EP0428171B1 - Electrolysis cell for the manufacture of peroxo- and perhalogenate compounds - Google Patents

Description

The invention relates to an electrolytic cell for the anodic production of peroxo compounds, e.g. of peroxodisulfates, peroxomonosulfates, peroxodiphosphates, and the corresponding acids; and of perhalogenates and their acids, in particular perchlorates or perchloric acid.

Membrane electrolysis cells, mostly of the filter press type, have been gaining technical importance in the industrial production of chlorine and sodium hydroxide for several years. However, the numerous cell constructions described in the magazine and patent literature are not suitable for the production of, for example, peroxodisulfates or peroxodisulfuric acid, because the anode material used in the chlor-alkali electrolysis cells, mostly based on titanium support / mixed oxide made from Group VIII metals and titanium, is technically used to form peroxodisulfate not suitable because its current efficiency and its stability are too low. The current yield can be increased to technically interesting values when using iridium-containing mixed oxides, but only if fluoride-containing anolyte additives are used, which, however, soon destroy the coating and thus render the anode unusable (cf.Fukuda et al., Electrochimica Acta 24 (1979) , 363-365).

The efforts to develop membrane cells for the electrolytic production of peroxo or perhalogenate compounds have so far not led to technically useful solutions. A major reason for this is the lack of long-term resistant anode materials or composite electrodes made therefrom, which can be used in the form of sheets in electrodes and cell constructions in a way that is inexpensive to process and process. Composite electrodes of this type should consist, for example, of a titanium or tantalum base which is homogeneous, is connected flatly and firmly with a platinum foil overlay. Indeed, the manufacture of peroxo compounds still relies on the use of solid platinum as the only technically usable anode material. Composite electrodes, in which a platinum layer was produced by cathodic deposition from galvanic platinum baths or platinum salt melts, have an insufficient adhesive strength, an insufficient service life and an unsatisfactory current efficiency.

In the manufacture of the usual anodes, it was necessary to fix the platinum metal in the form of wires, strips or foils on the metal base titanium or tantalum, which is resistant to the electrolyte, by means of locally limited - i.e. non-flat - connections, such as by point or Roll seam welding or by mechanical pressing devices. These welding or mechanically formed contact points are not liquid-tight and are therefore accessible to the electrolyte; Experience has shown that they are destroyed over time by corrosion and arcing, after which the platinum parts are wholly or partially lifted off the surface and are lost to the electrolysis process. The degree of utilization for the platinum metal invested in an electrolysis plant is therefore limited. It is far from reaching the arithmetic value that results when the quotient "installed platinum weight / specific platinum consumption per ton of product" is formed. With a homogeneous, adherent platinum coating of 50 µm, for example at an anodic current density of 9 kA / m², a runtime of 15 to 20 years could be achieved in the electrolytic extraction of potassium peroxodisulfate, but in technical operation, mechanically pressed platinum foils are used on an titanium tube as anode support a maximum of only 3 years as the lifespan. Then the composite anode, which has partially lost the platinum foil mechanically, is with to be provided with a new edition or to be replaced by a new anode.

Electrolysis cells which are constructed using partially contacted composite electrodes are known (cf. J. Balej and H. Vogt, "Electrochemical Reactors", Progress Process Engineering 22 (1984), 371-389). The electrolytic cells for the production of peroxodisulfuric acid require a separator which separates the cathode compartment from the anodically formed peroxodisulfate, so that its reduction on the cathode surface is reduced or prevented. Various constructions use platinum foil strips as anodes, which are fixed to tantalum sheet by roll seam welding (i.e. only locally). In other electrolysis cells, platinum wire is used, which is either fixed on flat titanium wire meshes by spot welding or wound spirally around a silver wire coated with tantalum and attached to it by, for example, spot welding. With these cell constructions, an anodic current density of 5 kA / m², based on the platinum surface, cannot be exceeded, since otherwise the current load on the contact points between the support and platinum will be too high, which would then lead to their destruction by heating and corrosion. Cells for the production of salts of peroxodisulfuric acid have a similar structure. However, constructions without a separator or diaphragm can also be used here if the peroxodisulfate is precipitated as a salt during the electrolysis and the electrolyte flows through the cell sufficiently quickly.

