WO2018054646A1

WO2018054646A1 - Device for continuous operation of an electrolysis cell having a gaseous substrate and gas diffusion electrode

Info

Publication number: WO2018054646A1
Application number: PCT/EP2017/071292
Authority: WO
Inventors: Günter Schmid; Helmut Eckert; Ralf Krause; Christian Reller; Bernhard Schmid; Dan Taroata
Original assignee: Siemens Aktiengesellschaft
Priority date: 2016-09-20
Filing date: 2017-08-24
Publication date: 2018-03-29
Also published as: DE102016217989A1; CN109715861A; US20190226105A1; AU2017332322A1; EP3475469A1; AU2017332322B2

Abstract

The invention relates to a method for continuous operation of an electrolysis cell having a gaseous substrate, wherein an electrolyte is supplied to the electrolysis cell by an electrolyte inflow, and an electrolyte flow out of the electrolysis cell into the gas chamber occurs via a gas diffusion electrode, wherein electrolyte is suctioned out of the gas chamber through a connection between the gas chamber and the electrolyte inflow. The invention further relates to a device for carrying out the method.

Description

description

Apparatus for the continuous operation of an electrolytic cell with gaseous substrate and gas diffusion electrode

The present invention relates to a method for continu ^¬ tinuous operation of an electrolytic cell with gaseous Sub ^¬ strat, wherein an electrolyte of the electrolysis cell is supplied by an electrolyte flow, and a flow of electrolyte from the electrolytic cell in the gas space takes place through a gas diffusion ^¬ electrode, electrolyte from the Gas space is sucked through a connection between the gas space and the electrolyte inflow, and an apparatus for performing the method.

The burning of fossil fuels currently covers about 80% of global energy needs. As a result of these incineration processes in 2011, worldwide approx

Emitted 34,032.7 million tonnes of carbon dioxide (C0 ₂ ) into the atmosphere. This release is the easiest way to dispose of even large amounts of CO2 (lignite power plants over 50000 tons per day).

The discussion about the negative impact of the greenhouse gas CO2 on the climate has meant that we think about a How To ^¬ derverwertung of CO2. Thermodynamic sailed ^¬ hen is very low CO2, and can therefore hardly be reduced again to useful products. In nature, the CO2 process of photosynthesis to carbohydrate ^¬ th. This temporally and on a molecular level spatially divided into many sub-steps process is very difficult to copy on an industrial scale. The currently more efficient compared to pure photocatalysis way represents the electrochemical reduction of CO2 S. A hybrid is the light-supported electrolysis or the electrically assisted under ^¬ photocatalysis. Both terms are synonymous to USAGE ^¬, depending on the perspective of the viewer. As in the photosynthesis in the process below to ^¬ driving electric power (if necessary, photo assisted) which is obtained from renewable sources such as wind and sun, CO ₂ in an energetically higher quality product (such as CO, CH _4, C ₂ H ₄ , etc.) converted. The required amount of energy in this reduction corresponds in the ideal case, the Burn ^¬ voltage energy of fuel and should only regenerati ^¬ ven sources. An overproduction of renewable energies is not continuously available, but currently only at times with strong sunlight and strong wind. However, with the continued expansion of renewable energy sources, this will continue to increase in the near future.

The electrochemical reduction of CO ₂ to Festkörperelektro ^¬ offers in aqueous electrolyte solutions a variety of product options which in the following Table 1, taken from Y. Hori, Electrochemical CO ₂ reduction on metal electrodes, in: C. Vayenas, et al. (Eds.), Modern Aspects of Electrochemistry, Springer, New York, 2008, pp. 89-189, are shown.

Table 1: Faraday efficiencies for carbon dioxide on various metal electrodes

Electrode CH 4 C ₂ H ₄ c ₂ H ₅ OH c ₃ H ₇ OH CO HCOO ^" H ₂ Total

Cu 33 .3 25 .5 5. 7 3. 0 1.3 9.4 20.5 103.5

Au 0. 0 0. 0 0. 0 0. 0 87.1 0.7 10.2 98.0

Ag 0. 0 0. 0 0. 0 0. 0 81.5 0.8 12.4 94.6

Zn 0. 0 0. 0 0. 0 0. 0 79.4 6.1 9.9 95.4

Pd 2. 9 0. 0 0. 0 0. 0 28.3 2.8 26.2 60.2

Ga 0. 0 0. 0 0. 0 0. 0 23.2 0.0 79.0 102.0

Pb 0. 0 0. 0 0. 0 0. 0 0.0 97.4 5.0 102.4

Hg 0. 0 0. 0 0. 0 0. 0 0.0 99.5 0.0 99.5

In 0. 0 0. 0 0. 0 0. 0 2.1 94.9 3.3 100.3

Sn 0. 0 0. 0 0. 0 0. 0 7.1 88.4 4.6 100.1

Cd 1. 3 0. 0 0. 0 0. 0 13.9 78.4 9.4 103.0

Tl 0. 0 0. 0 0. 0 0. 0 0.0 95.1 6.2 101.3

Ni 1. 8 0. 1 0. 0 0. 0 0.0 1.4 88.9 92.4

Fe 0. 0 0. 0 0. 0 0. 0 0.0 0.0 94.8 94.8

Pt 0. 0 0. 0 0. 0 0. 0 0.0 0.1 95.7 95.8

Ti 0. 0 0. 0 0. 0 0. 0 0.0 0.0 99.7 99.7 When operating such electrolysis cells for CO 2 reduction, it has been shown that electrolyte passes through a gas diffusion electrode (GDE) and leads to an accumulation of electrolyte in the gas space. Both in the case of flow-through and flow-by, the electrolyte loses the solvent, in particular water, as a result of the gas flow, as a result of which salt deposits occur in the gas space and, particularly disadvantageously, in the GDE itself. These lead to the loss of selectivity and ultimately to the failure of the electrode or the electrolyzer.

DE 10 2012 204 041 A1, eg sections [0007], [0008], [0041], and [0059], or DE 10 2013 011 298 A1 describes the mode of operation of an "oxygen-consuming cathode". It also describes that electrolyte passes through the GDE. In DE 10 2012 204 041 AI is also described that it can lead to clogging of the pores of the GDE.

