SEPARATION OF IMPURITIES IN A PROCESS FOR HYDROLYTICALLY DEPOLYMERIZING A POLYAMIDE

Abstract

The present invention relates to a process for separating at least one -caprolactam oligomeric compound CPO from a stream S.sub.R comprising said at least one CPO and -caprolactam monomeric compound CPM.

Claims

1.-16. (canceled)

17. A process for separating at least one -caprolactam oligomeric compound CPO from a stream S.sub.R comprising said at least one CPO and -caprolactam monomeric compound CPM, the process comprising (i) providing an aqueous liquid stream S.sub.R comprising CPM dissolved in water at a concentration c.sub.R(CPM), CPM having a boiling point T.sub.CPM, wherein S.sub.R further comprises the at least one CPO at a concentration c.sub.R(CPO), CPO having a boiling point T.sub.CPO with T.sub.CPO>T.sub.CPM; (ii) preparing an aqueous liquid mixture M.sub.E comprising the stream S.sub.R provided according to (i); (iii) subjecting the mixture M.sub.E according to (i) to evaporation conditions in an evaporation unit E.sub.1, obtaining an aqueous vapor stream S.sub.V1 and an aqueous liquid stream S.sub.L1, wherein S.sub.V1 comprises CPM at a concentration c.sub.V1(CPM) with c.sub.V1(CPM)>c.sub.R(CPM), wherein S.sub.L1 comprises the at least one CPO at a concentration c.sub.L1(CPO) with c.sub.L1(CPO)>c.sub.R(CPO) and comprises CPM at a concentration c.sub.L1(CPM) with c.sub.L1(CPM)<c.sub.R(CPM); (iv) dividing the stream S.sub.L1 according to (iii) into a first stream S.sub.L11 and a second stream S.sub.L12, wherein S.sub.L11 and S.sub.L12 have the same chemical composition as S.sub.L1; (v) passing the stream S.sub.L12 obtained according to (iv) to a downstream treatment stage; wherein preparing the aqueous liquid mixture M.sub.E according to (ii) comprises mixing the stream S.sub.R with the stream S.sub.L11.

18. The process of claim 17, wherein the stream S.sub.R provided according to (i) exhibits a CPM concentration in the range of from 15 to 90 weight-%; and a CPO concentration in the range of from 0.5 to 10 weight-%; wherein the stream S.sub.V1 obtained according to (iii) exhibits a CPM concentration in the range of from 65 to 99 weight-%; wherein the stream S.sub.V1 obtained according to (iii) preferably exhibits a CPO concentration in the range of from 0 to 0.4 weight-%; wherein the stream S.sub.L1 obtained according to (iii) exhibits a CPM concentration in the range of from 0.1 to 10 weight-%; and a CPO concentration in the range of from 1 to 10 weight-%.

19. The process of claim 17, wherein preparing the aqueous liquid mixture M.sub.E according to (ii) further comprises, prior to mixing the stream S.sub.R with the stream S.sub.L11, heating the stream S.sub.L11 obtained from (iv) to a temperature in the range of from 200 to 270 C.

20. The process of claim 19, wherein heating the stream S.sub.L11 comprises passing the stream S.sub.L11 through a heat exchanger H.sub.1; or wherein preparing the aqueous liquid mixture M.sub.E according to (ii) comprises mixing the stream S.sub.R provided according to (i) with the stream S.sub.L11 obtained from (iv) and heating the combined stream to a temperature in the range of from 200 to 270 C., wherein heating the combined stream comprises passing the stream S.sub.L11 through a heat exchanger H.sub.1.

21. The process of claim 17, wherein the evaporation in the evaporation unit E.sub.1 according to (iii) is carried out in one or more stirred vessels, or in one or more film evaporators, or in one or more stirred vessels and in one or more film evaporators.

22. The process of claim 17, wherein the evaporation conditions according to (iii) comprise an evaporation temperature T.sub.E1 of the mixture M.sub.E, wherein T.sub.E1 is in the range of from 200 to 270 C., and wherein the evaporation conditions according to (iii) further comprise an evaporation pressure p.sub.E1.

23. The process of claim 17, wherein the evaporation conditions according to (iii) further comprise a residence time t.sub.E1 in the evaporation unit E.sub.1, wherein t.sub.E1 is in the range of from 1 min to 5 h.

24. The process of claim 17, wherein according to (iv), the stream S.sub.L1 is divided into the first stream S.sub.L11 and the second stream S.sub.L12 at a mass ratio m(S.sub.L12):m(S.sub.L11) in the range of from 0.01:1 to 0.02:1.

25. The process of claim 17, wherein the downstream treatment stage according to (v) comprises one or more of an evaporation unit; a depolymerization unit for depolymerizing at least one of the at least one -caprolactam oligomeric compound CPO comprised in the stream SL12; a separation unit for separating at least one solid residue from the stream S.sub.L12; a processing unit for processing at least one solid residue comprised in the stream S.sub.L12; an incineration stage for incinerating at least one solid residue comprised in the stream S.sub.L12.

