Chlorine dioxide is generated by electrochemical oxidation of sodium chlorite in an anode compartment of a cation-exchange membrane-divided cell and is recovered in a suitable recipient medium by passing the chlorine dioxide through a hydrophobic microporous membrane. Water balance in a continuous operation is maintained by removing water from the anolyte by transporting the same partly across the hydrophobic microporous membrane in vapor form and partly across the cation-exchange membrane.

Chlorine dioxide generation for water treatment

An improved electrolytic process and apparatus are disclosed for oxidizing or reducing inorganic and organic species, especially in dilute aqueous solutions. The electrolytic reactor (100) includes an anode (101), a cathode (102) and a monobed of cation exchange material (116) in contact with the anode (101) as the primary electrode for oxidation and anion exchange material in contact with the cathode (102) as the primary electrode for reduction. The monobed (116) includes both modified ion exchange material, modified to have active semiconductor junctions to enhance the oxidation or reduction, and unmodified ion exchange material to enhance diffusion of the ions through the monobed. The monobed may be divided into segments including one or more particulate ion exchange resin segments (108, 110) and one or more ion exchange membrane segments (104, 106).

Electrolytic process and apparatus for the controlled oxidation and reduction of inorganic and organic species in aqueous solutions

There are provided methods for preparing lithium hydroxide. For example, such methods can comprise submitting an aqueous composition comprising a lithium compound to an electrolysis under conditions suitable for converting at least a portion of said lithium compound into lithium hydroxide.

Processes for preparing lithium hydroxide

There are provided methods for preparing lithium carbonate. For example, such methods can comprise reacting an aqueous composition comprising lithium hydroxide with CO2 by sparging the CO2 the said composition, thereby obtaining a precipitate comprising the lithium carbonate. The methods can also comprise inserting at least a portion of the precipitate into a clarifier and obtaining a supernatant comprising lithium bicarbonate and a solid comprising the lithium carbonate, separating the solid from the supernatant; and heating the supernatant at a desired temperature so as to at least partially convert the lithium bicarbonate into lithium carbonate.

Processes for preparing lithium carbonate

Chlorous acid is generated from a chlorite salt precursor, a chlorate salt precursor, or a combination of both by ion exchange. The ion exchange material facilitates the generation of chlorous acid by simultaneously removing unwanted cations from solution and adding hydrogen ion to solution. Chlorine dioxide is generated in a controlled manner from chlorous acid by catalysis. Chlorine dioxide can be generated either subsequent to the generation of chlorous acid or simultaneously with the generation of chlorous acid. For catalysis of chlorous acid to chlorine dioxide, the chlorous acid may be generated by ion exchange or in a conventional manner. Ion exchange materials are also used to purify the chlorous acid and chlorine dioxide solutions, without causing degradation of said solutions, to exchange undesirable ions in the chlorous acid and chlorine dioxide solutions with desirable ions, such as stabilizing ions, and to adjust the pH of chlorous acid and chlorine dioxide solutions.

Methods for making chlorous acid and chlorine dioxide

The formation of sodium sulfate by-product in sulfuric acid-based chlorine dioxide generating processes is decreased and preferably eliminated entirely, by effecting electrochemical treatment of sodium ion-containing feed materials for the generator to remove sodium ions and to add hydrogen ions. Sodium hydroxide may be produced as a by-product. The process is generally applicable to the electrochemical treatment of alkali metal chlorates, alkali metal sulfates and mixtures thereof to produce acidified solutions useful in providing chlorate ion-containing feeds to such chlorine dioxide generating processes or for other purposes.

Electrochemical processing of aqueous solutions

A greater yield of chlorine dioxide from a chlorine dioxide generating process is obtained by providing acidic or acidity-generating components in the product chlorine dioxide solution to provide a chlorine dioxide solution having a pH below about 5.5.

Method of improving yield of chlorine dioxide generation processes

Chlorine dioxide is formed by reduction of sodium chlorate in a sulphuric acid-containing reaction medium. Sulphuric acid is introduced to the reaction medium in air atomized form to promote rapid and efficient mixing of the sulphuric acid, thereby avoiding chlorine dioxide decomposition at hot spots resulting from inefficient mixing of acid with the reaction medium.

Acid introduction in chlorine dioxide production

Chlorine dioxide is produced at high efficiency in a continuous process effected using hydrogen peroxide as the reducing agent in a single vessel generator-evaporator-crystallizer at the boiling point of the reaction medium under sub-atmospheric pressure. The reaction medium is maintained under steady state continuous operation with a residual chlorine concentration while having no residual hydrogen peroxide concentration in the reaction medium.

Hydrogen peroxide-based chlorine dioxide generation process

Chlorine dioxide is produced at high efficiency by reduction of sodium chlorate with methanol in an aqueous acid reaction medium at a total acid normality below 7 with the reaction medium being at its boiling point while a subatmospheric pressure is applied thereto and having a chlorate concentration of at least about 20 molar By employing such conditions, the tendency is eliminated for the reaction to be subject to white-outs in the absence of added chloride ion In this way, the chlorine content of product aqueous chlorine dioxide solution arising from this source is eliminated

Bechberger Edward J

Papers

Electrochemical processing of aqueous solutions

Method of improving yield of chlorine dioxide generation processes

Acid introduction in chlorine dioxide production

Hydrogen peroxide-based chlorine dioxide generation process

Methanol-based chlorine dioxide process