PROCESS AND APPARATUS FOR PRODUCTION OF ONE OR MORE ELECTROLYSIS PRODUCTS

[0001]The present invention relates to a process and an apparatus for producing one or more electrolysis products, in particular hydrogen and/or oxygen, using one or more electrolysis cells, in particular one or more electrolysis cells having a proton exchange membrane.

BACKGROUND OF THE INVENTION

[0002]The production of hydrogen using electrolysis cells having proton exchange membranes (PEM) is known. In such electrolysis cells, a solid polymer electrolyte, the proton exchange membrane, is used. The proton exchange membrane is used to conduct protons, to separate the product gases, and to electrically isolate the anode and cathode sides from one another. The use of electrolysis cells having proton exchange membranes can overcome some of the problems regarding partial load operation and the low possible flow densities that occur in conventional alkaline electrolysis.

[0003]Due to the comparatively high pressure of the produced hydrogen when using electrolysis cells having proton exchange membranes, consumers can be supplied directly. The high flow densities that can be used lead to comparatively low operating costs, in particular in cases in which dynamic electrical energy sources such as wind and sun are used, where peaks in energy supply cannot otherwise be utilized.

[0004]The polymer electrolyte allows the use of thin membranes of, for example, approximately 100 to 200 μm, alongside simultaneously high pressures. This leads to low ohmic losses, which are primarily caused by the conduction of protons through the membrane and the formation of pressurized hydrogen. Due to its solid structure, the polymer electrolyte membrane has a low gas transition rate, which can lead to very high product gas purity. This can be advantageous in particular as regards storage safety and direct use, for example in a fuel cell.

[0005]The anode reaction in an electrolysis cell having a proton exchange membrane is commonly referred to as an oxygen evolution reaction (OER). At the anode, the liquid reactant water is supplied to the catalyst and oxidized to form oxygen, protons and electrons:

[0006]The cathode reaction is commonly referred to as a hydrogen evolution reaction (HER). In this case, the supplied electrons are combined with the protons conducted through the membrane, thereby producing gaseous hydrogen:

[0007]In addition to hydrogen from the cathode side, the oxygen formed on the anode side of corresponding electrolysis cells can also be used. The present invention may relate to the recovery of hydrogen on the cathode side and oxygen on the anode side.

[0008]The object of the present invention is to improve the production of hydrogen and/or oxygen, in particular using electrolysis cells having a proton exchange membrane, and in particular to make it safer and more reliable.

DISCLOSURE OF THE INVENTION

[0009]Against this background, the present invention proposes a process and an apparatus for producing one or more electrolysis products, in particular hydrogen and/or oxygen, and in particular using an electrolysis cell having a proton exchange membrane, said process and apparatus having the features of the independent claims. Each of the embodiments are the subject matter of the dependent claims and of the description below.

[0010]Although the present invention is described below predominantly with reference to an electrolysis process in which a proton exchange membrane is used, embodiments of the present invention in which other electrolysis techniques are used can in principle also be used, in particular if problems addressed in the present invention occur there in the same way or in a comparable way. Reference to an electrolysis process with a proton exchange membrane is made merely for simplification and without the intention of limiting the present invention thereto.

[0011]If the term “an” electrolysis cell, in particular having “a” proton exchange membrane (in each case in the singular), is mentioned here, this should be understood to mean that embodiments of the present invention are typically realized having multiple such electrolysis cells, wherein corresponding electrolysis cells can in particular be part of a known type of electrolysis cell stack, in which a plurality of such electrolysis cells are present. In the case of an electrolysis process using proton exchange membranes, in such a stack a plurality of arrangements each comprising an anode, a proton exchange membrane and a cathode are provided, which are separated from one another by separating devices and means for water feed and means for gas withdrawal. The means for water feed and means for gas withdrawal can be connected to feed and collecting lines, respectively, that serve the entire stack. In other types of electrolysis, a similar stack structure can be provided and corresponding feed and collecting lines can also be used here. Arrangements having multiple electrolysis cell stacks can also be used. Below, reference is made, among other things, to an “electrolysis arrangement,” which is to be understood in particular to mean equipment which has one or more electrolysis cell stacks, each typically containing multiple electrolysis cells.

