CA1190889A - Solid polymer electrolyte chlor-alkali cell - Google Patents

Abstract

ABSTRACT

Disclosed is a solid polymer electrolyte electrolytic cell having a fluorocarbon permionic membrane with carboxylic acid groups, interposed between the anolyte and catholyte. The cathode may be a depolarized cathode, e.g., a peroxy compound depolarized cathode, a redox couple depolarized cathode, or an oxidant-complex depolarized cathode. The cathode may be a boride, e.g., titanium, diboride, an intercalation compound of carbon and fluorine, or a transition metal., e.g., iron, cobalt, or nickel. The elec-trocatalysts, e.g., the anode and cathode, may be adhered to the permionic membrane by chemdeposition. The anode may be particulate with hydrophobic material. The individual anode particles may be silicone extended. The electrolytic process using the cell may be carried out at high pressure to obtain liquid chlorine, which is then separated from the brine. The cell may be horizontal, with internal heat exchange means. In the case of a bipolar cell, the bipolar conductor element may be silicone, or a titanium alloy, and may have heat transfer and reagent feed means incorporated therein.

Description

~s~

SOLID POLYMER E~ECTROLYTE CHLOR-ALKALI CELL

Description of the Invention Solid polymer electrolyte chlor alkali cells have a cation selec-tive permionic membrane with an anodic electrocatalyst embedded in and on the anodic surface of the membrane, tllat is in and on the anolyte facing surface of the permionic membrane, and a cathodic hydro~yl evolution cata- -lyst, i.e., a cathodic electrocatalyst, embedded in and on the cathodic surface of the membrane, that is the catholyte facing surface of the per mionic membrane. In an alternative exemplifica~ion, a cathode depolarizer, also known equivalently as an HO2- disproportionation catalyst, is present on the cathodic surace, that is the catholyte facing surface of the penni-onic membrane. This HO2- disproportionation catalyst serves to depolari~e the cathode and avoid the formation of gaseous hydrogen.
Solid polymer electrolyte chlor alkali bipolar electroly~ers herein contemplated offer the advantages of high production per unit volume ~5 o~ electrolyæer, high current efficiency, high current density, and in an alternative exemplification, the avoidanre of gaseous products and the concomi ~ant aux;liaries necessitated by gaseous products.
In the solid polymer electrolyte chlor alkali process aqueous alkali metal chloride, such as sodiu[n chloride or potassium chloride,

2~ contacts the anodic surface of the solid polymer electrolyte. An electrical potential is imposed across the cell with chlorine being evolved at the anodic surEace of the solid polymer electrolyte.
Alkali metal ion, that is sodium ion or potassium ion, is trans~
ported across the solid polymer electrolyte permionic membrane to the .~

cathodic hydroxyl evolution catalyst on the opposite surface of the permi-onic membrane. ~e alkali metal ion, that is the sodium ion or potassium ion is transported with its water oE hydration, but with substantially no transport of bulk electrolyte.
Hydroxyl ion is evolved at the eathodic hydroxyl ion evolution catalyst as is hydrogen. However, in an alternative e~emplification, a cathod;c depolarization catalyst, i.e., an H02- disproportionation catalyst, is present in the vicinity of the cathodic surface of the oermionic mem-brane and an o~idant is fed to the catholyte compartment to avoid the gen-eration of gaseous cathodic products.

The Figures FIG. 1 is an e~ploded view o~ a bipolar, solid polymer electro-lyte electrolyzer.
FIG. 2 is a perspective view of a solid polymer electrolyte unit of the bipolar electrolyzer shown in FIG. 1.
FIG. 3 is a cutaway elevation of the solid polymer electrolyte Ullit shown in FIG. 2.
FIG. 4 is a cutaway elevation, in ~reater ~agnification of the solid polymer electrolyte sheet shown in the unit of FIGS. 2 and 3.
FIG. 5 i8 a perspective view of the distributor showing one forrn of electrolyte feed and recovery.
FIG. 6 is a cutaway side elevation of the distributor shown in FIG. 5 FIG. 7 is a perspective view of one exemplification of the bipolar element shown in FIG. l.
FIG. 8 is a cutaway side elevation of ~he bipolar ele~ent ~hown in FIG. 7.

FIG. 9 is a perspective view of an alternative exempli~ication of a bipolar element having heat exchange means pas~ing therethrough.
FIG. 10 is a cutaway side elevation of the bipolar element shown in FIG. 9.
FI~. 11 is a perspective view of an alternative exemplification of a bipolar element having distributor means combined with the bipolar element.
FIG. 12 is a cutaway side elevation of the bipolar element shown ;n FIG. 11.
FIG. 13 is a schematic cutaway side elevation of the solid polymer electrolyte electrolytic cell.
FIG. 14 is a schematic of the solid polymer electrolyte chlor-alkali process.

Detailed Description oE the Invention The chlor alkali cell shown schematically in FIG. 14 has a solid polymer electrolyte 31 with a permionic membrane 33 therein. The permionic membrane 33 has all anodic surface 35 with chlorine catalys~ 37 thereon and a cathodic surface 41 with cathodic hydroxyl evolution catalyst 43 thereon.
Also shown is an external power supply connected to the anodic catalyst 37 by distributor 57 and connected to the cathodic catalyst 43 by distrib~ltor 55.
Brine is fed to the anodic side of ~he solid polymer electrolyte 31 where it contacts the anodic chlorine evolution catalyst 37 on the anodic surface 35 of the permionic membrane 31. The chlorine, present as chloride ion in the solution, forms chlorine according to the reaction:
2 Cl~ - ~~~7` C12 ~ 2e~

3 ~ ~ ~

The a1kali meta] j.on, that is sodium ion or potassium ion, shown in Figure 14 as sodium iOtl., and its water of hydration, passes through the permionic membrane 33 to the cathodic side 41 of the pernionic membrane 33.
Water is fed to the catholyte compartment both externally, ancl as water of hydration passing through the permionic membrane 31. The stoichiometric reaction at the cathodic hydroxyl evolution catalyst is:
~12 -~ - 011 + H
In an a].ternative exempli.fication, a cathode depolarizing catalyst and an oxidant are present whereby to avoid the generation of gaseous hydrogen.
The structure for accomplishing this reaction is shown generally :Ln Figure 13 where electrolytic cell 11 is shown with walls 21 and a permi-onic membrane 33 therebetween. The permionic membrane 33 has an anodic surface 35 and an anodic electrocatalyst 37 on the anocdic surface 35, and a cathodic surface lll with cathodic electrocatalyst 43 thereon. In an alternative exemplification, a cathode depo].ari.~ation catalyst, that is an ~2 disproportionation catalyst (not shown) -is in the vicini.ty of the cathodic surface 41 of the membrane 33 whereby to avoid the evolution of llydrogell gas.
~leans for conducting el.ectrical current from the walls 21 to the solid polymer electrolyte 31 are as shown as distributor packing 57 in the allol.yte compartment 39 whi.ch conducts current from the wall 21 to the anodic chlorine evolution catalyst 37, ancl distributor packing 55 in the catholyte compartment 45 which conducts current from the wal.l 21 to the cathodic hydroxyl evolution catalyst 43.
In a preferred exemplification, the distributor packings, 55 and 57 also provide turbulence and mixing of the respective electrolytes. This avoids concentration polarization, gas bubble effects, stagnation, and dead space.

In cell operation, brine is fed to the anolyte conpartment 39 through brine inlet 81a and depleted brine is withdra~m frorn the anolyte compartment 39 through brine outlet 81b~ lhe anolyte liquor may be removed as a chlorine gas cvntaining froth, or liquid chlorine and liquid brine may be removed together.
Water is fed to the catholyte compartment 45 through water feed means 10la to maintain the alkali ~etal hydroxide liquid thereby avoiding deposition of solid alkali ~etal hydroxide on the membrane 33. Additionally, oxidant may be fed to the catholyte compartment 45, for example when an HO2-disproportionation catalyst is present, whereby to avoid formation of hydrogen gas and to be able to withdraw a totally liquid cathode product.
One particularly desirable cell structure is a bipolar electro-lyzer utilizing a solid polymer electrolyte. FIG. 1 is an exploded view of a bipolar solid polymer electrolyte electrolyzer. The electrolyzer is shown ~ith two solid polymer electrolytic cells ll and 13. There could however be many rnore such cells in the electrolyzer l. The limitation on l:he number of cells, ll and 13, in the electrolyzer 1 is imposed by recti-fier and transfonner capabilities as well as the possibilities of current leakage. Ilowever, electrolyzers containing upwards from 150 or even 200 or more cells are within the contemplation of the art utilizing presently available rectifier and transformer technologies.
Individual electrolytic celL ll contains a solid polymer electro-lyte unit 31 shown as a part of the electrolyzer in FIG. l, individually in FIG. 2, in partial cutaway in FIG. 3, and in higher magnification in FIG. 4 with the catalyst particles 37 and 43 exaggerated. Solid polymer elctrolyte unit 31 is also shown schematically in FIGS.13 and 14.

~ 57 The solid poly~er electrolyte unit 31 includes a permionic mem-brane 33 with "anodic chlorine evolution catalyst 37 on the anodic sur-face 35 of the permionic membrane 33 and cathodic hydroxyl evolution catalyst 43 on the cathodic surface 41 of the permionic membrane 33.
The cell boundaries, may be, in the case of an intennediate cell of the electrolyzer 1, a pair of bipolar units 21 also called bipolar back-plates. In the case of the fil-st and last cells of the electrolyzer, such as cells 11 and 13 shown in FIG. 1, a bipolar unit 21 is one boundary of the individual electrolytic cell~ and end plate 71 is ~he opposite boundary of the electrolytic cell. The end plate 71 has inlet means for brine feed 81a, outlet means for brine removal 81b, inlet means water feed lOla5 and hydroxyl solution removal lOlb. Additionally, when the cathode is depo-larized, oxidant feed, not shown would also be utilized. The end plate 71 also includes current connectors 79.
In the case of an monvpolar cell, the end units would be a pair of end plates 71 as described above.
The end plate 71 and the bipolar units 21 provide gas tight and electrolyte tight integrity Eor the individual cells. A~ditionally, the end plate 71 and the bipolar units 21 provide electical conductivity, as ~ell as in various embodiments, electrolyte feed and gas recovery.
The bipolar unit 21, shown in FIGS. 7 and 8 has anolyte resist-ant surface 23 facing the anodic surface 35 and anodic catalyst 37 of one cell 11. The anolyte resistant surface 35 contacts the anolyte liquor and forms the boundary of the anolyte compartment 39 of the cell. The bipolar unit 21 also has a catholyte resistant surface 25 facing the cathodic surface 41 and cathode catalyst 43 of the solid polymer electrolyte 31 oE
the next adjacent cell 13 of electroly~er 1.

