SE440921B - Electrolysis procedure - Google Patents

Abstract

In this is described an electrolytic cell with an electrolyte in the form of a solid polymer, in which the cell presents a permionic carboxy-acid membrane arranged between the anolyte and the catolyte. The cathode can be a depolarised cathode, e.g. one with a peroxide compound depolarised cathode, one with a redox pair depolarised cathode or one with an oxidant-complex depolarised cathode. The cathode can be a boride, e.g. titanium diboride, an intercalation compound of carbon and fluorine or a transition metal, e.g. iron, cobalt or nickel. Electrocatalysts, e.g. anode and cathode, can be brought to adhere to the permionic membrane through chemical deposition. The anode can be in the form of a particle with hydrophobic material. The individual anode particles can be silicon extended. The electrolysis procedure can be carried out at high pressure, whereby one obtains liquid chlorine, which is thereafter separated from the salt solution. The cell can be horizontal and be provided with an inner heat exchanging organ. In the case of a bi-polar cell, the bi-polar conductor element can be made of silicon or a titanium alloy as well as having a heat conducting and reagent supply organ incorporated therein.<IMAGE>

Description

Electrolyte, 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, whereby chlorine develops at the anode surface of the solid polymer electrolyte.

Alkali metal ion, i.e. sodium ion or potassium ion, is transported across the permionic membrane of solid polymer electrolyte to the cathodic hydroxyl evolution catalyst on the opposite surface of the permionic membrane. The alkali metal ion, ie the sodium ion or the potassium ion, is transported with its hydrated water but practically without any transport of bulk electrolyte.

Hydroxyl ion develops at the cathodic hydroxyl ion evolution catalyst, which also applies to hydrogen. In an alternative embodiment, however, a cathodic depolarization catalyst, i.e. an HO 2 'disproportionation catalyst, is present in the vicinity of the cathodic surface of the permionic membrane, and an oxidant is fed to the catholyte compartment to avoid the formation of gaseous cathodic products.

The invention will now be elucidated in more detail in connection with the accompanying drawings, for which: Fig. 1 is an exploded view of a bipolar electrolyzer with phase polymer electrolyte.

Fig. 2 is a perspective view of a solid polymer electrolyte unit in the bipolar electrolyzer shown in Fig. 1.

Fig. 3 is a cross-sectional view of the solid polymer electrolyte unit of Fig. 2.

Fig. 4 is a cross-sectional view, on a larger magnification, of the solid polymer electrolyte sheet shown in the unit of Figs. 2 and 3.

Fig. 5 is a perspective view of the distribution device showing a form of electrolyte supply and discharge. Fig. 6 is a cross-sectional view of the distribution device shown in Fig. 5.

Fig. 7 is a perspective view of a variant of the bipolar element shown in Fig. 1.

Fig. 8 is a cross-sectional view of the bipolar element shown in Fig. 7.

Fig. 9 is a perspective view of an alternative variant of a bipolar element, through which heat exchange means pass.

Fig. 10 is a sectional view of the bipolar element shown in Fig. 9. Fig. 11 is a perspective view of an alternative embodiment of a bipolar element, where distribution means are combined with the bipolar element.

Fig. 12 is a sectional view of the bipolar element shown in Fig. 11.

Fig. 13 is a schematic cross-sectional side view of the electrolytic cell with solid polymer electrolyte.

Fig. 14 is a schematic view of the chlor-alkali process using a solid polymer electrolyte.

The chlor-alkali cell schematically shown in Fig. 14 has an electrolyte 31 in the form of a solid polymer with a permionic membrane 33 therein. The permionic membrane 33 has an anodic surface 35 with chlorine catalyst 37 thereon and a cathodic surface 41 with cathodic hydroxyl evolution catalyst Ä3 thereon. Furthermore, an external current source is shown, which is connected to the anodic catalyst 37 via the distribution device 57 and connected to the cathodic catalyst 43 via the distribution device 55.

Saline is fed to the anode 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. The chlorine, which is present as the chloride ion in the solution, forms chlorine according to the reaction: 2c1 '__; C12 + 2e 'The alkali metal ion, ie sodium ion or potassium ion, which is shown in Fig. 14 as sodium ion, and its hydrated water, passes through the permionic membrane 33 to the cathode side 41 of the permeable membrane 33. Water is led to the catholyte compartment both externally and as hydrated water , which passes through the permionic membrane 31. The stoichiometric reaction of the cathodic hydroxyl evolution catalyst is: H 2 O + e '-_> OH' + H According to an alternative variant, a cathode depolarization catalyst and an oxidant are present, thereby avoiding the formation of gaseous hydrogen.

The structure or structure for effecting this reaction is generally shown in Fig. 13, where an electrolytic cell II is shown with walls 21 and a permionic membrane 33 therebetween.

The permionic membrane 33 has an anodic surface 35 and an anodic electrocatalyst 37 on the anodic surface 35 and a cathodic surface 41 with cathodic electrocatalyst 43 thereon. According to an alternative variant, there is a cathode depolarization catalyst. that is, a HO 2 'disproportionation catalyst (not shown), in the vicinity of the cathodic surface 41 of the membrane 33, thereby avoiding evolution of hydrogen gas.

Means for conducting electric current from the walls 21 to the solid polymer electrolyte 31 are shown as distribution device 5? in the anolytic compartment 39, which device conducts current from the wall 21 to the anodic chlorine evolution catalyst 37, and a distribution device 55 in the catholytic compartment 45, which device conducts current from the wall 21 to the cathodic hydroxyl evolution catalyst 43.

According to a preferred variant, the distribution devices 55 and 57 also give turbulence and mixing of resp. electrolytes. This avoids concentration polarization, gas-bubble effects, stagnation and dead space.

During operation of the cell, saline is passed to the anolyte compartment 39 through the saline inlet 81a, and depleted saline is discharged from the anolyte compartment 39 through the saline outlet 81b.

The anolyte liquid containing liquid chlorine and liquid brine is removed. Water is led to the catholyte compartment 45 through water supply means 10la so that the alkali metal hydroxide liquid is maintained, thereby avoiding the deposition of solid alkali metal hydroxide on the membrane 33. In addition, oxidant can be passed to the catalyst compartment 45, e.g. when an H 2 O 2 disproportionation catalyst is present, thereby avoiding the formation of hydrogen gas and thereby being able to remove a completely liquid cathode product.

A particularly desirable cell structure is a bipolar electrolyzer in which an electrolyte in the form of a solid polymer is used. Fig. 1 is an exploded view of a bipolar electrolyzer with an electrolyte in the form of a solid polymer. The electrolyzer is shown with two electrolytic cells 11 and 13 with solid polymer. However, there may be many more such cells in the electrolyser 1. The limitation on the number of cells, l1 and 13, in the electrolyser 1 depends on the rectifier and transformer capacity and on the possibility of current leakage. Electrolysers containing upwards of 150 or 1: .¿> .m-. however, zoo or more cells are possible in this art using fine; available rectifier and transformer technology. A single electrolytic cell 11 contains a solid polymer electrolyte unit 31, which is shown as part of the electrolyzer in Fig. 1, individually in Fig. 2, in partial section in Fig. 3 and with a larger magnification in Fig. 4 with the catalyst particles 37 and 43 exaggerated. The solid polymer electrolyte unit 31 is also shown schematically in FIG. 13 and 14.

The solid polymer electrolyte unit 31 comprises a permionic membrane 33 with anodic chlorine evolution catalyst 37 on the anode surface 35 of the permionic membrane 33 and cathodic hydroxyl evolution catalyst 43 on the cathode surface 41 of the permionic membrane 33.

The cell boundaries for an intermediate cell in the electrolyser 1 can consist of a pair of bipolar units 21, which are also called bipolar support plates. In the case of the first and last cells of the electrolyser, such as cells 11 and 13 shown in Fig. 1, a bipolar unit 21 is one boundary of the individual electrolytic cell, while the end plate 71 is the opposite boundary of the electrolytic cell. The end plate 71 has inlet means 8la for supplying saline solution, outlet means 8lb for removing saline solution, inlet means 10a for supplying water and means 10b for removing hydroxyl solution. When the cathode is depolarized, the supply of oxidant is also used, which, however, is not shown in the present case. The end plate 71 also includes current conductor 79.

In the case of monopolar cell, the end units would be a pair of end plates 71 as described above. The end plate 71 and the bipolar units 21 make the individual cells gas-tight and electrolyte-tight. In addition, the end plate 71 and the bipolar units 21 provide electrical conductivity and in various embodiments electrolyte supply and gas recovery.

The bipolar unit 21 shown in Figs. 7 and 8 has an anolyte-resistant surface 23 facing the anodic surface 35 and the anodic catalyst 37 in a cell II. The anolyte-resistant surface 35 contacts the anolyte liquid and forms the boundary of the anolyte compartment 39 of the cell. The bipolar unit 21 also has a catholyte-resistant surface 25 facing the cathode surface 41 and the cathode catalyst 43 in the solid polymer electrolyte 31 in the immediately following cell 13 in the electrolyzer. l.

The anolyte-resistant surface 23 may be made of an anodic oxide-film-forming metal, i.e., a metal which forms an acid-resistant oxide film when exposed to aqueous acidic solutions. The anodic oxide film-forming metals include titanium, tantalum, tungsten, niobium, hafnium and zirconium, as well as alloys of titanium, such as titanium with yttrium, titanium with palladium, titanium with molybdenum and titanium with nickel. Alt. the anolyte-resistant surface may be made of silicon or a silicide.

The bipolar unit 21 may be made of two sheets, plates or laminates, 23 and 25. The surface 23 facing the anolyte may be made of an anodic oxide film-forming metal, as described above. According to one embodiment, however, the anolyte-facing surface 23 of the bipolar unit 21 is made of an alloy of an anodic oxide film-forming metal, which is characterized by improved resistance to hydride formation and crevice corrosion.

