EP0356805B1 - Process for the production of alkali dichromates and chromic acid - Google Patents
Process for the production of alkali dichromates and chromic acid Download PDFInfo
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- EP0356805B1 EP0356805B1 EP89115033A EP89115033A EP0356805B1 EP 0356805 B1 EP0356805 B1 EP 0356805B1 EP 89115033 A EP89115033 A EP 89115033A EP 89115033 A EP89115033 A EP 89115033A EP 0356805 B1 EP0356805 B1 EP 0356805B1
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- chromic acid
- dichromate
- alkali
- electrolysis
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- KRVSOGSZCMJSLX-UHFFFAOYSA-L chromic acid Substances O[Cr](O)(=O)=O KRVSOGSZCMJSLX-UHFFFAOYSA-L 0.000 title claims description 22
- AWJWCTOOIBYHON-UHFFFAOYSA-N furo[3,4-b]pyrazine-5,7-dione Chemical compound C1=CN=C2C(=O)OC(=O)C2=N1 AWJWCTOOIBYHON-UHFFFAOYSA-N 0.000 title claims description 22
- 238000000034 method Methods 0.000 title claims description 19
- 238000004519 manufacturing process Methods 0.000 title claims description 6
- 239000003513 alkali Substances 0.000 title description 20
- 238000005868 electrolysis reaction Methods 0.000 claims description 17
- 239000007788 liquid Substances 0.000 claims description 16
- 239000012528 membrane Substances 0.000 claims description 16
- SOCTUWSJJQCPFX-UHFFFAOYSA-N dichromate(2-) Chemical compound [O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O SOCTUWSJJQCPFX-UHFFFAOYSA-N 0.000 claims description 13
- WGLPBDUCMAPZCE-UHFFFAOYSA-N Trioxochromium Chemical compound O=[Cr](=O)=O WGLPBDUCMAPZCE-UHFFFAOYSA-N 0.000 claims 2
- 229910052783 alkali metal Inorganic materials 0.000 claims 1
- -1 alkali metal dichromate Chemical class 0.000 claims 1
- 229910001413 alkali metal ion Inorganic materials 0.000 claims 1
- 239000000243 solution Substances 0.000 description 39
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 12
- JHWIEAWILPSRMU-UHFFFAOYSA-N 2-methyl-3-pyrimidin-4-ylpropanoic acid Chemical compound OC(=O)C(C)CC1=CC=NC=N1 JHWIEAWILPSRMU-UHFFFAOYSA-N 0.000 description 9
- 150000002500 ions Chemical class 0.000 description 5
- 238000005341 cation exchange Methods 0.000 description 4
- KIEOKOFEPABQKJ-UHFFFAOYSA-N sodium dichromate Chemical compound [Na+].[Na+].[O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O KIEOKOFEPABQKJ-UHFFFAOYSA-N 0.000 description 4
- 150000001768 cations Chemical class 0.000 description 3
- JOPOVCBBYLSVDA-UHFFFAOYSA-N chromium(6+) Chemical compound [Cr+6] JOPOVCBBYLSVDA-UHFFFAOYSA-N 0.000 description 3
- 239000012535 impurity Substances 0.000 description 3
- 229910001415 sodium ion Inorganic materials 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 229910001220 stainless steel Inorganic materials 0.000 description 2
- 239000010935 stainless steel Substances 0.000 description 2
- 229910052719 titanium Inorganic materials 0.000 description 2
- 239000010936 titanium Substances 0.000 description 2
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- 229920000557 Nafion® Polymers 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 239000011575 calcium Substances 0.000 description 1
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 description 1
- 239000000920 calcium hydroxide Substances 0.000 description 1
- 229910001861 calcium hydroxide Inorganic materials 0.000 description 1
- 229910001424 calcium ion Inorganic materials 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- HTXDPTMKBJXEOW-UHFFFAOYSA-N dioxoiridium Chemical compound O=[Ir]=O HTXDPTMKBJXEOW-UHFFFAOYSA-N 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 229910000457 iridium oxide Inorganic materials 0.000 description 1
- 150000007522 mineralic acids Chemical class 0.000 description 1
- 150000007524 organic acids Chemical class 0.000 description 1
- 235000005985 organic acids Nutrition 0.000 description 1
- BPUBBGLMJRNUCC-UHFFFAOYSA-N oxygen(2-);tantalum(5+) Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[Ta+5].[Ta+5] BPUBBGLMJRNUCC-UHFFFAOYSA-N 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 229910000029 sodium carbonate Inorganic materials 0.000 description 1
