Note: Descriptions are shown in the official language in which they were submitted.
12Z5964
.
MONOPOLAR, BIPOLAR A~D/OR HYBRID MEMBR~E CELL
.: :
: : Many important basic chemicals which are utilized
,in~;modern society are produced by electrolysis.
Nearly all:of the chlorine and caustic used in the
5 . world today is produced by the electrolysis of aqueous
sodium chloride (brine) solutions. There is increas-
ing interest in the electrolysis of water, the produc-
tion of oxygen a~d:particul~arly, hydrogen which is
findin~ ever increasing~use in our society. Other
uses of electrolysis include electro-organic
synthesis, batteries and the like, and even more com-
mon applications~such as water purification systems
.and swimming pool chlorinators.
Flowing mercury cathode cells and diaphragm cells
have provided the~bulk of the electroIytic production
of chlorine and caustic. In more recent times, the
membrane-type electrolytic cell has gained popularity
` because of~its ease of operation and, particularly,
; because of:its lack of polluting effluents such as
: 20 from mercury or the use of carcinogenic material such
'
lZZS91~4
,
as asbestos. Membrane-type electrolytic cèlls gen-
erally comprise an anode chamber and a cathode chamber
which are defined on their common side by a hydrau-
lically impermeable ion-exchange membrane, several
types of which are now commercially available but are
generally fluorinated polymeric materials.
Membrane-type electrolysis cells generally com-
prise one of two distinct types, that is the mono-
polar-type in which the electrodes of each cell are
-directly connected to a source a power supply, or the
bipolar-type in which adjoining cells in a cell bank
have a co~mon electrode assembly therebetween, said
electrode assembly being cathodic on one side and
anodic on the other.
_ However, in the past these two designs have been
so different that few parts of these electrolytic
cells have been interchangeable. Thus, each type of
cell has required substantially completely different
components for each. Further, even when components
~have been similar they have generally required com-
pletely separate manufacturing tools and processes.
Several designs of both monopolar and bipolar
membrane cells incorporate a pair of formed metal pan
structures which define the anode and cathode com-
partment when similar pans are assembled in a facingrelationship with a membrane interposed therebetween.
Cells of this type are described in U. S. Patents
4,017,375 and 4,108,752, for example.
Because of the rigorous corrosive conditions
existing in the electrolytes of both the anode and
cathode chambers, it has been necessary to form the
anode and cathode pan out of material which is
resistant to the electrolyte. In most cases, anode
pans were formed from titanium or other valve metals
_or their alloys in sheet form. Similarly, cathode
~ - \
3~25964
~ 3
pans were formed from ferrous metals such as steel,
stainless steel, as well as metals such as nickel. An
example af such pans in a monopolar cell is described
in U.S. Patent 4,244,802. However, a disadvantage is
-this patent requires expensive lamination o~ the
highly conductive metal outer layer to the pan, which
is unnecessary when pans are employed in the present
invention.
In a bipolar cell the electrical connections
- between the anodelcathode parts of a bipolar element
have provided serious design problemsD Due to the
different corrosive environments of the anode and
cathode the parts are made of diffexent materia]s.
Electrically connecting these materials has been done
-in several ways, each with some inherent dis-
advantages. For example, the use of titanium/stud
bonded plates has had the problem of hydrogen dif-
fusing throu~h the stud plate and hydriding the
titanium and thereby destroying the bond. Trimetal
(titanium/copper/steel) plates have overcome the
hydriding problem, but at a cost that is extremely
high. Other forms of oechanical connections have been
dificult because of the requirements of internal
bolts or fasteners to apply the joint pressure re-
~quired to make these mechanical connections viable.
In a monopolar cell, in addition to the necessityof corrosion resistance, there is the necessity of
conducting current from the external power source
into, and out of, the monopolar elements and evenly
_distributing the current across the active electrode
surfaces. In order to carry and distribute this cur-
rent with low ohmic losses (especially in large area
electrodes) a low resistance conductor must be used.
This conductor may be made of a large cross section of
~the corrosion-resistant metal or of a smaller cross
.
~ - ~
:~L2ZS96q~
-- 4 --
section of a metal such as copper or alumihum, for
example, which has a specific resistance 5 to 50 times
lower than the corrosion-resistant metals. Obviously,
these low resistance metals must be protected from
corrosion by the electrolytes in order to make them
~ viable materials for use in electrolytic cells.
One method used in the past to help alleviate
problems of getting electric current to the electrode
active area while maintaining low structural voltage
losses and even current distribution across the mem-
brane in monopolar membrane electrolyzers has been to
use a copper conductor bar with suitable corrosion--
resistant metal bonded or clad to the copper. The
disadvantages of this approach are high manufacturing
costs, limited shape and size availability, difficult
welding, chamber width limited by the width of the
conductor bar, interference with electrolyte flow,
longer current paths necessary due to conductor
spacing causing uneven current distribution to the
membrane, problems of sealing the cells where the
conductor bars pass through the cell structure, high
cost dictating a higher current density and therefore
high structural IR losses and the requirement of
removal of conduc~or bars before electrodes can be
recoated. (IR is an abbreviation from the Ohm's Law
equation, V = IR, which means voltage equals current
multipli~ed by resistance. Thus, by IR, we intend
voltage.)
A second approach which has been used in the past
is to eliminate the copper and carry the current in
the corrosion-resistant metal electrode structure.
