Recycling method

Abstract

The present invention relates to a method for recycling a composite, wherein the composite comprises a fibre and polybutylene terephthalate (PBT), the method comprising: (a) contacting the composite with a solvent solution comprising ortho dichlorobenzene (oDCB) such that the PBT dissolves in the solvent solution to form a solvate and separates from the fibre; (b) isolating the fibre from the solvate.

Description

[0001] RECYCLING METHOD

[0002] Field of the invention

[0003] The present invention relates to a method for recycling a composite material comprising polybutylene terephthalate.

[0004] Background of the invention

[0005] Polybutylene terephthalate (PBT) is a thermoplastic engineering polymer that is widely used in various industries due to its excellent mechanical properties, chemical resistance, and electrical insulation capabilities. PBT composites, which are reinforced with materials such as glass fibres, carbon fibres, or mineral fillers, further enhance these properties, making them suitable for high-performance applications in the automotive, electronics, and consumer goods sectors.

[0006] Despite the widespread use and benefits of PBT composites, their disposal poses significant environmental challenges. Traditional disposal methods, such as landfilling and incineration, are not sustainable due to the long degradation time of PBT and the release of harmful substances during incineration. Consequently, there is a growing need for effective recycling methods that can recover valuable materials from PBT composites and reduce environmental impact.

[0007] Current recycling techniques for PBT composites primarily involve mechanical recycling, where the material is shredded and reprocessed. However, this method often leads to a degradation of the material's properties, limiting its reuse in high-performance applications.

[0008] The present invention addresses the need for an efficient and sustainable method for recycling PBT composites. By developing a novel recycling process, this invention aims to improve the recovery of high-quality materials from PBT composites, thereby contributing to environmental sustainability and resource conservation.

[0009] Summary of the invention

[0010] The present invention seeks to address the problem above by providing a chemical recycling method which comprises contacting a PBT composite with a solvent solution comprising ortho dichlorobenzene. This allows for the PBT to be separated from any composite material, such as a fibre and / or filler, and subsequently breaking the polymer down into an oligomeric form such that the oligomeric form can be used in other processes.

[0011] Advantageously, the present recycling method results in a polymeric solution comprising PBT, wherein the PBT can be used as a feedstock in the production of cyclic poly(l,4- butylene terephthalate) (cPBT).

[0012] A first aspect of the present invention is a method for recycling a composite, wherein the composite comprises a fibre and polybutylene terephthalate (PBT), the method comprising:

[0013] (a) contacting the composite with a solvent solution comprising ortho dichlorobenzene (oDCB) such that the PBT dissolves in the solvent solution to form a solvate and separates from the fibre;

[0014] (b) isolating the fibre from the solvate.

[0015] Description of the figures

[0016] Examples of the present invention will now be described in detail with reference to the accompanying figures, in which:

[0017] Figure 1 is a process flow diagram of an embodiment of the invention and depicts unit operations of a process for obtaining: i) cPBT; and ii) acidic-terminated oligomeric PBT; from an input stream of PBT composite.

[0018] Figure 2a shows the nature of a composite material on contact with an oDCB solution, as is referred to in example 2.

[0019] Figure 2b shows the nature of a composite material after contact with an oDCB solution, as is referred to in example 2.

[0020] Detailed description of the invention

[0021] Unless indicated otherwise, all technical and scientific terms used herein will have their common meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0022] The term "comprising" or variants thereof will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. The term "consisting" or variants thereof is to be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, and the exclusion of any other element, integer or step or group of elements, integers or steps.

[0023] When used herein in relation to a specific value (such as an amount), the term "about" (or similar terms, such as "approximately") will be understood as indicating that such values may vary by up to 10% (particularly, up to 5%, such as up to 1%) of the value defined. It is contemplated that, at each instance, such terms may be replaced with the notation "±10%", or the like (or by indicating a variance of a specific amount calculated based on the relevant value). It is also contemplated that, at each instance, such terms may be deleted.

[0024] The term "atmospheric boiling point" is understood to mean the boiling point of a liquid at atmospheric pressure. Atmospheric pressure is 1 atm (101,325 Pa).

