target enrichment stage output material, with a flow rate typically between 50 and 200 mL / min. The dust filter uses a sintered metal filter with a pore size of 0.1 micrometers. The dehumidifying cold trap uses semiconductor cooling to lower the dew point of the sample gas to below -20 degrees Celsius to avoid interference from moisture on the analytical instrument. The pretreated sample gas then enters the isotope abundance analyzer. The analytical instrument can be an online mass spectrometer or a tunable diode laser absorption spectrometer. Taking a laser spectrometer as an example, it utilizes… 12 CO and 13 CO or 12 CO2 and 13 The differences in characteristic absorption lines of CO2 in the near-infrared band are used to output the carbon isotope abundance ratio in real time through wavelength scanning and second harmonic detection techniques. 13 C abundance and 12 The ratio of C abundance or 13 The percentage of carbon atoms in total carbon. The measurement cycle of the analytical instrument is typically 1 to 5 seconds, with a measurement accuracy of ±1 / 1000 of an abundance unit. The abundance ratio data output by the analytical instrument is transmitted in real time to the central control system via digital communication protocols such as Modbus or Profibus.

[0091] The comparison and deviation calculations are performed within the control system. The preset target abundance value R_set is set according to product order requirements; for example, when production requires an abundance of 10%. 13 For product C, R_set equals 10%. The control system reads the real-time abundance ratio R_actual from the analyzer each control cycle and calculates the deviation e, which is equal to R_set minus R_actual. Simultaneously, the deviation change rate Δe is calculated to determine the trend of the abundance ratio. To improve control stability, a rolling average value can be used as R_actual, taking the average of the most recent 10 to 30 sampling cycles.

[0092] Dynamically adjusting key process parameters is the core execution step of closed-loop control. The selection and adjustment direction of key process parameters depend on the comparison results. The specific operation is as follows: If the deviation e is positive and its absolute value exceeds the control dead zone, i.e., R_actual is lower than R_set, the product... 13 Insufficient carbon abundance necessitates enhancing the system's separation driving force. Enhancement measures include reducing the space velocity (WHV) of the target enrichment stage oxidation step. A specific method for reducing the WHV is to adjust the flow rate setpoint of the feed mass flow controller for this oxidation reactor downwards, for example, by reducing it by 5% to 10% each time according to the deviation. After reducing the WHV, the residence time is prolonged. 13 C is preferentially oxidized more fully at the active sites of the catalyst, resulting in more complete product oxidation. 13 The carbon abundance will increase. Simultaneously, the reaction temperature of the oxidation step can be moderately reduced; within the low-temperature operating range, lower temperatures generally result in a higher separation factor. However, adjustments must be made cautiously, with each reduction not exceeding 2 degrees Celsius to avoid excessive decreases in reaction rate leading to insufficient conversion. Another enhancement measure is to adjust the temperature of one or more reduction steps upstream of the target enrichment stage. Appropriately increasing the reduction step temperature, such as from 400 degrees Celsius to 420 degrees Celsius, can improve the carbon dioxide reduction conversion rate, thus enhancing the enrichment of the carbon dioxide entering the next oxidation step. 13 The increased carbon monoxide flow rate further enhances the performance of downstream processes. 13 C accumulation rate.

[0093] If the deviation e is negative and its absolute value exceeds the control dead zone, i.e., R_actual is higher than R_set, the product... 13 Excessive carbon abundance, while exceeding quality requirements, may consume excessive energy and raw materials, necessitating a moderate reduction in the separation driving force. Reduction measures include appropriately increasing the space velocity or reaction temperature in the oxidation step, with each adjustment being comparable to the enhancement process. When adjusting, priority should be given to the parameter whose change causes the least disturbance to the system. Typically, the space velocity should be adjusted first, followed by the oxidation temperature, and finally the reduction temperature, as the reduction step has greater thermal inertia and a slower response time due to temperature changes.

[0094] For the differentiated adjustment of the preliminary enrichment zone and the refined enrichment zone, if the product abundance deviation stems from insufficient concentration in the front end of the system, the space velocity or temperature parameters of the first K stages in the preliminary enrichment zone are adjusted first; if the deviation stems from the refining efficiency in the later stages, the operating parameters of stages K+1 to N in the refined enrichment zone are adjusted first. After adjustment, the control system continues to monitor the change of R_actual in each control cycle. After the system response stabilizes, the deviation is compared again until the deviation falls within the control dead zone. This closed-loop control mode of real-time online monitoring and feedback adjustment ensures that the entire system always maintains the optimal operating point, ensuring batch consistency and long-term stability of the carbon isotope abundance ratio of the final product, meeting the requirements of high-end applications such as... 13C-breath test materials have strict requirements for the accuracy of isotope abundance.

[0095] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. The above descriptions are only preferred embodiments of this application. It should be noted that due to the limitations of written expression, while there are objectively infinite specific structures, those skilled in the art can make several improvements, modifications, or changes without departing from the principles of this invention, and can also combine the above technical features in an appropriate manner. These improvements, modifications, changes, or combinations, or the direct application of the inventive concept and technical solution to other situations without modification, should all be considered within the scope of protection of this application.

