DD140262A5 - METHOD FOR CONTINUOUS PRODUCTION OF CHLORINE - Google Patents

Description

06/22/1979

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Process for the continuous production of chlorine Field of application of the invention

The invention relates generally to a process for producing halogens and alkali metal hydroxides by electrolysis of aqueous alkali metal halide salts.

More particularly, the invention is directed to a process of producing chlorine and sodium hydroxide by electrolysis of brine in a cell having a solid polymer electrolyte membrane with at least one surface having a catalytic anode and / or cathode connected is"

Characteristic of the known technical solutions

The production of halogens, such as chlorine, by electrolysis of sodium chloride solution with lye (HaOH) as a second product is of great industrial importance. The chlorine / alkali industry produces millions of tons of chlorine and caustic soda every year. The principal electrolytic processes by which chlorine has been produced are the so-called mercury cell method and the diaphragm cell method = The mercury method excludes the electrolysis of an alkali metal

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Chloriälösung in a cell between a graphite or metal anode ein _s which is also referred to as dimensionally stable anode.

Chlorine is liberated at the anode, and the alkali metal migrates into the mercury to form a corresponding amalgam. "This amalgam is then reacted in a decomposition reaction with water to produce caustic soda and hydrogen." For all practical purposes, the mercury cell process is for the preparation of Chlorinated outdated "Mercury is such a dangerous substance, and the regulations governing the control of mercury and other types of pollution have become so severe that the days of the mercury cell are over." However, mercury cells are also expensive and complex for chlorine production in this impurity aspect Use of mercury itself causes problems in terms of the size and complexity of Stage ₅ , since care was required in the handling of this material. "In addition, mercury is expensive - and must be used in large quantities. Further, the need for decomposition causes «- stage of the formed.Amalgams.including the belonging equipment, - caustic soda and. Exploiting hydrogen, an additional price increase »

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Although no mercury is used in the diaphragm parts, it does contain porous electrodes - which are separated by a microporous diaphragm. "The space between the electrodes is mixed with brine. filled and separated by a microporous diaphragm, which may take the form of an overlying porous diaphragm which separates the cathode electrolyte (hereinafter called "catholyte" for short) and the anode electrolyte (hereinafter called "anolyte") chambers one from the other The serious disadvantages of a diaphragm cell is that the pores in the diaphragm allow mass transport or hydraulic flow of the sodium chloride solution through the diaphragm. As a result, the catholyte contains "broth" produced at the cathode, "considerable amounts of sodium chloride." This means the production of a "contaminated and diluted brine." On the other hand, the hydroxide produced at the cathode can pass through the porous diaphragm to the anode. where it is electrolyzed oxygen production "the formation of oxygen at the anode is for various reasons adverse oxygen-not only to a" contamination of Chlore _s formed there but also takes the anode to "

Since the. Maasentransport between the chambers so many. Unwanted effects has _s -ist a number of arrangements. have been proposed to remedy or at least partly resolve these problems * One of them

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is the maintenance of a pressure difference across the diaphragm so as to minimize the mass transport of the electrolyte between the anolyte and catholyte chamber. However, these solutions have in the best case been considered to be only partially effective. "

In order to eliminate the disadvantages associated with the diaphragm cell and the mass transport through the porous diaphragm, it has been proposed to use "selective ionic permeability membranes in cells for chlorine generation" to separate the anolyte from the catholyte chamber. These permeability-selective membranes used in these cells are typically cationic membranes which allow the selective passage of positive cations and minimize the passage of negatively charged anionone. Since these membranes are not porous, they hinder the return migration of the liquor from the catholyte chamber into the amino chamber and similarly prevent the transport of the brine anolyte into the catholyte chamber and the dor-ti-ge Dilution of the lye "It has been found, however, that even the membrane parts still have certain disadvantages, which limit their application to a great extent". One of the main disadvantages of the. Cell membrane-is. That they require a high cell tension. This high cell fission is only partly attributable to the use of the membrane, and is chiefly due to the fact that electrodes are known in the known cells of Meinbrank

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be used in the spatial distance from the diaphragm "As a result of this spatial distance between the electrodes and the membrane, the cell in addition to the Spannimgsabfall across the membrane voltage drop in the electrolyte between the electrodes and the membrane _s and these cells are subject to further a voltage drop due to Gas bubble formation or mass transfer «Since the catalytic electrodes are located at a distance from the membrane, the chlorine is generated at a distance of άβτ membrane. This leads to the formation of a gaseous layer between the electrode and the membrane. This gaseous layer interrupts the electrolyte path between the electrode and the membrane and thereby partially blocks the ions from the membrane. This interruption of the electrolytic path between the electrode and the membrane naturally leads to a further voltage drop Increases cell tension required to produce chlorine and, apparently, reduces the cell's voltage efficiency. "

Aim of the invention miff

Ziel.der invention is to provide a -einfachen _s economic and industrially applicable process for the production of halogen and alkali metal ".ydroxiden by electrolysis of brines *

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The invention is based on the concept of 'developing a suitable membrane for the separation of the anode axaxamer from the cathode chamber and arranging the electrodes more expediently to the membrane'.

The process according to the invention for the continuous production of chlorine by electrolysis of alkali metal chlorides is characterized by the following stages:

a) continuous introduction of an aqueous alkali metal chloride solution into the anode compartment of an electrolytic cell in which the anode compartment is separated from the cathode compartment by a cation selective ion exchange membrane,

b) contacting this solution with a porous gas-permeable _s ks.talytischen anode electrode iet connected to the anode of the chamber facing side of the membrane and embedded therein, whereby the catalytic! Places in the. Electrode in contact with the ion-exchanging remnants of the membrane, so that the electrolysis can take place directly at the interface between the membrane and the electrode and against a porous, gas-permeable, cathodic cathode selectode on the other side of the membrane.

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c) continuously introducing a stream of water into the cathodic chamber and contacting it with the catalytic cathode electrode to provide a source of hydroxy ions at the cathode and to continuously rinse the cathode electrode to dilute the liquor formed therein;

d) supplying current to the electrodes to electrolyze the alkali metal chloride to produce chlorine at the anode and water to produce alkali metal hydroxide and hydrogen at the cathode and

e) Continuous removal of chlorine from the anode chamber and from lye and hydrogen from the cathode chamber *

According to the invention, the aqueous solution is brought into contact with a porous, gas-permeable, catalyst-bound anode of bound, reduced noble metal oxides, box-shaped isomers of bound, temperature-stabilized, reduced oxides of ruthenium, of bound, reduced oxides of ruthenium and made of graphite

The aqueous solution may erfindungsgomäß also be brought into contact with any of a porous gas-permeable _s, catalytic anode, in which the reduced oxides of ruthenium are further stabilized by a content of the reduced metal oxides ₅ 'are selected from

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the reduced oxides of iridium, tantalum, titanium, job, or hafnium,

Erfindiingsgemäß particularly an aqueous HaCl- ^ solution in contact with a porous ₉ is gas permeable? catalytic anode made of bound, reduced oxides of ruthenium and reduced oxides of iridium, for example with 5 to 25 % of reduced oxides of iridium ,

For example, the aqueous solution may also be contacted with a porous, gas-permeable, catalytic anode of bound reduced oxides of ruthenium and reduced oxides of tantalum.

The process according to the invention can also be carried out for the continuous production of chlorine from brine. The following steps are carried out %

a) continuous introduction of an acidified brine in the anode chamber. an electrolytic cell, ~. wherein the / modenkammer is separated from the cathode chamber by a cation selective ion exchange membrane ₉

b) continuously introducing a stream of water 3 into the cathode chamber 5

c) electrolyzing the acidified salsalt at a

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porous, gas - permeable, - catalytic anode, which is connected to a surface of the membrane and embedded in this, in order to discharge chloride at the anode zn and to minimize the evolution of oxygen _s .

d) simultaneous electrolyzing of water at a. porous, gas-permeable, catalytic cathode on the opposite side of the membrane to produce liquor and hydrogen, wherein the cathode is continuously rinsed with water to dilute the resulting liquor and the migration of the liquor through the membrane to the anode as low as possible keepν and

e) Continuous removal of chlorine from the anode compartment and from lye and hydrogen from the compartment chamber *

Er.findunga according to a Höl-angeeänerte brine is elektrölyeiert at the anode · whose Säurekonaentration maintained at above ₅₁ O 2 mol Hol wii? CU

The. The process is carried out in such a way, that the acidified brine in Koniakt with. a porous, gas-permeable anode of bonded, reduced Edolmetallosiden and the water in contact with a porous düjiiieü _s gaadurchlässigen catalytically t; L sch en cathode of gebimc? ... the BIIT the membrane connected enes Edelnstallteilchexi and in this one

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are bedded, with the thickness of the cathode not exceeding 0.025 mm in order to allow the penetration of water through the cathode to the interface between the cathode and the membrane, so that the liquor formed there is diluted.

