CA1075199A - Electrolytic cell and method for the production of oxyhalogens - Google Patents
Electrolytic cell and method for the production of oxyhalogensInfo
- Publication number
- CA1075199A CA1075199A CA181,534A CA181534A CA1075199A CA 1075199 A CA1075199 A CA 1075199A CA 181534 A CA181534 A CA 181534A CA 1075199 A CA1075199 A CA 1075199A
- Authority
- CA
- Canada
- Prior art keywords
- cell
- compartment
- electrodes
- anodes
- cathodes
- 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
Links
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
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
- C25B11/036—Bipolar electrodes
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
Abstract
ELECTROLYTIC CELL AND METHOD FOR
THE PRODUCTI?E OF OXYHALOGENS
ABSTRACT OF THE DISCLOSURE
Multi-polar electrolytic cells for manufacturing oxyhalogen compounds include terminal compartments containing monopolar electrodes, and a number of bipolar electrode compart-ments interposed between the terminal compartments, each compartment being substantially enclosed and non-communicating with the other compartments. Open-ended electrically insulating conduits extending form the walls of each compartment are adapted to provide a current leakage path and efficient circulation of electrolyte solution through each compartment when the cell is immersed in a reaction tank containing electrolyte solution.
Dimensionally stable anodes and cathodes in each compartment are generally foraminous sheets interleaved in horizontal position but may also be interleaved solid sheets disposed vertically or intermediate horizontal and vertical positions. The cell structure provides an excellent path for circulation of the electrolyte during electrolysis and minimized electric current leakage between adjacent compartments. A process for the preparation of sodium chlorate is described.
THE PRODUCTI?E OF OXYHALOGENS
ABSTRACT OF THE DISCLOSURE
Multi-polar electrolytic cells for manufacturing oxyhalogen compounds include terminal compartments containing monopolar electrodes, and a number of bipolar electrode compart-ments interposed between the terminal compartments, each compartment being substantially enclosed and non-communicating with the other compartments. Open-ended electrically insulating conduits extending form the walls of each compartment are adapted to provide a current leakage path and efficient circulation of electrolyte solution through each compartment when the cell is immersed in a reaction tank containing electrolyte solution.
Dimensionally stable anodes and cathodes in each compartment are generally foraminous sheets interleaved in horizontal position but may also be interleaved solid sheets disposed vertically or intermediate horizontal and vertical positions. The cell structure provides an excellent path for circulation of the electrolyte during electrolysis and minimized electric current leakage between adjacent compartments. A process for the preparation of sodium chlorate is described.
Description
~'7~
r3AClC_ROOND OF Tl-lr INVPNl10 1) Field oE the Inveotion This invention relates to multipolar electrolytic cells for tlle Use in the production of oxyhalogen compounds such as sodiurn chlorate by electrolysis of an all<ali metal halide such as sodium chloride. More specifically, this invention relates to mul tipolar electrolytic cells including bipolar electrodes which provide excellent electrolyte solution circulation and high current efficiency in the production of oxyhalogen solutions.
r3AClC_ROOND OF Tl-lr INVPNl10 1) Field oE the Inveotion This invention relates to multipolar electrolytic cells for tlle Use in the production of oxyhalogen compounds such as sodiurn chlorate by electrolysis of an all<ali metal halide such as sodium chloride. More specifically, this invention relates to mul tipolar electrolytic cells including bipolar electrodes which provide excellent electrolyte solution circulation and high current efficiency in the production of oxyhalogen solutions.
2) Descrie~rl of the Prior Art Multipolar electrolytic cells including bipolar electrodes have been used for 10 the production of oxyhalogen compounds since this type of cell is compact and does not :~ reguire electric current lead and exposed metallic mcmbers connecting tlle busbars to the intermediate electrodes. By rnaking elec~trical connections to the terrninal multipolar electrodes only and circulating electrolyte through the compartments intermediate, the terminal electrodes corrosion and con~amination of the electrolyte by the evolved gases r eacting with exposed parts connected to the inter-nediate electrodes is avoided. In the production of sodium chlorate, sodiurn chloricie ' electrolyte is decomposed by electrolytic action to rapidly form ions which subsequently by a much slower chemical reaction combine to form sodium chlorate. In ~! order to maintain good current efficiency and optimum reaction conditions, the 20 electrolytic cell is generally positioned within a reaction tank. To assure optimum operating conclitions, the electrolyte should circulate rapidly and turbulently through the cell and then circulate between tl1e reaction tank and electrolytic cell a~ a rate which provides minimum time for reaction of the products of electrolysis in the cell and maximum residence time for completion of the chemical reaction of the products " ::
in 'the reaction tank. As the electrolyte passes in parallel flow upwardly through the cell units, It is subjected to electrolysis and hydrogen gas is generated at the cathode surface of each cell ~mit. The continuous circulation of the electrolyte in the above-described parallel p~ttern is caused prirnarily by the generation of hycirogen gas bubbles at the ~cathode surface. During the residence time in `the holding tank, the ~75~L9~
relatively slow chc~-nical reacLlon involYirlg the combination of hypochlorous aci(i ancl hypochlorite ion accorcling to the equation ~ CIO t OCI = C103 ~ 211CI takes place, the hypoclllorous ackl and hypoclllorite ions being generated by the relativel~ fas~
electrolytic reaction in the cell unit. Considerable heat is generated during the electrolysis in the cell units, and to insure ef Eicient performance at the overall operating conditions and for stability of the materials of construction, it is necessary to provide for removal of the generated heat. Cooling coils are generally irnmersed in the reaction or holding tank to maintain suitable operating temperatures.
~ 'Yhen suitable chemical and pH conditions are maintained in the operation 10 of multipolar electrolytic cells, current efficiency is dependent primarily on the rate of flow of the electrolyte solution through the cell units, the currcnt leakage loss and holding tank residence time. Maximum current leakage occurs througll the inlets and ~- outlets and, to some extent, around the edges of the bipolar plates of the cell units.
To maintain minimum current leakage, it has previously been considered necessary to isolate solwtion flow to the cell units be Eore the electrolyte enters the unit by providing as long a leal<age path through the inlets and ou-tlets ~s is practicable.
Solution inlet and outlet openings have been provided on the sidewalls of the cell chamber9 and to avoid current leakag~e, the openings ha~e been extended l~y means of electrically insulating pipes or other conduits communicating with the inlets and 20 outlets at the sidewalls of the cell chamber. ~xtension of the inlets and outlets boy the ., i~ use of an insulating block having bored holes communicating wi1h the inlets and outlets of the sidewalls of a cell chamber is disclosed in U.S. Patent No. 33405,051. To prevent communication between the adjacent cell compartments and the attendant leaka~e of electrolyte9 the eclges of the bipolar electro~es have been sealed to the side and bottom cell walls and also have been located in grooves on the sidewalls.
Althou,,h the above-described prior art cel~ designs have reduced current leakage, the problems of efficient cell operation have not been satisfactorily resolved.
The use of the inlet and outlet tubes connected to the openings in the sidewalls of the chamber have restricted circulation of the electrolyte by virtue of the length and 30 small diameter of the tubes. Since a high rate of circwlatlon is required to provide ;::
in 'the reaction tank. As the electrolyte passes in parallel flow upwardly through the cell units, It is subjected to electrolysis and hydrogen gas is generated at the cathode surface of each cell ~mit. The continuous circulation of the electrolyte in the above-described parallel p~ttern is caused prirnarily by the generation of hycirogen gas bubbles at the ~cathode surface. During the residence time in `the holding tank, the ~75~L9~
relatively slow chc~-nical reacLlon involYirlg the combination of hypochlorous aci(i ancl hypochlorite ion accorcling to the equation ~ CIO t OCI = C103 ~ 211CI takes place, the hypoclllorous ackl and hypoclllorite ions being generated by the relativel~ fas~
electrolytic reaction in the cell unit. Considerable heat is generated during the electrolysis in the cell units, and to insure ef Eicient performance at the overall operating conditions and for stability of the materials of construction, it is necessary to provide for removal of the generated heat. Cooling coils are generally irnmersed in the reaction or holding tank to maintain suitable operating temperatures.
~ 'Yhen suitable chemical and pH conditions are maintained in the operation 10 of multipolar electrolytic cells, current efficiency is dependent primarily on the rate of flow of the electrolyte solution through the cell units, the currcnt leakage loss and holding tank residence time. Maximum current leakage occurs througll the inlets and ~- outlets and, to some extent, around the edges of the bipolar plates of the cell units.
To maintain minimum current leakage, it has previously been considered necessary to isolate solwtion flow to the cell units be Eore the electrolyte enters the unit by providing as long a leal<age path through the inlets and ou-tlets ~s is practicable.
