Highly heat-integrated process for preparing purified epsilon-caprolactam from polyamide 6

Abstract

A process for preparing purified ε-caprolactam from polyamide 6 contained in a solid material M, wherein the process comprises preparing an aqueous liquid stream comprises ε-caprolactam, subjecting this liquid stream to depressurization in an evaporation unit from which aqueous vapor streams SEV1, SEV2 and SEV3 are obtained which have different pressures and which are then used as heat source for heat-consuming purification units used for preparing a purified ε-caprolactam.

Description

[0001]Highly heat-integrated process for preparing purified epsilon-caprolactam from polyamide 6 The present invention relates to a process for preparing purified ε-caprolactam from polyamide 6 comprising hydrolytically depolymerizing polyamide 6 contained in a solid material, wherein downstream of the depolymerization stage, heat contained in the stream obtained from depolymerization is highly efficiently used within the overall process to obtain purified ε- caprolactam. Polyamide, and in particular polyamide 6 being characterized by the formula (–NH–(CH2)5–CO–)n, can be found in numerous materials, such as packaging, engineering plastics from automotive and textile filaments. The latter represents about 40 % of the polyamide 6 global market. At present, only a very small part of the textile filaments is recycled while it represents a significant percentage of the global CO2emissions. There is thus a need to recycle polyamide 6 from such materials. Processes for alkaline depolymerizing a polyamide exists. Further, the processes in the art are energy-intensive processes. Thus, there is a constant need to provide an improved process for depolymerizing a polyamide able to overcome these issues. Surprisingly, it was found that the process of the present invention according to which polyamide is hydrolytically depolymerized, wherein the stream obtained from depolymerization is suitably processed so as to obtain aqueous vapor streams having different pressures and wherein these aqueous vapor streams are further used as tailor-made heat sources in different depolymerization downstream stages ultimately leading to purified ε-caprolactam, is a robust and, at the same time, a highly heat-effective process. Thus, the process of the present invention permits to reduce the overall energy consumption compared to known processes for depolymerization of a polyamide. Further, using the inventive heat-integrated process permits to reduce the CO2footprint, an essential feature of any up-to-date industrial-scale process. In particular, the present invention relates to a process for preparing purified ε-caprolactam from polyamide 6 contained in a solid material M, the process comprising (i) preparing an aqueous liquid stream SRcomprising ε-caprolactam dissolved in water, comprising (i.1) providing the solid material M comprising the polyamide 6, and providing an aqueous liquid stream SW; (i.2) preparing an aqueous depolymerization mixture based on the solid material M and the aqueous liquid stream SW provided according to (i.1); (i.3) subjecting the aqueous depolymerization mixture prepared according to (i.2) to depolymerization conditions in a chemical reaction unit UR, said depolymerization conditions comprising a depolymerization temperature TD at a depolymerization pressure pD, obtaining in UR a liquid aqueous reaction mixture MR comprising ε- caprolactam dissolved in water; (i.4) removing the aqueous liquid stream SRfrom UR, wherein SRcomprises ε-caprolactam at an ε-caprolactam concentration cSR and wherein SR has a pressure pSR with 0.95 pD ≤ pSR≤ pDand a temperature TSRwith 0.95 TD≤ TSR≤ TD; (ii) subjecting the liquid aqueous stream SR obtained according to (i.4) to depressurization in an evaporation unit UE, obtaining from UEaqueous vapor streams SEV1, SEV2and SEV3, wherein SEV1 has a pressure pEV1 and a temperature TEV1, wherein SEV2 has a pressure pEV2 and a temperature TEV2, and wherein SEV3 has a pressure pEV3 and a temperature TEV3, wherein pEV1> pEV2> pEV3; and further obtaining from UEan aqueous liquid stream SLcomprising ε-caprolactam at an ε-caprolactam concentration cSLwith cSL> cSR; (iii) passing the aqueous liquid stream SL obtained according to (ii) through a heat-consuming purification unit UP comprising at least two heat-consuming purification sub-units UP1 and UP2, obtaining from UPa stream SCPLcomprising ε-caprolactam at an ε-caprolactam concentration cSCPL with cSCPL >> cSL; (iv) providing at least part of the heat consumed in UP1 by SEV3 or a part stream thereof, thereby obtaining from SEV3or the part stream thereof an at least partially condensed aqueous stream SEL3having a pressure pEL3and a temperature TEL3with TEL3≤ TEV3; and providing at least part of the heat consumed in UP2 by SEV2 or a part stream thereof, thereby obtaining from SEV2or the part stream thereof an at least partially condensed aqueous stream SEL2having a pressure pEL2and a temperature TEL2with TEL2≤ TEV2; (v) subjecting at least part of the aqueous stream SEL3 and at least part of the aqueous stream SEL2 to heat exchange in a heat exchange unit UH, wherein at least part of the heat transferred in UHis provided by the aqueous vapor stream SEV1or a part stream thereof, thereby obtaining from SEL3and SEL2an aqueous liquid stream SRWhaving a temperature TRW with TRW > TEL3 and TRW > TEL2, and obtaining from SEV1 or the part stream thereof an at least partially condensed aqueous stream SEL1having a temperature TEL1with TEL1≤ TEV1; (vi) recycling at least part of the stream SRWand at least part of the stream SEL1into the reaction unit UR. No specific limitations exist how the aqueous depolymerization mixture according to (i.2) is provided. Preferably, preparing the aqueous depolymerization mixture according to (i.2) comprises (i.2.1) melting in a melting unit UMthe solid material M provided according to (i.1), obtaining a liquid stream SMhaving a temperature TSMat a pressure pSM; (i.2.2) admixing in a pre-reaction unit UPR the stream SM obtained according to (i.2.1) with the stream SW provided according to (i.1) and having a temperature TSW at a pressure pSW, obtaining a liquid reaction feed stream SFhaving a temperature TSFat a pressure pSF; (i.2.3) feeding the stream SFobtained according to (i.2.2) as the depolymerization mixture into the chemical reaction unit UR. Regarding the temperatures according to (i.2.1), (i.2.2) and (i.2.3) above, it is preferred that at least one of the following relations, more preferably at least two of the following relations, more preferably at least all of the following relations apply: 0.8 ≤ TSF / TD≤ 1.05; 0.6 ≤ TSM / TSF≤ 1.2; and 0.8 ≤ TSW / TSF ≤ 1.2. Regarding the pressures according to (i.2.1), (i.2.2) and (i.2.3) above, it is preferred that at least one of the following relations, preferably at least two of the following relations, more preferably at least all of the following relations apply: 0.9 ≤ pSF / pD ≤ 1.05; 0.9 ≤ pSM / pSF≤ 1.05; and 0.9 ≤ pSW / pSF≤ 1.05. Regarding the temperatures and pressures according to (i.2.1), (i.2.2) and (i.2.3) above, it is more preferred that at least one of the following combinations of temperature and pressure relations, more preferably at least two of the following combinations of temperature and pressure relations, more preferably all of the following combinations of temperature and pressure relations apply: 0.8 ≤ TSF / TD≤ 1.05 and 0.9 ≤ pSF / pD≤ 1.05; 0.6 ≤ TSM / TSF≤ 1.2 and 0.9 ≤ pSM / pSF≤ 1.05; and 0.8 ≤ TSW / TSF ≤ 1.2 and 0.9 ≤ pSW / pSF ≤ 1.05. Regarding the pre-reaction unit UPRaccording to (i.2.2), it is preferred that it is a mixing unit comprising a dynamic mixing unit, or a static mixing unit, or a dynamic mixing unit and a static mixing unit. Preferably, the pre-reaction unit UPR according to (i.2.2) comprises more preferably consists of a static mixing unit. Regarding the melting unit UM according to (i.2.2), it is preferred that it comprises, more preferably consists of an extruder, i.e. a melt extruder. Generally, said extruder can be designed according to the specific needs of the process, preferably, for example, as a single-screw extruder or a twin-screw extruder. Therefore, it is preferred that the pre-reaction unit UPR according to (i.2.2) comprises, preferably consists of, a mixing unit, preferably a static mixing unit, and the melting unit UMcomprises, preferably consists of an extruder, preferably a single-screw extruder or a twin-screw extruder. More preferably, the melting unit UMis equipped with a degassing system, wherein the process further comprises removing a gas stream SGM from UM during melting in UM. Preferably, the gas stream SGMhas a temperature TGMat a pressure pGM, wherein 0.95 ≤ TGM / TSM≤ 1.05. Still more preferably, the gas stream SGMremoved from UMis subjected to scrubbing in a scrubbing unit US, preferably to one or more of wet scrubbing and dry scrubbing, more preferably to wet scrubbing, wherein said wet scrubbing preferably comprises passing the gas stream SGMinto a scrubbing column, preferably a packed scrubbing column. Preferably, between the melting unit UM and the pre-reaction unit UPR, a melt pump unit is arranged, in particular in case the pressure of the stream leaving the UMis lower than the pressure desired for the stream to exhibit when entering the pre-reaction unit UPR. In this case, the melt pump unit may serve for bringing the stream leaving the UM to its desired pressure. More preferably, between the melting unit and the melt pump unit, a filtration unit UF is arranged through which the stream leaving the melting unit UMis passed, preferably for ensuring safe operation of the downstream melt pump unit. More preferably, said filtration unit UFis designed for separating particles having a particle size in the range of from 100 to 500 micrometer, preferably in the range of from 200 to 400 micrometer, from the stream leaving the melting unit UM. Regarding the mixing ratio of streams SW and SM according to (i.2.1), no specific restrictions exist. Preferably, according to (i.2.1), SWand SMare admixed in UPRat a mixing ratio (mW / kg) / (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. According to (i.3), the aqueous depolymerization mixture prepared according to (i.2) is subjected to depolymerization conditions in a chemical reaction unit UR, said depolymerization conditions comprising a depolymerization temperature TDat a depolymerization pressure pD. Preferably, TDis in the range of from 230 to 335 °C and pDis in the range of from 40 to 140 bar, more preferably TD is in the range of from 250 to 320 °C and pD is in the range of from 40 to 125 bar, more preferably TDis in the range of from 270 to 310 °C and pDis in the range of from 40 to 110 bar. Preferably according to the present invention, the reaction unit UR according to (i.3) comprises z chemical reactors Ri, i=1…z, wherein z is in the range of from 1 to 10, preferably in the range of from 1 to 8, more preferably in the range of from 1 to 6, more preferably in the range of from 1 to 5, more preferably in the range of from 1 to 4, more preferably in the range of from 1 to 3. More preferably, 2 or 3, more preferably 3 chemical reactors Ri, are used. If z > 1, it is preferred that at least 2 reactors Ri, preferably z reactors Riare serially coupled, wherein - the stream SFis fed into Ri, with i = 1; - an aqueous liquid stream Si containing ε-caprolactam dissolved in water is removed from reactor Ri and fed into the reactor Ri+1, with i < z; - the aqueous liquid stream Szcontaining ε-caprolactam dissolved in water is removed from the reactor Rzas the stream SR. According to the present invention, in every reactor Ri, a depolymerization temperature TDi at a depolymerization pressure pDiis maintained, wherein, independently of each other, TDiis in the range of from 230 to 335 °C and pDiis in the range of from 40 to 140 bar, preferably wherein TDiis 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. Further according to the present invention, if z > 1, the z reactors Riare vertically arranged, with R1being the top-most reactor and Rzbeing the bottom-most reactor. In this case, it is preferred that a stream Si obtained from a reactor Ri is transferred to the following downstream reactor Ri+1 by gravity, preferably by gravity only. Regarding the specific design of the one or more reactors used according to the process of the present invention, it is preferred that at least one, preferably z reactors Ri, are stirred tank reactors. More preferably, at least one, more preferably every stirred tank reactor Rihas, independently from each other, from 2 to 6 compartments, preferably from 2 to 5 compartments, more preferably from 2 to 4 compartments. More preferably, said compartments are serially arranged, more preferably serially and vertically arranged, wherein 2 adjacent compartments are preferably separated by a divider which comprises at least one flow-through opening. More preferably, wherein at least one compartment comprised in a reactor Ricomprises at least one agitator, wherein more preferably every compartment of every reactor Ri comprises at least one agitator, wherein more preferably, every compartment of every reactor Ri comprises one agitator, wherein the process comprises agitating the depolymerization mixture in a given compartment for at least part of the time during subjecting to depolymerization conditions in said compartment. Generally, the polyamide 6 depolymerization conditions in the chemical reaction unit UR according to (i.3) further comprise a total residence time tD of the aqueous depolymerization mixture in the unit UR, preferably in the z reactors Ri, more preferably in the z stirred tank reactors Ri. According to the present invention, it is preferred that at least 85 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-% of the aqueous depolymerization mixture have a tDin the range of from 30 to 90 min. In particular in the preferred case as described above according to which stirred tank reactors exhibiting the said compartments are used with z > 1, it is preferred that the residence time of an aqueous depolymerization mixture in a reactor Ri is tDi, wherein 0.90 ≤ (tDi / tDi+1) ≤ 1.10, preferably 0.95 ≤ (tDi / tDi+1) ≤ 1.05. Thus, according to the present invention, a very narrow residence time distribution can be achieved. Preferably according to the present invention, no polyamide 6 depolymerization catalyst such as a mineral acid and / or a zinc salt such as zinc chloride, zinc acetate or zinc triflate is added for preparing the stream SFto be subjected to hydrolytic polyamide 6 depolymerisation conditions in the reaction unit UR. Further according to the present invention, the process preferably comprises removing from at least one reactor Ri, preferably from all z reactors Ri, a respective gas stream SGi, wherein a given gas stream SGi has a temperature TGi at a pressure pGi, and wherein 0.95 ≤ TGi / TDi ≤ 1.05. More preferably, the process of the present invention further comprises combining at least one of the gas streams SGi, preferably all streams SGi, with the gas stream SGMobtained from the melting unit UM and as described above, prior to subjecting the gas stream SGM to scrubbing as defined above. According to the present invention, it is possible to provide the solid material M according to (i.1) according to any suitable method. According to a preferred method, (i.1) comprises (i.1.1) providing the solid material M in a delivering unit UMD, wherein UMDpreferably comprises one or more of at least one big bag station and at least one a bulk container station; (i.1.2) passing the solid material M provided according to (i.1.1) via a first connecting line from the unit UMDto a material collecting unit UMC, preferably a collecting drum, wherein the first connecting line preferably comprises one or more of at least one material receiving and discharge unit UMRD, at least one first material feeding unit UFMF, and at least one first particle separation unit UFMPS; (i.1.3) passing the solid material M from the unit UMCvia a second connecting line to the unit UM, wherein the second connecting line preferably comprises one or more of at least one second material feeding unit USMF, at least one second particle separation unit USMPS, and at least one metal detector. Preferably, the first connecting line according to (i.1.2) comprises at least one unit UMRD, more preferably at least one hopper, more preferably at least one one-zone hopper, and further comprises at least one unit UFMF, preferably at least one rotary feeder, and preferably further comprises at least particle separation unit UFMPS, more preferably at least one filter, more preferably at least one mesh filter. Preferably, for passing the solid material M via a first connecting line from the unit UMD to the unit UMC, at least one gas stream SG is passed through the first connecting line, said at least one gas stream preferably comprising, more preferably consisting of air or lean air, wherein prior to being passed through the first connecting line, the at least one gas stream is preferably pre-treated by at least one of filtrating, compressing and cooling, more preferably by filtrating, compressing and cooling. Preferably, the second connecting line according to (i.1.3) comprises at least two units USMF, preferably comprising a rotary feeder and a loss-in-weight feeder, wherein more preferably, the rotary feeder is arranged upstream of the loss-in-weight feeder, and further comprises a unit USMPS, preferably a vibrating screen. Preferably according to the present invention, according to (i.1), the solid material M is provided, preferably provided to UM, in the form of granules, wherein the particle size distribution of said granules is preferably characterized by one or more of the following pairs of values, more 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. Regarding the composition of the solid material M, it is preferred that from 10 to 100 weight-%, more preferably from 30 to 100 weight-%, more preferably from 50 to 100 weight-%, more preferably from 80 to 100 weight-%, of the solid material M consist of the polyamide 6. Also 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. 