Note: Descriptions are shown in the official language in which they were submitted.
r~ 4S6
This invention relates to an improved electrolysis
process and an improved electrolytic cell employing an ion
exchange membrane as a diaphragm between the anode and cathode.
The novel process and electrolytic cell can be used for
a variety of purposes, including for example the production of
sodium hydroxide, chlorine and hydrogen from saline water, -
the production of lithium hydroxide, potassium hydroxide,
iodine, bromine, chloric acid, bromic acid, persulfuric acid,
etc., and the production of adiponitrile from acrylonitrile,
and the like.
Generally speaking, when a cation exchange membrane is
employed as a diaphragm, desalted interfacial layers are
formed on the anode side of the membrane, because the trans-
port number oE catLons throllgh tllc meml)rane Ls usual:Ly 80~
o~ grenter, wl)LI.c that o~ tl~e catioTls througll the anoLyte ls
50% or :Lesu unless the ano:ly~e Ls strongly ac:ld:Lc. Because oE
the dlfferential in transport numbers, desalted interfacial
layers are formed during operatlon in direct proportion to the
difference between the transport numbers through the membrane
and through the anolyte. The salt concentration of a desalted
interfacial layer i8 inversely proportional to the current
dens:Lty, directly proportional to the salt concentratlon in `~
the anolyte and inversely proportLonal to the thickness of the
interfacLal layer. There thus exlsts a current density whereby
the salt concentration in the interface is 0, namely the
limiting current density.
However, even if electrolysis is perforn~ed with a current
density which is not more than the limiting current density,
electrical conductivity is impaired by the presence of a
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thick interfacial layer, thus requiring a higher electrolysis
voltage. Moreover, as is well known, iE electrolysis is
performed with a current density which i9 more than the limiting
current density, electrolysis occurs in the interfacial layer.
In order to perform elec~rolysis as econornica:Lly as possible,
it is necessary to keep the thickness of the interfacial layer
as th:in as possible, in order to perform the electrolysis under
low electrolysis voltage and high current density.
Previously for this purpose it has been proposed to
inerease the flow veloeity of anolyte or to provide a spaeer
between the anode and the eation exchange membrane in order to
obtain a uniform spaeing and lmprove turbulenee effeets (for
example, refer to Rutler et al U.S. Patent No. 3,0l7,338,
:lsslle(l January 16, 1962). Furttlermore, when n spneer is providetl,
~here ~s no e()ntclet betweell t:he nllod~ arld ~lle catlon exchclnge
menlbrane or between thL catllode and the ecltion exchange n~elllbrane,
thus preventing burning of the membrane which ean be caused by
loeallzed high current passage due to contact. However, when
a spacer ls provided, it is very dlffieult to maintain a spaeing
of 1 mm or less. When eleetrolysis :is conducted with accompanying
generation of gas from the anode, a spacer tends to retain
~enerated ~as and thus shLeld currellt passage with an attendant
LnerLase of electroLys:ls volt~ge.
It has now been found that electrolysis can stably be
performed without using a spaeer when the eation exchange membrane
is maintained pressed toward the anode by keeping the inner
pressure of the eathode chamber higher than that of the anode
ehamber.
Thus, the eleetrolysis proeess of the present invention
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is characterized by maintaining a i~igher inner pressure in the
cathode chamber of the electrolytic cell than that in the anode
chamber. The inner pressure differential can be maintained in
several ways, for example by adjusting the differences in gas
pressure at the chamber exits, or by adjusting the amount of
electrolyte supplied to each chamber.
According to the process of the present invention, the
- cation exchange membrane is never brought into direct contact
with the anode because they are separated by the gas generated
from the anode. Furthermore, the invention is free from the
phenomenon of localized high current passage through the cation
exchange membrane which can result i.n burning of the membrane. ;:
Since the space between the anode and the cat:ion exchange
membrane can be very smal:l. and s:Lnc:e the :LnterFclc:l.al desalted
:Layer on tlle membrlne :Ls cont:Lnuoll,ly stlrred by t:he p,as
! ~enernted erom tlle ~no(le, the tll:l.clcllels oE the :Lnt~lrEne:i.n:L
layer i8 mln:Lm:L~ed and tlll~s the l:Lm:Lting current clensLty ~.
increased remarkably. A lower electrolysis voltage can thus be
employed.
When the inner pressure in the cathode chamber is equal
to that in the anode chamber, the electrolysis voltage is unstab:Le
bec~use the positlon of the cation exchange membrane ls not
f:i.xed llnd eun somet:lm~s contact e:ltller tlle canode or tlle cathode.
~s can be seen Erom the Eollow:Ln~ exalllp:LQs and rcferential
examples, electrolysis voltage can fluetuate about 0.~ V by ~.
contact of the cation exchange membrane with one of the electrodes.
