CA1088456A - Electrolytic cell with cation exchange membrane and gas permeable electrodes - Google Patents
Electrolytic cell with cation exchange membrane and gas permeable electrodesInfo
- Publication number
- CA1088456A CA1088456A CA221,570A CA221570A CA1088456A CA 1088456 A CA1088456 A CA 1088456A CA 221570 A CA221570 A CA 221570A CA 1088456 A CA1088456 A CA 1088456A
- Authority
- CA
- Canada
- Prior art keywords
- anode
- cathode
- gas
- electrolysis
- cation exchange
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/34—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis
- C25B1/46—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis in diaphragm cells
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B3/00—Electrolytic production of organic compounds
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
- C25B9/70—Assemblies comprising two or more cells
- C25B9/73—Assemblies comprising two or more cells of the filter-press type
- C25B9/77—Assemblies comprising two or more cells of the filter-press type having diaphragms
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Inorganic Chemistry (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
In an electrolytic cell having a cation exchange membrane as a diaphragm partitioning said cell into cathode and anode chambers, electrolysis of an aqueous electrolyte solution is conducted while generating gas at the anode by maintaining the pressure within the cathode chamber higher than that within the anode chamber. Some difficulties caused when electrolyzing an aqueous alkali metal halide solution to form alkali metal hydroxide in the cathode chamber are overcome by adjusting the anolyte to a pH <3.5. A preferred electro-lytic cell for use in the process is also disclosed.
In an electrolytic cell having a cation exchange membrane as a diaphragm partitioning said cell into cathode and anode chambers, electrolysis of an aqueous electrolyte solution is conducted while generating gas at the anode by maintaining the pressure within the cathode chamber higher than that within the anode chamber. Some difficulties caused when electrolyzing an aqueous alkali metal halide solution to form alkali metal hydroxide in the cathode chamber are overcome by adjusting the anolyte to a pH <3.5. A preferred electro-lytic cell for use in the process is also disclosed.
Description
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 jl/ -2-.~,~ '' ' ! .
.' `. :. ' ' ` '. , : ' -: ," ,; ' ' .` i ,' ..
. , '. . . :.
389LS~;
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 jl/ -3-.' , , , ' , .
, .; ~ . , ~ 8~45~
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 . ..
. ~ ~
. ~
~ '' . . ' ~ .
' ~ , ' : ~ . ~ ; - .
,: . .: :
: ~ . . : : ., ~81~3~5~6 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.
~' jl/ -5-.' i~ ' ..
.. . .. . . . . . . . . . . . . .... .
~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.
jl/ -6- ~, . . , : . , .
'.. . ~ . . ... :
., , . , . .. : ., . . :', 8~
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 hm :: , . - - . - ,. . . . . .
-, . ,:
. . . . . , . : . . . : , . .
`' ~L0~84~5;6 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 ;
jl/ -8-. ~'~``' , .
.
. .
.
`: : ' ': .' . ~ . :
,: ~ . ~ ., , ,.,, . . : ' .' ' :: ....... , .~ . , . : :
., : , .
ii6 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_ bm:
.
~ 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 ,,3, jl/ -10- .
'' ~ ~' ' , ' ,, ' "-, ' . :. ., 4S~
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.
.
. . - , ~
', 1 ', ` ~ ` ~ . ~ ` '' , . , , ' ' ~ ~ ' , , '' ' " , ', ' ' ' .
LS~, 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 ~; j]/-12-. - . . ... . .
.
~, . . . .
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.
:: . :'. '.
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
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 jl/ -2-.~,~ '' ' ! .
.' `. :. ' ' ` '. , : ' -: ," ,; ' ' .` i ,' ..
. , '. . . :.
389LS~;
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 jl/ -3-.' , , , ' , .
, .; ~ . , ~ 8~45~
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 . ..
. ~ ~
. ~
~ '' . . ' ~ .
' ~ , ' : ~ . ~ ; - .
,: . .: :
: ~ . . : : ., ~81~3~5~6 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.
~' jl/ -5-.' i~ ' ..
.. . .. . . . . . . . . . . . . .... .
~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.
jl/ -6- ~, . . , : . , .
'.. . ~ . . ... :
., , . , . .. : ., . . :', 8~
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 hm :: , . - - . - ,. . . . . .