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. Preferably according to the present invention, the solid material M provided according to (i.1) comprises, preferably consists of, a waste material, preferably one or more of a textile waste material and an engineering plastics waste material, more preferably of a textile waste material. Regarding the evaporation unit UEaccording to (ii), it is preferred that it comprises two evaporation sub-units UE1 and UE2, wherein more preferably, UE1 and UE2 are serially coupled. While there is no specific restriction regarding the respective design, it is preferred that at least one evaporation sub-unit comprises, preferably consists of a flash drum, wherein it is more preferred that the evaporation sub-unit UE1 comprises, preferably consists of a flash drum and that the evaporation sub-unit UE2 comprises, preferably consists of a flash drum. Preferably according to the present invention, (ii) comprises (ii.1) subjecting the liquid aqueous stream SR obtained according to (i.4) to depressurization in the evaporation sub-unit UE1, obtaining from UE1an aqueous vapor stream SEV1Ahaving the pressure pEV1, and further obtaining an at least partially aqueous liquid stream SLU1; (ii.2) dividing the stream SEV1A, obtaining the stream SEV1 and a stream SEV1B having the pressure pEV1; (ii.3) subjecting the stream SEV1Bto depressurization in a unit UV1, UV1preferably comprising a valve, more preferably a pressure relief valve, obtaining the stream SEV2; (ii.4) subjecting the stream SLU1 obtained according to (ii.1) to depressurization in UE2, obtaining from UE2an aqueous vapor stream SEV3Aand the liquid stream SL. Preferably, the aqueous vapor stream SEV3A obtained according to (ii.4) is the aqueous vapor stream SEV3. Further preferably according to the present invention, obtaining the stream SEV3further comprises one or more of (ii.5.1) and (ii.5.2): (ii.5.1) separating a stream SEV1Cfrom the stream SEV1A, obtained according to (ii.1), the stream SEV1Chaving the pressure pEV1; subjecting the stream SEV1Cto depressurization in a unit UV2, UV2 preferably comprising a valve, more preferably a pressure relief valve, obtaining a stream SEV3B having the pressure pEV3; (ii.5.2) separating a stream SEV2Afrom the stream SEV2obtained according to (ii.3), the stream SEV2Ahaving the pressure pEV2; subjecting the stream SEV2Ato depressurization in a unit UV3, UV3 preferably comprising a valve, more preferably a pressure relief valve, obtaining a stream SEV3Chaving the pressure pEV3; and further comprises (ii.6) admixing one or more of the streams SEV3B obtained according to (ii.5.1) and the stream SEV3C obtained according to (ii.5.2) to the stream SEV3A obtained according to (ii.4), obtaining the stream SEV3. Preferably according to the process of the present invention, the following pressures and temperatures are realized: - pD is preferably 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 TD is preferably 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; - pEV1is 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 TEV1 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; - pEV2is 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; - pEV3is 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 TEV3is 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. Further preferably according to the process of the present invention, the following is realized as far as the pressures of the at least partially condensed aqueous streams relative to the pressures of the respective aqueous vapour streams, and as far as the temperature differences between the aqueous vapor streams and the respective at least partially condensed aqueous streams at these pressures is concerned: - 0.95 pEV1≤ pEL1≤ pEV1; and ΔTVL1 = TEV1 - TEL1 is in the range of from 2 to 10 °C, preferably in the range of from 3 to 8 °C, more preferably in the range of from 4 to 6 °C; - 0.95 pEV2≤ pEL2≤ pEV2; and ΔTVL2= TEV2- TEL2is in the range of from 15 to 40 °C, preferably in the range of from 18 to 32 °C, more preferably in the range of from 20 to 30 °C; - 0.95 pEV3≤ pEL3≤ pEV3; and ΔTVL3= TEV3- TEL3is in the range of from 10 to 30 °C, preferably in the range of from 12.5 to 27.5 °C, more preferably in the range of from 15 to 25 °C. In case of latent heat comprised in the aqueous vapour streams, the temperature differences ΔTVL1, ΔTVL2, ΔTVL3may become zero, and the following is realized: - 0.95 pEV1 ≤ pEL1 ≤ pEV1; and ΔTVL1= TEV1- TEL1is in the range of from 0 to 10 °C, preferably in the range of from 0 to 8 °C, more preferably in the range of from 0 to 6 °C; - 0.95 pEV2 ≤ pEL2 ≤ pEV2; and ΔTVL2 = TEV2 - TEL2 is in the range of from 0 to 40 °C, preferably in the range of from 0 to 32 °C, more preferably in the range of from 0 to 30 °C; - 0.95 pEV3≤ pEL3≤ pEV3; and ΔTVL3 = TEV3 - TEL3 is in the range of from 0 to 30 °C, preferably in the range of from 0 to 27.5 °C, more preferably in the range of from 0 to 25 °C. According to a preferred process of the present invention, at least part of the at least partially condensed stream SEL2 and at least part of the at least partially condensed stream SEL3 are suitably combined, and the respectively combined stream is subjected to heating prior to being suitably recycled to the reaction unit UR. According to this preferred process, the respective heat for heating said combined stream is at least partially provided by the aqueous vapor stream SEV1or a part stream thereof. Therefore, the present invention also relates to the above-described process, wherein (v) and (vi) comprise (v) combining at least part of the stream SEL2and at least part of the stream SEL3in a unit UC, obtaining a combined aqueous liquid stream SC, and subjecting at least part of the aqueous liquid stream SC to heat exchange in a heat exchange unit UH, wherein at least part of the heat transferred in UHis provided by the aqueous vapor stream SEV1or a part stream thereof, thereby obtaining from SCan aqueous liquid stream SRWhaving a temperature TRW > TC, and obtaining from SEV1 or the part stream thereof an at least partially condensed aqueous stream SEL1having a temperature TEL1with TEL1< TEV1, the process further comprising combining at least part of the stream SEL1in UCwith SEL2or the part stream thereof and the stream SEL3 or the part stream thereof; (vi) recycling at least part of the stream SRW into the reaction unit UR. Generally, according to the present invention, the heat-consuming purification unit UPcomprises two or more heat-consuming purification sub-units UP1 and UP2 for different ε-caprolactam purification tasks downstream of the hydrolytic depolymerization stage. Each of the heat- consuming purification sub-units UP1and UP2may consist of one single purification sub-unit or of two or more purification sub-units. According to a preferred design of the process of the present invention, the heat-consuming purification sub-units UP1 comprises two or more purification sub- units UP1(j), j=1..m, m ≥ 2, and the heat-consuming purification sub-units UP2comprises two or more purification sub-units UP2(k), k=1..n, n ≥ 2. More preferably according to the present invention, the two or more purification sub-units UP1(j) comprise a water separation unit UWS and a crystallization unit UCR, and the two or more purification sub-units UP2(k) comprise at least one distillation column. More preferably according to the present invention, the two or more purification sub-units UP1(j) comprise a water separation unit UWS and a crystallization unit UCR, and the two or more purification sub-units UP2(k) comprise a distillation unit UDI and one or more of a high-boiler separation unit UHSand a chemical treatment unit UCT. More preferably according to the present invention, the two or more purification sub-units UP1(j) comprise a water separation unit UWS and a crystallization unit UCR, and the two or more purification sub-units UP2(k) comprise a distillation unit UDI, a high-boiler separation unit UHSand a chemical treatment unit UCT. Accordingly, it is preferred according to the present invention to prepare different aqueous vapor streams from the streams SEV2 and SEV3, and use these different streams as suitable heat sources for said different heat-consuming purification sub-units. Therefore, the present invention also relates to the above-described process, comprising (iii) passing the aqueous liquid stream SL obtained according to (ii) through a heat-consuming purification unit UPat least comprising m heat-consuming purification sub-units UP1(j), j=1..m, m ≥ 2, and n heat-consuming purification sub-units UP2(k), k=1..n, n ≥ 2 obtaining from UPa stream SCPLcomprising ε-caprolactam at an ε-caprolactam concentration cSCPLwith cSCPL >> cSL; (iv) dividing the stream SEV3 in at least m part streams SEV3(j) having a temperature TEV3(j) = TEV3and a pressure pEV3(j) = pEV3, and dividing the stream SEV2in at least n part streams SEV2(k) having a temperature TEV2(j) = TEV2and a pressure pEV2(j) = pEV2; and providing at least part of the heat consumed in UP1(j) by SEV3(j), thereby obtaining from SEV3(j) an at least partially condensed aqueous stream SEL3(j) having a pressure pEL3(j) and a temperature TEL3(j) with TEL3(j) < TEV3(j); and providing at least part of the heat consumed in UP2(k) by SEV2(k), thereby obtaining from SEV2(k) an at least partially condensed aqueous stream SEL2(k) having a pressure pEL2(k) and a temperature TEL2(k) with TEL2(k) < TEV2(k); (v) subjecting at least parts of the aqueous streams SEL3(j) and SEL2(k) to heat exchange in a heat exchange unit UH, wherein at least part of the heat transferred in UHis provided by the aqueous vapor stream SEV1 or a part stream thereof, thereby obtaining from the streams SEL3(j) and the streams SEL2(k) an aqueous liquid stream SRWhaving a temperature TRWwith TRW> TEL3(j) and TRW> TEL2(k), and obtaining from SEV1or the part stream thereof an at least partially condensed aqueous stream SEL1 having a temperature TEL1 with TEL1 < TEV1; (vi) recycling at least part of the stream SRW and at least part of the stream SEL1 into the reaction unit UR. According to the process of the present invention, it is preferred that according to (iii), the m heat- consuming purification sub-units UP1(j) comprise one or more of a water separation unit UWSand a crystallization unit UCR, wherein the water separation unit UWSpreferably comprises one or more of an evaporator arranged upstream of a flash tank and a film evaporator, more preferably one or more of an evaporator arranged upstream of a flash tank and a falling film evaporator, and wherein the crystallization unit UCRpreferably comprises at least one heat exchanger preferably for providing a heating medium used for crystallization purposes. More preferably, a stream SEV3(j) is used for providing at least part of the heat consumed by the evaporator arranged upstream of the flash tank comprised in the water separation unit UWS, thereby obtaining a stream SEL3(j). Further, more preferably, another stream SEV3(j) is used for providing at least part of the heat consumed in the water separation unit UWS, thereby obtaining a stream SEL3(j). Yet further more preferably, a stream SEV3(j) is used for providing at least part of the heat consumed by the at least one heat exchanger of the crystallization unit UCR, thereby obtaining a stream SEL3(j). This heat exchanger, for example, may be used for providing hot water for the crystallization unit UCR. Further according to the process of the present invention, it is preferred that according to (iii), the n heat-consuming purification sub-units UP2(k) comprise a distillation unit UDI, wherein UDIpreferably comprises at least one distillation column, preferably at least two distillation columns, more preferably at least three distillation columns, more preferably at least three serially arranged distillation columns. More preferably, in at least one of the distillation columns, preferably in each distillation column, a first stream SEV2(k1) is passed as a direct heating medium through a heating jacket of said distillation column, thereby obtaining a first stream SEL2(k1), and second stream SEV2(k2) is passed as an indirect heating medium through a heat exchanger, preferably a heat exchanger used for sump evaporation of said distillation column, thereby obtaining a second stream SEL2(k2). More preferably, the distillation in at least one distillation column is carried out as a vacuum distillation, and the process further comprises operating at least one vacuum generating means, preferably at least one vacuum ejector, with at least one stream SEV2(k). According to the present, it may be conceivable that, prior to using a stream SEV2(k) as heating medium in one or more of said distillation columns and depending on the specific configuration of the respective distillation column, the pressure of SEV2(k) is suitably reduced, preferably for example to a range of from 3 to 4 bar. As indicated above, it is preferred according to the process of the present invention that the purification unit UPcomprises a heat-consuming water separation unit UWS, a heat-consuming distillation unit UDI and a heat-consuming crystallization unit UCR. According to this preferred design, the process preferably comprises feeding the stream SLcomprising ε-caprolactam at a concentration cSLto UWS, obtaining from UWSa stream SUWScomprising ε-caprolactam at a concentration cSUWS, feeding the stream SUWSto the distillation unit UDI, obtaining from UDI a stream SUDI comprising ε-caprolactam at a concentration cSUDI, and feeding the stream SUDIinto the crystallization unit UCR, obtaining from UCRthe stream SCPLcomprising ε-caprolactam at the concentration cSCPL, wherein cSL< cSUWS< cSUDI< cSCPL. Further according to the process of the present invention, it is preferred that according to (iii), the n heat-consuming purification sub-units UP2(k) further comprise a high-boiler separation unit UHS. In said high-boiler separation unit UHS, one or more compounds X are separated from the stream fed into UHS wherein said one or more compounds have a boiling point higher than the boiling point of ε-caprolactam. Preferably according to the present invention, the high-boiler separation carried out in UHScomprises (a) providing the stream SUWS, having a temperature TSUWS and exhibiting a total concentration cSUWS(X) of the one or more compounds X and a concentration cSUWS(C) of monomeric ε-caprolactam; (b) producing in an evaporation unit UE1from the stream SUWSan aqueous at least partially vaporous stream SV1 and a liquid stream SL1, comprising (b.1) passing the stream SUWSprovided according to (a) into the unit UE1, preparing in the unit UE1from the stream SUWSan evaporation mixture ME1having an evaporation temperature TE1 at an evaporation pressure pE1 with TE1 > TSUWS, wherein the one or more one organic compounds X have a boiling point TBX and ε-caprolactam has a boiling point TBCwith TBX> TE1≥ TBCat the evaporation pressure pE1; (b.2) removing the stream SV1from the evaporation unit UE1, the stream SV1having a temperature TV1 with TV1 ≤ TE1 and exhibiting a total concentration cV1(X) of one or more compounds X and a concentration cV1(C) of monomeric ε-caprolactam with