Electrolysis method, electrolysis cell, electrolysis system, use and device

Abstract

The invention relates to a method for the extraction of carbon dioxide, comprising the following steps: a) anodic oxidation of hydrogen to obtain an acidic oxidation product; b) converting the acidic oxidation product with an aqueous solution containing a basic carbonate, in particular having a pH of > 7 to 9, to obtain an acidic aqueous solution; c) removing carbon dioxide from the acidic aqueous solution to obtain a carbon dioxide gas and a degassed acidic aqueous solution; d) subjecting the acidic components of the degassed acidic aqueous solution to cathodic reduction to produce cathodically produced hydrogen while also producing an aqueous alkaline solution having a pH of 9.4 to > = 8.

Description

Technical Field

[0001] The present invention relates to a method for extracting carbon dioxide, in particular from seawater or a gas containing carbon dioxide, in particular air or a point source, an electrolyser for extracting carbon dioxide, an electrolysis system comprising such an electrolyser, the use of such an electrolyser in an apparatus for the electrolytic extraction of carbon dioxide from seawater or a gas containing carbon dioxide, in particular air or a point source, and an apparatus for the electrolytic extraction of carbon dioxide from seawater. Background Art

[0002] With the increasing concentration of atmospheric CO2 and the resulting increase in global average temperature, systems for extracting CO2 from the atmosphere are becoming increasingly important. In addition to direct air capture (DAC) from ambient air, there are also technical possibilities for extracting or recovering CO2 from carbonate-containing aqueous solutions, in particular seawater.

[0003] Electrochemical methods can decompose water into alkaline and acidic components. In an acidic environment, the chemical balance changes from through Shift towards CO2 and H2O (see equation (1) below).

[0004]

[0005] Common electrochemical methods for splitting water into acidic and alkaline streams typically use one or more ion exchange membranes. These membranes selectively allow cations (CEM) or anions (AEM) to pass through. In addition, bipolar membranes (BPMs) can be used to separate aqueous systems into acidic (H + ) flow and alkaline (OH - )flow.

[0006] The so-called E-CEM (electrocatalytic cation exchange module) system has two cation exchange membranes between electrodes. Here, water flows through all three separated compartments. By applying a voltage, the proton concentration in the middle compartment increases due to H + The pH value is thus lowered, making it possible to extract CO2 from the solution. The energy consumption of such a system is about 20,000 kWh / t-CO2.

[0007] Compared to E-CEM systems, bipolar membrane electrodialysis systems (BPMED) are more energy efficient, requiring about 920 kWh / t-CO2 or 1,400 kWh / t-CO2 to extract CO2 from aqueous solution. Redox reactions such as the formation of H2 (HER) and O2 (OER) from H2O can be suppressed using a redox-active electrolyte stream that circulates directly at the cathode or anode. Preferred electrolytes include systems containing Fe(II) and Fe(III) ions, such as potassium hexacyanoferrate (II) and potassium hexacyanoferrate (III), but other compounds can also be used. At the bipolar membrane, water molecules are decomposed into acidic (H + ) flow and alkaline (OH - The acidic stream can be used to recover CO2, while the alkaline stream is used to alkalize process water.

[0008] To date, the highest energy efficiency for CO2 recovery from aqueous systems based on the state of the art has been achieved using an electrochemical hydrogen cycle (EHL). This setup involves three compartments. The cathode compartment is filled with seawater, producing H2 and OH at the cathode. - The resulting hydrogen is directed into the anode compartment. There, H2 is oxidized to H + , and is transferred to the intermediate compartment to acidify the incoming seawater.

[0009] Nanofiltration is often necessary for electrochemical methods of removing or recovering carbon dioxide from seawater. If high pH conditions exist in certain parts of the system, such as in the cathode compartment, this can lead to mineral precipitation of divalent magnesium or calcium ions. These ions are necessary to maintain high seawater alkalinity and thus the ability to reabsorb atmospheric carbon dioxide. In addition, the precipitated minerals can contaminate the system, causing problems such as electrode scaling, which will increase energy costs over time.

[0010] Nanofiltration is a highly complex and expensive process, with operating costs estimated at €0.20 per cubic meter of water treated. To extract one ton of CO2 from seawater with a dissolved CO2 concentration of 2.2 mM with 90% efficiency, 11,477 m3 of CO2 would be required. 3 The calculation shows that for one ton of CO2 extracted, the nanofiltration alone would cost around 2,000 euros.

[0011] The present invention therefore aims to reduce or eliminate these disadvantages. Summary of the invention

[0012] The above objects are achieved by the invention as defined in the independent claims.

[0013] According to a first aspect, the present invention relates to an electrolysis process for carbon dioxide extraction, in particular a continuously operated electrolysis process, comprising the following steps:

[0014] a) performing anodic oxidation on hydrogen to obtain an acidic oxidation product;

[0015] b) converting the acidic oxidation product with an aqueous solution containing an alkaline carbonate, in particular having a pH of >7 to 9, to obtain an acidic aqueous solution;

[0016] c) removing carbon dioxide from the acidic aqueous solution to obtain carbon dioxide gas and a degassed acidic aqueous solution;

[0017] d) subjecting the degassed acidic aqueous solution to cathode reduction of an acidic component to obtain cathode-generated hydrogen and an alkaline aqueous solution having a pH of 10 to ≥ 7.1.

[0018] According to a second aspect, the present invention provides an electrolyser for carbon dioxide extraction, comprising:

[0019] Anode compartment,

[0020] Intermediate compartments, and

[0021] A cathode compartment, wherein

[0022] The intermediate compartment is arranged between the anode compartment and the cathode compartment; the anode compartment is connected to the intermediate compartment via a first transport membrane;

[0023] The cathode compartment is connected to the intermediate compartment via a second transport membrane;

[0024] The anode compartment and the cathode compartment are fluidly connected via a hydrogen line;

[0025] The middle compartment has an inlet and an outlet, the outlet being fluidly connected to a carbon dioxide extraction device, and the carbon dioxide extraction device being fluidly connected directly to the inlet of the cathode compartment via a liquid line.