To ensure the maintenance of a higher inner pressure in the .
eathode ehamber, in spite of generated gas indueed pressure
fluctuati.ons, it i.s preferred to maintain the inner pressure
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of the cathode chamber at least about 0.02 atmospheres higher
than that of the anode chamber. ~owever, too large a pressure
differential can result in damage to the electrolytic cell
components, and accordingly the pressure differential is normally
ma:intained in the range of from about 0.02 to 0.48 atmospheres.
When the invention is utilized in the electrolysis of
saline water, thus resulting in the production of sodium
hydroxide in the cathode chamber, the hydroxy ion (OH ) which
migrates through the ion exchange membrane immediately contacts
the anode. Such contact brings about several disadvantages,
namely the formation of a perchlorate or an increase in the
amount of oxygen present in the generated chlorine gas.
It has been discovered that these disadvantages can be
avoided by maintaining the p~1 value of the anolyte at 3.5 or
les.~, as can clearly be see1l Erom the resu:Lts oE th~ ~ol:10wLn~
ex1)crL1nent.
1~X~ RLMEN'l'
. __ _ _
Electrolysis was performed with an electrolytic current
; density of 50 ~mp./dm2 and at a temperature of 90C using an
electrolytic cell having anode and cathode chambers separated
by a cation exchange membrane having an effective electrolytic
membrane area of 5 cm x 5 cm. ~ metal plate coated with a
so:l;ld so:1utlon o~ ruthcnlum oxlde was used as the anode and an
lron plate as the cathode. ~.2 N sallne water was circulated
in tlle anode chamber and an aqueous caustlc soda solution,
adjusted to 17%, was circulated in the cathode chamber. The
internal pressure of the cathode chamber was maintained
apprximately 0.39 atmospheres higher than that of the anode
chamber.
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~S~8~4~i6
Table 1 shows the rate of formation of chloric acid
estimated from the amount of chloric acid ion produced.
Table 2 shows the relation between pH value of the saline
watcr and the percentage of gaseous oxygen in the gaseous chlorine.
Table 1
Hydrogen ion ConcentrationRate of formation of
_ _of saline water_ CQO3 (g/lit. hr)
pH= 1.0 0.00
p~l = 2.0 0.00
pH= 3.0 <0.05
pH= 3.5 0.05
p~ O 0.09
p~ I.5 0.39
p~l = 5.0 0 ~5
'l'abLe 2
Hydrogen ion(A) amoullt of(B) amount of
concentration CQ2 gas gener- 0~ gas gener- (B)/(A)
o saline water ated (li~./hr.) ated (l:it./hr.) (%)
[ll ] = 0.9 N 5.12 16.9 x 10 9 0.33
[ll ~ = 0.1 N 5.08 20.8 x ]0 9 0.41
pEl = 1 5.07 23.3 x 10 3 0 . ll6
p~ .5 5.L230.2 x 10 3 0.59
y~l ~ 3.5 5.2~ 3:L.2 x :lO 3 0 . 60
pll - ~ 5.08 55.3 x 10 9 1 . 09
pH = 4.5 5.02 74.3 x 10 3 1.48
p~l = 5 5.00 192.2 x 10 3 3.84
'~o keep the pH of the anolyte at or below 3.5, a mineral
ac-Ld or a mixture of mineral acids, e.g. IICQ, ll2SO", HNO3, etc.,
may be added to the anolyte. HCQ is particularly preferred.
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The concentration of the acid is typically 0.5 N or less since
a higher concentration lowers current efEiciency.
The acid may be added directly to the anode chamber
or admixed before hand with saline water and then supplied to
the anode chamber.
The advantages of the process of the present
invention can be realized even when flat plate electrodes are
employed. However, the advantages are particularly conspicuous
when electrolysis is performed using gas-permeable metallic
electrodes while discharging gas generated from the electrodes
back of the electrodes.
"Gas-permeable metallic electrode" is intended to
identify an electrode made of metallic material having many
interst;ices o~ openings. Examples oE gas-permeable metallic
electrodes include expanded sheets, multi-rod sheets,
perforated sheets, meshes, etc. For anodic use, it is
particularly preferred that the electrode be coated with a
noble metal oxide.
Gas-permeable metallic electrodes are preferably
employed when gas is generated during electrolysi.s. Furthermore,
the structure of the electrolytic cell is preferably such that
the dis-tance between the electrode and inside of the par-tition
wall in each chamber is greater than that between the electrode
and the cation exchange membrane, such that gas generated on an
electrode surface at the current passing portion diffuses into
the circulating electrolyte behind the electrode to minimize
the gas content between the electrode and cation exchange
membrane. ~hen generated gas is permitted to ascend behind the
electrode by employing a gas-permeable metallic electrode and an
electrolytic cell where the non~current passing space kehind the
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electrode in each chamber is larger than the space between
the electrodes in the cation exchange membrane, a downcomer is
preferably provided between partition walls and the gas-ascending space.