cV1(C) > cSUWS(C) and cV1(X) < cSUWS(X); (b.3) removing the stream SL1 from the evaporation unit UE1, the stream SL1 having a temperature TL1 with TL1 = TE1 and exhibiting a total concentration cL1(X) of one or more compounds X and a concentration cL1(C) of monomeric ε-caprolactam with cL1(C) < cE1(C) and cL1(X) > cSUWS(X); (c) producing in a separation unit US1 from the stream SV1 an aqueous vapor stream SV2 and a liquid stream SL2, comprising (c.1) passing the stream SV1 removed from the evaporation unit UE1 according to (b.2), optionally after cooling, into the separation unit US1and subjecting the stream SV1, optionally the stream after cooling, in the separation unit US1 to separation conditions; (c.2) removing the stream SV2 from the separation unit US1, the stream SV2 having a temperature TV2with TL0< TV2≤ TV1and exhibiting a total concentration cV2(X) of one or more compounds X and a concentration cV2(C) of monomeric ε-caprolactam; (c.3) removing the stream SL2 from the separation unit US1, the stream SL2 having a temperature TL2 with TL2 = TV2 and exhibiting a total concentration cL2(X) of one or more compounds X and a concentration cL2(C) of monomeric ε-caprolactam with cL2(X) > cV2(X) and cL2(C) < cV2(C); (d) passing the aqueous stream SV2 obtained from the separation unit US1 according to (c.2) as stream SUHSto the unit UDI. According to the present invention, the separation unit US1according to (c) is a heat-consuming unit, wherein at least part of the heat consumed in US1 is provided by a stream SEV2(k) according to the present invention, obtaining a respective stream SEL2(k). Preferably, the separation unit US1comprises, more preferably consists of, a droplet separator, preferably selected from the group consisting of a hydrocyclone, a demister plate, and an absorption tower, wherein more preferably, US1 is a hydrocyclone. According to this preferred design, the process preferably comprises feeding the stream SLcomprising ε-caprolactam at a concentration cSLto UWS, obtaining from UWSa stream SUWScomprising ε-caprolactam at a concentration cSUWS, feeding the stream SUWSto the high-boiler separation unit UHS, obtaining from UHS a stream SUHS comprising ε-caprolactam at a concentration cSUHS, feeding the stream SUHSto the distillation unit UDI, obtaining from UDIa stream SUDIcomprising ε-caprolactam at a concentration cSUDI, and feeding the stream SUDIinto the crystallization unit UCR, obtaining from UCR the stream SCPL comprising ε-caprolactam at the concentration cSCPL, wherein cSL < cSUWS < cSUHS < cSUDI < cSCPL. Further according to the process of the present invention, it is preferred that according to (iii), the n heat-consuming purification sub-units UP2(k) further comprise, preferably in addition to the high- boiler separation unit UHSas described herein, a chemical treatment unit UCT. According to the present invention, it is preferred that UCTis suitably integrated in the distillation unit UDI. In the preferred case where UDI comprises three serially arranged distillation columns as described above, with the upstream-most column D1, the column D2 in the middle and the downstream-most column D3, it is preferred that UCTis arranged downstream of D1and upstream of D2. With regard to this preferred arrangement of three serially arranged distillation columns D1, D2, and D3, the distillation carried out in UDI preferably comprises (α) providing the feed stream to the first distillation column D1, the stream SUWS, the stream SUWScomprising ε-caprolactam at a concentration cSUWS(C), one or more organic compounds X at a total concentration cSUWS(X), one or more organic compounds Y at a total concentration cSUWS(Y), and water at a concentration cSUWS(W), wherein water has a boiling point TW, ε-caprolactam has a boiling temperature TC, the one or more organic compounds X have a boiling temperature TX, and the one or more organic compounds Y have a boiling temperature TY, with TY < TC < TX; (β) separating water from the stream SUWS, comprising a distillation in a first distillation column D1, obtaining from D1a vapour top stream ST1comprising water at a concentration cST1(W) > cSUWS(W), and further obtaining from D1 a liquid bottoms stream SB1 comprising ε-caprolactam at a concentration cSB1(C) > cSUWS(C), the one or more organic compounds X at a total concentration cSB1(X) > cSUWS(X), and the one or more organic compounds Y at a total concentration cSB1(Y) > cSUWS(Y); (γ) separating the one or more compounds X from at least a part of the stream SB1, comprising a distillation in a second distillation column D2, obtaining from D2 a top stream ST comprising ε-caprolactam at a concentration cST2(C) < cSB1(C) and the one or more organic compounds Y at a total concentration cST2(Y) > cSB1(Y), further obtaining from D2 a bottom stream SB2 comprising the one or more organic compounds X at a total concentration cSB2(X) > cSB1(X) and optionally ε-caprolactam at a concentration cSB2(C) < cSB1(C), and obtaining from D2a side stream SS2comprising ε-caprolactam at a concentration cSS2(C) > cSB1(C); (δ) separating the one or more compounds Y from at least a part of the stream ST2, comprising a distillation in a third distillation column D3, obtaining from D3a top stream ST3comprising the one or more compounds Y at a total concentration cST3(Y) > cST2(Y), and obtaining from D3 a bottom stream SB3 comprising ε-caprolactam at a concentration cSB3(C) > cST2(C); wherein either the stream SS2and / or the stream SB3is / are passed to a downstream treatment as the stream SUDI. According to another design of the process of the present invention, the chemical treatment unit is arranged downstream of the distillation unit UDI and upstream of the crystallization unit UCR. Preferably according to the present invention, the chemical treatment carried out in UCTcomprises (a) providing a stream SOX comprising at least one oxidizing agent preferably comprising a permanganate; (b) preparing an oxidation reaction educt mixture MOEfrom the stream SOXand the ε-caprolactam feed stream passed into UCT, preferably the ε-caprolactam feed stream obtained from the distillation column D1 as described below or the ε-caprolactam feed stream SUDIas described below, comprising one or more oxidizable organic compounds A, and subjecting the mixture MOEto oxidation reaction conditions, obtaining an oxidation reaction product stream SOP comprising ε-caprolactam, further comprising one or more oxidation reaction products AP obtained from the oxidation of at least a part of the one or more compounds A, and optionally further comprising a part of the one or more organic compounds A; (c) providing a stream SOB comprising at least one hydroxide, wherein the at least one hydroxide comprised in the stream SOBpreferably comprises, more preferably consists of, at least alkali metal hydroxide, wherein more preferably, the at least one alkali metal hydroxide comprises, more preferably consists of, sodium hydroxide; (d) admixing the stream SOB provided according to (c) with the stream SOP obtained according to (b) and subjecting the resulting mixture to basic treatment conditions, obtaining a chemically treated stream SUCT; (e) passing the stream SUCT to either the column D2 or to UCR. According to the present invention, one or more of the apparatus used for subjecting the mixture MOEto oxidation reaction conditions according to (b) and the apparatus used for the basic treatment according to (d), preferably the apparatus used for the basic treatment according to (d), is a heat-consuming unit, wherein at least part of the heat consumed therein is provided by a stream SEV2(k) according to the present invention, obtaining a respective stream SEL2(k). Preferably, said apparatus used for the basic treatment according to (d) comprises, more preferably consists of, a reactor, preferably a stirred reactor, more preferably a continuous stirred tank reactor (CSTR). According to the preferred design wherein UCT is arranged downstream of UDIand upstream of UCR, the process preferably comprises feeding the stream SLcomprising ε-caprolactam at a concentration cSL to UWS, obtaining from UWS a stream SUWS comprising ε-caprolactam at a concentration cSUWS, feeding the stream SUWS to the distillation unit UDI, obtaining from UDIa stream SUDIcomprising ε-caprolactam at a concentration cSUDI, feeding the stream SUDIinto the chemical treatment unit UCT, obtaining from UCTa stream SUCTcomprising ε-caprolactam at a concentration cSUCT, and feeding the stream SUCT into the crystallization unit UCR, obtaining from UCRthe stream SCPLcomprising ε-caprolactam at the concentration cSCPL, wherein cSL< cSUWS< cSUDI< cSUCT< cSCPL. Regarding the preferred process of the present invention according to which at least m at least partially condensed aqueous streams SEL3(j) and at least n at least partially condensed aqueous streams SEL2(k) are obtained, it is preferred that (v) and (vi) comprise (v) combining at least one of the streams SEL2(k) or a part stream thereof, preferably all streams SEL2(k) or part streams thereof, and at least one of the streams SEL3(j) or a part stream thereof, preferably all streams SEL3(j) or part streams thereof, in a unit UC, obtaining a combined aqueous liquid stream SC, and subjecting at least a part of the aqueous liquid stream SC to heat exchange in a heat exchange unit UH, wherein at least part of the heat transferred in UHis provided by the aqueous vapor stream SEV1or a part stream thereof, thereby obtaining from SCan aqueous liquid stream SRWhaving a temperature TRW> TC, and obtaining from SEV1 or the part stream thereof an at least partially condensed aqueous stream SEL1having a temperature TEL1with TEL1< TEV1, the process further comprising combining at least a part of the stream SEL1in UCwith SEL2and SEL3; (vi) recycling at least part of the stream SRW into the reaction unit UR. According to the process of the present invention, it may be preferred to further feed, in addition to at least one of the streams SEL2(k) or a part stream thereof, preferably all streams SEL2(k) or part streams thereof, and at least one of the streams SEL3(j) or a part stream thereof, preferably all streams SEL3(j) or part streams thereof, as indicated above, at least one liquid aqueous stream SPinto UC. This at least one aqueous stream SPcan be, for example, an aqueous stream obtained from processing the stream SL in the purification unit UP. By way of example, at least one liquid aqueous stream SP may be obtained in the water separation unit UWS as described above and / or at least one liquid aqueous stream SPmay be obtained in the distillation unit UDIas described above, i.e. these liquid aqueous streams are obtained in the course of the overall ε- caprolactam purification process wherein water is separated from the aqueous stream SL in order to ultimately obtain purified crystalline ε-caprolactam. Further, in addition to the at least one liquid aqueous stream SP, at least one further liquid aqueous stream SE can be fed into UC, wherein at least one further liquid aqueous stream SEcan be a fresh water stream, such as a fresh water make-up stream intended to at least partially compensate for a loss of water realized in the course of the overall process. Therefore, the present invention also relates to a process which further comprises feeding at least one liquid aqueous stream SP and optionally at least one liquid aqueous stream SE into UC and combining SP and optionally SE in UC with the streams SEL2 and SEL3, and the streams SEL2(k) and SEL3(j), respectively, wherein SPis an aqueous stream obtained from the purification unit UPand wherein SE is a fresh water stream. Preferably, the aqueous stream SP is obtained as optionally combined stream of at least one or more of the water separation unit UWS as described above and the distillation unit UDIas described above. According to the process of the present invention, it may be preferred to pass the stream SRW, prior to recycling at least part of SRWinto the reaction unit UR, through a heat exchange unit UH2, obtaining a heated stream SWhaving a temperature in the range of from 0.95 TDto 1.05 TD. By way of example, the heat used for heating at least part of SRW in UH” to the described temperature may be provided by hot oil. In this case, the process preferably further comprises (vi) recycling at least part of the stream SRWas part of the stream SWinto the reaction unit UR. In the course of the overall process of the present invention, it may be preferred to pass one or more streams through respective filtration units. By way of preferred examples, the process of the present may comprise one or more of - passing the stream SR, upstream of UE, through a filtration unit UF1; - passing the stream SL, upstream of UP, through a filtration unit UF2; - passing the stream SLU1, upstream of UE2, through a filtration unit UF3. Generally, the process of the present invention is a continuous process, a semicontinuous process or a batch process. It is conceivable that one or more stages of the process are carried out in a continuous manner, and one or more stages are carried out in a suitable semi-continuous and / or in a suitable batch-type manner so that the overall process can be classified as a continuous process. The process of the present invention represents a highly heat-integrated, economically and ecologically superior process for recovering ε-caprolactam, in particular from polyamide 6 containing waste material. Preferably, the heat efficiency ηEFFof the process of the present invention is at least 80 %, preferably in the range of from 80 to 100 %, more preferably in the range of from 90 to 100 %, with ηEFF = (ΔHUP1 + ΔHUP2 + ΔHUH) / ΔHSR wherein ΔHUP1is the total heat demand of the purification sub-unit UP1according to (iii); ΔHUP2is the total heat demand of the purification sub-unit UP2according to (iii); ΔHUH is the total heat transferred in the heat exchange unit UH according to (v); ΔHSRis the amount of usable energy contained in the stream SRobtained according to (i.4). More preferred ranges of ηEFFmay be from 97 to 100 % or from 98 to 100 % or from 99 to 100 %. Preferably according to the present invention, at least one of, more preferably at least two of, more preferably the three following relative quantities are realized: - ΔHUP1(rel) = ΔHUP1 / (ΔHUP1+ ΔHUP2+ ΔHUH) is preferably in the range of from 30 to 50 %, more preferably in the range of from 35 to 45 %; - ΔHUP2(rel) = ΔHUP2 / (ΔHUP1 + ΔHUP2 + ΔHUH) is preferably in the range of from 15 to 30 %, more preferably in the range of from 20 to 25 %; - ΔHUH(rel) = ΔHUH / (ΔHUP1 + ΔHUP2 + ΔHUH) is preferably in the range of from 30 to 45 %, more preferably in the range of from 35 to 40 %; with the proviso that ΔHUP1(rel) + ΔHUP2(rel) + ΔHUH(rel) = 1. Generally, the stream SCPL obtained according to (iii), i.e. the purified ε-caprolactam stream, can be used for any suitable purpose. According to a preferred use of the stream SCPL, the process of the present invention further comprises providing at least part of the stream SCPL obtained according to (iii) to a polyamide 6 production unit UPP, wherein the polyamide 6 produced in UPPis preferably provided as a feedstock to a textile material producing unit UTP, from which unit UTP(A) a textile material MT is obtained which is brought onto the market, wherein, after the life- time TMTof said textile material MTit is at least partially collected as textile waste material in a textile material collecting unit UTC; (B) remaining material MR is obtained as textile waste material; wherein at least part of the textile waste material according to (A), or at least part of the textile waste material according to (B), or at least part of the textile waste material according to (A) and at least part of the textile waste material according to (B) is suitably provided to URas SM, preferably via UM. According to a preferred use of the stream SCPL, the process of the present invention further comprises providing at least part of the stream SCPL obtained according to (iii) to a polyamide 6 production unit UPP, wherein the polyamide 6 produced in UPP is preferably provided as a feedstock to an engineering plastics material producing unit UEP, from which unit UEP(A) an engineering plastics material MEis obtained which is brought onto the market, wherein, after the life-time TME of said engineering plastics material ME it is at least partially collected as engineering plastics waste material in an engineering plastics material collecting unit UEC; (B) remaining material MR is obtained as engineering plastics waste material; wherein at least part of the engineering plastics waste material according to (A), or at least part of the engineering plastics waste material according