Method for recycling polyolefin containing waste

Abstract

Disclosed is a method for recycling polyolefin containing waste by using a solvent with a specific Hansen parameter and contacting this mixture with a liquid filtration aid before separating the polyolefin from the mixture. The method includes the steps of mixing the polyolefin containing waste with a solvent having a Hansen parameter .sub.H from 0.0 to 3.0 MPa.sup.1/2; contacting this mixture with a liquid filtration aid having a Hansen parameter .sub.H>4.0 MPa.sup.1/2; and separating the polyolefin from the mixture.

Claims

1. A method for recycling a polyolefin containing waste comprising the following steps: a) mixing the polyolefin containing waste with a solvent having a Hansen parameter .sub.H from 0.0 to 3.0 MPa.sup.1/2; b) contacting the mixture from a) with a liquid filtration aid having a Hansen parameter .sub.H4.0 MPa.sup.1/2.; and c) separating the polyolefin from the mixture.

2. The method according to claim 1, wherein the polyolefin is selected from the group consisting of PE, PP, LDPE, HDPE, LLDPE, and mixtures thereof.

3. The method according to claim 1, wherein the solvent is selected from the group consisting of hydrocarbon compounds.

4. The method according to claim 3, wherein the hydrocarbon compounds are aliphatic hydrocarbon compounds.

5. The method according to claim 4, wherein the aliphatic hydrocarbon compounds are cyclo, linear, or branched aliphatic hydrocarbon compounds.

6. The method according to claim 1, wherein the liquid filtration aid contains at least one fluid with a Hansen-parameter .sub.H from 4.0 to 38.0 MPa.sup.1/2.

7. The method according to claim 6, wherein the liquid filtration aid forms a miscibility gap with the solvent.

8. The method according to claim 1, wherein the liquid filtration aid is at least one fluid selected from the group consisting of mono-/poly-hydroxy hydrocarbons with 2 to 12 carbon atoms.

9. The method according to claim 1, wherein the liquid filtration aid is at least one fluid selected from the group consisting of 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-pentanol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 1,2,3-propanetriol, 1,2,4-butanetriol, 1,2,3-butanetriol, 2-(hydroxymethyl)-1,3-propanediol, 1,3,5-pentanetriol, 2,3,4-pentanetriol, 2-(hydroxymethyl)-2-methyl-propanediol, 2-propene-1-ol, propene-2-ol, 3-butene-1-ol, 2-buten-1-ol, 3-buten-2-ol, 1-butene-2-ol, (E)-2-Buten-1-ol, (Z)-2-Buten-1-ol, 2-methyl-2-propen-1-ol, 2-methyl-prop-1-en-1-ol, cyclopropylcarbinol, cyclobutanol, 1-penten-3-ol, 3-methyl-3-buten-1-ol, (Z)-2-penten-1-ol, 3-methyl-2-buten-1-ol, 2-methyl-3-buten-2-ol, (E)-2-penten-1-ol, 2-methyl-2-buten-1-ol, 4-penten-1-ol, 3-penten-2-ol, 2-penten-1-ol, 4-penten-2-ol, (Z)-2-penten-1-ol, (Z)-3-Penten-1-ol, 3-methyl-3-buten-2-ol, 3-penten-1-ol, (E)-2-penten-1-ol, (E)-3-penten-1-ol, 2-methyl-3-buten-1-ol, 2-penten-1-ol, pent-2-en-1-ol, 2-methyl-(E)-2-butenol, trans-3-penten-2-ol, 1-penten-3-ol, (Z)-pent-3-en-2-ol, (E)-pent-3-en-2-ol, prop-1-en-1,2-dimethyl-1-ol, 1-ethylcyclopropanol, 1-methylcyclopropanemethanol, cyclopentanol, cyclobutanemethanol, cyclopropylmethylcarbinol, 1,2-cyclopentanediol, and any combination thereof.

10. The method according to claim 1, wherein the polyolefin containing waste is selected from the group consisting of green dot collection waste, industrial waste, household-waste, bulky waste, packaging waste, rigid plastic waste and mixtures thereof and comprises or consists of multilayered plastic material and contaminant, wherein the multilayered plastic material contains at least one layer with at least 80.0 wt.-% of a polyolefin and at least another layer with at least 80.0 wt.-% of another polymer or polymer blend and optionally, a further layer comprising more than 20.0 wt.-% metal and/or paper.

