DD142456A5 - METHOD AND DEVICE FOR CHLORINCALIELECTROLYSIS - Google Patents

Description

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description Title of the invention

"Method and apparatus for chlor-alkali electrolysis" Fields of application of the invention;

The invention is in the field of large-scale production of chlorine and alkali by electrolysis of an alkali metal chloride solution

characteristic of the known technical solutions;

Chlorine and caustic lye are widely produced by the basic industry, and they are almost exclusively produced by electrolytic means from aqueous solutions of alkali metal halides, especially sodium chloride, for various industries. This electrolysis takes place primarily with diaphragm electrolysis cells. " In the diaphragmatic electrolysis process, the saline solution is continuously fed into the anode chamber, penetrating the diaphragm, which is usually asbestos flooded on a broken cathode. To reduce the migration back of the hydroxyl ions, the feed rate is adjusted so that the flow through the diaphragm is above the reaction rate, yielding a catholyte with as little unreacted IT sodium chloride as possible. The hydrogen ions are discharged at the cathode as hydrogen gas. "The catholyte is the

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lye, especially sodium hydroxide solution, and contains unreacted sodium chloride and other impurities; it must be concentrated and purified in order to come to a marketable caustic soda or sodium chloride, which can be recycled back into the process · The evolution of hydrogen requires high voltages, which decreases the current efficiency of a cell, equivalent to lower effectiveness with respect to caustic soda and chlorine »

With the advent of dimensionally stable anodes and various coating compositions, which reduced electrode spacing, the cells became more efficient in terms of current efficiency.

Hydraulically impermeable membranes in electrolysis cells largely permit the selective migration of certain ions, so that impurities can be excluded from the desired product. This saves on expensive cleaning and concentration stages. Recently, great progress has been made in improving the effectiveness of the anode side and the membrane or membrane However, so far the cathode side has received less attention in order to achieve a further increase in the current efficiency of the cathodes. This would, however, result in a considerable energy saving in the production of chlorine and caustic. In a conventional electrolytic cell with anode, Cathode and between a diaphragm runs at the cathode following reaction:

2H ₂ O + 2e ~ -> H ₂ + 2 OH * "·

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The potential of this reaction over a standard hydrogen electrode is -0.83 V · The desired reaction under ideal conditions would be:

2H ₂ O + O ₂ + 4e → 4OiT,

whose potential is +0.40 V, in other words, this theoretically means a voltage saving of 1.23 V. »The energy required for the hydrogen, which is an undesirable reaction in conventional electrolysis cells, can not be effectively compensated in the industry by utilization of the hydrogen formed, since it is a generally undesirable product in this reaction. Although some applications have been found for this excess hydrogen, but do not make a distinction between the cost of electrical energy to develop the hydrogen, so that - if the hydrogen evolution could be avoided - electrical energy can be saved and thus the cost price for chlorine and Lye would be relieved «

An oxygen electrode provides a way to inhibit this reaction by consuming electrochemically active oxygen to form water and delivering electrons to the cathode according to the following equation:

2 H ₂ O + O ₂ + Ae " " - »» 4 OH * "·

It is readily apparent that this reaction is all the more energy efficient, as the vaporization does not take place at the cathode and the potential is reduced. This is achieved by feeding a gas containing acid, such as air or oxygen

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Enriched air, to the oxygen side of a Sästoffstoffelektrode, where the oxygen has easy access to the electrolytically active surface, so that this oxygen is consumed in the manner indicated above. However, this requires a somewhat different construction of the electrolytic cell, by providing a Sästoffstoffkammer on the cathodic side of the cathode, in which the oxygen can be introduced.

As such, acid-electrolyte electrodes are well-known after NASA's extensive development work on fuel cells using an oxygen electrode and a hydrogen anode since 1960 has resulted in the generation of electric power for spacecraft by reacting hydrogen with oxygen Supported development work on various components of fuel cells, including the acidic electrode, the conditions and environment in which an oxygen electrode works are very different between the fuel cell and a chlor-alkali electrolytic cell. While much of the new technology is from NASA projects for the Chloralkali electrolysis of value, in particular with regard to the development of an oxygen electrode ,, is further development work to adapt the oxygen electrode to the Um required as is the case with chloralkali electrolysis cells ©

It has already been considered to use oxygen electrodes in chlor-alkali electrolysis cells in order to improve their effectiveness, which is then theorized.

