CA1194835A - Electrochemical apparatus and process for manufacturing halates - Google Patents

Abstract

Abstract An apparatus for manufacture of halate may comprise an electrolytic cell including a plurality of monopolar dimensionally stable anodes and cathodes, means for positioning them in spaced and paired relationship within units comprising two anode-cathode pairs with two inner cathodic surfaces on a base structure and two outer anode surfaces, each anode surface facing a cathodic surface and being separated therefrom, with enclosure means above each unit for trapping gas generated between the anodes and cathodes of the unit and transmitting it to a passageway through which it and electrolyte move upwardly and help to circulate electro-lyte in the cell, to one capable of producing halate at the same rate and at a lower current density; a method is provided for improving the performance which comprises: installing in the cell additional electrode units and replacing at least a portion of the enclosure means with an enlarged means for enclosing the tops of of a plurality of such units, including an original and an added unit, and connecting said enlarged means for such plurality of units with an original single vertical passageway for circulation of generated gas and electrolyte upwardly through the cell

Description

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~ 1 --I~is invention rela~es to a method of converting an apparatus for the ~anufacture of halate, especially sodium chlor~
ate.
This application is a division of Canadian Patent ~pplication serial no.344,391 filed on January 25, 1980.
More part~cularly, it relates to a method and apparatus, capable of efficiently operating at lcw current densities, which includes a greater number of electrode pairs than previously employed in cells of similar capacity and which operates at a lower current density. Such an apparatus may be made by modifi-cation of a higher current density electrochemical halate cell.
mus the invention particularly relates to a process ~or effecting such conversion and for producing chlorate more efficiently at lower curren~ densities.
Electrochemical apparatuses and processes for the nanufacture of chlorates and particularly, for the manufacture of sodium chlorate, are well knc~l and are widely employed com~ercially for m~kin~ such co~pounds. It is known to produce chlorine and sodium hydroxide by the electrolysis of brine and to make sodi~m hypochlorite by reaction of such products when no diaphra~s or membranes are utilized in an electrolytic cell and it is kno~n that hypochlorite is convertible to sodium chlvrate and sodium chloride, the latter of which ma~ be recycled in the elec-trolytic process.

In ~he U.S. patent 3,732,153, granted May B, 1~73 to Cyri1 J. Harke, John C. Parkinson and John E. ~urrey, and ass;gned to Hooker Chemical;Corporation, there is disclosed a chlorate cell in which monop~lar dimensionally stable anodes are positioned about cathodes in units, gas- and liquid electrolyte-containing reaction product generated between the anodes and cathodes of such a unit are collected in an enclosure at the top of such units and are carried upward~y through a passageway, a g~s is remoYed from the top o~ the cell and electrolyte is circulated downwardly through baffled passages to near the tops of the electrode units and then through non-baffled passageways between the units to the bottom of the celli from whence it moves upwardly between the electrodes.
The Harke et al. patent is the closest prior art known to the present inventor although the references cited during prosecution of the patent (U.S. p~tents 3~291,714j 3,475,313; 3,553,088;
3,574,095; and 3,657,102; and French patent 1,284,779) may also be considered as relevant, to a limited extent.
The present invention is an important improvement over the apparatuses and processes of U.S. pateilt 3,732,153 when, as now, conservation of electrical energy in vital~ It provides means for ready product;on of a lower current density chlorate sell of higher operating efficiency at the same current rating~as the Harke et al.
cell whîch may be of substantially the same cell design except for modificat~ons in the numbers of electrodes or electrode units and ;n the constructions of enclosures ~nd some passageways for cir-culation of electrolyte through the cell. By means of the present invention much of the same structure and materials utilized for making the Harke et al. cell may be employed in the cons~ruction of the present cells and the Harke et ai. type cells may be modified and converted ~o cells within the present invention9 if so desired.