[0025] In a first aspect, the invention provides a method for recycling a composite wherein the composite comprises a fibre and polybutylene terephthalate (PBT), the method comprising:

[0026] (a) contacting the composite with a solvent solution comprising ortho dichlorobenzene (oDCB) such that the PBT dissolves in the solvent solution to form a solvate and separates from the fibre;

[0027] (b) isolating the fibre from the solvate.

[0028] In some embodiments of the first aspect, step (b) may be performed through filtration, in other embodiments, the fibre may be isolated by simply removing it from the surface of the solvate, for example by using tweezers.

[0029] In some embodiments of the first aspect, the method further comprises:

[0030] (a) cooling the solvate such that the PBT precipitates;

[0031] (b) filtering the solvate to isolate the PBT precipitate; and

[0032] (c) drying the PBT precipitate.

[0033] In some embodiments of the first aspect, the solvent solution comprises oDCB in a concentration of greater than 50 weight % of the solvent solution, such as greater than 60, 70, 80, 90, 95, 98 or 99 weight %. Preferably, the solvent solution consists essentially of oDCB. In some embodiments of the first aspect, prior to step (a), the solvent solution is heated to reflux. It may be that the solution is refluxed at approximately 180 °C, since this is the atmospheric boiling point of oDCB.

[0034] In some embodiments of the first aspect, in step (a), the solvent solution comprising the composite is heated to reflux. It may be that the solution is refluxed at approximately 180 °C.

[0035] In some embodiments of the first aspect, the solvent solution comprising the composition is heated to reflux for at least about 1 minute. In preferred embodiments the solvent solution is heated to reflux for at least about 5 minutes, for at least about 10 minutes, for at least about 15 minutes, for at least about 20 minutes, for at least about 25 minutes, for at least about 30 minutes, for at least about 40 minutes, for at least about 50 minutes, for at least about 1 hour, for at least about 1.5 hours, or for at least about 2 hours. In more preferred embodiments the solvent solution is heated to reflux for at least about 5 minutes.

[0036] In some embodiments of the first aspect, the solvent solution comprising the composition is heated to reflux for between about 1 minute and about 2 hours, between about 2 minutes and about 1.5 hours, between about 3 minutes and about 1 hour, between about 4 and about 50 minutes, between about 5 and about 40 minutes, between about 6 and about 30 minutes, between about 7 and about 20 minutes, between about 8 and about 15 minutes, or between about 9 and about 12 minutes, such as about 10 minutes. In preferred embodiments, the solvent solution comprising the composition is heated to reflux for between about 5 and about 30 minutes.

[0037] In some embodiments of the first aspect wherein the method comprises steps (c) to (e), in step (c), the solvate is cooled to below approximately 100 °C, such as below approximately 95, 90, 85, 80, 75, 70, 65, 60, 55 or 50 °C. In preferred embodiments, the solvate is cooled to approximately 50 °C.

[0038] In some embodiments of the first aspect, wherein the method comprises steps (c) to (e), the method further comprises:

[0039] (d) dissolving the dried PBT precipitate in oDCB.

[0040] In some embodiments of the first aspect, the method further comprises:

[0041] (e) carrying out azeotropic distillation to form an anhydrous solution comprising oDCB and PBT; (f) performing a depolymerisation reaction, wherein the depolymerisation reaction comprises contacting the anhydrous solution of step (g) with a depolymerisation catalyst to form a depolymerisation product stream comprising cPBT and oligomeric PBT.

[0042] In some embodiments of the first aspect, the method comprises steps (a) to (b), followed by steps (g) to (h), such that steps (c) to (f) are omitted. In such an embodiment the skilled person will appreciate that once the fibre is isolated from the solvate comprising oDCB and PCB, (for example by filtration), the solvate can be azeotropically distilled to form the anhydrous solution before undergoing depolymerisation.

[0043] In some embodiments of the first aspect, the method comprises:

[0044] (a) contacting the composite with a solvent solution comprising ortho dichlorobenzene (oDCB) such that the PBT dissolves in the solvent solution to form a solvate and separates from the fibre;

[0045] (b) isolating the fibre from the solvate;

[0046] (g) carrying out azeotropic distillation of the solvate to form an anhydrous solution comprising oDCB and PBT;

[0047] (h) performing a depolymerisation reaction, wherein the depolymerisation reaction comprises contacting the anhydrous solution of step (g) with a depolymerisation catalyst to form a depolymerisation product stream comprising cPBT and oligomeric PBT.

