Method for recovering polyurethane polymer from waste polymer textile material comprising polyester fibers and polyurethane fibers

Abstract

A method of recovering polyurethane polymer from waste polymer textile material comprising polyester fibers and polyurethane fibers is described. The method comprises: providing a waste polymer textile material in a shredded or cut form; contacting the waste polymer textile material in shredded or cut form with a polar aprotic solvent at a temperature of 25 to 125 DEG C so that the polyurethane is at least partially dissolved in the polar aprotic solvent while the polyester is substantially unaffected; separating the polyester from a solvent mixture comprising the polar aprotic solvent and the polyurethane dissolved therein by solid-liquid separation; precipitating the polyurethane dissolved in the solvent mixture; separating the precipitated polyurethane from the solvent mixture to obtain a polyurethane polymer and a used polar aprotic solvent; and optionally reusing the used polar aprotic solvent.

Description

Technical Field

[0001] This invention relates to the field of obtaining useful products from waste polymer textile materials. Specifically, it relates to a method for recovering polyurethane polymers from waste polymer textile materials comprising polyester and polyurethane fibers. The method of this invention is environmentally friendly because, in addition to the waste polymer textile materials, any solvents used in the method can be recycled. Background Technology

[0002] Polymer textiles are now widely used in a variety of products, such as carpets, clothing, coverings, and bedding. Because waste polymer textiles increasingly consist of blends of polymers, each contributing to specific desired properties, the reuse and disposal of post-consumer textiles is complex. For example, polyurethane polymer fibers, such as elastane or Lycra, are increasingly used in items like jeans and sportswear to impart elasticity. In this case, polyester fibers can provide other desired properties, such as strength, durability, and breathability.

[0003] In order to reuse the raw materials from which waste polymer textiles are made, it is necessary to effectively separate the various components, and therefore a suitable separation method is required.

[0004] While mechanical separation of fibers has been attempted, recent methods aim to separate components chemically. One such method, disclosed in CN110790980A, involves contacting waste polyester fiber material with an organic solvent having a boiling point of 20 to 230°C at a temperature of 20 to 180°C. Soluble fibers other than polyester are dissolved, filtered, and the filtrate is distilled. The organic solvent can be recovered, but this requires expensive fractionation. The dissolution temperature varies depending on the type of soluble polymer that needs to be removed. For example, dissolving polyurethane requires a temperature of 130 to 150°C.

[0005] A drawback of the known methods is that different solvents are required for each soluble polymer. Polyurethane requires a polar aprotic solvent, nylon requires formic acid, and cyclohexanone is needed to separate polylactic acid fibers. Each solvent may leave a residue in the polyester in a certain amount, which severely limits the further use of the polyester. Furthermore, due to the relatively high dissolution temperatures used, the dissolved polymer may not be effectively separated from the solvent, thus the solvent may contain impurities. This hinders their reuse, which is undesirable from an environmental perspective.

[0006] Therefore, there is a need for an improved method for recovering polyurethane polymers from waste polymer textile materials containing polyester and polyurethane fibers, a method that does not have the disadvantages of the prior art, or at least has fewer disadvantages. Another objective is to provide a more cost-effective and robust improved separation method without generating more waste streams. Yet another objective is to provide an improved method for recovering other soluble polymers besides polyurethane polymers from waste polymer textile materials containing polyester and polyurethane fibers. Summary of the Invention

[0007] This invention provides a method as described in claim 1. A method for recovering polyurethane polymers from waste polymer textile materials containing polyester fibers and polyurethane fibers includes the following steps: a) Provide waste polymer textile materials in shredded or diced form; b) Contact waste polymer textile material in shredded or cut form with a polar aprotic solvent at a temperature of 25 to 125°C, so that the polyurethane is at least partially dissolved in the polar aprotic solvent while the polyester is substantially unaffected. c) Separating polyester from a solvent mixture containing a polar aprotic solvent and polyurethane dissolved therein by solid-liquid separation; d) Precipitate the polyurethane dissolved in the solvent mixture; e) Separate the precipitated polyurethane from the solvent mixture to obtain the polyurethane polymer and the polar aprotic solvent used. f) In step b), the previously used polar aprotic solvent is reused.

[0008] The result is that polyurethane polymers are soluble in polar aprotic solvents at dissolution temperatures ranging from 25 to 125°C, and also at higher temperatures. This method not only allows for the removal of polyurethane polymers from waste polymer textile materials but also enables the recycling of polyurethane polymers into usable polymers. The polyurethane polymers can be used directly as raw materials for subsequent processes, such as fiber manufacturing (spinning) processes. The inventors have found that the relatively low dissolution temperature of 25 to 125°C allows for the preservation of the soluble polymer, particularly the relatively high molecular weight of the polyurethane polymer. This makes it directly usable in subsequent processes that convert the polymer into usable articles, while also demonstrating that it can extract the polymer more efficiently from polar aprotic solvents. This allows for the direct reuse of polar aprotic solvents in this method and prevents or limits solvent disposal and / or subsequent distillation. Detailed Implementation

[0009] Waste polymer textile materials can be supplied in suitable forms, where they are provided in relatively small pieces, such as shredded or cut. Shredding involves cutting the waste polymer textile material in a shredder. This may produce blocks of some length, such as strips or ribbons. Waste polymer material can also be cut into even smaller blocks, typically with linear dimensions of 0.1 to 10 cm. The typical density of such loosely cut blocks of waste polymer textile material is 10 to 50 g / dm³. 3 For example, approximately 20 g / dm 3 The density of waste textile materials can be reduced, for example, by fluffing. For instance, fluffy textile materials can be obtained through fibrillation, in which the textile material is punctured and torn with needles. In this form, the waste textile material contains relatively small, loose fibrous pieces of material and a relatively large amount of air between the fibrous pieces. The density of textiles in the loose fibrous form is approximately 5 to 10 g / dm³. 3 In the industrial sector, sorted waste polymer textile materials are typically supplied in large bags, where the textile material is compressed to approximately 170 to 310 g / dm³. 3 or even up to 500 g / dm 3 The method of the present invention allows for the processing of waste polymer textile materials having the above-mentioned density. Therefore, a suitable density range is 5 to 500 g / dm³. 3 Preferred concentration: 80 to 400 g / dm 3 More preferably 100 to 380 g / dm 3 And the optimal value is 120 to 350 g / dm 3 .