to (B), or at least part of the engineering plastics waste material according to (A) and at least part of the engineering plastics waste material according to (B) is suitably provided to UR as SM, preferably via UM. Thus, the present invention also relates to the use of the stream SCPL, obtainable or obtained by a process as described above, for preparing polyamide 6, said use preferably further comprising employing said polyamide 6 as a feedstock for preparing one or more of a textile material and an engineering plastics material, more preferably for preparing a textile material. Accordingly, the present invention also relates to a method for preparing polyamide 6, said method comprising employing SCPL, obtainable or obtained by a process as described above, as a starting material, wherein said method preferably further comprises employing said polyamide 6 as a feedstock for preparing one or more of a textile material and an engineering plastics material, more preferably for preparing a textile material. Generally, the present invention also relates to the use of the stream SCPL, obtainable or obtained by a process as described above, for preparing one or more of a polymer and a polymer product; or to a method for preparing one or more of a polymer and a polymer product, said method comprising employing the stream SCPL, obtainable or obtained by a process as described above, as a starting material. Accordingly, the present invention also relates to the use or the method as described above, wherein the polymer, or the polymer product, or the polymer and the polymer product is or are in the form of at least one of a granulate, a strand, a rod, a plate, a pipe, a foil, a layer, a film, a sheet, a fiber, a filament, a coating, an extruded article, a molded article, a soft foam, a half-rigid foam and a rigid foam. Accordingly, the present invention also relates to the use or the method as described above, wherein the polymer, or the polymer product, or the polymer and the polymer product comprises or comprise polyamide 6 and optionally at least one further polymeric compound, said polyamide 6 being at least partially obtainable or obtained from SCPL, said SCPLbeing obtainable or obtained by a process as described above, wherein the at least one further polymeric compound preferably comprises one or more of at least one polyamide 6.6, at least one polyethylene terephthalate, at least one polyurethane, at least one polyester, at least one cellulose material, and at least one rubber material comprising one or more of at least one natural rubber material and at least one synthetic rubber material. Accordingly, the present invention also relates to the use or the method as described above, wherein the polymer, or the polymer product, or the polymer and the polymer product is or are one of the following or a part of one of the following: - a part of a car, preferably a cylinder head cover, an engine cover, a housing for a charge air cooler, a charge air cooler flap, an intake pipe, an intake manifold, a connector, a gear wheel, a fan wheel, a cooling water box, a housing or a housing part for a heat exchanger, a coolant cooler, a charge air cooler, a thermostat, a water pump, a radiator, a fastening part or a part of a battery system for electromobility, a dashboard, a steering column switch, a seat, a headrest, a center console, a transmission component, a door module, a car exterior for an A, a B, a C or a D pillar cover, a spoiler, a door handle, an exterior mirror, a windscreen wiper, a windscreen wiper protection housing, a decorative grill, a cover strip, a roof rail, a window frame, a sunroof frame, an antenna panel, a headlight, a taillight, an airbag, a top mount, an oil pan, a fuel cell, a heat shield and / or a cushion; - a cloth, an apparel, preferably a shirt, trousers, a pullover, a boot, a shoe, a shoe sole, a tight, a yarn, a fabric, and / or or jacket; - an electrical part, preferably an electrical component, an electronic passive component, an electronic active component, a printed circuit board, a housing component, a foil, a line, a switch such as a microswitch, a plug, a socket, a distributor, a relay, a resistor, a capacitor, an inductor, a bobbin, a lamp, a diode such as an LED, a transistor, a connector, a regulator, an integrated circuit (IC), a processor, a controller, a memory, a sensor, a microbutton, a semiconductor, a reflector housing for example for light-emitting diodes, a fastener for an electrical and / or an electronic component, a spacer, a bolt, a strip, a slide-in guide, a screw, a nut, a film hinge, a snap hook (snap-in), and / or a spring tongue; - a consumer and / or a pharmaceutical product, preferably a tennis string, a climbing rope, a bristle, a brush, an artificial grass, a 3D printing filament, a grass trimmer, a zipper, a hook and loop fastener, a paper machine clothing, an extrusion coating, a fishing line, a fishing net, an offshore line and rope, a vial, a syringe, an ampoule, a bottle, a sliding element, a spindle nut, a chain conveyor, a plain bearing, a roller, a wheel, a gear, a roller, a ring gear, a screw and spring damper, a hose, a pipeline, a cable sheathing, a socket, a switch, a cable tie, a fan wheel, a carpet, a box and / or a bottle for cosmetics, a mattress, a cushion, an insulation; - a packaging for the food industry, preferably a mono- and / or multi-layer blown film, a cast film (mono- and / or multi-layer), a biaxially stretched film, a laminating film. Accordingly, the present invention also relates to the use or the method as described above, wherein the polymer, or the polymer product, or the polymer and the polymer product contains or contain polyamide 6, obtainable or obtained from SCPL, said SCPLbeing obtainable or obtained by a process as described above, in an amount of 1 weight-% or more, preferably 2 weight-% or more, more preferably 5 weight-% or more, more preferably 15 weight-% or more, more preferably 30 weight-% or more, more preferably 40 weight-% or more, more preferably 60 weight-% or more, more preferably 80 weight-% or more, more preferably 90 weight-% or more, more preferably 95 weight-% or more; and / or in an amount of 100 weight-% or less, preferably 95 weight-% or less, more preferably 90 weight-% or less, more preferably 50 weight-% or less, more preferably 25 weight-% or less, more preferably 10 weight-% or less. 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 preparing purified ε-caprolactam from polyamide 6 contained in a solid material M, the process comprising (i) preparing an aqueous liquid stream SRcomprising ε-caprolactam dissolved in water, comprising (i.1) providing the solid material M comprising the polyamide 6, and providing an aqueous liquid stream SW; (i.2) preparing an aqueous depolymerization mixture based on the solid material M and the aqueous liquid stream SW provided according to (i.1); (i.3) subjecting the aqueous depolymerization mixture prepared according to (i.2) to depolymerization conditions in a chemical reaction unit UR, said depolymerization conditions comprising a depolymerization temperature TD at a depolymerization pressure pD, obtaining in URa liquid aqueous reaction mixture MRcomprising ε-caprolactam dissolved in water; (i.4) removing the aqueous liquid stream SR from UR, wherein SR comprises ε- caprolactam at an ε-caprolactam concentration cSR and wherein SR has a pressure pSRwith 0.95 pD≤ pSR≤ pDand a temperature TSRwith 0.95 TD≤ TSR≤ TD; (ii) subjecting the liquid aqueous stream SR obtained according to (i.4) to depressurization in an evaporation unit UE, obtaining from UEaqueous vapor streams SEV1, SEV2and SEV3, wherein SEV1has a pressure pEV1and a temperature TEV1, wherein SEV2 has a pressure pEV2 and a temperature TEV2, and wherein SEV3 has a pressure pEV3 and a temperature TEV3, wherein pEV1 > pEV2 > pEV3; and further obtaining from UEan aqueous liquid stream SLcomprising ε-caprolactam at an ε-caprolactam concentration cSLwith cSL> cSR; (iii) passing the aqueous liquid stream SL obtained according to (ii) through a heat- consuming purification unit UPcomprising at least two heat-consuming purification sub-units UP1and UP2, obtaining from UPa stream SCPLcomprising ε-caprolactam at an ε-caprolactam concentration cSCPL with cSCPL >> cSL; (iv) providing at least part of the heat consumed in UP1 by SEV3 or a part stream thereof, thereby obtaining from SEV3or the part stream thereof an at least partially condensed aqueous stream SEL3having a pressure pEL3and a temperature TEL3with TEL3≤ TEV3; and providing at least part of the heat consumed in UP2 by SEV2 or a part stream thereof, thereby obtaining from SEV2or the part stream thereof an at least partially condensed aqueous stream SEL2having a pressure pEL2and a temperature TEL2with TEL2 ≤ TEV2; (v) subjecting at least part of the aqueous stream SEL3 and at least part of the aqueous stream SEL2to heat exchange in a heat exchange unit UH, wherein at least part of the heat transferred in UHis provided by the aqueous vapor stream SEV1or a part stream thereof, thereby obtaining from SEL3 and SEL2 an aqueous liquid stream SRW having a temperature TRWwith TRW> TEL3and TRW> TEL2, and obtaining from SEV1or the part stream thereof an at least partially condensed aqueous stream SEL1 having a temperature TEL1with TEL1≤ TEV1; (vi) recycling at least part of the stream SRW and at least part of the stream SEL1 into the reaction unit UR. 2. The process of embodiment 1, wherein preparing the aqueous depolymerization mixture according to (i.2) comprises (i.2.1) melting in a melting unit UM the solid material M provided according to (i.1), obtaining a liquid stream SMhaving a temperature TSMat a pressure pSM; (i.2.2) admixing in a pre-reaction unit UPR the stream SM obtained according to (i.2.1) with the stream SW provided according to (i.1) and having a temperature TSW at a pressure pSW, obtaining a liquid reaction feed stream SFhaving a temperature TSFat a pressure pSF; (i.2.3) feeding the stream SF obtained according to (i.2.2) as the depolymerization mixture into the chemical reaction unit UR; wherein 0.8 ≤ TSF / TD ≤ 1.05 and 0.9 ≤ pSF / pD ≤ 1.05; 0.6 ≤ TSM / TSF ≤ 1.2 and 0.9 ≤ pSM / pSF ≤ 1.05; and 0.8 ≤ TSW / TSF≤ 1.2 and 0.9 ≤ pSW / pSF≤ 1.05. 3. The process of embodiment 2, wherein the pre-reaction unit UPR according to (i.2.2) comprises, preferably consists of, a mixing unit, preferably a static mixing unit, and wherein the melting unit UMcomprises, preferably consists of an extruder, preferably a single-screw extruder or a twin-screw extruder. 4. The process of embodiment 2 or 3, wherein according to (i.2.1), SWand SMare admixed in UPRat a mixing ratio (mW / kg) / (mP / kg) in the range of from 1:1 to 20:1, preferably in the range of from 2:1 to 15:1, more preferably in the range of from 5:1 to 10:1, wherein mW is the amount of water comprised in SWand mPis the amount of polyamide 6 comprised in SM. 5. The process of any one of embodiments 1 to 4, wherein the reaction unit UR according to (i.3) comprises z chemical reactors Ri, i=1…z, wherein z is in the range of from 1 to 10, preferably in the range of from 1 to 8, more preferably in the range of from 1 to 6, more preferably in the range of from 1 to 5, more preferably in the range of from 1 to 4, more preferably in the range of from 1 to 3. 6. The process of embodiment 5, wherein at least 1, preferably z reactors Ri, are stirred tank reactors. 7. The process of any one of embodiments 1 to 6, wherein providing the solid material M according to (i.1) comprises (i.1.1) providing the solid material M in a delivering unit UMD, wherein UMD preferably comprises one or more of at least one big bag station and at least one a bulk container station; (i.1.2) passing the solid material M provided according to (i.1.1) via a first connecting line from the unit UMDto a material collecting unit UMC, preferably a collecting drum, wherein the first connecting line preferably comprises one or more of at least one material receiving and discharge unit UMRD, at least one first material feeding unit UFMF, and at least one first particle separation unit UFMPS; (i.1.3) passing the solid material M from the unit UMCvia a second connecting line to the unit UM, wherein the second connecting line preferably comprises one or more of at least one second material feeding unit USMF, at least one second particle separation unit USMPS, and at least one metal detector. 8. The process of any one of embodiments 1 to 7, wherein according to (i.1), the solid material M is provided, preferably provided to UM, in the form of granules, wherein the particle size distribution of said granules is preferably characterized by one or more of the following pairs of values, preferably by two or more of the following pairs of values, more preferably by the following three pairs of values: - a D10 value of the particle width in the range of from in the range of from 0.1 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. 9. The process of any one of embodiments 1 to 8, wherein from 10 to 100 weight-%, preferably from 30 to 100 weight-%, more preferably from 50 to 100 weight-%, more preferably from 80 to 100 weight-%, of the solid material M consist of the polyamide 6. 10. The process of any one of embodiments 1 to 9, wherein the solid material M provided according to (i.1) comprises, preferably consists of, a waste material, preferably one or more of a textile waste material and an engineering plastics waste material, more preferably of a textile waste material. 11. The process of any one of embodiments 1 to 10, wherein the evaporation unit UE according to (ii) comprises two evaporation sub-units UE1and UE2, wherein UE1and UE2are preferably serially coupled. 12. The process of embodiment 11, wherein at least one evaporation sub-unit, preferably the two evaporation sub-units UE1and UE2comprise, preferably consist of a flash drum. 13. The process of embodiment 11 or 12, wherein (ii) comprises (ii.1) subjecting the liquid aqueous stream SR obtained according to (i.4) to depressurization in the evaporation sub-unit UE1, obtaining from UE1an aqueous vapor stream SEV1A having the pressure pEV1, and further obtaining an at least partially aqueous liquid stream SLU1; (ii.2) dividing the stream SEV1A, obtaining the stream SEV1and a stream SEV1Bhaving the pressure pEV1; (ii.3) subjecting the stream SEV1B to depressurization in a unit UV1, UV1 preferably comprising a valve, more preferably a pressure relief valve, obtaining the stream SEV2; (ii.4) subjecting the stream SLU1obtained according to (ii.1) to depressurization in UE2, obtaining from UE2 an aqueous vapor stream SEV3A and the liquid stream SL. 14. The process of embodiment 13, wherein the aqueous vapor stream SEV3Ais the aqueous vapor stream SEV3. 15. The process of embodiment 13, wherein obtaining the stream SEV3further comprises one or more of (ii.5.1) and (ii.5.2): (ii.5.1) separating a stream SEV1C from the stream SEV1A, obtained according to (ii.1), the stream SEV1C having the pressure pEV1; subjecting the stream SEV1C to depressurization in a unit UV2, UV2preferably comprising a valve, more preferably a pressure relief valve, obtaining a stream SEV3Bhaving the pressure pEV3; (ii.5.2) separating a stream SEV2A from the stream SEV2 obtained according to (ii.3), the stream SEV2Ahaving the pressure pEV2; subjecting the stream SEV2Ato depressurization in a unit UV3, UV3preferably comprising a valve, more preferably a pressure relief valve, obtaining a stream SEV3C having the pressure pEV3; and further comprises (ii.6) admixing one or more of the streams SEV3Bobtained according to (ii.5.1) and the stream SEV3Cobtained according to (ii.5.2) to the stream SEV3Aobtained according to (ii.4), obtaining the stream SEV3. 