Electrolysis cell, electrolysis tank and CO2 reduction method

Abstract

The present invention relates to electrolytic cells, electrolyzers and methods for the electrochemical reduction of carbon dioxide on an industrial scale. [Selected figure] Figure 1

Description

[Technical field]

[0001] The present invention describes electrolysis cells, electrolysers and methods for the electrochemical reduction of carbon dioxide on an industrial scale. [Background technology]

[0002] The production of basic chemicals, such as carbon monoxide, methanol, ethane, propane, formaldehyde or synthesis gas, is currently based on fossil raw materials. The shortage of such raw materials and the associated CO 2 By increasing emissions, we need to conserve fossil fuel resources such as natural gas and oil, and at the latest reduce the amount of CO released. 2 CO after being used as a material at the end of the life cycle of products manufactured from basic chemicals due to the combustion of and resulting global warming 2 To avoid emissions of CO2, sustainable synthesis methods are essential.

[0003] In addition, CO is used as a raw material for synthesis. 2 It is useful to use CO from various processes, e.g., steel manufacturing or the incineration of household waste. 2 This will help to slow down the increase in global warming.

[0004] The use of renewable energy, for example from wind energy, hydroelectric or solar power plants, among other things, reduces CO2 emissions as a feedstock. 2 This, combined with the use of , makes this new process particularly sustainable.

[0005] Therefore, the electrolysis process is particularly suitable for producing the above-mentioned basic chemicals in a sustainable manner.

[0006] Since basic chemicals are typically produced on a scale of at least 1000 metric tons, CO 2The electrolysis process using CO2 must be made available on a large scale. To produce industrial quantities of products using electrolysis, electrolyzers with large electrolysis cells and multiple electrolysis cells are required. Here, industrial production is defined as more than 0.1 kg of CO2 per electrolysis cell. 2 / (h*m 2 For this purpose, electrolytic cells with an electrode area of ​​2 m² or more per electrolytic cell are usually used, as is known, for example, from chlor-alkali electrolysis. The electrolytic cells are arranged together in groups of up to 100 cells in racks. Several racks then form electrolytic cells. The CO 2 The electrochemical reaction preferably takes place at a gas diffusion electrode connected as a cathode and can in principle take place according to the reaction shown by way of example below: [ka] Where CO 2 is converted to CO and hydroxide ions, and hydrogen can also be produced in a secondary reaction.

[0007] It is common to all known processes that gas diffusion electrodes are used for the electrochemical reaction and that for the operation of the gas diffusion electrodes an industrial scale cell structure in which the gas diffusion electrodes can be installed and operated must be available.

[0008] For example, industrial electrolytic cells used in chloralkali electrolysis usually have a capacity of 1 m per electrolytic cell. 2 The electrolytic cells have an electrode area of ​​more than 100. More than 100 electrolytic cells are connected together to form an electrolytic cell. A large number of electrolytic cells are then used for on-site production.

[0009] The operation of gas diffusion electrodes requires special measures in industrial electrolyzers.

[0010] Therefore, in the industrial use of gas diffusion cathodes, care must be taken to ensure that the gas diffusion electrode (GDE) used for this purpose has an open pore structure and is installed between the electrolyte space and the gas space. The internal structure of the GDE must allow the gas reaction to take place at the three-phase boundary between the electrolyte, the catalyst, and the gas as close as possible to the electrolyte. This boundary layer is stabilized by the hydrophobicity of the GDE material. However, it was found that this stabilization, brought about by the surface tension of the electrolyte at the electrode surface, only allows a finite pressure gradient between the gas and liquid sides of the GDE. If the gas-side pressure is too high, the gas will eventually break through the GDE and the function of the GDE is destroyed in this area. That is, here the electrolysis process is locally interrupted. On the other hand, if the liquid pressure is too high, the three-phase boundary is shifted out of the catalyst area of ​​the GDE until the GDE is filled with electrolyte, and further pressure increase leads to liquid leakage of the electrolyte into the gas space. As a result, the function of the GDE is destroyed as well and the desired reaction does not take place.

[0011] In the case of vertical electrode arrangements, such as those usefully used in industrial electrolysers, this leads to a limitation of the construction height of the electrolysis cell, due to the inability to operate the gas diffusion electrodes at excessively high gas or liquid pressures. Typical industrial construction heights of the electrodes of electrolysis cells exceed 30 cm, usually about 100-150 cm. In the case of membrane electrolysis with a construction height of more than 10 cm, the gas already enters from the gas space into the cathode-electrolyte gap between the GDE and the membrane in the upper region of the electrolysis cell. Thus, the industrially achievable construction height remains limited to about 20-30 cm, making industrially economical utilization of the electrolysers currently available on the market difficult.

[0012] Industrial electrochemical CO 2 Industrial-scale cell concepts for the reduction have not yet been described or are not available: the first experiments were always carried out only on a small laboratory cell scale, with construction heights less than 10 cm, and the problems of construction height and pressure difference between the gas space and the electrolyte space therefore did not play any role. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] WO2003 / 042430A2 Summary of the Invention [Problem to be solved by the invention]

[0014] Therefore, the object of the present invention is to 2 The present invention provides an apparatus and method for operating a gas diffusion electrode on an industrial scale, whereby more than 0.1 kg of CO is converted in the GDE. 2 / h*m 2 means the amount of production that reacts electrochemically.

[0015] CO or CO / H 2 CO to form the mixture 2 The electrochemical reduction of O at a gas diffusion electrode is essentially known in principle from chlor-alkali membrane electrolysis. 2 This is different from the electrochemical reduction of O 2 In the reduction of CO / H, hydroxide ions are formed from oxygen gas, resulting in a decrease in volume. The GDE consumes oxygen, resulting in a decrease in partial pressure. However, the CO / H 2 CO to form 2 The reduction of CO 2 Gas to gas volume (CO or CO / H 2 ), so that no partial pressure drop occurs. This requires a specific mode of operation, especially on the cathode side of the electrolysis cell.

[0016] As mentioned above, industrial quantities of CO are 2 No industrial electrolysis process or apparatus is known to date that can be produced from [Means for solving the problem]

[0017] The above technical objective is to provide a method for producing CO2 on an industrial scale in accordance with the present invention. 2 The electrolytic cell of the present invention comprises at least a cathode half shell (1) having a cathode (11), a gas space (4) connected to a first gas supply conduit (5) for carbon dioxide gas and to a first gas discharge conduit (6) for the gaseous reaction products, in particular carbon monoxide, hydrogen and unreacted carbon dioxide gas, a catholyte inlet (13), and a catholyte outlet (14), an anode half-shell (2); and a separator (3) arranged between the anode half-shell (2) and the cathode half-shell (1) for separating the anode space (15) and the cathode space (16); said anode half-shell (2) has at least a second gas exhaust conduit (7) for the anode reaction products, in particular oxygen and possibly carbon dioxide, an anolyte inlet (8), and an anolyte outlet (9) and an anode (10), further comprising power leads (31, 32) for connecting the anode and the cathode to a DC voltage source, the cathode (11) being configured as a gas diffusion electrode for reacting carbon dioxide gas; the cathode (11), the anode (10) and the separator (3) Perpendicular to the main dimension a gap (12) for the passage of catholyte (17) by the falling liquid film principle is placed between the separator (3) and the cathode (11). [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic vertical cross-sectional view of an electrolytic cell Z. [Diagram 2] FIG. 2 shows the introduction and discharge of anolyte through a common outlet for multiple electrolysis cells. [Diagram 3] FIG. 3 illustrates the introduction and discharge of anolyte through separate outlets for multiple electrolysis cells. [Figure 4] FIG. 4 shows the introduction and discharge of catholyte from multiple electrolysis cells. [Diagram 5]FIG. 5 shows the introduction and exhaust of gases at the cathode. [Figure 6] Figure 6 shows a schematic diagram of the overall process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] In a preferred embodiment of the present invention, the separator is an ion exchange membrane or diaphragm, and the separator is particularly preferably an ion exchange membrane.