An especially preferred group of such alloys are alloys of titanium and one or more rare earth metals.

Intended rare earth metals include scandium, yttrium and lanthanides. The lanthanides are lanthanum, cerium, praseodymium neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. Thus, when the term "rare earth metals" is used in the present case, it is intended to include scandium, yttrium and lanthanides.

The alloying element for the rare earth metal may be one or more rare earth metals. For example, it may be scandium or yttrium or cerium or lanthanum or lanthanum and yttrium or lanthanum and cerium. Usually, the alloying additive to the rare earth metal is yttrium.

The amount of rare earth metal alloying substance should be at least a threshold amount sufficient to reduce or even dominate the uptake of hydrogen by the titanium. This is usually at least about 0.01% by weight, although smaller amounts have positive effects. The maximum amount of rare earth metal alloying substance should be low enough to essentially avoid the formation of a two-phase system. In general, it is less than about 2% by weight of rare earth metal for the rare earth metals yttrium, lanthanum, cerium, gadolinium and erbium, although amounts up to about 4 or even 5% by weight of this can be tolerated without adverse effects, and less than about 7% by weight of rare earth metal for the rare earth metals scandium and europium, although amounts up to 10% by weight can be tolerated without harmful effects, mäng iëïïë fi ï 10 15 20 25 50 55 40 8001377-4 . In general, the amount of rare earth metal is from about 0.01 to about 1 weight percent and preferably from about 0.015 to about 0.05 weight percent.

The titanium alloy can also contain various impurities without harmful effect. These pollutants include iron in amounts that are normally above about 0.01% or even 0.1% and often as high as 1%, vanadium and tantalum in amounts up to about 0.1% or even 1%, oxygen in amounts up to about 0.1% by weight and carbon in amounts up to about 0.1% by weight. d Alt. the anolyte-facing surface 23 of the bipolar moiety may be an isomorphic beta-phase alloy of titanium with molybdenum or an isomorphic alloy of titanium with other transition metal, such as palladium, nickel and iron, e.g. when the iron content is less than 0.015% by weight. Isomorphic alloys of titanium and the above transition metals provide improved resistance to crevice corrosion and hydrogen uptake. The amount of the transition metal, ie iron, nickel, palladium or molybdenum, should be high enough to improve the resistance to crevice corrosion as well as the resistance to hydrogen uptake but low enough to avoid the formation of a second phase.

The catholyte-resistant surface 25 can be made of any material which is resistant to conc. caustic solutions containing either oxygen or hydrogen or both. Such materials include iron, steel, stainless steel and the like.

The two members 23 and 25 of the bipolar unit 21 may be sheets of titanium and iron or sheets of the other of the above materials, and in addition there may be a hydrogen barrier arranged between the anode surface 25 and the cathode surface 25, thereby avoiding transport. of hydrogen through the cathode surface 25 in a bipolar unit to the anode surface 23 in the bipolar unit.

The hydrogen barrier or hydrogen barrier layer, which is arranged (arranged) between the anode surface 25 and the cathode surface 25 in the bipolar unit 21, is a material which impedes 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 suites, organic resins and paints. Alt. metals with hydrogen barrier properties 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. The best hydrogen barrier result is obtained when the hydrogen barrier coating is molybdenum, rhodium, iridium, silver, gold, manganese, zinc, cadmium, lead, copper or tungsten. Especially preferred are copper.

The hydrogen barrier can be a sheet or a plate. Alt. it may be a deposited film or coating. According to yet another embodiment, the hydrogen barrier may be detonation plated on one or both members of the bipolar unit 21.

According to an alternative variant shown in fia. 9 and 10, heat exchanger lines 121 pass through the bipolar unit 21.

These heat exchange lines 121 transport cold liquid or cold gas for extraction of heat from the electrolyzer, e.g. I2R-generated heat as well as reaction heat. This enables the use of a lower pressure when the electrolyser is under pressure, such as when liquid chlorine is the desired product or when oxygen is supplied under pressure, or both.

According to yet another variant of the bipolar solid polymer electrolyte electrolyzer, which embodiment is shown in Figs. 11 and 12, the bipolar unit 21 performs electrolyte supply and distribution function. Thus, in addition to or instead of the distribution device 51, the conduit 133 extends from the tube 11a to the interior of the bipolar unit 21 and then to a porous or open element 131, which distributes the electrolyte.

Analogously to the opposite electrolyte, supply is made through tubes 143 to a porous or open surface 141 on the opposite surface of the bipolar unit.

The individual electrolysis cells 11 and 13 in the bipolar electrolyzer 1 also comprise distribution means 51, which may be arranged or arranged between the ends of the cell, i.e. between the bipolar unit 21 or the end wall 71 and the solid polymer electrolyte 31. This distribution means is shown in fig. 1 and individually in Figs. 5 and 6 with the catholyte liquid lines 105a and 105b and the catholyte supply 11a and the catholyte outlet 11b.

The peripheral wall 53 of the distributor 51 is shown as a circular ring. It makes the electrolyzer 1 as well as the cells 11 and 13 electrolyte-tight and gas-tight.

The gasket, which may be caustic resistant or sodium hydroxide resistant, such as gasket 55, or resistant to acidified chlorinated brine and chlorine, such as gasket 57, is preferably elastic or recurrent, conductive and substantially non-catalytic. This means that the gasket 55 of the catholyte unit in the catholyte compartment 45 has a higher hydrogen evolution or hydroxyl ion evolution overvoltage than the cathode catalyst 43, thereby avoiding electrolytic evolution of cathode product thereon. Similarly, the gasket 57 in the anolyte compartment 59 has higher chlorine evolution overvoltage and higher oxygen evolution overvoltage than the anode catalyst 57, thereby avoiding the development of chlorine or oxygen thereon.

Gaskets 55 and 57 help conduct current from the boundary of the cell, such as the bipolar unit 21 or end plate 71, to the solid polymer electrolyte 51. This necessitates high electrical conductivity. This power line is made at the same time as product development is avoided thereon, as has been described above. Similarly, the material must have a minimum of contact resistance at the solid polymer electrolyte 51 and at the boundaries of the individual cell 11, e.g. the end wall 71 or the bipolar unit 21.

Furthermore, the distribution gasket 55, 57 distributes and diffuses the electrolyte in the anolyte compartment 59 or the catholyte compartment 45, thereby avoiding concentration polarization, building up of stationary gas and liquid pockets and building up solid deposits, such as potassium hydroxide or sodium hydroxide deposits.

The gasket 55, 57 may be carbon, e.g. in the form of graphite, carbon felt, carbon fibers, porous graphite, activated carbon or the like.

Alt. the gasket may be a metal blanket, a metal fiber, a metal sponge, metal grid, graphite grid, metal mesh, graphite mesh or clamps or springs or the like, such clamps or springs abutting the solid polymer electrolyte and the bipolar unit 21 in the end plate 71.

According to yet another variant, the current conductor and the current distribution means 51, which provide electrical contact between the cell walls 21,71, and the solid polymer electrolyte 51, may be a sheet of fine wire mesh or mesh resting on the catalyst 37,33, and electrically and mechanically in series with the cell's 11 end walls 21.71. The electrical and mechanical connecting means may be constituted by first and second resilient metal means, the first resilient metal means abutting the catalyst 37,33, and the second resilient metal member abutting the end wall 21,71 of the cell. The two resilient metal members are removably connected. This means they can POOR QUALITY. The distribution means 55 and 57. abut each other during compression, or they may be clamped together. Alt. the gasket 51, 57, may be a gasket such as rings, spheres, cylinders or the like, which are tightly packed so as to obtain high conductivity and low electrical contact resistance.

According to a variant, the saline supply line 87a and the saline discharge line 87b as well as the supply line 11a for water and oxidant and the discharge line 11b for catholyte liquid can be combined with distribution means 51, 51. In this variant, the supply lines 87a and 11a extend into the packing 55 and 57 , while the discharge lines 87b and lll b extend outwards from the gasket 55 and 57.

According to an alternative variant, the reagent supply and product recovery can take place via a microporous distribution device, e.g. microporous hydrophilic or microporous hydrophobic films, which rest against the solid polymer electrolyte 51 and during compression. In an embodiment where the supply is to microporous films on the solid polymer electrolyte 51, the catalyst particles 57 and 45 may be present in the microporous film as well as in the surface of the solid polymer electrolyte 55 and 41.

As described above, the individual solid polymer electrolyte electrolysis cells 11 and 15 comprise the solid polymer electrolyte 51 having a permionic membrane 55, on whose anode surface 55 there is anode catalyst 57 and on whose cathode surface 41 there is cathode catalyst 45. The boundaries of the cell may consists of a bipolar unit 21 or an end plate 71, the electrical contact between the boundaries and the solid polymer electrolyte 51 taking place via distribution means 51. Furthermore, there are reagent supply lines 87a and 11a and product discharge lines 87b and 11b. In addition, there must be means for providing and maintaining an electrolyte-tight and gas-tight seal, such as gasket 61. Although gasket 61 is shown only between the walls 71 and the bipolar units 21 and the distribution means 51, it is understood that additional or alternative gasket (s) 61 can be arranged between the distribution means 51 and the solid polymer electrolyte 51.

Gaskets in contact with the anolyte compartment 59 should be made of any material that is resistant to acidified, chlorinated brine as well as to chlorine. Such materials include unfilled silicone rubber as well as various resilient or elastic fluorocarbon materials. 10 15 20 25 BO 55 40 ll 8001377-4 The gaskets 61 in contact with the catholyte compartment 45 may be made of any material which is resistant to conc. caustic soda or sodium hydroxide.

