Method for separating co2 from air and providing concentrated co2

Abstract

The present invention relates to a method and an apparatus for extracting CO2 from a gaseous medium, in particular ambient air, using a CO2 separation apparatus having: a CO2 scrubber that has a gas inlet and a gas outlet, a sorbent inlet at an upper end of the CO2 scrubber, and a first intermediate tank for receiving a CO2-enriched sorbent from the CO2 scrubber; and an electrodialysis apparatus for separating CO2 into a release medium. The method comprises the following steps: enriching the sorbent with CO2 in the CO2 scrubber and feeding the CO2-enriched sorbent into the first intermediate tank; discharging a first partial quantity of the enriched sorbent from the first intermediate tank into the electrodialysis apparatus; and recirculating a second partial quantity of the enriched sorbent from the first intermediate tank into the CO2 scrubber. The method is configured to be carried out continuously, semi-continuously or batchwise.

Description

[0001] Description

[0002] Process for the separation of CO2 from air and provision of concentrated CO2

[0003] The invention relates to a method for separating CO2 from the air and for providing concentrated CO2, as well as to a device for separating CO2 from the air and providing concentrated CO2.

[0004] The emission of carbon dioxide into the atmosphere is currently considered a major driver of climate change. Carbon capture and storage (CCS) technologies are efficient and effective methods for reducing carbon dioxide emissions into the atmosphere.

[0005] Common methods for capturing carbon dioxide include absorption, adsorption, membrane-based systems, electrochemical separation, and cryogenic separation. The absorption of carbon dioxide in an aqueous solvent can be used to purify exhaust gases from power plants and industrial facilities.

[0006] Furthermore, it is desirable to capture carbon dioxide directly from the ambient air and release or store it in a controlled manner. Known methods for adsorbing carbon dioxide directly from the ambient air include direct air capture (DAC) processes.

[0007] The published patent application (DE 102020 004 542 A1) describes several options for binding and releasing carbon dioxide from a gas mixture on a laboratory scale. Various methods are presented for loading an amine-containing sorbent, such as homogenizing the sorbent with a gas mixture or absorbing the CO2 onto a sorbent in a gas scrubbing column. Furthermore, options for precipitating the bound CO2 as a solid, as well as electrolytically releasing CO2 from an acceptor medium, are described. Furthermore, a recirculation of the sorbent after loading and subsequent discharging with CO2 in a direct path between a gas scrubbing column for loading and an electrodialysis device for discharging, is described.The known processes have the disadvantage that high carbon dioxide concentrations are often required in the gas phase to be purified (the above-mentioned publication describes an experimental setup with a CO2 content of 48 vol%), for example, to ensure a sufficiently loaded absorber solution for efficient release by electrodialysis. This prevents efficient operation of such systems, for example, for the purification of ambient air.

[0008] Furthermore, it is not possible with the known methods to keep a higher concentration of the sorbent in solution without by-products such as carbonates precipitating as solids.

[0009] Furthermore, there is currently little information on the operation of CO2 scrubbers for separating CO2 from ambient air. The low partial pressure of CO2 makes cost-effective CO2 scrubbing for DAC processes unpromising, as a correspondingly high air volume would have to be supplied to an absorber tower to bind a significant amount of CO2 from the ambient air to or into a sorbent in a reasonable time.

[0010] In addition, the air tends to become enriched with water up to the respective saturation partial pressure, which, depending on the inlet humidity, can lead to high water loss from an aqueous sorbent. Quantitative statements regarding water loss and the energy balance for a system beyond the laboratory scale depend on several environmental conditions and the specific large-scale setup and are not generally available.

[0011] The object of the present invention is to provide a method and a device for the efficient absorption and controlled release of gaseous carbon dioxide from the ambient air, which at least partially overcomes the disadvantages of the previous methods.

[0012] Furthermore, the present device for carrying out the method according to the invention is intended to record and optimize process-economic parameters for the regeneration or purification of, for example, ambient air from CO2 addition, since the system according to the invention can be operated on a pilot plant scale. For example, site-specific parameters could be recorded. At the same time, data on the material and energy consumption of such a "CO2 scrubbing system" or CO2 separation device could be generated beyond the laboratory scale.

[0013] This object is achieved by the inventive method according to claim 1 and the inventive device according to claim 10.

[0014] Further advantageous embodiments of the invention emerge from the subclaims and the following description of preferred embodiments of the present invention.

[0015] A method according to the invention for recovering CO2 from a gaseous medium, in particular ambient air, using a CO2 separation device with a CO2 scrubber with a gas supply and a gas discharge, a sorbent supply at an upper end of the CO2 scrubber and a first intermediate tank for receiving a CO2-enriched sorbent from the CO2 scrubber; and an electrodialysis device for separating CO2 into a release medium comprises the following process steps:

[0016] - Enriching the sorbent with CO2 in the CO2 scrubber;

[0017] - Supply of the CO2-enriched sorbent into the first intermediate tank;

[0018] - Discharging a first portion of the enriched sorbent from the first intermediate tank into the electrodialysis device; and

[0019] - Returning a second portion of the enriched sorbent from the first intermediate tank to the CO2 scrubber. The process is designed to be carried out continuously, semi-continuously, or batchwise.

[0020] A gaseous medium can be ambient air, but it can also be industrial gases, exhaust gases, gas mixtures, point sources and the like, with the method described herein of CO2 and / or other water-soluble gases, such as nitrogen oxides (e.g. NO X ) be exempted.

[0021] The process according to the invention is carried out in a CO2 separation device. This device is designed to first bind gaseous CO2 to a sorbent and then release it from the sorbent in a controlled manner as a gas. It can be collected and stored in a concentrated form.

[0022] Such a separation device includes a CO2 scrubber. The CO2 scrubber can be a column with packed elements, also referred to below as an "absorber column," such as a trickle-bed column. The packing elements can be Raschig rings or other types of packing. These packing elements have a large surface area and can thus provide a large reaction surface for the absorption process.