[0020] Suitable ion exchange membranes are in particular configured as cation exchange membranes and capable of conducting cations from the anode space to the cathode space. These are known in the prior art. Alternatively, it is possible to use anion exchange membranes which transport anions from the cathode space to the anode space. It is preferred to use cation exchange membranes. In conventional ion exchange membranes, the ion transport is also related to the transport of water, which depends on the set concentrations of the anolyte and catholyte, the temperature and the operating conditions.

[0021] Suitable diaphragms are in particular all known diaphragms that tightly separate the anode space from the cathode space, in particular from the cathode gap. Here, the diaphragm should in particular have a tightness (bubble point) of more than 10 mbar, preferably more than 300 mbar, particularly preferably more than 1000 mbar. In particular, the diaphragm should be inert to the electrolyte and the reactant gases and stable at the operating temperature. Diaphragms for electrolysis are known from the prior art.

[0022] The electrolysis cell is intended for use in electrolysis on an industrial scale, which means in particular that the construction height of the electrolysis cell is at least 30 cm and therefore differs significantly from laboratory and laboratory cells.

[0023] A major consequence of using such structural heights is that measures must be taken to prevent both catholyte and gas from passing through the gas diffusion electrode.

[0024] In a preferred embodiment, the vertical Main dimension in direction is at least 30 cm, preferably at least 60 cm, particularly preferably at least 100 cm. Such a construction height makes it possible to operate the electrolysis cell according to the principle of a falling film (catholyte) in the cathode space without any catholyte or gas permeation through the gas diffusion electrodes.

[0025] As the cathode, CO 2 It is preferred to use gas diffusion electrodes containing electrocatalysts for the reduction, in particular gas diffusion electrodes made based on silver and / or silver oxide as electrocatalyst, preferably on silver particles, and applied in compaction together with a powdered fluoropolymer, in particular PTFE powder, as a non-conductive binder to a metallic or non-metallic, conductive or non-conductive support. It is preferred to use metallic conductive supports for compaction.

[0026] Instead of the powdered fluoropolymers, it is in principle also possible to use other polymer powders having comparable properties (i.e. inert to the electrolyte, in particular at the reaction temperatures and high current densities, and processable in the manufacture of GDEs), in particular polyalkylenes, particularly preferably polyethylene, polypropylene or partially fluorinated polymers.

[0027] In another preferred embodiment of the electrolysis cell of the invention, a means for slowing down the flow of catholyte (hereinafter referred to as a "flow brake") is provided in the gap between the membrane and the GDE. In this way, the residence time of the catholyte in the gap in front of the cathode can be controlled. The flow brake is particularly preferably configured as a non-conductive, inert sheet-like woven structure.

[0028] The flow brake may in particular consist of a porous sheet-like textile structure, particularly preferably a woven fabric, stretched loop knit fabric or shaped loop knit fabric arranged in the gap. Alternatively, mechanical internal structures in the gap may be envisaged to provide a horizontal electrolyte flow or a flow of electrolyte at a slight angle to the horizontal, resulting in a meandering electrolyte flow. The material of the flow brake may in particular be hydrophilic, as in the case of the flow brake described in Example 1 of WO2003 / 042430A2, for example, or may be hydrophobic, depending on the choice of flow conditions or the viscosity of the catholyte. Preferred materials are as described above.

[0029] To ensure that the gap is always sufficiently supplied with electrolyte, the introduction of catholyte can preferably be carried out by a distribution channel connecting a catholyte supply conduit to the gap. To ensure that the distribution channel is always filled with electrolyte, the distribution channel can have an overflow (not shown) through which excess electrolyte supplied can be drained.

[0030] In this case, the gas diffusion electrodes seal the distribution channels and the gaps from the gas space.

[0031] Contact between the gas diffusion electrode (GDE) and the power lead in the cathode space is advantageously and preferably made via a resiliently mounted conductive structure. This can be configured, for example, as a rigid structure in the form of an expanded metal mounted on a spring, electrically contacting the GDE from the side of the gas space. In order to maintain the size of the gap between the GDE and the separator under a compressive load (for example by electrical contact), a spacer is placed in the gap between the separator and the GDE. The function of the spacer can also be performed by the flow brake, if the latter has sufficient mechanical stability and rigidity under a compressive load on the surface.

[0032] In a preferred embodiment of the electrolysis cell of the present invention, a second gas discharge conduit for the anode reaction products is connected to the upper end of the anode space; a first gas discharge conduit for the gaseous reaction products, in particular carbon monoxide, hydrogen and unreacted carbon dioxide gas, is connected to the upper end of the gas space; and a gas supply conduit for carbon dioxide is connected to the lower end of the gas space. The introduction of carbon dioxide can be preferably carried out through a gas distribution channel, for example a pipe having a number of holes as a gas inlet arranged in the electrolysis cell, so that carbon dioxide can be supplied to the electrode surface and the reaction products can be discharged uniformly across the width of the electrolysis cell.

[0033] CO fed to the cathode half shell 2 The amount of CO is at least 0.5 times the amount of charge passed per current, calculated according to the reaction equation above. If more hydrogen is to be produced, a substoichiometric amount of CO is required. 2 If hydrogen production is to be avoided, CO 2 In this case, CO 2 The amount is preferably a multiple of the stoichiometric amount required depending on the current flowing. In particular, 0.5% to 800% more CO than theoretically required. 2 can also be introduced.

[0034] In a further preferred variant of the electrolytic cell of the invention, the second gas discharge conduit is connected to a separation device for separating carbon dioxide from oxygen, which is connected to the gas supply conduit via a carbon dioxide conduit so that the separated carbon dioxide can be recycled to the electrolytic cell. The separated oxygen, depending on its purity, can be passed directly for further use for other chemical reactions.

[0035] CO 2 In a preferred embodiment of the electrolytic cell for reducing to CO, an aqueous solution of an alkali metal bicarbonate, preferably potassium bicarbonate, caesium bicarbonate or sodium bicarbonate, particularly preferably potassium bicarbonate, is used as catholyte.

[0036] Independently of this, an aqueous solution of an alkali metal bicarbonate, preferably potassium bicarbonate, cesium bicarbonate or sodium bicarbonate, particularly preferably potassium bicarbonate, is used as the anolyte in a further preferred embodiment of the electrolytic cell. The salts in the anolyte and catholyte preferably have the same cationic species.

[0037] To increase the electrical conductivity, electrolyte salts inert with respect to the anodic or cathodic reactions and preferably having the same cationic species, such as alkali metal sulfates or alkali metal hydrogen sulfates; in particular salts selected from among the sulfates or hydrogen sulfates of potassium, cesium and sodium; particularly preferably potassium hydrogen sulfate, can be added independently to both the anolyte and the catholyte. The total concentration of the salts is preferably 0.1 to 2 moles per liter, and particularly preferably an electrolyte is used which has a conductivity of more than 10 S / m (S is Siemens and m is meters) at 25 ° C.

[0038] In a particularly preferred variant of the electrolytic cell of the invention, when the same electrolyte salt is used for the anolyte and the catholyte, the catholyte outlet is installed at the lower end of the gap, the catholyte inlet is installed above the gap on the cathode half-shell and the catholyte outlet is connected to a catholyte collection pipe in which the catholyte from the catholyte outlets of the electrolytic cell join together, and the anolyte from the anolyte outlets of the electrolytic cell join together in a collection tube for the anolyte (see, for example, FIG. 1).

