Method for controlling a caprolactam crystallization process

Abstract

A crystallization unit U for carrying out an ε-caprolactam crystallization process, wherein the unit U comprises crystallization sub-units UC(H), a batch drum sub-unit UB and a stream distribution sub-unit UD connecting UB and UC(H); an ε-caprolactam crystallization process carried out in the crystallization unit U; and a method for controlling the ε-caprolactam crystallization process carried out in the unit U.

Description

Method for controlling a caprolactam crystallization processThe present invention relates to a crystallization unit for carrying out an E-caprolactam crystallization process, said E-caprolactam crystallization process, and a method for controlling this process. Further, the present invention relates to the respectively obtained highly purified E-caprolactam and its use as an educt material, preferably for preparing polyamide 6.Polyamide, and in particular polyamide 6 characterized by the formula (-NH-(CH2)5-CO-)n, can be found in numerous materials, such as packaging, engineering plastics from automotive and textile filaments. The latter represents about 40 % of the polyamide 6 global market. At present, only a very small part of the textile filaments is recycled while it represents a significant percentage of the global CO2 emissions. There is thus a need to recycle polyamide 6 from such materials.Songcheng Wang et al., "Development of suspension melt crystallization: a review”, Chemical Engineering Research and Design 201 (2024) 372-388 focuses on the advancements made in suspension melt crystallization techniques over the past two decades, specifically in process modelling, equipment development, and applications.US 2022 / 089545 A1 relates to a caprolactam production process, and particularly to a refining process and a refining system of caprolactam.US 4,787,985 A relates to a counter-current process for purifying chemicals using crystal purification. The unit process has a purification and recovery section which contain substantially identical stages. In operation, the unit process purifies the chemical by utilizing sequential recrystallizer. The size and purity of the crystals increases from the last recrystallizer in the recovery section through each subsequent stage to the last recrystallizer in the purification section.CN 104072419 A relates to a method of purification and a purifying plant of crude E-caprolactam that contains impurities.US 2012 / 330006 A1 relates to a method of manufacturing E-caprolactam by crystallizing raw E-caprolactam containing an impurity, that was obtained by Beckmann rearrangement of cyclohexanoneoxime.Such recycling suitably involves subjecting materials containing polyamide 6, in particular textile materials, to a depolymerization stage and subjecting the respectively obtained crude depolymerization mixture comprising E- caprolactam to downstream purification. Such purification process for E-caprolactam downstream of the depolymerization step is not a straight-forward task, for example due to the various possible chemical compositions of waste materials comprising polyamide 6 which form the educt materials for the recycling process.According to the present invention, it was found that a crystallization process is a suitable final step of the above- mentioned downstream purification of crude E-caprolactam streams obtained from depolymerization, and the respectively obtained purified E-caprolactam can be used, for example, as educt material for subsequent polymerization reaction, in particular to prepare polyamide 6. However, in particular in view of the various possible chemical compositions of waste materials comprising polyamide 6, there was also the need for providing a crystallization process which allows for adapting the crystallization process to possibly different chemical compositions of mixtures obtained from one or more purification stages downstream of the depolymerization stage and upstream of the crystallization stage.Therefore, the present invention relates to a crystallization unit U for carrying out an E-capro-lactam crystallization process, wherein the unit U comprises(1) h crystallization sub-units Uc(H), H = 1 ...h and h > 2, wherein each crystallization sub-unit UC<H) comprises s crystallizer WC(S(H», S(H) = 1 ...S and s > 1 ; a stream transportation line LC(H) passing through the s crystallizer WC(S(H», comprising an entry and exit point EC(H) connected to the stream distribution sub-unit UD according to (3) and further comprising controllable means MEC(HJ for passing a stream from UD into LC<H) and for passing a stream from LC(H) to UDI(2) a batch drum sub-unit UB comprising k batch drums B(i) with I = 1 ...k and k > 2, wherein k is preferably in the range of from 2 to 20, wherein each batch drum B(i) is equipped with controllable means MBO) for passing a stream from B(i) via the stream distribution sub-unit UD according to (3) to at least one of EC(H>; a crude E-caprolactam feed stream transportation line Lso to at least one batch drum B(i);(3) a stream distribution sub-unit UD connecting UB and the h sub-units UC<H), the sub-unit UD comprising(3.1) for each drum B(i) with I = 1 ...k(3.1.1) at least one of a stage stream transportation line Ls<Hi)(i) from B(i) to at least one EC<HI) and a stage stream transportation line Ls<H2)(i) from B(i) to at least one EC<H2), H1 + H2, wherein Ls<Hi)(i) comprises at least one controllable means MLS(HI)O) for passing a stream from B(i) to Ec(W) and l_s<H2)(i) comprises at least one controllable means MLs<H2)(i) for passing a stream from B(i) to Ec(H2>;(3.1 .2) at least one of a back stream transportation line LB<H i)(i) from EC<HI) to B(i) and a back stream transportation line LB<H2)(i) from EC<H2) to B(i), wherein LBCHIJG) comprises at least one controllable means MLBCHIJG) for passing a stream from EC(HI> to B(i) and LB<H2)(i) comprises at least one controllable means MLB<H2)(i) for passing a stream from EC<H2) to B(i);(3.2) a final residue stream transportation line LR<H3) , H3 + H1 ,H2, for removing a final crystallization residue stream SRF from a transportation line LC(H) via EC<H), wherein LR<H3) comprises at least one controllable means MLR<H3) for removing said final residue stream SRF from LC(H>;(3.3) a final fine product stream transportation line LF<H4), H4 + H1,H2,H3, for removing a final fine crystallization product stream SPF from a transportation line LC<H) via EC(H), wherein LF<H4> comprises at least one controllable means MLF<H4) for removing said final fine product stream SPF from LC(H>.With regard to the number of crystallization sub-units UC<H), it is preferred that 2 < h < 10, more preferably 2 < h < 8, more preferably 2 < h < 6, more preferably 2 < h < 4, more preferably h = 2 or h = 3, more preferably h = 2. As far as the number of crystallizers C(S(H» comprised in the crystallization sub-units UC<H) is concerned, it is preferred that independently for each H, 1 < s < 5, more preferably 1 < s < 4, more preferably 1 < s < 3, more preferably s = 1 or s = 2, more preferably s = 2.Further according to the present invention, the batch drum sub-unit UB comprises k batch drums B(i) wherein k is at least 2. Preferably, k > 3, more preferably k > 4. Therefore, preferred values of k are, for example, in the range of from 2 to 20 or in the range of from 3 to 15. More preferably, 4 < k < 10, more preferably 4 < k < 9, more preferably 4 < k < 8. Thus, 4 or 5 or 6 or 7 or 8 batch drums B(i) may be preferred.Regarding the controllable means MEC(H> for passing a stream from UD into LC(H) and for passing a stream from LC<H) to UD which are comprised in the stream transportation line LC(H), it is preferred that at least one of said controllable means MEC<H), preferably each of said controllable means MEC<H), comprises, preferably consists of a valve. Other controllable means, however, which attain the same object of either passing a stream from UD into LC(H) or for passing a stream from LC(H> to UD, depending on the status of the crystallization proceedings, are also conceivable.Regarding the crystallizers C(S(H», it is conceivable to employ any design thereof exhibiting a suitable heatable and coolable surface. However, it is preferred that at least one of the crystallizers C(S(H», preferably each crystallizer C(S(H» is configured as a shell-and-tube heat exchanger. In this regard, it is more preferred that said crystallizer C(S(H» is configured as a vertically mounted shell-and-tube heat exchanger which comprises an entry point for passing a heat transfer medium (HTM) into the shell and an exit point for removing the heat transfer medium from the shell.According to the present invention, it is still more preferred that at least one crystallization sub-unit UC<H), preferably each crystallization sub-unit UC<H) comprises at least 2 crystallizers C(S(H». which are arranged in series. According to this preferred design, a given crystallization sub-unit UC<H) further comprises a circular stream transportation line LC(H) which passes through the at least 2 crystallizers C(S(H». Further according to this design, a stream which is passed from the batch drum unit UB to a given stream transportation line LC(H) is transported from the respective entry and exit point EC<H) through the transportation line LC(H) to a first crystallizer C(S(H», is passed through said first crystallizer C(S(H» in which a first crystallization stage is carried out, and the remaining stream is then further transported through the transportation line LC<H) to a second crystallizer C(S(H», is passed through said second crystallizer C(S(H» in which a second crystallization stage is carried out, and the remaining stream is then furthertransported through the transportation line LC<H) to either one or more further crystallizer WC(S(H» before the finally remaining stream is removed through the transportation line LC(H) via the entry and exit point EC<H) from the crystallization sub-unit Uc(H). In this context, it is noted that it may be conceivable that a given entry and exit point EC(H) is configured as an entry point and, separately, an exit point.Further according to the present invention, it is preferred that at least one, preferably each crystallization sub-unit Uc(H) comprises controllable means MLC(H) for circulating a stream through LC(H). While there is no specific restriction concerning the design of said controllable means MLC(H), it is preferred that at least one of the controllable means MLC(H). preferably each controllable means MLC<H), comprises, preferably consists of a stream circulation pump. More preferably, said controllable means MLC(H) are arranged downstream of EC<H) and upstream C(S(H». Therefore, for the preferred case when a crystallization sub-unit comprises at least 2 crystallizers WC<S(H), it is preferred that said controllable means MLC(H) are arranged downstream of EC<H) and upstream of the first crystallizer CS(H». According to the present invention, it may be conceivable that more than one controllable means MLC(H) are comprised in a crystallization sub-unit Uc(H). It is preferred that a given crystallization sub-unit UC<H) comprises one controllable means MLC(H), more preferably one stream circulation pump.Preferably, at least one of the transportation lines LC<H), preferably each transportation line LC(H), is connected to at least one, preferably one expansion drum BEC<H). Such expansion drum BEC(H> was found to be advantageous to allow for compensating density changes during crystallization. More preferably, a given expansion drum BEC(H> is openly connected to a suitable off-gas system which may comprise, for example, a breather drum such as a cooled breather drum. According to the present, it may be advantageous to suitably install a level measurement in an expansion drum BEC(H), for example to determine the crystallization progress and / or control the temperature of a heating medium used during crystallization in a crystallizer C(S(H» configured as a shell-and-tube heat exchanger.Preferably, each crystallizer C(S(H» is completely filled with the feed stream for crystallization and does not comprise a gas phase. The at least one expansion drum BEC(H> may allow for maintaining each crystallizer C(S(H» being completely filled with the feed stream while the filling of the at least one expansion drum BEC(HJ may vary, for example due to being openly connected to a suitable off-gas system.Generally, every transportation line according to the present invention can be configured as an individual transportation line. However, it is also possible or may be even preferred that two or more transportation lines suitably share at least one common section.Generally, it is preferred that the crystallization unit UC<H) for carrying out an E-caprolactam crystallization process, said E-caprolactam crystallization process, and a method for controlling this process relate to melt crystallization, more preferably to layer melt crystallization, more preferably to solid layer crystallization or dynamic layercrystallization, and even more preferably to dynamic layer crystallization. Alternatively, or in addition thereto, static crystallization may be applied.In view of the above, a preferred crystallization unit of the present invention is a unit U wherein h = 2 and s = 2, and wherein the unit U comprises(1) two crystallization cycle sub-units Uci and Uc2, wherein(1.1) the first crystallization cycle sub-unit Uci comprises a first crystallizer Wci(1) and a second crystallizer Wci(2); a circular stream transportation line Lei passing through Wci(1) and Wci(2), comprising an entry and exit point Eci connected to the stream distribution sub-unit UD according to (3) and further comprising controllable means MLCI for circulating a stream through Lei, wherein Eci comprises controllable means MECI for passing a stream from UD into Lei and for passing a stream from Lei to UD;(1 .2) the second crystallization cycle sub-unit Uc2 comprises a first crystallizer Wc2(1) and a second crystallizer Wc2(2); a circular stream transportation line I_c2 passing through Wc2(1) and Wc2(2), comprising an entry and exit point Ec2 connected to the stream distribution sub-unit UD according to (3) and further comprising controllable means MLC2 for circulating a stream through I_c2, wherein Ec2 comprises controllable means MEC2 for passing a stream from UD into I_c2 and for passing a stream from LC2 to UD;(2) a batch drum sub-unit UB comprising k batch drums B(i) with i = 1 ...k and k > 4, wherein each batch drum B(i) is equipped with controllable means MB(I) for passing a stream from B(i) via the stream distribution sub-unit UD according to (3) to at least one of Eci and Ec2; a crude E-caprolactam feed stream transportation line Lso to at least one batch drum B(i);(3) a stream distribution sub-unit UD connecting UB, UCI and Uc2, the sub-unit UD comprising(3.1) for each drum B(i) with i = 1 ...k(3.1.1) at least one of a stage stream transportation line Lsi (i) from B(i) to Eci and a stage stream transportation line Ls2(i) from B(i) to Ec2, wherein Lsi (i) comprises at least one controllable means MLSI (I) for passing a stream from B(i) to Eci and Ls2(i) comprises at least one controllable means MLS2(I) for passing a stream from B(i) to Ec2;(3.1.2) at least one of a back stream transportation line LBI(I) from Eci to B(i) and a back stream transportation line LB2(I) from Ec2 to B(i), wherein LBI (i) comprises at least one controllable means MLBI (I) for passing a stream from Eci to B(i) and l_B2(i) comprises at least one controllable means MLB2(I) for passing a stream from Ec2 to B(i);(3.2) a final residue stream transportation line LRI for removing a final crystallization residue stream SRF from Lei via Eci, wherein LRI comprises at least one controllable means MLRI for removing said final residue stream from Lei;(3.3) a final fine product stream transportation line LF2 for removing a final fine crystallization product stream SPF from LC2 via Ec2, wherein LF2 comprises at least one controllable means MLF2 for removing said final fine product stream SPF from l_c2.Preferably, each crystallizer Wci(1 ), Wci(2), Wc2(1) and Wc2(2) is configured as a shell-and-tube heat exchanger, more preferably as a vertically mounted shell-and-tube heat exchanger, comprising an entry point for passing a heat transfer medium into the shell and an exit point for removing the heat transfer medium from the shell. Preferably, each controllable means MLCI and MLC2 comprises, more preferably consists of a stream circulation pump and each controllable means MECI and MEC2 comprises, preferably consists of a valve. Preferably, the controllable means MLCI are arranged downstream of Eci and upstream Wci(1 ), and the controllable means MLC2 are arranged downstream of EC2 and upstream Wc2(1). Preferably, each controllable means MLC(I) comprises a valve and a pump, preferably a valve and a pump arranged downstream of said valve. Preferably, the transportation line Lei is connected to an expansion drum BECI which is preferably arranged downstream of Wci(1) and upstream of Wci(2), and the transportation I_c2 is connected an expansion drum BEC2 which is preferably arranged downstream of Wc2(1) and upstream of Wc2(2).Preferably, the batch drum sub-unit UB further comprises, for at least one of the batch drums B(i), preferably for all batch drums B(i), a back mixing transportation line LMB(I) equipped with controllable means MLMB(I) for passing a stream from B(i) via MB(I) back into B(i).Preferably, each controllable means MECI, MEC2, MLSI(I), MLS2(I), MLBI(I), MLB2(I), MLMB(I), MLRI, and MLF2 comprises, more preferably consists of a valve.In addition to the k batch drums B(i) of the batch drum sub-unit UB, the crystallization unit U of the present invention preferably comprises a final crystallization residue batch drum BR which is equipped with controllable means MR for passing a stream from BR to a further use, wherein said batch drum BR is connected to the transportation line LRI . Further in addition to the k batch drums B(i) of the batch drum sub-unit UB, the crystallization unit U of the present invention preferably comprises a final crystallization fine product batch drum BF equipped with controllable means MF for passing a stream from BF to a further use, wherein said batch drum BF is connected to the transportation line LF2. More preferably, at least one of the controllable means MR and MF, more preferably each of the controllable means MR and MF comprises, more preferably consists of a valve.According to the present invention, it may be conceivable that downstream of the controllable means MF, a static crystallization sub-unit USCR is arranged, wherein it may be preferred that at least a part of what is removed from the final crystallization fine product batch drum BF is subjected to further crystallization.In particular in order to avoid encrusting and / or blocking issues in the course of the crystallization process, it is preferred that the parts of the crystallization unit of the present invention which come and / or may come into contact with streams and / or mixtures comprising E-caprolactam are heatable to temperatures of at least the melting point of caprolactam. In terms of controlling said temperature, a respective part of the crystallization unit may be equipped with one or more suitable temperature sensors. More preferably, at least one, more preferably each controllable means, each batch drum B(i) and each transportation line is configured to be heatable to a temperature of at least 50 °C, preferably at least 60 °C, more preferably at least 70 °C, the crystallization unit U further comprising means MH for heating each controllable means, each batch drum B(i) and each transportation line. More preferred respective temperature ranges are from 70 to 90 °C or from 70 to 80 °C.Preferably according to the present invention, the crude E-caprolactam feed stream transportation line Lso comprises, upstream of the at least one batch drum B(i), an analytical unit UA for analysing a crude E-caprolactam feed stream So to be passed into B(i) with respect to at least one crude E-caprolactam feed quality parameter selected from the group consisting of an E-caprolactam purity QGC(SO), an APHA value QAPHA(SO), a permanganate absorption number QPAN(SO), and an UV absorption Quv(So). Depending on the results of the analysis carried out in UA in view of the desired characteristics of E-caprolactam obtained as final fine product stream, the crystallization process of the present invention is controlled according to the present invention as described herein. Therefore, according to the present invention, it is particularly preferred that the crystallization unit U further comprising a control sub-unit UDP which, more preferably, comprises a computer-supported control system for controlling at least one controllable means, preferably all controllable means.Generally, the crystallization unit according to the present invention may be operated as a stand-alone unit. Preferably, however, the crystallization unit of the present is part of (comprised in) a plant PDP for depolymerization of polyamide 6 and purification of E-caprolactam obtained from said depolymerization. While there are no specific restrictions regarding such a plant with the sole proviso that directly upstream of the crystallization unit U, a crude E- caprolactam is provided which can be subjected to crystallization in U, it is preferred that the plant PDP comprises a melting and mixing unit for preparing a depolymerization mixture from a solid material M comprising polyamide, the material M preferably being a waste material, more preferably a textile waste material and / or an engineering plastic waste material, the melting and mixing unit being arranged upstream of a preferably hydrolytic depolymerization unit for depolymerizing polyamide 6 comprised in said depolymerization mixture, the depolymerization unit being arranged upstream of a purification unit for purifying E-caprolactam obtained from said depolymerization unit, the purification unit comprising at least one ofone or more water separation units, one or more high boiler separation units for separating organic compounds from E-caprolactam having a higher boiling point than E-caprolactam, and one or more distillation units.More preferably, said purification unit is arranged upstream of the crystallization unit U, wherein more preferably, the crystallization unit U is the downstream-most unit of said plant PDP.Therefore, the present invention also relates to a plant PDP for depolymerization of polyamide 6 and purification of E- caprolactam obtained from said depolymerization, said plant PDP comprising the crystallization unit U according to the present invention, and further comprising a melting and mixing unit, preferably a melting unit UM and a pre-reaction mixing unit UPR, for preparing a depolymerization mixture from a solid material M comprising polyamide 6, the material M preferably being a waste material, more preferably a textile waste material and / or an engineering plastic waste material, the melting and mixing unit being arranged upstream of a preferably hydrolytic depolymerization unit UR for depolymerizing polyamide 6 comprised in said depolymerization mixture, the depolymerization unit being arranged upstream of a purification unit UP for purifying E-caprolactam obtained from said depolymerization unit, the purification unit comprising at least one of one or more water separation units Uws, one or more high boiler separation units Ui for separating organic compounds fromE-caprolactam having a higher boiling point than E-caprolactam, and one or more distillation units UDI; optionally a chemical treatment unit UOD; wherein said purification unit UP is preferably arranged upstream of the crystallization unit U, wherein more preferably, the crystallization unit U is the downstream-most unit of said plant PDP.Optionally or preferably, said plant PDP is part of (comprised in) an integrated polyamide 6 plant Pi which comprises said plant PDP and which further comprises a polyamide 6 production plant PPA. Said integrated plant Pi further comprises a transportation line LCPL for passing purified E-caprolactam from PDP to PPA and preferably a transportation line Ls for passing an aqueous recycle stream from PPA to PDP.Therefore, the present invention also relates to an integrated polyamide 6 plant Pi which comprises the plant PDP as described above and which further comprises a polyamide 6 production plant PPA, said integrated plant Pi further comprising a transportation line LCPL for passing purified E-caprolactam from PDP to PPA and preferably a transportation line Ls for passing an aqueous recycle stream from PPA to PDP.Crystallization process carried out in the crystallization unit UThe present invention also relates to an E-caprolactam crystallization process which is carried out in the crystallization unit as described herein, wherein the process comprises(i) providing a liquid crude feed stream So comprising E-caprolactam, wherein So has a temperature of at most 70 °C and exhibits an E-caprolactam purity QGC(SO), an APHA value QAPHA(SO), a permanganate absorption number QPAN(SO) and a UV absorption Quv(So);(ii) passing the stream So into a batch drum B(i), 1 < I < k, wherein k is preferably in the range of from 2 to 20;(iii) subjecting the content of the batch drum B(i) to crystallization comprising n crystallization stages P(x) carried out in at least one sub-unit UC<H) with 1 < n < (k-i+1) and x = 1 ...n, wherein n is preferably in the range of from 1 to 41 , and further comprising m crystallization stages C(y) carried out in at least one sub-unit UC<HI) with0 < m < (i-1) and y = 1...m for m > 0, wherein H1 A H2, wherein m is preferably in the range of from 1 to 19; (iii.1 ) wherein a crystallization stage P(x) comprises(iii.1.1) passing a stage stream Ss(x+i-1) comprising at least a part of the content of a batch drumB(x+i-1 ) from said batch drum B(x+i-1 ) via the transportation line LS(H2)(X-H-1 ) and the entry and exit point EC<H2) into the transportation line LC(H2>;(iii.1.2) passing the stream Ss(x+i-1) through the transportation line LC<H2) with the means MLC<H2), thereby passing through the at least one crystallizer Wc(s(H2», wherein in Wc(s(H2», e- caprolactam comprised in Ss(x+i-1 ) crystallizes and remains as crystallized solid in Wc(s(H2»;(iii.1.3) removing a residue stream SR(X-H-1) from the transportation line Lc(H2) via EC<H2), wherein the stream SR(X-H-1 ) is depleted in E-caprolactam compared to the stream Ss(x+i-1 ); and(1.3.1) passing the stream SR(X-H-1) via the transportation line LR<H3) as final residue stream SRF via MLR(H3> to optional further use; or(1 .3.2) passing the stream SR(X-H-1 ) via the transportation line LB(H2)(X+I-2) into the batch drum B(x+i-2);(iii.1.4) transferring the crystallized solid in Wc(s(H2» into a liquid product stream Sp(x+i-1), said transferring into a liquid product stream preferably comprising heating the crystallized solid to a temperature of at least the melting point of the crystallized solid;(iii.1.5) removing the stream Sp(x+i-1) from the transportation line LC<H2) via EC<H2), wherein the stream Sp(x+i-1 ) is concentrated in E-caprolactam compared to the stream Ss(x+i-1 ), and(1.5.1) passing the stream Sp(x+i-1) via the transportation line LF<H4) as final E- caprolactam fine product stream SPF via MLF<H4) to further use; or(1 .5.2) passing the stream Sp(x+i-1 ) via the transportation line LB(H2)(X-H) into the batch drum B(x+i);(iii.2) wherein a crystallization stage C(y) comprises(iii.2.1 ) passing a stage stream Ss(i-y) comprising at least a part of the content of a batch drumB(i-y) from said batch drum B(i-y) via the transportation line Ls(Hi)(i-y) and the entry and exit point EC(HIJ into the transportation line LC(HI>;(111.2.2) passing the stream Ss(i-y) through the transportation line LC(HI) with the means MC<HI), thereby passing through the at least one crystallizer WC(S(HI», wherein in WC(S(HI», e- caprolactam comprised in Ss(i-y) crystallizes and remains as crystallized solid in WC(S(HI»;(111.2.3) removing a residue stream SR(i-y) from the transportation line LC(HI), wherein the stream SR(i-y) is depleted in E-caprolactam compared to the stream Ss(i-y); and(2.3.1) passing the stream SR(i-y) via the transportation line LR<H3> as final residue stream SRF via MLR(H3> to optional further use; or(2.3.2) passing the stream SR(i-y) via the transportation line LB<Hi)(i-y-1 ) into the batch drum B(i-y-1);(111.2.4) transferring the crystallized solid in WC(S(HI» into a liquid product stream Sp(i-y);(111.2.5) removing the stream Sp(i-y) from the transportation line LC(HI> via EC<HI), wherein the stream Sp(i-y) is concentrated in E-caprolactam compared to the stream Ss(i-y), and passing the stream Sp(i-y) via the transportation line l_B(Hi)(i-y+1 ) into the batch drum B(i-y+1).As far as the crystallization process carried out in a preferred crystallization unit of the present invention as described herein is concerned, such process comprises(I) providing a liquid crude feed stream So comprising E-caprolactam, wherein So has a temperature of at most 70 °C and exhibits an E-caprolactam purity QGC(SO), an APHA value QAPHA(SO), a permanganate absorption number QPAN(SO) and a UV absorption Quv(So);(ii) passing the stream So into a batch drum B(i), 1 < I < k, wherein k is preferably in the range of from 2 to 20;(ill) subjecting the content of the batch drum B(i) to crystallization comprising n crystallization stages P(x) carried out in Uc2 with 1 < n < (k-i+1) and x = 1 ...n, wherein n is preferably in the range of from 1 to 41, and further comprising m crystallization stages C(y) carried out in Uci with 0 < m < (i-1) and y = 1 ...m for m > 0, wherein m is preferably in the range of from 1 to 19;(ill.1 ) wherein a crystallization stage P(x) comprises(ill.1.1) passing a stage stream Ss(x+i-1) comprising at least a part of the content of a batch drum B(x+i-1) from said batch drum B(x+i-1) via the transportation line Ls2(x+i-1) and the entry and exit point Ec2 into the circular stream transportation line I_c2;(ill.1.2) passing the stream Ss(x+i-1) through the circular transportation line I_c2 with the means MLC2, thereby passing through the first crystallizer Wc2(1) and the second crystallizer Wc2(2), wherein in Wc2(1) and Wc2(2), E-caprolactam comprised in Ss(x+i-1 ) crystallizes and remains as crystallized solid in Wc2(1) and Wc2(2);(ill.1.3) removing a residue stream SR(X+I-1 ) from the transportation line Lc2 via Ec2, wherein the stream SR(X+I-1 ) is depleted in E-caprolactam compared to the stream Ss(x+i-1 ); and(1.3.1) passing the stream SR(X-H-1) via the transportation line LRI as final residue stream SRF via MLRI to optional further use; or(1 .3.2) passing the stream SR(X+I-1 ) via the transportation line LB2(X-H-2) into the batch drum B(x+i-2);(ill.1.4) transferring the crystallized solid in Wc?