Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
This invention relates to an improved cationic
exchange membrane, a process for making that membrane, and
apparatus which is used in the process. More particularly,
the membrane is a fluorinated cation exchange membrane,
one important use of which is to separate the anode and
cathode compartments of a chloralkali cell.
Fluorinated polymers containing pendant side
chains containing sulfonyl groups are now well-known,
and their use as ion exchange membranes is also known.
It is desirable to have an ion exchange membrane which
is supported, i.e., which contains a material which
imPartS physical strength to the fluorinated polymer,
so that the physical strength of ~he complete membrane
construction is greater than that of a film of the
fluorinated polymer. Heretofore,methods for supporting
such membranes have not been adequate, for if films of
desirable thickness were employed complete encapsulation
of the support material was not effected, and if complete
encapsulation of the support material were to be assured
excessively thick films of fluorinated polymer were
required. Such excessive film thickness not only increases
~he cost of the membrane, but i~ also reduces the
usefulness of the membrane for ion exchange purposes
because the increased thickness leads to higher operating
voltage and higher power consumption. If the support
material is not completely encapsulated, the membrane
will leak or will in use ultimately rupture at the
non-encapsulated points and will then leak, and thus its
3Q usefulness is impaired.
A method which has been proposed to overcome
the abo~e problems and deficiencies is that of U~S.
Patent 3,770,5~7 wherein a film o fluorinated polymer
which contains pendant side chains containing -SO2L
f~l
~ ~,5~7~
groups, where L is F or C1, is treated on one surace
with an alkali me~al hydroxide, an alkaline earth metal
hydroxide or ammonium hydroxide, to form a hydrolyzed
surface layer wherein the functional groups are in the
-(SO3)jM form, where M is alkali metal, alkaline eaxth
metal or ammonium, and ~ is ~he valence of M, followed
by contacting the -SO2L surface of the film with a
support m~terial, and applying a differential pressure
to the contacted support material and the film, the
pressure on the opposite surface of the support material
from that which is contacting the fluorinated polymer
being at least 5 inche~ (127 mm) of mercury less than
the pressure on the surface of the fluorinated polymer
film opposite to that contacting the support material,
for a sufficient period of time to cause ~he support
material which is in contact with said film to become
completely encapsulated within the film of fluQrinated
polymer while heating the film and support material at
a temperature of from 240-320C. The resulting laminate
is then subjected to a second hydrolysis treatment with
alkali me~al hydroxide, alkaline earth me~al hydroxide
or ammonium hydroxide after which it is ready for use
for ion exchange purposes. This method has the
disadvantage of adding an additional processing step in
the formation of the supported structure, and many
additional hours o processing time are required to
effect the surface hydrolysis step in the hydroxide
treating bath used. Additionally this method cannot be
used for luorina~ed~~olymers whlch cont~in carboxylic
functional groups because the hydrolysis step would
lead to carboxylic acid groups or salts thereof, which
easily decarboxylate at the temperatures ~mployed in
forming the supported construction.
It is a principal ob~ect of the inv ntion to
provide novel web supported membranes of exceptional
uniformity. In the novel web reinforced membranes the
sulfonyl and carboxyl groups can be either in melt
, . . . . . .. .. ... . .. .... . . .. . .. .. . . . . . .. .. . . . . .. ..
6~6~8
fabricable form, or, after hydrolysis or other suitable
chemical reaction, can be in ion exchange form.
It is another objec~ of ~his invention to
pro~ide a process for forming a supported structure o~
S fluorinated polymers which contain pendant side chains
containing either sulfonyl groups or carboxyl groups or
both, which method leads to a completely encapsulated
s~pported structure, and which eliminates the necessity
for a surface hydrolysis step.
It is a further object to provide apparatus
adapted for carrying out the process of the invention
specified immediately above.
Other objects will be apparent from the
continuing description.
SUMMARY O~ THE INVENTION
According to the present invention~ there is
provided a reinforced membrane which consists essentially
of at least two layers of melt fabricable fluorinated
polymer which contains side chains containing sulfonyl
~ and/or carhoxyl groups in melt fabricable form/ and a
woven reinforcing fabric comprising warp and fill strands,
there being at l-east one layer of a said fluorinated poly-
mer on each side of said re.inforcing fabric, the warp and
fill strands of said reinforcing fabric defining windows
be~.Jeen saîd strands, each la~er of fluorinated polymer
in at least 70% of the area in each of at least 90%
of said windows being of uniform thickness within plus
or minus 10%.
There is also provided according to the inven-
tion reinforced membranes in ion exchange ~OLm madeby hydrolyzing or otherwise chemically modifying such
melt fabricable membranes.
There is additionally provided according tQ
the invention a process for continuously forming a
reinforced membrane comprising
(1) continuously bringing at least two films of
~ 1~S~7~
, . ,
melt-fabricable fluorinated polymer which contain side
chains containing sulfonyl and/or carboxyl unctional
groups in melt fabricable form and a web of reinforcing
material into face-to-face contact such that proximate
surfaces of two of said films contact opposite planar
surfaces of said web, and moving the resulting combination
of said films and said web vertically, unsupported
except at two opposite edges thereof,
(2) remo~ing air from between said films at the two
opposite edge portions thsreof,
(3) applying heat to the two outermost opposite planar
film surfaces, first in the center portions thereof and
progressi~ely moving toward and including the edge
portions thereof, and
(4) cooling the resulting reinforced membrane.
There is further provided according to the
invention appaxatus fox making a reinorced membrane,
comprlslng,
(1) a frame, and mounted on said frame,
(2~ means for guiding at least two con~inuous webs of
film and a continuous web of reinforcing material into
face-to~face contact such that proximate surfaces of two
of said webs of film contact opposite sides of sai~
web of .reinforcing material,
(3) two sets of flexible endless belts which cooperate
to engage opposite sides of the resulting assembly of
said webs at the edge portions thereof and to transport
said assembly, each set consisting o~ two belts, one
belt of each set having a series of perforations along
its entire length, each set of belts extending beyond
an edge of said assembly, and guide means for said
belts,
t4) vacuum means including two vacuum ma~ifolds, one
manifold adjacent each said perforated belt, for removing
air from between said films of said assembly at the edge
portions thereof through said perforations,
(5~ two banks of heaters, one bank adjacent each exposed
film surface, each bank consisting of a plurality of
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.~
heaters disposed for heating first the center portion
of said assembly and ~hen progressively toward and
including the edges thereof as said assembly is transported
therebetween, to fuse said assembly into a reinforced
membrane,
(6) means for guiding said assembly between said banks
of heaters,
(7) a wind-up for collecting said reinforced membrane, and
(8) means for driving ~aid wind-up.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure l depicts schematically a side view o~
the apparatus of the invention.
