PROCESS FOR THE RECOVERY OF EPSILON-CAPROLACTAM FROM NYLON 6-CONTAINING MULTI- COMPONENT MATERIAL

Abstract

The present invention provides an improved process for the recovery of -caprolactam from Nylon 6 comprising multi-component material, in particular multi-layered film. Further, the invention provides a plant configured to carry out the process of the invention, and the recovered e-caprolactam obtainable by the process of the invention that has a product carbon footprint of less than 2.5 kg CO.sub.2 equivalent per kg purified e-caprolactam (based on data originating from ecoinvent version 3.7.1; location: Europe).

Claims

1. A process for recovering purified -caprolactam derived from a Nylon 6-containing multi-component material in an industrial scale plant with a production capacity for -caprolactam of at least 500 tons/year if operated all the time, wherein the plant comprises a Nylon 6-depolymerization section comprising one or more depolymerization reactors that are operated in at least one of series and parallel, a recovery section comprising one or more condensers, and a purification section comprising one or more pieces of extraction equipment, one or more pieces of solvent switch equipment, and one or more pieces of distillation equipment, and wherein the process comprises the steps of: a) providing a pre-concentrated Nylon 6-containing material that has been obtained by extracting a Nylon 6-containing multi-component material with one or more organic solvents to obtain a solid pre-concentrated Nylon 6-containing material, which is enriched in Nylon 6 as compared to the Nylon 6-containing multi-component material; b) depolymerizing the pre-concentrated Nylon 6-containing material in the depolymerization section in the presence of water to obtain a vapor stream comprising water and -caprolactam in a weight to weight ratio of 2:1 to 15:1; c) recovering crude -caprolactam from said vapor stream in the recovery section; and d) purifying said crude -caprolactam in the purification section to obtain purified F-caprolactam, wherein the purification comprises the steps of (i) extracting the crude g-caprolactam with an organic solvent, whereby an aqueous phase and an organic phase are obtained, and wherein the organic phase comprises the organic solvent, g-caprolactam and impurities; (ii) switching the solvent by replacing the organic solvent at least partially with water, whereby an aqueous phase comprising water, -caprolactam and impurities with lower- or higher-boiling points than -caprolactam is obtained and wherein the solvent switch step (ii) is selected from a process based on back-extraction with water, and a process based on solvent swap distillation, in which the organic solvent is distilled off and water is charged; and (iii) obtaining purified -caprolactam by distillative removal of impurities with lower- or higher-boiling points than -caprolactam; wherein after step d)(i), the organic phase obtained in step d)(i) is washed with water or with an aqueous alkaline solution; wherein step d)(ii) is followed by oxidation by an oxidant selected from potassium permanganate, sodium permanganate and hydrogen peroxide; and wherein the Nylon 6-containing multi-component material is a multi-layer packaging film that is a thin sheet with a thickness of less than 1 mm and contains at least one layer comprising or consisting of Nylon 6 and at least one layer not comprising Nylon 6, wherein the at least one layer comprising or consisting of Nylon 6 is sandwiched in between two or more layers not comprising Nylon 6.

2-4. (canceled)

5. The process according to claim 1, wherein the weight fraction of Nylon 6 in the Nylon 6-containing multi-component material ranges from 1 wt. % to 75 wt. %, based on the total weight of the Nylon 6-containing multi-component material.

6. The process according to claim 1, wherein the extracting in step a) comprises the steps of (i) adding the one or more organic solvents to the Nylon 6-containing multi-component material; (ii) performing a phase separation to obtain a liquid extract phase comprising solvent and dissolved components from the Nylon 6-containing multi-component material and an at least partially solid phase comprising undissolved components of the Nylon 6-containing multi-component material and optionally solvent; (iii) removing the solvent from the liquid extract phase and, if present therein, also from the at least partially solid phase to obtain two solid phases, one of which is the pre-concentrated Nylon 6-containing material that is enriched in Nylon 6 as compared to the Nylon 6-containing multi-component material that is used as starting material.

