WO2024251758A1

WO2024251758A1 - Process for hydrolytically depolymerizing a polyamide

Info

Publication number: WO2024251758A1
Application number: PCT/EP2024/065380
Authority: WO
Inventors: Stefan Blei; Faissal-Ali El-Toufaili; Oliver Bey; Vikram Raghavendhar RAVIKUMAR; Bart Vander Straeten; Michael Schreiber; Bao Liu; Christian Dienes
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2023-06-06
Filing date: 2024-06-05
Publication date: 2024-12-12
Anticipated expiration: 2025-12-06
Also published as: MX2025014674A; AR132876A1; KR20260019627A; TW202506641A; EP4724421A1; AU2024286546A1; CN121399096A

Abstract

A process for hydrolytically depolymerizing a polyamide 6 comprised in a solid material M, the process comprising providing the solid material M; melting in a melting unit U_M the solid material M, obtaining a liquid stream S_M having a temperature T_SM at a pressure p_SM; providing a liquid aqueous stream S_W having a temperature T_SW at a pressure p_SW; admixing in a pre-reaction unit U_PR the stream S_M with the stream S_W, obtaining a liquid reaction feed stream S_F having a temperature T_SF at a pressure p_SF; feeding the stream S_F into a chemical reaction unit U_R; subjecting the stream S_F in the reaction unit U_R to polyamide 6 depolymerization conditions comprising a polyamide 6 depolymerization temperature T_D at a polyamide 6 depolymerization pressure p_D, obtaining in U_R an aqueous depolymerization mixture comprising ε-caprolactam dissolved in water; removing an aqueous liquid reactor exit stream S_R from U_R, the stream S_R comprising ε-caprolactam dissolved in water; wherein 0.8 ≤ T_SF/T_D ≤ 1.05 and 0.9 ≤ p_SF/p_D ≤ 1.05.

Description

Process for hydrolytically depolymerizing a polyamide

The present invention relates to a process for hydrolytically depolymerizing a polyamide prepared from c-caprolactam and an apparatus for carrying out a process for hydrolytically depolymerizing a polyamide prepared from c-caprolactam, preferably for carrying out the aforementioned process.

Polyamide, and in particular polyamide 6 being characterized by the formula (-NH-(CH2)5-CO-)_n, can be found in numerous materials, such as packaging, engineering plastics from automotive and textile filaments. The latter represents about 40 % of the polyamide 6 global market. At present, only a very small part of the textile filaments is recycled while it represents a significant percentage of the global CO2 emissions. There is thus a need to recycle polyamide 6 from such materials. Processes for alkaline depolymerizing a polyamide exists. Thus, there is a need to provide an improved process for depolymerizing a polyamide able to overcome these issues.

According to the present invention, it was found that an efficient depolymerization reaction wherein polyamide 6 is hydrolytically hydrolyzed can be realized when upstream of the chemical reaction unit in which the depolymerization reaction actually takes place, a specific sequence of a melting unit and a pre-reaction unit is realized. Further, it was found that the process can be rendered even more efficient if a specific design of the chemical reaction unit is realized. Based thereon, and in combination with specific sequences of stages upstream and in particular downstream of said chemical reaction unit allowing for the recycling of water and a very effective use of process-internal heat, an advantageous overall process for recycling materials containing polyamide 6 can be provided by the present invention.

Therefore, the present invention relates to a process for hydrolytically depolymerizing a polyamide 6 comprised in a solid material M, the process comprising

(i) providing the solid material M;

(ii) melting in a melting unit UM the solid material M provided according to (i), obtaining a liquid stream SM having a temperature TSM at a pressure PSM;

(iii) providing a liquid aqueous stream Sw having a temperature Tsw at a pressure psw;

(iv) admixing in a pre-reaction unit UPR the stream SM obtained according to (ii) with the stream Sw provided according to (iii), obtaining a liquid reaction feed stream SF having a temperature TSF at a pressure PSF;

(v) feeding the stream SF obtained according to (iv) into a chemical reaction unit UR;

(vi) subjecting the stream SF in the reaction unit UR to polyamide 6 depolymerization conditions comprising a polyamide 6 depolymerization temperature TD at a polyamide 6 depolymerization pressure PD, obtaining in UR an aqueous depolymerization mixture comprising c-caprolactam dissolved in water;

(vii) removing an aqueous liquid reactor exit stream SR from UR, the stream SR comprising E- caprolactam dissolved in water; wherein 0.8 < TSF/TD 1 .05 and 0.9 < PSF/PD 1 .05. Preferably according to the present invention, no polyamide 6 depolymerization catalyst such as a mineral acid, such as one or more of hydrochloric acid, nitric acid, sulphuric acid and phosphoric acid, and/or a zinc salt such as zinc chloride, zinc acetate or zinc triflate is added for preparing the stream SF to be subjected to hydrolytic polyamide 6 depolymerisation conditions according to (vi).

Preferably, 0.6 < TSM/TSF 1.05 and 0.9 < PSM/PSF 1.05. According to the present invention, one or more of the following ranges may be preferred: 0.6 < TSM/TSF 0.7; 0.7 < TSM/TSF 0.8;

0.8 TSM/TSF - 0.9; 0.9 TSM/TSF - 1 -0; 1.0 TSM/TSF - 1.05.

Further preferably, 0.8 < TSW/TSF 1.3 and 0.9 < psw/psF 1 .05. Further according to the present invention, one or more of the following ranges may be preferred: 0.8 < TSW/TSF 0.9;

0.9 TS /TSF - 1 -0; 1.0 ^ TSW/TSF - 1.1 ; 1.1 - TSW/TSF - 1.2; 1.2 ^ TSW/TSF - 1 -3.

Regarding the pre-reaction unit UPR according to (iv), no specific limitations exist, provided that a liquid reaction feed stream SF having the temperature TSF at the pressure PSF can be obtained. Preferably, the pre-reaction unit UPR according to (iv) comprises, more preferably consists of a mixing unit, wherein more preferably, said mixing unit is a static mixing unit. The term “static mixing unit” as used herein refers to an arrangement of mixing elements which are installed in a pipe or duct, and which operate essentially without moving parts, preferably entirely without moving parts. According to the present invention, it may be preferred that said mixing unit is configured as a suitable pipe junction of the pipe for the stream SM and the pipe for the stream Sw, wherein no specific mixing elements are present.

According to the present invention, it is preferred that according to (iv), Sw and SM are admixed in UPR at a mixing ratio (mw/kg) I (mp/kg) in the range of from 1 :1 to 20:1 , more preferably in the range of from 2:1 to 15:1 , more preferably in the range of from 5:1 to 10:1 , wherein mw is the amount of water comprised in Sw and m? is the amount of polyamide 6 comprised in SM. Preferred ranges are, for example, from 5:1 to 6:1 or from 6:1 to 7:1 or from 7:1 to 8:1 from 8:1 to 9:1 or from 9:1 to 10:1.

Regarding the melting unit UM according to (ii), no specific limitations exist, provided that a liquid stream SM having the temperature TSM at the pressure PSM can be obtained. Preferably, the melting unit UM according to (ii) comprises a kneader or an extruder, more preferably an extruder, wherein more preferably, the melting unit UM according to (ii) consists of an extruder, wherein more preferably, the extruder is a single-screw extruder or a twin-screw extruder, more preferably a twin-screw extruder. More preferably, the solid material M which is provided according to (i) and which has a temperature which is lower than TSM is fed into the extruder and melted therein while being conveyed through the extruder. Preferably, the temperature of solid material which is fed into the extruder has a temperature in the range of from 10 to 50 °C, more preferably in the range of from 15 to 40 °C, more preferably in the range of from 20 to 30 °C. Further preferably, the solid material is fed into the extruder at a pressure in the range of from 0.75 to 5 bar, more preferably in the range of from 0.85 to 3 bar, more preferably in the range of from 0.95 to 1.5 bar. For melting the material M, the extruder is preferably equipped with suitable heating means so as to respectively heat up the material M, wherein when leaving the extruder, the liquid stream SM has the temperature TSM. Said suitable heating means can be arranged in a manner so that the extruder exhibits one heating zone or more than one heating zones. It is conceivable that for feeding the solid material M, the extruder has more than one feeding zone. Further according to the present invention, the extruder can be operated either starve-fed or flood-fed.

Preferably, the melting unit UM, preferably the extruder, is equipped with a degassing system which serves for removing one or more gases during the melting process in the extruder. While it is generally conceivable that the extruder has more than one degassing zone, it is preferred that it has one degassing zone. Preferably, the degassing zone located directly before the pressure build-up in the extruder discharge zone. If the melting unit UM, preferably the extruder, is equipped with a degassing system, the process preferably comprises removing a gas stream SGM from UM during melting according to (ii). Preferably, said gas stream SGM has a temperature TGM at a pressure PGM, wherein 0.95 < TGM/TSM 1.05, preferably 0.95 < TGM/TSM 1.0. Preferably according to the present invention, the stream SGM obtained from the melting unit UM is subjected to scrubbing in a scrubbing unit Us, preferably to one or more of wet scrubbing and dry scrubbing, more preferably to wet scrubbing, wherein said wet scrubbing preferably comprises passing the gas stream SGM into a scrubbing column, preferably a packed scrubbing column. Prior to being subjected to scrubbing, the stream SGM obtained from the melting unit UM is preferably subjected to cooling, preferably in a vacuum system via which the stream SGM is preferably removed from the melting unit UM.

According to the present invention, the stream SM has a pressure PSM wherein said pressure PSM is preferably in the range 0.9 < PSM/PSF 1 .05 and wherein PSF is in the range 0.9 < PSF/PD 1 .05. As discussed below, the polyamide 6 depolymerization pressure PD is preferably in the range of from 40 to 140 bar. Therefore, it is preferred according to the present invention that the pressure PSM is higher, more preferably significantly higher than the pressure at which the solid material M is fed into the melting unit UM, preferably into the extruder. According to the present invention, it may be conceivable that this increase in pressure is achieved in the extruder itself. However, it is particularly preferred that for achieving said increase in pressure is achieved by a suitable compression device which is comprised in the melting unit UM, for example a compression device which is arranged downstream of the extruder. According to this preferred arrangement, it may be preferred that the liquid stream leaving the extruder is at essentially the same pressure as the solid material which is fed into the extruder, wherein said liquid stream is then suitably compressed in said compression device to result in the stream SM having the temperature TSM at the pressure PSM. Preferably according to the present invention, said compression device comprises, more preferably consists of, at least one suitably gear pump, wherein is more than one gear pump is installed, it is preferred that at least two gear pumps are serially arranged. Further according to the present invention, it may be preferred to pass the liquid stream SM leaving the melting unit UM through a filter unit UF before it is admixed with the liquid aqueous stream Sw according to (iv). Preferably, downstream of the melting unit UM and upstream of the reaction unit UR, a filtration unit UF is arranged, preferably a filtration unit UF for separating particles having a particle size in the range of from 100 to 500 micrometer, preferably in the range of from 200 to 400 micrometer, from the liquid stream SM, wherein the process comprises passing the stream liquid stream SM through UF, prior to admixing according to (iv). Yet further, if the melting unit UM comprises a compression device as described above, it may be preferred to pass the liquid stream, preferably obtained from the extruder, through said filter device UF before the stream is passed through the compression device.

Further according to the present invention, it is possible that the melting unit UM comprises more than one melting apparatus, preferably more than one extruder, wherein, for example, two or more extruders can be arranged in parallel.

Regarding the polyamide 6 depolymerization conditions according to (vi), it is preferred that TD is in the range of from 230 to 330 °C and PD is in the range of from 40 to 140 bar, more preferably TD is in the range of from 250 to 320 °C and PD is in the range of from 40 to 125 bar, more preferably TD is in the range of from 270 to 310 °C and PD is in the range of from 40 to 110 bar.

Therefore, preferred ranges for TD are, for example, from 270 to 280 °C or 280 to 290 °C or 290 to 300 °C or 300 to 310 °C, and preferred ranges for PD are, for example, from 40 to 55 bar or from 55 to 70 bar or from 70 to 85 bar or from 85 to 100 bar or from 100 to 110 bar.

