EP0050373A1 - Cellule d 'electrolyse et procédé pour la fabrication d'halogène - Google Patents

Cellule d 'electrolyse et procédé pour la fabrication d'halogène Download PDF

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Publication number
EP0050373A1
EP0050373A1 EP81108662A EP81108662A EP0050373A1 EP 0050373 A1 EP0050373 A1 EP 0050373A1 EP 81108662 A EP81108662 A EP 81108662A EP 81108662 A EP81108662 A EP 81108662A EP 0050373 A1 EP0050373 A1 EP 0050373A1
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Prior art keywords
membrane
cathode
layer
overvoltage
screen
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EP81108662A
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German (de)
English (en)
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EP0050373B1 (fr
Inventor
Oronzio De Nora
Gian Nicola Martelli
Antonio Nidola
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Oronzio de Nora SA
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Oronzio de Nora SA
Oronzio de Nora Impianti Elettrochimici SpA
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Priority claimed from IT8025483A external-priority patent/IT8025483A0/it
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Publication of EP0050373A1 publication Critical patent/EP0050373A1/fr
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/60—Constructional parts of cells
    • C25B9/65—Means for supplying current; Electrode connections; Electric inter-cell connections
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
    • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
    • C25B9/23—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms comprising ion-exchange membranes in or on which electrode material is embedded

Definitions

  • the invention herein is directed to electrolysis of an aqueous electrolyte and is particularly concerned with generating elemental halogen by electrolyzing an aqueous halide, such as hydrochloric acid or alkali metal chloride to generate elemental chlorine.
  • an aqueous halide such as hydrochloric acid or alkali metal chloride
  • a solid polymer electrolyte cell is characterized by an ion exchange membrane, which separates the electrodes of the cell and by the fact that one or preferably both electrodes are in contact with the membrane.
  • the solid polymer electrolyte cells present (with respect to conventional.membrane cells in which the cathode and frequently both anode and cathode are separated from the membrane), several advantages useful in different electrolysis processes. More precisely :
  • the ion permeable diaphragms are cation exchange polymers in the form of thin flexible sheets or membranes. Generally, they are imperforate and do not permit a flow of anolyte into the cathode chamber but it has also been suggested that such membranes may be provided with some small perforations to permit a small flow of anolyte therethrough, although the bulk of the work appears to have been accomplished with imperforate membranes.
  • Typical polymers which may be used for this purpose include fluorocarbon polymers such as polymers of trifluoroethylene or tetrafluoroethylene or copolymers thereof which contain ion exchange groups.
  • the ion exchange groups normally are cationic groups including sulfonic acid, sulfonamide, carboxylic acid, phosphoric acid and the like, which are attached to the fluorocarbon polymer chain through carbon and which exchange cations. However, they may also contain anion exchange groups.
  • Typical such membranes have the general formula : or
  • Such membranes include typically those fluorocarbon ion exchange polymers manufactured by the Du Pont Company under the trade name "Nafion” and by Asahi Glass Company of Japan under the trade name "Flemion”.
  • Patents which describe such membranes include British Patent No. 1,184,321 and U.S. Patent No. 3,282,875 and U.S. No. 4,075,405.
  • the cathode In cells of the type contemplated, the cathode is in close proximity to or in direct contact with the ion exchange membrane. They must be sufficiently permeable to permit rapid escape of evolved gas from the points of their evolution and to provide ready access of liquid electrolyte to these points as well as rapid removal of evolved alkali or other electrolysis products produced from such points. Thus the electrodes are normally quite porous.
  • electrode material in the form of very fine powder of catalytic material i.e. platinum group metal or oxide is mixed with an inert polymeric binder, mainly polytetrafluoroethylene (PTFE).
  • PTFE polytetrafluoroethylene
  • the mixture is sintered and hot-pressed in a suitable mold, in the form of extremely thin and sufficiently coherent porous 'film or layer . Said films are then hot-pressed onto the 'membrane surface to obtain a permanent adhesion to the membrane.
  • Methods of producing such electrodes are described in certain patents assigned to the General Electric Company. One patent which describes such methods is U.S. Patent No. 3,297,484.
  • an adherent and porous layer of metal resistant to corrosion and electrocatalytic on the membrane surface, which may or may not be preroughened by chemical reduction and deposition of the metal from solutions.
  • Said methods are defined "electroless" to distinguish them from the galvanic deposition. This method is described in the Italian Patent Applications SNs 24829 A/79 and 20489 A/80.
  • cathodic efficiency is relatively low, for example 85% or below and that oxygen in appreciable concentration, for example above 0.5 to 1% or more by volume, is evolved in the chlorine produced.
  • the high alkalinity may induce dehydration of the membrane with consequent decrease of the electrical conductivity, moreover the high concentration gradient increases the back-diffusion of the hydroxyl ion toward the anode with a resulting loss of the faraday efficiency.
  • membranes which has a weaker acidic section or surface on the cathode side and on the anode side.
  • membranes have been provided wherein the anode side comprises sulfonic or phosphonic groups and the cathode side comprises a cation exchange layer in which the acid groups are largely or even completely carboxylic.
  • the membrane is sulfonic acid or salt thereof on the anode side whereas on the cathode side the membrane surface is largely sulphonamide.
