EP0011886B1 - Preparation of oxy-halogenated acids and their salts by electrolysis - Google Patents
Preparation of oxy-halogenated acids and their salts by electrolysis Download PDFInfo
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- EP0011886B1 EP0011886B1 EP79200618A EP79200618A EP0011886B1 EP 0011886 B1 EP0011886 B1 EP 0011886B1 EP 79200618 A EP79200618 A EP 79200618A EP 79200618 A EP79200618 A EP 79200618A EP 0011886 B1 EP0011886 B1 EP 0011886B1
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- ions
- calcium
- electrolysis
- sea water
- purified
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- 238000005868 electrolysis reaction Methods 0.000 title claims description 17
- 150000003839 salts Chemical class 0.000 title claims description 6
- 239000002253 acid Substances 0.000 title claims description 3
- 150000007513 acids Chemical class 0.000 title claims 2
- 239000012266 salt solution Substances 0.000 claims description 14
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 12
- 239000013535 sea water Substances 0.000 claims description 12
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 11
- 229910001424 calcium ion Inorganic materials 0.000 claims description 10
- 229910001425 magnesium ion Inorganic materials 0.000 claims description 10
- 238000000034 method Methods 0.000 claims description 10
- 239000000920 calcium hydroxide Substances 0.000 claims description 9
- 229910001861 calcium hydroxide Inorganic materials 0.000 claims description 9
- JLVVSXFLKOJNIY-UHFFFAOYSA-N Magnesium ion Chemical compound [Mg+2] JLVVSXFLKOJNIY-UHFFFAOYSA-N 0.000 claims description 8
- 229910021645 metal ion Inorganic materials 0.000 claims description 8
- 239000000243 solution Substances 0.000 claims description 8
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 claims description 6
- VTHJTEIRLNZDEV-UHFFFAOYSA-L magnesium dihydroxide Chemical compound [OH-].[OH-].[Mg+2] VTHJTEIRLNZDEV-UHFFFAOYSA-L 0.000 claims description 6
- 239000000347 magnesium hydroxide Substances 0.000 claims description 6
- 229910001862 magnesium hydroxide Inorganic materials 0.000 claims description 6
- BHPQYMZQTOCNFJ-UHFFFAOYSA-N Calcium cation Chemical compound [Ca+2] BHPQYMZQTOCNFJ-UHFFFAOYSA-N 0.000 claims description 5
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 5
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 claims description 4
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 claims description 4
- 239000000460 chlorine Substances 0.000 claims description 4
- 229910052801 chlorine Inorganic materials 0.000 claims description 4
- 229910000019 calcium carbonate Inorganic materials 0.000 claims description 2
- 150000001875 compounds Chemical class 0.000 claims description 2
- 239000002244 precipitate Substances 0.000 claims description 2
- WQYVRQLZKVEZGA-UHFFFAOYSA-N hypochlorite Chemical compound Cl[O-] WQYVRQLZKVEZGA-UHFFFAOYSA-N 0.000 description 12
- 239000003792 electrolyte Substances 0.000 description 9
- 239000010410 layer Substances 0.000 description 9
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 8
- 239000011575 calcium Substances 0.000 description 7
- -1 sodium hypochlorite Chemical class 0.000 description 7
- 239000012535 impurity Substances 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 5
- WGKMWBIFNQLOKM-UHFFFAOYSA-N [O].[Cl] Chemical class [O].[Cl] WGKMWBIFNQLOKM-UHFFFAOYSA-N 0.000 description 4
- QWPPOHNGKGFGJK-UHFFFAOYSA-N hypochlorous acid Chemical compound ClO QWPPOHNGKGFGJK-UHFFFAOYSA-N 0.000 description 4
- 238000001556 precipitation Methods 0.000 description 4
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 3
- 239000005708 Sodium hypochlorite Substances 0.000 description 3
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 3
- 239000003513 alkali Substances 0.000 description 3
- 150000004649 carbonic acid derivatives Chemical class 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 150000004679 hydroxides Chemical class 0.000 description 3
- 229910000510 noble metal Inorganic materials 0.000 description 3
- SUKJFIGYRHOWBL-UHFFFAOYSA-N sodium hypochlorite Chemical compound [Na+].Cl[O-] SUKJFIGYRHOWBL-UHFFFAOYSA-N 0.000 description 3
- 229910052719 titanium Inorganic materials 0.000 description 3
- 239000010936 titanium Substances 0.000 description 3
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000012267 brine Substances 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005265 energy consumption Methods 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 239000011777 magnesium Substances 0.000 description 2