Tantalum or titanium anodes coated with platinum foils are also used for the production of perhalates, in particular for the production of perchloric acid and its salts. In terms of service life and yields, these offer advantages over graphite anodes coated with lead dioxide. Platinate-coated titanium has so far been technically used for production not proven by perchlorates. For reasons similar to the anodes used to date for the production of peroxodisulfates, the anodic current densities of 5 kA / m 2 cannot be exceeded even in the production of perchloric acid or perchlorates.

It is therefore an object of the present invention to provide an electrolysis cell suitable for producing peroxo and perhalogenate compounds, with which the service life corresponding to the platinum content of the composite anode can be achieved and which enables a high current density and low energy consumption. This object is achieved with the present invention.

The invention relates to an electrolysis cell of the filter press type consisting of alternately arranged, provided with electrolyte feed cathodes and anodes, which is characterized in that the cathodes and anodes consist of cuboid hollow bodies, between which there are frame-shaped seals, and which are liquid-tight and insulated from one another via these seals are connected to a cell package, the cathode hollow bodies are permeable to liquid and gas, the anode hollow bodies have openings for the transport of the anolyte in and out above and below the platinum support, and the effective anode surface through the platinum metal layer consisting of a valve metal support and a platinum support thereon, which are available is formed by hot isostatic pressing (HIP) of a platinum foil on a valve metal carrier.

The platinum foil preferably has a thickness of 20 to 100 μm, and in particular 50 μm.

Tantalum or niobium, and in particular titanium, is preferably used as the valve metal. The thickness of the valve metal carrier (valve metal sheet) is preferably chosen so that that it can be easily processed into electrodes and can be stably installed in appropriate cell constructions; the thickness is preferably 1 to 6 mm, in particular 2 to 4 mm, and primarily 3 mm.

The welding of the composite sheets produced by hot isostatic pressing (HIP; diffusion welding) can be carried out using suitable, known welding techniques, e.g. by TIG welding or laser technology. The welding zone must be absolutely free of platinum, otherwise alloys are created that are not corrosion-resistant.

Preferred configurations of this electrolysis cell, which can be used individually or in combination, are listed below: The platinum foil has a thickness of 20 to 100 μm. The valve metal is titanium, niobium or tantalum. The valve metal carrier has a thickness of 1 to 6 mm. Separators are located between the hollow cathode bodies (1) and the hollow anode bodies (2), by means of which the catholyte spaces are separated from the anolyte spaces. The separator consists of a fluorinated cation exchange membrane containing sulfonic acid groups. It lies on the openwork, liquid and gas permeable cathode surface and is attached at a distance of 0.5 to 5 mm to the platinum anode surface. The active cathode parts (12) of the hollow cathode body (1) are perforated. They are roughened and / or provided with a coating which reduces the cathode polarization. The openings above and below the platinum support for the supply and removal of the anolyte are slit-shaped openings or are formed by a large number of adjacent bores. The width of the slot-shaped openings or the diameter of the bores increases from the electrolyte feed or discharge (52, 62) to the opposite side. The anode hollow bodies are equipped with inlets and outlets for a coolant (71, 72) and consist of three chambers, from which the upper and lower serve the electrolyte guide and the middle of the rear cooling of the active anode surfaces. The sealing material for the frame-shaped seals (3) is a vinylidene fluoride-hexafluoropropylene copolymer.

Another object of the invention is the use of an electrolytic cell according to the invention for the electrolytic production of peroxo and perhalogenate compounds.