The phenomenon of salt deposits is particularly dominant in electrolysers, which convert a gaseous substrate on a gas diffusion electrode into gaseous substrates.

There is thus a need for a method and an apparatus with which these can be reduced by electrolytic passage be ^¬-related problems or failures.

The present inventors have found an operating mode in which salt migration occurs so that an electrolysis cell still runs stably. In particular, an off ^¬ salt electrolyte can be avoided and a good electrolysis performance can be obtained over a long period despite passing through the electrode. According to a first aspect, the present invention relates to a method for the continuous operation of a gaseous substrate electrolysis cell, wherein

an electrolyte is supplied to the electrolytic cell by an electrolyte flow, and

an electrolyte flow from the electrolysis cell into the gas space takes place through a gas diffusion electrode, the electrolyte is collected from the electrolyte flow into the gas space in a collecting area in the gas space, and the collected electrolyte is sucked out of the latter, wherein the suction through a connection between the gas space and the electrolyte inflow takes place.

Furthermore, the present invention relates in a broad aspect ren ^¬ a device for continuous operation of an electrolytic cell with gaseous substrate comprising an electrolytic cell comprising

an anode,

a cathode, wherein at least one of the anode and the cathode is formed as a gas ^¬ diffusion ^electrode , and

a cell space adapted to be filled with an electrolyte and into which the anode and the cathode are at least partially inserted;

a supply for electrolyte, which is adapted to the

Cell space to supply electrolyte;

a gas chamber which is designed to supply a gaseous substrate of a gas diffusion electrode ^¬, wherein the gas space is provided on a side remote from the cell chamber side of the gas diffusion electrode;

a supply for a gaseous substrate, which is ^¬ forms is to supply the gaseous space to the gaseous substrate; a collection area in the gas space, which is designed to collect electrolyte in the gas space; and

a connection between the gas space and the supply for

Electrolyte, which is designed to dissipate electrolyte which has been collected in the collecting area in the gas space, from this.

Further aspects of the present invention can be found in the dependent claims and the detailed description.

The accompanying drawings are intended to illustrate embodiments of the present invention and to provide a further understanding thereof. In the context of the description, they serve to explain concepts and principles of the invention. Other embodiments and many of the stated advantages will become apparent with reference to the drawings.

The elements of the drawings are not necessarily to measure ^¬ scale shown to each other. Identical, functionally identical and identically acting elements, features and components are in the figures of the drawings, unless otherwise stated, each provided with the same reference numerals. Figures 1 to 5 show schematically exemplary representations of a possible construction of an electrolytic cell according to an embodiment of the present invention.

FIG. 6 shows schematically an embodiment of an electrolysis system for CO 2 reduction without the inventive design of the connection between electrolyte supply and gas diffusion electrode.

Figure 7 shows schematically an embodiment of an electrolysis plant for C02 reduction with gas diffusion electric ^¬ de. Figure 8 shows schematically the construction of a Venturi nozzle.

FIGS. 9 to 13 schematically show different embodiments for controlling the suction of electrolyte from a collecting area in the gas space of a device with gas diffusion electrode and electrolyte passage.

The present invention relates in a first aspect to a method for continuously operating an electrolytic cell with a gaseous substrate, wherein

an electrolyte is supplied to the electrolytic cell by an electrolyte flow, and

an electrolyte flow from the electrolytic cell takes place in the gas space through a gas diffusion electrode, the electrolyte from the, in particular unwanted, electrolyte flow in the

Gas space is collected in a collection area in the gas space, and the collected electrolyte is sucked out of this, wherein the suction takes place through a connection between the gas space and the electrolyte inflow. The flow of electrolyte is particularly unavoidable according to certain embodiments.

The method described is for all electrolytic cells with gaseous substrate and in particular gas diffusion electrode but is preferably used for electrolysis of CO ₂ or CO, for example to CO or hydrocarbons. It is therefore described in particular in connection with the C0 ₂ ~ electrolysis to CO or hydrocarbons, as I said but not limited thereto. For Kohlendio ^¬ xidelektrolyse determined according to this execution ^¬ form gas diffusion electrodes as cathodes are used which precious metals such as silver or gold, for example, silver and / or copper (for example, for hydrocarbon formation in the C0 ₂ - eduction) comprise or consist of.

If an oxygen-consuming electrode is provided as the gas diffusion electrode, it may for example consist of or at least comprise silver.

Suitable gaseous substrates are generally all gaseous substrates which can be used in electrolysis, such as carbon dioxide, carbon monoxide, oxygen, etc., for example carbon dioxide or carbon monoxide. Also, the electrolyte is not particularly limited in the process and may include, for example, those which are usually used in electro ^¬ lyses. According to certain embodiments, the electrolyte comprises water, ie it is an aqueous electrolyte in which conductive salts can be dissolved. Suitable salts for example, those with alkali metal cations such as Na ^+, K ^+, etc. and with suitable anions, for example Halogenanio- NEN such as Cl ^~, Br ^~, etc., sulfate and / or sulfonate, carboxylic bonat- and / or hydrogen carbonate ions , etc., and / or mixtures thereof into consideration, it also being possible ionic liquids can also be used in solution to ^¬ additionally or alternatively, if necessary.

The gas diffusion electrode is understood to mean an electrode through which the gaseous substrate is introduced into the electrolysis cell. This is not particularly limited in terms of their structure and is particularly designed porous. By a suitable adjustment of hydrophilicity and / or hydrophobicity in the gas diffusion electrode (GDE), in this case also, according to certain embodiments, the flow of electrolyte from the electrolysis cell, in which the electrolyte is introduced and the electrolysis takes place, in the gas space through which the gaseous substrate is supplied, set the ^¬ the. Thus, for example, in the method according to the invention as well as in the device according to the invention, the gas diffusion electrode can be produced by adjusting its hydrophobicity / hydrophilicity so that a certain electrolyte flow through it is made possible. The setting can be suitably made and is not particularly limited.

