NO800391L - CHLORAL CALCIUM WITH SOLID POLYMER ELECTROLYT. - Google Patents

Abstract

Chloral alkali cell (11) having a solid polymer electrolyte unit (31). The electrolyte unit (31) comprises a permionic membrane (33) having an anodic chlorine evolution catalyst (37) on the anodic surface (35) and a cathodic hydroxyl evolution catalyst (43) on the cathodic surface (41) .The cathode material is preferably selected from titanium, vanadium, niobium, tantalum, chromium and tungsten compounds and the cathode may be depolarized with a peroxy compound, with a pair of redox or with an oxidizing complex. The anode is preferably particulate and consists of a hydrophobic material which may be diluted with silicon. The catalysts (37) and (43) may be bonded to the permionic membrane (33) by chemical application. an electrolyzer (1). Use of the electrolyser (1). occurs under high pressure to obtain liquid chlorine. '

Description

The present invention relates to a chloralkali cell with a solid polymer electrolyte.

Chloralkali cells with solid polymer electrolyte have

a cation selective,. permionic membrane with an anodic electro-. catalyst imposed in and. on the anodic surface of the membrane, i.e. in and on the anolyte facing the surface of the permionic membrane, and a cathodic hydroxyl evolution catalyst, i.e. a cathodic electrocatalyst placed in and on the catholyte surface of the membrane, i.e. the catholyte facing surface of the permionic membrane. In an alternative example, a cathode depolarizer, also known as an HC₂ disproportionation catalyst, is present on the cathodic surface, ie the catholyte facing the surface of the permionic membrane. This H02 disproportionation catalyst serves to depolarize the cathode and prevent the formation of gaseous hydrogen.

Chloralkali bipolar electrolyzes with. solid polymer electrolyte, has advantages in terms of high production per unit volume of electrolysis, high current efficiency, high current density and avoiding gaseous products and associated additional equipment as necessary due to gaseous products.

In the solid polymer electrolyte chloralkali process, aqueous alkali metal chloride, such as sodium chloride •■.>■_ or potassium chloride, comes into contact with the anodic surface of the solid polymer electrolyte. An electric potential is applied across the cell and chlorine is evolved at the anodic surface of the solid polymer electrolyte.

The alkali metal ion, i.e. sodium ion or potassium ion, is transported across the solid polymer electrolyte permionic membrane to the cathodic hydroxyl evolution catalyst on the opposite surface of the permionic membrane. The alkali metal ion, i.e. sodium ion or potassium ion, is transported with its water of hydration, but largely without'. transport of electrolyte mass-.

Hydroxyl ion is evolved on the cathodic hydroxyl ion evolution catalyst and likewise hydrogen. An alternative example is a cathodic depolarization catalyst, i.e., an H0 2 ~ disproportionation catalyst present near the cathodic surface of the permionic membrane, and an oxidizing agent is added to the catholyte chamber to prevent the formation of gaseous cathodic products. Fig. 1 is a bipolar electrolyser with solid polymer electrolyte, where the parts are shown apart. Fig. 2 is a perspective view of a solid polymer electrolyte unit in the bipolar electrolyser shown in Fig. 1. Fig. 3 is a section of the solid polymer electrolyte unit shown in fig. 2. Fig. 3 is a section, at greater magnification, of the solid polymer electrolyte surface shown in the unit of Fig. 2 and 3-Fig. 5 is a perspective view of a distributor showing one form of electrolyte feed and recovery. Fig. 6 is a side section of the distributor shown in fig. 5.

Fig. 7 is a perspective sketch of an embodiment

of the bipolar. element shown in fig. 1.

Fig. 8 is a. section of the bipolar element shown

in fig. 7-Fig. 9 is a perspective sketch of an alternative embodiment of a bipolar element with water exchange devices passed through the element.

Fig. 10 is a section of the bipolar element

shown in fig. 9.