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- XTEGARKTQYYJKE-UHFFFAOYSA-M Chlorate Chemical class [O-]Cl(=O)=O XTEGARKTQYYJKE-UHFFFAOYSA-M 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- 229910000640 Fe alloy Inorganic materials 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- 229910000990 Ni alloy Inorganic materials 0.000 description 1
- 229910001854 alkali hydroxide Inorganic materials 0.000 description 1
- 150000008044 alkali metal hydroxides Chemical class 0.000 description 1
- 239000010405 anode material Substances 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 230000003311 flocculating effect Effects 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 159000000003 magnesium salts Chemical class 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 239000010955 niobium Substances 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 239000011241 protective layer Substances 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229910052715 tantalum Inorganic materials 0.000 description 1
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Images
Classifications
-
- 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
- C25B1/24—Halogens or compounds thereof
- C25B1/26—Chlorine; Compounds thereof
Definitions
- the invention relates to a process for the production of chlorine oxygen acids or their salts by electrolysis of sea water or salt solutions containing contaminating metal ions.
- Magnesium hydroxide tends to adhere to the cathode or settle on the walls of the electrolysis chamber, thereby hindering the flow of the electrolyte and reducing the efficiency.
- the growing deposits mainly clog the space between the anode and cathode in the electrolysis chamber, making continuous cell operation impossible for a long time.
- smooth, uninterrupted sheets have been used as cathodes, and a certain ratio of the flow rate and the concentration of the electrolyte has been provided for an increased flow rate (DE-A 26 19 497).
- the invention has for its object to achieve a reduction or control of the formation of deposits on the cathode during the electrolysis of sea water or salt solutions containing contaminating metal ions to obtain solutions of chlorine-oxygen acids or their salts, advantages of known methods being used without their disadvantages to have to put up with.
- the invention now consists in operating the electrolysis cell with unpurified sea water or unpurified salt solution until a layer is formed on the electrodes
- Compounds of the contaminating metal ions, in particular calcium and / or magnesium ions are deposited in a sufficient strength and effect a current efficiency of more than 90%, and that then the calcium and / or magnesium ions contained in the unpurified sea water or in the unpurified saline solution by adding sodium hydroxide solution and / or calcium hydroxide as well as sodium carbonate at a pH of more than 9 precipitates in whole or in part, if necessary separates and feeds the cleaned solution to the electrolysis cell.
- Adequate layer thickness is understood in the sense of the invention to mean a layer thickness which is sufficient to achieve a current efficiency of more than 90%.
- this is fed to the electrolyzer in carrying out the method according to the invention until a sufficient layer thickness is reached.
- the current efficiency slowly increases over time until values of over 90% are reached. This increase generally takes place over a period of 5 to 30 hours, the cell voltage generally increasing by 0.2 to 0.3 volt with the same current density. After this deposition phase, the cell voltage continues to increase and this increase is 1 to 1.5 volts within 100 to 2000 hours, depending on the concentration of contaminating ions.
- the supply of the unpurified salt solution is switched off by the method according to the invention and the purified salt solution is then fed to the electrolyte.
- the impurities which are predominantly contained in the salt solution in the form of calcium and / or magnesium ions or iron ions, are precipitated by adding sodium hydroxide solution and / or calcium hydroxide and sodium carbonate or soda at a pH of over 9.
- the magnesium ions are precipitated by the hydroxyl ions of the calcium hydroxide, the calcium ions by the carbonate ions and magnesium hydroxide or calcium carbonate is precipitated.
- the precipitation of the impurities is usually brought about completely. In some cases it can Depending on the local conditions of the electrolysis cells, it may be sufficient if the majority of the impurities are precipitated.
- the precipitation products can also remain wholly or partly in the finely divided state in the brine or saline solution.
- contaminations of, for example, calcium and magnesium salts in amounts of about 5 mg Ca ++ / I or 1 mg Mg ++ / I are deposited on the cathodes in the brine and gradually cause a layer to form.
