Control for optimized electrolyte supply of electrodes of an electrolyser

Abstract

A device and a method are described, 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 achieved in particular by individually adjusting the volume flow introduced into a given cell element, while simultaneously controlling the pressure of the liquid, electrolyte-containing composition in the electrolyte distribution system.

Description

[0001] 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.

[0002] 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. Typically, as is known from chlor-alkali electrolysis, cell elements with an electrode area of ​​more than 2 m² per electrolysis cell are used. The cell elements are grouped, for example, up to 100 units in an electrolysis rack. Several racks then form an electrolyzer. The capacity of an industrial electrolyzer, for example for chlorine production, is currently up to 30,000 tons per year of chlorine and the respective equivalents of sodium hydroxide or hydrogen.

[0003] Regardless of the electrode type chosen, several electrolyzers are typically operated in parallel in corresponding electrolysis plants. As described, for example, in DE19641125, 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").

[0004] The supply of operating fluids to the cell elements, particularly 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 an electrolysis cell room can be found, for example, in Ullmann's Encyclopedia of Industrial Chemistry, chapter "Chlorines".

[0005] The operation of the electrodes in an electrolyzer, particularly one with gas diffusion electrodes, requires a minimum electrolyte supply 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 electrolyte distribution requirement.

[0006] 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.

[0007] 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).The flow rate of the electrolyte supplied to the electrolyzer is regulated for this purpose so that all level indicators show optimal supply. For example, a transparent tube serving as an overflow for electrolyte solution from the cell element and as a level indicator should be full and have a static level – also referred to as the electrolyte level – meaning it should be full 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 flow rate of the electrolyte supplied to the electrolyzer, does not allow all cell elements to be adjusted to the optimal supply of electrolyte solution to the electrodes, e.g., the electrolyte level in the overflow tube.The regulation of optimal supply is therefore improved by valves for fine-tuning the volume flow directed into the individual cell element. However, this type of control still leads to problems during the operation of the electrolysis process.

[0008] 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.

[0009] 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. This reduction in flow rate, and the resulting insufficient supply of electrolyte solution to each individual cell element, can lead to an electrolyte deficiency at the affected electrode. This can cause the electrical operating voltage at the undersupplied electrode to rise to such an extent that, in the worst-case scenario, the entire electrolyzer is shut down and fails for safety reasons.This results in an undesirable and costly production outage.

[0010] 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.

[0011] 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 the overflow tube of many cell elements, pressure is exerted on the electrodes, especially in the upper region of gas diffusion electrodes. Additionally, a larger quantity of electrolyte flows out through 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, leading to pressure changes in the outlet system for the gas supplied as a reactant and negatively impacting the gas distribution / supply within the cell element.This also results in an undesirable increase in cell voltage.

[0012] The task was therefore to provide a control system that enables reliable, effective, and easy-to-use operation of the electrodes in an electrolyzer, as well as simple adjustment of the optimal electrolyte supply to the electrodes, indicated by a level sensor (e.g., adjusting the electrolyte level in the overflow tube). This would minimize the number of cell elements with over- or under-supply of electrolyte solution without affecting neighboring cell elements, thus preventing excessive wear on the electrodes, particularly on the gas diffusion electrode. Furthermore, the system should minimize over-supply of electrolyte solution when the current changes, especially when the current decreases.

[0013] 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 The pressure of the electrolyte solution introduced into the electrolyte distribution system is measured and adjusted (preferably by a control system comprising at least one pressure setting unit and at least one control device) such that an absolute pressure in the range of 1.20 to 6.00 bar is present in the electrolyte distribution system, at least one partial flow is diverted from the main electrolyte flow introduced for each cell element, 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.

[0014] It has been shown that the problem is solved by the method according to the invention. Optimal electrolyte supply 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.

[0015] 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.

[0016] 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).

[0017] An aqueous solution of at least one electrolyte selected from at least one electrolyte of the group NaCl, NaOH, KOH, KCl, HCl, NaHCO 3 , KHCO 3 is preferably used as the electrolyte solution.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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 drop 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 volumetric flow rate is ensured, for example, by ensuring that, in an electrolyzer with a number n of cell elements operated in parallel, the volumetric flow rate of the main electrolyte flow before its 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.