26. The process of claim 17, wherein the downstream treatment stage according to (v) comprises an evaporation unit, the process further comprising (vi) subjecting the stream S.sub.L12 to evaporation conditions in an evaporation unit E.sub.2, obtaining an aqueous vapor stream S.sub.V2 and a liquid stream S.sub.L2 wherein S.sub.V2 comprises CPM at a concentration c.sub.V2(CPM) with c.sub.V2(CPM)>c.sub.L12(CPM), and CPO at a concentration c.sub.V2(CPO) with c.sub.V2(CPO)<c.sub.L12(CPO); wherein S.sub.L2 comprises the at least one CPO at a concentration c.sub.L2(CPO) with c.sub.L2(CPO)c.sub.L12(CPO); (vii) passing the stream S.sub.L2 obtained according to (vi) to a downstream treatment stage.

27. The process of claim 26, wherein the evaporation in the evaporation unit E.sub.2 according to (vi) is carried out in one or more stirred vessels, or in one or more film evaporators, or in one or more stirred vessels and in one or more film evaporators.

28. The process of claim 26, wherein the evaporation conditions according to (vi) comprise an evaporation temperature T.sub.E2 of the stream S.sub.L12, wherein T.sub.E2 is in the range of from 200 to 300 C., and wherein the evaporation conditions according to (vi) further comprise an evaporation pressure p.sub.E2.

29. The process of claim 26, wherein the evaporation conditions according to (vi) further comprise a residence time t.sub.E2 in the evaporation unit E.sub.2, wherein t.sub.E2 is in the range of from 1 s to 5 min.

30. The process of claim 26, wherein the downstream treatment stage according to (vii) comprises one or more of a depolymerization unit for depolymerizing at least one of the at least one -caprolactam oligomeric compound CPO comprised in the stream S.sub.L2; a separation unit for separating at least one solid residue from the stream S.sub.L2; a processing unit for processing at least one solid residue comprised in the stream S.sub.L2; an incineration stage for incinerating at least one solid residue comprised in the stream S.sub.L2.

31. The process of claim 17, the process further comprising (viii) passing the aqueous vapor stream S.sub.V to a water removal unit W.sub.U for separating CPM from water.

32. The process of claim 17, wherein providing the stream S.sub.R according to (i) comprises (i.1) preparing an aqueous liquid mixture M.sub.WC containing CPM dissolved in water and CPO, comprising (i.1.1) providing an aqueous liquid stream S.sub.W; (i.1.2) providing a solid material M containing a polyamide prepared from -caprolactam; (i.1.3) preparing a mixture of the solid material M provided according to (i.1.2) and the aqueous liquid stream S.sub.W provided according to (i.1.1); (i.1.4) preparing an aqueous liquid mixture M.sub.WP comprising the polyamide dissolved in water from the mixture prepared according to (i.1.3); (i.1.5) subjecting the aqueous liquid mixture M.sub.WP prepared according to (i.1.4) to depolymerization conditions in a chemical reactor unit R.sub.U, obtaining the aqueous liquid mixture M.sub.WC comprising CPM dissolved in water and CPO; (i.2) optionally subjecting the aqueous mixture M.sub.WC obtained according to (i.1.5) to depressurization in a depressurization unit D.sub.U, obtaining an aqueous vapor stream S.sub.VD and an aqueous liquid stream S.sub.C, S.sub.C comprising CPM dissolved in water and CPO; (i.3) optionally passing the aqueous mixture M.sub.WC obtained according to (i.1.5) or the aqueous liquid stream S.sub.C, obtained according to (i.2) to solid-liquid separation in a solid-liquid separation unit SL.sub.U, obtaining an aqueous liquid stream S.sub.L comprising CPM dissolved in water and CPO; (i.4) separating water from the aqueous liquid mixture M.sub.WC obtained according to (i.1.5) or from the aqueous liquid stream S.sub.C obtained according to (i.2) or from the aqueous liquid stream S.sub.L obtained according to (i.3) by evaporation in an evaporation unit E.sub.U comprising least two evaporation sub-units E.sub.U1 and E.sub.U2, obtaining at least one aqueous vapor stream S.sub.VE and the aqueous liquid stream S.sub.R.