~ 3 -In accordance with the invention there is provided a method ~or converting an apparatus for ~nufacture of halate, comprising an electrolytlc cell includiny a plurality of mono-polar di~ensIonally stable anodes and cathodes, means for posi-tioning them in spaced and pa.ired rel.ation~ship within units ccmprising two anode-cathode pairs with two inner cathodic surfaces on a base structure and t~o outer anode surfaces, each anode surface facing a cathod-ic surface and being separated therefrom, with enclosure means above each unit for trapping ~as generated between the anodes and cathodes of the unit and transmitting it to a p~ssageway through which it and electrolyte move upwardly and help to circulate electrolyte in the cell, to one capable of producing halate at the same rate and at a lo~er c~Drrent density which comprises: installing in said cell additional electrode units and replacing at least a p~rtion of the enclosure means with an enlarged means for enclosing the tops of a plurality of such units, including an origina]. and an added unit, and connecting said enlarged means for such plurality of units with an original single vertical passageway for circulation of generated gas and electrolyte upw~rdly throug~ the cell.
In a particular embo11ment any spaces be.tween electrode units are re~oved and installed units are spaced apart from other such units by anode conductors. In particular spaces may be remo~ed between at least t~o units without installation of an e~larged enclosure and an additional unit so as to provide an enlarged passageway for circulation of electrolyte downwardly through the cell.

mere ls disclosed here~n an apparatus for the manu-:Eacture of a halate which ccn~?rises an electrolytic cell including a plu~ality of monopolar dimensionaTly stable anodes and cathodes in spaced and paired relationship with one another, said anodes being holdable to the cell at a side thereof and being re-movable from the cell through a side thereof, means for applying positive and negative electrical potentials to the.anodes and cathodes, respectively, and means for moving electrolyte in the . cell so that it conducts current between the anodes and the ~o cathodes o~ the anode-cathode pa;rs, passes between the anodes and cathodes of the pairs and is at least part;ally electroly~ed thereby to hypohalite and gaseous electrolysis produEt3 which means for moving the electrolyte include clearance passageways between anodes and cathodes of the pairs for conducting such ~5 hypohalite~ electrolyte and gaseous electrolysis product upwardly, an enclosure co~ering the tops of at least four such passageways between anode and cathode pqirs and narrowing down to a passageway less than 1/10 the horizontal cross-sectional area of such en-closure and extending upwardly from it to an upper part of the cell, which enclosure and upw~rdly extending passageway guide . gas and liquld moving upwardly from the clearance passageways~
. and a passage to conduct hypohalite downwardly past baffles to a lower portion of the cell, said passage containing said hypohalite ~or a long enough period of time during operation of the cell to convert a substantial proportion thereof to halate, means for w;thdrawing halate-containing liquor from the cell.after it has . descended through the baffled:passage to the lower portion of ; the cell? means for feeding halide to the cell to replace that consumed in the preparation o~ withdrawn halate and means for withdrawing a gaseous product of electrolysis from the upper part of the cell~ Also within the invention is the uti.lization in chlorate cells of circulating means which pass the gas product~
electroly~e mixtures from between at least four anode-cathode '': ' ' ' . .

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pairs or at least two units~ each containing two anode-cathode pairs, upwardly in the cell through a single passageway. Addi-tionally, the invention relates to: methods of converting higher' current density chlorate cells of the Harke et a1. type to lower c~rrent density cellsi lower current density e7ectroche~ical . .processes for the manufacture'of chlorate; .improved spacers employed to maintain the desired separation or clearance between anode and cathodes in such cells, and anode supports.
The invention will be readily understood by.reference to ~he accompanying drawing and the present description, inoluding - . the working examples and the following explanation of the drawing~
in which:
- . FIG. 1 is a part;ally cut~way and sectioned side ele- ..
. . vational view of an electrochemical ceil of this inv~ntion;
15 . . FIG. 2 is a partiàlly cutaway and sectioned end ele- .' vational view of'the cell of FIG. 1, with electrical conn'ectors ' shown; . ~ ' FIG. 3 is an enlarged view oF portions of anode-cathode assembl;es of FI~. 1, showing a covering enclosure and an upwardly leading passageway which, in combination, serve to convey e~ectro- .
: -lyte and gas upwardly from spaces between anodes and cathodes of a plurality of electrode uni~s thereof; and FIG. 4 is a modifi~d perspective view of parts of several . . .pairs of anode-ca~hode ~ssembl;es and'circalating means, showing ' 25 ~' passageways for upward flow of gas-containing reaction products ; . and for downward flow of.electrolyte.
- .' In'the following description'of the illustrative apparatus ''oF the invention, where reference is made to the"production of' . sodium chlorate from an aqueous solution of sodium chloride it will 'be evident that this is ~or the purpose of simplicity oF descrip-. tion because it is possible to make other halates, such as potassium - chlorate and'sodium bromate, by similar methods with the same or -- ':

