Background of the invention
[0001] Fluorinated polymers containing pendant side chains having functional groups are
used as ion exchange membranes for electrochemical cells, particularly as membranes
in chloralkali electrolytic cells. Typically, the side chains on the fluorinated polymers
contain sulfonyl or carboxyl groups or both. In the use of such membranes in electrolytic
cells, the desired performance characteristics are obtained using a particularly thin
membrane. It is desirable to minimize the thickness of this membrane, to reduce the
operating voltage of the electrolytic cell. However, the thin membranes are difficult
to handle without damage or tearing during installation in the electrolytic cells.
Accordingly, the thin membranes are frequently reinforced with woven or nonwoven webs.
However, such reinforcing webs, in the operation of an electrolytic cell, cause uneven
current distribution and increased operating voltage.
[0002] US--A-4 021 327 refers to fluorocarbon- polymer based cation permeable separators.
The separator is reinforced with supporting fibers which are initially contained in
a fabric which also contains sacrificial fibers which are subsequently removed from
the fabric.
Summary of the invention
[0003] The instant invention provides an improved reinforced fluorinated polymer membrane
which exhibits adequate strength for normal installation procedures without increasing
the operating voltage of the cell.
[0004] Specifically, the instant invention provides, in a fluorocarbon cation exchange membrane
consisting of (a) at least one fluorinated polymer having side chains containing sulfonyl
and/or carboxyl groups and (b) a reinforcing web embedded in the fluorinated polymer,
characterized in that the entire reinforcing web is degradable by hypochlorite. _
__ __
[0005] The invention further provides a process for the continuous production of alkali
metal hydroxide which comprises continuously providing an aqueous alkali metal halide
solution to the anode compartment of an electrolytic cell having an anode, a cathode,
and a cation exchange membrane separating the anode and the cathode; electrolyzing
the solution; and continuously removing alkali metal hydroxide solution, hydrogen,
and halogen from the electrolytic cell, wherein the cation exchange membrane consists
of (a) at least one fluorinated polymer having side chains containing sulfonyl and/or
carboxyl groups and (b) a reinforcing web embedded in the fluorinated polymer, characterized
in that the entire reinforcing web is degradable by hypochlorite.
[0006] The invention further provides an electrolytic cell having an anode, a cathode, and
a cation exchange membrane separating the anode and the cathode, wherein the cation
exchange membrane consists of (a) at least one fluorinated polymer having side chains
containing sulfonyl and/or carboxyl groups and (b) a reinforcing web embedded in the
fluorinated polymer, characterized in that the entire reinforcing web is degradable
by hypochlorite.
Detailed description of the invention
[0007] The fluorocarbon cation exchange membranes which can be used in the instant invention
have side chains containing either or both sulfonyl and carboxyl groups.
[0008] Polymers having sulfonyl functional groups typically contain pendant side chains
having
groups wherein R
f is F, Cl, or a C, to C
'o perfluoroalkyl radical, and preferably F. Ordinarily, the functional group in the
side chains of the polymer will be present in terminal
groups. Fluorinated polymers of this kind and their preparation are disclosed in United
States Patents 3,282,875, 3,560,568, 3,718,627 and 3,041,317, hereby incorporated
by reference. Perfluorinated polymers are preferred because of their inertness to
a wide variety of chemicals. The equivalent weight of these polymers is generally
about from 1000 to 1600.
[0009] The fluorinated polymers having carboxyl functional groups are typically polymers
having a fluorinated hydrocarbon backbone chain to which are attached the functional
groups or pendant side chains which in turn carry the functional groups.
[0010] Fluorinated polymers of this kind and their preparation are disclosed in British
Patent 1,145,445, United States Patents 3,506,635, 4,116,888 and 3,852,326, all hereby
incorporated by reference. Preferred monomers for use in the preparation of such polymers
are found in United States Patents 4,121,740 and 3,852,326, also hereby incorporated
by reference. For chlor-alkali cells, perfluorinated polymers are preferred.
