Method and device for the desorption of CO2 adsorbed on a sorbent and the use of water and / or steam

Abstract

The present invention describes a method for desorbing CO2 adsorbed on a sorbent, comprising a step of supplying water and / or water vapor from an exhaust gas stream of a cathode (31) of an aqueous electrolysis cell (30) to the sorbent (13).

Description

State of the art

[0001] One greenhouse gas responsible for global warming is carbon dioxide (CO2). There is therefore a worldwide effort to isolate CO2 from the air and then either convert it into other products through synthesis, or to store it permanently in liquid or solid form, for example in underground storage facilities. There are systems with which CO2 can be removed and isolated from the air on a large scale. Such systems are known as direct air capture systems (DAC systems) and comprise an adsorption or desorption chamber (ADC) into which ambient air is introduced, from which CO2 is selectively chemically or physically bound to a liquid or solid sorbent (also known as an adsorbent), thus removing it from the air. When the adsorbed CO2 is needed, it is desorbed from the sorbent by heating and, if necessary, negative pressure, and can then either be stored or reused.

[0002] Heating during the desorption process is typically performed with steam, which is used to flush the sorbent. This flushing process requires a high energy input. Furthermore, the water must be largely free of gas residues, such as oxygen, which could otherwise impair further reactions.

[0003] The present invention provides a method and a device for desorbing CO2 from a sorbent in a simple and energy-saving manner, while avoiding byproducts, particularly gaseous byproducts, including oxygen. Furthermore, the use of water and / or steam from an exhaust stream of a cathode of an aqueous electrolysis cell is also described. Disclosure of the invention

[0004] The process according to the invention enables cost- and energy-efficient desorption of CO2 adsorbed (and / or absorbed) on a sorbent by using water or water vapor from an aqueous electrolysis cell for desorption. The aqueous electrolysis cell is not specifically limited and can, for example, be a water electrolysis cell for water splitting or a CO2 electrolysis cell in which hydrogen and water vapor are present in the gas stream at the cathode. Since water electrolysis generally does not produce any dissolved substances, a water electrolysis cell is the preferred aqueous electrolysis cell.

[0005] The sorbent (absorbent or adsorbent) is not specifically restricted and can be either liquid or solid at room temperature and ambient pressure and can be inorganic, organic, polymeric, or non-polymeric in nature. Particularly suitable sorbents have amine groups to which CO2 preferentially adsorbs. WO 2022 / 013197A1 teaches suitable sorbents as an example. Other suitable sorbents can include (modified) activated carbon, cellulose, silica, zeolites, metal-organic frameworks, mixed metal oxides, covalent-organic frameworks, or polymer-based ion exchange resins, among others. According to the invention, the sorbent comprises CO2 adsorbed and / or absorbed thereon (both binding options are possible).

[0006] At least a portion of the water used to desorb CO2 from the loaded sorbent originates from an exhaust stream from the cathode of an aqueous electrolysis cell. For example, in water electrolysis, water is fed to a water electrolysis cell, which is decomposed into oxygen at the anode and hydrogen at the cathode using an electric current. The hydrogen formed at the cathode may contain residual water. Any oxygen passing through a membrane arranged between the cathode and the anode is also catalytically converted to water on the cathode side, so that the cathode exhaust gas (= exhaust stream from the cathode) consists essentially of hydrogen and water.

[0007] The water from the hydrogen-water mixture can be separated in a water separator and fed into the sorbent. A similar operation is achieved with other aqueous electrolysis processes.

[0008] It goes without saying that in addition to the at least one aqueous electrolysis cell, several aqueous electrolysis cells can also be present and the water and / or water vapor from any two or more aqueous electrolysis cells can be supplied to the sorbent.

[0009] It is advantageous if the water still has residual heat or is at least partially present in the form of water vapor, because the residual heat in the water or water vapor can then be effectively used for the desorption of CO2 from the sorbent. If the desorption of CO2 is carried out under negative pressure (e.g., 50 mbar absolute to 400 mbar absolute), water temperatures from room temperature (20 °C) to 80 °C are particularly suitable.

[0010] The process therefore has at least the following two advantages: Firstly, preheated water is reused, namely for the desorption of CO2. Furthermore, the water originating from the aqueous electrolysis cell contains essentially no foreign gases, such as oxygen, so that desorption with the water (this also includes water vapor) from the aqueous electrolysis cell does not introduce any foreign substances into the CO2 to be isolated, and any adsorption sites released by the sorbent are not blocked by oxygen. However, entrained solids generally do not pose a problem, as they can be easily separated from the released CO2.