- PXLIDIMHPNPGMH-UHFFFAOYSA-N sodium chromate Chemical compound [Na+].[Na+].[O-][Cr]([O-])(=O)=O PXLIDIMHPNPGMH-UHFFFAOYSA-N 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 229910001427 strontium ion Inorganic materials 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 229910001936 tantalum oxide Inorganic materials 0.000 description 1
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
- C25B1/22—Inorganic acids
Definitions
- the invention relates to processes for the production of alkali dichromates and chromic acid by electrolysis of monochromate and / or dichromate solutions in electrolytic cells whose anode and cathode spaces are separated by cation exchange membranes, an anolyte liquid containing dichromate and / or chromic acid and in the cathode space in the anode space an alkaline alkali ion-containing catholyte liquid is formed.
- alkali monochromate solutions or suspensions are introduced into the anode compartment of the cell and converted into an alkali dichromate solution by selectively passing alkali ions through the membrane be transferred to the cathode compartment.
- alkali dichromate or alkali monochromate solutions or a mixture of alkali dichromate and alkali monochromate solutions are introduced into the anode compartment and converted into solutions containing chromic acid.
- sodium monochromate and / or sodium dichromate solutions are used for these processes.
- the solutions formed in the anode compartments of the cells are concentrated, it being possible for crystallization of sodium dichromate to take place, for example, at 80 ° C. and that of chromic acid at 60-100 ° C.
- the crystallized products are separated off, optionally washed and dried.
- an alkaline alkali ion-containing catholyte liquid is obtained in the cathode compartment, which can consist, for example, of an aqueous sodium hydroxide solution or, as described in CA-A-739 447, of an aqueous solution containing sodium carbonate.
- the object of the invention was to provide processes for the production of alkali dichromate and chromic acid by electrolysis which do not have the disadvantages described.
- the invention thus relates to processes for the preparation of alkali dichromates and chromic acid by electrolysis of monochromate and / or dichromate solutions in electrolytic cells, the anode and cathode spaces of which are separated by cation exchange membranes, with anolyte liquid containing dichromate and / or chromic acid and alkaline alkali ions in the cathode space -containing catholyte liquids are formed, which is characterized in that the catholyte liquids are periodically replaced by a solution with a pH less than 6.
- the method according to the invention is carried out while maintaining the electrolysis current.
- the catholyte liquids are preferably periodically replaced by a solution with a pH less than 1. Suitable solutions are inorganic acids such as sulfuric acid, phosphoric acid, hydrochloric acid as well as organic acids with different concentrations.
- the catholyte liquids are periodically replaced by a solution containing chromic acid. It is advantageous to use a solution containing chromic acid, the content of which is 10-900 g chromic acid per liter. This solution can of course also contain proportions of alkali dichromate.
- the process according to the invention is preferably operated in such a way that the catholyte liquids are replaced by a solution with a pH of less than 6 after an electrolysis time of 1-100 days.
- the timing of this measure depends on the content of polyvalent cations in the monochromate and / or dichromate solutions and on the anodic current density. If the cations are very low, the liquid can be exchanged even after a period of more than 100 days.
- the electrolytic cells used in the examples consisted of anode compartments made of pure titanium and cathode compartments made of stainless steel. Cation exchange membranes from DuPont with the designation Nafion® 324 were used as membranes.
- the cathodes were made of stainless steel and the anodes were made of expanded titanium with an electrocatalytically active layer of tantalum oxide and iridium oxide. Such anodes are described, for example, in US Pat. No. 3,878,083.