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similar apparatuses and therefore it should be considered that the description also applies to apparatuses and processes for making halates.
Electrochemical cell 11, as shown in FIG. 1, may be con-sidered to be composed of an upper section 13 and a lower section 15. The upper section is mprimarily for the retention of hyp0-chlorite and electrolyte and for conversion of the hypochlorite to chlorate by a time reaction. The bottom portion, which may be considered as being the eletrolytic portion, is for electrolysis of brine (an aqueous solution of sodium chloride) to hydrogen, chloring and sodium hydroxide, the latter two of which react to form hypochlorite. Also, in the larger spaces 16 and 18, respec-tively, between inactive electrode surfaces and beneath the elec-trodes, conversion of hypochlorite to chlorate amy also take place.
Electrolytic units 17 and 19 each include anodes 21 and 23 for the one unit and 25 and 27 for the other, which anodes may be in sheet of plate form. Such anodes are strengthened by horizontal channels 26 and have anode conductors 29 welded to their inactive sides, which also helps to rigidify the anode. The anodes are bent along vertival corners to form ends 28, which further stiffen them. They are also supported on ledges 100, of steel angle iron as shown, covered on the top thereof with an insulating material, preferably a synthetic organic polymer, most preferably polytetra-fluorethylene (Teflon?). The anodes and the attached channels and conductor rods are removable from the cell at sides thereof by unfastening plates 30 and withdrawing held anode assemblies.
Although solid sheet anodes may be employed, and normally are made primarily of a valve metal coated with noble metal on the active side thereof, perforated metals, expanded metals and screens may also be used and in the present description are considered to be interchangeable with smooth surfaced anodes 8~5 , and sheets where such are described. Also materials of.construc-tion for the anodes may be changed to suitablè substitutes. Anode conductor rods 29 normally extend horizontally and will preferably . . be titanium clad over a copper core.
The anodes of each "unit" are located about ca~hode sub-assemblies 31 and 33, in which cathodes 35 and 37 for sub-assembly : 31 and 39 and 41 for sub-assembly 33,.respectively, are joined to-: - gether by means of internal wall-spacers 43 and'45, respectively. ' ' ~ In cathode sub-assembly 31 open spaces 47 are for circulation of ' 10 cooling water, when desired ~nd it is preferred that such water -. : move through such sub-assembly from bottom to top in generally . hor;~ontal paths, mo~ing from one space to another through ver-' .- tical.openings or passageways through or at the ends of spacers '; ' 43. Add;tionally, a heat exch~nger ~not illustrated) may be present : 15 .in the cell top section if warranted. A titanium tube exchanger ' . ;s preferred and the coolant, usually water, can also circulate ':' . through the cathodes (and anode conductors, etc., when employed). `.. ;
.. Atop a pair-of adjacent electrode units~ each o~ which . includes two anodes and two cathodes and in which each of the ~' 20 ''anode-cathode pa;rs defines a clearance passageway in which electrolyte is electrolyzed, there is positioned enclosure 49 ~ . comprising.a vertical wali 51 having an outwardly flaring bo~tom -. ' .` .portion 53, a hori~ontal "ceil;ng" 55 and an upwardly extend;ng ' -... .
'. passage 57 defined by vertical wa11s 59. Enclosure 49 encloses ~.'...... 25 . or covers a pair of un;ts 17.and 19 and collects gas and upwardly . ~.
." ....... circulat;ng electrolyte and reaction product from said units and - .'~ ~ ;
'. ' ' from the passage~ays between the reactive electrodes thereof and ; .~ .. directs such materials upwardly through p~ssage'570 -As-is seen ' ' by reference to FIG. 4 passage 57 and walls 59 are parts of the upper section of the electrochemical cell. B.~ffle passage 61, defined by walls 59 and baffles 63, together ~ith vertical channel members 65 give the assembly strength.