Figure 2 depicts schematically a front view of a
portion of the apparatus of the invention.
Figure 3 is a pictorial view of a detail at
one edge portion of tll~ apparatus of the invention.
Figure 4 is a photograph, at a magnification
of 60, of a cross-section of a membrane of the inve~tion,
cut in a direction parallel to the machine direction of
the lamination process.
Figure 5 is a photograph, at a magnification of
60, of a cross-section of the same membrane as in Figure
4, but cut in a direction perpendicular to the machine
direction of the lamination process.
DETAILED DESCRIPTION OF THE INVENTION
Referring first to Figure 1, it should be
understood that the various elements o~ the apparatus
of the invention are joined either directly or indirectly
to a frame 1 by means of various supports, of which
30 supports 2 and 3 are typical, the remaining supports not
being shown for simplicity.
Melt fabricable films ll and 12 of fluorinated
polymer containing sulfonyl and/or carboxyl groups, to
be described more fully below, and a web of reinforcing
35 material 13, also to be described more fully below, are
unwound from supply rolls 14, 15 and 16, respectively,
in the direction of the arrows show~. Films ll and 12
S S7 ~
and web 13 are brouyht together over guide roll 17, and
further guided through the apparatus around guide rolls
18 and 19.
Flexible belts 20 and 21 cooperate to contact
opposite sides of one edge portion of the assembly of
films 11 and 12 and web 13. Belts 20 and 21 are suitably
maae of a thin impervious material such as stainless
steel about 5 to 20 mils (0.13 to 0.5 mm) thick. Belts
20 and 21 move in the direction of the arrows shown.
Belt 20 is guided in a path around rolls 18
and 22. Roll 2~ is mounted so as to be movable
vertically by means of air-ac~ua~ed cylinders, no~ shown.
I~ this way roll 22 presses against belt 20 to create a
positive tension which prevents the belt from slipping
on the rolls it contacts.
Belt 20 is restrained from wandering laterally
along the indicated rolls by use of two guide blocks 23
and 24 within which it passes just beore it contacts
rolls 18 and 22, respectively. Each guide block is
fabrica~ed from two members (not sepaxately shown) held
together by screws. The first member is in the shape
of a rectangular solid having machined in one face a
shallow depression, about 0.2~ mm (la mils) deep for a
belt 0.2 mm (8 mils) thick, and ahout 1/16 inch (about
1.5 mm) wider than the width of belt 20~ and
the second member in the form of a rectangular ~olid is
secured by screws to the first member over the machined
depression to form a slot through which belt 20 passes.
The second member of the guide block is placed in positio~
only after endless belt 20 has been positioned in the
machined depression. Guide blocks 23 and 24 are suitably
fabricated from aromatic polyimide resin filled with
graphite as is disclosed in U.5. Patent 3,179,631.
Belt 20 contains a series of perforations along
its entire length, not shown in Figure 1, but which will
b more fully explained below.
Belt 21 is guided in a path around rolls 17,
18, 19, 25, 26 and 27. Belt 21 is restrained from
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wandering laterally along those rolls by use of flanges
between which bel~ 21 runs on rolls 26 and 27.
The shaft o~ roll 26 i5 mounted with a screw
adjustment for mo~ing roll 26 toward and away from belt
S 21 to permit increasing or decreasing the tension on belt
21. In this way the tension on belt 21 can be adjusted
so that it will not slip.
A second set of belts, not shown in Figure l
but identical to belts 20 and 21, similarly grips the
second edge portion of the assembly of films 11 and 12
and web 13O
Roll 28 is a resilient rubber roll which is
urged by air actuated cylinders toward roll 18 to press
belts 20 and 21, films ll and 12, and web 13 into
intimate contact and against roll 18.
A vacuum manifold 2~, whose operation will be
more fully explained below, is positioned adjacent
perforated belt 20. Pipe 30 serves to join vacuum
manifold 29 to a vacuum source not shown. A second
vacuum manifold, not shown in Figure 1 but identical to
vacuum manifold 29, is positioned adjacent to the second
perforated belt referred to above but al50 not shown
in Figure 1.
A seal.ng shoe 35 to be described in detail
~5 below presses against belt 21 and urges belts ~0 and 21
ilms 11 and 12 and web 13 toward vacuum maniold 29.
A similar sealing shoe is used in cooperation with the
second set of belts not shown in this view.
Two banks of heaters (not shown in Figure 1)
contained within housin~s 31 and 32 are positioned on
opposite sides of the assembly of films ll and 12 and
web 13. The heaters serve ~o soften films ll and 12
sufficiently to permit the assembly of ~ilms 11 and 12
and web 13 to be fused into a membrane. The membrane
33 thus foxmed is collected on wind-up 34O
Wind-up 34 And rolls 17 and 18 are driven.
They provide the driving force for moving the membrane
.. . .. . . .. . .. ..
~65~7~
and assembly of film5 11 and 12 and web 13 through th~
apparatu6. The remaining rolls in the apparatus all can
be idler rolls.
Rolls 17 and 18 are suitahly co~ered with a
textured surface such as a fine emery cloth. This pro~
vides a high enough coefficient of friction of the roll
against films 11 and 12 to prevent the films and also
belts 20 and 21 from slipping against these driven rolls.
certain elements in Figure 1 are drawn as not in
contact with one another for clarity in showing them,
whereas it should be understood that they are in contact
during operation. Thus, in ~igure 1, vacuum manifold ~s
shown as not in contact with belt 20, the latter is
shown as not in contact with the assembly of webs 11, 12
and 13, the latter is shown as not in contact with belt
21, and the latter is shown as not in contact with seal-
ing shoe 35, whereas during operation these pairs of
elements are in fact in contact.
In Figure 2, a partial front view of the
apparatus, are seen rolls 18, 19 and 22, with belt 20
shown passing over rolls 18 and 22 and being restrained
from lateral movement by guide block 23. A second simi~
lar belt 42, not seen in Figure 1, passes over rolls 18
and 41, and is also seen in this view. Belt 42 also i5
restrained from lateral movement by a guide block 42.
The second guide block ~4 for belt 20, and a similar sec-
ond guide block for belt 42 are not shown in this view.
Roll 41 is mounted to be movable vertically in
the same manner as is roll 22. Both rolls 22 and 41 are
made of resilient rubber.
Belt 20 has a series of perforations 44 along
the ~ntire length thereof, only ssme of which are shown
in Figure 2. Similarly, belt 42 has a series of perfora
tions 45 along the entire length thereof, only some o
which are shown in Figure 2. Housing 31 contains a ba~k
of heating elemsnts 46~ which typically may be radiant
or infrared heating elements. Housing 32, not shown in
.9
~ ~5~7~
Figure 2, contains a similar bank o~ heating elements.