[0011] This means that energy from the aqueous electrolysis cell, which is stored in the water or water vapor of the exhaust gas from the cathode of the electrolysis cell, is reused for the desorption of CO2, so that the process is characterized by a good energy balance and, due to the purity of the water or water vapor, CO2 can be isolated with high purity and thus quality.

[0012] The subclaims show preferred developments of the invention.

[0013] More preferably, the sorbent is introduced into an adsorption or desorption chamber (ADC) of a CO2 separation device (10), in particular a direct air capture system (DAC system). DAC systems as used according to the invention are known from the prior art and are described, for example, in WO 2021 / 259760 A1. The sorbent contained in the ADC serves, on the one hand, for the adsorption (and / or absorption) of CO2 from the air and, on the other hand, for the desorption of high-purity CO2, which can be intended for further syntheses or storage. The ADC can be equipped with corresponding supply lines for air (for the adsorption of CO2) and water (water vapor) (for the desorption of CO2), and outlet lines for air, water, and the isolated CO2. A water circuit from the outlet of the ADC to the inlet of the ADC is also possible.Furthermore, heat exchangers can be provided for introducing or removing heat from the various streams flowing into or out of the ADC. Pumps can also be installed in the lines to increase the flow rate. Furthermore, a negative pressure device (e.g., in the form of a vacuum pump) can be provided to reduce pressure and thus facilitate the desorption of the CO2 bound to the sorbent. Coupling an aqueous electrolysis cell with a DAC system improves the overall energy balance of both systems, allowing for the sustainable isolation of high-purity CO2 from the air.

[0014] Preferably, the water and / or steam from the aqueous electrolysis cell can be introduced into the DAC system at one or more different points. One possibility is to introduce the water and / or steam directly at the inlet of the ADC. This process is particularly advantageous when the water has a higher temperature and is present in the form of steam, because then very little of the water's or steam's energy is wasted by pumping it through pipes. Instead, the water and / or steam is introduced into the ADC as quickly as possible to desorb CO2.

[0015] According to another possibility, which can be used alternatively or additionally, the water and / or steam is introduced into a water supply line at the inlet of the ADC. This process is particularly advantageous if the water and / or steam originating from the aqueous electrolysis cell is to be mixed with additional (tempered) water before being fed into the ADC.

[0016] According to another option, which can be used alternatively or additionally, the water and / or steam is fed into a condensate storage tank of the DAC system. The condensate storage tank is usually located at the outlet of the DAC and is connected to the DAC via a water supply line, forming a circuit between the outlet of the DAC and the inlet of the DAC. The circuit can contain the condensate storage tank and, if necessary, other components, such as heat exchangers, supply lines for additional streams, and pumps.

[0017] Further advantageously, the water supply line of the DAC system comprises an evaporation unit, and the water and / or steam is introduced into the water supply line upstream and / or downstream of the evaporation unit. Upstream introduction is particularly used when the residual heat of the water from the aqueous electrolysis cell is low (in particular below 50 °C), because then this water is brought to a higher, suitable temperature, if necessary together with additional water that is fed to the ADC. However, if the residual heat is high, in particular if the water from the aqueous electrolysis cell is in the form of steam, its temperature is sufficient and it does not have to be passed through the evaporation unit. The evaporation unit, which is in particular in the form of a heat pump, can then heat additional water to be fed to the ADC.

[0018] The above options for introducing water and / or steam into the DAC system can be used individually or in any combination. Introducing the water and / or steam into the condensate storage tank is particularly suitable, as the water from the condensate storage tank can then be fed into the ADC in a targeted manner, namely only during the desorption of CO2, thus allowing water and / or steam to be introduced into the DAC system circuit independently of an ongoing adsorption or desorption reaction.

[0019] To further conserve resources, it may be advantageous to feed the water and / or steam exiting the ADC to the aqueous electrolysis cell. This recirculates the water between the aqueous electrolysis cell and the DAC system, saving not only energy costs but also water.

[0020] To ensure that the respective electrolysis reaction can proceed unhindered, the water and / or steam exiting the ADC is advantageously fed to a water purifier and / or an electrolyte purifier of the aqueous electrolysis cell. This ensures that the water is further purified or appropriately treated before entering the electrolysis cell.

[0021] Furthermore, the invention also discloses a device for desorbing CO2 from a sorbent comprising adsorbed CO2. The device is suitable for carrying out the method described above. Accordingly, the advantages, advantageous developments, and embodiments of the method and the device are mutually applicable.

