PL119244B1 - Method of manufacture of halogens and alkali metal hydroxides by means of electrolysis of alkali metal halidesmetallov putem ehlektroliza galogenidov hhelochnykh metallov - Google Patents

Description

The subject of the invention is a method for producing halogens and alkali metal hydroxides by electrolysis of aqueous solutions of alkali metal halides in an electrolyzer having an anode and cathode separated by a diaphragm. Production of halogens, especially chlorine, by electrolysis of solutions of alkali metal halides, with simultaneous preparation alkali metal hydroxides, especially sodium hydroxide, is carried out on a very large scale. For this purpose, one of two electrolytic processes is usually used, namely in an electrolyzer with a mercury cathode or in a diaphragm electrolyzer. In the first of these processes, a graphite or metal anode of fixed dimensions is used and chlorine is released on this anode, while the alkali metal accumulates on the mercury cathode, forming an alkali metal amalgam. This amalgam is then reacted with water to obtain sodium hydroxide and hydrogen. However, this method is now obsolete for the production of chlorine. First of all, it is very difficult to carry out this process while complying with regulations regarding environmental pollution of mercury, and besides, mercury is relatively expensive, which is of great importance, especially due to the large dimensions of electrolysers for the production of chlorine. Additionally, this process is complicated by the need to use equipment to decompose the amalgam in order to produce sodium hydroxide and hydrogen. Although no mercury is used in diaphragm electrolysers, these electrolysers have porous electrodes separated by a porous diaphragm. The space between the electrodes is filled with a sodium chloride solution, i.e. brine and a separated microporous membrane that separates the cathode space from the anode space. A serious disadvantage of such electrolysers is that the pores in the membrane enable mass transfer, i.e. the hydraulic flow of sodium chloride solutions through this membrane, which makes that catholyte, i.e. sodium hydroxide produced at the cathode, contains significant amounts of sodium chloride, and is therefore contaminated and diluted. On the other hand, the hydroxide produced at the cathode can return through the porous diaphragm to the anode, where it undergoes electrolysis, producing oxygen, which is undesirable for many reasons. Namely, it not only pollutes the chlorine, but also attacks the anode. The flow of anolyte and catholyte between both spaces is very undesirable, so a number of measures have already been proposed to limit or eliminate this flow. One of such measures is maintaining different pressure on both sides of the diaphragm, but such a procedure is only partially effective. It has also been proposed to use diaphragms that selectively allow ions to pass through, usually cation exchange diaphragms, enabling a selective flow of anions. with a negative charge. Since these diaphragms are not porous, they prevent the flow of hydroxide from the cathode space to the anode space, as well as the flow of brine from the anode space to the cathode space, thanks to which the hydroxide is not diluted and contaminated. However, it was found that Such diaphragm electrolysis has a number of disadvantages, and above all, high voltage. The reason for this is only partly the characteristics of the diaphragm itself, and largely the fact that known diaphragm electrolysers use electrodes physically distant from the diaphragm. As a result of this distance between the electrodes and the diaphragm, in addition to the reduction of the product of the current R by the resistance I through the membrane, there is also a decrease in this product in the electrolyte between the electrodes and the diaphragm before the ion transfer, and thereafter there is a decrease voltage caused by the generation of gas bubbles or mass transfer. Namely, since the catalytic electrodes are far from the diaphragm, chlorine is produced far from the diaphragm and as a result, a gaseous layer is formed between the electrode and the diaphragm, which interrupts the path of the electrolyte between the electrode and the diaphragm, partially separating the ions from the diaphragm. This interruption of the electrolyte path causes an additional decrease in the IR product, and thus increases the voltage necessary to produce chlorine, obviously changing the voltage efficiency of the electrolyzer. K The method according to the invention does not has the disadvantages described above. According to the invention, halogens, e.g. chlorine or bromine, are produced by electrolysis of an aqueous solution of an alkali metal halide, e.g. sodium chloride, carried out on electrolyzer electrodes physically and permanently bonded to the surface of the diaphragm. permeable liquid electrolyte, so there is a gas. produced directly on the surface of the diaphragm, and the ion stream does not flow through the electrolyte. An electrochemically active substance is directly and inseparably bound to the surface of this diaphragm, preferably constituting particles of platinum group metals, oxides of such metals, etc., which is an electronically active catalyst. The part of the electrolyzer carrying the electron stream, hereinafter referred to as the current collector, is separated from the electrode where the gas is produced. The electrochemically active catalyst is permanently connected to the diaphragm and the contacts with the current collector are only sufficient to enable the transfer of current. 55 These basic features distinguish the solution according to the invention from known solutions, according to which the electrodes are made of metallic material, i.e. electrically conductive, and have a surface covered with an electrochemically active substance. Typically, such a coating consists of electrically conductive valve metals such as titanium, tantalum, etc., covered with electrochemically active metals of the platinum group or the like. Since this electrochemically active catalyst is an integral part of the electrically conducting elements in such a solution, gas generation takes place in the electrolyte and the ion stream flows through the electrolyte before reaching the ion-transferring diaphragm. In contrast, in the solution according to the invention, electrochemically the active catalyst is not an integral part of the electrically conducting elements, i.e. the receiver, but is permanently connected to the diaphragm and thus the gas production reaction is moved to the boundary surface between the diaphragm and this catalyst. In this way, disruptions to the flow of the ion stream through the bubbles of the produced gas are almost completely avoided, which occurs in known solutions. Moreover, the stream of ions, i.e. alkali metal cations or hydrogen, does not need to pass through the liquid electrolyte and thus avoids the drop in the IR product described above. According to the invention, the electrolysis of an aqueous solution of an alkali metal halide is carried out in an electrolyzer in which the polymeric cationic diaphragm is permanently bonded at a number of points to at least one electrode, forming an electrode-diaphragm assembly. Voltage is supplied to this assembly by contacting it with a current-carrying current collector having an overvoltage surface for hydrogen or halogen higher than the corresponding overvoltage of the electrode connected to the diaphragm. The