Method of concentrating alkali metal hydroxide in hybrid cells having cation selective membranes

Claim 2

A process for the production of alkali metal hydroxide and electrical energy which comprises: (a) introducing flow of an aqueous solution of at least one alkali metal hydroxide as anolyte through an anode compartment of at least one hybrid cell, the hybrid cell comprising a gas diffusion type anode having first and second surfaces, a membrane selectively permeable to cations and having first and second surfaces, and a gas diffusion type cathode having first and second surfaces, the first surface of said anode and the first surface of said membrane forming said anode compartment, the first surface of said cathode forming with said second surface of said membrane a cathode compartment; the formed anode compartment having an inlet and an outlet, and the formed cathode compartment having an inlet and an outlet, said anolyte flowing from the inlet to the outlet of said anode compartment (b) introducing flow of an aqueous fluid medium receptive to alkali metal ions as catholyte through said cathode compartment from the inlet to the outlet; (c) causing, by a flow of current through an external load between said cathode and said anode generated by oxidation of hydrogen supplied to the second surface of said gas diffusion type anode and generation of hydroxide ions by reduction of an oxygen-containing gas supplied to the second surface of the gas diffusion type cathode, alkali metal ions to selectively pass from the anolyte through said membrane to the catholyte in said cathode compartment to form, with cathode generated hydroxide ions, an aqueous solution of alkali metal hydroxide; (d) withdrawing from said cathode compartment the catholyte which is more concentrated in respect to alkali metal hydroxide than the aqueous media introduced to said cathode compartment; and (e) withdrawing from said anode compartment an aqueous solution depleted in alkali metal hydroxide.

Claim 3

A process as claimed in claim 1 in which the aqueous solution of alkali metal hydroxide introduced to said anode compartment is a solution comprising up to about 25 percent by weight alkali metal hydroxide.

Claim 4

A process as claimed in claim 2 in which the solution withdrawn from said anode compartment contains alkali metal hydroxide in a concentration above about 0.01 percent by weight.

Claim 5

A process as claimed in claim 1 in which the aqueous alkali metal hydroxide solution withdrawn from said cathode compartment contains alkali metal hydroxide in an amount up to about 50 percent by weight.

Claim 6

A process as claimed in claim 4 in which the aqueous solution of at least one alkali metal hydroxide introduced to said anode compartment is a solution comprising up to about 25 percent by weight alkali metal hydroxide.

Claim 7

A process as claimed in claim 1 in which the aqueous solution of at least one alkali metal hydroxide introduced to said anode compartment is a solution comprising up to about 25 percent by weight medium hydroxide.

Claim 8

A process as claimed in claim 6 in which the solution exiting the cathode compartment contains sodium hydroxide in a concentration up to about 50 percent by weight.

Claim 9

A process as claimed in claim 1 in which air flows over a second surface of the gas diffusion type cathode opposite said first surface in a quantity sufficient to remove water from the cathode to concentrate the solution of alkali hydroxide flowing through the cathode compartment.

Claim 10

A process as claimed in claim 1 in which the oxygen-containing gas is air.

Claim 11

A process as claimed in claim 1 in which the flow of anolyte from the inlet to the outlet of the anode compartment and the flow of catholyte from the inlet to the outlet of the cathode compartment are respectively substantially in one direction without appreciable mixing, back convection or diffusion of molecules and ions contained in said anolyte and catholyte.

Claim 12

A process for the production of sodium hydroxide from the aqueous effluent of a cathode compartment of a chloralkali cell and electrical energy which comprises: (a) introducing as anolyte flow of an aqueous effluent solution of at least one chloralkali cell, said solution comprising sodium hydroxide and sodium chloride as anolyte to an anode compartment of at least one hybrid cell, the hybrid cell comprising a gas diffusion type anode having first and second surfaces, a membrane permeable to sodium ions and having first and second surfaces, and a gas diffusion type cathode having first and second surfaces, the first surface of said anode and the first surface of said membrane forming the anode compartment, and the first surface of said gas diffusion type cathode forming with the second surface of said membrane a cathode compartment, the formed anode compartment, having and inlet and an outlet, and the formed cathode compartment, having an inlet and an outlet, said anolyte flowing from the inlet to the outlet of said anode compartment; (b) introducing flow of an aqueous fluid medium receptive to sodium ions as catholyte from the inlet to the outlet of said cathode compartment; (c) supplying an oxygen-containing gas to said second surface of said gas diffusion type cathode and hydrogen to the second surface of said gas diffusion type anode; (d) causing, by a flow of current through said chloralkali cell from said gas diffusion type cathode to said gas diffusion type anode of the hybrid cell and generated by oxidation of hydrogen at said gas diffusion type anode and generation of hydroxide ion by reduction of oxygen at said gas diffusion type cathode, sodium ions to selectively pass through said membrane to said cathode compartment to form with cathode generated hydroxide ions an aqueous solution of sodium hydroxide; (e) removing from said cathode compartment catholyte which is more concentrated in respect to sodium hydroxide than the solution introduced to said anode compartment; and (f) removing from said anode compartment an aqueous solution depleted in sodium hydroxide.