(1) and Wc2(2) into a liquid product stream Sp(x+i-1);(ill.1.5) removing the stream Sp(x+i-1) from the transportation line I_c2 via Ec2, wherein the streamSp(x+i-1 ) is concentrated in E-caprolactam compared to the stream Ss(x+i-1 ), and(1.5.1) passing the stream Sp(x+i-1) via the transportation line LF2 as final E-caprolactam fine product stream SPF via MLF2 to further use; or(1 .5.2) passing the stream Sp(x+i-1 ) via the transportation line l_B2(x+i) into the batch drum B(x+i);(ill.2) wherein a crystallization stage C(y) comprises(111.2.1) passing a stage stream Ss(i-y) comprising at least a part of the content of a batch drum B(i-y) from said batch drum B(i-y) via the transportation line Lsi(i-y) and the entry and exit point Eci into the circular stream transportation line Lei;(111.2.2) passing the stream Ss(i-y) through the circular transportation line Lei with the means MLCI , thereby passing through the first crystallizer Wci(1) and the second crystallizer Wci(2), wherein in Wci(1) and Wci(2), E-caprolactam comprised in Ss(i-y) crystallizes and remains as crystallized solid in Wci(1) and Wci(2);(111.2.3) removing a residue stream SR(i-y) from the transportation line Lei, wherein the stream SR(i-y) is depleted in E-caprolactam compared to the stream Ss(i-y); and(2.3.1) passing the stream SR(i-y) via the transportation line LRI as final residue stream SRF via MLRI to optional further use; or(2.3.2) passing the stream SR(i-y) via the transportation line LBi(i-y-1 ) into the batch drum B(i-y-1);(111.2.4) transferring the crystallized solid in Wci(1) and Wci(2) into a liquid product stream Sp(i-y);(111.2.5) removing the stream Sp(i-y) from the transportation line Lei via Eci, wherein the stream Sp(i-y) is concentrated in E-caprolactam compared to the stream Ss(i-y), and passing the stream Sp(i-y) via the transportation line l_Bi(i-y+1 ) into the batch drum B(i-y+1).More preferably, m is in the range of from 1 to 15, more preferably in the range of from 2 to 10, more preferably in the range of from 3 to 9. Independent thereof, more preferably, n is in the range of from 1 to 31, more preferably in the range of from 3 to 26, more preferably in the range of from 3 to 21 .For a crystallization process which is carried out in a specific crystallization unit according to the present invention, the Figure 1 of the present invention and the respective description of the Figure 1 herein further illustrate the overall process concept.Prior to step (ii) of passing the stream So into a batch drum B(i), it is preferred that each controllable means, each batch drum B(i) and each transportation line, independently of each other, is heated to a temperature of at least 50 °C, preferably of at least 60 °C, preferably to a temperature of at least 70 °C, more preferably to a temperature in the range of from 70 to 90 °C, more preferably in the range of from 70 to 80 °C, via the means MH which are described herein in the context of the crystallization unit U.Preferably according to the present invention, each crystallization stage P(x) according to (ill.1 ) is characterized by a freezing ratio F(P(x)) and wherein, independently of each other, each freezing ratio F(P(x)) is at least 0.4, preferably at least 0.45, more preferably at least 0.5, more preferably at least 0.55, more preferably at least 0.60, more preferably at least 0.65. The freezing ratio F(P(x)) is defined asF(P(x)) = m(SP(x+i-1)) I m(Ss(x+i-1)) wherein m(Sp(x+i-1)) is the mass of the liquid product stream Sp(x+i-1) according to (ill.1.4) and m(Ss(x+i-1)) is the mass of the stage stream Ss(x+i-1) according to (ill.1.1).Further preferably according to the present invention, each crystallization stage C(y) according to (ill.2) is characterized by a freezing ratio F(C(y)) and wherein, independently of each other, each freezing ratio F(C(y)) is at least 0.4, preferably at least 0.45, more preferably at least 0.5, more preferably at least 0.55, more preferably at least 0.60, more preferably at least 0.65. The freezing ratio F(C(y)) is defined asF(C(y)) = m(Sp(i-y)) / m(Ss(i-y)) wherein m(Sp(i-y)) is the mass of the liquid product stream Sp(i-y) according to (ill.2.4) and m(Ss(i-y)) is the mass of the stage stream Ss(i-y) according to (iii.2.1).Yet further preferably according to the present invention, each crystallization stage P(x) according to (ill.1 ) is characterized by a freezing ratio F(P(x)) and wherein, independently of each other, each freezing ratio F(P(x)) is at least 0.4, preferably at least 0.45, more preferably at least 0.5, more preferably at least 0.55, more preferably at least 0.60, more preferably at least 0.65, and each crystallization stage C(y) according to (ill.2) is characterized by a freezing ratio F(C(y)) and wherein, independently of each other, each freezing ratio F(C(y)) is at least 0.4, preferably at least 0.45, more preferably at least 0.5, more preferably at least 0.55, more preferably at least 0.60, more preferably at least 0.65.Preferably according to the present invention, each crystallization stage P(x) according to (ill.1 ) is characterized by an effective distribution coefficient D(P(x)) and wherein, independently of each other, each effective distributioncoefficient D(P(x)) is in the range of from 0.1 to 0.8, preferably in the range of from 0.2 to 0.7, more preferably in the range of from 0.3 to 0.6. The effective distribution coefficient D(P(x)) is defined asD(P(x)) = CIM(SP(X+I-1 )) I CIM(SS(X+I-1 )) wherein CIM(SS(X+I-1)) is the concentration of impurities contained in the stage stream Ss(x+i-1) according to (ill.1.1) and CIM(SP(X+I-1)) is the concentration of impurities, determined via GC as described in Reference Example 1.1 herein, contained in the product stream Sp(x+i-1) according to (ill.1.4), wherein the term "impurity” refers to any chemical compound other than E-caprolactam. Further preferred ranges of D(P(x)) may be from 0.35 to 0.55, from 0.35 to 0.50, or from 0.35 to 0.45.Further preferably according to the present invention, each crystallization stage C(y) according to (ill.2) is characterized by an effective distribution coefficient D(C(y)) and wherein, independently of each other, each effective distribution coefficient D(C(y)) is in the range of from 0.1 to 0.8, preferably in the range of from 0.2 to 0.7, more preferably in the range of from 0.3 to 0.6. The effective distribution coefficient D(C(y)) is defined asD(C(y)) = CiM(SP(i-y)) I CiM(Ss(i-y)) wherein CiM(Ss(i-y)) is the concentration of impurities, determined via GC as described in Reference Example 1.1 herein, contained in the stage stream Ss(i-y) according to (ill.2.1) and CiM(Sp(i-y)) is the concentration of impurities contained in the product stream Sp(i-y) according to (ill.2.4), wherein the term "impurity” refers to any chemical compound other than E-caprolactam. Further preferred ranges of D(C(y)) may be from 0.35 to 0.55, from 0.35 to 0.50, or from 0.35 to 0.45.The concentration of impurities contained in the product stream, preferably for the determination of effective distribution coefficient D as outlined above, may generally be determined via GC as indicated above, and also via the APHA color, PAN values, or UV / Vis absorption values, said values preferably determined as described in Reference Example 1 herein.The concentration of impurities contained in the product stream may preferably be determined via the APHA color, more preferably via the APHA color was determined in accordance with ISO 8112. The determination of the APHA color is also illustrated in Reference Example 1 herein.The concentration of impurities contained in the product stream may preferably be determined via PAN values, more preferably via the PAN values determined in accordance with DIN ISO 8660.The concentration of impurities contained in the product stream may preferably be determined via UV / Vis absorption values, more preferably via the UV / Vis absorption values determined at a wavelength of 290 nm in accordance with DIN ISO 7059.Yet further preferably according to the present invention, each crystallization stage P(x) according to (ill.1 ) is characterized by an effective distribution coefficient D(P(x)) and wherein, independently of each other, each effective distribution coefficient D(P(x)) is in the range of from 0.1 to 0.8, preferably in the range of from 0.2 to 0.7, more preferably in the range of from 0.3 to 0.6, and each crystallization stage C(y) according to (ill.2) is characterized by an effective distribution coefficient D(C(y)) and wherein, independently of each other, each effective distribution coefficient D(C(y)) is in the range of from 0.1 to 0.8, preferably in the range of from 0.2 to 0.7, more preferably in the range of from 0.3 to 0.6.According to (ill.1.4) of the process of the present invention, the crystallized solid is transferred into a liquid product stream Sp(x+i-1 ). Preferably, said transferring of the crystallized solid into a liquid product stream comprises (ill.1.4.1) increasing the temperature of the crystallized solid in Wc(s(H2» close to the melting point of pure E- caprolactam, obtaining a further residue stream SR(X+I-1 ), and removing said further residue stream SR(X+I-1 ) from the transportation line LC<H2) via Ec(H2) according to (ill.1.3);(ill.1.4.2) transferring the remaining crystallized solid in Wc(s(H2» into a liquid product stream Sp(x+i-1 ).According to a preferred process of the present invention described herein, said transferring of the crystallized solid into a liquid product stream according to (ill.1.4) preferably comprises(ill.1.4.1) increasing the temperature of the crystallized solid in at least one of Wc2(1) and Wc2(2), preferably in Wc2(1) and Wc2(2), close to the melting point of pure E-caprolactam, obtaining a further residue stream SR(X+I-1 ), and removing said further residue stream SR(X+I-1 ) from the transportation line I_c2 via Ec2 according to (ill.1.3);(ill.1.4.2) transferring the remaining crystallized solid in Wc2(1) and Wc2(2) into a liquid product stream Sp(x+i-1 ).According to (ill.2.4) of the process of the present invention, the crystallized solid is transferred into a liquid product stream Sp(i-y). Preferably, said transferring of the crystallized solid into a liquid product stream comprises(111.2.4.1) increasing the temperature of the crystallized solid in WC(S(HI» close to the melting point of pure E- caprolactam, obtaining a further residue stream Sp(i-y), and removing said further residue stream Sp(i-y) from the transportation line LC(HI) via EC<HI) according to (ill.2.3);(111.2.4.2) transferring the remaining crystallized solid in WC(S(HI» into a liquid product stream Sp(i-y).According to a preferred process of the present invention described herein, said transferring of the crystallized solid into a liquid product stream according to (ill.2.4) preferably comprises(111.2.4.1) increasing the temperature of the crystallized solid in at least one of Wci(1) and Wci(2), preferably in Wci(1) and Wci(2), close to the melting point of pure E-caprolactam, obtaining a further residue stream SR(i-y), and removing said further residue stream SR(i-y) from the transportation line Lei via Eci according to (iii.2.3);(111.2.4.2) transferring the remaining crystallized solid in Wci(1) and Wci(2) into a liquid product stream Sp(i-y).Generally, there are no specific restrictions how the liquid crude feed stream So comprising E-caprolactam according to (I) is provided. However, it is particularly preferred that providing the liquid crude feed stream So comprising E-caprolactam according to (I) comprises(1.1) providing a stream SM comprising a solid material M comprising polyamide 6;(1.2) preparing an aqueous depolymerization mixture based on the stream SM provided according to (1.1);(1.3) subjecting the depolymerization mixture prepared according to (1.2) to polyamide 6 depolymerization conditions in a reaction unit UR, obtaining a liquid aqueous stream S comprising E-caprolactam dissolved in water at a concentration CSR, the stream SR further comprising one or more impurities;(1.4) passing the aqueous stream SR into a purification unit UP, obtaining from the stream SR the stream So comprising E-caprolactam at a concentration co with co » CR.Also preferably, the stream So provided according to (I) is obtainable or obtained by a method comprising(1.1) providing a stream SM comprising a solid material M comprising polyamide 6;(1.2) preparing an aqueous depolymerization mixture based on the stream SM provided according to (1.1);(1.3) subjecting the depolymerization mixture prepared according to (1.2) to polyamide 6 depolymerization conditions in a reaction unit UR, obtaining a liquid aqueous stream SR comprising E-caprolactam dissolved in water at a concentration CSR, the stream SR further comprising one or more impurities;(1.4) passing the aqueous stream SR into a purification unit UP, obtaining from the stream SR the stream So comprising E-caprolactam at a concentration co with co »> CR.The process of the present invention and the crystallization unit of the present invention, due to their flexibility in choosing, for example, a suitable batch drum B(i) into which the stream So is passed and a suitable number of crystallization stages P(x) and C(y), respectively, exhibit unique characteristics in particular for streams So which are not entirely predictable in terms of their chemical composition. Such streams So are, further in particular, obtained from recycling streams which, due to uncertainty which recycling feedstock is used, may lead to streams So varying in chemical composition. Therefore, it is particularly preferred according to the present invention that the solid material M comprised in the stream SM provided according to (1.1) comprises, more preferably consists of, a waste material, wherein said waste material more preferably comprises, more preferably consists of, one or more of at least one textile waste material and at least one engineering plastics waste material, more preferably comprises, more preferably consists of at least one textile waste material. Preferably from 10 to 99 weight-%, more preferably from 30 to 98.5 weight-%, more preferably from 50 to 98 weight-%, more preferably from 80 to 98 weight-%, of the solidmaterial M consist of polyamide 6, wherein, in addition to polyamide 6, the solid material M preferably comprises one or more further organic polymeric compounds, more preferably including, but not limited to, one or more of at least one elastane; at least one polyamide 6.6; at least one semiaromatic polyamide including one or more of polyamide 6T and polyamide 61; at least one polyethylene terephthalate; at least one polyurethane; at least one polyester; at least one polyether; at least one polyvinyl chloride; at least one natural fiber material such as wool and cotton; at least one cellulose material; at least one natural elastomer; at least one synthetic elastomer; at least one copolymer of two or more of said polymeric compounds including statistical copolymers, gradient copolymers, alternating copolymers, block copolymers, and graft copolymers; and at least one rubber material comprising one or more of at least one natural rubber material and at least one synthetic rubber material.Prior to being provided to the process of the present invention, the waste material can be suitably sorted. In this regard, it is possible to spread the collected textile waste material on a conveyor, which spreading can be carried out either manually and / or mechanically. Thereafter, the respectively spread textile waste material is subjected to sorting, either by composition and / or by color. Sorting can be carried out either manually and / or optically. If carried out optically, the sorting preferably comprises an infrared sorting, more preferably a near-infrared sorting and / or a midinfrared sorting. Optionally, prior to sorting, the textile waste material can be subjected to a suitable metal removing step. If a metal removing step is carried out, ferrous elements are preferably separated, for example by suitable magnetic means, and / or non-ferrous elements are preferably separated, for example by suitable eddy current separating means. After said sorting, the respectively obtained textile waste material can be subjected to a further treatment, such as cutting and / or milling.Generally, the solid material M can be provided according to any suitable method. Preferably according to the present invention, providing the solid material M comprises providing the solid material M in a delivering unit which preferably comprises one or more of at least one big bag station and at least one a bulk container station; passing the provided solid material M via a first connecting line from the delivering unit to a material collecting unit, preferably a collecting drum, wherein the first connecting line preferably comprises one or more of at least one material receiving and discharge unit, at least one first material feeding unit, and at least one first particle separation unit U; passing the solid material M from the material collecting unit via a second connecting line to a melting unit UM as described herein, wherein the second connecting line preferably comprises one or more of at least one second material feeding unit, at least one second particle separation unit, and at least one metal detector.Preferably, the solid material M may be provided in the form of granules, wherein the particle size distribution of said granules is preferably characterized by one or more of the following pairs of values, preferably by two or more of the following pairs of values, more preferably by the following three pairs of values: a D10 value of the particle width in the range of from in the range of from 0.1 to 15 mm and a D10 value of the particle length in the range of from 0.3 to 15 mm;a D50 value of the particle width in the range of from in the range of from 0.2 to 20 mm and a D50 value of the particle length in the range of from 0.5 to 20 mm; a D90 value of the particle width in the range of from in the range of from 0.3 to 30 mm and a D90 value of the particle length in the range of from 0.8 to 30 mm.Generally, the aqueous depolymerisation mixture according to (i .2) can be prepared according to any method.Preferably, preparing the aqueous depolymerization mixture according to (i.2) comprises melting in a melting unit UM the solid material M, obtaining the liquid stream SM having a temperature TSM at a pressure PSM; admixing in a prereaction unit UPR the stream SM with an aqueous stream Sw having a temperature Tsw at a pressure psw, obtaining a liquid reaction feed stream SF having a temperature TSF at a pressure PSF; feeding the stream SF obtained according to as the depolymerization mixture into the chemical reaction unit UR. AS far as this process design is concerned, it is preferred that0.8 < TSF / TD 1 .05 and 0.9 < PSF / PD 1 .05;0.6 < TSM / TSF 1.2 and 0.9 < PSM / PSF 1.05; and0.8 — TSW / TSF — 1.2 and 0.9 — psw / psF — 1 .05.The pre-reaction unit UPR preferably comprises, more preferably consists of, a mixing unit, preferably a static mixing unit, and wherein the melting unit UM comprises, preferably consists of an extruder, preferably a single-screw extruder or a twin-screw extruder. Further, it is preferred that Sw and SM are admixed in UPR at a mixing ratio (mw / kg) I (mp / kg) in the range of from 1 : 1 to 20:1 , more preferably in the range of from 2:1 to 15:1 , more preferably in the range of from 5: 1 to 10:1 , wherein mw is the amount of water comprised in Sw and mp is the amount of polyamide 6 comprised in SM.As far as the hydrolytic depolymerization according to the present invention is concerned, it is preferred that the depolymerization pressure PD in the unit UR is in the range of from 40 to 140 bar, more preferably in the range of from 40 to 125 bar, more preferably in the range of from 40 to 110 bar; and the depolymerisation temperature TD in the unit UR is in the range of from 230 to 335 °C, more preferably in the range of from 250 to 320 °C, more preferably in the range of from 270 to 310 °C.Preferably, the reaction unit UR comprises z chemical reactors R, i=1 ...z, wherein z is in the range of from 1 to 10, preferably in the range of from 1 to 8, more preferably in the range of from 1 to 6, more preferably in the range of from 1 to 5, more preferably in the range of from 1 to 4, more preferably in the range of from 1 to 3. If z > 1 , is preferred that at least 2 reactors R, more preferably all z reactors R, are serially coupled, wherein the stream SF is fed into R, with i = 1 ; an aqueous liquid stream Si containing E-caprolactam dissolved in water is removed from reactor R and fed into the reactor +i, with i < z;the aqueous liquid stream Szcontaining E-caprolactam dissolved in water is removed from the reactor Rzas the stream SR; wherein in every reactor R, a depolymerization temperature TDI at a depolymerization pressure PDI is maintained, wherein, independently of each other, TDI is in the range of from 230 to 330 °C and PDI is in the range of from 40 to 140 bar, preferably wherein TDI is in the range of from 250 to 320 °C and PDI is in the range of from 40 to 125 bar, more preferably wherein TDI is in the range of from 270 to 310 °C and PDI is in the range of from 40 to 110 bar. For z > 1, it is preferred that the z reactors R are vertically arranged, with Ri being the top-most reactor and Rzbeing the bottom-most reactor, wherein Si obtained from Rj is transferred to Ri+i by gravity, preferably by gravity only. More preferably, at least 1, preferably all z reactors R, are continuous stirred tank reactors (CSTR). Preferably, every continuous stirred tank reactor R has, independently from each other, from 2 to 6 compartments, more preferably from 2 to 5 compartments, more preferably from 2 to 4 compartments, said compartments preferably being serially, more preferably being serially and vertically arranged, wherein 2 adjacent compartments are separated by a divider which comprises at least one flow-through opening. Preferably at least one compartment comprised in a reactor R comprises at least one agitator, wherein more preferably every compartment of every reactor R comprises at least one agitator, wherein more preferably, every compartment of every reactor R comprises one agitator, and the process comprises agitating the depolymerization mixture in a given compartment for at least part of the time during subjecting to depolymerization conditions in said compartment. Preferably, the polyamide 6 depolymerization conditions further comprise a total residence time to of the aqueous depolymerization mixture in the unit U , preferably in the z reactors R, more preferably in the z continuous stirred tank reactors, wherein at least 85 weight- %, preferably at least 90 weight-%, more preferably at least 95 weight-% of the aqueous depolymerization mixture have a to in the range of from 30 to 90 min. More preferably, the residence time of an aqueous depolymerization mixture in a reactor R is toi and 0.90 < (tra I bi+i) 1 .10, more preferably 0.95 < (toi I toi+i) 1 .05.If the solid material M comprises one or more elastanes, the aqueous liquid stream SR obtained from the depolymerization reaction usually contains one or more decomposition products which are formed from the one or more elastanes, for example in the course of the depolymerization reaction in UR. Additionally or alternatively, one or more decomposition products form the one or more elastanes may also be formed in the melting unit UM which is described above. By way of example, said one or more decomposition products from the one or more elastanes preferably include at least one of aniline, butanediol, butanediol oligomers including, for example, butandediol dimer and butanediol trimer, and 4,4’-methylenedi ani line (MDA) and isomers thereof such as 2, 4'-methy lenedianil ine and 2,2'-methylenedianiline.Preferably according to the present invention, the purification unit UP according to (1.4) comprises a water separation unit Uws and a distillation unit UDI, and the process preferably comprises feeding the stream SR to Uws, obtaining from Uws a stream Sws comprising E-caprolactam at a concentration cws, feeding the stream Sws to the distillation unit UDI, obtaining from UDI the stream So comprising E-caprolactam at a concentration co, wherein CR < cws «< co.The symbol “«<” compared to the symbol “<” indicates that, for example, the ratio cws I CR is significantly lower than the ratio co I cws.Further preferably, the water separation unit Uws comprises at least two water separation sub-units Uwsi and Uws2, preferably two serially coupled water separation sub-units Uwsi and Uws2, wherein the stream S is fed into Uwsi, wherein downstream of Uwsi and upstream of Uws2, a separation unit Ui is preferably located, the process comprising obtaining from Uwsi an aqueous stream Swsi, feeding the stream Swsi into the separation unit Ui, obtaining from Ui an aqueous stream Si, and feeding the stream Si into the unit Uws2, wherein in Ui, one or more of impurities are separated from Swsi, thereby obtaining from Ui an impurity stream Si, said impurities preferably comprising at least one impurity comprised in SR, wherein at least one of said impurities is an organic compound having a higher boiling point than E-caprolactam, the separation unit Ui being a high boiler separation unit.With regard to the specific apparatus design of the sub-unit Uwsi and sub-unit Uws2, it is preferred that the sub-unit Uwsi comprises one or more of a falling film evaporator, a flash tank, a forced circulation evaporator, and a distillation column, more preferably one or more of a falling film evaporator and a flash tank, more preferably a falling film evaporator and a flash tank, and that the sub-unit Uws2 comprises one or more of a falling film evaporator, a flash tank and a distillation column, more preferably a distillation column.As far as the high boiler separation unit Ui is concerned, no specific restrictions exist provided that in said unit Ui, compounds can be at least partially separated which have a higher boiling point than E-caprolactam. It was found that the waste material which are most preferably used as the solid material M will contain certain compounds which, either prior to or after depolymerization of polyamide 6, lead to a stream comprising E-caprolactam and compounds having a higher boiling point than E-caprolactam. Due to possibly different chemical compositions of said waste material, however, these compounds having a higher boiling point than E-caprolactam will usually differ from time to time, both with regard to the content in the stream to be purified and in chemical nature. Regarding the chemical nature of the high boiler compounds, a comparatively high uncertainty exists, simply in view of the unpredictable chemical composition of the materials subjected to depolymerization and, finally, high boiler separation according to the present invention. However, when developing the process of the present invention, numerous elaborate experiments were carried out, and it was found that in a majority of situations, the one or more compounds comprised in the stream Swsi preferably comprise at least one of at least one aromatic amine which includes at least one of an aromatic monoamine, an aromatic diamine, an aromatic triamine and an aromatic tetramine; at least one aliphatic amine which includes at least one of an aliphatic monoamine, an aliphatic diamine and an aliphatic triamine; at least one aliphatic amide; at least one aromatic alcohol which includes at least one of an aromatic monool and an aromatic diol; at least one aliphatic alcohol which includes at least one of an aliphatic monool and an aliphatic diol;at least one aromatic acid; at least one and aliphatic acid; at least one E-caprolactam oligomer; at least other compound selected from the group consisting of one or more cleavage products of dyes such as optionally chlorinated aromatic diamines, one or more water-soluble oligomeric cellulose cleavage products, and one or more water-soluble oligomers of terephthalic acid and hexamethylenediamine.Yet further, it was found that the at least one aromatic amine preferably includes one or more of 4, 4'-methylenedi anil! ne (MDA), isomers thereof such as 2,4’-methylenedianiline and 2,2’-methylenedianiline, and polymethylen polyphenylen polyamines (pMDA); the at least one aliphatic amine and the at least one aliphatic amide preferably include one or more of hexamethylenediamine adipate, 6-aminocaproic acid and oligomers thereof, including 6-aminocaproic acid dimer and higher oligomers such as 6-aminocaproic acid trimer, 6-aminocaproic acid tetramer, 6- aminocaproic acid pentamer, 6-aminocaproic acid hexamer, N'-(6-aminohexyl)hexane-1,6-diamine, N- methylhexane-1,6-diamine, 6-amino-hexanamide, derivatives of E-caprolactam other than E-caprolactam oligomers and having a boiling point higher than E-caprolactam such as 1-(6-aminohexyl)azepan-2-one; the at least one aliphatic alcohol preferably includes one or more of butanediol and oligomers thereof, including butanediol