In the apparatus and process here depicted, the
assembly of films and reinforcing material to be
fabricated into a membrane is transported upwardly from
roll 18 and around roll 19. Heater elements 46 are
arrayedin a chevron-shaped array for the purpose o~
first heating the center portion of the assembly and then
progressively laterally in ko~h d~ctions to and including
the edge portions of the assembly~ and it is ~or this
reason that the center of the chevron-shaped array points
downward. In this manner, entrapment of air bubbles
between the films as they are laminated is less likely
to oocur.
In the pictorial view of Figure 3 is ound a
view of belts 20 and 21 and an edge of films 11 and 12
and reinforcing material 13, with each element in turn
broken away so as to reveal the relationship of these
elements to one another. As seen in Figure 3, an edge
of each of films 11 and 12 and of reinforcing material 13
extends between belts 20 and 21. Belts 20 and 21 are
suitably of the same width, typically 5-15 centimeters
(2-6 inches) and are positioned to be in register with
one another. As indicated above, belt 20 has a series
of perforations 44 along the entire length thereof.
The combination of belts 20 and 21 and
assembly of films 11 and 12 and reinforcing material 13
moves upwardly, with belt 20 moving slidably against and
in contact with vacuum manifold 29.
Vacuum manifold 29 comprises a body 51 and a
face plate 52. Body 51 is fabricatad to have a wide deep
recess along most of its length, except for the extreme
end portions thereof which are not recessed, the recess
becoming interior chamber S3 of the manifold, and is
suitably made of a metal such as aluminum. Face plate
52 is fabricated to have a 510t 54 along most of its
length, except for the extreme end portions thereof
which are not slotted, the slot communicating with
1.0
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chamber 53, and is suitably made o~ a graphite-filled
phenolic resin so that bel~ 20 will easily slide against
it even when drawn against it by vacuum and pressed
against it by sealing shoe 35. The body 51 and face
plate 52 are held together by screws 55, and sealed
together with a silicone rubber cement. Interior
chamber 53 is connected to vacuum means, as was
explained in relation to Figure 1 above. Belt 20 and
vacuum manifold 29 are so positioned that perforations
44 and slot 54 are in register with one another.
Typically, perforations 44 are about 6 mm in diameter
a~d slot 54 is about 3 mm wide. Sealing shoe 35 is
urged against belt 21 by a series of spri~.g-loaded
brackets, of which bracket 56 is typical. Bracket 56
is secured to the body 51 of vacuum manifold 29 by a
screw 57. Bracket 56 is linked to, but spaced apart
from, sealing shoe 35 by a bolt 58 and nuts not shown.
A spring 59 surrounding the shaft of bolt 58 urges seal-
ing shoe 35 against belt 21.
In operation, when a vacuum is drawn in
vacuum chamber 53, air is drawn through slot 54. This
in turn draws belt 20 into contact with face plate 52 of
vacuum manifold 29. As belt 20 moves upward, it moves
in sliding contact with face plate 52. In turn, all of
films 11 and 12, reinforcing material 13, and belt 21
are drawn into contact with one anvther and with ~elt
20. The outermost portions 60 and 61 of belts 20 and 21,
respectively, orm a temporary seal against one another.
Similarly, film 11 forms a temporary seal against the
inner portion 62 of belt 20, and film 12 forms a tempo-
rary seal against the inner portion 63 of belt 21.
R~sidual air trapped between ilms 11 and 12 is then
drawn from between them, between the strands of reinforc-
ing material 13, and through perforations 44 and slot 54
into vacuum manifold 29. S~aling shoe 35 presses against
the edge portions o~ belt 21 and thus aids in establishing
and maintaining the temporary vacuum seals.
11
~l 1 6S G7 ~
12
In this way films ll and 12 are brought into intimate
contact with reinforcing material 13, and are sealed
into intimate contact with it as the assembly of films
and reinforcing material passes between the hea~ers.
Films 11 and 12 are suitably of the same width
and are pa3sed ~hrough the apparatus in register with
on~ another. However, film 12 may be wider than film ll
without impairing the operation of the apparatus and
removal of the entrapped air from between the films.
The web supported membranes of the invention
are characterized by having exceptional unifo~mity.
Woven reinforcing fabrics comprise warp and ill strands
which meet at croscover points termed junctions, and
which define openings between the strands termed
windows. In the membxanes of the invention each layer
of fluorinated polymer in at least 70~, pre~erably 75%,
of the area in each of a~ least 90~, preferably 95~,of
~hewindows is of uniform thickness within plus or minus
10%, preferably plus or minus 5~. Addi~ionally, i~ is
preferred that the ~otal thickness o fluorinated pol~mer
which covers both sides of the strands is at least 80%,
preferably 85%, of the a~era~e total thickness of the
polymer in the portion of the windows which is uniform
within plus or minus 10%.
Figures 4 and 5 are photographs at 60X magni-
fication of cross-sections of a me~rane of the invention
cut in directions parallel and perpendicular, respec-
- - tively, to the machine directions of the lamination
process. The membrane was made by laminating a film
0.051 mm (2 mils3 thick of a copolymer of
perfluoro(3,6-dioxa-4-methyl-7-oc~sulfonyl fluoride) and tetra-
fluoroethylene having an equivalent ~eisht of llO0 bo each side o a
fabric of fluorocarbon polymer filaments (0.127 mm, or 5
mil, diameter) in a Leno weave having 68% open area. This
membrane is similar to that firs~ prepared in Example 1
below~ before the ethylene diamine treatment of that
example.
12
1 1 6 ~
The membranes of the invention are prepared
from componen~ polymer films which have a ~hick~ess
ranging from as low as 0.013 mm (0.5 mil) up to several
mils. As t~e membrane will generally be prepared from
two or three such polymer films, the thickn~ss of
polymer in ~he resulting membrane will generally lie in
the range of about 0.025 to 0.:25 mm (1 to 10 mils).
Membranes can be made using either the same or
different thickness of polymer on each side o~ the
reinforcing material. In some cases the polymer on one
side of the reinforced material will be made up o layers
of two different polymer films, which can be blocked
together before the lami~ation process is carried out.
During lamination the bank of heaters on one side of the
assemb~y of webs to be laminated can be heated to a
higher or lower temperature than the bank of heaters on
the opposite side, or both banks of heaters can be
heated to the same temperature.
When the same thic~ness of the same or similar
polymer films are used on each side of the reinforcin~
material and the heaters axe operated at the same
temperature, the polymer films are drawn substantially
equally into the window areas of the reinforcing material
during fabrication, and the two opposite sur~aces of
the resulting membrane are therefore similar~y contoured.