16. The process of any one of embodiments 1 to 15, wherein - pD is in the range of from 40 to 140 bar, preferably in the range of from 40 to 125 bar, more preferably in the range of from 40 to 110 bar; and TDis in the range of from 230 to 335 °C, preferably in the range of from 250 to 320 °C, more preferably in the range of from 270 to 310 °C; - pEV1 is in the range of from 13 to 19 bar, preferably in the range of from 14 to 18 bar, more preferably in the range of from 15 to 17 bar; and TEV1is in the range of from 170 to 230 °C, preferably in the range of from 180 to 220 °C, more preferably in the range of from 190 to 210 °C; - pEV2 is in the range of from 5 to 11 bar, preferably in the range of from 6 to 10 bar, more preferably in the range of from 7 to 9 bar; and TEV2is in the range of from 150 to 210 °C, preferably in the range of from 160 to 200 °C, more preferably in the range of from 170 to 190 °C; - pEV3 is in the range of from 0.95 to 1.5 bar, 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 in the range of from 90 to 140 °C, preferably in the range of from 100 to 130 °C, more preferably in the range of from 110 to 120 °C. The process of any one of embodiments 1 to 16, wherein - 0.95 pEV1 ≤ pEL1 ≤ pEV1; and ΔTVL1 = TEV1 - TEL1 is in the range of from 2 to 10 °C, preferably in the range of from 3 to 8 °C, more preferably in the range of from 4 to 6 °C; - 0.95 pEV2 ≤ pEL2 ≤ pEV2; and ΔTVL2 = TEV2 - TEL2 is in the range of from 15 to 40 °C, preferably in the range of from 18 to 32 °C, more preferably in the range of from 20 to 30 °C; - 0.95 pEV3≤ pEL3≤ pEV3; and ΔTVL3 = TEV3 - TEL3 is in the range of from 10 to 30 °C, preferably in the range of from 12.5 to 27.5 °C, more preferably in the range of from 15 to 25 °C. The process of any one of embodiments 1 to 17, wherein (v) and (vi) comprise (v) combining at least part of the stream SEL2 and at least part of the stream SEL3 in a unit UC, obtaining a combined aqueous liquid stream SC, and subjecting at least part of the aqueous liquid stream SCto heat exchange in a heat exchange unit UH, wherein at least part of the heat transferred in UH is provided by the aqueous vapor stream SEV1or a part stream thereof, thereby obtaining from SCan aqueous liquid stream SRWhaving a temperature TRW> TC, and obtaining from SEV1or the part stream thereof an at least partially condensed aqueous stream SEL1 having a temperature TEL1 with TEL1 < TEV1, the process further comprising combining at least part of the stream SEL1 in UC with SEL2or the part stream thereof and the stream SEL3or the part stream thereof; (vi) recycling at least part of the stream SRWinto the reaction unit UR. The process of any one of embodiments 1 to 18, comprising (iii) passing the aqueous liquid stream SLobtained according to (ii) through a heat- consuming purification unit UP at least comprising m heat-consuming purification sub- units UP1(j), j=1..m, m ≥ 2, and n heat-consuming purification sub-units UP2(k), k=1..n, n ≥ 2 obtaining from UPa stream SCPLcomprising ε-caprolactam at an ε-caprolactam concentration cSCPLwith cSCPL>> cSL; (iv) dividing the stream SEV3 in at least m part streams SEV3(j) having a temperature TEV3(j) = TEV3and a pressure pEV3(j) = pEV3, and dividing the stream SEV2in at least n part streams SEV2(k) having a temperature TEV2(j) = TEV2and a pressure pEV2(j) = pEV2; and providing at least part of the heat consumed in UP1(j) by SEV3(j), thereby obtaining from SEV3(j) an at least partially condensed aqueous stream SEL3(j) having a pressure pEL3(j) and a temperature TEL3(j) with TEL3(j) < TEV3(j); and providing at least part of the heat consumed in UP2(k) by SEV2(k), thereby obtaining from SEV2(k) an at least partially condensed aqueous stream SEL2(k) having a pressure pEL2(k) and a temperature TEL2(k) with TEL2(k) < TEV2(k); (v) subjecting at least parts of the aqueous streams SEL3(j) and SEL2(k) to heat exchange in a heat exchange unit UH, wherein at least part of the heat transferred in UHis provided by the aqueous vapor stream SEV1 or a part stream thereof, thereby obtaining from the streams SEL3(j) and the streams SEL2(k) an aqueous liquid stream SRWhaving a temperature TRWwith TRW> TEL3(j) and TRW> TEL2(k), and obtaining from SEV1or the part stream thereof an at least partially condensed aqueous stream SEL1having a temperature TEL1 with TEL1 < TEV1; (vi) recycling at least part of the stream SRW and at least part of the stream SEL1 into the reaction unit UR. 20. The process of embodiment 19, wherein according to (iii), the m heat-consuming purification sub-units UP1(j) comprise one or more of a water separation unit UWSand a crystallization unit UCR, wherein the water separation unit UWSpreferably comprises one or more of an evaporator arranged upstream of a flash tank and a film evaporator, more preferably one or more of an evaporator arranged upstream of a flash tank and a falling film evaporator, and wherein the crystallization unit UCRpreferably comprises at least one heat exchanger preferably for providing a heating medium used for crystallization purposes. 21. The process of embodiment 20, wherein a stream SEV3(j) is used for providing at least part of the heat consumed by the evaporator arranged upstream of the flash tank comprised in the water separation unit UWS, thereby obtaining a stream SEL3(j). 22. The process of embodiment 20 or 21, wherein a stream SEV3(j) is used for providing at least part of the heat consumed in the water separation unit UWS, thereby obtaining a stream SEL3(j). 23. The process of any one of embodiments 20 to 22, wherein a stream SEV3(j) is used for providing at least part of the heat consumed by the at least one heat exchanger of the crystallization unit UCR, thereby obtaining a stream SEL3(j). 24. The process of any one of embodiments 20 to 23, wherein according to (iii), the n heat- consuming purification sub-units UP2(k) comprise a distillation unit UDI, wherein UDI preferably comprises at least one distillation column, preferably at least two distillation columns, more preferably at least three distillation columns, more preferably at least three serially arranged distillation columns, and wherein the n heat-consuming purification sub- units UP2(k) preferably further comprise one or more of a high-boiler separation unit UHSand a chemical treatment unit UCT, more preferably a high-boiler separation unit UHSand a chemical treatment unit UCT. 25. The process of embodiment 24, wherein in at least one of the distillation columns, preferably in each distillation column, a first stream SEV2(k1) is passed as a direct heating medium through a heating jacket of said distillation column, thereby obtaining a first stream SEL2(k1), and second stream SEV2(k2) is passed as an indirect heating medium through a heat exchanger, preferably a heat exchanger used for sump evaporation of said distillation column, thereby obtaining a second stream SEL2(k2). The process of embodiment 24 or 25, wherein the distillation in at least one distillation column is carried out as a vacuum distillation, wherein the process further comprises operating at least one vacuum generating means, preferably at least one vacuum ejector, with at least one stream SEV2(k). The process of any one of embodiments 24 to 26, wherein the purification unit UPcomprises a heat-consuming water separation unit UWS, a heat-consuming distillation unit UDI and a heat-consuming crystallization unit UCR, the process comprising feeding the stream SLcomprising ε-caprolactam at a concentration cSLto UWS, obtaining from UWSa stream SUWScomprising ε-caprolactam at a concentration cSUWS, feeding the stream SUWSto the distillation unit UDI, obtaining from UDI a stream SUDI comprising ε-caprolactam at a concentration cSUDI, and feeding the stream SUDIinto the crystallization unit UCR, obtaining from UCRthe stream SCPLcomprising ε-caprolactam at the concentration cSCPL, wherein cSL < cSUWS < cSUDI < cSCPL; wherein the purification unit UP preferably further comprises a heat-consuming high-boiler separation unit UHS, the process preferably comprising feeding the stream SLcomprising ε-caprolactam at a concentration cSLto UWS, obtaining from UWSa stream SUWScomprising ε-caprolactam at a concentration cSUWS, feeding the stream SUWS to the high-boiler separation unit UHS, obtaining from UHS a stream SUHScomprising ε-caprolactam at a concentration cSUHS, feeding the stream SUHSto the distillation unit UDI, obtaining from UDIa stream SUDI comprising ε-caprolactam at a concentration cSUDI, and feeding the stream SUDI into the crystallization unit UCR, obtaining from UCR the stream SCPL comprising ε-caprolactam at the concentration cSCPL, wherein cSL< cSUWS< cSUHS< cSUDI< cSCPL. The process of any one of embodiments 19 to 27, wherein (v) and (vi) comprise (v) combining at least one of the streams SEL2(k) or a part stream thereof, preferably all streams SEL2(k) or part streams thereof, and at least one of the streams SEL3(j) or a part stream thereof, preferably all streams SEL3(j) or part streams thereof, in a unit UC, obtaining a combined aqueous liquid stream SC, and subjecting at least a part of the aqueous liquid stream SCto heat exchange in a heat exchange unit UH, wherein at least part of the heat transferred in UHis provided by the aqueous vapor stream SEV1or a part stream thereof, thereby obtaining from SC an aqueous liquid stream SRW having a temperature TRW> TC, and obtaining from SEV1or the part stream thereof an at least partially condensed aqueous stream SEL1having a temperature TEL1with TEL1< TEV1, the process further comprising combining at least a part of the stream SEL1 in UC with SEL2 and SEL3; (vi) recycling at least part of the stream SRWinto the reaction unit UR. The process of embodiment 28, further comprising feeding at least one liquid aqueous stream SPand optionally at least one liquid aqueous stream SEinto UCand combining SP and optionally SE in UC with the streams SEL2 and SEL3, and the streams SEL2(k) and SEL3(j), respectively, wherein SPis an aqueous stream obtained from the purification unit UPand wherein SE is a fresh water stream. 30. The process of embodiment 29, wherein the aqueous stream SPis obtained as optionally combined stream of at least one or more of the water separation unit UWSas defined in embodiment 20 and the distillation unit UDI as defined in embodiment 24. 31. The process of any one of embodiments 1 to 30, comprising passing the stream SRW, prior to recycling at least part of SRW into the reaction unit UR, through a heat exchange unit UH2, obtaining a heated stream SW having a temperature in the range of from 0.95 TD to 1.05 TD. 32. The process of any one of embodiments 1 to 31, wherein (vi) comprises (vi) recycling at least part of the stream SRW as part of the stream SW into the reaction unit UR. 33. The process of any one of embodiments 1 to 32, preferably as far as being dependent on embodiment 13, comprising one or more of - passing the stream SR, upstream of UE, through a filtration unit UF1; - passing the stream SL, upstream of UP, through a filtration unit UF2; - passing the stream SLU1, upstream of UE2, through a filtration unit UF3. 34. The process of any one of embodiments 1 to 33, exhibiting a heat efficiency ΔHEFFof at least 80 %, preferably in the range of from 80 to 100 %, more preferably in the range of from 90 to 100 %, with ηEFF = (ΔHUP1 + ΔHUP2 + ΔHUH) / ΔHSR wherein ΔHUP1is the total heat demand of the purification sub-unit UP1according to (iii); ΔHUP2 is the total heat demand of the purification sub-unit UP2 according to (iii); ΔHUHis the total heat transferred in the heat exchange unit UHaccording to (v); ΔHSRis the amount of usable energy contained in the stream SRobtained according to (i.4). 35. The process of embodiment 34, wherein at least one of, more preferably at least two of, more preferably the three following relative quantities are realized: - ΔHUP1(rel) = ΔHUP1 / (ΔHUP1 + ΔHUP2 + ΔHUH) is preferably in the range of from 30 to 50 %, more preferably in the range of from 35 to 45 %; - ΔHUP2(rel) = ΔHUP2 / (ΔHUP1+ ΔHUP2+ ΔHUH) is preferably in the range of from 15 to 30 %, more preferably in the range of from 20 to 25 %; - ΔHUH(rel) = ΔHUH / (ΔHUP1 + ΔHUP2 + ΔHUH) is preferably in the range of from 30 to 45 %, more preferably in the range of from 35 to 40 %; with the proviso that ΔHUP1(rel) + ΔHUP2(rel) + ΔHUH(rel) = 1. The process of any one of embodiments 1 to 35, being a continuous process, a semicontinuous process or a batch process. The process of any one of embodiments 1 to 36, further comprising providing at least part of the stream SCPLobtained according to (iii) to a polyamide 6 production unit UPP, wherein the polyamide 6 produced in UPPis preferably provided as a feedstock to a textile material producing unit UTP, from which unit UTP (A) a textile material MT is obtained which is brought onto the market, wherein, after the life-time TMTof said textile material MTit is at least partially collected as textile waste material in a textile material collecting unit UTC; (B) remaining material MR is obtained as textile waste material; wherein at least part of the textile waste material according to (A), or at least part of the textile waste material according to (B), or at least part of the textile waste material according to (A) and at least part of the textile waste material according to (B) is suitably provided to UR as SM, preferably via UM. The process of any one of embodiments 1 to 37, further comprising providing at least part of the stream SCPL obtained according to (iii) to a polyamide 6 production unit UPP, wherein the polyamide 6 produced in UPPis preferably provided as a feedstock to an engineering plastics material producing unit UEP, from which unit UEP(A) an engineering plastics material ME is obtained which is brought onto the market, wherein, after the life-time TMEof said engineering plastics material MEit is at least partially collected as engineering plastics waste material in an engineering plastics material collecting unit UEC; (B) remaining material MR is obtained as engineering plastics waste material; wherein at least part of the engineering plastics waste material according to (A), or at least part of the engineering plastics waste material according to (B), or at least part of the engineering plastics waste material according to (A) and at least part of the engineering plastics waste material according to (B) is suitably provided to URas SM, preferably via UM. Use of SCPL, obtainable or obtained by a process according to any one of embodiments 1 to 38, for preparing polyamide 6, said use preferably further comprising employing said polyamide 6 as a feedstock for preparing one or more of a textile material and an engineering plastics material, more preferably for preparing a textile material. A method for preparing polyamide 6, said method comprising employing SCPL, obtainable or obtained by a process according to any one of embodiments 1 to 38, as a starting material, wherein said method preferably further comprises employing said polyamide 6 as a feedstock for preparing one or more of a textile material and an engineering plastics material, more preferably for preparing a textile material. Use of SCPL, obtainable or obtained by a process according to any one of embodiments 1 to 38, for preparing one or more of a polymer and a polymer product; or a method for preparing one or more of a polymer and a polymer product, said method comprising employing SCPL, obtainable or obtained by a process according to any one of embodiments 1 to 38, as a starting material. 42. The use or the method of embodiment 41, wherein the polymer, or the polymer product, or the polymer and the polymer product is or are in the form of at least one of a granulate, a strand, a rod, a plate, a pipe, a foil, a layer, a film, a sheet, a fiber, a filament, a coating, an extruded article, a molded article, a soft foam, a half-rigid foam and a rigid foam. 43. The use or the method of embodiment 41 or 42, wherein the polymer, or the polymer product, or the polymer and the polymer product comprises or comprise polyamide 6 and optionally at least one further polymeric compound, said polyamide 6 being at least partially obtainable or obtained from SCPL, said SCPLbeing obtainable or obtained by a process according to any one of embodiments 1 to 36, wherein the at least one further polymeric compound preferably comprises one or more of at least one polyamide 6.6, at least one polyethylene terephthalate, at least one polyurethane, at least one polyester, at least one cellulose material, and at least one rubber material comprising one or more of at least one natural rubber material and at least one synthetic rubber material. 