Non-pure hydrogen assisted seawater carbon capture method and system

Abstract

The invention relates to the technical field of H2 preparation and CO2 capture, and discloses a non-pure hydrogen assisted seawater carbon capture method and system. The method comprises the following steps: softening seawater to remove calcium and magnesium ions; introducing dehydrated and dedusted non-pure hydrogen into an anode chamber of the electrochemical reactor, oxidizing under the action of a catalyst to generate protons, and migrating the protons to an acidification chamber through an ion exchange membrane to react with carbonate in the softened seawater to generate soluble CO2; cO2 is extracted through a vacuum stripping method; the seawater in the cathode chamber is subjected to a hydrogen evolution reaction to generate hydrogen and alkaline water, and hydrogen is extracted; synthesizing hydrocarbons such as methane and methanol from the captured CO2 and H2 under the action of a catalyst; the extracted acidic and alkaline waste liquid is mixed and neutralized to be close to neutral and then is discharged. According to the invention, industrial waste gas resource utilization, seawater low-carbon capture and high-efficiency hydrogen production collaboration are realized, and the method has the advantages of low energy consumption, low cost, environmental friendliness and high added value of products.

Description

Technical Field

[0001] This invention relates to the fields of hydrogen preparation and carbon dioxide capture and application in seawater, and more particularly to a non-pure hydrogen-assisted seawater carbon capture method and system. Background Technology

[0002] Currently, direct air capture technology has made some progress, but it faces significant challenges: the concentration of CO2 in the atmosphere is extremely low (approximately 420 ppm), requiring the processing of large amounts of air, resulting in high energy consumption, huge equipment investment, and expensive capture costs. In contrast, the ocean, as a vast natural carbon sink, stores approximately 93% of the Earth's CO2, with about 2%–3% existing as dissolved carbon dioxide gas and the remaining 97%–98% in combined bicarbonate and carbonate forms. The dissolved CO2 concentration in its surface seawater (100 mg / L) is more than 140 times that of the atmosphere (0.7 mg / L). Acidifying seawater to release and capture CO2 is equivalent to indirectly capturing atmospheric CO2 (the carbon dioxide balance between atmosphere and seawater: CO2(g) <=> CO2(aq)). Removing CO2 from seawater can indirectly reduce the carbon dioxide content in the atmosphere, mitigating the greenhouse effect; the resulting seawater medium can absorb more carbon dioxide from the atmosphere without affecting the ocean's pH.

[0003] Currently, the main method used in direct air capture technology is amine absorption, which utilizes an amine solution to chemically absorb carbon dioxide from flue gas, followed by heating and desorption. While the technology is relatively mature, it is energy-intensive, requires large equipment, and is costly. The main method for capturing carbon dioxide in seawater is electrochemical methods. However, this method involves an oxygen evolution reaction at the anode, which is energy-intensive, and the product is relatively singular (only carbon dioxide), resulting in low overall economic efficiency.

[0004] Many industrial processes, such as chlor-alkali, oil refining, and chemical manufacturing, produce hydrogen-rich byproduct gases, and biomass gasification also generates hydrogen-containing mixtures. These gases are often not utilized efficiently, and direct emission or combustion leads to resource waste and environmental pollution. Maximizing the value of hydrogen in byproduct gases while simultaneously achieving low-energy carbon capture is a current technological challenge.

[0005] Therefore, developing a circular process that can organically combine industrial waste gas utilization, seawater acidification carbon capture, and efficient hydrogen production to overcome the shortcomings of existing technologies such as high energy consumption, simple processes, and high costs, and to achieve resource synergy, energy reduction, and product value-added, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] To address the aforementioned technical issues, a non-pure hydrogen-assisted seawater carbon capture method and system are provided. By cleverly coupling electrochemical acidification, hydrogen evolution reaction, and carbon capture process, the system achieves efficient extraction of hydrogen from industrial gases, low-energy capture of carbon dioxide from seawater, and subsequent resource utilization.