[0011] Polymers are preferred in which the carbon atom adjacent to the carboxyl group bears
one, and especially two, fluorine atoms. Also preferred are perfluorinated polymers.
The equivalent weight of the polymers having carboxyl functional groups is preferably
about from 500 to 1500.
[0012] The membranes used in the instant invention comprise single layers of polymers having
sulfonyl or carboxylic functional groups, single layers of polymer containing both
types of functional groups, as well as laminar structures containing different polymers
or different equivalent weights of similar polymers. Such laminar structures are preferred.
[0013] The central feature of the present invention is a reinforcing web embedded in the
fluorinated polymer which is degraded by hypochlorite. Thus, the reinforcing web provides
added strength for the membrane during manufacturing operations and the installation
of the membrane in an electrolytic cell, but, because of its degradability in hypochlorite,
is disintegrated in operation. The oxidation of the reinforcing web to low molecular
weight products results in its removal from the membrane. The disintegration of the
reinforcing web eliminates the areas in the membrane that typically cause higher operating
voltages. These deficiencies were noted with the use of reinforcing polymers such
as polytetrafluoroethylene which are resistant to degradation.
[0014] A wide variety of reinforcing webs can be used in the present invention. These include
woven and knitted fabrics as well as nonwoven felts and papers and randomly dispersed
fibrils. The particular composition of the reinforcing web can also vary widely, including
most natural and synthetic fibers. Representative of reinforcing fibers that can be
used are those of cotton, linen, silk, rayon, acetate, nitrocellulose, nylon, polyester,
polyvinyl alcohol, polyacrylonitriles, polyolefins and cellulose. Of the nonwoven
materials which can be used in the present invention, lightweight tissue paper has
been found particularly satisfactory. Among the woven fabrics which can be used, a
low denier rayon is particularly preferred.
[0015] An important factor in the present invention is that the reinforcing web be embedded
in the fluorinated polymer. That is, the reinforcing web must not be present throughout
the entire thickness of the cation exchange membrane, since this would produce passages
through the entire thickness of the membrane after the reinforcing wex was degraded
and removed. Preferably, the reinforcing web is completely encapsulated in the fluorinated
polymer. In the event that a laminar structure is used as the fluorocarbon cation
exchange membrane, such as one containing a first fluorinated polymer having sulfonic
groups and a second fluorinated polymer having carboxylic acid groups, the reinforcing
web is preferably embedded in the fluorinated polymer having sulfonic acid groups
in the pendant side chains.
[0016] The thickness of the reinforcing web can vary with the total thickness of the fluorocarbon
cation exchange membrane. However, in general, the reinforcing web has a thickness
of about from 25 to 127 µm and preferably of about from 50 to 101 pm.
[0017] The cation exchange membranes of the present invention exhibit increased structural
integrity and are resistant to tears often encountered in the installation of such
membranes in an electrolytic cell. This structural integrity is achieved without the
presence of permanent reinforcing materials such as perfluorinated polymer webs. However,
after a period of operation in an electrolytic cell, the reinforcing web is degraded
so as to not interfere with the electrical conduction of the membrane. In fact, the
voids remaining after disintegration of the reinforcing web actually aid in electrical
conduction, thereby further reducing the voltage requirements of the operating cell.
The period for degradation of the reinforcing web will, of course, vary with the particular
material selected, the thickness of the reinforcing web and the operating conditions
of the cell. In general, however, the period of degradation will vary from several
hours to up to two months.
[0018] The membranes of this invention can be used in any known membrane electrochemical
cell, especially cells for the electrolysis of brine. Among these cells are those
in which the gap or spacing between the electrodes is no greater than about 3 mm.
The membrane can be held in contact with either the anode or the cathode with the
aid of a hydraulic head in one cell compartment, or with an open-mesh or grid or woven
spacer to urge the membrane against the electrode. It is often advantageous for the
membrane to be in contact with both porous anode and porous cathode in narrow-gap
cells of this type. Such arrangements minimize the resistance contributed by the anolyte
and catholyte, thus providing for operation at low. voltage. The membranes of this
invention can also be used in a solid polymer electrolyte or composite electrode/membrane
arrangement, in which a thin porous anode and/or porous cathode are attached directly
to the membrane surface, and rigid current collectors can also be used in contact
with these electrodes.