According to the present invention, the reaction unit UR according to (v) comprises at least one reactor in which the liquid stream SF is subjected to depolymerization conditions according to (vi). Preferably, the reaction unit UR according to (v) comprises z chemical reactors R, i=1 ...z, wherein z is in the range of from 1 to 10, preferably in the range of from 1 to 8, more preferably in the range of from 1 to 6, more preferably in the range of from 1 to 5, more preferably in the range of from 1 to 4, more preferably in the range of from 1 to 3. More preferably, the reaction unit UR according to (v) comprises 3 reactors Ri, R2 and R3.

If the reaction unit UR according to (v) comprises more than one reactor R, i.e. if z > 1 , it is preferred that at least 2 reactors R, preferably all z reactors R are serially coupled, wherein according to (v), the stream SF is fed into R, with i = 1 ; an aqueous liquid stream Sj containing e-caprolactam dissolved in water is removed from reactor R and fed into the reactor R+i, with i < z; according to (vii), the aqueous liquid stream S_z containing e-caprolactam dissolved in water is removed from the reactor R_z as the stream SR; wherein in every reactor R, a depolymerization temperature TDI at a depolymerization pressure poi is maintained, wherein, independently of each other, TDI is in the range of from 230 to 330 °C and poi is in the range of from 40 to 140 bar, preferably wherein TDI is in the range of from 250 to 320 °C and poi is in the range of from 40 to 125 bar, more preferably wherein TDI is in the range of from 270 to 310 °C and poi is in the range of from 40 to 110 bar. Regarding the preferred arrangement of three reactors Ri, R2 and R3, it is preferred that these three reactors are serially coupled, wherein according to (v), the stream SF is fed into R1; an aqueous liquid stream Si containing e-caprolactam dissolved in water is removed from reactor R1 and fed into the reactor R2; an aqueous liquid stream S2 containing e-caprolactam dissolved in water is removed from reactor R2 and fed into the reactor R3; according to (vii), the aqueous liquid stream S3 containing e-caprolactam dissolved in water is removed from the reactor R3 as the stream SR; wherein in the reactor R1, a depolymerization temperature TDI at a depolymerization pressure PDI is maintained, wherein TDI is in the range of from 230 to 330 °C and PDI is in the range of from 40 to 140 bar, preferably wherein TDI is in the range of from 250 to 320 °C and PDI is in the range of from 40 to 125 bar, more preferably wherein TDI is in the range of from 270 to 310 °C and PDI is in the range of from 40 to 110 bar; wherein preferred ranges for TDI are, for example, from 270 to 280 °C or 280 to 290 °C or 290 to 300 °C or 300 to 310 °C, and preferred ranges for PDI are, for example, from 40 to 55 bar or from 55 to 70 bar or from 70 to 85 bar or from 85 to 100 bar or from 100 to 110 bar; wherein in the reactor R2, a depolymerization temperature TD2 at a depolymerization pressure PD2 is maintained, wherein TD2 is in the range of from 230 to 330 °C and PD2 is in the range of from 40 to 140 bar, preferably wherein TD2 is in the range of from 250 to 320 °C and PD2 is in the range of from 40 to 125 bar, more preferably wherein TD2 is in the range of from 270 to 310 °C and PD2 is in the range of from 40 to 110 bar; wherein preferred ranges for TD2 are, for example, from 270 to 280 °C or 280 to 290 °C or 290 to 300 °C or 300 to 310 °C, and preferred ranges for PD2 are, for example, from 40 to 55 bar or from 55 to 70 bar or from 70 to 85 bar or from 85 to 100 bar or from 100 to 110 bar; wherein in the reactor R3, a depolymerization temperature TD3 at a depolymerization pressure PD3 is maintained, wherein TD3 is in the range of from 230 to 330 °C and PD3 is in the range of from 40 to 140 bar, preferably wherein TD3 is in the range of from 250 to 320 °C and PD3 is in the range of from 40 to 125 bar, more preferably wherein TD3 is in the range of from 270 to 310 °C and PD3 is in the range of from 40 to 110 bar; wherein preferred ranges for TD3 are, for example, from 270 to 280 °C or 280 to 290 °C or 290 to 300 °C or 300 to 310 °C, and preferred ranges for PD3 are, for example, from 40 to 55 bar or from 55 to 70 bar or from 70 to 85 bar or from 85 to 100 bar or from 100 to 110 bar.

According to the present invention, it is preferred that for z > 1 , the z reactors R are vertically arranged, with R1 being the top-most reactor and R_z being the bottom-most reactor, wherein Sj obtained from R is transferred to R+i by gravity, preferably by gravity only. Regarding the preferred arrangement of three reactors R1, R2 and R3, it is preferred that the reactors R1, R2 and R3 are vertically arranged, with R1 being the top-most reactor and R3 being the bottom-most reactor, wherein Si obtained from Ri is transferred to R2 by gravity, preferably by gravity only, and wherein S2 obtained from R2 is transferred to R3 by gravity, preferably by gravity only.

Regarding the specific design of the one or more reactors R, it is preferred that at least one reactor R is an stirred tank reactor, and more preferably all z reactors are stirred tank reactors. Regarding the preferred arrangement of three reactors R1, R2 and R3, it is preferred that the reactors R1, R2 and R3 are stirred tank reactors.

While there are no general restrictions regarding the specific design of said stirred tank reactors, it is particularly preferred according to the present invention that at least one stirred tank reactor R, preferably every stirred tank reactor R, has, independently from each other, preferably from 2 to 6 compartments, more preferably from 2 to 5 compartments, more preferably from 2 to 4 compartments, said compartments preferably being serially, more preferably being serially and vertically arranged, wherein 2 adjacent compartments are separated by a divider which comprises at least one flow-through opening. Preferably at least one compartment comprised in a reactor R comprises at least one agitator, wherein more preferably, every compartment of every reactor R comprises at least one agitator, wherein more preferably, every compartment of every reactor R comprises one agitator, wherein the process comprises agitating the depolymerization mixture in a given compartment for at least part of the time during subjecting to depolymerization conditions in said compartment. Regarding the preferred arrangement of three reactors R1, R2 and R3, it is more preferred that the stirred tank reactor R1 has 3 vertically and serially arranged compartments wherein every compartment comprises an agitator, the stirred tank reactor R2 has 3 vertically and serially arranged compartments wherein every compartment comprises an agitator, and the stirred tank reactor R3 has 3 vertically and serially arranged compartments wherein every compartment comprises an agitator. Particular reference is made to Figure 5 of the present invention and its respective description.

Alternatively, regarding the specific design of said stirred tank reactors, it is particularly preferred according to the present invention that at least one stirred tank reactor R, preferably every stirred tank reactor R, has, independently from each other, preferably from 2 to 6 compartments, more preferably from 2 to 5 compartments, more preferably from 2 to 4 compartments, said compartments preferably being serially, more preferably being serially and vertically arranged, wherein said reactor R comprises at least one agitator and wherein 2 adjacent compartments are formed by, and separated by, one or more suitable components of said agitator such as blades comprised in the agitator, wherein the process comprises agitating the depolymerization mixture in a given compartment for at least part of the time during subjecting to depolymerization conditions in the reactor compartment. In this regard, and further regarding the preferred arrangement of three reactors R1, R2 and R3, it is more preferred that the stirred tank reactor R1 has 2 vertically and serially arranged compartments formed by, and separated by, said suitable components of the agitator comprised in R1, the stirred tank reactor R2 has 2 vertically and serially arranged compartments formed by, and separated by, said suitable components of the agitator comprised in R2, and the stirred tank reactor R3 has 2 vertically and serially arranged compartments formed by, and separated by, said suitable components of the agitator comprised in R₃.

Preferably according to the present invention, the polyamide 6 depolymerization conditions according to (vi) further comprise a total residence time to of the aqueous depolymerization mixture in the unit UR, preferably in the z reactors R, more preferably in the z stirred tank reactors, wherein at least 85 weight-%, preferably at least 90 weight-%, more preferably at least 95 weight-% of the aqueous depolymerization mixture have a to in the range of from 30 to 90 min. The term “total residence time” as used in this context of the present invention refers to the sum of the residence times in all chemical reactors R mentioned above. In particular for z > 1 , it is preferred that the residence time of an aqueous depolymerization mixture in a reactor R is toi and wherein 0.90 < (toi I toi+i) 1.10, preferably 0.95 < (toi I toi+i) 1.05. Therefore, according to the present invention, it is preferred that a narrow residence time distribution is realized. Regarding the preferred arrangement of three reactors Ri, R2 and R3, it is more preferred that the residence time of the aqueous depolymerization mixture in the reactor R1 is toi , the residence time of the aqueous depolymerization mixture in the reactor R2 is tD2 and the residence time of the aqueous depolymerization mixture in the reactor R3 is tD3, and wherein 0.90 < (toi I tD2) 1.10, preferably 0.95 < (toi I tD2) 1 -05, and wherein 0.90 < (tD21 to₃) 1.10, preferably 0.95 < (tD21 tos) 1.05.

Preferably according to the present, at least one of the reactors R, preferably all reactors R have one or more outlet means for removing a gas stream from the respective reactor R, i.e. outlet means for degassing the respective reactor R. Therefore, the process of the present invention preferably comprises removing from at least one reactor R, preferably from all z reactors R, a respective gas stream SGI, a given gas stream SGI having a temperature TGI at a pressure PGI, wherein 0.95 < TGI/TDI 1.05. Regarding the preferred arrangement of three reactors R1, R2 and R3, the process more preferably comprises removing from R1 a gas stream SGI , SGI having a temperature TGI at a pressure PGI , wherein 0.95 < TGI/TDI 1 .05, removing from R2 a gas stream SG2, SG2 having a temperature TG2 at a pressure PG2, wherein 0.95 < TG2/TD2 1 .05, and removing from R3 a gas stream SGS, SGS having a temperature TGS at a pressure PGS, wherein 0.95 < TGS/TDS 1 .05. According to the present invention, it may be preferred that the process further comprises combining at least one of the gas streams SGI, more preferably all streams SGI, more preferably the gas streams SGI , SG2 and SGS with the gas stream SGM as described hereinabove, preferably prior to subjecting the gas stream SGM to scrubbing as described hereinabove.

Generally, there are no specific restrictions how the solid material M is provided according to (i). Preferably, providing the solid material M according to (i) comprises

(1.1) providing the solid material M in a delivering unit UMD, wherein UMD preferably comprises one or more of at least one big bag station and at least one a bulk container station;

(1.2) passing the solid material M provided according to (i.1) via a first connecting line from the unit UMD to a material collecting unit UMC, preferably a collecting drum, wherein the first connecting line preferably comprises one or more of at least one material receiving and discharge unit UMRD, at least one first material feeding unit UFMF, and at least one first particle separation unit UFMPS;

(i.3) passing the solid material M from the unit UMC via a second connecting line to the unit UM, wherein the second connecting line preferably comprises one or more of at least one second material feeding unit USMF, at least one second particle separation unit USMPS, and at least one metal detector.

Preferably, the first connecting line according to (i.2) comprises at least one unit UMRD, preferably at least one hopper, more preferably at least one one-zone hopper, and further comprises at least one unit UFMF, preferably at least one rotary feeder, and preferably further comprises at least particle separation unit UFMPS, more preferably at least one filter, more preferably at least one mesh filter.

Further preferably, for passing the solid material M via a first connecting line from the unit UMD to the unit UMC, at least one gas stream SG is passed through the first connecting line, said at least one gas stream preferably comprising, more preferably consisting of air or lean air, wherein prior to being passed through the first connecting line, the at least one gas stream is preferably pretreated by at least one of filtrating, compressing and cooling, more preferably by filtrating, compressing and cooling.

Further preferably, the second connecting line according to (i.3) comprises at least two units USMF, preferably comprising a rotary feeder and a loss-in-weight feeder, wherein more preferably, the rotary feeder is arranged upstream of the loss-in-weight feeder, and further comprises a unit USMPS, preferably a vibrating screen.

