Process for separating solids from an aqueous stream comprising epsilon-caprolactam

Abstract

A process for separating solids from a liquid aqueous stream SR comprising monomeric ε-caprolactam dissolved in water and exhibiting a solids content cR, the process comprising (i) preparing the stream SR, comprising providing a stream SM comprising a solid material M comprising polyamide 6; preparing an aqueous depolymerization mixture based on SM; and subjecting the depolymerization mixture to polyamide 6 depolymerization conditions in a reaction unit UR, obtaining the stream SR; (ii) subjecting the stream SR to solid-liquid separation conditions in a solid-liquid separation unit USL comprising at least one centrifuge, obtaining from USL a liquid aqueous stream SP comprising ε-caprolactam and exhibiting a solids content cP, the unit USL exhibiting a total separation efficiency ΘT ≥ 70 %.

Description

Process for separating solids from an aqueous stream comprising epsilon-caprolactamThe present invention relates to a process for separating solids from a liquid aqueous stream SR comprising monomeric E-caprolactam dissolved in water and further relates to a separation unit for carrying out said process.Polyamide, and in particular polyamide 6, can be found in numerous materials, such as packaging, engineering plastics from automotive and textile filaments. The latter represents about 40 % of the polyamide 6 global market. At present, only a very small part of the textile filaments is recycled while it represents a significant percentage of the global CO2 emissions. In case said recycling is carried out, a process involving a hydrolysis stage was found to be a promising strategy.It was found that from such a hydrolysis stage, a depolymerization mixture is obtained which comprise, in addition to E-caprolactam as the envisaged depolymerization product, also solid components. In order to further purify said depolymerization mixture with respect to the valuable product E-caprolactam, it turned out to be advantageous to separate said solids efficiently from the depolymerization mixture. Depending on the composition of the waste material to be recycled, the solids in the depolymerization mixture may have varying compositions.WO 2024 / 200493 A1 relates to an integrated recycling process, specifically for recycling E-caprolactam from a solid material which comprises a polymer prepared from E-caprolactam, specifically polyamide 6.WO 2023 / 187036 A1 relates to a heat-integrated process for hydrolytically depolymerizing a polyamide prepared from E-caprolactam, said polyamide being contained in a solid material M.US 5656 757 A relates to a process for the recovery of monomers from multi-component, hydrolyzable polymeric waste materials, particularly caprolactam from waste materials that include nylon 6.Gama Nuno et al., "Solvolysis of Nylon: A Pathway to Sustainable Recycling and Circular Economy”, Sustainability, vol. 16, no. 22, 2024-11-08, page 9725 discloses a method for the chemical recycling of PA waste using hydrochloric acid.Anonymous, "Different separation technologies / Alfa Laval”, 2024-03-26, pages 1 to 3 discloses a separation unit for solid / liquid separation comprising a decanter centrifuge, a disk centrifuge and a filter in series.EP 4306 620 A1 discloses a method for processing of liquefied waste plastics (LWP), said method comprising the steps of subjecting a liquefied waste plastic-based feedstock to heat treatment (HT processing) in an aqueous solution comprising alkali metal hydroxide and / or alkaline earth metal hydroxide to form a heat treated effluent, transferring the heat treated effluent to a separator, subjecting said heat treated effluent to phase separation toisolate at least an oil phase comprising treated LWP and an aqueous phase comprising contaminated material, and recycling at least a part of the aqueous phase back to the HT processing step.JP 2011 / 132283 A relates to a method and apparatus for continuously reducing solids present in a plastic cracked oil produced by cracking of a plastic with a decanter and a disk-type centrifuge arranged in series.CN 215 841 795 U relates to an extracting solution centrifugal filtration equipment, in particular to a system for continuous centrifugal filtration and residual liquid recovery of a natural pigment extracting solution.Surprisingly, it was found that such separation can be carried out if for said separation, a centrifuge is used. In particular, it was found that a two-step separation process using a centrifuge in each step is advantageous.Therefore, the present invention relates to a process for separating solids from a liquid aqueous stream SR comprising monomeric E-caprolactam dissolved in water and exhibiting a solids content CR I weight-%, the process comprising(i) preparing the stream SR, comprising(i.1 ) providing a stream SM comprising a solid material M comprising polyamide 6;(1.2) preparing an aqueous depolymerization mixture based on SM;(1.3) subjecting the depolymerization mixture prepared according to (i.2) to polyamide 6 depolymerization conditions in a reaction unit U , obtaining the stream SR;(ii) subjecting the stream SR obtained from (i) to solid-liquid separation conditions in a solid-liquid separation unitUSL comprising at least one centrifuge, obtaining from USL a liquid aqueous stream SP comprisingE-caprolactam and exhibiting a solids content CP I weight-%, and further obtaining from USL at least one solid residue stream Ss exhibiting a solids content cs I weight-%, said unit USL exhibiting a total separation efficiency 0T according to formula (I)0T(%) = 100with ST s 70 %.Regarding 0T, it is preferred that 0T S 75 %, more preferably 0T S 80 %, more preferably 0T S 85 %, more preferably 0T s 90 %, more preferably 0T S 95 %.Preferably according to the present invention, solids content CR of the stream SR is in the range of from 0.1 to 4 weight-%, preferably in the range of from 0.15 to 3 weight-%, more preferably in the range of from 0.2 to 2 weight-%. Preferably at least 85 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-% of the stream SR which is subjected to (ii) consist of monomeric E-caprolactam and water, based on the total weight of SR. Preferably, the stream SR which is subjected to (ii) exhibits a monomeric E-caprolactam concentration CE of at least 5 weight-%, more preferably of at least 10 weight-%, based on the total weight of SR. Preferably, the stream SR whichis subjected to (ii) has a temperature TR in the range of from 75 to 150 °C, preferably in the range of from 80 to 130 °C, more preferably in the range of from 85 to 110 °C.According to the present invention, the "solids content” as referred to herein describes the quantity of solid particles suspended or dissolved in a liquid. The solid particles includes all suspended particles that can be removed by, for example, filtration or sedimentation. The solids content refers to the percentage of solid particles - either suspended or dissolved - present in a liquid. It is typically expressed as a mass percentage (% mass / mass) of the total sample. Preferred determination methods for the solid content include, but are not limited to gravimetric determination: a sample is filtered and the residue is dried on the filter and weighed; conductivity measurement: enables the determination as dissolved ions influence the electrical conductivity of the water; spectrophotometry: measures the turbidity of the water as an indirect indicator of the solids content; Online measuring devices: allows for real-time monitoring of the solids content and enables a rapid response to deviations if desired.The solids content may be determined by drying a sample at a specific temperature (e.g., 103 °C to 105 °C) until its weight is constant, then dividing the final dry weight by the original wet weight and multiplying by 100.According to the present invention, preferably, the solids content is determined as follows:• A known quantity of the liquid sample is placed in a pre-weighed container;• The sample is dried in an oven (typically at 103— 105°C) until all moisture is removed;• The container is cooled in a desiccator and reweighed;The solids content is then calculated as follows:Solids content (%) = (Weight after drying - Tare weight) I (Initial sample weight - Tare weight) x 100.Preferably according to the present invention, at least one centrifuge comprised in USL is a decanter centrifuge. According to a preferred embodiment of the present invention, the unit USL comprises at least two serially arranged centrifuges, wherein two or more of the at least two serially arranged centrifuges exhibit the same operating principle or wherein two or more of the at least two serially arranged centrifuges exhibit different operating principles, wherein it is more preferred that two or more of the at least two serially arranged centrifuges exhibit different operating principles. Still more preferably, the unit USL comprises exactly two serially arranged centrifuges which, more preferably, exhibit different operating principles.Therefore, the centrifuges comprised in the unit USL are two serially arranged centrifuges Ci and C2, C2 being arranged downstream of Ci, and wherein (II) comprises(ii.1 ) subjecting SR obtained from (i) to solid-liquid separation conditions in Ci, obtaining an aqueous liquid stream SIM exhibiting a solids content CIM I weight-% and further obtaining a solid residue stream Ssi exhibiting a solids content csi I weight-%;(ii.2) subjecting SIM to solid-liquid separation conditions in 02, obtaining the aqueous liquid stream SR, and further obtaining a solid residue stream Ss2 exhibiting a solids content 0321 weight-%; wherein Ci exhibits a separation efficiency 0ci according to formula (la) ecl(%) = 100wherein C2 exhibits a separation efficiency 0c2 according to formula (lb) aC2(%> = ioo db)wherein 0ci s 70 % and 0c2 90 %.Values such as 0ci s 75 % or 0ci s 80 % or 0ci s 85 % or 0ci s 90 % are conceivable. Further, values such as 0c2 > 92 % or 0c2 94 % or 0c2 96 % or 0c2 98 % or 0c2 99 % are conceivable.The centrifuge Ci is preferably operated in semi-continuous mode or in continuous mode, more preferably in continuous mode. The centrifuge C2 is preferably operated in semi-continuous mode or in continuous mode, more preferably in continuous mode.It is preferred that the centrifuge Ci is a two-phase decanter, and it is further preferred that the centrifuge C2 is a self-discharging two-phase disc separator with intermittent solid discharge.Therefore, according to a preferred embodiment, the present invention relates to a process for separating solids from a liquid aqueous stream S comprising monomeric E-caprolactam dissolved in water and exhibiting a solids content CR I weight-%, the process comprising(I) preparing the stream SR, comprising(1.1) providing a stream SM comprising a solid material M comprising polyamide 6;(1.2) preparing an aqueous depolymerization mixture based on SM;(1.3) subjecting the depolymerization mixture prepared according to (1.2) to polyamide 6 depolymerization conditions in a reaction unit UR, obtaining the stream SR;(ii) subjecting the stream SR obtained from (I) to solid-liquid separation conditions in a solid-liquid separation unit USL comprising two serially arranged centrifuges Ci and C2 which preferably exhibit different operating principles, C2 being arranged downstream of Ci, with Ci being a two-phase decanter and C2 is a self-discharging two-phase disc separator with intermittent solid discharge, said subjecting comprising (ii.1 ) subjecting SR obtained from (I) to solid-liquid separation conditions in Ci, obtaining an aqueous liquid stream SIM exhibiting a solids content CIM I weight-% and further obtaining a solid residue stream Ssi exhibiting a solids content csi I weight-%;(ii.2) subjecting SIM to solid-liquid separation conditions in 02, obtaining the aqueous liquid stream SR, and further obtaining a solid residue stream Ss2 exhibiting a solids content 032 1 weight-%; wherein Ci exhibits a separation efficiency 0ci according to formula (la) ecl(%) = 100wherein C2 exhibits a separation efficiency 0c2 according to formula (lb) aC2(%> = ioo db)wherein 0ci s 70 % and 0c2 90 %.Preferably, the stream SIM which is subjected to (ii.2) has a temperature TIM in the range of from 75 to 140 °C, preferably in the range of from 80 to 120 °C, more preferably in the range of from 85 to 100 °C. Ranges of from 85 to 90 °C or from 90 to 95 °C or from 95 to 100 °C are conceivable.According to the present invention, when preparing preparing the stream SR, depolymerization is carried out in an aqueous medium. In an aqueous medium, depending on the respective temperature and pressure, monomeric E-caprolactam is present in