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In FIG. 3 supporting member 67, held to enclosure 49 in the interior thereof~ is shown resting on cathode spacer-supports 43 and 45, jo;ned to enclosure wall 51 and in contact with en-closure cover or ceiling 55. Through such enclosure parts the cathodes, which are held to the cell walls, support the enclosure . and baffle structure. Member 67 is an insulator, preven-ting short circuiting of elec.trodes ~nd also serves to ma;ntain a desired distance between the cathodes, sub-assembly top and the riser passageway structure for passage upwardly of reaction products and electrolyte. It is preferably a synthetic polymer, e.q., . Tro~idur~HT (.PVDC).
To maintain the desired distance between anodic and cathodic surfaces and thereby help to better regulate voltage drop ~ between anodes and cathodes the present invention preferably utilizes synthetic organic polymeric buttons 69, which preferably are mounted on the anodes by insertion through openings 71 therein.
- Such "buttons" are preferably of an inert polymer of yood physical : characteristics for the application~ such as.polytetrafluoro-: ethylene, sold under the trade markTeflon~ and have "heads" of controlled-thickness SQ as to regulate the electrode gap by bear-ing against both anode and cathode. Preferably such gap will be - thereby regulated so as to be from:Ø05 to 0.4 cm., preferab1y 0.08 to 0.32 cm. and most preferably about 0.15 tD
0.25 cm. . .-. Electricity is conducted to the present cell via conductor - -73, connectors 75 and anode conductors 29 and is transmitted from - the.cell via its conductive wall 77, usually of steel, and con-nectors 79 and 81. The cell is supported on concrete piers 83 . and has a top 85 of titanium, like that described in U.S. patent;
30 4~039,420. The walls of the top section of the cell, especially if of synthetic plastic material, which is sometimes employed, . :~ trade mark , . . ~`' ' :' ..................................... ~, , ~ ~, . . .
'~ . . . '' ' . '' ' 3~5 ~ay be reinforced with horizontal channels or ribs ~7.' The upper.
cell section 13 is held to the cell bo~om se~ion 15 by flanged connections 89. - .
. In operation the cell is charged with sodium chlor;de '' ~ 5 ~solu~ion at the desired concentration, usually saturated and acidic, cooling water is circulated through the cathodes and/or . .
~hrough a titanium tube type heat exchanger in the cell top, if des;red~ and the current is turned on. In the reac~ion or clear-ance spaces between the anodes and cathodes sodium hydroxide, chlorine and hydrogen are generated and the sodium hydroxide and chlorine react to produce sodium hypochlorite.' The hydrogen and ~he aqueous sodium hypochlorite rise past the electrodes, entrained '' ., in one another~ are directed by the enclosure covering the tops of the reactive cle~rance passageways to the r;ser passage (one , 15 riser passage for each.four or more reactant passageways, as illustrated). to the top of ,the cell where the gas fills yas space `~. 91 abo~e electrolyte iigu;d 92 ~nd the liquid proceeds,.to travel -: downwardly through the baffled passages. sSome gas is removed through outlet 95, wh~ch also serves for nitrogen purging. Make-20 ,. up feed is charged through inlet 'fitting ~3. The sodium hypo-.chlorite solution, which ;s at First dilute,'is returned down~ardly to the cell bottom past thQ baffles ~nd through opening 16 between inactive electrode surfaces of electrode units and by other paths ', . ~, at sides and ends of the cell. Desirably at least 20% and prefer-25 -. , ably 30 to 90% of the hypochlorite,passing downwardly through the . . ..
' , ,.'baffled passageway is con~erted-to chloraite in one pass. After .' ..
: ' .'. ,suf~icient'circulation of electrolyte past the electrodes the ' ' .
- ., : 'concentrat;on of so~um chlorate produced from the hypochlorite ~.intermediate product -is high enough to allow withdrawal of some ~ . .
. 30 ~ ' such solution as product. Such withdrawal may be effected.
. . .:through drain line 97. A portion of the amount withdrawn may , .. ~ , . , . . ;
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be m;xed with sa~.urated sodium chloride solution, resaturated by additîon of sodiu~ chloride crystals, acidified w;th hydro-chloric acid, chlorine or a mixture thereof, heated or cooled, as desired (with cooling usually being effected), and returned to the cell near the top, as through fitting 95, or at the bottom thereoF, if desired. The process is run continuously in ---such manner but it may also be batch operated. In other embodi-ments of the .nvention sodium'chloride and acid are added to the electrolyte feed back to the cell and no chlorate solution re-moved from the cell is returned to it (éxcept after chlorate re-moval).
Under preferred conditions of operation the w rrent density is maintained at 0.28 to 0.40 ampere per square centimeter, e.g., 0.35 ampere/sq. cm., the potential is of 2.3 to 3.1 volts, e.g.~ 3.0 volts, the concentration of sodium chlor;de in the aqueous electroly~e is maintained at from about 100 to 1~0 gra~s per liter, 'e.g., 130 grams/liter, and the tempera~ure is in the range o~ 50 to 85C., preFerably 60 to 85C. and most preFerably about 80C., ' so that in the event of minor changes therein the temperature will not exceed 85C. The pH of the electrolyte will be maintained at - about 6 to 6.5 by the addition of hydrochloric acid or chlorine ' 'to the returning electrolyte so that such' returning electrolyte - will have a pH of about 4 to 5. Current efficiencies Qbtained are about 93 to 97% on a continuous basis and are often superior to ~ 25 ~current efficiencies obtained in continuous commercial practice' ; with higher current densities, e.gO~ 0.6 to 1 ampere per square centimeter. HoweVer, the real superiority of the present operation is in its lower voltage which leads to significant savings of ~ ' electric power. '-- 30 '' It has been found that to obtain useful circulationin the present cells, in which the clearance distances between ~ :
active electrodes are in th'e 0.05 to 0.4 cm. width range, the - linear vel'ocity of liquid (exclusiYe of gas, except dissolved gas) . ' ' . ' . ' ~

