CO2 trapping system and method based on seawater grading pretreatment and electrochemical coupling

Abstract

The invention discloses a CO2 trapping system and method based on seawater grading pretreatment and electrochemical coupling. The system comprises a seawater grading pretreatment unit, an electrochemical coupling trapping unit and a CO2 separation and collection unit. The seawater grading pretreatment unit is used for removing suspended matters step by step and retaining carbonate through a triple filtering device, and preparing desalted seawater by utilizing a reverse osmosis device to meet electrolysis requirements; the electrochemical coupling trapping unit adopts a three-compartment structure including an anode chamber, a middle compartment and a cathode chamber, a cation exchange membrane and a proton exchange membrane are combined, protons generated by an anode are migrated to the middle compartment to react with seawater carbonate to generate CO2, and cathode hydrogen evolution and anode oxygen evolution are synchronously realized; and the CO2 separating and collecting unit is used for collecting high-purity CO2 through a membrane separation and vacuum negative pressure technology. According to the method, the problem of local consumption of deep and far sea wind power is solved, collaborative coupling of seawater purification, CO2 capture and green hydrogen preparation is realized, the green fuel synthesis cost is reduced, and the method has remarkable environmental and economic benefits.

Description

Technical Field

[0001] This invention belongs to the fields of carbon capture and storage (CCUS), new energy consumption and comprehensive utilization of seawater. Specifically, it relates to a CO2 capture system and method based on seawater graded pretreatment and electrochemical coupling, which is particularly suitable for the on-site consumption of deep-sea wind power generation. Background Technology

[0002] The ocean is Earth's largest carbon sink, storing approximately 93% of CO2 and removing 30-40% of anthropogenic carbon emissions annually, making it crucial for maintaining global carbon balance. However, with rising atmospheric CO2 concentrations, ocean acidification caused by excessive CO2 absorption is seriously threatening marine ecosystems. Traditional carbon capture technologies are mostly designed for point source emissions and are difficult to apply directly to vast ocean areas.

[0003] In recent years, electrochemical-based CO2 capture technology from seawater has gradually attracted attention. This technology uses electricity to drive an electrochemical reaction to extract CO2 from seawater, which can alleviate ocean acidification, protect the ecosystem, and effectively utilize intermittent green electricity such as offshore wind power. At the same time, the process can produce hydrogen (H2) and oxygen (O2) as byproducts, providing raw materials for the production of green fuels such as methane and methanol, thus achieving both environmental and economic benefits.

[0004] However, existing electrochemical CO2 capture technologies for seawater face many challenges in practical applications: (1) Challenges in seawater pretreatment: Seawater contains a large amount of suspended solids (silt, microorganisms, debris, etc.) and dissolved salts. If directly introduced into an electrochemical device, the suspended solids will clog the electrodes, block the flow channels, contaminate or even damage the ion exchange membrane, resulting in a sharp decline in system efficiency and high maintenance costs. Traditional single filtration methods are difficult to balance filtration accuracy and efficiency.

[0005] (2) Low reaction efficiency: Traditional single-chamber or double-chamber electrolytic cells are difficult to achieve efficient directional migration of protons, resulting in low CO2 generation rate and easy cross-contamination of products.

[0006] (3) Low system integration: The existing seawater pretreatment, electrochemical capture and gas separation units are mostly independent modules, lacking overall optimization design, resulting in large system size and high energy consumption, making it difficult to deploy on deep-sea platforms with limited space.

[0007] Therefore, there is an urgent need in this field for an efficient, stable, and economical seawater CO2 capture technology that can adapt to complex seawater quality, has a high degree of system integration, can synergistically produce high-purity hydrogen and CO2, and is suitable for on-site consumption of deep-sea wind power. Summary of the Invention