Fig. 11 is a perspective sketch of an alternative embodiment of a bipolar element with distributor devices combined with the bipolar element. Fig. 12 is a side section of the bipolar element shown in fig. 11. Fig. 13 is a schematic side section of an electrolytic cell with solid polymer electrolyte. Fig. 1H is a schematic representation of a chloralkali process with a solid polymer electrolyte. The chloral calyx which. is shown schematically in fig. 1*1 'has a solid polymer electrolyte 31 with a permionic membrane 33 in it. The permionic membrane 33 has an anodic surface 35 with a chlorine catalyst 37 thereon and the cathodic surface 41 with a cathodic hydroxyl evolution catalyst 43 thereon. One also sees an external power supply connected to the anodic catalyst 37 by means of the distributor 57 and connected to the cathodic catalyst 43 by means of the distributor 55. Brine is supplied to the anodic side of the solid polymer electrolyte 31, where it comes into contact with the anodic chlorine evolution catalyst 37 on the anodic surface 35 of the permionic membrane 31- Chlorine, which is present as chloride ion in solution, forms chlorine gas according to the equation: ; The alkali metal ion, i.e. sodium ion or potassium ion, shown in fig. 14 as sodium ion, and its water of hydration, pass through the permionic membrane 33 to the cathodic side 41 of the permionic membrane 33. Water is supplied to the catholyte chamber. both from the outside and as hydration water that is passed through the permionic membrane 31 The stoichiometric reaction at the cathodic hydroxyl evolution catalyst is: ; In an alternative example, a cathode depolarization catalyst and an oxidizing agent are present to prevent gaseous hydrogen from forming. The structure for producing this reaction is shown generally in FIG. 13, where an electrolytic cell is shown with walls 21 and a permionic membrane 33 between them. The permionic membrane 33 has an anodic surface 35 and an anodic electrocatalyst 37 on the anodic surface 355 and a cathodic surface 41 with a cathodic electrocatalyst 43 on it. In an alternative example, a cathodic depolarization catalyst, i.e., an HC>2 disproportionation catalyst (not shown) is located near the cathodic surface 41 of the membrane 33 to avoid the formation of hydrogen gas. Devices for passing electrical current from the wall 21 to the solid polymer electrolyte 31 are shown as the distributor 57 in the anolyte chamber 39 which carries current from the wall 21 to the anodic chlorine evolution catalyst 37 5 and the distributor 55 in the catholyte chamber 45 which carries current from the wall 21 to the cathodic hydroxyl evolution catalyst 43. In a preferred embodiment, the flow dividers 55 and 57 also provide turbulence and mix the respective electrolytes. This prevents concentration polarization, gas bubble effects, stagnation and dead space. ;During the operation of the cell, brine is supplied to the anolyte chamber 39 through the brine inlet 8la and used brine is extracted from the anolyte chamber 39 through the brine outlet 8lb. Anolyte liquid can be removed as a foam containing chlorine gas, or liquid chlorine and liquid brine can be removed together. ;Water is supplied to the catholyte chamber 45 through the water supply 101a to keep the alkali metal hydroxide liquid and avoid the application of solid alkali metal hydroxide to the membrane. when.a H02 disproportionation catalyst is present, in this way.to.avoid the formation of hydrogen gas and to be able to withdraw a total liquid cathode product. A particularly desirable cell structure is a bipolar electrolyser which uses a solid polymer electrolyte. Fig. 1 shows such a bipolar electrolyser with a solid polymer electrolyte, and the parts are separated. The electrolyzer is shown with two electrolytic cells with available polymer 11 and 13. It can. however, there may be many more such cells in the electrolyser 1. The limitation on the number of cells, 11 and 13, in the electrolyser 1 is imposed by the rectifier and transformer possibilities and likewise by the possibilities of "current leakage". Electrolysers containing up to .150 or more; and with .200 or more cells is, however, within what is possible, if one uses available rectifiers and transformer technologies.; Individual electrolyte cells 11 contain a solid polymer electrolyte unit 31 shown as part of the electrolyser in Fig. 1, individually in Fig. 2 , in partial section in Fig. 3 and in larger magnification in Fig. 4, where the catalyst particles 37 and 43 are excessively large. The solid polymer electrolyte unit 31 is also shown schematically in Figs. 13 and 14. The solid polymer electrolyte unit 31 comprises a permionic membrane 33 with an anodic chlorine evolution catalyst 37 on the anodic surface 35 of the permionic membrane 33 and a cathodic hydroxyl evolution catalyst 43; on the n cathodic surface 41 of the permionic membrane 33. The cell boundaries can, when it concerns an intermediate cell in the electrolyser 1, be a pair of bipolar units 21 also called bipolar back plates. When it comes to the first and last cells in the electrolyser, such as cells 11 and 13 shown in fig. 1, a bipolar unit 21 is a boundary for the individual electrolytic cell, and. end plate 71 is the opposite interface for the electrolytic cell. The end plate 71 has supply devices for brine feeding 8la, outlet for removing brine 8lb, inlet for water supply 101a and removal of hydroxyl ;101b. In addition, a supply for oxidizing agent, which is not shown, will also be used when the cathode is depleted. The end plate 71 also includes the current connections 79 - When it is a monopolar cell, the end units will 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 for the individual cells. In addition, the end plate 71 and the bipolar units 21 provide electrical conductivity, and likewise in the various designs, electrolyte supply and gas recovery. ;The bipolar unit 21, which is shown. in fig. 7 and 8, has an anolyte-resistant surface 23 facing. the anodic surface 35 and anodic. catalyst 37 on one of the cells 11. The anolyte-resistant surface 35 comes into contact with the anolyte liquid and forms the interface to the anolyte chamber 39 in the cell. The bipolar unit 21 also has a catholyte-resistant surface 25 which faces the cathodic surface 4l and the cathode catalyst 43 in the solid polymer electrolyte 31 in the next neighboring cell 13 in the electrolyser 1. The anolyte-resistant surface 23 can be made of valve metal, i.e. metal which forms an acid-resistant oxide film when exposed to aqueous acid solutions. Valve metal includes titanium, tantalum, tungsten, vanadium, hafnium and zirconium and likewise alloys of titanium, such as titanium with yttrium, titanium with palladium, titanium with molybdenum and titanium with nickel. Optionally, the anolyte-resistant surface can be made of silicon or a silicide; The bipolar unit 21 can be made of two plates or laminates 23 and 25. The surface .23 facing the anolyte can be made of v single metal as described above. According to one embodiment, however, the surface 23 facing the anolyte in the bipolar unit 21 is made of an alloy of valve metal which is characterized by increased resistance to hydride formation and pitting corrosion. A particularly prominent group of such alloys are alloys of titanium and a rare earth metal or metals. Rare earth metals considered include scandium, yttrium and lanthanides. The lanthanides are lanthanum, cerium, praesodymium, neodymium, promethium, samerium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and tutetium. When the term "rare earth metals" is used, it shall include scandium, ytterium and the tantanides. ;The alloy consisting of a rare earth metal can. be one or more rare earth metals. E.g. can it be scandium or ytterium or cerium, .or lanthanum or lanthanum and ytterium or lanthanum and cerium. Usually the additive will all be ytterium. ;The amount of rare earth metal used as an alloying agent should be at least the threshold value that is sufficient to reduce or dominate the uptake of hydrogen by titanium. This is usually at least approx. 0.01% by weight though. smaller amounts have a positive impact. The maximum amount of rare earth metals used as an alloying agent should be low enough to avoid any significant formation of a two-phase system. Usually this is less than approx. 2 wt-% rare earth metal for the rare earth metals yttrium, lan-, tinium, cerium, gadolinium and erbium although amounts up to 4 or even 5 wt-% can be tolerated without harmful effects, and less than approx. 7 wt% rare earths for the rare earth metals scandium and europium, although amounts up to 10 wt% can be tolerated without adverse effects. Usually, the amount of rare earth metals is from approx. 0.01-approx. 1% by weight, and preferably from approx. 0.015-approx. 0.05% by weight. ;Titanium alloys can also contain various impurities without adverse effects. These impurities include iron in amounts that are usually above approx. 0.01$ or even 0.1$, and often as high as 1%, vanadium and tantalum in amounts up to approx. 0.1$ or even up to 1%, oxygen in amounts up to 0.1% by weight and carbon in amounts up to approx. ;0.1% by weight. ;Possibly it can surface 23 in it. bipolar unit facing the anolyte be an isomorph beta phase alloy of titanium with molybdenum or an isomorph alloy of titanium with other transition metals, such as palladium, nickel and iron, e.g. where the iron content is less than approx. 0.05% by weight. Isomorphous alloys of titanium and the above-mentioned transition metals provide increased resistance to pitting corrosion and hydrogen uptake. The amount of transition metal, e.g. iron, nickel, palladium or molybdenum, should be sufficiently high to increase pitting corrosion resistance and hydrogen uptake resistance, but low enough to avoid the formation of another phase. The catholyte-resistant surface 25 can be provided by any material resistant to concentrated, corrosive solutions such as in-'. holds either oxygen or hydrogen or both. Such metals include iron, steel, stainless steel etc. ;The two parts 23 and 25 in the bipolar unit 21. can. be plates of titanium and iron, plates of the other metals listed above, and there may additionally be a hydrogen barrier placed between the anodic surface 23 and the cathodic surface 25, to avoid the transport of hydrogen through the cathodic surface 25 of a bipolar unit to the anodic surface 23 of the bipolar unit. The hydrogen barrier, which is placed between the anodic surface 23 and the cathodic surface 25 of the bipolar unit 21, is a material that inhibits the flow of hydrogen, e.g. a material with low hydrogen solubility. or permeability. The hydrogen barrier can be a non-conductive material, such as silicates and glass, organic resins and paints. Optionally, metals that have properties such as a hydrogen barrier can be used. Suitable results can be obtained with vanadium, chromium, manganese, cobalt, nickel, copper, zinc, niobium, molybdenum, silver, cadmium, rhodium, tantalum, tungsten, iridium and gold. Best hydrogen barrier results are provided when the hydrogen barrier coating is molybdenum, rhodium, iridium, silver, gold, manganese, zinc, cadmium, lead, copper or tungsten. Especially preferred ;. are cups. ;The hydrogen barrier can be a plate.- Optionally, it can be an applied film or a coating. In another embodiment, the hydrogen barrier can be detonation applied to one or both parts of the bipolar unit 21..; In an alternative embodiment shown in fig. 9 and 10, heat exchange lines 121 are passed through the bipolar unit 21. These heat exchange units 121 carry coolant or cooled gas to remove heat from the electrolyser, e.g. In 2 R generated heat and likewise the reaction heat<. >This makes it possible to use . a lower pressure when the electrolyser is under pressure, and when liquid chlorine is the desired product or when. oxygen is supplied under pressure or both. Another example of a bipolar electrolyser with solid polymer electrolyte, shown in Figs. 11 and 12, the electrolyte feeding and distribution function is carried out by means of the bipolar unit 21. In addition until, instead of the distributor 21, the line 133 thus extends from the line 115a to the interior of the bipolar unit 21, then, to a porous or open element 131 which distributes the electrolyte. Analogously for the opposite electrolyte, the feeding takes place through the tube 143 to a porous or open surface 141 on the opposite surface of the bipolar unit. The individual electrolytic cells 11 and 13 in the bipolar electrolyser 1 also comprise distribution devices 51 which can be placed between the ends of the cell, i.e. between the bipolar unit 21 or the end wall 71 and the solid polymer electrolyte 31. These distribution devices are shown in fig. 1. and individually in fig. 5 and 6 with lines for the catholyte liquid 105a and 105b and the catholyte supply Illa and catholyte recovery 111b. The side wall 53 of the distributor 51 is shown as a circular ring. It provides an electrolyte-tight and gas-tight integrity to the electrolyser 1 and likewise to the cells 11 and .13-The gasket which can be etch-resistant as . packings 55 or, resistant to acidic, chlorinated brine and chlorine such as packing 57, is preferably soft, conductive and largely non-catalytic. That is that the packing 55 in the catholyte unit,' in the catholyte chamber 45' has a higher hydrogen evolution or hydroxyl ion evolution over the voltage drop than the cathode catalyst 43 in order to avoid electrolytic evolution of cathodic product on it. In a similar way, the packing 57 in the anolyte chamber 39 has a higher chlorine development over the voltage drop and a higher oxygen development over the voltage drop than the anodic catalyst 37 in order to avoid the development of chlorine or oxygen on this.. The packing 55 and 57 serve to conduct current from the boundary of the cell, such as the bipolar unit 21 or the end plate 71, to the solid polymer electrolyte 31- This necessitates high electrical conductivity.' The management is carried out while avoiding product development as described above. In a similar way, the material must have a minimum of contact resistance at the solid polymer electrolyte 31 and at the interfaces in the individual cell 11, die. the end wall 71 or bipolar unit 21. ;The distribution packings 55, 57 further distribute and diffuse the electrolyte in the anolyte chamber 39 or the catholyte chamber 45 to avoid concentration polarization, build-up of stagnant gas and liquid pockets, and build-up of solid coatings, such as potassium hydroxide or sodium hydroxide coatings. The packing 55, 57 can be carbon, e.g. in the form of graphite, carbon felt, carbon fibres, porous graphite, activated carbon etc. Optionally, the packing can be metal felt, metal fiber, metal sponge, metal mesh, graphite mesh or clamps and springs etc., and such clamps or springs abut against the solid polymer electrolyte and the bipolar unit 21; and on the bipolar unit 21 of the end plate 71; According another embodiment can be the current collector and the current distribution devices 51" which provide. electrical contact between the cell walls 21, 71 and the solid polymer electrolyte 31, be a plate of fine mesh, which abuts the catalyst. 