..., r: «o '*; fW '-'.

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table would be possible; However, the oxygen electrodes found little interest in common effective and economical electrodes in electrolysis cells for the production of chlorine and alkali. While it has been recognized that a suitable oxygen electrode is necessary for the realization of the theoretical efficiencies, in the chloralkali electrolysis special process measures are necessary, which differ from those in fuel cells, since an electric potential is sought, which is responsible for the formation of chlorine and alkali and, moreover, oxygen-containing gas must be supplied to the electrochemical reaction. However, it has been found advantageous to develop a procedure for oxygen electrodes which are directed to the optimization of theoretically achievable efficiencies with such oxygen electrodes in chloroalkali cells.

Kiel of the invention

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The object of the invention is therefore a procedure for oxygen electrodes for improving and optimizing the energy yield in the context of chloralkali electrolysis. One measure according to the invention is to adjust the pressure of the gas to be fed to the oxygen electrode. Another feature is the adjustment of the total gas flow to the oxygen electrode additional feature is the wetting of the gas stream to optimize the yield and increase the life of the oxygen electrode "Finally, the Perahaltung of contaminants, such as CO ₂ > to provide from the oxygen electrode to be supplied gas

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Explanation of the essence of the invention

The invention thus relates to a chloralkali electrolysis in a cell containing a cathode chamber and an anode chamber separated by a membrane or an oxygen chamber separated from the cathode chamber by an oxygen electrode, the alkali metal halide solution being fed into the anode chamber and an aqueous electrolyte being fed into the cathode chamber and one introduces oxygen-containing gas into the oxygen chamber at an overpressure with such a flow rate that provides oxygen in a superstoichiometric amount for the reaction. · From the anode chamber is derived halogen gas and from the cathode chamber alkali hydroxide solution «While maintaining an overpressure in the oxygen chamber maintains, the oxygen-depleted gas is discharged from the cathode chamber »

It has been found that it is desirable to introduce high concentration, molecular oxygen-containing, condione dioxide-depleted gas into the oxygen chamber. For the chlorine and alkali extraction is fed as anolyte alkali metal chloride solution and the oxygen chamber a carbon dioxide-free oxygen-containing humidified gas supplied with pressure at such a flow rate that the 1.5 to lOfache stoichiometrically required amount of oxygen is made available, "Here, the moisture content of the oxygen-containing Regulated gas; In addition, the oxygen pressure in the oxygen chamber is controlled and the feed rate of the oxygen-containing gas is ",

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The invention will be explained in more detail with reference to the accompanying figures.

Pig * 1 is a schematic cross section of a cell used in the invention and

Fig. 2 is a diagram in which the relationship

between the total flow rate, the pressure difference and the cathode potential can be taken *

The electrolytic cell 12 after 3 ig # 1 is monopolar; such cells - usually in larger numbers - are on a common foundation or the like, as is common practice "The cell itself may consist of a metallic or plastic material, such as steel, nickel, titanium or other valve metals, but also polyvinyl chloride, Polyethylene, polypropylene, fiberglass or many other materials * Yentilia metals may be called aluminum, molybdenum, kiob, titanium, tungsten, zirconium and their alloys *

In the cell 12 is the anode 14, partition or membrane 16 and the cathode 18, so that in the cell, the anode chamber 20, cathode chamber 22 and Säuerst off chamber 24 are formed.

The anode is generally made of a metal material, but may also be graphite, as was formerly common. However, today, generally active materials which are capable of withstanding the anolyte are employed, such as yenmetal metals. Preferred for this purpose Cost, Availability and Electrochemical Properties Titanium * The titanium substrate or the G-round body can

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Such as solid sheet metal, expanded metal, mesh or mesh with a high open-area or porous titanium with a density of 30 to 70 $ of pure Titaas, as obtained by cold compacting titanium powder. Porous titanium is preferred in some cases, primarily because of its long durability and structural integrity. Optionally, one can reinforce the porous titanium with a titanium mesh for large area electrodes.