With such a structure, the generated gas can qui'ckly migrate
from the front of the electrode to the gas-ascending space
behind the electrode, thereby permitting an electrolyte with a
low gas content to exist in the space between the cation exchange
membrane and the electrode and permitting the electrolyte to
circulate and stir the men~brane surface and the electrode surface
to minimi~e voltage drop. Thus, electrolysis can be carried
out with high current density.
For the purpose of illustrat:ing electrolytic cells suitable
for practiclng tlle process of the presenl: invent:ion, reEerence
may bc had to thc annexe(l drclwlngs, :Ln whlch:
L6 1 schcmcltic cross-sectLotl oE an c:Lec~rolytic ce:ll
LLlu~l~rcltlng ~ile prlnctp:l.c oE ~lle lllVen~:LOII;
Fig. 2 is a perspective back v:Lew of the electIode shown
in Fig. l;
Fig. 3 is a perspective view of an electrode oE an electro- -
lytic cell;
Fig. ~ is a partial cross-section of a bipolar electrolytlc
cel:L;
; 'I~'Lp. 5 :Ls a perspcct:Lve v:Lew, pnrt]y in scct:Lon, oE a
b:iuolar eletrolytlc cell vlewcd from the anocle s:Lde; and
Fig. 6 is a schematic slde elevation of a bipolar electrolytic
cell.
Referring now to Fig. 1, 2 represents a metal anode of
expanded sheet structure. During electrolysis, bubbles of
chlorine gas form on the current passlng side of the anode ;
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surface Since the space formed by support 71 behind the
an~de 2 is larger than that between the cation exchange
membrane and the anode, the gas migrates behind the anode,
accompanied by a flow of anolyte, and ascends. The face of
the anode is preferably of the construction illustrated in
Fig. 1 so that gas which is generated spontaneously migrates
as shown by the small arrows. The larger arrows represent
the flow of electrolyte even when the anode surface is flat,
and not slanted in the manner shown in Fig. l; a similar flow
pattern of electrolyte and gas occurs as long as the space
behind the anode is larger than that between the anode and the
membrane. However, better performance seems to be obtained
utili~ing an anode o the configuration illustrated in Fig. 1.
Chlorine yas which is evolved can be discharged ~rom
outlet 75. The electrolyte descends through downcomer 113
between -the gas-ascending space and the partition wall 111 and
between the cation exchange membrane 1 and anode 2, as shown by
the larger arrows. In Fig. 1 and Fig. 2, 72 is a partition
wall between the gas-ascending space and the downcomer 113 and
also serves as a conductive plate. 73 is a spacer and 112 a
conductive rod.
In processes where gas is generated at the cathode,
liquid flow can be promoted and the ratio of gas to liquid
decreased by employing a cathode chamber having a structure
equivalent to that shown in Fig. 1 and Fig. 2. In a preferred
embodiment, a ca-thode chamber of larger volume than that of the
anode chamber is employed to avoid current shielding by generated
gas.
In industrial applications, a bipolar system electrolytic
_9_
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.
~ aS6
cell is preferably employed, since it is easy to increase the
voltage of the direct current source and reduce the current
quantity. In bipolar system electrolytic cells, anode chambers
and cathode chambers are serially alternated, separated from
each other by means oE cation exchange membranes and parti.tion
walls.
The cathodes and anodes are placed on both sides of cation
exchange membranes as closely as manufacturing will permit. An
anode chamber is of course provided between the anode and the
partition wall, and likewise a cathode chamber for processes
involving cathodic generation of gas.
In a bipolar system electrolytic cell, back to back anodes
and cathodes are electrically connected to eacll other via the
part.l.t:Lon wal:l.
Thc Ca~i.OII exchange nlelllbraQec; nnd part:lt:k)n wnll9 are :E:lat,
and l)re~erably vert:lca:l. and pnra:l.:lel to eacll othel, to provlde
for easy gas separation. Controlling plates, to improve
gaseous separation, can be employed in both anode and cathode
chambers.
~ccording to the process of the present invention, the
inner pressure of cathode chambers is maintained higher than
tlla~ o.E anode chclmbers, to prevent cathode contact by the cation
excllange membranes. ~s long as the structure .ls such that
cathocles and anodes are arranged at flxed intervals, there i.s no
need to provide spacers between the cathodes and cation exchange
membranes. In processes where gas is cathodically generated,
it is also preferred to omit cathodic spacers to minimize gas
retention and attendant current shielding.
A bipolar system electrolytic cell, suitable for practicing
the process of the present invention, consists of an assembly
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wherein a multiplicity of electrolytic cell units are combined
by the interposition oE cation exchange membranes 1 between each
unit, each cell unit comprising an anode and a cathode separated
by a partition wall 111 and electrically connected by means of
a condllctive rod 112.
