Control for the optimized supply of electrolyte to electrodes of an electrolyzer

Abstract

The invention relates to a device and a method for the optimized distribution of a liquid electrolyte-containing composition to electrodes, each of which is located in half-cells of the cell elements of an electrolyzer, the half-cells preferably being equipped with gas diffusion electrodes. The electrolyte-containing composition is distributed to said electrodes in particular by carrying out, for individual cell elements, individual adjustments to the volume flow introduced into the cell element in question while at the same time controlling the pressure of the liquid electrolyte-containing composition in the electrolyte distributor system.

Description

[0001] 2024PF30090 - Abroad

[0002] - 1 -

[0003] "Regulation for optimized electrolyte supply to electrodes of an electrolyzer"

[0004] The invention relates to a device and a method, each for the optimized distribution of a liquid, electrolyte-containing composition onto electrodes located in half-cells of the cell elements of an electrolyzer, wherein said half-cells are preferably equipped with gas diffusion electrodes. The distribution of the electrolyte-containing composition onto said electrodes is additionally achieved, in particular, by regulating the pressure of the liquid, electrolyte-containing composition present in the electrolyte distribution system.

[0005] For the industrial production of basic chemicals, electrolysis processes must be scaled up to large-scale industrial production (several thousand tons per year). To produce large quantities of product using electrolysis, large-area electrolysis cells and electrolyzers with a large number of electrolysis cells, known as cell elements, are necessary. As is common in chlorine-alkali electrolysis, cell elements with an electrode area of ​​more than 2 m² are typically used. 2 Each electrolysis cell uses a cell element. The cell elements are grouped together in an electrolysis rack, for example, up to 100 units. Several racks then form an electrolyzer. The capacity of an industrial electrolyzer, e.g., for chlorine production, is currently up to 30,000 tons per year of chlorine and the respective equivalents of sodium hydroxide or hydrogen.

[0006] Regardless of the electrode type chosen, several electrolyzers are typically operated in parallel in corresponding electrolysis plants. As described, for example, in DE 19641125, each electrolyzer comprises several individual cell elements connected hydraulically in parallel, which are subjected to electric current in either a series circuit ("bipolar electrolyzers") or a parallel circuit ("monopolar electrolyzers").

[0007] The supply of operating media to the cell elements, in particular liquid electrolyte-containing solutions (e.g., anolyte for the anode and catholyte for the cathode), and the removal of the products generally occur via operating piping systems that connect the electrolyzers to the corresponding processing plants and to which the electrolyzers are connected in parallel. Typical arrangements of electrolyzers and piping systems in 2024PF30090 - Abroad

[0008] - 2 - information about an electrolysis cell room can be found, for example, in Ullmann's Encyclopedia of Industrial Chemistry, chapter "Chlorines".

[0009] The operation of the electrodes in an electrolyzer, particularly one with gas diffusion electrodes, requires a minimum supply of electrolyte for each cell element via a flow of the necessary electrolyte solutions. This flow has a defined volumetric flow rate to ensure efficient electrolysis with minimal electrode failure or wear. To achieve this, the liquid electrolyte composition must be adequately distributed to the electrodes located in the half-cells of the respective cell elements within the electrolyzer. The operation of electrolyzers with gas diffusion electrodes is particularly sensitive to the requirement of precise electrolyte distribution.

[0010] During operation, the electrodes in each cell element should be in contact with a liquid, electrolyte-containing solution, ideally at least on one electrode surface. To enable the operator to ensure this optimal electrode supply and to verify the actual supply to each electrode, cell elements often include devices that function as level indicators. Such a level indicator can be, for example, an electronic or mechanical measuring device, such as a transparent tube designed as an overflow for electrolyte solution from the cell element.

[0011] The distribution of electrolyte solution to the individual electrodes of the cell elements is typically controlled by adjusting the flow rate of the electrolyte solution, which is drawn from a storage container and fed to the electrolyzer as a fluid stream. The amount of electrolyte solution required for electrode operation and the necessary flow rate of the fluid stream supplied to the electrolyzer are determined by the number of electrodes to be supplied and the cell design used. Thus, in electrolyzers with multiple electrodes or cell elements, the optimal supply to the electrodes is adjusted by controlling the flow rate of the supplied liquid electrolyte solution (hereinafter referred to as the electrolyte flow).For this purpose, the volume flow of the electrolyte stream supplied to the electrolyzer is regulated in such a way that all level indicators show the optimal supply, i.e., for example, a transparent hose that serves as an overflow for electrolyte solution from abroad.

[0012] - 3 -

[0013] The electrolyte level indicator, which also serves as a cell element, should be filled and have a static electrolyte level – also known as the electrolyte level – meaning it should be filled but show no outflow of electrolyte solution. Outflow of electrolyte solution is also called overflow. However, it has been found that the conventional control concept, which regulates the volumetric flow rate of the electrolyte supplied to the electrolyzer, does not allow for the adjustment of all cell elements to the optimal supply of electrolyte solution to the electrodes, e.g., the electrolyte level in the overflow tube. Therefore, the regulation of the optimal supply is improved by valves for fine-tuning the volumetric flow rate supplied to each individual cell element. Nevertheless, this type of control leads to problems during the operation of the electrolysis process.

[0014] The concept of regulating the flow rate in combination with the valve position for each cell element means that, despite various adjustments by opening and closing the valves, it cannot be guaranteed that all cell elements, or at least 95% of them, receive an optimal supply, as indicated, for example, by the electrolyte level in the overflow tube. In electrolyzers with a transparent overflow tube as a level indicator, it has been observed that, for example, when many cell elements have an overflow in the overflow tube, partially closing a valve can reduce the amount of electrolyte flowing to the overflowing cell element. However, other cell elements that initially had an electrolyte level in the overflow tube then begin to overflow. This, in turn, necessitates readjusting the valves on the newly overflowing cell elements until a normal electrolyte level is reached.This iterative adjustment process is very time-consuming and cannot fully achieve the optimal distribution of the electrolyte solution onto the electrodes.

[0015] A faulty control setting can lead to an insufficient supply of electrolyte solution during operation. A reduction in the flow rate of the electrolyte supplied to the electrolyzer can cause even a slight reduction in this flow rate to result in cell elements that previously contained electrolyte no longer containing any electrolyte. These cell elements must then be individually readjusted at their respective valves. Due to this reduction in flow rate and the resulting insufficient supply of electrolyte solution to the individual cell element, the affected electrode of cell element 2024PF30090 - Abroad can be damaged.

[0016] - 4 - an electrolyte undersupply can occur, and the electrical operating voltage at the undersupplied electrode can rise to such an extent that, in the worst case, the entire electrolyzer is shut down and fails for safety reasons. This is associated with an undesirable and costly production downtime.

[0017] Furthermore, it was found that an excessively high electrolyte flow rate (e.g., indicated by the continuous overflow through the overflow hose, which acts as a level indicator) results in increased electrolyte pressure on the electrode, particularly in the upper region of the cell, specifically on the gas diffusion electrode directly below the electrolyte distribution channel when using gas diffusion electrodes. This causes irreversible damage to the electrode, especially the gas diffusion electrode, in this area over the medium term, leading to an undesirable increase in cell voltage, a reduction in electrode lifespan, and necessitating premature electrode replacement.

[0018] Furthermore, it was observed that when the current is changed, particularly when it is reduced, the number of cell elements that were previously optimally supplied (e.g., those with a sufficient electrolyte level in the overflow tube) overflows. For example, if electrolyte solution overflows from many cell elements via the overflow tube, pressure is exerted on the electrodes, especially in the upper region of gas diffusion electrodes. Additionally, a larger quantity of electrolyte flows out via the overflow tube. This overflow occurs when gas diffusion electrodes are operated, flowing into the outlet system for the gas supplied as a reactant and then into the electrolyte drainage system. The overflowing electrolyte solution must be discharged along with the excess gas, which leads to pressure changes in the outlet system for the gas supplied as a reactant and negatively affects the gas distribution / supply within the cell element.This also results in an undesirable increase in cell voltage.