Through the passage or passage of the electrolyte through the gas diffusion electrode, salt formation or salt precipitation on the gas diffusion electrode could occur in previously known processes. For a better understanding of the present invention, this phenomenon is likely Darge by way of example in connection with reference to various methods ^¬, in which the method according to the invention or which he ^¬ invention modern apparatus can be used.

It should be noted that the reflux of the electrolyte can simultaneously serve to eliminate or avoid salt deposits in the GDE. The phenomenon of salt precipitation can occur here in a variety of operations.

For example, in a chlorine alkali electrolysis with an oxygen-consuming electrode, it can be represented as follows:

According to the prior art, is continuously fed in chloralkali electric ^¬ lyse the anolyte compartment of sodium chloride as wässri- ge solution. At the anode, chloride (Cl ^~ ) is oxidized to chlorine (CI ₂ ) leaving the electrolysis cell.

2 Cl - * CI ₂ + 2e (charge neutrality) The released electrodes are transported by the applied voltage source to the cathode. In order to obtain electroneutrality of the overall system, a membrane results in a corresponding covalent cation stream.

At the cathode, water is reduced in the classical membrane process.

H2O + 2e ^~ - * H-2 + 2 OH ^~ (charge neutrality)

The negative charges can be compensated by cations, in this example, Na ^+, ie the OH generated at the cathode ^~ - ions can continuously leave the cathode compartment, for example as a caustic soda solution.

In the case of the use of an oxygen- ^consuming cathode as a gas diffusion electrode, no hydrogen is formed, but rather water. The enthalpy of water formation can reduce the necessary system voltage, so that less energy is consumed.

H ₂ 0 + Q ₂ + 2e ^" - * H ₂ 0 + 2 OH ^" (charge neutrality)

The oxygen-consuming cathode chlor-alkali electrolysis is loading for example of silver, which educts tion can be used to also CO to C0 ₂ ^~.

For charge equalization, cations, eg Na ⁺ ions, move in the direction of the cathode space, which must be continuously removed from the electrolyte in the form of sodium bicarbonate.

One possible anode reaction is here e.g. with oxygen as follows:

H ₂ 0 -> 0 ₂ + 2 H ⁺ + 2 e ^" A continuous operation is possible with a game as electrolysis at ^¬ when the pH Balancing catholyte and

^¬ be mixed anolyte and outside the electrolytic cell continuously ge. However, this is expensive. In erfindungsgemä- KISSING method, however, a continuous mixture of anolyte and catholyte outside the electrolysis cell can SUC ^¬ gen. Of course, anolyte and catholyte may be the same as electrolyzer ^¬ th, but can also be different. Another possibility consists, for example, the anolyte sau ^¬ he make so that only protons pass through a membrane towards the cathode. Possibly. Here a concentra ^¬ onsausgleich must be inserted so that protons are discharged active overall through the membrane, as with other cations, water molecules. Of course, this measure can also be taken additionally in the method according to the invention.

A salt deposition in the gas space or gas supply space can then arise through the following process. At the back of the porous cathode can hydroxide ions, in the above mentioned

Examples arise together with the corresponding cations (Na ⁺ , K ⁺ , etc.) penetrate, which can form salts and can be deposited on the back of the electrode or in the pores.

Another example is the electrolytic reduction of carbon dioxide. At the cathode, different pro ^¬-products can occur in all operating modes depending on the electrode material.

Examples:

Carbon monoxide: C0 ₂ + 2 e ^" + H ₂ 0 - * CO + 2 OH ^"

Ethylene: 2 C0 ₂ + 12 e ^" + 8 H ₂ 0 -> C ₂ H ₄ + 12 OH ^"

Methane: C0 ₂ + 8 e ^" + 4 H ₂ 0 -> CH ₄ + 4 OH ^"

Ethanol: 2C0 ₂ + 12 e ^" + 9H ₂ 0 -> C ₂ H ₅ OH + 12 OH ^"

Monoethylene glycol: 2 CO ₂ + 10 e ^" + 8 H ₂ O -> HOC ₂ H ₄ OH + 10 OH ^" Salt separation in the gas space can then take place by the following process. Hydroxide ions, which are formed in the abovementioned examples, together with the corresponding cations (Na ⁺ , K ⁺ , etc.) can penetrate to the rear side of the porous cathode. Depending on the pH value, the corresponding bicarbonate or carbonate can be deposited in conjunction with CO ₂

(Salt deposition, salinization).

According to the invention, therefore, the electrolyte is collected in a collecting region in the gas space and the collected electrolyte is sucked out of it, so that no electrolyte remains in the gas space, so that no salt separation takes place through solvent removal.

The collecting area here is not particularly limited, in ^¬ if he can collect the electrolyte, for example as a liquid or solution, and insofar from this the collected electrolyte can be sucked out, for example, through an opening or a drain with appropriate discharge device, which with is connected to the electrolyte inlet and thus forms a connection between the gas space and the electrolyte flow. According to certain embodiments, the collection area takes place at a lower end of the gas space, preferably below a level (as seen from the bottom) of the gas ^¬ diffusion electrode respectively, so that the electrolyte can flow after passing into the gas space by gravity downwardly below the lower end so that it does not remain too long at the gas diffusion electrode, for example, the Rücksei ^¬ te and / or in pores thereof. The connection between the gas space and the electrolyte inflow preferably takes place by means of an opening or an outflow in the collecting area in the gas space, preferably at a lower end of the collecting area.

The connection between the gas space and the electrolyte inflow is not particularly limited and can be done, for example, by suitable pipes, hoses, etc., eg pipes, the material preferably being adapted to the material of a recirculated electrolyte collected in the collecting area can, and for example, the material for a supply or supply device for the electrolyte correspond, which is also not particularly limited and may be formed, for example, as a tube. According limited hours ^¬ th embodiments of the collection area in the gas space is not provided with the gas diffusion electrode in contact. The tubes are not particularly limited in their further shape, but in accordance with certain embodiments have a circular cross-section in order to allow a good transport or flow of the electrolyte.