Solution inlet and outlet openings have been provided on the sidewalls of the cell chamber9 and to avoid current leakag~e, the openings ha~e been extended l~y means of electrically insulating pipes or other conduits communicating with the inlets and 20 outlets at the sidewalls of the cell chamber. ~xtension of the inlets and outlets boy the ., i~ use of an insulating block having bored holes communicating wi1h the inlets and outlets of the sidewalls of a cell chamber is disclosed in U.S. Patent No. 33405,051. To prevent communication between the adjacent cell compartments and the attendant leaka~e of electrolyte9 the eclges of the bipolar electro~es have been sealed to the side and bottom cell walls and also have been located in grooves on the sidewalls.
Althou,,h the above-described prior art cel~ designs have reduced current leakage, the problems of efficient cell operation have not been satisfactorily resolved.
The use of the inlet and outlet tubes connected to the openings in the sidewalls of the chamber have restricted circulation of the electrolyte by virtue of the length and 30 small diameter of the tubes. Since a high rate of circwlatlon is required to provide ;::
- 3 - ~
, . .
75~
both maximum retention time :Ln the reaction tank and sufflcient cooling of the electro,lyte ~y contact witll the cooling coils, the use of such tubes reduces the operating and current efficiency.
SUMMA~Y OF T~E INVENT ON , Therefore, it is a primary object of this invention to provide a multipolar electrolytic cell for manufacture of oxy-halogen compounds wherein electrical current leakage is minlmized and current efficiency is optimized.
A further object of this invention is to provide a multipolar electrolytic cell for production of oxyhalogen compouncls wherein efficient circulation of the electrolyte solution and optimum control of the temperature and pH range of the electrolyte solution can be maintained.
A further object is to provide an economical and ' efficient process for the preparation of oxyhalogen compounds.
These and other objects are accomplished by this ', ~ invention by provision of a multipolar electrolytic cell '- comprising a cell chamber which is substantially enclosed and separated into cell compartments by parallel spaced electrically insulating and solution separating electrolyte partitions. Bipolar electrodes, preferably horizontally disposed and foraminous, are positioned in interleaved fashion in each compartment and arranged to communicate electrically between the liquid-tight compartments. Vertical bipolar electrodes may also be arranged in the individual compartments '' .,:
~ and may be solid or foraminous. Monopolar electrodes mounted ~ .
in each of the two terminal compartments interleaved with portions of the bipolar electrodes of opposite polarity function ;30 to supply and withdraw electric current to and from the ter-minal compartments, respectively.
Thus, in accordance with the present teachings, a "' " ''' ~. - . : . .. .
substantially enclosed :Llquld tlght multlpolar electrolytlc cell is provided. Such cell comprlses a cell chamber havlng a top, a bottom, a side and end walls wlth a plurality of vertical parallel electrlcally lnsulating partitions spaced longitudlnally of the cell and dlvlcling the cell lnto lndlvidual compartments. At least two electrically insulated substantial:Ly vertically oriented conduits are provided associated with each individual compartment, the conduits being adapted to supply electrolyte to the lower portion and to withdraw electrolyte from the upper portion of each individual compartment. A
plurality of parallel dimensionally stable anodes is provided assembled in spaced face~to-face relation in one terminal compartment and adapted to receive a number of cathodes inter-leaved with the anodes. Means are provided for supporting the anodes in assembled position with means being provided for supplying electric current to the anodes. A plurality of parallel cathodes assembled in close:Ly spaced face-to-face , relation to the otherterminal compartment and are adapted to receive a number of anodes interleaved with the cathodes.
Means is provided for supporting the cathodes in assembled 'I position with means for withdrawing current from the cathodes.
A plurality of bipolar electrode assemblies is provided inter-posed between the terminal compartments with each bipolar electrode assembly comprising a plurality of parallel bipolar ; electrodes in closely spaced face-to-face relation and each bipolar electrode oE each bipolar electrode assembly extends through each partition of the cell, one portion of each bipolar electrode on one side of each partition being of one polarity and the other portion of each bipolar electrode on the opposed side of each partition being of opposite polarity to the one portion. The portions of the bipolar electrode which extend ; through the partition separate the terminal anode assembly 1 ~ -4a-''''i ~
; . -- ~ . . , . , . , : , . . .
Erom adJacent cells and are cathode lnterleaved with the anodes of the termlnal anode assembly. The portions of the bipolar electrodes extendlng through the partltlons separatlng the termlnal cathode assembly from ad~acent cells are dimensionally stable anodes interleaved with the cathodes. All other bipolar electrode portions of the bipolar electrode assemblies are interleaved with bipolar electrode portions of opposite polarlty.
The outstanding feature of this lnventlon ls the provision of the combination of a substantially enclosed electrolytic multipolar cell unit with an upper open-ended conduit vertically disposed above a plurality oE electrodes in each compartment a sufficient distance to provide rapid circulation of electrolyte through the entire electrode assembly ot the compartmeDt when gases are generated at the ~ . .
., ~ 30~
J
b-, ,~ :
5~9 electrode surfclces. The tetm "chirr)ney effect" whelever i-t occurs in this specification ancl claims means -the rapicl ancl turbulc!nt circukltion of elcctrolyte provided by the combination of an upper open-enclecl condui-t disposecl ver~iccllly above an electrode assembly, which concluit can be considered analogous to a chirnney, a subs-tantially enclosed cell cornpartrnent or unit and the gases evolved at the electrode surIaces.
When an electrolytic cell of such structure is placed within a reaction or holcling tank containing electrolyte solution, the electrolyte solution is causecl to circulate rapidly through each individua.l compartment. The combination of the compartrnents being substantially enclosed, with the exception of the upper and lower conduit openings, the 10 vertical disposition of the upper conduit, the openings in the horizontally spaced electrodes or the open channels bet\l/een the ver-tically or intermediately spacecl electrodes, and the gas bubb.les rising from ~he electrode surfaces cause the solution to rapidly and turbulently pass through the cell. The circulation of the electrolyte is believed to be induced by a solution displacement phenornena, or "chimney effect."
The portion of the electrolyte solution within the cell containing gas bubbles is less dense than the solution outside the cell which does not contain bubbles so tllat the heavier solution enters the cell through the lower conduit and displaces the less dense solution within the cell ancl causes it to flow through the upper conduit and into the retention vessel. While the upper and lower conduits each enhance electrolyte 20 circulation, the relationship of the length to diameter of the cond~lits is adjustecl to minimize current leakage dependene on individual cell desigrl. Thus, the advantages of .
excellent circulation of the electrolyte and good current efficiency are provided by virtue of the cell structure of this invention. If the temperature must be controlled for a particular product such as the manufacture o:E sodiurn chlorate, cooling coils are arranged in the reaction tank in which the electrolytic cell is clisposed. The excellent .~ circulation characteristics of the cell also provide advantageous, sirnple control of a . .
~. ~ predetermined temperature of the electrolyte solution during residence time in the : reaction tank.
The above objec~s and advantages of the invention will be apparent to those 30 sl~illed in the art from the following specification, the appended claims and by ~ .
, . :,. . ,' . : . ' : .
- . . :. .
,' , ' ' ' . :' , '~ ; ;.: ' ~ ' '. :
~.~D175~
reEerence to the clrawings wherein like numerals insofar as practical represent the same or similar parts, and in which:
I~IG. l is a side elevation of one embodiment of a multipolar cell of this invention illustrating a cell ~herein horizontally disposed foraminous electrodes are utilized.
FIG. 2 is an end view taken alon~ line 2-2 of FIG. 1 illustrating the cell disposed in a reaction or holding tanl~ ~0, in which cooling coils may optionally be positioned and illustrating the flow of the electrolyte solution tllrough the cell.
I~IG. 3 is a side elevational view of another ernbodiment of a rnultipolar 10 electrolytic cell of tlle present invention illustrating a cell in which solid vertical electrocles are incorporated~
FIG. I~ is a secLion as in FIG. 2 wherein the cooling coils are cleleted for clarity of illustration and the upper and lower conduits are carried by respective upper and lower portions of a sicle wall.
FICl. 5 is a modification of FIG. l illustrating an embGdiment of the cell where the conduits are the same length as the thickness of the top and bottom walls of each compartment.
Referring to the drawings, a cell chamber is shown generally at 10 having a top wall or cover 13, end walls ll, a bottom wall 12, and side walls 9 (not shown).
20 Solution separating and electrically insulating partitions l~, divide the chamber into unit compartments. In ~iG. 1, compartments 167 17, 18 and l9 are interposed hori-zontally between terminal compartments 15 and 20. Open-ended conduits 21 and 22, respectively, carried by ~he top and bottom wall of each compartment are in communication with the interior oE said compartment for circulation of the electrolyte by inflow through the lower or bottom conduit and withdrawal through the upper or top conduit. The plurality of dimensionally stable foraminous anodes 27 are disposed in horizontal substantially parallel spaced face-to-face relation in one terminal compart-ment 15 of the cell. The plurality of foraminous cathodes 31 are positioned in horizontal parallel closely spaced face-to-face relativn in ~erminal compartment 20.