- electrolytic cells are used in the method according to the invention, for example electrolytic cells with alternating vertical anodes and cathodes.
- the electrode spacing is, for example, 2 to 5 mm and the electrolyte with a flow rate of 0.3 to 2 m / s is electrolyzed at a current density of 2 to 25 A / dm 2 .
- the temperature of the electrolyte can be 10 to 50 ° C and the pH can range from 7 to 10.
- the cathodes consist of electrically conductive, wear-resistant metal materials, for example titanium, nickel, or iron and nickel alloys.
- the anode material can be graphite.
- anodes are titanium, niobium or tantalum electrodes coated with noble metal or noble metal oxide or so-called dimensionally stable anodes, in which the electrocatalytic effect of mixed oxides originates from noble metals and film-forming metals, in particular titanium.
- the chlorine reacts with the sodium hydroxide solution to form sodium hypochlorite according to:
- hypochlorous acid Sodium hypochlorite reacts with water to form hypochlorous acid
- reaction (1) or reaction (2) depends on the pH of the environment. If the pH is> 5, the entire active chlorine is in the form of hypochlorous acid and hypochlorite ions. The higher the pH value, the greater the proportion of hypochlorite ions.
- the advantages of the method according to the invention can be seen in the fact that a targeted layer formation on the cathodes occurs uniformly in all electrolysis cells of the system.
- the thin passive layer of a certain thickness deposited according to the invention prevents an excessive reduction of the hypochlorite ions, thus increases the yield of hypochlorite and makes cell cleaning unnecessary or reduces it to a very considerable extent.
- FIG. 1 shows the efficiency of hypochlorite cells as a function of the running time.
- a plant with 8 cells connected in series was operated with sea water at 28 ° C. at a rate of 20 m 3 / h.
- the current strength was slowly increased from 500 A to 5,000 A over a total of 30 hours.
- the voltage rose from 25 to 35 V.
- the content of active chlorine in the form of NaOCI rose from 0.2 g / l to 2.8 g / l in the same period.
- the current yield ran according to the diagram in FIG. 1, ie without the addition of precipitation chemicals, the current yield would asymptotically approach the value of 100%, but at the same time the voltage would increase and the pollution would increase, so that after 2,000 hours at the latest the plant would be shut down subsequent acid washing would be required.
Description
Die Erfindung betrifft ein Verfahren zur Gewinnung von Chlorsauerstoffsäuren bzw. deren Salze durch Elektrolyse von Meerwasser oder verunreinigende Metallionen enthaltenden Salzlösungen.The invention relates to a process for the production of chlorine oxygen acids or their salts by electrolysis of sea water or salt solutions containing contaminating metal ions.
Bei der Elektrolyse von Meerwasser oder von verunreinigende Metallionen, wie Ca- oder Mg-Ionen enthaltenden Salzlösungen, treten bei der Gewinnung von Chlorsauerstoffsäuren bzw. deren Salze, wie Natriumhypochlorit, auch heute noch Schwierigkeiten auf, welche die kommerzielle Nutzung und die Wirtschaftlichkeit belasten. Die in derartigen Salzlösungen enthaltenen Calcium- oder Magnesiumionen reagieren mit den an der Kathode erzeugten Hydroxylionen unter Bildung von Calcium- und Magnesium- hydroxid und gegebenenfalls Carbonaten.In the electrolysis of sea water or of contaminating metal ions, such as salt solutions containing Ca or Mg ions, difficulties still arise today in the production of chlorine-oxygen acids or their salts, such as sodium hypochlorite, which are detrimental to commercial use and economy. The calcium or magnesium ions contained in such salt solutions react with the hydroxyl ions generated at the cathode to form calcium and magnesium hydroxide and possibly carbonates.
