A segmented current rise-stabilization-steady-state maintenance coupled continuous process for the electroreduction of carbon dioxide to ethylene at high current density

Abstract

This invention discloses a segmented current rise-stabilization-steady-state maintenance coupled continuous process for the electroreduction of carbon dioxide to produce ethylene at high current density. The process uses a flowing electrolyzer as the reactor and a gas diffusion electrode with a copper-based catalyst layer as the cathode. Carbon dioxide gas is continuously introduced into the cathode side, and an alkaline electrolyte is added to and circulated into the electrolysis system. During the start-up phase, a segmented current rise procedure is used to gradually establish a stable cathode reaction interface, enabling continuous ethylene production within the target high current density region, and maintaining the operating state within a preset steady-state maintenance window. When the operating state deviates from the steady-state maintenance window, a deviation correction operation is performed to restore operation to the target high current density. This process achieves long-term stable continuous production of ethylene from carbon dioxide electroreduction at high current density and has good engineering application prospects.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide electrochemical conversion technology, specifically relating to a segmented current rise-stabilization-steady-state maintenance coupled continuous process for the electroreduction of carbon dioxide to ethylene at high current density. Background Technology

[0002] The electroreduction of carbon dioxide is an important technological route that uses electrical energy to drive the conversion of carbon dioxide into high-value-added chemicals, enabling the high-value utilization of carbon resources under relatively mild conditions. Among the many products of carbon dioxide electroreduction, ethylene is an important basic chemical raw material, widely used in the production of polyethylene, ethylene oxide, ethylene glycol, and other products. Therefore, developing carbon dioxide electroreduction technology to produce ethylene is of great significance.

[0003] In existing technologies, copper-based catalytic systems are widely used for the electroreduction of carbon dioxide to produce ethylene due to their ability to promote carbon-carbon coupling reactions. To improve carbon dioxide supply efficiency and reaction current density, flow cell reactors and gas diffusion electrodes are increasingly being applied to carbon dioxide electroreduction systems to overcome the problems of low carbon dioxide solubility and poor mass transfer efficiency in traditional submerged reactors.

[0004] However, under high current density conditions, the existing carbon dioxide electroreduction process for ethylene production still has the following shortcomings: First, when the system switches from low-load operation to high-current-density operation, the cathode reaction interface is prone to fluctuations in carbon supply and local mass transfer imbalance. Secondly, during long-term continuous operation, problems such as increased voltage fluctuations, unstable ethylene formation, and operational degradation are likely to occur. Third, existing technologies lack systematic operating procedure design for high current density continuous production processes, especially lacking coupled control processes for the start-up, stabilization and stable production stages. Fourth, existing continuous processes often only focus on achieving the target current density, without integrating the design of the reaction interface establishment process and steady-state maintenance process under high current density, which is not conducive to long-term stable operation.

[0005] Therefore, it is necessary to provide a carbon dioxide electroreduction process for ethylene production that can establish a stable reaction interface under high current density conditions, maintain steady-state production, and is suitable for long-term continuous operation. Summary of the Invention

[0006] The purpose of this invention is to provide a segmented current rise-stabilization-steady-state maintenance coupled continuous process for the electroreduction of carbon dioxide to produce ethylene under high current density, in order to solve the problems in the prior art such as the difficulty in establishing a stable reaction interface under high current density operating conditions, large fluctuations in operation during continuous production, significant performance degradation during long-term operation, and insufficient stability in the continuous generation of ethylene.

[0007] In existing carbon dioxide electroreduction processes for ethylene production, although the use of flow cell reactors and gas diffusion electrodes has improved the problem of limited carbon dioxide mass transfer to some extent, making it possible for the system to operate at higher current densities, the following shortcomings still exist in actual continuous production: During the start-up phase, if the system is directly and rapidly increased to the target high current density region, it is easy to cause insufficient establishment of the cathode-side reaction interface, resulting in problems such as local carbon supply shortage, local mass transfer imbalance, and instability of the gas-liquid-solid three-phase interface; During continuous production, as the operating time increases, the system is prone to phenomena such as increased cell voltage, fluctuations in the composition of the outlet product, changes in the circulating liquid level, and a gradual deviation of the operating state from the stable region, which in turn affects the continuity and stability of ethylene production.

[0008] Especially for flow cell systems using a gas diffusion electrode with a copper-based catalyst layer as the cathode, at 500–600 mA / cm 2 When operating at high current densities, the system is highly sensitive to start-up methods, gas supply conditions, electrolyte circulation conditions, and continuous operation management. Current technologies typically focus on the catalyst material itself or single reaction conditions. However, a systematic and effective solution is lacking for how to design a process program that enables the system to first establish a stable interface before transitioning to high-current-density continuous production, maintain a steady-state window during continuous operation, and promptly correct deviations from the steady-state window to achieve long-cycle continuous ethylene production.

