Low energy chlorate electrolytic cell and process

Inactive Publication Date: 2005-01-20
JACKSON JOHN R +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0010] In the electrolysis process of the invention, electrolytic cells having as a cell separator a low transport efficiency alkali metal ion permselective membrane or an hydrophilic, microporous diaphragm are used for the production of an alkali metal chlorate. In order to provide a process with greater electrical efficiency, the uncatalyzed mild steel or titanium cathodes utilized in commercial, prior art cells for the production of an alkali metal chlorate are replaced in the cells of the invention with either catalytic, metal cathodes or gas-diffusion cathodes, which are depolarized by feeding air or oxygen to the cathode. To utilize such cathodes without cathode corrosion, the anolyte and catholyte compartments must be separated by a microporous diaphragm or a low transport efficiency alkali metal ion permselective cationic membrane. The electrolysis process of the invention can be carried out with essentially no losses of chlorine, produced in the process, and, in the absence of hexavalent chromium values, derived from the addition of sodium chromate or sodium bichromate to the electrolyte, thus providing economic as well as environmental advantages. The use of a hydrophilic, microporous diaphragm in the electrolysis process of the invention req

Problems solved by technology

The use of hexavalent chromium in the electrolyte is disadvantageous economically as well as environmentally, as set forth in U.S. Pat. No. 5,104,499 to Millet and U.S. Pat. No. 4,295,951 to Bommaraju et al.
Because of the presence of the highly oxidizing hypochlorite ions in the electrolyte solution, activated cathode

Method used

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Examples

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examples 1-4

Forming No Part of this Invention

[0027] In order to demonstrate the reduced power usage that can be expected where a precious metal oxide coated cathode is substituted for the titanium or mild steel cathodes presently utilized in commercial sodium chlorate electrolysis cells, a comparison was made of these cathodes as well as an oxygen reduction cathode by measuring the single electrode potential of these cathode materials against a saturated calomel reference electrode. The conditions for measuring the single electrode potentials of these cathode materials were as follows: Sodium hydroxide electrolyte—one molar, current density—one amp per square inch, temperature—30 to 40 degrees centigrade. Where an oxygen reduction cathode was used, pure oxygen was fed to the cathode. Cathodes of titanium and mild steel, represent commercial cathodes utilized for the production of sodium chlorate. The precious metal oxide coated cathode was a mixture of platinum and ruthenium oxides thermally d...

example 5

[0036] A pilot plant size plate and frame type electrolytic cell electrolysis process for the production of sodium chlorate is described in which the anode and cathode compartments are separated by a microporous diaphragm.

[0037] The anode used in the cell was a platinum-iridium oxide coated titanium expanded mesh substrate. The activated cathode was a platinum-ruthenium oxide coated nickel expanded mesh substrate. The electrode size was 3 inches by 10 inches providing a total of 30 square inches of active surface area. The microporous diaphragm utilized to separate the anolyte and catholyte compartments of the cell was a hydrophilic polyvinylidene fluoride sheet sold under the trademark Duropore® by the Millipore Corporation. This diaphragm had a pore diameter of about 0.1 micron, a thickness of 110 plus or minus 30 microns, and a porosity of 70%.

[0038] During the operation of the cell, the current input was measured at 35 amps or 1.17 amps per square inch current density. The tem...

example 6

[0041] Example 5 was repeated, except that in the process, using a plate and frame type electrolytic cell, an hydrophilic, polytetrafluoroethylene, microporous diaphragm sold under the trademark Advantec® by Advantec MSF, Inc. was used to separate the anode and cathode compartments of the cell.

[0042] The same cathode and anode as those described in Example 5 were used. The diaphragm pore diameter was 0.1 micron, the thickness was 25 plus or minus 1 microns, and the porosity was 71%. The current input was 35 amps or 1.17 amps per square inch current density. The temperature of both the anolyte and catholyte solutions was maintained at about 65 degrees centigrade by steam heat exchangers. The differential hydraulic pressure from the catholyte to the anolyte compartment was maintained at 4 inches of water.

[0043] In the process, purified brine was first acidified to a pH of about 3.5 to remove carbonate ions before being fed, at a rate of about 1.56 milliliters per minute, to the cath...

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Abstract

Alkali metal chlorates are produced by electrolyzing an anolyte contained in an anode compartment of an electrolytic cell, the anode and cathode compartments separated by means of a permselective membrane having low alkali metal ion transport efficiency. The final chlorate product can be directly crystallized from the electrolyzed anolyte or fed directly to a chlorine dioxide generator. Alternatively, a microporous, hydrophilic diaphragm can be substituted for the permselective membrane provided that the catholyte compartment is maintained at a higher hydraulic pressure than the hydraulic pressure in the anolyte compartment.

Description

BACKGROUND OF THE INVENTION [0001] (1) Field of the Invention [0002] This invention relates to an electrolytic cell, a low transport efficiency alkali metal ion permselective membrane, and a cyclic electrolysis process for the preparation of an alkali metal chlorate in an aqueous medium from the corresponding alkali metal chloride. [0003] (2) Description of Related Art [0004] It is known in this art to form sodium chlorate by the electrolysis of sodium chloride using a sodium chlorate electrolyte which is a mixture of sodium chloride and sodium chlorate at concentrations close to the saturation point. In the prior art commercial process, an electrolytic cell is used in which the anode and cathode are exposed to the same electrolyte; the cell not being divided into cathode and anode compartments by a porous barrier, diaphragm, or membrane. At the anode in such a cell, chlorine is evolved and at the cathode, hydrogen is evolved. Hydrogen produced at the cathode and chlorine produced a...

Claims

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Application Information

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IPC IPC(8): C25B1/26C25B13/04C25B13/08
CPCC25B1/265C25B13/08C25B13/04
Inventor JACKSON, JOHN R.ZHAO, MINGCHUAN
Owner JACKSON JOHN R
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