Preferably, the thickness of the cathode may also be about 0.012 mm

The method-is in particular performed in such a way - that the acidified brine is brought into contact with a porous, gas permeable, catalytic anode of bonded, temperature stabilized, ·-reduced oxides of ruthenium * and in particular such _s that the acidified brine in contact with a porous , gas-permeable, catalytic anode is made of bound, reduced oxides of ruthenium and reduced oxides of iridium.

In the present invention, the process for producing halogen and alkali metal hydroxide can be carried out by electrolyzing an aqueous alkali metal halide solution between an anode and a cathode separated by a cation exchange membrane one of the electrodes comprises thermally-stabilized, reduced oxides of platinum-group metals comprising the membrane. Mim have a gas- and electrolyte-permeable catalytically © electrode

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It is advantageous that the reduced oxides associated with the membrane comprise a plurality of th.ermis.h stabilized "reduced platinum group metal oxide particles", in particular, that a layer of thermally stabilized, reduced oxide platinum group metal particles be bonded to opposite sides of the membrane to create gas and electrolyte turolic _s catalytic anode and cathode electrodes.

In this case, for example, the thermally stabilized reduced oxide particles of a platinum group metal can be bonded by means of a fluorocarbon polymer.

Brfindungsgemäß the particles thermally stabilized oxides of ruthenium can be thermally stabilized by a content of, reduced oxides of reduced oxides of iridium, tantalum, titanium or hafnium _s liobs are further stabilized "

The inventive method sum Halo ™ gen and.Alkalimetallhydroxid by electrolysis of aqueous alkali metal halide solution by means of a pair of catalytic! Electrodes separated by an ion-permeable membrane are characterized in particular by using an electrode. which is a Yielsahl of thermally stabilized, realized oxide particles of platinum group metals,

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bound to the side of the membrane facing the cathode

According to the invention, the process for producing chlorine by electrolysis of an aqueous alkali metal chloride-electrolyte between an anode and a cathode, which are separated by an ion exchange membrane, the. Flow of the aqueous electrolyte through the membrane limited by performing the electrolysis with a cathode comprising a thin layer of particles of platinum group metal or conductive oxides thereof, wherein the layer is connected to one side of the membrane and in Contact is with a current distributor, which is exposed to the electrolyte and has a hydrogen overvoltage which is higher than that of the cathodic particle layer.

The current distributor is in contact with a solid electrolyte comprising an alkali hydroxide.

In carrying out the process for producing chlorine by electrolysis of an aqueous alkali metal chloride between an anode and a cathode separated by an ion exchange membrane, which is restricted from flowing through aqueous electrolyte, Is the electrolysis carried out with a cathode _? which comprises a thin particle layer consisting of a pi-group metal or conductive oxides thereof

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stehts this layer being in contact with one side of the membrane and with a current ¥ _s issuer is exposed to the aqueous solution Älkalimetallchlorid and having a surface 'higher than the Chlorüberspannung- Anodenteilchenschieht *

The particles are bound together by means of a fluorocarbon polymer «.

The anode layer is connected to a cation exchange membrane ·

In particular, the anode layer is associated with a fluorocarbon polymer-ion exchange membrane containing sulfonic acid groups. "

The process for producing halogens and alkali metal hydroxides by electrolyzing aqueous alkali metal halides between an anode and a cathode passing through a cation exchange polymer membrane of? are separate from each other -is in particular - characterized by _? -that at least one of the electrodes attached a variety Electrically, conductive _s catalytic particles ^ to the membrane _s having to provide a gas- and electrolyte-permeable electrode ;, wherein the cathode side of the membrane has a lower water content than the remaining portion. ", a Anicnensperrschicht au ^ which rejects the HydroxyHonen

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and keeps the diffusion of alkali through the membrane to the anode at a minimum level.

Incidentally, the composite membrane is a laminate of two layers in which the cathode-side anion rejection property is larger than that on the anode side si. For example, the membrane is a polymeric fluorocarbon cationic membrane having an anion-eroding sulfonamide barrier layer on the cathode side _e

In accordance with the invention, a cathode made of a plurality of electrically conductive particles is connected to the sulfonyl layer on the cathode side of the membrane and connected to the anode side of conductive particles.

The method according to the invention has a number of significant advantages * '

Erfindungegemäß are halogens _s b "B" _s Broa chlorine etc _"s through the electrolysis of an aqueous alkali metal halide solution ,, Zo B * a Kacl _Lb'sung-9 produced at the anode of an electrolytic cell" containing a solid polymer electrolyte in a Porm Kationenaustauschermenibran _t to the , To separate cell into a catholyte and anolyte Kaimaer «The catalytic electrodes at which chlorine-and lye are produced are very thin ,, porous, gas-permeable ones? catalytically ^ electrodes connected to opposite surfaces of the membrane

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and embedded in them, so that the chlorine is generated directly at the interface from electrode to membrane. * This causes the electrodes to have very low overvoltages for the chlorine ion discharge and the generation of alkali.

The catalytic! Electrodes v / iron catalytic Substantive to _s the at least one reduced platinum ™ gruppenmetalloxid comprises which has been thermally stabilized by heating of the reduced oxide in the presence of oxygen * In a preferred AusfUhrungs form, the electrodes of such oxide particles "with polytetrafluoroethylene particles Examples of useful platinum group metals are platinum, palladium, iridium.

The preferred reduced metal oxides for chlorine production are the reduced oxides of ruthenium or iridium. * The electrocatalyst can be one of its reduced platinum group metal oxide _? such as ruthenium oxide, iridium dioxide, platinum oxide, etc. It has been found, however, that mixtures or alloys of reduced platinum group metal oxides are more stable. An electrode of reduced ruthenium oxide with up to 25 % reduced iridivunoside, and preferably on - 25 Gexi * - reduced iridium oxide has been found to be very stable "graphite or. Another conductive extender is added in an amount of up to 50 % Qex, and preferably from 10" to 30% by weight * The extender should

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excellent conductivity and low halogen over voltage have and it should θehr be much cheaper than the platinum group metals, so that it is possible to provide a ₅ considerably cheaper, yet highly effective electrode "

One or more reduced oxides of a valve metal _s, such as titanium, tantalum, mob. Zirconium, 'hafnium, vanadium',. or tungsten may be added to stabilize the electrode against oxygen, chlorine and the generally harsh electrolysis conditions. Up to 50% by weight of the valve metal is useful with the preferred amount being in the range of 25-50% by weight. - $ was lying

At least one of the catalytic electrodes is connected to the liquid-impermeable ion-transporting membrane. By connecting one or both of the electrodes to the membrane, the electrolyte voltage drop between the electrodes and the membrane becomes minimal. siert, as well as the. Gas mass transport, since no gas layer is formed between the electrode and the membrane «.

This leads to a considerable reduction of

Cell voltage and the significant economic benefits that result ". "...

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The invention is explained in more detail using an exemplary embodiment ©. .. ... ......

In the accompanying drawing show

1 is a representation of an electrolytic cell of the present invention %

Fige'2 an ecbematische Darotellung the cell and

^{1 of} the reactions taking place in different parts of the cell *

In FIG. 1, denoted at 10 is a halogen electrolysis cell consisting of a cathode gray 11 and an anode 12 space separated by a solid polymer electrolyte membrane 13, the membrane 13 preferably being a hy dra ti wobbled _s passage! gkeits? · .is selective cation '* With the opposite surfaces of the membrane 13 electrodes are connected, "the particles of einem.Fluorkohlenstoff _$ as Teflon ^ uiiifassens with thermally stabilized," re "~ äusierten oxides of ruthenium (RuCX.) , or iridium (IrO. ,,) or stabilized reduced oxides of ruthenium = · iridium (RuIr) O.,. Rutheniura-Uitan (RuTi) O, Ruthenium = »

-tu,. -Λ · '

Ossntal-Iridiura (RaTaIr) O or Ruthenium Graphite "The cathode 14 is connected to one side of the membrane 13, preferably embedded in the same, and not catalyzed by an anode 29

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connected to the opposite side of the membrane 13 and preferably embedded in this. The Teflon-bonded cathode 14 is similar to the anode catalyst. Suitable catalyst materials include finely divided metals such as platinum, palladium, gold, silver _s manganese, cobalt or nickel, spinels or reduced platinum group metal oxides such as Pt-Ir 0, Pt-Ru-O, graphite and suitable combinations of the aforementioned materials eino. , '

Current collectors in the form of metal screens 15 and 1.6 are pressed against the electrodes. The whole unit of membrane 13 and electrode '· is firmly supported by the cathode chamber 11 and anode chamber 12 forming housing elements mediating the seals 17 and 18, wherein the seals 17? 18 are made of any material which - with respect to the cell environment, _s namely alkali, - chlorine, oxygen, .wäßrigem sodium chloride in Palee the electrolysis of brine, and HCl, HBr in .Falle other hydrogen halides, resistant ._ or inert "One form of Such seal 175 18 is a filled rubber seal sold by Irving Moore. Company, Cambridge, Mass under the trade name EPDM.

