U.S. patent number 3,910,827 [Application Number 05/348,349] was granted by the patent office on 1975-10-07 for diaphragm cell.
This patent grant is currently assigned to PPG Industries, Inc.. Invention is credited to Hugh Cunningham, Carl W. Raetzsch, John F. Van Hoozer.
United States Patent |
3,910,827 |
Raetzsch , et al. |
October 7, 1975 |
Diaphragm cell
Abstract
A novel diaphragm cell (electrolyzer) useful for electrolyzing
brines to produce chlorine and sodium hydroxide is disclosed which
is constructed of a plurality of single cells. Such single cells
are made up from bipolar electrodes which have a plurality of
finger-like, dimensionally stable anodes extending in one direction
outwardly from a support wall and a plurality of finger-like
cathodes extending in the opposite direction from the support wall.
In its assembled state, the electrolyzer is made up of one or more
single cells in which cathodes of one bipolar electrode are
interleaved between anodes of the adjacent bipolar electrode to
form a single cell. An especially effective bipolar electrode has
hollow anodes having spaced pairs of anode surfaces. In a preferred
embodiment the support wall (or backplate) has a titanium surface
on its anode side and an iron surface on its catholyte side.
Inventors: |
Raetzsch; Carl W. (Corpus
Christi, TX), Van Hoozer; John F. (Pittsburgh, PA),
Cunningham; Hugh (Corpus Christi, TX) |
Assignee: |
PPG Industries, Inc.
(Pittsburgh, PA)
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Family
ID: |
26856807 |
Appl.
No.: |
05/348,349 |
Filed: |
April 5, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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160339 |
Jul 7, 1971 |
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54816 |
Jul 14, 1970 |
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836082 |
Jun 24, 1969 |
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Current U.S.
Class: |
205/511; 204/253;
204/254; 204/268; 204/269; 204/278; 204/283; 204/284;
204/290.13 |
Current CPC
Class: |
C25B
9/70 (20210101); C25B 9/19 (20210101) |
Current International
Class: |
C25B
9/18 (20060101); C25B 9/06 (20060101); C01b
007/06 (); C01b 011/26 (); C01d 001/08 () |
Field of
Search: |
;204/252,253,254,255,256,258,268,269,270,278,283,284,98,128,129,29F |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Edmundson; F. C.
Attorney, Agent or Firm: Goldman; Richard M.
Parent Case Text
RELATED APPLICATION
This is a continuation of application Ser. No. 160,339, filed July
7, 1971, which is a continuation-in-part of application Ser. No.
54,816, filed July 14, 1970, and application Ser. No. 836,082,
filed June 24, 1969, all now abandoned.
Claims
We claim:
1. A method of operating a bipolar electrolyzer having a plurality
of individual bipolar units in back-to-back bipolar configuration,
with a peripheral wall around each individual bipolar unit; an
anolyte chamber and a catholyte chamber in each individual bipolar
unit, the anolyte chamber and catholyte chamber of an individual
bipolar unit being separated from each other by a backplate having
a surface of a ferrous metal on the catholyte side and titanium on
the anolyte side; a plurality of hollow, wedge-shaped, inward and
upward louvered, valve metal anodes in said anolyte chamber, said
valve metal anodes having an electrically conductive surface
thereon; valve metal conductors between the base of said valve
metal anode wedges and the titanium surface of said backplate; the
bases of said hollow, wedge-shaped, inward and upward louvered,
valve metal anodes being held securely against said valve metal
conductors; a plurality of hollow, wedge-shaped, metal cathodes in
said catholyte chamber; said hollow, wedge-shaped metal cathodes
being spaced from and electrically connected to the ferrous metal
surface of said backplate; the hollow, wedge-shaped, valve metal
anodes of one bipolar unit and the hollow, wedge-shaped cathodes of
the next adjacent bipolar unit being interleaved between and
uniformly spaced from each other and forming a single electrolytic
cell therebetween; and a diaphragm therebetween dividing said
single electrolytic cell into an anolyte chamber and a catholyte
chamber; which method comprises feeding sodium chloride brine into
each of the individual electrolytic cells; passing an electrical
current through the electrolyzer from the cathodes of one cell
through the backplate to the anodes of the next adjacent cell in
the electrolyzer; evolving chlorine in the anolyte chamber;
collecting the evolved chlorine within the hollow, wedge-shaped
anodes between the inward and upward louvered metal walls thereof,
thereby imparting an upward circulatory motion to anolyte liquor
within the hollow, wedge-shaped anodes; recovering said chlorine at
the top of said anolyte chamber; evolving hydrogen and caustic soda
in said catholyte chamber; recovering said hydrogen at the top of
said catholyte chamber; and recovering catholyte liquor from said
catholyte chamber.
2. The method of operating a bipolar electrolyzer of claim 1
wherein said hollow, wedge-shaped, inward and upward louvered,
valve metal anodes have an electrically conductive surface only on
the interior surfaces thereof and wherein chlorine is evolved only
within the hollow, wedge-shaped anodes.
3. The method of operating a bipolar electrolyzer of claim 1
comprising passing the electrical current from a cathode of one
cell through an electrode support means which extends through an
opening in the backplate, to an anode mounting means of the next
adjacent cell of the electrolyzer, and from the anode mounting
means to an anode mounted thereon.
4. The method of operating a bipolar electrolyzer of claim 1
comprising collecting the evolved hydrogen gas in a chamber in the
upper portion of the bipolar unit and recovering catholyte liquor
from a separate chamber in the lower portion of the bipolar
unit.