When the heaters are operated at different temperatures,
the film on the side heated to the lower temperature is
less easily drawn into the window areas, so ~h~
contour o~ the curface of the resulting membrane on that
side will be smoother or flatter than the contour on the
opposite side which was ~eated to the higher temperatureO
When different thicknesses of pol~mer film are
used on opposite sides of the reinforcing material, and
the heaters are operated at the same temperature, the
sidP having the greater thickness of polymer will be
less easily drawn into the window areas cf the
reinforcing material, and the surface of that sid~ will
have a smoother or flatter contour than the con~our of
1~
~ ~65678
14
the opposite side having a thinner layer of pol~mer~
When di~ferent thicknesses of polymer are used on the
two opposing sides of the reinforcing material and it
is desired to have ~ membrane having approximately the
same surace contour on each side, the bank of heaters
on the side having the greater thickness of polymer can
be heated to a somewhat higher tempexature so as to
permit the polymer on both sides of the reinforcing
material to be equally drawn into the window areas.
Among the preferred membrane constructions are
those having polymer with sulfonic functional groups
on both sides of the reinforcing material~ those having
polymer with carboxylic functional groups on both sides
of the reinforcing material, those having polymer with
sulfonic functional groups on one side of the reinforcing
material and carboxylic functional groups on the other
side of the reinforcing material, and those having
polymer with sulfonic functional groups on one side of
the reinforcing material and a layer of polymer with
sulfonic functional groups and also a layer of polymer
with carboxylic functional:sroUPs on the other side
of the reinforcing material such that the polymer with
carboxylic functional groups constitutes the exposed
surface layer.
A problem which is sometimes encountered with
a chloralkali cell which employs a membrane to separake
the anode and cathode compartments i~ gas blinding on
the cathode side of the membrane. One of the advantages
of the present invention is its ability to make membranes
having a smoother or flatter surface on one side of the
membrane as comp~red to the other side. A membran~
prepared to have one relatively smooth or flat side can
be positioned in a chloralkali cell such that the smoother
side faces toward the cathode so as to alleviate the
problem of entrapment of gas bubbles in recesses on the
membrane surface facing the cathode. M~mbranes fabricated
to have two different polymers on the two di~ferent
14
~ 16567~
surfaces, for example polymer having sulfonic acid or
salt functional groups on one sur~ace and polymer having
sulfonamide functional groups or carboxylic functional
groups on the other surface are generally positioned in
a chloralkali. cell with the latter surface facing
toward the cathode, inasmuch as that pol~mer composition
is more e~fective in suppressing back-migration of
hydroxyl ion through the membrane. In such membranes
it is ~hexeforepreferred that the membrane surface
having carboxylic or sulfonamide functional groups
have a flatter contour than the other surface.
The melt-abricable polymer having sulfonyl
~unctional groups is typically a polymer ha~ing a
fluorinated hydrocarbon backbone chain to which are
attached the functional groups or pendant side chains
which in turn carry the functional groups. The pendant
side chains can contain, for example, -CF-CF2-S02F
Rf
groups wherein Rf is F, Cl, or a Cl to C10 perfluoroalkyl
radical. Ordinarily, the functional group in ~he side
chains of the polymer will be present in terminal
-O-CF-CF2SO2F groups.
Rf
Examples of fluorinated polymers of this kind axe
disclosed in U~S.P. 3,28~,875, U.S.P. 3,560,S~8 and
U.S.P. 3,718,627. More specifically, the pol~ners can
be prepared from monomers which are fluorinated or
fluorine substituted vinyl compounds. The polymers are
made from at least two monomers, with at least one o~
the monomers coming from each o~ th~ two groups
described below.
The first group is fluorinated vinyl compounds
such as vinyl fluoride, hexafluoropropylene, ~inylidene
fluoride, trifluoroethylene,chIorotriflu~roethylene, -
per1uoro(alkyl vinyl ether), tetra1uoroethylene andmixtures thereof. In the case of copolymers which will
be used in electrolysis of brine, the precursor vinyl
monomer desirably will ~ot contain hydrogen.
1~
~567~
1.6
The second group is the sul~onyl-containing
monomers containing the precursor gxoup -CF-CF2-SO2F,
wherein R~ is as defined aboveO Additional examples
can be represented by the general formula
CF2=CF-Tk-CF2SO2F wherein T is a bifunctional fluorinated
radical comprising 1 to ~ carbon atoms, and k is 0 or 1.
Substituent atoms in T include fluorine, chlorine, or
hydrogen, although generally hydrogen will be excluded
in use of the copolymer for ion exchange in a chlor-
alkali cell. The most preferred polymers are free of
both hydrogen and chlorine attached to carbon, i.
they are perfluorinated, for gxeatest stability in
harsh en~ironmentsO The T xadical of ~he formula above
can be either branched or unbranched, i.e., straight~
chain, and can ha~e one or more ether linkages. It i5
preferred that the vinyl radical in this group of
sulfonyl fluoride containing comonomers be joined to
the T group through an ether linkage, i.e., that the
comonomer be of the formula CF2=CF-O-T--CF2 SO2F.
Illustrative of such sulfonyl fluoride containing
comonomers are CF2=CFOCF2CF2SO2F,
CF2-CFOCF2 1CFOCF2CF2~;02F,
CF3
CF2=CFOCF2fFOCFz~FOCF2CF2S02F,
CF3 CF3
CF2=CFCF2CF2SO2F, and
CF2--CFocF2cFocF2cF2~;o2F
fF2
CF3.
The most preferred sulfonyl fluoride contain
ing comonomar is perfluoro(3,6 dioxa-4-methyl 7
octenesulfonyl fluoride),
16
5 67 ~
17
CF2=CFOCF2fFOCF2CF2SO~F.
c~3
The sulfonyl-containing monomers are disclosed
5 in such references as U.S.P. 3,282,875, U~S.P~ 3,041,317,
U.S.P. 3,718,627 and U.S.P. 3,560,568~
A preferred class of such polymers is
represented by pol~mers having the repeating units
~ CX2- CX2 11~ _
~F
,~ ~
CF-Rf
CF2
. SO2F n
wherein
m is 3 to 15,
n i5 1 to 10,
p is 0, 1 or 2,
the X's taken together are four fluorines or three
fluorines and one chlorine,
Y is P or CF3, and
Rf is F, C1 or a Cl to Clo perfluoroalkyl
radical.
A most preferred copol~mer is a copolymer of
tetrafluoroethylene and perfluoro~3,6-dioxa-4-methyl-7
30 octenesulfonyl fluoride) which comprises 20 to 65
percent, preferably~ 25 to 50 percent by weight of the
latter.