-, . ,:
. . . . . , . : . . . : , . .
`' ~L0~84~5;6 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 ;
jl/ -8-. ~'~``' , .
.
. .
.
`: : ' ': .' . ~ . :
,: ~ . ~ ., , ,.,, . . : ' .' ' :: ....... , .~ . , . : :
., : , .
ii6 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_ bm:
.
~ 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 ,,3, jl/ -10- .
'' ~ ~' ' , ' ,, ' "-, ' . :. ., 4S~
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.
.
. . - , ~
', 1 ', ` ~ ` ~ . ~ ` '' , . , , ' ' ~ ~ ' , , '' ' " , ', ' ' ' .
LS~, 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 ~; j]/-12-. - . . ... . .
.
~, . . . .
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.
:: . :'. '.
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.
~, ,, , q.
,, . . . : . , ..
.
. ' ~ ' .
' ' ' , ' ' : ' ~' 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~
jl/ -15-. ,,, , ., '''.,, ..'; '"'"": ' ' ." ~,..: ., ' .:
', ' ' ~ . , . ,` ' ' ,' ~ ' , ; ' 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.
' . ~.
: . . . -: . . . . , . . , , . : . . . . . . ... . .
, ,: .. ~ . : . . . . ,: . : . . : ~ . ~ . , , . . :
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)
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.
~, ,, , q.
,, . . . : . , ..
.
. ' ~ ' .
' ' ' , ' ' : ' ~' 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~
jl/ -15-. ,,, , ., '''.,, ..'; '"'"": ' ' ." ~,..: ., ' .:
', ' ' ~ . , . ,` ' ' ,' ~ ' , ; ' 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.
' . ~.
: . . . -: . . . . , . . , , . : . . . . . . ... . .
, ,: .. ~ . : . . . . ,: . : . . : ~ . ~ . , , . . :
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 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, :' ~
. - ,. , .: , . , , , ~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-. .
.
. :,- ~ , , - , 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-, . : . :: .
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 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, :' ~
. - ,. , .: , . , , , ~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-. .
.
. :,- ~ , , - , 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-, . : . :: .
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a process for the electrolysis of an aqueous electrolyte solution in an electrolytic cell having an anode and a cathode and having a cation exchange membrane as a diaphragm partitioning said cell into cathode and anode chambers which comprises conducting electrolysis while generating gas at the anode, the improvement comprising maintaining the pressure within the cathode chamber higher than that within the anode chamber.
2. A process as claimed in Claim 1, wherein electrolysis is conducted while discharging the gas generated at the anode on the side of the anode remote from the cation exchange membrane.
3. A process as claimed in Claim 1, wherein electrolysis is conducted while gas is being generated at the cathode by using an electrolytic cell having cathode chambers of larger volume than the anode chambers, the gases generated at the respective electrodes being discharged on the sides of the respective electrodes remote from the cation exchange membrane.
4. A process as claimed in Claim 1, 2 or 3, wherein the pressure within the cathode chamber is maintained about 0.2 to 0.48 atmospheres higher than that within the anode chamber.
5. A process as claimed in Claim 1 or 2, wherein a gas-permeable metallic plate is used as the anode.
6. A process as claimed in Claim 3, wherein gas-permeable metallic plates are used as the anode and the cathode, respectively.
7. A process as claimed in Claim 3, wherein the aqueous electrolyte solution is saline water.
8. A process as claimed in Claim 7, wherein mineral acid is added to the anolyte to maintain the pH value of said anolyte at 3.5 or less.