[0009] Therefore, this invention proposes an integrated continuous production process that couples "segmented current ramp-up and stabilization" with "steady-state control." This process does not simply increase the carbon dioxide electroreduction system to a target current density, but rather designs functional zones for the start-up and continuous production stages. This allows the system to establish the reaction interface and stabilize the mass transfer state before entering the high current density production zone. After entering the continuous production stage, a preset steady-state window and offset correction measures ensure that the system remains within a stable operating range conducive to continuous ethylene production for as long as possible. Thus, this invention improves the feasibility, stability, and scale-up value of continuous ethylene production under high current density conditions.

[0010] The technical solution adopted in this invention is as follows: 1. Reactor Construction Steps A flow electrolytic cell is used as the carbon dioxide electroreduction reactor. The flow electrolytic cell includes a gas chamber, a cathode gas diffusion electrode, a cathode chamber, an ion exchange membrane, an anode chamber, and an anode. The carbon dioxide electroreduction reaction takes place in the cathode chamber, while the corresponding electrode reaction, preferably the oxygen evolution reaction, takes place in the anode chamber. The cathode gas diffusion electrode is a gas diffusion electrode supported on a copper-based catalyst layer, and the anode is an oxygen evolution anode.

[0011] The gas diffusion electrode is made of carbon paper, with a copper-based catalyst loaded on one side at a loading rate of 0.5-2 mg / cm³. 2 The purpose of adopting the above structure is to balance gas transport, electron conduction, and catalytic activity, so that carbon dioxide can form a relatively stable gas-liquid-solid three-phase reaction interface on the cathode side, thereby providing a basis for the generation of ethylene at high current densities.

[0012] Furthermore, the copper-based catalyst comprises a rare earth metal Ce-doped cuprous oxide substrate and an organic cation layer in situ modified on the surface of the substrate.

[0013] Furthermore, the preparation method of the copper-based catalyst includes the following steps: S1: Dissolve Cu source, Ce source and imidazole cationic liquid in deionized water to obtain a homogeneous precursor solution; S2: Add alkali to the precursor solution in step S1, adjust the pH to 10-13, and then stir at a constant temperature for 10-60 min to obtain the precursor suspension. S3: Add a reducing agent solution dropwise to the precursor suspension in step S2. After the addition is complete, continue the reaction system under constant temperature and sealed reaction for 0.5-2 hours. During this process, copper ions are reduced to cuprous oxide and accompanied by in-situ lattice doping of cerium atoms. At the same time, imidazole cations in the solution are in-situ coated on the surface of the generated catalyst through non-covalent interaction. S4: The copper-based catalyst is then obtained by washing, drying, and grinding.

[0014] Further, in step S1, the molar amount of Ce source is 5-20% of the molar amount of Cu source, the molar ratio of imidazole cationic liquid to Cu source is 0.8-1.2:1, and the imidazole cationic liquid is one or more of 1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide or 1-butyl-3-methylimidazolium tetrafluoroborate; The temperature for constant temperature stirring in step S2 is 30-40℃, and the stirring time is 20-40 minutes. The constant temperature reaction temperature in step S3 is 30-40℃, and the reaction time is 0.8-1.5h.

[0015] 2. Continuous raw material supply steps Carbon dioxide gas is continuously introduced into the cathode side. The carbon dioxide is preferably supplied at a constant flow rate to avoid adverse effects on the reaction interface caused by gas supply fluctuations. Preferably, the carbon dioxide flow rate is 5–20 sccm, more preferably 10 sccm. An alkaline electrolyte, which is a potassium hydroxide aqueous solution with a concentration of 0.5–2 M, is added to and circulated in both the cathode and anode chambers, preferably 1 M.

[0016] The electrolyte is circulated rather than discharged after a single use. This is to maintain ion conductivity and system continuity under continuous production conditions. Preferably, the circulation flow rate of the alkaline electrolyte in the cathode and anode chambers is 20–200 mL / min, more preferably 50–150 mL / min. By maintaining stable electrolyte circulation, the system homogeneity during continuous operation can be improved, and the adverse effects of local concentration differences, resistance fluctuations, or liquid level changes on continuous production can be reduced.

[0017] 3. Steps for segmented current rise and stabilization One of the core aspects of this invention is that, during the reactor start-up phase, the system is not directly raised to 500–600 mA / cm². 2 Instead of targeting the high current density region, a segmented current ramp-up process is adopted to gradually establish a stable cathode reaction interface and a continuous production base.

[0018] The segmented current rise and stabilization steps preferably include the following stages: (1) Low current density stabilization stage: During this stage, the current density is controlled at 50–150 mA / cm². 2 The preferred operating time is 0.5–2 hours. The main function of this stage is to gradually establish an initial stable state at the cathode-side reaction interface, allowing the gas diffusion electrode with the copper-based catalyst layer to establish its working state under relatively mild conditions, thus reducing the abrupt disturbances caused by the system directly entering high-load operation.