[0019] The task was therefore to provide a control system that enables fail-safe, effective, and easy-to-use operation of the electrodes of an electrolyzer, as well as allowing for simple adjustment of the optimal supply of electrolyte solution to the electrodes, detectable by a level indicator (e.g., adjusting the electrolyte level in the overflow hose), so that the number of cell elements with over- or under-supply of electrolyte solution is specifically minimized without affecting neighboring cell elements. 2024PF30090 - Abroad

[0020] - 5 - thus avoiding detrimental high wear occurring at the electrode, particularly at the gas diffusion electrode. Furthermore, an oversupply of electrolyte solution when the current changes, especially when the current decreases, should be minimized.

[0021] A first object of the invention, which solves the problem, is a method for distributing a liquid composition as an electrolyte solution to several cell elements of an electrolyzer, wherein a main stream of the electrolyte solution is distributed as the main electrolyte stream through an electrolyte distribution system to half-cells of several cell elements to supply the electrodes located therein, and for this purpose the main electrolyte stream supplied to the electrolyzer is introduced into an electrolyte distribution system and there divided into several partial streams, provided that

[0022] - the pressure of the electrolyte solution introduced into the electrolyte distribution system is measured in the electrolyte distribution system and adjusted (preferably by a control system containing at least one pressure setting unit and at least one control device) such that an absolute pressure in the electrolyte distribution system is in the range of 1.20 to 6.00 bar,

[0023] - from the main electrolyte flow introduced for each cell element, at least one partial flow is diverted, the volume flow of each diverted partial flow being adjusted, this adjusted partial flow being discharged from the electrolyte distribution system and introduced into a half-cell of the respective cell element.

[0024] It has been shown that the problem is solved by the method according to the invention. Optimal supply of electrolyte solution to the electrodes can be achieved more easily by adjusting the amount of electrolyte solution for the cell elements without significant effort, without affecting the other cell elements, and without risk of electrolyzer failure. The electrodes are optimally supplied with electrolyte solution even with changing current and can be operated reliably. Electrode wear is reduced. 2024PF30090 - Abroad

[0025] - 6 -

[0026] According to the invention, an "electrolyte solution" is understood to be a liquid composition which, in addition to at least one liquid solvent, also contains at least one dissolved electrolyte, e.g. an aqueous solution of sodium chloride.

[0027] For the process according to the invention, an aqueous, liquid composition is preferably suitable as the electrolyte solution, in which at least one electrolyte is dissolved and which has an electrical conductivity at 25°C that is greater than the electrical conductivity of double-distilled water measured at 25°C. The total concentration of the electrolytes in the aqueous electrolyte solution is preferably 0.1 to 12 mol / L, wherein, in particular, electrolyte solutions with a conductivity at 25°C of greater than 10 S / m are used (S stands for Siemens and m for meters).

[0028] An aqueous solution of at least one electrolyte selected from at least one electrolyte of the group NaCl, NaOH, KOH, KCl, HCl, NaHCO3, KHCO3 is preferably used as the electrolyte solution.

[0029] Unless explicitly defined, a substance (or composition) is "liquid" if it exists in the liquid state at 20°C and 1013 mbar. A substance (or composition) is "solid" if it exists in the solid state at 20°C and 1013 mbar. A substance (or composition) is "gaseous" if it exists as a gas at 20°C and 1013 mbar.

[0030] Volume flow rate is a physical quantity and indicates how much volume of a medium (e.g., electrolyte solution) is transported through a defined cross-section per unit of time.

[0031] In the method according to the invention, at least one partial flow is diverted from the main electrolyte flow introduced into the electrolyte distribution system for each cell element. The volumetric flow rate of each diverted partial flow is adjusted, and this adjusted partial flow is discharged from the electrolyte distribution system and introduced into a half-cell of the respective cell element. The volumetric flow rate of each partial flow is thus adjusted individually for each partial flow. With respect to the electrolyte flow, the respective cell elements are therefore operated in parallel. 2024PF30090 - Abroad

[0032] - 7 -

[0033] Furthermore, in a preferred embodiment, it is advantageous if the volume flow of each partial flow dispensed from the electrolyte distribution system and directed to each cell element has a volume flow between 100 and 900 L / h, preferably in the range of 450 to 700 L / h.

[0034] In a further embodiment, it has proven preferable according to the invention if the adjustment of the volume flow of each branched partial flow is carried out by a separate pressure loss unit as a control device. Suitable pressure loss units include, for example, an orifice plate or a valve (such as an electronically controlled valve or a manually adjustable valve). Consequently, in a further preferred embodiment of the method according to the invention, the volume flow is adjusted by a pressure loss unit comprising at least one orifice plate and / or at least one valve.According to the invention, it is therefore particularly preferred if the volumetric flow rate of each partial flow discharged from the electrolyte distribution system is adjusted by a pressure loss unit such that electrolyte solution flows to each cell element at a volumetric flow rate between 100 and 900 L / h, preferably in the range of 450 to 700 L / h. The quantity of electrolyte solution to be introduced for the process according to the invention is thus preferably a volumetric flow rate between 100 and 900 L / h, preferably in the range of 450 to 700 L / h, per electrolysis cell. This volume flow rate is ensured, for example, by ensuring that, in an electrolyzer with a number n of cell elements operated in parallel, the volume flow rate of the main electrolyte flow before introduction into the electrolyte distribution system is between n • 100 L / h and n ■ 900 L / h, preferably in the range of n ' 450 and n ' 700 L / h.

[0035] In a further preferred embodiment, the volume flow rate of the main electrolyte flow is first set to a value between n • 100 L / h and n • 900 L / h, preferably in the range of n ' 450 and n ' 700 L / h, and then the volume flow rate of each branched partial flow is adjusted.

[0036] In the method according to the invention, the electrolyzer is supplied with electrolyte solution not only by adjusting the volume flow rate but also by adjusting the pressure (preferably via a control system). For this adjustment, the pressure of the electrolyte solution to be introduced into the electrolyte distribution system is regulated and set to a defined value. 2024PF30090 - Foreign

[0037] - 8 -

[0038] The pressure (setpoint) of the electrolyte solution in the electrolyte distribution system must be increased. The pressure of the electrolyte solution in the electrolyte distribution system must be higher than the ambient pressure (atmospheric pressure), i.e., at least 1.20 bar, preferably at least 1.25 bar, more preferably at least 1.30 bar, and further preferably at least 1.50 bar, so that all cell elements can be supplied with a sufficient quantity of electrolyte solution. An upper limit of 6.00 bar for the absolute pressure of the electrolyte solution in the electrolyte distribution system has proven practical, preferably 4.00 bar, and particularly preferably 3.20 bar.

[0039] Suitable absolute pressures for the electrolyte solution in the electrolyte distribution system have proven to be those falling within at least one of the following ranges from the list below: 1.20 to 6.00 bar, 1.20 to 4.00 bar, 1.20 to 3.20 bar, 1.25 to 6.00 bar, 1.25 to 4.00 bar, 1.25 to 3.20 bar, 1.30 to 6.00 bar, 1.30 to 4.00 bar, 1.30 to 3.20 bar, 1.50 to 6.00 bar, 1.50 to 4.00 bar, 1.50 to 3.20 bar. This list will also be referenced in the following text.

[0040] In a preferred embodiment of the method, the pressure is adjusted via a control system, which includes at least one pressure adjustment unit and at least one control device. The pressure adjustment unit can be, for example, at least one flow control element (such as an orifice plate or a valve) or a dispensing device (such as a pump). The control device, for example, an electronic control device, is configured to electronically control the pressure adjustment unit (such as a flow control element and / or a pump) to maintain a setpoint specified by the control device and to regulate it based on the absolute pressure of the electrolyte solution in the electrolyte distribution system, as determined by the pressure measuring device. In this context, the pressure of the electrolyte solution in the electrolyte distribution system is preferably measured by a pressure measuring device.

