EP1167579B1 - Chlor-alkali electrolytic process in membrane cells using non-purified salt - Google Patents

Chlor-alkali electrolytic process in membrane cells using non-purified salt Download PDF

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EP1167579B1
EP1167579B1 EP01114430A EP01114430A EP1167579B1 EP 1167579 B1 EP1167579 B1 EP 1167579B1 EP 01114430 A EP01114430 A EP 01114430A EP 01114430 A EP01114430 A EP 01114430A EP 1167579 B1 EP1167579 B1 EP 1167579B1
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anode
membrane
process according
cathode
chlorine
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German (de)
French (fr)
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EP1167579A1 (en
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Jakob Dr.-Ing. Jörissen
Simon Dipl.-Ing.(Fh) Schnitzler
Ulrich Dipl.-Ing. Stemick
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Siemens AG
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Siemens AG
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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
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/34—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis
    • C25B1/46—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis in diaphragm cells

Definitions

  • Chlorine-based disinfectants for drinking water and swimming pools are indispensable because of their long-term effectiveness, especially for the disinfection of swimming pool water.
  • the use, and especially the transport and storage of elemental chlorine are associated with safety risks. Its use in water can lead to the undesirable formation of toxic chlorinated compounds from organic contaminants.
  • sodium hypochlorite solutions An alternative to the use of elemental chlorine is the use of sodium hypochlorite solutions.
  • the use of sodium hypochlorite solutions has the following advantages: The transport and handling of sodium hypochlorite are less dangerous than with chlorine gas, and inconvenience is easier to manage.
  • sodium hypochlorite solutions are very easy to dose and the hypochlorous acid formed from the sodium hypochlorite in the water at neutral pH acts as a strong oxidizer but is not chlorinating.
  • the process according to the invention relates to systems based on brine-based membrane cells.
  • US Pat. No. 4,230,544 describes a device and a corresponding chloralkali electrolysis process in which the electrolytic process, in particular in the anode space, is controlled by the pH value and the selection of the electrode. This is done in such a way that the amount of oxygen formed at the anode or the current efficiency of the oxygen production and the current efficiency of the membrane for the transfer of hydroxide ions from the cathode space to the anode space are chemically substantially equivalent.
  • the object of the invention is therefore to provide a chloralkali electrolysis process in which, in spite of the simplifications required for small installations (no brine cleaning, no complete degassing) a stable and reliable condition is achieved.
  • the abovementioned disadvantages of the hitherto available small plants should be avoided, but at the same time the chloralkali electrolysis process according to the invention should at least be equal in terms of costs.
  • a produced by further processing of the products of chlorine electrolysis sodium hypochlorite solution should show optimum product quality.
  • FIG. 4 shows by way of example the acidic state of the membrane obtained in carrying out the chloralkali electrolysis process according to the invention in the device according to the invention or a part thereof, namely the electrolysis cell.
  • the chloralkali electrolysis process according to the invention is characterized in that the membrane is in an acid state during electrolysis.
  • the term "acidic" state or “alkaline” state of a membrane has hitherto been known to the person skilled in the art within the context of the reaction of unpurified sodium sulfate with sodium hydroxide solution and sulfuric acid [Jörissen, J .; Simmrock, KH: "The behavior of ion exchange membranes in electrolysis and electrodialysis of sodium sulphate", J. Appl. Electrochem. 21 (1991) 869-876; Jörissen, J .: “Ion Exchange Membranes in Electrolysis and Electro-Organic Synthesis", Progress Reports VDI, Series 3, No. 442, VDI-Verlag Dusseldorf (1996)].
  • the membrane (e) is usually destroyed by the use of impure brine by the then contained in it impurities such as calcium and magnesium salts. This happens due to precipitation of these substances on / in the membrane.
  • the chloralkali electrolysis process according to the invention is characterized by an acidic environment for the membrane;
  • the irreversible damage to the membrane is prevented by the impurities present in the non-purified brine.
  • the precipitates occur, as has been shown in the invention, in the chlorine electrolysis only in the alkaline, but not in the acidic area. If an acidic environment is present in the membrane according to the invention, the contaminants contained in the brine can pass through the membrane.
  • the acidic environment is ensured according to the invention by producing oxygen at the anode simultaneously with the chlorine.
  • Hydrogen ions (H 3 O + ) are produced as a by-product of oxygen production, which acidify the anolyte very strongly. Since only a dilute sodium hydroxide solution, in the range of 2 to 5 wt .-% NaOH, is present in the cathode compartment in the inventive method, an acidic environment is stable in the membrane. Therefore, an acidic boundary layer is formed by the hydrogen ions in front of the membrane in the cathode compartment. The membrane therefore has no direct contact with the sodium hydroxide solution and is in an acidic state.
  • the acidic state of the membrane is stabilized by the fact that - unlike the hitherto customary small systems for Chlorelektrolyse- the chlorine gas in the form of a Magersolenfrelen chlorine gas is removed from the anode compartment.
  • the achievable by the selected process conditions operating state of the method according to the invention reliably prevents deposits in the membrane and can be maintained long-term stable.
  • the chloride concentration of the anolyte in the anode compartment is below the saturation limit in the chloralkali electrolysis process according to the invention, preferably below 50 g / l, particularly preferably in a range from 35 to 45 g / l.
  • the anode-side supply of saturated brine is carried out according to the invention preferably by means of one of the following methods, namely level control, hydrostatic pressure control, conductivity measurement, density measurement or a combination thereof. Such methods are known to the person skilled in the art.
  • the cathode-side supply of softened water is controlled according to the invention via a measurement of the voltage of the cell, a conductivity measurement and / or density measurement.
  • the method according to the invention is particularly advantageous, since the water supplied on the cathode chamber side is softened tap water.
  • the membrane separating the anode space and the cathode space is in an acidic state. Therefore, a single-layer membrane is preferably used. However, this is not a mandatory requirement of the method, as long as it is ensured that the boundary layer separating the cathode and the anode space is in the acidic state, as shown in FIG. 4. In a two-layer membrane, however, ensuring an acidic state is not reliably possible.
  • a cation exchange membrane is used to maintain the acidic state of the membrane separating the anode and cathode compartments.
  • the membrane is one formed on the basis of one or more polymers derivatized with acidic groups.
  • acidic groups which provide the cation exchange function in the membrane are preferably sulfonic acid groups.
  • the polymer must be one which is stable under the conditions of the chloralkali electrolyte according to the invention for an extended period of time, the requirements for the membrane in carrying out the process according to the invention not being as stringent as the conditions for a corresponding membrane in the chlorine electrolysis are in large plants.
  • This is due, inter alia, to the lower stresses of the membrane in this respect in the context of the method according to the invention, since, for example, the concentration of NaOH in the cathode compartment can be kept substantially lower in comparison with the large-scale industrial chloralkali electrolysis method ( ⁇ 33% by weight NaOH).
  • polymer membranes based on perfluorinated hydrocarbons for example for the membrane separating the cathode and the anode space, e.g. Nafion® from DuPont.
  • anodes are preferably used, on whose surfaces it comes in addition to the formation of chlorine gas from the chloride ions and also for the production of oxygen by oxidation of water.
  • the usual dimensionally stable anodes for the chloralkali electrolysis on the basis of titanium, coated with ruthenium-titanium oxides, are optimized for minimal oxygen formation and therefore not very suitable for the process according to the invention.
  • the strongly acidic anolyte according to the invention only little oxygen is produced on them. In addition, they are destroyed in conditions that lead to increased oxygenation.
  • an anode which is formed from a multi-layer material based on titanium and is not destroyed with increased oxygen formation.
  • Conventional titanium anodes are suitable for oxygen evolution, as can be used, for example, in steel strip galvanizing or in sodium sulfate electrolysis.
  • Such electrodes whose support material consists of titanium are coated with mixed oxides based on iridium oxide and tantalum oxide. Examples of such preferably used electrodes based on the above-mentioned metals are, for example, Electro Chemical Services / Eltech type EC600 or EC625, or equivalent types from Heraeus Elektrochemie GmbH.
  • the chloralkali electrolysis process according to the invention is particularly suitable for producing a chlorine bleach or aqueous sodium hypochlorite solution from the aqueous sodium hydroxide solution produced on the cathode side and the chlorine gas produced on the anode side.
  • a combined reactor is used after the chloralkali electrolysis process according to the invention, in the upper, that is the supply line of NaOH / H 2 nearest area, hydrogen is separated from the sodium hydroxide, in the central region of the Reaction of the chlorine is carried out with the sodium hydroxide solution and in the lower part of the resulting sodium hypochlorite solution is cooled.
  • the lower area is the area closest to the Cl 2 supply line.
  • This example was performed in a laboratory cell with 52 mm diameter active area (about 20 cm 2 membrane area).
  • the anode used was a titanium sheet (Heraeus Elektrochemie GmbH, Rodenbach, Industriestr. 17, 63517 Rodenbach), which was provided with a coating suitable for the simultaneous development of chlorine and oxygen.
  • the cathode was a chrome nickel steel sheet (material No. 1.4571).
  • the cell was formed from two 40 mm wide cell chambers sandwiched by a Nafion® 424 membrane (Dupont, Wilmington, Delaware, USA) and terminated by the electrodes. The distances between the electrodes and the membrane were thus each 40 mm.
  • the cell walls were made of glass or acrylic glass (PMME) to observe the membrane and to detect precipitations immediately.
  • the mixing of the cell chambers was carried out with magnetic stirring cores.
  • a saturated brine of evaporated salt tablets (Axal®, Solvay, Hans-Böckler-Allee 20, 30173 Hannover) flowed into the anode compartment via a level control without any further cleaning measures.
  • the feed to the cathode compartment was controlled so that the sodium hydroxide concentration reached 4 wt .-%.
  • the current density was 2.25 kA / m 2 .
  • the brine supply to the anode compartment turned to just under 30 g / h.
  • a concentration of 3.6% by weight of NaCl and of 0.3% by weight of HCl was analyzed.
  • the water transport through the membrane with the Na + and H + ions increased so high that the supplied brine was completely transported away in the form of the gases chlorine and oxygen as well as through the membrane (no anolyte effluent).
  • the current yield for chlorine and caustic soda was 65 to 70%.
  • the sodium hypochlorite solution produced therefrom in an absorber had a pH of 11-12 and excellent stability.
  • the experimental plant ran for a total of three months under these conditions (about 2000 hours). After dissecting the cells, both the membranes and the electrodes were in perfect condition.
  • a second test facility with 62 mm diameter of the active area (about 30 cm 2 membrane area) was constructed with expanded metal electrodes, so that the electrode spacing could be lowered to about 2 mm.
  • the coating of the titanium anode was carried out by the company Electro Chemical Services / Eltech.
  • a cathode made of expanded titanium metal was used. This is not attacked by hypochlorite, which arises in the breaks from the membrane penetrating chlorine.
  • the plant ran with 2.25 kA / m 2 current density in the cycle of 6 hours of operation and 6 hours break 8 months. This corresponds to a mere operating time of about 2800 hours.
  • the current yield for chlorine and caustic soda was constant at about 50%.
  • the cell voltage started after switching on at room temperature with about 4.1 volts and then reached after approximately one hour of heating to about 55 ° C constant about 3.8 volts. There was no deterioration in the results throughout the trial period. The membrane remained completely clear.
  • a cell with an electrode area of 450 cm 2 was tested.
  • the Magersole feed was level controlled using a small reservoir with float switch.
  • the cell was operated with a current of 100A at a voltage of about 4.1V.
  • the production capacity of this plant was about 70 g / h. After a trial period of about 2 months with daily interruptions, 300 hours of continuous operation resulted in very constant relationships in current, voltage and generation quantity. After disassembly of the cell membranes and electrodes were in perfect condition.