According to certain embodiments, the suction takes place by the electrolyte inflow exerts a suction effect on the gas space. This can ensure that not too much electrolyte accumulates in the collection area and thus comes as ^¬ to the gas diffusion electrode in contact also can be minimized or prevented thereby an influence on the gas supply. According to certain embodiments, the gas supply does not take place from the collecting area in the gas space, so that the electrolyte is not flowed through by the gas or bubbled through. Nevertheless, the collection area is located in the gas space, so it is also in contact with the feed for the gaseous substrate.

The inventive apparatus which can be used for the invention ^shown SSE process thus preferably includes a collection area for electrolyte of the following gravity at the lower end of the gas diffusion electrode or below it. Gas space and electrolyte feed are preferably connected in such a way that the electrolyte feed exerts a suction effect on the gas space.

For example, this can be achieved by the Verbin ^¬ extension is in the form of a venturi nozzle, Laval nozzle or similar from ^¬ designed, wherein the compound is preferably carried out in the region in which the respective nozzle is tapered and the Elek trolyt ^¬ thus at the supply an increased speed ^¬ has. According to certain embodiments, therefore, the suction effect arises in that the connection between the gas space and the electrolyte inflow comprises a Venturi nozzle, through which the electrolyte inflow to the electrolysis cell takes place. Again, the connection to the gas space is preferably at a tapered point of the Venturi nozzle.

Basically, the present approach is based on the principle of the venturi nozzle, which is illustrated schematically in FIG. 8 and exemplified with the connection to the gas space L2. The principle is based on the fact that the flow velocity of a medium flowing through a pipe is inversely proportional to a changing pipe cross-section. That is, the speed is greatest where the cross section of the tube is smallest. According to the law of Bernoulli, in addition, in a flowing fluid (gas or liquid), an increase in speed is accompanied by a pressure drop. Accordingly, for a nozzle according to FIG. 8, pi> p2, where pi is the pressure of the supplied electrolyte in the direction of flow in front of the nozzle and P2 the pressure of the electrolyte in the smallest cross section of the nozzle as well as the connection to the gas space L2 and vi is the velocity of the electrolyte in the flow direction in front of the nozzle and V2 is the velocity of the electrolyte in the smallest cross-section of the nozzle. This relationship can be used for aspirating the electrolyte from the collection area in the

Exploiting gas space.

The Venturi nozzle, as well as a Laval nozzle, is not particularly limited in shape in so far as the cross-section of the nozzle in the flow direction of the supplied electrolyte initially decreases. The shape of the cross section is not particularly limited and may be ^¬ be round, elliptical, square, rectangular, triangular, etc., however, is approximately in accordance with certain embodiments. Also, a symmetrical nozzle shape is preferred.

In addition, the Venturi nozzle, as well as a Laval nozzle, also not limited in their design, wherein preferably the connection to the gas space or collecting area in the gas space takes place at the narrowest point of the nozzle.

The line L2 (at which the pressure p2 prevails) is connected in FIG. 8 to the gas space of the electrolysis cell, which accumulates the electrolyte.

According to certain embodiments, the suction of the electrolyte from the gas space takes place periodically. In this way it can be ensured that the electrolyte which has passed through the GDE is regularly sucked off, but on the other hand there is also a sufficiently long period for the electrolysis without any interference through the suction. According to certain embodiments, the suction is carried out in such a way that not all of the electrolyte is sucked out of the collecting area in order to better stabilize the pressure in the system and to prevent a transfer of gaseous substrate into the compound. According to certain embodiments, a transfer of gaseous substrate into the connection between the gas space and the supply for electrolyte is prevented or prevented.

A periodic suction, in particular with the Favor ^¬ th characteristics to achieve, the periodic suction is carried out in accordance with certain embodiments by a control mechanism which controls the periodic suction.

This control mechanism is not further limited and will be further described in detail hereinafter with reference to various embodiments. By Regelmecha ^¬ mechanism in particular, in accordance with certain embodiments, the connection between the gas chamber and the supply of electrolyte from the supply of electrolyte, for example perio ^¬ disch be sealed or closed, for example by a closure, such as a Flüssigkeitsver- circuit, the may be located anywhere in the connection between the gas space and the supply for electrolyte, for example as a valve, for example, on a pipe bond near the electrolyte supply, for example at a T-piece, or as a closure on a discharge from the in ^¬ play collection area in the gas space, for example in the form of a float. The control mechanism may Example ^¬ as an opening of the closure depends on measurements and sensor data induce, for example, using a fill level of the electrolyte in the collecting area, but may also be formed automatically or mechanically or mechanically self-regulating, without a measurement must be made.

Thus, the apparatus according limited hours ^¬ th embodiments contains at least a control mechanism, preferably a liquid seal and a Regelmecha ^¬ mechanism which opens the access to the electrolyte flow when a certain filling level of the collecting area is reached. The re ^¬ gel mechanism can also be integrated with the liquid closure, for example, when using a float.

According to certain embodiments, the control mechanism is mechanically formed. Hereby, the cost of Ver ^¬ bond between gas space and supply for electrolyte can be kept as low as possible.

According to certain embodiments of the control mechanism comprises a float which is located in the collecting area in the gas space, and allows the drain to be connected between the gas space and the electrolyte flow, depending on the level of the electric ^¬ LYTEN in the collecting area in the gas space, wherein the

Float, for example, periodically opened. It should be noted that the gas chamber must be connected not only to the GDE, but also may include another area of the gas supply, such as a tundish, wel ^¬ ches can be seen, for example, toward the floor below the GDE before ^¬ and where the permeated Electrolyte can flow. According to certain embodiments, the float is referred to as a cone or truncated cone, for example as Plug formed with the tip of the cone or the circular surface of the truncated cone with the smaller size protrudes into the connection between the gas space and the supply for electrolyte. With the truncated cone may be, which closes the opening of the connection between the gas space and the supply of electrolyte in the collecting area of the gas space ER reaches a "wedge-shape". Preference is given here, the float is made of a material which has a respective closure si ^¬ cherstellt, on the other hand not th through the electrolytically and / or the gaseous substrate is attacked, for ^¬ play, on elastomer or thermosetting resins. to adjust the density ceramic fillers may be employed. the density can also be adjusted, for example, by fluorination of the plastics material. Instead of Floats but other locking devices such as flaps, etc., may be provided.