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. .~3~ 5 past the e1ectrodes (in the clearance passage~ay) is desirably in the range of 0.5 to 7 meters per second, preferably being from 4 to 6 meters per second,'and the preferred linear velocity through the clownward baffled passages is 1 to 20%, preferably 3 to 10% ~-- 5-- thereof. The velocities through ~he passageways below the b~`fled passayeway and between inactive electrodes from the bottom of the baff1ed passageways to the bottom of the cell normally and pre- -. ferably are from 10 to lC0%9 more preferably 20 to 60% of the linear velocity of the electrolyzed liquid moving upwardly between the active electrodes. To regulate such linedr velocities the total cross-sect;onal area of the inactive passageways between - the electrodes will usually be from 10 to 100%, e.g., 40% of the .total of the cross-sectional areas of the active clearance passage-ways. Thus, the widths of such areas, when from 20 to 200 active passageways are present and when from 2 to 1~ larger-downwardly . passageways are present, will usually be in the range of from 5 to 100 times the active clearance passageway width. Normally from 5 to 50 enclosures, each over from 2 to 4 electrode units containing from 4 to 8 clearance passageways between'anode and ' cathode pairs will be present. Preferably from 10 to 20 en-. closures and from 2 to 5 larger passageways will be utilized.
The proportion of larger passageways to electrode units (each unit containing two anode-cathode pairs) will normally be in the range of 1:4 to 1:10. Also, to help maintain desired flow the 25 cross-sectional area of the upwardly directed passages from the .enclosures will be from 2 to 10%, preferably from 4 to 8% and more preferably about 6% o~ the cross-sectional areas of the enclosures, said cross-secti~nal areas being measured horizon-: tally (as is the case for measur;ng such areas of clearances . and passageways previously-mentioned).
The present invention results in substantial advantages over the prior art when electrical energy conservation is a prime . ~ ' .

