Electrochemical production of syngas and related methods

Abstract

The invention relates to a method of producing a syngas mixture comprising: removing CO2 from air by exposing the air to a carbon-depleted alkaline catholyte capture solution, thereby obtaining a carbon-enriched catholyte capture solution comprising HCO3 ‑ ; passing the carbon-enriched catholyte capture solution comprising HCO3 ‑ to a catholyte compartment of an electrolyser, the electrolyser further comprising an anolyte compartment comprising an anolyte solution and a interlayer compartment disposed between the catholyte compartment and the anolyte compartment and comprising an interlayer solution; electrolyzing a first portion of HCO3 ‑ , thereby forming a syngas mixture, and electrolyzing the anolyte solution to produce protons (H + ); causing a second portion of HCO3 ‑ to migrate from the catholyte compartment to the interlayer compartment and causing protons to migrate from the anolyte compartment to the interlayer compartment; acidifying the migrated HCO3 ‑ with the protons, thereby forming CO2, separating the CO2 from the interlayer solution; passing the separated CO2 to the catholyte compartment and electrochemically reducing the CO2. The invention also relates to a system for carrying out such a method.

Description

Technical Field

[0001] This invention relates to the electrochemical generation of syngas using a bicarbonate solution. It specifically relates to a cathode electrolyte capture solution recycling system equipped with an electrolyzer that internally generates high-purity CO2. Background Technology

[0002] The increasing levels of carbon dioxide (CO2) in the atmosphere is a pressing environmental problem. Various methods have been developed to capture CO2 from point sources and the atmosphere (in short, from the air) and to store the captured CO2. Among these, direct air capture (DAC) systems have attracted attention. These systems capture (remove) CO2 directly from the air by employing chemical processes or adsorbents (e.g., highly alkaline solutions).

[0003] However, one of its drawbacks is the high energy consumption required to release the captured CO2 from the adsorbent / solution, which negatively impacts the overall energy efficiency of the process and may even make it less economically viable compared to other CO2 removal processes. Furthermore, using or storing the captured CO2 for other applications typically requires additional steps and resources.

[0004] Another such application is the production of syngas, a mixture of carbon monoxide, hydrogen, methane, carbon dioxide, and water vapor. Traditional syngas production methods, such as steam reforming or partial oxidation of hydrocarbons, typically involve complex processes and high energy consumption. Furthermore, they can produce harmful byproducts or pollutants, leading to environmental and health problems.

[0005] Syngas production from electrochemical reduction of CO2: Current status and prospective implementation, S. Hernández, M. Amin Farkhondehfal et al., *Green Chemistry*, Vol. 10, 2017, https: / / doi.org / 10.1039 / C7GC00398F, provides a review of existing electrolytic processes combining carbon dioxide reduction and hydrogen evolution reaction with water or proton reduction to produce syngas. The electrochemical reduction of CO2 in aqueous solutions leads to the formation of carbon monoxide, formic acid, methane, and other hydrocarbons. Although initiating the reduction reaction requires a high cell potential, this reaction requires minimal cell potential (1.47 V to 1.94 V if the anodic reaction is water oxidation). Typical electrolyzer setups show that the cathode and anode sides remain separate, and there is no interaction between them.

[0006] One drawback of the aforementioned system is the unsatisfactory purity of the syngas, necessitating further downstream purification. Therefore, a more efficient and sustainable method is needed to capture CO2 from the atmosphere and use it for syngas production.

[0007] WO2018 / 215174 discloses an electrolyzer having a cathode space containing a cathode, separated from a salt bridge space by an ion exchange membrane containing an anion exchanger, and an anode space containing an anode, located on the opposite side of the salt bridge space and separated from it by an ion exchange membrane containing a cation exchanger. CO2 is introduced into the cathode space via a cathode electrolyte reservoir, specifically CO2 dissolved in an aqueous cathode electrolyte solution. In the cathode space, two reactions occur: CO2 reacts with water to reduce to CO, and OH- is generated therefrom. - It also undergoes a competitive neutralization reaction with CO2 to form HCO3. - The overall reaction is as follows: 3 CO2 + H2O → CO + 2 HCO3 - The bicarbonate ions formed migrate into the salt bridge space, where they react with protons migrating from the anode space to form CO2 and water. The formed CO2 is advantageously returned to the cathode electrolyte reservoir.

[0008] One drawback of the above method is its limited operating life and unsatisfactory CO production. More specifically, those skilled in the art will understand that the reduction of CO2 to CO and its reaction with OH-... - Neutralizing competition, OH - It is generated at the cathode during the hydrolysis of water and the reduction of CO2 to form hydrogen and CO, respectively. This neutralization consumes a large amount of CO2, leading to the formation of bicarbonate ions (HCO3-). - ) and carbonate ions (CO3) 2- The formation of OH-. This limits the concentration of dissolved CO2 in the cathode electrolyte that can be reduced to CO, and the OH- produced during the CO2 reduction reaction. - This leads to an increase in the pH of the cathode space. Based on CO2 and HCO3... - and CO3 2- As shown in the Bjerrum diagram, an increase in pH shifts the equilibrium towards HCO3-. - and CO3 2- The shift in direction will therefore lead to further neutralization of CO2, thus reducing the amount of CO2 available for reduction to CO and further increasing the pH. Once a pH of approximately 10 is reached (as shown in the Yellum diagram), the concentration of CO2 becomes negligible, and CO production ceases. Therefore, only hydrogen (water hydrolysis) will form in the cathode space, while CO2 will form in the salt bridge space. Summary of the Invention

[0009] The present invention aims to overcome one or more of the aforementioned disadvantages. Its object is to provide a method for producing syngas that uses CO2 captured from a CO2-containing gas stream (e.g., from a point source or the atmosphere, hereinafter referred to as air), i.e., a method combining CO2 capture from the air with syngas production. Another object is to provide a method that has reduced energy consumption compared to known CO2 capture and syngas production methods in the prior art, thereby making the method more energy-efficient and more environmentally friendly (i.e., more sustainable). Yet another object is to provide a method for producing syngas with high purity. In other words, these methods aim to both remove carbon dioxide from the air and produce high-quality syngas. Another object is to provide a method with low yields of harmful byproducts or pollutants, thereby reducing its environmental footprint.

[0010] Another object of the present invention is to provide an apparatus for performing or implementing such a method combining CO2 capture and syngas production.