Claim 13

A process for the production of sodium hydroxide from the aqueous effluent of a cathode compartment of a chloralkali cell and electrical energy which comprises: (a) introducing as anolyte flow of an aqueous effluent solution of at least one chloralkali cell, said solution comprising sodium hydroxide and sodium chloride as anolyte to an anode compartment of at least one hybrid cell, the hybrid cell comprising a gas diffusion type anode having first and second surfaces, a membrane permeable to sodium ions and having first and second surfaces, and a gas diffusion type cathode having first and second surfaces, the first surface of said anode and the first surface of said membrane forming the anode compartment, and the first surface of said gas diffusion type cathode forming with the second surface of said membrane a cathode compartment, the formed anode compartment, having and inlet and an outlet, and the formed cathode compartment, having an inlet and an outlet, said anolyte flowing from the inlet to the outlet of said anode compartment; (b) introducing flow of an aqueous fluid medium receptive to sodium ions as catholyte from the inlet to the outlet of said cathode compartment; (c) supplying an oxygen-containing gas to said second surface of said gas diffusion type cathode and hydrogen to the second surface of said gas diffusion type anode; (d) causing, by a flow of current through said chloralkali cell from said gas diffusion type cathode to said gas diffusion type anode of the hybrid cell and generated by oxidation of hydrogen at said gas diffusion type anode and generation of hydroxide ion by reduction of oxygen at said gas diffusion type cathode, sodium ions to selectively pass through said membrane to said cathode compartment to form with cathode generated hydroxide ions an aqueous solution of sodium hydroxide; (e) removing from said cathode compartment catholyte which is more concentrated in respect to sodium hydroxide than the solution introduced to said anode compartment; and (f) removing from said anode compartment an aqueous solution depleted in sodium hydroxide.

Claim 14

A process as claimed in claim 11 in which air flows over said second surface of the cathode in a quantity sufficient to remove water from the cathode to concentrate the sodium hydroxide solution passing through the cathode compartment.

Claim 15

A process as claimed in claim 11 in which the aqueous effluent solution of the chloralkali cell introduced to said anode compartment is a solution comprising up to about 25 percent by weight sodium hydroxide and up to 15 percent by weight sodium chloride.

Claim 16

A process as claimed in claim 13 in which the solution withdrawn from said anode compartment contains sodium hydroxide in concentration above about 0.01 percent by weight.

Claim 17

A process as claimed in claim 13 in which the solution exiting the cathode compartment contains sodium hydroxide in a concentration up to about 50 percent by weight.

Claim 18

A process as claimed in claim 11 in which the aqueous effluent solution of the chloralkali cell introduced to said anode compartment comprises from about 10 to about 15 weight percent sodium hydroxide and up to about 15 weight percent sodium chloride.

Claim 19

A process as claimed in claim 16 in which the solution withdrawn from said anode compartment contains sodium hydroxide in concentration above about 0.01 percent by weight.

Claim 20

A process as claimed in claim 16 in which the solution exiting the cathode compartment contains sodium hydroxide in a concentration up to about 50 percent by weight.

Claim 21

A process as claimed in claim 11 in which the solution exiting the cathode compartment contains sodium hydroxide in a concentration up to about 50 percent by weight.

Claim 22

A process as claimed in claim 11 in which the hydrogen supplied to the anode is hydrogen generated by the chloroalkali cell.

Claim 23

A process as claimed in claim 11 in which the oxygen-containing gas is air.