The electrolytic cell according to the invention is formed from rectangular, rectangular hollow bodies for cathodes and anodes, which are isolated from one another by frame-shaped seals and are connected to one another in a liquid-tight manner, e.g. are screwed. The anode hollow body has an opening for the supply and removal of the anolyte, preferably a slot-shaped opening or a number of holes, above and below the rectangular platinum support.

Separators are preferably located between the anode and cathode bodies; the separators are expediently clamped between the frame-shaped seals. A separator made of a fluorinated cation exchange membrane (KIA membrane) containing sulfonic acid groups is preferably used to produce the peroxo compounds, e.g. a cation exchange membrane of the type NAFION® 423 (semipermeable membranes based on poly (perfluoroalkylene) sulfonic acid).

The separator preferably lies on the perforated, liquid and gas permeable cathode surface; the distance of the separator from the smooth, flat platinum anode surface (platinum layer of the composite anode) is preferably 0.5 to 5 mm.

When using a cation exchange membrane, e.g. of type NAFION® 423, it was surprisingly found that this can not only be used up to approx. 5 kA / m² - in chlor-alkali electrolysis using membrane cells a maximum of 3 to 5 kA / m² can be achieved in continuous operation. Long-term loads of up to 15 kA / m² also had no effect on the function and durability of the cation exchange membrane. This is of great importance because a technical electrolysis plant for the production of peroxo or perhalogenate compounds can be operated significantly above the nominal output if the electrolysis cell is suitable for overloads. When using the electrolysis cell according to the invention, this effect can be used and it allows the ohmic heat generation caused by the excessive power consumption to be dissipated.

The active cathode parts in the cathode hollow bodies preferably consist of a sheet provided with openings, e.g. Expanded metal, perforated sheet or blind plates.

The composite anodes are used in the cells according to the invention with a smooth, uninterrupted platinum surface, that is to say not as, for example, expanded metal. The electrolysis cell is preferably operated with a hydrostatic overpressure in the anode compartment of more than 0.02 bar (2000 Pa) compared to the cathode compartment. This is sufficient to press the cation exchange membrane against the cathode made of perforated material and thus to ensure the necessary distance between the anode surface and the KIA membrane. In order to keep the cell voltage low, this distance should preferably not exceed 5 mm, and in particular 3 mm. If suitably chosen electrolysis conditions are observed, anodic product current yields of 92 to 96% can be achieved with the arrangement according to the invention; the amount of gaseous oxygen anodically formed as a by-product is therefore so small that even with a 0.5 mm distance between Anode and separator no disturbing gas bubble effect occurs. Flow speeds of> 0.3 m / sec should preferably be maintained. Since the cathode material is perforated and is preferably made of expanded metal, the electrolytically generated hydrogen can easily escape "to the rear".

In a further preferred embodiment of the cathode, the surface of the cathode is removed by mechanical and / or chemical measures, e.g. by sandblasting and / or etching in acids, provided with a finely structured roughening; the resulting increase in surface area results in a reduction in the cathode polarization (hydrogen overvoltage), corresponding to a reduction in the effective cathodic current density, as a result of which the cell voltage is reduced to the same extent. This depolarization effect can be enhanced by coating the effective cathode surfaces with metals and / or oxides from group VIII of the Periodic Table of the Elements, this coating then advantageously being produced with a surface-rich microstructure. The cathode material is preferably stainless steel.

The openings in the anode hollow bodies above and below the preferably rectangular platinum support for the supply and removal of the anolyte are preferably slit-shaped openings or are formed by a large number of bores lying side by side. The width of the slit-shaped openings or the diameter of the bores is preferably from the electrolyte supply or discharge seen from the opposite side larger.

The anode hollow bodies are preferably designed such that the back of the active anode surfaces are cooled can, they are provided with inlets and outlets for a coolant, especially for cooling water.

In an expedient embodiment, the anode hollow bodies are designed in such a way that they consist of three chambers, the upper and lower of which serve to guide the electrolyte and the middle to cool the rear of the active anode surfaces.