30 The anodes 27 and cathodes 31 are proYided with apertures at one end thereoE and are ~'~
, ~
~, .. . .
. ' , ,., : , : . , .
., , 7s~g held in assc-rnblecl positic,rl l~y threaclecl pos-ts 2~ ~Y~tcndirlg through -the apertures in the electrodes, spacing of the elecirodes being provicled by apertured shirns mour)tecl on support posts 28 between adjacent electrodes. Conductor bars 26 are also mounted on posts 28 for supplying electrical current to the electrode assembly and may additionally serve as electrode separators. Threaclecl nuts 29 are connected to threaded posts 28 to hold the electrodes in assernbled position. The posts are provided with bases 32 for supporting the electrode assernblies on the bottom wall 12. Copper rods 24 extend through the top wall of the chamber and ~re ehrcadably connec-ted to the conductor bars carried by the electrode assemblics of terrninal compartrncnts 15 10 and 20, respectively. Electrically nonconductin~ tubes 2~a con~structed o~ plastic or ceramic rnaterial, inert to the cell environment, surround the copper rods ancl exter-d above the level of solution in the retention tank for preventing corrosion of the copper rods. Electrically insulated tubes 25 also constructed of suitable plastic or ceramic material and preferably of polyvinylidene chloride are arranged concentrically with and spaced from the electrically nonconducting tubes 25a to prevent electrical current leakage through the solutioll in ~he retention tank to the terminal cell compartrnen-~s.
Tubes 25 are made of sufficient length to prov;de a long electrical current path and of such diameter as to establish a sutficiently narrow gap between the periphery of tubes 25a and the inner walls of tubes 25 to minimize the cross sectional area available for 20 current leakage. The copper rods are connected to a power source, not showrI~ and serve to supply and withdraw electric current to the cell. In the preferred embodiment, the electrodes are all horizontally disposed and, with the exception of thc assembly of the monopolar dimensionally stable anodes horizontally disposed in one terminal compartment and the assernbly of monopolar cathodes in the other terminal compartment, the electrodes of the cell are all interleaved foraminous bipolar electrodes 34 common to adjacent compartmer.ts of the cell. The foraminous bipolar electrodes 34 are constructed and arranged so that the assemblies o~ bipolar electrodes in cell compartments 169 17, 18 and 19 which compartments are horizontally interposed between the terminal electrode assembly compartments comprise a 30 plurality of foraminous parallel subs-tantially horizontal dimensionally stable anocle . .: .
S~
portions 35 aclaptecl to receive a plurality of forarninous parallel substantially horizontal cathocle portions 3G in c~osely spaced substarltially face-lo ~ace relation to each anode portion. The bipolar electrodes 34 are arrangecl so that one portion of the electrode of one polarity is positioned in one compartment and the other portion of opposite polarity extends into an adjacent compartment. In this manner, the bipolar electrodes of tile assembly are alternately arranged in polarity both in vertical and end-to-end or longitudinal position throughout the cell. The bipolar electrodes are mounted on the supporting posts through apertures located at their miclpoints, each end being of opposite electrical charge in adjacent hori~ontally interposed cells. In the 10 terminal anode assembly of compartment 15, the cathode portion 36 of each hipolar electrode in the compartment is positioned anci closely spaced in substantially face-to-face relation to each dimensionally stable anode 27. The dimensionally stahle anode portion 35 of each bipolar electrode includecl in the terminal cathocle assernbly ; compartment 20 is arranged in substantially face-to face closely spaced relation to each cathode. All the remaining electrodes are interleaved foraminous bipolar electrodes common to two adjacent cells. The bipolar electrodes have apertures at intermediate points and are mounted in the same manner as the terminal electrocles by posts extending through the apertures and positloning the electrodes in spaced relation by means of shims. Posts 28, the spacers and the connecting nuts may be constructed 20 of any electrically conductive metal resistant to the cell environmer,t; generally, they .1 - are made of a valve metal, preerably titanium. The conductor bars in each terminal compartment are required to be electrically conductive and any conductive metal may be used. Generally, a valve metal, preferably titanium, is used. The posts provided with attached bases 32 serve as support and assembling means for the electrodes and ! ~ are generally completely enclosed within the electrically insulating partitions 14. The ~; anodes 27 of the terminal compartment assembly as noted are supported by the posts at their apertured ends and at their other ends terminate at a point just short of the partition opposed to the apertured end. The cathodes of the terminal compar~ment 20 are arranged in the same manner and terminate just short o the partition opposed to 30 their apertured ends~ The interleaved bipolar electrodes are positioned so that each ~ .
: ' ' '~ ' ' .'' . " " ,. . .
:: . ........................ .. . .
3~
anodc portion arld c~ch cathoàe portion will terminat( short of the parti~ion ollposecl to their apertured micl-points. Such arrangement avoids short circui-ting of tlle cell electrode assemblies by preventing contact o~ the electrodes with cell elements having an opposite electrical charge. Supporting legs 23 are mounted on the bottorn cell ~all and are adapted to supl)ort the cell when it is positioned within an outer solution retaining tank.
In the above-described embodiments, the electrodes are all horizontally disposed and foraminous in construction. However, it shoukl be un(lerstood that the electrodes can be mounted in vertlcal position by the same means of support and 10 assembly, the only variations bcin~ the positioning of the electrodes at right angles to the arrangement shown in FIG. 1. In vertical position, the clectro(le shccts may bc solid or foraminous dependent on optimum operating eEficiency. Solid sheets may be used if sufficient space is present between adjacent electrodes or electrode segments to permit unobstructed rapid passage of electrolyte.
The dimensionally stable anodes 27 and bipolar anode portions 35 cornprise an electricaily conductiYe substrate with a surface coating thereon of a solid solution of at least one precious metal oxide and at least one valve metal oxide. The electrically conductive substrate may be any metal which is not adversely affected by the cell environment during use and also has the capability, if a breakdown in the 20 surface coting develops, of preventing detrimental reaction of the electrolyte with the substrate. The geometrical configuration of the anodes may vary provided anodes of suitable shape for forming the structural assembly are used. Generally, the substrate is selected from the valve metals including titanium, tantalum, niobium and ~.irconiurn.
Expanded mesh titanium sheet is preferred at the present time Eor the horizontally disposed anodes.
~'~ In the solid solutions, an interstitial atom of a valve metal oxide crystal lattice host structure is replaced with an atom of precious metal. This solid solution structure distinguishes the coating from physical mixtures of the oxides since pure ~i ~valve metal oxides are, in fact, insulators. Such substitutional solid solutions are 30 electrically conductive, catalytic and electrocatalytic.
,~ .
_ 9 _ .
In the above-lnentiollcd solid solution host structure, the valve rnetals includc titaniuln, tantalurn, niobium and zirconh~m, while the implanted precious r-ne-tals encompass platinum, ruthenium, pallaclium, iridium, rodiurn and osmium.
Titanium dioxide-ruthenium dioxide solid solutions are preferred at this time. The molar ratio of valve metal to precious metal varies between 0.2-5:1, approxirnately 2:1 being presently preferred.
If desired, the solid solutions may be modified by the addition of other components which may either enter into the solid solution itself or adrnix with same to attain a desired result. For instance, it is known that a portion of the precious rnetal 10 oxide, up to 50 percent, may be replaced with tin dioxide without substantial detrimental effect on the overvoltage. Likewise, the solid solution may be modified by the addition of cobalt compounds particularly cobalt titanate. Solid solutions rnodified ~/ by the addition of cobalt titanate, which serves to stabilize and extend the life of the solid solutionj are described more completely in Canadian Patent No. 9~8,~90, issued ~une 11, 197~. Other partial substitutions and additions are encompassed. Another ;~ type of dimensionally stable anode coating whicl- may be used with good results in tne practice of this invention consists of mixtures of chemically and mechanically inert organic polymers and solid solutions of valve metal and precious metal oxides as at least a partial-coating on the electrically conductive subs-trate. Particularly useful 20 materials in such anode coatings are the above-described solicl solutions in admixture with fluorocarbon polymers such as polyvinyl fluoride, polyvinylidene fluoricle and the like coated on at least part of the surface of an electrlcally conductive substrate `; consisting of the above-described valve metals which rnay be mixed with other suitable metals.
1~ One other type of dimensionally stable anode capable of satisfactory use in Jj:~ : ' this invention consists of a valve metal substrate bearing a coating of precious metals or precious metal alloys, particularly platinum and alloys thereof on at least par~ of its Sul face.
The above- mentioned preferred solid solution coatin~s are described in 30 more detail in British E'atent No. 1,1959871.
~: - 10-.