37, 43 and electrically and mechanically in series with the end walls 21, 71 of the cell 11. The electrical and mechanical contact can be provided by means of first and second flexible metal devices, the first flexible metal device abutting the catalyst 37 , 43, dg the second flexible metal device rests against the wall 21, 71 in the cell. The two flexible metal devices can be removed together. That is that they lie against each other under pressure or that they can be fastened together. Optionally, the packing 51, 57' can be packing such as rings, balls, cylinders or the like, packed tightly to obtain high conductivity and low electrical contact resistance. In one embodiment, the brine supply 87a and the brine outlet 87-b, and likewise the supply of water and oxidizing agent Illa and recovery of the catholyte liquid 111b, can be combined with the distributors_ 51»51 In such an embodiment, the supply 87a and Illa extend into the packings 55 and 57, and the outlet 87b and 111b extend from the packings 55 and 57. In an alternative embodiment, the reagent supply and product recovery can be a microporous distributor, e.g. microporous, hydrophilic or microporous, hydrophobic films that lie against the solid polymer electrolyte 31 and under pressure from the distribution devices 55 and 57. In an embodiment where the supply is microporous films on the solid polymer- . electrolyte 31, the catalyst particles 37 and 43 can be in the microporous film and likewise on the surface of the solid polymer electrolyte 35 and 41. As described above, the individual electrolyte cells 11 and 13 with solid polymer electrolyte comprise a solid polymer electrolyte 31 with a permionic membrane 33 with an anodic catalyst 37 on the anodic surface 35 thereof, and a cathodic catalyst 43 on the cathodic surface thereof. The interface in the cell can be a bipolar unit 21 or an end plate 71, where the electrical line between the interfaces and the solid polymer electrolyte 31 is the distribution devices 51. The reagent supply 87a and Illa and the product recovery 87b and 111b are also provided. In addition, there must be devices to maintain an electrolyte-tight, gas-tight seal such as the gasket 6l. While the gasket 61 is only shown between the walls 71 and bipolar units 21, and the distributors 51, it is understood that additional or alternative gaskets 61 may be located between the distributor 51 and the solid polymer electrolyte '31. Gaskets in contact with the anolyte chamber 39 should be made of any material that is resistant to acidic, chlorine-containing brine and likewise to chlorine. Such materials include unfilled silicone rubber and likewise various resistant fluorocarbon materials.. The gaskets 61 in contact with the catholyte chamber 45 may be made of any material resistant to concentrated caustic soda. '. A particular, satisfactory floating system is shown generally in fig. 1, where the brine is supplied to the electrolyser 1 through the brine line 8la in the end unit 71, e.g. with a hydrostatic pressure. The brine is then fed through line 83a into the "0" ring or gasket 61 to and through line 85a in the distributor 51 on the cathodic side 45 of cell 11, and then to and through line 89a therein; solid polymer unit 31 to the 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 the line 8la passing through the distributor 51 and the outlet 87a which leads the electrolyte to the anolyte chamber. The flow then continues from line 91a in the distributor 51 to line 93a in the next "0" ring or gasket through line 95a in the bipolar unit 21 and on to the next cell 13, where the liquid flow is largely as described above. Brine is distributed by means of the packing 57 in the distributor 51 inside the anolytic chamber 39- Distribution a<y>the brine sweeps chlorine from the anodic surface 35 and anodic catalyst 37 to avoid chlorine stagnation. ;The used brine is drawn out through the outlet 87b in the distributor 51 to the return line 91b, e.g. at partial vacuum or reduced pressure. The return is through the return line 89 in the solid polymer electrolyte unit 31, the line 85b in the cathodic distributor 51, the line 83b in the "0" ring or gasket 6l to the outlet 8lb, where spent brine is recovered from the electrolyser 1.; While the brine supply is shown with an inlet system and an outlet system, i.e. recovery of used brine and chlorine through the same outlets, it is understood that used brine and chlorine can be recovered separately. It is also understood that depending on the internal pressure in the anolyte chamber 39 and the temperature of the anolyte liquid in the anolyte chamber, chlorine can either be a liquid or a gas. ;Water and oxidizing agent enter the electrolyser 1 through inlet 101a in end unit 71. Water and oxidizing agent then continue through line 103a in the "0" ring or gasket 6l to line 105a and "T" in the cathodic distributor 51 on therein cathodic side 45 of the cell 11. The "T" outlet comprises the line 105 and the outlet Illa. Water and oxidizing agent are led by means of the outlet Illa in the ring 53 in the distributor 51 to the catholyte-resistant packing 55 inside the catholyte chamber 45 in the cell 11. The cell liquid, i.e. the aqueous alkali metal hydroxide, such as sodium hydroxide or potassium hydroxide, is recovered from the cathodic surface 41 of the solid polymer electrolyte permionic membrane 3.3 by means of water introduced into the cell 11. When oxidizing agent is present, the liquid can be recovered through the outlet 111b. When there is no oxidizing agent, gas and liquid can both be recovered through 111b, or in an alternative embodiment, a separate gas recovery line not shown can be used. While the electrolyser is shown with a common feed for oxidizing agent and water, and with a common recovery for gas and liquid, it can be. three lines present, Illa, 111b and a third line, not shown, for water supply and oxidizing agent supply and liquid recovery. Optionally, there may be three lines 111b and a third line, which is not shown, for water supply, recovery of liquid and recovery of gas. ;Returning to the general flow in the electrolyser 1, line 105a continues to line 107a in the solid polymer electrolyte unit 31 to line 109a in the anodic distributor 51 which continues through line 113a in the "0" ring or gasket 61; and then to the wire 115a in the bipolar unit 21, where the same path through the individual cell 13 is followed as in cell 11. In a similar way, the network can be continued in further cells. ;Recovery of product is shown from the distributor 51 through the outlet 111b to the line 105b and then to the ;line 103b in the "0" ring or gasket 61 to the outlet 101b in the end wall 71 ;While the flow is described as to and through the distributors 51, which described above, the flow can also be through other paths. E.g. the inlet and outlet or both could be in the bipolar unit 21, and the bipolar unit would then be equipped with porous films or outlet tubes from the unit 21. Alternatively, the inlet and outlet or both could be part of the solid polymer electrolyte unit 31. While the flow is described as parallel to each individual cell 11 and 13, there can also be a flow in series. When series flow of the brine is used, the "T" one, outlet .87 line 91 may be an L rather than a T. In an embodiment where series flow is used, there will be a lower brine depletion in each cell, while partially depleted brine from one cell is carried to the next cell for further utilization. Similarly, when flow in series is used for the catholyte liquid, the T, the conduit 105" outlet 111 will be an L. When flow in series is used, the flow may be co-current with high sodium 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 electrolyser can either be positioned horizontally or vertically, i.e. the bipolar electrolyser. 1 can have solid polymer electrolyte units 31 with either a horizontal membrane 33. or a vertical membrane 33- Preferably, the membrane 33 is horizontal with the anodic surface 35 on top of the permionic membrane 33 and the cathodic surface 4l on the bottom of the permionic membrane 33. A horizontal embodiment gives different advantages. During low-pressure operation, chlorine bubbles flow up through the anolyte chamber 39- In the catholyte chamber 45, a horizontal pla ssing prevent the build-up of concentrated alkali metal hydroxide on the bottom surface 41 of the permionic membrane 33, while the bottom surface 41 of the permionic membrane 33 is wetted with alkali metal hydroxide. When oxidizing agent is . present, and in particular a gaseous oxidizing agent, in addition the horizontal location will allow the oxidizing agent to be in contact with the cathodic surface 4l of the permionic membrane 33-; In this solid polymer electrolyte 31 contains a permionic membrane 33- The permionic membrane 33 should be chemically resistant, cation selective, with an anodic chlorine evolution catalyst 37 on the anodic surface 35 and a cathodic hydroxyl evolution catalyst 43 on the cathodic surface 41. ;The permionic membrane 33 of fluorocarbon resin used in the solid polymer electrolyte 31 is characterized by the presence of cation selective ion exchange groups , where the ion exchange capacity in the membrane, the concentration of ion exchange groups in the membrane based on water absorbed in the membrane and the glass transition temperature in the membrane material. The fluorocarbon resins used have the parts: ; where X is -F, -Cl, -H, or -CF^ ; X' is -F, -Cl, -H, -CF3 or CF3 (CF2)m-, where m is an integer from 1-5; and where Y is -A, - -A, -P-A, or -O-(CF2)n (P,Q,R)-A. ;In the unit (P, Q, R) P is - (CF2 )a( CXX' )fe (C.F2 )c , Q is (-CF2-0-CXX<»>)d, R is (-CXX' -0-CF2) and (P, Q, R) contain one or more of P,. Q and R. ;O is the phenylene group; n is 0 or - 1, a, b, c, d and e are integers. from 0-6. ;The typical groups Y have the structure with the acid group A, connected to a carbon atom which is connected ;. to fluorine atom. These include- ^CF^-^A and side chains which either have compounds such as: -0-fCF2^xA, ; where x, y and z are 1-10 respectively; Z and R are respectively -F or a C1_10. Perfluoroalkyl group, and A is the acid group as defined below. When it concerns copolymers with olefinic and olefinic acid parts as described above, it is preferred to have 1-40. mol%, and preferably 3-20 mol% of olefinic acid subunits to produce a membrane with ion exchange capacity in the desired range. ;A is an acid group selected from the group consisting of of ; ; or a group that can be converted into one of the aforementioned groups by hydrolysis or by neutralization. In a particularly preferred embodiment of the invention, A can either be -C00H or a functional group which can. converted to -COOH by hydrolysis or neutralization such as -CN, -COF, -COC1, -COOR-^-CO0M, -CONR^; R-1 is a C1-10 alkyl group and R2 and R3 are either hydrogen or C-1 to C10 alkyl groups, including perfluoroalkyl groups or both. M is hydrogen or alkali metal; when M is an alkali metal, it is preferably sodium or potassium. ;In an embodiment of the invention where A is ;-C0NR2R-j,. and.where R and R are hydrogen, or a C 1 to C 10 alkyl group, including a perfluoroalkyl group, the cathodic surface 41 of the permionic membrane 33 can have ion exchange groups in carboxylic acid form, while the anodic surface of the permionic. membrane has ion exchange groups in amide or N-substituted amide form. The use of amide groups or N-substituted amide groups on the anodic surface 35 of the permionic membrane 33 serves to make the cathodic surface 35 hydrophobic. This prevents chlorine stagnation on the membrane 33. The membrane 33 can be converted into an amide or N-substituted amide group during the synthesis, or after the catalyst 37 has been applied to it or inserted into it, e.g. by reaction with ammonia or an amine. ;In an alternative embodiment, A can either be ;-SO^H or a functional group that can be converted to;-SO-jH by hydrolysis or neutralization, or formed from .,-SQ3H such as -SC^M' , (S02- NH) M", -SC^NH-I^-N}^ or -S02NR2|R5NRljR6; M' is an alkali metal; M".is H, NH^, an alkali metal or j ordal alkali metal; is H, Na or K; R5 is a C1 -C8 alkyl group, (R-L)2NRg or R1NRg(R2)zNRg, Rg is H, Na, K or -SO2; and R 1 is a C 2 -C 6 alkyl group. ;The membrane under consideration has an ion exchange capacity of from 0.5-2.0 mg equivalents per g dry polymer, and preferably from approx. 0.9-approx. 1.8 mg equivalents per g dry polymer, and in a particularly preferred embodiment from approx. 1.1-approx. 1.7 mg equivalents per g dry polymer.' ;When the ion exchange capacity is less than approx. 0.5 mg equivalents per g of dry polymer, the current efficiency is low at the high concentrations of alkali metal hydroxide considered here, while when the ion exchange capacity is greater than approx. 