Process for producing sodium hydroxide and ammonium sulfate from sodium sulfate
First Claim
1. A process for producing sodium hydroxide, which process comprises electrolysing an aqueous solution of sodium sulfate in an electrolytic cell having at least one anode compartment and at least one cathode compartment, said anode compartment containing an anolyte and having an anode located therein, said cathode compartment containing a catholyte and having a cathode located therein, said anode compartment and said cathode compartment being separated from the sodium sulfate solution by an anion selective ion exchange membrane and a cation selective ion exchange membrane, respectively, wherein during the process ammonia is added to the anolyte to at least partially neutralize sulfuric acid produced in the anode compartment.
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Abstract
A process for producing sodium hydroxide and ammonium sulfate by electrolysing an aqueous solution of sodium sulfate is disclosed. The process is carried out in a three-compartment electrolytic cell having a central compartment separated from an anode and a cathode compartment by, respectively, anion selective and cation selective ion exchange membrane. The solution of sodium sulfate is circulated through the central compartment, while solutions of sodium hydroxide and ammonium sulfate are circulated, respectively, through the cathode and the anode compartment. During the process, ammonia is added to the anolyte to at least partially neutralize sulfuric acid produced in the anode compartment and reduce the back migration of protons from the anolyte into the central compartment. As a result, high purity ammonium sulfate of commercial value higher than that of sulfuric acid is produced with high current efficiency and in concentrations higher than those achievable for sulfuric acid.
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Citations
24 Claims
- 1. A process for producing sodium hydroxide, which process comprises electrolysing an aqueous solution of sodium sulfate in an electrolytic cell having at least one anode compartment and at least one cathode compartment, said anode compartment containing an anolyte and having an anode located therein, said cathode compartment containing a catholyte and having a cathode located therein, said anode compartment and said cathode compartment being separated from the sodium sulfate solution by an anion selective ion exchange membrane and a cation selective ion exchange membrane, respectively, wherein during the process ammonia is added to the anolyte to at least partially neutralize sulfuric acid produced in the anode compartment.
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2. A process for producing sodium hydroxide and ammonium sulfate, which method comprises:
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passing a solution of sodium sulfate through a central compartment of a three-compartment electrolytic cell having a cathode compartment and an anode compartment separated from the central compartment by a cation selective ion exchange membrane and an anion selective ion exchange membrane, respectively; passing a catholyte through the cathode compartment and an anolyte through the anode compartment; passing a direct electric current between an anode and a cathode located in the anode compartment and the cathode compartment, respectively, thus producing sodium hydroxide in the cathode compartment and sulfuric acid in the anode compartment; at least partially neutralizing sulfuric acid produced in the anode compartment by adding ammonia to the anolyte.
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24. A process for producing sodium hydroxide, which process comprises electrolysing an aqueous solution of sodium sulfate in an electrolytic cell having at least one anode compartment and at least one cathode compartment, said anode compartment containing an anolyte and having an anode located therein, said cathode compartment containing a catholyte and having a cathode located therein, said anode compartment and said cathode compartment being separated from the sodium sulfate solution by an anion selective ion exchange membrane and a cation selective ion exchange membrane, respectively, wherein during the process ammonia is added to the anolyte to at least partially neutralize sulfuric acid produced in the anode compartment, and wherein the cation selective ion exchange membrane is a stable perfluorinated cation exchange membrane, the anion selective ion exchange membrane is made of an organic polymer having amino functionality attached thereto, the cathode is a nickel cathode and the anode is a DSA-O2 anode and sulfuric acid is neutralized to maintain the anolyte at a pH of from about 0.5 to about 3.5.
Specification