Since the electrical resistance of the corrosion
resistant metal (e.g., titanium, nickel, stainless
steel) is high compared to copper and aluminum, the
voltage loss is increased and the length of the
122S969L
-- 5 --
.
current path must be kept as short as poss~ble (i.e.,
small electrode dimension parallel to the current
path). This then limits the size of an electrode
active area, increases the sealing perimeter to active
area ratio, and requires many smaller components to
~ create the same total active area. Thus, a larger
active area to sealing perimeter would also provide
the additional benefit of a more efficient use of the
membrane area (i.e., active area/purchased area ratio
is higher). Current distribution in connection to
external buswork is also difficult with this approach.
Therefore, the advantages of this invention are
to reduce the ohmic loss in monopolar or bipolar
electrolyzer structures, by reducing the electrical
resistance due to structuxal components and mechanical
connection problems,~to improve current distribution,
to allow for greater electrode active areas and to
decrease the sealing perimeter to active area ratio.
In one aspect, these advantages are enhanced in
the bipolar me~mbrane-type ceIl by using novel low
pressure, high surface contact area, low current
density mechanical connections between the back plates
of the anode and cathode elements of a bipolar
electrode assembly. In another aspect of the instant
invention, a similar novel low pressure, high surface
area contact between the back plates of the cells in
the assemblies of a hybrid electrolyzer combination of
monopolar and/or bipolar cells is utilized.
This invention also provides a structure for
membrane cells which requires little or no retro~
fitting. As newer and better electrode elements are
developed they may be retrofit without loss of the
novel current distributor member and/or the novel
monopolar, bipolar, or hybrid cell to cell low pres-
sure contact feature.
:'.
~ i
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~L2Z596a~
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~ lis invention also contemplates a cathode
design, anode design, and current distributor member
design which are usable for both bipolar and monopolar
membrane cell arrangements without modification
allowing a single production of items to be used in
~ both types of electrolyzers by simply changing the
assembly sequence. Because of this unique ability
another electrolyz~r configuration is contemplated
which is a hybrid or combination monopolar, and/or
bipolar arrangement of cells within one electrolyzer.
The hybrid electrolyzer then may comprise a number of
monopolar sections electrically arranged in a series
(i.e. bipolar) fashion or a number of bipolar sections
electrically arranged in parallel (i.e. monopolar)
fashion or any combination of bipolar and monopolar.
The advantages are abillty to select electrolyzer
current to match a convenient or existing rectifier
capacity,~avoid the shortcomings of bipolar design
(such as current leakage, single current path through
electrolyzer, high voltage circuits), avoid the
shortcomings of monopolar design (reduction in amount
of buswork required, lower current circuits). Other
advantages and configurations of a hybrid design will
be readily apparent to those skilled in the art.
Additional advantages of the invention include
the ability to change current distributor members
without changing other components, the ability to
change cell elements without changing other com-
ponents, the ability to allow for current density
changes optimizing power cost versus capital costs,
and the ability to obviate any need for conductor bars.
Therefore, the present invention providec for a
filter press electrolyzer comprising at least one
electrolytic cell for electrolytic processes; said
electroIyzer being provided with end plates which fo~m
~L2259~;4
7 - :
end walls for said electrolyzer; said cell having
vertically disposed electrode assemblies and at least
one membrane positioned therein; said cell including
means for introducing and removing liquids, gases and
eLectrical energy; said electrode assemblies having
back plates of electrically conductive material which
is corrosion resistant to the internal cell conditions
and through which current is introduced into and
removed from the electrodes; the improvement
comprising an electrical connection between an
opposing electrode assembly back plate and a current
supply means via a contact joint wherein the
dimensions of electrical contact area are
substantially the same as the dimensions of said
electrode assemblies of said cell, and said contact
joint comprises a low pressure, high surface contact
area, low current density mechanical connection
without metallurgical bonding, and wherein said
current supply means is selected from an anode back
pIate, a cathode back plate, a current distributor
member, or combinations thereof, whereby said
electrical contact joint is separated from the
electrolyte via the opposing back plate.
The present invention also provides for use of
the electrolyzer in the above paragraph to produce
caustic and halogen from brine.
The present invention also provides for a process
for the production of caustic and halogen from brine
comprising the steps of (1) placing brine in intimate
contact with a filter press electrolyzer comprising at
least one electrolytic cell for electrol~tic
processes; said electrolyzer being provided with end
plates which form end walls for said electrolyzer;
said cell having vertically disposed electrode
assemblies and at least one membrane positioned
.~,
:I.ZZ5~64
-- 8 --
.
therein; said cell including means for introducing and
removing li~uids, gases and electrical energy; said
electrode assemblies having back plates of
electrically conductive material which is corrosion
resistant to the internal cell conditions and through
which current is introduced into and removed from the
electrodes; and (2) introducing electrical energy into
said cell thereby producing caustic and halogen; the
improvement in said process comprising an electrical
connection between an opposing electrode assembly back
plate and a current supply means via a contact joint
wherein the dimensions of electrical contact area are
substantially the same 2S the dimensions of said
electrode assemblies of said cell, and said contact
joint comprises a low pressure, high surface contact
area, low current density mechanical connection
without metallurgical bonding, and wherein said
curren~ supply means is selected from an anode back
plate, a cathode back plate, a current distributor
member, or combinations thereofj whereby said
electrical contact joint is separated from the
electrolyte via the opposing back plate.
The current supply means referred to in the
paragraphs above may be an anode back plate, may be a
cathode back plate, or may be a current distributor
member.
Figure 1 is an exploded view of a monopolar
filter press electrolytic cell of the invention;
Figure 2 is an exploded view of a cell.