2.0 mg equivalents per g dry polymer, the current efficiency in the membrane is too low. ;The content of ion exchange groups per g absorbed water is from c-a. 8 mg equivalents per g of absorbed water, to approx. 30 mg equivalents; per g absorbed water, and preferably from approx. 10 mg equivalents per g.absorbed water to approx. 28 rag equivalents per g absorbed water, and in a preferred embodiment from approx. 14 mg equivalents per ;g absorbed water to approx. 26 mg equivalents per g absorbed water. When the content of ion exchange groups per unit weight absorbed water is less than approx. 8 mg equivalents per g or over approx. 30 mg equivalents per g, the power efficiency is too low. The glass transition temperature is preferably at least approx. 20°C below the temperature of the electrolyte. When the electrolyte temperature is between 95-110°C, the glass transition temperature in the membrane material of fluorocarbon resin is below approx. 90°C and in a particularly preferred embodiment below 70°C. But the glass transition temperature should be above approx. -8o°C to provide satisfactory tensile strength in the membrane material. Preferably, the glass transition temperature is from approx. -80°C to approx. 70°C, and in a particularly preferred version from approx. -80°C to approx. 50°C. ;When the glass transition temperature in the membrane is within approx. 20°C of the electrolyte or higher than the temperature in the electrolyte, the resistance in the membrane will increase, and the permeability selectivity in the membrane will decrease. By the glass transition temperature is meant the temperature below which the polymer segments are not energetic enough either to move past each other or in relation to each other in the case of segmented, Brownian movements. That is below the glass transition temperature, the only reversible response in the polymer under load is stretching, while above the glass transition temperature the response in the polymer under load will be a segmented rearrangement to compensate for the externally applied load. ;The permionic membrane materials of fluorocar-. bon resin that has been assessed has a water permeability of less than approx. 100 ml per hour per m<2>at 60°C in four normal sodium chloride at pH 10, and preferably less than 10 ml per hour. per m at 60 C in four normal sodium chloride at pH 10. Water permeabilities higher than approx. ; 100 ml per hour per m 2 , measured as described above, can lead to an impure alkali metal hydroxide product. ;The electrical resistance in the dry membrane should be from approx. 0.5-approx. 10 ohms per cm 2, and preferably from approx. 0.5~cai 7 ohm per cm. Preferably, the permionic membranes of fluorinated resin have a molecular weight, i.e. a degree of polymerization, which is sufficient to give a volumetric flow rate of approx. 100 ml^ per second at a temperature of from 150-300°C. ;The thickness of the membrane 33 should be such that one. gets a membrane 33 that is strong enough to withstand pressure stresses and manufacturing processes, e.g. application of catalyst particles, but sufficiently thin to avoid high electrical resistance. Preferably, the membrane is from 10-1000 microns thick, and in a preferred embodiment from 50-200 microns thick. In addition, internal reinforcement or increased thickness, or cross-linking can be used, or possibly lamination can be used to provide a strong membrane. In a preferred embodiment, the permionic membrane comprises devices for introducing anolyte liquid into the interior of the permionic membrane. This prevents crystallization of alkali metal chloride salts in the permionic membrane 33- A method for achieving this may include wicks such as e.g. extends up to or past the anodic catalyst 37. According to another embodiment, the means for introducing anolyte liquid into the interior of the permionic membrane may comprise hydrophilic or wettable fibers that extend up to or past the anodic catalyst 37 or to and with microtubes that extend up, ;to and past the anode catalyst 37-;As considered here,' the devices for introducing anolyte liquid into the interior of the permionic membrane draw water or anolyte liquid into the membrane past the hydration water which is linked to the electrolytically entrained al .potassium metal ions. This is to prevent crystallization of alkali metal chloride, such as sodium chloride or potassium chloride in the membrane. In a preferred embodiment, the electrocatalysts 37 and 43 and the membrane 33 are a unit. While this can be achieved by having the electrocatalysts 37 and 4 3 on the distributor packings 55 and 57 with the distributors 55 and 57 held in a pressure relationship to the diaphragm 33».ei? it is preferred to provide a film of the electrocatalysts 37 and 43 on the permionic membrane 33. The film 37, 43 is usually from approx. 10-approx. 200 micron thick, and preferably from approx. 25-approx. 125 micron thick, and ideally from approx. 50-approx. 150 micron thick. ;Electrocatalyst-permionic membrane unit 31 should have the dimension stability, resistance to chemical and thermal degradation, electrocatalytic activity and preferably the catalyst particles should be finely distributed and 2 porous with at least approx. 10 m surface per g catalyst particle 43. Application of the catalyst 37 and 43 to the permionic membrane 33 can be achieved by pressing the particles 37 and 43 into a molten, semi-molten, liquid, plastic or thermoplastic permionic membrane 33 during heating. That is the membrane is heated above the glass transition temperature, preferably above the temperature at which the membrane 33. can be deformed by pressure alone. According to yet another embodiment, the particles 37 and 4.3 can be pressed into the partially polymerized, permionic membrane 33, or pressed into a partially crosslinked, permionic membrane 33, and the polymerization or crosslinking is carried forward, for example, by raising or lowering the temperature, adding initiator, adding additional monomer or use of ionizing radiation or the like. According to another embodiment of the method according to the invention, where further polymerization is carried out, the particles 37 and 43 can be introduced into the partially polymerized, permionic membrane 33. Then a monomer of hydrophobic polymer can be applied to the surface, by e.g. an initiator, and is copolymerized, in situ, with the partially polymerized permionic membrane 33 to provide a hydrophobic surface with exposed particles 37 and 43. In this way, the catalyst particles 37 and 43 can be present with a hydrophobic surface e.g. to protect the anodic surface 35 from chlorine, or to protect the cathodic surface 41 from crystallization or precipitation of alkali metal hydroxide, or to increase the depolarization when a cathodic HC^" disproportionation catalyst is present on the cathodic surface 41 of the permionic membrane According to another embodiment of the invention, the permionic membrane parts can be cross-linked, for example after the application of catalyst particles, to increase the hydrophobic character of the membrane surface. The cross-linking agent which can be reacted during the formation or after the anode materials have been applied on a partially polymerized, permionic membrane. Suitable crosslinking agents include divinylbenzenes, e.g., perfluorinated divinylbenzenes. Other suitable crosslinking agents include perfluorinated dienes, such as hexafluorobutadiene, octafluoropentadiene, including 1, 3, and 1, 4 dienes, and decafluorohexadiene, including 1,3 and 1,4 and 1,5 dienes.Generally, crosslinking mi dled a divinylbenzene or perfluorinated C4~C5;diene, and especially hexafluorobutadiene. According to another embodiment, anode electrocatalyst 37 can be diluted with silicon. That is that when the anode electrocatalyst 37 is a particle, the particles can be coated with silicon particles, e.g. silicon particles coated with a suitable chlorine evolution catalyst. Additional silicon particles, e.g. coated silicon particles, silicon particles with silicide and silicon particles with a silicon surface, can. be on the anodic surface 35 of the permionic membrane 33j both to provide conduction between the anode particles and as an anode catalyst. ;According to this embodiment, low overvoltage anode particles are provided which comprise an electroconductive surface which is electrolyte resistant, such as metallic platinum or ruthenium oxide on an electroconductive substrate which is partially or completely, and preferably mainly, composed of silicon in the elemental state (to . difference from silicides which can be considered compounds of silicon and another metal). When silicon is present in an elemental state, it contains impurities or additives, e.g. boron, phosphorus or the like, or silicides of various metals dispersed through the silicon which can give conductivity and/or strength to the silicon. Elemental silicon is usually a continuous phase, where other agents are dissolved or dispersed. ;The silicon particles should be electrically conductive; and should be at least as electrically conductive as graphite, e.g. should silicon have a bulk conductivity. in excess of 10 2 (ohm-centimeter) 1 and preferably 10^ (ohm-centimeter) ^ or higher. Substantially pure silicon, i.e. silicon with a purity greater than 99.995 atomic %, is at best a poor conductor, and can be characterized as a non-conductor with a resistivity of only about 1 ohm-centimeter. It is known that by adding small, even trace amounts of boron, phosphorus or other materials, the resulting silicon compound will be electrically conductive. According to the invention, it has been demonstrated that, with appropriate care, a silicon substrate can be obtained in a form which is inert to anodic attack, and such substrates can be effectively used to provide support for a conductive surface. ;Elementary silicon containing up to 2%,;and even up to 5% boron or up. to 2% phosphorus and small amounts of other impurities, has been shown to have the desired resistance to anodic attack by aqueous sodium chloride. ;The silicon can also contain iron, e.g. up to 40% by weight when phosphorus and boron are present, as phosphorus and boron have a corrosion-inhibiting effect. ;The silicon particles can also contain silicides. Particularly preferred are silicides. with a catalytic effect or a conductivity-increasing effect such as silicides of groups IV, V and VI, e.g. TiSi2, SrSi2, VSi2, NbSi2, ;TaSi2 and WSI2 and the heavy metal silicides, e.g. CrSi, Cr^Si^, CrSI, CrSi2 and MoSi2 and likewise the cobalt silicides ;CoSi2. According to another embodiment of the method according to the invention, the catalysts 37 and 4-3 can be chemically applied, e.g. by means of hypophosphite or borohydride reduction, or electro-applied to the permionic membrane 33 In addition, there may be a subsequent activation of the catalyst, e.g. by simultaneous application of a leachable material with a less leachable material and subsequent activation by washing out the more leachable material. According to another embodiment, a surface of catalyst 37 and 43 can be applied to the permionic membrane by electrophoresis, by laser application or by photo application. According to another embodiment of the method according to the invention, a catalytic coating 37 and 43 can be applied to the permionic membrane 33 using a chelate of a metal which reacts with. the acid groups of the permionic membrane 33. Typically, the catalyst 37 and 43 on the surface of the permionic membrane 33 is a catalyst containing a noble metal, such as platinum group metal or an alloy of platinum group metal. and an intermetallic compound; of a platinum group metal or oxide, carbide, nitride, boron, silicide or sulfide of a platinum group metal. Such catalysts containing noble metals are characterized by a high surface area and an ability to either be bound to a hydrophobic particle or to be embedded in a hydrophobic film. In addition, the catalyst containing noble metal can be a partially reduced oxide, or soot, so. ;as platinum soot or palladium soot or applied electrically or chemically. The catalysts 37 and 43 can also be an intermetallic compound of other metals, including precious metals and non-precious metals. Such intermetallic compounds include, pyrochlores, delafossites, spinels, perovskites, bronzes, tungsten bronzes, silicides, nitrides, carbides and borides. ;Especially desirable, cathodic catalysts; which may be present on the solid polymer electrolyte. "permionic membrane 33" includes steel, stainless steel, cobalt, nickel, alloys of nickel or "iron," compounds of nickel, especially porous nickel with molybdenum, tantalum, tungsten, titanium, columbium and the like and boride, electrically conductive, electrically active borides , nitrides, silicides and carbides, such as platinum group metal silicides, nitrides, carbides and borides and titanium diboride. Other cathodic catalysts 43 which may be present on the cathodic surface 41 of the permionic membrane include platinum group metals, e.g. .platinum, palladium, ruthenium, osmium, iridium and rhodium, both as a smooth coating for coatings with a high surface, eg "soot" with a surface ;of more than 10 m 2 per g. ;As assessed here , the permionic membrane 33, or a surface thereof, e.g. the anodic surface 35 or the cathodic surface 4l, is brought into contact with a reducing agent, a complexing agent, a buffer and a compound of the metal or compounds of those metals so m must be applied. The reducing agent may be a borohydride reducing agent or a hypophosphite reducing agent. The borohydride solution should contain 1-5 g per liter of borohydride, e.g. sodium or potassium borohydride, and preferably 1.5-2.5 g per liters of borohydride.. ;When the coating is on a synthetic* permionic membrane 3.3, rather than on a metal substrate, sequential contact is particularly desirable. In sequential contact, the membrane 33 is first brought into contact with the reducing agent, and then with compounds of the metals to be applied.