11. The method according to claim 10, wherein the another polymer or polymer blend is selected from the group consisting of polyesters, polyethers, polyvinylacetate, polyvinylalcohols, ethylenevinylalcohols, polyamides, polyacrylates, polycarbonates, polyurethanes, aromatic polymers, blends thereof, and copolymers thereof.

12. The method according to claim 10, wherein the contaminant is selected from the group consisting of glass, fillers, flame retardants, papers, colorants, printing inks, whiteners, bonding agents, coatings, inert contaminants, foams, adhesives, metals, heavy metals, volatile organic substances, aromatic substances, halogenated aromatic substances, halogenated hydrocarbons, biologically degradable dirt, residual foodstuff, wood, textile fibres, natural fibres, and any combination thereof.

13. The method according to claim 1, wherein a temperature of 75 to 200 C. is applied in steps a) and b).

14. The method according to claim 1, wherein a temperature of 25 to 260 C. is applied in step c).

15. The method according to claim 1, wherein the mixture of step a) comprises from 2.0 to 40 wt.-% polymer.

16. The method according to claim 1, wherein the contacting time in step b) is at least 0.5 min.

17. The method according to claim 1, wherein the volume of the liquid filtration aid in step b) is from 0.5 to 100 wt.-%, in relation to the mixture of waste and solvent coming from step a).

18. The method according to claim 1, wherein the mixture is subjected to a separation process prior to step c).

19. The method according to claim 1, wherein the separation in step c) is effected by evaporation of the solvent or by addition of a precipitant followed by precipitation and mechanical separation of the polyolefin.

20. The method according to claim 1, wherein the separated polyolefin is directly fed into an extruder and processed to a polyolefin granulate compound, masterbatch or film or dried in a drying process and cooled to room temperature.

Description

EXAMPLE A

PE from Post-Industrial Film Waste

(1) Multilayer packaging films have been cut into pieces of approximately 1-5 cm.sup.2 and used as input samples. All input samples have been dissolved by a multifold polyolefin-extraction in several 100 mL and 1 L batches. The temperature that has been applied in this extraction step in order to dissolve PE is 100-125 C. The residence time which was found sufficient for a complete extraction of PE was 15-30 min.

(2) A1) Coarse filtration without filtration aid

(3) After extraction of the waste material the extract solution has been filtered coarsely by means of simple tea strainers with two different sieve sizes, 500 m and 100 m, respectively).

(4) From the TiO.sub.2-pigmented multilayer film, the achieved filtered PE-solutions were white coloured. These solutions were dried. The resulting PE-powders were molten with a melt-flow-index-equipment (MFI-equipment). X-ray fluorescence (XRF) measurements were performed to check the content of TiO.sub.2-pigments. A titanium content of 2.2 wt.-% Ti has been found.

(5) A2) Fine filtration without filtration aid

(6) As an effect of the different colour of some input samples the extracted PE-dispersion (solution with impurities) was coloured light yellow or pink from dissolved parts of the colouring ink.

(7) In order to achieve a white or even natural non-coloured PE, the yellow/pink hot extract solution has been filtered by means of a 1-L heated pressurized (cake) filtration (Temp. 110 C.; 0.3-2 bar; Seitz depth filter sheet T1500, 28 cm.sup.2 filter area). The filter showed a pore size of less than 5 m and was successful in removing some of the TiO.sub.2-pigments. Solutions with a weight ratio of 4.0 to 8.0% PE could be filtered easily with a fresh filter device, but repeatedly after filtration of 70-85 g of white-pigmented PE (depending on concentration this number correlates to from 1000 to 1750 g of PE-dispersion) the filter was blocked.

(8) The MFI-strand which has been produced after drying was still white. The XRF-measurement which was performed to check the content of TiO.sub.2-pigments revealed a titanium content of 1.3 wt.-% Ti.

(9) A3) Improved fine filtration with filtration aid

(10) After extraction of the waste material a filtration aid has been added to the extract solution. The mixture of extract solution and filtration aid has been separated by sedimentation and filtered by means of a 1-L heated pressurized (cake) filtration (Temp. 110 C.; 0.3-2 bar; 28 cm.sup.2 filter area). An MFI-strand of the filtered material has been produced and examined by XRF-measurements. The titanium content was 0.0028 wt.-%.

(11) Thus, a very high purification efficiency of 99.9% with respect to the TiO.sub.2-pigments could be achieved.