.: . ~
~ '; ~ ~ ' ' " " '' , ', , :
~ he calhodes 31 ancl hipolar cathode pOI tions 3G may be any rnetal capable o-~ sustaining the corrosive cell concli-~ions ancl a usef~ll rnetal is generally selected from the group consisting of stair)less steel, nickel, titanium, steel, lead and platinum. In some cases, the cathodes may be coated with the solid solu-tions al~ove-clescribed for coating the dimensionally stable anodes.
The bipolar ~node portions 35 and the bipolar cathode portions 36 are arranged in closely spaced face-to-face relation between insulating partitions ll~. It is desirable to maintain elecLrode close spacing thereby establishing minirnum eleclrical resistance of the electrolyte between the electrodes to insure optirnurn currcnt 10 efficiency. Consequently, the electrocles are spaced as close as practically possible and maintainecl free from electrical contact by el~ctrlcally nor)colldllctive separators interwoven through, or positioned within, the openings of the foraminous electrodes.
When flat or cylindrical elements are used as separa-tors, they are generally interwoven through alternate openings on the faces of the electrodes disposecl near the cdges but may also be interwoven through other portions of the electrodes. Other types of spacers capable of satisfactory use are elect-ically nonconductive strips provided with projections adapted to be tightly positiolled within the forarninous electrode openings and button-type members such as semi-spherical elements arranged on opposite sides of the elec~rode openings and joined by an engaging member, such as a shaft cr stem, 20 extendin~ through the electrode openings. The separators are positioned to prevent electrical contact or shorting between the electrodes and, at the same time, provide maximum flow of the electrolyte through the openings in the electrode~ The electrically nonconductive separators should be constructed of materials inert to the cell environment and may have any suitable geometric configuration. Generally, the separators are polyvinylidene chloride, polyvinyl chloride, chlorinated polyvinyl chloride, polyvinyl fluoride, ~etrafluoroethylene and the like ancl may be of solid or hollow, cylindrical, ~lat or other suitable config-lrationO
The bipolar electrodes are generally of unitary electrically conductive base constructionj each dimensionally stable anode portion of the base bearing a solid 30 solution coating which may be one of the above-described solid solution coatin~s~ the .
, , . . . . . ..
., , , S.~g cathode portion being the ullcoat~cl electricLIlly conductive rnet~l of -the base. The cathode portion in sorne cases rnay also be coated in the same manner as the dirnensionally stable anode segment. Other suitable electrically conduc-tive coatings may be applied to at least a part of the surface of the anode portion. Such coatings as platinum and alloys thereof and other noble metals are also suitable as conductive coatings.
The cell is useful Eor the manuEclcture of alkali metal chlorate by a process which comprises the steps of introducing an aqueous alkali metal halide solu-tion into the cell compartments, imposing an electrical potential across the clectrodes to 10 electrolyze the all<ali metal halide sol~ltion, the temperature of the solution being maintained at about 60C to about 80C and the pH of the solution beinK maintained at~about 6.0 to about 7.5 during electrolysis and recovering alkali rnetal chlora-te irom the electrolyzed solution. The cell is initially positioned within a surrounding tank in such manner that the conduits ex-tending frorn the bottom wall of each compartment are spaced from lhe base of the enclosing tank to permit entrance of the solution, and ;1 the conduits ex-tending from the top wall of eacll compartment are below the top edges of the side walls of the tank. The halide is introduced into the surrounding tank to completely cover the cell including the condui ts carried by the top wall of each compartment. A decomposition potential is then imposed across- the cell for 20 electrolysis. During electrolysis, gases generated at the electrode surfaces lower the density of the solution within the cells.
The l'chirnney effect" described above causes the solution in the tank surrounding the cell to enter the open conduits carried by the bottom wall or a lower portion of a side wall of each compartment and flow rapidly upwardly through the entire electrode assembly of each compartment where electrolysis occurs and to exit rapidly through the open-ended vertical conduit in or extending from the top wall or upper portion of a side wall of each compartment into the tank surrounding the cell. A
cooling coil 8 is preferably arranged within the enclosure tank 9 for ternperature control.
. ,: , ~'', ~ .
.1 ~ : - , :
:
.. . . .
~137~i~9~
Since the unit compartrnents or ce~ls ;;rc completely enclose(l with tlle exception oE opcn conduits carried by the top al-cl bottom walls, the solution flows very rapidly and vigorously through the entire electrocle asscrnbly. In this manner, sodium hypochlorite is rapidly producecl electrochemical!y wi~h very lirnited simultaneous production of sodiurn chlorate. After the solution cxi ts frorn the ceJI, sufficient residence ~ime is provided in the surroundillg tank for chemical convelsion of the hypochlorite to chlorate by the large volume of solution contained in the tank and tirne lapse during circulation through the tank ancl reen~ry to the cell. The design of thc cell thus enables production of all<ali metal chlorate in the most efficient manner since 10 the major amount of chlorate is procluced chemically rather tharl by the more expensive electrochemical reaction.
Although the use of one rnultipolclr electrolyLic cell of this inventiorl has been illustrated and described, any desired nurnber of such cells may be arranged in an electrolyte-containing tank of sufficient size for complete immersion of the cells therein. The specific number of cells and tanks selected will depend orl ~conornic and other practical operating factors such as availa~le space desired, quantity of pro~uct and the like. If desired, the tanl<s may be arranged in banks, rows or slacked formation. Also, the electrolyte from each tank surrounding an individual or number of multipolar cells may be circulated to a common product recovery tank.
As noted above, the conduits carried by the walls of each cornpartrnent are of sufficient lengtlI and vertical orientation to prevent significant electric current leakage from the cell. The length will vary widely in accordance with the wall thicknessS voltage utilized, number of cells ancl other related design factors.
,i~ The conduits may be apertures of the same length as the thickness of walls if such length in combination with the contributing related factors prevents significant current leakage and contrlbutes to circulation velocity. This modification of the cell structure is illustratecl in FIG. 5 and is particularly suitable where a small number of .~ .
; ~ multipolar cells are positioned in a single retention tank.
:~
.~
, , .
.. ~ ,. . , . . ,. , , . ~ , . .
The folJo~l/ing exarnp~es of 1;hc production of sodium chlorate presen~ed below are intended for purposes oL illustration only ancl are not $o be considered limitative of the invention in any manner.
Example 1 A multipolar clectrolytic ccll of the type illustrated in FIGS. 1 and 2 was arranged in an uncovered tanl< having a volume capaci-ty abou-t 5 times greater than the cell and side walls of greater height than the combined lleight of the cell and the conduits projecting from the top walls of the cell. The external tank was filled with saturated brine solution containing about 310 g/l of sodium chloride and about 0~5 g/l of sodium dichromate. Direct current was appliecl to the electrodes of the cell to 10 electrolyze the solution. Gases were immediately evolved at the electrode surfaces and a rapid and turbulerlt circulation o~ he solution through a.ll the cornpartrnents of the cell, into the open-ended conduits of the bottom walls, througll the assembly of elcctrodes in each compartment and througll the open-ended conduit in the top wall of each compar~ment resulted. The cell was operated for a period of about 16 hours by continuously introducing saturated brine of the same composilion, as initially utili~ed, into the tank surrounding the cell, elec$rolyzing the solution in the cell while rnaintaining the temperature of the solution at about 60C and the pH at about 7.0, withdrawing the electrolyzed hrine from the external tank, recovering sodium ch.lorate therefrom, fortifying the depl~ted brine with saturated brine and recirculating the 2û fortified brine to the multipolar cell.
The average current efficiency during this period was 91~ percent and the average quantity of sodium chlorate product obtained was 380 g/l.
Exam~
The same prccedure was followed as in Example 1 ~vith the exception that the saturated brine solution contained about 2.0 g/l sodiurn clichrornate $he pH was maintained at 6.7 and the cell was con~inuously operated for a period of 15 hours. l he . . ~ . . ~ -: . . -. , . .
~37~
average current efficiency cluring this period w,~s 93 percent an~l the average amount of sodium chlorate obtained was 316 g/l.
The above examples clearly illusLrate that the present invention provides for the production of alkali metal chlolates at efficiencies much higher than those available in conventional multipolar cells used for clllorate production.
.
.~ ' .....
,, .
, ~ '
, . .
75~
both maximum retention time :Ln the reaction tank and sufflcient cooling of the electro,lyte ~y contact witll the cooling coils, the use of such tubes reduces the operating and current efficiency.
SUMMA~Y OF T~E INVENT ON , Therefore, it is a primary object of this invention to provide a multipolar electrolytic cell for manufacture of oxy-halogen compounds wherein electrical current leakage is minlmized and current efficiency is optimized.
A further object of this invention is to provide a multipolar electrolytic cell for production of oxyhalogen compouncls wherein efficient circulation of the electrolyte solution and optimum control of the temperature and pH range of the electrolyte solution can be maintained.
A further object is to provide an economical and ' efficient process for the preparation of oxyhalogen compounds.