Figure 3 is a plan view partial cross section of
the monopolar filter press electrolytic cell of the
invention;
Figure 4 is a cross sectional view of an integral
manifold;
Figure 5 is a graphic view of a monopolar cathode
~ lZ~S96g
- 9 -
assembly;
Figure 6 is a graphic view of a monopolar anode
assembly;
Figure 7 is an exploded partial cross sectional
view of one integral manifolding assembly of the in-
~ vention;
Figure 8 is an exploded view of a bipolar filter
press electrolytic cell of the invention;
; Figure 9 is an explod~d view of one version of a
hybrid polarity filter press electrolytic cell of the
invention;
Figure 10 is an elevation view partial cross
section of a bipolar section of a filter press
electrolytic cell of the invention;
Figure 11 is an elevation view partial cross
section o a monopolar section of a filter press
hybrid polarity electrolytic cell of the invention;
Figure 12 is a plan view partial cross section of
one version of a hybrid polarity section of a filter
press electrolytic cell of the invention;
Figure 13 is a graphic view of a cathode pan;
Figure 14 is a graphic vlew of an anode pan;
The present invention relates to an electrolyzer
having a monopolar filter press electrolytic cell for
use in electrolytic processes. Cells of this type
generally contain anodes, cathodes, membranes and are
contained within bulkheads connected by tie rods which
may or may not be spring loaded. The monopolar em-
bodiment of the present invention contemplates having
current distributor members situated between adjacent
cathodes and between adjacent anodes thereby allowing
current to be brought into and removed from said
anodes and cathodes within said cells via the novel
low pressure, low current density, high area
connection of the present invention.
~225g6~
- 10 -
The present invention also relates to an electro-
lyzer having a bipolar filter press electrolytic cell
for use in electrolytic processes. Cells of this type
generally contain bipolar electrode assemblies, and
membranes, and are contained within bulkheads con-
~ nected by tie rods which may or may not be spring
loaded. In one embodiment, the bipolar embodiment of
the present invention contemplates the present, novel
current distributor member situated between each end
plate and a bipolar electrode assembly, with an anodeside facing one end plate and a cathode side facing
the other end plate, thereby allowing current to be
brought into and remo~ed from said cells via the novel
low pressure, low current density, high area
connection of the present invention. Further,
conducting eIectrical current from cell to cell is
accomplished via a novel low pressure, high surface
contact area, low current density mechanical
connections between the back plates of the anode and
cathode elements of the bipolar electrode assemblies.
Also, the present invention relates to an elec-
trolyzer having a;hybrid combination monopolar and/or
bipolar cells arranged within one electrolyzer for use
in electrolytic processes. Electrolyzers of this type
may be made up of a number of bipolar sections
arranged in a monopolar fashion, that is each bipolar
section electrically connected in parallel within the
end walls of one electrolyzer; or it may be made up of
a number of monopolar sections arranged in a bipolar
fashion, that is each monopolar section electrically
connected in series within the end walls of one
electrolyzer: the electrical connections to the
electrodes being made using the novel low pressure
high area, connection between either a current
distributor member of the back plate of another
,
122S~64
-- 11 -- . ..
.
electrode. Also, the hybrid embodiment of the present
invention contemplates any arrangement of monopolar
and/or bipolar assemblies within one electrolyzer.
The hybrid embodiment contemplates use of the novel
low pressure, high area, low current density
- connection, with the contact area for said connection
substantially the same dimensions of the active area
of said electrodes.
For the monopolar, bipolar, and hybrid embodi-
ments also, there is provided a method of sealing thesystem so as to prevent leakage of feedstocks and
products produced in said cell as well as there is
provided a means, either external or integral, of
receiving raw materials and removing resulting pro-
ducts. Also provided is a method of introducing and
removing electrical energy into and out of the cells.
This electrical system is generally referred to as a
bus system and in the pre3ent invention is external to
the cells.
Anodes suitable for use in the instant invention
comprise an anode back plate and an active anode sur-
face area.
In a preferred embodiment, the active anode sur-
face area comprises a foraminous anode of a type which
is generally known in the art comprising valve metal
substrate having an electrocatalytic coating applied
thereto of precious metals and/or oxides thereof,
transition metal oxides and mixtures of any of these
materials. The anode member is generally planar in
form and may be constructed of any foraminous material
such as expanded metal mesh, perforated plate or wire
screening. It is to be understood that this
foraminous material has a high surface area and large
number of points of contact with the membrane brought
about by having a large number of small perforations,
~ ~L22S964
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- 12 -
for example: expanded metal mesh having what is
commonly known as having "micromesh size" pores. Also
suitable i8 a reticulated anode of titanium metal
coated with DSARTM (an electrocatalytic coating~
5 such as described in Canadian patent application
Serial No. 432,055, in the name of Harney et al.
This active anode area is mechanically and
electrically attached to the anode back plate
preferably by welding. Further, preferably, the
active anode area is attached to the back plate via
springs. Thus, the anode may be spring loaded against
the membrane to help provide a large number of points
of contact. These springs may take many forms and be
of various metals, preferably the same metal as used
to form the active anode area. The welding may take
the form of resistance welding, TIG welding (tungsten
inert gas~ welding), elect~on beam welding, diffusion
welding (diffusion bonding) and laser welding for
example. Presently preferred at this time is the
technique of resistance welding.
It is to be understood, however, that in using a
reticulated anode the active reticulate material may
` be cast in place and diffusion bonded into the pan or
may be welded by any of the above suitable welding
techniques.