[0019] (2) Intermediate current density transition stage: After the low current density stabilization stage, the current density is increased to 200-350 mA / cm. 2 The preferred operating time is 0.5–3 hours. The main function of this stage is to further transition the gas supply, interfacial reaction, and system mass transfer state to high-load operating conditions, so that the system has good interfacial stability and continuous operation adaptability before entering the target high current density region.

[0020] (3) High current density introduction stage: After completing the above stabilization and transition, the current density will be further increased to 500-600 mA / cm. 2The system then enters the continuous ethylene production stage. Compared to directly increasing the current density to the target high current density, the segmented current increase method described above can reduce the risk of operational fluctuations during the start-up phase and improve the success rate of the system entering the high current density stable region.

[0021] In other words, this invention enables the system to smoothly transition from the startup state to a high-current-density continuous production state through three consecutive functional stages: low-load stabilization, medium-load transition, and high-load introduction. This phased approach to establishing the operational foundation is one of the key features that distinguishes this invention from existing direct current boosting or single constant-current operation processes.

[0022] 4. Steady-state maintenance steps When the system reaches 500–600 mA / cm 2 After reaching the target high current density region, this invention does not simply understand continuous operation as "keeping the current constant", but further manages the operating status of the continuous production stage by setting a steady-state holding window.

[0023] The steady-state maintenance window includes one or more of the following metrics: Slot voltage fluctuation range; Fluctuation range of cathode outlet gas composition; Range of fluctuation in circulating electrolyte level; Fluctuation range of electrolyte circulation status; If necessary, the range of variation in the total flow rate of the cathode outlet gas should also be included.

[0024] Preferably, the voltage fluctuation of the cell does not exceed 5% to 15% of the stable operating baseline value; preferably, when the circulating electrolyte level is lower than 90% of the initial level, it is considered that the level has deviated from the steady-state window; preferably, when one or more of the proportions of ethylene, hydrogen, or carbon monoxide in the cathode outlet product composition experience continuous abnormal fluctuations, it can also be determined that the operating state has deviated from the steady-state maintenance window.

[0025] The "steady-state holding" mentioned in this invention essentially transforms the control of high-current-density continuous production processes from simple setpoint control to control of the operating state window. In other words, it no longer focuses solely on "whether it is operating at 500 mA / cm²". 2 Or 600mA / cm 2 Instead of focusing solely on the steady-state condition, the system is simultaneously monitored to ensure that the operating status remains within a stable range conducive to the continuous production of ethylene. As long as the operating indicators remain within the aforementioned steady-state maintenance window, the system can be considered to be in a steady-state production stage suitable for continuous ethylene production.

[0026] 5. Offset Correction Steps During long-term continuous operation, the system may gradually deviate from the steady-state maintenance window due to factors such as prolonged operation time, changes in the circulating liquid, and changes in the reaction interface state. To address this, the present invention further designs a deviation correction step to pull the system back to the stable operating region after deviation occurs.

[0027] When a deviation from the steady-state holding window is detected, a correction operation is performed. The correction operation includes at least one of the following: Short-term reduction of current density; Add deionized water and / or fresh electrolyte; Partial replacement of the circulating electrolyte; Replace all circulating electrolytes.

[0028] Preferably, the short-term reduction of current density involves reducing the target high current density to 20%–50% of it, maintaining this for 5–30 minutes, and then restoring it to the target high current density. Preferably, the partial electrolyte replacement ratio is 20%–100% of the total volume of the circulating electrolyte. Preferably, electrolyte replenishment is performed when the circulating electrolyte level is lower than 90% of the initial level. Preferably, partial or complete electrolyte replacement is performed every 48–120 hours to reduce the adverse effects of electrolyte state changes on production stability during long-term continuous operation.

[0029] The aforementioned offset correction step is not intended as a standalone interruption, but rather as an integral part of the steady-state maintenance process. It is triggered and implemented as needed during continuous production based on the operational status. Through this step, the system can be promptly adjusted back to a suitable continuous production state when signs of deviation appear, thereby extending the sustainable operating time of high-current-density continuous ethylene production.

[0030] 6. Continuous production steps After the phased current ramp-up and stabilization are completed and the system enters the target high current density production zone, it is maintained in continuous operation under ambient temperature and pressure conditions. The target high current density is preferably 500 mA / cm². 2 Above and not higher than 600 mA / cm 2 The continuous operating time should be no less than 100 hours, preferably no less than 200 hours.

[0031] In this stage, carbon dioxide undergoes an electroreduction reaction on the cathode side, continuously generating gaseous products including ethylene. By coupling the segmented current rise stabilization step, the steady-state maintenance step, and the offset correction step, this invention enables better accessibility and maintainability of the high current density continuous production stage.

[0032] 7. Product Export and Collection Steps The gaseous products generated on the cathode side are continuously exported, condensed, demisted, and separated into gas and liquid components before collection. Further purification may be performed if necessary to obtain ethylene products. Preferably, during continuous operation, one or more of the following are monitored online: cathode outlet gas composition, tank voltage, and circulating liquid level. The determination of whether to proceed with the offset correction step is based on the monitoring results.