7. The process according to claim 1, wherein an organic solvent is used for the extracting in step a) that preferentially dissolves at least one of non-Nylon 6 compounds from the Nylon 6-containing multi-component material and Nylon 6 from the Nylon 6-containing multi-component material.

8. The process according to claim 1, further comprising at least one additional step selected from: (i) prior to the extracting in step a) the Nylon 6-containing multi-component material has been subjected to at least one additional pre-treatment step comprising a washing step and a mechanical size reduction step; and (ii) wherein the depolymerization of the pre-concentrated Nylon 6-containing material in step b) is conducted at a temperature ranging from 180 C. to 400 C.; and (iii) wherein the water present in step b) is in the form of steam, which is preferably charged to the depolymerization section in step b) as super-heated steam having a temperature ranging from 220 C. to 575 C.

9. The process according to claim 1, wherein the depolymerization of the pre-concentrated Nylon 6-containing material in step b) is carried out in the absence or presence of a catalyst, wherein the catalyst is selected from an acid and a base catalyst, the acid catalyst being selected from the group consisting of orthophosphoric acid, boric acid, sulfuric acid, organic acid, organic sulfonic acid, salts of the aforementioned acids, Al.sub.2O.sub.3 and SiO.sub.2, and combinations thereof, and the base catalyst being selected from the group consisting of alkali hydroxide, alkali salt, alkaline earth hydroxide and alkaline earth salts, organic bases and solid bases, and combinations thereof.

10. The process according to claim 1, wherein prior to the distillative removal in step d)(iii), an alkali metal hydroxide, is added.

11. The process according to claim 1, wherein prior to the distillative removal in step d)(iii) an aqueous phase comprising water, -caprolactam and impurities with lower or higher boiling points than -caprolactam is obtained by at least partially replacing the organic solvent with water, and wherein the solvent replacement step is selected from a process based on reextraction with water, and a process based on solvent replacement distillation, in which the organic solvent is distilled off and water is charged.

12. The process according to claim 1, wherein in the purification section used in step d) further comprises an addition of crude -caprolactam obtained from a Beckmann rearrangement of cyclohexanone oxime with the crude -caprolactam that is recovered in step c).

13-15. (canceled)

16. The process according to claim 5, wherein the weight fraction of Nylon 6 in the Nylon 6-containing multi-component material ranges from 1 wt. % to 60 wt. % based on the total weight of the Nylon 6-containing multi-component material.

17. The process according to claim 5, wherein the weight fraction of Nylon 6 in the Nylon 6-containing multi-component material ranges from 2 wt. % to 35 wt. %.

18. The process according to claim 5, wherein the weight fraction of Nylon 6 in the Nylon 6-containing multi-component material ranges from 3 wt. % to 25 wt. %.

19. The process according to claim 8, wherein the depolymerization of the pre-concentrated Nylon 6-containing material in step b) is conducted at a temperature ranging from 200 C. to 350 C.

20. The process according to claim 8, wherein the depolymerization of the pre-concentrated Nylon 6-containing material in step b) is conducted at a temperature ranging from 220 C. to 340 C.

21. The process according to claim 8, wherein the depolymerization of the pre-concentrated Nylon 6-containing material in step b) is conducted at a temperature ranging from 240 C. to 325 C.

22. The process of claim 8, wherein the water present in step b) is in the form of steam, which is preferably charged to the depolymerization section in step b) as super-heated steam having a temperature ranging from 275 C. to 500 C.

23. The process of claim 9, wherein the acid catalyst is orthophosphoric acid.

24. The process of claim 9, wherein the base catalyst is selected from the group consisting of: sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, and potassium hydrogen carbonate.