An aqueous brine is introduced through an electrolyte inlet 19 which communicates with the chamber interior 20. Spent electrolyte and halogens such as chlorine are removed through an outlet conduit 21.

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A cathode inlet conduit 22 communicates with the cathode compartment 11 _s for introduction of cathode space electrolyte ₉ water or aqueous HaOH, which is more dilute than that formed electrochemically at the interface electrode / electrolyte

The water serves two separate functions «A part of the water gets under. Generation of hydroxyl anions is electrolyzed, and these hydroxy-1 anions combine with the ionic cations transported through the membrane 13 to form alkalis (HaOH). However, the wax also rinses the embedded cathode electrode 14 $ around the membrane / electrode electrode. boundary surface. 14 concentrated highly concentrated liquor, to dilute and so a diffusion of the liquor through the membrane 13 back into the / moden ~ Blektrolyträum 12 as possible au hold * The cathode outlet 24 is in communication with the cathodic space 11 for the removal of the dilute liquor, plus any at the Cathode 14 Discharged Hydrogen and Excess Water * An energy carrying cable 23 is inserted into the Kathoderirauai 11 eings ™, and a comparable unillustrated cable is inserted into the Anodc chamber 12 * These cables connect the current conducting Coles sieves 16 and * 15 respectively Power source ©

FIG. 2 illustrates the reactions taking place in the cell 10 during the electrolysis of a valtäßrigan brine, and serves to understand the process of the invention of the process of lead electrolysis

20 - 2

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in the way the cell 10 works.

An aqueous solution of sodium chloride is introduced into the anode compartment 12, which is separated from the cathode compartment 11 by the cationic membrane 13. The membrane 13 is a composite membrane having a layer 26 of high water content (20 to 35 % < based on the dry weight of the membrane) on the anode side and a low water content layer 27 (5 to 15 % ₉ based on the dry weight of the membrane) both are separated by a Teflon fabric 28.

In order to optimize the cathode performance, the membrane 13 is provided with a cathode-side ion-rejecting barrier to repel the hydroxyl ions and to block or minimize the re-migration of the liquor to the anode 29. The repellent properties of the cathode-side anion-repellent barrier layer can be further enhanced by chemically modifying the perfluorosulfonic acid membrane on the cathode side to form a thin layer of low-water-content polymer. B. happen? That the polymer is converted to form a substituted sulfonamide membrane layer. The cathode layer 27 has a high equivalent weight or is converted to a weak acid form (SuIfonami.d), and thereby the water content of this part of the composite membrane 13 is increased

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the ability of the film to salt reject and. minimize the diffusion of sodium hydroxide through the membrane 13 back to the anode 29. The membrane 13 may also be a homogeneous film of low water content polymer such as Mfion 150, perfluororic acid, etc.

The Teflon-bonded catalysts of reduced noble metal oxides contain at least one thermal. stabilized, reduced pia tintaetal oxide, such as E.uthenium _s iridium or ruthenium-iridium with or without additive, reduced oxides of titanium, ilobium or tantalum and particles of graphite. These catalysts are pressed into the surface of the membrane 13. The metal sieves 15? 16 trained current collectors, for the sake of clarity? in Pigur 2 are shown only partially, are against the surface of the catalytic! , Electrodes pressed and connected to the positive or * negative terminal of the energy source ^ to create the Elektrosylsepotential between the cell electrodes zn . The sodium chloride solution _s .die. is _s -v / ird-at the anode 23 to produce chlorine _s as exemplified by the bubbles 30 in Figure 2. _s- electrolyzed. ...... The HatriuTrrionen Ha "'" are by the. Membrane 13 is transported to the cathode 14. A stream denoted 31 is introduced into the cathode space or water or aqueous UaOH and acts as KathoXyto. This aqueous stream 31 rinses the surface of the Teflon-bonded catalytic converter.

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see cathode 14 »to dilute the liquor formed at the interface of membrane 13 to cathode 14 and thereby reduce the back diffusion of the liquor through the membrane 13 to the anode 29.

A portion of the water catholyte is electrolyzed at the cathode 14 to form hydroxyl ions and gaseous hydrogen. "The hydroxy ions combine with the sodium ions transported through the membrane .1.3 to form sodium hydroxide at the interface from the membrane 13 to the electrode." The sodium hydroxide slightly wets the teflon part of the bonded electrode and migrates to the surface where it is diluted by the aqueous stream purging the surface of the electrode. Using the water flushing of the cathode 14 14 concentrated sodium hydroxide in the range of 5 to 6 4 _{5 S} 5 is formed molar "Something of dem'Natriumhydroxid, which is indicated by the arrow 33 at the cathode ,, however, migrates through the membrane 13 to the. Anode 29-back * The sodium hydroxide transported to the anode 29 is produced to produce water and oxygen 5 as by the. Blistering 34 shown, oxidized This is a parasitic reaction,

which reduced the efficiency of the cathodic current

Oxygen production at the anode 29 is undesirable, as this can have detrimental effects on the electrode and the membrane 13. In addition, the oxygen dilutes the GhIOr ₉ produced at the anode 29, so that an adequate amount of oxygen is produced.

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The treatment in the different parts of the cell is the following:

Anode reaction: 2 Cl- * Cl _? t + 2e "'(1)

(Principle). ,

Membrane »Transport 2Ia ⁺ + HgO. (2)

Cathode reaction: 2HgO- »20H" + H ₂ t ~ 2e "° (3a),

2Na ⁺ -5- 20H ". 2HaOH (3b)

Anode reaction: 4OH ~~~ ⁵ 0 ~ * \ + 2HpO + 46 ^ (4)

Overall reaction? 23JaCl + 2 "H ₂ 0- ^ 2NaOH + Cl _? T + H ₉ -f (5) (principle)

The new arrangement 53ur electrolysis of aqueous solutions of SaI25lauge which is written into the present application be _"s is characterized by the fact that the catalytic sites of the electrodes at Kationenauatauschermeinbr-in direct contact with and. the ion-exchanging acid radicals connected to the polymer chain _s . These acid-exchanging radicals are sulfonic acid radicals SO 2 H 2 HgO or carboxyaromatic radicals COOH 2 H "O. There is therefore neither the iinolytic nor the catholyte chamber. any a be ~ Bierkensvierten Spannungaabfallc Such electrolyte Spannungeabfall is characteristic in which the electrode and the membrane are separated from each other for the existing systems and methods _s, it UIID there can ₅ 5 volts in the order of Oj2 to O * The elimination or at least considerable Reduction of this voltage »

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If one of the main advantages of the present invention is because it has a very significant effect on the total cell voltage and the economy of the process.

Since chlorine is generated directly at the interface of the anode to the membrane, there is also no voltage drop due to the so-called "bubble effect," which is a gas injection and mass transport loss due to the interruption or blockage of the electrolyte path between the electrode and the membrane.

