Electrochemical methods for production of alkali metal hydroxides without the co-production of chlorine
First Claim
1. A method for producing an alkali metal hydroxide without the simultaneous production of chlorine, which comprises the steps of:
- a) providing an electrochemical cell comprising a hydrogen consuming anode and an alkali metal hydroxide producing cathode;
b) introducing an electrolyte solution into said electrochemical cell, said solution comprising a salt selected from the group consisting of an alkali metal carbonate, alkali metal bicarbonate, and mixtures thereof;
c) impressing a voltage across said anode and cathode to produce alkali metal hydroxide and hydrogen at the cathode;
d) feeding a source of hydrogen to said hydrogen consuming anode while maintaining said electrolyte solution in said electro-chemical cell at a pH>
7 to produce carbon dioxide and water, ande) facilitating the discharge of carbon dioxide at said anode at a sufficient rate to maintain cell voltages at <
2.6 V and at a current density of at least 100 mA/cm2.
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Abstract
Methods for the electrolysis of aqueous solutions of alkali metal carbonates and bicarbonates for the production of alkali metal hydroxides at current efficiencies of >85 percent without the simultaneous co-production of halogen or acid can be performed at very low, commercially attractive cell voltages and at high current densities in single or two solution compartment cells with carbon dioxide as the only substantive co-product by maintaining cell pH at >7. The methods are also especially suitable for retrofitting existing chlor-alkali facilities for shifting the balance of production in favor of caustic soda at peak demands. The methods may also be performed with fuel cell configurations for even more attractive operating economics.
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Citations
39 Claims
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1. A method for producing an alkali metal hydroxide without the simultaneous production of chlorine, which comprises the steps of:
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a) providing an electrochemical cell comprising a hydrogen consuming anode and an alkali metal hydroxide producing cathode; b) introducing an electrolyte solution into said electrochemical cell, said solution comprising a salt selected from the group consisting of an alkali metal carbonate, alkali metal bicarbonate, and mixtures thereof; c) impressing a voltage across said anode and cathode to produce alkali metal hydroxide and hydrogen at the cathode; d) feeding a source of hydrogen to said hydrogen consuming anode while maintaining said electrolyte solution in said electro-chemical cell at a pH>
7 to produce carbon dioxide and water, ande) facilitating the discharge of carbon dioxide at said anode at a sufficient rate to maintain cell voltages at <
2.6 V and at a current density of at least 100 mA/cm2. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A method for producing an alkali metal hydroxide without the simultaneous production of chlorine, which comprises the steps of:
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a) providing an electrochemical cell comprising a hydrogen consuming anode in an anolyte compartment, a high performance cathode in a catholyte compartment and a cell divider positioned therebetween; b) introducing an electrolyte solution into said anolyte compartment, said solution comprising a salt selected from the group consisting of an alkali metal carbonate, alkali metal bicarbonate, and mixtures thereof; c) introducing an aqueous solution into said catholyte compartment, said aqueous solution comprising alkali metal cartions from said anolyte compartment; d) impressing a voltage across said anode and cathode to produce alkali metal hydroxide and hydrogen at the cathode; e) feeding a source of hydrogen to said hydrogen consuming anode while maintaining the electrolyte solution in said anolyte compartment at a pH >
7 to produce carbon dioxide and water, andf) maintaining a sufficient concentration of said alkali metal salt in solution in said anolyte compartment and at a sufficiently high temperature while facilitating the discharge of carbon dioxide at said anode to provide a cell voltage of <
2.0 V at a current density of at least 100 mA/cm2 and a alkali metal hydroxide current efficiency in the range of about 90 to about 95 percent. - View Dependent Claims (22, 23, 24, 25, 26)
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27. A method for producing an alkali metal hydroxide without the simultaneous production of chlorine, which comprises the steps of:
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a) providing an electrochemical cell comprising a hydrogen consuming anode and a gas consuming cathode; b) introducing an electrolyte solution into said electro-chemical cell, said solution comprising a salt selected from the group consisting of an alkali metal carbonate, alkali metal bicarbonate, and mixtures thereof; c) feeding a source of gas to said gas consuming cathode selected from the group consisting of air, oxygen and mixtures thereof; d) impressing a voltage across said anode and cathode to produce alkali metal hydroxide at the cathode, and e) feeding a source of hydrogen to said hydrogen consuming anode while maintaining said electrolyte solution in said electro-chemical cell at a pH >
7 to produce carbon dioxide and water at said anode. - View Dependent Claims (28, 29, 30, 31, 32, 33, 34)
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35. In a method of producing alkali metal hydroxide without the simultaneous production of chlorine in an electrochemical cell comprising a hydrogen consuming anode and an alkali metal hydroxide producing cathode in which an electrolyte solution is introduced into said electrochemical cell comprising a salt selected from the group consisting of alkali metal carbonate, alkali metal bicarbonate and mixtures thereof;
- impressing a voltage across said anode and cathode to produce alkali metal hydroxide and hydrogen at said cathode, and feeding the hydrogen to said hydrogen consuming anode to produce carbon dioxide and water while maintaining said electrolyte solution at a pH >
7,the improvement comprising operating said electrochemical cell with a hydrogen consuming anode comprising a polymer selected from the group consisting of non-ionic and ionic charged types to provide a cell voltage of <
2.6 V and at a current density of at least 100 mA/cm2. - View Dependent Claims (36, 37, 38, 39)
- impressing a voltage across said anode and cathode to produce alkali metal hydroxide and hydrogen at said cathode, and feeding the hydrogen to said hydrogen consuming anode to produce carbon dioxide and water while maintaining said electrolyte solution at a pH >
Specification