The float 9 can close off an inflow of electrolyte from the collecting area 2 of the gas space 1 for connection, in particular a Venturi nozzle or Venturi unit, in an off state, as illustrated in FIGS. 11 to 13, which represent various embodiments with the float 9 , As shown in Figure 11, the pressure difference between the pressure in the gas chamber _G p and the pressure p2 in the connection to the Venturi nozzle in an off state to an ^¬ additional force Fi on the float exerts, through the

Pressure difference is conditional. In the flow-through mode, the pressure in the gas space is integral (not at the nozzle) higher than in the electrolyte. As the amount of electrolyte in the collection area 2 increases, an upward force F2 is generated on the float 9. The float 9, or another closure, is designed so that from a certain level of the

Float the opening 3a of the connection between the gas space and the supply of the electrolyte 3 to Venturi nozzle releases. The nozzle sucks the electrolyte from the gas space 1 until the float 9 closes the opening again. The density of the float is smaller than that of the electrolyte. With ^¬ guides 9a, which for example from the same material Rial as the float can be, a better closure of the opening 3a can be ensured.

The dimensions of the float 9 may be designed so that the valve is preferably 2 times per minute or less white ^¬ ter preferably 1 times per minute or less opens. The groove ^¬ Zung a float 9 simultaneously provides a hysteresis in the entire system so that vibrations can be avoided. The float 9 and the supply of the electrolyte in the Venturi nozzle are preferably selected so that the ^{Sammelbe ¬} rich 2 is not completely emptied. This is intended to prevent a gaseous substrate such as CO ₂ from being additionally removed from the gas space 1 and the pressure p _G in the gas space 1 to drop sharply.

Figure 12 shows a further embodiment of the gas space 1 with collection area 2, in which the float 9 but has a different plug shape, in which still join on both sides of the truncated cone cylinder, on the one hand to achieve better closure, on the other hand, but also the buoyancy of Float targeted adjust by ^{¬ for} example, the mass of the float is changed. In Figure 13, the float 9 is formed in a conical shape, whereby the return of the electrolyte from the collecting region 2 for supplying the electrolyte 3 can be done slowly and thus large fluctuations in the supply can be avoided.

The device with a float 9 can be used both in the flow-through (with gas supply through the electrode) and in the backflow operation (with gas supply along the electrode and diffusion of the gas through the electrode).

In Durchströmbetrieb is approximately the integral pressure P _G ^_ P ₂ in the gas space 1 is usually higher, which pushes the float 9, in addition to its own weight, on the connection to the electrolyte. On the float 9 therefore usually a slightly larger force F ₂ must be expended to the opening 3a and thus to open the connection. The force F _{2 to be applied} is also determined by the size of the opening _{3 a} .

In Hinterströmbetrieb the integral pressure should

Gas space / electrolyte of P ~ _G ^_ P ₂ in the off Elek ^¬ trolysesystem preferably be approximately equal. When switched on, an electrolyte flow through the GDE back into the gas space occurs due to the occurring potentials

Float 9 closes the connection through the Venturi effect and its own weight. From a certain level, the opening 3a is opened and overflowed electrolyte is fed back into the electrolyte circuit.

As an alternative or in addition to a float, another regulating mechanism may be provided, such as another

Closure, e.g. a valve which can be closed by a regulator. Of course, several valves can be provided. According to certain embodiments, the suction is regulated by a valve, which regulates the connection between the gas space and the electrolyte inflow.

The valve is coupled in accordance with certain embodiments with a level sensor for electrolyte in the gas space via a controller, wherein the control of the valve is based on a Mes ^¬ sung a level sensor. The level measurement can be done, for example, electronically, optically, based on a pressure measurement, etc., and the level sensor is not particularly limited.

A corresponding system with valves is shown schematically in FIGS. 9 and 10. As shown in FIG. 9, the control device can take place by means of, for example, electrical, sensor technology and corresponding valves 4. In this case, the fill level in the collection area 2 can be measured, for example, by means of a pressure sensor 5. One appropriately designed controller 6, for example, provided as Pmax / Pmin valve control unit, opens a between the

Line L2 (not shown) and the gas space with Sammelbe ^¬ rich 2 located valve 4 when exceeding a specified upper pressure limit p _max . By the pressure difference

Ap = p _max - p2, the accumulated electrolyte is again withdrawn from the gas space 1 and fed back to the electrolyte circuit, for example. If a pressure p _m i _n in the gas chamber 1 falls below, the valve 4 is closed again. Thus, the level of the electrolyte passing through the GDE into the gas chamber can be maintained at a predefined level, thus avoiding salt formation on the backside of the GDE.

Equivalent, the level measurement can alternatively be done via a magnetic float 7 and reed switch 8, as shown in Figure 10 by way of example.

According to certain embodiments, the salt concentration in the electrolyte is chosen so that no salt deposition takes place during operation, ie the electrolysis. These

Concentration can be suitably determined, for example, according to the solubility of a conducting salt, etc. in the electrolyte. In a further aspect, the present invention relates to an apparatus for continuously operating a gaseous substrate electrolytic cell comprising

an electrolytic cell comprising:

an anode,

a cathode,

wherein at least one of the anode and the cathode is formed as a gas diffusion electrode, and

a supply for electrolyte, which is adapted to the

Cell space to supply electrolyte; a gas chamber which is designed to supply a gaseous substrate of a gas diffusion electrode ^¬, wherein the gas space is provided on a side remote from the cell chamber side of the gas diffusion electrode;

a connection between the gas chamber and the supply of electrolyte which is adapted electrolyte which Sam ^¬ melbereich was collected in the gas space to dissipate therefrom.

The device described is suitable for all electrolysis cells with gaseous substrate (CO ₂ , CO) and gas diffusion electrode. In certain embodiments, the device is for CO ₂ electrolysis to CO or hydrocarbons. With the device according to the invention, the inventive method can be carried out.

The supply for electrolyte, the gas space, the collection area in the gas space and the connection between the gas space and the supply for electrolyte have already been discussed in connection with the method according to the invention and thus preferably correspond to those discussed above. In addition, these are not particularly limited.