Preferably according to (i), the solid material M is provided, preferably provided to UM, in the form of particles, wherein the particle size distribution of said particles is preferably characterized by one or more of the following pairs of values, preferably by two or more of the following pairs of values, more preferably by the following three pairs of values: a D10 value of the particle width in the range of from in the range of from 0.3 to 15 mm and a D10 value of the particle length in the range of from 0.3 to 15 mm; a D50 value of the particle width in the range of from in the range of from 0.5 to 20 mm and a D50 value of the particle length in the range of from 0.5 to 20 mm; a D90 value of the particle width in the range of from in the range of from 0.8 to 30 mm and a D90 value of the particle length in the range of from 0.8 to 30 mm.

More preferred pairs of values are, for example: a D10 value of the particle width in the range of from in the range of from 2 to 4 mm and a D10 value of the particle length in the range of from 3.5 to 5.5 mm; a D50 value of the particle width in the range of from in the range of from 2.5 to 4.5 mm and a D50 value of the particle length in the range of from 4 to 7 mm; a D90 value of the particle width in the range of from in the range of from 3 to 5 mm and a D90 value of the particle length in the range of from 4.5 to 8.5 mm.

The term “particle” as used in this context of the present invention comprises optionally preformed granules, and also comprises shredded pieces.

Preferably from 10 to 100 weight-%, more preferably from 30 to 100 weight-%, more preferably from 50 to 100 weight-%, more preferably from 60 to 100 weight-%, more preferably from 70 to 100 weight-%, more preferably from 80 to 100 weight-%, of the solid material M provided according to (i) consist of the polyamide 6. If the polyamide 6 content of the solid material M is less than 100 weight-%, it may be preferred that the solid material M additionally comprises one or more elastanes. Generally, the solid material M may comprise, in addition to polyamide 6, at least one further polymeric compound, wherein the at least one further polymeric compound preferably comprises one or more of at least one polyamide 6.6; at least one semiaromatic polyamide including one or more of polyamide 6T and polyamide 6I; at least one polyethylene terephthalate; at least one polyurethane; at least one polyester; at least one polyether; at least one polyvinyl chloride; at least one natural fiber material such as wool and cotton; at least one cellulose material; at least one natural elastomer; at least one synthetic elastomer; at least one copolymer of two or more of said polymeric compounds including statistical copolymers, gradient copolymers, alternating copolymers, block copolymers, and graft copolymers; and at least one rubber material comprising one or more of at least one natural rubber material and at least one synthetic rubber material. Further, in addition to polyamide 6, the solid material M may further comprise one or more of at least one pigment material and at least one glass fiber material.

Preferably, the solid material M provided according to (i) comprises, more preferably consists of, a waste material, more preferably one or more of a textile waste material and an engineering plastics waste material, more preferably a textile waste material. Generally, the solid material M provided according to (i) may consist of one single material or from several different materials, i.e. it consists of w chemical materials Mj with j=1 ..w and w>1 . Further according to the present invention, preferably at least one of the chemical materials Mj, more preferably every chemical material Mj comprises, preferably consists of a waste material, said waste material preferably comprising, more preferably consisting of at least one textile waste material. If w>1 , the respective two or more materials may have different chemical compositions which are not subject to any specific restrictions with the proviso that the solid material M exhibits the composition as discussed above.

According to the present invention, it is preferred that from 90 to 100 weight-%, more preferably from 91 to 100 weight-%, more preferably from 92 to 100 weight-%, more preferably from 93 to 100 weight-%, more preferably from 94 to 100 weight-%, more preferably from 95 to 100 weight- % of the liquid aqueous stream Sw provided according to (iii) consist of water. More preferred ranges may be from 96 to 100 weight-% or from 97 to 100 weight-% or from 99 to 100 weight-% or from 99 to 100 weight-%. Preferably according to the present invention, providing the liquid aqueous stream Sw according to (iii) comprises generating an aqueous stream comprising at least part of the water comprised in the stream SR, and feeding at least part of said generated aqueous stream back to the chemical reaction unit UR as the aqueous stream Sw or as part thereof.

Regarding said recycling of water, it is possible, for example, that the process comprises subjecting the stream SR obtained from the chemical reaction unit UR, optionally after subjecting SR to filtration, to thermal water separation, obtaining an aqueous stream Sx; and feeding at least part of the aqueous stream Sx back to the chemical reaction unit UR as part of the aqueous stream Sw, wherein said thermal water separation preferably comprises one or more of distilling and falling film evaporating. Preferably, generating the aqueous stream Sx may comprise distilling the stream SR obtained from the reaction unit UR, optionally after subjecting SR to filtration, obtaining the stream Sx. Said distilling preferably may be carried out in a distillation column at a bottoms temperature preferably in the range of from 70 to 140 °C, more preferably in the range of from 80 to 120 °C, more preferably in the range of from 90 to 110 °C, and a top pressure preferably in the range of from 0.5 to 1.5 bar, more preferably in the range of from 0.7 to 1.2 bar, more preferably in the range of from 0.8 to 1 .1 bar, wherein the stream Sx is obtained at the top of the distillation column. Further, said distilling preferably may comprise subjecting the vapor top stream to condensation, obtaining a liquid stream Sx, wherein at least a part of the liquid stream Sx is fed back to the chemical reaction unit UR as part of the aqueous stream Sw. Said liquid stream Sx obtained from condensation may preferably be divided into 2 streams, wherein a first stream obtained from dividing is fed back to the chemical reaction unit UR as part of the aqueous stream Sw and a second stream is fed back to the top of the distillation column, wherein the volume ratio of the first stream relative to the second stream is preferably in the range of from 10:1 to 0.5:1 , more preferably in the range of from 7:1 to 1 :1 , more preferably in the range of from 5:1 to 2:1.

Regarding said recycling of water, it is preferred according to the process of the present invention wherein according to (vii), the stream SR comprising e-caprolactam dissolved in water at a concentration CSR, the stream SR further comprising one or more impurities, that the process further comprises

(viii) passing the liquid aqueous stream SR into an evaporation unit UE, obtaining from SR a liquid aqueous stream SL comprising e-caprolactam dissolved in water at a concentration CSL with CSL > CSR, and further obtaining from SR one or more aqueous vapor streams Sv;

(ix) passing the aqueous stream SL into a heat-consuming purification unit UP, obtaining from SL a stream SCPL comprising e-caprolactam at a concentration CSCPL with CSCPL » CSL, and further obtaining from SL one or more aqueous streams SRW, wherein at least part of the heat consumed in UP is provided by at least one of the one or more streams Sv, thereby obtaining from the at least one stream Sv at least one at least partially condensed aqueous stream Svw;

(x) recycling at least one stream Svw at least partially to the reaction unit UR and at least one stream SRW at least partially to the reaction unit UR. The recycling according to (x) preferably comprises

(x.1 ) feeding the at least one stream Svw and the at least one stream SRW into a water treatment unit Uw, obtaining from Uw at least one aqueous recycle stream Sw;

(x.2) recycling the at least one aqueous stream Sw at least partially to the reaction unit UR.

The water treatment unit Uw preferably comprises a water recovery unit UWR and a waste water unit Uww, wherein (x.1 ) preferably further comprises

(x.1 .1 ) feeding the at least one stream Svw and the at least one stream SRW into the water recovery unit UWR, obtaining from UWR the at least one aqueous recycle stream Sw and at least one aqueous stream Ssw;

(x.1 .2) feeding the at least one stream Ssw to the waste water unit Uww, obtaining from Uww, at least one waste water stream Sww.

The purification unit UP preferably comprises one or more of a heat-consuming water separation unit Uws, a heat-consuming distillation unit UD and a heat-consuming crystallization unit Uc, more preferably two or more of a heat-consuming water separation unit Uws, a heat-consuming distillation unit UD and a heat-consuming crystallization unit Uc, more preferably a heatconsuming water separation unit Uws, a heat-consuming distillation unit UD and a heat-consuming crystallization unit Uc, wherein at least part of the heat consumed in one or more of Uws, UD and Uc is provided by at least one of the one or more streams Sv.

For such purification unit UP, the process preferably comprises one or more of (a-1 ), (a-2) and (a- 3); more preferably at least two or more of (a-1 ), (a-2) and (a-3); more preferably (a-1 ), (a-2) and (a-3):

(a-1 ) obtaining at least one at least partially condensed aqueous stream Svwi from Uws;

(a-2) obtaining at least one at least partially condensed aqueous stream Svw2 from UD;

(a-3) obtaining at least one at least partially condensed aqueous stream Svws from Uc; wherein the process further comprises feeding one or more Svwi, Svw2 and Svws; preferably two or more Svwi, Svw2 and Svws; more preferably Svwi, Svw2 and Svws into the water treatment unit Uw as defined in embodiment 29.

Preferably, at least one of the streams SRW is obtained from Uws.

Preferably, the purification unit UP comprises a heat-consuming water separation unit Uws, a heat-consuming distillation unit UD and a heat-consuming crystallization unit Uc, wherein the process comprises feeding the stream SL comprising e-caprolactam at a concentration CSL to Uws, obtaining from Uws a stream Uws comprising e-caprolactam at a concentration Cuws, feeding the stream Sows to the distillation unit UD, obtaining from UD a stream SUD comprising e-caprolactam at a concentration CUD, and feeding the stream SUD into the crystallization unit Uc, and obtaining from Uc a stream SCPL comprising e-caprolactam at a concentration CSCPL, wherein CSL < Cuws < CUD < CSCPL- Preferably, the water separation unit Uws comprises at least two heat-consuming water separation sub-units Uwsi and Uws2, more preferably two serially coupled heat-consuming water separation sub-units Uwsi and Uws2, wherein the stream SL is preferably fed into Uwsi and wherein at least part of the heat consumed in one or more of Uwsi and Uws2 is preferably provided by at least one of the one or more streams Sv.

For such water separation unit Uws, the process preferably comprises one or more of (b-1 ) and (b-2) preferably (b-1 ) and (b-2):

(b-1 ) obtaining at least one at least partially condensed aqueous stream Svwn from Uwsi; (b-2) obtaining at least one at least partially condensed aqueous stream Svwi2 from U s2.

Further for such water separation unit Uws, it is preferred that at least one aqueous stream SRWI is obtained from Uwsi and at least one aqueous stream SRW2 is obtained from Uws2, and wherein at least one of SRWI and SRW2, preferably SRWI and SRW2 are fed into Uw.

Yet further for such water separation unit Uws, it is preferred that downstream of Uwsi and upstream of Uws2, a separation unit Ui is located, wherein the process preferably comprises obtaining from Uwsi an aqueous stream Suwsi, feeding the stream Suwsi into the separation unit Ui, obtaining from Ui an aqueous stream Sui, and feeding the stream Sui into the unit Uws2, wherein in Ui, one or more of impurities are separated from Suwsi, thereby obtaining from Ui an impurity stream Si, said impurities preferably comprising at least one impurity comprised in SR according to (vii).

Preferably, the evaporation unit UE comprises two or more evaporation sub-units, wherein the process preferably comprises obtaining at least two vapor streams Svi and Sv2, passing the vapor stream Svi to at least one heat-consuming unit and passing the vapor stream Sv2 to at least one heat-consuming unit, wherein the vapor streams Svi and Sv2 differ from each other in either pressure and/or temperature.

Preferably, downstream of UR, at least one solid-liquid separation unit is arranged, wherein it is preferred that at least one of the streams SL and SR is passed through at least one solid-liquid separation unit prior to being passed to the next downstream unit.

According to the present invention, it is preferred that the solid material M provided according to (i) comprises, preferably consists of, a waste material, preferably one or more of a textile waste material and an engineering plastics waste material, more preferably of a textile waste material.

Regarding the stream SCPL described above, i.e. the purified s-caprolactam stream, is may be preferred that said stream SCPL is passed to a polyamide 6 production unit UPP where it is employed as starting material. If need be, one or more further streams SNCPL can be additionally passed to UPP, said streams comprising non-recycled s-caprolactam, i.e. s-caprolactam from a conventional source. The respectively prepared polyamide 6 material preferably may then be passed to a unit UTP where it is used as a starting material for preparing a material comprising polyamide 6, preferably a textile material comprising polyamide 6. If need be, one or more further streams SNPAS can be additionally passed to UTP, said streams comprising non-recycled polyamide 6, i.e. polyamide 6 from a conventional source. Depending on the type of material prepared in UTP, also further streams comprising one or more starting materials other than polyamide 6 can be passed to UTP. The material, preferably the textile material MT obtained from UTP then preferably goes into the market and remains there for a given lifetime TMT. Thereafter, the respective end-of-life material is suitably collected in a collecting unit UTC, preferably a textile material collecting unit, from which it is suitably passed as the solid material M or as part of the solid material M to the process as described above, optionally after sorting as described herein.