[0012]When reference is made here to an “anode side” or “cathode side” of an electrolysis cell, an electrolysis cell stack or an electrolysis arrangement of any kind, these terms typically refer to the cathode sides or anode sides of the electrolysis cells of corresponding cell stacks as a whole. A gas withdrawn from this/these cathode side(s) (overall) is also referred to as “cathode gas” or “cathode extraction gas” below. The same applies to gases withdrawn from the anode side, i.e., an “anode gas” or an “anode extraction gas”. These gases are typically gas mixtures.

[0013]The cathode gas is rich in hydrogen, the anode gas is rich in oxygen, although the cathode gas may also contain a smaller proportion of oxygen and the anode gas may contain a smaller proportion of hydrogen. However, the anode gas typically contains more hydrogen than the cathode gas contains oxygen, since hydrogen typically transfers more easily to the anode side than oxygen transfers to the cathode side. As mentioned, high product purities can be achieved by the use of proton exchange membranes and therefore the cathode gas contains very little oxygen. However, other electrolysis techniques can also produce hydrogen-rich cathode gas and oxygen-rich anode gas each containing the other gas in a relatively small concentration. The term “rich” can in particular be a content of more than 90%, 95%, 99% or 99.5% on a volumetric, quantity or molar basis.

[0014]In particular in electrolysis with proton exchange membranes, the anode gas is withdrawn together with water on the anode side, i.e., a biphasic stream or biphasic mixture is initially discharged from the anode side. After separation into a gas phase and a liquid phase, the former can, in conventional processes, be fed, for example, to oxygen recovery or released into the atmosphere.

[0015]A main problem with regard to the biphasic stream or biphasic mixture containing oxygen and water results from its possible hydrogen content. Driven by the pressure gradient through the proton exchange membrane, for example, hydrogen can pass through this proton exchange membrane, albeit by permeation, but increased when defects or cracks occur. For example, in scenarios of low load, in standby or in the case of defects, this hydrogen content may possibly reach the lower explosion limit (LEL) of approximately 4% hydrogen in oxygen. A corresponding transition of hydrogen can, in principle, also occur in other electrolysis techniques.

[0016]The (lower) explosion limit of a gas indicates the content in a gas mixture from which ignition or explosion is possible if the oxygen content is sufficient at the same time. The latter is always the case when it comes to oxygen-rich anode extraction gas or the aforementioned biphasic stream.

[0017]An explosion is an uncontrolled burn-off of a flammable gas mixture with a laminar flame front. An explosion substantially differs from a detonation by the speed of the propagation.

[0018]In the case of an explosion, this is below the speed of sound; in the case of a detonation, this is typically significantly above the speed of sound. Explosions and detonations of gas mixtures in containers and pipelines result in a massive increase in pressure which can lead to the bursting of the containers and corresponding consequential damages. Typically, in an explosion, a pressure increase by a factor of ten can be assumed. The effects of a detonation are significantly more severe. Here, the pressure increase factor may be 50 or more. An explosion may morph into a detonation after a certain start-up length and a minimum concentration of fuel and oxygen.

[0019]An ignition source in the region within, and downstream of, an electrolysis cell, for example having a proton exchange membrane or a corresponding stack, cannot be completely ruled out. Thus, the possible ignition of the explosive gas mixture must be assumed when designing a corresponding apparatus.

[0020]The oxyhydrogen reaction proceeds very quickly, resulting in very rapidly spreading flame speeds that are above the speed of sound. Therefore, an explosion can transition into a detonation even in small spaces and pipelines. For a detonation scenario, very high explosion pressure conditions must be taken into account in the design.

[0021]Even if an explosion or detonation occurs “only” in a separator for separating the biphasic stream, damage can occur in other regions, in particular downstream equipment such as pumps or heat exchangers or an electrolysis cell or a stack itself, because the explosion pressure is transferred thereto via the incompressible fluid (water).

