Method for operating an electrochemical plant for gas separation and electrochemical plant

Abstract

The invention relates to a method for operating an electrochemical plant (1) for gas separation, in particular for carbon dioxide separation, in which an ionic liquid (2) enriched with the gas to be separated is supplied to at least one electrochemical cell (3), the gas in the electrochemical cell (3) is separated by changing a process parameter at an electrode (4) and the ionic liquid (2) depleted by the separated gas is discharged from the at least one electrochemical cell (1). Furthermore, the invention relates to an electrochemical system (1) which is suitable for carrying out the inventive method or individual steps of the method.

Description

[0001] The present invention relates to a method for operating an electrochemical plant for gas separation, in particular for carbon dioxide separation. Furthermore, the invention relates to an electrochemical plant for gas separation that is suitable for carrying out the method or that can be operated according to the method. State of the art

[0002] Electrochemical cells used for carbon dioxide capture have two electrodes that are electrically connected and separated by a separator. Both the separator and the electrodes are saturated with an ionic liquid, which ensures charge balance within the electrochemical cell. At the first electrode, located on the cathode side, a gas, such as carbon dioxide, is captured from a gas stream through an electrochemical process. Gas capture is initiated by a change in temperature, pressure, or electrical voltage. It is reversible, meaning that changing the temperature or pressure back to the initial state, or removing or reversing the voltage, causes a controlled release of the previously captured gas. A second electrode, located on the anode side, acts as an electron donor and provides the electrons necessary for the capture reaction.

[0003] To increase efficiency and the amount of bound gas, a large number of electrochemical cells are stacked and electrically connected in practical applications. Within an electrochemical cell are supply channels through which exhaust gas is fed into the cell, and especially into the first electrode on the cathode side, as input gas, and the processed exhaust gas is removed as output gas. The supplied gas stream typically originates from combustion processes or other production processes that generate gas mixtures as exhaust gas or byproducts. These gas mixtures often contain carbon dioxide.

[0004] In electrochemical cells, this gas stream comes into contact with the ionic liquid surrounding the electrodes. The ionic liquid is able to dissolve the gas to be captured from the gas stream. The dissolved gas diffuses through the ionic liquid to the cathode-side electrode, where it is then captured by an electrochemical reaction. The resulting concentration gradient within the ionic liquid leads to a constant diffusion current of dissolved gas to the cathode-side electrode until it is saturated with the gas to be captured. To extract the captured gas, the depleted exhaust gas is removed from the electrochemical cell by means of a vacuum, so that the captured gas can be released as pure as possible and in a high concentration.

[0005] One of the disadvantages of this process is the complex and, in particular, time-consuming vacuuming of the electrochemical cell. This increases the process time and thus reduces the throughput of the electrochemical cell. Another disadvantage is that the concentration gradient within the ionic liquid during gas phase deposition at the cathode-side electrode leads to a low gas concentration of the ionic liquid in contact with the electrode. This, in turn, reduces the efficiency of the electrochemical deposition reaction and increases the process time. Furthermore, the exhaust gas supplied to the electrochemical cells, since it originates from production processes, contains a high degree of impurities, such as dirt particles, soot, water, or other combustion products.These are absorbed by the ionic liquid and partially accumulate on the electrodes, further reducing the efficiency of the electrochemical deposition reactions.

[0006] The present invention is concerned with the objective of solving the disadvantages of the prior art described above and increasing the efficiency of the electrochemical plant.

[0007] To solve the problem, a method for operating an electrochemical gas separation plant with the features of claim 1 is proposed. Furthermore, an electrochemical plant suitable for carrying out the method or partial steps thereof is proposed. Advantageous embodiments of the invention are described in the respective dependent claims. Disclosure of the invention

[0008] Method for operating an electrochemical plant for gas separation, in particular for carbon dioxide separation, in which an ionic liquid enriched with the gas to be separated is supplied to at least one electrochemical cell, the gas in the electrochemical cell is separated by changing a process parameter at an electrode and the ionic liquid, depleted by the separated gas, is discharged from the at least one electrochemical cell.

[0009] By enriching the ionic liquid with the gas to be separated outside the electrochemical cell, the gas to be separated is supplied to the electrochemical cell via the ionic liquid. This eliminates the need to remove any gas from the cell by vacuuming after the gas has been separated. The complex vacuuming step is thus eliminated, simplifying and accelerating the gas separation process. Consequently, the efficiency of the gas separation increases.