electrodes used according to the invention contain as a catalytic substance at least one reduced metal oxide of the platinum group, thermally fixed by heating the reduced oxides in the presence of oxygen Preferably, these electrodes are a fluorocarbon derivative (polytetrafluoroethylene particles) bonded to reduced metal oxides from the platinum group, e.g. platinum, palladium, iridium, rhodium. ruthenium and osmium, with reduced ruthenium or iridium oxides being particularly preferred for the production of chlorine. Single, reduced platinum group oxides can be used as the electrocatalyst, but it has been found that mixtures or alloys of such oxides are more durable. For example, electrodes made of reduced ruthenium oxides containing up to 25%, and preferably 5-25% by weight, of iridium oxide are very durable. Fillers in the form of graphite or other electrically conductive substances can be used, e.g. ruthenium titanium can be added in an amount of up to 50 %, V and especially 10-30% by weight. Such a filler should have good electrical conductivity with low halogen overvoltage and should be significantly less expensive than platinum group metals, enabling the production of cheaper but highly efficient electrodes. In order to make these electrodes resistant to the effects of oxygen, chlorine and the harsh conditions of electrolysis, ¬ to use the addition of one or more reduced valve metal oxides, such as titanium, tantalum, niobium, zirconium, hafnium, vanadium and tungsten, in an amount of up to 50% by weight, preferably 25-50% by weight. At least one catalytic 119 244 -electrode is connected to a diaphragm which does not allow liquid to pass through but allows ions to pass through. By bonding the electrodes to the diaphragm, the decrease in the IR product in the electrolyte between the electrodes and the diaphragm is reduced, as well as the losses during gas mass transfer, because a gas layer is formed between the electrode and the diaphragm. Thus, a significant reduction in the electrolyzer voltage is achieved, which constitutes a significant economic advantage. 10 The invention is described in detail below with reference to the drawing, in which Fig. 1 shows an axonometric view of the electrolyzer used in the process according to the invention without an external cover, and Fig. 2 shows a vertical cross-section of the diaphragm with the anode and cathode, indicating the reactions taking place. during electrolysis. According to Fig. 1, the electrolyzer 10 consists of a cathode compartment 11 and an anode compartment 12, separated by a diaphragm 13 made of solid polymeric electrolyte, preferably a hydrated, selectively permeable cation exchange diaphragm. Bonded to the surfaces of the diaphragm 13 are electrodes containing particles of a fluorocarbon, e.g. a product from the Dupont 25 Company known as Teflon, and these particles are bound to stabilized, reduced oxides of ruthenium RuOx or iridium IrOx, or stabilized, reduced oxides of ruthenium-iridium (RuIr)Ox, ruthenium-titanium (Ru 30 Ti)Ox, ruthenium-titanium-iridium (RuTiIr)Ox, ruthenium-tanthallium-iridium (RuTaIr)Ox or ruthenium-graphite. On one side, the cathode 14 is mounted on the surface of the diaphragm and bonded to it, while on the other side, an anode, not shown in FIG. containing a catalyst. Suitable catalysts are finely divided metals such as platinum, palladium, gold, silver, as well as spirals, manganese, cobalt, nickel, reduced oxides of metals from the platinum group (Pt-Ir)Ox, (Pt-Ru)Ox, graphite and their combinations. Current collectors 15 and 16 are pressed against the electrodes. The entire diaphragm/electrode set is fixedly mounted between the elements of the space cover 11 and 12 by means of seals 17 and 18, made of any inert material or from ¬ resistant to the effects of the environment prevailing in the electrolyzer, namely chlorine, oxygen, aqueous sodium chloride solution and sodium hydroxide. Such seals can be used, for example, filled rubber seals manufactured by the Irving Moore Company, Cambridge, United States. under the name of the EPDM seal. 95 The anolyte in the form of an aqueous solution of sodium chloride, i.e. brine, is introduced through conduit 19, connected to the anode space chamber 20. The spent electrolyte and chlorine gas are discharged through conduit 21, passing through the sheath. The wire 22 connects to the cathode space 11 and serves to supply it with catholyte, water or an aqueous NaOH solution with a dilution greater than the dilution of the hydroxide produced electrochemically at the 6% electrode/electrolyte interface. Water performs two functions, namely part of it undergoes electrolysis, giving hydroxyl anions, which combine with sodium cations transferred to the diaphragm and sodium hydroxide is produced. In addition, water flows through the cathode and dilutes the highly concentrated hydroxide produced at the diaphragm/cathode interface, reducing hydroxide recycling by diffusion through the diaphragm into the anode space. Conduit 23 serves to remove dilute sodium hydroxide and hydrogen from the cathode space 11 , which is released at the cathode. This wire is also used to drain excess water from the cathode space 11. The power cable 24 is introduced into the cathode space and a similar cable, not shown in the drawing, is introduced into the anode space. These cables connect the electrically conductive grids 15 and 16 to a source of electrical energy. Figure 2 shows schematically the reactions taking place in the electrolyzer during brine electrolysis and explains the operation of the electrolyzer. An aqueous sodium chloride solution is introduced into the anode compartment, which is separated from the cathode compartment by diaphragm 13. In order to improve cathodic efficiency, diaphragm 13 has an ion-repellent barrier layer on the cathode side to repel hydroxyl ions and prevent or at least reduce the back migration of the alkali metal hydroxide to the anode. The diaphragm 13, as described in detail below, is a composite diaphragm having on the anode side a layer 26 of high water content (20-35"% by weight based on the dry weight of the diaphragm) and on the cathode side a layer 27 of low water content. water (5-15"% by weight in relation to the dry weight of the diaphragm), both layers being separated by a Teflon cloth 28. The anion repulsion capacity of the cathode-side barrier layer can be further increased by chemically modifying the cathode-side diaphragm and producing a thin layer of polymer with a low water content. According to one variant, this is achieved by modifying the polymer by forming a membrane layer from a substituted sulfonamide. For example, a layer 27 with a high milliequivalent weight value is used. water MEW, or transforms it into a weak acid (sulfonamide), thus reducing the water content in this part of the laminated membrane. This increases the ability of the membrane to repel salt and reduces the diffusion of sodium hydroxide through the membrane back to the anode. The membrane may also be a homogeneous membrane with a low water content (Mafion 150, perfluorocarboxylic acid, etc.). A Teflon-bonded reduced noble metal oxide catalyst containing stabilized reduced oxides of ruthenium or iridium or ruthenium and iridium, optionally with the addition of reduced oxides of titanium, niobium or tantalum, and graphite, is pressed into the surfaces 8 ny 13., Current collectors 15 and 16, shown on {ig. 2 only partially, are pressed to the surfaces of the catalytic electrodes and connected, respectively, to