[0011] Another objective is to provide a method that has an improved operating life (the time the system can produce syngas) compared to existing methods. More specifically, the objective is to provide a method that, even when compared to methods based on CO2 and HCO3... - and CO3 2- The latter, such as Yerumtu Figure 7 Synthesis gas can be generated at a higher pH value as expected (as shown in the figure).

[0012] In this disclosure, the terms "syngas" and "syngas mixture" are used interchangeably, referring to a mixture comprising CO / H2 and optionally CO2, or a mixture substantially composed of CO / H2 and optionally CO2. Advantageously, the concentration of CO2 in the syngas is equal to or less than 50% by volume, preferably equal to or less than 40% by volume, more preferably equal to or less than 30% by volume, for example equal to or less than 20% by volume. In other words, the syngas advantageously comprises CO and H2, or is substantially composed of CO and H2.

[0013] In this disclosure, the term "high-purity gas" refers to a gas having a purity of at least 95% by volume, preferably at least 98% by volume, more preferably at least 99% by volume, and most preferably at least 99.5% by volume, as measured by gas chromatography (GC). This term is particularly used in this disclosure to refer to carbon dioxide and carbon monoxide having high purity.

[0014] When high purity is used in combination with syngas, the latter is considered as a high purity mixture of CO / H2 and optionally CO2, i.e., a mixture consisting essentially of CO / H2 and optionally CO2, wherein the content of impurities (typically O2 and / or N2) in the syngas is less than 5% by volume, preferably less than 2% by volume, more preferably less than 1% by volume, and most preferably less than 0.5% by volume.

[0015] In this disclosure, the term "high alkalinity solution or liquid" is used to refer to a solution or liquid having a pH value of 9 or higher, preferably 9.5 or higher, more preferably 10 or higher, such as 11 or higher, or up to 13.5.

[0016] According to a first aspect of this disclosure, a method for generating a syngas mixture as set forth in the appended claims is provided. This method for generating a syngas mixture incorporates the removal of carbon dioxide from the air, wherein the carbon dioxide extracted from the air is used to generate syngas.

[0017] Methods for generating syngas mixtures involve removing CO2 from air containing carbon dioxide (CO2) by exposing air to a carbon-lean alkaline cathode electrolyte capture solution. The CO2 contained in the exposed air is absorbed by the carbon-lean alkaline cathode electrolyte capture solution and forms bicarbonate ions (HCO3-). - This process yields a product containing bicarbonate ions (HCO3-). - The carbon-rich cathode electrolyte capture solution. Using carbon dioxide removed from the atmosphere (air) to generate syngas reduces the environmental footprint of this method.

[0018] The method also includes containing HCO3 - A carbon-rich cathode electrolyte capture solution is fed into the cathode electrolyte chamber of the electrolyzer. The electrolyzer also includes an anode electrolyte chamber and an intermediate chamber, the latter disposed between the cathode electrolyte chamber and the anode electrolyte chamber. The anode electrolyte chamber contains the anode electrolyte solution. The intermediate chamber contains the intermediate layer solution. The cathode electrolyte chamber contains the cathode, and the anode electrolyte chamber contains the anode.

[0019] Electrolysis is carried out in an electrolyzer. More specifically, for the first part of HCO3... - Electrolysis is performed to form a syngas mixture. Additionally, the anolyte solution is also electrolyzed to produce protons (H+). + ).

[0020] Under the influence of the electrochemical potential of the electrolyzer, the second part of HCO3 - Protons migrate from the cathode electrolyte chamber to the intermediate chamber, and protons migrate from the anolyte chamber to the intermediate chamber.

[0021] Advantageously, the molar ratio of the first part to the second part is 25:75 to 0.1:99.9, preferably 20:80 to 0.2:99.8, and more preferably 10:90 to 0.5:99.5.

[0022] After migration, the migrating bicarbonate ions react with the migrating protons, thereby causing the migrating HCO3- to... - It is acidified by protons and forms CO2, which is contained in the intermediate layer solution.

[0023] Advantageously, the CO2 formed in the acidification step has a purity of at least 95% by volume, preferably at least 98% by volume, more preferably at least 99% by volume, and most preferably at least 99.5% by volume, as measured by gas chromatography (GC).

[0024] Advantageously, the carbon-deficient alkaline cathode electrolyte capture solution has a high alkalinity, i.e., advantageously has a pH value of 9 to 12.5, preferably 9.5 to 12, more preferably 10 to 12. The inventors have noted that the system can unexpectedly operate at pH values ​​equal to or higher than 9, preferably equal to or higher than 10, more preferably equal to or higher than 11, and even up to pH 13.

[0025] Advantageously, the carbon-deficient alkaline cathode electrolyte capture solution contains one or a combination of KOH, KHCO3, and K2CO3.

[0026] Advantageously, the method further includes separating CO2 from the intermediate layer solution. Advantageously, the method further includes returning the now CO2-free (separated) intermediate layer solution to the intermediate layer chamber of the electrolyzer. Returning the intermediate layer solution allows for reuse and recycling, which contributes to the efficiency and sustainability of the method, as there is no loss or waste of the intermediate layer solution.

[0027] Advantageously, the method further includes feeding the separated CO2 into the cathode electrolyte chamber. Upon entering the cathode electrolyte chamber, the CO2 is electrochemically reduced to form carbon monoxide (CO). Advantageously, the resulting CO, as part of the syngas mixture, has a high purity, i.e., a purity of at least 95% by volume, preferably at least 98% by volume, more preferably at least 99% by volume, and most preferably at least 99.5% by volume, as measured by GC.

[0028] In the context of this disclosure, "feeding separated CO2 into the cathode electrolyte chamber" and "allowing CO2 into the cathode electrolyte chamber" should be understood as feeding CO2 directly into the cathode electrolyte chamber, i.e., feeding CO2 itself, i.e., as a gas, into the cathode electrolyte chamber. Therefore, this term does not include delivering CO2 in dissolved form (e.g., CO2 dissolved in a liquid (such as water)) or in the form of water-saturated CO2.

[0029] Advantageously, the separated CO2 is directly fed into the cathode of the cathode electrolyte chamber.

