Methods and apparatus for desorbing CO2 adsorbed on adsorbents, and uses of water and / or water vapor.

Abstract

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

Description

Existing technology

[0001] The greenhouse gas causing global warming is carbon dioxide (CO2). Therefore, efforts are underway worldwide to separate CO2 from the air and then either synthesize it into other products or permanently store it in liquid or solid form, such as in underground storage facilities. Equipment capable of removing and separating CO2 from the air on an industrial scale is now available. This equipment, known as a direct air capture system (DAC), comprises an adsorption or desorption chamber (ADK) placed in ambient air to selectively bind CO2 to a liquid or solid adsorbent (also called an adsorbent) via chemical or physical means, thus removing it from the air. When the adsorbed CO2 is needed, it is desorbed again from the adsorbent by heating and optionally applying negative pressure, and can then be stored or further utilized.

[0002] Heating during desorption is typically performed using steam, which is also used to wash away the adsorbent. This washing process requires a high energy input. Furthermore, the water must be essentially free of gaseous residues, such as oxygen, which could otherwise interfere with further reactions.

[0003] This invention provides a method and apparatus for desorbing CO2 from an adsorbent in a simple and energy-efficient manner, wherein byproducts, particularly gaseous byproducts, such as oxygen, are avoided. Furthermore, the invention also describes the use of water and / or water vapor in the exhaust gas stream from the cathode of an aqueous electrolytic cell.

[0004] Invention disclosure The method of this invention achieves the desorption (and / or absorption) of CO2 adsorbed on an adsorbent in a cost-effective and energy-efficient manner, wherein desorption is carried out using water or water vapor from an aqueous electrolyzer. The specific type of aqueous electrolyzer is not limited; for example, it can be a water electrolyzer for water splitting or a CO2 electrolyzer, wherein hydrogen and water vapor are present in the gas flow at the cathode. Since water electrolysis typically does not produce dissolved substances, an aqueous electrolyzer is preferred.

[0005] The specific nature of the adsorbent (absorbent or adsorbent) is not limited; it can be liquid or solid at room temperature and normal pressure, and can be inorganic, organic, polymeric, or non-polymeric. Particularly suitable adsorbents contain amine groups, on which CO2 is preferably adsorbed. WO 2022 / 013197A1, for example, teaches suitable adsorbents. Other suitable adsorbents may include (modified) activated carbon, cellulose, silica, zeolite, metal-organic frameworks, mixed metal oxides, covalent organic frameworks, or polymer-based ion exchange resins, etc. According to the invention, the adsorbent comprises CO2 adsorbed and / or absorbed thereon (either combination is acceptable).

[0006] At least a portion of the water used to desorb CO2 from the loaded adsorbent originates from the waste gas stream at the cathode of an aqueous electrolyzer. For example, in water electrolysis, water is supplied to the electrolyzer, where it is decomposed into oxygen at the anode and into hydrogen at the cathode by the aid of an electric current. The hydrogen generated at the cathode may contain residual water. Oxygen that may pass through the membrane located between the cathode and anode is also catalytically converted into water on the cathode side; therefore, the cathode waste gas (= cathode waste gas stream) is primarily composed of hydrogen and water.

[0007] The water in the hydrogen and water mixture can be separated at a water separator and supplied to the adsorbent. Similar operations are used in other aqueous electrolysis processes.

[0008] It goes without saying that, in addition to the at least one aqueous electrolytic cell, there may be multiple aqueous electrolytic cells, and water and / or water vapor from two or more arbitrary aqueous electrolytic cells may be supplied to the adsorbent.

[0009] Advantageously, the water also contains residual heat or is at least partially in the form of water vapor, because the residual heat in the water or water vapor can then be effectively used to desorb CO2 from the adsorbent. If the desorption of CO2 is carried out under negative pressure conditions (e.g., 50 mbar absolute to 400 mbar absolute), a water temperature of room temperature (20°C) to 80°C is particularly suitable.

[0010] Therefore, this method has at least two advantages: First, the preheated water is reused, i.e., for CO2 desorption. Second, the water from the aqueous electrolysis cell is essentially free of foreign gases such as oxygen, so the desorption using water (including water vapor) from the aqueous electrolysis cell does not introduce foreign substances into the CO2 to be separated, and the adsorption sites of the released adsorbent are not blocked by oxygen. Conversely, entrained solids generally do not pose a problem, as they can be easily separated from the released CO2.