[0023] Furthermore, a gas supply and gas discharge are provided, allowing a CO2-containing gas stream, such as ambient air, to be fed into the CO2 scrubber and a CO2-poor gas stream to be discharged again. The gas supply and gas discharge can be achieved, for example, via a suction fan positioned at an upper air inlet, which draws CO2-containing ambient air into the separation device through a lower air inlet. This allows the gas stream flowing in from below to flow through the CO2 scrubber and form the continuous phase.

[0024] In the process according to the invention, CO2 is absorbed by a flowable sorbent. The sorbent can be a liquid, a solvent, or an aqueous solution of a sorbent. Examples of known liquids for absorbing CO2 include amine-containing ionic liquids. Examples of known solvents for absorbing CO2 include monoethanolamine (MEA), ammonia, and the like. The sorbents used according to the invention are preferably solutions of amines, diamines, and tertiary amines, amino acids, and amino acid salts.

[0025] The sorbent is fed into the CO2 scrubber through a sorbent inlet at its upper end. The sorbent can be dispersed, for example, by atomizing or breaking it up into fine droplets. This can be achieved using a nozzle. This increases the absorption surface of the sorbent. The sorbent can trickle through the CO2 scrubber, forming the dispersed phase.

[0026] A device for carrying out the method according to the invention further comprises a first intermediate tank and an electrodialysis unit. The CO2-enriched sorbent is collected in the first intermediate tank, and the dissolved or absorbed CO2 is transferred into a release medium in the electrodialysis unit. The release medium can be an aqueous solution of a proton donor, such as an organic acid.

[0027] A method according to the invention comprises enriching the sorbent with CO2 in the CO2 scrubber. As already described above, the divided sorbent can trickle through the CO2 scrubber. The packing of the CO2 scrubber allows the sorbent to be distributed over a large surface area, creating a large contact area between the CO2-containing gas stream flowing in from below and the sorbent. The enrichment of the sorbent with CO2 can occur by binding CO2 to the sorbent and subsequently dissolving it as an anion.

[0028] In the process according to the invention, the enriched sorption solution, i.e., the CO2-laden sorbent, is fed into the first intermediate tank. This can be done, for example, through a tank located directly at the lower end of the CO2 scrubber, into which the enriched sorbent can flow. However, there can also be a pipe connection that conveys the loaded sorbent from the CO2 scrubber into the first intermediate tank.

[0029] According to the invention, a first portion of the enriched sorbent is fed into the electrodialysis device. This can occur when the sorbent is sufficiently enriched, for example, when it is determined that saturation with CO2 has been reached.

[0030] Simultaneously or alternatively, in the process according to the invention, a second portion of the enriched sorbent from the first intermediate tank can be returned to the CO2 scrubber. This can serve to further load the partially CO2-enriched sorbent with CO2, thus achieving a higher concentration of absorbed CO2 in the sorbent, which has a beneficial effect on the subsequent electrodialysis.

[0031] Surprisingly, it was found that during the loading of the sorbent with carbon dioxide, the inventive circulation in the absorber column does not lead to precipitation of water-insoluble carbonates or bicarbonates. Furthermore, it was surprisingly observed that the solubility in water of, for example, arginine as a sorbent increases during or after loading with carbon dioxide.

[0032] Accordingly, the CO2 bound by the process according to the invention can be completely regenerated to gaseous CO2 without any losses due to salting-out effects or flocculation of poorly soluble or insoluble carbonates or bicarbonates.

[0033] The process according to the invention is designed to be carried out continuously, semi-continuously, or batchwise. As a continuous process, the absorption and release steps can take place in a continuous cycle. As a batchwise process, absorption and release (i.e., electrodialysis) can be carried out completely separately. In a semi-continuous process, for example, electrodialysis can be switched on once sufficient absorption has occurred.

[0034] In a first embodiment, the method also comprises the steps:

[0035] - Depletion of the CO2-enriched sorbent in the electrodialysis device;

[0036] - Discharging a first portion of the depleted sorbent into a second intermediate tank;

[0037] - Discharging a second portion of the depleted sorbent into the first intermediate tank; and

[0038] Feeding a portion of depleted sorbent from the second intermediate tank to an upper end of the CCh scrubber.

[0039] In this embodiment, the sorbent enriched in the CO2 scrubber is depleted in the electrodialysis unit. Dissolved (or absorbed) CO2 is removed from the sorbent by electrodialysis and released in gaseous form. Electrodialysis is a process in which a voltage is applied to, for example, an aqueous medium. By using selective ion exchange membranes in the dialysis chambers and bipolar membranes in the intermediate chambers, the bound or absorbed CO2, which may be present in the sorbent solution, for example, as carbonate or bicarbonate ion and as such can desorb from the sorbent, can pass through an anion exchange membrane (AAM) and be converted to carbon dioxide in the anolyte chamber and released in a controlled manner as a gas into a release medium.

[0040] Furthermore, in this embodiment, a portion of the CO2-depleted (or regenerated) sorbent can be discharged into a second intermediate tank. The second intermediate tank can be located downstream of the electrodialysis unit; accordingly, the CO2-laden sorbent can be regenerated by electrodialysis and then fed into the second intermediate tank.

[0041] Since, according to the invention, the supply of CO2-enriched sorbent can, as already described above, not only come directly from the CO2 scrubber but also from the first intermediate tank, the release of CO2 from the sorbent by electrodialysis can also occur independently of continuous absorption of CO2 by the sorbent in the CO2 scrubber. Furthermore, the method in this exemplary embodiment can also be carried out in such a way that the regenerated sorbent does not have to be supplied directly to the CO2 scrubber; accordingly, regenerated sorbent can be kept in the second intermediate tank until the absorption of CO2 by the regenerated sorbent is to take place again. For this purpose, the sorbent from the second intermediate tank can be fed to an upper end of the CO2 scrubber, where it is again finely divided and is available for the absorption of CO2 in the CO2 scrubber.

[0042] Through electrodialysis, the dissolved and absorbed carbon dioxide is released as a gas in a controlled manner. Controlled release involves, for example, dehumidification and compression, followed by introduction of carbon dioxide into gas cylinders for storage and / or later use, for example, in organic synthesis. The carbon dioxide thus obtained can be used for further synthesis in the production of e-fuels.

