EP1740739B1 - Electrochemical cell - Google Patents

Electrochemical cell Download PDF

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Publication number
EP1740739B1
EP1740739B1 EP05732004.6A EP05732004A EP1740739B1 EP 1740739 B1 EP1740739 B1 EP 1740739B1 EP 05732004 A EP05732004 A EP 05732004A EP 1740739 B1 EP1740739 B1 EP 1740739B1
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EP
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Prior art keywords
electrolyte
gap
gas
overflow
electrochemical cell
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EP05732004.6A
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German (de)
French (fr)
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EP1740739A1 (en
Inventor
Fritz Gestermann
Andreas Bulan
Hans-Dieter Pinter
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Covestro Deutschland AG
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Covestro Deutschland AG
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B15/00—Operating or servicing cells
    • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
    • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms

Definitions

  • the invention relates to an electrochemical cell, at least consisting of an anode half-cell with an anode, a cathode half-cell with a cathode and an ion exchange membrane arranged between anode half-cell and cathode half-cell, wherein the anode and / or the cathode is a gas diffusion electrode.
  • the invention further relates to a process for the electrolysis of an aqueous solution of alkali chloride.
  • WO 01/57290 An electrolytic cell with a gas diffusion electrode is known in which a porous layer is provided in the gap between the gas diffusion electrode and the ion exchange membrane. The electrolyte flows from top to bottom over the porous layer under the action of gravity through the gap.
  • the porous layer according to WO-A 01/57290 may consist of foams, wire nets or the like.
  • an electrolytic cell with gas diffusion electrode for the electrolysis of a sodium chloride solution in which a layer of a hydrophilic material is in the gap between the gas diffusion electrode and the ion exchange membrane.
  • the layer of hydrophilic material preferably has a porous structure containing a corrosion-resistant metal or resin.
  • a porous structure for example, nets, fabrics or foams can be used.
  • Sodium hydroxide, the electrolyte flows down the layer of hydrophilic material down to the bottom of the electrolytic cell under gravity.
  • EP-A 1 033 419 an electrolytic cell with gas diffusion electrode as a cathode for the electrolysis of a sodium chloride solution known.
  • a hydrophilic porous material through which the electrolyte flows.
  • porous material metals metal oxides or organic materials are considered, provided they are corrosion resistant.
  • Porous layers also have the disadvantage that gas which has once entered the porous structure, from this difficult to get out again.
  • the gas can accumulate, whereby the above-mentioned disadvantages arise.
  • Gas from the gas space can also pass from the gas space into the gap through the gas diffusion electrode under operating conditions.
  • gas diffusion electrodes tend to pass more gas at non-wetted sites, so that the effect amplifies.
  • the object of the present invention is therefore to provide an electrolytic cell which avoids the disadvantages of the prior art.
  • the invention relates to an electrochemical cell, at least consisting of an anode half-cell with an anode, a cathode half-cell with a cathode and an ion exchange membrane arranged between anode half-cell and cathode half-cell, wherein the anode and / or the cathode is a gas diffusion electrode, between the gas diffusion electrode and the ion exchange membrane Gap, an electrolyte inlet above the gap and an electrolyte drain below the gap and a gas inlet and a gas outlet is arranged, characterized in that the electrolyte inlet is connected to an electrolyte reservoir and has an overflow.
  • the electrolyte flows in the gap between gas diffusion electrode and ion exchange membrane from top to bottom through the half cell. Accordingly, in the electrolysis cell according to the invention there is an electrolyte feed above the gap and an electrolyte drain below the gap. The gap is completely filled by the flowing electrolyte.
  • the remaining space of the half-cell behind the gas diffusion electrode i. the space on the side facing away from the ion exchange membrane of the gas diffusion electrode, which is referred to as gas space, is filled with gas.
  • the gas is supplied to the gas space through the gas inlet and discharged through the gas outlet.
  • the Elektolytzulauf forms horizontally above the gap a channel which extends over the entire width of the electrochemical cell.
  • the electrolyte can be fed uniformly over the entire width from above into the gap between the gas diffusion electrode and the ion exchange membrane.
  • the electrolyte feed for example, has numerous openings which are directed downwards, over which the electrolyte flows during operation of the electrolytic cell into the gap.
  • a gap-shaped or slot-shaped opening may be provided, which extends over the entire width of the gap.
  • the electrolyte leaves the half-cell via the electrolyte drain and enters an electrolyte reservoir, wherein the electrolyte effluent must be immersed in the electrolyte reservoir to an uncontrolled gas flow through the electrolyte reservoir from cell to cell (in case of several electrolysis cells connected to an electrolyzer).
  • the electrochemical cell according to the invention is also referred to as a falling film cell.
  • Their trouble-free operation depends crucially on the safe supply of the electrode with electrolyte.
  • the width may be more than 2000 mm. This means that a uniform feeding of the electrode with electrolyte over the entire width must be guaranteed.
  • gas diffusion electrode is used as the electrode, gas can enter from the gas space through the gas diffusion electrode into the gap between the gas diffusion electrode and the ion exchange membrane. The gas must be able to be reliably removed from the gap, since an accumulation of gas in the gap must be avoided.
  • the uniform feeding of the gas diffusion electrode with electrolyte, which flows in the gap between gas diffusion electrode and ion exchange membrane from top to bottom, is achieved in the electrolysis cell according to the invention in that the electrolyte feed is connected to an electrolyte reservoir and has an overflow.
  • the electrolyte reservoir is preferably located 30 to 200 cm above the electrolyte inlet.
  • the electrolyte flows from the storage tank into the electrolyte inlet. From the electrolyte feed, the electrolyte flows e.g. via a slit-shaped opening in the gap between gas diffusion electrode and ion exchange membrane.
  • the electrolyte reservoir is connected via a pump to the electrolyte inlet.
  • the electrolyte reservoir can in principle be arranged at any desired location, for example below the electrochemical cell. With the help of the pump, the electrolyte is pumped with the desired form in the electrolyte inlet.
  • the electrolyte reservoir may, in principle, be connected at any location to the electrolyte inlet, e.g. at one end of the electrolyte inlet.
  • electrolysis cells according to the invention are connected to form an electrolyzer, a single electrolyte reservoir can be used to supply all the electrolysis cells of the electrolyzer.
  • each of the electrolysis cells can be equipped with a separate storage tank.
  • the electrolyte inlet according to the invention has an overflow.
  • the overflow preferably has a height of 0 to 190 cm, more preferably 1 to 190 cm above the entry into the gap. In principle, the height of the overflow can be less than 1 cm; The overflow is at the same level as the entry into the gap.
  • the overflow ensures that during operation of the electrolysis cell always accumulates a certain amount of electrolyte in the electrolyte feed. It is crucial for the height of the overflow to accumulate a large amount of electrolyte in the electrolyte feed sufficient to continuously supply electrolyte to the gap across its entire width.
  • a valve, a diaphragm, for example in the form of a perforated disc, or the like may be provided in the supply line, which connects the electrolyte reservoir with the electrolyte inlet.
  • a valve, a diaphragm for example in the form of a perforated disc, or the like may be provided in the supply line.
  • the targeted overflow of the electrolyte from the electrolyte inlet allows a uniform feeding of the gap with electrolyte over the entire width of the electrode and a safe discharge of gas from the gap.
  • the overflow stream prevents the level of electrolyte in the electrolyte feed from dropping enough for the falling film of the electrolyte in the gap to break off. Furthermore, the overflow ensures, inter alia, that gas bubbles which rise from the gap in the electrolyte feed are transported away with the electrolyte.
  • the overflow can in principle be positioned at any point along the electrolyte inlet. He can e.g. be provided at one end of the electrolyte inlet.
  • the overflow is designed according to the invention as an overflow channel.
  • Such an overflow channel can be arranged either outside or inside the cathode half cell. Excess electrolyte, which does not flow down the gap, flows from the electrolyte feed into the overflow channel and is removed from the overflow channel from the electrolytic cell, e.g. discharged into an electrolyte tank.
  • the overflow channel can be designed, for example, as a hose or pipe, possibly with a perforated cover or the like.
  • the overflow channel is e.g. directed upwards. This can e.g. be designed as a U-shaped channel, so that excess electrolyte first fills the connected to the electrolyte inlet leg of the U-shaped overflow channel and drains over the second leg again.
  • the overflow channel is directed upwards, e.g. U-shaped
  • the height between the upper vertex of the upflow channel and the electrolyte inlet (hereinafter referred to g) is preferably 0 to 190 cm, particularly preferably 1 to 190 cm. Likewise, this applies to any form of overflow.
  • the overflow channel can also be embodied as a standpipe or vertical shaft, channel or the like within the electrolysis half-cell.
  • the excess electrolyte is hereby removed from the electrolysis cell and passed, for example, into a collecting container.
  • the entry into the standpipe is preferably at least 1 cm above the Level of the gap to ensure uniform feeding across the full width of the cell.
  • the discharged via the overflow electrolyte is preferably passed into a collection container.
  • a collection container This may be achieved, for example, by a channel located outside the electrolytic cell, e.g. a hose or pipe done.
  • the collecting container may be connected to the storage container so that the electrolyte can be pumped from the collecting container into the storage container and re-supplied to the electrolytic cell.
  • the amount of electrolyte flowing from the receiver tank into the electrolyte feed depends on the height difference between the liquid level of the electrolyte in the feed tank and the liquid level in the electrolyte feed.
  • the height difference thus defined is also referred to below as h.
  • the liquid level in the electrolyte feed in turn, depends on the height of the overflow, which determines how much the electrolyte in the electrolyte feed is dammed up. If the electrolyte is supplied by means of a pump from the storage tank to the electrolyte feed, the amount of electrolyte which is conveyed into the electrolyte feed depends on the delivery head h of the pump.