Magnesiumhydroxid neigt dazu, an der Kathode zu haften oder sich an den Wänden der Elektrolysekammer abzusetzen und dadurch die Strömung des Elektrolyten zu behindern und den Wirkungsgrad herabzusetzen. Die anwachsenden Ablagerungen verstopfen vor allem den Raum zwischen Anode und Kathode in der Elektrolysekammer, wodurch für längere Zeit ein kontinuierlicher Betrieb der Zelle unmöglich wird. Zur Vermeidung dieser Schwierigkeiten hat man bereits nach bekannten Vorschlägen zur elektrolytischen Herstellung von Hypochlorit glatte, nicht unterbrochene Bleche als Kathoden verwendet und bei erhöhter Strömungsgeschwindigkeit ein bestimmtes Verhältnis von Strömungsgeschwindigkeit und Konzentration des Elektrolyten vorgesehen (DE-A 26 19 497). Auch hat man in bekannten Elektrolysezellen zur Gewinnung von Hypochlorit aus Meerwasser durch bauliche Maßnahmen eine gerichtete Elektrolytströmung bestimmter Geschwindigkeit eingestellt (DE-B 1956156). Bei der Herstellung von Alkalichloraten durch Elektrolyse von Alkalichloridlösungen ist es ferner bekannt, dem Elektrolyten Alkalihydroxid oder Carbonat zur Herabsetzung der Stromverluste zuzufügen. Bei derartigen Verfahren ist es ebenfalls bekannt, schwer lösliche Hydroxide, wie Calcium- oder Magnesiumhydroxid dem Elektrolyten zuzusetzen und diese Hydroxide während des ganzen Verlaufs der Elektrolyse in dem Elektrolyten suspendiert zu halten (DE-B 90 060). Schließlich ist es bekannt, unerwünschte Metallionen aus Salzlösungen, die für die Chloralkali-Elektrolyse bestimmt sind, durch Ausflockung der Eisen-, Magnesium- und Calciumionen als Carbonate bzw. Hydroxide zu entfernen (CH-A 505751).Magnesium hydroxide tends to adhere to the cathode or settle on the walls of the electrolysis chamber, thereby hindering the flow of the electrolyte and reducing the efficiency. The growing deposits mainly clog the space between the anode and cathode in the electrolysis chamber, making continuous cell operation impossible for a long time. To avoid these difficulties, according to known proposals for the electrolytic production of hypochlorite, smooth, uninterrupted sheets have been used as cathodes, and a certain ratio of the flow rate and the concentration of the electrolyte has been provided for an increased flow rate (DE-A 26 19 497). In known electrolysis cells for obtaining hypochlorite from sea water, a directed electrolyte flow of a certain speed has been set by constructional measures (DE-B 1956156). In the production of alkali chlorates by electrolysis of alkali chloride solutions, it is also known to add alkali hydroxide or carbonate to the electrolyte in order to reduce the current losses. In such processes it is also known to add poorly soluble hydroxides, such as calcium or magnesium hydroxide, to the electrolyte and to keep these hydroxides suspended in the electrolyte throughout the course of the electrolysis (DE-B 90 060). Finally, it is known to remove unwanted metal ions from salt solutions which are intended for chlor-alkali electrolysis by flocculating the iron, magnesium and calcium ions as carbonates or hydroxides (CH-A 505751).
Der Erfindung liegt die Aufgabe zugrunde, eine Verringerung bzw. Steuerung der Ansatzbildung auf der Kathode während der Elektrolyse von Meerwasser oder verunreinigende Metallionen enthaltenden Salzlösungen zur Gewinnung von Lösungen von Chlorsauerstoffsäuren bzw. deren Salze zu erzielen, wobei Vorteile bekannter Verfahren genutzt werden, ohne deren Nachteile in Kauf nehmen zu müssen.The invention has for its object to achieve a reduction or control of the formation of deposits on the cathode during the electrolysis of sea water or salt solutions containing contaminating metal ions to obtain solutions of chlorine-oxygen acids or their salts, advantages of known methods being used without their disadvantages to have to put up with.
