Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND
1. Field of the Invention
This invention relates to the use of an endless
band or continuous sheet of porous polymeric diaphragm
material attached to its own support members as a replace-
ment for asbestos diaphragms now found in the conventional
diaphragm electrolyti.c cell.
2. Description of the Prior Art
The production of chlorine from an aqueous alkali
metal chloride solution by the use of a diaphragm electro-
lytic cell is well known. This type of cell is described
in some detail in the well-known textbook Chlorine, Its
Manufacture Properties and Uses, J. S. Sconce, Editor,
American Chemical Society Monograph No. 154, Reinhold
Publishing Corporation, New York, New York (1962~ beginning
at page 90. Among the cells described therein is the
Hooker cell which has a finger-type of cathode construction.
Thîs cell and other similarly described diaphragm cells
employ as the diaphragm an asbestos diaphragm made in situ
from a water~-based slurry. The asbestos slurry-type
diaphragm has an important advantage in the cells inasmuch
as the diaphragm conforms to the convoluted contours of the
cathode and presents no attachment problems. The cathode
~ fingers are particularly fabricated from wire screen mesh
so that the asbestos diaphragms can be deposited on the
cathode from the asbestos slurry. The use of other types
of asbestos such as asbestos paper wrapped over the finger-
type cathode and sealed at the top and bottom with cement
and putty provide a poor seal and loss of current
efficiency.
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There are economic advantages in replacing the
asbestos diaphragms by new types of preformed continuous
sheet diaphragms, in particular,power and steam savings.
Also with the commercialization of metal anodes which last
a long time~ e.g., ~ to 5 years, a durable diaphragm which
lasts as long as the anode would e~fect savings in cell
maintenance and reconstruction. Furthermore, health
problems which may be involved with the handling oE
asbestos would be minimiæed by the replacing of asbestos
diaphragms with preformed continuous sheet diaphragms.
The use of other materials as the diaphragm in
electrolytic apparatus appears to be limited to situations
where the anode/cathode configuration is such that the
diaphragm material can be maintained as a ~lat sheet simply
by stretching between the opposing anode and cathode. An
early patent, U. S. 1,464,689, discloses simply stretching
a diaphragm material between a pair of cooperating jaws
when the anode is flat. A later U. S. patent, U. S.
3,~35,074, discloses that in an electrodialysis apparatus
having a flat ~ertical anode and a flat vertical cathode at
opposite ends of the unit the diaphragm or membrane between
the two electrodes can be installed with one free endj if
desired.
- SUMMARY OF THE INVENTION
In accordance with the invention there is provided
in a diaphragm-type cell for the production of chlorine and
caustic from aqueous alkali metal chloride solutions having
a plurality of anodes mounted at the bottom of said cell,
a cathode between adjacent anodes and spaced between each
~o cathode and anode a diaphragm which divides the celL into
anolyte and catholyte compartments the improvement which
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comprises;
a diaphragm assembly composed of an upper
diaphragm support, a lower diaphragm
support and a continuous diaphragm
extending from said upper support to
said lower support, both. said diaphragm
supports being made of an electrically
non-conductive polymeric composition~
said lower support resting on or adjacent
to the bottom of said cell and having
: openings therein whi:ch allow said
anodes to extend through said lower
support, said diaphragm being in
mechanical connect1on with.said upper
- and lower supports so that all of the
flow of electrolyte.from th.e anode to
:the cathode is through said diaphragm,
~ said diaphragm being maintainable ln
: ~ place without the use of keepers, : :
:20 ~ retainers or the like, said cathode
: being àt all times separated from saidanode by said dlaphragm and/or upper and
lower diaphragm supports.
- DESCRIPTION OF THE DRP~WINGS
,
FIG. 1 is a side sectional view of a conventional
diaphragm electrolytic cell showing the present invention
installed th.erein.
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FIG. 2 is a top cross-sectional view of t~e
electrolytic cell taken along ].ine 2-2 of FIG. 1.
FIG. ~ is an expanded schematic drawing showing
the elements of the in~ention and their reLationship to the
conventional diaphragm elec.trolytic cell.