  • an overflow channel may be provided which is arranged substantially horizontally. Excess electrolyte can also be removed from the electrolysis cell via such a horizontally arranged overflow channel.
  • the pressure in the electrolyte inlet can be set by selecting the height g of the overflow channel. As the pressure increases, more electrolyte can be passed through the gap. Thus, the gap can be acted upon at different current densities with different amounts of electrolyte. This is advantageous, for example, if the electrolyte is strongly concentrated at high current densities, which can cause damage to the ion exchange membrane. However, this can be avoided if the electrolyte is passed through the gap with a larger volume flow.
  • the pressure in the electrolyte inlet can be set in a targeted manner. It is important to note that g is less than or equal to h.
  • the advantage of the electrolysis cell according to the invention is that due to the simple principle of the free overflow a uniform feeding of the gap between the gas diffusion electrode and the ion exchange membrane and the safe removal of gas from the gap is possible.
  • the flow velocity in the gap can be easily regulated by means of the overflow.
  • a dangerous for the gas diffusion electrode dynamic pressure increase in the gap between gas diffusion electrode and membrane can be avoided, which could be caused for example by direct injection of the electrolyte by means of a pump without functioning free overflow of the electrolyte inlet.
  • Oxygen, air or oxygen-enriched air (hereinafter referred to simply as oxygen) is supplied from a template (also referred to as a gas collection container), preferably below the gas space, in the gas space of the half-cell with gas diffusion electrode.
  • the supply takes place via a gas distribution pipe as gas inlet uniformly over the entire width of the half-cell.
  • the unused oxygen is removed in the upper part of the half-cell via a gas outlet from the gas space.
  • the gas supply can also take place in the upper region and the gas removal in the lower region of the electrolysis half-cell.
  • the gas outlet is connected to the electrolyte reservoir, so that the electrolyte reservoir simultaneously serves as a gas reservoir for excess oxygen.
  • the unused oxygen is supplied from the gas space via a gas line as a gas outlet to the electrolyte reservoir, wherein the gas line preferably dips below the liquid level of the electrolyte. If the gas line immersed in the electrolyte reservoir and at the same time the electrolyte discharge is immersed in the electrolyte reservoir, the dipping of the gas line in the electrolyte reservoir must not be deeper than the immersion of the electrolyte discharge in the reservoir. The excess oxygen can be recycled for optimal utilization.
  • the electrolyte reservoir simultaneously serves as a gas collection container, has the advantage that only a storage container is required for the oxygen and the electrolyte.
  • the electrolyte reservoir can also be arranged below the electrolytic cell, wherein the electrolyte is conveyed from the electrolyte reservoir into the electrolyte inlet by means of a pump, provided that the free flow of the electrolyte excess is ensured via the overflow channel (control over not over-flowed overflow channel).
  • the gas outlet is connected to a gas collecting container and the gas space is closed relative to the gap.
  • the gas space can, for example by means of a Plate, such as a metal plate, be completed against the gap.
  • the gas collecting container is a separate collecting container, flows in the excess oxygen via a gas line as a gas outlet. In this way, the oxygen pressure can be adjusted independently of the pressure conditions in the gap.
  • the gas space has drainage openings at the lower end.
  • flow guide structures are provided in the gap.
  • the flow guide structures prevent a free fall of the electrolyte in the gap, so that the flow velocity is reduced compared to the free fall. At the same time, however, the electrolyte must not accumulate in the gap due to the Strömungsleit Weg.
  • the flow guide structures are selected so that the pressure loss of the hydrostatic liquid column in the gap is compensated. Examples of flow guiding structures are made WO 03/042430 and WO 01/57290 known.
  • the flow guiding structures may also consist of thin plates, foils or the like, which have openings for flowing through the electrolyte. They are transversal, i. perpendicular or oblique, arranged to the flow direction of the electrolyte in the gap.
  • the plate-shaped Strömungsleit Jardin are preferably inclined relative to the horizontal, wherein they are inclined either only in one axis or in both axes. If the flow guide structures are arranged obliquely to the flow direction, they can be inclined both in the direction of the ion exchange membrane and in the direction of the gas diffusion electrode. In addition, the flow guiding structures may be inclined across the width of the electrochemical cell.
  • Another object of the invention is a process for the electrolysis of an aqueous alkali halide solution in the electrochemical cell according to the invention.
  • the method is characterized in that the electrolyte from the electrolyte reservoir is supplied in excess to the electrolyte inlet, the electrolyte flows from the electrolyte inlet into the gap and out of the gap into the electrolyte outlet and flows away from the electrolyte inlet via the overflow.
  • An excess of electrolyte in the electrolyte feed means in the context of the present invention that the electrolyte feed is always filled evenly over the entire width at least with an electrolyte film.
  • electrolyte inlet always a certain level of electrolyte must be present over the entire width of the electrolyte inlet. This is best ensured if always a certain amount of electrolyte flows not only through the gap, but also via the overflow from the electrolyte feed.
  • the excess of the electrolyte which is removed via the overflow is 0.5 to 30% by volume, particularly preferably 1 to 20% by volume.
  • the amount of electrolyte that a falling film cell requires for its trouble-free operation depends only on the type of falling film cell, but not on the selected current densities. Therefore, the excess electrolyte must be set only once at the beginning of the electrolysis operation and only kept constant during operation.
  • the effective height ratio h to g must be selected so that the necessary for the optimal operation of the electrolytic cell electrolyte concentration in the gap.
  • the electrochemical cell according to the invention can be used for different electrolysis processes, in which at least one electrode is a gas diffusion electrode.
  • the gas diffusion electrode functions as a cathode, more preferably as an oxygen-consuming cathode, wherein the gas supplied to the electrochemical cell is an oxygen-containing gas, e.g. Air, oxygen-enriched air or oxygen itself.
  • the cell according to the invention is preferably used for the electrolysis of an aqueous solution of an alkali metal halide, in particular of sodium chloride.
  • the gas diffusion electrode is constructed, for example, as follows:
  • the gas diffusion electrode consists at least of an electrically conductive carrier and an electrochemically active coating.
  • the electrically conductive carrier is preferably a mesh, woven, braided, knitted, nonwoven or foam of metal, in particular of nickel, silver or silver-plated nickel.
  • the electrochemically active coating preferably consists of at least one catalyst, e.g. Silver (I) oxide, and a binder, e.g. Polytetrafluoroethylene (PTFE).
  • the electrochemically active coating may be composed of one or more layers.
  • a gas diffusion layer for example of a mixture of carbon and polytetrafluoroethylene, can be provided, which is applied to the support.
  • electrodes of titanium may be used, which are e.g. coated with ruthenium-iridium-titanium oxides or ruthenium-titanium oxide.
  • ion exchange membrane a commercially available membrane, e.g. from DuPont, e.g. Nafion® NX2010.
  • FIG. 1 an embodiment of an electrochemical cell according to the invention is shown in longitudinal section. Electrolyte flows out of the electrolyte reservoir 7 via an electrolyte feed line 8 into the electrolyte inlet 10 of the electrolysis half cell with gas diffusion electrode 4 (FIG. FIG. 2 ).
  • the electrolyte reservoir 7 is disposed above the electrolyte inlet 10.
  • the electrolyte feed 10 extends longitudinally over the entire width of the electrolysis half cell above the gap 11 (FIG. FIG. 2 ).
  • the height difference between the liquid level in the receiver tank 7 and the liquid level in the electrolyte inlet 10 is designated by h.
  • the electrolyte flows uniformly over the entire width of the electrolysis half-cell via the electrolyte inlet 10 into the gap 11 (FIG. FIG. 2 ). In the gap 11, the electrolyte flows down into the electrolyte outlet 20 (FIG. FIG. 2 ) leading to the gas space 5 ( FIG. 2 ), and from the electrolyte drain 20 via an electrolyte discharge 15 into an electrolyte reservoir 14.
  • the gas space 5 is terminated with a metal plate, e.g. a sheet, 23 separated from the electrolyte effluent 20.
  • a metal plate e.g. a sheet, 23 separated from the electrolyte effluent 20.
  • the oxygen pressure can thus be adjusted independently of the pressure conditions in the gap 11 and brought to optimum operating conditions for the gas diffusion electrodes. Drainage holes (not shown here) allow drainage of possibly accumulated condensate from the back of the gas diffusion electrode.
  • the electrolysis half-cell has an overflow channel 13, which in the illustrated embodiment is U-shaped, with the apex of the U-shaped channel pointing upwards.
  • an additional overflow channel 12 is provided, which is arranged substantially horizontally. Excess electrolyte, which does not flow off in the gap 11, flows via the overflow channel 12 into a side channel 21, which is arranged vertically to the side of the electrolysis half-cell and dissipates excess electrolyte downwards. Excess electrolyte is collected in the electrolyte reservoir 14.
  • the gas distribution pipe 18 thus forms the gas inlet into the electrolysis half cell.
  • Unconsumed oxygen can leave the gas space 5 via a gas line 9 as a gas outlet and flow into the electrolyte reservoir 7.
  • the electrolyte reservoir 7 also serves as a gas collection container.
  • a pump 30 is provided, which pumps electrolyte from the collecting container 14 into the storage container 7.
  • FIG. 2 shows the electrolytic cell according to FIG. 1 in cross section. It consists of an anode half-cell 1 with an anode 6 and a cathode half-cell 22 with a gas diffusion electrode 4 as a cathode.
  • the two half-cells 1, 22 are separated from each other by an ion exchange membrane 3. Between the ion exchange membrane 3 and the gas diffusion electrode 4 there is a gap 11. Behind the gas diffusion electrode 4, a gas space 5 is arranged. The gas space 5 thus forms the rear space behind the gas diffusion electrode 4.
  • electrolyte flows from the electrolyte inlet 10 into the gap 11 and from the gap 11 in the electrolyte effluent 20 until the electrolyte is finally collected via the electrolyte discharge 15 in the electrolyte reservoir 14.
  • Gas which flows via the gas distribution pipe 18 into the gas space 5, can flow via the gas outlet 9 into the electrolyte reservoir 7 above the electrolytic cell.
  • a metal plate 23 separates the gas space 5 from the electrolyte outlet 20.