Bei einem Verfahren der genannten Art zur Gewinnung von Chlorsauerstoffsäuren bzw. deren Salze durch Elektrolyse von Meerwasser oder verunreinigende Metallionen enthaltenden Salzlösungen besteht die Erfindung nun darin, daß man die Elektrolysezelle so lange mit ungereinigtem Meerwasser oder ungereinigter Salzlösung betreibt, bis auf den Elektroden eine Schicht aus Verbindungen der verunreinigenden Metallionen, insbesondere Calcium- und/oder Magnesiumionen, in einer hinreichenden und einen Stromwirkungsgrad von mehr als 90 % bewirkenden Stärke abgeschieden ist, und daß man dann die in dem ungereinigten Meerwasser oder in der ungereinigten Salzlösung enthaltenen Calcium- und/oder Magnesiumionen durch Zusatz von Natronlauge und/oder Calciumhydroxid sowie Natriumcarbonat bei einem pH-Wert von über 9 ganz oder teilweise ausfällt, gegebenenfalls abtrennt und die gereinigte Lösung der Elektrolysezelle zuführt. Unter hinreichender Schichtstärke wird im Sinne der Erfindung eine Schichtdicke verstanden, die ausreicht, einen Stromwirkungsgrad von mehr als 90 % zu erreichen.In a method of the type mentioned for the production of chlorine oxygen acids or their salts by electrolysis of sea water or salt solutions containing contaminating metal ions, the invention now consists in operating the electrolysis cell with unpurified sea water or unpurified salt solution until a layer is formed on the electrodes Compounds of the contaminating metal ions, in particular calcium and / or magnesium ions, are deposited in a sufficient strength and effect a current efficiency of more than 90%, and that then the calcium and / or magnesium ions contained in the unpurified sea water or in the unpurified saline solution by adding sodium hydroxide solution and / or calcium hydroxide as well as sodium carbonate at a pH of more than 9 precipitates in whole or in part, if necessary separates and feeds the cleaned solution to the electrolysis cell. Adequate layer thickness is understood in the sense of the invention to mean a layer thickness which is sufficient to achieve a current efficiency of more than 90%.
Unabhängig von der Konzentration der Verunreinigungen in der Salzlösung wird diese in Durchführung des erfindungsgemäßen Verfahrens solange dem Elektrolyseur zugeführt, bis eine hinreichende Schichtdicke erreicht ist. Während des Aufbaus der Schicht aus insbesondere Calcium- und Magnesium-hydroxid und - carbonaten zu dieser Schichtstärke steigt die Stromausbeute langsam mit der Zeit an bis Werte von über 90 % erreicht werden. Dieser Anstieg erfolgt im allgemeinen in einem Zeitraum von 5 bis 30 Stunden, wobei die Zellenspannung bei gleicher Stromdichte in aller Regel um 0,2 bis 0,3 Volt ansteigt. Nach dieser Abscheidungsphase steigt die Zellenspannung weiter an und dieser Anstieg beträgt in Abhängigkeit von der Konzentration an verunreinigenden Ionen 1 bis 1,5 Volt innerhalb von 100 bis 2000 Stunden. Sobald Stromausbeuten von 90 % erreicht sind, wird nach dem erfindungsgemäßen Verfahren die Zufuhr der ungereinigten Salzlösung abgestellt und nunmehr gereinigte Salzlösung dem Elektrolyten zugeführt. Die Verunreinigungen, die überwiegend in Form von Calcium- und/oder Magnesiumionen oder Eisenionen in der Salzlösung enthalten sind, werden durch Zusatz von Natronlauge und/oder Calciumhydroxid sowie Natriumcarbonat bzw. Soda bei einem pH-Wert von über 9 ausgefällt. Bei Verwendung von Calciumhydroxid und Natriumcarbonat werden die Magnesiumionen durch die Hydroxylionen des Calciumhydroxids, die Calciumionen durch die Carbonationen niedergeschlagen und Magnesiumhydroxid bzw. Calciumcarbonat ausgefällt. Die Fällung der Verunreinigungen wird in aller Regel vollständig herbeigeführt. In manchen Fällen kann es in Abhängigkeit von den örtlichen Gegebenheiten der Elektrolysezellen ausreichend sein, wenn der überwiegende Teil der Verunreinigungen ausgefällt wird.Regardless of the concentration of the impurities in the salt solution, this is fed to the electrolyzer in carrying out the method according to the invention until a sufficient layer thickness is reached. During the build-up of the layer, in particular calcium and magnesium hydroxide and carbonates to this layer thickness, the current efficiency slowly increases over time until values of over 90% are reached. This increase generally takes place over a period of 5 to 30 hours, the cell voltage generally increasing by 0.2 to 0.3 volt with the same current density. After this deposition phase, the cell voltage continues to increase and this increase is 1 to 1.5 volts within 100 to 2000 hours, depending on the concentration of contaminating ions. As soon as current yields of 90% have been reached, the supply of the unpurified salt solution is switched off by the method according to the invention and the purified salt solution is then fed to the electrolyte. The impurities, which are predominantly contained in the salt solution in the form of calcium and / or magnesium ions or iron ions, are precipitated by adding sodium hydroxide solution and / or calcium hydroxide and sodium carbonate or soda at a pH of over 9. When using calcium hydroxide and sodium carbonate, the magnesium ions are precipitated by the hydroxyl ions of the calcium hydroxide, the calcium ions by the carbonate ions and magnesium hydroxide or calcium carbonate is precipitated. The precipitation of the impurities is usually brought about completely. In some cases it can Depending on the local conditions of the electrolysis cells, it may be sufficient if the majority of the impurities are precipitated.