Therefore, according to the present invention, the process may preferably further comprise providing the stream SCPL to a polyamide 6 production unit UPP, wherein the polyamide 6 produced in UPP is preferably provided as a feedstock to a textile material producing unit UTP, from which unit UTP

(A) a textile material MT is obtained which is brought onto the market, wherein, after the lifetime TMT of said textile material MT, it is at least partially collected as textile waste material in a textile material collecting unit UTC_;

(B) remaining material MR is obtained as textile waste material; wherein at least part of the textile waste material according to (A), or at least part of the textile waste material according to (B), or at least part of the textile waste material according to (A) and at least part of the textile waste material according to (B) is suitably provided to UR via UM.

Therefore, the present invention also relates to the use of SCPL, obtainable or obtained by a process as described hereinabove, for preparing polyamide 6, said use preferably further comprising employing said polyamide 6 as a feedstock for preparing a textile material.

Further, the present invention also relates to a method for preparing polyamide 6, said method comprising employing SCPL, obtainable or obtained by a process as described hereinabove, as a starting material, wherein said method preferably further comprises employing said polyamide 6 as a feedstock for preparing a textile material.

Further according to the present invention, the process may preferably further comprise providing the stream SCPL to a polyamide 6 production unit UPP, wherein the polyamide 6 produced in UPP is preferably provided as a feedstock to an engineering plastics material producing unit UEP, from which unit UEP

(A) an engineering plastics material ME is obtained which is brought onto the market, wherein, after the life-time TME of said engineering plastics material ME it is at least partially collected as engineering plastics waste material in an engineering plastics material collecting unit UEC;

(B) remaining material MR is obtained as engineering plastics waste material; wherein at least part of the engineering plastics waste material according to (A), or at least part of the engineering plastics waste material according to (B), or at least part of the engineering plastics waste material according to (A) and at least part of the engineering plastics waste material according to (B) is suitably provided to UR as SM, preferably via UM.

Therefore, the present invention also relates to the use of SCPL, obtainable or obtained by a process as described hereinabove, for preparing polyamide 6, said use preferably further comprising employing said polyamide 6 as a feedstock for preparing an engineering plastics material.

Further, the present invention also relates to a method for preparing polyamide 6, said method comprising employing SCPL, obtainable or obtained by a process as described hereinabove, as a starting material, wherein said method preferably further comprises employing said polyamide 6 as a feedstock for preparing an engineering plastics material.

According to a further aspect, the present invention relates to an integrated process for preparing polyamide 6, comprising

(a) preparing a stream SCPL according to a process as described herein, said stream SCPL comprising purified e-caprolactam;

(P) passing the stream SCPL to a polyamide 6 production unit UPA;

(y) subjecting the stream SCPL in UPA to e-caprolactam polymerization conditions, obtaining from UPA a polyamide 6 material MP and a stream comprising water and one or more £-caprolactam oligomers;

(5) optionally subjecting to stream comprising water and one or more e-caprolactam oligomers to concentration with respect to the one or more e-caprolactam oligomers in at least one concentration stage, obtaining a concentrated stream comprising water and one or more £-caprolactam oligomers;

(E) passing the optionally concentrated stream comprising water and one or more £-caprolactam oligomers into at least one of the melting unit UM and the water separation sub-unit Uws2 described herein.

Preferably, the optionally concentrated stream comprising water and one or more £-caprolactam oligomers according to (E) further comprises £-caprolactam, i.e. monomeric £-caprolactam.

Further preferably, said integrated process comprises

(y) subjecting the stream SCPL in UPA to £-caprolactam polymerization conditions, obtaining from UPA a polyamide 6 material MP and a stream SEW comprising water at a concentration CE (W), £-caprolactam at a concentration CE (C), and one or more £-caprolactam oligomers at a total concentration CE (O);

(5) subjecting the stream SE to concentration, comprising

(6.1) subjecting the stream SEW to concentration in a first concentration unit Uci, obtaining from Uci a concentrated stream Sci comprising water at a concentration Cci(W), £-caprolactam at a concentration Cci(C), and one or more e-caprolactam oligomers at a total concentration Cci(O), with Cci(W) < CEW(W), CCI (C) > CEW(C) and

Cci(O)> CEW(O), and further obtaining from Uci an aqueous stream Swi comprising water at a concentration Cwi(W) > CEW(W);

(5.2) subjecting the stream Sci to concentration in a second concentration unit Uc2, obtaining from Uc2 a concentrated stream Sc2 comprising one or more e-caprolactam oligomers at a total concentration Cc2(O), with Cc2(O) > Cci(O), and further obtaining from Uc2 an aqueous stream Sw2 comprising water at a concentration Cw2(W) and £-caprolactam at a concentration Cw2(C), with Cw2(W) > Cwi(W) and Cw2(C) > Cwi(C);

(E) passing the stream Sc2 to the sub-unit UM and the stream Sw2 to the sub-unit Uws2.

As described above, the stream SEW which is obtained from the polyamide 6 polymerization unit UPA comprises water, monomeric £-caprolactam and one or more £-caprolactam oligomers. Usually, this aqueous stream SE furher comprises one or more further organic compounds other than monomeric £-caprolactam and one or more £-caprolactam oligomers. Therefore, it is preferred that the stream SEW further comprises one or more organic compounds X other than £-caprolactam and oligomers thereof at a total concentration CEW(X), the process according to (5) comprising

(5.1 ) subjecting the stream SEW to concentration in a first concentration unit Uci, obtaining from Uci a concentrated stream Sci comprising water at a concentration Cci(W), £-caprolactam at a concentration Cci(C), one or more £-caprolactam oligomers at a total concentration Cci(O) and one or more organic compounds X at a total concentration Cci(X), with Cci(W) < CEW(W), CCI (C) > CEW(C), C_CI (O)> C_EW(O) and c_Ci(X)> c_Ew(X), and further obtaining from Uci an aqueous stream Swi comprising water at a concentration

Cwi(W) > CEW(W);

(5.2) subjecting the stream Sci to concentration in a second concentration unit Uc2, obtaining from Uc2 a concentrated stream Sc2 comprising one or more £-caprolactam oligomers at a total concentration Cc2(O) and one or more organic compounds X at a total concentration Cc2(X), with Cc2(O) > Cci(O) and Cc2(X) > Cci(X), and further obtaining from Uc2 an aqueous stream Sw2 comprising water at a concentration Cw2(W) and £-caprolactam at a concentration Cw2(C), with Cw2(W) > Cwi(W) and Cw2(C) > Cwi(C).

More preferably according to the present invention, (y) comprises

(y.1 ) passing the stream SCPL and preferably an aqueous stream SAQO to a polymerization stage STo, obtaining from STo a polyamide 6 crude product stream SPAI and an aqueous stream SWAI ;

(y.2) passing the stream SPAI and preferably an aqueous stream SAQI to a granulation stage STi, obtaining from STi a crude granulated polyamide 6 material MPA2 and an aqueous stream SwA2;

(y.3) passing the material MPA2 and preferably an aqueous stream SAQ2 to an extraction stage ST2, obtaining from ST2 a purified granulated polyamide 6 material MPAS and an aqueous stream SWAS; (y.4) passing the material MPAS to a drying stage ST3, obtaining from ST3 the polyamide 6 material MP and an aqueous stream SWA4.

Assuming that some of the polyamide 6 material obtained from the production unit UPA does not meet the specifications, the process may preferably further comprise passing at least some of said material MPR to the unit UM.

The process of the present invention as described above may preferably be a continuous process. However, one or more process steps may be carried out in a batch-type mode, and one or more steps may be carried out in a semicontinuous mode.

The present invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and back-references as indicated. In particular, it is noted that in each instance where a range of embodiments is mentioned, for example in the context of a term such as "The process of any one of embodiments 1 to 4", every embodiment in this range is meant to be explicitly disclosed for the skilled person, i.e. the wording of this term is to be understood by the skilled person as being synonymous to "The process of any one of embodiments 1 , 2, 3 and 4". Further, it is explicitly noted that the following set of embodiments represents a suitably structured part of the general description directed to preferred aspects of the present invention, and, thus, suitably supports, but does not represent the claims of the present invention.

1 . A process for hydrolytically depolymerizing a polyamide 6 comprised in a solid material M, the process comprising

(i) providing the solid material M;

(vi) subjecting the stream SF in the reaction unit UR to polyamide 6 depolymerization conditions comprising a polyamide 6 depolymerization temperature TD at a polyamide 6 depolymerization pressure PD, obtaining in UR an aqueous depolymerization mixture comprising e-caprolactam dissolved in water;

(vii) removing an aqueous liquid reactor exit stream SR from UR, the stream SR comprising e-caprolactam dissolved in water; wherein 0.8 < TSF/TD 1.05 and 0.9 < PSF/PD 1 .05.

2. The process of embodiment 1 , wherein 0.6 < TSM/TSF 1.05 and 0.9 < PSM/PSF 1 .05. 3. The process of embodiment 1 , wherein 0.8 < TSW/TSF 1 .3 and 0.9 < psw/psF 1.05.

4. The process of any one of embodiments 1 to 3, wherein the pre-reaction unit UPR according to (iv) comprises, preferably consists of, a mixing unit, preferably a static mixing unit.

5. The process of any one of embodiments 1 to 4, wherein according to (iv), Sw and SM are admixed in UPR at a mixing ratio (n kg) I (mp/kg) in the range of from 1 :1 to 20:1 , preferably in the range of from 2:1 to 15:1 , more preferably in the range of from 5:1 to 10:1 , wherein mw is the amount of water comprised in Sw and m? is the amount of polyamide 6 comprised in SM.

6. The process of any one of embodiments 1 to 5, wherein the melting unit UM comprises, preferably consists of an extruder, preferably a single-screw extruder or a twin-screw extruder.

7. The process of any one of embodiments 1 to 6, preferably of embodiment 6, wherein the melting unit UM is equipped with a degassing system, wherein the process comprises removing a gas stream SGM from UM during melting according to (ii), said gas stream SGM having a temperature TGM at a pressure PGM, wherein 0.95 < TGM/TSM 1.05.

8. The process of embodiment 7, wherein the gas stream SGM removed from UM is subjected to scrubbing in a scrubbing unit Us, preferably to one or more of wet scrubbing and dry scrubbing, more preferably to wet scrubbing, wherein said wet scrubbing preferably comprises passing the gas stream SGM into a scrubbing column, preferably a packed scrubbing column.

9. The process of any one of embodiments 1 to 8, wherein downstream of the melting unit UM and upstream of the reaction unit UR, a filtration unit UF is arranged, preferably a filtration unit UF for separating particles having a particle size in the range of from 100 to 500 micrometer, preferably in the range of from 200 to 400 micrometer, from the liquid stream SM, wherein the process comprises passing the stream liquid stream SM through UF, prior to admixing according to (iv).

10. The process of any one of embodiments 1 to 9, wherein according to (vi), TD is in the range of from 230 to 330 °C and PD is in the range of from 40 to 140 bar, preferably wherein TD is in the range of from 250 to 320 °C and PD is in the range of from 40 to 125 bar, more preferably wherein TD is in the range of from 270 to 310 °C and PD is in the range of from 40 to 110 bar.

11 . The process of any one of embodiments 1 to 10, wherein the reaction unit UR according to (v) comprises z chemical reactors R, i=1 ...z, wherein z is in the range of from 1 to 10, preferably in the range of from 1 to 8, more preferably in the range of from 1 to 6, more preferably in the range of from 1 to 5, more preferably in the range of from 1 to 4, more preferably in the range of from 1 to 3.

