SELECTIVE DEPOLYMERISATION OF POLYAMIDE 6 TO PRODUCE CAPROLACTAM FROM MIXTURES OF CAPROLACTAM-CONTAINING POLYMERS AND POLYURETHANE-CONTAINING POLYMERS, IN PARTICULAR POLYURETHANE BLOCK COPOLYMERS

Abstract

A process for obtaining caprolactam from mixtures of caprolactam-containing polymers and polyurethane-containing polymers, in particular polyurethane block copolymers, by depolymerization, wherein the depolymerization of the mixture is performed in the presence of 0.05% to 5% by weight of a base at a temperature of 250? C. to 350? C. and a pressure of 5 to 700 mbar and wherein the caprolactam is obtained in gaseous form.

Claims

1.-13. (canceled)

14. A process for obtaining caprolactam from mixtures of caprolactam-containing polymers and polyurethane-containing polymers by depolymerization, wherein the depolymerization of the mixture is performed in the presence of 0.05% to 5% by weight of a base at a temperature of 250? C. to 350? C. and a pressure of 5 to 700 mbar and wherein the caprolactam is obtained in gaseous form.

15. The process according to claim 14, wherein the depolymerization of the mixture is performed in the presence of 0.05% to 3% by weight of a base.

16. The process according to claim 14, wherein the depolymerization is performed at a temperature of 270? C. to 350? C.

17. The process according to claim 14, wherein the depolymerization is performed at a pressure of 8 to 200 mbar.

18. The process according to claim 14, wherein the water content of the mixture during the depolymerization is not more than 5% by weight.

19. The process according to claim 14, wherein the base is a compound selected from the group consisting of alkali metal oxides, alkali metal hydroxides, and alkali metal carbonates.

20. The process according to claim 14, wherein the process is performed in a depolymerization reactor.

21. A process for obtaining caprolactam from a mixture of caprolactam-containing polymers with polyurethane-containing polymers by depolymerization, comprising the steps of: (A) heating the mixture to a temperature of 220? C. to 300? C. to obtain a melt (S), (B) adding a base before, during or after step (A), (C) charging the melt (S) into at least one depolymerization reactor, (D) heating the melt (S) to a temperature of 250? C. to 350? C. to obtain gaseous caprolactam (C), (E) discharging the gaseous caprolactam from the depolymerization reactor to leave behind a residue.

22. The process according to claim 21, wherein the water content of the mixture in step (C) is not more than 5% by weight.

23. The process according to claim 21, wherein the pressure in step (D) is 5 to 700 mbar.

24. A caprolactam produced by a process according to claim 14.

25. A method for producing polycaprolactam- and/or caprolactam-containing copolymers and/or polymer mixtures comprising the use of the caprolactam according to claim 24.

26. A method for producing fibers comprising the use of the caprolactam according to claim 24.

Description

EXAMPLES

Example 1 (According to the Invention)

[0092] Depolymerization of a PA6 (polyamide 6)/polyurethane block copolymer mixture:

[0093] An 80:20 PA6/polyurethane block copolymer mixture (textile from INDITEX/Nextil) (402 g) was admixed with 2% KOH (Bernd Kraft, ultrapure potassium hydroxide pellets) (8 g) and melted in a TCF 2.5 twin-screw kneader (LIST Technology AG, Switzerland). A vacuum of 80-100 mbar abs. was then established and at an internal temperature of 300? C. the PA6 in the mixture was depolymerized over 2.5 h. The caprolactam formed was withdrawn overhead in gaseous form and then condensed at 74? C. The resulting caprolactam melt was cooled to obtain solid caprolactam. 290 g of caprolactam (90% based on PA6 content of starting mixture) were obtained. The product was analyzed by gas chromatography and had a purity of 90% by weight.

Examples 2 and 3 (Comparative Examples)

[0094]

TABLE-US-00002 Example Starting material Caprolactam purity [% by wt.] 2 Ultramid B36 97 3 Ultramid B3WG6 (70% PA6) 95-97

[0095] Example 2 was carried out analogously to the inventive example. Ultramid B36 was used instead of the 80:20 PA6/polyurethane block copolymer mixture.

Example 3

[0096] In a twin-screw compounding extruder 15 kg/h of a mixture of Ultramid B3WG6 and 2% KOH (Bernd Kraft, ultrapure potassium hydroxide pellets) based on the total amount (200 g of KOH per 10 kg of Ultramid B3WG6) were melted at 245? C. and supplied to a CKR 25 C twin-screw kneader reactor with discharge screw (LIST Technology AG, Switzerland). At a temperature of 271? C. and a vacuum of 35 mbar absolute the obtained polyamide 6 was depolymerized (residence time about 1 h). The caprolactam formed was withdrawn overhead in gaseous form and then condensed at 89? C. The resulting caprolactam melt was cooled to obtain solid caprolactam. The inert constituents, KOH and residual amounts of polyamide 6 were conveyed continuously via a discharge screw into a collecting vessel which was likewise under vacuum. 9.68 kg/h of caprolactam (94% based on the PA6 content of the starting mixture) were obtained. The product was analyzed by gas chromatography and had a purity of 95-97% by weight.

Example 4 (Inventive)

[0097] Depolymerization of a PA6 (Polyamide 6)/Polyurethane Block Copolymer Mixture in a Continuous Process:

[0098] In a twin-screw compounding extruder 13 kg/h of a mixture of a PA6/spandex mixture (80:20) and 2% KOH (Bernd Kraft, ultrapure potassium hydroxide pellets) based on the total amount (200 g of KOH per 10 kg of PA6/spandex) were melted at 245? C. and supplied to a CKR 25 C twin-screw kneader reactor with discharge screw (LIST Technology AG, Switzerland).

[0099] At a temperature of 300? C. and a vacuum of 60 mbar absolute the obtained polyamide 6 was depolymerized (residence time about 1 h). The caprolactam formed was withdrawn overhead in gaseous form and then condensed at 130? C. The resulting caprolactam melt was cooled to obtain solid caprolactam. The remaining constituents, KOH and residual amounts of polyamide 6 were conveyed continuously out of the kneader reactor via a discharge screw into a collecting vessel which was likewise under vacuum. 9.4 kg/h of caprolactam (94% based on the PA6 content of the starting mixture) were obtained. The product was analyzed by gas chromatography and had a purity of 87-88% by weight.