[0023] 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.

[0024] 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 brought to a defined pressure (setpoint) within the electrolyte distribution system. 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.

[0025] 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.

[0026] 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.

[0027] 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 absolute pressure of the electrolyte solution prevailing in the electrolyte distribution system is selected and set (preferably via the control system). This setpoint lies 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" is understood to mean that the selected setpoint pressure in the electrolyte distribution system is maintained by the pressure control system within a tolerable pressure fluctuation, with 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 setpoint 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 most preferably in the range of 1.20 to 3.20 bar, and maintained within a maximum deviation of ± 50 mbar from the setpoint.

[0028] 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 greater 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 storage 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 lies in one of the ranges 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.When electrolyte solution is drawn from the reservoir, the hydrostatic pressure of the resulting main electrolyte flow can be maintained, for example, by a pumping system to refill the reservoir with electrolyte solution from another storage tank. However, the pressure of the main electrolyte flow can also be generated directly by a pump during extraction from a storage tank, without the need for a reservoir, and adjusted such that the pressure, determined by at least one measuring device, lies within the range of an absolute pressure from the aforementioned list, more preferably within the range of 1.20 to 6.00 bar, more preferably within the range of 1.25 to 4.00 bar, and most preferably within 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.

[0029] In a further preferred embodiment of the electrolyzer, during operation, the electrolyte solution introduced into the respective cell elements is removed from the respective cell elements, fed into an electrolyte drain system, and combined there 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, serving 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 electrolyte drain 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 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. 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.

[0030] 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.

[0031] 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.

[0032] 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, caused 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 gas-side electrode assembly (GDE). If the gas-side pressure is too high, the gas eventually breaks through the GDE, disrupting its function in this region; that is, the electrolysis process is locally interrupted. Conversely, if the liquid pressure is too high, the three-phase boundary shifts out of the catalyst region of the GDE until the GDE is flooded with electrolyte solution, and further pressure increases lead to liquid breakthrough of the electrolyte solution into the gas phase. This also disrupts the function of the GDE, and the desired reaction does not occur.

[0033] In a preferred embodiment of the method, an electrolyzer usable in the inventive process contains at least one cell element for the use of at least one gas diffusion electrode, containing 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 CO2 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 a second half-shell equipped with a further electrode and having 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, . 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 branched off from the main electrolyte flow in the electrolyte distribution system can be introduced into the first half-shell of the electrolysis cell.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] Suitable ion exchange membranes are, in particular, 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, the temperature, and the operating conditions.

[0038] 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).

[0039] 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.

[0040] Suitable separators include diaphragms such as the Zirfon™ Pearl diaphragm (manufacturer Agfa), which is made of PTFE and zirconium dioxide.

[0041] In a further, particularly preferred embodiment of the process according to the invention, 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 with a powdered fluorine-containing polymer, in particular PTFE powder, as a non-conductive binder on a metallic or non-metallic, conductive or non-conductive support. 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.

[0042] Instead of powdered fluoropolymers, other polymer powders with comparable properties (i.e., in particular inert towards electrolyte at reaction temperature and high current density and processable in the production of the GDE) are also suitable, in particular polyalkylenes, especially preferably polyethylene, polypropylene or partially fluorinated polymers.

[0043] 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: (i) an anode half-cell comprising an anode half-shell with an anode compartment; (ii) a cathode half-cell comprising a cathode half-shell with a cathode compartment, which in turn has at least one catholyte compartment containing at least one catholyte inlet and at least one catholyte gap; (iii) at least one separator for separating the anode compartment of the anode half-shell from the cathode compartment of the cathode half-shell; (iv) a gas diffusion electrode, the largest surface 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.

[0044] 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 10 2004 018748 A1.

[0045] WO 2005 / 100640A1, EP 2 652 176 A and WO 2001 / 057290 A1.

[0046] 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.

[0047] 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 WO2003042430A2, Example 1, or hydrophobic, depending on the choice of flow conditions or the viscosity of the electrolyte solution. The preferred materials are described above.

[0048] 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.

[0049] 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).

[0050] 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.