[0022] The device according to the invention comprises a desorption chamber. The desorption chamber contains the sorbent, which can be in liquid or solid form and, in particular, forms an adsorbent bed. The sorbent is configured to reversibly adsorb (and / or absorb) CO2 from the air.

[0023] The device further comprises at least one aqueous electrolysis cell. It goes without saying that, in addition to the at least one aqueous electrolysis cell, several aqueous electrolysis cells may be present.

[0024] A water electrolysis cell to be used for this purpose comprises a cathode at which hydrogen is formed from water, with a water separator arranged in an exhaust gas line of the cathode in order to separate the hydrogen formed from the residual water.

[0025] The device further comprises an electrolysis wastewater line for water and / or steam from the water separator to the desorption chamber, so that water and / or steam from the aqueous electrolysis cell, which is particularly present in the form of a water electrolysis cell, can be used directly to desorb CO2 from the sorbent after separation from the hydrogen. For this purpose, the water separator and the desorption chamber are connected to each other by the electrolysis wastewater line, so that as little residual heat as possible can escape from the water and / or steam, thus enabling the desorption of CO2 to be carried out as efficiently and energy-efficiently as possible.

[0026] The device couples two different reaction systems together in such a way that energy in the form of (warm) water and / or steam is transferred from one reaction system (aqueous electrolysis cell) to another reaction system that carries out the desorption reaction. Because the water emerging from the cathode of the aqueous electrolysis cell and separated from it has a high degree of purity and is essentially free of oxygen, the desorption reaction is not impaired, and the resulting adsorption sites of the sorbent are not blocked by oxygen.

[0027] According to an advantageous development, the desorption chamber is part of a DAC system and thus an ADC. The DAC system further comprises a water supply line to the inlet of the ADC for supplying water to the ADC. This allows for better control of the introduction of water and / or water vapor from the exhaust gas of the aqueous electrolysis cell into the ADC and avoids heat losses.

[0028] The DAC system also advantageously includes a condensate storage tank at a CO2 outlet of the ADC. This opens up the possibility of temporarily storing water that is only required for the desorption reaction in the ADC, so that water can be temporarily stored while the ADC adsorbs CO2 from the air. A water separator can advantageously be installed upstream of the condensate storage tank so that pure CO2 can be isolated and removed from the DAC system before entering the condensate storage tank.

[0029] It is particularly advantageous for the electrolysis wastewater line to be directly connected to the water supply line. This embodiment is particularly preferred when the water exiting the electrolysis process has a high temperature (at least 50 °C) or is in the form of water vapor and the ADC is in desorption mode.

[0030] Furthermore, the DAC system of the device according to the invention advantageously comprises an evaporation unit in the water supply line. The evaporation unit serves to convert water into steam and, due to its very good energy efficiency, is designed, in particular, as a heat exchanger. The water to be evaporated in the evaporation unit can be external water, water from the condensate storage tank, or water from the exhaust gas of the water electrolysis cell.

[0031] A further advantageous development provides that the electrolysis wastewater line is connected to the water supply line upstream and / or downstream of the evaporation unit. An upstream feed of the electrolysis wastewater line is advantageous when the water from the exhaust gas of the aqueous electrolysis cell has a low temperature and is converted to water vapor upon passing through the evaporation unit. A downstream feed has the advantage of allowing a very short path to the ADC, which is particularly desirable when the water obtained from the exhaust gas of the aqueous electrolysis cell has a high temperature and is present in particular in the form of water vapor. Both guides can also be combined with one another in the device, so that one or the other feed can be selected depending on the temperature of the water obtained from the exhaust gas of the water electrolysis.Suitable supply line blocking mechanisms may be provided for this purpose.

[0032] It is particularly advantageous that the electrolysis wastewater line is connected to the condensate storage tank, as this allows water to be transferred from the water electrolysis cell to the DAC system at any time and then used specifically when the desorption reaction is running.

[0033] The device also advantageously comprises a discharge line for water and / or steam from the condensate storage tank to the inlet of the aqueous electrolysis cell. This creates a water circuit between the aqueous electrolysis cell and the DAC system, allowing not only energy to be saved but also water to be effectively conserved. The energy and product balance of the device is thereby significantly improved.

[0034] It goes without saying that the device described above can comprise further components or elements, such as storage tanks, vacuum systems, sensors for pressure, CO2 and temperature, etc. Since aqueous electrolysis cells and DAC systems are known to those skilled in the art, further details are unnecessary.