[0007] The technical means employed in this invention are as follows:

[0008] A method for carbon capture in seawater assisted by non-pure hydrogen includes the following steps: Step S1, Seawater pretreatment: The seawater is softened to remove calcium and magnesium ions, resulting in softened seawater. Step S2, Electrochemical Acidification and Proton Generation: Impure hydrogen gas is introduced into the anode chamber of the electrochemical reactor, where an electrochemical oxidation reaction occurs under the action of the anode catalyst to produce protons (H). + The protons migrate through the ion exchange membrane to the acidification chamber; simultaneously, the softened seawater is introduced into the acidification chamber as an aqueous solution containing carbonates. Step S3, Carbon dioxide extraction: In the acidification chamber, the migrating protons react with carbonate and bicarbonate ions in the softened seawater to generate dissolved carbon dioxide; carbon dioxide is extracted from the acidified low-concentration acid water by vacuum stripping. Step S4, Hydrogen generation and extraction: In the cathode chamber of the electrochemical reactor, the seawater introduced undergoes a hydrogen evolution reaction under the action of the cathode catalyst to generate hydrogen and high-concentration alkaline water; the proton generation rate and hydrogen evolution rate are adjusted by controlling the voltage across the electrodes, thereby adjusting the output of CO2 and H2. Step S5, hydrocarbon generation: The CO2 captured in step 3 and the H2 captured in step S4 undergo a catalytic reaction in the presence of a catalyst to synthesize hydrocarbons. Step S6, waste liquid neutralization and discharge: The low-concentration acidic water after CO2 extraction in S3 is mixed with the high-concentration alkaline water after H2 extraction in S4 to make the mixture neutral, and then discharged into the sea.

[0009] Furthermore, the softening treatment in step S1 includes a chemical precipitation method to reduce the total content of calcium and magnesium ions after treatment to 10 ppm or less.

[0010] Furthermore, the non-pure hydrogen gas in step S2 includes one or more of the following: industrial by-product hydrogen, biomass gas, water gas, and coke oven gas. The main component of the industrial by-product hydrogen is hydrogen gas, and it also contains one or more of methane, carbon monoxide, carbon dioxide, nitrogen, water vapor, and nitrogen oxides. The main components of biomass gas are one or more of hydrogen, carbon monoxide, carbon dioxide, methane, or ethane. The main components of water gas are carbon monoxide and hydrogen. The main components of coke oven gas are hydrogen, methane, and one or more other hydrocarbons.

[0011] Furthermore, the electrode catalyst in step S2 is a transition metal catalyst; the main components of the transition metal catalyst are one or more of Pt, Ni, Co, and Ir.

[0012] Furthermore, in step S3, the vacuum stripping method is operated at a pressure controlled between 1 kPa and 50 kPa.

[0013] Furthermore, in step S4, the output of carbon dioxide and hydrogen is adjusted by controlling the cell voltage of the electrochemical reactor between 1.0V and 5.0V.

[0014] Furthermore, the catalytic reaction in step S5 is a hydrogenation reaction; the synthesized hydrocarbon is one or more of methane, methanol, and formic acid.

[0015] Furthermore, the electrochemical reactor is a three-chamber electrolytic cell, comprising an anode chamber, an acidification chamber, and a cathode chamber in sequence; a first ion exchange membrane is disposed between the anode chamber and the acidification chamber, and a second ion exchange membrane is disposed between the acidification chamber and the cathode chamber.

[0016] Furthermore, the first ion exchange membrane is a proton exchange membrane, used to allow protons to selectively enter the acidification chamber from the anode chamber; the second ion exchange membrane is a cation exchange membrane, used to allow sodium ions to enter the cathode chamber from the acidification chamber.

[0017] Furthermore, the cation exchange membrane is prepared by modifying a proton exchange membrane by soaking it in a 1-4M NaCl solution to enhance sodium ion selectivity. In this step, a sodium chloride solution is used to modify the proton exchange membrane, transforming it into a sodium ion exchange membrane.