  • halogen is effectively generated by electrolyzing an aqueous halide in an electrolytic cell having a pair of opposed electrodes separated by an ion permeable separation preferably an ion exchange polymer and where at least one electrode, preferably the cathode, has two surfaces.
  • the first surface is resistant to electrodic and electrolytic attack and has a low overvoltage being readily capable of functioning as an electrode'and evolving electrolysis product by electrolysis.
  • the second such surface has a higher overvoltage (hydrogen overvoltage in the case of the cathode surface or chlorine overvoltage in the case of anode surface) and is between the lower overvoltage surface and the membrane, generally being in direct contact with or even bonded to the membrane.
  • both surfaces are electro- conductive and are capable of being polarized as an electrode. Furthermore both surfaces are in direct electrical contact so that there is little or substantially no potential difference between them.
  • the cathode may comprise an electroconductive porous metal coating disposed on and bonded to the cathode side of the membrane.
  • the intermediate cathode section may be in the form of an electroconductive grid-or grate with relatively high hydrogen overvoltage electroconductive surface which is pressed against the cathode side of the membrane.
  • the first or rear most cathode section has a lower hydrogen overvoltage surface than that of the front coating or grid engaging the membrane a major portion and even substantially all of cathodic electrolysis occurs at points spaced by the spacer or barrier from the membrane as distinguish ed from on or close to the membrane surface.
  • the cathode where the major electrolysis takes place Ls readily porous and permits ready flow including lateral flow of catholyte therethrough.
  • it may be in the form of fine mesh flexible electroconductive metal screen having to 10 mesh openings per centimeter or a mat of undulating wire screen or a combination of these elements.
  • the openings are relatively large and thus provide channels adjacent to the points of contact between the conductive spacer and the main cathode section whereby catholyte may flow edgewise along the cathode surface and adjacent these points thereby sweeping away evolved alkali from the front portion of the cathode as well as from the areas more remote from the membrane.
  • the spacer, barrier or intermediate section is itself quite thin often being less than 5 microns.
  • the remaining active section is at least 100 microns thick and this is two or more or even 10 or more times the thickness of the spacer. This permits flowing catholyte to have access to the front portions of the cathode a distance only equal to the spacer thickness thereby reducing the probability of localized high alkali concentrations undergoing formation at the membrane surface.
  • the spacer is of the same or substantially the same surface composition as the main cathode section some electrolysis may take place on the spacer or in the pores thereof. This amount is reduced by providing a barrier or spacer of higher hydrogen overvoltage than the hydrogen overvoltage of the major active cathode area.
  • the more active cathode may have a surface - comprising a platinum group metal or oxide thereof which has a very low hydrogen overvoltage.
  • the intermediate layer can have an electroconductive surface of a metal or oxide which is higher in overvoltage.
  • a thin porous layer of silver or copper metal or an iron or nickel screen may be used for this purpose.
  • other conductive materials which are resistant to corrosion in the alkaline cathode area may also be used.
  • the intermediate section in any case is porous and permeable to electrolyte. Being quite electroconductive, it may co-operate in transmitting current to'the more remove active cathode areas without serious increase in overall voltage.
  • the intermediate cathode section comprises a thin porous film of silver particles deposited on the membrane surface for example by chemical reduction or electroless deposition.
  • the ratio between empty and solid spaces in such a deposit or layer often ranges from 1.2 to 0.5.
  • one surface of the membrane is roughened by sandblasting or other method and then the roughened surface is swelled or hydrated with an alkali mild hydroxide solution, preferably diluted aqueous caustic soda or aqueous potash.
  • the alkali treated surface is contacted with a salt solution of the metal to be deposited, preferably silver in the form of a reducible compound such as silver .nitrate; the membrane is then contacted with a solution containing hydroquinone.
  • the hydroquinone due to the high alkalinity existing at the surface of the membrane, previously treated with the alkali solution, oxidizes the quinone reducing the metal ions absorbed on the membrane surface to metal.
  • the reduction proceeds until the alkalinity at the . membrane surface falls.
  • the reduction progresses only while adequate soda or potash is available at the membrane surface to neutralize evolved hydrogen ion or acidity generated with the oxidation of hydroquinone to quinone.
  • the reduction stops as the alkalinity due to the soda or potash previously absorbed on the membrane is consumed and the pH of the surface proceeds to or toward neutrality or an acidic state.
  • the metal grains formed at the surface do not act as catalytic sites for a further reduction of the metal and the coating thus obtained is finely dispersed highly porous and uniform, with metal grains therein being very small and the coating is quite thin.
  • the amount of the deposited metal is strictly determined by the availability of caustic soda and potash in the surface layer of the membrane, it is possible to control the amount and depth of deposited metal by limiting the depth of penetration of soda or potash within the membrane and contacting the pretreated membrane with the solution of the salt of metal to be reduced and then with the solution containing hydroquinone in quick succession.
  • one surface of the hydrated membrane is brought in contact with the caustic solution for a time comprised between 30 and 120 seconds, only on the surface to be treated, so that the diffusion of the soda or potash with the membrane takes place at largely or completely the surface whereon the electrode has to be applied.
  • the temperature is the room-temperature, although other temperatures may be considered as well.
  • the concentration of the caustic solution is another determining factor on the depth of penetration of the soda or potash within the thickness of the membrane.
  • a diluted solution tends to swell more the membrane and therefore to facilitate the penetration of soda or caustic.