The anolyte res;stant surface 23 can be fabricated of a valve rnetal, that is a metal which forms an ~cid resistant oxide film upon exposure to aqueous acidic solutions. The valve metals include titanium, tantalum, tungsten, columbium9 hafnium, and zirconium, as well as alloys of titanium, such as titanium with yttrium, titanium with palladium, titanium with molybdenum, and titanium with nickel. Alternatively, the anolyte resistant surface may be fabricated of silicon or a silicide.
The bipolar unit 21 may be fabricated of two sheets, plates, or laminates, 23, 25. The surface 23 facing the anolyte may be fabricated of a valve metal, a~ described hereinabove. However, according to one --exemplification~ the anolyte facing surface 23 of the bipolar unit 21 is fabricated of an alloy of a valve metal characteri~ed by enhanced resist-ance to hydride formation and crevice corrosion.
One particularly outstanding group of such alloys are alloys oE
titanium and a rare earth metal or metals. Contemplated rare earth metals include scandium, yttrium, and the lanthanides. The lanthanides are ~S c ~ "y, cl r; ~
lanthanum, cerium, praesodyMium, neodyrnium, promethium, s~ n, europium, ~adolinium, terbiurn, dysprosium, holrnium, erbium, thulium, ytterbium, and lutetium. Whenever ~he term "rare earth metals" is used herein, i~ is intended to encompass scandium, i~t-t~ um, and the lanthanides.
The rare earth metal alloying agent may be one or more rare earth metals. For example, it may be scandium or yttrium or cerium, or lanthanum ) C-A W~rl or L~t-h~u and y~trium or lanthanum and ceriumO Most commonly, the rare earth metal alloying addition will be yttriurn.
The amount of rare earth metal alloying agent should be at least a threshold amount sufficient to diminish or even dominate the uptalce of hydrogen by the titanium. This is generally at least about 0.01 weight percent, although lesser amounts have positive effects. The maximum amount of rare earth metal alloying agents should be lo~ enough to avoid substan-tial formation of a two phase system. Generally, this is less than about 2 weight percent rare earth metal for the rare earth me~.als yttrium, lan-f J~ C? ~um, cerium, gadolinium, and erbium although amounts up to about 4 or even 5 percent by weight thereof can be tolerated without adverse effects, and less than about 7 weight percent rare earth for the rare earth metals scandium and europium, although amounts up to 10 percent by weight may be fo/~r~fe~
~ r~ e~ without deleterius effects. Generally the amount of rare earth ~etal is from about 0.01 weight percent to about 1 weight percent9 and preferably from about 0.015 weight percent to about 0.05 weight percent.
The titanium alloy may also contain various impurities without deleterious effect. These impurities include iron in amounts normally above about 0.01 percent or even 0.1 percent and frequently as high as 1 percent, vanadium and tantalum in amounts up to about 0.1 percent or e~en 1 percent oxygen in amounts up to about 0.1 weight percent, and carbon in amounts up to about 0.1 ~eight percent.
Alternatively~ the anolyte facing surEace 23 of the bipolar unit may be an isomorphous beta phase alloy of titanium with rnolybdenum or an isomorphous alloy of titanium ~ith other transition metal, such as palladium, nickel and iron, e.g., where the iron content ir; less than 0.05 weight per-cent iron. Isomorphous alloys of titanium and the above transition metals offer enhanced resistance to crevice corrosion and hydrogen uptalce. The amount of the transition metal~ i.e.~ ironJ nickel, palladium, or molyb denum, should be high enough to enhance the crevice corrosion resistance and hydrogen uptake resis~ance but low enough to avoid formation of a second phase.

9~3 The catholyte resistance surface 25 may be fabricated of any material resistant to concentrated caustic solutions containing either oxygen or hydrogen or both. Such materials include iron, steel, stainless steel and the like.
The two rnembers 23 and 25 of the bipolar unit 21 mzy be sheets of titanium and iron, shee~s of the other materials specified above, and there may additionally be a hydrogen barrier interposed between the anodic sur~ace 23 and cathodic surface 25~ whereby to avoid the transport of hydrogen through the ca~hodic surface 25 oE a bipolar unit to the anodic surface 23 of the bipolar unit.
The hydrogen barrier, interposed between the anodic surface 23 and cathodic surface 25 of the bipolar unit 21, is a material that impedes the flow of hydrogen, e.g., é3 material with a low hydrogen solubility or permeability. The hydrogen barr er may be a nonconductive material such as silicates and glasses, organic resins, and paints. Alternatively, metals having hydrogen barrier properties may be used. Suitable results may be obtained with vanadium, chromium, manganese, cobalt, nickel~ copper, ~inc, niobium, molybdenum, silver, cadmium, rhodium tantalu~, tungsten, iridium, and gold. Best hydrogen barrier results are obtained when the hydrogen barrier coating is molybdenum, rhodium, iridium, silver, gold, manganese, zinc, cadlnium, lead, copper or tungsten. Especially preferred is copper.
The hydrogen barrier may be of slleet or plate. Alternatively, it may be a deposited film or coating. According to a still further e~em-plification the hydrogen barrier may be detonation clad to one or both members of the bipolé3r unit 21.
In an alternative exemplification shown in FIGS. 9 and lO~ heat exchanger conduits 121 pass through the bipolar unit 210 These heat exchanger conduits 121 carry cool liquid or cool gas to extract heat from the electrolyzerl for example I2R generated heat as well as the heat of reaceion. This enables a 1O~7er pressure to be used when the electrolyzer is pressurized, as ~hen a liquid chlorine is the desired product or when oxygen is fed under pressure or both.
In a still further exemplification of the bipolar solid pol~ner electrolyte electrolyzer, shown in Figures 11 and 12 the electrolyte feed and distribution function is performed by the bipolar unit 21. Thusl in addition to or in lieu of distributor 51, line 133 extends fro~ conduit 115a to the interior of the bipolar unit ~1 then to a porous or open ele-ment 131 which distributes the electrolyte. Analogously for the opposite electrolyte, feed is through pipe 143 to a porous or open surface 141 on the opposite surface of the bipolar unit.
The individual electrolytic cells 11 and 13 of bipolar electro-lyzer 1 also include distributor means Sl which may be imposed between the ends of the cell, that is between the bipolar unit 21 or end wall 71 and the solid polymer electrolyte 31. This distributor means is shown in FIG. 1 and individually in FIGS. 5 and 6 with the catholyte liquor COII-duits 105a and 105b and the catholyte feed 111a and catholyte recovery lllb.
The peripheral wall 53 of the distributor 51 is shown as a circu-lar ring. It provides electrolyte tight and gas tight integrity to the electroly2er 1 as well as to the cells 11 and 13.
The packing, which may be caustic resistant as packing 559 or acidified chlorinated brine and chlorine resistant, as packing 57, is pref-erably resilient, conductive, and substantially noncatalytic. That is, packing 55 of the catholyte unit, in the catholyte compartment 45 has f,f>
a higher hydrogen evolution or hydroxyl ion evolution over voltage-~hen ~3~