Cathodes suitable for use in the present inven-
tion may be generally described as comprising a
cathode back plate and an active cathode surface
area. In a preferred embodiment the present invention
contemplates a cathode pan preferably stamped from a
planar sheet of nickel, iron, steel, stainless ~teel,
or other similar alloy material. The active cathode
surface area is likewise made of a material such as
iron, steel, stainless ~teel, or other similar alloy
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`I ~12259~;4L !
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- ~3 -
material. The cathode active ~urface area is forami-
nous in nature and preferably i~ a reticulate metal
member formed as described, i.e. in Canadian Application
Serial No . 429,606, in the name of Stewart et al.
It is understood, however, that nickel
mesh, steel mesh, etc., and spring loaded systems
similar to tho~e described hereinabove in rela~ion to
anodes are also suitable. Also, other known types of
cathodes for use in zero gap and/or finite gap cells
are suitable for use in the current invention.
The cathode active surface area is electrically,
and mechanically attached to the cathode pans. In the
case of the cathodes being fabricated from metal mesh
analogous to the mesh anodes described hereinabove
welding is the preferred method of at achment. In the
case of fabricating the reticulated cathodes the pre-
ferred method of attachment is plating, most
preferably galvanic plating. This contact can be
realized solely by mechanical pressure if so desired.
Finally, while the anodes and cathodes have been
described ln their relationship to ~he preferred
embodiment of the instant invention, namely a membrane
gap cell (7ero gap cellj, it is to be clearly under-
stood that whether or not the cell has a finite gapbetween membrane and electrode or not is not critical
to the present invention. Thus, the present invention
is also completely suitable for use in finite gap
cell~ which are well known and understood in the art
and therefore will not be further described herein.
In the preferred embodiment, the electrodes of
the present invention utilize pans with a single back
plate configuration. Thus pans for the anodes and
pans for the cathodes are both formed on similar dies
and are substantially identical in size and shape.
122S964
- 14 -
.
The differences in them being: the manifoldiny
arrangement used which allows the proper fluids to
enter and exit the particular area, i.e., cathode aréa
or anode area, and the materials of the pans; the
anode pan generally being made of a valve metal
~ preferably titanium or a titanium alloy or other metal
resistant to corrosive conditions of the anode
chamber, and the cathode pan being made of nickel,
steel, stainless steel or alloys thereof or other
metals resistant to corrosive conditions of the
cathode chamber; the location of the sealing means or
groove to contain the sealing means.
The pans are formed to create an integral frame
attached to the back plate which forms a chamber for
containing electrolytes and electrode active areas.
The back plate is generally planar and preferably
flexible to allow it to conform to a current
distributor member or another electrode back plate to
provide a good electrical connection. ~he frame of
the pan may contain an area which may be rigidified by
applying a grouting or filler material and also
contain a face area which may be sealed by flat
gaskets, o-rings or other gasket shapes when pans are
arranged in a facing relation with a membrane
therebetween.
One purpose of rigidifying the pans with a grout
or filler material is to provide a reinforcement of
thin pan metal enabling it to withstand a compressive
gasket force without collapse thus allowing economic
use of the expensive corrosion resistant metals
through the use of thin material, i.e., on the order
of .015 to 0.10 inch (.038 to 0.254 cm) thick sheet
metal. Other purposes include making handling of the
electrodes easier and increasing the internal pressure
holding capacity.
~ .
~` ~225969~
- 15 -
Suitable for use as grouting or filler materials
are, for exampie, thermoplastics, elastomers, resins,
urethanes, formed metal shapesj and various
polyfluorinated materials. Presently preferred are
epoxy group and fiberglass reinforced polyester or
~ vinyl esters. The grout or filler materials may be
"cast in place" or prefabricated and subsequently
placed-and/or bonded in place. In either case, it is
advantageous to be able to remove these materials
relatively easily for electrode recoating processes.
In a preferred embodiment, the instant invention
contemplates anode pans generally of a valve metal
sheet stamped into the form of a pan. The preferable
anode material is titanium metal or an alloy thereof.
The anode active surface area is electrically and
physically attached to the anode pan.
The present invention also contemplates that the
electrode enclosure may be a frame which forms the
chamber to contain the electrolytes and the
electrodes, and the frame may be detachable from the
back plate in lieu of being permanently attached to
the back plate. The frame may be of alternate
materials, such as plastic, metals, et cetera. The
perimeter frame is a separate member which is gasketed
25 to the electrode structure as opposed to the pan.
80th anode and cathode elements are completed by a
frame to create an enclosure for the electrolytes
surrounding the electrodes and provide means of feed
and discharge through passages in the frame. The
frame is gasketed to the corrosion resistant plate
around its perimeter and also gasketed on the opposite
side which will seal to the membrane, thus creating
the electrode enclosure. Anode and cathode elements
are alternately stacked with membranes between and
compressed by end plates ~bulkheads) and tie rods.
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The frames may be (1) molded of any suitable corrosion
resistant plastic (anode: Kynar@, CPVC~ Teflons~,
elastomers, ABS, etc., cathode: CPVC, polypropylene,
ABS, elastomers, Teflo-ns~, etc.) or (2) fabricated by
welding, gluing, etc. of these plastic materials, or
- (3) fabricated of solid or tube - hollow - corrosion
resistant metals (anode: titanium or alloys, cathode:
steel, nickel, stainless steel, etc.) fabrication
being by pressing, drawing, roll forming, welding,
extruding, forging, etc. or a combination. The
gasketing may be "O" rings, flat gaskets, extruded
gaskets or other well known means ~U.S. #4,344,633).