[0011] Therefore, the energy from the aqueous electrolytic cell in the water or water vapor stored in the exhaust gas at the cathode of the electrolytic cell is reused for CO2 desorption, thus the method is characterized by a good energy balance, and furthermore, due to the purity of the water or water vapor, high-purity and therefore high-quality CO2 can be separated.

[0012] The dependent claims describe preferred extensions of the invention.

[0013] More preferably, the adsorbent is introduced into the adsorption or desorption chamber (ADK) of a CO2 separation device (10), particularly a direct air capture device (DAC device). The DAC device used according to the invention is well known in the prior art, for example described in WO 2021 / 259760 A1. The adsorbent contained in the ADK is used, on the one hand, to adsorb (and / or absorb) CO2 from the air, and on the other hand, to desorb high-purity CO2, which can be used for further synthesis or for storage. The ADK may be equipped with corresponding air supply lines (for CO2 adsorption) and water (water vapor) supply lines (for CO2 desorption), as well as exhaust lines for air, water, and separated CO2. A water circulation loop from the outlet to the inlet of the ADK may also be provided. Furthermore, a heat exchanger may be used to introduce or remove heat from the different streams set to enter and leave the ADK, wherein pumps may also be present in the lines to increase the flow rate. Additionally, a negative pressure device (e.g., in the form of a vacuum pump) may be provided to reduce pressure, thereby promoting the desorption of CO2 bound to the adsorbent. The coupling of the aqueous electrolyzer with the DAC device improves the overall energy balance of the two systems, thereby enabling the separation of high-purity CO2 from the air in a sustainable manner and type.

[0014] Preferably, water and / or water vapor from an aqueous electrolyzer can be introduced into the DAC device at one or more different sites. One possible approach is to introduce water and / or water vapor directly at the ADK inlet. This method is particularly advantageous when the water is at a higher temperature and especially in the form of water vapor, because there is significantly less energy wasted by pumping water or water vapor through the line, and the water and / or water vapor are introduced into the ADK via the fastest route to desorb CO2.

[0015] Water and / or steam may be introduced into the water supply line leading to the ADK inlet, depending on another possible alternative or supplementary method. This method is particularly advantageous if the water and / or steam from the aqueous electrolyzer should be mixed with further (temperature-controlled) water before being introduced into the ADK.

[0016] Alternatively or as a supplement, water and / or steam may be introduced into the condensate tank of the DAC device. The condensate tank is typically located at the outlet of the ADK and connected to the ADK via a water supply line, thus forming a loop between the ADK outlet and inlet. Within this loop, the condensate tank and optional other components, such as heat exchangers, other feed lines, and pumps, may be installed.

[0017] More advantageously, the water supply line of the DAC device includes an evaporation unit, with water and / or water vapor introduced into the supply line upstream and / or downstream of the evaporation unit. Upstream introduction is particularly useful when the residual heat of the water from the aqueous electrolyzer is low (especially below 50°C), as the water can then be optionally heated to a higher suitable temperature along with further water introduced into the ADK. However, if the residual heat is high, especially when the water from the aqueous electrolyzer is in the form of water vapor, its temperature is sufficient and there is no need for an evaporation unit. In this case, the evaporation unit (especially in the form of a heat pump) can heat the further water introduced into the ADK.

[0018] The aforementioned methods for introducing water and / or water vapor into the DAC device can be used individually or in any combination. It is particularly suitable to introduce water and / or water vapor into a condensate tank, as this allows water to be selectively supplied to the ADK from the condensate tank, i.e., only during CO2 desorption. Therefore, water and / or water vapor can be introduced into the DAC device's circulation loop regardless of whether an adsorption or desorption reaction is in progress.

[0019] To further conserve resources, it may be advantageous to supply water and / or steam discharged from the ADK to an aqueous electrolyzer. This would allow water to circulate between the aqueous electrolyzer and the DAC equipment, saving not only energy costs but also water.

[0020] To ensure the smooth execution of their respective electrolytic reactions, the water and / or water vapor discharged from ADK are advantageously supplied to the water processor and / or electrolyte processor of the aqueous electrolyzer. This ensures that the water is purified or treated again before entering the electrolyzer.