[0010] In another embodiment, the density of the waste polymer textile material is 5 to 500 g / dm³. 3 For example, 100 to 500 g / dm 3 For example, 150 to 500 g / dm 3 For example, 200 to 500 g / dm 3 For example, 250 to 500 g / dm 3 Another embodiment provides waste polymer textile materials with a density of 5 to 450 g / dm³. 3 For example, 5 to 400 g / dm 3 For example, 5 to 350 g / dm 3 For example, 5 to 300 g / dm 3 .

[0011] Providing waste polymer textile materials in cut form may be advantageous, and is preferred. This implementation can improve the separation of different fibers in the waste polymer textile materials.

[0012] Waste textile materials include polyester and polyurethane fibers. Polyurethane contains organic units linked by urethane bonds and can be formed by reacting polyisocyanates with polyols. Terephthalate polymers are a class of polyesters containing a terephthalate backbone. The most common example of a terephthalate polymer is polyethylene terephthalate, also known as PET. Alternative examples include polybutylene terephthalate, polypropylene terephthalate, pentaerythritol terephthalate, and their copolymers, such as copolymers of polyethylene terephthalate and polyethylene glycols, such as polyethylene oxide glycol and poly(tetramethylene glycol) copolymers. PET is one of the most common polymers, and there is a strong desire to recycle it by depolymerizing it into reusable raw materials.

[0013] Waste polymer textile materials in shredded or cut form are contacted with a polar aprotic solvent, for example, by adding a polar aprotic solvent to the waste polymer textile materials. In the context of this application, the term "polar" also includes "dipole." Solvents are generally classified according to their polarity and are classified as polar and nonpolar based on their dielectric constant. In the context of this application, solvents with a dielectric constant greater than about 5 are considered polar. Solvents are also aprotic. Aprotic solvents lack acidic protons due to the absence of hydroxyl and amino groups. Therefore, aprotic solvents do not act as proton donors in hydrogen bonding, but they can be proton acceptors. Suitable polar aprotic solvents include, but are not limited to, dichloromethane (DCM), tetrahydrofuran (THF), ethyl acetate, acetonitrile, dimethylformamide (DMF), dimethylacrylurea, dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), acetone, hexamethylphosphoric triamine (HMPT), N-methylpyrrolidone (NMP), pyridine, and sulfolane. Preferred polar aprotic solvents have a dielectric constant greater than 10, more preferably greater than 20, and most preferably greater than 30. DCM and THF are less preferred, and DMF is particularly less preferred. Biosolvents may also be used, such as dihydro-L-glucanone (Cyrene), alkyl levulinates such as methyl levulinate, ethyl levulinate, or propyl levulinate, γ-valerolactone, alkyl lactates such as methyl lactate, ethyl lactate, and propyl lactate, furfural, furfuryl alcohol, levulinic acid, or mixtures thereof.

[0014] The mixture is heated to a temperature range of 25 to 125°C until the polyurethane polymer dissolves. For the purpose of recovering the polyurethane polymer from the mixture, the temperature is preferably 40 to 110°C, more preferably 60 to 100°C, and most preferably 70 to 90°C. Heating typically takes place for 15 minutes to 8 hours, more preferably 1 to 7 hours, and most preferably 2 to 6 hours. The pressure is typically 90 to 200 kPa, such as atmospheric pressure. The heating step results in the formation of a slurry comprising polyester and dissolved polyurethane. At the selected dissolution temperature and duration, the polyurethane dissolves at least partially, while the polyester remains undissolved and substantially unaffected. Heating is preferably carried out until the polyurethane is substantially completely dissolved. However, this is not considered necessary. Small amounts, such as up to 10% by weight relative to the initial amount of polyurethane, for example up to 5% by weight, preferably up to 3% by weight, or even up to 1% by weight, may remain undissolved.

[0015] Step b) of the above method, which dissolves polyurethane in a polar aprotic solvent, can be carried out by adding a suitable catalyst. However, preferably, no catalyst is added in step b).

[0016] Following the dissolution step, the slurry undergoes solid-liquid separation, in which the polyester is separated from the solvent mixture comprising a polar aprotic solvent and dissolved polyurethane. Any suitable solid-liquid separation method can be used, such as centrifugation or filtration, or a combination of these methods. Typically, the filtration step is carried out on a coarse filter, resulting in a filtrate. Thus, the polyester is separated from the solvent mixture by retaining it on the filter, while the solvent mixture passes through the filter as a liquid, possibly in the form of small particles. The mesh size of the filter is preferably not too small to allow the liquid to pass through; and not too large to retain the polyester.

[0017] After collecting the filtrate containing the solvent mixture, the polyurethane present in the solvent mixture is precipitated and separated from the solvent mixture. The polyurethane can then be further processed or reused. Preferably, the mesh size is less than 10 µm, more preferably 5 to 9 µm. In addition to mesh size, the pressure used may also play a role, with larger negative pressures generally allowing for smaller mesh sizes. This embodiment is suitably carried out by providing the solvent mixture or slurry in a filter chamber containing a filter, wherein a negative pressure is applied to the filter.

[0018] Useful embodiments provide a method in which precipitating the polyurethane dissolved in the solvent mixture in step d) comprises adding water to the solvent mixture, wherein the solvent mixture is optionally cooled to a temperature below the contact temperature of step b) before, during, or after the addition of water. Adding hot water in the form of an aqueous solution or a mixture of alcohol and water is not excluded.

[0019] In another improved embodiment, the added water (or aqueous solution) is at a temperature of 1 to 100°C, more preferably 5 to 50°C, even more preferably 10 to 40°C, and most preferably 15 to 30°C at ambient pressure. As a result, the addition of relatively cold water to the solvent mixture significantly improves the separation of precipitated and subsequently precipitated polyurethane, particularly when combined with a relatively low dissolution temperature of 60 to 100°C, more preferably 70 to 90°C.

[0020] The advantage of the claimed method is that the recovered polyurethane has a relatively high molecular weight. This allows for its reuse without further processing. In an embodiment of the claimed method, the number-average molecular weight Mn of the polyurethane polymer obtained in step e) is at least 50,000 Da, more preferably at least 65,000 Da, and most preferably at least 90,000 Da. Alternatively, the weight-average molecular weight Mw of the polyurethane polymer obtained in step e) is at least 100,000 Da, more preferably at least 130,000 Da, and most preferably at least 180,000 Da. Mn and Mw are determined by gel permeation chromatography at 40 °C using DMF and 0.02 m of lithium bromide as eluents. The sample may show a bimodal distribution with a secondary peak at the lower molecular weight. In all cases, Mn and Mw are defined according to the dominant peak (major peak) in the molecular weight distribution.