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Description

Die Erfindung betrifft eine elektrochemische Zelle, wenigstens bestehend aus einer Anodenhalbzelle mit einer Anode, einer Kathodenhalbzelle mit einer Kathode und einer zwischen Anodenhalbzelle und Kathodenhalbzelle angeordneten Ionenaustauschermembran, wobei die Anode und/oder die Kathode eine Gasdiffusionselektrode ist. Die Erfindung betrifft ferner ein Verfahren zur Elektrolyse einer wässrigen Lösung von Alkalichlorid.The invention relates to an electrochemical cell, at least consisting of an anode half-cell with an anode, a cathode half-cell with a cathode and an ion exchange membrane arranged between anode half-cell and cathode half-cell, wherein the anode and / or the cathode is a gas diffusion electrode. The invention further relates to a process for the electrolysis of an aqueous solution of alkali chloride.

Aus WO 01/57290 ist eine Elektrolysezelle mit Gasdiffusionselektrode bekannt, bei der in dem Spalt zwischen der Gasdiffusionselektrode und der Ionenaustauschermembran eine poröse Schicht vorgesehen ist. Der Elektrolyt strömt von oben nach unten über die poröse Schicht unter Einwirkung der Schwerkraft durch den Spalt. Die poröse Schicht gemäß WO-A 01/57290 kann aus Schäumen, Drahtnetzen oder dergleichen bestehen.Out WO 01/57290 An electrolytic cell with a gas diffusion electrode is known in which a porous layer is provided in the gap between the gas diffusion electrode and the ion exchange membrane. The electrolyte flows from top to bottom over the porous layer under the action of gravity through the gap. The porous layer according to WO-A 01/57290 may consist of foams, wire nets or the like.

In US 6 117 286 ist ebenfalls eine Elektrolysezelle mit Gasdiffusionselektrode zur Elektrolyse einer Natriumchlorid-Lösung beschrieben, in der sich eine Schicht aus einem hydrophilen Material im Spalt zwischen der Gasdiffusionselektrode und der Ionenaustauschermembran befindet. Die Schicht aus hydrophilem Material hat vorzugsweise eine poröse Struktur, welche ein korrosionsbeständiges Metall oder Harz enthält. Als poröse Struktur können z.B. Netze, Gewebe oder Schäume verwendet werden. Natriumhydroxid, der Elektrolyt, strömt unter der Schwerkraft über die Schicht aus hydrophilem Material nach unten auf den Boden der Elektrolysezelle.In US 6 117 286 Also, an electrolytic cell with gas diffusion electrode for the electrolysis of a sodium chloride solution is described, in which a layer of a hydrophilic material is in the gap between the gas diffusion electrode and the ion exchange membrane. The layer of hydrophilic material preferably has a porous structure containing a corrosion-resistant metal or resin. As a porous structure, for example, nets, fabrics or foams can be used. Sodium hydroxide, the electrolyte, flows down the layer of hydrophilic material down to the bottom of the electrolytic cell under gravity.

Weiterhin ist aus EP-A 1 033 419 eine Elektrolysezelle mit Gasdiffusionselektrode als Kathode zur Elektrolyse einer Natriumchlorid-Lösung bekannt. In der Kathodenhalbzelle, in der der Elektrolyt, von dem Gasraum durch eine Gasdiffusionselektrode getrennt, nach unten strömt, ist ein hydrophiles, poröses Material vorgesehen, durch das der Elektrolyt strömt. Als poröses Material kommen Metalle, Metalloxide oder organische Materialien in Betracht, sofern sie korrosionsbeständig sind.Furthermore, it is off EP-A 1 033 419 an electrolytic cell with gas diffusion electrode as a cathode for the electrolysis of a sodium chloride solution known. In the cathode half-cell in which the electrolyte, separated from the gas space by a gas diffusion electrode, flows downward, there is provided a hydrophilic porous material through which the electrolyte flows. As porous material metals, metal oxides or organic materials are considered, provided they are corrosion resistant.

Bei den aus dem Stand der Technik bekannten Elektrolysezellen mit Gasdiffusionselektrode ist nicht sicher gestellt, dass der Spalt zwischen Gasdiffusionselektrode und Ionenaustauschermembran aufgrund des porösen Materials vollständig mit Elektrolyt gefüllt werden kann. Dies ist nachteilig, da hierdurch Bereiche in dem Spalt entstehen, in denen sich Gas befindet und ansammelt. In diesen Bereichen kann kein elektrischer Strom fließen. Strom fließt ausschließlich durch elektrolytgefüllte Bereiche in dem Spalt, sodass lokal eine höhere Stromdichte entsteht, die eine höhere Elektrolysespannung zur Folge hat. Sammelt sich das Gas an der Ionenaustauschermembran, so ist diese nicht mehr vollständig benetzt und kann aufgrund des fehlenden Elektrolyten beschädigt werden.In the known from the prior art electrolysis cells with gas diffusion electrode is not ensured that the gap between the gas diffusion electrode and ion exchange membrane can be completely filled with electrolyte due to the porous material. This is disadvantageous because it creates areas in the gap in which gas is located and accumulates. No electrical current can flow in these areas. Current flows only through electrolyte-filled areas in the gap, so locally creates a higher current density, which has a higher electrolysis voltage result. If the gas collects on the ion exchange membrane, it is no longer completely wetted and can be damaged due to the missing electrolyte.

Poröse Schichten haben weiterhin den Nachteil, dass Gas, welches einmal in die poröse Struktur eingetreten ist, aus dieser nur schwierig wieder heraus gelangen kann. Innerhalb der porösen Schicht kann sich das Gas ansammeln, wodurch die oben genannten Nachteile entstehen. Gas aus dem Gasraum kann unter Betriebsbedingungen auch aus dem Gasraum in den Spalt durch die Gasdiffusionselektrode hindurchtreten. Darüber hinaus neigen Gasdiffusionselektroden dazu, an nicht benetzten Stellen vermehrt Gas durchzulassen, so dass sich der Effekt verstärkt.Porous layers also have the disadvantage that gas which has once entered the porous structure, from this difficult to get out again. Within the porous layer, the gas can accumulate, whereby the above-mentioned disadvantages arise. Gas from the gas space can also pass from the gas space into the gap through the gas diffusion electrode under operating conditions. In addition, gas diffusion electrodes tend to pass more gas at non-wetted sites, so that the effect amplifies.

Die Aufgabe der vorliegenden Erfindung besteht demnach darin, eine Elektrolysezelle bereitzustellen, welche die Nachteile des Standes der Technik vermeidet.The object of the present invention is therefore to provide an electrolytic cell which avoids the disadvantages of the prior art.

Gegenstand der Erfindung ist eine elektrochemische Zelle, wenigstens bestehend aus einer Anodenhalbzelle mit einer Anode, einer Kathodenhalbzelle mit einer Kathode und einer zwischen Anodenhalbzelle und Kathodenhalbzelle angeordneten Ionenaustauschermembran, wobei die Anode und/oder die Kathode eine Gasdiffusionselektrode ist, zwischen der Gasdiffusionselektrode und der Ionenaustauschermembran ein Spalt, ein Elektrolytzulauf oberhalb des Spaltes und ein Elektrolytablauf unterhalb des Spaltes sowie ein Gaseintritt und ein Gasaustritt angeordnet ist, dadurch gekennzeichnet, dass der Elektrolytzulauf mit einem Elektrolytvorlagebehälter verbunden ist und einen Überlauf aufweist.The invention relates to an electrochemical cell, at least consisting of an anode half-cell with an anode, a cathode half-cell with a cathode and an ion exchange membrane arranged between anode half-cell and cathode half-cell, wherein the anode and / or the cathode is a gas diffusion electrode, between the gas diffusion electrode and the ion exchange membrane Gap, an electrolyte inlet above the gap and an electrolyte drain below the gap and a gas inlet and a gas outlet is arranged, characterized in that the electrolyte inlet is connected to an electrolyte reservoir and has an overflow.

Im Betrieb der erfindungsgemäßen elektrochemischen Zelle strömt der Elektrolyt in dem Spalt zwischen Gasdiffusionselektrode und Ionenaustauschermembran von oben nach unten durch die Halbzelle. Dementsprechend befindet sich in der erfindungsgemäßen Elektrolysezelle ein Elektrolytzulauf oberhalb des Spaltes und ein Elektrolytablauf unterhalb des Spaltes. Der Spalt ist dabei vollständig von dem strömenden Elektrolyt angefüllt. Der übrige Raum der Halbzelle hinter der Gasdiffusionselektrode, d.h. der Raum auf der der Ionenaustauschermembran abgewandten Seite der Gasdiffusionselektrode, welcher als Gasraum bezeichnet wird, ist mit Gas gefüllt. Das Gas wird dem Gasraum durch den Gaseintritt zugeführt und durch den Gasaustritt abgeführt.During operation of the electrochemical cell according to the invention, the electrolyte flows in the gap between gas diffusion electrode and ion exchange membrane from top to bottom through the half cell. Accordingly, in the electrolysis cell according to the invention there is an electrolyte feed above the gap and an electrolyte drain below the gap. The gap is completely filled by the flowing electrolyte. The remaining space of the half-cell behind the gas diffusion electrode, i. the space on the side facing away from the ion exchange membrane of the gas diffusion electrode, which is referred to as gas space, is filled with gas. The gas is supplied to the gas space through the gas inlet and discharged through the gas outlet.