In general, this base body or the substrate has a coating which protects it against passivation, so as to obtain a so-called dimensionally stable anode in this way. Many of these coatings contain a noble metal, noble metal oxide alone or together with a valve metal oxide or other electrocatalytically active, but corrosion resistant material. These dimensionally stable anodes are known and widely used (U.S. Patent Nos. 3,236,756, 3,623,498, 3) 711 385, 3 751 296 and 3 933 616) o Another known coating consists of tin, titanium and ruthenium oxides (US Pat. Nos. 3,776,834 and 3,855,092). Other known coatings include tin and antimony in combination with titanium. and ruthenium oxides (US Pat. No. 3,875,043) and tantalum iridium oxide (US Pat. No. 3,878,083) *

As a partition or membrane, a wide variety of products can be used. Primarily hydraulically impermeable cation-exchange membranes are suitable and which specifically thin layers based on fluorinated copolymers having pendant sulphonic acid groups _e laterally fluorinated Such copolymers are derived from monomers:

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(D,

their SOgF groups are converted into sulfonic acid groups, and monomers of the formula

where R is the grouping

U)

and R ^{1 is 1} Ioror or a fluoroalkyl group having 1 to 10 carbon atoms, Y is fluorine or CF ,, X is fluorine, chlorine or CF ₅ and X ^{1 is} X or

(B)

and m can be 1, 2 or 3, η is O or 1 and a is O or 1 to 5 * The copolymers have w her oily units of the formulas

(3)

and

The equivalent weight of these copolymers should be between about 800 and 1600. Preferred are copolymers having a water absorption of at least about $ 25, since higher cell voltages are required for a given current density with less water absorption. "The membrane starch (unlaminated) of at least about 0.2 mm requires higher cell voltages, resulting in lower current efficiency «

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Because of the 'large surface area of the membranes in large scale cell plants, the membrane sheet is laminated or impregnated onto a hydraulically permeable, electrically nonconductive, inert reinforcement, such as a woven or nonwoven material of asbestos fibers, glass fibers, polytetrafluoroethylene, or the like. to have an unbroken membrane sheet on at least one side of the reinforcement, thereby largely preventing leakage (U.S. Patent Nos. 3,041,317, 3,282,875, 3,624,053, 3,784,399, British Patent No. 1,184,321 to JTAi ¹ IOH ¹¹⁾ · ·

Copolymers of formulas (3) and (4) may also contain other ion-exchanging groups, such as the carboxyl group in either the acid, ester or salt form, such that the copolymers contain SO ₂ I ¹ COOR ² instead of SO ₂ and R ^{2 is} hydrogen, a Alkali metal ion or an organic radical is basically one can say that such membrane materials may contain exchange groups or functional groups which are converted into Au stau shear group η, or a functional group in which an exchange group can easily be introduced, such as Residues of carbonic acid, nitrogen-containing acids, silicic acid, phosphoric acid or telluric acid or their salts or esters. Sulfuric acid, chloric acid, arsenic acid, selenic acid

Also suitable as the membrane material is a scaffold copolymer of tetrafluoroethylene and hexafluoropropylene and grafted onto this scaffold. Styrene and ot-methylstyrene in a ratio of 1: 1. These graft copolymers are then sulfonated or carbonated to give the ion exchange properties. Scaffolding

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such membrane materials sit high chemical resistance.

Another membrane material is polymers with pendent carboxylic or sulfonic acid groups whose backbone chain is derived from the polymerization of a polyvinyl aromatic compound with a monovinyl aromatic compound in an inorganic solvent under conditions such that evaporation of the solvent is prevented so as to generally obtain copolymeric substances. Basically, however, products made of polyvinylaromatics correspond to $ 100.

Suitable polyvinylaromatics are: divinylbenzenes, divinyltoluenes, divinylnaphthalenes, divinyldiphenyls, diphenylvinyl ethers, their substituted alkyl derivatives, such as dimethyldivinylbenzenes and similar polymerizable aromatics, which are polyfunctional with respect to the vinyl groups.