- the distance between the electrodes and the membrane was 1.5 mm in all cases.
- Sodium dichromate solutions with a content of 900 g / l Na2Cr2O7 ⁇ 2 H2O were introduced into the anode compartments with the levels of impurities listed in the individual examples.
- the electrolysis temperature was 80 ° C in all cases.
- the sodium dichromate solutions used in this experiment had the following levels of impurities:
- the rate of introduction of the sodium dichromate solutions was chosen so that a molar ratio of sodium ions to chromium (VI) of 0.8 was established in the anolyte leaving the cell.
- a white deposit had formed in the membrane, which essentially consisted of calcium hydroxide.
- the cell voltage at this point was 4.04 V.
- the anodes had to be replaced several times due to insufficient durability.
- the procedure for dissolving and removing the storage was as follows: The cathodically formed 20% sodium hydroxide solution was first replaced by water in the cathode compartment of the cell and then by a solution containing CrO3- and Na2Cr2O7 ⁇ 2 H2O with a pH value of less than 1. This solution had the following composition: 30.3% Na2Cr2O7 ⁇ 2 H2O 30.3% CrO3 39.4% H2O.
- the sodium dichromate solution used had the following levels of impurities:
- the sodium dichromate solutions used in this example had the following contamination levels:
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- Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
- Inorganic Compounds Of Heavy Metals (AREA)
Description
Die Erfindung betrifft Verfahren zur Herstellung von Alkalidichromaten und Chromsäure durch Elektrolyse von Monochromat- und/oder Dichromat-Lösungen in Elektrolysezellen, deren Anoden-und Kathodenräume durch Kationenaustauschermembranen getrennt sind, wobei im Anodenraum eine Dichromat- und/oder Chromsäure-haltige Anolytflüssigkeit und im Kathodenraum eine alkalische Alkaliionen-haltige Katholytflüssigkeit ensteht.The invention relates to processes for the production of alkali dichromates and chromic acid by electrolysis of monochromate and / or dichromate solutions in electrolytic cells whose anode and cathode spaces are separated by cation exchange membranes, an anolyte liquid containing dichromate and / or chromic acid and in the cathode space in the anode space an alkaline alkali ion-containing catholyte liquid is formed.
Gemäß der US-A-3 305 463 und der CA-A-739 447 erfolgt die elektrolytische Herstellung von Alkalidichromaten und Chromsäure (CrO₃) in Elektrolysezellen, deren Elektrodenräume durch eine Kationenaustauschermembran getrennt sind.According to US-A-3 305 463 and CA-A-739 447, the electrolytic production of alkali dichromates and chromic acid (CrO₃) takes place in electrolysis cells, the electrode spaces of which are separated by a cation exchange membrane.
Bei der Erzeugung von Alkalidichromaten werden Alkalimonochromatlösungen oder -suspensionen in den Anodenraum der Zelle eingeleitet und in eine Alkalidichromatlösung umgewandelt, indem Alkaliionen selektiv durch die Membran in den Kathodenraum überführt werden. Zur Herstellung von Chromsäure werden Alkalidichromat- oder Alkalimonochromatlösungen oder eine Mischung von Alkalidichromat- und Alkalimonochromatlösung in den Anodenraum eingeleitet und in Chromsäure-haltige Lösungen überführt. In der Regel kommen für diese Prozesse Natriummonochromat- und/oder Natriumdichromatlösungen zum Einsatz.In the production of alkali dichromates, alkali monochromate solutions or suspensions are introduced into the anode compartment of the cell and converted into an alkali dichromate solution by selectively passing alkali ions through the membrane be transferred to the cathode compartment. To prepare chromic acid, alkali dichromate or alkali monochromate solutions or a mixture of alkali dichromate and alkali monochromate solutions are introduced into the anode compartment and converted into solutions containing chromic acid. As a rule, sodium monochromate and / or sodium dichromate solutions are used for these processes.
