JPS58181879A - Halogen electrolysis manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention generally relates to a method and apparatus for producing halogens and alkali metal hydroxides by electrolysis of aqueous solutions of alkali metal halides.

More specifically, the present invention relates to a method for producing chlorine and sodium hydroxide by electrolyzing a saline solution in an electrolytic cell using an electrocatalytic anode and a cathode bonded to at least one surface of a diaphragm; It is related to the device.

Advantageously, the present invention provides an electrolytic cell containing an anode compartment and an anode compartment separated by a solid polymeric electrolyte in the form of a stable, selectively cation-permeable ion exchange membrane. When generating a halogen, such as chlorine, by electrolyzing an aqueous solution of an alkali metal halide, at least one thermally stabilized reduced oxide of a platinum group metal may be used. An electrode with electrocatalytic action (hereinafter referred to as a catalytic electrode) is used in a form bonded to the surface of the ion exchange membrane, and a saline solution is brought into contact with the anode and water or Na
A saline solution is electrolyzed by contacting the OH' aqueous solution with the cathode to produce chlorine at the anode and hydrogen and caustic at the cathode. In doing so, the cell diaphragm serves as an anion blocker to block hydroxide ions and block back migration of caustic alkali to the anode, thereby increasing the cathode current efficiency of the electrolytic cell and the process. It is preferable to have a barrier layer on the cathode side.

Electrolysis of sodium chloride aqueous solution produces chlorine-like ha[]
The production of gen, with the production of caustic alkali (NaOH) as a by-product, constitutes a major industry. mosquito)
The chlorine-alkali industry produces hundreds of thousands of tons of chlorine and caustic soda annually.

The main electrolytic methods conventionally used for producing chlorine are the so-called mercury method and the diaphragm method. The mercury method is a method in which an aqueous alkali metal chloride solution is electrolyzed in an electrolytic cell with a graphite or metal anode (DSA - dimensionally stable wA electrode) and a mercury cathode. Chlorine is liberated at the @ pole and the -h alkali metal is precipitated in the mercury in the form of an alkali metal amalgam. Alkali metal amalgam is processed by a decomposition reaction that reacts the amalgam with water to produce caustic soda and hydrogen.

However, the mercury process is obsolete for all practical purposes for the production of chlorine. Mercury is an extremely toxic substance, and the ordinance standards for regulating mercury and other citron contaminants are becoming so strict that the days of mercury laws are said to be over. However, beyond the pollution and environmental problems associated with the use of mercury methods for chlorine production, mercury method electrolysers are NN and expensive. The use of mercury itself presents problems in that it is complicated by the size of the bath and the care required in handling the mercury. Mercury is expensive and must be used extensively.

A notable economic problem associated with the mercury process is the cost of the cracking process and associated equipment to produce caustic soda and hydrogen.

On the other hand, diaphragm electrolysers do not use mercury and have electrodes with pores separated by microporous diaphragms.

The gap between the electrodes is separated by micropores ms, which can be filled with saline solution and take the form of an overlying porous diaphragm separating the cathode and anode compartments.

One of the significant disadvantages of membrane electrolyzers is that mass transfer or flow of the sodium chloride solution occurs across the membrane through the pores in the membrane1, so that the catholyte, i.e. also at the cathode, The caustic solution produced is contaminated with substantial amounts of sodium chloride. This results in the production of impure and dilute caustic. On the other hand, the hydroxide formed at the cathode can migrate back through the porous diaphragm to the anode, so that the hydroxide is electrolyzed at the anode to produce oxygen. Oxygen production at the anode is highly undesirable for a variety of reasons. That is, the production of oxygen at the anode not only provides less pure chlorine, but the oxygen also attacks the anode.

Is the anolyte and catholyte transferred between the two alyte compartments? This results in a number of undesirable effects, such as those mentioned above, and a number of improvements have been proposed to minimize or completely overcome these disadvantages. One is to maintain a pressure differential across the membrane such that mass transfer of electrolyte between the catholyte and catholyte compartments is minimally inhibited. However, such solutions are only partially effective at best.

11i! To overcome the disadvantages associated with the use of membrane electrolyzers and mass transfer of electrolyte through porous membranes, ion-selective permselectors are used to separate anolyte and catholyte in chlorine-generating electrolyzers. It was suggested that a diaphragm be used.

The ion-selective permselective membranes used in these electrolytic cells are mainly C-cationic bamboo membranes in order to selectively pass negatively charged anions. Since these membranes are not porous, they prevent the caustic from migrating back from the catholyte compartment to the anolyte compartment and likewise allow the saline anolyte to be transferred to the catholyte compartment to dilute the caustic. It has a slope that prevents However, it has been recognized that diaphragm electrolysers still have certain drawbacks, which limit their widespread use.

One of the main drawbacks of the diaphragm electrolyzers known to date is that they have high sliding voltages.

Only a portion of the sliding voltage is due to the properties of the diaphragm itself, and a significant portion of this is due to the fact that known diaphragm cell designs utilize electrodes that are physically spaced from the diaphragm. This is due to the point. As a result of the physical gap between the electrode and the diaphragm, the electrolyzer not only creates an IR drop across the diaphragm, but also provides an electrolyte IR drop in the electrolyte between the electrode and the diaphragm prior to ion transport. C
chlorine is generated at a distance from the diaphragm. As a result, a gas layer is formed between the electrode and the diaphragm. This gas layer obstructs the passage of electrolyte between the electrode and the diaphragm, thereby partially sealing the ions from the diaphragm. Such obstruction of electrolyte passage between the electrode and the diaphragm, of course, also leads to additional IR reduction, which increases the sliding voltage required for chlorine generation, with the result that the voltage efficiency of the cell is clearly reduced.

The advantages of the invention will become apparent from the description below.

According to the invention, an aqueous solution of an alkali metal halide, for example an aqueous NaCl solution, is electrolyzed using an electrolytic cell containing a solid polymer electrolyte in the form of a cation exchange membrane, which divides the cell into a catholyte compartment and an anolyte compartment. By doing so, halogens, ie, chlorine, bromine, etc., are generated at the anode. The catalytic north pole, which allows chlorine and caustic to be generated in situ, is a thin, porous, gas permeable catalytic electrode that allows chlorine to be generated at the electrode-diaphragm interface by separation. This results in an electrode with extremely low overpotentials for chlorine release and caustic production.

