NL8200153A - MEMBRANE, ELECTROCHEMICAL CELL, AND ELECTROLYSIS METHOD. - Google Patents

Abstract

An ion exchange membrane which comprises at least a layer of fluorinated polymer which contains -COONa or -COOK groups, and optionally a layer of fluorinated polymer which contains -SO3Na or -SO3K groups, which membrane contains therein a microporous polytetrafluoroethylene sheet which has been stretched in at least one direction, and which membrane has been fabricated by melt lamination, is described. The membrane may optionally have an external reinforcing fabric adhered to one surface thereof. Such membrane can be used as the separator between the compartments of a chloralkali cell, and such a cell operates at low voltage, high current efficiency, and low power consumption. <IMAGE>

Description

.......... "ï i v 1 N.0, 30,6i * 6

* T

Membrane, electrochemical cell * and electrolysis process

Fluorinated ion exchange polymers with functional carboxylic and / or sulfonic acid groups or salts are known in the art. A principal use of such polymers is as a component of a membrane used to separate the anode and cathode compartments of a chlor-alkali electrolytic cell. Such a membrane can be in the form of a reinforced or non-reinforced film or laminar structure.

It is desirable for use in a chlor-alkali cell that a membrane provide low voltage operation and high current efficiency and thereby low energy consumption to provide products of high purity at low cost, especially with a view to energy costs are increasing all the time. It is also desirable that the membrane be rigid so as to withstand damage during manufacture and installation in such a cell. Since films of the best available ion exchange polymers have a low tear strength, it has been found necessary to reinforce them by manufacturing membranes with a reinforcement therein, such as a reinforcing fabric.

However, the use of a reinforcement in the membrane is not entirely favorable. A disadvantageous effect is that the use of reinforcement, such as a fabric *, results in a thicker membrane, which in turn leads to application at higher voltage because the greater thickness has a greater electrical resistance. Attempts to lower the resistance by using thinner films in the manufacture of reinforced membranes are often unsuccessful because the film breaks in some of the windows of the fabric during membrane manufacture, resulting in a membrane with leaks. ("Windows" is understood to mean the open areas of a fabric 30 between adjacent threads of the fabric.) A leaking membrane is undesirable as it allows anolyte and catholyte to flow into the opposite cell compartment, thereby reducing the flow efficiency and the fabricated products, and thick low polymer at the nodes of threads in a reinforcing fabric also form areas of high resistance ("nodes" means the intersections where threads meet the warp direction in the weft direction) · 8200153 i> 2

It is a object of the present invention to provide an ion exchange membrane which operates at low voltage and high current efficiency, thereby operating at lower power consumption and yet has good tear resistance. Another object is to provide a thin, strong ion exchange membrane. Other objects will become clear below.

Briefly, according to the invention, there is provided a melt-exchanged ion exchange membrane containing at least one layer of fluorinated polymer, containing functional -COONa or 10 -COOK groups, and which membrane therein contains a layer of microporous polytetrafluoroethylene containing in at least one direction is strengthened.

More specifically, according to one aspect of the invention there is provided an ion exchange membrane containing a layer of fluorinated polymer having functional -C00M groups, wherein M is Na or K, and fully embedded therein a microporous polytetrafluoroethylene sheet, which is in stretched in at least one direction, which membrane is made by heat-lamination.

According to another aspect of the invention, there is provided an ion-exchange membrane comprising a first layer of a first fluorinated polymer containing -C00M functional groups, a second layer of a second fluorinated polymer containing functional -SO, M groups, wherein M is Na or K and fully embedded therein contains a microporous polytetrafluoroethylene sheet, which is stretched in at least one direction, which membrane is made by heat-lamination.

Also, according to the invention, there is provided an electrochemical cell having such an ion exchange membrane as a component thereof and an electrolysis process using such an ion exchange membrane.

The membranes of the present invention are usually prepared from one or more layers of fluorinated polymer containing -C00R and / or -SC ^ W functional groups, wherein R is a lower carbon alkyl group and WF or Cl and a web of 35 carrier material.