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Abstract

Chlor-alkali electrolysis comprises using an electrolysis cell having an anode chamber with an anode separated from a cathode chamber with a cathode by a membrane. Water is fed to the side of the cathode chamber and a saturated sodium chloride (NaCl) solution is fed to the side of the anode chamber. A mixture of aqueous sodium hydroxide and hydrogen gas is produced by electrolysis on the cathode side, and chlorine gas is produced on the anode side forming a lean sol. The membrane is in the acid state. The mixture of aqueous sodium hydroxide and hydrogen gas is removed on the cathode outlet of the electrolysis cell and the chlorine gas and oxygen are removed on the anode side of the cell. An Independent claim is also included for an apparatus for carrying out the process. Preferred Features: The chlorine gas removed on the anode side is free from lean sol. The aqueous sodium hydroxide has a concentration of less than 20, preferably 2-5 wt.% NaOH. The membrane is a cation exchange membrane, preferably made of a polymer derivative with sulfonyl groups. The polymer is a polymer based on perfluorinated hydrocarbons. The aqueous sodium hydroxide and the chlorine are used in the production of a chlorine bleaching solution. The anode is coated with mixed oxides based on iridium oxide and tantalum oxide.

Description

Die Erfindung betrifft ein Chloralkalielektrolyse-Verfahren unter Einsatz einer Membranzelle, wobei das Verfahren die Schritte umfasst, dass

  • einer Elektrolysezelle, die durch Unterteilung mit einer Membran einen Anodenraum mit einer Anode und einen Kathodenraum mit einer Kathode aufweist, kathodenraumseitig Wasser und anodenraumseitig eine gesättigte Sole, das heißt NaCI-Lösung zugeführt wird,
  • durch Elektrolyse kathodenraumseitig ein Gemisch von wässriger Natronlauge und Wasserstoffgas hergestellt und anodenraumseitig unter Bildung einer Magersole Chlorgas hergestellt wird, wobei sich die Membran im sauren Zustand befindet,
  • am kathodenraumseitigen Auslass der Elektrolysezelle das Gemisch von Natronlauge und Wasserstoffgas entnommen wird und am anodenraumseitigen Auslass der Elektrolysezelle Chlorgas und Sauerstoffe entnommen werden und eine anodenseitige Zufuhr an gesättigter Sole lediglich in dem Umfange erfolgt, dass der Verbrauch an Anolyt ausgeglichen wird.
The invention relates to a chloralkali electrolysis method using a membrane cell, the method comprising the steps of
  • an electrolysis cell which has an anode space with an anode and a cathode space with a cathode by division with a membrane, cathode side water and anode space side a saturated brine, that is NaCl solution is supplied
  • a mixture of aqueous sodium hydroxide solution and hydrogen gas is produced on the cathode chamber side by electrolysis and chlorine gas is produced on the anode chamber side to form a brine gas, the membrane being in the acidic state,
  • the mixture of sodium hydroxide solution and hydrogen gas is withdrawn from the cathode compartment-side outlet of the electrolytic cell and chlorine gas and oxygen are removed from the anode compartment-side outlet of the electrolysis cell, and an anode-side supply of saturated brine is effected only to the extent that the consumption of anolyte is compensated.

Desinfektionsmittel auf der Basis von Chlor für Trinkwasser und Schwimmbäder sind wegen ihrer Langzeitwirkung insbesondere für die Desinfektion von Schwimmbeckenwasser unverzichtbar. Die Anwendung sowie vor allem der Transport und die Lagerung von elementarem Chlor sind jedoch mit Sicherheitsrisiken verbunden. Sein Einsatz kann im Wasser zur unerwünschten Bildung toxischer chlorierter Verbindungen aus organischen Verunreinigungen führen. Außerdem hat Chlor eine Absenkung des pH-Wertes durch die als Koppelprodukt entstehende Salzsäure zur Folge.Chlorine-based disinfectants for drinking water and swimming pools are indispensable because of their long-term effectiveness, especially for the disinfection of swimming pool water. However, the use, and especially the transport and storage of elemental chlorine are associated with safety risks. Its use in water can lead to the undesirable formation of toxic chlorinated compounds from organic contaminants. Besides, has Chlorine results in a lowering of the pH by the hydrochloric acid formed as by-product.

Als Alternative zum Einsatz von elementarem Chlor bietet sich die Verwendung von Natriumhypochlorit-Lösungen an. Der Einsatz von Natriumhypochlorit-Lösungen hat die folgenden Vorteile: Der Transport und die Handhabung von Natriumhypochlorit sind weniger gefährlich als bei Chlorgas, Havariefälle sind leichter beherrschbar. Außerdem lassen sich Natriumhypochlorit-Lösungen sehr einfach dosieren und die aus dem Natriumhypochlorit im Wasser bei neutralem pH-Wert gebildete hypochlorige Säure wirkt als starkes Oxidationsmittel, ist aber nicht chlorierend.An alternative to the use of elemental chlorine is the use of sodium hypochlorite solutions. The use of sodium hypochlorite solutions has the following advantages: The transport and handling of sodium hypochlorite are less dangerous than with chlorine gas, and inconvenience is easier to manage. In addition, sodium hypochlorite solutions are very easy to dose and the hypochlorous acid formed from the sodium hypochlorite in the water at neutral pH acts as a strong oxidizer but is not chlorinating.

