SE446199B - Procedure for electrolysis of an aqueous solution of an alkali metal halide - Google Patents

Abstract

1523047 Cation exchange membranes for brine electrolysis cells ASAHI KASEI KOGYO KK 2 July 1976 [9 July 1975(2) 31 March 1976] 27654/76 Heading C7B [Also in Divisions B5 and C3] Electrolytic cells, especially for brine, have the anode and cathode compartments separated by a cation exchange membrane comprising a fluorocarbon polymer containing pendant carboxylic groups of formula -OCF2COOM, where M is hydrogen, ammonium, quaternary ammonium or metal. The said groups are obtained by reduction of -OCF 2 CF 2 SO 3 X groups (see Division C3), and the membrane may contain residual groups of this type. Preferred membranes contain -OCF 2 COOM groups on one surface, which faces the cathode, and -OCF 2 CF 2 SO 3 M groups on the opposite surface. The membrane may be formed from a single film, or may be a composite of two polymeric films, and in either case it may further include a reinforcing layer, e.g. a fabric formed from PTFE fibres. The 27 specific examples describe a variety of such membranes and their application in the electrolysis of brine, the starting copolymers being of tetrafluoroethylene and perfluoro (3, 6-dioxa- 4-methyl-7-octene sulphonyl fluoride, in some cases with a further monomer which is hexafluoropropene, perfluoropropyl vinyl ether or perfluoro- 3, 6-dioxa-5-methyl-nonene-1.

Description

HO 7907834-1 The disadvantage of such a low efficiency can be reduced by lowering the yield capacity of the sulfonic acid groups to less than 0.7 milliequivalents per gram of the H-form of the dry resin. However, such a reduction results in a severe reduction in the electrical conductivity of the membrane and a proportional increase in energy consumption. This solution is therefore not without financial difficulties US-PS 3,909,378 discloses composite cation exchange membranes which contain sulfonic acid components such as ion exchange group and which comprise two polymers of different equivalent weight (EW), i.e. number of grams of polymer, which contains an equivalent weight of functional group in the ion exchanger.

When such membranes are used in the electrolysis of aqueous solutions of sodium chloride, high efficiencies are obtained by carrying out the electrolysis with the side having polymers with higher EW, of the composite membrane against the cathode. For high efficiencies coupled with 1 energy consumption, the EW value of the polymer with higher EW must be increased and the 3 - a _thickness reduced as much as possible. However, it is extremely difficult to produce a composite cation exchange membrane having an efficiency not less than 90 L by means of membranes containing only sulfonic acid groups, I US-PS 3,78A,399, DT-OS 2 H37 595 and DT-OS 2 HH? 540, cation exchange membranes are proposed in which the surface layers against the cathode of the fluorocarbon exchange membranes contain sulfonamide groups, salts thereof, or N-monosubstituted sulfonamide groups. However, these membranes lack time in electrochemical and chemical stability.

DE-A-1 QÄ1 BH? describes the use of "two cation exchanger foils", i.e. to use two foils of cation exchange membrane; concretely expressed, to use a membrane consisting of a polymeric fluorine: hydrocarbon in the anode side and a membrane consisting of a polymeric fluorine-free material in the cathode side. DD-B-939 990 discloses a membrane in which sulfonic acid groups are formed by grafting the mixture of styrene and divinylbenzene (both of which are hydrocarbons) onto one side of the base film followed by sulfonation thereof, while carboxylic acid groups are formed by introducing ethyl acetate. acrylate (a hydrocarbon) on the other side of the base film for saponification thereof and the ion exchange groups are in both cases bound to hydrocarbons.

US-A-3 773 63u discloses a perfluorosulfonic acid membrane (Nafion), which can be described as conventional technology and does not provide any connection with or suggestion of the perfluorocarboxylic acid membrane.

JP 75-H1791 (CA vol 83, 1975, 80å03c) describes a membrane flfl, 10 20 25 §O 5 79Ü7834-1i which is produced by making a film with a thickness of L, 3 mm with a hot press from the powders of a polymer , obtained by grafting a perfluorovinyl carboxylic acid type monomer corresponding to the formula CF2 = CFE0X or CF2 wherein X represents F or OZ, wherein Z represents H, an alkyl group having 1-E carbon atoms, NHH or an alkali metal, n = 2-12 , to a homopolymer of a monomer of the perfluoroethylene type, corresponding to the formula: = cF0 (cr2) ncoX XOW] F 1 C .: | C wherein X represents F, CF 3, Cl or a copolymer of two or more kinds of monomers selected from the above and, if necessary, performing hydrolysis thereof to obtain an ion exchange membrane.

DE-B2? 2 EOU 622 relates to an ion exchange membrane for electrolysis and describes the provision of a neutral layer on the surface of a membrane with a functional group A (defined in lines 63-68 in the 5th column) for the purpose of improving current efficiency.

DE-B2-2 510 071 is written by Seko, who is one of the inventors of the present invention. This literature does not describe the side chain structure of -OCFQCOOM and its effect concretely.

The present invention relates to a process for electrolyzing an aqueous solution of an alkali metal halide by means of cation exchange membranes which effectively prevent re-migration of hydroxyl ions and enable a constant electrolysis process with higher efficiency than conventional fluorocarbon cation exchange membranes.

Membranes characterized by the presence of carboxylic acids, when used in electrolytic cells, especially when used in cells for electrolysis of sodium chloride for the production of aqueous sodium hydroxide, have many advantages over conventional cation exchange membranes. A particular advantage of the durability of the membranes, and it has been found that the efficiency with respect to the current of the membranes remains stable at well over 90% even after many months of operation. The present invention relates to a process for the electrolysis of an aqueous solution of an alkali metal halide to produce the corresponding halogen and alkali metal hydroxide, characterized in that an electrolytic cell comprising an anode is used. part and a cathode part separated by a membrane, comprising (a) a perfluorocarbon polymer containing protruding carboxylic acid groups of the formula: I -ocF2CooM wherein M is hydrogen, ammonium, quaternary ammonium and / or metal ions, (b) a perfluorocarbon polymer having cation exchange groups consisting essentially of sulfonic acid groups -OCF 2 CF 2 SO 3 M, wherein M is as defined above, wherein the fluorocarbon polymer (a) is present as a surface stratum having a thickness of at least about 100 Å on one side of the membrane, wherein the side of the membrane containing the surface name is facing the cathode side of the cell.

In its simplest form, the cation exchange membrane is a film-forming perfluorocarbon polymer. The film can be varied widely depending on the purposes of There is no particular limit as to the thickness, a thickness of 13 to 508 mm is suitable for many purposes.

The preferred embodiments of the membrane are characterized by the presence that the fluorocarbon polymer (a) is present as a stratum on the surface, which stratum is at least about 100 Å thick, and the polymer is substituted with protruding carboxylic acid groups having the above-mentioned thickness film. but usually the formula. The membrane according to the invention can be classified into two major groups. One group consists of a single-layer film, in which the equivalent weight (EW) of the cation grips is uniform throughout the membrane. The second group consists of two-layer films, in which a first film with a higher EW value and a second film with a lower EN value are combined. In either case, the specific fluorocarbon polymer as defined above may be present either homogeneously throughout the film or as a stratum on a surface of or within the membrane. However, the membrane may sometimes have Strata on opposite sides of the membrane in the indicated groups. As previously mentioned, according to the preferred embodiment with two-layer films, the first film with the higher EW value is; equipped with the specific perfluorocarbon polymer, preferably as a surface stratum having a thickness of at least 100 Å on the surface located on the side opposite the side laminated with the second film. For practical reasons, the membrane is usually reinforced with reinforcing material, which consists of woven textile material of inert fibers and porous films of inert polymers, preferably polytetrafluoroethylene fibers. The reinforcing material is suitably embedded in the membrane on the side opposite to the stratum of the present specific perfluorocarbon polymer. In the two-layer film, the reinforcing material is suitably embedded in the second film with the lower EW value.

For the sake of simplicity, a detailed explanation is given in the following mainly with reference to single-layer films with a surface stratum on the membrane. The structure of the first film in the bilayer membrane with respect to functional groups is substantially the same as in the single layer film. When the membrane is used in electrolysis, the side carrying the stratum is placed in the electrolytic cell so that it faces the cathode side in order to achieve the remarkable effects according to the invention.

Since the cationic membranes of the invention are derived from sulfonic acid groups which are substituted with fluorocarbon copolymers, they may in fact contain any predetermined proportion of sulfonic acid groups, or derivatives thereof.