The first polymer layer to which the present invention pertains is usually a carboxylic acid polymer having a fluorinated hydrocarbon backbone to which are attached the functional groups or side chains, which in turn contain the functional groups kO. For example, the side chains may contain the groups of formula 1 8200153 ii 3 »where g is F or CF ^ t is 1 to 12 and V is -COOR or -CN, where R is an alkyl group with a small number of carbon atoms * Usually the functional group in the side chains of the polymer are present in terminal groups of formula 2 * Examples of fluorinated polymers of this kind are described in British Patent No. 1, 145, 445 and U.S. Pat. Nos. 4,116,888 and 3 * 506,635. In particular, the polymers can be prepared from monomers which are fluorinated or fluorine substituted vinyl compounds. The polymers are usually prepared from at least two monomers. At least one monomer is a fluorinated vinyl compound such as vinyl fluoride, hexafluoropropene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, perfluoro (alkyl vinyl ether), tetrafluoroethylene and mixtures thereof. In the case of copolymers which will be used in the electrolysis of saline solutions, the vinyl monomer precursor desirably does not contain hydrogen. Additionally, at least one monomer is a fluorinated monomer containing a group that can be hydrolyzed to a carboxylic acid group, for example a carbaloxy group or nitrile group, in a side chain as set forth above.

By "fluorinated polymer" is meant a polymer in which after loss of the group R by hydrolysis to ion-exchange form, the number of F atoms is at least 90% of the number of F atoms and H atoms.

The monomers, with the exception of the R group in -C00R, will preferably contain no hydrogen, especially when the polymer is to be used in the electrolysis of saline and most preferably will be free in severe environments are of both hydrogen and chlorine, ie are perfluorinated; the R group need not be fluorinated since it is lost during hydrolysis when the functional groups are converted to ion exchange groups.

One example of a suitable type of monomer containing carboxylic acid groups is represented by the formula cf ^ or oocf ^ cfocoor 2 2, s d.

where R is alkyl with a. is a small number of carbon atoms, T is F or CF_ and 82 0 0 1 5 3

* * I

k s is 0, 1 or 2.

Those monomers in which s is 1 are preferred because their preparation and separation in good yield is accomplished more easily than when s is 0 or 2. The compound 5 CF- = CF0CF-CF0CF_C00CH_ 2 2, 2 3 CF ^ is a particularly useful monomer · Such monomers can be prepared, for example, from compounds of the formula CF = CF (OCF-CF) OCF-CF-S0 F 2 2 , S 2 2 2

Y.

wherein s and Y are as defined above, by (1) saturating the terminal vinyl group with chlorine to protect it in subsequent steps by converting it to a CF2C1-CFC1 group, (2) oxidation with nitrogen dioxide to converting the -0CF2CF2S02F group to an -0CF2C0F group, (3) esterification with an alcohol, such as methanol to form a 15 -0CF2G00CH2 group, and (4) dechlorination with zinc dust to give the final CF2 = CF- regenerate group. It is possible to replace steps (2) and (3) in this order by steps (a) reduction of the -0CF2CF2SC> 2E group to a sulfinic acid, -0CF2CF2S02H or its alkali or alkaline earth metal salt by treatment with a sulfite salt or hydrazine , (b) oxidation of the sulfinic acid or salt thereof with oxygen or chromic acid to form -CF 2 CO 2 H groups or metal salts thereof and (c) esterification to -OCF 2 OCH 2 according to known methods; this sequence is described in more detail in South African Patent No. 25 78/2224. Preparation of copolymers thereof is described in

South African Patent 78/2221.

Another example of a suitable type of carboxylic acid containing monomer is represented by the formula CF = CF40CF HF} 0CF - CF - V u 2 ƒ S 2 1 I s 30 where V is -C00R or -CN, R alkyl having a lower number of carbon atoms, YF or CF_, g is F or CF ^ and 33 s is 0, 1 or 2.

The most preferred monomers are those wherein V is -C00R, wherein R is a small number alkyl group 8200153 '9 carbon atoms, generally having 1 to 5 carbon atoms * due to the polymerization convenience and conversion to the ionic form *

Those monomers in which s is 1 are also preferred because their preparation and separation in good yield is accomplished more easily than when s is 0 or 2. Preparation of these monomers where V is -COOB where R is an alkyl group having a small number of carbon atoms * and copolymers thereof are described in U.S. Pat. 131 «7 ^ -0. The compounds 10 CF- = CF0CF-CFQCF.CF- C00CH, and 2 2, 2 2 5 cf3 CF2 = CF0 (CF2 CFO) 2 CF2 GF2C00CH ^ GF3 the preparation of which is described here * are particularly suitable · Preparation of monomers * in which V is -CN * is described in U.S. Pat. No. 3,552,326.

