Carbon conversion system and method for direct air capture coupled to solid oxide electrolysis

Abstract

The present application relates to carbon paving set and carbon conversion technical field, especially to direct air capture coupling solid oxide electrolysis carbon conversion system and method, wherein, carbon conversion system, including: direct air capture module, solid oxide electrolysis tank module, solid oxide electrolyysis tank module and direct air capture module are connected through heat energy recovery path, and heat energy recovery path is configured to utilize the reaction waste heat generated by solid oxide electrolysis tank module to drive the adsorbent regeneration process of direct air capture module.Direct air capture module includes adsorption reactor and buffer tank.The present application is through adopting the carbon conversion system, airflow fluctuation is smoothed as quasi-steady state by buffer tank, and the stable air inlet of solid oxide electrolysis tank is guaranteed;The reaction waste heat of solid oxide electrolysis tank is guided to be used for adsorbent regeneration, and the overall energy consumption of system is reduced;The composite cathode modified by cation doping can adapt to the dynamic fluctuation of wide range CO2 concentration, and the operation stability of system is improved.

Description

Technical Field

[0001] This invention relates to the field of carbon deposition and carbon conversion technology, and in particular to a carbon conversion system and method that couples direct air capture with solid oxide electrolysis. Background Technology

[0002] Existing high-temperature solid oxide electrolyzer technology faces a significant challenge in practical applications: feedstock adaptability. Traditional processes typically require high-purity, high-concentration CO2 gas (generally not less than 90% by volume) as the electrolysis feedstock. This requirement leads to a strong dependence on upstream carbon capture or separation processes: while industrial point-source capture yields relatively high concentrations of CO2 gas, its supply is geographically limited, making distributed deployment difficult; and it cannot achieve in-situ, continuous, and integrated conversion from low-concentration (e.g., approximately 400 ppm by volume) CO2 capture from ambient air to the synthesis of high-value chemicals.

[0003] Therefore, the existing technology still needs further development and improvement. Summary of the Invention

[0004] This invention proposes a carbon conversion system and method that couples direct air capture with solid oxide electrolysis. By integrating and coupling direct air capture with a solid oxide electrolyzer, it aims to solve the problems of poor airflow stability and low energy utilization efficiency faced by existing carbon conversion technologies. Specifically:

[0005] In a first aspect, a carbon conversion system comprising direct air capture coupled with solid oxide electrolysis, wherein:

[0006] A direct air capture module is used to capture and enrich carbon dioxide from ambient air to generate a carbon-containing feedstock gas stream. The direct air capture module includes an adsorption reactor and a buffer tank, wherein the buffer tank is configured to convert the pulsed gas stream generated by the adsorption reactor into a quasi-steady-state gas stream.

[0007] A solid oxide electrolytic cell module is used to receive the carbon-containing raw material gas stream and perform electrolytic conversion. The solid oxide electrolytic cell module includes a composite cathode, which is prepared by using perovskite oxide as a matrix and modifying it with cation doping.

[0008] The solid oxide electrolyzer module and the direct air capture module are connected via a heat recovery path, which is configured to use the waste heat generated by the solid oxide electrolyzer module to drive the adsorbent regeneration process of the direct air capture module.

[0009] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0010] As a preferred technical solution, in the carbon conversion system, the adsorption reactor is filled with a selective adsorption material, which is selected from at least one of solid amine composite materials, metal-organic framework materials, or porous materials modified with alkali metals or alkaline earth metals.

[0011] As a preferred technical solution, in the carbon conversion system, the substrate of the composite cathode is a perovskite structure oxide, and cations are doped into the lattice of the substrate or modified on the surface of the substrate to induce the generation of oxygen vacancies on the surface of the composite cathode.

[0012] As a preferred technical solution, in the carbon conversion system, the cation is selected from Li + Na + K + 、Rb + and Cs + Any one of the following; the perovskite structure oxide is Sr2Fe 1.5 Mo 0.5 O 6-δ .

[0013] As a preferred technical solution, in the carbon conversion system, the direct air capture module further includes:

[0014] The temperature control module is used to control the switching between the adsorption temperature and the desorption temperature of the adsorption reactor;

[0015] The pressure control module is used to regulate the pressure inside the adsorption reactor;

[0016] A carrier gas supply device is used to introduce a purging medium into the adsorption reactor.

[0017] As a preferred technical solution, the carbon conversion system wherein the direct air capture module is configured with a conventional regeneration mode and a deep regeneration mode; the conventional regeneration mode regenerates the adsorbent through a combination of temperature-driven and pressure-driven purging; the deep regeneration mode removes stubborn impurities by heating the adsorption reactor to a temperature higher than that of the conventional regeneration mode and performing dry purging.

[0018] As a preferred technical solution, in the carbon conversion system, a dehumidification and drying unit is further provided between the direct air capture module and the solid oxide electrolysis cell module. The dehumidification and drying unit is used to adjust the relative humidity of the raw material airflow before entering the solid oxide electrolysis cell module to a preset range.

[0019] Secondly, a carbon conversion method based on the carbon conversion system described above, comprising the following steps:

[0020] Carbon dioxide is captured from ambient air using a direct air capture module;

[0021] By controlling the desorption conditions of the direct air capture module, the captured carbon dioxide is enriched and buffered and stabilized to form a continuous carbon-containing raw material gas flow.

[0022] The carbon-containing raw material gas stream is introduced into the solid oxide electrolytic cell module for electrolysis, converting it into carbon-containing chemicals;

[0023] The heat energy generated by the solid oxide electrolyzer module is collected and fed back to the direct air capture module to drive the regeneration of the adsorbent.