Die Verwendung handelsüblicher Chlorbleichlaugen, das heißt der Natriumhypochlorit-Lösungen ist jedoch mit den folgenden Nachteilen verbunden :However, the use of commercially available chlorine bleach solutions, ie the sodium hypochlorite solutions, has the following disadvantages:

Die fertig zu beziehenden, hochkonzentrierten Chlorbleichlaugen sind nur über eine gewisse Zeit stabil, das heißt, sie zerfallen im Laufe der Zeit, erreichen ihre Desinfektionswirkung nicht mehr und führen unerwünschte Nebenprodukte mit sich.The ready-to-use, highly concentrated chlorine bleach solutions are stable only for a certain time, that is, they disintegrate over time, no longer achieve their disinfecting effect and carry unwanted by-products.

Die Kosten für die handelsübliche Bleichlauge sind in Europa im Vergleich zur äquivalenten Menge Chlorgas bzw. im Vergleich zu vor Ort mittels Elektrolyse hergestellter Lösung sehr hoch.The cost of the commercial bleaching liquor is very high in Europe compared to the equivalent amount of chlorine gas or compared to locally produced by electrolysis solution.

Aus den genannten Gründen bietet es sich an, mit Hilfe einer geeigneten Elektrolyse-Anlage die Natriumhypochlorit-Lösung direkt vor Ort herzustellen. Dies erfolgt üblicherweise mittels der Chloralkalielektrolyse, auch Chlorelektrolyse genannt.For the reasons mentioned above, it makes sense to produce the sodium hypochlorite solution directly on site with the aid of a suitable electrolysis plant. This is usually done by means of the chloralkali electrolysis, also called chlorine electrolysis.

Das Prinzip der Chlorelektrolyse ist seit vielen Jahren bekannt. Es wird in der industriellen Chlorherstellung im großen Maßstab seit vielen Jahren erfolgreich eingesetzt.The principle of chlorine electrolysis has been known for many years. It has been used successfully in large scale industrial chlorine production for many years.

In der Desinfektionstechnik für die Wasseraufbereitung existieren zur Zeit Anlagen auf der Grundlage von Membranzellen sowie Anlagen auf der Grundlage von Durchlaufzellen, wie in der Fig. 1 gezeigt ist.In the disinfection technique for water treatment, there are currently facilities based on membrane cells and systems based on flow cells, as shown in FIG.

Das erfindungsgemäße Verfahren betrifft Anlagen auf der Grundlage von Membranzellen auf Solebasis.The process according to the invention relates to systems based on brine-based membrane cells.

Übliche Membranzellen-Elektrolyseverfahren arbeiten, wie nachfolgend erläutert:

  • Die Membran teilt die Elektrolysezelle in einen Anoden- und Kathodenraum;
  • der Anodenraum ist der Raum zwischen Anode (positiver Elektrode) und Membran, bei gelochten Anoden zusätzlich der Raum hinter der Anode;
  • der Kathodenraum ist der Raum zwischen Kathode (negativer Elektrode) und Membran, bei gelochten Kathoden zusätzlich der Raum hinter der Kathode;
  • zwischen Anode und Kathode liegt eine elektrische Gleichspannung an;
  • in den Anodenraum wird die Salzsole zudosiert. Die Salzsole enthält hauptsächlich gelöste (hydratisierte) Chlorid- und Natrium-Ionen;
  • in den Kathodenraum wird Wasser zudosiert;
  • an der Anode wird aus den Chlorid-Ionen Chlorgas produziert;
  • Kationenaustauscher-Membranen sind im Idealfall nur für gelöste (hydratisierte) Kationen durchlässig;
  • die Natrium-Ionen in der Salzsole können die Membran passieren und gelangen in den Kathodenraum;
  • an der Kathode werden aus dem zudosierten Wasser Wasserstoffgas und Hydroxid-lonen gebildet;
  • aus den Natrium- und Hydroxid-lonen entsteht Natronlauge;
  • auf Grund der an den Elektroden ablaufenden Reaktionen und dem damit verbundenen lonentransport durch die Membran fließt zwischen Anode und Kathode der Zellstrom;
  • als Maß für die Wirksamkeit der Membran wird die Stromausbeute angegeben. Sie gibt den Anteil des Zellstroms an, der für die Bildung der gewünschten Produkte (Chlor und Natronlauge) verwendet wird;
  • die in den Anodenraum zudosierte Sole reagiert nur zu einem Teil ab. Die Sole verlässt den Anodenraum mit reduziertem Salzgehalt (Magersole). In der Zelle löst sich ein Teil des produzierten Chlors in der Magersole. Die Magersole wird nach Durchlaufen des Entgasungsbehälters wieder in einem Salzlösebehälter aufgesättigt und im Kreislauf gefahren, so dass kein Salz verloren geht.
  • durch den Einsatz von Kationenaustauscher-Membranen, lässt sich salzfreie Natronlauge (Kathodenseite) und Chlorgas erzeugen, das von der Magersole abgetrennt wird.
Conventional membrane cell electrolysis methods operate as explained below:
  • The membrane divides the electrolytic cell into an anode and cathode space;
  • the anode space is the space between anode (positive electrode) and membrane, with perforated anodes additionally the space behind the anode;
  • the cathode space is the space between cathode (negative electrode) and membrane, with perforated cathodes additionally the space behind the cathode;
  • between anode and cathode is a DC electrical voltage;
  • in the anode compartment, the brine is added. The brine contains mainly dissolved (hydrated) chloride and sodium ions;
  • water is added to the cathode compartment;
  • At the anode chlorine gas is produced from the chloride ions;
  • Cation exchange membranes are ideally permeable only to dissolved (hydrated) cations;
  • the sodium ions in the brine can pass through the membrane and enter the cathode compartment;
  • At the cathode hydrogen gas and hydroxide ions are formed from the dosed water;
  • Sodium hydroxide is formed from the sodium and hydroxide ions;
  • due to the reactions taking place at the electrodes and the associated ion transport through the membrane, the cell current flows between the anode and the cathode;
  • as a measure of the effectiveness of the membrane, the current efficiency is specified. It indicates the proportion of cell flow used for the formation of the desired products (chlorine and caustic soda);
  • the brine metered into the anode compartment only reacts to a certain extent. The brine leaves the anode compartment with reduced salt content (Magersole). In the cell, part of the chlorine produced dissolves in the brine holly. The brine brine is saturated again after passing through the degassing in a brine and circulated so that no salt is lost.
  • through the use of cation exchange membranes, salt-free caustic soda (cathode side) and chlorine gas can be generated, which is separated from the brine sols.

Bei industriellen Großanlagen ist das Membran-Verfahren für die ChloralkaliElektrolyse seit etwa zwanzig Jahren Stand der Technik in der chemischen Industrie. In großchemischen Anlagen wird zur Minimierung der Prozesskosten mit einem sehr großen Aufwand alles getan, um den Energiebedarf der Anlage zu minimieren. Die Hauptrolle kommt dabei der Reinigung der Sole zu, die bis in den Spurenbereich frei von Störstoffen und Chlor sein muss.In industrial large-scale plants, the membrane process for the chloralkali electrolysis has been state of the art in the chemical industry for about twenty years. In large-scale plants everything is done to minimize the process costs with a great effort to minimize the energy requirements of the plant. The main role is to clean the brine, which must be free of impurities and chlorine down to the trace area.

Dies wurde möglich durch Entwicklung von chemisch ausreichend stabilen Kationenaustauscher-Membranen auf der Basis perfluorierter Polymere (z.B. Nafion® , DuPont). Außerdem wird zur Senkung des Energieaufwandes die Sole - neben der sowieso üblichen Fällung - mit Hilfe spezieller lonenaustauscher gereinigt, damit die Membran nicht durch Ablagerungen von Calcium- und MagnesiumVerbindungen zerstört wird. Die Konzentrationen der Störstoffe wird mit dieser Technik auf Werte unterhalb von 50 ppb abgesenkt. Zum Vergleich: Handelsübliches Siedesalz weist typische Calcium-Konzentrationen von ca. 0,14% auf.This has been made possible by the development of chemically stable cation exchange membranes based on perfluorinated polymers (e.g., Nafion®, DuPont). In addition, to reduce the energy consumption, the brine is - in addition to the usual precipitation - cleaned with the help of special ion exchanger, so that the membrane is not destroyed by deposits of calcium and magnesium compounds. The concentrations of the impurities are lowered with this technique to values below 50 ppb. For comparison: Commercially available evaporated salt has typical calcium concentrations of about 0.14%.