[0008] To address the aforementioned issues, this invention provides a CO2 capture system and method based on graded pretreatment and electrochemical coupling of seawater. By constructing a collaborative system of "graded pretreatment of seawater - electrochemical coupling capture - CO2 separation and collection", the system performs graded filtration of seawater and efficient CO2 separation, solving the problems of on-site consumption of deep-sea wind power and seawater acidification, and achieving the dual goals of carbon reduction and seawater resource utilization.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: On one hand, this invention proposes a CO2 capture system based on seawater staged pretreatment and electrochemical coupling, comprising: (1) Seawater grading pretreatment unit, used to provide suitable raw materials for electrochemical reaction, includes: a triple filtration device and a reverse osmosis device. The triple filtration device is used to filter the raw seawater step by step to remove suspended solids to avoid clogging / corrosion of the electrochemical device components and retain the carbonates in the seawater. The inlet of the reverse osmosis device is connected to the outlet of the triple filtration device to desalinate part of the seawater after triple filtration and produce desalinated seawater. Its core function is to adapt to the electrolysis reaction requirements of the cathode chamber and anode chamber and avoid the interference of high salinity on the electrode reaction. (2) Electrochemically coupled trapping unit, which is the core of the system, includes a middle compartment, a cathode compartment, an anode compartment, a catalyst, a solid electrolyte, a DC voltage source, and membrane components for separating the compartments; the inlet of the middle compartment is directly connected to the outlet of the triple filtration device for introducing carbonate-rich seawater after triple filtration; the inlets of the cathode compartment and the anode compartment are respectively connected to the outlet of the reverse osmosis device for introducing desalinated seawater; the membrane components include a cation exchange membrane disposed between the cathode compartment and the middle compartment, and a proton exchange membrane disposed between the anode compartment and the middle compartment, to achieve selective ion permeation and directional proton migration; (3) CO2 separation and collection unit, including membrane separation device and vacuum pump; the inlet of the membrane separation device is connected to the outlet of the intermediate compartment for purifying the generated CO2; the vacuum pump is connected to the outlet of the membrane separation device for providing negative pressure to collect the purified CO2.

[0010] Furthermore, the triple filtration device consists of a coarse filter, a medium filter, and a fine filter connected in series; the coarse filter is an 80-120 μm cyclone filter used to remove suspended solids with a particle size ≥ 80 μm; the medium filter is a 20-40 μm cyclone filter used to remove suspended solids with a particle size ≥ 20 μm; and the fine filter is a 3-7 μm precision filter used to remove fine particles with a particle size ≤ 7 μm.

[0011] Furthermore, the cation exchange membrane allows cations to pass through while retaining anions and gases, preventing cross-contamination between the cathode chamber and the intermediate compartment; the proton exchange membrane has high proton conductivity, ensuring that protons generated at the anode migrate directionally to the intermediate compartment, and the proton conductivity of the proton exchange membrane at 25°C is ≥0.01 S / cm.

[0012] Furthermore, the seawater treated by the aforementioned triple filtration device has a suspended solids content of ≤1 mg / L and a carbonate retention rate of ≥95%.

[0013] Furthermore, the desalination rate of the reverse osmosis device is ≥99%; the DC voltage source provides an electric field for the electrolysis reaction; and the electrolysis reaction temperature is controlled at 20-60℃.

[0014] Furthermore, the catalyst includes a cathode catalyst disposed in the cathode chamber and an anode catalyst disposed in the anode chamber; the cathode catalyst is a platinum-based catalyst or a nickel-based catalyst, used to promote the hydrogen evolution reaction; the anode catalyst is an iridium-based catalyst or a ruthenium-based catalyst, used to promote the oxygen evolution reaction and proton generation.

[0015] Furthermore, the solid electrolyte is a strong cation exchange resin (such as sodium styrene-divinylbenzene sulfonated copolymer) or inert ceramic particles; the solid electrolyte is filled in the intermediate compartment, the cathode compartment, and the anode compartment.

[0016] Furthermore, the membrane separation device uses a CO2 selective permeation membrane made of polyimide, polysulfone, or ceramic, with a CO2 rejection rate ≥98%; the vacuum pump is a dry screw vacuum pump or a Roots vacuum pump with a pumping speed of 10-50 m³ / h. 3 / h, with an ultimate vacuum degree ≤10 Pa.