[0018] Furthermore, each reaction process in the anode chamber, acidification chamber, and cathode chamber is carried out at a temperature of 20~50℃, an operating pressure of atmospheric pressure or 2~40 bar, and an operating current of 1~50A; and / or, the vacuum stripping method in step S3 is operated at a vacuum degree of -0.09MPa~-0.1MPa.

[0019] Furthermore, in step S6, the pH value of the mixture is adjusted to 7.0-8.0 before being discharged.

[0020] Furthermore, the process also includes a heat recovery step, in which the waste heat generated by the catalytic reaction in step S5 is used to preheat seawater or maintain the temperature of the electrochemical reactor to improve energy efficiency.

[0021] Furthermore, the CO2 and H2 produced in steps S3 and S4 can be recycled, and the unreacted gas is returned to the catalytic reactor to improve the conversion rate of hydrocarbon synthesis.

[0022] The present invention also discloses a system for implementing the above method, comprising: Seawater pretreatment unit for softening seawater; The three-chamber electrochemical reactor has a hydrogen-containing waste gas inlet in the anode chamber, a softened seawater inlet in the acidification chamber, and a softened seawater inlet in the cathode chamber. A gas separation unit, connected to the acidification chamber and the cathode chamber respectively, is used to separate carbon dioxide and hydrogen. A catalytic synthesis reactor, the inlet of which is connected to the carbon dioxide outlet and hydrogen outlet of the gas separation unit; The waste liquid mixing and neutralization unit has its inlet connected to the liquid outlets of the acidification chamber and the cathode chamber, respectively.

[0023] Compared with the prior art, the present invention has the following advantages: This invention innovatively uses non-pure hydrogen gases such as industrial by-product hydrogen, biomass gas, water gas, or coke oven gas as a source of protons. At the same time, it uses seawater as raw material and combines hydrogen production, carbon capture, and wastewater treatment processes to reduce waste emissions, which is in line with the concepts of green chemical industry and circular economy.

[0024] This invention utilizes electrochemical acidification to release CO2 from seawater instead of the traditional acid addition method, resulting in significantly lower energy consumption compared to traditional capture technologies such as amine absorption. Simultaneously, it leverages low-cost, high-yield waste resources—industrial by-product hydrogen or biomass gas—as a hydrogen production source, reducing hydrogen production costs. The anode and cathode waste liquids are neutralized and discharged, avoiding the chemical consumption and subsequent treatment costs associated with acid-base neutralization.

[0025] The entire process uses seawater and by-product gas as the main raw materials, and the final products are high-value-added hydrocarbons and near-neutral water. It achieves negative carbon dioxide emissions and resource utilization of industrial waste gas, resulting in significant environmental benefits.

[0026] By adjusting the applied voltage, the proton generation rate and hydrogen evolution rate can be flexibly adjusted, thereby precisely controlling the output of CO2 and H2 to adapt to different production needs. The operation is simple and the response is fast. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the overall process of a non-pure hydrogen-assisted seawater carbon capture method according to the present invention.

[0029] Figure 2 This is a schematic diagram of the structure of the electrochemical reactor (three-chamber electrolyzer) used in this invention. Detailed Implementation

[0030] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0033] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0034] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms 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, and therefore should not be construed as a limitation on the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0035] For ease of description, spatial relative terms such as "above," "over," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation besides the orientation of the device as described in the figures. For example, if the device in the figures is inverted, a device described as "above" or "above" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0036] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0037] As described in the background section, current industrial production processes generate large amounts of industrial byproducts such as hydrogen, biomass gas, water gas, and coke oven gas. The hydrogen in these industrial waste gases is not being fully utilized. To address this problem...