[0010] Since the gas to be separated is dissolved in the ionic liquid and is supplied to the electrochemical cell along with the ionic liquid, mass transport into the electrochemical cell is improved. The flow of the ionic liquid through the electrochemical cell creates turbulence, which leads to a homogeneous mixing of the dissolved gas in the liquid and thus improves the mass transport of the gas to be separated to the electrode of the electrochemical cell. This leads to an acceleration of the electrochemical reaction.

[0011] The flow of the ionic liquid and the dissolved gas through the electrochemical cell also prevents the formation of a concentration gradient within the ionic liquid. This is because the ionic liquid constantly supplies the electrochemical cell with the gas to be deposited. Since the efficiency of the electrochemical reactions increases with the gas concentration in the ionic liquid, the efficiency of the electrochemical cell also increases. This is particularly advantageous at high charging rates of the electrochemical cells, as a high diffusion resistance then develops between the gas already deposited and the gas dissolved in the ionic liquid. This resistance is compensated for by the increased gas concentration in the ionic liquid.

[0012] Preferably, the depleted ionic liquid is removed via a circuit, enriched with the gas to be separated, and fed back to the at least one electrochemical cell. This means that the ionic liquid is recirculated, thus saving ionic liquid. Furthermore, the recirculation and reuse of the ionic liquid eliminates the need for a storage container for the ionic liquid.

[0013] Preferably, the ionic liquid is introduced into a chamber for enrichment with the gas to be separated, through which a gas mixture containing the gas to be separated is passed. The enrichment of the ionic liquid with the gas to be separated thus takes place in a chamber and therefore always outside the electrochemical cell. The gas mixture containing the gas to be separated can be controlled as it enters and exits the chamber. The ionic liquid is preferably sprayed into the chamber. The ionic liquid is thus present in the chamber as fine droplets or a liquid mist, which greatly increases the surface area of ​​the ionic liquid, enabling it to absorb the gas to be separated more effectively. This promotes the enrichment of the ionic liquid with the gas to be separated.

[0014] Preferably, the enriched ionic liquid is supplied to the electrochemical cell using a pump unit. The pump unit provides a simple and therefore cost-effective way to supply the ionic liquid to the electrochemical cell. Furthermore, the flow rate of the ionic liquid through the electrochemical cell can be adjusted using the pump unit.

[0015] Advantageously, the enriched ionic liquid is passed upstream of the at least one electrochemical cell through at least one filter unit. The filter unit removes unwanted liquids and / or solids from the ionic liquid, preventing them from entering the electrochemical cell. These unwanted liquids and / or solids could be, for example, byproducts from the gas mixture or exhaust gas containing the gas to be separated. If these byproducts enter the electrochemical cell, they can accumulate on the cell's electrodes and negatively affect the electrochemical reaction within the cell.In conventional gas separation processes, the ionic liquid present in the electrochemical cell is neither exchanged nor cleaned, which can lead to deposits of byproducts and thus to premature aging of the electrodes and a reduction in the efficiency of gas separation in the electrochemical cell. These undesirable effects can be avoided through recirculation and prior cleaning of the ionic liquid. The filter unit therefore results in a long service life and increased efficiency of the electrochemical cell.

[0016] In a further development of the invention, it is proposed that by changing the process parameter again, gas previously deposited at the electrode is released and discharged from the electrochemical cell via a separate outlet. This measure is carried out particularly when the corresponding electrode of the electrochemical cell is saturated in order to regenerate it. Furthermore, the previously deposited gas can thus be utilized. The quality of the released gas is an important characteristic in this context. Controlled release allows the purity and thus the quality of the previously deposited gas to be increased.

[0017] Preferably, the supply of the enriched ionic liquid to the electrochemical cell is temporarily interrupted by closing a shut-off valve integrated into the circuit. This method of interrupting the supply of the ionic liquid is particularly relevant for maintenance and / or cleaning processes, as well as for the release of previously deposited gas. If the ionic liquid were to continue to be supplied to the electrochemical cell during the release of the previously deposited gas, the cell would become re-enriched with the gas and the gas would be released uncontrollably. In this case, less of the previously deposited gas would be released. Therefore, preferably, the supply of the enriched ionic liquid to the electrochemical cell is temporarily interrupted during the release of the gas previously deposited at the electrode by closing a shut-off valve integrated into the circuit.