[0021] To improve the reusability of used polar aprotic solvents, an embodiment of the method is provided, wherein added water is separated from the used polar aprotic solvent obtained in step e) before the polar aprotic solvent is reused according to step f). Since the boiling point of the added water is typically deviated from (and in most embodiments is lower than) the boiling point of the polar aprotic solvent used in the method, separation can be easily achieved by evaporating the water.

[0022] The amount of polar aprotic solvent that may remain in the polyester after step c) can be further reduced by embodiments of the method in which the polyester obtained in step c) is squeezed and / or washed in a suitable washing liquid, such as water or a polyol. For example, squeezing can be performed in a pressurizing device, such as a pressure roller. Washing or rinsing can be performed in one step or repeated in multiple steps, such as by providing the polyester in a washing tank.

[0023] In another preferred method according to its implementation, the method further includes the following steps:

[0024] g) Contact the polyester obtained in step c) with an alcohol solvent at a temperature of 50 to 200°C to further dissolve any remaining polyurethane in the alcohol solvent, while the polyester remains substantially unaffected; and

[0025] h) Separate the polyester from the polyol solvent mixture containing alcohol solvents, residual polyurethane that may be dissolved in the alcohol solvent mixture, and any residual polar aprotic solvents by solid-liquid separation.

[0026] In this embodiment, contacting the polyester with an alcohol solvent and then separating the polyester from the solvent mixture represents the second step, which differs from the first step of contacting the polyester with a polar aprotic solvent, and occurs after the first step. This can be carried out in the same manner as described above with the polar aprotic solvent in the first step.

[0027] The second step allows for a further reduction in the amount of polar aprotic solvents present in the polyester, as well as a reduction in the amount of elastic fibers in the polyester. This is important because small amounts of polar aprotic solvents and / or elastic fibers in the polyester can lead to discoloration in other downstream processes, such as processes where the polyester is depolymerized to its monomers. As will be further disclosed below, the addition of alcohol solvents does not cause this problem, since alcohol solvents are used in the polyester depolymerized via glycolysis anyway. According to an embodiment of the method, the amount of polar aprotic solvents still present in the polyester after step h) is less than 1:1, more preferably less than 1:2, even more preferably less than 1:5, and most preferably less than 1:10, relative to the amount of alcohol solvents in the alcohol solvent mixture. As a result, the amount of aprotic solvents present in the polyester after step h) is very low, which significantly prevents discoloration of the polyester (and the bis(2-hydroxyethyl) terephthalate, abbreviated as BHET, produced after depolymerization). Surprisingly, this can be achieved in this embodiment involving the second step. Without wishing to be bound by any theory, in step g) of this implementation, the aprotic solvent is evaporated to a degree that will not cause any problems with the polyester or the BHET discoloration that may occur after the optional depolymerization step.

[0028] Step g) of the preferred method is preferably carried out at a temperature of 110°C to 190°C, more preferably 120°C to 170°C, and even more preferably 130°C to 150°C.

[0029] The alcohol solvent can be selected from monools, diols, and triols. Preferably, non-halogenated alcohols are used. More preferably, polyols are used. Smaller chain alcohols are preferred, such as C6 to C10 monools, and equally preferred are C2 to C10 diols, more preferably C2 to C8 diols. Examples of such diols are vicinal diols and geminal diols. Examples of suitable alcohols include 1-hexanol, 3-methyl-1-pentanol, 4-methyl-1-pentanol, 1-heptanol, 2-heptanol, 3-heptanol, 4-heptanol, 1-octanol, 2-octanol, 2-ethyl-1-hexanol, 4-methyl-3-heptanol, 5-methyl-3-heptanol, 2,2,3-trimethyl-3-pentanol, 1-nonanol, 2-nonanol, 3-nonanol, 4-nonanol, 5-nonanol, 7-methyl-1-octanol, 2,6-dimethyl-4-heptanol, 3,5-dimethyl-4-heptanol, 3,5,5-trimethyl-1-hexanol, 1-decanol, and 1,4-phenylenediol. Alcohols, ethylene glycol (1,2-ethylene glycol) and diethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,2-pentanediol, hexane-1,2-diol, hexane-1,6-diol, heptane-1,2-diol, heptane-1,7-diol, octane-1,2-diol, octane-1,8-diol, nonane-1,3-diol, nonane-1,9-diol, decane-1,2-diol, decane-1,10-diol, undecane-1,2-diol, undecane-1,11-diol, dodecane-1,2-diol and dodecane-1,12-diol. In a suitable embodiment, the preferred alcohol to be used in the second step comprises a diol, more preferably an alkylene glycol, selected from ethylene glycol (1,2-ethylene glycol), propylene glycol (1,3-propanediol), 1,4-butanediol, and 1,5-pentanediol.

[0030] Another advantage of the two-step implementation is that it can be used to remove polymers other than polyurethane present in waste polymer textile materials. In this implementation, the waste polymer textile material also contains polyamide fibers, which are dissolved in step g) and then separated from the polyester in step h). The separation is preferably performed as disclosed above for the separation of polyurethane.

[0031] Polyamides comprise macromolecules with repeating units linked by amide bonds (e.g., O=C-NH-C). Synthetic polyamides include materials such as nylon, aromatic polyamides, and sodium polyaspartate. Polyamides may also include aliphatic polyamides such as PA 6 and PA 66, polyphthalamides such as PA 6T, and aromatic polyamides. Synthetic polyamides are commonly used in textiles, automotive applications, carpets, and sportswear due to their high durability and strength.

[0032] Another embodiment relates to a method in which the waste polymer textile material also comprises acrylic polymer fibers, said acrylic polymer being dissolved in step b), and the dissolved acrylic polymer being separated from the first mixture in step d). Surprisingly, the removal of the acrylic polymer, such as polyacrylonitrile, can be carried out in a single-step embodiment using the same polar aprotic solvent used to remove polyurethane. Another advantage of using such a polar aprotic solvent is that the acrylic polymer can be dissolved therein at relatively low temperatures, for example, 25 to 80°C, more preferably 30 to 65°C, and most preferably 40 to 50°C. After separation of the polyester from the solvent mixture, the dissolved acrylic polymer remains dissolved in the solvent mixture and does not precipitate therein. For example, the acrylic polymer can be removed from the polar aprotic solvent by fractionation.

[0033] In another embodiment of the method, the waste polymer textile material also contains functional additives, such as dyes, and the functional additives are dissolved in a polar aprotic solvent, and in step d), the functional additives are separated from the polyester using the polar aprotic solvent.

