Method and apparatus for making aqueous chlorine dioxide

A process for producing chloride dioxide, comprising the steps of:

• A providing an aqueous acid solution comprising
• 1 a hydroxy carboxylic acid that is capable of temporarily transferring chlorine from an alkali metal salt of chlorite ion, but substantially does not form a salt with an alkali metal salt of a chlorite ion, and
• 2a companion acid that substantially does not react with an alkali metal salt chlorite ion;
• B combining, in a vessel, (i) an alkali metal salt of a chlorite ion, and (ii) said aqueous acid solution, to yield an aqueous reaction solution;
• wherein chlorite ions are produced in said aqueous reaction solution, and said chlorite ions react with said hydroxy carboxylic acid present therein to yield an aqueous product solution that comprises chlorine dioxide but is substantially free of chlorous acid, and wherein a sufficient amount of companion acid is provided in A to maintain the pH of the aqueous reaction solution at a value of .ltoreq.4;
• and
• C withdrawing at least a portion of the chlorine dioxide from the aqueous product solution and separating chlorine dioxide present in said product solution from the remaining components in said product solution.

A process for producing chlorine dioxide, comprising the steps of:

• A providing an aqueous acid solution comprising
• 1 a hydroxy carboxylic acid that is capable of temporarily transferring chlorine from an alkali metal salt of chlorite ion, but substantially does not form a salt with an alkali metal salt of a chlorite ion, and
• 2 a companion acid that substantially does not react with an alkali metal salt of a chlorite ion;
• B combining, in a vessel, (i) an alkali metal salt of a chlorite ion, and (ii) said aqueous acid solution to yield an aqueous reaction solution;
• C maintaining pH of the aqueous reaction solution at a value of .ltoreq.4 during the reaction of (i) and (ii) by,
• 1flowing inert gas through said aqueous acid solution comprising said hydroxy carboxylic acid and said companion acid, wherein a portion of either or both acids is entrained to yield an acid gas that comprises said inert gas and acid, and
• 2 flowing said acid gas into the aqueous reaction solution, so that at least a portion of the acid in said acid gas is absorbed into the aqueous reaction solution;
• D maintaining the temperature of the vessel contents within the range of from about 20.degree. C. to about 60.degree. C.,
• wherein chlorite ions are produced in said aqueous reaction solution, and said chlorite ions react with said hydroxy carboxylic acid present therein to yield an aqueous product solution that comprises chlorine dioxide but is substantially free of chlorous acid, and
• E flowing an inert gas through at least a portion of said product solution which has been removed from said vessel, wherein at least a portion of the chlorine dioxide in said product solution is entrained in said inert gas to yield a product gas comprising inert gas and chlorine dioxide and
• F flowing the product gas into a trap comprising an aqueous liquid to separate at least a portion of the chlorine dioxide from the inert gas, thereby yielding an aqueous chlorine dioxide solution.

A process for the continuous production of chlorine dioxide, comprising the steps of:

• A providing an aqueous acid solution comprising
• 1 a hydroxy carboxylic acid that is capable of temporarily transferring chlorine from an alkali metal salt of chlorite ion, but substantially does not form a salt with an alkali metal salt of a chlorite ion, and
• 2 a companion acid that substantially does not react with an alkali metal salt of a chlorite ion;
• B combining, in a vessel, (i) an alkali metal salt of a chlorite ion, and (ii) said aqueous acid solution to yield an aqueous reaction solution;
• C maintaining pH of the aqueous reaction solution at a value of .ltoreq.4 during the reaction of (i) and (ii);
• D maintaining the temperature of the vessel contents at from about 30.degree. C. to about 45 (degree sign),
• wherein chlorite ions are produced in said aqueous reaction solution, and said chlorite ions react with said hydroxy carboxylic acid present therein to yield an aqueous product solution that comprises chlorine dioxide but is substantially free of chlorous acid;
• E transferring at least a portion of the product solution into a chlorine dioxide stripper in which inert gas is passed into intimate contact with acid product solution, thereby yielding a product gas comprising said inert gas and entrained chlorine dioxide, wherein said product gas also may contain unreacted hydroxy carboxylic acid and/or companion acid;
• F optionally flowing the product gas into a condenser to condense any unreacted hydroxy carboxylic acid and/or companion acid present therein;
• G flowing the product gas, optionally received from the condenser, into a chlorine dioxide absorber, wherein the product gas is contacted with an aqueous liquid to yield an aqueous chlorine dioxide solution and a scrubbed inert gas.