Note: Descriptions are shown in the official language in which they were submitted.
1036540
Background of the Invention - '
Alkali metal halates, sucll as soclium chlorate, may be prepared ..
electrolytical.ly. In the electrolytic preparation of alkali metal . .
.... ..
halates, alkali meLal halide i5 eed to an electrolytlc cell. E`or
example, ln the case oE a clllorata cell, alkul-l. matal clnlorlda i~ ~ecl
to tlle ccll. Ilyclro~ell i5 evolved at tlle cn~llocle and alkali mctaL
hydroxicle is proclucc-l a~jacellt to tlle cathode. Clllorlllc ancl hydroxyl .``
ion comc into cont;lct ~.ltll1n tha clectro.l.ytc cllam~ar alld rcact accorcllnl~
.
, ~ , . . .
to equation (i), 1036540
(i) Cl2 + 2011 > (Cl +l 0) l + c~ 0
thereby ~ormLng hypochlorite ion. The hypochlorite ion, in which the
chlorine has a valence oE -~l, may be se:Lf-oxidlzed to`a chlorite ion,
in which the chlorine has a valence of -~3, and a chloride ion, in which -'
the chlorine ha6 a valence of -l, according to reaction (ii).
(ii) (Cl O) -t (Cl 0) ~ 3 )-l C:L~l
The c~hlorlte lon, Ln turn, Ls oxic1L~ec1 by hypo(:hlorlte lon
to chlorate Lon Ln whlctl thc clllt)rlllc ha~ vn'lc11c~ Or 15, ~4 ~hOWII :L1I
reactLon (LLi).
(iLi) (CL 3 2) l ~ (C:L lo) ~(Cl 503) l ~ Cl
The starting polnt of the electrolytlc alkall 1netal halate
process is the alkali metal halide, e.g , sodium chloride, in which the
halogen has a valence of -l. The halogen in ttle alkali metal halate has
a valence of +5. Therefore, the valence change n-ecessary for the
production of alkali metal halate is from -l to +5, a total of +6.
In this way, 6 Faradays are required for the production of l equivalent
of the alkali metal halate.
In the electro~ysis of an acldic solution oE an alkali metal
halide, a hypohalite'solution is first produced containing little free
hypohalous acid. tlowever, :Ln the presence oE a mLneral acLd 8UCII as
chromic acid or sulfuric acid, the concentration of hypohalous acid is
increased, and the oxidation of the hypohalous acid by hypo11alite ions
pro~!uces halnt'e ion, halogen, and hydrogen. 11ydrogen Lo11s then react
.
~ 2 --
.
.. _ _ . .. . . ..... ... .. ..
~.()36S4~
to form more hypohalous ion and the process continues with the formation
of halate ion in all parts oE the electrolyte. Side reactions, e.g.,
the evolution of oxygen at the cathode, and the reaction of nascent'hydro-
gen with oxygen containing ions, may be reducecl by tile addition of
chromate lon, l.e., sodlum chromlte lnto the electroLyte thereby favoring
the evolution of halite ion.
The chemical formation of halate ion takes place throughout
the entire cell, and in fact throughout the system wherever halite ion
and hypohallte lon are present.
In ~he operatlon oE SOdlll01 ch:Lorate cells oE the prlor arl:, -
the comblnatLon Oe tlliclc eLectrodes 111d lc)W CUrrCrlt dellS:L~:.Le~l e.~.,
Less than about L00 ampere.s per sqllare Eoot, llrovldc~cl n ce'L'L op~ratLn~
temperature oE about 50 to about 65~. I:n sllcll ceLLs soLIcl sodlum
chlorlde had to be substantlally continuously addecl to the cell.
Ln a batch chlorate cell operatLon, aEter the celL llquor is
recovered from the cell it is clarified, e.g., by fi:Ltration, and then
fed to an evaporator for concentration. Afterward, separation occurs
and crystallized sodium chloride is recovered. The cell liquor may then
be returned to sa'turating means for adjustment to desired brine
strength and returned to the cell. In a continuous chlorate cell pro- -
cess, without evaporation or removal of sodium chloride, the cell
liquor is cooled to crystallize the sodlum chlorate then returned to
the cell.
Sumlllary oE the InvellLLoll
According to this invention, bipolar halate cells are pro- -
vlded havlng compacct electrolysis volullles, but permlCtLn~ ~he use of
large cell bodl-s, l.e., ce:Ll bocl:Les characterizecl by large electrolyte
,.'~ .
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~365~6~
volumes. In this way, a small volume is utilized ~or electrolysis while
a large volume is provided for the chemical Eormation of halate ion.