[0041] For this purpose, the electrolyte solution to be introduced into the electrolyzer is pressurized in the method according to the invention (for example, by means of a pump and / or a control valve and / or by means of an elevated storage tank, preferably at least by means of a pump), and the pressure prevailing in the electrolyte distribution system is adjusted (preferably by the control system). To carry out the pressure control, a setpoint value of the electrolyte solution is set (preferably via the control system).

[0042] - 9 -

[0043] The absolute pressure of the electrolyte solution prevailing in the distribution system is selected and set within one of the ranges from the aforementioned list, more preferably in the range of 1.20 to 6.00 bar, more preferably in the range of 1.25 to 4.00 bar, and particularly preferably in the range of 1.20 to 3.20 bar. In a particularly preferred and effective embodiment, the aforementioned setpoint is additionally kept constant by the pressure control system during operation, especially during electrode operation. "Constant" means that the selected setpoint pressure in the electrolyte distribution system is maintained by the pressure control system within a tolerable pressure fluctuation of a maximum deviation of ± 50 mbar from the setpoint.The absolute pressure of the electrolyte solution introduced into the electrolyte distribution system is therefore preferably set to a defined target value within the aforementioned range, more preferably in the range of 1.20 to 6.00 bar, particularly in the range of 1.25 to 4.00 bar, and especially preferably in the range of 1.20 to 3.20 bar, and maintained within a deviation of a maximum of ± 50 mbar from the target value.

[0044] Advantageously, for optimized pressure control, the pressure of the main electrolyte flow upstream of the control system (especially upstream of the control system) should preferably be higher than the selected setpoint pressure in the electrolyte distribution system. Therefore, in a further preferred embodiment, it has proven beneficial to draw the electrolyte solution from a storage tank to provide the main electrolyte flow in such a way that the pressure of the resulting main electrolyte flow upon entry into the control system is higher than the pressure in the electrolyte distribution system. This pressure can be generated, for example, by a pump and / or an elevated storage tank. In the case of an elevated tank, the pressure of the electrolyte solution in the main electrolyte flow is generated as hydrostatic pressure.In such an embodiment, it is preferred if the main electrolyte flow is supplied by a withdrawal device for extracting electrolyte from an elevated reservoir as a storage tank, wherein during the supply the pressure in the electrolyte distribution system is determined via at least one measuring device and the pressure is adjusted via a control system such that the absolute pressure determined with the measuring device is in one of the ranges from the aforementioned list 2024PF30090 - Abroad.

[0045] - 10 - is, further preferably, in the range of an absolute pressure of 1.20 to 6.00 bar, more preferably in the range of 1.25 to 4.00 bar, and particularly preferably in the range of 1.20 to 3.20 bar. When electrolyte solution is withdrawn from the elevated reservoir, the hydrostatic pressure of the resulting main electrolyte flow can, for example, be additionally maintained by a pumping system for refilling the elevated reservoir with electrolyte solution from another storage tank. However, the pressure of the electrolyte solution of the main electrolyte stream can also be generated directly by the power of a pump when drawing from a storage tank, without an elevated reservoir, and adjusted such that the pressure determined with at least one measuring device is in the range of an absolute pressure from the aforementioned list, more preferably in the range of an absolute pressure of 1.20 to 6.00 bar, more preferably in the range of 1.25 to 4.00 bar, and particularly preferably in the range of 1.20 to 3.20 bar.In a further preferred embodiment of the method according to the invention, the main electrolyte flow is supplied by a withdrawal device for extracting electrolyte solution from a storage container. During supply, the pressure in the electrolyte distribution system is measured by at least one measuring device, and the pressure is adjusted by at least one flow control element (preferably a valve with a throttle valve or a valve) of a control system, which can be used to regulate the main electrolyte flow, and / or by regulating the quantity withdrawn by the withdrawal device, such that the pressure determined by the measuring device lies within the range from the aforementioned list, more preferably within the range of an absolute pressure of 1.20 to 6.00 bar, more preferably within the range of 1.25 to 4.00 bar, and particularly preferably within the range of 1.20 to 3.20 bar. At least one pump particularly preferably serves as the withdrawal device.

[0046] In a further preferred embodiment of the method, during operation of the electrolyzer, the electrolyte solution introduced into the respective cell elements is, from each cell element, discharged from the respective cell elements into an electrolyte drain system and there combined to form a main electrolyte drain stream from all cell elements of the electrolyzer. For this purpose, the individual cell elements of the electrolyzer are connected, for example, via a cell element drain to a common drain line provided for all cell elements of the electrolyzer, which serves as the electrolyte drain system for the main electrolyte drain stream. It proved advantageous if the pressure control is set such that the absolute pressure in the 2024PF30090 - Abroad

[0047] - 11 -

[0048] The pressure in the electrolyte drainage system is not higher than the absolute pressure in the respective cell elements. In this preferred embodiment, it is therefore advantageous if the electrolyte solution is discharged from the cell elements into an electrolyte drainage system and the absolute pressure in the electrolyte drainage system is equal to or lower than the absolute pressure in the respective cell elements. Furthermore, it is particularly preferred if the differential pressure between the electrolyte distribution system and the electrolyte drainage system is between 0.30 and 5.00 bar, preferably in the range of 0.40 to 2.50 bar.

[0049] In a further preferred embodiment of the method, the electrolyte solution from the cell elements is discharged into an electrolyte drainage system, wherein the absolute pressure in the electrolyte drainage system is in the range of 1.00 to 1.40 bar, preferably in the range of 1.10 to 1.30 bar.

[0050] The method according to the invention is particularly well suited for the application of optimized operation of gas diffusion electrodes supplied with electrolyte solution. For this purpose, in a further embodiment, the partial currents supplied from the electrolyte distribution system are each introduced into an electrolysis cell of the electrolyzer, which is equipped with at least one gas diffusion electrode. It is preferred if the partial currents supplied from the electrolyte distribution system are each introduced into a separate half-cell of a cell element, said half-cell being equipped with a gas diffusion electrode, preferably with a gas diffusion electrode as the cathode.

[0051] The operation of gas diffusion electrodes requires additional special measures. For example, when using gas diffusion cathodes in technical applications, it is important to note that the gas diffusion electrode used (hereinafter referred to as GDE) has an open-pore structure and is installed between the electrolyte space and the gas space of a cell element's half-shell. The electrolyte space of the half-shell is filled with electrolyte solution, which comes into contact with the GDE. The GDE is supplied with gas via the gas space of the half-shell. The internal structure of the GDE must allow the gas reaction to occur as close as possible to the electrolyte solution at the three-phase interface between the electrolyte solution, electrocatalyst, and gas. This interface is stabilized by the hydrophobicity of the GDE material.However, it turns out that this stabilization, which is caused by the surface tension of the electrolyte at the electrode surface, only applies to a finite pressure gradient 2024PF30090 - Abroad.

[0052] - 12 - 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 GDE's function will be disrupted in this area; that is, the electrolysis process will be locally interrupted. Conversely, if the liquid pressure is too high, the three-phase boundary will shift out of the catalyst region of the GDE until the GDE is flooded with electrolyte solution, and further pressure increases will lead to liquid breakthrough of the electrolyte solution into the gas space. This will also disrupt the GDE's function, and the desired reaction will not occur.