[0038] like Figure 1 , Figure 2 As shown in the figure, an embodiment of the present invention discloses a non-pure hydrogen-assisted seawater carbon capture method, comprising: Step S1, Seawater pretreatment: The seawater is softened to remove calcium and magnesium ions, resulting in softened seawater. Step S2, Electrochemical Acidification and Proton Generation: Impure hydrogen gas is introduced into the anode chamber of the electrochemical reactor, where an electrochemical oxidation reaction occurs under the action of the anode catalyst to produce protons (H). +The protons migrate through the ion exchange membrane to the acidification chamber; simultaneously, the softened seawater is introduced into the acidification chamber as an aqueous solution containing carbonates. In step S3, within the acidification chamber, the migrating protons react with carbonate and bicarbonate ions in the softened seawater to generate dissolved carbon dioxide, which is then extracted from the acidified low-concentration acid water using a vacuum stripping method. In step S4, the seawater introduced into the cathode chamber of the electrochemical reactor undergoes a hydrogen evolution reaction under the action of the cathode catalyst to generate hydrogen gas and high-concentration alkaline water. The proton generation rate and hydrogen evolution rate can be adjusted by controlling the voltage across the electrodes, thereby adjusting the output of CO2 and H2. In step S5, the CO2 captured in S3 and the H2 captured in S4 undergo a catalytic reaction in the presence of a catalyst to synthesize hydrocarbons. Step S6, waste liquid neutralization and discharge: The low-concentration acidic water after CO2 extraction in S3 is mixed with the high-concentration alkaline water after H2 extraction in S4 to make the mixture neutral, and then discharged into the sea.

[0039] Based on the above method, a direct current is applied to both ends of the electrolytic cell. Under certain operating current, flow rate, and temperature conditions, a driving force for ion migration is generated. At the anode, non-pure hydrogen from industrial by-products such as hydrogen, biomass gas, water gas, or coke oven gas is efficiently utilized. Under the action of a catalyst, it is converted into protons, which then cross the proton exchange membrane and enter the acidification chamber. This converts the seawater carbonate solution in the acidification chamber into carbonic acid, which can then be extracted using a vacuum stripping device. Metal cations in the acidification chamber permeate through the cation exchange membrane into the cathode chamber, where they react with OH- generated in the cathode chamber. - The mixture is combined to form an alkaline aqueous solution. A hydrogen evolution reaction occurs at the cathode, producing hydrogen gas. The acidic solution extracted in the acidification chamber is mixed with the high-concentration alkaline solution produced in the cathode chamber at a volume ratio of approximately 1:1.05. The resulting solution has a pH of approximately 7.8, close to neutral, meeting emission standards and can be directly discharged into the sea. The acidification level and hydrogen evolution rate can be adjusted by regulating the voltage across the electrodes, thereby flexibly controlling the production of CO2 and H2. Optionally, the obtained carbon dioxide and hydrogen can be synthesized into hydrocarbons through a catalytic reaction and sold as a byproduct. This not only significantly reduces the investment cost of carbon dioxide capture and utilization processes, promoting industrial applications, but also further enhances overall production efficiency.

[0040] Because natural seawater is rich in Ca 2+ and Mg 2+ Directly introducing seawater into the electrolytic cell will cause hydroxide precipitates to form, which will not only clog the liquid flow channels and contaminate the electrodes, but also adhere to the surface of the ion exchange membrane, leading to its failure. To avoid this phenomenon, such as... Figure 1As shown, before entering the acidification and cathode chambers, natural seawater undergoes softening treatment using chemical precipitation and filtration. Seawater is passed into a container containing an appropriate amount of sodium carbonate solution to promote the reaction of calcium and magnesium ions with sodium carbonate, forming insoluble calcium carbonate and magnesium carbonate precipitates. To ensure the effectiveness of the reaction, the concentration of the sodium carbonate solution is typically chosen to be between 0.1 mol / L and 0.3 mol / L. The specific concentration can be adjusted according to the initial concentration of calcium and magnesium ions in the seawater, usually about 10 to 30 grams of sodium carbonate per liter of seawater. The mixed solution is stirred for reaction, generally for 30 minutes to 1 hour, to ensure complete reaction and the conversion of calcium and magnesium ions into insoluble precipitates. After the reaction is complete, the seawater enters the filtration step, using a filter screen or microfiltration membrane to filter the reacted liquid and remove the precipitates. The softened seawater after filtration should have a total calcium and magnesium ion content reduced to below 8 ppm.