[0034] Preferred polar aprotic solvents include dimethylacetamide (DMAc), which has shown increased separation efficiency of polyurethanes compared to the use of another polar aprotic solvent, such as dimethylformamide (DMF).

[0035] The weight ratio of the polar aprotic solvent to the textile waste material can vary over a wide range, but is preferably higher than 1:1. In a preferred embodiment, the weight ratio of the textile waste material to the polar aprotic solvent is 1:2 to 1:40, more preferably 1:5 to 1:35, even more preferably 1:10 to 1:25, and most preferably 1:15 to 1:20. Lower ratios use less solvent and are preferred.

[0036] Preferred embodiments provide a method in which the polyester comprises polyethylene terephthalate and / or the polyurethane comprises a polyether-polyurea copolymer, such as an elastic fiber.

[0037] In another embodiment, the acrylic polymer that may be present in the waste polymer textile material includes polyacrylonitrile fibers. Polyacrylonitrile polymers refer to homopolymers of acrylonitrile and copolymers of acrylonitrile with one or more copolymerizable monomers. These copolymers preferably contain at least 70% by weight, preferably more than 85% by weight, of acrylonitrile, and at most 30% by weight, preferably less than 15% by weight, of copolymerizable monomers. Copolymerizable monomers may include addition monomers containing olefinic double bonds, such as methyl acrylate, methyl methacrylate, ethyl acrylate, chloroacrylic acid, ethyl methacrylate, acrylic acid, methacrylic acid, acrylamide, methacrylamide, butyl acrylate, methacrylonitrile, butyl methacrylate, vinyl acetate, vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, vinylidene bromide, allyl chloride, methyl vinyl ketone, vinyl formate, vinyl chloroacetate, vinyl propionate, styrene, vinyl stearate, vinyl benzoate, vinylpyrrolidone, etc. Alkenylpiperidine, 4-vinylpyridine, 2-vinylpyridine, N-vinylphthalimide, N-vinylsuccinimide, methyl malonate, N-vinylcarbazole, methyl vinyl ether, itaconic acid, vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, methyl allyl sulfonic acid, vinyl furan, 2-methyl-5-vinylpyridine, naphthalene, itaconic acid ester, chlorostyrene, vinyl sulfonate, styrene sulfonate, allyl sulfonate, methyl allyl sulfonate, vinylidene fluoride, 1-chloro-2-bromoethylene, α-methylstyrene, ethylene, and propylene, etc.

[0038] Waste polymer textile materials may contain a variety of polymer materials. In a preferred embodiment, a method is provided in which the waste polymer material comprises 85 to 99% by weight of polyester, 1 to 15% by weight of polyurethane, and optionally polyamide and / or acrylic polymers, totaling 100% by weight. The amount of polyamide in the waste polymer textile material can be up to 15% by weight, more preferably up to 10% by weight, and most preferably up to 5% by weight. The amount of acrylic polymer in the waste polymer textile material can be up to 15% by weight, more preferably up to 10% by weight, even more preferably up to 5% by weight, and most preferably up to 2% by weight. It should be noted that the presence of polyamide and acrylic polymer fibers in the waste polymer textile material is optional and not essential to the present invention.

[0039] In another aspect of the invention, a method further comprising the following steps is provided.

[0040] i) Add a reactive solvent to disperse the polyester recovered after step h), and obtain a dispersion; j) Add a depolymerization catalyst to the dispersion; k) Under reactive conditions, the polyester is depolymerized to obtain monomers and / or oligomers dissolved in a reactive solvent; The reactive solvent mentioned herein comprises an alcohol solvent, optionally an alcohol solvent obtained from step h).

[0041] A preferred method of depolymerization is glycolysis, which is preferably catalytic. Typically, due to the preferred use of ethylene glycol, a reaction mixture comprising at least one monomer containing bis(2-hydroxyethyl) terephthalate (BHET) can be formed. An example of suitable depolymerization via glycolysis is known in WO2016 / 105200 in the name of the applicant. According to this process, terephthalate polymers are depolymerized via glycolysis in the presence of a specially designed catalyst. At the end of the depolymerization process, water is added, and phase separation occurs. This allows for the separation of a first phase containing the BHET monomer from a second phase containing the catalyst, oligomers, and additives. The first phase may contain impurities in dissolved form as well as dispersed particles. The BHET monomer can be obtained by crystallization.

[0042] High purity is required for the reuse of depolymerized raw materials. It is well known that any contaminant can affect subsequent polymerization reactions of the raw materials. Furthermore, since terephthalate polymers are used in food and medical applications, stringent regulations apply to prevent health problems. This invention allows for the achievement of such high purity.

[0043] The depolymerization step involves glycolysis, in which the ethylene glycol solvent is also a reactant for obtaining BHET and other final byproducts, rather than terephthalic acid, which would be generated, for example, during hydrolysis. The polymer concentration in the reaction mixture or dispersion is typically 1 to 30% by weight of the total weight of the reaction mixture, although concentrations outside this range are also possible.

[0044] The amount of ethylene glycol (EG) in the reaction mixture can be selected within a wide range. In useful embodiments, the weight ratio of EG to the polymer is 20:10 to 100:10, more preferably 40:10 to 90:10, and most preferably 60:10 to 80:10.

[0045] In step k), the reaction mixture can be heated to a suitable temperature, preferably maintained during depolymerization. Depolymerization can be carried out at a temperature of at least 160°C, preferably at least 180°C, and more preferably at least 190°C. The temperature can be conveniently selected within the range of 160°C to 250°C. More preferably, the depolymerization step can include monomer formation within a temperature range of 185°C to 225°C. A suitable pressure in the depolymerization reactor is 1 to 5 bar, preferably above 1.0 bar, and more preferably below 3.0 bar.

[0046] During the depolymerization step, the average residence time of the BHET monomer can range from 30 seconds to 3 hours, or even longer. To stop the depolymerization reaction and / or deactivate the catalyst, the temperature can be lowered to 160°C or below, but preferably not lower than 85°C.

[0047] This invention can be carried out using any catalyst suitable for this purpose. Suitable catalysts include heterogeneous catalysts. In the depolymerization method according to the embodiment, the catalyst forms a dispersion in the reaction mixture during step c). Other suitable catalysts include homogeneous catalysts. These catalysts do not form a dispersion but are typically dissolved in the reaction mixture during step c).