44. The use or the method of any one of embodiments 41 to 42, wherein the polymer, or the polymer product, or the polymer and the polymer product is or are one of the following or a part of one of the following: - a part of a car, preferably a cylinder head cover, an engine cover, a housing for a charge air cooler, a charge air cooler flap, an intake pipe, an intake manifold, a connector, a gear wheel, a fan wheel, a cooling water box, a housing or a housing part for a heat exchanger, a coolant cooler, a charge air cooler, a thermostat, a water pump, a radiator, a fastening part or a part of a battery system for electromobility, a dashboard, a steering column switch, a seat, a headrest, a center console, a transmission component, a door module, a car exterior for an A, a B, a C or a D pillar cover, a spoiler, a door handle, an exterior mirror, a windscreen wiper, a windscreen wiper protection housing, a decorative grill, a cover strip, a roof rail, a window frame, a sunroof frame, an antenna panel, a headlight, a taillight, an airbag, a top mount, an oil pan, a fuel cell, a heat shield and / or a cushion; - a cloth, an apparel, preferably a shirt, trousers, a pullover, a boot, a shoe, a shoe sole, a tight, a yarn, a fabric, and / or or jacket; - an electrical part, preferably an electrical component, an electronic passive component, an electronic active component, a printed circuit board, a housing component, a foil, a line, a switch such as a microswitch, a plug, a socket, a distributor, a relay, a resistor, a capacitor, an inductor, a bobbin, a lamp, a diode such as an LED, a transistor, a connector, a regulator, an integrated circuit (IC), a processor, a controller, a memory, a sensor, a microbutton, a semiconductor, a reflector housing for example for light-emitting diodes, a fastener for an electrical and / or an electronic component, a spacer, a bolt, a strip, a slide-in guide, a screw, a nut, a film hinge, a snap hook (snap-in), and / or a spring tongue; - a consumer and / or a pharmaceutical product, preferably a tennis string, a climbing rope, a bristle, a brush, an artificial grass, a 3D printing filament, a grass trimmer, a zipper, a hook and loop fastener, a paper machine clothing, an extrusion coating, a fishing line, a fishing net, an offshore line and rope, a vial, a syringe, an ampoule, a bottle, a sliding element, a spindle nut, a chain conveyor, a plain bearing, a roller, a wheel, a gear, a roller, a ring gear, a screw and spring damper, a hose, a pipeline, a cable sheathing, a socket, a switch, a cable tie, a fan wheel, a carpet, a box and / or a bottle for cosmetics, a mattress, a cushion, an insulation; - a packaging for the food industry, preferably a mono- and / or multi-layer blown film, a cast film (mono- and / or multi-layer), a biaxially stretched film, a laminating film. 45. The use or the method of any one of embodiments 41 to 44, wherein the polymer, or the polymer product, or the polymer and the polymer product contains or contain polyamide 6, obtainable or obtained from SCPL, said SCPLbeing obtainable or obtained by a process according to any one of embodiments 1 to 36, in an amount of 1 weight-% or more, preferably 2 weight-% or more, more preferably 5 weight-% or more, more preferably 15 weight-% or more, more preferably 30 weight-% or more, more preferably 40 weight-% or more, more preferably 60 weight-% or more, more preferably 80 weight-% or more, more preferably 90 weight-% or more, more preferably 95 weight-% or more; and / or in an amount of 100 weight-% or less, preferably 95 weight-% or less, more preferably 90 weight-% or less, more preferably 50 weight-% or less, more preferably 25 weight-% or less, more preferably 10 weight-% or less. As far as the embodiment 45 is concerned, the respective amounts are preferably determined based on identity preservation and / or segregation and / or mass balance and / or book and claim chain of custody models, more preferably based on mass balance, more preferably the International Sustainability and Carbon Certification (ISCC) standard. As far as the embodiments 41 to 45 are concerned, preparing the polymer, the polymer product, or the polymer and the polymer product may comprise one or more synthesis steps and can be performed by conventional synthesis and technics well known to the person skilled in the art. Examples of the synthesis steps are described in “Industrial Organic Chemistry”, 3rdvolume, Wiley-VCH, 1997; ISBN: 978-3-527-28838-0; „Kunststoffhandbuch“, 11 volumes in 17 sub- volumes, Carl Hanser Verlag, especially volume 6, „Polyamide“, 1stedition, 1966; “Injection Molding Reference Guide, 4thedition, CreateSpace Independent Publishing Platform, 2011, ISBN: 978-1466407824; WO 2008 / 155271 A1 and WO 2013 / 139827 A1, each of which is incorporated herein by reference. The term „bar“ as used in the context of the present invention refers to the absolute pressure, also referred to as „bar(abs)“ or as “bara”. The 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. Preferred aspects of the present invention are further illustrated in the Figures 1 to 12 as described hereinunder. Description of the figures Fig.1 illustrates a process according to the present invention. In a reaction unit UR, a depolymerization mixture (not shown) which is based on an a solid material M and an aqueous liquid stream is subjected to polyamide 6 depolymerization conditions, and from the reaction unit UR, an aqueous liquid stream SRcomprising ε-caprolactam dissolved in water is obtained. This stream SRis then subjected to depressurization conditions in an evaporation unit UE from which aqueous vapor streams SEV1, SEV2 and SEV3 are obtained, as well as an aqueous liquid stream SL. The liquid stream SLis then passed to a purification unit UPwhere it is purified with respect to the oligomeric compound ε-caprolactam. From UP, a respectively purified stream SCPLis obtained. The unit UP comprises at least two heat-consuming purification sub-units UP1 and UP2 (not shown), and at least part the heat consumed in UP1 is provided by SEV3 and at least part the heat consumed in UP2is provided by SEV2. Due to this heat transfer, condensation takes place, and from the vapor streams SEV2and SEV3, liquid streams SEL2and SEL3are obtained which are passed the a heat exchange unit UH from which, based on the streams SEL2 and SEL3, a respectively heated liquid aqueous stream SRWis obtained which is recycled to the reaction unit UR as a source of water for the hydrolytic polyamide 6 depolymerization reaction. The heat for obtaining the stream SRWbased on SEL1and SEL2is provided by the aqueous vapor stream SEV1which, after heat transfer in UH, is obtained as (condensed) liquid stream SEL1 which, as SRW, is recycled to the reaction unit UR as a source of water for the hydrolytic polyamide 6 depolymerization reaction. Fig.2 illustrates a process according to the present invention. In this figure, and further to Fig. 1, the two (different) heat-consuming purification sub-units UP1 and UP2 (not shown in Fig.1) comprised in UPare shown wherein the heat consumed in UP1is at least partially provided by the stream SEV3 (from which, due to the heat transfer, the liquid stream SEL1 is obtained), and wherein the heat consumed in UP2 is at least partially provided by the stream SEV2 (from which, due to the heat transfer, the liquid stream SEL2is obtained). Fig.3 illustrates a process according to the present invention. In this figure, and further to Figs. 1 and 2, a preferred was of preparing the depolymerization mixture in the reaction unit URis shown. A solid material M comprising polyamide 6 and a liquid aqueous stream SWare provided. The solid material M is melted in a melting unit UM from which a melt stream SM is obtained. This stream SM is admixed with the stream SW in a pre-reaction UPR, and resulting mixed stream is then passed to the reaction unit URwhere it is subjected, as depolymerization mixture, to polyamide 6 depolymerization conditions. Fig.4 illustrates a process according to the present invention. In this figure, and further to Figs. 1 to 3, a preferred way of treating the stream SEL1is shown. The stream SEL1, obtained from SEV1used for heating purposes in UH, is not directly recycled back to UR as shown in Figs.1 and 3, but first fed into a unit UC where it is combined with the liquid streams SEL2 and SEL3 obtained from the purification unit UP. The respectively combined liquid stream SCis then passed through UHand thereby heated. From UH, the liquid aqueous stream SRWis obtained which is then recycled to the reaction unit UR (via UPR) as a source of water for the hydrolytic polyamide 6 depolymerization reaction. Fig.5 illustrates a process according to the present invention. In this figure, and further to Fig. 4, a preferred way of recycling the stream SRW is shown. The liquid aqueous stream SRW obtained from UH, prior to being recycled to UR, is admixed with a fresh water stream SW, and the resulting aqueous liquid stream, also referred to SW, is then passed into UR(via UPR) as a source of water for the hydrolytic polyamide 6 depolymerization reaction. Fig.6 illustrates a process according to the present invention. In this figure, it is shown that prior to being recycled to UR, the liquid aqueous stream SRW is further heated in the heat exchange unit UH2. A fresh water stream (not shown) can be admixed, either, for example, to the stream SCprior to being fed into UC, and / or can be admixed with SEL1prior to being passed into UC, and / or can be fed directly into UC, and / or can be admixed to SRWprior to being fed into UH2, and / or to SW according to this Fig.6 prior to being fed into UPR. Further in this figure, it is shown that an aqueous stream SPwhich is obtained from the purification unit UPis additional passed into UC. By way of example, the stream SP can be obtained from one or more distillation columns comprised in UPor from one or more other evaporation devices comprised in UP. The stream SPcan also be a combined stream of two or more aqueous streams obtained from UP, wherein it is also possible that two or more of these aqueous streams obtained from UP are fed separately into UC. Fig.7 illustrates a process according to the present invention. In this figure, a preferred way of providing the aqueous vapor streams SEV1, SEV2 and SEV3 in UE is shown. First, the stream aqueous liquid SRobtained from the reaction unit UR(not shown) is fed into a first evaporation unit UE1 from which a first aqueous vapor stream SEV1A (having a pressure pEV1) and an aqueous liquid stream SLU1 are obtained. SLU1 is then passed to a first evaporation unit UE2. The stream SEV1Ais divided, and one of the respectively obtained vapor streams is the stream SEV1which is used according to the present invention preferably for hearting purposes in the heat exchange unit UH. The other part of the stream, SEV1B, is passed to depressurization in the unit UV1 from which the stream SEV2is obtained which has the pressure pEV2which is lower than the pEV1. Further, from the evaporation unit UE2, the stream SEV3Ais obtained which, if not treated further, is the stream SEV3 having the pressure pEV3 which in turn is lower than pEV2. Further from UE2, the liquid stream SL is obtained which is then passed to the purification unit UP. Fig.8 illustrates a process according to the present invention. In this figure, further to figure 7, a further preferred way of providing the aqueous vapor streams SEV1, SEV2 and SEV3 in UE is shown. Further to what is described in the context of figure 7, the stream SEV1A, prior to being divided in the streams SEV1Band SEV1, is divided to obtain the stream SEV1Chaving the pressure pEV1. SEV1C is subjected to depressurization in the unit UV2 from which the stream SEV3B is obtained, having the pressure pEV3. Further, the stream SEV2 obtained from UV1 having the pressure pEV2is divided, obtaining the stream SEV2A(and the remaining stream SEV2), wherein SEV2Ahas the pressure pEV2. SEV2Ais subjected to depressurization in the unit UV3from which the stream SEV3C is obtained, having the pressure pEV3. The streams SEV3B and SEV3C can then be used for heating purposes as such. In this figure 8, it is shown that both streams are combined with the stream SEV3A, resulting in the combined stream SEV3. The streams SEV1, SEV2and SEV3according to the present invention can, irrespective how they are prepared in UE, fed in respective steam pipe systems and passed to the respective units where part streams of SEV1, SEV2and SEV3are taken from the respective pipe systems and fed into the individual heat- consuming units. Fig.9 illustrates a process according to the present invention. In this figure, a preferred arrangement of heat-consuming purification sub-units comprised in UPis shown. According to this arrangement, the liquid stream SL is first passed to a water separation unit UWS. It is noted that one or more water streams (not shown) obtained by this water separation together may form at least a part of the stream SPdescribed herein. The heat consumed in UWSfor water separation purposes is at least partially provided by the aqueous vapor stream SEV3(1) which is a part stream of SEV1 obtained from UE. From UWS, a stream SUWS is obtained which is sent to further purification in a distillation unit UDI. In this figure 9, it is assumed, for example, that UDIcomprises two distillation columns. For each of these distillation columns, an individual vapor stream is provided by dividing the stream SEV2obtained from UE. From UDI, a stream SUDIis obtained which is sent to a crystallization unit UCR for further purification and from which the (final) stream SCPL is obtained containing the purified ε-caprolactam. The heat consumed in UCR for crystallization purposes is at least partially provided by the stream SEV3(2), a part stream of SEV3. From these heat-consuming purification sub-units, the respective (condensed) liquid streams SEL3(1), SEL3(2), SEL2(1) and SEL2(2) are obtained which are then preferably combined (not shown) and suitably recycled according to the present invention to UR (not shown). Fig.10 illustrates a process according to the present invention. In this figure, a preferred arrangement of heat-consuming purification sub-units comprised in UP is shown. According to this arrangement, the liquid stream SLis first passed to a water separation unit UWS. It is noted that one or more water streams (not shown) obtained by this water separation together may form at least a part of the stream SP described herein. The heat consumed in UWS for water separation purposes is at least partially provided by the aqueous vapor stream SEV3(1) which is a part stream of SEV1obtained from UE. From UWS, a stream SUWSis obtained which is sent to further purification in a high-boiler separation unit UHS. In this high-boiler separation unit UHS, a hydrocyclone, for example, is present for the operation of which a vapor stream SEV2(3) is provided by dividing the stream SEV2obtained from UE. From UHS, a stream SUHSis obtained which is sent to further purification in a distillation unit UDI. In this figure 10, as in figure 9, it is assumed, for example, that UDI comprises two distillation columns. For each of these distillation columns, an individual vapor stream is provided by (further) dividing the stream SEV2obtained from UE. From UDI, a stream SUDIis obtained which is sent to a crystallization unit UCRfor further purification and from which the (final) stream SCPL is obtained containing the purified ε-caprolactam. The heat consumed in UCR for crystallization purposes is at least partially provided by the stream SEV3(2), a part stream of SEV3. From these heat-consuming purification sub-units, the respective (condensed) liquid streams SEL3(1), SEL3(2), SEL2(1), SEL2(2) and SEL2(3) are obtained which are then preferably combined (not shown) and suitably recycled according to the present invention to UR (not shown). Fig.11 illustrates a process according to the present invention. In this figure, compared with what is shown in figure 10, a preferred arrangement of the distillation unit UDI comprised in UP is shown. According to this preferred arrangement, the distillation unit UDI comprises three (serially arranged) distillation columns D1, D2and D3. For each of these distillation columns, an individual vapor stream (streams SEV2(1), SEV2(2) and SEV2(3)) is provided by (further) dividing the stream SEV2 obtained from UE. In addition to the three distillation columns, the distillation unit UDI further comprises a chemical treatment unit UCTarranged downstream of D1and upstream of D2. In this chemical treatment unit UCT, a reactor such as a stirred reactor, for example, is present for the operation of which a vapor stream SEV2(4) is provided by dividing the stream SEV2 obtained from UE. From these heat-consuming purification sub-units, the respective (condensed) liquid streams SEL3(1), SEL3(2), SEL2(1), SEL2(2), SEL2(3), SEL2(4) and SEL2(5) are obtained which are then preferably combined (not shown) and suitably recycled according to the present invention to UR(not shown). Fig.12 illustrates a process according to the present invention. In this figure, compared with what is shown in figure 11, the chemical treatment unit UCTis arranged downstream of the distillation unit UDI and upstream of the crystallization unit UCR. According to this process, the stream SUDI which is obtained from UDI is passed to UCT from which a stream SUCT is obtained which is then passed to UCR. From these heat-consuming purification sub-units, the respective (condensed) liquid streams SEL3(1), SEL3(2), SEL2(1), SEL2(2), SEL2(3), SEL2(4) and SEL2(4) are obtained which are then preferably combined (not shown) and suitably recycled according to the present invention to UR (not shown).