[0026] According to a third aspect, the invention relates to an electrolysis system comprising at least one electrolysis cell according to the second aspect of the invention.

[0027] According to a fourth aspect, the invention relates to the use of an electrolyser according to the second aspect of the invention in an apparatus for the electrolytic extraction of carbon dioxide from seawater.

[0028] According to a fifth aspect, the present invention relates to an apparatus for electrolytically extracting carbon dioxide from seawater, comprising an electrolysis cell according to the second aspect of the present invention or an electrolysis system according to the third aspect of the present invention.

[0029] According to a sixth aspect, the invention relates to the use of an electrolyser according to the second aspect of the invention in an apparatus for the electrolytic extraction of carbon dioxide from a gas containing carbon dioxide, in particular from air or a point source.

[0030] According to a seventh aspect, the present invention relates to an apparatus for electrolytically extracting carbon dioxide from a gas containing carbon dioxide, in particular from air or a point source, comprising an electrolysis cell according to the second aspect of the invention or an electrolysis system according to the third aspect of the invention.

[0031] Technical Effects of the Invention

[0032] These aspects of the invention enable significantly more energy-efficient process operation than previous methods for carbon dioxide electrowinning. In addition, these aspects reduce mineral precipitation of carbonate-containing solutions, especially in the cathode compartment, even in the presence of divalent cations. This results in gentler process operation because cathode maintenance intervals are extended. This is particularly due to reduced scaling of the cathode material by reducing precipitation of calcium and / or magnesium hydroxides. At the same time, divalent cations such as Mg 2+ and Ca 2+ Can be returned to the sea, eliminating the need for nanofilters. This has ecological advantages by allowing further absorption of CO2 via carbonates, and economic benefits by eliminating the need for expensive and maintenance-intensive nanofilters. In addition, the present invention allows not to deviate significantly from the pH of seawater, for example about 8.1. This avoids discharging effluent from electrolysis into the sea at a pH lower than seawater. Therefore, the present method is beneficial for marine ecosystems in terms of pH because it avoids ocean acidification.

[0033] Furthermore, utilizing these aspects of the invention may improve the energy efficiency of extracting carbon dioxide from air because lower voltages may be achieved.

[0034] More details of the technical effects achieved by the present invention can be found in the detailed description.

[0035] definition

[0036] Unless otherwise specified, all technical terms used herein correspond to the understanding of ordinary professionals.

[0037] The term "carbon dioxide extraction" is broadly understood to mean the removal of carbon dioxide in gaseous form from a carbonate-containing aqueous solution using H + The cation formally converts the carbonate / bicarbonate to dihydrogen carbonate, which decomposes into water and carbon dioxide gas as shown in equation (1) above.

[0038] The term "acidic" is to be broadly understood to mean an "acidic aqueous solution" having a pH value of < 7. Thus, "pH neutral" means a pH value of 7.

[0039] The term "alkaline" or "basic" is also broadly understood to refer to a "basic aqueous solution" having a pH value >7.

[0040] The term "pH value" corresponds to the understanding of ordinary technicians and can be measured with a pH meter. The pH values ​​disclosed herein can be measured, for example, using a VOLTCRAFT PHT-200 pH value and oxidation-reduction potential (ORP) combination meter. The following technical specifications of the measuring device are provided below:

[0041] Measuring range (mV): -1999 to 1999mV

[0042] Accuracy (mV): ±0.5%

[0043] Accuracy (pH):

[0044] ±(0.02pH+2d)

[0045] Automatic temperature compensation

[0046] yes

[0047] Operating temperature 0 to 50°C

[0048] Resolution 0.01

[0049] Power supply (details)

[0050] 9V

[0051] Dimensions (L x W x H) 68 x 30 x 195 mm Weight

[0052] 250g

[0053] high:

[0054] 195mm

[0055] length:

[0056] 68mm

[0057] width:

[0058] 30mm

[0059] Measuring range (pH)

[0060] 0-14pH

[0061] calibration

[0062] Factory standard (no certificate)

[0063] monitor

[0064] number

[0065] interface

[0066] RS-232

[0067] Measurement functions

[0068] pH

[0069] Redox (ORP)

[0070] Maximum pH measurement range

[0071] 14pH

[0072] Minimum pH measurement range

[0073] 0pH

[0074] Product Type

[0075] Combined measuring device

[0076] The specified measuring devices are factory calibrated to standards and can be additionally calibrated with pH buffer solutions (pH=4 and pH=7) included in the delivery.

[0077] The term "acidic oxidation product" is to be understood broadly, and without being bound by a particular theory, to refer to the proton-form product of the oxidation of diatomic hydrogen, particularly hydrogen gas. The proton-form product may be present as H3O + (aq) Solvation exists in aqueous solution, Cl - (aq) It may be present as a counter anion and / or as part of a solid electrode material and / or solid membrane material, enabling transport of proton products via known mechanisms. In addition to chloride, products derived from acids such as H2SO4, HCO3 - Other counter anions of H2CO3, H3BO3 and HBr may also be present in all of the abovementioned cases.

[0078] The term "carbonate-containing aqueous solution" is to be understood broadly and includes carbonates in any chemical form. A "carbonate-containing aqueous solution" is usually alkaline, with a pH of >7 to 9, >7 to 9.4, or >7 to 10. This means that the aqueous solution contains dissolved carbonate (CO3 2- ) and / or bicarbonate. An example of a "carbonate-containing aqueous solution" is seawater. A carbonate-containing aqueous solution contains in particular divalent cations, such as magnesium, calcium and / or strontium. In addition, a carbonate-containing aqueous solution may also contain monovalent cations, such as sodium.

[0079] The term "seawater" is used interchangeably and equivalently with "brine" and "saline water" and refers broadly to aqueous solutions derived from saline bodies, particularly saline seas such as oceans. Of course, the exact chemical composition can vary depending on the location where the seawater is collected. For example, the composition provided by Kester, DR, Duedall, IW, Connors, DN and Pytkowicz, RM (1967), Preparation of Artificial Seawater Archived 2008-12-17. Limnology & Oceanography, 12, 176–179), which is incorporated by reference, is used as an approximate example. According to this publication, Tables 1 and 2 are provided as approximate examples of seawater compositions.