[0048] Several possible heterogeneous depolymerization catalysts are based on ferromagnetic and / or ferrimagnetic materials. Additionally, antiferromagnetic materials, synthetic magnetic materials, paramagnetic materials, and superparamagnetic materials can also be used, such as materials containing at least one of Fe, Co, Ni, Gd, Dy, Mn, Nd, and Sm, and preferably materials containing at least one of O, B, C, and N, such as iron oxides like ferrite, magnetite, hematite, and maghemite. The catalyst particles may comprise nanoparticles.

[0049] Catalyst particles catalyze depolymerization reactions. In such depolymerization reactions, individual molecules of the condensation polymer are released from a solid polymer, such as a semi-crystalline polymer, via a catalytic reaction. This release results in the dispersion of the polymer material into a reactive solvent and / or the dissolution of individual polymer molecules in the reactive solvent. This dispersion and / or dissolution is thought to further enhance the depolymerization of the polymer into monomers and oligomers.

[0050] Suitable catalysts include transition metals in metallic or ionic form. Ionic forms include free ions in solution and ions in ionic or covalent bonds. An ionic bond is formed when one atom transfers one or more electrons to another atom. A covalent bond is an interatomic connection formed by two atoms sharing electron pairs. Transition metals can be selected from the first transition metal system, also known as 3d orbital transition metals. More specifically, transition metals are selected from iron, nickel, and cobalt. However, iron and nickel particles are preferred because cobalt is unhealthy and iron and nickel particles can be formed in a pure form. Alloys of various transition metals can also be used.

[0051] If the catalytic particles are made of metal, an oxide surface can be provided, which can further enhance catalysis. The oxide surface can be formed independently, through contact with air, through contact with water, or can be intentionally applied.

[0052] Iron-containing particles are the preferred choice. In addition to being magnetic, iron-containing particles have been found to catalyze the depolymerization of PET, for example, converting 70 to 90% of the PET to monomer within an acceptable reaction time of up to 6 hours, depending on the catalyst loading and other processing factors, such as the PET / solvent ratio.

[0053] Non-porous metal particles, particularly transition metal particles, can be suitably prepared by the thermal decomposition of carbonyl complexes, such as iron pentacarbonyl and nickel tetracarbonyl. Alternatively, iron oxide and nickel oxide can be prepared by exposing the metal to oxygen at higher temperatures, such as 400°C and above. Non-porous particles may be more suitable than porous particles because they may be less exposed to alcohols, thus exhibiting less corrosion, and can be reused more frequently for catalysis. Furthermore, due to the limited surface area, any oxidation of the surface may lead to a reduction in the number of metal ions, resulting in a lower level of ions present in the product stream as leaching contaminants to be removed from the product stream.

[0054] Another suitable class of catalysts includes particles based on alkaline earth metals selected from beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba) and their oxides. Preferred alkaline earth metal oxides are magnesium oxide (MgO). Other suitable metals include, but are not limited to, titanium (Ti), zirconium (Zr), manganese (Mn), zinc (Zn), aluminum (Al), germanium (Ge), and antimony (Sb), as well as their oxides and further alloys. Noble metals, such as palladium (Pd) and platinum (Pt), are also suitable. MgO and ZnO have also been found to catalyze the depolymerization of PET, for example, with a conversion rate of 70% to 90% to monomers within acceptable reaction times, but this depends on catalyst loading and other processing factors, such as the PET / solvent ratio. Suitable catalysts based on hydrotalcite have also been considered.

[0055] Preferably, the catalyst particles are selected such that they are substantially insoluble in (alcohol) reactive solvents, even at higher temperatures above 100°C. Oxides that readily dissolve in alcohols such as ethylene glycol at higher temperatures, such as amorphous SiO2, are less suitable.

[0056] The preferred catalyst concentration is 1% by weight or less relative to the amount of PET. Good results have also been achieved with catalyst loadings below 0.2% by weight or even below 0.1% by weight relative to PET. This low catalyst loading is highly advantageous, and the method of the present invention allows for the recovery of increased amounts of nanoparticle catalyst.

[0057] According to the present invention, the surface area of ​​the non-porous particles is suitably less than 10 m². 2 / g, more preferably up to 5 m 2 / g, or even more preferably up to 1 m 2 / g. In another embodiment, the surface area is at least 3 m². 2 / g. Porosity appropriately less than 10 -2 cm 3 / g, or, for example, up to 10 -3 cm 3 / g. Porous particles can also be used, which typically exhibit a larger surface area.

[0058] In the depolymerization method according to the embodiments, the catalyst forms a dispersion in the reaction mixture during mixing and / or depolymerization. A particularly preferred heterogeneous catalyst that can be used in this invention is a catalyst complex comprising catalyst particles and a catalyst entity associated with the catalyst particles, for example, connected to the catalyst particles by a linking group. The catalyst entity comprises an ionic liquid containing a positively charged cationic portion and a negatively charged anionic portion. The catalyst particles are preferably nanoparticles, more preferably magnetic particles, and magnetic particles are preferably used in methods in which a catalyst recovery step is performed using a magnetic attraction between a magnet and the particles. The catalyst particles themselves may also exhibit catalytic activity.

[0059] The catalyst complex (ABC) comprises three distinguishable elements: (nano)particles (A), a bridging portion containing a linking group (B), which is chemically linked to the particles, for example, by covalent bonding or physically linked to the particles, for example, by adsorption, and a catalyst entity (C) associated with the particles (A), for example, by chemical bonding, such as covalent bonding, to the linking group. The linking group preferably does not completely cover the surface of the nanoparticles, for example, in core-shell particles.

[0060] The particles of the claimed catalyst complex are preferably based on ferromagnetic and / or ferrimagnetic materials. Additionally, antiferromagnetic materials, synthetic magnetic materials, paramagnetic materials, and superparamagnetic materials can also be used, such as materials containing at least one of Fe, Co, Ni, Gd, Dy, Mn, Nd, and Sm, and preferably containing at least one of O, B, C, and N, such as iron oxides, like ferrite, hematite (Fe₂O₃), magnetite (Fe₃O₄), and maghemite (Fe₂O₃, γ-Fe₂O₃). Considering cost, relatively inexpensive particles, such as those containing iron (Fe), are preferred even when the catalyst complex of the present invention is fully or largely recovered. Another advantage of iron or iron oxide particles is that they have the highest saturation magnetization, which makes particle separation easier by magnetic separators. And even more importantly, iron oxide (nano) particles have a positive effect on the degradation reaction. The iron oxide may also contain other elements, such as cobalt and / or manganese, as in CoFe₂O₄.