[0030] Advantageously, the method further includes separating the syngas mixture from the cathode electrolyte capture solution to obtain a carbon-lean alkaline cathode electrolyte capture solution. Advantageously, at least a portion of the carbon-lean alkaline cathode electrolyte capture solution is reused to remove CO2 from CO2-containing air, which reduces the amount of waste stream generated in the process and thus reduces the environmental footprint of the process.

[0031] According to a second aspect of this disclosure, a synthesis gas mixture generation system as set forth in the appended claims is provided.

[0032] The syngas mixture generation system includes a CO2 capture system fluidly connected to the cathode electrolyte chamber of the electrolyzer. The electrolyzer also includes an anode electrolyte chamber and an intermediate chamber disposed between the cathode electrolyte chamber and the anode electrolyte chamber. The cathode electrolyte chamber contains the cathode. The anode electrolyte chamber contains the anode.

[0033] Advantageously, the cathode is a metallic silver gas diffusion electrode (GDE).

[0034] Advantageously, the electrolyzer also includes a first membrane located between the cathode electrolyte chamber and the intermediate chamber. In other words, the cathode electrolyte chamber and the intermediate chamber are advantageously separated by the first membrane. Advantageously, the first membrane allows negatively charged ions, especially HCO3-, to pass through. - Through.

[0035] Advantageously, the electrolyzer also includes a second membrane located between the anolyte chamber and the intermediate chamber. In other words, the anolyte chamber and the intermediate chamber are advantageously separated by the second membrane. Advantageously, the second membrane allows positively charged ions, especially protons (H+), to pass through. + (through)

[0036] Advantageously, the CO2 capture system (11) includes a direct air capture system (DAC system), or is essentially composed of a direct air capture system (DAC system).

[0037] Advantageously, the syngas mixture generation system further includes a first gas-liquid separator fluidly connected to the outlet of the intermediate chamber. Advantageously, a first outlet of the first gas-liquid separator is fluidly connected to the inlet of the intermediate chamber. Advantageously, a second outlet of the first gas-liquid separator is fluidly connected to the inlet of the cathode electrolyte chamber.

[0038] Advantageously, the syngas mixture generation system also includes a second gas-liquid separator that is fluidly connected to the outlet of the cathode electrolyte chamber of the electrolyzer and the inlet of the CO2 capture system.

[0039] Optionally, but advantageously, the syngas mixture generation system further comprises a catholyte capture solution reservoir in fluid connection with the outlet of the second gas-liquid separator and the inlet of the CO2 capture system. In other words, when present, the catholyte capture solution reservoir is advantageously located between the second gas-liquid separator and the CO2 capture system, and is configured to store the carbon-depleted alkaline catholyte capture solution in use.

[0040] Alternatively or additionally, but advantageously, the optional catholyte capture solution reservoir is further in fluid connection with the outlet of the CO2 capture system and the inlet of the catholyte chamber of the electrolyzer. In other words, when present, the catholyte capture solution reservoir is advantageously located between the CO2 capture system and the catholyte chamber of the electrolyzer, and is configured to store the carbon-rich catholyte capture solution comprising bicarbonate ions in use. Brief Description of the Drawings

[0041] Aspects of the present invention will now be described in more detail with reference to the accompanying drawings, in which like reference numerals designate like features, and in the accompanying drawings: Figure 1 schematically illustrates operations for capturing carbon dioxide from air and generating a syngas mixture according to a first embodiment of the present invention.

[0042] Figure 2 schematically illustrates operations for capturing carbon dioxide from air and generating a syngas mixture according to a second embodiment of the present invention.

[0043] Figure 3 shows a schematic diagram of a syngas generation system according to the present invention.

[0044] Figure 4 shows another schematic diagram of another syngas generation system according to the present invention.

[0045] Figures 5A to 5F respectively show the Faradaic efficiency of electrochemical conversion of CO2 to syngas, the flow rate of internally generated CO2, the pH value of the catholyte capture solution, the syngas composition, the cell potential, and the electrical conductivity over time according to the first embodiment.

[0046] Figures 6A to 6F respectively show the flow rate of internally generated CO2 for electrochemical conversion of CO2 to syngas, the cell potential, the pH value of the catholyte capture solution, the syngas composition, the carbon efficiency, and the impurities in the gas contained in the interlayer solution over time according to the second embodiment.

[0047] Figure 7 shows the Bjerrum diagram of CO2, HCO3 - and CO3 2- . Detailed Implementation

[0048] In the following paragraphs, on the one hand, refer to Figure 1 and Figure 2 On the other hand, refer to Figure 3 ,in Figure 1 and Figure 2 The present invention relates to a method for generating a synthesis gas mixture and its operation (steps). Figure 3 The synthesis gas mixture generation system relating to the present invention is configured to perform... Figure 1 and Figure 2 The method.

[0049] The method includes a CO2 capture operation or step 100 performed in a CO2 capture system 1. The CO2 capture system 1 is configured to expose air containing carbon dioxide to a cathode electrolyte capture solution capable of absorbing at least a portion, preferably substantially all, of the CO2 from the air.

[0050] The cathode electrolyte capture solution capable of absorbing CO2 from the air is a highly alkaline solution and carbon-deficient. A preferred example of such a solution is an aqueous solution containing one or a combination of KOH, KHCO3, and K2CO3.

[0051] More specifically, when the pH of the carbon-lean cathode electrolyte capture solution is between 9 and 12.5, the solution advantageously contains KHCO3 and K2CO3. When the pH of the carbon-lean cathode electrolyte capture solution is between 12.5 and 14, the solution advantageously contains KOH and K2CO3. Advantageously, the carbon-lean cathode electrolyte capture solution contains at least KHCO3, i.e., advantageously has a pH of 9.5 to 12.5. The inventors have discovered that when the carbon-lean cathode electrolyte capture solution contains at least KHCO3, the solution exhibits high selectivity for CO2.

[0052] A particularly preferred cathode electrolyte capture solution capable of absorbing CO2 is a KHCO3 solution with a molar concentration of up to 3.4 M at room temperature; especially molar concentrations of 0.5 M to 3.4 M, more particularly 1 M to 3.4 M, and even more particularly 2 M to 3.4 M, such as about 3 M KHCO3 solutions, all molar concentrations determined at room temperature. The inventors unexpectedly discovered that when the cathode electrolyte capture solution capable of absorbing CO2 is a KHCO3 solution, the lower concentration (molar concentration) allows for higher selectivity for CO2 absorption and allows for a higher cell potential in the electrolyzer.