Claim 24

A process as claimed in claim 11 in which the flow of anolyte from the inlet to the outlet of the anode compartment and the flow of catolyte from the inlet to the outlet of the cathode compartment are respectively substantially in one direction without appreciable mixing, back convection or diffusion of molecules and ions contained in said anolyte and catholyte.

Claim 25

A process for preparing a concentrated, substantially sodium chloride free, aqueous solution of sodium hydroxide from the aqueous effluent solution of the cathode compartment of a chloralkali cell, which effluent solution comprises sodium hydroxide and sodium chloride, and simultaneously producing electrical energy which comprises: (a) introducing said solution as anolyte flow to an anode compartment of a hybrid cell, the hybrid cell comprising a gas diffusion type anode having first and second surfaces, a membrane permeable to sodium ions and having first and second surfaces, and a gas diffusion type cathode having first and second surfaces, the first surface of said anode and the first surface of said membrane forming the anode compartment, the first surface of said gas diffusion type cathode, and the second surface of said membrane forming a cathode compartment, the formed anode compartment having an inlet and an outlet, and the formed cathode compartment, having an inlet and an outlet, said anolyte flowing from the inlet to the outlet of said anode compartment; (b) introducing flow of an aqueous fluid medium receptive to sodium ions as catholyte from the inlet to the outlet of said cathode compartment; (c) supplying air to the second surface of said gas diffusion type cathode in a quantity sufficient to remove water from the catholyte and hydrogen, generated by said chloralkali cell, to the second surface of said anode; (d) causing, by a flow of current through said chloralkali cell from said cathode to said gas diffusion type anode to the hybrid cell and generated by oxidation of hydrogen at said gas diffusion type anode and generation of hydroxide ion by reduction of oxygen from the air at said gas diffusion type cathode, sodium ions to selectively pass through said membrane to said cathode compartment to form with cathode generated hydroxide ions an aqueous solution of sodium hydroxide; (e) withdrawing from said cathode compartment catholyte which is more concentrated in respect to sodium hydroxide than the solution introduced to said anode compartment; and (f) removing from said anode compartment an aqueous solution depleted in sodium ions.

Claim 26

A process for preparing a concentrated, substantially sodium chloride free, aqueous solution of sodium hydroxide from the aqueous effluent solution of the cathode compartment of a chloralkali cell, which effluent solution comprises sodium hydroxide and sodium chloride, and simultaneously producing electrical energy which comprises: (a) introducing said solution as anolyte flow to an anode compartment of a hybrid cell, the hybrid cell comprising a gas diffusion type anode having first and second surfaces, a membrane permeable to sodium ions and having first and second surfaces, and a gas diffusion type cathode having first and second surfaces, the first surface of said anode and the first surface of said membrane forming the anode compartment, the first surface of said gas diffusion type cathode, and the second surface of said membrane forming a cathode compartment, the formed anode compartment having an inlet and an outlet, and the formed cathode compartment, having an inlet and an outlet, said anolyte flowing from the inlet to the outlet of said anode compartment; (b) introducing flow of an aqueous fluid medium receptive to sodium ions as catholyte from the inlet to the outlet of said cathode compartment; (c) supplying air to the second surface of said gas diffusion type cathode in a quantity sufficient to remove water from the catholyte and hydrogen, generated by said chloralkali cell, to the second surface of said anode; (d) causing, by a flow of current through said chloralkali cell from said cathode to said gas diffusion type anode to the hybrid cell and generated by oxidation of hydrogen at said gas diffusion type anode and generation of hydroxide ion by reduction of oxygen from the air at said gas diffusion type cathode, sodium ions to selectively pass through said membrane to said cathode compartment to form with cathode generated hydroxide ions an aqueous solution of sodium hydroxide; (e) withdrawing from said cathode compartment catholyte which is more concentrated in respect to sodium hydroxide than the solution introduced to said anode compartment; and (f) removing from said anode compartment an aqueous solution depleted in sodium ions.

Claim 27

A process as claimed in claim 23 in which the flow of anolyte from the inlet to the outlet of the anode compartment and the flow of catolyte from the inlet to the outlet of the cathode compartment are respectively substantially in one direction without appreciable mixing, back convection or diffusion of molecules and ions contained in said anolyte and catholyte.