In Fig. 3, 2 is a gas-permeable metallic anode, having
behind it, separated by a partition wall, a cathode. 75 is an
outlet for anode gas and 76 an outlet for cathode gas. 77 is
an inlet for anolyte and 78 an inlet for catholyte. 81 is a
support and 82 a side bar. A downcomer, as in Fig. 1, is
employed for the purpose of increasing the ascending velocity
of the gas-liquid mixture in the space behind the porous
electrode. Without a downcomer, the descendlng velocity oE
~he li(lu:Ld between the membrane and the electrode is somewhnt
:I.ower and can result ln gas be:LIlg present :Ln tlle s[~ace between
the Incmbr~lne and the e:loc~rode. Wh:L:Le thls Ls oE no sub6t~nt:Lal
concern, it is preferred that the d:Lmensions of the downcomer
be determined according to operational current density and the
spacing between the electrode and the membrane.
Anode and cathode Illeshes are fixed on the mesh supports
71 by suitable means such as weldlng, etc. The mesh support
7:l and the conductor pipes 112 must of course be made o-f a metal
rcslstarlt to corros:lon by the electro:Lyte.
Generally speaklng, when the e:Lectrodes o~f a bLpolar
system electrolytic cell are in the form of flat plates, each
electrode may be used as a partition wall between cathode and
anode chambers. However, with porous electrodes, it is necessary
to use a separate partition wall. Any material can be utili~ed
for such a partition wall, if compatible with the electrolyte,
3G the electrolysis products, the electrolytic temperature, etc.
.
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Examples of su-Ltable partition walls include plastic plates,
metal plates, plastic-lined plates, concrete plates and
explosion bonded titanium/irol~ plates.
As cathode materials, gas-permeable iron plates such as
iron meshes, nets, poro~s plates and the like or iron plates
plated with nickel or a nickel alloy are suitable. The ratio
of the area of the openings to that of the metal of the mesh,
or the diameter of the rods and breadth of the interstices, can
be suitably selected to aid in gas discharge. It is important
5~ eS t~
l~{?~r7 that there be sufficient ~ss~ throug~h th~ cathode to permit
.1'.~
gas to freely migrate from the front to the back, while still
maintaining acceptable mechanlcal strength of the cathode.
Any kind of cation exchange membrane can be utilized.
In general, membranes made of a polylllel of a perfL~toros~llEonlc
acLd compound; s~l:Lfonlc acLd typo catloll exctlclnge membrancs
prel)ared by polymer:lxcltion oE styrcllc-dlviny:L benzetle ~ol.lt)wed
by sulEonatlon; carboxyllc acLd type cation exchan~e membranes
prepared by polymerization oE acrylic acid-divinyl benzene;
phosphoric acid type cation exchange membranes; and the like may
be employed. From a standpoint oE chlor:ine resistance, membranes
prepared from s~lbstrates of fluoro~contaln:Lng compounds are
preferred. The cation exchange membrclnes employed in the process
are preferably hlgh in catlon permst-~:Lect:Lvity, low Ln electric
reslstance and as thln as poss:Lble wlthout permlt~:Lng reverse
diffusion. Furthermore, it is desirable that the cation
exchange membranes be free from swelling or shrinkage induced
deformation under electrolysis conditions and, to this end, can
be reinforced by Teflon~ nets or other materlals.
; The process of the present inventlon can be utilized in
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8~S~
any electrolysis process whereill cation exchange membranes are
employed, whether it be merely a dual compartment or a multi
compartment system.
The distance between the membrane and the 'electrodes in
an electrolytic cell is determined by taking the manner of
gas discharge, as well as other factors, into consideration.
In general, the spacing is normally from 0.5 to 5 mm, prefera'bly
from 0.5 to 1.5 mm, dependent upon the limits of mechanical
precision.
Electrolysis can be performed at any desired temperature
in the range of from about 20 to 200 C, preferably from about
50 to 100C, dependent upon the materials employed. '~
Current density normally ranges from about 10 to 200 ~/dm2.
It is preferably as high as possible, as long as an extreme ' '
voltage rise is no~ effected. A suitable economical current
- density is higher than that in the case of prior art diaphragm
processes, namely from about 20 to 80 A/dm2. '~;'''' '
When electrolyzing aqueous sodium chloride solutions, a
'purified saturated or nearly saturated aqueous sodium chloride
solution is employed as the anolyte, as in conventional processes.
The aqueous sodium chloride anolyte solution is supplied
to each anode chamber in an amount selected to obtain a '
utilization efficiency of from 5 to 50æ. Water or a dilute
aqueous caus~ic soda solution is supplied as catholyte to the
..
'cathode chamber to maintain the concentration of the outlet
caus~tic soda constant.
The present invention is :illustrated in more detail in
~ .
the following examples.
:: . :'. '.
I3-
EX~MPLE I
The method of the present invention was practiced
utilizing a bipolar system electrolytic cell as illustrated in
Fig. 4 of the accompanying drawings.