The catalytic electrode is a reduced oxide of at least one platinum group metal (
The catalytic material comprises at least one reduced platinum group metal oxide which is thermally stabilized by heating the reduced oxide in the presence of oxygen. In one preferred embodiment, the electrode comprises a fluorocarbon (
polytetrafluoroethylene particles). Examples of useful platinum group metals are platinum, palladium, iridium, rhodium, luteum and osmium. Preferred reduced metal oxides for the production of chlorine are reduced oxides of ruthenium or iridium. The electrode catalyst is ruthenium oxide,
Although it can be a single reduced platinum group metal oxide such as iridium oxide, platinum oxide, etc., it has been found that mixtures or alloys of reduced platinum group metal oxides are more stable. For example, electrodes consisting of a reduced oxide of ruthenium containing up to 25% by weight of reduced oxide of iridium, preferably from 5 to 25% by weight, have been found to be very stable.

up to 50% by weight, preferably 10-30% by weight of graphite or other conductive fillers, such as ruthenium-coated titanium
can be added in an amount of The extender should have good conductivity and low halogen overvoltage and be substantially cheaper (i
It should be substantially cheaper than the platinum group metals so as to provide a flexible yet highly effective electrode.

Addition of reducing oxides of one or more pulp metals such as titanium, tantalum, niobium, zirconium, hernonium, vanadium or tungsten to stabilize the electrode against oxygen, chlorine and generally harsh electrolytic conditions It can be forced. Although 50% by weight valve metal can be effectively used, it is preferred to use 25 to 50% by weight. At least one of the catalytic electrodes is coupled to a liquid-impermeable, ion-transporting membrane. By bonding -b or both of the electrodes to the diaphragm, transport losses of the gaseous body due to the formation of a gas layer between the electrode and the diaphragm are prevented to a minimum, so that
The drop in electrolyte IR between the electrode and the diaphragm is kept to a minimum.
Ill be taken. This results in a substantial reduction in sliding voltage and significant economic advantages resulting from this reduction.

The novel features of the invention are defined in the claims. However, in order to more clearly illustrate the invention itself, its mechanism and method of operation, together with its objects and advantages, the invention will now be further described with reference to the drawings.

In FIG. 1 showing a schematic diagram of an electrolytic cell that is a feature of the present invention, the electrolytic cell generally designated as 10 has a catholyte chamber 11,
There is a solid polymer electrolyte membrane 13 separating the anolyte compartment 12, preferably a hydrated permselective cation exchange membrane. The surface of the diaphragm 13 on the anode side is coated with a stabilized reduced oxide of ruthenium or iridium (R
uOx) or (lrox), stabilized reduced oxide of ruthenium-iridium (RIJ lr) Ox
, stabilized reduced oxide of rhdenium-titanium (RU
ll) ○×, stabilized reduced oxide of ruthenium-titanium-iridium (Ru T i lr ) OX, stabilized reduced oxide of ruthenium-tantalum-iridium ( Ru Ta lr ) OX or stabilized ruthenium-graphite Nororocarbons bonded to reduced oxides such as
An electrode consisting of particles of fluorocarbon, sold by the company, is attached. 14'c A small cathode is bonded to and embedded in one side of the diaphragm, and a catalytic anode, not shown, is bonded to and embedded in the opposite side of the diaphragm. The cathode bonded with Teflon is similar to the anode catalyst. Suitable catalytic materials include finely divided metals such as platinum, palladium, gold, silver, spinel, manganese, cobalt, nickel, reduced oxides of platinum group metals, such as Pt.
-1rOx, Pt-RuOx, etc., graphite and appropriate combinations thereof.

Current collectors 15 and 16 in the form of metal screens are pressed against the electrodes. The entire septum Ill/electrode assembly is
The gaskets 17 and 18 are rigidly supported between the shells 1 and 12 and are made of any material that is resistant or inert to the tank environment, i.e., chlorine, oxygen, thorium chloride and aqueous caustic solution. ing. One form of gasket is manufactured by the United States, Massachusetts,
E from l rVinQ MOOre in Cambridge.
It is a filled rubber gasket sold under the trademark PDM.

A saline solution as the anolyte is introduced through the electrolyte port 19 communicating with the anode v20. The spent electrolyte and chlorine gas are removed through the outlet conduit 21 and further through the shell. The cathode inlet conduit 22 communicates with the cathode chamber 11 and serves to introduce catholyte, water or an aqueous NaOH solution (more dilute than that formed electrochemically at the bridge/electrolyte interface) into the cathode V. Motsu. Water serves two different functions. However, some of the water is electrolyzed to form hydroxyl (OH) anions, which combine with sodium cations that are transported toward the diaphragm to form caustic (NaOH) anions.
form. Water also flows across the embedded cathode and separates the gap! It dilutes the extremely high concentration of caustic that forms at the I/electrode interface, thereby minimizing diffusion of caustic back across the diaphragm into the anolyte chamber. The cathode outlet conduit 23 communicates with the cathode chamber 11 and serves to remove the diluted caustic and any hydrogen released at the cathode and any excess water. A power cable 24 is led into the cathode compartment, and a similar cable, not shown, is led into the anode compartment. These cables connect the conductive wire meshes 15 and 16 to a power source.

FIG. 2 is a diagrammatic illustration of the reactions that take place in the cell during electrolysis of a saline solution, and is useful for understanding the electrolytic method of the present invention and the function of the electrolytic cell. An aqueous solution of sodium chloride is introduced into the anode chamber, which is separated from the cathode chamber by a cation diaphragm 13. For optimal cathode efficiency, the diaphragm is provided with an ion-blocking barrier layer on its cathode side to block hydroxide ions and prevent or minimize back migration of caustic to the anode. The diaphragm 13 has a high water content (20-35% based on the dry weight of the diaphragm) 1ii26. on the anode side, as detailed below. ij and Teflon cloth 28
A composite membrane is formed with the cathode side m27 having a low water content (5-15% of the dry weight of the membrane) separated therefrom by the membrane. The ion blocking properties of the anion blocking barrier layer on the cathode side can be further enhanced by chemically modifying the perfluorosulfonic acid membrane on the cathode side to form a thin layer of shrub-containing polymer. - In embodiments, this is achieved by modifying the polymer to form a substituted sulfonamide diaphragm layer.

The cathode side layer 27 thus has a high MEW (the ivy is converted to a weak acid form (sulfonamide), which can thus reduce the water content in this part of the laminated membrane.