The method according to the invention is advantageous

for transition metals, and particularly favorable for group VII transition metals. It is particularly beneficial for the simultaneous application of two group VIII metals with different resistance and for chemical leaching and subsequent leaching of the less resistant metal.

The borohydride is preferably an alkali metal borohydride, such as sodium or potassium borohydride. The transition metal is. present in the second solution as a soluble salt, e.g. a citrate, oxalate, glycolate, sulfate or chloride. Buffers and the complexing agent can be the acid and the alkali metal salt of the same organic compound, e.g. sodium citrate and citric acid, sodium oxalate and oxalic acid and the like. Optionally, an inorganic acid, e.g.

phosphoric acid and sodium phosphite are used.

The complexing agent and the buffer serve to keep group VIII metal ions in solution, e.g. at pH from 6-8.

In a particularly preferred embodiment comprises

the cathodic electrocatalyst .43 porous nickel containing an effective amount, ie a surge reducing or surge stabilizing amount of group IVB, VB, VIB or VIIB transition metal'. These transition metals include titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technitium and rhenium. The preferred materials are titanium, zirconium, hafnium, vanadium, niobium, tantalum, molybdenum and tungsten. Particularly preferred are titanium, tantalum, zirconium and mdlbyden.

Nickel is usually over approx. 50% and less than approx. 95%, and usually from approx. 65-approx. 90% nickel, calculated as nickel metal, basis total weight of porous, active surface.

The second transition metal is present in the porous catalytic surface 43 in a hydrogen overvoltage reducing amount. This is over approx. 2, 5, preferably over approx. 5, but below approx. 50, and usually from approx. 10-approx. 35% by weight, calculated as metal, base total nickel calculated as metal and other transition metal calculated as metal in the surface. Usually, 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 surfaces consisting mainly of another transition metal, e.g. titanium, tantalum, zirconium or molybdenum.

While the mechanism for the hydrogen overvoltage lowering effect of the second transition metal is not fully understood, it is known that porous threads of e.g. molybdenum alone are high in hydrogen overvoltage, but that low hydrogen overvoltage over extended periods of the electrolysis can be observed when other transition metals as described above, e.g. molybdenum is used together with porous nickel. When it comes to molybdenum, it is assumed that molybdenum depolarizes or catalyzes a step of the hydrogen evolution process. For this reason, the upper limit of the second transition metal is below the concentration where the surface has hydrogen overvoltage properties of the second transition metal, d<y>s. under approx. 50% and usually below approx. 35%•

The second transition metal itself may be present as an elemental metal, i.e. elemental molybdenum, titanium, tantalum, zirconium or tungsten with a formal valence of 0, as an alloy with nickel or as an alkali resistant compound such as a carbide, nitride, boride, sulphide, phosphide, oxide or other compound insoluble in concentrated alkali metal hydroxide. Preferably, the second transition metal is present on the surface 43 with nickel as the elemental metal or an alloy with nickel or a carbide.

A particularly prominent cathode 43 according to the invention is one which has a porous surface 43 of nickel and molybdenum containing approx. 82% nickel and approx. 18% molybdenum, where the basis is total nickel and molybdenum, and which has a porosity of approx. 0.7 and a thickness of approx. 75-approx. 500 micrometres.

According to another embodiment of the method

according to the invention, the cathode is produced by applying a .

film of nickel, the other transition metal and a leaching

bare material on the permionic membrane 33, and then wash out the leachable material.

The washable material can be any

any metal or compound that can be applied together with nickel and the other transition metal or with nickel compounds and compounds of the other transition metal,

and washed out using a strong acid or a strong base without washing out significant amounts of nickel and

the other transition metal or causes substantial degradation or poisoning of nickel or the other transition metal.

The film can be applied to the permionic membrane. 33 by electroapplication of nickel, the other transition metal and a washable material, or by a simultaneous application of solid particles, or by chemical application, e.g. by hypo-phosphite application, or by borohydride application of nickel compounds, compounds of the other transition metal and leachable materials, or even by application and thermal decomposition of organic compounds of nickel, the other, transition metal and. washable materials, e.g. application and thermal decomposition of alcoholates and resinates.

According to a particularly desirable embodiment of the method for producing the electrode according to the invention, fine particles are introduced, e.g. in the order of 0.5-70 micrometers in diameter, of nickel, the other transition metal or a compound thereof and a leachable material in a partially polymerized, permionic membrane 33/ after which the polymerization ends, with leaching of the leachable materials either before or after the polymerization. Optionally, the particles can be introduced into a heated, thermoplastic, permionic membrane 33- .

The leachable materials may be present in the nickel particle or as separate particles. Typical leachable compounds include copper, zinc, gallium, aluminium, tin, silicon or the like. Particularly preferred are nickel particles containing approx. 3-approx. 70% nickel,.where the rest is aluminum as Raney alloy.

After the polymerization of the partially polymerized membrane 33 has ended, or after cooling of the heated, thermoplastic membrane 33, the particles 43 can be washed out, e.g. in alkali: such as 0.5 normal caustic soda or 1 normal caustic soda, to remove the leachable material, e.g. aluminium, and then rinsed with water. It is of course understood that some of the washable material can remain in the porous electrode surface 43 without any harmful effect. Thus, e.g. where Raney-nickel-aluminum alloy and molybdenum are deposited, in the membrane 33, the surface may contain nickel, molybdenum and aluminum after leaching. The resulting surface can e.g. contain amorphous nickel, crystalline molybdenum nickel-aluminium alloys and traces of aluminum oxide.

According to another embodiment according to the invention, the surface 43 may contain boron or phosphorus. These materials, which are assumed to be applied during borohydride or hypophosphite application, stabilize the voltage characteristics of the cathodic electrocatalyst 43.

The cathodic electrocatalyst 43 described above, while useful with perfluorinated ion exchange membranes 33 in general, will find particular application in ion exchange membranes 33 having carboxylic acid groups as described above.

Nickel is usually present over approx. 50%, and less than approx. 95%, and usually from approx. 65~approx. 90% nickel, calculated as nickel metal, where the basis is the total weight of the porous, active surface.

The second transition metal is present in the porous catalytic surface 43 in a hydrogen bias reducing amount. This is over approx. 2.5, and preferably over approx. 5%, but below approx. 50%, and usually from approx.

10-approx. 35% by weight, calculated as metal, where the basis is total nickel calculated as metal and other transition metal calculated as metal in the surface. Usually, the amount of other transition metal in the surface is large enough to have

a hydrogen overvoltage lowering effect, but low enough to avoid the high overvoltage identified with porous surfaces that are mainly other transition metal,

e.g. titanium, tantalum, zirconium or molybdenum.

While the mechanism for the hydrogen surge- . lowering effect of the other transition metal is not clearly understood, it is known that porous films of e.g. molybdenum alone are high in hydrogen overvoltage, but that a low hydrogen overvoltage over extended periods of electrolysis can be observed, when another transition metal as described above, e.g., molybdenum, is used together with pqrøa nickel. When it comes to molybdenum, it is assumed that molybdenum will depolarize or catalyze a step in the hydrogen evolution process. For this reason, the upper limit for the second transition metal is below the concentration where the surface has hydrogen overvoltage properties of the second transition metal, i.e. below approx. 50% and usually below approx. J>5% •

The second transition metal itself may be present as elemental metal, i.e. as elemental molybdenum, titanium,

■tantalum, zirconium or tungsten with a formal valence of

0 or as an alloy with nickel or an alkali-resistant compound, such as a carbide, nitride, boride, sulfide, phosphide, oxide, or other compound insoluble in concentrated alkali metal hydroxide. Preferably, the second transition metal present in the surface 43 is nickel as elemental metal, or an alloy with nickel or a carbide.

A particularly prominent cathode 43 according to the invention is one which has a porous surface 43 of nickel and molybdenum, which contains approx. 82% nickel by weight and approx.

18% by weight molybdenum, where the basis is total nickel and molybdenum

and which has a porosity of approx. 0.7 and a thickness of approx. 75-approx. 500 micrometers.

According to another embodiment of the method according to the invention, the cathode is produced by applying a film of nickel, the other transition metal and a leaching

bare material, on the permionic membrane 33 and then wash out the leachable material.

The leachable material can be any metal or compound that can be co-applied with nickel and the other transition metal. or with nickel compounds and compounds of the other transition metal,

and is washed out using a strong acid or a strong base without washing out significant amounts of nickel and the other transition metal and causing significant degradation, or poisoning of the nickel or the other transition metal

metal.

The film can be applied to the permionic membrane 33 by electro-application of nickel, the other transition metal, and a washable material or by simultaneous application of solid particles, or by chemical application, e.g. in case of hypophosphite-. application or by borohydride application of nickel compounds, compounds of the other transition metal and leachable materials, or even by application and thermal decomposition of organic compounds of nickel, the other transition metal and leachable materials, e.g. application and thermal decomposition of alcoholates or, resinates.

According to a particularly preferred embodiment of the method for producing the electrode according to the invention, fine particles are introduced, e.g. in the order of 0.5-70 micrometers in diameter, of nickel, the other transition metal or a compound thereof<p>g a leachable material in a partially polymerized, permionic membrane 33, after which the polymerization is terminated, with leaching of the leachable materials either before or.after polymerization. Alternative particles can be lowered into a heated, thermoplastic, permionic membrane 33-

The leachable materials may be present in the particle with nickel or as separate particles.

Typical leachable compounds include copper, zinc, gallium, aluminium, tin, silicon and the like. Particularly preferred are nickel particles containing from 30-70% nickel, the remainder being aluminum such as Raney alloy.

After completion of the polymerization of the partially polymerized membrane 33, or cooling of the heated, thermoplastic membrane 33, the particles 43 can be washed out, e.g. in alkali, such as 0.5 normal caustic

.soda. or 1 normal caustic soda, to remove the washable material, e.g. aluminium, then rinse with water. It is of course understood that some of the leachable material can remain in the porous electrode surface 43 without adverse effect. Thus, e.g. when it comes to Raney-nickel-aluminum alloy and

molybdenum which has been introduced into the membrane 33, the surface 43 may contain nickel, molybdenum and aluminum after leaching - the resulting surface may e.g. contain amorphous nickel, crystalline molybdenum, nickel-aluminium alloys and traces of aluminum oxide.