In Fig. ~, the eation exchange membrane 1 is a sulfonic
acid type cation exchange membrane composed mainl~ of fluorine
resin. The anode 2 was preparecl by expanding a titanium plate
of 1.5 mm thickness into a perforated plate of 60% porosity
and then eoating the perforated plate with a solid solution
eomprising 55 mol % of ruthenium oxide, 40 mol ~ of titanium
oxide and 5 mol % of z:ireonium oxide. Cathode 3 is a perforated
plate prepared by expanding an :iron plate of 1.6 mm thiekness
to a porosity of 60%.
Both the anode 2 nlld c:ntllocl~ 3 nre :l.2 m lrl Length and
2.~ m :Ln wldtll ancl are maLntnllled vertLctll. nnd pnraLlol to enel
otller and separated by a dLstanee oE 2 mm. The partition wa:Ll
4 was obtaLned by explosion bonding a titan:ium plate of 1 mm
thickness onto an iron plate 6 of 9 mm thiekness, and positioned
so that the titanium s:Lde faees the anode. The spaee between
the anode 2 and titanium side 5 of the part:ition wall has been
eleetrieally eonneeted by being welded to a t:Ltanlum plate
rlb 7 of ll mm thLelcness, 25 mm wldth and ].2 m length. Thus an
anode ehamber ~ having n w:ldth of 25 mm :L8 prov:Lcled behind the
anode. Rlb 7, whleh ls vertleal, has been provided with holes
10 mm in diameter to faeilitate hori~ontal mlxing of gases or
anolyte.
The spaee between the eathode 3 and the iron side 6 of the
partition wall Ls eleetrieally eonnected by welding to an iron
plate rib 9 of 6 mm thiekness, ~5 mm width and 1.2 m length.
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Thus a cathode chamber 10 having a width of 45 mm is provided
behind the cathode. Rib 9, which like rib 7 is also vertical,
is also provided with holes of 10 mm in diameter to facilitate
horizontal mixing of gases or catholyte.
The anode and cathode chambers are surrounded by an iron
frame 11 of 16 mm thickness the iron is lined with a 2 mm thick
titanium plate wherever exposed to anolyte. :[ron frame 11 is
equipped with a charging nozzle 13 and discharging noz~le l~i
for the anolyte, and a charging nozzle 15 and discharging nozzle
16 for the catholyte.
7~t Units of the above described electrolytic cells are
serially arranged with cation exchange n~embranes 1 :interposed
betwcen ind:Lviclun]. cells. ~n ethy:lene-prol)ylc~llc r~lbber packing
17 .Ls LQterposed botwecen the iron rrame :Ll ~:cc~Lc)lls t() mnLrltaLn
n 2 mn1 spacL~ etweell oplc)secl ~IQodcs and catllodc!4 allcl ~o prcvellt
e:Lectrolyte leakagc. No spacers are ut:LLi~ecl in the current
passage portions between the anodes ancl cation exchange membranes
or between the cathodes and cation exchange membranes. On one
end of the unit, as shown ln F:Lg. 6, there is provided an
electrolytic cel] unit 18 having only an anocle cllamber, and on
the other end an electrolyt:Lc cell un:it 19 hav:Lng only a catilode
cllalnber. The unlts are p:Lacecl on a ~iLter pres~: stancl to
as~:embLe the bi.l~olar sy~telll e:Lcctro:LytLc ceL:I.
With reference to Fig. 6, a direct current voltage is
applied to both ends of the bipolar system electrolytic cell so
that the current flows in series through the individual cell
units. Catholyte and anolyte are individually charged from
respective headers through f:Lexible hoses into the individual
cell units, and then discharged. The catholyte :is charged fro~
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4S6
a catholyte tank througll a catholyte header into the cathodechamber of each cell by means of a pump. Subsequently, the
catholyte, in the form of a gas-liquid mixture, is discharged,
recycled in the catholyte tank, and submitted to gas-liquid
separation. Likewise, the anolyte is charged from an anolyte
tank through an anolyte header into the anode chamber of each
cell by means of a pump. Subsequently the anolyte, in the
form of a gas-liquid mixture, is discharged, recycled in the
anolyte tank, and subjected to gas-liquid separation.
Electrolysis was performed utili~ing an aqueous sodium
chloride solution as the anolyte and an aqueous sodium hydroxide
solution as the catholyte. Both catllolyte and anolyte were
charged at a rate of 600 liters per hour. Saturated aqueous
~ m chlorLde and hydrocll:Lorlc acLd were added l:o the anolyte
tanlc to ohtlLn a sod:ium chlorlde conccn~rntioll oE 2.5 N aln(l a
pll o~ 3 nt the anoJy~e challlL)cr ~ tlet. Pllre water was adde(l
to the catholyte tank to obtain 1 sodiulll hydroxLde concentra~io
o~ 5 N at the cathode chamber outlet. The cathode and anode
chambers were maintained at a temperature of 90C. A direct
current was applied at a current density of 50 ~/dm2, i.e. a
direct current of 1~.200 amperes.