Membranes suitable for use in the instant in-
vention are of several types which now are com-
mercially available but are generally fluorinatedpolymeric materials which have surface modifications
necessary to perform the ion-exchange function. One
presently preferred material is a perfluorinated co-
polymer having pendent cation exchange functional
groups. These perfluorocarbons are a copolymer of at
least two monomers with one monomer being selected
from a group including vinyl fluoride, hexafluoro-
propylene, vinylidene fluoride, trifluoroethylene,
chlorotrifluoroethylene, perfluoro(alkylvinyl ether),
tetrafluoroethylene and mixtures thereof.
The second monomer often is selected from a group
of monomers usually containing an SO2F or sulfonyl
fluoride pendant group. Examples of such second mono-
mers can be generically represented by the formula
CF2= CFRlSO2F. Rl in the generic formula is a
bifunctional perfluorinated radical comprising gen-
erally 1 to 8 carbon atoms but upon occasion as many
as 25. One restraint upon the generic formula is a
general requirement for the presence of at least one
fluorine atom on the carbon atom adjacent the -SO2F
ZZ59~
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- 17 - -
group, particularly where the functional group exists
as the -(-S02~H)mQ form. In this form, U can be
hydrogen or an alkali or alkaline earth metal cation
and m is the valence of Q. The Rl generic formula
portion can be of any suitable or conventional con-
figuration, but it has been found preferably that the
vinyl radical comonomer join the Rl group through an
ether linkage.
Such perfluorocarbons, generally are available
commercially such as through E.I. duPont, their pro-
ducts being known generally under the trademark
~AFION~TM. Perfluorocarbon copolymers containing
perfluoro (3,6-dioxa--4-methyl-7-octenesulfonyl
fluoride) comonomer have found particular acceptance
in C12 cells. Where sodium chloride brine is
utilized for making chloralkali products from an
electrochemical cell, it has been found advantageous
to employ membranes having their preponderant bulk
comprised of perfluorocarbon copolymer having pendant
sulfonyl fluoride derived functional groups, and a
relatively thin layer of perfluorocarbon copolymer
having carbonyl fluoride derived functional groups
adjacent one membrane surface. It is presently
preferred to have these membranes further modified
with inorganic surface treatments which impregnate the
surface of said membranes with metallic materials such
as, i.e. ZrO2, and TiO2. This modification i8
believed to help prevent the problem of gas bubble
~uildup along the membrane electrode interface. By
removing this problem the cell is able to operate more
efficiently. A more detailed description of this type
of membrane modification can be found in
Canadian Patent 1,173,105, in the name of Covitch et al.
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25964
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.
The present invention utilizes a novel current
distributor member for introducing curren~ into or
removing it from the cells. It is used in monopolar
cells, or in bipolar cells at the connections to the
external power source, or in hybrid cells to connect
to external power sources or other sections of the
electrolyzer. This results in the ability evenly and
with lower IR losses to introduce and to distribute
current into and out of the cell without the
constriction of cell size due to the IR loss of the
anodes and cathodes. This is possible by utilizing
current distributor members having dimensions of
electrical contact that are substantially the same as
the dimensions of the electrode assemblies. It is
15- possible, of course, to utilize current distributor
members which are smaller dimensionally than the
electrode assemblies with the clear understanding that -~
as the size of the current distributor member is
reduced the IR losses will increase. Obviously, there
be point at~which the I~ losses become too great to be
acceptable. Likewise, it is clear that the current
distributor members may be dimensior.aIly greate~ in
size than the electrode assemblies. However, since
this would not increase the contact area it would
provide no advantage. By "dimensionally" is meant the
dimensions of length and width which determine the
surface area available for mechanical and electrical
contact with the electrode assemblies. Since copper
and aluminum are far better conductors of current than
valve metals, certain stainless steel alloys cells may
be greater in size while maintaining an acceptably low
IR loss level. It is to be understood, however, that
while copper and aluminum are preferred because of the
weight and cost savings and lower volume of metal
needed, any conductive metal will work if enough
~Z2S964
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-- 19 --
volume is provided to carry the necessary current with
acceptable IR losses. In addition, this novel current
distributor member allows for higher current densities
to be used within the cell and therefore allows for
greater caustic and chlorine production from a cell
- that must be run at a lower current density per unit
area.
The current distributor member is generally a
solid copper planar sheet but may also be any suitable
conductor having sufficient cross sectional area to
carry the required current with low IR loss and good
current distribution. Suitable examples of these
other conductive metals include, for example, nickel,
iron, steel, as well as alloys of these metals and
alloys of copper and aluminum.
In the preferred embodiment in monopolar cells
and the monopolar cell assemblies in hybrid cell
systems the current distributor members are placed
between anode pans with the back side of each pan
acing the current distributor member to form a single
monopolar anode element. Likewise, current
distributor members are placed between cathode pans
with the back side of each pan facing the current
distributor member to form a single monopolar cathode
element.
In the preferred embodiment in bipolar cells and
in the bipolar sections of the current distribution
system of hybrid cells there is a current distributor
member between each cell back plate and a bipolar
electrode assembly, an anode side facing one back
plate and a cathode side facing the other back plate.
The current distributor members protrude past the side
of the cell on one side only. The members between
adjacent anodes extend on one side while the members
between adjacent cathodes extend on the opposite
~ 122~64
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side. This extension is then used to connèct via a
bus system, to tne power source or other sections of
the electrolyzer. The manner of connecting the
buswork to the current distributor members is not
critical and methods are well known in the art and
~ therefore will not be further discussed herein.