25. The process of claim 10, wherein the alkali metal hydroxide is NaOH.

26. The process according to claim 11, wherein the step of at least partially replacing the organic solvent with water, further comprises one or more of the following steps: a. oxidation by an oxidant selected from potassium permanganate, sodium permanganate and hydrogen peroxide; b. treatment with an acidic cation exchange resin and/or a basic anion exchange resin; and c. hydrogenation in the presence of a hydrogenation catalyst selected from Raney nickel, nickel on silica, nickel on aluminum oxide, ruthenium on aluminum oxide, rhodium on aluminum oxide, platinum on carbon and palladium on carbon.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0224] In the following, the invention will be described with reference to the Figures, which depict certain embodiments of the invention. The invention, however, is as defined in the claims and as generally described herein. It should not be limited to the embodiments shown for illustrative purposes in the Figures below.

[0225] FIG. 1 is a schematic of the process of the invention comprising processing steps performed in a Nylon 6-pre-concentration section, a depolymerization section, a recovery section and a purification section.

[0226] FIG. 2 illustrates three embodiments of the Nylon 6 pre-concentration step a) of the process of the invention, in which the Nylon 6-containing multi-component material is extracted with organic solvent(s) to obtain a pre-treated Nylon 6 containing phase, which is enriched in Nylon 6.

[0227] FIG. 2a depicts an embodiment of the Nylon 6 pre-concentration step a) of the process of the invention, in which non-Nylon 6 compounds are preferentially extracted from the Nylon 6-containing multi-component material to obtain the pre-concentrated Nylon 6-containing material, which is enriched in Nylon 6.

[0228] FIG. 2b depicts an embodiment of the Nylon 6 pre-concentration step a) of the process of the invention, in which Nylon 6 is preferentially extracted from the Nylon 6-containing multi-component material to obtain the pre-concentrated Nylon 6-containing material, which is enriched in Nylon 6.

[0229] FIG. 2c depicts an embodiment of the Nylon 6 pre-concentration step a) of the process of the invention, in which extraction of non-Nylon 6 compounds from the Nylon 6-containing multi-component material is combined with the extraction of Nylon 6 from the resulting Nylon 6-containing phase, which is enriched in Nylon 6 to obtain a Nylon 6-containing phase, which is further enriched in Nylon 6.

DETAILED DESCRIPTION OF THE DRAWINGS

[0230] The process of the invention is schematically illustrated in FIG. 1. The process comprises the following sections: [0231] Nylon 6-pre-concentration section [A], in which the Nylon 6-containing multi-5 component material [1] is treated with an (organic) solvent [2] to obtain a pre-concentrated Nylon 6-containing material, which is enriched in Nylon 6 [3] and a second phase that comprises non-Nylon 6-compounds [4]; [0232] Depolymerization section [B], in which the pre-treated Nylon 6, which is enriched in Nylon 6 [3] is depolymerized to -caprolactam, that is discharged as an -caprolactam-containing product vapor stream [5]. In addition, residual material [6] is discharged. Superheated steam [7] and optionally catalyst [8] are charged to the depolymerization section [B]; [0233] Recovery section [C], in which crude -caprolactam [9] is recovered from the -caprolactam-containing product vapor stream [5] that is discharged from the depolymerization section [B]; and [0234] Purification section [D], in which crude -caprolactam [9] that is discharged from the recovery section [C] is purified to yield high purity -caprolactam [10].

[0235] FIG. 2a depicts an embodiment of an extraction in a Nylon 6-pre-concentration section [A], in which the Nylon 6-containing multi-component material [1] is treated with a solvent [2] that preferentially extracts non-Nylon 6 compounds from the Nylon 6-containing multi-component material [1] to obtain a pre-concentrated Nylon 6-containing material, which is enriched in Nylon 6 [3] and a second phase [4] that is enriched in non-Nylon 6-compounds.

[0236] FIG. 2b depicts an embodiment of an extraction in a Nylon 6-pre-concentration section [A], in which the Nylon 6-containing multi-component material [1] is treated with a solvent [2] that preferentially extracts Nylon 6 from the Nylon 6-containing multi-component material [1] to obtain a pre-concentrated Nylon 6-containing material, which is enriched in Nylon 6 [3] and a second phase [4] that is enriched in non-Nylon 6-compounds.