[0021] Furthermore, an apparatus for desorbing CO2 from an adsorbent containing adsorbed CO2 is also disclosed according to the present invention. This apparatus is suitable for carrying out the method described above. Therefore, the advantages, advantageous extensions, and implementation methods of this method and apparatus are mutually applicable.

[0022] The apparatus of the present invention includes a desorption chamber. The desorption chamber contains an adsorbent, which may be in liquid or solid form, particularly constituting an adsorbent bed. The adsorbent is configured to reversibly adsorb (and / or absorb) CO2 from the air.

[0023] Furthermore, the device includes at least one aqueous electrolytic cell. It goes without saying that, in addition to the at least one aqueous electrolytic cell, multiple aqueous electrolytic cells may also exist.

[0024] The water electrolysis cell for this purpose includes a cathode where hydrogen is generated from water, wherein a water separator is provided in the exhaust gas line of the cathode to separate the generated hydrogen from the residual water.

[0025] Furthermore, the device includes an electrolytic wastewater pipeline for outputting water and / or water vapor from the water separator to the desorption chamber, so that water and / or water vapor from an aqueous electrolytic cell, particularly an aqueous electrolytic cell in the form of a water electrolytic cell, can be directly used to desorb CO2 from the adsorbent after separation from hydrogen. For this purpose, the water separator and the desorption chamber are interconnected via the electrolytic wastewater pipeline, allowing as little residual heat as possible to escape from the water and / or water vapor, thus enabling CO2 desorption to proceed as efficiently and energy-savingly as possible.

[0026] This device couples two different reaction devices to transfer energy in the form of (warm) water and / or steam from one reaction device (aqueous electrolysis cell) to another reaction device that performs the desorption reaction. Since the water discharged and separated from the cathode of the aqueous electrolysis cell is highly pure and essentially oxygen-free, the desorption reaction is unaffected, and the adsorption sites of the released adsorbent are not blocked by oxygen.

[0027] According to an advantageous extension, the desorption chamber is part of the DAC device, and therefore the ADK, and the DAC device also includes a water supply line to the ADK inlet for introducing water into the ADK. This allows for better control of the introduction of water and / or water vapor from the exhaust gas from the aqueous electrolyzer into the ADK and avoids heat loss.

[0028] More advantageously, the DAC device also includes a condensate storage tank at the CO2 outlet of the ADK. This enables the temporary storage of water that is only necessary for the desorption reaction in the ADK, allowing water to be temporarily stored while the ADK adsorbs CO2 from the air. Advantageously, a water separator can be present upstream of the condensate storage tank to separate pure CO2 and discharge it from the DAC device before it enters the condensate storage tank.

[0029] Particularly advantageously, the electrolysis wastewater line is directly connected to the water supply line. This embodiment is particularly preferred when the water discharged from electrolysis has a high temperature (at least 50°C) or is present in the form of water vapor and ADK is present in desorption mode.

[0030] Furthermore, advantageously, the DAC device of the present invention includes an evaporation unit in the water supply line. This evaporation unit is used to convert water into water vapor and is specifically designed as a heat exchanger due to its extremely high energy efficiency. The water to be evaporated in the evaporation unit can be external water, water from a condensate storage tank, or water from waste gas from a water electrolysis cell.

[0031] Another advantageous extension specifies that the electrolytic wastewater line is connected to the water supply line upstream and / or downstream of the evaporation unit. An upstream supply of the electrolytic wastewater line is advantageous when the water in the exhaust gas from the aqueous electrolysis cell has a low temperature and is converted into water vapor as it flows through the evaporation unit. A downstream supply has the advantage of enabling a very short path through the ADK, which is particularly ideal when the water obtained from the exhaust gas of the aqueous electrolysis cell has a high temperature and is especially present in the form of water vapor. These two methods can also be combined in the unit so that one or the other supply can be selected based on the temperature of the water obtained from the exhaust gas of water electrolysis. For this purpose, a suitable supply line shut-off mechanism can be specified.

[0032] Of particular advantage, the electrolytic wastewater line is connected to the condensate storage tank, as this allows water to be delivered from the water electrolysis cell to the DAC device at any time and then used selectively as needed during the desorption reaction.

[0033] Advantageously, the device includes a discharge line for water and / or water vapor from a condensate storage tank to the inlet of the aqueous electrolyzer. This creates a water circulation loop between the aqueous electrolyzer and the DAC equipment, thereby saving not only energy but also water. Consequently, the energy and product balance of the device is significantly improved.