[0080] Table 1: Information on the approximate composition of salts by weight in seawater.

[0081] Weight salt

[0082] Salt Molecular weight <![CDATA[g kg -1 Solution]]> Sodium chloride (NaCl) 58.44 23.926 <![CDATA[Sodium sulfate (Na2SO4)]]> 142.04 4.008 Potassium sulfate (KCl) 74.56 0.677 <![CDATA[Sodium bicarbonate (NaHCO3)]]> 84.00 0.196 Potassium Bromide (KBr) 119.01 0.098 <![CDATA[Boric acid (H3BO3)]]> 61.83 0.026 Sodium fluoride (NaF) 41.99 0.003

[0083] Table 2: Information on the approximate composition of bulk salts in seawater.

[0084] Volumetric salt

[0085] Salt Molecular weight <![CDATA[mol kg -1 Solution]]> <![CDATA[Magnesium chloride (MgCl2·6H2O)]]> 203.33 0.05327 <![CDATA[Calcium chloride (CaCl2·2H2O)]]> 147.03 0.01033 <![CDATA[Strontium chloride (SrCl2·6H2O)]]> 266.64 0.00009

[0086] The term "degassed acidic aqueous solution" refers broadly to an aqueous solution having a pH < 7 from which carbon dioxide gas has been substantially completely removed. Such a degassed acidic solution can be obtained by extracting carbon dioxide gas from the acidic aqueous solution, for example via a membrane contactor. Such a degassed acidic aqueous solution particularly retains divalent cations, such as magnesium and / or calcium. Specifically, the degassed acidic aqueous solution contains ≤10 wt%, preferably ≤5 wt% carbon dioxide, wherein the mass percentages are based on the initial mass of carbon dioxide present as carbonate and / or bicarbonate in the alkaline carbonate-containing aqueous solution. In other words, the separation efficiency is at least 90%, preferably at least 95%.

[0087] The term "acidic component" generally refers to protons in the form of water, i.e., H3O + (aq).

[0088] The term "fluid connection" is to be understood in a broad sense and refers in particular to a connection between two electrolysis cells, such as a pipeline, which is designed to transport a fluid, such as a liquid or a gas such as hydrogen, from one electrolysis cell to another electrolysis cell. Such an electrolysis cell may include a cathode compartment, an anode compartment, or an intermediate compartment located between the anode compartment and the cathode compartment.

[0089] The term "gas containing carbon dioxide" is understood in a broad sense. In particular, such a gas may include air. Those skilled in the art are familiar with the composition of air at a given location or understand methods for measuring this composition. In addition, "gas containing carbon dioxide" may also originate from a point source. A point source is typically an industrial source of CO2, wherein the process generates more carbon dioxide gas than is normally present in the air. Examples include flue gases from industrial processes such as cement production and / or coal combustion. Based on the total volume of the wet gas, a point source may contain a gas having a carbon dioxide content of about 10 mol% to 25 mol%, in particular 14 mol% to 21 mol%. Such a gas may also have a carbon dioxide content of about 10 vol% to 20 vol%. In general, the mass / volume / molar fraction of carbon dioxide in the gas containing carbon dioxide is substantially non-critical to the function of the present invention and its various aspects.

[0090] exist Figure 4 A sample process for capturing carbon dioxide from a gas containing carbon dioxide is illustrated in . For CO2 absorption, various technical configurations can be considered. For example, for low CO2 concentrations such as in air, it may be advantageous to expose the gas to an alkaline solvent using a cross-flow method with a cooling tower-like structure. For higher CO2 concentrations, such as in flue gases from industrial processes, a tower that uses a countercurrent principle to contact the gas with an alkaline aqueous solution may be more suitable technically and economically. In addition, the carbonate-containing aqueous solution may also contain monovalent cations, such as sodium. The carbonate-containing aqueous solution may contain monovalent cations, such as sodium or potassium, in particular or exclusively. These monovalent cations can be paired, for example, with counter anions selected from sulfate, perchlorate, nitrate, iodide, or a combination thereof. Specifically, the dissolved salt can be selected from Na2SO4, K2SO4, NaClO4, KClO4, NaNO3, KNO3, NaI, KI. The term "alkaline carbonate-containing aqueous solution" is used equivalently to "carbonate-containing aqueous solution". BRIEF DESCRIPTION OF THE DRAWINGS

[0091] Figure 1 An embodiment of an electrolysis cell according to the invention is shown.

[0092] Figure 2 An embodiment of an electrolysis system according to the invention having a monopolar configuration is shown.

[0093] Figure 3 An exemplary Pourbaix diagram of water is illustrated.

[0094] Figure 4 An embodiment of an electrolysis system for extracting carbon dioxide from a carbon dioxide-containing gas according to the present invention is shown.

[0095] Figure 5An embodiment of an electrolysis system according to the invention having a bipolar configuration is shown. DETAILED DESCRIPTION

[0096] The embodiments shown below illustrate advantageous configurations of the invention and should not be understood as limiting the scope of the invention. Unless otherwise stated, the features of the various embodiments within different aspects of the invention may be freely combined.

[0097] Electrolysis method:

[0098] According to a first aspect, the invention relates to an electrolysis process for carbon dioxide extraction, in particular a continuously operated electrolysis process, comprising the following steps:

[0099] a) performing anodic oxidation on hydrogen to obtain an acidic oxidation product;

[0100] b) removing the acidic oxidation products with an aqueous solution containing alkaline carbonates, such as seawater, in particular with a pH of >7 to 9, to obtain an acidic aqueous solution;

[0101] c) extracting carbon dioxide from the acidic aqueous solution to obtain carbon dioxide gas and a degassed acidic aqueous solution;

[0102] d) subjecting the acidic components of the degassed acidic aqueous solution to cathode reduction, wherein an alkaline aqueous solution is further obtained, wherein an alkaline aqueous solution having a pH of 10 to ≥7.1 or 9.4 to ≥8 is further obtained. In particular, the pH value may be 9.2 to ≥8, specifically 8.5 to ≥8, optionally 8.8 to ≥7.1, or further optionally 8.0 to ≥7.1. A range of 8.4 to ≥7.1 is also possible. The pH value is measured at the cathode compartment outlet using the disclosed method.