[0051] 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., expanded metal, mounted on springs, electrically contacts the GDE from the gas compartment side. To maintain the dimensions of the gap between the GDE and the separator under pressure, e.g., from the electrical contact, spacers are installed in the gap between the separator and the GDE. The flow brake can also perform the function of the spacer if it possesses sufficient mechanical stability and stiffness under pressure across its surface.Another object of the invention is a device configured for carrying out the method according to the invention for distributing liquid composition as an electrolyte solution onto 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 pressure control 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 the device additionally includes at least one pressure measuring device configured to measure the pressure of electrolyte solution in the electrolyte distribution system, the pressure adjustment unit being 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, determined by the pressure measuring device, in the range of 1.20 to 6.00 bar; the electrolyte distribution system having several branches for electrolyte solution, each in fluid communication with a cell element, wherein electrolyte solution can be carried through the branches and each branch has at least one adjustment unit for adjusting the volume flow rate of the electrolyte solution delivered to the respective individual cell element.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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, controlling the pressure adjustment unit (e.g. the pumping capacity of the pump or the flow rate of a flow control device) to achieve the setpoint and adjusting the pressure accordingly.

[0056] 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 said pressure range) and, 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.

[0057] It is particularly preferred if the pressure control unit includes, in addition to the 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.

[0058] 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 these branches, and each branch has at least one adjustment unit for adjusting the volume flow rate 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.

[0059] 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.

[0060] Gas diffusion electrodes such as those mentioned in the previously described embodiments of the method are also preferred for the device.

[0061] 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: (i) an anode half-cell comprising an anode half-shell with an anode compartment; (ii) a cathode half-cell comprising a cathode half-shell with a cathode compartment, which in turn has at least one catholyte compartment containing at least one catholyte inlet and at least one catholyte gap; (iii) at least one separator for separating the anode compartment of the anode half-shell from the cathode compartment of the cathode half-shell; (iv) a gas diffusion electrode, the largest surface of which is oriented at a distance along the separator surface, forming a catholyte gap; wherein each branch of the electrolyte distribution device is in fluid connection with each catholyte inlet.

[0062] 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.

[0063] In another preferred embodiment of the method according to the invention, using the aforementioned cell elements, it has proven advantageous if, to ensure sufficient supply of the catholyte gap with electrolyte solution, the electrolyte solution is preferably supplied to the catholyte gap via a distribution channel. For this purpose, said cell elements additionally include 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 gas-tight from the gas space.

[0064] 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).

[0065] The invention will now be explained using a specific embodiment, without limiting it to that embodiment: The invention is illustrated by way of example using a chlor-alkali electrolysis process and a device configured for this purpose (see Figure 1). Fig. 2 , 3 and 4 ) illustrated. It depicted the process in a cathode hemisphere. 26 located catho 14, which was equipped as a gas diffusion electrode (SDE) according to EP 1 728 897 A2, via a main electrolyte current 19 and corresponding distribution system 10supplied with aqueous sodium hydroxide solution (alkali) as the electrolyte solution. At the cathode 14 Gaseous oxygen reacted with water to form hydroxide ions, which reacted with the sodium ions passing through the ion exchange membrane (separator). 27 from the anode 34 come, forming an aqueous sodium hydroxide solution. However, the process according to the invention 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 A1.

[0066] In all the following examples, an NaCl-SVK electrolyzer was used. 1 with a number n = 158 elements connected in parallel in the main electrolyte current, as an accumulation Z(n) operated ( Fig.1 For example 1 below as a comparison, Fig.2 for the following example according to the invention (2). A single cell element Zcontains an anode half-shell 25 and a cathode half-shell 26, which uses an ion exchange membrane as a separator 27 are separate.

[0067] The anode half-shell 25 A stream of an aqueous solution of sodium chloride with a concentration of ~300 g / L was supplied. The process parameters for the operation of the anode half-shell were... 25 These correspond to the state of the art for chlor-alkali electrolysis and are largely independent of the operating mode of the cathode half-shell and have no influence on the process according to the invention.

[0068] 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.

