PROCESS FOR DE-POLYMERIZATION OF STYRENIC MONOMER-CONTAINING POLYMERS AND FOR RETRIEVAL OF STYRENIC MONOMERS

Abstract

The invention relates to an improved process for providing purified styrenic monomers, such as styrene, from styrene-containing polymer waste. Styrene-containing waste is depolymerized in a suitable reactor, and the depolymerization products are condensed and separated in a three-step distillation process.

Claims

1-17. (canceled)

18. A process for retrieving styrenic monomer from a polymer mixture (P), the polymer mixture (P) comprising: (A) 1 wt-% to 99.8 wt-%, related to the total weight of polymer mixture (P), of a styrenic polymer comprising: i. 70 wt-% to 100 wt-%, related to the total weight of (A), of repeating units derived from a styrenic monomer selected from styrene and alpha-methylstyrene; ii. 0 wt-% to 30 wt-%, related to the total weight of (A), of repeating units derived from dienes; iii. 0 wt-% to 2 wt-%, related to the total weight of (A), of repeating units derived from other radically co-polymerizable monomers; (B) 0.1 wt-% to 98.9 wt-%, related to the total weight of polymer mixture (P), of a mixture of polymers other than polymer (A); (C) 0.1 wt-% to 30 wt-%, related to the total weight of polymer mixture (P), of organic or inorganic polymer additives and auxiliaries; and optionally (D) 0 wt-% to 50 wt-%, related to the total weight of polymer mixture (P), of impurities such as, but not limited to, food waste, dirt, packaging residues or moisture, the process comprising the steps of: I) feeding the polymer mixture (P) into a pyrolysis zone of a pyrolysis reactor and subjecting it to a temperature of 300° C. to 650° C., in particular 300° C. to 550° C., measured as the average temperature of the polymer mixture (P) at the inner surface of the reactor wall during the reaction runtime, during which at least partial decomposition of the component (A) to styrenic monomers takes place, and a gas containing said styrenic monomers is formed; II) condensing the condensable substances including styrenic monomers from the gas formed in step I) at a cooling rate of more than 500° C./min (500 K/min); III) fractionating the condensed substances from step II) in a distillation column (X), wherein in step Ill), a fraction (a1) comprising styrenic monomers is withdrawn through a side outlet from the distillation column (X), at a position above 65% to 95% and below 35% to 5% of the total number of theoretical stages; a fraction (a2) comprising heavy boilers is collected at the bottom of the distillation column (X); a fraction (a3) comprising light boilers is collected at the head of the distillation column (X); and the distillation column (X) is operated at a bottom pressure of 200 hPa (150 mmHg) to 533 hPa (400 mmHg), a head pressure of 133 hPa (100 mmHg) to 400 hPa (300 mmHg), a bottom temperature of 200° C. to 300° C., and a head temperature of 40° C. to 80° C.

19. The process according to claim 18, wherein the polymer mixture (P) comprises 80 wt-% to 99.8 wt-%, related to the total weight of polymer mixture (P), of the styrenic polymer (A) and 0.1 wt-% to 19.9 wt-%, related to the total weight of polymer mixture (P) of the mixture of polymers (B).

20. The process according to claim 18, wherein a stabilizer or radical scavenger is added to the condensable substances in step II).

21. The process according to claim 18, further comprising the step IV) fractionating fraction (a1) obtained in step III) in a distillation column (Y).

22. The process according to claim 21, wherein in step IV) a fraction (b1) comprising styrenic monomers and components with a higher boiling point than the styrenic monomers is withdrawn from the bottom of the distillation column (Y) and a fraction (b2), comprising components with a lower boiling point than the styrenic monomers is withdrawn from the head of the distillation column (Y).

23. The process according to claim 21, wherein the distillation column (Y) is operated at a bottom pressure of 160 hPa (120 mmHg) to 347 hPa (260 mmHg), a head pressure of 40 hPa (30 mmHg) to 147 hPa (110 mmHg), a bottom temperature of 80° C. to 120° C., and a head temperature of 50° C. to 80° C.