[0061] According to the present invention, the catalyst particles used in the catalyst complex may be at least partially coated with a protective coating. The coating may also serve to stabilize the catalyst, keeping the particles suspended. Therefore, at least a portion of the surface of the catalyst particles may be coated with materials such as polyethyleneimine (PEI), polyethylene glycol (PEG), silicone oil, fatty acids such as oleic acid or stearic acid, silanes, mineral oil, amino acids, polyacrylic acid, or polyvinylpyrrolidone (PVP). Carbon may also be used as a coating material. The coating may be removed before or during the catalytic reaction. Methods of coating removal may include, for example, a solvent washing step before use in the reactor, or combustion in air. However, coating removal is not always necessary.

[0062] Preferably, the catalyst particles are selected such that they are substantially insoluble in (alcohol) reactive solvents, even at higher temperatures above 100°C. Oxides that readily dissolve in alcohols such as ethylene glycol at higher temperatures, such as amorphous SiO2, are less suitable.

[0063] It was found that the catalyst particles are preferably small enough to enable the catalyst complex to function as a catalyst, thereby degrading the terephthalate polymer into smaller units, wherein the yield of these smaller units, particularly the yield of their monomers, is sufficiently high for commercial use. It was also found that the nanoparticles are preferably large enough to allow the catalyst complex of the invention to be reused by recycling the catalyst complex. Suitable catalyst particles have an average diameter greater than 1 μm, with a maximum of 3 μm and greater. Suitable nanoparticles have an average diameter from 2 to 500 nm, or even a maximum of 1 μm.

[0064] In examples of the catalyst complexes of the present invention, the magnetic particles have an average diameter of 2 nm to 500 nm, preferably 3 nm to 100 nm, more preferably 4 nm to 50 nm, for example 5 to 10 nm. It has been found that small particles of 5 to 10 nm are optimal, for example, in terms of the yield and recovery of the catalyst complex. Note that the term "size" refers to the average diameter of the particles, where the actual diameter of the particles may vary slightly due to their characteristics. Furthermore, aggregates may also form, for example, in solution. The size of these aggregates is typically 50 to 200 nm, for example 80 to 150 nm, such as about 100 nm.

[0065] Particle size and its distribution can be measured by light scattering, for example using a Malvern dynamic light scattering instrument, such as the NS500 series. A more laborious method is to take representative electron microscope images and measure the size of individual particles on the images; this is generally applicable to smaller particle sizes, but equally applicable to larger particle sizes. For the average particle size, the mean can be taken. In approximation, the size with the most particles or the median size can be used as the average.

[0066] The catalyst entity of the present invention comprises at least two parts. The first part relates to a positively charged (cationic) portion. The second part relates to a negatively charged (anionic) portion, which is typically a salt complex portion. The negative and positive charges typically cancel each other out. In terms of conversion and selectivity, the positively and negatively charged portions have been found to have a synergistic and enhancing effect on the degradation process of waste terephthalate polymers.

[0067] The positively charged portion (cation) can be aromatic or aliphatic, and / or heterocyclic. The cationic portion can be aliphatic and is preferably selected from guanidine (carbamimidoylazanium), ammonium, phosphonium, and sulfonium. The non-aromatic or aromatic heterocyclic portion preferably comprises a heterocycle having at least one, preferably at least two, heteroatoms. The heterocycle can have 5 or 6 atoms, preferably 5 atoms. The positively charged portion can be an aromatic portion, which preferably has a stable positive charge. Typically, the cationic portion carries a delocalized positive charge. The heteroatom can be, for example, nitrogen (N), phosphorus (P), or sulfur (S). Suitable aromatic heterocycles are pyrimidines, imidazoles, piperidines, pyrrolidines, pyridines, pyrazoles, oxazoles, triazoles, thiazoles, methimazoles, benzotriazoles, isoquinolines, and viologen-type compounds (e.g., having two coupled pyridine ring structures). Imidazole structures are particularly preferred, which produce imidazoleium ions. Particularly suitable cationic moieties having N as a heteroatom include imidazolium (a 5-membered ring with two N atoms), piperidinium (a 6-membered ring with one N atom), pyrrolidineonium (a 5-membered ring with one N atom), and pyridinium (a 6-membered ring with one N atom). Preferred imidazolium cationic moieties include butylmethylimidazolium (bmim). + ) and dialkylimidazolium. Other suitable cationic moieties include, but are not limited to, triazolium (a 5-membered ring with 3 N), thiazolylium (a 5-membered ring with N and S) and (iso)quinolineium (two 6-membered rings with N (naphthalene)).

[0068] In a preferred method, the cationic portion of the catalyst entity is selected from at least one of imidazolium, piperidinium, pyridinium, pyrrolidineium, sulfonium, ammonium, and phosphonium groups.

[0069] The cationic moiety may have one or more substituents, preferably one or more substituents being alkyl moieties. In specific examples, the alkyl moiety has a length of C1 to C6, for example, C2 to C4. In particular examples, the imidazolium group has two substituents R1 and R2 respectively attached to one of the two nitrogen atoms; the piperidinium group has two substituents R1 and R2 attached to its nitrogen atom; the pyridinium group has two substituents R1 and R2, wherein one of the two substituents R1 and R2 is attached to its nitrogen atom; the pyrrolidineium group has two substituents R1 and R2 attached to its nitrogen atom; the sulfonium group has three substituents R1, R2, and R3 attached to its sulfur atom; the ammonium group has four substituents R1, R2, R3, and R4 attached to its nitrogen atom; and the phosphonium group has four substituents R1, R2, R3, and R4 respectively attached to its phosphorus atom.

[0070] The negatively charged portion (anion) may be related to anionic complexes, but can alternatively be a simple ion, such as a halide. It may involve a salt complex portion, preferably a metal salt complex portion, which has a metal ion with a +2 or +3 charge, such as Fe. 3+ Al 3+ Ca 2+ Zn 2+ and Cu 2+ And negatively charged counterions, such as halogen ions, like Cl- - F - and Br - In this example, the salt contains Fe. 3+ The salt complex portion, such as halide ions, like FeCl4 - Alternatively, counterions that do not contain metal salt complexes, such as halide ions, are used.