A particularly satisfactory flow system is generally shown in Fig. 1, where the brine is fed to the electrolyzer 1 via the brine inlet 81a in the end unit 71, e.g. with a hydrostatic head. The saline solution then passes through line 85a in the O-ring or gasket 61 to and through line 85a in the distributor 51 on the cathode side 45 of the cell 11 and then through line 89a in the solid polymer unit 51 to the anodic distributor 51 on the anode side 55 of the solid polymer. 51 in the electrolytic cell ll. At the distribution device 51 there is a T-opening and outlet with the line 9la passing through the distribution device 51 and outlet 87a which delivers electrolyte to the anolyte chamber. The flow then continues from line 9la in the distributor 51 to line 95a in the next O-ring or packing through line 95a in the bipolar unit 21 and then to the next cell 15, where the fluid flow is substantially as described above. saline solution is distributed by means of the gasket 57 in the distribution device 51 inside the anolyte compartment 59. Through the distribution of the saline solution, chlorine is swept from the anodic surface 55 and the anodic catalyst 57, whereby chlorine stagnation is avoided.

The depleted saline solution is taken out through outlet 87b in the distribution device 51 to the return line 91b, e.g. by means of partial vacuum or reduced pressure. The return then takes place through the return line 89b in the solid polymer electrolyte unit 51, the line 85b in the cathodic distribution device 51, the line 85b in the O-ring or the seal 61 to the outlet 8lb, where the depleted saline solution is recovered from the electrolyser 1.

Water and oxidant enter the electrolyzer 1 through inlet 10a1a in the end unit 71. The water and oxidant then continue through line 105a in the O-ring or seal beer to line 10aa and "T" in the cathodic distribution device 51 on the cathode side 45 of the cell 11. fr-outlet includes line 1o5a een line llla. Water and oxidant are delivered via the outlet 11a in the ring 55 of the distributor 51 to the catholyte-resistant gasket 55 inside the catholyte chamber 45 in the cell 11. The cesium hydrogen, i.e. the aqueous alkali metal hydroxide, such as sodium m-"fl- * trooa QUALIW-i- ~ 10 Hydroxide or potassium hydroxide, is recovered from the cathodic surface 41 of the solid polymer electrolyte permionic membrane 53 by means of the water fed into the cell 11. When oxidant is present, liquid is recovered through the outlet 111b. If there is no oxidant, liquid can be recovered through 111b. Although the electrolyzer is shown with a common supply of oxidant and water and with a common recovery for gas and liquid, there may be three pipelines, llla, lllb and a third pipeline, which is not shown, for water supply, oxidant supply or liquid recovery, alternatively there may be three lines 11a, 11b and a third line not shown, for water supply, liquid recovery or ga. recovery. To return to the total flows in the electrolyzer 1, line 105a continues to line 107a in the solid polymer electrolyte unit 31 to line 107a in the anodic distribution device 51, which continues through to line 11a in the O-ring or gasket 61 and then to the line 115a in the bipolar unit 21, where the same path through the individual cell 15 is followed as in cell 11. Similarly, the network can continue in additional cells.

The recovery of product is shown to take place from the distribution device 51 through the outlet 11b to the line 105b and then to line 105b in the O-ring or the gasket 61 to the outlet 10b in the end wall 71. Although the flow has been described to and through distribution devices 51, as has described above, the flow can also take place by other means. For example, the inlet or outlet or both may be located in the bipolar unit 21, which would support porous film or outlet pipes from the unit 21. Alt. the inlet or the outlet or both parts may form part of the solid polymer electrolyte unit 51. While the flow has been described as being parallel 1377-4 to each individual cell 11 and 13, it may also be a series flow.

When using a series flow of the brine, the T, outlet 87 line 91, may be an L rather than a T.

In one embodiment where serial flow is used, lower saline depletion occurs in each cell, with partially depleted saline from one cell being fed to the next cell for further partial depletion.

Correspondingly, when there is a series flow of catholyte liquid, the T, line 105 outlet III, may be an L.

When series flow is utilized, the flow may occur in cocurrent with high sodium or high potassium ion concentration gradients across the solid polymer electrolyte 33.or in countercurrent with lower sodium or potassium ion concentration gradients over the individual solid polymer electrolyte units 31.

The bipolar electrolyzer can be either horizontally or vertically arranged, i.e. the bipolar electrolyzer 1 can have a solid polymer electrolyte unit 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 41 on the bottom of the permionic membrane 33. various advantages. up through the anolyte compartment 39.

A Horizontal Design Offers When operating under low pressure, chlorine bubbles flow in the cathode surface compartment 45, the horizontal configuration prevents the build-up of concentrated alkali metal hydroxide on the bottom surface 41 of the permionic membrane 33, while allowing the bottom surface 41 of the permionic membrane 33 to be wetted. with alkali metal hydroxide.

In addition, when oxidant is present, especially gaseous oxidant, the horizontal configuration allows the oxidant to be in contact with the cathodic surface 41 of the permionic membrane 33.

The solid polymer electrolyte 31 contains a permionic membrane 33.

The permionic membrane 33 should be chemically resistant, cation-selective, with anodic chlorine evolution catalyst 37 on the anode surface 35 and cathodic hydroxyl evolution catalyst 43 on the cathode surface 41 thereof.

The permionic fluorocarbon resin membrane 33 used to provide the solid polymer electrolyte 31 is characterized by the presence of evaporation-selective ion exchange groups, ion exchange capacity of 10 Å, bonded to a carbon atom bonded to a fluorine atom. lä 8001377-4 membrane, concentration of ion exchange groups in the membrane on the basis of water absorbed in the membrane and the glass transition temperature of the membrane material.

The fluorocarbon resins referred to herein have the units:% CF2-CXX'è and ~ (- cnz-c-Xè Y wherein x is -F, -cl, -H or -crf X 'is -F, -cl, -H, - crj or cr (cF2) m-; m is an integer of 1-5; one Y is -A, -ø-A, -PA, or -o- (cF2) n (P, Q, n) - A.

In the unit (P, Q, n), P is - (cH2) a (c> o <') b (cF2) c, Q is (-CF2-O-CXX') d, R is (-CXX'-O -CF 2) e and (P, Q, R) contain one or more of P, Q, R. ø is the phenylene group; n is 0 or 1; a, b, c, d and e are integers of O-6. . The typical groups for Y have the structure with the acid group, 4 V. These include {CF2àkA, and side chains with ether linkages, such as: éO - éCFaà-XA, {--0-CF2-? FàyA, éO-CFg-slFàxšO-CFa- CFgåyA and ZZ -O-CF2 {CF2-O-§F§X {CF2åy {CF2-O-? F) ZA; wherein x, y and z are resp.

- Z B 1 to 10; Z and R are respectively. -F or a C1-C10 perfluoroalkyl group, and A is the acid group defined below.

In the case of copolymers with the olefinic and olefinic acid units described above, it is preferred to have 1-40 mole percent and especially 3-20 mole percent, of the olefinic acid units in the preparation of a membrane which exhibits an ion exchange capacity within the desired range.

A is a carboxylic acid group -COOH, m- or a functional group which can be converted to -COOH by hydrolysis or by neutralization, such as -CN, -COF, -COCl, -COORI, -COOM, -CONRERB; R 1 is a C 1 -C 10 alkyl group and R 2 and R 3 are either hydrogen or C 1 -C 10 alkyl groups, including perfluoroalkyl groups, or both.

M is hydrogen or an alkali metal; when M is an alkali metal, it is most preferably sodium or potassium.

In the embodiment of the present invention where A is -CONR 2 R 5 and where R and R are hydrogen, or a C 1 -C 10 alkyl group, including a perfluoroalkyl group, the cathode surface of the permionic membrane may be 41 ha the ion exchange groups in carboxylic acid form, while the anodic surface of the permionic membrane has the ion exchange groups in amide or N-substituted amide form. The arrangement of amide groups or N-substituted amide groups on the anode surface 35 of the permionic membrane 33 helps to make the cathodic surface 35 hydrophobic. This prevents chlorine stagnation on the membrane 33.

The membrane 33 can be converted to an amide or N-substituted amide group during synthesis or after the catalyst 37 has been deposited thereon or embedded therein, e.g. by reaction with ammonia or an amine. The membrane material has an ion exchange capacity of from about 0.5 to about 2.0 mg equivalents per gram of dry polymer, and preferably from about 0.9 to about 1.8 mg equivalents per gram of dry polymer, and in a particularly preferred embodiment from about 1.1 to about 1.7 mg equivalents per gram of dry polymer.

When the ion exchange capacity is less than about 0.5 mg equivalents per gram of dry polymer, the current efficiency is low at the present high concentrations of alkali metal hydroxide, while when the ion exchange capacity is greater than about 2.0 mg equivalents per gram of dry polymer, the current efficiency of the membrane is too law.

The amount of ion exchange groups per gram of absorbed water is from about 8 mg equivalents per gram of absorbed water to about 30 mg equivalents per gram of absorbed water and preferably from about 10 mg equivalents per gram of absorbed water to about 28 mg equivalents per gram of absorbed water and in a preferred variant about 14 mg equivalents_per gram of absorbed water to about 26 mg equivalents per gram of absorbed water.

When the proportion of ion exchange groups per unit weight of absorbed water is less than about 8 mg equivalents per gram or above about 30 mg equivalents per gram, the current efficiency is too low.

The glass transition temperature is preferably at least about QOOC below the temperature of the electrolyte. When the electrolyte temperature is between about 95 and 10 ° C, the glass transition temperature of the permionic fluorocarbon resin membrane material is below about 90 ° C and in a particularly preferred variant below about 70oC.

