A process apparatus and method for selectively capturing carbonate or bicarbonate in seawater

Abstract

The application discloses a process equipment and method for selectively capturing carbonate or bicarbonate in seawater, and the process equipment comprises a capacitive CO2 removal device which is assembled in the order of a cathode shell, a cathode electrode, a gasket, a separator, an anode electrode and an anode shell, a first titanium sheet is arranged in the cathode shell, a second titanium sheet is arranged in the anode shell, a water inlet is arranged at the lower part of the anode shell, and a water outlet is arranged at the upper part of the anode shell. The application realizes the selective capture and conversion of carbonate in seawater by improving the existing capacitive deionization technology, coating a substance capable of specifically combining with divalent cations on activated carbon, attracting and capturing divalent cations by the electrode after electrification, combining the captured cations with anions to form metal salt precipitation by reversing the electrode polarity, and the operation is sustainable, low in energy consumption and low in cost, and the application provides an innovative and optimized scheme for the field of carbon dioxide treatment and carbon dioxide mineralization in seawater.

Description

Technical Field

[0001] This invention belongs to the field of chemical engineering and devices, and relates to a process equipment and method for selectively capturing carbonate or bicarbonate ions in seawater. Background Technology

[0002] To reduce residual carbon dioxide emissions from human activities, it is necessary to remove carbon dioxide directly from the atmosphere and oceans. This process, known as Direct Air Capture (DAC), employs advanced (electro)chemical processes to capture trace amounts of carbon dioxide from the atmosphere, which is then regenerated by controlling fluctuations in temperature or pressure. The released carbon dioxide is subsequently purified and pressurized before being transported for utilization or storage. Due to the extremely low concentration of carbon dioxide in the atmosphere (approximately 410 ppm) and the complex, multi-step nature of the process, the energy consumption of current DAC technologies is prohibitively high (200–365 kJ / mol) for ton-scale implementations. -1 CO2). In addition, the substantial capital and maintenance costs associated with DAC systems (over $100 million) -1 CO2 poses an additional barrier, hindering the widespread adoption of this technology.

[0003] The ocean is the largest carbon sink, with an effective carbon dioxide concentration of 2.1 mmol / kg in seawater. -1 The concentration of carbon dioxide in the ocean is 120 times that in the atmosphere. Therefore, capturing carbon dioxide from seawater (also known as "direct ocean capture," DOC) offers an attractive alternative for carbon removal and also helps mitigate ocean acidification.

[0004] To date, two strategies for capturing ocean carbon dioxide have been reported: the pH fluctuation method and the Ca / Mg-based mineral cycle. In the pH fluctuation method, seawater is broken down into acid and alkali via electrodialysis. The acid is used to acidify the seawater, promoting the conversion of carbonate and bicarbonate ions into dissolved carbon dioxide, which is then extracted from the seawater via a membrane contactor. The alkali is then used to neutralize the acidified seawater, and the resulting neutralized seawater is discharged back into the ocean. The Ca / Mg-based mineral cycle involves the calcination of minerals such as limestone (CaCO3), a process that produces CaO while releasing carbon dioxide. The CaO is then introduced into the seawater to increase its alkalinity, thereby promoting the conversion of bicarbonate to carbonate. The resulting carbonate reacts with Ca... 2+ Ions combine to form CaCO3, creating an efficient closed loop. In both cases, the chemical processes involved can be very expensive in terms of energy consumption, with the most efficient DOC technologies consuming between 130 and 200 kilojoules per mole of carbon dioxide.