Preferred embodiments of electrolysis cells according to the invention are illustrated in the accompanying figures.

Figures 1 and 2 show schematically the structure of an electrolysis cell according to the invention:
The electrolytic cell essentially consists of two end cathodes 18 of identical construction (mirror image symmetrical), a plurality of rectangular hollow bodies for cathodes 1 and anodes 2, seals 3 which are pressed between the alternating anodes and cathodes by means of threaded rods 4 in a liquid-tight manner and the electrodes of opposite polarity isolate from each other. If necessary, separators (not shown) are present which separate the differently composed electrolytes of the cathode and anode compartments from one another; separators are preferably used for separators known for chlor-alkali electrolysis, in particular cation exchange membranes of the type NAFION® 423 (semipermeable membranes based on poly (perfluoroalkylene) sulfonic acid) ). The separators lie between the seal 3 and the frame of the cathode 1 in such a way that electrolyte leakage ("wicking" of the cation exchange membrane to the outside) is reliably prevented by a protruding edge of the seal.

Each of the rectangular, rectangular cathode or anode hollow bodies has pipe sockets 51, 61, 52, 62 for the supply 51, 52 or discharge 61, 62 of catholyte or anolyte (respectively in diametrical position 51/61 or 52/62) . These pipe sockets, which are arranged alternately with the polarity are flexibly connected to the inlet 91, 92 or outlet manifolds 101, 102 of the cell packet. The anode hollow bodies also have pipe sockets for the supply and discharge 72 of cooling water.

The cooling of the anode hollow bodies enables electrolysis operation with current densities of up to 15 kA / m² and more, because it reliably prevents the heating of the anode surface caused by ohmic voltage losses and thus guarantees a high product yield with low oxygen development.

This anode cooling also has a particularly favorable effect in the synthesis of peroxodisulfuric acid and perchloric acid, where particularly low temperatures are to be maintained.

On both sides or on one side, the hollow anode bodies have 2 connection lugs for the power supply (positive polarity), which is carried out by means of flexible copper elbows from copper power supply rails. Analogously, the cathode hollow bodies 1 are connected to the negative pole of the rectifier; the power connection takes place above and / or below the cathodes.

3 to 5 show embodiments for the structure of the anode hollow body 2 described in FIGS. 1 and 2 in cross section (FIG. 3), in plan view (FIG. 4) and in section of plane AB of FIG. 4 (FIG. 5).

The flat, cuboid anode hollow body comprises two opposite anode base surfaces made of the actual anode parts 22 covered with platinum foil, side boundaries 21 and diametrically arranged coolant connections 71, 72. There are electrolyte feeds and discharges below and above the anode parts 22/21/22/21 each with a pipe socket 52, 62 and an end plate 8 are provided. The pipe connections are positioned diametrically opposite on the anode hollow body.

The electrolyte supply parts of the anode are welded to the anode hollow body in such a way that a slot or a series of bores for the inflow and outflow of the anolyte are provided between the anode part 22 and the end plate 8.

The anode support body (anode pad) is formed from so-called valve metals, preferably titanium. The welding of the composite sheets produced by hot isostatic pressing (e.g. a platinum foil of 50 µm thickness on a 3 mm thick titanium sheet) can be carried out with the help of suitable welding techniques, e.g. TIG welding or laser technology. The welding zone must be absolutely free of platinum, otherwise alloys are created that are not corrosion-resistant. After the welding process, the hollow anode body is brought into a completely flat state at its edges, which are contacted with the frame seal 3 (see FIG. 1), if necessary by mechanical finishing.

The inside of the anode part 22/21/22/21 can contain elements to increase the Reynolds number, e.g. Flow baffles included (not shown). Likewise, the electrolyte supply parts of the anode body can be provided with internals for leveling the flow.

FIGS. 6 and 7 show embodiments for the construction of a cathode hollow body according to FIG. 1 in section (FIG. 6) and in plan view (FIG. 7).