[0053] The inventors noted that the system can unexpectedly operate at pH values ​​equal to or higher than 9, preferably equal to or higher than 10, more preferably equal to or higher than 11, and even up to pH 13.

[0054] When exposed to air containing CO2, the carbon-lean alkaline cathode electrolyte captures CO2 from the air, thereby generating bicarbonate ions (HCO3-) in the solution. - The process yields a carbon-rich cathode electrolyte capture solution. Advantageously, operation 100 is driven by the chemical affinity between CO2 in the air and the composition of the carbon-depleted alkaline cathode electrolyte capture solution.

[0055] Advantageously, CO2 capture system 1 is a direct air capture system. A direct air capture system can be any such system known in the art.

[0056] The carbon-rich cathode electrolyte capture solution containing bicarbonate ions is then guided (i.e. fed) into the cathode electrolyte chamber 4 of the electrolyzer 3 in subsequent feed operation 101. The electrolyzer also includes an anode electrolyte chamber 5 and an intermediate chamber 6 located between the cathode electrolyte chamber 4 and the anode electrolyte chamber 5.

[0057] The cathode electrolyte chamber 4 contains a cathode. The cathode can be any cathode known in the art for electrolysis. A preferred example of a suitable cathode within the cathode electrolyte chamber 4 is a metallic silver gas diffusion electrode (GDE).

[0058] The anolyte chamber 5 contains an anode. The anode can be any anode known in the art for electrolysis. The anolyte chamber also contains components capable of forming protons (H+) during electrolysis. + The anolyte solution is a solution containing H2SO4. Preferred examples of suitable anolyte solutions are aqueous solutions containing H2SO4, such as 0.5 M to 3 M H2SO4 solutions, preferably 0.75 M to 2 M H2SO4 solutions, and more preferably 0.5 M H2SO4 solutions.

[0059] The intermediate chamber (6) contains an intermediate solution. Preferred examples of such solutions are aqueous solutions containing one or a combination of KOH, KHCO3, and K2CO3. Advantageously, the carbon-lean cathode electrolyte capture solution contains at least KHCO3. The inventors have found that when the carbon-lean cathode electrolyte capture solution contains at least KHCO3, the solution exhibits high selectivity for CO2. The inventors have unexpectedly discovered that higher concentrations (molar concentrations) allow for higher flow rates of protons to reach the intermediate chamber, thereby improving the efficiency of the method and system.

[0060] A particularly preferred intermediate layer solution is a KHCO3 solution with a molar concentration of up to 3.4 M at room temperature; especially molar concentrations of 0.5 M to 3.4 M, more particularly 1 M to 3.4 M, and even more particularly 2 M to 3.4 M, such as about 2 M KHCO3 solutions, all molar concentrations measured at room temperature. The inventors unexpectedly discovered that when the intermediate layer solution is a KHCO3 solution, the lower concentration (molar concentration) allows for higher selectivity for CO2 absorption and allows for a higher cell potential in the electrolyzer.

[0061] The carbon-rich cathode electrolyte capture solution containing bicarbonate ions in the cathode electrolyte chamber (4) is electrolyzed during electrolysis operation 102. More specifically, the first portion of bicarbonate ions contained in the carbon-rich cathode electrolyte capture solution undergoes an electrochemical reaction facilitated by the electrodes (anode and cathode) of the electrolyzer. This electrochemical reaction converts these bicarbonate ions into a mixture of hydrogen and carbon monoxide (CO), collectively referred to as syngas. This syngas can be used as a fuel gas for energy production in various applications.

[0062] Advantageously, the electrolysis operation 102 achieves a carbon efficiency of approximately 80%, where carbon efficiency is defined as the proportion of carbon in the bicarbonate that is converted into syngas components.

[0063] The electrolysis operation 102 also includes the electrolysis of the anolyte solution in the anolyte chamber 5 of the electrolyzer 3, thereby generating protons.

[0064] When the cathode electrolyte solution is an aqueous solution, the electrolysis operation 102 also advantageously includes the electrolysis of water to hydrogen (H₂O + 2e⁻) in the cathode electrolyte chamber. - → H2 + 2OH - ).

[0065] Advantageously, the OH- produced during water electrolysis - It tends to react with the bicarbonate ions in the first part to produce carbonate ions and water, which is then electrolyzed into H2.

[0066] The second portion of bicarbonate ions contained in the carbon-rich cathode electrolyte capture solution migrates from the cathode electrolyte chamber 4 to the intermediate layer chamber 6, i.e., to the intermediate layer solution, during migration operation 103.

[0067] The molar ratio of bicarbonate ions in the first phase to those in the second phase depends on the pH of the cathode electrolyte trapping solution in the cathode electrolyte chamber. More specifically, the migration of bicarbonate ions into the intermediate chamber is related to the reaction of bicarbonate ions with OH-. -The reaction competition. Advantageously, the molar ratio of bicarbonate ions in the first part to bicarbonate ions in the second part is 25:75 to 0.1:99.9, preferably 20:80 to 0.2:99.8, more preferably 10:90 to 0.5:99.5.

[0068] Simultaneously with the bicarbonate ion migration, the migration operation 103 also includes the migration of protons from the anolyte chamber 5 to the same intermediate chamber 6, i.e., migration into the intermediate solution.

[0069] Advantageously, the migration operation 103 occurs due to the electrochemical gradient present in chambers 4, 5, and 6 of the electrolyzer.

[0070] Advantageously, the electrolyzer 3 also includes a first membrane 7 located between the cathode electrolyte chamber 4 and the intermediate chamber 6. In other words, the first membrane 7 separates the cathode electrolyte trapping solution from the intermediate layer solution. When the electrolyzer 3 includes this first membrane 7, migrating bicarbonate ions pass from the cathode electrolyte chamber 4 through the first membrane 7 into the intermediate chamber 6. In other words, the first membrane 7 allows bicarbonate ions to permeate. More specifically, bicarbonate ions migrate across the first membrane 7 due to the electrochemical gradient established across it.

[0071] Advantageously, the first membrane 7 is an anion exchange membrane (AEM), i.e., a membrane that allows negatively charged ions to pass through. Advantageously, the first membrane does not allow positively charged ions to pass through. In other words, the first membrane 7 is advantageously a selective membrane that allows only negatively charged ions to pass through while blocking other ions.