[0024] As a preferred technical solution, the carbon conversion method wherein the solid oxide electrolyzer module is controlled to operate in co-electrolysis mode by adjusting the desorption parameters of the direct air capture module and introducing water vapor into the carbon-containing feed gas stream in a proportional manner, thereby producing syngas with an adjustable hydrogen-to-oxygen ratio.

[0025] Beneficial effects: Compared with existing technologies, this invention, by employing the aforementioned carbon conversion system, smooths airflow fluctuations into a quasi-steady state through a buffer tank, ensuring stable air intake for the solid oxide electrolyzer module; the waste heat from the solid oxide electrolyzer module is directed for adsorbent regeneration, reducing the overall energy consumption of the system; the cation-doped modified composite cathode can adapt to dynamic fluctuations in CO2 concentration over a wide range, improving the system's operational stability. This achieves in-situ, continuous, and integrated conversion from low-concentration (approximately 400 ppm volume fraction) CO2 capture from ambient air to the synthesis of high-value chemicals. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the overall structure of the carbon conversion system provided in an embodiment of the present invention.

[0028] Figure 2 This is a schematic diagram of the direct air capture module provided in an embodiment of the present invention.

[0029] Figure 3This is a schematic diagram of the SOEC electrolytic stack provided in an embodiment of the present invention.

[0030] Figure 4 This is a schematic diagram illustrating the working principle and reaction mechanism of the electrolysis unit provided in an embodiment of the present invention.

[0031] Figure 5 The current-voltage polarization curves of Li and Na doping in direct air capture mode are provided for embodiments of the present invention.

[0032] Figure 6 Impedance characteristics of Li and Na doping in direct air trapping mode provided in embodiments of the present invention.

[0033] Figure 7 The voltage-time curve of a single cell performing a CO2 capture-release-electrolysis cycle in direct air capture mode is provided for an embodiment of the present invention. Detailed Implementation

[0034] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0035] In the description of the embodiments of the present invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0036] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0037] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0038] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0039] like Figure 1 As shown, the system mainly consists of a direct air capture module 100, a solid oxide electrolyzer module 200, and a heat recovery path 300 connecting the two. The gas outlet of the direct air capture module 100 is connected to the air inlet of the solid oxide electrolyzer module 200 via a pipeline, and the heat outlet of the solid oxide electrolyzer module 200 is connected to the heat inlet of the direct air capture module 100 via the heat recovery path 300. The main function of the direct air capture module 100 is to selectively adsorb CO2 from ambient air and, under specific conditions, desorb and release the enriched CO2 to form a feed gas stream for the solid oxide electrolyzer module 200. The solid oxide electrolyzer module 200 electrolyzes the CO2 in the feed gas stream into CO under high-temperature conditions, or co-electrolyzes CO2 and H2O into syngas (H2 / CO mixture). The heat recovery path 300 conducts the high-temperature waste heat generated during the operation of the solid oxide electrolyzer module 200 to the direct air capture module 100, providing energy for the thermal regeneration process of the adsorbent.

[0040] like Figure 2As shown, in one embodiment of the present invention, the direct air capture module 100 includes at least one adsorption reactor 110. The adsorption reactor 110 can be a fixed-bed reactor, filled with a selective adsorption material for selectively adsorbing CO2 from the flowing ambient air. The selective adsorption material has a high adsorption capacity and selectivity for CO2, while also meeting the requirement of effective regeneration under medium and low temperature conditions. In a specific embodiment, the adsorption material is a solid amine-based composite material, which uses porous silica or alumina as a carrier, with primary, secondary, or tertiary amine functional groups grafted onto the inner surface of the pores. The amine functional groups can undergo a reversible chemisorption reaction with CO2, exhibiting a high CO2 adsorption capacity at room temperature (typically 2–4 mmol / g), and achieving effective thermal regeneration within a temperature range of 80–120°C.

[0041] In another specific embodiment, the adsorbent is a metal-organic framework (MOF). This type of material forms a crystalline porous material with a regular pore structure through the coordination assembly of metal nodes and organic ligands. Its pore size and surface functional groups can be controlled during the synthesis stage, thereby endowing the material with selective recognition and adsorption capabilities for CO2. Compared to amine-based materials, some MOFs can maintain a high adsorption capacity even under low CO2 partial pressure conditions, making them suitable for directly capturing CO2 at levels of 400 ppm from the atmosphere.

[0042] In another specific embodiment, the adsorbent is a porous material modified with an alkali metal or alkaline earth metal, such as a composite adsorbent prepared by impregnating activated carbon or alumina with potassium carbonate (K2CO3). The introduction of alkali metal salts makes the surface of the adsorbent alkaline, which is beneficial for the selective adsorption of acidic gas CO2.

[0043] The aforementioned adsorbent materials can be used alone or mixed in proportion and filled into the adsorption reactor 110 to meet various performance requirements such as adsorption capacity, selectivity, and regeneration energy consumption. The operation of the adsorption reactor 110 includes an adsorption stage and a regeneration (desorption) stage, which alternate sequentially. During the adsorption stage, ambient air is introduced by a fan or blower and passes through the adsorption bed at a certain flow rate. CO2 is selectively adsorbed, and the purified gas is discharged. During the regeneration stage, the adsorbed CO2 is desorbed from the surface of the adsorbent material by heating, depressurizing, or introducing a purge medium, resulting in a CO2-rich gas flow output.

[0044] To achieve continuous operation of multiple towers in parallel, in another embodiment, the direct air capture module 100 includes at least two adsorption reactors 110, each reactor alternating between the adsorption phase and the regeneration phase, thereby ensuring a continuous output of CO2-rich gas flow.