Also, the supply of the gaseous substrate, which is adapted to supply the gas space to the gaseous substrate, is not particularly limited insofar as it is capable of supplying gas, and preferably is not affected by the gas, and may be used, for example, as a pipe , Hose or the like may be formed.

In addition, the device according to the invention may also have a discharge device for electrolyte and / or a liquid or dissolved product and / or a discharge device for a gaseous product and / or unconsumed gaseous substrate, which are not particularly limited. The electrolytic cell in the inventive device environmentally holds at least an anode and a cathode, of which min ^¬ a is least formed as a gas diffusion electrode, and a cell space which is adapted to be filled with an electric ^¬ LYTEN and in which the anode and the cathode are at least partially incorporated. It is not excluded according to the invention that both the anode and the Ka ^¬ method are formed as a gas diffusion electrode. According to certain embodiments, the anode is formed as a gas diffusion ^¬ electrode. According to certain embodiments, the cathode is designed as a gas diffusion electrode. According be ^¬ voted embodiments is reacted electrolytically at the cathode carbon dioxide or carbon monoxide, so the cathode formed such that they can convert carbon dioxide, for example, as copper (C0 _2, CO) and / or silver-containing ^¬ (C0 ₂₎ gas diffusion electrode.

The electrolysis cells used correspond for example to those of the prior art, which are shown schematically in Figures 1 to 5, wherein in the figures cells are shown with membrane M, which may not be present in the device according to the invention, according to certain embodiments, however, applies and which can separate an anode space I and a cathode space II. Such a

Membrane is present, this is not particularly limited and adapted for example to the electrolysis, for example, the electrolyte and / or the anode and / or cathode reaction.

The electrochemical reduction, for example of CO ₂ , takes place in an electrolysis cell, which usually consists of an anode and a cathode compartment. FIGS. 1 to 5 show examples of a possible cell arrangement. For each of these cell arrangements, a gas diffusion electrode according to the invention can be used, for example as a cathode. By way of example, the cathode compartment II in FIGS. 1 and 2 is designed so that a catholyte is supplied from below and then leaves the cathode compartment II upwards. Alternatively, however, the catholyte can also be supplied from above, as for example with falling film electrodes. At the anode A, which is electrically connected to the cathode K by a current source for providing ^¬ position of the voltage for the electrolysis, the oxidation of a substance found in the anode chamber I instead of being conces- introduced from below for example with an anolyte, and Anolyte with the product of the oxidation then leaves the anode compartment. In the example shown in figures 1 and 2, 3-chamber structure, a reaction gas such as carbon dioxide, by the gas diffusion electrode, here for ^¬ (not shown in detail as GDE) by way of the cathode K are conveyed into the cathode compartment II for reducing, by way of example Hinterströmbetrieb as in Figure 1 or in the flow-through operation in Figure 2. Although not shown are also embodiments with porous anode A conceivable. In FIGS. 1 and 2, the spaces I and II are separated by a membrane M. In contrast, in the PEM (proton or ion exchange membrane) structure of Figure 3, the gas diffusion electrode as cathode K (also not shown in detail as GDE) and a porous anode A directly on the membrane M, whereby the anode space I is separated from the cathode compartment II. The structure in Figure 4 corresponds to a mixed form of the structure of Figure 2 and the structure of Figure 3, wherein on the catholyte side, a structure with the gas diffusion electrode and gas supply G is provided in Durchströmbetrieb, as shown in Figure 2, whereas on the anolyte side, a structure as in Figure 3 is provided. Of course, mixed forms or other embodiments of the exemplified electrode spaces are conceivable. Also conceivable are embodiments without membrane. Thus, according to certain embodiments, the cathode-side electrolyte and the anode-side electrolyte may be identical, and the

Electrolysis cell / electrolysis unit can come out without membrane ^¬ . However, it is not excluded that the electrolysis cell in such embodiments, a membrane However, this is associated with additional effort in terms of the membrane as well as the applied voltage. Catholyte and anolyte can be mixed again outside the electrolysis cell ^¬ optional.

Figure 5 corresponds to the structure of Figure 4, here, as ^¬ derum the gas supply G takes place as in Figure 1 in Hinterströmbetrieb and the reactant and product through E and P are shown.

Figures 1 to 5 are schematic representations. The electrolysis cells of Figures 1 to 5 can also be assembled into mixed variants. For example, the anode compartment may be designed as a PEM half cell, as in FIG. 3, while the cathode compartment consists of a half cell, which has a certain volume of electrolyte between the membrane and

Includes electrode, as shown in Figure 1. The membrane can also be configured as a multilayer, so that separate supply of anolyte or catholyte is made possible. Separation effects are achieved in aqueous electrolytes, for example by the hydrophobicity of intermediate layers. Nevertheless, conductivity can be ensured if conductive groups are integrated in such separation layers. The membrane may be an ion-conducting membrane, or a separator, which causes only a mechanical separation and is permeable to cations and anions.

By using the gas diffusion electrode according to the invention, it is possible to build a three-phase electrode. For example, a gas can be fed from the rear to the electrically active front side of the electrode in order to carry out an electrochemical reaction there. Also, according to certain embodiments, the gas diffusion electrode may only be trailing behind, ie, a gas such as CO ₂ is conducted past the rear of the gas diffusion electrode relative to the electrolyte, which gas may then pass through the pores of the gas diffusion electrode and the product may be removed at the rear. Preference is given to the gas flow during Inverse flows in reverse to the flow of the electrolyte, so that depressed liquid such as electrolyte can be removed.

According to certain embodiments, the connection between the gas space and the supply for electrolyte comprises a Venturi nozzle or another nozzle such as a Laval nozzle, preferably a Venturi nozzle.