5. A method of operating a bipolar electrolyzer having a plurality
of individual bipolar units in back-to-back bipolar configuration,
with a peripheral wall around each individual bipolar unit; an
anolyte chamber and a catholyte chamber in each individual bipolar
unit, the anolyte chamber and catholyte chamber of an individual
bipolar unit being separated from each other by a backplate having
a surface of a ferrous metal on the catholyte side and titanium on
the anolyte side; a plurality of hollow, wedge-shaped, inward and
upward louvered, titanium anodes, in said anolyte chamber, said
titanium anodes having an electrically conductive surface only on
the interior surfaces thereof; titanium conductors between the base
of said hollow, wedge-shaped, titanium anodes and the titanium
surface of said backplate; the bases of said hollow, wedge-shaped,
inward and upward louvered, titanium anodes being held securely
against said titanium conductors; a plurality of hollow,
wedge-shaped, metal cathodes in said catholyte chamber; said
hollow, wedge-shaped metal cathodes being spaced from and
electrically connected to the ferrous metal surface of said
backplate; the hollow, wedge-shaped, titanium anodes of one bipolar
unit and the hollow, wedge-shaped cathodes of the next adjacent
bipolar unit being interleaved between and uniformly spaced from
each other and forming a single electrolytic cell therebetween; and
a diaphragm therebetween dividing said single electrolytic cell
into an anolyte chamber and a catholyte chamber; which method
comprises feeding sodium chloride brine into each of said
individual electrolytic cells; passing an electrical current
through said electrolyzer from the cathodes of one cell through the
backplate to the anodes of the next adjacent cell in the
electrolyzer; evolving and collecting chlorine within the hollow,
wedge-shaped anodes between the inward and upward louvered walls
thereof, thereby imparting an upward circulatory motion to anolyte
liquor within the anode wedges; recovering said chlorine at the top
of the anolyte chamber; evolving hydrogen and caustic soda in the
catholyte chamber; recovering said hydrogen at the top of the
catholyte chamber; and recovering catholyte liquor from the
catholyte chamber.
6. The method of operating a bipolar electrolyzer of claim 5
comprising passing the electrical current from a cathode of one
cell through an electrode support means which extends through an
opening in the backplate, to an anode mounting means in the next
adjacent cell, and from the anode mounting means to an anode
mounted thereon.
7. The method of operating a bipolar electrolyzer of claim 5
comprising collecting the evolved hydrogen gas in a chamber in the
upper portion of the bipolar unit and recovering catholyte liquor
from a separate chamber in the lower portion of the bipolar
unit.
8. A method of operating a bipolar electrolyzer having a plurality
of individual bipolar units in back-to-back bipolar configuration,
with a peripheral wall around each individual bipolar unit; an
anolyte chamber and a catholyte chamber in each individual bipolar
unit, the anolyte chamber and catholyte chamber of an individual
bipolar unit being separated from each other by a backplate having
a surface of a ferrous metal on the catholyte side and titanium on
the anolyte side; a plurality of hollow, wedge-shaped, inward and
upward louvered, valve metal anodes in said anolyte chamber, said
valve metal anodes having an electrically conductive surface only
on the interior surfaces thereof; valve metal conductors between
the base of said hollow, wedge-shaped, valve metal anodes, and the
valve metal surface of said backplate; the bases of said hollow,
wedge-shaped, inward and upward louvered, valve metal anodes being
held securely against said valve metal conductors; a plurality of
hollow, wedge-shaped, metal cathodes in said catholyte chamber;
said hollow, wedge-shaped, metal cathodes being spaced from and
electrically connected to the ferrous metal surface of said
backplate, the hollow, wedge-shaped, valve metal anodes of one
bipolar unit and the hollow, wedge-shaped cathodes of the next
adjacent bipolar unit being interleaved between and unformly spaced
from each other and forming a single electrolytic cell
therebetween; and a diaphragm therebetween dividing said single
electrolytic cell into an anolyte chamber and a catholyte chamber;
which method comprises feeding sodium chloride brine into each of
said individual electrolytic cells; passing an electrical current
through said electrolyzer from the cathode of one cell through an
electrode support means which extends through an opening in the
backplate, to an anode mounting means, in the next adjacent cell,
and from the anode mounting means to an anode mounted thereon;
evolving and collecting chlorine within the hollow, wedge-shaped,
valve metal anodes between the inward and upward louvered walls
thereof, thereby imparting an upward circulatory motion to the
anolyte liquor within the hollow, wedge-shaped anodes; recovering
said chlorine at the top of said anolyte chamber; evolving hydrogen
and caustic soda in said catholyte chamber; collecting the evolved
hydrogen gas in a chamber in the upper portion of the bipolar unit
and recovering the hydrogen gas therefrom; and recovering catholyte
liquor from a separate chamber in the lower portion of the bipolar
unit.
9. A method of operating a bipolar electrolyzer having a plurality
of individual bipolar units in back-to-back bipolar configuration,
with a peripheral wall around each individual bipolar unit; an
anolyte chamber and a catholyte chamber in each individual bipolar
unit, the anolyte chamber and catholyte chamber of an individual
bipolar unit being separated from each other by a backplate having
a surface of a ferrous metal on the catholyte side and titanium on
the anolyte side; said bipolar unit having a chamber for the
collection of gases in the upper portion thereof, in communication
with the catholyte side of the backplate, and a separate chamber
for the collection of liquid in the lower portion thereof in
communication with the catholyte side of the backplate; a plurality
of hollow, wedge-shaped, inward and upward louvered, titanium
anodes in said anolyte chamber, said titanium anodes having an
electrically conductive surface only on the interior surfaces
thereof; internally threaded titanium conductors between the base
of said titanium anode wedges and the titanium surface of said
backplate; the bases of said hollow, inward and upward louvered,
titanium anode wedges being held securely against said titanium
conductors by a threaded, titanium screw; a plurality of hollow,
wedge-shaped, ferrous metal cathodes in said catholyte chamber;
said hollow, wedge-shaped ferrous metal cathodes being spaced from
and electrically connected to the ferrous metal surface of said
backplate; the hollow, wedge-shaped, titanium anodes of one bipolar
unit and the hollow, wedge-shaped cathodes of the next adjacent
bipolar unit being interleaved between and uniformly spaced from
each other and forming a single electrolytic cell therebetween; and
an asbestos diaphragm on said hollow, wedge-shaped cathodes
dividing said single electrolytic cell into an anolyte chamber and
a catholyte chamber; which method comprises continuously feeding
sodium chloride brine into each of said individual electrolytic
cells; passing an electrical current through said electrolyzer from
the cathode of one cell through an electrode support means which
extends through an opening in the backplate, to an anode mounting
means, and from the anode mounting means to an anode of the next
adjacent cell in the electrolyzer; evolving and collecting chlorine
within the hollow, wedge-shaped, anodes between the inward and
upward louvered walls thereof, thereby imparting an upward
circulatory motion to anolyte liquor within the hollow,
wedge-shaped anodes; recovering said chlorine at the top of said
anolyte chamber; evolving hydrogen and caustic soda in said
catholyte chamber; collecting the evolved hydrogen gas in the
chamber in the upper portion of the bipolar unit; continuously
recovering chlorine from said chamber, and recovering catholyte
liquor from the separate chamber in the lower portion of the
bipolar unit.
