~'7~
r3AClC_ROOND OF Tl-lr INVPNl10
1) Field oE the Inveotion
This invention relates to multipolar electrolytic cells for tlle Use in the
production of oxyhalogen compounds such as sodiurn chlorate by electrolysis of an
all<ali metal halide such as sodium chloride. More specifically, this invention relates to
mul tipolar electrolytic cells including bipolar electrodes which provide excellent
electrolyte solution circulation and high current efficiency in the production of
oxyhalogen solutions.
2) Descrie~rl of the Prior Art
Multipolar electrolytic cells including bipolar electrodes have been used for
10 the production of oxyhalogen compounds since this type of cell is compact and does not
:~ reguire electric current lead and exposed metallic mcmbers connecting tlle busbars to
the intermediate electrodes. By rnaking elec~trical connections to the terrninal
multipolar electrodes only and circulating electrolyte through the compartments
intermediate, the terminal electrodes corrosion and con~amination of the electrolyte
by the evolved gases r eacting with exposed parts connected to the inter-nediate
electrodes is avoided. In the production of sodium chlorate, sodiurn chloricie
' electrolyte is decomposed by electrolytic action to rapidly form ions which
subsequently by a much slower chemical reaction combine to form sodium chlorate. In
~! order to maintain good current efficiency and optimum reaction conditions, the
20 electrolytic cell is generally positioned within a reaction tank. To assure optimum
operating conclitions, the electrolyte should circulate rapidly and turbulently through
the cell and then circulate between tl1e reaction tank and electrolytic cell a~ a rate
which provides minimum time for reaction of the products of electrolysis in the cell
and maximum residence time for completion of the chemical reaction of the products
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in 'the reaction tank. As the electrolyte passes in parallel flow upwardly through the
cell units, It is subjected to electrolysis and hydrogen gas is generated at the cathode
surface of each cell ~mit. The continuous circulation of the electrolyte in the above-
described parallel p~ttern is caused prirnarily by the generation of hycirogen gas
bubbles at the ~cathode surface. During the residence time in `the holding tank, the
~75~L9~
relatively slow chc~-nical reacLlon involYirlg the combination of hypochlorous aci(i ancl
hypochlorite ion accorcling to the equation ~ CIO t OCI = C103 ~ 211CI takes place,
the hypoclllorous ackl and hypoclllorite ions being generated by the relativel~ fas~
electrolytic reaction in the cell unit. Considerable heat is generated during the
electrolysis in the cell units, and to insure ef Eicient performance at the overall
operating conditions and for stability of the materials of construction, it is necessary
to provide for removal of the generated heat. Cooling coils are generally irnmersed in
the reaction or holding tank to maintain suitable operating temperatures.
~ 'Yhen suitable chemical and pH conditions are maintained in the operation
10 of multipolar electrolytic cells, current efficiency is dependent primarily on the rate
of flow of the electrolyte solution through the cell units, the currcnt leakage loss and
holding tank residence time. Maximum current leakage occurs througll the inlets and
~- outlets and, to some extent, around the edges of the bipolar plates of the cell units.
To maintain minimum current leakage, it has previously been considered necessary to
isolate solwtion flow to the cell units be Eore the electrolyte enters the unit by
providing as long a leal<age path through the inlets and ou-tlets ~s is practicable.
Solution inlet and outlet openings have been provided on the sidewalls of the cell
chamber9 and to avoid current leakag~e, the openings ha~e been extended l~y means of
electrically insulating pipes or other conduits communicating with the inlets and
20 outlets at the sidewalls of the cell chamber. ~xtension of the inlets and outlets boy the
.,
i~ use of an insulating block having bored holes communicating wi1h the inlets and outlets
of the sidewalls of a cell chamber is disclosed in U.S. Patent No. 33405,051. To
prevent communication between the adjacent cell compartments and the attendant
leaka~e of electrolyte9 the eclges of the bipolar electro~es have been sealed to the side
and bottom cell walls and also have been located in grooves on the sidewalls.
Althou,,h the above-described prior art cel~ designs have reduced current
leakage, the problems of efficient cell operation have not been satisfactorily resolved.