  • a concentrated solution tends to shrink the membrane, making it more impervious to the internal diffusion of soda or potash.
  • the aqueous alkaline solution used in a soda solution between 2.5 and 20% by weight of NaOH.
  • the diffusion of soda within the membrane is therefore controlled by adjusting the contacting time through the concentration of the solution and the temperature.
  • the membrane surfaced is promptly rinsed with deionized and distilled water, and then contacted with the solution of the metal salt to be reduced.
  • this is a solution of silver nitrate with normality between 0.01 and 1 N, more preferably between 0.1 and 0.5 N.
  • the temperature is the room temperature, though different temperatures may be considered.
  • the treating times for this metal salt range from 30 to 120 sec., considering that a diluted solution requires a time longer than a more concentrated solution.
  • the membrane is again rinsed and the surface treated with alkali and then silver salt is contacted with an aqueous solution containing from 10 to 30% of a reducing agent which reduces the metal salt and generates hydrogen ion, such as hydroquinone, for a time ranging from 1 to 15 minutes.
  • a reducing agent which reduces the metal salt and generates hydrogen ion, such as hydroquinone
  • the membrane may be contacted with soda on both surfaces, whenever it is desired to apply the electrode coating on both surfaces, before proceeding to the reduction with hydroquinone.
  • alkali solutions such as sodium carbonate, or potassium carbonate solutions.
  • the coatings obtained with this embodiment of the present .nvention are exceptionally uniform with a thickness which may range from 0.025 to 0.5 micron the thickness being largely controlled by controlling the depth of penetration of the alkali .nd the subsequent absorption of metal salts.
  • the lateral reesistivity of the metal films thus obtained may range between .5 to 10 Ohm centimeters.
  • a reducing agent such as hydroquinone which enerates hydrogen ion in the course of reducing metal salt o metal is especially effective where it is desired to apply a metal coating to a cation exchange membrane and to avoid metal deposition within the interior of the membrane sheet.
  • the cation exchange material is itself acidic except to the extent where the exchange groups have been neutralized 'any generation of hydrogen ion reduces pH.
  • the metal salt reduction takes place only under an alkaline pH, the reduction stops as the alkalinity falls. Hence, if only the surface is contacted with alkali for a time insufficient to allow substantial alkali penetration below the surface reduction of metal is restricted to the depth of alkali penetration.
  • the invention is particularly applicable to diaphragms or membranes wherein one side or face thereof is less acidic or comprises a weaker acid than the other.
  • a membrane having predominately sulfonic groups on one .side and predominately carboxylic groups on the other side an effective silver coating is applied to the weaker acid side, i.e. the carboxylic side.
  • the coating is applied to the weaker acid side, i.e. the sulfonamid side.
  • the carboxylic side may also contain some sulfonic groups, if desired.
  • the membrane is thus coated with a thin electroconductive porous layer bonded thereto at least on one face.
  • This membrane is installed in a cell with the coating on the cathode side.
  • Such a cell has an electroconductive cathode section which is installed to bear against the above silver coating on its rear face (face remove from the membrane) and this cathode section has a lower hydrogen overvoltage than the porous silver coating.
  • the intermediate cathode section may comprise a screen or grid which is open to electrolyte and gas flow and which is merely pressed against or even embedded in the membrane so long as electrolyte has free access to its surface and evolved gas can escape therefrom.
  • Ordinary iron or nickel screen or graphite cloth which is thin and flexible so that it can bend to accomodate for irregularities in the membrane contour and can permit free electrolyte flow :may be used for this purpose.
  • Such screens are electroconductive and have a surface which can function as a cathodic surface but at a higher voltage because of its high hydrogen overvoltage surface.
  • This screen is backed by the first or principal cathode screen which may be in the form of one or a stack of electroconductive screens and/or and electroconductive compressible wire mat which has a lower overvoltage surface than the intermediate screen.
  • the electrode area of the low overvoltage surface substantially exceeds often by 25-50% or more the electrode area of the higher overvoltage surface of the front or intermediate cathode section.
  • the cathode may comprise a single structure such as a compressible electroconductive mat or a screen or grill work with two electroconductive electrode surfaces one of which has a lower hydrogen overvoltage aligned with respect to the membrane so that the high overvoltage surface bears against the membrane with the lower overvoltage surface being spaced therefrom.
  • the higher overvoltage cathode surface may comprise metallic iron or nickel or silver, silver alloy etc.
  • lower overvoltage surface may comprise a platinum group metal or electroconductive oxide (platinum, ruthenium, palladium etc.) as a coating on a nickel or iron screen as an alloy or mixed oxide of such platinum group metal and nickel.
  • platinum group metal or electroconductive oxide platinum, ruthenium, palladium etc.
  • such lower overvoltage surface may comprise a conductive sulfide such as nickel or iron sulfide or mixtures thereof with iron or nickel metal or oxide.
  • the difference in hydrogen overvoltage between the two surfaces should not be excessive and preferably they do not differ by more than about 0.5 volts at current densities in the range of 2 to 5 KA/m 2 and preferably comprised between 0.1 and 0.5 volts.
  • the membrane surface may be roughened or abraded, for example by sandblasting,sputter etching, embossing or other means to increase its surface area.
  • the cathode is then pressed into unbonded contact with such rough surface.
  • the surface area of the abraded surface of a membrane of given size generally is at least about 25 percent and often 50% of above greater than the surface area of a membrane of such size or dimension with a smooth surface.