[0022]The present invention, in its various embodiments, allows safer solutions for such cases and overcomes the disadvantages of the prior art. Conventionally, a corresponding explosion- or detonation-proof design is at best very expensive and at worst technically unfeasible. Protection of downstream equipment by pressure relief valves or rupture disks can traditionally also be problematic, because the pressure wave of the explosion or detonation propagates very quickly, i.e., at approximately 3000 m/s.

[0023]For example, from the publication by N. Briguglio, F. Pantò, S. Siracusano, A. S. Aricò, “Enhanced performance of a PtCo recombination catalyst for reducing the H₂ concentration in the O₂ stream of a PEM electrolysis cell in the presence of a thin membrane and a high differential pressure,” Electrochimica Acta 344 (2020) 136153, it is known to equip a membrane electrode assembly (MEA) in a corresponding electrolysis process with a recombination catalyst. In particular, this is used within the anode, where the permeated hydrogen meets the evolved oxygen. The recombination catalyst catalyzes a reaction between hydrogen and oxygen to form water, allowing the hydrogen content to be reduced. Other conventional embodiments may comprise equipping a proton exchange membrane with a corresponding recombination catalyst.

[0024]The present invention, however, proposes a process for producing one or more electrolysis products using an electrolysis arrangement, wherein the term “electrolysis arrangement” is expressly referred to in the above explanations.

[0025]In the proposed process, anode gas and water are withdrawn from the electrolysis arrangement in a biphasic mixture.

[0026]The proposed process further comprises the feeding of the biphasic mixture or a portion thereof into a separator arrangement which, for example, has one or more separators for phase separation, in the simplest case simple containers with, if necessary, installations conducive to separation. In the separator arrangement, water is separated from the biphasic mixture or from the portion thereof that is fed into the separator arrangement.

[0027]The proposed process further comprises the treating of separator gas from the separator arrangement in a catalysis arrangement which is designed to convert hydrogen with oxygen into water and has a corresponding catalyst. In this way, hydrogen can be removed at least to the extent that, if necessary in conjunction with further process steps, a sufficient reduction of the hydrogen content is achieved. The separator gas is, in particular, gas that accumulates in an upper region of a separator and that originates from the gas phases of the different streams fed in and, if applicable, additional gas streams fed in.

[0028]Finally, the proposed process comprises the feedback of catalysis gas, which is, in particular, correspondingly depleted in hydrogen and contains reaction water from the catalysis conversion, from the catalysis arrangement into the separator arrangement. This allows the water contained in the mixture to be separated using the same equipment used for the initial phase separation of the biphasic mixture in the proposed process.

[0029]The anode gas and the separator gas may contain oxygen and, to a lesser extent, hydrogen, whereby the hydrogen content in the separator gas is lower than in the anode gas due to the feedback of the catalysis gas and the correspondingly formed cycle, and the catalysis gas is depleted of hydrogen by treatment in the catalysis arrangement.

[0030]In contrast to the prior art, the proposed solution therefore involves not locating the recombination catalyst in the membrane or another structure close to or connected to the membrane in a membrane electrode assembly, but in a separate device, namely a catalysis unit through which a recycle stream flows, which is formed using the separator gas from a separator device.

[0031]By using embodiments of the present invention, a number of advantages can be achieved compared to the prior art. These comprise, for example, that the recombination catalyst does not impose any restrictions on the implementation or optimization of the electrolysis membrane and the membrane electrode assembly. Restrictions on the design of the recombination catalyst or its provision due to boundary conditions associated with application to the membrane are also eliminated. Advantages of the proposed process and its embodiments further comprise that no complete depletion of hydrogen is carried out in the catalysis unit used, because a corresponding cycle can be run through multiple times, and effective depletion is possible with sufficient throughput, even if depletion in a single run should be insufficient.