Claims

1. A carbon isotope enrichment cycle process based on low-temperature selective oxidation of carbon monoxide, implemented using a selective oxidation-reduction coupled cycle system consisting of N cascaded enrichment stages, wherein... N is an integer greater than 1; the process is characterized by comprising the following steps: Within each enrichment level, the following steps are performed sequentially: Oxidation step: Using a catalyst, carbon monoxide is selectively catalytically oxidized at -20~100℃ to produce carbon dioxide enriched with heavy carbon isotopes and residual carbon monoxide enriched with light carbon isotopes. Separation steps: The product from the above steps is subjected to alkaline solution and / or organic amine solution to absorb carbon dioxide, and unreacted carbon monoxide enriched with light carbon isotopes is obtained; the absorbed carbon dioxide is released again by acid or heating treatment to obtain carbon dioxide enriched with heavy carbon isotopes. Reduction step: Under high temperature conditions of 200~600℃, carbon dioxide enriched with heavy carbon isotopes is reduced by at least one reducing substance selected from hydrogen, metal oxide, sulfite, and metal powder to generate carbon monoxide enriched with heavy carbon isotopes; wherein the conversion rate of the reduction process is ≥90%, ensuring the separation effect of carbon isotopes by selective oxidation. Joint execution is performed between the enrichment levels described at each level: Enriched material transfer: The carbon dioxide enriched with heavy carbon isotopes produced in the previous oxidation step is reduced by the reduction step to obtain carbon monoxide enriched with heavy carbon isotopes, which is then fed into the next oxidation step as carbon monoxide raw material. Depleted material recycling: The carbon monoxide enriched with light carbon isotopes produced in the subsequent separation step is returned to the previous oxidation step; The cascade coupling of the oxidation step, the separation step, and the reduction step enables the directional enrichment of carbon isotopes.

2. The carbon isotope enrichment and recycling process based on low-temperature selective oxidation of carbon monoxide according to claim 1, characterized in that: The reaction temperature for the oxidation step is -20 to 100°C.

3. The carbon isotope enrichment and recycling process based on low-temperature selective oxidation of carbon monoxide according to claim 1, characterized in that: The catalyst is selected from at least one of noble metal catalysts, transition metal oxide catalysts, supported noble metal catalysts, and supported transition metal oxide catalysts.

4. The carbon isotope enrichment and recycling process based on low-temperature selective oxidation of carbon monoxide according to claim 1, characterized in that: The oxidation step achieves the desired effect by controlling the reaction space velocity and catalyst particle size. 13 Preferential oxidation of C.

5. The carbon isotope enrichment and recycling process based on low-temperature selective oxidation of carbon monoxide according to claim 4, characterized in that: In the oxidation step, the reaction space velocity is controlled at 1000~10000 h⁻¹. -1 Within the specified range, and controlling the catalyst particle size between 20 and 200 mesh; through the synergistic effect of the reaction space velocity and the catalyst particle size, the residence time of the reactants at the active sites of the catalyst and the diffusion mass transfer process are regulated, so as to achieve higher reactivity. 12 C preferentially diffuses away from the reaction site, thereby causing the C-containing 13 Carbon monoxide (C) accumulates at active sites and is preferentially oxidized, resulting in enrichment. 13 C carbon dioxide and enrichment 12 Residual carbon monoxide of C.

6. The carbon isotope enrichment and recycling process based on low-temperature selective oxidation of carbon monoxide according to claim 5, characterized in that: For enrichment stages 1 through K, a preliminary enrichment zone is configured, employing a first parameter combination where the reaction space velocity is 5000 ~ 10000 h⁻¹. -1 The catalyst particle size is 40-200 mesh to prioritize ensuring the system's material throughput. For the K+1 to Nth enrichment stages, a fine enrichment zone is configured, employing a second parameter combination where the reaction space velocity is 1000-5000 h⁻¹. -1 The catalyst has a particle size of 20 to 60 mesh to prioritize improving the single-stage separation accuracy; where K is an integer between 1 and N.

7. The carbon isotope enrichment and recycling process based on low-temperature selective oxidation of carbon monoxide according to claim 6, characterized in that: Prior to each oxidation step, the following steps are also included: The carbon monoxide feedstock entering this oxidation step is adjusted to a preset physical state, which enables the oxidation step to operate stably within a preset operating window; the preset operating window is the range of operating conditions that can effectively cause catalytic oxidation reaction and avoid thermodynamic remixing of carbon isotopes.

8. The carbon isotope enrichment and recycling process based on low-temperature selective oxidation of carbon monoxide according to claim 7, characterized in that: Before adjusting the carbon monoxide feedstock entering this oxidation step to a preset physical state, the process also includes the following steps: The temperature of the carbon monoxide feedstock input in the oxidation step of this stage is monitored in real time, and it is determined whether the temperature is within the preset temperature range corresponding to the preset operation window.

9. The carbon isotope enrichment and recycling process based on low-temperature selective oxidation of carbon monoxide according to claim 7, characterized in that: The process of adjusting the carbon monoxide feedstock entering this oxidation step to a preset physical state includes the following steps: The physical state parameters of the carbon monoxide feedstock are monitored in real time, including the rate of change of temperature over time or the rate of change of pressure over time. Determine whether the physical state parameter exceeds the corresponding preset fluctuation threshold; If the physical state parameter exceeds the preset fluctuation threshold, the temperature and / or pressure of the carbon monoxide raw material are adjusted until the physical state parameter is lower than the corresponding preset fluctuation threshold.

10. The carbon isotope enrichment and recycling process based on low-temperature selective oxidation of carbon monoxide according to claim 1, characterized in that: It also includes the following steps: Real-time online monitoring of the carbon isotope abundance ratio of output materials at at least one target enrichment level; The carbon isotope abundance ratio is compared with a preset target abundance value to obtain the comparison result; Based on the comparison results, at least one key process parameter of the target enrichment stage or its upstream enrichment stage is dynamically adjusted so that the carbon isotope abundance ratio of the output material approaches the preset target abundance value. The key process parameters include at least one of the reaction temperature of the oxidation step, the reaction space velocity, and the temperature of the reduction step.

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