[0045] In one embodiment of the present invention, the direct air capture module 100 further includes a buffer tank 120. The buffer tank 120 is disposed on the pipeline between the gas outlet of the adsorption reactor 110 and the air inlet of the solid oxide electrolysis cell module 200.

[0046] The CO2 desorption rate in the regeneration stage of the adsorption reactor 110 changes dynamically with the bed temperature and pressure, causing the output gas flow rate and CO2 concentration to fluctuate in a pulse-like manner over time. The solid oxide electrolyzer module 200 has high requirements for the stability of the inlet gas. Large fluctuations in the inlet gas flow rate and composition can lead to increased electrode polarization loss, decreased electrolysis efficiency, and even thermo-chemical stress damage to the cathode material.

[0047] The buffer tank 120 provides a certain gas storage volume to homogenize and stabilize the upstream pulsed gas flow, transforming it into a quasi-steady-state gas flow with relatively stable flow rate and concentration before it is delivered to the solid oxide electrolyzer module 200. The volume of the buffer tank 120 is designed based on the scale of the adsorption reactor 110 and the peak desorption flow rate to ensure that, under the most unfavorable operating conditions, the fluctuation range of the output gas flow rate is controlled within the acceptable range of the solid oxide electrolyzer module 200.

[0048] In one specific embodiment, the buffer tank 120 is equipped with a pressure sensor and a flow regulating valve to maintain a stable outlet airflow through feedback control.

[0049] In one embodiment of the present invention, the direct air capture module 100 further includes a temperature control module 130, a pressure control module 140, and a carrier gas supply device 150.

[0050] The temperature control module 130 is configured to control the switching between the adsorption temperature and the desorption temperature of the adsorption reactor 110. During the adsorption stage, the adsorption reactor 110 is maintained at a relatively low adsorption temperature (usually 20-40°C, i.e., close to the ambient temperature) to facilitate the chemical adsorption of CO2. During the regeneration stage, the temperature control module 130 provides heat to the bed through built-in heating elements (such as electric heating wires, hot fluid heat exchange tubes) or external heat exchangers to raise the reactor temperature to the desorption temperature (usually 80-150°C), thereby promoting the desorption of CO2 from the surface of the adsorption material.

[0051] In one embodiment of the invention, the heating source for the temperature control module 130 is the waste heat from the solid oxide electrolyzer conducted through the heat recovery path 300. The solid oxide electrolyzer module 200 operates at a high temperature of 700–850°C. The high-temperature gas (mainly hot gas flow containing O2) generated on its anode side, as well as the radiant and conductive heat emitted by the stack body, are cooled to a suitable temperature by the heat exchanger in the heat recovery path 300 and then used as the regeneration heat source for the direct air capture module 100.

[0052] The pressure control module 140 is configured to regulate the pressure within the adsorption reactor 110. In one specific embodiment, the pressure control module 140 includes a vacuum pump and a pressure regulating valve. During the regeneration phase, the pressure control module 140 evacuates the reactor, reducing the bed pressure (e.g., to 5–20 kPa absolute pressure), which helps achieve effective CO2 desorption at lower temperatures, thereby reducing regeneration heat consumption. During the adsorption phase, the pressure control module 140 maintains the reactor at near-atmospheric pressure. This regeneration strategy, coupled with temperature swing adsorption (TSA) and pressure swing adsorption (PSA), can be flexibly adjusted under different operating conditions to obtain optimal energy utilization efficiency and CO2 recovery rate.

[0053] The carrier gas supply device 150 is configured to introduce a purge medium into the adsorption reactor 110. During the regeneration stage, by introducing an appropriate amount of purge gas (such as dry air, nitrogen, or water vapor) into the bed, the partial pressure of CO2 in the bed can be reduced, accelerating CO2 desorption and carrying the desorbed CO2 to the outlet, thereby improving desorption efficiency. In one specific embodiment, when water vapor is selected as the purge medium, the desorption output gas stream contains both CO2 and H2O. This mixed gas stream can be directly introduced into the solid oxide electrolyzer module 200 for co-electrolysis of CO2 and H2O to produce H2 / CO syngas, in which case no additional water vapor addition device is required. In another specific embodiment, dry air or nitrogen is selected as the purge medium, and CO2 is the main component of the desorption gas stream, which is suitable for the operation mode of the solid oxide electrolyzer module 200 electrolyzing CO2 alone.

[0054] In one embodiment of the present invention, the direct air capture module 100 is configured with a conventional regeneration mode and a deep regeneration mode, which can be flexibly switched according to the actual state of the adsorbent material.

[0055] The conventional regeneration mode is suitable for normal cycle operation. In this mode, the temperature control module 130 raises the bed temperature of the adsorption reactor 110 to the conventional desorption temperature (e.g., 80–120°C), while the pressure control module 140 reduces the bed pressure, and the carrier gas supply device 150 introduces an appropriate amount of purge medium. The synergistic effect of temperature-driven and pressure-driven purge ensures that CO2 on the adsorption material is fully desorbed. After one regeneration cycle, the CO2 adsorption capacity of the material is basically restored to the initial level.

[0056] The deep regeneration mode is suitable for situations where, after prolonged operation, the adsorbent surface accumulates stubborn impurities such as moisture and organic pollutants, leading to an irreversible decrease in adsorption capacity. In this mode, the temperature control module 130 raises the bed temperature to a level significantly higher than that of the conventional regeneration mode (e.g., 150–200°C), and the carrier gas supply device 150 introduces dry purging gas (low-humidity air or inert gas) to dry and purge the bed. The higher processing temperature helps break the strong interaction between impurities and adsorption sites, allowing stubborn impurities to be removed and restoring the effective active area and functional group density of the adsorbent material. The operation frequency of the deep regeneration mode is typically much lower than that of the conventional regeneration mode, for example, once every tens to hundreds of conventional cycles.