[0069] To supply each cathode with alkali as an electrolyte solution, the necessary quantity 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 ) filled with lye. The lye enters a catholyte gap 17 via the filled distribution channel 24 and then flows downwards through the catholyte gap 17, which is filled with a fabric as a flow restrictor. The complete filling of the distribution channel 24 and thus of the catholyte gap 17 is ensured by this, or can also be verified by the lye level in the overflow hose 15 ( Fig. 3 ) is present. 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.

[0070] The caustic solution flowing from the element enters the caustic solution drain system 13 via the caustic solution drain hose 16. The caustic solution from the caustic solution drain system 13 is then directed into the caustic solution storage tank 2. A portion of the caustic solution is drawn from the storage tank and reused. Caustic solution is taken from the storage tank 2, diluted with water 4 to 31.0 wt.%, and returned to the electrolyzer 1.

[0071] The cathode hemisphere was equipped with a gas diffusion electrode, serving as the cathode. 14 for the reduction of oxygen using silver as an electrocatalyst (this SVK was manufactured according to EP 1 728 896 A2). The cathode hemisphere 26Pure oxygen continued to be supplied in an amount equal to 1.5 times the amount consumed by the flow. Unused oxygen was discharged via the oxygen outlet header (not shown in the figures). The amount of caustic solution that would have accumulated in elements with overflow was also discharged. 15 on the overflow hoses of the distribution channel 24 drained away (see also Fig.3 ). Both overflowing lye and from each cell element via the lye drain hose. 16 The applied lye solution (concentration 32.2 wt% NaOH; temperature: 86.8 °C) is directed onto the lye drainage system. 13 guided. The absolute pressure in the lye drainage system 13 The pressure was 1.218 bar. A more detailed description of the cell elements used in Examples 1 and 2 follows. Z is the Fig. 4 to be extracted ( vide infra ) .

[0072] The applied electric current was 12,200 A, and the amount of oxygen supplied was 682 m³ / h (standard conditions).

