Method and apparatus for electrochemically generating oxygen

Abstract

The present invention provides a method for manufacturing an oxygen-containing gas product (10), in which an aqueous feedstock (1) is electrolyzed (E) to obtain an oxygen-rich and hydrogen-containing anode feed gas (2) and an oxygen-depleted and hydrogen-rich cathode feed gas (14). The anode feed gas is at least partially subjected to a catalytic reaction (C) for hydrogen to form water to obtain a first mixture (4) with low hydrogen content. A first portion of the first mixture (4) is recycled to the anode feed gas (2) downstream of the electrolysis (E) and upstream of the catalytic reaction (C), and at least a second portion of the first mixture is used to form the oxygen-containing gas product. In addition, an apparatus for implementing this method is also provided.

Description

[0001] The present invention relates to a method and an apparatus for electrochemically producing oxygen. Background Art

[0002] Generally, there are various options for providing oxygen as a gas. Widely used options include, for example, air separation, in which air is first liquefied and then fractionated.

[0003] Electrochemical reactions of different oxygen-containing compounds, such as water or carbon dioxide, are also known and provide oxygen. However, in most cases, the oxygen formed cannot be utilized as a product, but escapes from the process and is discarded.

[0004] Depending on the specific application, extremely high requirements may be placed on the purity of the oxygen. Therefore, it is necessary to separate as many impurities as possible from the oxygen. In addition, there are usually the following problems in the process of handling oxygen: the equipment components exposed to a higher oxygen concentration must be implemented to be corrosion-resistant.

[0005] In addition, in a gas mixture with a higher oxygen concentration, depending on the specific composition of the components, an explosive mixture that poses a safety risk may be formed. This is especially the case when the oxygen comes from an electrolysis process that forms hydrogen.

[0006] Although hydrogen is usually formed on the cathode side during the electrolysis process; due to the high mobility of small hydrogen molecules, it is impossible to prevent the oxygen formed on the anode side of the electrolysis from being contaminated by hydrogen that passes through the membrane separating the anode side and the cathode side, such as a proton exchange membrane (PEM), an anion exchange membrane (AEM), or a solid oxide high-temperature membrane (SOEC) of a solid oxide electrolysis cell.

[0007] In principle, the following reactions occur during electrolysis.

[0008] For the case of PEM electrolysis :

[0009] At the anode: H2O → 1 / 2O2 + 2H + + 2e -

[0010] At the cathode: 2e - + 2H + → H2

[0011] For the case of AEM electrolysis :

[0012] At the anode: 2OH - → 1 / 2O2 + 2H2O + 2e -

[0013] At the cathode: 2e - + 2H2O → H2 + 2OH -

[0014] For the case of SOEC electrolysis :

[0015] At the anode: 2O 2- →O2 + 4e -

[0016] At the cathode: H2O + 2e - →H2 + O 2-

[0017] As described above, other oxygen-containing compounds can also be electrolyzed to obtain oxygen. If the isolate used is not anhydrous, the above reactions may occur as side reactions. Therefore, the formation of hydrogen must be taken into account in any case.

[0018] Before describing the present invention in detail, it is first necessary to explain some terms used herein.

[0019] Unless otherwise clearly stated, the composition, concentration, and ratio of the mixture given within the scope of this application relate to the volume composition, concentration, or volume ratio of the dry, i.e., anhydrous, mixture.

[0020] In the language of this patent application, if the proportion of one or more components of a gas mixture exceeds 50%, 60%, 70%, 80%, 90%, 95%, 98%, 99%, 99.9%, or 99.99%, the gas mixture is rich in this one or more components. In the case of multiple components, the proportion refers to the sum of the respective proportions.

[0021] Correspondingly, if the mixture is not rich in one or more components, i.e., the proportion of this component in the mixture is less than 50%, 40%, 30%, 20%, 10%, 5%, 2%, 1%, 0.1%, or 0.01%, the mixture lacks this one or more components.