[0005] Carbon capture processes must be integrated with downstream carbon dioxide conversion or storage to effectively achieve carbon removal targets. One strategy involves converting carbon dioxide into smaller molecules, including carbon monoxide (CO), ethylene (C2H4), and alcohols (CH3OH, C2H6O), via CO2 electrolysis, thereby enabling the production of carbon-neutral chemicals and fuels. However, this method only provides short-term carbon dioxide storage, ranging from a few months to a few years. Furthermore, the energy consumption associated with CO2 electrolysis is typically 600–800 kJ / mol. -1 CO2 causes the total energy consumption of the entire carbon capture and utilization cycle to be 730–1165 kJ / mol. -1 CO2. Captured carbon dioxide can also be mineralized with natural silicates, offering a more durable solution compared to short-term storage as fuel. However, mineralization typically takes several years, which is insufficient for the required rapid carbon dioxide capture rate. Rapid mineralization requires silicate pretreatment with an energy input of 150–250 kJ / mol per mole of carbon dioxide. -1 CO2. Furthermore, the global implementation costs of DAC / DOC and their environmental impact on ecosystems (due to the use / generation of acids / bases) remain uncertain. These concerns collectively drive our development of a chemical-free, low-energy scheme for capturing and utilizing ocean carbon dioxide with minimal impact on the marine environment.

[0006] In summary, the high carbon concentration in the ocean presents a new solution compared to direct air capture (DAC) technology, making it possible to capture carbon dioxide directly from seawater. Direct ocean capture methods based on pH fluctuations and Ca / Mg mineral cycles offer an attractive alternative for carbon removal, but the high energy consumption in these processes remains a challenge. On the other hand, carbon dioxide mineralization offers advantages over short-term storage, but a low-energy, rapid mineralization method without additional input is still lacking.

[0007] Therefore, a more environmentally friendly and efficient solution is needed to achieve the goal of sustainable climate development. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides an apparatus and method for selectively capturing carbonate or bicarbonate ions in seawater, which converts carbonate or bicarbonate ions, the form of carbon dioxide in the ocean, into substances such as calcium carbonate without the need for any reactants or chemicals. The process and structure are simple and inexpensive.

[0009] The present invention adopts the following technical solution.

[0010] A first aspect of the present invention provides a process apparatus for selectively capturing carbonate or bicarbonate ions in seawater, comprising a capacitor CO2 removal device, the capacitor CO2 removal device comprising: a cathode shell, a first titanium sheet, a cathode electrode, a gasket, a separator, an anode electrode, an anode shell, an inlet, a second titanium sheet, and an outlet; the apparatus is assembled in the order of cathode shell, cathode electrode, gasket, separator, anode electrode, and anode shell, the first titanium sheet being disposed inside the cathode shell, the second titanium sheet being disposed inside the anode shell, the inlet being disposed at the lower part of the anode shell, and the outlet being disposed at the upper part of the anode shell.

[0011] Preferably, the electrode is a material that generates double-layer capacitance and adsorbs ions, serving as a cathode or anode substrate.

[0012] Preferably, the electrode surface is coated with a substance that binds to divalent cations, wherein the substance that binds to divalent ions is any one of organic compounds containing -COOH or -HSO3 in its structure.

[0013] Preferably, the capacitor CO2 removal device uses a solution with a carbonate concentration of 0.001M to 1M and a calcium ion concentration of 0.001M to 5M as the ion source and electrolyte.

[0014] Preferably, the electrode is either an electrode with a substance that binds to divalent cations coated on one side, or an electrode with both sides coated with a substance that binds to divalent cations.

[0015] Preferably, the device further includes a cation exchange membrane or anion exchange membrane between the electrode and the pad.

[0016] A second aspect of the present invention provides a process method for selectively capturing carbonate or bicarbonate ions in seawater, based on the aforementioned process equipment for selectively capturing carbonate or bicarbonate ions in seawater, comprising the following steps:

[0017] Step 1: Assemble the capacitor CO2 removal device and introduce the solution;

[0018] Step 2: Apply voltage to the device, applying a negative potential to the cathode side and a positive potential to the anode side;

[0019] Step 3: Reverse the positive and negative terminals of the power supply to convert the original cathode electrode in Step 2 into the anode electrode;

[0020] Step 4: Repeat steps 2-3 to obtain solid salt particles from the introduced solution, selectively capturing carbonate or bicarbonate ions in seawater.

