EP2495353A2 - Method for operating an oxygen-consuming electrode - Google Patents

Abstract

Operating oxygen consuming electrode as cathode for electrolysis of alkali chlorides or hydrochloric acid, in an electrochemical cell, comprises at least partially heating oxygen containing process gas that is supplied to electrode, using a heat source of electrolysis, preferably by heat exchange with a process stream obtained by electrolysis or with a process stream that is reprocessed subsequent to electrolysis, before contacting with the oxygen consuming electrode, to a temperature that is not > the temperature of cathode chamber in the cell or to less than 50[deg] C, preferably less than 10[deg] C.

Description

The invention relates to a method for conditioning an oxygen-containing process gas in an electrochemical process, in which a gas diffusion electrode, in particular an oxygen-consuming electrode is used. Electrochemical processes here are in particular the chlor-alkali and hydrochloric acid electrolysis with oxygen-consuming electrodes.

By using gas diffusion electrodes, energy savings can be achieved with different electrochemical processes, moreover, the formation of undesirable or uneconomical by-products is avoided.

An example of a gas diffusion electrode is the Oxygen Consumption Electrode (SVE). Oxygen-consuming electrodes are used, inter alia, in the chloralkali electrolysis, hydrochloric acid electrolysis, fuel cell technology or in metal / air batteries.

The invention is based on known per se oxygen-consuming electrodes, which are formed as gas diffusion electrodes and usually comprise an electrically conductive carrier and a gas diffusion layer with a catalytically active component.

Various proposals for operating the oxygen-consuming electrodes in electrolytic cells in technical size are known in principle from the prior art. The basic idea is to replace the hydrogen-developing cathode of the electrolysis (for example, in the chloralkali electrolysis) by the oxygen-consuming electrode (cathode). An overview of the possible cell designs and solutions may be published by Moussallem et al "Chlor-Alkali Electrolysis with Oxygen Depolarized Cathodes: History, Present Status and Future Prospects", J. Appl. Electrochem. 38 (2008) 1177-1194 , are taken.

Prior art oxygen-consuming electrodes are used in various arrangements in electrochemical processes, such as the generation of electricity in fuel cells or in the electrolytic production of chlorine from aqueous solutions of sodium chloride. A more detailed description of the chlorine-alkali electrolysis with oxygen-consuming electrode is located in Journal of Applied Electrochemistry, Vol. 38 (9) pages 1177-1194 (2008 ). Examples of electrolysis cells with Sauerstoffverzehrelektroden are the writings EP 1033419B1 . DE 19622744C1 and WO 2008006909A2 refer to.

The electrolysis of sodium chloride or hydrochloric acid is operated on an industrial scale in plants with capacities of up to more than 1 million t chlorine / year. In addition to the electrolyzers, the plants also contain facilities for the treatment of chlorine and caustic soda and, if a conventional electrolysis without SVE is operated, for hydrogen. Descriptions of the work-up procedures can be found, for example, in the sections "Chlorine" and "Sodium Hydroxide" Online edition of Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag GmbH & Co. KG, Weinheim ,

Another development direction for the use of SVE technology in chlor-alkali electrolysis is the ion exchange membrane, which separates the anode from the cathode compartment in the electrolytic cell, without attaching sodium hydroxide solution directly to the SVE. This arrangement is also referred to as zero gap arrangement in the prior art. This arrangement is also commonly used in fuel cell technology. The disadvantage here is that the forming sodium hydroxide must be passed through the SVE to the gas side and then flows down to the SVE. It must not come to a clogging of the pores in the SVE by the sodium hydroxide or crystallization of caustic soda in the pores. It has been found that very high sodium hydroxide concentrations can also occur in this case, with the ion exchange membrane not being stable in the long term against these high concentrations ( Lipp et al, J. Appl. Electrochem. 35 (2005) 1015 - Los Alamos National Laboratory "Peroxide formation during chlorine-alkali electrolysis with carbon-based ODC ").