The specific fluorocarbon polymer, which constitutes the stratum of the invention, may contain from 10 to 100 mole percent carboxylic acid substituents based on the sum of cation exchange groups. As the distance from the surface increases, the relative percentage of carboxylic acid substituents usually decreases, and the relative percentage of sulfonic acid substituents increases. According to preferred embodiments of the invention, only one surface has predominantly carboxylic acid substituents, and the amount of sulfonic acid groups increases with the distance from this surface, until the opposite surface has predominantly sulfonic acid groups. According to the invention, the cation exchange membrane contains (a) a perfluorocarbon polymer containing protruding carboxylic acid groups of the formula -OCF2COOM and (b) a perfluorocarbon polymer having cation exchange groups consisting essentially of the sulfonic acid groups ~ OCF2CF2SO3M. According to the most suitable form of reinforced membrane, the surface stratum is present only on the side opposite to the reinforced side, and the remaining part consists essentially of a perfluorocarbon polymer with the sulfonic acid groups -OCF 2 CF 2 SO 3 M as cation exchange groups.

It has been observed that the presence of carboxylic acid groups on the surface of the cation exchange membrane, especially on the surface facing the cathode, remarkably attenuates re-migration of hydroxyl ions from the cathode compartment during the electrolysis of aqueous solutions of alkali metal. I-OCF2CF2SO3M by saponification. 7907834-1 6 polytetrafluoroethylene films were used as reinforcing materials. If reinforcing materials are used, it is particularly convenient to embed them in the polymer membrane. This can easily be done at, for example, elevated temperature and reduced pressure as shown in the examples.

Of all these different constructions, those membranes in which carboxyl groups predominate on one surface and sulfone groups predominate on the other are particularly preferred. In composite membranes, the film having the higher EW value preferably carries the carboxyl groups.

The fluorocarbon-containing starting polymer having sulfonic acid groups such as side chains is prepared by copolymerizing a fluorinated ethylene and a vinyl fluorocarbon monomer having a sulfonyl fluoride group of the general formula (I) below: 'F with 1 to 5 carbon atoms and n denotes an integer having the value 0-3), if necessary together with a monomer consisting of hexafluoropropylene, CF3CF = CF2 and compounds of the general formula (II) F (CF2) ¿0 (? FCF2O) pCF = CF2 CF3 üarieß denotes an integer with the value 1-3 and p an integer with (II) 'the value 0-2), whereby a polymer with the side chain -OCFZCFZSOZF is obtained, which forms the obtained polymer in in the form of a membrane, after which the side chain -OCF 2 CF 2 SO 2 F in the indicated polymer is converted to the group Typical examples of fluorinated ethylene are vinylidene fluoride, tetrafluoroethylene and chlorotrifluoroethylene. Of these, tetrafluoroethylene is preferred.

Typical examples of vinyl fluorocarbon monomers having a sulfonyl fluoride group having the general formula given are, for example, the following: FSO2CF2CF2OCF = CF2 ESO2CF20çFQF20CFsCF¿ - CF3 _ FS02ChzCF2OçFCÉ2O? the vinyl fluorocarbon monomers having an active sulfonyl fluoride group, perfluoro (3,6-dioxa-U-methyl-7-octenesulfonyl fluoride), FSO 2 CF 2 CF 2 O, FCF 2 OCF = CF 2 are preferred.

A typical example of a fluorovinyl ether of formula (II) which, if necessary, participates in the copolymerization is perfluoromethyl vinyl ether.

The process of the present invention can be applied to all the sulfonyl-substituted polymers described in U.S. Pat. No. 3,909,373. It is advantageous if the membrane is first formed with the sulfonyl-substituted polymer, which is then converted by the reactions described in more detail in the following, to a membrane according to the invention.

The preferred copolymer composition for the starting materials is such that the content of fluorinated ethylene monomer is 30 to 90% by weight, preferably NO to 75% by weight, and the content of perfluorovinyl monomer bearing the sulfonyl fluoride group is 70 to 10% by weight, preferably 60 to 25% by weight. . The materials are formed according to methods well known in the art of homopolymerization or copolymerization of fluorinated ethylenes.

The polymerization can be carried out in either aqueous or non-aqueous systems. The polymerization is usually carried out at temperatures from 0 to 200 ° C under a pressure of 98 kPa to 19.6 MPa.

The polymerization is often carried out in a non-aqueous system in a fluorinated solvent. Examples of such non-aqueous solvents are 1,2,2-trichloro-1,2,2-trifluoroethane and perfluorocarbons such as perfluoromethylcyclobutane, perfluorooctane and perfluorobenzene. The polymerization in aqueous systems is carried out by contacting the monomers with an aqueous solvent containing a free radical initiator and a dispersant to produce a slurry of polymer particles, or by other well known methods.

After the polymerization, the resulting polymer is formed into a membrane by any of the many well known techniques available. for this purpose .u It is suitable that the copolymer has an EW value in the range 1000 to 2000. A membrane with a low EW value is desirable to the extent that the electrical resistance is proportionally low. A membrane of a copolymer with an extremely low EN value is not desirable, since the mechanical strength will then not be sufficient; A copolymer with an extremely high EW value cannot be easily formed into a membrane. The most suitable range for the EW value is thus between 1000 and 1500. A typical example of a fluorovinyl ether of formula (II) which, if necessary, participates in the copolymerization is perfluoromethyl vinyl ether.

The preparation of the present membrane can be applied with all the sulfonyl-substituted polymers described in U.S. Pat. No. 3,909,378. It is advantageous if the membrane is first formed with the sulfonyl-substituted polymer, which is then converted by the reactions described in more detail in The preferred copolymer composition for the starting materials is such that the content of fluorinated ethylene monomer is 30 to 90% by weight, preferably 40 to 75% by weight, and the content of perfluorovinyl monomer, which ceases to be the sulfonyl fluoride group, is 70%. to 10% by weight, preferably 60 to 25% by weight. The materials are formed according to methods well known in the art of homopolymerization or copolymerization of fluorinated ethylenes.

The polymerization can be carried out in either aqueous or non-aqueous systems. The polymerization is usually carried out at temperatures from 0 to 200 ° C under a pressure of 98 kPa to 19.6 MPa. Often the polymerization is carried out in a non-aqueous system in a fluorinated solvent. Examples of such non-aqueous solvents are 1,2,2-trichloro-1,2,2-trifluoroethane and perfluorocarbons, such as perfluoromethylcyclobutane, perfluorooctane and perfluorobenzene. The polymerization in aqueous systems is carried out by contacting the monomers with an aqueous solvent, containing a free radical initiator and a dispersant to produce a slurry of polymer particles, or by other well known methods.

After the polymerization, the resulting polymer is formed into a membrane by any of the many well known techniques available for this purpose. It is suitable that the copolymer has an EW value in the range 1000 to 2000. A membrane with a low BW value is desirable to the extent that the electrical resistance is proportionally low. A membrane of a co-polymer with an extremely low EW value is not desirable, since the mechanical strength will then not be sufficient. A copolymer with an extremely high Ew value cannot be easily formed into a membrane. The most suitable range for the EW value is thus between 1000 and 1500. After the molding to the membrane, the copolymer can be laminated to a reinforcing material, such as textile material, to improve the mechanical strength, as reinforcing material is textile material of polytetrafluoroethylene fibers most suitable. The indicated stratum should preferably be on the surface opposite the side on which the reinforcing material is applied.

When the cation exchange membrane has two bonded films, which also constitutes a preferred embodiment of the invention as stated above, the two kinds of copolymers with different EW values are prepared according to the polymerization methods described above, after which the composite film is formed and manufactured. The first film should have an EW value of at least 150 greater than the EW value of the second film and also a thickness not exceeding half the total thickness. The thickness of the first film should preferably be as small as possible, since the electrical resistance is greatly increased as the EW value increases.

Therefore, the thickness of the first film, which depends on its EW value, should be 50% or less of the total thickness, preferably H5 to 10%.

It is important that the first film with the higher EW value is in the form of a continuous film formed parallel to the surface of the membrane.

The total thickness of the composite cation exchange membrane usually has a lower limit of 100 μm and no upper limit, but the thickness varies with the type of ion exchange group used, the strength required for the copolymer as an ion exchange membrane, the type of electrolytic cell. and operating conditions. The upper limit is usually set with regard to the economy and other practical factors.

The composite membrane can be laminated with textile material or other suitable reinforcing materials in order to improve the mechanical strength of the membrane. The reinforcing material is preferably embedded in the second film. As reinforcing materials, polytetrafluoroethylene fiber materials are most suitable. In the preparation of the products according to the invention, the pendant sulfonyl groups are transferred in the form denoted by the formulas: -ocrzcszsozx '(A) and / or -ocF2cF2so¿ \\ 0 ~ ocF cr so -' 2 2 2 _ wherein X represents halogen, in particular fluorine or chlorine, hydroxyl, alkyl (B) W having up to H carbon atoms, aryl or OZ, wherein Z represents a metal atom, in particular an alkali metal atom, alkyl having up to H to U carbon atoms or aryl, to -OCF 2 COOM by treatment with a reducing agent.