13 Yet another suitable type of carboxylic acid-containing monomer is that with a -OiCF ^^ COOCH ^ group, where v is 2 to 12, such as CF_ = CF-0 (CF_), GOOCH and CF = CF0CF_CF (CF> 0 (CF ) _C00CH.

The preparation of such monomers and copolymers thereof is described in Japanese Pat. Nos. 3 ^ 86/77 and 28586/77 and 20 in British Pat. No. 1,145 »Mf5 ·

Another group of polymers containing carboxylic acid groups is represented by polymers having the repeating units of formula 3, wherein q is 3 to 15, 25 r is 1 to 10, s is 0, 1 or 2, and t is 1 to 12 wherein the groups X taken together are four fluorine atoms or three fluorine atoms and a chlorine atom is IF or CF, 5 g is F or CF and 3 R is an alkyl group with a small number of carbon atoms.

A preferred group of copolymers is that of tetrafluoroethylene and a compound of the formula CF- = CF0 (GF_CF0) (CF_) COOR, 2 2, n 2 m ï wherein 82 0 0 1 5 3 6

# X

η Ο, 1 or 2, m is 1, 2, 3 or if, YF or CF_ and R is GEj, C ^ H ^ or · Such copolymers to which the present invention pertains can be prepared according to known methods, for example, U.S. Pat. Nos. 3 * 528,954 and 4,131,740 and South African Patent 78/2225.

When a layer of sulfonyl polymer is present, it is usually a polymer with a fluorinated hydrocarbon backbone to which are attached the functional groups or side chains which in turn carry the functional groups. For example, the side chains can be -GF-GF ^ SQ ^ W groups, where R ^ F, Cl, or a per-

Rf is fluoroalkyl of 1 to 10 carbon atoms and F is W or Cl, preferably F. Usually, the functional group in the side chains of the polymer will be present in -O-CF-CF ^ SO ^ F terminal groups. Examples of fluorinated polymers of this type are described in U.S. Pat. Nos. 3 * 282,875 »3 * 580,568 and 3,718,627. More specifically, the polymers can be prepared from monomers which are fluorinated or fluorine substituted vinyl compounds. The polymers are prepared from at least two monomers, with at least one of the monomers from each of the two groups described below.

At least one monomer is a fluorinated vinyl compound such as vinyl fluoride, hexafluoropropene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, perfluoro (alkyl vinyl ether), tetrafluoroethylene and mixtures thereof. In the case of copolymers which will be used for the electrolysis of saline solutions, the vinyl monomer precursor desirably does not contain hydrogen.

The second group are the sulfonyl-containing monomers, which contain the precursor group -CF-CF ^ -SO ^ F, where R ^ as before

Rf is defined. Additional examples can be represented by the general formula CF ^ CF-T ^ -CF ^ SO ^ F, where T is a bifunotional fluorinated group containing 1 to 8 carbon atoms and k is 0 or 1. Substituent atoms in T include fluorine, chlorine or hydrogen, although hydrogen will generally be excluded 820 0 15 3 / * 7 when using the ion exchange copolymer in a chloroalkali cell. The most preferred polymers are both hydrogen-free and chlorine-bonded to carbon, that is, they are perfluorinated for the greatest stability in severe environments. The I group of the preceding formula can be either branched or non-branched. be branched, i.e. have a straight chain and may contain one or more ether bonds. It is preferred that the vinyl group in this group of sulfonyl fluoride-containing comonomers is linked to the T group by an ether-10 bond, i.e. that the corona monomer has the formula CF ^ CF-OTC ^ -SO ^ F. Examples of such sulfonyl fluoride containing comonomers are cf2 = cfogf2cf2so2f, CFo = CF0CF_CF0CF.CF_S0-F, fa d. | fa fa fa cf3 15 CF2 = CF0CF2CF0CF2GF0CF2CF2S02F, CF CF_ »3 5 GF2 = CFCF2CF2S02F and the compound of formula k ·

The most preferred sulfonyl fluoride-containing comonomer is perfluoro (3,6-dioxa-if-methyl-7-octene sulfon-20-fluoride), CF2 = CFOCF2CF0CF2CF2S02F.

gf3

The sulfonyl-containing monomers are described in U.S. Pat. Nos. 3 * 282 * 875, 3.0VU317 * 3, 7, 627 and 3,560,568.