[0073] The characters describe: Fig. 1 Schematic representation of an electrolyte supply with pure alkali volume control (not according to the invention): The Fig.1 This is explained in more detail in Example 1. Fig. 2 Inventive method / device - pressure control: The Fig.2 This will be explained in more detail in Example 2. Fig. 3 Schematic representation of a partial flow branch according to the invention 20 including inflow 18 and process 16 of electrolyte solution (catholyte) for a cathode 14 of a single NaCl SVK cell element Z: The cross-section through the electrolysis cell Z This occurred on the side of the cathode hemisphere between the separator and the flow brake of the catholyte gap. 17. From the storage container2 is via a pump 5 a water-based NaOH solution (alkali, 32.2 wt%) was taken, which was diluted by adding water. 4 is brought to a concentration of 31.0 wt.% and pumped into a pipe in the supply line. 19 guided electrolyte main flow is brought with a starting value of the volume flow (see example 2), which is measured at the flow measuring device. 7 The electrolyte flow is measured and monitored. The main electrolyte flow passes through a pressure adjustment unit. 8 and is then transferred to an electrolyte distribution system 10 introduced. There, the main electrolyte flow is transferred into n = 158 substreams. Each of these substreams has its own branch. 20 and each partial flow is routed via the branch 20 and the catholyte inflow 18 into the distribution channel 24 introduced above and along the catholyte gap filled with a flow brake17 This process is carried out. To ensure optimal supply to the entire surface of the gas diffusion electrode (i.e., the cathode). 14) To ensure proper functioning with electrolyte solution, the adjustment unit is used. 11 (like a control valve) the volume flow in the branch 20 adjusted in such a way that the transparent overflow hose of the overflow 15 An electrolyte level is reached; the electrolyte is visible but does not overflow. 15 off. Meanwhile, the electrolyte distribution system 10 prevailing absolute pressure of the electrolyte as measured by the pressure gauge 9 measured and in the control device 12 The pressure is compared to a target value. If the pressure deviates from the target value, the control device initiates a change. 12, that the pressure is controlled by the regulating valve of the pressure setting device 8The pressure is readjusted to the setpoint so that it remains within a tolerance deviation of ±50 mbar from the setpoint. The electrolyte solution is drained via the caustic soda hose. 16 The solution is extracted from the cell element and introduced into the caustic soda drainage system. From there, the caustic soda is returned via the electrolyte recirculation system. 23 If necessary, after cleaning (not shown) put back into the storage container 2 introduced. Fig. 4 Schematic representation of a section through a single NaCl SVK cell element Z, as used in examples 1 and 2: In Fig.4 A cell element is illustrated according to the principle of falling film, in which the anode half-shell is located between 25 and cathode half-shell 26 an ion exchange membrane as a separator 27 is positioned, which is the anode space 28 from the cathode space 29 separates. The cathode compartment comprises the gas compartment. 30,a catholyte gap 17 and the catholyte flow 16. During operation, the gas space is accessed 30 via the first gas supply line 31 in particular the gaseous reactant of the SVK (e.g. O 2 ) is introduced and the gaseous reaction products via a first gas discharge. 32 derived for gaseous reaction products and excess reactant. The gas space 30 is designed in such a way that the gas supply line 31 introduced reactant with the separator 27 turned away and the gas space 30 facing surface of the SVK 14 can get in touch, and that after contacting the SVK 14 remaining residual gas from the gas vent 32 can be drained away. The catholyte gap 17 is defined as the space between the separator 27 and the separator 27 facing surface of the SVK 14 defined. In the catholyte gap 17The flow brake is located there. 33, the flow of the water through the catholyte inflow 18 The catholyte inflow is regulated by the introduced catholyte. 18 defines the space for introducing catholyte and for supplying catholyte to the distribution channel 24. The separator 27 The flow brake makes contact over a large area 33, which in turn cover the entire area of ​​the SVK 14 contacted. The catholyte is taken from the catholyte drain. 16 from the cathode hemisphere 26 led out. The SVK 14 It features a supported gas diffusion layer with silver as an electrocatalyst. Here, the SVK 14 installed in the electrolysis cell in such a way that the SVK 14 with a material permeability between catholyte gap 17 and catholyte flow 16 in the electrolysis cell is oriented so that during operation the catholyte is drawn from the catholyte gap 17 exits and from the catholyte flow16 is released. The electrolysis cell of the Fig.4 It also shows an anolyte inflow. 35 and an anolyte drainage 36 on, through which the anode space 28 and the anode contained therein 34 The electrolysis cell is supplied with an anolyte current. It also contains a power line for the cathode to provide electricity. 21 and a power line for the anode 22, which contact the respective half-shell 25, 26 and each via electrically conductive connections 40, 41 Current from the respective hemisphere 25, 26 to the corresponding electrode 14, 34 delivers. The SVK 14 is via a rigid, electrically conductive structure 37 supplied with electricity via breakthroughs for gas and electrolyte, which are located at the SVK 14 rests on the anode half-shell. 25 and cathode half-shell 26 are via the flange areas 38a and 38bcontacted and each with a seal 39 Sealed. At least the separator. 27 It is fixed via the aforementioned flange areas between the half-shells. The overflow 15 is located at the distribution channel 24 on the front face of the cell element and is not in Fig.4 shown (see here) Fig.3 ). The reference symbols describe:

