Process for preparing fluorocarboxylic acids

1. A process for preparing fluorocarboxylic acid in which acidification reaction treatment and washing treatment are continuously carried out, the process comprising:

subjecting a fluorocarboxylate-containing aqueous solution to acidification reaction treatment in the presence of sulfuric acid so as to form a sulfate-containing fluorocarboxylic acid phase; and

subjecting the fluorocarboxylic acid phase to washing treatment using an aqueous sulfuric acid solution,

wherein said acidification and said washing are carried out at a temperature at which said fluorocarboxylic acid is a liquid.

2. The process of claim 1 , wherein the fluorocarboxylate has the general formula

X—RfCOOM

in which X is a hydrogen atom, a fluorine atom or a chlorine atom; M is a monovalent alkali metal or ammonium ion; and Rf is a linear or branched fluoroalkyl group of 4 to 14 carbons.

3. The process of claim 1 , wherein the fluorocarboxylate has the general formula

X—(CF 2 ) m —O—(CF(CF 3 )CF 2 O) n —CF(CF 3 )COOM

in which X is a hydrogen atom, a fluorine atom or a chlorine atom; m is an integer from 1 to 10; n is an integer from 0 to 5; and M is a monovalent alkali metal or ammonium ion.

4. The process of claim 1 , which comprises maintaining an aqueous phase that is present in acidification reaction treatment at a sulfuric acid concentration of about 2 to 95 wt %.

5. The process of claim 1 , which comprises carrying out the washing treatment in a liquid-liquid heterophase dispersed system composed of an aqueous phase and an organic phase, and maintaining the aqueous phase at a sulfuric acid concentration of about 2 to 95 wt %.

6. The process of claim 5 , which comprises continuously carrying out the washing treatment by countercurrent contact between the organic phase and the aqueous phase.

7. The process of claim 1 , which comprises continuously carrying out the acidification reaction treatment and washing treatment, using a differential contacting extraction column, by feeding the fluorocarboxylate-containing aqueous solution and the aqueous sulfuric acid solution to the extraction column so that they flow countercurrent to each other.

8. The process of claim 7 , wherein the extraction column is a Karr column.

9. The process of claim 1 , wherein the fluorocarboxylate comprises C 7 F 15 COONa.

10. The process of claim 1 , wherein the fluorocarboxylate comprises C 7 F 15 COONH 4 .

11. The process of claim 1 , wherein M is selected from the group consisting of sodium, potassium and ammonium ion.

12. A process for preparing fluorocarboxylic acid in which acidification reaction treatment and washing treatment are carried out, the process comprising:

subjecting a fluorocarboxylate-containing aqueous solution to acidification reaction treatment in the presence of sulfuric acid so as to form a sulfate-containing fluorocarboxylic acid phase; and

subjecting the fluorocarboxylic acid phase to washing treatment using an aqueous sulfuric acid solution,

wherein said acidification and said washing are carried out at a temperature at which said fluorocarboxylic acid is a liquid, and at least one of said acidification reaction treatment and washing treatment is carried out batchwise.

13. A process for preparing fluorocarboxylic acid in which acidification reaction treatment and washing treatment are carried out, the process comprising:

subjecting a fluorocarboxylate-containing aqueous solution to acidification reaction treatment in the presence of sulfuric acid so as to form a sulfate-containing fluorocarboxylic acid phase; and

subjecting the fluorocarboxylic acid phase to washing treatment using an aqueous sulfuric acid solution,

wherein said acidification and said washing are carried out at a temperature at which said fluorocarboxylic acid is a liquid, and at least one of said acidification reaction treatment and washing treatment is carried out continuously.