A preferred group of such polymers> 25 · is represented by polymers having the repeating units of formula 5 »where h is 3 to 15, j is 1 to 10, p is 0, 1 or 2, 30 is the symbols X together are four fluorine atoms or three fluorine atoms and one chlorine atom are »TF or CF, and is

Ef is F, Cl or a perfluoroalkyl group of 1 to 10 carbon atoms.

A most preferred copolymer is an 8200153-8 copolymer of tetrafluoroethylene and perfluoro (3'-6-dioxa-1-methyl-7-octenesulfonyl fluoride) containing 20 to 65 wt.%, Preferably 25 to 50 wt. weight SÓ of the latter contains

Such copolymers used in the present invention can be prepared by general polymerization techniques developed for homo- and copolymerizations of fluorinated ethenes, in particular those used for tetrafluoroethylene, which have been described in the literature. aqueous techniques for the preparation of the copolymers include those of US Pat. No. 3,0VI,317, said by polymerizing a mixture of the major monomer therein, such as tetrafluoroethylene, and a fluorinated ethylene, which contains a sulfonyl fluoride group, in the presence of a free radical initiator, preferably a perfluorocarbon peroxide or azo compound, at a temperature in the range of 0-200 ° C and at pressures in the range of 10y to 2 x 10r pascals or higher. The non-aqueous polymerization can, if desired, be carried out in the presence of a fluorinated solvent. Suitable fluorinated solvents are inert, liquid perfluorinated hydrocarbons, such as perfluoromethylcyclohexane, perfluorodimethylcyclobutane, perfluorooctane, perfluorobenzene and the like, and inert, liquid chlorofluorocarbons such as 1,1,2-trichloro-1,2,2-trifluoroethane and the like ·

Water-containing techniques for the preparation of the copolymer include contacting the monomers with an aqueous medium containing a free-radical initiator to obtain a suspension of polymer particles in non-water-wetted or granular form, such as disclosed in U.S. Pat. No. 2,393,967, or the contact of the mono-3 lakes with an aqueous medium containing both a free-radical initiator and a telogen inactive dispersant to obtain an aqueous colloidal dispersion polymer particles and coagulating the dispersion as described, for example, in U.S. Patent Nos. 2,559,752 and 2,593,583.

A copolymer containing various types of functional groups can also be used as a film component for the manufacture of the membrane of the invention. For example, a terpolymer prepared from a monomer selected from the group of non-40 functional monomers as described above, a monomer from 8200153 9 the group of the above-described carboxylic acid monomers, and additionally a monomer from the above-described group of sulfonyl monomers, can be prepared and used as one of the film components for the manufacture of the membrane.

It is furthermore possible as a film component of the membrane. to use a film »which is the mixture of two or more polymers · For example, a mixture of a polymer having sulfonyl groups in melt-ready form with a polymer having carboxylic acid groups in a melt-ready form can be prepared and used as one of the membrane component films of the present invention.

In addition, it is possible to use a laminar film as one of the component films in the manufacture of the membrane. For example, a film with a layer of a copolymer with sulfonyl groups in melt-formable form and a layer of a copolymer with carboxylic acid groups in melt-formable form can also be used as one of the component films in the manufacture of the membrane of the invention

An essential component of the membrane of the invention 20 is a layer of a first fluorinated polymer containing functional -COONa or -COOK groups having an equivalent weight in the range of IfOO to 2000, most preferably 1000 to 1100, and which has a thickness in the range of 13 to 250 microns, preferably 25 to 75 microns.

The membrane of the invention may contain, optionally in adhesive contact with this layer of first fluorinated polymer, an optional component, which is a layer of a second fluorinated polymer, which contains functional -SO2 III or -SQ2 K groups. , which has an equivalent weight in the range of 800 to 2000, most preferably 1100 to 1200, and which has a thickness in the range of 13 to 150 microns »preferably 13 to 75 microns When this second layer is present , the thickness of the first layer of the first fluorinated polymer should be 13 to 150 microns, preferably 13 to 75 microns, and the thickness of the first. 35 and second layer together should be in the range of from 26 to 250 microns, preferably from 26 to 150 microns.