[0071] The linking group may include a bridging portion for connecting the catalyst entity to the catalyst particles. By connecting the catalyst entity to the catalyst particles, the catalyst entity and particles of the present invention are bonded together via bridging portions. This connection typically involves, on the one hand, a physical or chemical bond between the bridging portion and the catalyst entity, and on the other hand, a physical or chemical bond between the bridging portion and the catalyst particles. Specifically, multiple bridging portions are connected to or bonded to the surface regions of the catalyst particles of the present invention. Suitable bridging portions include weak organic acids, silicon-containing groups, and silanols. Thus, more specifically, the bridging portion includes a functional group for bonding with the particulate oxide and a second linking group for bonding with the catalyst entity. The functional group is, for example, a carboxylic acid, an alcohol, a silicic acid group, or a combination thereof. Other acids, such as organic sulfonic acids, are not excluded. The linking group includes, for example, a terminal alkyl chain connected to a cationic portion, and the alkyl chain is typically C1 to C6, such as propyl and ethyl. The linking group may be connected to a cationic portion, such as a preferred imidazolium portion. In the attached state, the BC complex may contain, for example, an imidazolium having two alkyl groups, such as butylmethylimidazolium (bmim+) or ethylmethylimidazolium.

[0072] A suitable bridging portion is provided as a reactant, wherein the linking group is functionalized to chemically react with the catalyst entity. For example, suitable functionalization of the linking group provides substituted alkyl halides. Suitable reactants include, for example, 3-chloropropyltrialkoxysilane and 3-bromopropyltrialkoxysilane. The alkoxy group is preferably ethoxy, although methoxy or propoxy is not excluded. Trialkoxysilanes are preferred, although dialkyldialkoxysilanes and trialkylmonoalkoxysilanes are not excluded. In the latter case, the alkyl group is preferably a lower alkyl group, such as C1 to C4 alkyl groups. At least one alkyl group is then functionalized, for example with a halogen, as described above.

[0073] The reactants are then reacted with a catalyst entity. Preferably, the reaction generates a positive charge on the cationic entity, more specifically on the heteroatom, but preferably largely delocalized within the heterocyclic cationic moiety. For example, the reaction is a reaction of a (substituted) haloalkane with a heteroatom-containing (e.g., nitrogen) cationic moiety, which generates a bond between the heteroatom and the alkyl group. Thus, the heteroatom carries a positive charge, and the halide ion carries a negative charge. Subsequently, the negatively charged halide ion can be enhanced by adding a Lewis acid to form a metal salt complex. One example is the conversion of chloride ions to FeCl4. - .

[0074] According to the present invention, the amount of the bridging portion and the catalyst entity bonded thereto is (moles of bridging portion / grams of magnetic particles) 5. 10 -6 Up to 0.1, preferably 1 10 -5 Up to 0.01, more preferably 2 10 -5 Up to 10 -3 For example, 4 10 -5 Up to 10 -4 For the efficient optional recovery of the catalyst complex, a relatively large amount of catalyst is preferred; however, for the amount of catalyst and its cost, an even smaller amount of catalyst is preferred.

[0075] It is worth noting that homogeneous catalysts are more difficult to recover from the product stream. In some cases, such catalysts may even be unrecoverable. However, they can be recovered, for example, before the crystallization of the BHET monomer, but this would require specific measures to overcome the problem. Therefore, heterogeneous catalysts are preferably used in embodiments of the method of the present invention.

[0076] In a preferred embodiment, the amount of catalyst that can be used relative to the weight of the polymer is 0.001 to 20% by weight, more preferably 0.01 to 10% by weight, and most preferably 0.01 to 5% by weight.

[0077] This invention provides an efficient method for recovering polyurethane and optionally other polymers, such as polyamides and acrylic polymers, from waste textile materials containing polyesters, such as PET. The method is relatively robust, substantially insensitive to the presence of additives and impurities, and preferably uses a limited amount of solvent. Therefore, the method of this invention is particularly suitable for waste textile material streams, such as those from clothing or carpets. Furthermore, the residual polyester is ready for further processing, particularly depolymerization, because residual substances, such as polymers, degraded polymers, and solvents, have been effectively removed prior to further processing.

[0078] In embodiments of the present invention, relatively high purity BHET monomers after depolymerization can also be provided. In the context of this invention, high purity may mean relatively low amounts of polar aprotic solvents, such as DMAc, and / or relatively low amounts of polyurethane polymers present in the pretreated and depolymerized BHET monomers. The amounts of polar aprotic solvents and polyurethane polymers in BHET can be conveniently measured by the total nitrogen content. According to the present invention, BHET products with a total nitrogen content of less than 1000 ppm, more preferably less than 800 ppm, even more preferably less than 500 ppm, and most preferably less than 300 ppm can be obtained by embodiments of the method of the present invention. Other achievable BHET products have a total nitrogen content of less than 150 ppm, preferably less than 100 ppm, more preferably less than 30 ppm, even more preferably less than 15 ppm, and still more preferably less than 10 ppm. In other embodiments of the method, BHET products with a total nitrogen content of more than 0.06 ppm, preferably more than 0.07 ppm, more preferably more than 0.08 ppm, and even more preferably more than 0.09 ppm can be obtained. The above embodiments can combine a total nitrogen content range, for example, a total nitrogen content of 0.06 to 1000 ppm, preferably 0.07 to 800 ppm, even more preferably 0.08 to 500 ppm, and most preferably 0.09 to 300 ppm.

[0079] Another measure of the purity of the BHET monomers obtained after depolymerization is their color, such as the color displayed in the well-known CIELAB color space, which covers the entire range of human color perception. (Brightness value L) Define black as 0 and white as 100. The axis is associated with the opposite colors of green and red; negative values ​​point to green, and positive values ​​point to red. The axis ultimately represents the opposite of blue and yellow, with negative values ​​pointing to blue and positive values ​​pointing to yellow. The inventors discovered that b This is particularly relevant to the color of the BHET monomers obtained from characterization, as yellowing appears to be dominant. In fact, b It appears to be a good indicator of the presence of residual products of elastic fibers (degraded into polyols and colored diurethanes, isocyanates, and glycol esters) and optional PAN.

[0080] The results show that b can be obtained through the implementation scheme of this method. BHET products with values ​​below 2, such as below 1.5, below 1.0, or below 0.5. The BHET products that can be obtained through embodiments of the method of the present invention... The value is greater than 0, for example, greater than 0.05 or greater than 0.1. If b If the value is below 0, the BHET product will be too blue. The above implementation scheme can be combined into b The range of values.

[0081] In the implementation plan, it is stated that " A BHET product that can be obtained by the method claimed herein” It can be replaced with " A BHET product obtained by the method claimed herein” .