the positive and negative terminals of the source of electrical energy, thereby obtaining a potential on the electrolyzer electrodes. The sodium chloride solution introduced into the anode compartment undergoes electrolysis at the anode 29 and is obtained chlorine, shown in Fig. 2 in the form of bubbles 30. Sodium ions Na+ are transferred through the diaphragm 13 to the cathode 14. A stream of water or an aqueous NaOH solution, marked with arrow 31, is introduced into the cathode space and constitutes the catholyte. An aqueous stream flows through the surface associated with the cathode, readily producing a concentrated sodium hydroxide solution at the diaphragm/cathode interface and reducing the return of this hydroxide by diffusion through the diaphragm to the anode. Part of the water in the catholyte is electrolyzed at the cathode. in an alkaline medium, giving OH- hydroxyl ions and hydrogen gas. The hydroxyl ions combine with the sodium ions transferred through the diaphragm and produce sodium hydroxide at the diaphragm/electrode contact surface. This hydroxide easily wets the Teflon that is part of the bonded electrode and migrates to the surface, where it is diluted by the water stream flowing through the electrode surface. A concentrated sodium hydroxide solution of 4.5-6.5 M is easily produced at the cathode, and even after dilution, some sodium hydroxide (arrow 33) migrates back through the diaphragm 13 to the anode, where it is oxidized to give consuming water and oxygen, shown in Fig. 2 in the form of bubbles 34, This is, of course, an undesirable reaction, reducing the current efficiency of the cathode. The production of oxygen is also undesirable because it may have a harmful effect on the electrode and the diaphragm, and besides dilutes the chlorine produced at the anode, so oxygen must be removed. The following reactions take place in various parts of the cell. At the anode (main reaction): 2Cl--*ClJ+2e- Transfer through the diaphragm: 2Na++H20 At the cathode 2H20-*20H-+H2t-2e 2Na+ +20H--*2NaOH At the anode (harmful reaction): 40H--0.+ 2H20+4e- Total (main reaction): 2NaCl+2HaO-*2NaOH+Cl2+N2 ( 1) (2) (3a) (3b) io 15 20 25 30 35 40 45 50 55 (4) (5) 60 The electrolysis process of aqueous solutions of alkali metal halides according to the invention is carried out in an electrolyzer in which the catalytic the sides of the electrodes are in direct contact with the cation exchanger membrane and acidic ion-exchanging radicals associated with the polymeric framework, which may be sulfonic acid radicals S03HXH20 or carboxylic acid radicals COOHXH20. Due to this, there is no noteworthy decrease in the IR product in the anolyte or catholyte. This drop is characteristic of systems in which the diaphragm and the electrode are separated and may amount to 0.2-0.5V. Avoiding this voltage drop is, of course, one of the main benefits obtained when using the process according to the invention, because it has This influences the voltage used in the process and provides economic benefits: In addition, because the chlorine is produced directly at the contact surface of the anode with the diaphragm, there is no voltage drop caused by gas bubbles and by interrupting or blocking the electrolyte path between the electrode and diaphragm. As stated above, in known electrolytic systems chlorine is released on the catalytic electrode separated from the diaphragm and creates a gaseous layer in the space between the diaphragm and the electrode, causing an interruption of the path between the electrode collector and the diaphragm, hindering the passage of Na+ ions , thereby causing a voltage drop. The Teflon-bonded catalytic electrode contains the above-mentioned reduced oxides of platinum group metals, such as ruthenium, iridium or ruthenium iridium, in order to reduce the overvoltage of chlorine evolution at the anode. Reduced ruthenium oxides are used, fixed by the action of the produced chlorine and oxygen. These oxides are fixed primarily by heat treatment, namely heating at a temperature lower than that at which the oxides begin to decompose to produce pure metal. Preferably, heating is carried out at a temperature of 350-750°C for 0.5-5 6 hours, especially at a temperature of 550-600°C within 1 hour. Further fixation involves the use of reduced ruthenium oxides mixed with graphite and/or with reduced oxides of platinum group metals, such as IrO* in an amount of 5-25%, preferably 25% by weight calculated as iridium, or with oxides of platinum, rhodium, etc. , as well as with reduced valve metal oxides, such as, for example, TiO* in an amount of 25-50% by weight or tantalum oxides in an amount of 25% by weight or more. It has also been found that by bonding a three-component alloy of titanium oxides with Teflon, tenu and iridium Ru, Ir, Ti)Ox, tantalum, ruthenium and iridium (Ru, Ir, Ta)Ox or ruthenium, iridium and titanium (RuIrTi)Ox, durable anodes are obtained that are useful for a long period of time. In the case of ternary alloys, cuts are those in which the content of reduced iridium oxides is 5-25% by weight, the content of reduced ruthenium oxides is about 50% by weight, and the rest is a valve metal such as titanium. In binary alloys containing reduced oxides ruthenium and titanium, the titanium content is preferably 50% by weight, the rest being ruthenium. Titanium is less expensive than ruthenium or iridium, so its use provides economic benefits, and it also makes the electrode resistant to the effects of chlorine and oxygen in an acidic environment. Niobium, tantalum, zirconium or hafnium are used as other valve metals, replacing titanium. Alloys of reduced platinum group metal oxides and reduced titanium oxides or other valve metals are mixed with Teflon to obtain a homogeneous mixture. The Teflon content in the anode is 15-50%, preferably 20-30% by weight. In the tests described below, Teflon T-30 from Dupont Corporation was used, but other fluorocarbons can also be used with the same effect. Platinum group metal etc. is usually used in an amount of at least 0.6 mg, and preferably 1-2 mg per 1 cm* of anode surface. Current collectors for the anode may have the form of a grid or a dense mesh made of platinized niobium, ensuring good contact with the electrode surface. Expanded titanium mesh coated with ruthenium oxide, iridium oxide, transition metal oxide, or a mixture thereof may also be used. Another type of anode collector is a mesh coated with a noble metal or noble metal oxide, attached to the plate by welding or other bonding. Anode collector current contacting the bonded anode layer has an overvoltage for chlorine that is higher than the surface layer of the catalytic anode, which reduces the probability of an electrochemical reaction on its surface, e.g. chlorine release, because such reactions occur more easily on the anode surface due to its lower overvoltage for chlorine and due to the greater drop in the IR product on the way to the collector grid. The cathode is preferably a bonded mixture of platinum black Teflon particles, with the platinum black content being 0.4-4 mg per 1 cm2 of the cathode surface. However, as stated above, other catalytically active substances may also be used, such as palladium, gold, silver, spinels, manganese, cobalt, nickel or graphite, or reduced oxides such as those used at the anode, e.g. RuIrO* , etc. The cathode, like the anode, is preferably embedded and bonded to the surface of the cation exchanger membrane. The cathode is quite thin, its thickness is 0.05-0.08 mm or less, and preferably about 0.013 mm. It is porous and contains a small amount of Teflon. The thickness of the cathode may be important, namely it limits the penetration of water or an aqueous NaOH solution through the cathode, which reduces the current efficiency of the cathode. Preferably, electrolysers are used having cathodes with a thickness of 0.013-0.05 mm, containing platinum black and 15% by weight of bound Teflon. When such an electrolyzer operates at a temperature of 8-91°C and brine containing 1 liter is fed to the anode. 