[0237] FIG. 2c depicts an embodiment of an extraction in a first Nylon 6-pre-concentration section [A], in which the Nylon 6-containing multi-component material [1] is treated with a solvent [2] that preferentially extracts non-Nylon 6 compounds from the Nylon 6-containing multi-component material [1] to obtain a pre-treated Nylon 6 containing phase, which is enriched in Nylon 6 [3] and a second phase [4] that is enriched in non-Nylon 6-compounds. In a second Nylon 6-pre-concentration section [A], the pre-concentrated Nylon 6-containing material, which is enriched in Nylon 6 [3] is treated with a second solvent [2] that preferentially extracts Nylon 6 from the pre-concentrated Nylon 6-containing material, which is enriched in Nylon 6 [3] to obtain a pre-treated Nylon 6 comprising phase, which is further enriched in Nylon 6 [3] and a further phase [4] that is enriched in non-Nylon 6-compounds.

[0238] The present invention is illustrated by, but not intended to be limited to, the following examples.

EXAMPLES

[0239] The starting material that was used in the Examples 1 and 2 and 4 and in the Comparative Examples were waste multi-layered packaging films, comprising layers of polyethylene and Nylon 6. The Nylon 6 layers were buried in the used waste multi-layered packaging films, i.e., sandwiched in between other layers and therefore not well accessible.

[0240] The Nylon 6-pre-concentration step a) of the waste multi-layered packaging films can be performed as described in EP0849312 or in DE102016015198, wherein polyethylene is selectively dissolved at elevated temperatures in an organic solvent, e.g., white spirit (Sigma-Aldrich; CAS number 68551-17-7) or methylcyclohexane, whereby the resulting mixture comprises undissolved Nylon 6 and an organic solution comprising organic solvent and dissolved polyethylene. Undissolved Nylon 6 material is obtained after separation of the organic solution from the resulting mixture. The resulting undissolved Nylon 6 material can be dried and optionally densified by melting under nitrogen and subsequently converted into solid particles that are enriched in Nylon 6 as compared to the Nylon 6-containing multi-component starting material.

[0241] To determine the quality of the obtained -caprolactam, the following parameters were measured: The permanganate absorption number of -caprolactam was determined (PAN: ISO 8660PlasticsDetermination of permanganate absorption number of caprolactamSpectometric method, second edition ISO 8660; 2002). Moreover the absorbance at wavelength of 290 nm was measured (E290: ISO 7059Caprolactam for industrial useDetermination of absorbance at a wavelength of 290 nm; 1982). Additionally, the volatile bases content was determined (Volatile bases (VB): ISO 8661Caprolactam for industrial useDetermination of volatile bases contentTitrimetric method after distillation, 1988). Finally, the alkalinity or acidity is determined by titration at a temperature of 25 C. using a Tashiro indicator in a 1:2 ratio of 0.1 wt./v.sub.Ethanol % Methylene blue: 0.1 wt./v.sub.Ethanol % Methyl red, which is grey at its end point. A flask containing water and indicator is first titrated to grey, then X grams of an aqueous -caprolactam solution containing Y wt. % -caprolactam (as determined by refractive index) is added and the solution is titrated back to grey using a 0.01 N H.sub.2SO.sub.4 solution (in case the solution is alkaline) or a 0.01 N NaOH solution (in case the solution is acidic).

[0242] Alkalinity is then given by:

[00001]$\mathrm{Alkalinity}\left(\mathrm{mmol}/\mathrm{kg}\mathrm{caprolactam}\right)=v*t*1000/\left(X*Y\right)$ [0243] Where: [0244] v=volume of H.sub.2SO.sub.4 solution added (ml) [0245] t=normality of H.sub.2SO.sub.4 solution (=0.01 N) [0246] X=weight of sample (g) [0247] Y=concentration -caprolactam (wt. %)

[0248] Acidity is then given by:

[00002]$\mathrm{Acidity}\left(\mathrm{mmol}/\mathrm{kg}\mathrm{caprolactam}\right)=v*t*1000/\left(X*Y\right)$ [0249] Where: [0250] v=volume of NaOH solution added (ml) [0251] t=normality of NaOH solution (=0.01 N) [0252] X=weight of sample (g) [0253] Y=concentration -caprolactam (wt. %)

[0254] -caprolactam, that can be used for all major polymerization applications, without dilution with purer qualities of -caprolactam, fulfils all of the following specifications: [0255] PAN: max. 5 [0256] E290: max. 0.05 [0257] VB: max. 0.5 mmol/kg [0258] Alkalinity: max. 0.1 mmol/kg [0259] Acidity: max. 0.1 mmol/kg

Example 1

Depolymerization of Nylon 6 and Recovery of -Caprolactam.

[0260] The material used for depolymerization and the further processing steps as described below can be any Nylon 6-containing multi-component material or derivative thereof. The particular material that was used in the following examples was enriched in Nylon 6 as compared to Nylon 6-containing multi-component starting material and was prepared as described above from waste multi-layered packaging films.

[0261] The enriched in Nylon 6 starting material was shaped into pearl-like solid particles (diameter: 3 to 4 mm). The polyethylene content in the undissolved Nylon 6 material was about 1 wt. % as determined by TGA (Thermal Gravimetric Analysis).

[0262] In step b), 33.6 g of the pearl-like solid particles and 9.8 grams of 20 wt. % phosphoric acid were charged to a Premex high pressure autoclave. First, the reactor content was heated under nitrogen and subsequently superheated steam was injected continuously at a rate of 4 grams per minute during the 120-minute reaction. The temperature and the pressure in the reactor were maintained at 260 C. and 0.11 MPa, respectively. During the reaction a vapor stream was continuously discharged from the reactor.

[0263] In step c), to recover crude -caprolactam from the obtained vapor, the latter was cooled to 20 C. The condensate that composed of on average 28.3 grams of -caprolactam, most of the remainder being water, was concentrated by evaporation in a rotavap (rotary evaporator) that was operated under vacuum (9.5 kPa; water bath temperature was ca. 65 C.) to an -caprolactam concentration of on average 49.6 wt. %. (The resulting mixture, crude -caprolactam, is the mixture to be purified.)

[0264] Step b) and step c) were repeated five times. The five mixtures were combined and the resulting solution was used as stock solution in the following Examples and Comparative Experiments.

[0265] This EXAMPLE shows that crude -caprolactam can be obtained in good yield and without operational issues by depolymerization of Nylon 6 that originates from discarded Nylon 6 waste multi-layered packaging films.

Example 2

Purification by Extraction, Caustic Wash, Reextraction, Oxidation and Distillation.

[0266] In step d)(i) 70 gram of crude -caprolactam that was obtained in EXAMPLE 1 was extracted one time with 100 gram and nine times with 50 gram solvent mixture MIBC/cyclohexane (50 wt. %: 50 wt. %) at 25 C. The ten resulting -caprolactam phases comprising solvent mixtures were combined and washed with 7 gram aqueous caustic solution (2 wt. %). Subsequently, the washed -caprolactam comprising solvent mixture was extracted six times with 50 gram of water at 25 C. The six resulting aqueous -caprolactam phases were combined. Water and residual solvent mixture were distilled out of the aqueous -caprolactam phase whereby a concentrated -caprolactam solution with a water content of 50 wt. % was obtained. The resulting mixture was treated with 0.2 wt. % KMnO.sub.4 with regard to -caprolactam at 50 C. for 2 hours. The solids formed were then removed from the oxidized reaction product by means of a filtration. 75 mmol of aqueous sodium hydroxide per kg -caprolactam was then added to the resulting aqueous -caprolactam solution.