In prior art systems, the chlorine-donating catalytic electrode is separated from the membrane. The gas is formed directly at the electrode and results in a gas layer in the space between the membrane and electrode *. This interrupts the electrolyte path between the electrode collector and the membrane and blocks the passage of ions, thereby increasing the voltage drop. -

The PTFE-containing catalytic electrode contains reduced oxides of platinum group metals, such as ruthenium, iridium or ruthenium-iridium, in order to minimize the chlorine overvoltage at the anode. The reduced Rutheniuraoxide are stabilized against chlorine and oxygen evolution, to obtain a stable anode »The stabilization is initially

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by temperature stabilization, d * tu by heating the reduced ruthenium moxides to a temperature below that at which decomposition into pure metal begins. " Thus, "die..reduzierten Oxide 6h 30 to 350 min - 750 ⁰ G-heated, preferably for one hour at Temperaturen'Im range 550-600 ⁰ C ^ The Teflon-bonded reduced Rutheniumoslde the anode can be further stabilized by mixing with graphite and /., or mixing with the reduced oxides of other platinum metals _s as iridium IrO _T in a range of. 5 to 25% of iridium, with 25% being preferred, or with which ETCE ₅ Rh of Pt or with reduced oxides "of valve metals Titanium TiO, with 25 to 50 % of TiO2 being preferred, or 'tantalum (25 $ or more) "It has also been found that a ternary alloy of reduced oxides of titanium, ruthenium and iridium (Ru ₅ Ir ₉ Ti) 0 or of tantalum, ruthenium and iridium (Ru, 'Ir, Ta) 0_,

which is bonded with Teflon is very effective in producing a stable long-lived anode. In the case of the ternary alloy, the composition preferably consists of 5 to 25 % by weight of redox oxide of iridium, about 50% by weight of reduced ruthenium oxides and the rest is a valve metal such as titanium. "Pure a binary alloy of reduced oxides of peithenium and titanium which contains the preferred electrode- a lot of 50 G-ewe ~% titanium. and the remainder is ruthenium * titanium has the added advantage that it is much cheaper than ruthenium, or iridium 'and that it is therefore an effective *

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This is a diluent that reduces costs while stabilizing the electrode in an acid environment and against HCl, chlorine and oxygen evolution. Other valve metals, such as Mob, tantalum zirconium or hafnium, can be used in the electrode structure instead of titanium ·· ..

The alloys of the reduced noble metal oxides, together with the reduced oxides of titanium or other valve metals, are mixed with Teflon to form a homogeneous mixture. The Teflon content of the anode may range from 15 to 50% by weight, although 20 to 30% by weight. -% are preferred. The Teflon used is the material sold by the Dupont Corporation under the trade designation T-30, although other fluorocarbons may be used equally. Typical noble metal gene amounts for the anode lie at 0.6 mg / cm of the electrode surface, the preferred range being 1 to 2 mg / cm. The current collector for the anode may be a platinum-plated willow net with fine bottles, with good contact to the electrode surface is obtained. However, a stretched titanium teta coated with ruthenium oxide, iridium oxide, valve metal oxide or mixtures thereof may also be used as the collector structure for the anode. another possible anode collector structure may be a noble metal or "oxide" clad network attached to a Ti or Ti alloy plate by welding or bonding i

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The anode-crystal collector engaged with the bonded anode layer ₉ has a higher chlorine overvoltage than the catalytic surface layer of the anode electrode. This reduces the likelihood of the electrochemical reaction, such as the chlorine reaction at the flow distributor surface _s because these reactions are more likely due to the lower overpotential on the electrokata3.ytic anode electrode surface © and because the voltage drop across the collector is greater «

The cathode preferably eats a bound mixture of oil particles and Pia tins c.hwara with a platinum black amount of O ₅ 4 to 4 ffig / cm. However, _β can equally well, the other, above of katalytieichen materials are benutst · The cathode is similar to the anode is preferably connected to the surface of the Kationenaus'tausehermembran and is embedded in this .The cathode very thin with a thickness-tone about 0 _? 05-bis. O ram ₉₀₇₅ or less and having about vorsugsweise O _5, 012 ma thickness .hergestellt _s it is porous and has a low Teflon content to "

The thickness, the cathode can be quite significant * It can in reduced Waoser or by. The rinsing and penetration of aqueous. Kassn be Haoh reflected in the cathode _s reducing 4ie effectiveness of Kathodenstroaes »Cells. They were made with thin cathodes of about 012, here-about O ₅ 05 ffini thickness of platinum black with 15 % Teflon. The current effect of

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Cells with thin cathodes. Amounted to about 80 % at 5 molar WaOH, at 88 to 91 ⁰ C and a supply of 290 g MaCl / 1 to the anode. With a 0.075 mm thick cathode of ruthenium and graphite, the current efficiency was 54 % with 5molarer FaOH reduced · The following Table A shows the relationship of current efficiency to thickness and indicates that thicknesses not exceeding 0.05 to 0.075 mm have the best performance * ~.

Table A cathode Cathode thickness (mm) Current Effectiveness in % (at cell platinum black 0.05-0.075 64 (4.0) 1 platinum black 0.05-0.075 73 (4,5) CVI Pia t i ns chwarζ 0.025-0.05 15 (3,1) 3 platinum black 0.025 »0.05 82 (5) 4 platinum black 0,012 78 (5.5) 5 5 % platinum »black on graphite. - 0,075 78 (3.0) 6 15 % ' Ru 0 on graphite 0,075 54 (5.0) 7 Platinized graphite web 0.25-037 57 (5) 8th

The electrode is gas-permeable _s made so that at the interface between the electrode and membrane

22 «6» 1979 APC25B / 2O9 54 476 11

evolved gases-easily. It is made porous to allow penetration of the rinse water to the interface between the electrode and the membrane where the IaOH is formed, and to allow access of the salty brine to the membrane and the catalytic elec- trode. This helps to thin it the formed highly concentrated IaOIl ₅ before. she likes the teflon and on. the electrode surface ', where it is further diluted by the water flowing over the electrode surface. «It is important to dilute the ifaOH at the interface between membrane and electrode, because there the concentration at the -. Teflon content should not exceed 15 to 30 Geviv-fo "as Teflon is hydrophobic * With good porosity, a limited Teflon content _s a thin cross section and a rinsing liquid of water or dilute lye the KaOH concentration is controlled by the migration of NaOH through the. To reduce membrane; which is further supported by an anion-repellent barrier layer on the Kathoäenseite *

-V / ground carefully selected the Stroiakollektor for Kathode.muß since the attacks many materials at the cathode existing highly corrosive alkali, in particular during the cell iet off * The current collector may be a Hickelnetz seiru && winding lye

22.6.1979 .-. "APC25B / 209 54 476 11

resistant to. However, the current collector can also be made from a sheet of corrosion-resistant steel, onto which a mesh of corrosion-resistant steel is welded. Another cathode current collector structure, which is resistant or inert to alkaline solution, is graphite or graphite in combination with a nickel mesh pressed onto the plate and against the surface of the electrode.

The cathode current collector which is in engagement with the bonded cathode layer is made of a material having a higher hydrogen overvoltage than that of the catalytic cathode surface. The likelihood of an electrochemical reaction, such as hydrogen evolution at the current collector, is therefore reduced because of the lower overpotential on the electrode and because the cathode electrode shields the current collector to some extent.

The membrane 13 is preferably a stable hydrated cationic membrane formed by ion transport. Selectivity is excellent. The cation exchange membrane allows the passage of positively charged ITa - trium cationi and minimizes the passage of negatively charged anions. There are different types of ion exchange resins »! be processed into membranes to the selective transport of cations. .enable. Two types are the so-called sulfonic acid cations »

22 * 6,1979 APC25B / 2O9 498 54 476 11

exchange resins and the carboxylic acid cation exchangers ™ Bsi the sulfonic acid resins, which are preferred j are the ion-exchanging groups hydrated sulfonic acid residues SO ^ H χ Ho ^ »by sulfonation with. The ion-exchanging acid radicals are non-mobile within the membrane but solid with the polymer chain. which ensures that the electrolyte concentration does not change.

The sulfone acid groups having perfluorocarbon cation exchange membranes are preferably _t . since they ensure excellent cation transport, are highly stable and are unaffected by acids and strong oxidants, and they also have excellent thermal stability and are essentially invariable over time. " A specific preferred group of cationic polymer membranes is derived from US Pat DuPont Company sold under the trade name .Kaf ion, this is a membrane? in which the polymer is a hydrated copolymer of poly (tetrafluoroethylene) and polysulfonyIfluoridvinylather i.S5t _? having pendant sulfonic acid groups = These membranes are used in the hydrogen form, more commonly those obtained by the manufacturer. Form. Is the ion exchange capacity of a given sulfonic acid cation exchange membrane. depending on the molyequivalent weight dey SO. ^ ~ H residue per gram of dry polymer ₆ The greater the concentration of sulfonate

. ' , , · 22.6.1979

APC25B / 2Q9 498. 54 476 11

is acidic, the greater the ion exchange capacity and the greater the ability of the. hydrated membrane _s transport cations. However, as the ion exchange capacity of the membrane increases, the water content also increases and the ability of the membrane to repel salt decreases.