[0022] In the language used herein, a gas or mixture that does not contain one or more components means that it is extremely lacking in this component, and its proportion is less than 1000 ppm, 100 ppm, 10 ppm, 1 ppm, 100 ppb, 10 ppb, or 1 ppb. The proportion of the component that the gas or mixture does not contain is especially less than the detection limit of this component.

[0023] A gas or mixture rich in one or more components means a gas or mixture having a concentration of one or more components higher than that of the initial gas or initial mixture. Compared with the corresponding initial gas, a gas rich in a certain component especially has at least 1.1, 1.3, 2, 3, 10, 30, 100, 300, or 1000 times the proportion of this component.

[0024] Accordingly, compared with the corresponding initial gas, a gas with a low content of a certain component especially has a proportion of this component that is at most 0.001, 0.003, 0.01, 0.03, 0.1, 0.3, 0.5, or 0.9 times.

[0025] If a part of a gas or a mixture is mentioned hereinafter, it may mean using a volume ratio of the gas or the mixture, which is at most 100% of the total standard volume of the original gas or the original mixture, and the composition of the gas or the mixture is the same as that of the original gas or the original mixture, or using a gas or a mixture formed only by certain components of the original gas or the original mixture. That is, this part of the gas or the mixture has the same or different composition from the original gas or the original mixture.

[0026] In the language used herein, an explosion means a slight explosion, bursting, or detonation.

[0027] The object of the present invention is to release oxygen obtained in the electrolysis reaction from hydrogen through catalytic oxidation and prevent excessive temperature rise during the catalytic reaction. Summary of the Invention

[0028] The solution of the present invention to achieve the above object is a method and an apparatus for electrochemically producing oxygen having the characteristics of the present invention. The technical solution is the subject of the following description.

[0029] Oxygen in the hydrogen-rich gas (cathode feed gas) generated by electrolysis can react with hydrogen to form water and be removed from the hydrogen-rich gas together with the water that has not reacted during electrolysis. Within the scope of the present invention, this conventional technique for removing oxygen is used to remove hydrogen impurities in the oxygen-rich gas (anode feed gas) formed on the anode. Different from the conventional oxygen content in the typical cathode feed gas, the hydrogen content in the anode feed gas is usually higher because the cathode side usually operates at a greater pressure.

[0030] The solution of the present invention to achieve the above object is that, downstream of the electrolysis unit, the anode feed gas containing oxygen and part of hydrogen obtained from the raw materials in the electrolysis unit is at least partially subjected to a catalytic reaction of hydrogen and oxygen to form water in a manner to obtain a low-hydrogen intermediate mixture, wherein a first part of the intermediate mixture is recycled to the anode feed gas downstream of the electrolysis and upstream of the catalytic reaction. A second part of the low-hydrogen intermediate mixture is used to form an oxygen-containing gas product. As described above, the "first part of the intermediate mixture" is the pure quantity ratio of the intermediate mixture, but it can also refer to the ratio containing other substances obtained in subsequent steps. The same applies to the "second part of the intermediate mixture".

[0031] By applying the measures proposed in the present invention, the hydrogen concentration in the corresponding equipment components is reduced. In particular, the hydrogen concentration is reduced in such a way that the adiabatic temperature rise in the catalytic reaction is limited to a certain expected value. The advantage is that ordinary adiabatic reactors with lower costs can be applied. Thus, there is no need to use an isothermal reactor solution at a higher cost.

[0032] According to the present invention, by recycling a first portion of a low-hydrogen (especially hydrogen-free or hydrogen-lean) intermediate mixture downstream of the electrolysis to the anode feed gas, even when the hydrogen concentration in the anode feed gas is relatively high, the hydrogen content there can still be diluted to an unproblematic value, enabling the oxygen in the anode feed gas to be purified and utilized. Downstream of the hydrogen removal, the hydrogen is already present at an unproblematic concentration due to being removed accordingly.

