Note: Descriptions are shown in the official language in which they were submitted.
This invention concerns, generally, an electrolyti
I cell with anocles cover-ed by an ion-selective membrane whercin
the cathode is formed by a static, porous bed of small con- I
' ducting particles, extending between the walls of the cathodej
compartment and the walls Or the membranes and pressing said ¦
membranes against the anodes. In particular, the invention
relates to a cell for the electrolysis Or aqueous solutions Or;
alkali metal halides, although it may be used for carrying
out other electrolysis reactions, such as the electrolysis
of other salts which undergo decomposition under electrolysis
conditions, ror the electrolysis of IICl solutions, the
; electrolysis of water, organic and inorganic oxidations and
reductions, etc.
~ecent]y, electrolytic cells have been developed
which use ion exchange mernbranes instead of the more
; traditional asbestos diaphragms)especially for brine electro-
~ lysis. Although they are electrolytically conductive under
`i Iloperating conditions, such rnembranes are substantially
~- liMpermeable to the hydrodynamic flow of liquids and gases.
, In operation, the alkali metal halide brine is introduced
- into the anodic compartmentl where gaseous halogen develops
on the surfaces of the anode. The alkali metal ions are
select~ively transported across the cationic membrane into
~the cathodic compartment, where the a]kali metal ions combine
1 25 i with the hydroxyls generated on the cathode by electrolysis
of the water to form alkali metal hydroxide.
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Cells wlth cationic membranes offer numerous
~advantages over the conventional diaphragm cells. They perrni ;
' the production of relatively pure solutions of alkali metal
' hydroxide, not diluted with brine as in the case of the
porous diaphragms, where subsequent separation and purifica-
tion of the hydroxide is required, and also permit a more
efficient and simplified operation of the electrolysis
process.
, To fully utili%e the ch~iracteristics of the non-
porous membranes, it is desirable to reduce to a minimum
' the distance between electrodes (i.e., the interelectrodic
gap), which reduction has a remarkable effect on the opera~
ting voltage and hence on the energy efficiency of the
electrolytic process.
, Commercial membranes are sensitive to current I -
density, which must be maintained within certain optimal
~ limits for efficient operation of the membrane. The current ¦
i density should be ncarly constant over the entire surface,
,,so as to avoid the occurence of mechanical and electrical
' stresscs, which would irreversibly damage the membrane.
In the known membrane cells~ the optimation Or these
parameters depends to a large extent on the structural
tolerance limits and, in view of the size of the electrode
surfaces in the commercial cells, relative to the ever
25 l smallcr electrode spacings (of the order of some millimeters)
the inevitable deviations from the most exact parallelism
between the anodic and cathodic surfaces cause more or less
marked var~atiol-s of the urrent density ove~ tho surlaoe o
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of the membr~ne. As a re!,ult., past ~forts to assure a correct curren~ denslt~
locally, on various areas o~ the membrane, have not been successful.
In one partlcular aspect the present invention provides an
electrolysis cell comprising an anode compartment containing an elec-troly-te per-
meable anode and a cathode compartment containing a cathode separated by an ion
exchange membrane supported on the electrolyte permeable anode, means to impress
an electrolysis current on the cell, means for introducing catholyte to the cathode
compartment, means for introducing catholyte to the cathode compartment, means for
removing spen-t anolyte and electrolysis products from the anode compartment and
means for removing spent catholyte and electro~ysis products from the cathode
compartment, the cathode being a porous static bed of electrically conductive
catholyte-resistant particulate filling material which presses the membrane
against the anode.
In another particular aspect the present invention provides an
electrolytic cell comprising a container of cathodically resistant metal, a valve
metal top on said container electrically insulated from said container, at least
one tubular valve metal anode connected to and extending from said top sub-
stantially to the bottom of said container, perforations through a portion of the walls
- of said anode inside said container and an imperforate portion of said anode extending
from just below the top of said container to said valve metal top, said anode being
open at both ends, an ion permeable membrane on the perforated walls of said anode,
a porous, static bed of electrically conductive particulate cathodic filling material
between said membrane and the walls of said container, openings into the tubular
anode through the bottom of said container, means to feed electrolyte into the
bottom of said tubular anode, means to elec~rically insulate said anode at the top
and bottom from said container, means to convey positive electric current to said
anode, means to convey negative electric current from said container, means to
conduct gaseous products produced on said anode and electrolyte out of said
container, means to conduct gaseous cathodic products produced in said container
out of said container, means to lntroduce liquid into the cathodic compartment of
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cm/
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said container between said mcmbrane and the w~l.ls of s~id con-tainer and rneans
to convey liquid cathoclic products out oE said container.