cathodic catalyst 43 in order to avo:icl the electrolytic evolution of cathodic product thereon. Similarly~ the paclcin~ 57 in the anolyte compart-ment 39 has a higher chlorine evolution over voltage and higher oxygen evolution over voltage than the anodic catalyst 37 whereby the evolution of chlorine or oxygen thereon is avoided.
The packing 55, and 57 serves to conduct current from the boundary of the cell such as bipolar unit 21 or end plate 71, to the solid polymer electrolyte 31. This necessitates a high electrical conductivity. The conduction is carried out while avoiding product evolution thereon, as described above. Similarly, the material must have a minimum of contact resistance at the solid polymer electrolyte 31 and at the boundaries of the individual cell 11, e.g., end wall 71 or bipolar unit 21.
Furthermore, the distributor packing 55, 57 distributes and dif-fuses the electrolyte in the anolyte compartment 39 or catholyte compartment 45 whereby to avoid concentration polariæation, the build up of stagnant gas and liquid pockets, and the build up of solid deposits such as potassium hydroxide or sodium hydroxide deposits.
The packing 55, 57 may be carbon, for example in the form of grapllite, carbon felt, carbon fibers, porous graphite, activated csrbon or the .lilce. Alternc~tively, the packing may be a metal felt, a metal fiber, a metal. sponge, metal screen, graphite screen, metal mesh, graphite mesh, or cl.:ips or springs or the like, such clips or spring~s bearing on the solid polyn~er electrolyte and on the bipolar unit 21 of the end plate 71.
According to a further exemplification of this invention9 the current collector and current distributor means, 51, providing electrical contact between the cell walls, 21, 71, and the solid polymer electrolyte 31, may be a sheet of fine gauge screen or mesh, bearing upon the cata]yst 37, 43, an~ electrically and mechanically in series with the end walls 21, 71S of the cell 11. Tlle electrical and mechanical connector may be provided by first and second resilient metal means~ the first resilient metal means bearing upon the catalyst 37, 43, and ~he second resilient metal means bearing upon the end wall 21, 71, of the cell. The two resilient metal means are removably joined. That is they may bear upon each other under compression, or they may be clipped together. Alternatively, the packing 51, 57 may be packing as rings, spheres, cylinders or the 1ike, packed tightly to obtain high conductivity and low electrical contact resistance.
In one exemplification the brine feed 87a and brine withdrawal S7b, as well as the water and oxidant feed 111a, and catholyte liquor recovery 111b, may be combined with distributors 51,51. In such an exempli-fication the feed 87a and feed llla extend into the packing 55 and 57 and the withdrawa].~37b and recovery 111b extends from the packing 55 and 57.
In an alternative exemplification the reagent feed may be to and product recovery may be from a microporous distributor, for example micro-porous hydrophilic or microporous hydrophobic films bearing upon the solid polymer electrolyte 31 and under compression by the distributor means 55 and 2~ 57. In an exemplification where the feed is to microporous Eilms upon the solid polymer electrolyte 31, the catalyst particles 37 and 43 may be in the mlcroporous film as well as on the surEace of the solid polymer electro-1yte 35 and l~1~
~ s described above, individual solid polymer electrolyte electro-lytic cell 11 and 13 inc]udes a solid polymer electrolyte 31 wi~h a permi-onic membrane 33 having anodic catalyst 37 on the anodic surface 35 thereof, and cathodic catalyst 43 on the cathodic surface 41 thereof. The boundaries of the cell may be a bipolar unit 21 or an end plate 71, with electrical conduction between the boundaries and the solid polymer electrolyte 31 being by distributor means 51. Reagent feed 87a and llla and product recovery 87b and lllb are also provided. Additionally, there mus~ be provided means for ~aintain;ng and providing an electrolyte ~ight, gas tight seal as gasket 61. While gasket 61 is only shown between walls 71 and bipolar units 21, and the distributors 51, it is to be understood that additionally or alter~atively, gasket 61 may be interposed between the distributors 51, and the solid polymer electrolyte 31.
Gaskets in contact with the anolyte compartment 39 should be made of any material that i5 resistant to acidified, chlorinated brine as well as to chlorine. Such materials include unfilled silicon rubber as well as various resilient fluorocarbon materials.
The gaskets 61 in contact with the catholyt~ compartment 45 may '``~ l5 be fabricated of any ~aterial which is =~t to concentrated caustic soda.
One particularly satisfactory flo~ system is shown generally in FIG. 1 where the brine is fed to the electroly~er 1 through brine inlet 81a in the end unit 71, e.g., with a hydrostatic head. The brine then passes through conduit 83a in the "O" ring or gasket 61 to and through conduit 85a in the distributor 51 o~ the cathodic side 45 cf cell 11, and thence to and through conduit 89a in the solid polymer unit 31 to anodic distributor 51 on the anodic side 35 of the solid polymer 31 of the electrolytic cell 11.
At the distributor 51 there is a "T" opening and outlet with conduit 91a passing through the distributor 51 and outlet 37a clelivering electrolyte to the anolyte chamber. The flow then continues, from conduit 91a in distrib-utor 51 to conduit 93a in the next "O" ring or gaslcet through conduit 95a in the bipolar unit 21 and on to the next ~ell 13 where ~he fluid flow is substantially as described above. Brine is distributed by the packing 57 in the distributor 51 within the anolyte compartment 39. Distribution of the brine sweeps chlorine from the anodic surface 35 and anodic catalyst 37 to avoid chlorine stagnation.
The depleted brine is drawn through outlet 87b of the distribu-tor 51 to return conduit 91b e.g. by partial ~acuum or reduced pressure.
The return is then through return conduit 89b in the solid polymer electro-lyte unit 31, the conduit 85b in the cathodic distributor 51, conduit 83b in the "0" ring or gasket 61 to outlet 81h where the depleted brine is recovered from the electrolyzer 1.
While the brine feed has been sho~n with one inlet system and one outlet system~ i~e. the recovery of depleted brine and chlorine through the same outlets, it is to be understood that depleted brine and chlorine ~ay be separltely recovered. It is also to be understood, that depending upon the internal pressure of the anolyte co~partment 39 and the temperature of the anolyte liquor within the anolyte compartment, the chlorine may either be a liquid or a gas.
Water and oxidant e~ter the electrolyzer 1, through inlet lOla in the end unit 71. The water and o~idant then proceed through conduit 103a in the "O" ring or gaske~ 61 to conduit 105a and "T" in cathodic disribu-tor 51 on the cathodic side 45 of cell 11. The "T" outlet includes conduit 105a and outlet llla. Water and oxidan~ are delivered by outlet llla in ring 53 of the distributor 51 to the catholyte resistant packing 55 within the catholyte chamber 45 of cell 11. The cell liquor, t'nat is the aqueous alkali metal hydroxide, such as sodium hydroxide or potassium hydroxide, is recovered from the cathodic surface 41 of the solid polymer electrolyte -- lL~ --permionic me~brane 33 by the water carried into the cell 11~ When oxidant îs present~ liquid is recovered through the outlet lllb. When there i9 no oxidant, ga~ and liquid may both be recovered through lllb, or, in a~
alternative exemplification, a separate gas recovery line~ not shown, may be utilized.
While, the electrolyzer is shown with common feed for oxidant and water, and with common recovery for gas and liquid, there may be three conduits present, llla, lllb and a third conduit, not shown, for water feed, oxidant feed, and liquid recovery. Altertlatively, there may be three conduits llla, lllb and a third conduit, not shown, for water feed, liquid recovery and gas recovery.
Returning to overall flows in the electrolyæer 1, conduit iO5a continues to conduit 107a of the solid polymer electrolyte unit 31 to conduit lO9a of the anodic distributor 51 which continues through to con-duit 113a of the O ring or gasket 61 thenc~ to conduit 115a of the bipolar unit 21, where the sa~e path through individual cell 13 is followed as in cell 11~ Similarly the network ~ay be continued fo} further cells.
The recovery of product is shown as being from distributor 51 through outlet lllb to conduit 105b thence to conduit 103b in the O ring or gnsket 61 to outlet lOlb in the end wall 71.
While the flow is de~cribed as being to and through distribu-tors 51, as described above, the flow could also be through other pa~hs.
For examplel the inlet or outlet or both could be in ~he bipolar unit 21 which bipolar unit would carry porou~ film or outlet pipes from unit 21.
Alternatively, the inlet or outlet or both could be part of the solid polymer electrolyte unit 31.

While the flow is de~cribed as being in parallel to each indi-~idual cell 11 and 13, it could be serial flow. ~here serial flow of the brine i9 utilized, the T, outlet 87-conduit 9l can be an L rather than a T.
In an exemplification where serial flow is utilized, there would be lower brine depletion in each cell, with partially depleted brine from one cell fed to the next cell for further partial depletion. Similarly, where there is serial flow of the catholyte liquor, the T, conduit 105-outlet 111 could be an L.
Where serial flow is utilized the 10w could be concurrent with high scdium or high potassium ion concentration gradients across the solid polymer electrolyte 33 or countercurrent with lower sodium or potassium ion concentration gradients across the individual solid polymer electrolyte units 31.
The bipolar electrolyzer may be either horiæontally or verti-cally arrayed, that is the bipolar electrolyzer l may have a solid polymer electrolyte ullits 31 with either a hori~ontal membrane 33 or a lertical membrane 330 Preferably the membrane 33 is horizontal with the anodic surface 35 on top of the permionic membrane 33 and the cathodic surface 41 on the bottom of the permionic membrane 33. A horizontal design offers various advantages. Under low pressure operation, chlorine bubbles flow up through the anolyte compartment 39. In the catholyte compartment 45, the horizontal conflguration pre~ents the build up of concentrated alkali metal hydroxide on the bottom surface 41 of the permionic membrane 339 while allowing for the bottom surface 41 of the permionic membrane 33 to be 'wet with alkali metal hydroxide. Additionally, where oxidant is present~ espe-cially gaseous oxidant, the hori~ontal configuration allows the oxidant to be in contact with the cathodic surface 41 of the permionic l~embrane 33.

The solid polymer electrolyte 31 contains a permionic membrane 33.
The permionic membrane 33 should be chemically resistane, cation selective, with anodic chlorine eYolution catalyst 37 on the anodic surface 35 and cathodic, hydro~yl evolution catalyst 43 on the cathodic surface 41 thereof.
The flurocarbon resin permionic membrane 33 used in providing the solid polymer e~ectrolyte 31 is characteri~ed by the presence of cation selective ion exchange groups, the ion exchange capacity of the membrane, the concentration of ion exchange groups in ehe membrane on the basis of water absorbed in the membrane, and the glass transition eemperature of the membrane material.
o~ rL~
f~ ~ The ~ resins herein contemplated have the moieties:
~',~
~CF2-CXX'~ and ~CF2 -C -X~
y where X is -F, -Cl, -I~, or -CF3; X' i~ -F~ -Cl, ~ CF3 or CF3 ~CF2)m-;
m i5 an integer of 1 to 5; and Y is -A, -~ A, -P-A, or -0-(CF2)n (P, Q, R)-A.
In the unit (P, Q, R), P i9 --(CF2)a(CXX~)b(CF2)c, Q is (-CF2-0-cxx )d~
R is (-CXX'-0-CF2)e, and (P, ~, R) contains one or more of P, Q. R.
~ is the phenylene group; n is 0 or 1; a, b, c, d and e are int.egers from 0 to 6.
The typical groups of Y have the structure with the acid group, A, connected to a carbon atom which is connected to a fluorine atom. These include ~CF2~XA, and side chains having ether linkages suc~ as: 0-~CF2~A9 ~-0-CF2-CF~yA, ~O~CF2-CF~x~O-CF2-CF2~yA, and -0-CF2~CF2-O~CF~x~CF2~y~CF2 Z Z Z

-O-CF~zA where x, y, and z are respeGtively l to lO; Z and R are respec-tively -F or a Cl~lo perfluoroalkyl group, and A is the acid group as defined below.
In the case of copolymers having the olefinic and olefi~-acid r~ f~
! ! moieties above described, it is ~ r~ y to have 1 to 40 mole percent, and preferably especially 3 to 20 ~ole percen~ of the olefin-acid moiety units in order to produce a membrane having an ion-exchange capacity within the desired range.
A i6 an acid group chosen rom the group consisting of -COOH
-P03H2, and -P2~2 -or a group which may be converted to one of the afoeesaid groups by hydrolysis or by neutrali~ation.
In a particularly preferred exemplification of this invention, A
may be either -COOH, or a functional group which can be converted to -COOH
by hydrolysis or neutralization such as -CN, -COF, -COCl, -COORl, -COO~, -CONR2R3; Rl is a Cl_lo alkyl g~oup and R2 and R3 are either hydrogen or Cl ~o Clo alkyl groups, including perfluoroalkyl groups, or both. M is hydrogen or an alkali metal; when M is an alkali me~al it is most prefera-bly sodium or potassium.
In the exemplification of this invention where A is -CONR2R3, and where R and R are hydrogen, or a Cl to Clo alkyl group, including a perfluoroalkyl group, the cathodic surface 41 of the permionic mel~brane 33 may have the ion exchange groups in the carboxylic acid form, while the anodic surface of the permlonic membrane has the ion e~change groups in the amide or N-substituted amide form. The provision of amide ~roups or N-substituted amide groups on the anodic surface 35 of the permionic membrane 33 serves to render the cathodic surface 35 hydrophobic. This prevents chlorine stagnatlon on the membrane 33.
The membrane 33 may be converted to an amide or N-substituted amide group during synthesis, or after the catalyst 37 has been deposited thereon or embedded therein, e.g., by reaction with ammonia or an amine.
In an alternative exemplification A may be either -S03H or a functional group which can be converted to -S03H by hydrolysis or neutrali-zation, or formed from -S03H such as -S03M', (S02-NH) M", -S02~-Rl-NH23 or -S02NR4R5NR4R6; M' is an alkali metal; M" is H, NH4 an alkali metal or an alkali earth metal; R4 is H Na or K; R5 is a C3 to C6 alkyl group, (R1)2 NR6, or RlNR6(R2)z NR6; R6 is H, Na, K or -S02; and Rl is a C2-C6 alkyl group.
The membrane material herein contemplated has an ion exchange capacity from about 0.5 to about 2.0 milligram equivalents per gram of dry polymer, and preferably from about 0.9 to about 1.8 milligram equivalents per gram of dry polymer, and in a particularly preferred e~emplification, from about l.l to about 1.7 milligram equivalents per gram of dry polymer.
When the ion exchange capacity is greater than about 2.0 milligrams equi-valents per gram of dry polymer, the current efficiency of the membrane is too low.