With regard to both the polymer with carboxylic acid functionality and the polymer with sulfonyl functionality above an equivalent weight of 2000, the electrical similar resistance becomes too high and below the indicated lower limits of the equivalent weight, the mechanical properties become bad due to excessive swelling of the polymer. The relative amounts of the comonomers that form the polymer can be controlled or selected so that the polymer has a desired equivalent weight 5. The equivalent weight above which the resistance of a film or membrane becomes too high for practical application in an electrolytic cell varies slightly with the thickness of the film or membrane. For thinner films and membranes, equivalent weights of up to about 2000 may be permitted. For most purpose-10. ends, however, and for films of conventional thickness, a value no greater than about 1 ^ 00 is preferred

A second essential component of the membrane is a micro-porous polytetrafluoroethylene sheet. This sheet may be a film or an extrusion product which has been microporified or treated with some microporizing agent. This sheet should have a thickness in the range of 2.5 to 250 microns, preferably 15 to 75 microns, and has an open cell porosity with a pore size in the range 0.01 to 20 microns, preferably 3 to 15 microns . By "pore size" is meant an average size of the pores present.

This microporous sheet is a sheet that is stretched in at least one direction so that it will be tough and thus impart toughness to the membrane of the invention. Stretching results in orientation of the polymer in the sheet. The ability of the microporous sheet to provide toughness in the thin membranes of the invention is an important aspect of the invention. The use of an oriented sheet also ensures a form-retaining stable membrane. The sheet may be a sheet stretched in two mutually perpendicular directions; such a sheet has both a greater orientation and a greater toughness and gives a membrane which is resistant to tearing in all directions.

One such typical microporous sheet is a microstructured poly-tetrafluoroethylene sheet characterized by knots interconnected by fibrils manufactured by high speed stretching at an elevated temperature of a non-sintered, dried paste extrusion product of polytetrafluoroethylene as disclosed in U.S. Patent 3,962,155 and commercially available from WL Gore & Associates, Ine., under the tradename Gore-Tex.

Zj.0 When the membrane contains only the first layer of the first 82 0 0 1 5 3 - 11 fluorinated polymer »the microporous sheet will be placed in this first layer and must be fully embedded therein. As used herein, the term "fully embedded" means that the pores of the microporous sheet are filled with the first and / or second fluorinated polymer »which will or will subsequently be converted into an ion exchange polymer» but that fibers of polytetrafluoroethylene, which form part of the microporous sheet, may protrude beyond the surface of the membrane

When the membrane contains both a first layer of a first fluorinated polymer and a second layer of a second fluorinated polymer, the microporous sheet may be placed in either layer or at the boundary of the layers and thus in both layers stretch out. For a membrane intended for use in a chloroalkali electrolysis process, the microporous sheet 15 will preferably be predominant in the second layer and most preferably entirely in the second layers, the membrane will be used with the second layer facing the anode of the cell · In any case, the microporous sheet is fully embedded in the obtained composite structure.

The membranes of the invention may also contain another optional component, which is a woven or knitted reinforcement fabric, deposited externally on the membrane adjacent one of the surfaces, preferably the exposed surface of the above-described second layer.

In the case of a woven fabric, weaving products such as a normal braid and a fine weave are suitable. The threads of the fabric can be monofilament-like or multi-stranded.

The wires are per-halocarbon polymer wires. As used herein, the term "perhalocarbon polymer" is used for a polymer which has a carbon chain, which may or may not contain ether-oxygen bonds therein and which is completely substituted with fluorine atoms or with fluorine and chlorine atoms. Preferably, the perhalocarbon polymer is a perfluorocarbon polymer, since it has greater chemical inertness. Typically, such polymers include homopolymers prepared from tetrafluoroethylene and copolymers of tetrafluoroethylene with hexafluoropropene and / or perfluoro (alkyl vinyl ethers) with alkyl groups of 1 to 10 carbon atoms, such as perfluoro (propyl vinyl ether). An example of a most preferred wire material is po-ifO lytetrafluoroethylene. Threads made from chlorotrifluoroethylene 82 0 0 1 5 3 12 polymers are also suitable

In order to have a suitable strength in the fabric for lamination and in the membrane after lamination, the threads should have a denier of 50 to 600, preferably 200 to 1000 (denier is 5g / 9000m thread).

The fabric will usually have a thread count in the range of 1.6 to 16 threads / cm on both warp and weft, preferably 3 to 10 threads / cm.