In yet another particular aspect the present invention provides
an electrolysis cell comprising a cathodic container, a valve metal cover for said
container, a plurality of tubular valve metal anodes with walls permeable to liquids
inside said container and secured to ~he cover of said container, tubular ion exchange
membranes on the outer surfaces of said tubular anodes delimiting and hydraulically
separating the cathodic compartment inside said container from the anodic compartment
inside said tubular anodes, a bottom~closure for said container means in said closure
forming hydraulic connection between the interior of said tubular anodes and an
electrolyte, distributor external to the cathodic container, a static, porous bed
of conductive particulate filling material resistant to the cathodic conditions
in said cathodic container to a height just below the cover of the container,
pressing said membranes against said anodes, said static, porous hed being in
electrical contact with the inner walls of the cathodic container and functioning
as the cathodic at the surface adjacent to said membranes, a tank for receiving
impoverished electrolyte and anodic gas connected with the upper ends of said
tubular anodes, means for passing electrolysis current between said anodes and
the cathodic of the cell and means for recovering gaseous and liquid products
from the cathodic compartment.
In yet another particular aspect the present invention provides
the method of reducing the interelectrode g~p in an electrolysis cell having an
anode compartment, a cathode compartment, a porous and permeable anode in the anode
j compartment and a cathode in the cathode compartment, an ion exchange membrane
i between the anode and the cathode compartment and means to pass an electrolysis
current through said cell, which comprises pressing said membrane against said
porous anode surface by a porous, static bed of conducting particulate filling
material between the walls of sald cathode compartment and said membrane and con-
ducting electric current through said anode, said membrane and said particulate
~ ~illing material between said membrane and the walls of said cathode compartment.
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In a further particular aspect th~ present lnvention E~rovldes
an electrolysis cell havincl an anode compartment and a cathode compartment,
electrodes comprising an anode and a ca-thode, means to pass an electrolysis
current between said anode and said cathode and an ion exchanye membrane between
said electrodes, the method of reducing the interelectrodic gas to approximately
- the thickness of said membrane, which comprises placing said membrane against one
of said electrodes, pressing said membrane against said electrode by a porous,
static bed of conduc-ting particulate filling material between said membrane and the
other electrode, and passing the electrolysis current bctween said electrodes
through said static bed.
In still a further particular aspect the present invention provides
an electrolytic cell having electrocatalytically coa-ted valve metal anodes, a cathode
and ion selective cationic membranes substantially impermeable to the flow of liquids
and gases therethrough, between the anodes and cathodes, the method of maintaining
; the current density substantially constant and of reducing mechanical and electrical
stresses on said membranes which comprises applying said membranes on said anodes,
substantially filling the space between the membranes and the electrically conducting
walls of the cathodes with, porous cathodic filling material in the form of chips,
balls, beads, cylinders, Raschig rings, metallic wool or other particles or strands
pressing said mbranes against said anodes, passing an electrolysis current from
said anodes through said membranes and said filling material to the electrically
conducting walls of said cathodes and collecting the anodic gases and liquids
separate from the cathodic gases and liquids.
Various other advantages of the invention will become apparent
from the description which follows.
The preferred embodiment of the cell of this invention comprises
a cathodic container of steel or other conductive material resistant to corrosion
in the catholyte environment which is closed at the upper end by a plate or cover
' of titanium or other valve metal, which is passivatable under conditions of
anodic polarization and which has at least one but preferably a serles of tubular
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anodes welded into holes i.n the tltanlum cover plate which extend almost the
entlre depth of the contalner, with the walls of the tubular anodes (except the
upper part of the anode walls near the welds to the titanium plate) perforated
so as to be permeable to liqui.ds and gases.
The anodes are dimensionally stable and, -typlcal].y, are of
titanium or other valve metal, coated on at .Least part of the active surface with
an electroconducting, electrocatalytlc deposit of material resistant to the anodic
conditions and not passivatable, preferably a deposit of noble metals such as
platinum, palladium, rhodium, ruthenium and
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iridium, or oxides or mixed oxides thereof. The lower ends fof the tubular anodes are closed by plugs Or inert, pre- f
ferably plastic, material provided with coaxial threaded
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holes. The permeable walls of the tubular anodes are com-
: pletely covered externally by the membranes so as to delimit
the anodic compartment inside the tubular anodes.