[0053] In a preferred embodiment of the process, an electrolyzer usable in the inventive method comprises at least one cell element for the use of at least one gas diffusion electrode, comprising a first half-shell equipped with a gas diffusion electrode as an electrode (e.g., as a cathode), wherein the gas diffusion electrode divides the half-shell into a gas space and an electrolyte space (in particular, an electrolyte space (e.g., catholyte space) containing at least one electrolyte inlet (e.g., catholyte inlet) and at least one electrolyte gap (e.g., catholyte gap)), and the half-shell on the gas side of the gas diffusion electrode connects the gas space with at least one gas inlet (and optionally with at least one gas outlet for residual gas (e.g., residual oxygen gas when using an oxygen-consuming cathode as the GDE) and / or gaseous reaction products (e.g.,in a CCh electrolysis, in particular carbon monoxide and hydrogen), and on the electrolyte side of the gas diffusion electrode has the electrolyte chamber with an inlet for an electrolyte solution and an outlet for the electrolyte solution, and has a second half-shell equipped with a further electrode and an electrolyte chamber with at least one inlet for an electrolyte solution and at least one outlet for the electrolyte solution, and a separator arranged between the first half-shell and the second half-shell for spatial separation of the electrolyte chambers of the respective half-shells, and electrical current lines for connecting the respective electrodes to a DC voltage source, 2024PF30090 - Foreign.

[0054] - 13 - wherein at least the inlet for an electrolyte solution of the first half-cell is connected to the electrolyte distribution system in such a way that at least one partial flow diverted from the main electrolyte flow in the electrolyte distribution system can be introduced into the first half-shell of the electrolysis cell.

[0055] Nickel or nickel alloys have proven to be the preferred material for constructing the respective half-shells. However, in a particularly preferred embodiment of the electrolysis cell suitable for the process, all electrolyte-contacting parts of the electrolysis cell are made of nickel and have a tarnish-corrosion protection layer of gold. It is also conceivable, in principle, to use inert plastics as alternative construction materials or as materials for the inner coating of the cathode side of the cell at operating temperatures below 90°C, provided that these are chemically resistant to the electrolytes and gases at the given temperature.

[0056] In this embodiment, it is particularly preferred if the gas diffusion electrode, the further electrode and the separator are arranged vertically with their main extent in the respective cell element, and a gap for the passage of the electrolyte solution is located between the separator and the gas diffusion electrode according to the principle of a falling liquid film.

[0057] In a further, preferred embodiment of the method according to the invention, the separator is an ion exchange membrane or a diaphragm; in particular, the separator is an ion exchange membrane.

[0058] Suitable ion exchange membranes are, in particular, those designed as cation exchange membranes that can transfer cations from the anode compartment to the cathode compartment. These are generally known from the prior art. Alternatively, anion exchange membranes that transport anions from the cathode compartment to the anode compartment can also be used. Cation exchange membranes are preferred. With conventional ion exchange membranes, ion transport is also associated with water transport, which depends on the selected concentrations of the anolyte and catholyte, temperature, and operating conditions. 2024PF30090 - Foreign

[0059] - 14 -

[0060] Suitable separators include ion exchange membranes, such as well-known cation exchange membranes like fumasep F 1075-PK (manufacturer: Fumatech GmbH) and the type Nafion N 324 (manufacturer: Chemours Company).

[0061] Suitable diaphragms include all known diaphragms that provide a gas-tight seal between the anode compartment and the cathode compartment, specifically between the cathode gap and the anode compartment. The diaphragm should ideally have a gas tightness (bubble point) of more than 10 mbar, preferably more than 300 mbar, and most preferably more than 1000 mbar. Furthermore, the diaphragm should be inert to the electrolyte and reaction gases and stable at operating temperatures. Diaphragms for electrolysis are generally known from the prior art.

[0062] Suitable separators include diaphragms such as the Zirfon™ Pearl diaphragm (manufacturer Agfa), which is made of PTFE and zirconium dioxide.

[0063] In a further, particularly preferred embodiment of the inventive process, the gas diffusion electrodes are used at least as a cathode, which in particular contains an electrocatalyst for O2 or CO2 reduction. This electrocatalyst is preferably based on silver and / or silver oxide, and preferably on silver particles. It is compacted onto a metallic or non-metallic, conductive or non-conductive support with a powdered fluorine-containing polymer, in particular PTFE powder, as a non-conductive binder. A metallic, conductive support is preferably used for compaction. Nickel meshes, gold-plated nickel meshes, silver meshes, PTFE-coated glass fiber supports, carbon fiber fabrics or carbon-based knits / structures, as well as supports based on polymers such as polypropylene or polyethylene, are preferably used as supports for manufacturing the gas diffusion electrodes.A particularly suitable gas disposal device (GDE) for the method according to the invention is an oxygen consumption cathode (SVK), the provision of which is described in publication EP 1728896 A2, to which explicit and full reference is made.

[0064] Instead of powdered fluoropolymers, other polymer powders with comparable properties (i.e., in particular inert towards the electrolyte at reaction temperature and high current density and processable in the production of the GDE) can also be used. 2024PF30090 - Abroad

[0065] - 15 - in question, in particular polyalkylenes, especially preferably polyethylene, polypropylene or partially fluorinated polymers.

[0066] If a GDE is used as an electrode in an embodiment of the inventive method, an embodiment of the method is particularly preferred in which the cell elements of the electrolyzer used therein each contain at least:

[0067] (i) an anode half-cell containing an anode half-shell with an anode space;

[0068] (ii) a cathode half-cell comprising a cathode half-shell with a cathode space comprising at least one catholyte space comprising at least one catholyte inlet and at least one catholyte gap;

[0069] (iii) at least one separator to separate the anode compartment of the anode half-shell from the cathode compartment of the cathode half-shell;

[0070] (iv) a gas diffusion electrode, the largest of which is oriented at a distance along the separator surface, forming a catholyte gap; and the partial flow intended for the respective cell element is introduced into the catholyte inlet.

[0071] If the catholyte inlet is located above the catholyte gap, the corresponding cell elements are operated according to the falling film principle (falling film cell principle). When operating according to the falling film cell principle in accordance with the prior art, a basic principle exists, for example for chlor-alkali electrolysis, which is known from the following publications: EP 150 017 A, DE 10333853 A1, DE 102004 018748 A1.

[0072] WO 2005 / 100640A1, EP 2 652 176 A and WO 2001 / 057290 Al.

[0073] In another preferred embodiment of the process according to the invention, in which these special cell elements are used, a means for slowing the flow of the partial current introduced into the half-cell, hereinafter referred to as a flow brake, is provided in the catholyte gap of the electrolysis cells used in the process, between the membrane and the gas discharge device (GDE). This allows the residence time of the introduced electrolyte solution in the gap in front of the GDE to be controlled. The flow brake is particularly preferably designed as an electrically non-conductive, inert textile surface. 2024PF30090 - Abroad

[0074] - 16 -

[0075] The flow restrictor can consist, in particular, of a porous textile fabric, preferably a woven, knitted, or crocheted material, arranged in the gap. Alternatively, mechanical components within the gap are also conceivable, enabling a horizontal or slightly angled electrolyte flow, resulting in a meandering flow of the electrolyte solution. The material of the flow restrictor can be hydrophilic, such as the flow restrictor known from W02003042430A2, Example 1, or hydrophobic, depending on the choice of flow conditions or the viscosity of the electrolyte solution. The preferred materials are described above.

[0076] In another preferred embodiment of the inventive method, using said special cell elements, it has proven advantageous if, for the adequate supply of the catholyte gap with electrolyte solution, the electrolyte solution is preferably supplied to the catholyte gap via a distribution channel that connects the catholyte inlet for electrolyte solution to the catholyte gap in the cell element. The gas diffusion electrode seals the distribution channel and the catholyte gap gas-tight from the gas space.

[0077] To ensure that the distribution channel is always filled with electrolyte solution, it can have an overflow (not shown in the figures) through which any excess electrolyte solution can be discharged. This overflow is preferably designed such that the electrolyte level or overflow can be detected, e.g., via a transparent section (e.g., by using transparent materials).

[0078] In a further embodiment of the method for operating gas diffusion electrodes, the electrolyzer is particularly preferably designed such that the individual cell elements are bipolarly connected to each other and the end elements are provided with current supply and current discharge plates.