Since the conversion to a carboxylic acid group takes place chemically, it can be controlled so as to obtain products with virtually any desired degree of carboxylation.

The starting polymers are usually formed from sulfonyl fluoride-substituted compounds, which remain intact during the polymerization. The sulvyl uriuri groups can be treated directly with a reducing agent for transfer to the carboxylic acid groups. Alternatively, they may first be converted to any of the other sulfonic acid derivatives defined in the formulas (A) and (B) indicated by known reactions, and then converted to carboxylic acid groups. The sulfonyl chloride groups are particularly preferred because of their higher reactivity. It is therefore more desirable to transfer the sulfonyl fluoride group to another derivative of sulfonic acid, as defined above in connection with the definition of X. Such reactions can be readily carried out according to known methods. W The formation of the carboxylic acid group can take place by any of many routes. It can be formed by reduction to a sulfinic acid with a relatively weak reducing agent followed by heat treatment as shown in the following: I I of X red. _ \ -OCF CF _-------- <7 _ 0CF2CF2SO2M 2 2502 A r z OCFECOOM. The transfer to carboxylic acid groups can be more easily carried out, as M in the indicated formulas represents hydrogen. Alternatively, the treatment can be carried out stepwise, whereby a sulfinic acid is initially formed and this is transferred to a carboxyl group by means of a strong reducing agent. This can be done as follows: 2 eds. ”J W 1-OCF2CF2SO2X ------- fa 0CF2CF2SO¿M; ocrgcoom.

With some reducing agents, the treatment of the sulfonic group can directly give the carboxyl group as follows. It is convenient that the concentration of sulfinic acid groups in the final product is relatively low. Accordingly, it may be desirable, but not necessary, to oxidize the sulfonic acid groups to sulfonic acid groups. 7907834-1 according to the following scheme: -ocrzcrgsozm -------, = - ocrzcrzsošra This can be done according to known methods, which use aqueous mixtures of sodium hydroxide and hypochlorite.

The reducing agents that can be used in accordance with the present invention are exemplified below. Those skilled in the art are well aware of these reducing agents and many other similar reducing agents as well as methods in which these reducing agents are used. However, some reducing agents, such as hydrazine having amino groups, which may form sulfonamide groups, as described in DT-OSS2 H37 395, are not suitable for use in the present invention and therefore are not within the scope of the present invention either.

The first group reducing agent consists of metal hydrides of the general formula MeLHu, wherein Me represents an alkali metal atom and L an aluminum or boron atom, or Me'Hx, wherein Me 'represents an alkali metal atom or an atom of an alkaline earth metal and x represents an integer having a value of 1 to 2. Examples of reducing agents of this kind are lithium aluminum hydride, lithium borohydride, potassium borohydride, sodium borohydride, sodium hydride and calcium hydride.

The reducing group of the second group consists of inorganic acids which have reducing effects, such as hydrogen iodide, hydrogen bromide, phosphoric acid, hydrogen sulphide and arsenic acid.

The reducing agent of the third group consists of mixtures of. metals and acids. Examples of these mixtures are tin, iron, zinc and zinc amalgam and the acids may be hydrochloric acid, sulfuric acid and acetic acid. The fourth group's reducing agent consists of compounds of metals with low valence rates. Examples of these compounds are stannous chloride, ferrous sulphate and titanium (III) trichloride. They can be used together with such acids as hydrogen chloride and sulfuric acid.

The reducing agent of the fifth group consists of organic metal compounds. Examples of such reducing agents are butyllithium, Grignard reagent, triethylaluminum and triisobutylaluminum.

The reducing agent of the sixth group consists of inorganic acid salts which have a reducing effect and similar compounds. Examples of such reducing agents are potassium iodide, sodium iodide, potassium sulfate, sodium sulfite, ammonium sulfite, sodium sulfite, sodium dithionite, sodium phosphite, sodium arsenic, sodium polysulfide and phosphorus trisulfide. HO 7907834-1 The reducing agent of the seventh group consists of mixtures of metals and water, steam, alcohols or alkalis. Examples of metals that can be used in the mixtures are sodium, lithium, aluminum, magnesium, zinc, iron and amalgams thereof. Examples of alkalis are alkali hydroxides and alcoholic alkalis. One of the reducing agents in the eighth group consists of organic compounds with reducing effects, such as triethanolamine and acetaldehyde.

From the par nenrparma listed above, it has been shown that those belonging to the second, third, fourth and sixth groups are preferable.

The optimal conditions for treatment with a reducing agent are selected depending on the selected reducing agent and on the type of the substituent X in the SOZX group. Usually the reaction temperature varies between -50 ° C and 250 ° C, preferably between 0 ° C and 150 ° C, and the reducing agent is used in the form of a gas, liquid or solution. As solvents for the reaction one can use water, polar organic solvents such as methanol, tetrahydrofuran, diglyme, acetonitrile, propionitrile or benzonitrile, or non-polar organic solvents such as n-hexane, benzene or cyclohexane or mixtures. of such solvents.

The amount of reducing agent is not less than the equivalent weight of the sulfonyl group present in the surface. Usually the reducing agent was used in large excess. The pH of the reaction system is selected on the basis of the particular reducing agent used.

The reaction can be carried out under reduced, normal or elevated pressure. In reactions using gaseous reducing agent, the elevated pressure can improve the reaction rate.

The reaction time usually varies between one minute and 100 hours.

When the cation exchange membrane is reinforced with a reinforcing material, the treatment with reducing agent preferably takes place on the side which is opposite the side added with reinforcing material.

The course of the reaction can be followed by analysis of the IR absorption spectrum of the membrane and this is particularly illustrated in the working examples.

The main bands when following the reaction are as follows: saifonyikioria 11:20 cnfl sulfinic acid salt 940 cm_l sulfinic acid salt 1010 cm_l carboxylic acid 1780 cm_l carboxylic acid 1690 cm_l _ The specific functional groups have been shown to be uniform substances with a neutralization point at approximately 2.5 pKa 10 15 20 25 30 35 uo 13 79o7ss4-1 in going from measurements of electrical resistance and IR spectrum at varying pH. These functional groups show characteristic absorption at 1780 emil (H-form) and at 1690 cmnI (Na-form). Furthermore, when converted to chlorides by treatment with PCI5 / POCl3, they have been found to have characteristic absorption at 180 cm -1. By these measurements they are identified as carboxylic acid groups. In elemental analysis by the combustion method it has been found that the sulfur atoms The fluorine atom has been observed to disappear by two atoms per one exchange group by the alizarin complex method, based on these analytical results and the fact that carboxylic acids are formed when reducing agents do not contain any carbon atom in an atmosphere in the absence of carbon atoms, it is confirmed that the indicated functional SruPPs consist of - OCF2COOïš This product obtained in the reaction corresponding to the indicated structure is also confirmed by measuring NMR spectrum of C the polymer reaction and performed with ~ monomer having the functional group -OCF2CF2SO2X.

The products obtained during the treatment with the reducing agent can have three typical forms. These forms are: 1) All the -COOM groups required are formed, 2) Not all -COOM groups required are formed and -SO 2 M- groups may be present, 3) Substantially all -SOZM groups is present.

In the first case, no further treatment is required.

In the second and third cases, there are two options. A stronger reducing agent can be used or the -SOZM groups can be transferred to the carboxylic acid group by heat treatment, which is advantageous when M represents hydrogen. The heating can take place at a selected practical pressure at a temperature between 60 ° C and 400 ° C for a period of 15 to 120 minutes. Preferred conditions with respect to efficiency and economy are atmospheric pressure; 100 ° C to 200 ° C and 30 ° C for 60 minutes. Any remaining sulfonic acid groups can be converted to sulfonic acid groups if desired. This conversion of the sulfinic acid group to the sulfonic acid group can be easily carried out if the former group is subjected to oxidation in an aqueous solution containing 1 to 10 1 NaCl 2 or in an aqueous solution with 1 to 30% H 2 O 2 at 100 ° C for 2 to 2 hours. The reducing agent used in the present process is selected, as in the case of ordinary organic reactions, taking into account a variety of factors, such as the nature of the substituent X in the SOEX group, the nature of the reducing agent, the nature of the solvent to be used, the reaction temperature, the concentration, the pH, the reaction time and the reaction pressure. The reducing agents which can be used according to the present invention can be broadly divided on the basis of their reactions in the following manner. The first group reducing agent can be used for virtually all SOZX groups. Occasionally the reaction proceeds too far to form a product which turns out to be an alcohol.