[0057] In one embodiment of the present invention, a dehumidification and drying unit 160, an air valve 170, and a flow meter 180 are further provided between the direct air capture module 100 and the solid oxide electrolysis cell module 200.

[0058] While adsorbing CO2, the direct air capture module 100 inevitably adsorbs moisture from the ambient air, which is then desorbed along with CO2 during the regeneration stage, resulting in a certain amount of water vapor in the feed gas stream. For the solid oxide electrolyzer module 200, an appropriate amount of water vapor in the intake air is helpful for participating in the co-electrolysis reaction, but if the water vapor content is too high or too low, it will affect the electrolysis performance and the stability of the cathode material.

[0059] The dehumidification and drying unit 160 is configured to regulate the relative humidity of the feed gas flow entering the solid oxide electrolyzer module 200, maintaining it within a preset range. In one specific embodiment, the dehumidification and drying unit 160 uses a silica gel or molecular sieve packed column to remove excess moisture from the gas flow through physical adsorption, controlling the relative humidity at a low level (e.g., below 5%), suitable for the pure CO2 electrolysis mode of the solid oxide electrolyzer. In another specific embodiment, when the system needs to operate in co-electrolysis mode, the dehumidification and drying unit 160 can be used in conjunction with a water vapor addition device to adjust the ratio of water vapor to CO2 in the feed gas flow to a target value (e.g., an H2O:CO2 molar ratio of 1:1 to 3:1) before inputting it into the solid oxide electrolyzer module 200 to produce syngas with a specific H2 / CO ratio.

[0060] The dehumidification and drying unit 160 enables the system to flexibly respond to raw material airflow under different humidity conditions, ensuring the stable operation of the solid oxide electrolytic cell module 200, while avoiding electrode material degradation caused by abnormal intake humidity.

[0061] Combination Figure 3As shown, in one embodiment of the present invention, the solid oxide electrolyzer module 200 includes a fuel cell assembly 210, inlet and outlet gas pipelines (not shown), and a power supply system 220. The fuel cell assembly 210 is composed of a plurality of individual cells 211 stacked together, each individual cell including a cathode (fuel electrode), an electrolyte layer, and an anode (air electrode). In CO2 electrolysis mode, the feed gas flow is introduced into the cathode side through the inlet gas pipeline, and CO2 gains electrons at the cathode interface and is reduced to CO, producing O2. 2- Ions are conducted to the anode side through the dense oxide electrolyte, where they are oxidized to O2 and discharged.

[0062] The solid oxide electrolyzer module 200 typically operates in the range of 700–850°C. Within this temperature range, the oxide ion-conducting electrolyte (such as yttrium-stabilized zirconium oxide, YSZ) exhibits sufficiently high ionic conductivity, while the electrochemical reactions at the cathode and anode possess favorable kinetic conditions.

[0063] Combination Figure 4 As shown, in this embodiment, during the operation of the electrolysis unit, when the power supply system 220 applies a DC voltage, the raw material gas enters the cathode chamber through the inlet and undergoes an electrochemical reduction reaction at the porous cathode 2110 to generate syngas and oxygen ions (O2). 2- Synthesis gas is discharged from the outlet. Oxygen ions migrate to the anode side via the dense electrolyte 2111 and undergo an oxidation reaction on the surface of the porous anode 2112 to generate oxygen. This oxygen is carried by the purge air flowing through the anode flow field and is finally discharged from the system through the oxygen-enriched air outlet, thus completing the conversion of electrical energy into chemical energy.

[0064] During operation, the power supply system 220 applies a DC voltage to the fuel cell stack, driving the following electrochemical reaction: carbon dioxide and water vapor from the inlet undergo a reduction reaction on the cathode surface:

[0065] CO2 + 2e - → CO + O 2-

[0066] H2O + 2e - →H2+ O 2-

[0067] The generated syngas is discharged from the outlet. Simultaneously, the generated oxygen ions (O₂)... 2- Under the influence of an electric field, it migrates through the dense electrolyte layer to the anode, where it undergoes an oxidation reaction.

[0068] 2O 2- → O2 + 4e -

[0069] The generated oxygen is discharged from the system through the outlet along with the purge airflow, completing the entire electrochemical energy and matter conversion cycle.

[0070] The composite cathode used in the solid oxide electrolytic cell module 200 of one embodiment of the present invention is one of the important technical innovations of the present invention. This composite cathode uses perovskite oxide as a substrate, and its electronic structure and surface chemical properties are controlled by cation doping.

[0071] Perovskite oxides have the general formula ABO3, where the A-site is typically an alkaline earth metal or rare earth metal ion, and the B-site is typically a transition metal ion. These oxides possess advantages such as good high-temperature chemical stability and tunable mixed conductivity (possessing both electronic and oxygen ion conductivity), making them one of the important candidate systems for cathode materials in solid oxide electrolyzers.

[0072] In one specific embodiment, the substrate of the composite cathode is a double perovskite oxide Sr2Fe. 1.5 Mo 0.5 O 6-δ (Hereinafter referred to as SFM). In SFM, Sr occupies the A-site, while Fe and Mo jointly occupy the B-site, forming an ordered or partially ordered double perovskite superstructure. SFM exhibits high mixed electronic-ionic conductivity, in which Fe exhibits variable valence characteristics (Fe... 3+ / Fe 2+ Fe 4+ / Fe 3+ This endows the material with good redox reversibility. δ represents the stoichiometric deviation of oxidation, and its value reflects the concentration of oxygen vacancies in the material's crystal lattice. Under a reducing atmosphere (the working atmosphere on the cathode side of CO2 electrolysis), Fe in SFM will undergo partial reduction, generating a certain amount of oxygen vacancies, which helps CO2 surface adsorption and activation.