[0267] In step d)(ii), a distillative removal of water and impurities with lower or higher boiling points than -caprolactam was performed. Subsequently, water and impurities with lower boiling points than -caprolactam were removed as top products by distillation under reduced pressure in a batch-wise operated distillation set-up. Finally, purified -caprolactam was recovered as top product at 300 Pa, while the impurities with higher boiling points compared to -caprolactam remained as bottom product in the distillation set-up. The specifications of the purified -caprolactam were: [0268] PAN: 5 [0269] E290: 0.023 [0270] VB: 0.167 [0271] Alkalinity: 0.044

[0272] From this EXAMPLE, it can be concluded that purified -caprolactam that meets the required specifications for major polymerization applications can be obtained from depolymerized waste multi-layered packaging film pieces from which polyethylene was removed by extraction and was purified by extraction with an organic solvent, oxidation and distillation.

Comparative Experiment 1

Purification by Distillation.

[0273] 0.75 mmol of aqueous sodium hydroxide per kg -caprolactam was added to 35 gram of crude -caprolactam that was obtained in EXAMPLE 1. This mixture was then distilled according to the procedure described in EXAMPLE 2. The specifications of the purified -caprolactam were: [0274] PAN: 73.5 [0275] E290: 0.531 [0276] VB: 0.718 [0277] Acidity: 7.643

[0278] This COMPARATIVE EXPERIMENT shows that the quality of -caprolactam that is obtained from depolymerization of waste multi-layered packaging film pieces from which polyethylene was removed by extraction and was purified by distillation is very poor as it does not meet any of the required specifications for major polymerization applications.

Comparative Experiment 2

Purification by Oxidation and Distillation.

[0279] 35 gram of crude -caprolactam that was obtained in EXAMPLE 1 was treated with 0.2 wt. % KMnO.sub.4 with regard to -caprolactam at 50 C. for 2 hours. The solids formed were then removed from the oxidized reaction product by means of a filtration. 0.75 mmol of aqueous sodium hydroxide per kg -caprolactam was then added to the resulting aqueous -caprolactam solution. This mixture was then distilled according to the procedure described in EXAMPLE 2. The specifications of the purified -caprolactam were: [0280] PAN: 11.7 [0281] E290: 0.324 [0282] VB: 0.657 [0283] Acidity: 2.991

[0284] This COMPARATIVE EXPERIMENT shows that the quality of -caprolactam that is obtained from depolymerization of waste multi-layered packaging film pieces from which polyethylene was removed by extraction and was purified by oxidation and distillation is very poor as it does not meet any of the required specifications for major polymerization applications.

Comparative Experiment 3

Purification by Extraction, Caustic Wash, and Reextraction.

[0285] 70 gram of crude -caprolactam that was obtained in EXAMPLE 1 was extracted one time with 100 gram and nine times with 50 gram solvent mixture MIBC/cyclohexane (50 wt. %: 50 wt. %) at 50 C. The ten resulting -caprolactam phases comprising solvent mixtures were combined and washed with 7 gram aqueous caustic solution (2 wt. %). Subsequently, the washed -caprolactam comprising solvent mixture was reextracted six times with 50 g of water at 25 C. The six resulting aqueous -caprolactam phases were combined. Water and residual solvent mixture were distilled out of the aqueous -caprolactam phase whereby a concentrated -caprolactam solution with an -caprolactam content of 50.4 wt. % was obtained. The specifications of the purified -caprolactam were: [0286] PAN: 82 [0287] E290:1.2

[0288] This COMPARATIVE EXPERIMENT shows that the quality of -caprolactam that is obtained from depolymerization of waste multi-layered packaging film pieces from which polyethylene was removed by extraction and was purified by extraction and reextraction is very poor as it does not meet all the required specifications for major polymerization applications.

Comparative Experiment 4

Purification by Extraction, Caustic Wash, Reextraction and Oxidation.