As monovinylaromatics which are generally present as impurities in the commercially available polyvinylaromatics, mention may be made of: styrene, the vinyltoluene isomers, vinylnaphthalenes, vinylthenylbenzenes, vinylchlorobenzenes, vinylxylenes and their oO-substituted alkyl derivatives, such as ot-methylvinylbenzene. If highly pure polyvinylaromatics are used. For example, it is sometimes desirable to add monovinyl aromatics such that the polyvinyl aromatics make up 30 to 80 mole percent of the polymerizable species

To dissolve the polymerizable material prior to polymerization are solvents which are inert for this are, d _u h _o en not with & monomers or poly

, 1 Il! . ( r \

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mereη to react, and a boiling point of at least 6O ⁰ C possession medium are miscible are «

have at least 6O ⁰ C and with the SuIfonie

The polymerization can be carried out in a conventional manner using heat, pressure or catalysts and is carried to an insoluble, infusible gel within the entire volume of the solution. These gels are then sulfonated to such an extent that there are no more than 4 equivalents of sulfonic acid groups per mole of polyvinyl aromatic in the polymer and not less than 1 equivalent of sulfonic acid groups per 10 moles of poly- and monovinyl aromatics in the polymer. These membrane materials can also be applied to reinforcements (US Pat. Nos. 2,731,408, 2,731,411, 3,887,499 - "IONICS CR6").

The membrane materials can still be improved by a chemical surface treatment. In general, the laterally pendant groups are reacted with substances which give a less polar bond and therefore are able to absorb several water molecules by hydrogen bonding. This leads to a narrowing of the pore size of the membrane material, so that less water of hydration with the cations are transferred through the membrane. Thus, the pendent groups can be reacted with ethylenediamine to link two via the two nitrogen atoms of ethylenediamine. With a membrane thickness of 0.18 mm, the surface treatment should be done to a depth of about 15 / μm on one side by adjusting the reaction time. This gives good conductivity and cation exchange capacity with low residual hydroxyl ion migration in conjunction with water migration

r f.Λ η -in 7 ü ***; £. / 7>S; -:

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The partition 16 may also be a porous diaphragm made of any material resistant to the electrolyte with suitable bubble pressure and electrical conductivity. An example of this is an asbestos diaphragm which is either in the form of an asbestos paper or deposited as an asbestos web from a paser slurry in the vacuum Asbestos fiber material can be added as a further modification of plastics, in particular fluorinated, in the context of the production of the diaphragm. However, it is also possible to render plastics themselves porous to such an extent that they possess the properties of a diaphragm. However, this is all known in the field of chloralkali electrolysis.

The third essential part of the electrolysis is the cathode. In this case, according to the invention, it is necessarily an acid-substance cathode. An oxygen electrode can be defined as an electrode to which molecular oxygen is supplied to lower the voltage below the fourth necessary for the evolution of hydrogen. The body for an oxygen cathode is generally a current drain, generally made of a metal material or metal carbon may also be present. This metal material is generally cheap, commonly available building materials of low cost, easy availability, and resistance to chemical corrosion as occurs at the cathode of electrolytic cell. Examples include iron, nickel, lead and tin and various alloys, such as mild steel, corrosion-resistant steel, bronze, monel and cast iron, this body is preferably compared to the

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Catholytes are stable and have excellent electrical conductivity. "In general, a porous material such as a mesh is used for the acidic cathode. Nickel, but also tantalum, titanium, silver, gold, and clad bodies are preferred in terms of cost price, durability, and required stress , On one side of this body is a coating of a porous Materrals either compressed as such, to adhere to the llickelgrundkörper, or by being fixed thereon by means of a binding substance, so as to obtain a porous base material. A preferred porous base material is coal. Within the pores of the oxygen cathode is fixed a catalyst for combining molecular oxygen with water molecules to form hydroxyl groups. These catalysts are generally those based on silver or a platinum metal such as palladium, ruthenium, gold, iridium, rhodium, osmium or Rhenium; but may also be semi-precious or non-noble metals, alloys, metal oxides or organometallic complexes. In general, such electrodes contain a hydrophobic substance to prevent wetting of the electrode. Of course, the porosity of the charcoal, the amount and type of catalyst of influence on the voltages required for the electrolysis and the achieved power efficiencies and lifetimes (US-PS 3 423 247).