290 g of NaCl, then when producing sodium hydroxide with a concentration of 5 m on the cathode, the current efficiency at the same current density of 32.4 A/dm2 is approximately &Q% of the theoretical efficiency, while when using a ruthenium-graphite cathode with thickness 0.08 mm, the current efficiency under the same conditions decreases to 54%. Table A shows the dependence of the current efficiency on the cathode thickness, and these results show that it is most advantageous to use cathodes with a thickness of not more than 0.05-0.08 mm. is Table A Electrolyzer number 1 " Z 3 4i 5 6 7 8 Cathode platinum black platinum black platinum black platinum black platinum black 5% by weight platinum black on graphite 15% by weight RuOx platinized graphite cloth Cathode thickness in millimeters 0.05-^0.08 .0.015^0.08 0.0|2f5—0S05 0.10125—fl,0'3 0.01i3 0.08 0.08 0.215—0.38 Current efficiency in % and NaOH concentration 6|4 73 75 82 78 78 54 57 4.0 m 4.5i m 3.1 m 5 m 5.5 m 3.0, m 5.0 ml 5 m The electrode should be permeable to gas to allow easy escape of gases generated at the contact surface of the electrode 35 with the diaphragm. It should also be porous so that water can penetrate to the contact surface of the cathode with the diaphragm, where NaOH is produced, and so that the supplied brine has easy access to the diaphragm. catalytic surfaces of the electrode. 40 The penetrating water dilutes the sodium hydroxide, which is highly concentrated when produced, and this dilution occurs before the NaOH wets the Teflon and reaches the electrode surface, where it is further diluted by the water washing the electrode. It is important to dilute NaOH on the surface where the electrode contacts the diaphragm, because that is where its concentration is the highest. Since Teflon is hydrophobic, in order to allow water to pass through the cathode, the Teflon content in the cathode should not be higher than 15 —30% by weight. With good porosity, limited Teflon content and small electrode thickness, thanks to the water or diluted NaOH solution that flows around the electrode, the NaOH concentration can be regulated so as to limit the migration of NaOH through the diaphragm. Moreover, this return migration of sodium hydroxide can be further limited by creating a separating layer on the surface of the cathode, repelling anions. The current collector for the cathode should be carefully selected, because the alkali on the cathode strongly corrodes many plastics, especially when the electrolyzer is stopped. The current collector119 2 11 may have the form of a nickel mesh, because nickel is resistant to alkalis. It is also possible to produce collectors in the form of stainless steel plates to which a stainless steel mesh is welded. Graphite current collectors are also resistant to the action of alkali B, possibly with a nickel mesh pressed into the graphite plate on the side facing the electrode. The cathode current collector in contact with the bonded cathode layer is made of a material 10 having a higher overvoltage for hydrogen. than the surface of the electrocatalytic cathode. Thanks to this, the possibility of electrochemical reactions, such as the production of hydrogen in the current collector, is limited. The cathode also covers the collectors to some extent. The diaphragm 13 is preferably a durable, hydrated cation exchanger diaphragm which is characterized by the ability to selectively transmit ions, namely, it allows sodium cations with a positive charge to pass through and limits the penetration of negatively charged anions. Various resin ion exchangers can be used to produce such diaphragms. One group of such resins are cation exchange resins called sulfonic acid resins, and the second group are cation exchange resins called carboxylic acid resins. In the first of these groups, which is particularly preferably used for the production of diaphragms, the ion-exchange groups are hydrated sulphonic acid radicals SO3HXH20, bound to the polymer skeleton by sulfonation. These acid radicals are not mobile in transition, but are permanently bound to the polymer skeleton, thanks to which the electrolyte concentration does not fluctuate continuously. , . » As mentioned above, perfluorocarbon-rosulfonic acids are preferably used for the production of diaphragms because they enable very good cation transfer, are very durable, are not affected by acids and strong oxidants, are very resistant to heat and practically do not change over time. A particular type of such cation exchanger semi-meric diaphragms suitable for the process of the invention is the "Nafion" material from the Dupont Company, which is a hydrated copolymer of polytetrafluoroethylene (PTFE) with polysulfonyl fluorinyl ether containing attached sulfone groups. These diaphragms can be used in their hydrogen form, i.e. in the form in which they are usually supplied by the manufacturer. Ion exchange capacity (IQ of a membrane made of such a resin depends on the value of the milliequivalent (MEW) of SO groups per 1 g of polymer in the dry state ¬ chym. 55 The higher the concentration of sulfonic acid groups, the greater the exchange capacity, i.e. the ability to pass cations through the hydrated membrane. However, as the ion exchange capacity of the diaphragm increases, its water content also increases and the diaphragm's ability to repel salt decreases. The rate at which sodium hydroxide migrates from the cathode to the anode therefore increases as its ion exchange capacity increases, resulting in a decrease current efficiency of the cathode, as well as the production of oxygen at the anode, with its accompanying inconveniences. For these reasons, the preferred ion exchange membrane for brine electrolysis is a laminate consisting of a thin (0.05 mm thick) cation exchange resin membrane with a milliequivalent weight of sulfonic groups MEW = 1500, with a low water content (5-15% by weight). , strongly repelling salt and bonded with a Teflon cloth to a membrane with a thickness of 0.1 mm or more, having a high ion exchange capacity and a milliequivalent weight MEW = 1100. An example of such laminates is the "Nafion 315" laminate produced by the Dupont Company, as well as other Nafion laminates 355, 376, 390, 227 and 214. In these laminates, the cathode side is a thin layer or film of resin with a low water content (5-15% by weight), in order to provide the best possible repulsion. salt, while the anode side of such a diaphragm is a membrane with a high water content, increasing the ability to exchange ions. The ion-exchange diaphragm is prepared by soaking in an alkali metal hydroxide solution with a concentration of 3-8 m for 1 hour in order to give the diaphragm its form. sulfonate and in order to achieve a constant water content in the membrane and the ion transfer capacity of the membrane. When producing laminated membranes in which the membranes are bonded with a Teflon cloth, it is sometimes advantageous to clean the membrane or the Teflon cloth by maintaining a temperature