The conterlt of ion e~change ~roups per gram of absorbed water is from about 8 milligram equivalents per gram of zbsorbed water to about 30 milligram equivalents per gram of absorbed water and preferably from about 10 milligram equivalent~ per gram of absorbed water eO about 28 milligram equivalents per gram of absorbed water3 and in a preferred exemplification from about 14 miLligram equivalents per gram of absorbed ~ater to about 26 milligram equivalents per gram of absorbed water. When the content of ion exchange groups per unit weight of absorbed water is less ~han about 8 milligram equivalents per gram or above abouL 30 milligram equivalents per gram the current efficiency i5 too low.
The glass transition temperature is preferably at least about 20C below the temperature of the electrolyte. When the electrolyte temperature i9 between about 95~C and 110C, the glass tran~ition tempera-ture of the fluorocarbon resin permionic ~embrane material is below about lS 90C and in a partic~larly preferred exemplification below about 70C.
Ilowever, the glass transition te~perature should be above about -80C in order ~o provide satisfactory tensile strength of the membrane material~
Preferably the glass transition temperature is from about ~80C to about 70C and in a particularly preferred exemplification fro~ about minus 80C
to about 50C.
When the glass transition temperature of the membrane is within about 20C of tbe electrolyte or higher than the temperature of the electro-lyte the resistance of the membrane increases and the perm selectivity of the membrane decreases. By glass transition temperature is meant the temperature below which the polymer segments are not energetic enough to either move past one another or wikh respect to one anoeher by segmen~al Brownian motion. That i8, below the gLass transition temperature~ the only reversib]e response of the polymer to stresses is strain while above the glass transition tempera~ure the response of the polymer to stress is segmental rearrangement to relieve the externally applied stress.
The fluorocarbon resin permionic membrane materials contemplated herein have a water permeability of less than about 100 milliliters per hour per square meter at 60 C in four normal sodium chloride a~ a pll of 10 and preferably lower than 10 milliliters per hour per square meter at 60C
in four normal sodium chloride of the p~l of 10. Water permeabilities higher than about 100 milliliters per hour per square meter, measured as described above, may result in an impure alkali metal hydroxide product.
The electrical resistance of the dry membrane should be from about 0.5 to about 10 ohms per square centimeter and preferably from about 0.5 to about 7 ohms per square centimeter.
Preferably the fluorinated-resin permionic membrane has a mole cular weight, i.e., a degree of polymerization, sufficient to give a volu-metric flow rate of abou~ 100 cubic millimeters per second at a temperature of from about 150 to about 300C.
The thickness of the permionic membrane 33 should be such as to provide a membrane 33 that is strong enough to withstand pressure changes ~0 ~nd manufacturing processes, e.g., the adhesion of the catalyst particles, but thin enough to avoid high electrical resistivity. Preferably the membrane is from 10 to 1000 microns thick and in a preferred exempllfication from about 50 to about 200 microns thick. Additionally, internal reinforce-ment, or increased thickness, or crosslinking may be utilized, or even lamination may be utilized in order to provide a strong membrane.
In a preferred exemplification, the permionic membrane includes means for carrying anolyte liquor into the interior of the permionic membrane. This prevents crystallization of alkali metal chloride salt~
within the permionic m~mbrane 33. The means for accomplishing this may include ~icking means, for example, extending up to or beyond the anodic catalyst 37. According to a further exemplification, t'ne means for carry~
ing anolyte liquor into the interior of the permionic membrane may include hydrophilic or wettable fibers extending up to or beyond the anode catalyst 37 or even microtubes extendirlg up to or beyond the anode ca~alys~ 37.
As herein contemplated, the means for carrying the anolyte liquor into the int~rior of the perm;onic membrane draw water or anolyte liquor into the membrane beyond the water of hydration associated with the electro- -lytically carried alkali metal ions. This is to prevent the crystalli~ation of alkali metal chloride such as sodium chloride or potassium chloride in the membrane.
In a preferred exemplification ~he electrocatalysts 37 and 43 and the membrane 33 are one unit. While thi~ may be provided by having the electrocatalysts 37 and 43 on the distributor packing 55 a~d 57, with the di~tributor 55 and 51 maintai~ed in a comptessive relationship with the membrane 33, it is preferred to provide a ilm of the electrocatalyst 37 and 43 on the permionic membrane 33. The film 37,43 is generally from about lO ~nicrons to about 200 microlls ehicki preferably from about 25 ~o about 175 micron~ thick and ideally from about 50 to about 150 microns thick.
The electrocatalyst-permionic ~embrane unit 31 should have dimen~ional stability, resis~ance ~o chemical and thermal degrada~ion, electrocatalytic activity, and preferably the catalyst particles should be -finely divided and porous ~ith at least about lO square meters of surface area per gram of catalyst particle, 43.

~3~

Adherence o the catalyst, 37 and 43, to the permionic membrane 33 may be provided by pressing the particles 37, 43 into a molten, semi-molten, fluid, plastic, or thermoplastic permionic membrane 33 at elevated tempera-tures. That is, the membrane is heated above its glass ~ransition tem-perature preferably above the ~emperature a~ which the membrane 33 may be deformed by pressure alone. According to a still further exemplifica tion, the particles 37 and 43 may be pressed into a partially polymeri~ed permionic membrane 33 or pressed into a partially crvss-linked permionic membrane 33 and the polymerization or crosslinking carried forward, for example, by raising or lo~ering the temperature, adding initiator, adding additional monomer~ or the use of ionizing radiat;on, or the like.
According to a further exemplification of the method of this invention, where further polymerization is carried out, the particles 37,43 may be embedded in the partially polymerized permionic membrane 33.
Thereafter~ a monomer of a hydrophobic polymer can be applied to the surface, with, for e~ample, an initiator, and ropolymerized, in situ, with the partially polymerized permionic membrane 33, whereby to provide a hydrophobic surface having exposed particles 37,43. In this way, the catalyst particles 37,43 may be present witb the hydrophobic surface, e.g., to protect the anodic surface 35 from chlorine, or to protect the cathodic ~urface 41 from crystallization or solidification of alkali metal hydroxide, or to enhance depolarization as when a cathodic H02- disproportionation catalyst is present on tne cathodic surface 41 of the permionic membrane.
According to a further exemplification of this in~ention, the permionic membrane moieties may be cross linked, e.g., after catalyst par- -ticle deposition, to enhance the hydrophobic character of ~he membrane surface. The cross linking agent which may react during formation or after the anode materials have been deposited on a partially polymeri~ed permionic membrane. Suitable cross linking a~ents include the divinyl benzenes, e.g., the perfluorinated divinyl benzenes. Other suitable cross linking agents include perfluorinated dienes, as hexafluorobutadiene, octafluoropentadiene including the 1, 3, and 1, 4 dienes, and decafluorohexadiene, including the 1,3, the 1,4, and the ],5 dienes. Most commonly the cross linking agent is a divinyl ben~ene or perfluorinated C4 to C6 diene, especially hexafluoro-butadiene.
According to an alternative exemplification the anode electro-catalyst 37 may be extended with silicon. That is, where the anode elec-trocatalyst 37 is in particle form, the particles may be coated silicon particles, i.e., silicon particles coated with a suitable chlorine evolution catalyst. Additionally silicon particles, e.g., coated silicon particles, silicide surfaced silicon particles, and silicide particles having a silicon surface, may be on the anodic surface 35 of the permionic membrane 33, both to provide conductivity between anode particles and as an anode catalyst.
According to this exemplificationg anode particles are provided having a low overvoltage which comprises an electrolyte resistant electro-conductive surface such as metallic platinum or ruthenium oxide on an 2n electroconductive substrate composed partlally or completely and preferably predomlnantly of silicon in the elemental state (as distinguished from s:Llicicles which may be regarded as compounds of silicon and another metal)~
l~hile the silicon is in the elemental state it contains innpurities, doping agents or additives, e.g., boron, phosphorus, etc., or silicides of certain metals dispersed through the silicon which impart conductivity and/or strength to the silicon. The elemental silicon generally is a continuous phase with the other agents dissolved or dispersed therein.

The silicon par~icles should be electroconductive and should be at least as electroconductive as graphite, e.g., silicon should have a bulk electrical conductivity in excess of 102 (ohm-centimeters) 1 and preferably 104 (ohm-cen~imeters) 1 or higher. Substantially pure silicon, e.g., silicon having a purity in excess of 99.995 atomic percent, is at most a poor conductor, and may even be characterized as a non-conductor having a resistivity of only about 1 ohm-contimers. It is known that by incorporat-ing small, even trace amounts of boron, phosphorus, or other materials, the resulting silicon composition will be electroconductive. According to this invention it has been found that with proper precaution the silicon sub-strate can be provided in a form which is inert to anodic attack and such substrates can be effectively used to support the conductive surface.
Elemental silicon containing up to 2 percent or even up to 5 per-cent boron or up to 2 percent phosphorus and negligible amounts of other impurities have been found to have the desired inertness to anodic attack by aqueous sodium chloride.
The silicon may also contain iron, e.g., up to about ~lO weight percent when phosphorus or boron is present, the phosphorus and boron having a eorrosion inhibiting effect.
The silicon particles may also contain silicides. Especially preferred are silicides havin~ a catalytic effect or a conductivity enhanc-ing effect, as the silicides of metals of Group IV, V, and VI, e.g., TiSi2, SrSi2, VSi2, NbSi2, TaSi2, and WSI2 and the heavy metal silicides, e.g., CrSi, Cr5Si3, CrSI, CrSi2 and MoSi2 as well as cobalt silicides CiSi2.
According to a still further e~emplification of the method of this invention, the catalysts 37,43 may be chemical depositecl, e.g., by ; hypophosphite or borohydride reduction, or be electrodeposited on the 38~

permionic membrane 33. ~dditionally, there may be subsequent activation of the catalyst9 for example9 by codeposition of a leachable material with a less leachable m3terial and subsequent activation by leaching out the more leachable material.
According to a still further exemplification, a surface of catalyst 37,43 may be applied to the permionic membrane by electrophoretic deposition, by sputtering, by laser deposition, or by photodeposition.
According to a still further exemplification of the method of this invention, a catalytic coating 37,43 may be applied to the permionic membrane 33 utili~ing a chelate of a metal which reacts with the acid groups of the pe~mionic membrane 33.
Typically, the catalyst 37,43 on the surface of the permionic membrane 33 is a precious metal-containing catalyst, such as a plaeinum group metal or alloy of a platinum group metal or an intermetallic compound lS of a platinum group metal or oxide, carbide, nitride, boride, silicideg or s~llphide of a platinum group metal. Such precious metal-containing cata-lysts are characteriæed by a high surface area and the cap~bility of either being bonded to ~ hydrophobic particle or being embedded in the hyd~opho-bic film. Additionally, the precious metal-containing catalyst may be a partially reduced oxide, or a black, such as platinum black or palladium black, or an electrodeposit or chemical depos;t.
The catalysts 37,43 may also be an intermetall;c compound of other metaLs, including precious metals or non-precious metals. Such intermetallic co~pounds include pyrochlores, delafossi~es, spinels, perov-skites, bronzesg tungsten bronzes, silicides, nitrides, carbides and borides.