[0079] In a further preferred embodiment of the method, the gas diffusion electrode (GDE) is preferably contacted with the current supply in the cathode compartment via an elastically mounted, electrically conductive structure. This structure can be designed such that a rigid structure, e.g., in the form of expanded metal, mounted on springs, electrically contacts the GDE from the gas compartment side. To maintain the dimensions 2024PF30090 - Abroad

[0080] - 17 - To prevent pressure from opening the gap between the GDE and the separator, e.g., due to electrical contact, spacers are installed in the gap between the separator and the GDE. The flow restrictor can also perform the function of the spacer if it has sufficient mechanical stability and rigidity under pressure across its surface.A further object of the invention is a device configured for carrying out the method according to the invention for distributing a liquid composition as an electrolyte solution to several cell elements of an electrolyzer, comprising at least one storage container for electrolyte solution; at least one electrolyzer with several cell elements, each of which in turn has at least one half-cell for receiving the electrolyte solution stored in the storage container; at least one supply line for electrolyte solution, wherein this supply line contains at least one unit for adjusting the pressure of the main electrolyte flow to be carried in the supply line and this supply line is in fluid communication at least with the storage container and at least via an electrolyte distribution system with the storage container and the said cell elements of existing electrolyzers; wherein.

[0081] - the device additionally includes at least one pressure measuring device configured to measure the pressure of electrolyte solution in the electrolyte distribution system,

[0082] - the pressure adjustment unit is configured such that it can, via a control device, change the pressure of the electrolyte solution carried in the supply line and introduced into the electrolyte distribution system such that the electrolyte solution carried in the electrolyte distribution system has an absolute pressure in the range of 1.20 to 6.00 bar, as determined by the pressure measuring device; the electrolyte distribution system has several branches for electrolyte solution, each connected to a cell element in fluid communication, wherein electrolyte solution can be carried through the branches and the branches each 2024PF30090 - Abroad

[0083] - 18 - have at least one adjustment unit for adjusting the volume flow of the electrolyte solution delivered to each individual cell element.

[0084] A fluid connection is understood to be a device that connects device components and through which a substance, which can exist in any state of matter, can be transported as a fluid flow from one device component to the next, for example, a supply line in the form of a pipe. The term "in fluid connection" means that the named device components are connected to each other via a fluid connection.

[0085] The storage container of the device according to the invention can be designed in further embodiments as described in the method according to the invention.

[0086] The device according to the invention comprises at least one unit for pressure setting, at least one control device provided for this purpose, and at least one pressure measuring device.

[0087] By means of the aforementioned pressure adjustment unit, the pressure of the main electrolyte flow in the supply line can be changed via the control device to carry out the method according to the invention and its previously described embodiments, such that the specified pressure of the electrolyte solution introduced into the electrolyte distribution system is maintained. It is particularly preferred if, in a further embodiment, the pressure adjustment unit is configured such that it sets the absolute pressure of the electrolyte solution introduced into the electrolyte distribution system to a setpoint value determined via the control device and lying within the range of 1.20 to 6.00 bar, particularly in the range of 1.25 to 4.00 bar, and especially preferably from 1.30 to 3.20 bar, and maintains this value within a deviation of a maximum of ± 50 mbar from the setpoint value.In a further preferred embodiment, the pressure adjustment unit is controlled via the control device by comparing the pressure determined by the pressure measuring device in the electrolyte distribution system with the specified pressure range of absolute pressure from 1.20 to 6.00 bar as the setpoint (preferably with a fixed, constant setpoint (see embodiment of the method) that lies within the said pressure range) and, if there is a deviation from the setpoint, the pressure adjustment unit (e.g. the 2024PF30090 - foreign.

[0088] - 19 -

[0089] The pump's output (or the flow rate of a flow control device) is controlled to achieve the setpoint and the pressure is adjusted accordingly.

[0090] The pressure adjustment unit can preferably be configured as described previously in the further embodiments of the method. In a preferred embodiment, the pressure adjustment unit is selected from at least one control valve and / or at least one pump. In a further preferred embodiment, the control valve and / or the pump output is controlled via the control device by comparing the pressure determined by the pressure measuring device in the electrolyte distribution system with the predetermined absolute pressure range of 1.20 to 6.00 bar (or one of the aforementioned preferred pressure ranges, in particular in the range of 1.25 to 4.00 bar, most preferably from 1.30 to 3.20 bar) as a setpoint (preferably with a fixed, constant setpoint that lies within the aforementioned pressure range). If there is a deviation from the setpoint, the pressure adjustment unit, e.g.,The pump's pumping capacity adjusts the pressure accordingly to achieve the target value.

[0091] It is particularly preferred if the pressure control unit includes, in addition to at least one pump, at least one flow control device, which is connected in the supply line between the inlet to the electrolyte distribution system and the at least one pump. In this embodiment, the pump output can remain constant, and the pressure can be adjusted via the flow control device. A suitable flow control device is, for example, a valve with a throttle valve, and in particular a valve with an electrically adjustable throttle valve.

[0092] The device according to the invention necessarily includes an electrolyte distribution system, which has several branches for electrolyte solution, each connected to a cell element in fluid communication. Electrolyte solution can be passed through the branches, and each branch has at least one adjustment unit for adjusting the volume flow of the electrolyte solution delivered to the respective individual cell element. According to the invention, it has proven preferred if the at least one adjustment unit is selected from a pressure loss unit. It is particularly preferred if the at least one pressure loss unit contains at least one orifice plate and / or at least one valve. 2024PF30090 - Foreign

[0093] - 20 -

[0094] As mentioned in a preferred embodiment of the method according to the invention, it is also a preferred embodiment of the device if said half-cell is equipped with a gas diffusion electrode, preferably with a gas diffusion electrode as the cathode.

[0095] Gas diffusion electrodes such as those mentioned in the previously described embodiments of the method are also preferred for the device.

[0096] If at least one gas diffusion electrode is used in the device according to the invention, it has proven to be a very preferred embodiment of the device if the cell elements of the existing electrolyzers each contain at least:

[0097] (i) an anode half-cell containing an anode half-shell with an anode space;

[0098] (ii) a cathode half-cell comprising a cathode half-shell with a cathode space comprising at least one catholyte space comprising at least one catholyte inlet and at least one catholyte gap;

[0099] (iii) at least one separator to separate the anode compartment of the anode half-shell from the cathode compartment of the cathode half-shell;

[0100] (iv) a gas diffusion electrode, the largest of which is oriented at a distance along the separator surface forming a catholyte gap, wherein a branch of the electrolyte distribution device is in fluid communication with a catholyte inlet.

[0101] For this embodiment of the device, embodiments of the components contained therein, individually or in combination, are again preferred as those mentioned in the previously described embodiments of the method.

[0102] In another preferred embodiment of the inventive method, using the aforementioned cell elements, it has proven advantageous to supply the catholyte gap with sufficient electrolyte solution preferably via a distribution channel. For this purpose, said cell elements additionally contain 2024PF30090 - Foreign

[0103] - 21 -

[0104] (v) a distribution channel extending along the opening of the catholyte gap facing the catholyte inlet and connecting the catholyte inlet for electrolyte solution to the catholyte gap, wherein the gas diffusion electrode seals the distribution channel and the catholyte gap from the gas space in a gas-tight manner.

[0105] To ensure that the distribution channel is always filled with electrolyte solution, it can have an overflow through which any excess electrolyte solution can be drained. This overflow is preferably designed in such a way that the electrolyte level or overflow can be detected, e.g., via a transparent section (e.g., by using transparent materials).

[0106] The invention will now be explained using a specific embodiment, without limiting it to that embodiment:

[0107] The invention is illustrated by way of example using a chlorine-alkali electrolysis process and a device configured for this purpose (see Figs. 2, 3 and 4). In this process, the cathode 14, located in a cathode hemisphere 26 and equipped as a gas diffusion electrode (GDE) according to EP 1 728 897 A2, was supplied with aqueous sodium hydroxide solution (alkali) as the electrolyte solution via a main electrolyte flow 19 and a corresponding distribution system 10. At the cathode 14, gaseous oxygen reacted with water to form hydroxide ions, which, together with the sodium ions arriving from the anode 34 via the ion exchange membrane (separator) 27, formed an aqueous sodium hydroxide solution. However, the inventive method can be used on any other comparably equipped electrolyzer, such as one in which CO2 is converted to CO at the gas diffusion electrode, as described in WO 2020 / 057998 Al.