[0019] In any of the above arrangements, either or both of the electrodes can have a catalytically
active surface layer of the type known in the art for lowering the overvoltage at
an electrode. Such electrocatalyst can be of a type known in the art, such as those
described in U.S. Patents 4,224,121 and 3,134,697, and published UK Patent Application
GB 2,009,788A. Preferred cathodic electrocatalysts include platinum black, Raney nickel
and ruthenium black. Preferred anodic electrocatalysts include platinum black and
mixed ruthenium and iridium oxides.
[0020] The membranes described herein can also be modified on either surface or both surfaces
thereof so as to have enhanced gas release properties, for example by providing optimum
surface roughness or smoothness, or, preferably, by providing thereon a gas- and liquid-permeable
porous non-electrode layer. Such non-electrode layer can be in the form of a thin
hydrophilic coating or spacer and is ordinarily of an inert electroinactive or non-electrocatalytic
substance. Such non-electrode layer should have a porosity of 10 to 99%, preferably
30 to 70%, and an average pore diameter of 0.01 to 2000 um, preferably 0.1 to 1000
pm, and a thickness generally in the range of 0.1 to 500 pm, preferably 1 to 300 ¡.rm.
A non-electrode layer ordinarily comprises an inorganic component and a binder; the
inorganic component can be of a type as set forth in published UK Patent Application
GB 2,064,586A, preferably tin oxide, titanium oxide, zirconium oxide, or an iron oxide
such as Fe
20
3 or Fe
30
4. Other information regarding non-electrode layers on ion-exchange membranes is found
in published European Patent Application 0,031,660, and in Japanese Published Patent
Applications 56-108888 and 56-112487.
[0021] The binder component in a non-electrode layer, and in an electrocatalyst composition
layer, can be for example, polytetrafluoroethylene, a fluorocarbon polymer at least
the surface of which is hydrophilic by virtue of treatment with ionizing radiation
in air or a modifying agent to introduce functional groups such as -COOH or -S0
3H (as described in published UK Patent Application GB 2,060,703A) or treatment with
an agent such as sodium in liquid ammonia, a functionally substituted fluorocarbon
polymer or copolymer which has carboxylate or sulfonate functional groups, or polytetrafluoroethylene
particles modified on their surfaces with fluorinated copolymer having acid type functional
groups (GB 2,064,586A). Such binder can be used in an amount of about from 10 to 50%
by wt. of the non-electrode layer or of the electrocatalyst composition layer.
[0022] Composite structures having non-electrode layers and/or electrocatalyst composition
layers thereon can be made by various techniques known in the art, which include preparation
of a decal which is then pressed onto the membrane surface, application of a slurry
in a liquid composition (e.g., dispersion or solution) of the binder followed by drying,
screen or gravure printing of compositions in paste form, hot pressing of powders
distributed on the membrane surface, and other methods as set forth in GB 2,064,586A.
Such structures can be made by applying the indicated layers onto membranes in melt-fabricable
form, and by some of the methods onto membranes in ion-exchange form; the polymeric
component of the resulting structures when in melt-fabricable form can be hydrolyzed
in known manner to the ion-exchange form.
[0023] Non-electrode layers and electrocatalyst composition layers can be used in combination
in various ways on a membrane. For example, a surface of a membrane can be modified
with a non-electrode layer, and an electrocatalyst composition layer disposed over
the latter. It is also possible to place on a membrane a layer containing both an
electrocatalyst and a conductive non-electrode material, e.g. a metal powder which
has a higher overvoltage than the electrocatalyst, combined into a single layer with
a binder. One preferred type of membrane is that which carries a cathodic electrocatalyst
composition on one surface thereof, and a non-electrode layer on the opposite surface
thereof.