[0103] The anodic oxidation of hydrogen in step a) can occur in aqueous solution or via a gas diffusion electrode such as a zero-gap electrode. The acidic oxidation product formally corresponds to H in the following equation (2): + :

[0104] H2→2H + +2e - E 0 =0V(2)

[0105] H + Can be used as H3O + (aq)or as part of the solid electrode and / or membrane material in aqueous solution. The exact form of the acidic oxidation product (H+) is not critical, as long as it can be used in step b). In certain embodiments, the hydrogen in step a) can be oxidized at the gas diffusion electrode without the use of an aqueous solution, requiring only minimal humidification of the hydrogen. Oxidizing the hydrogen reduces the energy requirements of the process because the generation of oxygen is unnecessary. Figure 3 As shown, the redox potential of hydrogen oxidation is significantly lower than the redox potential of water oxidation to produce oxygen.

[0106] Using the acidic oxidation product, step b) involves the conversion of the carbonate-containing aqueous solution. For example, the oxidation product from step a) can be produced in the anode compartment, while the reaction in step b) occurs in the intermediate compartment of the electrolyzer, which can be arranged between the cathode compartment and the anode compartment. The acidic oxidation product can be contacted with the carbonate-containing aqueous solution via a transport membrane for conversion. Preferably, the carbonate-containing aqueous solution has a pH of about ≥8 to about 8.5. The conversion in step b) particularly involves a chemical reaction as described by equation (1) to form dissolved carbon dioxide. Since the acidic oxidation product is used for the conversion, dissolved carbon dioxide is present after the conversion in step b). In the subsequent step c), in particular, carbon dioxide gas is removed via a membrane contactor that can be arranged outside the intermediate compartment and downstream of step c). Thus, carbon dioxide is removed from the acidic aqueous solution to obtain a degassed acidic aqueous solution with a pH <7. In step d), which particularly occurs in the cathode compartment, the degassed acidic aqueous solution and the acidic components in the water such as H + (aq) is reduced, wherein hydrogen and hydroxide ions are generated, producing an alkaline aqueous solution with a pH of about 10 to ≥7.1 or 9.4 to ≥8 or in one of the above ranges. In particular, the alkaline aqueous solution has a pH of about >7.1 to 9 or 8 to 9, preferably >7.1 to 8.5 or 8 to 8.5, such as about 8.1. These reactions are formally carried out according to the following equations (3) and (4):

[0107] 2H + +2e - →2H2,E 0 ≈0,24V@pH=4(3)

[0108] H2O+2Na + +2e - →2NaOH+H2,E 0 =-0.48V@pH=8.1(4)

[0109] The method according to the first aspect of the present invention can be operated at a DC voltage of <1.5 V, in particular ≤1.3 V. In this context, the sodium cations in equation (4) are in particular transported from the intermediate compartment to the cathode compartment, for example via a transport membrane. The reactions described by equations (3) and (4) in step d) lead to the following significant technical advantages of the present invention.

[0110] In step d), the alkaline aqueous solution reaches a pH range of 10 to ≥7.1 or 9.4 to ≥8 or one of the above ranges to reduce the tendency of divalent cations such as magnesium and / or calcium, which are particularly present in the carbonate-containing aqueous solution, to precipitate as solid hydroxide precipitates. This pH range is achieved by the presence of a degassed acidic aqueous solution in step d). In particular, as explained above, the degassed acidic aqueous solution may include divalent cations such as magnesium and / or calcium. By the reduction reaction in equation (3) and the further water reduction in equation (4), an alkaline aqueous solution with a pH of 9.4 to ≥7 is obtained. Beyond this range, the pH value will be too high, resulting in unfavorable precipitation of the hydroxide, which leads to significant scaling of the cathode discussed above. By reducing hydroxide precipitation, divalent cations such as calcium, magnesium and / or strontium can be retained in the carbonate-containing aqueous solution without the need for expensive and maintenance-intensive nanofilters to remove them. Reducing or avoiding impurities caused by precipitated hydroxides also improves efficiency, as such impurities generally lead to reduced energy efficiency. Excessive hydroxide precipitation will lower the pH of the alkaline aqueous solution, which is undesirable.

[0111] It is advantageous to reintroduce the alkaline aqueous solution into a salty water such as the sea, because the presence of divalent cations allows further binding of carbon dioxide. Therefore, the pH level achieved also has ecological benefits. Another ecological advantage is that there is no need to discharge acidic wastewater into a salty water such as the sea; on the contrary, the alkaline aqueous solution has an environmentally friendly pH value. The low pH in seawater can also lead to the release of CO2 into the atmosphere.

[0112] Surprisingly, it was also found that the partially acidic environment caused by the introduction of a degassed acidic aqueous solution at the cathode (see equation (2) above) leads to more energy-efficient hydrogen generation due to kinetic and thermodynamic advantages.

[0113] Before the carbonate-containing aqueous solution is introduced in step b), nitrogen and oxygen can be removed from the solution. For example, it is possible to use a membrane contactor.

[0114] The electrolysis method according to the first aspect may be carried out using an electrolysis cell as described in the second aspect of the invention. The method may also be used to extract carbon dioxide from a gas containing carbon dioxide such as air or a point source.

[0115] In certain embodiments, the hydrogen produced at the cathode in step d) is transferred to step a) and oxidized in step a). In other words, the method comprises a hydrogen cycle (oxidation in step a), reduction in step b), reoxidation in step d). Thus, the present invention can generate hydrogen to a large extent autonomously, reducing the need for an external hydrogen supply. Since hydrogen production is generally energy intensive, the hydrogen cycle represents a significant efficiency saving.