12. The process of embodiment 11 , wherein if z > 1 , at least 2 reactors R, preferably z reactors R are serially coupled, wherein according to (v), the stream SF is fed into R, with i = 1 ; an aqueous liquid stream Sj containing e-caprolactam dissolved in water is removed from reactor R and fed into the reactor R+i, with i < z; according to (vii), the aqueous liquid stream S_z containing e-caprolactam dissolved in water is removed from the reactor R_z as the stream SR; wherein in every reactor R, a depolymerization temperature TDI at a depolymerization pressure poi is maintained, wherein, independently of each other, TDI is in the range of from 230 to 330 °C and poi is in the range of from 40 to 140 bar, preferably wherein TDI is in the range of from 250 to 320 °C and poi is in the range of from 40 to 125 bar, more preferably wherein TDI is in the range of from 270 to 310 °C and poi is in the range of from 40 to 110 bar.

13. The process of embodiment 12, wherein for z > 1 , the z reactors R are vertically arranged, with Ri being the top-most reactor and R_z being the bottom-most reactor, wherein Sj obtained from R is transferred to R+i by gravity, preferably by gravity only.

14. The process of any one of embodiments 11 to 13, wherein at least 1 , preferably z reactors R, are stirred tank reactors.

15. The process of embodiment 14, wherein every stirred tank reactor R has, independently from each other, from 2 to 6 compartments, preferably from 2 to 5 compartments, more preferably from 2 to 4 compartments, said compartments preferably being serially, more preferably being serially and vertically arranged, wherein 2 adjacent compartments are separated by a divider which comprises at least one flow-through opening.

16. The process of embodiment 15, wherein at least one compartment comprised in a reactor R comprises at least one agitator, wherein preferably every compartment of every reactor R comprises at least one agitator, wherein more preferably, every compartment of every reactor R comprises one agitator, wherein the process comprises agitating the depolymerization mixture in a given compartment for at least part of the time during subjecting to depolymerization conditions in said compartment.

17. The process of any one of embodiments 1 to 16, preferably of any one of embodiments 11 to 16, more preferably of embodiment 15 or 16, wherein the polyamide 6 depolymerization conditions according to (vi) further comprise a total residence time to of the aqueous depolymerization mixture in the unit UR, preferably in the z reactors R, more preferably in the z stirred tank reactors, wherein at least 85 weight-%, preferably at least 90 weight-%, more preferably at least 95 weight-% of the aqueous depolymerization mixture have a to in the range of from 30 to 90 min. The process of embodiment 17 as far as embodiment 17 is dependent on any one of embodiments 11 to 16 with z > 1 , preferably on embodiment 15 or 16 with z > 1 , wherein the residence time of an aqueous depolymerization mixture in a reactor Rj is toi and wherein 0.90 < (toi I toi+i) 1.10, preferably 0.95 < (toi I toi+i) 1.05. The process of any one of embodiments 11 to 18, comprising removing from at least one reactor R, preferably from all z reactors R, a respective gas stream SGI, a given gas stream SGI having a temperature TGI at a pressure PGI, wherein 0.95 < TGI/TDI 1.05. The process of embodiment 19, further comprising combining at least one of the gas streams SGI, preferably all streams SGI, with the gas stream SGM as defined in embodiment 7, prior to subjecting the gas stream SGM to scrubbing as defined in embodiment 8. The process of any one of embodiments 1 to 20, wherein providing the solid material M according to (i) comprises

(1.1 ) providing the solid material M in a delivering unit UMD, wherein UMD preferably comprises one or more of at least one big bag station and at least one a bulk container station;

(1.3) passing the solid material M from the unit UMC via a second connecting line to the unit UM, wherein the second connecting line preferably comprises one or more of at least one second material feeding unit USMF, at least one second particle separation unit USMPS, and at least one metal detector. The process of embodiment 21 , wherein the first connecting line according to (i.2) comprises at least one unit UMRD, preferably at least one hopper, more preferably at least one one-zone hopper, and further comprises at least one unit UFMF, preferably at least one rotary feeder, and preferably further comprises at least particle separation unit UFMPS, more preferably at least one filter, more preferably at least one mesh filter. The process of embodiment 21 or 22, wherein for passing the solid material M via a first connecting line from the unit UMD to the unit UMC, at least one gas stream SG is passed through the first connecting line, said at least one gas stream preferably comprising, more preferably consisting of air or lean air, wherein prior to being passed through the first connecting line, the at least one gas stream is preferably pre-treated by at least one of filtrating, compressing and cooling, more preferably by filtrating, compressing and cooling.

24. The process of any one of embodiments 21 to 23, wherein the second connecting line according to (i.3) comprises at least two units USMF, preferably comprising a rotary feeder and a loss-in-weight feeder, wherein more preferably, the rotary feeder is arranged upstream of the loss-in-weight feeder, and further comprises a unit USMPS, preferably a vibrating screen.

25. The process of any one of embodiments 1 to 24, wherein according to (i), the solid material M is provided, preferably provided to UM, in the form of granules, wherein the particle size distribution of said granules is preferably characterized by one or more of the following pairs of values, preferably by two or more of the following pairs of values, more preferably by the following three pairs of values: a D10 value of the particle width in the range of from in the range of from 0.3 to 15 mm and a D10 value of the particle length in the range of from 0.3 to 15 mm; a D50 value of the particle width in the range of from in the range of from 0.5 to 20 mm and a D50 value of the particle length in the range of from 0.5 to 20 mm; a D90 value of the particle width in the range of from in the range of from 0.8 to 30 mm and a D90 value of the particle length in the range of from 0.8 to 30 mm.

26. The process of any one of embodiments 1 to 25, wherein from 10 to 100 weight-%, more preferably from 30 to 100 weight-%, more preferably from 50 to 100 weight-%, more preferably from 60 to 100 weight-%, more preferably from 70 to 100 weight-%, more preferably from 80 to 100 weight-%, of the solid material M consist of the polyamide 6.

27. The process of any one of embodiments 1 to 26, wherein providing the liquid aqueous stream Sw according to (iii) comprises generating an aqueous stream comprising at least part of the water comprised in the stream SR, and feeding at least part of said generated aqueous stream back to the chemical reaction unit UR as the aqueous stream Sw or as part thereof.

28. The process of any one of embodiments 1 to 27, wherein according to (vii), the stream SR comprising e-caprolactam dissolved in water at a concentration CSR, the stream SR further comprising one or more impurities, the process further comprising

(x) recycling at least one stream Svw at least partially to the reaction unit UR and at least one stream SR at least partially to the reaction unit UR.

29. The process of embodiment 28, wherein the recycling according to (x) comprises (x.1) feeding the at least one stream Svw and the at least one stream SRW into a water treatment unit Uw, obtaining from Uw at least one aqueous recycle stream Sw;

30. The process of embodiment 29, wherein the water treatment unit Uw comprises a water recovery unit UWR and a waste water unit Uww, wherein (x.1) further comprises

(x.1.1 ) feeding the at least one stream Svw and the at least one stream SRW into the water recovery unit UWR, obtaining from UWR the at least one aqueous recycle stream Sw and at least one aqueous stream Ssw;

31 . The process of any one of embodiments 28 to 30, wherein the purification unit UP comprises one or more of a heat-consuming water separation unit Uws, a heat-consuming distillation unit UD and a heat-consuming crystallization unit Uc, preferably two or more of a heat-consuming water separation unit Uws, a heat-consuming distillation unit UD and a heatconsuming crystallization unit Uc, more preferably a heat-consuming water separation unit Uws, a heat-consuming distillation unit UD and a heat-consuming crystallization unit Uc, wherein at least part of the heat consumed in one or more of Uws, UD and Uc is provided by at least one of the one or more streams Sv.

32. The process of embodiment 31 , comprising one or more of (i-1 ), (i-2) and (i-3); preferably at least two or more of (i-1), (i-2) and (i-3); more preferably (i-1), (i-2) and (i-3):

(i-1) obtaining at least one at least partially condensed aqueous stream Svwi from Uws;

(i-2) obtaining at least one at least partially condensed aqueous stream Svw2 from UD;

(i-3) obtaining at least one at least partially condensed aqueous stream Svws from Uc; the process further comprising feeding one or more Svwi, Svw2 and Svws; preferably two or more Svwi, Svw2 and Svws; more preferably Svwi, Svw2 and Svws into the water treatment unit Uw as defined in embodiment 29.

33. The process of embodiment 31 or 32, wherein at least one of the streams SRW is obtained from Uws. 34. The process of any one of embodiments 28 to 33, wherein the purification unit UP comprises a heat-consuming water separation unit Uws, a heat-consuming distillation unit UD and a heat-consuming crystallization unit Uc, the process comprising feeding the stream SL comprising e-caprolactam at a concentration CSL to Uws, obtaining from Uws a stream Uws comprising e-caprolactam at a concentration Cuws, feeding the stream Sows to the distillation unit UD, obtaining from UD a stream SUD comprising e-caprolactam at a concentration CUD, and feeding the stream SUD into the crystallization unit Uc, and obtaining from Uc a stream SCPL comprising e-caprolactam at a concentration CSCPL, wherein

CSL < Cuws < CUD < CSCPL.

35. The process of any one of embodiments 28 to 34, wherein the water separation unit Uws comprises at least two heat-consuming water separation sub-units Uwsi and Uws2, preferably two serially coupled heat-consuming water separation sub-units Uwsi and Uws2, wherein the stream SL is fed into Uwsi and wherein at least part of the heat consumed in one or more of Uwsi and Uws2 is provided by at least one of the one or more streams Sv.

36. The process of embodiment 35, comprising one or more of (ii-1) and (ii-2) preferably (ii-1 ) and (ii-2):

(ii-1 ) obtaining at least one at least partially condensed aqueous stream Svwn from Uwsi; (ii-2) obtaining at least one at least partially condensed aqueous stream Svwi2 from Uws2.

37. The process of embodiment 36, wherein at least one aqueous stream SRWI is obtained from Uwsi and at least one aqueous stream SRW2 is obtained from Uws2, and wherein at least one of SRWI and S_RW2, preferably S_RWi and S_RW2 are fed into U_w.

38. The process of any one of embodiments 35 to 37, wherein downstream of Uwsi and upstream of Uws2, a separation unit Ui is located, the process comprising obtaining from Uwsi an aqueous stream Suwsi, feeding the stream Suwsi into the separation unit Ui, obtaining from Ui an aqueous stream Sui, and feeding the stream Sui into the unit Uws2, wherein in Ui, one or more of impurities are separated from Suwsi, thereby obtaining from Ui an impurity stream Si, said impurities preferably comprising at least one impurity comprised in SR according to (vii).

39. The process of any one of embodiments 28 to 38, wherein the evaporation unit UE comprises two or more evaporation sub-units, the process comprising obtaining at least two vapor streams Svi and Sv2, passing the vapor stream Svi to at least one heat-consuming unit and passing the vapor stream Sv2 to at least one heat-consuming unit, wherein the vapor streams Svi and Sv2 differ from each other in either pressure and/or temperature.