Zur Erzeugung von Alkalidichromat- oder Chromsäurekristallen werden die in den Anodenräumen der Zellen gebildeten Lösungen eingeengt, wobei die Kristallisation von Natriumdichromat beispielsweise bei 80°C und die von Chromsäure bei 60-100°C erfolgen kann. Die auskristallisierten Produkte werden abgetrennt, gegebenenfalls gewaschen und getrocknet.To generate alkali dichromate or chromic acid crystals, the solutions formed in the anode compartments of the cells are concentrated, it being possible for crystallization of sodium dichromate to take place, for example, at 80 ° C. and that of chromic acid at 60-100 ° C. The crystallized products are separated off, optionally washed and dried.
Im Kathodenraum wird bei beiden Prozessen eine alkalische Alkaliionen-haltige Katholytflüssigkeit erhalten, die beispielsweise aus einer wäßrigen Natriumhydroxid-Lösung oder, wie in der CA-A-739 447 beschrieben, aus einer wäßrigen Natriumcarbonat-haltigen Lösung bestehen kann.In both processes, an alkaline alkali ion-containing catholyte liquid is obtained in the cathode compartment, which can consist, for example, of an aqueous sodium hydroxide solution or, as described in CA-A-739 447, of an aqueous solution containing sodium carbonate.
Bei der Durchführung der Verfahren kommt es zur Bildung von Einlagerungen von Verbindungen mehrwertiger Ionen, insbesondere von Erdalkaliverbindungen, die die Funktionsfähigkeit der Membran bereits nach kurzer Zeit verschlechtern, bis hin zum völligen Ausfall der Membran. Ursache dieser Einlagerungen sind geringe Gehalte an mehrwertigen Kationen, insbesondere Calcium- und Strontiumionen, in den als Elektrolyt verwendeten Alkalidichromat- und/oder Alkalimonochromatlösungen, wie sie in technischen Verfahren, beschrieben in Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Volume A 7, 1986, S. 67-97, erhältlich sind.When the processes are carried out, compounds of polyvalent ions, in particular alkaline earth compounds, are formed, which deteriorate the functionality of the membrane after a short time, up to the complete failure of the membrane. The cause of these deposits are low levels of polyvalent cations, especially calcium and strontium ions, in the alkali dichromate and / or alkali monochromate solutions used as electrolyte, as are available in technical processes described in Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Volume A 7, 1986, pp. 67-97.
Die Aufgabe der Erfindung bestand darin, Verfahren zur Herstellung von Alkalidichromat und Chromsäure durch Elektrolyse bereitzustellen, die die beschriebenen Nachteile nicht aufweisen.The object of the invention was to provide processes for the production of alkali dichromate and chromic acid by electrolysis which do not have the disadvantages described.
Überraschend wurde nun gefunden, daß die genannten Nachteile nicht auftreten, wenn die Katholytflüssigkeit periodisch durch eine Lösung mit einem pH kleiner 6 ersetzt wird.Surprisingly, it has now been found that the disadvantages mentioned do not occur if the catholyte liquid is periodically replaced by a solution with a pH less than 6.
Gegenstand der Erfindung sind somit Verfahren zur Herstellung von Alkalidichromaten und Chromsäure durch Elektrolyse von Monochromat- und/oder Dichromatlösungen in Elektrolysezellen, deren Anoden- und Kathodenräume durch Kationenaustauschermembranen getrennt sind, wobei in Anodenraum Dichromat und/oder Chromsäure-haltige Anolytflüssigkeiten und im Kathodenraum alkalische Alkaliionen-haltige Katholytflüssigkeiten entstehen, welches dadurch gekennzeichnet ist, daß die Katholytflüssigkeiten periodisch durch eine Lösung mit einem pH kleiner 6 ersetzt wird.The invention thus relates to processes for the preparation of alkali dichromates and chromic acid by electrolysis of monochromate and / or dichromate solutions in electrolytic cells, the anode and cathode spaces of which are separated by cation exchange membranes, with anolyte liquid containing dichromate and / or chromic acid and alkaline alkali ions in the cathode space -containing catholyte liquids are formed, which is characterized in that the catholyte liquids are periodically replaced by a solution with a pH less than 6.