Im allgemeinen ist es zweckmäßig, die ausgefällten Verunreinigungen abzutrennen, beispielsweise durch Filtration unter gegebenenfalls Zusatz von Filtrierhilfsmitteln. In Fällen relativer Unempfindlichkeit von Elektrolysezellen gegen feinverteilte Feststoffe können die Fällungsprodukte jedoch auch ganz oder teilweise in feinverteiltem Zustand in der Speisesole bzw. Salzlösung verbleiben.In general, it is expedient to separate off the precipitated impurities, for example by filtration with the addition of filter aids where appropriate. In cases where electrolysis cells are relatively insensitive to finely divided solids, the precipitation products can also remain wholly or partly in the finely divided state in the brine or saline solution.
Es ist auch bekannt, daß bereits Verunreinigungen von z.B. Calcium- und Magnesiumsalzen in Mengen von etwa 5 mg Ca++/I bzw. 1 mg Mg++/I in der Speisesole auf den Kathoden niedergeschlagen werden und allmählich eine Schichtbildung herbeiführen.It is also known that contaminations of, for example, calcium and magnesium salts in amounts of about 5 mg Ca ++ / I or 1 mg Mg ++ / I are deposited on the cathodes in the brine and gradually cause a layer to form.
In dem erfindungsgemäßen Verfahren werden übliche Elektrolysezellen verwendet, beispielsweise Elektrolysezellen mit abwechselnd angeordneten vertikalen Anoden und Kathoden. Der Elektrodenabstand beträgt beispielsweise 2 bis 5 mm und der Elektrolyt mit einer Strömungsgeschwindigkeit von 0,3 bis 2 m/s wird bei einer Stromdichte von 2 bis 25 A/dm2 elektrolysiert. Die Temperatur des Elektrolyten kann 10 bis 50 °C betragen und der pH-Wert kann im Bereich von 7 bis 10 liegen. Die Kathoden bestehen aus elektrisch leitenden, verschleißfesten Metallwerkstoffen, beispielsweise Titan, Nickel, oder Eisen-und Nickellegierungen. Das Anodenmaterial kann Graphit sein. Besonders geeignete Anoden sind jedoch mit Edelmetall oder Edelmetalloxid beschichtete Titan-, Niob- oder Tantal-Elektroden oder sogenannte dimensionsstabile Anoden, bei denen die elektrokatalytische Wirkung von Mischoxiden von Edelmetallen und filmbildenden Metallen, insbesondere Titan, ausgeht.Conventional electrolytic cells are used in the method according to the invention, for example electrolytic cells with alternating vertical anodes and cathodes. The electrode spacing is, for example, 2 to 5 mm and the electrolyte with a flow rate of 0.3 to 2 m / s is electrolyzed at a current density of 2 to 25 A / dm 2 . The temperature of the electrolyte can be 10 to 50 ° C and the pH can range from 7 to 10. The cathodes consist of electrically conductive, wear-resistant metal materials, for example titanium, nickel, or iron and nickel alloys. The anode material can be graphite. However, particularly suitable anodes are titanium, niobium or tantalum electrodes coated with noble metal or noble metal oxide or so-called dimensionally stable anodes, in which the electrocatalytic effect of mixed oxides originates from noble metals and film-forming metals, in particular titanium.
Bei der elektrolytischen Herstellung von Hypochlorit aus Meerwasser oder Salzlösung laufen folgende chemischen Reaktionen an den Elektroden ab.The following chemical reactions take place at the electrodes in the electrolytic production of hypochlorite from sea water or saline.