[0116] In certain embodiments, the acidic oxidation product from step a) is transported via a first transport membrane to be converted in step b), and the first transport membrane is in contact with a solution containing alkaline carbonate at the point where the acidic oxidation product leaves. For example, the first transport membrane may include a gas diffusion electrode, a gas diffusion layer (GDL) and / or a zero gap membrane electrode (CEM). The gas diffusion layer may also be considered to be a part of the first transport membrane. In particular, the first transport membrane may include a perfluorosulfonic acid membrane. Preferably, such a transport membrane is based on perfluorosulfonic acid / polytetrafluoroethylene copolymers. The material for the transport membrane may be further or alternatively particularly selected from: a membrane based on PTFE / PTFE (polytetrafluoroethylene / Teflon), a hydrocarbon membrane, a sPPS (sulfonated polyphenylsulfone) membrane. Examples include membranes known by the names Nafion, Gore, Fumasep, Fumapem, Aquivion and / or Xion, preferably Nafion or Gore-Select membranes. In particular, the acidic oxidation product may be generated in the anode compartment in step a) and diffuse through the first transport membrane, the reaction in step b) taking place in the intermediate compartment.

[0117] In certain embodiments, metal cations such as sodium cations are transferred from the carbonate-containing aqueous solution to the cathode reduction step d) via a second transport membrane during the reaction. The second transport membrane can have the same characteristics as the first transport membrane described above. Specifically, sodium cations from the carbonate-containing aqueous solution can be transported from the intermediate compartment to the cathode compartment via the second transport membrane to perform step d). These cations are used to formally balance the charge, as described in Equation (4).

[0118] In certain embodiments, the pH of the degassed acidic aqueous solution is less than 5. Specifically, the pH may be about 2 to less than 5, preferably 3 to about 4.5. This pH value may be achieved by anodization in step 1. Acidic pH provides the above advantages.

[0119] According to certain embodiments, the degassed acidic aqueous solution in step d) may also be contacted with an alkaline aqueous solution. For example, due to the reduction described by equation (4), the alkaline aqueous solution may accumulate in the cathode compartment over time, generating a pH gradient, because the degassed acidic aqueous solution at the inlet is acidic.

[0120] Electrolyzer for CO2 extraction

[0121] According to a second aspect, the present invention relates to an electrolyser for carbon dioxide extraction, comprising:

[0122] Anode compartment,

[0123] Intermediate compartments, and

[0124] A cathode compartment, wherein

[0125] The intermediate compartment is located between the anode compartment and the cathode compartment; the anode compartment is connected to the intermediate compartment via a first transport membrane;

[0126] The cathode compartment is connected to the intermediate compartment via a second transport membrane;

[0127] The anode compartment and the cathode compartment are fluidly connected via a hydrogen line;

[0128] The middle compartment has an inlet and an outlet, the outlet being fluidly connected to a carbon dioxide extraction device, and the carbon dioxide extraction device being fluidly connected directly to the inlet of the cathode compartment via a liquid line.

[0129] Of course, the electrolyzer also includes the features and technical effects of the electrolysis method. Specifically, the electrolyzer according to the second aspect of the present invention is designed to perform the electrolysis method described in the first aspect of the present invention. Therefore, the electrolyzer can also be used to extract carbon dioxide from seawater.

[0130] In addition, the electrolyzer can be used in a method of extracting carbon dioxide from a gas containing carbon dioxide, such as air or a point source. In this case, a solvent-air contactor as described herein can be used.

[0131] Specifically, the anode compartment is configured to perform step a) of the method according to the first aspect of the invention. Furthermore, the intermediate compartment is specifically configured to perform step b) of the method according to the first aspect of the invention. Thus, the cathode compartment is configured to perform step d) of the method according to the first aspect of the invention. In addition, the carbon dioxide extraction device is configured to perform step c) of the method according to the first aspect of the invention.

[0132] In certain embodiments, the carbon dioxide extraction device is selected from a membrane contactor, preferably 3M Liqui-Cel, a heat exchanger, and combinations thereof. Preferably, a membrane contactor is used. In the case of a heat exchanger, it is configured to heat the acidic aqueous solution to enable the carbon dioxide gas to be degassed.

[0133] Specifically, the first transport membrane is an ion transport membrane configured to transfer acidic oxidation products from the anode compartment to the cathode compartment. Additionally or alternatively, the second transport membrane can be configured as an ion transport membrane designed to transfer monovalent cations such as sodium cations from the intermediate compartment to the cathode compartment.

[0134] As is apparent from the previous explanations in the description, the electrolyser does not comprise a nanofilter.

[0135] Furthermore, in particular, apart from the carbon dioxide extraction, no additional operations are performed between the outlet of the intermediate compartment and the inlet of the cathode compartment. Specifically, the fluid connection between the outlet of the intermediate compartment and the inlet of the cathode compartment does not include any additional mixing device, ensuring that the pH of the acidic aqueous solution and the degassed acidic aqueous solution remains substantially constant.

[0136] In certain embodiments, the anode compartment includes an anode material in direct contact with the first transport membrane. The anode active material is specifically selected from platinum, nickel / iron, nickel / cobalt, nickel, cobalt / platinum, stainless steel, iridium, iridium oxide, ruthenium, ruthenium oxide, palladium and combinations thereof. Preferably, the anode active material is platinum. The anode material can be configured as a zero gap electrode, and there is no gap between the anode material and the first transport membrane. In addition, the anode material can be applied to a carrier. Such a carrier can be selected from iron, steel, titanium, carbon paper or a combination thereof. Alternatively, the anode can be configured as a gas diffusion electrode. For example, the gas diffusion electrode can include a product variant of the Gore-Primea series.

[0137] In certain embodiments, a device for removing oxygen and nitrogen from the aqueous solution containing alkaline carbonate may be provided before the inlet of the intermediate compartment. Such a device may be configured similarly to a carbon dioxide extraction device.

[0138] In certain embodiments, the anode compartment may include an external supply of hydrogen. This allows compensating for any hydrogen deficiency that may occur during hydrogen recirculation.