The rate at which the sodium hydroxide migrates from the cathode to the anode side increases with ion exchange capacity. The back migration reduces the efficiency of the cathode current and also results in oxygen production at the anode with all the undesirable consequences associated therewith. The preferred ion exchange membrane for use in brine electrolysis is therefore a laminate composed of a thin film (about 0.05 mm thick) with a weight equivalent to 1500 and a low water content (5 to 15 %) with high salt absorbency. _s solution connected to a film having a thickness of about 0.1-mm or more, high lonenaustausohkapazität, .einem Milliäquivale nt weight of 1100 and a Teflon fabric. A form of such layer concentration is sold by DuPont under the trade name Haiion 315. Other forms of laminates or construction. NEN _s in which the cathode side layer of a thin Harsfilm low water content (5 to 15%) is "in order to optimize the salt rejection, while the anode side of the membrane to promote the ion-exchange" capacity, a film with a high water content, are

22.6 * 1979 APC25B / 209. 54 476 11

the trade names Hafion 355, 37β _? 39O _s 227 and 214 available *

The ion exchange membrane is prepared by soaking it in caustic (3 to 8 molar) for one hour to determine the membrane's water content and its ion re-ionization properties. In the membrane of the Teflon fabric-bonded layer membrane, it may be desirable to use the membrane or membrane Teflon tissue is to be purified by 3 minutes to 4 hours by refluxing under 70% EHO

The cathode-side barrier layer should have a low water content based on the water absorption of the persulfonic acid groups. * This results in a more effective anion (hydroxyl) abstraction. By bubbling or repelling the hydroxyl ions, the re-migration of the alkali is considerably reduced the current efficiency of the cell increases, and the acid. In an alternative laminate construction, the cathode side layer of the membrane is chemically modified to convert the sulfonic acid group to one with less water absorption. This can be achieved by reacting a surface layer of the polymer with the formation of a layer of sulfonamide groups, there are various possible methods for the formation of the sulfonamide surface layer. Such a process involves reacting the surface of the sulfonamide

22.6.1979 ._ APC25B / 209 54 476 11

Hafion membrane in the sulfone fluoride form with amines such as ethylenediamine to form the substituted sulfonamide membranes. This sulfonamide layer acts as. a very effective barrier for anions. By repelling the hydroxyl ions on the cathode side, the re-migration of the liquor is obviously considerably reduced.

The reduced platinum group metal oxides of ruthenium, IridiuiBSj of ruthenium / iridium, etc. with or without the reduced oxides of the valve metals, such as titanium or titanium. , of graphite containing the Teflon particles under. Formation of the porous gas-permeable catalytic electrodes are obtained by thermal decomposition of the mixed metal salts in the absence or presence of excess sodium salts, eg. B »of the Hitrats,

Carbonates etc. *. ... ν. ".. ... /. ; ..

The manufacturing process is a modification of the Adams process of platinum production by the concomitant use of thermally decomposable halides of iridium, titanium or ruthenium, eg of iridium chloride, ruthenium chloride or titanium chloride. For example, to prepare the binary oxide (Ru, Ir) O, the finely divided ones Salts of ruthenium and iridium in the same weight ratio of ruthenium and iridium mixed together as desired in the binary oxide. An excess of sodium nitrate or equivalent alkali metal salts is added and the mixture is stirred for 3 hours at 500 to 600 ^° C. in a silica dish

22 · 6.1979.

APC25B / 209 498 54 476 11

melted ^ The resulting product is thoroughly ge. wash to remove the remaining nitrates and halides. Thereafter, the suspension of the mixed or alloyed oxides is reduced electrochemically at room temperature or by passing hydrogen bubbles through the mixture. The product is thoroughly dried, ground and sieved through an IT nylon mesh, the particles typically having a diameter of about 37 ρ-τα after sieving.

The alloy of the reduced oxides of ruthenium and. Iridium is ο then stabilized .thermisch by einstündigss heating to a temperature of 500 to 600 ⁰ C. Thereafter, the electrode by mixing the reduced, thermally stabilized platinum group metal oxides with Polytetrafluoräthylenteilchen ago * A commercially available product is Teflon T-30 of DU

The reduced KdelraetalloxicSe how. However, RuO _x can also be mixed with a conductive carrier such as graphite transition metal carbides and valve metals to improve stability and require only small amounts of precious metal (0 _s 5 rag / cm)

In the case of using a graphite Ruthaniiun electrode, the powdered, graphite, (like Poco ~ Graph.it 1748 of the Union Oil Coipany) laj.t 15 to 30 $ .. Teflon T mixed with this graphite and Teflon kiechung

22.6 · 1979 APC25B / 209 498 54 476 11.

one mixes the reduced metal oxides.

The mixture of noble metal oxide particles and Teflon particles or of graphite and the reduced oxide particles are placed in a mold and heated until the mass is sintered into a decal shape, which is then bonded to the surface of the membrane by application of pressure and heat embeds.

Various methods can be used to bond and embed the electrode in the membrane, including the method described in detail in U.S. Patent No. 3,134,697, in which the electrode structure is pressed into the surface of a partially polymerized ion exchange membrane, whereby the sintered, porous, gas-absorbing particle mixture integral with the membrane and is embedded in the surface thereof.

For chlorine production to Ano Iy t chamber · 930 cm ^2/108 performs aqueous alkali metal chloride solution, such as NaCl, in the ".. The feed rate is-preferably in the range. Of 200 to 2000 ml / min. / MA / cm ² . the brine concentration should be in the range of _2? 5 · to 5 moles (150 ~ 300 g / l) are held, wherein a 5 molar solution is preferred as the cathode current efficiency increases directly with the concentration of the solution. at the same time the increased brine concentration reduces the oxygen evolution at the anode, which happens through water electrolysis. "With decreasing concentration

'22.6.1979

 , APC25B / 209 498

54 476 ir

On the other hand, the evolution of oxygen in the anolyte increases because of the relative amount of water present at the anode, which competes with the IaCl for competition. catalytic. Reaction sites. As water concentration increases with decreasing saline-eye concentration, water increasingly becomes electrolyzed at the anode with evolution of oxygen. Water electrolysis at the anode also reduces cathodic efficiency, since the H-ions produced by electrolysis of water pass through the membrane and interfere with the membrane

xy! ions underwater combine to form. these hydroxy ions are not available for formation. "

By maintaining the above flow rate in the anolyte chamber, it is ensured that the anode is continuously supplied with fresh brine. "

When the feed rate decreases, the brine residence time and, in particular, the residence time of the spent brine increases. This exhausted brine with its relatively high water content is then present at the anode for a longer time, resulting in increased water electrolysis with associated oxygen production and transport the hydrogen ions through the membrane logo CNRS logo INIST. Both the concentration of brine and the rate of feed influence the development of deodorant

22.6.1979 APC25B / 209 54 476 11

Stoffs at the anode and the transport of hydrogen ions through the membrane.

It may also be desirable to carry out the electrolysis at higher than atmospheric pressure to promote the removal of the gaseous electrolysis products. By pressurizing the anolyte and catholyte chamber, the size of the gas bubbles formed at the electrodes is reduced. The smaller gas bubbles are more easily dissolved Another benefit is the elimination or reduction of the formation of gas films on the electrode surface which can block the access of the anolyte or catholyte solution to the electrode. in which only one electrode is connected to the membrane, the reduction of the particle size reduces the voltage losses due to the gas barriers and the mass transport in the space between the non-bonded electrode and the membrane, since the electrolyte path is less interrupted by the smaller bubbles

Oxygen can be generated at the anode, but also due to the return of sodium hydroxide from the cathode. This IJaOH migrates through the membrane due to the steep concentration gradient at the membrane interface, and the limited capacity of the cationic membranes to repel salts is a puncture

39 - 209'4

22.6 * 1979 APC25B / 2O9 498 54 476 11

of the water content, of the membrane "For a 5 molar sodium hydroxide solution, 5 to 30% by weight of the sodium hydroxide formed in the cathode migrates through the membrane. back depending on the type of membrane used "At the anode, oxygen is then formed by the electrochemical oxidation of the 0H ~ = anions according to the following equation.

4 0H ~ - »2H ₂ O + O ₂ f + 4e".

The percentage of the oxygen produced by the leaching at the anode is about half the weight percent of caustic. Therefore, when 5 to 30 weight ~ -% of the liquor to the anode migrate _s then develop there 2 1/2 to 15 volume η · -% Sauerstoff.- By using a sheet or other membrane in which the membrane ^ Kathodenseite.der a film with a high equivalent weight ,, low water content and increased ability to repel anions (hydroxyl), the migration of the liquor to the anode can be limited «

In addition, oxygen production at the anode can be further reduced by acidification of the brine solution. "The H 'ions of the acidified brine combine with the hydroxyl ions, preventing oxidation of the hydroxyl ions." Oxygen evolution can be an order of magnitude or more (of 5 to 10% by volume of oxygen to 0 ^ 2 to .O ₅ 4% by volume) may be reduced by adding at least 0 _t , 25 moles of HCl to the brine.