[0021] Preferably, in step 1, the device is composed of any one of "anode-cation exchange membrane-anion exchange membrane-cathode", "anode-cation exchange membrane-cathode", "anode-anion exchange membrane-cathode" or "anode-cathode".

[0022] Preferably, in step 2, the applied voltage is applied for 0-100 hours.

[0023] Preferably, in steps 2 and 3, the applied voltage is 0V-4V.

[0024] The beneficial effects of this invention are that, compared with the prior art,

[0025] (1) This invention uses an electrochemical device as a capacitor CO2 removal device, which mainly consists of a shell, anode, cathode, and separator. Based on capacitor deionization technology, a novel carbon capture device with an improved design on the cathode electrode is used. A layer of material that can absorb divalent cations is coated on the activated carbon on the negative charge side. By reversing the electrode polarity, it combines with divalent anions in seawater to obtain a precipitate, thereby achieving sustainable, low-energy-consumption, and low-cost capture of carbon dioxide from seawater. The device uses seawater as the electrolyte, eliminating the need for additional conductive additives. It has a simple structure, low cost, and can still achieve ideal results after scale-up, possessing potential for practical industrial applications.

[0026] (2) The steps of this invention are simple. This invention directly utilizes a material layer coated with adsorbed divalent cations as the core, and selectively collects metal cations (such as Ca) through a reverse electrode method. 2+ Mg 2+ (etc.), thereby selectively capturing carbonate ions in seawater to achieve the purpose of cyclically capturing carbon dioxide, effectively avoiding the cumbersome steps of previous methods;

[0027] (3) The present invention has low energy consumption, no extra chemical reaction occurs in the capacitor removal carbon dioxide technology, low energy consumption and high economic benefits, and can effectively optimize carbon dioxide capture and conversion technology, and has great application potential. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a capacitor-controlled CO2 reactor.

[0029] Figure 2 This is a photograph of a capacitor-to-CO2 reactor.

[0030] Figure 3 A schematic diagram of the structure of Nafion, which has the ability to bind with divalent cations;

[0031] Figure 4 A schematic diagram of the structure of a cation exchange resin that has a binding interaction with divalent cations;

[0032] Figure 5 This is a graph showing the selective binding of sulfonic acid compounds to calcium ions.

[0033] Figure 6 SEM image of calcium carbonate produced in the experiment;

[0034] Figure 7 The XRD pattern of the calcium carbonate produced in the experiment;

[0035] Figure 8 A graph showing the relationship between applied voltage and the calcium carbonate produced;

[0036] In the diagram: 1. Cathode shell; 2. First titanium sheet; 3. Cathode electrode; 4. Gasket; 5. Spare mesh; 6. Anode electrode; 7. Anode shell; 8. Inlet; 9. Second titanium sheet; 10. Outlet. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, other embodiments obtained by those skilled in the art without creative effort are all within the protection scope of this invention.

[0038] like Figure 1-2 As shown, Embodiment 1 of the present invention provides a process device for selectively capturing carbonate or bicarbonate ions in seawater, namely a capacitor CO2 removal device. The capacitor CO2 removal device includes: a cathode shell 1, a first titanium sheet 2, a cathode electrode 3, a gasket 4, a separator 5, an anode electrode 6, an anode shell 7, a water inlet 8, a second titanium sheet 9, and a water outlet 10.

[0039] The membrane electrode electrolytic cell is assembled in the following order: cathode shell 1, cathode electrode 3, gasket 4, separator 5, anode electrode 6, and anode shell 7. The first titanium sheet 2 is disposed inside the cathode shell 1, the second titanium sheet 9 is disposed inside the anode shell 7, the water inlet 8 is disposed at the lower part of the anode shell, and the water outlet 10 is disposed at the upper part of the anode shell.