As noted above, in the cell of the anode, partition and cathode three chambers are formed, namely the anode chamber, the cathode chamber and the oxygen chamber. In the chloralkali electrolysis, the anode chamber is fed via the salt feed line

·. j η ί η "ιr;Q> Ί Π-. \>,

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26 The alkali halide solution is supplied. The chlorine extraction is primarily sodium or potassium chloride. The catholyte is introduced via the feed line 28, it must contain sufficient water molecules to provide the required hydroxyl ions for the reaction Oxygen supply 30 is a acid-containing gas, preferably introduced from carbon dioxide-freed and humidified air or humidified pure oxygen, Ohlor is discharged through the halogen discharge line 32 and lye on the Katholytableitung 34 · The deoxygenated gas or the residual oxygen leave the oxygen chamber above 36 ,

In the oxygen-depolarized three-chamber line for chlor-alkali electrolysis used according to the invention, a pressure gradient prevails across the porous cathode after the pressure in the oxygen chamber is higher than in the cathode chamber. The higher pressure, which need not be overpressure, but de facto a negative pressure , promotes mass transfer of oxygen-containing gas into the cathode, and thus prevents oxygen depletion in the reaction zone within the cathode, thereby extending the life of the cathode. This pressure difference is based on the partial pressure of the oxygen when pure oxygen is not used.

If the supply of depolarizing gas into the oxygen chamber is increased, the mass transfer of oxygen at the reactive sites of the cathode is improved. This is especially important when pure oxygen is not used. Molecular oxygen is passed through the catalyst site within the porous body of the cathode

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consumed. When oxygen is consumed, additional quantities must be constantly available and, consequently, it must be constantly fed to the oxygen chamber 24 oxygen-containing gas. The preferred feed is between 0 and 10 times the stoichiometrically required oxygen, with about 2.5 being preferred.

If air is used as the oxygen-containing gas, it is necessary to remove CO ₂ before it is introduced into the oxygen chamber, because this leads to the formation of carbonate deposits on the cathode, which very significantly influences the service life and the current yield, including the required cell voltage. If the main part of the COg is removed, the problem is largely solved »

But even the presence of nitrogen in the air can cause problems, since it dilutes oxygen, penetrates into the pores of the cathode and must first diffuse back from these, since it is not consumed by the reaction. As a result, the activity of the catalyst is reduced within the pores of the cathode, so that a deterioration of the current efficiency and an increase in the cell voltage are the result. This disadvantage can be largely overcome by significantly increasing the air supply, thereby reducing the cell voltage to a minimum and increasing the current efficiency to a maximum.

The oxygen cathodes in electrolysis cells, the evaporation and the mass transport problems may provide ") This can be overcome by lifting up the relative Eeuchte the oxygen-containing gas by passing it through water at a temperature of 40 to 70 ⁰ C.

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flow, giving it a relative humidity of about 85. This reduces the evaporation and drying of the cathodes, which can lead to a lifting of the porous material from the massive body of the cathode and thus to an increase in the mass transfer through the porous surfaces · The gas temperature should be about 40 to 90O ⁰ C.

Humidifying the gas seems to have another effect. The evaporation, which leads to a mass transfer from the water of the cathode chamber in the cathode, causes crystallization of pesticides from the electrolyte, which can significantly affect the life of the cathode by clogging of the pores. By moistening the oxygen-containing gas, the evaporation or evaporation is largely suppressed by a liquid transfer is limited from the Kathodenkanmer.

If the dew point of the gas supplied to the cathode is higher than the surface temperature of the cathode, water condenses on the cathode surface. However, this places occupy the oxygen mass transfer, so that a considerable drop in power of a particular oxygen cathode is observed. Therefore, the dew point of the gas must be adjusted in consideration of these two adverse effects, i. the dew point must be a few degrees above the surface temperature of the cathode, and the relative humidity must reach such a value that the evaporation is suppressed. It should be noted that higher operating temperatures reduce the required cell voltages, but also shorten the life of the cathode. As optimum, a temperature of

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60 to 85 ⁰ C ·

Aüsführungsbeispiele

The invention will be further illustrated by the following Seispiele.

example 1

An oxygen cathode according to US Pat. No. 3,423,245 was used in an electrolytic cell in such a way that the side of the acidic substance chamber and the nickel side of the cathode chamber face away from one another. A dimensionally stable anode with a catalyst layer of tantalum and iridium oxides was arranged at a distance of about 7 cm parallel to the oxygen cathode. Into the oxygen chamber was fed at a flow rate of about 790 cnr / ^mi - & C0 ₂ -free air, d _e h. about 21 times the stoichiometric amount for a current density in the cell of 15 »5 A / dm