The reducing agents of the second, third and fourth groups are particularly effective when used for sulfonyl halide groups with relative: high reactivization. . The reducing agents of the fifth, sixth, seventh and eighth groups are also effective when used on sulfonyl halide groups, but the use of these reducing agents often yields only the sulfinic acid. The use of the -SOZF group requires particularly careful selection of reaction conditions, as it may give hydrolysis in the presence of reducing agents from the sixth, seventh and eighth groups.

It is possible to transfer the -50201 group directly to the carboxylic acid group without going through the sulfinic acid intermediate. The conversion can be carried out, for example, by subjecting the membrane of the fluorocarbon polymer, which carries the -SQ2Cl group, to elevated temperature and / or over-irradiation and / or -zg with an organic or inorganic peroxide.

Of course, the reaction can be applied to other monomers with similar side chains. Thus, the fluorocarbon monomers having sulfinic acid groups or carboxylic acid groups can be readily synthesized by the indicated reaction.

It should be noted that the final effect of the treatment with a reducing agent can be illustrated by the following reaction scheme: _ .i ____.; _________; OCFZCFZCOBM 7 The membranes of the invention have many advantages of which ~ OCF2C00M. .some have already been mentioned. During the electrolysis of the aqueous solution of the alkali metal halide, the part of the fluorocarbon polymer which carries carboxylic acid groups in the cation exchange membrane is preferably facing the catholyte side. Therefore, even in the case of electrolysis for the production of high concentration of sodium hydroxide, the membrane effectively prevents the re-migration of hydroxyl ions and enables the electrolysis to proceed with high efficiency with respect to the current. In particular, if a cation exchange membrane of two-layer structure is used, such as a diaphragm in electrolysis of an aqueous solution of sodium chloride, it can be achieved that the re-migration of hydroxyl ions is effectively prevented and the efficiency with respect to current can be maintained. at a high level by leaving the layers with a high EW value obtained during the treatment with the reducing agent facing the cathode side of the electrolytic cell. Consequently, this cation exchange membrane enables the energy consumption per unit to be reduced and the purchase price of the product to be reduced proportionally and the membrane therefore becomes extremely advantageous from a commercial point of view.

The environment is usually acidic in the anode compartment during electrolysis of an aqueous solution of sodium chloride. In view of the fact that the apparent pKa value of the carboxylic acid is in the order of 2 to 3, the presence of the thin layer of carboxylic acid groups in the anode space causes an increase in the potential and is therefore disadvantageous. Compared to conventional membranes, the present membranes have the following advantages in terms of the manufacturing process. The production of cation exchange membranes from fluorocarbon polymers which are substituted with carboxylic acid groups has hitherto proved to be extremely difficult.

This is because suitably_substituted fluorocarbon monomers are extremely difficult to_synthesize. In addition, copolymers of such monomers with perfluorovinyl monomers are extremely sensitive to thermal decomposition and they can not be thermally formed into a membrane by conventional extrusion techniques. According to the present invention, the stated difficulties are reduced by converting the sulfonic acid group of the fluorocarbon polymer to a carboxylic acid group. The following examples are intended to further illustrate the invention.

Example 1. T . The polymerization temperature was maintained at U5 ° C and the pressure was maintained at 505 kPa during the copolymerization. The yield capacity of the obtained polymer, measured after saponification, was 0.95 mg equivalents / gram of dry resin.

This copolymer was formed during heating into a 0.3 mm thick film. This was then saponified in a mixture of 2.5N sodium hydroxide / 50 percent methanol at 60 ° C for 16 hours, transferred to the H-form in 1N hydrochloric acid and heated at 120 ° C under reflux for 20 hours in a mixture ( lzl) of phosphorus pentachloride and phosphorus oxychloride for conversion to sulfonyl chloride form. After completion of the reaction, the copolymer membrane was washed with carbon tetrachloride, after which an A.T.R. spectrum was obtained, which showed a strong absorption band at 1-20 gcm / l characteristic of sulfonyl chloride. In a solution of crystal violet, the membrane was not stained. Between layers of acrylic resin, two layers of this membrane were fixed by means of gaskets of polytetrafluoroethylene. The frames were immersed in an aqueous 57% hydrogen iodide solution so that one surface of each membrane was reacted at 80 ° C for 2 hours. The A.T.R. spectrum of the membrane was then recorded. In the spectrum, the absorption band at 1420 redistributing sulfonyl chloride had disappeared and an absorption band at 1780 cm -1 characterizing the carboxylic acid group had become visible. In a solution of crystal violet, a 15 μm thick layer was stained on a surface of the membrane. The surface cation exchange groups were found to be carboxylic acid groups (100%) according to the A.T.B. spectrum. When saponifying this membrane in an aqueous solution of 5N disodium hydroxide / SO percent methanol at 60 ° C for 16 hours, a homogeneous and strong cation exchange membrane was obtained. 7-In an aqueous OQIN sodium hydroxide solution, this membrane showed a specific conductivity of 10.0 x 10 -3 mho / cm.

This membrane specific conductivity was determined by initial conversion to total Na form; the membrane was kept in a constantly renewing bath of an aqueous 0.1N sodium hydroxide solution at about 25 ° C for 10 hours, after which the membrane was charged with a thousand-period alternating current in an aqueous 0.1N sodium hydroxide solution at 25 ° C to measure the electrical voltage of the membrane. resistance. The indicated Na form of the electrolytic diaphragm was equilibrated in an aqueous 2.5 N sodium hydroxide solution at 90 ° C for 16 hours, inserting it into an electrolytic cell so that the treated surface faced the cathode side. The diaphragm was then used as a membrane in the electrolysis of sodium chloride and its efficiency with respect to the current was measured. The result was 95 percent. The electrolytic cell had a working surface of 15 rounds (5 cm x 3 cm) comprising an anode compartment and a cathode compartment separated by the cationic membrane. A metallic, dimensionally stable DSA anode was used and an iron plate was used. such as cathode. An aqueous 3N sodium chloride 3 pH solution was circulated through the anode chamber and an aqueous 35% sodium hydroxide solution through the cathode chamber at 90 ° C.

Under these conditions, an electric current was passed between the electrodes with the current density of 50 amperes / dmz. The efficiency was calculated by dividing the amount of sodium hydroxide formed in the cathode chamber per hour by the theoretical value calculated on the basis of the amount of electricity passed. Z Comparative Example 1.

The sulfonyl chloride form of the membrane obtained in Example 1 was saponified in a mixture of 2.5N sodium hydroxide / 50 percent methanol.

The sulfonic acid form formed of the ion exchange membrane was tested for specific conductivity and efficiency with respect to current but under the conditions used in Example 1. The values found were 1.3.0 x 10 -3 mho / cm and 55 3. 5 ', respectively. Example 2.. The polymerization of Example 1 was repeated in the same manner but the pressure was maintained at 606 kPa during the polymerization. The yield capacity of the obtained polymer was Ö, 79 milligram equivalents / gram dry resin; The copolymer was formed under heating into a 0.3 mm thick film. The membrane was transferred to sulfonyl chloride form under the same conditions as in Example 1. A surface of the membrane was reacted with an aqueous 57% hydrogen iodide solution at 80 ° C for 30 hours.

Then, the A.T.R. spectrum of the treated surface of the membrane was taken.

In the spectrum, the absorption band at 1U20 cm -1 characteristic of the sulfonyl group had disappeared and an absorption band at 1780 cm -1 characteristic of the carboxylic acid group had become visible. In a solution of crisis; The cation exchange groups on the surface were found to consist of carboxylic acid groups (100 L) according to the ATR spectrum. This membrane was saponified in a solution of 2.0N sodium hydroxide / 50% methanol at 60 ° C for 10 hours and then treated in a aqueous 2.5% sodium hypochlorite solution at 90 ° C for 16 hours The resulting membrane was treated in a solution containing 2.0N sodium hydroxide and 50% methanol at 90 ° C for 16 hours.

This membrane ATR spectrum showed the characteristic absorption of a salt of a carboxylic acid group at 1690 cm -1 on the surface reacted with the hydrogen iodide, and an absorption characteristic of a salt of sulfonic acid was observed at 1055 cm on the opposite surface, 'The specific conductivity of the membrane was 6.5 x 10-3 mho / cm. The efficiency with respect to the current was measured under the same conditions as in Example 1 with the surface treated with the hydrogen iodide having the absorption band at 1M? 0 cm -1 7907834-1 '18 iodide facing the cathode chamber and the efficiency Víäïß itself amounts to - 9ü '%. The alkali concentration in the cathode chamber was maintained at 30% and after a continuous current flow for 1500 hours, the efficiency with respect to the current was found to be as high as 93.2 2.

Comparative Example_2. The sulfonyl chloride form of the membrane obtained in Example 2 was saponified in a solution of 2.5N sodium hydroxide / 50 percent methanol.