[0108] In all subsequent examples, an NaCl-SVK electrolyzer 1 with a number n = 158 elements connected in parallel in the main electrolyte flow was operated as a collection Z(n) (Fig. 1 for subsequent example 1 for comparison, Fig. 2 for subsequent example 2 according to the invention). A single cell element Z contains an anode half-shell 25 and a cathode half-shell 26, which are separated by an ion exchange membrane as a separator 27.

[0109] An anode half-shell 25 was supplied with a stream of an aqueous solution of sodium chloride with a concentration of ~300 g / L. The process parameters for the operation of the anode half-shell 25 correspond to the state of the art for a Chi or alkaline ionization system. 2024PF30090 - Foreign

[0110] - 22 -

[0111] Electrolysis is largely independent of the operating mode of the cathode half-shell and has no influence on the method according to the invention.

[0112] To supply the electrolyte to each cathode half-shell 26, the sodium hydroxide solution contained in a storage container 2 was first extracted by pump 5 to provide the main electrolyte flow. The concentration of the electrolyte solution (31.0 wt% NaOH) was then adjusted by adding water 4. In the electrolyte distribution system 10, a branch 20 of a partial flow was generated for each cell element from the main electrolyte flow carried in the electrolyte solution supply line 19. Each of these partial flows of the electrolyte solution was then supplied to the corresponding cell element via the catholyte inlet 18 of the respective cell element.

[0113] To supply each cathode with alkali as an electrolyte solution, the required amount of alkali to the individual cell elements of the chlor-alkali-SVK electrolyzer 1 was first adjusted by opening or closing the valve 11, which was installed for each branch 20 of the electrolyte solution between the electrolyte distribution system 10 and each catholyte inlet 18 of each cell element Z. Within the cell element, the distribution channel 24 located above the catholyte gap 17 (see also Fig. 3) was thus filled with alkali. The alkali then flows through the filled distribution channel 24 into a catholyte gap 17 and subsequently downwards through the catholyte gap 17, which is filled with a fabric acting as a flow restrictor. The complete filling of the distribution channel 24 and thus of the catholyte gap 17 is thereby ensured, or can also be checked by verifying that a caustic solution level is present in the hose of the overflow 15 (Fig. 3).Thus, the amount of lye for each cell element Z is adjusted with the valve 11 provided for this purpose so that no lye flows over the overflow 15, but that the level of lye in the transparent tube of the overflow 15 is visible.

[0114] The caustic solution flowing from the element enters the caustic solution drainage system 13 via the caustic solution drainage hose 16. The caustic solution from the caustic solution drainage system 13 is directed into the caustic solution storage tank 2. A partial flow of the caustic solution is drawn from the storage tank and reused. Caustic solution is taken from storage tank 2, diluted with water 4 to 31.0 wt.%, and returned to the electrolyzer 1. 2024PF30090 - Abroad

[0115] - 23 -

[0116] The cathode hemisphere was equipped with a gas diffusion electrode, cathode 14, for the reduction of oxygen over silver as an electrocatalyst (this cathode hemisphere was manufactured according to EP 1 728 896 A2). Pure oxygen was supplied to the cathode hemisphere 26 in an amount corresponding to 1.5 times the oxygen consumed by the current. Unused oxygen was discharged via the oxygen outlet header (not shown in the figures). The amount of caustic solution that flowed from the overflow tubes of the distribution channel 24 in elements with overflow 15 (see also Fig. 3) was also discharged. Both the overflowed caustic solution and the caustic solution discharged from each cell element via the caustic outlet tube 16 (concentration 32.2 wt% NaOH; temperature: 86.8 °C) were directed to the caustic outlet system 13. The absolute pressure in the lye drainage system 13 was 1.218 bar.A more detailed description of the cell elements Z used in Examples 1 and 2 can be found in Fig. 4 (vide infra).

[0117] The applied electric current was 12,200 A, and the amount of oxygen supplied was 682 m³. 3 / h (standard conditions).

[0118] The characters describe:

[0119] Fig. 1: Schematic representation of an electrolyte supply with pure alkali volume control (not according to the invention):

[0120] Figure 1 is explained in more detail in Example 1.

[0121] Fig. 2: Inventive method / inventive device - pressure control: Fig. 2 is explained in more detail in Example 2.

[0122] Fig. 3: Schematic representation of a partial flow branch 20 according to the invention, including inlet 18 and outlet 16 of electrolyte solution (catholyte) for a cathode 14 of a single NaCl SVK cell element Z: The section through the electrolysis cell Z was taken on the side of the cathode half-shell between the separator and the flow restrictor of the catholyte gap 17. A water-based NaOH solution (lye, 32.2 wt%) is drawn from the storage tank 2 via a pump 5, which is brought to a concentration of 31.0 wt% by the addition of water 4 and is introduced by the pump into a main electrolyte flow in the supply line 19 with a starting volume flow rate (see Example 2), which is measured and controlled at the flow measuring device 7. The main electrolyte flow passes through a pressure control unit 2024PF30090 - Abroad

[0123] - 24 -

[0124] 8 and is then introduced into an electrolyte distribution system 10. There, the main electrolyte flow is divided into n = 158 partial flows. Each of these partial flows has its own branch 20 and is introduced via the branch 20 and the catholyte inlet 18 into the distribution channel 24, which runs above and along the catholyte gap 17 filled with a flow restrictor. To ensure optimal supply of the entire surface of the gas diffusion electrode (i.e., the cathode 14) with electrolyte solution, the volume flow in the branch 20 is adjusted via the adjustment unit 11 (i.e., a control valve) such that an electrolyte level is established in the transparent overflow tube of the overflow 15; the electrolyte is visible but does not flow out via the overflow 15.Meanwhile, the absolute pressure of the electrolyte in the electrolyte distribution system 10 is measured by the pressure gauge 9 and compared with a setpoint in the control device 12. If the pressure deviates from the setpoint, the control device 12 causes the pressure to be readjusted to the setpoint via the control valve of the pressure adjustment device 8, so that the pressure remains within a tolerance deviation of ±50 mbar from the setpoint. The electrolyte solution is discharged from the cell element via the caustic soda drain hose 16 and introduced into the caustic soda drain system. From there, the caustic solution is returned to the storage tank 2 via the electrolyte return line 23, possibly after cleaning (not shown).

[0125] Fig. 4: Schematic representation of a section through a single NaCl SVK cell element Z, as used in Examples 1 and 2:

[0126] Figure 4 illustrates a falling film cell element in which an ion exchange membrane is positioned as a separator 27 between the anode half-shell 25 and the cathode half-shell 26, separating the anode compartment 28 from the cathode compartment 29. The cathode compartment comprises the gas space 30, a catholyte gap 17, and the catholyte outlet 16. During operation, the gaseous reactant of the SVK (e.g., O2) is introduced into the gas space 30 via the first gas inlet 31, and the gaseous reaction products are discharged via a first gas outlet 32 ​​for gaseous reaction products and excess reactant. The gas space 30 is designed such that the reactant introduced via the gas inlet 31 comes into contact with the surface of the SVK 14 facing away from the separator 27 and towards the gas space 30.

[0127] - 25 -

[0128] Contact can be made and the residual gas remaining after contacting the SVK 14 can be discharged from the gas outlet 32.

[0129] The catholyte gap 17 is defined as the space between the separator 27 and the surface of the SVK 14 facing the separator 27. The flow restrictor 33, which regulates the flow of the catholyte introduced through the catholyte inlet 18, is located in the catholyte gap 17. The catholyte inlet 18 defines the space for introducing catholyte and for supplying it to the distribution channel 24. The separator 27 makes contact with the flow restrictor 33 over its entire surface, which in turn makes contact with the SVK 14 over its entire surface. The catholyte is discharged from the cathode hemisphere 26 via the catholyte outlet 16.