The flat, rectangular cathode hollow body 1 consists of the electrochemically active cathode parts 12, which are welded to the lateral edges with U-profiles 13 and 14, the cathode parts 12 being able to be designed, for example, as expanded metal, perforated sheet metal or as blind plates. In the event of In a cell without a separator, the cathode can also be equipped with metal sheets (instead of expanded metal), the cathode then being constructed like the anode and thus can also be cooled. The electrolyte supply and discharge pipes 61 are located below and above the cathode parts 12. The pipe connections are positioned diametrically opposite on the hollow cathode body.

Both cathode parts are welded to one another along the lines a-b-c-d, as a result of which the hollow cathode body, which is closed to the outside, is formed. It can contain internals (not shown) to equalize the electrolyte flow and the current distribution.

Stainless steel is preferably used as the material for the cathode body. In particular, stainless steel from WSt has been used to produce the peroxo or perhalogenate compounds. No. 1.4539 proven. The stainless steel parts are welded using suitable, known welding techniques. After the welding process, the cathode body is brought into a completely flat state at its edges 17, which are contacted with the frame seal and possibly with the separator, if necessary by mechanical finishing.

To achieve a low cathode polarization, the cathode plates 12 are generally roughened; it can take place on the finished cathode body, for example (after covering the sealing edges 17) by means of sandblasting and / or by means of a pickling paste. To further intensify the depolarization effect, the cathode plates can be processed according to methods known per se, for example with Raney nickel (for example by flame or plasma spraying), or thermally with mixed oxides composed of Ti, Ta and / or Zr on the one hand and Pt, Ru and / or on the other hand Ir, coat. If necessary (e.g. with Raney pads), extractable parts (such as aluminum or magnesium) are removed in alkaline or acidic solutions.

The "end cathodes" 18 of the electrolytic cell consist of hollow bodies closed on one side; the side facing the inside of the cell either consists of a "perforated", that is to say liquid and gas permeable, or of a smooth metal sheet which leaves slots or bores at the top and bottom, while the opposite side consists of a solid metal plate 19 and forms the cell wall (see Fig. 1).

The electrolytic cell consists of n anodes and n + 1 cathodes. A (double) anode built in accordance with the invention with two 0.06 m² of platinum surface takes up 0.6 kA of current per anode at the current densities of 5 kA / m² previously used in technology. However, the electrolytic cell according to the invention can be operated with 1 kA as a permanent load and with 1.8 kA peak load. The current densities customary in the prior art for the production of peroxo compounds in cells (with separators) divided can be considerably exceeded in the electrolysis cell according to the invention. An appropriately equipped electrolysis system can therefore absorb peak electricity (e.g. night electricity) from electricity providers relatively quickly and flexibly; on the other hand, it can be operated down to 2 kA / m² without loss of load.

Because of its compact design, the electrolysis cell according to the invention only requires no space (space requirement). For example, for a 8.33 kA / m² electrolysis cell for the production of ammonium peroxodisulfate (APS) for 7 kA nominal current consumption - corresponding to a production of approx. 28 kg / h APS - only one parking space of 0.7 x 0.7 m² with a height of approx. 1 m is required. The cells usual up to now require a multiple of this space.

With an appropriate selection of the sealing material between the hollow electrode bodies, cell service lives can be reduced achieve that are at least 5 years; this considerably reduces the maintenance effort compared to the cells that are now in use. Suitable seals are, for example, seals made of Viton® (a heat and chemical-resistant, vulcanizable fluoroelastomer based on vinylidene fluoride-hexafluoropropylene copolymers); With these seals, the compression on the outside is limited by round or rectangular parts made of materials that are resistant to the electrolyte (eg ceramics, polyvinylidene fluoride, IT seals). In this way, a defined distance between the cell segments and a defined seal compression can be set.