Especially desirable cathodic ca~alysts which may be present on the solid polymer electrolyte permionic membrane 33 as a first transition metal include steel, stainless steel, cobalt, nickel9 alloys of nickel or iron, compositions of nickel, especially porous nickel with molybdenum, tantalum, tungsten, titanium, columbium or the like, and boride, electri--cally conductive electrically active borides, nitrides, silicides and carbides, such as, the platinum group metal silicides, nitrides, carbides and borides and titanium diboride.
Other cathodic catalysts 43 tha~ may be present on the cathodic surface 41 of the permionic membrane include the platinum group metals, e.g., platinum, palladium, ruthenium, osmium, iridium, and rhodium, both as smooth deposits for as high surface area deposits9 e.g., "blacks" having a surface area in excess of 10 square meters per gram, As herein contemplated, the permionic membrane 33, or one surface thereof, e.g., the anodic surface 35 or cathodic surface 41, is contacted with a reducing agent, a complexing agent, a buffer, and a compound of the metal, or compounds of the metals to be deposited. The reducing agent may be a borohydride reducing agent or a hypophosphite reducing agent. The borohydride solution should contain 1 to 5 grams per liter of borohydride, e.g., sodium or potassium borohydride, and preferably 1.5 to 2.5 grams per liter of borohydride.
l~here the deposition is on a synthetic permionic membrane, 33, rather than a metal substrate9 sequential contact is particularly desirable.
In se~uential contact the membrane 33, is first contacted with the reducing agent, and thereafter with the compounds of the metals to be deposited.
The method of this invention is advantageous with transition metals, and is particularly advantageous with group VIII transition metals as the first ~ransition metals. It is especially useful for the codeposition of two Group ~III metals of dissimilar resistance to chemical leachants~ and the subsequent leaching of the less resistant metal.
The borohydride is preferably an alkali metal borohydride, as sodium or potassium borohydride. The transition metal is present in the second solution as a soluble salt, eOg., a citrete, oxalate, glycolate, sulfate, or chloride. The buffer and the complexing agent may be the acid and the alkali metal salt of the same organic union, e.g., sodium citrate and citric acid, sodium oxalate and oxalic acid, and the like. Alterna-tively an inorganic acid, e.g., phosphoric acid and sodium phosphite may beused, The complexing agent and buffer serve to maintain the Group VIII
metal ions in solution, e.g., at the pH of 6 to 8.
In a particularly preferred exemplification the cathodic electro-catalyst 43 comprises porous nickel which contains an effective amount, i.e., an overvoltage reducing or overvoltage stabilizing amount of a second transition metal of Group IVB, VB, VI~ or VIIB. These transition metals include titanium9 zirconium, hafnium, vanadium, columbium, tantalum, chromium, molybdenum, tungsten, manganese, technetium, and rhenium. The preferred materials are titanium, zirconium, hafnium, vanadium, columbium, tantalum~ molybdenum, and tungsten. Especially preferred are titanium, tan~alum, 2irconium, and molybdenum.
The nickel is generally above about 50% and less than about 95%, and generally from about 65 to about 90 percent nickel, calculated as nickel metal, basls total weight of the porous active surface.
The second transition metal is present in the porous cataly~ic surface 43 in a hydrogen overvoltage lowering amount. This is above about ~ 28 -2.5% preferably above about 5%, but below about 50%, and generally from about 10 to about 35 weight percent, calculated as me~al, basis total nickel calculated as metal and second transition metal calculated as metal in the surfacef Generally~ the amount of the second transition metal in the surface is high enough to have a hydrogen overvoltage lowering effect, but low enough to avoid the high overvoltage identified with porous sur-faces that are mainly the second transition metal e.g., titanium, tantalum, ~irconium, or molybdenum.
While the mechanism of the hydrogen overvoltage lowering effect of second transition metal is not clearly understood3 it is known that porous films of, e.g.~ molybdenum alone are high in hydrogen overvoltage9 but that a low hydrogen overvoltage over extended periods of electrolysis is observed when a second transition metal as hereinabove described, e.g.
molybdenum, is used in conjunction with porous nickel. In the case of molybdenum, the molybdenum is believed to depolarize or cataly~e one step of the hydrogen evolution process. For this reason, the upper limit of the second transition metal is below the concentration at which the porous catalytic surface has the hydrogen overvoltage properties of the second transition metal, i.e., below about 50 percent and generally below about ?.0 35 percent.
The second transition metal itself may be present as the elemen-tal metal that is as elemental molybdenum, titanium, tantalum, ~irconium, or tungsten having a formal valence of 0, as an alloy with nickel or as an alkali-resistant compound such as a carbide, nitride, boride, sulfide, phosphide, o~ide, or other co~lpound that is insoluble in concentrated alkali metal hydroxide. Preferably, the second transition metal is present in the surface 43 with nickel as the elemental metal, an alloy with nickel, or a carbide.

One pa~ticularly outstanding cathode 43 of this invention is one having a porous surface 43 of nickel and molybdenum containing abo~t 82 weight percent nickel, and about 18 ~eight percent molybdenum basis total nickel and molybdenum and having a yorosity of about .7 and a thick-ness of about 75 to about 500 micrometers.
According to a further exemplification of ~he method of this invention, ~he cathode herein ccntempl~ted is prepared by depositing a film of nickel, the second transition metal, and a leachable material on the permionic membrane 33 and thereafter leaching out the l~achable material.
~ a /
The leachable material may be any metal or~compound t~at can be co-deposited with nickel and the second transition metal or with nickel compounds and compounds of the second transieion metal and leached out by a strong acid or strong base without leaching out significant quantities of the nickel or the second transition metal or causing significant deteriora-tion or poisoning of the nickel or the second transition metal.
The film may be deposited on the permionic membrane 33 by elec-trodeposition of nickel, the second transition metal, and a leachable material, or by codeposition of solid particles, or by chemical depo~ition for example, by hypophosphite deposition or by borohydride deposition o nickel compounds, co~pound& of the second transition metal and leachable materials~ or even by deposition and thermal decomposit;on of organic com pounds of nickel, the second transitlon metal, and leachable materials, for exa~ple, deposition and thermal decomposition of alcoholates or resinatesO
According to one part;cularly desirable exel~plification of the method of preparing the elec~rode of this invention, fine particles for exa~ple, on the order of about 0.5 to 70 micrometers in diameter, of ~ 30 -$~

nickel, the second transition metal or a compound thereof, and a leachable material are embedded in a partially polymeri~ed permionic membrane 33 and the polymerization then comple~ed, with leaching of the leachable material either before or after polymerization. Alternatively, ~he particles may be embedded in a heated thermoplastic permionic membrane 33.
The leachable materials may be present in the particle with the nickel or may be separate particles. Typical leachablP compounds include copper, zinc, gallium, aluminum, tin, silicon, or the like. Especially preferred are nickel particles containing about 3 to about 70 percent nickel, balance aluminum as Raney alloy.
After completion of polyMerization of the partially polymerized membrane 33, or cooling of the heated thermoplastic membrane 33, the particles 43 may be leached, e.g., ;n alkali such as 0.5 normal caustic soda or l normal caustic soda~ in order to remove the leachable material, e.g., alu~inum, and ~hereafter rinsed with wa~er. It is, of course to be understood that some oE the leachable material may remain in the porous electrode surface 43 without deleteriou~ effect. Thus, for example, where Raney nickel-aluminum alloy, and molybdenum are embedded in the membrane 33 the surface may contain nickel, molybdenum, and aluminum, after leaching.
The resulting surface, may, for example, con~ain amorphous nickel, crystal- -line molybdenum nickel-aluminum alloys and traces oE alumina.
According to a still further exempl;fication of the invention herein contemplatedg the surface 43, may contain boron or phosphorous.
These materials, believed to be deposited during borohydride or hypo-phosphite deposition, stabilize the voltage characteristics of th~ ca~hodic electrocatalyst 43.

8~

The cathodic electrocatalyst, 43, hereinabove described, while useful with perfluorinated ion exchange membranes 33 generally, finds especial utility in ion exchange membranes 33 having carboxylic acid groups as described hereinabove.

In the electrolysis of alkali metal chloride brines, such as potassium chloride and sodium chloride brines in solid polymer electrolytic cell, especially one having carboxylic acid-type permionic membrane, 33, purity of the brine is of significant importance. The content of transi-tion metals in the brine should be less than 40 parts per million, and preferably less than 20 parts per million, whereby to avoid fouling the permionic membrane 33. The pH of the brine should be low enough to avoid precipitatiOn of magnesium ions. The calcium content should be less than 50 parts per billion, and preferably less than 20 parts per billion. The brine should be substantially free of organic carbon compounds, especially, where the chlorine is to be recovered directly from the cell as a liquid and utilized in a further process, for example, an organic synthesis process such as a vinyl chloride manufacturing process, wi~hout further treatment.
The brine treatment may be carried out by various methods in order to attain the degrees of purity called for. For example, phosphate precipi-tation may be used to remove calcium, for example, as the calcium apatite or as a calcium fluoroapatite. Additionally, an ion exchange resin can be utilized to purify the brine.
Preferably the ion exchange resin is a chelating ion exchange ~0 resln. In this way the multifunctionality removes multivalent metal impurities, e.g.9 alkaline earth metal ions and transitlon metal ions.
The water fed to the catholyte compartment ~5 should be sub-stantially free of carbon dioxide and carbonates whereby to prevent the ormation and deposition of carbonate on the permionic membrane 33.
Preferably3 the feed is deioni~ed water.