Description

[0117] The present invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and back-references as indicated. In particular, it is noted that in each instance where a range of embodiments is mentioned, for example in the context of a term such as The process of any one of embodiments 1 to 3, every embodiment in this range is meant to be explicitly disclosed for the skilled person, i.e. the wording of this term is to be understood by the skilled person as being synonymous to The process of any one of embodiments 1, 2 and 3. 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. [0118] 1. A process for separating at least one -caprolactam oligomeric compound CPO from a stream S.sub.R comprising said at least one CPO and -caprolactam monomeric compound CPM, the process comprising [0119] (i) providing an aqueous liquid stream S.sub.R comprising CPM dissolved in water at a concentration c.sub.R(CPM), CPM having a boiling point T.sub.CPM, wherein S.sub.R further comprises the at least one CPO at a concentration c.sub.R(CPO), CPO having a boiling point T.sub.CPO with T.sub.CPO>T.sub.CPM; [0120] (ii) preparing an aqueous liquid mixture M.sub.E comprising the stream S.sub.R provided according to (i); [0121] (iii) subjecting the mixture M.sub.E according to (i) to evaporation conditions in an evaporation unit E.sub.1, obtaining an aqueous vapor stream S.sub.V1 and an aqueous liquid stream S.sub.L1, wherein S.sub.V1 comprises CPM at a concentration c.sub.V1(CPM) with c.sub.V1(CPM)>c.sub.R(CPM), wherein S.sub.L1 comprises the at least one CPO at a concentration c.sub.L1(CPO) with c.sub.L1(CPO)>c.sub.R(CPO) and comprises CPM at a concentration c.sub.L1(CPM) with c.sub.L1(CPM)<c.sub.R(CPM); [0122] (iv) dividing the stream S.sub.L1 according to (iii) into a first stream S.sub.L11 and a second stream S.sub.L12, wherein S.sub.L11 and S.sub.L12 have the same chemical composition as S.sub.L1; [0123] (v) passing the stream S.sub.L12 obtained according to (iv) to a downstream treatment stage; wherein preparing the aqueous liquid mixture M.sub.E according to (ii) comprises mixing the stream S.sub.R with the stream S.sub.L11. [0124] 2. The process of embodiment 1, wherein the stream S.sub.R provided according to (i) has a temperature in the range of from 100 to 150 C., preferably in the range of from 110 to 145 C., more preferably in the range of from 120 to 140 C. [0125] 3. The process of embodiment 1 or 2, [0126] wherein the stream S.sub.R provided according to (i) exhibits a CPM concentration in the range of from 15 to 90 weight-%, preferably in the range of from 20 to 75 weight-%, more preferably in the range of from 25 to 60 weight-%; and a CPO concentration in the range of from 0.5 to 10 weight-%, preferably in the range of from 0.5 to 7 weight-%, more preferably in the range of from 0.5 to 4 weight-%; [0127] wherein the stream S.sub.V1 obtained according to (iii) exhibits a CPM concentration in the range of from 65 to 99 weight-%, preferably in the range of from 65 to 90 weight-%, more preferably in the range of from 65 to 80 weight-%; wherein the stream S.sub.V1 obtained according to (iii) preferably exhibits a CPO concentration in the range of from 0 to 0.4 weight-%, preferably in the range of from 0 to 0.3 weight-%, more preferably in the range of from 0 to 0.2 weight-%; [0128] wherein the stream S.sub.L1 obtained according to (iii) exhibits a CPM concentration in the range of from 0.1 to 10 weight-%, preferably in the range of from 0.5 to 7.5 weight-%, more preferably in the range of from 1 to 5 weight-%; and a CPO concentration in the range of from 1 to 10 weight-%, preferably in the range of from 1.5 to 10 weight-%, more preferably in the range of from 2 to 10 weight-%. [0129] 4. The process of any one of embodiments 1 to 3, wherein preparing the aqueous liquid mixture M.sub.E according to (ii) further comprises, prior to mixing the stream S.sub.R with the stream S.sub.L11, heating the stream S.sub.L11 obtained from (iv) to a temperature in the range of from 200 to 270 C., preferably in the range of from 210 to 270 C., more preferably in the range of from 220 to 270 C. [0130] 5. The process of embodiment 4, wherein heating the stream S.sub.L11 comprises passing the stream S.sub.L11 through a heat exchanger H.sub.1. [0131] 6. The process of embodiment 4 or 5, wherein according to (ii), the stream S.sub.R provided according to (i) and the stream S.sub.L11 obtained from heating are mixed in the evaporation unit E.sub.1. [0132] 7. The process of any one of embodiments 4 to 6, wherein prior to mixing the stream S.sub.R with the stream S.sub.L11, the stream S.sub.R provided according to (i) is not heated. [0133] 8. The process of any one of embodiments 1 to 3, wherein preparing the aqueous liquid mixture M.sub.E according to (ii) comprises mixing the stream S.sub.R provided according to (i) with the stream S.sub.L11 obtained from (iv) and heating the combined stream to a temperature in the range of from 200 to 270 C., preferably in the range of from 210 to 270 C., more preferably in the range of from 220 to 270 C. [0134] 9. The process of embodiment 8, wherein heating the combined stream comprises passing the stream S.sub.L11 through a heat exchanger H.sub.1. [0135] 10. The process of embodiment 8 or 9, wherein prior to mixing the stream S.sub.R with the stream S.sub.L11, the stream S.sub.R provided according to (i) is not heated. [0136] 11. The process of any one of embodiments 1 to 10, wherein the evaporation in the evaporation unit E.sub.1 according to (iii) is carried out in one or more stirred vessels, or in one or more film evaporators, or in one or more stirred vessels and in one or more film evaporators; wherein