However, the glass transition temperature should be above about -80 ° C for the membrane material to exhibit satisfactory tensile strength. Preferably, the glass transition temperature is in the range from about -80 to about 70 ° C and in a particularly preferred variant between about -80 and about 5000.

Poor: QUALITY 10 15 20 25 30 55 40. chloride at pH 10. 8001377-4 16 When the glass transition temperature of the membrane is within about 20 ° C from the temperature of the electrolyte or higher than the temperature of the electrolyte, the resistance of the membrane increases, while its permeability selectivity decreases. By glass transition temperature is meant the temperature below which the polymer segments are not energetic enough to either move past each other or in relation to each other by means of Brownian segment movement. Below the glass transition temperature, in other words, the only reversible response of the polymer to stresses is elongation, while the polymer's response to stresses above the glass transition temperature is segment regrouping to relieve the externally applied stress.

The present permionic fluorocarbon resin membrane material has a water permeability of less than about 100 ml per hour per mg at 6000 in four N sodium chloride at a pH of 10 and preferably less than 10 ml per hour per mg at 6000 in 4 N sodium. about 100 ml per hour and per m2, measured as described above, can result in a crude alkali metal hydroxide product.

The electrical resistance of the dry membrane should be from about 0.5 to about 10 ohms per cm2 0.5 to about 7 ohms per cm2.

Preferably, the permionic fluorinated resin membrane has a molecular weight, i.e. a degree of polymerization, which is sufficient to give a volumetric flow rate of about 100 mmHs per second at a temperature of from about 150 to about 30,000.

The thickness of the permionic membrane 33 should be such as to obtain a membrane 33 which is strong enough to withstand temporary pressure changes and manufacturing processes, e.g. adhesion of the catalyst particles, but thin enough to avoid high electrical resistivity. Preferably the membrane is from 10 to 1000 thick and in a particularly preferred embodiment from about 50 to about 200 thick. In addition, internal reinforcement, or increased thickness, or crosslinking can be used or even; lamination to provide a strong and preferably from about membrane.

In a preferred variant, the permionic membrane includes means for transporting anolyte liquid into the interior of the permionic membrane. This prevents crystallization of alkali metal chloride salts within the permionic membrane 33.

The means for achieving this may involve braided or f 6 up binder "§? Â% (§Éš'§§ï§É ¥ ïÃEÉ ¿10 15 20 25 30 35 40 N 8ÛÛ1377'4 woven means, which e.g. up to or past the anodic catalyst 37. According to another embodiment, the means for transporting anolyte liquid into the interior of the permionic membrane may comprise hydrophilic or wettable fibers extending up to or past the anode catalyst 37, or even microtubes, extending up to or past the anode catalyst 37.

In the present case, the means for transporting the anolyte liquid into the interior of the permionic membrane draws water or anolyte liquid into the membrane past the hydrate water connected to the electrolytically transported alkali metal ions.

This prevents crystallization of alkali metal chloride, such as sodium chloride or potassium chloride, in the membrane.

According to a preferred variant, the electrocatalysts 37 and 43 and the membrane 33 are one unit. Although this can. provided by having the electrocatalysts 37 and 43 on the packer 55 and 57 of the distributor, the distributor 55 and 57 being kept in compressive contact with the membrane 33, it is convenient to arrange a film of the electrocatalysts 37 and 43 on the permionic membrane 33 The film 37, 43 is usually from about 10 to about 200 microns thick, preferably from about 25 to about 175 microns thick, ideally from about 50 to about 150 microns thick.

The electrolyte and permionic membrane unit 31 should have dimensional stability, chemical and thermal degradation resistance, and electrocatalytic activity, and preferably the catalyst particles should be atomized and porous with at least about 10 m 2 of surface area per g of catalyst particle, 43.

Adhesion of the catalyst 37 and 43, to the permionic membrane 33 can be accomplished by pressing the particles 37 and 43 into a molten, semi-molten, liquid, plastic or thermoplastic, permionic membrane 33 at elevated temperature.

This means that the membrane is heated to a temperature above its glass transition temperature, preferably above the temperature at which the membrane 33 can be deformed only by means of pressure.

According to another embodiment, the particles 37 and 43 may be pressed into a partially polymerized permionic membrane 33 or pressed into a partially crosslinked permionic membrane 33 and the polymerization or crosslinking may be continued, e.g. by raising or lowering the temperature, adding initiator, adding additional monomer or using ionizing radiation or the like.

POOR QUALITY '10 15 20 25 30 55 H0' 8001377-4 18 According to another variant, when further polymerization is carried out, the particles 37, H3 can be embedded in the partially polymerized permonic membrane 33. Thereafter, a monomer of a hydrophobic polymer can be applied to the surface with e.g. an initiator and copolymerized in situ with the partially polymerized permionic membrane 33, thereby providing a hydrophobic surface with exposed particles 37, 43. In this way, the catalyst particles 37, 43 may be present on the hydrophobic surface, t. ex. to protect the anodic surface 35 from chlorine or to protect the cathodic surface 41 from crystallization or solidification of alkali metal hydroxide or to increase the depolarization, such as when a cathodic HO 2 disproportionation catalyst is present on the cathodic surface 41 of the permionic membrane.

According to another variant, the permionic membrane units can be crosslinked, for example after deposition of catalyst particles, so that the hydrophobic character of the membrane surface is increased. The crosslinker may react during molding or after the anode materials have been deposited on a partially polymerized permionic membrane. Suitable bridging agents include the divinylbenzenes, e.g. the 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-, 1,4- and 1,5-dienes. The bridging agent is usually a divinylbenzene or perfluorinated G4-C6 diene, especially hexafluorobutadiene.

According to an alternative variant, the anode electrocatalyst 37 may be extended with silicon. In other words, when the anode electrocatalyst 37 is a particle, the particles may be coated silicon particles, i.e. silicon particles coated with a suitable chlorine evolution catalyst In addition, silicon particles, e.g. Coated silicon particles, silicon surface silicon particles and silicon surface silicon particles are present on the anodic surface 35 of the permionic membrane 33 to provide both conductivity between anode particles and to act as an anode catalyst.

According to this variant, low overvoltage anode particles are provided, which comprise an electrolyte-resistant electrically conductive surface, such as metallic platinum or ruthenium oxide, on an electrically conductive substrate, which is partially or completely and preferably predominantly silicon 1 elemental state ( unlike silicides, which can be considered as compounds of silicon and other metals). While the silicon is in the elemental state, it contains impurities, dopants or additives, e.g. boron, phosphorus, etc., or silicides of certain metals dispersed in said silicon, which impart to said silicon conductivity and / or strength. Said elemental silica usually has a continuous phase with the other agents dissolved or dispersed therein.

The silicon particles should be electrically conductive and should be at least as electrically conductive as graphite; for example silicon should have an electrical bulk conductivity exceeding 102 (ohm-cm) -1 and preferably 104 (ohm-cm) -1 or higher. Essentially pure silicon, e.g. silicon with a purity exceeding 99,995 atomic percent, is at best a poor conductor and can t.o.m. characterized as a non-conductor with a resistivity of only about 1 ohm-cm. It is known that by incorporating small and t.o.m. trace amounts of boron, phosphorus or other materials provide a silicon composition which is electrically conductive. It has been found that with appropriate precautions the silicon substrate can be provided in a form which is inert to anodic attack, and such substrates can be effectively used to support the conductive surface.

Elemental silicon containing up to 2% or more up to 5% boron or up to 2% phosphorus and negligible amounts of other pollutants have been shown to be inert to the desired extent against anodic attack of aqueous sodium chloride.

The silicon in question may also contain iron, e.g. up to about 40% by weight, when phosphorus or boron is present, wherein said phosphorus and boron have a corrosion-inhibiting effect.

The silicon particles may also contain silicides. Particularly preferred are silicides with catalytic effect or conductivity-promoting effect, such as the silicides of metals from groups IV, V and VI, e.g. TiSi2, SrSi2, VSi2, NbSi2, TaSi2 and WSi2 as well as the heavy metal silicides, e.g. CrSi, Cr5Si3, CrSi, CrSi2 and MoSi2 as well as cobalt silicides CoSi2.

According to yet another variant, the catalysts 37, ü5 can be chemically deposited, e.g. by hypophosphite or borohydride reduction, or electrodeposition on the permionic membrane 33. In addition, subsequent activation of the catalyst may occur, e.g. by simultaneous deposition of a leachable material and a less leachable material and subsequent activation by leaching of the more leachable material. According to yet another variant, a surface of catalyst 37, U3 foot Q fl š fl m 10 15 20 25 30 35 Ä0 8001377-4 20 can be applied to the permionic membrane by electrophoretic deposition, by sputtering, by laser deposition or by photoeposition.

According to another variant, a catalytic coating 37, ë3 can be applied to the permionic membrane 33 using a chelate of a metal which reacts with the acid groups on the permionic membrane 33.

Typically, the catalyst 37, 43 on the surface of the permionic membrane 33 is a noble metal-containing catalyst, such as a platinum group metal or an alloy of a platinum group metal or an intermetallic compound of a platinum group metal or an oxide, carbide, nitride , boride, silicide or sulphide of a platinum group metal.

Such noble metal-containing catalysts are characterized by high surface area and ability to either bind to a hydrophobic particle or be embedded in the hydrophobic film. tínasyart chemical deposition.

In addition, the noble metal-containing catalyst may be a partially reduced oxide, or a "black" material, such as pla- or palladium black, or an electrodeposition, or Catalysts 37, 43 may also be an intermetallic compound of other metals, including noble metals and non-noble metals. Such intermetallic compounds include pyrochlorine compounds, delafossites, spinels, perovskites, bronzes, tungsten bronzes, silicides, nitrides, carbides and borides.