These and other objects are accomplished by this ', ~ invention by provision of a multipolar electrolytic cell '- comprising a cell chamber which is substantially enclosed and separated into cell compartments by parallel spaced electrically insulating and solution separating electrolyte partitions. Bipolar electrodes, preferably horizontally disposed and foraminous, are positioned in interleaved fashion in each compartment and arranged to communicate electrically between the liquid-tight compartments. Vertical bipolar electrodes may also be arranged in the individual compartments '' .,:
~ and may be solid or foraminous. Monopolar electrodes mounted ~ .
in each of the two terminal compartments interleaved with portions of the bipolar electrodes of opposite polarity function ;30 to supply and withdraw electric current to and from the ter-minal compartments, respectively.
Thus, in accordance with the present teachings, a "' " ''' ~. - . : . .. .
substantially enclosed :Llquld tlght multlpolar electrolytlc cell is provided. Such cell comprlses a cell chamber havlng a top, a bottom, a side and end walls wlth a plurality of vertical parallel electrlcally lnsulating partitions spaced longitudlnally of the cell and dlvlcling the cell lnto lndlvidual compartments. At least two electrically insulated substantial:Ly vertically oriented conduits are provided associated with each individual compartment, the conduits being adapted to supply electrolyte to the lower portion and to withdraw electrolyte from the upper portion of each individual compartment. A
plurality of parallel dimensionally stable anodes is provided assembled in spaced face~to-face relation in one terminal compartment and adapted to receive a number of cathodes inter-leaved with the anodes. Means are provided for supporting the anodes in assembled position with means being provided for supplying electric current to the anodes. A plurality of parallel cathodes assembled in close:Ly spaced face-to-face , relation to the otherterminal compartment and are adapted to receive a number of anodes interleaved with the cathodes.
Means is provided for supporting the cathodes in assembled 'I position with means for withdrawing current from the cathodes.
A plurality of bipolar electrode assemblies is provided inter-posed between the terminal compartments with each bipolar electrode assembly comprising a plurality of parallel bipolar ; electrodes in closely spaced face-to-face relation and each bipolar electrode oE each bipolar electrode assembly extends through each partition of the cell, one portion of each bipolar electrode on one side of each partition being of one polarity and the other portion of each bipolar electrode on the opposed side of each partition being of opposite polarity to the one portion. The portions of the bipolar electrode which extend ; through the partition separate the terminal anode assembly 1 ~ -4a-''''i ~
; . -- ~ . . , . , . , : , . . .
Erom adJacent cells and are cathode lnterleaved with the anodes of the termlnal anode assembly. The portions of the bipolar electrodes extendlng through the partltlons separatlng the termlnal cathode assembly from ad~acent cells are dimensionally stable anodes interleaved with the cathodes. All other bipolar electrode portions of the bipolar electrode assemblies are interleaved with bipolar electrode portions of opposite polarlty.
The outstanding feature of this lnventlon ls the provision of the combination of a substantially enclosed electrolytic multipolar cell unit with an upper open-ended conduit vertically disposed above a plurality oE electrodes in each compartment a sufficient distance to provide rapid circulation of electrolyte through the entire electrode assembly ot the compartmeDt when gases are generated at the ~ . .
., ~ 30~
J
b-, ,~ :
5~9 electrode surfclces. The tetm "chirr)ney effect" whelever i-t occurs in this specification ancl claims means -the rapicl ancl turbulc!nt circukltion of elcctrolyte provided by the combination of an upper open-enclecl condui-t disposecl ver~iccllly above an electrode assembly, which concluit can be considered analogous to a chirnney, a subs-tantially enclosed cell cornpartrnent or unit and the gases evolved at the electrode surIaces.
When an electrolytic cell of such structure is placed within a reaction or holcling tank containing electrolyte solution, the electrolyte solution is causecl to circulate rapidly through each individua.l compartment. The combination of the compartrnents being substantially enclosed, with the exception of the upper and lower conduit openings, the 10 vertical disposition of the upper conduit, the openings in the horizontally spaced electrodes or the open channels bet\l/een the ver-tically or intermediately spacecl electrodes, and the gas bubb.les rising from ~he electrode surfaces cause the solution to rapidly and turbulently pass through the cell. The circulation of the electrolyte is believed to be induced by a solution displacement phenornena, or "chimney effect."
The portion of the electrolyte solution within the cell containing gas bubbles is less dense than the solution outside the cell which does not contain bubbles so tllat the heavier solution enters the cell through the lower conduit and displaces the less dense solution within the cell ancl causes it to flow through the upper conduit and into the retention vessel. While the upper and lower conduits each enhance electrolyte 20 circulation, the relationship of the length to diameter of the cond~lits is adjustecl to minimize current leakage dependene on individual cell desigrl. Thus, the advantages of .
excellent circulation of the electrolyte and good current efficiency are provided by virtue of the cell structure of this invention. If the temperature must be controlled for a particular product such as the manufacture o:E sodiurn chlorate, cooling coils are arranged in the reaction tank in which the electrolytic cell is clisposed. The excellent .~ circulation characteristics of the cell also provide advantageous, sirnple control of a . .
~. ~ predetermined temperature of the electrolyte solution during residence time in the : reaction tank.
The above objec~s and advantages of the invention will be apparent to those 30 sl~illed in the art from the following specification, the appended claims and by ~ .
, . :,. . ,' . : . ' : .
- . . :. .
,' , ' ' ' . :' , '~ ; ;.: ' ~ ' '. :
~.~D175~
reEerence to the clrawings wherein like numerals insofar as practical represent the same or similar parts, and in which:
I~IG. l is a side elevation of one embodiment of a multipolar cell of this invention illustrating a cell ~herein horizontally disposed foraminous electrodes are utilized.
FIG. 2 is an end view taken alon~ line 2-2 of FIG. 1 illustrating the cell disposed in a reaction or holding tanl~ ~0, in which cooling coils may optionally be positioned and illustrating the flow of the electrolyte solution tllrough the cell.
I~IG. 3 is a side elevational view of another ernbodiment of a rnultipolar 10 electrolytic cell of tlle present invention illustrating a cell in which solid vertical electrocles are incorporated~
FIG. I~ is a secLion as in FIG. 2 wherein the cooling coils are cleleted for clarity of illustration and the upper and lower conduits are carried by respective upper and lower portions of a sicle wall.
FICl. 5 is a modification of FIG. l illustrating an embGdiment of the cell where the conduits are the same length as the thickness of the top and bottom walls of each compartment.
Referring to the drawings, a cell chamber is shown generally at 10 having a top wall or cover 13, end walls ll, a bottom wall 12, and side walls 9 (not shown).
20 Solution separating and electrically insulating partitions l~, divide the chamber into unit compartments. In ~iG. 1, compartments 167 17, 18 and l9 are interposed hori-zontally between terminal compartments 15 and 20. Open-ended conduits 21 and 22, respectively, carried by ~he top and bottom wall of each compartment are in communication with the interior oE said compartment for circulation of the electrolyte by inflow through the lower or bottom conduit and withdrawal through the upper or top conduit. The plurality of dimensionally stable foraminous anodes 27 are disposed in horizontal substantially parallel spaced face-to-face relation in one terminal compart-ment 15 of the cell. The plurality of foraminous cathodes 31 are positioned in horizontal parallel closely spaced face-to-face relativn in ~erminal compartment 20.
30 The anodes 27 and cathodes 31 are proYided with apertures at one end thereoE and are ~'~
, ~
~, .. . .
. ' , ,., : , : . , .
., , 7s~g held in assc-rnblecl positic,rl l~y threaclecl pos-ts 2~ ~Y~tcndirlg through -the apertures in the electrodes, spacing of the elecirodes being provicled by apertured shirns mour)tecl on support posts 28 between adjacent electrodes. Conductor bars 26 are also mounted on posts 28 for supplying electrical current to the electrode assembly and may additionally serve as electrode separators. Threaclecl nuts 29 are connected to threaded posts 28 to hold the electrodes in assernbled position. The posts are provided with bases 32 for supporting the electrode assernblies on the bottom wall 12. Copper rods 24 extend through the top wall of the chamber and ~re ehrcadably connec-ted to the conductor bars carried by the electrode assemblics of terrninal compartrncnts 15 10 and 20, respectively. Electrically nonconductin~ tubes 2~a con~structed o~ plastic or ceramic rnaterial, inert to the cell environment, surround the copper rods ancl exter-d above the level of solution in the retention tank for preventing corrosion of the copper rods. Electrically insulated tubes 25 also constructed of suitable plastic or ceramic material and preferably of polyvinylidene chloride are arranged concentrically with and spaced from the electrically nonconducting tubes 25a to prevent electrical current leakage through the solutioll in ~he retention tank to the terminal cell compartrnen-~s.