The membrane can be made from the component layers of film and the microporous sheet using heat and pressure. Temperatures of about 200 ° C to 300 ° C are usually required to melt the polymer films used and allow for the microporous sheet to be fully embedded in the film, and when two films are used, to fuse the films together; however, the required temperature may even be above or below this range and will depend on the particular polymer used or the specific polymers used. The choice of a suitable low temperature in each specific case will be obvious, because a too short will trigger shooter / embedding of the microporous sheet 20, as evidenced by high opacity and will shorten to achieve a suitable degree of adhesion of the films to each other, when there are two films and too high temperature will cause leakage · Pressures of only k 7 approximately 2 x 10 pascals up to pressures above 10 pascals can be used 25 · A hydraulic press is a suitable device for the manufacture of the membrane, in which case typical pressures in the range of 2 x 105 to 107 pascals are ·

Another device suitable for the continuous preparation of the membrane contains a hollow roller with an internal heater and an internal vacuum source. The hollow roller contains a series of circumferential slots on the surface which allow the internal vacuum source to draw component materials toward the hollow roller. The vacuum pulls the component materials from the membrane onto the hollow roller, such that conventional air

L

35 presses against the component materials are in the range 5x10 5 to 10 pascals. A curved stationary plate with a blast heating device faces the top surface of the hollow roller with a space of about 6 mm between their two surfaces.

ifO During a lamination test, porous separating paper 8200153 13 'is used in contact with the hollow roll as a support material to prevent adhesion of any component material to the roll surface and to allow the vacuum materials to pass component materials in the direction of the hollow roll to pull. Feed and take off means are provided for the component materials and the product. In the feed means, one guide roller of smaller diameter than the hollow roller is present for unloading paper and component materials. The feed and take-off means are positioned so that component materials can pass around the hollow roller over a length of about 5/6 of its circumference. A different guide roller is provided for the release paper, which allows its separation from the other materials. Collection means are provided for the release paper and the membrane product.

For use in ion exchange applications and in cells, for example a chlor-alkali cell for the electrolysis of saline solutions, all functional groups must be converted to ionizable functional groups at the membrane. These groups are -C00M groups and, when present, -SO4M groups, where M is sodium or potassium. Such conversion is usually and expediently carried out by hydrolysis with acid or base, so that the various functional groups, as described above in connection with the polymers to be melted, are converted to the free acids or the alkali metal salts thereof, respectively. Such hydrolysis can be performed with a water-containing solution of an inorganic acid or an alkali metal hydroxide. Hydrolysis with base is preferred as it is faster and more complete. Use of warm solutions, such as at about the boiling point of the solution, is preferred for rapid hydrolysis. The time required for hydrolysis 30 increases with the thickness of the structure. It is also advantageous to include a water-miscible organic compound, such as dimethyl sulfoxide, in the hydrolysis bath. The free carboxylic and sulfonic acids can be converted into salts with sodium hydroxide or potassium hydroxide.

The membrane of the invention is impermeable to the hydraulic flow of liquid. (A diaphragm, which is porous, allows the hydraulic flow of fluid through it without change in composition, while an ion exchange membrane allows the selective permeation by ions and permeation of fluid by kO diffusion, so that the material containing the membrane 8200153 • 'η penetrates, differs in composition from the liquid in contact with the membrane). It is easy to determine whether or not there is hydraulic flow of liquid through a gas or liquid leak test. A major use of the ion exchange membrane of the invention is in electrochemical cells. Such a cell contains an anode, an anode compartment, a cathode, a cathode compartment and a membrane, which is placed to separate the two compartments. An example is a chloroalkalic cell. * The copolymers used in the layers described herein must have a sufficiently high molecular weight to produce films that are at least moderately strong in both the melt-prepared precursor form and the hydrolyzed ion exchange form.

Example I

In a hydraulic press with heatable plates measuring 20 cm x 20 cm, a piece of a film of a copolymer of the transfluorine and methyl methyl fluorine (if, 7-di oxa-5-methyl-8-nonenoate) of equivalent weight was placed of 1050, which piece of film had a thickness of 36 to 3 microns and was circular with a diameter of 12.5 cm, and a piece of "Gore-Tex" sheet as described above, which piece of sheet had a thickness of 25 microns, was circular with a diameter of 12.5 cm and a pore size of 0.5 micrometers. The film and microporous sheet assembly was covered with a.