[0043] The advantage of recycling the regenerated sorbent either to the first or second intermediate tank in the present embodiment allows, compared to existing processes, a process in which the sorbent does not have to be pumped through the electrodialysis membranes, which has a positive effect on the service life of the dialysis membranes. Since the column and dialysis unit can have different heights and flow rates, the height of the column would have to be achieved using a pump. If there is direct recycling from the dialysis chamber to the column, the use of a pump carries the risk of accelerated wear of the dialysis membrane.

[0044] The absorption and release of carbon dioxide with the embodiment described here can occur either continuously, semi-continuously, or intermittently. This is advantageous because electrodialysis proceeds faster than the absorption of, for example, carbon dioxide by a sorbent. Accordingly, absorption requires a higher throughput.

[0045] Accordingly, in one embodiment, the electrodialysis can be switched on intermittently (or batchwise), for example when a certain amount of saturated sorbent is available (for example, provided in the first intermediate tank).

[0046] In addition, thanks to the use of intermediate tanks and the possibility(s) of recirculation, the process can also be operated continuously. The choice of process control may depend on, for example, site parameters, gas concentrations in the ambient air, plant size, and the like.

[0047] In a further embodiment, the enrichment and depletion of the sorbent with CO2 is determined by a saturation criterion. This can be achieved by measuring the electrical conductivity of the sorbent. Since water-soluble gas molecules such as carbon dioxide dissolve in solution as anions, the electrical conductivity of the sorbent solution increases during the absorption of, for example, carbon dioxide into a sorbent. According to this embodiment, saturation of the sorbent with, for example, carbon dioxide can be determined by the fact that the conductivity of the sorbent no longer increases. The solution is then considered saturated. In an analogous manner, the regeneration of the sorbent, i.e., by a corresponding decrease in the electrical conductivity of the sorbent, can also be monitored.

[0048] Measuring electrical conductivity as a saturation parameter of the sorbent enables the determination of the saturation level in direct operation, meaning that sampling and external measurement of the CO2 loading concentration, for example, via gas chromatography, are not necessary. Furthermore, the absorption and desorption process can be monitored in situ by measuring conductivity, and process parameters can be adjusted accordingly to the current absorption and desorption status of the sorbent.

[0049] The conductivity of the sorption solution during the absorption process can be measured, for example, as it exits the CO2 scrubber, using a conductivity sensor. If the conductivity of the sorbent continues to increase, e.g., during the process, the sorbent can be fed back into the CO2 scrubber until a constant conductivity value is measured. The saturated, loaded sorbent can then be stored in the first intermediate tank for batch electrodialysis operation. Alternatively, or simultaneously, the sorbent can be fed directly from the first intermediate tank to the electrodialysis in continuous operation, or partially in semi-continuous operation.

[0050] For example, the conductivity during the desorption process is first determined before the loaded sorbent enters the electrodialysis unit and then after it leaves the electrodialysis unit. By measuring the conductivity, the regeneration of the sorbent can be determined, e.g., by determining that the electrical conductivity is no longer decreasing or has reached a predetermined value.

[0051] In another embodiment, the sorbent comprises an aqueous solution of at least one amine. This can be a primary, secondary, or tertiary amine. Amines have a free electron pair on the nitrogen atom, which allows them to accept a proton and thus act as bases in aqueous solution, producing OH' ions.

[0052] In a further embodiment, the sorbent comprises an aqueous solution of at least one agent containing a guanidine group. Like amines, guanidine groups form bases in aqueous solution upon addition of a proton, which improves the absorption process of CO2 by the sorbent (e.g., by the amine or guanidine group), as explained in more detail below.

[0053] In another embodiment, the sorbent comprises an arginine solution. Arginine is a basic amino acid that, in addition to an amine group, also has a guanidine group and is therefore very well suited for absorbing carbon dioxide in aqueous solution. The chemical processes involved in the absorption of, for example, carbon dioxide by an amino acid are described in more detail below.

[0054] In a further embodiment, the concentration of the sorbent can be increased during the recycling of the sorbent without, for example, carbonates and bicarbonates precipitating as solids. Surprisingly, it was found that with the recycling according to the invention, no precipitation of solids or flocculation occurs. Increasing the concentration of the sorbent, such as arginine in aqueous solution, during the recycling of the absorption leads to an even higher binding or absorption rate of gas molecules to the sorbent. It was further found that the solubility of arginine increases after loading with carbon dioxide compared to the solubility of pure arginine in water (solubility of 148 g / l at RT). For example, if the sorbent is an arginine solution, the concentration can initially be between 0.5 and 2 mol / L and can be increased during the process.In another embodiment, the release takes place by means of electrodialysis using an acid. The acid serves to provide protons, which facilitates the dissociation of carbonate or bicarbonate ions into carbon dioxide and water. Accordingly, the bound CO2 is released in gaseous form into the acid as the release medium. The acid can be an organic acid. The requirements for the acid used are, on the one hand, high electrical conductivity of the acid, with migration in the applied electric field of electrodialysis being as low as possible. This can also occur if an acid anion has a molecular size that is too large to pass through the ion exchange membranes of the electrodialysis chambers.

[0055] In one embodiment, the release medium comprises citric acid.

[0056] The present invention further relates to a device for extracting CO2 from a gaseous medium, comprising a unit for gas supply and gas removal, a unit for sorbent supply, a CO2 scrubber, and a first intermediate tank. The elements are designed and arranged to carry out the method according to the invention.

[0057] As mentioned above, the gas supply and gas removal can be achieved through a suction fan mounted at an upper opening, which serves as the air outlet, while ambient air is introduced as a gas through a lower opening, which serves as the air inlet. The ambient air can be analyzed for its composition and properties (e.g., water content, CO2 content, temperature, etc.) at the inlet and outlet. Furthermore, the ambient air can be adjusted to the desired process parameters, i.e., conditioned, at the inlet. Furthermore, the ambient air can be filtered at the inlet to remove, for example, dust, pollen, soot, and the like.