The resulting sulfonic acid type ion exchange membrane was tested for specific conductivity and efficiency under the same conditions as in Example 1. The values obtained were 7.0 x 10 .37 mho / cm and 65%, respectively. Example 3; A terpolymerization was carried out with the monomers of Example 1 plus perfluoropropyl vinyl ether according to the procedure described in Example 1. When the obtained membrane was subjected to the same procedure f as in Example 1, it was found that the efficiency was as high as for the membrane according to Example 1.

Example Å The terpolymerization was carried out with the monomers of Example 1 plus perfluoro-3,6-dioxa ¥ 5 * methylnone-1, CF3CF2CF20CF (CF3) CF2- ~ OCF = CF2. When the obtained membrane was subjected to the same experiment as in Example 1, similar results were obtained.

Example 5.

A sulfonyl fluoride type membrane having a yield capacity of 0565 milligram equivalents / gram dry resin was obtained in a similar manner to Example 1. The membrane was plated in a flask and tetrahydrofuran was added. Lithium borohydride was added in large excess and the resulting reaction system was heated under reflux for 50 hours.

After completion of the reaction, the A.T.R. spectrum of the membrane was measured. In spectrum 1 characteristic of the sulfonyl fluoride practically disappeared and a larger absorption band at 1690 cm -1 characteristic of -CO0Li as well as small absorption bands at 9ü0 cm -1 and 1010 cm -1 characteristic of sulfinic acid salts became visible instead. This membrane was allowed to stand in a watery, ten percent percent reading of crystal violet (containing 10 percent ethanol) for three minutes and then a cross section of the membrane was examined under a microscope.

The microscopic observation revealed a strongly stained layer with a thickness of about 10 μm on each surface of the membrane.

The content of carboxylic acid groups in the surface layers when determined by the A.T. Ru spectrum was about 60 percent. Example 6 clay polymerization was carried out with the monomers of Example 1 plus hexafluoropropylene according to the procedure described in Example 1.

When the obtained membrane was examined in a similar manner as in Example 1, similar results were obtained. . ÉšeE22è_l- '. The sulfonyl chloride form of the membrane of Example 1 was reduced in aqueous 35% phosphoric acid solution at 80 ° C for 10 hours. According to the A.T.R. spectrum, the absorption band at the 1H 2 O cm-1 characteristic sulfonyl chloride group had disappeared, but the absorption band at 1780 om-1 characteristic of the carboxylic acid group was not very strong. When the membrane was washed with water and treated in an H7% hydrogen bromide solution at 8000 for 20 hours, the intensity of the absorption band increased at 1780 cm -1, which band is characteristic of the carboxylic acid group. According to the ATR spectrum, the cation exchange groups on the surface amounted to 90 1. tp 'When the membrane saponified with ice aqueous solution of 2.5N sodium hydroxide / 50 percent methanol and then the ATR spectrum of the membrane was taken up, the absorption caused by the carboxylic acid group I by 1780 cm'l shifted towards an absorption at l690 cm-1 characteristic of the carboxylic acid salt. Absorption of low intensity induced by the sulfinic acid salt group was visible at 9H0 and 1010 cm -1. The specific conductivity and efficiency of the membrane with respect to the current were found to be 9.5-x 10 -3 mho / cm 2 and 92 percent, respectively, when measured under the conditions described in Example 1.

Example 8. The sulronyl chloride form of the membrane (0.65 meq / g) obtained in a manner similar to that of Example 1 was refluxed in an aqueous solution of tin and hydrochloric acid for 50 hours after which time the ATR spectrum of the membrane was taken up. . In the spectrum, the absorption band characteristic of the sulfonyl chloride group had disappeared and a sharp absorption band at 1780 cm -1 characteristic of the carboxylic acid group had become visible. The carbosylic acid groups were present on the surface (100%) according to the A.T.R. spectrum; This membrane was saponified in an aqueous solution of 2.5N sodium hydroxide / 50 percent methanol. The specific conductivity and efficiency of the preselected membrane were found to amount to 2.0 x 10 -3 mho / cm and 96 percent, respectively, when measured under the same conditions as in Example 1 and an alkali concentration in the cathode chamber of 20%.

Example 9. Example 8 was repeated but an aqueous solution of stannous chloride and hydrochloric acid was used in place of the aqueous solution of tin and hydrochloric acid and similar results were obtained.

Example 10. The sulfonyl chloride form of the membrane obtained in Example 1 was immersed in an aqueous 15% sodium sulfide solution under a continuous stream of nitrogen at 60 ° C for one hour. After completion of the reaction, the A.T.R. spectrum of the membrane was measured. In the spectrum, the absorption band at 120 DEG C., characteristic of the sulfonyl chloride group, had completely disappeared, and sharp absorption bands at C10 cm @ 3 and 1010 cm @ -1, characteristic of sulfonic acid salts, had become visible. The membrane was converted to H-form by immersing it in a 1N hydrochloric acid solution at 60 ° C for 10 hours and heating it in a nitrogen atmosphere at 150 ° C for 120 minutes. It was then converted to the Na form by immersing it in a 2.5N sodium hydroxide solution and measuring the A.T.R. spectrum.

In the spectrum, the absorption bands at 9H0 ~ cm_l and 1010 cm_l characteristic of the sulfinic acid salts had completely disappeared and a strong absorption band at 1690 cm -1 characteristic of the carboxylic acid salt had become visible. According to the A.T.R. spectrum, the cation exchange groups on the surface were carboxylic acid groups (100%). The membrane was immersed in an aqueous solution of 2.1 ONE sodium hydroxide / 50% methanol to saponify the sulfonyl chloride groups still remaining inside the membrane. The specific conductivity and efficiency of the saponified membrane were found when measured under the same conditions as in Example 1 to be 9.2 x 10 -3 mm / cm and 95 percent, respectively. When the efficiency with respect to the current was measured under the same conditions as in Example 1, but the alkali concentration in the cat room was fixed at H0 percent, the value was obtained 95 Percent.

Comparative Example 3. In the sulfonyl chloride form of the membrane obtained in Example 1, it was saponified in an aqueous solution of 2.5N sodium hydroxide / 50% methanol. The efficiency with respect to the current for the saponified membrane amounted to 52 per cent when measured under the same conditions as in Example 1, however, the alkali concentration in the catheter was fixed at 40 per cent.

Example ll. The procedure of Example 110 was repeated but 5% potassium iodide solution was used instead of the aqueous 15% sodium sulfide solution. The results were similar to those obtained in Example 10. Example 21 Two sheets of the sulfonyl chloride form of the membrane obtained according to Example 1 were fixed in frames similar to those used in Example 1. The frames were immersed in triethanolamine so that one surface of each membrane was reacted at 80 ° C for 20 hours. A.T.R. spectra for the treated surfaces of each membrane were recorded. In the spectrum, 1 characteristic of the sulfonyl chloride group in the absorption band at 1U20 cm -1 had disappeared and strong absorption bands at 9H0 cm -1 and 1010 cm -1 marking for the sulfinic acid salts had become visible. The membrane was saponified in an aqueous solution of 2.5N sodium hydroxide / 50 percent - ol, then heated in 12N hydrochloric acid at 90 ° C for 30 hours, transferred back to the Na form using 2.5N sodium hydroxide, after which the ATR spectrum was measured A sharp absorption band, characteristic of a carboxylic acid salt, became visible at 1690 cm The absorption bands at 90 ° cm -1 and 1010 cm -1 had practically disappeared.The proportion of carboxylic acid, oxoxy acid groups in the form of cation exchange groups on the surface was 85% according to measurement of ATR spectrum. 0 The specific conductivity of this membrane was found to be to 11.0 x 10-3 mho / cm when measured under the same conditions as in Example 1.

The efficiency with respect to the current for the membrane was 89 per cent when measuring with the treated surface facing the cathode chamber.

Example 13- The sulfonyl chloride form of the membrane obtained in Example 1 was reacted in a 5% hexane-tetrahydrofuran solution of butyllithium at 60 ° C for 8 hours, after which the A.T.R. spectrum was taken. In the spectrum, the absorption band of the sulfonyl chloride group was reduced at 1 cm -1, characteristic of the sulfinic acid salt appeared. with about 60 percent and the absorption bands at 930 and 1010 cm_l Example lä.

The sulfonyl chloride form of the membrane obtained in Example 1 was saponified, transferred to the H-form with hydrochloric acid, dried thoroughly and reacted in a tetrahydrofuran solution of lithium aluminum hydride at 0 ° C for 20 hours. In the A.T.R. spectrum, an absorption band at 177 cm -1 characteristic of the carboxylic acid group was faintly visible.

Example 15.