[0073] However, unmodified SFM exhibits insufficient surface oxygen vacancy concentration and CO2 activation rate to support efficient electrocatalytic conversion when processing low-concentration CO2. To address this issue, one embodiment of the present invention involves the controlled doping of SFM with low-valent cations to further modulate its catalytic performance.

[0074] In one embodiment of the present invention, the cation used to dope and modify the composite cathode substrate is selected from alkali metal ions, including Li + Na + K + 、Rb + and Cs + At least one of them.

[0075] There are two doping methods: one is to incorporate cations into the matrix lattice in a solid solution form (lattice doping); the other is to modify the surface of the matrix with cations in the form of nanoparticles or thin films (surface modification). Both methods can induce additional oxygen vacancies on the surface of the composite cathode, thereby enhancing the material's CO2 adsorption and activation capabilities.

[0076] In one specific embodiment, Na + To create a cation-doped powder, Na₂CO₃ solution was uniformly dispersed on the surface of SFM powder using an impregnation method. After sintering, the Na₂CO₃ solution was then... + Some of the Na diffuses into the SFM lattice, while some remains on the particle surface, forming nanoscale Na compounds. + (Ionic radius approximately 0.102 nm) compared to Sr 2+ The size difference between the 0.144 nm and typical B-site ions (0.060–0.072 nm) leads to local lattice distortion, resulting in charge imbalance. The system maintains electroneutrality by generating oxygen vacancies. Experiments show that with appropriate amounts of Na... + The composite cathode with doping (e.g., Na / SFM molar ratio of 0.2) showed a significant increase in CO2 electrolysis current density compared to unmodified SFM at a CO2 volume fraction of 50%, and maintained high electrocatalytic activity even when the CO2 volume fraction was reduced to 30%, demonstrating good wide concentration adaptability.

[0077] In another specific embodiment, using Li + To prepare a Li-doped SFM composite cathode, Li₂CO₃ was mixed with SFM precursor powder and co-sintered using a solid-state method. + The introduction of [a specific substance] gives the material surface a certain degree of hydrophilicity, which is beneficial to the adsorption and activation of water molecules on the cathode surface, and exhibits a good synergistic catalytic effect in the CO2 / H2O co-electrolysis mode.

[0078] In yet another specific embodiment, K + K-doped SFM composite cathodes were prepared using methods similar to impregnation or co-sintering to dope the cations. It should be noted that the above three doping examples demonstrate the regulatory mechanisms and effects of different alkali metal cations on the electrocatalytic performance of SFM. + and Cs + The doping modification is similar in principle to that of the alkali metal cations mentioned above, and can be carried out by referring to the same preparation method.

[0079] The composite cathode of one embodiment of the present invention can maintain effective electrocatalytic activity over a wide range of CO2 concentrations, which is the basis for the stable operation of the coupling system of the present invention.

[0080] The mechanism lies in the fact that the additional oxygen vacancies generated by cation doping serve as active sites for CO2 adsorption and activation. Under quasi-steady-state gas flow conditions (CO2 volume fraction 15–50%), the high concentration of oxygen vacancies still ensures a sufficient number of CO2 molecules are effectively captured and activated on the cathode surface, maintaining the continuous progress of the CO2 electrolysis reaction. When the inlet CO2 concentration increases to the percentage level, the abundant active sites effectively suppress the increase in electrode polarization loss, maintaining a high conversion efficiency.

[0081] Furthermore, the introduction of alkali metal cations optimizes the covalent nature and reversible redox properties of the transition metal-oxygen bond (MO bond). Appropriately enhanced MO bond covalent nature facilitates the activation and dissociation of adsorbed CO2 (CO2→CO+O). 2- Simultaneously, reversible Fe redox (Fe 3+ Fe 2+ This ensures the continuous regeneration of active sites during the electrolysis process, preventing the cathode from becoming inactive due to depletion of active sites or excessive oxidation under wide concentration dynamic fluctuation conditions.

[0082] Figures 5-6 These are the test results obtained during the operation of the DAC system according to the present invention.

[0083] The testing method involved in this embodiment is as follows: SFMNa / Li-SDC (weight ratio 7:3) was used as the positive electrode for testing. At 800°C, the test was conducted at 30 mV s. -1 Linear scan voltammetry (LSV) curves were recorded at scan rates from 0.05 V to 1.8 V. The EIS of a single cell at 800°C and 1.5 V was measured within a scan frequency range of 0.1 Hz to 105 Hz.

[0084] in, Figure 5 These are the test results from the linear sweep voltammetry (LSV) method. Single-cell I-V curves for SFM–SDC, SFMLi–SDC, and SFMNa–SDC cathodes were tested at 800°C. At 1.5 V, the corresponding current densities reached 1.61 A cm⁻¹. -2 (SFM-SDC), 1.75 A cm -2 (SFMLi- SDC) and 2.14 A cm -2 (SFMNa- SDC). Figure 6 The total polarization resistance of a single cell is 0.52 Ω cm² for SFM- SDC at 800°C and 1.5 V, 0.1907 Ω cm² for SFMLi- SDC, and 0.1275 Ω cm² for SFMNa- SDC.

[0085] In one embodiment of the present invention, the heat recovery path 300 includes a heat exchanger and a heat-conducting pipe. The high-temperature waste heat generated during the operation of the solid oxide electrolytic cell module 200 mainly comes from two aspects: first, the enthalpy carried by the high-temperature oxygen-rich flow (temperature above 700°C) on the anode side during discharge; second, the Joule heat generated by the irreversible polarization loss of the stack body.