[0048] In other embodiments of the first aspect, the method comprises:

[0049] (a) contacting the composite with a solvent solution comprising ortho dichlorobenzene (oDCB) such that the PBT dissolves in the solvent solution to form a solvate and separates from the fibre;

[0050] (b) isolating the fibre from the solvate;

[0051] (c) cooling the solvate such that the PBT precipitates;

[0052] (d) filtering the solvate to isolate the PBT precipitate;

[0053] (e) drying the PBT precipitate;

[0054] (f) dissolving the dried PBT precipitate in oDCB.

[0055] (g) carrying out azeotropic distillation to form an anhydrous solution comprising oDCB and PBT;

[0056] (h) performing a depolymerisation reaction, wherein the depolymerisation reaction comprises contacting the anhydrous solution of step (g) with a depolymerisation catalyst to form a depolymerisation product stream comprising cPBT and oligomeric PBT. In some embodiments of the first aspect, the anhydrous solution comprising oDCB and PBT comprises less than about 1000 ppm water, such as less than about 900, about 800, about 700, about 600, about 500, about 400, about 300, about 200, about 100, about 80, about 60, about 40, about 20, about 10, about 5, or about 2 ppm water. Preferably the anhydrous comprises less than 10 ppm water, such as less than 5 ppm water.

[0057] The skilled person will understand a depolymerisation catalyst to be a catalyst which facilitates the breaking down of polymer chains in shorter polymer chains. These shorter polymer chains may be liner, such as oligomeric PBT, or cyclic, such as cPBT.

[0058] In some embodiments of the first aspect, step (h) is carried out at reflux for at least about 30 minutes, for at least about 40 minutes, for at least about 50 minutes, for at least about 1 hour, for at least about 1.5 hours, for at least about 2 hours, for at least about 2.5 hours, or for at least about 3 hours. In preferred embodiments, step (h) is carried out at reflux for at least about 2 hours. It may be that the solution is refluxed for at least about 2 hours at approximately 180 °C.

[0059] In some embodiments of the first aspect the depolymerisation catalyst is a titanium catalyst, such as an organotitante catalyst. In some embodiments, the catalyst may include at least one member selected from the group consisting of 2-ethylhexyl titanate, tetrakis- (2-ethyl- hexyl) titanate, tetrabutyl titanate, tetra isopropyl titanate, analkoxy titanate, titaniummethoxide, titanium ethoxide, diisopropoxide bis(2,4-pentanedionate ), and butanediol titanate. In preferred embodiments, the catalyst comprises tetra isopropyl titanate.

[0060] In preferred embodiments of the first aspect, the depolymerisation catalyst comprises 4 mole parts butanediol and 1 mole part 2-methyl-2,4-pentandiol (hexylene glycol) per molar part of tetra isopropyl titanate. In preferred embodiments, the depolymerisation catalyst consists of 4 mole parts butanediol and 1 mole part 2-methyl-2,4-pentandiol (hexylene glycol) per molar part of tetraisopropyl titanate.

[0061] In some embodiments of the first aspect, the method further comprises:

[0062] (i) heating the depolymerisation product stream of step (h) to obtain a secondary product stream comprising cPBT and acid-terminated oligomeric PBT. In some embodiments of the first aspect, step (i) is performed at pressure, to avoid vaporisation of the solvent, and at a temperature of at least about 200 °C, at least about 210 °C, at least about 220 °C, at least about 230 °C, at least about 240 °C, or at least about 250 °C.

[0063] In preferred embodiments of the first aspect, step (i) is performed at a pressure of at least about 1.5 atmospheres, at least about 2.0 atmospheres, at least about 2.5 atmospheres, at least about 3.0 atmospheres, at least about 3.5 atmospheres, at least about 4.0 atmospheres, at least about 4.5 atmospheres, or at least about 5.0 atmospheres.

[0064] In preferred embodiments of the first aspect, step (i) is performed at approximately 250 °C and at approximately 3.0 atmospheres.