c 25 pressure of 3 23 x 10 pascals for 1 minute, after preheating for 1 minute, heated to 220 ° C. The resulting composite structure had a thickness of about 6 µm micrometers and was nearly transparent, indicating complete embedding of the microporous sheet in the copolymer film layer. The composite structure 30 was placed in a mixture of 7 wt.% Water, 15 wt.% Dimethyl sulfoxide and 11 wt.% Potassium hydroxide for 1 hour at 80 ° C to hydrolyze the -G00CII groups, whereby an ion exchange membrane was provided with -COOK groups. The membrane was washed thoroughly with water and mounted in a small chloroalkali cell, p 35 The cell was operated for 8 days at 80 G / ampere / dm and a 20 wt% starting salt solution concentration to prepare alkali at 32 wt% at a current efficiency of 93.7 - 96.3 a voltage of 3 »59 - 3» 73 volts and an energy consumption of 2523 -2658 kWh / metric ton. During the hydrolysis, the functional L + O groups of the membrane became -COQNa groups.

8200153 15

For comparison, a copolymer film as described above * except that it had a thickness of 51 micrometers and without a microporous sheet therein * was hydrolyzed as described above »soaked in 30 wt% aqueous NaOH for 2 hours» mounted in a small chloroalkali cell and Operated for 8 days under the same conditions as above to prepare lye at a current efficiency of 94 * 9 - 99 * 9 # * © ea voltage of 4 * 02 - 418 volts and a power consumption of 2790 -2863 kwh / metric ton.

Example II

In the hydraulic press described in Example I, a piece of film of a copolymer such as that of Example I was "diameter 12.5 cm, thickness 25 micrometers, a piece of fabric, diameter 12.5 cm and a piece between the film and the fabric" Gore-Tex sheet as described above, diameter 12.5 ohm thickness 25 microns, pore size 3 to 5 mm. ((The fabric had 10 threads / cm polytetrafluoroethylene yarn of 200 denier in the warp and 10 threads / cm of polytetrafluoroethylene yarn of 400 denier in the weft, in a very fine fabric and had a thickness of 175 micrometers)).

The microporous sheet, fabric and film assembly was heated at 270 ° C for 1 minute 6o under 1.06 x 10 pascals, after preheating for 1 minute. The resulting composite structure had excellent mechanical strength and was free from leakage when tested under a vacuum of 1.65 x 10 · pascals. The composite structure was placed in an aqueous solution containing 32 wt% NaOH and 10 wt% methanol at room temperature for 2 hours to hydrolyze the -COOCH 4 groups to provide an ion exchange membrane with -COONa groups . The membrane is suitable as a separation between the compartments of electrochemical cells.

INDUSTRIAL APPLICABILITY

The ion exchange membrane of the present invention is a technical advance over the membranes of the prior art. It exhibits improved behavioral properties when used as a membrane in a chlor-alkali cell, including low voltage and high current efficiency operation and therefore lower power consumption. As a result, there is a significant saving in operating costs resulting from the reduced energy consumption. The membrane of the invention also reduces chlorine gas wear on the anolyte side of the membrane during the electrolysis of saline.

The ion exchange membrane of the invention can also be used in the electrolysis of water to oxygen and hydrogen and in the Donnan dialysis and electrodialysis processes.

82 0 0 1 5 3

Claims (24)