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~consideration. It has been found when operatin~ at lower current densities, such as those herein described, that lower voltages '`
may be utilized and by increasing the area of active electrolytic _ ! surfaces the samë chlorate production can be obtained, The savings in electricity, often a small proportion and sometimes only ~ few or se~eral percent, are substantial over lengthly periods~ often ~.being in the hundreds of ~housands o~ dollars per year for relative- ' ' . :'.
ly small cell houses. Th'e eff;ciency of operation can be raised . :' by.operating at temper~tures in the range given'and especially . lOin the upper part of such ranye but care will be taken to avoid ' . ha~ing continuous Operatihg temperatures exceed 85C. becaus2 at - such temperatures oxygen product;~n may sometimes exceed the de-: s~red l;mit of 3X by vo~ume of the hydrogen m~de. Simil~rly if ..'. ,circulat;on speeds are increased unduly the percentage of chlorine will a~so be increased objectionably beyond the 2 or 3 percent . : limit tgaS percentages are measured by ~olume).
- ; , Although the present cells are for low current density operation, when necessary they may be operated at higher current ' -'. .densit~es9 thereby increasing chlorate production and giv.in3 the .' . chlorate'plant a higher degree of flexibility to respond to demand.
When cells of the.present type are constructed they may.be compara-.tively easily modified by removal of alternate electrode units and shortening of the enc~osures so as to cover only the remaining .. units.' Then should electrical energy no longer be a seriously 25 limiting factor~ such cells m~y be operated at higher.current ~ . densities and the'remoVed electrodes, if desired, may be ~mployed '.
' : ~ .,-'in other cells. Similarly, and as is more often the case, exist-':- ing cells of the Harke et al. type may be readily converted to : .' : : ' .low current density cel~s by addition of electrode units between 30 " those present, coupled with.extension of the enclosures. When ~''such modif;cations are made it is noted that the widths of the .-:` . . ' ' . . ; . : ,- ,''~
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. - 13 -alternate or second electrode units to be installed may be such that there is no need for additional spacers between the units because the anode conductors function as such spacers. Such modifications between cells of the high and low current density .. ~.types may be.made ~ith substantially no changes in the upper ce~
portions, including thé tops, baffles and riser passages, and little or no change in the tank.of the bottom section, the supports : therefor and the original électrode units.thereo~. The "new"
electrode units being installed may have the cathode sub-assemblies . : -10 . wider than usual and Qf heav.ier walls because of the absence of ~ ~ internal supports but they will usually.be made lighter than the .. : "original" electrode units so as to diminish cell weight, to ~ minimize the need for modification of the cell box and electrode . supports and aiso bec~use cool;ng Pffected by passage of.coolant ~5 within the original cathode sub-assemblies, may often be su fficient, : . due to lower EI losses, so that additional cooling will not be re-... .. . quired. I~- more-cool~ng is desirable it may be ef~ected elsewhere :; . in the cell, e.g.., the cel1 top, w;th an addition~l heat exchanger or the second cathode sub-assembl;çs may be modified to provide ~ for internal.cooling.
The modified enclosure over a plurality o~ electrode ~ units does not result in d;minished flow.of products of electro-~.lysis through the riser passageway because by lowering the current ~:: density to approximately half that previously employed, while - 25 .increasing the active electrode surface proportionally, essentially . .. .. the same quan~ity of electrolysis product results as does when the . ;
"unmodif~ed".Harke et.-al. cell is employed. The riser passagew~y, `
~ :: . . being directly aboYe one electrode unit, despite the f~ct.that it i~ asymmetrically mounted with respect to a pair ur othe plurality ~h 30 . ~of such un;ts, has products from the ~l;gned electrode unit moved directly upwardly through the riser, helping to draw ~long products ..