Description
THE INVENTION
The invention is concerned with an electrolytic cell (or
electrolyzer) in which aqueous alkali metal salts (e.g., sodium
chloride) are electrolyzed to form chlorine and alkali metal
hydroxide (so called alkali chlorine cells) of the type which
includes a succession of vertical electrodes in which dimensionally
stable anodes alternate with cathodes carrying a diaphragm. It is
particularly concerned with the arrangement and configuration of
the anodes and cathodes on a support wall (or backplate) and with
means for securing the electrodes to the support wall. It is also
concerned with a special bipolar electrode configuration which
among other things is characterized by hollow anodes having spaced
pairs of anodic surfaces.
A variety of types of alkali-chlorine electrolytic cells employing
a bipolar electrode assembly and a permeable diaphragm have been
known in the past. The present trend in this type of cell is to
provide within a single cell housing a plurality of individual cell
units utilizing bipolar electrode structures. See U.S. Pat. Nos.
2,858,263 and 3,337,443. In such an electrode structure, the anodes
of one cell are positioned in a back-to-back relationship with the
cathodes of the adjacent cell and electrical contact is maintained
between the two. The supporting wall for the anodes and cathodes in
the back-to-back relationship functions to physically separate the
cells within the over-all cell housing.
The present invention provides an improved bipolar alkali-halogen
diaphragm cell of the described type. The present invention
provides a diaphragm cell which is particularly light in weight and
easy to assemble and disassemble. It provides a unique, highly
advantageous bipolar electrode configuration which advantageously
effects brine circulation within the cell, reduces (even
substantially eliminates) the problems of gas binding in the
interelectrode space and utilizes efficiently metallic anodes. The
present invention furthermore provides a diaphragm cell having
improved electrical connection between the cathode and anode.
Herein the term cell unit is used to describe the back-to-back
bipolar assembly of the anodes of one cell with the cathode of the
adjacent cell. Each cell thus is made up of cathodes from one cell
unit (i.e. the bipolar electrode thereof) interleaved and spaced
from anodes of the next adjacent cell unit (i.e. the bipolar
electrode thereof). Each cell unit thus includes as a principal
component a bipolar electrode assembly. The cathodes
characteristically have elongated hollow portions which are
interleaved or interpositioned with and spaced from the anodes of
the next adjacent cell unit. The cathodes are constructed of metal
wire screening or the like perforated sheeting and are covered with
a permeable diaphragm, for example asbestos. The metal wire
screening may be of any suitable metal, for example, steel or,
alternatively, nickel or chromium or other metal sufficiently
resistant to corrosion under the conditions prevailing in the
catholyte during electrolysis.
The finger-like anode elements may be provided by a single sheet or
wall-like element or according to a particular preferred embodiment
are hollow and comprise a pair of laterallyspaced vertical walls.
These walls, in one embodiment, may be open along the outer end of
the elements or alternatively closed or substantially closed at the
outer end. Electrolyzers with hollow anodes are constructed so as
to provide for the presence of electrolyte in the hollow of the
anode. Anodic products, notably gaseous chlorine can form and/or
collect behind the anode surface directly facing the surface of the
adjacent cathode. This is gases, notably elemental chlorine can and
does collect in the hollow of the anode, and hence its accumulation
in the interelectrode space is minimized or avoided. Electrolyte is
also free to circulate in the electrolyzer and to move in the anode
hollow. Such circulation of gas and electrolyte is especially
noticeable (and enhanced) with metallic anode side walls of
previous material, such as when the walls are of rods, screen,
expanded metal mesh, perforated plate or louvered plate.
These anodes are constructed of any suitable chlorineresistant
metal such as titanium or like valve metal, e.g., tantalum and
tungsten, having an electroconductive surface of a platinum group
metal or the oxide of a platinum group metal. one or both surfaces
of the hollow anodes will have this electroconductive surface.
Characteristically, the sheet or wall-like anodes are thin, e.g.,
less than about a half inch thick. The term single-cell is used to
describe the cell formed by the finger-like anodes from one bipolar
electrode (or of one cell unit) which are interleaved with the
finger-like cathodes from an adjacent bipolar electrode (or of the
adjacent cell unit).
Another important component of the cell unit (and bipolar
electrode) is the supporting wall or backplate. As shown in the
specific embodiments hereinafter described, the backplate may serve
one or more purposes including that of (1) the prime structural
element for supporting the plurality of anodes and cathodes which
make up the cell unit, (2) the principal structure which divides
the entire electrolytic cell (electrolyzer) into its component
cells (single cells) and (3) the conductor by which the current
flows from cell to cell. For the backplate to perform such
functions it should be of appropriate construction and materials.
One especially useful type of electroconductive backplate has its
anodic side (or surface) of titanium (or like valve metal) and its
cathodic surface of steel. These surfaces are each resistant enough
to the respective cell environments to which they are exposed
during cell operation to provide for long backplate life.
In the drawings:
FIG. 1 shows a perspective view illustrating generally the bipolar
cell of the present invention with portions of the cell housing
broken away.
FIG. 2 shows in cross-section an enlarged portion of the electrodes
taken along the line II--II in FIG. 1 illustrating the relationsip
of the cell units to the cells in the cell housing.
FIGS. 3-12 illustrate various embodiments for mounting the
electrodes to the support wall in the cell units of the bipolar
cell.
FIGS. 13-15 show another preferred embodiment of the present
invention.
Bipolar diaphragm cell 10 as shown in FIG. 1 is constructed of a
plurality of cell units such as cell units 11, 12, 13 and 14 which
form single cells 18, 19, and 20. The end cell unit 11 provides a
cathode half cell and the end cell unit 14 provides an anodic half
cell. The intermediate cell units 12 and 13 are bipolar providing
an anodic surface in the direction of cell unit 11 and a cathodic
surface in the direction of cell unit 14.