Chlorine gas was generated at the allode and hydrogen gas
at the catllode. Tlle d:LEEerence betweell the :Lnner pressllre o~
tlle cathode chalnber and that oE the anode chambe~ was contro:Lled
by controlling the inner pressures of the anolyte and catholyte
tanks, and the pressure difference between the two chambers
measured by means of a mercury manometer. The relationship
between the pressure differential and electrolysis voltage per
unit cell is shown in Table 3.
16-
'
. ~.
: . . . -: . . . . , . . , , . : . . . . . . ... . .
, ,: .. ~ . : . . . . ,: . : . . : ~ . ~ . , , . . :
Table 3
Pressure difference Electrolysis voltage
(m water column) (volts)
4 4.11
0 3.7 - 3.9
~ 0.2 3.72
+ 1 3.65
+ 2 3.65
+ 5 3.65
Note: The mark "+" shows that the inner pressure
of the cathode chamber was higher than that
of the anode chaMber.
The effectiveness of the present invention is bel:;eved
clear from Table 3.
The electro:Lytic ce:l.l was d:L~assellll)led rlnd Lnsl)ecte(l; no
bnr~lLn~ or other dnmage of the catLon exc:hc~ c~ elllbrane wn~:
observecl.
_X~M~LE II
An electrolytic cell similar to that of Example I, the
titanium plate rib 7 and lron plate rib 9 were varied :in width,
thereby varying the widths of the cathode and anode chambers.
Electrolysis was then conducted as in Example I, except:
that the electrolysLs temperclt:ure was 70~C, the current dens:ity
was 30 ~/dm2, the spac:lllg bet~/een tlle catllode ~Ind nno(le was
5 mm, and the inner pressure of the cathode chamber maintained
2 mm (water column) higher than that of the anode chamber.
The variations in electrolysis voltage per unit cell are
shown in Table 4.
~ 30
- '
~ 17-
. .:
5~
Table 4
Width of Width of Electrolysis
cathode chamber anode chamber voltage
(mm) (mm) (volts)
3.26
3.25
3.27
3.29
3.33 :-
3.45
3.39
: 20 ~0 3.3~
3.29
3.27
3.~,
. ~0 3.~.6
Rl,l~ TI~I. IEXA~II'I,Ii. I
The elecL-rolysis of Examp:Le I was repe~ted, util:i~lug the
same electrolytic cell as in Example I, except that spacers
having a porosity of 60%, and which had been prepared by Eorming
cuts in a 1 mm thick Teflon cloth and expancling the thu~: treated
cloth, were inserted individual.ly between the anocle and the
catlon exchange membrane and between the cathocle and the cat:ion
exchallge membrane. No dc~press:Lon o~ electro:Ly::ac; vo:ltage, as
cllsplayecl by the present :invent:lon, was observed no n~atter how
the pressure differenkial between the anode and cathode chambers
was varied. Moreover, the electrolysis voltage reached 3.7 -
.. volts at a current density of 12 A/dm2; the high current density
and low electrolysis voltage as in Examp.le I could not be attained.
jl/ -18.-
, ... . .
,., ~ ,,1 .
: : . , , . . : , , , , . : ,
~L0~4~6
EXAMPLE III
:
Using a two eompartment electrolytic cell having an eEfect- -
ive electrolytic membrane area of 5 cm x 5 cm, a 2.5 N aqueous
sGdium chloride solution was recycled through a 5 lite~
vessel and the anode chamber, and an aqueous 17% caustic soda
solution recycled through a similar 5 liter vessel and the
cathode chamber. The electrolytes were maintained at 75C
and eontinuous eleetrolysis performed for 120 hours under a
current density which was 50 A/dm2 at both the eation exchange
membrane surface and the anode plate surface. During eleetrolysis,
the anolyte was maintained at a eoneentration in the range of
2.3 to 3.0 N by intermittently adding reagent grade solid
sodium ehloride. A pE-I deteetor was llnked into the anolyte
elreulatlon plpe and employed to automntiea:l:ly eontIol the
adclLtlon oE hydrochlorlc aeld to maLnta:Ln an anolyte p~l of 2.0
~ 0.2. 'rhe lnner pressure of the eathode ehamber was malnta:Lned
1 mm (water column) hlgher than that of the anode chamber.
An anode havlng a solid solution of ruthenium oxide and
titanlum oxlde eoated on metallie tltanium was employed together
w:Lth a eathode having nlekel rhodanide plated iron surEaee. A
1 mm thiek sulfonie aeid type ion exehange membrane, having a
polypropylene fabrie eore materlal, was employed as the eation
exehange membrane.
There ~-&s no deteetable eh:lorle aeld lons in the anolyte
following 120 hours of eontlnuous eleetrolysis. The oxygen gas
eontent in the ehlorlne gas between the ll9th and 120th hour
was found to be 0.39%.
A eorresponding result was obtained upon repetition of
the example utillzing an anode havlng a portion of ruthenium or
jl/ -19
.