The lower end of the cathode container is closed
. li
. by a plate, prcferably of inert plast:ic material, and is
;~ provided with means for feeding brine or ot}ier anolyte into
. 10 the interior of the various tubular anodes, typically by
- means of inlets Or plastic material whose flanges form a
. seal against the bottom plate of the container. The anolytel
is fed through tubular connectors screwed into the th:readed
holcs Or the closing plugs of the tubular anodes.
fl The container in the preferred embodi.rnent is
!i provided with an outlet in the upper part for the emergence
, of the cathodic gas, with a discharge opening in the lower
Il part for discharge of the catholyte and with an inlet pipe
¦~l for recycling the dilute catholyte or ~rater into the
I., cathodic c.ompartment. The anodes welded to the cover of the fi
. container comrnunicate through the holes in the cover with a ¦
. c`namber above the container where the anodic gas separates
. from the electrolyte, escapes from an outlet and flows to a ¦
il gas recovery system and the electrolyte is recycled to a
I' resaturation systenn before reintroduced into the cell. . .
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The cathode of the cell consists of a porous,
static bed of loose, conducting cathodic materlal in the
form of chips, beads, balls, cylinders, Raschig rings,
metallic wool or other particles with which the container is¦
completely filled to a height corresponding at least to the ¦
height of the perrneable walls of the tubular anodes covered
by the membranes. The filling of cathodic material is in
contact with the inner walls of the container and with the
outer surfaces of the membranes on the various tubular
anodes and presses against the membranes. The conductive
cathoclic fil]ing material may be graphite, lead, iron,
nickel, cobalt, vanadiurn, molybdenurn, zinc, or alloys
thereof, intermetallic compounds, compounds of hydridization,
carbid-ization and nitridization of metals, or other materials
i having good conductivity and resistance to the cathodic
conditions.
l Materia]s exhibiting lo~ hydrogen overpotential
- l, such as iron, nickel and alloys thereof are particularly
1 suitable for brine electrolysis. On the contrary, for
' instances, for the reduction of FeIII to FeII in an acidic
sulfate catholyte solutlon using an anionic rnembrane and
evolving oxygen on the anode, particulate materials having al -
high hydrogen overpotential such as lead and lead alloys
i are preferable. The cathodic filling material may also com-l ;
~i prise p]astic, ceramic, or other inert, non conductive,
material coated with a layer of the electrically conductive
and cathodically resistant materials mentioned.
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The titanium plate or cover to which the tubular
' anodes are welded is ~Lnsulated from the cathod:Lc compartment
' by an insulating gasket. It is connected to the positive
terminal Or the current distribution network, and the
,; cathoclic compartment is connected to the negative terminal ¦
of the distribution network.
' The mass of the cathode filling is cathodically
polarized and functions as cathode and the porosity of the
static bed of cathodic material permits rapid evacuation of '
,' the cathodic gas and contributes to protect cathodically the,
,; inner walls of the cathode container. ! ~r
The electrode spacing is reduced to little more
than the thickness of the membranes by the local def'lection
~ of the electrolytic current flux lines on the geometrically
,, undefinecl surfaces of the cathode material, rcpresented by
, the particles of the bed directly adjacent to the surfaces
of the membrarles, and on the geometrically undefined sur-
' faces of the meshes of the permeable walls of the tubular
¦ anodes on which the membranes are applied.
I The spacing betueen the cathodic filling material
; ' and the anodes remains substantially constant throughout I
the electrolysis process. ¦
This conriguration of the cell produces excellent '
uniformity of the current density on the entire electrodic
', area, without s~ldden localized differences which would tend .`
¦ll to deteriorate the membranes by the creation of mechanical ,,
and electrical stresses.