Das erfindungsgemäße Verfahren wird unter Beibehaltung des Elektrolysestroms durchgeführt. Vorzugsweise werden die Katholytflüssigkeiten periodisch durch eine Lösung mit einem pH kleiner 1 ersetzt. Geeignete Lösungen sind anorganische Säuren, wie z.B. Schwefelsäure, Phosphorsäure, Salzsäure sowie auch organische Säuren mit unterschiedlichen Konzentrationen. In einer besonders bevorzugten Variante werden die Katholytflüssigkeiten durch eine Chromsäure-haltige Lösung periodisch ersetzt. Es ist vorteilhaft, eine Chromsäure-haltige Lösung zu benutzen, deren Gehalt 10-900 g Chromsäure pro Liter beträgt. Diese Lösung kann natürlich auch Anteile an Alkalidichromat enthalten.The method according to the invention is carried out while maintaining the electrolysis current. The catholyte liquids are preferably periodically replaced by a solution with a pH less than 1. Suitable solutions are inorganic acids such as sulfuric acid, phosphoric acid, hydrochloric acid as well as organic acids with different concentrations. In a particularly preferred variant, the catholyte liquids are periodically replaced by a solution containing chromic acid. It is advantageous to use a solution containing chromic acid, the content of which is 10-900 g chromic acid per liter. This solution can of course also contain proportions of alkali dichromate.
Das erfindungsgemäße Verfahren wird vorzugsweise so betrieben, daß die Katholytflüssigkeiten nach einer Elektrolysezeit von 1-100 Tagen durch eine Lösung mit einem pH-Wert kleiner 6 ersetzt wird. Der Zeitpunkt dieser Maßnahme ist abhängig vom Gehalt an mehrwertigen Kationen in der Monochromat- und/oder Dichromatlösungen sowie von der anodischen Stromdichte. Bei sehr geringen Gehalten dieser Kationen kann der Austausch der Flüssigkeit auch nach einem längeren Zeitraum als 100 Tagen erfolgen.The process according to the invention is preferably operated in such a way that the catholyte liquids are replaced by a solution with a pH of less than 6 after an electrolysis time of 1-100 days. The timing of this measure depends on the content of polyvalent cations in the monochromate and / or dichromate solutions and on the anodic current density. If the cations are very low, the liquid can be exchanged even after a period of more than 100 days.
Bei Durchführung des erfindungsgemäßen Verfahrens werden Einlagerungen vermieden bzw. gebildete Einlagerungen werden aufgelöst, wodurch die Lebensdauer der Membran erheblich verlängert wird, was einen kontinuierlichen und dauerhaften Betrieb der Elektrolyse gewährleistet.When carrying out the method according to the invention, deposits are avoided or formed deposits are dissolved, as a result of which the life of the membrane is considerably extended, which ensures continuous and permanent operation of the electrolysis.
Das erfindungsgemäße Verfahren wird anhand der folgenden Beispiele näher erläutert.The process according to the invention is explained in more detail with reference to the following examples.
Die in den Beispielen verwendeten Elektrolysezellen bestanden aus Anodenräumen aus Rein-Titan und Kathodenräumen aus Edelstahl. Als Membranen wurden Kationenaustauschermembranen der Firma DuPont mit der Bezeichnung Nafion® 324 verwendet. Die Kathoden bestanden aus Edelstahl und die Anoden aus Titanstreckmetall mit einer elektrokatalytisch aktiven Schicht aus Tantaloxid und Iridiumoxid. Solche Anoden sind beispielsweise in der US-A 3 878 083 beschrieben.The electrolytic cells used in the examples consisted of anode compartments made of pure titanium and cathode compartments made of stainless steel. Cation exchange membranes from DuPont with the designation Nafion® 324 were used as membranes. The cathodes were made of stainless steel and the anodes were made of expanded titanium with an electrocatalytically active layer of tantalum oxide and iridium oxide. Such anodes are described, for example, in US Pat. No. 3,878,083.