Der Elektolytzulauf bildet horizontal oberhalb des Spaltes einen Kanal, welcher sich über die gesamte Breite der elektrochemischen Zelle erstreckt. So kann mit Hilfe des kanalförmigen Elektrolytzulaufs der Elektrolyt gleichmäßig über die gesamte Breite von oben in den Spalt zwischen Gasdiffusionselektrode und Ionenaustauschermembran zugeführt werden. Dazu besitzt der Elektrolytzulauf z.B. zahlreiche Öffnungen, welche nach unten gerichtet sind, über die der Elektrolyt im Betrieb der Elektrolysezelle in den Spalt strömt. Anstelle von mehreren Öffnungen kann auch eine spalt- oder schlitzförmige Öffnung vorgesehen sein, welche sich über die gesamte Breite des Spaltes erstreckt. Der Elektrolyt verlässt die Halbzelle über den Elektrolytablauf und gelangt in einen Elektrolytsammelbehälter, wobei der Elektrolytablauf in dem Elektrolytsammelbehälter getaucht sein muss, um einen unkontrollierten Gasstrom über den Elektrolytsammelbehälter von Zelle zu Zelle (bei mehreren zu einem Elektrolyseur miteinander verbundenen Elektrolysezellen) zu vermeiden.The Elektolytzulauf forms horizontally above the gap a channel which extends over the entire width of the electrochemical cell. Thus, with the aid of the channel-shaped electrolyte feed, the electrolyte can be fed uniformly over the entire width from above into the gap between the gas diffusion electrode and the ion exchange membrane. For this purpose, the electrolyte feed, for example, has numerous openings which are directed downwards, over which the electrolyte flows during operation of the electrolytic cell into the gap. Instead of a plurality of openings, a gap-shaped or slot-shaped opening may be provided, which extends over the entire width of the gap. The electrolyte leaves the half-cell via the electrolyte drain and enters an electrolyte reservoir, wherein the electrolyte effluent must be immersed in the electrolyte reservoir to an uncontrolled gas flow through the electrolyte reservoir from cell to cell (in case of several electrolysis cells connected to an electrolyzer).

Die erfindungsgemäße elektrochemische Zelle wird auch als Fallfilmzelle bezeichnet. Ihr störungsfreier Betrieb hängt entscheidend von der sicheren Versorgung der Elektrode mit Elektrolyt ab. Bei einer technischen Elektrolysezelle kann die Breite mehr als 2000 mm betragen. Dies bedeutet, dass eine gleichmäßige Bespeisung der Elektrode mit Elektrolyt über die gesamte Breite gewährleistet sein muss. Wird als Elektrode eine Gasdiffusionselektrode eingesetzt, kann Gas aus dem Gasraum durch die Gasdiffusionselektrode hindurch in den Spalt zwischen Gasdiffusionselektrode und Ionenaustauschermembran eintreten. Das Gas muss aus dem Spalt zuverlässig abgeführt werden können, da eine Anreicherung von Gas in dem Spalt vermieden werden muss.The electrochemical cell according to the invention is also referred to as a falling film cell. Their trouble-free operation depends crucially on the safe supply of the electrode with electrolyte. In a technical electrolysis cell, the width may be more than 2000 mm. This means that a uniform feeding of the electrode with electrolyte over the entire width must be guaranteed. If a gas diffusion electrode is used as the electrode, gas can enter from the gas space through the gas diffusion electrode into the gap between the gas diffusion electrode and the ion exchange membrane. The gas must be able to be reliably removed from the gap, since an accumulation of gas in the gap must be avoided.

Die gleichmäßige Bespeisung der Gasdiffusionselektrode mit Elektrolyt, welcher in dem Spalt zwischen Gasdiffusionselektrode und Ionenaustauschermembran von oben nach unten strömt, wird in der erfindungsgemäßen Elektrolysezelle dadurch erzielt, dass der Elektrolytzulauf mit einem Elektrolytvorlagebehälter verbunden ist und einen Überlauf aufweist. In einer ersten Ausführungsform ist der Elektrolytvorlagebehälter vorzugsweise 30 bis 200 cm oberhalb des Elektrolytzulaufs angeordnet. Im Betrieb der Elektrolysezelle strömt der Elektrolyt aus dem Vorlagebehälter in den Elektrolytzulauf. Von dem Elektrolytzulauf strömt der Elektrolyt z.B. über eine spaltförmige Öffnung in den Spalt zwischen Gasdiffusionselektrode und Ionenaustauschermembran.The uniform feeding of the gas diffusion electrode with electrolyte, which flows in the gap between gas diffusion electrode and ion exchange membrane from top to bottom, is achieved in the electrolysis cell according to the invention in that the electrolyte feed is connected to an electrolyte reservoir and has an overflow. In a first embodiment, the electrolyte reservoir is preferably located 30 to 200 cm above the electrolyte inlet. During operation of the electrolytic cell, the electrolyte flows from the storage tank into the electrolyte inlet. From the electrolyte feed, the electrolyte flows e.g. via a slit-shaped opening in the gap between gas diffusion electrode and ion exchange membrane.

In einer weiteren Ausführungsform ist der Elektrolytvorlagebehälter über eine Pumpe mit dem Elektrolytzulauf verbunden. In dieser Ausführungsform kann der Elektrolytvorlagebehälter prinzipiell an beliebiger Stelle, beispielsweise unterhalb der elektrochemischen Zelle, angeordnet sein. Mit Hilfe der Pumpe wird der Elektrolyt mit dem gewünschten Vordruck in den Elektrolytzulauf gepumpt.In a further embodiment, the electrolyte reservoir is connected via a pump to the electrolyte inlet. In this embodiment, the electrolyte reservoir can in principle be arranged at any desired location, for example below the electrochemical cell. With the help of the pump, the electrolyte is pumped with the desired form in the electrolyte inlet.

Der Elektrolytvorlagebehälter kann prinzipiell an beliebiger Stelle mit dem Elektrolytzulauf verbunden sein, so z.B. an einem Ende des Elektrolytzulaufs.The electrolyte reservoir may, in principle, be connected at any location to the electrolyte inlet, e.g. at one end of the electrolyte inlet.

Werden mehrere erfindungsgemäße Elektrolysezellen zu einem Elektrolyseur verbunden, kann ein einziger Elektrolytvorlagebehälter für die Bespeisung aller Elektrolysezellen des Elektrolyseurs eingesetzt werden. Alternativ kann jede der Elektrolysezellen mit einem separaten Vorlagebehälter ausgestattet sein.If several electrolysis cells according to the invention are connected to form an electrolyzer, a single electrolyte reservoir can be used to supply all the electrolysis cells of the electrolyzer. Alternatively, each of the electrolysis cells can be equipped with a separate storage tank.

Der Elektrolytzulauf weist erfindungsgemäß einen Überlauf auf. Der Überlauf hat bevorzugt eine Höhe von 0 bis 190 cm, besonders bevorzugt 1 bis 190 cm über dem Eintritt in den Spalt. Prinzipiell kann die Höhe des Überlaufs weniger als 1 cm betragen; dabei liegt der Überlauf auf gleicher Höhe mit dem Eintritt in den Spalt. Der Überlauf gewährleistet, dass sich im Betrieb der Elektrolysezelle immer eine gewisse Menge Elektrolyt in dem Elektrolytzulauf aufstaut. Für die Höhe des Überlaufs ist entscheidend, dass er eine Menge Elektrolyt in dem Elektrolytzulauf aufstaut, die ausreicht, um den Spalt über seine gesamte Breite kontinuierlich mit Elektrolyt zu versorgen. Hierfür strömt gerade so viel Elektrolyt aus dem Elektrolytvorlagebehälter in den Elektrolytzulauf, dass der Überlauf gerade überläuft. In der Zuführleitung, welche den Elektrolytvorlagebehälter mit dem Elektrolytzulauf verbindet, kann ein Ventil, eine Blende, z.B. in Form einer Lochscheibe, oder dergleichen vorgesehen sein. Die gezielte Überlaufströmung des Elektrolyten aus dem Elektrolytzulauf erlaubt eine gleichmäßige Bespeisung des Spaltes mit Elektrolyt über die gesamte Breite der Elektrode sowie eine sichere Abführung von Gas aus dem Spalt. Die Überlaufströmung verhindert, dass der Elektrolytpegel in dem Elektrolytzulauf so weit abfällt, dass der Fallfilm des Elektrolyten in dem Spalt abreißt. Ferner gewährleistet der Überlauf unter anderem, dass Gasblasen, welche aus dem Spalt in den Elektrolytzulauf aufsteigen, mit dem Elektrolyten abtransportiert werden.The electrolyte inlet according to the invention has an overflow. The overflow preferably has a height of 0 to 190 cm, more preferably 1 to 190 cm above the entry into the gap. In principle, the height of the overflow can be less than 1 cm; The overflow is at the same level as the entry into the gap. The overflow ensures that during operation of the electrolysis cell always accumulates a certain amount of electrolyte in the electrolyte feed. It is crucial for the height of the overflow to accumulate a large amount of electrolyte in the electrolyte feed sufficient to continuously supply electrolyte to the gap across its entire width. For this purpose, just as much electrolyte flows from the electrolyte reservoir into the electrolyte inlet that the overflow is just overflowing. In the supply line, which connects the electrolyte reservoir with the electrolyte inlet, a valve, a diaphragm, for example in the form of a perforated disc, or the like may be provided. The targeted overflow of the electrolyte from the electrolyte inlet allows a uniform feeding of the gap with electrolyte over the entire width of the electrode and a safe discharge of gas from the gap. The overflow stream prevents the level of electrolyte in the electrolyte feed from dropping enough for the falling film of the electrolyte in the gap to break off. Furthermore, the overflow ensures, inter alia, that gas bubbles which rise from the gap in the electrolyte feed are transported away with the electrolyte.