This increases the salt blocking capacity of the coating and minimizes the disadvantage of sodium hydroxide migration across the membrane to the anode. This diaphragm is also a homogeneous coating of a low water content diaphragm. (Nafion-150, perfluorocarboxylic acid, etc.).

of a platinum group metal bonded to Teflon, containing a stabilized reduced oxide of ruthenium or iridium or ruthenium-iridium, with or without a reduced oxide of titanium, di-A or tantalum, and graphite. The reduced oxide catalyst is pressed against the surface of the diaphragm 3 as shown. Current collectors 15 and 16, only partially shown for clarity, are pressed against the surface of the catalytic electrode and are connected to the positive and negative terminals of the power source, respectively, to provide an electrolytic potential across the electrode. The sodium chloride solution introduced into the anode chamber is electrolyzed at the anode 29 to generate chlorine at the surface as illustrated schematically by bubble formation 30. Sodium ions (Na+) are transported across diaphragm 13 to cathode 14. A stream of water or Na OH aqueous solution shown at 31 is directed into the cathode chamber to act as the catholyte. This aqueous flow dilutes the caustic formed at the flow septum II/cathode interface across the surface of the Teflon-bonded catalytic cathode 14 and reduces back migration of caustic across the septum to the anode. .

A portion of the wood catholyte is electrolyzed at the cathode under alkaline reaction conditions to produce hydroxide ions (OH-) and gaseous hydrogen. These hydrogen ions combine with sodium ions transported across the membrane to form sodium hydroxide (caustic soda) on the septum GL/electrode interface. This sodium hydroxide readily wets the Teflon forming part of the bonded electrode and diffuses to the surface where it is diluted by the aqueous stream flowing across the electrode surface. 4.5-6.5M concentrated sodium hydroxide is easily produced at the cathode by sweeping the cathode with an aqueous solution.

Therefore, even with dilution, some sodium hydroxide remains in the diaphragm 13, as shown by arrow 33.
It moves back through to the anode. The sodium hydroxide transferred to the anode is oxidized to produce water and oxygen as shown by bubble formation at 34. Of course, this is a parasitic reaction that reduces the current efficiency of the cathode. The production of oxygen itself is undesirable since oxygen can have an adverse effect on the electrodes and diaphragms. Additionally, element II dilutes the chlorine produced at the anode and therefore requires treatment to remove oxygen. The reactions at various parts of the tank are similar to each other.

The novel configuration of the electrolysis of saline solutions described in the present invention is such that the catalytic sites in the electrode are the cationic diaphragms, and therefore the ion-exchangeable acid groups bonded to the polymer backbone (these groups are 5O3tlXHzO sulfonic acid groups). Roto C
00HXH20 carboxylic acid group). As a result, there is no appreciable IR drop in the anolyte or catholyte compartments (
This IR drop is usually called ``electrolyte IR drop'')
.

``Electrolyte IR reduction'' is characteristic of existing systems and methods in which the electrode and diaphragm are spaced apart.
The drop may be on the order of 0.2-0.5 volts. The elimination or substantial reduction of this voltage drop is of course one of the principal advantages of the present invention, since it has a clear and very significant effect on the overall sliding voltage and the economy of the method. Furthermore, since chlorine is generated directly at the interface between the anode and the diaphragm,
Caused by gas shielding and reduced mass transport due to obstruction or blockage of the electrolyte passage between the electrode and the diaphragm, the so-called ``bubble effect''11
No decrease in performance was observed in this case.

As mentioned above, in prior art systems, the catalytic electrode that releases chlorine is located at a distance from the diaphragm. The gas is directly deposited in the electrode, forming a gas layer in the gap between the diaphragm and the electrode, which actually destroys the electrolyte passage between the electrode and the diaphragm and blocks the passage of rNa+ ions.
This effectively increases the IR drop.

The catalytic electrode associated with the electrode teflon contains reduced oxides of the aforementioned platinum group metals, such as ruthenium, iridium, or ruthenium-iridium, to minimize chlorine overvoltage at the anode.

The reduced γ-ium oxide is stabilized against chlorine and oxygen to form a stable anode. Stabilization is first carried out by thermal stabilization, ie heating the reduced oxide of ruthenium to a temperature below the temperature at which decomposition of the reduced oxide to pure metal begins to occur. for example,
The reduced oxide is preferably heated to 350 DEG -750 DEG C. for 30 minutes to 6 hours. A preferred thermal stabilization treatment is accomplished by heating the reduced oxide to a temperature of 550° to 600°C for one hour. A Teflon-bonded anode containing a reduced oxide of ruthenium can be further prepared by mixing it with graphite and/or a reduced oxide of other platinum group metals, e.g.
r) Mixing OX with iridium in a proportion ranging from 5 to 25%, preferably 25% iridium, or with reduced oxides of platinum, rhodium, etc., and further reduced oxides of valve metals, e.g. (Ti). Stabilized by mixing with Ox (preferably Ti0X 25-50%) or reduced oxide of tantalum (25% or more). Furthermore, in producing stable, long-life single poles, ternary alloys of reduced oxides of titanium, ruthenium and iridium (RIJ, II-) are used.

Ti) Ox or ternary alloys of reduced oxides of tantalum, ruthenium a' and iridium (RIj, Ir.

The use of Ta)OX bonded to Teflon has been found to be very effective. In the case of ternary alloys,
The composition is preferably 5 to 25% reduced oxide of iridium, about 50% reduced oxide of ruthenium, and the remainder a transition metal such as titanium. For binary alloys of reduced oxides of ruthenium and titanium, titanium 50
Preferably, the balance by weight is ruthenium. Of course, titanium has the added advantage of being much cheaper than either ruthenium or iridium, thus reducing the price of the wA electrode, while at the same time stabilizing the anode under acidic conditions and reducing chlorine and oxygen release. It is also an effective bulking agent that stabilizes other transition metals,
For example, niobium (Nl), tantalum <la), zirconium (7r) or hafnium <Hf) may also be used as an alternative to [1] in this electrode structure.

An alloy of reduced oxides of noble metals and reduced oxides of titanium or other transition metals is mixed with Teflon to form a homogeneous mixture. The Teflon content of this anode is Teflon [1-15
~50% by weight, but Teflon 20-30% by weight
is preferred. Teflon is called Qupon with the name 1-30.
Although other fluorocarbons can be used as well. The typical amount of negative metal added to this anode is 1C11 on the electrode surface.
0.6-tusk per ', preferred range is 1-2-77
It is cII2. The TEPCO hardener for the anode can be a fine mesh platinum coated niobium screen that makes good contact with the electrode surface. Another possible use as an anode coating is an expanded titanium screen coated with ruthenium oxide, iridium oxide, transition metal oxides, and mixtures thereof. Yet another anode coating may be in the form of a noble metal or negative metal oxide coated screen attached by welding or bonding to the anode plate.