[0065] In some embodiments of the first aspect, the method further comprises:

[0066] (j) cooling the secondary product stream of step (i) such that the acid- terminated oligomeric PBT precipitates; and

[0067] (k) filtering the cooled secondary product stream of step (j) to isolate the acid- terminated oligomeric PBT precipitate and to yield a liquid filtrate comprising cPBT.

[0068] In some embodiments of the first aspect, in step (j), the secondary product stream of step (i) is cooled to below approximately 100 °C, such as below approximately 95, 90, 85, 80, 75, 70, 65, 60, 55 or 50 °C. In preferred embodiments, the secondary product stream is cooled to approximately 50 °C.

[0069] In some embodiments of the first aspect, the method further comprises:

[0070] (l) treating the liquid filtrate comprising cPBT with basic alumnia (AI2O3); and

[0071] (m) filtering the resulting solution and concentrating the filtrate to isolate cPBT.

[0072] In some embodiments of the first aspect, at least a portion of the acid-terminated oligomeric PBT is utilised downstream in the production of PBT.

[0073] In some embodiments of the first aspect, at least a portion of the PBT in the PBT composite for recycling, is PBT produced using at least a portion of the acid-terminated oligomeric PBT according to any of the above embodiments. In some embodiments of the first aspect, the fibre is selected from the list consisting of glass fibres, carbon fibres and / or basalt fibres. In a preferred embodiment, the fibre is a glass fibre.

[0074] In an embodiment of the first aspect, the composite may comprise a filler in addition to, or instead of, the fibre. Accordingly, the method is a method for recycling a composite, wherein the composite comprises a fibre and / or a filler, and polybutylene terephthalate (PBT), the method comprising:

[0075] (a) contacting the composite with a solvent solution comprising ortho dichlorobenzene (oDCB) such that the PBT dissolves in the solvent solution to form a solvate and separates from the fibre;

[0076] (b) isolating the fibre and / or filler from the solvate.

[0077] In an embodiment, the filler is selected from the list consisting of calcium carbonate and alumina.

[0078] In an embodiment, the filler is in the form of a microsphere.

[0079] Detailed description of the figures

[0080] FIG. 1 is a process flow diagram of an embodiment of the invention and depicts unit operations of a process for obtaining: i) cPBT; and ii) acidic-terminated oligomeric PBT; from an input stream of PBT composite.

[0081] In the flow diagram depicted in FIG. 1, one or more input streams 101 comprising composite material for recycling (e.g., PBT composite) is refluxed in a solvent of ortho dichlorobenzene (oDCB) at a temperature of approximately 180 °C in one or more unit operations 102. The PBT from the PBT composite dissolves to provide an output solvate stream 103 comprising PBT, and any insoluble composite material 104 is removed (e.g., fibres, glass fibres etc) and this may optionally be separately recycled.

[0082] The output solvate stream comprising PBT 103 is then provided in an input stream to one or more unit operations 105. The one or more unit operations 105 may comprise cooling the solution to facilitate the precipitation of PBT followed by filtration to isolate the PBT precipitate. In such an embodiment, in practice unit operation 105 may be the same vessel as unit operation 102 which was used to dissolve the initial input stream of PBT composite in oDCB, or alternatively it may be a separate vessel. Alternatively, the one or more unit operations 105 may comprise a filtration step to remove any undissolved particulate. This filtration may be performed above 150 °C so as to keep the PBT dissolved in oDCB.

[0083] Alternatively, unit operation 105 may optionally be omitted such that output stream 103, comprising oDCB and dissolved PBT, feeds directly into stream 106.

[0084] The PBT isolated from unit operation 105 is then optionally dried before being introduced into one or more input streams 106 to one or more depolymerisation (cyclisation) reactors 107 and refluxed at approximately 180 °C at atmospheric pressure. The one or more input streams 106 also comprises solvent (oDCB) and a depolymerisation titanium catalyst. In the process of FIG. 1, an output stream 108 of the depolymerization reaction may comprise cPBT product in oDCB solvent, as well as byproducts including, for example, residual oligomeric PBT, catalyst residue, (tetra hydrofuran) THF complexes, and other compounds.

[0085] The output stream 108 from the depolymerisation step then provides the one or more input streams for a second reactor 109 which is refluxed at approximately 180 °C and 3 atmospheres (45 psi). In practice, it may be that reactor 1, 107, and reactor 2, 109, are the same vessel. Alternatively, they may be separate vessels.