40. The process of any one of embodiments 28 to 39, wherein downstream of UR, at least one solid-liquid separation unit is arranged, wherein preferably at least one of the streams SL and SR is passed through at least one solid-liquid separation unit prior to being passed to the next downstream unit. The process of any one of embodiments 28 to 40, further comprising providing the stream SCPL to a polyamide 6 production unit UPP, wherein the polyamide 6 produced in UPP is preferably provided as a feedstock to a textile material producing unit UTP, from which unit UTP

(A) a textile material MT is obtained which is brought onto the market, wherein, after the life-time TMT of said textile material MT, it is at least partially collected as textile waste material in a textile material collecting unit UTC_;

(B) remaining material MR is obtained as textile waste material; wherein at least part of the textile waste material according to (A), or at least part of the textile waste material according to (B), or at least part of the textile waste material according to (A) and at least part of the textile waste material according to (B) is suitably provided to UR via UM. The process of any one of embodiments 1 to 41 , wherein from 90 to 100 weight-%, preferably from 91 to 100 weight-%, more preferably from 92 to 100 weight-%, more preferably from 93 to 100 weight-%, more preferably from 94 to 100 weight-%, more preferably from 95 to 100 weight-% of the liquid aqueous stream Sw provided according to (iii) consist of water. The process of any one of embodiments 1 to 42, being a continuous process, a semicontinuous process or a batch process. The process of any one of embodiments 1 to 43, wherein the solid material M provided according to (i) comprises, preferably consists of, a waste material, preferably one or more of a textile waste material and an engineering plastics waste material, more preferably of a textile waste material. Use of SCPL, obtainable or obtained by a process according to any one of embodiments 28 to 44, for preparing polyamide 6, said use preferably further comprising employing said polyamide 6 as a feedstock for preparing one or more of a textile material and an engineering plastics material, more preferably for preparing a textile material. A method for preparing polyamide 6, said method comprising employing SCPL, obtainable or obtained by a process according to any one of embodiments 28 to 44, as a starting material, wherein said method preferably further comprises employing said polyamide 6 as a feedstock for preparing one or more of a textile material and an engineering plastics material, more preferably for preparing a textile material. 47. Use of SCPL, obtainable or obtained by a process according to any one of embodiments 28 to 44, for preparing one or more of a polymer and a polymer product; or a method for preparing one or more of a polymer and a polymer product, said method comprising employing SCPL, obtainable or obtained by a process according to any one of embodiments 28 to 44, as a starting material.

48. The use or the method of embodiment 47, wherein the polymer, or the polymer product, or the polymer and the polymer product is or are in the form of at least one of a granulate, a strand, a rod, a plate, a pipe, a foil, a layer, a film, a sheet, a fiber, a filament, a coating, an extruded article, a molded article, a soft foam, a half-rigid foam and a rigid foam.

49. The use or the method of embodiment 47 or 48, wherein the polymer, or the polymer product, or the polymer and the polymer product comprises or comprise polyamide 6 and optionally at least one further polymeric compound, wherein the at least one further polymeric compound preferably comprises one or more of at least one polyamide 6.6; at least one semiaromatic polyamide including one or more of polyamide 6T and polyamide 61; at least one polyethylene terephthalate; at least one polyurethane; at least one polyester; at least one polyether; at least one polyvinyl chloride; at least one natural fiber material such as wool and cotton; at least one cellulose material; at least one natural elastomer; at least one synthetic elastomer; at least one copolymer of two or more of said polymeric compounds including statistical copolymers, gradient copolymers, alternating copolymers, block copolymers, and graft copolymers; and at least one rubber material comprising one or more of at least one natural rubber material and at least one synthetic rubber material.

50. The use or the method of any one of embodiments 47 to 49, wherein the polymer, or the polymer product, or the polymer and the polymer product is or are one of the following or a part of one of the following: a part of a car, preferably a cylinder head cover, an engine cover, a housing for a charge air cooler, a charge air cooler flap, an intake pipe, an intake manifold, a connector, a gear wheel, a fan wheel, a cooling water box, a housing or a housing part for a heat exchanger, a coolant cooler, a charge air cooler, a thermostat, a water pump, a radiator, a fastening part or a part of a battery system for electromobility, a dashboard, a steering column switch, a seat, a headrest, a center console, a transmission component, a door module, a car exterior for an A, a B, a C or a D pillar cover, a spoiler, a door handle, an exterior mirror, a windscreen wiper, a windscreen wiper protection housing, a decorative grill, a cover strip, a roof rail, a window frame, a sunroof frame, an antenna panel, a headlight, a taillight, an airbag, and/or a cushion; a cloth, an apparel, preferably a shirt, trousers, a pullover, a boot, a shoe, a shoe sole, a tight and/or or jacket; an electrical part, preferably an electrical component, an electronic passive component, an electronic active component, a printed circuit board, a housing component, a foil, a line, a switch such as a microswitch, a plug, a socket, a distributor, a relay, a resistor, a capacitor, an inductor, a bobbin, a lamp, a diode such as an LED, a transistor, a connector, a regulator, an integrated circuit (IC), a processor, a controller, a memory, a sensor, a microbutton, a semiconductor, a reflector housing for example for light-emitting diodes, a fastener for an electrical and/or an electronic component, a spacer, a bolt, a strip, a slide-in guide, a screw, a nut, a film hinge, a snap hook (snap-in), and/or a spring tongue; a consumer and/or a pharmaceutical product, preferably a tennis string, a climbing rope, a bristle, a brush, an artificial grass, a 3D printing filament, a grass trimmer, a zipper, a hook and loop fastener, a paper machine clothing, an extrusion coating, a fishing line, a fishing net, an offshore line and rope, a vial, a syringe, an ampoule, a bottle, a sliding element, a spindle nut, a chain conveyor, a plain bearing, a roller, a wheel, a gear, a roller, a ring gear, a screw and spring damper, a hose, a pipeline, a cable sheathing, a socket, a switch, a cable tie, a fan wheel, a carpet, a box and/or a bottle for cosmetics, a mattress, a cushion, an insulation; a packaging for the food industry, preferably a mono- and/or multi-layer blown film, a cast film (mono- and/or multi-layer), a biaxially stretched film, a laminating film.

51 . The use or the method of any one of embodiments 47 to 50, wherein the polymer, or the polymer product, or the polymer and the polymer product contains or contain polyamide 6 in an amount of 1 weight-% or more, preferably 2 weight-% or more, more preferably 5 weight-% or more, more preferably 15 weight-% or more, more preferably 30 weight-% or more, more preferably 40 weight-% or more, more preferably 60 weight-% or more, more preferably 80 weight-% or more, more preferably 90 weight-% or more, more preferably 95 weight-% or more; and/or in an amount of 100 weight-% or less, preferably 95 weight-% or less, more preferably 90 weight-% or less, more preferably 50 weight-% or less, more preferably 25 weight-% or less, more preferably 10 weight-% or less.

As far as the embodiment 51 is concerned, the respective amounts are preferably determined based on identity preservation and/or segregation and/or mass balance and/or book and claim chain of custody models, more preferably based on mass balance, more preferably the International Sustainability and Carbon Certification (ISCC) standard.

As far as the embodiments 47 to 51 are concerned, preparing the polymer, the polymer product, or the polymer and the polymer product may comprise one or more synthesis steps and can be performed by conventional synthesis and technics well known to the person skilled in the art. Examples of the synthesis steps are described in “Industrial Organic Chemistry”, 3^rd volume, Wiley-VCH, 1997; ISBN: 978-3-527-28838-0; „Kunststoffhandbuch“, 11 volumes in 17 subvolumes, Carl HanserVerlag, especially volume 6, „Polyamide“, 1^st edition, 1966; “Injection Molding Reference Guide, 4^th edition, CreateSpace Independent Publishing Platform, 2011 , ISBN: 978-1466407824; WO 2008/155271 A1 and WO 2013/139827 A1 , each of which is incorporated herein by reference. The term „bar“ as used herein refers to „bar(abs)”, i.e. bar (absolute), sometimes also referred to “bara”.

The term “textile material” as used herein covers textile raw materials and non-textile raw materials that are processed by various methods into linear, planar and spatial structures. It concerns the linear textile structures produced from them, such as yarns, twisted yarns and ropes, the sheet-like textile structures, such as woven fabrics, knitted fabrics, braids, stitch- bonded fabrics, nonwovens and felts, and the three-dimensional textile structures, i.e. body structures, such as textile hoses, stockings or textile semi-finished products; and it further concerns those finished products which, using the aforementioned products, are brought into a saleable condition by making up, opening up and/or other operations for onward transmission to the processor, the trade or the end consumer. The term “textile waste material” as used herein covers a textile material as defined above, the inherent value of which has been consumed from the perspective of its current holder and, thus, is an end-of-life material for said holder.

The term “engineering plastics” as used herein refers to high-performance plastics grades which possess physical properties enabling them to perform for prolonged use in structural applications, over a wide temperature range, under mechanical stress, and in difficult chemical and physical environments used for example to fabricate plastic parts replacing traditional engineering materials like metals and ceramics. Engineering plastics specifically apply in the fabrication of mechanical parts across several industries such as automotive, medical, electrical and electronics, aerospace, construction and consumer products. The term “engineering plastics waste material” as used herein covers an engineering plastics material as defined above, the inherent value of which has been consumed from the perspective of its current holder and, thus, is an end-of-life material for said holder.

The term “elastane” as used herein is also referred to as “spandex”, and common brand names for spandex include Lycra, Elaspan, Acepora, Creora, Inviya, Roica, Dorlastan, Linel or ESPA.

In the context of the present invention, a term “X is one or more of A, B and C”, wherein X is a given feature and each of A, B and C stands for specific realization of said feature, is to be understood as disclosing that X is either A, or B, or C, or A and B, or A and C, or B and C, or A and B and C. In this regard, it is noted that the skilled person is capable of transfer to above abstract term to a concrete example, e.g. where X is a chemical element and A, B and C are concrete elements such as Li, Na, and K, or X is a temperature and A, B and C are concrete temperatures such as 10 °C, 20 °C, and 30 °C. In this regard, it is further noted that the skilled person is capable of extending the above term to less specific realizations of said feature, e.g. “X is one or more of A and B” disclosing that X is either A, or B, or A and B, or to more specific realizations of said feature, e.g. ‘ is one or more of A, B, C and D”, disclosing that X is either A, or B, or C, or D, or A and B, or A and C, or A and D, or B and C, or B and D, or C and D, or A and B and C, or A and B and D, or B and C and D, or A and B and C and D. Preferred aspects of the present invention are further illustrated in the Figures 1 to 14 as described hereinunder.

Description of the figures

Fig. 1 illustrates a process according to the present invention. A suitably provided solid material M comprising polyamide 6 is fed into a melting unit UM from which a liquid stream SM is obtained and further passed to a pre-reaction unit UPR where it is admixed with a liquid aqueous stream Sw. A liquid stream SF which is obtained from the unit UPR is then passed to a reaction unit UR where it is subjected to polyamide 6 depolymerization conditions to obtain an aqueous depolymerization mixture which comprises e-caprolactam dissolved in water. From the unit UR, an aqueous liquid reactor exit stream SR comprising e-caprolactam dissolved in water then removed.

Fig. 2 illustrates a process according to the present invention. In addition to the process design shown in Fig. 1 , the melting unit UM according to Fig. 2 is equipped with a degassing system. Via this degassing system, a gas stream SGM is removed which is obtained when the solid material M is melted in UM. The stream SGM is then passed to a scrubbing unit Us.

Fig. 3 illustrates a process according to the present invention. In addition to the process design shown in Fig. 2, a filtration unit UF is arranged downstream of the melting unit UM and upstream of the reaction unit UR. The stream SM which is obtained from the unit UM is passed through this filtration unit and, downstream of UF, is passed as suitably filtrated stream SM to the pre-reaction unit UPR.

Fig. 4 illustrates a process according to the present invention. Compared to the process design shown in Fig. 3, a preferred design of the reaction unit UR is shown. According to this preferred design, the unit UR consists of three reactors Ri, R2 and R3 which are arranged in series and which are preferably vertically arranged. The stream SSF which is obtained from the pre-reaction unit UPR is fed into the reactor R1 where it is subjected to polyamide 6 depolymerization conditions, and from which a liquid aqueous stream Si is obtained which comprises e-caprolactam dissolved in water and further comprises non-depolymerized polyamide 6. The stream Si is then passed, preferably by gravity only, to the reactor R2 where it is subjected to polyamide 6 depolymerization conditions, and from which a liquid aqueous stream S2 is obtained which comprises e-caprolactam dissolved in water und further comprises non-depolymerized polyamide 6. The stream S2 is then passed, preferably by gravity only, to the reactor R3 where it is subjected to polyamide 6 depolymerization conditions, and from which a liquid aqueous stream S3 is obtained which comprises e-caprolactam dissolved in water. This stream S3 is then removed as the stream SR from the reaction unit UR.