[0130] The SVK 14 features a supported gas diffusion layer with silver as an electrocatalyst. The SVK 14 is integrated into the electrolysis cell such that it is oriented with a permeability between the catholyte gap 17 and the catholyte outlet 16 within the electrolysis cell, allowing the catholyte to exit the catholyte gap 17 and be discharged through the catholyte outlet 16 during operation.

[0131] The electrolysis cell of Fig. 4 further comprises an anolyte inlet 35 and an anolyte outlet 36, through which the anode chamber 28 and the anode 34 located therein are supplied with the anolyte current. In addition, the electrolysis cell includes a current line for the cathode 21 and a current line for the anode 22, which contact the respective hemispheres 25, 26 and supply current from the respective hemispheres 25, 26 to the corresponding electrode 14, 34 via electrically conductive connections 40, 41. The anode 34 is supplied with current via a rigid, electrically conductive structure 37 with openings for gas and electrolyte, which rests against the anode 34.

[0132] The anode half-shell 25 and the cathode half-shell 26 are contacted via the flange areas 38a and 38b and sealed with a gasket 39 each. At least the separator 27 is fixed between the half-shells via the aforementioned flange areas.

[0133] The overflow 15 is located on the distribution channel 24 at the front face of the cell element and is not shown in Fig. 4 (see Fig. 3 here). 2024PF30090 - Abroad

[0134] - 26 -

[0135] The reference symbols describe:

[0136] 1 Electrolyzer with a number n cell elements Z as a collection Z(n)

[0137] 2 storage containers (here: storage containers for lye for withdrawal 3 or dilution 4 while obtaining electrolyte solution (catholyte))

[0138] 3. Extraction device for produced lye

[0139] 4. Adding water to adjust the electrolyte concentration of the electrolyte-

[0140] Distribution system 10 guided electrolyte main flow

[0141] 5 Extraction device (here: pump)

[0142] 6 Unit for flow control (here control valve e.g. flap)

[0143] 7 Flow measuring device (here: volume flow measurement)

[0144] 8 Unit for pressure adjustment (here control valve e.g. flap)

[0145] 9 Pressure measuring device

[0146] 10 Electrolyte distribution system

[0147] 11 Adjustment unit for setting the value in each individual cell element of the n

[0148] Cell elements delivered volume flow of the electrolyte solution (here: implemented as: valves for regulating the electrolyte solution (alkali) to each individual

[0149] Cell element

[0150] 12 Control device

[0151] 13. Lye drainage system

[0152] 14 Cathode (here: gas diffusion electrode as SVK)

[0153] 15 Overflow of the individual cell element (overflow hose, preferably transparent to the

[0154] Level control

[0155] 16 Catholyte drain with alkali drain hose of the individual cell element

[0156] 17 Catholyte gap

[0157] 18 Catholyte inflow of the respective cell element

[0158] 19 Supply line for electrolyte solution, in fluid connection with the storage tank 2 and the individual cell elements at least via the electrolyte distribution unit 10

[0159] 20 Branch for electrolyte solution

[0160] 21 Power line cathode

[0161] 22 Power line anode

[0162] 23 Electrolyte recycling (here: concentrated alkali as extracted catholyte) 2024PF30090 - Abroad

[0163] - 27 -

[0164] 24 Distribution channel (arranged within the individual cell element above the cathode along the catholyte gap 17)

[0165] 25 anode half-shell

[0166] 26 Cathode half-shell

[0167] 27 Separator

[0168] 28 Anode compartment

[0169] 29 The cathode space is the entire volume defined by the cathode hemisphere 26, which contains, in addition to the cathode 14, the catholyte gap 17 and the gas space 30.

[0170] 30 Gas space

[0171] 31 Gas supply line

[0172] 32 Gas discharge

[0173] 33 Flow brake

[0174] 34 Anode

[0175] 35 Anolyte inflow

[0176] 36 Anolyte drainage

[0177] 37 electrically conductive, perforated structures for powering the SVK 14

[0178] 38a Flange area

[0179] 38b Flange area

[0180] 39 Seal

[0181] 40 Electrically conductive connection of the anode 34 with anode half-shell 25

[0182] 41 electrically conductive connection from the cathode 14 and the elastic structure 37 with the cathode hemisphere 26

[0183] Z single cell element

[0184] Z(n) A collection of a number n individual cell elements that are contained in an electrolyzer 2024PF30090 - Abroad

[0185] - 28 -

[0186] Examples

[0187] Example 1: Comparison example with volume flow control but without pressure control

[0188] The electrolyzer described above, with the electrolyte supply operation shown in Fig. 1, was supplied by pump 5 with 85 m³ / h. 3 The pump was supplied with sodium hydroxide solution per hour. Behind the pump was a control element 6 in the form of a control valve 6. Between the pump 5 and the control valve 6 was a flow measuring device 7 as a volume flow detection system in the form of a magnetic inductive flow meter.

[0189] With a main electrolyte flow rate of 85 m³ 3 The calculated starting value of the volume flow rate of each partial flow in the branch is 20,537.97 L / h (i.e., 85,000 L / h).

[0190] The transparent overflow tubes 15, which acted as level indicators, were then checked to ensure that the distribution channel 24 of each of the 158 cell elements was optimally supplied with electrolyte solution, thus allowing for optimal distribution of the solution across the cathode 14. 52 elements were in the overflow, while the other 106 elements had a caustic solution level in the caustic overflow tube 15. The caustic solution flow rate to the elements with caustic solution overflow was reduced by carefully closing valve 11 until no further overflow was observed. Closing valve 11 prevented overflow in all elements with overflow. It was then observed that other elements, which previously had no overflow, now overflowed. The number of overflowing elements could not be reduced. The caustic solution quantity of

[0191] 85 m 3 / h over 83 m 3The flow rate was reduced by [per hour]. During this process, the fill level of one cell element dropped so drastically that no caustic solution was visible in the caustic solution overflow hose of overflow 15. Within one minute, the cell voltage of this cell element rose above the maximum permissible cell voltage value, causing the electrolyzer to shut down. With the power off, it was observed that 145 of the 158 cell elements were now overflowing. The valve 11 of the element exhibiting the sharp voltage increase was opened by 30%. After restarting the system, 32 elements were still overflowing. The valve 11 of all overflowing elements was closed until no overflow was visible. It was then observed again that some of the elements that had previously been at electrolyte level were now overflowing. The number of overflowing cell elements could not be reduced. [Reference number: 2024PF30090 - Abroad]

[0192] - 29 - To avoid electrolyzer failure during further reduction of the caustic solution volume, the valves 11 of the cell elements without overflow were opened by 10% and then the caustic solution volume was reduced to 81m 3 The flow rate was reduced. It was then determined that 17 elements were still in the overflow, and their valves were further closed. Subsequently, an overflow was detected in 8 cell elements that previously had an electrolyte level of 15 in the overflow. No further adjustments were made.

[0193] Example 2: Inventive method - pressure control

[0194] The electrolyzer 1 of Fig. 1, described above, was equipped with a pressure control system, as shown in Fig. 2. During operation, the electrolyzer 1 of Fig. 2 was supplied with sodium hydroxide solution by the pump 5, as previously described. A flow rate sensing system 7, in the form of a magnetic inductive flow meter, was located downstream of the pump. A control device 8, in the form of a flap, was installed downstream of the pump. A pressure sensing system 9, in the form of a pressure transmitter, was located downstream of the flap. An absolute pressure of 2.7 bar, to be set in the electrolyte distribution system 10, was specified as a control target via the control unit 12, which is connected to the pressure measuring device 9. The valves 11 to all cells were opened to 30%. After commissioning, 19 cell cells overflowed at the overflow 15, at which point the valve 11 was closed until no further overflow was visible. The absolute pressure in the electrolyte distribution system 10 remained constant.No other cell element overflowed. The caustic solution volume was measured at flow meter 79 m³ / h. 3 / h measured. With a main electrolyte flow rate of 79 m³ / h. 3 / h (i.e. 79,000 L / h) the calculated starting value of the volume flow of each partial flow in branch 20 is 500.00 L / h.

