# US 8,541,540 B2 · Continuous process for the extraction of polyamide-6

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- Number: US 8,541,540 B2
- Document ID: US8541540B2
- Status: Granted
- Kind: B2
- Application number: 12/542,743
- Filed: 2009-08-18
- Published: 2010-02-25
- Granted: 2013-09-24
- Earliest claimed: 2008-08-19
- Assignees: Lurgi Zimmer GmbH
- Applicants: Klaus Kirsten; Manfred Albrecht; Franz Samlitschka
- Inventors: Klaus Kirsten; Manfred Albrecht; Franz Samlitschka
- Web page: https://patentgrep.com/patent/US8541540B2

## CPC

- C08G 69/14: Lactams
- B01D 11/0288: {Applications, solvents}
- B29B 9/065: {under-water, e.g. underwater pelletizers}
- C07D 201/16: Separation or purification
- C07D 223/10: attached in position 2
- C08G 69/16: Preparatory processes
- C08G 69/46: Post-polymerisation treatment
- C08J 3/12: Powdering or granulating
- B29K 2077/00: Use of {PA, i.e.} polyamides, e.g. polyesteramides {or derivatives thereof}, as moulding material
- C08J 2377/02: Polyamides derived from omega-amino carboxylic acids or from lactams thereof (C08J2377/10 takes precedence)
- Y02P 20/582: Recycling of unreacted starting or intermediate materials
- C08G: MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- B01D: SEPARATION (separating solids from solids by wet methods B03B, B03D; by pneumatic jigs or tables B03B; by other dry methods B07; magnetic or electrostatic separation of solid materials from solid materials or fluids, separation by high-voltage electric fields B03C; centrifuges, vortex apparatus B04; presses per se for squeezing-out liquid from liquid-containing material B30B9/02; treatment of water C02F, e.g. softening by ion-exchange C02F1/42; {arrangements of air intake cleaners in gas turbine plants F02C7/05} ; arrangements or mounting of filters in air-conditioning, air-humidification or ventilation F24F13/28)
- B29B: PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
- C07D: HETEROCYCLIC COMPOUNDS (macromolecular compounds C08)
- C08J: WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H (working, e.g. shaping, of plastics B29)
- B29K: INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR {MOULDS, } REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

A continuous process is disclosed for the extraction of monomeric caprolactam and its oligomers as the raw polymer product obtained in the polymerization of polyamide-6 in which no fresh water, but processing water or previously used extraction water is used for the granulation.

## Claims

### Claim 1

A continuous process for preparing polyamide-6 from caprolactam, which comprises the steps of:
(a) polymerizing caprolactam at elevated temperature to obtain a polymer melt mixture of polyamide-6, caprolactam, and oligomers of caprolactam;
(b) granulating the polymer melt mixture of polyamide-6, caprolactam, and oligomers of caprolactam to obtain chips of polyamide-6 that also contain caprolactam and oligomers of caprolactam;
(c) following step (b), extracting from the chips of polyamide-6, the extractable caprolactam and oligomers of caprolactam, using a stream of extraction water having at most 15% by weight of caprolactam monomers or oligomers to obtain a wet polyamide-6 product containing about 10% water by weight, a stream of extract water rich in extractable caprolactam and oligomers of caprolactam, and a first stream of recycled circulating water containing a low amount of caprolactam and caprolactam oligomers relative to the stream of extract water, and passing the first stream of recycled circulating water containing a low amount of caprolactam and caprolactam oligomers from the extraction to the granulation of step (b), whereby passing the first stream of recycled circulating water containing the low amount of caprolactam and caprolactam oligomers, as a sole source of water for the granulation, avoids any need to add fresh water to the granulation, avoids any need to evaporate said water to recover the polyamide-6, the extractable caprolactam and the oligomers of caprolactam and serves to pre-extract caprolactam and oligomers of caprolactam from the polymer melt following step (a); and
(d) following the granulation of step (b) removing a second stream of recycled circulating water containing a higher amount of caprolactam and caprolactam oligomers in the range of 4 to 6%, relative to the low amount in the first stream of recycled circulating water, and passing the second stream of recycled circulating water from the granulation to the extraction.

### Claim 2 (depends on 1)

The process defined in claim 1, wherein according to step (c), the first stream of recycled circulating water containing the low amount of caprolactam and caprolactam oligomers contains about 1 to 2% by weight of caprolactam and caprolactam oligomers.

### Claim 3 (depends on 1)

The process defined in claim 1, wherein according to step (c), the first stream of recycled circulating water containing the low amount of caprolactam and caprolactam oligomers contains less than 1% by weight of caprolactam and caprolactam oligomers.

### Claim 4 (depends on 1)

The process defined in claim 1, wherein following step (c) the wet polyamide-6 product containing about 10% water by weight is dried to produce a dry polyamide-6 and a condensate.

### Claim 5 (depends on 1)

The process defined in claim 1 wherein following step (c) the stream of extract water rich in extractable caprolactam and oligomers of caprolactam has a concentration of caprolactam and oligomers of caprolactam of about 4 to 15% by weight.

### Claim 6 (depends on 5)

The process defined in claim 5 wherein the stream of extract water rich in extractable caprolactam and oligomers of caprolactam has a concentration of caprolactam and oligomers of caprolactam of about 10% by weight.

### Claim 7 (depends on 5)

The process defined in claim 5 wherein following step (c) the stream of extract water rich in extractable caprolactam and oligomers of caprolactam is channeled to a caprolactam recovery process for separating caprolactam from water by evaporation at 103 to 115° C., the recovered caprolactam is concentrated to a range of 60 to 85% by weight and returned to the polymerization of step (a).

### Claim 8 (depends on 1)

The process defined in claim 1 wherein according to step (c) the first stream of recycled circulating water containing a low amount of caprolactam and caprolactam oligomers, relative to the stream of extract water, has an extract content of approximately 1 to 2%.