[0035] The invention also describes the use of water or steam from an exhaust stream of a cathode of an aqueous electrolysis cell for the desorption of CO2 adsorbed on a sorbent. This use allows energy and thus costs to be saved for the desorption, so that the desorption of CO2 is characterized by a high degree of sustainability.

[0036] In light of the above advantages, it is particularly preferred that the sorbent is incorporated into an ADK of a DAC plant. Short description of the drawings

[0037] Embodiments of the invention are described in detail below with reference to the accompanying drawings. In the drawing: Fig. 1 shows a schematic device according to an embodiment of the invention. Embodiments of the invention

[0038] The figure shows only the components, aspects, and elements essential to the invention. All other components, aspects, and elements are omitted for clarity.

[0039] Fig. 1 shows a device 1 for desorbing CO2 from a sorbent 13 and simultaneously illustrates a method for desorbing CO2.

[0040] In detail, Fig. 1 a device 1 comprising a DAC system 10 and an electrolysis cell 30.

[0041] The DAC system 10 comprises an ADC 11, which contains a sorbent 13 in a reaction chamber 12, which is configured to reversibly adsorb and / or absorb CO2. Both binding options of the CO2 to the sorbent are expressly possible and depend solely on the choice of sorbent 13.

[0042] The sorbent 13 is in the form of an adsorption bed and may comprise any supported or unsupported substance that reversibly binds CO2.

[0043] The ADK 11 has an air inlet 14 through which ambient air is admitted into the ADK 11 and from which CO2 is to be isolated. The air can be blown into the air inlet 14 via a pump 15.

[0044] The residual air remaining after the adsorption of CO2 on the sorbent 13 can be discharged from the air outlet 16 of the ADK 11.

[0045] The ADK 11 also has a water inlet 17 through which hot water and / or steam can be introduced into the ADK 11 during the desorption process to desorb the CO2 stored on the sorbent.

[0046] In addition, the ADC 11 has a CO2 outlet 18 from which the water and the desorbed CO2 are discharged. The mixture can pass through the heat exchanger 19, allowing liquid water to be separated and gaseous CO2 to be discharged via the pump 20. The separated water can be stored in the condensate tank 21 and fed back to the water inlet 17 for further desorption.

[0047] The line present between the condensate reservoir 21 and the water inlet 17 is a water supply line 22. The water supply line 22 can be directly connected to the condensate reservoir 21 on one side and to the water inlet 17 on the other side. Preferably, however, at least one evaporation unit 23, which can be designed in the form of a heat exchanger, is located in the water supply line 22. In addition, a further pump 24 can be provided upstream of the evaporation unit 23, with which water is supplied from the condensate reservoir 21 to the evaporation unit 23, where the water is brought to the desired temperature suitable for desorbing the CO2 from the sorbent.

[0048] The aqueous electrolysis cell 30, which is designed here as a water electrolysis cell, comprises a cathode 31, where hydrogen is formed from water, and an anode 32, where oxygen is formed from water. The hydrogen and residual water exit the cathode 31 as an exhaust stream via the exhaust line 33, which is fed to a water separator 34, from which water is separated from the exhaust stream, leaving pure hydrogen behind and can be discharged from the system.

[0049] The anode exhaust gas exiting the anode 32 can also pass through a water separator 35, leaving pure oxygen behind. The water from the anode exhaust gas can be pumped through a water conditioner 36 and an electrolyte conditioner 40 via the water supply line 38 and fed back into the electrolysis reaction by pumping with pump 39. This ensures effective water use.

[0050] The water separated from the cathode exhaust gas in the water separator 34 is fed to the ADC 11. Various options A, B, and C are available for this purpose, all of which lead with a dashed line from the electrolysis cell 30 to the ADC system 10. At least one of the electrolysis wastewater lines 37 A to C is formed, and water and / or steam from the anode exhaust gas of the aqueous electrolysis cell 30 is fed to the ADC 11 via this electrolysis wastewater line 37 A to C.

[0051] According to option A, the water and / or steam is connected directly to the water supply line 22 of the DAC system 10 via the electrolysis waste water line 37 A.

[0052] According to option B, the water and / or steam is connected to the water supply line 22 of the DAC system 10 via the electrolysis waste water line 37 B upstream of the evaporation unit 23.

[0053] According to option C, the water and / or steam is connected to the condensate storage tank 21 via the electrolysis waste water line 37 C.