of 70°C under reflux cooling within 3-4 hours. As mentioned above, the layer constituting a barrier on the cathodic side should contain a small amount of water in relation to the content of sulfone groups*, because then a more effective repulsion of the anion (hydroxyl group) is achieved, thus the return of alkali metal hydroxide is significantly reduced and the current efficiency of the electrolyzer increases and the production of oxygen at the anode is limited. The diaphragm layer on the cathode side can also be chemically modified, namely by modifying the functional groups of the polymer surface layer so that it has the ability to absorb water. through this layer was lower than the corresponding capacity of the sulfonic acid layer. This can be achieved by reacting the surface layer of the polymer to form a layer with sulfonamide groups. Various reactions can be used for this purpose, and one of them is to react the surface of the Nafion diaphragm in the form of fluorosulfonyl with amines, e.g. with ethylene diamine. The formed sulfonamide layer constitutes a very effective barrier layer against anions, and thus the return of alkali metal hydroxide is significantly reduced. Reduced oxides of metals from the platinum group and optionally together with reduced oxides of transition metals or graphite, bonded with time. Teflon fabrics to obtain porous, gas-permeable catalytic electrodes, are prepared by thermal decomposition of a mixture of metal salts in the absence or presence of an excess of sodium salts such as nitrates, carbonates, etc. This process is a modification of the Adams method of preparation platinum by incorporating thermally decomposable halides of iridium, titanium or ruthenium, such as iridium chloride, ruthenium chloride or titanium chloride. For example, in the case of a binary alloy (ruthenium, iridium)Ox, finely divided salts of ruthenium and iridium are mixed in a ratio corresponding to the given weight ratio of ruthenium to iridium in the melt, then an excess of sodium nitrate or another alkali metal salt is added and the mixture is melted in a silica pot at a temperature of 500-600°C for 3 hours. The obtained product is washed thoroughly with water to remove the remains of nitrates and halides, and then the aqueous suspension of mixed and molten oxides is reduced at room temperature in a known manner using the carbon electrode method or by passing hydrogen through the suspension. The product is dried thoroughly, ground and sieved through a nylon sieve. After sieving, the product particles usually have a diameter of 3.7 micrometers. The obtained alloy of reduced ruthenium and iridium oxides is then thermally stabilized by heating it at a temperature of 500-600°C for 1 hour. Electrodes are prepared by mixing the obtained product with particles of polytetrafluoroethylene, i.e. Teflon, preferably Teflon T-30. Reduced noble metal oxides such as RuOx can be mixed with an electrically conductive carrier, e.g. graphite, valve metal carbides or valve metals, thereby improving product durability and enabling the use of lower amounts of platinum group metals (0 .5 mg per 1 cm*). When using graphite with ruthenium, powdered graphite is mixed with Teflon used in an amount of 15-30% by weight in relation to the weight of the mixture, and then mixed with reduced ruthenium oxides. A mixture of particles of the noble metal with particles of Teflon or graphite and reduced oxides are placed in a mold and heated until sintered, and then deposited on the surface of the diaphragm and bonded to it using hot pressure. Various methods can be used to bond the electrode to the diaphragm, including the method given in the patent description of St. Zj. Am. No. 3134697. This method involves pressing an electrode into the surface of a partially polymerized resin constituting an ion-exchange membrane, obtaining a permanent bond of the baked, porous mixture of gas-absorbing particles with the membrane. In the process of producing chlorine, brine is introduced into the anode compartment, i.e. an aqueous solution of an alkali metal chloride, e.g. sodium chloride. At a current density of 10.8A/dm2, brine is preferably supplied in the amount of 21.5-215 ml per minute and per 1 dm* of the active surface of the electrolyzer. The concentration of the brine should be 2.5-5 m, i.e. 150-300 g/litre, and it is preferable to use brine with a concentration of 5 m, i.e. about 300 g/litre, because the cathode current efficiency increases in proportion to the increase in concentration. brine, and, moreover, increasing the brine concentration reduces the evolution of oxygen at the anode as a result of water electrolysis. s As the anolyte concentration decreases, the evolution of oxygen increases because a relatively larger amount of water at the anode competes with NaCl in the electrolysis reaction, i.e., a larger amount of water is electrolyzed and thus the amount of oxygen released increases. Electrolysis of water at the anode also reduces the current efficiency of the cathode, because hydrogen ions produced by hydrolysis pass through the diaphragm and combine with hydroxyl ions to give water, rather than the desired alkali metal hydroxide. By maintaining the anolyte inflow within the limits given above, a constant supply of anolyte is ensured. feeding fresh starting product to the anode. At a lower feed rate, its residence time increases, and especially the residence time of the exhausted brine in the electrolyzer. The exhausted brine contains a relatively large amount of water and its presence at the anode for a long time causes undesirable electrolysis of water with the production of oxygen and the transfer of hydrogen ions through the diaphragm. Thus, both the brine concentration and its feed rate influence the evolution of oxygen at the anode and the transfer of hydrogen ions through the diaphragm. u In order to facilitate the removal of gaseous electrolysis products, electrolysis can be carried out at a pressure higher than atmospheric. Such an increase in pressure in the anode and cathode spaces also reduces the size of gas bubbles produced on the electrodes. Smaller gas bubbles detach from the electrode surface more easily, and therefore are easier to remove from the electrolyzer. Moreover, this reduces the formation of gas coatings on the surface of the electrodes, which may hinder access of the anolyte and catholyte to the electrodes. In an electrolyzer with a hybrid system, in which only one electrode is connected to the diaphragm, the reduction of the dimensions of the gas bubbles causes reducing obscuration by gas and reducing voltage losses during mass transfer in the space between the diaphragm and the electrode not connected to it, due to the fact that with smaller dimensions of the gas bubbles, the gaps in the electrolyte path are reduced. As above mentioned, the evolution of oxygen at the anode due to water electrolysis can be prevented, or at least limited, by using the above-mentioned brine feed rate and maintaining a high brine concentration. However, oxygen may also be evolved at the anode as a result of sodium hydroxide returning from the cathode. This hydroxide migrates through the diaphragm due to the high concentration on the surface between the diaphragm and the electrode, and the low ability of the cation exchange diaphragms to repel salt is, as stated above, dependent on the water content in the diaphragm. In the case of a NaOH solution with a concentration of 5 m 5-30% by weight of NaOH produced at the cathode returns