[0039] Therefore, when the same electrolyte salt is used by the anolyte and the catholyte, an electrolysis cell is preferred, characterized in that the catholyte outlet is installed at the lower end of the gap, the catholyte inlet is arranged above the gap on the cathode half-shell, and the catholyte outlet is connected, in the case of several catholyte outlets, more preferably via one collection tube conduit, to an electrolyte collection facility, in which the catholyte from the catholyte outlet and the anolyte from the anolyte outlet are mixed. In the case of several anolyte outlets, it is particularly preferred that a collector is installed between the anolyte outlet and the electrolyte collection facility.

[0040] Before the catholyte and anolyte are mixed together, the two solutions are preferably fed separately to a gas removal unit, where the gases dissolved or dispersed in the electrolyte are separated. The anolyte is thus substantially free of oxygen, and the catholyte is free of carbon monoxide and hydrogen. This ensures that no CO 2 The anolyte containing oxygen is CO / H 2 The catholyte may then be mixed with the degassed electrolyte anolyte to prevent it from mixing with the catholyte containing gas to form an explosive gas mixture.

[0041] If necessary, the electrolyte can be heated or cooled by means of a heat exchanger to set a predetermined inlet temperature of the electrolyte to the anode and cathode spaces. If necessary, appropriate amounts of electrolyte salt or water can be added to set the electrolyte concentration. Similarly, more concentrated or more dilute electrolyte solutions can be introduced into the electrolytic cell to set the desired inlet concentration.

[0042] In a further preferred embodiment of the electrolytic cell of the invention, the first gas discharge conduit is connected to a gas separation unit for separating carbon monoxide, hydrogen and unreacted carbon dioxide gases, in particular via a collection conduit connecting the first gas discharge conduit of the electrolytic cell to further similar gas discharge conduits of other electrolytic cells.

[0043] In this particular embodiment of the cell according to the invention, the gas separation unit preferably comprises a recirculation conduit for the separated carbon dioxide gas, which recirculation conduit is connected to the first gas supply conduit for carbon dioxide gas and to the gas space. In particular, the distribution conduits connecting the recirculation conduit to the first gas supply conduit for carbon dioxide gas of the electrolytic cell and further to the similar first gas supply conduit of the other electrolytic cell may be interconnected.

[0044] The gas separation unit also preferably has an exhaust conduit for the separated carbon monoxide, which is connected to a chemical production plant for chemical conversion of the carbon monoxide to a chemical intermediate, or the separated carbon monoxide can be fed to a collection conduit or storage for further use.

[0045] Typical intermediates are, for example, phosgene, isocyanates or bisphenols which are used for the preparation of industrial polymers, in particular polyurethanes or polycarbonates.

[0046] The gas separation unit also preferably has an outlet conduit for the separated hydrogen, which in turn is connected to a hydrogen pipe network or to a distribution facility for hydrogen.

[0047] In a preferred embodiment of the invention, the second gas exhaust conduit for the anode reaction product is connected to a second gas separation unit for separating carbon dioxide from oxygen, which is connected to the gas supply conduit via a carbon dioxide conduit and optionally via a distribution conduit.

[0048] In a further particularly preferred variant of the electrolysis cell (see, for example, FIG. 2), the second gas discharge conduit for the anodic reaction product and the anolyte discharge conduit form one unit and are connected to a gas / liquid separator in the external collection conduit. The gas / liquid separator separates the CO 2 and O 2 The anolyte is fed to a second gas removal unit and the gas is separated from the electrolyte. 2 and O2 The electrolyte from the electrolyte collection facility is then re-fed to the anolyte inlet via an external distribution conduit for the anolyte.

[0049] In a further particularly preferred variant of the electrolysis cell, the electrolyte recirculation conduits (for the catholyte and / or the anolyte, as appropriate) optionally have a supply conduit for mixing in water or a more concentrated electrolyte and a mixing unit for mixing the depleted electrolyte (e.g. the anolyte) with the more concentrated electrolyte or, if necessary, in water or a less concentrated electrolyte.

[0050] Nickel and nickel alloys are the preferred materials for the construction of the cathode half shell. However, in a particularly preferred embodiment of the electrolysis cell, all parts in contact with the electrolyte in the electrolysis cell are made of nickel with a gold start-up corrosion protection layer. It is also conceivable to use polymers that are inert at operating temperatures below 90° C. as alternative construction materials or materials for the internal coating of the cathode side of the cell, as long as they are chemically resistant to the electrolyte and gases at the given temperature.

[0051] The preferred materials of construction of the anode half-shell can be nickel and nickel alloys, titanium or titanium alloys. It is also particularly preferred that all parts in contact with the electrolyte in the electrolysis cell have a gold anti-corrosion layer in the region of the anode half-shell. Here again, inert polymers with sufficient heat resistance and mechanical strength can be used as alternatives as well as materials of construction or materials for the inner coating of the anode side of the electrolysis cell.

[0052] The present invention further relates to a method for producing CO 2 on an industrial scale by membrane or diaphragm electrolysis. 2the electrolytic cell according to the invention, characterized in that it comprises a plurality of electrolytic cells according to the invention, which are electrically connected to one another in a bipolar manner.

[0053] The electrolytic cell is particularly preferably constructed in such a way that the individual electrolytic cells are connected to one another in a bipolar manner and the end elements are provided with power inlet or outlet plates.

[0054] The connections of the anolyte supply conduits and the catholyte supply conduits with the corresponding electrolyte discharge conduits of the individual electrolysis cells are preferably connected to each other via external connection conduits with distributors or collectors. A further preferred embodiment of the electrolysis cell according to the invention is characterized in that a collector for the anolyte, a collector for the catholyte, a distributor for the catholyte and a gas distributor for the reactant gases as well as a gas collector for the product gas are provided to connect the supply and discharge conduits of the various electrolysis cells. In particular, the supply conduits of at least 10 electrolysis cells are connected to the distributor and the discharge conduits of at least 4 electrolysis cells are connected to the collector. The introduction of the anolyte is therefore carried out via distribution conduits for the anolyte (see, for example, FIG. 2). From these distribution conduits, the anolyte is supplied to the elements connected to the anode space in each case via flexible connections, for example flexible pieces of tubing. The anolyte conveyed from the anode space and the gases produced therein (mainly oxygen and carbon dioxide) are again supplied to the collection conduits. This outer collection conduit can function as a gas / liquid separator so that the gas can be fed via a further separate conduit to an optional second gas separation unit for separation of oxygen and carbon dioxide. From the connecting conduit, the anolyte is fed to the second gas separation unit and then to the electrolyte collection facility.

[0055] The introduction of the catholyte can take place via an external distribution conduit, from which it is fed via a flexible connection, for example a flexible piece of tubing, to the electrolysis cells connected thereto and in these electrolysis cells to the internal distribution channel of the cathode in each case. The catholyte flowing out of the gap is fed again via an outlet into the external collector conduit. In order to prevent gas from entering the external collector conduit from the cathode space via the outlet, the outlet may be configured to be immersed in the electrolyte present in the collector conduit and form a seal.