Der Abstand der Elektroden zur Membran betrug in allen Fällen 1,5 mm. In die Anodenräume wurden Natriumdichromatlösungen mit einem Gehalt von 900 g/l Na₂Cr₂O₇·2 H₂O mit den in den einzelnen Beispielen aufgeführten Gehalten an Verunreinigungen eingeleitet.The distance between the electrodes and the membrane was 1.5 mm in all cases. Sodium dichromate solutions with a content of 900 g / l Na₂Cr₂O₇ · 2 H₂O were introduced into the anode compartments with the levels of impurities listed in the individual examples.
Den Kathodenräumen wurde Wasser mit einer solchen Geschwindigkeit zugeführt, so daß 20 %ige Natronlauge die Zellen verließ. Die Elektrolysetemperatur betrug in allen Fällen 80°C.Water was supplied to the cathode compartments at such a rate that 20% sodium hydroxide solution left the cells. The electrolysis temperature was 80 ° C in all cases.
Die bei diesem Versuch verwendeten Natriumdichromatlösungen wiesen folgende Gehalte an Verunreinigungen auf:
Diese Lösungen wurden in der beschriebenen Elektrolysezelle elektrolytisch in Chromsäure-haltige Lösungen umgewandelt. Die dabei eingestellte Stromdichte betrug 1 kA pro m² der projizierten, der Membran zugewandten Flächen der Anode und der Kathode, wobei die der Membran zugewandte Fläche der Anode 10 cm · 3,6 cm betrug.These solutions were converted electrolytically into solutions containing chromic acid in the electrolysis cell described. The current density set was 1 kA per m 2 of the projected areas of the anode and cathode facing the membrane, the area of the anode facing the membrane being 10 cm × 3.6 cm.
Die Geschwindigkeit des Einleitens der Natriumdichromatlösungen wurde so gewählt, daß sich in dem die Zelle verlassenden Anolyten ein molares Verhältnis von Natriumionen zu Chrom(VI) von 0,8 einstellte. Nach einer Elektrolysezeit von 167 Tagen hatte sich in der Membran eine weiße Einlagerung gebildet, die im wesentlichen aus Calciumhydroxid bestand. Die Zellspannung lag zu diesem Zeitpunkt bei 4,04 V. Während der Laufzeit der Elektrolyse mußten die Anoden wegen unzureichender Haltbarkeit mehrfach ausgewechselt werden.The rate of introduction of the sodium dichromate solutions was chosen so that a molar ratio of sodium ions to chromium (VI) of 0.8 was established in the anolyte leaving the cell. After an electrolysis time of 167 days, a white deposit had formed in the membrane, which essentially consisted of calcium hydroxide. The cell voltage at this point was 4.04 V. During the electrolysis, the anodes had to be replaced several times due to insufficient durability.
Zur Auflösung und Entfernung der Einlagerung wurde nun wie folgt verfahren: Die kathodisch gebildete 20 %ige Natronlauge wurde im Kathodenraum der Zelle zunächst durch Wasser und dann durch eine CrO₃- und Na₂Cr₂O₇ · 2 H₂O-haltige Lösung mit einem pH-Wert kleiner 1 ersetzt. Diese Lösung wies folgende Zusammensetzung auf:
30,3 % Na₂Cr₂O₇ · 2 H₂O
30,3 % CrO₃
39,4 % H₂O.The procedure for dissolving and removing the storage was as follows: The cathodically formed 20% sodium hydroxide solution was first replaced by water in the cathode compartment of the cell and then by a solution containing CrO₃- and Na₂Cr₂O₇ · 2 H₂O with a pH value of less than 1. This solution had the following composition:
30.3% Na₂Cr₂O₇ · 2 H₂O
30.3% CrO₃
39.4% H₂O.
Nach einer Stunde Elektrolyse wurde die Lösung im Kathodenraum wieder zunächst durch Wasser und dann durch 20 %ige Natronlauge ersetzt. Nach dieser Behandlung waren die weißen Einlagerungen nahezu vollständig entfernt und die Zellspannung war auf 3,73 V zurückgegangen.After one hour of electrolysis, the solution in the cathode compartment was replaced first by water and then by 20% sodium hydroxide solution. After this treatment, the white deposits were almost completely removed and the cell voltage had dropped to 3.73 V.