When used in a film or m~mbrane to separate
the anode and cathode compartments of an electrolysis
35 cell, 5uch as a chloralkali cell, the polymer after
conversion to ionizable form ~hould have a total ion
17
~ 1~S67~
18
exchange capacity of 0.5 to i.6 meq~g (milliequival~nts/
gram), preerabl~ from 0.8 to 1.2 meq/g. Below an ion
exchange capacity of 0~5 meq/~, the electrical resis-
tivity becomes too high, and above 1.6 meq/g ~he
mechanical properties are poor because o~ excessive
swelling of the polymer. The values o~ m and n in ~he
above formula of the copolymer should be adjusted or
chosen such that the polymer has an equivalent weight
no greater than about 2000, preferably no greater than
about 1600, for use as an ion exchange barrier in an
electrolytic cell. The equivalent weight above which
the resistance of a film or membrane becomes too high
for practical use in an electrolytic cell varies
somewhat with the thickness of the film or membrane.
For thinner films and membranes, equivalent weights up
to about 2000 can be tolerated. For mos~ purposes,
however, and for films of ordinary thickness, a ~alue
no greater than about 1600 is preferred.
Such copolymers used in the p~esent invention
can be prepared by general polymerization techniques
developed for homo- and copolymerizations o~ fluorina~ed
ethylenes, particularly those employed for tetrafluoro-
ethylene which are described in the literature.
Nonaqueous techniques for preparing the copolymers
include that of U.S.P. 3,041,317, that is, by the
polymerization of a mixture of the major monomer therein,
such as tetrafluoroethylene, and a fluorinat~d ethylene
containing a sulfonyl fluoride group in the presence of
a free radical initiator, preferably a perfluorocarbon
39 peroxide or azo compound, a~ a temperature in ~he
range 0-200C. and at pressures in the range 1-200 or
more atmospheres. ~he nonaqueous polymerization mayv
if de~ired, be carried out in the presence o~ a
fluorinated sol~ent. Suitzble fluorinated solve~ts
are inert, liquid, perfluorinated hydroc~rbons, ~uch
as per~luoromethylcyclohexane, perfluorodimethyl-
cyclobutane, pexfluorooctane, perfluorobenzens and the
1~
~6~6
L9
like, and inert, liquid chlorofluorocarbons such as
1,1,2-trichloro 1,2,2-trifluoroethane, and the like.
Aqueous techniques for preparing the copolymer
include contacting the monomers with an aqueous medium
containing a free-radical initiator to obtain a slurry
of polymer particles in non-water-wet or granular form,
as disclosed in U.S. Patent 2,393,967, or contacting
the monomers with an aqueous medium containing both a
free-radical initlator and a telogenically inactive
dispersing agen~, to obtain an aqueous colloidal
dispersion of polymer particles, and coagulating the
dispersion, as disclosed, for example, in
U.S.P. 2,559,752 and U.S.P. 2,593,583.
The melt-fabricable polymer haviny carboxylic
functional groups is typically a polymer having a
fluorinated hydrocarbon backbone chain to which are
attached the functional groups or pendant side chains
which in turn carry the functional groups~ The
pendant side chains can contain, for ~xample ~ CF ~ W
~ BJ~
groups wherein ~ is ~ or CF3, t is 1 to 12, and W is
-COOR or -CN, where R is lower alkyl. Ordinarily, the
functional group in the side chains of the polymer will
be present in terminal -t CF ~ W groups. Examples
of fluorinated polymers of this kind are disclosed .in
British Patent 1,145,445 and U.S. 3,506,635. More
specifically, the polymers can be prepared from monomers
which a.re fluorinated or fluorine substituted vinyl
compounds. The pol~mers are usually made from at least
two monomers. At least one monomer is a 1uorinated
vinyl compound from the first group de~cribed herein-
above in reference to polymers containing -S02F groups.
Addi~ionally, at least one monomer is a fluorinated
monomer which contains a group which can ~e hydrolyzed
to a carboxylic acid ~roup, e.g., a carboalkoxyl or
nitrile group, in a side chain a~ se~ forth abo~e.
1~
1 ~65678
~.o
Again in this case, as in the case of ~he pol~mers
having -SO2~ groups, the monomers~ with ~he exception
of the R group in the -COOR, will preferably not
contain hydrogen, especially if the polymer will be
5 used in the electrolysis of brine, and for greatest
stability in harsh environments, most preferably will
be free of both hydrogen and chlorine, i.e., will be
per~luorinated; the R group need not be fluorinated as
it is lost duriny hydrolysis when the functional
groups are converted to ion-exchange groups.
One exemplary suitable type of carbo~yl
containing monomer is represented by the formula
CF~=CF~OCF2CF~OCF2-COOR
lS wherein
R is lower alkyl,
Y is F or CF3, and
s is 0, 1 or 2.
Those monomexs wherein s is 1 are preferred because
their preparation and isolation in good yield is more
easily accomplished than when s is 0 or 2.
The compound
CF2=CFOCF2CFOCF2cooCH3
CF3
is an especially useful monomer. Such monomer~ can be
prepared, for example, from compounds having the
formula CF2=CFtOCF2CF~OCF2CF2SO2F
wherein s and Y are as defined above, by (1) saturating
3Q the terminal vinyl group with chlorine to protect it in
subsequent steps by converting it to a CF2Cl-CFCl-
group; (2~ oxidation with nitrogen dioxide to convertthe -OCF2CF2SO2F group to an -OCF2COF group;
(3) es~eri~ication with an alcohol such as methanol to
form an -OCF2COOC~3 group; and (4) dechlorination with
zinc dust to regenerate the terminal CF2=CF group.
It is also possible to replace steps (2) and (3) o
~0
11~5~78
21
this sequence by the steps (~) reduc~ion of the
-OCF2CF2SO2F group to a sulfinic acid, -OCF2CF2SO2H, ~r
alkali metal or alkaline earth metal salt thereor ~y
treatment with a sulfite salt or hydrazine; (b) oxida-
tion of the sul~inic acid or salt thereof with oxygenor chromic acid, whereby -OCF2COOH groups or metal salts
thereof are formed; and ~c) esterification to
-OCF2COOCH3 by known methods; this se~uence is more
fully described in Canadian A~plication No. 301 530 in the
names of W. G. Grot, CO J. Molnar and P. R. Resnick,
filed 1978 April 18. Prepar~tion of copolymers
thereof is described in Canadian Appllcation No. 301 588
in the names of C. J. Molnar and P. R. Resnick, ~iled
1978 April 18.
Another exemplary suitable type of carboxyl-
containing monomer is represented by the formula
CF2=CF~OCF2CF~ OC 2-CF -
Y
wherein
V is -COOR or -CN,
R is lower alkyl,
Y is F or CF3,
~ is F or CF3, and
s is 0, 1 or 2.