The acidic chamber was set to about 110 g / cm (gauge) whereupon the oxygen bleed 36 was correspondingly throttled. This pressure was maintained during the experiment. As the catholyte, a caustic containing about 400 g / l NaOH was introduced into the cathodic chamber and continuously moved with the help of a magnetic stirrer

The cathode was conditioned by electrolysis at 60 ^° C., a current density of about 5 A / dm, for one day. After completion of the conditioning, the current density was increased to about 15.5 A / dm and the air feed, pressure, temperature and current density were kept constant during further testing. It will

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pointed out that these experiments were carried out only with sodium hydroxide solution as the electrolyte, but not worked as Chloralkalizelle. However, the results obtained thereby largely correspond to those obtained in operation as a chloralkali electrolytic cell, since the anode or the electrode spacing are not critical factors, the anode must only be resistant to "the alkali"

The cathodes were conditioned at low current density, since it was believed that the catalytic platinum layer was partially oxidized during storage of the cathodes prior to use. This conformation greatly restores catalytic efficiency without adversely affecting the cathode. Slow penetration of less noble catalysts, however, can be detrimental

The current connection was made on the side of the cathode, because of this it was easier to obtain good electrical contact than on the coal side. The cathode voltage was determined to be mercury / mercury oxide standard and changed from 0.31 on the first day to to -1.03 on the 98th day, then the attempt was canceled. The lifetime of the cathode under these conditions was 2 350 tu

Example 2

In a modification of Example 1, an air flow rate of 220 cnr / mia, corresponding to approximately 6 times the stoichiometric amount of oxygen, was maintained in this eel. The reference voltage changed from -0.43 at the first Sag to -2.27 at 52 _O day "The

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Cathode life was only 1 240 h ". This shows that at higher flow rates the potentials are lower and the lifetime is better «

Example 3

In a modification of Example 1, oxygen was passed to the oxygen chamber at a flow rate of 150 c / min. This corresponded to about 19 times the stoichiometrically required amount of oxygen for a current density of 15 »5 A / dm." In this Pail, the power connection was made on the coal side of the cathode. The cathode was conditioned at .... 'o. ·

a current density of 5 A / dm for about 24.5 hours.

Then, the current density became 10 A / dm for 24 hours

ο increased and finally to about 15.5 A / dm, being held during the experiment · The reference voltage changed from the 2nd lag from -0.38 to -0.42 at the 293. lag. The experiment was aborted only because it detected a peeling of the cathode. Cathode life: about 70.3oh. It is also emphasized again that at higher flow speed and greater Savserstoffangebot at a lower potential, the life of the cathode is slightly improved.

Example 4

According to Example 1, an oxygen cathode at about 85 ⁰ C and a current density of 31 A / dm was tested with an electrolyte containing 300 g / l UaOH, in this Pail as membrane the above-described ITAS ¹ IOlT was applied to this experiment were various Cathodes used and the available Sellenspannungea determined and found from the percentage voltage difference by avoiding the evolution of hydrogen

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cathode av. Cell voltage V Voltage reduction V # Stablnetζ 4,335 O-electrode Pt catalyst Oo 3,039 1,296 30 2 O electrode Ag catalyst Oo 3,306 1,029 24 2 O electrode Ag catalyst air 3,536 0,799 18

As a result, oxygen catalysis exhibits superior performance over a rod catalyst that undergoes hydrogen evolution.