[0040] The electrode material is a material that can generate double-layer capacitance and adsorb ions, and serves as a cathode or anode substrate.

[0041] In a preferred but non-limiting embodiment of the present invention, activated carbon, which is currently the mainstream and widely commercially available material, is loaded onto a current collector graphite sheet as an electrode substrate. It is inexpensive and can generate a relatively stable double-layer capacitance when energized, and is therefore widely used.

[0042] More preferably, the material used to generate double capacitance is not limited to the activated carbon electrode in this study; any material or mixture capable of generating double-layer capacitance is acceptable, such as MnO2, metal oxides, metal composites, etc.

[0043] like Figure 3 , Figure 4 As shown, the electrode surface is coated with a cation exchange resin that binds to divalent ions. The coated cation exchange resin has abundant sulfonic acid groups, which have a strong binding effect with divalent cations and can selectively adsorb divalent cations in seawater, such as calcium ions and magnesium ions.

[0044] In a preferred but non-limiting embodiment of the present invention, the selected substance having the ability to bind with cations is not limited to the cation exchange resin in this study. Any substance having the ability to bind with cations is acceptable, including but not limited to small molecule organic compounds containing sulfonic acid groups, polymers containing carbonyl groups, polymers containing sulfonic acid groups, organic compounds containing sulfonate groups, polymers containing sulfonate groups, polymers containing carbonyl groups, etc., wherein the cations in the organic compounds or polymers containing sulfonate groups are all cations with a weaker binding effect than calcium ions, including but not limited to metal ions such as Li, Na, K, Be, Mg, and Al.

[0045] The inventors noted that the selected functional group was compatible with Ca2+. + The bonding strength is moderate, which can effectively capture Ca2+. + The ions can also release Ca2+ during the formation of calcium carbonate precipitate. + This design avoids both excessively strong bonds that prevent the formation of calcium carbonate precipitate and excessively weak bonds that lead to the formation of unwanted CaSO4 precipitate, thereby increasing the Ca2+ precipitate concentration. + The selectivity and efficiency of the entire process.

[0046] It is worth noting that in the specific implementation of this invention, in Embodiment 1, one electrode is coated with cation exchange resin, and the other is a pure activated carbon electrode. In Embodiment 2, both electrodes are coated with electrodes that selectively adsorb cations. In the double-sided coated electrode design, both electrodes can adsorb cations in the first step, achieving the same experimental effect. Furthermore, regardless of whether it is single-sided or double-sided coated, the polarity of both electrodes is variable throughout the operation of the device, depending on the sign of the applied voltage.

[0047] The capacitor-based carbon dioxide removal device also uses seawater or a solution with a concentration similar to that of ionized seawater as the ion source and electrolyte.

[0048] In a preferred but non-limiting embodiment of the present invention, the selected seawater or a solution with a concentration similar to that of ionized seawater should contain the main ions calcium ions and carbonate ions, which are used to absorb calcium ions and further react with carbonate ions to capture and transform carbonate ions, and ultimately achieve the purpose of mineralizing carbon dioxide.

[0049] More preferably, the carbonate concentration in the solution with a similar seawater concentration is 0.001M to 1M, and the calcium ion concentration is 0.001M to 5M.

[0050] It is worth noting that the types and concentrations of other ions in the solution are not necessary conditions, but only preferred conditions. The solution itself can be used as a conductive electrolyte, without the need for additional conductive additives.

[0051] In a preferred but non-limiting embodiment of the present invention, adding a cation exchange membrane or anion exchange membrane between the electrode and the gasket in the capacitor carbon dioxide removal device is an optimized choice but not a necessary condition.

[0052] In this embodiment, the electrochemical device used does not have anion / cation exchange membranes added between the electrodes and the separator. Adding anion / cation exchange membranes can weaken the common ion effect and promote the experiment. The experimental effect can be achieved without adding anion / cation exchange membranes.