[0024] Membranes which carry thereon one or more electrocatalyst layers, or one or more
non-electrode layers, or combinations thereof, can be employed in an electrochemical
cell in a narrow-gap or zero-gap configuration as described above.
[0025] The membranes of this invention, after degradation of the reinforcing web, have another
surprising advantage. They are more resistant to the deleterious effect of Na
2SO
4 in the brine than corresponding membranes containing carboxylic or carboxylic and
sulfonyl ion exchange resins and a perfluorocarbon reinforcing web, but never having
contained a degradable reinforcing web. The control membranes suffer deleterious effects
when the brine contains 30 g/I or even as little as 10 g/I. Na
2S0
4. The current efficiency deteriorates somewhat after a few weeks and Na
IS0
4 crystals may appear in the cathode surface of the laminar structure, especially close
to the perfluorocarbon threads. With the membrane of the present invention, these
deleterious effects are not observed.
[0026] The invention is further illustrated in the following specific examples:
Example 1
[0027] A reinforced cationic ion exchange membrane was prepared by thermally bonding together
two polymeric layers. A cathode surface layer was used consisting of 51 µm of a copolymer
of tetrafluoroethylene (TFE) and methyl perfluoro (4,7-dioxa-5-methyl-8-noneate) (EVE)
and having an equivalent weight of 1080. An anode surface layer was used consisting
of 127 pm of a copolymer of TFE and perfluoro (3,6-dioxa-4-methyl-7-octenesulfonyl
fluoride) (PSEPVE) and having an equivalent weight of 1100. The anode layer was impregnated
into 102 pm of two-ply facial tissue paper.
[0028] The laminate was made in two steps using a heated platen press. In the first step
the TFE/ PSEPVE copolymer was pressed into the tissue paper at 270°C and 3.23 MPa
for 1 min. In the second step the TFE/EVE layer was thermally bonded at 250°C at 1.1
MPa for 1 min. The resulting laminate was hydrolyzed in a bath containing 30% dimethyl
sulfoxide (DMSO) and 11% potassium hydroxide (KOH) for 20 minutes at 90°C. The resulting
construction was leak-free as determined by a vacuum leak checker. The laminate was
treated with a hot solution of 5% sodium hypochlorite (NaOCI) where it was found that
the paper was leached out after about 1 hour.
[0029] A portion of the laminate so treated was mounted wet in a laboratory chloralkali
cell having an active area of 45 cm
2 between a dimensionally stable anode and a mild steel expanded metal cathode. The
cell was operated at 80°C with a current density of 3.1 KA/m
2. The anolyte salt content was held at 200 gpl. Water was added to the catholyte to
maintain the concentration of the caustic produced at 32±1%.
[0030] After 6 days on line the cell was performing well at 3.70 volts and 95.1% current
efficiency.
Example 2
[0031] If the following procedure is carried out, the indicated results will be expected.
[0032] A cationic ion exchange membrane containing a temporary reinforcement is prepared
by thermally bonding together the following layers in the order specified.
[0033] A. A cathode surface layer consisting of a 25 µm film of TFE/EVE having an equivalent
weight of 1080.
[0034] B. A 76 pm layer of TFE/PSEPVE having an equivalent weight of 1100.
[0035] C. A reinforcing cloth having a thickness of 71.1 pm consisting of 50 denier rayon
fiber with a warp and fill thread count of 29.5 threads/cm.
[0036] D. An anode surface layer consisting of 25 pm of a TFE/PSEPVE copolymer having an
equivalent weight of 1100.
[0037] This construction is thermally bonded and hydrolyzed. The resulting laminate shows
improved tear resistance over a non-reinforced construction of similar thickness.
If tested in a laboratory cell under the conditions of Example 1, except that the
cell is operated at 90°C, after 7 days of operation the membrane is expected to perform
well at 3.63 volts and 95% current efficiency. After 7 days of operation, removal
and examination of the membrane will indicate a substantial total dissolution of the
rayon fibers, leaving a pattern of channels where the fabric had been.