[0072] Advantageously, the selective permeability of the first membrane 7 is achieved through its ionic properties. Advantageously, the first membrane 7 comprises, or is substantially composed of, a polymer matrix containing a fixed positive charge, a polymer matrix adapted to attract and allow the passage of negatively charged ions while repelling positively charged ions.

[0073] Advantageously, the electrolyzer 3 also includes a second membrane 8 located between the anolyte chamber 5 and the intermediate chamber 6. In other words, the second membrane 8 separates the anolyte solution from the intermediate solution. When the electrolyzer 3 includes this second membrane 8, migrating protons pass from the anolyte chamber 5 through the second membrane 8 into the intermediate chamber 6. In other words, the second membrane 8 allows protons to permeate. More specifically, protons migrate across the second membrane 8 due to the electrochemical gradient established across it.

[0074] Advantageously, the second membrane 8 is a cation exchange membrane (CEM), i.e., a membrane that allows positively charged ions to pass through. In other words, the second membrane 8 is advantageously a selective membrane that allows only positively charged ions to pass through while blocking other ions.

[0075] Advantageously, the selective permeability of the second membrane 8 is achieved through its ionic properties. Advantageously, the second membrane 8 comprises, or is substantially composed of, a polymer matrix containing a fixed negative charge, a polymer matrix adapted to attract and facilitate the passage of cations (such as protons) while repelling negatively charged ions.

[0076] Advantageously, the first membrane 7 and the second membrane 8 possess excellent chemical stability to withstand the electrolytic environment and sufficient mechanical strength to maintain their structure during operation. Furthermore, the first membrane 7 and the second membrane 8 advantageously exhibit high resistance to fouling. It will be understood that fouling of membranes 7 and 8 will negatively impact the efficiency of migration operation 103 and any subsequent process operations, and may result in energy loss.

[0077] The presence of the selectively permeable first membrane 7 and the second membrane 8 facilitates the migration operation 103.

[0078] After bicarbonate ions and protons migrate into the intermediate chamber, acidification 104 of the bicarbonate ions and protons occurs. This acidification operation 104 produces carbonic acid, which decomposes into CO2 and water. In other words, acidification operation 104 results in the intermediate layer solution containing CO2 and water. The acidification reaction is represented by the following equation: H + + HCO3 - → CO2 + H2O. This reaction is promoted by the concentration gradient of protons and bicarbonate ions.

[0079] The inventors discovered that the electrolyzer 3, including the intermediate chamber 6 as described above, creates an environment isolated from the cathode electrolyte chamber 4 of the electrolyzer, in which the interaction of bicarbonate ions and protons can occur without negatively impacting syngas production during electrolysis operation 102. The presence of the first membrane 7 and the second membrane 8 further enhances this. In particular, the acidification reaction is further promoted by the electrochemical potentials across membranes 7 and 8.

[0080] The efficiency of acidification step 104 depends on, but is not limited to, the properties of the optional first membrane 7 and second membrane 8, the ion concentration, and the design of the intermediate liquid chamber 6 of the electrolyzer.

[0081] Advantageously, the electrolysis operation 102, the migration operation 103 and the acidification operation 104 are carried out simultaneously in the electrolyzer 3.

[0082] Now for reference Figure 2 and Figure 3 , and no longer refer to Figure 1 The method of the present invention may further include a separation operation 105. The separation operation 105 is advantageously carried out in a first gas-liquid separator 9. The first gas-liquid separator 9 may be any separator known in the art for separating gas dissolved in a liquid from the liquid.

[0083] Separation operation 105 includes separating the carbon dioxide formed in the intermediate layer solution during acidification operation 104 from the intermediate layer solution. Advantageously, depending on the type of gas-liquid separator used, separation operation 105 typically includes adjusting physical conditions such as pressure and / or temperature to cause dissolved carbon dioxide to form bubbles and rise to the upper part of the first gas-liquid separator 9.

[0084] Following separation operation 105, the method further includes a feeding operation 106, in which the resulting CO2-lean intermediate layer solution is recycled (i.e., fed) back to the intermediate layer chamber 6 of the electrolyzer 3. This recycling operation 106 allows for a sustained supply of "fresh" (i.e., CO2-lean) intermediate layer solution for the ongoing acidification operation 104. Therefore, no intermediate layer solution is wasted, resulting in its efficient utilization, thereby reducing the environmental footprint of the method and system and increasing its sustainability.

[0085] Following separation operation 105, the method further includes step 107, which involves transferring the separated carbon dioxide to the cathode electrolyte chamber 4 of the electrolyzer 3, wherein the carbon dioxide is electrochemically reduced to CO at the cathode in reduction operation 108. More specifically, step 107 involves transferring the separated carbon dioxide itself as a gas to the cathode electrolyte chamber. The inventors have discovered that by introducing gaseous carbon dioxide, which can be directly used for reduction to CO, the neutralization to bicarbonate ions (CO2 + OH-) is restricted. - → HCO3 - ) and carbonate ions (CO2 + 2OH-) - → CO3 2- + H2O) -- This is the competitive reaction that will occur when the separated carbon dioxide dissolves in the cathode electrolyte capture solution, leading to the continuous electrochemical conversion of CO2.

[0086] The cathode, particularly the GDE, provides surface area for the reduction reaction 108, allowing interaction between CO2 and the electrode surface. CO2 reacts with electrons to form CO, which are advantageously provided by the external circuitry of the electrolyzer 3. The reduction reaction is driven by an applied potential across the electrolyzer 3 and is characterized by Faraday efficiency, indicating the proportion of electrons available for the desired reaction to produce CO. Carbon efficiency characterizes the effectiveness of converting the carbon content of CO2 into the desired syngas components.

[0087] Advantageously, the electrolysis operation 102, the migration operation 103, the acidification operation 104, the separation operation 105 and the transfer reaction 107, and the feed operation 106, if present, are carried out simultaneously in the electrolyzer 3.