[0053] Embodiment 2 of the present invention provides a process for selectively capturing carbonate or bicarbonate ions in seawater, comprising the following steps:

[0054] Step 1: Assemble the capacitor carbon dioxide removal device and introduce the solution;

[0055] In a preferred but non-limiting embodiment of the present invention, the device is composed of any one of the following: "anode-cation exchange membrane-anion exchange membrane-cathode", "anode-cation exchange membrane-cathode", "anode-anion exchange membrane-cathode", or "anode-cathode".

[0056] More preferably, simulated seawater is continuously introduced into the device at a rate of 1.2 mL / min.

[0057] Step 2: Apply voltage to the device, applying a positive potential to the cathode side and a negative potential to the anode side, so that the anode electrode can selectively capture cations;

[0058] In a preferred but non-limiting embodiment of the invention, the applied voltage is 0.4-1.2 volts.

[0059] It is worth noting that 0.4-1.2 volts is the optimal voltage range for the experiment, and voltages of 0-4 volts and above 1.2 volts can also achieve the experimental results.

[0060] Step 3: Reverse the positive and negative terminals of the power supply to convert the original cathode electrode in Step 2 into the anode electrode, so that the electrode on this side has the ability to attract anions;

[0061] In a preferred but non-limiting embodiment of the present invention, the voltage application time is 0-100h.

[0062] It is worth noting that, due to the unique nature of the electrode reversal strategy, the positive and negative electrodes, as well as the anode and cathode, on each side are variable. When energized in step 2, the side with the negative electrode (coated with the ion-adsorbing material) acts as the cathode, while the other electrode becomes the anode, connected to the positive electrode. When the power is reversed, the cathode that was originally connected to the negative electrode becomes the anode connected to the positive electrode, and vice versa. That is, the electrode coated with the cation-adsorbing material is connected to the negative potential cathode in step 2, absorbing cations; in step 3, after the power is reversed, it becomes the positive electrode, the anode, absorbing anions. This device operates by repeatedly reversing the polarity of the positive and negative electrodes. Step 4 repeats steps 2-3, allowing the device to obtain solid salt particles from the introduced solution, thus selectively capturing carbonate ions from seawater.

[0063] Among them, the solid salt particles are solid insoluble substances formed by divalent cations and anions, including but not limited to calcium carbonate, magnesium carbonate, calcium sulfate, magnesium sulfate, or magnesium hydroxide and calcium hydroxide that may be formed.

[0064] In a preferred but non-limiting embodiment of the present invention, the generated solid particles are primarily calcium carbonate. For example... Figure 8 As shown, the mass of calcium carbonate solid particles obtained varies under different voltages, and the total amount of calcium carbonate particles obtained increases with the increase of the applied voltage.

[0065] More preferably, such as Figure 5-7 As shown, the present invention can also use XPS, SEM, XRD and other methods to detect the generated products, determine the composition of the experimental products, and determine the mass of the generated products by weighing.

[0066] It is worth noting that this invention performs energy and carbon emission calculations and economic benefit assessments on the implementation process: This study calculates the energy consumption during the operation based on Joule's law and the carbonate conversion pathway, and finally concludes that the reactor device for selectively adsorbing divalent cations has significant advantages in terms of energy consumption and economic cost.

[0067] The energy consumption generated during the implementation of the technology is:

[0068]

[0069] Where |I(t)| is the current value (A) during the operation of the device, U(V) is the voltage applied in the device, and dt is the operating time of the device (s). The mass (g) of calcium carbonate obtained during the operation of the device. is the molar mass of CaCO3.

[0070] The beneficial effects of this invention are that, compared with the prior art,

[0071] (1) The present invention uses an electrochemical device as a capacitor carbon dioxide removal device, which is mainly composed of a shell, anode, cathode and separator. It has a simple structure, low cost, and can still achieve ideal results after scale-up, and has the potential for practical industrial application.