In addition to being the preferred planar sheets,
said current distributor members may also be sheets
having calendered, dimpled, corrugated or serrated
surfaces or having an interface material attached to,
or inserted between, said surfaces as well as having
conductive compounds, i.e., greases containing parti-
cles of conductive metals distributed therein on its
surfaces. The reason for these surface modifications,
if used~, is to help improve the electrical contact
between the current distributor members and the anodes
and/or cathodes by ensuring that the highest amount of
mechanical surface contact is maintained and contact
resistance is minimized between said current members
and said anodes or cathodes. Further, it is
contemplated that the thickness of the current
distributor members may vary across the length of the
member based on~the current and voltage requirements,
to~reduce cost, for the particular sized cell. It is
understood that if such tapered~ members are used that
the taper of the anodes and the taper of the cathode
members between the cathodes are reversed so as to
provide a parallel stack of cells to be compressed
between the bulkheads. Finally, the current
distributor member may also be used to provide struc-
tural support for the cell.
With respect to monopolar, bipolar, or hybrid,
the current distributor member or electrode back plate
is held in mechanical contact with an electrode back
plate over a substantial portion of the total area, by
2Z5964
- 21 -
hydraulic or static pressure of the electr~lytes in
the pans, by the spring pressure o~ the anode and/or
cathode structures and by supports being compressed in
the filter press arrangement by the bulkhead-tie rod
assemblies. The novel electrical connection is made
outside the cell so that it is separated from the
electrolyte via the back plate. The back plate
restrains the electrolyte so that the electrolyte does
not contact the novel electrical connection. The
pressure applied is in the range of from about 0.5 to
100 psi, (0.035 to 7.03 kg/cm2), preferably in the
range of from about 1 to 20 psi(0.0703 to 1.403
kg/cm2). Increased pressure reduces contact
resistance. Normally for generally known mechanical
connection of electrical joints (i.e., bus work) in
the art a low area, high pressure (i.e., 500 - 5000
psi) (35.15 to 351.5 kg/cm2) joint is used to get a
low specific joint resistance and current densities
across the joint are high (i.e., 200 - 2000 asi) (31 -
310 amps/cm2) with the joint contact voltage lossequal to the product of specific resistance times
current density. Also, other factors such as "current
stream- line" effects enter into the total voltage
loss across this type of mechanical joint. In the
case of the contact of the current distributor to the
back plate or contact of the back plate to the back
plate of the present invention, the joint pressure is
lower (1 - 20 psi) (0.0703 to 1.403 kg/cm2) yielding
a higher specific resistance, but the joint area is
very large yielding a low current density (i.e., 0.5
to 10 asi) (0.0775 to 1.55 amps/cm2) and thus a low
ohmic loss across the joint. For example, a copper to
titanium joint, as might be used on the anode,
operating at 3 asi (0.465 amps/cm2) with a pressure
of 5 psi (0.3515 kg/cm2) (specific resistance of 3.5
2596~ ~
.
- 22 -
x 10 3 ohm-in2) (22.58 x lO 3 ohms/cm2) wo~ld
have a voltage loss of 1.05 x lO 2 volts, and a
copper to nickel joint, as might be used on the
cathode, operating at 3 asi (0.465 amps/cm2) with a
pressure of 5 psi (0.3515 kg/cm2) (specific
resistance 7.7 x 10 5 ohm-in~) (49.68 x 10 5
ohms/cm2) would have a voltage loss of 2.33 x lO 4
volts. The aifference between the copper to titanium
and the copper to nickel is due to differences in
contact resistance due to different materials and
different surface preparations, oxides, etc.
Modifications to the metal surfaces or the use of
interface materials to take advantage of lower contact
resistance o~ various metals is further discussed
hereinbeloW.
A thin pan is preferred because it is flexible
and conforms to the current distributor member or the
mating back pan in a connection creating a large con-
tact area. Additionally, materials such as con-
*
ductive reticulates (sponge metal), Multilam , con-
ductive wools and the like may be used as an interfacein contact with the current distributor member or back
plates to increase the contact area. Because contact
resistance is also dependent upon the materials in
contact, the distributor member and/or the pan may be
coated with a`material as an interface to make the
contact resistance lower. Suitable examples include,
~or example, coatings and plating of metals such as
silver, gald, platinum, nickel and copper by methods
such as, for example, plasma spraying, painting,
flame spraying, sputtering, vapor deposition and
combinations of the above.
In addition to the above materials, sealing means
such as a gasket may be placed between the distributor
member and pan or frame, or between anode and cathode
-
~,
*Trademark
- ~L22sg64
- 23 -
elements of bipolar electrode assemblies. This seal-
ing means is located so as to be around the current
distributor member and/or anode element and cathode
element perimeter to prevent entrance of corrosive
elements which can oxidize the contact and thereby
increase resistance and may also employ a conductive
and/or anti-oxidation material.
The key to the success of the use of these
connections is the fact that the low current densities
10 required, i.e., approximately 0.5 to 10 asi (0.0775 to
1.55 amps/cm2), with pressures at the joint of
approximately less than 1 to about 100 psi (0.0703 to
7.03 kg/cm2) results in low IR losses at a high
resistance junction (joint).
The bulkheads, tie rods and associated equipment
used to hold the cells in place and seal the cells are
those generally well known in the art. They are sized
to~be generally the same size as the cells to be
pressed between said bulkheads and generally are con-
structed of heavy gauge steel. The bulkheads and tie
rods may or may not be electrically isolated from the
cells as is preferable in each particular use. Since
these types of materials are well known and understood
in the art further description will not be given
herein.