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Another advantage of the preferred embodiment of
the cell of this inventiorl, which comprises a plurality of
tubular anodes, is its compactness, as the ratio between
` the extent of the electrode surfaces and the volume occupied
by the cell is much greater than in prior cornmercial
membrane cells~ ¦
~he drawings of the preferred embodiment illustrate
the anodes as circular tubes in a rectangular container,
which is preferred because of the greater uniformity of the
~ current density and lower cost. It will be understood,
ho~ever, that anodes tubes of other shapes, such asoval,
rectangular, hexagonal and other polygonal shapes, may be ' -
used and are within the scope of the word "tubes" as used
herein and that the cel.l container can be rectangular,
cylindrical or other shapes. A less prererred embodiment
of the invention is a cyli.ndrical container housing a single,
concentric cylindrical anode; however, according to this
ernbodlment a number of cells are necessary to attain the
" desired capacity. It wi]l also be understood that while
,' the cell of this :invention is described in connection with
the production of chlorine, it may be used for electrolytic
processes producing other products.
i In the accompanylng drawings, which illustrate
the preferred ermbodiment of this invention, Fig. 1 ls a
25 !~ sectional view and Fig. 2 is a sectional plan view along
line 1-1 of Fig. 1, with parts above the section line
illu erate~ n hlsl~ e~.
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As illustrated in Fig. 1, the cell comprises a
rectangular cathodic container 1 of steel or nickel, or
alloys thereof, or of other conductive and cathodicallY
resistant metal. A cover 2 of titanium or other anodically
passivatable valve metal, bolted to the container 1, closes
the container at the top. An insulating gaslcet 3 is
provided between the cathodic container 1 and the titanlum
cover 2. Tubular anodes 4 of titanium are welded in holes
; in the cover 2 and extend above the cover as illustrated.
The walls of tubular anodes 4 are provided with holes or
.
; other perforations, which begin at a short ~istance below
the cover 2 and extend to the bottom of the anodes ll. The
perforated portions 6 of the anodes may be formed of
reticulated or expanded titanium sheet welded to the
imperforate top section 5, or formed integrally therewith.
The surface of the perforated portions 6 o~ the tubular
anodes 4 is suitably coated with an electrocatalytic deposlt,
which is non-passivatable and resistant to anodic condltions
typically containing noble metals or oxides of noble metals.l
The tubular anodes are closed at the lower end by a plug or ¦
closure 7 of tltanium welded to the lower end of each anode
4, or, preferably, as indicated in Fig. 1, Or chemically
resistant plastic material, such as PVC or the liXe~ provided
uith a coax:ial, threaded hole 7a. -¦ ;
The cationic membrane 8, preferably tubular, is
slipped over the anodes 4 and fastened to the imperforate
top of the anodes and to the outer cylindrical surface of
the plug 7 by means of bands of plastic material 9. This
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Stelling i5 particlllarly easy and forms a perfect hydraulif
seal between the membranes and the perrorated sections of
the anodes 4 which is dirficult to obtain in conventional
filter press cells.
i The cationic membrane 8 is preferably permeable to
cations and impermeable to the hydrodynamic flow of the
liquid and gas. Suitable materials for themembraneS are
fluoridized polymers or copolymers containing sulfonic
groups. Such materials are sufficiently flexible and are
produced in tubular form by extrusion or hot gluing of
flat sheets. The thickness of such membranes is in the
order Or one-tenth of a m:illimeter.
The container 1 is turne(l 180 to facilitate fill-
ing and is filled with the cathodic material 10. The
I container is then closed with a rectangular plate 11 per~
forated at the base of each of the anodes 4 and, preferably,¦
Il of inert plast~c material. A rectangular brine distribution, -
¦~ box 12, also Or inert plastic material, is welded to the
: !i plate 11 and is closed by a closure plate 13 equipped with
l a brine inlet opening 14. A ~asket may be provided between
!j the plate 11 and the flanged bottom of the rectangular
container 1. The flanges Or the plate 11 may be bolted to
the bottom flange on container 1 and the closure plate 13
~I may be bolted to the bottom of the distribution box 12. The
I brine distribution box is connccted to the interior of the
~ i~ anodes 4 by means Or tubular connectors 15, which are
1 1l¦ flanged at one end and threaded into the threaded holes 7a
~ o~ the closure plu~s 7 e~ls or kasketk 16 aro pro~1ded
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between the rlanges on the connectors 15 and the brine
; distribution bo~ 12.
The cathodic compartment is filled with particulat~
material to about the top of the permeable sections 6 of the
' tubular anodes 4~
The cathodic container is provided, near the upper
part, at a level higher than that Or the particulate bed 10, !
with one or more outlets 17 for hydrog~en and, in its lower
part, with at least one adjustable gooseneck outlet 18 for
' i
. 10 discharging the ca-tholyte.