The device according to the invention may further comprise a regulating mechanism, which is designed to regulate the discharge of the electrolyte to the collecting area in the gas space

This control mechanism is not further limited and ^corresponds , for example, to those described in connection with the method according to the invention. By the control mechanism in particular, in accordance with certain embodiments, the connection between the gas chamber and the supply of electrolyte from the supply of electrolyte, for example perio ^¬ disch be sealed or closed, for example by a closure, such as a Flüssigkeitsver- circuit, which in the connection between the gas space and the supply for electrolyte can be located anywhere, for example as a valve, formed for example at a Rohrver ^¬ bond near the electrolyte supply, for example at a tee, or as a closure to an outflow from, in ^¬ example Collection area, in the gas space, for example in the form of a float. The control mechanism may Example ^¬ as an opening of the closure depends on measurements and sensor data induce, for example, using a fill level of the electrolyte in the collecting area, but may also be formed automatically or mechanically, without the need for measurement must be made.

Thus, the apparatus according limited hours ^¬ th embodiments contains at least a control mechanism, preferably a liquid seal and a Regelme ^¬ mechanism which opens the access to the electrolyte flow when a certain level of collection area is reached. The regulating mechanism may in this case also be integrated with the liquid closure, for example when using a float.

According to certain embodiments, the control mechanism comprises a float, which is provided in the collecting area in the gas space and is designed to periodically interrupt the connection between the gas space and the supply for electrolyte. The float can hereby be designed as desired, as long as it can interrupt the connection between the gas space and the supply for electrolyte. According to certain embodiments, the float is formed as a cone or truncated cone, wherein the tip of the cone or the circular surface of the truncated cone with the smaller size protrudes into the connection between the gas space and the supply for electrolyte.

According to certain embodiments, the control mechanism comprises a valve in the connection between the gas space and the supply for electrolyte, which is coupled to a level sensor in the gas space and a regulator, wherein the level ^¬ sensor and the controller are adapted to the valve in the To regulate the connection between the gas space and the supply for electrolyte depending on the level of the electrolyte in the gas space.

According to certain embodiments, the erfindungsge ^¬ Permitted device comprises a plurality of electrolysis cells or a stack of electrolysis cells, in which at least one of the anode and the cathode is in each case designed as a gas diffusion electrode, which electrolysis cells then each have a gas space at least, of each with either a feed for Electrolyte for all cells or with multiple feeds for electrolyte for all cells, for example, also separate Zu ^¬ guides for electrolyte for each cell, is connected via a connection between the gas space and the corresponding supply for electrolyte. The several electrolysis cells can then merge into a cell stack (eg, 100 or more cells) to save space. In such a stack is then in particular for reasons of space, the use of

Floats as a control mechanism or self-regulating system advantageous. According to certain embodiments, such devices with multiple Elektrolysezel ^¬ len or cell stacks can thus be found for example, 100 or more cells application, wherein here also the use of

Floats for the regulation of the connection between the

Gas space and the corresponding supply for electrolyte is advantageous.

In addition, the device according to the invention may comprise further constituents which are present in an electrolysis plant, that is to say in addition to the current source for the electrolysis different cooling and / or heating devices, etc. These further constituents of the device, for example an electrolysis plant, are not further limited and can be suitably provided.

The above embodiments, refinements and developments can, if appropriate, be combined with one another as desired. Further possible refinements, developments and implementations of the invention also include combinations of previously or not explicitly mentioned combinations

The following with respect to the embodiments described features of the invention. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention.

The invention will be illustrated below with reference to some exemplary embodiments which, however, do not limit the same. Examples

All experiments, as well as the comparative examples and examples were carried out at room temperature of about 20 ° C - 25 ° C, unless otherwise stated.

Comparative Example 1

A device for CO 2 electrolysis without connection of electrolyte and gas supply is shown in FIG.

An electrolysis is shown in which carbon dioxide is reduced on the cathode side and water is oxidized on the anode A side. On the side of the anode reaction of chloride to chlorine, bromide to bromine, sulfate could examples play held to peroxodisulfate (with or without gas development ^¬ lung), etc.. As the anode A, Example ^¬ as platinum is suitable, and as the cathode K of copper. The two electro ^¬ spaces of the electrolysis cell are separated by a membrane M from Nafion ®. The integration of the cell in a system with anolyte and catholyte 20 is 10 (or. Figure 7 with Gasdiffusi ^¬ onselektrode, s Comparative Example 2) in the figure 6 without gas diffusion electrode shown. Anodenseits water is supplied with ElektrolytZusätzen 12 via an inlet 11 in an electrolyte reservoir. However, it is not excluded that water is also supplied to or instead of the inlet 11 at a different location of the anolyte circuit 10, since, according to FIG. 6, the electrolyte reservoir 12 can also be used for gas separation. From the electrolyte reservoir 12, the electrolyte is pumped by means of the pump 13 into the anode compartment, where it is oxidized. The product is then pumped back into the electric ^¬ lyte reservoir 12 where it ter 26 can be discharged into the Produktgasbehäl-. Via a product gas outlet 27, the product gas can be removed from the product gas container 26. Of course, the separation of the product gas can also be done elsewhere. This results in a Anolyte circuit 10, since the electrolyte is also circulated on the anode side.

On the cathode side 20 is in the catholyte as a carbon dioxide dioxide over a C02 ~ inlet placed in an electrolyte-supply container 21 ^¬ 22, where it is, for example, physically dissolved. By means of a pump 23, this solution is brought into the cathode compartment, where the carbon dioxide is reduced at the cathode K, for example to CO on a silver cathode. An optional further pump 24 then pumps the solution obtained at the cathode K containing CO and unreacted CO 2 to a gas separation vessel 25, where the product gas containing CO 2 can be discharged into a product gas tank 26. The product gas can be taken from the product gas container 26 via a product gas outlet 27. Of the

In turn, electrolyte is pumped out of the gas separation vessel back to the electrolyte reservoir 21 where carbon dioxide may again be added. Here too, only an exemplary arrangement of a catholyte circuit 20 is indicated, the individual device components of the

Katholytkreislaufs 20 may also be arranged differently, for example by the gas separation is already carried out in the cathode compartment. Preferably, the gas separation and the Gassätti ^¬ tion done separately ie in one of the container, the electrolyte is saturated with CO2 and then pumped as a solution without gas bubbles through the cathode compartment. The gas that emerges from the cathode compartment, then accounts for a large proportion of CO, since CO2 itself remains dissolved because it was consumed and thus the concentration in the electrolyte is slightly lower.