Introduction of brine, caustic, water and removal
of hydrogen, chlorine, caustic, anolyte and catholyte
may be accomplished either by internal, integral, or
external manifolding. In the case where external
manifolding is utilized suitable materials for
carrying the various fluids and gases are well known
in the art and will not be further described herein.
In the case of internal or integral manifolding, the
inlets and outlets may be constructed of materials
that are normally attacked by the chemicals under the
~ .
~22596~
-
- 24 -
conditions of use but which are lined with plastics or
organic polymeric materials which are inert under the
conditions of practice. Preferably, however, the
integral manifolding is constructed of titanium metal
s or nickel metal as the case warrants for particular
inputs and outputs, inlets and outlets, and said inte-
gral and/or internal manifolding is electrically iso-
lated from the individual cells preferably by being
physically spaced so as not to be in contact with the
cells of polarity not desired in that particular mani-
fold line.
The bipolar filter press zero gap electrolytic
cells of the present invention, for example, are pre-
ferably configured such that an anode element pan back
faces a cathode element pan back; on either exposed
active surface face of said anode elements and said
cathode elements is a membrane which is in physical
contact with said exposed active surfaces and then on
either side of the exposed surfaces of said membranes
are opposite polarity active surface areas. This stack
assembly is repeated until the desired number of cells
is reached and then a single current distributor
member is placed at each end.
The monopolar filter press zero gap electrolytic
cells of the present invention are preferably con-
figured such that two anode pan backs face each other
and are separated by a current distributor member. On
either exposed active surface face of said anodes is a
membrane which is in physical contact with said anodes
and then on either side of the exposed surfaces of
said membranes are cathodes in pairs back to back with
current distributor members in between each pair~
This stack assembly is repeated until the desired
number of cells is reached. Bulkheads are provided
for either the monopolar or bipolar cell on either end
`` ~ILZ~5969~
- 25 -
with connecting tie rods and associated pa~aphernalia
to contain said so produced cells. It is to be
understood that sealing of said stack is provided by
either gaskets or O-rings, both of which are known and
conventional in the art. It is further understood
~ that the appropriate face or channeling necessary for
gaskets and/or O-rings are provided in the respective
anode and cathode pans.
The present invention is more fully described by
reference to the appended drawings and the discussion
hereinbelow.
Figures 1, and 3-7 relate to the monopolar
embodiment of the present invention. Figure 1 shows a
preferred embodiment of the present invention as it
relates to a monopolar cell configuration. Figure 1
shows an assembly (l) consisting of a piurality of
vertically disposed anode assemblies (4) and cathode
assemblies (5~ in physical contact with the
permselective membranes (6) (zero gap). Also shown
are integral discharge and inlet ports (100).
Additionally bulXheads (2) and tie rods (3) are
illustrated. Figure 2 shows an exploded view of a
filter press cell, as used in Example 1 and Example
2. As in Figure 1 the cell (1) comprises bulkheads
(2), tie rods (3), anode assembly (4), cathode
assembly (5) and membrane (6). Figure 3 shows a
partial cross sectional plan view of Figure 1. This
view shows anode pans (10) located on either side of
current distributor member (30). LiXewise cathodes
pans (20) are located on either side of current
distributor members (30). The anode pans have active
anode areas (11) attached to said pans via springs
` (12) and also incorporate a sealing means (13).
Similarly the cathode pans (20) have active cathode
areas (21) attached to them, in this particular case
.
~2S964
- - 26 -
reticulate without springs, and also utilize a sealing
means (23). These anode and cathode assemblies are
alternated and are in contact with and separated by
membranes (6). Spacers (40) are utilized as necessary
to maintain proper cell dimensions. Finally, grouting
material (50) for making the pans more rigid is
shown. Figure 4 is a cross sectional view of one
embodiment of integral manifolding showing the
position of the integral manifold (100) with rela-
tion to membranes (6), spacers (40), cathodes as-
semblies (5) and anode assemblies (4). Integral mani-
fold (100) is comprised of spacer (101), sealing means
(103), manifold sealing means (106) and manifold sec-
tions (107). Figure 5 shows a monopolar cathode
assembly (5) in greater detail. Shown are two cathode
pans (20), active cathode area (21), sealing means
(23), current distributor member (30) and integral
manifolds (100). Similarly, Figure 6 illustrates a
monopolar anode assembly (4) comprising two anode pans
(10), active anode area (11), sealing means ~13),
current distributor member (30) and integral manifolds
(100). Figure 7 represents a detailed view of an
integral manifolding embodiment showing an anode
assembly (4), a cathode assembly (5) and in integral
manifold tlOO). Specifically, the integral manifold
(100) is shown as comprising spacer section ~lOl),
sealing means (103), coupler (104) and manifold
sections (107). Also shown are current distributor
member (30) and spacer (40). Obviously, however, the
manifold sections (102) and spacer sections (101) of
the cathode manifolding are reversed for the anode
manifolding.
Figure 8 shows a preferred embodiment of a
bipolar electrolyzer of the present invention as it
relates to cell configuration. Figure 8 shows a
``` ~LZ25964
- - 27 - ~
.
bipolar cell assembly (32) consisting of a;plurality
of vertically disposed anode pan assemblies ~35) and
cathode pan assemblies (36) in physical contact with'
the permselective membranes (37) (zero gap). A single
current distributor member (61) is located on each end
of the electrolyzer and interace material (38) are
located between and in contact with the backs of
adjacent anode and cathode pan assemblies. Also shown
are integral discharge and inlet ports (131~. Ad-
ditionally bulkheads (33) and tie rods (34) are illus-
trated.