equilibrium with E-aminocaproic acid, also referred to as 6-aminocaproic acid. Thus, whenever according to the present invention, monomeric E-caprolactam is described as being present in an aqueous medium, the respective amount or the respective concentration of monomeric E-caprolactam refers to the sum of monomeric E-caprolactam and E-aminocaproic acid. This equilibrium can be shifted essentially completely to the side of monomeric E-caprolactam, in particular, for example, in the distillation stage UDI or the crystallization stage UC .According to the present invention, in another preferred embodiment, at least one centrifuge comprised in USL is a three phase decanter centrifuge. A three phase decanter is a special type of decanter centrifuge that separates three phases from each other in a single continuous process, e.g.:• Solids• Heavy liquid (e.g., water)• Light liquid (e.g., oil).This technique is also known as three-phase separation and is based on the different densities of the components and their immiscibility. According to a more preferred embodiment of the present invention, the unit USL comprises at least two serially arranged centrifuges, wherein two or more of the at least two serially arranged centrifuges exhibit the same operating principle, or wherein two or more of the at least two serially arranged centrifuges exhibit different operating principles. It is more preferred that two or more of the at least two serially arranged centrifuges exhibit different operating principles, and wherein at least one of the at least two serially arranged centrifuges is a three phase decanter centrifuge, more preferably wherein one of the at least two serially arranged centrifuges is a three phase decanter centrifuge. Still more preferably, the unit USL comprises exactly two serially arranged centrifugeswhich, more preferably, exhibit different operating principles, and more preferably, one of said two serially arranged centrifuges is a three phase decanter centrifuge.When the centrifuge Ci is a three phase decanter, said centrifuge is preferably operated in semi-continuous mode or in continuous mode, more preferably in continuous mode. The centrifuge C2 is preferably operated in semi-continuous mode or in continuous mode, more preferably in continuous mode.It is preferred that the centrifuge Ci is a three-phase decanter, and it is further referred that the centrifuge C2 is a self-discharging two-phase disc separator with intermittent solid discharge. Employing a three phase decanter advantageously combines different separation steps and may make potential additional separation steps redundant, thus maintaining overall cost effectiveness of the process.Therefore, according to a preferred embodiment, the present invention relates to a process for separating solids from a liquid aqueous stream SR comprising monomeric E-caprolactam dissolved in water and exhibiting a solids content C I weight-%, the process comprising(I) preparing the stream SR, comprising(1.1) providing a stream SM comprising a solid material M comprising polyamide 6;(1.2) preparing an aqueous depolymerization mixture based on SM;(1.3) subjecting the depolymerization mixture prepared according to (1.2) to polyamide 6 depolymerization conditions in a reaction unit UR, obtaining the stream SR;(ii) subjecting the stream SR obtained from (I) to solid-liquid separation conditions in a solid-liquid separation unit USL comprising two serially arranged centrifuges Ci and C2 which preferably exhibit different operating principles, C2 being arranged downstream of Ci, with Ci being a three-phase decanter and C2 is a self-discharging two-phase disc separator with intermittent solid discharge, said subjecting comprising (ii.1 ) subjecting SR obtained from (I) to solid-liquid separation conditions in Ci, obtaining an aqueous liquid stream SIM exhibiting a solids content CIM I weight-% and further obtaining a solid residue stream Ssi exhibiting a solids content csi I weight-%;(ii.2) subjecting SIM to solid-liquid separation conditions in C2, obtaining the aqueous liquid stream SR, and further obtaining a solid residue stream Ss2 exhibiting a solids content Cs21 weight-%; wherein Ci exhibits a separation efficiency 0ci according to formula (la) ecl(%) = 100wherein C2 exhibits a separation efficiency 0c2 according to formula (lb)wherein 0ci s 70 % and 0c2 90 %.Preferably, the stream SIM which is subjected to (ii.2) has a temperature TIM in the range of from 75 to 140 °C, preferably in the range of from 80 to 120 °C, more preferably in the range of from 85 to 100 °C. Ranges of from 85 to 90 °C or from 90 to 95 °C or from 95 to 100 °C are conceivable.As mentioned above, the composition of the stream SR, among others with regard to the nature of the solids, may vary depending on the composition of the waste material to be depolymerized. In view of these varying streams S , It was found that it in particular as far the centrifuge C2, preferably the self-discharging two-phase disc separator with intermittent solid discharge is concerned, it is advantageous to operate C2 with flexible operating parameters which can be adapted to the varying streams SR and, therefore, to the varying streams SIM. Thus, the present invention also relates to a method of controlling the process of the present invention, said controlling comprising determining the composition of the stream SIM and adapting the operating parameters of the centrifuge C2, in particular of the self-discharging two-phase disc separator with intermittent solid discharge, to the respectively determined composition of the stream SIM. This method of controlling can be supported, or can be entirely carried out, by a computer-supported control system.Preferably, the unit USL further comprises a feed unit UFI, wherein the process preferably further comprises passing the stream SIM via the unit UFI to (ii.2). More preferably, the unit UFI comprises one or more of a feed drum and a feed pump. Preferably, the feed drum is stirred and / or heated, more preferably stirred and heated.According to a preferred embodiment of the present invention, the unit USL further comprises a filter unit F arranged downstream of the downstream-most centrifuge, preferably downstream of C2, the process further comprising (ii.3) subjecting the stream SR, preferably obtained from (ii.2), to solid-liquid separation conditions in F, obtaining an aqueous liquid stream SPF.Preferably, the unit USL further comprises a feed unit UF2, wherein the process preferably further comprises passing the stream SP via the unit UF2 to (ii.3). More preferably, the unit UF2 comprises one or more of a feed drum and a feed pump. Preferably, the feed drum is stirred and / or heated, more preferably stirred and heated.Preferably, the stream SPF obtained according to (ii.3) exhibits a solids content CPF I weight-% of at most 0.2, preferably of at most 0.1, more preferably of at most 0.05. Also preferably, the stream SPF obtained according to (ii.3) exhibits a solids content CPF / weight-% in the range of from 0 to 0.2, more preferably in the range of from 0 to 0.1, more preferably in the range of from 0 to 0.05.Therefore, according to a preferred embodiment, the present invention relates to a process for separating solids from a liquid aqueous stream SR comprising monomeric E-caprolactam dissolved in water and exhibiting a solids content CR I weight-%, the process comprising(i) preparing the stream SR, comprising(i.1 ) providing a stream SM comprising a solid material M comprising polyamide 6;(1.2) preparing an aqueous depolymerization mixture based on SM;(1.3) subjecting the depolymerization mixture prepared according to (1.2) to polyamide 6 depolymerization conditions in a reaction unit UR, obtaining the stream S ;(ii) subjecting the stream SR obtained from (I) to solid-liquid separation conditions in a solid-liquid separation unit USL comprising two serially arranged centrifuges Ci and C2 which preferably exhibit different operating principles, C2 being arranged downstream of Ci, with Ci being a two-phase decanter and C2 is a self-discharging two-phase disc separator with intermittent solid discharge, said subjecting comprising (ii.1 ) subjecting SR obtained from (I) to solid-liquid separation conditions in Ci, obtaining an aqueous liquid stream SIM exhibiting a solids content CIM I weight-% and further obtaining a solid residue stream Ssi exhibiting a solids content csi I weight-%;(11.2) subjecting SIM to solid-liquid separation conditions in C2, obtaining the aqueous liquid stream SR, and further obtaining a solid residue stream Ss2 exhibiting a solids content 0321 weight-%;(11.3) subjecting the stream SP obtained from (ii.2) to solid-liquid separation conditions in F, obtaining an aqueous liquid stream SPF; wherein Ci exhibits a separation efficiency 0ci according to formula (la) ecl(%) = 100wherein C2 exhibits a separation efficiency 0c2 according to formula (lb)Sc2(%) = 100wherein 0ci s 70 % and 0c2 90 %.Regarding the solid material M according to (1.1), it is preferred that it comprises, more 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. 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 solid material M consist of polyamide 6, wherein, in addition to polyamide 6, the solid material M preferably 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 polyamide 6.6; at least one semiaromatic polyamide including one or more of polyamide 6T and polyamide 6I; at least one polyethylene terephthalate; at least one polyurethane; at least one polyester; at least one polyether; at least one polyvinyl chloride; at least one natural fiber material such as wool and cotton; at least one cellulose material; at least one natural elastomer; at least one synthetic elastomer; at least one copolymer of two or more of said polymeric compounds including statistical copolymers, gradient copolymers, alternating copolymers, block copolymers, and graft copolymers; and at least one rubber material comprising one or more of at least one natural rubber material and at least one synthetic rubber material.Prior to being provided to the process of the present invention, the 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 be subjected to a suitable metal removing step. If a metal removing step is carried out, ferrous elements 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 further treatment, such as cutting and / or milling.Generally, the solid material M can be provided according to any suitable method. Preferably according to the present invention, providing the solid material M comprises providing the solid material M in a delivering unit which 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 delivering unit to a material collecting unit, preferably a collecting drum, wherein the first connecting line preferably comprises one or more of at least one material receiving and discharge unit, at least one first material feeding unit, and at least one first particle separation unit U; passing the solid material M from the material collecting unit via a second connecting line to a melting unit UM as described herein, wherein the second connecting line preferably comprises one or more of at least one second material feeding unit, at least one second particle separation unit, and at least one metal detector.Preferably, the solid material M may be 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 and a D10 value of the particle length in the range of from 0.3 to 15 mm; a D50 value of the particle width in the range of from in the range of from 0.2 to 20 mm and a D50 value of the particle length in the range of from 0.5 to 20 mm; a D90 value of the particle width in the range of from in the range of from 0.3 to 30 mm and a D90 value of the particle length in the range of from 0.8 to 30 mm.In particular in case the solid material M provided in the stream SM comprising a solid material M comprising polyamide 6 according to (1.1) comprises one or more elastanes, it is preferred that the crystallized E-caprolactam obtainable or obtained by the process of the present invention exhibits a polytetrahydrofuran content in the range of from 0 to 10 weight-ppm, more preferably in the range of from 0 to 5 weight-ppm, more preferably in the range of from 0 to 1 weight-ppm; and / or an aniline content in the range of from 0 to 10 weight-ppm, more preferably in the range of from 0 to 5 weight-ppm, more preferably in the range of from 0 to 1 weight-ppm; and / ora methylene diphenyl diamine (MDA), isomers and oligomers content in the range of from 0 to 10 weight-ppm, more preferably in the range of from 0 to 5 weight-ppm, more preferably in the range of from 0 to 1 weight-ppm; and / or a butanediol content in the range of from 0 to 500 weight-ppm, more