[0017] The present invention also proposes a method for CO2 capture using the system described above, comprising the following steps: S1. Seawater classification and pretreatment: The raw seawater is filtered through a triple filtration device in sequence to remove suspended solids while retaining carbonates. Then, the filtered seawater is divided into two paths: the first path is directly sent to the middle compartment of the electrochemical coupling collection unit; the second path is sent to the reverse osmosis unit for desalination treatment. After obtaining desalinated seawater, it is sent to the cathode and anode compartments of the electrochemical coupling collection unit respectively. S2, Electrochemical Coupling Collection: Electrolysis is carried out by applying a DC voltage to the cathode chamber and the anode chamber under the action of a catalyst and a solid electrolyte; An oxygen evolution reaction occurs in the anode chamber, producing protons (2H₂O - 4e⁻). - = O2↑ + 4H + The protons migrate through the proton exchange membrane to the intermediate compartment; In the intermediate compartment, the migrating protons react with bicarbonate ions in the seawater to produce CO2 gas (CO3). 2- +2H + =CO2↑ +H2O or HCO3 - + H + = CO2↑ + H2O); Hydrogen evolution reaction occurs in the cathode chamber to produce hydrogen gas (2H₂O + 2e⁻). - = H2↑ + 2OH - ); S3, CO2 Separation and Collection: The CO2-containing gas generated in the intermediate compartment is passed into a membrane separation device for purification to obtain high-purity CO2. The purified CO2 is then collected under negative pressure provided by a vacuum pump, completing carbon capture. Simultaneously, hydrogen produced in the cathode chamber and oxygen produced in the anode chamber are collected. 。

[0018] Furthermore, the intermediate compartment is circulated with seawater that has been triple-filtered and retains carbonates, while the cathode and anode compartments are circulated with desalinated seawater that has undergone reverse osmosis pretreatment. The membrane modules have clearly defined functions: the cation exchange membrane is used to separate the cathode compartment and the intermediate compartment, allowing cations to pass through while retaining anions and gases, preventing cross-contamination between the cathode and intermediate compartments; the proton exchange membrane is used to separate the anode compartment and the intermediate compartment, with a proton conductivity ≥0.01 S / cm (25℃), ensuring the directional and efficient migration of protons. Furthermore, in step S3, the CO2 purified by the membrane separation device has a purity of ≥99% and a collection efficiency of ≥90%; the collected CO2 and hydrogen can be synthesized on-site into green fuels such as methanol and methane.

[0019] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) Excellent economic efficiency of new energy consumption: CO2, hydrogen, oxygen and desalinated seawater are produced simultaneously. Hydrogen does not need to be transported over long distances and can be directly synthesized with captured CO2 on the deep-sea platform to synthesize green fuels such as methanol and methane, which significantly reduces storage and transportation costs and improves the economic feasibility of deep-sea wind power.

[0020] (2) System stability and long lifespan: The unique “seawater graded pretreatment” process accurately removes suspended solids of different particle sizes through three-stage filtration while retaining carbonates, effectively solving the problems of electrode poisoning and membrane blockage caused by seawater impurities; the reverse osmosis desalinated seawater is used in the electrolysis chamber, avoiding side reactions caused by high salinity and extending the equipment lifespan.

[0021] (3) High reaction efficiency: The three-compartment structure combined with the synergistic effect of cation exchange membrane and proton exchange membrane realizes the directional and efficient migration of protons and the selective permeation of ions, which greatly improves the CO2 generation rate and current efficiency.

[0022] (4) Significant environmental benefits: Directly capturing CO2 from seawater helps alleviate ocean acidification and protect marine ecology; at the same time, it achieves seawater purification (removing suspended solids and some salt), promoting the efficient use of marine resources.

[0023] (5) Strong adaptability: The system has a compact structure and adjustable parameters of each unit (voltage, flow rate, membrane material), making it compatible with seawater quality in different sea areas. It is particularly suitable for the space constraints and operation requirements of deep-sea wind power platforms. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall structure of the system of the present invention; Figure 2 This is a detailed structural schematic diagram of the electrochemical coupling trapping unit of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0026] like Figure 1 and Figure 2 As shown, this embodiment of the invention provides a CO2 capture system based on seawater graded pretreatment and electrochemical coupling, including a seawater graded pretreatment unit, an electrochemical coupling capture unit, and a CO2 separation and collection unit.

[0027] The raw seawater first enters the seawater classification and pretreatment unit. This unit consists of a triple filtration system, consisting of a 100μm cyclone filter (removing suspended solids ≥100μm), a 30μm cyclone filter (removing suspended solids ≥30μm), and a 5μm precision filter (removing fine particles ≤5μm), connected in series via pipelines. After three-stage filtration, the suspended solids content of the seawater is reduced to below 1 mg / L, and the carbonate retention rate exceeds 95%. Subsequently, the filtered seawater is divided into two streams: one stream (approximately 2000 mL / min) is directly transported as a carbon source to the intermediate compartment of the subsequent electrochemical coupling and trapping unit; the other stream enters the reverse osmosis unit for desalination at an operating pressure of approximately 2 MPa, with a desalination rate >99.5%. The desalinated seawater produced is then transported to the cathode and anode chambers at a total flow rate of approximately 500 mL / min.