Particularly desirable cathodic catalysts, which may be present on the permionic membrane: 33 of solid polymer electrolyte, include steel, stainless steel, cobalt, nickel, nickel or iron alloys, nickel compositions, especially porous nickel with molybdenum, tantalum, tungsten , titanium, niobium or the like, and boride, electrically conductive, electrically active borides, nitrides, silicides and carbides such as the platinum group metal silicides, nitrides, carbides and borides and titanium diboride.

Other cathodic catalysts 43, which may be present on the cathodic surface 41 of the permeable membrane, include the platinum group metals, e.g. platinum, palladium, ruthenium, osmium, iridium and rhodium, both as even deposits for high surface area deposits, e.g. "black" material with a surface area exceeding 10 m2 per gram.

In the present case, the permionic membrane 33 or a surface thereof, e.g. the anodic surface 35 or the cathodic Y * lm dl ævf fi x ~: LV '' ß fi * x Y f 1 å va »i 10 15 20 25 30 35 40 2, 8001577-4 surface 41, in contact with a reducing agent, a complexing agents, a buffer and a compound of the metal, or compounds of the metals to be deposited. The reducing agent may be a borohydride reducing agent or a hypophosphite reducing agent.

The borohydride solution should contain 1-5 g of borohydride per liter, e.g. sodium or potassium borohydride, and preferably 1.5-2.5 g of borohydride per liter.

When the deposition takes place on a synthetic permionic membrane, 55, instead of on a metal substrate, subsequent contact is particularly desirable. Upon subsequent contact, the membrane 33 is first brought into contact with the reducing agent and then with the compounds of the metals to be deposited.

The process is advantageous in connection with transition metals and especially advantageous in connection with transition metals from group VII. It is especially useful for the simultaneous deposition of two metals of group VIII with click-like resistance to chemical leaching agents, whereby later the less resistant metal is leached.

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, for example a citrate, oxalate, glycolate, sulphate or chloride. The buffer substance and the complexing agent may be the acid and alkali metal salt of the same organic compound, e.g. sodium citrate and citric acid, sodium oxalate and oxalic acid, and the like. Alt. an inorganic acid can be used, e.g. phosphoric acid and sodium phosphite. The complexing agent and the buffer substance help to keep the metal ions of the Group VIII metal in solution, e.g. at pH 6-8.

According to a particularly preferred variant, the cathodic electrocatalyst 43 comprises porous nickel which contains an effective amount, i.e. an overvoltage reducing or overvoltage stabilizing amount, of a transition metal of group IVB, VB, VIB or VIIB. These transition metals include titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technetium and rhenium. The preferred materials are titanium, zirconium, hafnium, vanadium, niobium, tantalum, molybdenum and tungsten.

Particularly preferred are titanium, tantalum, zirconium and molybdenum.

The nickel in question usually constitutes over about 50% and less than about 95%, preferably between about 65 and about 90%, nickel, calculated ,, _, __ ~ .P °° R, §füF: LIfïi2i_ 10 15 20 25 30 35 40 8001377-4 22 as nickel metal, based on the total weight of the porous active surface.

The second transition metal is present in the porous É catalytic surface 43 in a hydrogen overvoltage lowering amount. This A is above about 2.5% by weight, preferably above about 5% by weight but below about 50% by weight, and usually from about 10% to about 35% by weight, calculated as metal, on the basis of total nickel calculated as metal and transition metal calculated as metal in the surface . In general, 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 which occurs in connection with porous surfaces which predominantly consist of the other transition metal, e.g. titanium, tantalum, zirconium or molybdenum. y Although the mechanism of the hydrogen surge-reducing effect-. ten_of the second transition metal is not fully clarified, it is known that porous films of e.g. only molybdenum has a high hydrogen overvoltage but that low hydrogen overvoltage during long electrolysis periods is observed when a second transition metal, such as this has been described above, e.g. molybdenum, is used together with porous In the case of molybdenum, said molybdenum is assumed to depolarize by this nickel. or catalyze a step in the hydrogen evolution process. For this reason, the upper limit of the second transition metal is below the concentration at which the surface has the hydrogen overvoltage properties that apply to the second transition metal, ie below about 50% and usually below about 35%.

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

An especially preferred cathode H3 is a cathode with a porous surface ÄB of nickel and molybdenum containing about 82% by weight of nickel and about 18% by weight of molybdenum, calculated on total nickel and molybdenum, and with a porosity of about 0.7 and a thickness of from about 75 "to about 500 10 15 20 25 BO 55 H0 23 8001377-4 According to another variant, the cathode in question is prepared by depositing a film of nickel, the second transition metal and a leachable material on the permionic membrane 35, after which the leachable material is leached out. .

The leachable material may be any metal or compound which can be deposited simultaneously with nickel and the second transition metal or together with nickel compounds and compounds of the second transition metal and leached with a strong acid or a strong base without appreciable quantities of nickel or other transition metal is leached out or without significant destruction or poisoning of the nickel or other transition metal in question.

The film can be deposited on the permionic membrane 55 by electrodeposition of nickel, the second transition metal and a leachable material or by simultaneous deposition of solid particles or by chemical deposition or chemical deposition, e.g. by hypophosphite deposition or by borohydride deposition of nickel compounds, compounds of the second transition metal and leachable materials or t.o.m. by deposition and thermal decomposition of organic compounds of nickel, the second transition metal and leachable materials, e.g. deposition and thermal decomposition of alcoholates or resinates.

According to a particularly preferred variant of the method for manufacturing the electrode, fine particles are embedded, e.g. of the order of about 0.5 to 70 microns in diameter, of nickel, the second transition metal or a compound thereof and a leachable material in a partially polymerized permionic membrane 53, after which the polymerization is completed, whereby leaching of the leachable material takes place either before or after the polymerization. Alternatively, the particles may be embedded in a heated thermoplastic permionic membrane 33.

The leachable materials may be present in the particle together with nickel or they may be separate. Typical leachable compounds include copper, especially particles. zinc, gallium, aluminum, tin, silicon or similar. preferred are nickel particles containing from about 3 to about 70% nickel, the remainder being aluminum as Raney alloy.

After completion of polymerization of the partially polymerized membrane 33, or cooling of the heated thermoplastic membrane 35, the particles 45 can be leached, e.g. in alkali, such as 0.5 normal sodium hydroxide or normal sodium hydroxide, for the purpose of removing the leachable material, e.g. aluminum, and then rinsed with water. It is of course understood that a certain part of the leachable material can remain in the porous electrode surface 43 without any harmful effect. Thus, when e.g. Raney nickel-aluminum alloy and molybdenum are embedded in the membrane 33, the surface may contain nickel, molybdenum and aluminum after leaching. The resulting surface can e.g. contain amorphous nickel, crystalline molybdenum-nickel-aluminum alloys and traces of alumina.

According to another variant, the surface H3 may contain boron or phosphorus. These materials. which is assumed to be deposited during borohydride or hypophosphite deposition stabilizes the stress properties of the cathodic electrocatalyst 43.

The nickel in question usually constitutes more than about 50% and - less than about 95%, usually from about 65 to about 90%, nickel, calculated as nickel metal, on the basis of the total weight of the porous active surface.

The second transition metal is present in the porous catalytic surface 45 in a hydrogen overvoltage lowering amount. This is above about 2.5% by weight, preferably above about 5% by weight but below about 50% by weight, and is usually from about 10% to about 35% by weight, calculated as metal, based on total nickel, calculated as metal, and other transition metals. , counted as metal, in the surface. In general, the amount of the second transition metal in the surface is high enough to obtain a hydrogen overvoltage lowering effect, but it must be low enough to avoid the high overvoltage which applies to porous surfaces which mainly consists of the second transition metal, e.g. titanium, tantalum, zirconium or molybdenum. Although the mechanism of the hydrogen overvoltage lowering effect of the second transition metal is not fully understood, it is known that porous films of e.g. only molybdenum has a high hydrogen overvoltage but that low hydrogen overvoltage during long electrolysis periods is observed when a second transition metal, as described above, eg, molybdenum, is used together with porous nickel. In the case of molybdenum, the molybdenum in question is assumed to depolarize or catalyze a step in the hydrogen evolution process.

For this reason, the upper limit of the second transition metal is below the concentration at which the surface has the hydrogen overvoltage properties of the second transition metal. the transition metal, i.e. below about 50% and usually below about 35%.

The second transition metal may itself be present as elemental metal, ie as 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, which is insoluble in conc. alkali metal hydroxide. Preferably, the second transition metal is present in the surface 43 together with nickel as an elemental metal, as an alloy with nickel or as a carbide.

A particularly favorable cathode H3 is a cathode having a porous surface H3 of nickel and molybdenum containing about 82% by weight of nickel and about 18% by weight of molybdenum, based on total nickel and molybdenum and having a porosity of about 0.7 and a thickness of about 75 to about 500 / um.

According to yet another variant of the method, the cathode in question is prepared by depositing a film of nickel, the second transition metal and a leachable material on the permionic membrane 33, after which the leachable material is leached out.

The leachable material may be any metal or compound which can be deposited simultaneously with nickel and the second transition metal or together with nickel compounds and compounds of the second transition metal and leached with a strong acid or a strong base, without leaching appreciable quantities. of the nickel or other transition metal in question or causing significant destruction or poisoning of the nickel or other transition metal in question.

The film can be deposited on the permionic membrane 53 by electrodeposition of nickel, the second transition metal and a leachable material or by simultaneous deposition of solid particles or by chemical deposition, e.g. by hypophosphite deposition or by borohydride deposition of nickel compounds, compounds of the second transition metal and leachable materials or even by deposition and thermal decomposition of organic compounds of nickel, the second transition metal and leachable materials, e.g. deposition and thermal decomposition of alcoholates or resinates.