A process for recycling the unconsumed oxygen from the electrolysis into the electrolysis is known in DE10149779 A1 described. In the in DE10149779 A1 described method, the added fresh oxygen is expanded in a gas jet pump, the resulting suction pressure is used to suck the coming out of the electrolysis cell, unused oxygen. In the nozzle there is an intimate mixing of fresh oxygen with recycled oxygen.

In principle, a small amount of hydrogen can be formed in all electrolyses with SVE by side reaction, which then leaves the electrolysis cell with the excess oxygen. In the return of the coming out of the cell, hydrogen-containing oxygen, the hydrogen accumulates and it can lead to ignitable mixtures. To avoid a dangerous accumulation of hydrogen, but also a disturbing enrichment of other foreign gases, a portion of the gas stream leaving the cell is removed from the circulation as purge gas. Another safeguard against dangerous enrichments of hydrogen is the in DE 10342148 described removal by means of a catalytic oxidation.

In DE10159372 A1 For example, heating and humidification of the process gas are referred to as possible embodiments of an electrochemical half-cell with SVE, but without further disclosure of accurate temperature control, concentrations, and the like.

The heating of process gases generally takes place in process engineering by means of a heat exchanger, which is heated by an external energy source such as steam. The temperature of the process gas is controlled by appropriate control devices. The control equipment requires additional investment, the use of an additional external energy source also increases the investment costs and also increases the overall energy consumption of the process.

The object of the present invention is to provide a process for the heating of process gas for use in electrolysis cells with oxygen-consuming electrodes, which overcomes the above disadvantages.

The specific object of the present invention is to provide a method which enables the heating of oxygen-containing starting gas in the electrochemical production of chlorine by means of electrolyzer with SVE with minimal equipment and control engineering effort and without additional energy input.

A particular object of the present invention is to provide a method which enables heating and additionally humidification of oxygen-containing educt gas in the electrochemical production of chlorine by means of electrolyzer with SVE with minimal equipment and control engineering effort and without additional energy input

The object is achieved by using existing heat sources for heating the oxygen-containing process gas in the electrolysis process itself or in the subsequent work-up procedure.

The invention relates to a method for operating an oxygen-consuming electrode as a cathode for the electrolysis of alkali chlorides or hydrochloric acid - in the case of hydrochloric acid by reacting protons and oxygen - at the electrode in an electrochemical cell, characterized in that the oxygen-containing process gas supplied to the electrode at least partially using a heat source from the electrolysis, in particular by heat exchange with a selected process stream, which is obtained from the electrolysis, or with one of the electrolysis subsequent reclaimed process stream is heated prior to contact with the oxygen-consuming electrode to a temperature which corresponds at most to the temperature of the catholyte in the cell or by less than 50 ° C, preferably less than 20 ° C, more preferably less than 10 ° C. below.

The oxygen is typically supplied in excess due to the process, unused oxygen is removed from the cell again. The excess of oxygen can be chosen over a wide range, usually the excess is usually 5-100% of the amount required for the reaction. The oxygen discharged from the cell is mixed with fresh oxygen and returned to the cell. To avoid an accumulation of undesirable foreign gases, a small part, usually 0.5-20% of the oxygen removed from the cell, is removed from the circulation in a purge stream.

Pure oxygen (> 99% by volume O ₂ ) is preferably used for the supply of fresh oxygen. However, it is also possible to use a gas with a lower oxygen concentration (90-99% by volume O ₂ ) or oxygen-enriched air (30-99% by volume). 95 vol .-% O ₂ ) are used. In principle, the use of air in the chlor-alkali electrolysis with SVE conceivable, in which case especially CO ₂ -free air should be used to avoid the alkali carbonate formation. The terms "process gas" and "reactant gas" given in the following explanations each include oxygen-containing gas mixtures, including pure oxygen. Oxygen is obtained technically from air by liquefaction and subsequent distillative separation (cyrogenic separation), by selective absorption / desorption on suitable absorbents (PSA). Another, less common method is the separation by membranes. The cryogenic separation usually provides a very pure oxygen of> 99.9 vol .-% O ₂ , while with the pressure swing or membrane separation process usually oxygen with 90 - 95 vol .-% O _{2 is} produced. The oxygen from such sources usually contains only small traces of water (<1 ppm).