813~

The recharging or regenera~ion of the chelating ion exchange res m is critical. The regeneration by the non~oxidi~ing acid should y~ r~ 7~
~$ remove almost all multi~ e~t cations. This may be acco~plished by, e.g.,utilizing lO to 2 bed volumes of 0.5 to 5 normal hydrochloric acid, and preferably lO to 20 or more bed volumes of 2 to 3 normal hydrochloric acid as the regenerating fluid.
Dilute mineral acids, e.g., from about O.l to lO normal, and preferably from about 0.5 to 5 normal are utilized as the regenerants.
Non-oxidizing acids are preferred to avoid damage to the resin. Suitable acids include the hydrogen halides, e~pecially hydrochloric acid.
The strength of ~he acid ~hould be high enough to withdraw cations from the resin, i.e., above about O.l normal, and preferably above about 0.5 normal, but low enough to avoid dehydratin~ the membrane, i.e., below about lO normal. I~ this way a brine may be obtained that contains less than 20 parts per million transition metals, and less than 20 parts per billion alkaline earth metals.
In the operation of the c811, short residence ti~e in the anolyte compart~en~ 39 for ~he brine depletion of about lO to about 15 percen~
allows the utili~ation of brine as a coolant and avoids concentration polarization. However, higher brine depletions, for example, 30, 40, even 50, 60 or 70 percent, ~ay be utili~ed.
The temperature of ~he cell may be above 9 degrees C.~ especially when the brine is lo~ in pH whereby to reduce chlorine hydrate formation.
Alternatively, the ~emperature of the cell may be ~aintained below 9C., whereby to enhance chlorine hydrate formation and allow the recovery of a slurry of brine and chlorine hydrate.

The cell temperature ~hould be low enough so that when liquid chlorine i~ recovered fro~ a pressurized cell th~ pressure n~ces~ary t~
maintain the chlorine liquid is low enough to still permit conventional c~nstruction techniques rather than high pressure tec~niqu~s to be utilized.
The pre~sure-temperature data of liquid chlo~ine is reproduced in Table I.

TABLE I
VAPOR PRESSURE OF LIQUID CHLORINE
Gage Pressure, Te~pera~ure Po~nds p~r 10C. ~F. Square Inch -30 -22 3.1 -25 -13 7.2 -20 - 4 13.4 -15 ~5 17.2 15-10 14 23.5 - 5 23 30.6 + 5 41 47.8 58.2 2015 59 6~.9 68 81.9 77 95.4 ~6 111.7 129.9 2540 104 149.0 113 170.
122 193.1 131 218.1 140 24~.8 30~5 149 271.0 158 302.4 ~5 167 335.7 176 370.9 185 409.1 35~0 194 448.~ _ 203 492.2 105 221 5~6 130 2~6 888 ~5140 284 1035 _ .~S
~?~

When the electrolyzer is operated to recover liquid chlorine, the pressure should be high enough to maintain the chlorine liquid. In this way, liquid chlorine and depleted brine may be recovered together, the liquid chlorine separated from the brine, the brine then cooled to convert any chlorine therein to chlorine hydrate, which i8 further separated from the brine, and the brine refortified in salt, repurified and returned to the cell while the chlorine hydrate separated therefrom is heated to form chlorine.
The pressure in the electrolyzer should be high enough to allow ~aseous ni~ro~en and oxygen to be vented from ehe cell and the cell auxil-iaries, without evaporating significant amounts of liquid chlorine. When operating to produce li~uid chlorine the temperature of the cell should be below about lOO~C., whereby to maintain the design pressure on the electro~
ly~er below about 600 pounds per square inch gage. Preferably, the temper-ature of the cell should be below about 50C. whereby to allo~ design pres-sure of the cell to be below about 200 pounds per square inch. However, the desired temperature and pressure of the cell ~ay depend upon the end use of the liquid chlorine and the required vapor pressure and temperature of the liquid chlorine. As a practical matter, the pressure within the cell i8 dependen~ more upon the pressure of ~be auxiliaries and end use of the chlorine rat~er ~han the structural components of the cell.
High pressure is particula~ly advantageous, on the catholyte side 45 of the individual electrolytic cell 119 where the cathodic reaction is depolariæed, as the hi8b pressure serves to force the depolarizer into the catalyst 43 and disprcportionate the H0~
When the electrolyzer 1 is operated at a high enough pressure to form liquid chlorine within the anolyte compartments 37, the chlorine r ,. 3~) and the depleted brine m~y be recovered fro~ the electrolyzer's liql~ids.
~iquid chlorine is relatively immiscible with brine ~ ~he pressures herein contemplated. For this reason the liquid chlorine may be easily separated from the brine, as by centrifugation, filtrstion, or other viscosity, surface tension, or density dependent means.
Thereafter the separated liquid chlorine ~ay be stored or uti-lized as liquid without liquefaction. However, the liquid chlorine consti-tutes only 2 to 5 mole percent of the liquids handled in the anolyte compartment. While most of the chlorlne will be recovered and separated as a substantially pure liquid, some will be solubilized in the brine. The chlorine in the brine may be recoYered by cooling the brine to 90, e.g., by liquid chlorine evaporation cooling, whereby to convert the soluble chlorine contained in the brine to chlorine hydrate. The chlorine hydrate, a yellow crystalline material3 may be separated from the depleted b~ine, and e.g.~ heated to form chlorine.
In the operation of the cell, the removal of stagnant chlorine pockets from the anodic surface and the removal of solid, crystallized, or highly concentrated liquid alkali metal hydroxides from the cathodic sur-face 41 of the permionic membrane 33 may be carried out utilizing ultra-sonic vibration of the permionic membrane 33, or by the use of a pulsed current. Where a pulsed current is utili~ed it may be pulsed direct cur-rent, rectieied alternating current,or rectified half~wave alternating cur-rent. Particularly preferred is pulsed direct current having a frequency of from about 10 to about 40 cycles per second, and preferably about ~0 to about 30 cycles per second.
The catholyte liquor recovered from the cell typically will contain iQ excess of 20 weight percent ~lkali metal hydroxide. Where9 as ~ 7 ;,.~.

38~

in a preferred exemplification, the permionic membrane 33 is a carboxylic acid membrane, as described hereinabove, the catholyte liquor may contain in excess of 30 to 35 percent, for example 40 or even 45 or more weight percent alkali metal hydroxide.
The current dens;ty of the solid polymer electrolyte electrolytic cell 11 may be higher than that in a conventional permionic membrane or diaphragm cell, for example, in excess of 200 amperes per square foot, and preferably in excess of 400 amperes per square foot. According to one pre-ferred exemplification of this invention9 slectrolys;s may be carried out at a curren~ density of 800 ur even 1,200 amperes per square foot, where the current density is defined as total current passing through the cell divided by the surface area of one side of the per~ionic ~embrane 33.
A~cording to a particularly preferred exe~plification of the method of this invention, the cathode may be depolarized whereby to elimi-nate the formation of gaseous cathodic products. In operatio~ ~ith the depolarized cathode, oxidant i9 fed to the cathodic surface 41 of the solid polymer electroly~e 31 while providing a s~ able catalyst 43 in contact ~ith the cathodic surface 41 of the solid polymer electrolyte 31 whereby to avoid evolution of gaseous hydrogen. In this way, when th~ electrolyzer, l, and elec~rolytic cell, ll, i5 maintained at an elevated pressure, as described he.reinabove, the evolution of gaseous yroducts can be largely avoided, as can the problems associated therewith.
In the process of producing alkali metal hydroxide and chlorine by electrolyzing an alkali metal chloride brine9 such as an aqueous solution ~5 of sodium chloride or potassîum chloride, the alkali metal chloride solution is fed into the cell, a voltage i8 i~posed across the cell, chlorine is evolved at the anode, alkali metal hydroxide is produced in the electrolyte ~- 3~
,~

in contact with the cathode, and hydrogen may be evolved at the cathoder The overall anode reaction is:
2Cl- -~ C12 ~ 2e~ (l) while the overall cathode reaction i8:
2H20 ~ 2e~ ~ 1l2 ~ 20H (2) More precisely, ~he ca~hode reaction is reported to be:

E~2O ~ e -> HadS ~ OH (3) by which the monatomic hydrogen is adsorbed OlltO the surface of the cathode.
In basic media~ the adsorbed hydrogen is reported to be desorbed according to one of two alternative processes:

2Hadg ~ H2 or (4) Hads ~ H20 ~ e - ~ H2 +OH

The hydrogen desorption step, i.e., reac~ion (4) or reaction (5)9 is reported ~o be the hydrogen overvoltage determining step. That is, it is the rate controlling step and its activation energy corresponds to the cathodic hydrogen overvoltage. The cathode voltage for the hydrogen ~volution reaction (2) is on the order of about 1.5 to 1.6 volts versus a saturated calo~el electrode (SCE~ on iron in basic media of which the hydro~en overvoltage component is about 0.4 to 0.5 volt.

One method of reducing the cathode voltage is to provide a sub- - -stitute reaction for the e~olu~ion of gaseous hydrogen, ~hat iS9 to provide a reaction where a liquid product i9 formed rather han gaseous hydrogen.
Thus, water may be formed ~here an oxidant is fed to the cathode. The oxidant may be a gaseous oxidant such as oxygen, air, or thP like. Alter-2S natively, the oxidant may be a liquid oxidant such as ~ F~e~-~e~ e, a hydrvperoxide, hydrogen pero~ide or a peroxy acid or the like.

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When the oxidant is oxygen, e.g., as air or as gaseous oxygen, the following react;oll is believed to take place at the rathode:

2 ~ 2H20 + 4e ~ 40H- (6) This reaction is postuLated to be an electron ~ranser reaction:

2 + H20 + 2e~ -> H02 + ~H (7) follow~d by a surface reaction:

2~02 ~~~-~ 2 ~ 20H- (8) It is believed tha~ the predominant reaction on the hydrophobic ~urface is reaction ~7), uith reaction (8) occurring on the surfaces of the ].0 catalyst particles 43 dispersed in and through the cathode surface 41 of the. solid polymer elect~olyte 33. Such catalyst particles include particles oE electrocatalysts as described hereinbelow. In this way, the high overvolta~e hydrogen desorption step is elimina~ed.
Where the oxidant is a peroxy co~pound, the follo~ing reaction is believed to take place at the cathode: -RCOO- ~ 2H20 ~ 2e~ - ~ RCOH ~ 30~1- (9) .