Da die erwähnten Membranen nicht vollständig selektiv sind, sondern zu einem Anteil von ca. 4 - 10% des elektrischen Stroms auch Hydroxid-lonen aus dem Kathodenraum in den Anodenraum gelangen lassen, enthält die aus der Zelle ablaufende Sole neben Chlor auch Hypochlorit. Beide Stoffe müssen aus den folgenden Gründen entfernt werden:

  • Austreten von Chlorgas;
  • das in der Sole enthaltene Chlor kann im Solekreislauf - insbesondere bei der Wiederaufsättigung mit Salz - aus der Sole ausgasen und führt zu Umweltbelastungen und Korrosionsschäden;
  • Schädigung der lonenaustauscher für die Solereinigung;
  • gelöstes Chlor und Hypochlorit in der Sole zerstören die lonenaustauscher;
  • Bildung von Chlorat;
  • aus dem Hypochlorit in der Magersole kann durch verschiedene Reaktionen Chlorat entstehen, das sich im Kreislauf anreichert und zu Störungen führt.
Since the membranes mentioned are not completely selective, but also allow hydroxide ions to pass from the cathode compartment into the anode compartment to a proportion of about 4 to 10% of the electrical current, the brine which leaves the cell contains hypochlorite in addition to chlorine. Both substances must be removed for the following reasons:
  • Leakage of chlorine gas;
  • the chlorine contained in the brine can outgas from the brine in the brine circuit, in particular during re-saturation with salt, and leads to environmental pollution and corrosion damage;
  • Damage to the ion exchangers for brine cleaning;
  • dissolved chlorine and hypochlorite in the brine destroy the ion exchangers;
  • Formation of chlorate;
  • Chlorochlorate can be formed from the hypochlorite in the brine brine by various reactions, which accumulates in the circulation and leads to disturbances.

Zur Entfernung von Chlorat und Hypochlorit durch Reaktion zu Chlor wird Salzsäure zugefügt. Um das Chlor vollständig aus der Sole zu entfernen, wird die Entchlorung im allgemeinen durch Vakuum-Entgasung durchgeführt. Eventuell noch enthaltenes Restchlor wird durch Natriumsulfit chemisch reduziert.To remove chlorate and hypochlorite by reaction to chlorine hydrochloric acid is added. In order to completely remove the chlorine from the brine, the dechlorination is generally carried out by vacuum degassing. Any remaining chlorine is chemically reduced by sodium sulfite.

Neben den vorstehend diskutierten Großanlagen sind auf dem Markt auch sog. Kleinanlagen erhältlich, die nach dem folgenden, in Fig. 2 erläuterten Grundprinzip arbeiten. Das Grundprinzip dieser Anlagen ist das gleiche wie das der großchemischen Anlagen. Allerdings wurden aus Kostengründen einige Vereinfachungen durchgeführt:

  • Die Sole wird aus Siedesalz und enthärtetem Wasser bereitet.
  • Es wird keinerlei Reinigung der Sole durchgeführt.
  • Die Magersole wird nicht vollständig entchlort. Daraus ergibt sich ein normaler Restchlorgehalt der Magersole von 5 bis 8 g/l.
  • Um ein Ausgasen des Chlors zu verhindern, wird zusätzlich ein Teil der entstehenden Natronlauge in die Magersole dosiert.
In addition to the large systems discussed above, so-called small systems are also available on the market, which operate according to the following basic principle explained in FIG. 2. The basic principle of these systems is the same as that of large-scale plants. However, for reasons of cost, some simplifications have been made:
  • The brine is prepared from vacuum salt and softened water.
  • There is no cleaning of the brine.
  • The lager brine is not completely dechlorinated. This results in a normal residual chlorine content of the Magersole of 5 to 8 g / l.
  • In order to prevent outgassing of the chlorine, a portion of the resulting caustic soda is additionally dosed into the broth.

Aus diesen Vereinfachungen ergeben sich in der Praxis die folgenden Probleme:

  • Die in der Anlage verwendete Sole weist sehr hohe Konzentrationen von Störstoffen auf.
  • Da keine Ausschleusung aus dem Solekreislauf vorgesehen ist, steigt die Konzentration der Störstoffe stetig an. Dabei bilden sich jedoch in der Membran am Übergang vom sauren Medium des Anodenraums zum alkalischen Medium des Kathodenraums häufig Ausfällungen, vor allem von Calcium- und Magnesiumsalzen, die anfangs zu einem starken Anstieg der Zellspannung und schließlich zu einer irreversiblen Schädigung der Membran führen. Dies geschieht häufig schon nach relativ kurzen Laufzeiten.
  • Durch den hohen Chlorgehalt der Sole kommt es zur verstärkten Bildung von Chlorat.
  • Durch die Zugabe von Natronlauge in die nicht vollständig entchlorte Magersole wird die Entwicklung von Chlorat unterstützt.
  • Durch Nebenreaktionen, die durch die Zugabe der Natronlauge verstärkt werden, kann es zu massivem Austritt von Chlorgas aus dem Salzlösebehälter kommen.
  • Da ein Teil der erzeugten Natronlauge der Magersole zudosiert wird, fehlt dieser in der erzeugten Natriumhypochlorit-Lösung, und sie weist nicht zu Hypochlorit umgesetztes Chlor auf. Dies beeinträchtigt die Stabilität des Produktes und kann zu einem Austritt von Chlorgas aus dem Produkt führen.
These simplifications result in the following problems in practice:
  • The brine used in the plant has very high concentrations of impurities.
  • Since no discharge from the brine circuit is provided, the concentration of impurities steadily increases. In the membrane, however, precipitations often form in the membrane at the transition from the acid medium of the anode space to the alkaline medium of the cathode space, especially of calcium and magnesium salts, which initially lead to a sharp increase in cell voltage and finally to irreversible damage to the membrane. This often happens after a relatively short period of time.
  • The high chlorine content of the brine causes increased formation of chlorate.
  • The addition of caustic soda to the incompletely dechlorinated brine sols helps to promote the development of chlorate.
  • By side reactions, which are enhanced by the addition of caustic soda, it can lead to massive leakage of chlorine gas from the brine.
  • Since some of the caustic soda produced is added to the brine, it is absent in the sodium hypochlorite solution produced, and it does not have chlorine converted to hypochlorite. This affects the stability of the product and may result in the release of chlorine gas from the product.

Es ist aufgrund des anlagentechnischen Aufwands und des Preises nicht möglich, die genannten Probleme der Kleinanlagen mit den Mitteln des großchemischen Verfahrens zu lösen.It is not possible due to the technical complexity and the price to solve the problems of small plants mentioned by means of large-scale process.

US-A 4,230,544 beschreibt eine Vorrichtung und ein entsprechendes Chloralkalielektrolyse-Verfahren, bei dem der elektrolytische Vorgang insbesondere im Anodenraum über den pH-Wert und die Wähl der Elektrode gesteuert wird. Dies erfolgt in der Weise, dass sich die Menge des an der Anode gebildeten Sauerstoffs beziehungsweise die Stromeffizienz der Sauerstofferzeugung und die Stromeffizienz der Membran für die Übertragung von Hydroxidionen vom Kathodenraum zum Anodenraum chemisch im Wesentlichen äquivalent sind.US Pat. No. 4,230,544 describes a device and a corresponding chloralkali electrolysis process in which the electrolytic process, in particular in the anode space, is controlled by the pH value and the selection of the electrode. This is done in such a way that the amount of oxygen formed at the anode or the current efficiency of the oxygen production and the current efficiency of the membrane for the transfer of hydroxide ions from the cathode space to the anode space are chemically substantially equivalent.

Aufgabe der Erfindung ist es daher, ein Chloralkalielektrolyse-Verfahren bereitzustellen, bei dem trotz der bei Kleinanlagen notwendigen Vereinfachungen (keine Solereinigung, keine vollständige Entgasung) ein stabiler und betriebssicherer Zustand erreicht wird. Insbesondere sollen die vorstehend erwähnten Nachteile der bislang verfügbaren Kleinanlagen vermieden werden, wobei jedoch gleichzeitig das erfindungsgemäße Chloralkalielektrolyse-Verfahren in Bezug auf die Kosten diesen zumindest ebenbürtig sein soll. Außerdem soll eine durch Weiterverarbeitung der Produkte der Chlorelektrolyse hergestellte Natriumhypochlorit-Lösung eine optimale Produktqualität zeigen.The object of the invention is therefore to provide a chloralkali electrolysis process in which, in spite of the simplifications required for small installations (no brine cleaning, no complete degassing) a stable and reliable condition is achieved. In particular, the abovementioned disadvantages of the hitherto available small plants should be avoided, but at the same time the chloralkali electrolysis process according to the invention should at least be equal in terms of costs. In addition, a produced by further processing of the products of chlorine electrolysis sodium hypochlorite solution should show optimum product quality.