[0088] Those skilled in the art will understand that the bicarbonate ions in the carbon-rich cathode electrolyte capture solution are hydrolyzed indirectly rather than directly during electrolysis operation 102. In other words, the term "electrolysis of bicarbonate ions in the first part" should be understood in this disclosure as its indirect conversion into syngas. More specifically, water (advantageously present) in the cathode electrolyte capture solution is electrolyzed into hydrogen and OH- in the cathode electrolyte chamber. - The pH of the cathode electrolyte capture solution and, consequently, the pH within the cathode electrolyte chamber, affects the first portion of HCO3 in the carbon-rich cathode electrolyte capture solution. - Will react with the formed OH - The reaction forms CO3 2- And water (the so-called neutralization reaction), in which the latter will be electrolyzed to produce hydrogen gas and OH-. - Meanwhile, the CO2 transferred to the cathode electrolyte chamber in step 107 is reduced to CO.

[0089] The inventors unexpectedly discovered that the method including step 107—which thus includes introducing CO2 into the cathode electrolyte chamber to form a combination of bicarbonate ions (formed by capturing CO2 from the air, as described above) and CO2 (i.e., generated in situ in the intermediate chamber by acidification of bicarbonate ions)—favors the reduction of CO2 to CO rather than its neutralization (CO2 and OH-). - The reaction produces bicarbonate and carbonate ions. Although carbonate ions are still formed, causing the pH in the cathode electrolyte chamber to increase over time (as is also the case in prior art methods and systems), the waste or loss of CO2 due to reactions other than reduction to CO is significantly reduced. This results in a highly efficient CO2 reduction reaction, and (albeit unexpectedly) allows the method and system of the present invention to continue operating at pH values ​​exceeding the maximum operating pH of prior art systems and methods (pH 10, as shown in the Yellum diagram). Figure 7 Operate at a pH value of approximately 13 (maximum pH 13).

[0090] In other words, while the methods and systems of this disclosure still exhibit the known pH increase due to the formation of bicarbonate ions, they possess improved operational life because the systems and methods of this invention remain operable at the pH at which prior art systems and methods cease to function. Not wishing to be bound by any theory, the inventors attribute this unexpected effect to the reaction of CO2 as CO2 gas and HCO3-. -The combined CO2 is fed into the cathode electrolyte chamber, rather than just CO2 (which is typically dissolved in water in prior art methods). Furthermore, the high pH of the lean-carbon cathode electrolyte capture solution leaving the cathode electrolyte chamber can even be considered advantageous, as the higher pH allows for a higher CO2 capture yield. In other words, although there is a known pH elevation in the systems and methods of the present invention, because the methods and systems of the present invention continue to operate (within the electrolyzer) at pH values ​​much higher than those of prior art systems and methods, CO2 can be removed from CO2-containing air more efficiently via the lean-carbon cathode electrolyte capture solution in the CO2 capture system compared to prior art solutions and systems.

[0091] It was also unexpectedly found that when the feeding of bicarbonate ions into the cathode electrolyte chamber was stopped, and thus the removal of CO2 from the air in the CO2 capture system was stopped, and thereafter only the CO2 generated in the intermediate chamber was fed into the cathode electrolyte chamber (step 107), the method of the present invention also operated well, exhibiting operational stability for a duration of at least 250 hours, preferably at least 400 hours, and more preferably at least 500 hours.

[0092] Advantageously, when the method includes step 107, CO2 is introduced into the cathode electrolyte chamber near the cathode, preferably directly at the cathode. This has the advantage that CO2 can be immediately utilized by the cathode. Although it is still related to CO2 being reacted with OH- - While neutralizing competition, CO2 available directly at the cathode will be more easily reduced than when introduced elsewhere in the cathode electrolyte chamber. This advantageously leads to a higher CO yield.

[0093] CO is a component of syngas, therefore operations 107 and 108 enhance syngas production. Furthermore, since the CO2 produced in operation 104 advantageously has high purity, i.e., at least 95% by volume, preferably at least 98% by volume, more preferably at least 99% by volume, and most preferably at least 99.5% by volume as measured by gas chromatography (GC), the resulting CO also has high purity, i.e., at least 95% by volume, preferably at least 98% by volume, more preferably at least 99% by volume, and most preferably at least 99.5% by volume as measured by GC, thereby maximizing the efficiency of the syngas production method of the present invention.

[0094] The method also advantageously includes a separation step 109, in which the syngas is separated from the cathodic electrolyte capture solution to obtain a cathodic electrolyte capture solution with reduced carbon content, i.e., a carbon-lean alkaline cathodic electrolyte capture solution. Separation operation 109 is advantageously carried out in a second gas-liquid separator 10. The second gas-liquid separator 10 can be any separator known in the art for separating gases dissolved in a liquid from liquids.

[0095] Advantageously, depending on the type of gas-liquid separator used, separation operation 109 typically involves adjusting physical conditions such as pressure and / or temperature, which allows the gas to be released from the liquid solution.

[0096] Advantageously, following the separation operation 109, the method further includes a transfer operation 110, in which at least a portion, preferably all, of the lean syngas and carbon-lean alkaline cathode electrolyte capture solution is recycled back to the CO2 capture system 1, where it can be reused in the next CO2 capture operation 100. This recycling operation 110 improves the efficiency and sustainability of the entire method because less solution is wasted / discarded.

[0097] Now for reference Figure 4 The syngas mixture generation system 20 may also include a cathode electrolyte capture solution reservoir 19. The cathode electrolyte capture solution reservoir is configured to store cathode electrolyte capture solution during use. More specifically, operation 110 may include a sub-step of transferring a carbon-lean alkaline cathode electrolyte capture solution from the second gas-liquid separator 10 to the cathode electrolyte capture solution reservoir 19. Figure 2 (not shown in the image), and the sub-step of transferring at least a portion of the carbon-depleted alkaline cathode electrolyte capture solution from reservoir 19 to CO2 capture system 1 .... Figure 2 (Not shown in the image).

[0098] Additionally or alternatively, but advantageously, operation 101 may include the sub-step of transferring a carbon-rich cathode electrolyte capture solution from the CO2 capture system 1 to the cathode electrolyte capture solution reservoir 19. Figure 1 and Figure 2 (not shown in the image), and the sub-step of transferring at least a portion of the carbon-rich cathode electrolyte capture solution from the reservoir 19 to the cathode electrolyte chamber 4 of the electrolyzer 3 .... Figure 1 and Figure 2 (Not shown in the image).

[0099] Advantageously, the cathode electrolyte capture solution reservoir 19 is able to maintain a stable flow of the cathode electrolyte capture solution, thereby contributing to the efficiency of the system and the entire method.