The anode current collector that engages the bonded anode layer has a higher chlorine overpotential than the catalytic anode surface layer of the anode. This reduces the probability that electrochemical reactions, such as chlorine evolution, will occur on the current distributor surface. This is because these reactions are more likely to occur on the catalytic anode surface, which has a lower overvoltage and higher IR drop relative to the TEPCO screen.

The cathode was prepared by 1) adding []n particles and platinum black to a condition where the addition of platinum black was ≠0.
Binding mixture C mixed at a ratio of 4 to 41R')/cn'
It is preferable that there be. As mentioned above, palladium,
Other catalytic materials such as gold, silver, spinel, iron, cobalt, nickel, graphite and reduced oxides used on the anode (such as Rulr○x) may be used as well. The cathode also
Like the anode, it is preferably bonded to and embedded in the surface of the cation diaphragm. The cathode is formed to be very thin, ie, 2 to 3 mils or less, preferably about 0.5 mils thick, porous, and with a low Teflon content.

The thickness of the cathode can be very important. As the roughness increases, the water or jtNaOH aqueous solution flow and permeability of the cathode decreases, and the cathode current efficiency also decreases due to silting. Form an electrolytic cell with a thin (approximately 0.5 to 2.0 mil thick) platinum black-15% tenolone bonded cathode. The w ratio of electrolytic cells with these thin cathodes is 2902/L.
H was about 80%. When using a 3.0 mil thick Ru-graphite cathode, the current efficiency is 5M Na0Hr5.
It decreased to 4%. Table A shows the relationship between current efficiency CE and cathode depth and shows that cathodes with thicknesses not exceeding 2 to 3 mils give the best performance.

Table A Tank Cathode Cathode thickness
Current efficiency - (mil)
% (MNa ○to()1 Platinum black
2~3 64 (4,0M)2
Shirokane black 2-3 73
(4,bM)3 Shirokane black 1~2
7”:v (3,1M) 4 Shirokane black 1~2 82 (5M
)5 Shirokane black 0.5
78(5,5M)6 5% platinum black on graphite
3 78 (3, OM) 7 5% Ru Ox on graphite 3 54
(5,0M>8 Platinum coated graphite cloth 10~
The 15 57 (5M) electrode is formed to be gas permeable so that gas generated at the electrode/diaphragm interface can easily leak out. The porosity is such that water can penetrate the cathode/diaphragm interface where Na 2 OH is formed and the saline feed has easy access to the catalytic sites of the membrane and electrode. The former, water penetration into the cathode/diaphragm interface, occurs during the initial formation of NaOH, which wets the Teflon and rises to the electrode surface where it is further diluted by water flowing across the electrode surface. Helps dilute very high concentrations of NaOH before it becomes saturated. The dilution effect at the diaphragm interface, where the NaOH concentration is highest, is important. To achieve maximum water penetration at the cathode, the Teflon content should not exceed 15-30% because Teflon is hydrophobic.

By filling the trabeculae with good porosity, limited Teflon content, thin cross-section and flow of water or diluted NaOH, the Na0t−1 concentration can be increased beyond the diaphragm.
controlled to reduce the tendency for OH migration to occur. In addition to the use of water or diluted NaOH streams for the purpose of controlling the structural properties of the cathode and reducing the WJ and Na0HII degrees, the reverse of UNaOH can be achieved by providing a 7-ion blocking barrier layer on the cathode side. Migration can be further reduced.

The area between the current collectors for the cathode should not be cleaned, as the extremely corrosive caustic alkali present in the cathode will attack many materials, especially during outages.
The numbers must be carefully selected. The current collector takes the form of a nickel jaw screen as nickel is resistant to caustic. The current collecting space may also be comprised of a stainless steel electrode plate and a stainless steel screen welded thereto. Another cathode current collector structure that is resistant or inert to caustic solutions is graphite or graphite in combination with an electrode plate pressed against its surface. The cathode current collectors that engage the bonded cathode layers are formed from a material that has a higher hydrogen overpotential than the catalytic cathode surface.

This also reduces the probability of electrochemical reactions such as hydrogen evolution occurring on the current distributor. These reactions are more likely to occur on the cathode surface because the catalytic cathode surface has a lower overpotential and the cathode shields the current collector to some extent.

Diaphragm Membrane 13 is preferably a stable hydrated cation exchange membrane characterized by ion transport selectivity. The cation exchange membrane allows the passage of positively charged sodium cations and minimizes the passage of negatively charged anions. Various types of ion exchange resins can be used to make membranes that provide selective transport of cations. Two types of resins are so-called sulfonic acid type cation exchange resins and carboxylic acid type cation exchange resins. In a preferred type of sulfonic acid-type cation exchange resin, the ion exchange group is a hydrated sulfone bonded to the polymer backbone by sulfonation. group (803HXH20). These ion-exchangeable acid groups are fixedly bound to the polymer backbone without movement within the diaphragm, thereby ensuring that the electrolyte concentration does not fluctuate.

As previously mentioned, perfluorocarbon sulfonic acid type cation exchange resin membranes provide excellent cation transport, are extremely stable, are not attacked by acids and strong oxidants, have excellent thermal stability, and are essentially unchanged over time. Therefore, it is preferable. A particular group of preferred cationic polymeric membranes is available under the trade name "Nafion".
These membranes are a hydrated copolymer of polytetrafluoroethylene (PTFE) and vinyl sulfonyl fluoride containing pendant sulfonic acid groups. These membranes are of the hydrogen type, which is the type they are usually obtained from manufacturers.

The ion exchange capacity (IEC) of a given sulfonic acid-type cationic polymer membrane is 803 millimeters per 12 ml of dry polymer.
ght, MEW). The higher the concentration of sulfonic acid type groups, the greater the ion exchange capacity and therefore the greater the cation transport capacity of the hydration membrane. However, as the ion exchange capacity of the membrane increases, the water content increases and the salt rejection capacity of the membrane decreases.

Therefore, the rate of migration of sodium hydroxide from the cathode side to the anode side increases with IEC. This results in a decrease in cathode current efficiency (CE) and also in the evolution of oxygen at the anode, with all the attendant undesirable consequences. Thus, one example of a preferred ion exchange resin membrane for use in saline electrolysis is a high ion exchange capacity, 1100 MEW, bonded to a 4 mil or thicker film with Teflon holes.
EW, low water content <5-15%), cation exchange I/JA #3 with high salt blocking ability! It is a stacked pigeon body made of a thin film of 2 mils thick. An example of a laminated structure is available from Dupont under the trade name Narion 315.
Other types of laminated structures commercially available are Nafion 355, 376.3.
90,227.214, whose cathodic side consists of a thin layer or III membrane of resin with a low water content (5-15%) that provides optimal salt rejection capacity, while the anode side of the diaphragm increases ion exchange capacity. It has a structure that is a thin film with high water content.