The electrolytic cells according to the invention can also be operated without separators, e.g. for the production of potassium or sodium peroxodisulfate with simultaneous precipitation of the salts and for the production of sodium perchlorate (with the addition of sodium dichromate as cathodic top layer former).

The invention will now be explained in more detail with reference to the following examples, without being restricted thereto.

Examples example 1

An electrolytic cell according to the invention is made up of 7 anodes which are coated on both sides with 0.06 m² (0.255 x 0.235) platinum foil of 50 μm thickness on a 3 mm thick Ti sheet by hot isostatic pressing (HIP), and 8 cathode bodies, the active ones Cathode surfaces consist of expanded metal with a mesh size of 12.7 x 6 mm, web width 2 mm. It is equipped with a KIA membrane NAFION® 423 with a thickness of 330 µm (support fabric PTFE), which rests on the cathode and is set to a distance of 2.5 mm from the anode surface using an IT-supported VITON® seal.

The cathode surfaces were treated by sandblasting and chemical pickling in dilute sulfuric acid (1: 1) in such a way that the surface roughness was medium (gray color).

The anolyte consists of 0.2 M H₂SO₄, 2.6 M (NH₄) ₂SO₄, 0.9 M (NH₄) ₂S₂O₈ and an addition of ammonium thiocyanate (4.5 g / kg produced (NH₄) ₂S₂O₈ at 40 ° C). A solution of 1 M H₂SO₄ and 3.5 M (NH₄) ₂SO₄ is used as the catholyte.

With a current consumption of 7 kA corresponding to an anodic current density of 8.33 kA / m², ammonium peroxodisulfate is generated with a current efficiency of 92 to 96%; with a residence time of the anolyte in the electrode gap of 0.35 sec. adjusted with the help of a circulation pump. Over the course of 40 hours, 1.120 kg of product (dried, chemically pure) are obtained by crystallization, centrifugation, washing and drying. The voltage of the electrolytic cell remained in the range of 6.4 to 6.6 volts. This results in an energy requirement of 1.6 kWh / kg of product.

Example 2

In an electrolytic cell according to Example 1, 5 M H₂SO₄ is used as the anolyte. With current densities of 10 kA / m², corresponding to a current consumption of 9.4 kA, peroxodisulfuric acid is obtained at 8 ° C with a current efficiency of 88%, the maintenance of which requires the addition of NH₄SCN.

Example 3

To produce potassium peroxodisulfate, the electrolytic cell according to Example 1 is advantageously without a cation exchange membrane used under the following conditions:
Electrolyte: 2.1 M H₂SO₄, 1.4 M K₂SO₄, 0.3 M K₂S₂O₈;
1.5 g NaSCN / kg K₂S₂O₈ produced;
Current density: 9 kA / m², corresponding to 7.56 kA
Cell current;
Temperature: 25 ° C.
At a cell voltage of 5.9 volts, potassium peroxodisulfate is precipitated from the electrolyte (suspension electrolyte) with a current efficiency of 75% and removed from the electrolyte by means of customary separation and cleaning steps. Energy requirement: 1.56 kwh / kg.

Example 4

In an electrolysis cell according to Example 3, a solution of 3.0 M H₂SO₄, 2.8 M Na₂SO₄ and 0.2 M Na₂S₂O₈ with the addition of 12 g NaSCN per kg of Na₂S₂O₈ produced at 8 kA / m² is electrolyzed. Temperature: 25 ° C. The residence time of the electrolyte in the electrode gap does not exceed 0.4 s. If the electrolyte composition is kept constant, sodium peroxodisulfate (NPS) precipitates from the suspension electrolyte with a current efficiency of 62%. With a voltage of 6.2 volts, the energy requirement is 2.25 kWh / kg.