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from the other such electrode unit. The asymmetric mounting on the enclosure al'lows for continued use of one ~omplete side there-of, so that only one side has to be replaced and even that replace-ment can be effected by substitution of new skirt and flaring - -- 5 portions and extension of the roof-portion of the'already existing -(in a Harke et al. structure) other side of the riser. In some ' instances, where desired, electrode dr riser and enclosure po~
sitions may be adjusted so that the riser is symmetrically located with respect to the electrodes but such is not necessary and often may be undesirable, involvîng additional changes in cell structures. Sim;larly, the locations of the larger lower vertical passageways may be altered but it is preferred to have these symmetrically located away from the cell ends and separate from each other, e.g., separated by 20 to 50% of the electrode units present.
In addition to the basic improvements recited over prior art chlorate cells of similar'types it should also be noted that the utilization of the present polymeric plastic spacing buttons provides an exce11ent method for regulating inter-electrode clearance distances and thereby promoting uniformity of electro-' '`' lysis and electrochemical reaction. The buttons are easily in-stalled, firmly held in place and provide a positive-means for accurately setting distances between electrode working surfaces.
It is preferred that they be installed through holes in the anode ' 25 walls by ;nsertion through such ~alls and by expansion'of a non-- critical side so as to maintain the buttons in place. Such ex-pansion can be effected by: press-fus;ng such non-critical sides;
thread fastening a "n~t" onto a threaded shaft of the spacer passing thrcugh the anode wa~l opening; fusion of a cap onto the button shaft'passing through the opening;'or by other suitable means. The important aspect is to make the "buttons" bet~een the electrodes of desired uniform thickness and to have them held 1~9~5 firmly in place against the active anode wall in pressing contact with the cathode.
Although various aspects of the electrolytic cell of this invention have been described other details of the construction - may be Found ;n-U.S.-paten~ 3,732,153. ~
The subject material referred to includes various descriptions of materials of construction, fittings, assemblies and operations which will be e~idently relatable to the present invention by one of sk;ll in the art.
lo The following example illustrates the operation of the present appara~us in the production of sodium chlorate. -However, the method described ;s illustrative only, the inventi~n may be employed for making other halates and the processes described may be ~aried. In the example and in the specification and claims all parts are by weight and all temperatures are in ~. unless otherwise indicated.
EXAMPLE
An electrolyt;c cell (or electrochemical apparatus) of the type described in FIG'S. 1-4 is made by the described modi-f;cat;on of a corresponding cell such as that of U.S. patent 3,732,153. The electrolytic cell measures approximately 1.2 by