  • a square membrane sheet one meter square has an overall or enclosed area of one square meter.
  • the sheet may be roughened enough to increase its surface area to 1.25 - 1.5 square meters or even higher although the overall area or its bulk edge to edge cross sectional area enclosed by the periphery of the sheet remains the same.
  • the depth of penetration of the pitted or roughened area is small, rarely exceeding about 25 micron and generally the depth of the roughened area is below 10 microns, generally being below 5 microns. Also the average distance between crests of the roughened area is small, rarely exceeding 50 microns and preferably being below 10 microns, usually being 0.1 to 5 microns.
  • the roughening of the membrane surfaces may be achieved by sandblasting the membrane with sand-or quartz particles of 50 to 150 microns for a few seconds up to one or two minutes.
  • the cell comprises an anode end plate 103 and a cathode end plate 110, both mounted in a vertical plane with each end-plate in the form of a channel having side walls respectively enclosing an anode space 106 and a cathode space 111.
  • Each end plate also has a peripheral seal surface on side-walls projecting on each side of the cell from the plane of the respective end plate, 104 being the anode seal surface and 112 being the cathode seal surface.
  • These surfaces bear against a membrane or diaphragm 105 which stretches across the enclosed space between the side walls separating anode from cathode.
  • this membrane is provided on the cathode side with the roughened surface with a cathode screen bearing against the rough surface.
  • the membrane may be coated with silver, copper or the like porous coating 205 as described above.
  • the anode 108 may comprise a relatively rigid uncompressible sheet of expanded titanium metal or other perforate, anodically resistant substrate, preferably having a non- passivable coating thereon such as a metal or oxide or mixed oxide of a platinum group metal.
  • This sheet is sized to fit within the side walls of the anode back plate and is supported.. rather rigidly by spaced electroconductive metal or graphite ribs 109 which are fastened to and project from the web or base of the anode end plate 103.. The spaces between the ribs provide for ready flow of anolyte which is fed into the bottom and withdrawn from the top of such spaces.
  • the entire end plate and ribs may be of graphite and alternatively, it may be of titanium clad steel or other suitable material.
  • the rib ends bearing against the anode sheet 108 may or not be coated, e.g. with platinum or like metal to improve electrical contact and the anode sheet 108 may, if desired, be welded to the ribs 109.
  • the anode rigid foraminous sheet 108 is held firmly in an upright position.
  • This sheet may be of expanded metal having upwardly inclining openings 10 directed away from the membrane (see Fig. 2) to deflectrising gas bubbles towards the space 109 and away from the membrane.
  • the screen 108a usually a fine mesh screen provides a density of contacts of extremely low area with the membrane in excess of at least 30 contacts per square centimeter. It may be spot welded to the coarse anode screen 108 or not, as desired.
  • ribs 120 extend outward from the base of the cathode end plate 110 a distance which is a fraction of the entire depth of the cathode space 111. These .ribs are spaced across the cell to provide parallel space for vertical electrolyte flow from bottom to top and engage the cathode which is in sheet or layer form, i.e. it's thickness dimension is much less than its width and height.
  • the cathode end plate and ribs may be made of steel or a nickel iron alloy or other cathodically resistant electroconductive material.
  • On the conductive ribs 120 is welded a relatively rigid pressure plate 122 which is perforate and readily allows circulation of electrolyte from one side thereof to the other.
  • the pressure plate is electroconductive and serves to impart cathodic polarity to the electrode and to apply pressure thereto and it may be made of expanded metal or heavy screen of steel, nickel, copper or alloys thereof.
  • a relatively fine flexible screen 114 bears against the rough surface of the membrane or against the coating 205, if present on the cathode side of the active area of diaphragm 105.
  • This screen because of its flexibility and relative thinness, assumes the contours of the diaphragm and therefore that of anode 108.
  • a metal screen mat 113 is disposed behind the screen and this compressible mat is cathodic and serves as part of the cathode.
  • the screen 114 is composed of nickel wire or other electroconductive cathodically resistant wire which has a surface of low hydrogen overvoltage (lower than the silver) and may be coated with a low hydrogen overvoltage coating such as coating of a platinum group metal or oxide thereof.
  • two or more electroconductive metal screens are interposed between the rough membrane surface and the compressible mat 113.
  • a screen of relatively higher hydrogen overvoltage in direct contact with the membrane surface and a second screen or bank of screens which have a surface or relatively lower hydrogen overvoltage behind but in contact with the higher overvoltage screen.
  • the high overvoltage screen surface may be of iron or steel or nickel whereas the surface of the more remote screen or screens may comprise a coating of platinum group metal or conductive oxide thereof or nickel sulfide or other low overvoltage coating.
  • the differential in hydrogen overvoltage between the two types of surfaces ranges from 0.05 to 0.5 volts, rarely being above 0.6 volts.
  • the screen surfaces are in close electrical contact with each other since the screens are pressed tightly together and against the membrane by the compressible mat and are essentially at the same electrical potential.
  • the screens advantageously are fine in mesh and provide many contacts of low area with the membrane and with the next adjacent screen, usually being at least 30 contacts per square . centimeter.
  • a compressible electroconductive wire mat 113 is disposed between the cathode screen 114 and the cathode pressure plate 122.