Example 5

In an electrolysis cell according to Example 3, sodium perchlorate is produced from NaClO₃ solution, the following conditions being met:
Initial values: 4 to 6 M NaClO₃, 0.5 to 1 M NaClO₄;
Final values: 0.3 to 0.5 M NaClO₃; 7 to 9 M NaClO₄;
a concentration of 2 to 5 g / l Na₂Cr₂O₇ is maintained in the electrolyte to form a cathodic cover layer;
Current density: 5 kA / m² (up to 15 kA / m² peak load);
Current consumption: 6 kA; Current efficiency: 95%;
Cell voltage: 4.6 volts; Energy consumption approx. 2600 kWh / t;
Temperature: 35 ° C; pH = 4.4 to 5.3.

Using a cation exchange membrane, the cells of the invention are also suitable for the production of HClO₄ according to the process of DE-PS 10 31 288.

In all electrolyses operated using a cation exchange membrane, pure hydrogen is formed on the cathode which, after having passed through a washing system, can be used directly for chemical or thermal purposes.

Claims (15)

1. Electrolysis cell of the filter press type for the production of peroxy or perhalogenate compounds of alternatingly arranged cathodes and anodes provided with electrolyte feeds, characterised in that the cathodes (1) and anodes (2) consist of quadrate-shaped hollow bodies between which are present frame-shaped seals (3) and which, via these seals (3), are connected liquid-tight and insulated from one another to give a cell pile, the cathode hollow bodies (1) are liquid- and gas-permeable, the anode hollow bodies (2) possess, above and below a platinum layer, openings for the introduction and removal of the anolyte and the effective anode surface is formed by the platinum metal layer of a composite anode of a valve metal substrate and a platinum layer present thereon, obtainable by hot isostatic pressing of a platinum foil on to a valve metal carrier.
2. Electrolysis cell according to claim 1, characterised in that the platinum foil possesses a thickness of 20 to 100 µm.
3. Electrolysis cell according to one of claims 1 or 2, characterised in that the valve metal is tantalum, niobium or titanium.
4. Electrolysis cell according to one of claims 1 to 3, characterised in that the valve metal carrier possesses a thickness of 1 to 6 mm.
5. Electrolysis cell according to one of the preceding claims, characterised in that, between the cathode hollow bodies (1) and the anode hollow bodies (2), are present separators by means of which the catholyte chambers are separated from the anolyte chambers.
6. Electrolysis cell according to one of the preceding claims, characterised in that the separator consists of a fluorinated, sulphonic acid group-containing cationic exchanger membrane.
7. Electrolysis cell according to one of the preceding claims, characterised in that the separator lies on the perforated, liquid- and gas-permeable cathode surface.
8. Electrolysis cell according to one of claims 5 to 7, characterised in that the separator is installed at a distance of 0.5 to 5 mm from the platinum anode surface.
9. Electrolysis cell according to one of the preceding claims, characterised in that the effective cathode parts (12) of the cathode hollow body (1) are perforated.
10. Electrolysis cell according to one of the preceding claims, characterised in that the effective cathode parts (12) are roughened and/or provided with a coating reducing the cathode polarisation.
11. Electrolysis cell according to one of the preceding claims, characterised in that the openings for the introduction and removal of the anolyte present above and below the platinum layer are slit-shaped openings or are formed by a plurality of bores lying next to one another.
12. Electrolysis cell according to claim 11, characterised in that the width of the slit-shaped openings or the diameter of the bores becomes larger seen from the electrolyte introduction side (52) towards the opposite side.
13. Electrolysis cell according to one of the preceding claims, characterised in that the anode hollow bodies are provided with inlets and outlets for a cooling agent (71,72) and that they consist of three chambers of which the upper and lower ones serve for conducting the electrolyte and the middle one for cooling the rear side of the active anode surface.
14. Electrolysis cell according to one of the preceding claims, characterised in that the sealing material for the frame-shaped sealings (3) is a vinylidene fluoride-hexafluoropropylene co-polymer.
15. Use of an electrolysis cell according to one of claims 1 to 14 for the production of peroxy and perhalogenate compounds.

Images