[0032]The present invention and embodiments thereof reduce, in particular, safety risks caused by hydrogen on the anode side due to membrane rupture or local damage in an improved and simpler manner compared to the prior art. Application to the membrane or in a membrane electrode assembly would have no or only a limited effect in this case. This can be considered as a design case for the recombination catalyst, thereby reducing and possibly eliminating corresponding risks.

[0033]Operating scenarios that may result in critical hydrogen concentrations (this particularly includes hydrogen concentrations of more than 2 percent by volume, i.e., approximately 50% of the lower explosion limit) can occur during downtime, i.e., at 0% load, and at partial load, for example at 20% load. In the former case, the apparatus can be operated in standby mode, the corresponding pumps run at minimal load, and no more hydrogen and oxygen are produced. However, in the example of an electrolysis process with a proton exchange membrane, the cathode side is still filled with hydrogen at approximately 30 bar overpressure, which diffuses through the membrane to the anode side as a result of the pressure difference. The water stream at the anode transports the diffused hydrogen into the downstream separator. Hydrogen accumulates there. Hydrogen and oxygen continue to be produced at partial load. Hydrogen diffuses through the membrane to the anode, flows together with the oxygen into the separator and also accumulates there.

[0034]Conventionally, corresponding apparatuses are shut down at 50% of the lower explosion limit, i.e., a detected hydrogen concentration of 2 percent by volume. During operating scenarios in which the hydrogen concentration exceeds this value, a purge gas can be supplied to the separator to dilute the hydrogen. The present invention allows at least a partial dispensing with such measures.

[0035]The recombination catalyst can be designed such that the use of oxygen as an electrolysis product without a downstream reactor to reduce the hydrogen content in the oxygen is possible even at low load conditions. This is conventionally also carried out catalytically (so-called CatOx). In certain embodiments, the invention makes it possible to dispense with a separate oxygen withdrawal step. In particular, the invention provides in embodiments that the one electrolysis product or one of the plurality of electrolysis products is oxygen, which is withdrawn as further separator gas from the separator arrangement and/or as further catalysis gas downstream of the catalysis arrangement. The latter alternative achieves higher purity, but may require a larger blower for the catalysis arrangement.

[0036]Typically, the separator gas recycled, i.e., passed through the catalysis unit, comprises a certain proportion of the total separator gas, while the remainder can be used as the electrolysis product. This proportion can be, in particular, 25 to 75 times, 40 to 60 times, or approximately 50 times the volume assumed to transfer from the cathode side to the anode side in the event of a membrane rupture.

[0037]Product purity can also be adjusted by appropriately adjusting the recirculation volume. In certain embodiments, a corresponding adjustment can also ensure that the hydrogen content upstream of the catalysis unit is sufficiently low so that the catalysis unit itself does not represent an ignition source.

[0038]In embodiments of the invention, multiple electrolysis cells arranged in multiple electrolysis cell stacks may be used in the electrolysis arrangement, wherein the one or at least one of multiple biphasic streams is formed by combining anode extraction gas and water from multiple electrolysis cell stacks.

[0039]In certain embodiments, the separator gas can be supplied to the catalysis unit by means of a compressor or a blower. As a result, the separator gas is heated by the heat of compression. This can be specifically exploited to promote the catalysis reaction. The separator gas can also be provided in dry form, i.e., without condensed water, which also promotes reactions in catalysis.

[0040]In embodiments of the invention, the catalysis gas or a portion thereof can be treated with water before being fed back into the separator arrangement, in particular in order to lower a temperature downstream of the catalysis process and thus, for example, to maintain a design temperature of the downstream equipment.

[0041]Within the scope of the present invention, in particular, the temperature development in the catalyst bed of the catalysis unit due to the hydrogen conversion can be monitored comparatively easily, in particular in contrast to temperature monitoring of the membrane surfaces. In this way, hydrogen breakthrough or membrane rupture can be easily detected. This provides a comparatively simple analysis (hydrogen content as a function of temperature) that is superior to other analysis methods in this stream and for this application. In corresponding embodiments of the invention, it can therefore be provided that a temperature detection is carried out in the one or at least one of the plurality of catalysis units, and that, in particular on the basis of the temperature detection, a defect diagnosis of one or more electrolysis membranes in the one or more electrolysis cells is carried out. For example, a defect can be detected if a temperature value exceeds a temperature threshold. For example, with a typical hydrogen content as explained above, the temperature typically increases by 10 to 40 K across the catalysis unit. In contrast, with a breakthrough of hydrogen, a temperature increase of 100 to 300 can be observed.