  • the mat 113 is a crimped corrugated or wrinkled compressible wire-mesh fabric which fabric is advantageously an open mesh knitted-wire mesh of the type described in U.S. application for United States Letters Patent Serial No. 102629 filed December 11, 1979 wherein the. wire strands are knitted into a relatively flat fabric with interlocking loops.
  • This fabric is then crimped or wrinkled into a wave or undulating form with the waves being close together, for example 0.3 to 2 centimeters apart, and the overall thickness of the compressible fabric is 2 to 10 millimeters.
  • the crimps may be in a zig-zag or herringbone pattern and the mesh of the fabric is coarser, i.e. has a larger pore size than that of screen 114. Both the screen 114 and the mat generally have pore or void size substantially larger than the pore size of coating 205.
  • this undulating fabric 113 is disposed in the space between the finer mesh screen or screens 114 and the more rigid expanded metal pressure plate 122.
  • the undulations extend across the space and the void ratio of the compressed fabric is, notwithstanding compression, preferably higher than 75%; preferably between 85 and 96%, of the apparent volume occupied by the fabric.
  • the waves extend in a vertical or inclined direction so that channels -for upward free flow of gas and electrolyte are provided which channels are not substantially obstructed by the wire of the fabric. This is true even when the waves extend across the cell from one side to the other because the mesh openings in the sides of the waves permit free flow of fluids.
  • the end-plates 110 and 103 are clamped together and bear against membrane 105 or a gasket shielding the membrane from the outside atmosphere disposed between the end walls.
  • the clamping pressure compresses the undulating fabric 113 against the finer screen or screens 114 and the metal coating or the roughened membrane to the thickness substantially less than the fabric in it uncompressed state. This in turn presses the screen 114 against the membrane and thus, the anode surface of the membrane presses against anode 108a.
  • substantially saturated sodium chloride aqueous solution is fed into the bottom of the anolyte compartment of the cell and flows upward through channels or spaces 105 between ribs 109 and depleted brine and evolved chlorine escapes from the top of the cell.
  • Water or dilute sodium hydroxide is fed into the bottom of the cathode chamber and rises through channels 111 as well as through the voids of the compressed mesh sheet 113 and evolved hydrogen and alkali is withdrawn from the top of the cell.
  • Electrolysis is caused by imparting a direct current electric potential between the anode and cathode end plates.
  • At least the upper openings in pressure plate 122 are louvered to provide an inclined outlet directed upwardly away from the compressed fabric 113 whereby some portion of evolved hydrogen and/or electrolyte escapes to the rear electrolyte chamber 111.' Therefore, the vertical spaces at the back of the pressure plate 122 and the space occupied by compressed mesh 113 are provided for upward catholyte and gas flow.
  • aqueous brine containing from 140 to 300 grams per liter of sodium chloride is circulated within the anode compartment of the cell.
  • Chlorine is evolved at the anode, while the solvated ions tend to migrate through the cation membrane and reach the cathode where caustic soda of substantial concentration above 15-20% by weight and hydrogen is evolved.
  • Solutions containing 25 to 40% by weight of alkali metal hydroxide may be produced with anode and cathode efficiencies above 90% frequently above 95%.
  • the cathodically polarized section includes the end plate 110 and pressure plate 122 mat 113 and the screen or assembly of screens 114 which bear against the membrane.
  • the screen or the rear screen and/or the mat 113 is coated with a coating or surface which has a low or substantially negligible hydrogen overvoltage.
  • Typical coatings include a mixture of nickel and conductive ruthenium oxide, platinum black or platinum metal or other such coating of a low hydrogen overvoltage material.
  • the depth of this active area may be expanded by coating the compressible wire fabric 113 with the same material.
  • the coating becomes polarized as a cathode.
  • generation of caustic and chlorine at such coating is small or even substantially nonexistent relative to the amount generated on the screen 114 and or compressed fabric 113 for at least two reasons, first it has a higher hydrogen overvoltage than the surface on screen 114 or 113 and second because its area is comparatively smaller because it has a thickness less than 1 to 2 microns as discussed above. Consequently, only a small portion of the evolved caustic tends to back migrate toward the anode.
  • the thin silver layer may thus constitute a less active porous spacer element between the membrane and a more active cathode area where the bulk of the caustic is generated and swept away. This more larger active.area is readily permeable to edgewise electrolyte flow promoting rapid removal of caustic not only from the active cathode surfaces but from ; the pores of the thin silver coating.
  • the path of flow of evolved caustic through the coating is lengthened thus hindering although not necessarily completely preventing escape of caustic evolved therein.
  • this may tend-to promote the undesirable back migration discussed above.
  • it has been considered desirable to limit thickness of the layer to a maximum of 2 to 5 microns preferably not over 2 microns and more advantageously below one micron.
  • the active screen as well as the fabric 113 have openings much larger than the pores of the silver coating. Thus such openings may be 0.1 centimer wide or even more and in case of the fabric 113 the voids exceed the solid wire sections by several times. As a consequence electrolyte may flow in an edgewise direction through fabric 113 as illustrated in Fig. 2 as well in a ramdom path around, along and through the open mesh of screen 114.
  • a silver coating having a thickness below one micron, usually below 0.5 micron, is especially effective in promoting cathode efficiency of 95% or above
  • the silver coating may be thickned as by electrodeposition or further electroless coating so long as good porosity of the coating is_retained.