[0033] To ensure that an undesired high hydrogen concentration is not reached, it is particularly advantageous to provide sensors at specific locations in the manufacturing equipment, such as at the outlet of the electrolysis unit or in the catalytic reaction unit. These sensors can, for example, directly detect the hydrogen concentration and, in the case of exceeding a predetermined threshold, according to the present invention, dilute the anode feed gas with the first portion of the low-hydrogen intermediate mixture, for example, by opening a valve or by increasing the amount of the recycled low-hydrogen intermediate mixture.

[0034] Another advantageous technical solution of such sensors enables temperature monitoring, whereby the catalytic reaction can be cut off in a controlled or regulated manner, or the anode feed gas can be diluted again in a controlled or regulated manner. The advantage is that the catalytic reaction only starts when an undesired temperature rise is excluded, thus preventing excessive thermal load on the catalyst, which may cause damage or destruction of the catalyst.

[0035] Particularly advantageously, in the said method, the threshold value of the maximum hydrogen concentration can be changed according to other measured parameters, such as the pressure and / or temperature in the relevant equipment components, so as to achieve an efficient method implementation in the following aspects: recycling the hydrogen-free or hydrogen-lean gas to the anode feed gas only to the extent required, thereby, for example, saving the compression energy downstream of the catalytic reaction.

[0036] In all technical variants of the method and equipment of the present invention, it is particularly advantageous to use only the gas flow originally from the electrolysis for reducing the hydrogen concentration. This can prevent impurities from non-processes that are difficult to remove from the product gas, such as nitrogen or argon, from mixing into the process.

[0037] In one embodiment of the method, advantageously, the intermediate mixture is at least partially condensed in such a way as to obtain a fraction of the intermediate mixture with a lower water content and a condensate rich in water. The fraction of the intermediate mixture or a part thereof can be dried in such a way as to obtain an oxygen-containing gas product and a residual gas low in oxygen and rich in water, and the residual gas is partially or completely recycled in the aforesaid manner. In this embodiment, the residual gas or the recycled part thereof is the first part of the intermediate mixture mentioned several times, and the second part is provided in the form of an oxygen-containing gas product. The advantage is that water, which may cause interference in the gas product, does not enter the gas product.

[0038] In another advantageous embodiment of the method, the first part of the intermediate mixture recycled to the anode feed gas is formed by at least a part of the intermediate mixture and / or the fraction of the intermediate mixture and / or the residual gas and / or the gas product. The advantage is that only the gases already present in the process are used to reduce the hydrogen concentration. This prevents interfering impurities formed by the gases, which may be difficult to remove from the gas product, from mixing into the process.

[0039] Advantageously, the drying includes at least one temperature swing adsorption (TSA), because this temperature swing adsorption can be combined with the remaining method steps particularly efficiently. However, other forms of drying, such as pressure swing adsorption (PSA) or membrane methods, can also be applied.

[0040] Advantageously, upstream of the drying to be carried out subsequently, the fraction of the intermediate mixture remaining after the condensation described above is compressed and further condensed in such a way as to obtain another fraction of the intermediate mixture and another condensate, wherein at least a part of the other fraction of the intermediate mixture is sent for drying. In this way, a pressure favorable for drying can be set, and dehydration is carried out before drying. Thus, the size of the drying unit can be designed to be smaller.

[0041] In particular, each of the aforesaid condensates or both condensates together (if any) can be partially or completely recycled with the feedstock to carry out electrolysis. In this way, the method according to this embodiment can be carried out in a particularly material-saving manner.

[0042] In an advantageous embodiment, one or more process parameters including the hydrogen concentration and / or the gas temperature and / or the gas pressure are detected downstream of the electrolysis and / or in the catalytic reaction. In the case where one or more of these process parameters exceed a preset threshold value, the first part of the intermediate mixture is recycled to the anode feed gas. Particularly advantageously, the recycling amount of the intermediate mixture can also be continuously adjusted based on one or more of these process parameters. Thereby, on the one hand, it can be ensured that no potential dangerous situations occur during the implementation of the method, and on the other hand, an excessive recycling flow is prevented from causing unnecessary overloading of the equipment.