The most preferred monomers are tho~e wherein V is -COOR
wherein R is lower alkyl, generally Cl to C5, because o~
ease in polymerization and conversion to ionic form.
Those monomers wherein s is 1 are also preferred because
their preparation and isolation in good yield is more
easily accom~lished tha~ when n is 0 or 2~ Preparation
of ~hose monomers wherein ~ is -COOR where ~ is lower
alkyl, and copolymers thereof, is described in
U. S. Patent 4,131,740. ~he compound.
CF2=CFOCF2CFOCF2CF2COOC~3, and
c~3
C~ 2=CFO ( CF 2CF ) 2CF 2CF2( ~00CH3,
CF3 21
~1~5~7~
whose preparation is described therein, are especially
useful monomers. Prepara~ion of monomexs wherein V
is -CN is described in U.S. Patent 3,~52,326.
Yet another suitable ~ype of carboxyl-contain-
ing monomer is that having a terminal -O(CF2)vCOOCH3
group where v is from 2 to 12, such as
CF2=CF-O(CF2)3COOCH3 and CF2=CFOCF2CP(CF3)0~F2)3COOCH3
Preparation of such monomers and copolymers thereof is
described in Japanese Patent Publications 38586/77 and
28486/77, and in British Patent 1,145,445.
Anothër.class of carboxyl-containing
polymers is represented by polymers having the repeating
units
_ - CF - CF2- ~ CX2 - CX~
O
CF2
l s
.~
COOR r
wherein
q is 3 t~ 15,
r is } to 10,
s is 0, 1 or 2,
t is 1 ~o 12,
the X's taken together are our f~uorines or three
fluorines and one chlorine,
Y is F or CF3,
~ is F or CF3, and
R is lower alkyl.
The values and preferred values of the ion
exchange capacity and equivalent w ight of the
carboxylic containing copolymer should be in t~.e same
ranges as se~ forth above for copolymers con~aining
22
1 l 6 ~ G7
23
sulfonyl groups in ionizable orm. Similarly, the
same polymerization techniques as set forth above are
also suitable.
A copolymer which contains different types of
functional groups can also be used as one of the com-
ponent films in making the membrane vf the inventio~.
For exampl~, a terpolymer prepared from a monomer
chosen from the first group descxibed above, a monomer
from the second group descxibed above, and additionally
a monomer of ~he carboxylic ~ype from the third group
described above can be prepared and used as one of the
film components in making the membrane.
It is further possible to use as one of the
component films of the membrane a film which is a
blend of two or more polymers. For example, a blend
of a polymer having sulfonyl groups in melt-fabricable
form with a polymer having carboxyl groups in melt-
fabricable form can be prepared and used as one of the
component films of ~he membrane of this invention.
It is additionally possible to use a laminar
film as one of the component films in making the
membrane. For example, a film having a layer of a
copolymer having sulfonyl groups in melt-fabricable form
and a layer of a copolymer having carboxyl groups in
melt-fabricable form, can also be used as one of the.
component films in making the me~rane of the invention.
In the process of the in~ention, temperatures
of about 240C to 320C are ordinarily required to
fuse the polymer films employed, so as to form a unitary
membrane structure with the support ma~erial, and, when
more than two films are used~ to ~ake adjacent sheets
of film fuse together; the te~perature required may be
even above or below this ranae, howev~r, and will
depend on the specific poly~er or polymers used. Actual
heater temperatures as measured by a thermocouple
in the heater i~self will be higher than the indicated
film temperature, due to heat losses;
heater temperatures will vary with the
~ ~5~
24
type of heater, its placement, etc~, and will generally
~all in the xange of 350 ~o 500C. In the apparatus
described herein, heater temperatures of 400 to 475C
have been found suitable for making many membranes.
The choic20f a suitable temperature in any specific
case will be clear, inasmuch as too low a temperature
will fail to effec~ an adequate degree of adherence o
the films to the reinforcement member and to each othex,
and too high a temperature will cause gas bubbles to
~orm between or within ~he polymer films in ~he window
areas and will cause the films to sag and form non-
uniform layers.
The reinforcement abric for encapsulation
within the membrane is suitably a woven or nonwoven
fabric. Woven fabrics include those of ordinary weave,
and warp knit fabrics. A woven fabric is preferred for
a membrane to be used in an electrolysis cell. Fabrics
prepared from either monofilament or from multistranded
yarns can be used. The fabric should be able to
withstand a temperature from about 240~C to about 320C.,
since these temperatures are employed in the laminating
steps. With this proviso, the individual reinforcing
fibers can be made from conventional materials, since
their main purpose is to strengthen the membrane. Due
to chemical inertness, reinforcement materials made
from perfluorinated polymers have been found to be
preferred. The polymers include those made from
tetrafluoroethylene and copolymers of tetrafluoroethylene
with hexafluoropropylene and per~luoro(alkyl ~inyl ethers)
with alkyl being 1 to 10 carbon atoms such as perfluoro
(propyl vinyl ether). An example of a most preferred
reinforcement material is polytetrafluoroethylene.
Supporting fibers made from chlorotrifluoroethylene
p~lymers are also useful. Other suitable reinforcin~
materials include quartz and glass. Such reinforcemenk
materials and their use to strengthen polymers in a
mexbrane are well known in the prior art.
24
1 ~5~7~
~ ther reinforcin~ members in sheet-like ~orm
can also be used in the process of the invention. 'rhese
in~lude various metals and alloys such as stainless
steel and titanium in ~he form of screen or expande~
mesh, sheets of perhalogenated polymers such as poly-
tetrafluoroethylene in the form of expanded mesh, fabric
of graphite fibers, netting of various polymers such as
polypropylene or oriented polyethylene, and fiberglass.