  • this coating is less than about 5 microns and rarely above one or two microns in thickness.
  • the metal coating 205 is porous, the coating may appear continuous to the naked eye. Thus the pores or voids are much smaller than those in either the screen or the mat. This small pore size may be the reason the coating appears to be a barrier which may restrain back migration of alkali to the area of the anode.
  • the cell is capable of operation at cathode Faraday efficiencies of 95% and above with less than 0.5% if even substantially no oxygen in chlorine evolved at the anode. In contrast where the coating is omitted cathode efficiencies of 85-88% and oxygen concentration of 1-2% by volume in the chlorine have been observed.
  • the cation exchange membrane is a sheet having a hick- ness of 0.3 millimeters constituted by two layers of cation resin laminated together with an interlayer of polytetrafluoroethylene screen as mechanical support, one layer is made of a copolymer of tetrafluoroethylene and perfluorovinylether sulfonyl fluoride (or acid) having an equivalent weight of 1100 and the other layer consisting of a copolymer of tetrafluoroethylene and a perfluorovinyleter containing carboxylic groups and having an equivalent weight approximately in the same ranges.
  • the membrane is then hydrated by soaking in a deionized and distilled water for about 2 hours at a temperature from 60 to 80°C.
  • the membrane is then placed on the bottom of a watertight container consisting in a flat bottom and a frame laid on the perimeter of the membrane with the carboxylic side up.
  • An aqueous solution containing 10% by weight of caustic soda is poured on the membrane at room temperature and left for 60 seconds. Then the solution is removed and the membrane surface was quickly rinsed with distilled water.
  • An aqueous solution 0.15 N of silver nitrate is then poured on the treated carboxylic surface of the sheet in the same container, at room temperature, and left for 60 seconds.
  • the membrane surface is rinsed again with distilled water and an aqueous solution containing 20% of hydroquinone is then poured on the sheet in the container and left for 10 minutes.
  • a silver layer is deposited on the carboxylic side of the membrane coating the sulfonic acid side of the membrane uncoated.
  • the weight of silver is about 0.5 grams per square meter of membrane surface.
  • the morphology of the silver layer deposited on the carboxylic side of membrane is then observed under an electronic microscope.
  • the silver layer appears constituted by finely dispersed crystals having dimensions varying from 0.01 micron to 0.1 micron.
  • the thickness of the silver layer substantially corresponds to the sizes of the crystals and the porosity degree, expressed as the ratio between full and empty spaces of the projected area, is comprised between 1.2 and 0.5 and ranges from 0.1 to 0.5 micron.
  • Figure 3 is an enlargement, magnified 80.000 times, of the silver electrode so deposited on the membrane.
  • Figure 4 shows an enlargement at a signification of 10,000, of a palladium electrode obtained via following the reduction method disclosed in Example 1 of the Italian Patent application SN 20.489 A/80. :
  • the palladium electrode obtained via "electroless” exhibits a typical structure of growth with large modular grains and agglomerates, several (about 10) micron thick and the membrane appears to be completely shielded by the metallic layers, conversely the silver electrode of the invention shows a thinner structure characterized by finely dispersed smaller grains with a high porosity degree.
  • the lateral resistivity of the silver electrodic layer measured by a microhmeter is about 7 ohm centimeters.
  • the membrane/electrode system obtained according to the method of the foregoing example was arranged in a laboratory cell similar to that illustrated in figs. 1 and 2 and consisting of two compartments separated by the coated membrane with the silver coating on the cathode side.
  • the anode was an expanded sheet of titanium, coated with an electrocatalytic layer of titanium and ruthenium mixed oxide supplied by Permelec S.p.A. of Milan, under the trade mark of DSA( R ).
  • the low overvoltage cathode section was a micronet with 9 meshes per cm., galvanically coated with an alloy of nickel (50%) and ruthenium (50%), directly pressed against the silver layer deposited on the membrane surface.
  • the current conducting system comprised an undulating crimped resilient mat about 0.5 centimeters thick made of knitted nickel wire having a diameter of 0.11 millimeters pressed against the micro-net by means of an expanded sheet made of low-carbon containing steel, substantially rigid and connected to the negative pole of the electric current source.
  • the electrode surface was about 240 x 240 millimeters.
  • Oxygen in the chlorine below 0.2 percent is observed in this type of experiment.
  • cation membrane sheet have been coated on the carboxylic layer surface with silver electrode prepared according to the method described in Example 1, varying opportunely the conditions for controlling the quantity and therefore the thickness of the electrodic layer.
  • the membrane treated- is a fluorocarbon polymer cation ; exchange membrane which is a laminate of two layers.
  • One of these layers is a copolymer of a polyfluoroethylene (tetrafluoroethylene) and a perfluorovinylether-sulfonylfluoride (or/and) having an equivalent weight of about 1100.
  • the other layer is a sheet of a copolymer of the polyfluoroethylene (tetrafluoroethylene) and a perfluoroethylene other which contains carboxylic groups. This carboxylic sheet also has an equivalent weight of about 1100.
  • the two layers are laminated together with an interlayer of polytetrafluoroethylene screen to provide mechanical support.
  • the thickness of the membrane is 0.3 millimeters.
  • the treated sheet is assembled in different cells of the type described above after conditioning by heating at about 80°C in an aqueous solution containing 2-3 percent by weight of sodium chloride until the dimensions of the sheet (swelling) has stabilized.