According to a particularly desirable variant of the method for manufacturing the electrode, fine particles are embedded, e.g. of sizez ~ .i., _......._.._...__...._.

PGO-R QUALITY 10 15 20 25 30 35 RO 8001377-4 26 from about 0.5 to 70 / mn in diameter, of nickel, the second transition metal or a compound thereof and a leachable material in a partially polymerized permionic membrane 33, whereupon the polymerization is completed, whereby leaching of the leachable material takes place either before or after the polymerization. Alternative particles can be embedded in hot heated thermoplastic permionic membrane 33.

The leachable materials may be present in the particle together with the nickel in question, or they may be separate particles. Typical leachable compounds include copper, zinc, gallium, aluminum, tin, silicon or the like.

Particularly preferred are nickel particles, containing from about 50 to about 70% nickel, the remainder being aluminum, as Raney alloy.

After completion of the polymerization of the partially polymerized membrane 53, or cooling of the heated thermoplastic membrane 33, the particles 43 can be leached, e.g. in alkali, such as 0.5 normal caustic soda or l normal caustic soda, in order to remove the leachable material, e.g. aluminum, and then rinsed with water. It is of course understood that a certain amount of the leachable material can remain in the porous electrode surface ÄB without harmful effects. Thus, when e.g. Raney nickel-aluminum alloy and molybdenum are embedded in the membrane 35, the surface 45 may contain nickel, molybdenum and aluminum after leaching. The resulting surface can e.g. contain amorphous nickel, crystalline molybdenum, nickel-aluminum alloys and traces of alumina.

In the electrolysis of alkali metal chloride solutions, such as potassium chloride and sodium chloride solutions in a solid polymer electrolysis cell, especially a cell with a carboxylic acid type permionic membrane 33, the purity of the saline solution is of significant importance.

The content of transition metals in the saline solution should be less than 40 parts per million and preferably less than 20 parts per million, thereby avoiding growth or coating of the permionic membrane 33. The pH of the saline solution should be sufficiently low to avoid precipitation of magnesium ions.

The calcium content should be less than 50 billionths and preferably less than 20 billionths. The saline solution should be practically free of organic carbon compounds, especially when chlorine is to be extracted directly from the cell as a liquid and used in another process, e.g. an organic synthesis process, such as a vinyl chloride production process, without further treatment. Salt-: nav-_ .Ewa status: 10 15 20 25 30 35 The solution treatment can be carried out in different ways in order to achieve the desired degree of purity. For example, phosphate precipitation can be used to remove calcium, e.g. as calcium apatite or as calcium fluoroapatite. Furthermore, an ion exchange resin can be used to purify the brine.

Preferably, the ion exchange resin is a chelating ion exchange resin. In this way, with the help of the multifunctionality, pollutants in the form of polyvalent metals are removed, e.g. ions of alkaline earth metals and ions of transition metals.

The water passed to the catalyst compartment 45 should be substantially free of carbon dioxide and carbonates, thereby avoiding the formation and deposition of carbonate on the permionic membrane 55. Preferably, the water is supplied in the form of deionized water. The regeneration or regeneration of the chelating ion exchange resin is critical. The regeneration with non-oxidizing acid should remove virtually all polyvalent cations. This can be achieved by e.g. uses from 10 to 2 bed volumes of from 0.5 to 5 normal hydrochloric acid and preferably from 10 to 20 bed volumes or even more of from 2 to 5 normal hydrochloric acid as regeneration fluid.

Diluted mineral acids, e.g. from about 0.1 to 10 normal, and preferably from about 0.5 to 5 normal, are used as non-oxidizing acids are preferred, in order to be Among suitable acids may be mentioned hydrogenating agents. Avoid damaging the resin. the halides, especially hydrochloric acid.

The acid strength should be high enough for cations to be expelled from the resin, ie above about 0.1 normal and preferably above about 0.5 normal, but low enough to avoid dehydration of the membrane, ie below about 10 normal .

In this way, a saline solution can be obtained which contains less than 20 million parts of transition metals and less than 20 billion parts of alkaline earth metals.

During operation of the cell, short residence times in the anolyte compartment 59 allow for a depletion of a saline solution of about 10 to about 15% use of saline as a coolant and an avoidance of concentration polarization. Higher saline depletion, e.g. 30, 40 or even. 50, 60 or 70%, seek can be used. The electrolysis process according to the invention involves feeding aqueous alkali metal chloride salt solution to an electrolytic cell having an anolyte compartment ~ which is separated from a catalyst compartment by means of an electrolyte in the form of solid polymer, the solid polymer electrolyte comprising a fluorinated cation exchange membrane having carboxylic acid groups as ion exchange groups, an anodic electrocatalyst on its anodic surface and a cathodic electrocatalyst on its cathodic surface, applying an electric potential over the solid polymer electrolyte, and chlorine is extracted from the anolyte compartment and alkali metal hydroxide from the catholyte compartment, the cell being operated at a sufficient pressure below about N MPa overpressure and such a temperature that the chlorine in the anolyte compartment is kept in liquid form, liquid chlorine and depleted saline are extracted from the cell, and separating the liquid chlorine from the depleted brine n. The cell temperature can be above 9 ° C, especially when the saline solution has a low pH value, thereby reducing the formation of hydrochloride. Alt. For example, the temperature of the cell can be kept below 9 ° C, thereby increasing the formation of hydrochloride and enabling the dilution of a saline solution and hydrochloride.

The cell temperature should be low enough that the pressure required to keep the chlorine liquid should be low enough to still allow the use of conventional construction techniques instead of high pressure techniques. Pressure temperature data for liquid chlorine are given in Table I.

TABLE I Vapor pressure for liquid chlorine Temperature, OC Overpressure. MPa -30 0.021 -25 0.050 -20 ”0.092 -15 0.119 -10 '0.162 - 5 0.211 0 0.268 + 5 0.350 10 o, uo2 15 0.475 20 0.565 25 0.658 29 8001577-4 Table I cont. Vapor pressure for liquid chlorine Temperature, OC Overpressure. MPa 50 0.771 5 35 0.896 40 1.028 45 1.179 50 1.332 55 1.505 10 60 1 1.682 65 1.870 70 2.087 75 2.316 80 2.559 15 85 2.823 90 5.097 95 5.396 100 3.70 105 4.04 20 110 4.40 115 4.79 120 5.22 125 5.67 150 6.13 25 ”šš Éiïâ According to the invention, liquid chlorine and depleted saline solution can be recovered together, the liquid chlorine is separated from the saline solution, the saline solution is then cooled to convert any. chlorine therein to chlorohydrate, which is further separated from the brine, and the brine is reinforced with respect to salt, purified again and returned to the cell, while the chlorohydrate separated therefrom is heated to form chlorine.

The pressure in the electrolyser should be high enough to allow gaseous nitrogen and oxygen to escape from the cell and the auxiliaries belonging to the cell, without expelling appreciable amounts of liquid chlorine. When operating the cell to produce liquid chlorine, the temperature of the cell should be below about 10,000, thereby maintaining the pressure of the electrolyzer below about 4 MPa overpressure. Preferably, the temperature of the cell should be kept below about 40 5000, thereby allowing the cell pressure to be kept unier about in irooà QUALITY 10 15 20 25 30 55 40 8001377-4 30 1.4 MPa overpressure. However, the desired temperature and pressure of the cell may depend on the final use of the liquid chlorine and the required vapor pressure and the required temperature of the liquid chlorine. In practice, the pressure inside the cell is more dependent on the pressure in the auxiliary means and the end use of the chlorine than on the structural components of the cell.

High pressure is particularly advantageous on the catholyte side 45 of the individual electrolytic cell 11, where the cathode reaction is depolarized, since the high pressure helps to force the depolarizer into the catalyst 43 and disproportionate HO2_.

The chlorine and the depleted saline solution are extracted from the electrolyzer fluids. Liquid chlorine is relatively immiscible with saline at the pressures referred to here. For this reason, the liquid chlorine can be easily separated from the brine, such as by centrifugation, filtration or any other viscosity, surface tension or density dependent means.

Thereafter, the separated liquid chlorine can be stored or used as a liquid without condensation. However, the liquid chlorine makes up only from 2 to 5 mole percent of the liquids present in the anolyte compartment. Although most of the chlorine will be recovered and separated in the form of a substantially pure liquid, a certain amount thereof will be solubilized in the saline solution. The chlorine in the brine can be recovered by cooling the brine to 900, e.g. by cooling the evaporated liquid chlorine, whereby the soluble chlorine contained in the brine is converted into chlorohydrate. The hydrochloride, which is a yellow crystalline material, can be separated from the depleted saline solution and e.g. heated to form chlorine.

During operation of the cell, the removal of stagnant chlorine pockets from the anode surface and the removal of solid, crystallized or highly concentrated liquid alkali metal hydroxides from the cathode surface 41 of the permionic membrane 33 can be performed using ultrasonic vibration of the permionic membrane 33 or by using pulses. . When pulsating current is used, it can consist of pulsed direct current, rectified alternating current or rectified half-wave alternating current. Particularly preferred is pulsed direct current with a frequency of from about 10 to about 40 cycles per second and preferably from about 20 to about 30 cycles per second. 150011 QUALYH 10 The catholyte liquid recovered from the cell typically contains over 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 catholyte liquid may contain over 30 to 55% by weight, e.g. 40 or t.o.m. 45% by weight or more of alkali metal hydroxide.

The current density of the electrolysis cell II with solid polymer electrolyte may be higher than that of a conventional cell with a permionic membrane or diaphragm, e.g. more than 2150 A per m2 and preferably more than 4300 A per m2. According to a particularly preferred embodiment of the present invention, electrolysis can be performed at a current density of 8600 or even 12900 A per m2, the current density being defined as the total current passing through the cell divided by the surface area of one side of the permionic membrane 35.