In the electrolysis of alkali metal chloride brine, such as potassium chloride and sodium chloride brine in an electrolytic cell with solid polymer, and especially one which has a permionic membrane of the carboxylic acid type 33, the purity of the brine is of particular importance. The content of transition metals in the sheets should be less than 40 parts per million, and preferably

less than 20 parts per million, to avoid damage to it

permionic membrane 33- pH in the bed 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 sheet should be substantially free of organic compounds, especially when chlorine is to be removed directly from the cell as a liquid and used in a further process, e.g. an organic synthesis process such as the production of vinyl chloride without further treatment. The lacquer treatment can be carried out using different methods to achieve the desired purity. E.g. can phosphate precipitation be used to remove calcium e.g. such as calcium apatite or calcium fluorapatite. In addition, ion exchange resin can be used to clean the sheet.

Preferably, the ion exchange resin is a chelated ion exchange resin. In this way, the multivalent functionality will remove multivalent metal impurities,

e.g. jpr alkali metal ions and transition metal ions.

The water supplied to the catholyte chamber 45 should be largely free of carbon dioxide and carbonates to prevent the formation and precipitation of carbonate on the permionic membrane 33. Preferably, the supply is deionised water..

The charging or regeneration of the ion exchange resin is critical. Regeneration using non-oxidizing acid should remove almost all multivalent cations. This can be achieved by e.g. to use 10-2 column volumes of Q.5-5 normal hydrochloric acid, and preferably 10-20 or more column volumes of .2-3 normal hydrochloric acid as regeneration liquid.

Diluted mineral acids, e.g. from 0.1-10 normal, and preferably from approx. 0.5-5 normal, used as regenerating agents. Non-oxidizing acids are preferred to avoid damage to the resin. Suitable acids include hydrogen halides and especially hydrochloric acid.

The strength of the acid should be strong enough to draw cations from the resin, ie above approx. 0.1 normal, and preferably above 0.5 normal, but low enough to avoid dehydration of the membrane, ie below approx. 10 normal. In this way one can get a lackey. that contain less than 20 parts per million transition metals and less than 20 parts per billion alkaline earth metals.

During the operation of the cell, a short residence time in the anolyte chamber 39 for drawing off the bed of from 10 to approx. 15% make it possible to use iake as a coolant and prevent concentration polarization. Higher lake utilization_ e.g. 30, 40 and even 50, 60 or 70% can be used.

The temperature in the cell can be above 9°c, and especially when the bed : has a low pH to reduce chloride hydrate formationsT. Optionally, the temperature in the cell can be kept below 9°C in order to

increase chloral hydrate formation and allow recovery of a slurry of brine and chloral hydrate.

The cell temperature should be sufficiently low

so that when liquid chlorine is removed from a pressurized cell, the pressure is which is necessary to keep the chlorine liquid,

low enough to allow conventional concentration methods rather than high pressure methods. Pressure-temperature data for liquid chlorine are reproduced in Table I.

When the electrolyser is operated to recover liquid chlorine, the pressure should be high enough to keep the chlorine liquid. In this way, liquid chlorine and used brine can be recycled together,

liquid chlorine is separated from the sheet, the sheet is then cooled to convert any chlorine in it into chlorine hydrate which is separated from the sheet, and the sheet, fortified with regard to salt, is cleaned again and returned to the cell, while the chlorine hydrate which is separated from it is heated to form chlorine.

The pressure in the electrolyser should be high enough to allow gaseous nitrogen and oxygen to be blown off the cell and cell equipment, without significant amounts of liquid chlorine evaporating. When liquid chlorine is to be produced, the temperature in the cell should be below 100°C to keep the concentration pressure in the electrolyser below 42 kg/cm pressure. Preferably, the temperature in the cell should be below 50°C, for

to allow concentration pressure in the cell of less than 14 kg/cm . However, the desired temperature and pressure in the cell may depend on the final use of liquid chlorine and the required vapor pressure and temperature in the liquid chlorine. For practical reasons, the pressure in the cell is more dependent on the pressure in the surrounding parts and the final use of chlorine than on the structural components of the cell.

High pressure is generally preferred on the catholytic side 45 of the individual electrolytic cell 11, where the cathodic reaction is depolarized,

as high pressure serves to force depolarizing agent into the catalyst 4.3 and disproportionate H02.

When the electrolyser 1 is used at sufficiently high pressure so that liquid chlorine can be formed in the anolyte chamber 37, chlorine and used brine can be removed from the electrolyser liquids. Liquid chlorine is relatively miscible with brine at the current pressures. For this reason, liquid chlorine can be easily separated from the sheet, e.g. by centrifugation, filtration or other viscosity, surges

or density-dependent means.

The separated liquid chlorine can then be stored or used as a liquid without further liquefaction. flow-

final chlorine, however, makes up 2-5 - mol% of the liquids handled in the anolyte chamber. Although most of the chlorine will be recovered and excreted as a largely clean liquid, some will dissolve in the bed linen. Chlorine in the sheet can be recovered by cooling the sheet to 90°C, e.g. upon cooling by evaporating liquid chlorine, thereby converting soluble chlorine in the sheet into chlorine hydrate. Chlorine hydrate, a yellow, crystalline material, can be separated from the used sheet and, for example, heated so that chlorine is formed.

During 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 surface. 41 of the permionic membrane 33, is performed using ultra-sonic vibration on the permionic membrane 33 or using pulsating current. When the pulsating current is used, it can be pulsating direct voltage, rectified alternating current or rectified half-wave alternating current. Particularly preferred is pulsed direct voltage with a frequency

on from 10-approx. 40 cycles per second, and preferably from

about. 20-approx. 30 cycles per second.

The catholytic fluid recovered from

the cell will usually contain in excess of 20% by weight of alkali metal hydroxide. When, as in a preferred embodiment, the permionic membrane 33 is a carboxylic acid membrane, as described above, the catholytic liquid may contain in excess of 30-35%, e.g. 40 or even 45 or more wt% alkali metal hydroxide.

The current density in the electrolytic cell with solid polymer electrolyte 11 can be higher than in a conventional permionic membrane or diaphragm cell,

e.g. of more than 0.22 ampere per cm 2, and preferably of more than 0.44 amperes per cm. According to a preferred embodiment of the invention, electrolysis can be carried out with a current density of 0.88 or even 1.32 amperes per cm<2>, where the current density is defined as total current that pass-

ers through the cell divided by the surface area on one side of the permionic membrane 33-

According to a particularly preferred embodiment of the Freiri process according to the invention, the cathode is depolarized to eliminate the formation of gaseous, cathodic products - When operating with a depolarized cathode, oxidizing agent is added to the cathode surface 41 of the solid polymer electrolyte 31 while providing a suitable catalyst 43 in contact with the cathodic surface 41 of the solid polymer electrolyte 31 to avoid the development of gaseous hydrogen. In this way, the development of gaseous products can largely be avoided when the electrolyser 1 and the electrolytic cell 11 are kept at a high pressure as described above, and problems associated with this can also be avoided.

In the process of producing alkali metal hydroxide and chlorine by electrolyzing an alkali metal chloride brine, such as an aqueous solution of sodium chloride or potassium chloride, the alkali metal chloride solution is supplied to the cell, a voltage is applied to the cell, chlorine is evolved at the anode, alkali metal hydroxide is produced in the electrolyte

in contact with the cathode, and hydrogen may be evolved, on the cathode. The general anode reaction is:

while the general cathodic reaction is:

More specifically, the cathode reaction can be expressed as: where monatomic hydrogen is absorbed on the surface of the cathode. In basic media, the absorbed hydrogen is desorbed in one of two alternative processes:

The hydrogen desorption step, i.e. reaction 4 or reaction 5> is believed to be the step that determines hydrogen overvoltage; That is that it is the rate-controlling step and the activation energy corresponds to the cathodic hydrogen overvoltage. The cathode voltage for the hydrogen evolution reaction 2 is of the order of 1.5-1.6 volts against a saturated calomel electrode (SCE) on iron in basic media, where the hydrogen overvoltage component is. from 0.4-0.5 volts.

One method of reducing the cathode voltage is to provide a substitution reaction for the evolution of gaseous hydrogen, i.e. to provide a reaction where a liquid product is formed rather than gaseous hydrogen. Thus, water can be formed when an oxidizing agent is supplied to the cathode. The oxidizing agent can be a gaseous oxidizing agent, such as oxygen, air or the like. Optionally, the oxidizing agent can be a liquid, oxidizing agent, such as hydrogen peroxide, a hydroperoxide, hydrogen peroxide and a peroxy acid or the like.

When the oxidizing agent is oxygen, e.g. air or gaseous oxygen, the following reaction is assumed to take place at the cathode:

This reaction is believed to be an electron-transfer reaction: followed by a surface reaction:

It is assumed that the predominant reaction on a hydrophobic surface is reaction J, while reaction 8 takes place on the surface of the catalyst particles 43 dispersed in and through the cathode surface 41 of the solid polymer electrolyte 33.

Such catalyst particles include particles of electrocatalysts as described below. In this way, the desorption step with high hydrogen overvoltage is eliminated.

When the oxidizing agent is a peroxy compound, it is assumed that the following reaction takes place at the cathode:

It is assumed that this reaction is an electron transfer reaction followed by a surface reaction.

Suitable organic oxidizing agents are organic compounds containing a reducible peroxy bond, C-0-0-. Suitable oxidizing agents include organic peroxides, organic hydroperoxides and organic peracids, also referred to as peroxyacids. A preferred group of organic oxidizing agents are organic hydroperoxides. Particularly prominent organic oxidizing agents are organic hydroperoxides that give alcohols that are soluble in water.

in all proportions, those hydroperoxides which give alcohols which have limited solubility in water and those hydroperoxides which have alcohols which are poorly soluble in water. E.g. particularly prominent hydroperoxides are methyl hydroperoxide which gives methyl alcohol, ethyl hydroperoxide which gives ethyl alcohol, n-propyl hydroperoxide which gives n-propyl alcohol, i-propyl hydroperoxide which gives i-propyl alcohol and t-butyl hydroperoxide which gives t-butyl alcohol. Also useful for the method according to the invention are those hydroperoxides which give alcohols with limited solubility in water, so

such as n-butyl hydroperoxide which gives n-butyl alcohol, sec-butyl hydroperoxide which gives sec-butyl alcohol, i-butyl hydroperoxide which gives i-butyl alcohol and t-pentyl hydroperoxide which gives t-pentyl alcohol. Optionally, these hydroperoxides can be used which give as cathodic reduction products, poorly

soluble alcohols, such as n-pentyl hydroperoxide which gives n-pentyl alcohol, i-pentyl hydroperoxides which give i-pentyl alcohols, s-pentyl hydroperoxides which give s-pentyl alcohols and neopentyl hydroperoxide which gives. ne.opentyl alcohol as cathodic reduction products. Also useful are cumene hydroperoxide which gives cumyl alcohol and ethylbenzene hydroperoxide which gives methyl-phenylcarbinol.