preferably in the range of from 0 to 300 weight-ppm, more preferably in the range of from 0 to 100 weight-ppm, more preferably in the range of from 0 to 50 weight-ppm, more preferably in the range of from 0 to 10 weight-ppm; and / or an ethylene glycol content in the range of from 0 to 500 weight-ppm, more preferably in the range of from 0 to 300 weight-ppm, more preferably in the range of from 0 to 100 weight-ppm, more preferably in the range of from 0 to 50 weight-ppm, more preferably in the range of from 0 to 10 weight-ppm.When subjecting the stream SR obtained from (i) to solid-liquid separation conditions in a solid-liquid separation unit USL any solids in the stream S can be effectively separated. The solid material M according to (i.1 ) may preferably comprises, more preferably consist 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, any may thus comprise some components which remain solid after depolymerization in (i) . The separation, preferably employing a two-phase decanter or three phase decanter as indicated above, thus allows for effective removal of the remaining solids from stream SR in a cost-effective manner.In this context of the present invention, the term "E-caprolactam oligomer” encompasses E-caprolactam dimer and higher oligomers, such as E- caprolactam trimer, E-caprolactam tetramer, E-caprolactam pentamer, E-caprolactam hexamer; the term "6-aminocaproic acid” or "E-aminocaproic acid "encompasses 6-aminocaproic 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; the term "aniline” encompasses aniline as such and further encompasses derivatives thereof, such as aniline containing one or more methyl groups, and / or one or more halogen residues, and / or one or more additional amino groups, and / or one or more benzyl groups, wherein examples of such aniline derivatives may include N-methyl aniline and aminotoulene. Methylene dianiline as described hereinunder is not an aniline derivative according to the present invention: the term "methylene di ani line” encompasses 4,4’-methylenedi aniline (MDA) and isomers thereof such as 2,4’-methylenedianiline and 2,2’-methylenedianiline; the term "butanediol” encompasses butanediol as such and oligomers thereof, including butanediol dimer and higher oligomers such as butanediol trimer; the term "ethylene glycol” encompasses ethylene glycol as such and oligomers thereof, including diethylene glycol and higher oligomers such as triethylene glycol.In each case, the respective content refers to an individual compound encompassed by the respective general term. For example with respect to the E-caprolactam oligomer content, the term "an E-caprolactam oligomer content in the range of from 0 to 10 weight-ppm” refers to an E-caprolactam dimer content in the range of from 0 to 10 weight-ppm, an E-caprolactam trimer content in the range of from 0 to 10 weight-ppm, an E-caprolactam tetramer content in the range of from 0 to 10 weight-ppm, an E-caprolactam pentamer content in the range of from 0 to 10 weight-ppm, an E-caprolactam hexamer content in the range of from 0 to 10 weight-ppm, etc.If the solid material M comprises one or more elastanes, the aqueous liquid stream SR 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 U .Generally, the aqueous depolymerisation mixture according to (i .2) can be prepared according to any method. Preferably, preparing the aqueous depolymerization mixture according to (i.2) comprises melting in a melting unit UM the solid material M, obtaining the liquid stream SM having a temperature TSM at a pressure PSM; admixing in a prereaction unit UPR the stream SM with an aqueous stream Sw having a temperature Tsw at 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 that0.8 < TSF / TD 1 .05 and 0.9 < PSF / PD 1 .05;0.6 < TSM / TSF 1.2 and 0.9 < PSM / PSF 1.05; and0.8 — TSW / TSF — 1.2 and 0.9 — psw / psF — 1 .05.The pre-reaction unit UPR preferably comprises, more preferably consists of, a mixing unit, preferably a static mixing unit, and wherein the melting unit UM comprises, preferably consists of an extruder, preferably a single-screw extruder or a twin-screw extruder. Further, it is preferred that Sw and SM are admixed in UPR at a mixing ratio (mw / kg) I (mp / kg) in the range of from 1 :1 to 20:1, more preferably in the range of from 2:1 to 15:1, more preferably in the range of from 5:1 to 10:1, wherein mw is the amount of water comprised in Sw and mp is the amount of polyamide 6 comprised in SM.As far as the hydrolytic depolymerization according to (i.3) is concerned, it is preferred that the depolymerization pressure PD in the unit UR is in the range of from 40 to 140 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 TD in the unit UR is 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 UR comprises z chemical reactors R, i=1 ...z, wherein z is in the range of from 1 to 10, preferably in the range of from 1 to 8, more preferably in the range of from 1 to 6, more preferably in the range offrom 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 R, more preferably all z reactors R, are serially coupled, wherein the stream SF is fed into R, with 1 = 1; an aqueous liquid stream Si containing E-caprolactam dissolved in water is removed from reactor R and fed into the reactor +i, with i < z; the aqueous liquid stream Szcontaining E-caprolactam dissolved in water is removed from the reactor Rzas the stream SR; wherein in every reactor R, a depolymerization temperature TDI at a depolymerization pressure PDI is maintained, wherein, independently of each other, TDI is in the range of from 230 to 330 °C and PDI is in the range of from 40 to 140 bar, preferably wherein TDI is in the range of from 250 to 320 °C and PDI is in the range of from 40 to 125 bar, more preferably wherein TDI is in the range of from 270 to 310 °C and PDI is in the range of from 40 to 110 bar. For z > 1, it is preferred that the z reactors R are vertically arranged, with Ri being the top-most reactor and Rzbeing the bottom-most reactor, wherein Si obtained from Rj is transferred to Rj+i by gravity, preferably by gravity only. More preferably, at least 1, preferably all z reactors R, are continuous stirred tank reactors (CSTR). Preferably, every continuous stirred tank reactor R has, 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 R comprises at least one agitator, wherein more preferably every compartment of every reactor R comprises at least one agitator, wherein more preferably, every compartment of every reactor R comprises one agitator, 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 to of the aqueous depolymerization mixture in the unit U , preferably in the z reactors R, 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 to in the range of from 30 to 90 min. More preferably, the residence time of an aqueous depolymerization mixture in a reactor R is toi and 0.90 < (fo I bi+i) 1.10, more preferably 0.95 < (fo I bi+i) 1.05.If the solid material M comprises one or more elastanes, the aqueous liquid stream SR obtained 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 or more elastanes may also be formed in the melting unit UM which is described above. By way of example, 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'-methy lenedianili ne (MDA) and isomers thereof such as 2,4'-methy lenedianil ine and 2,2'-methylenedianiline.With regard to the depolymerization carried out in UR, it is especially preferred that no polyamide 6 depolymerization catalyst such as a mineral acid and / or a zinc salt such as zinc chloride, zinc acetate or zinc tritiate is used for said depolymerization.According to a preferred embodiment, the process of the present invention further comprises, after (1.3) and before (ii),(1.4) removing a part of the water from the stream S , preferably in an evaporation unit UE.Preferably, (1.4) comprises subjecting the stream SR obtained according to (1.3) to depressurization in an evaporation unit UE, obtaining from UE the aqueous liquid stream SR to be subjected to (ii) and further obtaining from UE at least one aqueous vapor stream SEV, preferably three aqueous vapor streams SEV, wherein a first stream SEVI has a pressure PEVI and a temperature TEVI, a second stream SEV2 has a pressure PEV2 and a temperature TEV2, and a third stream SEV3 has a pressure PEV3 and a temperature TEV3, wherein PEVI > PEV2 > PEV3, whereinPEVI is preferably in the range of from 13 to 19 bar, more preferably in the range of from 14 to 18 bar, more preferably in the range of from 15 to 17 bar; and TEVI is preferably in the range of from 170 to 230 °C, more preferably in the range of from 180 to 220 °C, more preferably in the range of from 190 to 210 °C;PEV2 is preferably in the range of from 5 to 11 bar, more preferably in the range of from 6 to 10 bar, more preferably in the range of from 7 to 9 bar; and TEV2 is preferably in the range of from 150 to 210 °C, more preferably in the range of from 160 to 200 °C, more preferably in the range of from 170 to 190 °C;PEV3 is preferably in the range of from 0.95 to 1 .5 bar, more preferably in the range of from 1 .0 to 1 .4 bar, more preferably in the range of from 1.1 to 1.3 bar; and TEV3 is preferably in the range of from 90 to 140 °C, more preferably in the range of from 100 to 130 °C, more preferably in the range of from 110 to 120 °C.According to the present invention, it is preferred that the purified stream obtained from the separation unit USL is subjected to further purification with regard to the valuable product E-caprolactam. Therefore, the present invention preferably further comprises(ill) subjecting the stream SP or the stream SPF as defined herein to further purification in a purification UP, obtaining from UP a stream SCPL comprising monomeric E-caprolactam at a concentration of at least 99 weight-%, preferably of at least 99.5 weight-%, more preferably of at least 99.8 weight-%, more preferably of at least 99.9 weight-%; wherein UP comprises one or more of at least one water separation unit Uws, at least one high-boiler separation unit UHS, at least distillation unit UDI and at least one crystallization unit UCR.Preferably, the at least one high-boiler separation unit UHS is arranged downstream of Uws, the at least distillation unit UDI arranged downstream of UHS, and, if present, the at least one crystallization unit UCR is arranged downstream of UDI.Therefore, according to a preferred embodiment, the present invention relates to a process for purifying a liquid aqueous stream SR comprising monomeric E-caprolactam dissolved in water and exhibiting a solids content C I weight-%, the process comprising(I) preparing the stream SR, comprising(1.1) providing a stream SM comprising a solid material M comprising polyamide 6;(1.2) preparing an aqueous depolymerization mixture based on SM;(1.3) subjecting the depolymerization mixture prepared according to (1.2) to polyamide 6 depolymerization conditions in a reaction unit UR, obtaining the stream SR;(1.4) preferably removing a part of the water from the stream SR, preferably in an evaporation unit UE;(ii) subjecting the stream SR obtained from (I) to solid-liquid separation conditions in a solid-liquid separation unit USL comprising two serially arranged centrifuges Ci and C2 which preferably exhibit different operating principles, C2 being arranged downstream of Ci, with Ci being a two-phase decanter and C2 is a self-discharging two-phase disc separator with intermittent solid discharge, said subjecting comprising (ii.1 ) subjecting SR obtained from (I) to solid-liquid separation conditions in Ci, obtaining an aqueous liquid stream SIM exhibiting a solids content CIM I weight-% and further obtaining a solid residue stream Ssi exhibiting a solids content csi I weight-%;(11.2) subjecting SIM to solid-liquid separation conditions in C2, obtaining the aqueous liquid stream SR, and further obtaining a solid residue stream Ss2 exhibiting a solids content 0321 weight-%;(11.3) subjecting the stream SP obtained from (ii.2) to solid-liquid separation conditions in F, obtaining an aqueous liquid stream SPF; wherein Ci exhibits a separation efficiency 0ci according to formula (la) ecl(%) = 100wherein C2 exhibits a separation efficiency 0c2 according to formula (lb)wherein 0ci s 70 % and 0c2 90 %;(ill) subjecting the stream SPF to further purification in a purification UP, obtaining from UP a stream SCPL comprising monomeric E-caprolactam at a concentration of at least 99 weight-%, preferably of at least 99.5 weight-%, more preferably of at least 99.8 weight-%, more preferably of at least 99.9 weight-%; wherein UP comprises one or more of at least one water separation unit Uws, at least one high-boiler separation unit UHS, at least distillation unit UDI and at least one crystallization unit UCR.Still further according to the present invention, it may be preferred that the valuable product, the highly purified stream SCPL, is used to prepare polyamide 6 which then can be further processed to, for example, textile materials, engineering plastics material, and the like. Therefore, the present invention may preferably further comprise (iv) subjecting the stream SCPL to polyamide 6 polymerization conditions, obtaining polyamide 6 recycled from the solid material M.Therefore, according to a preferred embodiment, the present invention relates to a process for recycling polyamide 6, the process comprising(I) preparing the stream SR, comprising(1.1) providing a stream SM comprising a solid material M comprising polyamide 6;(1.2) preparing an aqueous depolymerization mixture based on SM;(1.3) subjecting the depolymerization mixture prepared according to (1.2) to polyamide 6 depolymerization conditions in a reaction unit U , obtaining the stream SR;(1.4) preferably removing a part of the water from the stream SR, preferably in an evaporation unit UE;(ii) subjecting the stream SR obtained from (I) to solid-liquid separation conditions in a solid-liquid separation unit USL comprising two serially arranged centrifuges Ci and C2 which preferably exhibit different operating principles, C2 being arranged downstream of Ci, with Ci being a two-phase decanter and C2 is a self-discharging two-phase disc separator with intermittent solid discharge, said subjecting comprising (ii.1 ) subjecting SR obtained from (I) to solid-liquid separation conditions in Ci, obtaining an aqueous liquid stream SIM exhibiting a solids content CIM I weight-% and further obtaining a solid residue stream Ssi exhibiting a solids content csi I weight-%;(11.2) subjecting SIM to solid-liquid separation conditions in C2, obtaining the aqueous liquid stream SR, and further obtaining a solid residue stream Ss2 exhibiting a solids content 0321 weight-%;(11.3) subjecting the stream SP obtained from (ii.2) to solid-liquid separation conditions in F, obtaining an aqueous liquid stream SPF; wherein Ci exhibits a separation efficiency 0ci according to formula (la) ecl(%) = 100wherein C2 exhibits a separation efficiency 0c2 according to formula (lb)Sc2(%) = 100wherein 0ci s 70 % and 0c2 90 %;(ill) subjecting the stream SPF to further purification in a purification UP, obtaining from UP a stream SCPL comprising monomeric c-caprolactam at a concentration of at least 99 weight-%, preferably of at least 99.5 weight-%, more preferably of at least 99.8 weight-%, more preferably of at least 99.9 weight-%; wherein UP comprises one or more of at least one water separation unit Uws, at least one high-boiler separation unit UHS, at least distillation unit UDI and at least one crystallization unit UCR;(iv) subjecting the stream SCPL to polyamide 6 polymerization conditions, obtaining polyamide 6 recycled from the solid material M.Preferably, (iv) comprises(a) providing the stream SCPL;(|3) passing the stream SCPL to a polyamide 6 production plant UPAG;(y) subjecting the stream SCPL to E-caprolactam polymerization conditions, obtaining from UPA6 a polyamide 6 material MP and a stream comprising water and one or more E-caprolactam oligomers;(5) optionally subjecting to stream comprising water and one or more E-caprolactam oligomers to concentration with respect to the one or more E-caprolactam oligomers in at least one concentration stage, obtaining a concentrated stream comprising water and one or more E-caprolactam oligomers;(E) preferably passing the optionally concentrated stream comprising water and one or more E-caprolactam oligomers into at least one of the melting unit UM as defined herein and the water separation unit Uws as defined herein, wherein (y) preferably comprises(y.1 ) passing the stream SCPL and preferably an aqueous stream SAQO to a polymerization stage STo, obtaining from STo a polyamide 6 crude product stream SPAI and an aqueous stream SWAI;(y.2) passing the stream SPAI and preferably an aqueous stream SAQI to a granulation stage ST 1, obtaining from STi a crude granulated polyamide 6 material MPA2 and an aqueous stream SWA?;(y.3) passing the material MPA2 and preferably an aqueous stream SAQ2 to an extraction stage ST2, obtaining from ST2 a purified granulated polyamide 6 material MPA3 and an aqueous stream SWAS;(y.4) passing the material MPA3 to a drying stage ST3, obtaining from ST3 the polyamide 6 material MP and an aqueous stream SWA4; wherein more preferably, at least a part of the stream SWAS; obtained according to (y.3) is passed as feed stream to one or more of Ci and C2 as defined herein, preferably to C2 as defined herein. Assuming that some of the polyamide 6 material obtained from the production plant UPA6 does not meet the specifications, the process may preferably further comprise passing at least some of said material MPR to the unit UM.The present invention further relates to polyamide 6, obtainable or obtained by a process comprising steps (I), (II), (II) and (iv) as defined herein.The present invention further relates to a process comprising steps (I), (ii) and (ill) as defined herein, further comprising providing at least part of the stream SCPL to a polyamide 6 production unit UPA6, wherein the polyamide 6 produced in UPA6 is preferably provided 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 the lifetime 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 MRTE 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 solid material M according to (1.1).The present invention further relates to a process comprising steps (I), (II) and (ill) as defined herein, further comprising providing at least part of the stream SCPL to a polyamide 6 production unit UPA6, wherein the polyamide 6produced in UPA6 is preferably provided 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 least partially collected as engineering plastics waste material in an engineering plastics material collecting unit UEC;(B) remaining material MREP is obtained as engineering plastics waste material; wherein at least part of the engineering plastics waste material according to (A), or at least part of the engineering plastics waste material according to (B), or at least part of the engineering plastics waste material according to (A) and at least part of the engineering plastics waste material according to (B) is suitably provided as solid material M according to (1.1).Further, the present invention relates to a separation unit USL for separating solids from a liquid aqueous stream SR according to a process as defined herein, said unit USL comprising(A) two serially arranged centrifuges Ci and C2 exhibiting the same or different operating principles, preferably different operating principles, wherein more preferably, the centrifuge Ci is a two-phase decanter and the centrifuge C2 is a self-discharging two-phase disc separator with intermittent solid discharge;(B) a feed unit UFI arranged downstream of Ci and upstream of C2, the unit UFI preferably comprising one or more of a feed drum and a feed pump; and a feed unit UF2 arranged downstream of C2 and upstream of F as defined in (C), the unit UF2 preferably comprising one or more of a feed drum and a feed pump;(C) a filter unit F arranged downstream of C2; wherein Ci exhibits a separation efficiency 0ci according to formula (la) ecl(%) = 100wherein C2 exhibits a separation efficiency 0c2 according to formula (lb)wherein 0ci s 70 % and 0c2 90 %.Further, the present invention relates to a separation unit USL for separating solids from a liquid aqueous stream SR comprising monomeric E-caprolactam dissolved in water and exhibiting a solids content CR I weight-% with CR being preferably in the range of from 0.1 to 4 weight-%, more preferably in the range of from 0.15 to 3 weight-%, more preferably in the range of from 0.2 to 2 weight-%, said separating comprising(ii.1 ) subjecting SR to solid-liquid separation conditions in Ci, obtaining an aqueous liquid stream SIM exhibiting a solids content CIM I weight-% and further obtaining a solid residue stream Ssi exhibiting a solids content csi I weight-%;(ii.2) subjecting SIM to solid-liquid separation conditions in C2, obtaining an aqueous liquid stream SR, and further obtaining a solid residue stream Ss2 exhibiting a solids content Cs21 weight-%;(ii.3) preferably subjecting the stream SP to solid-liquid separation conditions in a filter unit F, obtaining an aqueous liquid stream SPF; said unit USL comprising(A) two serially arranged centrifuges Ci and C2 exhibiting the same or different operating principles, preferably different operating principles, wherein more preferably, the centrifuge Ci is a two-phase decanter and the centrifuge C2 is a self-discharging two-phase disc separator with intermittent solid discharge;(B) a feed unit UFI for passing the stream SIM via the unit UFI to (ii .2), the unit UFI preferably comprising one or more of a feed drum and a feed pump; and a feed unit UF2 for passing the stream SP via the unit UF2 to (ii.3), the unit UF2 preferably comprising one or more of a feed drum and a feed pump;(C) a filter unit F arranged downstream of C2 for subjecting the stream SP obtained from (ii.2) to solid-liquid separation conditions in F.According to another aspect, the present invention relates to a process as defined herein, comprising the step of converting at least a part of one or more of the solid residue streams according to (ii), preferably at least a part of one or more of the stream Ssi according to (ii.1) and the stream Ss2 according to (ii.2), and / or a chemical material obtainable or obtained by the process as defined herein to obtain a product Q. According to yet another aspect, the present invention relates to a process comprising the steps of using the separation unit USL as described herein to obtain one or more solid residue streams, preferably a stream Ssi and a stream Ss2, and / or a chemical material, and preferably converting at least a part of one or more of the solid residue streams, preferably at least a part of one or more of the stream Ssi and the stream Ss2, and / or a chemical material to obtain a product Q.Preferably, the product Q is selected from: building block or monomer; or polymer, preferably polymer A, polymer composition, preferably polymer composition A, or polymer product, preferably polymer product A; or industrial use polymer, industrial use surfactant, descaling compound, industrial use biocide, industrial use solvent, industrial use dispersant, composition thereof or formulation thereof; or agrochemical composition, agrochemical formulation auxiliary or agrochemically active ingredient; or active pharmaceutical ingredient or intermediate thereof, pharmaceutical excipient, animal feed additive, human food additive, dietary supplements, aroma chemical or aroma composition; or aqueous polymer dispersion, preferably polyurethane or polyurethane - poly (meth)acry late hybrid polymer dispersion, emulsion, binder for paper and fiber coatings, UV-curable acrylic polymer for hot melts and coatings polyisocyanates, hyperbranched polyester polyol, polymeric dispersant for inorganic binder compositions, unsaturated polyester polyol or 100% curable composition; or cosmetic surfactant, emollient, wax, cosmetic polymer, UV filter, further cosmetic ingredient or composition or formulation thereof; or polymer B, polymer composition B, coating composition, other functional composition, foil, molded body, coating or coated substrate.Preferably, the content of the at least a part of one or more of the solid residue streams according to (II), more preferably at least a part of one or more of the stream Ssi according to (II.1) and the stream Ss2 according to (II.2), and / or a chemical material obtainable or obtained by the process as described herein in the product Q is 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 the content of the at least a part of one or more of the solid residue streams according to (ii), more preferably at least a part of one or more of the stream Ssi according to (ii.1 ) and the stream Ss2 according to (ii.2), and / or a chemical material obtainable or obtained by the process as described herein in the product Q is 100 weight-% or less, preferably 95 weight-% or less, more preferably 90 weight-% or less, more preferably 50 weight-% or less, more preferably 25 weight-% or less, more preferably 10 weight-% or less; and preferably wherein the content is determined based on identity preservation and / or segregation and / or mass balance and / or book and claim chain of custody models, preferably based on mass balance, preferably the International Sustainability and Carbon Certification (ISCC) standard.The publication Prior Art Disclosure; Issue 684; paragraphs

[1000] to

[8005] ; ISSN: 2198-4786; published: February 12, 2024 will be regarded as Reference RF1, which is incorporated herein by reference in its entirety. Preferably, the product Q referred to in the preceding paragraph is a product as described in Reference RF1; paragraphs

[1000] to

[8005] , Preferably, the process described herein is further a process for the production of a product, preferably product Q.The converting step to obtain the product Q preferably comprises one or more step(s) as described below and can be performed by conventional methods well known to a person skilled in the art. The converting step preferably comprises one or more step(s) selected from: recycling, preferably depolymerizing, gasifying, pyrolyzing, and / or steam cracking; and / or purifying, preferably crystallizing, (solvent) extracting, distilling, evaporating, hydrotreating, absorbing, adsorbing and / or subjecting to ion exchanger; and / or assembling, preferably foaming, synthesizing, chemical conversion, chemically transforming, polymerizing and / or compounding; and / or forming, preferably foaming, extruding and / or molding; and / or finishing, preferably coating and / or smoothing.In addition, the one or more step(s) are described in detail in Reference RF1; paragraphs

[1000] to

[8005] ,The term "building block”, as used in the context of the product Q herein, comprises compounds, which are in a gaseous or liquid state under standard conditions of 0°C and 0.1 MPa. Building blocks are typically used in chemical industry to form secondary products, which provide a higher structural complexity and / or higher molecular weightthan the building block on which the secondary product is based. The building block is preferably selected from the group consisting of hydrogen, carbon monoxide, carbon dioxide, ethylene oxide, ethylene glycols, syngas comprising a mixture of hydrogen and carbon monoxide, alkanes, alkenes, alkynes and aromatic compounds. The alkanes, alkenes, alkynes and aromatic compounds comprise in particular 1 to 12 carbon atoms, respectively.The term "monomer”, as used in the context of the product Q herein, comprises molecules, which can react with each other to form polymer chains by polymerization. The monomer is preferably selected from the group consisting of (meth)acrylic acid, salts of (meth)acrylic acid; in particular sodium, potassium and zinc salts; (meth)acrolein and (meth)acrylates. (Meth)acrylates comprising 1 to 22 carbon atoms are preferred, in particular comprising 1 to 8 carbon atoms. The terms (meth)acrylic acid, (meth)acrolein or (meth)acrylate relate to acrylic acid, acrolein or acrylate and also to methacrylic acid, methacrolein or methacrylate, where applicable. Further, the monomer can be selected from hexamethylenediamine (HMD) and adipic acid.The building block can further be an intermediate compound. The term "intermediate compound”, as used in the context of the product Q herein, comprises organic reagents, which are applied for formation of compounds with higher molecular complexity. The intermediate compound can be selected for example from the group consisting of phosgene, polyisocyanates and propylene oxide. The polyisocyanates are in particular aromatic di- and polyisocyanates, preferably toluene diisocyanate (TDI) and / or diphenylmethane diisocyanate (MDI).The building block and the monomer and typical converting step(s) to obtain the building block or monomer are described in more detail in paragraphs

[1000] to

[1012] of Reference RF1.The term "polymer A”, as used in the context of the product Q herein, comprises thermoplastic, e.g., polyamide or thermoplastic polyurethane, thermoset, e.g., polyurethane, elastomer, e.g., polybutadiene, or a copolymer or a mixture thereof and is defined in more detail in paragraphs

[2001] to

[2007] of Reference RF1.The term "polymer composition A”, as used in the context of the product Q herein, comprises all compositions comprising a polymer as described above and one or more additive(s), e.g. reinforcement, colorant, modifier and / or flame retardant, and is defined in more detail in paragraph

[2008] of Reference RF1.The term "polymer product A”, as used in the context of the product Q herein, comprises any product comprising the polymer A and / or polymer composition A as described above and is defined in more detail in paragraphs

[2009] and

[2010] of Reference RF1 .The step(s) to obtain the polymer, preferably polymer A, polymer composition, preferably polymer composition A or polymer product, preferably polymer product A is / are described in more detail in paragraph

[2011] of Reference RF1 .The term "industrial use polymer”, as used in the context of the product Q herein, comprises rheology, polycarboxylate, alkoxylated polyalkylenamine, alkoxylated polyalkylenimine, polyether-based, dye inhibition and soilrelease cleaning polymers defined in more detail in paragraphs

[3035] to

[3044] of Reference RF1. The term "industrial use surfactant”, as used in the context of the product Q herein, comprises non-ionic, anionic and amphoteric industrial use surfactants defined in more detail in paragraphs

[3008] to

[3034] of Reference RF1. The term "industrial use descaling compound”, as used in the context of the product Q herein, comprises non-phosphate based builders (NPB) and phosphonates (CoP) described in more detail in paragraphs

[3001] to

[3005] of Reference RF1. The term "industrial use biocide”, as used herein, refers to a chemical compound that kills microorganisms or inhibits their growth or reproduction defined in more detail in paragraphs

[3006] to

[3007] of Reference RF1. The term "industrial use solvent”, as used in the context of the product Q herein, comprises alkyl amides, alkyl lactamides, alkyl esters, lactate esters, alkyl diester, cyclic alkyl diester, cyclic carbonates, aromatic aldehydes and aromatic esters defined in more detail in paragraphs

[3045] to

[3055] of Reference RF1. The term "industrial use dispersant”, as used in the context of the product Q herein, comprises anionic and non-ionic industrial use dispersants defined in more detail in paragraphs

[3056] to

[3058] of Reference RF1. The term "composition and / or formulation thereof' with reference to the industrial use polymers, industrial use surfactants, descaling compounds and / or industrial use biocides refers to industrial use compositions and / or institutional use products and / or fabric and home care products and / or personal care products defined in more detail in paragraph

[3059] of Reference RF1. The converting step(s) to obtain the industrial use polymer, industrial use surfactant, descaling compound and / or industrial use biocide are defined in more detail in paragraph

[3060] of Reference RF1. The converting steps to obtain the industrial use composition or formulation of the industrial use polymer, industrial use surfactant, descaling compound and / or industrial use biocide are defined in more detail in paragraph

[3061] of Reference RF1.The term "agrochemical composition”, as used in the context of the product Q herein, typically relates to a composition comprising an agrochemically active ingredient and at least one agrochemical formulation auxiliary. Examples of agrochemical compositions, active ingredients and auxiliaries are described in more detail in Reference RF1, paragraph

[4001] ,The agrochemical composition may take the form of any customary formulation. The agrochemical compositions are prepared in a known manner, e.g. described by Mollet and Grubemann, Formulation technology, Wiley VCH, Weinheim, 2001; or Knowles, New developments in crop protection product formulation, Agrow Reports DS243, T&F Informa, London, 2005. The converting step(s) to obtain the agrochemically active ingredients and auxiliaries may be conducted in analogy to the production step(s) of their analogues that are based on petrochemicals or other precursors that are not gained by recycling processes. In addition, conversion to compounds mentioned in sections "Polymer” and "Cosmetic surfactant, emollient, wax, cosmetic polymer, UV filter, further cosmetic ingredient or compositions or formulations thereof' may be performed as described in these sections as well as the respective paragraphs in Reference RF1.The term active pharmaceutical ingredients and / or intermediates thereof, as used in the context of the product Q herein, comprises substances that provide pharmacological activity or other direct effect in the diagnosis, cure, mitigation, treatment, or prevention of disease, or to affect the structure or any function of the body. Intermediatesthereof are isolated products that are generated during a multi-step route of synthesis of an active pharmaceutical ingredient. The term pharmaceutical excipients, as used in the context of the product Q herein, comprises compounds or compound mixtures used in compositions for various pharmaceutical applications, which are not substantially pharmaceutically active on itself. Active pharmaceutical ingredients and / or intermediates thereof and pharmaceutical excipients are defined in more detail in paragraph

[5001] of Reference RF1.The converting step(s) to obtain the active pharmaceutical ingredients and / or intermediates thereof and pharmaceutical excipients may comprise one or more synthesis steps and can be performed by conventional synthesis and techniques well known to a person skilled in the art.The terms animal feed additives, human food additives, dietary supplements, as used in the context of the product Q herein, comprises Vitamins, Pro-Vitamins and active metabolites thereof including intermediates and precursors, especially Vitamin A, B, E, D, K and esters thereof, like acetate, propionate, palmitate esters or alcohols thereof like retinol or salts thereof and any combinations thereof; Tetraterpenes, especially isoprenoids like carotenoids and xanthophylls including their intermediates and precursors as well as mixtures and derivates thereof, especially beta carotene, Canthaxanthin, Citranaxanthin, Astaxanthin, Zeaxanthin, Lutein, Lycopene, Apo-carotenoids, and any combinations thereof; organic acids, especially formic acid, propionic acid and salts thereof, such as sodium, calcium or ammonium salts, and any combinations thereof, such as but not limited to mixtures of formic acid and sodium formiate, propionic acid and ammonium propionate, formic acid and propionic acid, formic acid and sodium formiate and propionic acid, propionic acid and sodium propionate and formic acid and sodium formiate; glycerides of carboxylic acids and short and medium chain fatty acids, conjugated linoleic acids, such as omega-6 fatty acid (C18:2) methyl ester and 1 ,2-propandiol and beverage stabilizers, such as polyvinylpyrrolidone-polymer or polyvinylimidazole / polyvinylpyrrolidone-copolymer. Animal feed additives, human food additives and dietary supplements are defined in more detail in paragraph

[5002] of Reference RF1.The converting step(s) to obtain the animal feed additives, human food additives, dietary supplements may comprise one or more synthesis steps and can be performed by conventional synthesis and techniques well known to a person skilled in the art.The terms aroma chemical and aroma composition as used in the context of the product Q herein, comprise a volatile organic substance with a molecular weight between 70-250 g / mol comprising a functional group with a carbon skeleton of C5-C16 carbon atoms comprising linear, branched, cyclic, for example with a ring size of C5-C18, bicyclic or tricyclic aliphatic chains and but not necessarily one or more unsaturated structural elements like double bonds, triple bonds, aromatics or heteroaromatics and preferably the one or more additional functional groups are selected from alcohol, ether, ester, ketone, aldehyde, acetal, carboxylic acid, nitrile, thiol, amine. In one aspect, the aroma chemical is a terpene-based aroma chemical, for example selected from monoterpenes and monoterpenoids, sesquiterpenes and sesquiterpenoids, diterpenes, triterpenes or tetraterpenes. Aroma chemicals can be combinedwith further aroma chemicals to give an aroma composition. Aroma chemicals and aroma compositions are defined in more detail in paragraph

[5003] of Reference RF1.The converting step(s) to obtain the aroma chemical and aroma composition may comprise one or more synthesis steps and can be performed by conventional synthesis and techniques well known to a person skilled in the art.The term "aqueous polymer dispersion”, as used in the context of the product Q herein, comprises aqueous composition(s) comprising dispersed polymer(s) and is defined in more detail in the section

[6001] entitled "aqueous polymer dispersion” of Reference RF1. The dispersed polymer(s) may be selected from acrylic emulsion polymer(s), styrene acrylic emulsion polymer(s), styrene butadiene dispersion(s), aqueous dispersion(s) comprising composite particles, acrylate alkyd hybrid dispersion(s), polyurethane(s) (including UV-curable polyurethanes) and polyurethane - poly(meth)acrylate hybrid polymer(s). The term "emulsion polymer”, as used herein, comprises polymer(s) made by free-radical emulsion polymerization. Aqueous polyurethane dispersion(s) are defined in more detail in the section

[6002] entitled "Polyurethane dispersions” of Reference RF1. UV-curable polyurethane(s) is / are defined in more detail in the section

[6017] of Reference RF1. Polyurethane - poly(meth)acrylate hybrid polymer(s) is / are defined in more detail in the section

[6016] of Reference RF1.The term "polymeric dispersant”, as used in the context of the product Q herein, comprises preferably polymer(s) comprising polyether side chain, in particular polycarboxylate ether polymer(s) and polycondensation product(s) defined in more detail in paragraph

[6020] entitled "Polymeric dispersant” of Reference RF1.The converting (polymerization) step(s) to obtain the aqueous polymer dispersion(s) comprising emulsion polymer(s) is / are defined in more detail in the section

[6003] entitled "Emulsion polymerization” of Reference RF1.The converting (polymerization) step(s) to obtain the aqueous polyurethane dispersion(s) is / are defined in more detail in the section

[6014] entitled "Process for the preparation of aqueous poly-urethane dispersions” and section [6017)] entitled "Aqueous UV-curable polyurethane dispersions, their preparation and use and compositions containing them” of Reference RF1.Composition(s) and uses of aqueous polymer dispersion(s) and of polymeric dispersant(s) are defined in more detail in the following sections of Reference RF1 : section

[6004] entitled "Uses of aqueous polymer dispersions”, section

[6005] entitled "Binders for architectural and construction coatings” section

[6006] entitled "Binders for paper coating” section

[6007] entitled "Binders for fiber bonding” section

[6008] entitled "Adhesive polymers and adhesive compositions” section

[6015] entitled "Aqueous polyurethane dispersions suitable for use in coating compositions”section

[6016] entitled "Aqueous polyurethane - poly(meth)acrylate hybride polymer dispersions suitable for use in coating compositions” section

[6017] entitled "Aqueous UV-curable polyurethane dispersions, their preparation and use and compositions containing them” section

[6018] entitled "Inorganic binder compositions comprising polymeric dispersants and their use”

[6019] 100% curable coating compositionsUV-crosslinkable poly(meth)acrylate(s) and its / their uses are defined in more detail in section

[6009] entitled "UV-crosslinkable poly(meth)acrylates for use in UV-curable solvent-free hot melt adhesives and their use for making pressure-sensitive self-adhesive articles” of Reference RF1.Polyisocyanate(s), composition(s) comprising them and their uses are defined in more detail in section

[6010] entitled "Polyisocyanates” of Reference RF1.Hyperbranched polyester polyol(s) and its / their uses are defined in more detail in section

[6011] entitled "Organic solvent based hyperbranched polyester polyols suitable for use in coating compositions” of Reference RF1. The converting step(s) to obtain the hyperbranched polyester polyols is / are defined in more detail in the section

[6012] entitled "Preparation of organic solvent based hyperbranched polyester polyols” of Reference RF1 . Coating composition(s) comprising hyperbranched polyester polyol(s), polyisocyanate(s) and additive(s) and substrate(s) coated therewith are defined in more detail in section

[6013] entitled "Organic solvent based two component coating compositions comprising hyperbranched polyester polyols and polyisocyanates” of Reference RF1.Unsaturated polyester polyol(s), solvent-based coating composition(s) comprising said unsaturated polyester polyol(s) and substrate(s) for coating with said coating composition(s) are defined in more detail in section

[6018] entitled "Organic solvent based coating composition comprising unsaturated polyester polyols” of Reference RF1 . 100% curable coating composition(s) is / are defined in more detail in section

[6019] of Reference RF1.Polymeric dispersant(s) for inorganic binder compositions is / are defined in more detail in section

[6020] of Reference RF1. The inorganic binder composition(s) comprising the polymeric dispersants and their use are defined in more detail in section

[6021] of Reference RF1. The converting step(s) to obtain the polymeric dispersant(s) are defined in more detail in section

[6020] of Reference RF1. The term "inorganic binder composition” comprising the polymeric dispersant(s), as used herein, comprises preferably in particular hydraulically setting compositions and compositions comprising calcium sulfate and is defined in more detail in section

[6021] of Reference RF1 entitled "Inorganic binder compositions comprising the polymeric dispersant and their use”. Specific building material formulation(s) comprising polymeric dispersant(s) or building product(s) produced by a building material formulation comprising a polymeric dispersant are disclosed in more detail in section

[6021] of Reference RF1.The term "cosmetic surfactant”, as used in the context of the product Q herein, comprises non-ionic, anionic, cationic and amphoteric surfactants and is defined in more detail in paragraph

[7002] of Reference RF1 . The term "emollient”, as used in the context of the product Q herein, refers to a chemical compound used for protecting, moisturizing, and / or lubricating the skin and is defined in more detail in paragraph

[7003] of Reference RF1. The term "wax”, as used in the context of the product Q herein, comprises pearlizers and opacifiers and is defined in more detail in paragraph

[7004] of Reference RF1 . The term "cosmetic polymer”, as used in the context of the product Q herein, comprises any polymer that can be used as an ingredient in a cosmetic formulation and is defined in more detail in paragraph

[7005] of Reference RF1 . The term "UV filter”, as used in the context of the product Q herein, refers to a chemical compound that blocks or absorbs ultraviolet light and is defined in more detail in paragraph

[7006] of Reference RF1 . The term "further cosmetic ingredient”, as used in the context of the product Q herein, comprises any ingredient suitable for making a cosmetic formulation. Several sources disclose cosmetically acceptable ingredients. E. g. the database Cosing on the internet pages of the European Commission discloses cosmetic ingredients and the International Cosmetic Ingredient Dictionary and Handbook, edited by the Personal Care Products Council (PCPC), discloses cosmetic ingredients. The term "composition and / or formulation thereof” with reference to the cosmetic surfactant, emollient, wax, cosmetic polymer, UV filter and / or further cosmetic ingredient refers to personal care and / or cosmetic compositions or formulations defined in more detail in paragraph

[7007] of Reference RF1 . The converting step(s) to obtain the cosmetic surfactant, emollient, wax, cosmetic polymer, UV filter or further cosmetic ingredient is / are defined in more detail in paragraph

[7008] of Reference RF1.The terms "polymer B”, "polymer composition B”, "coating composition”, "other functional composition”, "foil”, "molded body”, "coating” and "coated substrate” are well known to the person skilled in the art and are defined in more detail from paragraph

[8000] to

[8005] of Reference RF1.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 term "textile material” as used herein covers textile raw materials and non-textile raw materials that are processed by various methods into linear, planar and spatial structures. It concerns the linear textile structures produced from them, such as yarns, twisted yarns and ropes, the sheet-like textile structures, such as woven fabrics, knitted fabrics, braids, stitch-bonded fabrics, nonwovens and felts, and the three-dimensional textile structures, i.e. body structures, such as textile hoses, stockings or textile semi-finished products; and it further concerns those finished products which, using the aforementioned products, are brought into a saleable condition by making up, opening up and / or other operations for onward transmission to the processor, the trade or the end consumer. The term "textile waste material” as used herein covers a textile material as defined above, the inherent value of which has been consumed from the perspective of its current holder and, thus, is an end-of-life material for said holder.The term "engineering plastics” as used herein refers to high-performance plastics grades which possess physical properties enabling them to perform for prolonged use in structural applications, over a wide temperature range,under mechanical stress, and in difficult chemical and physical environments used for example to fabricate plastic parts replacing traditional engineering materials like metals and ceramics. Engineering plastics specifically apply in the fabrication of mechanical parts across several industries such as automotive, medical, electrical and electronics, aerospace, construction and consumer products. The term "engineering plastics waste material” as used herein covers an engineering plastics material as defined above, the inherent value of which has been consumed from the perspective of its current holder and, thus, is an end-of-life material for said holder.The present invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and back-references as indicated. In particular, it is noted that in each instance where a range of embodiments is mentioned, for example in the context of a term such as "The process of any one of embodiments 1 to 4", every embodiment in this range is meant to be explicitly disclosed for the skilled person, i.e. the wording of this term is to be understood by the skilled person as being synonymous to "The process of any one of embodiments 1, 2, 3 and 4". Further, it is explicitly noted that the following set of embodiments represents a suitably structured part of the general description directed to preferred aspects of the present invention, and, thus, suitably supports, but does not represent the claims of the present invention.1 . A process for separating solids from a liquid aqueous stream SR comprising monomericE-caprolactam dissolved in water and exhibiting a solids content CR I weight-%, the process comprising(I) preparing the stream SR, comprising(1.1) providing a stream SM comprising a solid material M comprising polyamide 6;(1.2) preparing an aqueous depolymerization mixture based on SM;(1.3) subjecting the depolymerization mixture prepared according to (1.2) to polyamide 6 depolymerization conditions in a reaction unit UR, obtaining the stream SR;(ii) subjecting the stream S obtained from (I) to solid-liquid separation conditions in a solid-liquid separation unit USL comprising at least one centrifuge, obtaining from USL a liquid aqueous stream SP comprising E-caprolactam and exhibiting a solids content CP I weight-%, and further obtaining from USL at least one solid residue stream Ss exhibiting a solids content cs I weight-%, said unit USL exhibiting a total separation efficiency 0T according to formula (I)0T(%) = 100with ST s 70 %.2. The process of embodiment 1, wherein 0T S 80 %, preferably 0T S 90 %, more preferably 0T S 95 %.3. The process of embodiment 1 or 2, wherein CR is in the range of from 0.1 to 4 weight-%, preferably in the range of from 0.15 to 3 weight-%, more preferably in the range of from 0.2 to 2 weight-%.4. The process of any one of embodiments 1 to 3, wherein at least 85 weight-%, preferably at least 90 weight-%, more preferably at least 95 weight-% of SR subjected to (ii) consist of monomeric E-caprolactam and water, based on the total weight of S .5. The process of any one of embodiments 1 to 4, wherein SR subjected to (II) exhibits a monomeric E-caprolactam concentration CE of at least 5 weight-%, preferably of at least 10 weight-%, based on the total weight of SR.6. The process of any one of embodiments 1 to 5, wherein SR subjected to (II) has a temperature TR in the range of from 75 to 150 °C, preferably in the range of from 80 to 130 °C, more preferably in the range of from 85 to 110 °C.7. The process of any one of embodiments 1 to 6, wherein at least one centrifuge comprised in USL is a decanter centrifuge.8. The process of any one of embodiments 1 to 7, wherein the unit USL comprises at least two serially arranged centrifuges.9. The process of embodiment 8, wherein two or more of the at least two serially arranged centrifuges exhibit the same operating principle.10. The process of embodiment 8, wherein two or more of the at least two serially arranged centrifuges exhibit different operating principles.11 . The process of embodiment 9 or 10, preferably of embodiment 10, wherein the centrifuges comprised in the unit USL are two serially arranged centrifuges Ci and C2, C2 being arranged downstream of Ci, and wherein (ii) comprises(ii.1 ) subjecting SR obtained from (I) to solid-liquid separation conditions in Ci, obtaining an aqueous liquid stream SIM exhibiting a solids content CIM I weight-% and further obtaining a solid residue stream Ssi exhibiting a solids content csi I weight-%;(ii.2) subjecting SIM to solid-liquid separation conditions in C2, obtaining the aqueous liquid stream SR, and further obtaining a solid residue stream Ss2 exhibiting a solids content Cs21 weight-%; wherein Ci exhibits a separation efficiency 0ci according to formula (la) ecl(%) = 100wherein C2 exhibits a separation efficiency 0c2 according to formula (lb)Sc2(%) = 100wherein 0ci s 70 % and 0c2 90 %.12. The process of embodiment 11, wherein Ci is operated in semi-continuous mode or in continuous mode, preferably in continuous mode, and wherein 02 is operated in semi-continuous mode or in continuous mode, preferably in continuous mode.13. The process of embodiment 11 or 12, wherein Ci is a two-phase decanter and wherein the centrifuge 02 is a self-discharging two-phase disc separator with intermittent solid discharge.14. The process of embodiment 11 or 12, wherein Ci is a three phase decanter and wherein the centrifuge 02 is a self-discharging two-phase disc separator with intermittent solid discharge.15. The process of any one of embodiments 11 to 14, wherein the unit USL further comprises a feed unit UFI, the process further comprising passing the stream SIM via the unit UFI to (ii .2), the unit UFI preferably comprising one or more of a feed drum and a feed pump.16. The process of any one of embodiments 1 to 15, preferably of any one of embodiments 11 to 15, wherein the unit USL further comprises a filter unit F arranged downstream of the downstream-most centrifuge, preferably downstream of 02, the process further comprising(ii.3) subjecting the stream SR, preferably obtained from (ii.2), to solid-liquid separation conditions in F, obtaining an aqueous liquid stream SPF.17. The process of embodiment 16, wherein SPF exhibits a solids content CPF I weight-% of at most 0.2, preferably of at most 0.1, more preferably of at most 0.05.18. The process of embodiment 16 or 17, wherein the unit USL further comprises a feed unit U F2, the process further comprising passing the stream SP via the unit UF2 to (ii.3), the unit UF2 preferably comprising one or more of a feed drum and a feed pump.19. The process of any one of embodiments 1 to 18, wherein the solid material M according to (1.1) comprises, more 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.20. The process of any one of embodiments 1 to 19, preferably embodiment 19, wherein from 10 to 99 weight-%, preferably from 30 to 98.5 weight-%, more preferably from 50 to 98 weight-%, more preferably from 80 to 98 weight-%, of the solid material M consist of polyamide 6, wherein, in addition to polyamide 6, the solid material M preferably comprises one or more further organic polymeric compounds, more preferably including, but notlimited to, one or more of at least one elastane; at least one polyamide 6.6; at least one semiaromatic polyamide including one or more of polyamide 6T and polyamide 6I; at least one polyethylene terephthalate; at least one polyurethane; at least one polyester; at least one polyether; at least one polyvinyl chloride; at least one natural fiber material such as wool and cotton; at least one cellulose material; at least one natural elastomer; at least one synthetic elastomer; at least one copolymer of two or more of said polymeric compounds including statistical copolymers, gradient copolymers, alternating copolymers, block copolymers, and graft copolymers; and at least one rubber material comprising one or more of at least one natural rubber material and at least one synthetic rubber material. The process of any one of embodiments 1 to 20, preferably embodiment 19 or 20, wherein the solid material M comprises one or more elastanes. The process of embodiment 21 , wherein the crystallized E-caprolactam obtainable or obtained by the process of the present invention exhibits a polytetrahydrofuran content in the range of from 0 to 10 weight-ppm, more preferably in the range of from 0 to 5 weight-ppm, more preferably in the range of from 0 to 1 weight-ppm; and / or an aniline content in the range of from 0 to 10 weight-ppm, more preferably in the range of from 0 to 5 weight-ppm, more preferably in the range of from 0 to 1 weight-ppm; and / or a methylene diphenyl diamine (MDA), isomers and oligomers content in the range of from 0 to 10 weight-ppm, more preferably in the range of from 0 to 5 weight-ppm, more preferably in the range of from 0 to 1 weight- ppm; and / or a butanediol content in the range of from 0 to 500 weight-ppm, more preferably in the range of from 0 to 300 weight-ppm, more preferably in the range of from 0 to 100 weight-ppm, more preferably in the range of from 0 to 50 weight-ppm, more preferably in the range of from 0 to 10 weight-ppm; and / or an ethylene glycol content in the range of from 0 to 500 weight-ppm, more preferably in the range of from 0 to 300 weight-ppm, more preferably in the range of from 0 to 100 weight-ppm, more preferably in the range of from 0 to 50 weight-ppm, more preferably in the range of from 0 to 10 weight-ppm. The process of any one of embodiments 1 to 22, further comprising, after (1.3) and before (II), (1.4) removing a part of the water from the stream SR, preferably in an evaporation unit UE. The process of any one of embodiments 1 to 23, further comprising(ill) subjecting the stream SR, or the stream SPF as defined in embodiment 15, to further purification in a purification UP, obtaining from UP a stream SCPL comprising monomeric E-caprolactam at a concentration of at least 99 weight-%, preferably of at least 99.5 weight-%, more preferably of at least 99.8 weight-%, more preferably of at least 99.9 weight-%; wherein UP comprises one or more of at least one water separation unit Uws, at least one high-boiler separation unit UHS, at least distillation unit UDI and at least one crystallization unit UCR.The process of embodiment 24, further comprising(iv) subjecting the stream SCPL to polyamide 6 polymerization conditions, obtaining polyamide 6 recycled from the solid material M. Polyamide 6, obtainable or obtained by a process according to embodiment 25. The process of embodiment 26, further comprising providing at least part of the stream SCPL to a polyamide 6 production unit UPA6, wherein the polyamide 6 produced in UPA6 is preferably provided 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 the lifetime 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 MRTE 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 solid material M according to (1.1). The process of embodiment 24, further comprising providing at least part of the stream SCPL to a polyamide 6 production unit UPA6, wherein the polyamide 6 produced in UPA6 is preferably provided 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 least partially collected as engineering plastics waste material in an engineering plastics material collecting unit UEC;(B) remaining material MREP is obtained as engineering plastics waste material; wherein at least part of the engineering plastics waste material according to (A), or at least part of the engineering plastics waste material according to (B), or at least part of the engineering plastics waste material according to (A) and at least part of the engineering plastics waste material according to (B) is suitably provided as solid material M according to (1.1). A separation unit USL for separating solids from a liquid aqueous stream SR comprising monomeric E-caprolactam dissolved in water and exhibiting a solids content CR I weight-% with CR being preferably in the range of from 0.1 to 4 weight-%, more preferably in the range of from 0.15 to 3 weight-%, more preferably in the range of from 0.2 to 2 weight-%, said separating comprising(ii.1 ) subjecting SR to solid-liquid separation conditions in Ci, obtaining an aqueous liquid stream SIM exhibiting a solids content CIM I weight-% and further obtaining a solid residue stream Ssi exhibiting a solids content csi I weight-%;(11.2) subjecting SIM to solid-liquid separation conditions in C2, obtaining an aqueous liquid stream SR, and further obtaining a solid residue stream Ss2 exhibiting a solids content Cs21 weight-%;(11.3) preferably subjecting the stream SP to solid-liquid separation conditions in a filter unit F, obtaining an aqueous liquid stream SPF; said unit USL comprising(A) two serially arranged centrifuges Ci and C2 exhibiting the same or different operating principles, preferably different operating principles, wherein more preferably, the centrifuge Ci is a two-phase decanter and the centrifuge C2 is a self-discharging two-phase disc separator with intermittent solid discharge;(B) a feed unit UFI for passing the stream SIM via the unit UFI to (ii.2), the unit UFI preferably comprising one or more of a feed drum and a feed pump; and a feed unit UF2 for passing the stream SP via the unit UF2 to (ii.3), the unit UF2 preferably comprising one or more of a feed drum and a feed pump;(C) a filter unit F arranged downstream of C2 for subjecting the stream SP obtained from (ii.2) to solid-liquid separation conditions in F. A process, preferably according to any one of embodiments 1 to 25, comprising the step of converting at least a part of one or more of the solid residue streams according to (ii), preferably at least a part of one or more of the stream Ssi according to (ii.1 ) and the stream Ss2 according to (ii.2), and / or a chemical material obtainable or obtained by the process according to any one of embodiments 1 to 25 to obtain a product Q. A process comprising the steps of using the separation unit USL according to embodiment 29 to obtain one or more solid residue streams, preferably a stream Ssi and a stream Ss2, and / or a chemical material, and preferably converting at least a part of one or more of the solid residue streams, preferably at least a part of one or more of the stream Ssi and the stream Ss2, and / or a chemical material to obtain a product Q. The process of embodiment 30 or 31 , wherein the product Q is selected from: building block or monomer; or polymer, preferably polymer A, polymer composition, preferably polymer composition A, or polymer product, preferably polymer product A; or industrial use polymer, industrial use surfactant, descaling compound, industrial use biocide, industrial use solvent, industrial use dispersant, composition thereof or formulation thereof; or agrochemical composition, agrochemical formulation auxiliary or agrochemically active ingredient; or active pharmaceutical ingredient or intermediate thereof, pharmaceutical excipient, animal feed additive, human food additive, dietary supplements, aroma chemical or aroma composition; or aqueous polymer dispersion, preferably polyurethane or polyurethane - poly (meth)acrylate hybrid polymer dispersion, emulsion, binder for paper and fiber coatings, UV-curable acrylic polymer for hot melts and coatings polyisocyanates, hyperbranched polyester polyol, polymeric dispersant for inorganic binder compositions, unsaturated polyester polyol or 100% curable composition; orcosmetic surfactant, emollient, wax, cosmetic polymer, UV filter, further cosmetic ingredient or composition or formulation thereof; or polymer B, polymer composition B, coating composition, other functional composition, foil, molded body, coating or coated substrate.33. The process of any one of embodiments 30 to 32, wherein the content of the at least a part of one or more of the solid residue streams according to (ii), preferably at least a part of one or more of the stream Ssi according to (II.1) and the stream Ss2 according to (II.2), and / or a chemical material obtainable or obtained by the process according to any one of embodiments 1 to 25 in the product Q is 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 wherein the content of the at least a part of one or more of the solid residue streams according to (II), preferably at least a part of one or more of the stream Ssi according to (II.1) and the stream Ss2 according to (II.2), and / or a chemical material obtainable or obtained by the process according to any one of embodiments 1 to 22 in the product Q is 100 weight-% or less, preferably 95 weight-% or less, more preferably 90 weight-% or less, more preferably 50 weight-% or less, more preferably 25 weight-% or less, more preferably 10 weight-% or less; and preferably wherein the content is determined based on identity preservation and / or segregation and / or mass balance and / or book and claim chain of custody models, preferably based on mass balance, preferably the International Sustainability and Carbon Certification (ISCC) standard.It is explicitly noted that the above-disclosed 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.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 term "textile material” as used herein covers textile raw materials and non-textile raw materials that are processed by various methods into linear, planar and spatial structures. It concerns the linear textile structures produced from them, such as yarns, twisted yarns and ropes, the sheet-like textile structures, such as woven fabrics, knitted fabrics, braids, stitch-bonded fabrics, nonwovens and felts, and the three-dimensional textile structures, i.e. body structures, such as textile hoses, stockings or textile semi-finished products; and it further concerns those finished products which, using the aforementioned products, are brought into a saleable condition by making up, opening up and / or other operations for onward transmission to the processor, the trade or the end consumer. The term "textile waste material” as used herein covers a textile material as defined above, the inherent value of which has been consumed from the perspective of its current holder and, thus, is an end-of-life material for said holder.The term "engineering plastics” as used herein refers to high-performance plastics grades which possess physical properties enabling them to perform for prolonged use in structural applications, over a wide temperature range, under mechanical stress, and in difficult chemical and physical environments used for example to fabricate plastic parts replacing traditional engineering materials like metals and ceramics. Engineering plastics specifically apply in the fabrication of mechanical parts across several industries such as automotive, medical, electrical and electronics, aerospace, construction and consumer products. The term "engineering plastics waste material” as used herein covers an engineering plastics material as defined above, the inherent value of which has been consumed from the perspective of its current holder and, thus, is an end-of-life material for said holder.

Claims

Claims1. A process for separating solids from a liquid aqueous stream SR comprising monomericE-caprolactam dissolved in water and exhibiting a solids content OR I weight-%, the process comprising(i) preparing the stream SR, comprising(i.1 ) providing a stream SM comprising a solid material M comprising polyamide 6;(1.2) preparing an aqueous depolymerization mixture based on SM;(1.3) subjecting the depolymerization mixture prepared according to (i.2) to polyamide 6 depolymerization conditions in a reaction unit U , obtaining the stream SR;(ii) subjecting the stream SR obtained from (i) to solid-liquid separation conditions in a solid-liquid separation unit USL comprising at least one centrifuge, obtaining from USL a liquid aqueous stream SP comprising E-caprolactam and exhibiting a solids content CP I weight-%, and further obtaining from USL at least one solid residue stream Ss exhibiting a solids content cs I weight-%, said unit USL exhibiting a total separation efficiency 0T according to formula (I)0T(%) = 100with ST s 70 %.

2. The process of claim 1 , wherein 0T S 80 %, preferably 0T S 90 %, more preferably 0T S 95 %.

3. The process of claim 1 or 2, wherein CR is in the range of from 0.1 to 4 weight-%, preferably in the range of from 0.15 to 3 weight-%, more preferably in the range of from 0.2 to 2 weight-%.

4. The process of any one of claims 1 to 3, wherein at least 85 weight-%, preferably at least 90 weight-%, more preferably at least 95 weight-% of SR subjected to (ii) consist of monomeric E-caprolactam and water, based on the total weight of SR, and wherein SR subjected to (ii) exhibits a monomeric E-caprolactam concentration CE preferably of at least 5 weight-%, more preferably of at least 10 weight-%, based on the total weight of SR.

5. The process of any one of claims 1 to 4, wherein SR subjected to (ii) has a temperature TR in the range of from 75 to 150 °C, preferably in the range of from 80 to 130 °C, more preferably in the range of from 85 to 110 °C.

6. The process of any one of claims 1 to 5, wherein the unit USL comprises at least two serially arranged centrifuges, wherein two or more of the at least two serially arranged centrifuges exhibit the same operating principle or wherein two or more of the at least two serially arranged centrifuges exhibit different operating principles, wherein more preferably, two or more of the at least two serially arranged centrifuges exhibit different operating principles.

7. The process of claim 6, wherein the centrifuges comprised in the unit USL are two serially arranged centrifuges Ci and 02, C2 being arranged downstream of Ci, and wherein (ii) comprises(ii.1 ) subjecting SR obtained from (i) to solid-liquid separation conditions in Ci, obtaining an aqueous liquid stream SIM exhibiting a solids content CIM I weight-% and further obtaining a solid residue stream Ssi exhibiting a solids content csi I weight-%;(11.2) subjecting SIM to solid-liquid separation conditions in C2, obtaining the aqueous liquid stream SR, and further obtaining a solid residue stream Ss2 exhibiting a solids content 0321 weight-%; wherein Ci exhibits a separation efficiency 0ci according to formula (la) ecl(%) = 100wherein C2 exhibits a separation efficiency 0c2 according to formula (lb)Sc2(%) = 100wherein 0ci s 70 % and 0c2 90 %.

8. The process of claim 7, wherein Ci is a two-phase decanter and wherein the centrifuge C2 is a self-discharging two-phase disc separator with intermittent solid discharge.

9. The process of claim 7 or 8, wherein the unit USL further comprises a feed unit UFI, the process further comprising passing the stream SIM via the unit UFI to (ii.2), the unit UFI preferably comprising one or more of a feed drum and a feed pump.

10. The process of any one of claims 1 to 9, preferably of any one of claims 7 to 9, wherein the unit USL further comprises a filter unit F arranged downstream of the downstream-most centrifuge, preferably downstream of C2, the process further comprising(11.3) subjecting the stream SR, preferably obtained from (ii.2) as defined in claim 7, to solid-liquid separation conditions in F, obtaining an aqueous liquid stream SPF; wherein SPF exhibits a solids content CPF I weight-% preferably of at most 0.2, more preferably of at most 0.1, more preferably of at most 0.05.11 . The process of claim 10, wherein the unit USL further comprises a feed unit UF2, the process preferably further comprising passing the stream SP via the unit UF2 to (ii.3), the unit UF2 preferably comprising one or more of a feed drum and a feed pump.

12. The process of any one of claims 1 to 11, wherein the solid material M according to (1.1) comprises, more 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 from 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 solid material M consist of polyamide 6, wherein, in addition to polyamide 6, the solid material M preferably 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 polyamide 6.6; at least one semiaromatic polyamide including one or more of polyamide 6T and polyamide 6I; at least one polyethylene terephthalate; at least one polyurethane; at least one polyester; at least one polyether; at least one polyvinyl chloride; at least one natural fiber material such as wool and cotton; at least one cellulose material; at least one natural elastomer; at least one synthetic elastomer; at least one copolymer of two or more of said polymeric compounds including statistical copolymers, gradient copolymers, alternating copolymers, block copolymers, and graft copolymers; and at least one rubber material comprising one or more of at least one natural rubber material and at least one synthetic rubber material.

13. The process of any one of claims 1 to 12, further comprising(iii) subjecting the stream SR, or the stream SPF as defined in claim 9, to further purification in a purification UP, obtaining from UP a stream SCPL comprising monomeric E-caprolactam at a concentration of at least 99 weight-%, preferably of at least 99.5 weight-%, more preferably of at least 99.8 weight-%, more preferably of at least 99.9 weight-%; wherein UP comprises one or more of at least one water separation unit Uws, at least one high-boiler separation unit UHS, at least distillation unit UDI and at least one crystallization unit UCR.

14. A separation unit USL for separating solids from a liquid aqueous stream SR according to a process as defined in any one of claims 7 to 11 , said unit USL comprising(A) two serially arranged centrifuges Ci and C2 exhibiting the same or different operating principles, preferably different operating principles, wherein more preferably, the centrifuge Ci is a two-phase decanter and the centrifuge C2 is a self-discharging two-phase disc separator with intermittent solid discharge;(B) a feed unit UFI arranged downstream of Ci and upstream of C2, the unit UFI preferably comprising one or more of a feed drum and a feed pump; and a feed unit UF2 arranged downstream of C2 and upstream of F as defined in (C), the unit UF2 preferably comprising one or more of a feed drum and a feed pump;(C) a filter unit F arranged downstream of C2; wherein Ci exhibits a separation efficiency 0ci according to formula (la) ecl(%) = 100wherein C2 exhibits a separation efficiency 0c2 according to formula (lb)Sc2(%) = 100wherein 0ci s 70 % and 0c2 90 %.

15. A process, preferably according to any one of claims 1 to 13, comprising the step of converting at least a part of one or more of the solid residue streams according to (ii), preferably at least a part of one or more of the stream Ssi according to (ii.1 ) and the stream Ss2 according to (ii.2), and / or a chemical material obtainable or obtained by the process according to any one of claims 1 to 13 to obtain a product Q; and / or a process comprising the steps of using the separation unit USL according to claim 14 to obtain a stream Ssi and a stream Ss2, and / or a chemical material, and preferably converting at least a part of one or more of the stream Ssi and the stream Ss2, and / or the chemical material to obtain a product Q.

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