through the diaphragm, depending on its type.119 244 15 16 15 Oxygen is produced at the anode by electrochemical oxidation of OH- ions according to the following equation: 40-^ pH2O+O2+4e- 5 The amount of oxygen produced at the anode by the migration of the alkali metal hydroxide is, in percent by volume, about half the amount of hydroxide in percent by weight. For example, 2.5-15% by volume of oxygen is produced when 10 5-30% by weight of hydroxide migrates to the anode. As mentioned above, this migration can be limited by using a laminated diaphragm or one in which the cathode side is a layer or film. resin cation exchanger with a high sulfonic acid equivalent, low water content and hydroxyl anion repellent. In addition, however, the production of oxygen at the anode can be limited not only by reducing the transfer of hydroxide through a diaphragm with an increased salt repulsion capacity, but also by acidifying the brine. Hydrogen ions Jti+ from the acidified brine combine with hydroxyl ions OH-, which prevents the oxidation of the latter. The oxygen evolution of 5-10% by volume can be reduced to 0.2-0.4% by volume by adding hydrochloric acid with a concentration of at least 0.25 m. -.'¦¦"*¦¦¦¦ "-v;. When the hydrochloric acid concentration is lower, the amount of oxygen released increases rapidly from 0.2-0.4% to the amount normally produced, i.e. 5-110% by volume. To ensure optimal electrolysis process, highly pure salt must be used. lanka, i.e. containing few calcium and magnesium ions. The content of these ions should be 0.5 parts per million or less, otherwise calcium and magnesium penetrate the diaphragm, causing its destruction. At a concentration of these ions of more than 20 parts per million, the operation of the electrolyzer becomes seriously disturbed after only a few days. The brine should therefore be purified so that it contains less than 2, and preferably less than 0.5 parts of calcium and magnesium per million parts of brine. 45 At a current density of 32.4 A/dm2, the operating voltage of electrolysers having the bonded electrodes described above is 2.9-3.6 V, depending on the electrode composition, and electrolysis is preferably carried out at a temperature of 80-90 °C; because at such an elevated temperature, the electrolyzer voltage and overall efficiency are much better. This is confirmed by tests with an electrolyzer operating at a current density of 32.4 A/dm2 and having a Teflon-bonded mixture of reduced ruthenium and iridium oxides, carried out at different temperatures. At a temperature of 90°C, the electrolyzer voltage was 3.02 V , and at a temperature of 35°C it increased to 3.6 V. An electrolyzer operating at a current density of 21.5 A/dm2 at a temperature of 90°C required a voltage of 2.6 V, and at a temperature of 35°C the voltage increased up to 3.15 V. Therefore, from the point of view of overall efficiency, it is preferable to use a temperature of 80-90°C. Although, as stated above, the voltage of the electrolyzer decreases at lower current densities, it is preferable to use the density current of 32.4 A/dm2 or higher, due to lower investment costs, namely the size and cost of the device for producing a specific amount of chlorine and/or alkali metal hydroxide per day. Electrolysers are made of materials resistant to the action of brine. , and chlorine in the anode compartment and to the action of highly concentrated alkali metal hydroxide and hydrogen in the cathode compartment. The end plates of the electrolyzer can be made of titanium or stainless steel, and the seals can be made of filled rubber, e.g. EPDM. , oxides of transitional metals or mixtures thereof bonded to a titanium plate, or meshes covered with a precious metal or its oxide, attached to a palladium-titanium plate. Cathodic current collectors may be made of nickel, mild steel or stainless steel in the form of plates having a welded stainless steel mesh. They may also consist of nickel plates with a nickel mesh attached to them. Other materials resistant to the action of alkali metal hydroxide and hydrogen, such as graphite, can also be used to produce cathode current collectors. As stated above, the materials used to produce current collectors should have an overvoltage for hydrogen at the cathode and at the towards the anode an overvoltage for chlorine higher than the corresponding voltage of the cathode or anode, in order to avoid an electrochemical reaction, such as the evolution of hydrogen and/or chlorine, which reactions should occur more easily on the catalytic surfaces of the electrodes, and especially on the surface nor between these anodes and the diaphragm. Examples. In tests aimed at illustrating the process according to the invention, namely the influence of various parameters on the efficiency of the electrolyzer for brine electrolysis, and especially on the operating voltage of the electrolyzer, electrolysers containing ion-exchange diaphragms bonded with Teflon with electrolyzers introduced into the diaphragms were used. ¬ oxides with reduced oxides of noble metals. Table L shows the influence of various oxides of noble metals on the voltage of electrolysers. These electrolysers had electrodes containing various combinations of noble metal oxides given in the table, bound to Teflon particles and inserted into a diaphragm with a thickness of .15 mm. In all tests, electrolysis was carried out at a current density of 32.4 A/dm2, at a temperature of 90°C, and brine was introduced with a concentration of 5 m, i.e. 290 g/liter, in an amount of 200-2000 ml/minute. One of these electrolysers was constructed in the same way as known electrolyzers and contained an anode of permanent shape, placed at a certain distance from the diaphragm, as well as a cathode in the form of a stainless steel mesh placed at a similar distance. This electrolyzer worked in the same conditions as the remaining electrolysers used in the process carried out in accordance with the invention. The results given in Table 1 prove that the electrolysers used according to the invention operate at a voltage of 2.9-3.6 V, while the known electrolyzer (in Table 4) required the same conditions voltage higher by 0.6-1.5 V* The benefits achieved according to the invention are clearly visible. Diaphragms made of the above-described Nafion materials, manufactured by Dupont Corporation, were used in the electrolysers. 10 18 electrolyzers operating at higher current densities (32.4 and 43 A/dms) in accordance with the invention, with lower investment costs and the electrolyzer operates at a voltage approximately IV lower than known electrolyzers. Table 3 shows the relationship between cathode current efficiency and oxygen evolution. The tests were carried out in an electrolyzer with anodes and cathodes with reduced noble metal oxide, bonded with Teflon and inserted into a cationite diaphragm. A saturated aqueous solution of sodium chloride was electrolyzed at a temperature of 90°C, using a current density of 32.4 A/dm2 and distributing the brine- Table 1 Electrolyzer number 1 2 3 4 5 6 7 1 8 9 10 11 Anode 6 mg/cm2 (Ru 25% Ir)Ox 6 mg/cm2 (Ru 25% Ir)Ox 6 mg/cm2 (Ru 25% Ir)Ox Permanently sized mesh anode, spaced from the diaphragm 4 mg/cm2 (Ru 50% Ti)Ox 4 mg/cm2 (Ru 25% Ir 25% Ta)Ox 6 mg/cm2 (RuOx - graphite) 6 mg/cm2 (RuO)x 6 mg/cm2 (Ru - 5% Ir)Ox 2 mg/cm2 (IrOx) 2 mg/cm2 (IrOx) Cathode 4 mg/cm2 platinum black 4 mg/cm2 platinum black 4 mg/cm2 platinum black Stainless steel mesh, separated from the diaphragm 4 mg/cm2 platinum black 4 mg/cm2 platinum black 2 mg/cm2 