The bipolar cell 10 may be provided with only one intermediate cell
unit having but one bipolar electrode such as cell unit 12.
Alternatively, the cell unit 10 may include two or more (frequently
12 or 15) intermediate cell units, as desired. The intermediate
cell units may be identically constructed.
The cell unit 13, for example, has a frame 21 including a backplate
22, which serves as a partition between single cells 19 and 20, and
peripheral walls 23, 24, 25 and 26. The frame 21 may be constructed
of iron and steel. However, the anodic side of the backplate 22 and
the inner surfaces of walls 23, 24, 25 and 26 should have a
suitable protective coating, such as of rubber, in order to prevent
corrosion. Alternatively, the frame 21 may be of titanium plate or
titanium clad steel plate. The peripheral walls, such as wall 24,
each includes a pair of flanges 27 and 28 that allow for bolting
the cell unit 13 to similar flanges on the adjacent cell units 12
and 14. Of course, the bolts are suitably insulated electrically
from the cell units and sealing gaskets are provided between the
meeting surfaces of the adjacent flanges. Thus, the container for
the single cell 19 is provided by the backplate 22 of cell unit 13,
the peripheral walls 23, 24, 25 and 26 and the backplate 22 of cell
unit 12.
The backplate 22 in the electrolytic cell illustrated in FIG. 1 has
at least one opening 34 which allows brine to flow from one cell
compartment to the next thereby providing an equal level of brine
in each single cell. The backplate 22 further includes openings 33
for mounting of the cathode 16 and 17 thereon as hereinafter
described. The upper portion of backplate 22 provides means for
removing the cathodic gas product, for example, hydrogen, from the
cell such means including a chamber 37 defined by wall 38 and the
upper peripheral wall 25. The wall 38 has an opening 39 for passage
of hydrogen formed in the hereinafter described cathodic zone in
the cell into chamber 37. The hydrogen gas is removed from chamber
37 through pipe 41. A pipe 42 in the upper peripheral wall 25 is
provided for removal of the anodic gas product, for example,
chlorine gas which is formed in the anodic zone of the cell. A pipe
43 is provided in upper peripheral wall 25 for passage of brine
into the single cell. The cell products such as caustic soda are
removed from the cathodic zone of the cell through pipe 44 in the
wall 24.
The cathode 16, as shown in FIGS. 1 and 2, includes a backscreen 47
spaced from plate 22 and finger-like cathode elements 46 which
extend perpendicularly from the backscreen 47. The finger-like
cathode elements are preferably wedge shaped as shown in FIGS. 1
and 2, thus facilitating achievement of near zero gap (or
interelectrode space) between the anode and cathode fingers.
However, the side walls comprising each cathode could be
substantially parallel with each other. The cathode fingers 46 and
the back screen 47 may be constructed of material conventionally
used in diaphgram cell cathodes for example, the type of screen
disclosed in U.S. Pat. No. 3,337,443. Cathode finger 46 includes
the side walls 45 and 50 which are joined at their outermost end
and at their upper and lower edge thus forming a chamber 70
enclosed except for the end which open into the chamber 75 defined
by the backplate 22 and the backscreen 47. The chambers 70 and 75
of each of the multiplicity of cathode elements associated with the
one cell unit together comprise the cathodic zone (in which the
catholyte is contained) of the single cell 20. Each cathode element
comprising cathode fingers 46 and the backscreen 47 is electrically
interconnected to the backplate 22 and its corresponding anode 17
of the cell unit. The screen of the cathode fingers 46 and
backscreen 47 is covered with permeable diaphragm suitably of
non-woven asbestos fabric. Alternatively, the permeable diaphragm
may be a permionic membrane. The permeable diaphragm prevents undue
mixing of the catholyte and anolyte and allows for the collection
of anodic and cathodic gases. The chambers 70 and 75 communicate
with the cathodic gas collection chamber 37 through the opening 39
in wall 38.
The cathode fingers 46 each have a plurality of horizontal bars 48
including laterally extending flanges 49 for supporting the screen
forming the cathode fingers and for conducting electrical current
to the cathodes. The bars 48 may be constructed of the same type of
material as used in backplate 22, for example, iron or steel.
The anodes 17 (FIGS. 1 and 2) are finger-shaped and extend
outwardly from the backplate 22. Anode 17 includes a pair of
laterally-spaced walls 61 and 62 and a rear wall 63. The walls 61
and 62 may be solid plate or may be of a foraminous or louvered
sheet material. Anode 17 has a horizontal bar 64 with
laterally-extending flanges 66 for support of the walls 61 and 62.
The walls 61 and 62 preferably are disposed so that their outer
surfaces are at an angle which is complementary to the angle
provided between the pair of adjacent cathode fingers 46. Thus,
when the electrodes are in position of operation shown in FIG. 2, a
uniform space (electrode gap) is provided between the outer,
opposed, facing surfaces of the respective anodes and cathodes. The
anode 17 including walls 61, 62 and 63 as well as the horizontal
bar 64 and flanges 66 and 67 may be constructed of any suitable
anodically-resistant material, preferably titanium. The outer
surfaces of solid walls 61 and 62 should be coated with a suitably
anodically-resistant electroconductive surface such as a platinum
group metal or the oxide of a platinum group metal such as
platinum, rhodium, palladium, ruthenium, rhenium, and osmium,
mixtures and alloys of these metals, and/or one or more oxides of
these metals. In addition, the electroconductive surface may also
contain oxides of other metals, some of which will improve the
anode's performance including oxides of titanium, lead, manganese,
cobalt, iron, chromium, tantalum and silicon. If the walls 61 and
62 are foraminous sheets, then the outer and/or inner surfaces may
be coated with such metal or metal oxide.