[0042]In the 0% load scenario explained above, the amount of oxygen required for recombination may not be sufficient. In this case, an oxygen stream, e.g. carbon dioxide-free air, can be fed into the separator arrangement so that the hydrogen can be converted into water. The current purging of the separator is complex and costly. The purging must function in all scenarios, including power outages. This involves expenditure on equipment, regulatory burden, etc. For this purpose, up to 300 kg/h of nitrogen, for example, is required for purging. This is avoided by the present invention.

[0043]In other words, the proposed process having the features explained above can be carried out in a first process mode, wherein the process comprises a second process mode in which less electrolysis oxygen is produced on the anode side than in the first process mode, or no electrolysis oxygen is produced. The second process mode can comprise substantially the same process steps, i.e., optionally the withdrawing of anode gas and water from the electrolysis arrangement in a biphasic mixture, the feeding of the biphasic mixture or a portion thereof into the separator arrangement, the treating of separator gas from the separator arrangement in the catalysis arrangement and the feedback of catalysis gas from the catalysis arrangement into the separator arrangement, wherein the anode gas in this embodiment can, however, be oxygen-free or more depleted in oxygen than in the first process mode and oxygen can be fed into the separator arrangement. The separator gas may also be richer in oxygen than the anode extraction gas, thus ensuring hydrogen depletion in the catalysis unit.

[0044]As mentioned, the one or more catalysis units may be configured in particular to reduce a hydrogen content in a gas portion of the one or more biphasic streams to less than 50% of the lower explosion limit. Thus, gas purging or the like may be dispensed with.

[0045]In a corresponding process, a catalyst material selected from the materials explained in more detail below can be used in the one or more catalysis units.

[0046]In embodiments of the present invention, the catalyst may be a platinum or palladium material and/or a platinum or palladium alloy, for example with cobalt and/or nickel, on a support material. Iridium or ruthenium may also be used as an alternative or additional active material. In embodiments of the present invention, suitable support materials include, for example, aluminum oxide or dialuminium trioxide, silicon dioxide or cerium oxide. In principle, all inert or active carrier materials can be used in embodiments of the invention.

[0047]Non-limiting examples of a suitable catalyst comprise, for example, a platinum content of 0.05 to 0.3% by molar or mass basis, a palladium content of 0.05 to 0.3% by molar or mass basis, and a support made of or comprising dialuminum trioxide. Specific examples of platinum and palladium contents are 0.15% each.

[0048]In principle, a suitable catalyst should meet requirements such as high activity and the ability to withstand oxidizing conditions (a reducing environment).

[0049]For alloys that can also be used, reference can be made to specialist literature such as N. Briguglio et al., Electrochimica Acta 344 (2020) 136153. Suitable alloys can be used, in particular, to increase the activity of the catalyst. Examples include the use of a platinum-cobalt alloy with platinum-to-cobalt alloy ratios of, for example, 85:15 atomic percent or 50:50 to 95:5 atomic percent, or platinum or palladium-nickel alloys with corresponding ratios.

[0050]According to embodiments of the invention, the purging of the separator for mitigation purposes is no longer required. The amounts of oxygen required in 0% load operation are typically less than 5 kg/h, very small compared to the required amounts of purge gas. An extension of the operating range in the sense of a reduction of the minimum load of a corresponding electrolyzer may also be possible in embodiments of the invention.

[0051]An apparatus for producing one or more electrolysis products is also the subject of the present invention, with reference to the corresponding independent patent claim for the features of the apparatus.

[0052]For further features and advantages of a corresponding apparatus and embodiments thereof, reference is expressly made to the above explanations relating to the process proposed according to the invention and its embodiments, since they apply in the same way here.