dimer and higher oligomers such as butanediol trimer, including polytetrahydrofuran; the at least one aromatic acid and the at least one aliphatic acid preferably include one or more of terephthalic acid and adipic acid; the at least one E-caprolactam oligomer preferably includes one or more of E-caprolactam dimer E- caprolactam trimer, E-caprolactam tetramer, E-caprolactam pentamer, and E-caprolactam hexamer.Regarding the high boiler separation carried out in said separation unit Ui, it is preferred that at least one of the following methods A, B and C is applied:A. Providing a stream SLO (preferably being the stream Swsi described hereinabove) having a temperature TLO and exhibiting a total concentration CLO(X) of the one or more compounds X having a higher boiling point than E-caprolactam and a concentration CLO(C) of monomeric E-caprolactam; producing in an evaporation unit UEI from the stream SLO an aqueous at least partially vaporous stream Svi and a liquid stream SLI, comprising passing the stream SLO into the unit UEI, preparing in the unit UEI from the stream SLO an evaporation mixture MEI having an evaporation temperature TEI at an evaporation pressure PEI with TEI > TLO, wherein the one or more one organic compounds X have a boiling point TBX and E-caprolactam has a boiling point TBC with TBX > TEI - TBC at the evaporation pressure PEI;removing the stream Svi from the evaporation unit UEI, the stream Svi having a temperature Tvi with Tvi TEI and exhibiting a total concentration cvi(X) of one or more compounds X and a concentration Cvi(C) of monomeric E-caprolactam with cvi(C) > CLO(C) and cvi(X) < CLO(X); removing the stream SLI from the evaporation unit UEI, the stream SLI having a temperature TLI with Tn = TEI and exhibiting a total concentration CLI(X) of one or more compounds X and a concentration CLI(C) of monomeric E-caprolactam with CLI(C) < CEI(C) and CLI(X) > CLO(X); producing in a separation unit Usi from the stream Svi an aqueous vapor stream Sv2 and a liquid stream SL2, comprising passing the stream Svi removed from the evaporation unit UEI, optionally after cooling, into the separation unit Usi and subjecting the stream Svi, optionally the stream after cooling, in the separation unit Usi to separation conditions; removing the stream Sv2 from the separation unit Usi, the stream Sv2 having a temperature Tv2 with TLO < Tv2^ Tvi and exhibiting a total concentration cv2(X) of one or more compounds X and a concentration cv2(C) of monomeric E-caprolactam; removing the stream SL2 from the separation unit Usi, 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 E-caprolactam with CL2(X) > cv2(X) and Ci_2(C) < cv2(C); passing the aqueous stream Sv2 obtained from the separation unit Usi to a water separation unit.B. Providing a stream SLO (preferably being the stream Swsi described hereinabove) having a temperature TLO and exhibiting a total concentration CLO(X) of the one or more compounds X, a concentration CLO(C) of monomeric E-caprolactam, and a concentration CLO(W) of water; providing a non-aqueous stripping gas stream SGO comprising at least one inert gas G and having a temperature TGO with TGO > TLO; producing in a stripping unit Usi from the stream SLO an aqueous gas stream Svi and a liquid stream SLI, comprising passing the stream SLO and the stream SGO into the stripping unit Usi; bringing the stream SLO and the stream SGO in the stripping unit Usi at stripping conditions into contact with each other, wherein the stripping conditions comprise a stripping pressure ps and wherein at the stripping pressure ps, the one or more one organic compounds X comprised in the stream SLO have a boiling point TBX and monomeric E-caprolactam has a boiling point TBC with TBX > TBC; removing the stream Svi from the stripping unit Usi, the stream Svi having a temperature Tvi with TLO < Tvi < TGO and exhibiting a total concentration cvi(X) of one or more compounds X, a concentration cvi(C) of monomeric E-caprolactam, a concentration Cvi(W) of water and a concentration Cvi(G) of the at least one inert gas G, with cvi(C) > CLO(C) and cvi(X) < CLO(X); removing the stream SLI from the stripping unit Usi, the stream SLI having a temperature TLI withTLO < TLI < TGO and exhibiting a total concentration CLI(X) of one or more compounds X and a concentration CLI(C) of monomeric E-caprolactam, with CLI(X) > Cvi(X) and CLI(C) < Cvi(C); producing in a separation unit Us2 from the stream Svi an aqueous gas stream Sv2 and a liquid stream SL2, comprising passing the stream Svi removed from the stripping unit Usi into the separation unit Us2 and subjecting the stream Svi in the unit Us2 to separation conditions; removing the stream Sv2 from the separation unit Us2, the stream Sv2 exhibiting a total concentration cv2(X) of one or more compounds X, a concentration cv2(C) of monomeric E-caprolactam, a concentration cv2(W) of water and a concentration cv2(G) of the at least one inert gas G, with cv2(W) < cvi(W); removing the stream SL2 from the separation unit Us2, the stream SL2 exhibiting a total concentration cL2(X) of one or more compounds X, a concentration Ci_2(C) of monomeric E-caprolactam and a concentration CL2(W) of water, with CL2(X) > Cv2(X), Ci_2(C) > Cv2(C), and CL2(W) < Cv2(W).C. Providing a stream SLO (preferably being the stream Swsi described hereinabove) having a temperature TLO and exhibiting a total concentration CLO(X) of the one or more compounds X, a concentration CLO(C) of monomeric E-caprolactam, and a concentration CLO(W) of water; providing an aqueous stripping gas stream SGO having a temperature TGO with TGO > TLO; producing in a stripping unit Usi from the stream SLO an aqueous gas stream Svi and a liquid stream SLI, comprising passing the stream SLO and the stream SGO into the stripping unit Usi; bringing the stream SLO and the stream SGO in the stripping unit Usi at stripping conditions into contact with each other, wherein the stripping conditions comprise a stripping pressure ps and wherein at the stripping pressure ps, the one or more one organic compounds X comprised in the stream SLO have a boiling point TBX and monomeric E-caprolactam has a boiling point TBC with TBX > TBC; removing the stream Svi from the stripping unit Usi, the stream Svi having a temperature Tvi with TLO < Tvi < TGO and a total concentration cvi(X) of one or more compounds X, a concentration cvi(C) of monomeric E-caprolactam and a concentration Cvi(W) of water, with cvi(C) > CLO(C) and cvi(X) < CLO(X); removing the stream SLI from the stripping unit Usi, the stream SLI having a temperature TLI with TLO < TLI < TGO and exhibiting a total concentration CLI(X) of one or more compounds X and a concentration CLI(C) of monomeric E-caprolactam, with CLI(X) > Cvi(X) and CLI(C) < Cvi(C); producing in a separation unit Us2 from the stream Svi an aqueous gas stream Sv2 and an aqueous liquid stream SL2, comprising passing the stream Svi removed from the stripping unit Usi into the separation unit Us2 and subjecting the stream Svi in the unit Us2 to separation conditions;removing the stream Sv2 from the separation unit Us2, the stream Sv2 exhibiting a total concentration cv2(X) of one or more compounds X, a concentration cv2(C) of monomeric E-caprolactam, and a concentration cv2(W) of water with cv2(W) < Cvi(W); removing the stream SL2 from the separation unit Us2, the stream SL2 exhibiting a total concentration cL2(X) of one or more compounds X, a concentration CL2(C) of monomeric E-caprolactam and a concentration CL2(W) of water, with CL2(X) > Cv2(X), CL2(C) > Cv2(C), and CL2(W) < cv2(W); producing in a separation unit Us3 from the stream SL2 an aqueous gas stream Sv3 and a liquid stream SL3, comprising passing the stream SL2 removed from the separation unit Us2 into the separation unit Us3 and subjecting the stream SL2 in the unit Us3 to separation conditions; removing the stream Sv3 from the separation unit Us3, the stream Sv3 exhibiting a concentration cvs(W) of water with cvs(W) > CL2(W); removing the stream SL3 from the separation unit Us3, the stream Su exhibiting a concentration Ci_3(C) of monomeric E-caprolactam and a concentration CL3(W) of water, with CLS(C) > cv2(C) and CL3(W) < CV2(W).According to the present invention, it may be further preferred that the purification unit UP further comprises, optionally upstream and preferably downstream of the distillation unit UDI, a chemical treatment unit UOD, and the process preferably comprises obtaining the stream So from UOD. AS far as the chemical treatment in the unit UOD is concerned, the process of the present invention preferably comprises providing a preferably liquid stream SDI comprising E-caprolactam from the distillation unit UDI, said stream SDI further comprising one or more oxidizable organic impurity compounds IOE; providing a stream Sox comprising at least one permanganate; preparing an oxidation reaction educt mixture MOE from the stream SDI and the stream Sox, and subjecting the mixture MOE to oxidation reaction conditions, obtaining an oxidation reaction product stream SP comprising E- caprolactam, further comprising one or more oxidation products IOD obtained from the oxidation of at least a part of the one or more compounds IOE, and optionally further comprising a part of the one or more organic compounds IOE; separating, optionally after filtration, at least a part of the one or more oxidation products IOD and optionally at least a part of organic compounds IOE from the stream SP, obtaining the stream So.The at least one permanganate comprised in the stream Sox preferably comprises, more preferably consists of, at least alkali metal permanganate, wherein more preferably, the at least one alkali metal permanganate comprises one or more of sodium permanganate and potassium permanganate. Preferably from 0.5 to 100 weight-% of the stream Sox consist of permanganate. Therefore, generally, it is conceivable that the permanganate is used in its solid form. Preferably, the stream Sox provided according to (b) further comprises water, wherein it is more preferred that the oxidation reaction educt mixture MOE exhibits a permanganate concentration, calculated as MnC , in the range offrom 0.005 to 5 weight-%, more preferably in the range of from 0.01 to 3 weight-%, more preferably in the range of from 0.05 to 1 weight-%. Yet further, the oxidation reaction conditions preferably comprise a temperature TOE of the mixture MOE in the range of from 40 to 140 °C, more preferably in the range of from 60 to 100 °C, more preferably in the range of from 70 to 90 °C. Still further preferably, the mixture MOE further comprises water. Preferably, subjecting the mixture MOE to oxidation reaction conditions is carried out in an oxidation reaction unit UOR comprised in the chemical treatment unit UOD, wherein the unit UOR preferably comprises one or more of at least one continuous stirred tank reactor and at least one tube reactor. Further preferably, the chemical treatment process of the present invention further comprises providing a stream SB comprising at least one hydroxide, wherein the oxidation reaction educt mixture MOE is prepared from the stream SUD or the stream SCR, and from the stream Sox and the stream SB.The at least one hydroxide comprised in the stream SB preferably comprises, more preferably consists of, at least alkali metal hydroxide, wherein more preferably, the at least one alkali metal hydroxide comprises, more preferably consists of, sodium hydroxide. Preferably from 0.5 to 100 weight-% of the stream SB consist of hydroxide. Therefore, generally, it is conceivable that the hydroxide is used in its solid form. Preferably, the stream SB further comprises water, wherein it is more preferred that the oxidation reaction educt mixture MOE prepared according to (c) exhibits a hydroxide concentration, calculated as OH, in the range of from 0.005 to 0.75 weight-%, more preferably in the range of from 0.01 to 0.5 weight-%, more preferably in the range of from 0.1 to 0.25 weight-%. According to the present invention, it may be preferred that separating at least a part of the one or more oxidation products IQD and optionally at least a part of organic compounds IOE from the stream SP comprises subjecting the stream SP to distillation in a distillation unit UDT which is comprised in, i.e. is part of, the chemical treatment unit UOD. In this case, a stream SDT is obtained from the distillation unit UDT which comprises E-caprolactam, wherein this stream SDT is the stream So.Preferably, the unit UDT comprises one or more distillation columns, more preferably one or two distillation columns, wherein at least one distillation column is optionally configured as side stream column or as divided wall column. According to the process of the present invention, the distillation unit UDT can be design so as to accomplish one of the following separation tasks: a simple evaporation of E-caprolactam; separating one or more light boiling compounds from E-caprolactam; separating one or more high boiling compounds from E-caprolactam; separating one or more high boiling compounds and one or more light boiling compounds from E-caprolactam in one side-stream distillation column; or in two separate distillation columns; or in one divided wall distillation column; or in one side stream distillation column, and a further distillation column wherein in said further distillation column one or more light boiling compounds; or where one or more high boiling compoundsare separated from E-caprolactam.Method of controlling the crystallization process carried out in the crystallization unit UAs mentioned herein, the process of the present invention is characterized in particular, among others, by its flexibility in view of possible varying chemical compositions of the stream So, and, therefore, the possibility to use the crystallization unit U for dealing with said varying chemical compositions using the following method of controlling the process of the present invention.Therefore, the present invention also relates to a method for controlling an E-caprolactam crystallization process as described herein, carried out in a crystallization unit U as described herein, the method comprising(a) providing parameters a parameter space Q(SF) of the final E-caprolactam fine product stream SPF to be obtained by the process according to (iii.1.5.1) as described herein to a control unit UDP;(b) providing operating characteristics of the h crystallization sub-units UC<H) to the control unit UDP;(c) determining, prior to passing the stream So into a batch drum B(i) according to (ii), parameters of a parameter space Q(So) of the stream So in the analytical unit UA, wherein the parameters of Q(So) correspond to the parameters of Q(SF); and passing the parameters of Q(So) to the control unit UDP;(d) determining in the control unit UDP, based on the parameters of the parameter space Q(SF) provided according to (a) and further based on the operating characteristics of the h crystallization sub-units UC<H) provided according to (b), the number of crystallization cycles P(x) and the number of crystallization cycles C(y) necessary to change the parameters of Q(So) to the parameters of Q(SF), and further determining the batch drum B(i) into which the crude E-caprolactam feed stream So is to be passed;(e) determining, in the control unit UDP, operation instructions for the controllable means of the batch drum subunit UB, the stream distribution sub-unit UD and the h crystallization sub-units UC<H) to realize number of crystallization cycles P(x) and the number of crystallization cycles C(y) determined according to (d);(f) carrying out a crystallization process as described herein, comprising passing the operation instructions determined according to (e) to the controllable means.According to a preferred process of the present invention carried out in a preferred crystallization unit U according to the present invention, the preferred method for controlling said process comprises(a) providing parameters a parameter space Q(SF) of the final E-caprolactam fine product stream SPF to be obtained by the process according to (iii.1.5.1) as described herein to a control unit UDP;(b) providing operating characteristics of the crystallization cycle sub-units Uci and Uc2 to the control unit UDP;(c) determining, prior to passing the stream So into a batch drum B(i) according to (ii), parameters of a parameter space Q(So) of the stream So in the analytical unit UA, wherein the parameters of Q(So) correspond to the parameters of Q(SF); and passing the parameters of Q(So) to the control unit UDP;(d) determining in the control unit UDP, based on the parameters of the parameter space Q(SF) provided according to (a) and further based on the operating characteristics of the crystallization cycle sub-units Uci and Uc2 provided according to (b), the number of crystallization cycles P(x) and the number of crystallization cycles C(y) necessary to change the parameters of Q(So) to the parameters of Q(SF), and further determining the batch drum B(i) into which the crude E-caprolactam feed stream So is to be passed;(e) determining, in the control unit UDP, operation instructions for the controllable means of the batch drum subunit UB, the stream distribution sub-unit UD and the crystallization cycle sub-units Uci and Uc2 to realize number of crystallization cycles P(x) and the number of crystallization cycles C(y) determined according to (d);(f) carrying out a crystallization process as described herein, comprising passing the operation instructions determined according to (e) to the controllable means.With regard to the parameter space Q(SF), every chemical or physical parameter can be used with the proviso that it can be determined in the analytical unit UA. Preferably, the parameter space Q(SF) comprises one or more of the E- caprolactam purity QGC(SF), the APHA value QAPHA(SF), the permanganate absorption number QPAN(SF), and the UV absorption QUV(SF), preferably at least QGC(SF) and QAPHA(SF). According to preferred methods and processes of the present invention,QGC(SF) is preferably at least 99.5 area-%, more preferably at least 99.8 area-%, more preferably at least 99.9 area-%;QAPHA(SF) is preferably at most 6, more preferably most 5, more preferably at most 4;QPAN(SF) is preferably at most 6, more preferably at most 5, more preferably at most 4;QUV(SF) is preferably at most 0.1 , more preferably at most 0.07, more preferably at most 0.05.Yet further according to preferred methods and processes of the present invention, more preferably according to the preferred methods and processes being characterized by the preferred ranges of QGC(SF), QAPHA(SF), QPAN(SF) and QUV(SF) described above, the parameter space Q(So) preferably comprises one or more of the E-caprolactam purity QGC(SO), the APHA value QAPHA(SO), the permanganate absorption number QPAN(SO), and the UV absorption Quv(So), preferably at least QGC(SO) and QAPHA(SO). According to preferred methods and processes of the present invention, at least one of the following, preferably at least two of the following relations are met, wherein more preferably, said at least two relations comprise one or more of the relations for QGC(SO) and QAPHA(SO):QGC(SO) < QGC(SF);QAPHA(SO) > QAPHA(SF);QPAN(SO) > QPAN(SF);Quv(So) > QUV(SF).According to said relations, it may be preferred that:QGC(SO) is at most 99.4 area-% for QGC(SF) being at least 99.5 area-%, more preferably at most 99.7 area-% for QGC(SF) being at least 99.8 area-%, more preferably at most 99.8 area-% for QGC(SF) being at least 99.9 area-%;QAPHA(SO) is at least 30;QPAN(SO) is at least 30;Quv(So) is at least 0.4.According to the present, it may be conceivable that prior to passing the stream So into the batch drum B(i), water is added, and the concentration of E-caprolactam is respectively decreased. Conceivable values of QGC(SO) are at least 90 area-% such as from 90 to 98 area-%.Integrated process for preparing polyamide 6According to a further aspect, the present invention relates to an integrated process for preparing polyamide 6, comprising(a) preparing a stream SPF according to a process as described herein, said stream SRF comprising purified E- caprolactam;(p) passing the stream SPF to a polyamide 6 production plant PPA;(y) subjecting the stream SPF in PPA to E-caprolactam polymerization conditions, obtaining from PPA a polyamide 6 material MP and a stream comprising water and one or more E-caprolactam oligomers;(5) optionally subjecting to stream comprising water and one or more E-caprolactam oligomers to concentration with respect to the one or more E-caprolactam oligomers in at least one concentration stage, obtaining a concentrated stream comprising water and one or more E-caprolactam oligomers;(E) passing the optionally concentrated stream comprising water and one or more E-caprolactam oligomers into at least one of the melting unit UM as described herein and the separation unit Uws2 as described herein.Preferably, the optionally concentrated stream comprising water and one or more E-caprolactam oligomers according to (E) further comprises E-caprolactam, i.e. monomeric E-caprolactam. Further preferably, said integrated process comprises(y) subjecting the stream SPF in PPA to E-caprolactam polymerization conditions, obtaining from PPA a polyamide 6 material MP and a stream SEW comprising water at a concentration CEW(W), E-caprolactam at a concentration CEW(C), and one or more E-caprolactam oligomers at a total concentration CEW(O);(5) subjecting the stream SEW to concentration, comprising(5.1) subjecting the stream SEW to concentration in a first concentration unit UCRI, obtaining from UCRI a concentrated stream Sci comprising water at a concentration Cci(W), E-caprolactam at a concentration cci (C), and one or more E-caprolactam oligomers at a total concentration cci (O), with Cci(W) < CEW(W),Cci(C) > CEW(C) and Cci(O) > CEW(O), and further obtaining from UCRI an aqueous stream Swi comprising water at a concentration Cwi(W) > CEW(W);(5.2) subjecting the stream Sci to concentration in a second concentration unit UCR2, obtaining from UCR2 a concentrated stream Sc2 comprising one or more E-caprolactam oligomers at a total concentration cc2(O), with cc2(O) > Cci(O), and further obtaining from UCR2 an aqueous stream Sw2 comprising water at a concentration cw2(W) and E-caprolactam at a concentration Cw2(C), with cw2(W) > Cwi(W) and cw2(C) > Cwi(C);(E) passing the stream Sc2 to the melting sub-unit UM and the stream Sw2 to the separation unit Uws2.As described above, the stream SEW which is obtained from the polyamide 6 polymerization plant PPA comprises water, monomeric E-caprolactam and one or more E-caprolactam oligomers. Usually, this aqueous stream SEW further comprises one or more further organic compounds other than monomeric E-caprolactam and one or more E- caprolactam oligomers. Therefore, it is preferred that the stream SEW further comprises one or more organic compounds V other than E-caprolactam and oligomers thereof at a total concentration CEW(V), the process according to (5) comprising(5.1) subjecting the stream SEW to concentration in a first concentration unit UCRI, obtaining from UCRI a concentrated stream Sci comprising water at a concentration Cci(W), E-caprolactam at a concentration cci (C), one or more E-caprolactam oligomers at a total concentration Cci(O) and one or more organic compounds V at a total concentration cci (V), with Cci(W) < CEW(W), CCI (C) > CEW(C), CCI(O)> CEW(O) and cci(V) > CEW(V), and further obtaining from Uci an aqueous stream Swi comprising water at a concentration Cwi(W) > CEW(W);(5.2) subjecting the stream Sci to concentration in a second concentration unit UCR2, obtaining from UCR2 a concentrated stream Sc2 comprising one or more E-caprolactam oligomers at a total concentration cc2(O) and one or more organic compounds V at a total concentration Cc2(V), with cc2(O) > Cci(O) and cc2(V) > cci (V), and further obtaining from Uc2 an aqueous stream Sw2 comprising water at a concentration cw2(W) and E- caprolactam at a concentration Cw2(C), with cw2(W) > Cwi(W) and cw2(C) > Cwi(C).More preferably according to the present invention, (y) comprises(y.1 ) passing the stream SPF and preferably an aqueous stream SAQO to a polymerization stage STo, obtaining from STo a polyamide 6 crude product stream SPAI and an aqueous stream SWAI;(y.2) passing the stream SPAI and preferably an aqueous stream SAQI to a granulation stage ST 1, obtaining from STi a crude granulated polyamide 6 material MPA2 and an aqueous stream SWA2;(y.3) passing the material MPA2 and preferably an aqueous stream SAQ2 to an extraction stage ST2, obtaining from ST2 a purified granulated polyamide 6 material MPA3 and an aqueous stream SWAS;(y.4) passing the material MPA3 to a drying stage ST3, obtaining from ST3 the polyamide 6 material MP and an aqueous stream SWA4.In particular regarding the process of the present invention comprising (y.1 ) to (y.4) above, it is preferred that the stream Swi obtained from UCRI according to (5) is passed back to the polyamide 6 production plant PPA. More preferably, the stream Swi is passed back to PPA as at least part of one or more of the streams SAQO, SAQI and SAQ2.Assuming that some of the polyamide 6 material obtained from the production plant PPA does not meet the specifications, the process may preferably further comprise passing at least some of said material MPR to the unit UM.Optional seedingOptionally, seeding may be included. During seeding, a small mass of crystals is added in order to start the crystallization, or to provide sufficient surface area.For example, in case seeding is applied during the purification step in the process, the crystallization loop may be filled with E-caprolactam. Subsequently, this E-caprolactam may be drained. The remaining liquid E-caprolactam film on the crystallizer tube may be crystallized by decreasing the temperature of the crystallizer tube wall to the seeding temperature. As a next step, the crystallizer tube may be pre-heated to a temperature below the freezing temperature of the feed to maintain the crystallized layer on the crystallizer tube for seeding, e.g. as a seeding layer.Computer programYet further, the present invention relates to a computer program, comprising instructions which, when the program is executed by the computer-supported control system according to embodiment 25, cause the system to perform the method for controlling the process as described herein. Still further, the present invention relates to a non-transient computer-readable medium containing instructions which, when executed by one or more processors, cause the one or more processors to perform the program described hereinabove.Further aspectAccording to a further aspect, the present invention relates to a process, preferably to the process as described herein, which comprises the step of converting the final residue stream SRF obtainable or obtained as described herein and / or the final E-caprolactam fine product stream SPF obtainable or obtained as described herein and / or a chemical material obtainable by or obtained by the process as described herein to obtain a product cp. Yet further, the present invention relates to a process comprising the step of using the crystallization unit U as described herein to obtain a final residue stream SRF and / or a final E-caprolactam fine product stream SPF; and preferably converting the final residue stream SRF and / or the final E-caprolactam fine product stream SPF to obtain a product cp.Preferably, the product cp is selected from:building block or monomer; or polymer, preferably polymer A, polymer composition, preferably polymer composition A, or polymer product, preferably polymer product A; or industrial use polymer, industrial use surfactant, descaling compound, industrial use biocide, industrial use solvent, industrial use dispersant, composition thereof or formulation thereof; or agrochemical composition, agrochemical formulation auxiliary or agrochemically active ingredient; or active pharmaceutical ingredient or intermediate thereof, pharmaceutical excipient, animal feed additive, human food additive, dietary supplements, aroma chemical or aroma composition; or aqueous polymer dispersion, preferably polyurethane or polyurethane - poly(meth)acrylate hybrid polymer dispersion, emulsion, binder for paper and fiber coatings, UV-curable acrylic polymer for hot melts and coatings polyisocyanates, hyperbranched polyester polyol, polymeric dispersant for inorganic binder compositions, unsaturated polyester polyol or 100% curable composition; or cosmetic surfactant, emollient, wax, cosmetic polymer, UV filter, further cosmetic ingredient or composition or formulation thereof; or polymer B, polymer composition B, coating composition, other functional composition, foil, molded body, coating or coated substrate.Regarding this process from which the product cp, is obtained, it is preferred: that the content of SRF and / or MPF and / or the chemical material in the product cp is 1 weight-% or more, preferably 2 weight-% or more, more preferably 5 weight-% or more, more preferably 15 weight-% or more, more preferably 30 weight-% or more, more preferably 40 weight-% or more, more preferably 60 weight-% or more, more preferably 80 weight-% or more, more preferably 90 weight-% or more, more preferably 95 weight-% or more; and / or that the content of the content of SRF and / or MPF and / or the chemical material in the product cp is 100 weight-% or less, preferably 95 weight-% or less, more preferably 90 weight-% or less, more preferably 50 weight-% or less, more preferably 25 weight-% or less, more preferably 10 weight-% or less; and preferably wherein the content is determined based on identity preservation and / or segregation and / or mass balance and / or book and claim chain of custody models, preferably based on mass balance, preferably the International Sustainability and Carbon Certification (ISCC) standard.The publication Prior Art Disclosure; Issue 684; paragraphs