This reaction is postulated to be an electron transfer reaction followed by a surface reaction.
Suitahle organic oxidants are those orga~ic compounds con~ainin&
a reducible peroxy bond~ C-O-O-. Su;table oxidants include organic peroxides, organic hydroperoxides, and organic peracids, also referred to as peroxy acids. One preferred group of organic oxidants are organic hydroperoxides.
Particularly outstanding organic oxidants are organic hydroperoxides ! ~ 40 , j'~

yielding alcohols that are soluble in water in all proportions, those hydroperoxides yielding alcohols that are of limited solubility in water, and those hydroperoxides yielding alcohols that are sparingly soluble in water. For example, particularly outstanding hydroperoxides are methyl hydroperoxide yielding methyl alcohol, ethyl hydroperoxide yielding e~hyl alcohol 9 n-propyl hydroperoxide yielding n-propyl alcohol, i-propyl hydro-peroxide yielding i-propyl alcohol, ~nd t-butyl hydroperoxide yieldi~g t-butyl alcohol. Also useful in the method of this invention are those hydroperoxides yielding alcohols oE limited solubility in water such as n-butyl hydroperoxide yielding n-butyl alcohol, sec-butyl hydroperoxide yielding sec-butyl alcohol, i-butyl hydroperoxide yielding i-butyl alcohol~
and t-pentyl hydroperoxide yielding t-pentyl alcohol. Alternatively, those hydroperoxides may be used which yield as cathodic reduction products spar-ingly soluble alcohols, such a~ n-pentyl hyd~operoxide yielding n~pentyl alcohol, i-pentyl hydropero~ides yielding i-pentyl alcohols, s-pentyl hydroperoxides yielding s-pentyl alcohols, and neopentyl hydroperoxide yielding neopentyl alcohol as cathodic reduction products. Also useful are cumene hydroperoxide yielding cumyl alcohol and ethylben7ene hydroperoxide yielding me~hyl phenyl carbinol.
Another group of hydroperoxides useful in carrying out the method of this invention are dihydroperoxides. Dihydroperoxides yield glycols as a reaction product when added to the catholyte cha~ber of an electrolytic cell as herein contemplated. The preferred dihydroperoxides are those that are completely miscible in water or those ~hat are at least partially soluble in waterO The preferred dihydroperoxides are the dihy- -droperoxides of the C3 to Clo alkyls with the dihydroperoxides of the C6 to Clo alkyls being especially preferred. Such dihydroperoxides include hexane dihydroperoxide, heptane dihydroperoxide, octane dihydropero~ide, nonane dihydroperoxide, and decane dihydroperoxide.
While alcohols~ ketones, aldehydes, and glycols are referred to herein, they may only be formed as intermediates and may be further reacted, as by dehydration to give olefines and ethers, or by reaction with other additives as organic acids to yield esters or to yield alkali metal salts of alcohols.
Where the intermediate product is an alcohol, the alcohol may be further reacted to yield ethersO The alcohol may be separated from the cell liquor and further reacted in order to form the ether, e.g., by reaction with an alkylating agent, e.g., an alkyl sulfate. Thus, where the organic oxidant is ertiary butyl hydroperoxide~ the intermediate recovered from the catholyte eompartment is tertiary butyl alcohol. The tertiary butyl alcohol may be removed f~om the cell9 separated from the cellliquor, e.g., by distillation, and reacted with, e.g., methyl sulfate, to yield methyl tertiary butyl e~her. Methyl tertiary butyl ether finds utility as an a~tomoti~e f~el additive.
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Particularly d~}~e~ hydropero~ides are Chose yielding alcohols that are soluble in ~ater in all proportions and are useful in various industrial processes ~ example~ t-butyl hydropero~ide yielding t-butyl alcohol as a cathodic reduction product, t-butyl alcohol being useful as an automotive anti-knock compound.
DialXyl peru~ides, having the iormula RlOOR2 where Rl and R2 m~y be -CH3, -C2Hs, -G3H7, -C4Hg, -C}l2CH ~ CH2, or any other dialkyl peroxide soluble in water or soluble in organic solvents may be used in the method of this invention. In addition to the dialkyl pero~ides, the polyoxides having thR formula RlOnR2, where n is 3 or 4 may be used in the method of this inv~ntion as may the cycloperoxides having the formula Rl - 0 - 0 - R2.

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Peroxy acids, also known as peracids, ha~ing the formula R(C03H) where R may be ll, -CH3, -CH2Cl, -C2Hs, -(n C3H7), -(i C4Hg), - -n-C5H~
and any other peracid soluble in water or soluble in organic solvents may be used in ehis invention. Also, acyl peroxides or other peroxy acid precursors may be uiliæed in the method of this invention. Additionally, aryl diperoxy acids may be used in the method of this inventionO
While the method of this invention is described with respect to organic o~idizers such as organic peroxides, organic hydroperoxides (having the general formula R - O - O - H) and organic peroxy acids (having the general formula RC03H), it is to be understood that various derivatives of the organic oxidizers may also be used. For example, the method of this invention may be practiced with s~lts of the organic o~idizers, e.g., salts of organic hydroperoxides (having the formula R - O - O - M) and salts of organic peroxy acids (having the formula RC03~), where M i8 a cationic lS species chosen from the group consis~ing of alkali metals, alkaline earth metals~ and the ammonium radical. Of the alkali metals lithiu~, sodium, potassium, rubidium, and cesium, most frequently the alkali metal will be sodium or potassium. Of the alkaline earth metals berylli~n, magnesium, calcium, strontium, and barium, most frequently the alkaline earth metal will be magnesium or calcium. Generally, when the catholyte liquor is an aqueous alkali metal hydro~idej MOH, the organic oxidi~er either is the hydrogen form (e.g., R - O - O - H, R - O - O - R, RC03H), or the alkali metal salt (e.g., R - O - O M, RC03M), where M i~ the same alkali metal in the hydroxide and the organic oxidizer.
According to the method of this invention utilizing organic peroxy oxidants, the cathod~ reaction products oE the oxidant are recovered from the catholyte chamber 45 along with the cell liquor. The cathodic ~ 43 ,~

reduction products of ~he oxidant may be partially or ~otally gases or vapors such as methyl alcohol, ethyl alcohol, n propyl alcohol, i~propyl alcohol, or t-butyl alcohol. Alternatively, the products may be liquids recovered with the cell liquor such as methyl alcohol, ethyl alcohol, n~propyl alcohol, i-propyl alcohol, t-butyl alcohol, sec-butyl alcohol, i-butyl alcohol, n-butyl alcohol~ or t-pentyl alcohol9 n-pentyl alcohol, i-pentyl alcohol, or amyl alcohol or the cathodic product may be emulsions or suspensions of e~cess amounts of sparingly soluble alcohols, such as jec-butyl alcohol, i-butyl alcohol, n-butyl alcohol, t-pentyl alcohol, n pentyl alcohol, i-pentyl alcohol, or amyl alcohol. Where the cathodic reduction product of the oxidant is recovered either as a gas or as both a gas and a liquid such as methyl alcohol, ethyl alcohol~ n-propyl alcohol, i-propyl alcohol, or t-butyl alcohol, the ~athodic reduction product is separated from both the water vapor and gRS phase and recovered. Alterna-tively, where the cathodic reduction product of the oxidant is recovered as a liquid, either in solution with water or as suspension or emulsion in water, such as ~ethyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, sec-butyl alcohol, t-butyl alco-hoL, t-pentyl alcohol, n-pentyl alcohol, i-pentyl alcohol, neopentyl alco-hol, or s-pentyl alcohol, the cathodic reduction product may be separated fro~n the cell liquor by methods well known in the art such as fractional distillation, e~traction, adsorption, stripping, other phase separaeion techniques, or ~he like and recovered.
According to one exemplification of this in~ention9 tertiary butyl alcohol is produced during the electrolysis of sodium chloride brine. In this exemplification of the invention, sodium chloride brin~ is fed to an anolyte chamber 39 o an electrolytic cell ll~ tertiary butyl hydroperoxide ~/~
:~r~

i5 fed to a catholyte chamber 45 of the cell and an electrical current is passed from an anode 37 of the cell 11 to a cathode 43 of the cell 11 whereby chlorine i5 evolved at the anode and tertiary butyl alcohol and acetone are formed in the catholyte chamber. An aqueous catho]yte liquor containing sodium hydro~ide, tertiary butyl alcohol, acetone, and excess tertiary butyl hydroperoxide is recovered from the catholyte chamber 45 of the cell 11.
Ther~ater, an aqueous catholyte cell liquor containing sodium hydroxide, tertiary butyl alcohol, a carbonyl, e.g., acetone, and excess tert;ary butyl hydroperoxide, most likely as the sodium salt, is recovered from the cell 11. With a tertiary butyl hydroperoxide feed and a tertiary butyl alcohol product, an azeotrope may be formed upon evaporation and subsequent recovery and distillation of the cell liquor. This a~eotrope contains 11.76 percent water and 88.~4 percent tertiary butyl alcohol.
In the emhodiment of this invention where an excess of tertiary butyl hydroperoxide is fed to the cell, the tertiary butyl alcohol recovered as an azeotrope, the hydroperoxide salt of sodium, e.g., Na+ [(CH333C00-], may be crystallized out of concentrated aqueous caustic soda solution, e.g., caustic soda solution containing in excess of 40 weight percent caustic soda. This sodiuTn salt of tertiary butyl hydroperoxide may then be recirculated to the catholyte chamber 45 of a cell 11,13.
According to a fur~her exemplification of ~his i~vention, the m p Je.
cell liquor may be fed to another cell 13, for ~1~, to the catholyte chamber 45 thereof, whereby to provide a catholyte liquor enhanced in alkali metal hydro~ide content and di~iDished in organic oxidant content.
The remaining organic oxidant may then be further reduced in the subsequent cell or cells, with the cell liquor, in order to produc~ more by-product, e.g., Inore ke~one, aldehyde, acid, alcohol, or glycol, and a high strength alkali metal hydroxide solution. In this exemplification serial flow of the cathode li~uor, eOg., through a bipolar electrolyzer, 1, may be utili~.ed.
According to a still further exemplification o the method of this invention the oxidant may be a redox couple, i.e., a reduction-oxida- -tion co~ple, where the oxidant is reduced inside the cell and thereafter oxidized outside the cell, as for return to the cell. One suitable redox couple i5 a copper compound which can be fed to the cell 11 as a ~ c compound, reduced to a cuprous compound at ~he cathode 43, and recovered from the catholyte compartment 45 as a cuprous compound. Thereafter, the cuprous compound ~ay be oxidized to a cupric oompou~d outside of the electrolyzer 1, and returned to the electrolyzer. Suitable copper couples include chelated copper couples such as phthalocyanines.
According to a further e~emplification of the method of this invention, where a redox couple is utilized, the redox couple may be a quinone-hydroquinone redox couple. In this case the quinone is electro-lytically reduced to hydroquinone at the cathode 43, hydroquinotle i9 recovered from the catholyte liquor 45, and oxidiæed to quinone externally of the ceil.
According to a further exe~lplification of the method of this invention, solid oxygen carriers may be fed ~o the catholy~e compartment 45, and recovered partially freed of oxygen. These include manganese ~II) I/~ r y ~ n ~' r, e.
complexes, transition metal pe~al~ey;~e tetrasulfonate complexes, and binuclear copper (II~ co~plexes of l-phenyl-1,3,5-hexane ~ ~.
The cathode catalysts useful in carrying out the method of this invention are those having properties as H02- disproportionation catalysts, i.e., catalysts that are capable of catalyzing the surface reaction 2H02- -~> ~2 ~ 20H- (10).