[0053]The same also applies to an apparatus which, according to one embodiment of the invention, is configured to carry out a process according to any embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWING

[0054]Embodiments of the invention will be described below purely by way of example and with reference to the accompanying drawings, in which:

[0055]FIGS. 1 and 2 illustrate apparatuses for explaining the background of the invention, and

[0056]FIG. 3 illustrates an apparatus according to an embodiment of the invention.

EMBODIMENTS OF THE INVENTION

[0057]The embodiments described below are described solely for the purpose of assisting the reader in understanding the features claimed and previously discussed. They are merely representative examples and are not intended to be considered to be exhaustive and/or limiting with respect to the features of the invention. It goes without saying that the advantages, embodiments, examples, functions, features, structures and/or other aspects described above and below are not to be considered to limit the scope of the invention as defined in the claims, or to limit equivalents to the claims, and that other embodiments may be used and changes made without departing from the scope of the claimed invention.

[0058]Different embodiments of the invention may comprise, have, consist of, or substantially consist of further expedient combinations of the described elements, components, features, parts, steps, means, etc., even if such combinations are not specifically described herein. Furthermore, the disclosure may comprise other inventions that are presently not claimed, but which may be claimed in the future, in particular when comprised in the scope of the independent claims.

[0059]Explanations relating to devices, equipment, arrangements, systems, etc. according to embodiments of the present invention may also apply to procedures, processes, methods, etc. according to the embodiments of the present invention, and vice versa. Elements, process steps, etc. that are identical, have the same effect, correspond in terms of their function, are structurally identical or have a similar structure can be indicated by identical reference signs.

[0060]The present invention and embodiments thereof are explained below with reference to an electrolysis process with a proton exchange membrane. As mentioned multiple times, however, the invention is not limited to this.

[0061]FIG. 1 illustrates an apparatus for explaining the background of the present invention and is designated as a whole by 100.

[0062]In the example shown, the apparatus comprises electrolysis arrangements 10 in the form of or as part of two electrolysis cell stacks 110 and 120. A plurality of electrolysis cells is present and the electrolysis arrangements 10 have an anode side 11 and a cathode side 12. The components mentioned are illustrated in a highly simplified manner. Other components such as fans are not shown. For the sake of clarity, valves and control devices, measuring sensors and the like have also been omitted.

[0063]Water 101 is supplied to the anode side of each electrolysis cell. During operation, oxygen is formed on the anode side(s) 11 by the oxygen evolution reaction, which is transported away from the anode side(s) 11 in a biphasic stream or a biphasic mixture 102 with water. As mentioned, this biphasic stream 102, or a gas portion thereof referred to here as “anode gas” or “anode extraction gas” contains certain amounts of hydrogen, which can lead to the problems mentioned above. Furthermore, the hydrogen evolution reaction on the cathode side(s) 12 produces hydrogen, which is transported away from the cathode side(s) 12 in the form of a hydrogen stream 103.

[0064]In the apparatus 100 illustrated here, a catalysis arrangement 20 is provided in which the combined extraction gases from the anode sides 11 of the electrolysis arrangements 10 are catalytically processed in a biphasic mixture with water such that at least a portion of the hydrogen is catalytically converted with a portion of the oxygen into water. If required, i.e., in particular in the aforementioned 0% load cases, additional oxygen can be supplied in a source stream 104, which can, for example, be carbon dioxide-free air.

[0065]In the example shown, the correspondingly processed biphasic mixture is fed in the form of a source stream 105 into a separator arrangement 30, in which the water content is separated in the form of a hydrogen stream 106. In this way, substantially pure oxygen can be recovered in the form of a source stream 107 and, for example, supplied to a drying process, compression process, etc. (not shown) if recovery as an electrolysis product is intended.

[0066]FIG. 2 shows a further apparatus to illustrate the background of the present invention and is designated as a whole by 200.