The cathode 16 and anode 17 are mounted on backplate 22 by
electrode support means 52 (FIG. 2). The electrode support means 52
includes a block 53 which extends through opening 33 in backplate
22 and is secured therein such as by welding. The block 53 may be
constructed of iron rod or other electrically conductive,
cathodically-resistant material and has an opening 54 there through
for reception of screw 56. The screw 56 is threadedly engaged in
opening 57 in the corresponding horizontal bar 48 of cathode finger
46. The screw 56 holds the backscreen 47 and the cathode finger 46
snugly against a shoulder 58 of block 53 to provide good electrical
contact. The opening 54 in block 53 has an enlarged portion 59 of
sufficient size to permit the head of the screw 56 to be disposed
there within. The rear wall 63 of anode 17 has an opening 68
through which anode mounting screw 69 extends for threaded
engagement in the enlarged portion 59 of opening 54 in the block
53. The open outer end of anode 17 provides access to screw 69 for
mounting and dismounting of anode 17. The screw 69 holds the anode
17 securely against block 53 and backplate 22 thus providing good
electrical contact. The screw 69 should be of an
anodically-resistant electrically conductive material such as
titanium. Sealing gasket 71 may be provided between the anode 17
and the backplate 22, thereby preventing any anolyte from reaching
the block 53 which, if it were to happen, might result in
corrosion. Seal 73 is provided between screw 69 and the backwall
63, thereby preventing leakage of anolyte through opening 68 and
into contact with the block 53.
The end cell unit 14 is constructed identical to cell unit 13
except that cell unit 14 does not include a cathode. In other
words, the only electrodes mounted on cell unit 14 are anodes. The
anodes may extend through the backplate and be welded or bolted to
a copper bus bar.
Cell unit 11 is constructed of a backplate 77 which may be bolted
to cell unit 12. Cell unit 11 has a cathode 78 including a
backscreen 79 and finger-like cathodes 80. Cathode 78 may be
mounted on plate 77 in a manner identical to the mounting of
cathode 16 on backplate 22 of cell unit 13.
The cell units 11, 12, 13 and 14 are bolted together, forming
single cells 18, 19 and 20, and the bolts are suitably insulated to
prevent shorting between cell units. Alternatively, the cell units
may be secured together by tie rods in a manner conventionally used
in filter press type cells. The single cells 18, 19 and 20 are
electrically connected in series. During a typical operation, brine
is continuously added to each of the single cells through the
corresponding pipe 43. The openings 34 between single cells permit
equilization of the brine level in each single cell. The openings
34 further prevent any one of the single cells from going dry, for
example, due to a stoppage in pipe 43. The brine is electrolyzed in
the single cell with anodic products, such as chlorine gas being
formed in the anodic zone and cathodic products, such as hydrogen
gas and caustic soda being formed in the cathodic zone. In those
instances where each anode includes a pair of laterally spaced
walls (e.g., as shown in some detail in FIGS. 3 and 12) of pervious
material anodic gaseous products can and will collect in the hollow
of the anode (bounded by the walls) and rise to the top of the cell
for removal via pipe outlet 42. The diaphragm prevents back
migration of the cathodic products into the anodic zone.
As illustrated in FIG. 1, anodes 17 have their walls open and
terminating above the bottom lower wall of the cell unit. This
permits liquid communication between the interelectrode space and
the hollow space within the anode. Electrolyte can thus also
circulate behind the anode walls, and the anolyte in such cell
configurations can be regarded as including electrolyte present
both between the cathode and anode as well as within the hollow of
the anode.
With perforate (pervious) anode walls, chlorine readily collects
and rises in the hollow space defined by the space walls of the
anode. As this chlorine collects and rises within the hollow, it
will cause movement of electrolyte. With anode walls spaced close
enough (usually spaced laterally less than 5 inches, more often
between 1/2 and 3 inches) and especially when the electrolyzer is
operated with reasonably high current densities, the rising
chlorine gas will lift upwardly electrolyte in the hollow.
Electrolyte (anolyte liquor) circulation can primarily be provided
in this fashion by the lift due to rising chlorine gas.
With those electrolyzers having bipolar electrodes with hollow
electrodes as herein contemplated, brine feed to the electrolyzer
need not be directly into the interelectrode gap. Brine, for
example, can be introduced wherever convenient (other than to the
catholyte); it can be fed into the hollow space of the anodes, if
desirable.
It is found that with previous hollow anodes, electrolyzers of the
type herein described function especially well and evidence
ruggedness of performance. For example, shorting usually attributed
heretofore in other cells to touching (or undue closeness) of
anodic surface and diaphragm is no longer a frequent event even
though there may be some slight misalignment or touching of anode
to diaphragm (or cathode surface which has lost diaphragms.)
Further preferred embodiments of electrode support means are shown
in FIGS. 3-12. The bipolar cell units 12A-12I shown in these
Figures are constructed substantially like cell unit 12 except for
the electrode design and electrode support means.
The electrode support means 52A (FIGS. 3 and 4) includes an
elongated bar or current gatherer 81 which is typical of the
current gatherer used in cell units 12A through 12H. The current
gatherer is welded to the cathode finger 46A and has openings (not
shown) through which cathodic products formed in fingers 46A may
pass to the chamber 75A. A metal block 82 is secured to bar 81 such
as by welding. The metal block 82 extends through an opening 83 in
backscreen 47A and is secured to backplate 22A by screw 84. The
screw 84 extends through opening 87 in backplate 22A and is
threadedly engaged in opening 88 in block 82. Preferably, the head
89 of screw 84 is countersunk into backplate 22A thereby providing
a flat surface against which anode 16A (FIG. 4) may be mounted The
electrode support means 52A further includes a screw 91 which
secures the anode 16A (FIG. 4) or anode 17A (FIG. 3) to backplate
22A. The head 92 of screw 91 is preferably welded to backplate 22A.
In the embodiment illustrated in FIG. 3 screw 91 is situated along
the same axis as that of screw 84 whereas FIG. 4 shows an
embodiment where screw 91 is offset from screw 84. In both
embodiments, screw 91 extends through an opening 93 in backplate
22A and an opening 94 in the rear wall 63A of anode 17A (or 16A).
The nut 96 is tightened down on screw 91 and draws anode 17A or 16A
snugly and securely against backplate 22A. A seal 97 may be
provided between anode 17A and backplate 22A, thereby preventing
any leakage between the cathodic compartment and the anodic
compartment. A seal 90, such as a Thred Seal (Trademark of Parker
Seal Company), is provided between nut 96 and wall 63A.
The bipolar cell unit 12B (FIG. 5) includes an anode 17B, a
backplate 22B, and a cathode 16B. The electrode support means 52B
includes an enlongated bar 101 which is secured to cathode finger
46B, for example, by welding. Openings, not shown, are provided in
bar 101 through which cathodic products may pass. A rod 102 which
is threaded at one end is secured to bar 101, such as by welding.