Der Überlauf kann prinzipiell an beliebiger Stelle entlang des Elektrolytzulaufs positioniert sein. Er kann z.B. an einem Ende des Elektrolytzulaufs vorgesehen sein.The overflow can in principle be positioned at any point along the electrolyte inlet. He can e.g. be provided at one end of the electrolyte inlet.

Der Überlauf ist erfindungsgemäß als Überlaufkanal ausgeführt. Ein solcher Überlaufkanal kann entweder außerhalb oder innerhalb der Kathodenhalbzelle angeordnet sein. Überschüssiger Elektrolyt, welcher nicht in dem Spalt nach unten strömt, fließt aus dem Elektrolytzulauf in den Überlaufkanal und wird aus dem Überlaufkanal aus der Elektrolysezelle z.B. in einen Elektrolytsammelbehälter abgeführt. Der Überlaufkanal kann beispielsweise als Schlauch oder Rohr, gegebenenfalls mit Lochblende oder dergleichen, ausgeführt sein. Der Überlaufkanal ist z.B. nach oben gerichtet. Dieser kann z.B. als U-förmiger Kanal ausgeführt sein, so dass überschüssiger Elektrolyt zunächst den mit dem Elektrolytzulauf verbundenen Schenkel des U-förmigen Überlaufkanals anfüllt und über den zweiten Schenkel wieder abfließt.The overflow is designed according to the invention as an overflow channel. Such an overflow channel can be arranged either outside or inside the cathode half cell. Excess electrolyte, which does not flow down the gap, flows from the electrolyte feed into the overflow channel and is removed from the overflow channel from the electrolytic cell, e.g. discharged into an electrolyte tank. The overflow channel can be designed, for example, as a hose or pipe, possibly with a perforated cover or the like. The overflow channel is e.g. directed upwards. This can e.g. be designed as a U-shaped channel, so that excess electrolyte first fills the connected to the electrolyte inlet leg of the U-shaped overflow channel and drains over the second leg again.

Ist der Überlaufkanal nach oben gerichtet, z.B. U-förmig, so beträgt die Höhe zwischen dem oberen Scheitelpunkt des nach oben gerichteten Überlaufkanals und dem Elektrolytzulauf (nachfolgend mit g bezeichnet) bevorzugt 0 bis 190 cm, besonders bevorzugt 1 bis 190 cm. Analog gilt dies für jede Form des Überlaufs.If the overflow channel is directed upwards, e.g. U-shaped, the height between the upper vertex of the upflow channel and the electrolyte inlet (hereinafter referred to g) is preferably 0 to 190 cm, particularly preferably 1 to 190 cm. Likewise, this applies to any form of overflow.

In einer weiteren Ausführungsform kann der Überlaufkanal auch als Standrohr oder vertikaler Schacht, Kanal oder dergleichen innerhalb der Elektrolysehalbzelle ausgeführt sein. Der überschüssige Elektrolyt wird hierüber aus der Elektrolysezelle abgeführt und z.B. in einen Sammelbehälter geleitet. Der Eintritt in das Standrohr liegt bevorzugt mindestens 1 cm über dem Niveau des Spaltes, damit eine gleichmäßige Bespeisung über die volle Breite der Zelle gewährleistet ist.In a further embodiment, the overflow channel can also be embodied as a standpipe or vertical shaft, channel or the like within the electrolysis half-cell. The excess electrolyte is hereby removed from the electrolysis cell and passed, for example, into a collecting container. The entry into the standpipe is preferably at least 1 cm above the Level of the gap to ensure uniform feeding across the full width of the cell.

Der über den Überlauf abgeführte Elektrolyt wird vorzugsweise in einen Sammelbehälter geleitet. Dies kann beispielsweise durch einen außerhalb der Elektrolysezelle angeordneten Kanal, z.B. ein Schlauch oder Rohr erfolgen. Der Sammelbehälter kann mit dem Vorlagebehälter verbunden sein, so dass der Elektrolyt aus dem Sammelbehälter in den Vorlagebehälter gepumpt und der Elektrolysezelle erneut zugeführt werden kann.The discharged via the overflow electrolyte is preferably passed into a collection container. This may be achieved, for example, by a channel located outside the electrolytic cell, e.g. a hose or pipe done. The collecting container may be connected to the storage container so that the electrolyte can be pumped from the collecting container into the storage container and re-supplied to the electrolytic cell.

Die Menge an Elektrolyt, welche aus dem Vorlagebehälter in den Elektrolytzulauf strömt, ist von der Höhendifferenz zwischen dem Flüssigkeitspegel des Elektrolyten in dem Vorlagebehälter und dem Flüssigkeitspegel in dem Elektrolytzulauf abhängig. Die so definierte Höhendifferenz wird nachfolgend auch mit h bezeichnet. Der Flüssigkeitspegel in dem Elektrolytzulauf wiederum ist von der Höhe des Überlaufs abhängig, welche bestimmt, wie stark der Elektrolyt in dem Elektrolytzulauf aufgestaut wird. Wird der Elektrolyt mittels einer Pumpe aus dem Vorlagebehälter dem Elektrolytzulauf zugeführt, ist die Menge an Elektrolyt, welche in den Elektrolytzulauf gefördert wird, von der Förderhöhe h der Pumpe abhängig.The amount of electrolyte flowing from the receiver tank into the electrolyte feed depends on the height difference between the liquid level of the electrolyte in the feed tank and the liquid level in the electrolyte feed. The height difference thus defined is also referred to below as h. The liquid level in the electrolyte feed, in turn, depends on the height of the overflow, which determines how much the electrolyte in the electrolyte feed is dammed up. If the electrolyte is supplied by means of a pump from the storage tank to the electrolyte feed, the amount of electrolyte which is conveyed into the electrolyte feed depends on the delivery head h of the pump.

In einer weiteren Ausführungsform der erfindungsgemäßen Elektrolysezelle kann alternativ oder zusätzlich zu einem nach oben gerichteten Überlaufkanal oder einem Standrohr, Schacht, Kanal oder dergleichen ein Überlaufkanal vorgesehen sein, welcher im Wesentlichen horizontal angeordnet ist. Auch über einen solchen horizontal angeordneten Überlaufkanal kann überschüssiger Elektrolyt aus der Elektrolysezelle abgeführt werden.In a further embodiment of the electrolysis cell according to the invention, alternatively or in addition to an upwardly directed overflow channel or a standpipe, manhole, channel or the like, an overflow channel may be provided which is arranged substantially horizontally. Excess electrolyte can also be removed from the electrolysis cell via such a horizontally arranged overflow channel.

Wird mehr Elektrolyt zugegeben, als über den z.B. U-förmigen Überlaufkanal und den Spalt ablaufen kann, so erhöht sich der Druck des Elektrolyten in dem kanalförmigen Elektrolytzulauf oberhalb des Spaltes. Erfindungsgemäß ist durch Wahl der Höhe g des Überlaufkanals der Druck im Elektrolytzulauf einstellbar. Mit Erhöhung des Druckes kann mehr Elektrolyt durch den Spalt geführt werden. Somit kann der Spalt bei unterschiedlichen Stromdichten mit unterschiedlicher Elektrolytmenge beaufschlagt werden. Dies ist beispielsweise vorteilhaft, wenn bei hohen Stromdichten der Elektrolyt stark aufkonzentriert wird und dadurch Schäden an der Ionenaustauschermembran entstehen können. Dies kann jedoch vermieden werden, wenn der Elektrolyt mit einem größeren Volumenstrom durch den Spalt geführt wird. Durch Variation des Verhältnisses der Höhendifferenzen zueinander, also das Verhältnis von h zu g, kann der Druck in dem Elektrolytzulauf gezielt eingestellt werden. Es ist darauf zu achten, dass g kleiner oder gleich h ist.If more electrolyte is added than over the e.g. U-shaped overflow channel and the gap can run, so the pressure of the electrolyte in the channel-shaped electrolyte inlet increases above the gap. According to the invention, the pressure in the electrolyte inlet can be set by selecting the height g of the overflow channel. As the pressure increases, more electrolyte can be passed through the gap. Thus, the gap can be acted upon at different current densities with different amounts of electrolyte. This is advantageous, for example, if the electrolyte is strongly concentrated at high current densities, which can cause damage to the ion exchange membrane. However, this can be avoided if the electrolyte is passed through the gap with a larger volume flow. By varying the ratio of the height differences to one another, that is to say the ratio of h to g, the pressure in the electrolyte inlet can be set in a targeted manner. It is important to note that g is less than or equal to h.

Der Vorteil der erfindungsgemäßen Elektrolysezelle liegt darin, dass durch das einfache Prinzip des freien Überlaufs eine gleichmäßige Bespeisung des Spalts zwischen der Gasdiffusionselektrode und der Ionenaustauschermembran sowie die sichere Abführung von Gas aus dem Spalt möglich ist. Darüber hinaus kann die Strömungsgeschwindigkeit im Spalt auf einfache Weise mit Hilfe des Überlaufs reguliert werden. Außerdem kann eine für die Gasdiffusionselektrode gefährliche dynamische Druckerhöhung im Spalt zwischen Gasdiffusionselektrode und Membran vermieden werden, welche z.B. durch direkte Einspeisung des Elektrolyten mittels einer Pumpe ohne funktionierenden freien Überlauf des Elektrolytzulaufs verursacht werden könnte.The advantage of the electrolysis cell according to the invention is that due to the simple principle of the free overflow a uniform feeding of the gap between the gas diffusion electrode and the ion exchange membrane and the safe removal of gas from the gap is possible. In addition, the flow velocity in the gap can be easily regulated by means of the overflow. In addition, a dangerous for the gas diffusion electrode dynamic pressure increase in the gap between gas diffusion electrode and membrane can be avoided, which could be caused for example by direct injection of the electrolyte by means of a pump without functioning free overflow of the electrolyte inlet.