Fig. 5 shows a preferred design of a reactor R used according to the present invention. If more than one reactor R is used, as, for example, described hereinabove in the context of Fig. 4, it is preferred that every reactor Rj exhibits this preferred design. Fig. 5 shows a reactor R which is an stirred tank reactor. In Fig. 5, the following reference numbers are used:

(1 ) vertically arranged three-compartment reactor R

(2) outlet means for degassing the reactor

(3) outlet means for removing a liquid reaction mixture from R

(4) inlet means for feeding a liquid stream into R, such as the stream SF into Ri

(5) heating jacket

(6.1) top compartment

(6.2) middle compartment

(6.3) bottom compartment

(7.1) agitator of top compartment

(7.2) agitator of middle compartment

(7.3) agitator of middle compartment

(8) drive unit for agitators according to (7.1 )-(7.3)

(9.1) divider between top and middle compartment with flow-through opening

(9.2) divider between middle and bottom compartment with flow-through opening

(10.1) inlet means for passing heating medium into the heating jacket (5)

(10.2) outlet means for removing heating medium from the heating jacket (5)

Fig. 6 illustrates a process according to the present invention. Compared to the process design shown in Fig. 4, a preferred design is shown how the solid material M is provided. According to Fig. 6, the solid material is provided in a delivering unit MMD which, for example, may comprise one or more big bag stations and/or one or more bulk container stations. From the unit UMD, the material is then passed to a suitably material collecting unit MMC which preferably comprises, more preferably consists of a drum. From the unit MMC, the material is then suitably passed to the melting unit UM.

Fig. 7 illustrates a process according to the present invention. Compared to the process design shown in Fig. 6, a preferred process is shown how the solid material is passed from the delivering unit UMD to the collecting unit UMC via a first connecting line. The unit UMD according to Fig. 7 comprises, for example, one bulk container station from which material M is passed to a particle separation unit UFMPS(1 ), and two big bag stations, wherein from the first big bag station, material M is passed to a particle separation unit UFMPS(2.1 ) and wherein from the second big bag station, material M is passed to a particle separation unit UFMPS(2.2). From UFMPS(1 ), material M is then passed through a feeding unit UFMF(1 ), such as a rotary feeder, and via UFMF(1 ), it is passed and optionally distributed to the receiving and discharge means UMRD(3), preferably a hopper, and UMRD(4), preferably a hopper. Further, from UFMPS(2.1 ), material M is then passed to a receiving and discharge means UMRD(2.1 ), preferably a hopper, and from UMRD(2.1 ) through a feeding unit UFMF(2.1 ), such as a rotary feeder, and via UFMF(2.1 ), it is passed and optionally distributed to the receiving and discharge means UMRD(3) and UMRD(4). Likewise, from UFMPS(2.2), material M is then passed to a receiving and discharge means UMRD(2.2), preferably a hopper, and from UMRD(2.2) through a feeding unit UFMF(2.2), such as a rotary feeder, and via UFMF(2.2), it is passed and optionally distributed to the receiving and discharge means UMRD(3) and UMRD(4). From either UMRD(3) and/or UMRD(4), material M is then passed to the collecting unit UMC via either the unit UFMF(3), preferably a rotary feeder, and/or the unit UFMF(4), preferably a rotary feeder. Further in Fig. 7, gas streams SG(1 ), SG(2) and SG(3) are shown which are passed into the respective sections of the first connecting line to (pneumatically) transport material M to the respective downstream units as shown. At least one of said gas streams, preferably all gas streams are preferably subject to gas filtration, followed by compression and subsequent cooling, prior to being passed into the respective sections of the first connecting line (not shown).

Fig. 8 illustrates a process according to the present invention. Compared to the process design shown in Fig. 6, a preferred process is shown how the solid material is passed from the collecting unit UMC, preferably comprising a collecting drum, to the melting unit UM via a second connecting line. According to Fig. 8, the solid material M is passed from the unit UMC through a first feeding unit USMF(1 ), such as a rotary feeder, to a particle separation unit USMPS such as a vibrating screen. From USMPS, material M is then passed to a second feeding unit USMF(2), preferably a loss-in weight feeding means such as a loss-in-weight screw from which the material M is then suitably passed to the melting unit UM. Preferably, the preferred process upstream of the unit UM as shown in Fig. 8 is to be seen in connection with the preferred process as shown in Fig. 6.

Fig. 9 illustrates a process according to the present invention. Compared to the process design shown in Fig. 4, it is further shown that a gas stream SGI is obtained in and removed from each reactor Rj comprised in the unit UR. These gas streams, specifically SGI , SG2 and SGS are then suitably combined and passed to a scrubber unit Us. It is noted that the streams SGI may also be passed to the unit Us separately (alternative not shown). It is further conceivable that one or more of the streams SGI are combined, prior to being fed into Us, with the gas stream SGM obtained from the melting unit UM (alternative not shown).

Fig. 10 illustrates a process according to the present invention. In Fig. 10, a preferred sequence of stages downstream of the reaction unit UR are shown, as well as a preferred recycling of water via the stream Sw. According to the process of Fig. 10, a liquid aqueous stream S3 is obtained and removed as the stream SR from the last reactor R3 of the unit UR which comprises c- caprolactam and one or more impurities. This stream SR is then passed to an evaporation unit UE from which a liquid aqueous stream SL and one or more aqueous vapor streams Sv are obtained and removed; in Fig. 10, only one vapor stream Sv is shown. The stream SL has a higher c- caprolactam concentration than the stream SR. The stream SL is then passed to a heatconsuming purification unit UP where a further purification with regard to c-caprolactam occurs. From the stream SL which is fed into UP, a product stream SCPL is finally obtained which comprises c-caprolactam at a concentration which is significantly higher than the c-caprolactam concentration of the stream SL. According to the process of the present invention, at least a part of the heat consumed in the purification unit UP is at least partially provided by at least one of the one or more vapor streams Sv and based on Sv, one or more at last partially condensed aqueous streams Svw are obtained and removed from UP; only one stream Svw is shown in Fig. 10. Yet further from the purification unit UP, one or more aqueous streams SRW are obtained from SL. At least one stream Svw is then at least partially recycled to the reaction unit UR, and also at least one stream SRW is at least partially recycled to the reaction unit UR wherein, for said recycling purposes, the streams Svw and SRW are passed into a water treatment unit Uw from which a stream Sw is obtained which is then (at least partially) recycled as aqueous stream Sw (or part thereof) to the reaction unit UR. Further from Uw, one or more waste water streams Sww are obtained which are not recycled to the process. Preferably, the water treatment unit Uw comprises a water recovery unit UWR and optionally a waste water unit Uww. Preferably, the streams Svw and SRW are passed into the water treatment unit Uw where they are suitably purified and/or suitably collected in order to obtain the one or more aqueous recycle streams. Streams which are obtained from such purification may then be passed to the waste water treatment unit Uww from which a waste water stream Sww is obtained.

Fig. 11 illustrates a process according to the present invention. The process according to Fig. 11 shows the further use of the stream SCPL, i.e. the purified s-caprolactam. According to the present invention, stream SCPL is preferably passed to a polyamide 6 production unit UPP where it is employed as starting material. If need be, one or more further streams SNCPL can be additionally passed to UPP, said streams comprising non-recycled s-caprolactam, i.e. s-caprolactam from a conventional source. The respectively prepared polyamide 6 material is then passed to a unit UTP where it is used as a starting material for preparing a material comprising polyamide 6, preferably a textile material comprising polyamide 6. If need be, one or more further streams SNPAS can be additionally passed to UTP, said streams comprising non-recycled polyamide 6, i.e. polyamide 6 from a conventional source. Depending on the type of material prepared in UTP, also further streams comprising one or more starting materials other than polyamide 6 can be passed to UTP. The material, preferably the textile material MT obtained from UTP then goes into the market and remains there for a given lifetime TMT. Thereafter, the respective end-of-life material is suitably collected in a collecting unit UTC, preferably a textile material collecting unit, from which it is suitably passed as stream the SM or as part of the stream SM to the reaction unit UR preferably via a unit UM for providing the stream SM to UR. Such unit UM usually comprises any apparatus by which the preferably solid material M can be suitably passed to the reaction unit UR. Preferably, UM comprises apparatuses such as one or more silos, one or more hoppers, one or more truck unloading stations, one or more big bag unloading station, and the like. Further in Fig. 11 , it is shown that in the production unit UTP, remaining material MR is obtained from the production process, i.e. material which is not comprised in MT. By way of example, MR may be in the form of textile cuttings. This material can be fed, either via UTC and/or directly via UM, to UR as the stream SM or as part of stream SM, preferably according to processes illustrated in Figs. 6, 7 and 8 hereinabove.

Fig. 12 illustrates a process according to the present invention. Compared to Fig. 11 , a preferred design of the unit UP is shown, i.e. the process as shown in Fig. 12 shows a preferred way of purifying the stream SL with respect to e-caprolactam. According to this process, the stream SL is first passed to a water separation unit Uws from which the one or more streams SRW are obtained which are then preferably passed to the water treatment unit Uw as already shown in Fig. 11 . Further, at least one of the streams Sv is passed to Uws for at least partially meeting the heat demand of Uws; based on this at least one stream Sv passed to Uws, one or more at least partially condensed streams Svwi are obtained and preferably further passed to the water treatment unit Uw, specifically UWR. The stream Sows comprising e-caprolactam is then preferably passed to a distillation unit UD for further purification with respect to e-caprolactam. Further, at least one of the streams Sv is passed to UD for at least partially meeting the heat demand of UD; based on this at least one stream Sv passed to UD, one or more at least partially condensed streams Svw2 are obtained and preferably further passed to the water treatment unit Uw, specifically UWR. The stream SUD comprising e-caprolactam is then preferably passed to a crystallization unit Uc for further purification with respect to e-caprolactam. Further, at least one of the streams Sv is passed to Uc for at least partially meeting the heat demand of Uc; based on this at least one stream Sv passed to Uc, one or more at least partially condensed streams Svws are obtained and preferably further passed to the water treatment unit Uw, specifically UWR.

Fig. 13 illustrates a process according to the present invention. Compared to Fig. 13, a preferred design of the unit Uws is shown, i.e. the process as shown in Fig. 13 shows a preferred way of separating water from the stream SL. According to this process, the stream SL is first passed to a first stage of water separation, carried out in the unit Uwsi. From Uwsi, a stream Suwsi comprising e-caprolactam is then passed to an intermediate treatment stage Ui where impurities may be removed. The thus purified stream Sui obtained from Ui is then further passed to a second stage of water separation, carried out in the unit Uws2. From said unit Uws2, a stream Suws2 comprising e-caprolactam is obtained which corresponds to the stream Sows as shown in Fig. 12 and which is then preferably passed to the distillation unit UD. From the intermediate unit Ui, a stream Si comprising the respectively separated impurities is removed which, depending on the amount and/or the chemical nature of the impurities, may be put to further use. According to this process, one or more aqueous streams SRWI are obtained which are then preferably passed to the water treatment unit Uw, specifically UWR. Further according to this process, one or more aqueous streams SRW2 are obtained which are then preferably passed to the water treatment unit Uw, specifically UWR. Preferably, at least one of the streams Sv is passed to Uwsi for at least partially meeting the heat demand of Uwsi; based on this at least one stream Sv passed to Uwsi, one or more at least partially condensed streams Svwn are obtained and preferably further passed to the water treatment Uw, specifically UWR. Preferably, at least one of the streams Sv is passed to Uws2 for at least partially meeting the heat demand of Uws2; based on this at least one stream Sv passed to Uws2, one or more at least partially condensed streams Svwi2 are obtained and preferably further passed to the water treatment Uw, specifically UWR.

Fig. 14 illustrates a process according to the present invention. Compared to Fig. 13, the preferred recycling loop as already shown in Fig. 11 hereinabove is additionally shown, as well as the treatment of the gas streams S_Gi obtained in and removed from the reactors Ri, R2 and R3, as already shown in Fig. 9 hereinabove.

Claims

(i) providing the solid material M;

(vii) removing an aqueous liquid reactor exit stream SR from UR, the stream SR comprising e-caprolactam dissolved in water; wherein 0.8 < TSF/TD 1 .05 and 0.9 < PSF/PD 1.05.

2. The process of claim 1 , wherein 0.6 < TSM/TSF 1 .05 and 0.9 < PSM/PSF 1 .05 and wherein 0.8 TS /TSF ^ 1.3 and 0.9 PS /PSF - 1.05.