; '22.6.1979 ._

; , APC25B / 209. 54 476 11

If the HCl concentration less than 0.25 mol, the oxygen evolution increases from 0.2 to 0.4 vol ', quickly normally observed without the acidification _/ amounts, for "example of 5-10 vol %.

PUr the optimal implementation of the process, the brine purity must be very high, z. For example, the Ca ⁺⁺ and Mg ⁺⁺ content should be low, and should be kept at 0.5 ppm or less to avoid deterioration of the membrane by absorption of calcium and magnesium ions. A concentration of these ions above 20 ppm leads to a deterioration in the performance of the cell within days. The brine must therefore be purified to keep the salt content of calcium and magnesium ions to less than 2 ppm and preferably less than 0.5 ppm.

At 325 mA / cm, the operating voltage of the cell is located with bonded electrodes in the range of 2: 9 to 3.6 volts depending on the electrode composition, and the supplied brine is preferably maintained at a temperature of 80 ..-> 90 ⁰ C because Cell voltage and overall efficiency of the cell at the higher operating temperatures can be considerably improved »-Z-. For example, a cell with a teflon bonded electrode was prepared from the reduced oxide of a ruthenium / iridium mixture at various temperatures with a current density of 325 ° C ^; mA / cm operated. At 90 ⁰ C, the cell voltage was 3 _s 02 volts At 35 ⁰ C, the cell voltage increased to 3.6 volts »For a

22.6.1979 APC25B / 2O9 498 54 476 11

Current density of 215 mA / cm, the cell at 90 ⁰ O required a cell voltage of 2 _S 6 YoIt * At the above-mentioned Stromdichte.stieg the cell voltage in operation at. 35 ⁰ C to 3 "15 volts" A temperature range of 80 - 90 ⁰ C is therefore with regard to the total. Efficacy * Although preferably the cell voltage falls at lower current densities _s of operating with a

Current density at 325 raA / era prefers _s since economic operation in relation to the invested capital is possible ₉ 2.Bo in view of the size and the cost of a plant, which is necessary to a given tonnage To produce chlorine and / or lye on a daily basis.

The cell is made of such materials ₉ opposite brine and chlorine in the case of / molytkaimner and against highly concentrated caustic and hydrogen in the KatoIytkammer. resistant or inert "The end plates of the cell can therefore be made of pure titanium or stainless steel, and the filled rubber clearings such as EPDM ₆ Me anode core collectors can be made of platinum hot tapes, stretched titanium tubing with RuQ 'j IrO * valve metal oxides and the blends of which are coated and attached to a titanium plate or a noble metal or noble metal oxide clad epoxy attached to a palladium / titanium plate. The cathode coupler collector may be a plate of nickel carbon steel or stainless steel _s eein with a letz

22.6.1979 APC25B / 209 498 54 476 11

welded from corrosion-resistant steel or a plate to which is connected a network. "Other materials such as graphite, which are resistant to leach or inert and are not subject to hydrogen embrittlement, can also be used for producing the cathode tromkollektors.

The advantages of the invention will now be explained in more detail by way of examples.

Examples

Cells were constructed and tested that included ion-exchange membranes and Teflon-bonded electrodes with reduced noble metal oxide embedded in the membrane to show and, in particular, the effect of the various parameters on cell efficacy in brine electrolysis to illustrate the operating voltage characteristics of the cell.

Table I illustrates the effect on the cell voltage of the various combinations of reduced noble metal oxides. The cells were equipped with electrodes having various specific combinations of reduced noble metal oxides bound with Teflon particles and embedded in a 0.15 mm thick cationic ion exchange membrane. The cell was injected at a current density of about 325 mA / cm at 90 G delivery rates from 200 to 2000 ml / min and

.. 22.6.197.9

APC25B / 209 54 476 11

operated at a concentration of the supplied of 5 mol »

One cell was constructed in accordance with the prior art and included a dimensionally stabilized anode spaced from the membrane and a cathode mesh made of corrosion resistant steel similarly spaced. Biese control cell was operated under the same conditions «

From the data given in Table I it can be seen that in the method according to the invention the cell operating potentials ranged from 2 _S 9 to 3p6 YoIt * Compared with a cell according to the prior art, the control cell Έτο 4 »was under the same operating conditions a spiciness improvement from O ₅ 6 to 1j5? realized the resulting operational efficiencies and economic benefits are clearly visible »

Table I

Cell anode

Cathode supply- current- "Temp" - C flow

salt density (V) wi'rk-

lye mA / cmr. ·. col-

fcelt

Membrane (5 molar HaOH)

6 mg / cm 4 mg / cm 5 molar (Ru, 25% platinum (290 g / l) Ir) O black

ρ ρ

6mg / cm 4mg / cnr "(Ru, 25% platinum-Ir) O ^

black

6mg / cm (R

dimensionless 15Tetζ of ⁿ ionsiaä- körrosißig static onsbebile constant Hetzanode steel in the exhaust distance from the stand of d "Membrane Membrane

ρ ρ

4 mg / cm 4 * mg / cm ⁿ (Ru, 50% platinum Ti) O black

ρ ρ

4 mg / cm 4 mg / cm "(Ru ₅ 25% platinum-Ir-25% black Ta) O ^

323

323

323

323

323

323

3.2 - 3.3 90

3.3 - 3.6 90

2.9

90

4.2 - 4.4 90

3.6 - 3.7 90

3.5-3.6 90

%

%

DuPont Hafion laminate '

DuPont 1500 EW 'Nafion

DuPont 1500 EW Uafion

DuPont 1500 EW Uafion

DuPont

Nafion ..

315 laminate

DuPont Nafion laminate

Q)

£ 3

03 .p U O

Ö Cj COrH

ο is

-ρ

^ ί4 βΗ • Ρ · Η CÖ Φ CO £: Co X

So α>

Feo

I Cj

rH CÖ O Pi

t © CM

s · ρ a

OXl O

U Ό .ρ · η CO rrt

"Ή

«I-i cö ω co co fxO

bö £

£ G) CÖ lsi -P r ~ I

 XI

CÖ

C) 'Ö O

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r-i

in

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(Λ CM

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CM

cm.

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CM CA

CM

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p. 60

S 2 φ a:

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CA

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• Ρ «-0 EJ O E!

Ο <-> .J-PhOCs- Q ϊ-ΪΞ JO -H · Η I Ρ - «<Η 0 S £ &<$; P ^ it-q CA O ί ω O σ \ ο cn in «Η CA CA ! I

CA

CA CM CA

CA

CA CM CA

CJ

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r-i O

H

od u

^ • H CÖ bO-f »^

Θ GJXl rH O CQ

in

CA

-P

• P Ö CÖ Ej O EJ O · ΗΉ

p4 ^ h a

P CÖ CÖ

in

VO

VO

it

CA

OJ CA

CA CJ CA

OJ

ta

^'0 X

O. Ej

TiO-P g:

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rh

LA 1.,, CM CM S C o ^fx S O I r - * { • ^ o ^K ,O fr-i Ö Γ, 60 H R H S-!

22.6.1979 APC25B / 209 54 476 11

'' '' '·' / '.. · ..' ... ..

A cell similar to cell # 7 of Table I was constructed and operated at 90 ° with the addition of saturated brine. The cell potential (.'V). as a function of the current density is given in the following Table II »

Table II current density (mA / cm) Zellspannung_ (V) 430 323 215. 108 3.2 2.9 2.7 2.4 •

These results show that the cell operating potential decreases with reduced current density. However, the relationship of current density to cell voltage determines-but the relationship between operating and capital costs of chlorine electrolysis. However, it is clear that even at very high current densities (about 325 and 430 mA / cm) significant improvements in cell voltage are realized in the chlorine production process of the present invention.

Table III illustrates the effect of cathodic stron activity on oxygen evolution. A Teflon-bonded catalytic anode cell and reduced noble metal cathode embedded in an ion exchange membrane underwent SO ² C under

22 * 6 * 1979 APC25B / 209 498 54 476 11.

Addition of a saturated brine with a current density of 323 mA / cm v.nd. a feed rate of 2 to 5 ml / min / 6 _s 25 cm of the electrode surface operated »The percentage by volume of oxygen in the chlorine was determined as a puncture of the cathodic current efficiency &

Tabelle__III Oxygen development (Yol-fo) cathodic . "2.2 4.0 5 _$ & 8.9 89 86 04 80

Table IV illustrates the. Controlling effect of the acidification of the brine on the evolution of oxygen. The oil transfer ratio of the oxygen in the chlorine was determined for various HCl concentrations in the brine.