platinum black 4 mg/cm2 platinum black 4 mg/cm2 platinum black 4 mg/cm2 platinum black 4 mg/cm2 platinum black Electrolyzer voltage V 3.2—3.3 3.3—3.6 2.9 4.2-4.4 3.6—3.7 3.5—3.6 3.0 3 .4 3.4-3.7 3.1-3.5 3.2—3.6 Current efficiency % 85 78 66 81 85 86 89 83 73 80 65 Diaphragm (NaOH 5m) Nafion 315 laminate Nafion 1500 " EW Nafion 1500 EW Nafion 1500 EW Nafion 315 laminate Nafion 315 Nafion 315 Nafion 1500 EW t Nafion 1500 EW Nafion laminate Nafion 315 laminate In electrolyzer no. 7 from table 1, electrolysis was carried out at a temperature of 90°C, introducing a saturated aqueous solution of sodium chloride home and office The electrolyzer voltage was adjusted depending on the current density. The results are given in table 2. Table 2 Electrolyzer voltage 1 V 3.2 2.9 2.7 1 2.4 Current density A/dm2 43 32.4 21.5 10.8 50 55 60 These results indicate that the operating voltage of the electrolyzer trolizer decreases as the current density decreases, but it should be emphasized that even at a cone of 31-77.5 ml per minute and 1 dm2 of electrode area. Oxygen content in chlorine in percent by volume as a function of cathode current efficiency. Table 3 Cathode current efficiency % 89 86 84 | 80 Amount of oxygen released f (% by volume) f i 2.2 4.0 5.8 I 8.9 f Table 4 illustrates the effect of brine acidification on oxygen evolution. The oxygen content in chlorine19 in % by volume was determined for different concentrations of HC1 in brine. Table 4 Molar concentration of HC1 in brine 0.05 0.075 0.10 0.15 0.25 Oxygen content in chlorine (% by volume) 2.5 1.5 0 .9 0.5 0.4 The data in Table 4 show that the evolution of oxygen due to the electrochemical oxidation of the returning OH- ions decreases as the hydroxyl anions chemically react with the hydrogen cations to produce water. In electrolyzer no. 1 from table 1, electrolysis of a saturated aqueous solution of NaCl, acidified with 0.2 m HCl, was carried out. The process was carried out at a current density of 32.4 A/dm2 at a temperature of 35-90°C and the electrolyzer voltage was measured at various temperatures. The test results are given in Table 5. In electrolyzer No. 7 from Table 1, electrolysis of an aqueous NaCl solution with a concentration of 290 g/liter, not acidified with hydrochloric acid, was carried out. The process was carried out at a temperature of 35-90°C at a current density of 21.5 A/dm2 and the electrolyzer voltage was measured at various temperatures. The results are given in Table 5 after conversion to work at a current density of 32.4 A/dm2, the results before conversion are given in brackets. thus limiting the return migration of sodium hydroxide to the anode side. The anode was a layer connected to the diaphragm containing (Ru 25 Ir) Oz particles bound with Teflon T-30 in an amount of 20% by weight. This layer contained 6 mg of precious metal per 1 cm2. On the other side, the diaphragm was bonded to the cathode in the form of platinum black particles mixed with 15% by weight of Teflon T-30 as a binder. There was 4 mg of platinum black per 1 cm2 of cathode surface. An aqueous NaCl solution with a concentration of 280-315 g/liter was introduced into the anode space, and distilled water was also introduced into this space. Electrolysis was carried out at a current density of 32.7 A/dm2, at a temperature of 85-90°C. The results of these tests are given in table 6. 1 Voltage 1 of electrolyzer no. 1 3.65 3.38 3.15 3.10 3.05 3.02 Voltage of electrolyzer no. 2 at 32.4 A/dma 3.50 (3.15) 3.30 (2.08) 3.12 (2.78) 3.05 (2.72) 2.97 (2.65) 2.95 (2.63) Tempera- | round 1 °C 35 45 65 75 85 90 The results given in table 5 show that the most favorable operating voltage is obtained at a temperature of 80-90°C, but it should be noted that even at a temperature of 35°C the operating voltage of these electrolysers used in accordance with the invention is at least 0.5 V lower than in the case of known electrolysers in which chlorine is produced at a temperature of 90°C. Electrolysers have been made containing complex diaphragms, having barrier layers on the cathode side, breathing anions. These layers consisted of chemically modified sulfanomides. The diaphragms were 1.9 mm thick and made of Nafion material manufactured by Dupont Corporation. The cathode side of each diaphragm was made to a depth of 0.38 mm and subjected to a reaction with 10-19 20 30 35 40 45 90 55 60 Table 6 Electrolyzer number 1 2 1 3 Electrolyzer voltage 2.68 2.78 2.76 Temperature °C 85 89 90 NaOH concentration 5.1 m 4.8 m 4 .8 m Cathode efficiency-1 % 89.6 87.6 1 91.6 1 These data prove that the use of a sulfonamide barrier layer significantly improves the cathode current efficiency without affecting the operating voltage of the electrolyzer. In such electrolysers, a total current efficiency of about 88-92% was obtained, which shows that the diaphragms associated with such electrodes enable the process to be carried out with a current efficiency much better than when using known methods of brine electrolysis. The best results are obtained using for NaCl electrolysis, electrolyzers in which both electrodes are connected to the surface of the ion-transferring diaphragm, but significant benefits are also achieved by using electrolyzers in which only one of the electrodes is connected to the ion-transferring diaphragm. In such hybrid electrolysers, the benefits are smaller than in the case of electrolyzers having both electrodes connected to the diaphragm, but they are still significant compared to the processes carried out in known electrolysers, namely the operating voltage is lower by 0.3-0.5 V Comparative tests were carried out by electrolyzing brine in electrolysers with both electrodes connected to the diaphragm and in hybrid electrolysers in which only the anode or only the cathode was connected to the diaphragm. At the same time, the process was carried out under the same conditions in known electrolysers, in which none of the electrodes was connected to the diaphragm. In all cases, Nafion 315 diaphragms were used, the process was carried out at a temperature of 90°C, adding brine with a concentration of approximately 290 gj/liter. Platinum black was used on the cathode in an amount of 2.15119 244 21 22 mg/cm2, and on the anode ! RuOx with graphite, Ru with graphite or RuOx in the amount of 4.3 mg/cm2. The current efficiency at a current density of 32.4 A/dm2 was almost the same in all cases (84-85% for NaOH 0.5 m). The test results are given in Table 7. As can be seen, electrolyzer No. 1 with both electrodes connected to the diaphragm operates at a voltage almost 1 V lower than the operating voltage of the known electrolyzer No. 6, in which the electrodes are not connected to the diaphragm. Hybrid electrolyzers have a voltage 0.4-0.6 V higher than electrolyzer no. 1, but 0.3-0.5 V lower than the known electrolyzer no. 6. f Electrolyzer no. 1 1 2 3 4 5 6 Ta Anode RuOx-graifit bonded platinum niobium mesh, unbonded platinum niobium mesh, unbonded Ru-graphite bonded RuOx bonded platinum niobium mesh, unbonded bale 7 Cathode black platinum bonded platinum black bonded platinum black bonded nickel mesh unbonded nickel mesh unbonded nickel mesh unbonded Voltage | at a current density of 32.4 A/dm2 2.9 3.5 34 i i 3.5 3.3 3.8 N The results given in the examples prove that the method of producing chlorine by electrolysis of brine according to the invention is much more advantageous than the known ones methods and enables the production of chlorine at the anode and hydrogen and highly pure alkali metal hydroxide at the