Another group of hydroperoxides which are useful in carrying out the method according to the invention are dihydroperoxides. Dihydroperoxides give glycols as a reaction product when they are added to the catalytic chamber in an electrolytic cell considered here. The preferred dihydroperoxides are those which are completely miscible in water and those which are at least partially soluble in water.

The preferred dihydroperoxides are dihydroperoxides of <C>^<-C>^q alkyls with dihydroperoxides of cg"C]-Q alkyls being particularly preferred. Such dihydroperoxides include hexane dihydroperoxide, heptane dihydroperoxide, octane dihydroperoxide, nonane dihydroperoxide and decane dihydroperoxide.

While alcohols, ketones, aldehydes and glycols are mentioned here, it is possible that they are only formed as intermediates and that they are reacted further such as by dehydration to olefins and ethers or by reaction with other additives such as organic acids to esters and alkali metal salts of alcohols.

When the intermediate product is an alcohol, the alcohol can be converted further into ethers. The alcohol can be separated from the cell fluid and further reacted to form the ether, e.g.

by reaction with an alkylating agent, e.g. an alkyl sulfate. When the organic, oxidizing agent, thus

is tertiary butyl hydroperoxide, the intermediate recovered from the catholyte chamber is tertiary butyl alcohol. The tertiary butyl alcohol can be removed from the cell, separated from the cell fluid, e.g. by distillation, and is reacted with, for example, methyl sulphate to methyl tertiary butyl ether. Methyl tertiary butyl ether can be used as an additive to fuel for motor vehicles.

Particularly desirable hydroperoxides are those which give alcohols which are soluble in water in all proportions and which are useful in various industrial processes or, for example, t-butyl hydroperoxide which gives t-butyl alcohol as a cathodic reduction product, where t-butyl alcohol can be used as an anti - knocking agent in motor vehicles..

Dialkyl peroxides with the formula R-^OOR^, where R^

and R2kan. be -CH^, -C^, ~ cj>^, ~ ci^ E9> ~ CH2CH = CH2

or another dialkyl peroxide which. is soluble in water or soluble in organic solvents, can be used according to the method according to the invention. In addition to dialkyl peroxides, polyoxides with the formula Ri0nR2'nvor. n is 3 or 4 is used in the method according to the invention,

and likewise cycloperoxides with the formula R^ 0 - 0. R2-Peroxyacids, which are also called peracids, with the formula R(CO 3 H), where R can be -H, --CH^,. -CHgCl, -CgH,

-(n-C-jH^), -(i-C^H^), ■-.-n-C^H^^) and other' peracids which

are soluble in water or soluble in organic solvents, can be used in the invention. Acyl peroxides and other peroxy acid precursors can also be used in the method according to the invention. In addition, aryl diperoxy acids can be used in the method according to the invention.

Although the method according to the invention is described with regard to organic, oxidizing agents, so

such as organic peroxides, organic hydroperoxides (with

the general formula R - 0 - 0 - H) and organic peroxyacids (with the general formula RCO^H), it is understood that various derivatives of organic oxidizing agents can also be used. E.g. can the method according to the invention be used with salts of organic, oxidizing agents, e.g. salts of organic hydroperoxides (with the formula R - 0 - 0 - M) and salts of organic peroxyacids (with the formula RCI-^M), where M is a cationic group selected from the group consisting of alkali metals, alkaline earth metals and the ammonium radical. Of the alkali metals lithium, sodium,

. potassium, rubidium and cesium, will usually be alkali metals.

be sodium or potassium. Of the alkaline metals beryllium,

magnesium, calcium, strontium and barium, the alkaline earth metal will usually be magnesium or calcium. When the catholytic liquid is an aqueous alkali metal hydroxide, MOH, the organic oxidizing agent is usually present either in hydrogen form (e.g. R - 0 0 - H, R - 0 - 0 - R, RCO^H) or in

form of alkali metal salt (e.g. R - 0 - 0 M, RCO^M), where M is the same alkali metal in the hydroxide and in the organic oxidizing agent..

When, according to the method according to the invention, organic peroxy oxidizing agents are used, the cathode reaction products of the oxidizing agent are recovered from the catholyte chamber 45 together with the cell fluid. The cathodic reduction products of the oxidizing agent can be partially or completely gases or vapors, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol or t-butyl alcohol. Optionally, the products can be liquids recovered from the cell fluid, 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-butyl alcohol, n- pentyl alcohol, i-pentyl alcohol or amyl alcohol or the cathodic product can be emulsions or suspensions of excess amounts of poorly soluble alcohols, such as sec-butyl alcohol, i-butyl alcohol, n-butyl alcohol, t-butyl alcohol, n-pentyl alcohol, i- pentyl alcohol or amyl alcohol. When the cathodic reduction product of the oxidizing agent is recovered either as a gas or both as a gas and as a liquid, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol or t-butyl alcohol, the cathodic reduction product is separated from both the water vapor and gas -phase and is recovered. Optionally, when the cathodic reduction product of the oxidizing agent is recovered as a liquid, either in solution with water or as a suspension or emulsion in water,., such as methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol , i-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, t-pentyl alcohol, n-pentyl alcohol, i-pentyl alcohol, rieo<p>ent<y>lal<k>ohol or s-pentyl alcohol, .the cathodic reduction product can be separated

from the cell fluid by methods known per se, so

as fractional distillation, extraction, absorption, stripping, ing or phase separation techniques or the like and recovered

According to a method according to the invention, tertiary butyl alcohol is produced during the electrolysis of sodium chloride brine. In this embodiment, the sodium chloride solution is supplied to the anolyte chamber 39 therein. electrolytic cell 11, tertiary butyl hydroperoxide is supplied to the catholyte chamber. 45 in the cell, and an electric current is passed from the anode 37 in the cell 11 to the cathode 43 in the cell 11, after which chlorine is evolved at the anode and tertiary butyl alcohol and acetone are formed in the catholyte chamber. An aqueous catholyte liquid containing sodium hydroxide, tertiary butyl alcohol, acetone and excess tertiary butyl hydroperoxide is recovered from the catholyte chamber 45 of the cell 11.

An aqueous catholyte cell fluid containing sodium hydroxide, tertiary butyl alcohol, a carbonyl, e.g. acetone, and an excess of tertiary butyl alcohol, probably together with sodium salt, ■ from cell 11. With a tertiary butyl hydroperoxide feed and a tertiary butyl alcohol product, an azeotrope can be formed by evaporation and subsequent recovery and distillation of the cell liquid. This azeotrope contains 11.76% water and 88.24% tertiary butyl alcohol.

In one embodiment of the invention, where an excess of tertiary butyl hydroperoxide is supplied to the cell, the tertiary butyl alcohol is recovered as an azeotrope, the hydroperoxide salt of sodium, e.g. Na<+>[ (CH^^COO-], can

is crystallized from concentrated, aqueous caustic soda solution, e.g. a caustic soda solution containing more

than 40% by weight of caustic soda. This sodium salt of ter-

tertiary butyl hydroperoxide can then be recycled to the catholyte chamber 4 5 in cells 11 and 13•

according to a further method according to the invention, the cell fluid can be supplied to the other cell, e.g.

13, to the catholyte chamber 45 therein, to provide a catholyte liquid which is increased with regard to alkali metal hydroxide content and reduced content of organic oxidizing agent.

The remaining, organic, oxidizing agent can then be further reduced in a subsequent cell or cells, /down. the cell fluid, to produce more by-product, e.g. more ketone, aldehyde, acid, alcohol or glycol and a high strength alkali metal hydroxide solution. In this embodiment, serial flow of cathode liquid, e.g. through a bipolar electrolyzer 1 is used.

According to yet another embodiment of the method according to the invention, the oxidizing agent can be a redox couple, e.g. a reduction-oxidation pair, where the oxidizing agent is reduced inside the cell and then oxidized outside the cell, to be returned to the cell. A suitable redox couple is a copper compound which can be supplied to the cell 11 as a copper. (II) compound, is reduced to a copper (II) compound at the cathode 43 and is recovered from the catholyte chamber 45 as a copper (II) compound. The copper (II) compound can then be oxidized to a copper (III) compound outside the electrolyser 1, and returned to the electrolyser. Suitable copper complexes include chelated copper pairs, such as phthalocyanines.

According to another embodiment of the method according to the invention, where a redox couple is used, the redox couple can be a quinone-hydroquinone redox couple. ■ In this case. quinone is electrolytically reduced to hydroquinone at the cathode 43, hydroquinone is recovered from the catholyte<y>box 45 and oxidized to quinone outside the cell.

According to another embodiment of the method, according to the invention, solid oxygen carriers can be supplied to the catholyte chamber 45 and recovered partially freed of oxygen. These include manganese (II) complexes, transition metal phthalocyanine tetrasulfonate complexes and binuclear copper (II) complexes of 1-phenyl-1,3,5_hexanethiorate.

Cathode catalysts which are useful in performing sen of the method according to the invention, are those who have properties as H02 disproportionation catalysts, i.e. catalysts capable of catalyzing the surface reaction ... _. ■ In addition, the catalyst should either be able to catalyze the electron transfer reaction

or to be used together with such a catalyst. The catalysts considered here should also be chemically resistant to the catholyte liquid.

Satisfactory HO^<->disproportionation catalysts include carbon, Group VIII transition metals, which are iron, cobalt, nickel, ■ palladium, ruthenium, rhodium, platinum, osmium, iridium, and compounds thereof.