Sauerstoff, Luft oder mit Sauerstoff angereicherte Luft (nachfolgend vereinfacht als Sauerstoff bezeichnet) wird aus einer Vorlage (auch als Gassammelbehälter bezeichnet), vorzugsweise unterhalb des Gasraums, in den Gasraum der Halbzelle mit Gasdiffusionselektrode zugeführt. Die Zuführung erfolgt über ein Gasverteilerrohr als Gaseintritt gleichmäßig über die gesamte Breite der Halbzelle. Der nicht verbrauchte Sauerstoff wird im oberen Bereich der Halbzelle über einen Gasaustritt aus dem Gasraum abgeführt. Alternativ kann die Gaszufuhr auch im oberen Bereich und die Gasabfuhr im unteren Bereich der Elektrolysehalbzelle erfolgen.Oxygen, air or oxygen-enriched air (hereinafter referred to simply as oxygen) is supplied from a template (also referred to as a gas collection container), preferably below the gas space, in the gas space of the half-cell with gas diffusion electrode. The supply takes place via a gas distribution pipe as gas inlet uniformly over the entire width of the half-cell. The unused oxygen is removed in the upper part of the half-cell via a gas outlet from the gas space. Alternatively, the gas supply can also take place in the upper region and the gas removal in the lower region of the electrolysis half-cell.

In einer ersten Ausführungsform ist der Gasaustritt mit dem Elektrolytvorlagebehälter verbunden, so dass der Elektrolytvorlagebehälter gleichzeitig als Gassammelbehälter für überschüssigen Sauerstoff dient. Der nicht verbrauchte Sauerstoff wird dabei aus dem Gasraum über eine Gasleitung als Gasaustritt dem Elektrolytvorlagebehälter zugeführt, wobei die Gasleitung bevorzugt unter den Flüssigkeitsspiegel des Elektrolyten abtaucht. Wird die Gasleitung im Elektrolytvorlagebehälter getaucht und ist gleichzeitig auch die Elektrolytableitung in dem Elektrolytsammelbehälter getaucht, so darf die Tauchung der Gasleitung im Elektrolytvorlagebehälter nicht tiefer sein, als die Tauchung der Elektrolytableitung im Sammelbehälter. Der überschüssige Sauerstoff kann zur optimalen Ausnutzung rezykliert werden.In a first embodiment, the gas outlet is connected to the electrolyte reservoir, so that the electrolyte reservoir simultaneously serves as a gas reservoir for excess oxygen. The unused oxygen is supplied from the gas space via a gas line as a gas outlet to the electrolyte reservoir, wherein the gas line preferably dips below the liquid level of the electrolyte. If the gas line immersed in the electrolyte reservoir and at the same time the electrolyte discharge is immersed in the electrolyte reservoir, the dipping of the gas line in the electrolyte reservoir must not be deeper than the immersion of the electrolyte discharge in the reservoir. The excess oxygen can be recycled for optimal utilization.

Diese bevorzugte Ausführungsform, bei welcher der Elektrolytvorlagebehälter gleichzeitig als Gassammelbehälter dient, hat den Vorteil, dass für den Sauerstoff und den Elektrolyten nur ein Vorlagebehälter benötigt wird. Es ist jedoch ebenfalls möglich, für den Sauerstoff und den Elektrolyten jeweils eine unabhängige Vorlage bereitzustellen. In diesem Fall kann der Elektrolytvorlagebehälter auch unterhalb der Elektrolysezelle angeordnet sein, wobei der Elektrolyt aus dem Elektrolytvorlagebehälter in den Elektrolytzulauf mittels einer Pumpe gefördert wird, sofern der freie Ablauf des Elektrolytüberschusses über den Überlaufkanal gewährleistet ist (Kontrolle über nicht vollflächig durchströmten Überlaufkanal).This preferred embodiment, in which the electrolyte reservoir simultaneously serves as a gas collection container, has the advantage that only a storage container is required for the oxygen and the electrolyte. However, it is also possible to provide an independent template for the oxygen and the electrolyte, respectively. In this case, the electrolyte reservoir can also be arranged below the electrolytic cell, wherein the electrolyte is conveyed from the electrolyte reservoir into the electrolyte inlet by means of a pump, provided that the free flow of the electrolyte excess is ensured via the overflow channel (control over not over-flowed overflow channel).

In einer alternativen Ausführungsform ist der Gasaustritt mit einem Gassammelbehälter verbunden und der Gasraum gegenüber dem Spalt abgeschlossen. Dies bedeutet, dass auch im unteren Bereich des Gasraums, wo der Elektrolyt aus dem Spalt abfließt, der Elektrolyt nicht in den Gasraum eintreten und sich dort aufstauen kann. Der Gasraum kann beispielsweise mittels einer Platte, z.B. einer Metallplatte, gegenüber dem Spalt abgeschlossen sein. In dieser Ausführungsform ist der Gassammelbehälter ein separater Sammelbehälter, in den überschüssiger Sauerstoff über eine Gasleitung als Gasaustritt strömt. Auf diese Weise kann der Sauerstoffdruck unabhängig von den Druckverhältnissen im Spalt eingestellt werden. In dieser Ausführungsform weist der Gasraum am unteren Ende Drainageöffnungen auf.In an alternative embodiment, the gas outlet is connected to a gas collecting container and the gas space is closed relative to the gap. This means that even in the lower region of the gas space, where the electrolyte flows out of the gap, the electrolyte can not enter the gas space and can accumulate there. The gas space can, for example by means of a Plate, such as a metal plate, be completed against the gap. In this embodiment, the gas collecting container is a separate collecting container, flows in the excess oxygen via a gas line as a gas outlet. In this way, the oxygen pressure can be adjusted independently of the pressure conditions in the gap. In this embodiment, the gas space has drainage openings at the lower end.

In einer bevorzugten Ausführungsform sind Strömungsleitstrukturen in dem Spalt vorgesehen. Die Strömungsleitstrukturen verhindern einen freien Fall des Elektrolyten in dem Spalt, so dass die Strömungsgeschwindigkeit gegenüber dem freien Fall verringert ist. Gleichzeitig darf sich jedoch der Elektrolyt in dem Spalt aufgrund der Strömungsleitstrukturen nicht aufstauen. Die Strömungsleitstrukturen sind so gewählt, dass der Druckverlust der hydrostatischen Flüssigkeitssäule in dem Spalt kompensiert wird. Beispiele für Strömungsleitstrukturen sind aus WO 03/042430 und WO 01/57290 bekannt.In a preferred embodiment, flow guide structures are provided in the gap. The flow guide structures prevent a free fall of the electrolyte in the gap, so that the flow velocity is reduced compared to the free fall. At the same time, however, the electrolyte must not accumulate in the gap due to the Strömungsleitstrukturen. The flow guide structures are selected so that the pressure loss of the hydrostatic liquid column in the gap is compensated. Examples of flow guiding structures are made WO 03/042430 and WO 01/57290 known.

Die Strömungsleitstrukturen können auch aus dünnen Platten, Folien oder dergleichen bestehen, welche Öffnungen zum Durchströmen des Elektrolyten aufweisen. Sie sind quer, d.h. senkrecht oder schräg, zur Strömungsrichtung des Elektrolyten in dem Spalt angeordnet. Die plattenförmigen Strömungsleitstrukturen sind vorzugsweise gegenüber der Horizontalen geneigt, wobei sie entweder nur in einer Achse oder in beiden Achsen geneigt sind. Sind die Strömungsleitstrukturen schräg zur Strömungsrichtung angeordnet, können sie sowohl in Richtung der Ionenaustauschermembran als auch in Richtung der Gasdiffusionselektrode geneigt sein. Darüber hinaus können die Strömungsleitstrukturen über die Breite der elektrochemischen Zelle geneigt sein.The flow guiding structures may also consist of thin plates, foils or the like, which have openings for flowing through the electrolyte. They are transversal, i. perpendicular or oblique, arranged to the flow direction of the electrolyte in the gap. The plate-shaped Strömungsleitstrukturen are preferably inclined relative to the horizontal, wherein they are inclined either only in one axis or in both axes. If the flow guide structures are arranged obliquely to the flow direction, they can be inclined both in the direction of the ion exchange membrane and in the direction of the gas diffusion electrode. In addition, the flow guiding structures may be inclined across the width of the electrochemical cell.

Ein weiterer Gegenstand der Erfindung ist ein Verfahren zur Elektrolyse einer wässrigen Alkalihalogenid-Lösung in der erfindungsgemäßen elektrochemischen Zelle. Das Verfahren zeichnet sich dadurch aus, dass der Elektrolyt aus dem Elektrolytvorlagebehälter im Überschuss dem Elektrolytzulauf zugeführt wird, der Elektrolyt von dem Elektrolytzulauf in den Spalt und aus dem Spalt in den Elektrolytablauf strömt sowie von dem Elektrolytzulauf über den Überlauf abfließt.Another object of the invention is a process for the electrolysis of an aqueous alkali halide solution in the electrochemical cell according to the invention. The method is characterized in that the electrolyte from the electrolyte reservoir is supplied in excess to the electrolyte inlet, the electrolyte flows from the electrolyte inlet into the gap and out of the gap into the electrolyte outlet and flows away from the electrolyte inlet via the overflow.