[0139] In certain embodiments, the cathode compartment may have a side opposite to the second transport membrane, with the cathode compartment inlet positioned closer to the opposite side than the second transport membrane. This may result in alkalinization of the aqueous solution in the cathode compartment, creating a high pH gradient between the cathode and the second transport membrane. As a result, the transport of cations into the cathode compartment is significantly improved.

[0140] In certain embodiments, the inlet of the cathode compartment and the inlet of the middle compartment may be arranged so that the liquid flow entering the cathode compartment flows in a countercurrent or parallel manner to the liquid flow entering the middle compartment through the electrolyzer. In particular, the advantage of the countercurrent arrangement is that the same pH gradient direction is maintained, promoting the movement of positively charged cations into the cathode compartment.

[0141] In certain embodiments, the cathode compartment comprises a cathode material, preferably selected from platinum, nickel, titanium, carbon paper or a combination thereof. Platinum is particularly preferred as the cathode active material. Carbon paper with a coated Pt / C catalyst is particularly preferred.

[0142] In certain embodiments, the method according to the first aspect of the invention is carried out at a total pressure above atmospheric pressure, in particular between 2 and 50 bar.

[0143] The electrolytic cell according to the first aspect of the invention may be operated at a temperature below 100° C. Specifically, the electrolytic cell may be operated at 60° C. to 80° C. Additionally, the electrolytic cell may be operated at a temperature of at least 95° C. but below 100° C.

[0144] Electrolysis system

[0145] According to a third aspect, the invention relates to an electrolysis system comprising at least one electrolysis cell according to the second aspect of the invention.

[0146] Of course, such an electrolysis system is designed to perform the method according to the first aspect of the present invention. Therefore, the electrolysis system includes the method steps of the first aspect of the present invention, and the corresponding technical advantages. This also applies to the electrolytic cell according to the first aspect of the present invention.

[0147] For example, multiple electrolyzers can be used together in an electrolysis system. These electrolyzers can be connected in a stacked configuration. For example, two electrolyzers can share an anode compartment. Another electrolyzer can be connected to the two electrolyzers via a shared cathode. Another electrolyzer can be connected via a shared anode compartment, and so on.

[0148] Uses of electrolyzers

[0149] According to a fourth aspect, the invention relates to the use of an electrolyser according to the second aspect of the invention in an apparatus for the electrolytic extraction of carbon dioxide from seawater.

[0150] According to a sixth aspect, the invention relates to the use of an electrolyser according to the second aspect of the invention in an apparatus for electrolytically extracting carbon dioxide from a gas containing carbon dioxide, in particular from air or a point source. In this case, a solvent-air contactor as described herein can be used.

[0151] The uses according to the fourth and sixth aspects include the technical features, effects and advantages of the method described in the first aspect and the electrolytic cell described in the second aspect.

[0152] Equipment for the electrolytic extraction of carbon dioxide from seawater or from gases containing carbon dioxide:

[0153] According to a fifth aspect, the present invention relates to an apparatus for electrolytically extracting carbon dioxide from seawater, comprising an electrolysis cell according to the second aspect of the present invention or an electrolysis system according to the third aspect of the present invention.

[0154] Such a device may be located in a saline body of water such as the sea. The device may also be operated using seawater as the carbonate-containing solution.

[0155] According to a seventh aspect, the present invention relates to an apparatus for electrolytically extracting carbon dioxide from a gas containing carbon dioxide, in particular from air or a point source, comprising an electrolysis cell according to the second aspect of the invention or an electrolysis system according to the third aspect of the invention. In this case, a solvent-air contactor as described herein can be used.

[0156] In addition, the device according to the fifth aspect or the seventh aspect can also be operated by the method according to the first aspect of the present invention. In order to avoid repetition, it should be noted that the device includes the features, technical advantages and effects described in the first aspect, the second aspect, the third aspect and the fourth aspect of the present invention.

[0157] Description of the drawings

[0158] The following drawings illustrate exemplary embodiments of the invention and are not to be considered limiting.

[0159] Figure 1An exemplary embodiment of an electrolyzer 1 for extracting carbon dioxide from seawater according to a second aspect of the present invention is shown. Fresh alkaline seawater with a pH of about 8.1 is introduced into a first membrane contactor 17a via a first inlet line 13, which removes oxygen and nitrogen from the seawater. Alkaline seawater is introduced into an intermediate compartment 51 via a second inlet line 14, and the intermediate compartment 51 is arranged between an anode compartment 50 containing an anode 45 and a cathode compartment 52 containing a cathode 46. The anode compartment 50 and the intermediate compartment 51 are separated by a first ion transport membrane 61, which is configured to transport protons from the anode compartment 50 to the intermediate compartment 51. The intermediate compartment 51 and the cathode compartment 52 are separated by a second ion transport membrane 62, which is configured to transport sodium ions from the intermediate compartment 51 to the cathode compartment 52. These electrochemical reactions are powered by an AC voltage source 44. In the anode compartment 50, hydrogen is oxidized at the anode 45 to produce acidic oxidation products. The acidic oxidation product is transferred to the middle compartment 51 via the first ion transport membrane 61, where it reacts with seawater to form an acidic aqueous solution. Hydrogen for oxidation is transported from the cathode compartment 52 to the anode compartment 50, for example, via the hydrogen pipeline 23, where hydrogen is generated at the cathode 46. The acidic aqueous solution formed in the middle compartment contains dissolved carbon dioxide generated according to equation (1). The acidic aqueous solution (pH of about 4) is guided to the second membrane contactor 17b and the third membrane contactor 17c through the first outlet pipeline 4, where carbon dioxide gas is removed. The degassed acidic aqueous solution (pH of about 4) is then transferred to the cathode compartment 52 via the second outlet pipeline 5. In the cathode compartment, there is a pH gradient (lighter shading represents a lower pH, darker shading represents a higher pH). The gradient is generated as the degassed acidic aqueous solution is introduced at the cathode inlet 55 while hydroxide ions are generated at the cathode 46. According to the flow path in the cathode compartment 52, the degassed acidic aqueous solution is neutralized by the hydroxide ions. In addition, during the formation of hydrogen according to equation (3), the pH increases as the protons are consumed. Thus, an alkaline aqueous solution with a pH>8.1 is formed in the cathode compartment, which can be returned to the sea via the seawater outlet line 11.