[0058] As already mentioned above, the sorbent supply in the device according to the invention can be fed either from a storage tank containing sorbent or from regenerated sorbent from the second intermediate tank, or from not yet fully loaded sorbent from the first intermediate tank. According to the invention, the sorbent is finely divided upon entering the CO2 scrubber. Accordingly, the sorbent supply can be configured as a pipeline with a nozzle at the end.

[0059] The CO2 scrubber of the device according to the invention can, as already mentioned above, be designed as a column with packed elements, for example in the form of a trickle-bed column, also known as a fixed-bed reactor. A fixed-bed reactor is characterized in that a liquid can flow through a solid bed or packing. A trickle-bed column, in the sense of the device according to the invention, is a fixed-bed reactor through whose solid bed or packing a liquid flows on the one hand and a gas on the other. The gas stream penetrates the trickle-bed reactor from bottom to top as a continuous phase, while the liquid flows from top to bottom through the solid bed or packing of packed elements.

[0060] The first intermediate tank of the device according to the invention can either be mounted below the CO2 scrubber so that the loaded sorbent flows directly from the CO2 scrubber into the tank. However, it can also be supplied via a pipeline. The tank itself can be a stainless steel tank with an appropriate capacity (i.e., tailored to the respective absorption capacity of the system).

[0061] The individual elements of the device according to the invention are designed and arranged so that they can carry out the method according to the invention.

[0062] In a further embodiment, the device according to the invention is further equipped with an electrodialysis unit and a second intermediate tank.

[0063] An electrodialysis unit is a device for electrodialysis. Electrodialysis is an electrochemical process in which ionic components can be removed from a solution using ion exchange membranes and the driving force of an electric field. Ionic compounds are reduced in one circuit (diluate) and concentrated in another (concentrate).

[0064] The electrodialysis unit can be constructed, for example, from two electrode end plates with membranes stacked between them. The anode can be made of nickel or stainless steel, the cathode of stainless steel. Cell frames are inserted between the membranes as spacers for the supply and removal of the loaded sorbent. The cell frame thickness can be, for example, 0.5 mm, which accordingly defines the membrane spacing. The cell frame size can be, for example, 50 x 50 cm. The membrane package can consist of 16 cell pairs. In such a design, the effective membrane surface area corresponds to 1750 cm 2Further scaling up to industrial scale is possible. In this exemplary embodiment, the device further comprises a second intermediate tank located downstream of the electrodialysis unit. The second intermediate tank can be made of stainless steel and connected to the electrodialysis unit via a pipeline.

[0065] In a further embodiment, the device according to the invention is further equipped with a first bypass which recirculates the sorbent from the first intermediate tank into the CO2 scrubber for further absorption. In this case, it can be determined, for example, by means of a conductivity sensor that the conductivity of the sorbent continues to rise upon exiting the CO2 scrubber and before entering the first intermediate tank. This can be used to determine, for example, that the sorbent is not yet fully saturated with bicarbonate or carbonate ions (i.e. the sorbent is not yet fully loaded with CO2) and can be passed from the first intermediate tank into the first bypass, from where the sorbent can be fed back into the absorber column from above. This can be done using a pump attached to the first bypass.

[0066] The conductivity sensor can also be located in the first intermediate tank and measures the conductivity of the solution or liquid within it. If the conductivity value in the first intermediate tank stops increasing, it can be determined, for example, that the sorbent is saturated, and the absorption cycle can be terminated.

[0067] In a further embodiment, the device according to the invention comprises a second bypass that returns the sorbent from the second intermediate tank to the CO2 scrubber, whereby the second bypass bypasses the electrodialysis unit. Due to their design, the CO2 scrubber and the electrodialysis unit have a height difference of several meters. As a result, without the use of a second intermediate tank and second bypass, the regenerated absorber solution would have to be pumped through the electrodialysis unit to compensate for this height difference, which leads to increased membrane wear on the dialysis membranes. The second bypass allows the regenerated absorber solution (or the sorbent) to be collected in the second intermediate tank and from there pumped back to the level of the CO2 scrubber, from where it can be fed to the scrubber for further CO2 absorption.

[0068] According to another embodiment, to protect the dialysis membranes, it is possible to feed the regenerated absorber solution to the first intermediate tank directly from the electrodialysis chamber via a third bypass. Since the height difference of the CO2 scrubber does not have to be overcome, this can be done without the use of a pump, thus protecting the electrodialysis membranes. As already described above, the at least partially regenerated absorber solution can thus be fed back into the absorption circuit in the CO2 scrubber.

[0069] The device according to the invention can further be equipped with a heat exchanger unit and a heat pump. For example, it can be advantageous to cool the incoming ambient air to an optimal temperature for absorption using a cooling unit (i.e., a first heat exchanger). By using an additional heat exchanger, the CO2-laden sorbent can be heated to an optimal temperature for electrodialysis (e.g., a temperature between 30°C and 50°C). For example, the two heat exchangers can be coupled with a heat pump, resulting in optimal and energetically advantageous heat utilization of the device according to the invention.

[0070] The purpose of cooling or, in general, preconditioning the incoming ambient air is to increase the hydrophilic interactions between the gas molecules to be dissolved and the aqueous absorber solution (i.e. the sorbent) and thus to ensure a better transition of the gas molecules into the water phase.

[0071] Heating the sorbent for electrodialysis accordingly utilizes the opposite effect, namely increasing the hydrophobic interactions in the system, which promotes the release of dissolved gas molecules from the water phase.

[0072] In a further embodiment, the device according to the invention is further equipped with sensors suitable for measuring the electrical conductivity, temperature, pH, pressure, flow rate, current, and voltage, as well as the humidity of the gas streams and / or liquids used. These parameters can be determined for the sorbent before / after absorption, as well as before / after electrodialysis, for the gaseous medium before / after entering the absorber column, and for the CO2 released after exiting the electrodialysis unit.

[0073] The use of sensors in the device according to the invention also enables sensor-based and sensor-monitored operation of the system, which can be largely autonomous. The use of sensors enables the use of control technology that, depending on the measured parameters, operates the device according to the invention either intermittently or continuously, or decides on the activation of one of the bypasses or intermediate tanks described above.