The use of the inlet and outlet tubes connected to the openings in the sidewalls of the
chamber have restricted circulation of the electrolyte by virtue of the length and
30 small diameter of the tubes. Since a high rate of circwlatlon is required to provide
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both maximum retention time :Ln the reaction tank and sufflcient
cooling of the electro,lyte ~y contact witll the cooling coils,
the use of such tubes reduces the operating and current
efficiency.
SUMMA~Y OF T~E INVENT ON ,
Therefore, it is a primary object of this invention to
provide a multipolar electrolytic cell for manufacture of oxy-
halogen compounds wherein electrical current leakage is
minlmized and current efficiency is optimized.
A further object of this invention is to provide a
multipolar electrolytic cell for production of oxyhalogen
compouncls wherein efficient circulation of the electrolyte
solution and optimum control of the temperature and pH range
of the electrolyte solution can be maintained.
A further object is to provide an economical and
' efficient process for the preparation of oxyhalogen compounds.
These and other objects are accomplished by this ',
~ invention by provision of a multipolar electrolytic cell
'- comprising a cell chamber which is substantially enclosed
and separated into cell compartments by parallel spaced
electrically insulating and solution separating electrolyte
partitions. Bipolar electrodes, preferably horizontally
disposed and foraminous, are positioned in interleaved fashion
in each compartment and arranged to communicate electrically
between the liquid-tight compartments. Vertical bipolar
electrodes may also be arranged in the individual compartments ''
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~ and may be solid or foraminous. Monopolar electrodes mounted
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in each of the two terminal compartments interleaved with
portions of the bipolar electrodes of opposite polarity function
;30 to supply and withdraw electric current to and from the ter-
minal compartments, respectively.
Thus, in accordance with the present teachings, a
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substantially enclosed :Llquld tlght multlpolar electrolytlc cell
is provided. Such cell comprlses a cell chamber havlng a top,
a bottom, a side and end walls wlth a plurality of vertical
parallel electrlcally lnsulating partitions spaced
longitudlnally of the cell and dlvlcling the cell lnto lndlvidual
compartments. At least two electrically insulated substantial:Ly
vertically oriented conduits are provided associated with each
individual compartment, the conduits being adapted to supply
electrolyte to the lower portion and to withdraw electrolyte
from the upper portion of each individual compartment. A
plurality of parallel dimensionally stable anodes is provided
assembled in spaced face~to-face relation in one terminal
compartment and adapted to receive a number of cathodes inter-
leaved with the anodes. Means are provided for supporting the
anodes in assembled position with means being provided for
supplying electric current to the anodes. A plurality of
parallel cathodes assembled in close:Ly spaced face-to-face
, relation to the otherterminal compartment and are adapted to
receive a number of anodes interleaved with the cathodes.
Means is provided for supporting the cathodes in assembled
'I position with means for withdrawing current from the cathodes.
A plurality of bipolar electrode assemblies is provided inter-
posed between the terminal compartments with each bipolar
electrode assembly comprising a plurality of parallel bipolar
; electrodes in closely spaced face-to-face relation and each
bipolar electrode oE each bipolar electrode assembly extends
through each partition of the cell, one portion of each bipolar
electrode on one side of each partition being of one polarity
and the other portion of each bipolar electrode on the opposed
side of each partition being of opposite polarity to the one
portion. The portions of the bipolar electrode which extend
; through the partition separate the terminal anode assembly
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Erom adJacent cells and are cathode lnterleaved with the anodes
of the termlnal anode assembly. The portions of the bipolar
electrodes extendlng through the partltlons separatlng the
termlnal cathode assembly from ad~acent cells are dimensionally
stable anodes interleaved with the cathodes. All other bipolar
electrode portions of the bipolar electrode assemblies are
interleaved with bipolar electrode portions of opposite polarlty.
The outstanding feature of this lnventlon ls the
provision of the combination of a substantially enclosed
electrolytic multipolar cell unit with an upper open-ended
conduit vertically disposed above a plurality oE electrodes in
each compartment a sufficient distance to provide rapid
circulation of electrolyte through the entire electrode
assembly ot the compartmeDt when gases are generated at the
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electrode surfclces. The tetm "chirr)ney effect" whelever i-t occurs in this specification
ancl claims means -the rapicl ancl turbulc!nt circukltion of elcctrolyte provided by the
combination of an upper open-enclecl condui-t disposecl ver~iccllly above an electrode
assembly, which concluit can be considered analogous to a chirnney, a subs-tantially
enclosed cell cornpartrnent or unit and the gases evolved at the electrode surIaces.