[0100] The syngas mixture generation system may also include an anolyte reservoir 24, which is configured to store a portion of the anolyte solution, thereby allowing an optimal amount of anolyte solution to be present in the anolyte chamber 5 of the electrolyzer 3.

[0101] Advantageously, the method and system of the present invention allow the production of a synthesis gas comprising 40 to 60 vol% hydrogen, 40 to 30 vol% CO, and 25 to 10 vol% carbon dioxide, for example, a synthesis gas comprising 50 vol% H2, 40 vol% CO, and 10 vol% CO2.

[0102] Example Example 1 The electrolyzer used a four-layer flow cell separated by an Ag-based gas diffusion electrode (GDE) and containing a cation exchange membrane (CEM, Nafion 117) and an anion exchange membrane (AEM, Fumasep FAA-3-50).

[0103] 5 L of 2 M KHCO3 solution was used as the carbon-lean alkaline cathode electrolyte capture solution and was refreshed between the Ag GDE and CEM. 5 L of 0.5 M H2SO4 was used as the anolyte solution and was refreshed between the AEM and the anode (DSA plate). 0.5 L of 2 M KHCO3 solution was used as the intermediate layer solution and was refreshed between the CEM and AEM.

[0104] In the first experiment, essentially pure carbon dioxide was supplied to the catholyte chamber containing a 2 M KHCO3 solution (as a carbon-deficient alkaline catholyte trapping solution). This was achieved by applying 100 mA·cm⁻¹. -2 A constant current density was used to test the effect of CO2 delivery rate on the selectivity of CO2 conversion to syngas in a metal Ag-based gas diffusion electrode (GDE) cathode. An external CO2 supply to the cathode electrolyte chamber and thus to the cathode was gradually increased (every 20 hours) from 50 mL / min. -1 Reduce to 0 mL / min -1 The step size is 10 mL / min. -1 In addition to an externally supplied, essentially pure CO2, CO2 generated internally in the intermediate chamber is also continuously supplied to the cathode after separation from the intermediate solution. Electrolysis lasted for nearly 540 hours, with the external CO2 supply ceasing 100 hours after the start of the test.

[0105] The Faraday efficiency of CO production in the measurement system varies with the duration of electrolysis. Figure 5A The results are shown, and it is clear from the graph that only at least 20 mL / min is needed. -1 External CO2 is introduced into the system, having only a limited impact on the Faraday efficiency of CO, which remains at approximately 78% (compared to approximately 22% for hydrogen). Once the external CO2 decreases to 10 mL / min... -1 The Faraday efficiency of CO also decreases to approximately 55%. Once the external CO2 concentration drops to 0 mL / min... -1 The Faraday efficiency of CO further decreases but remains relatively constant at around 45%. This means that a minimum external CO2 supply is required to ensure a sufficiently high CO Faraday efficiency. It will be understood that this supply could come from CO2 captured (removed) from the air, while in the experiment a substantially pure CO2 stream was used for analytical reasons.

[0106] It was also noted that after the external CO2 supply was shut off (starting from 100 hours), the CO2 reduction reaction in the cathode electrolyte chamber (at the cathode) was maintained solely by internally generated CO2 gas (produced in the intermediate layer solution via acidification of bicarbonate ions), at a constant flow rate of approximately 15 mL / min. -1 ( Figure 5B The flow rates of the gas separated from the intermediate layer solution and the synthesis gas generated in the cathode electrolyte chamber are measured by a volumetric flow meter (supplier: BPC).

[0107] It was also noted that during the electrolysis reaction, as the reaction proceeded, the pH of the cathode electrolyte capture solution gradually increased to a value of 9.8. Figure 5C The pH of the cathode electrolyte capture solution was measured using a Hach PHC301 probe. As the pH increased, the ability of the cathode electrolyte capture solution to absorb unreacted CO2 from the cathode increased. Therefore, the concentration of unreacted CO2 escaping from the cathode electrolyte chamber as a syngas component decreased, such as... Figure 5D As shown. It was also noted that shortly after the external CO2 supply ceased, the syngas composition was rich in hydrogen (45% to 60%) and carbon monoxide (30% to 50%). The composition of the gas separated from the intermediate layer solution and the syngas generated in the cathode electrolyte chamber was analyzed by gas chromatography.

[0108] It was also noted that after 500 hours of experimentation, the battery potential increased from 4.5 V to approximately 7 V (see [link to experiment]). Figure 5E This is believed to be due to the dilution of the intermediate layer solution, caused by the formation of water when bicarbonate ions acidify with protons. This is further confirmed by the abrupt change in conductivity caused by the dilution starting from 100 hours (the moment the external carbon dioxide supply ceases). Figure 5F Electrochemical tests were performed using a VMP3 potentiostat (supplier: BioLogic). Conductivity was measured using a CDC401 probe.

[0109] Example 2 The electrolyzer used a four-layer flow cell separated by another Ag-based gas diffusion electrode (GDE) (containing 10 wt.% less argon than the GDE of Example 1) and containing a cation exchange membrane (CEM, Nafion 117) and an anion exchange membrane (AEM, Fumasep FAA-3-50).

[0110] 5 L of 2 M KHCO3 solution was used as the carbon-lean alkaline cathode electrolyte capture solution and was refreshed between the Ag GDE and CEM. 5 L of 0.5 M H2SO4 was used as the anolyte solution and was refreshed between the AEM and the anode (DSA plate). 0.5 L of 2 M KHCO3 solution was used as the intermediate layer solution and was refreshed between the CEM and AEM.

[0111] At 100 mA.cm -2 Electrolysis was carried out at a constant current density for 650 hours without an external CO2 supply. In other words, in Example 2, the CO2 supply to the cathode and cathode electrolyte chamber consisted solely of CO2 generated by acidified bicarbonate ions and released from the intermediate layer solution. Similar to Example 1, it is again noted that in the absence of an external carbon dioxide supply, the dilution of the intermediate layer solution ultimately leads to a reduction in CO2 release from it. This is due to... Figure 6A The decrease observed after more than 400 hours of continuous operation indicates an increase in battery potential. Figure 6B In addition, an increase in pH of the cathode electrolyte capture solution was measured. Figure 6C This prevents CO2 from escaping from the cathode electrolyte capture solution, as demonstrated by analysis of the composition of the syngas released from the cathode / cathode electrolyte chamber over time. Figure 6D ).from Figure 6C It is also clear that the system continues to operate at pH values ​​as high as approximately 13, which is significantly superior to existing systems that cease reducing CO2 to CO at pH 10. This also results in an extended duration of effective operation of the system and method of the present invention. Figure 6D It is clear that the CO2 fraction gradually decreases over time, while the carbon efficiency increases accordingly. Figure 6E The composition of the gas from the intermediate layer solution was also analyzed. Figure 6F The display shows impurities that change over time, with the amount of impurities changing over time not exceeding 0.5% by volume. In other words, high-purity CO2 gas was generated by acidifying bicarbonate ions in the intermediate layer solution.