[0041] like Figure 1 As shown, the principle of the electrode catalytic process in the anode chamber is as follows: H2-2e - →2H + In the anode chamber, industrial by-product hydrogen or biomass gas introduced from the outside undergoes preliminary dehydration and dust removal, at a concentration of 2 Nm³. 3 A flow rate of / h is introduced into the anode chamber, and after passing through a titanium electrode coated with a Pt / Ir2 composite catalyst, combustible components such as hydrogen in the by-product gas are electrochemically oxidized to generate H+ under a cell voltage of 2.5V. The H+ migrates to the acidification chamber through a proton exchange membrane. This method can efficiently utilize hydrogen from industrial by-product hydrogen or hydrogen in biomass gas.

[0042] A stream of softened seawater is introduced into the acidification chamber at a certain flow rate. Dissolved inorganic carbon (carbonate and bicarbonate ions) in the seawater reacts with protons transported across the membrane from the anode chamber. The reaction principle in the acidification chamber is as follows: H + + CO3 - →HCO3 - H + +HCO3 - →H2CO3; H2CO3→H2O+CO2(g). H2CO3 is produced in seawater. Protons migrating from the anode continuously acidify the seawater, causing the pH to decrease. When the seawater pH drops below 4.5, carbonic acid accumulates to a certain value, and the acidified seawater has a pH ≈ 4.5. This seawater then enters a vacuum stripping tower, where CO2 gas is extracted under an operating pressure of 20 kPa, achieving a purity of over 90%. The low-concentration acidic water after CO2 extraction is temporarily stored. Another stream of softened seawater is introduced into the cathode chamber at a certain flow rate. The cathode chamber uses carbon paper electrodes coated with a Pt / C catalyst. Under the influence of an electric field, the seawater undergoes a hydrogen evolution reaction: H₂O + 2Na₂O +→H2(g) + NaOH: Water molecules combine with sodium ions that have permeated through the ion-exchange membrane in the acidification chamber. These ions are then decomposed into hydrogen and hydroxide ions by the catalytic action of the cathode electrode, generating a high-concentration alkaline sodium hydroxide solution with a pH of approximately 11.5, and producing high-purity hydrogen gas (>99.9%). The hydrogen gas is collected after gas-liquid separation. By adjusting the tank voltage to a stable 2.2V, the yields of CO2 and H2 reach their predetermined design values. The first ion exchange membrane between the anode and acidification chambers of the electrochemical reactor is a proton exchange membrane, Nafion 117. The second ion exchange membrane between the acidification and cathode chambers is a Nafion membrane modified by soaking in 1-4M NaCl solution for 48 hours. + The selective permeability is significantly improved. In this embodiment, 3M NaCl is preferred.

[0043] In some embodiments, in order to improve the reaction rate at the anode and cathode inside the electrolytic cell, a suitable catalyst is used for catalysis. The catalyst used at the anode is a composite of Pt and IrO2 in a mass ratio of 1:8, and the catalyst used at the cathode is a Pt / C catalyst.

[0044] In some embodiments, in order to prevent other gases from mixing into the carbon dioxide removed from acidified seawater and to improve the purity of carbon dioxide, the seawater is degassed before being introduced into the electrolytic cell to remove dissolved gases. Degasting equipment is used, and the degasting equipment can be a vacuum degasser or a degasting membrane.