[0074] Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:

[0075] Fig. 1 schematically shows an embodiment of the presented method;

[0076] Fig. 2 shows schematically a simplified structure of the absorption and release system; and

[0077] Fig.3 shows schematically a detailed structure of the absorption and release system.

[0078] An embodiment of a simplified process according to the invention is shown in Fig. 1. Here, the focus will be on the chemical reactions and interactions that occur in the process according to the invention; a detailed description of the process according to the invention is provided with reference to Fig. 2.

[0079] In Fig. 1, CO2 is absorbed from the air by bringing the air into contact with a liquid absorber solution in a CCh scrubber (10). For this purpose, air is introduced into the CO2 scrubber from below (V1), and the absorber solution, which is dispersed at the top of the CO2 scrubber, flows countercurrently from top to bottom through the CCh scrubber (V2).

[0080] An aqueous amino acid solution, preferably an arginine solution, is used as the sorbent or absorber solution. It is known that basic amino acids dissolved in water enhance the reaction of gases (in this case CO2) with water to form water-soluble compounds. The reason for this lies in the chemical structure of amino acids. The generic formula of an amino acid is HOOC-CHR-NH2.

[0081] Amino acids possess a carboxyl group and a primary or secondary amine group as reactive groups, which allows them to undergo an intramolecular acid-base reaction. This involves an internal transfer of a proton from the carboxyl group to the amine group, resulting in a dipolar, zwitterionic form of the amino acid.

[0082] In the formula below, (1) corresponds to the non-ionic and (2) to the dipolar zwitterionic form of an amino acid:

[0083]

[0084] Amino acids are ampholytes, meaning they can react as acids or bases because the deprotonated carboxyl group can accept protons and the protonated amine group can donate protons. In aqueous solution, they usually exist as zwitterions.

[0085] In acidic solution, amino acids react as bases; accordingly, the carboxyl group of an amino acid is protonated in acidic solution, so that the cation form of the amino acid is formed by the protonated ammonium group (R-NH3 + ) results.

[0086] In basic solution they react as acids, accordingly the amine group is not protonated (i.e. as R-NH2) and the carboxyl group is deprotonated (i.e. as R-COO'), resulting in the anion form of the amino acid.

[0087] At the isoelectric point of an amino acid, the pH value of the solution is adjusted so that the amino acid is electrically neutral to the outside, i.e. the charges in the molecule cancel each other out.

[0088] When dissolved in water, the following equilibria are established in which the amino acid assumes its zwitterionic form (2):

[0089] (acidic) (zwitterion) (basic)

[0090] The amphoteric nature of amino acids is important when considering them as solvents for CO2 capture.

[0091] The following describes, by way of example, the reactions that occur during the absorption of CO2 by a sorbent in the CO2 scrubber (10). In the present embodiment, an amino acid salt solution is used as the sorbent. The absorption of CO2 by the amino acid salt solution occurs with the formation of a bivalent carbamate anion ('OOC-CHR-NH-COO'). Absorption in the aqueous medium occurs with the formation of bicarbonate (HCO3') according to the following reaction equations:

[0092] The hydroxyl ions (OH') in equations 2 and 3 are, as mentioned above, generated by the action of amino acids as weak bases in aqueous solution:

[0093] After its formation, the carbamate anion (from equation 2) hydrolyzes to form bicarbonate and free amine:

[0094] Another possible reaction for the absorption of gaseous CO2 is the base-catalyzed bicarbonate formation:

[0095] Substituents on the a-carbon of an amino acid create instability in the resulting carbamate molecule, which promotes carbamate hydrolysis. The thus released amine can then react with other CO2 molecules, thus binding them by absorption. Thus, the hydrolysis of the carbamate leads to increased CO2 absorption into the absorber solution, i.e., the aqueous solution of the sorbent.

[0096] The degree of hydrolysis is determined, for example, by the concentration of the amine, the pH of the solution, and the chemical stability of the carbamate. CO2 absorption is increased when all absorbed CO2 is present as bicarbonate (HCO3'). Solutions with a higher bicarbonate-to-carbamate ratio exhibit greater desorption rates in electrodialysis and produce a desirable, leaner desorbed solution. The kinetics of CCh uptake are dominated by the formation of the carbamate anion (Equation 2). The formation of the carbamate anion occurs almost instantaneously upon contact of the amine-containing sorbent with the gas mixture and represents the rate-determining step.

[0097] In contrast, base-catalyzed bicarbonate formation (Equation 6) is significantly slower. The contribution of Equation 3 to the kinetics of the absorption process can be important at very low CO2 loadings, where the pH of the solution is high. However, this reaction becomes slower with increasing CO2 uptake compared to the reaction with an amine.

[0098] Returning to Fig. 1, the CO2 from the supplied air stream is bound to the sorbent in the CO2 scrubber (10). CO2-free or low-CO2 gas leaves the CO2 scrubber (10) at the top (V9), and the CO2-laden absorber solution is pumped (V3) from the bottom of the column into the electrodialysis unit (20). The bottom of the column can be designed as a first intermediate tank (11).

[0099] By means of an electrodialysis unit (20), the bound CO2, which is present in solution in the form of HCOa' as described above, is separated (V8) from the sorbent and the released gaseous CO2 is then concentrated (V4).

[0100] Electrodialysis is an electrochemical process in which ionic or ionogenic components can be removed from a solution and separated from one another using one or more ion exchange membranes with an applied electric field as the driving force.

[0101] In the simplified embodiment shown in Fig. 1, ionic compounds are reduced in one circuit (diluate) and concentrated in another (concentrate). In the electrodialysis used here, the diluate chamber (2) and concentrate chamber (3) are separated from each other by an anion exchange membrane (AAM) (6). An anion exchange membrane is a membrane semipermeable to anions.

[0102] The CO2-laden sorbent is fed into the diluate chamber (V3). Bicarbonate anions (HCOa') migrate from the diluate chamber (2) through the AAM (6) in the direction of the arrow in Fig. 1 into the adjacent concentrate chamber (3). Further migration toward the anode is prevented by the downstream bipolar membrane (BPM) (5). A BPM (5) separates the concentrate chamber (3) from the anode chamber (4), and the diluate chamber (2) from the cathode chamber (1).