Claims

1. A method for producing a syngas mixture, comprising: - Carbon dioxide (CO2) is removed from air containing carbon dioxide by exposing it to a carbon-deficient alkaline cathode electrolyte capture solution, thereby obtaining a solution containing bicarbonate ions (HCO3-). - The carbon-rich cathode electrolyte capture solution. - Will contain HCO3 - The carbon-rich cathode electrolyte capture solution is fed into the cathode electrolyte chamber (4) of the (101, 101a, 101b) electrolyzer (3), the cathode electrolyte chamber (4) containing a cathode, wherein the electrolyzer (3) further includes an anode electrolyte chamber (5) containing an anode and an anode electrolyte solution, and an intermediate layer chamber (6) disposed between the cathode electrolyte chamber (4) and the anode electrolyte chamber (5) and containing an intermediate layer solution. - Electrolysis of HCO3 in the first part of (102) - This forms a syngas mixture, and the anolyte solution is electrolyzed to produce protons (H+). + ), - Make the second part of HCO3 - The protons migrate (103) from the cathode electrolyte chamber (4) to the intermediate chamber (6), and from the anolyte chamber (5) to the intermediate chamber (6), wherein the migration step (103) is driven by the electrochemical potential of the electrolyzer (3). - In the intermediate chamber (6), HCO3 migrating by proton acidification (104) - This forms CO2, which is contained in the intermediate layer solution. - Separate (105) the CO2 from the intermediate layer solution, and - The separated CO2 is fed into the cathode electrolyte chamber (4) (107) and electrochemically reduced (108) the CO2 to form carbon monoxide (CO).

2. The method according to claim 1, wherein the CO2 formed in the acidification step (104) has a purity of at least 95% by volume, preferably at least 98% by volume, more preferably at least 99% by volume, and most preferably at least 99.5% by volume, as measured by gas chromatography (GC).

3. The method according to any one of the preceding claims, wherein the carbon-deficient alkaline cathode electrolyte capture solution has a pH value of 9 to 12.

5.

4. The method according to any one of the preceding claims, wherein the carbon-deficient alkaline cathode electrolyte capture solution comprises one or a combination of KOH, KHCO3 and K2CO3.

5. The method according to any one of the preceding claims further includes feeding a CO2-free intermediate layer solution into the intermediate layer chamber (6) of the electrolyzer (3) (106).

6. The method according to any one of the preceding claims, wherein the CO has a purity of at least 95% by volume, preferably at least 98% by volume, more preferably at least 99% by volume, and most preferably at least 99.5% by volume, as measured by GC.

7. The method according to any one of the preceding claims, wherein the separated CO2 is directly fed into the cathode of the cathode electrolyte chamber (107).

8. The method according to any one of the preceding claims further includes separating (109) the synthesis gas mixture from the cathode electrolyte capture solution to obtain a carbon-lean alkaline cathode electrolyte capture solution, wherein at least a portion of the carbon-lean alkaline cathode electrolyte capture solution is reused to remove (100) CO2 from air containing CO2.

9. A synthesis gas mixture generation system (1, 20) comprising a CO2 capture system (11) fluidly connected to a cathode electrolyte chamber (4) of an electrolyzer (3), the electrolyzer (3) further comprising an anode electrolyte chamber (5) containing an anode and an intermediate chamber (6) disposed between the cathode electrolyte chamber (4) and the anode electrolyte chamber (5), wherein the cathode electrolyte chamber (4) contains a cathode, wherein the system further comprises a first gas-liquid separator (9) fluidly connected to an outlet (13) of the intermediate chamber (6), wherein a first outlet (14) of the first gas-liquid separator (9) is fluidly connected to an inlet (12) of the intermediate chamber (6), and wherein a second outlet (15) of the first gas-liquid separator (9) is fluidly connected to an inlet (16) of the cathode electrolyte chamber (4).

10. The synthesis gas mixture generation system (1, 20) according to claim 9, wherein the electrolyzer (3) further comprises a first membrane (7) located between the cathode electrolyte chamber (4) and the intermediate chamber (6), wherein the first membrane (7) allows negatively charged ions to pass through.

11. The syngas mixture generation system (1, 20) according to claim 10, wherein the first membrane (7) allows HCO3 to be generated. - Through.

12. The synthesis gas mixture generation system (1, 20) according to any one of claims 9 to 11, wherein the electrolyzer (3) further comprises a second membrane (8) located between the anolyte chamber (5) and the intermediate chamber (6), wherein the second membrane (8) allows positively charged ions to pass through.

13. The syngas mixture generation system (1, 20) according to claim 12, wherein the second membrane (8) allows protons (H) to pass through. + (through) 14. The synthesis gas mixture generation system (1, 20) according to any one of claims 9 to 13, wherein the CO2 capture system (11) includes a direct air capture system.

15. The syngas mixture generation system (1, 20) according to any one of claims 9 to 14, further comprising a second gas-liquid separator (10) in fluid connection with the outlet (17) of the cathode electrolyte chamber (4) of the electrolyzer (3) and the inlet (18) of the CO2 capture system (11).

16. The syngas mixture generation system (20) according to any one of claims 9 to 14, further comprising a second gas-liquid separator (10) fluidly connected to the outlet (17) of the cathode electrolyte chamber (4) of the electrolyzer (3), and a cathode electrolyte capture solution reservoir (19) fluidly connected to the outlet (21) of the second gas-liquid separator (10), the outlet (22) of the CO2 capture system (11), the inlet (18) of the CO2 capture system (11), and the inlet (23) of the cathode electrolyte chamber (4) of the electrolyzer (3).

17. The synthesis gas mixture generation system according to any one of claims 9 to 16, wherein the cathode is a metallic silver gas diffusion electrode (GDE).

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