[0086] A heat exchanger is located at the heat outlet of the solid oxide electrolysis cell module 200. It uses the waste heat from the high-temperature side to heat the heat exchange medium (such as heat transfer oil, high-pressure steam, or air), reducing the heat level to the regeneration temperature range (80–200°C) required by the direct air capture module 100. The heat exchange medium, cooled by the heat exchanger (not shown), is transported via a heat transfer pipeline (not shown) to the temperature control module 130 of the direct air capture module 100, providing a heat source for the regeneration heating of the adsorption reactor 110.

[0087] Through the above-mentioned heat recovery path, the high-temperature waste heat of the solid oxide electrolytic cell module 200 can be effectively utilized, avoiding the dependence of the direct air capture module 100 on external energy for adsorbent regeneration, thus reducing the overall energy consumption of the system and improving energy utilization efficiency.

[0088] An embodiment of the carbon conversion system of the present invention includes a direct air capture module 100 and a solid oxide electrolyzer module 200. The direct air capture module 100 includes a fixed-bed adsorption reactor 110 filled with solid amine-based composite adsorbent material and a buffer tank 120 with a volume of 50 L. The adsorption reactor 110 alternately performs adsorption (at ambient temperature and pressure, adsorption time approximately 30 minutes) and regeneration (120°C, 0.01 MPa, N2 purging, regeneration time approximately 20 minutes). The resulting CO2-rich gas flow (CO2 volume fraction 15–80%, dynamically changing with the regeneration process) is smoothed in the buffer tank 120 and then input into the solid oxide electrolyzer module 200 at a relatively stable flow rate (±10% fluctuation). The solid oxide electrolyzer module 200 contains a stack of 10 single cells, each cell using YSZ electrolyte, with the anode being perovskite-type La. 0.8 Sr 0.2 MnO3 (LSM) is used, with a Na-doped SFM composite cathode (Na / SFM molar ratio 0.2). The fuel cell stack operates at 800°C and an applied voltage of 1.5 V / cell. Heat recovery path 300 recovers heat from the 800°C tail gas on the anode side via an anode tail gas heat exchanger, cooling it to 130°C for regeneration heating of the adsorbent in the direct air capture module 100.

[0089] The technical advantages of this embodiment are as follows: the buffer tank effectively eliminates the gas inlet fluctuations caused by the intermittent operation of the adsorption reactor, and the solid oxide electrolyzer operates stably under quasi-steady-state gas inlet conditions; the Na-doped SFM cathode maintains high CO electrolysis selectivity (CO selectivity > 90%) within a dynamic range of CO2 volume fraction of 15-50%; and the heat recovery path uses the waste heat of the solid oxide electrolyzer for adsorbent regeneration, reducing the external heat consumption of the system by about 60%.

[0090] One embodiment of the carbon conversion system of the present invention further extends the above-described device. The direct air capture module 100 includes two adsorption reactors 110 (operating alternately to achieve near-continuous output), and the buffer tank 120 has its volume increased to 100L. The direct air capture module 100 is also equipped with a temperature control module 130 (embedded with a heat exchanger tube to receive waste heat from the heat recovery path), a pressure control module 140 (including a vacuum pump, which can reduce the bed pressure to 8 kPa during the regeneration stage), and a carrier gas supply device 150 (which can switch between supplying dry air or water vapor). A dehumidification and drying unit 160 (molecular sieve drying column, which can control the relative humidity of the outlet airflow to be below 3%) is provided between the direct air capture module 100 and the solid oxide electrolyzer module 200. The cathode of the solid oxide electrolyzer module 200 uses Li-doped SFM (Li / SFM molar ratio 0.2) and operates at 800°C.

[0091] When the CO2 pure electrolysis mode needs to be operated, the dehumidification and drying unit 160 turns on the drying function to reduce the humidity of the raw material airflow to below 3% RH before it is input into the solid oxide electrolysis cell to produce high-purity CO.

[0092] When co-electrolysis mode is required, the dehumidification and drying unit 160 switches to humidity control mode. By quantitatively supplementing water vapor into the gas flow, the H2O:CO2 molar ratio is adjusted to the target value, and the solid oxide electrolyzer produces syngas with an H2 / CO molar ratio that can be adjusted between 0.5 and 3.0.

[0093] In addition, after running several hundred regeneration cycles, by switching to deep regeneration mode (180°C, dry air purging), the organic impurities and strongly adsorbed moisture accumulated on the adsorbent material are removed, so that the adsorption capacity is restored to more than 95% of the initial value.

[0094] The technical advantages of this embodiment are as follows: the parallel operation of the dual towers significantly improves the continuous output capability of the system; the vacuum pressure-temperature coupling regeneration reduces the regeneration energy consumption by about 20% compared with simple temperature regeneration; the setting of the dehumidification and drying unit allows the system to flexibly switch between pure electrolysis and co-electrolysis operation modes, and effectively protects the cathode of the solid oxide electrolytic cell from damage caused by high humidity intake; the deep regeneration mode effectively extends the service life of the adsorbent material.

[0095] One embodiment of the present invention provides a carbon conversion method based on the above-described carbon conversion system, comprising the following steps:

[0096] Step S100: Start the direct air capture module 100, and continuously introduce ambient air into the adsorption reactor 110 at a flow rate of approximately 1000 L / min via a blower. Under normal temperature (approximately 25°C) and atmospheric pressure conditions, the solid amine-based composite adsorbent material in the adsorption bed selectively chemically adsorbs CO2 from the air. After air with a CO2 volume fraction of approximately 400 ppm passes through the bed, the outlet CO2 volume fraction drops to below 100 ppm (CO2 adsorption rate >75%). The adsorption operation lasts for approximately 25–35 minutes, and when the bed adsorption capacity is close to saturation, switch to the regeneration stage.