22.6 * 1979 APC25B / 209 498 '54 476 11 Table IV Acid (HCl) -7 O ₂ (Vol-g) 0.05 2.5 0,075 1.5 0.10 0.9 0.15 0.5 0.25 0.4

From these data it is clear that the evolution of oxygen due to the electrochemical oxidation of the migrated OH "is reduced by preferentially reacting the OH""with the H ⁺ to form HgO.

A cell similar to cell Hr * 1 of Table I was constructed and operated at 323 mA / cm to supply saturated NaCl solution which had been acidified with 0.2 η HCl. The cell voltage was measured at various operating temperatures of 35 to 90 ° C.

A cell similar to the cell Ir * 7 of Table I was constructed and operated at 215 mA / cm to supply a solution (about 5 molar) containing 290 g NaCl / L which was not acidified. The cell voltage wurde.bei various operating temperatures from 35 to 90 ⁰ C measured "The results were converted" to a current density of 323 mA / cm

22.6.1979 APC25B / 2O9 54 476 11

Table V

Cell '! Ir. 1 voltage (V) Cell Hr, 7 voltage (V) ₂ converted to 323 mA / cm ^ measured at 215 mA / cm-) (3.15.) temper 3.65. 3.50 (2.98) 35 3.38 3.30 (2.91 45 3.2 3.20 (2.78) 55 3.15 3.12 (2.72) 65   3.10 3.05 (2.65) .75 3.05 2 _f 97 (2.63) 85 3 * 02 2.95 90

Show these results? that the best operating voltage in the range of 80 to 90 ⁰ C is obtained * It is, however it Iiinsuweiaen "that even at 35 ⁰ C, the voltage ndt erfindungsgeniäßen the catalyst and! Iektro3.ysator at least ₅ O, S volts is better than the chlorine ISlektroly'satoren 'according to your state of the art _s which were operated at 90 ⁰ C "·

Bs'., Became a series of _; Cells with composite membranes designed in each case the anion-repellent barrier layers on the cathode side in the form of · chemically modified. ._ .. SulfonaiiddscMchten atifwiesen ^ The membranes were 0 _s Art'ο 187 mm thick membranes of the lonely Dupont of -Rande Is be * ™ drawing-Haiion sold the cathode side of the membrane to dignity .to einer.Tiefe 0 _f .037 Wn. by reacting. ncLt ethylenediamine to form the sulfonamides

22.6.1979 "APC25B / 209 498 54 476 11

Barrier layer modified to promote hydroxyl ion repellency and minimize leach back to anode side. An anode of (Ru, 25 Ir) O particles with 20 % T-30 Teflon binder and a precious metal amount of 6 mg / cm 2 connected to the membrane A cathode of platinum black particles mixed with 15 % T-30 Teflon binder and a quantity of 4 mg platinum black / cm was connected to the other side of the membrane.

A brine solution having a concentration of 280 to 315 g / l of HaGl was supplied to the anode compartment and distilled water was charged into the cathode compartment. Cells were treated with a current density of 325 mA / cm and at a temperature of 85 - operated 90 ⁰ G "were obtained the following results.

Cell voltage Table VI • NaOH-concentration in mol Cathode efficiency in %. cell 2.68 2.78 2.76 Temperature Sc 5.1 4.8 4.8 - 89.6 87.6 91.6 1 2 3 85 ° 89 ° 90 °

These results show that the use of a composite membrane with a cathode-side anion-rejecting barrier layer of chemically modified sulfonamide leads to a considerable improvement in the cathode ».

22.6 * 1979 APC25B / 2O9 498 54 476 11

Current efficiency results without affecting the voltage efficiency of the process. This clearly demonstrates that the use of such a membrane with associated electrodes results in considerable improvements in the efficiency of the current and thus in the overall economy of the process.

When the BaGl electrolysis is carried out in a cell in which both electrodes are connected to the surface of an ion-transporting membrane, a maximum improvement is achieved. "However, the improved performance of the process is achieved for all structures5 in which at least one of the structures. Electrodes are connected to the surface of the ion-transporting membrane * Such a cell is called a hybrid cell * - The improvement in such a hybrid cell is slightly lower than in a cell ₅ in which both electrodes are connected to the membrane «. Nevertheless, the improvement in a hybrid cell is significantly better, namely O ₅ 3 to 0 _s 5 VoXt than in the cells of the prior art *

A series of cells were constructed and brine electrolysis carried out in order to compare the results of cells with two. the membrane connected electrodes with the results in hybrid cells, in which either only ·, the anode or only. the cathode was connected to the membrane, and to compare with a cell according to the prior art, in which none of

, 22.6.1979

: - , 'APC25B / 209

': ' · · Λ ^: - ^; ';/' / '·; · '- - ^; , ; ':. ^: ... ^: '-; ^: / ^{54 476 11} '

Electrodes connected to the membrane *,

All of these cells were made with membrane 'from' ion-315, the cells were operated at 90 ⁰ C and there was a liquor feed with a concentration of about 290 g / 1 * The amount of catalyst bound electrode was for platinum black at the cathode 2 g / 930 ice; ² and on the anode for RuO "graphite and RuO 4 g / 930 cm ... The current efficiency at 323 mA / a * was for all the cells is substantially equal to (84 to 85% for 5 molar NaOH) _e Die'Tabelle shows YII the cell voltages for the different cells «. - ·.

Table VII

Ze3.1e anode

Ru graphite (bound)

Platinum-plated kiob net (not bound)

Platiniertes Eiöbnetz (unbound)

Ru graphite (bound)

cathode

Platinum Swaris (bound)

Platinum black (bound)

Platinum black (bound)

Nickelnets (not bound)

Cell voltage bJ ₁ 32 3 roA / cm

3,5 '.

3 ₉ 4

3.5

.22.6.1979.

APC25B / 2Q9 54 476 11

(Continuation)

Cell anode

Ru O ^ (bound)

Platiniert.es' Mobnetz (not -gebun the)

cathode

Mickey net (not tied up)

-Nick Inet ζ (not bound)

cell voltage

3 * 3

3 $ 8

The cell spamming with. Two cells are equipped with electrodes. It is almost 1 volt better than the cell of the prior art in which none of the electrodes was a Teflon-bonded electrode and listed under cell no. 6 Cathode Nos. _6, 2, and 3 and the bonded-anode hybrid cells Ir o 4 and 5 are 0.4 to 0.6 volts worse than those with two bound electrodes, but still around O ₅ 3 to 0.5 Volt better than the cell Nr © without a Teflon-bound electrode »

Reacting the brine and dee water ™. katholj; th of catalytic .Elektroden that are directly connected to the kationisc-hsn membrane and embeds in this turned j develop zn at the cathode um chlorine at the anode and hydrogen and high purity Lange, is a much better process for producing Chlorine from Sai.islauge made possible * This arrangement contains the catalytic sites in the electrodes

'06.22.1979. ·

APC25B / 209 54 476 11

in direct contact with the membrane and the acid-exchanging residues in the membrane and this results in a much more voltage efficient process, in that the required cell potential is considerably lower (up to 1 volt or more) than in known processes. "The use of the highly effective fluorocarbon-bound reduced noble metal oxide catalysts as well as the fluorocarbon graphite / reducted precious

metal oxide catalysts with low overvoltages improve the effectiveness of the process »

The term "valve metal" used in the present application is defined in U.S. Patent No. 3,948,451 and denotes a subset of transition metals, e.g. B.Ti, Ta, Zr, Mo and W include ·. These valve metals conduct the flow in the anodic direction and resist the flow passage in the cathodic direction. "They are resistant to the electrolyte and the conditions in an electrolytic cell, e.g. As for the production of chlorine and HaOH, sufficiently resistant to be used for it as an electrode material.