The process gas stream entering the electrolysis cell should if possible have a temperature which corresponds to the temperature in the cell or which is only slightly below the temperature in the electrolysis cell. Otherwise, a temperature gradient occurs within the electrolysis cell and, as a consequence, an uneven distribution of the electrolysis power and material flows over the surface of the electrode, which results in reduced performance and permanent damage to the diaphragm and SVE.

The moisture content of the entering into the electrolysis cell oxygen should, if possible, be so high that at least the amount of water transported with the exiting oxygen is compensated. Since the water content in the purge stream is no longer returned to the cell, at least this part must be tracked, in arrangements without recycling the educt gas according to the total amount of water discharged. When operating the cell in Zero Gap arrangement in which the SVE has contact with the ion exchange membrane, it is customary that by moistening the oxygen flow additional amounts of water are introduced into the electrolytic cell to a too high, harmful for the membrane concentration of the alkali or even a Crystallize the alkali hydroxide to avoid. To moisten the oxygen, the water must be evaporated, for which energy must be supplied.

The heating can be carried out in particular in such a way that only the freshly supplied to the process oxygen-containing gas is heated with a heat source from the electrolysis. In arrangements without recirculation of the excess oxygen, this is the given design, but it can also be carried out with recycling of the oxygen-containing process gas. When recycling the excess oxygen, the heating can also take place in such a way that only the reduced by a proportion of exhaust gas flow recycled oxygen-containing process gas is combined with the freshly supplied oxygen and the combined gas stream is heated with a heat source from the electrolysis. The discharge of the exhaust gas stream serves to enrich the oxygen-containing process gas with undesired minor components such as. To avoid hydrogen or inert gases in a circulation of the oxygen-containing process gas.

According to the invention, the heating of the oxygen-containing process gas takes place by using process heat, which is obtained in the electrolysis process and / or a downstream processing of process streams. Preference is given to using process heat with a low energy level, ie heat sources having a temperature of <150 ° C., preferably <120 ° C., particularly preferably <100 ° C., for the heating. Preference is given to the use of secondary heat sources by direct heat exchange in a heat exchanger. However, it can also be an indirect heat exchange by interposing a further heat transfer medium.

In a preferred embodiment of the invention, the chlorine gas taken from the anode side of the electrochemical cell is used as the process stream for the heat exchange for heating the oxygen-containing process gas.

In another preferred embodiment of the invention, the catholyte leaving the cell and / or anolyte used to heat the oxygen-containing process gas is used as the process flow for the heat exchange.

Preference is also given to a method in which cooling waters, condensates or secondary steam from an alkali metal hydroxide evaporation plant connected downstream of the electrolysis cell are used for heating the oxygen-containing process gas.

The heating and humidification of the oxygen-containing process gas is particularly preferably carried out by passing the process gas through alkali lye discharged from the catholyte circuit, in particular sodium hydroxide solution.

Particular preference is given to using as the process stream for the heating and humidification of the oxygen-containing process gas condensed vapors from the electrochemical cell downstream Alkalilauge-, in particular sodium hydroxide evaporation, the heat exchange is carried out in particular by passing the oxygen-containing process gas through the condensed vapors.

The use of process heat, which is obtained in the electrolysis process and / or the downstream workup simultaneously reduces the need for cooling energy, which further increases the efficiency and environmental impact of the process.