[0028] The electrochemically coupled trapping unit employs a three-compartment electrolytic cell structure. The middle compartment is filled with filtered seawater (containing bicarbonate) from the pretreatment unit. The cathode and anode compartments are filled with desalinated seawater from the reverse osmosis unit. A homogeneous cation exchange membrane separates the cathode and middle compartments, while a perfluorosulfonic acid proton exchange membrane separates the anode and middle compartments. A Pt / C catalyst is loaded in the cathode compartment as the cathode catalyst, and an IrO2 catalyst is loaded in the anode compartment as the anode catalyst. Each compartment is filled with sodium-type styrene-divinylbenzene sulfonated copolymer resin as the solid electrolyte. A 3V DC voltage source is applied to the cathode and anode, and the system electrolysis temperature is maintained at 60°C.

[0029] When electricity is applied, an oxygen evolution reaction occurs in the anode chamber: 2H₂O - 4e⁻ - = O2↑ + 4H + The protons produced (H + Driven by an electric field, the protons pass through the proton exchange membrane into the intermediate compartment. Inside the intermediate compartment, the protons react with HCO3- in the seawater. - Reaction: HCO3 - + H + The reaction CO2↑ + H2O continuously produces CO2 gas. Hydrogen evolution occurs in the cathode chamber: 2H2O + 2e- - = H2↑ + 2OH - Na produces hydrogen gas. + Cations migrate from the intermediate compartment to the cathode compartment through the cation exchange membrane to maintain electroneutrality.

[0030] The CO2 separation and collection unit comprises a membrane separation device and a miniature dry screw vacuum pump. The CO2-containing gas mixture generated in the intermediate chamber enters the membrane separation device, which is made of polyimide hollow fiber membrane. This membrane exhibits high selectivity for CO2; driven by the negative pressure provided by the vacuum pump (system pressure maintained at tens of Pascals), CO2 preferentially permeates through the membrane wall for purification, achieving a purity of up to 99.2%. The purified CO2 is then drawn into a CO2 collection container (such as a small cryogenic storage tank) for storage, with a collection efficiency of approximately 90%. Simultaneously, hydrogen generated at the cathode is extracted through a hydrogen collection port, and oxygen generated at the anode is extracted through an oxygen collection port; both can be subsequently utilized, providing raw materials for the on-site synthesis of green fuels.

[0031] Test results: The system ran continuously for 100 hours without any film blockage or electrode corrosion.

[0032] The CO2 generation rate is 15 mmol / h·cm², and the current efficiency reaches 85%.

[0033] The purity of the CO2 product is ≥99%, and the purity of the hydrogen product is ≥99.5%.

[0034] In summary, this invention provides a CO2 capture system and method based on seawater graded pretreatment and electrochemical coupling. Through unique process flow design and unit integration, it effectively solves the problems of difficult seawater pretreatment, numerous electrolysis side reactions, and low system efficiency in existing technologies. This system is compact, stable in operation, low in energy consumption, and produces high-purity gas. It is particularly suitable for integration with deep-sea wind power and offshore oil platforms to achieve negative CO2 emissions and on-site consumption of green electricity, possessing extremely high industrial application value and broad market prospects.

[0035] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A CO2 capture system based on seawater staged pretreatment and electrochemical coupling, characterized in that, include: A seawater classification and pretreatment unit, used to provide suitable feedstock for electrochemical reactions, includes: The triple filtration system and reverse osmosis system are used to filter the raw seawater step by step, removing suspended solids and retaining carbonates. The inlet of the reverse osmosis unit is connected to the outlet of the triple filtration unit, and is used to pre-treat part of the seawater after triple filtration to produce desalinated seawater. An electrochemically coupled trapping unit includes an intermediate compartment, a cathode compartment, an anode compartment, a catalyst, a solid electrolyte, a DC voltage source, and membrane modules for separating the compartments. The inlet of the intermediate compartment is directly connected to the outlet of the triple filtration device for introducing carbonate-rich seawater after triple filtration. The inlets of the cathode and anode compartments are respectively connected to the outlets of the reverse osmosis device for introducing desalinated seawater. The membrane modules include a cation exchange membrane disposed between the cathode compartment and the intermediate compartment, and a proton exchange membrane disposed between the anode compartment and the intermediate compartment. The CO2 separation and collection unit includes a membrane separation device and a vacuum pump; the inlet of the membrane separation device is connected to the outlet of the intermediate compartment for purifying the generated CO2; the vacuum pump is connected to the outlet of the membrane separation device for providing negative pressure to collect the purified CO2.