Claims (6)

22 * 6,1979 APC25B / 209 54 476 11 A process for the continuous production of chlorine by electrolysis of alkali metal chlorides, characterized by the following steps: a) continuous introduction of an aqueous alkali metal chloride solution into the anode chamber of an electrolytic cell in which the anode chamber is separated from the cathode chamber by a cation-selective ion exchange copolymer; b) contacting this solution with a porous gas-permeable catalytic ariode electrode connected to and embedded in the side of the mergebrane facing the anode-core, the catalytic gas being thereby introduced. Sites in the electrode are in contact with the ion-exchanging remnants of the membrane so that the electrolysis can take place directly on the interface between the membrane and the electrode and against a porous gas-permeable catalytic cathode electrode on the other side of the membrane. c) continuously introducing a stream of water into the cathode diarrhea and placing it in contact with the catalytic © η cathode electrode to recover a source of hydroxyl ions at the cathode. 06/22/1979. APG25B / 209 498 54 476 11 and to continuously purge the cathode electrode for yerdimming the liquor formed therej d) supplying current to the electrodes to electrolyze the alkali metal chloride to produce chlorine at the anode and water to produce alkali metal hydroxide and hydrogen at the cathode and e) continuously removing chlorine from the anode compartment and from caustic and hydrogen from the cathode compartment. · 2 * The method according to Point.1, characterized in that the aqueous solution into contact with a porous gas-permeable _s, catalytic anode of bonded, reduced noble metal oxides brought 3 «method, according to point 2, characterized in that the aqueous solution in contact with a porous? gas-permeable, catalytic anode of bound, temperature-stabilized _s "reduced oxides of ruthenium is brought. 4 * Method according to item 3 *, characterized in that - the aqueous solution is in contact with a porous, gas-permeable catalytic anode consisting of bound, reduced oxides of ruthenium and graphite. 22.6.1979 APC25B / 2O9 498 54 476 11 is brought « Procedure according to item 3 or 4 $ indicated by "that-the-watery. Solution-in contact with a porous, gas-permeable, catalytic anode in which the reduced oxides of ruthenium are further reduced by a content of Stabilized metal oxides selected from the reduced oxides of iridium, tantalum, titanium's mob or hafnium * Method according to item 5, characterized in that. an aqueous solution of UaeCl is brought into contact with a porous gas-permeable catalytic anode of bound reduced oxides of ruthenium and reduced oxides of iridium. 7 ". Procedure-by-point. 6, characterized in that the aqueous solution of EaOl is in contact with a porous, gas-permeable, catalytic anode of bound »reduced oxides of ruthenium and from 5 to 25% by weight of reduced oxides of Iridium is brought *. 8 "Process according to item 6 or 7" characterized in that the aqueous HaCl solution is in contact with an oil. röserij gas-permeable ^ catalytic anodes of bound, reduced oxides of ruthenium and 25 reduced oxides of iridium is brought * 22 * 6 * 1979. ._ APC25B / 2P9 498 54 476 11 9 * Method according to item 5 _S, characterized in that the aqueous solution is in contact with a porous, gas-permeable, catalytic. Anode of bound reduced oxides of ruthenium and reduced oxides of tantalum is brought * 10 * Process for the continuous production of chlorine from brine, characterized by the following stages a) continuously introducing an acidified brine into the anode compartment of an electrolytic cell, the anode compartment being separated from the cathode compartment by a cation selective ion exchange membrane, b) continuous introduction of a stream of water into the cathode chamber, c) electrolyzing the acidified brine on a porous, gas-permeable, catalytic anode connected to and embedded in a surface of the membrane to discharge chloride at the anode and minimize oxygen evolution . d) equilibrium electrolysis of water an.a porous, gas-permeable, catalytic cathode. I on the opposite side of the membrane to generate liquor and hydrogen there, the j 22.6.1979 APC25B / 209 498 54 476 11 The cathode is continuously rinsed with water in order to dilute the lye there and minimize the migration of the lye through the membrane to the anode, and e) continuous removal of chlorine from the anode and nkammer and lye and hydrogen from the cathode chamber. 11 · Procedure by item. 10, characterized in that an HGl-acidified brine is electrolyzed at the anode, whose acid concentration is kept above 0.2 moles of HCl * 12 * Method according to item 10 or 11 _s, characterized in that the acidified brine is in contact with; a porous gas-permeable anode of bound, reduced metal oxide and the water in contact with a thin, porous gas-permeable, caustic. bonded cathodes of bonded precious metal, which are connected to and embedded in the membrane _? The thickness of the cathode does not exceed 0 _s 025-awn .. to allow water to pass through the cathode to the interface. between the cathode and the membrane. to dilute the liquor formed there. 13 "Method" according to point T2 _S, characterized in that the thickness of the cathode is approximately O ₃ , 012 mm « 22 * 6 * 1979 APC25B / 2Ö9 498 54 476 11 ' 14 "Process according to items 10 to 13, characterized in that the acidified brine is in contact with a porous salt. .gas-permeable »catalytic * anode is prepared from bound, temperature-stabilized, reduced oxides of ruthenium» Method according to item 14, characterized in that the acidified brine is brought into contact with a porous, gas-permeable, catalytic anode made of bound ruthenium oxides and reduced iridium oxides. " A process for producing halogen and alkali metal hydroxide, characterized in that an aqueous alkali metal halide solution is electrolysed between an anode and a cathode separated by a cation exchange membrane. wherein at least one of the electrodes comprises thermally stabilized reduced platinum group metal oxides bound to the membrane to form a gas and electrolyte permeable catalytic electrode. Procedure by point. 16 _f characterized in that the associated with the membrane reduced oxides include a plurality of thermally stabilized, reduced oxide particles of a platinum group metal. - 22 * 6.1979 'APC25B / 209 54 476 11 A method according to item 16 or 17, characterized in that a layer of thermally stabilized5 reduced-platinum group moiety particles is bonded to opposite sides of the membrane to form gas and electrolyte permeable catalytic anode and cathode electrodes create « 19 "Method according to item 17 or 18, characterized in that the thermally stabilized, reduced oxide particles of a platinum group metal are connected by means of a carbonyl polymer" The method of item 19, characterized in ^ that the particles are thermally stabilized reduced oxides of ruthenium _s which are further stabilized by a content of thermally stabilized, reduced oxides of reduced oxides of iridium, tantalum, Titan, niobium or "hafnium. 21 «A method for producing halogen and Alkaliine ta 1 lh? / Dr oxide durcIi electric Iy se aq i GSR A IkaIimetallhalogenid '~ solution · means of a pair of catalytic electrodes _{5, s} are separated from one another, by an ion-™ permeable membrane gekennzeichnet- -through that one uses an electrode _r clie a multiplicity thermally stabilized,. Oxidized oxide particles of platinum group metals bound to the side of the membrane facing the cathode. includes * • 22 * 6 _O 1979 ''. ·, · '-. , APC25B / 2O9 54 476 11. 22. A method for producing chlorine by electrolysis of an aqueous Alkaliinetallchlorid electrolyte between an anode and a cathode ₉ which are separated by an ion exchange membrane j which limits the flow of des.wäßrigen electrolyte through the membrane, characterized in that the electrolysis with a Cathode comprising a thin layer of particles of platinum group metal or conductive oxides thereof, wherein the layer is bonded to one side of the membrane and in contact with a current distributor exposed to the electrolyte and having a hydrogen overvoltage is higher than that of the cathodic particle layer. 23 * Method according to item 22 _S, characterized in that the distributor is in contact with an electrolyte containing an alkali metal hydroxide « Method for producing chlorine by electrolysis of an aqueous alkali metal chloride between an anode and a cathode separated by an ion exchange membrane which restricts the passage of aqueous electrolyte, characterized in that the electrolysis is carried out with a cathode containing a thin particle Layer composed of a platinum group metal or conductive oxides thereof 22.6.1979 APC25B / 2Ö9 498 .54 476 11 Layer is in contact with one side of the membrane and with a current distributor exposed to the aqueous solution of alkali metal chloride and having a surface with higher chlorine absorption than the anode particle layer * 25 "" / learn after item 24, characterized by "that the particles are bound together by means of a fluorocarbon polymer" Method according to item 25, characterized in that the anode layer is connected to a cation exchange membrane. 27 * Process according to item 26, characterized in that the anode layer is connected to a fluorocarbon-containing fluorocarbon toff polybier ~ cation exchange membrane © Process for the preparation of halogens and alkali metal hydroxides by electrolyzing aqueous alkali metal halides between a. _S anode and a cathode which are separated from one another by a cation exchange membrane, characterized in that at least one ,, DER electrodes a plurality of electrically leitender-, catalytic .. Particles ;, ge build en to the membrane, has a gas- and eloktrolytransmittent. Electrode zn sheep, with the cathode side of the membrane ge ge 22 * 6 * 1979 APC25B / 209 54 476 11 has a lower water content than the remaining part to form an anion barrier layer which repels the hydroxyl ions and keeps the diffusion of alkali through the membrane to the anode at a minimum value. 29 «Procedure under point 28 _? characterized in that the composite membrane is a laminate of two layers in which the property for repelling anions on the cathode side is larger than on the anode side * Process according to item 29 », characterized in that the membrane is a polymeric fluorocarbon cation exchange membrane having an anion-repellent sulfonamide barrier layer on the cathode side _e Method according to item 30, characterized in that a cathode composed of a plurality of electrically conductive particles is connected to the sulfonamide layer located on the cathode side of the membrane ". 32 * method according to point 31 _s characterized -by "that is connected to the anode side of the membrane an anode of a plurality of electrically conductive particles" For this // page drawing