the evaporation in the evaporation unit E.sub.1 according to (iii) is preferably carried out in one or more continuous stirred-tank reactors, or in one or more falling film evaporators, or in one or more continuous stirred-tank reactors and in one or more falling film evaporators; wherein the evaporation in the evaporation unit E.sub.1 according to (iii) is more preferably carried out in one or more continuous stirred-tank reactors, wherein more preferably, if evaporation in E.sub.1 is carried out in more than one continuous stirred-tank reactors, the continuous stirred-tank reactor are arranged in parallel. [0137] 12. The process of embodiment 11, wherein the one or more stirred vessels and the one or more film evaporators are equipped with heating means to indirectly providing heat for the evaporation carried out in E.sub.1, the process comprising passing a heating medium through said heating means, wherein said heating means are preferably heating jackets. [0138] 13. The process of any one of embodiments 1 to 12, preferably of embodiment 11 or 12, wherein the evaporation conditions according to (iii) comprise an evaporation temperature T.sub.E1 of the mixture M.sub.E, wherein T.sub.E1 is in the range of from 200 to 270 C., preferably in the range of from 210 to 270 C., more preferably in the range of from 220 to 270 C., and wherein the evaporation conditions according to (iii) further comprise an evaporation pressure p.sub.E1, wherein p.sub.E1 is preferably less than 1 bar(abs). [0139] 14. The process of embodiment 13, wherein p.sub.E1 is in the range of from 10 to 900 mbar(abs), preferably in the range of from 10 to 850 mbar(abs), more preferably in the range of from 10 to 800 mbar(abs). [0140] 15. The process of any one of embodiments 1 to 14, preferably of any one of embodiments 11 to 14, wherein the evaporation conditions according to (iii) further comprise a residence time t.sub.E1 in the evaporation unit E.sub.1, wherein t.sub.E1 is in the range of from 1 min to 5 h, preferably in the range of from 5 min to 4 h, more preferably in the range of from 10 min to 3 h. [0141] 16. The process of any one of embodiments 1 to 15, wherein according to (iv), the stream S.sub.L1 is divided into the first stream S.sub.L11 and the second stream S.sub.L12 at a mass ratio m(S.sub.L12):m(S.sub.L11) in the range of from 0.01:1 to 0.02:1. [0142] 17. The process of any one of embodiments 1 to 16, wherein the downstream treatment stage according to (v) comprises one or more of [0143] an evaporation unit; [0144] a depolymerization unit for depolymerizing at least one of the at least one -caprolactam oligomeric compound CPO comprised in the stream S.sub.L12; [0145] a separation unit for separating at least one solid residue from the stream S.sub.L12; [0146] a processing unit for processing at least one solid residue comprised in the stream S.sub.L12, [0147] an incineration stage for incinerating at least one solid residue comprised in the stream S.sub.L12. [0148] 18. The process of any one of embodiments 1 to 17, wherein the downstream treatment stage according to (v) comprises an evaporation unit, the process further comprising [0149] (vi) subjecting the stream S.sub.L12 to evaporation conditions in an evaporation unit E.sub.2, obtaining an aqueous vapor stream S.sub.V2 and a liquid stream S.sub.L2 wherein S.sub.V2 comprises CPM at a concentration c.sub.V2(CPM) with c.sub.V2(CPM)>c.sub.L12(CPM), and CPO at a concentration c.sub.V2(CPO) with c.sub.V2(CPO)<c.sub.L12(CPO); wherein S.sub.L2 comprises the at least one CPO at a concentration c.sub.L2(CPO) with c.sub.L2(CPO)c.sub.L12(CPO); [0150] (vii) passing the stream S.sub.L2 obtained according to (vi) to a downstream treatment stage. [0151] 19. The process of embodiment 18, [0152] wherein the stream S.sub.V2 obtained according to (vi) exhibits a CPM concentration in the range of from 50 to 100 weight-%, preferably in the range of from 60 to 100 weight-%, more preferably in the range of from 80 to 100 weight-%; and a CPO concentration in the range of from 0 to 0.5 weight-%, preferably in the range of from 0 to 0.3 weight-%, more preferably in the range of from 0 to 0.1 weight-%; [0153] wherein the stream S.sub.L2 obtained according to (vi) exhibits a CPO concentration in the range of from 1 to 10 weight-%, preferably in the range of from 1.5 to 10 weight-%, more preferably in the range of from 2 to 10 weight-%. [0154] 20. The process of embodiment 18 or 19, wherein the evaporation in the evaporation unit E.sub.2 according to (vi) is carried out in one or more stirred vessels, or in one or more film evaporators, or in one or more stirred vessels and in one or more film evaporators; wherein the evaporation in the evaporation unit E.sub.2 according to (vi) is preferably carried out in one or more film evaporators; wherein the evaporation in the evaporation unit E.sub.2 according to (vi) is more preferably carried out in one or more wipe film evaporators, wherein more preferably, if evaporation in E.sub.2 is carried out in more than one wipe film evaporators, the wipe film evaporators are arranged in parallel. [0155] 21. The process of embodiment 20, wherein the one or more stirred vessels and the one or more film evaporators are equipped with heating means to indirectly providing heat for the evaporation carried out in E.sub.2, the process comprising passing a heating medium through said heating means, wherein said heating means are preferably heating jackets. [0156] 22. The process of any one of embodiments 18 to 21, wherein the evaporation conditions according to (vi) comprise an evaporation temperature T.sub.E2 of the stream S.sub.L12, wherein T.sub.E2 is in the range