[0033] The essence of this invention does not lie in simply limiting a specific current density value, electrolyte concentration, or carbon dioxide flow rate, but rather in proposing a process control logic suitable for high-current-density continuous ethylene production systems: first establish stability, then increase load; first maintain steady state, then continue production; and promptly correct and restore production when deviations from steady state occur. Specifically, this invention divides the high-current-density continuous ethylene production process into multiple stages with different process functions, so that the start-up stage and the continuous production stage are no longer isolated, but coupled through a continuous process chain of "segmented current increase for stabilization - steady-state maintenance - deviation correction." This significantly improves the system's ability to enter a stable operating state from an initial state under high current density and reduces the possibility of fluctuations and attenuation during long-term continuous operation. In other words, this invention transforms the high-current-density carbon dioxide electroreduction ethylene production from a "single-point operation problem" into a "process coupling control problem," thus making the entire continuous process more suitable for engineering implementation.

[0034] Compared with the prior art, the present invention has the following beneficial effects: 1) This invention uses a segmented current ramping process to gradually transition the system from low load to high load operation, avoiding the interface abrupt changes and operational fluctuations caused by directly entering the target high current density, which is conducive to establishing a stable cathode reaction interface.

[0035] 2) This invention integrates the stabilization stage and the continuous production stage. Through the coupling concept of "stabilization-steady state maintenance", the high current density ethylene production process is transformed from simple target value operation to controlled process state operation, thereby improving the controllability of continuous production.

[0036] 3) By setting a steady-state holding window and implementing offset correction when the operating state deviates from the window, this invention helps to reduce the adverse effects of liquid level changes, voltage fluctuations and product composition fluctuations during long-term continuous operation, thereby enhancing the stability of continuous ethylene production under high current density conditions.

[0037] 4) The process described in this invention can be carried out at room temperature and pressure, the process conditions are mild, and it is easy to combine with existing flow cell systems and gas diffusion electrode systems, which has good engineering application prospects.

[0038] 5) This invention is not only applicable to achieving 500-600 mA / cm 2The continuous production of ethylene under high current density, and through process procedures and operational status management, has improved the feasibility of continuous operation for more than 200 hours, showing good potential for continuous production and scale-up. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Without departing from the spirit and substance of the present invention, those skilled in the art can make various equivalent substitutions or modifications based on the content disclosed in the present invention, all of which should fall within the scope of protection of the present invention.

[0040] This invention provides a segmented current ramp-up and steady-state maintenance coupled continuous process for the electroreduction of carbon dioxide to produce ethylene at high current density. The core of this process lies in: during the system start-up phase, a stable reaction interface suitable for continuous high-current-density production is gradually established through segmented current ramp-up; after entering the target high-current-density production stage, the system's operating state is maintained within a preset steady-state maintenance window by monitoring the cell voltage, cathode outlet gas composition, circulating liquid level, and circulation status; when the operating state deviates from the steady-state maintenance window, the system's steady state is restored through offset correction methods such as liquid replenishment, liquid replacement, and short-term current reduction, thereby improving the stability and continuous operation capability of the continuous production process for the electroreduction of carbon dioxide to produce ethylene.

[0041] The reactor used in this invention is a flow electrolysis cell reactor.

[0042] In this invention, carbon dioxide gas is continuously introduced into the cathode side. The carbon dioxide gas can be pure carbon dioxide or a mixture containing carbon dioxide; in the preferred embodiment, pure carbon dioxide is used. Preferably, the carbon dioxide flow rate is controlled at 5–20 sccm, more preferably 10 sccm. Using a relatively stable and continuous gas supply method helps reduce the impact of gas-side fluctuations on the cathode reaction interface, thereby facilitating the continuous generation of ethylene under high current density continuous operation conditions.

[0043] Alkaline electrolyte is added to and circulated in both the cathode and anode chambers. The electrolyte is preferably an aqueous solution of potassium hydroxide, with a concentration preferably between 0.5 and 2 M, more preferably 1 M. The electrolyte is circulated, preferably at a flow rate of 20 to 200 mL / min, more preferably 50 to 150 mL / min. The purpose of this circulation is to ensure relatively stable ion conduction conditions and liquid phase state during continuous production, reducing the adverse effects on the reactor caused by localized changes in liquid level, concentration, or conduction state during long-term operation.

[0044] This invention specifically emphasizes that the system should not be directly introduced into a reactor at a pressure of 500–600 mA / cm² during reactor startup.2 Instead of targeting the high current density region, this invention employs a segmented current ramp-up procedure to gradually establish a stable reaction interface. The reason for this is that directly entering a high current density operating state in a flowing electrolyzer and gas diffusion electrode system can easily cause abrupt changes at the cathode interface within a short period. This makes it difficult for the local carbon supply state, interface wetting state, and mass transfer state to adapt in a timely manner, resulting in significant fluctuations in the continuous high current density operation. Therefore, this invention divides the start-up process into multiple functional stages, enabling the reactor to gradually transition from the initial state to a continuous production state.