When an electrolytic cell of such structure is placed within a reaction or holcling tank
containing electrolyte solution, the electrolyte solution is causecl to circulate rapidly
through each individua.l compartment. The combination of the compartrnents being
substantially enclosed, with the exception of the upper and lower conduit openings, the
10 vertical disposition of the upper conduit, the openings in the horizontally spaced
electrodes or the open channels bet\l/een the ver-tically or intermediately spacecl
electrodes, and the gas bubb.les rising from ~he electrode surfaces cause the solution to
rapidly and turbulently pass through the cell. The circulation of the electrolyte is
believed to be induced by a solution displacement phenornena, or "chimney effect."
The portion of the electrolyte solution within the cell containing gas bubbles is less
dense than the solution outside the cell which does not contain bubbles so tllat the
heavier solution enters the cell through the lower conduit and displaces the less dense
solution within the cell ancl causes it to flow through the upper conduit and into the
retention vessel. While the upper and lower conduits each enhance electrolyte
20 circulation, the relationship of the length to diameter of the cond~lits is adjustecl to
minimize current leakage dependene on individual cell desigrl. Thus, the advantages of
.
excellent circulation of the electrolyte and good current efficiency are provided by
virtue of the cell structure of this invention. If the temperature must be controlled
for a particular product such as the manufacture o:E sodiurn chlorate, cooling coils are
arranged in the reaction tank in which the electrolytic cell is clisposed. The excellent
.~ circulation characteristics of the cell also provide advantageous, sirnple control of a . .
~. ~ predetermined temperature of the electrolyte solution during residence time in the
: reaction tank.
The above objec~s and advantages of the invention will be apparent to those
30 sl~illed in the art from the following specification, the appended claims and by
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reEerence to the clrawings wherein like numerals insofar as practical represent the
same or similar parts, and in which:
I~IG. l is a side elevation of one embodiment of a multipolar cell of this
invention illustrating a cell ~herein horizontally disposed foraminous electrodes are
utilized.
FIG. 2 is an end view taken alon~ line 2-2 of FIG. 1 illustrating the cell
disposed in a reaction or holding tanl~ ~0, in which cooling coils may optionally be
positioned and illustrating the flow of the electrolyte solution tllrough the cell.
I~IG. 3 is a side elevational view of another ernbodiment of a rnultipolar
10 electrolytic cell of tlle present invention illustrating a cell in which solid vertical
electrocles are incorporated~
FIG. I~ is a secLion as in FIG. 2 wherein the cooling coils are cleleted for
clarity of illustration and the upper and lower conduits are carried by respective upper
and lower portions of a sicle wall.
FICl. 5 is a modification of FIG. l illustrating an embGdiment of the cell
where the conduits are the same length as the thickness of the top and bottom walls of
each compartment.
Referring to the drawings, a cell chamber is shown generally at 10 having a
top wall or cover 13, end walls ll, a bottom wall 12, and side walls 9 (not shown).
20 Solution separating and electrically insulating partitions l~, divide the chamber into
unit compartments. In ~iG. 1, compartments 167 17, 18 and l9 are interposed hori-
zontally between terminal compartments 15 and 20. Open-ended conduits 21 and 22,
respectively, carried by ~he top and bottom wall of each compartment are in
communication with the interior oE said compartment for circulation of the electrolyte
by inflow through the lower or bottom conduit and withdrawal through the upper or top
conduit. The plurality of dimensionally stable foraminous anodes 27 are disposed in
horizontal substantially parallel spaced face-to-face relation in one terminal compart-
ment 15 of the cell. The plurality of foraminous cathodes 31 are positioned in
horizontal parallel closely spaced face-to-face relativn in ~erminal compartment 20.