According to a particularly preferred variant, the cathode can be depolarized, thereby eliminating the formation of gaseous cathode products. When using the depolarized cathode, oxidant is fed to the cathode surface 41 of the solid polymer electrolyte 31, while arranging a suitable catalyst 43 in contact with the cathode surface H1 of the solid polymer electrolyte 31, thereby avoiding evolution of gaseous hydrogen. When in this way the electrolyzer 1 and the electrolytic cell 11 are kept at elevated pressure, as has been described above; For example, the development of gaseous products can largely be avoided, which also applies to the problems associated with it. In the process for producing alkali metal hydroxide and chlorine by electrolysis of an alkali metal chloride salt solution, such as an aqueous solution of sodium chloride or potassium chloride, the alkali metal chloride solution is passed into the cell, whereupon a voltage is applied across the cell to form chlorine alkali in the anode. the electrolyte in contact with the cathode and hydrogen can develop at the cathode. The total anode reaction is: 201- --- à C12 + 2e "(1) while the total cathode reaction is: 2H2o + ae '----; ~ H2 + zone" (2) More precisely, the cathode reaction is reported to be: H20 + e '----> Hads + oH' (3) according to which monoatomic hydrogen is adsorbed on the cathode surface. media reported the adsorbed hydrogen is desorbed according to one of I basic veins _ .. _... _. __ _ PooR oÜALm 10 15 20 25 30 35 40 _ fed to the cathode. 8001377-4 32 two alternative processes: 2Hads --- ä H2 or _ (4) Hads + H20 + e '--9 H2 + OH (5) The hydrogen desorption step, ie reaction (4) or reaction (5), is stated to be the hydrogen overvoltage determining step. This means that it is the speed regulating step, and its activation energy corresponds to the cathode hydrogen overvoltage. The cathode voltage for the hydrogen evolution reaction (2) is of the order of about 1.5 to 1.6 volts relative to a saturated calomel electrode (SCE) on iron in basic media, where the hydrogen overvoltage component is from about 0.4 to 0.5 volts.

One way to reduce the cathode voltage is to produce a substitute reaction for the evolution of gaseous hydrogen, i.e. to produce a reaction in which a liquid product is formed instead. Thus water can be formed when an oxidant The oxidant may be a gaseous oxidant, such as Alt. the oxidant may be a gaseous hydrogen liquid. oxygen, air or the like. shaped oxidant, such as hydrogen peroxide, a hydroperoxide, hydrogen peroxide or a peroxyacid or the like. When the oxidant is oxygen, e.g. in the form of air or gaseous oxygen, the following reaction is assumed to take place at the cathode: '(6) O 2 + 2H 2 O + nä' __; 4oH '_) This reaction is assumed to be an electron transfer reaction: _ 02 + H20 + ae' ---> H02 '+ oH' (7) followed by a surface reaction: 21102 '-> 02 + 2oH' (8) It it is assumed that the predominant reaction on the hydrophobic surface is reaction (7), reaction (8) taking 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, such as will be described below. In this way, the high hydrogen overvoltage desorption step is eliminated.

When the oxidant is a peroxy compound, the following reaction is believed to take place at the cathode: Rcopo '+ 2H 2 O + ae' ---> RcoH + 3oH '(9) This reaction is believed to be an electron transfer reaction followed by a surface reaction.

Suitable organic oxidants are those organic compounds which contain a reducible peroxy bond, C-O-O-. Suitable oxidants include organic peroxides, organic hydroperoxides and organic peracids, which are also called peroxyacids.

A preferred group of organic oxidants are organic hydroperoxides. Particularly advantageous organic oxidants are organic hydroperoxides which give alcohols which are soluble in water in all proportions, those hydroperoxides which give alcohols which have limited solubility in water, and those hydroperoxides which give alcohols which are soluble in water. For example, particularly advantageous 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 in the process of the present invention are those hydroperoxides which give alcohols with limited solubility in water 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 to give t-pentyl alcohol. Alt. For example, such hydroperoxides can be used which, as cathode reduction products, give sparingly soluble alcohols, such as n-pentyl hydroperoxide to give n-pentyl alcohol, i-pentyl hydroperoxides to give i-pentyl alcohols, s-pentyl hydroperoxides to give s-pentyl alcohols and neopentyl hydroperoxide to give nopenthol red oxide. Also useful are cumene hydroperoxide, which gives cumyl alcohol, and ethylbenzene hydroperoxide, which gives methylphenylcarbinol.

Another group of hydroperoxides useful in the practice of the process of the present invention are dihydroperoxides. Dihydroperoxides give glycols as a reaction product when added to the catholyte chamber of an electrolytic cell according to the present invention. The preferred dihydroperoxides are those which are completely miscible with water or those which are at least partially soluble in water. The preferred dihydroperoxides are dihydroperoxides of C3-C10-alkyls, with the dihydroperoxides of the C6-C10-alkyl groups being especially preferred.

Such dihydroperoxides include hexane dihydroperoxide, heptane dihydroperoxide, octane hydroperoxide, nonanedihydroperoxide and decanedihydroperoxide.

While alcohols, ketones, aldehydes and glycols are referred to herein, they can be formed only as intermediates and can be further reacted, such as by dehydration to form pORO QUALITY and m olefins and ethers. or by reaction with other additives, such as organic acids, to form esters or to form alkali metal salts of alcohols.

When the intermediate is an alcohol, this alcohol can be further reacted to form 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. Thus, when the organic oxidizing agent is tertiary butyl hydroperoxide, the intermediate recovered from the catholyte compartment is tertiary butyl alcohol. The tertiary butyl alcohol can be recovered from the cell, separated from the cell fluid, e.g. by distillation, and reacted with e.g. methyl sulfate to form methyl tertiary butyl ether. Methyl tertiary butyl ether is useful as a car fuel additive.

Particularly desirable hydroperoxides are those which yield alcohols which are soluble in water in all proportions and are useful in various industrial processes. Som ex. may be mentioned t-butyl hydroperoxide which gives t-butyl alcohol as a cathode reduction product, whereby t-butyl alcohol is useful as an octane enhancer for cars.

Dialkyl peroxides having the formula R10OR2, where R1 and R2 can be -CH3, -CEH, -CEH7, -CHH9, -CH2CH = CH2, or any other dialkyl peroxide that is soluble in water or soluble in organic solvents can be used in the process of the present invention. In addition to the dialkyl peroxides, the polyoxides of the formula R10nR, where n is 3 or 4, can be used in the process of the present invention, which also applies to the cyclperoxides of the formula B1-O-O-B2.

Peroxyacids, also known as peracids, of the formula mcoñn), where R may be -H, -cny 011201, mans, - (n-c5H7), - (i-CÄH9), - (n-C5H11), and which as horse other peracid, which is soluble in water or soluble in organic solvents, can be used. Furthermore, acyl peroxides or other peroxyacid precursors can be used in the process. In addition, aryldiperoxy acids can also be used.

While the process is described with respect to organic oxidizing agents, such as organic peroxides, organic hydroperoxides (with the general formula R -O- O -H) and organic peroxyacids (with the general formula RCOBH), it is understood that various derivatives of the organic peroxides oxidizing agents can also be used. Exem- 10 15 '20 25 30 35 H0 c _l _______, ____ c_? a Q 35 8001377-4 pelvis, the process can be practiced with salts of the organic oxidizing agents, e.g. salts of organic hydroperoxides (of the formula R - O - O - M) and salts of organic peroxyacids (of the formula RCO3M), where M is a catechinical group selected from the group consisting of alkali metals, alkaline earth metals and ammonium radicals. Of the alkali metals lithium, sodium, potassium lrubidium and cesium, the alkali metal is usually sodium or potassium. Of the alkaline earth metals beryllium, magnesium, calcium, strontium and barium, the alkaline earth metal is usually magnesium or calcium. Generally, when the catholyte liquid is an aqueous alkali metal hydroxide, MOH; the organic oxidizing agent is either in hydrogen form (eg R - O - O - H, R - O - O - R, RCOBH) or the alkali metal salt (eg R - O - O - M, RCO3M), where M is the same alkali metal in the hydroxide and the organic oxidizing agent.

Using organic peroxioxidants, the cathode reaction products are recovered from the oxidant from the catholyte chamber H5 together with the cell fluid. The cathodic reduction products of the oxidant may be partially or totally gases or vapors, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol or t-butyl alcohol. Alt. the products may be liquids recovered with 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-pentyl alcohol, n-pentyl alcohol, alcohol or amyl alcohol, or the cathode product may be emulsions or suspensions of excess amounts of sparingly soluble alcohols, such as sec-butyl alcohol, i-butyl alcohol, n-butyl alcohol, t-pentyl alcohol, n-pentyl alcohol, i-pentyl alcohol or amyl alcohol. When the cathode reduction product of the oxidant is recovered either as a gas or as both a gas and a liquid, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol or t-butyl alcohol, the cathodic reduction product is separated from both the water vapor and the gas phase and recovered. Alt. when the cathodic reducing 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, neopentyl alcohol or s-pentyl alcohol, the cathodic reduction product is separated from the cell fluid by "uz fl lhlïï 10 20 25 30 35 # 0 80013. well known in the art, such as fractional distillation, extraction, adsorption, stripping, other phase separation techniques or the like, and recovered.