,:
~: . . . '~ . , ,, ,'; . `' . . : ~' ' ' ' . , ' ''
- lq.~8~56
platinum precipitated in admixture in the noble metal coating. -
EXAMPLE IV
..
Using the same apparatus as in Example III, 4.2 N
aqueous sodium chloride solution was recycled through the 5
liter vessel and the anode chamber, and an aqueous 17% caustic
soda solution recycled through the other 5 liter vessel and ~he
cathode. The electrolytes were maintained at 90C and
electrolysis performed with a current density of 50 A/dm2 at
both the cation exchange membrane surface and the anode plate
surface.
During electrolysis the sodium chloride concentration
of the anolyte was maintained within the range of ~.2 N ~ 0.2 N
by intermittently adding solid sodium chloride, The anolyte
was sampled from time to time to measure the acid concentration
and adjusted to 0.2 N ~ 0.1 N by the addition of hydrochloric
acid. The inner pressure of the cathode chamber was maintained
1 m (water column~ higher than the anode cham~er.
A plate electrode having a 3 ~ thickness ruthenium
oxide coating on a 1 mm thick titanium alloy was employed as
the anode, and an iron plate as the cathode. A 0.7 mm thick
i caxboxylic acid type ion exchange membrane, having a poly-
prop~lene cloth core, was used as the cation exchange membrane.
Electrolysis was performed and the amounts of caustic
soda and chloric acid formed during electrolysis measured.
Additionally, the composition of the chlorine gas formed during
the one hour preceding completion o electrolysis was analyzed.
i The amount of caustic soda formed was 687.1 g, which
is 92.1~i of the theoretical amount. No chloric acid formation
was observed in the anolyte. The proportion of oxygen gas
3C contained in the chlorine gas formed during the 1 hour preced:Lng ccmpletion
-20-
hn~ ~ . .. . . . . .. . . .
. ,. , . , - . : ., . : , :
. , . ' . .' ' . . : '' .' ' ' : ': '.. .. ' , : ' .
:... . ~ ' . ,. :, , ,, . , :. . ..
~(~8~456
of electrolysis ~7as 0.44%.
EXA~IPLE V
An aqueous sodium chloride solution was electrol.yzed over
a lengthy period of time utilizi.ng an electrolytic cell assembly
com~osed of three pairs of two compartment electrolytic cells,
connected in series, having an effective electrolytic area of
100 dm2 (100 cm x 100 cm).
... .
A sulfonic acid type cation exchange resin membrane
eomposed mainly of fluorine resin was employed. -
During electrolysis, the anolyte was controlled to provide
a concentration of 290 to 310 g/Q of sodium chloride in the
anolyte charged to the electrolytic cell and a sodium chl.oride
concentration oE 2~0 to 260 g/Q :in the anolyte cIi.scharged from
~IIe electrt).Lyt:Lc ce.l.l by eIllploy:Lng ~I rocycle system :Lnvol.v:Lng
recyc.I.l.ng oE th(~ aIlol.yte througII ~he e:I.ectro:I.yti.c cel.I., a
dl:Lutc aquet)us sodlum cI~:l.oI::LcIe solutlon tank, a sod:ium chlorlde
dissolution tower, an ion exchange resin tower for removal of
calc:ium and magnes:ium and a saturated sodium chloride solution
pur:iEi.cation tank, respectively.
20 Hydrochloric acid was added to the anolyte to mainta:in a
p~I of about 2.5 :Ln the anolyte discharg:Lng from the electrolytic
ce:L:I
The catholyte was ma:I.ntal.ned at n concentratlon oE about
17~ sodium hydroxlde. :
.Electrolysis was performed while maintaining the inner ..
pressure of the cathode chamber about 0.3 m (water column) higher
than that of the anode chamber. :
Electrolysis was continuously performed for 65 days ~about
1600 hours) at a temperature of 75~C and a current density of :
21- :
,~,,c, :' ~
. - ,. , .: ,
. , , ,
56
~0 ~/dm2.
The chloric acid ion concentration was periodically measured
during electrolysis, and during the first 20 days of electrolysis
increased little by little. ~ter 25 days of electrolysis, the
chloric acid concentration became substantially constant in an
amount of about 0.2 g/Q and electrolysis proceeded stably
without any detrimental efEect such as a decrease in sodium
chloride solubility.
The proportion of oxygen gas in the chlorine gas averaged
in the rang2 of from O.l to 0.2%.
The current efficiency, based on the amount of sodium
hydroxide formed, was about 95~.
The anode utilized was prepared by coating a l.5 mm
thickness tltan:Lu1n mesh havlng a poroslty oE 60~ w~th a solid
solutlon compr:Lslng 70 mol ~ oE ruthellL~ oxL(1e, 20 mol % o~
tltan:Lu1n oxlde anc1 lO moL % o~ zLrconlu1n ox:Lde. L'he cathoc1e
utl:Ll~ed was a 1.5 mm th:Lck :Lron mesh havlng a porosity of 60%.