[0097] Step S200: Waste heat generated by the operation of the solid oxide electrolysis cell module 200 (using 130°C hot water as the heat exchange medium) is input into the temperature control module 130 via the heat recovery path 300 to heat the bed in the adsorption reactor 110. Simultaneously, the pressure control module 140 starts the vacuum pump to reduce the bed pressure to approximately 10 kPa, and a suitable amount of dry N2 is introduced into the bed as a purge medium via the carrier gas supply device 150. Under the combined action of temperature, pressure, and purge, CO2 desorbs from the surface of the adsorbent material and is output from the adsorption reactor 110 with the purge gas flow, forming a CO2-rich gas flow with a CO2 volume fraction of 15–80% (varying with the desorption process).

[0098] Step S300: The CO2-rich gas flow enters the buffer tank 120 and, after homogenization and pressure stabilization, forms a quasi-steady-state gas flow with a flow fluctuation of less than ±8% and a relatively stable CO2 volume fraction, which is continuously input to the cathode side of the solid oxide electrolysis cell module 200.

[0099] Step S400: The solid oxide electrolytic cell module 200 operates at 800℃ and an applied voltage of 1.5 V / section. CO2 on the cathode side undergoes an electrochemical reduction reaction on the Na-doped SFM composite cathode: CO2 + 2e → CO + O 2- The generated CO is discharged from the cathode side outlet along with the exhaust gas, and O 2- Ions are conducted to the anode side via the YSZ electrolyte, where they are oxidized to O2 and discharged: O 2-→ 1 / 2O2+2e - The CO volume fraction in the outlet gas stream on the cathode side is approximately 60–75% (the remainder is mainly unconverted CO2). After subsequent separation units (such as pressure swing adsorption separation or membrane separation), CO product gas with a purity of ≥99% can be obtained.

[0100] Step S500: The high-temperature oxygen-enriched tail gas (approximately 780°C) discharged from the anode side of the solid oxide electrolysis cell module 200 exchanges heat with the heat exchange medium through the heat recovery path 300, transferring heat to the circulating hot water (heating it to 130°C). The circulating hot water is then transported to the direct air capture module 100 via a heat-conducting pipeline for adsorbent regeneration heating in step S200. The anode tail gas temperature at the heat exchanger outlet drops to approximately 100°C before being discharged.

[0101] The above steps S100 to S500 constitute a continuous operating cycle. Steps S100 (adsorption) and S200 to S300 (regeneration + gas supply) are carried out synchronously through the alternating operation of two adsorption reactors. The solid oxide electrolysis cell module 200 continuously operates in a steady state, and the system as a whole realizes the continuous conversion of CO2 from atmospheric capture to CO products.

[0102] The technical advantages of this method embodiment are as follows: the overall energy consumption of the system for capturing CO2 from the atmosphere (including adsorption fan energy consumption, regeneration heating energy consumption, and electrolysis energy consumption) is reduced by about 25% compared to the traditional route of high-purity CO2 supply + solid oxide electrolyzer; the entire process does not require external CO2 cylinders or liquid CO2 storage and transportation, making it suitable for deployment in distributed scenarios without centralized carbon sources; the system's single CO2 conversion rate is about 55-65%, and unconverted CO2 can be recycled back to the adsorption unit for recapture, resulting in an overall carbon utilization rate of more than 80%.

[0103] One embodiment of the present invention provides a method for performing CO2 / H2O co-electrolysis to produce syngas on the above-described system. Based on the above method, the following adjustments are made to steps S200 and S300:

[0104] Step S201: The carrier gas in the regeneration stage is switched from dry N2 to water vapor (relative humidity of about 80%, provided by the steam generator in the carrier gas supply device). The water vapor serves as the purging medium, carrying the desorbed CO2 while also mixing with the feed gas flow, so that the gas flow output from the adsorption reactor 110 contains both CO2 and H2O, with an H2O:CO2 molar ratio of approximately 1.5:1.

[0105] Step S301: The dehumidification drying unit 160 switches to the humidity adjustment mode and further fine-tunes the H2O:CO2 molar ratio (target value is 2:1) to ensure that the airflow enters the cathode side of the solid oxide electrolysis cell module 200 with a controlled water-carbon ratio.

[0106] Step S401: The solid oxide electrolyzer module 200 operates in co-electrolysis mode at 800℃ and an applied voltage of 1.5 V / section, with CO2 electrolysis (CO2 + 2e) occurring simultaneously on the cathode side. - →CO+O 2-) and H2O electrolysis (H2O + 2e- → H2 + O) 2- Taking the two reactions with a feed ratio of H2O:CO2 = 2:1 as an example, the theoretical output of syngas with an H2 / CO molar ratio of approximately 2:1 (close to the optimal feed ratio for methanol synthesis). By adjusting the amount of steam used in the desorption stage of the DAC module (i.e., adjusting the H2O:CO2 feed ratio) and the operating temperature and voltage of the solid oxide electrolyzer, the H2 / CO molar ratio can be flexibly adjusted within a wide range of 0.5 to 3.0 to adapt to the feedstock requirements of different downstream catalytic processes (such as Fischer-Tropsch synthesis requiring an H2 / CO ratio of approximately 2:1, methanation requiring an H2 / CO ratio of approximately 3:1, and methanol synthesis requiring an H2 / CO ratio of approximately 2:1).

[0107] The resulting syngas, after preliminary purification by pressure swing adsorption (VPSA), can be used as feedstock for a Fischer-Tropsch synthesis unit. It can then be converted to C by iron-based or cobalt-based catalysts at 200–350 °C and 1–3 MPa. 5+ Liquid hydrocarbons (synthetic oils) can also be converted into methanol via a methanol synthesis unit (copper-zinc-aluminum catalyst, 250℃, 5 MPa), and then dehydrated to produce dimethyl ether (DME). Both upstream and downstream conversion processes are mature industrial technologies, and their detailed principles will not be elaborated here.