[0045] In some embodiments, in order to better control the rate of carbon dioxide and hydrogen production, the reaction rate of the electrolyzer can be accelerated by adjusting the seawater flow rate, with the optimal seawater flow rate being 8~50 L / min.

[0046] Collected CO2 and H2 are mixed at a molar ratio of 1:4 and subjected to methanation in a fixed-bed reactor equipped with a Ni-based catalyst at 320°C and 20 bar to synthesize methane gas. Alternatively, methanol can be synthesized by mixing CO2 and collected H2 at a molar ratio of 1:5 in a fixed-bed reactor equipped with a Cu-Zn-Al catalyst at 280°C and 15 bar. Formic acid can also be synthesized by mixing CO2 and collected H2 at a molar ratio of 1:1 in a fixed-bed reactor equipped with a Pd / Ru complex catalyst at 110°C and 10 bar. Depending on the type of catalyst and the temperature setting, one or more of methane, methanol, or formic acid can be synthesized.

[0047] In some embodiments, when electro-acidification is incomplete, some carbon dioxide will dissolve in the aqueous solution, resulting in bicarbonate as the product of the acidification process. Therefore, when it is necessary to increase the carbon dioxide yield, the voltage of the electrolyzer should be increased as much as possible to ensure a more complete acidification process. Since catalytic reactions are exothermic, the heat generated can be used to heat water or steam as industrial byproducts. Unreacted carbon dioxide and hydrogen from the catalytic reaction can be recycled back into the reactor to increase the yield of the final product and the conversion rate of carbon dioxide and hydrogen. Example This embodiment uses hydrogen (approximately 80% purity, containing impurities such as carbon dioxide and methane) produced by a chemical plant and seawater from the Bohai Sea as raw materials to implement the cyclical process of electrochemical acidification synergistic hydrogen production and carbon capture of by-product gas described in this invention. The specific steps are as follows: First, 1000 liters of seawater were taken and 100 kg of sodium carbonate (Na₂CO₃) was added to achieve a final concentration of 20 wt%. The mixture was stirred for 30 minutes to allow calcium and magnesium ions in the seawater to react with the sodium carbonate, forming an insoluble precipitate. After the reaction, the precipitate was removed using a precipitation filtration method, yielding softened seawater. Testing showed that the total calcium and magnesium ion content in the treated seawater was reduced to 10 ppm or less, meeting the requirements for subsequent electrochemical reactions.

[0048] The softened seawater was divided into two streams. One stream was fed into the acidification chamber of the electrochemical reactor at a flow rate controlled at 15 L / min. The other stream was mixed with by-product gas from the chemical plant. After preliminary dehydration and dust removal, the by-product gas was discharged at a rate of 2 Nm³. 3 A flow rate of / h is introduced into the anode chamber. The anode chamber uses a titanium electrode coated with a Pt and Ir2 composite catalyst, and the catalytic reaction is carried out at a voltage of 2.5V to promote proton generation. At this time, the protons (H) generated by the anode reaction... + The protons migrate through the proton exchange membrane to the acidification chamber, where they react with carbonate and bicarbonate ions in seawater to produce carbon dioxide.

[0049] In the acidification chamber, migrating protons react with carbonate ions (CO3-) from seawater. 2- ) and bicarbonate (HCO3) - The ions react to form dissolved carbon dioxide (CO2). Acidified seawater (pH reduced to approximately 4.5) enters a vacuum stripping tower, where CO2 gas is extracted at an operating pressure of 20 kPa, achieving a purity of over 95%, with an energy consumption of approximately 690 kWh / ton. -1 CO2. Temporarily store the low-concentration acidic solution after CO2 extraction.

[0050] Another stream of softened seawater was introduced into the cathode chamber at a flow rate of 15 L / min. The cathode chamber used a carbon paper electrode coated with a Pt / C catalyst. Under the influence of an electric field, the seawater underwent a hydrogen evolution reaction, producing high-purity hydrogen gas (>99.9%) and highly concentrated alkaline water (pH rises to approximately 11.5). The hydrogen gas was collected after gas-liquid separation. By adjusting the power supply, the cell voltage was stabilized at 2.2V, at which point the yields of CO2 and H2 reached the predetermined design values.