FIG. 4 is a side cross-sectional view of the
conventional diaphragm electrolytic cell wherein an
optional modification of the invention has been installed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
:
The present invention, as shown in FIG. 1, is
installed in a typical electrolytic diaphragm cell having
cell bottom and bus bar means 10 which is coated a non-
conductive sealant layer 12 and through which sealant layer
12 protrudes a~series of spaced anode metal stems 40 for
connecting anodes 24-with bus bar means 10. The stem 40 is
secured to the bus bar means 10 by use of nut 42. The cell
is`completed with the installation of cell sides 16 and
cell top 14 along with weak cell liquor outlet 18, hydrogen
outlet 20 and chlorine outlet 22, the exact positioning of
the foregoing outlets being a matter of choice. The porous
cathode 26 is typically made of a ferrous metal with a
woven wire construction although other means of fabricating
can be employed. The cathode 26 is so formed that it will
be one continuous piece but containing a series of openings
or passageways through which the anodes 24 can pass and most
of the surface of cathode 26 will be parallel to the anodes
24. As a matter of convenience, the cathode 26/diaphragm
36 assembly can be prepared prior to insertion o diaphragm
36 into the cell. This can be conveniently accomplished
~0 by attaching each of the continuous sheet or endless belt
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diaphragm 36 to the lower diaphragm support 30, then
lowering the cathode 26 down onto the lower diaphragm
support 30 so that the diaphragm 36 extends upwardly
through the passageways previously provided for the anode
24 and, ~hereafter~ applying the upper diaphragm support 32
to the other edge of the endless band diaphragm 36. This
assembly is then set into the cell so that the anode 24
extends through the passageways made by the diaphragm 36
which parallels the passageways of the cathode 26. The
cathode 26 and lower diaphragm support 30 are then placed
in mechanical and electrical attachment with the cell so
that proper position of the cathode 26 and diaphragm 36
will be maintained. Gas seals ~not shown) between sidewall
16 and lower diaphragm support 30 and between sidewall 16
and upper diaphragm support 32 complete the separation
between the cathode and anode chambers.
The spaci~l relationships between the anode 2~,
diaphragm 36 and cathode 26 are more clearly~shown in the
top cross-sectional view of FIG. 2. In this view it will
be noted that the anode 2~ is surrounded by diaphragm 36
and the diaphragm 36 i9 in turn surrounded by the cathode 26.
Both the diaphragm 36 and the cathode 26 having a fixed
spaced relationship with the anode 24 whereby at any given
- point on the surface of anode 24 the cathode ?6 and diaphragm
36 are in substantially the same spaced position as at any
other point on anode 24 . In no case is anode 24 in contact
with cathode 26 each being at all times distinctly separated
from eac~ other by diaphragm 36, l'he diaphragm ~6 thereby
forms an anolyte and catholyte chamber for each anode 24 or
cathode 26 pair.
The invention is illustrated schematically in
FIG. 3 wherein the expanded drawing shows an anode 24
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embedded in cell bottom 10 and extending through the non-
conductive sealant layer 12. The lower diaphragm support 30
contains slots or openings which accommodate the insertion of
anode 24. The cathode 26 ~s of woven wire-mesh construction
and is so woven that it has openings shaped corresponding to
the openings or slots in the lower diaphragm support 30 but
of a slightly larger nature thereby accommodating the endless
belt diaphragm 36 which is attached to the lower diaphragm
support 30 and the upper diaphragm support 32 which has the
same configuration as the lower diaphragm support 30.
The lower diaphragm support 30 and the upper
diaphragm support 32 are constructed of a chemically inert,
electrically non-conducting thermoplastic material such as
polyolefin derived from an olefin containing 2 to 4 carbon
atoms including polyethylene, polypropylene, polybutene-1 and
mixtures thereof~ poIytetrafluoroethylene, copolymers of
tetrafluoroethylene and polyperfluoroalkoxy compounds,
chlorofluoropolyethylene, polyvinylidene fluoride polymers
and acrylonitrile butadiene styrene terpolymers. The
properties of these polymers are improved by adding inert,
non-conducting yet reinforcing fillers.such as asbestos,
glass fibers, mica, kaolin or carbon black. An exemplary
composition for use in thls invention is an asbestos filled
polypropylene composition, such as disclosed in British Patent
1,246,034. Another equally suitable material is a polytetra-
fluoroethylene polymer or copolymer. The upper diaphragm
support 32 and the lower diaphragm support 30 are made from
the foregoing polymeric materials in such a manner that the
support me.mbers 30, 32 are both..
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electr.ically non-conducting and are incapable of permitting
the flow of electrolyte from one chamber to the other
chamber. It is also within the scope of this invention
to make the support frames 30, 32 out of a suitable metal
or wire which is completely covered and encased with an
insulating polymeric ma~erlal disclosed above.
The endless bel.t diaphragm 36 can be made ou~ of
the same polymeric material as the diaphragm support
members 30, 32 are made out of or it can be one of the
other suitable polymeric materials, e.g., those enumerated
above. The endless belt diaphragm 36, however, is so
fabricated with`appropriate physical, chemical and electro-
chemical properties that it is porous and will permit the
flow of electrolyte from one chamber to the other chamber.