1. A fluorocarbon cation exchange membrane consisting of (a) at least one fluorinated
polymer having side chains containing sulfonyl and/or carboxyl groups and (b) a reinforcing
web embedded in the fluorinated polymer, characterized in that the entire reinforcing
web is degradable by hypochlorite.
2. A cation exchange membrane of claim 1 wherein the reinforcing web has a thickness
of about from 25 to 125 um.
3. A cation exchange membrane of claim 1 wherein the reinforcing web is nonwoven.
4. A cation exchange membrane of claim 3 wherein the reinforcing web consists of tissue
paper.
5. A cation exchange membrane of claims 1 wherein the reinforcing web is a woven fabric.
6. A cation exchange membrane of claim 5 wherein the woven fabric is rayon.
7. A cation exchange membrane of claim 1 wherein the fluorinated polymer is a laminar
structure comprising a perfluorosulfonic acid resin bonded to a perfluorocarboxylic
acid resin and the reinforcing web is embedded in the perfluorosulfonic acid polymer.
8. A cation exchange membrane of claim 7 wherein the perfluorosulfonic acid resin
has an equivalent weight of about from 1000 to 1600 and the perfluorocarboxylic acid
resin has an equivalent weight of about from 500 to 1500.
9. A cation exchange membrane of Claim 1 further comprising a gas- and liquid-permeable
porous layer of electrocatalyst composition on at least one surface thereof.
10. A cation exchange membrane of Claim 1 further comprising a gas- and liquid-permeable
porous non-electrode layer on at least one surface thereof.
11. A process for the continuous production of alkali metal hydroxide which comprises
continuously providing an aqueous alkali metal halide solution to the anode compartment
of an electrolytic cell having an anode, a cathode, and a cation exchange membrane
separating the anode and the cathode; electrolyzing the solution; and. continuously
removing alkali metal hydroxide solution, hydrogen, and halogen from the electrolytic
cell, wherein the cation exchange membrane consists of (a) at least one fluorinated
polymer having side chains containing sulfonyl and/or carboxyl groups, and (b) a reinforcing
web embedded in the fluorinated polymer, characterised in that the entire reinforcing
web is degradable by hypochlorite.
12. A process of Claim 11 further comprising applying to at least one surface of the
cationic ion exchange membrane a gas- and liquid-permeable porous layer of electrocatalyst
composition.
13. A process of Claim 11 further comprising applying to at least one surface of the
cationic ion-exchange membrane a gas- and liquid-permeable porous non-electrode layer.
14. A process of Claim 11 further comprising applying to at least one surface of the
resulting cationic ion-exchange membrane at least one gas- and liquid-permeable porous
layer selected from electrocatalyst composition and non-electrode material.
15. An electrolytic cell having an anode, a cathode, and a cation exchange membrane
separating the anode and the cathode, wherein the cation exchange membrane consists
of (a) at least one fluorinated polymer having side chains containing sulfonyl and/or
carboxyl groups, and (b) a reinforcing web embedded in the fluorinated polymer, characterized
in that the entire reinforcing web is degradable by hypochlorite.
16. An electrolytic cell of Claim 15 wherein the gap between the electrodes is no
greater than about 3 mm.
1. Eine Fluorkohlenstoff - Kationenaustauschermembran, bestehend aus (a) mindestens
einem fluorhaltigen Polymeren mit Seitenketten, die Sulfonyl- und/oder Carboxylgruppen
enthalten, und (b) einem in das fluorhaltige Polymere eingebettete Verstärkungsgewebe,
dadurch gekennzeichnet, dass das gesamte Verstärkungsgewebe durch Hypochlorit abbaubar
ist.
2. Eine Kationenaustauschermembran nach Anspruch 1, bei der das Verstärkungsgewebe
eine Dicke von etwa 25 bis 125 um hat.
3. Eine Kationenaustauschermembran nach Anspruch 1, in der das Verstärkungsgewebe
ein Vliesstoff ist.
4. Eine Kationenaustauschermembran nach Anspruch 3, in der das Verstärkungsgewebe
aus Seidenpapier besteht.