[0045] In this embodiment of the invention, the preparation method of the copper-based catalyst includes the following steps: ① Preparation of the mixed precursor solution: Accurately weigh 399.3 mg of copper acetate monohydrate and 109.6 mg of cerium ammonium nitrate (NH4)2Ce(NO3)6, ensuring that the molar amount of Ce is 5-20% of the molar amount of Cu. Simultaneously weigh 174.7 mg of 1-butyl-3-methylimidazolium chloride (BmimCl) as an organic modifier. Add the above three powders to a 40 mL beaker. ② Dissolution and stirring: Place the beaker in a water bath at a constant temperature of 35℃ and continuously stir at 500 rpm using a magnetic stirrer until all solids are completely dissolved, yielding a clear blue-green mixed solution. ③ In-situ coprecipitation: Under the conditions of maintaining a constant temperature of 35℃ and stirring at 500 rpm, slowly add 4 mL of a 2 mol / L sodium hydroxide (NaOH) aqueous solution to the above blue-green solution, adjusting the pH to approximately 12. Continue stirring at a constant temperature for 30 minutes, at which point a uniform suspension will form in the solution. ④ In-situ Reduction and Assembly: Subsequently, under the same stirring and temperature conditions, 4 mL of a 2 mol / L aqueous solution of hydroxylamine hydrochloride (NH₂OH·HCl) was slowly added dropwise as a reducing agent. After the addition was complete, the reaction system was sealed and the reaction was continued at 35°C for 1 hour. During this process, copper ions were reduced to cuprous oxide, accompanied by in-situ lattice doping of cerium atoms. Simultaneously, imidazole cations in the solution were in-situ coated on the surface of the generated catalyst through non-covalent interactions. ⑤ Centrifugation and Washing: After the reaction was completed, the reaction solution was cooled to room temperature. The suspension was transferred to centrifuge tubes and centrifuged at 8000 rpm for 10 minutes, discarding the supernatant. The bottom precipitate was collected and ultrasonically washed 5 times each with deionized water and anhydrous ethanol, respectively, to thoroughly remove free chloride ions and unreacted impurities. ⑥ Drying and Collection: The washed precipitate was placed in a vacuum drying oven and vacuum dried at 55°C for 12 hours. After drying, the sample is taken out and ground into a uniform fine powder in an agate mortar, thus obtaining an organically functionalized cerium-doped copper-based catalyst.

[0046] Preparation of the cathode gas diffusion electrode in the examples: ① Catalyst slurry preparation: Weigh 10 mg of the catalyst powder prepared above and add it to a mixed solvent containing 1 mL of isopropanol and water (isopropanol:water = 3:1 volume ratio), followed by the addition of 20 μL of 5% Nafion solution. Place the mixture in an ultrasonic cleaner and ultrasonically disperse it in an ice-water bath for 30 minutes to prepare a uniform catalyst ink. ② Electrode coating: Take the treated carbon paper (1 cm × 1 cm in size) and uniformly drop-coat the above catalyst ink onto one side surface of the carbon paper, controlling the catalyst loading to be 1.0 mg / cm. 2 The coated carbon paper is allowed to air dry naturally at room temperature and then used as the working electrode.

[0047] Example 1: 500 mA / cm 2 Segmented current rise-to-stabilization and steady-state maintenance coupled continuous production under certain conditions This embodiment uses a flow electrolytic cell as the carbon dioxide electroreduction reactor. The flow electrolytic cell includes a gas chamber, a cathode gas diffusion electrode, a cathode chamber, an ion exchange membrane, an anode chamber, and an anode. The anode is an oxygen evolution anode (made of platinum sheet with a purity > 99.99%).

[0048] Before operation, carbon dioxide gas is introduced into the cathode-side gas chamber at a flow rate of 10 sccm. 1 M KOH aqueous solution is added to both the cathode and anode chambers as circulating electrolyte, maintaining separate circulation of the electrolyte in each chamber. The initial volume of the circulating electrolyte can be set according to the reactor size and the capacity of the circulation system. In this embodiment, it is sufficient to meet the requirements of continuous operation and facilitate subsequent liquid level monitoring. Liquid level changes are recorded during the circulation process.

[0049] During the startup phase, a segmented current ramping approach is adopted, specifically including: The first stage is the low current density stabilization stage, where the current density is controlled at 100 mA / cm². 2 The process lasts for 1 hour. The main function of this stage is to transition the cathode interface from its initial state to its working state, and to gradually establish a stable correlation between carbon dioxide supply, electrode surface reaction, and liquid phase environment.

[0050] The second stage is the intermediate current density transition stage, where the current density is increased to 300 mA / cm². 2 This process is maintained for 2 hours. The purpose of this stage is to further adapt the system to higher load operating conditions, preparing it for the target high current density continuous production stage.

[0051] The third stage is the high current density introduction stage, which increases the current density to 500 mA / cm². 2 And it began to enter the continuous production stage.