Ein Überschuss an Elektrolyt im Elektrolytzulauf bedeutet im Sinne der vorliegenden Erfindung, dass der Elektrolytzulauf stets gleichmäßig über die gesamte Breite wenigstens mit einem Elektrolytfilm gefüllt ist. Während also im Betrieb der Elektrolysezelle stets Elektrolyt über den Spalt abfließt, muss gleichzeitig im Elektrolytzulauf stets ein gewisser Elektrolytpegel auf der gesamten Breite des Elektrolytzulaufs vorhanden sein. Dies ist am besten dann gewährleistet, wenn stets eine bestimmte Elektrolytmenge nicht nur über den Spalt, sondern auch über den Überlauf aus dem Elektrolytzulauf abfließt.An excess of electrolyte in the electrolyte feed means in the context of the present invention that the electrolyte feed is always filled evenly over the entire width at least with an electrolyte film. Thus, while in operation of the electrolytic cell always flows electrolyte through the gap, at the same time in the electrolyte inlet always a certain level of electrolyte must be present over the entire width of the electrolyte inlet. This is best ensured if always a certain amount of electrolyte flows not only through the gap, but also via the overflow from the electrolyte feed.

Vorzugsweise beträgt der Überschuss des Elektrolyten der über den Überlauf abgeführt wird 0,5 bis 30 Vol%, besonders bevorzugt 1 bis 20 Vol.%.Preferably, the excess of the electrolyte which is removed via the overflow is 0.5 to 30% by volume, particularly preferably 1 to 20% by volume.

Wesentlich ist, dass die Elektrolytmenge, die eine Fallfilmzelle zu ihrem störungsfreien Betrieb benötigt, nur von der Bauart der Fallfilmzelle abhängt, nicht jedoch von den gewählten Stromdichten. Daher muss der Elektrolytüberschuss nur einmal zu Beginn des Elektrolysebetriebs eingestellt und während des Betriebs lediglich konstant gehalten werden. Das effektive Höhenverhältnis h zu g muss so gewählt werden, dass sich die für den optimalen Betrieb der Elektrolysezelle notwendige Elektrolytkonzentration in dem Spalt einstellt.It is essential that the amount of electrolyte that a falling film cell requires for its trouble-free operation depends only on the type of falling film cell, but not on the selected current densities. Therefore, the excess electrolyte must be set only once at the beginning of the electrolysis operation and only kept constant during operation. The effective height ratio h to g must be selected so that the necessary for the optimal operation of the electrolytic cell electrolyte concentration in the gap.

Die erfindungsgemäße elektrochemische Zelle kann für unterschiedliche Elektrolyseverfahren eingesetzt werden, in denen mindestens eine Elektrode eine Gasdiffusionselektrode ist. Vorzugsweise fungiert die Gasdiffusionselektrode als Kathode, besonders bevorzugt als Sauerstoffverzehrkathode, wobei das der elektrochemischen Zelle zugeführte Gas ein sauerstoffhaltiges Gas ist, z.B. Luft, mit Sauerstoff angereicherte Luft oder Sauerstoff selbst. Bevorzugt wird die erfindungsgemäße Zelle für die Elektrolyse einer wässrigen Lösung eines Alkalihalogenids, insbesondere von Natriumchlorid, verwendet.The electrochemical cell according to the invention can be used for different electrolysis processes, in which at least one electrode is a gas diffusion electrode. Preferably, the gas diffusion electrode functions as a cathode, more preferably as an oxygen-consuming cathode, wherein the gas supplied to the electrochemical cell is an oxygen-containing gas, e.g. Air, oxygen-enriched air or oxygen itself. The cell according to the invention is preferably used for the electrolysis of an aqueous solution of an alkali metal halide, in particular of sodium chloride.

Im Falle der Elektrolyse einer wässrigen Natriumchloridlösung ist die Gasdiffusionselektrode beispielsweise wie folgt aufgebaut: Die Gasdiffusionselektrode besteht wenigstens aus einem elektrisch leitfähigen Träger und einer elektrochemisch aktiven Beschichtung. Der elektrisch leitfähige Träger ist bevorzugt ein Netz, Gewebe, Geflecht, Gewirke, Vlies oder Schaum aus Metall, insbesondere aus Nickel, Silber oder versilbertem Nickel. Die elektrochemisch aktive Beschichtung besteht vorzugsweise wenigstens aus einem Katalysator, z.B. Silber(I)-Oxid, und einem Binder, z.B. Polytetrafluorethylen (PTFE). Die elektrochemisch aktive Beschichtung kann aus einer oder mehreren Schichten aufgebaut sein. Zusätzlich kann eine Gasdiffusionsschicht, beispielsweise aus einer Mischung aus Kohlenstoff und Polytetrafluorethylen, vorgesehen sein, welche auf den Träger aufgebracht wird.In the case of the electrolysis of an aqueous sodium chloride solution, the gas diffusion electrode is constructed, for example, as follows: The gas diffusion electrode consists at least of an electrically conductive carrier and an electrochemically active coating. The electrically conductive carrier is preferably a mesh, woven, braided, knitted, nonwoven or foam of metal, in particular of nickel, silver or silver-plated nickel. The electrochemically active coating preferably consists of at least one catalyst, e.g. Silver (I) oxide, and a binder, e.g. Polytetrafluoroethylene (PTFE). The electrochemically active coating may be composed of one or more layers. In addition, a gas diffusion layer, for example of a mixture of carbon and polytetrafluoroethylene, can be provided, which is applied to the support.

Als Anode können beispielsweise Elektroden aus Titan eingesetzt werden, welche z.B. mit Ruthenium-Iridium-Titan-Oxiden oder Ruthenium-Titanoxid beschichtet sind.As the anode, for example, electrodes of titanium may be used, which are e.g. coated with ruthenium-iridium-titanium oxides or ruthenium-titanium oxide.

Als Ionenaustauschermembran kann eine handelsübliche Membran, z.B. der Fa. DuPont, z.B. Nafion® NX2010, eingesetzt werden.As the ion exchange membrane, a commercially available membrane, e.g. from DuPont, e.g. Nafion® NX2010.

Die erfindungsgemäße Elektrolysezelle, welche sich für die Elektrolyse einer wässrigen Natriumchloridlösung eignet, besitzt einen Spalt zwischen Gasdiffusionselektrode und Ionenaustauschermembran vorzugsweise mit einer Breite von 0,2 bis 5 mm, besonders bevorzugt von 0,5 bis 3 mm. Nachfolgend wird die Erfindung anhand der beigefügten Zeichnungen näher erläutert. Es zeigen:

Figur 1
einen schematischen Längsschnitt durch eine Ausführungsform der erfindungsgemäßen Elektrolysezelle
Figur 2
einen schematischen Querschnitt durch die erfindungsgemäße Elektrolysezelle nach Figur 1.
The electrolysis cell according to the invention, which is suitable for the electrolysis of an aqueous sodium chloride solution, has a gap between gas diffusion electrode and ion exchange membrane, preferably with a width of 0.2 to 5 mm, particularly preferably 0.5 to 3 mm. The invention will be explained in more detail with reference to the accompanying drawings. Show it:
FIG. 1
a schematic longitudinal section through an embodiment of the electrolytic cell according to the invention
FIG. 2
a schematic cross section through the electrolysis cell according to the invention FIG. 1 ,

In Figur 1 ist eine Ausführungsform einer erfindungsgemäßen elektrochemischen Zelle im Längsschnitt dargestellt. Elektrolyt strömt aus dem Elektrolytvorlagebehälter 7 über eine Elektrolytzuleitung 8 in den Elektrolytzulauf 10 der Elektrolysehalbzelle mit Gasdiffusionselektrode 4 (Figur 2). Der Elektrolytvorlagebehälter 7 ist oberhalb des Elektrolytzulaufs 10 angeordnet. Der Elektrolytzulauf 10 verläuft längs über die gesamte Breite der Elektrolysehalbzelle oberhalb des Spaltes 11 (Figur 2). Die Höhendifferenz zwischen dem Flüssigkeitspegel in dem Vorlagebehälter 7 und dem Flüssigkeitspegel in dem Elektrolytzulauf 10 ist mit h bezeichnet.In FIG. 1 an embodiment of an electrochemical cell according to the invention is shown in longitudinal section. Electrolyte flows out of the electrolyte reservoir 7 via an electrolyte feed line 8 into the electrolyte inlet 10 of the electrolysis half cell with gas diffusion electrode 4 (FIG. FIG. 2 ). The electrolyte reservoir 7 is disposed above the electrolyte inlet 10. The electrolyte feed 10 extends longitudinally over the entire width of the electrolysis half cell above the gap 11 (FIG. FIG. 2 ). The height difference between the liquid level in the receiver tank 7 and the liquid level in the electrolyte inlet 10 is designated by h.

Der Elektrolyt strömt gleichmäßig über die gesamte Breite der Elektrolysehalbzelle über den Elektrolytzulauf 10 oben in den Spalt 11 (Figur 2). In dem Spalt 11 fließt der Elektrolyt nach unten in den Elektrolytablauf 20 (Figur 2), der zum Gasraum 5 (Figur 2) hin offen ist, und von dem Elektrolytablauf 20 über eine Elektrolytableitung 15 in einen Elektrolytsammelbehälter 14.The electrolyte flows uniformly over the entire width of the electrolysis half-cell via the electrolyte inlet 10 into the gap 11 (FIG. FIG. 2 ). In the gap 11, the electrolyte flows down into the electrolyte outlet 20 (FIG. FIG. 2 ) leading to the gas space 5 ( FIG. 2 ), and from the electrolyte drain 20 via an electrolyte discharge 15 into an electrolyte reservoir 14.