Die eingesetzte Natriumdichromatlösung hatte folgende Gehalte an Verunreinigungen:
Die elektrolytische Umwandlung dieser Lösung in eine Chromsäure-haltige Lösung erfolgte bei 3 kA/m² der projizierten vorderen Fläche der Anode, wobei diese Fläche 11,4 cm · 6,7 cm betrug. Die Geschwindigkeit des Einleitens der Natriumdichromatlösung wurde so eingestellt, daß sich in dem die Zelle verlassenden Anolyten ein molares Verhältnis von Natriumionen zu Chrom(VI) von 0,8 einstellte.The electrolytic conversion of this solution into a solution containing chromic acid was carried out at 3 kA / m 2 of the projected front surface of the anode, this surface being 11.4 cm × 6.7 cm. The rate of introduction of the sodium dichromate solution was adjusted so that a molar ratio of sodium ions to chromium (VI) of 0.8 was established in the anolyte leaving the cell.
Nach 12 Tagen Betrieb der Zelle hatten sich, verbunden mit einem Anstieg der Zellspannung von anfänglich 4,10 V auf 5,24 V, weiße Einlagerungen in der Membran gebildet. Zur Auflösung und Entfernung dieser Einlagerungen wurde wie im Beispiel 1 beschrieben verfahren, wobei in diesem Fall die Zeit der Elektrolyse mit der CrO₃- und Na₂Cr₂O₇ · 2 H₂O-haltigen Lösung im Kathodenraum 10 Minuten betrug. Nach der Behandlung waren die weißen Einlagerungen weitestgehend entfernt, was auch der Rückgang der Zellpsannung auf 4,85 V zeigte.After 12 days of operation of the cell, associated with an increase in the cell voltage from initially 4.10 V to 5.24 V, white deposits had formed in the membrane. To dissolve and remove these deposits, the procedure was as described in Example 1, in which case the time for electrolysis with the solution containing CrO₃- and Na₂Cr₂O₇ · 2 H₂O in the cathode compartment was 10 minutes. After the treatment, the white deposits were largely removed, which was also shown by the decrease in cell voltage to 4.85 V.
Die in diesem Beispiel eingesetzten Natriumdichromatlösungen wiesen folgende Gehalte an Verunreinigung auf:
Die elektrolytische Umwandlung dieser Lösungen erfolgte bei 3 kA/m² der projizierten Anodenfläche von 11,4 cm · 6,7 cm. In dem die Zelle verlassenden Anolyten wurden durch Variation der Einleitungsgeschwindigkeit der Natriumdichromatlösungen molare Verhältnisse von Natriumionen zu Chrom(VI) von 0,46 bis 0,55 eingestellt.The electrolytic conversion of these solutions took place at 3 kA / m² of the projected anode area of 11.4 cm × 6.7 cm. In the anolyte leaving the cell, molar ratios of sodium ions to chromium (VI) of 0.46 to 0.55 were set by varying the rate of introduction of the sodium dichromate solutions.
Nach einer Elektrolysezeit von 28 Tagen hatten sich wieder weiße Einlagerungen in der Membran gebildet. Die Zellspannung lag zu diesem Zeitpunkt bei 3,96 V. Die Auflösung und Entfernung der Einlagerungen erfolgte wie im Beispiel 1 beschrieben.After an electrolysis time of 28 days, white deposits had formed in the membrane again. At this point in time the cell voltage was 3.96 V. The dissolution and removal of the deposits was carried out as described in Example 1.
Nach der Behandlung waren die weißen Einlagerungen nahezu vollständig entfernt und die Zellspannung war auf 3,75 V zurückgegangen.After the treatment, the white deposits were almost completely removed and the cell voltage had dropped to 3.75 V.