[0056] The introduction of gas into the cathode space is preferably carried out via an external distribution conduit (see, for example, FIG. 5). From this external distribution conduit, the gas is supplied via a connection to the cathode coupled thereto via a gas supply conduit. The connection of the cathode half shell to the distribution conduit can be carried out, for example, via a flexible piece of tubing. In a particularly preferred embodiment, in the electrolysis cell, the gas can be distributed over the width of the electrolysis cell via a distribution system, so that a uniform flow of gas from the bottom up occurs and a sufficient amount of carbon dioxide gas can be supplied to the GDE. In order to supply the gas of the gas space to the GDE, an internal structure can be installed in the gas space, which brings about a swirling of the gas flow. This can likewise ensure that the reaction products and excess unreacted carbon dioxide gas are discharged again from the electrolysis cell. The gas from the gas space enters again into the outer collection tube conduit via the outlet. The connection between the cathode outlet and the collection tube conduit can again be carried out via a flexible piece of tubing. The gas from the outer collection conduit can be CO, H 2 and unreacted CO 2 The CO separated in the gas separation unit is then fed to a gas separation facility to separate the CO 2 The gas, together with fresh carbon dioxide gas, is returned to the cathode space via the outer distribution line.

[0057] The electrolytic cell of the present invention is preferably operated at an absolute pressure in the range of 900 mbar (900 hPa) to 2000 mbar (2000 hPa).

[0058] CO 2 As gas diffusion electrodes for the reduction of to CO, it is particularly preferred to use silver-based GDEs, in particular those produced according to the measures disclosed in European patent EP-A 1 728 896, particularly preferably according to the examples described therein. The porosity of the catalytically active layer (calculated from the amount of raw material used and the material density divided by the volume of the electrode calculated from the geometric dimensions of area and thickness minus the volume of the support) is particularly preferably greater than 10%, but can be less than 80%.

[0059] To avoid undesirable buoyancy effects caused by the light product gases CO and hydrogen, carbon dioxide is preferably fed into the gas space to generate a gas velocity close to the rear side of the gas diffusion electrode of 0.001-15 m / s, preferably 0.01-10 m / s. The gas velocity is calculated from the volumetric flow rate of the introduced gas or gas mixture and the area of ​​the distance from the GDE to the separator multiplied by the gap width. When adjusting the amount of gas, the amount is calculated according to the current flowing and the resulting charge amount, and the stoichiometrically required CO. 2 Care must be taken to ensure that the amount of the solution is not less than at least 0.5 times the amount of the solution.

[0060] The gas velocity is maintained in the above-mentioned range of 0.001 to 15 m / s, preferably 0.01 to 10 m / s, preferably by structural means. This can be achieved, for example, by keeping the gas space in the region between the gas diffusion electrode and the support structure for the gas diffusion electrode as narrow as possible. Thus, for industrial electrolysis cells, the distance from the gas diffusion electrode to the rear wall of the cathode should be no more than 5 cm, preferably no more than 4 cm, particularly preferably no more than 2 cm. Also conceivable are flow-directing internal structures in the region between the gas diffusion electrode and the support structure for the gas diffusion electrode, in order to prevent undesirable chimney effects. Furthermore, internal structures that make the gas flow turbulent in the region between the gas diffusion electrode and the support structure are also possible. This can be achieved, for example, by the installation of porous structures, such as metal or polymer foams, or knitted, braided or woven fabrics.

[0061] As supports for the manufacture of GDEs, it is preferred to use gold-plated nickel mesh, silver mesh, PTFE-coated glass fiber supports, woven carbon fiber or C-based knitted fabrics / structures, and supports based on polymers, such as polypropylene or polyethylene.

[0062] Separating the anode and cathode chambers with a separator helps to avoid mixing of the electrolytes and avoid electrochemical short circuits. Without a separator, gases formed at the anode could be further reduced at the cathode, resulting in the formation of an electrochemical short circuit, reducing the current yield and potentially compromising the economics of the process. Additionally, hydrogen and / or carbon monoxide produced in the GDE could form explosive gas mixtures with oxygen produced at the anode.

[0063] According to a preferred embodiment of the electrolysis cell, if an ion exchange membrane is used as separator, it is preferable to use known cation exchange membranes, for example of the type Nafion N 324 (manufacturer: Chemours Company), in particular Nafion N 324 fumasep F 1075-PK (manufacturer: Fumatech GmbH).

[0064] According to a preferred embodiment of the electrolysis cell, if a diaphragm is used as a separator, any diaphragm known for electrolysis can be used, for example a Zirfon™ Pearl (manufacturer: Agfa) type diaphragm made of PTFE and zirconium oxide.

[0065] The electrolysis cell is advantageously constructed in particular such that the separator is placed directly on the anode. The anode is electrically conductively connected to the anode half shell. The anode is preferably constructed with a hollow space shaped to conduct the gas (e.g. oxygen gas) formed at the anode to the rear side of the anode facing away from the separator. As anode structure, it is possible to use, for example, expanded metal or any other anode structure known from the prior art. A preferred design of the electrolysis cell of the invention is further characterized in that the anode is placed on the separator at a point, line or area contact of the anode. This allows the gas generated at the anode to be conducted to the rear side of the anode facing away from the separator. Gas present between the anode and the separator can cause an increase in the electrolysis voltage, which may impair the electrolysis process or the economics of the electrolysis process. Furthermore, the placement of the separator on the anode avoids damage to the separator during operation. The generation of gas results in pressure fluctuations, which in turn cause the separator to move back and forth during electrolysis, which in the long term may cause mechanical damage with the consequence of cracks, thus compromising the gas / liquid separation effect.

[0066] The pressure difference at which the separator is pressed against the anode is at least 10 mbar in such a preferred embodiment of the invention.

[0067] Furthermore, the present invention relates to the production of CO2 on an industrial scale by membrane electrolysis with a gas diffusion electrode as the cathode. 2The method is characterized in that it is carried out in an electrolytic cell as described above, the separator being an ion exchange membrane, and includes the following steps: - introducing a catholyte, which is an aqueous solution containing at least an alkali metal bicarbonate, into the gap between the ion exchange membrane and the cathode via the catholyte inlet; - introducing an anolyte into the anode space via the anolyte inlet, the anolyte being an aqueous solution containing at least an alkali metal bicarbonate; - introducing a flow of carbon dioxide gas into the gas space through a first gas supply conduit; - setting the electrolysis voltage at the power leads and - discharging the reacted catholyte at a catholyte outlet; - Discharging the anode reaction products consisting of anolyte and product gases, the anolyte being discharged through an anolyte outlet and the product gases oxygen and possibly CO 2 is discharged through a second gas discharge conduit or the anolyte and the product gas are discharged together through a special conduit; - at least CO, unreacted CO from the gas space via a first gas exhaust pipe; 2 and optionally discharging a gaseous cathode reaction product consisting of hydrogen; - CO, unreacted CO 2 , and optionally hydrogen gas mixture into its components, and unreacted CO 2 recirculating the first gas to the first gas supply line; - setting an initial concentration of alkali metal bicarbonate in the discharged anolyte and catholyte; and - Recirculating the catholyte to the catholyte inlet and the anolyte to the anolyte inlet (8).

[0068] Furthermore, the present invention relates to the production of CO2 on an industrial scale by diaphragm electrolysis at a gas diffusion electrode as the cathode. 2The method is carried out in an electrolytic cell as described above, the separator being a diaphragm, and is characterized in that it comprises the following steps: - introducing a catholyte (17), which is an aqueous solution containing at least an alkali metal bicarbonate, into the gap (12) between the diaphragm (3) and the cathode (11) via the catholyte inlet (13); - introducing an anolyte, which is an aqueous solution containing at least an alkali metal bicarbonate, into the anode space (15) via the anolyte inlet (8), - introducing a carbon dioxide gas stream (33) into the gas space (4) through a first gas supply conduit (5), - setting the electrolysis voltage on the power leads (31) and (32); - discharging the reacted catholyte at a catholyte outlet (14); - discharging the anode reaction products consisting of anolyte and product gas, the anolyte being discharged through the anolyte outlet (9) and the product gas oxygen being discharged through the second gas discharge conduit (7) or the anolyte and the product gas being discharged together, in particular via the conduit (70), - from the gas space (6) via a first gas outlet pipe (6), at least CO, unreacted CO 2 and optionally discharging a gaseous cathode reaction product consisting of hydrogen; - CO, unreacted CO 2 , and optionally hydrogen into its components, and unreacted CO 2 to the first gas supply pipe (5); - setting an initial concentration of alkali metal bicarbonate in the discharged anolyte and catholyte; and - Recirculating the catholyte to the catholyte inlet (13) and the anolyte to the anolyte inlet (8).

[0069] In a preferred embodiment of the method, the carbon dioxide gas is humidified with water vapor before being fed into the electrolysis cell and into the gas space. Here, the carbon dioxide gas is charged with an amount of water such that the water vapor partial pressure of the catholyte in the cell corresponds to the water vapor partial pressure of the carbon dioxide gas fed. This allows water to be added to the electrolyte inside the gas diffusion electrodes at the phase interface, preventing water from being extracted. It may be necessary to heat the fed carbon dioxide gas so that a sufficient amount of water can be absorbed by the carbon dioxide.

[0070] The two novel methods (membrane electrolysis and diaphragm electrolysis) are preferably carried out in such a way that the gas velocity in the gas space close to the rear side of the gas diffusion electrode is between 0.001 m / s and 15 m / s, preferably between 0.01 m / s and 10 m / s.

[0071] In a further preferred embodiment, the two novel processes (membrane electrolysis and diaphragm electrolysis) are carried out such that the drift velocity of the catholyte flowing from top to bottom through the gap is between 0.2 cm / s and 15 cm / s, preferably between 1 cm / s and 10 cm / s. Independently, the volumetric flow rate of the anolyte in the anode half shell is less than 10 l / (h*m 2 )~300 l / (h*m 2 ) (where "l" is the volume of anolyte in liters, "h" is time, and "m 2 " is the area of ​​the anode).

[0072] The invention will now be described by way of example with reference to the drawings, in which: EXAMPLES

[0073] General description of the construction of the electrolytic cell or cell according to the invention Cathode Half Shell The cathode half shell 1 has an electrolyte inlet 13 and an electrolyte outlet 14, and also a gas supply 5 and a gas exhaust 6 (see FIG. 1).

[0074] The introduction of electrolyte 13 into the cathode half-shell 1 is performed from above, and the supplied catholyte 17 flows downwards along the gas diffusion electrode (GDE) 11 from above. Here, the catholyte 17 flows downwards through the gap 12 between the ion exchange membrane 3 and the GDE 11. To avoid excess electrolyte flowing into the gap 12, a flow brake 24 is installed in the gap 12.

[0075] The flow brake 24 is made from a porous woven fabric of PTFE, as described in WO 2003 / 042430 A2.

[0076] In order to ensure that the gap is always supplied with sufficient catholyte 17, the introduction takes place via a distribution channel 34. To ensure that the distribution channel 34 is always filled with catholyte 17, this channel can have an overflow (not shown here) via which the excess catholyte 17 supplied can be drained.

[0077] The contact between the GDE 11 and the power inlet lead 31 in the cathode space is made via a resiliently mounted conductive structure 35. This resilient structure 35 rests on a rigid nickel metal structure in the form of an expanded metal (not shown in FIG. 1). The expanded metal is conductively connected by means of a rigid connection 91 to the cathode half-shell. The GDE 11 is mounted on the resilient structure 35 and is electrically contacted from the side of the gas space 4. The cathode half-shell 1 is in electrical contact with the anode half-shell 2 of another adjacent electrolysis cell Z2 in case of a bipolar connection of several electrolysis cells Z1 or with the power supply plate 62. The outermost anode half-shell 2 is correspondingly electrically connected to the power outlet plate 63.

[0078] A gas supply 5 for the introduction of carbon dioxide 33 into the gas space 4 takes place in the lower part of the gas space 4, while an exhaust conduit 6 for the gaseous reaction products from the cathode space 16 is arranged in the upper region of the gas space 4. In order to prevent gas from leaving the cathode space 16 together with the electrolyte via the catholyte outlet 14, the outlet 14 is preferably arranged in such a way that it can be introduced submerged in an external collector conduit 43 for the catholyte in one variant. Such submersion is known (see, for example, DE 10 2005 027 735 A1).

[0079] In the electrolytic cell E, the discharge conduit 14 and the supply conduit 13 for the catholyte are coupled to a plurality (n) of electrolytic cells Z1, Z2, ... Z(n) via an external connection conduit-collector 43 or distributor 42 in fluid connection (Figure 4). Similarly, the gas discharge conduit 6 and the gas supply conduit 5 are joined via an external connection conduit-collector 45 or distributor 44- (Figure 5). Similar couplings of the anolyte supply conduit 8 from the distributor 40 and the anolyte discharge conduit 9 at the collector 41 are shown in Figure 3. A gas discharge conduit 7 for the anode gas is collected and can be generated via a similar collection conduit (not shown) and a second gas separation unit 20 (FIG. 3), or the anode gas is discharged from the anolyte space 15 via a connecting conduit 70 together with the anolyte and separated into an electrolyte stream (in conduit 9a) and an anode gas (in conduit 41a) in a collector 41b configured as a gas / liquid separation device (FIG. 2). The anode gas is then fed via conduit 41a to the second gas separation unit 20, where it is separated into oxygen and CO 2 and are separated.

[0080] The catholyte that is combined in collector 43 through catholyte outlet 14 is preferably fed via catholyte outlet 14a to a gas removal facility 74 where the catholyte is stripped of any remaining dissolved or dispersed hydrogen and carbon monoxide (see FIG. 6) and these remaining gases are discarded or combusted.

[0081] Oxygen-free electrolyte is removed from the gas removal facility 72 via outlet 9b and is fed to the electrolyte recovery facility 19. From here, the electrolyte can be distributed to the anode and cathode after adjustment of the concentration by addition of water or a more dilute or concentrated electrolyte solution 18. From the electrolyte collection facility 19, the electrolyte is brought to the required inlet temperature by means of a heat exchanger (not shown) and fed via distributors 42 and 40 to the electrolysis cells via conduits 8 and 13 (see FIG. 6).

[0082] The anolyte mixed in the collector 41 via outlet 9 is preferably fed via conduit 9a to a gas removal facility 72 where residual gases such as oxygen are removed from the anolyte. These residual gases are either discarded or reused, depending on their quantity.

[0083] The deoxygenated anolyte is fed to an electrolyte collection facility 19 via conduit 9b.

[0084] As gas removal facility 72 or 74 it is possible to use a stripping column known per se.

[0085] The basis for operation is an active electrode area of ​​at least 0.1 m 2 An electrolytic cell Z having a flow rate of at least 25 l / (h*m) is used. The electrolytic cell Z has a width of at least 10 cm. The height of the electrodes is at least 30 cm. The electrolyte feed rate to the GDE is typically 25 l / (h*m 2 )~500l / (h*m 2 ), where "l" is the volume of catholyte delivered (in liters), h is time, and m 2 is the area of ​​the installed GDE.

[0086] The drift velocity of the catholyte 17 flowing downward from the top through the gap 12 formed by the GDE 11 and the separator 3 is typically between 0.2 cm / s and 15 cm / s.

[0087] The gap 12 between the GDE 11 and the separator (ion exchange membrane 3) is at least 30 cm high and 10 cm wide, with a gap width of at least 0.1 mm.

[0088] Used as catholyte 17 is an aqueous solution of an alkali metal hydrogen carbonate or a mixture thereof, for example sodium or potassium hydrogen carbonate. As electrolyte salts further salts such as alkali metal sulfates or hydrogen sulfates can be added. The total concentration of the salts is preferably 0.1-2 mol / l, and an electrolyte is used which has a conductivity of more than 10 S / m at 25 ° C (S is Siemens and m is meters). The measurement of the conductivity can be carried out using a commercially available conductivity meter.

[0089] The outlet temperature of the catholyte from the cathode half shells 1 to 14 is not more than 85° C., preferably not more than 60° C., particularly preferably not more than 45° C. The temperature of the catholyte 17 supplied to the cell Z is adjusted so as to comply with the outlet temperature.

[0090] Excess CO 2 33 is fed into the gas space 4 of the cathode half-shell 1 via the inlet 5. Here, CO 2 The amount is preferably a multiple of the stoichiometric amount required depending on the current flowing. From 0.5% to 800% more CO than theoretically required 2 will be added.

[0091] Introduced CO 2 In order to obtain a better distribution of the CO introduced, a gas distributor in the form of a flexible tube with holes (not shown here) can be used in the electrolysis cell Z, which allows the CO 2 Uniform distribution of and transport of the reaction products can be achieved.

[0092] Catholyte Circuit The catholyte 17 removed from the cathode half shell 1 by the cathode outlet 14 contains CO, H 2 , and excess CO 2The gas mixture may still contain residues consisting of:

[0093] The first separation takes place, for example, in a suitably dimensioned collection conduit 43 to which the gas / liquid mixture from the electrolytic cells Z is supplied. The collection conduit 43 has at least one liquid outlet 14a and a gas discharge channel (not shown). The gas discharge channel is connected to a gas collection conduit 45. The gas collection conduit 45 is connected to the gas outlet 6 of the cathode element 1. The gas collection conduit 45 carries the gas from all the electrolytic cells Z to the gas separation unit 21.

[0094] Catholyte 17 from gas collection conduit 43 is fed to gas removal unit 74 via conduit 14a.

[0095] The electrolyte is resupplied to the electrolytic cell Z from an electrolyte collection facility 19. The composition of the electrolyte can be pre-tested and, if necessary, replenished with water and the above-mentioned salts to ensure that electrolyte having the same concentration is always resupplied to the electrolytic cell Z.

[0096] Electrolyte is returned from the electrolyte collection facility 19, for example by means of a pump, to the electrolytic cell Z via the heat exchanger and distributor pipe conduits 40, 42.

[0097] CO, H from electrolysis cell Z 2 and excess CO 2 Further processing of the mixture separated from the external collecting conduit 45 is carried out, for example, as follows: - Cooling of the gas mixture in a heat exchanger.

[0098] The condensate obtained by cooling can, for example, be returned to the electrolyte circuit.

[0099] -Excessive or unreacted CO 2This can be done by means of membrane treatment and / or by means of amine scrubs. In the case of amine scrubs, various ethanolamine / water mixtures or other amines such as monoethanolamine are used as the absorption medium. 2 The removal of CO takes place in a scrubbing column at near atmospheric pressure. Gas flows from the bottom up through the scrubbing column, while the amine solution flows countercurrently, removing CO. 2 The loaded scrubbing solution can be regenerated by the introduction of heat and then reused. The released CO 2 is resupplied to the electrolysis element. 2 In principle, CO removal from power plants requires 2 Removal techniques are available (SSchmidt, VGB PowerTech 12 / 2013).

[0100] -Separated CO 2 New CO required 2 and is fed back into the electrolysis cell.

[0101] The separation of the remaining CO and hydrogen is then carried out by membrane processes and / or using cold boxes, which are known in principle and are used to separate H 2 These are cold chambers operated at low temperatures to separate CO from coal. In these processes, temperatures below -180 °C are achieved. These cooling chambers are used for the separation of synthesis gas and can be commercially tailored for specific users.

[0102] -The hydrogen obtained from the cold box is passed for further use.

[0103] The carbon monoxide obtained from the cold box is subjected to further use, for example to produce phosgene and downstream products for polymer production.

[0104] To avoid the accumulation of impurities in the electrolyte circuit, in some cases a small amount of electrolyte (for both the anolyte and catholyte) is separated and discarded.

[0105] Gas Diffusion Electrode As gas diffusion electrodes (GDEs), it is particularly preferred to use silver-based GDEs, such as those described in European patent EP 2398101, which are highly effective in reducing CO 2 The porosity of the catalytically active layer is more than 10% and less than 80%, calculated from the material density of the raw material used.

[0106] The GDE is manufactured as follows: 3.5 kg of a powder mixture consisting of 5% by weight of PTFE powder, 88% by weight of silver(I) oxide and 7% by weight of silver powder (e.g. type 331 manufactured by Ferro) was mixed in an Eirich mixer, model R02, equipped with a star swirl as mixing element, at a rotation speed of 6000 rpm so that the temperature of the powder mixture did not exceed 55°C. In total, mixing was carried out three times with a mixing time of 50 seconds and three times with a mixing time of 60 seconds. After mixing, the powder mixture was sieved using a sieve with a mesh opening of 1.0 mm. The sieved powder mixture was then applied to a conductive support element. The support element was a wire mesh made of silver, with a wire thickness of 0.14 mm and a mesh opening of 0.5 mm. The application was carried out using a template with a thickness of 2 mm, and the powder was applied using a sieve with a mesh opening of 1.0 mm. The excess powder protruding above the thickness of the mold was removed by means of a scraper. After removing the template, the support with the applied powder is pressed by means of a roller press with a pressing force of 0.45 kN / cm. The gas diffusion electrode is recovered from the roller press. The porosity of the gas diffusion electrode is about 50%.

[0107] Separator Separating the anode and cathode chambers makes it possible to avoid mixing of the electrolytes and thus avoid electrochemical short circuits. Without a separator, the gas formed at the anode would be further directly reduced at the cathode, which would reduce the current yield and could lead to electrochemical short circuits that would undermine the economics of the process. Furthermore, the hydrogen and / or carbon monoxide formed at the GDE could form explosive gas mixtures with the oxygen formed at the anode. As separators, it is particularly preferred to use cation exchange membranes, for example fumasep F 1075-PK from Fumatech, or of the Nafion N 324 type (manufacturer: Chemours Company), in particular Nafion N 324. Suitable diaphragms are, for example, Zirfon™ pearls (manufacturer: Agfa), which are composed of PTFE and zirconium dioxide. For example, the cation exchange membrane Nafion N 324 is used.

[0108] The electrolysis cell is constructed such that a separator is placed on the anode structure, the anode being configured with a hollow space that directs the gas produced at the anode to the side facing away from the separator. As an anode structure it is possible to use, for example, an expanded metal, but also other structures known from the prior art.

[0109] The pressure with which the separator is pressed against the anode is preferably greater than 10 mbar.

[0110] Anode Space The anode half-shell 2 of the electrolysis cell Z comprises, for example, an anolyte inlet 8, an anolyte outlet 9, a second gas outlet conduit 7 through which the formed gas is discharged, and an anode 10. The anode 10 is conductively connected to the anode half-shell 2 via a lead 90 (FIG. 1).

[0111] Anolyte 15a is supplied to the lower part of the anode space 15 through anolyte inlet 8 and is removed via anolyte outlet 9 at the upper part of the anode space 15. Catholyte 17 and anolyte 15a therefore flow countercurrently through the electrolysis cell Z.

[0112] The anolyte 15a is selected as a function of the anodic reaction: in this case where oxygen is exhausted at the anode 10, the same electrolyte is used as the anolyte 15a and the catholyte 17.

[0113] The anolyte 15a supplied to the anode half shell 2 therefore consists of an aqueous electrolyte containing, for example, alkali metal bicarbonates, to which other inert salts have also been added to increase the electrical conductivity. Such salts include alkali metal sulfates, alkali metal hydrogen sulfates or mixtures thereof. The total concentration of alkali metal ions in the electrolyte solution is in particular between 0.01 mol / l and 2 mol / l.