According to one variant, tertiary butyl alcohol is produced during the electrolysis of sodium chloride brine. In this variant, sodium chloride salt solution is passed to an anolyte chamber 39 in an electrolytic cell II, whereby tertiary butyl hydroperoxide is passed to a catholyte chamber 45 in the cell and electric current is passed from an anode 37 in the cell III to a cathode 43 in the cell III, whereby chlorine is discharged. develops 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 in cell ll.a W Then from the cell ll an aqueous catholyte cell fluid containing sodium hydroxide, tertiary butarbonyl, e.g. acetone, and excess tertiary butyl hydroperoxide, probably as the sodium salt. With the addition of tertiary butyl hydroperoxide and a product in the form of tertiary butyl alcohol, an azeotrope can be formed upon evaporation and subsequent recovery and distillation of the cell fluid. This azeotrope contains 11: 76% water and 88.24% tertiary butyl alcohol.

In the variant where an excess of tertiary butyl hydroperoxide is fed to the cell, the tertiary butyl alcohol recovered as an azeotrope, the hydroperoxide salt of sodium, e.g. Naff® (CH 3) 3 COO- /, is crystallized from a concentrated aqueous solution of sodium hydroxide, e.g. a caustic soda solution containing more than 40% by weight of sodium hydroxide. This sodium salt of tertiary butyl hydroperoxide can then be recycled to the catholyte chamber H5 in a cell 11,15.

According to yet another variant, the cell fluid can be fed to another cell 13, e.g. to its catholyte chamber H5, thereby providing a catholyte liquid having elevated alkali metal hydroxide content and decreased organic oxidant content. The remaining organic oxidant can then be further reduced in the subsequent cell or cells together with the cell fluid, in order to provide additional by-product, eg more ketone, aldehyde, acid, alcohol or glycol and a high strength alkali metal hydroxide solution. In this embodiment, serial flow of the catholyte liquid, e.g. by a bipolar electrolyzer 1, be used.

According to yet another variant of the process, the oxidant www-sf ".- Pooïá QUALITY 10 15 20 25 50 35 BO 37 8001377-4 may be a redox pair, i.e. a reduction oxidation pair, where the oxidant is reduced inside the cell and then oxidized outside for return to A suitable redox pair, which can be fed to cell 11 as a cuprous compound, is reduced to a cuprous compound at the cathode H5 and recovered from the cathode compartment H5 as a cuprous compound, then the cuprous compound can be oxidized to a cuprous compound outside the electrolyzer 1 and returned to the cell. Suitable copper pairs include chelated copper pairs, the cell, such as a copper precursor such as phthalocyanines.

According to another variant of the process, when a redox pair is used, this redox pair may be a quinone-hydroquinone redox pair. In this case, the quinone is electrolytically reduced to hydroquinone at the cathode H3, whereby hydroquinone is recovered from the catholyte liquid H5 and oxidized to quinone outside the cell.

Another variant of the process means that solid oxygen carriers can be led to the cathode surface compartment H5 and partially recovered from oxygen. These include manganese (II) complexes, transition metal phthalocyanine tetrasulfonate complexes and binuclear copper (II) complexes of 1-phenyl-1,5,5-hexane priorate.

The cathode catalysts useful in the practice of the process are those which exhibit properties such as HOš disproportionation catalysts, ie catalysts capable of catalyzing the surface reaction 2HO 2 '-ïa-02 + 20H' (10). In addition, the catalyst should either have the ability to catalyze the electron transfer reaction O 2 + H 2 O + ae "-> HO 2" + OH 'or to be used with such a catalyst. (ll) The catalysts in question should also be chemically resistant to the catalytic fluid. Satisfactory HO 2 'disproportionation catalysts include carbon, the 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. can be present as metals, as alloys and as intermetallic compounds. When e.g. nickel is used, it can be mixed with Mo, Ta or Ti. These mixtures help to maintain low cathode voltage over long electrolysis periods.

Any metal from group IIIB, IVB, VB, VIB, Transition metal - 3293cc 91mm. 10 15 20 25 30 35 40 be a boride of a transition metal. VIIB, IB, IIB or IIIA, including alloys and mixtures thereof, which metal or alloy is resistant to the catholyte, can be used as cathode coating 43 or catalyst on the surface of the membrane 33.

Furthermore, solid metalloids, such as phthalocyanines of the Group VIII metals, perovskites, tungsten bronzes, spinels, delafossites and pyrochloro compounds, among others, can also be used as catalytic surface 43 on the membrane 33.

Particularly preferred catalysts are the platinum group metals, compounds of the platinum group metals, e.g. oxides, carbides, silicides, phosphides and nitrides thereof, as well as intermetallic compounds and oxides thereof, such as the rutile form RuO2-TiO2 with semiconducting properties.

According to another variant, the catechelectrocatalyst, i.e. the electron transfer catalyst for the reaction H 2 O + e '--e oH "+ H The transition metals which give borides with the required chemical resistance to concentrated aqueous alkali metal hydroxides and which have a surface catalytic activity for the above group , 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 , eg titanium, vanadium, niobium, tantalum, chromium, and tungsten, especially preferred are titanium diboride, TiB2.

According to another preferred variant, an intercalation compound of carbon and fluorine can be used as cathode catalyst H3.

By intercalation compound of carbon and fluorine is meant a carbonaceous material which is crystallized in a graphite layer lattice with the layer atoms separated from each other by a distance of about 1.41 Angstroms, the layers being separated by larger distances, e.g. at least about 3.35 Angstroms, and wherein fluorine atoms are present between the layers. In the case in question, the carbon layers in the intercalation compound may be pleated, as is the case for carbon monofluoride of the empirical formula (CFX), where X is between 0.68 and 0.995. Alt. For example, the carbon layers in the intercalation compound may be substantially planar, as is the case for tetracarbon monofluoride of the empirical formula (CFX), where X is between 0.25 0Ch 0.5Q -__ Included in the present IIM- ~ ...._, _________ ~ m PWR eff 10 15 20 25 50 35 UO _ torn. 39 8001377-4 cases are also various intermediate compounds and non-stoichiometric compounds.

Intercalation compounds of carbon and fluorine are also called They are characterized by an infrared spectrum having an absorption band at 120 cm cm -1. fluorinated graphites and graphite fluorides.

Catalyst 43 in the form of a carbon-fluorine intercalation compound may have incorporated therein a HO2 disproportionation catalyst.

When a gaseous oxidant, such as air or oxygen, is used, the electron transfer portion of the catalyst is hydrophilic, while the surface reaction portion may be hydrophilic or hydrophobic and preferably hydrophobic. The surface reaction catalyst is hydrophobic or is embedded in or supported by a hydrophobic film. The hydrophobic film may be a porous hydrophobic material, such as graphite or a film of a fluorocarbon polymer on the catalyst surface reaction catalyst described above, and the electron transfer catalyst should be in the immediate vicinity. They may be mixed, or they may be different surfaces of the same particles. For example, a particularly desirable catalyst may be provided by a microporous film on the permionic membrane surface 41 with catalyst 43 supported by a hydrophobic microporous film. of each other.

According to another variant, in which a depolarized cathode is used, the electrodes can be dripping electrodes, ie electrodes which drip oxidizing agents. When using dripping electrodes, the oxidant is distributed through the distribution device 51 to the catalytic particles H3, thereby avoiding contact with catholyte liquid in the catholyte compartment 45. Alternatively, the oxidant can be provided by means of a second distribution means, which abuts the cathode surface U1 of the permionic membrane 33 or against the catalytic particles H3.

The oxidant can be supplied in gaseous form, including excess air or oxygen. When excess air or oxygen is used, this excess of air or oxygen acts as a heat exchange medium, keeping the temperature low enough to keep the vapor pressure of the liquid chlorine low.

Alt. multiple oxidants can be used, such as air and oxygen, or air and a peroxy compound, or oxygen and a peroxy compound, or air or oxygen and a redox pair. When air or oxygen is used as the oxidizing agent, it (it) should be substantially free (free) from carbon dioxide, thus avoiding carbonate formation on the cathode.

POOlï QUALITY 10 15 we 8001377-4 M0 The use of a horizontal cell is particularly advantageous when cathode depolarization is used. Particularly satisfactory is the arrangement where the anode surface 55 of the permionic membrane 53 and the anodic catalyst 37 are located on top of the permionic membrane 31 and the cathodic surface 41 and the cathode catalyst 43 are located on the underside of the permionic membrane 35. This avoids soaking of the oxidation catalyst, i.e. the HO 2 - disproportionation catalyst, with alkali metal hydroxide, while producing a thin film of alkali metal hydroxide at the membrane surface 41 adjacent the cathode surface and improving the contact with the catalyst 43 and the oxidant. Although the method of the present invention has been described in connection with specific examples and embodiments thereof, the scope of patent protection is not intended to be limited thereto other than as set forth in the appended claims.

Claims (4)

9 ”aoo1z77-4 PATENT REQUIREMENTS An electrolysis process, which comprises feeding aqueous alkali metal chloride salt solution to an electrolytic cell having an anolyte compartment separated from a catholyte compartment by a solid polymer electrolyte, the solid polymer electrolyte comprising a fluorinated cationic agroalkyl bromine group arboxyl group arbor on its anodic surface and a cathodic electrocatalyst on its cathodic surface, that an electric potential is applied across the solid polymer electrolyte, and that chlorine is extracted from the anolyte compartment and alkali metal hydroxide from the cathode surface compartment sufficient pressure below about 4 MPa overpressure and such a temperature that the chlorine in the anolyte compartment is kept in liquid form, that liquid chlorine and depleted saline are taken out of the cell, and that the liquid chlorine is separated from the depleted saline solution. Process according to claim 1, in which chlorine is recovered from the depleted saline solution. 3. A process according to claim 2, characterized in that the depleted salt solution is cooled, thereby forming chlorohydrate, and in separating the chlorine hydrate from the known salt solution._ 4. A process according to claim 3, in which the depleted salt solution is cooled to below 9 ° C, characterized in that hydrochloride is formed. pooa QUNÅW