Claims

Claims 1. A process for preparing purified ε-caprolactam from polyamide 6 contained in a solid material M, the process comprising (i) preparing an aqueous liquid stream SRcomprising ε-caprolactam dissolved in water, comprising (i.1) providing the solid material M comprising the polyamide 6, and providing an aqueous liquid stream SW; (i.2) preparing an aqueous depolymerization mixture based on the solid material M and the aqueous liquid stream SW provided according to (i.1); (i.3) subjecting the aqueous depolymerization mixture prepared according to (i.2) to depolymerization conditions in a chemical reaction unit UR, said depolymerization conditions comprising a depolymerization temperature TDat a depolymerization pressure pD, obtaining in UR a liquid aqueous reaction mixture MRcomprising ε-caprolactam dissolved in water; (i.4) removing the aqueous liquid stream SRfrom UR, wherein SRcomprises ε- caprolactam at an ε-caprolactam concentration cSR and wherein SR has a pressure pSR with 0.95 pD ≤ pSR ≤ pD and a temperature TSR with 0.95 TD ≤ TSR ≤ TD; (ii) subjecting the liquid aqueous stream SRobtained according to (i.4) to depressurization in an evaporation unit UE, obtaining from UE aqueous vapor streams SEV1, SEV2and SEV3, wherein SEV1has a pressure pEV1and a temperature TEV1, wherein SEV2has a pressure pEV2and a temperature TEV2, and wherein SEV3has a pressure pEV3 and a temperature TEV3, wherein pEV1 > pEV2 > pEV3; and further obtaining from UE an aqueous liquid stream SL comprising ε-caprolactam at an ε-caprolactam concentration cSLwith cSL> cSR; (iii) passing the aqueous liquid stream SLobtained according to (ii) through a heat- consuming purification unit UP comprising at least two heat-consuming purification sub-units UP1and UP2, obtaining from UPa stream SCPLcomprising ε-caprolactam at an ε-caprolactam concentration cSCPLwith cSCPL>> cSL; (iv) providing at least part of the heat consumed in UP1 by SEV3 or a part stream thereof, thereby obtaining from SEV3 or the part stream thereof an at least partially condensed aqueous stream SEL3having a pressure pEL3and a temperature TEL3with TEL3≤ TEV3; and providing at least part of the heat consumed in UP2by SEV2or a part stream thereof, thereby obtaining from SEV2 or the part stream thereof an at least partially condensed aqueous stream SEL2having a pressure pEL2and a temperature TEL2with TEL2≤ TEV2; (v) subjecting at least part of the aqueous stream SEL3 and at least part of the aqueous stream SEL2 to heat exchange in a heat exchange unit UH, wherein at least part of the heat transferred in UHis provided by the aqueous vapor stream SEV1or a part stream thereof, thereby obtaining from SEL3and SEL2an aqueous liquid stream SRWhaving a temperature TRW with TRW > TEL3 and TRW > TEL2, and obtaining from SEV1 or the partstream thereof an at least partially condensed aqueous stream SEL1 having a temperature TEL1with TEL1≤ TEV1; (vi) recycling at least part of the stream SRW and at least part of the stream SEL1 into the reaction unit UR.

2. The process of claim 1, wherein from 10 to 100 weight-%, preferably from 30 to 100 weight- %, more preferably from 50 to 100 weight-%, more preferably from 80 to 100 weight-%, of the solid material M consist of the polyamide 6, wherein the solid material M provided according to (i.1) preferably comprises, more preferably consists of, a waste material, preferably one or more of a textile waste material and an engineering plastics waste material, more preferably of a textile waste material.

3. The process of claim 1 or 2, wherein the evaporation unit UEaccording to (ii) comprises two evaporation sub-units UE1 and UE2, wherein UE1 and UE2 are preferably serially coupled, and wherein preferably at least one evaporation sub-unit, more preferably the two evaporation sub-units UE1and UE2comprise, preferably consist of a flash drum.

4. The process of claim 3, wherein (ii) comprises (ii.1) subjecting the liquid aqueous stream SRobtained according to (i.4) to depressurization in the evaporation sub-unit UE1, obtaining from UE1an aqueous vapor stream SEV1A having the pressure pEV1, and further obtaining an at least partially aqueous liquid stream SLU1; (ii.2) dividing the stream SEV1A, obtaining the stream SEV1and a stream SEV1Bhaving the pressure pEV1; (ii.3) subjecting the stream SEV1B to depressurization in a unit UV1, UV1 preferably comprising a valve, more preferably a pressure relief valve, obtaining the stream SEV2; (ii.4) subjecting the stream SLU1obtained according to (ii.1) to depressurization in UE2, obtaining from UE2 an aqueous vapor stream SEV3A and the liquid stream SL; wherein the aqueous vapor stream SEV3Ais the aqueous vapor stream SEV3.