Erfindungsgemäß werden diese Aufgaben dadurch gelöst, dass ein Chloralkalielektrolyse-Vertahren unter Einsatz einer Membranzelle bereitgestellt wird, wobei das Verfahren die Schritte umfasst, dass

  • einer Elektrolysezelle, die durch Unterteilung mit einer Membran einen Anodenraum mit einer Anode und einen Kathodenraum mit einer Kathode aufweist, kathodenraumseitig Wasser und anodenraumseitig eine gesättigte NaCI-Lösung zugeführt wird,
  • durch Elektrolyse kathodenraumseitig ein Gemisch von wässriger Natronlauge und Wasserstoffgas hergestellt und anodenraumseitig unter Bildung einer Magersole Chlorgas hergestellt wird, wobei sich die Membran im sauren Zustand befindet,
  • am kathodenraumseitigen Auslass der Elektrolysezelle das Gemisch von Natronlauge und Wasserstoffgas entnommen wird und
  • am anodenraumseitigen Auslass der Elektrolysezelle Chlorgas und Sauerstoff entnommen werden und eine anodenseitige Zufuhr an gesättigten Sole lediglich in dem Umfange erfolgt, dass der Verbrauch an Anolyt ausgeglichen wird.
According to the invention, these objects are achieved by providing a chloralkali electrolysis method using a membrane cell, the method comprising the steps of
  • an electrolysis cell which, by division with a membrane, has an anode space with an anode and a cathode space with a cathode, water is supplied on the cathode space side and a saturated NaCl solution on the anode space side,
  • a mixture of aqueous sodium hydroxide solution and hydrogen gas is produced on the cathode chamber side by electrolysis and chlorine gas is produced on the anode chamber side to form a brine gas, the membrane being in the acidic state,
  • the mixture of sodium hydroxide solution and hydrogen gas is withdrawn from the cathode compartment-side outlet of the electrolysis cell, and
  • At the anode chamber-side outlet of the electrolytic cell, chlorine gas and oxygen are taken off and an anode-side supply of saturated brine takes place only to the extent that the consumption of anolyte is compensated.

Die Erfindung wird nachfolgend und durch die beigefügten Zeichnungen sowie die Beispiele näher erläutert.The invention is explained in more detail below and by the accompanying drawings and the examples.

Es zeigen die Figuren:

  • Fig. 1 zeigt die verschiedenen Anlagetypen für die Wasseraufbereitung gemäß dem Stand der Technik.
  • Fig. 2 zeigt eine übliche Kleinanlage zur Herstellung von Chlorbleiche.
The figures show:
  • Fig. 1 shows the various plant types for water treatment according to the prior art.
  • Fig. 2 shows a conventional small plant for the production of chlorine bleach.

Das erfindungsgemäße Verfahren und die entsprechende Vorrichtung ist beispielhaft in der Fig. 3 beschrieben.The method according to the invention and the corresponding device are described by way of example in FIG.

Fig. 4 zeigt modellhaft den bei der Durchführung des erfindungsgemäßen Chloralkalielektrolyse-Verfahrens in der erfindungsgemäßen Vorrichtung beziehungsweise einem Teil derselben, nämlich der Elektrolysezelle, erzielten sauren Zustand der Membran.4 shows by way of example the acidic state of the membrane obtained in carrying out the chloralkali electrolysis process according to the invention in the device according to the invention or a part thereof, namely the electrolysis cell.

Das erfindungsgemäße Chloralkalielektrolyse-Verfahren zeichnet sich dadurch aus, dass sich bei der Elektrolyse die Membran in einem sauren Zustand befindet. Der Begriff des "sauren" Zustandes beziehungsweise "alkalischen" Zustandes einer Membran ist dem Fachmann bislang im Rahmen der Reaktion von ungereinigtem Natriumsulfat zu Natronlauge und Schwefelsäure bekannt [Jörissen, J.; Simmrock, K. H.: "The behaviour of ion exchange membranes in electrolysis and electrodialysis of sodium sulphate", J. Appl. Electrochem. 21 (1991) 869-876; Jörissen, J.: "Ionenaustauscher-Membranen in der Elektrolyse und elektro-organischen Synthese", Fortschritt-Berichte VDI, Reihe 3, Nr. 442, VDI-Verlag Düsseldorf (1996)].The chloralkali electrolysis process according to the invention is characterized in that the membrane is in an acid state during electrolysis. The term "acidic" state or "alkaline" state of a membrane has hitherto been known to the person skilled in the art within the context of the reaction of unpurified sodium sulfate with sodium hydroxide solution and sulfuric acid [Jörissen, J .; Simmrock, KH: "The behavior of ion exchange membranes in electrolysis and electrodialysis of sodium sulphate", J. Appl. Electrochem. 21 (1991) 869-876; Jörissen, J .: "Ion Exchange Membranes in Electrolysis and Electro-Organic Synthesis", Progress Reports VDI, Series 3, No. 442, VDI-Verlag Dusseldorf (1996)].

Wie vorstehend erwähnt, wird die Membran(e) üblicherweise bei Verwendung von ungereinigter Sole durch die dann in ihr enthaltenen Störstoffe wie Calcium- und Magnesiumsalze zerstört. Dies geschieht aufgrund von Ausfällungen dieser Stoffe an/in der Membrane.As mentioned above, the membrane (e) is usually destroyed by the use of impure brine by the then contained in it impurities such as calcium and magnesium salts. This happens due to precipitation of these substances on / in the membrane.

Das erfindungsgemäße Chloralkalielektrolyse-Verfahren ist - wie bereits erwähnt-durch ein saures Milieu für die Membran gekennzeichnet; damit wird die irreversible Schädigung der Membran durch die in der nicht gereinigten Sole vorhandenen Störstoffe verhindert. Die Ausfällungen treten nämlich, wie sich im Rahmen der Erfindung gezeigt hat, bei der Chlorelektrolyse nur im alkalischen, nicht aber im sauren Bereich auf. Liegt in der Membran erfindungsgemäß ein saures Milieu vor, können die in der Sole enthaltenen Störstoffe die Membran passieren.As already mentioned, the chloralkali electrolysis process according to the invention is characterized by an acidic environment for the membrane; Thus, the irreversible damage to the membrane is prevented by the impurities present in the non-purified brine. The precipitates occur, as has been shown in the invention, in the chlorine electrolysis only in the alkaline, but not in the acidic area. If an acidic environment is present in the membrane according to the invention, the contaminants contained in the brine can pass through the membrane.

Das saure Milieu wird erfindungsgemäß dadurch sichergestellt, dass an der Anode gleichzeitig mit dem Chlor auch Sauerstoff produziert wird. Als Nebenprodukt bei der Sauerstoff-Erzeugung fallen Wasserstoffionen (H3O+) an, diese säuern den Anolyten sehr stark an. Da im Kathodenraum bei dem erfindungsgemäßen Verfahren eine nur verdünnte Natronlauge, im Bereich von 2 bis 5 Gew.-% NaOH, vorhanden ist, liegt in der Membran stabil ein saures Milieu vor. Vor der Membran im Kathodenraum bildet sich daher durch die Wasserstoffionen eine saure Grenzschicht aus. Die Membran hat daher keinen direkten Kontakt mit der Natronlauge und befindet sich in einem sauren Zustand.The acidic environment is ensured according to the invention by producing oxygen at the anode simultaneously with the chlorine. Hydrogen ions (H 3 O + ) are produced as a by-product of oxygen production, which acidify the anolyte very strongly. Since only a dilute sodium hydroxide solution, in the range of 2 to 5 wt .-% NaOH, is present in the cathode compartment in the inventive method, an acidic environment is stable in the membrane. Therefore, an acidic boundary layer is formed by the hydrogen ions in front of the membrane in the cathode compartment. The membrane therefore has no direct contact with the sodium hydroxide solution and is in an acidic state.