. ~ ~, . . .

Additonally, the catalyst should either be capable of catalyzing the electro~ transfer reaction 2 ~~ ~2 ~ 2e ~ HO2 ~ OH- (ll), or of being used in conjunction with such a catalyst. The catalysts herein contemplated should also be chemically resistant to the catholyte liquor.
Satisfactory HO~- disproportionation catalysts include carbon, the transition metals of Group VIII, being iron, cobalt, nickel, palladium, ruthenium, rhodium, platinum, osmium, iridium, and compounds thereof. Additionally, other catalys~s such as copper, lead and oxides of lead may be used. The transition metals may be present as the metals~ as alloys, and as intermetallic compounds. For example, when nickel is used, it may be ad~ixed with Mo, Ta, or Ti. These admixtures serve to main~ain a low cathodic voltage over extended periods of electrolysis.
Any metal of Group III B, IV B, V B, VI B, VII B, I B, II B, or III ~, including alloys and mixtures thereof, which metal or alloy is resistant to the satholyte can be used as ~he cathode coating 43 or catalyst on the surface of the ~embrane 33.
Additionally, solid n~etalloids, such as phthalocyanines of the Group VIII ~etals, perovskites, tungsten bron~es, spinel~, delafossites, and pyrochlores, among others, may be used as a catalytic surface 43 of the membrane 33.
Particularly preferred catalysts are the platinum group metals, compounds of platinum group metals, e.g., oxides, carbides, ~ilicides, phosphides, and nitrides ~hereof, and ;ntermetallic compounds and oxides thereof, such as rutile form Ru02-TiO2 having semi-conducting properties.

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According to a further exemplification of this invention, the cathode electrocatalyst, ~hat is, the electron transfer catalyst for the reaction }120 ~ e~ - ~ OH- + H
may be a borîde of a transition metal. The transition metals providing borides of requisite chemical resistance to concentrated aqueous alkali metal hydro~ides, and ha~ing surface catalytic act;vity for the aforemen-tioned reaction are the transition metals of Groups IVB, VBg and VIB of periodic tahle. These metals are titanium, zirconium, hafnium, vanadium, niobium (columbium), tantalum, chro~iu~, ~olybdenum, and tungsten. Pre-ferred among the transition of groups IVB, Vb and VIB are those providing borides of higher chemical resistance, e.g., titanium, vanadium, niobium (columbium), tantalum, chromium, and tungsten. Especially preferred is titanium diboride, TiB2.
lS According to a preferred exemplification of this invention, an intercalation compound of carbon and fluorine may be used aæ the catbodic catalyst 43.
~y an intercalation compound of carbon and fluorine is meaQt a carbonaceous material crystall;zed in a graphitic layer lattice with the layer atoms being approximately 1.41 angstroms apart, the layer~ being a greater distance apart, e.g., at least about 3.35 angstroms, and with fluorine atoms present between the layers. As herein contemplated, the carbon layers within the intercalation compound may be puckered~ as postu-lated for carbon monofluoride having the empi~ical formula (CFX) where x is between 0.68 and 0.995. Alternatively, the carbon layers within the intercalation compound may be substantially planar, as postulated for tetracarbon monofluoride having the empirical formula (CF~ where x is 8~

between 0.25 and 0.30. Also contemplated herein are various intermediate and non-stoichiometric compounds.
Intercalation compounds of carbon and fluorine are also referred to as fluorinated graphites and graphite fluorides. They are characterized by an infrared spectrum showing an absorption band at 1220 centimeters 1.
The carbon~fluorine intercalation compound catalyst 43 herein contemplated may have incorporated therein an H02-disproportionation catalyst.
Where a gaseous oxidant, as air or oxygen iR utilized, the portion of the catalyst intended for electron transfer is hydrophilic whilo the portion intended for the surface reaction may be hydrophilic or hydrophobic and preferably hydrophobic. The surface reaction catalyst is hydrophobic or i9 embedded in or carried by a hydrophobic film. l~e hydrophobic film may be a porous hydrophobic material such as graphite or a filtn of a fluorocarbon polymer on the catalyst. The surface reaction catalyst, as described above, and the electron tr2nsfer catalyst should be i~ close proximity. They may be admixed, or they may be different surfaces of the same particle. For example, a particularly desirable catalyst may be provided by a microporous film on the permionic membrane surface 41 with catalyat 43 carried by a hydrophobic microporous filmA
According to a further exemplification of this invention utili~ing a depolarized cathode, the electrodes can be weeping electrodes, iOe., electrodes that weep oxidant. In the utili~ation of weepi~g electrodes, the oxidant is distributed through the distributor 51 to the catalytic particles 43 thereby avoiding contact with catholyte liquor in the catholyte compartment 45. Alternatively, the oxidant may be provided by a second distributor means, bearing upon the cathodic surface 41 of the permionic membrane 33 or upon the catalytic particles 43.

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The feed of oxidant may be gaseous, including ~xcess air or oxygen. Where excess air or oxygen is utilized, the excess air or oxygen serves as a heat exchange mediurn to maintain the temperature low enough to keep the liquid chlorine vapor pressure low. Alternatively, the use of multiple oxidants, su~h as air and oxygen, or air and a pero~y compound, or oxygen and a pero~y compoundJ or air or oxygen and a redox coupLe, may be utili~ed. Where air or oxygen is used as the oxidant, it should be sub-stantially free of carbon dioxide whereby to avoid carbonate formation on the cathode.
Utilization uf a horizontal ~ell is particularly advantageous where cathode depolarization is utilized. Especially satisfactory is the arrangement where the anodic surface 35 of the permionic membrane 33 and the anodic catalyst 37 are on top of the permionic membrane 31 and the cathodic surface 41 and cathodic catalyst 43 are on the bottom of the permionic membrane 33. This avoids flooding the oxidation catalyst, that is, the H02- disproportionation catalyst, ~ith alkali metal hydroxide, while providing a thin film of alkali metal hydroxide at the rnembrane surface 41 adjaceat to the cathode surfaceand enhances the contact of the catalyst 43 and the oxidant.
While the method of this invention has been described ~ith refer- -ence to specific exe~plifications, embodir~en~s, and examples, the scope is not to be limited except as limited by the clairns appended hereto.

,~

, . . .

Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of electrolysis comprising feeding aqueous alkali metal chloride to an electrolytic cell having an anolyte compartment separated from a catholyte compartment by a solid polymer electrolyte, the solid polymer electrolyte comprising a permionic membrane having an anodic electrocatalyst on the anodic surface thereof and a cathodic electrocatalyst on the cathodic surface thereof; wherein the permionic membrane is a fluorocarbon permionic membrane having carboxylic acid ion exchange groups, an ion exchange capacity of 0.5 to 2.0 milliequivalents per gram of dry polymer, and a glass transition temperature above -80°C
but below 20°C below the electrolyte temperature; imposing an electrical potential across the solid polymer electrolyte, withdrawing chlorine from the anolyte compartment and alkali metal hydroxide liquor from the catholyte compartment, said alkali metal hydroxide liquor containing at least 30 weight percent alkali metal hydroxide.

2. A method as claimed in claim 1 wherein the polymer has ether linkages in carboxylic acid bearing side chain.

3. A method as claimed in claim 1 which comprises maintaining the hydrostatic pressure within the anolyte compartment above the vapor pressure of the evolved chlorine.

4. A method as claimed in claim 1 wherein the cathode bearing upon the cathodic surface of the permionic membrane comprises a boride of a transition metal.

5. A method as claimed in claim 1 wherein liquid chlorine with depleted anolyte liquor is withdrawn from the anolyte compartment and the liquid chlorine separated from the depleted anolyte liquor.

6. A method as claimed in claim 5 comprising cooling the depleted anolyte liquor whereby to form chlorine hydrate, and separating the chlorine hydrate from the depleted anolyte liquor.

7. A method as claimed in claim 6 comprising cooling the depleted anolyte liquor to below 9 degrees centigrade.

8. A method as claimed in claim 1 comprising providing a catalyst comprising an intercalation compound of carbon and fluorine on the cathodic side of the solid polymer electrolyte, and feeding an oxidant to the catholyte compartment.

9. A method as claimed in claim 8 wherein the cathodic surface of the permionic membrane has a hydrophilic portion and a hydrophobic portion in contact with oxidant and wherein the hydrophilic portion comprises the intercalation compound of carbon and fluorine.

10. A method as claimed in claim 9 wherein the oxidant is oxygen.

11. A method as claimed in claim 8, 9 or 10 wherein the intercalation compound of carbon and fluorine has the empirical formula CFX where x is from 0.25 to 1.0

12. A method as claimed in claim 1 comprising feeding an organic peroxide to the catholyte compartment of the electrolytic cell and providing a catalyst for the reduction of the organic peroxide in contact with the cathodic surface of the permionic membrane whereby to substantially eliminate evolution of hydrogen gas.

13. A method as claimed in claim 12 wherein the peroxide is hydrogen peroxide, an organic hydroperoxide, organic peroxide, organic peroxy acid or a derivative thereof.

14. A method of electrolysis as claimed in claim 1 wherein said permionic membrane further includes a hydrogen oxidation catalyst on said cathodic surface thereof, and is substantially horizontally disposed with the anodic electrocatalyst on the top surface thereof and the cathodic electrocatalyst on the bottom surface thereof, and a film of aqueous alkali metal hydroxide is maintained on the bottom surface of said membrane, oxidant being supplied at the membrane bottom surface, so as to avoid flooding of cathodic catalyst.