A distribution or spray tube 24, above the level of
theparticulate material 10, extends hori~ontally over sub-
stantially the entire length of the container 1 and is
I equippcd ~lith a series of holes so as to permit the addition
l Or water or catholyte to the cathodic compartment for dilut-
I ing and regulating the conccntration of the alkali metal
; I hydroxide produced in the cathode compartment.
Preferably, water is continuously added into the
I cathodic compartment through the distribution tube 24, in
, order to dilute the hydroxide formed at the cathode and
maintain the hydroxide concentration Or the catholyte erfluer t
, rrom the cell within 25% and 43% by weight.
' Each Or the tubular anodes ~1 is connected at the
I top to a rectangular tank 19 extending over the entire top
li f the cell container 1. The electrolyte level in the tank
19 is maintained constant by a gooseneck discharge tube 20
for the electrolyte. The electrolyte discharged rrom tube 20
, is sent to the resaturation system before being recycled
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into the cell through the elect~olyte inlet 14.
The halogen produced on the anodes separates from
the electrolyte in tank 19 and escapes through outlet 21.
, The plate or cover 2 to which the tubular anodes 4
1 are welded is directly connected to the positive terminal Or
the electric power supply by means o~ the connection 22 and
the cathodic container 1 is connected to the negative
terminal by means of connection 23.
Fig. 2 is a sectional view along the line 1-1 o~
Fig. 1, with the elements Or the cell described with refer-
ence to Fig. 1 indicated by the same numerals. The locatlon
o~ the distribution tube 24 is indicated by bro'~en lines ¦
above the level of the particles Or cathodic material 10 in
the cathode container 1.
~i ~ The cell shown comprises six tubu]ar anodes in a
rcctangular casing, but it wi]l be understood that the
nunber o~ anodes may be varied in the transversè direction,
j, that more rows o~ anodes may be used, that the shape of the ¦
Il cell and the anodes may be di~rerent from that illustrated
1 and that other modifications and changes May be made within ¦
the spirit and scope o~ our invention.
The extent of the cylindrical sur~aces of the
tubular anodes 4 is very large relative to the volume of
;~ the container 1, which permits high production rates in
!l a compact cell, at substantially equal current density
; Il' throughout the cell when compared to the cells commonly used
¦, commercially. In operation, concentrated brine (120-310
- ¦, g/ltr) o~ NaCl, ror example, is fed through the inlet 14 int
I distribution b~x 12 tDd rises throu~h each ~r the tubular
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anodes 4, on the electrocatalytically coated surfaces of
which chlorine forms. The sodium ions traverse the catlonic¦
membrane and combine with the hydroxyls released at the
cathode by electrolysis of the water, forming sodlum hydr- ¦
', oxide. The chlorine rises through the electrolyte contained
. j inside the tubular anodes 4 and into tank 19, where it
' separates from the liquid and escapes through the outlet 21.
The rising chlorine bubbles provide a rapid upward flow of
the electrolyte in the tubes 4.
The impoverished brine flows through the constant
level outlet 20 and is recycled to the resaturation system , ~r
before being reintroduced into the cell through the inlet 14.'
The.hydrogen released on the surfaces of the porous
,; cathode bed adjacent the rnembrane 8 rises through the
1~ paJticle bed 10 and collects in the upper space of the
cathodic container, whence it escapes through the outlet 17.
The sodiurn hydroxide solution is discharged through the
adjustable gooseneck 18. The adjustable gooseneck 18 .
' maintains the level.of the catholyte at substantially the
n same level as the top of the cathodic bed 10.
The catholyte may be cycled through a recovery
system for the sodium hydroxide located outside the cell
and t4e effluent~ dilute sodium hydroxide solution,rein-
troduced into the cathodic compartment through the distribu-
1 tion tube 24.
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The operat:i.ng temperature may vary between 30 and
. 1000C and is pre~erably maintained at about 85C. The pH
of the anolyte may vary between 1 and 6 and the current
l density may be between 1000 and 5000 ~/m2.
' While the cell and method of this invention have
been described with reference to the illustrative drawings~
it is understood that numerous changes and alternati.ves may
be used within the scope of this invention, that other
. electrolysis processes may be carried out in the a,oparatus
. described, that instead of titanium, other valve metals
; such as tantalum, ~irconium, molybdenum, niobium, tungsten
and yttrium may be used in the construction ofthecell and that~
the static, conductive, particulate material may be used in
other forrns of electrolysis cells.
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