An der Anode :
An der Kathode :
Das Chlor reagiert mit der Natronlauge unter Bildung von Natriumhypochlorit gemäß :
Natriumhypochlorit reagiert mit Wasser unter Bildung von Hypochlorsäure
Hypochlorsäure dissoziiert gemäß
Das Überwiegen von Reaktion (1) oder Reaktion (2) hängt von dem pH-Wert des Milieus ab. Bei einem pH-Wert > 5 liegt das gesamte Aktivchlor in Form von Hypochlorsäure und Hypochlorit-lonen vor. Dabei ist der Anteil an Hypochlorit-Ionen umso größer je höher der pH-Wert ist.The predominance of reaction (1) or reaction (2) depends on the pH of the environment. If the pH is> 5, the entire active chlorine is in the form of hypochlorous acid and hypochlorite ions. The higher the pH value, the greater the proportion of hypochlorite ions.
Die Vorteile des erfindungsgemäßen Verfahrens sind darin zu sehen, daß in sämtlichen Elektrolysezellen der Anlage gleichmäßig eine gezielte Schichtbildung auf den Kathoden erfolgt. Die erfindungsgemäß abgeschiedene dünne Passivschicht bestimmter Stärke unterbindet eine zu starke Reduktion der Hypochloritionen, erhöht somit die Ausbeute an Hypochlorit und erübrigt die Zellenreinigung bzw. vermindert sie in einem ganz erheblichen Umfang.The advantages of the method according to the invention can be seen in the fact that a targeted layer formation on the cathodes occurs uniformly in all electrolysis cells of the system. The thin passive layer of a certain thickness deposited according to the invention prevents an excessive reduction of the hypochlorite ions, thus increases the yield of hypochlorite and makes cell cleaning unnecessary or reduces it to a very considerable extent.
Die Erfindung wird nachstehend und beispielhalf gemäß dem Diagramm der Figur 1 erläutert, worin der Wirkungsgrad von Hypochloritzellen in Abhängigkeit von der Laufzeit dargestellt ist.The invention is explained below and by way of example according to the diagram in FIG. 1, which shows the efficiency of hypochlorite cells as a function of the running time.
Eine Anlage mit 8 hintereinandergeschalteten Zellen wurde mit Meerwasser von 28 °C mit einer Menge von 20 m3/h betrieben. Über insgesamt 30 Stunden wurde die Stromstärke langsam von 500 A auf 5 000 A erhöht. Die Spannung stieg dabei von 25 auf 35 V. Der Gehalt an aktivem Chlor in Form von NaOCI stieg in demselben Zeitraum von 0,2 g/I auf 2,8 g/I. Die Stromausbeute verlief gemäß dem Diagramm der Fig. 1, d.h. ohne Zusatz von Fällchemikalien würde sich die Stromausbeute asymptotisch dem Wert 100 % nähern, gleichzeitig würde aber die Spannung ansteigen und die Verschmutzung zunehmen, so daß nach spätestens 2 000 h eine Stillegung der Anlage mit anschließender Säurewäsche erforderlich werden würde. Während bei Normalbetrieb der Spannungsabfall pro Zelle ca. 4,5 V und die Stromausbeute 96 % beträgt, steigt die Spannung bei verschmutzten Zellen auf bis zu 6 V und die Stromausbeute kann fast 100 % betragen. Der Gleichstrom-Energieverbrauch beträgt im ersten Falle bei Normalbetrieb 3,6 kWh/kg CI2, in zweiten Falle mit verschmutzten Zellen 4,5 kWh/kgCl2. Dieser Anstieg im Energieverbrauch und die Notwendigkeit des regelmäßigen Waschens kann durch Fällung der Verunreinigungen verhindert werden, wenn man erfindungsgemäß mit dieser Fällung beginnt, nachdem sich eine Schutzschicht von hinreichender Stärke auf den Kathoden gebildet hat.A plant with 8 cells connected in series was operated with sea water at 28 ° C. at a rate of 20 m 3 / h. The current strength was slowly increased from 500 A to 5,000 A over a total of 30 hours. The voltage rose from 25 to 35 V. The content of active chlorine in the form of NaOCI rose from 0.2 g / l to 2.8 g / l in the same period. The current yield ran according to the diagram in FIG. 1, ie without the addition of precipitation chemicals, the current yield would asymptotically approach the value of 100%, but at the same time the voltage would increase and the pollution would increase, so that after 2,000 hours at the latest the plant would be shut down subsequent acid washing would be required. While during normal operation the voltage drop per cell is approx.4.5 V and the current yield is 96%, the voltage increases when the cells are dirty up to 6 V and the current yield can be almost 100%. The direct current energy consumption is 3.6 kWh / kg CI 2 in normal operation in the first case, and 4.5 kWh / kgCl 2 in the second case with dirty cells. This increase in energy consumption and the need for regular washing can be prevented by precipitating the impurities if, according to the invention, this precipitation starts after a protective layer of sufficient strength has formed on the cathodes.