24. The process according to claim 21, further comprising the step of: V) separating the fraction comprising styrenic monomers obtained in step IV) in a distillation column (Z), wherein a fraction (c1) comprising styrenic monomers is withdrawn from the head of the distillation column (Z); and a fraction (c2), comprising components with a higher boiling point than the styrenic monomers, is collected at the bottom of the distillation column (Z); wherein the distillation column (Z) is operated at a bottom pressure of 133 hPa (100 mmHg) to 467 hPa (350 mmHg), a head pressure of 13 hPa (10 mmHg) to 133 hPa (100 mmHg), a bottom temperature of 80° C. to 150° C., and a head temperature of 45° C. to 100° C.

25. The process according to claim 21, wherein the distillation column (Y) in step IV) comprises at least 50 theoretical stages.

26. The process according to claim 18, wherein the component (B) is a mixture of polymers selected from the group consisting of polyolefins; hydrogenated or non-hydrogenated ethylenepropylene-diene-rubber (EPDM); polyvinyl chloride (PVC); chlorinated polyvinyl chloride (c-PVC); polycarbonates; polyamides; and polyesters.

27. The process according to claim 18, wherein the component (B) contains iv. 0 wt-% to 1 wt-%, related to the total weight of polymer mixture (P), of PVC or c-PVC; v. 0 wt-% to 35 wt-%, related to the total weight of polymer mixture (P), of polyolefins, hydrogenated EPDM or non-hydrogenated EPDM; vi. 0 wt-% to 10 wt-%, related to the total weight of polymer mixture (P), of hydrogenated or non-hydrogenated styrene-butadiene copolymers comprising at least 15 wt-% butadiene based on the total weight of styrene-butadiene copolymer; and vii. 0 wt-% to 5 wt-%, related to the total weight of polymer mixture (P), of polyesters, polycarbonates or polyamides, provided that the amount of components selected from groups iv., v., vi. and vii. sums up to at least 0.1 wt-%, related to the total weight of polymer mixture (P).

28. The process according to claim 18, wherein the component (C) contains viii. 0 wt-% to 10 wt-%, related to the total weight of polymer mixture (P), of water; ix. 0 wt-% to 1 wt-%, related to the total weight of polymer mixture (P), of halogenated substances; x. 0 wt-% to 10 wt-%, related to the total weight of polymer mixture (P), of inorganic or organic dyes or pigments; xi. 0 wt-% to 10 wt-%, related to the total weight of polymer mixture (P), of lubricants, waxes or amides of long chain organic acids; xii. 0 wt-% to 5 wt-%, related to the total weight of polymer mixture (P), of emulsifiers or soaps; xiii. 0 wt-% to 5 wt-%, related to the total weight of polymer mixture (P), of paper or cardboard; xiv. 0 wt-% to 1 wt-%, related to the total weight of polymer mixture (P), of metals, metal oxides or metal salts; xv. 0 wt-% to 10 wt-%, related to the total weight of polymer mixture (P), of further fillers; and xvi. 0 wt-% to 2 wt-%, related to the total weight of polymer mixture (P), of other additives such as UV stabilizers, HALS, hindered phenols, disulfite stabilizers, quenchers or absorbers, provided that the amount of components selected from groups viii., ix., x., xi., xii., xiii., xiv., xv., and xvi. sums up to at least 0.1 wt-%, related to the total weight of polymer mixture (P).

29. The process according to claim 18, wherein shear force and/or pressure are additionally applied to the polymer mixture (P) in the pyrolysis reactor in step I).

30. The process according to claim 18, wherein at least 3 theoretical stages are located below the position at which the condensed substances from step II) are introduced into the distillation column (X) in step III) and at least 17 theoretical stages are located above the position at which the condensed substances from step II) are introduced into the distillation column (X) in step III).

31. The process according to claim 18, wherein fraction (a2) collected at the bottom of the distillation column (X) in step III) is re-introduced into the pyrolysis zone of the pyrolysis reactor in step I).

32. The process according to claim 18, wherein the styrenic monomer retrieved by the process is styrene.

33. The process according to claim 18, wherein the distillation column (X) contains trays.

34. The process according to claim 24, wherein the distillation column (Z) contains more than 10 theoretical stages.

35. The process according to claim 24, wherein the distillation column (Z) is a packed column.

36. The process according to claim 18, wherein the distillation column (X) contains 20 to 40 theoretical stages.

37. The process according to claim 21, wherein the feed of the distillation column (Y) is located at a position above 20% to 80% of the total number of theoretical stages of distillation column (Y) and below 80% to 20% of the total number of theoretical stages of distillation column (Y).