cathode. By using direct contact of the electrodes with the diaphragm containing acid radicals, a higher current efficiency of the process is achieved, in which an operating voltage lower by about 1 V from the voltage in known processes, and the use of catalysts with low overvoltage described above also contributes to improving the process efficiency. Patent claims 1. Method of producing halogens and alkali metal hydroxides by electrolysis of alkali metal halides between the anode and the electrolyzer cathode, which electrodes are separated from each other by a polymeric cation exchange membrane, at least one of the electrodes contains an electrically conductive catalytic substance and is permanently bonded in numerous points with the diaphragm, creating a uniform electrode-diaphragm complex, characterized in that the electrolysis process is carried out using at least one electrode whose electrically conductive catalytic substance is in direct contact with the diaphragm and voltage is applied to this electrode connected with the diaphragm by means of a conductive electric current of the collector, causing its surface to contact the surface of this electrode, and a collector is used whose surface has an overvoltage for hydrogen or halogen higher than the overvoltage of the electrode surface associated with the diaphragm. 2. The method according to claim The method of claim 1, characterized in that at least one gas- and electrolyte-permeable electrode is used, containing a catalytic substance in the form of particles bound to the diaphragm on the cathode side. 3. The method according to claim The method of claim 1, characterized in that at least one gas- and electrolyte-permeable electrode is used, formed by a diaphragm having on the anode side consisting of numerous electrically conductive particles of a catalytic substance introduced into the diaphragm. 4. The method according to claim 1 or 2 or 3, characterized in that heat-set particles of reduced metal oxides from the platinum group are used as the electrically conducting and catalytically acting particles introduced in the diaphragm. 5. The method according to claim 4, characterized in that heat-set particles of reduced platinum group metal oxide bonded with a fluorocarbon are used. 6. The method according to claim 4, characterized in that heat-set particles of reduced ruthenium oxides are used, further fixed by the introduction of heat-set, reduced oxides of metals such as iridium, tantalum, titanium, niobium or hafnium. 7. The method according to claim The method of claim 1, characterized in that a diaphragm is used whose cathode side has a lower water content than the rest of the diaphragm. 8. The method according to claim 1 or 7, characterized in that a diaphragm is used in the form of a laminate of two layers, the ability of which to repel anions is greater on the cathode side than on the anode side. 9. The method according to claim 8, characterized in that a diaphragm is used which is a polymeric fluorocarbon cation exchanger having on the cathode side a barrier sulfonamide layer that repels the anodes. 10. The method according to claim 1, characterized in that the aqueous solution of alkali metal chloride is contacted with an anode made of bonded, heat-set ruthenium oxides. 11. The method according to claim 1, characterized in that at least one electrode is used containing a mixture of graphite particles and a metal from the platinum group and/or a metal oxide of the 2nd group of platinum. 12. The method according to claim 10, characterized in that the aqueous solution of alkali metal chloride is contacted with an anode made of bound ruthenium and graphite oxides reduced in the alkali metal chloride solution. The concentration of HC1 in the anode is maintained at 13. The method according to claims 10, characterized in that at least 0.2 molar. FIG.2 ZGK 5 Btm, order 90*2 — 95 copies Price PLN 100 PL PL PL

Claims (13)

1. Patent claims 1. Method of producing halogens and alkali metal hydroxides by electrolysis of alkali metal halides between the anode and cathode of the electrolyzer, which electrodes are separated from each other by a polymeric cation exchange membrane, at least one of the electrodes contains electrically conductive - 10 15 20 25 30 35 40 45 50 55 65 catalytic substance and is permanently bonded to the diaphragm at numerous points, creating a uniform ejectrode-diaphragm complex, characterized in that the electrolysis process is carried out using at least one an electrode whose electrically conductive catalytic substance is in direct contact with the diaphragm and a voltage is applied to this electrode associated with the diaphragm by means of an electrically conductive collector, causing its surface to come into contact with the surface of this electrode, and a collector is used whose surface has an overvoltage for hydrogen or halogen higher than the overvoltage of the electrode surface connected to the diaphragm. 2. The method according to claim The method of claim 1, characterized in that at least one gas- and electrolyte-permeable electrode is used, containing a catalytic substance in the form of particles bound to the diaphragm on the cathode side. 3. The method according to claim The method of claim 1, characterized in that at least one gas- and electrolyte-permeable electrode is used, formed by a diaphragm having on the anode side consisting of numerous electrically conductive particles of a catalytic substance introduced into the diaphragm. 4. The method according to claim 1 or 2 or 3, characterized in that heat-set particles of reduced metal oxides from the platinum group are used as the electrically conducting and catalytically acting particles introduced in the diaphragm. 5. The method according to claim 4, characterized in that heat-set particles of reduced platinum group metal oxide bonded with a fluorocarbon are used. 6. The method according to claim 4, characterized in that heat-set particles of reduced ruthenium oxides are used, further fixed by the introduction of heat-set, reduced oxides of metals such as iridium, tantalum, titanium, niobium or hafnium. 7. The method according to claim The method of claim 1, characterized in that a diaphragm is used whose cathode side has a lower water content than the rest of the diaphragm. 8. The method according to claim 1 or 7, characterized in that a diaphragm is used in the form of a laminate of two layers, the ability of which to repel anions is greater on the cathode side than on the anode side. 9. The method according to claim 8, characterized in that a diaphragm is used which is a polymeric fluorocarbon cation exchanger having on the cathode side a barrier sulfonamide layer that repels the anodes. 10. The method according to claim 1, characterized in that the aqueous solution of alkali metal chloride is contacted with an anode made of bonded, heat-set ruthenium oxides. 11. The method according to claim 1, characterized in that at least one electrode is used containing a mixture of graphite particles and a metal from the platinum group and/or a metal oxide of the 2nd group of platinum. 12. The method according to claim 10, characterized in that the aqueous solution of alkali metal chloride is contacted with an anode made of bound ruthenium and graphite oxides reduced in the alkali metal chloride solution. HC1 concentration maintained at the anode 13. The method according to claim 10, characterized in that it is at least 0.2 molar. FIG. 2 ZGK 5 Btm, resident 90*2 — 95 copies Price PLN 100 PL PL PL