# US 6,720,437 B2 · Fluorinated carboxylic acid recovery and reuse

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- Number: US 6,720,437 B2
- Document ID: US6720437B2
- Status: Granted
- Kind: B2
- Application number: 10/060,995
- Filed: 2002-01-30
- Published: 2002-10-17
- Granted: 2004-04-13
- Earliest claimed: 2001-02-07
- Assignees: E. I. Du Pont de Nemours and Company
- Inventors: Clay Woodward Jones; Ta-Wei Fu
- Web page: https://patentgrep.com/patent/US6720437B2

## CPC

- C07C 51/42: Separation; Purification; Stabilisation; Use of additives
- C07C: ACYCLIC OR CARBOCYCLIC COMPOUNDS

## Abstract

Fluorinated carboxylic acid, used as a surfactant in fluoropolymerization in aqueous media, can be recovered by scrubbing from the exhaust gas of the dryer during polymer drying and, after concentration and treatment with alumina, directly reused in fluoropolymerization in aqueous media.

## Claims

### Claim 1

A process for the recovery and recycle of fluorinated carboxylic acid contained in the exhaust gas produced from the drying of fluoropolymer that has been polymerized in aqueous media containing fluorinated carboxylic acid comprising:
a) scrubbing the exhaust gas to produce a scrubber solution containing fluorinated carboxylic acid,
b) concentrating said scrubber solution to produce a concentrated scrubber solution,
c) contacting the concentrated scrubber solution with alumina to produce a recovered fluorinated carboxylic acid solution, and
d) directly reusing said recovered fluorinated carboxylic acid solution in a fluoropolymerization in aqueous dispersion.

### Claim 2 (depends on 1)

The process of claim 1 wherein said fluorinated carboxylic acid is a perfluorinated carboxylic acid.

### Claim 3 (depends on 1)

The process of claim 1 wherein said fluorinated carboxylic acid is perfluorooctanoic acid.

### Claim 4 (depends on 1)

The process of claim 1 wherein said scrubbing produces a scrubber solution containing about 500 to about 5000 parts per million fluorinated carboxylic acid.

### Claim 5 (depends on 1)

The process of claim 1 wherein said concentrating produces a concentrated scrubber solution containing about 1 to about 35% by weight fluorinated carboxylic acid.

### Claim 6 (depends on 1)

The process of claim 1 wherein said recovered fluorinated carboxylic acid solution contains no more than about 30 parts per million fluoride ion.

### Claim 7 (depends on 1)

The process of claim 1 wherein the recovered fluorinated carboxylic acid solution has an APHA color below about 100.

### Claim 8 (depends on 1)

The process of claim 1 wherein the alumina has a surface area from about 100 m2/g to about 1000 m2/g.

### Claim 9 (depends on 1)

The process of claim 1 wherein the recovered fluorinated carboxylic acid solution has a pH of about 4 to about 9.