Bei dem erfindungsgemäßen Verfahren ist es möglich, den sauren Zustand der Membran automatisch aufrechtzuerhalten. Dies ergibt sich durch das Zusammenspiel der Wirkungen der verschiedenen Parameter des erfindungsgemäßen Verfahrens, insbesondere aus der Chlor- und der Sauerstoff-Entwicklung am Anodenmaterial, verursacht durch die Variation des Solezuflusses in den Anodenraum.In the method according to the invention, it is possible to automatically maintain the acidic state of the membrane. This results from the interaction of the effects of the various parameters of the method according to the invention, in particular from the evolution of chlorine and oxygen at the anode material, caused by the variation of the brine inflow into the anode compartment.

Bei einer besonders bevorzugten Verfahrensführung wird der saure Zustand der Membran dadurch stabilisiert, dass - anders als bei den bislang üblichen Kleinanlagen zur Chlorelektrolyse- das Chlorgas in Form eines magersolenfrelen Chlorgases dem Anodenraum entnommen wird. Der durch die gewählten Verfahrensbedingungen erreichbare Betriebszustand des erfindungsgemäßen Verfahrens vermeidet zuverlässig Ablagerungen in der Membrane und lässt sich langzeitstabil aufrechterhalten.In a particularly preferred procedure, the acidic state of the membrane is stabilized by the fact that - unlike the hitherto customary small systems for Chlorelektrolyse- the chlorine gas in the form of a Magersolenfrelen chlorine gas is removed from the anode compartment. The achievable by the selected process conditions operating state of the method according to the invention reliably prevents deposits in the membrane and can be maintained long-term stable.

Anodenseitig braucht bei dem erfindungsgemäßen Verfahren eine Zufuhr an gesättigter Sole insbesondere lediglich in dem Umfange zu erfolgen, dass der durch die Elektrolyse bedingte Verbrauch an Anolyt ausgeglichen wird. Im Unterschied zu den bislang üblichen Chlorelektrolyse-Verfahren wird die im Anodenraumvorhandene Magersole also nicht rezirkuliert, somit kommt es auch nicht zu den vorstehend erwähnten nachteiligen Effekten wie Anstieg der Konzentration an Störionen und so weiter.On the anode side, in the method according to the invention, a supply of saturated brine in particular needs to be carried out only to the extent that the consumption of anolyte caused by the electrolysis is compensated. In contrast to the chlorine electrolysis method customary hitherto, therefore, the magnesole present in the anode compartment is not recirculated, so that the abovementioned adverse effects such as an increase in the concentration of interfering ions and so on do not occur.

Die Chloridkonzentration des Anolyten im Anodenraum liegt bei dem erfindungsgemäßen Chloralkalielektrolyse-Verfahren unterhalb der Sättigungsgrenze, bevorzugt unterhalb von 50 g/l, besonders bevorzugt in einem Bereich von 35 bis 45 g/l.The chloride concentration of the anolyte in the anode compartment is below the saturation limit in the chloralkali electrolysis process according to the invention, preferably below 50 g / l, particularly preferably in a range from 35 to 45 g / l.

Die anodenseitige Zufuhr an gesättigter Sole erfolgt erfindungsgemäß bevorzugt mittels eines der nachfolgenden Verfahren, nämlich Niveauregulierung, hydrostatische Druckregelung, Leitfähigkeitsmessung, Dichtemessung oder auch einer Kombination davon. Derartige Verfahren sind dem Fachmann bekannt.The anode-side supply of saturated brine is carried out according to the invention preferably by means of one of the following methods, namely level control, hydrostatic pressure control, conductivity measurement, density measurement or a combination thereof. Such methods are known to the person skilled in the art.

Die kathodenseitige Zufuhr an enthärtetem Wasser wird erfindungsgemäß über eine Messung der Spannung der Zelle, eine Leitfähigkeitsmessung und/oder Dichtemessung geregelt. Das erfindungsgemäße Verfahren ist ganz besonders vorteilhaft, da das kathodenraumseitig zugeführte Wasser enthärtetes Leitungswasser ist.The cathode-side supply of softened water is controlled according to the invention via a measurement of the voltage of the cell, a conductivity measurement and / or density measurement. The method according to the invention is particularly advantageous, since the water supplied on the cathode chamber side is softened tap water.

Für das erfindungsgemäße Chloralkalielektrolyse-Verfahren ist es-wie bereits erwähnt - wesentlich, dass sich die den Anodenraum und den Kathodenraum trennende Membran in einem sauren Zustand befindet. Deshalb wird bevorzugt eine einschichtige Membran verwendet. Dies ist jedoch keine zwingende Voraussetzung des Verfahrens, so lange sichergestellt ist, dass die den Kathoden- und den Anodenraum trennende Grenzschicht sich im sauren Zustand befindet, wie es in Fig. 4 gezeigt ist. Bei einer zweischichtigen Membran ist die Sicherstellung eines sauren Zustandes jedoch nicht zuverlässig möglich.As already mentioned, it is essential for the chloralkali electrolysis process according to the invention that the membrane separating the anode space and the cathode space is in an acidic state. Therefore, a single-layer membrane is preferably used. However, this is not a mandatory requirement of the method, as long as it is ensured that the boundary layer separating the cathode and the anode space is in the acidic state, as shown in FIG. 4. In a two-layer membrane, however, ensuring an acidic state is not reliably possible.

Bei dem erfindungsgemäßen Verfahren wird zur Aufrechterhaltung des sauren Zustandes der den Anoden- und Kathodenraum trennenden Membran eine Kationenaustauschermembran verwendet. Bei der Membran handelt es sich insbesondere um eine solche, die auf der Grundlage eines oder mehrerer Polymere gebildet ist, das beziehungsweise die mit sauren Gruppen derivatisiert ist/sind. Derartige bevorzugt eingesetzte saure Gruppen, die die Kationenaustauscherfunktion in der Membran bereitstellen, sind bevorzugt Sulfonsäuregruppen.In the method according to the invention, a cation exchange membrane is used to maintain the acidic state of the membrane separating the anode and cathode compartments. In particular, the membrane is one formed on the basis of one or more polymers derivatized with acidic groups. Such preferably used acidic groups which provide the cation exchange function in the membrane are preferably sulfonic acid groups.

Bei dem Polymer muss es sich um eines handeln, das unter den Bedingungen der erfindungsgemäßen Chloralkalielektroyse auch auf längere Zeit stabil ist, wobei die Anforderungen an die Membran im Rahmen der Durchführung des erfindungsgemäßen Verfahrens nicht so strikt wie die Bedingungen für eine entsprechende Membran bei der Chlorelektrolyse in Großanlagen sind. Dies liegt unter Anderem an den in dieser Hinsicht niedrigeren Beanspruchungen der Membran im Rahmen des erfindungsgemäßen Verfahrens, da beispielsweise die Konzentration an NaOH im Kathodenraum im Vergleich mit den großindustriellen Chloralkalielektrolyse-Verfahren (≈ 33 Gew.-% NaOH) wesentlich geringer gehalten werden kann. Andererseits ist es der große Vorteil des erfindungsgemäßen Chloralkalielektrolyse-Verfahrens, dass ungereinigtes Siedesalz als Basis für die Sole verwendet werden kann, ohne dass es zu den bei der Verwendung dieses Ausgangsmaterials bekannten Nachteilen käme.The polymer must be one which is stable under the conditions of the chloralkali electrolyte according to the invention for an extended period of time, the requirements for the membrane in carrying out the process according to the invention not being as stringent as the conditions for a corresponding membrane in the chlorine electrolysis are in large plants. This is due, inter alia, to the lower stresses of the membrane in this respect in the context of the method according to the invention, since, for example, the concentration of NaOH in the cathode compartment can be kept substantially lower in comparison with the large-scale industrial chloralkali electrolysis method (~33% by weight NaOH). On the other hand, it is the great advantage of the chloralkali electrolysis process according to the invention that unpurified vacuum salt as the basis for the brine can be used without the disadvantages known in the use of this starting material.

Erfindungsgemäß werden für die den Kathoden- und den Anodenraum trennende Membran bevorzugt Polymer-Membranen auf der Basis perfluorierter Kohlenwasserstoffe eingesetzt, z.B. Nafion® der Firma DuPont.According to the invention, it is preferred to use polymer membranes based on perfluorinated hydrocarbons, for example for the membrane separating the cathode and the anode space, e.g. Nafion® from DuPont.