5. The process of claim 4, wherein obtaining the stream SEV3 further comprises one or more of (ii.5.1) and (ii.5.2): (ii.5.1) separating a stream SEV1Cfrom the stream SEV1A, obtained according to (ii.1), the stream SEV1Chaving the pressure pEV1; subjecting the stream SEV1Cto depressurization in a unit UV2, UV2 preferably comprising a valve, more preferably a pressure relief valve, obtaining a stream SEV3Bhaving the pressure pEV3; (ii.5.2) separating a stream SEV2Afrom the stream SEV2obtained according to (ii.3), the stream SEV2A having the pressure pEV2; subjecting the stream SEV2A to depressurization in a unit UV3, UV3 preferably comprising a valve, more preferably a pressure relief valve, obtaining a stream SEV3Chaving the pressure pEV3; and further comprises(ii.6) admixing one or more of the streams SEV3B obtained according to (ii.5.1) and the stream SEV3Cobtained according to (ii.5.2) to the stream SEV3Aobtained according to (ii.4), obtaining the stream SEV3.

6. The process of any one of claims 1 to 5, wherein - pDis in the range of from 40 to 140 bar, preferably in the range of from 40 to 125 bar, more preferably in the range of from 40 to 110 bar; and TD is in the range of from 230 to 335 °C, preferably in the range of from 250 to 320 °C, more preferably in the range of from 270 to 310 °C; - pEV1 is in the range of from 13 to 19 bar, preferably in the range of from 14 to 18 bar, more preferably in the range of from 15 to 17 bar; and TEV1is in the range of from 170 to 230 °C, preferably in the range of from 180 to 220 °C, more preferably in the range of from 190 to 210 °C; - pEV2 is in the range of from 5 to 11 bar, preferably in the range of from 6 to 10 bar, more preferably in the range of from 7 to 9 bar; and TEV2is in the range of from 150 to 210 °C, preferably in the range of from 160 to 200 °C, more preferably in the range of from 170 to 190 °C; - pEV3 is in the range of from 0.95 to 1.5 bar, 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 TEV3is in the range of from 90 to 140 °C, preferably in the range of from 100 to 130 °C, more preferably in the range of from 110 to 120 °C.

7. The process of any one of claims 1 to 6, wherein - 0.95 pEV1 ≤ pEL1 ≤ pEV1; and ΔTVL1 = TEV1 - TEL1 is in the range of from 2 to 10 °C, preferably in the range of from 3 to 8 °C, more preferably in the range of from 4 to 6 °C; - 0.95 pEV2≤ pEL2≤ pEV2; and ΔTVL2 = TEV2 - TEL2 is in the range of from 15 to 40 °C, preferably in the range of from 18 to 32 °C, more preferably in the range of from 20 to 30 °C; - 0.95 pEV3≤ pEL3≤ pEV3; and ΔTVL3 = TEV3 - TEL3 is in the range of from 10 to 30 °C, preferably in the range of from 12.5 to 27.5 °C, more preferably in the range of from 15 to 25 °C.

8. The process of any one of claims 1 to 7, wherein (v) and (vi) comprise (v) combining at least part of the stream SEL2 and at least part of the stream SEL3 in a unit UC, obtaining a combined aqueous liquid stream SC, and subjecting at least part of the aqueous liquid stream SCto heat exchange in a heat exchange unit UH, wherein at least part of the heat transferred in UH is provided by the aqueous vapor stream SEV1 or a part stream thereof, thereby obtaining from SC an aqueous liquid stream SRW having a temperature TRW> TC, and obtaining from SEV1or the part stream thereof an at least partially condensed aqueous stream SEL1having a temperature TEL1with TEL1< TEV1, the process further comprising combining at least part of the stream SEL1 in UC with SEL2or the part stream thereof and the stream SEL3or the part stream thereof;(vi) recycling at least part of the stream SRW into the reaction unit UR.

9. The process of any one of claims 1 to 8, comprising (iii) passing the aqueous liquid stream SL obtained according to (ii) through a heat- consuming purification unit UPat least comprising m heat-consuming purification sub- units UP1(j), j=1..m, m ≥ 2, and n heat-consuming purification sub-units UP2(k), k=1..n, n ≥ 2 obtaining from UP a stream SCPL comprising ε-caprolactam at an ε-caprolactam concentration cSCPL with cSCPL >> cSL; (iv) dividing the stream SEV3in at least m part streams SEV3(j) having a temperature TEV3(j) = TEV3 and a pressure pEV3(j) = pEV3, and dividing the stream SEV2 in at least n part streams SEV2(k) having a temperature TEV2(j) = TEV2 and a pressure pEV2(j) = pEV2; and providing at least part of the heat consumed in UP1(j) by SEV3(j), thereby obtaining from SEV3(j) an at least partially condensed aqueous stream SEL3(j) having a pressure pEL3(j) and a temperature TEL3(j) with TEL3(j) < TEV3 (j); and providing at least part of the heat consumed in UP2(k) by SEV2(k), thereby obtaining from SEV2(k) an at least partially condensed aqueous stream SEL2(k) having a pressure pEL2(k) and a temperature TEL2(k) with TEL2(k) < TEV2(k); (v) subjecting at least parts of the aqueous streams SEL3(j) and SEL2(k) to heat exchange in a heat exchange unit UH, wherein at least part of the heat transferred in UHis provided by the aqueous vapor stream SEV1or a part stream thereof, thereby obtaining from the streams SEL3(j) and the streams SEL2(k) an aqueous liquid stream SRWhaving a temperature TRWwith TRW> TEL3(j) and TRW> TEL2(k), and obtaining from SEV1or the part stream thereof an at least partially condensed aqueous stream SEL1having a temperature TEL1 with TEL1 < TEV1; (vi) recycling at least part of the stream SRW and at least part of the stream SEL1 into the reaction unit UR: wherein according to (iii), the m heat-consuming purification sub-units UP1(j) preferably comprise one or more of a water separation unit UWS and a crystallization unit UCR; wherein the water separation unit UWSpreferably comprises one or more of an evaporator arranged upstream of a flash tank and a film evaporator, more preferably one or more of an evaporator arranged upstream of a flash tank and a falling film evaporator; wherein the crystallization unit UCR preferably comprises at least one heat exchanger preferably for providing a heating medium used for crystallization purposes.

10. The process of claim 9, wherein - a stream SEV3(j) is used for providing at least part of the heat consumed by the evaporator arranged upstream of the flash tank comprised in the water separation unit UWS, thereby obtaining a stream SEL3(j); - a stream SEV3(j) is used for providing at least part of the heat consumed in the water separation unit UWS, thereby obtaining a stream SEL3(j); - a stream SEV3(j) is used for providing at least part of the heat consumed by the at least one heat exchanger of the crystallization unit UCR, thereby obtaining a stream SEL3(j).

11. The process of claim 9 or 10, wherein according to (iii), the n heat-consuming purification sub-units UP2(k) comprise a distillation unit UDI, wherein UDI preferably comprises at least one distillation column, preferably at least two distillation columns, more preferably at least three distillation columns, more preferably at least three serially arranged distillation columns, wherein preferably in at least one of the distillation columns, more preferably in each distillation column, a first stream SEV2(k1) is passed as a direct heating medium through a heating jacket of said distillation column, thereby obtaining a first stream SEL2(k1), and second stream SEV2(k2) is passed as an indirect heating medium through a heat exchanger, preferably a heat exchanger used for sump evaporation of said distillation column, thereby obtaining a second stream SEL2(k2); wherein the distillation preferably in at least one distillation column is carried out as a vacuum distillation, wherein the process more preferably further comprises operating at least one vacuum generating means, preferably at least one vacuum ejector, with at least one stream SEV2(k); the n heat-consuming purification sub-units UP2(k) preferably further comprising one or more of a high-boiler separation unit UHS and a chemical treatment unit UCT, more preferably a high-boiler separation unit UHS and a chemical treatment unit UCT.

12. The process of any one of claims 9 to 11, wherein (v) and (vi) comprise (v) combining at least one of the streams SEL2(k) or a part stream thereof, preferably all streams SEL2(k) or part streams thereof, and at least one of the streams SEL3(j) or a part stream thereof, preferably all streams SEL3(j) or part streams thereof, in a unit UC, obtaining a combined aqueous liquid stream SC, and subjecting at least a part of the aqueous liquid stream SC to heat exchange in a heat exchange unit UH, wherein at least part of the heat transferred in UHis provided by the aqueous vapor stream SEV1or a part stream thereof, thereby obtaining from SCan aqueous liquid stream SRWhaving a temperature TRW > TC, and obtaining from SEV1 or the part stream thereof an at least partially condensed aqueous stream SEL1having a temperature TEL1with TEL1< TEV1, the process further comprising combining at least a part of the stream SEL1in UC with SEL2 and SEL3; (vi) recycling at least part of the stream SRW into the reaction unit UR.

13. The process of any one of claims 1 to 12, exhibiting a heat efficiency ΔHEFFof at least 80 %, preferably in the range of from 80 to 100 %, more preferably in the range of from 90 to 100 %, with ηEFF= (ΔHUP1+ ΔHUP2+ ΔHUH) / ΔHSRwherein ΔHUP1 is the total heat demand of the purification sub-unit UP1 according to (iii); ΔHUP2 is the total heat demand of the purification sub-unit UP2 according to (iii); ΔHUHis the total heat transferred in the heat exchange unit UHaccording to (v); ΔHSRis the amount of usable energy contained in the stream SRobtained according to (i.4).

14. The process of claim 13, wherein at least one of, more preferably at least two of, more preferably the three following relative quantities are realized: - ΔHUP1(rel) = ΔHUP1 / (ΔHUP1 + ΔHUP2 + ΔHUH) is preferably in the range of from 30 to 50 %, more preferably in the range of from 35 to 45 %; - ΔHUP2(rel) = ΔHUP2 / (ΔHUP1+ ΔHUP2+ ΔHUH) is preferably in the range of from 15 to 30 %, more preferably in the range of from 20 to 25 %; - ΔHUH(rel) = ΔHUH / (ΔHUP1 + ΔHUP2 + ΔHUH) is preferably in the range of from 30 to 45 %, more preferably in the range of from 35 to 40 %; with the proviso that ΔHUP1(rel) + ΔHUP2(rel) + ΔHUH(rel) = 1.

15. The process of any one of claims 1 to 14, being a continuous process, a semicontinuous process or a batch process.

16. Use of SCPL, obtainable or obtained by a process according to any one of claims 1 to 15, for preparing one or more of a polymer and a polymer product, wherein the polymer, or the polymer product, or the polymer and the polymer product is or are in the form of at least one of a granulate, a strand, a rod, a plate, a pipe, a foil, a layer, a film, a sheet, a fiber, a filament, a coating, an extruded article, a molded article, a soft foam, a half-rigid foam and a rigid foam; and wherein the polymer, or the polymer product, or the polymer and the polymer product comprises or comprise polyamide 6 and optionally at least one further polymeric compound, said polyamide 6 being at least partially obtainable or obtained from SCPL, said SCPLbeing obtainable or obtained by a process according to any one of claims 1 to 15, wherein the at least one further polymeric compound preferably comprises one or more of at least one polyamide 6.6, at least one polyethylene terephthalate, at least one polyurethane, at least one polyester, at least one cellulose material, and at least one rubber material comprising one or more of at least one natural rubber material and at least one synthetic rubber material.

17. The use of claim 16, wherein the polymer, or the polymer product, or the polymer and the polymer product is or are one of the following or a part of one of the following: - a part of a car, preferably a cylinder head cover, an engine cover, a housing for a charge air cooler, a charge air cooler flap, an intake pipe, an intake manifold, a connector, a gear wheel, a fan wheel, a cooling water box, a housing or a housing part for a heat exchanger, a coolant cooler, a charge air cooler, a thermostat, a water pump, a radiator, a fastening part or a part of a battery system for electromobility, a dashboard, a steering column switch, a seat, a headrest, a center console, a transmission component, a door module, a car exterior for an A, a B, a C or a D pillar cover, a spoiler, a door handle, an exterior mirror, a windscreen wiper, a windscreen wiper protection housing, a decorative grill, a cover strip, a roof rail, a window frame, a sunroof frame, an antenna panel, a headlight, a taillight, an airbag, a top mount, an oil pan, a fuel cell, a heat shield and / or a cushion; - a cloth, an apparel, preferably a shirt, trousers, a pullover, a boot, a shoe, a shoe sole, a tight, a yarn, a fabric, and / or or jacket;- an electrical part, preferably an electrical component, an electronic passive component, an electronic active component, a printed circuit board, a housing component, a foil, a line, a switch such as a microswitch, a plug, a socket, a distributor, a relay, a resistor, a capacitor, an inductor, a bobbin, a lamp, a diode such as an LED, a transistor, a connector, a regulator, an integrated circuit (IC), a processor, a controller, a memory, a sensor, a microbutton, a semiconductor, a reflector housing for example for light-emitting diodes, a fastener for an electrical and / or an electronic component, a spacer, a bolt, a strip, a slide-in guide, a screw, a nut, a film hinge, a snap hook (snap-in), and / or a spring tongue; - a consumer and / or a pharmaceutical product, preferably a tennis string, a climbing rope, a bristle, a brush, an artificial grass, a 3D printing filament, a grass trimmer, a zipper, a hook and loop fastener, a paper machine clothing, an extrusion coating, a fishing line, a fishing net, an offshore line and rope, a vial, a syringe, an ampoule, a bottle, a sliding element, a spindle nut, a chain conveyor, a plain bearing, a roller, a wheel, a gear, a roller, a ring gear, a screw and spring damper, a hose, a pipeline, a cable sheathing, a socket, a switch, a cable tie, a fan wheel, a carpet, a box and / or a bottle for cosmetics, a mattress, a cushion, an insulation; - a packaging for the food industry, preferably a mono- and / or multi-layer blown film, a cast film (mono- and / or multi-layer), a biaxially stretched film, a laminating film.

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