The rod 102 extends through opening 103 in backplate 22B. A nut 104
is threadedly engaged with rod 102, thereby securing cathode 16B in
place. Preferably, a seal 106 such as a Thred Seal (Trademark of
Parker Seal Company) is provided between nut 104 and backplate 22B.
The seal 106 prevents leakage of catholyte through backplate 22B to
its anodic side. The rear wall 63B of anode 16B in this embodiment
is a double wall including wall portions 107 and 108. The wall
portion 107 may be of steel but the wall portion 108 must be of an
anodically-resistant material such as titanium. The wall portion
107 has an opening 109 through which rod 102 extends. A nut 111
secures a wall portion 107 to the backplate 22B. The side walls 61
B and 62B extend over wall portion 107 and are welded thereto. A
screw 112 extends through opening 113 in wall portion 108. The
screw 112 may be threadedly engaged in a suitable opening in rod
102. Alternatively, the screw 112 may be off set from rod 102,
threadedly engaged in a suitable opening in wall portion 107, or
screw 112 may be threadedly engaged in a nut disposed on the side
of wall portion 107 toward backplate 22B. The screw 112 thereby
secures wall portion or cover 108 to wall portion 107. A seal 114
is disposed between wall portion 108 and wall portion 107 and
prevents arolyte from contacting wall portion 107. A further seal
116 is disposed between anode 16B and the backplate 22B.
The bipolar cell unit 12C (FIG. 6) includes an anode 17C, cathode
16C and backplate 22C. The anodes 17C and cathodes 16C are secured
to the backplate 22C by the electrode support means 52C. The
electrode support means 52C includes an elongated bar 121 which is
welded to the finger cathode 46C. Bar 121 has openings therein for
passage of cathodic products. A rod 122 is secured to bar 121 and
extends through an opening 123 in backplate 22C. The electrode
support means 52C further includes a nut 124 which is threadedly
engaged with rod 122. The nut 124 serves to hold the cathode 16C in
spaced relationship to the backplate 22C. A nut 125 is threadedly
engaged with rod 122 thereby securing cathode 16C to the backplate
22C. A seal 126 may be located between nut and backplate 22C. The
anode 17C includes side walls 61C, 62C, and rear wall 63C. The rear
wall 63C includes an opening 128 through which extends a screw 129.
Screw 129 is threadedly engaged in rod 122 and secures the anode
17C to the backplate 22C. The screw 129 draws rear surface 127 of
wall 63C into electrical contact with rod 122 and nut 125. Seals
131 and 132 are provided to prevent leakage of anolyte into contact
with parts which are of materials not resistant to the anolyte,
notably steel parts such as rod 122 and backplate 22C.
The cell unit 12D (FIG. 7) includes an anode 17D, cathode 16D, and
backplate 22D. The electrode support means 52D in this embodiment
comprises an elongated bar 141 which is welded to the cathode
finger 46D, the electrode support means 52D further includes the
connecting block 142 which is attached to bar 141 such as by
welding. Th block 142 extends through an opening 143 in backplate
22D. The anode 17D is secured in place by screw 144 which extends
through opening 146 in rear wall 63D and is threadedly engaged in
opening 147 in block 142. The block 142, if desired, may be welded
to the backplate 22D.
The electrode support means 52E of bipolar cell unit 12E (FIG. 8)
includes an elongated bar or current gatherer 151 which is welded
to the cathode finger 46E. The electrode support means 52E further
includes a rod 152 which is welded to the bar 151 and extends
through an opening 153 in backplate 22E. A nut 154 is threadedly
engaged with rod 152 thereby holding cathode 16E in place. A seal
156 may be provided between nut 154 and the backplate 22E. The rod
152 extends through an opening 157 in the rear wall 63E of anode
17E. A threaded cap 158 is threadedly engaged with rod 152 thereby
holding anode 17E in place. A seal 159 is provided between cap 158
and the rear wall 63E. A seal 160 is provided between the anode 17
E and the backplate 22E.
The electrode support means 52F of bipolar cell unit 12F (FIG. 9)
includes an elongated bar 171 which is welded to cathode finger
46F, a block 172 which is welded to bar 171 is threaded to that the
nut 173 may be tightened against the rear screen 47F. The block 172
has a portion 174 of reduced diameter which extends through the
opening 176 in the backplate 22F. The block 172 has a shoulder 177
which abuts against the backplate 22F thereby holding the
backscreen 47F at a point spaced from backplate 22F. The screw 178
secures anode 17F to the backplate 22F. The screw 178 extends
through opening 179 in rear wall 63F and is threadedly engaged in
opening 181 in the block 172. The screw 178 holds the meeting
surfaces of wall 63F and block 172 in electrical contact with one
another. A seal 182 is provided between the head of screw 178 and
wall 63F and a seal 183 is provided between anode 17F and backplate
22F. The seals 182 and 183 may be of EPDM rubber (ASTM designation)
which has excellent resistance to corrosion and remains resilient
even after extended periods of cell operation at high
temperatures.
The bipolar cell unit 12G (FIG. 10) has an electrode support means
52G including a current gatherer 191 which is welded to the cathode
finger 46G. A threaded rod 192 is welded to the current gatherer
191. A nut 193 is threadedly engaged with rod 192 and securely
holds the backscreen 47G against electrode finger 46G. A nut 194 is
threadedly engaged with rod 192 and holds the cathode 16G in a
position spaced laterally from the backplate 22G. The rod 192
extends through opening 196 in the backplate 22G. The anode 17G in
this embodiment is a single sheet or plate-like element, i.e., in
contrast to the embodiments illustrated in FIGS. 2 to 9, includes
only one side wall comprised of a plate of titanium or a titanium
group metal having an electroconductive surface on both sides
thereof. This side wall 61G, when the cell is operating, is
disposed substantially equi-distant between opposed cathode fingers
of each cathode of the appropriate cathode pair (not shown) of the
adjacent cell unit. The anode 17G further includes a rear wall 63G
which is welded to anode side wall 61G. The rear wall 63G has an
opening 197 through which a screw 198 extends for threaded
engagement in an opening 199 in the rod 192. The screw 198 securely
holds the anode 17G in place against the backplate 22G.