(12) For extract solutions of the same PE-concentration an increase in the service life of the filter by a factor of 20 could be achieved by using a filtration aid whilst also maintaining the purification performance.

EXAMPLE B

PE from Post-Consumer Flexible Waste

(13) Post-consumer flexible waste material has been extracted and filtered in the same way as described in example A.

(14) B1) Coarse filtration without filtration aid

(15) Subsequently, the extract solution has been filtered by means of a coarse filter such as in example A1. The resulting coarsely filtered PE-solution has a green-brown (olive) colour and showed many fine dispersed dark-grey impurities. A microscopic analysis (frame size: 0.4 mm.sup.2) of a film blown from the finely filtered material has revealed that the filtration has not been effective. The sample contained 2678 particles formed by impurities. Their size can be derived from the particle size distribution diagram in FIG. 1. The biggest particles show a considerable size of up to 400 m.

(16) B2) Fine filtration without filtration aid

(17) The impurities caused blocking of the applied fine filter after filtration of 10 g PE only.

(18) B3) Fine filtration with a solid filter aid

(19) The use of a massive excess of a solid filter aid (25% related to dissolved PE), e.g. Celite, could increase the throughput up to 35 g PE (dissolved in hot solutions of 3.5% to 8.5% concentration).

(20) B4) Fine filtration of the supernatant

(21) To the same extent as in example B3 the fine-filtration throughput was increased by using the supernatant after 1 h to 2.0 h sedimentation of the coarse-filtered PE-solution.

(22) Thus (even with applied accelerated sedimentation of the hot PE-solution in centrifugal field) there were no means to achieve a robust (long-lasting) fine filtration of the PE-solution by non-expensive methods (affordable by the low commercial price of the recovered PE). E.g. the cost of single-use dead end filters and/or consumption of filter aids including their later disposal are much too high for achieving a profitable application.

(23) And from a technical view the throughput of the fine-filter is too low in relation to the necessary cleaning/CIP-expenses, filter media and used solvent amounts for rinsing. Additionally, the very small flows would require an expensive large filter device: A post-consumer-PE-dispersion of 5.8% concentration could be filtered at a rate of 0.001 g PE/(bar.Math.cm.sup.2.Math.s) only.

(24) B5) Fine filtration with a liquid filtration aid

(25) A liquid filtration aid was added to the already coarsely filtered PE-solution. The liquid filtration aid was a second polar solvent, e.g. an alcohol, which accelerated the sedimentation of the impurities. As a result either a) a homogeneous liquid phase with a solid precipitate consisting in insoluble impurities or b) a second liquid phase was obtained. The settled impurities were separated mechanically from the PE-containing phase without any loss of PE.

(26) Blocking of the fine filter only occurs at PE-amounts as high as 500-900 g when solutions of 4.5 wt.-% to 8.0 wt.-% PE are used. In comparison to the filter blocking observed in example B1) this is an improvement factor of almost 2 orders of magnitude.

(27) A pc-PE-dispersion of 5.6 wt.-% concentration could be filtered at a rate of 0.1 g PE/(bar.Math.cm.sup.2.Math.s). Necessary filter devices can be much smaller (cheaper) than in comparative example B4.

(28) The microscopic analysis (frame size: 0.4 mm.sup.2) of a film which has been blown from the PE recyclate confirmed that also the amount of impurities could be reduced considerably. The sample contained only 44 particles formed by impurities. This corresponds to reduction of impurities (fines) by means of liquid filtration aid of 98%. Additionally, it can be concluded from the particle size distribution diagram in FIG. 2 that the impurities in the recyclate are smaller (only up to 100 m) than in the case of a filtration without a liquid filter aid (compare to FIG. 1).

(29) Moreover, after the process, the filtration aid fluid showed enrichments of bonding agents and other polymeric materials, such as adhesives and/or polystyrene based polymers. FIGS. 3 and 4 provide evidence for that.

(30) In FIG. 3 the infrared spectrum of the material which has been isolated from the liquid filtration aid after it has been used in the recycling process (1) shows an absorption at the same wavenumbers as a the sample of a pure PE-based bonding agent with maleic anhydride (2). In FIG. 4 the IR-spectrum of the isolated precipitate (4) shows considerable agreement with the infrared spectrum of a pure polyurethane based coating (3). Without the use of the liquid filtration aid, these impurities would have been found in the final product, the PE-recyclate.