In einer besonderen Ausführungsform ist der Gasraum 5 mit einer Metallplatte als Abschluss, z.B. einem Blech, 23 von dem Elektrolytablauf 20 getrennt. In Verbindung mit einer von der Vorlage 7 unabhängigen Sauerstoffvorlage (hier nicht dargestellt) kann damit der Sauerstoffdruck unabhängig von den Druckverhältnissen im Spalt 11 eingestellt und auf für die Gasdiffusionselektroden optimale Betriebsbedingungen gebracht werden. Drainageöffnungen (hier nicht dargestellt) ermöglichen eine Abfuhr von möglicherweise angefallenem Kondensat von der Rückseite der Gasdiffusionselektrode.In a particular embodiment, the gas space 5 is terminated with a metal plate, e.g. a sheet, 23 separated from the electrolyte effluent 20. In conjunction with an oxygen template independent of the original 7 (not shown here), the oxygen pressure can thus be adjusted independently of the pressure conditions in the gap 11 and brought to optimum operating conditions for the gas diffusion electrodes. Drainage holes (not shown here) allow drainage of possibly accumulated condensate from the back of the gas diffusion electrode.

Erfindungsgemäß weist die Elektrolysehalbzelle einen Überlaufkanal 13 auf, der in der dargestellten Ausführungsform U-förmig ist, wobei der Scheitel des U-förmigen Kanals nach oben weist. Außerdem ist in der dargestellten Ausführungsform ein zusätzlicher Überlaufkanal 12 vorgesehen, welcher im Wesentlichen horizontal angeordnet ist. Überschüssiger Elektrolyt, welcher nicht in dem Spalt 11 abfließt, strömt über den Überlaufkanal 12 in einen Seitenkanal 21, welcher im Wesentlichen seitlich der Elektrolysehalbzelle vertikal angeordnet ist und überschüssigen Elektrolyten nach unten abführt. Überschüssiger Elektrolyt wird in dem Elektrolytsammelbehälter 14 aufgefangen.According to the invention, the electrolysis half-cell has an overflow channel 13, which in the illustrated embodiment is U-shaped, with the apex of the U-shaped channel pointing upwards. In addition, in the illustrated embodiment, an additional overflow channel 12 is provided, which is arranged substantially horizontally. Excess electrolyte, which does not flow off in the gap 11, flows via the overflow channel 12 into a side channel 21, which is arranged vertically to the side of the electrolysis half-cell and dissipates excess electrolyte downwards. Excess electrolyte is collected in the electrolyte reservoir 14.

Ist der Überschuss an Elektrolyt so groß, dass dieser nicht alleine über den Spalt 11 und den Überlaufkanal 12 abgeführt werden kann, fließt ein Teil des Elektrolyten über den U-förmigen Überlaufkanal 13 in den Seitenkanal 21 nach unten ab. Die Höhendifferenz zwischen dem Scheitel des Überlaufkanals 13 und dem Flüssigkeitspegel in dem Elektrolytzulauf 10 ist mit g bezeichnet.If the excess of electrolyte is so large that it can not be removed by way of the gap 11 and the overflow channel 12 alone, part of the electrolyte flows downward via the U-shaped overflow channel 13 into the side channel 21. The height difference between the apex of the overflow channel 13 and the liquid level in the electrolyte inlet 10 is designated by g.

Unterhalb des Spaltes 11 verläuft ebenfalls längs der Elektrolysehalbzelle ein Gasverteilerrohr 18 mit Öffnungen 19, über die Sauerstoff aus einem Gasvorlagebehälter 17 in den Gasraum 5 der Elektrolysehalbzelle strömt. Das Gasverteilerrohr 18 bildet somit den Gaseintritt in die Elektrolysehalbzelle. Nicht verbrauchter Sauerstoff kann über eine Gasleitung 9 als Gasaustritt den Gasraum 5 verlassen und in den Elektrolytvorlagebehälter 7 strömen. In der dargestellten Ausführungsform dient der Elektrolytvorlagebehälter 7 zugleich als Gassammelbehälter.Below the gap 11 also runs along the electrolysis half-cell, a gas distribution pipe 18 with openings 19, flows through the oxygen from a gas storage tank 17 into the gas space 5 of the electrolysis half-cell. The gas distribution pipe 18 thus forms the gas inlet into the electrolysis half cell. Unconsumed oxygen can leave the gas space 5 via a gas line 9 as a gas outlet and flow into the electrolyte reservoir 7. In the illustrated embodiment, the electrolyte reservoir 7 also serves as a gas collection container.

Ferner ist in der Ausführungsform gemäß Figur 1 eine Pumpe 30 vorgesehen, welche Elektrolyt aus dem Sammelbehälter 14 in den Vorlagebehälter 7 pumpt.Further, in the embodiment according to FIG FIG. 1 a pump 30 is provided, which pumps electrolyte from the collecting container 14 into the storage container 7.

Figur 2 zeigt die Elektrolysezelle gemäß Figur 1 im Querschnitt. Sie besteht aus einer Anodenhalbzelle 1 mit einer Anode 6 und einer Kathodenhalbzelle 22 mit einer Gasdiffusionselektrode 4 als Kathode. Die beiden Halbzellen 1, 22 sind durch eine Ionenaustauschermembran 3 voneinander getrennt. Zwischen der Ionenaustauschermembran 3 und der Gasdiffusionselektrode 4 befindet sich ein Spalt 11. Hinter der Gasdiffusionselektrode 4 ist ein Gasraum 5 angeordnet. Der Gasraum 5 bildet somit den Rückraum hinter der Gasdiffusionselektrode 4. FIG. 2 shows the electrolytic cell according to FIG. 1 in cross section. It consists of an anode half-cell 1 with an anode 6 and a cathode half-cell 22 with a gas diffusion electrode 4 as a cathode. The two half-cells 1, 22 are separated from each other by an ion exchange membrane 3. Between the ion exchange membrane 3 and the gas diffusion electrode 4 there is a gap 11. Behind the gas diffusion electrode 4, a gas space 5 is arranged. The gas space 5 thus forms the rear space behind the gas diffusion electrode 4.

Wie in Figur 2 dargestellt, strömt Elektrolyt aus dem Elektrolytzulauf 10 in den Spalt 11 und von dem Spalt 11 in den Elektrolytablauf 20, bis der Elektrolyt schließlich über die Elektrolytableitung 15 in dem Elektrolytsammelbehälter 14 aufgefangen wird. Gas, welches über das Gasverteilerrohr 18 in den Gasraum 5 strömt, kann über den Gasaustritt 9 in den Elektrolytvorlagebehälter 7 oberhalb der Elektrolysezelle strömen. Eine Metallplatte 23 trennt den Gasraum 5 von dem Elektrolytablauf 20.As in FIG. 2 shown, electrolyte flows from the electrolyte inlet 10 into the gap 11 and from the gap 11 in the electrolyte effluent 20 until the electrolyte is finally collected via the electrolyte discharge 15 in the electrolyte reservoir 14. Gas, which flows via the gas distribution pipe 18 into the gas space 5, can flow via the gas outlet 9 into the electrolyte reservoir 7 above the electrolytic cell. A metal plate 23 separates the gas space 5 from the electrolyte outlet 20.

Claims (10)

  1. An electrochemical cell at least consisting of an anode half-cell (1) with an anode (6), a cathode half-cell (22) with a cathode (4) and an ion-exchange membrane (3) arranged between the anode half-cell (1) and the cathode half-cell (22), the anode (6) and/or the cathode (4) being a gas diffusion electrode and there being arranged a gap (11) between the gas diffusion electrode (4) and the ion-exchange membrane (3), an electrolyte feed inlet (10) above the gap (11) and an electrolyte drain (20) beneath the gap (11) together with a gas inlet (18) and a gas outlet (9), characterised in that the electrolyte feed inlet (10) is connected via an electrolyte feed line (8) to an electrolyte holding vessel (7) and comprises an overflow, the overflow taking the form of an overflow channel (12; 13) and the pressure in the electrolyte feed inlet (10) being adjustable by choosing the height g of the overflow channel.
  2. An electrochemical cell according to claim 1, characterised in that the electrolyte holding vessel (7) is arranged 30 to 200 cm above the electrolyte feed inlet (10).
  3. An electrochemical cell according to claim 1, characterised in that the electrolyte holding vessel (7) is connected via a pump with the electrolyte feed inlet (10).
  4. An electrochemical cell according to any one of claims 1-3, characterised in that the height of the overflow amounts to 0 to 190 cm.
  5. An electrochemical cell according to claim 1, characterised in that the overflow channel is a U-shaped channel (13), the vertex of which points upwards.
  6. An electrochemical cell according to claim 1, characterised in that the overflow channel takes the form of a standpipe or shaft.
  7. An electrochemical cell according to any one of claims 1-6, characterised in that the gas outlet (9) is connected with the electrolyte holding vessel (7).
  8. An electrochemical cell according to any one of claims 1-6, characterised in that the gas outlet (9) is connected with a gas collecting vessel and the gas space (5) is shut off from the gap (11).
  9. A process for electrolysing an aqueous alkali halide solution in an electrochemical cell according to any one of claims 1-8, characterised in that the electrolyte is supplied in excess from the electrolyte holding vessel (7) to the electrolyte feed inlet (10), the electrolyte flows from the electrolyte feed inlet (10) into the gap (11) and from the gap (11) into the electrolyte drain (20) and flows away from the electrolyte feed inlet (10) via the overflow.
  10. A process according to claim 9, characterised in that the excess of electrolyte amounts to 0.5 to 30 vol.%, preferably to 1 to 20 vol.%.
EP05732004.6A 2004-04-17 2005-04-09 Electrochemical cell Active EP1740739B1 (en)

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