The ion exchange membrane is immersed in caustic alkali <3-8M> for 1 hour to adjust the membrane's water content and ion transport performance to be maintained constant. In the case of I441ii septa bonded together by a Teflon cloth, the septum or Teflon cloth was washed in 70% rIaast for 3 to 4 hours.
It is desirable to clean by refluxing for a period of time.

As already briefly pointed out, the barrier layer on the cathode side should be characterized by a low water content, based on water-absorbing persulfonic acid groups. This results in more efficient anion (hydroxide) rejection. By sequestering or blocking the hydroxide ions, caustic backmigration is substantially reduced, thereby increasing cell current efficiency and reducing oxygen evolution at the anode. In another layered structure, the layer on the cathode side of the diaphragm is chemically modified. For example, the functional groups in the surface layer of the polymer are modified to have lower water absorption than sulfonic acid type membranes.

This is accomplished by reacting the surface layer of the polymer to form a layer of sulfonamide groups. Various reactions can be used to form the sulfonamide type surface layer. One way to do this is to use sulfonyl fluoride type C.
A method in which the surface of a certain Nafion membrane is reacted with an amine such as ethylene diamine (EDA) to form a substituted sulfonamide membrane. This sulfonamide layer acts as a highly effective barrier layer for anions. By blocking the hydroxyl anion on the cathode side, the back migration of the caustic alkali (NaOH) is clearly substantially reduced.

Electrode Manufacture Reduced oxides of platinum group metals such as ruthenium, iridium, ruthenium-iridium, alone or together with reduced oxides of transition metals such as titanium or graphite, are combined with Teflon particles to form porous gas-permeable catalysts. Electrodes are formed, the manufacture of which is accomplished by pyrolyzing the mixed metal salts in the presence or absence of excess sodium salts, such as nitrous salts, carbonates, etc. A practical method of production is a modification of the Adahus process for platinum production by incorporating pyrolizable halogenides of iridium, titanium or ruthenium, such as salts of these metals such as iridium chloride, luium chloride or titanium chloride. - For example, in the case of 0x binary alloys (ruthenium, iridium), finely divided salts of ruthenium and iridium are placed in the alloy (mixed in the same proportion as the desired ruthenium and iridium ◆tannification). And this is the excessive woman'ie4Mt
Thorium or equivalent alkali metal salt is incorporated and the mixture is melted in a silica dish at 500°C to 600'Cr for 3 hours. The residue is washed sufficiently to remove any remaining nitrates and halides.

The resulting mixed and alloyed oxide suspension was subjected to electrolytic carbon reduction technology (e+electrocarbon red).
LIct i.

(n technique) or alternatively by bubbling hydrogen through the mixture. The product is thoroughly dried, ground and sieved through a nylon mesh screen. After sieving, the particles have a particle size of 37 μm (μ).

The alloy of reduced oxides of ruthenium and iridium is then thermally stabilized by heating to 500-600'C for 1 hour. The electrode is made by mixing a thermally stabilized reduced oxide of a platinum group metal with "Teflon" polytetrafluoroethylene particles. One suitable example of such Teflon particles is Teflon particles. -Du with the name of 30
It is sold by Pont.

Reduced oxides of precious metals such as Ru Qx improve their stability and reduce the use of precious metals (0°51 S/am
') for graphite, transition metal carbide, transition metal like 8
Can be mixed with monoelectric carriers.

In the case of graphite-ruthenium, powdered graphite (e.g. -1
- Manufactured by On Oil [oco grap old e 174]
8) with 15-30% Teflon (e.g. T-30) and mix this graphite-Teflon mixture with reduced gold jlfside.

A mixture of noble metal particles and Teflon powder is charged into a mold with a mixture of graphite and reduced oxide particles and heated until the composition is sintered into a decal II shape, which is then sintered into a diaphragm. bonding and embedding by application of pressure and heat to the surface of. Various methods can be used to attach and implant the electrodes to the septum.

An example is my own U.S. Pat. No. 3.134.69.
This is the method described in Item 7. In this method, the electrode structure is pressed onto the surface of a partially polymerized ion exchange membrane, thereby integrally bonding the sintered, porous, gas-absorbing particle mixture to the membrane and embedding it into the membrane surface. let them get involved.

Process Parameters Base yarn generation is carried out by introducing an aqueous alkali metal chloride solution, such as NaCl, into the anolyte chamber. The feed rate is preferably in the range of 200 to 2000 A/min/ft2/100 ASF. The saline solution concentration should be in the range 2,5-5 M (150-30 (1/l)), with a 5 molar solution at ~300 n/p being preferred since cathodic current efficiency increases linearly with concentration.

At the same time, as the saline concentration increases, the generation of oxygen at the anode due to water electrolysis decreases. As the anolyte concentration decreases, the relative amount of water present at the anode to compete for contact reaction sites with NaCf increases and thus oxygen evolution increases.

As a result, an additional amount of water is electrolyzed at the anode.
Generate elements. Water electrolysis at the anode further reduces cathode efficiency. This is because hydrogen ions H4 produced by water electrolysis move across the diaphragm and form hydroxide ions (
This is because it combines with OH-) to produce water and thus reduces the hydroxide ions available for the production of caustic alkali.

As previously discussed, by maintaining the flow rate of the saline solution introduced into the anolyte chamber within a specified range, the anode is constantly supplied with fresh feedstock.

of raw materials when the feed rate decreases? l! The transaction time, especially the residence time of the spent saline feed, increases. The longer the spent material (with a relatively high water content) remains at the anode, the more likely it is that the electrolysis of water will increase, with the concomitant production of 81I elements and migration of hydrogen ions across the membrane. is brought about. Therefore, both the concentration level of the saline solution and its feed rate affect the evolution of oxygen at the anode and the migration of hydrogen ions through the diaphragm.

Additionally, it may be desirable to conduct the electrolysis under superatmospheric pressure to enhance the removal of gaseous electrolysis products. Pressurizing the anolyte and catholyte compartments to a pressure above atmospheric pressure reduces the size of bubbles that form at the electrodes.