[0051] Collected CO2 and H2 were mixed at a molar ratio of 1:4 and subjected to methanation in a fixed-bed reactor containing a Ni-based catalyst. The reaction time was maintained for 30 minutes at 320°C and 20 bar to synthesize methane gas. The conversion rate was as high as 75%, and the purity of the methane was over 95%.

[0052] The low-concentration acidic water after CO2 extraction is mixed with the high-concentration alkaline water produced at a volume ratio of approximately 1:1.05. The resulting solution has a pH of approximately 7.8, which is close to neutral and meets the discharge standards. It is then directly discharged into the sea.

[0053] In summary, it can be seen that the above embodiments of the present invention achieve the following technical effects: This innovative process uses non-pure hydrogen, such as industrial by-product hydrogen, biomass gas, water gas, or coke oven gas, as a source of protons. It also uses seawater as a raw material and combines hydrogen production, carbon capture, and wastewater treatment processes to reduce waste emissions, which aligns with the concepts of green chemistry and circular economy.

[0054] Electrochemical acidification is used to release carbon dioxide from seawater instead of the traditional acid addition method, resulting in significantly lower energy consumption than traditional capture technologies such as amine absorption. Simultaneously, low-cost, high-yield waste resources—industrial by-product hydrogen or biomass gas—are utilized as hydrogen production sources, reducing hydrogen production costs. Neutralization and discharge of anode and cathode wastewater avoids the consumption of chemicals for acid-base neutralization and subsequent treatment costs. The entire process uses seawater and by-product gas as the main raw materials, and the final products are high-value-added methane and near-neutral water. It achieves negative carbon dioxide emissions and resource utilization of by-product waste gas, resulting in significant environmental benefits.

[0055] The catalytic reaction of CO2 and H2 is an exothermic reaction. The heat generated by the reaction can be reasonably recovered and used to preheat the solution with a heat exchange device, so that the electrolyzer operates at the optimal temperature and achieves the highest efficiency, while reducing energy waste. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for carbon capture in seawater assisted by non-pure hydrogen gas, characterized in that, Includes the following steps: Step S1, Seawater pretreatment: The seawater is softened to remove calcium and magnesium ions, resulting in softened seawater. Step S2, Electrochemical Acidification and Proton Generation: Impure hydrogen gas is introduced into the anode chamber of the electrochemical reactor, where an electrochemical oxidation reaction occurs under the action of the anode catalyst to generate protons; the protons migrate to the acidification chamber through the ion exchange membrane; simultaneously, the softened seawater is introduced into the acidification chamber as an aqueous solution containing carbonates; Step S3, Carbon dioxide extraction: In the acidification chamber, the migrating protons react with carbonate and bicarbonate ions in the softened seawater to generate dissolved carbon dioxide; carbon dioxide is extracted from the acidified low-concentration acid water by vacuum stripping. Step S4, Hydrogen generation and extraction: In the cathode chamber of the electrochemical reactor, the seawater introduced undergoes a hydrogen evolution reaction under the action of the cathode catalyst to generate hydrogen and high-concentration alkaline water; the proton generation rate and hydrogen evolution rate can be adjusted by controlling the voltage across the electrodes, thereby adjusting the output of CO2 and H2. Step S5, hydrocarbon generation: The CO2 captured in S3 and the H2 captured in S4 undergo a catalytic reaction in the presence of a catalyst to synthesize hydrocarbons. Step S6, waste liquid neutralization and discharge: The low-concentration acidic water after CO2 extraction in S3 is mixed with the high-concentration alkaline water after H2 extraction in S4 to make the mixture neutral, and then discharged into the sea.