[0054] Option C and thus electrolysis waste water line 37 C is preferred because it can use the water and / or steam from the aqueous electrolysis cell 30 independently of the reaction currently taking place in the ADK 11, so that heat losses are reduced.

[0055] Furthermore, in order to save water, a discharge line 25 for water and / or water vapor from the condensate storage tank 21 to the inlet of the aqueous electrolysis cell 30 can be formed in the DAC system 10, which discharge line opens into the water conditioner 36 or the electrolyte conditioner 40.

[0056] The device is characterized by high energy efficiency, which primarily results from the fact that (hot) water and / or water vapor from an anode exhaust gas of an aqueous electrolysis cell 30 is fed to an ADC 11, so that less additional energy is required to heat the water used for desorption during the desorption reaction of CO2 from a sorbent in the ADC 11. Furthermore, the water separated from the anode exhaust gas and fed to the ADC 11 is essentially free of condensing gases and, above all, oxygen, so that the desorption reaction can take place unhindered and vacated adsorption sites are not occupied by oxygen or other gases. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] WO 2022 / 013197A1

[0005] WO 2021 / 259760 A1

[0013]

Claims

[1] Method for the desorption of CO2 adsorbed on a sorbent, comprising a step of supplying water and / or water vapor from an exhaust gas stream of a cathode (31) of an aqueous electrolysis cell (30) to the sorbent (13). [2] Method according to claim 1, wherein the sorbent (13) is introduced into an adsorption or desorption chamber (11) of a CO2 separation device (10), in particular a direct air capture system (10). [3] Method according to claim 2, wherein the water and / or the water vapor of the aqueous electrolysis cell (30) is introduced into a condensate reservoir (21) of the CO2 separation device (10) and / or directly to the inlet of the adsorption or desorption chamber (11) and / or into a water supply line (22) to the inlet of the adsorption or desorption chamber (11). [4] Method according to claim 3, wherein the water supply line (22) comprises an evaporation unit (23) and the water and / or the water vapor is introduced into the water supply line (22) upstream and / or downstream of the evaporation unit (23). [5] Method according to one of claims 2 to 4, wherein the water and / or water vapor emerging from the adsorption or desorption chamber (11) is fed to the aqueous electrolysis cell (30). [6] Method according to claim 5, wherein the water and / or the water vapor emerging from the adsorption or desorption chamber (11) is fed to a water conditioner (36) and / or an electrolyte conditioner (40) of the aqueous electrolysis cell (30). [7] Device (1) for desorbing CO2 from a sorbent comprising adsorbed CO2, the device (1) comprising: - a desorption chamber comprising the sorbent (13) - an aqueous electrolysis cell (30) comprising: ◯ a cathode (31), wherein a water separator (34) is arranged in an exhaust gas line (33) of the cathode (31), - an electrolysis waste water line (37) for discharging water and / or water vapor from the water separator (34) to the desorption chamber (11). [8] Device (1) according to claim 7, wherein the desorption chamber is part of a CO2 separation device (10), in particular direct air capture system (10) and thus an adsorption or desorption chamber (11), and the CO2 separation device (10), in particular direct air capture system (10), further comprises: - a water supply line (22) to the inlet of the adsorption or desorption chamber (11) for supplying water into the adsorption or desorption chamber (11). [9] Device (1) according to claim 8, wherein the CO2 separation device (10) further comprises a condensate storage (21) at a CO2 outlet of the adsorption or desorption chamber (11). [10] Device (1) according to one of claims 8 or 9, wherein the electrolysis waste water line (37) is directly connected to the water supply line (22). [11] Device (1) according to one of claims 8 to 10, wherein the water supply line (22) comprises an evaporation unit (23). [12] Device (1) according to claim 11, wherein the electrolysis waste water line (37) is connected to the water supply line (22) upstream and / or downstream of the evaporation unit (23). [13] Device (1) according to one of claims 9 to 12, wherein the electrolysis waste water line (37) is connected to the condensate storage (21). [14] Device (1) according to one of claims 9 to 13, further comprising a discharge line (25) of water and / or water vapor from the condensate storage (21) to the inlet of the aqueous electrolysis cell (30). [15] Use of water or water vapor from an exhaust gas stream of a cathode (31) of an aqueous electrolysis cell (30) for desorption of CO2 adsorbed on a sorbent (13). [16] Use according to claim 15, wherein the sorbent (13) is introduced into an adsorption or desorption chamber (11) of a CO2 separation device (10), in particular a direct air capture system (10).

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