[0160] Figure 2 An example of a monopolar configuration of an electrolysis system 100a according to the third aspect of the invention is depicted. The arrows represent material input and output, as shown in FIG. Figure 1 Only components relevant to this discussion are labeled with reference numerals. In this configuration, the first electrolytic cell 1a and the second electrolytic cell 1b are connected via their anode compartments 50. In addition, the third electrolytic cell 1c is connected to the second electrolytic cell 1b via the cathode 46. An additional electrolytic cell 1n may be connected to the third electrolytic cell 1c via a common anode compartment 50, as shown. Figure 2 Indicated by the ellipsis in , and so on.

[0161] For illustration purposes, Figure 3 The Pourbaix diagram of water is shown.

[0162] Figure 4 An example of an apparatus 200 according to the third aspect of the invention is illustrated, which is capable of performing the method described in the first aspect. A gas, such as air, is introduced into the apparatus 200 via an air supply system 30, which gas can pass through an air-liquid contactor 31, where the gas is absorbed into an alkaline aqueous solution. The resulting carbonate-containing aqueous solution is then mixed with an acidic aqueous solution in a mixing container 32, so that, for example, carbon dioxide gas can be removed from the system via one or more membrane contactors 33. The degassed acidic solution is then divided into two parts and directed to an electrolytic cell 34 according to the second aspect of the invention. A first portion of the degassed acidic solution is directed to an intermediate compartment 52, where it reacts with an acidic oxidation product from the anode compartment 51. A second portion of the degassed acidic aqueous solution is directed to a cathode compartment 53, where it undergoes reduction to produce an alkaline aqueous solution. Subsequently, hydrogen can be separated from the alkaline aqueous solution in the gas-water separator 35, where the hydrogen can be fed into the anode compartment 51, where the hydrogen is oxidized into protons according to the above reaction equation, and the protons are fed into the intermediate compartment 52, for example, via the first ion transport membrane 61.

[0163] Figure 5 An example of a bipolar configuration of an electrolysis system 100b according to the third aspect of the invention is depicted. The arrows represent material input and output, as shown in FIG. Figure 1 Only components relevant to this discussion are labeled with reference numerals. In this configuration, the first electrolytic cell 1a and the second electrolytic cell 1b are connected via their anode compartments 50. According to the stacking technique described above, another electrolytic cell 1n can in turn be connected to an adjacent electrolytic cell via the anode compartment 50, which is located at Figure 2 , represented by three dots, and so on.

[0164] Examples

[0165] Experimental setup

[0166] The experiment corresponds to Figure 4The electrolysis was carried out in a device of the configuration shown. As described in the second aspect of the invention, the electrolytic cell used in the experiment consists of an electrolytic cell comprising two steel end plates, a graphite collector with an integrated flow field on the anode side, and a titanium mesh collector on the cathode side. The flow field of the middle compartment is made of PTFE with a thickness of 1 mm. The seal is made of a gasket using PTFE and FKM. Two Nafion cation exchange membranes are used. A carbon fiber diffusion medium is used as the diffusion medium for the two electrodes. Platinum carbon is used as a catalyst for the two electrodes, wherein the catalyst is applied to the gas diffusion medium on the anode side and directly applied to the membrane on the cathode side using a transfer method.

[0167] The electrolyte used in the experiment was a 0.5 M sodium chloride distilled water solution with a conductivity of 30 mS / cm.

[0168] A Zahner Elektrik Zennium Pro model potentiostat / galvanostat was used for power supply and measurements.

[0169] A peristaltic pump, Shenchen LabN6III with two pump heads, was used to circulate the liquid. The electrolyte flow rate was set at 80 mL / min. In addition to the hydrogen separated using a gas-liquid separator, an external hydrogen supply was regulated via a Bronkhorst mass flow controller model F201-CV.

[0170] Experimental Description

[0171] The electrolyzer was equipped with two graphite flow fields on both the anode and cathode sides. Two types of FKM-based gaskets were used, with thicknesses of 0.2 mm and 0.3 mm, respectively. The 0.3 mm thick gasket was placed between the graphite flow field and the membrane. The thinner 0.2 mm gasket was placed between the membrane and the middle compartment flow field.

[0172] For all experiments, the flow rate was kept constant at 80 mL / min. The active cell area was 10.2 cm 2 , and the applied current varied between 0.02A, 0.05A, and 0.1A during the experiments.

[0173] Different fluid flow configurations

[0174] Two experimental series were performed, each differing only in the fluid flow configuration. In the first experiment, the cathode compartment and the intermediate compartment were fed from the same tank containing a 0.5 M electrolyte deionized water solution. The electrolyte had a pH of 7.3 before being introduced into the cell.

[0175] In the second experiment, the outlet of the middle compartment was fluidically connected to the inlet of the cathode compartment. As a result, the pH at the outlet of the middle compartment matched the pH at the inlet of the cathode compartment, which is the main difference from the first experiment.

[0176] result

[0177] As described above, the experiments conducted according to the invention measured the voltage for different applied currents. The results of the experiments in which the same solution with a slightly alkaline pH was introduced into both the intermediate compartment and the cathode compartment are shown in Table 3. Table 4 shows the measured values ​​for the system according to the invention. In this case, the pH at the outlet of the intermediate compartment was the same as the pH at the inlet of the cathode compartment, expressed as pH 中间，OUT =pH 阴极，IN .

[0178] Table 3: Cell voltage and pH values ​​measured with introduction of the same solution, wherein the pH at the inlet to both the cathode compartment and the intermediate compartment is the same.

[0179]

[0180] The comparative examples were determined according to the experimental setup and procedure described by L. Yan et al., ACS Energy Lett. 2022, 7, 1947–1952.

[0181] Table 4: pH values ​​measured at the inlet and outlet of the intermediate compartment and the cathode compartment according to the invention.