In the embodiment illustrated in FIG. 10, the anode component of
the cell unit is in the form of a thin anodicallyresistant
vertically disposed sheet or plate having substantially parallel
flat surfaces of appropriate electroconductive material upon which
anolyte products of electrolysis (e.g., chlorine) form. When
assembled in the electrolytic cell, each thin anode plate (of which
there are a plurality in each cell unit) is interleaved between,
but spaced laterally of opposed cathode fingers of adjacent
cathodes extending outwardly from the adjacent cell unit.
The vertical edge of the sheet-like anode terminates parallel to
and spaced from the backplate of the adjacent cell unit. The
lateral distance (spacing) from this anode edge to the backplage
cathodic face will be substantially greater (at least three times
greater, but rarely more than 20 times) than the space between the
anode face and opposed cathode fingers (electrode gap), thus
favoring current flow between opposed cathode and anode faces. A
typical lateral space will be from 2 to 8 inches.
These anodes desirably are quite thin, usually considerably less
than one inch in thickness (distance between the anode's parallel
faces), notably about 0.5 inches or less (rarely less than 0.2
inch). When the sheet-like anodes are of mesh, thickness as herein
intended considers the mesh as if it were a solid plate.
The cell unit 12H (FIG. 11) includes an electrode support means 52H
having a current gatherer 211 which is welded to the finger cathode
46H. The current gatherer 211 may be a discontinuous bar, thus
permitting cathodic products to pass from the finger to the space
between the screws 47H and plate 22H. A threaded rod 212 is welded
to the current gatherer 211. A nut 213 is threadedly engaged with
rod 212 for purposes of holding the backscreen 47H securely against
the fingered electrode 46H. The electrode support 52H further
includes a nut 214 for controlling the extent to which the threaded
rod 212 extends through the opening 216 in the backplate 22H. Ribs
223 are provided for spacing scren 47H from plate 22H. The ribs 223
may be of steel or other material chemically resistant to the
catholyte conditions and are welded to plate 22H. The screen 47H is
slightly flexible, thus permitting adjustment of rod 212 with
respect to backplate 22H. The anode assembly 17H in this embodiment
carries a narrow anode member 217, including a pair of side walls
61H and 662H which are welded to the rear wall 63H. A screw 219
extends through opening 221 in rear wall 63H and is threadedly
engaged in the opening 222 in rod 212. The screw 219 securely
retains the anode 17B against the backplate 22H and maintains
excellent electrical contact between the meeting surfaces of wall
63H and rod 212.
The cell unit 12I (FIG. 12) includes cathodes 16I and anodes 17I
which are mounted on a backplate 22I such as by electrode support
means 52I. The cathodes 16I may be constructed substantially like
cathodes 16 shown in FIGS. 1 and 2. However, in this instance the
rear portions 225 and 226 of side walls 45I and 50I are flared
thereby providing fingers 46I with a wider base for resting against
back screen 47I and permitting flexing of cathode 16I during
adjustment of the block 228 with respect to backplate 22I.
The electrode support means 52I includes a current gatherer 227
which is an elongated bar having openings therein through which
cathode products may pass. The current gatherer 227 is welded to
side walls 45I and 50I of cathode 16I. The electrode support means
52I includes a threaded rod 228 which is welded to the current
gatherer 227 and extends through opening 229 in backscreen 47I and
opening 230 in backplate 22I. A nut 233 is threadedly engaged with
rod 228 and retains cathode finger 46I securely against backscreen
47I. Nut 234 is threadedly engaged with rod 228 and holds the
cathode 16I, including backscreen 47I and finger 46I, securely
against backplate 22I. A screw 236, preferably of titanium metal,
extends through opening 237 in rear wall 63I of anode 17I and is
threadedly engaged in opening 235 in rod 228. A titanium thread
seal washer 238 is provided between anode 17I and backplate 22I. A
plurality of spacer bars 241 are provided between backscreen 47I
and backplate 22I. The bars 241 hold the cathode 17I spaced from
the backplate 22I and may be constructed of any material which is
corrosion resistant in a cathode environment, for example, steel or
copper. The ring nut 234 adjusts the distance rod 228 extends
through plate 22I, thus assuring proper contact between the
surfaces of wall 63I and rod 228. Furthermore, use of ring nut 234
permits use of a smaller screw 236 than would otherwise be
necessary. The rear wall 63I may be a continuous wall the full
length of the anode 17I or may be comprised of a plurality of
discontinuous wall portions, for example, one such wall portion
being provided for each electrode support means. Alternatively, all
of the anodes 17I for a cell unit could be mounted on a single rear
wall 63I.
Furthermore, wall 22I could serve as the rear wall of anodes 17I in
which case wall (backplate) 22I may ideally be a titanium clad
steel plate and anode walls 61I and 62I may be welded thereto. Wall
22I thus is provided on its anodic face with a titanium surface (an
electroconductive material chemically resistant to the anolyte
environment) and on its cathodic side with an iron surface (an
electroconductive material resistant to the catholyte environment).
Although, because of availability, cost and structural strength,
backplates of titanium clad steel are specially preferred,
backplates may have surfaces of other materials meeting certain
electrical and corrosion resistant standards.
In lieu of a steel cathodic surface, the backplate may be of other
adequately electroconductive catholyte resistant materials such as
ferrous metals (iron, alloys of iron including various steels),
nickel, copper, gold, cobalt, platinum, silver lead and chromium,
or mixtures thereof. Useful metals for the cathodic faces thus are
those which do not readily form hydrides (by reaction with atomic
hydrogen in the catholyte) and which are electroconductive. Metals
whose resistivity is less than 50 microhms per cubic centimeter (at
20.degree.C.) are thus useful, while those with resistivities
greater than 1 but less than about 20 microhms per cubic centimeter
are especially useful.
On its side exposed to the anolyte, the backplate's anodic surface
may be of other so called valve metals or precious metals such as
tantalum, niobium, platinum, zirconium, ruthenium, palladium,
rhodium and irridium. The surface of titanium actually exposed to
anolyte has thin protective titanium oxide film which usually
develops in situ if not preformed. These metals and oxides are
resistant to the anolyte conditions to which they are exposed, and
particularly are resistant to chlorination, for example. Other
oxides which have satisfactory corrosion resistant properties
include magnetite and lead oxide.