[0067]The apparatus 200 illustrated in FIG. 2 differs from the apparatus 100 illustrated in FIG. 1 in particular in that a catalysis arrangement 20 is present for each electrolysis cell stack 110, 120 and only the biphasic mixture processed here is combined to form the source stream 105. Further embodiments, multiple arrangements of catalysis units, etc. are possible in any desired variants without departing from the scope of the present invention.

[0068]FIG. 3 illustrates an apparatus according to one embodiment of the present invention and is designated as a whole by 300.

[0069]In the example shown, the apparatus 300 comprises, without limiting the present invention in any way, electrolysis devices 10 and two electrolysis cell stacks 110 and 120, as in the previously explained apparatuses 100 and 200. The electrolysis devices 10 each have an anode side 11 and a cathode side 12. As before, the components mentioned are illustrated in a highly simplified manner. Other components such as fans are not shown. As before, valves and control devices, measuring sensors, sensors and the like have been omitted for the sake of clarity.

[0070]Water from a water stream 101b is supplied to each of the electrolysis devices 10 on the anode side. The water stream 101b can be branched off from a water feed stream 101, as illustrated in FIG. 3, but a separate provision of a corresponding water stream 101b is also possible.

[0071]During operation, as already explained, oxygen is formed on the anode side(s) 11 by the oxygen evolution reaction, which is transported away from the anode side(s) 11 in a biphasic mixture 102 with water. As mentioned, this biphasic mixture 102, or a gas portion thereof referred to here as “anode gas” contains certain amounts of hydrogen, which can lead to the problems mentioned above. Furthermore, the hydrogen evolution reaction on the cathode side(s) 12 produces hydrogen, which is transported away from the cathode side(s) 12 in the form of a hydrogen stream 103.

[0072]In the apparatus 300, the biphasic mixture 102 is fed into a separator device 30 without prior catalysis treatment in a catalysis device 20, as occurs in the apparatuses 100 and 200, in which the water content is separated in the form of a hydrogen stream 106. The gas phase withdrawn from the separator device 30, which is referred to here as separator gas 108, therefore still contains hydrogen in the apparatus 300, in contrast to apparatuses 100 and 200, which is withdrawn by means of the catalysis device 20. For this purpose, a partial stream 108a of the source stream 108 is fed into the catalysis device 20 via a compressor or a blower 40; a remaining partial stream 108b is discharged from the apparatus 300.

[0073]In the embodiment of the invention illustrated here, the catalysis device 20 is not supplied with the combined withdrawal gases from the anode sides 11 of the electrolysis cells 10 in a biphasic mixture with water as before, but only with the gas phase 108 from the separator device 30 or a corresponding partial stream 108a. In the catalysis device 20, at least a portion of the hydrogen is catalytically converted with a portion of the oxygen into water. If required, i.e., in particular in the aforementioned 0% load cases, additional oxygen can also be provided here in a source stream 104, which can, for example, be carbon dioxide-free air, but which is fed here into the separator device 30.

[0074]The gas phase from the separator device 30 processed in the catalysis device 20, i.e., the correspondingly processed partial stream 108a, designated by 109 in FIG. 3, is free or substantially free of hydrogen, but contains water of reaction from the catalysis and possibly water already contained previously. This source stream 109 can now be quenched, i.e., combined, with water from a water stream 101a in order to lower the temperature. Like the water stream 101b, the water stream 101a can also be branched off from a feed water stream 101 or provided separately. A correspondingly obtained collection stream is returned to the separator 30.

[0075]By means of the recycling realized in this way, the hydrogen content in the separator 30 can be reduced overall, so that the hydrogen content in the source stream 108 or 108b can be reduced overall to a value that is non-critical in the sense explained above. The source stream 108b can therefore be safely fed, for example, to a drying process, compression process, etc. (also not shown here), if recovery is intended.

[0076]An advantage of the apparatus 300 compared to the apparatuses 100 and 200 is that only one catalysis unit 20 can be used for a plurality of electrolysis cell stacks 110, 120, which, moreover, does not have to achieve complete hydrogen removal in a single run due to the recycling.