30 The anodes 27 and cathodes 31 are proYided with apertures at one end thereoE and are
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held in assc-rnblecl positic,rl l~y threaclecl pos-ts 2~ ~Y~tcndirlg through -the apertures in the
electrodes, spacing of the elecirodes being provicled by apertured shirns mour)tecl on
support posts 28 between adjacent electrodes. Conductor bars 26 are also mounted on
posts 28 for supplying electrical current to the electrode assembly and may
additionally serve as electrode separators. Threaclecl nuts 29 are connected to
threaded posts 28 to hold the electrodes in assernbled position. The posts are provided
with bases 32 for supporting the electrode assernblies on the bottom wall 12. Copper
rods 24 extend through the top wall of the chamber and ~re ehrcadably connec-ted to
the conductor bars carried by the electrode assemblics of terrninal compartrncnts 15
10 and 20, respectively. Electrically nonconductin~ tubes 2~a con~structed o~ plastic or
ceramic rnaterial, inert to the cell environment, surround the copper rods ancl exter-d
above the level of solution in the retention tank for preventing corrosion of the copper
rods. Electrically insulated tubes 25 also constructed of suitable plastic or ceramic
material and preferably of polyvinylidene chloride are arranged concentrically with
and spaced from the electrically nonconducting tubes 25a to prevent electrical current
leakage through the solutioll in ~he retention tank to the terminal cell compartrnen-~s.
Tubes 25 are made of sufficient length to prov;de a long electrical current path and of
such diameter as to establish a sutficiently narrow gap between the periphery of tubes
25a and the inner walls of tubes 25 to minimize the cross sectional area available for
20 current leakage. The copper rods are connected to a power source, not showrI~ and
serve to supply and withdraw electric current to the cell. In the preferred
embodiment, the electrodes are all horizontally disposed and, with the exception of thc
assembly of the monopolar dimensionally stable anodes horizontally disposed in one
terminal compartment and the assernbly of monopolar cathodes in the other terminal
compartment, the electrodes of the cell are all interleaved foraminous bipolar
electrodes 34 common to adjacent compartmer.ts of the cell. The foraminous bipolar
electrodes 34 are constructed and arranged so that the assemblies o~ bipolar electrodes
in cell compartments 169 17, 18 and 19 which compartments are horizontally
interposed between the terminal electrode assembly compartments comprise a
30 plurality of foraminous parallel subs-tantially horizontal dimensionally stable anocle
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portions 35 aclaptecl to receive a plurality of forarninous parallel substantially
horizontal cathocle portions 3G in c~osely spaced substarltially face-lo ~ace relation to
each anode portion. The bipolar electrodes 34 are arrangecl so that one portion of the
electrode of one polarity is positioned in one compartment and the other portion of
opposite polarity extends into an adjacent compartment. In this manner, the bipolar
electrodes of tile assembly are alternately arranged in polarity both in vertical and
end-to-end or longitudinal position throughout the cell. The bipolar electrodes are
mounted on the supporting posts through apertures located at their miclpoints, each end
being of opposite electrical charge in adjacent hori~ontally interposed cells. In the
10 terminal anode assembly of compartment 15, the cathode portion 36 of each hipolar
electrode in the compartment is positioned anci closely spaced in substantially face-to-
face relation to each dimensionally stable anode 27. The dimensionally stahle anode
portion 35 of each bipolar electrode includecl in the terminal cathocle assernbly
; compartment 20 is arranged in substantially face-to face closely spaced relation to
each cathode. All the remaining electrodes are interleaved foraminous bipolar
electrodes common to two adjacent cells. The bipolar electrodes have apertures at
intermediate points and are mounted in the same manner as the terminal electrocles by
posts extending through the apertures and positloning the electrodes in spaced relation
by means of shims. Posts 28, the spacers and the connecting nuts may be constructed
20 of any electrically conductive metal resistant to the cell environmer,t; generally, they
.1 - are made of a valve metal, preerably titanium. The conductor bars in each terminal
compartment are required to be electrically conductive and any conductive metal may
be used. Generally, a valve metal, preferably titanium, is used. The posts provided
with attached bases 32 serve as support and assembling means for the electrodes and
! ~ are generally completely enclosed within the electrically insulating partitions 14. The
~; anodes 27 of the terminal compartment assembly as noted are supported by the posts
at their apertured ends and at their other ends terminate at a point just short of the
partition opposed to the apertured end. The cathodes of the terminal compar~ment 20
are arranged in the same manner and terminate just short o the partition opposed to
30 their apertured ends~ The interleaved bipolar electrodes are positioned so that each
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3~
anodc portion arld c~ch cathoàe portion will terminat( short of the parti~ion ollposecl to
their apertured micl-points. Such arrangement avoids short circui-ting of tlle cell
electrode assemblies by preventing contact o~ the electrodes with cell elements having
an opposite electrical charge. Supporting legs 23 are mounted on the bottorn cell ~all
and are adapted to supl)ort the cell when it is positioned within an outer solution
retaining tank.