[0074] 1 Electrolyzer with a number of n cell elements Z as a collection Z(n) 2 storage containers (here: storage container for lye for dispensing) 3 or dilution 4 3. Extraction device for produced lye 4. Water addition to adjust the electrolyte concentration to the electrolyte distribution system 105 Extraction device (here: pump) 6 Flow control unit (here: control valve, e.g., flap) 7 Flow measuring device (here: volumetric flow measurement) 8 Pressure control unit (here: control valve, e.g., flap) 9 Pressure measuring device 10 Electrolyte distribution system 11 Adjustment unit for adjusting the volumetric flow rate of the electrolyte solution delivered to each individual cell element of the n cell elements (here: designed as: valves for regulating the electrolyte solution (caustic soda) to each individual cell element) 12 Control device 13 Caustic soda drain system 14 Cathode (here: gas diffusion electrode as SVK) 15 Overflow of the individual cell element (overflow hose, preferably transparent for level control) 16 Catholyte drain with caustic soda drain hose of the individual cell element 17 Catholyte gap 18 Catholyte inlet of the respective cell element 19 Supply line for Electrolyte solution, in fluid connection with the storage container 2and the individual cell elements at least via the electrolyte distribution unit 10 20 Branch for electrolyte solution 21 Cathode electrical conductor 22 Anode electrical conductor 23 Electrolyte return (here: concentrated alkali as the catholyte removed) 24 Distribution channel (within the individual cell element above the cathode along the catholyte gap) 17 (arranged) 25 Anode half-shell 26 Cathode half-shell 27 Separator 28 Anode compartment 29 Cathode compartment is the entire area divided by the cathode half-shell 26 defined volume which is next to the cathode 14 among other things the catholyte gap 17 and the gas space 30 Contains: 30 Gas space 31 Gas inlet 32 ​​Gas outlet 33 Flow restrictor 34 Anode 35 Anolyte inlet 36 Anolyte outlet 37 Electrically conductive, perforated structure for powering the SVK 14 38a Flange area 38b Flange area 39 Gasket 40 Electrically conductive connection of the anode 34 with anode half-shell 2541 Electrically conductive connection from the cathode 14 and the elastic structure 37 with the cathode half-shell 26 Zindividual cell element Z(n) An assembly of a number n individual cell elements that are contained in an electrolyzer Beispiele Example 1: Comparison example with volume flow control but without pressure control

[0075] The electrolyzer described above operates according to the electrolyte supply mechanism. Fig. 1 was pumped 5 It was supplied with 85 m³ / h of sodium hydroxide solution. A control device was located behind the pump. 6 in the form of a control valve 6. Between pump 5 and the control valve 6 There was a flow metering device 7 als Volume flow measurement system in the form of a magnetic inductive flow meter.

[0076] With a main electrolyte flow rate of 85 m³ / h (i.e., 85,000 L / h), the calculated initial value of the flow rate of each branch is 20 537.97 L / h.

[0077] Then, the transparent hoses of the overflow, which act as level indicators, were checked. 15 checked whether the distribution channel 24 Each of the 158 cell elements was optimally supplied with electrolyte solution, thus optimally distributing it across the surface of the cathode. 14 can be distributed. 52 elements were in the overflow, the other 106 elements had a lye level in the lye overflow hose. 15 a reduction in the caustic solution flow rate to the elements with caustic solution overflow by carefully closing the valve. 11 The test was carried out until no further overflow could be observed. For all elements with overflow, closing the valve confirmed that the problem had stopped. 11Overflow was to be avoided. It was subsequently observed that other elements, which previously had no overflow, now overflowed. The number of overflowing elements could not be reduced. The caustic solution flow rate was reduced from 85 m³ / h to 83 m³ / h. During this reduction, the fill level of one element dropped significantly, resulting in no caustic solution remaining in the overflow hose. 15 This was noticeable. 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 current off, it was determined that 145 of the 158 cell elements were now in overflow mode. The valve on the element exhibiting the sharp voltage increase was opened. 11 The valve was opened by 30%. After restarting the system, 32 elements were still overflowing. The valve was opened on all elements with overflow. 11The valves were closed until no overflow was visible. It was then observed again that some of the cells that had previously been at electrolyte level were now overflowing. The number of cells with overflow could not be reduced. To prevent electrolyzer failure with a further reduction in the amount of lye, the valves were closed. 11 The overflow valves of the cell elements were opened by 10%, and then the caustic solution flow rate was reduced to 81 m³ / h. It was then observed that 17 elements were still in the overflow, and their valves were further closed. Following this, the electrolyte level in the overflow was checked on 8 cell elements. 15 An overflow was detected. No further adjustments were made. Example 2: Inventive method - pressure control

[0078] The previously described electrolyzer 1 of the Fig. 1 was, as in Fig.2 The electrolyzer is shown, equipped with a pressure regulator. 1 the Fig.2 through the pump 5 As previously described, it was filled with sodium hydroxide solution. A flow rate monitoring system was located behind the pump. 7 in the form of a magnetic inductive flow meter. A control device was installed downstream of the pump. 8 It was built in the form of a flap. Behind the flap was a pressure sensing system. 9 in the form of a pressure transmitter. It was connected to the pressure measuring device. 9 related control unit 12 a system within the electrolyte distribution system 10 The absolute pressure to be set is specified as a control parameter of 2.7 bar. The valves 11 All elements were opened to 30%. After commissioning, 19 cell elements were operating at overflow. 15 over, at which the valve 11It was closed until no overflow was visible. The absolute pressure remained in the electrolyte distribution system. 10 constant. No other cell element overflowed. The amount of lye was measured at the flow meter. 7 measured at 79 m³ / h. With a main electrolyte flow rate of 79 m³ / h (i.e., 79,000 L / h), the calculated initial flow rate of each branch is... 20 500.00 L / h.