[0195] With a main electrolyte flow rate of 85 m³ 3 The calculated starting value of the volume flow rate of each partial flow in the branch is 20,537.97 L / h (i.e., 85,000 L / h).

[0196] The pressure control thus enabled a simple and effective adjustment of the volume flow of the electrolyte solution and the corresponding fill level within the individual cell element, without the electrolyzer having to be switched off due to an increase in the cell voltage of one of the cell elements.

Claims

2024PF30090 - Ausland - 30 - P a t e n t a n s p r ü c h e 1. A method for distributing a liquid composition as an electrolyte solution to several cell elements of an electrolyzer, wherein a main stream of the electrolyte solution is distributed as the main electrolyte stream through an electrolyte distribution system to half-cells of several cell elements for supplying the electrodes located therein, characterized in that the main electrolyte stream supplied to the electrolyzer is introduced into an electrolyte distribution system and there divided into several partial streams, provided that the pressure of the electrolyte solution introduced into the electrolyte distribution system is measured in the electrolyte distribution system and adjusted such that an absolute pressure in the range of 1.20 to 6.00 bar is present in the electrolyte distribution system, and at least one partial stream is diverted from the introduced main electrolyte stream for each cell element, wherein the volume flow of each diverted partial stream is adjusted.This adjusted partial flow is dispensed from the electrolyte distribution system and introduced into a half-cell of the respective cell element.

2. Method according to claim 1, characterized in that the pressure of the electrolyte solution introduced into the electrolyte distribution system is measured in the electrolyte distribution system and adjusted such that an absolute pressure in the electrolyte distribution system is in the range of 1.20 to 4.00 bar, preferably in the range of 1.20 to 3.20 bar.

3. Method according to one of the preceding claims, characterized in that the electrolyte solution from the cell elements is discharged into an electrolyte drainage system and the absolute pressure in the electrolyte drainage system is equal to or lower than the absolute pressure in the respective cell elements.

3. Method according to one of the preceding claims, characterized in that the electrolyte solution from the cell elements is discharged into an electrolyte drainage system and the absolute pressure in the electrolyte drainage system is in the range of 1.00 to 1.40 bar, preferably in the range of 1.10 to 1.30 bar. 2024PF30090 - Abroad - 31 - 4. Method according to one of the preceding claims, characterized in that the electrolyte solution from the cell elements is discharged into an electrolyte drainage system and the differential pressure between the electrolyte distribution system and the electrolyte drainage system is 0.30 to 5.00 bar, preferably in the range of 0.40 to 2.50 bar.

5. Method according to one of the preceding claims, characterized in that the absolute pressure of the electrolyte solution introduced into the electrolyte distribution system is set to a predetermined target value in the said range and maintained within a deviation of a maximum of ± 50 mbar from the target value.

6. Method according to one of the preceding claims, characterized in that the volume flow of each partial flow discharged from the electrolyte distribution system is adjusted by a pressure loss unit such that electrolyte solution flows to each cell element at a volume flow rate between 100 and 900 L / h, preferably 450 - 700 L / h.

7. Method according to one of the preceding claims, characterized in that the volume flow is adjusted by a pressure loss unit comprising at least one orifice plate and / or at least one valve.

8. Method according to one of the preceding claims, characterized in that partial currents discharged from the electrolyte distribution system are each introduced into a separate half-cell of a cell element, wherein said half-cell is equipped with a gas diffusion electrode, preferably with a gas diffusion electrode as the cathode.

9. Method according to one of the preceding claims, characterized in that the cell elements of the electrolyzer each contain at least: (i) an anode half-cell containing an anode half-shell with an anode space; (ii) a cathode half-cell comprising a cathode half-shell with a cathode space comprising at least one catholyte space comprising at least one catholyte inlet and at least one catholyte gap; 2024PF30090 - Abroad - 32 - (iii) at least one separator to separate the anode compartment of the anode half-shell from the cathode compartment of the cathode half-shell; (iv) a gas diffusion electrode, the largest of which is oriented at a distance along the separator surface, forming a catholyte gap; and the partial flow intended for the respective cell element is introduced into the catholyte inlet.

10. Method according to one of the preceding claims, characterized in that, for the provision of the main electrolyte flow, electrolyte solution is taken from a storage container in such a way that the pressure of the resulting main electrolyte flow before adjustment and before entry into the electrolyte distribution system is greater than the pressure in the electrolyte distribution system.

11. Method according to one of the preceding claims, characterized in that the main electrolyte flow is supplied by a withdrawal device for taking electrolyte solution from a storage container, wherein during the supply the pressure in the electrolyte distribution system is measured via at least one measuring device and the pressure is adjusted via at least one flow control device usable for regulating the main electrolyte flow, preferably a fitting with a throttle valve or a valve, a control system and / or via the regulation of the quantity taken off by the withdrawal device such that the pressure determined with the measuring device is in the range of an absolute pressure of 1.20 to 6.00 bar.

12. Device for distributing a liquid composition as an electrolyte solution to several cell elements (Z(n)) of an electrolyzer (1), comprising at least one storage container (2) for electrolyte solution; at least one electrolyzer (1) with several cell elements (Z(n)), each of which in turn has at least one half-cell for receiving the electrolyte solution stored in the storage container; at least one supply line (9) for electrolyte solution, wherein this supply line (9) has at least one unit for adjusting the pressure (8) of the electrolyte solution to be supplied in the supply line (9). 2024PF30090 - Abroad - 33 - main flow contains and this supply line is in fluid connection at least with the storage tank (2) and at least via an electrolyte distribution system (10) with the said cell elements (Z) of existing electrolyzers (1); wherein - the device additionally includes at least one pressure measuring device (9) configured to measure the pressure of electrolyte solution in the electrolyte distribution system (10), - the pressure setting unit (8) is configured such that it can change the pressure of the electrolyte solution carried in the supply line (9) and introduced into the electrolyte distribution system (10) via a control device (12) such that the electrolyte solution carried in the electrolyte distribution system (10) has an absolute pressure in the range of 1.20 to 6.00 bar as determined by the pressure measuring device (9); - the electrolyte distribution system (10) has several branches (20) for electrolyte solution, each connected to a cell element (Z) in fluid communication, wherein electrolyte solution can be passed through the branches (20) and the branches (20) each have at least one adjustment unit (11) for adjusting the volume flow of the electrolyte solution delivered to the respective individual cell element.

13. Device according to claim 12, characterized in that the adjustment unit (11) is a pressure loss unit, preferably comprising at least one aperture and / or at least one valve.

14. Device according to claim 12 or claim 13, characterized in that said half-cell is equipped with a gas diffusion electrode (14), preferably with a gas diffusion electrode as the cathode. 2024PF30090 - Abroad - 34 - 15. Device according to one of claims 12 to 14, characterized in that the cell elements (Z) of the existing electrolyzers (1) each contain at least: (i) an anode half-cell comprising an anode half-shell (25) with an anode space (28); (ii) a cathode half-cell, comprising a cathode half-shell (26) with a cathode space (29) which in turn comprises at least one catholyte space which comprises at least one has a catholyte inlet (18) and contains at least one catholyte gap (17); (iii) at least one separator (27) to separate the anode compartment (28) of the anode half-shell (25) from the cathode compartment (29) of the cathode half-shell (26); (iv) a gas diffusion electrode (14) which is oriented with its largest area at a distance along the separator surface forming a catholyte gap (17), wherein a branch (20) of the electrolyte distribution device (10) is in fluid communication with a catholyte inlet (18).

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