[0043] Furthermore, advantageously, in the case of exceeding a predetermined limit value of this or these process parameters, in particular the temperature increase in the catalytic reaction, the anode feed gas can be discharged from the process, in particular blown out. This can protect the equipment in cases where the reduction of the hydrogen concentration is not sufficient to limit the heat generation.

[0044] It can also be advantageous to carry out the catalytic reaction at the adsorption pressure at which drying is also carried out and / or to carry out the electrolysis at the pressure at which drying is also carried out, and / or to increase the pressure of the cycle to the pressure level of the catalytic reaction, because in this way the entire process is carried out substantially at a uniform pressure level.

[0045] Advantageously, the anode feed gas or feed oxygen can be heated by heat exchange with the first mixture before the catalytic reaction to save process heat. During this process, the water contained in the product stream can also be at least partially condensed, which also saves energy during condensation.

[0046] According to the invention, there is provided an apparatus for manufacturing an oxygen-containing gas product with an electrolysis unit, the apparatus being adapted to electrolyze a water-containing feedstock in such a way as to obtain an anode feed gas rich in oxygen and hydrogen and a cathode feed gas poor in oxygen and rich in hydrogen. A catalytic reaction unit is provided, which is adapted to at least partially carry out a catalytic reaction for generating water from hydrogen on the anode feed gas in such a way as to obtain a low-hydrogen intermediate mixture. There are a number of components adapted to recycle a first part of the intermediate mixture to the anode feed gas downstream of the electrolysis and upstream of the catalytic reaction. The apparatus also has a number of components adapted to form an oxygen-containing gas product with a second part of the intermediate mixture.

[0047] Advantageously, the apparatus is also provided with a number of components adapted to carry out the method according to any one of the above advantageous technical solutions. Description of the Drawings

[0048] Other advantages, embodiments and other details of the invention will be described in detail below with reference to the drawings, in which

[0049] Figure 1 a preferred embodiment of the method of the invention is shown in the form of a schematic block diagram, and

[0050] Figure 2 another preferred embodiment of the method of the invention is shown in the form of a schematic block diagram, the method in particular using high-pressure electrolysis.

[0051] In the Figure 1 illustrated embodiment of the invention, a feedstock 1 consisting mostly of water is electrolyzed E. During this process, a cathode feed gas 14 poor in oxygen and rich in hydrogen and an anode feed gas 2 rich in oxygen and hydrogen are formed.

[0052] At least a part of the anode feed gas is used as feedstock 3 for the catalytic reaction C, in which an intermediate mixture 4 that is low in hydrogen relative to the anode feed gas is formed. In the catalytic reaction C, hydrogen contained in the anode feed gas 2 in a certain proportion, for example, in a proportion of 0.1% to 2%, reacts with a part of the oxygen that constitutes the main part of the anode feed gas 2 to form water. Thereby, the hydrogen concentration downstream of the catalytic reaction C is effectively reduced.

[0053] In the embodiment shown here, a first condensation K1 is carried out on the intermediate mixture 4 leaving the catalytic reaction C, in which an intermediate mixture fraction 5 with a lower water content relative to the intermediate mixture 4 and a water-rich condensate 6 are formed. The intermediate mixture fraction 5 is compressed to the adsorption pressure level and cooled. After cooling, a further condensation K2 is carried out on the compressed intermediate mixture fraction 5, in which another intermediate mixture fraction 8 with a lower water content relative to the intermediate mixture fraction 5 and another condensate 9 are formed. The condensates 6, 9 are at least partially recycled together with the feedstock 1 to carry out the electrolysis E.