of from 200 to 300 C., preferably in the range of from 215 to 300 C., more preferably in the range of from 230 to 300 C., and wherein the evaporation conditions according to (vi) further comprise an evaporation pressure p.sub.E2, wherein p.sub.E2 is preferably less than 1 bar(abs). [0157] 23. The process of embodiment 22, wherein p.sub.E2 is in the range of from 10 to 900 mbar(abs), preferably in the range of from 10 to 850 mbar(abs), more preferably in the range of from 10 to 800 mbar(abs). [0158] 24. The process of any one of embodiments 18 to 23, wherein the evaporation conditions according to (vi) further comprise a residence time t.sub.E2 in the evaporation unit E.sub.2, wherein t.sub.E2 is in the range of from 1 s to 5 min, preferably in the range of from 5 s to 4 min, more preferably in the range of from 10 s to 3 min. [0159] 25. The process of any one of embodiments 18 to 24, wherein the downstream treatment stage according to (vii) comprises one or more of [0160] a depolymerization unit for depolymerizing at least one of the at least one -caprolactam oligomeric compound CPO comprised in the stream S.sub.L2; [0161] a separation unit for separating at least one solid residue from the stream S.sub.L2; [0162] a processing unit for processing at least one solid residue comprised in the stream S.sub.L2; [0163] an incineration stage for incinerating at least one solid residue comprised in the stream S.sub.L2. [0164] 26. The process of any one of embodiments 1 to 25, preferably of any one of embodiments 18 to 25, the process further comprising [0165] (viii) passing the aqueous vapor stream S.sub.V1, preferably the aqueous vapor stream S.sub.V1 and the aqueous vapor stream S.sub.V2, more preferably a combined stream of the aqueous vapor stream S.sub.V1 and the aqueous vapor stream S.sub.V2, to a water removal unit W.sub.U for separating CPM from water, wherein the water removal unit preferably comprises at least one distillation column, more preferably from 1 to 3 distillation columns, more preferably 2 or 3 distillation columns, more preferably 3 distillation columns, wherein, if the water removal unit W.sub.U comprises more than one distillation column, the distillation columns are preferably serially arranged. [0166] 27. The process of embodiment 26, wherein the bottoms stream of at least one distillation column, preferably the bottoms stream of the downstream-most distillation column is recycled into the evaporation unit E.sub.1. [0167] 28. The process of any one of embodiments 1 to 27, wherein providing the stream S.sub.R according to (i) comprises [0168] (i.1) preparing an aqueous liquid mixture M.sub.WC containing CPM dissolved in water and CPO, comprising [0169] (i.1.1) providing an aqueous liquid stream S.sub.W; [0170] (i.1.2) providing a solid material M containing a polyamide prepared from -caprolactam; [0171] (i.1.3) preparing a mixture of the solid material M provided according to (i.1.2) and the aqueous liquid stream S.sub.W provided according to (i.1.1); [0172] (i.1.4) preparing an aqueous liquid mixture M.sub.WP comprising the polyamide dissolved in water from the mixture prepared according to (i.1.3); [0173] (i.1.5) subjecting the aqueous liquid mixture M.sub.WP prepared according to (i.1.4) to depolymerization conditions in a chemical reactor unit R.sub.U, obtaining the aqueous liquid mixture M.sub.WC comprising CPM dissolved in water and CPO; [0174] (i.2) optionally subjecting the aqueous mixture M.sub.WC obtained according to (i.1.5) to depressurization in a depressurization unit D.sub.U, obtaining an aqueous vapor stream S.sub.VD and an aqueous liquid stream S.sub.C, S.sub.C comprising CPM dissolved in water and CPO; [0175] (i.3) optionally passing the aqueous mixture M.sub.WC obtained according to (i.1.5) or the aqueous liquid stream S.sub.C, obtained according to (i.2) to solid-liquid separation in a solid-liquid separation unit SL.sub.U, obtaining an aqueous liquid stream S.sub.L comprising CPM dissolved in water and CPO; [0176] (i.4) separating water from the aqueous liquid mixture M.sub.WC obtained according to (i.1.5) or from the aqueous liquid stream S.sub.C obtained according to (i.2) or from the aqueous liquid stream S.sub.L obtained according to (i.3) by evaporation in an evaporation unit E.sub.U comprising least two evaporation sub-units E.sub.U1 and E.sub.U2, obtaining at least one aqueous vapor stream S.sub.VE and the aqueous liquid stream S.sub.R. [0177] 29. The process of embodiment 28, wherein the solid material M provided according to (i.1.2) comprises, preferably consists of waste material, wherein said waste material preferably comprises textile waste material. [0178] 30. The process of embodiment 28 or 29 insofar as embodiments 28 or 29 are dependent on any one of embodiments 18 to 25, wherein according to (vii), passing the liquid stream S.sub.L2 to a downstream treatment stage comprises [0179] (vii.1) dividing the stream S.sub.L2 into a first stream S.sub.L21 and a second stream S.sub.L22, wherein S.sub.L21 and S.sub.L22 have the same chemical composition as S.sub.L2; [0180] (vii.2) recycling the stream S.sub.L21 into the chemical reactor unit according to (i.1.5); [0181] (vii.3) passing the stream S.sub.L22 to a downstream treatment stage. [0182] 31. The process of embodiment 30, wherein the downstream treatment stage according to (vii.3) comprises one or more of [0183] a separation unit for separating at least one solid residue from the stream S.sub.L22; [0184] a processing unit for processing at least one solid residue comprised in the stream S.sub.L22; [0185] an incineration stage for incinerating at least one solid residue comprised in the stream S.sub.L22.