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP26775/74 | 1974-03-09 | ||
| JP49026775A JPS50120493A (en) | 1974-03-09 | 1974-03-09 | |
| JP11255674 | 1974-09-30 | ||
| JP112556/74 | 1974-09-30 | ||
| JP14174574A JPS5168477A (en) | 1974-12-10 | 1974-12-10 | Kairyosareta denkaihoho |
| JP141745/74 | 1974-12-10 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1088456A true CA1088456A (en) | 1980-10-28 |
Family
ID=27285534
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA221,570A Expired CA1088456A (en) | 1974-03-09 | 1975-03-07 | Electrolytic cell with cation exchange membrane and gas permeable electrodes |
Country Status (8)
| Country | Link |
|---|---|
| BR (1) | BR7501374A (en) |
| CA (1) | CA1088456A (en) |
| DE (1) | DE2510396C3 (en) |
| FR (1) | FR2263034B1 (en) |
| GB (1) | GB1487284A (en) |
| IT (1) | IT1034107B (en) |
| NL (1) | NL169618C (en) |
| SE (1) | SE432447B (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2658189C2 (en) * | 1976-12-22 | 1979-02-15 | Metallgesellschaft Ag, 6000 Frankfurt | Process for the electrochemical production of olefin oxide |
| USRE30864E (en) | 1977-06-27 | 1982-02-09 | Olin Corporation | Process for electrolysis in a membrane cell employing pressure actuated uniform spacing |
| US4142950A (en) * | 1977-11-10 | 1979-03-06 | Basf Wyandotte Corporation | Apparatus and process for electrolysis using a cation-permselective membrane and turbulence inducing means |
| IT1118243B (en) * | 1978-07-27 | 1986-02-24 | Elche Ltd | MONOPOLAR ELECTROLYSIS CELL |
| DE2914870A1 (en) * | 1979-04-12 | 1980-10-30 | Hoechst Ag | METHOD FOR CHLORINE AND COOLING THE ANOLYTE OF ALKALI HALOGENIDE ELECTROLYSIS |
| US4265719A (en) * | 1980-03-26 | 1981-05-05 | The Dow Chemical Company | Electrolysis of aqueous solutions of alkali-metal halides employing a flexible polymeric hydraulically-impermeable membrane disposed against a roughened surface cathode |
| DK501485A (en) * | 1984-11-05 | 1986-05-06 | Dow Chemical Co | ELECTROLYTE CELL AND METHOD OF OPERATING THE SAME |
| US4822460A (en) * | 1984-11-05 | 1989-04-18 | The Dow Chemical Company | Electrolytic cell and method of operation |
| GB9224372D0 (en) * | 1992-11-20 | 1993-01-13 | Ici Plc | Electrolytic cell and electrode therefor |
| CN118241225B (en) * | 2024-05-27 | 2024-08-16 | 山东菜央子盐场有限公司 | Method for extracting bromine from chlorine-free brine |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1196631A (en) * | 1966-05-31 | 1970-07-01 | Monsanto Co | Electrolytic Diaphragm Cell |
| US3496077A (en) * | 1967-12-18 | 1970-02-17 | Hal B H Cooper | Electrolyzing of salt solutions |
| BE790369A (en) * | 1971-10-21 | 1973-04-20 | Diamond Shamrock Corp | METHOD AND APPARATUS FOR THE PREPARATION OF HYDROXIDES FROM HIGH PURE ALKALINE METALS IN AN ELECTROLYTIC TANK. |
-
1975
- 1975-03-06 GB GB9388/75A patent/GB1487284A/en not_active Expired
- 1975-03-06 SE SE7502502A patent/SE432447B/en not_active IP Right Cessation
- 1975-03-07 BR BR1374/75A patent/BR7501374A/en unknown
- 1975-03-07 NL NLAANVRAGE7502738,A patent/NL169618C/en not_active IP Right Cessation
- 1975-03-07 CA CA221,570A patent/CA1088456A/en not_active Expired
- 1975-03-07 FR FR7507198A patent/FR2263034B1/fr not_active Expired
- 1975-03-07 IT IT21049/75A patent/IT1034107B/en active
- 1975-03-10 DE DE2510396A patent/DE2510396C3/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| IT1034107B (en) | 1979-09-10 |
| DE2510396C3 (en) | 1987-01-22 |
| FR2263034B1 (en) | 1978-03-17 |
| DE2510396A1 (en) | 1975-09-11 |
| NL169618B (en) | 1982-03-01 |
| DE2510396B2 (en) | 1980-04-17 |
| NL7502738A (en) | 1975-09-11 |
| SE7502502L (en) | 1975-09-10 |
| SE432447B (en) | 1984-04-02 |
| GB1487284A (en) | 1977-09-28 |
| NL169618C (en) | 1982-08-02 |
| BR7501374A (en) | 1976-11-30 |
| FR2263034A1 (en) | 1975-10-03 |
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