Smaller gas bubbles are significantly more easily separated from the electrode and electrode surface, whereby removal of gaseous electrolysis products from the electrolytic cell is more easily accomplished. Furthermore, the additional advantage is obtained of eliminating or minimizing the formation of gaseous films on the electrode surfaces, which can prevent the rapid access of anolyte and catholyte to the electrodes. A type of hybrid tank in which only two electrodes are connected to a diaphragm.
In the case of the cell structure, the reduction in the size of the bubbles results in a reduction in gas shielding and mass transfer in the gap between the non-bonding electrode and the membrane (based on the "bubble effect parameter").
IR reduction) decreases. This is because the obstruction of the electrolyte passage is less in the case of smaller bubbles.

Oxygen generation As already pointed out, lli! is based on water electrolysis! Oxygen evolution at the poles can be minimized by keeping the flow rate within the above range and keeping the saline concentration high. However, oxygen can also be generated at the anode by back migration of sodium hydroxide from the cathode.

NaOH migrates across the diaphragm due to the high concentration gradient across the diaphragm interface and the limited salt-stopping capacity of the cationic diaphragm, which is a function of the water content of the diaphragm, as discussed above.

For a 5M NaOH solution, a trowel of about 5 to 30 wt. % of butrium hydroxide formed at the cathode moves back across the diaphragm depending on the diaphragm used. Oxygen is produced at the anode by electrochemical oxidation of ON- according to the equation:

40H-→2H20+02 +48- The volume percent of oxygen produced at the anode based on the transfer of caustic is about ten of the weight percent of the caustic. Therefore, if 5-30% of the caustic were to be transferred back to the anode, 2-15% by volume of oxygen would be evolved. As previously mentioned, the migration of caustic to the anode is caused by the fact that the cathode side of the diaphragm is coated with a layer of cation-exchange resin or a cation-exchange resin with a low water content, which increases the diaphragm's anion (hydroxyl ion) blocking ability. This may be limited by the use of certain laminated or other diaphragms.

However, in addition to minimizing caustic migration across the membrane by enhancing the salt-rejection capacity of the membrane, M-tree formation at the anode can be further reduced by acidifying the saline solution. Hydrogen ions (H+) from the acidified saline solution combine with hydroxide ions (OH'') and this prevents oxidation of the hydroxide ions.

Oxygen evolution is reduced by an order of magnitude or more (0.2-0.4 from 5-10% by volume of II element) by the addition of at least 0.25M HCl.
% by volume). When HCI is at a lower concentration than Ol, 25M, the oxygen evolution is between 0.2 and 0.
4 The level normally observed from each ship% immediately, i.e. 5
It increases to ~10% by volume.

For optimal operation of the method and electrolyzer of the invention, the purity of the saline water must be high, in other words Ca+1
．． M! 11" content should be low. Calcium and magnesium ion content is kept at 0.5 ppm or less to avoid deterioration of the membrane due to exchange of calcium and magnesium ions in the raw saline into the membrane. At concentrations above 20 ppm, the performance of the electrolyzer deteriorates significantly within a few days.

The combined, saline solution has a total content of calcium and magnesium ions of less than 2 pp-, preferably 0.5
It must be purified to keep it below ppph.

At 300 ASF, the operating voltage of the coupled electrode electrolyzer is C2,9 to 3.6 volts depending on the composition of the electrodes, in which case the feedstock is preferably maintained at a temperature of 80 to 90C. This is because the sliding voltage and overall efficiency of operation are substantially improved at higher operating temperatures. for example,
When an electrolytic cell operating at 300 AS and using a reduced oxide combined with Teflon of a ruthenium-iridium mixture was operated at various temperatures, 90"C'C- had a sliding voltage of 3.02 volts and 35 ℃ the sliding voltage increased to 3°6 volts and 200 amps/h ft (
ASF), the electrolyzer operated at 90° C. required a sliding voltage of 2.6 volts. At the same current density, 3
When operated at 5°C, the sliding voltage increased to 3.15 volts. Therefore, from the perspective of overall operational efficiency, it is 80 to 90.
A temperature range of 0.degree. C. is preferred. As previously mentioned, the sliding voltage decreases at lower current densities, but operation at current densities of 300 amps/sq. Operation at such current densities is preferred since it is economical in terms of the size and price of the equipment required to provide the current density.

The material of the electrolytic cell is one that is resistant or inert to saline and chlorine in the case of the anolyte compartment, and resistant to high concentrations of caustic alkali and hydrogen in the case of the catholyte compartment. For example, the terminal of the electrolytic cell is made of pure titanium or stainless steel, and the gasket is of a filled rubber type such as T1) DM.

The anode current collector may be a platinum-coated niobium wire mesh, a titanium expanded wire mesh coated with RuQx, Ir0X, a transition metal oxide, or a mixture thereof mounted on a titanium plate, or a bonded precious metal or bonded noble metal mesh mounted on a palladium-titanium plate, as described above. It may be manufactured from noble metal oxide coated wire mesh. The cathode current collector may be a base made of nickel, mild steel, or stainless steel W4 with a stainless steel wire mesh or a nickel wire mesh welded to the base. Other materials such as graphite that are caustic resistant or inert and not susceptible to hydrogen embrittlement can also be used in the manufacture of the anode current collector.

As already pointed out, all of these current collectors have a higher hydrogen overpotential in the case of the cathode and a higher chlorine overpotential in the case of the anode, and therefore are more likely to settle hydrogen and/or chlorine. Electrochemical reactions occur preferentially on the catalytic surface of the electrode, particularly at the interface between the catalytic anode and the diaphragm. .

EXAMPLE An electrolytic cell incorporating an ion-exchange membrane with a Teflon-bonded metal-carrying oxide electrode embedded in the membrane was fabricated and various parameters related to the effectiveness of the electrolytic cell in the electrolysis of saline solutions were investigated. were tested to illustrate the effect of the cell and especially to illustrate the operating voltage characteristics of the cell.

Table 1 illustrates the effect of various combinations of noble metal reduced oxides on sliding voltage. Electrolysers were constructed with electrodes consisting of various specific combinations of noble metal reduced oxides combined with Teflon particles and embedded in a 6 mil thick cationic membrane.

Each electrolyzer was charged with a 5M saline solution feed of 200 to 200 ml at a current density of 300 amps/sq. ft. at 90°C.
It was operated using a feed rate of 00 cc/min.

The comparative electrolytic cell had a four-way stabilizing anode (DSA) placed apart from the Urallll according to the prior art and a stainless steel S+ cathode wire mesh placed separately in the same way, and this comparative test electrolytic cell was also the same. operated under the conditions.