2.4 meters and is about 2.4 meters high. It is equipped with - platinum-iridium plated titan;um anodes and with carbon stee1 cathodes and the anode conductors are titaniunn c!ad copper. The preferred coating on the titan;um anode is a 70:30 platinum:
iridium composition. The cell box is of carbon steel and the cell top is of titanium. The enclosure, riser passageway, baffles and baffled passages are of titanium.
A brine solution containing 140 9./1. of NaCl (in the 130-160 9./1. range) is circulated through the cell and -Fills the , , .
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cell to a distance about 15 cm. from the top thereo-F. Such brine solution is subsequently employed as a makeup feed too. The feed rate' i5 about 21 liters per minute, ~he takeoff of chlorate-con-taining liquor is the same ~nd about 70~ (60-80%~ of the feed is recircula~ed material. The ;nlet kemperature of the brine is ' a~out 55C. (in the 40-60C. range) but it is soon heated up to 'cell'operating temperature, which is such that ~he liquid drawn '~off from the cell is a~ abou~ 80~C. ~in the 50-8~C. range~.
' Chlorine gas is fed in with the makeup brine and sometimes with the recirculated electrolyte ~o acidify the liquor entering the electrolytic zone. Acidific~t;on of the feed is to a pH of ~bout 5.2 (în the-4.8 to 5.7 range) so ~ha~ the liquor drawn ' off has a pH of about 6.5 (;n the 6.1 to 6.8 range).' `- ; After cîrculation of electrolyte has begun operation ' 15 of the cell is started. The cell voltage is found to be about ' 3 volts (in the 2.9 to 3.2 volt range~, with a current density - ' of 0.35 ampere/sg. cm. (in the 0.28 to 0.4 ampere/sq. rlm. range).
When the ci rcul ati ng electrolyte has increased in sodium chlorate ~ ' `content to 450 9./1. ~350-5QO 9./1. rangej liquor is taken off ~ at the bo~tom of the cell from that circulating-~'nd--is made up ~w;th feed brine. Takeoff and-~akeup operations are conducted 'continuously. The liquor rémoved analyzes 130 g./l. o~ NaCl ~'(120-150 g./~. range), 450 9.11. of NaClG3 ~nd 2.5 g./l. of '-- NaOCl (2-4 9./1. range). -Gas removed frcm'the cell top portion :25 'of ~he apparatus, which contains about twice the Yolume of the active bo~tom sec~ion thereof, analyzes less than 1% of'chlorine ~ ~.
and less than 3% ~2.3%~ of oxygen, the b~lance being hydrogen. ' ' ' . ' ! .', Operations of the cell are continued and -Feeds and ~; takeofFs are regulated so as to maintain elèctroly~ic'and ~ :
' electrochemical equ;l;br~a and to permit takeoff o-F cell liquor - at the analysis indicated. Under such oper~ting conditions it ; ~ is found that cell efficiency is about 93~ or better. ~he -. - - : ~ -:
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' ~ - 17 -'v~rious component parts of the cell withstand well the operating conditions and the chemicals wi~h which they come into contact, `:and repairs and replacements are no~ necessitated for periods ''of over a year.
. _5~ SimiJarly, operations of the apparatus under Dther ' ~ ' ' conditions previously described and under conditions like those ' of this example, modified as indicated previously, result in efficient productions of sodium chlorate ~nd other metal chlorates.
'- '"~ The'plastic button spacers are'found to hold up well ;' - lO with use o~ the cell and accurately maintain spacings between ; electrodes and facilitate up~ard flow ~they do not channel the electrolyte, as do vertica~ line spacers). In pract;ce the ~; buttons are usually ci~cular, 0.8 to l.5 cm. in diameter, and ' ~ arranged in a regular staggered (or diamond~ pattern about 8 to ;20 cm. apart, e.g., l3 cm. apart. About 30 to lO0 are used per : 5~;` anode cathode pair, e.g., 55 in the-present example.
' '' The in~ention has been described with respect to ~; '"' Yario~s illustrations and examples thereof but is not to be ;,'considered as limited to these because it'will be clea'r to one ` 20 ''skilled in the art that equiv~lents ans substitutes may be .. . .. . . . .
'' ,employed without'dep~rting from the spirit of the invention or - going outside the scope thereof.
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Claims (3)

The embodiments of the invention in which an exclusive property or privilege is claimed is defined as follows:

1. A method for converting an apparatus for manufacture of halate, comprising an electrolytic cell including a plurality of monopolar dimensionally stable anodes and cathodes, means for positioning them in spaced and paired relationship within units comprising two anode-cathode pairs with two inner cathodic surfaces on a base structure and two outer anode surfaces, each anode surface facing a cathodic surface and being separated therefrom, with enclosure means above each unit for trapping gas generated between the anodes and cathodes of the unit and transmitting it to a passageway through which it and electrolyte move up-wardly and help to circulate electrolyte in the cell, to one capable of producing halate at the same rate and at a lower current density which comprises: installing in said cell additional electrode units and replacing at least a portion of the enclosure means with an enlarged means for enclosing the tops of a plurality of such units, including an original and an added unit, and connecting said enlarged means for such plurality of units with an original single vertical passageway for circulation of generated gas and electrolyte upwardly through the cell.

2. A method according to claim 1, wherein any spacers between electrode units are removed and installed units are spaced apart from other such units by anode connectors.

3. A method according to claim 2, wherein spacers are removed between at least two units without installation of an enlarged enclosure and an additional unit so as to provide an enlarged passage-way for circulation of electrolyte downwardly through the cell.