[0186] In the context of the present invention, it is noted that the term polyamide prepared from -caprolactam as used herein refers to polyamide 6 being characterized by the formula (NH(CH.sub.2).sub.5CO).sub.n. In the context of the present invention, an -caprolactam monomeric compound CPM is an -caprolactam monomer. The term, bar as used in the context of the present invention refers to bar(abs), i.e. bar (absolute), sometimes also referred to bara.

[0187] The term textile material covers textile raw materials and non-textile raw materials that are processed by various methods into linear, planar and spatial structures. It concerns the linear textile structures produced from them, such as yarns, twisted yarns and ropes, the sheet-like textile structures, such as woven fabrics, knitted fabrics, braids, stitch-bonded fabrics, nonwovens and felts, and the three-dimensional textile structures, i.e. body structures, such as textile hoses, stockings or textile semi-finished products; and it further concerns those finished products which, using the aforementioned products, are brought into a saleable condition by making up, opening up and/or other operations for onward transmission to the processor, the trade or the end consumer.

[0188] The term textile waste material covers a textile material as defined above, the inherent value of which has been consumed from the perspective of its current holder and, thus, is an end-of-life material for said holder.

[0189] In the context of the present invention, a term X is one or more of A, B and C, wherein X is a given feature and each of A, B and C stands for specific realization of said feature, is to be understood as disclosing that X is either A, or B, or C, or A and B, or A and C, or B and C, or A and B and C. In this regard, it is noted that the skilled person is capable of transfer to above abstract term to a concrete example, e.g. where X is a chemical element and A, B and C are concrete elements such as Li, Na, and K, or X is a temperature and A, B and C are concrete temperatures such as 10 C., 20 C., and 30 C. In this regard, it is further noted that the skilled person is capable of extending the above term to less specific realizations of said feature, e.g. X is one or more of A and B disclosing that X is either A, or B, or A and B, or to more specific realizations of said feature, e.g. X is one or more of A, B, C and D, disclosing that X is either A, or B, or C, or D, or A and B, or A and C, or A and, or B and C, or B and D, or C and D, or A and B and C, or A and B and, or B and C and D, or A and B and C and D.

DESCRIPTION OF THE FIGURES

[0190] FIG. 1 is a schematic representation of a production unit used for the process according to preferred embodiments of the invention

[0191] The production unit comprises an evaporation unit E.sub.1, a dividing means D and a mixing means M. An aqueous liquid stream S.sub.R comprising CPM dissolved in water at a concentration c.sub.R(CPM), CPM having a boiling point T.sub.CPM, wherein S.sub.R further comprises the at least one CPO at a concentration c.sub.R(CPO), CPO having a boiling point T.sub.CPO with T.sub.CPO>T.sub.CPM is admixed with a stream S.sub.L11, obtaining the aqueous liquid mixture M.sub.E. The aqueous liquid mixture M.sub.E is fed to evaporation conditions into the evaporation unit E.sub.1, obtaining an aqueous vapor stream S.sub.V1 and an aqueous liquid stream S.sub.L1. S.sub.V1 comprises CPM at a concentration c.sub.V1(CPM) with c.sub.V1(CPM)>c.sub.R(CPM). S.sub.L1 comprises the at least one CPO at a concentration c.sub.L1(CPO) with c.sub.L1(CPO)>c.sub.R(CPO) and comprises CPM at a concentration c.sub.L1(CPM) with c.sub.L1(CPM)<c.sub.R(CPM). The aqueous liquid stream S.sub.L1 is divided in two streams S.sub.L11 and S.sub.L12. S.sub.L11 and S.sub.L12 have the same chemical composition as S.sub.L1. The aqueous liquid stream S.sub.L12 Is passed through a downstream treatment not shown in FIG. 1 and the aqueous liquid stream S.sub.L11 is recycled and mixed with SR.

[0192] FIG. 2 is a schematic representation of a production unit used for the process according to preferred embodiments of the invention

[0193] As in FIG. 1, the production unit comprises an evaporation unit E.sub.1 and a dividing means D. However, compared to FIG. 1, the production unit further comprises a heat exchanger H.sub.1 and does not comprise a mixing means M. The aqueous liquid stream S.sub.R is fed into the evaporation unit E.sub.1 and the aqueous liquid stream S.sub.L11, prior to be recycled as a feed component into E.sub.1, is passed through H.sub.1 for heating. M.sub.E is thus formed in E.sub.1. Apart from said differences, the process illustrated in FIG. 2 is carried out as the one illustrated in FIG. 1.