From this test data, it is readily observed that in the method of the present invention, the cell operating potential is in the range of 2.9 to 3.6 volts. Typical electrolytic cell by conventional technology (control electrolytic cell N
0.6~ under the same operating conditions when compared with oy4)
A sliding voltage improvement of 1.5 volts has been achieved. The operational efficiency and the economic benefits it brings are very obvious.
Saline feed Current density 2 6 capes/-4 capes/- (R025%Ir')OX pt I
5°03 6
'f/aw' (Ru 2!4Ir') OX 54wII/-4 Cape/-3o.

(Ru 50 vomit Ti) OX Pt black 6 4
'af/sw' 41197-300 (Ru
254Ir-25 rumor Ta) OX pt black 7
6 cape/-2 cape/cal”
5 o.

(Rub!-Graphite) Pt%8
6q/ew” 4 Cape/a/
300 (uuoz) pt
Black 9 6Mf/al 4 Cape/lJ
5 n
0(Ru-5Ir)OX Pt black ID 2 ``I/am' 4 W
q/ml 500(I
rOx) Pt black 112 "F/ml"4'9/at"
S00(IrM)
Pt Kurosuri Voltage Temperature C, L Separation Pusafion 2990° 66% Dupont 1500 E
VNafl, 0wa 4.2-4.4 90° 81% Dupon
t 4500 EVafxon 315 Naflon 10 90' 89% Dupont 1
lafion315 Nafion 5.4 80085qk Dupont 15
00KW Nafion 14-17 90' 75% Dupont
4500 EVafion An electrolytic cell similar to cell No. 7 in Table 1 was constructed and operated at 90"C with a saturated saline solution feed. Sliding voltage (
V) was observed as a function of current density (ASF) and is shown in Table 2.

No. H Surface voltage (V) Current density (ASF) 3, 2
400 2,9 300 2,7 200 2.4 100 This data shows that the cell operating voltage decreases as the current density decreases. However, the relationship between current density and sliding voltage is a matter of the trade-off between operating costs and capital equipment costs for chlorine electrolysis.

However, extremely high current density (300-400
Even in ASF), significant improvements in sliding voltage (of 1 volt or more) are achieved in the chlorine production process of the present invention.

Table m illustrates the effect of cathode current efficiency on oxygen evolution. An electrolytic cell with a Teflon-bonded noble metal reduced oxide catalyst anode and cathode embedded in a cation diaphragm was heated at 90'C, at a saturated saline concentration, at a current density of 300 ASF and at a current density of 300 ASF per square inch of electrode area. min 2~5cc
It was operated at a feed rate of . The volume percent of oxygen in chlorine was measured as a function of cathodic current efficiency.

Table m Table Cathode current efficiency (%) Oxygen evolution - (volume %) 89
2,2 86 4,0 84 b, 8 80 8,9 Table 1V illustrates the controlling effect that acidification of saline solutions has on oxygen evolution. The volume φ% of oxygen in chlorine was measured for various concentrations of 1" cl in saline solution. 05 2. 50.07
5 1. 50, 1
0. 90, 15
0.50, 25 0. 4 It is clear from this data that oxygen evolution due to electrochemical oxidation of back-transferred OH'' is reduced by preferentially chemically reacting OH- with H+ to form H2O.

Assemble an electrolytic cell similar to cell No. 31 in Table 1 and
．． 3 using a saturated NaCl feed acidified with 2M HCl.
It was operated at 00ASF. The sliding voltage was measured at various operating temperatures from 35 to 90°C.

Assemble an electrolytic cell similar to tank No. 7 in Table 1 and
(1/L (~5M) NaCl) raw Ft (1! non-sexualized) was used at 20 OASF.

The sliding voltage was measured at various operating temperatures from 35 to 90°C. This data was converted to 300 ASF standard.

Chapter V Table 545 Engineering 50 (515) hs 538 550 (L9&) 45 52 520 (2,9) 55 515 512 (2,78)! 5110
AO5 (472) 75405 2-97 (2,
45) 85 This data shows that the best operating voltage is obtained in the range of 80-90°C. However, it should be noted that even at 35°C, the sliding voltage using the method and electrolyzer of the present invention is at least 0.5 volts better than a conventional chlorine electrolyzer operating at 90°C. be.

A number of electrolytic cells were assembled with composite membranes having an anion-blocking cathode-side barrier layer in the form of a chemically modified sulfonamide layer. These diaphragms were 7.5 mil diaphragms of the type sold by E, I, DuDOnt under the trade name Nafion. The (Ru25 1r) Ox particles were modified to a thickness of 1.5 mils by reaction with ethylenediamine <FDA> to form a sulfonamide barrier layer to minimize back migration of alkali to the anode side. and 20% King-30 Teflon binder, containing 116 m7/cm2 of precious metals.
An anode of: - Platinum gold 14 consisting of platinum black particles and 15% 1-30 Teflon binder
A cathode of 1'iJ/ee+2 was attached to the opposite side of the septum.

280-3151/I Na Cj! A saline solution with Ili was fed into the cathode compartment and distilled water was fed into the cathode compartment. These electrolyzers are rated at 304 amperes/100,000 ft (△
Operating at a flow density of 5 F-) and a humidity of 85-90 DEG C., the following sliding voltages, caustic degrees and cathode efficiencies were achieved using composite anion-blocking barrier layers.

1 2.68 85 5.1 89.62 2.
78 89 4.8 87.632.7690
4.8 91. The data show that by using a composite membrane with a chemically modified sulfone, amide-type cathode-side anion-blocking barrier layer, the cathode current efficiency can be increased without affecting the sliding current efficiency of this electrolytic method. This clearly shows that substantial improvements can be made. Approximately 88% to approximately 92%
Current efficiencies of 100% are achieved in the process carried out in this type of electrolyzer. This demonstrates that by using such a diaphragm with associated electrodes, a substantial improvement in current efficiency and therefore in the economics of the overall process is achieved.

The greatest improvement is achieved when the electrolysis of Na 2 Ci+ is carried out in an electrolytic cell in which both electrodes are bonded to the surface of an ion permeable membrane. However, the improved performance of this method is achieved for all electrolytic cells (hybrid cells) of construction in which at least -h of the electrodes are bonded to the surface of the ion-permeable membrane.

The improvement in such a hybrid structure is somewhat less than in the case where both electrodes are bonded to the membrane surface. However, the improvement is quite significant (0.3 to 0.5 volt improvement over the voltage required for known methods).