Such sheet-like member can be large or s~all in it~
dimensions, and following preparation of ~he article
having two sheets bf a 1uorinated polyme~ said polymer
having sulfonyl groups in melt~a~ricable form, adhered to
opposite sides of such reinforcing member, it can be in
flat form or cut and/or shaped into other desirable
forms such as small cylinders or saddles, or merely
rolled into spiral form for insertion into a reactor
such as a tube or column. Especially when shaping into
such forms is desirable, support members having some
.. . . . . . ........................ .. . _ . .. .
degree of stiffness are desirable. A~ter hydrolysis o~
2~ t~e sulfonyl groups to sulLonate groups with a base
and subsequent acidification to form sulfonic acid groups,
articles of this kind are useful as a catalyst for
catalyzing any chemical reaction catalyzed by hydrogen
ion or a strong acid, e.g., alkylation of aromatic
compounds such as the reaction of benzene a~d ethylene
at 160C to form ethylbenzene. Said hydrolysis with a
base and acidification to form sulfonic acid groups
can be carried out either he~ore or after said cutting,
shaping into desirable forms, or rolling into spiral
form. For preparation of such axticles with the
process and apparatus disclosed herein, the reinforcing
member can be of any configuration so long as air can
be remo~ed from between the two films and from within
the reinforcing member through the edge-conveyor belts~
Any reinforcing member having raised portions on its
surface, on either a macroscopic of microscopic scale,
is suitable. For example, such members can be porous,
5 ~ 7 ~
26
~r have an open-cell ~tructure. Sheets which are nonpoxous Ln the
thickness dixection, but which have sur~ace roughne.~s in a random
or repe~ting pattern such as projections or fuxraws, 50 long
as the air can be rem~ed from between the two ~ilms, can also
be used as the reinforcement. The fluorinated polymer having
sulfonyl gYoups used in articles used as a catalyst is preferably
a-perluorinated polymer. Catalysts made by the process disclosed
herein make highly efficient use of the polymer by ~ e of the
polymer being l~ryely in the ~orm of a uniform thin layer.
For use in ion exchange applications and in
cells, for example a chloralkali cell for electrol~sis
of brine, the membrane should have all of the ~unctional
groups converted to ioni2able functional groups.
Ordinarily and preferably these will be sulfonic acid
and carboxylic acid groups, or alkali metal salts
thereof. Such conversion i5 ordinarily and conveniently
accomplished by hydrolysis with acid or base, such
that the various functional groups dascribed abo~e in
relation to the melt-fabricable polymers are converted
respectively to the free acids or the alkali metal
salts thereo. Such hydrolysis can be carried out with
an aqueous solution of a mineral acid or an alkali
metal hydroxide. Base hydroly~is is preferred as it
is faster and more complete. Use of hot solutions,
such as near the boiling point of the solution, i5
preferred for rapid hydrolysis. The time required for
hydrolysis increases with the thickness of the ~truc-
ture. It is also of advantage to include a water~
miscible organic compound such as dimethylsulfoxide in
the hy~rolysis bath.
Before carrying out the hydrolysis described
in the previous paragraph, it is also possible to
chemically modi~y one surface of the membrane by means
other than hydrolysis. This can be especially desirable
in the case of a memhrane all of whose component films
are prepared from polymers which contain sulfonyl
functional groups and which is intended to be used in
a chloralkali cell. In such a case, it is possible to
26
~ 1~5~
27
treat one surface of the mer.~brane whose functional
groups are still in sul~onyl fluoride or sulfonyl
chloride form with a mono- or ~olyfunc~ional amine,
such as butylamine or ethylenediamine. Such techniques
5 are described in, for example, U~S. Patents 4,085,071
and 3,969,285. Following amine treatment the membrane
is then subjected to a hydrolysis treatment such as
that described in the paragraph immediately above.
The various copolymers used in the blends
described herein should be of high enough molecular
weight to produce tough films in both the melt-fabricable
precursor form and in the hydroly~ed ion-exchange form.
To further illustrat the innovative aspects
of the present invention, the ~ollowing examples are
provided.
EXP~IPLE 1
.. . . . ..
A membrane of symmetrical cross-sec~ion was
prepared on apparatus as described hereinabove
as follows.
A fabric woven from perfluorocarbon pol~mer
monofilaments was encapsulated between a pair of similar
films of fluorinated polymer containing sulfonyl groups.`
The films were each of a copolymer of perfluoro(3,6-dioxa~
4-methyl-7-octenesulfonyl fluoride) and tetrafluoroethylene
having an equi~alent weight of 1150 and of an equal
thickness of 2 mils (51 micrometers). The fabric was
woven from per1uorocarbon polymer monofilament of ~00
denier ~.005 inches diameter, or 0.127 mm) having
a ~hread count of 34-38 per inch (13-15 per cm) in the
warp dixection and 17-18 per inch t6 7 per cm~ in the
fill or weft direction.
During lamination the films and fabric fo~ming
the web were passed between chevron-shaped heater plates,
each of 6 inch (0.15 meter) effective heated length
maintained at 4~0QC (heater temperature measured by
thermocouple) at a rate of 12 inches/minute (5.08 X 10-3
meters/sec.). The amount of vacuum applied at the fabric
27
1 165B7~
28
edges through the perfoxated edge-conveyor belt was 26.5
i~ches of mercury below atmosphPric pressure, or
11.5 x 103 Pa absolute pressure.
This laminate was then subjected to a post-
treatment with a solution of ethylene diamine on oneface only so as to form a catholyte barrier layer to
enhance its efficiency when used as an ion-exchange
membrane in a chlor-alkali cell. The treating solution
contained 20 ml of ethylene diamine in 80 ml of dimethyl-
sulfoxide which had previously been dried over a molecu-
lar sieve of 4 A (Angstrom) size. Th~ membra~e was
treated for 90 minutes at room kemperature in this
solution. ~he depth of ~reatment penetratio~ was 0.3
mils (~.5 microns) as measured by staining a cross~
section of the membrane with Merpacyl*orange R dye which
showed up the modified sur~ace layer.
After water-washing and hydrolysis, the
membrane was tested in a chlor-alkali cell for 54 days
of con~inuous operation. The a~erage voltage observed
was 3.85 volts at an average current efficiency of 90~,
equivalent to a power consumption of 2857 KW-hr/metric
ton of NaOH when producing NaOH of ~9~ concentration at
a current density of 31 amps/decimeter2(2 ASI). Other
test conditions were as follows: ~he inlet brine
(less than 0.1 ppm calcium) was saturated and the rate
was adjusted to yield an exit brine concentration of
240 gms/liter. Anolyte temperature was 80C.
Example 2
The same apparatus and reinforcement fabric
were used as in Example 1. To one side of the fabric
was applied a 51-micrometer t2-mil) film o a copolymer
of perfluoro~3,6-dioxa-4-methyl-7-octenesulfonyl
fluoride~ and tetrafluoroethylene having an equivalent
weight of 1100. To the other side of the fa~ric was
35 applied a pair of pre-blocked films as follows: one
film was a 51-micrometer film as just described and the
other film was a ~5-micrometer (l-mil) film of a melt
*denotes trade mark 28
7 8
2~
extruded blend of 75% by w~. of a copolymer of methyl
perfluoro(4,7-dioxa-5-methyl-8-nonenoate) and tetra-
fluoroethylene having an equivalen~ wei~ht o~ 1050 and
25% by wt. of a copolymer of perfluoro(3,6-dioxa-4-msthyl-
5 7-octenesul~onyl fluoride) and tetrafluoroethylene having
an equivalent weight of 1100; the films were pre-blocked
by passing them simultaneously between a pair of nip-rolls
to press them together~ each film being separately trained
around the periphery of its respectivé nip-roll so that
the films did not touch until the nip was reached, so as
to achieve a rolling wedge effect which precludes
entrainment of air between the films, because any
entrained air would lead to formation of bubbled, deformed
areas during formation of the membrane as a result of
expansion o~ the air during heating; the resulting
blocked "bi-film" was used in ~ormation of the membrane
with the sulfon~l ~luoride film placed against the
reinforcing fabric. -During lamination, the che~ron-
shaped heaters at the side having the 76-micrometer
"bi-film" were maintained at 440C, and on the other
side at 420C (both heater temperatures measured by
thermocouple), the line speed was 5.1 mm/sec, and the
vacuum at the edge conveyors was 27.5 inches of mercury
below atmospheric pressure t8.2 KPa absolute pressure).