Tubes 25 are made of sufficient length to prov;de a long electrical current path and of such diameter as to establish a sutficiently narrow gap between the periphery of tubes 25a and the inner walls of tubes 25 to minimize the cross sectional area available for 20 current leakage. The copper rods are connected to a power source, not showrI~ and serve to supply and withdraw electric current to the cell. In the preferred embodiment, the electrodes are all horizontally disposed and, with the exception of thc assembly of the monopolar dimensionally stable anodes horizontally disposed in one terminal compartment and the assernbly of monopolar cathodes in the other terminal compartment, the electrodes of the cell are all interleaved foraminous bipolar electrodes 34 common to adjacent compartmer.ts of the cell. The foraminous bipolar electrodes 34 are constructed and arranged so that the assemblies o~ bipolar electrodes in cell compartments 169 17, 18 and 19 which compartments are horizontally interposed between the terminal electrode assembly compartments comprise a 30 plurality of foraminous parallel subs-tantially horizontal dimensionally stable anocle . .: .
S~
portions 35 aclaptecl to receive a plurality of forarninous parallel substantially horizontal cathocle portions 3G in c~osely spaced substarltially face-lo ~ace relation to each anode portion. The bipolar electrodes 34 are arrangecl so that one portion of the electrode of one polarity is positioned in one compartment and the other portion of opposite polarity extends into an adjacent compartment. In this manner, the bipolar electrodes of tile assembly are alternately arranged in polarity both in vertical and end-to-end or longitudinal position throughout the cell. The bipolar electrodes are mounted on the supporting posts through apertures located at their miclpoints, each end being of opposite electrical charge in adjacent hori~ontally interposed cells. In the 10 terminal anode assembly of compartment 15, the cathode portion 36 of each hipolar electrode in the compartment is positioned anci closely spaced in substantially face-to-face relation to each dimensionally stable anode 27. The dimensionally stahle anode portion 35 of each bipolar electrode includecl in the terminal cathocle assernbly ; compartment 20 is arranged in substantially face-to face closely spaced relation to each cathode. All the remaining electrodes are interleaved foraminous bipolar electrodes common to two adjacent cells. The bipolar electrodes have apertures at intermediate points and are mounted in the same manner as the terminal electrocles by posts extending through the apertures and positloning the electrodes in spaced relation by means of shims. Posts 28, the spacers and the connecting nuts may be constructed 20 of any electrically conductive metal resistant to the cell environmer,t; generally, they .1 - are made of a valve metal, preerably titanium. The conductor bars in each terminal compartment are required to be electrically conductive and any conductive metal may be used. Generally, a valve metal, preferably titanium, is used. The posts provided with attached bases 32 serve as support and assembling means for the electrodes and ! ~ are generally completely enclosed within the electrically insulating partitions 14. The ~; anodes 27 of the terminal compartment assembly as noted are supported by the posts at their apertured ends and at their other ends terminate at a point just short of the partition opposed to the apertured end. The cathodes of the terminal compar~ment 20 are arranged in the same manner and terminate just short o the partition opposed to 30 their apertured ends~ The interleaved bipolar electrodes are positioned so that each ~ .
: ' ' '~ ' ' .'' . " " ,. . .
:: . ........................ .. . .
3~
anodc portion arld c~ch cathoàe portion will terminat( short of the parti~ion ollposecl to their apertured micl-points. Such arrangement avoids short circui-ting of tlle cell electrode assemblies by preventing contact o~ the electrodes with cell elements having an opposite electrical charge. Supporting legs 23 are mounted on the bottorn cell ~all and are adapted to supl)ort the cell when it is positioned within an outer solution retaining tank.
In the above-described embodiments, the electrodes are all horizontally disposed and foraminous in construction. However, it shoukl be un(lerstood that the electrodes can be mounted in vertlcal position by the same means of support and 10 assembly, the only variations bcin~ the positioning of the electrodes at right angles to the arrangement shown in FIG. 1. In vertical position, the clectro(le shccts may bc solid or foraminous dependent on optimum operating eEficiency. Solid sheets may be used if sufficient space is present between adjacent electrodes or electrode segments to permit unobstructed rapid passage of electrolyte.
The dimensionally stable anodes 27 and bipolar anode portions 35 cornprise an electricaily conductiYe substrate with a surface coating thereon of a solid solution of at least one precious metal oxide and at least one valve metal oxide. The electrically conductive substrate may be any metal which is not adversely affected by the cell environment during use and also has the capability, if a breakdown in the 20 surface coting develops, of preventing detrimental reaction of the electrolyte with the substrate. The geometrical configuration of the anodes may vary provided anodes of suitable shape for forming the structural assembly are used. Generally, the substrate is selected from the valve metals including titanium, tantalum, niobium and ~.irconiurn.
Expanded mesh titanium sheet is preferred at the present time Eor the horizontally disposed anodes.
~'~ In the solid solutions, an interstitial atom of a valve metal oxide crystal lattice host structure is replaced with an atom of precious metal. This solid solution structure distinguishes the coating from physical mixtures of the oxides since pure ~i ~valve metal oxides are, in fact, insulators. Such substitutional solid solutions are 30 electrically conductive, catalytic and electrocatalytic.
,~ .
_ 9 _ .
In the above-lnentiollcd solid solution host structure, the valve rnetals includc titaniuln, tantalurn, niobium and zirconh~m, while the implanted precious r-ne-tals encompass platinum, ruthenium, pallaclium, iridium, rodiurn and osmium.
Titanium dioxide-ruthenium dioxide solid solutions are preferred at this time. The molar ratio of valve metal to precious metal varies between 0.2-5:1, approxirnately 2:1 being presently preferred.
If desired, the solid solutions may be modified by the addition of other components which may either enter into the solid solution itself or adrnix with same to attain a desired result. For instance, it is known that a portion of the precious rnetal 10 oxide, up to 50 percent, may be replaced with tin dioxide without substantial detrimental effect on the overvoltage. Likewise, the solid solution may be modified by the addition of cobalt compounds particularly cobalt titanate. Solid solutions rnodified ~/ by the addition of cobalt titanate, which serves to stabilize and extend the life of the solid solutionj are described more completely in Canadian Patent No. 9~8,~90, issued ~une 11, 197~. Other partial substitutions and additions are encompassed. Another ;~ type of dimensionally stable anode coating whicl- may be used with good results in tne practice of this invention consists of mixtures of chemically and mechanically inert organic polymers and solid solutions of valve metal and precious metal oxides as at least a partial-coating on the electrically conductive subs-trate. Particularly useful 20 materials in such anode coatings are the above-described solicl solutions in admixture with fluorocarbon polymers such as polyvinyl fluoride, polyvinylidene fluoricle and the like coated on at least part of the surface of an electrlcally conductive substrate `; consisting of the above-described valve metals which rnay be mixed with other suitable metals.
1~ One other type of dimensionally stable anode capable of satisfactory use in Jj:~ : ' this invention consists of a valve metal substrate bearing a coating of precious metals or precious metal alloys, particularly platinum and alloys thereof on at least par~ of its Sul face.
The above- mentioned preferred solid solution coatin~s are described in 30 more detail in British E'atent No. 1,1959871.
~: - 10-.
.: . ~
~ '; ~ ~ ' ' " " '' , ', , :
~ he calhodes 31 ancl hipolar cathode pOI tions 3G may be any rnetal capable o-~ sustaining the corrosive cell concli-~ions ancl a usef~ll rnetal is generally selected from the group consisting of stair)less steel, nickel, titanium, steel, lead and platinum. In some cases, the cathodes may be coated with the solid solu-tions al~ove-clescribed for coating the dimensionally stable anodes.
The bipolar ~node portions 35 and the bipolar cathode portions 36 are arranged in closely spaced face-to-face relation between insulating partitions ll~. It is desirable to maintain elecLrode close spacing thereby establishing minirnum eleclrical resistance of the electrolyte between the electrodes to insure optirnurn currcnt 10 efficiency. Consequently, the electrocles are spaced as close as practically possible and maintainecl free from electrical contact by el~ctrlcally nor)colldllctive separators interwoven through, or positioned within, the openings of the foraminous electrodes.
When flat or cylindrical elements are used as separa-tors, they are generally interwoven through alternate openings on the faces of the electrodes disposecl near the cdges but may also be interwoven through other portions of the electrodes. Other types of spacers capable of satisfactory use are elect-ically nonconductive strips provided with projections adapted to be tightly positiolled within the forarninous electrode openings and button-type members such as semi-spherical elements arranged on opposite sides of the elec~rode openings and joined by an engaging member, such as a shaft cr stem, 20 extendin~ through the electrode openings. The separators are positioned to prevent electrical contact or shorting between the electrodes and, at the same time, provide maximum flow of the electrolyte through the openings in the electrode~ The electrically nonconductive separators should be constructed of materials inert to the cell environment and may have any suitable geometric configuration. Generally, the separators are polyvinylidene chloride, polyvinyl chloride, chlorinated polyvinyl chloride, polyvinyl fluoride, ~etrafluoroethylene and the like ancl may be of solid or hollow, cylindrical, ~lat or other suitable config-lrationO
The bipolar electrodes are generally of unitary electrically conductive base constructionj each dimensionally stable anode portion of the base bearing a solid 30 solution coating which may be one of the above-described solid solution coatin~s~ the .