The secondary heat sources used in accordance with the method according to the invention can, in addition to the energy for heating the oxygen-containing process gas, additionally supply the energy which is required for preferential humidification of the oxygen-containing process gas for the evaporation of the water. The humidification of the oxygen-containing process gas is carried out in a manner known to those skilled in the art, for example by passage through a water column or by a trickle column charged with water. The amount of water supplied via the humidification is chosen such that at least the water discharged with the potential exhaust gas flow is replaced.

When operating a SVE in an electrochemical process, a large number of secondary heat sources are available for heating the oxygen-containing process gas, which are to be explained in more detail below for the chlor-alkali electrolysis, but without wishing to limit the invention to these examples.

Thus, the chlorine gas discharged from the electrolysis can be used as a heat source. The chlorine removed from the electrolysis has the temperature of the electrolytic cell and thus a temperature which is preferred for the process gas feed into the cell. During the workup of the chlorine discharged from the electrolysis cell, it is typically cooled before further drying and purification (see Ullmann's Encyclopedia of Industrial Chemistry, chapter "Chlorine", Wiley-VCH Verlag GmbH & Co. Kg, Weinheim ). As a rule, the cooling takes place with external cooling media, for example cooling tower water. When using the heat of the electrolysis removed chlorine to preheat the process gas thus additional external cooling energy is saved. The heat exchange between the oxygen-containing process gas and the chlorine is preferably carried out in a countercurrent heat exchanger. The design of the heat exchanger takes place in a manner known to the expert. Thus, plate heat exchangers, shell and tube heat exchangers or other embodiments can be used. Suitable materials are the oxygen and chlorine resistant materials known to those skilled in the art. A preferred durable material is titanium. The variant described here is also characterized by the fact that no control elements for the temperature control are needed, overheating of the oxygen-containing process gas is not possible, the process gas is brought to the prevailing in the electrolytic cell temperature level.

Further heat sources for the heating of the oxygen-containing process gas are process streams from the anolyte and / or the catholyte circuit. Due to electrical losses in the electrolytic cell, both anolyte and catholyte process streams heat up during electrolysis. The heating increases with increasing current density. To avoid boiling of the electrolytes, the process streams in the circuits must be cooled. The cooling takes place according to the prior art with external cooling media, for example cooling tower water. The heat generated in the anolyte and / or catholyte cycle is sufficient in normal operation to bring the fresh oxygen for the SVE to the required temperature level. When starting the cells and during partial load operation with low current density, it may be necessary to use additional energy sources for warming up the oxygen in addition to the waste heat from the anolyte and / or the catholyte circuit.

For warming up the oxygen-containing process gas, additional secondary heat sources from the electrolysis downstream work-up processes for products from the electrolysis can be used independently of the aforementioned heat sources, for example, the waste heat resulting from chlorine work-up or evaporation of the sodium hydroxide solution. For example, the sodium hydroxide solution is concentrated in a conventional manner from the concentration of about 32% achieved in the electrolysis by distillation to the commercial concentration of 50% (cf. Ullmann's Encyclopedia of Industrial Chemistry, chapter "Sodium Hydroxides", Wiley-VCH Verlag GmbH & Co Kg, Weinheim ). In this evaporation vapors are generated, which must be condensed by cooling. The concentrated caustic soda leaves the last evaporation stage, for example, at a temperature of> 150 ° C and is cooled down to a temperature of typically <50 ° C for storage and transport. Both the released for the condensation of the vapors as well as the cooling of the hot caustic soda Heat can therefore be used preferably in each case for the preheating of the oxygen-containing educt gas. It is also possible to use steam at a low pressure level, as can be generated, for example, during cooling of the sodium hydroxide solution above 150 ° C. or by relaxing condensate, for preheating the oxygen-containing educt gas.

Furthermore, steam condensates or condensates, which occur during the heating of the evaporation plant, can be used in particular for the preheating of the oxygen-containing educt gas.

The secondary heat sources to be used in accordance with the method according to the invention can additionally supply the energy which is required for wetting the oxygen-containing process gas with water for the evaporation of the water.