Because of the increased electrolyte temperaturé oE the electrolyte, due
to the hlgher current denslties obtainecl with tneta:L e:lectrodes, the
solubllity oE alkaLl metal halates in ceL;l li~luor is increased. The
large cell volume relative to electrode volume provides a longer cell
residence time. The combination of higller temperatur~, higher halate
solubllity, and longer resLdence time provi(les higller concentrations oE
halate in the cell LL~Iuor. Tlle lon~er resldence times a:llows more of
the halate to be formed by che~nlcaL reactioll ratiler tllan by electrolysLs,
~hereby prov:Ldlng a Illgller current efCLcLellcy. Tlle IILgller ~elllperal:u~e
allows a brine feed to be utllLxecl ratllel^ tllall solLd saLt Eeed.
~ ccording to th:Ls invention, a blpo:Lar aLkali metal llalate
cell i9 provideclllavln~ a plura]lty of indlvidual bipolar units elec-
trically in series. ~ach bipolar Urlit hns a number of indlvidual con- -
ductor elements. ~n individual conductor element contains a metal
anode mounted on one side and a metal cathode mounted on the opposite
side. Individual insulators correspond to each pair of individual con-
ductors and-are interposed between a pair of individual conductors.
In this way, an individual insulator is interposed between a pair of
adjacent, individual conductors, and an individual conductor is inter-
.
posed between a pair of adjacent, individual insulators. ~ach indi-
vidual bipolar unit further includes compressive means, imposing a com-
pressive. Eorce upon a combLnatLon oE alternatLng l.nsu:La~:ors and con-
ductors. In this way a rigid bipolar unLt is provided.
The bipolar units are arrayed :Ln bipolar conEiguratioll with
the anodes of one bLpolar unLt Lnter.Leaved betweell a pair oE cathodes
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~36540
of a subsequent bipolar unit. The anodes of a bi.polar unit and catl-odes
of the subsequent bipolar unit are separated from each other by the
insulators, referred to above, of both of the bipolar units. In the
same way, the cathodes of a bipolar unit are interleaved between a pair
of anodes of a prlor blpolar unit, with the cat:l~odes of the blpolar
unLt, and the anodes Oe the prlor b1polar unlt be:LIlg rieparated from each
other by tile insulatlng means of the pair of bipo.1ar UllitS.
.' '
Detailed Description
Ttle inventioll may be understood by reEerellce to the appended
171gures. In the Flgures: -
Flgure 1 ls a part:i.al cutaway l~e~rsl~ectl.ve v l.eW oE the e.Lec-.
trolytLc ce:Ll of tll:Ls :LIlvent:Lon.
F:Lgure 2 1s a perspectlve, partla:Lly-exploded view of a seg-
ment of a pair of adjacent bipolar units oE the electrolytic cell of
thls lnventlon.
Figure 3 ls a plan view of three bipolar unlts of the electro-
lytlc cell of this lnventlon. Flgure 4 is a side elevation of a bipolar
unlt of the electrolytic cell of thls lnventlon.
The bipolar electrolyzer l of this invention contalns a
plurality of bipolar units 21 through 24 in series with the subsequent
and adjacent bipolar units ln the electrolyzer, thereby deflnlng a
plurallty of adjacent individual blpolar cells ll through 14. Blpolar
conflguratlon ~ay be understood by conslderlng the current flow. Elec-
trlcal current trave:l.s froM an anode 51 oE onc cel:L .L.L a~tache-l to the
first blpolar unlt 21 of that cell :Ll to the cathode 6:L of the ce:L1.
The cathode 6L is attached to the second blpolar unlt 22 of the cell ll.
_5 _
';
~03t;5~0
The current then passes from the cathode 61 through the conducting means
30 of the bipolar unit 22 to the anode 51 connected to the bipolar unit
22 which is in turn the anode 51 of the next adjacent cell 12 in the
electrolyzer 1.
The anodes 51 of the bipolar unit 22 are interleaved between
the cathodes 61 of the next adjacent bipolar unit 23. The cathodes 61
of the bipolar unit 23 are interleaved between the anodes 51 of the
immediately preceding bipolar unit 22. Direct short circuits between
the anodes 51 and cathodes 61 of adjacent bLpolar unlts 21 and 22 are
prevented by the insulating méans 40 as wi;Ll be more EllLly described
hereinafter.