[0114] The pH of the anolyte 15a supplied to the anode half shell is preferably 4-9.

[0115] The anolyte 15a extracted from the anode half shell 2 preferably has an alkali metal ion concentration of 0.01 mol / l to 2 mol / l.

[0116] The pressure in the anode half shell can be set to a value between 0 and 500 mbar lower than the pressure in the cathode half shell.

[0117] The volumetric flow rate of the anolyte 15a through the inlet 8 is 10 l / (h*m 2 ) to 300l / (h*m 2 ) is supplied to the anode half shell.

[0118] The exit temperature of the electrolyte from the anode half shell is preferably not more than 85° C., preferably not more than 60° C., particularly preferably not more than 45° C. The temperature of the anolyte supplied to the electrolytic cell Z can be regulated by means of a heat exchanger so as to respect the exit temperature.

[0119] The mixture of produced oxygen, possibly carbon dioxide and anolyte removed from the anode half shell 2 is first fed via conduit 70 to an external collector conduit 41b, which has at least one liquid outlet 9a and a gas exhaust channel 41a.

[0120] In the variant with separate discharge of the anolyte and the reactant gases (FIG. 3), the produced oxygen together with the carbon dioxide is conveyed from the anode half-shell 2 via the gas discharge conduit 7, optionally dried and fed to the second gas separation unit 20. The CO separated in the second gas separation unit 20 2 is returned to the gas space 4 of the cathode half-shell 1 via line 5. Oxygen 52 is collected and sent for further use.

[0121] In the variant with separate discharge of anolyte and reactant gases (FIG. 3), the anolyte 15a is conveyed out of the anode half-shell 2 via conduit 9 and fed to a collection conduit 41. The anolyte 15a is mixed with the residual oxygen and CO 2 The anolyte is then fed via conduit 9a to a gas removal unit 72 for residual degassing of oxygen, and the anolyte from which residual oxygen has been removed is fed via conduit 9b to the electrolyte collection facility 19.

[0122] The catholyte 17 exiting the cathode half shell 2 via the outlet 14 is fed to an external collection conduit 43 (FIG. 4). Any entrained carbon monoxide or hydrogen is collected from the collection conduit 43 and separated into CO / H 2 The catholyte 17 is conveyed through a conduit 14a to a collection conduit 45 for the remaining CO / H 2 The gas enters the gas removal unit 74 for removing CO and H.2 The catholyte from which the electrolyte has been removed is supplied to an electrolyte collection facility 19 via line 14b.

[0123] From the electrolyte collection facility 19, the combined electrolyte is resupplied to the electrolytic cell Z, the composition of which is previously tested and, if necessary, replenished with water and / or the above-mentioned salts via a supply conduit 18 so that the same concentrations of anolyte 15a and catholyte 17 can always be recirculated to the electrolytic cell Z.

[0124] From the electrolyte collection facility 19, the electrolyte is removed by means of a pump and fed via a heat exchanger and a connecting conduit to the anode half shell and further via a heat exchanger to the cathode half shell (not shown).

[0125] Connecting electrolytic cells to form an electrolytic cell The individual electrolytic cells Z1, Z2, ..., are assembled in a rack with a number of at least 10 and not more than 100 elements. The discharge conduits 14; 9 for the electrolyte, the supply conduits 8, 13 for the electrolyte, the gas discharge conduits 7; 70; 6 and the gas supply conduits 5 are connected between the electrolytic cells by means of external collectors or distributors, as described above.

[0126] Electrical isolation If several electrolytic cells Z are connected in series in a bipolar manner in an electrolytic cell E, the total voltage on the electrolytic cell increases with each further electrolytic cell Z, increasing the risk of stray currents. Therefore, careful electrical separation of the electrolyte streams feeding and draining from the individual electrolytic cells must be performed. In particular, when the total voltage exceeds 200 V, electrically insulating tubes or pipes are used between the fluidly connected connecting conduits and the electrolytic cells.

[0127] Here, the polymer is selected, for example, so that it is chemically resistant to the electrolyte and reactive gases used, and also thermally resistant.

[0128] Preferably, polymers such as polypropylene, polyethylene or PTFE (polytetrafluoroethylene) can be used.

[0129] Example 1 (Present Invention) An electrolysis unit was used consisting of an electrolysis cell E with individual electrolysis cells Z, Z1, Z2, ..., Z(n) connected to each other in a bipolar manner in an electrolysis cell rack (not shown). 2 Each individual electrolysis cell Z(n) has an active electrode area of ​​1000 nm. Each individual electrolysis cell Z(n) has an anode half-shell 2 made of titanium and a dimensionally stable commercial anode 10 with a platinum coating from Umicore, Platinode®, for oxygen evolution. The cathode half-shell is made of nickel. All parts of the cathode half-shell 1 in contact with the catholyte 17 are plated. All parts in electrical contact with the gas diffusion electrode 11 are plated as well. As gas diffusion electrode 11, a silver-PTFE-based electrode (manufactured as described above) is used. The anode half-shell 2 and the cathode half-shell 1 are separated by an ion exchange membrane 3 of the Nafion 324 type (manufacturer: Chemours).

[0130] The voltage across the electrolytic cell is set on the rectifier so that a current of 7590 A flows.

[0131] Each electrolytic cell Z was operated as follows: A 15% strength by weight potassium bicarbonate solution 15a is fed to the anode half shell 2 via the feed conduit 8 with a mass flow rate of 400 kg / h and a temperature of 35° C. 2266 g / h oxygen and 12461 g / h CO 2 A gas mixture consisting of oxygen and CO is removed from the anode half shell 2 via the discharge line 7. In addition, a potassium bicarbonate solution with a concentration of 8.8% by weight is removed from the anode half shell 2 via the discharge line 9 at a rate of 358.9 kg / h and at a temperature of 42° C. 2 The mixture of gas with CO 2 33 to a second gas separation unit 20 which separates oxygen 52. 233 is CO fed into the gas space 4 of the cathode half-shell 1 via a feed conduit 5 2 It is added to the volumetric flow 53 .

[0132] A 15% strength by weight potassium bicarbonate solution 17 is fed to the cathode half-shell 1 via the feed conduit 13 with a mass flow rate of 600 kg / h and a temperature of 30° C. The temperature of the solution leaving the cathode half-shell 1 via the discharge conduit 14 is 45.3° C. and the potassium bicarbonate content of the solution is 18.5% by weight. The exit mass flow rate is 640.1 kg / h.

[0133] The anolyte 15a leaving the anode half-shell 2 is fed to an external collector conduit 41. From there, the anolyte 15a is fed to a gas removal installation 72 for removing residual amounts of oxygen. The gas removal unit 72 consists of a stripping column (not shown) with a diameter of 50 cm and a height of 200 cm. Nitrogen flows countercurrently to the catholyte introduced from above through a distributor nozzle with a volume flow of 100 l / h. O 2 The free electrolyte may be removed from the stripping column and fed to an electrolyte collection facility 19.

[0134] The catholyte 17 leaving the cathode half-shell 1 through the conduit 14 is fed to the external collector conduit 43. The catholyte 17 is connected through the conduit 14a to a gas removal unit 74. The gas removal unit 74 consists of a stripping column (not shown) with a diameter of 50 cm and a height of 200 cm. Nitrogen flows countercurrently to the catholyte introduced from above through a distribution nozzle with a volumetric flow rate of 100 l / h. CO and H 2 The free catholyte 17 is removed from the stripping column and fed via line 14b to an electrolyte collection facility 19. The stripped gas is fed to an incineration unit.