Figure 9 shows a preferred embodiment of one
version o~ a hybrid polarity electrolyzer of the
pxesent invention. As in Figure 8 the cell (32)
comprises bulkheads (33), tie rods (34), anode
assemblies (35), cathode assemblies (36), membranes L,'
(37), interface material (38), current distributors
(61) and integral discharge and inlet ports (131).
Figure 10 shows a partial cross sectional elevation
view of Figure 8. This view shows anode pans (35j and
cathode pans (36). Located on either end of the
electrolyzer is a single current distributor member
(61). The anode pans have active anode areas (42)
attached to said pans via springs (43) and also
~5 incorporate a sealing means (4~). Similarly the
cathode pans (36) have active cathode areas (52)
a,ttached to them, in this particular case reticulate
without springs, and also utilize a sealing means
(54). These anode and cathode assemblies are
alternated and are in contact with and separated by
membranes (37). Interface materials (38) are utilized
as necessary to help maintain proper electrical con-
tact. Finally, grouting material (81) for making the
pans more rigid is shown. It is understood that as
many cells as desired may be placed between the bulk-
.
- ~L225964
.
- 28 -
heads, in a variety of monopolar and/or bipolar
sections arranged and connected together in an
electroly~er. Figure 11 shows a partial cross
sec~ional elevation view of a monopolar electrolyzer
or a monopolar section of a hybrid polarity
electrolyzer. This view shows anode pans (35) located
on either side of current distributor member (61).
Likewise cathode pans (36) are located on either side
of current distributor members (61). The anode pans
have active anode areas (42) attached to said pans via
springs (43) and also incorporate a sealing means
(44). Similarly the cathode pans (36) have active
cathode areas (52) attached to them, in this
particular case reticulate without springs, and also
utilize a sealing means (54). These anode and cathode
assemblies are alternated and are in contact with and
separated by membranes (37). Spacers (71) are
utilized as necessary to maintain proper cell
dimensions. Finally, grouting material (81) for
making the pans more rigid is shown. Finally,
insulators (91) are shown. Figure 12 shows a partial
cross sectional plan view of Figure 9. This view
shows anode pans (35) and cathode pans (36) as well as
membranes (37), interface materials (38), current
distributor members (61), insulators (91), grouting
material (81), cathode active area (52), cathode
sealing means (54), anode sealing means 544), anode
active area (42) and anode springs (43). Figure 13
shows a detailed view of a cathode pan assembly (36)
with cathode pan (51), cathode active area (52),
sealing means (54) and integral discharge and inlet
ports (131). Figure 14 shows a detailed view of an
anode pan assembly (35) with anode pan (41), anode
active area (42), sealing means (44) and integral
discharge and inlet ports (131).
IZ25~364
.
- 29 - - -
The present invention is further illustrated by
the examples which follow without any intention of
being limited thereby.
ExAMæLE 1
This example shows how contact resistance and
therefore low voltage drop between the current dis-
tributor member and the anode as well as between the
current distributor and the cathode.
An electrolytic cell having an active surface
10 area of 10 inches (25.4 cm) by 30 inches (76.2 cm) was
assembled utilizing a compressible spring loaded
titanium DSARTM anode and a reticulate nickel
cathode made following the teaching of Canadian
Patent Application No. 432,055. The cell
also utilized a NAFIONRTM membrane separator between
the anode and cathode. The cell was run at zero gap.
There was a copper reticulate member positioned at the
anode back surface and a copper current distribution
member positioned against the copper reticulate. There
was also a copper current distributor member posi-
tioned against the cathode back surface. Electrolube,
a conductive grease, was utilized between the anode
back and copper current distributor as well as between
the cathode back and copper current distributor.
At 2 asi (0.31 amps/cm2), contact resistance
between the current distributor member and the anode
was approximately 10 mV and approximately 3 mV between
the current distributor member and the cathode. These
contact res1stances were measured using a millivolt
meter from the back o~ the pan to the current- distributor member.
~ZZ5964
- 30-32 -
. .
.
EXAMPLE 2
This example shows the usefulness of a reticulate
interface material.
The 300 square inch (1935 cm2) monopolar cell
~ 5 was operated with a compressible mesh DSA coated
anode and a reticulate cathode fabricated a~ described
in Canadian Application No. 429,606
in the name of Stewart et al, with a NaCl electro-
lyte feed. The membrane was a NAFIONRTM ion
exchange membrane. The cell was run both with and
without a copper reticulate material, of substantially
the same surface area as the active membrane area,
placed between the back of the titanium anode plate
and the copper metal current distributer member, also
having a surface area substantially the same ac the
active membrane area. At a current density of 2 asi
(0.31 amps/cm2j, the contact resistance between the
back of the anode plate and the current distributer
member was 64 mV without the copper reticulate
interface material and 12 mV when the copper
reticulate interface material was utilized. The
benefit of using this embodiment of the invention to
reduce contact resistance is thus, clearly
demonstrated.
While the invention has been described in the
above-identified examples and by way of the
above-identified drawings, other embodiments have been
suggested, and deviations and modifications from those
embodiments will occur to those skilled in the art
upon reading and understanding of the foregoing speci-
fication. It is intended that all such embodiments be
included within the scope of the invention as defined
only by the appended claims.
