RECYCLING METHOD FOR STYRENE-CONTAINING PLASTIC WASTE

Abstract

The invention relates to a method for economically using styrene-containing plastic waste as raw material for new high-quality plastic products as part of a raw material recycling process, optionally having the steps of pre-treating a styrene-containing starting material, decomposing the styrene-containing starting material in a suitable reactor, discharging and collecting the resulting gases and condensing the low-molecular products in a suitable separator, separating the collected low-molecular components of the previous step by means of a fractioning distillation process, and optionally additionally decomposing the styrene oligomers in a steam cracker.

Claims

1-13. (canceled)

14. A process for the pyrolytic depolymerization of a styrene-containing plastics waste (K) consisting of the components A, B1, B2, B3 and C: A: 0.1 to 100% by weight, based on the entirety of components A, B1, B2 and B3, of at least one styrene-containing polymer comprising at least 40% of styrene, based in each case on component A, and up to 60% by weight, based on component A, of rubber and/or other comonomers which do not interrupt the pyrolysis process; B1: 0 to 60% by weight, based on the entirety of A, B1, B2 and B3, of polyolefin or polyolefin mixtures; B2: 0 to 60% by weight, based on the entirety of A, B1, B2 and B3, of other polymers, differing from A and B1; B3: 0 to 20% by weight, based on the entirety of A, B1, B2 and B3, of conventional plastics additives and conventional plastics auxiliaries; C: 0 to 50% by weight, based on the entirety of A, B1, B2 and B3, of other foreign substances, dirt and moisture; the process comprising the steps of: i) decomposing the styrene-containing plastics waste (K) in a suitable reactor via introduction of thermal energy and optionally of shear energy, where the plastics waste (K) to be decomposed is introduced into a pyrolysis zone of the reactor and is pyrolyzed there at an average temperature of 250° C. to 500° C. measured at the inner surface of a reactor wall during the reaction time, where the residence time in the pyrolysis zone of the plastics waste (K) to be pyrolyzed is 0.1 to 60 minutes, and where the styrene component of the styrene-containing plastics waste (K) is at least to some extent decomposed to give styrene monomers and styrene oligomers; ii) discharging and collecting the gases produced in step i) and condensing the low-molecular-weight products comprising the resultant styrene monomers, in a suitable separator; iii) fractionating, by means of fractional distillation, the condensed low-molecular-weight constituents of the previous step comprising the resultant styrene monomers.

15. The process as claimed in claim 14, characterized in that in a further step iv) the resultant styrene oligomers from step i), and also any styrene oligomers present before step i), are introduced into a steam cracker.

16. The process as claimed in claim 14, characterized in that the quantity present of component A, based on the entirety of components A, B1, B2 and B3, is at least 1% by weight.

17. The process as claimed in claim 14, characterized in that the quantity present of component A, based on the entirety of components A, B1, B2 and B3, is at least 10% by weight.

18. The process as claimed in claim 14, where component A comprises 0 to 10% by weight, based on component A, of one or more comonomers from the group consisting of acrylonitrile, vinyl chloride, methyl methacrylate and alpha-methylstyrene.

19. The process as claimed in claim 14, where the proportion of component B1 is 0.1 to 50% by weight, based on the entirety of components A, B1, B2 and B3.

20. The process as claimed in claim 14, where the proportion of component C is 0.1 to 30% by weight based on the entirety of components A, B1, B2 and B3.

21. The process as claimed in claim 14, where the quantity of component A present is at least 50% by weight, based on the entirety of components A, B1, B2 and B3, where the quantity of component B1 present is at least 10% by weight, based on the entirety of components A, B1, B2 and B3, and the proportion of component C is 0.1 to 20% by weight, based on the entirety of components A, B1, B2 and B3.

22. The process as claimed in claim 14, where the pyrolysis temperature in step i) is in the range 280 to 470° C. and the residence time in step i) is in the range 1 to 45 minutes.

23. The process as claimed in claim 14, where the pyrolysis reactor in step i) is selected from the group consisting of twin-screw extruders, fluidized-bed reactors and microwave reactors.

24. The process as claimed in claim 14, where shear energy is additionally introduced in step i) into the styrene-containing plastics waste (K).

25. The process as claimed in claim 14, where the pyrolysis reactor in step i) comprises no catalyst.

26. The process as claimed in claim 14, where the styrene-containing plastics waste (K) is subjected in a preceding step o) to a pretreatment comprising one or more of the following steps, where the sequence of the steps is not fixed and multiple repetition of steps is also possible: manual sorting to remove disruptive substances, washing, comminution, automatic sorting in suitable systems.