All electrodes are fully coupled (both electrodes are coupled), hybrid (anode-only and cathode-only), and conventional non-coupled tanks. In order to compare the results obtained using the uncoupled version, a number of electrolytic cells were assembled and electrolysis of saline solutions was carried out.

All four electrolyzers were equipped with Nafion 315 membranes.
The assembled tank C1 was operated at U9'O<0>C using approximately 290' l/i) of saline solution raw material. The content of catalytic material in the combined electrodes is 2/[[2] for platinum black at the cathode and RuOx - graphite and RuOx at the anode.
It was 4G/ft2.

The current efficiency at 300 ASF is virtually the same for all electrolysers (84-85 for 5 M NaOH)
%)Met. Table V1 shows cell voltage characteristics for various electrolytic cells.

Table 1 ++ Hibiki 1--Kanka □1 Mu side--■1--One salary--□11
1□111 It is observed that the sliding voltage of the fully Teflon bonded cell N0.1 is one volt better C than the sliding voltage of the control cell N006 which is not bonded to any Teflon according to the prior art. Hybrid cathode coupling tank No.

2 and NO33 and hybrid anode bonding tank no.

4 and N085 are fully Teflon bonded baths N0
11, but still 0.3 to 0.5 volts better than the prior art method performed in a bath without any Teflon-bonded electrodes. .

By reacting an aqueous saline anolyte and an aqueous catholyte over a catalytic electrode bonded directly to and embedded in the cationic membrane to generate chlorine at the anode and hydrogen and high purity caustic at the cathode. It will be appreciated that an extremely superior method of producing chlorine from saline solution can be provided. By adopting such a configuration, the electrocatalytic sites in the electrode are brought into direct contact with the diaphragm and the acid exchange groups in the diaphragm, which is significantly better than known methods at the required sliding voltage (1). A method with higher voltage efficiencies is provided for voltage efficiency such as volts or higher.Highly efficient noble metal reducing oxide catalysts bonded to fluorocarbons and fluorocarbon graphite-negative metal reducing oxides The catalyst is used at low overpotentials, further improving the efficiency of the process of the invention.

[Brief Description of the Drawings] Fig. 1 is a schematic diagram of an electrolytic cell used in the method of the present invention, and Fig. 2 is an illustration of the electrolytic cell used in the method of the present invention. FIG. 1 is an illustrative diagram illustrating the reaction that occurs. 11...Cathode chamber, 12...Anode chamber,]
3...Diaphragm, 14...Cathode, 15.1
6... Current collector, 17° 18... Gasket, 19... Electrolyte inlet, 20...
Anode chamber, 21...Anode chamber exit, 22...
・Gloomy entrance, 23...Cathode exit, 26...
...Anode side layer, 27...Cathode side layer, 28...
...Teflon cloth, 29...Continued from page 1 0 Inventor Russell Mason Dempsey No. 4 Hamilton Homestead Circle, Massachusetts, United States of America Procedure? Minamishosho (method> 58.5.26 Showa year)
Mr. Kazuo Wakasugi, Commissioner of the Japan Patent Office 1 Description of the case Patent Application No. 184777 filed in 1984 2 Name of the invention Method for electrolytic production of halogen 3 Relationship to the amendment case Applicant's address United States of America, 12305, New York State , Schenectaday, River Road) Name: General I Left Electric Company Representative name: Samson Herzgots 4 Agent address: 4th floor, QI Wa Building, 1-14-14 Akasaka, Minato-ku, Tokyo 107 Japan General Electric Co., Ltd. Company/Far East Patent Department 5, Date of amendment order: April 6, 1982, 6 Details subject to amendment @ and drawing 7, contents of amendment as attached. However, there are no changes to the content due to the engraving.

Claims (1)

[Claims] 1. An integrated structure consisting of an electrode and a diaphragm by separating an anode and a cathode by a cation-exchange polymer diaphragm, at least one of the electrodes containing a conductive catalyst substance, and bonding to the diaphragm at a plurality of locations. In the method h, in which a halogen and an alkali metal hydroxide are generated by electrolysis of an alkali metal hydroxide between the two electrodes, at least -
The electrolysis is carried out using the catalytic material of the electrode of h in direct contact with the diaphragm, and a potential is applied to the bonded electrode via a conductive current collector whose surface is in contact with the bonded electrode. The above method for electrolytically producing gen and alkali metal hydroxide, wherein 2. The catalytic material of at least one electrode is comprised of a plurality of particles, the particles being bonded to the cathode side of the diaphragm and embedded within the diaphragm to form an electrode permeable to gas and electrolyte. The method described in Scope 1. 3. The anode bonded to and embedded in the anode side of the diaphragm is composed of a plurality of conductive catalyst particles and forms an electrode permeable to C gas and electrolyte. h method according to any of item 2. 4. Claims 1 to 3, characterized in that the conductive catalyst particles are thermally stabilized reduced oxide particles containing MeOX of a metal selected from platinum group metals.
The method described in any one of paragraphs. b. Process h according to claim 4, characterized in that the thermally stabilized reduced oxide particles of a platinum group metal are bonded by a fluorocarbon polymer. 6. The particles are a thermally stabilized reduced oxide of ruthenium, and include a thermally stabilized reduced oxide selected from reduced oxides of iridium, tantalum, titanium, niobium or hafnium. 5. A method according to claim 4, characterized in that the method is stabilized historically by. 7. The cathode side of the diaphragm has less moisture than the rest of the diaphragm, which eliminates hydroxyl ions and minimizes the diffusion of alkali through the diaphragm to the anode. l! 2. A method according to claim 1, characterized in that ii. 8. Either claim 1 or 7, wherein the diaphragm is a two-layer laminate, and the property of blocking anions is greater on the cathode side than on the anode side. The method described in. 9. The method according to claim 8, wherein the diaphragm is a fluorocarbon polymer chlorine exchange diaphragm and has a sulfonamide barrier layer on the cathode side for blocking anions. 10. Process according to claim 1, characterized in that the aqueous solution is contacted with an anode consisting of a bonded thermally stabilized reduced oxide of ruthenium. ]1. at least one electrode is graphite, platinum group metal and/or
11. A method according to any one of claims 1 to 10, characterized in that it comprises a particle mixture of or oxides thereof. 12. A special feature characterized in that the aqueous solution is brought into contact with an anode made of a reduced ruthenium oxide and graphite combined together.
+The method according to claim 10. 13. Process according to claim 10, characterized in that the alkali metal chloride in contact with the anode is maintained at 11 degrees of at least 0.25 molar HCl.