[0079] With a main electrolyte flow rate of 85 m³ / h (i.e., 85,000 L / h), the calculated initial value of the flow rate of each branch is 20 537.97 L / h.

[0080] 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

1. 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 electrolyte main stream through an electrolyte distribution system to half-cells of several cell elements for supplying the electrodes located therein, characterized by the fact thatThe main electrolyte stream supplied to the electrolyzer is introduced into an electrolyte distribution system and divided there into several partial streams, provided that: - the pressure of the electrolyte solution introduced into the electrolyte distribution system is measured and adjusted in such a way that an absolute pressure in the range of 1.20 to 6.00 bar is present in the electrolyte distribution system; - at least one partial stream is diverted from the introduced main electrolyte stream for each cell element, whereby the volume flow of each diverted partial stream is adjusted, this adjusted partial stream is discharged from the electrolyte distribution system and introduced into a half-cell of the respective cell element.

2. Method according to claim 1, characterized by the fact thatThe pressure of the electrolyte solution introduced into the electrolyte distribution system is measured and adjusted in such a way 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 by the fact 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 by the fact 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. 4.Method according to one of the preceding claims, characterized by the fact 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 by the fact that The absolute pressure of the electrolyte solution introduced into the electrolyte distribution system is set to a predetermined target value within the specified range and maintained within a maximum deviation of ± 50 mbar from the target value.

6. Method according to one of the preceding claims, characterized by the fact thatThe volume 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 volume flow rate between 100 and 900 L / h, preferably 450 - 700 L / h.

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

8. Method according to one of the preceding claims, characterized by the fact that Partial currents dispensed 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 by the fact thatThe cell elements of the electrolyzer each contain at least: (i) an anode half-cell, comprising an anode half-shell with an anode compartment; (ii) a cathode half-cell, comprising a cathode half-shell with a cathode compartment, which in turn has at least one catholyte compartment containing at least one catholyte inlet and at least one catholyte gap; (iii) at least one separator for demarcating the anode compartment of the anode half-shell from the cathode compartment of the cathode half-shell; (iv) a gas diffusion electrode, the largest surface of which is oriented at a distance along the separator surface, forming a catholyte gap; and the partial current intended for the respective cell element is introduced into the catholyte inlet.

10. Method according to one of the preceding claims, characterized by the fact thatTo provide 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 entering the electrolyte distribution system is greater than the pressure in the electrolyte distribution system.

11. Method according to one of the preceding claims, characterized by the fact thatThe main electrolyte flow is supplied by a withdrawal device for extracting 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 withdrawn 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) contains at least one unit for pressure control (8) of the main electrolyte flow to be carried in the supply line (9) and this supply line is in fluid communication at least with the storage container (2) and at least via an electrolyte distribution system (10) with the said cell elements (Z) of the electrolyzers (1) present;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 determined by the pressure measuring device (9) in the range of 1.20 to 6.00 bar;- the electrolyte distribution system (10) has several branches (20) for electrolyte solution, each branch being in fluid communication with a cell element (Z), 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 by the fact 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 by the fact that said half-cell is equipped with a gas diffusion electrode (14), preferably with a gas diffusion electrode as the cathode.

15. Device according to one of claims 12 to 14, characterized by the fact thatThe cell elements (Z) of the existing electrolyzers (1) each comprise at least: (i) an anode half-cell comprising an anode half-shell (25) with an anode compartment (28); (ii) a cathode half-cell comprising a cathode half-shell (26) with a cathode compartment (29), which in turn comprises at least one catholyte compartment, which includes at least one catholyte inlet (18) and at least one catholyte gap (17); (iii) at least one separator (27) for separating 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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