27. The process as claimed in claim 14, where component A comprises at least one styrene-containing polymer comprising at least 50% of styrene; component B1 is polyolefin or polyolefin mixtures selected from polyethylene, polypropylene and mixtures containing them; component B2 is a polymer, differing from A and B1, selected from polycarbonates, polyesters, polyamides, polyvinyl chloride, and mistuxtures thereof.

28. The process as claimed in claim 22, where the pyrolysis temperature in step i) is in the range 300 to 450° C. and the residence time in step i) is in the range 2 to 30 minutes.

Description

EXPLANATION OF THE DRAWINGS

[0087] FIG. 1 shows an example of a GC-MS analysis of the reaction products from example 1.

[0088] FIG. 2 shows an example of a GC analysis of the reaction products from example 2.

[0089] The invention is illustrated by the examples, figures and claims below.

EXAMPLES

[0090] In order to demonstrate the suitability of styrene-containing plastics wastes, polymers are heated in flasks to 350° C. to 450° C. This temperature is the average temperature of the reaction mixture in the interior of the reaction vessel during the reaction time.

TABLE-US-00002 TABLE 2 Inventive examples and comparative examples Inv. Ex. 1 Inv. Ex. 2 V1 V2 V3 V4 Inv. Ex. 3 Inv. Ex. 4 (K) PS GPPS PS 468N PP PP Co- LDPE LLDPE Mixture of Mixture of 158 N (impact- Homo- polymer 60% GPPS 60% GPPS modified polymer 158 N 158 N poly- polystyrene polystyrene styrene) and 40% PP and 40% homo- LDPE polymer Main Styrene Styrene Waxy Waxy Waxy Waxy Styrene Styrene products of monomer monomer sub- sub- sub- sub- monomer monomer thermal and and stances stances stances stances and styrene and styrene cracking styrene styrene oligomers oligomers oligomers oligomers V = comparative examples

Inventive Example 1

[0091] The polymer samples are decomposed in a glass apparatus consisting of round-bottomed flask with heating jacket, Liebig condenser and cold trap. The commercially available polystyrene (PS GPPS 158 N, producer: INEOS Styrolution, Frankfurt) for decomposition is charged to the round-bottomed flask, input weight being 100 g. A vacuum pump is used to generate subatmospheric pressure in the apparatus. The residual pressure in the apparatus is 45 mbar. The start temperature of the reaction is 370° C., measured between heating jacket and flask.

[0092] Formation of condensate starts at a jacket temperature of 460° C. At a jacket temperature of 550° C. the reaction has concluded. The average reaction temperature is 460° C. During the entire running time of the experiment, the reaction products are collected in two stages, firstly in a cryostat at −40° C. and then in a cold trap cooled to −196° C. by liquid nitrogen. The yield of condensate is 95.4%, based on the quantity of polystyrene used.

[0093] The reaction products produced are characterized by means of GC-MS

[0094] (Agilent 7890A gas chromatograph, Agilent DB-1 column with He carrier gas), see FIG. 1. Table 3 describes the composition of the reaction products.

TABLE-US-00003 TABLE 3 Composition of reaction products from inventive example 1 Proportion in Proportion based on Component condensate starting material Styrene monomer 37.25% 35.63% Styrene dimer 19.73% 18.82% Styrene trimer 32.37% 30.88% Total proportion of styrene 89.35% 85.23% and styrene oligomers

[0095] In the next step, the condensate is fractionated by fractional distillation. This is achieved by distillation with a Vigreux column at subatmospheric pressure generated by a membrane pump (starting pressure 50 mbar). A distillation pig is used to collect the various fractions, and the low-boiling-point fraction is collected in a cold trap cooled by liquid nitrogen. The distillation temperature here is increased from room temperature to 490° C. (flask jacket temperature). The resultant fractions are characterized by gas chromatography (see table 4). The expression “low boilers” here means all of the substances evolved from the condensate to be fractionated that change to the gas phase at a lower temperature than styrene monomer, styrene dimer and styrene trimer. The expression “high boilers” here means all of the substances evolved from the condensate to be fractionated that change to the gas phase at a higher temperature than styrene monomer, styrene dimer and styrene trimer.