[0194] FIG. 3 is a schematic representation of a production unit used for the process according to preferred embodiments of the invention

[0195] The process illustrated by FIG. 3 represents an alternative to the process illustrated by FIG. 2. As in FIG. 1, the production unit comprises an evaporation unit E.sub.1, a dividing means D and a mixing means M. However, compared to FIG. 1, the production unit further comprises a heat exchanger H.sub.1, said heat exchanger H.sub.1 is positioned downstream of the mixing means M and upstream of E.sub.1. Thus, H.sub.1 heats the combined streams, preferably to a temperature in the range of from 200 to 270 C., more preferably in the range of from 210 to 270 C., more preferably in the range of from 220 to 270 C. Apart from said differences, the process illustrated in FIG. 3 is carried out as the one illustrated in FIG. 1.

[0196] FIG. 4 is a schematic representation of a production unit used for the process according to preferred embodiments of the invention

[0197] As in FIG. 3, the production unit comprises an evaporation unit E.sub.1, a dividing means D, a mixing means M and a heat exchanger H.sub.1. However, compared to FIG. 3, the production unit further comprises a second evaporation unit E.sub.2. The aqueous liquid stream S.sub.L12 is fed to evaporation conditions in the second evaporation unit E.sub.2, obtaining an aqueous vapor stream S.sub.V2 and a liquid stream S.sub.L2. S.sub.V2 comprises CPM at a concentration c.sub.V2(CPM) with c.sub.V2(CPM)>c.sub.L12(CPM), and CPO at a concentration c.sub.V2(CPO) with c.sub.V2(CPO)<c.sub.L12(CPO). S.sub.L2 comprises the at least one CPO at a concentration c.sub.L2(CPO) with c.sub.L2(CPO)c.sub.L12(CPO). The liquid stream S.sub.L2 is passed through a downstream treatment stage not shown in FIG. 4. Apart from said differences, the process illustrated in FIG. 4 is carried out as the one illustrated in FIG. 3.

[0198] FIG. 5 is a schematic representation of a production unit used for the process according to preferred embodiments of the invention

[0199] As in FIG. 4, the production unit comprises an evaporation unit E.sub.1, a dividing means D, a mixing means M, a heat exchanger H.sub.1 and a second evaporation unit E.sub.2. However, compared to FIG. 4, the production unit further comprises a water removal unit W.sub.U for separating CPM from water. The water removal unit W.sub.U comprises 3 distillation columns serially arranged. The bottoms stream of the downstream-most distillation column is recycled into the evaporation unit E.sub.1. The aqueous vapor stream S.sub.V1 and the aqueous vapor stream S.sub.V2 are mixed and the combined stream is passed through the water removal unit W.sub.U. Apart from said differences, the process illustrated in FIG. 5 is carried out as the one illustrated in FIG. 4.

[0200] FIG. 6 is a schematic representation of a production unit used for the process according to preferred embodiments of the invention

[0201] As in FIG. 5, the production unit comprises an evaporation unit E.sub.1, a dividing means D, a mixing means M, a heat exchanger H.sub.1, a second evaporation unit E.sub.2 and a water removal unit W.sub.U for separating CPM from water. However, compared to FIG. 5, the production unit further comprises, upstream of M and E.sub.1, a chemical reactor unit R.sub.U, a depressurization unit D.sub.U, a solid-liquid separation in a solid-liquid separation unit SL.sub.U and an evaporation unit E.sub.U comprising least two evaporation sub-units E.sub.U1 and E.sub.U2. A solid material M containing a polyamide prepared from -caprolactam and an aqueous liquid stream S.sub.W are fed to depolymerization conditions in a chemical reactor unit R.sub.U, obtaining the aqueous liquid mixture M.sub.WC comprising CPM dissolved in water and CPO. The aqueous liquid mixture M.sub.WC is passed through a depressurization unit D.sub.U, obtaining an aqueous vapor stream S.sub.VD and an aqueous liquid stream S.sub.C. S.sub.C comprising CPM dissolved in water and CPO. The aqueous liquid stream S.sub.C is subjected to solid-liquid separation by passing through the solid-liquid separation unit SL.sub.U, obtaining an aqueous liquid stream S.sub.L comprising CPM dissolved in water and CPO. Then, water is separated from aqueous liquid stream S.sub.L by evaporation in E.sub.U comprising E.sub.U1 and E.sub.U2, obtaining an aqueous vapor stream S.sub.VE and the aqueous liquid stream S.sub.R. The aqueous liquid stream S.sub.R is then treated as in the process illustrated in FIG. 5.