The sulfonyl fluoride form of a 0.20 mm thick membrane was prepared according to a procedure similar to the procedure described in Example 1. A surface of the membrane was saponified with an aqueous solution of 2.5N sodium hydroxide / 50 percent methanol. The membrane was spread with the non-saponified surface downwards on a flat woven material 10 20 25 50 than 79Û7834 “1 -D m of polytetrafluoroethylene with a thickness of 0.15 mm with warp yarns and weft yarns, both of H00 denier multifilament, with a report of warp and weft of 16 yarns per cm. The membrane and the material were heated to 27,000, the membrane being simultaneously drawn against the material by means of a vacuum for embedding the material in the membrane as a reinforcing material.

This membrane was transferred to the sulfonyl chloride form by the same method as used in Example 1. With acrylic resin frames, two such membranes were held together with the material-reinforced surface on the inside. The frames containing the two adjacent membranes were immersed in an aqueous H7% hydrogen bromide solution and reacted at 80 ° C for 20 hours. After completion of the reaction, the membranes were removed, saponified in an aqueous solution of 2.5N sodium hydroxide / 50 percent methanol and further oxidized in a solution of 2.5N sodium hydroxide / 2.5 percent sodium hypochlorite at 90 ° C for 16 hours. The specific conductivity and degree of wettability of the membrane with a considerable percentage when measured under the same conditions as in Example 1 and with those on the current were found to amount to 5.0 x 10 mho / cm and 95 respectively the treated surface facing the cathode.p Comparative Example U. _ The reinforced membrane obtained in Example 15 was saponified. The specific conductivity and efficiency of the saponified membrane amounted to 6.0 x 10 mho / cm and 58 percent, respectively, when measured under the same conditions as in Example 1.

Example 16.

The treated membrane obtained in Example 1, after oxidation (with 2.5N NaOH / 2.5% NaClO), was subjected to different durability tests by immersing the membrane in an M5% sodium hydroxide solution or in a 5% sodium hypochlorite solution at 9000 for 500 hours. Then, the A.T; R spectrum of the treated surface of the membrane was recorded. In the spectrum, an absorption band was observed at 1690 cm -1, which band is characteristic of the carboxylic acid group. When the membrane is transferred to the H-form in 1N hydrochloric acid, the absorption is shifted: to 1780 cm -1 unchanged during the durability test. The specific conductivity and efficiency of the membrane when measured after the durability test under the same conditions as in Example 1 amounted to -9.9 x 10-5 mho / cm and 9U percent for the sample that had been subjected to the durability test in the H5 percent sodium hydroxide and to 10.2 x, which shows that the membrane was practically ldf3 mho / cm and 96 percent for the sample tested in the 5% sodium hypochlorite solution. The results show that the membrane was absolutely unchanged during the durability tests. 10 17 20 25 30 35 NO 23 7907834-1 Example 17.

The sulfonyl chloride form of the membrane obtained in Example 1 was saponified, transferred to the H-form with 1N hydrochloric acid, dried thoroughly and treated with phosphorus pentoxide suspended in phosphorus oxychloride at 110 ° C for 24 hours. After this treatment, the A.T.R. spectrum was measured, observing absorption bands at 1H6O and lü7O cm_1, characteristic of the sulfonic anhydride. The membrane was reacted with lithium aluminum hydride under the same conditions as in Example 11, giving similar results. Example 18. The procedure of Example 2 was repeated but the order of saponification and oxidation was reversed. The results were similar to those obtained in Example 2.

Example 19. The procedure of Example 1 was repeated, but the reaction in the hydrogen iodide solution was carried out at H0 ° C for four hours and after the saponification the reaction in the hydrogen iodide solution was repeated at 80 ° C for 25 hours.

The resulting membrane was oxidized in an aqueous solution of 2.5N sodium hydroxide / 2.5 percent sodium hypocritite and then the specific conductivity and efficiency were measured under the same conditions as in Example 1. The values obtained were 11.0 x 10 -3 mho / cm 3, respectively. g9U percent.

Example 20. A polytetrafluoroethylene powder and glass fibers were mixed. The mixture was compression molded at a pressure of 29 MPa to form a polytetrafluoroethylene film having a thickness of 1 millimeter. The film was heated in an electric furnace at 32,000 for one hour to melt the polytetrafluoroethylene powder, and then the melt was treated with hydrogen fluoride to dissolve the glass phase. Consequently, a neutral membrane with a porous structure was obtained.

This neutral membrane was coated three times with a 1,2,2-trichloro-1,2,2-trifluoroethane solution of a copolymer of tetrafluoroethylene and perfluoro (3,6-dioxa-U-methyl-7-octenesulfonyl fluoride) with a the yield capacity of 1.2 milligram equivalents / gram of dry resin which copolymer was obtained in a polymerization process similar to the procedure described in Example 1. The solvent was evaporated from the covered membrane. Then, the coating was pressed on the membrane at 270 ° C for 10 minutes to form a laminate having a thickness of 50 μm.

Under the same conditions as in Example 1, this membrane was transferred to the sulfonyl chloride form and reacted with hydrogen iodide gas at 100 ° C in the HO hours ATT .. spectrum showed that the absorption band 10 H0 7907834-1 f characteristic of the sulfonyl chloride group, had completely disappeared and that sharp absorption band at 178 DEG C., characteristic of carboxylic acid, had become visible.D Example 21. The tetrafluoroethylene and perfluoro-3,6-dioxa-U-methyl-7-octenesulfonyl fluoride were copolymerized in 1,2-trichloro-1,2,2-trifluoroethane in the presence of perfluoropropionyl peroxide as the polymerization initiator, the polymerization temperature being maintained at USOC and the pressure being maintained at H90 kPa during the polymerization. The resulting polymer is identified as polymer 1. The copolymerization was repeated on the same but the pressure was maintained at 29H kPa during the polymerization, and polymer 2 is obtained.

A portion of each of these polymers was subjected to hydrolysis in a mixture of aqueous SN sodium hydroxide solution and methanol (1: 1 by volume) at 90 ° C for 16 hours for transfer to the sodium sulfonate form. The yield capacity of the sodium sulfonate form of the polymer was found to be 0.7 H milliequivalents / gram dry resin for polymer 1 and Q, 91 milliequivalents / gram dry resin for polymer 2., V '7 Polymer 1 and polymer 2 were formed in heat to separate membranes. with a thickness of 51 μm and l0l μm. The two membranes were laid against each other and formed during heating into a composite membrane. The composite membrane was treated in the indicated hydrolysis system for transfer to the sodium sulfonate form of the composite membrane.

The composite membrane was converted to H-form by treatment in an aqueous 1N hydrochloric acid solution and then transferred to the sulfonyl chloride form by reaction with a mixture of phosphorus pentachloride and phosphorus oxychloride (gravimetric ratio 1: 1) at 120 ° C for 40 hours. After completion of the reaction, the composite membrane was washed for four hours under reflux in carbon tetrachloride and dried in vacuo at 00 ° C, the ATR spectrum of the dried membrane revealed that in both the polymer of polymer 1 and of polymer 2 there were absorption bands those of the sulfonyl chloride at 1H20 cm -1 while the absorption due to the sulfonic acid group at 1060 cm -1 had completely disappeared.

Two films of the composite membrane were held against each other with membrane sides with polymer.2 facing inwards and in this position the films were fixed in frames of acrylic resin by means of gaskets of polytetrafluoroethylene. The frames were immersed in an aqueous 57% hydrogen iodide solution so that only the free surfaces (membrane sides with polymer 1) would be reacted at 80 ° C for 50 hours. The membranes were washed with water at 60 ° C for 50 minutes. IR spectrum for each treated surface 1 was measured. In the spectrum, the absorption band at IU20 cm-1 for the sulfonyl chloride had completely disappeared and an absorption band at 1780 cm-1 characteristic of the carboxylic acid group had appeared. In a solution of crystal violet, a stained layer about 0.8 μm wide was observed on the side of the membrane containing polymer 1.

According to the A.T.R. spectrum, the cation exchange groups on the surface were found to be carboxylic acid groups (100%).

The membrane was saponified in an aqueous solution of 2.5N sodium hydroxide / 50 percent methanol at 60 ° C for 16 hours and then the A.T.R. spectrum was taken. In the spectrum, the absorption band of the carboxylic acid group shifted to 1690 om-1 for the side of the membrane containing polymer 1. On the side of the membrane containing polymer 2, there was an absorption band at 1055 cm -1 characteristic of sodium sulfonate.

The membrane was immersed in an aqueous 2.5% sodium hypochlorite solution and oxidized at 90 ° C for 16 hours.

The specific conductivity of the resulting membrane was 5.2 x 10 -3 mho / cm when measured in an aqueous 0.1N sodium hydroxide. solution. The specific conductivity of the membrane was determined after complete conversion to the Na form, the membrane being kept in a constantly renewing bath of an aqueous 0.1N sodium hydroxide solution at normal room temperature for 10 hours until equilibrium was reached after which the membrane was subjected to 1000-periodide alternating current. in an aqueous 0.1 N soda solution at 25 ° C to measure the electrical resistance of the membrane.