TABLE-US-00004 TABLE 4 Characterization of the fractions from inventive example 1 Total propor- Temper- tion of Propor- ature Propor- Propor- Propor- Propor- Propor- styrene and tion of of heating tion of tion of tion of tion of tion of styrene fraction, medium low high styrene styrene styrene oligomers based on Fraction (° C.) boilers boilers monomer dimer trimer in fraction condensate 1 82 8.94% — 91.06% — — 91.06% 0.80% 2 86 1.17% — 98.83% — — 98.83% 28.03% 3 88 — — 100.00% — — 100.00% 10.80% 4 95 — — 100.00% — — 100.00% 5.20% 5 116 — — 100.00% — — 100.00% 2.23% 6 125 — 0.42% 99.58% — — 99.58% 1.88% 7 133 — 0.71% 99.29% — — 99.29% 0.48% 8 141 — 1.56% 98.44% — — 98.44% 1.18% 9 451 4.66% 21.12% 39.57% 31.88% 2.76% 74.21% 0.50% 10 453 — 11.71% 23.07% 64.20% 1.02% 88.29% 0.50% 11 453 — 7.76% 8.61% 60.84% 22.79% 92.24% 2.83% 12 490 — 8.67% 8.86% 79.63% 2.83% 91.06% 12.83% Cold 0.96% 4.83% 86.74% 6.85% 0.61% 91.32% 0.63% trap Residue 32.15% in flask

Inventive Example 2

[0096] The experiment is repeated by analogy with inventive example 1, using impact-modified polystyrene (PS 486N, producer: INEOS Styrolution). PS 486N polystyrene is an impact-resistant amorphous polystyrene (HIPS) with melt volume flow rate (melt volume rate 200° C./5 kg load, ISO 1133) about 4 cm.sup.3/10 min.

[0097] The starting temperature of the reaction is 370° C., measured between heating jacket and flask. Formation of condensate starts at a jacket temperature of 450° C. At a jacket temperature of 550° C. the reaction has concluded. During the entire running time of the experiment, the reaction products are collected in two stages, firstly in a cryostat at −40° C. and then in a cold trap cooled to −196° C. by liquid nitrogen. The yield of condensate is 82.2%, based on the quantity of polystyrene used. The reaction products produced are characterized by means of gas chromatography (Agilent 7890A gas chromatograph, Agilent HP-5 column with argon carrier gas, detection by flame ionization, solvent THF), see FIG. 2.

[0098] Table 5 describes the composition of the reaction products.

TABLE-US-00005 TABLE 5 Composition of reaction products from inventive example 2 Proportion in Proportion based on Component condensate starting material Styrene monomer 52.59% 43.23% Styrene dimer 6.50% 5.34% Styrene trimer 10.48% 8.61% Total proportion of styrene 69.57% 57.18% and styrene oligomers

[0099] In the next step, the condensate is fractionated by fractional distillation. This is achieved by distillation with a Vigreux column at subatmospheric pressure generated by a membrane pump. A distillation pig is used to collect the various fractions, and the low-boiling-point fraction is collected in a cold trap cooled by liquid nitrogen. The distillation temperature here is increased from room temperature to 160° C. (flask jacket temperature). The resultant fractions are characterized by gas chromatography (see table 6). The expression “low boilers” here means all of the substances evolved from the condensate to be fractionated that change to the gas phase at a lower temperature than styrene monomer, styrene dimer and styrene trimer. The expression “high boilers” here means all of the substances evolved from the condensate to be fractionated that change to the gas phase at a higher temperature than styrene monomer, styrene dimer and styrene trimer. Table 6 collates styrene monomer, styrene dimer and styrene dimer within a single column.

TABLE-US-00006 TABLE 6 Characterization of fractions from inventive example 2 Temper- Propor- ature Propor- Propor- Propor- tion of of heating tion of tion of tion of fraction medium low high styrene based on Fraction (° C.) boilers boilers monomer condensate 1 78 48.88% 2.34% 48.78% 3.35% 2 80 41.97% 4.05% 55.68% 2.60% 3 100 15.80% 7.09% 77.11% 39.55% 4 118 5.95% 8.94% 85.11% 5.45% 5 130 2.42% 7.73% 89.85% 0.45% 6 145 1.35% 8.33% 90.32% 0.53% 7 149 0.80% 15.16% 84.04% 0.13% 8 160 2.53% 17.90% 79.57% 0.25% Cold trap 60.94% 1.23% 37.83% 1.23% Residue 46.48% in flask

[0100] Analogous experiments are carried out with a polymer blend made of 85% by weight of polystyrene (A), 8% by weight of aromatic polycarbonate (B2), 2% by weight of conventional additives (B3) and 5% of foreign substances (C).