CA1164408A - Corrosion resistant electrolytic cell - Google Patents
Corrosion resistant electrolytic cellInfo
- Publication number
- CA1164408A CA1164408A CA000385971A CA385971A CA1164408A CA 1164408 A CA1164408 A CA 1164408A CA 000385971 A CA000385971 A CA 000385971A CA 385971 A CA385971 A CA 385971A CA 1164408 A CA1164408 A CA 1164408A
- Authority
- CA
- Canada
- 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.)
- Expired
Links
Landscapes
- Electrodes For Compound Or Non-Metal Manufacture (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An electrolytic cell comprising an anode, a cathode and iron-containing metals exposed to the interior portions of the cell which are maintained at about the same electrical potential as the cathode.
These materials are covered with a protective coating to minimize corrosion during operation of the cell.
An electrolytic cell comprising an anode, a cathode and iron-containing metals exposed to the interior portions of the cell which are maintained at about the same electrical potential as the cathode.
These materials are covered with a protective coating to minimize corrosion during operation of the cell.
Description
t'~
CORROSION RESISTANT ELECT~OLYTIC CELL
The present invention resides in electrolytic cells having iron-containing materials exposed to the interior portions of the cell and maintained at about the s~me 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 investi-gated means to reduce the energy consumed by electro-lytic 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/~inc alloy being electroplated onto a nickel-coated, iron substrate, wherein the zinc is subsequently leached from the Ni/Zn alloy by an alka-line solution. A similar process is shown in NetherlandsPatent 75-07550, laid open to inspection January 20, 1976.
27,905-F -1-1~l6~
Accordingly, the present invention resides in an eleetrolytic cell wherein voltage and pH eonditions place iron-containing components of the cell into a state of ionization causing deterioration of the com-ponents, said cell comprising an anode in an anodechamber; a cathode in a cathode chamber; said iron-eontaining components being exposed to the interior porti~n of th~ ~th~ ch~mher and electrieally eon-nected to the cathode; and wherein at least a portion of the surface of the iron-eontaining eomponents is eoated with a proteetive coating at a level sufficient to minimize ionization of iron to thereby prevent eon-tamination of the products by electrolysis.
The Figure is a Pourbaix diagram showing the potential vs pH for an iron-water system at 25C.
The Figure shows the oxidation state of iron as a function of pH and voltage at 25C in an iron--water system. If the iron-containing parts of the eell exposed to pH and voltage eonditions which put them into area A of the Pourbaix diagram, iron wlll exist as Fe. Conditions eorresponding to area B, will cause iron to exist as HFeO2. In area C, iron will exist as a mixture of Fe3O4 and HFeO2.
In area D, iron will exist as Fe3O4 while in area E, iron will exist as Fe203. pH and voltage conditions corresponding to areas A, D and E will eause iron to exist in a solid state. However, if iron-eontaining parts are subjected to pH and voltage conditions eorresponding to areas B or C, iron will ionize and cause iron impurities in the eleetrolytie produets.
Although vol~age reduetion teehniques are economieal, in ~hat they save energy, it has been 27,905-F -2-9t(t~
discovered that there are problems associated with such techniques. One of the more serious problems is the fact that frequently the elec~rolytic products contain a greater amount of impurities than do products pro-duced from conventional cells. For example, when lowovervoltage cathodes are used in a chlor-alkali elec-trolytic process, it has been found that the caustic pr~uced fre~uent~y c~ntains a greater concentration of iron than caustic produced from cells using conventional cathodes. Since low overvoltage cathodes are typically coated with nickel or some other corrosion-resistant metal coating, it is surprising that ~he iron contamin-ation in such a cell is greater than when conventional iron or steel cathodes are used.
It has been found that the 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 contam-ination 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 partialIy 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.
27,905-F -3-Examples of some coatings which may be used are nickel, titanium, vinyl ester resins, epoxy and various other plastics. Nickel, however, is the preferred coating since it confoxms nicely to the physical and chemical requirements of the coating.
Optionally, the backscreen or other iron-containing parts of the cell may be constructe~ fr~m the materials which have been listed as being good protective coatings. For example, the backscreen may be a nickel screen, rather than a nickel-coated iron screen.
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 condi-tions 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 main-tained 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.~., the cell conditions enter areas ~ and/or C of the Figure where HFeO2 will form and iron will ionize. Ionization of the iron-containing parts will cause iron contamination of the products of the cell.
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 27,905-F -4-iron will ionize. In such a system, any iron-containi~g 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 minimi~e iron contamination of the productsO
It should be understood that the Pourbaix diagram which was selected for illustration of the invention is for 25C in an aqueous system which is chloride free. However, most electrolytic cells operate at elevated temperatures. For example, chlor-alkali cells normally operate at 50-100~. The voltag~
re~uired 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 25C, the voltage to cause ionization at 100C in chloride-containing systems will be slightly different.
The following examples illustrate the inven-tion in a chlor-alkali electrolytic cell. However, it should be well understood that the invention may be used in any electrolytic cell wherein an aqueous solu-tion is electrolyzed and wherein there are iron-containing parts electrically connected with the cathode or parts which are maintained at a voltage about the same as that of the cathode.
Exam~le Four 11 square foot cathodes were tested in diaphragm chlor-alkali cells: One conventional low-carbon steel cathode having an uncoated backscreen; onelow overvoltage cathode having an uncoated backscreen;
27,905-F -5-and two low overvoltage cathodes, each having a back-screen coated with a protective nickel coating. The protective coating was applied by electroplating a steel cathode with a nickel-zinc alloy, then removing the æinc by soaking in an alkaline solution, leaving a high-surface area nickel coating.
Each of the cells was fed a sat7lrated Na~l brine solution and was maintained at a temperature of about 70C. The same brine source fed all cells, thus the brine for each cell had the same iron content.
Upon start-up, each of the cells was operated at approximately 800 amps and produced an approximately 10 weight percent NaOH catholyte solution. The conven-tional 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. However, the two low overvoltage cathodes having a nickel coated backscreen produced catholytes having 0.7 and 0.5 ppm Fe, respectively.
After operating several weeks at 800 amps, the current on each cell was lowered to 150 amps, thus reducing the cathode overvoltage. At 150 amps, 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 four cells were then shut down for a few days and restarted. Upon start-up, the standard steel cathode cell produced a catholyte having 1.7 ppm Fe;
27,905-F -6-4(k~
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 havi~g 0.5 ppm Fe.
27,905-F -7-
CORROSION RESISTANT ELECT~OLYTIC CELL
The present invention resides in electrolytic cells having iron-containing materials exposed to the interior portions of the cell and maintained at about the s~me 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 investi-gated means to reduce the energy consumed by electro-lytic 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/~inc alloy being electroplated onto a nickel-coated, iron substrate, wherein the zinc is subsequently leached from the Ni/Zn alloy by an alka-line solution. A similar process is shown in NetherlandsPatent 75-07550, laid open to inspection January 20, 1976.
27,905-F -1-1~l6~
Accordingly, the present invention resides in an eleetrolytic cell wherein voltage and pH eonditions place iron-containing components of the cell into a state of ionization causing deterioration of the com-ponents, said cell comprising an anode in an anodechamber; a cathode in a cathode chamber; said iron-eontaining components being exposed to the interior porti~n of th~ ~th~ ch~mher and electrieally eon-nected to the cathode; and wherein at least a portion of the surface of the iron-eontaining eomponents is eoated with a proteetive coating at a level sufficient to minimize ionization of iron to thereby prevent eon-tamination of the products by electrolysis.
The Figure is a Pourbaix diagram showing the potential vs pH for an iron-water system at 25C.
The Figure shows the oxidation state of iron as a function of pH and voltage at 25C in an iron--water system. If the iron-containing parts of the eell exposed to pH and voltage eonditions which put them into area A of the Pourbaix diagram, iron wlll exist as Fe. Conditions eorresponding to area B, will cause iron to exist as HFeO2. In area C, iron will exist as a mixture of Fe3O4 and HFeO2.
In area D, iron will exist as Fe3O4 while in area E, iron will exist as Fe203. pH and voltage conditions corresponding to areas A, D and E will eause iron to exist in a solid state. However, if iron-eontaining parts are subjected to pH and voltage conditions eorresponding to areas B or C, iron will ionize and cause iron impurities in the eleetrolytie produets.
Although vol~age reduetion teehniques are economieal, in ~hat they save energy, it has been 27,905-F -2-9t(t~
discovered that there are problems associated with such techniques. One of the more serious problems is the fact that frequently the elec~rolytic products contain a greater amount of impurities than do products pro-duced from conventional cells. For example, when lowovervoltage cathodes are used in a chlor-alkali elec-trolytic process, it has been found that the caustic pr~uced fre~uent~y c~ntains a greater concentration of iron than caustic produced from cells using conventional cathodes. Since low overvoltage cathodes are typically coated with nickel or some other corrosion-resistant metal coating, it is surprising that ~he iron contamin-ation in such a cell is greater than when conventional iron or steel cathodes are used.
It has been found that the 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 contam-ination 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 partialIy 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.
27,905-F -3-Examples of some coatings which may be used are nickel, titanium, vinyl ester resins, epoxy and various other plastics. Nickel, however, is the preferred coating since it confoxms nicely to the physical and chemical requirements of the coating.
Optionally, the backscreen or other iron-containing parts of the cell may be constructe~ fr~m the materials which have been listed as being good protective coatings. For example, the backscreen may be a nickel screen, rather than a nickel-coated iron screen.
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 condi-tions 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 main-tained 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.~., the cell conditions enter areas ~ and/or C of the Figure where HFeO2 will form and iron will ionize. Ionization of the iron-containing parts will cause iron contamination of the products of the cell.
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 27,905-F -4-iron will ionize. In such a system, any iron-containi~g 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 minimi~e iron contamination of the productsO
It should be understood that the Pourbaix diagram which was selected for illustration of the invention is for 25C in an aqueous system which is chloride free. However, most electrolytic cells operate at elevated temperatures. For example, chlor-alkali cells normally operate at 50-100~. The voltag~
re~uired 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 25C, the voltage to cause ionization at 100C in chloride-containing systems will be slightly different.
The following examples illustrate the inven-tion in a chlor-alkali electrolytic cell. However, it should be well understood that the invention may be used in any electrolytic cell wherein an aqueous solu-tion is electrolyzed and wherein there are iron-containing parts electrically connected with the cathode or parts which are maintained at a voltage about the same as that of the cathode.
Exam~le Four 11 square foot cathodes were tested in diaphragm chlor-alkali cells: One conventional low-carbon steel cathode having an uncoated backscreen; onelow overvoltage cathode having an uncoated backscreen;
27,905-F -5-and two low overvoltage cathodes, each having a back-screen coated with a protective nickel coating. The protective coating was applied by electroplating a steel cathode with a nickel-zinc alloy, then removing the æinc by soaking in an alkaline solution, leaving a high-surface area nickel coating.
Each of the cells was fed a sat7lrated Na~l brine solution and was maintained at a temperature of about 70C. The same brine source fed all cells, thus the brine for each cell had the same iron content.
Upon start-up, each of the cells was operated at approximately 800 amps and produced an approximately 10 weight percent NaOH catholyte solution. The conven-tional 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. However, the two low overvoltage cathodes having a nickel coated backscreen produced catholytes having 0.7 and 0.5 ppm Fe, respectively.
After operating several weeks at 800 amps, the current on each cell was lowered to 150 amps, thus reducing the cathode overvoltage. At 150 amps, 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 four cells were then shut down for a few days and restarted. Upon start-up, the standard steel cathode cell produced a catholyte having 1.7 ppm Fe;
27,905-F -6-4(k~
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 havi~g 0.5 ppm Fe.
27,905-F -7-
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electrolytic cell wherein voltage and pH conditions place iron-containing components of the cell into a state of ionization causing deteriora-tion 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.
2. The cell of claim 1 wherein the protective coating is a metal selected from nickel or titanium or an alloy of said metals.
3. The cell of claim 1, including means for impressing a sufficient voltage on the anode and the cathode to cause electrolytic reactions to occur;
wherein said voltage maintains the iron containing components at a voltage level about the same as the voltage of the cathode.
wherein said voltage maintains the iron containing components at a voltage level about the same as the voltage of the cathode.
4. The cell of claim 3 wherein the cathode is maintained at a voltage of from -0.8 to -1.1 volts, vs. Normal Hydrogen Electrode.
5. The cell of claim 3 or 4 wherein the means for maintaining the iron-containing materials at a voltage approximately the same as that of the cathode is an electrical connection between the cathode and the iron-containing materials.
6. The cell of claim 1, 2 or 3 wherein the cathode is a low-overvoltage cathode.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000385971A CA1164408A (en) | 1981-09-15 | 1981-09-15 | Corrosion resistant electrolytic cell |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000385971A CA1164408A (en) | 1981-09-15 | 1981-09-15 | Corrosion resistant electrolytic cell |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1164408A true CA1164408A (en) | 1984-03-27 |
Family
ID=4120964
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000385971A Expired CA1164408A (en) | 1981-09-15 | 1981-09-15 | Corrosion resistant electrolytic cell |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1164408A (en) |
-
1981
- 1981-09-15 CA CA000385971A patent/CA1164408A/en not_active Expired
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US5162079A (en) | Process and apparatus for control of electroplating bath composition | |
| US4555317A (en) | Cathode for the electrolytic production of hydrogen and its use | |
| CA1335973C (en) | Process for preparing quaternary ammonium hydroxides | |
| NO142314B (en) | ELECTRODE FOR ELECTROCHEMICAL PROCESSES. | |
| US3663414A (en) | Electrode coating | |
| US4279709A (en) | Preparation of porous electrodes | |
| US4169775A (en) | Protection of the low hydrogen overvoltage catalytic coatings | |
| US4087337A (en) | Rejuvenation of the efficiency of sea water electrolysis cells by periodic removal of anodic deposits | |
| US4100049A (en) | Coated cathode for electrolysis cells | |
| US4906340A (en) | Process for electroplating metals | |
| US3974051A (en) | Production of hypochlorite from impure saline solutions | |
| US4311567A (en) | Treatment of permionic membrane | |
| US4586998A (en) | Electrolytic cell with low hydrogen overvoltage cathode | |
| Moats et al. | Mesh-on-lead anodes for copper electrowinning | |
| US3254015A (en) | Process for treating platinum-coated electrodes | |
| CA1164408A (en) | Corrosion resistant electrolytic cell | |
| USRE34191E (en) | Process for electroplating metals | |
| US4312723A (en) | Corrosion resistant electrolytic cell | |
| CA1161783A (en) | Method of preventing deterioration of palladium oxide anode | |
| EP0074431A1 (en) | Corrosion resistant electrolytic cell | |
| US4488947A (en) | Process of operation of catholyteless membrane electrolytic cell | |
| GB914515A (en) | Process for the electrolytic production of hyper-pure zinc | |
| US3202594A (en) | Process for activating platinum electrodes | |
| US4412894A (en) | Process for electrowinning of massive zinc with hydrogen anodes | |
| US4085014A (en) | Elimination of impurities from sea water cell feed to prevent anode deposits |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |