Color-stable aqueous mixture comprising recovered liquid caprolactam

Abstract

A process for preparing a liquid ε-caprolactam mixture MF, comprising providing a stream SM comprising a solid material M comprising polyamide 6; preparing an aqueous depolymerization mixture based on SM; subjecting the depolymerization mixture to polyamide 6 depolymerization conditions in a reaction unit UR, obtaining a liquid aqueous stream SR comprising ε-caprolactam dissolved in water, the stream SR further comprising one or more impurities; and optionally passing the liquid aqueous stream SR into an evaporation unit UE, obtaining from SR a liquid aqueous stream SL comprising ε-caprolactam dissolved in water; passing the stream SR, optionally the stream SL, into an ε-caprolactam purification unit UP and obtaining from the unit UP the mixture MF; or obtaining from the unit UP a mixture MT having an ε-caprolactam purity ΩGC(MT) of at least 99 %, an APHA value ΩAPHA(MT) of at most 20 and a water content xH2O(MT) of at most 0.05 weight-%, based on the total weight of the mixture MT, and adding water to the mixture MT, obtaining the mixture MF; wherein the mixture MF has an ε-caprolactam purity ΩGC(MF) of at least 99 %, an APHA value ΩAPHA(MF) of at most 20 and a water content xH2O(MF) of at least 0.1 weight- %, based on the total weight of the mixture MF.

Description

[0001]Color-stable aqueous mixture comprising recovered liquid caprolactamThe present invention relates to a process for preparing a highly pure liquid mixture whichcomprises ε-caprolactam and which is color-stable when stored at low temperatures, whereinsaid mixture is prepared by subjecting a solid material which comprises polyamide 6 to hydrolytic depolymerization and purifying the resulting depolymerization mixture with respect toε-caprolactam. Further, the present invention relates to a method of storing said mixture, andfurther relates to the respectively stored mixture. Still further, the present invention relates to the use of the optionally stored mixture for preparing polyamide 6, and thus to a full polyamide 6 (orε-caprolactam) recycle loop.Polyamide 6 characterized by the formula (–NH–(CH2)5–CO–)n, can be found in numerousmaterials, 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 CO2emissions. There is thus a need to recycle polyamide 6 from such materials. The purificationprocess for ε-caprolactam downstream of the depolymerization step is not a straight-forward task,for example due to the various possible chemical compositions of waste materials comprising polyamide 6 which form the educt materials for the recycling process. Once a respectivelypurified mixture comprising ε-caprolactam is obtained from depolymerisation and downstreampurification stages, such mixture is advantageously re-used as an educt for polymerization, in particular for preparing polyamide 6, thus realizing a recycle loop. However, it is not guaranteed that such a mixture can be used as educt material immediately after its preparation. Often times, it will be necessary to store said mixture for a certain period of time prior to further use. As far as such storing is concerned, it is necessary that in the course thereof, the quality of the mixture is kept essentially constant, in particular as far as the color properties, most commonly expressed interms of the APHA color values. The APHA color scale, also referred to as the Hazen scale or asthe Platinum Cobalt scale, is a color standard named for the American Public Health Association.Yet further, it is desirable that such storing can be carried out under economically advantageous conditions, such as comparatively low temperatures. WO 2023 / 144338 A1 discloses a process for recovering purified ε-caprolactam from materialderived from polyamide 6 comprising fishing nets in a plant, wherein the plant comprises adepolymerization section, a recovery section, and a purification section.Surprisingly, it was found that a highly pure mixture ε-caprolactam which is obtained fromhydrolytic depolymerisation and subsequent purification and which exhibits a certain minimum content of water has the desired storing properties. Therefore, the present invention relates to a process for preparing a liquid ε-caprolactam mixture MF, the process comprising(i) providing a stream SM comprising a solid material M comprising polyamide 6;(ii) preparing an aqueous depolymerization mixture based on SM;(iii) subjecting the depolymerization mixture prepared according to (ii) to polyamide 6depolymerization conditions in a reaction unit UR, obtaining a liquid aqueous stream SRcomprising ε-caprolactam dissolved in water at a concentration cSR, the stream SR further comprising one or more impurities; and optionally passing the liquid aqueous stream SR intoan evaporation unit UE, obtaining from SRa liquid aqueous stream SLcomprising ε- caprolactam dissolved in water at a concentration cSLwith cSL> cSR, and further obtaining from SR one or more aqueous vapor streams SV;(iv) passing the stream SR, optionally the stream SL, into an ε-caprolactam purification unit UP,and (iv.1) obtaining from the unit UP the mixture MF; or(iv.2) obtaining from the unit UP a mixture MT having an ε-caprolactam purity ΩGC(MT) of atleast 99 %, an APHA value ΩAPHA(MT) of at most 20 and a water content xH2O(MT) of at most 0.05 weight-%, based on the total weight of the mixture MT, and adding water to the mixture MT, obtaining the mixture MF; wherein the mixture MF has an ε-caprolactam purity ΩGC(MF) of at least 99 %, an APHAvalue ΩAPHA(MF) of at most 20 and a water content xH2O(MF) of at least 0.1 weight-%, basedon the total weight of the mixture MF. Preferably at least 99 weight-%, preferably at least 99.1 weight-%, more preferably at least 99.2 weight-%, more preferably at least 99.3 weight-%, more preferably at least 99.4 weight-%, more preferably at least 99.5 weight-%, more preferably at least 99.6 weight-%, more preferably at least 99.7 weight-%, more preferably at least 99.8 weight-%, more preferably at least 99.9 weight-% of the mixture MFconsist of ε-caprolactam and water. It is preferred that ΩGC(MF) is at least 99.5 %, more preferably at least 99.6 %, more preferably atleast 99.7 %, more preferably at least 99.8 %, more preferably at least 99.9 %. Further, it ispreferred that ΩAPHA(MF) is at most 15, more preferably at most 12.5, more preferably at most 10,more preferably at most 7.5, more preferably at most 5. Still further, it is preferred that xH2O(MF) isin the range of from 0.1 to 10 weight-%, more preferably in the range of from 0.15 to 9 weight-%, more preferably in the range of from 0.2 to 8 weight-%, more preferably in the range of from 0.35to 7 weight-%, more preferably in the range of from 0.5 to 6 weight-%. Suitable ranges of xH2O(MF)may include from 0.5 to 2 weight-% and from 2 to 4 weight-% and from 4 to 6 weight-%. Therefore, mixtures MFare more preferred for which ΩGC(MF) is at least 99.9 %, ΩAPHA(MF) is at most 5, and xH2O(MF) is in the range of from 0.5 to 6 weight-%. Preferably, the mixture MFhas a temperature in the range of from 20 to 80 °C, more preferably in the range of from 35 to 77 °C, more preferably in the range of from 50 to 75 °C. Optionally or preferably, the mixture MF is further characterized by one or more of a permanganate absorption number ΩPAN(MF) and an UV absorption ΩUV(MF). ΩPAN(MF) ispreferably at most 20, more preferably at most 15, more preferably at most 10. ΩUV(MF) ispreferably at most 0.75, more preferably at most 0.25, more preferably at most 0.1. Therefore,mixtures MF are more preferred for which ΩPAN(MF) is at most 10 and ΩUV(MF) is at most 0.1. Thus, more preferred are mixtures MF for which ΩGC(MF) is at least 99.9 %, ΩAPHA(MF) is at most5, xH2O(MF) is in the range of from 0.5 to 6 weight-%, ΩPAN(MF) is at most 10 and ΩUV(MF) is atmost 0.1. Regarding the determination of the values of ΩGC, ΩAPHA, ΩUVand ΩPAN, reference is made to the Reference Examples hereinbelow. Preferably according to the present invention, the purification unit UP according to (v) comprises a water separation unit UWSand a distillation unit UD, and the process preferably comprises feeding the stream SR, optionally the stream SL, to UWS, obtaining from UWS a stream SUWS comprising ε- caprolactam at a concentration cUWS, feeding the stream SUWS to the distillation unit UD, obtainingfrom UD the mixture MF comprising ε-caprolactam at a concentration cMF, wherein cSR < cUWS <<<cMF, preferably wherein cSL < cUWS <<< cMF.The symbol “<<<” compared to the symbol “<” indicates that, for example, the ratio cUWS / cSRis significantly lower than the ratio cMF / cUWS.Further preferably, the water separation unit UWS comprises at least two water separation sub- units UWS1and UWS2, preferably two serially coupled water separation sub-units UWS1and UWS2, wherein the stream SR, optionally the stream SL, is fed into UWS1, wherein downstream of UWS1and upstream of UWS2, a separation unit UI is preferably located, the process comprising obtaining from UWS1an aqueous stream SUWS1, feeding the stream SUWS1into the separation unit UI, obtaining from UIan aqueous stream SUI, and feeding the stream SUIinto the unit UWS2, wherein in UI, one or more of impurities are separated from SUWS1, thereby obtaining from UI an impurity stream SI, said impurities preferably comprising at least one impurity comprised in SR according to (iii), wherein at least one of said impurities is an organic compound having a higher boiling point than ε-caprolactam, the separation unit UIbeing a high boiler separation unit. With regard to the specific apparatus design of the sub-unit UWS1and sub-unit UWS2, it is preferred that the sub-unit UWS1comprises one or more of a falling film evaporator, a flash tank, a forced circulation evaporator, and a distillation column, more preferably one or more of a falling film evaporator and a flash tank, more preferably a falling film evaporator and a flash tank, and that the sub-unit UWS2comprises one or more of a falling film evaporator, a flash tank and a distillation column, more preferably a distillation column.As far as the high boiler separation unit UI is concerned, no specific restrictions exist providedthat in said unit UI, compounds can be at least partially separated which have a higher boiling point than ε-caprolactam. It was found that the waste material which are most preferably used as the solid material M according to (i) will contain certain compounds which, either prior to or afterdepolymerization of polyamide 6 according to (iii), lead to a stream comprising ε-caprolactam andcompounds having a higher boiling point than ε-caprolactam. Due to possibly different chemical compositions of said waste material, however, these compounds having a higher boiling pointthan ε-caprolactam will usually differ from time to time, both with regard to the content in thestream to be purified and in chemical nature. According to a preferred process stage of thepresent invention, said high boiler separation in the unit UIcomprises(α) obtaining the stream SUWS1 from the water separation sub-unit UWS1,wherein this stream hasa temperature TUWS1 and exhibits a total concentration cL0(Ψ) of one or more compounds Ψwhich have a higher boiling point than ε-caprolactam further have a concentration cL0(C) of monomeric ε-caprolactam;(β) producing in an evaporation unit UE1 from the stream SUWS1 an aqueous at least partiallyvaporous stream SV1 and a liquid stream SL1, comprising (β.1) passing the stream S UWS1 into the unit UE1, preparing in the unit UE1 from the streamSUWS1 an evaporation mixture ME1 having an evaporation temperature TE1 at an evaporation pressure pE1 with TE1 > TUWS1, wherein the one or more one organic compounds Ψ have a boiling point TBX and ε-caprolactam has a boiling point TBC withTBX > TE1 ≥ TBC at the evaporation pressure pE1;(β.2) removing the stream SV1 from the evaporation unit UE1, the stream SV1 having atemperature TV1 with TV1 ≤ TE1 and exhibiting a total concentration cV1(Ψ) of one ormore compounds Ψ and a concentration cV1(C) of monomeric ε-caprolactam withcV1(C) > cUWS1(C) and cV1(Ψ) < cUWS1(Ψ); (β.3) removing the stream SL1 from the evaporation unit UE1, the stream SL1 having atemperature TL1with TL1= TE1and exhibiting a total concentration cL1(Ψ) of one or more compounds Ψ and a concentration cL1(C) of monomeric ε-caprolactam withcL1(C) < cE1(C) and cL1(Ψ) > cUWS1(Ψ);(γ) producing in a separation unit US1 from the stream SV1 an aqueous vapor stream SV2 and aliquid stream SL2, comprising (γ.1) passing the stream SV1 removed from the evaporation unit UE1 according to (β.2),optionally after cooling, into the separation unit US1 and subjecting the stream SV1, optionally the stream after cooling, in the separation unit US1to separation conditions; (γ.2) removing the stream SV2from the separation unit US1, the stream SV2having a temperature TV2 with TUWS1 < TV2 ≤ TV1 and exhibiting a total concentration cV2(Ψ) ofone or more compounds Ψ and a concentration cV2(C) of monomeric ε-caprolactam;(γ.3) removing the stream SL2from the separation unit US1, the stream SL2having a temperature TL2 with TL2 = TV2 and exhibiting a total concentration cL2(Ψ) of one ormore compounds X and a concentration cL2(C) of monomeric ε-caprolactam with cL2( Ψ) > cV2(Ψ) and cL2(C) < cV2(C);(δ) passing the aqueous stream SV2 obtained from the separation unit US1 according to (γ.2) tothe water separation sub-unit UWS2.Generally, it is preferred that preparing the mixture ME1comprises agitating, preferably mechanical agitating, more preferably stirring. Therefore, the unit UE1 preferably comprises a stirred reactor, more preferably a stirred tank reactor, more preferably a continuous stirred tankreactor. The separation unit US1 preferably comprises, more preferably consists of, a dropletseparator, preferably selected from the group consisting of a hydrocyclone, a demister plate, and an absorption tower, more preferably a hydrocyclone. Regarding the temperature TUWS1 of the stream SUWS1 according to (α), it is preferred that TUWS1 is in the range of from 75 to 120 °C, more preferably in the range of from 80 to 110 °C, morepreferably in the range of from 85 to 100 °C. As far as the chemical composition of the streamSUWS1 is concerned, it is preferred that the sum of the concentrations cUWS1(C) and cUWS1(Ψ),cUWS1(C) + cUWS1(Ψ), is at least 60 weight-%, more preferably in the range of from 60 to 95 weight- %, more preferably in the range of from 70 to 90 weight-%, more preferably in the range of from80 to 85 weight-%, in each case based on the total weight of the stream SUWS1. Further in thestream SUWS1, the weight ratio of the one or more compounds Ψ to monomeric ε-caprolactam ispreferably in the range of from 50:50 to 5:95. Suitable range include, for example, 50:50 to 40:60, or 45:50 to 35:65, or 40:60 to 30:70, or 35:65 to 25:75, or 30:70 to 20:80, or 25:75 to 15:85, or20:80 to 10:90, or 15:85 to 5:95. According to the present invention, in particular in case theprocess of the present invention is carried out as a continuous process, the concentration of Ψ inSUWS1 may change over time, depending on which specific material M is fed into the process. Inparticular for this scenario, the inventive high boiler separation allows for producing a stream SV2 having an essentially constant and very low high boiler concentration cV2(Ψ). Regarding the chemical nature of the high boiler compounds, a comparatively high uncertainty exists, simply in view of the unpredictable chemical composition of the materials subjected to depolymerization and, finally, high boiler separation according to the present invention. However, when developing the process of the present invention, numerous elaborate experiments were carried out, and it was found that in a majority of situations, the one or more compounds comprised in the stream SUWS1preferably comprise at least one of- at least one aromatic amine which includes at least one of an aromatic monoamine, anaromatic diamine, an aromatic triamine and an aromatic tetramine;- at least one aliphatic amine which includes at least one of an aliphatic monoamine, analiphatic diamine and an aliphatic triamine;- at least one aliphatic amide;- at least one aromatic alcohol which includes at least one of an aromatic monool and anaromatic diol;- at least one aliphatic alcohol which includes at least one of an aliphatic monool and analiphatic diol;- at least one aromatic acid;- at least one and aliphatic acid;- at least one ε-caprolactam oligomer;- at least other compound selected from the group consisting of one or more cleavageproducts of dyes such as optionally chlorinated aromatic diamines, one or more water- soluble oligomeric cellulose cleavage products, and one or more water-soluble oligomers of terephthalic acid and hexamethylenediamine. Yet further, it was found that- the at least one aromatic amine preferably includes one or more of 4,4’-methylenedianiline(MDA), isomers thereof such as 2,4’-methylenedianiline and 2,2’-methylenedianiline, and polymethylen polyphenylen polyamines (pMDA);- the at least one aliphatic amine and the at least one aliphatic amide preferably include oneor more of hexamethylenediamine adipate, 6-aminocaproic acid and oligomers thereof, including 6-aminocaproic acid dimer and higher oligomers such as 6-aminocaproic acid trimer, 6-aminocaproic acid tetramer, 6-aminocaproic acid pentamer, 6-aminocaproic acid hexamer, N'-(6-aminohexyl)hexane-1,6-diamine, N-methylhexane-1,6-diamine, 6-amino- hexanamide, derivatives of ε–caprolactam other than ε–caprolactam oligomers and havinga boiling point higher than ε–caprolactam such as 1-(6-aminohexyl)azepan-2-one;- the at least one aliphatic alcohol preferably includes one or more of butanediol andoligomers thereof, including butanediol dimer and higher oligomers such as butanediol trimer, including polytetrahydrofuran;- the at least one aromatic acid and the at least one aliphatic acid preferably include one ormore of terephthalic acid and adipic acid;- the at least one ε-caprolactam oligomer preferably includes one or more of ε–caprolactamdimer ε–caprolactam trimer, ε–caprolactam tetramer, ε–caprolactam pentamer, and ε–caprolactam hexamer. According to the present invention, it is further preferred that the purification unit UP further comprises, downstream of the distillation unit UD, one or more of a crystallization unit UCR and achemical treatment unit UOD, and the process preferably comprises obtaining the mixture MF fromUCRor from UOD. As far as the chemical treatment in the unit UODis concerned, the process of the present invention preferably comprises(a) providing a preferably liquid stream SUD comprising ε-caprolactam from the distillation unitUD or a preferably liquid stream SCR comprising ε-caprolactam from the crystallization unitUCR, said stream SUDor said stream SCRfurther comprising one or more oxidizable organic impurity compounds X, wherein the stream SUD or the stream SCR has an ε-caprolactampurity ΩGC(SC) of at least 99 % and exhibits a weight ratio rXC of the one or more organic compounds X relative to ε-caprolactam;(b) providing a stream SO comprising at least one permanganate;(c) preparing an oxidation reaction educt mixture MOE from the stream SUD and the stream SO,or from the stream SSCR and the stream SO, and subjecting the mixture MOE to oxidation reaction conditions, obtaining an oxidation reaction product stream SP comprising ε-caprolactam, further comprising one or more oxidation products Y obtained from the oxidation of at least a part of the one or more compounds X, and optionally further comprising a part of the one or more organic compounds X, wherein the stream SP exhibitsa weight ratio rXCP of organic compound X relative to ε-caprolactam with 0 ≤ rXCP < rXC andfurther exhibits a weight ratio rYCP of the one or more products Y relative to ε-caprolactam with rYCP > 0;(d) separating at least a part of the one or more oxidation products Y and optionally at least apart of organic compound X from the stream SP, obtaining the mixture MFor the mixture MTexhibiting a weight ratio rYCT of oxidation product Y relative to ε-caprolactam with0 ≤ rYCT < rYCP, and further exhibiting a weight ratio rXCT of organic compound X relative toε-caprolactam with 0 ≤ rXCT < rXC.The at least one permanganate comprised in the stream SO provided according to (b) preferably comprises, more preferably consists of, at least alkali metal permanganate, wherein more preferably, the at least one alkali metal permanganate comprises one or more of sodiumpermanganate and potassium permanganate. Preferably from 0.5 to 100 weight-% of the streamSO provided according to (b) consist of permanganate. Therefore, generally, it is conceivable thatthe permanganate is used in its solid form. Preferably, the stream SO provided according to (b)further comprises water, wherein it is more preferred that the oxidation reaction educt mixture MOE prepared according to (c) exhibits a permanganate concentration, calculated as MnO4, in the range of from 0.005 to 5 weight-%, more preferably in the range of from 0.01 to 3 weight-%, more preferably in the range of from 0.05 to 1 weight-%. Yet further, the oxidation reaction conditions according to (c) preferably comprise a temperature TOEof the mixture MOEin the range of from 40 to 140 °C, more preferably in the range of from 60 to 100 °C, more preferably in the range of from70 to 90 °C. Still further preferably, the mixture MOE prepared according to (c) further compriseswater. Preferably, subjecting the mixture MOE to oxidation reaction conditions is carried out in anoxidation reaction unit UOR comprised in the chemical treatment unit UOD, wherein the unit UOR preferably comprises one or more of at least one continuous stirred tank reactor and at least one tube reactor. Further preferably, the process of the present invention further comprises providing a stream SB comprising at least one hydroxide, wherein the oxidation reaction educt mixture MOEaccording to (c) is prepared from the stream SUDor the stream SCR, and from the stream SOand the stream SB. The at least one hydroxide comprised in the stream SB preferably comprises, more preferably consists of, at least alkali metal hydroxide, wherein more preferably, the at least one alkali metalhydroxide comprises, more preferably consists of, sodium hydroxide. Preferably from 0.5 to 100weight-% of the stream SB consist of hydroxide. Therefore, generally, it is conceivable that thehydroxide is used in its solid form. Preferably, the stream SB further comprises water, wherein it ismore preferred that the oxidation reaction educt mixture MOE prepared according to (c) exhibits ahydroxide concentration, calculated as OH, in the range of from 0.005 to 0.75 weight-%, more preferably in the range of from 0.01 to 0.5 weight-%, more preferably in the range of from 0.1 to 0.25 weight-%.Preferably according to the present invention, the one or more oxidizable organic compounds Xhave a boiling point δX / °C with 0.5 ≤ (δX / δC) ≤ 1.5, δC / °C being the boiling point of ε-caprolactamand wherein at least one of the one or more oxidation products Y has a boiling point δY / °C with δY / °C ≠ δC / °C, wherein the difference Δδ between the boiling points δY and δC is preferably at least1 °C. Usually, the one or more oxidizable organic compounds X will have a higher boiling pointthan ε-caprolactam; however, it is conceivable that there are oxidizable organic compounds having a lower boiling point than ε-caprolactam, for example certain aldehydes and / or ketones.According to the present invention, it may be preferred that separating at least a part of the oneor more oxidation products Y and optionally at least a part of organic compound X from the stream SP according to (d) comprises subjecting the stream SP obtained according to (c) todistillation in a distillation unit UDT which is comprised in, i.e. is part of, the chemical treatment unitUOD. In this case, a stream SDT is obtained from the distillation unit UDT which comprisesε-caprolactam, wherein this stream SDT is the mixture MF or the mixture MT. Preferably, the unitUDT comprises one or more distillation columns, more preferably one or two distillation columns,wherein at least one distillation column is optionally configured as side stream column or asdivided wall column. According to the process of the present invention, the distillation unit UDT canbe design so as to accomplish one of the following separation tasks:- a simple evaporation of ε-caprolactam;- separating one or more light boiling compounds from ε-caprolactam;- separating one or more high boiling compounds from ε-caprolactam;- separating one or more high boiling compounds and one or more light boiling compoundsfrom ε-caprolactam -- in one side-stream distillation column; or-- in two separate distillation columns; or-- in one divided wall distillation column; or-- in one side stream distillation column, and a further distillation column wherein in saidfurther distillation column --- one or more light boiling compounds; or where--- one or more high boiling compoundsare separated from ε-caprolactam. It may be preferred that prior to being subjected to separating according to (d), the stream SPobtained from (c) is subjected to filtration.According to the process of the present invention, the purification unit UP may further comprise acrystallization unit UCR, wherein the process comprises obtaining from the distillation unit UDa stream SUD comprising ε-caprolactam at a concentration cUD, and feeding the stream SUD to the crystallization unit UCR, obtaining from UCRthe mixture MFcomprising ε-caprolactam at the concentration cMF.Further according to the present invention, the purification unit UP may further comprise achemical treatment unit UOD, wherein the process comprises obtaining from the distillation unit UDa stream SUDcomprising ε-caprolactam at a concentration cUDand feeding the stream SUDto thechemical treatment unit UOD, obtaining from UOD the mixture MF comprising ε-caprolactam at theconcentration cMF.Yet further according to the present invention, the purification unit UP may further comprise achemical treatment unit UOD and a crystallization unit UCR, wherein the crystallization unit UCR islocated downstream of the distillation unit UD and the chemical treatment unit UOD is locateddownstream of the crystallization unit UCR, wherein the process comprises obtaining from the distillation unit UD a stream SUD comprising ε-caprolactam at a concentration cUD, feeding the stream SUDto the crystallization unit UCR, obtaining from the crystallization UCRa stream SCRcomprising ε-caprolactam at a concentration cCR, and feeding the stream SCR to the chemicaltreatment unit UOD, obtaining from UODthe mixture MFcomprising ε-caprolactam at the concentration cMF.Still further according to the present invention, the purification unit UP may further comprise achemical treatment unit UOD and a crystallization unit UCR, wherein the chemical treatment unitUOD is located downstream of the distillation unit UD and the crystallization unit UCR is locateddownstream of the unit UCR, wherein the process comprises obtaining from the distillation unit UDa stream SUDcomprising ε-caprolactam at a concentration cUD, feeding the stream SUDto the chemical treatment unit UOD , obtaining from the chemical treatment unit UOD a stream SODcomprising ε-caprolactam at a concentration cOD, and feeding the stream SOD to the crystallizationunit UCR, obtaining from UCR the mixture MF comprising ε-caprolactam at the concentration cMF.As described above, according to (iv.2), the process of the present invention may comprisepassing the stream SR, optionally the stream SL, into an ε-caprolactam purification unit UP, andobtaining from the unit UPa mixture MThaving an ε-caprolactam purity ΩGC(MT) of at least 99 %, an APHA value ΩAPHA(MT) of at most 20 and a water content xH2O(MT) of at most 0.05 weight-%, based on the total weight of the mixture MT. Preferably, xH2O(MT) is in the range of from 0 to 0.05 weight-%, more preferably in the range of from 0 to 0.01 weight-%, more preferably in the rangeof from 0 to 0.001 weight-%. Further preferably, ΩGC(MT) is at least 99.5 %, more preferably atleast 99.8 %, more preferably at least 99.9 %. Yet further preferably, ΩAPHA(MT) is at most 20,more preferably at most 15, more preferably at most 10. Therefore, it is more preferred thatxH2O(MT) is in the range of from 0 to 0.001 weight-%, ΩGC(MT) is at least 99.9 %, and ΩAPHA(MT) isat most 10. Optionally or preferably, the mixture MTis further characterized by one or more of a permanganate absorption number ΩPAN(MT) and an UV absorption ΩUV(MT), wherein ΩPAN(MT) is at most 20, preferably at most 15, more preferably at most 10, and wherein ΩUV(MT) is at most0.75, preferably at most 0.25, more preferably at most 0.1. Therefore, it is more preferred thatxH2O(MT) is in the range of from 0 to 0.001 weight-%, ΩGC(MT) is at least 99.9 %, ΩAPHA(MT) is atmost 10, ΩPAN(MT) is at most 10, and ΩUV(MT) is at most 0.1.As described above, according to (i), a stream SM is provided which comprises a solid material Mcomprising polyamide 6. Preferably, the material M comprises, preferably consists of, waste material, wherein said waste material more preferably comprises, more preferably consists of, one or more of at least one textile waste material and at least one engineering plastics waste material, more preferably comprises, more preferably consists of at least one textile waste material; wherein preferably from 10 to 99 weight-%, more preferably from 30 to 98.5 weight-%, more preferably from 50 to 98 weight-%, more preferably from 80 to 98 weight-% of the material M consist of polyamide 6; wherein preferably, in addition to polyamide 6, the material M comprises one or more further organic polymeric compounds, more preferably including, but not limited to, one or more of at least one elastane, at least one polyethylene terephthalate, at least one polytetrahydrofuran, at least one polyamide 6.6, at least one polyurethane, at least one polyester, at least one cellulose material, and at least one rubber material comprising one or more of at least one natural rubber material and at least one synthetic rubber material. Prior to being provided to the process of the present invention, the collected textile waste material can be suitably sorted. In this regard, it is possible to spread the collected textile waste material on a conveyor, which spreading can be carried out either manually and / or mechanically. Thereafter, the respectively spread textile waste material is subjected to sorting, either by composition and / or by color. Sorting can be carried out either manually and / or optically. If carried out optically, the sorting preferably comprises an infrared sorting, more preferably a near-infrared sorting and / or a mid-infrared sorting. Optionally, prior to sorting, the textile waste material can besubjected to a suitable metal removing step. If a metal removing step is carried out, ferrouselements are preferably separated, for example by suitable magnetic means, and / or non-ferrous elements are preferably separated, for example by suitable eddy current separating means. After said sorting, the respectively obtained textile waste material can be subjected to a furthertreatment, such as cutting and / or milling.Generally, the solid material M can be provided according to any suitable method. Preferablyaccording to the present invention, providing the solid material M comprises providing the solidmaterial 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; passing the provided solid material M via a first connecting line from the unit UMDto 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 onefirst particle separation unit UFMPS; passing the solid material M from the unit UMC via a secondconnecting 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. Generally, the solid material M may be provided from different sources if desired. For example, the collected textile waste material as a source of the solid material M may origin from different textile waste material sources and may be combined, and then the collected textile waste material can be suitably sorted as indicated above. The textile waste material may generally have different grades of quality, different grades of impurities and different material combinations.Nevertheless, such material is of course suitable for the process in accordance with the presentinvention. The ε-caprolactam for the process in accordance with the present invention may be obtained via hydrolytic depolymerisation and subsequent purification as described in the contextof the present invention, which, depending from the sources and the quality of the materialcollected and sorted, may result in slight variation of the properties of the solid material M while of course still being suitable for the process described herein. Preferably, the solid material M is provided 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 0.1 to 15 mm anda 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 0.2 to 20 mm anda 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 0.3 to 30 mm anda D90 value of the particle length in the range of from 0.8 to 30 mm. Generally, the aqueous depolymerisation mixture according to (ii) can be prepared according to any method. Preferably, preparing the aqueous depolymerization mixture according to comprises melting in a melting unit UM the solid material M, obtaining a liquid stream SM having atemperature TSM at a pressure pSM; admixing in a pre-reaction unit UPR the stream SM with anaqueous stream SWhaving a temperature TSWat a pressure pSW, obtaining a liquid reaction feed stream SF having a temperature TSF at a pressure pSF; feeding the stream SF obtained according to as the depolymerization mixture into the chemical reaction unit UR. As far as this process design is concerned, it is preferred that 0.8 ≤ TSF / TD≤ 1.05 and 0.9 ≤ pSF / pD≤ 1.05; 0.6 ≤ TSM / TSF ≤ 1.2 and 0.9 ≤ pSM / pSF ≤ 1.05; and 0.8 ≤ TSW / TSF≤ 1.2 and 0.9 ≤ pSW / pSF≤ 1.05; wherein TDis the depolymerization temperature and pDis the depolymerization pressurecomprised by the polyamide 6 depolymerization conditions in the reaction unit UR.The pre-reaction unit UPRpreferably comprises, more preferably consists of, a mixing unit, preferably a static mixing unit, and wherein the melting unit UMcomprises, preferably consists ofan extruder, preferably a single-screw extruder or a twin-screw extruder. Further, it is preferredthat SWand SMare admixed in UPRat a mixing ratio (mW / kg) / (mP / kg) in the range of from 1:1 to20:1, more preferably in the range of from 2:1 to 15:1, more preferably in the range of from 5:1 to10:1, wherein mW is the amount of water comprised in SW and mP is the amount of polyamide 6 comprised in SM. As far as the hydrolytic depolymerization according to the present invention is concerned, it ispreferred that the depolymerization pressure pD in the unit UR is in the range of from 40 to140 bar, more preferably in the range of from 40 to 125 bar, more preferably in the range of from 40 to 110 bar; and the depolymerisation temperature TDin the unit URis in the range of from 230 to 335 °C, more preferably in the range of from 250 to 320 °C, more preferably in the range of from 270 to 310 °C. Preferably, the reaction unit URcomprises z chemical reactors Ri, 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. If z > 1, is preferred that at least 2 reactors Ri, morepreferably all z reactors Ri, are serially coupled, wherein- the stream SF is fed into Ri, with i = 1;- an aqueous liquid stream Si containing ε-caprolactam dissolved in water is removed fromreactor Riand fed into the reactor Ri+1, with i < z;- the aqueous liquid stream Sz containing ε-caprolactam dissolved in water is removed fromthe reactor Rz as the stream SR; wherein in every reactor Ri, a depolymerization temperature TDi at a depolymerization pressure pDiis maintained, wherein, independently of each other, TDiis 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 offrom 270 to 310 °C and pDi is in the range of from 40 to 110 bar. For z > 1, it is preferred that thez reactors Riare vertically arranged, with R1being the top-most reactor and Rzbeing the bottom- most reactor, wherein Si obtained from Ri is transferred to Ri+1 by gravity, preferably by gravityonly. More preferably, at least 1, preferably all z reactors Ri, are continuous stirred tank reactors(CSTR). Preferably, every continuous stirred tank reactor Rihas, independently from each other, 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 Ri comprises at least one agitator, wherein more preferably every compartment of every reactor Ricomprises at least one agitator, wherein more preferably, every compartment of every reactor Ricomprises one agitator, and 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. Preferably, the polyamide 6 depolymerization conditions further comprise a total residence time tDof the aqueous depolymerization mixture in the unit UR, preferably in the z reactors Ri, more preferably in the z continuous 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 tDin the range of from 30 to 90 min. More preferably, the residence time of an aqueous depolymerization mixture in a reactor Riis tDiand0.90 ≤ (tDi / tDi+1) ≤ 1.10, more preferably 0.95 ≤ (tDi / tDi+1) ≤ 1.05.If the solid material M comprises one or more elastanes, the aqueous liquid stream SRobtained from the depolymerization reaction usually contains one or more decomposition products which are formed from the one or more elastanes, for example in the course of the depolymerization reaction in UR. Additionally or alternatively, one or more decomposition products form the one ormore elastanes may also be formed in the melting unit UM which is described above. By way ofexample, said one or more decomposition products from the one or more elastanes preferably include at least one of aniline, butanediol, butanediol oligomers including, for example, butandediol dimer and butanediol trimer, and 4,4’-methylenedianiline (MDA) and isomers thereof such as 2,4’-methylenedianiline and 2,2’-methylenedianiline.According to the present invention, it is preferred that preparing the stream SR according to (iii) ina hydrolytic depolymerization reaction is carried out in the absence of a polyamide 6 depolymerization catalyst such as a mineral acid and / or a zinc salt such as zinc chloride, zincacetate or zinc triflate, i.e. that no such polyamide 6 depolymerization catalyst is used forpreparing or is contained in the depolymerisation mixture to be subjected to depolymerisation conditions. Generally, the process of the present invention can be designed as a continuous process, asemicontinuous process, or a batch process.As described hereinabove, the mixture MF of the present invention having a certain minimum content of water is suitable to be stored and, after storing, till exhibits advantageous characteristics, in particular with respect to its APHA color. Therefore, the process of the present invention may further comprise(v) storing the mixture MF obtained according to (iv) at a temperature of the mixture of at most80 °C under an inert gas atmosphere for a storage time ΔtΣ, obtaining a stored mixture MS,wherein the storage time ΔtΣ is at least 1 d.Preferably according to (v), the mixture MF is stored under exclusion of light. Further preferablyaccording to (v), the storage time ΔtΣis at least 7 d, more preferably at least 14 d, more preferablyin the range of from 14 to 28 d. Still further preferably according to (v), the inert gas atmospherecomprises one or more of nitrogen and argon. Further according to the present invention, it ispreferred that the mixture MFis stored according to (v) at a storing temperature δSof the mixture MF in the range of from 20 to 80 °C, preferably in the range of from 25 to 80 °C, more preferablyin the range of from 35 to 77 °C, more preferably in the range of from 50 to 75 °C. Furtheraccording to the present invention, it is preferred that the mixture MF is stored according to (v) ata storing pressure pS of the inert gas atmosphere in the range of from 0.5 to 10 bar, morepreferably in the range of from 0.75 to 5 bar, more preferably in the range of from 1 to 2 bar. Further according to the present invention, it is preferred that the storing according to (v) comprises agitating, preferably mechanically agitating, more preferably stirring the mixture MFfor at least part of the storage time ΔtΣ, preferably for essentially the entire storage time ΔtΣ. It was further found that it may be advantageous to carry out the storing according to (v) at a temperature which is in a specific functional relationship to the water content of the mixture MF. Specifically, it may be preferred that during storing according to (v), (δS / °C) = – 2.6 ^ (xH2O(MF) / weight-%) + CSwherein CS = 77 ± 10, preferably CS = 77 ± 5.Further, the present invention also relates to a method of storing a mixture MF comprising ε-caprolactam and water and having a purity ΩGC(MF)of at least 99 %, an APHA value ΩAPHA(MF) ofat most 20 and a water content xH2O(MF) of at least 0.1 weight-%, based on the total weight of themixture MF, wherein said method comprises storing the mixture MF at a temperature of themixture of at most 80 °C under an inert gas atmosphere for a storage time ΔtΣ, obtaining a storedmixture MS, wherein the storage time ΔtΣ is at least 1 d.As far as said method of storing is concerned, it is preferred that at least 99 weight-%, preferably at least 99.1 weight-%, more preferably at least 99.2 weight-%, more preferably at least 99.3 weight-%, more preferably at least 99.4 weight-%, more preferably at least 99.5 weight-%, more preferably at least 99.6 weight-%, more preferably at least 99.7 weight-%, more preferably at least 99.8 weight-%, more preferably at least 99.9 weight-% of the mixture MFconsist of ε- caprolactam and water. It is preferred that as far as the method of storing is concerned, ΩGC(MF) is at least 99.5 %, more preferably at least 99.6 %, more preferably at least 99.7 %, more preferably at least 99.8 %, more preferably at least 99.9 %. Further, it is preferred that ΩAPHA(MF) is at most 15, more preferably at most 12.5, more preferably at most 10, more preferably at most 7.5, more preferably at most 5. Still further, it is preferred that xH2O(MF) is in the range of from 0.1 to 10 weight-%, more preferably in the range of from 0.15 to 9 weight-%, more preferably in the range of from 0.2 to 8 weight-%, more preferably in the range of from 0.35 to 7 weight-%, more preferably in the range of from 0.5 to 6 weight-%. Suitable ranges of xH2O(MF) may include from 0.5 to 2 weight-% and from 2 to 4 weight-% and from 4 to 6 weight-%. Therefore, mixtures MFare more preferred for which ΩGC(MF) is at least 99.9 %, ΩAPHA(MF) is at most 5, and xH2O(MF) is in the range of from 0.5 to 6 weight-%. Optionally or preferably as far as the method of storing is concerned, the mixture MFis further characterized by one or more of a permanganate absorption number ΩPAN(MF) and an UV absorption ΩUV(MF). ΩPAN(MF) is preferably at most 20, more preferably at most 15, morepreferably at most 10. ΩUV(MF) is preferably at most 0.75, more preferably at most 0.25, morepreferably at most 0.1. Therefore, mixtures MF are more preferred for which ΩPAN(MF) is at most10 and ΩUV(MF) is at most 0.1. Thus, more preferred are mixtures MF for which ΩGC(MF) is at least99.9 %, ΩAPHA(MF) is at most 5, xH2O(MF) is in the range of from 0.5 to 6 weight-%, ΩPAN(MF) is atmost 10 and ΩUV(MF) is at most 0.1.Preferably, as far as the method of storing is concerned, the mixture MF is obtainable or obtained by a process comprising the steps (i) to (iv) as described above, Further regarding said method of storing, it is preferred that the mixture MF is stored underexclusion of light. Further preferably regarding said method of storing, the storage time ΔtΣ is atleast 7 d, more preferably at least 14 d, more preferably in the range of from 14 to 28 d. Still further regarding said method of storing, the inert gas atmosphere comprises one or more ofnitrogen and argon. Further preferably regarding said method of storing, the mixture MF is storedat a storing temperature δSof the mixture MFin the range of from 20 to 80 °C, preferably in the range of from 25 to 80 °C, more preferably in the range of from 35 to 77 °C, more preferably inthe range of from 50 to 75 °C. Further preferably regarding said method of storing, the mixture MFis stored according to (v) at a storing pressure pS of the inert gas atmosphere in the range of from 0.5 to 10 bar, more preferably in the range of from 0.75 to 5 bar, more preferably in the range offrom 1 to 2 bar. Further preferably regarding said method of storing, it is preferred that the storingaccording to (v) comprises agitating, preferably mechanically agitating, more preferably stirring the mixture MF for at least part of the storage time ΔtΣ, preferably for essentially the entire storage time ΔtΣ. It was further found that it may be advantageous to carry out the method of storing at a storing temperature which is in a specific functional relationship to the water content of the mixture MF. Specifically, it may be preferred that during storing, (δS / °C) = – 2.6 ^ (xH2O(MF) / weight-%) + CSwherein CS = 77 ± 10, preferably CS = 77 ± 5.Generally, in the context of the present, a value Ω(MF) such as ΩGC(MF) and ΩAPHA(MF) refers tothe respective value Ω(MF) essentially immediately after the preparation of the mixture MF, inparticular to the respective value Ω(MF) prior to storing.The present invention generally also relates to a liquid mixture MF comprising ε-caprolactam andwater and having a purity ΩGC(MF) of at least 99 %, an APHA value ΩAPHA(MF) of at most 20 anda water content xH2O(MF) of at least 0.1 weight-%, based on the total weight of the mixture MF, said mixture MF preferably being obtainable or obtained by a process according to a process asdescribed above comprising steps (i) tom (iv), the mixture MF exhibiting a storage stability ΣΔt aftera storage time Δt, wherein ΣΔt is characterized by an APHA value ΩAPHA(Δt).If Δt is 14 d and the storage stability Σ14 after said storage time is characterized by an APHA valueΩAPHA(14), it is preferred that- if ΩAPHA(MF) is less than 5, ΩAPHA(14) ≤ 10;- if ΩAPHA(MF) is in the range of from 5 to 8, ΩAPHA(14) ≤ 2 ΩAPHA(MF);- if ΩAPHA(MF) > 8, ΩAPHA (14) ≤ 1.5 ΩAPHA(MF)).If Δt is 28 d and the storage stability Σ28 after said storage time is characterized by an APHA valueΩAPHA(28), it is preferred that- if ΩAPHA(MF) is less than 4, ΩAPHA(28) ≤ 10;- if ΩAPHA(MF) is in the range of from 4 to 8, ΩAPHA(28) ≤ 3 ΩAPHA(MF);- if ΩAPHA(MF) > 8, ΩAPHA(28) ≤ 2 ΩAPHA(MF).Further according to the present invention, the storage stability ΣΔt after a storage time Δt may befurther characterized by one or more of a permanganate absorption number ΩPAN(Δt) and an UV absorption ΩUV(Δt).If Δt is 14 d and the storage stability Σ14 after said storage time is characterized by one or more ofa permanganate absorption number ΩPAN(14) and an UV absorption ΩUV(14), it is preferred that- if ΩPAN(MF) is less than 5, ΩPAN(14) ≤ 10;- if ΩPAN(MF) is in the range of from 5 to 8, ΩPAN(14) ≤ 1.5 ΩPAN(MF);- if ΩPAN(MF) > 8, ΩPAN(14) ≤ 1.25 ΩPAN(MF);and- if ΩUV(MF) is less than 0.02, ΩUV(14) ≤ 0.05;- if ΩUV(MF) is in the range of from 0.02 to 0.03, ΩUV(14) ≤ 3 ΩUV(MF);- if ΩUV(MF) > 0.03, ΩUV(14) ≤ 1.25 ΩUV(MF).If Δt is 28 d and the storage stability Σ28 after said storage time is characterized by one or more ofa permanganate absorption number ΩPAN(28) and an UV absorption ΩUV(28), it is preferred that- if ΩPAN(MF) is less than 5, ΩPAN(28) ≤ 10;- if ΩPAN(MF) is in the range of from 5 to 8, ΩPAN(28) ≤ 3 ΩPAN(MF);- if ΩPAN(MF) > 8, ΩPAN(28) ≤ 2 ΩPAN(MF);and- if ΩUV(MF) is less than 0.025, ΩUV(28) ≤ 0.05;- if ΩUV(MF) is in the range of from 0.025 to 0.05, ΩUV(28) ≤ 3 ΩUV(MF);- if ΩUV(MF) > 0.05, ΩUV(28) ≤ 2 ΩUV(MF).The present invention generally also relates to a stored liquid mixture MS comprisingε-caprolactam and water, wherein the mixture MS is obtainable or obtained by a process asdescribed above comprising the step (v).For said stored mixture MS, it is preferred that it exhibits an APHA value ΩAPHA(14) after a storagetime Δt of 14 d, wherein- if ΩAPHA(MF) is less than 4, ΩAPHA(14) ≤ 10;- if ΩAPHA(MF) is in the range of from 4 to 8, ΩAPHA(14) ≤ 2 ΩAPHA(MF);- if ΩAPHA(MF) > 8, ΩAPHA(14) ≤ 1.5 ΩAPHA(MF).For said stored mixture MS, it is further preferred that it exhibits an APHA value ΩAPHA(28) after astorage time Δt of 28 d, wherein- if ΩAPHA(MF) is less than 4, ΩAPHA(28) ≤ 10;- if ΩAPHA(MF) is in the range of from 4 to 8, ΩAPHA(28) ≤ 3 ΩAPHA(MF);- if ΩAPHA(MF) > 8, ΩAPHA(28) ≤ 2 ΩAPHA(MF).The said stored mixture MSmay be further characterized by one or more of a permanganate absorption number ΩPAN(Δt) and an UV absorption ΩUV(Δt).If the storage time Δt is 14 d, it is preferred for the mixture MS that- if ΩPAN(MF) is less than 5, ΩPAN(14) ≤ 10;- if ΩPAN(MF) is in the range of from 5 to 8, ΩPAN(14) ≤ 1.5 ΩPAN(MF);- if ΩPAN(MF) > 8, ΩPAN(14) ≤ 1.25 ΩPAN(MF);and- if ΩUV(MF) is less than 0.01, ΩUV(14) ≤ 0.05;- if ΩUV(MF) is in the range of from 0.01 to 0.03, ΩUV(14) ≤ 3 ΩUV(MF);- if ΩUV(MF) > 0.03, ΩUV(14) ≤ 1.25 ΩUV(MF).If the storage time Δt is 28 d, it is preferred for the mixture MS that- if ΩPAN(MF) is less than 5, ΩPAN(28) ≤ 10;- if ΩPAN(MF) is in the range of from 5 to 8, ΩPAN(28) ≤ 3 ΩPAN(MF);- if ΩPAN(MF) > 8, ΩPAN(28) ≤ 2 ΩPAN(MF);and- if ΩUV(MF) is less than 0.025, ΩUV(28) ≤ 0.05;- if ΩUV(MF) is in the range of from 0.025 to 0.04, ΩUV(28) ≤ 1.5 ΩUV(MF);- if ΩUV(MF) > 0.03, ΩUV(28) ≤ 1.25 ΩUV(MF).The present invention further relates to the use of a mixture MFas described hereinabove and / or a mixture MSas described hereinabove as an educt material for a chemical process, preferably for a polymerization reaction, more preferably for preparing polyamide 6.The present invention still further relates to a method for preparing polyamide 6, comprising(A) preparing a mixture MF according to a process as described hereinabove comprisingsteps (i) to (iv), and / or providing a mixture MF as described hereinabove; (B) optionally storing the mixture MF at storage conditions as defined hereinabove in thecontext of the process step (v), obtaining a stored mixture MS; (C) subjecting the mixture MF prepared and / or provided according to (A) and / or the mixture MSaccording to (B) to polyamide 6 polymerization conditions.The present invention still further relates to polyamide 6 as such, obtainable or obtained by saidmethod, wherein said polyamide has n APHA value of at most 10, preferably of at most 9, more preferably of at most 8.The present invention still further relates to a process as described above, which processcomprises providing at least part of the mixture MF, or of the mixture MS, to a polyamide 6production unit UPP, wherein the polyamide 6 produced in UPP is preferably provided as afeedstock to a textile material producing unit UTP, from which unit UTP(A) a textile material MTE is obtained which is brought onto the market, wherein, after thelifetime TMTE of said textile material MTE, it is at least partially collected as textile waste material in a textile material collecting unit UTC;(B) remaining material MRE 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 as material M according to (i).The present invention still further relates to a process as described above, which processcomprises providing at least part of the mixture MF, or of the mixture MS, to a polyamide 6production unit UPP, wherein the polyamide 6 produced in UPP is preferably provided as afeedstock to an engineering plastics material producing unit UEP, from which unit UEP(A) an engineering plastics material MEP is obtained which is brought onto the market, wherein,after the lifetime TMEPof said engineering plastics material MEP, it is at least partially collected as engineering plastics waste material in an engineering plastics materialcollecting unit UEC;(B) remaining material MRE is obtained as engineering plastics waste material;wherein at least part of the engineering plastics waste material according to (A), or at least part ofthe engineering plastics waste material according to (B), or at least part of the engineering plasticswaste material according to (A) and at least part of the engineering plastics waste materialaccording to (B) is suitably provided as material M according to (i).The present invention still further relates to the use of the mixture MF as described hereinaboveor of the mixture MSas described hereinabove 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.The present invention still further relates to a method for preparing polyamide 6, said methodcomprising employing the mixture MF as described hereinabove or the mixture MS as describedhereinabove as a starting material, wherein said method preferably further comprises employingsaid 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.The present invention still further relates to the use of the mixture MF as described hereinaboveor of the mixture MS as described hereinabove for preparing one or more of a polymer and apolymer product; or a method for preparing one or more of a polymer and a polymer product, saidmethod comprising employing the mixture MF as described hereinabove or the mixture MS asdescribed hereinabove as a starting material.Preferably according to said use or said method of above, 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.Further preferably according to said use or said method of above, the polymer, or the polymerproduct, or the polymer and the polymer product comprises or comprise polyamide 6 and optionally at least one further polymeric compound, said polyamide 6 being at least partiallyobtainable or obtained from the mixture MF as described hereinabove or from the mixture MS asdescribed hereinabove, wherein the at least one further polymeric compound preferablycomprises one or more of at least one polyamide 6.6, at least one polyethylene terephthalate, atleast one polyurethane, at least one polyester, at least one cellulose material, and at least onerubber material comprising one or more of at least one natural rubber material and at least one synthetic rubber material.Further preferably according to said use or said method of above, the polymer, or the polymerproduct, 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 aircooler, 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, a top mount, an oil pan, a fuel cell, a heat shield and / or a cushion;- a cloth, an apparel, preferably a shirt, trousers, a pullover, a boot, a shoe, a shoe sole, a tight,a yarn, a fabric, and / or or jacket;- an electrical part, preferably an electrical component, an electronic passive component, anelectronic 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, anintegrated 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, anut, 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, abristle, 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.Further preferably according to said use or said method of above, the polymer, or the polymerproduct, or the polymer and the polymer product contains or contain polyamide 6, obtainable orobtained from the mixture MF as described hereinabove or from the mixture MS as describedhereinabove in an amount of 1 weight-% or more, preferably 2 weight-% or more, more preferably5 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 90weight-% or less, more preferably 50 weight-% or less, more preferably 25 weight-% or less,more preferably 10 weight-% or less. 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 thecontext 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 preparing a liquid ε-caprolactam mixture MF, the process comprising(i) providing a stream SM comprising a solid material M comprising polyamide 6;(ii) preparing an aqueous depolymerization mixture based on SM;(iii) subjecting the depolymerization mixture prepared according to (ii) to polyamide 6depolymerization conditions in a reaction unit UR, obtaining a liquid aqueous stream SR comprising ε-caprolactam dissolved in water at a concentration cSR, the stream SR further comprising one or more impurities; and optionally passing the liquid aqueousstream SRinto an evaporation unit UE, obtaining from SRa liquid aqueous stream SLcomprising ε-caprolactam dissolved in water at a concentration cSL with cSL > cSR, and further obtaining from SRone or more aqueous vapor streams SV; (iv) passing the stream SR, optionally the stream SL, into an ε-caprolactam purification unitUP, and (iv.1) obtaining from the unit UP the mixture MF; or(iv.2) obtaining from the unit UP a mixture MT having an ε-caprolactam purity ΩGC(MT)of at least 99 %, an APHA value ΩAPHA(MT) of at most 20 and a water content xH2O(MT) of at most 0.05 weight-%, based on the total weight of the mixture MT, and adding water to the mixture MT, obtaining the mixture MF; wherein the mixture MF has an ε-caprolactam purity ΩGC(MF) of at least 99 %, anAPHA value ΩAPHA(MF) of at most 20 and a water content xH2O(MF) of at least 0.1weight-%, based on the total weight of the mixture MF.2. The process of embodiment 1, wherein ΩGC(MF) is at least 99.5 %, more preferably at least99.8 %, more preferably at least 99.9 %.3. The process of embodiment 1 or 2, wherein ΩAPHA(MF) is at most 15, preferably at most 10,more preferably at most 5.4. The process of any one of embodiments 1 to 3, wherein the mixture MF has a temperaturein the range of from 20 to 80 °C, preferably in the range of from 35 to 77 °C, more preferably in the range of from 50 to 75 °C.5. The process of any one of embodiments 1 to 4, wherein xH2O(MF) is in the range of from 0.1to 10 weight-%, preferably in the range of from 0.2 to 8 weight-%, more preferably in the range of from 0.5 to 6 weight-%.6. The process of any one of embodiments 1 to 5, wherein the mixture MF is furthercharacterized by one or more of a permanganate absorption number ΩPAN(MF) and an UV absorption ΩUV(MF), wherein ΩPAN(MF) is at most 20, preferably at most 15, more preferably at most 10, and wherein ΩUV(MF) is at most 0.75, preferably at most 0.25, more preferably at most 0.1.7. The process of any one of embodiments 1 to 6, wherein the purification unit UP according to(v) comprises a water separation unit UWSand a distillation unit UD, the process preferably comprising feeding the stream SR, optionally the stream SL, to UWS, obtaining from UWS astream SUWS comprising ε-caprolactam at a concentration cUWS, feeding the stream SUWS to the distillation unit UD, obtaining from UD the mixture MF comprising ε-caprolactam at aconcentration cMF, wherein cSR< cUWS<<< cMF, preferably wherein cSL< cUWS<<< cMF.8. The process of embodiment 7, wherein the water separation unit UWS comprises at leasttwo water separation sub-units UWS1and UWS2, preferably two serially coupled water separation sub-units UWS1 and UWS2, wherein the stream SR, optionally the stream SL, is fedinto UWS1, wherein downstream of UWS1 and upstream of UWS2, a separation unit UI is preferably located, the process comprising obtaining from UWS1an aqueous stream SUWS1, feeding the stream SUWS1into the separation unit UI, obtaining from UIan aqueous stream SUI, and feeding the stream SUI into the unit UWS2, wherein in UI, one or more of impurities are separated from SUWS1, thereby obtaining from UI an impurity stream SI, said impurities preferably comprising at least one impurity comprised in SRaccording to (iii), wherein at least one of said impurities is an organic compound having a higher boiling point than ε-caprolactam, the separation unit UI being a high boiler separation unit.9. The process of embodiment 7 or 8, wherein the purification unit UP further comprises,downstream of the unit UD, one or more of a crystallization unit UCR and a chemical treatment unit UOD, the process comprising obtaining the mixture MF from UCR or from UOD.10. The process of embodiment 9, wherein the chemical treatment in the unit UOD comprises(a) providing a preferably liquid stream SUD comprising ε-caprolactam from the distillationunit UD or a preferably liquid stream SCR comprising ε-caprolactam from thecrystallization unit UCR, said stream SUDor said stream SCRfurther comprising one or more oxidizable organic impurity compounds X, wherein the stream SUD or the stream SCR has an ε-caprolactam purity ΩGC(SC) of at least 99 % and exhibits a weight ratiorXCof the one or more organic compounds X relative to ε-caprolactam; (b) providing a stream SO comprising at least one permanganate;(c) preparing an oxidation reaction educt mixture MOE from the stream SUD and thestream SO, or from the stream SSCRand the stream SO, and subjecting the mixture MOE to oxidation reaction conditions, obtaining an oxidation reaction product stream SP comprising ε-caprolactam, further comprising one or more oxidation products Yobtained from the oxidation of at least a part of the one or more compounds X, and optionally further comprising a part of the one or more organic compounds X, whereinthe stream SPexhibits a weight ratio rXCPof organic compound X relative to ε-caprolactam with 0 ≤ rXCP < rXC and further exhibits a weight ratio rYCP of the one ormore products Y relative to ε-caprolactam with rYCP > 0;(d) separating at least a part of the one or more oxidation products Y and optionally atleast a part of organic compound X from the stream SP, obtaining the mixture MFor the mixture MT exhibiting a weight ratio rYCT of oxidation product Y relative to ε-caprolactam with 0 ≤ rYCT < rYCP, and further exhibiting a weight ratio rXCT of organiccompound X relative to ε-caprolactam with 0 ≤ rXCT < rXC.11. The process of embodiment 10, wherein the at least one permanganate comprised in thestream SOprovided according to (b) comprises, preferably consists of, at least alkali metal permanganate, wherein more preferably, the at least one alkali metal permanganate comprises one or more of sodium permanganate and potassium permanganate.12. The process of embodiment 10 or 11, wherein from 0.5 to 100 weight-% of the stream SOprovided according to (b) consist of permanganate.13. The process of any one of embodiments 10 to 12, wherein the stream SO providedaccording to (b) further comprises water.14. The process of any one of embodiments 10 to 13, wherein the oxidation reaction eductmixture MOEprepared according to (c) exhibits a permanganate concentration, calculated as MnO4, in the range of from 0.005 to 5 weight-%, preferably in the range of from 0.01 to 3 weight-%, more preferably in the range of from 0.05 to 1 weight-%.15. The process of any one of embodiments 10 to 14, wherein the oxidation reaction conditionsaccording to (c) comprise a temperature TOE of the mixture MOE in the range of from 40 to 140 °C, preferably in the range of from 60 to 100 °C, more preferably in the range of from 70 to 90 °C.16. The process of any one of embodiments 10 to 15, wherein the mixture MOE preparedaccording to (c) further comprises water.17. The process of any one of embodiments 10 to 16, wherein subjecting the mixture MOE tooxidation reaction conditions is carried out in an oxidation reaction unit UOR comprised in the chemical treatment unit UOD, wherein the unit UORpreferably comprises one or more of at least one continuous stirred tank reactor and at least one tube reactor.18. The process of any one of embodiments 10 to 17, further comprising providing a stream SBcomprising at least one hydroxide, wherein the oxidation reaction educt mixture MOEaccording to (c) is prepared from the stream SUD or the stream SCR, and from the stream SO and the stream SB.19. The process of embodiment 18, wherein the at least one hydroxide comprised in the streamSB comprises, preferably consists of, at least alkali metal hydroxide, wherein more preferably, the at least one alkali metal hydroxide comprises, more preferably consists of, sodium hydroxide.20. The process of embodiment 18 or 19, wherein from 0.5 to 100 weight-% of the stream SBconsist of hydroxide.21. The process of any one of embodiments 18 to 20, wherein the stream SB further compriseswater.22. The process of any one of embodiment 18 to 21, wherein the oxidation reaction eductmixture MOE prepared according to (c) exhibits a hydroxide concentration, calculated as OH, in the range of from 0.005 to 0.75 weight-%, preferably in the range of from 0.01 to 0.5 weight-%, more preferably in the range of from 0.1 to 0.25 weight-%.23. The process of any one of embodiments 10 to 22, wherein the one or more oxidizableorganic compounds X have a boiling point δX / °C with 0.5 ≤ (δX / δC) ≤ 1.5, δC / °C being theboiling point of ε-caprolactam and wherein at least one of the one or more oxidationproducts Y has a boiling point δY / °C with δY / °C ≠ δC / °C, wherein the difference Δδ betweenthe boiling points δYand δCis preferably at least 1 °C.24. The process of any one of embodiments 10 to 23, wherein separating at least a part of theone or more oxidation products Y and optionally at least a part of organic compound X from the stream SPaccording to (d) comprises subjecting the stream SPobtained according to (c) to distillation in a distillation unit UDT, comprised in the chemical treatment unit UOD, obtaining from the distillation unit UDT a stream SDT comprising ε-caprolactam as the mixtureMF or the mixture MT, wherein the unit UDT comprises one or more distillation columns,preferably one or two distillation columns, wherein at least one column is optionally configured as side stream column or as divided wall column.25. The process of any one of embodiments 10 to 24, wherein prior to being subjected toseparating according to (d), the stream SP obtained from (c) is subjected to filtration.26. The process of any one of embodiments 9 to 25, wherein the purification unit UP furthercomprises a crystallization unit UCR, the process comprising obtaining from the distillation unit UD a stream SUD comprising ε-caprolactam at a concentration cUD, and feeding the stream SUDto the crystallization unit UCR, obtaining from UCRthe mixture MFcomprisingε-caprolactam at the concentration cMF.The process of any one of embodiments 9 to 25, wherein the purification unit UP furthercomprises a chemical treatment unit UOD, the process comprising obtaining from thedistillation unit UD a stream SUD comprising ε-caprolactam at a concentration cUD andfeeding the stream SUDto the chemical treatment unit UOD, obtaining from UODthe mixtureMF comprising ε-caprolactam at the concentration cMF.The process of any one of embodiments 9 to 25, wherein the purification unit UP furthercomprises a chemical treatment unit UOD and a crystallization unit UCR, wherein the crystallization unit UCR is located downstream of the distillation unit UD and the chemicaltreatment unit UOD is located downstream of the crystallization unit UCR, the processcomprising obtaining from the distillation unit UDa stream SUDcomprising ε-caprolactam at a concentration cUD, feeding the stream SUD to the crystallization unit UCR , obtaining fromthe crystallization UCR a stream SCR comprising ε-caprolactam at a concentration cCR, andfeeding the stream SCRto the chemical treatment unit UOD, obtaining from UODthe mixtureMF comprising ε-caprolactam at the concentration cMF.The process of any one embodiments 9 to 25, wherein the purification unit UP furthercomprises a chemical treatment unit UODand a crystallization unit UCR, wherein thechemical treatment unit UOD is located downstream of the distillation unit UD and thecrystallization unit UCRis located downstream of the unit UCR, the process comprising obtaining from the distillation unit UDa stream SUDcomprising ε-caprolactam at a concentration cUD, feeding the stream SUD to the chemical treatment unit UOD , obtaining from the chemical treatment unit UOD a stream SOD comprising ε-caprolactam at aconcentration cOD, and feeding the stream SOD to the crystallization unit UCR, obtaining fromUCR the mixture MF comprising ε-caprolactam at the concentration cMF.The process of any one of embodiments 1 to 29, wherein xH2O(MT) is in the range of from 0to 0.05 weight-%, preferably in the range of from 0 to 0.01 weight-%, more preferably in therange of from 0 to 0.001 weight-%.The process of any one of embodiments 1 or 30, wherein ΩGC(MT) is at least 99.5 %,preferably at least 99.8 %, more preferably at least 99.9 %.The process of any one of embodiments 1 to 31, wherein ΩAPHA(MT) is at most 20,preferably at most 15, more preferably at most 10.The process of any one of embodiments 1 to 32, wherein the mixture MT is furthercharacterized by one or more of a permanganate absorption number ΩPAN(MT) and an UV absorption ΩUV(MT), wherein ΩPAN(MT) is at most 20, preferably at most 15, more preferably at most 10, and wherein ΩUV(MT) is at most 0.75, preferably at most 0.25, more preferably at most 0.1.34. The process of any one of embodiments 1 to 33, wherein the material M according to (i)comprises, preferably consists of, waste material, wherein said waste material more preferably comprises, more preferably consists of, one or more of at least one textile waste material and at least one engineering plastics waste material, more preferably comprises, more preferably consists of at least one textile waste material; wherein preferably from 10 to 99 weight-%, more preferably from 30 to 98.5 weight-%, more preferably from 50 to 98 weight-%, more preferably from 80 to 98 weight-% of the material Mconsist of polyamide 6;wherein preferably, in addition to polyamide 6, the material M comprises one or more further organic polymeric compounds, more preferably including, but not limited to, one or more of at least one elastane, at least one polyethylene terephthalate, at least onepolytetrahydrofuran, at least one polyamide 6.6, at least one polyurethane, at least one polyester, at least one cellulose material, and at least one rubber material comprising one or more of at least one natural rubber material and at least one synthetic rubber material.35. The process of any one of embodiments 1 to 34, further comprising(v) storing the mixture MF obtained according to (iv) at a temperature of the mixture of atmost 80 °C under an inert gas atmosphere for a storage time ΔtΣ, obtaining a storedmixture MS, wherein the storage time ΔtΣ is at least 1 d.36. The process of any one of embodiments 1 to 35, wherein according to (v), the mixture MF isstored under exclusion of light.37. The process of any one of embodiments 1 to 36, wherein according to (v), the storage timeΔtΣis at least 7 d, more preferably at least 14 d, more preferably in the range of from 14 to 28 d.38. The process of any one of embodiments 1 to 37, wherein according to (v), the inert gasatmosphere comprises one or more of nitrogen and argon, preferably argon.39. The process of any one of embodiments 1 to 38, wherein according to (v), the mixture MF isstored at a storing temperature δSof the mixture MFin the range of from 20 to 80 °C, preferably in the range of from 25 to 80 °C, more preferably in the range of from 35 to 77°C, more preferably in the range of from 50 to 75 °C, preferably at a storing pressure pS of the inert gas atmosphere in the range of from 0.5 to 10 bar, more preferably in the range offrom 0.75 to 5 bar, more preferably in the range of from 1 to 2 bar.40. The process of embodiment 39, wherein during storing according to (v),(δS / °C) = – 2.6 ^ (xH2O(MF) / weight-%) + CSwherein CS = 77 ± 10, preferably CS = 77 ± 5.41. A method of storing a mixture MF comprising ε-caprolactam and water and having a purityΩGC(MF)of at least 99 %, an APHA value ΩAPHA(MF) of at most 20 and a water contentxH2O(MF) of at least 0.1 weight-%, based on the total weight of the mixture MF, said mixture MF being obtainable or obtained by a process according to any one of embodiments 1 to 34, said method comprising storing the mixture MFat a temperature of the mixture of at most 80 °C under an inert gas atmosphere for a storage time ΔtΣ, obtaining a stored mixtureMS, wherein the storage time ΔtΣ is at least 1 d.42. The method of embodiment 41, wherein the mixture MF is stored under exclusion of light.43. The method of embodiment 41 or 42, wherein the storage time ΔtΣ is at least 7 d, morepreferably at least 14 d, more preferably in the range of from 14 to 28 d.44. The method of any one of embodiments 41 to 43, wherein the inert gas atmospherecomprises one or more of nitrogen and argon.45. The method of any one of embodiments 41 to 44, wherein the mixture MF is stored at astoring temperature δS of the mixture MF in the range of from 20 to 80 °C, preferably in the range of from 25 to 80 °C, more preferably in the range of from 35 to 77 °C, more preferably in the range of from 50 to 75 °C preferably at a storing pressure pS of the inertgas atmosphere in the range of from 0.5 to 10 bar, more preferably in the range of from0.75 to 5 bar, more preferably in the range of from 1 to 2 bar.46. The method of embodiment 45, wherein during storing,(δS / °C) = – 2.6 ^ (xH2O(MF) / weight-%) + CSwherein CS = 77 ± 10, preferably CS = 77 ± 5.47. A liquid mixture MF comprising ε-caprolactam and water and having a purity ΩGC(MF) of atleast 99 %, an APHA value ΩAPHA(MF) of at most 20 and a water content xH2O(MF) of at least0.1 weight-%, based on the total weight of the mixture MF, said mixture MF preferably being obtainable or obtained by a process according to any one of embodiments 1 to 34, the mixture MF exhibiting a storage stability ΣΔt after a storage time Δt, wherein ΣΔt ischaracterized by an APHA value ΩAPHA(Δt).48. The mixture of embodiment 47, wherein Δt is 14 d and the storage stability Σ14 after saidstorage time is characterized by an APHA value ΩAPHA(14), wherein- if ΩAPHA(MF) is less than 5, ΩAPHA(14) ≤ 10;- if ΩAPHA(MF) is in the range of from 5 to 8, ΩAPHA(14) ≤ 2 ΩAPHA(MF);- if ΩAPHA(MF) > 8, ΩAPHA (14) ≤ 1.5 ΩAPHA(MF)).49. The mixture of embodiment 47 or 48, wherein Δt is 28 d and the storage stability Σ28 aftersaid storage time is characterized by an an APHA value ΩAPHA(28), wherein- if ΩAPHA(MF) is less than 4, ΩAPHA(28) ≤ 10;- if ΩAPHA(MF) is in the range of from 4 to 8, ΩAPHA(28) ≤ 3 ΩAPHA(MF);- if ΩAPHA(MF) > 8, ΩAPHA(28) ≤ 2 ΩAPHA(MF).50. The mixture of any one of embodiments 47 to 49, wherein the storage stability ΣΔt after astorage time Δt is further characterized by one or more of a permanganate absorptionnumber ΩPAN(Δt) and an UV absorption ΩUV(Δt).51. The mixture of embodiment 50, wherein Δt is 14 d and the storage stability Σ14 after saidstorage time is characterized by one or more of a permanganate absorption numberΩPAN(14), wherein -if ΩPAN(MF) is less than 5, ΩPAN(14) ≤ 10;- if ΩPAN(MF) is in the range of from 5 to 8, ΩPAN(14) ≤ 1.5 ΩPAN(MF);- if ΩPAN(MF) > 8, ΩPAN(14) ≤ 1.25 ΩPAN(MF);and an UV absorption ΩUV(14), wherein -if ΩUV(MF) is less than 0.02, ΩUV(14) ≤ 0.05;- if ΩUV(MF) is in the range of from 0.02 to 0.03, ΩUV(14) ≤ 3 ΩUV(MF);- if ΩUV(MF) > 0.03, ΩUV(14) ≤ 1.25 ΩUV(MF).52. The mixture of embodiment 50 or 51, wherein Δt is 28 d and the storage stability Σ28 aftersaid storage time is characterized by one or more of a permanganate absorption numberΩPAN(28), wherein -if ΩPAN(MF) is less than 5, ΩPAN(28) ≤ 10;- if ΩPAN(MF) is in the range of from 5 to 8, ΩPAN(28) ≤ 3 ΩPAN(MF);- if ΩPAN(MF) > 8, ΩPAN(28) ≤ 2 ΩPAN(MF);and an UV absorption ΩUV(28), wherein- if ΩUV(MF) is less than 0.025, ΩUV(28) ≤ 0.05;- if ΩUV(MF) is in the range of from 0.025 to 0.05, ΩUV(28) ≤ 3 ΩUV(MF);- if ΩUV(MF) > 0.05, ΩUV(28) ≤ 2 ΩUV(MF).53. A liquid mixture MS comprising ε-caprolactam and water, obtainable or obtained by aprocess according to any one of embodiments 35 to 40.54. The mixture of embodiment 53, having an APHA value ΩAPHA(14) after a storage time Δt of14 d, wherein -if ΩAPHA(MF) is less than 4, ΩAPHA(14) ≤ 10;- if ΩAPHA(MF) is in the range of from 4 to 8, ΩAPHA(14) ≤ 2 ΩAPHA(MF);- if ΩAPHA(MF) > 8, ΩAPHA(14) ≤ 1.5 ΩAPHA(MF).55. The mixture of embodiment 53 or 54, having an APHA value ΩAPHA(28) after a storage timeΔt of 28 d, wherein- if ΩAPHA(MF) is less than 4, ΩAPHA(28) ≤ 10;- if ΩAPHA(MF) is in the range of from 4 to 8, ΩAPHA(28) ≤ 3 ΩAPHA(MF);- if ΩAPHA(MF) > 8, ΩAPHA(28) ≤ 2 ΩAPHA(MF).56. The mixture of any one of embodiments 53 to 55, having one or more of a permanganateabsorption number ΩPAN(14) and an UV / Vis absorption ΩUV(14) after a storage time Δt,wherein -if ΩPAN(MF) is less than 5, ΩPAN(14) ≤ 10;- if ΩPAN(MF) is in the range of from 5 to 8, ΩPAN(14) ≤ 1.5 ΩPAN(MF);- if ΩPAN(MF) > 8, ΩPAN(14) ≤ 1.25 ΩPAN(MF);and wherein -if ΩUV(MF) is less than 0.01, ΩUV(14) ≤ 0.05;- if ΩUV(MF) is in the range of from 0.01 to 0.03, ΩUV(14) ≤ 3 ΩUV(MF);- if ΩUV(MF) > 0.03, ΩUV(14) ≤ 1.25 ΩUV(MF).57. The mixture of any one of embodiments 53 to 56, having one or more of a permanganateabsorption number ΩPAN(28) and an UV / Vis absorption ΩUV(28) after a storage time Δt,wherein -if ΩPAN(MF) is less than 5, ΩPAN(28) ≤ 10;- if ΩPAN(MF) is in the range of from 5 to 8, ΩPAN(28) ≤ 3 ΩPAN(MF);- if ΩPAN(MF) > 8, ΩPAN(28) ≤ 2 ΩPAN(MF);and wherein -if ΩUV(MF) is less than 0.025, ΩUV(28) ≤ 0.05;- if ΩUV(MF) is in the range of from 0.025 to 0.04, ΩUV(28) ≤ 1.5 ΩUV(MF);- if ΩUV(MF) > 0.03, ΩUV(28) ≤ 1.25 ΩUV(MF).58. Use of the mixture MF according to any one of embodiments 47 to 52 or the mixture MSaccording to any one of embodiments 53 to 57 as an educt material for a chemical process,preferably for a polymerization reaction, more preferably for preparing polyamide 6.59. A method for preparing polyamide 6, comprising(A) preparing a mixture MF according to a process according to any one of embodiments1 to 34, and / or providing a mixture MF according to any one of embodiments 47 to 52; (B) optionally storing the mixture MF at storage conditions as defined in any one ofembodiments 35 to 40, obtaining a stored mixture MS; (C) subjecting the mixture MF prepared and / or provided according to (A) and / or themixture MS according to (B) to polyamide 6 polymerization conditions.60. Polyamide 6, obtainable or obtained by a method according to embodiment 59, having anAPHA value of at most 10, preferably of at most 9, more preferably of at most 8.61. The process of any one of embodiments 1 to 34, or 35 to 40, further comprising providing atleast part of the mixture MF, or of the mixture MS, to a polyamide 6 production unit UPP, wherein the polyamide 6 produced in UPP is preferably provided as a feedstock to a textilematerial producing unit UTP, from which unit UTP(A) a textile material MTE is obtained which is brought onto the market, wherein, after thelifetime TMTEof said textile material MTE, it is at least partially collected as textile waste material in a textile material collecting unit UTC; (B) remaining material MRE 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 as material M according to (i).62. The process of any one of embodiments 1 to 34, or 35 to 40, further comprising providing atleast part of the mixture MF, or of the mixture MS, to a polyamide 6 production unit UPP, wherein the polyamide 6 produced in UPP is preferably provided as a feedstock to anengineering plastics material producing unit UEP, from which unit UEP(A) an engineering plastics material MEP is obtained which is brought onto the market,wherein, after the lifetime TMEPof said engineering plastics material MEP, it is at least partially collected as engineering plastics waste material in an engineering plastics material collecting unit UEC; (B) remaining material MRE is obtained as engineering plastics waste material;wherein at least part of the engineering plastics waste material according to (A), or at leastpart of the engineering plastics waste material according to (B), or at least part of theengineering plastics waste material according to (A) and at least part of the engineeringplastics waste material according to (B) is suitably provided as material M according to (i).63. Use of the mixture MF according to any one of embodiments 47 to 52 or of the mixture MSaccording to any one of embodiments 53 to 57 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.64. A method for preparing polyamide 6, said method comprising employing the mixture MFaccording to any one of embodiments 47 to 52 or the mixture MS according to any one of embodiments 53 to 57 as a starting material, wherein said method preferably furthercomprises 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.65. Use of the mixture MF according to any one of embodiments 47 to 52 or of the mixture MSaccording to any one of embodiments 53 to 57 for preparing one or more of a polymer anda polymer product; or a method for preparing one or more of a polymer and a polymerproduct, said method comprising employing the mixture MFaccording to any one of embodiments 47 to 52 or the mixture MSaccording to any one of embodiments 53 to 57 as a starting material.The use or the method of embodiment 65, wherein the polymer, or the polymer product, orthe 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.The use or the method of embodiment 65 or 66, wherein the polymer, or the polymerproduct, or the polymer and the polymer product comprises or comprise polyamide 6 andoptionally at least one further polymeric compound, said polyamide 6 being at least partiallyobtainable or obtained from the mixture MFaccording to any one of embodiments 47 to 52or from the mixture MS according to any one of embodiments 53 to 57, wherein the at leastone further polymeric compound preferably comprises one or more of at least one polyamide 6.6, at least one polyethylene terephthalate, at least one polyurethane, at least one polyester, at least one cellulose material, and at least one rubber material comprising one or more of at least one natural rubber material and at least one synthetic rubber material.The use or the method of any one of embodiments 65 to 67, wherein the polymer, or thepolymer 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 chargeair 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, anexterior 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, a top mount, an oil pan, a fuel cell, a heat shield and / or a cushion;- a cloth, an apparel, preferably a shirt, trousers, a pullover, a boot, a shoe, a shoe sole, atight, a yarn, a fabric, 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, acast film (mono- and / or multi-layer), a biaxially stretched film, a laminating film.69. The use or the method of any one of embodiments 65 to 68, wherein the polymer, or thepolymer product, or the polymer and the polymer product contains or contain polyamide 6,obtainable or obtained from the mixture MFaccording to any one of embodiments 47 to 52 or from the mixture MSaccording to any one of embodiments 53 to 57 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, morepreferably 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 69 is concerned, the respective amounts are preferably determinedbased 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 65 to 69 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”, 3rdvolume, Wiley-VCH, 1997; ISBN: 978-3-527-28838-0; „Kunststoffhandbuch“, 11 volumes in 17 sub- volumes, Carl Hanser Verlag, especially volume 6, „Polyamide“, 1stedition, 1966; “Injection Molding Reference Guide, 4thedition, 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 in the context of the present invention refers to the absolute pressure,also referred to as „bar(abs)“ or as “bara”.The abbreviation „d“ as used in the context of the present invention in terms as a physical unitdescribes the time interval “day”, i.e. a time interval of (24 ± 1) h, preferably (24 ± 0.5) h. Forexample, a time period of 14 d refers to (336 ± 1) h, preferably (336 ± 0.5) h, and a time period of28 d refers to (672 ± 1) h, preferably (672 ± 0.5) h. 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 tothe processor, the trade or the end consumer. The term “textile waste material” as used hereincovers 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 engineeringmaterials like metals and ceramics. Engineering plastics specifically apply in the fabrication ofmechanical parts across several industries such as automotive, medical, electrical andelectronics, 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 present invention is further illustrated by the following Reference Examples, Examples, and Comparative Examples. Reference Example 11.1 Determination of the APHA color of ε-caprolactamThe APHA color was determined in accordance with ISO 8112. In principle, the extinction E of a 50 % by weight aqueous ε-caprolactam solution is determined in a cuvette of length l = 5 cm at awavelength λ = 390 nm and expressed in Hazen units (platinum-cobalt scale). For doing so, themeasured extinction E is multiplied by the factor f = 150. The Hazen units (platinum-cobalt scale) are defined as the color of a solution containing, in 1 l water, 1 mg platinum in the form of hexachloroplatinum(IV) acid in the presence of 2 mg cobalt(II) chloride hexahydrate. The Hazen units correspond to the APHA units. A standard solution of 500 Hazen units as prepared asfollows: 1.000 g cobalt(II) chloride hexahydrate (CoCl2 ^ 6 H2O) and 1.245 g potassiumhexachloroplatinate(IV) (K2PtCl6) are dissolved in 100 ml hydrochloric acid having a of 1.19 g / ml. The solution is transferred into a 1000 ml volumetric flask which is filled to the calibration mark.This solution contains 500 mg platinum and corresponds to 500 Hazen units. A specific amountof ε-caprolactam, usually in the range of from 5 to 50 g, is dissolved in a 250 Erlenmeyer flask in50 ml distilled water. The solution is mixed and left until the air bubbles have disappeared. The 2cuvettes of the spectrophotometer (which is suitable for measurements at a wavelength λ = 390nm) are filled with distilled water, placed in the beam path, and the spectrophotometer is adjustedat λ = 390 nm to E = 0. Then, the distilled water is removed from the sample cuvette, followed byfilling this cuvette with the ε-caprolactam solution. Then, the extinction E of this solution isdetermined at λ = 390 nm (E390) against the comparative cuvette containing distilled water. Thecolor number X (Hazen units, platinum-cobalt scale) is calculated as X = E ^ f = 150 ^ E390. X isrounded to the next integer.1.2 Determination of the purity of ε-caprolactamThe purity of ε-caprolactam and the respective amounts of impurities was determined via GC- FID / MS using GC (Agilent 7890A) coupled with two MSDs (Agilent 5975C) for electron impactionisation and chemical ionisation. The respective area-% values obtained from the measurementrepresent the GC purity values ΩGCaccording to the present invention.1.3 Determination of the PAN of ε-caprolactamThe PAN values were determined in accordance with DIN ISO 8660.1.4 Determination of the UV-Vis absorption of ε-caprolactamThe UV / Vis absorption values were determined at a wavelength of 290 nm in accordance with DIN ISO 7059. Reference Example 2 For determining a storage stability ΣΔtafter a storage time Δt, 10-25 g of a given material werestored under exclusion of light in a glass vessel under an inert (argon) gas atmosphere for a pre-determined time Δt at constant temperature in the respective examples and comparativeexamples under constant stirring with a Teflon-coated magnetic stir bar at 250-500 rpm. Thetemperatures were kept constant in an oil bath using a contact thermometer. During the measurement, it was ensured that the respective material and never less than 15 % of the gas atmosphere were maintained at the respective temperature.Reference Example 3: Storing stability of petrochemically derived ε-caprolactamε-caprolactam (15.0 g), which was prepared via the reaction sequence (i) cyclohexane oxidationwith air (ii) oximation using hydroxylamine sulfate (iii) Beckmann rearrangement (oleum / sulphuric acid catalysed), with the following specifications:ΩUV = 0.03; ΩAPHA = 2; ΩPAN = 3; ΩGC = 99.9 %;was stored under inert atmosphere and light exclusion for 28 days at 85 °C. The following specifications were observed after 28 days:ΩUV(28) = 0.16; ΩAPHA(28) = 4; ΩPAN(28) = 8.This Reference Example 3 shows that a (conventionally) synthesized ε-caprolactam can bestored for 28 d at 85 °C, and the specifications after 28 d, in particular ΩAPHA(28) and ΩPAN(28), did not change much so that it can be concluded that the material exhibits a good storage stability Σ28.Comparative Example 1: Insufficient storing stability of recovered ε-caprolactamDepolymerized and purified ε-caprolactam (15.0 g) with the following specifications:ΩUV(MT) = 0.03; ΩAPHA(MT) = 2; ΩPAN(MT) = 7; ΩGC(MT) = 99.9 %;was stored under inert atmosphere and light exclusion for 14 and 28 days at 85 °C.The following specifications were observed after 14 days:ΩUV(14) = 0.28; ΩAPHA(14) = 5; ΩPAN(14) = 13.The following specifications were observed after 28 days:ΩUV(28) = 0.87; ΩAPHA(28) = 23; ΩPAN(28) = 23.Compared to Reference Example 3, the ε-caprolactam according to Comparative Example 1 wasnot obtained from conventional synthesis but via hydrolytic depolymerisation and subsequent purification as described in the context of the present invention, leading to an ε-caprolactam mixture MT. For this mixture MT of recovered ε-caprolactam which exhibited the samecharacteristics ΩUV, ΩAPHA, ΩPAN, and ΩGC as the ε-caprolactam according to Reference Example3, it was found that the storage conditions of Reference Example 2 led to an insufficient stability, as can be seen, for example, from the huge relative increase of the ΩAPHA value withΩAPHA(28) = 12.5 ΩAPHA(MT), or of the ΩUV value with ΩUV(28) = 29 ΩUV(MT).Comparative Example 2: Insufficient storing stability of recovered ε-caprolactamThe ε-caprolactam according to Comparative Example 2 was not obtained from conventionalsynthesis but recovered via hydrolytic depolymerisation and subsequent purification as describedin the context of the present invention, leading to an ε-caprolactam mixture MT. Thisdepolymerized and purified ε-caprolactam (15.0 g) had the following specifications:ΩUV(MT) = 0.73; ΩAPHA(MT) = 10; ΩPAN(MT) = 21; ΩGC(MT) = 99.9 %;was stored under inert atmosphere and light exclusion 28 days at 85 °C. The following specifications were observed after 28 days:ΩUV(28) = 1.68; ΩAPHA(28) = 54; ΩPAN(28) = 33.As for the material of Comparative Example 1, an insufficient storage stability was observed, forexample in view of the relative increase in the ΩAPHA value with ΩAPHA(28) = 5.4 ΩAPHA(MF).Example 1: Storing stability of recovered ε-caprolactamThe same material as in Comparative Example 2 was used, where based on the recovered ε-caprolactam as obtained from hydrolytic depolymerisation and subsequent purification, anaqueous mixture MF was prepared which was then stored at the storage conditions according to the present invention. In particular, the depolymerized and purified ε-caprolactam (15.0 g) employed had the following specifications:ΩUV(MF) = 0.73; ΩAPHA(MF) = 10; ΩPAN(MF) = 21; ΩGC(MF) = 99.9 %.This material was stored under inert argon atmosphere and light exclusion for 28 days at 70 °Cas a mixture comprising 2.0 weight -% of demineralized water. The following specifications were observed after 28 days:ΩUV(28) = 0.73; ΩAPHA(28) = 19; ΩPAN(28) = 20.Compared to the respective specifications of Comparative Example 2, all values ΩUV(28),ΩAPHA(28) and ΩPAN(28) showed a significantly lower increase, if at all. In particular, it was foundthat ΩAPHA(28) = 1.9 ΩAPHA(MF); ΩUV(28) = 1.0 ΩUV(MF); ΩPAN(28) = 0.95 ΩPAN(MF).Example 2 Storing stability of recovered ε-caprolactamThe ε-caprolactam which was employed was recovered via hydrolytic depolymerisation andsubsequent purification as described in the context of the present invention, leading to an ε-caprolactam mixture MF. The depolymerized and purified ε-caprolactam (15.0 g) had the followingspecifications:ΩAPHA(MF) = 5; ΩGC(MF) = 99.9 %.and was stored under inert atmosphere and light exclusion 28 days at 70 °C as a mixture comprising 2.0 weight -% of demineralized water. The following specification was observed after 28 days: ΩAPHA(28) = 11. It was found that, as can be seen from ΩAPHA(28) = 2.2 ΩAPHA(MF), the aqueous mixture of the present invention led to an advantageous storage stability of the recovered ε-caprolactam.Example 3: Storing stability of recovered ε-caprolactamThe ε-caprolactam which was employed was recovered via hydrolytic depolymerisation andsubsequent purification as described in the context of the present invention, leading to an ε-caprolactam mixture MF. The depolymerized and purified ε-caprolactam (15.0 g) had the followingspecifications:ΩUV(MF) = 0.03; ΩAPHA(MF) = 1; ΩPAN(MF) = 4; ΩGC(MF) = 99.9 %;and was stored under inert atmosphere and light exclusion for 14 and 28 days at 70 °C with 2.0weight-% of demineralized water.The following specifications were observed after 14 days:ΩUV(14) = 0.03; ΩAPHA(14) = 1; ΩPAN(14) = 4.The following specifications were observed after 28 days:ΩUV(28) = 0.04; ΩAPHA(28) = 3; ΩPAN(28) = 5.It was found that, as can be seen from all values, the aqueous mixture of the present invention led to a very advantageous storage stability of the recovered ε-caprolactam.Example 4: Storing stability of recovered ε-caprolactamThe ε-caprolactam which was employed was the ε-caprolactam of Example 3, i.e. the materialwith the following specifications:ΩUV(MF) = 0.03; ΩAPHA(MF) = 1; ΩPAN(MF) = 4; ΩGC(MF) = 99.9 %.Compared to Example 3, the material which was subjected to storing for 28 d was a differentaqueous mixture, namely a mixture comprising 5.0 weight-% of demineralized water. The storingwas carried out at 60 °C at otherwise identical conditions as in Example 3. The following specifications were observed after 28 days:ΩUV(28) = 0.04; ΩAPHA(28) = 1; ΩPAN(28) = 3.It was found that, as can be seen from all values, the aqueous mixture of the present invention led to a very advantageous storage stability of the recovered ε-caprolactam.

Claims

Claims1. A process for preparing a liquid ε-caprolactam mixture MF, the process comprising(i) providing a stream SM comprising a solid material M comprising polyamide 6;(ii) preparing an aqueous depolymerization mixture based on SM;(iii) subjecting the depolymerization mixture prepared according to (ii) to polyamide 6depolymerization conditions in a reaction unit UR, obtaining a liquid aqueous stream SR comprising ε-caprolactam dissolved in water at a concentration cSR, the stream SR further comprising one or more impurities; and optionally passing the liquid aqueousstream SR into an evaporation unit UE, obtaining from SR a liquid aqueous stream SL comprising ε-caprolactam dissolved in water at a concentration cSL with cSL > cSR, and further obtaining from SRone or more aqueous vapor streams SV; (iv) passing the stream SR, optionally the stream SL, into an ε-caprolactam purification unitUP, and (iv.1) obtaining from the unit UP the mixture MF; or(iv.2) obtaining from the unit UP a mixture MT having an ε-caprolactam purity ΩGC(MT)of at least 99 %, an APHA value ΩAPHA(MT) of at most 20 and a water content xH2O(MT) of at most 0.05 weight-%, based on the total weight of the mixture MT, and adding water to the mixture MT, obtaining the mixture MF; wherein the mixture MF has an ε-caprolactam purity ΩGC(MF) of at least 99 %, anAPHA value ΩAPHA(MF) of at most 20 and a water content xH2O(MF) of at least 0.1weight-%, based on the total weight of the mixture MF.

2. The process of claim 1, wherein ΩGC(MF) is at least 99.5 %, more preferably at least 99.8%, more preferably at least 99.9 % and ΩAPHA(MF) is at most 15, preferably at most 10,more preferably at most 5.

3. The process of claim 1 or 2, wherein the mixture MF has a temperature in the range of from20 to 80 °C, preferably in the range of from 35 to 77 °C, more preferably in the range of from 50 to 75 °C.

4. The process of any one of claims 1 to 3, wherein xH2O(MF) is in the range of from 0.1 to 10weight-%, preferably in the range of from 0.2 to 8 weight-%, more preferably in the range of from 0.5 to 6 weight-%.

5. The process of any one of claims 1 to 4, wherein the purification unit UP according to (v)comprises a water separation unit UWS and a distillation unit UD, the process preferablycomprising feeding the stream SR, optionally the stream SL, to UWS, obtaining from UWS a stream SUWS comprising ε-caprolactam at a concentration cUWS, feeding the stream SUWS to the distillation unit UD, obtaining from UD the mixture MF comprising ε-caprolactam at aconcentration cMF, wherein cSR< cUWS<<< cMF, preferably wherein cSL< cUWS<<< cMF; wherein the water separation unit UWS preferably comprises at least two water separation sub-units UWS1and UWS2, more preferably two serially coupled water separation sub-unitsUWS1 and UWS2, wherein the stream SR, optionally the stream SL, is fed into UWS1, wherein downstream of UWS1and upstream of UWS2, a separation unit UIis preferably located, the process preferably comprising obtaining from UWS1 an aqueous stream SUWS1, feeding thestream SUWS1 into the separation unit UI, obtaining from UI an aqueous stream SUI, and feeding the stream SUIinto the unit UWS2, wherein in UI, one or more of impurities are separated from SUWS1, thereby obtaining from UIan impurity stream SI, said impurities preferably comprising at least one impurity comprised in SR according to (iii), wherein at least one of said impurities is an organic compound having a higher boiling point than ε-caprolactam, the separation unit UIbeing a high boiler separation unit; wherein the purification unit UP preferably further comprises, downstream of the unit UD, one or more of a crystallization unit UCR and a chemical treatment unit UOD, the process comprising obtaining the mixture MFfrom UCRor from UOD.

6. The process of claim 5, wherein the chemical treatment in the unit UOD comprises(a) providing a preferably liquid stream SUD comprising ε-caprolactam from the distillationunit UD or a preferably liquid stream SCR comprising ε-caprolactam from thecrystallization unit UCR, said stream SUD or said stream SCR further comprising one or more oxidizable organic impurity compounds X, wherein the stream SUD or the stream SCR has an ε-caprolactam purity ΩGC(SC) of at least 99 % and exhibits a weight ratiorXCof the one or more organic compounds X relative to ε-caprolactam; (b) providing a stream SO comprising at least one permanganate;(c) preparing an oxidation reaction educt mixture MOE from the stream SUD and thestream SO, or from the stream SSCRand the stream SO, and subjecting the mixture MOE to oxidation reaction conditions, obtaining an oxidation reaction product stream SP comprising ε-caprolactam, further comprising one or more oxidation products Yobtained from the oxidation of at least a part of the one or more compounds X, and optionally further comprising a part of the one or more organic compounds X, whereinthe stream SP exhibits a weight ratio rXCP of organic compound X relative to ε-caprolactam with 0 ≤ rXCP < rXC and further exhibits a weight ratio rYCP of the one ormore products Y relative to ε-caprolactam with rYCP > 0;(d) separating at least a part of the one or more oxidation products Y and optionally atleast a part of organic compound X from the stream SP, obtaining the mixture MF or the mixture MTexhibiting a weight ratio rYCTof oxidation product Y relative to ε-caprolactam with 0 ≤ rYCT < rYCP, and further exhibiting a weight ratio rXCT of organiccompound X relative to ε-caprolactam with 0 ≤ rXCT < rXC;7. The process of claim 6, wherein the at least one permanganate comprised in the stream SOprovided according to (b) comprises, preferably consists of, at least alkali metal permanganate, wherein more preferably, the at least one alkali metal permanganate comprises one or more of sodium permanganate and potassium permanganate, wherein preferably from 0.5 to 100 weight-% of the stream SOprovided according to (b) consist of permanganate and wherein the stream SO provided according to (b) preferably furthercomprises water;wherein the oxidation reaction educt mixture MOE prepared according to (c) exhibits a permanganate concentration, calculated as MnO4, preferably in the range of from 0.005 to 5 weight-%, more preferably in the range of from 0.01 to 3 weight-%, more preferably in the range of from 0.05 to 1 weight-%; wherein the oxidation reaction conditions according to (c) comprise a temperature TOEof the mixture MOEpreferably in the range of from 40 to 140 °C, more preferably in the range of from 60 to 100 °C, more preferably in the range of from 70 to 90 °C; wherein the mixture MOE prepared according to (c) preferably further comprises water;wherein subjecting the mixture MOEto oxidation reaction conditions is carried out in an oxidation reaction unit UOR comprised in the chemical treatment unit UOD, wherein the unit UOR preferably comprises one or more of at least one continuous stirred tank reactor and at least one tube reactor.

8. The process of claim 6 or 7, further comprising providing a stream SB comprising at leastone hydroxide, wherein the oxidation reaction educt mixture MOEaccording to (c) is prepared from the stream SUDor the stream SCR, and from the stream SOand the stream SB, wherein the at least one hydroxide comprised in the stream SB preferably comprises, more preferably consists of, at least alkali metal hydroxide, wherein more preferably, the at least one alkali metal hydroxide comprises, more preferably consists of, sodium hydroxide, wherein preferably from 0.5 to 100 weight-% of the stream SBconsist of hydroxide, wherein the stream SB preferably further comprises water, wherein the oxidation reaction educt mixture MOEprepared according to (c) exhibits a hydroxide concentration, calculated as OH, preferably in the range of from 0.005 to 0.75 weight-%, more preferably in the range of from 0.01 to 0.5 weight-%, more preferably in the range of from 0.1 to 0.25 weight-%.

9. The process of any one of claims 6 to 8, wherein the one or more oxidizable organiccompounds X have a boiling point δX / °C with 0.5 ≤ (δX / δC) ≤ 1.5, δC / °C being the boilingpoint of ε-caprolactam and wherein at least one of the one or more oxidation products Yhas a boiling point δY / °C with δY / °C ≠ δC / °C, wherein the difference Δδ between the boilingpoints δYand δCis preferably at least 1 °C, wherein separating at least a part of the one or more oxidation products Y and optionally at least a part of organic compound X from the stream SP according to (d) preferably comprises subjecting the stream SP obtained according to (c) to distillation in a distillation unit UDT, comprised in the chemical treatment unit UOD, obtaining from the distillation unit UDT a stream SDT comprising ε-caprolactam asthe mixture MF or the mixture MT, wherein the unit UDT preferably comprises one or more distillation columns, more preferably one or two distillation columns, wherein at least one column is optionally configured as side stream column or as divided wall column.

10. The process of any one of claims 5 to 9, wherein the purification unit UP further comprises acrystallization unit UCR, the process comprising obtaining from the distillation unit UDa stream SUDcomprising ε-caprolactam at a concentration cUD, and feeding the stream SUDto the crystallization unit UCR, obtaining from UCR the mixture MF comprising ε-caprolactam at the concentration cMF;or wherein the purification unit UP further comprises a chemical treatment unit UOD, the process comprising obtaining from the distillation unit UDa stream SUDcomprising ε-caprolactam at a concentration cUD and feeding the stream SUD to the chemical treatment unit UOD, obtaining from UOD the mixture MF comprising ε-caprolactam at the concentrationcMF; or wherein the purification unit UP further comprises a chemical treatment unit UOD and acrystallization unit UCR, wherein the crystallization unit UCR is located downstream of the distillation unit UD and the chemical treatment unit UOD is located downstream of thecrystallization unit UCR, the process comprising obtaining from the distillation unit UDa stream SUD comprising ε-caprolactam at a concentration cUD, feeding the stream SUD to the crystallization unit UCR , obtaining from the crystallization UCR a stream SCR comprising ε-caprolactam at a concentration cCR, and feeding the stream SCR to the chemical treatmentunit UOD, obtaining from UOD the mixture MF comprising ε-caprolactam at the concentrationcMF; or wherein the purification unit UPfurther comprises a chemical treatment unit UODand a crystallization unit UCR, wherein the chemical treatment unit UOD is located downstream ofthe distillation unit UD and the crystallization unit UCR is located downstream of the unit UCR, the process comprising obtaining from the distillation unit UD a stream SUD comprising ε-caprolactam at a concentration cUD, feeding the stream SUD to the chemical treatment unitUOD, obtaining from the chemical treatment unit UODa stream SODcomprising ε-caprolactam at a concentration cOD, and feeding the stream SOD to the crystallization unit UCR, obtainingfrom UCR the mixture MF comprising ε-caprolactam at the concentration cMF.

11. The process of any one of claims 1 to 10, wherein xH2O(MT) is in the range of from 0 to 0.05weight-%, preferably in the range of from 0 to 0.01 weight-%, more preferably in the range of from 0 to 0.001 weight-%, wherein ΩGC(MT) is at least 99.5 %, preferably at least 99.8 %, more preferably at least 99.9 %, and wherein ΩAPHA(MT) is at most 20, preferably at most 15, more preferably at most 10.

12. The process of any one of claims 1 to 11, wherein the material M according to (i)comprises, preferably consists of, waste material, wherein said waste material more preferably comprises, more preferably consists of, one or more of at least one textile waste material and at least one engineering plastics waste material, more preferably comprises, more preferably consists of at least one textile waste material; wherein preferably from 10 to 99 weight-%, more preferably from 30 to 98.5 weight-%, more preferably from 50 to 98 weight-%, more preferably from 80 to 98 weight-% of the material M consist of polyamide 6; wherein preferably, in addition to polyamide 6, the material M comprises one or more further organic polymeric compounds, more preferably including, but not limited to, one or more of at least one elastane, at least one polyethylene terephthalate, at least one polytetrahydrofuran, at least one polyamide 6.6, at least one polyurethane, at least one polyester, at least one cellulose material, and at least one rubber material comprising one or more of at least one natural rubber material and at least one synthetic rubber material.

13. The process of any one of claims 1 to 12, further comprising(v) storing the mixture MF obtained according to (iv) at a temperature of the mixture of atmost 80 °C under an inert gas atmosphere for a storage time ΔtΣ, obtaining a storedmixture MS, wherein the storage time ΔtΣ is at least 1 d;wherein according to (v), the mixture MF is stored preferably under exclusion of light, thestorage time ΔtΣ is preferably at least 7 d, more preferably at least 14 d, more preferably in the range of from 14 to 28 d, the inert gas atmosphere preferably comprises one or more of nitrogen and argon, and the mixture MFis stored at a storing temperature δSof the mixture MF preferably in the range of from 20 to 80 °C, preferably in the range of from 25 to 80 °C, more preferably in the range of from 35 to 77 °C, more preferably in the range of from 50 to 75 °C.

14. The process of claim 13, wherein during storing according to (v),(δS / °C) = – 2.6 ^ (xH2O(MF) / weight-%) + CSwherein CS = 77 ± 10, preferably CS = 77 ± 5.

15. A method of storing a mixture MF comprising ε-caprolactam and water and having a purityΩGC(MF)of at least 99 %, an APHA value ΩAPHA(MF) of at most 20 and a water contentxH2O(MF) of at least 0.1 weight-%, based on the total weight of the mixture MF, said mixture MFpreferably being obtainable or obtained by a process according to any one of claims 1 to 12, said method comprising storing the mixture MFat a temperature of the mixture of at most 80 °C under an inert gas atmosphere for a storage time ΔtΣ, obtaining a stored mixtureMS, wherein the storage time ΔtΣ is at least 1 d.

16. A liquid mixture MF comprising ε-caprolactam and water and having a purity ΩGC(MF) of atleast 99 %, an APHA value ΩAPHA(MF) of at most 20 and a water content xH2O(MF) of at least0.1 weight-%, based on the total weight of the mixture MF, said mixture MFpreferably being obtainable or obtained by a process according to any one of claims 1 to 12, the mixture MFexhibiting a storage stability ΣΔt after a storage time Δt, wherein ΣΔt is characterized by anAPHA value ΩAPHA(Δt); wherein for Δt being 14 d and the storage stability Σ14 after said storage time beingcharacterized by an APHA value ΩAPHA(14), it is preferred that -if ΩAPHA(MF) is less than 5, ΩAPHA(14) ≤ 10;- if ΩAPHA(MF) is prefin the range of from 5 to 8, ΩAPHA(14) ≤ 2 ΩAPHA(MF);- if ΩAPHA(MF) > 8, ΩAPHA (14) ≤ 1.5 ΩAPHA(MF));and wherein for Δt being 28 d and the storage stability Σ28 after said storage time beingcharacterized by an an APHA value ΩAPHA(28), it is preferred that -if ΩAPHA(MF) is less than 4, ΩAPHA(28) ≤ 10;- if ΩAPHA(MF) is in the range of from 4 to 8, ΩAPHA(28) ≤ 3 ΩAPHA(MF);- if ΩAPHA(MF) > 8, ΩAPHA(28) ≤ 2 ΩAPHA(MF).

17. A liquid mixture MS comprising ε-caprolactam and water, obtainable or obtained by aprocess according to claim 13 or 14, said mixture MS having an APHA value ΩAPHA(14) aftera storage time Δt of 14 d, wherein- if ΩAPHA(MF) is less than 4, ΩAPHA(14) ≤ 10;- if ΩAPHA(MF) is in the range of from 4 to 8, ΩAPHA(14) ≤ 2 ΩAPHA(MF);- if ΩAPHA(MF) > 8, ΩAPHA(14) ≤ 1.5 ΩAPHA(MF);and further having an APHA value ΩAPHA(28) after a storage time Δt of 28 d, wherein- if ΩAPHA(MF) is less than 4, ΩAPHA(28) ≤ 10;- if ΩAPHA(MF) is in the range of from 4 to 8, ΩAPHA(28) ≤ 3 ΩAPHA(MF);- if ΩAPHA(MF) > 8, ΩAPHA(28) ≤ 2 ΩAPHA(MF).

18. Use of the mixture MF according to claim 16 or the mixture MS according to claim 17 as aneduct material for a chemical process, preferably for a polymerization reaction, more preferably for preparing polyamide 6; and / or a method for preparing polyamide 6,comprising (A) preparing a mixture MF according to a process according to any one of claims 1 to 12,and / or providing a mixture MF according to claim 16; (B) optionally storing the mixture MF at storage conditions as defined in claim 13 or 14,obtaining a stored mixture MS; (C) subjecting the mixture MF prepared and / or provided according to (A) and / or themixture MS according to (B) to polyamide 6 polymerization conditions;wherein said polyamide 6, obtainable or obtained by said use or said method has an APHA value of at most 10, preferably of at most 9, more preferably of at most 8.

19. The process of any one of claims 1 to 12, or 13 or 14,further comprising providing at least part of the mixture MF, or of the mixture MS, to a polyamide 6 production unit UPP, wherein the polyamide 6 produced in UPP is preferablyprovided as a feedstock to a textile material producing unit UTP, from which unit UTP(A) a textile material MTE is obtained which is brought onto the market, wherein, after thelifetime TMTEof said textile material MTE, it is at least partially collected as textile waste material in a textile material collecting unit UTC; (B) remaining material MRE 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 as material M according to (i);and / or further comprising providing at least part of the mixture MF, or of the mixture MS, to a polyamide 6 production unit UPP, wherein the polyamide 6 produced in UPP is preferablyprovided as a feedstock to an engineering plastics material producing unit UEP, from which unit UEP(A) an engineering plastics material MEP is obtained which is brought onto the market,wherein, after the lifetime TMEP of said engineering plastics material MEP, it is at leastpartially collected as engineering plastics waste material in an engineering plastics material collecting unit UEC; (B) remaining material MRE is obtained as engineering plastics waste material;wherein at least part of the engineering plastics waste material according to (A), or at leastpart of the engineering plastics waste material according to (B), or at least part of theengineering plastics waste material according to (A) and at least part of the engineeringplastics waste material according to (B) is suitably provided as material M according to (i).

20. Use of the mixture MF according to claim 16 or of the mixture MS according to claim 17 forpreparing one or more of a polymer and a polymer product; or a method for preparing oneor more of a polymer and a polymer product, said method comprising employing the mixture MFaccording to claim 16 or the mixture MSaccording to claim 17 as a starting material; wherein the polymer, or the polymer product, or the polymer and the polymer product preferably 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; wherein the polymer, or the polymer product, or the polymer and the polymer product preferably comprises or comprise polyamide 6 and optionally at least one further polymeric compound, said polyamide 6 being at least partially obtainable or obtained from the mixture MF according to claim 16 or from the mixture MS according to claim 17, wherein the at leastone further polymeric compound preferably comprises one or more of at least one polyamide 6.6, at least one polyethylene terephthalate, at least one polyurethane, at least one polyester, at least one cellulose material, 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 preferably 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 chargeair 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, aheadlight, a taillight, an airbag, a top mount, an oil pan, a fuel cell, a heat shield and / or a cushion; -a cloth, an apparel, preferably a shirt, trousers, a pullover, a boot, a shoe, a shoe sole, atight, a yarn, a fabric, 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, aline, a switch such as a microswitch, a plug, a socket, a distributor, a relay, a resistor, acapacitor, 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, afishing 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, acast film (mono- and / or multi-layer), a biaxially stretched film, a laminating film;wherein the polymer, or the polymer product, or the polymer and the polymer productpreferably contains or contain polyamide 6, obtainable or obtained from the mixture MFaccording to claim 16 or from the mixture MSaccording to claim 17 in an amount of 1 weight-% or more, 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-% ormore; and / or in an amount of 100 weight-% or less, preferably 95 weight-% or less, morepreferably 90 weight-% or less, more preferably 50 weight-% or less, more preferably 25 weight-% or less, more preferably 10 weight-% or less.