[0289] The concentrated -caprolactam solution with an -caprolactam content of 50.4 wt. % that was obtained in COMPARATIVE EXPERIMENT 3 was treated with 0.04 wt. % KMnO.sub.4 with regard to -caprolactam at 50 C. for 2 hours. The solids formed were then removed from the oxidized reaction product by means of a filtration. The specifications of the purified -caprolactam were: [0290] PAN: 83 [0291] E290:3.01

[0292] This COMPARATIVE EXPERIMENT shows that the quality of -caprolactam that is obtained from depolymerization of waste multi-layered packaging film pieces from which polyethylene was removed by extraction and was purified by extraction, reextraction and oxidation is very poor as it does not meet all the required specifications for major polymerization applications.

Example 3

Calculation of Product Carbon Footprint of Purified -Caprolactam

[0293] A continuous process according to the invention for the production of purified -caprolactam from waste multi-layered packaging films, comprising layers of polyethylene and Nylon 6 was simulated. The Nylon 6 content of these waste multi-layered packaging films, comprising layers of polyethylene and Nylon 6 was 20 wt. %.

[0294] The process included: [0295] Cutting waste multi-layered packaging films, comprising layers of polyethylene and Nylon 6 in small pieces; [0296] Washing with water of the small pieces of waste multi-layered packaging films, comprising layers of polyethylene and Nylon 6; [0297] Drying by centrifugation of the washed small pieces of waste multi-layered packaging films, comprising layers of polyethylene and Nylon 6; [0298] Extraction of polyethylene with white spirit; [0299] Separation of non-dissolved solid pre-concentrated Nylon 6-containing material by centrifugation; [0300] Washing of non-dissolved solid pre-concentrated Nylon 6-containing material with water; [0301] Separation of washed non-dissolved solid pre-concentrated Nylon 6-containing material and aqueous extract by centrifugation; [0302] Decolorization of the polyethylene comprising white spirit solution by treatment with active carbon; [0303] Recovery of polyethylene from the polyethylene comprising white spirit solution by cooling and partial evaporation of the white spirit; [0304] Melting and pelletization of recovered polyethylene; [0305] Melting and pelletization of washed non-dissolved solid pre-concentrated Nylon 6-containing material; [0306] Depolymerization of Nylon 6 in the pelletized Nylon 6-containing material under influence of H.sub.3PO.sub.4 and superheated steam; [0307] Recovery of crude -caprolactam by partial condensation of vapors discharged from depolymerization reactor; [0308] Evaporative concentration of crude -caprolactam to 80 wt. % -caprolactam; [0309] Counter-current extraction of concentrated crude -caprolactam with benzene; [0310] Washing of organic extract with diluted caustic solution; [0311] Counter-current extraction of washed organic extract with water; [0312] Evaporative concentration of aqueous extract; [0313] Oxidation of the concentrated extract with KMnO.sub.4 and then filtration of the oxidized reaction product to remove solids formed; [0314] Addition of caustic; [0315] Recovery of pure -caprolactam by vacuum distillation.

[0316] The main products of this process are polyethylene and pure -caprolactam. The pure -caprolactam recovery yield is about 0.8 kg pure -caprolactam per kg Nylon 6 in the waste multi-layered packaging films, comprising layers of polyethylene and Nylon 6. The obtained by-products are incinerated with energy recovery.

[0317] The product carbon footprint of purified -caprolactam was calculated based on the consumption figures of raw materials, and utilities of the above described process are based on data originating from ecoinvent version 3.7.1. The distribution of the environmental impact between the products purified -caprolactam and polyethylene in the Nylon 6-pre-concentration section was based on the weight ratio of these products.

[0318] The outcome revealed that the product carbon footprint of purified -caprolactam obtained from multi-layered packaging films, comprising layers of polyethylene and Nylon 6 is less than 2 ton CO.sub.2 eq./ton of -caprolactam (location: Europe).

Example 4

Depolymerization of Nylon 6 and Recovery of -Caprolactam.

[0319] The material used for depolymerization and the further processing steps as described below was enriched in Nylon 6 as compared to Nylon 6-containing multi-component starting material and was prepared as described above from waste multi-layered packaging films. The enriched in Nylon 6 starting material was shaped into pearl-like solid particles (diameter: 3 to 4 mm). The polyethylene content in the undissolved Nylon 6 material was about 1 wt. % as determined by TGA (Thermal Gravimetric Analysis).