[1000] to

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

[1000] to

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

[1000] to

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

[1000] to

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

[2001] to

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

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

[2009] and

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

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

[3035] to

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

[3008] to

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

[3001] to

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

[3006] to

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

[3045] to

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

[3056] to

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[6006] entitled "Binders for paper coating” section

[6007] entitled "Binders for fiber bonding” section

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[8000] to

[8005] of Reference RF1.The 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 crystallization unit 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 crystallization unit of any one of embodiments 1, 2, 3 and 4". 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 ofembodiments 1 , 2, 3 and 4". 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 method 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 method 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 crystallization unit U for carrying out an E-caprolactam crystallization process, wherein the unit U comprises(1) h crystallization sub-units Uc(H), H = 1 ...h and h > 2, wherein each crystallization sub-unit UC<H) comprises s crystallizer WC(S(H», S(H) = 1 ...S and s > 1 ; a stream transportation line LC(H) passing through the s crystallizer WC(S(H», comprising an entry and exit point EC<H) connected to the stream distribution sub-unit UD according to (3) and further comprising controllable means MEC<H) for passing a stream from UD into LC(H) and for passing a stream from LC(H) to UD;(2) a batch drum sub-unit UB comprising k batch drums B(i) with I = 1 ...k and k > 2, wherein k is preferably in the range from 2 to 20, wherein each batch drum B(i) is equipped with controllable means MBO) for passing a stream from B(i) via the stream distribution sub-unit UD according to (3) to at least one of EC(H>; a crude E-caprolactam feed stream transportation line Lso to at least one batch drum B(i);(3) a stream distribution sub-unit UD connecting UB and the h sub-units UC<H), the sub-unit UD comprising(3.1) for each drum B(i) with I = 1 ...k(3.1.1) at least one of a stage stream transportation line Ls<Hi)(i) from B(i) to at least one Ec(W) and a stage stream transportation line Ls<H2)(i) from B(i) to at least one EC<H2), H1 + H2, wherein Ls<Hi)(i) comprises at least one controllable means MLS(HI)O) for passing a stream from B(i) to EC<HI) and Ls<H2)(i) comprises at least one controllable means MLs<H2)(i) for passing a stream from B(i) to EC(H2>;(3.1 .2) at least one of a back stream transportation line LB<H i)(i) from EC<HI) to B(i) and a back stream transportation line LB<H2)(i) from Ec(H2) to B(i), wherein LB(HI)O) comprises at least one controllable means MLB(HI)O) for passing a stream from EC<HI) to B(i) and Ls(H2)(i) comprises at least one controllable means MLB<H2)(i) for passing a stream from EC(H2> to B(i);(3.2) a final residue stream transportation line LR<H3) , H3 + H1 ,H2, for removing a final crystallization residue stream SRF from a transportation line LC(H) via EC<H), wherein LR<H3) comprises at least one controllable means MLR<H3) for removing said final residue stream SRF from LC(H>;(3.3) a final fine product stream transportation line LF<H4), H4 + H1,H2,H3, for removing a final fine crystallization product stream SPF from a transportation line LC<H) via EC(H), wherein LF<H4> comprises at least one controllable means MLF<H4) for removing said final fine product stream SPF from LC(H). The crystallization unit U of embodiment 1, wherein 2 < h < 10, preferably 2 < h < 8, more preferably2 < h < 6, more preferably 2 < h < 4, more preferably h = 2 or h = 3, more preferably h = 2. The crystallization unit U of embodiment 1 or 2, wherein independently for each H, 1 < s < 5, preferably 1 < s < 4, more preferably 1 < s < 3, more preferably s = 1 or s = 2, more preferably s = 2. The crystallization unit U of any one of embodiments 1 to 3, wherein k > 3, preferably k > 4. The crystallization unit U of any one of embodiments 1 to 4, wherein at least one of the controllable means MEC(H), preferably controllable means MEC<H), comprises, preferably consists of a valve. The crystallization unit U of any one of embodiments 1 to 5, wherein at least one of the crystallizer WC(S(H», preferably each crystallizer WC(S(H» is configured as a shell-and-tube heat exchanger, preferably as a vertically mounted shell-and-tube heat exchanger, comprising an entry point for passing a heat transfer medium into the shell and an exit point for removing the heat transfer medium from the shell. The crystallization unit U of any one of embodiments 1 to 6, wherein at least one crystallization sub-unit Uc(H), preferably each crystallization sub-unit Uc(H) comprises at least 2 crystallizer WC(S(H» and further comprises a circular stream transportation line LC(H) passing through the at least 2 crystallizer WC(S(H», wherein the at least one crystallization sub-unit Uc(H), preferably each crystallization sub-unit Uc(H) further comprises controllable means MLC(H) for circulating a stream through LC(H). The crystallization unit U of embodiment 7, wherein at least one of the controllable means MLC(H), preferably each controllable means MLC<H), comprises, preferably consists of a stream circulation pump. The crystallization unit U of embodiment 7or 8, wherein the controllable means MLC(H) are arranged downstream of EC<H) and upstream WC(S(H» The crystallization unit U of any one of embodiments 1 to 9, wherein at least one of the transportation lines LC(H), preferably each transportation line LC(H), is connected to an expansion drum BEC<H).The crystallization unit U of any one of embodiments 1 to 10, wherein h = 2 and s = 2, wherein the unit U comprises(1) two crystallization cycle sub-units Uci and Uc2, wherein(1.1) the first crystallization cycle sub-unit Uci comprises a first crystallizer Wci(1) and a second crystallizer Wci(2); a circular stream transportation line Lei passing through Wci(1) and Wci(2), comprising an entry and exit point Eci connected to the stream distribution sub-unit UD according to (3) and further comprising controllable means MLCI for circulating a stream through Lei, wherein Eci comprises controllable means MECI for passing a stream from UD into Lei and for passing a stream from Lei to UD;(1 .2) the second crystallization cycle sub-unit Uc2 comprises a first crystallizer Wc2(1) and a second crystallizer Wc2(2); a circular stream transportation line I_c2 passing through Wc2(1) and Wc2(2), comprising an entry and exit point Ec2 connected to the stream distribution sub-unit UD according to (3) and further comprising controllable means MLC2 for circulating a stream through I_c2, wherein Ec2 comprises controllable means MEC2 for passing a stream from UD into I_c2 and for passing a stream from I_c2 to UD;(2) a batch drum sub-unit UB comprising k batch drums B(i) with i = 1 ...k and k > 4, wherein each batch drum B(i) is equipped with controllable means MB(I) for passing a stream from B(i) via the stream distribution sub-unit UD according to (3) to at least one of Eci and Ec2; a crude E-caprolactam feed stream transportation line Lso to at least one batch drum B(i);(3) a stream distribution sub-unit UD connecting UB, UCI and Uc2, the sub-unit UD comprising(3.1) for each drum B(i) with i = 1...k(3.1.1) at least one of a stage stream transportation line Lsi (i) from B(i) to Eci and a stage stream transportation line Ls2(i) from B(i) to Ec2, wherein Lsi (i) comprises at least one controllable means MLSI(I) for passing a stream from B(i) to Eci and Ls2(i) comprises at least one controllable means MLS2(I) for passing a stream from B(i) to Ec2;(3.1.2) at least one of a back stream transportation line l_Bi(i) from Eci to B(i) and a back stream transportation line l_B2(i) from Ec2 to B(i), wherein LBI (i) comprises at least one controllable means MLBI(I) for passing a stream from Eci to B(i) and LB2(I) comprises at least one controllable means MLB2(I) for passing a stream from Ec2 to B(i);(3.2) a final residue stream transportation line LRI for removing a final crystallization residue stream SRF from Lei via Eci, wherein LRI comprises at least one controllable means MLRI for removing said final residue stream from Lei;(3.3) a final fine product stream transportation line LF2 for removing a final fine crystallization product stream SPF from I_c2 via Ec2, wherein LFI comprises at least one controllable means MLF2 for removing said final fine product stream SPF from Lei ■12. The crystallization unit U of embodiment 11, wherein each crystallizer Wci(1), Wci(2), Wc2(1) and Wc2(2) is configured as a shell-and-tube heat exchanger, preferably as a vertically mounted shell-and-tube heat exchanger, comprising an entry point for passing a heat transfer medium into the shell and an exit point for removing the heat transfer medium from the shell.13. The crystallization unit U of embodiment 11 or 12, wherein each controllable means MLCI and MLC2 comprises, preferably consists of a stream circulation pump and wherein each controllable means MECI and MEC2 comprises, preferably consists of a valve.14. The crystallization unit U of any one of embodiments 11 to 13, wherein the controllable means MLCI are arranged downstream of Eci and upstream Wci(1), and wherein the controllable means MLC2 are arranged downstream of Ec2 and upstream Wc2(1).15. The crystallization unit U of any one of embodiments 11 to 14, wherein each controllable means MB(I) comprises a valve and a pump, preferably a valve and a pump arranged downstream of said valve.16. The crystallization unit U of any one of embodiments 11 to 15, wherein the transportation line Lei is connected to an expansion drum BECI, preferably arranged downstream of Wci(1) and upstream of Wci(2), and the transportation I_c2 is connected an expansion drum BEC2 preferably arranged downstream of Wc2(1) and upstream of Wc2(2).17. The crystallization unit U of any one of embodiments 11 to 16, wherein the batch drum sub-unit UB further comprises for at least one of the batch drums B(i), preferably for all batch drums B(i), a back mixing transportation line LMBO) equipped with controllable means MLMBO) for passing a stream from B(i) via MB(I) back into B(i).18. The crystallization unit U of any one of embodiments 11 to 17, wherein 4 < k < 10, preferably 4 < k < 9, more preferably 4 < k < 8.19. The crystallization unit U of any one of embodiments 11 to 18, wherein each controllable means MECI, MEC2, MLSIO), Mi_s2(i), MLBIO), Mi_B2(i), MLMBO), MLRI, and MLF2 comprises, preferably consists of a valve.The crystallization unit U of any one of embodiments 11 to 19, further comprising a final crystallization residue batch drum BR equipped with controllable means M for passing a stream from BR to a further use, wherein said batch drum BR is connected to the transportation line LRI, and further comprising a final crystallization fine product batch drum BF equipped with controllable means MF for passing a stream from BF to a further use, wherein said batch drum BF is connected to the transportation line LF2, wherein each controllable means MR and MF preferably comprises, more preferably consists of a valve. The crystallization unit U of embodiment 20, wherein downstream of MF, a static crystallization sub-unit USCR is arranged. The crystallization unit U of any one of embodiments 1 to 21 , preferably of any one of embodiments 11 to 21 , wherein each controllable means, each batch drum B(i) and each transportation line is configured to be heatable to a temperature of at least 50 °C, preferably at least 60 °C, more preferably at least 70 °C, the crystallization unit U further comprising means MH for heating each controllable means, each batch drum B(i) and each transportation line. The crystallization unit U of any one of embodiments 1 to 22, preferably of any one of embodiments 11 to 22, wherein upstream of the at least one B(i), the crude E-caprolactam feed stream transportation line Lso comprises an analytical unit UA for analysing a crude E-caprolactam feed stream So to be passed into B(i) with respect to at least one crude E-caprolactam feed quality parameter selected from the group consisting of an E-caprolactam purity QGC(SO), an APHA value QAPHA(SO), a permanganate absorption number QPAN(SO), and an UV absorption Quv(So). The crystallization unit U of any one of embodiments 1 to 23, preferably of any one of embodiments 11 to 23, further comprising a control sub-unit UDP. The crystallization unit U of any one of embodiments 1 to 24, preferably of any one of embodiments 11 to 25, further comprising a computer-supported control system for controlling at least one controllable means, preferably all controllable means, said computer-supported control system preferably being a part of the subunit UDP according to embodiment 24. The crystallization unit U of any one of embodiments 1 to 24 comprised in a plant PDP for depolymerization of polyamide 6 and purification of E-caprolactam obtained from said depolymerization, said plant PDP preferably comprising a melting and mixing unit for preparing a depolymerizaton mixture from a solid material M comprising polyamide, the material M preferably being a waste material, more preferably a textile waste material and / or an engineering plastic waste material, the melting and mixing unit being arranged upstream ofa preferably hydrolytic depolymerization unit for depolymerizing polyamide 6 comprised in said depolymerizaton mixture, the depolymerization unit being arranged upstream of a purification unit for purifying E-caprolactam obtained from said depolymerization unit, the purification unit comprising at least one of one or more water separation units, one or more high boiler separation units for separating organic compounds from E-caprolactam having a higher boiling point than E-caprolactam, and one or more distillation units, said purification unit being arranged upstream of the crystallization unit U, wherein more preferably, the crystallization unit U is the downstream-most unit of said plant PDP, and wherein said plant PDP is optionally or preferably comprised in an integrated polyamide 6 plant Pi, said integrated polyamide 6 plant Pi comprising said plant for PDP and further comprising a polyamide 6 production plant PPA, said integrated plant Pi further comprising a transportation line LCPL for passing purified E-caprolactam from PDP to PPA and a transportation line Ls for passing an aqueous recycle stream from PPA to PDP. An E-caprolactam crystallization process carried out in a crystallization unit according to any one of embodiments 1 to 26, the process comprising(i) providing a liquid crude feed stream So comprising E-caprolactam, wherein So has a temperature of at most 70 °C and exhibits an E-caprolactam purity QGC(SO), an APHA value QAPHA(SO), a permanganate absorption number QPAN(SO) and a UV absorption Quv(So);(ii) passing the stream So into a batch drum B(i), 1 < i < k, wherein k is preferably in the range of from 2 to 20;(iii) subjecting the content of the batch drum B(i) to crystallization comprising n crystallization stages P(x) carried out in at least one sub-unit U C<H2) with 1 < n < (k-i+1 ) and x = 1 ... n, wherein n is preferably in the range of from 1 to 41, and further comprising m crystallization stages C(y) carried out in at least one sub-unit Uc(Hi) with 0 < m < (i-1) and y = 1 ...m for m > 0, wherein H1 A H2, wherein m is preferably in the range of from 1 to 19;(iii.1 ) wherein a crystallization stage P(x) comprises(iii.1.1) passing a stage stream Ss(x+i-1) comprising at least a part of the content of a batch drum B(x+i-1 ) from said batch drum B(x+i-1 ) via the transportation line LS(H2)(X-H-1 ) and the entry and exit point EC<H2) into the transportation line LC(H2>;(iii.1.2) passing the stream Ss(x+i-1) through the transportation line LC<H2) with the means Mc(H2), thereby passing through the at least one crystallizer Wc(s(H2», wherein in Wc(s(H2», E-caprolactam comprised in Ss(x+i-1 ) crystallizes and remains as crystallized solid in Wc(s(H2»;(iii.1.3) removing a residue stream SR(X-H-1) from the transportation line Lc(H2) via EC<H2), wherein the stream SR(X+I-1 ) is depleted in E-caprolactam compared to the stream Ss(x+i-1); and(1.3.1) passing the stream SR(X+I-1 ) via the transportation line LR<H3> as final residue stream SRF via MLR<H3) to optional further use; or(1 .3.2) passing the stream SR(X+I-1 ) via the transportation line LB(H2)(X-H-2) into the batch drum B(x+i-2);(ill.1.4) transferring the crystallized solid in Wc(s(H2» into a liquid product stream Sp(x+i-1);(ill.1.5) removing the stream Sp(x+i-1) from the transportation line LC<H2) via EC<H2), wherein the stream Sp(x+i-1 ) is concentrated in E-caprolactam compared to the stream Ss(x+i-1), and(1.5.1) passing the stream Sp(x+i-1) via the transportation line LF<H4) as final E- caprolactam fine product stream SPF via MLF<H4) to further use; or(1 .5.2) passing the stream Sp(x+i-1 ) via the transportation line LB(H2)(X-H) into the batch drum B(x+i);(ill.2) wherein a crystallization stage C(y) comprises(111.2.1) passing a stage stream Ss(i-y) comprising at least a part of the content of a batch drum B(i-y) from said batch drum B(i-y) via the transportation line Ls<Hi)(i-y) and the entry and exit point EC<HI) into the transportation line LC(HI>;(111.2.2) passing the stream Ss(i-y) through the transportation line LC(HI) with the means MC(HI), thereby passing through the at least one crystallizer WC(S(HI», wherein in WC(S(HI», E-caprolactam comprised in Ss(i-y) crystallizes and remains as crystallized solid in WC(S(HI»;(111.2.3) removing a residue stream SR(i-y) from the transportation line LC(HI), wherein the stream SR(i-y) is depleted in E-caprolactam compared to the stream Ss(i-y); and(2.3.1) passing the stream SR(i-y) via the transportation line LR<H3) as final residue stream SRF via MLR(H3> to optional further use; or(2.3.2) passing the stream SR(i-y) via the transportation line LB<Hi)(i-y-1 ) into the batch drum B(i-y-1);(111.2.4) transferring the crystallized solid in WC(S(HI» into a liquid product stream Sp(i-y);(111.2.5) removing the stream Sp(i-y) from the transportation line LC(HI> via EC(HI>, wherein the stream Sp(i-y) is concentrated in E-caprolactam compared to the stream Ss(i-y), and passing the stream Sp(i-y) via the transportation line i-B(Hi)(i-y+1) into the batch drum B(i-y+1). The E-caprolactam crystallization process of embodiment 27, carried out in a crystallization unit according to any one of embodiments 11 to 27, the process comprising(i) providing a liquid crude feed stream So comprising E-caprolactam, wherein So has a temperature of at most 70 °C and exhibits an E-caprolactam purity QGC(SO), an APHA value QAPHA(SO), a permanganate absorption number QPAN(SO) and a UV absorption Quv(So);(ii) passing the stream So into a batch drum B(i), 1 < I < k, wherein k is preferably in the range of from 2 to 20;(ill) subjecting the content of the batch drum B(i) to crystallization comprising n crystallization stages P(x) carried out in Uc2 with 1 < n < (k-i+1) and x = 1 ...n, wherein n is preferably in the range of from 1 to 41 , and further comprising m crystallization stages C(y) carried out in Uci with 0 < m < (i-1) and y = 1 ...m for m > 0, wherein m is preferably in the range of from 1 to 19;(ill.1 ) wherein a crystallization stage P(x) comprises(ill.1.1) passing a stage stream Ss(x+i-1) comprising at least a part of the content of a batch drum B(x+i-1 ) from said batch drum B(x+i-1 ) via the transportation line Ls2(x+i-1) and the entry and exit point Ec2 into the circular stream transportation line I_c2;(ill.1.2) passing the stream Ss(x+i-1) through the circular transportation line I_c2 with the means MLC2, thereby passing through the first crystallizer Wc2(1) and the second crystallizer Wc2(1), wherein in Wc2(1) and Wc2(2), E-caprolactam comprised in Ss(x+i-1 ) crystallizes and remains as crystallized solid in Wc2(1) and Wc2(2);(ill.1.3) removing a residue stream SR(X+I-1 ) from the transportation line Lc2 via Ec2, wherein the stream SR(X+I-1 ) is depleted in E-caprolactam compared to the stream Ss(x+i-1 ); and(1.3.1) passing the stream SR(X+I-1 ) via the transportation line LRI as final residue stream SRF via MLRI to optional further use; or(1 .3.2) passing the stream SR(X+I-1 ) via the transportation line LB2(X-H-2) into the batch drum B(x+i-2);(ill.1.4) transferring the crystallized solid in Wc2(1) and Wc2(2) into a liquid product stream SP(x+i-1);(ill.1.5) removing the stream Sp(x+i-1) from the transportation line I_c2 via Ec2, wherein the stream Sp(x+i-1 ) is concentrated in E-caprolactam compared to the stream Ss(x+i-1 ), and(1.5.1) passing the stream Sp(x+i-1) via the transportation line LF2 as final E- caprolactam fine product stream SPF via MLF2 to further use; or(1.5.2) passing the stream Sp(x+i-1) via the transportation line LB2(X-H) into the batch drum B(x+i);(ill.2) wherein a crystallization stage C(y) comprises(iii.2.1) passing a stage stream Ss(i-y) comprising at least a part of the content of a batch drum B(i-y) from said batch drum B(i-y) via the transportation line Lsi(i-y) and the entry and exit point Eci into the circular stream transportation line Lei;(111.2.2) passing the stream Ss(i-y) through the circular transportation line Lei with the means Mei, thereby passing through the first crystallizer Wci(1) and the second crystallizer Wci(1 ), wherein in Wci(1) and Wci(2), E-caprolactam comprised in Ss(i-y) crystallizes and remains as crystallized solid in Wci(1) and Wci(2);(111.2.3) removing a residue stream SR(i-y) from the transportation line Lei, wherein the stream SR(i-y) is depleted in E-caprolactam compared to the stream Ss(i-y); and(2.3.1) passing the stream SR(i-y) via the transportation line LRI as final residue stream SRF via MLRI to optional further use; or(2.3.2) passing the stream SR(i-y) via the transportation line l_Bi(i-y-1 ) into the batch drum B(i-y-1);(111.2.4) transferring the crystallized solid in Wci(1) and Wci(2) into a liquid product stream Sp(i-y);(111.2.5) removing the stream Sp(i-y) from the transportation line Lei via Eci, wherein the stream Sp(i-y) is concentrated in E-caprolactam compared to the stream Ss(i-y), and passing the stream Sp(i-y) via the transportation line l_Bi(i-y+1 ) into the batch drum B(i-y+1). The process of embodiment 27 or 28, comprising, prior to (ii), heating each controllable means, each batch drum B(i) and each transportation line, independently of each other, to a temperature of at least 50 °C, preferably of at least 60 °C, preferably to a temperature of at least 70 °C, more preferably to a temperature in the range of from 70 to 90 °C, more preferably in the range of from 70 to 80 °C, via the means MH. The process of any one of embodiments 27 to 29, wherein each crystallization stage P(x) according to (ill.1 ) is characterized by a freezing ratio F(P(x)) and wherein, independently of each other, each freezing ratio F(P(x)) is at least 0.4, preferably at least 0.45, more preferably at least 0.5, more preferably at least 0.55, more preferably at least 0.60, more preferably at least 0.65, wherein the freezing ratio F(P(x)) is defined as