2. The CO2 capture system based on seawater staged pretreatment and electrochemical coupling according to claim 1, characterized in that, The triple filtration device consists of a coarse filter, a medium filter, and a fine filter connected in series. The coarse filter is an 80-120 μm cyclone filter used to remove suspended solids with a particle size ≥ 80 μm. The medium filter is a 20-40 μm cyclone filter used to remove suspended solids with a particle size ≥ 20 μm. The fine filter is a 3-7 μm precision filter used to remove fine particles with a particle size ≤ 7 μm.

3. The CO2 capture system based on seawater staged pretreatment and electrochemical coupling according to claim 1, characterized in that, The cation exchange membrane allows cations to pass through while retaining anions and gases, preventing cross-contamination between the cathode chamber and the intermediate compartment. The proton exchange membrane has high proton conductivity, ensuring that protons generated at the anode migrate directionally to the intermediate compartment. The proton conductivity of the proton exchange membrane at 25°C is ≥0.01 S / cm.

4. The CO2 capture system based on seawater staged pretreatment and electrochemical coupling according to claim 2, characterized in that, The seawater treated by the aforementioned triple filtration device has a suspended solids content of ≤1 mg / L and a carbonate retention rate of ≥95%.

5. A CO2 capture system based on seawater staged pretreatment and electrochemical coupling according to claim 2, characterized in that, The desalination rate of the reverse osmosis unit is ≥99%.

6. The CO2 capture system based on seawater staged pretreatment and electrochemical coupling according to claim 1, characterized in that, The catalyst includes a cathode catalyst disposed in the cathode chamber and an anode catalyst disposed in the anode chamber; the cathode catalyst is a platinum-based catalyst or a nickel-based catalyst, used to promote the hydrogen evolution reaction; the anode catalyst is an iridium-based catalyst or a ruthenium-based catalyst, used to promote the oxygen evolution reaction and proton generation.

7. A CO2 capture system based on seawater staged pretreatment and electrochemical coupling according to claim 1, characterized in that, The solid electrolyte is a strong cation exchange resin or inert ceramic particles; the solid electrolyte is filled in the intermediate compartment, the cathode compartment, and the anode compartment.

8. A CO2 capture system based on seawater staged pretreatment and electrochemical coupling according to claim 1, characterized in that, The membrane separation device uses a CO2 selective permeation membrane made of polyimide, polysulfone, or ceramic, with a CO2 rejection rate of ≥98%; the vacuum pump is a dry screw vacuum pump or a Roots vacuum pump with an ultimate vacuum of ≤10 Pa.

9. A method for CO2 capture using the system described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Seawater classification and pretreatment: The raw seawater is filtered through a triple filtration device in sequence to remove suspended solids while retaining carbonates; then, the filtered seawater is divided into two paths: the first path is directly transported to the middle compartment of the electrochemical coupling collection unit. The second route is sent to the reverse osmosis unit for desalination. After obtaining desalinated seawater, it is sent to the cathode chamber and anode chamber of the electrochemical coupling collection unit respectively. S2, Electrochemical Coupling Collection: Electrolysis is performed by applying a DC voltage to the cathode and anode chambers; An oxygen evolution reaction occurs in the anode chamber to produce protons, which then migrate through the proton exchange membrane to the intermediate compartment. In the intermediate compartment, the migrating protons react with bicarbonate ions in the seawater to generate CO2 gas. Hydrogen gas is produced by the hydrogen evolution reaction in the cathode chamber. S3, CO2 separation and collection: The CO2-containing gas generated in the intermediate compartment is passed into the membrane separation device for purification, and the purified CO2 is collected under the negative pressure provided by the vacuum pump.

10. The method according to claim 9, characterized in that, In step S3, the CO2 purified by the membrane separation device has a purity of ≥99% and a collection efficiency of ≥90%; the collected CO2 and hydrogen can be synthesized into green fuel on-site.

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