[0052] During continuous production, the system operates continuously at ambient temperature and pressure, and the following indicators are monitored: (1) Slot voltage; (2) Composition of the cathode outlet gas; (3) Circulating electrolyte level.

[0053] Among them, the cell voltage can serve as an important indicator of whether the system has experienced operational deviation; the composition of the cathode outlet gas can be used to determine whether the continuous ethylene production state is stable; and the circulating liquid level can reflect whether the liquid phase conditions have changed significantly during continuous operation.

[0054] In this embodiment, the steady-state maintenance window is set as follows: the tank voltage deviates from the stable operating baseline by no more than 10%, and the circulating liquid level is not lower than 90% of the initial level. Within this window, the system is considered to be in the steady-state maintenance stage of high current density continuous production.

[0055] The offset correction operation will be performed if any of the following conditions are met: (1) The tank voltage deviates from the stable operating baseline value by more than 10%; (2) The circulating fluid level is lower than 90% of the initial level; (3) The composition of the cathode outlet gas exhibits continuous abnormal fluctuations.

[0056] The offset correction operation includes: fluid replenishment and short-term flow reduction.

[0057] The replenishment process involves adding deionized water and / or pre-prepared 1 M KOH solution to the circulating liquid system to restore the liquid level to near the initial level. Short-term current reduction is to reduce the current density from 500 mA / cm² 2 Reduced to 200 mA / cm 2 After 10 minutes, it was restored to 500 mA / cm. 2 Continue production.

[0058] The cathode outlet gas is condensed and dehydrated before being introduced into the analysis system for analysis, and the product gas is continuously collected. Operational results show that, using the segmented upflow build-up-steady-state maintenance coupling process described in this invention, the system can achieve a flow rate of 500 mA / cm². 2 It can maintain continuous operation for more than 200 hours at high current density and keep ethylene production continuous.

[0059] Example 2: 600 mA / cm 2 Continuous production implementation under certain conditions The reactor structure, cathode type, anode type, gas supply method, and electrolyte system used in this embodiment are the same as those in Example 1. Carbon dioxide is continuously introduced into the cathode side at a flow rate of 10 sccm; the electrolytes in the cathode and anode chambers are 1 M KOH aqueous solutions, which are circulated separately.

[0060] The difference in this embodiment is that the target high current density production stage is set to 600 mA / cm². 2 .

[0061] During the startup phase, a segmented flow ramping procedure is also used: In the first stage, the current density is controlled at 100 mA / cm². 2 Run for 1 hour; In the second stage, the current density is controlled at 300 mA / cm². 2 Run for 2 hours; In the third stage, the current density was further increased to 600 mA / cm². 2 It then enters the continuous production stage.

[0062] At 600 mA / cm 2 During continuous production, the tank voltage, outlet gas composition, and circulating liquid level are also monitored. The steady-state maintenance window can be set as follows: the tank voltage deviates from the stable operating baseline by no more than 15%, and the circulating liquid level is maintained at more than 90% of the initial level.

[0063] When the operating state deviates from the steady-state holding window, an offset correction operation is performed. The offset correction operation preferably includes: (1) The current density was reduced from 600 mA / cm 2 The voltage briefly dropped to 250 mA / cm 2 Lasts 5–15 minutes; (2) Replenish the fluid to restore the circulating fluid level; (3) Partial fluid replacement may be necessary.

[0064] In this embodiment, partial electrolyte replacement can be understood as draining a portion of the original electrolyte from the circulation system and replenishing it with a corresponding volume of fresh 1 M KOH aqueous solution. The electrolyte replacement ratio can be 20% to 50% of the total volume of the circulating liquid.

[0065] The results show that, using the above process procedure, even at 600 mA / cm 2 Under higher current density conditions, the system can still enter and maintain a continuous production state, and has a good ability to continuously generate ethylene.

[0066] Example 3: Introducing a continuous production method with periodic partial solution replacement Based on Example 1, this embodiment further introduces a periodic partial fluid replacement rule to enhance the ability to maintain steady state during long-term operation.

[0067] Specifically, during continuous production, a partial electrolyte change is performed every 72 hours. During a partial electrolyte change, 30% of the original electrolyte is removed from the circulating system, and an equal volume of fresh 1 M KOH aqueous solution is added. If, before 72 hours, the tank voltage rises by more than 15% above the baseline value, the circulating liquid level drops significantly, or the composition of the outlet gas fluctuates continuously, a partial electrolyte change can be performed earlier.

[0068] In this embodiment, the remaining parameters are the same as in Embodiment 1, namely: The cathode is a gas diffusion electrode supported on a copper-based catalyst layer; The carbon dioxide flow rate is 10 sccm; The startup phase uses 100 mA / cm 2 -300 mA / cm 2 -500 mA / cm 2 The segmented current boosting method; Continuous production stage at 500 mA / cm 2 Run it.

[0069] By introducing periodic partial liquid replacement, the adverse effects of changes in the circulating liquid state during long-term operation can be reduced. Results show that this method helps reduce tank voltage fluctuations, improves steady-state maintenance during continuous production, and extends the operating time of continuous ethylene production at high current densities.