For the humidification preheated water can preferably be used at a temperature which is equal to or higher than the temperature of the oxygen-containing process gas. The temperature of the water can in particular be selected so that the oxygen-containing process gas after leaving the moistening apparatus already has the intended for introduction into the electrolysis cell temperature. The process gas can also be brought to moistening in a further heat exchanger to the intended temperature.

The heating of the water is preferably carried out via a heat exchanger by using one of the aforementioned process streams as a heat source. However, it can also be used directly for the humidification of the oxygen-containing process gas in particular in the system resulting warm condensate. For example, when the sodium hydroxide solution is concentrated in an evaporation apparatus, condensed vapors form, which can be used directly for the humidification of the process gas. Also, instead of water, the typically discharged from the electrolysis, typically about 32 wt .-% sodium hydroxide solution for the humidification of the oxygen-containing process gas can be used. This variant has the further advantage that less water has to be evaporated in the downstream evaporation.

The humidification of the oxygen-containing process gas can also be done with cold water or with water having a temperature lower than the temperature of the supplied oxygen. Such a method has advantages, for example, if the water content in the process gas is to be limited, or if the aparative effort is to be kept low. In this variant, the process gas cools when moistening and is then reheated. For the heating, one of the aforementioned heat sources is used. It may also be advantageous to preheat the water used for moistening with one of the heat sources, even if the temperature of the water is below the intended temperature of the process gas. This is especially true advantageous if a defined moisture content below the saturation limit is provided for the process gas introduced into the electrolysis cell.

The above-described variants of the oxygen preheating can also be freely combined with each other, if this appears procedurally expedient.

In a further embodiment, steam with a low pressure level, which is obtained, for example, in the evaporation plant, used for humidification and heating of the oxygen-containing process gas. Use is made, for example, by injecting this vapor into the process gas stream.

The novel process is preferably carried out such that the oxygen-containing gas mixture supplied to the electrolysis cell, in particular a mixture of fresh oxygen and recycled oxygen, reduces the temperature in the cell by less than 50 ° C., preferably by less than 20 ° C., more preferably by less than 10 ° C falls below.

The recycling and mixing of the oxygen can be done according to the in DE 10149779A1 described method by means of a gas jet pump. However, the recycling and mixing of the oxygen can also be carried out in another manner known to the person skilled in the art. Thus, the oxygen discharged from the electrolysis cell can be sucked off by means of a pump or a compressor, compressed and then mixed with the fresh oxygen in a mixing device. The mixture can also take place immediately upon introduction into the electrode chamber.

The process according to the invention can be used independently of the quality of the freshly supplied oxygen. Thus, the new method can be used particularly preferably in electrochemical processes with an SVE and the supply of pure oxygen (> Vol.-99% O ₂ ). The new method can also be used in electrochemical processes with an SVE and the supply of highly enriched oxygen (90-99 vol .-% O ₂ ) or enriched oxygen (30 - 95 vol .-% O ₂ ) or CO ₂ -free air ( <100 ppm CO ₂ ) are used.

Preference is therefore given to an embodiment of the new method, which is characterized in that the oxygen-containing gas mixture fed to the electrode has a proportion of 30-95 vol.% Oxygen, preferably an oxygen content of 90-99 vol.%, Particularly preferably an oxygen content of > 99% by volume.

Also preferred is a process in which the oxygen-containing gas mixture supplied to the electrode has a CO ₂ content of <100 ppm.

The process according to the invention can be used independently of the stoichiometric excess of the oxygen introduced into the cell and also independently of the proportion of discharged exhaust gas. The process can be used in particular at the usual 1, 0.05 to 2-fold stoichiometric excess and a purge gas stream of 0.5 to 20% of the recirculated educt gas.

The method can basically be used in all electrochemical processes with an SVE.