  • the cell has anodes as described above comprising expanded titanium metal with a ruthenium oxide coating thereon.
  • a ruthenium oxide coated titanium screen is interposed between 'the expanded metal and the anode (sulfonic) side of the membrane.
  • the sheets are installed with the sandblasted carboxylic surface on the cathode side.
  • the cathode comprises a cathode backplate and pressure plate engaging a compressible knitted metal crimped compressible mat 113 which compresses against the screen or screens which in turn are pressed against the membrane surface.
  • the cells are operated circulating ⁇ aqueous brine containing 215 to 225 grams per liter of sodium chloride through the anolyte compartment and aqueous sodium hydroxide through the catholyte compartment with enough alkali hydroxide withdrawn and water added to the catholyte to maintain the hydroxide concentration at 30% by weight NaOH. Voltage imposed is enough to achieve the specified current density.
  • the anode used comprised titanium screen pressed against a finer titanium screen which was pressed against the membrane. Both screens were coated with conductive ruthenium oxide.
  • Sodium chloride solution containing 230 grams per liter of NaCl and having a pH of 3.5 was circulated at a temperature of 65-75°C through the anolyte chamber. The current density was 3000 Amperes per square meter. In all the cases the membrane has been sandblasted on the cathode side with quartz particles for 30 seconds.
  • the cathode alignment was as stated in table V. The results were as follows :
  • the above process may be conducted in the electrolysis of aqueous alkali metal chloride containing 150 to 325 grams- per liter of alkali metal chloride and the amount of water fed to the catholyte chamber being controlled to produce a convenient concentration of NaOH ranging from 5 to 40 or more, preferably 25 to 40 percent NaOH by weight.
  • Other alkali metal halides or other aqueous halides including hydrochloric acid and other metal halides may be electrolyzed to produce the corresponding halogens (chlorine, bromide include etc.).
  • water may be electrolyzed with the cell herein described to produce oxygen and hydrogen.
EP81108662A 1980-10-21 1981-10-21 Cellule d 'electrolyse et procédé pour la fabrication d'halogène Expired EP0050373B1 (fr)

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
IT8025483A IT8025483A0 (it) 1980-10-21 1980-10-21 Elettrocdi per celle ad elettrolita solido applicati sulla superficie di membrane scambiatrici di ioni e procedimentodi prparazione ed uso degli stessi.
IT2548380 1980-10-21
US21217280A 1980-12-02 1980-12-02
US212172 1980-12-02
US06/268,431 US4381979A (en) 1980-10-21 1981-05-29 Electrolysis cell and method of generating halogen
US268431 1981-05-29

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EP0050373A1 true EP0050373A1 (fr) 1982-04-28
EP0050373B1 EP0050373B1 (fr) 1988-06-01

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Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0066102A1 (fr) * 1981-05-26 1982-12-08 Asahi Glass Company Ltd. Cellule d'électrolyse à membrane échangeuse d'ions et procédé d'électrolyse l'utilisant
EP0066127A1 (fr) * 1981-05-22 1982-12-08 Asahi Glass Company Ltd. Cellule électrolytique à membrane échangeuse d'ions
EP0066101A1 (fr) * 1981-05-26 1982-12-08 Asahi Glass Company Ltd. Cellule d'électrolyse à membrane échangeuse d'ions et procédé d'électrolyse l'utilisant
FR2519030A1 (fr) * 1981-12-30 1983-07-01 Gen Electric Procede de production de produit caustique, ensemble unitaire membrane-electrode et structure d'electrodes multicouches
EP0124125A2 (fr) * 1983-05-02 1984-11-07 De Nora Permelec S.P.A. Cellule d'électrolyse et méthode de production d'halogène
EP0170419A2 (fr) * 1984-07-02 1986-02-05 Olin Corporation Cellule à densité de courant élevée
US4615775A (en) * 1979-08-03 1986-10-07 Oronzio De Nora Electrolysis cell and method of generating halogen
FR2624885A1 (fr) * 1987-12-17 1989-06-23 Commissariat Energie Atomique Ensemble electrodes-electrolyte polymere solide utilisable par exemple pour l'electrolyse de l'eau, et son procede de fabrication
EP0390157A2 (fr) * 1989-03-31 1990-10-03 United Technologies Corporation Cellule d'électrolyse et méthode d'utilisation
EP0629015A1 (fr) * 1993-04-30 1994-12-14 De Nora Permelec S.P.A. Cellule électrochimique comportant des membranes d'échange d'ions et des plaques bipolaires métalliques
WO1996011507A1 (fr) * 1994-10-11 1996-04-18 E.I. Du Pont De Nemours And Company Procede d'application de particules a activite catalytique sur une membrane
WO1996013073A1 (fr) * 1994-10-20 1996-05-02 Hoechst Aktiengesellschaft Membrane metallisee echangeuse de cations
US5639360A (en) * 1991-05-30 1997-06-17 Sikel N.V. Electrode for an electrolytic cell, use thereof and method using same