Description

EXAMPLES

[0075] Polymer mixtures (P) were heated in a flask to 350° to 450° C. This temperature is the average temperature of the polymer waste at the inner surface of the reactor wall during the reaction runtime. The results of depolymerization are summarized in Table 3.

TABLE-US-00003 TABLE 3 Examples (E), reference Example (R) and comparative examples (C) R1 C2 E2 C3 E3 C4 E4 C5 E5 (P) PS* PS* + 10% PS* + 1% PS* + 2% PS* + 0.5% PS* + 10% PS* + 2% PS* + 20% PS* + 5% Novodur Novodur PVC***** PVC***** PET*** PET*** Styrolux Styrolux P2H-AT** P2H-AT** 3G55**** 3G55**** Main mono- and mono- and mono- and trial mono- and mono- and mono- and mono- and mono- and products oligo- oligo- oligo- stopped oligo- oligo- oligo- oligo- oligo- styrene styrene + styrene + due to styrene + styrene + styrene + styrene + styrene + not identified few not formation lesser HCl not identified not identified not identified not identified products + identified of HCl formation products + products + products + products + black residue products + depoly- black residue less black black residue less black low amount of merisation residue residue black residue can still than in C4 than in C5 be conducted Styrene 70% <70% <70% n/a <70% <70% <70% <70% <70% yield Obser- — >10 ppm HCN <10 ppm HCN HCl fume Black residue Less Black residue Less vation black residue black residue *general purpose polystyrene (PS GPPS 158 N, INEOS Styrolution, Frankfurt) **representative of a typical ABS (Novodur, INEOS Styrolution) ***polyethylene terephthalate ****representative of a typical styrene-butadiene copolymer (INEOS Styrolution) *****polyvinyl chloride

DESCRIPTION OF THE DRAWING (FIG)

[0076] The drawings are schematic flow diagram of a particularly preferred embodiment of the process of the present invention, starting with step III).

[0077] It is an exemplary embodiment and is not meant to limit the invention. The drawing displays that the condensed substances (6), which are obtained after the pyrolysis step I) and the condensation step II), are introduced into a distillation column (1), which corresponds to distillation column (X). At the same time a first polymerization inhibitor (7) is introduced into the distillation column (1).

[0078] The light boilers (8), corresponding to fraction (a3), are partially removed from the head of the distillation column (1) and are partially condensed by a condenser (5) and reintroduced into the distillation column (1). The heavy boilers (9), corresponding to fraction (a2) are partially removed from the bottom of the distillation column (1) and are partially reboiled in a reboiler (4) and reintroduced into the distillation column (1).

[0079] The mixture comprising styrenic monomers (11) corresponding to fraction (a1) is withdrawn from distillation column (1) through a side draw (10) and introduced into a distillation column (2), corresponding to distillation column (Y). At the same time a second polymerization inhibitor (12) is introduced into the distillation column (2).

[0080] The fraction comprising ethylbenzene (13), corresponding to fraction (b2), is partially removed from the head of the distillation column (2) and is partially condensed by a condenser (5) and reintroduced into the distillation column (2). The fraction comprising styrenic monomers (14), corresponding to fraction (b1) is partially withdrawn from the bottom of the distillation column (2) and is partially reboiled in a reboiler (4) and reintroduced into the distillation column (2). The withdrawn portion of the fraction (14) is introduced into a distillation column (3), corresponding to distillation column (Z).

[0081] In the distillation column (3) a fraction comprising heavy boilers (15) corresponding to fraction (c2), is partially withdrawn from the bottom of the distillation column (3) and is partially re-boiled in a reboiler (4) and reintroduced into the distillation column (3).

[0082] The withdrawn part of fraction (15) is combined in a mixing utility (17) with the heavy boilers (9) withdrawn from the distillation column (1) to form a residue (18), which may be reintroduced into the pyrolysis reactor.

[0083] A second fraction (16), corresponding to fraction (c1), is partially removed from the head of the distillation column (3) and is partially condensed by a condenser (5) and reintroduced into the distillation column (3). The withdrawn fraction (16) is collected as the product, essentially consisting of styrenic monomers, e.g. styrene.