[0135] 36511g / h CO 2 is fed into the gas space 4 of the cathode half-shell 1 via the gas feed pipe 5. This amount is equal to the theoretically required CO2 The temperature was 25°C. 2 is saturated with water at 25° C. This is done by injecting water into the supply conduit 5. 2 The gas velocity is approximately 0.06 m / s at 25° C. The proportion of water vapor in the gas was not taken into account in this calculation.

[0136] The reaction gas mixture is fed to the gas space 4 via the outlet conduit 6 of the gas collection conduit 45. The gas from the gas collection conduit 45 is CO, H 2 and excess or unreacted CO 2 (FIG. 5) are fed to the gas separation unit 21 to separate: Carbon monoxide: 2577 g / h, Hydrogen: 99 g / h, CO 2 : 20000g / h. Separated CO 2 33 is fed to the gas recirculation conduit 53 in the first part of the gas separation unit 21 and recycled to the cathode half shell 1 via the gas distribution conduit 44 of the gas supply conduit 5. The CO / H 33 from the first stage of gas separation in the gas separation unit 21 2 A side stream of the mixture is sent to the chemical synthesis of methanol (not shown). 2 The mixture is fed to a second stage of a gas separation unit 21 which separates hydrogen and CO, and the separated gases are sent to further chemical synthesis, in particular CO is fed to a process for producing isocyanates, where phosgene is produced from CO and chlorine in the first stage and the obtained phosgene is further processed to obtain isocyanates.

[0137] Thus, in industrial electrolysis, 2 It has been shown that it is possible to convert it into CO, and, among other things, provide a sustainable production method for producing the required industrial quantities of CO. [Explanation of symbols]

[0138] 1 Cathode half shell 2 Anode half shell 3 Separator (diaphragm, ion exchange membrane) 4 Gas space (cathode) 5 First gas supply conduit for carbon dioxide (cathode space) 6 First gas exhaust conduit for gaseous reaction products (cathode space) 7 Second gas exhaust conduit for the anode reaction products (anode space) 8 Anolyte Inlet 9 Anolyte outlet 9a Oxygen-containing anolyte output stream to gas scavenger Oxygen-free anolyte outflow 10 Anode 11 Cathode (GDE) 12 Catholyte gap 13 Catholyte inlet 14 Catholyte outlet 14a CO / H from recovery facility 43 to gas removal unit 74 2 Containing catholyte outflow stream 14b CO / H 2 Free catholyte outflow 15 Anode Space 15a Anolyte 16 Cathode space 17 Catholyte 18 Supply conduit for water or concentrated or diluted electrolyte for concentration setting 19 Electrolyte recovery equipment 20 CO 2 / O 2 A second gas separation unit for separation 21 CO / H 2 / CO 2 Gas separation unit for 24 Flow Brake 31 Cathode power lead 32 Anode power lead 33 Carbon Dioxide 34 Distribution Channels 35 Elastic Structure 40 External distributor tube conduit for anolyte inlet 8 41 Outer collector tube conduit for anolyte outlet 9 41a O 2 / CO 2Gas exhaust pipe 41b Outer collector tube conduit for mixed anolyte with gas / liquid separation and gas discharge conduit 70 (gas and electrolyte discharge) 42 External distributor tube conduit for catholyte inlet 13 43 Outer collector tube conduit for catholyte outlet 14 44 External distributor conduit from gas supply conduit 5 to cathode 45 External collector conduit for first gas exhaust conduit 6 from the cathode 50 CO gas 51H 2 gas 52 O 2 gas 53 CO 2 recirculation line 60 Power supply to edge electrolytic cell 61 Power outlet from end electrolytic cell 62 Power Plate 63 Power Outlet Plate 70 Gas and electrolyte discharge from the anode 72 Oxygen gas removal equipment 74 Gas removal equipment for hydrogen and carbon monoxide 90 Conductive connection between anode and anode half shell 91 Conductive connection of GDE 7 and elastic structure 35 to cathode half shell Z Electrolysis Cell E Electrolytic cell

Claims

1. Electrolysis cell for electrochemical reaction of CO 2 on an industrial scale, comprising A cathode half-shell (1) having a rear wall; a cathode (11); a gas space (4) connected to a first gas supply conduit (5) for carbon dioxide gas and a first gas discharge conduit (6) for gaseous reaction products; a cathode liquid inlet (13); and a cathode liquid outlet (14), at least including: An anode half-shell (2); and a separator (3) disposed between the anode half-shell (2) and the cathode half-shell (1) for separating an anode space (15) and a cathode space (16); the anode half-shell (2) having at least a second gas discharge conduit (7) for anode reaction products, an anode liquid inlet (8), an anode liquid outlet (9), and an anode (10). Further including power leads (31, 32) for connecting the anode and the cathode to a DC voltage source. The distance from the cathode (11) to the rear wall of the cathode half-shell is 5 cm or less. The cathode (11) is configured as a gas diffusion electrode for reacting carbon dioxide gas; the cathode (11), the anode (10), and the separator (3) are arranged vertically with respect to the main dimensions; and a gap (12) for the passage of the cathode liquid (17) based on the principle of a falling liquid film is disposed between the separator (3) and the cathode (11), characterized in that it is an electrolytic cell.

2. The electrolytic cell according to claim 1, characterized in that the separator (3) is an ion exchange membrane or a diaphragm.

3. The electrolytic cell according to claim 1 or 2, characterized in that the main dimension of the cathode (11) in the vertical direction is at least 30 cm.

4. The electrolytic cell according to at least one of claims 1 to 3, characterized in that the main dimension of the cathode (11) in the vertical direction is at least 60 cm.

5. The electrolytic cell according to at least one of claims 1 to 4, characterized in that the cathode (11) is configured as a gas diffusion electrode based on silver and / or silver oxide as an electrocatalyst and has a powdered fluoropolymer as a non-conductive binder compressed on a metal or non-metal, conductive or non-conductive support. **Claim 6**: The second gas discharge conduit (7) for the anode reaction product is connected to the upper end of the anode space (15); the first gas discharge conduit (6) for the gaseous reaction product is connected to the upper end of the gas space (4); and the first gas supply conduit (5) for the carbon dioxide gas is connected to the lower end of the gas space (4). An electrolytic cell according to at least one of claims 1 to 5. **Claim 7** The second gas discharge conduit (7) for the anode reaction product is connected to a second gas separation unit (20) for separating carbon dioxide from oxygen; the second gas separation unit is connected to the gas supply conduit (5) via a carbon dioxide conduit. An electrolytic cell according to at least one of claims 1 to 6. **Claim 8** The cathode liquid is a bicarbonate of an alkali metal. An electrolytic cell according to at least one of claims 1 to 7. **Claim 9** The anode liquid is a bicarbonate of an alkali metal. An electrolytic cell according to at least one of claims 1 to 8. **Claim 10** The first gas discharge conduit (6) is connected to a gas separation unit (21) for separating carbon monoxide, hydrogen and unreacted carbon dioxide gas. An electrolytic cell according to at least one of claims 1 to 9. **Claim 11** The gas separation unit (21) has a recirculation conduit (53) for the separated carbon dioxide gas, and the recirculation conduit (53) is connected to the first gas supply conduit (5) for carbon dioxide gas via a distribution conduit (44). An electrolytic cell according to claim 10. **Claim 12** The gas separation unit (21) has a discharge conduit for the separated carbon monoxide, and the discharge conduit is connected to a chemical production plant for the chemical reaction of carbon monoxide. An electrolytic cell according to claim 10 or 11. **Claim 13** The gas separation unit (21) has a discharge conduit for the separated hydrogen, and the discharge conduit is connected to a hydrogen pipe network or a distribution plant for hydrogen. An electrolytic cell according to at least one of claims 10 to 12.

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