The electrolysis takes place in FIG. 6 by adding current via a current source (not shown).

In order to supply the electrolyte and the dissolved CO2 in the electrolyte with time-varying pressure of the electrolysis unit, 20 Ven ^¬ tile 30 are introduced in the anolyte and 10 catholyte circuit, which are controlled by a control device, not shown, and thus the supply to Anolyte and catholyte control to the anode or cathode, whereby the supply is carried out with variable pressure and product gas can be flushed out of the respective electrode cells.

The valves 30 are in the figure before the inlet in the

Electrolysis cell shown, but can also be provided, for example, after the outlet of the electrolytic cell and / or at other locations of the anolyte or 10 Katholytkreislauflaufs 20. Also, a valve 30 in Anolytkreis- run may for example be in front of the inlet into the electrolysis cell, while the valve is located in the catholyte 20 behind the Elektrolysezel ^¬ le, or vice versa. During operation of the cell, salt formation occurred at the cathode K.

Comparative Example 2 The device shown in FIG. 7 corresponds to the device in Comparative ^Example 1, in which case the cathode K is designed as a gas diffusion electrode through which it flows.

During operation of the cell, salt formation also occurred at the cathode K.

example 1

The structure in Example 1 corresponds to that in Comparative Example 2, but the valves 30 are omitted and instead a Venturi nozzle is provided in the catholyte circuit 20, which is connected to the supply for CO ₂ in the gas space corresponding to the structure in Figure 11. Under "normal" operating conditions, a service life of more than 1000 h could be proven. When operating conventional electrolysis cells, it has been shown that electrolyte passes through gas diffusion electrodes (GDE) and leads to an accumulation of electrolyte in the gas space. Both in flow-through (flow-through) and back-flow operation (flow-by) loses the electrolyte by the gas flow Lösungs ^¬ medium, especially water, which occur in the gas space and particularly detrimental in the GDE even salt deposits. These lead to the loss of selectivity and ultimately to the failure of the electrode or the electrolyzer.

This problem can be solved by the electrolytic cell is added to a stackbare, preferably purely mechanical Verbin ^¬ connection between the gas space and electrolyte flow, which may the passing into the gas space liquid is preferably periodically vacuum. The device preferably consists of a unit sucking on the "Venturi principle" and a float providing the necessary hysteresis, The amount of electrolyte flowing through the GDE can be achieved, for example, by adjusting the hydrophilicity of the GDE.

With the device according to the invention and the method according to the invention, a continuous operation can be ensured in the electrolysis cell. The device is much easier to integrate, especially in large-scale electrolysis cells than in small laboratory cells.

Claims

claims

1. A method for the continuous operation of an electrolytic cell with gaseous substrate, wherein

an electrolyte is supplied to the electrolysis cell by an electrolyte flow, and

an electrolyte flow from the electrolytic cell in the

Gas space through a gas diffusion electrode takes place, the electrolyte is collected from the electrolyte flow into the gas space in a collection area in the gas space, and the collected electrolyte is sucked out of this, wherein the suction takes place through a connection between the gas space and the electrolyte inflow. 2. The method of claim 1, wherein the suction takes place by the electrolyte inflow a suction effect on the

Gas space exercises.

3. The method of claim 2, wherein the suction effect arises by the connection between the gas space and the electrolyte inflow comprises a Venturi nozzle through which the electrolyte inflow to the electrolytic cell takes place.

4. The method according to any one of the preceding claims, wherein the suction of the electrolyte from the gas space is periodic.

5. The method of claim 4, wherein the periodic suction is performed by a control mechanism that regulates the periodic suction.

6. The method of claim 5, wherein the control mechanism me ^¬ chanically formed. 7. The method of claim 6, wherein the control mechanism

comprises a float, which is located in the collecting area in the gas space and the outflow to the connection between the gas space and the electrolyte inflow depending on the filling allows the electrolyte in the collection area in the gas space, the float is opened periodically.

Method according to one of the preceding claims, wherein the suction is controlled by a valve which controls the Ver ^¬ bond between the gas space and the electrolyte inflow.

The method of claim 8, wherein the valve is coupled to a level sensor for electrolyte in the gas space via a regulator, wherein the regulation of the valve is based on a measurement of a level sensor.

Apparatus for continuously operating an electrolytic cell with a gaseous substrate, comprising

an electrolytic cell comprising:

an anode,

a cathode,

wherein at least one of the anode and the cathode as

Gas diffusion electrode is formed, and

a cell space that is designed with a

To be filled electrolyte and in which the anode and the cathode are at least partially incorporated;

a supply of electrolyte adapted to supply electrolyte to the cell space;

a gas chamber which is designed to supply a gaseous substrate of Gasdiffusi ^¬ onselektrode, wherein the gas space is provided on a side remote from the cell chamber side of the gas diffusion electrode;

a supply for a gaseous substrate, which is designed to supply the gas space to the gaseous substrate ^¬ ;

a collection area in the gas space, which is designed to collect electrolyte in the gas space; and

a connection between the gas space and the supply for electrolyte, which is designed to electrolyte, which was collected in the collection area in the gas space to dissipate from this.

11. The apparatus of claim 10, wherein the connection between the gas space and the supply for electrolyte comprises a venturi nozzle.

12. Device according to claim 10 or 11, further comprising a regulating mechanism, which is designed to regulate the discharge of the electrolyte from the collecting area in the gas space.

13. The apparatus of claim 12, wherein the control mechanism comprises a float, which is provided in the collecting area in the gas space and is adapted to interrupt the connection between the gas space and the supply of electrolyte periodically.

14. The apparatus of claim 13, wherein the float is formed as a cone or truncated cone, wherein the tip of the cone or the circular surface of the truncated cone with the smaller size protrudes into the connection between the gas space and the supply for electrolyte. 15. The apparatus of claim 12, wherein the control mechanism comprises a valve in the connection between the gas space and the supply for electrolyte, which is coupled to a level ^¬ sensor in the gas space and a controller, wherein the level sensor and the controller are adapted to To regulate valve in the connection between the gas space and the supply for electrolyte depending on the level of the electrolyte in the gas space.