F(P(x)) = m(Sp(x+i-1)) I m(Ss(x+i-1)), wherein m(Sp(x+i-1)) is the mass of the liquid product stream Sp(x+i-1) according to (ill.1.4) and m(Ss(x+i-1)) is the mass of the stage stream Ss(x+i-1) according to (ill.1.1). The process of any one of embodiments 27 to 30, wherein each crystallization stage C(y) according to (ill.2) is characterized by a freezing ratio F(C(y)) and wherein, independently of each other, each freezing ratio F(C(y)) is at least 0.4, preferably at least 0.45, more preferably at least 0.5, more preferably at least 0.55, more preferably at least 0.60, more preferably at least 0.65, wherein the freezing ratio F(C(y)) is defined as F(C(y)) = m(Sp(i-y)) I m(Ss(i-y)), wherein m(Sp(i-y)) is the mass of the liquid product stream Sp(i-y) according to (ill.2.4) and m(Ss(i-y)) is the mass of the stage stream Ss(i-y) according to (ill.2.1).32. The process of any one of embodiments 27 to 31, wherein each crystallization stage P(x) according to (ill.1 ) is characterized by an effective distribution coefficient D(P(x)) and wherein, independently of each other, each effective distribution coefficient D(P(x)) is in the range of from 0.1 to 0.8, preferably in the range of from 0.2 to 0.7, more preferably in the range of from 0.3 to 0.6, wherein an effective distribution coefficient D(P(x)) is defined as D(P(x)) = CIM(SR(X-H-1 )) I CIM(SS(X+I-1 )), wherein CIM(SS(X+I-1 )) is the concentration of impurities contained in the stage stream Ss(x+i-1) according to (ill.1.1) and CIM(SR(X-H-1)) is the concentration of impurities, determined via GC as described in Reference Example 1.1 herein, contained in the product stream Sp(x+i-1) according to (ill.1.4), wherein the term "impurity” refers to any chemical compound other than E- caprolactam.33. The process of any one of embodiments 27 to 32, wherein each crystallization stage C(y) according to (ill.2) is characterized by an effective distribution coefficient D(C(y)) and wherein, independently of each other, each effective distribution coefficient D(C(y)) is in the range of from 0.1 to 0.8, preferably in the range of from 0.2 to 0.7, more preferably in the range of from 0.3 to 0.6, wherein an effective distribution coefficient D(C(y)) is defined as D(C(y)) = CiM(Sp(i-y)) I CiM(Ss(i-y)), wherein CiM(Ss(i-y)) is the concentration of impurities contained in the stage stream Ss(i-y) according to (iii.2.1) and CiM(Sp(i-y)) is the concentration of impurities, determined via GC as described in Reference Example 1.1 herein, contained in the product stream Sp(i-y) according to (ill.2.4), wherein the term "impurity” refers to any chemical compound other than E-caprolactam.34. The process of any one of embodiments 27 to 33, preferably according to any one of embodiments 28 to 33, wherein transferring the crystallized solid into a liquid product stream Sp(x+i-1) according to (ill.1.4) comprises (ill.1.4.1) increasing the temperature of the crystallized solid in Wc(s(H2» close to the melting point of pureE-caprolactam, obtaining a further residue stream SR(X+I-1), and removing said further residue stream SR(X+I-1) from the transportation line LC<H2) via EC<H2) according to (ill.1.3);(ill.1.4.2) transferring the remaining crystallized solid in Wc(s(H2» into a liquid product stream Sp(x+i-1 ); and preferably comprises(ill.1.4.1) increasing the temperature of the crystallized solid in at least one of Wc2(1) and Wc2(2), preferably in Wc2(1) and Wc2(2), close to the melting point of pure E-caprolactam, obtaining a further residue stream SR(X+I-1 ), and removing said further residue stream SR(X+I-1 ) from the transportation line Lc2 via Ec2 according to (ill.1.3);(ill.1.4.2) transferring the remaining crystallized solid in Wc2(1) and Wc2(2) into a liquid product stream Sp(x+i-1).35. The process of any one of embodiments 27 to 34, preferably according to any one of embodiments 28 to 33, wherein transferring the crystallized solid into a liquid product stream Sp(i-y) according to (ill.2.4) comprises(111.2.4.1 ) increasing the temperature of the crystallized solid in WC(S(HI» close to the melting point of pure E-caprolactam, obtaining a further residue stream SR(i-y), and removing said further residue stream SR(i-y) from the transportation line LC(HI) via EC<HI) according to (ill.2.3);(111.2.4.2) transferring the remaining crystallized solid in WC(S(HI» into a liquid product stream Sp(i-y); and preferably comprises(111.2.4.1) increasing the temperature of the crystallized solid in at least one of Wci(1) and Wci(2), preferably in Wci(1) and Wci(2), close to the melting point of pure E-caprolactam, obtaining a further residue stream SR(i-y), and removing said further residue stream SR(i-y) from the transportation line Lei via Eci according to (ill.2.3);(111.2.4.2) transferring the remaining crystallized solid in Wci(1) and Wci(2) into a liquid product stream Sp(i-y). The process of any one of embodiments 27 to 35, wherein providing the liquid crude feed stream So comprising E-caprolactam according to (I) comprises(1.1) providing a stream SM comprising a solid material M comprising polyamide 6;(1.2) preparing an aqueous depolymerization mixture based on the stream SM provided according to (1.1);(1.3) subjecting the depolymerization mixture prepared according to (1.2) to polyamide 6 depolymerization conditions in a reaction unit UR, obtaining a liquid aqueous stream SR comprising E-caprolactam dissolved in water at a concentration CSR, the stream SR further comprising one or more impurities;(1.4) passing the aqueous stream SR into a purification unit UP, obtaining from the stream SR the stream So comprising E-caprolactam at a concentration co with co » CR. The process of embodiment 36, wherein the solid material M according to (1.1) comprises, more preferably consists of, waste material, wherein said waste material more preferably comprises, more preferably consists of, one or more of at least one textile waste material and at least one engineering plastics waste material, more preferably comprises, more preferably consists of at least one textile waste material, wherein preferably from 10 to 99 weight-%, more preferably from 30 to 98.5 weight-%, more preferably from 50 to 98 weight-%, more preferably from 80 to 98 weight-%, of the solid material M consist of polyamide 6, wherein, in addition to polyamide 6, the solid material M preferably comprises one or more further organic polymeric compounds, more preferably including, but not limited to, one or more of at least one elastane; at least one polyamide 6.6; at least one semiaromatic polyamide including one or more of polyamide 6T and polyamide 6I; at least one polyethylene terephthalate; at least one polyurethane; at least one polyester; at least one polyether; at least one polyvinyl chloride; at least one natural fiber material such as wool and cotton; at least one cellulose material; at least one natural elastomer; at least one synthetic elastomer; at least one copolymer of two or more of said polymeric compounds including statistical copolymers, gradient copolymers, alternating copolymers, block copolymers, and graft copolymers; and at least one rubber material comprising one or more of at least one natural rubber material and at least one synthetic rubber material.A method for controlling an E-caprolactam crystallization process according to any one of embodiments 27 to 37, carried out in a crystallization unit according to any one of embodiments 1 to 26, the method comprising(a) providing parameters a parameter space Q(SF) of the final E-caprolactam fine product stream SPF to be obtained by the process according to (iii.1.5.1) to a control unit UDP;(b) providing operating characteristics of the h crystallization sub-units UC<H) to the control unit UDP;(c) determining, prior to passing the stream So into a batch drum B(i) according to (ii), parameters of a parameter space Q(So) of the stream So in the analytical unit UA, wherein the parameters of Q(So) correspond to the parameters of Q(SF); and passing the parameters of Q(So) to the control unit UDP;(d) determining in the control unit UDP, based on the parameters of the parameter space Q(SF) provided according to (a) and further based on the operating characteristics of the h crystallization sub-units Uc(H) provided according to (b), the number of crystallization cycles P(x) and the number of crystallization cycles C(y) necessary to change the parameters of Q(So) to the parameters of Q(SF), and further determining the batch drum B(i) into which the crude E-caprolactam feed stream So is to be passed;(e) determining, in the control unit UDP, operation instructions for the controllable means of the batch drum sub-unit UB, the stream distribution sub-unit UD and the h crystallization sub-units UC<H) to realize number of crystallization cycles P(x) and the number of crystallization cycles C(y) determined according to (d);(f) carrying out a crystallization process according to any one of embodiments 27 to 35, comprising passing the operation instructions determined according to (e) to the controllable means; preferably a method for controlling an E-caprolactam crystallization process according to any one of embodiments 28 to 37, carried out in a crystallization unit according to any one of embodiments 11 to 26, the method comprising(a) providing parameters a parameter space Q(SF) of the final E-caprolactam fine product stream SPF to be obtained by the process according to (iii.1.5.1) to a control unit UDP;(b) providing operating characteristics of the crystallization cycle sub-units Uci and Uc2 to the control unitUDP;(c) determining, prior to passing the stream So into a batch drum B(i) according to (ii), parameters of a parameter space Q(So) of the stream So in the analytical unit UA, wherein the parameters of Q(So) correspond to the parameters of Q(SF); and passing the parameters of Q(So) to the control unit UDP;(d) determining in the control unit UDP, based on the parameters of the parameter space Q(SF) provided according to (a) and further based on the operating characteristics of the crystallization cycle sub-units Uci and Uc2 provided according to (b), the number of crystallization cycles P(x) and the number of crystallization cycles C(y) necessary to change the parameters of Q(So) to the parameters of Q(SF), and further determining the batch drum B(i) into which the crude E-caprolactam feed stream So is to be passed;(e) determining, in the control unit UDP, operation instructions for the controllable means of the batch drum sub-unit UB, the stream distribution sub-unit UD and the crystallization cycle sub-units Uci and Uc2 to realize number of crystallization cycles P(x) and the number of crystallization cycles C(y) determined according to (d);(f) carrying out a crystallization process according to any one of embodiments 28 to 35, comprising passing the operation instructions determined according to (e) to the controllable means. The method of embodiment 38, wherein the parameter space Q(SF) comprises one or more of the E- caprolactam purity QGC(SF), the APHA value QAPHA(SF), the permanganate absorption number QPAN(SF), and the UV absorption QUV(SF), preferably at least QGC(SF) and QAPHA(SF), whereinQGC(SF) is preferably at least 99.5 area-%, more preferably at least 99.8 area-%, more preferably at least 99.9 area-%;QAPHA(SF) is preferably at most 6, more preferably most 5, more preferably at most 4;QPAN(SF) is preferably at most 6, more preferably at most 5, more preferably at most 4;QUV(SF) is preferably at most 0.1 , more preferably at most 0.07, more preferably at most 0.05; and wherein the parameter space Q(So) comprises one or more of the E-caprolactam purity QGC(SO), the APHA value QAPHA(SO), the permanganate absorption number QPAN(SO), and the UV absorption Quv(So), preferably at least QGC(SO) and QAPHA(SO), wherein at least one of the following, preferably at least two of the following relations are met, wherein more preferably, said at least two relations comprise one or more of the relations for QGC(SO) and QAPHA(SO):QGC(SO) < QGC(SF);QAPHA(SO) > QAPHA(SF);QPAN(SO) > QPAN(SF);Quv(So) > QUV(SF). A computer program, comprising instructions which, when the program is executed by the computer- supported control system according to embodiment 25, cause the system to perform the method according to embodiment 38 or 39. A non-transient computer-readable medium containing instructions which, when executed by one or more processors, cause the one or more processors to perform the program according to embodiment 40. A process, preferably according to any one of embodiments 27 to 35, more preferably according to any one of embodiments 28 to 35, comprising the step of converting the final residue stream SRF obtainable or obtained according to (ill.1.3.1) and / or the final residue stream SRF obtainable or obtained according to (ill.2.3.1) and / or the final E-caprolactam fine product stream SPF obtainable or obtained according to (ill.1.5.1) and / or achemical material obtainable by or obtained by the process according to any one of embodiments 27 to 35, preferably according to any one of embodiments 28 to 35, to obtain a product product cp. A process comprising the step of using the crystallization unit U according to any one of embodiments 1 to 26, preferably according to any one of embodiments 11 to 26, to obtain a final residue stream SRF and / or a final E- caprolactam fine product stream SPF; and preferably converting the final residue stream SRF and / or the final E- caprolactam fine product stream SPF to obtain a product cp. The process of embodiment 42 or 43, wherein the product cp is selected from: building block or monomer; or polymer, preferably polymer A, polymer composition, preferably polymer composition A, or polymer product, preferably polymer product A; or industrial use polymer, industrial use surfactant, descaling compound, industrial use biocide, industrial use solvent, industrial use dispersant, composition thereof or formulation thereof; or agrochemical composition, agrochemical formulation auxiliary or agrochemically active ingredient; or active pharmaceutical ingredient or intermediate thereof, pharmaceutical excipient, animal feed additive, human food additive, dietary supplements, aroma chemical or aroma composition; or aqueous polymer dispersion, preferably polyurethane or polyurethane - poly(meth)acrylate hybrid polymer dispersion, emulsion, binder for paper and fiber coatings, UV-curable acrylic polymer for hot melts and coatings polyisocyanates, hyperbranched polyester polyol, polymeric dispersant for inorganic binder compositions, unsaturated polyester polyol or 100% curable composition; or cosmetic surfactant, emollient, wax, cosmetic polymer, UV filter, further cosmetic ingredient or composition or formulation thereof; or polymer B, polymer composition B, coating composition, other functional composition, foil, molded body, coating or coated substrate. The process of any one of embodiments 42 to 44, wherein the content of the final residue stream SRF and / or the final E-caprolactam fine product stream SPF and I or the chemical material in the product cp is 1 weight-% or more, preferably 2 weight-% or more, more preferably 5 weight-% or more, more preferably 15 weight-% or more, more preferably 30 weight-% or more, more preferably 40 weight-% or more, more preferably 60 weight-% or more, more preferably 80 weight-% or more, more preferably 90 weight-% or more, more preferably 95 weight-% or more; and / or wherein the content of the final residue stream SRF and / or the final E-caprolactam fine product stream SPF and I or the chemical material in the product cp is 100 weight-% or less, preferably 95 weight-% or less, more preferably 90 weight-% or less, more preferably 50 weight-% or less, more preferably 25 weight-% or less, more preferably 10 weight-% or less; and preferably wherein the content is determined based on identity preservation and / or segregation and / or mass balance and / or book and claim chain of custody models,preferably based on mass balance, preferably the International Sustainability and Carbon Certification (ISCC) standard.The present invention is further illustrated by the following examples and figures.Short description of the figuresFigure 1 illustrates a crystallization unit U according to the present invention, a process of the present invention carried out therein, and a method of the present invention for controlling said process. Figure 1 shows a unit U comprising 2 crystallization sub-units Uci and Uci , a batch drum sub-unit UB comprising 4 batch drum B(i), i.e. k=4, and a stream distribution sub-unit UD connecting Uci , Uc2 and UB.The crystallization sub-unit Uci exhibits 2 crystallizers Wci(1) and Wci(2), i.e. s=2, which are connected via the transportation line Lei wherein Lei passes through Wci(1) and Wci(2) (dotted arrows). Heating and / or cooling of Wci(1) and Wci(2) is accomplished via a heat transfer medium HTM. The stream transportation line Lei further exhibits and entry and exit point Eci via which a stream is passed to and from the stream distribution sub-unit UD. Further, controllable means MECI are shown which serve for passing a stream from UD into Lei and for passing a stream from Lei to UD. Yet further, Lei comprises controllable means MLCI for circulating a stream through Lei. Between Wci(1) and Wci(2), the stream transportation line Lei is connected to an expansion drum BECI.The crystallization sub-unit Uc2 exhibits 2 crystallizers Wc2(1) and Wc2(2), i.e. s=2, which are connected via the transportation line I_c2 wherein I_c2 passes through Wc2(1) and Wc2(2) (dotted arrows). Heating and / or cooling of Wc2(1) and Wc2(2) is accomplished via a heat transfer medium HTM. The stream transportation line I_c2 further exhibits and entry and exit point Ec2 via which a stream is passed to and from the stream distribution sub-unit UD. Further, controllable means MEC2 are shown which serve for passing a stream from UD into I_c2 and for passing a stream from I_c2 to UD. Yet further, I_c2 comprises controllable means MLC2 for circulating a stream through l_c2. Between Wc2(1) and Wc2(2), the stream transportation line I_c2 is connected to an expansion drum BEC2.The stream distribution sub-unit UD according to Figure 1 exhibits 3 stage stream transportation lines Lsi(1 ), Lsi(2) and Lsi(3) via which streams are passed from the respective batch drums B(1), B(2) and B(3) to the crystallization sub-unit Uci. Further, 3 stage stream transportation lines Ls2(2), Ls2(3) and Ls2(4) are shown via which streams are passed from the respective batch drums B(2), B(3) and B(4) to the crystallization sub-unit Uc2.Further, the stream distribution sub-unit UD according to Figure 1 exhibits 3 back stream transportation lines LBI(1 ), LBI (2) and LBI (3) via which streams are passed from the crystallization sub-unit Uci to the respective batch drums B(1), B(2) and B(3). Further, 3 back stream transportation lines LB2(2), LB2(3) and LB2(4) are shown via which streams are passed from the crystallization sub-unit Uc2 to the respective batch drums B(2), B(3) and B(4).Further, the Figure 1 shows, comprised in the sub-unit UD, controllable means Mi_si(i), in particular MLSI(1 ), MLSI(2) and MLSI(3), which are used for passing a stream from the respective batch drum B(i) to the (in this case: entry) point Eci of the crystallization sub-unit Uci via the respective transportation line Lsi(i); controllable means Mi_s2(i), in particular MLS2(2), MLS2(3) and MLS2(4), which are used for passing a stream from the respective batch drum B(i) to the (in this case: entry) point Ec2 of the crystallization sub-unit Uc2 via the respective transportation line Ls2(i); controllable means MLBIO), in particular MLBI(1 ), MLBI(2) and MLBI(3), which are used for passing a stream from (in this case: exit) point Eci of the crystallization sub-unit Uci via the respective transportation line LBI (i); controllable means MLB20), in particular MLB2(2), MLB2(3) and MLB2(4), which are used for passing a stream from (in this case: exit) point Ec2 of the crystallization sub-unit Uc2 via the respective transportation line LB2(I) to the respective batch drum B(i). controllable means MLRI via which the final residue stream SRF obtained from the crystallization process is removed from the crystallization unit U via the transportation line LRI via (in this case: exit) point Eci ; controllable means MLF2 via which the final fine product stream SPF obtained from the crystallization process is removed from the crystallization unit U via the transportation line LF2 via (in this case: exit) point Ec2.It is noted that as shown in Figure 1, 2 or more transportation lines can be realized, over a certain length, by 1 single transportation line; reference is made, by way of example, to Lsi (3) and Ls2(3); or to the transportation line connecting, from left to right, MLRI(1), MLBI(1), MLSI(1), MLBI(2), MLSI(2), MLB(3) and MLSI(3). According to the present invention, it is also possible that each transportation line is realized as a separate transportation line.Further, the Figure 1 shows, comprised in the batch drum sub-unit UB, 4 batch drums B(1 ), B(2), B(3) and B(4) which further exhibit controllable means MB(I) for passing a stream from a given batch drum B(i) via the stream distribution sub-unit UD according to at least one of the crystallization sub-units Uci (via Eci) and Uc2 (via Ec2).Further, the Figure 1 illustrates a unit U (and a process carried out therein) which allows for varying the number of crystallization cycles by choosing, depending, among others, on the specific parameter space Q(SF) of the final E- caprolactam fine product stream SPF and parameter space Q(So) of the stream So passed to crystallization, the specific batch drum B(i) into which the stream So is fed.In particular, the unit U as shown in Figure 1 allows for passing the stream So into the batch drum B(4) via the stream transportation line Lso, in case only one crystallization cycle P(x) (one pure cycle) needs to be carried out (in Uc2). After crystallization, the respectively obtained residue stream is either passed via the transportation line LRI as final residue stream SRF via MLRI to optional further use (in accordance with (ill.1.3.1)) Alternatively, in accordance with (ill.1.3.2), this residue stream may be passed via the transportation line LB2(3) into the batch drum B(3).Further in particular, the unit U as shown in Figure 1 allows for passing the stream So into the batch drum B(3) via the stream transportation line Lso, in case 2 crystallization cycles P(x) (two pure cycles) need to be carried out (in Uc2). (In the following, only the crystallization cycles P(x) are discussed in detail.) In this case, among others, a stage stream S2(3) is passed from B(3) via Ls2(3) to Uc2 and subjected there to crystallization. The product stream SR(3), in this particular case not removed from the unit U as final product stream SPF via LF2, is passed via LB2(4) into the batch drum B(4). From B(4), a stage stream Ss(4) is then passed to Uc2 via Ls2(4), and the product stream SR(4) obtained from Uc2, i.e. the product stream after 2 (pure) cycles P(1) and P(2), is then removed from the unit U as stream SPF via LF2.Further in particular, the unit U as shown in Figure 1 allows for passing the stream So into the batch drum B(2) via the stream transportation line Lso, in case 3 crystallization cycles P(x) (three pure cycles) need to be carried out (in Uc2). (In the following, again, only the crystallization cycles P(x) are discussed in detail.) In this case, among others, a stage stream S2(2) is passed from B(2) via Ls2(2) to Uc2 and subjected there to crystallization (crystallization cycle P(1 )). The product stream SP(3), in this particular case not removed from the unit