EP0074431A1 - Cellule d'électrolyse résistant à la corrosion - Google Patents

Cellule d'électrolyse résistant à la corrosion Download PDF

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Publication number
EP0074431A1
EP0074431A1 EP81107331A EP81107331A EP0074431A1 EP 0074431 A1 EP0074431 A1 EP 0074431A1 EP 81107331 A EP81107331 A EP 81107331A EP 81107331 A EP81107331 A EP 81107331A EP 0074431 A1 EP0074431 A1 EP 0074431A1
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EP
European Patent Office
Prior art keywords
cathode
iron
cell
voltage
anode
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP81107331A
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German (de)
English (en)
Inventor
John Mark Mcintyre
Donald Lee Caldwell
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Dow Chemical Co
Original Assignee
Dow Chemical Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Dow Chemical Co filed Critical Dow Chemical Co
Priority to EP81107331A priority Critical patent/EP0074431A1/fr
Publication of EP0074431A1 publication Critical patent/EP0074431A1/fr
Ceased legal-status Critical Current

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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
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features

Definitions

  • the present invention resides in electrolytic cells having iron-containing materials exposed to the interior portions of the cell and maintained at about the same voltage as that of the cathode.
  • Electrolytic cells have found wide uses in modern industrial practice. However, with energy costs increasing, researchers in recent years have investigated means to reduce the energy consumed by electrolytic cells, following numerous approaches. Among the more common techniques used are the modification of the electrodes. For example, low overvoltage cathodes have been used; such cathodes have been described in numerous patents; among which are U.S. Patents 2,419,231; 3,272,728; 4,104,133; 4,170,536; 4,162,204; 4,024,044; 3,945,907 and 3,974,058.
  • Japanese Patent 31-6611 published August 7, 1956, discloses a nickel/zinc alloy being electroplated onto a nickel-coated, iron substrate, wherein the zinc is subsequently leached from the Ni/Zn alloy by an alkaline solution.
  • a similar process is shown in Netherlands Patent 75-07550, laid open to inspection January 20, 1976.
  • the present invention resides in- an electrolytic cell wherein voltage and pH conditions place iron-containing components of the cell into a state of ionization causing deterioration of the components, said cell comprising an anode in an anode chamber; a cathode in a cathode chamber; said iron-containing components being exposed to the interior portion of the cathode chamber and electrically connected to the cathode; and wherein at least a portion of the surface of the iron-containing components is coated with a protective coating at a level sufficient to minimize ionization of iron to thereby prevent contamination of the products by electrolysis.
  • the Figure is a Pourbaix diagram showing the potential vs pH for an iron-water system at 25°C.
  • the Figure shows the oxidation state of iron as a function of pH and voltage at 25°C in an iron--water system. If the iron-containing parts of the cell exposed to pH and voltage conditions which put them into area A of the Pourbaix diagram, iron will exist as Fe. Conditions corresponding to area B, will cause iron to exist as HFeO 2 - . In area C , iron will exist as a mixture of Fe 0 and HFeO 2 - . In area D, iron will exist as Fe 3 0 4 while in area E, iron will exist as Fe 2 0 3 . pH and voltage conditions corresponding to areas A, D and E will cause iron to exist in a solid state. However, if iron-containing parts are subjected to pH and voltage conditions corresponding to areas B or C, iron will ionize and cause iron impurities in the electrolytic products.
  • iron contamination present in the products produced by electrolysis when a low cathode voltage is used, comes from iron-containing cell parts which are exposed to the interior portions of the cell and are maintained at about the same voltage as the cathode.
  • An example of a source of iron contamination is a backscreen or some other type of cathode support that is frequently used in electrolytic cells. It has been found that if at least a portion of the iron-containing metallic parts of an electrolytic cell which are exposed to the interior portions of the cell are at least partially covered with a protective coating, iron contamination in the electrolytic products is minimized.
  • the protective coating used to coat the iron-containing parts of the cell should be stable at the applied electrical voltage, substantially stable at the temperature of the cell, substantially unreactive with the catholyte, and substantially stable at the pH.
  • nickel examples of some coatings which may be used are nickel, titanium, vinyl ester resins, epoxy and various other plastics.
  • Nickel is the preferred coating since it conforms nicely to the physical and chemical requirements of the coating.
  • the backscreen or other iron-containing parts of the cell may be constructed from the materials which have been listed as being good protective coatings.
  • the backscreen may be a nickel screen, rather than a nickel-coated iron screen.
  • the cathode When conventional iron or steel cathodes are used in an electrolytic cell for the electrolysis of water or a brine solution, the cathode is normally maintained at a voltage of approximately -1.1 to -1.2 volts vs. Normal Hydrogen Electrode (N.H.E.). The pH range is normally above approximately 13. These conditions would place iron-containing parts of_the cell into area A of the Figure. Any iron present on the cathode or any other iron in the cell which is maintained at a similar voltage will not ionize but will exist as Fe. However, if the voltage is reduced so that the cathode operates at approximately -0.8 volt to approximately -1.1 volts vs. N.H.E., the cell conditions enter areas B and/or C of the Figure where HFeO 2 will form and iron will ionize. Ionization of the iron-containing parts will cause iron contamination of the products of the cell.
  • N.H.E. Normal Hydrogen Electrode
  • the invention may be used in any electrolytic cell wherein a voltage and pH conditions place iron-containing parts of the cell under conditions where iron will ionize.
  • any iron-containing parts which are electrically connected with the cathode, or maintained at a voltage about the same as the cathode, will cause iron to ionize and will contaminate the products of the electrolysis.
  • the invention may be used to minimize iron contamination of the products.
  • the Pourbaix diagram which was- g elected for illustration of the invention is for 25°C in an aqueous system which is chloride free.
  • most electrolytic cells operate at elevated temperatures.
  • chlor-alkali cells normally operate at 50-100°C.
  • the voltage required to ionize iron under given pH ranges will vary with temperature, thus, while iron will ionize at voltages of about -0.8 to -1.1 volts vs. N.H.E. at 25°C, the voltage to cause ionization at 100°C in chloride-containing systems will be slightly different.
  • Each of the cells was fed a saturated NaCl brine solution and was maintained at a temperature of about 70°C.
  • each of the cells was operated at approximately 800 amps and produced an approximately 10 weight percent NaOH catholyte solution.
  • the conventional steel cathode cell produced a catholyte having 1.7 ppm Fe.
  • the low overvoltage cathode having an uncoated backscreen produced a catholyte having 1.6 ppm Fe.
  • the two low overvoltage cathodes having a nickel coated backscreen produced catholytes having 0.7 and 0.5 ppm Fe, respectively.
  • the current on each cell was lowered to 150 amps, thus reducing the cathode overvoltage.
  • the standard steel cathode cell produced a catholyte having 0.2 ppm Fe; the low overvoltage cathode having an uncoated backscreen produced a catholyte having 0.4 ppm Fe; and the two low overvoltage cathodes having nickel coated backscreens each produced catholytes having 0.06 ppm Fe.
  • the standard steel cathode cell produced a catholyte having 1.7 ppm Fe; the low overvoltage cathode cell having an uncoated backscreen produced a catholyte having 2.4 ppm Fe; and each of the two low overvoltage cathode cells having a coated backscreen produced catholytes having 0.5 ppm Fe.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrodes For Compound Or Non-Metal Manufacture (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
EP81107331A 1981-09-16 1981-09-16 Cellule d'électrolyse résistant à la corrosion Ceased EP0074431A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP81107331A EP0074431A1 (fr) 1981-09-16 1981-09-16 Cellule d'électrolyse résistant à la corrosion

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP81107331A EP0074431A1 (fr) 1981-09-16 1981-09-16 Cellule d'électrolyse résistant à la corrosion

Publications (1)

Publication Number Publication Date
EP0074431A1 true EP0074431A1 (fr) 1983-03-23

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Family Applications (1)

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EP81107331A Ceased EP0074431A1 (fr) 1981-09-16 1981-09-16 Cellule d'électrolyse résistant à la corrosion

Country Status (1)

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EP (1) EP0074431A1 (fr)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR562357A (fr) * 1921-03-05 1923-11-09 Perfectionnements aux électrolyseurs destinés à la fabrication de i'oxygène et de l'hydrogène
FR1397976A (fr) * 1963-04-25 1965-05-07 Pittsburgh Plate Glass Co Nouveaux types de doublages résistant à la corrosion pour récipients métalliques
FR2278798A1 (fr) * 1974-07-17 1976-02-13 Hooker Chemicals Plastics Corp Surface de cathode presentant une faible surtension d'hydrogene

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR562357A (fr) * 1921-03-05 1923-11-09 Perfectionnements aux électrolyseurs destinés à la fabrication de i'oxygène et de l'hydrogène
FR1397976A (fr) * 1963-04-25 1965-05-07 Pittsburgh Plate Glass Co Nouveaux types de doublages résistant à la corrosion pour récipients métalliques
FR2278798A1 (fr) * 1974-07-17 1976-02-13 Hooker Chemicals Plastics Corp Surface de cathode presentant une faible surtension d'hydrogene

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PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

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Effective date: 19830920

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Effective date: 19871005

RIN1 Information on inventor provided before grant (corrected)

Inventor name: CALDWELL, DONALD LEE

Inventor name: MCINTYRE, JOHN MARK