, , . . . . . ..
., , , S.~g cathode portion being the ullcoat~cl electricLIlly conductive rnet~l of -the base. The cathode portion in sorne cases rnay also be coated in the same manner as the dirnensionally stable anode segment. Other suitable electrically conduc-tive coatings may be applied to at least a part of the surface of the anode portion. Such coatings as platinum and alloys thereof and other noble metals are also suitable as conductive coatings.
The cell is useful Eor the manuEclcture of alkali metal chlorate by a process which comprises the steps of introducing an aqueous alkali metal halide solu-tion into the cell compartments, imposing an electrical potential across the clectrodes to 10 electrolyze the all<ali metal halide sol~ltion, the temperature of the solution being maintained at about 60C to about 80C and the pH of the solution beinK maintained at~about 6.0 to about 7.5 during electrolysis and recovering alkali rnetal chlora-te irom the electrolyzed solution. The cell is initially positioned within a surrounding tank in such manner that the conduits ex-tending frorn the bottom wall of each compartment are spaced from lhe base of the enclosing tank to permit entrance of the solution, and ;1 the conduits ex-tending from the top wall of eacll compartment are below the top edges of the side walls of the tank. The halide is introduced into the surrounding tank to completely cover the cell including the condui ts carried by the top wall of each compartment. A decomposition potential is then imposed across- the cell for 20 electrolysis. During electrolysis, gases generated at the electrode surfaces lower the density of the solution within the cells.
The l'chirnney effect" described above causes the solution in the tank surrounding the cell to enter the open conduits carried by the bottom wall or a lower portion of a side wall of each compartment and flow rapidly upwardly through the entire electrode assembly of each compartment where electrolysis occurs and to exit rapidly through the open-ended vertical conduit in or extending from the top wall or upper portion of a side wall of each compartment into the tank surrounding the cell. A
cooling coil 8 is preferably arranged within the enclosure tank 9 for ternperature control.
. ,: , ~'', ~ .
.1 ~ : - , :
:
.. . . .
~137~i~9~
Since the unit compartrnents or ce~ls ;;rc completely enclose(l with tlle exception oE opcn conduits carried by the top al-cl bottom walls, the solution flows very rapidly and vigorously through the entire electrocle asscrnbly. In this manner, sodium hypochlorite is rapidly producecl electrochemical!y wi~h very lirnited simultaneous production of sodiurn chlorate. After the solution cxi ts frorn the ceJI, sufficient residence ~ime is provided in the surroundillg tank for chemical convelsion of the hypochlorite to chlorate by the large volume of solution contained in the tank and tirne lapse during circulation through the tank ancl reen~ry to the cell. The design of thc cell thus enables production of all<ali metal chlorate in the most efficient manner since 10 the major amount of chlorate is procluced chemically rather tharl by the more expensive electrochemical reaction.
Although the use of one rnultipolclr electrolyLic cell of this inventiorl has been illustrated and described, any desired nurnber of such cells may be arranged in an electrolyte-containing tank of sufficient size for complete immersion of the cells therein. The specific number of cells and tanks selected will depend orl ~conornic and other practical operating factors such as availa~le space desired, quantity of pro~uct and the like. If desired, the tanl<s may be arranged in banks, rows or slacked formation. Also, the electrolyte from each tank surrounding an individual or number of multipolar cells may be circulated to a common product recovery tank.
As noted above, the conduits carried by the walls of each cornpartrnent are of sufficient lengtlI and vertical orientation to prevent significant electric current leakage from the cell. The length will vary widely in accordance with the wall thicknessS voltage utilized, number of cells ancl other related design factors.
,i~ The conduits may be apertures of the same length as the thickness of walls if such length in combination with the contributing related factors prevents significant current leakage and contrlbutes to circulation velocity. This modification of the cell structure is illustratecl in FIG. 5 and is particularly suitable where a small number of .~ .
; ~ multipolar cells are positioned in a single retention tank.
:~
.~
, , .
.. ~ ,. . , . . ,. , , . ~ , . .
The folJo~l/ing exarnp~es of 1;hc production of sodium chlorate presen~ed below are intended for purposes oL illustration only ancl are not $o be considered limitative of the invention in any manner.
Example 1 A multipolar clectrolytic ccll of the type illustrated in FIGS. 1 and 2 was arranged in an uncovered tanl< having a volume capaci-ty abou-t 5 times greater than the cell and side walls of greater height than the combined lleight of the cell and the conduits projecting from the top walls of the cell. The external tank was filled with saturated brine solution containing about 310 g/l of sodium chloride and about 0~5 g/l of sodium dichromate. Direct current was appliecl to the electrodes of the cell to 10 electrolyze the solution. Gases were immediately evolved at the electrode surfaces and a rapid and turbulerlt circulation o~ he solution through a.ll the cornpartrnents of the cell, into the open-ended conduits of the bottom walls, througll the assembly of elcctrodes in each compartment and througll the open-ended conduit in the top wall of each compar~ment resulted. The cell was operated for a period of about 16 hours by continuously introducing saturated brine of the same composilion, as initially utili~ed, into the tank surrounding the cell, elec$rolyzing the solution in the cell while rnaintaining the temperature of the solution at about 60C and the pH at about 7.0, withdrawing the electrolyzed hrine from the external tank, recovering sodium ch.lorate therefrom, fortifying the depl~ted brine with saturated brine and recirculating the 2û fortified brine to the multipolar cell.
The average current efficiency during this period was 91~ percent and the average quantity of sodium chlorate product obtained was 380 g/l.
Exam~
The same prccedure was followed as in Example 1 ~vith the exception that the saturated brine solution contained about 2.0 g/l sodiurn clichrornate $he pH was maintained at 6.7 and the cell was con~inuously operated for a period of 15 hours. l he . . ~ . . ~ -: . . -. , . .
~37~
average current efficiency cluring this period w,~s 93 percent an~l the average amount of sodium chlorate obtained was 316 g/l.
The above examples clearly illusLrate that the present invention provides for the production of alkali metal chlolates at efficiencies much higher than those available in conventional multipolar cells used for clllorate production.
.
.~ ' .....
,, .
, ~ '
Claims (15)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A substantially enclosed liquid-tight multipolar electrolytic cell comprising:
a cell chamber having top, bottom, side and end walls;
a plurality of vertical parallel electrically insulating partitions spaced longitudinally of the cell and dividing the cell into individual compartments;
at least two electrically insulated substantially vertically oriented conduits associated with each said individual compartment, said conduits adapted to supply electrolyte to the lower portion and withdraw electrolyte from the upper portion of each said individual compartment;
a plurality of parallel dimensionally stable anodes assembled in spaced face-to-face relation in one terminal compartment and adapted to receive a number of cathodes interleaved with said anodes;
means for supporting said anodes in assembled position;
means for supplying electric current to the anodes;
a plurality of parallel cathodes assembled in closely spaced face-to-face relation in the other terminal compartment adapted to receive a number of anodes interleaved with said cathodes;
means for supporting said cathodes in assembled position;
means for withdrawing current from the cathodes;
a plurality of bipolar electrode assemblies interposed between said terminal compartments;
each bipolar electrode assembly comprising a plurality of parallel bipolar electrodes in closely spaced face-to-face relation;
each bipolar electrode of each bipolar electrode assembly extending through each partition of the cell, one portion of each bipolar electrode on one side of each partition being of one polarity and the other portion of each bipolar electrode on the opposed side of each partition being of opposite polarity to said one portion;
the portions of the bipolar electrode extending through the partition separating the terminal anode assembly from adjacent cells being cathodes interleaved with the anodes of the terminal anode assembly;
the portions of the bipolar electrodes extending through the partition separating the terminal cathode assembly from adjacent cells being dimensionally stable anodes interleaved with the cathodes; and all other bipolar electrode portions of the bipolar electrode assemblies being interleaved with bipolar electrode portions of opposite polarity.
a cell chamber having top, bottom, side and end walls;
a plurality of vertical parallel electrically insulating partitions spaced longitudinally of the cell and dividing the cell into individual compartments;
at least two electrically insulated substantially vertically oriented conduits associated with each said individual compartment, said conduits adapted to supply electrolyte to the lower portion and withdraw electrolyte from the upper portion of each said individual compartment;
a plurality of parallel dimensionally stable anodes assembled in spaced face-to-face relation in one terminal compartment and adapted to receive a number of cathodes interleaved with said anodes;
means for supporting said anodes in assembled position;
means for supplying electric current to the anodes;
a plurality of parallel cathodes assembled in closely spaced face-to-face relation in the other terminal compartment adapted to receive a number of anodes interleaved with said cathodes;
means for supporting said cathodes in assembled position;
means for withdrawing current from the cathodes;
a plurality of bipolar electrode assemblies interposed between said terminal compartments;
each bipolar electrode assembly comprising a plurality of parallel bipolar electrodes in closely spaced face-to-face relation;
each bipolar electrode of each bipolar electrode assembly extending through each partition of the cell, one portion of each bipolar electrode on one side of each partition being of one polarity and the other portion of each bipolar electrode on the opposed side of each partition being of opposite polarity to said one portion;
the portions of the bipolar electrode extending through the partition separating the terminal anode assembly from adjacent cells being cathodes interleaved with the anodes of the terminal anode assembly;
the portions of the bipolar electrodes extending through the partition separating the terminal cathode assembly from adjacent cells being dimensionally stable anodes interleaved with the cathodes; and all other bipolar electrode portions of the bipolar electrode assemblies being interleaved with bipolar electrode portions of opposite polarity.