[0070] Example 4: Process Implementation Methods under Different Segmented Flow Rate Flow Procedures To illustrate that the segmented current increase procedure is not limited to a single numerical combination, this embodiment provides another segmented current increase scheme.

[0071] In this embodiment, the startup phase is set as follows: Phase 1: Current density is 80 mA / cm² 2 It runs for 1.5 hours; Second stage: Current density is 250 mA / cm² 2 Run for 1 hour; Phase 3: Current density is 400 mA / cm² 2 Run for 1 hour; Phase 4: Current density increases to 500 mA / cm² 2 It then enters the continuous production stage.

[0072] This embodiment illustrates that the segmented current boosting and stabilization process of the present invention is not limited to two or three stages, nor is it limited to a specific current density increasing path. As long as the process objective of "stabilization from low load - transition to intermediate load - introduction of target high load" can be achieved, it falls under the implementation of the segmented current boosting and stabilization process described in the present invention.

[0073] During continuous production, the tank voltage, outlet gas composition, and circulating liquid level were also monitored. Based on the steady-state maintenance window, corrective measures such as replenishment, partial liquid replacement, or short-term flow reduction were implemented. Results showed that a multi-stage gradual flow increase method can also achieve high current density continuous production and improve the smoothness of the system transitioning from the initial state to the steady-state production state.

[0074] Example 5: Implementation of Offset Correction Action Combination This embodiment illustrates that the offset correction step can employ a combination of various actions, rather than being limited to a single operation.

[0075] In this embodiment, the continuous production stage is set at 500 mA / cm. 2 Operation. During operation, if the tank voltage is detected to be continuously higher than the baseline value by more than 10% and the outlet gas composition shows significant fluctuations, the following combined offset correction procedure will be executed: Step 1: Reduce the current density from 500 mA / cm² 2 Reduced to 200 mA / cm 2 Lasts 10 minutes; Step 2: Add deionized water to restore the liquid level to more than 95% of the initial level; Step 3: Add the pre-prepared 1 M KOH solution to restore the system composition to the set level; Step 4: Restore to 500 mA / cm 2 Continue running.

[0076] If the system still does not return to the steady-state holding window after performing the above correction procedure, then a partial liquid replacement operation should be performed.

[0077] This embodiment illustrates that the offset correction in this invention is not a single fixed action, but rather a combination of one or more operations can be used to restore the steady-state operation of continuous production, depending on the detected offset type and degree.

[0078] Comparative Example 1: No segmented current ramping procedure is used To illustrate the role of the segmented current boosting and stabilization step in this invention, a comparative example is provided.

[0079] In this comparative example, the system was directly boosted to 500 mA / cm² instead of using a segmented current ramp-up procedure during the startup phase. 2Except for the above, the other conditions are the same as in Example 1, namely: The reactor is a flowing electrolytic cell; The cathode is a gas diffusion electrode supported on a copper-based catalyst layer; Carbon dioxide is introduced into the cathode side at a flow rate of 10 sccm; The electrolytes in the cathode and anode chambers are both 1 M KOH and are recycled separately. Operates at normal temperature and pressure.

[0080] The results showed that direct entry into 500 mA / cm 2 When operating at high current densities, the system is more prone to significant operational fluctuations during the start-up phase, which is detrimental to the formation of a stable reaction interface and results in poor stability during continuous production. Therefore, the segmented current ramp-up and stabilization method employed in this invention is beneficial for improving the accessibility and stability of continuous production at high current densities.

[0081] Comparative Example 2: No steady-state hold window or offset correction steps set To illustrate the role of the steady-state maintenance and offset correction steps in this invention, a comparative example is provided.

[0082] In this comparative example, the same segmented flow ramping procedure as in Example 1 is still used in the startup phase, but in the continuous production phase, no steady-state holding window is set, and no offset correction is implemented based on tank voltage, liquid level, or outlet gas composition.

[0083] The results show that during long-term continuous operation, the system is more prone to gradually deviating from the stable production state, with larger fluctuations in tank voltage, difficulty in timely recovery of liquid level changes, and a greater likelihood of continuous shifts in the composition of the outlet product, which is detrimental to the stable maintenance of continuous ethylene production. This indicates that the steady-state maintenance window and shift correction steps described in this invention play a crucial role in improving the long-term stability of the high-current-density continuous ethylene production process.

[0084] Comparative Example 3: Production using only constant current without replenishment or liquid replacement management. In this comparative example, the same reactor, cathode, electrolyte, and segmented upflow procedure as in Example 1 were used, but the process was modified to reach 500 mA / cm². 2 After the continuous production phase, no replenishment of liquid is performed, nor is partial or complete liquid replacement carried out.

[0085] The results show that as the operating time increases, the circulating fluid level gradually decreases, and the system's operating state is more likely to deviate from the steady-state maintenance window, resulting in a decrease in continuous operation capability. This indicates that managing the fluid level and circulating fluid state is one of the important conditions for achieving long-cycle, high-current-density continuous production.