In addition, other catalysts, such as copper, lead and oxides of lead can be used. The transition metals can be present as metals, as alloys or as intermetallic compounds. E.g. when nickel is used, this can be formed with Mo, Ta- or Ti. These mixtures serve to maintain a low cathodic voltage over extended electrolysis periods.

Any metal from group III B,

IV B, V B, VI B, VII B, I B', II B. or III A which include alloys or mixtures thereof, where the metal or alloy ■is permanent above the catholyte, can be used

as cathode coating 43 or catalyst. on the surface of the membrane 33.

In addition, solid metalloids, such as phthalocyanines of group VIII metals, perovskites, tungsten bronzes, spinels, delafossites and pyrochlores, among others, can a., is used as catalytic surface 43 on the membrane 33.

Particularly preferred catalysts are platinum group metals, compounds of platinum group metals,

e.g. oxides, carbides, silicides, phosphides and nitrides of these and intermetallic compounds and oxides of.

these, such as rutile form Ru02-Ti02 with semiconductor properties.

According to another aspect of the invention, the cathode electrocatalyst, i.e. the electron transfer catalyst for the reaction

be a boride of a transition metal. The transition metals which give borides with the desired chemical resistance to concentrated, aqueous alkali metal hydroxides: and which have a surface catalytic activity for the aforementioned reaction, are transition metals of groups IVB, VB and VIB in the periodic table. These metals are titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten. Preferred among the transition metals of groups IVB, VB and VIB are those which give borides with higher chemical resistance, e.g. titanium, vanadium, niobium, tantalum, chromium and tungsten. Particularly preferred is titanium diboride, TiB.

2

According to a preferred embodiment of the invention, an intercalation compound of carbon and fluorine can be used as cathodic catalyst 43.

By an intercalation compound of carbon and fluorine is meant a carbonaceous material•which crystallizes in a graphite structure, where the atoms in the layers are approx. 1.41 angstroms apart, while the layers have a greater distance, e.g. at least 3.35 angstroms, and where fluorine atoms are present between the layers. As considered here, the carbon layers in the intercalation compound may be humped as assumed for carbon monofluoride with the empirical formula (CFx), where x is between 0.68 and 0.995 - Optionally, the carbon layers in the intercalation compound may be largely planar, as assumed for tetracarbon monofluoride with the empirical formula (CFx), where x is between 0-, 25 and 0.30. Various intermediate and non-stoichiometric compounds are also considered here.

intercalation compounds of carbon and fluorine are also called fluorinated graphites and graphite fluorides.

They are characterized by an infrared spectrum with an absorption band at 1220 centimeters"1.

Carbon-fluorine intercalation compound catalyst 43 may be fed with an H0 2 ~ disproportionation catalyst.

When a gaseous oxidizing agent, such as air or oxygen, is used, the part of the catalyst that must . is used for electron transfer hydrophilic, while the part to be used for the surface reaction can be hydrophilic or hydrophobic, and preferably hydrophobic. The catalyst for the surface reaction is hydrophobic or introduced into or carried by the hydrophobic film. The hydrophobic film may be a porous hydrophobic material such as graphite or a film of a fluorocarbon polymer on the catalyst. The catalyst for the surface reaction, as described above, and the catalyst for the electron transfer should be close to each other. They can be mixed or they can be different surfaces on the same particle. E.g. a particularly favorable catalyst can be provided by means of a microporous film on the permionic membrane surface 41, where the catalyst 43 is supported by a hydrophobic, microporous film.

According to another embodiment of the method according to the invention, where a depolarized cathode is used, the electrode can be excretory electrodes, i.e. the electrode which excretes oxidizing agent. When using discharge electrodes, the oxidizing agent is distributed through the distributor 51 to the catalytic particles 43 and in this way avoids contact with the catholyte liquid in the catholyte chamber 45. Optionally, the oxidizing agent can be provided with the help of other distribution devices that are available. against the cathodic surface 41

of the permionic membrane 33 or against the catholytic particles 43.

The supply of oxidizing agent can be gaseous, including an excess of air or oxygen. When excess air or oxygen is used, excess air or oxygen serves as a heat exchange medium

to keep the temperature low enough for the vapor pressure to drop

liquid chlorine is kept low. Optionally, one can use several oxidizing agents, such as air and oxygen or air and a peroxy compound or oxygen and a peroxy compound or air or oxygen and a redox couple. When air and oxygen are used as oxidizing agents, it must be mostly free of carbon dioxide to avoid carbonate formation on the cathode.

The use of a horizontal cell is particularly advantageous when using cathode depolarisation. Particularly satisfactory is the arrangement, where the anode surface 35

on the permionic membrane 33 and the anodic catalyst 37 is on the top of the permionic membrane 33 and the cathodic surface 4l and cathode catalyst 43 is on the bottom

of the permionic membrane 33. This prevents the H02 disproportionation catalyst from being flooded with alkali metal hydroxide, while at the same time obtaining a thin film of alkali metal hydroxide on the membrane surface 41 near the cathode surface and increases the contact between the catalyst 43 and the oxidizing agent.

Although the method according to the invention has been described with reference to specific embodiments and examples, the scope of the invention is only limited by the appended claims.

Claims (16)

1. Electrolytic cell with solid polymer electrolyte with a permionic membrane with a cathode that abuts the cathodic surface thereof, characterized in that the cathode comprises a boride of a transition metal, 2. Electrolytic cell according to claim 1, characterized in that the boride is selected from the group consisting of borides of titanium, vanadium, niobium, tantalum, chromium. and tungsten... 3. Electrolytic cell according to claim 2, characterized in that the titanium boride is TiB^ . 4. Process for electrolysis where aqueous alkali metal chloride is supplied to an electrolytic cell with an anolyte chamber which is separated from a catholyte chamber by means of a. solid polymer electrolyte, wherein said solid polymer electrolyte comprises a permionic membrane with an anodic electrocatalyst on the anodic one. first surface thereof and a cathodic catalyst on the cathodic second surface thereof and applying an electrical potential over the solid polymer electrolyte and removes chlorine from the anolyte chamber and alkali metal hydroxide from the catholyte chamber, characterized by maintaining the hydrostatic pressure in the anolyte chamber above the vapor pressure of developed chlorine in order to thereby recover liquid chlorine from the anolyte chamber. 5. Process for electrolysis where aqueous alkali metal chloride brine is supplied to an electrolytic cell with an anolyte chamber separated from a catholyte chamber by means of a solid polymer electrolyte, where said solid polymer electrolyte comprises a permionic membrane of a fluorinated, polymeric carboxylic acid with an anodic electrocatalyst on the anodic surface of this and a cathodic electrocatalyst on the cathodic surface of this and applies an electric potential over the solid polymer electrolyte and removes chlorine from the anolyte chamber and alkali metal hydroxide from the catholyte chamber, characterized by - that therein solid polymer electrolyte is generally positioned horizontally with the anodic electrocatalyst on the top surface thereof and the cathodic electrocatalyst on the bottom surface thereof to conduct evolved chlorine away from the solid polymer electrolyte and provide a thin film of alkali metal hydroxide on the solid polymer electrolyte. 6. Process for electrolysis where an aqueous alkali metal chloride brine is supplied to an electrolytic cell with an anolyte chamber separated from a catholyte chamber by means of a solid polymer electrolyte, where. said solid polymer electrolyte .has an anodic electrocatalyst facing the anolytic chamber and a cathodic electrocatalyst, hydrogen oxidation catalyst facing the catholytic chamber, supplies an oxidizing agent to said catholyte chamber, applies an electrical potential across said polymer electrolyte and removes chlorine from the anolyte chamber . and alkali metal hydroxide- from the catholyte chamber, characterized by that the solid polymer electrolyte is generally placed horizontally with the anodic electrocatalyst on the top surface and the cathodic electrocatalyst on the bottom surface so as to maintain, a film of alkali metal hydroxide on the bottom surface of the solid polymer electrolyte and provides oxidizing agent at the solid polymer electrolyte surface to avoid overflow of the cathodic catalyst. 7. Electrolytic cell with a solid polymer electrolyte. with an anodic electrocatalyst on an anodic first surface thereof and a cathodic electrocatalyst on the opposite, cathodic second surface thereof and means for supplying oxidizing agent to said cathode disk other'surface of the solid polymer electrolyte, and an H02~ disproportionation catalyst in contact with the cathodic other surface of the aforementioned polymeric electrolyte, characterized in that the H02 disproportionation catalyst comprises a porous, electroconductive substrate with a porous, hydrophobic surface on this, where the H02~ disproportionation catalyst is mixed with the cathodic electrocatalyst. 8. Electrolytic cell according to claim 7, characterized in that the H02 disproportionation catalyst comprises a porous carbon substrate with one porous fluorocarbon surface. 9» Process for electrolysis where aqueous alkali metal chloride liquor is added. to.an electrolytic cell with an anolyte chamber separated from a catholyte chamber by means of a solid polymer electrolyte, where said solid polymer electrolyte consists of a fluorinated cation exchange membrane with carboxylic acid groups as ion exchange groups, an anodic electrocatalyst on the anodic surface thereof and a cathodic electrocatalyst on the cathodic surface of this, applies an electrical potential over said polymer electrolyte and carries away chlorine from the anolyte chamber and alkali metal hydroxide from the catholyte chamber, characterized in that moon carries away liquid chlorine and spent liquor from the cell and separates liquid chlorine from the spent liquor. 10. Method according to claim 9, characterized in that chlorine is recovered from the used . Lake. . 11. Method according to claim 10, characterized in that the spent brine is cooled to form chlorine hydrate and chlorine hydrate is separated from the brine. 12. Method according to claim 11, characterized in that the used brine is cooled to below 9°C to form chlorine hydrate. 13. Electrolytic cell with a solid polymer electrolyte consisting of a permionic membrane, an anodic electrocatalyst facing an anodic first surface, of the permionic membrane and a cathodic catalyst on a cathodic other surface of the permionic membrane, characterized in that said cathodic' electrocatalyst comprises, a first transition metal from group VIII. 14. Electrolytic cell according to claim 13, characterized in that. said cathodic electrocatalyst has a surface area of at least 10 m 2 /g. 15.. Electrolytic cell according to claim 13, characterized in that said cathodic electrocatalyst further comprises a transition metal selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, molybdenum and tungsten. 16. Electrolytic cell according to claim 15, characterized in that the second transition metal is molybdenum.