[0202] FIG. 7 is a schematic representation of a production unit used for the process according to preferred embodiments of the invention

[0203] As in FIG. 6, the production unit comprises an evaporation unit E.sub.1, a dividing means D, a mixing means M, a heat exchanger H.sub.1, a second evaporation unit E.sub.2 and a water removal unit W.sub.U for separating CPM from water and the production unit further comprises, upstream of M and E.sub.1, a chemical reactor unit R.sub.U, a depressurization unit D.sub.U, a solid-liquid separation in a solid-liquid separation unit SL.sub.U and an evaporation unit E.sub.U comprising two evaporation sub-units E.sub.U1 and E.sub.U2. The process illustrated in FIG. 7 is run as the process illustrated in FIG. 6 except that the liquid stream S.sub.L2 is divided in two streams, a first stream S.sub.L21 and a second stream S.sub.L22. S.sub.L21 and S.sub.L22 have the same chemical composition as S.sub.L2. The stream S.sub.L21 is recycled as a component of the aqueous liquid stream S.sub.W. The liquid stream S.sub.L22 is passed through a downstream treatment stage not shown in FIG. 7.

[0204] FIG. 8 is a schematic representation of a portion of the production unit used for the process according to preferred embodiments of the invention, namely the portion which provides S.sub.R

[0205] Said portion of the production unit comprises a reactor unit R.sub.U, a depressurization unit D.sub.U, a solid-liquid separation unit SL.sub.U and an evaporation unit E.sub.1 comprising two evaporation sub-units E.sub.U1 and E.sub.U2, said two units are serially coupled as shown in FIG. 8. The solid material M comprising the polyamide and an aqueous liquid stream S.sub.W are fed into the reactor unit R.sub.U and subjected to depolymerization conditions comprising a depolymerization temperature T.sub.D at a depolymerization pressure p.sub.D as detailed in the foregoing. An aqueous liquid stream M.sub.WC is removed from the bottom of R.sub.U, M.sub.WC comprising -caprolactam dissolved in water. The aqueous liquid stream M.sub.WC is fed into the depressurization unit D.sub.U obtaining an aqueous vapor stream S.sub.VD, and an aqueous liquid stream S.sub.C comprising -caprolactam dissolved in water. The aqueous vapor stream S.sub.VD is recycled as a component of the aqueous liquid stream S.sub.W, preferably after at least partial condensation. The aqueous liquid stream S.sub.C is passed through the solid-liquid separation unit SL.sub.U obtaining an aqueous liquid stream S.sub.SLU comprising -caprolactam dissolved in water. The aqueous liquid stream S.sub.L is then fed to evaporation in E.sub.1, in particular S.sub.L is fed to E.sub.U1. An aqueous vapor stream S.sub.VE1 is obtained from E.sub.U1 and an aqueous vapor stream S.sub.VE2 is obtained from E.sub.U2. The aqueous vapor streams S.sub.VE1 and S.sub.VE2 are recycled as a component of the aqueous liquid stream S.sub.W, preferably via condensation. Further, an aqueous liquid stream S.sub.R1 comprising -caprolactam dissolved in water is removed from E.sub.U1 and fed into E.sub.U2 and an aqueous liquid stream S.sub.R comprising -caprolactam dissolved in water is obtained and removed from E.sub.U2. The aqueous liquid stream S.sub.R is then further treated as disclosed in the foregoing and illustrated in FIGS. 1-7.

[0206] FIG. 9 is a schematic representation of a portion of the production unit used for the process according to preferred embodiments of the invention, namely the portion which provides S.sub.R

[0207] Said portion of the production unit comprises a reactor unit R.sub.U, a depressurization unit D.sub.U, a solid-liquid separation unit SL.sub.U and an evaporation unit E.sub.1 comprising two evaporation sub-units E.sub.U1 and E.sub.U2, said two units are serially coupled as shown in FIG. 9. The depressurization unit D.sub.U comprises a depressurization sub-unit DU11, a depressurization sub-unit DU12 and two solid-liquid separation units F1 and F2. The aqueous liquid stream M.sub.WC removed from the bottom of R.sub.U is passed through the solid-liquid separation unit F1, preferably filtration unit F1, wherein F1 preferably has a mesh size in the range of from 0.5 to 5 mm, more preferably in the range of from 1 to 3 mm, prior to being fed into the sub-unit DU11 to obtain an aqueous vapor stream S.sub.VD11, and an aqueous liquid stream S.sub.LD11 comprising -caprolactam dissolved in water. The aqueous liquid stream S.sub.LD11 is then passed through the solid-liquid separation unit F2, preferably filtration unit F2, wherein F2 preferably has a mesh size in the range of from 0.5 to 5 mm, more preferably in the range of from 1 to 3 mm, prior to being fed into the second depressurization sub-unit DU12, as a feed stream, to obtain an aqueous vapor stream S.sub.VD12, and the aqueous liquid stream S.sub.C comprising -caprolactam dissolved in water. The aqueous vapor streams S.sub.VD11 and S.sub.VD12 are recycled as a component of the aqueous liquid stream S.sub.W, preferably after at least partial condensation. Downstream of D.sub.U, the process is carried out as the process in FIG. 8.