Bei der Durchführung des erfindungsgemäßen Verfahrens werden außerdem bevorzugt solche Anoden verwendet, an deren Oberflächen es neben der Bildung von Chlorgas aus den Chlorid-Ionen auch zur Erzeugung von Sauerstoff durch Oxidation von Wasser kommt. Die üblichen dimensions-stabilen Anoden für die Chloralkali-Elektrolyse auf der Basis von Titan, beschichtet mit Ruthenium-Titan-Oxiden, sind auf minimale Sauerstoffbildung optimiert und deshalb für das erfindungsgemäße Verfahren wenig geeignet. Besonders bei Verwendung des erfindungsgemäß stark sauren Anolyten entsteht an ihnen nur wenig Sauerstoff. Außerdem werden sie bei Bedingungen, die zu erhöhter Sauerstoffbildung führen, zerstört.In carrying out the process according to the invention also such anodes are preferably used, on whose surfaces it comes in addition to the formation of chlorine gas from the chloride ions and also for the production of oxygen by oxidation of water. The usual dimensionally stable anodes for the chloralkali electrolysis on the basis of titanium, coated with ruthenium-titanium oxides, are optimized for minimal oxygen formation and therefore not very suitable for the process according to the invention. Especially when using the strongly acidic anolyte according to the invention, only little oxygen is produced on them. In addition, they are destroyed in conditions that lead to increased oxygenation.

Für die Erzeugung von Sauerstoff ist es besonders vorteilhaft, wenn eine Anode eingesetzt wird, die aus einem Mehrschichtenmaterial auf der Basis von Titan gebildet ist und bei erhöhter Sauerstoffbildung nicht zerstört wird. Geeignet sind übliche Titan-Anoden zur Sauerstoffentwicklung wie sie beispielsweise bei der Stahlbandverzinkung oder bei der Natriumsulfat-Elektrolyse verwendet werden können. Derartige Elektroden, deren Trägermaterial aus Titan besteht, sind mit Mischoxiden auf der Basis von Iridiumoxid und Tantaloxid beschichtet. Beispiele derartiger bevorzugt eingesetzter Elektroden auf der Basis der vorstehend erwähnten Metalle sind beispielsweise Electro Chemical Services/Eltech Typ EC600 beziehungsweise EC625, oder gleichwertige Typen von Heraeus Elektrochemie GmbH.For the production of oxygen, it is particularly advantageous if an anode is used, which is formed from a multi-layer material based on titanium and is not destroyed with increased oxygen formation. Conventional titanium anodes are suitable for oxygen evolution, as can be used, for example, in steel strip galvanizing or in sodium sulfate electrolysis. Such electrodes whose support material consists of titanium are coated with mixed oxides based on iridium oxide and tantalum oxide. Examples of such preferably used electrodes based on the above-mentioned metals are, for example, Electro Chemical Services / Eltech type EC600 or EC625, or equivalent types from Heraeus Elektrochemie GmbH.

Das erfindungsgemäße Chloralkalielektrolyse-Verfahren eignet sich insbesondere dazu, aus der kathodenseitig erzeugten wässrigen Natronlauge und dem anodenseitig hergestellten Chlorgas eine Chlorbleichlauge beziehungsweise wässrige Natriumhypochlorit-Lösung herzustellen.The chloralkali electrolysis process according to the invention is particularly suitable for producing a chlorine bleach or aqueous sodium hypochlorite solution from the aqueous sodium hydroxide solution produced on the cathode side and the chlorine gas produced on the anode side.

Bei einer besonders bevorzugten Verfahrensführung zu Herstellung der Chlorbleichlauge wird im Anschluss an das erfindungsgemäße Chloralkalielektrolyse-Verfahren ein Kombireaktor eingesetzt, in dessen oberem, das heißt der Zufuhrleitung von NaOH/H2 nächstgelegenen Bereich, Wasserstoff von der Natronlauge getrennt wird, in dessen mittleren Bereich die Reaktion des Chlors mit der Natronlauge erfolgt und in dessen unterem Bereich die entstehende Natriumhypochloritlösung gekühlt wird. Der untere Bereich ist derjenige Bereich, der der Zufuhrleitung für Cl2 am nächsten liegt.In a particularly preferred process for the preparation of the sodium hypochlorite, a combined reactor is used after the chloralkali electrolysis process according to the invention, in the upper, that is the supply line of NaOH / H 2 nearest area, hydrogen is separated from the sodium hydroxide, in the central region of the Reaction of the chlorine is carried out with the sodium hydroxide solution and in the lower part of the resulting sodium hypochlorite solution is cooled. The lower area is the area closest to the Cl 2 supply line.

Die Erfindung wird durch die nachfolgenden Beispiele näher erläutert, die jedoch nicht einschränkend zu verstehen sind.The invention is further illustrated by the following examples, which are not intended to be limiting.

Beispiel 1:Example 1:

Dieses Beispiel wurde in einer Laborzelle mit 52 mm Durchmesser der aktiven Fläche (ca. 20 cm2 Membranfläche) durchgeführt. Als Anode diente ein Titanblech (Heraeus Elektrochemie GmbH, Werk Rodenbach, Industriestr. 17, 63517 Rodenbach), das mit einer zur gleichzeitigen Entwicklung von Chlor und Sauerstoff geeigneten Beschichtung versehen war. Die Kathode war ein Chromnikkelstahlblech (Werkstoff-Nr. 1.4571). Die Zelle wurde aus zwei Zellkammern mit 40 mm Breite gebildet, zwischen denen eine Membrane Nafion® 424 (Dupont, Wilmington, Delaware, USA) eingespannt war und die durch die Elektroden abgeschlossen wurden. Die Abstände zwischen den Elektroden und der Membrane betrugen also je 40 mm. Die Zellwände bestanden aus Glas beziehungsweise Acrylglas (PMME), um die Membrane beobachten und Ausfällungen sofort erkennen zu können. Die Durchmischung der Zellkammern erfolgte mit Magnetrührkernen. In den Anodenraum floss eine gesättigte Sole aus Siedesalztabletten (Axal® , Solvay, Hans-Böckler-Allee 20, 30173 Hannover) ohne weitere Reinigungsmaßnahmen über eine Niveauregelung. Der Zulauf zum Kathodenraum wurde so geregelt, dass die Natronlauge-Konzentration 4 Gew.-% erreichte. Die Stromdichte betrug 2,25 kA/m2.This example was performed in a laboratory cell with 52 mm diameter active area (about 20 cm 2 membrane area). The anode used was a titanium sheet (Heraeus Elektrochemie GmbH, Rodenbach, Industriestr. 17, 63517 Rodenbach), which was provided with a coating suitable for the simultaneous development of chlorine and oxygen. The cathode was a chrome nickel steel sheet (material No. 1.4571). The cell was formed from two 40 mm wide cell chambers sandwiched by a Nafion® 424 membrane (Dupont, Wilmington, Delaware, USA) and terminated by the electrodes. The distances between the electrodes and the membrane were thus each 40 mm. The cell walls were made of glass or acrylic glass (PMME) to observe the membrane and to detect precipitations immediately. The mixing of the cell chambers was carried out with magnetic stirring cores. A saturated brine of evaporated salt tablets (Axal®, Solvay, Hans-Böckler-Allee 20, 30173 Hannover) flowed into the anode compartment via a level control without any further cleaning measures. The feed to the cathode compartment was controlled so that the sodium hydroxide concentration reached 4 wt .-%. The current density was 2.25 kA / m 2 .

Die Solezufuhr zum Anodenraum stellte sich auf knapp 30 g/h ein. Im Anodenraum wurde eine Konzentration von 3,6 Gew.-% NaCI und von 0,3 Gew.-% HCI analysiert. Bei dieser niedrigen Anolyt-Konzentration stieg dann der Wassertransport durch die Membrane mit den Na+- und H+-Ionen so hoch an, dass die zugeführte Sole vollständig in Form der Gase Chlor und Sauerstoff sowie durch die Membran abtransportiert wurde (kein Anolytablauf). Die Stromausbeute für Chlor und Natronlauge lag bei 65 bis 70 %. Die in einem Absorber daraus erzeugte Natriumhypochlorit-Lösung wies einen pH-Wert von 11-12 und eine ausgezeichnete Stabilität auf.The brine supply to the anode compartment turned to just under 30 g / h. In the anode compartment, a concentration of 3.6% by weight of NaCl and of 0.3% by weight of HCl was analyzed. At this low anolyte concentration, the water transport through the membrane with the Na + and H + ions increased so high that the supplied brine was completely transported away in the form of the gases chlorine and oxygen as well as through the membrane (no anolyte effluent). The current yield for chlorine and caustic soda was 65 to 70%. The sodium hypochlorite solution produced therefrom in an absorber had a pH of 11-12 and excellent stability.