[0018] Furthermore, for continuous gas separation, several electrochemical cells are preferably operated sequentially, with a time offset, so that gas is separated from the enriched ionic liquid in at least one electrochemical cell and bound to the electrode. This increases process stability and avoids dead times during the operation of the electrochemical cells. The amount of gas that can be separated per unit time in an electrochemical cell fluctuates during operation or during a separation cycle. This amount is highest at the beginning of the separation process, as there are no diffusion resistances yet. During the separation of the gas phase, the amount of bound gas from the electrochemical cell decreases per unit time. For this reason, staggered operation of several electrochemical cells leads to higher process stability, as an average separation rate is established.Furthermore, no gas can be captured from the exhaust gas temporarily during the release of the captured gas. However, ensuring a minimum amount of captured gas from the exhaust gas is crucial for many applications. The staggered operation of the electrochemical cells prevents all cells from being in the gas release phase simultaneously, thus ensuring gas capture by at least one electrochemical cell at all times.

[0019] Furthermore, an electrochemical plant for gas separation, in particular for carbon dioxide separation, is proposed. This plant features - at least one electrochemical cell, - a circuit through which an ionic liquid can be supplied to at least one electrochemical cell, as well as - a chamber that is integrated into the circuit upstream of at least one electrochemical cell and has a gas inlet and a gas outlet for a gas mixture containing the gas to be separated.

[0020] The proposed electrochemical system is particularly well-suited for carrying out the proposed process, thus achieving the same advantages. In particular, the proposed electrochemical system eliminates a process step, thereby reducing the gas separation process time. Furthermore, the mass transfer of the bound gas within the ionic liquid can be improved. Additionally, the formation of a concentration gradient within the ionic liquid is avoided. This ensures a continuous supply of an ionic liquid with a high concentration of bound gas to the electrode, thereby increasing the efficiency of the electrochemical reaction and the electrochemical cell.

[0021] Preferably, the chamber includes a spray unit for introducing the ionic liquid. The spray unit allows the ionic liquid to be introduced into the chamber in the form of very fine droplets or as a liquid mist. This increases the surface area and thus the absorption capacity of the ionic liquid. This means that more of the gas to be separated can be absorbed and supplied to the electrochemical cell.

[0022] Preferably, a pump unit is integrated into the circuit. The pump unit provides a widely available, simple, and therefore cost-effective way to supply the ionic liquid to the electrochemical cell. It also allows the flow rate of the ionic liquid through the electrochemical cell to be adjusted. Preferably, the pump unit is integrated into the circuit between the chamber and the at least one electrochemical cell.

[0023] Advantageously, a filter unit is integrated into the circuit. The filter unit prevents unwanted liquids and / or solids from entering the electrochemical cell along with the ionic fluid. Preferably, the filter unit is therefore integrated between the chamber and the at least one electrochemical cell.

[0024] In an advantageous embodiment of the invention, at least one shut-off valve is integrated into the circuit. This allows the inflow of ionic liquid into the electrochemical cell to be stopped, thereby facilitating maintenance and / or cleaning. Furthermore, the inflow of ionic liquid can be stopped during the release of previously separated gas to prevent the released gas from redissolving in the ionic liquid. Preferably, a first shut-off valve is integrated into the circuit upstream and a second shut-off valve downstream of the at least one electrochemical cell. The electrochemical cell can thus be completely isolated from the circuit.

[0025] The invention and its advantages are explained below with reference to the accompanying drawing / figure, which shows a schematic representation of a preferred embodiment of an electrochemical system according to the invention. Detailed description of the drawing

[0026] The figure shows an electrochemical system 1 for gas separation. This system comprises an electrochemical cell 3 and a circuit 5 through which an ionic liquid 2 can be supplied to the electrochemical cell 3. The ionic liquid 2 supplied to the electrochemical cell 3 flows around a first and a second electrode 4 of the electrochemical cell 3, which are separated from each other by a separator 14. The first electrode 4, on the cathode side, binds the gas to be separated, for example, carbon dioxide. The second electrode 4, on the anode side, provides electrons for this purpose.

[0027] A chamber 6 is integrated into circuit 5, through which a gas mixture containing the gas to be separated is passed during operation of the system 1. For this purpose, chamber 6 has a gas inlet 11 and a gas outlet 12. Simultaneously, chamber 6 has a spray unit 13 by means of which the ionic liquid 2 can be sprayed into chamber 6. The ionic liquid 2 dissolves the gas to be separated from the gas mixture and is thus enriched with the gas. With the aid of a pump unit 7, which is integrated into circuit 5 between chamber 6 and the electrochemical cell 3, the ionic liquid 2 enriched with the gas to be separated is supplied to the electrochemical cell 3. In doing so, it passes through a filter unit 8 integrated into circuit 5 upstream of the electrochemical cell 3, which separates unwanted liquids and / or solids from the ionic liquid 2 so that they do not enter the electrochemical cell 3.In electrochemical cell 3, the gas dissolved in the ionic liquid 2 is deposited or bound at the cathode-side electrode 4 of electrochemical cell 3. The depleted ionic liquid 2 is then returned to chamber 6 via circuit 5 to be re-enriched with gas.