In the above-described embodiments, the electrodes are all horizontally
disposed and foraminous in construction. However, it shoukl be un(lerstood that the
electrodes can be mounted in vertlcal position by the same means of support and
10 assembly, the only variations bcin~ the positioning of the electrodes at right angles to
the arrangement shown in FIG. 1. In vertical position, the clectro(le shccts may bc
solid or foraminous dependent on optimum operating eEficiency. Solid sheets may be
used if sufficient space is present between adjacent electrodes or electrode segments
to permit unobstructed rapid passage of electrolyte.
The dimensionally stable anodes 27 and bipolar anode portions 35 cornprise
an electricaily conductiYe substrate with a surface coating thereon of a solid solution
of at least one precious metal oxide and at least one valve metal oxide. The
electrically conductive substrate may be any metal which is not adversely affected by
the cell environment during use and also has the capability, if a breakdown in the
20 surface coting develops, of preventing detrimental reaction of the electrolyte with the
substrate. The geometrical configuration of the anodes may vary provided anodes of
suitable shape for forming the structural assembly are used. Generally, the substrate
is selected from the valve metals including titanium, tantalum, niobium and ~.irconiurn.
Expanded mesh titanium sheet is preferred at the present time Eor the horizontally
disposed anodes.
~'~ In the solid solutions, an interstitial atom of a valve metal oxide crystal
lattice host structure is replaced with an atom of precious metal. This solid solution
structure distinguishes the coating from physical mixtures of the oxides since pure
~i ~valve metal oxides are, in fact, insulators. Such substitutional solid solutions are
30 electrically conductive, catalytic and electrocatalytic.
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In the above-lnentiollcd solid solution host structure, the valve rnetals
includc titaniuln, tantalurn, niobium and zirconh~m, while the implanted precious
r-ne-tals encompass platinum, ruthenium, pallaclium, iridium, rodiurn and osmium.
Titanium dioxide-ruthenium dioxide solid solutions are preferred at this time. The
molar ratio of valve metal to precious metal varies between 0.2-5:1, approxirnately 2:1
being presently preferred.
If desired, the solid solutions may be modified by the addition of other
components which may either enter into the solid solution itself or adrnix with same to
attain a desired result. For instance, it is known that a portion of the precious rnetal
10 oxide, up to 50 percent, may be replaced with tin dioxide without substantial
detrimental effect on the overvoltage. Likewise, the solid solution may be modified by
the addition of cobalt compounds particularly cobalt titanate. Solid solutions rnodified
~/ by the addition of cobalt titanate, which serves to stabilize and extend the life of the
solid solutionj are described more completely in Canadian Patent No. 9~8,~90, issued
~une 11, 197~. Other partial substitutions and additions are encompassed. Another
;~ type of dimensionally stable anode coating whicl- may be used with good results in tne
practice of this invention consists of mixtures of chemically and mechanically inert
organic polymers and solid solutions of valve metal and precious metal oxides as at
least a partial-coating on the electrically conductive subs-trate. Particularly useful
20 materials in such anode coatings are the above-described solicl solutions in admixture
with fluorocarbon polymers such as polyvinyl fluoride, polyvinylidene fluoricle and the
like coated on at least part of the surface of an electrlcally conductive substrate
`; consisting of the above-described valve metals which rnay be mixed with other suitable
metals.
1~ One other type of dimensionally stable anode capable of satisfactory use in
Jj:~ : ' this invention consists of a valve metal substrate bearing a coating of precious metals
or precious metal alloys, particularly platinum and alloys thereof on at least par~ of its
Sul face.