[0108] The technical advantages of this method embodiment are as follows: the system can directly convert CO2 in the atmosphere and H2O in the ambient humidity into syngas with an adjustable H2 / CO ratio, forming a complete carbon utilization chain from air feedstock to liquid fuels or chemicals; the flexible and adjustable H2 / CO ratio enables the system to serve as a universal syngas supply platform, adaptable to various downstream product routes; the use of water vapor generated in the DAC regeneration stage to participate in co-electrolysis eliminates the need for a separate water vapor preparation unit, simplifying the system structure and further reducing energy consumption.

[0109] One embodiment of the present invention verifies the ability of a carbon conversion system to operate continuously and stably under conditions of large-scale dynamic fluctuations in inlet CO2 concentration. Figure 7 The results are from the CO2 electrolytic conversion operation of a single cell (with SFMNa-SDC as the positive electrode) in a CO2 capture-release-electrolysis cycle.

[0110] In this embodiment, ambient air is first continuously pumped into the capture device at room temperature until the adsorbent reaches saturation. Subsequently, carbon dioxide is continuously released at 105°C and at 0.5 A cm⁻¹. -2 Electrochemical conversion was carried out at 800°C. After 18 hours of continuous carbon dioxide release and electrolysis, the system was shut down to allow the adsorbent to re-adsorb carbon dioxide from the air until it reached saturation, followed by a second release-electrolysis cycle.

[0111] like Figure 7As shown, the single-cell electrolysis voltage with the SFMNa-SDC cathode rapidly increases in the initial stage of the first CO2 release cycle and then stabilizes. Once the adsorbent is resaturated with CO2, the electrolysis voltage during the second release and electrolysis process rapidly recovers to the level at the end of the first electrolysis and remains stable thereafter. Based on the CO and H2 generation rates, it can be estimated that during a single 18-hour release cycle, the coin cell (effective area: 0.28 cm²) can capture approximately 323.5 mL of CO2 (g) and 381.0 mL of water (g) from the air and convert them into CO (g) and H2 (g).

[0112] Finally, it should be noted that the above embodiments are only for illustrating the present invention and not for limiting the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that various combinations, modifications, or equivalent substitutions of the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention and should be covered within the scope of the claims of the present invention.

Claims

1. A carbon conversion system using direct air capture coupled with solid oxide electrolysis, characterized in that, include: A direct air capture module is used to capture and enrich carbon dioxide from ambient air to generate a carbon-containing feedstock gas stream. The direct air capture module includes an adsorption reactor and a buffer tank, wherein the buffer tank is configured to convert the pulsed gas stream generated by the adsorption reactor into a quasi-steady-state gas stream. A solid oxide electrolytic cell module is used to receive the carbon-containing raw material gas stream and perform electrolytic conversion. The solid oxide electrolytic cell module includes a composite cathode, which is prepared by using perovskite oxide as a matrix and modifying it with cation doping. The solid oxide electrolyzer module and the direct air capture module are connected through a heat recovery path, which is configured to use the waste heat generated by the solid oxide electrolyzer module to drive the adsorbent regeneration process of the direct air capture module. The adsorption reactor is filled with a selective adsorption material, which is selected from at least one of solid amine composite materials, metal-organic framework materials, or porous materials modified with alkali metals or alkaline earth metals. The composite cathode is based on a perovskite oxide structure, with cations doped into the lattice of the substrate or modified on the surface of the substrate to induce oxygen vacancies on the surface of the composite cathode. The direct air capture module also includes: The temperature control module is used to control the switching between the adsorption temperature and the desorption temperature of the adsorption reactor; The pressure control module is used to regulate the pressure inside the adsorption reactor; A carrier gas supply device is used to introduce a purging medium into the adsorption reactor. The direct air capture module is configured with a conventional regeneration mode and a deep regeneration mode; the conventional regeneration mode regenerates the adsorbent through a combination of temperature-driven and pressure-switching purge; the deep regeneration mode removes stubborn impurities by heating the adsorption reactor to a temperature higher than that of the conventional regeneration mode and performing a dry purge. A dehumidification and drying unit is also provided between the direct air capture module and the solid oxide electrolysis cell module. The dehumidification and drying unit is used to adjust the relative humidity of the raw material airflow before entering the solid oxide electrolysis cell module to a preset range.

2. The carbon conversion system according to claim 1, characterized in that, The cation is selected from Li + Na + K + 、Rb + and Cs + Any one of the following; the perovskite structure oxide is Sr2Fe 1.5 Mo 0.5 O 6-δ .

3. A carbon conversion method based on the carbon conversion system according to any one of claims 1-2, characterized in that, Includes the following steps: Carbon dioxide is captured from ambient air using a direct air capture module; By controlling the desorption conditions of the direct air capture module, the captured carbon dioxide is enriched and buffered and stabilized to form a continuous carbon-containing raw material gas flow. The carbon-containing raw material gas stream is introduced into the solid oxide electrolytic cell module for electrolysis, converting it into carbon-containing chemicals; The heat energy generated by the solid oxide electrolyzer module is collected and fed back to the direct air capture module to drive the regeneration of the adsorbent.

4. The carbon conversion method according to claim 3, characterized in that, By adjusting the desorption parameters of the direct air capture module and introducing water vapor into the carbon-containing feed gas stream in a proportional manner, the solid oxide electrolyzer module is controlled to operate in co-electrolysis mode, producing syngas with an adjustable hydrogen-to-oxygen ratio.

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