The Na form of the cation exchange membrane was equilibrated by immersing the membrane in an aqueous 2N sodium hydroxide solution at 90 DEG C. for 16 hours, after which the membrane was inserted into an electrolytic cell with the reacted surface, namely the polymer 1 side facing the cathode. The membrane was tested for efficiency in electrolysis of sodium chloride. The value turned out to be 9H percent.

The working surface of the electrolytic cell was 15 cm2 (5 cm X 3 cm). The cell comprised an anode space and a cathode space separated by the electrolytic membrane. A metal anode covered with a precious metal was used as the anode and an iron plate was used as the cathode. An aqueous BN sodium chloride solution of pH 3 was circulated through the anode compartment and an aqueous 30% sodium hydroxide solution was circulated through the cathode compartment at 90 ° C. Under these conditions, an electric current was passed through the saponified membrane was found to amount to 7.5 x 10 -6 between the electrodes with a current density of 50 amperes / dmg. The efficiency with respect to the current was calculated by dividing the amount of sodium hydroxide formed in the cathode chamber per hour by the theoretical value calculated on the basis of the amount of electricity passed.

The electric current was passed through the cell for 2000 hours.

Thereafter, the efficiency was measured with respect to the electricity and it turned out to be 93.8 percent. In Comparative Example 5.

The sulfonyl chloride form of the composite membrane obtained in Example 21 was saponified in a solution of 2.5N sodium hydroxide / 50 percent methanol. The specific conductivity and efficiency of 70 percent when measured under the same conditions as in Example 21.

Example 22.

The procedure of Example 21 was repeated but the order mho / cm and for saponification and oxidation was reversed. The specific conductivity and efficiency with respect to the current of the membrane were similar to the values obtained in Example 21.

Example 23. The procedure of Example 21 was repeated, but the membrane was reacted in an aqueous 20% potassium iodide solution at 60 ° C for 30 hours instead of the treatment with hydrogen iodide. After completion of the reaction, the A.T.R. spectrum of the treated surface was recorded. In the spectrum, absorption bands induced by the potassium sulfinate at 100 cm -1 and 940 cm -1 were observed that a surface layer having a thickness of 5 μm was stained on the side observed in a solution of crystal violet containing polymer 1.

The membrane was saponified under the same conditions as in Example 21 and then allowed to react in a 57% hydrogen iodide solution at 80 ° C for 30 hours. After completion of the reaction, the A.T.R. spectrum of the side of the membrane containing polymer was measured. In the spectrum, the absorption band caused by the potassium sulfinate had completely disappeared and an absorption band induced by the carboxylic acid appeared at 1780 cm-1. According to A.T.R. measurement, the cation exchange groups on the surface were carboxylic acid groups (about 100%). On the side of the membrane containing polymer 2, there was an absorption band developed from sulfonic acid at 100 cm -1. The membrane was further oxidized under the same conditions as in Example 21. The specific conductivity and efficiency 3 with respect to the current for the membrane was found to be 5.3 x 10 -10 10 15 20 '25 BO 35 ÄO 27 o 7907854-1 mho / cm respectively 94 percent.

Example ZN. A copolymer (polymer 3) was prepared by repeating the procedure of Example 21, keeping the pressure at 686 kPa during the polymerization.

The yield capacity of polymer 5 was found when measured according to the same procedure as in Example 21 to be 0.68 milliequivalents / gram of dry resin. Following the procedure of Example 21, a composite membrane containing the polymer with polymer 2, μl μm thick, and the membrane with polymer 3 having a thickness of 51 μm was prepared.

The composite membrane was subjected to hydrolysis in a mixture of an aqueous SN sodium hydroxide solution and methanol (1: 1 by volume) at 60 ° C for H0 hours and then transferred to the H-form by treatment in an aqueous 1N hydrochloric acid solution, after which it was again was converted to the ammonium sulfonate form by treatment in an aqueous 1N ammonia solution. The membrane was then reacted in a mixture of phosphorus pentachloride and phosphorus oxychloride (gravimetric ratio 1: 1) at 12,000 for 38 hours to convert to the sulfonyl chloride form.

The composite membrane was introduced into a flowing gas reaction system so that the polymer 3 side of the composite membrane was subjected to a contact reaction with 20.0% hydrogen iodide gas (with nitrogen as diluent gas) at 10,000 for 12 hours. A.T; R. spectra of the treated surface of the membrane were recorded. In the spectrum, an absorption band induced by carboxylic acid appeared at 1780 cm -1 and the absorption band induced by the sulfonyl chloride at 1120 cm -1 had disappeared. In a solution of crystal violet, a layer with a thickness of 10 μm was stained. According to the A.T.R. spectrum, about 100% of the cation exchange groups were carboxylic acid groups.

The composite membrane was then hydrolyzed, oxidized and introduced into an electrolysis cell with the side containing polymer 3 facing the cathode chamber. In this electrolysis system, the electrolysis of sodium chloride was carried out under the same conditions as in Example 21, keeping the concentration of sodium hydroxide circulating in the cathode chamber at 20 percent. The efficiency with respect to the current amounted to 97 percent and the specific conductivity amounted to H, 3 x 10 mho / cm.

The efficiency with respect to the current was when it was measured after 1700 hours of continuous passage of electric current 97.2 percent.

UI 10 20 30 U0 7907834-1 zß Jämförelseexemoel 6.

The sulfonyl chloride form of the composite membrane obtained in Example 2N was hydrolyzed in a solution of 2.5N sodium hydroxide / 50 percent methanol. The specific conductivity of the obtained membrane amounted to 5.2 x 10 -3 mho / cm. The membrane was subjected to electrolysis under the same conditions as in Example 2U with the polymer side facing the cathode chamber. The efficiency was 80.2 percent.

Example 25.

Two films of the sulfonyl chloride form of the membrane obtained in Example 24 were held together with the sides containing polymer 2 facing inwards and in this position they were fixed in acrylic resin frames, immersed in an aqueous 20% sodium sulfide solution and allowed to react under continuous flow. nitrogen at 70 ° C for two hours.

Upon completion of the reaction, an A.T.R. spectrum was recorded for the treated surface of the membrane. In the spectrum, the absorption band at 1320 cm -1, characteristic of the sulfonyl chloride group, had disappeared, while absorption bands at 1010 cm -1 and 9H0 cm -1, characteristic of the sulfonic acid salt, were observed.

The membrane was immersed in an aqueous 2.5% sodium hypochlorite solution at 70 ° C for 16 hours, after which the A.T.R. spectrum of the ~ .L membrane was measured. In the spectrum, the absorption bands at 1010 cm -1 and 90 ° cm -1 had disappeared and an absorption band at 1055 cm -1 characteristic of sodium sulfonate appeared.

Two films of the membrane, which had been treated with sodium sulfide as previously described, were washed with water and reattached to the frames so that the polymer 3 side was reacted in a solution of H7% hydrogen bromide at 80 ° C for 20 hours. The A.T.R. spectrum from the membrane showed a sharp absorption band induced by the carboxylic acid group at 1780 cm -1.

The membrane was saponified in an aqueous solution of 2.5N sodium hydroxide / 50 percent methanol and then a new A.T.R. spectrum was taken. 1 disappeared and one In the spectrum, the absorption band at 1780 cm -1 absorption band induced by the sodium carboxylate became visible at 1690 cm -1 and smaller absorption pathways induced by sulfinic acid salts became visible at 9H0 cm -1 and 1010 cm -1. An A.T.R. spectrum showed that about 90% of the cation exchange groups on the surface were carboxylic acid groups.

The membrane was then treated in an aqueous 2.5% sodium hypochlorite solution at 9000 for 16 hours. The specific conductivity of the treated membrane amounted to H, 6 x 10-5 mho / cm.

The efficiency with respect to the current was found to be 92 percent when measured under the same electrolytic conditions as in Example EB.

Virtually the same efficiency was maintained after 1700 hours of continuous current passage.

Example 26.

The membrane treated with sodium sulfide in Example 25 was saponified in an aqueous solution of 2.5N sodium hydroxide / 50 percent methanol at 6000 for 16 hours. The membrane was then treated in an aqueous 1N hydrochloric acid solution at 6,000 for 10 hours and then heated in air at 15,000 for one hour. The A.T.R. spectrum was recorded for the side of the membrane containing polymer 3. In the spectrum, absorption bands induced by the carboxylic acid group became visible at 177 cm -1.