EXAMPLE VI
~ copolymer of perfluoro[2-(2-fluorosulfonylethoxy)-propyl-
vinyl ether] with tetrafluoroethylene was molded into a membrane
of O.l mm thickness. The membrane was bonded with a Teflon~ net
and then hydrolyzed to prepare a cation exchange membrane having
a th:lckness oE 0.12 mm. The membrane was :Lmpregn1ted at 90C
wlth a monomer solutLon compr:Lslng 30 parts of styrene, 20 parts
of acrylic acicl and 30 parts of divinylbenzene, and then poly-
merized at 100C to obtain a cation exchange membrane. Using
the thus obtained membrane, cut into pieces of 1.2 m2 in area,
S0 pairs of bipolar system electrolytic cells were assembled.
Mesh electrodes, such as is shown in Figs. l, 2 and 3, were
jl/ -22-
. .
.
. :,- ~ , ,
- ,
S6
employed each having 1 m2 in effective area. The anodes were
prepared by expanding a 1.5 mm thick titanium plate which had been
fusion coated with ruthenium oxide and which were of the
configuration illustrated in Fig. ~. The cathocles were prepared
by plating a 1.5 mm thick iron mesh with nickel sulfide. The
conductors used to connect the electrodes were fastened by
screwing. In each chamber the spacing between the cation
exchange membrane and the electrodes was 2 mm.
The width of the gas-ascending space represented by 71 in
Fig. 1 was 30 mm, and the width of the downcomer was 7 mm.
Purified aqueous sodium chloride solution having a sodium
chloride concentration of 305 g/Q was recycled through the anode
chamber at a flow rate of 11,515 kQ/hr. Water was continuously
a(l(led to the so:Lut:Lon exit:ing the cathodc chc~ bor, In an alnount
oE l0,063 kg/llr , to adJuc;t the con(elltrltLorl o~ tlle sodLIlnl
llyd~oxIde so:L~Itloll to 20~. Tll(! lnner press-lro oE ~he cal:llo(le
challlber was malnta:Lned 2 m (water co]umn) higher than that of the
anode chamber.
Electrolysis was performed while applying a current of
5,000 amperes to the electrodes at each end. The amount of
chlorine anodically generated was 31~.5 kg/hr., and the amount
of 20% hydroxide solutiol~ obtalned from the cathode chamber was
:L5,21:L.8 kg/hr. Acldit:lonll:Ly, the amount of cathod:ical:Ly
gellerate(l hydrogen was 9,325 g/hr. Tlle current eEficiency WRS
95.1%, and the voltage of each electrode was 3.86 volts. The
operation proved to be capable of being stably performed for
a lengthy period of time.
~XAMPLE VII
A copolymer of perfluoro[2-(2-flllorosulfonylethoxy)-propyl-
jl/ -23-
:.
.' ~ ,
:.' . ' ` : ,
.. . . .
~ 8~;~45l~ vinyl ether] with tetrafluoroethylene was molcled into a membrane
of 0.12 mm thickness. The membrane was hydrolyzed, impregnated
at 80C with a solution of perfluoroacryllc acid, and then
polymerized to obtain a cation exchange membran'e of 0.144 mm
thickness and 1.2 m x 1.2 m in area. Using such a membrane,
50 pairs of electrolytic cells, of the type having a gas-liquid
separation chamber in the upper part of each cell as shown in
Figs. 1, 2 and 3, were assembled. The'structure was identical
in shape with that of Example VI, except for the gas-liq~lid
separation chambers and the anodes. The anodes used in this
example were prepared by hori~ontally arranging parallel
ruthenium oxide-coated titanium rods of 3 mm diameter with a
resultant 2 mm spac:ing hetween rocls. 'rhe e~Fectlve c~lrrellt
pa~;sage are~l oE eclch anode prove(l ~o be :l la~.
A pur:lrLccl ~q~lc-ous ~o(llllln cll'l.orlcle ~;olutloll h~lvlllg fl
socliulll chloricle concellt-r.ltion of 305 g/Q was recycled through
the anode chamber at a flow rate of 12,820 kQ/hr. Water was
continuously added to tile solut:ion discharging from the cathode
chamber, in an amount of 1,127.4 kg/hr., to maintain a sodium
hydroxide concentration in the solution of 31.1%.
Electrolysis was performed whlle apply:ing a c-lrrent oE
5,000 alllp~res to the electrocle~s Ln eclcll end. 'I'he amo~lllt of
anc)cllccllly generatecl ehlorLne was 3:Ll.2 kg/hr., the amount of
sodium hydroxide obtained from the cathode chamber discharge ~-
flow was 1,127.4 kg/hr., and the amount of hydrogen generated
was 9,325 g/hr. The current efficiency, based on the production
oE sodium hydroxide, was 96.1%, and the voltage of each electrode
was 3.95 volts. Again, electrolysis could be stably maintained
for a lengthy period of time.
~ 2~l-
, . : . :: .