EP0817297A2 (fr) * 1996-06-26 1998-01-07 De Nora S.P.A. Cellule électrochimique à membrane comportant des électrodes à diffusion gazeuse en contact avec des collecteurs métalliques poreux et plats pourvus de plages de contacts hautement distribuées
WO2004048643A1 (fr) * 2002-11-27 2004-06-10 Asahi Kasei Chemicals Corporation Cellule electrolytique bipolaire sans interstice
EP2746429A1 (fr) 2012-12-19 2014-06-25 Uhdenora S.p.A Électrolyseur

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB797565A (en) * 1956-03-29 1958-07-02 Lonza Electric & Chem Works A method of activating the cathode surfaces of electrolytic hydrogen generators
GB1534942A (en) * 1976-11-11 1978-12-06 Portals Water Treatment Ltd Electrode assembly for an electrolytic cell
US4214954A (en) * 1978-12-04 1980-07-29 Olin Corporation Plated metallic cathode with porous copper subplating

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB797565A (en) * 1956-03-29 1958-07-02 Lonza Electric & Chem Works A method of activating the cathode surfaces of electrolytic hydrogen generators
GB1534942A (en) * 1976-11-11 1978-12-06 Portals Water Treatment Ltd Electrode assembly for an electrolytic cell
US4214954A (en) * 1978-12-04 1980-07-29 Olin Corporation Plated metallic cathode with porous copper subplating

Cited By (25)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4615775A (en) * 1979-08-03 1986-10-07 Oronzio De Nora Electrolysis cell and method of generating halogen
EP0066127A1 (fr) * 1981-05-22 1982-12-08 Asahi Glass Company Ltd. Cellule électrolytique à membrane échangeuse d'ions
EP0066101A1 (fr) * 1981-05-26 1982-12-08 Asahi Glass Company Ltd. Cellule d'électrolyse à membrane échangeuse d'ions et procédé d'électrolyse l'utilisant
EP0066102A1 (fr) * 1981-05-26 1982-12-08 Asahi Glass Company Ltd. Cellule d'électrolyse à membrane échangeuse d'ions et procédé d'électrolyse l'utilisant
FR2519030A1 (fr) * 1981-12-30 1983-07-01 Gen Electric Procede de production de produit caustique, ensemble unitaire membrane-electrode et structure d'electrodes multicouches
EP0124125A2 (fr) * 1983-05-02 1984-11-07 De Nora Permelec S.P.A. Cellule d'électrolyse et méthode de production d'halogène
EP0124125A3 (en) * 1983-05-02 1985-05-15 Oronzio De Nora Impianti Elettrochimici S.P.A. Electrolysis cell and method of generating halogen
EP0170419A2 (fr) * 1984-07-02 1986-02-05 Olin Corporation Cellule à densité de courant élevée
EP0170419A3 (fr) * 1984-07-02 1987-10-14 Olin Corporation Cellule à densité de courant élevée
FR2624885A1 (fr) * 1987-12-17 1989-06-23 Commissariat Energie Atomique Ensemble electrodes-electrolyte polymere solide utilisable par exemple pour l'electrolyse de l'eau, et son procede de fabrication
EP0390157A2 (fr) * 1989-03-31 1990-10-03 United Technologies Corporation Cellule d'électrolyse et méthode d'utilisation
EP0390157A3 (fr) * 1989-03-31 1991-04-17 United Technologies Corporation Cellule d'électrolyse et méthode d'utilisation
US5639360A (en) * 1991-05-30 1997-06-17 Sikel N.V. Electrode for an electrolytic cell, use thereof and method using same
EP0580730B2 (fr) † 1991-05-30 1999-06-09 Sikel N.V. Electrode pour cellule electrolytique, son utilisation et procede l'utilisant
EP0629015A1 (fr) * 1993-04-30 1994-12-14 De Nora Permelec S.P.A. Cellule électrochimique comportant des membranes d'échange d'ions et des plaques bipolaires métalliques
WO1996011507A1 (fr) * 1994-10-11 1996-04-18 E.I. Du Pont De Nemours And Company Procede d'application de particules a activite catalytique sur une membrane
WO1996013073A1 (fr) * 1994-10-20 1996-05-02 Hoechst Aktiengesellschaft Membrane metallisee echangeuse de cations
US5906716A (en) * 1994-10-20 1999-05-25 Hoechst Aktiengesellschaft Metallized cation exchange membrane
EP0817297A2 (fr) * 1996-06-26 1998-01-07 De Nora S.P.A. Cellule électrochimique à membrane comportant des électrodes à diffusion gazeuse en contact avec des collecteurs métalliques poreux et plats pourvus de plages de contacts hautement distribuées
EP0817297A3 (fr) * 1996-06-26 1999-05-19 De Nora S.P.A. Cellule électrochimique à membrane comportant des électrodes à diffusion gazeuse en contact avec des collecteurs métalliques poreux et plats pourvus de plages de contacts hautement distribuées
WO2004048643A1 (fr) * 2002-11-27 2004-06-10 Asahi Kasei Chemicals Corporation Cellule electrolytique bipolaire sans interstice
US7323090B2 (en) 2002-11-27 2008-01-29 Asahi Kasei Chemicals Corporation Bipolar zero-gap type electrolytic cell
EP2039806A1 (fr) 2002-11-27 2009-03-25 Asahi Kasei Chemicals Corporation Cellule electrolytique bipolaire sans interstice
CN101220482B (zh) * 2002-11-27 2011-02-09 旭化成化学株式会社 复极式零间距电解池
EP2746429A1 (fr) 2012-12-19 2014-06-25 Uhdenora S.p.A Électrolyseur

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DE3176766D1 (en) 1988-07-07

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