EP0436146A1 - Process for the electrochemical regeneration of chromosulphuric acid - Google Patents
Process for the electrochemical regeneration of chromosulphuric acid Download PDFInfo
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- EP0436146A1 EP0436146A1 EP90123633A EP90123633A EP0436146A1 EP 0436146 A1 EP0436146 A1 EP 0436146A1 EP 90123633 A EP90123633 A EP 90123633A EP 90123633 A EP90123633 A EP 90123633A EP 0436146 A1 EP0436146 A1 EP 0436146A1
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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
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D21/00—Processes for servicing or operating cells for electrolytic coating
- C25D21/16—Regeneration of process solutions
- C25D21/18—Regeneration of process solutions of electrolytes
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- the invention relates to a method for the electrochemical regeneration of chromosulfuric acid, in which a novel electrolysis cell is used.
- electrodes made of lead or lead alloys and electrolytic cells with lead walls, for example steel troughs lined with lead, are usually used.
- a membrane cell for chlor-alkali electrolysis which consists of two half-shells, one half-shell made of titanium sheet and the other made of stainless steel or nickel sheet (see Bergner and Hannesen, GDCH Annual Conference on Angew. Electrochemistry, October 1984).
- the electrodes each consist of a blind sheet which is activated and inserted into the Half shell is welded.
- the electrodes are connected to the rear walls of the half-shells at regular intervals using corrugated strips.
- the two half-shells of a cell are separated from each other by a permeable membrane and seals.
- the task was to find a process in which the chromosulfuric acid is regenerated in a closed cell system and the resulting hydrogen can be obtained.
- the invention thus relates to a process for the electrochemical regeneration of chromosulphuric acid by anodic oxidation of Cr3+ ions to Cr6+ ions, the anolyte 20 to 200 g / dm3 total CrO3 and 100 to 600 g / dm3 H2SO4 and the catholyte 50 to Contains 500 g / dm3 H2SO4, characterized in that the regeneration is carried out in an electrolysis cell, which consists of two trough-like metal half-shells, the open sides of which face each other, with a plate or plate provided with holes or slits in the anode trough the anode tub is connected by corrugated strips, is located as the anode, there is a sheet in the cathode tub, which is connected to the cathode tub by corrugated tapes, is located as the cathode, the anode tub and cathode tub are separated from one another by a current-permeable, hydraulically sealing partition
- FIG. 1 shows an overall perspective view of an electrolysis cell
- FIG. 2 shows a section along the line II-II in FIGS. 1, 3 and 4
- FIG. 3 shows a section along the line III-III in FIGS. 1, 2 and 4
- FIG. 4 shows a plan view in the direction of arrow IV in FIGS. 1, 2 and 3.
- the cell consists of two trough-like metal half-shells (1) and (2).
- a perforated or slotted plate (3) perforated plate, expanded metal, or the like
- the plate (3) serves as an anode.
- a sheet (5) as the cathode, which is connected to the trough (2) via corrugated strips (6).
- the cathode consists of a simple sheet metal, sheet metal strips, perforated sheet metal, expanded metal or a sheet metal blind, preferably a sheet metal sheet.
- Anode tub (1) and cathode tub (2) are separated from each other by a current-permeable, hydraulically sealing partition (7) and seals (8) and (9). They are held together by two insulated steel frames (10) and (11). The screws (16) are insulated by means of plastic bushings (17) and plastic washers (18). There is an inlet pipe (12) for the anolyte on the underside of the anode tub (1), and an inlet pipe (14) for the catholyte on the cathode tub (2). The exhaust pipes (13) and (15) are located on the top of the trays (1) and (2).
- Figure 2 also shows the position of the corrugated strips (4) and (6) and the offset attachment of the inlet pipes (12) and (14).
- the circumferential steel frame (11) can finally be seen from FIGS. 3 and 4.
- the anode tub (1) and the corrugated strips (4) consist of titanium, while the cathode tray (2) and the corrugated strips (6) consist of nickel or a nickel alloy, for example ®Hastelloy.
- valve metals titanium, tantalum, vanadium and zirconium already used in chlor-alkali electrolysis are also suitable as materials for the anode (3) under the aggressive conditions of chromic acid electrolysis. Under anodic current load, these metals form a coherent oxide film on their surface, which protects the base material. If the surface of the anodes is not activated, the oxide layer formed prevents further current flow. Suitable activation layers for these metals for the chromic acid electrolysis are only electron-conducting oxides which have a high overvoltage in relation to oxygen, for example lead dioxide, manganese dioxide, tin dioxide, tantalum oxides or iridium oxides.
- One of the highest surge voltages for oxygen is characterized by lead dioxide, which is preferred. This results in the anodic electrochemical reaction on a titanium anode coated with PbO2 at current densities of 200 A / m2 to 2500 A / m2 current yields between 96% and 88%.
- Nickel and nickel alloys are suitable as materials for the cathode (5).
- sulfuric acid as the catholyte
- the reaction equation Discharges protons at the cathode and develops hydrogen, which leaves the cathode space in gaseous form.
- nickel is only resistant to 10 to 35% sulfuric acid if it is cathodically polarized. It must therefore be prevented that the nickel cathodes are exposed to sulfuric acid when de-energized.
- the hydrogen overvoltage on nickel is relatively low at 0.42 V at a current density of 100 A / m2, compared to quite high on lead under the same conditions at 1.09 v.
- the consequence of this is that when nickel is used as the cathode, a correspondingly lower cell voltage results.
- cation-active ion exchange membranes made of perfluorinated polymers with sulfonyl groups have proven their worth. They show excellent durability and selectivity in the electrolytes used up to temperatures of 110 ° C. The use of such membranes makes it possible to collect the cathodically developed hydrogen separately and to use it further.
- the electrolytic cell to be used and assembled according to the invention can be operated after filling catholyte into the cathode compartment and anolyte into the anode compartment and after pressing the power supply lines of a rectifier onto the anode tub and cathode tub rear wall.
- the continuous supply of catholyte and anolyte from storage tanks takes place via pumps at the lower end of the electrode space.
- the electrolyte leaves the cell.
- the anolyte with the desired composition is passed on for further use, the catholyte is continuously circulated through a buffer container and is concentrated again from time to time.
- the undesirable, to a small extent, developing oxygen (due to water decomposition) at the anode ensures sufficient mixing of the anolyte and supports the diffusion of Cr3+ to the anode surface.
- This effect can be intensified by additionally blowing inert gas into the anode compartment.
- This electrolysis cell is preferably not operated individually. Rather, multiple cells are pressed together in a cell frame by means of a pressing device rear wall to rear wall. This means that the current introduced at the beginning of the cell package with copper bars can flow through all cells and is derived from copper bars at the end of the package. Special contact strips ensure good current transfer between the cells. If the cells are operated in this way, a bipolar cell is present. All individual elements are connected in series.
- the concentration in the anolyte is 20 to 200, preferably 100 to 200, in particular 130 to 170 g / dm3 total CrO3 and 100 to 600, preferably 300 to 600, in particular 450 to 550 g / cm3 H2SO4.
- the catholyte contains 50 to 500, preferably 300 to 350 g / dm3 H2SO4.
- the electrolysis is carried out at a temperature of 40 to 110, preferably 80 to 110 ° C. and a current density of 100 to 2500, preferably 500 to 2500 A / m2.
- the electrolysis was carried out in a round laboratory membrane cell, which was composed of 2 glass dishes and was flange-sealed with two PTFE O-rings.
- the two glass bowls formed the cathode and anode space. They were separated by a polymer membrane made of a perfluorinated polymer, which was clamped between the two O-rings.
- the two circular electrodes were held eccentrically, the DC supply was via these holders.
- the spacing of the anode and cathode could be changed in relation to each other and to the membrane.
- Anolyte and catholyte were heated in the two cell halves with heating rods to 90 ° C and kept constant at this temperature during the electrolysis.
- the cathode consisted of non-activated nickel expanded metal, the anode made of titanium expanded metal, which was coated on all sides with electrodeposited PbO2.
- the cathode-anode distance was 8 mm.
- the catholyte was circulated through the cathode compartment with a constant throughput of 9 cm3 / h at all current densities.
- the electrolysis data obtained are shown in Table 1.
- a titanium expanded metal anode activated with a tantalum oxide / iridium oxide mixture was tested for suitability in a second glass cell, the structure of which corresponded completely to the cell described above.
Abstract
Chromschwefelsäure, die bei vielen organischen Reaktionen als Oxidationsmittel verwendet wird, kann mit Vorteil elektrochemisch regeneriert werden, wenn eine Elektrolysezelle eingesetzt wird, welche aus zwei wannenartigen Halbschalen (1) (2) mit dazwischen befindlicher stromdurchlässiger, hydraulisch abdichtender Trennwand (7) besteht. Auf diese Weise läßt sich auch der an der Kathode (5) entstehende Wasserstoff gewinnen und verwerten. <IMAGE>Chromosulfuric acid, which is used as an oxidizing agent in many organic reactions, can advantageously be regenerated electrochemically if an electrolysis cell is used which consists of two trough-like half-shells (1) (2) with a current-permeable, hydraulically sealing partition (7) in between. In this way, the hydrogen generated at the cathode (5) can also be obtained and utilized. <IMAGE>
Description
Die Erfindung bezieht sich auf ein Verfahren zur elektrochemischen Regenerierung von Chromschwefelsäure, bei welchem eine neuartige Elektrolysezelle verwendet wird.The invention relates to a method for the electrochemical regeneration of chromosulfuric acid, in which a novel electrolysis cell is used.
Bei der elektrochemischen Regenerierung von Chromschwefelsäure, welche bei Oxidationsprozessen eingesetzt war, werden üblicherweise Elektroden aus Blei oder Bleilegierungen und Elektrolysezellen mit Bleiwänden, beispielsweise mit Blei ausgekleidete Stahltröge verwendet.In the electrochemical regeneration of chromosulphuric acid, which was used in oxidation processes, electrodes made of lead or lead alloys and electrolytic cells with lead walls, for example steel troughs lined with lead, are usually used.
Der Nachteil der Verwendung von Blei oder Bleilegierungen besteht darin, daß die Anoden relativ schnell ihre Aktivität verlieren und nur beschränkt wiederverwertbar sind und daß an Kathoden aus Blei und Bleilegierung eine hohe Wasserstoffüberspannung auftritt (ca. 1,1 Volt). Es ist auch noch nicht gelungen, die Elektrolyse in geschlossenen Zellen durchzuführen und neben dem Cr⁶⁺ auch den auf der Kathodenseite entwickelten Wasserstoff zu gewinnen. Vielmehr muß der entstandene Wasserstoff von den mit Folien abgedeckten Zellen abgesaugt und mit Luft auf ein Verhältnis von etwa 50:1 verdünnt werden, um gefahrlos unterhalb der Explosionsgrenze von etwa 4 % H₂ in Luft arbeiten zu können. Diese Verfahrensweise ist unökonomisch und aus Gründen der Arbeitshygiene und des Umweltschutzes zu beanstanden.The disadvantage of using lead or lead alloys is that the anodes lose their activity relatively quickly and can only be recycled to a limited extent, and that a high hydrogen overvoltage occurs on lead and lead alloy cathodes (approx. 1.1 volts). It has also not yet been possible to carry out the electrolysis in closed cells and to obtain the hydrogen developed on the cathode side in addition to the Cr⁶⁺. Rather, the hydrogen produced must be suctioned off from the cells covered with foils and diluted with air to a ratio of approximately 50: 1 in order to be able to work safely below the explosion limit of approximately 4%
Bekannt ist eine Membranzelle für die Chloralkalielektrolyse, welche aus zwei Halbschalen besteht, wobei die eine Halbschale aus Titanblech und die andere aus Edelstahl oder Nickelblech gepreßt ist (vgl. Bergner und Hannesen, GDCH-Jahrestagung Angew. Elektrochemie, Oktober 1984). Die Elektroden bestehen aus je einem Jalousieblech, welches aktiviert und in die Halbschale eingeschweißt ist. In regelmäßigen Abständen werden die Elektroden mit den Rückwänden der Halbschalen durch Wellbänder verbunden. Die beiden Halbschalen einer Zelle sind durch eine durchlässige Membrane und Dichtungen voneinander getrennt.A membrane cell for chlor-alkali electrolysis is known, which consists of two half-shells, one half-shell made of titanium sheet and the other made of stainless steel or nickel sheet (see Bergner and Hannesen, GDCH Annual Conference on Angew. Electrochemistry, October 1984). The electrodes each consist of a blind sheet which is activated and inserted into the Half shell is welded. The electrodes are connected to the rear walls of the half-shells at regular intervals using corrugated strips. The two half-shells of a cell are separated from each other by a permeable membrane and seals.
Die Aufgabe bestand darin, ein verfahren zu finden, bei welchem die Chromschwefelsäure in einem geschlossenen Zellensystem regeneriert wird und der entstehende Wasserstoff gewonnen werden kann.The task was to find a process in which the chromosulfuric acid is regenerated in a closed cell system and the resulting hydrogen can be obtained.
Es wurde gefunden, daß die für die Chloralkalielektrolyse entwickelte Membranzelle grundsätzlich auch für die elektrochemische Regenerierung von Chromschwefelsäure geeignet ist.It has been found that the membrane cell developed for chlor-alkali electrolysis is in principle also suitable for the electrochemical regeneration of chromium-sulfuric acid.
Die Erfindung betrifft somit ein verfahren zur elektrochemischen Regenerierung von Chromschwefelsäure durch anodische Oxidation von Cr³⁺ -Ionen zu Cr⁶⁺-Ionen, wobei der Anolyt 20 bis 200 g/dm³ Gesamt-CrO₃ und 100 bis 600 g/dm³ H₂SO₄ und der Katholyt 50 bis 500 g/dm³ H₂SO₄ enthält, dadurch gekennzeichnet, daß die Regenerierung in einer Elektrolysezelle durchgeführt wird, welche aus zwei wannenartigen Metallhalbschalen besteht, deren offene Seiten einander zugewandt sind, wobei sich in der Anodenwanne eine mit Löchern oder Schlitzen versehene Platte aus Metall, die mit der Anodenwanne durch Wellbänder verbunden ist, als Anode befindet, sich in der Kathodenwanne ein Blech, welches mit der Kathodenwanne durch Wellbänder verbunden ist, als Kathode befindet, Anodenwanne und Kathodenwanne durch eine stromdurchlässige, hydraulisch abdichtende Trennwand und Dichtungen voneinander getrennt sind und durch eine Klemmvorrichtung zusammengehalten werden, die Temperatur 40 bis 110°C und die Stromdichte 100 bis 2500 A/m² beträgt.The invention thus relates to a process for the electrochemical regeneration of chromosulphuric acid by anodic oxidation of Cr³⁺ ions to Cr⁶⁺ ions, the anolyte 20 to 200 g / dm³ total CrO₃ and 100 to 600 g / dm³ H₂SO₄ and the catholyte 50 to Contains 500 g / dm³ H₂SO₄, characterized in that the regeneration is carried out in an electrolysis cell, which consists of two trough-like metal half-shells, the open sides of which face each other, with a plate or plate provided with holes or slits in the anode trough the anode tub is connected by corrugated strips, is located as the anode, there is a sheet in the cathode tub, which is connected to the cathode tub by corrugated tapes, is located as the cathode, the anode tub and cathode tub are separated from one another by a current-permeable, hydraulically sealing partition and seals and by a clamping device held together, the temperature 40 up to 110 ° C and the current density is 100 to 2500 A / m².
Die für das erfindungsgemäße verfahren zu verwendende Elektrolysezelle wird anhand der Figuren 1 bis 4 erläutert. Es zeigt Figur 1 eine perspektivische Gesamtansicht einer Elektrolysezelle, Figur 2 einen Schnitt entlang der Linie II-II in Figur 1, 3 und 4, Figur 3 einen Schnitt entlang der Linie III-III in Figur 1, 2 und 4 und Figur 4 eine Aufsicht in Richtung des Pfeiles IV in Figur 1, 2 und 3.The one to be used for the method according to the invention Electrolysis cell is explained with reference to Figures 1 to 4. 1 shows an overall perspective view of an electrolysis cell, FIG. 2 shows a section along the line II-II in FIGS. 1, 3 and 4, FIG. 3 shows a section along the line III-III in FIGS. 1, 2 and 4 and FIG. 4 shows a plan view in the direction of arrow IV in FIGS. 1, 2 and 3.
Gemäß Figur 1 besteht die Zelle aus zwei wannenartigen Metallhalbschalen (1) und (2). In der Anodenwanne (1) befindet sich eine gelochte oder geschlitzte Platte (3) (Lochblech, Streckmetall, oder ähnliches), welche mittels Wellbändern (4) mit der Anodenwanne (1) verbunden ist. Die Platte (3) dient als Anode. In der Kathodenwanne (2) befindet sich ein Blech (5) als Kathode, welches über Wellbänder (6) mit der Wanne (2) verbunden ist. Die Kathode besteht aus einem einfachen Blech, Blechstreifen, Lochblech, Streckmetall oder Jalousieblech, vorzugsweise aus einem Jalousieblech.According to Figure 1, the cell consists of two trough-like metal half-shells (1) and (2). In the anode trough (1) there is a perforated or slotted plate (3) (perforated plate, expanded metal, or the like) which is connected to the anode trough (1) by means of corrugated strips (4). The plate (3) serves as an anode. In the cathode trough (2) there is a sheet (5) as the cathode, which is connected to the trough (2) via corrugated strips (6). The cathode consists of a simple sheet metal, sheet metal strips, perforated sheet metal, expanded metal or a sheet metal blind, preferably a sheet metal sheet.
Anodenwanne (1) und Kathodenwanne (2) sind durch eine stromdurchlässige, hydraulisch abdichtende Trennwand (7) und Dichtungen (8) und (9) voneinander getrennt. Sie werden durch zwei miteinander isoliert verschraubte Stahlrahmen (10) und (11) zu einer Einheit zusammengehalten. Die Isolierung der Schrauben (16) erfolgt mittels Kunststoffbuchsen (17) und Kunststoffscheiben (18). An der Unterseite der Anodenwanne (1) befindet sich ein Zulaufrohr (12) für den Anolyten, an der Kathodenwanne (2) ein Zulaufrohr (14) für den Katholyten. An der Oberseite der Wannen (1) und (2) befinden sich die Abzugsrohre (13) und (15).Anode tub (1) and cathode tub (2) are separated from each other by a current-permeable, hydraulically sealing partition (7) and seals (8) and (9). They are held together by two insulated steel frames (10) and (11). The screws (16) are insulated by means of plastic bushings (17) and plastic washers (18). There is an inlet pipe (12) for the anolyte on the underside of the anode tub (1), and an inlet pipe (14) for the catholyte on the cathode tub (2). The exhaust pipes (13) and (15) are located on the top of the trays (1) and (2).
Figur 2 zeigt darüber hinaus die Lage der Wellbänder (4) und (6) sowie die versetzte Anbringung der Zulaufrohre (12) und (14).Figure 2 also shows the position of the corrugated strips (4) and (6) and the offset attachment of the inlet pipes (12) and (14).
Aus den Figuren 3 und 4 ist schließlich der umlaufende Stahlrahmen (11) zu erkennen.The circumferential steel frame (11) can finally be seen from FIGS. 3 and 4.
Die Anodenwanne (1) und die Wellbänder (4) bestehen aus Titan, während die Kathodenwanne (2) und die Wellbänder (6) aus Nickel oder einer Nickellegierung, beispielsweise ®Hastelloy, bestehen.The anode tub (1) and the corrugated strips (4) consist of titanium, while the cathode tray (2) and the corrugated strips (6) consist of nickel or a nickel alloy, for example ®Hastelloy.
Es wurde gefunden, daß die bereits in der Chlor-Alkali-Elektrolyse eingesetzten sog. "Ventilmetalle" Titan, Tantal, Vanadin und Zirkonium auch unter den aggressiven Bedingungen der Chromsäure-Elektrolyse als Werkstoffe für die Anode (3) geeignet sind. Diese Metalle bilden unter anodischer Strombelastung einen kohärenten Oxidfilm auf ihrer Oberfläche aus, der das Basismaterial schützt. Wird die Oberfläche der Anoden nicht aktiviert, verhindert die gebildete Oxidschicht den weiteren Stromfluß. Als geeignete Aktivierungsschichten für diese Metalle kommen für die Chromsäure-Elektrolyse nur elektronenleitende Oxide in Frage, die gegenüber Sauerstoff eine hohe Überspannung zeigen, beispielsweise Bleidioxid, Mangandioxid, Zinndioxid, Tantaloxide oder Iridiumoxide. Eine der höchsten Überspannungen für Sauerstoff zeichnet Bleidioxid aus, welches bevorzugt wird. So ergibt die anodisch ablaufende elektrochemische Reaktion
an einer mit PbO₂ beschichteten Titananode bei Stromdichten von 200 A/m² bis 2500 A/m² Stromausbeuten zwischen 96 % bis 88 %.It has been found that the so-called "valve metals" titanium, tantalum, vanadium and zirconium already used in chlor-alkali electrolysis are also suitable as materials for the anode (3) under the aggressive conditions of chromic acid electrolysis. Under anodic current load, these metals form a coherent oxide film on their surface, which protects the base material. If the surface of the anodes is not activated, the oxide layer formed prevents further current flow. Suitable activation layers for these metals for the chromic acid electrolysis are only electron-conducting oxides which have a high overvoltage in relation to oxygen, for example lead dioxide, manganese dioxide, tin dioxide, tantalum oxides or iridium oxides. One of the highest surge voltages for oxygen is characterized by lead dioxide, which is preferred. This results in the anodic electrochemical reaction
on a titanium anode coated with PbO₂ at current densities of 200 A / m² to 2500 A / m² current yields between 96% and 88%.
Als Werkstoffe für die Kathode (5) sind Nickel und Nickellegierungen, beispielsweise Hastelloy, geeignet. Bei Verwendung von Schwefelsäure als Katholyt werden nach der Reaktionsgleichung
Die Wasserstoffüberspannung an Nickel ist bei einer Stromdichte von 100 A/m² mit 0,42 V relativ niedrig, im Vergleich dazu an Blei unter den gleichen Bedingungen mit 1,09 v recht hoch. Dies hat zur Folge, daß bei Verwendung von Nickel als Kathode eine entsprechend niedrigere Zellenspannung resultiert.The hydrogen overvoltage on nickel is relatively low at 0.42 V at a current density of 100 A / m², compared to quite high on lead under the same conditions at 1.09 v. The consequence of this is that when nickel is used as the cathode, a correspondingly lower cell voltage results.
Als stromdurchlässige, hydraulisch abdichtende Trennwand (7) zwischen Anoden- und Kathodenraum haben sich kationenaktive Ionenaustauschermembranen aus perfluorierten Polymeren mit Sulfonyl-Gruppen bestens bewährt. Sie zeigen in den verwendeten Elektrolyten bis zu Temperaturen von 110°C eine hervorragende Beständigkeit und Selektivität. Die Verwendung derartiger Membranen ermöglicht es, den kathodisch entwickelten Wasserstoff separat aufzufangen und einer weiteren Nutzung zuzuführen.As a current-permeable, hydraulically sealing partition wall (7) between the anode and cathode compartments, cation-active ion exchange membranes made of perfluorinated polymers with sulfonyl groups have proven their worth. They show excellent durability and selectivity in the electrolytes used up to temperatures of 110 ° C. The use of such membranes makes it possible to collect the cathodically developed hydrogen separately and to use it further.
Die erfindungsgemäß zu verwendende und montierte Elektrolysezelle kann nach Einfüllen von Katholyt in den Kathodenraum und Anolyt in den Anodenraum und nach Anpressen von Stromzuführungen eines Gleichrichters auf die Anodenwannen- und Kathodenwannenrückwand betrieben werden. Die kontinuierliche Einspeisung von Katholyt und Anolyt aus vorratsbehältern erfolgt jeweils über Pumpen am unteren Ende des Elektrodenraumes. Am oberen Ende verläßt der Elektrolyt die Zelle. Der Anolyt mit der gewünschten Zusammensetzung wird der weiteren Verwendung zugeführt, der Katholyt wird ständig über einen Pufferbehälter im Kreislauf geführt und von Zeit zu Zeit wieder aufkonzentriert.The electrolytic cell to be used and assembled according to the invention can be operated after filling catholyte into the cathode compartment and anolyte into the anode compartment and after pressing the power supply lines of a rectifier onto the anode tub and cathode tub rear wall. The continuous supply of catholyte and anolyte from storage tanks takes place via pumps at the lower end of the electrode space. At the top end, the electrolyte leaves the cell. The anolyte with the desired composition is passed on for further use, the catholyte is continuously circulated through a buffer container and is concentrated again from time to time.
Die an sich unerwünschte, in geringem Umfang ablaufende Sauerstoffentwicklung (durch Wasserzersetzung) an der Anode sorgt für eine ausreichende Durchmischung des Anolyten und unterstützt die Diffusion von Cr³⁺ an die Anodenoberfläche. Dieser Effekt kann durch zusätzliches Einblasen von Inertgas in den Anodenraum verstärkt werden.The undesirable, to a small extent, developing oxygen (due to water decomposition) at the anode ensures sufficient mixing of the anolyte and supports the diffusion of Cr³⁺ to the anode surface. This effect can be intensified by additionally blowing inert gas into the anode compartment.
Vorzugsweise wird diese Elektrolysezelle nicht einzeln betrieben. Vielmehr werden in einem Zellengestell mehrere Zellen mittels einer Anpreßvorrichtung Rückwand an Rückwand zusammengepreßt. Damit kann der am Anfang des Zellenpakets mit Kupferschienen eingeleitete Strom durch alle Zellen fließen und wird am Ende des Pakets von Kupferschienen abgeleitet. Spezielle Kontaktstreifen sorgen für einen guten Stromübergang zwischen den Zellen. Werden die Zellen derartig betrieben, liegt eine Bipolarzelle vor. Alle Einzelelemente sind in Serie geschaltet.This electrolysis cell is preferably not operated individually. Rather, multiple cells are pressed together in a cell frame by means of a pressing device rear wall to rear wall. This means that the current introduced at the beginning of the cell package with copper bars can flow through all cells and is derived from copper bars at the end of the package. Special contact strips ensure good current transfer between the cells. If the cells are operated in this way, a bipolar cell is present. All individual elements are connected in series.
Die Konzentration im Anolyten beträgt 20 bis 200, vorzugsweise 100 bis 200, insbesondere 130 bis 170 g/dm³ Gesamt-CrO₃ und 100 bis 600, vorzugsweise 300 bis 600, insbesondere 450 bis 550 g/cm³ H₂SO₄. Der Katholyt enthält 50 bis 500, vorzugsweise 300 bis 350 g/dm³ H₂SO₄.The concentration in the anolyte is 20 to 200, preferably 100 to 200, in particular 130 to 170 g / dm³ total CrO₃ and 100 to 600, preferably 300 to 600, in particular 450 to 550 g / cm³ H₂SO₄. The catholyte contains 50 to 500, preferably 300 to 350 g / dm³ H₂SO₄.
Die Elektrolyse wird bei einer Temperatur von 40 bis 110, vorzugsweise 80 bis 110°C, und einer Stromdichte von 100 bis 2500, vorzugsweise 500 bis 2500 A/m² durchgeführt.The electrolysis is carried out at a temperature of 40 to 110, preferably 80 to 110 ° C. and a current density of 100 to 2500, preferably 500 to 2500 A / m².
Das erfindungsgemäße Verfahren soll an den folgenden Beispielen erläutert werden.The process according to the invention will be explained in the following examples.
Die Elektrolyse wurde in einer runden Labormembranzelle, die aus 2 Glasschalen zusammengesetzt war und über zwei O-Ringe aus PTFE abdichtend zusammengeflanscht war, durchgeführt. Die beiden Glasschalen bildeten den Kathoden- und Anodenraum. Sie waren durch eine Polymermembran aus einem perfluorierten Polymeren getrennt, die zwischen die beiden O-Ringe eingespannt war.The electrolysis was carried out in a round laboratory membrane cell, which was composed of 2 glass dishes and was flange-sealed with two PTFE O-rings. The two glass bowls formed the cathode and anode space. They were separated by a polymer membrane made of a perfluorinated polymer, which was clamped between the two O-rings.
Die beiden kreisrunden Elektroden waren exzentrisch gehaltert, über diese Halterungen erfolgte die Gleichstromzufuhr. Anode und Kathode konnten über Distanzstreifen in ihrem Abstand zueinander und zur Membran verändert werden. Anolyt und Katholyt wurden in den beiden Zellhälften mit Heizstäben auf 90°C aufgeheizt und während der Elektrolyse konstant bei dieser Temperatur gehalten.
Die Kathode bestand aus nicht aktiviertem Nickel-Streckmetall, die Anode aus Titan-Streckmetall, das mit galvanisch abgeschiedenem PbO₂ allseitig beschichtet war. Der Abstand Kathode-Anode betrug 8 mm.
Der Katholyt wurde dabei im Kreislauf durch den Kathodenraum gepumpt mit einem bei allen Stromdichten konstanten Durchsatz von 9 cm³/h. Die erhaltenen Elektrolysedaten zeigt Tabelle 1.
In einer zweiten Glaszelle, die in ihrem Aufbau der oben beschriebenen Zelle vollständig entsprach, wurde eine mit Tantaloxid/Iridiumoxid-Mischung aktivierte Titan-Streckmetallanode auf ihre Eignung getestet.
Bemerkenswert war die niedrige Zellenspannung von 1,92 V bei einer Strombelastung von 500 A/m² im Vergleich zu Beispiel 1. Allerdings war die Stromausbeute bezüglich CrO₃-Bildung von durchschnittlich nur 61 % bei einem vergleichsweise niedrigem Oxidationsgrad von 44 % geringer. Daraus resultierte ein relativ hoher Energiebedarf von 2,65 kWh/kg CrO₃ bei 500 A/m². Anodenseitig war eine stärkere Gasentwicklung (analysiert als O₂) festzustellen, die auf die niedrigere Sauerstoffüberspannung dieser Aktivierungsbeschichtung im Vergleich zu PbO₂ zurückzuführen ist. Mit steigender Strombelastung ging die Stromausbeute noch weiter zurück und erreichte z.B. bei 1 500 A/m² nur noch etwa 49 %.The low cell voltage of 1.92 V at a current load of 500 A / m² was remarkable in comparison to Example 1. However, the current yield with respect to CrO₃ formation was only 61% on average with a comparatively low degree of oxidation of 44%. This resulted in a relatively high energy requirement of 2.65 kWh / kg CrO₃ at 500 A / m². On the anode side, a stronger gas development (analyzed as O₂) was observed, which is due to the lower oxygen overvoltage Activation coating compared to PbO₂ is due. With increasing current load, the current yield decreased even further and only reached about 49% at 1,500 A / m², for example.
Die elektrolytische Regenerierung von Chromschwefelsäure wurde in einer Membranzelle wie in Figur 1 bis 4 beschrieben durchgeführt.
Claims (6)
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE3940978A DE3940978A1 (en) | 1989-12-12 | 1989-12-12 | METHOD FOR THE ELECTROCHEMICAL REGENERATION OF CHROMIUM ACIDIC ACID |
| DE3940978 | 1989-12-12 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0436146A1 true EP0436146A1 (en) | 1991-07-10 |
| EP0436146B1 EP0436146B1 (en) | 1994-04-20 |
Family
ID=6395298
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP90123633A Expired - Lifetime EP0436146B1 (en) | 1989-12-12 | 1990-12-08 | Process for the electrochemical regeneration of chromosulphuric acid |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US5045162A (en) |
| EP (1) | EP0436146B1 (en) |
| JP (1) | JPH05238736A (en) |
| DE (2) | DE3940978A1 (en) |
| DK (1) | DK0436146T3 (en) |
| ES (1) | ES2054203T3 (en) |
| IE (1) | IE65467B1 (en) |
| PT (1) | PT96157A (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4315411C2 (en) * | 1993-05-10 | 1995-04-27 | Lpw Anlagen Gmbh | Process for the regeneration of spent chromic acid solutions |
| DE4419683C2 (en) * | 1994-06-06 | 2000-05-04 | Eilenburger Elektrolyse & Umwelttechnik Gmbh | Bipolar filter press cell for anodic oxidation on platinum |
| DE19519177C2 (en) * | 1995-05-24 | 1999-05-12 | Warnecke Hans Joachim Prof Dr | Waste COD reduction method and apparatus |
| AT409764B (en) * | 1998-03-06 | 2002-11-25 | Treibacher Ind Ag | METHOD FOR OXIDATING VANADIUM |
| NZ331053A (en) * | 1998-07-21 | 2002-12-20 | Osmose New Zealand | Process for electrochemical generation of higher oxidate state values from lower oxidation state values above zero of transition metal(s) [eg; |
| FR2791662B1 (en) * | 1999-04-01 | 2001-06-22 | Conservatoire Nat Arts | PROCESS FOR THE ELECTROCHEMICAL TREATMENT OF EFFLUENTS, IN PARTICULAR TANNING EFFLUENTS, INCLUDING CHROMIUM SALTS |
| US6468414B1 (en) | 2001-02-16 | 2002-10-22 | Hydro-Quebec | Method of purification of a redox mediator before electrolytic regeneration thereof |
| GB2399349A (en) * | 2003-03-13 | 2004-09-15 | Kurion Technologies Ltd | Regeneration of chromic acid etching and pickling baths |
| JP3836833B2 (en) * | 2003-11-11 | 2006-10-25 | 山口 嘉春 | Hydrogen and oxygen mixed gas generator and its electrolyzer |
| DE102004023161A1 (en) * | 2004-05-07 | 2005-11-24 | Eilenburger Elektrolyse- Und Umwelttechnik Gmbh | Electrolysis cell with multilayer expanded metal cathodes |
| CN108103521B (en) * | 2017-12-22 | 2019-10-15 | 四川省银河化学股份有限公司 | A method of it improving electrolysis method and prepares quality of chromic anhydride |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2219806A1 (en) * | 1973-03-02 | 1974-09-27 | Basf Ag | Diaphragm cell for chromic-sulphuric acid prodn. - with membrane near cathode and high anode-cathode surface ratio |
| US4006067A (en) * | 1973-03-05 | 1977-02-01 | Gussack Mark C | Oxidation-reduction process |
| FR2354399A1 (en) * | 1976-06-11 | 1978-01-06 | Sarel | Sulpho:chromic and/or phospho:chromic regeneration cell - converts trivalent chromium to hexavalent state with controlled chromium migration |
| EP0189535A1 (en) * | 1985-01-16 | 1986-08-06 | Uhde GmbH | Electrolysis apparatus |
| WO1986005215A1 (en) * | 1985-02-27 | 1986-09-12 | Elin-Union Aktiengesellschaft Für Elektrische Indu | Method for the electrochemical oxidation of sulphuric acid chromium iii solutions into chromium vi solutions |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3761369A (en) * | 1971-10-18 | 1973-09-25 | Electrodies Inc | Process for the electrolytic reclamation of spent etching fluids |
-
1989
- 1989-12-12 DE DE3940978A patent/DE3940978A1/en not_active Withdrawn
-
1990
- 1990-10-31 US US07/606,437 patent/US5045162A/en not_active Expired - Fee Related
- 1990-12-08 ES ES90123633T patent/ES2054203T3/en not_active Expired - Lifetime
- 1990-12-08 EP EP90123633A patent/EP0436146B1/en not_active Expired - Lifetime
- 1990-12-08 DK DK90123633.1T patent/DK0436146T3/en active
- 1990-12-08 DE DE59005450T patent/DE59005450D1/en not_active Expired - Fee Related
- 1990-12-11 JP JP2401408A patent/JPH05238736A/en not_active Withdrawn
- 1990-12-11 IE IE446490A patent/IE65467B1/en not_active IP Right Cessation
- 1990-12-11 PT PT96157A patent/PT96157A/en unknown
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2219806A1 (en) * | 1973-03-02 | 1974-09-27 | Basf Ag | Diaphragm cell for chromic-sulphuric acid prodn. - with membrane near cathode and high anode-cathode surface ratio |
| US4006067A (en) * | 1973-03-05 | 1977-02-01 | Gussack Mark C | Oxidation-reduction process |
| FR2354399A1 (en) * | 1976-06-11 | 1978-01-06 | Sarel | Sulpho:chromic and/or phospho:chromic regeneration cell - converts trivalent chromium to hexavalent state with controlled chromium migration |
| EP0189535A1 (en) * | 1985-01-16 | 1986-08-06 | Uhde GmbH | Electrolysis apparatus |
| WO1986005215A1 (en) * | 1985-02-27 | 1986-09-12 | Elin-Union Aktiengesellschaft Für Elektrische Indu | Method for the electrochemical oxidation of sulphuric acid chromium iii solutions into chromium vi solutions |
Also Published As
| Publication number | Publication date |
|---|---|
| US5045162A (en) | 1991-09-03 |
| JPH05238736A (en) | 1993-09-17 |
| EP0436146B1 (en) | 1994-04-20 |
| ES2054203T3 (en) | 1994-08-01 |
| PT96157A (en) | 1991-09-30 |
| DE59005450D1 (en) | 1994-05-26 |
| IE65467B1 (en) | 1995-11-01 |
| IE904464A1 (en) | 1991-06-19 |
| DK0436146T3 (en) | 1994-08-08 |
| DE3940978A1 (en) | 1991-06-13 |
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