Likewise, the inventive method can be used in the operation of an alkaline fuel cell, in drinking water treatment, for example for the production of sodium hypochlorite or in the chlor-alkali electrolysis, in particular for the electrolysis of LiCl, KCl or NaCl.

The inventive method is preferably used in the use of an SVE in the chlor-alkali electrolysis and here in particular in the sodium chloride (NaC1) electrolysis or in a hydrochloric acid electrolysis.

The invention will be further explained by way of example in the following, without limiting the invention to the described embodiments.

Examples: example 1

FIG. 1 shows a NaCl electrolytic cell EA1 with anolyte circuit a and catholyte circuit b and a process gas circuit c with the conveying member P1. Chlorine gas d is removed from the anode. The anolyte is a partial stream e taken, which is used after dechlorination together with fresh water and solid sodium chloride for the preparation of a saturated NaCl solution e ', which is then introduced after cleaning back into the circuit. The catholyte circuit, a partial stream of sodium hydroxide solution is removed f. From the process gas cycle c, a partial stream g is removed as purge, and fresh oxygen h is supplied from a cryogenic air separation plant. The temperature of the electrolysis cell is 90 ° C. The anolyte and catholyte circuits are cooled via the heat exchangers WA 1 and WA 2. The chlorine gas is cooled in heat exchanger WA3 to about 40 ° C. Here, a part of the water present in the chlorine gas condenses.

In order to heat the process gas to the desired temperature, in one embodiment of the invention, the freshly supplied oxygen h is heated via the heat exchanger WA 4. Preferably, the heat exchange in a not shown here other execution against the cooled chlorine gas in such a way that WA 4 corresponds to the WA 3 and the oxygen is heated in the direct heat exchange against the hot chlorine gas, the heat exchange is preferably carried out in countercurrent. However, the heating can also be carried out in a further embodiment by means of a heat carrier circuit, preferably by means of a water cycle, so that the heat dissipated in WA3 is transferred to warm the oxygen in WA4. In a further embodiment, the heat dissipated from WA 1 or WA 2 by means of a heat carrier circuit is used to heat up the process gas in WA 4.

In a further embodiment, the process gas c is heated to the required temperature after discharge of the purge stream g and supply of the oxygen h in the heat exchanger WA5. In a variant not shown here, the heat exchange takes place against the cooled chlorine gas in such a way that heat exchanger WA 5 corresponds to the heat exchanger WA 3 and the process gas is heated in direct heat exchange against the hot chlorine gas, wherein the heat exchange is preferably carried out in countercurrent. However, the heating can also be carried out in a further embodiment by means of a heat carrier circuit, preferably by means of a water cycle, so that the dissipated in WA3 heat is transferred to the heating of the process gas in WA5. In a further embodiment, the heat dissipated from heat exchanger WA 1 or heat exchanger WA2 by means of a heat carrier circuit is used to heat up the process gas in WA5.

Example 2

In FIG. 2 further embodiments are exemplified, in which additionally the process gas is moistened.

In one embodiment, the freshly supplied oxygen h is heated in heat exchanger WA 1, wherein the heat energy as in the embodiments described above from one of the sources heat exchanger WA3, WA2 or WA1 comes. The oxygen stream h is then passed through the moistening apparatus KA 1 and the heated and humidified oxygen is supplied to the process gas circuit c. For moistening, an aqueous medium i is passed through the moistening apparatus KA1, which is either deionized water, condensate or caustic soda.

In a further embodiment, the process gas c is passed to the purge stream (g) and feed of the oxygen h through the humidifier KA 2 and then heated in the heat exchanger WA5, wherein the energy as in the embodiments described above from one of the sources WA3 , WA2 or WA1. For moistening, an aqueous medium i 'is passed through the moistening apparatus KA2, which is either deionized water, condensate or caustic soda.

Example 3

In FIG. 3 further embodiments are shown in which the heating and humidification done in an apparatus.