An lndlvidual bipolar unit 21 contaLns a pL~Irr;nLl~y oE lncllvl-
dual conducting means 30. The lndlviduaL conduct;LIlg means 30 are lnter-
posed between the cathodes 61 of one cell 11 on one slde oE the bipolar
unit 21 and the anodes 51 of the next adjacent cell 12 on the opposite
side of the bipolar unit 21. Current travels from the cathode 61 of
the prior cell 11 through the conducting means 30 of the bipolar unit 21
to the anode 51 of the next adjacent cell 12. The individual conductlng
means 30 includes an electrocondtictive, first metal member 3Z having an
anode 51 connected to one side thereof, an alkali resistant, electro- -
conductive, second metal member 34 having cathodes 61 connected to the
opposite side thereof, and a third metal member 36 betweenl and mechani-
cally and electrically connected to first 32 and second 34 metal members.
The first metal member 32, i.e., the acLd reslstant, electro-
conductlve metaJ member havlng the anode Sl connectcd ~heleto, Ls EabrL- -
cated of a materlal that i5 reslstant to anodic prod-lcts wl~lle retalnlllg
its electroconductlvity. Most commonly, the acid res:lstant metal mem-
ber ls Eabrlcated oE a va:Lve metal. The valve metals are those metals which
form an oxlde film when exposed to acldlc medla or to electroconductlve
.1 .
l -6-
r :l
1~36S~O
media under anodic conditions. The valve metals include titanium zir-
conium, hanium, vanadium, columbium, tantalum, and tungsten. Titanium,
tantalum, or tungsten, are the most commonly used valve metal for
electrolytic cell structural members because oE tlleir more low cost and
ready availability. Tltanlum is the preEerred materla:L Eor thls servlce
because of lts lowest cost relative to the other valve metaIs.
The first metal member or acid resistant, e:Lectroconductive
metal member 32 is showll in rectangular Eorm. This is because of the ;~
ready avallablllty o rectangular stock, the conEo~ LI.y to Lnsulatlng
means 40 as wLll be descrlbecl more Eully herelnaEter, ancl ease oE rlgldly
conneetlng the ano~es 51 substant:Lally parallel to eucll otller to the
metal member. Ilowever, 1~ HhouLcll)e utlder~toocl tlmt l:he ELr~t metaL mem-
ber may be cyl:Ln~trLeaL or oE otller sllape.
On the opposlte side oE the conductor 30 ls an alkali resis-
tant, electroconductive metal member 34 havlng cathode Eingers 61
connected thereto. PreEerably, the alkali resistant, electroconductive,
second metal member 34 is fabricated oE a material that is resistant to
cathode products such as hydroxyl ion while retaining its electro-
conductivity. Such materials include iron, steel, cobalt, nickel, and
the like. Most commonly, iron or steel is used.
While the second metal member 34 is shown rectangular in
form, it is to be understood that it may be of cylindrical or other
shape. Ilowever, a rectangular form is preÇerred because of the
availabillty oE rectangular stock, the eonformity to the lnsulatlng
means 40 as will be descrlbed more ully herelnaEter, and tlle ease o
welding the cathodes 61 thereto so as to provlde substantially parallel,
spaced cathode fingers 61.
--7--
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.. ..... .
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~L~36540
A third metal member 36 is interposed between, and mechanically
and electrically connected to said first metal member 32 and said
second metal member 34. ~he third metal member 36 is typ:Lcally fabri-
cated of a material that is electroconductive, and substantially imperme-
able to the flow of hydrogen. Such materlals lnclude copper, aluminum,
and lead. Most frequently copper is used. The thlrd member 36 provides
electrical conductivity between the cathodes 61 of one cell 11 an~ the
anodes 51 of the next adjacent cell 12 Additionally, the copper member
prevents the flow of nascent hydrogen from the cathode 61 through the
conductlng means ~ to the anode 51 oE tl~e next aclJacent cell.
The copper member 36 may be bonded ~o l:he ILrst mel:al member
or acld reslstant metul membcr 32 by weldlng, frLctLor~ weLcllll~, solderlng,
boltlng, or the like. 'rhe copper member 36 m~ly aLs~ L)e bonded to the alkali
resistant or second metal member 34 by welding, friction welding, soldering,
bolting or the llke.
The copper member 36 i9 shown in rectangular form because of
the ready availability of rectangular stock. ~lowever, it i9 to be under-
stood that the copper member 36 may be of cylindrical stock.
Electrodes 51 and 61 are mounted on the opposite surfaces of
the conductor 30~ Anodes 51 are connected to one side of the first
metal member 32. The anodes 51 are substantially parallel to each other
and extend from the first metal member 32. The anodes 51 themselves
are fabricated of an electroconductive, corrosion resistant metal.
Most commonly, the metal will be a valve me~al as described hereinbeeore,
witll titanium bein~ the preferred valve metal. l`lle anodes may be in
the form of a sheet or plate, or perforate sheet or a fora~inous
material such as expanded metal mesh.