[0086] In the second reactor 109 any catalyst residue present, for example from the depolymerisation titanium catalyst, will transition from a soluble, homogeneous form into an insoluble form with exposure to a sufficiently high temperature for a sufficient period of time. The precipitated catalyst residue can be separated from depolymerization reaction products, for example cPBT and residual oligomeric PBT, by any suitable separation technique, such as filtration, centrifugation, or decantation techniques. The ability to remove the titanium, without a water quench step, allows recycling of the residual oligomeric PBT, and subsequently cPBT, without a build-up of titanium in the overall integrated process.

[0087] In addition to catalyst precipitation in the second reactor 109 any residual oligomeric PBT in the output stream from the depolymerisation reactor 108 is transformed into the carboxylic acid-terminated oligomeric PBT species as shown in Reaction 1 as follows:

[0088] Reaction 1 - transformation of oligomeric PBT to acid-terminated oligomeric PBT

[0089] In the process of FIG. 1, following heating in rector 2 109, the output stream 110 is flash concentrated, unit operation 111, by venting to atmosphere causing oDCB solvent and THF to flash distil 112 due to their boiling point of 180 °C and 66 °C, respectively.

[0090] The output stream from the flash concentrator 111 comprising catalyst concentrated cPBT and acid-terminated oligomeric PBT 113 is then purified and worked-up in one or more unit operations 114 to provide output streams of cPBT 116 and acid-terminated oligomeric PBT 115. In the one or more purification and work-up unit operations 114, the input stream 113 is: i) cooled to approximately 50 °C to facilitate the precipitation of acid-terminated oligomeric PBT; ii) which is removed via filtration (to provide product stream 115); iii) The filtrate, rich in cPBT, is then treated with basic alumina (AI2O3); and iv) filtered and concentrated to provide a cPBT product stream 116.

[0091] The output stream of acid-terminated oligomeric PBT 115 is recycled into one or more input streams for one or more polycondensation unit operations 117 used in the production of PBT (e.g., high Mw PBT) 118. The polycondensation unit operations may be one described in US patent 7750109 (which is incorporated herein by reference). It may also have additional input streams comprising dimethyl terephthalate (DMT), butanediol (BDO), and a polymerisation titanium catalyst 116.

[0092] Examples

[0093] Example 1

[0094] To 300 mL oDCB heated to reflux was added ca. 5 grams of glass reinforced PBT derived from CBT polymerization. After heating this fabric at reflux for about 10 min, the PBT dissolved in oDCB and the glass fabric was removed with a pair of twizzers. The oDCB solution was cooled to 50 °C and the precipitated PBT was removed and dried.

[0095] To 130 mL of oDCB was added 1.76 g, 8 mMole of the above PBT. After complete dissolution, 34 mL of oDCB was removed by distillation to azeotropically remove all traces of water. To this dried solution was added 312 pL of a 0.77 Molar solution of the Titanium catalyst described in US Patent 7,750,109 B2. The subsequent reaction mixture was heated at reflux for two hrs. HPLC analysis demonstrated the characteristic oligomeric mixture of dimer, trimer, tetramer, etc.

[0096] The catalyst described in US Patent 7,750,109 B2 is Ti-(butanediol: 2-methyl-2,4- pentandiol). The catalyst was prepared by the following method:

[0097] A 100 mL flask equipped with a magnetic stir bar and fitted with a septum is flame dried under vacuum then filled with an inert gas. Tetraisopropyl titanate (15 mmol) is added followed by a mixture of diols (30 mmole total) then dry ortho dichlorobenzene (25 mL). After the addition of all reagents the flask is fitted with a short path distillation head and heated in an oil bath to 140° C. for about 1 hour. Isopropyl alcohol liberated from the reaction of tetra iso propyl titanate and the diols is collected and then the solution is heated in 200° C. oil to strip off 15 ml of the ortho dichlorobenzene to ensure that all isopropyl alcohol has been removed. Upon cooling the resulting solution is about 1 Min titanium. The catalyst is herein referred to by the abbreviation "Ti(BD:HG)(4: 1)".

[0098] Example 2

[0099] A glass fabric reinforced with a PBT composition was placed into a beaker comprising 300 mL of oDCB. This is shown in Figure 2a. In Figure 2a the woven nature of the glass fabric cannot be seen as it is coated with PBT.

[0100] The beaker, while the fabric was in contact with the oDCB, was heated at a temperature greater than 150 °C for approximately 1 minute. After approximately 1 minute the fabric was removed from the beaker. This is shown in Figure 2b. In Figure 2b, the woven nature of the glass fabric can be seen. This indicates that the PBT which previously coated the glass fabric has now dissolved in the oDCB and has separated from the glass fabric.

Claims

Claims1. A method for recycling a composite, wherein the composite comprises a fibre and polybutylene terephthalate (PBT), the method comprising:(a) contacting the composite with a solvent solution comprising ortho dichlorobenzene (oDCB) such that the PBT dissolves in the solvent solution to form a solvate and separates from the fibre;(b) isolating the fibre from the solvate.

2. The method according to claim 1, wherein the method further comprises:(c) cooling the solvate such that the PBT precipitates;(d) filtering the solvate to isolate the PBT precipitate; and(e) drying the PBT precipitate.

3. The method according to claim 1 or claim 2, wherein, prior to step (a), the solvent solution is heated to reflux.

4. The method according to any of claims 1 to 3, wherein in step (a), the solvent solution comprising the composite is heated to reflux.

5. The method according to claim 4, wherein the solvent solution comprising the composite is heated to reflux for between 5 and 30 minutes.

6. The method according to claim 2, wherein in step (c), the solvate is cooled to approximately 50 °C.

7. The method according to any one of claims 2 to 6, the method further comprising:(f) dissolving the dried PBT precipitate in oDCB.

8. The method according to any one of the preceding claims, the method further comprising:(g) carrying out azeotropic distillation to form an anhydrous solution comprising oDCB and PBT; and(h) performing a depolymerisation reaction, wherein the depolymerisation reaction comprises contacting the anhydrous solution of step (g) with a depolymerisation catalyst to form a depolymerisation product stream comprising cyclic poly(l,4-butylene terephthalate) (cPBT) and oligomeric PBT.

9. The method according to claim 8, wherein step (h) is carried out at reflux for at least 2 hours.

10. The method according to claim 8 or claim 9, wherein the depolymerisation catalyst is a titanium catalyst, preferably wherein the titanium catalyst comprises 4 mole parts butanediol and 1 mole part 2-methyl-2,4-pentandiol (hexylene glycol) per molar part of tetra iso propyl titanate.

11. The method according to any of claims 8 to 10, the method further comprising:(i) heating the depolymerisation product stream of step (h) to obtain a secondary product stream comprising cPBT and acid-terminated oligomeric PBT.

12. The method according to claim 11, wherein step (i) is performed at approximately 250 °C and at approximately 3 atmospheres.

13. The method according to claim 11 or claim 12, wherein the method further comprises:(j) cooling the secondary product stream of step (i) such that the acid- terminated oligomeric PBT precipitates; and(k) filtering the cooled secondary product stream of step (j) to isolate the acid- terminated oligomeric PBT precipitate and to yield a liquid filtrate comprising cPBT.

14. The method according to claim 13, wherein in step (j), the secondary product stream of step (i) is cooled to approximately 50 °C.

15. The method according to claim 13 or claim 14, wherein the method further comprises:(l) treating the liquid filtrate comprising cPBT with basic alumnia (AI2O3); and(m) filtering the resulting solution and concentrating the filtrate to isolate cPBT.

16. The method according to any of claims 11 to 15, wherein at least a portion of the acid-terminated oligomeric PBT is utilised downstream in the production of PBT.

17. The method according to any one of the preceding claims, wherein at least a portion of the PBT in the PBT composite for recycling is PBT produced using at least a portion of the acid-terminated oligomeric PBT according to any one of claims 11 to 15.

18. A method according to any one of the preceding claims, wherein the fibre is selected from the list consisting of glass fibres, carbon fibres and / or basalt fibres.

19. A method according to any one of the preceding claims, wherein the composite further comprises a filler, optionally wherein the filler is selected from the list consisting of calcium carbonate and alumina.

Images