5. Eine Kationenaustauschermembran nach Anspruch 1, in der das Verstärkungsgewebe
ein gewebter Stoff ist.
6. Eine Kationenaustauschermembran nach Anspruch 5, in der das Gewebe Reyon ist.
7. Eine Kationenaustauschermembran nach Anspruch 1, in der das fluorhaltige Polymere
eine Laminarstruktur ist, enthaltend ein Perfluorsulfonsäureharz, gebunden an ein
Perfluorcarbonsäureharz, und das Verstärkungsgewebe in das Perfluorsulfonsäurepolymere
eingebettet ist.
8. Eine Kationenaustauschermembran nach Anspruch 7, bei der das Perfluorsulfonsäureharz
ein Äquivalentgewicht von etwa 1000 bis 1600 und das Perfluorcarbonsäureharz ein Äquivalentgewicht
von etwa 500 bis 1500 hat.
9. Eine Kationenaustauschermembran nach Anspruch 1, die ferner eine gas- und flüssigkeitsdurchlässige
poröse Schicht einer Elektrokatalysator - Zusammensetzung auf mindestens einer ihrer
Oberfläche hat.
10. Eine Kationenaustauschermembran nach Anspruch 1, die ferner eine gas- und flüssigkeitsdurchlässige
poröse Nicht - Elektrodenschicht auf mindestens einer ihrer Oberfläche hat.
11. Ein Verfahren zur kontinuierlichen Herstellung von Alkalihydroxid, bei dem eine
wässrige Alkalihalogenidlösung kontinuierlich der Anodenkammer einer elektrolytischen
Zelle, die eine Anode, eine Kathode und eine Kationenaustauschermembran aufweist,
die die Anode und die Kathode trennt, zugeführt, die Lösung elektrolysiert und Wasserstoff
und Halogen aus der elektrolytischen Zelle entfernt wird, wobei die Kationenaustauschermembran
aus (a) mindestens einem fluorhaltigen Polymeren besteht, das Seitenketten, die Sulfonyl-
und/oder Carboxylgruppen enthalten, aufweist, sowie (b) ein Verstärkungsgewebe, das
in das fluorhaltige Polymere eingebettet ist, aufweist, dadurch gekennzeichnet, dass
das gesamte Verstärkungsgewebe durch Hypochlorit abbaubar ist.
12. Verfahren nach Anspruch 11, bei dem ferner auf mindestens eine Oberfläche der
Kationenaustauschermembran eine gas- und flüssigkeitsdurchlässige poröse Schicht einer
Elektrokatalysator - Zusammensetzung aufgebracht wird.
13. Verfahren nach Anspruch 11, bei dem ferner auf mindestens eine Oberfläche der
Kationenaustauschermembran eine gas- und flüssigkeitsdurchlässige poröse Nicht - Elektrodenschicht
aufgebracht wird.
14. Verfahren nach Anspruch 11, bei dem ferner auf mindestens eine Oberfläche der
entstandenen kationischen Austauschermembran mindestens eine gas- und flüssigkeitspermeable
poröse Schicht aufgebracht wird, die aus Elektrokatalysator - Zusammensetzungen und
Nicht - Elektrodenmaterial ausgewählt wird.
15. Eine elektrolytische Zelle mit einer Anode, einer Kathode und einer Kationenaustauschermembran,
welche die Anode und die Kathode trennt, wobei die Kationenaustauschermembran aus
(a) mindestens einem fluorhaltigen Polymeren mit Seitenketten, die Sulfonyl- und/oder
Carboxylgruppen haben, und (b) einem Verstärkungsgewebe, das in das fluorhaltige Polymere
eingebettet ist, besteht, dadurch gekennzeichnet, dass das gesamte Verstärkungsgewebe
durch Hypochlorit abbaubar ist.
16. Eine elektrolytische Zelle von Anspruch 15, in der der Spalt zwischen den Elektroden
nicht grösser als etwa 3 mm ist.