2. The cell according to Claim 1 wherein the substantially vertically oriented conduits are carried by an upper portion and a lower portion of each of two opposed side walls of each compartment, respectively.
3. The cell according to Claim 1 wherein the substantially vertically oriented conduits are carried by a top wall and a bottom wall of each compartment, respectively.
4. The cell of Claim 1 wherein all the electrodes are vertically disposed.
5. The cell of Claim 4 wherein the vertically disposed electrodes are nonforaminous solid sheets.
6. The cell according to Claim 1 wherein all the electrodes are disposed intermediate substantially horizontal and substantially vertical positions.
7. The cell according to Claim 6 wherein the electrodes are non-foraminous solid sheets.
8. The cell of Claim 1 wherein electrically insulated separators are positioned between adjacent electrode surfaces.
9. The cell of Claim 1 wherein the means for supplying current to the anodes of the terminal compartment and withdrawing current from the cathodes of the cathode terminal compartment consists of at least one current conducting rod, said rod having one end connected to a source of electric current and the other end connected to at least one conductor bar in electrical contact with said anodes and said cathodes, respectively.
10. The cell of Claim 1 wherein the dimensionally stable anodes consist essentially of a valve metal substrate bearing on at least part of its surface a coating of a solid solution of at least one precious metal oxide and at least one valve metal oxide.
11. The cell of Claim 1 wherein the dimensionally stable anodes consist essentially of a titanium metal substrate having a surface coating of a solid solution of titanium dioxide and ruthenium dioxide.
12. The cell of Claim 1 wherein the cathode is constructed of a metal selected from the group consisting of titanium, nickel, steel and stainless steel.
13. The cell of Claim 1 wherein the conduits are of the same length as the thickness of the top and bottom walls of each compartment.
14. The cell of Claim 1 wherein all the electrodes are substantially horizontally disposed.
15. The cell of Claim 14 wherein the substantially horizontally disposed electrodes are nonforaminous sheets.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US00291274A US3819503A (en) | 1972-09-22 | 1972-09-22 | Electrolytic cell for the production of oxyhalogens |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1075199A true CA1075199A (en) | 1980-04-08 |
Family
ID=23119646
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA181,534A Expired CA1075199A (en) | 1972-09-22 | 1973-09-20 | Electrolytic cell and method for the production of oxyhalogens |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US3819503A (en) |
| CA (1) | CA1075199A (en) |
Families Citing this family (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3997414A (en) * | 1975-05-05 | 1976-12-14 | Huron Chemicals Limited | Gas concentrated and cooled electrolytic cell |
| US4087344A (en) * | 1976-06-17 | 1978-05-02 | Huron Chemicals, Ltd. | Electrolytic cell |
| JPS53100998A (en) * | 1977-02-17 | 1978-09-02 | Kurorin Engineers Kk | Method of making alkali metal hypochlorite and electrolytic bath therefor |
| US4146443A (en) * | 1977-09-13 | 1979-03-27 | Phillips Petroleum Company | Introducing feed into externally circulating electrolyte in electrochemical process |
| US4332648A (en) * | 1979-12-17 | 1982-06-01 | Hooker Chemicals & Plastics Corp. | Electrolytic apparatus for the manufacture of alkali metal halate |
| US4332659A (en) * | 1979-12-17 | 1982-06-01 | Hooker Chemicals & Plastics Corp. | Electrolytic apparatus for the manufacture of alkali metal halate |
| US4372827A (en) * | 1980-11-10 | 1983-02-08 | Panclor S.A. | Novel horizontal diaphragmless electrolyzer |
| US4568440A (en) * | 1983-08-30 | 1986-02-04 | Eltech Systems Corporation | Bipolar electrolyzer having fixedly spaced apart electrodes |
| JP3101335B2 (en) * | 1991-03-11 | 2000-10-23 | クロリンエンジニアズ株式会社 | Electrolyzer for hypochlorite production |
| WO2011139893A1 (en) * | 2010-04-29 | 2011-11-10 | Etorus, Inc. | Dry cell electrolytic hydrogen generating system |
| US10787748B2 (en) | 2015-05-21 | 2020-09-29 | Avantium Knowledge Centre B.V. | Process for the preparation of an aromatic dicarboxylic acid |
| WO2016186505A1 (en) | 2015-05-21 | 2016-11-24 | Avantium Knowledge Centre B.V. | Process for the purification of a carboxylic acid-containing composition |
| EP3768642A4 (en) * | 2018-03-21 | 2021-11-17 | Axine Water Technologies Inc. | Electrolytic cell with bipolar electrodes for wastewater treatment |
| CN111302538B (en) * | 2019-11-21 | 2021-07-23 | 山东大学 | Reactor for generating hydroxyl radicals by bipolar electrode and application thereof |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA454734A (en) * | 1949-02-22 | Krebs And Co. A.G. | Electrolyser for producing oxygen compounds of chlorine | |
| GB1056889A (en) * | 1964-10-12 | 1967-02-01 | Albright & Wilson | Method and apparatus for performing electrolytic processes |
| US3503858A (en) * | 1964-11-26 | 1970-03-31 | Huron Nassau Ltd | Continuous electrolytic cell process |
| CA914610A (en) * | 1970-06-26 | 1972-11-14 | Chemetics International Ltd. | Multi-monopolar electrolytic cell assembly and system |
-
1972
- 1972-09-22 US US00291274A patent/US3819503A/en not_active Expired - Lifetime
-
1973
- 1973-09-20 CA CA181,534A patent/CA1075199A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US3819503A (en) | 1974-06-25 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA1075199A (en) | Electrolytic cell and method for the production of oxyhalogens | |
| CA1077436A (en) | Membrane electrolytic cell with concentric electrodes | |
| JPS5932548B2 (en) | Electrolysis method and electrolyzer | |
| US3791947A (en) | Electrolytic cell assemblies and methods of chemical production | |
| JPS63137191A (en) | Electrolytic cell for electrolytic precipitation of metal | |
| US3410784A (en) | Apparatus for performing electrolytic processes | |
| PL107640B1 (en) | DEVICE FOR ELECTROLYTIC DEPOSITION OF METAL FROM WATER SOLUTION AND THE METHOD OF ELECTROLYTIC SETTING OF METAL FROM WATER SOLUTION | |
| US3779889A (en) | Electrolytic cell for the manufacture of oxyhalogens | |
| HRP920972A2 (en) | FEATURES FOR THE TYPE FILTER FILTER PRESS AND ONE-POLE FILTER TYPE FILTER PRESS | |
| US4139449A (en) | Electrolytic cell for producing alkali metal hypochlorites | |
| US3930980A (en) | Electrolysis cell | |
| US4305806A (en) | Electrolysis device | |
| US4107024A (en) | Electrolytic cell with electrodes arranged as a hexagon | |
| US4075077A (en) | Electrolytic cell | |
| PL181797B1 (en) | External section of an electrodialyser | |
| SU1364243A3 (en) | Electrolyzer with horizontal mercury cathode | |
| US5720867A (en) | Process for the electrochemical recovery of the metals copper, zinc, lead, nickel or cobalt | |
| US4108756A (en) | Bipolar electrode construction | |
| EP0063420A1 (en) | Electrolyzers for the production of hydrogen | |
| US4568440A (en) | Bipolar electrolyzer having fixedly spaced apart electrodes | |
| SE445562B (en) | electrolysis | |
| JP3091617B2 (en) | Bipolar electrolytic cell | |
| US3864237A (en) | Bipolar diaphragmless electrolytic cells | |
| FI60890C (en) | SLUTEN BIPOLAER ELEKTROLYTISK CELL | |
| US3856652A (en) | Electrochemical cells |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |