EP0069504A2
Expired / Lapsed
EP
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Improved operation and regeneration of permselective ion-exchange membrane in brine electrolysis cells
Assignee: Dow Chemical Co
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Filing: 1982-06-22
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Granted: —
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Expires: 2002-06-22
Abstract
Abstract A method of operating and regenerating an electrolysis cell for electrolysing aqueous alkali metal halide solution and having permselective cation exchange membrane forming an anolyte and a catholyte compartment. The method comprises the steps of: feeding to and electrolyzing in said cell a brine which, at least prior to the brine's becoming part of the anolyte, contains no more than 5 ppm hardness (expressed as ppm calcium) and no more than 70 ppm carbon dioxide, carbonic acid, carbonate and bicarbonate (expressed as ppm CO2); regenerating the membrane by contacting the membrane on at least one of its sides with a solution capable of dissolving the multivalent cation compounds fouling the membrane for a time sufficient to dissolve a substantial amount of the compounds, the solution having a pH lower than the pH of the electrolyte which contacted that side of the membrane during the normal cell electrolysis.
Inventors
- 👤 Harry Stevens Burnley, Jr.
- 👤 Gary Russell Gantt
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-27 19:23
CPC Classifications
C; C25; C25B; C25B13/00; C25B1/00; C25B1/01; C25B1/34; C25B1/46; C25B15/00
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
170 words
A method of operation and regenerating an electrolysis cell for electrolysing an aqueous alkali metal halide solution (brine) to a halogen at the anode and an alkali metal hydroxide at the cathode, the cell containing a permselective cation exchange membrane disposed between the anode and cathode to form an anolyte and a catholyte compartment, which method comprises the steps of: feeding to and electrolyzing in said cell a brine which, at least at the time immediately prior to the brine's becoming part of the anolyte, contains no more than 5 ppm hardness (expressed as ppm calcium) and no more than 70 ppm "carbon oxide" (expressed as ppm C02); regenerating the membrane by contacting the membrane on at least one of its sides with a solution capable of dissolving the.multivalent cation compounds fouling the membrane for a time sufficient to dissolve a substantial amount of the compounds, the solution having a pH lower than the pH of the electrolyte which contacted that side of the membrane during the normal cell electrolysis.
Claim 2
Independent Claim
170 words
A method of operation and regenerating an electrolysis cell for electrolysing an aqueous alkali metal halide solution (brine) to a halogen at the anode and an alkali metal hydroxide at the cathode, the cell containing a permselective cation exchange membrane disposed between the anode and cathode to form an anolyte and a catholyte compartment, which method comprises the steps of: feeding to and electrolyzing in said cell a brine which, at least at the time immediately prior to the brine's becoming part of the anolyte, contains no more than 5 ppm hardness (expressed as ppm calcium) and no more than 70 ppm "carbon oxide" (expressed as ppm C02); regenerating the membrane by contacting the membrane on at least one of its sides with a solution capable of dissolving the.multivalent cation compounds fouling the membrane for a time sufficient to dissolve a substantial amount of the compounds, the solution having a pH lower than the pH of the electrolyte which contacted that side of the membrane during the normal cell electrolysis.
Claim 3
Dependent Claim
34 words
A method as claimed in Claim 1 wherein the brine fed to the cell contains less than 50 ppm carbon oxide during at least 50 percent of the normal electrolysis operation of the cell.
Claim 4
Dependent Claim
18 words
A method as claimed in Claim 1 or Claim 2 which further comprises drying the membrane after regeneration.
Claim 5
Independent Claim
27 words
A method as claimed in any one of the preceding claims wherein the membrane is regenerated in place in the cell and both compartments contain liquid solutions.
Claim 6
Dependent Claim
56 words
A method as claimed in Claim 4 wherein the membrane is regenerated after it has become fouled with compounds of multivalent cations accumulated from the brine fed to the cell during the normal cell electrolysis and the cell voltage is reduced to less than about 80 percent of the normal electrolysis voltage employed in the cell.
Claim 7
Dependent Claim
38 words
A method as claimed in Claim 4 or Claim 5 wherein during membrane regeneration the cell voltage is reduced to the cathodic protection voltage of the cell so that the cathode is afforded cathodic protection during membrane regeneration.
Claim 8
Independent Claim
31 words
A method as claimed in any one of Claims 4 to 6 wherein the pH of the solution in the anolyte chamber is decreased to less than 2.0 during membrane regeneration.
Claim 9
Independent Claim
29 words
A method as claimed in any one of Claims 4 to 7 wherein the solution in the catholyte chamber is maintained at a pH below 10 during membrane regeneration.
Claim 10
Independent Claim
25 words
A method as claimed in any one of Claims 4 to 8 wherein regeneration of the membrane is carried out for at least one hour.
Claim 11
Independent Claim
110 words
A method as claimed in any one of Claims 4 to 9 wherein the amount of carbon oxide employed in the brine feed of normal cell operation is less than 2 ppm; the pH of the solution in the anolyte compartment is maintained in a range of from 0.5 to about 2.0 during substantially most of the time required for membrane regeneration to be accomplished; wherein the pH of the solution in the catholyte compartment is maintained at a level below about pH 8 for at least half of the time during which membrane regeneration is carried out; and wherein membrane regeneration is carried out for at least ten hours.
Claim 12
Dependent Claim
90 words
A method as claimed in Claim 4, wherein the alkali metal halide solution is an aqueous sodium chloride solution, wherein the brine fed to the cell contains less than about 2 ppm carbon oxide, wherein during membrane regeneration, the cell voltage is reduced or turned off and the membrane is contacted with an anolyte solution having a decreased pH range of from O.5 to 2.0 and a catholyte solution having a pH of less than 8, and wherein regeneration of the membrane is carried out for at least one hour.
References Cited (Backward Citations)
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