U as final product stream SPF via LF2, is passed to the batch drum B(3) via LB2(3). From B(3), a stage stream Ss(3) is then passed via Ls2(3) to Uc2 and subjected there to crystallization (crystallization cycle P(2)). The product stream SP(3), again not removed from the unit U as final product stream SPF via LF2, is passed via LB2(4) into the batch drum B(4). From B(4), a stage stream Ss(4) is then passed to Uc2 via Ls2(4), and the product stream SP(4) obtained from Uc2 after the crystallization cycle P(3), i.e. the product stream after in total 3 (pure) cycles P(1 ), P(2) and P(3), is then removed from the unit U as stream SPF via LF2.Figure 2 illustrates a preferred design of the unit U with regard to one or more batch drums B(i). According to this design, a batch drum B(i) is further equipped with a back mixing transportation line LMB(I) which in turn is equipped with respective controllable means MLMBO) for passing a stream from B(i) via MB(I) back into B(i).Figure 3 illustrates a method according to present invention for controlling a process according to the present invention. Figure 3 shows a stream So to be passed to crystallization. Prior to passing the stream So to the crystallization process carried out in the crystallization unit U, in particular prior to passing the stream So into a specific batch drum B(i), parameters of a parameter space Q(So) of the stream So are determined in the analytical unit UA. The respectively obtained parameters are provided (dashed arrow) from the analytical unit UA to the control unit UDP. Further according to the method, the respective parameters of the parameter space Q(SF) of the final E-caprolactam fine product stream SPF to be obtained from the crystallization process are provided (dashed arrow) to the control unit UDP. Further, the operating characteristics of the crystallization sub-units used in the process (here: the operating characteristics OC(Uci) and 0C(Uc2) of the sub-units Uci and Uc2) are provided (dashed arrow) to the control unit UDP. Based on these input parameters, the number of crystallization cycles P(x) and the number of crystallization cycles C(y) are determined in UDP which are necessary to change the parameters of Q(So) to theparameters of Q(SF). Further in UDP, it is determined into which of the batch drums B(i) the crude E-caprolactam feed stream So is to be passed so as to allow for realizing said number of crystallization cycles P(x) and C(y). Based on the respective results, operating instructions 01 for the controllable means of the batch drum sub-unit UB, the stream distribution sub-unit UD and the crystallization sub-units are determined in UDP to realize said number of crystallization cycles P(x) and C(y). These operating instructions are then suitably passed (dashed arrows) to the respective controllable means Mi to Mz in the course of the crystallization process CP which controllable means then control (dotted arrows) the individual stages of the crystallization process CP accordinglyPreferably, determination and controlling as described are at least partially supported and / or carried out by a computer-supported control system which is a part of UDP or of which UDP consists of.ExamplesReference Example 1 : Measurement methods for determination of the parameters of the parameter space Q(So) and Q(SF)1 .1 Determination of QGC(SO) I QGC(SF)The purity of E-caprolactam and the respective amounts of impurities were determined via GC analysis. For GC analysis on purity of Caprolactam, samples were prepared in deionized water at concentration of approx. 200 mg / mL. Analysis was performed on a standard GC instrument equipped with a split / splitless injector and an FID. The injection volume was 1 piL (microL) at a split ratio of 15:1. The injector temperature was 250 °C. The instrument was operated in constant pressure mode at 14.5 psi (~ 1 bar), and nitrogen was used as carrier gas. Separation was performed on a Wax 52 CB column, 50 m x 0.32 mm, 1.2 pm from Agilent Technologies. The temperature program started with a ramp from 80 °C to 185 °C at a heating rate of 7 °C / min, and a hold time at 185 °C for 30 min. A second ramp was from 185 °C to 200 °C at a heating rate of 7 °C / min, and a hold time at 200 °C for 5 min. The detector (Flame Ionization Detector, FID) temperature was 250 °C. Evaluation of purity values QGC was based on area-% distribution, corrected by the content of water determined by Carl Fisher Method.1 .2 Determination of QAPHA(SO) I QAPHA(SF)The APHA color was determined in accordance with ISO 8112. In principle, the extinction E of a 50 % by weight aqueous E-caprolactam solution is determined in a cuvette of length I = 5 cm at a wavelength A = 390 nm and expressed in Hazen units (platinum-cobalt scale). For doing so, the measured extinction E is multiplied by the factor f = 150. The Hazen units (platinum-cobalt scale) are defined as the color of a solution containing, in 1 I water, 1 mg platinum in the form of hexachloroplatinum(IV) acid in the presence of 2 mg cobalt(ll) chloride hexahydrate. The Hazen units correspond to the APHA units. A standard solution of 500 Hazen units as prepared as follows: 1 .000 gcobalt(ll) chloride hexahydrate (C0CI2 ■ 6 H2O) and 1.245 g potassium hexachloroplatinate(IV) (faPtCle) are dissolved in 100 ml hydrochloric acid having a of 1.19 g / ml. The solution is transferred into a 1000 ml volumetric flask which is filled to the calibration mark. This solution contains 500 mg platinum and corresponds to 500 Hazen units. A specific amount of E-caprolactam, usually in the range of from 5 to 50 g, is dissolved in a 250 Erlenmeyer flask in 50 ml distilled water. The solution is mixed and left until the air bubbles have disappeared. The 2 cuvettes of the spectrophotometer (which is suitable for measurements at a wavelength A = 390 nm) are filled with distilled water, placed in the beam path, and the spectrophotometer is adjusted at A = 390 nm to E = 0. Then, the distilled water is removed from the sample cuvette, followed by filling this cuvette with the E-caprolactam solution. Then, the extinction E of this solution is determined at A = 390 nm (E390) against the comparative cuvette containing distilled water. The color number X (Hazen units, platinum-cobalt scale) is calculated as X = E ■ f = 150 ■ E390. X is rounded to the next integer.1 .3 Determination of QPAN(SO) I QPAN(SF)The PAN values were determined in accordance with DIN ISO 8660.1 .4 Determination of Quv(So) I Ouv(So)The UV / Vis absorption values were determined at a wavelength of 290 nm in accordance with DIN ISO 7059.Example 1 : Lab Scale Dynamic Layer CrystallizationIn order to mimic the most preferably large-scale crystallization process of the present invention, the following lab setup was used. This lab setup comprised a batch drum B(1 ), a product drum BF for receiving the final fine product stream obtained from the crystallization, and a residue drum BR for receiving the final residue stream obtained from the crystallization; a crystallization unit Uqi) comprising two crystallizers Wc(i(i» and Wc(2(i»; a circulation loop and a circulation pump; expansion drum connected to the top part of the circulation tube to compensate for density differences between liquid and solidified product as well as release of air.This lab setup in principle illustrates a crystallization unit U according to the present invention, as also shown in Figure 1 with respect to the afore-mentioned parts employed in the lab setup.All drums were connected to each other and to the crystallization cycle / loop via transportation lines (pipes / tubes) as defined herein. Tubes leading from the crystallizer towards a stage drum could be closed or opened via valves. The main part of the crystallizer was a tube. The outer wall (shell side) of the tube could be thermostated by a thermostatin a controlled manner by means of a heat transfer medium. E-caprolactam was crystallized out on the inner pipe surface by decreasing the temperature of the tube wall by means of the thermostat.For the experiment corresponding to a purification stage where optional seeding is applied, the crystallization loop was filled with E-caprolactam. Subsequently, this E-caprolactam was drained. The remaining liquid E-caprolactam film on the crystallizer tube was crystallized by decreasing the temperature of the crystallizer tube wall to the seeding temperature. As a next step, the crystallizer tube was pre-heated to a temperature below the freezing temperature of the feed to maintain the crystallized layer on the crystallizer tube. In a further step, the crystallizer loop was filled with the feed (molten E-caprolactam melt) from drum B(1 ). During this step, the crystallizer tube was kept below the freezing temperature (melting point) of the feed. After complete filling, the valves of the charging pipes were closed and circulation was started via the circulation pump. The wall temperature of the crystallizer tube was then decreased linearly within 1 h to the final crystallization temperature via the thermostat connected to the crystallizer tube.The temperature profile was chosen in order to crystallize I freeze out a certain fraction of the E-caprolactam in the feed mass of one batch (e.g. 40-70 weight-% based on the batch mass). When the final crystallization temperature was reached, the remaining liquid residues (mother liquor, enriched in impurities with respect to feed) were removed by opening the exit valve of the crystallization loop and the valve in the pipe towards the residue drum. After draining of the residues, the temperature of the tube wall of the crystallizer was increased above the melting point of the product crystals on the wall of the tube to melt off the crystallized E-caprolactam on the tube wall, i.e. product exhibiting a higher purity than the feed). This product was then transferred to the product where the purified E- caprolactam (fine product) was collected for further use.In order to further increase the purity of the obtained purified product, it was an option to apply sweating before the crystallized product mass was molten off. The time and the temperature were chosen with respect to the intended sweating mass, i.e. the liquid residuals sweated out of the crystal layer and the desired purification efficiency, i.e. the distribution coefficient. The liquid residues enriched with impurities, sweated out of the crystallizer, were then collected in the residue drum or the drum B(1 ). After reaching the final sweating temperature, the temperature of the crystallizer tube was increased to melt off the crystallized product mass on the tube wall. This product mass was then transferred to the product vessel.Preferably, the process in accordance with the present invention comprises a sweating step. More preferably, during sweating, up to 15 % by mass of the feed, such as from 0.1 to 15 % by mass of the feed or from 0.2 to 10 % by mass of the feed, are removed from the crystallized product mass on the tube wall by each sweating step. For sweating, the temperature of the crystallizer tube is increased, preferably over a time of up to 1 hour. The final sweating temperature is preferably 20 °C below or above the melting point of pure E-caprolactam, more preferably 15 °C below or above the melting point of pure E-caprolactam, more preferably 10 °C below or above the melting point of pure E-caprolactam, more preferably 5 °C below or above the melting point of pure E-caprolactam..After the crystallization loop was emptied, the next batch could be started and the aforementioned steps were respectively repeated. The respective temperature profile applied to the crystallizer tube via the heat transfer medium of the thermostat was adjusted according to the solid-liquid equilibrium of the feed, i.e. the purity of the feed determined prior to feeding it into the crystallization unit. All surfaces in contact with E-caprolactam, apart from the crystallizer tube, were thermostated so that any undesired crystallization was prevented.Table 1Summary of experimental results by performing crystallization trials as described in this example.<1> k corresponds to the effective distribution coefficient, which relates the measured "quality parameter” (parameter of the respective parameter space Q) of the stage product (molten crystallized mass) to the respective "quality parameter” of the stage feed (mixture intended to be crystallized). In this context, "effective” means that this parameter corresponds to an average "purity parameter” of the analysed sample (e.g. feed, product, residuals, and so forth). For example, for a determined GC purity of 99 area-% of the feed and 99.5 area-% of the molten product, the / Ceft.Gc is calculated as / ceff,Gc = (100-99.5) / (100-99) = 0.5. Consequently, values for the distribution coefficient < 1 indicate a purification effect and a value of 1 or >1 indicate no purification effect or a decrease in purity (e.g. product decomposition) with respect to the quality parameter (here GC purity). In an analogue way, the purification efficiency can be defined for other quality parameters. Notably, GC values stated were corrected by the water content of the sample.Example 2: Production-Scale Dynamic Layer CrystallizationAccording to the present invention, a production-scale (e.g. a cubic-meter scale) dynamic layer crystallization unit was used. The unit comprised six batch drums B(1) to B(6) for feed of crystallization stages 1 to 6, a product drum BF for receiving the final fine product stream SPF, and a residue drum BR for receiving the final residue stream SRF obtained from the crystallization; each stage drum B(1) to B(6) comprised an individual pump to fill stage feed from the stage drums into the crystallizers as well as to mix material within the stage drums; two crystallization sub-units Uci and Uc2, wherein each crystallization unit comprised two crystallizers Wci(1) and Wci(2), and Wc2(1) and Wc2(2), respectively; each of the crystallization sub-units Uci and Uc2 wereconnected to a separate heating and cooling unit that supplies heat transfer medium for temperature control; each crystallization sub-unit Uci and Uc2 also comprised a heat-traced circulation loop and a heat-traced circulation pump, and expansion drums BECI and BEC2 connected to the top part of the circulation pipe to compensate for density differences between liquid and solidified product as well as release of air.This production-scale setup in principle illustrates a crystallization unit according to the present invention, as also shown in Figure 1 with respect to the afore-mentioned parts employed in the production-scale setup.All drums were connected to each other and to the crystallization sub-units Uci and Uc2 via transportation lines (pipes) as defined herein. Pipes leading from the crystallizer towards a stage drum could be closed or opened via valves. The main part of each crystallizer was configured as a tube-bundle. The outer wall (shell side) of the tubes could be heated I cooled by a respective heating I cooling unit in a controlled manner by means of a heat transfer medium. E-caprolactam was crystallized out on the inner tube (product side) surface by decreasing the temperature of the tube wall by means of the heating I cooling unit.In the following, the procedure for a crystallization stage I batch is exemplarily illustrated for crystallization stage 4 for the case that stage drum B(4) receives the feed for the crystallization unit from upstream. The feed comprised E- caprolactam melt with impurities. The average quality parameters of the feed were evaluated as:GC purity: > 99.7 area-%UV(290 nm): 0.25PAN: 21.3The feed to be purified was received in stage drum B(4). For a crystallization stage where optional seeding (sometimes also referred to as priming) is applied, the pre-heated crystallization unit (pre-heated to above the melting point of pure caprolactam) was filled with E-caprolactam melt including impurities from the respective stage drum. Subsequently, this E-caprolactam melt was drained again to the stage drum of origin. In this way, the crystallizer tubes were wetted with E-caprolactam melt. The remaining liquid E-caprolactam "film” on the wetted crystallizer tubes was crystallized by decreasing the temperature of the crystallizer tube walls to the intended seeding temperature below the melting point of the E-caprolactam melt to wet the crystallizer tubes.After seeding, the crystallizer tubes were pre-heated to a temperature below the freezing temperature (e.g., the melting point) of the feed from stage drum B(4) to maintain the crystallized seeding layer on the crystallizer tubes. Next, the crystallizer sub-unit Uc2 was filled with the feed of molten E-caprolactam melt with impurities from stage drum B(4); this process step is also referred to as crystallization stage 4. During this step, the crystallizer tubes were kept below the freezing temperature (e.g., the melting point) of the feed. After complete filling, i.e. reaching a level in the expansion vessel BEC2 of approximately 80 to 90 %, the valves of the charging pipes were closed and circulation was started via the circulation pump in the circulation loop of crystallization sub-unit Uc2. The wall temperature of thecrystallizer tubes was then decreased essentially linearly within about 1 h to the final crystallization temperature via the heat transfer medium supplied by the heating I cooling system connected to the crystallizers. After the final crystallization temperature (i.e. after about 1 h) was reached, the residue liquid mass was released from the crystallization sub-unit Uc2 to the next (lower) stage drum B(3).In order to further increase the purity of the obtained crystallized material on crystallizer tube walls as the purified product, optionally sweating may be applied at this stage before the crystallized product mass is melted off. The time and the temperature may be chosen with respect to the intended sweating mass, i.e. the liquid residuals sweated out of the crystal layer and the desired purification efficiency, i.e. the distribution coefficient. The liquid residues enriched with impurities, sweated out of the crystallizer, can then collected in the next lower drum (e.g.: stage drum B(3)). After reaching the final sweating temperature, the temperature of the crystallizer tube may be further increased to melt off the crystallized product mass on the wall of the crystallizer tubes. This product mass may then transferred and collected in the next higher stage drum (here: stage drum B(5)).After the crystallization sub-unit Uc2 was emptied, the next batch was started in Uc2. The aforementioned procedure was repeated for crystallization stages 1 to 6, wherein material from stage drums B(1) to B(3) was crystallized in the crystallization sub-unit Uci (also referred to as the "yield cycle”), and melt in stage drums B(4) to B(6) was crystallized in the crystallization sub-unit Uc2 (also referred to as the "purification cycle”). In this setup, Uci could be operated in parallel to carrying out crystallization stages 1 to 3 (e.g., the yield cycle) while Uc2 was operated to carry out one of the crystallization stages 4 to 6 (e.g., the purification cycle).The melt purity with respect to E-caprolactam increased from stage drum B(1) to stage drum B(6). The stream with the lowest purity corresponded to residue stream SRF and the stream with the highest purity with respect to E- caprolactam corresponded to the product stream SPF that was obtained after having carried out stage 6 (e.g. corresponds to molten crystals after optional sweating is applied).The respective temperature profile applied to the crystallizer tubes via the heat transfer medium was adjusted according to the solid-liquid equilibrium (e.g. freezing temperature) of the feed, i.e. the purity of the feed determined prior to feeding it into the crystallization unit. The stage drum in which the feed for the crystallization unit was collected from upstream processes was chosen with respect to the purity of the feed determined prior to feeding it into the crystallization unit and the intended purity of the final product SPF. All surfaces in contact with E-caprolactam, apart from the crystallizer tubes were thermostated so that any undesired crystallization was prevented. The order which crystallization stage was executed was determined by the stage drum filling levels.Tables 2 and 3 hereinbelow summarize typical quality parameters obtained with the production scale setup (UV (290 nm) and PAN number of the melt) in the different "stages” for a production campaign carried out according to the procedure mentioned above. Clearly, the UV and the PAN number of the melt decrease (i.e. the purity increases)from the one obtained for the feed stream So with increasing stage drum number. The highest purity (lowest UV and PAN number) was obtained for the final product SPF (molten crystals after stage 6 crystallization) after three purification stages. Based on the obtained results from Table 2 and Table 3, the effective purification factors (i.e. distribution coefficient) Zceff,uv and keff. PAN were calculated.Due to the sampling procedure in the production plant, the quality parameter UV and PAN were determined from samples of the melt in the respective stage drums. The quality parameters for the "stage feed” were determined from a melt sample taken from the respective stage vessel, and the quality parameters for the stage product were taken from a sample of the next higher stage drum that collected the purified stage product and the residue of the next higher stage.The effective distribution coefficients / ceff,uv and keff.PAN for crystallisation stage 4 were determined as follows: a sample was taken from stage drum B(4); another sample was taken after stage 4 execution from stage drum B(5) in which the product of stage 4 was collected; the thus determined quality parameters were then put into relation to each other as follows: the respective quality parameter (e.g. UV number, PAN number) was put into relation from the next higher stage drum (which approximates the product purity) to the respective quality parameter in the current stage drum where the stage feed for crystallization was sent to the crystallizer in order to be crystallized.In this way, the effective distribution coefficients were calculated for the given values for Example 2a in Table 2 and Example 2b Table 3. The distribution coefficient relates the quality parameter from the sample of the stage feed drum either to the next drum that collected the crystallized product or to the final product stream SPF. An analogous procedure was applied for the other stages including the final residue stream SRF and final pure product stream SPFTable 2Summary of typical quality parameter UV (290 nm) and PAN number for stage streams obtained in a production campaign with the production-scale setup. Given values are rounded.Effective distribution coefficients determined based on UV(290 nm) and PAN values for samples taken from respective stage drums and final product stream SPF. Feed So given in Table 2 was collected for the trials in stage drum B(4). In this context,“effective” means that this parameter corresponds to an average “purity parameter” of the analysed sample (e.g. stage feed, material in next higher stage vessel with respect to the executed stage).Table 3 Summary of typical quality parameter UV (290 nm) and PAN number for stage streams obtained in a production campaign with the production-scale setup. Given values are rounded.<1> Distribution coefficients determined based on U V(290 nm) and PAN values for samples taken from respective stage drums and final product stream SPF. Feed SO given in Table 3 was collected for the trials in stage drum B(4).

Claims

1. Claims1 . A crystallization unit U for carrying out an E-caprolactam crystallization process, wherein the unit U comprises(1) h crystallization sub-units Uc(H), H = 1 ...h and h > 2, wherein each crystallization sub-unit UC<H) comprises s crystallizer WC(S(H», S(H) = 1...S and s > 1; a stream transportation line LC(H) passing through the s crystallizer WC(S(H», comprising an entry and exit point EC<H) connected to the stream distribution sub-unit UD according to (3) and further comprising controllable means MEC(HJ for passing a stream from UD into LC(H) and for passing a stream from LC(H) to UD;(2) a batch drum sub-unit UB comprising k batch drums B(i) with I = 1 ...k and k > 2, wherein each batch drum B(i) is equipped with controllable means MB(I) for passing a stream from B(i) via the stream distribution sub-unit UD according to (3) to at least one of EC(H>; a crude E-caprolactam feed stream transportation line Lso to at least one batch drum B(i);(3) a stream distribution sub-unit UD connecting UB and the h sub-units UC<H), the sub-unit UD comprising(3.1) for each drum B(i) with i = 1...k(3.1.1) at least one of a stage stream transportation line Ls<Hi)(i) from B(i) to at least one Ec(W) and a stage stream transportation line Ls<H2)(i) from B(i) to at least one EC<H2), H1 + H2, wherein Ls<Hi)(i) comprises at least one controllable means MLS<HI)(I) for passing a stream from B(i) to EC<HI) and Ls<H2)(i) comprises at least one controllable means MLS<H2)(I) for passing a stream from B(i) to EC(H2>;(3.1 .2) at least one of a back stream transportation line LB<H i)(i) from EC<HI) to B(i) and a back stream transportation line LB<H2)(i) from Ec(H2) to B(i), wherein LB(HI)O) comprises at least one controllable means MLB<HI)(I) for passing a stream from EC<HI) to B(i) and LB<H2)(i) comprises at least one controllable means MLB<H2)(I) for passing a stream from EC(H2> to B(i);(3.2) a final residue stream transportation line LR<H3) , H3 + H1,H2, for removing a final crystallization residue stream SRF from a transportation line LC(H) via EC<H), wherein LR<H3) comprises at least one controllable means MLR<H3) for removing said final residue stream SRF from LC(H>;(3.3) a final fine product stream transportation line LF(H4), H4 + H1,H2,H3, for removing a final fine crystallization product stream SPF from a transportation line LC<H) via EC(H), wherein LF<H4) comprises at least one controllable means MLF<H4) for removing said final fine product stream SPF from LC(H).

2. The crystallization unit U of claim 1 , wherein at least one of the crystallizer WC(S(H», preferably each crystallizer WC(S(H» is configured as a shell-and-tube heat exchanger, preferably as a vertically mounted shell-and-tubeheat exchanger, comprising an entry point for passing a heat transfer medium into the shell and an exit point for removing the heat transfer medium from the shell; wherein at least one crystallization sub-unit Uc(H), preferably each crystallization sub-unit UC<H) comprises at least 2 crystallizer WC(S(H» and further comprises a circular stream transportation line LC(H) passing through the at least 2 crystallizer WC(S(H», wherein the at least one crystallization sub-unit Uc(H), preferably each crystallization sub-unit UC<H) further comprises controllable means MLC(H) for circulating a stream through LC(H).

3. The crystallization unit U of claim 1 or 2, wherein h = 2 and s = 2, wherein the unit U comprises(1) two crystallization cycle sub-units Uci and Uc2, wherein(1.1) the first crystallization cycle sub-unit Uci comprises a first crystallizer Wci(1) and a second crystallizer Wci(2); a circular stream transportation line Lei passing through Wci(1) and Wci(2), comprising an entry and exit point Eci connected to the stream distribution sub-unit UD according to (3) and further comprising controllable means MLCI for circulating a stream through Lei, wherein Eci comprises controllable means MECI for passing a stream from UD into Lei and for passing a stream from Lei to UD;(1 .2) the second crystallization cycle sub-unit Uc2 comprises a first crystallizer Wc2(1) and a second crystallizer Wc2(2); a circular stream transportation line I_c2 passing through Wc2(1) and Wc2(2), comprising an entry and exit point Ec2 connected to the stream distribution sub-unit UD according to (3) and further comprising controllable means MLC2 for circulating a stream through I_c2, wherein Ec2 comprises controllable means MEC2 for passing a stream from UD into I_c2 and for passing a stream from I_c2 to UD;(2) a batch drum sub-unit UB comprising k batch drums B(i) with I = 1 ...k and k > 4, wherein each batch drum B(i) is equipped with controllable means MB(I) for passing a stream from B(i) via the stream distribution sub-unit UD according to (3) to at least one of Eci and Ec2; a crude E-caprolactam feed stream transportation line Lso to at least one batch drum B(i);(3) a stream distribution sub-unit UD connecting UB, UCI and Uc2, the sub-unit UD comprising(3.1) for each drum B(i) with I = 1 ...k(3.1.1) at least one of a stage stream transportation line Lsi (i) from B(i) to Eci and a stage stream transportation line Ls2(i) from B(i) to Ec2, wherein Lsi (i) comprises at least one controllable means Mi_si(i) for passing a stream from B(i) to Eci and Ls2(i) comprises at least one controllable means Mi_s2(i) for passing a stream from B(i) to Ec2;(3.1.2) at least one of a back stream transportation line l_Bi(i) from Eci to B(i) and a back stream transportation line l_B2(i) from Ec2 to B(i), wherein LBI (i) comprises at least onecontrollable means MLBI(I) for passing a stream from Eci to B(i) and LB2(I) comprises at least one controllable means MLB2(I) for passing a stream from Ec2 to B(i);(3.2) a final residue stream transportation line LRI for removing a final crystallization residue stream SRF from Lei via Eci, wherein LRI comprises at least one controllable means MLRI for removing said final residue stream from Lei;(3.3) a final fine product stream transportation line LF2 for removing a final fine crystallization product stream SPF from I_c2 via Ec2, wherein LFI comprises at least one controllable means MLF2 for removing said final fine product stream SPF from Lei ■4. The crystallization unit U of any one of claims 1 to 3, wherein each controllable means, each batch drum B(i) and each transportation line is configured to be heatable to a temperature of at least 50 °C, preferably at least 60 °C, more preferably at least 70 °C, the crystallization unit U further comprising means MH for heating each controllable means, each batch drum B(i) and each transportation line.

