# US 5,703,204 A · Method for reprocessing aqueous extract solutions obtained in the production of PA 6 or copolyamide

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- Number: US 5,703,204 A
- Document ID: US5703204A
- Status: Granted
- Kind: A
- Application number: 08/650,384
- Filed: 1996-05-20
- Granted: 1997-12-30
- Earliest claimed: 1995-05-31
- Assignees: Bayer Aktiengesellschaft
- Inventors: Andreas Gittinger; Claus Wulff; Heinrich Haupt; Karsten-Josef Idel
- Web page: https://patentgrep.com/patent/US5703204A

## CPC

- C08G 69/46: Post-polymerisation treatment
- C08G 69/16: Preparatory processes
- C08G 69/28: Preparatory processes
- C08G: MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS

## Abstract

The invention relates to a method for recycling (reprocessing) aqueous extract solutions obtained in the production of polyamides. The method for reprocessing the aqueous extract solutions obtained consists in that the aqueous extract solution is concentrated and polymerised, adding small amounts of dicarboxylic acid or polycarboxylic acid to the extract solution.

## Claims

### Claim 1

A method for reprocessing aqueous extract solutions obtained in the production of polyamide 6 or copolyamides containing not less than 70% by weight of repeating units derived from .epsilon.-caprolactam, which comprises obtaining and concentrating an aqueous extract solution, and adding 0.02 to 20 mmol of dicarboxylic acid or polycarboxylic acids per kg extract (dry matter) to the extract prior to, during or after concentration.

### Claim 2 (depends on 1)

A method as claimed in claim 1, further comprising polymerizing the aqueous extract solution, and wherein the dicarboxylic acid or polycarboxylic acids are added prior to, during or after concentration or during the, polymerization.

### Claim 3 (depends on 2)

The method according to claim 2, wherein additional polyamide-forming monomers are added for polymerization.

### Claim 4 (depends on 1)

A method according to claim 1, wherein 0.01 to 10 mmol of dicarboxylic or polycarboxylic acid are added.

### Claim 5 (depends on 1)

A method according to claim 1, wherein 1 to 6 mmol dicarboxylic or polycarboxylic acid are added.

### Claim 6 (depends on 1)

A method according to claim 1, wherein the dicarboxylic acids polycarboxylic acids are aliphatic or aromatic.

### Claim 7 (depends on 6)

A method according to claim 6, wherein the dicarboxylic or polycarboxylic acids are selected from C.sub.6 -C.sub.12 -alkyldicarboxylic acids, terephthalic acid, isophthalic acid and trimesic acid.

### Claim 8 (depends on 3)

A method according to claim 3, wherein the polyamide-forming monomers are lactams, aminocarboxylic acids or equimolar mixtures of diamines and dicarboxylic acids.

### Claim 9 (depends on 3)

A method according to claim 3, wherein 0 to 90 parts by weight of polyamide-forming monomers per 10 parts by weight of extract (dry matter) are added to the extract.

### Claim 10

In a process of reprocessing and polymerizing the aqueous extract solution from the production of polyamide 6 or copolyamides, the improvement which comprises increasing the rate of polymerization by addition of dicarboxylic acid or polycarboxylic acid to the extract.