[0103] The anode and cathode chambers contain the electrodes through which the external voltage, i.e. the electric field, is applied. During the electrodialysis process, H + and OH' ions are generated and released into the adjacent cell chamber. The H + -ions react in the concentrate chamber (3) with the HCOa' ions to form water and CO2:

[0104] The amine-containing sorbent remains in the diluate chamber (2) and is regenerated according to the following equation:

[0105] The sorbent thus prepared is then fed to the absorber column (10) for further CO2 separation from the air (V5).

[0106] While the CO2-laden sorbent flows into the diluate chamber (2) (V3) and CO2-free absorber solution exits this chamber (V5), the concentrate chamber (3) is part of a circuit with an aqueous acid as the absorption and release medium. The aqueous acid migrates neither toward the cathode through the AAM nor toward the anode through the BPM, but remains in the concentrate chamber (3). The migration of the acid anions toward the anode can be achieved, for example, by using a BPM with a cutoff in the range of 0.2-10 kDa, for example, using a bipolar nanofiltration (NF) membrane.

[0107] In a preferred embodiment of the present invention, the aqueous acid is citric acid, which is fed to the concentrate chamber (3) (V6). This reduces the pH in the concentrate chamber (3). The reaction according to equation 7 releases gaseous CO2, and the acid used is regenerated as a release medium (V8) and collected in a storage container (40). Any other aqueous solution of an organic or inorganic acid that has a very high electrical conductivity and is not electrophoretically transported in the direct current electric field, or alternatively has a molecular size larger than the cut-off (i.e., the pore size) of the BPM, can also be used as the release medium.

[0108] Hydrogen (H2) is produced as byproducts in the cathode chamber (1) and oxygen (O2) in the anode chamber (4). To remove these gases and prevent the oxyhydrogen reaction, NaOH flows from two different storage containers (50; 60) through the two electrode chambers in separate circuits.

[0109] The processes in the electrodialysis unit (20) will be described in more detail below.

[0110] As already mentioned, for the concentration of CO2 in the sorbent, a circulation through the CO2 scrubber (10) is advantageous, since this requires a higher throughput than the electrodialysis unit (20).

[0111] For example, a bypass allows the CO2 scrubber (10) to be designed smaller, which reduces investment costs.

[0112] Under conditions with high amino acid salt concentrations, precipitation of reaction products, complex formation, and salting-out effects can occur in known processes. By recirculating the absorption process in the CO2 scrubber (10) using a first bypass, the sorbent can be saturated with CO2. At the same time, the concentration of the sorbent in the absorber solution (such as arginine) can be gradually increased, resulting in increased CO2 uptake into the sorbent (or into the aqueous solution of the sorbent).

[0113] A higher CO2 content, corresponding to a high proportion of HCOa' ions in the loaded sorbent, promotes the efficient operation of electrodialysis, whereby more CO2 can be produced in concentrated form.

[0114] After the chemical reactions that take place during the process according to the invention have been described with reference to Fig. 1, the process control according to the invention will now be illustrated with reference to Fig. 2 using an arginine solution as the sorbent (or absorber solution). In a first step, ambient air is introduced into the CO2 scrubber (10) from below (V1). In parallel, fresh arginine solution is fed into the CO2 scrubber from above for commissioning (V2). The absorber solution trickles from top to bottom over packing elements (e.g. Raschig rings or other packing elements). The packing elements serve to increase the contact area between air and liquid.

[0115] The arginine solution absorbs part of the CO2 from the air stream and CCh-poor air escapes at the head of the CO2 scrubber (V9).

[0116] At the bottom of the CO2 scrubber, a first intermediate tank (11) is located to hold the loaded absorber solution. If the absorber solution is not yet sufficiently saturated with CO2, this design allows the CO2 scrubber to be circulated (V10), meaning the absorber solution can trickle through the CO2 scrubber several times until the absorber solution is saturated with CO2. For this purpose, the absorber solution is pumped from the first intermediate tank (11) to the top of the CO2 scrubber (10) via a first bypass (12).

[0117] The first bypass (12) is also used for the separate commissioning of the CO2 scrubber (10), ie without switching on the electrodialysis unit (20).

[0118] Once the absorber solution is sufficiently saturated with CO2, it is pumped from the first intermediate tank (11) into the electrodialysis unit (V3). Once the CO2 has been separated from the loaded absorber solution in the electrodialysis unit (20), the regenerated absorber solution can be returned to the CO2 scrubber (10) in two ways:

[0119] Firstly, the CCh-poor or CCh-free absorber solution can be fed into a second intermediate tank (22) (V12), as shown in Fig. 2, and from there to the head of the CO2 scrubber (10) (V11). Accordingly, a second bypass (13) is provided for this purpose, which can bypass the electrodialysis unit (20).

[0120] Secondly, the regenerated sorption solution or the regenerated sorbent can be fed directly from the electrodialysis unit (20) to the first intermediate tank (11) below the CO2 scrubber (10) via a third bypass (V13). A direct connection between the outlet of the electrodialysis unit (20) and the head of the CO2 scrubber (10) is not provided according to the invention, since, due to the design, there may be a height difference of several meters between the head of the CO2 scrubber (10) and the outlet of the electrodialysis unit (20). The regenerated absorber solution would have to be pumped up to the head of the CO2 scrubber (10) and pass through the electrodialysis unit (20), which would have a negative impact on the membrane stability of the dialysis membranes and ion exchange membranes.

[0121] A detailed arrangement of the individual elements as well as the control and sensor technology of the device according to the invention is explained with reference to Fig. 3.

[0122] In a preceding process step, the ambient air to be converted can be preconditioned. For this purpose, the ambient air is introduced into the CO2 scrubber (10) from below (V1). For this purpose, a suction fan is installed at the air outlet of the CO2 scrubber. In this way, ambient air is drawn from bottom to top into the CO2 scrubber.

[0123] The ambient air first flows through a filter to remove dust, pollen, etc. The air is adjusted to the desired temperature and humidity via a droplet eliminator and cooler, which can be a heat exchanger (WO).

[0124] Furthermore, the device according to the invention makes it possible to depict different air parameters for the investigation of different air conditions at different installation locations.

[0125] The temperature is controlled by a sensor (S4) and the air flow by a sensor (S5). The CCh content of the incoming air is monitored by the CCh sensor (S1), and the humidity and pressure are monitored by sensors (S2) and (S3).

[0126] The sorbent in the present embodiment is prepared using arginine and distilled or fully deionized water in concentrations of preferably 1 to 2 mol / L and stored in a first storage tank (30).

[0127] A pump (P1) pumps the fresh absorber solution from the top of the tank into the CO2 scrubber (10) (V2). It is then passed through a heat exchanger (W1) to adjust the absorber solution to a defined temperature. The absorber solution, which is fed to the top of the CO2 scrubber (10), is monitored for its temperature (S7), flow (S8), pressure (S9), and conductivity (S10) parameters.

[0128] The CC>2-poor or CCh-free air leaves the CO2 scrubber (10) at the head (V9), with its humidity parameters being recorded by sensor (S11), the CCh content by sensor (S12), and the temperature by sensor (S13). The operating temperature of the CO2 scrubber (10), for example, can be determined centrally via sensor (S6). Additional temperature sensors (without reference symbols) can be installed at various positions on the CO2 scrubber (10) to monitor the temperature along the entire length of the CO2 scrubber (10).

[0129] The conductivity of the absorber solution is continuously measured by a conductivity sensor (S14) to provide information about the CO2 loading of the sorbent. Alternatively or additionally, the conductivity of the sorbent can be continuously measured in the first intermediate tank (11) (sensor not shown in Fig. 3).

[0130] If the conductivity value of the sorption solution increases during operation of the absorber column (10), the absorber solution has not yet been saturated with CO2, meaning the sorbent can continue to absorb CO2 molecules. In one embodiment of the device according to the invention, a first bypass (12) is therefore provided to circulate the sorbent through the CO2 scrubber (10). For this purpose, the absorber solution, which is not yet fully loaded with CO2 and is detected by the conductivity sensor (S14), is pumped (V10) from the first intermediate tank (11) at the bottom of the CO2 scrubber (10) by means of a pump (P2) to the top of the CO2 scrubber (10), and the absorber solution can trickle through the CO2 scrubber again, where further CCh separation can take place. This process step can be repeated until the conductivity value, measured by the sensor (S14), remains constant.

[0131] Once the absorber solution is sufficiently saturated with CO2, it is pumped (V3) into the diluate chamber (2) of the electrodialysis unit (20) using the pump (P3). The loaded absorber solution is heated to a favorable temperature between 30°C and 50°C using a heat exchanger (W2). A slightly elevated temperature is beneficial for efficient electrodialysis, as it promotes hydrophobic interactions and thus the release of bicarbonate as CO2. The temperature of the CCh-rich absorber solution is controlled by a sensor (S21) before it enters the electrodialysis unit (20). The other parameters of flow, pH, conductivity, and pressure of the CCh-rich absorber solution are monitored by sensors (S22), (S23), (S24), and (S25).

[0132] The conductivity of the sorbent after loading is, for example, in the range between 8 and 12 mS, and the electrodialysis unit (20) can be operated with a slight overpressure between 1 and 2 bar (e.g. 1.6 bar).

[0133] In the electrodialysis unit (20), the CO2 is separated from the CCh-rich absorber solution (V8) and concentrated CO2 is released in gaseous form (V4). The parameters of current, voltage, temperature, and conductivity of the electrodialysis unit are recorded via sensors (S17), (S18), (S19), and (S20).

[0134] After electrodialysis, the at least partially regenerated sorbent can be collected in a second intermediate tank (22) (V12). The fill level of the second intermediate tank can be monitored, for example, via a fill level sensor (S37).

[0135] The CC>2-poor or regenerated absorber solution can be returned to the CO2 scrubber (10) in two ways. Firstly, the absorber solution can be fed into the second intermediate tank (22) (V12) and from there pumped by a pump (P3) to the head of the CO2 scrubber (10) via the bypass (13) (V11).

[0136] The conductivity of the CCh-free or regenerated absorber solution is monitored with a sensor (S36) at the outlet of the electrodialysis unit (20). Depending on the degree of loading of the sorbent, for example, it can be determined whether the absorber solution should be directed to the second intermediate tank (22) or the first intermediate tank (11) (see below).

[0137] Before re-entering (V11) into the CO2 scrubber (10), the absorber solution can pass through the heat exchanger (W1), allowing the absorber solution to be adjusted to a desired temperature.

[0138] The temperature, pressure, flow rate, and conductivity of the CCh-free or regenerated absorber solution are monitored by sensors (S7), (S8), (S9), and (S10) before entering the CO2 scrubber (10). The CCh-free or regenerated absorber solution trickles through the CO2 scrubber (10) along the packing and can again absorb CO2 from the incoming air.

[0139] The second option for feeding the CCh-free or regenerated absorber solution into the CO2 scrubber (10) is the direct feed line (V13) to the first intermediate tank (11), as already mentioned above. A direct connection between the outlet of the electrodialysis unit (20) and the head of the CO2 scrubber (20) is not provided, as the design can result in a height difference of several meters between the head of the CO2 scrubber (10) and the outlet of the electrodialysis unit (20). The regenerated absorber solution would have to be pumped up to the head of the CO2 scrubber (10), which would negatively impact the membrane stability of the dialysis membranes and the ion exchange membranes.

[0140] In addition to the circuit of the absorber solution through the diluate chamber (2) of the electrodialysis unit (20), there is a second circuit in which an organic or inorganic acid (e.g. citric acid) is passed from a storage container (40) through the concentrate chamber (3) of the electrodialysis unit (V6).

[0141] The acid is pumped from the storage container (40) into the concentrate chamber (3) of the electrodialysis unit (20) by a pump (P6). Before entering the electrodialysis unit (20), the pH value, flow rate, and conductivity of the acid are measured using sensors (S31), (S32), and (S33). The acid lowers the pH within the concentrate chamber (3). The pH value is preferably between 3 and 4.