1. Une membrane échangeuse de cations fluorocarbonée, constituée de (a) au moins un
polymère fluoré ayant des chaînes latérales contenant des groupes sulfonyle et/ou
carboxyle et (b) un tissu de renforcement enrobé dans le polymère fluoré, caractérisée
en ce que le tissu de renforcement entier est dégradable par un hypochlorite.
2. Une membrane échangeuse de cations selon la revendication 1, dans laquelle le tissu
de renforcement a une épaisseur d'environ 25 à 125 um.
3. Une membrane échangeuse de cations selon la revendication 1, dans laquelle le tissu
de renforcement est non-tissé.
4. Une membrane échangeuse de cations selon la revendication 3, dans laquelle le tissu
de renforcement consiste en papier de soie.
5. Une membrane échangeuse de cations selon la revendication 1, dans laquelle le tissu
de renforcement est un tissu tissé.
6. Une membrane échangeuse de cations selon la revendication 5, dans laquelle le tissu
tissé est de la rayonne.
7. Une membrane échangeuse de cations selon la revendication 1, dans laquelle le polymère
fluoré est une structure stratifiée comprenant une résine d'acide perfluorosulfonique liée à une résine d'acide perfluorocarboxylique et le tissu de renforcement
est enrobé dans le polymère d'acide perfluorosulfonique.
8. Une membrane échangeuse de cations selon la revendication 7, dans laquelle la résine
d'acide perfluorosulfonique a un poids équivalent d'environ 1000 à 1600 et la résine
d'acide perfluorocarboxylique a un poids équivalent d'environ 500 à 1500.
9. Une membrane échangeuse de cations selon la revendication 1, comprenant en outre
une couche poreuse de composition d'électro- catalyseur perméable aux gaz et aux liquides
sur au moins une de ses surfaces.
10. Une membrane échangeuse de cations selon la revendication 1, comprenant en outre
une couche poreuse non-électrode perméable aux gaz et aux liquides sur au moins une
de ses surfaces.
11. Un procédé pour la production continue d'un hydroxyde de métal alcalin, selon
lequel on fait arriver de manière continue une solution aqueuse d'un halogénure de
métal alcalin dans le compartiment anodique d'une cellule électrolytique ayant une
anode, une cathode et une membrane échangeuse de cations séparant l'anode et la cathode;
on électrolyse la solution, et on évacue de manière continue une solution d'hydroxyde
de métal alcalin, de l'hydrogène et un halogène de la cellule électrolytique, la membrane
échangeuse de cations étant constituée de (a) au moins un polymère fluoré ayant des
chaînes latérales contenant des groupes sulfonyle et/ou carboxyle et (b) un tissu
de renforcement enrobé dans le polymère fluoré, caractérisé en ce que le tissu de
renforcement entier est dégradable par un hypochlorite.
12. Un procédé selon la revendication 11, comprenant en outre l'application sur au
moins une surface de la membrane échangeuse de cations d'une couche poreuse de composition
d'électrocatalyseur perméable aux gaz et aux liquides.
13. Un procédé selon la revendication 11, comprenant en outre l'application sur au
moins une surface de la membrane échangeuse de cations d'une couche poreuse non-électrode
perméable aux gaz et aux liquides.
14. Un procédé selon la revendication 11, comprenant en outre l'application sur au
moins une surface de la membrane échangeuse de cations résultante d'au moins une couche
poreuse perméable aux gaz et aux liquides choisie parmi une composition d'électro-
catalyseur et une matière non-électrode.
15. Une cellule électrolytique ayant une anode, une cathode et une membrane échangeuse
de cations séparant l'anode et la cathode, où la membrane échangeuse de cations est
constituée de (a) au moins un polymère fluoré ayant des chaînes latérales contenant
des groupes sulfonyle et/ou carboxyle et (b) un tissu de renforcement enrobé dans
le polymère fluoré, caractérisée en ce que le tissu de renforcement entier est dégradable
par un hypochlorite.
16. Une cellule électrolytique selon la revendication 15, dans laquelle l'espace libre
entre les électrodes n'est pas plus grand qu'environ 3 mm.