5. The crystallization unit U of any one of claims 1 to 4, wherein upstream of the at least one B(i), the crude E- caprolactam feed stream transportation line Lso comprises an analytical unit UA for analysing a crude E- caprolactam feed stream So to be passed into B(i) with respect to at least one crude E-caprolactam feed quality parameter selected from the group consisting of an E-caprolactam purity QGC(SO), an APHA value OAPHA(SO), a permanganate absorption number QPAN(SO), and an UV absorption Quv(So).

6. The crystallization unit U of any one claims 1 to 5, comprised in a plant PDP for depolymerization of polyamide 6 and purification of E-caprolactam obtained from said depolymerization, said plant PDP preferably comprising a melting and mixing unit for preparing a depolymerizaton mixture from a solid material M comprising polyamide, the material M preferably being a waste material, more preferably a textile waste material and / or an engineering plastic waste material, the melting and mixing unit being arranged upstream of a preferably hydrolytic depolymerization unit for depolymerizing polyamide 6 comprised in said depolymerizaton mixture, the depolymerization unit being arranged upstream of a purification unit for purifying E-caprolactam obtained from said depolymerization unit, the purification unit comprising at least one of one or more water separation units, one or more high boiler separation units for separating organic compounds from E-caprolactam having a higher boiling point than E-caprolactam, and one or more distillation units, said purification unit being arranged upstream of the crystallization unit U, wherein more preferably, the crystallization unit U is the downstream-most unit of said plant PDP, and wherein said plant PDP is optionally or preferably comprised in an integrated polyamide 6 plant Pi, said integrated polyamide 6 plant Pi comprising said plant for PDP and further comprising a polyamide 6 production plant PPA, said integrated plant Pi furthercomprising a transportation line LCPL for passing purified E-caprolactam from PDP to PPA and a transportation line Ls for passing an aqueous recycle stream from PPA to PDP.

7. The crystallization unit U of any one claims 1 to 6, further comprising a computer-supported control system for controlling at least one controllable means, preferably all controllable means, said computer-supported control system preferably being a part of a control sub-unit UDP which is comprised in the unit U.

8. An E-caprolactam crystallization process carried out in a crystallization unit according to any one of claims 1 to 7, the process comprising(I) providing a liquid crude feed stream So comprising E-caprolactam, wherein So has a temperature of at most 70 °C and exhibits an E-caprolactam purity QGC(SO), an APHA value QAPHA(SO), a permanganate absorption number QPAN(SO) and a UV absorption Quv(So);(II) passing the stream So into a batch drum B(i), 1 < I < k, wherein k is preferably in the range of from 2 to 20;(ill) subjecting the content of the batch drum B(i) to crystallization comprising n crystallization stages P(x) carried out in at least one sub-unit U C<H2) with 1 < n < (k-i+1 ) and x = 1 ... n, wherein n is preferably in the range of from 1 to 41, and further comprising m crystallization stages C(y) carried out in at least one sub-unit UC<HI) with 0 < m < (i-1) and y = 1 ...m for m > 0, wherein H1 A H2; wherein m is preferably in the range of from 1 to 19,(ill.1 ) wherein a crystallization stage P(x) comprises(ill.1.1) passing a stage stream Ss(x+i-1) comprising at least a part of the content of a batch drum B(x+i-1 ) from said batch drum B(x+i-1 ) via the transportation line LS(H2)(X-H-1 ) and the entry and exit point EC<H2) into the transportation line LC(H2>;(ill.1.2) passing the stream Ss(x+i-1) through the transportation line LC<H2) with the meansMLC(H2>, thereby passing through the at least one crystallizer Wc(s(H2», wherein in Wc(s(H2», E-caprolactam comprised in Ss(x+i-1 ) crystallizes and remains as crystallized solid in Wc(s(H2»;(ill.1.3) removing a residue stream SR(X+I-1 ) from the transportation line Lc(H2) via EC<H2), wherein the stream SR(X+I-1 ) is depleted in E-caprolactam compared to the stream Ss(x+i-1); and(1.3.1) passing the stream SR(X+I-1 ) via the transportation line LR<H3) as final residue stream SRF via MLR<H3) to optional further use; or(1 .3.2) passing the stream SR(X+I-1 ) via the transportation line LB(H2)(X-H-2) into the batch drum B(x+i-2);(ill.1.4) transferring the crystallized solid in Wc(s(H2» into a liquid product stream Sp(x+i-1);(ill.1.5) removing the stream Sp(x+i-1) from the transportation line LC<H2) via EC<H2), wherein the stream Sp(x+i-1 ) is concentrated in E-caprolactam compared to the streamSs(x+i-1), and(1.5.1) passing the stream Sp(x+i-1) via the transportation line LF<H4> as final E- caprolactam fine product stream SPF via MLF<H4) to further use; or(1 .5.2) passing the stream Sp(x+i-1 ) via the transportation line LB(H2)(X-H) into the batch drum B(x+i);(ill.2) wherein a crystallization stage C(y) comprises(111.2.1) passing a stage stream Ss(i-y) comprising at least a part of the content of a batch drum B(i-y) from said batch drum B(i-y) via the transportation line Ls<Hi)(i-y) and the entry and exit point EC<HI) into the transportation line LC(HI>;(111.2.2) passing the stream Ss(i-y) through the transportation line LC(HI) with the means MC(HI), thereby passing through the at least one crystallizer WC(S(HI», wherein in WC(S(HI», E-caprolactam comprised in Ss(i-y) crystallizes and remains as crystallized solid in WC(S(HI»;(111.2.3) removing a residue stream Sp(i-y) from the transportation line LC(HI), wherein the stream Sp(i-y) is depleted in E-caprolactam compared to the stream Ss(i-y); and(2.3.1) passing the stream Sp(i-y) via the transportation line LR<H3) as final residue stream SRF via MLR(H3> to optional further use; or(2.3.2) passing the stream Sp(i-y) via the transportation line l_B(Hi)(i-y-1 ) into the batch drum B(i-y-1);(111.2.4) transferring the crystallized solid in WC(S(HI» into a liquid product stream Sp(i-y);(111.2.5) removing the stream Sp(i-y) from the transportation line LC(HI> via EC<HI), wherein the stream Sp(i-y) is concentrated in E-caprolactam compared to the stream Ss(i-y), and passing the stream Sp(i-y) via the transportation line LB<Hi)(i-y+1) into the batch drum B(i-y+1); wherein said process is preferably carried out carried out in a crystallization unit according to claim 4, the process preferably comprising(I) providing a liquid crude feed stream So comprising E-caprolactam, wherein So has a temperature of at most 70 °C and exhibits an E-caprolactam purity QGC(SO), an APHA value QAPHA(SO), a permanganate absorption number QPAN(SO) and a UV absorption Quv(So);(ii) passing the stream So into a batch drum B(i), 1 < I < k, wherein k is preferably in the range of from 2 to 20;(ill) subjecting the content of the batch drum B(i) to crystallization comprising n crystallization stages P(x) carried out in Uc2 with 1 < n < (k-i+1) and x = 1 ...n, wherein n is preferably in the range of from 1 to 41 , and further comprising m crystallization stages C(y) carried out in Uci with 0 < m < (i-1) and y = 1 ...m for m > 0, wherein m is preferably in the range of from 1 to 19;(ill.1 ) wherein a crystallization stage P(x) comprises(111.1.1) passing a stage stream Ss(x+i-1) comprising at least a part of the content of a batch drum B(x+i-1 ) from said batch drum B(x+i-1 ) via the transportation line Ls2(x+i-1) and the entry and exit point Ec2 into the circular stream transportation line Lc2i(ill.1.2) passing the stream Ss(x+i-1) through the circular transportation line I_c2 with the means Mc2, thereby passing through the first crystallizer Wc2(1) and the second crystallizer Wc2(1), wherein in Wc2(1) and Wc2(2), E-caprolactam comprised in Ss(x+i-1 ) crystallizes and remains as crystallized solid in Wc2(1) and Wc2(2);(ill.1.3) removing a residue stream SR(X+I-1) from the transportation line Lc2 via Ec2, wherein the stream SR(X+I-1 ) is depleted in E-caprolactam compared to the stream Ss(x+i-1 ); and(1.3.1) passing the stream SR(X+I-1) via the transportation line LRI as final residue stream SRF via MLRI to optional further use; or(1 .3.2) passing the stream SR(X+I-1 ) via the transportation line LB2(X-H-2) into the batch drum B(x+i-2);(ill.1.4) transferring the crystallized solid in Wc2(1) and Wc2(2) into a liquid product stream SP(x+i-1);(ill.1.5) removing the stream Sp(x+i-1) from the transportation line I_c2 via Ec2, wherein the stream Sp(x+i-1 ) is concentrated in E-caprolactam compared to the stream Ss(x+i-1 ), and(1.5.1) passing the stream Sp(x+i-1) via the transportation line LF2 as final E- caprolactam fine product stream SPF via MLF2 to further use; or(1.5.2) passing the stream Sp(x+i-1) via the transportation line l_B2(x+i) into the batch drum B(x+i);(ill.2) wherein a crystallization stage C(y) comprises(111.2.1) passing a stage stream Ss(i-y) comprising at least a part of the content of a batch drum B(i-y) from said batch drum B(i-y) via the transportation line Lsi(i-y) and the entry and exit point Eci into the circular stream transportation line Lei;(111.2.2) passing the stream Ss(i-y) through the circular transportation line Lei with the means Mei, thereby passing through the first crystallizer Wci(1) and the second crystallizer Wci(1), wherein in Wci(1) and Wci(2), E-caprolactam comprised in Ss(i-y) crystallizes and remains as crystallized solid in Wci(1) and Wci(2);(111.2.3) removing a residue stream SR(i-y) from the transportation line Lei, wherein the stream SR(i-y) is depleted in E-caprolactam compared to the stream Ss(i-y); and(2.3.1) passing the stream SR(i-y) via the transportation line LRI as final residue stream SRF via MLRI to optional further use; or(2.3.2) passing the stream Sp(i-y) via the transportation line l_Bi(i-y-1 ) into the batch drum B(i-y-1);(111.2.4) transferring the crystallized solid in Wci(1) and Wci(2) into a liquid product stream Sp(i-y);(111.2.5) removing the stream Sp(i-y) from the transportation line Lei via Eci, wherein the stream Sp(i-y) is concentrated in E-caprolactam compared to the stream Ss(i-y), and passing the stream Sp(i-y) via the transportation line l_Bi(i-y+1 ) into the batch drum B(i-y-Hl).

9. The process of claim 8, wherein each crystallization stage P(x) according to (ill.1 ) is characterized by a freezing ratio F(P(x)) and wherein, independently of each other, each freezing ratio F(P(x)) is at least 0.4, preferably at least 0.45, more preferably at least 0.5, more preferably at least 0.55, more preferably at least 0.60, more preferably at least 0.65, wherein the freezing ratio F(P(x)) is defined asF(P(x)) = m(SP(x+i-1)) I m(Ss(x+i-1)) wherein m(Sp(x+i-1)) is the mass of the liquid product stream Sp(x+i-1) according to (ill.1.4) and m(Ss(x+i-1)) is the mass of the stage stream Ss(x+i-1) according to (ill.1.1); and wherein each crystallization stage C(y) according to (ill.2) is characterized by a freezing ratio F(C(y)) and wherein, independently of each other, each freezing ratio F(C(y)) is at least 0.4, preferably at least 0.45, more preferably at least 0.5, more preferably at least 0.55, more preferably at least 0.60, more preferably at least 0.65, wherein the freezing ratio F(C(y)) is defined as F(C(y)) = m(Sp(i-y)) I m(Ss(i-y)), wherein m(Sp(i-y)) is the mass of the liquid product stream Sp(i-y) according to (iii.2.4) and m(Ss(i-y)) is the mass of the stage stream Ss(i-y) according to (iii.2.1); and wherein each crystallization stage P(x) according to (ill.1 ) is characterized by an effective distribution coefficient D(P(x)) and wherein, independently of each other, each effective distribution coefficient D(P(x)) is in the range of from 0.1 to 0.8, preferably in the range of from 0.2 to 0.7, more preferably in the range of from 0.3 to 0.6, wherein an effective distribution coefficient D(P(x)) is defined asD(P(x)) = CIM(SP(X+I-1 )) I CiM(Ss(x+i-1 )) wherein CIM(SS(X+I-1 )) is the concentration of impurities contained in the stage stream Ss(x+i-1 ) according to (ill.1.1) and CIM(SP(X+I-1)) is the concentration of impurities contained in the product stream Sp(x+i-1) according to (ill.1.4), wherein the term "impurity” refers to any chemical compound other than E-caprolactam; and wherein each crystallization stage C(y) according to (ill.2) is characterized by an effective distribution coefficient D(C(y)) and wherein, independently of each other, each effective distribution coefficient D(C(y)) is in the range of from 0.1 to 0.8, preferably in the range of from 0.2 to 0.7, more preferably in the range of from 0.3 to 0.6, wherein an effective distribution coefficient D(C(y)) is defined asD(C(y)) = CiM(Sp(i-y)) I CiM(Ss(i-y))wherein CiM(Ss(i-y)) is the concentration of impurities contained in the stage stream Ss(i-y) according to (iii.2.1) and CiM(Sp(i-y)) is the concentration of impurities contained in the product stream Sp(i-y) according to (iii.2.4), wherein the term "impurity” refers to any chemical compound other than E-caprolactam.

10. The process of claim 8 or 9, wherein transferring the crystallized solid into a liquid product stream Sp(x+i-1) according to (ill.1.4) comprises(ill.1.4.1) increasing the temperature of the crystallized solid in Wc(s(H2» close to the melting point of pure E-caprolactam, obtaining a further residue stream SR(X-H-I), and removing said further residue stream SR(X+I-1) from the transportation line LC<H2) via EC<H2) according to (ill.1.3);(ill.1.4.2) transferring the remaining crystallized solid in Wc(s(H2» into a liquid product stream Sp(x+i-1 ); and preferably comprises(ill.1.4.1) increasing the temperature of the crystallized solid in at least one of Wc2(1) and Wc2(2), preferably in Wc2(1) and Wc2(2), close to the melting point of pure E-caprolactam, obtaining a further residue stream SR(X+I-1 ), and removing said further residue stream SR(X+I-1 ) from the transportation line Lc2 via Ec2 according to (ill.1.3);(ill.1.4.2) transferring the remaining crystallized solid in Wc2(1) and Wc2(2) into a liquid product stream SP(x+i-1); wherein transferring the crystallized solid into a liquid product stream Sp(i-y) according to (iii.2.4) comprises(111.2.4.1) increasing the temperature of the crystallized solid in WC(S(HI» close to the melting point of pure E-caprolactam, obtaining a further residue stream SR(i-y), and removing said further residue stream Sp(i-y) from the transportation line LC(HI) via EC<HI) according to (ill.2.3);(111.2.4.2) transferring the remaining crystallized solid in WC(S(HI» into a liquid product stream Sp(i-y); and preferably comprises(111.2.4.1) increasing the temperature of the crystallized solid in at least one of Wci(1) and Wci(2), preferably in Wci(1) and Wci(2), close to the melting point of pure E-caprolactam, obtaining a further residue stream SR(i-y), and removing said further residue stream SR(i-y) from the transportation line Lei via Eci according to (ill.2.3);(111.2.4.2) transferring the remaining crystallized solid in Wci(1) and Wci(2) into a liquid product stream Sp(i-y).

11. The process of any one of claims 8 to 10, wherein providing the liquid crude feed stream So comprising E- caprolactam according to (I) comprises(1.1) providing a stream SM comprising a solid material M comprising polyamide 6;(1.2) preparing an aqueous depolymerization mixture based on the stream SM provided according to (1.1);(1.3) subjecting the depolymerization mixture prepared according to (1.2) to polyamide 6 depolymerization conditions in a reaction unit UR, obtaining a liquid aqueous stream SR comprising E-caprolactam dissolved in water at a concentration CSR, the stream SR further comprising one or more impurities;(i .4) passing the aqueous stream SR into a purification unit UP, obtaining from the stream SR the stream So comprising E-caprolactam at a concentration co with co » CR; wherein the solid material M according to (i.1) comprises, more preferably consists of, waste material, wherein said waste material more preferably comprises, more preferably consists of, one or more of at least one textile waste material and at least one engineering plastics waste material, more preferably comprises, more preferably consists of at least one textile waste material, wherein preferably from 10 to 99 weight-%, more preferably from 30 to 98.5 weight-%, more preferably from 50 to 98 weight-%, more preferably from 80 to 98 weight-%, of the solid material M consist of polyamide 6, wherein, in addition to polyamide 6, the solid material M preferably comprises one or more further organic polymeric compounds, more preferably including, but not limited to, one or more of at least one elastane; at least one polyamide 6.6; at least one polyethylene terephthalate; at least one polyurethane; at least one polyester; at least one polyether; at least one polyvinyl chloride; at least 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.

12. A method for controlling an E-caprolactam crystallization process according to any one of claims 8 to 11, carried out in a crystallization unit according to any one of claims 1 to 7, the method comprising(a) providing parameters a parameter space Q(SF) of the final E-caprolactam fine product stream SPF to be obtained by the process according to (ill.1.5.1) to a control unit UDP;(b) providing operating characteristics of the h crystallization sub-units UC<H) to the control unit UDP;(c) determining, prior to passing the stream So into a batch drum B(i) according to (II), parameters of a parameter space Q(So) of the stream So in the analytical unit UA, wherein the parameters of Q(So) correspond to the parameters of Q(SF); and passing the parameters of Q(So) to the control unit UDP;(d) determining in the control unit UDP, based on the parameters of the parameter space Q(SF) provided according to (a) and further based on the operating characteristics of the h crystallization sub-units Uc(H) provided according to (b), the number of crystallization cycles P(x) and the number of crystallization cycles C(y) necessary to change the parameters of Q(So) to the parameters of Q(SF), and further determining the batch drum B(i) into which the crude E-caprolactam feed stream So is to be passed;(e) determining, in the control unit UDP, operation instructions for the controllable means of the batch drum sub-unit UB, the stream distribution sub-unit UD and the h crystallization sub-units UC<H) to realize number of crystallization cycles P(x) and the number of crystallization cycles C(y) determined according to (d);(f) carrying out a crystallization process according to any one of embodiments 8 to 11 , comprising passing the operation instructions determined according to (e) to the controllable means.

13. The method of claim 12, wherein the parameter space Q(SF) comprises one or more of the E-caprolactam purity QGC(SF), the APHA value QAPHA(SF), the permanganate absorption number QPAN(SF), and the UV absorption QUV(SF), preferably at least QGC(SF) and QAPHA(SF), whereinQGC(SF) is preferably at least 99.5 area-%, more preferably at least 99.8 area-%, more preferably at least 99.9 area-%;QAPHA(SF) is preferably at most 6, more preferably most 5, more preferably at most 4;QPAN(SF) is preferably at most 6, more preferably at most 5, more preferably at most 4;QUV(SF) is preferably at most 0.1 , more preferably at most 0.07, more preferably at most 0.05; and wherein the parameter space Q(So) comprises one or more of the E-caprolactam purity QGC(SO), the APHA value QAPHA(SO), the permanganate absorption number QPAN(SO), and the UV absorption Quv(So), preferably at least QGC(SO) and QAPHA(SO), wherein at least one of the following, preferably at least two of the following relations are met, wherein more preferably, said at least two relations comprise one or more of the relations for QGC(SO) and QAPHA(SO):QGC(SO) < QGC(SF);QAPHA(SO) > QAPHA(SF);QPAN(SO) > QPAN(SF);Quv(So) > QUV(SF).

14. A computer program, comprising instructions which, when the program is executed by the computer- supported control system according to claim 7, cause the system to perform the method according to claim 12 or 13.

15. A process, preferably according to any one of claims 8 to 11, comprising the step of converting a chemical material obtainable by or obtained by the process according to any one of claims 8 to 11 to obtain a product cp; and / or a process, comprising the step of using the crystallization unit U according to any one of claims 1 to 7 to obtain a chemical material; and preferably converting the chemical material to obtain a product cp.

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