2. The non-pure hydrogen-assisted seawater carbon capture method according to claim 1, characterized in that: The softening treatment in S1 includes chemical precipitation, which reduces the total content of calcium and magnesium ions to 10 ppm or less after treatment.

3. The non-pure hydrogen-assisted seawater carbon capture method according to claim 1, characterized in that: The non-pure hydrogen in S2 includes one or more of the following: industrial by-product hydrogen, biomass gas, water gas, and coke oven gas. The main component of the industrial by-product hydrogen is hydrogen gas, and it also contains one or more of methane, carbon monoxide, carbon dioxide, nitrogen, water vapor, and nitrogen oxides. The main components of the biomass gas are one or more of hydrogen, carbon monoxide, carbon dioxide, methane, or ethane. The main components of the water gas are carbon monoxide and hydrogen. The main components of the coke oven gas are hydrogen, methane, and one or more other hydrocarbons.

4. The non-pure hydrogen-assisted seawater carbon capture method according to claim 1, characterized in that: The electrode catalyst in S2 is a transition metal catalyst; The main components of the transition metal catalyst are one or more of Pt, Ni, Co, and Ir; And / or, the vacuum stripping method in S3 has an operating pressure controlled between 1 kPa and 50 kPa.

5. The method for non-pure hydrogen-assisted seawater carbon capture according to claim 1, characterized in that: In S4, the output of carbon dioxide and hydrogen is adjusted by controlling the cell voltage of the electrochemical reactor between 1.0V and 5.0V.

6. The non-pure hydrogen-assisted seawater carbon capture method according to claim 1, characterized in that: The catalytic reaction in S5 is a hydrogenation reaction; the synthesized hydrocarbons are one or more of methane, methanol, and formic acid.

7. The non-pure hydrogen-assisted seawater carbon capture method according to claim 1, characterized in that: The electrochemical reactor is a three-chamber electrolytic cell, comprising an anode chamber, an acidification chamber, and a cathode chamber in sequence; a first ion exchange membrane is disposed between the anode chamber and the acidification chamber, and a second ion exchange membrane is disposed between the acidification chamber and the cathode chamber; The first ion exchange membrane is a proton exchange membrane, which allows protons to selectively enter the acidification chamber from the anode chamber; the second ion exchange membrane is a cation exchange membrane, which allows sodium ions to enter the cathode chamber from the acidification chamber.

8. The non-pure hydrogen-assisted seawater carbon capture method according to claim 1, characterized in that: The reactions in the anode chamber, acidification chamber, and cathode chamber are carried out at a temperature of 20~50℃, an operating pressure of atmospheric pressure or 2~40 bar, and an operating current of 1~50A; and / or, the vacuum stripping method in S3 is operated at a vacuum of -0.09MPa~-0.1MPa.

9. A non-pure hydrogen-assisted seawater carbon capture method according to claim 1, characterized in that: The pH of the mixture in step S6 is adjusted to 7.0-8.0 before being discharged; Furthermore, the method also includes a heat recovery step, in which the waste heat generated by the catalytic reaction in S5 is used to preheat seawater or maintain the temperature of the electrochemical reactor. And / or, The unreacted CO2 and H2 produced in S3 and S4 are returned to the catalytic reactor for recycling.

10. A system for implementing the method according to any one of claims 1 to 9, characterized in that, include: Seawater pretreatment unit for softening seawater; The three-chamber electrochemical reactor has a hydrogen-containing waste gas inlet in the anode chamber, a softened seawater inlet in the acidification chamber, and a softened seawater inlet in the cathode chamber. A gas separation unit, connected to the acidification chamber and the cathode chamber respectively, is used to separate carbon dioxide and hydrogen. A catalytic synthesis reactor, the inlet of which is connected to the carbon dioxide outlet and hydrogen outlet of the gas separation unit; The waste liquid mixing and neutralization unit has its inlet connected to the liquid outlets of the acidification chamber and the cathode chamber, respectively.

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