The endless belt diaphragm 36 is attached to the diaphragm
supports 30, ~2 in any one of several conventional
techniques used in fabricating pol~neric objects such as
heat-sealing, cementing or friction fit snap-in techniques
It is also:within the scope o this invention to use a
r~mbination of the attachment techniques mentioned above
to attach the dlaphragm 36 to the supports 30, 32. For
instance, the diaphragm 36 can be heat-sealed to the lower
or bottom support 30 and mechanically, i.e., friction fitted,
to the upper diaphragm support 32. The fabricated diaphragm
36 may properly be classified as a porous membrane, or a
felted fabric such as are presently employed in the various
phases ofelectrolytic cell technology. It is also known
in the cell technology to insert between diaphragm 36 and
the electrodes, either or both anode 2~ and cathode 263 an
iner~ screen (not shown) to facilitate and improve the
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functionlng of the cell. This modification can be used in
conjunction with the present invention~ if desired
While the invention has been set forth in terms
of the conventional woven wire screen cathodes 26 of the
Hooker and Diamond type cells, it is equally applicable to
and useful with cathodes 26 made of perforated metal plate
formed to a similar spacing arrangement.
The anode 24 can be either a solid metal sheet,
a woven wire arrangement or an expanded metal mesh as
desired, the exact co~figuration of the anode 24 being
beyond the scope of the present invention. Typically, the
anode 24 is made of a valve metal and, thereafter, coated.
By a valve metal it is meant metal of tungsten, titanium,
zirconium, tantalum and niobium. Preferably, titanium or
tantalum is employed and it is normally a commercially pure
grade such as electrolytic grade. Alloys of valve metals
can be employed as long as the alloy meets the criterion of
passivity, metal alloys which become passivated when
polarized anodically and can remain passive well beyond
anodic potential needed to convert a chloride ion to
chlorine The phen~menon of passivity in this connèction
is discussed in an article by Greene appearing in the
April 1962 issue of Corrosion, pages 136-t to 142-t,
wherein reference may be made to FI~. 1 of thP article
which describes typical active-passive transition of a metal
towards a corrosive medium. Titanium alloys of aluminum,
vanadium/ palladium9 chromium or tin can be;employed in
which the latter metals are present as less than 10 percent
of the alloy.
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It is also well known to coat the anode 24 with at
least one platinum group metaI or metal compound, e.g., oxide,
to enhance its utility. The platinum group metals include
platinum, ruthenium, osmium, rhodium, iridium and palladium
and alloys of two or more o the foregoing metals. Many means
for applying and the formulations of platinum group metals
and compounds for these coatings are known, for instance, see
U.S. Patents 3,632,498; 3,630,768; 3,616,446; 3l242,053;
and 3,177,131.
FIG. 4 shows an optional modification of the present
in~en~ion which is designed to secure the benefits of the
present invention to the diaphragm cell equipped with the
conventional Hooker woven wire cathode employed therein. The
Hooker woven wire type cathode is well known in the art and
generally disclosed in the Sconce textbook discussed above in
the background section. In this modification the cell bottom
and bus bar 10, the non-conductive sealant layer 12 and anodes
24 with metal stem 40 and retaining nut 42 remain positioned
without change as shown in FIG. 1. However, in contrast to the
cathode 26/diaphragm 36 arrangement of FIG. 1, the continuous
sheet or endless belt d;iaphragm 36, the lower diaphragm support
30 and upper diaphragm support 32 are rearranged so that they
form a series of equal distance-spaced closed openings on
both sides. This is accomplished by attaching the endless
belt diaphragm 36 to the anode 24 openings of the lower diaphragm
support 30 as previously disclosed. However, the upper
diaphragm support 32 is now realigned so that the prior axial
alignment of the openings in the lower diaphragm -
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support 30 and the openings in the upper diaphragm support
32 are completely otlt o:E register. From a top view the
openings in the upper support 32 are now spaced equidistant
from each two adjacent openings in the lower support 30.
The free end of the endless belt diaphragm 36 for attaching
to the upper diaphragm support 32 is now in register with
and contacting the solid portion of the upper diaphragm
support 32 which is equidistant spaced between two adjacent
openings shown in FIG. ~. When the diaphragm 36, upper
support 32 and lower support 30 are assembled, the diaphragm
36 is positioned around the anode 24 as before. However,
in this case, the Hooker woven wire cathode 26 is inserted
from above into the openings of the upper diaphragm support
32. In this case the cathode 26 is separated as before
from the anode 24 by the diaphragm 36 and the diaphragm
supports 30, 32. But, unlike the case as sho~n in FIGS. l,
2 and 3 the cathode 26 is not encased by the diaphragm 36
and diaphragm supports 30, 32 and can be disengaged from
the diaphragm 36 without disassembly of the diaphragm 36
diaphragm supports 32, 30 arrangement. Under this
arrangement the conventional diaphragm electrolytic cell
can be used as is without modification of the location of
the chlorine ou~let 22. Gas seal (not shown) between
sidewall 16 and lower diaphragm support 30 completes the
separation between the cathode and anode chambers.
Many other modifications and ramifications will
naturally suggest themselves to those skilled in the art
based on this disclosure. These ramifications and
modifications are intended to be comprehended as within
the scope of this invention.
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