Die Versuchsanlage lief insgesamt drei Monate unter diesen Bedingungen (etwa 2000 Stunden). Nach dem Zerlegen der Zellen waren sowohl die Membrane als auch die Elektroden in einem einwandfreien Zustand.The experimental plant ran for a total of three months under these conditions (about 2000 hours). After dissecting the cells, both the membranes and the electrodes were in perfect condition.

Beispiel 2:Example 2:

Eine zweite Versuchsanlage mit 62 mm Durchmesser der aktiven Fläche (ca. 30 cm2 Membranfläche) wurde mit Streckmetall-Elektroden aufgebaut, so dass der Elektrodenabstand auf etwa 2 mm abgesenkt werden konnte. Die Beschichtung der Titananode erfolgte durch die Firma Electro Chemical Services / Eltech. Um den intermittierenden Betrieb praktischer Produktionsanlagen für Natriumhypochlorit-Lösung, die nur bei Bedarf laufen, testen zu können, wurde eine Kathode aus Titan-Streckmetall eingesetzt. Diese wird nicht angegriffen von Hypochlorit, das in den Betriebspausen aus durch die Membran eindringendem Chlor entsteht. Die Anlage lief mit 2,25 kA/m2 Stromdichte im Takt von 6 Stunden Betrieb und 6 Stunden Pause 8 Monate. Dies entspricht einer reinen Betriebszeit von etwa 2800 Stunden. Die Stromausbeute für Chlor und Natronlauge lag konstant bei etwa 50 %. Die Zellspannung startete jeweils nach dem Einschalten bei Raumtemperatur mit ca. 4,1 Volt und erreichte dann nach einer rund einstündigen Aufheizphase auf ca. 55 °C konstant ca. 3,8 Volt. In der gesamten Versuchszeit war keine Verschlechterung der Ergebnisse zu beobachten. Die Membran blieb völlig klar.A second test facility with 62 mm diameter of the active area (about 30 cm 2 membrane area) was constructed with expanded metal electrodes, so that the electrode spacing could be lowered to about 2 mm. The coating of the titanium anode was carried out by the company Electro Chemical Services / Eltech. In order to test the intermittent operation of practical production facilities for sodium hypochlorite solution, which run only when needed, a cathode made of expanded titanium metal was used. This is not attacked by hypochlorite, which arises in the breaks from the membrane penetrating chlorine. The plant ran with 2.25 kA / m 2 current density in the cycle of 6 hours of operation and 6 hours break 8 months. This corresponds to a mere operating time of about 2800 hours. The current yield for chlorine and caustic soda was constant at about 50%. The cell voltage started after switching on at room temperature with about 4.1 volts and then reached after approximately one hour of heating to about 55 ° C constant about 3.8 volts. There was no deterioration in the results throughout the trial period. The membrane remained completely clear.

Beispiel 3:Example 3:

In einem weiteren Versuch wurde eine Zelle mit einer Elektrodenfläche von 450 cm2 getestet. Die Zufuhr der Magersole wurde mit Hilfe eines kleinen Vorlagebehälters mit Schwimmerschalter niveaugesteuert. Die Zelle wurde mit einem Strom von 100 A bei einer Spannung von ca. 4,1 V betrieben.In a further experiment, a cell with an electrode area of 450 cm 2 was tested. The Magersole feed was level controlled using a small reservoir with float switch. The cell was operated with a current of 100A at a voltage of about 4.1V.

Die Erzeugungsleistung dieser Anlage lag bei ca. 70 g/h. Nach einer Versuchszeit von ca. 2 Monaten mit täglichen Unterbrechungen ergaben sich 300 Betriebsstunden lang sehr konstante Verhältnisse in Strom, Spannung und Erzeugungsmenge. Nach dem Zerlegen der Zelle waren Membranen und Elektroden in einem einwandfreien Zustand.The production capacity of this plant was about 70 g / h. After a trial period of about 2 months with daily interruptions, 300 hours of continuous operation resulted in very constant relationships in current, voltage and generation quantity. After disassembly of the cell membranes and electrodes were in perfect condition.

Claims (15)

  1. Chloralkali electrolysis process using a membrane cell, wherein the process comprises the steps
    - an electrolysis cell which has an anode space having an anode and a cathode space having a cathode as a result of division by means of a membrane is supplied with water to the cathode space and a saturated brine, i.e. NaCl solution, to the anode space,
    - a mixture of aqueous sodium hydroxide and hydrogen gas is produced in the cathode space and chlorine gas is produced with formation of a depleted brine in the anode space by electrolysis, with the membrane being in the acid state,
    - the mixture of sodium hydroxide solution and hydrogen gas is taken off at the cathode space outlet of the electrolysis cell and
    - chlorine gas and oxygen are taken off at the anode space outlet of the electrolysis cell and saturated brine is fed in on the anode side only in the amount required to balance the consumption of anolyte.
  2. Process according to Claim 1, wherein the chlorine gas taken off on the anode side is free of depleted brine.
  3. Process according to Claim 1 or 2, wherein the sodium hydroxide solution produced in the cathode space has a concentration of less than 20% by weight of NaOH, preferably in the range from 2 to 5% by weight.
  4. Process according to any of the preceding claims, wherein the membrane is a single-layer membrane.
  5. Process according to any of the preceding claims, wherein the membrane is a cation-exchange membrane.
  6. Process according to any of the preceding claims, wherein the membrane is a membrane composed of a polymer which has been modified with sulphonyl groups.
  7. Process according to any of the preceding claims, wherein the polymer is a polymer based on perfluorinated hydrocarbons.
  8. Process according to Claim 7, wherein the introduction of saturated brine is regulated on the anode side by means of a method selected from among hydrostatic pressure regulation, conductivity measurement, density measurement and level regulation.
  9. Process according to any of the preceding claims, wherein the introduction of water on the cathode side is regulated by means of a method selected from among monitoring of the voltage of the cell, conductivity measurement and density measurement.
  10. Process according to any of the preceding claims, wherein the water fed to the cathode space is mains water.
  11. Process according to any of the preceding claims, wherein the aqueous sodium hydroxide produced on the cathode side and the chlorine gas produced on the anode side are used for producing a chlorine bleach liquor.
  12. Process according to Claim 11, wherein the chlorine bleach liquor is produced in a combination reactor in whose upper region hydrogen is separated from the sodium hydroxide solution, in whose middle region the reaction of the chlorine with the sodium hydroxide takes place and in whose lower region the sodium hypochlorite solution formed is cooled.
  13. Process according to any of the preceding claims, wherein a coated anode formed by a multilayer material based on titanium is used.
  14. Process according to Claim 13, wherein the coating of the anode consists essentially of mixed oxides based on iridium oxide and tantalum oxide.
  15. Process according to any of the preceding claims, wherein the chloride concentration of the anolyte in the anode space is below the saturation limit, preferably below 50 g/l, particularly preferably in a range from 35 to 45 g/l.
EP01114430A 2000-06-24 2001-06-15 Chlor-alkali electrolytic process in membrane cells using non-purified salt Expired - Lifetime EP1167579B1 (en)

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DE10031018A DE10031018B4 (en) 2000-06-24 2000-06-24 Chloralkali electrolysis process in membrane cells with electrolysis of untreated evaporated salt
DE10031018 2000-06-24

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EP1167579B1 true EP1167579B1 (en) 2006-09-27

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WO2004085709A1 (en) * 2003-03-25 2004-10-07 Gablenko Vyacheslav Georgievic Device for synthesising oxidants from agueous sodium chloride solution
DE102015003911A1 (en) 2015-03-27 2016-09-29 Eilenburger Elektrolyse- Und Umwelttechnik Gmbh Process for the disinfection of pool, drinking and service water as well as for the production of a disinfectant concentrate

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Publication number Priority date Publication date Assignee Title
US4230544A (en) * 1979-08-31 1980-10-28 Ionics Inc. Method and apparatus for controlling anode pH in membrane chlor-alkali cells
US4528077A (en) * 1982-07-02 1985-07-09 Olin Corporation Membrane electrolytic cell for minimizing hypochlorite and chlorate formation
DE29718331U1 (en) * 1997-10-17 1998-01-22 Dinotec Gmbh Electrolysis plant for the production of an aqueous sodium hypochlorite solution

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DE10031018A1 (en) 2002-01-31
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DE10031018B4 (en) 2007-02-22
DK1167579T3 (en) 2007-01-08

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