[0034] It goes without saying that the above-described apparatus may also include other components or elements, such as storage tanks, negative pressure devices, and sensors for pressure, CO2, and temperature. Since aqueous electrolysis cells and DAC devices are well known to those skilled in the art, they need not be described in detail here.

[0035] The invention also describes the use of water or water vapor in the exhaust gas stream from the cathode of an aqueous electrolytic cell for desorbing CO2 adsorbed on an adsorbent. Through this use, energy and therefore cost savings can be achieved for desorption, thus making the desorption of CO2 highly sustainable.

[0036] In view of the above advantages, it is particularly preferable to introduce the adsorbent into the ADK of the DAC device. Brief description of the attached diagram The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The drawings show: Figure 1 An illustrative apparatus according to one embodiment of the present invention.

[0038] Embodiments of the present invention This figure only depicts the basic components, aspects, and elements of the invention. For clarity, all other components, aspects, and elements have been omitted.

[0039] Figure 1The apparatus 1 for desorbing CO2 from adsorbent 13 is shown, and the method for desorbing CO2 is also explained.

[0040] Figure 1 The device 1 is shown in detail, which includes a DAC device 10 and an electrolytic cell 30.

[0041] The DAC device 10 includes an adsorbent 11 containing an adsorbent 13 in a reaction chamber 12, the adsorbent being configured to reversibly adsorb and / or absorb CO2. Both modes of binding of CO2 to the adsorbent are clearly feasible and depend solely on the choice of adsorbent 13.

[0042] The adsorbent 13 is formed in the form of an adsorption bed and may contain various supported or unsupported substances that reversibly bind CO2.

[0043] ADK 11 has an air inlet 14 through which ambient air enters ADK 11 and CO2 should be separated. The air can be blown into air inlet 14 by pump 15.

[0044] After CO2 is adsorbed onto the adsorbent 13, the remaining residual air can be discharged from the air inlet 16 of ADK 11.

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

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

[0047] The pipeline located between the condensate storage tank 21 and the water inlet 17 is the water supply line 22. The water supply line 22 can be directly connected at one end to the condensate storage tank 21 and the other end to the water inlet 17. However, preferably, the water supply line 22 contains at least one evaporation unit 23, which can be in the form of a heat exchanger. Furthermore, a further pump 24 can be installed upstream of the evaporation unit 23, which supplies water from the condensate storage tank 21 to the evaporation unit 23, where the water is heated to the required temperature for desorbing CO2 from the adsorbent.

[0048] The aqueous electrolyzer 30, designed as a water electrolyzer, includes a cathode 31 and an anode 32. Hydrogen is produced from water at the cathode 31, and oxygen is produced from water at the anode 32. Hydrogen and residual water are discharged from the cathode 31 as waste gas through waste gas line 33, which supplies water to a water separator 34. Water is separated from the waste gas stream in the water separator, allowing pure hydrogen to remain and be discharged from the system.

[0049] The anode exhaust gas discharged at anode 32 can also flow through water separator 35, leaving pure oxygen behind. Water from the anode exhaust gas can be supplied to the electrolysis reaction again via water processor 36 and electrolyte processor 40 through water supply line 38 and pumped by pump 39. This effectively utilizes water.

[0050] Water separated from the cathode exhaust gas in water separator 34 is supplied to ADK 11. Different possible pathways A, B, and C exist for this purpose, all connected to the ADC device 10 via dashed lines from the electrolytic cell 30. At least one of electrolytic wastewater lines 37 A to C is designed here, and water and / or water vapor from the anode exhaust gas of the aqueous electrolytic cell 30 are supplied to ADK 11 through these electrolytic wastewater lines 37 A to C.

[0051] According to possible method A, water and / or water vapor are directly connected to the water supply line 22 of the DAC device 10 via the electrolysis wastewater line 37A.

[0052] According to possible method B, water and / or water vapor are connected upstream of the evaporation unit 23 to the water supply line 22 of the DAC device 10 via the electrolysis wastewater line 37 B.

[0053] According to possible method C, water and / or water vapor are connected to condensate storage tank 21 via electrolytic wastewater line 37 C.

[0054] Option C and therefore the electrolytic wastewater pipeline 37 C are preferred because they can utilize water and / or steam from the aqueous electrolytic cell 30 independently of the reaction occurring in ADK 11, thereby reducing heat loss.