The above- mentioned preferred solid solution coatin~s are described in
30 more detail in British E'atent No. 1,1959871.
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~ he calhodes 31 ancl hipolar cathode pOI tions 3G may be any rnetal capable
o-~ sustaining the corrosive cell concli-~ions ancl a usef~ll rnetal is generally selected from
the group consisting of stair)less steel, nickel, titanium, steel, lead and platinum. In
some cases, the cathodes may be coated with the solid solu-tions al~ove-clescribed for
coating the dimensionally stable anodes.
The bipolar ~node portions 35 and the bipolar cathode portions 36 are
arranged in closely spaced face-to-face relation between insulating partitions ll~. It is
desirable to maintain elecLrode close spacing thereby establishing minirnum eleclrical
resistance of the electrolyte between the electrodes to insure optirnurn currcnt
10 efficiency. Consequently, the electrocles are spaced as close as practically possible
and maintainecl free from electrical contact by el~ctrlcally nor)colldllctive separators
interwoven through, or positioned within, the openings of the foraminous electrodes.
When flat or cylindrical elements are used as separa-tors, they are generally interwoven
through alternate openings on the faces of the electrodes disposecl near the cdges but
may also be interwoven through other portions of the electrodes. Other types of
spacers capable of satisfactory use are elect-ically nonconductive strips provided with
projections adapted to be tightly positiolled within the forarninous electrode openings
and button-type members such as semi-spherical elements arranged on opposite sides
of the elec~rode openings and joined by an engaging member, such as a shaft cr stem,
20 extendin~ through the electrode openings. The separators are positioned to prevent
electrical contact or shorting between the electrodes and, at the same time, provide
maximum flow of the electrolyte through the openings in the electrode~ The
electrically nonconductive separators should be constructed of materials inert to the
cell environment and may have any suitable geometric configuration. Generally, the
separators are polyvinylidene chloride, polyvinyl chloride, chlorinated polyvinyl
chloride, polyvinyl fluoride, ~etrafluoroethylene and the like ancl may be of solid or
hollow, cylindrical, ~lat or other suitable config-lrationO
The bipolar electrodes are generally of unitary electrically conductive base
constructionj each dimensionally stable anode portion of the base bearing a solid
30 solution coating which may be one of the above-described solid solution coatin~s~ the
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cathode portion being the ullcoat~cl electricLIlly conductive rnet~l of -the base. The
cathode portion in sorne cases rnay also be coated in the same manner as the
dirnensionally stable anode segment. Other suitable electrically conduc-tive coatings
may be applied to at least a part of the surface of the anode portion. Such coatings as
platinum and alloys thereof and other noble metals are also suitable as conductive
coatings.
The cell is useful Eor the manuEclcture of alkali metal chlorate by a process
which comprises the steps of introducing an aqueous alkali metal halide solu-tion into
the cell compartments, imposing an electrical potential across the clectrodes to
10 electrolyze the all<ali metal halide sol~ltion, the temperature of the solution being
maintained at about 60C to about 80C and the pH of the solution beinK maintained
at~about 6.0 to about 7.5 during electrolysis and recovering alkali rnetal chlora-te irom
the electrolyzed solution. The cell is initially positioned within a surrounding tank in
such manner that the conduits ex-tending frorn the bottom wall of each compartment
are spaced from lhe base of the enclosing tank to permit entrance of the solution, and
;1 the conduits ex-tending from the top wall of eacll compartment are below the top edges
of the side walls of the tank. The halide is introduced into the surrounding tank to
completely cover the cell including the condui ts carried by the top wall of each
compartment. A decomposition potential is then imposed across- the cell for
20 electrolysis. During electrolysis, gases generated at the electrode surfaces lower the
density of the solution within the cells.
The l'chirnney effect" described above causes the solution in the tank
surrounding the cell to enter the open conduits carried by the bottom wall or a lower
portion of a side wall of each compartment and flow rapidly upwardly through the
entire electrode assembly of each compartment where electrolysis occurs and to exit
rapidly through the open-ended vertical conduit in or extending from the top wall or
upper portion of a side wall of each compartment into the tank surrounding the cell. A
cooling coil 8 is preferably arranged within the enclosure tank 9 for ternperature
control.