Claims (5)
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE3829123 | 1988-08-27 | ||
| DE3829123A DE3829123A1 (en) | 1988-08-27 | 1988-08-27 | PROCESS FOR PREPARING ALKALIDICHROMATE AND CHROMIUM ACID |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| EP0356805A2 EP0356805A2 (en) | 1990-03-07 |
| EP0356805A3 EP0356805A3 (en) | 1990-04-18 |
| EP0356805B1 true EP0356805B1 (en) | 1992-05-20 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP89115033A Expired - Lifetime EP0356805B1 (en) | 1988-08-27 | 1989-08-15 | Process for the production of alkali dichromates and chromic acid |
Country Status (9)
| Country | Link |
|---|---|
| US (1) | US5094729A (en) |
| EP (1) | EP0356805B1 (en) |
| JP (1) | JP2839155B2 (en) |
| AR (1) | AR244811A1 (en) |
| BR (1) | BR8904280A (en) |
| CA (1) | CA1337807C (en) |
| DE (2) | DE3829123A1 (en) |
| MX (1) | MX170143B (en) |
| ZA (1) | ZA896499B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6063252A (en) * | 1997-08-08 | 2000-05-16 | Raymond; John L. | Method and apparatus for enriching the chromium in a chromium plating bath |
| RU2125120C1 (en) * | 1997-09-29 | 1999-01-20 | Иткин Герман Евсеевич | Method of electrolysis of aqueous solution of salt |
| CN101892490A (en) * | 2010-06-24 | 2010-11-24 | 中国科学院青海盐湖研究所 | Method for continuously preparing sodium dichromate by ionic membrane electrolysis |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA739447A (en) * | 1966-07-26 | W. Carlin William | Electrolytic production of chromic acid | |
| US1878918A (en) * | 1926-06-02 | 1932-09-20 | Electro Metallurg Co | Manufacture of chromic acid |
| US2333578A (en) * | 1939-06-16 | 1943-11-02 | Internat Smelting & Refining C | Electrolytic chromate production |
| US3305463A (en) * | 1962-03-16 | 1967-02-21 | Pittsburgh Plate Glass Co | Electrolytic production of dichromates |
| JPS5839916B2 (en) * | 1975-12-29 | 1983-09-02 | サイトウ カズオ | ROUKA CHROME SANYO EKI NO SAISEI SHIYORIHOHOOUOYOBISOUCHI |
| US4290864A (en) * | 1979-05-29 | 1981-09-22 | Diamond Shamrock Corporation | Chromic acid production process using a three-compartment cell |
-
1988
- 1988-08-27 DE DE3829123A patent/DE3829123A1/en not_active Withdrawn
-
1989
- 1989-05-25 AR AR89314753A patent/AR244811A1/en active
- 1989-08-08 MX MX017105A patent/MX170143B/en unknown
- 1989-08-15 EP EP89115033A patent/EP0356805B1/en not_active Expired - Lifetime
- 1989-08-15 DE DE8989115033T patent/DE58901477D1/en not_active Expired - Lifetime
- 1989-08-24 JP JP1216183A patent/JP2839155B2/en not_active Expired - Lifetime
- 1989-08-25 ZA ZA896499A patent/ZA896499B/en unknown
- 1989-08-25 BR BR898904280A patent/BR8904280A/en not_active Application Discontinuation
- 1989-08-25 CA CA000609441A patent/CA1337807C/en not_active Expired - Fee Related
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1991
- 1991-02-22 US US07/659,435 patent/US5094729A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| DE58901477D1 (en) | 1992-06-25 |
| JPH02102128A (en) | 1990-04-13 |
| CA1337807C (en) | 1995-12-26 |
| JP2839155B2 (en) | 1998-12-16 |
| US5094729A (en) | 1992-03-10 |
| EP0356805A3 (en) | 1990-04-18 |
| ZA896499B (en) | 1990-05-30 |
| MX170143B (en) | 1993-08-09 |
| BR8904280A (en) | 1990-04-17 |
| EP0356805A2 (en) | 1990-03-07 |
| AR244811A1 (en) | 1993-11-30 |
| DE3829123A1 (en) | 1990-03-01 |
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