[0055] In addition, to save water, a water and / or water vapor discharge line 25 can be formed in the DAC device 10 from the condensate storage tank 21 to the inlet of the aqueous electrolysis cell 30, which leads to the water processor 36 or the electrolyte processor 40.

[0056] The device is characterized by high energy efficiency, primarily due to the supply of (hot) water and / or steam from the anode exhaust gas of the aqueous electrolyzer 30 to the ADK 11. This reduces the additional energy required to heat the water used for desorption in the ADK 11 for the CO2 desorption reaction from the adsorbent. Furthermore, the water separated from the anode exhaust gas and delivered to the ADK 11 is essentially free of condensable gases, especially oxygen, allowing the desorption reaction to proceed smoothly and ensuring that the released adsorption sites are not occupied by oxygen or other gases.

Claims

1. A method for desorbing CO2 adsorbed on an adsorbent, comprising the step of supplying water and / or water vapor from a waste gas stream from the cathode (31) of an aqueous electrolytic cell (30) to the adsorbent (13).

2. The method according to claim 1, wherein the adsorbent (13) is introduced into the adsorption or desorption chamber (11) of the CO2 separation device (10), particularly the direct air capture device (10).

3. The method according to claim 2, wherein water and / or water vapor from the aqueous electrolysis cell (30) are introduced into the condensate storage tank (21) of the CO2 separation device (10), and / or directly into the inlet of the adsorption or desorption chamber (11), and / or into the water supply line (22) leading to the inlet of the adsorption or desorption chamber (11).

4. The method according to claim 3, wherein the water supply line (22) includes an evaporation unit (23), and water and / or water vapor are introduced into the water supply line (22) upstream and / or downstream of the evaporation unit (23).

5. The method according to any one of claims 2 to 4, wherein water and / or water vapor discharged from the adsorption or desorption chamber (11) is supplied to the aqueous electrolysis cell (30).

6. The method according to claim 5, wherein water and / or water vapor discharged from the adsorption or desorption chamber (11) is supplied to the water processor (36) and / or electrolyte processor (40) of the aqueous electrolysis cell (30).

7. An apparatus (1) for desorbing CO2 from an adsorbent containing adsorbed CO2, the apparatus (1) comprising: - Desorption chamber containing adsorbent (13) - An aqueous electrolytic cell (30) comprising: ○ Cathode (31), wherein a water separator (34) is installed in the exhaust gas pipeline (33) of the cathode (31). - Electrolytic wastewater pipeline (37), which is used to output water and / or water vapor from water separator (34) to desorption chamber (11).

8. The apparatus (1) according to claim 7, wherein the desorption chamber is part of the CO2 separation apparatus (10), particularly part of the direct air capture device (10), and is therefore an adsorption or desorption chamber (11), and the CO2 separation apparatus (10), particularly the direct air capture device (10), further comprises: - A water supply line (22) leading to the inlet of the adsorption or desorption chamber (11), which is used to supply water to the adsorption or desorption chamber (11).

9. The apparatus (1) according to claim 8, wherein the CO2 separation apparatus (10) further comprises a condensate storage tank (21) located at the CO2 outlet of the adsorption or desorption chamber (11).

10. The apparatus (1) according to any one of claims 8 or 9, wherein the electrolytic wastewater line (37) is directly connected to the water supply line (22).

11. The apparatus (1) according to any one of claims 8 to 10, wherein the water supply line (22) comprises an evaporation unit (23).

12. The apparatus (1) according to claim 11, wherein the electrolytic wastewater line (37) is connected to the water supply line (22) upstream and / or downstream of the evaporation unit (23).

13. The apparatus (1) according to any one of claims 9 to 12, wherein the electrolytic wastewater line (37) is connected to the condensate storage tank (21).

14. The apparatus (1) according to any one of claims 9 to 13, further comprising a water and / or water vapor discharge line (25) from the condensate storage tank (21) to the inlet of the aqueous electrolytic cell (30).

15. Use of water or water vapor in the exhaust gas stream from the cathode (31) of an aqueous electrolytic cell (30) for desorbing CO2 adsorbed on an adsorbent (13).

16. The use according to claim 15, wherein the adsorbent (13) is introduced into the adsorption or desorption chamber (11) of a CO2 separation device, particularly a direct air capture device (10).

Images