[0054] In Figure 1 the embodiment shown, drying T in the form of temperature swing adsorption (TSA) is carried out on this another intermediate mixture fraction 8, in which, in the adsorption stage, the residual water contained in the dried feedstock is adsorbed on the adsorbent. The oxygen contained in this another intermediate mixture fraction 8 is basically not adsorbed on the adsorbent and is converted into a gas product 10. In the desorption stage, the outlet towards the gas product 10 is closed, and the temperature of the TSA device or the drying T is increased by flowing a warm purge gas through it or by directly heating the adsorber. The molecules previously adsorbed on the adsorbent, especially water molecules, are thereby desorbed and can be transferred to the residual gases 11, 12, for example, using a purge gas (not shown) formed by the product stream 10. If most of the adsorbent is free of adsorbed water and other impurities, the temperature will decrease again, and another adsorption stage will start.

[0055] Advantageously, multiple TSA devices work in parallel and alternately, such that at any point in time at least one of the multiple TSA devices is in the adsorption stage. This can provide a continuous gas product stream 10.

[0056] In particular, it can be ensured that the vast majority of the adsorbed substances are re-desorbed, specifically by maintaining a relatively high temperature for a preset time, or by carrying out a concentration measurement in the residual gases 11, 12 downstream of the TSA device or the drying T. In the case where a time span is preset, the method can be advantageously controlled such that multiple TSA devices work alternately in the drying T, and the advantage of the concentration-related control is that the time of the desorption stage can be arranged as needed without being unnecessarily prolonged. This can improve the efficiency of the entire method.

[0057] At least a portion of the residual gas 12 can be recycled upstream of the catalytic reaction C to the anode feed gas or feedstock 3 to adjust the temperature rise of the catalytic reaction by reducing the hydrogen concentration. For the same purpose, a portion of another intermediate product fraction 8 can also be recycled upstream of the drying T as a control stream 13 to the anode feed gas 2 or feedstock 3.

[0058] Optionally, another portion of the residual gas 11 can be recycled downstream of the catalytic reaction C to the intermediate mixture 4 (not shown) or the intermediate mixture fraction 5. Thus, even if not used for temperature regulation in the catalytic reaction C, the product used as a purge gas can still be recycled to the process to increase the process yield.

[0059] In Figure 1 the illustrated embodiment, a series of sensors are integrated in the device to call information about the status of each method step, thereby regulating the temperature rise in the catalytic reaction C by adjusting the recycle streams 12 or 13. A hydrogen sensor detects the hydrogen concentration in different gas streams, such as the anode feed gas 2. Of course, the hydrogen concentration can also be detected at other locations (not shown), especially in the gas stream downstream of the catalytic reaction C to quantify the degree of reaction.

[0060] The temperature sensor 16 can also detect the temperature in the catalytic reaction C. With this information, it is possible to advantageously reduce or stop the supply of the anode feed gas or feedstock 3 to the catalytic reaction C in the case where the temperature rises sharply due to the catalytic reaction and there is a risk of catalyst degradation. In the case of such a temperature rise in the catalytic reaction, the anode feed gas can be intermittently discharged from the process until the temperature stabilizes again at an acceptable level for the process. However, the temperature detected by the temperature sensor 16 can also be used as a regulating variable for adjusting the control stream 13.

[0061] Figure 2 A preferred embodiment of the method according to the invention is schematically shown. In this embodiment, the electrolysis E is implemented in the form of high-pressure electrolysis, where the anode feed gas 2 is already at the adsorption pressure level. This advantageously allows the compression downstream of the catalytic reaction C to be omitted, and thus there is no need to implement a further condensation K2. In this case, only one compressor is required to recycle the residual gas in the drying T and a portion of the gas stream 8 used as the control stream 17 upstream of the drying. To eliminate the need for a separate compressor for the control stream 17, the residual gas in the drying T can be recycled together with the control stream 17 by the compressor, and downstream of the compressor, it is fed upstream (stream 12) or downstream (stream 11) of the catalytic reaction C according to the temperature regulation. Other aspects of the method implementation are the same as those described with reference to Figure 1 the method.

