Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing inorganic compound
Reexamination Certificate
1998-10-16
2001-03-20
Phasge, Arun S. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing inorganic compound
C205S510000
Reexamination Certificate
active
06203688
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is concerned with the electrolytic production of chlorine dioxide from chlorite ions. More particularly, the present invention relates to the electrochemical process and the electrolytic cell structure used to manufacture a high purity aqueous chlorine dioxide solution from a dilute aqueous alkali metal chlorite solution.
2. Description of the Art
It is known to produce chlorine dioxide electrolytically by the electro-oxidation of chlorite ions.
U.S. Pat. No. 2,163,793 describes an electrochemical chlorine dioxide generating process in which an aqueous solution of alkali metal chlorite and alkali metal chloride is electrolyzed in an electrolytic cell equipped with a porous diaphragm separating the anode and the cathode compartments.
British Patent No. 714,828 describes a process for the production of chlorine dioxide by electrolyzing an aqueous solution containing chlorite and a water-soluble salt of an inorganic oxy-acid other than sulfuric acid.
U.S. Pat. No. 2,717,237 discloses a method for producing chlorine dioxide by electrolysis of chlorite in the presence of a water-soluble alkali metal sulfate (e.g., sodium sulfate).
Japanese Patent Publication 81-158883, published Dec. 7, 1981, describes an electrolytic process for producing chlorine dioxide by electrolysis of chlorite in which the electrolyzed solution, at a pH of 2 or less, is fed to a stripping tank where air is introduced to recover the chlorine dioxide.
U.S. Pat. No. 4,542,008 describes an electrolytic process for chlorine dioxide production in which the sodium chlorite concentration of the solution leaving the anode compartment is measured by means of a photometric cell.
Published PCT International Patent Application WO 91/09158 and the corresponding U.S. Pat. No. 5,106,465 disclose a method of producing chlorine dioxide from alkali metal chlorite in an ion exchange compartment of a multi-compartment cell in which hydrogen ions generated in the anode compartment enter the ion exchange compartment through a cation exchange membrane, causing chlorite ion decomposition and forming chlorine dioxide.
PCT Published International Patent Application WO 94/26670 discloses a method of producing chlorine dioxide from sodium chlorite in which the gaseous product along with the water vapor is removed from the electrolyzed solution by means of a microporous, hydrophobic gas membrane. By removing water at the rate of its input to the anolyte, a continuous, environmentally innocuous operation with no undesired effluent can be effected.
While all the above mentioned patents and patent applications require the recirculation of the electrolyzed solution, PCT Published International Patent Application WO 91/09990 and its related U.S. Pat. Nos. (5,041,196, 5,084,149, 5,158,658, 5,298,280 and 5,294,319) teach an electrochemical process for producing chlorine dioxide from a dilute alkali metal chlorite solution in a single pass mode (i.e., with no recirculation of the anolyte) using a porous, high surface area anode. The product solution, in addition to chlorine dioxide, may also contain unconverted chlorite as well as undesired by-products, resulting from inefficiencies, such as chlorate or chloride ions.
The relative simplicity of the concept disclosed in WO 91/09990 and its related U.S. Patents makes it economically attractive. However, the presence of unconverted chlorite and undesired by-products in the product stream may preclude its use in many applications.
Therefore, there is a need for a chlorine dioxide generation process based on single pass mode with no recirculation of the anolyte wherein there is a high efficiency conversion of chlorite ions to chlorine dioxide per pass while minimizing the formation of undesired by-products.
BRIEF SUMMARY OF INVENTION
Surprisingly, it has been found that the combination of (1) using an electrochemical acidification cell to lower the pH value of the aqueous alkali metal chlorite feed to an optimum value before it enters the anode compartment of an electrochemical oxidation cell where the chlorite is converted to chlorine dioxide with (2) using an improved anolyte flow pattern in the electrochemical oxidation cell where the anolyte passes through a porous, high surface area electrode results in a substantially improved conversion efficiency per pass.
Accordingly, one aspect of the present invention is directed to a process for converting an aqueous, alkaline pH alkali metal chlorite solution to an aqueous chlorine dioxide-containing solution by:
(1) passing an aqueous, alkaline pH alkali metal chlorite solution through an electrochemical acidification cell having low surface area anode to produce an aqueous alkali metal chlorite solution having a pH less than 7; and then
(2) passing the aqueous alkali metal chlorite solution with the pH less than 7 through a porous, high surface area electrode in the anode compartment of an electrochemical oxidation cell to convert at least a portion of said alkali metal chlorite to chlorine dioxide and to produce an aqueous chlorine dioxide-containing solution.
In one particular preferred embodiment, the anode compartment of the electrochemical oxidation cell has a flow gap region between the porous high surface area electrode and the separator means (e.g., a membrane) that separates the anode compartment from the cathode compartment. The acidified alkali metal chlorite solution enters the anode compartment through the flow gap region and flows through the porous, high surface area anode, and exits the anode compartment on the backside of the anode and out the anode compartment.
In another preferred embodiment, the porous high surface anode occupies substantially all of the anode compartment and the acidified alkali metal chlorite enters the bottom of the anode compartment and passes upwardly through the porous high surface area anode and exits at the top of the anode compartment.
In another preferred embodiment of the present invention, the aqueous chlorine dioxide-containing solution is passed through a chlorine dioxide stripper or removal apparatus (e.g., a membrane based separation unit) to separate chlorine dioxide gas from the aqueous solution.
REFERENCES:
patent: 2163793 (1939-06-01), Logan
patent: 2717237 (1955-09-01), Rempel
patent: 4542008 (1985-09-01), Capuano et al.
patent: 4683039 (1987-07-01), Twardowski et al.
patent: 5041196 (1991-08-01), Cawlfield et al.
patent: 5084149 (1992-01-01), Kaczur et al.
patent: 5106465 (1992-04-01), Kaczur et al.
patent: 5158658 (1992-10-01), Cawlfield et al.
patent: 5294319 (1994-03-01), Kaczur et al.
patent: 5298280 (1994-03-01), Kaczur et al.
patent: 2182127 (1996-07-01), None
patent: 714828 (1954-09-01), None
patent: 56-158883 (1981-12-01), None
patent: 91/09158 (1991-06-01), None
patent: WO 91/09990 (1991-07-01), None
patent: WO 94/26670 (1994-11-01), None
The Chlorine Dioxide Handbook—Water Disinfection Series,—Donald F. Gates, pp. 86-87, No Date Available.
Kirk-Othmer—Encyclopedia of Chemical Technology—Fourth Ed. vol. 5, Carbon and Graphite Fibers to Chlorocarbons and Chlorohydrocarbons-C1—p. 986. No Date Available.
Cowley Gerald
Kaczur Jerry J.
Lipsztajn Marek
Phasge Arun S,.
Sim & McBurney
Sterling Pulp Chemicals, Ltd.
LandOfFree
Electrolytic process for producing chlorine dioxide does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrolytic process for producing chlorine dioxide, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrolytic process for producing chlorine dioxide will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2512824