Polymer Degradation

Abstract

A method of degrading a polymer into oligomers and/or monomers in a solvent, using a catalyst, and a functionalized magnetic particle comprising a catalyst being capable of degrading the polymer into oligomers and/or monomers. The present method and particle provide a high selectivity and a high conversion ratio.

Claims

1.-17. (canceled)

18. Method of degrading a homo- or copolymer into oligomers, trimers, dimers and/or monomers, comprising the steps of: providing the polymer in a suitable solvent, the polymer being in solid form, wherein the polymer is one or more of a polyester, a polyamide, a polycondensate and a polyether, wherein the solvent is a mono- or di-alcohol, adjusting temperature and pressure to reaction conditions, providing a catalyst complex being capable of degrading the polymer into oligomers and/or monomers, wherein the polymer, solvent and catalyst complex constitute a dispersion, wherein said catalyst complex comprising functionalized magnetic particles, wherein the functionalization comprises a bridging moiety and a catalyst entity bonded to the bridging moiety, said catalyst entity comprising an aromatic heterocyclic moiety, degrading the polymer by means of glycolysis over a period sufficient to degrade a significant portion thereof into oligomers, trimers, dimers and monomers, in which degradation of the polymer, the solvent functions as a reactant, recovering the catalyst complex, wherein a second solvent is provided as a washing agent, said second solvent being water, wherein the catalyst complex, oligomers trimers and dimers form a separate phase, and wherein monomers and the mono- or di-alcoholic solvent dissolve in the water, and retrieving monomers from the second solvent by means of crystallisation.

19. Method according to claim 18, wherein the polymer is a mixture of waste polymers.

20. The method as claimed in claim 19, wherein the said mixture comprises one or more of coloured polymers comprising color additives.

21. Method as claimed in claim 20, wherein said color additives go into the separate phase upon addition of the second solvent.

22. Method as claimed in claim 20, wherein the color additives comprise pigment.

23. Method according to claim 18, wherein the polymer is a polyester.

24. Method as claimed in claim 23, wherein the polyester is a poly carboxylic ester.

25. Method as claimed in claim 24, wherein the poly carboxylic ester is selected from polyethylene terephthalate (PET), polyethylene furanoate (PEF), polybutylene terephthalate (PBT), polytri-methylene terephthalate (PTT), polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyethylene adipate (PEA), polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), polyethylene naphthalate (PEN), Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and a polycondensate of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid (VECTRAN).

26. Method as claimed in claim 18, further comprising the step of providing oligomers obtained by degradation of the polymer to the solvent.

27. Method as claimed in claim 26, wherein the provision of catalyst complex comprising introducing a mixture of catalyst complex, oligomers, trimers, dimers and additives if any, which mixture is obtained in a preceding degradation process in the recovery step.

28. Method as claimed in claim 18, wherein the reaction conditions of degrading the homo- or copolymer is in the range of 170 C.-200 C.

29. Method as claimed in claim 18, wherein degradation of the polymer is carried out such that at least 99% of the polymer is degraded into oligomers, trimers, dimers and monomers.

30. Method as claimed in claim 18, wherein the solvent is a di-alcohol.

31. Method according to claim 18, wherein the degrading is performed during a period of 15 minutes-3 hours

32. Method as claimed in claim 18, wherein the amount of catalyst is 0.1-10 wt. %, relative to a total weight of polymer provided.

33. Method according to claim 18, wherein the polymer is provided as particles, pellets or granules, having a volume of 0.01 mm.sup.3-8 cm.sup.3.

34. Method as claimed in claim 32, wherein the volume is 0.03 mm.sup.3-1 cm.sup.3 per particle, pellet or granule.

35. Method according to claim 18, wherein the polymer is polyethylene terephthalate (PET) or polyethylene furanoate (PEF), the solvent is ethanediol, the catalyst entity comprises imidazolium, the bridging moiety is triethoxysilylpropyl, and the nanoparticle is one or more of magnetite, hematite, and maghemite.

Description

SUMMARY OF FIGURES

[0062] FIG. 1a-c shows chemical reactions and catalyst complexes.

[0063] FIG. 2 shows selectivity percentages of BHET.

DETAILED DESCRIPTION OF FIGURES

[0064] FIG. 1a shows chemical reactions. Therein poly(ethylene terephthalate) is degraded by using (bmim)FeCl.sub.4 in 1,2-ethanediol. As a result Terephthalic Acid Bis(2-Hydroxyethyl) ester (BHET) is formed. Further, it is shown that BHET can be converted into dimers and oligomers.

[0065] FIG. 1b shows a schematic representation of the present catalyst complex. Therein A represents a nanoparticle, B a bridging moiety, and C a catalyst entity with C1 being a positive catalyst moiety and C2 being a negative catalyst moiety.

[0066] FIG. 1c shows a nanoparticle A surrounded by a number of bridging moieties and catalyst entities.

[0067] FIG. 2 shows selectivity percentages of BHET (vertical axis), obtained from depolymerization of colored PET, as function of reaction time and amount of di-alcohol (1,2-ethanediol) (horizontal axes). The PET provided was cut into pieces of about 22 cm.sup.2. In another example pieces of about 0.30.3 cm.sup.2, and in a further example as small particles having an average diameter of 50 m. The size of the pieces was found to be not particularly relevant for the outcome. A reaction temperature was about 197 C. Results were obtained by varying a reaction time and amount of di-alcohol. For all degradation reactions performed, the corresponding PET conversion rates obtained are close to 100% (typically 99-99.99%, as no PET-pieces could be observed anymore in the solvent), which are considered to be very high. The selectivity rates (>90%, in a best case scenario so far >93%) are considered to be very high as well. The yield is as a result also >90%, and up to 93%. Even further the rates are obtained in a relatively short time frame. The selectivities are obtained with 2 wt. % catalyst (including bridging moiety and catalyst) relative to a total amount of polymer, respectively. So a small amount of catalyst is already sufficient.

[0068] So despite negative expectations that use of a catalyst complex would reduce selectivity, conversion and yield, the present method (and catalyst complex used therein) provides much better results e.g. in these respects than prior art methods (using a catalyst per se). Losses are already reduced from about 20-40% (prior art) to less than 7%.

Examples

[0069] Similar tests as above haven been performed on non-colored PET. The results thereof are in the same order of magnitude for both conversion and selectivity. As a consequence inventors conclude that a color additive has hardly any or no impact in this respect. Even further, additives, such as pigments, can be removed from the degradation products, with ease.

[0070] Similar tests as above have been performed on a wide range of raw (PET) material, e.g. polyester clothing, PET carpet, PET material from automotive industry, recycled PET, multi-layered PET trays containing other polymers, such as PE and PP. The results thereof are in the same order of magnitude for both conversion and selectivity, and thus for yield. As a consequence inventors conclude that the process is highly insensitive to different raw (PET) material and robust as well.

[0071] Similar tests were performed on amorphous (AMP) pellets and solid state polymerization (SSP) pellets. Again PET conversion and BHET selectivity were high. Values obtained for SSP pellets were somewhat lower, relatively. It is considered that possibly due to a somewhat longer chain length of the polymer to be degraded selectivity and conversion are somewhat jeopardized.

[0072] The invention although described in detailed explanatory context may be best understood in conjunction with the accompanying examples and figures. It should be appreciated that for commercial application it may be preferable to use one or more variations of the present system, which would similar be to the ones disclosed in the present application and are within the spirit of the invention.