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il936540
The anodes 51 are coated with an electroconductive material,
having low chlorine overvoltage. Typical materials useful for coating
metal anodes for use in electrolytic cells include the platinum group
metals, ruthenium, rhodium, palladium, osmium, iridium~ and platinum.
Alternatively, the coating compound m?y be an oxide of a platLnum group
metal such as ruthenium dioxide, rhodium trioxide, palladium dioxide,
osmium dioxide, iridium trioxide, or platinum dioxide. ~lternatively,
the coating compound may be an oxygen ContQining compoll~d of a platinum
group metal such as calclum ruthenate, calcLum rhodate, calc:lum ruthenlte,
calcium rhodi~e, the delaossLtes such as pIatinuIll cobrlltate or yallatIium
cobaltate, or a pyrochI.Qrc such a~ b:l~m~lth rathenate~ or bLfimlltlI rhoclnte.
Alternatively, the coatlng mater:Lal on ~he ~;urEace of L!le anotle may be
lead dioxide or other non-precious metal containing oxygen compounds.
The cathodeæ 61 are connected to the opposlte side of the
second metal member 34. The cathodes 61 are Eabrlcated oE an alkall
reslstant, hydroxyl ion resistant, electroconductive metal. The
cathodes 61 may be fabrlcated of iron~ steel, cobalt, nickel, iron,
manganese, or the like. Most commonly, they are fabricated or iron, or
steel, because of the ready availability thereoE. The cathodes may be
in the form of a sheet, plate, perforate sheet or plate, or foraminous
or expanded metal mesh. Most commonly, they are fabricated of iron, or
steel, because of the ready availability thereof. The cathodes may be
in the orm of a sheet, plate, perforate sheet or plate, or foraminous
or expanded metal mesh. Most commonly they have an open area from `;
about 35 to about 85 percent and preferably from about 65 to about
75 percent.
.
_ g _ :
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`- -` 036S~
As shown with particularity in Figs. 2 and 3, insulators
42 surround the individual connectors 36.
The insulators 42 correspond to the individual conductors 30
and are complimentary in shape to the individual conductors 30 so as to
totally cover and fit flush against the copper portion 36. In this way
the insulators 42 bear against the copper members 36 and provide a tight
fit therebetween, preventing contact of the copper members 36 by the
electrolyte.
The insulator means 40 are interposed between a pair of indi-
vidual conductors 30 and are arranged sequentially in an individual
bipolar unit in such a way that an insulator means 40 is interposed
between a pair of adjacent individual conductors 30 and an inclividual
conductor 30 is interposed between a pair of adjacent indtvlclual insu-
lator means 40.
lS The insu}ator means 40 include means for maintaining an inter-
electrode gap between the pair of electrodes 51 adjacent thereto and the
pair of electrodes 61 of a subsequent bipolar unit. The insulators also
include means for maintaining an inter-electrode gap between the pair of
electrodes of opposite charge adjacent thereto 61, and a pair of elec-
` 20 trodes 51 of the prior bipolar unit. The inter-electrode gap may be pro-
vided by means within the lnsulators such as a non-conductive structure
for engaging the electrodes of the prior bipolar unit, i.e., anodes Sl,
parallel to and spaced from the oppositely charged electrodes, i.e. the
;~ cathodes 61, of the bipolar unit. The insulator means 40 also include `
structure for engaging the electrodes of the subsequent bipclar unit,
i.e., cathodes 61, and maintaining them in a spaced relationship,
.~ . . . .
.~ .
,
~. - 10-
, . . .
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36S4 : :
i.e., parallel to and spaced from the oppositely charged electrodes 51, ~`
i.e., the anodes, of the bipolar unit. The structural mea~ or accom-
plishing this may include spaced slot means, grooves, notches, or
channels within the insulator. Alternatively, the means for maintaining
/ inter-electrode gap may include spaced wedges, extended frames, an extended
/ edge, or fin means, such as the extended edge 46 shown in Figures 2, 3,
and 4.
The individual insulating means 42 include compressible, elec-
trolyt~e resistant electrically non-conductive, i.e., electrically in-
sulative, means 42 on facing surfaces corresponding to facing surfaces of ;~
ad~acent conductors 30, 32, 34 and 36. The compressible means may be rubber,
polyethylene, Kynar *, Teflon *, or the like.