Claims (2)
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE2850575 | 1978-11-22 | ||
| DE19782850575 DE2850575A1 (en) | 1978-11-22 | 1978-11-22 | METHOD FOR THE ELECTROLYTIC PRODUCTION OF CHLORINE OXYGEN ACIDS OR. THEIR SALTS |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0011886A1 EP0011886A1 (en) | 1980-06-11 |
| EP0011886B1 true EP0011886B1 (en) | 1981-11-11 |
Family
ID=6055302
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP79200618A Expired EP0011886B1 (en) | 1978-11-22 | 1979-10-25 | Preparation of oxy-halogenated acids and their salts by electrolysis |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US4238302A (en) |
| EP (1) | EP0011886B1 (en) |
| JP (1) | JPS5573882A (en) |
| BR (1) | BR7907561A (en) |
| DE (2) | DE2850575A1 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5064514A (en) * | 1990-03-30 | 1991-11-12 | Olin Corporation | Apparatus for the production of chloric acid |
| US5616234A (en) * | 1995-10-31 | 1997-04-01 | Pepcon Systems, Inc. | Method for producing chlorine or hypochlorite product |
| US7611280B2 (en) * | 2003-12-16 | 2009-11-03 | Harco Laboratories, Inc. | EMF sensor with protective sheath |
| US20130248375A1 (en) * | 2012-03-02 | 2013-09-26 | Miox Corporation | Waste to Product On Site Generator |
| CN111039474A (en) * | 2019-12-26 | 2020-04-21 | 西安泰金工业电化学技术有限公司 | Power plant circulating water treatment system and method |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1044769A (en) * | 1963-11-05 | 1966-10-05 | George Joseph Crane | Production of chlorine dioxide from sodium chlorate feed stock containing sodium chloride |
| US3799849A (en) * | 1972-06-26 | 1974-03-26 | Hooker Chemical Corp | Reactivation of cathodes in chlorate cells |
| FR2244708B1 (en) * | 1973-09-25 | 1977-08-12 | Ugine Kuhlmann | |
| US3974051A (en) * | 1975-05-07 | 1976-08-10 | Diamond Shamrock Corporation | Production of hypochlorite from impure saline solutions |
| US4085014A (en) * | 1977-04-21 | 1978-04-18 | Diamond Shamrock Corporation | Elimination of impurities from sea water cell feed to prevent anode deposits |
| US4088550A (en) * | 1977-05-25 | 1978-05-09 | Diamond Shamrock Corporation | Periodic removal of cathodic deposits by intermittent reversal of the polarity of the cathodes |
-
1978
- 1978-11-22 DE DE19782850575 patent/DE2850575A1/en not_active Withdrawn
-
1979
- 1979-10-25 DE DE7979200618T patent/DE2961328D1/en not_active Expired
- 1979-10-25 EP EP79200618A patent/EP0011886B1/en not_active Expired
- 1979-11-05 US US06/091,312 patent/US4238302A/en not_active Expired - Lifetime
- 1979-11-21 BR BR7907561A patent/BR7907561A/en unknown
- 1979-11-22 JP JP15191779A patent/JPS5573882A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| DE2961328D1 (en) | 1982-01-14 |
| DE2850575A1 (en) | 1980-06-04 |
| EP0011886A1 (en) | 1980-06-11 |
| BR7907561A (en) | 1980-07-08 |
| JPS5573882A (en) | 1980-06-03 |
| US4238302A (en) | 1980-12-09 |
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