[0142] As a result of the displacement reaction, CO2 is released in gaseous form, and the citric acid is regenerated as a release medium (V8) and returned to the storage vessel (40). The still-moist CO2 is dehumidified using a cold trap (K1). Temperature control is achieved via sensor (S38). The flow rate and the CCh content of the released CO2 are measured by sensors (S34) and (S35). In a final step, the extracted CO2 is compressed and concentrated (V4), e.g., stored in gas cylinders. The volume flow of CO2 is, for example, between 20 and 270 l / h.

[0143] At the CO2 outlet, the quality of the concentrated CO2 can be determined, for example, using a gas chromatograph. Any by-products can be qualitatively and quantitatively detected and, if necessary, separated. In addition to the diluate circuit of the absorber solution (V11, V12, V13) and the concentrate circuit of the exemplary citric acid (V8, V6), the electrodialysis unit (20) has two separate base circuits. Aqueous NaOH solution is pumped into the cathode compartment (1) as catholyte from a third storage tank (50) by means of a pump (P4) in order to remove the hydrogen produced as a by-product. The flow rate and conductivity of the catholyte are monitored by sensors (S26) and (S27). The conductivity of the catholyte is advantageously between 30 and 40 mS / cm. For safety reasons, nitrogen is fed into the catholyte storage tank (50) to prevent the accumulation of hydrogen therein.The nitrogen flow is controlled by a sensor (S28).

[0144] Aqueous NaOH solution is pumped from another anolyte reservoir (60) into the anode chamber (4) by means of a pump (P5) to remove the oxygen produced as a byproduct. The flow and conductivity of the anolyte are monitored by sensors (S29) and (S30). The conductivity of the anolyte is advantageously between 30 and 40 mS / cm.

[0145] List of reference symbols

[0146] 1 cathode chamber

[0147] 2 Diluate chamber

[0148] 3 Concentrate chamber

[0149] 4 Anode chamber

[0150] 5 Bipolar ion exchange membrane (BPM)

[0151] 6 anion exchange membrane (AAM)

[0152] 10 CO2 scrubbers

[0153] 11 first intermediate tank

[0154] 12 first bypass

[0155] 13 second bypass

[0156] 14 third bypass,

[0157] 20 electrodialysis unit

[0158] 22 second intermediate tank

[0159] 30 first storage container

[0160] 40 second storage container

[0161] 50 third storage container

[0162] 60 fourth storage container

[0163] S1; S12; S35 CO2 sensor

[0164] S2; S11 humidity sensor

[0165] S3; S9; S25 pressure sensor

[0166] S4; S6; S7; S13; S19; S21; S38 temperature sensor

[0167] S5; S8; S22; S26; S28; S29; S32; S34 flow sensor

[0168] S10; S14; S20; S24; S27; S30; S33; S3 Conductivity sensor

[0169] S17 sensor for current measurement

[0170] S18 voltage sensor

[0171] S23; S31 pH sensor

[0172] S37 level sensor

[0173] P1 - P6 pump

[0174] WO; W1; W2 heat exchanger

[0175] K1 cold trap

Claims

Patent claims 1. A method for recovering CO2 from a gaseous medium, in particular ambient air, using a CO2 separation device, comprising: a CO2 scrubber (10) with a gas supply and a gas discharge, a sorbent supply at an upper end of the CO2 scrubber and a first intermediate tank (11) for receiving a CO2-enriched sorbent from the CO2 scrubber (10); and an electrodialysis device (20) for separating CO2 into a release medium; the method comprising: Enriching the sorbent with CO2 in the CO2 scrubber (10); Feeding the CO2-enriched sorbent into the first intermediate tank (11); Discharging a first portion of the enriched sorbent from the first intermediate tank (11) into the electrodialysis device (20); and Returning a second portion of the enriched sorbent from the first intermediate tank (11) to the CO2 scrubber (10); wherein the process is designed to be carried out continuously, semi-continuously, or batchwise.

2. The method of claim 1, further comprising: Depleting the CO2-enriched sorbent in the electrodialysis device (20); Discharging a first portion of the depleted sorbent into a second intermediate tank (22); Discharging a second portion of the depleted sorbent into the first intermediate tank (11); Feeding a portion of depleted sorbent from the second intermediate tank (22) to an upper end of the CO2 scrubber (10).

3. Method according to one of the preceding claims, wherein the enrichment and depletion of the sorbent is determined by means of a saturation criterion.

4. A process according to any one of the preceding claims, wherein the sorbent comprises an aqueous solution of at least one amine.

5. A method according to any one of the preceding claims, wherein the sorbent comprises an aqueous solution of at least one agent having a guanidine group.

6. A method according to any one of the preceding claims, wherein the sorbent comprises an aqueous arginine solution.

7. A method according to any one of the preceding claims, wherein the concentration of the sorbent is increased during the enrichment of the sorbent with CO2.

8. A method according to any one of the preceding claims, wherein the release medium comprises an acid.

9. The method of claim 8, wherein the acid comprises citric acid.

10. A device for recovering CO2 from a gaseous medium, comprising: a gas supply and gas removal unit; a sorbent supply unit; a CO2 scrubber (10); and a first intermediate tank (11), which are configured and arranged to carry out the method according to one of claims 1 to 10.

11. The apparatus of claim 10, further comprising: an electrodialysis unit (20); and a second intermediate tank (22).

12. The apparatus of claim 10, further comprising a first bypass (12) which recirculates the sorbent for absorbing CO2 from the first intermediate tank (11) to the CO2 scrubber (10).

13. Device according to one of claims 10 to 12, further comprising a second bypass (13) which returns the regenerated sorbent from the second intermediate tank (22) to the CO2 scrubber (10), the second bypass (13) bypassing the electrodialysis unit (20).

14. Device according to one of claims 10 to 13, further comprising a third bypass (14) which supplies the regenerated sorbent from the electrodialysis unit (20) to the first intermediate tank (11).

15. Device according to one of claims 10 to 14, wherein the device further comprises a sensor suitable for measuring at least one of the parameters: electrical conductivity, temperature, pH, pressure, flow, current and voltage, and humidity.

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