Interposed between a pair of the compresslble, lnsulativemeans 42 is a substantially incompressible, elec~rolyte resistant,
electrically non-conductive, electrically insulating means 44. The
subscantially incompressible means 44 may be H frames, channel frames,
or other shapes. The substantially incompressible electrolyte resistant
means 44 include the means 46 for maintaining alignment of electrodes
of adjacent bipolar units as shown with particularity in Figs. 2 and 3.
The individual bipolar units include compressive means 70
providing rigid bipolar structural units. As shown in Figs. 2 and 3,
the compressive means include an electrically insulative bolt means 70
extending through the individual insulating means 40 and the individual
conducting means 30 o~ the individual bipolar unit. The electrically
insulative bolt means 70 includes a core 71 of a structural material of
high tensile strength, e.g., iron or steel or other structural metal,
and may include a sheathing or coating thereon 73 of an electrically
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*Trade marks
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non-conductive material. ~ g4 ~o one exemplification, the compres-
sive means include iron or steel rod member 71 and a surface 73 of Kynar,
Teflon, or the like. At the opposite extreme ends oE the compressive
means, are bearin~ surface means 75 which are substan~ially co-extensive
wlth and bearlng upon an external palr oE insulating means 46 at the
extreme ends of the bipolar unit, and nuts i7.
The individual bipolar units 21 through 24 are assembled into
a plurality of individual cells 11 through 14 within a cell body 1.
The b:Lpolar unLts 21 thro-lgll 24 may be mo~n-teci on base struc-
tures 81 throllgh 84 wlthln the cell body 1. Thl.s glves e:Lectro:Lyte
volume under tllc e:Lectrode~, thereby a:llow:lll~, a:l.kal.:l. motal halate Eor-
matlon under the bLpolar unl~s 2:1 tllrougll 2l~ and above the b:l.polar
unlts 21 througll 24.
The bipolar unlts are shown generally at Fig. 1 and with spe-
clflc detall ln Plgs. 2, 3, and 4. As there shown, tlle bipolar units
are arrayed in series with subsequent and adjacent bipolar units of the
electrolytic cell.
The cell body 1 can be rubber-lined metal such as ethylene-
~ .
propylene-diene linei steel, neoprene lined steel, or the like. Addi-
tionally, the cell body l can be a concrete body.
The cell body 1 is closed at the top and includes means ~or
feeding brine to the cell and recovering the alkali metal chlorate and
hydrogen gas therefrom.
~ nder normal operating condltion6, wlth a sodium chloride
Eeed, the cell li.quor contalns from about 650 ~o about 750 grallls per
llter of sodium chlorate, from about 60 to about 125 grams per liter of
sodium chloride, approximately two grams per liter oE sodium cllcllrolllate
-12-
,
,,, .r~ .
~36540
added to improve the electrolytical efficiency of the cell, and trace
amounts of sodium hypochlorites. In the operation of the cell, the cur-
rent density is from about 200 to about 600 amperes per square foot.A residence time within the cell of from about 40 to about 250 milli-
llters per ampere is provided and preferably .Erom about 65 to aboùt -
200 milliliters per ampere. Tl~e p~l oE tlle cell lic!uor within the cell
is Erom about p~l 5.6 to about pll 6.9 and preferabl.y from about'pll 6 to
about pH 6.8. Under these conditions the temperature of the electrolyte
is from about 50C. to about 100C., frecluent:Ly :Ln excess o.E 80C. and
as hlgh as 95~C. or 98C. or even 100C. - ' :.
In the operat:Lon o~ the bLpQI.ar e:lecL:roly~:Lc ce:L:I., feed may
: either bc paral.:le:l ~eed, l.c., a p:Lura:L:L~y Oe .Ind:Lv:ld~ L Eoecls sub~tan-
tially correspond:Lng to each o~ the ln(l:lvlclual. cell~, or the feed may
be series f'eed, where:Ln the brine is fed at one end oE the celi and the
alka.ti metal chlorate i9 recovered at the opposite end oE the cell.
Generally, series feed is preferred, as the feed to tlle flrst cell is ':
,
low in hypochlorite ion concentration, thereby providing a high degree
of chemical formation of chlorate iQn and a high current.efficiency.
~ While the ceLl has been described with reference to the produc-
- tion of sodium chlorate from sodium chloride, it is to be understood
that the cell as herein described above may also be used for the produc-
tion of sodium bromate from sodium bromide brine, potassium chlorate
from potassium chloride brine,' and potassium bromate from potassium
bromide brine. Although the lnvention has been descr:Lbed w:Lth reference
to particu:Lar specl.Eic details ancl certa:Ln preferrecl exelllpl:Lfications,
it is not intended to thereby llmi~ the scope of this invention except
. ~ , . ' , .
insofar as the de'tails are recited ln the appended cla.Lms.'
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