[0028] The described process is repeated until the first electrode 4 on the cathode side is so saturated with the gas to be separated that saturation occurs. Once this is achieved, the electrochemical cell 3 is disconnected from the circuit 5 by closing a first shut-off valve 10 located upstream of the electrochemical cell 3 and a second shut-off valve 10 located downstream of the electrochemical cell 3. The gas bound in the cathode-side electrode 4 is then released by reversing the polarity of an electrical voltage applied to both electrodes 4 and discharged as pure, and in particular highly concentrated, gas from the electrochemical cell 3 through an outlet 9.

[0029] To restart the gas separation process, the shut-off valves 10 are reopened and ionic liquid 2 enriched with gas is supplied to the electrochemical cell 3 via the circuit 5.

[0030] The present figure shows an electrochemical system 1 with only one electrochemical cell 3. The system 1 can also have several electrochemical cells 3 to increase performance.

Claims

[1] Method for operating an electrochemical plant (1) for gas separation, in particular for carbon dioxide separation, in which an ionic liquid (2) enriched with the gas to be separated is supplied to at least one electrochemical cell (3), the gas in the electrochemical cell (3) is separated by changing a process parameter at an electrode (4) and the ionic liquid (2) depleted by the separated gas is discharged from the at least one electrochemical cell (3). [2] Method according to claim 1, characterized by , that the depleted ionic liquid (2) is removed via a circuit (5), enriched with the gas to be separated and fed back to the at least one electrochemical cell (3). [3] Method according to claim 1 or 2, characterized by, that the ionic liquid (2) is introduced into a chamber (6) for enrichment with the gas to be separated, through which a gas mixture containing the gas to be separated is passed, preferably the ionic liquid (2) being sprayed into the chamber. [4] Method according to any one of the preceding claims, characterized by , that the enriched ionic liquid (2) is supplied to the electrochemical cell (3) by means of a pump unit (7). [5] Method according to any one of the preceding claims, characterized by , that the enriched ionic liquid (2) is passed upstream of the at least one electrochemical cell (3) through at least one filter unit (8). [6] Method according to any one of the preceding claims, characterized by, that by changing the process parameter again, gas that was previously deposited at the electrode (4) is released again and discharged from the electrochemical cell (3) via a separate outlet (9). [7] Method according to any of the preceding claims, characterized by , that the supply of the enriched ionic liquid (2) to the electrochemical cell (3) is temporarily interrupted by closing a shut-off valve (10) integrated into the circuit (5), preferably during the release of the gas previously deposited at the electrode (4). [8] Method according to any one of the preceding claims, characterized by , that for continuous gas separation several electrochemical cells (3) are operated at different times, in particular successively, so that in at least one electrochemical cell (3) gas is separated from the enriched ionic liquid (2) and bound to the electrode (4). [9] Electrochemical plant (1) for gas separation, in particular for carbon dioxide separation, comprising - at least one electrochemical cell (3), - a circuit (5) through which an ionic liquid can be supplied to the at least one electrochemical cell (3), as well as - a chamber (6) which is integrated into the circuit upstream of the at least one electrochemical cell (3) and has a gas inlet (11) and a gas outlet (12) for a gas mixture containing the gas to be separated. [10] Plant according to claim 9, characterized by , that the chamber (6) has a spray unit (13) for introducing the ionic liquid into the chamber (6). [11] Plant according to claim 9 or 10, characterized by , that a pump unit (7) is integrated into the circuit (6), preferably between the chamber (6) and the at least one electrochemical cell (3). [12] Plant according to any one of claims 9 to 11, characterized by , that a filter unit (8) is integrated into the circuit (6), preferably between the chamber (6) and the at least one electrochemical cell (3). [13] Plant according to any one of claims 9 to 12, characterized by , that at least one shut-off valve (10) is integrated into the circuit (6), preferably a first shut-off valve (10) upstream and a second shut-off valve (10) downstream of the at least one electrochemical cell (3).

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