In one embodiment, the freshly supplied oxygen h in the moistening apparatus KA 1 is moistened and heated. The moistening apparatus KA1 1 is charged with a hot aqueous medium i, which is hot condensate from the sodium hydroxide evaporation plant, hot caustic soda (f), another hot aqueous stream from the process or deionized water, which means one of the waste heat was heated from one of the heat exchanger WA1, WA 2 or WA3.

In a further embodiment, the process gas c is humidified and heated after discharge of the purge stream g and supply of the oxygen h in the moistening apparatus KA 2. The moistening apparatus KA2 is charged with a hot aqueous medium i ', wherein it is is hot condensate from the caustic soda evaporation plant, hot caustic soda f, another hot aqueous stream from the process or deionized water, which was heated by means of one of the waste heat from one of the heat exchanger WA1, WA 2 or WA3.

Example 4

In an electrolysis apparatus with 10 cell elements ä 2.7 m ² , equipped with Nafion membrane N982® the Fa. Dupont and SVE, a NaCl solution of 220 g / l with current density of 4 kA / m ^{2 is} electrolyzed. In this case, the cathode chamber 33.8 Nm ³ / h of pure oxygen (> 99% O ₂ ), that is fed to 50% excess.

The supplied oxygen has a temperature of 80 ° C. The temperature is achieved by heating the fresh oxygen in countercurrent to chlorine gas discharged from the electrolysis apparatus before it is mixed with the residual gas stream reduced by the purge gas stream by means of a heat exchanger. This corresponds to the in FIG. 1 shown embodiment with the change that the heat exchanger WA 3 and WA 4 are replaced by a single heat exchanger, which is traversed by chlorine as the heat transfer medium and the fresh oxygen.

Claims (10)

A method of operating an oxygen-consuming electrode as a cathode for the electrolysis of alkali chlorides or hydrochloric acid in an electrochemical cell, characterized in that the oxygen-containing process gas supplied to the electrode at least partially using a heat source from the electrolysis, in particular by heat exchange with a selected process stream, from the electrolysis is obtained or a subsequent electrolysis refurbished process stream is heated prior to contact with the oxygen-consuming electrode to a temperature which corresponds at most to the temperature of the cathode space in the cell or by less than 50 ° C, preferably less than 20 ° C, more preferably less than 10 ° C. A method according to claim 1, characterized in that as the process stream for the heat exchange, the anode side of the electrochemical cell taken chlorine gas is used to heat the oxygen-containing process gas. A method according to claim 1 or 2, characterized in that is used as the process stream for the heat exchange of the cell leaving the catholyte and / or anolyte for heating the oxygen-containing process gas. Method according to one of claims 1 to 3, characterized in that cooling water, condensates or secondary steam from an electrolysis cell downstream alkali lye evaporation system for heating the oxygen-containing process gas can be used. Method according to one of claims 1 to 4, characterized in that the heating of the oxygen-containing process gas is carried out by passing the process gas through leached from the catholyte circuit alkali hydroxide. A method according to claim 1, characterized in that as a process stream for the heating of the oxygen-containing process gas condensed vapors from the electrochemical cell downstream alkali hydroxide evaporation are used, the heat exchange is carried out in particular by passing the oxygen-containing process gas through the condensed vapors. Method according to one of claims 1 to 6, characterized in that the oxygen-containing gas mixture supplied to the electrode accounts for 30-95% by volume. Oxygen, preferably an oxygen content of 90 to 99 vol .-%, particularly preferably has an oxygen content of> 99 vol .-%. Method according to one of claims 1 to 7, characterized in that the oxygen-containing gas mixture supplied to the electrode has a CO ₂ content of <100 ppm. Method according to one of claims 1 to 8, characterized in that the electrolysis is a chloralkali electrolysis, in particular a sodium chloride electrolysis Method according to one of claims 1 to 9, characterized in that the electrolysis is a hydrochloric acid electrolysis.

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