[0182]

[0183]

[0184] The results in Table 3 show qualitative agreement with the comparative example. The difference in the magnitude of pH fluctuations may be attributed to the lower flow rate of 40 mL / min in the comparative example. In both cases, at only 10 mA / cm 2 pH values ​​greater than 10 were observed at current densities of 1.5 Å. This would indicate a significant potential for divalent ion precipitation. Surprisingly, Table 4 shows that, in accordance with the present invention, redirecting the acidic solution into the cathode compartment significantly reduces the pH. This reduction ensures that divalent cations such as Ca can be avoided. 2+ or Mg 2+ Another noteworthy observation is that for all three current densities, the measured cell voltages were significantly lower than those of the control experiments, indicating that this approach can be operated more energy-efficiently.

[0185] Reference numerals list

[0186] 1 Electrolyzer

[0187] 1a The first electrolytic cell

[0188] 1b Second electrolytic cell

[0189] 1c The third electrolytic cell

[0190] ln Additional electrolytic cell

[0191] 11 Seawater export pipeline

[0192] 13 First inlet pipeline

[0193] 14 Second inlet pipeline

[0194] 17a First membrane contactor

[0195] 17b Second membrane contactor

[0196] 17c The third membrane contactor

[0197] 23 Hydrogen pipeline

[0198] 30 Air supply source

[0199] 31 Air-Solvent Contactor

[0200] 32 Mixing tank

[0201] 33 Desorption device

[0202] 34 Electrolyzer

[0203] 35 Gas-Liquid Separator

[0204] 44 DC power supply

[0205] 45 Anode

[0206] 46 Cathode

[0207] 50 Anode compartment

[0208] 51 Middle compartment

[0209] 52 cathode compartment

[0210] 55 Cathode inlet

[0211] 61 First Ion Transport Membrane

[0212] 62 Second ion transport membrane

[0213] 100a Electrolysis system with monopolar configuration

[0214] 100b Electrolysis system with bipolar configuration

[0215] 200 Equipment for direct air capture

Claims

1. An electrolysis method for carbon dioxide extraction, comprising the following steps: a) performing anodic oxidation on hydrogen to obtain an acidic oxidation product; b) converting the acidic oxidation product with an aqueous solution containing an alkaline carbonate, in particular having a pH of >7 to 9, to obtain an acidic aqueous solution; c) removing carbon dioxide from the acidic aqueous solution to obtain carbon dioxide gas and a degassed acidic aqueous solution; d) subjecting the degassed acidic aqueous solution to cathodic reduction of the acidic components to generate cathode-generated hydrogen and also generating an alkaline aqueous solution having a pH of 10 to ≥7.1 or 9.4 to ≥8.

2. The method according to claim 1, wherein the hydrogen produced at the cathode in step d) is transferred to step a) and oxidized in step a).

3. A process according to claim 1 or 2, wherein the acidic oxidation products from step a) are transported for conversion in step b) through a first transport membrane, which is in contact with the alkaline carbonate-containing aqueous solution at the exit point of the acidic oxidation products.

4. The method according to any one of the preceding claims, wherein metal cations from the carbonate-containing aqueous solution are transported during the reaction through a second transport membrane to step d) for cathode reduction.

5. The method according to any one of the preceding claims, wherein the pH of the degassed acidic aqueous solution is <5.

6. The process according to any one of the preceding claims, wherein the degassed acidic aqueous solution in step d) is contacted with a basic aqueous solution.

7. The process according to any one of the preceding claims, wherein the process is operated at a total pressure above atmospheric pressure, in particular between 2 and 50 bar.

8. An electrolyzer for carbon dioxide extraction, comprising: Anode compartment, Intermediate compartments, and A cathode compartment, wherein The intermediate compartment is arranged between the anode compartment and the cathode compartment; the anode compartment is connected to the intermediate compartment via a first transport membrane; The cathode compartment is connected to the intermediate compartment via a second transport membrane; The anode compartment and the cathode compartment are fluidly connected via a hydrogen line; The intermediate compartment has an inlet and an outlet, the outlet being fluidly connected to a carbon dioxide extraction device, and the carbon dioxide extraction device being fluidly connected directly to the inlet of the cathode compartment via a liquid line.

9. The electrolyser of claim 8, wherein the anode compartment contains an anode material in direct contact with the first transport membrane, and the anode material is in particular platinum.

10. An electrolyser according to claim 8 or 9, wherein means for removing oxygen and nitrogen from the aqueous solution containing alkaline carbonates are provided upstream of the inlet to the intermediate compartment.

11. An electrolyser according to any one of claims 8 to 10, wherein the anode compartment comprises an external supply of hydrogen.

12. The electrolytic cell according to any one of claims 8 to 11, wherein the cathode compartment has a side opposite to the second transport membrane, and the inlet of the cathode compartment is closer to the opposite side than the second transport membrane.

13. An electrolytic cell according to any one of claims 8 to 12, wherein the inlet of the cathode compartment and the inlet of the intermediate compartment are arranged so that the liquid flow entering the cathode compartment inlet flows in a countercurrent or parallel manner to the liquid flow entering the intermediate compartment inlet through the electrolytic cell.

14. The electrolytic cell of any one of claims 8 to 13, wherein the cathode compartment contains a cathode material, and the cathode material is selected from nickel, titanium or a combination thereof.

15. An electrolysis system comprising at least one electrolysis cell according to any one of claims 8 to 14.

16. Use of an electrolyser according to any one of claims 8 to 14 in an apparatus for electrolytic extraction of carbon dioxide from seawater.

17. An apparatus for electrolytically extracting carbon dioxide from seawater, comprising the electrolysis cell according to any one of claims 8 to 14 or the electrolysis system according to claim 15.

18. Use of an electrolyser according to any one of claims 8 to 14 in an apparatus for the electrolytic extraction of carbon dioxide from a gas containing carbon dioxide, in particular air or a point source.

19. An apparatus for electrolytically extracting carbon dioxide from a gas containing carbon dioxide, comprising the electrolysis cell according to any one of claims 8 to 14 or the electrolysis system according to claim 15.

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