The re5ultant laminate was hydrolyzed in a caustic
solution and then tested in a chloralkali cell. After
15 days of continuous operation, the voltage was 3.68
volts, and the current efficiency 98.7~, while prodlcing
30-32~ NaOH at 31 amps/decimeter2 at 80C, with an ~aCl
exit brine concentration of 230-235 gm/liter and an
ano~y*e pH o 4.2.
~ .
A membrane was prepared by laminating a 0.051-
mm (2-mil~ film of a copolymer of methyl perfluoro(4/7-
dioxa-5-methyl-8-nonenoate) and tetra1uoroethylene
having an equivalent weight of 1050 to each side of the
same reinforcement fabric as described in Example 1.
29
~ lS~
Lamination was carried out in the same apparatus at a
line speed of 5.1 mm/sec with the heaters in each bank
at 400C, and at a vacuum at the edge conveyors of 24
inches oE mercury below atmospheric pressure (20 X 103
Pa absolute pressure). After hydrolysis of the resulting
membrane to the carboxylate potassium salt form, it was
tested in a chloralkali cell under the s~andard operating
conditions as detailed in Example 2, and a voltage of
4.06 volts was observed at 98.3~ curxent efficiency
.
after 26 days of continuous operation.
Example 4
A membrane was prepared by laminating a 0.025-
mm ~l-mil) film a melt-extruded hlend of 75% by wt. of
a copolymer of methyl perfluoro(4,7-dioxa-5 methvl-8-
nonenoate3 and tetrafluoroethylene having an equivalentweight of 1050 and 25% by wt. of a copolymer of
perfluoro(3,6~dioxa-4-~ethyl-7-octenesulfonyl fluoride)
and tetrafluoroethylene having an equivalent weight of
1100 to each side of the same rein~orcement fabric as
described in Example 1. Lamination was carried out in
the same apparatus at a line speed of 5.1 mm/sec with
the heaters in each bank at 420~C, and at a vacuum at
the edge conveyors of 27 inches of mercury below
atmospheric pressure (9.9 x 103 Pa absolute pressure).
After hydrolysis, this membrane was tested in a chlor-
alkali cell under the standard conditions of Example 2,
and a voltage of 3.66 volts at 94.1% current efficiency
was observed after 14 days of continuous operation.
Example 5
In the apparatus of Example 1, two 0.051-mm
(2 mil) films of a copolymer of perfluoro(3,6-dioxa-4-
methyl-7-octenesulfonyl fluoride) and t~trafluoroethy~
lene having an equivalent weight of 1100 were brought
into contact with a non-woven uncalendered expanded
sheet of titanium metal (titanium sheet having a thick-
ness of 2.8 mils, or 0.071 mm~ expanded to have openings
9.8 mils, or 2.48 mm, by 4.9 mils~ or 1.245 mm), one
3~
11~5~7~
31
film on each side thereof. The chevron heatex~ w~re
set at 475C~, and a line speed of 24 inches per minute
(10.16 X 10-3 m/sec.~ and v~cuum at the edge conveyors
of 24 inches of mercury below atmospheric pressure
(20 x 103 Pa absolute pressure) were used. The
expanded metal ~eb provides a relAtively sti~f support
member for the films, and follo~ing hyarolysis of the
sulfonyl fluoride groups to sulfonate groups with a
caustic solution and subsequent acidification to form
sulfonic acid groups, the article so prepared, or after
subsequent cutting and/or shpaing, is useful as a
catalyst or various chemical reactions.
INDUSTRIAL APPLICABILITY
With the process and appaxatus described, ion
exchange membranes having general utility for ion
exchange purposes are prepared. Such includes selection
permeation or absorption of cations, and reverse osmosis.
A specific use for the membranes is in a chlor-
alkali cell such as disclosed in German patent application
2~ 2,251,660 published April 26, 1973, and Netherlands
patent application 72.17598 published June 29, 1973.
In a manner similar to ~hat disclosed therein, a
conventional chloralkali cell is employed wi~h the
distinction of using the novel membrane described herein
to separate the anode and ca~hode por~ions of the cellO
The web supported membrane of the present
invention possesses numerous technical advantages over
previously known membranes. This membrane possesses
exeptional uniformity. The warp and fill strands o the
support fabric are well covered on both sides of the
membrane by polymer. Prior art membranes made with thln
layers of fluorinated polymer invariably had either bare
junctions or junctions covered by only a thin polymPr
layer, and were thus vulnerable to abrasion and exposure
of the junctions of the strands; this invariably led to
rupture of the membrane and a short useful life. In
the present membrane, the strands and the junctions are
3~
S 6 7 ~
32
well covered by polymer on both .sides and thus have
greater resistance to abrasion and a longer useful life,
Furthermore, the greater uniformity of polymer filling
the window areas of the fabric, and the consequent
substantial elimination of window areas having only ~
thin layer of polymer therein, results in the elimina~ion
of.nonuniform current ~radientswhich lead to more
rapid deposition of calcium impurities in the thin
areas, which in turn leads to rupture of the thin areas
and short membrane life. Additionally, the greater
uniformity of the surface contours of the membrane of
this invention and the elimination of deep recesses in
the window areas substantially reduces the tendency for
gas blinding of membrane dur.ing use in a chloralkali
cell. Accordingly, the total thickness of the polymeric
material can be substantially reduced over prior art
membranes, with consequent improvement in efficiency
and reduction of ~ol~age when employed in electrolytic
processes such as the chloralkali process. Additionally,
~0 the membranes of the invention perform well during
chloralkali electrolysis when used under conditions of
high depletion of the feed brine. Furthermore, the
surface hydrolysis step of the prior art process for
making me~branes is eliminated. Also, the process
eliminates the step of stripping a membrane from a
laminating drum or other support surface which in many
cases led to a membrane having one surface textured or
embossed by the pattern of the support surface.
This application is a division of copending
application Serial No. 367 515, filed 1980 December 23.