As indicated, the respective anodic and cathodic sides of the
backplate are of different materials, the most exemplary
combination of which is titanium (on the anode side) and steel (on
the cathode side) in the form of a single sheet, e.g., titanium
clad steel. It is however possible to use a structure in which a
suitable electroconductive metal is sandwiched between the titanium
and steel, such as a copper sheet having titanium on its anode side
and steel on its cathode side.
The anodes 17I each include side walls 61I and 62I which are
laterally spaced from one another and which may be secured such as
by welding to a rear wall 63I. The side walls 61I and 62I of anode
17I are diverging rather than converging. In other words, the space
(and lateral distance) between walls 61I and 62I is less adjacent
rear wall 63I than it is at the edge opposite rear wall 63I. The
side walls 61I and 62I may have stiffening rods 242, if desired.
The stiffening rods 242 may be welded to the outer sides of walls
61I and 62I. In this embodiment, the cathode finger 46I lies
between the side walls 61I of one anode wall pair and 62I of the
wall of the next adjacent anode. For further strengthening
providing improved electrode spacing, the side wall 61I of one
anode finger 17I may be secured at the forward edge thereof to the
side wall 62I of that next adjacent anode finger, such as by
connector 243. The connector 243 in this instance includes a screw
244 which extends through an opening in wall 61I and is threadedly
engaged in nut 245. It is possible to bring the forward edges of
the anode walls substantially into touching contact by tightening
this connecting means. The nut 245 is secured to side wall 62I such
as by welding. The connector 243 alternatively may be a metal
clip.
Although the walls of each anode diverge as they extend outwardly
from rear wall 63I in this configuration, laterally spaced walls
62I and 61I each from one of two adjacent anodes which are
interposed between adjacent cathode fingers converge as they extend
towards cathodic backscreen 47I.
Cell 10J, shown in FIG. 13-15 is a further embodiment of the
present invention. Cell 10J is constructed similar to cell 10 of
FIG. 1. Cell 10J has a cell container or frame 21J which, if
desired, may be identical to frame 21 shown in FIG. 1. Cell 10J
further includes a plurality of wedge-shaped cathodes 16J and
anodes 17J which are mounted on backplate 22J by an electrode
support means 52J. In this embodiment, the thin edge 255 of
wedge-shaped electrodes lies in a horizontal plane or, in other
words, the thin edge of the electrodes extends perpendicular to the
vertical backplate 22J. The cathode 16J has a pair of side walls
45J and 50J, a bottom wall 252, and an outer end wall 253. The
walls 45J, 50J, 252 and 253 may be constructed of screen. The walls
45J and 50J, as shown in FIG. 14, converge upwardly. If desired,
baffles 254 (FIG. 13) may be provided in cathode 16J to force
product gases from the cathode wedges into the space between the
backstream 47J and the backplate 22J. The anode 17J includes a pair
of side walls 61J and 62J which are preferably constructed of
foraminous plates. The anode 17J further includes a backplate 63J.
The electrode support means 52J, shown in detail in FIG. 15, is
comprised of a current gathering bar 256 which is secured to walls
45J and 50J adjacent the open end of cathode 16J, for example, by
welding. The electrode support means 52J further includes a rod 257
which is secured to bar 256 and extends through openings in the
backplate 22J and rear wall 63J of anode 17J. A nut 258 is
threadedly engaged with rod 257, thereby securing anode 17J and
cathode 16J to the backplate 22J.
The anodes 17 thorugh 17J have generally been described as being
constructed of a titanium group metal with the walls 61-61J and
62-62J being solid plates and the titanium plates being platinized
on the side adjacent the cathode fingers 47-47J. The anodes 17-17J
may alternatively have side walls constructed of a pervious,
anodically-resistant plate, for example, of rod material, screen,
expanded metal mesh, perforated plate or louvered plate. The
pervious plate may be of titanium metal. In one preferred
embodiment, the pervious titanium plate has an electroconductive
surface, for example, of platinum, only on the side remote from the
cathode fingers. By so doing, the titanium metal forms a
non-conductive titanium oxide coating adjacent the diaphragm and
gas evolution during cell operation takes place on the back side of
the side walls, thus substantially reducing gas blinding and
turbulence in the diaphragm. Both sides (surfaces) of the perforate
anode may be provided with an electroconductive surface. When this
is done, it is usually the better practice for the
electroconductive surface facing the diaphragm to be thicker (1.5
to 5 times) than the coating on the other anode surface facing away
from the cathode and toward the hollow of the anode.
Chlorine which evolves on the front side (and thicker
electroconductive surface) of the anode wall nevertheless can move
through the openings in the perforate anode walls into the hollow
anode space. Louvered, perforate or expanded metal mesh or like
materials with openings facilitate such gas movement and also
permit anolyte to move from the electrode gap through the openings
into the anode hollow. With the louvers (or like openings) tilted
or fluted upwardly and inwardly toward the hollow space, gas and
liquid movement through the anode walls has imparted thereto an
upward movement component.
Furthermore, the side of the cathode backscreen and cathode fingers
toward the anode may be electrically insulated such as with a
rubber coating. By so doing, the cathodic gas products would be
produced on the back side of the cathode which would further reduce
gas blinding and back migration of caustic soda. This arrangment
would provide a highly-efficient cell, particularly if the porosity
of the diaphragm is slightly increased and the cell is operated at
a high brine flow rate and a high current density such as in excess
of 150, preferably in excess of 200, amperes per square foot of
cathode surface, as defined by length and breadth measurements of
the cathode. The cell of the present invention, especially when
using wedge-shaped foraminous anodes and cathodes, operates in a
very efficient manner when the anode-to-cathode gap (electrode gap)
is near zero, for example, generally less than 1/2 inch, typically,
1/8 to 1/4 inch and, preferably, the anode is directly against the
diaphragm.
Although the present invention has been described with reference to
specific details of particular embodiments thereof, it is not
intended thereby to limit the scope of the invention except insofar
as the specific details are recited in the appended claims. For
example, one skilled in the art may replace the nonwoven asbestos
fabric with a permionic membrane .
* * * * *