Claims

1. A segmented current rise-stabilization-steady-state maintenance coupled continuous process for the electroreduction of carbon dioxide to ethylene at high current density, characterized in that, Includes the following steps: Step 1: A flow electrolytic cell is used as the carbon dioxide electroreduction reactor. The flow electrolytic cell includes a gas chamber, a cathode gas diffusion electrode, a cathode chamber, an ion exchange membrane, an anode chamber, and an anode. Step 2: The cathode gas diffusion electrode is a gas diffusion electrode with a copper-based catalyst layer. Carbon dioxide gas is continuously introduced into the gas chamber on the cathode side, and alkaline electrolyte is added to and circulated in the cathode chamber and anode chamber respectively. Step 3: During the reactor start-up phase, a segmented upflow procedure is adopted to gradually move the system from the low current density region to the target high current density region in order to establish a stable cathode reaction interface. Step 4: Carry out the carbon dioxide electroreduction reaction in the target high current density region to continuously generate gaseous products containing ethylene, and maintain the reactor operation state within the preset steady-state holding window; continuously export and collect the gaseous products generated on the cathode side; Step 5: When the operating state deviates from the steady-state holding window, perform offset correction operation, and restore to the target high current density region to continue operation after offset correction; The target high current density region is 500-600 mA / cm². 2 .

2. The process according to claim 1, characterized in that, The segmented current boosting procedure includes a low current density stabilization stage, an intermediate current density transition stage, and a target high current density introduction stage.

3. The process according to claim 2, characterized in that, The current density during the low current density stabilization phase is 50-150 mA / cm². 2 Runs for 0.5-2 hours; The current density during the intermediate current density transition phase is 200-350 mA / cm². 2 It runs for 0.5-3 hours.

4. The process according to claim 1, characterized in that, The gas diffusion electrode is made of carbon paper, with a copper-based catalyst loaded on one side at a loading rate of 0.5-2 mg / cm³. 2 ; The copper-based catalyst comprises a rare earth metal Ce-doped cuprous oxide substrate and an organic cation layer in situ modified on the surface of the substrate.

5. The process according to claim 4, characterized in that, The preparation method of the copper-based catalyst includes the following steps: S1: Dissolve Cu source, Ce source and imidazole cationic liquid in deionized water to obtain a homogeneous precursor solution; S2: Add alkali to the precursor solution in step S1, adjust the pH to 10-13, and then stir at a constant temperature for 10-60 min to obtain the precursor suspension. S3: Add a reducing agent solution dropwise to the precursor suspension in step S2. After the addition is complete, continue the reaction system under constant temperature and sealed reaction for 0.5-2 hours. During this process, copper ions are reduced to cuprous oxide and accompanied by in-situ lattice doping of cerium atoms. At the same time, imidazole cations in the solution are in-situ coated on the surface of the generated catalyst through non-covalent interaction. S4: The copper-based catalyst is then obtained by washing, drying, and grinding.

6. The process according to claim 5, characterized in that, In step S1, the molar amount of Ce source is 5-20% of the molar amount of Cu source, the molar ratio of imidazole cationic liquid to Cu source is 0.8-1.2:1, and the imidazole cationic liquid is one or more of 1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide or 1-butyl-3-methylimidazolium tetrafluoroborate. The temperature for constant temperature stirring in step S2 is 30-40℃, and the stirring time is 20-40 minutes. The constant temperature reaction temperature in step S3 is 30-40℃, and the reaction time is 0.8-1.5h.

7. The process according to claim 1, characterized in that, The alkaline electrolyte is an aqueous solution of potassium hydroxide with a concentration of 0.5-2 M, preferably 1 M.

8. The process according to claim 7, characterized in that, The flow rate of carbon dioxide gas continuously introduced into the cathode side is 5-20 sccm, preferably 10 sccm; the circulation flow rates of the alkaline electrolyte in the cathode chamber and the anode chamber are 20-200 mL / min, preferably 50-150 mL / min.

9. The process according to claim 1, characterized in that, The steady-state maintenance window includes one or more of the following: cell voltage fluctuation range, cathode outlet gas composition fluctuation range, and circulating electrolyte level fluctuation range, wherein the cell voltage fluctuation does not exceed 5%-15% of the stable operating baseline value; The offset correction operation includes one or more of the following: briefly reducing the current density, adding deionized water, adding fresh alkaline electrolyte, partially replacing the circulating alkaline electrolyte, and completely replacing the circulating alkaline electrolyte.

10. The process according to claim 9, characterized in that, The short-term reduction of current density refers to reducing the target high current density to 20%-50% of it, maintaining it for 5-30 minutes, and then restoring it to the target high current density. During continuous operation, one or more of the following are monitored online: cell voltage, cathode outlet gas composition, and circulating electrolyte level. Based on the monitoring results, it is determined whether to perform the offset correction operation.