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Since the unit compartrnents or ce~ls ;;rc completely enclose(l with tlle
exception oE opcn conduits carried by the top al-cl bottom walls, the solution flows very
rapidly and vigorously through the entire electrocle asscrnbly. In this manner, sodium
hypochlorite is rapidly producecl electrochemical!y wi~h very lirnited simultaneous
production of sodiurn chlorate. After the solution cxi ts frorn the ceJI, sufficient
residence ~ime is provided in the surroundillg tank for chemical convelsion of the
hypochlorite to chlorate by the large volume of solution contained in the tank and tirne
lapse during circulation through the tank ancl reen~ry to the cell. The design of thc
cell thus enables production of all<ali metal chlorate in the most efficient manner since
10 the major amount of chlorate is procluced chemically rather tharl by the more
expensive electrochemical reaction.
Although the use of one rnultipolclr electrolyLic cell of this inventiorl has
been illustrated and described, any desired nurnber of such cells may be arranged in an
electrolyte-containing tank of sufficient size for complete immersion of the cells
therein. The specific number of cells and tanks selected will depend orl ~conornic and
other practical operating factors such as availa~le space desired, quantity of pro~uct
and the like. If desired, the tanl<s may be arranged in banks, rows or slacked
formation. Also, the electrolyte from each tank surrounding an individual or number
of multipolar cells may be circulated to a common product recovery tank.
As noted above, the conduits carried by the walls of each cornpartrnent are
of sufficient lengtlI and vertical orientation to prevent significant electric current
leakage from the cell. The length will vary widely in accordance with the wall
thicknessS voltage utilized, number of cells ancl other related design factors.
,i~ The conduits may be apertures of the same length as the thickness of walls
if such length in combination with the contributing related factors prevents significant
current leakage and contrlbutes to circulation velocity. This modification of the cell
structure is illustratecl in FIG. 5 and is particularly suitable where a small number of
.~ .
; ~ multipolar cells are positioned in a single retention tank.
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The folJo~l/ing exarnp~es of 1;hc production of sodium chlorate presen~ed
below are intended for purposes oL illustration only ancl are not $o be considered
limitative of the invention in any manner.
Example 1
A multipolar clectrolytic ccll of the type illustrated in FIGS. 1 and 2 was
arranged in an uncovered tanl< having a volume capaci-ty abou-t 5 times greater than the
cell and side walls of greater height than the combined lleight of the cell and the
conduits projecting from the top walls of the cell. The external tank was filled with
saturated brine solution containing about 310 g/l of sodium chloride and about 0~5 g/l
of sodium dichromate. Direct current was appliecl to the electrodes of the cell to
10 electrolyze the solution. Gases were immediately evolved at the electrode surfaces
and a rapid and turbulerlt circulation o~ he solution through a.ll the cornpartrnents of
the cell, into the open-ended conduits of the bottom walls, througll the assembly of
elcctrodes in each compartment and througll the open-ended conduit in the top wall of
each compar~ment resulted. The cell was operated for a period of about 16 hours by
continuously introducing saturated brine of the same composilion, as initially utili~ed,
into the tank surrounding the cell, elec$rolyzing the solution in the cell while
rnaintaining the temperature of the solution at about 60C and the pH at about 7.0,
withdrawing the electrolyzed hrine from the external tank, recovering sodium ch.lorate
therefrom, fortifying the depl~ted brine with saturated brine and recirculating the
2û fortified brine to the multipolar cell.
The average current efficiency during this period was 91~ percent and the
average quantity of sodium chlorate product obtained was 380 g/l.
Exam~
The same prccedure was followed as in Example 1 ~vith the exception that
the saturated brine solution contained about 2.0 g/l sodiurn clichrornate $he pH was
maintained at 6.7 and the cell was con~inuously operated for a period of 15 hours. l he
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average current efficiency cluring this period w,~s 93 percent an~l the average amount
of sodium chlorate obtained was 316 g/l.
The above examples clearly illusLrate that the present invention provides
for the production of alkali metal chlolates at efficiencies much higher than those
available in conventional multipolar cells used for clllorate production.
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