1. Ion exchange membrane characterized by the presence of a layer of fluorinated polymer, containing -COOM functional groups, in which M is sodium or potassium, and fully embedded therein, a microporous polytetrafluoroethylene sheet, which is stretched in at least one direction, which membrane is manufactured by melt lamination. Membrane according to claim 1, characterized in that the layer has a thickness in the range from 30 to 250 micrometers and the fluorinated polymer is a perfluorinated polymer with an equivalent weight in the range from 0000 to 2000. Membrane according to claim 1 or 2t, characterized in that the sheet has a thickness in the range of 2.5 to 250 micrometers and a pore size in the range of 0.01 to 20 micrometers. Membrane according to claims 1 to 3, characterized in that the layer has a thickness in the range of 13 to 75 micrometers, the perfluorinated polymer has an equivalent weight in the range of 1000 to 1100 and which sheet has a thickness of 20. range from 13 to 75 microns and a pore size in the range from 3 to 15 microns. Membrane according to claims 1 to if, with. characterized in that the sheet is stretched in at least two mutually perpendicular directions. Membrane according to claims 1 to 5, characterized in that the perfluorinated polymer is a copolymer of tetrafluoroethylene and CF 2 = CFOCF 1 CFOCF 1 CF 1 COOM. cf3 Membrane according to claims 1 to 6, characterized in that the membrane further comprises an outer carrier fabric adhered thereto, which fabric is woven or knitted, and consists of filaments of perfluorocarbon polymer. Membrane according to claims 1 to 4 », characterized in that the perfluorinated polymer is a copolymer of tetrafluoroethylene and CF = CFCKCF ^^ COOM» 35 CF- = CFOCF_CFOCF-COOM or CF- = CFOCF_CFO (CF _) _ COOM. U I Cm C. w eL I U ^ CF-, CF, Membrane according to claim 8, characterized in that the membrane further contains an external carrier fabric adhered thereto, which fabric is woven or knitted and consists of filaments of perfluorocarbon polymer. 8200153 ι 10 CF-, a CFOCF-, CF0CF_COOM or CF-, = CF0CF-CF0 (CFo) -. C00M. C 2 f W Cm Cm ^ c1 3 CF ^ CF ^ 10. Ion exchange membrane, characterized by the presence of a first layer of a first fluorinated polymer containing -C00M functional groups, a second layer of a second fluorinated polymer containing functional -SO2M groups, wherein M sodium or potassium, and fully embedded therein is a microporous polytetrafluoroethylene sheet, which is stretched in at least one direction, which membrane is made by melt lamination. Membrane according to claim 10, characterized in that each of the first and second layers has a thickness in the range from 13 to 150 micrometers, the two layers having a total thickness in the range from 26 to 250 micrometers, the first and second fluorinated polymers are each perfluorinated polymers, which first perfluorinated polymer has an equivalent weight in the range of 1000 to 2000 and which second perfluorinated polymer has an equivalent weight in a range of 800 to 2000. 12. Membrane according to claim 10 or 11, characterized in that the sheet has a thickness in the range from 2.5 to 250 micrometers and a pore size in the range from 0.01 to 20 micrometers. 20 Membrane according to claims 10 to 12, characterized in that each of the first and second layers has a thickness in the range of 13 to 75 micrometers and the two layers have a thickness in the range of 26 to 150 micrometers, which first perfluorinated polymer has an equivalent weight in the range of 1000 to 1100, which second perfluorinated polymer has an equivalent weight in the range of 1100 to 1200 and which sheet has a thickness in the range of 13 to 75 microns and an oriental size in the range from 3 to 15 micrometers. Membrane according to claims 10 to 13, characterized in that the sheet is stretched in two mutually perpendicular directions. Membrane according to claims 10 to 13, characterized in that the sheet is present at least predominantly in the second layer. Membrane according to claims 10 to 15, characterized in that the second perfluorinated polymer is a copolymer of tetrafluoroethylene and CF = CFOCF2CFOCF2CF2SO2M. CF ^ Membrane according to claims 10 to 16, characterized in that the first perfluorinated polymer is a copolymer 1 + 0 of tetrafluoroethylene and CF = CFOCF2CFOCF2CF2COOM. 82 0 0 1 5 3 0.5 ' 18. Membrane according to claims 10 to 17, characterized in that the membrane further contains an external carrier fabric adhered thereto, which fabric is woven or knitted and consists of filaments of perfluorocarbon polymer · 5 Membrane according to Claims 10 to 18, characterized in that the carrier fabric is adhered to the second layer 1 Membrane according to claims 10 to 16, characterized in that the first perfluorinated polymer is a copolymer of tetrafluoroethylene and CF_ = CF0 (CF_) COOM, 2 dj Membrane according to claim 20, characterized in that the membrane further comprises an external carrier fabric adhered thereto, which fabric is knitted or woven and consists of filaments of perfluorocarbon polymer. Membrane according to claim 21, characterized in that the carrier fabric is adhered to the second layer. 23. An electrochemical cell comprising an anode compartment, an anode placed within the anode compartment, a cathode compartment, a cathode placed within the cathode compartment and the membrane between the compartments according to claim 1, 6, 7, 8, 9, 10, 17, 19, 20 or 22. 24 · Method for the electrolysis of saline in a chlor-alkali cell containing an anode, an anode compartment, a cathode, a cathode compartment and a fluorine-containing cation exchange membrane separating the compartments to form caustic and chlorine characterized in that the membrane according to claim 1, 6, 7, 8, 9, 10, 17, 19, 20 or 22 is used as membrane. 8200153 1 1 1 1 1