Claims

1. A method for producing an oxygen-containing gas product (10), wherein an aqueous feedstock (1) is electrolyzed (E) to obtain an oxygen-rich and hydrogen-containing anode feed gas (2) and an oxygen-depleted and hydrogen-rich cathode feed gas (14), characterized in that, The catalytic reaction (C) of hydrogen to form water is at least partially carried out on the anode feed gas (2) to obtain a low-hydrogen intermediate mixture (4). A first portion of the intermediate mixture (4) is recycled to the anode feed gas (2) downstream of the electrolysis (E) and upstream of the catalytic reaction (C), and at least a second portion of the intermediate mixture (4) is used to form the oxygen-containing gas product.

2. The method according to claim 1, wherein at least a part of the intermediate mixture (4) is condensed (K1) to obtain an intermediate mixture fraction (5) with a lower water content and a water-rich condensate (6).

3. The method according to claim 2, wherein at least a part of the intermediate mixture fraction (5) is dried (T) to obtain the oxygen-containing gas product (10) and a low-oxygen and water-rich residual gas (12).

4. The method according to any one of the above claims, wherein at least a certain proportion of the intermediate mixture (4) and / or the intermediate mixture fraction (5) and / or the residual gas (12) and / or the gas product (10) is used to form the first portion of the intermediate mixture (4) recycled to the anode feed gas (2).

5. The method according to any one of claims 1-3, wherein the first portion of the intermediate mixture is recycled to the anode feed gas (2) or the anode-side feed (1) in an amount such that the volume fraction concentration of hydrogen in the anode feed gas (2) is at most 0.1%, 0.2%, 0.3%, 0.5%, 1% or 2% downstream of the recycling.

6. The method according to claim 3, wherein the drying includes temperature swing adsorption.

7. The method according to claim 3 or 6, wherein the intermediate mixture fraction (5) is compressed upstream of the drying (T) and further condensed (K2) to obtain another intermediate mixture fraction (8) and another condensate (9).

8. The method according to any one of claims 1-3, wherein at least one of the condensates (6, 9) is partially or fully recycled together with the feed (1) to carry out the electrolysis (E).

9. The method according to any one of claims 1-3, wherein one or more process parameters including hydrogen concentration and / or gas temperature and / or the difference between two gas temperatures and / or gas pressure are detected downstream of the electrolysis (E) and / or in the catalytic reaction (C), and wherein i) in the case where one or more of the process parameters exceed a preset threshold; or ii) the first portion of the intermediate mixture (4) is recycled to the anode feed gas (2) in an amount continuously adjusted according to the detected process parameters.

10. The method according to claim 9, wherein the anode feed gas (2) is discharged from the process in the case where one or more of the process parameters, especially the difference between two gas temperatures, exceed a predetermined limit value.

11. The method according to any one of claims 1 - 3, wherein the electrolysis (E) and / or the catalytic reaction (C) is carried out at the same pressure level at which the drying (T) is carried out; and / or, wherein the portion of the intermediate mixture (4) recycled to the anode feed gas (2) is compressed to the pressure level at which the catalytic reaction (C) is carried out.

12. The method according to any one of claims 1 - 3, wherein the anode feed gas (2) is heated by heat exchange with the intermediate mixture (4).

13. An apparatus for manufacturing an oxygen-containing gas product (10) with an electrolysis unit, the apparatus being adapted to electrolyze (E) a raw material (1) containing water in such a way as to obtain an anodic raw material gas (2) rich in oxygen and containing hydrogen and a cathodic raw material gas (14) poor in oxygen and rich in hydrogen, characterized in that: A catalytic reaction unit, which is adapted to carry out a catalytic reaction (C) of hydrogen generating water in such a way as to obtain a low - hydrogen intermediate mixture (4) with at least a part of the anode feed gas (2); a component, which is adapted to recycle a first part of the intermediate mixture (4) to the anode feed gas (3) downstream of the electrolysis (E) and upstream of the catalytic reaction (C), and to form the oxygen - containing gas product (10) with a second part of the intermediate mixture (4).

14. The apparatus according to claim 13, further comprising a component adapted to carry out all steps of the method according to any one of claims 2 to 12.

Images