3. The process of claim 1 or 2, wherein the pre-reaction unit UPR according to (iv) comprises, preferably consists of, a mixing unit, preferably a static mixing unit, wherein according to (iv), Sw and SM are admixed in UPR at a mixing ratio (mw/kg) I (mp/kg) preferably in the range of from 1 :1 to 20:1 , more preferably in the range of from 2:1 to 15:1 , more preferably in the range of from 5:1 to 10:1 , wherein mw is the amount of water comprised in Sw and m? is the amount of polyamide 6 comprised in SM; wherein the melting unit UM comprises, preferably consists of an extruder, preferably a single-screw extruder or a twin-screw extruder, wherein the melting unit UM is preferably equipped with a degassing system, the process preferably comprising removing a gas stream SGM from UM during melting according to (ii), said gas stream SGM having a temperature TGM at a pressure PGM, wherein preferably 0.95 < TGM/TSM 1.05, wherein the gas stream SGM removed from UM is preferably subjected to scrubbing in a scrubbing unit U_s.

4. The process of any one of claims 1 to 3, wherein downstream of the melting unit UM and upstream of the reaction unit UR, a filtration unit UF is arranged, preferably a filtration unit UF for separating particles having a particle size in the range of from 100 to 500 micrometer, preferably in the range of from 200 to 400 micrometer, from the liquid stream SM, wherein the process comprises passing the stream liquid stream SM through UF, prior to admixing according to (iv).

5. The process of any one of claims 1 to 4, wherein according to (vi), TD is in the range of from 230 to 330 °C and PD is in the range of from 40 to 140 bar, preferably wherein TD is in the range of from 250 to 320 °C and PD is in the range of from 40 to 125 bar, more preferably wherein TD is in the range of from 270 to 310 °C and PD is in the range of from 40 to 110 bar.

6. The process of any one of claims 1 to 5, wherein the reaction unit UR according to (v) comprises z chemical reactors R, i=1 ...z, wherein z is in the range of from 1 to 10, preferably in the range of from 1 to 8, more preferably in the range of from 1 to 6, more preferably in the range of from 1 to 5, more preferably in the range of from 1 to 4, more preferably in the range of from 1 to 3, wherein if z > 1 , at least 2 reactors R, preferably z reactors R are serially coupled, wherein according to (v), the stream SSF is fed into R, with i = 1 ; an aqueous liquid stream Sj containing e-caprolactam dissolved in water is removed from reactor R and fed into the reactor R+i, with i < z; according to (vii), the aqueous liquid stream S_z containing e-caprolactam dissolved in water is removed from the reactor R_z as the stream SR; wherein in every reactor R, a depolymerization temperature TDI at a depolymerization pressure poi is maintained, wherein, independently of each other, TDI is in the range of from 230 to 330 °C and poi is in the range of from 40 to 140 bar, preferably wherein TDI is in the range of from 250 to 320 °C and poi is in the range of from 40 to 125 bar, more preferably wherein TDI is in the range of from 270 to 310 °C and poi is in the range of from 40 to 110 bar, wherein for z > 1 , the z reactors R are preferably vertically arranged, with Ri being the top-most reactor and R_z being the bottom-most reactor, wherein Sj obtained from R is transferred to R+i preferably by gravity, more preferably by gravity only.

7. The process of claim 6, wherein at least 1 , preferably z reactors R, are stirred tank reactors, wherein preferably every stirred tank reactor R has, independently from each other, preferably from 2 to 6 compartments, more preferably from 2 to 5 compartments, more preferably from 2 to 4 compartments, said compartments preferably being serially, more preferably being serially and vertically arranged, wherein 2 adjacent compartments are separated by a divider which comprises at least one flow-through opening, wherein preferably at least one compartment comprised in a reactor R comprises at least one agitator, wherein more preferably every compartment of every reactor R comprises at least one agitator, wherein more preferably, every compartment of every reactor R comprises one agitator, wherein the process comprises agitating the depolymerization mixture in a given compartment for at least part of the time during subjecting to depolymerization conditions in said compartment; wherein the polyamide 6 depolymerization conditions according to (vi) preferably further comprise a total residence time to of the aqueous depolymerization mixture in the unit UR, more preferably in the z reactors R, more preferably in the z stirred tank reactors, wherein at least 85 weight-%, preferably at least 90 weight-%, more preferably at least 95 weight-% of the aqueous depolymerization mixture have a to in the range of from 30 to 90 min; wherein for z > 1 , the residence time of an aqueous depolymerization mixture in a reactor R is toi and wherein preferably 0.90 < (toi I toi+i) 1.10, more preferably 0.95 (toi I toi+i) - 1.05.

8. The process of claim 6 or 7, comprising removing from at least one reactor R, preferably from all z reactors R, a respective gas stream SGI, a given gas stream S_Gi having a temperature TGI at a pressure PGI, wherein 0.95 < TGI/TDI 1.05, the process preferably further comprising combining at least one of the gas streams SGI, preferably all streams SGI, with the gas stream SGM as defined in claim 3, prior to subjecting the gas stream SGM to scrubbing as defined in claim 3.

9. The process of any one of claims 1 to 8, wherein providing the solid material M according to (i) comprises

(1.3) passing the solid material M from the unit UMC via a second connecting line to the unit UM, wherein the second connecting line preferably comprises one or more of at least one second material feeding unit USMF, at least one second particle separation unit USMPS, and at least one metal detector; wherein the first connecting line according to (i.2) preferably comprises at least one unit UMRD, preferably at least one hopper, more preferably at least one one-zone hopper, and preferably further comprises at least one unit UFMF, preferably at least one rotary feeder, and preferably further comprises at least particle separation unit UFMPS, more preferably at least one filter, more preferably at least one mesh filter; wherein for passing the solid material M via a first connecting line from the unit UMD to the unit UMC, at least one gas stream SG is preferably passed through the first connecting line, said at least one gas stream preferably comprising, more preferably consisting of air or lean air, wherein prior to being passed through the first connecting line, the at least one gas stream is preferably pre-treated by at least one of filtrating, compressing and cooling, more preferably by filtrating, compressing and cooling; wherein the second connecting line according to (i.3) preferably comprises at least two units USMF, preferably comprising a rotary feeder and a loss-in-weight feeder, wherein more preferably, the rotary feeder is arranged upstream of the loss-in-weight feeder, and further comprises a unit USMPS, preferably a vibrating screen.

10. The process of any one of claims 1 to 9, wherein according to (i), the solid material M is provided, preferably provided to UM, in the form of granules, wherein the particle size distribution of said granules is preferably characterized by one or more of the following pairs of values, preferably by two or more of the following pairs of values, more preferably by the following three pairs of values: a D10 value of the particle width in the range of from in the range of from 0.3 to 15 mm and a D10 value of the particle length in the range of from 0.3 to 15 mm; a D50 value of the particle width in the range of from in the range of from 0.5 to 20 mm and a D50 value of the particle length in the range of from 0.5 to 20 mm; a D90 value of the particle width in the range of from in the range of from 0.8 to 30 mm and a D90 value of the particle length in the range of from 0.8 to 30 mm; wherein preferably from 10 to 100 weight-%, more preferably from 30 to 100 weight-%, more preferably from 50 to 100 weight-%, more preferably from 60 to 100 weight-%, more preferably from 70 to 100 weight-%, more preferably from 80 to 100 weight-%, of the solid material M consist of the polyamide 6.

11 . The process of any one of claims 1 to 10, wherein from 90 to 100 weight-%, preferably from 91 to 100 weight-%, more preferably from 92 to 100 weight-%, more preferably from 93 to 100 weight-%, more preferably from 94 to 100 weight-%, more preferably from 95 to 100 weight-% of the liquid aqueous stream Sw provided according to (iii) consist of water.

12. The process of any one of claims 1 to 11 , wherein the solid material M provided according to (i) comprises, preferably consists of, a waste material, preferably one or more of a textile waste material and an engineering plastics waste material, more preferably of a textile waste material.

13. The process of any one of claims 1 to 12, wherein according to (vii), the stream SR comprising e-caprolactam dissolved in water at a concentration CSR, the stream SR further comprising one or more impurities, the process further comprising

14. The process of claim 13, further comprising providing the stream SCPL obtained according to (ix) to a polyamide 6 production unit UPP, wherein the polyamide 6 produced in UPP is preferably provided as a feedstock to a textile material producing unit UTP, from which unit UTP

15. Use of SCPL, obtainable or obtained by a process according to claim 16 for preparing one or more of a polymer and a polymer product, wherein the polymer, or the polymer product, or the polymer and the polymer product is or are in the form of at least one of a granulate, a strand, a rod, a plate, a pipe, a foil, a layer, a film, a sheet, a fiber, a filament, a coating, an extruded article, a molded article, a soft foam, a half-rigid foam and a rigid foam; and wherein the polymer, or the polymer product, or the polymer and the polymer product comprises or comprise polyamide 6 and optionally at least one further polymeric compound, wherein the at least one further polymeric compound preferably comprises one or more of at least one polyamide 6.6; at least one semiaromatic polyamide including one or more of polyamide 6T and polyamide 6I; at least one polyethylene terephthalate; at least one polyurethane; at least one polyester; at least one polyether; at least one polyvinyl chloride; at least one natural fiber material such as wool and cotton; at least one cellulose material; at least one natural elastomer; at least one synthetic elastomer; at least one copolymer of two or more of said polymeric compounds including statistical copolymers, gradient copolymers, alternating copolymers, block copolymers, and graft copolymers; and at least one rubber material comprising one or more of at least one natural rubber material and at least one synthetic rubber material; wherein the polymer, or the polymer product, or the polymer and the polymer product is or are preferably one of the following or a part of one of the following: a part of a car, preferably a cylinder head cover, an engine cover, a housing for a charge air cooler, a charge air cooler flap, an intake pipe, an intake manifold, a connector, a gear wheel, a fan wheel, a cooling water box, a housing or a housing part for a heat exchanger, a coolant cooler, a charge air cooler, a thermostat, a water pump, a radiator, a fastening part or a part of a battery system for electromobility, a dashboard, a steering column switch, a seat, a headrest, a center console, a transmission component, a door module, a car exterior for an A, a B, a C or a D pillar cover, a spoiler, a door handle, an exterior mirror, a windscreen wiper, a windscreen wiper protection housing, a decorative grill, a cover strip, a roof rail, a window frame, a sunroof frame, an antenna panel, a headlight, a taillight, an airbag, and/or a cushion; a cloth, an apparel, preferably a shirt, trousers, a pullover, a boot, a shoe, a shoe sole, a tight and/or or jacket; an electrical part, preferably an electrical component, an electronic passive component, an electronic active component, a printed circuit board, a housing component, a foil, a line, a switch such as a microswitch, a plug, a socket, a distributor, a relay, a resistor, a capacitor, an inductor, a bobbin, a lamp, a diode such as an LED, a transistor, a connector, a regulator, an integrated circuit (IC), a processor, a controller, a memory, a sensor, a microbutton, a semiconductor, a reflector housing for example for light-emitting diodes, a fastener for an electrical and/or an electronic component, a spacer, a bolt, a strip, a slide-in guide, a screw, a nut, a film hinge, a snap hook (snap-in), and/or a spring tongue; a consumer and/or a pharmaceutical product, preferably a tennis string, a climbing rope, a bristle, a brush, an artificial grass, a 3D printing filament, a grass trimmer, a zipper, a hook and loop fastener, a paper machine clothing, an extrusion coating, a fishing line, a fishing net, an offshore line and rope, a vial, a syringe, an ampoule, a bottle, a sliding element, a spindle nut, a chain conveyor, a plain bearing, a roller, a wheel, a gear, a roller, a ring gear, a screw and spring damper, a hose, a pipeline, a cable sheathing, a socket, a switch, a cable tie, a fan wheel, a carpet, a box and/or a bottle for cosmetics, a mattress, a cushion, an insulation; a packaging for the food industry, preferably a mono- and/or multi-layer blown film, a cast film (mono- and/or multi-layer), a biaxially stretched film, a laminating film.