[0072] (2) The steps of this invention are simple. This invention directly utilizes a material layer coated with adsorbed divalent cations as the core, and selectively collects metal cations (such as Ca) through a reverse electrode method. 2+ Mg 2+ (etc.), thereby selectively capturing carbonate ions in seawater to achieve the purpose of capturing carbon dioxide, effectively avoiding the cumbersome steps of previous methods;

[0073] (3) The present invention has low energy consumption, no extra chemical reaction occurs in the capacitor removal carbon dioxide technology, low energy consumption and high economic benefits, and can effectively optimize carbon dioxide capture and conversion technology, and has great application potential.

[0074] 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 it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A process apparatus for selectively capturing carbonate or bicarbonate ions from seawater, comprising a capacitor-based CO2 removal unit, characterized in that: The capacitor CO2 removal device includes: a cathode shell (1), a first titanium sheet (2), a cathode electrode (3), a gasket (4), a mesh (5), an anode electrode (6), an anode shell (7), an inlet (8), a second titanium sheet (9), and an outlet (10); the device is assembled in the order of cathode shell (1), cathode electrode (3), gasket (4), mesh (5), anode electrode (6), and anode shell (7), the first titanium sheet (2) is disposed inside the cathode shell (1), the second titanium sheet (9) is disposed inside the anode shell (7), the inlet (8) is disposed at the lower part of the anode shell, and the outlet (10) is disposed at the upper part of the anode shell; The electrode is a material that generates double-layer capacitance and adsorbs ions, serving as a cathode or anode substrate; The electrode surface is coated with a substance that binds to divalent cations. By reversing the electrode polarity, it then binds to divalent anions in seawater to form a precipitate. The substance that binds to divalent ions is any organic compound containing -COOH or -HSO3 in its structure, and the selected functional group is related to Ca. 2+ The bond strength is moderate, which can effectively capture Ca. 2+ Ions can also release Ca during the formation of calcium carbonate precipitate. 2+ ; The capacitor CO2 removal device uses a solution with a carbonate concentration of 0.001M to 1M and a calcium ion concentration of 0.001M to 5M as the ion source and electrolyte.

2. The process equipment for selectively capturing carbonate or bicarbonate ions in seawater as described in claim 1, characterized in that: The electrode is either an electrode with a substance that binds to divalent cations coated on one side, or an electrode with both sides coated with a substance that binds to divalent cations.

3. The process equipment for selectively capturing carbonate or bicarbonate ions in seawater as described in claim 1, characterized in that: The device also includes a cation exchange membrane or anion exchange membrane between the electrode and the pad.

4. A process for selectively capturing carbonate or bicarbonate ions in seawater, based on the process equipment for selectively capturing carbonate or bicarbonate ions in seawater according to any one of claims 1-3, characterized in that: Includes the following steps: Step 1: Assemble the capacitor CO2 removal device and introduce the solution; Step 2: Apply voltage to the device, applying a negative potential to the cathode side and a positive potential to the anode side; Step 3: Reverse the positive and negative terminals of the power supply to convert the original cathode electrode in Step 2 into the anode electrode; Step 4: Repeat steps 2-3 to obtain solid salt particles from the introduced solution, selectively capturing carbonate or bicarbonate ions in seawater.

5. A process method for selectively capturing carbonate or bicarbonate ions in seawater as described in claim 4, characterized in that, In step 1, the device is composed of any one of "anode-cation exchange membrane-anion exchange membrane-cathode", "anode-cation exchange membrane-cathode", "anode-anion exchange membrane-cathode" or "anode-cathode".

6. A process method for selectively capturing carbonate or bicarbonate ions in seawater as described in claim 4, characterized in that, In step 2, the applied voltage is applied for 0-100 hours.

7. A process method for selectively capturing carbonate or bicarbonate ions in seawater as described in claim 4, characterized in that, In steps 2 and 3, the applied voltage is 0V-4V.

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