Example 5

According to Example 1, studies were made on an acidic cathode using air - without removal of CO ₂ - "The cathode was first supplied with oxygen and then switched to air" After less than 48 hours under air supply, the cathode had precipitated. This behavior is typical of cathodes, which air is supplied without first COp has been removed _o Hence the need for the removal of CO ₂ from the oxygen = containing gas to extend the life of oxygen cathode · The Operating conditions are of examples 1 to 3 · The following table shows the cell voltages and the loading voltages ο

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Cell voltage ν SEP versus Hg / HgO reference voltage Remarks -0.222 at 15.5 A / dm ² switched to compressed air 1.168 -0.255 at 5 A / dm ² "2 -0.212 1,044 -0.124 -0.354 0.995 -0.112 - -0.347 1,790 -0.461 Destroyed the cathode 1,768 -0.490 1,944 -1,066 1,940 2,034 2,120 2,745

Examples 6 to 12

According to Example 1 acidic cathodes were examined at varying air flow rate or varying pressure (Pig · 2) "From the diagram of Pig" 2 it follows that the cathode potential decreases with increasing flow velocity and with increasing pressures. In each Pail the air was moistened and free of carbon dioxide »

The experiments were terminated respectively when the reference voltage reached -1 and when exfoliation of the various layers occurred at the cathode. The flow rate of air or oxygen was plotted on a data sheet on the cathode behavior of the cells, namely the height in mm of a steel ball in a flow meter "Matheson # 601" (except example 3 "where number 602 was used)" The readings , were then placed in a flow

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speed cur / min converted using a calibration curve. The examples show the results in the cathode experiments in which the pressure difference was on the order of 200 g / cm. The difference in pressure is understood to mean the difference between the pressure on both sides of the cathode , In this case, the difference of the pressure in the oxygen chamber (100 g / cm gauge) and the average hydrostatic pressure which the electrolyte exerts on the other side of the cathode (10 g / cm) is about 100 g / cm. The hydrostatic pressure is calculated by multiplying the density of the electrolyte (1.33) by the mean height above the cathode, which is about 76 mm. It is estimated that the appropriate pressure difference may be 0.25 to 500 g / cm. It is believed that for cathodes operating at atmospheric pressure, or where the pressure in the oxygen chamber is not allowed to rise above atmospheric pressure, the cathode life is less than 1240 hours (Example 2). It should be noted that the examples refer exclusively to caustic soda as the electrolyte and were not operated as Chloralkalielektrolysezellen, since up to this time commercially were no porous cathodes. All the above experiments were carried out at a current density of 15.5 A / dm and this current density was used for the standardization; therefore, it does not represent an optimal value. It is expected that current densities of 31 A / dm and above can also be used. The experiments according to Examples 1 to 3 were carried out at 60 ⁰ C. Again, this is a value for standardization.

Claims (9)

invention claims 1) A method for Chloralkalielektrolyse in a cell with an anode chamber, a cathode chamber and in between a membrane or a diaphragm, characterized in that one introduces an oxygen chamber, which is located behind an oxygen cathode, under pressure molecular oxygen-containing gas, wherein the flow rate so that an excess of the amount of oxygen needed stoichiometrically for reaction with the hydrogen produced at the cathode is available at all times, and maintains an overpressure in the oxygen chamber. 2) Process according to item ¹ »characterized in that one maintains an overpressure of 0.25 to 500 g / cm ² . 3) Method according to item 2, characterized g e - Ice'na · records that one maintains an overpressure of 5 to 250 g / cm. 4) method according to; Item 3 », characterized in that one maintains an overpressure of 100 to 200 g / cm. / 2 211 S52 5) Method according to item 1 to 4, characterized in that maintaining such a flow rate in the oxygen chamber, that the 1.5 to 10 times stoichiometric Säuerst offmenge is available. 6) Method according to item 5, characterized in that a flow rate is maintained in the oxygen chamber such that 1.5 to 5 times the stoichiometric amount of oxygen is available 7) Process according to item ¹ to 6, characterized in that air is used as the oxygen-containing gas after deposition of carbon dioxide and optionally moistening. 8) Process according to item 7, characterized in that e η η is characterized in that one uses an oxygen-containing gas which is saturated with water vapor at 40 to 70 ⁰ C » 9) electrolytic cell for carrying out the method according to item 1 to 8 with an anode chamber with anode, a cathode chamber with cathode and in between a diaphragm or a membrane, characterized geke η η eichnet that the cathode is an oxygen cathode (8) and they are the oxygen chamber (24) into which an oxygen-containing, preferably humidified and preferably CO ₂ -free gas is supplied (30) and the oxygen-depleted gas is discharged again (36), and means for adjusting the moisture content, the pressure and the flow rate of the oxygen-containing Gases in the sow are first off chamber before eaten Hierza JLieiteo drawings