When this membrane was transferred to the salt form, an absorption band induced by the carboxylate appeared strongly at 1690 cm -1 and weaker absorption bands developed by sulfinic acid salts became visible at 1010 cm -1 and 9uo cm spectrum. Membrane. The surface cation exchange groups were found to be oxidized in an aqueous 2.5% sodium hypochlorite solution at 9000 for 16 hours. The specific conductivity of the oxidized membrane amounted to U, H x 10-5 mho / cm. The efficiency of the current for the membrane was 93 percent when measured under the same conditions as in Example 24. In Example 27. Tetrafluoroethylene and perfluoro-3,6-dioxa-H-methyl-7-octenesulfonyl chloride were emulsion polymerized at 70 ° C and a tetrafluoroethylene pressure of 0.5 MPa, using ammonium persulfate as initiator and the ammonium salt of perfluorooctanoic acid as emulsifier.

The polymer thus obtained was washed with water, hydrolyzed and then the yield capacity was measured titrimetrically. The yield capacity was found to be 0.80 milligram equivalents / gram in dry resin. This polymer is identified as polymer U.

In a process similar to the procedure of Example 21, polymer 2 used in Example 21 and polymer Ä were combined to form a composite membrane comprising a (polymer 2) membrane having a thickness of 101 μm and one (polymer H) -membrane, which had a thickness of 76 pm. This composite membrane was spread with (polymer 2) ~ side down on a woven material of polytetrafluoroethylene with a thickness of 0.15 mm, which material had multifilament weft yarns with the denier number H00 and warp yarns of multifilaments with the denier number 200 x 2 rap- ports of 10 yarn / cm each. The membrane and the textile material were heated at 270 ° C, the membrane being simultaneously pulled against the textile material 10 by means of a vacuum so that the textile material was embedded in the membrane as a reinforcing material.

This membrane was transferred to the sulfonyl chloride form in the same manner as described in Example 21. Two films of the membrane were held together with the (polymer 2) sides (the sides in which the textile material was embedded) facing inwards by means of acrylic resin frames. The (polymer Ü) sides of the membrane were reacted with hydrogen sulfide gas, which was fed in a continuous stream at 12,000 for 20 hours. 7 The membrane was removed; saponified in an aqueous solution of 2.5N sodium hydroxide / 50% methanol and then oxidized in a solution of 2.5N sodium hydroxide / 2.5% sodium hypochlorite at 90 ° C for 16 hours. The specific conductivity when measured according to the same method as in Example 21 was 3.2 x 10_3 mho / cm. The efficiency with respect to electricity was 9U percent. Even after 1,000 hours of continuous current passage, the efficiency with respect to the current was unchanged.

Comparative Example 7. The reinforced composite membrane obtained in Example 26 was saponified. The specific conductivity and efficiency with respect to the current of the resulting membrane: were 5.9 x 10-5 'mho / cm and 62.1 percent, respectively, when measured under the same conditions as in Example 21.

Example 28.

The fluorocarbon cation membrane, "Nafion No. 315" from E. I. DuPont de Nemours & Company, was immersed in an aqueous 1N hydrochloric acid solution at '60 ° C for 16 hours and then transferred to the ammonium sulfate form with a 1N aqueous ammonia solution. The membrane was dried in vacuo at 5000 for 16 hours and then reacted in a mixture of phosphorus pentachloride and phosphorus oxychloride (gravimetric ratio lzl) at 12000 for 40 hours. The A.T.R. spectrum of the surfaces with the equivalent weights 1500 and 1100, respectively, was recorded. In both spectra, the absorption band at 1060 cm -1 characteristic of the sulfonic acid group had disappeared and an absorption band of 1H 2 O cm -1 characteristic of the sulfonyl chloride could be observed.

Two films of the membrane were held together with the sides having the equivalent weight of 1100 facing inwards and the films were placed in acrylic resin frames, immersed in aqueous 57% hydrogen iodide solution and allowed to react at 80 ° C for 2 hours. After completion of the reaction, the membrane was washed with water and the A; T.R. spectrum of the side of the membrane having the equivalent weight of 1500 was taken up. In the spectrum, the absorption band at 1H20 cm-1 was characteristic of the sulfonyl chloride, for »\ J '| 10 15 20 25 BO UD 31 7907834-1 characteristic of the carboxylic acid group had become visible. In the A.T.R. spectrum obtained obtained and an absorption band at 1780 cm -1 for the side of the membrane having the equivalent weight of 1100, the absorption at 1120 cm -1 was characteristic of the sulfonyl chloride still intact.

This membrane was saponified in a solution of 2N sodium hydroxide / 50 percent methanol at 6000 for H0 hours. Thereafter, the membrane was oxidized in an aqueous 2.5% sodium hypochlorite solution at 9000 for 16 hours. Thereafter, the membrane was placed in an electrolytic cell with the side having the equivalent weight of 1500 facing the cathode, and the electrolysis of the sodium chloride was carried out under the same conditions as in Example ZÅ. The efficiency with respect to electricity was 96 percent. The specific conductivity was 2.0 x 10_3 mho / cm.

The efficiency of the membrane was when it was measured after 1500 hours of continuous current passage substantially unchanged.

Comparative Example 8. The sulfonyl fluoride form of the membrane prepared in Example 1 was fixed in a position between acrylic resin frames. Only one surface was allowed to react with a mixture of ammonia gas and air (about one volume percent) at room temperature for 15 hours. After completion of the reaction, a cross-section of the membrane was stained with methyl red, the stained layer developed by sulfonamide groups being found to have a depth of 0.02 mm only on the reacted surface. This membrane was subjected to saponification and equilibrated under the same conditions as in Example 1, after which the specific conductivity was measured and the result was 9.8 x 10 -3 mho / cm.

The efficiency with respect to the current was measured under the same conditions as in Example 1 with the surface with sulfonamide groups facing the cathode side, and in the measurement the value was obtained 87% for the efficiency.

After a continuous current passage for 1000 hours, the efficiency turned out to be as low as 80%.

Comparative Example 9.

The sulfonyl fluoride form of the membrane of Example 1 was treated on one surface with ethylenediamine at room temperature for 20 hours. After the reaction, the membrane was washed with diglyme and then with benzene and finally with water, which was heated to about 0 ° C. When a cross section of this membrane was treated with methyl red, only the treated surface was stained to a depth of 0.01 mm where the N-substituted sulfonamide was formed. This membrane was subjected to saponification and equilibrated under the same conditions as in Example 1. The specific conductivity was measured to be 0.2 X 10 -3 mho / cm. The efficiency with respect to the current was measured with the surface with N-substituted sulfonamide groups facing the cathode side under the same conditions as in Example 1, and the efficiency was found to be 91%.

After a continuous current passage for 1000 hours, the efficiency was as low as YÄ%.

Comparative Example 10.

The cation exchange membrane prepared in Comparative Example 9 was subjected to oxidative treatment with 2.5% aqueous sodium hypochlorite solution at 90 ° C for 16 hours. The efficiency with respect to the current was measured under the same conditions as in Example 1, the surface having N-substituted sulfonamide groups facing the cathode side and the efficiency being 76%. The formation of sulfonic acid groups was confirmed by the A.T.R. spectrum after the oxidative treatment.

Claims (2)

Ü 79Û7834 fi l Patentkrav. A process for the electrolysis of an aqueous solution of an alkali metal halide to produce the corresponding halogen and alkali metal hydroxide, characterized therefrom, which utilizes an electrolytic cell comprising an anode portion and a cathode portion separated by a membrane comprising (a) a perfluorocarbon polymer. , containing protruding carboxylic acid groups of the formula: Å -ocfzcoon wherein M is hydrogen, ammonium, quaternary ammonium and / or metal atoms, (hl a perfluorocarbon polymer having cation-If substituents consisting essentially of sulfonic acid groups wherein the fluorocarbon polymer (a) is present as a surface stratum having a thickness of at least about 100 Å on one side of the membrane, the side of the membrane containing the surface stratum facing the cathode side of the cell. 2. A method according to claim 1, characterized in that the membrane comprises two bonded polymer films, wherein a first film comprises a perfluorocarbon polymer containing protruding carboxylic acid groups, which can be illustrated by the formula: '-ocFcooM - wherein M is hydrogen, ammonium, quaternary ammonium and / or metal atoms; and a second film comprises a perfluorocarbon polymer containing protruding sulfonic acid groups, which may be illustrated by the formula: O-OCF 2 CF 2 SO 3 M wherein M is made of hydrogen, ammonium, quaternary ammonium and / or metal atoms, the equivalent weight of the polymer in each film ranging from and the equivalent weight of the polymer in the first film is at least 150 higher than the equivalent weight of the polymer in the second film and wherein the thickness of the first film is up to 50% of the total thickness, one side of the first film facing cell cathode. A compound according to any one of claims 1 to 2, wherein the alkali metal halide is sodium chloride.