[0320] In step b), 33.6 g of the pearl-like solid particles and 9.8 grams of 20 wt. % phosphoric acid were charged to a Premex high pressure autoclave. First, the reactor content was heated under nitrogen and subsequently superheated steam was injected continuously at a rate of 2.7 grams per minute during the 135-minute reaction. The temperature and the pressure in the reactor were maintained at 260 C. and 0.11 MPa, respectively. During the reaction a vapor stream was continuously discharged from the reactor.

[0321] In step c), to recover crude -caprolactam from the obtained vapor, the latter was cooled to 20 C. The condensate was composed of 26.1 grams of -caprolactam, most of the remainder being water.

[0322] Step b) and step c) were repeated by following the same procedure except that now 9.7 grams of 20 wt. % phosphoric acid were charged to a Premex high pressure autoclave and that the obtained condensate was composed of 26.9 grams of -caprolactam.

[0323] The two -caprolactam containing condensates were concentrated by evaporation in a rotavap (rotary evaporator) that was operated under vacuum (9.5 kPa; water bath temperature was ca. 65 C.) and thereafter combined to an -caprolactam concentration of 79.6 wt. %. The resulting stock solution, crude -caprolactam, is the mixture to be purified (see EXAMPLE 5).

[0324] The specifications of the crude -caprolactam were: [0325] PAN: 280 [0326] E290:2.14

[0327] This EXAMPLE shows that crude -caprolactam can be obtained in good yield and without operational issues by depolymerization of Nylon 6 that originates from discarded Nylon 6 waste multi-layered packaging films.

Example 5

Purification by Extraction, Reextraction, Oxidation and Distillation.

[0328] In step d)(i) 43.4 gram of crude -caprolactam that was obtained in EXAMPLE 4 was diluted to 68.9 wt. % by adding 6.7 g of water, the obtained solution was extracted one time with 77.5 gram and four times with 50 gram benzene at 25 C. The resulting organic extracts were combined and concentrated by evaporation in a rotavap that was operated under vacuum (9.5 kPa; water bath temperature was ca. 65 C.) to an -caprolactam concentration of about 24.5 wt. %. Subsequently, the -caprolactam comprising concentrated extract was 3 times batch-wise extracted with 25 gram water at a temperature of ca. 25 C. The three resulting aqueous -caprolactam phases were combined. Water and residual solvent mixture were distilled out of the aqueous E caprolactam phase whereby a concentrated -caprolactam solution with a water content of 49.5 wt. % was obtained. The specifications of the aqueous -caprolactam solution after reextraction were: [0329] PAN: 83 [0330] E290:1.15

[0331] The resulting mixture was treated with 0.2 wt. % KMnO.sub.4 with regard to -caprolactam at 50 C. for 2 hours. The solids formed were then removed from the oxidized reaction product by means of a filtration. 75 mmol of aqueous sodium hydroxide per kg -caprolactam was then added to the aqueous -caprolactam solution after oxidation. This mixture was then distilled according to the procedure described in EXAMPLE 2. The specifications of the purified -caprolactam were: [0332] PAN: <5 [0333] E290: <0.05 [0334] VB: <0.5 mmol/kg [0335] Alkalinity: <0.1 mmol/kg [0336] Acidity: <0.1 mmol/kg

[0337] From this EXAMPLE, it can be concluded that purified -caprolactam that meets the required specifications for major polymerization applications can be obtained from depolymerized waste multi-layered packaging film pieces from which polyethylene was removed by extraction and was purified by extraction with benzene, reextraction with water, oxidation and distillation.

[0338] While the present invention has been illustrated by means of several preferred embodiments, one of ordinary skill in the art will recognize that changes, modifications including conversion into a continuous mode of operation, and improvements can be made while still remaining within the scope and spirit of the present invention. Accordingly, no limitation upon the invention is intended, except as set forth in the appended claims.