[0082] The invention is illustrated in more detail by way of the following embodiments, which are exemplary and illustrative and do not limit the scope of the invention. Many variations will be apparent to those skilled in the art, whether obvious or not, and all fall within the scope of protection defined by the appended claims. In the accompanying drawings, Figure 1 The color measurements of the mother liquor (ML) and BHET obtained in Examples 3-1 to 3-3 and Comparative Experiment A according to embodiments of the present invention are schematically shown. Figure 2 schematically shown Figure 1 The correlation between color measurements and the amount of remaining elastic fibers in ML and dried BHET obtained according to embodiments 3-1 to 3-3 of the present invention and comparative experiment A; Figure 3 The average molecular weights (Mw and Mn) of the precipitated and extracted elastic fibers obtained according to the embodiment of the present invention and comparative experiment B are schematically shown. Figure 4 The diagram schematically illustrates the average molecular weights (Mw and Mn) of the precipitated and extracted elastic fibers obtained according to other embodiments of the invention and comparative experiment B; and Figure 5 The final results show the changes of Mw and Mn over time after pretreatment at 80°C for 4 hours according to the embodiment of the present invention.

[0083] Example

[0084] Initial waste materials

[0085] The obtained textile waste material contains approximately 95% by weight PET and 5% by weight elastic fibers. Besides the elastic fibers, the other materials contain nylon fibers and / or polyacrylonitrile (PAN) fibers. The fibers are interwoven, but different types of fibers may also be mixed together. PET fibers provide the most important properties for textile fabrics, while other fibers provide other properties, such as elastic fibers providing elasticity. When recycled, waste textile material is typically shredded in a mechanical recycling machine and may then be fiberized to produce fluff. Alternatively, shredded material blocks of waste textile material can be produced. Shredded material provided by sorters in large bags is not conducive to separating different fibers because the typical size of the shredded material is too large. Therefore, it is preferable to cut the waste material into smaller blocks.

[0086] One object of the present invention is to obtain a polyurethane polymer that can be directly reused without repolymerization or purification.

[0087] Additional materials used

[0088] N,N-Dimethylacetamide (DMAc, anhydrous, 99.8%) was obtained from Sigma-Aldrich as a polar aprotic solvent. Ethylene glycol (EG) was obtained from Sigma-Aldrich as an alcohol solvent. No catalyst was used when dissolving polyurethane in the polar aprotic solvents.

[0089] Nitrogen content analysis

[0090] The nitrogen content of extracted polyester was analyzed using a Trace Elemental Instruments XPLOR TN / TS analyzer according to ASTM D6069 and ASTM D4629. Nitrogen content analysis was also performed on unextracted waste fabrics, with the determined values ​​assumed to correspond to 5% by weight of elastic fibers in the waste fabrics. The nitrogen content was determined by oxidizing and burning the samples at approximately 1000°C using an ozone stream, according to the chemiluminescence method described above, in the presence of an oxidizing mixture of oxygen and argon, and compared with a calibration series.

[0091] Molecular weight analysis of extracted polyurethane

[0092] Gel permeation chromatography (GPC) was performed on a Viscotek GPC Max & TDA302 system. A GPC column 2 was used. 30cm Polargel M. Data were calculated using OmniSEC™, version 4 software. Dimethylformamide (DMF) containing 0.02 mg lithium bromide was used as the eluent at a flow rate of 0.8 ml / min. Approximately 200 mg of extracted elastic fibers, with an accuracy of 0.01 g, was dissolved in 10.0 ml of the eluent. The apparatus was calibrated using Agilent's linear PMMA standards (PMMA7 kit).

[0093] Polyurethane separation from PET / polyurethane textile waste

[0094] Example 1: Extraction at 80°C for 4 hours, with the addition of boiling water.

[0095] Polyester / elastic fiber (95 / 5 wt%) waste material was cut into roughly rectangular blocks, measuring approximately 2x2 to 5x5 cm. The total nitrogen content of the waste material was 1020 ppm. 10 g of fabric blocks, on a dry matter basis, were weighed and placed in a 250 ml round-bottom flask with 140 ml of DMAc solvent. The mixture was heated to 80°C in an oil bath using an Ika C-MAG HS 7 hot plate and maintained at this temperature for 4 hours with continuous mechanical stirring to decompose the polyurethane fibers and dissolve the polyurethane, as well as to extract it via solid-liquid extraction. After extraction, the remaining PET was filtered through a coarse filter to remove DMAc and dissolved polyurethane fibers via solid-liquid separation. To enhance the precipitation of polyurethane from the DMAc, boiling water was added at a 1:1 weight ratio to the initial amount of DMAc and stirred. The polyurethane precipitated immediately, forming floating blocks of elastic material. After 15 minutes, the degree of polyurethane precipitation from the DMAc solvent could be observed by the turbidity of the mixture. The resulting polyurethane precipitated in a 1:1 (w / w) DMAc / water solution was filtered under reduced pressure through a Buchner filter equipped with a paper filter with a pore size of 12 to 15 µm. Most of the polyurethane precipitate was recovered from the paper filter, while fine polyurethane precipitates passed through the paper filter, producing a turbid filtrate.

[0096] The number-average molecular weight (Mn) of the recovered polyurethane was determined to be 83,000 Da. The weight-average molecular weight (Mw) of the recovered polyurethane was 171,000 Da. These relatively high molecular weights resulted in improved precipitation of the polyurethane from the DMAc solvent.

[0097] Extraction efficiency assessment

[0098] The polyester fabric was then washed with 25 ml of DMAc, followed by 25 ml of ethylene glycol (EG), and filtered again through the same filter under reduced pressure. The washing process was repeated once more, followed by five washes with excess (approximately 150 ml) of deionized water. The extracted fabric was dried in a vacuum oven at 60°C, and the dry weight was determined. The residual total nitrogen in the PET fabric was 105 ppm, representing an extraction efficiency of approximately 90% compared to the starting material. It should be noted that the residual DMAc can partially explain the total nitrogen content, and the initial value of 1020 ppm may be higher as it exceeds the calibration range of the total nitrogen analyzer. The total nitrogen content of the precipitated and collected polyurethane was also measured, yielding a total organic nitrogen of 2600 ppm, again exceeding the calibration range.

[0099] Example 2: Extraction was performed at 80°C for 4 hours, and cold water was added to enhance precipitation.

[0100] Example 1 was repeated, but to further enhance the precipitation of polyurethane in DMAc, cold water at 40°C was added at a 1:1 weight ratio to the initial amount of DMAc and stirred. As a result, more polyurethane precipitated immediately and formed a bubbly, floating mass of elastic material. In fact, more polyurethane precipitate was recovered by the paper filter than in Example 1.

[0101] Example 3-1: Extraction at 80°C for 4 hours, followed by treatment with ethylene glycol (EG).

[0102] Polyester / elastic fiber (95 / 5 wt%) waste material was cut into approximately rectangular blocks, measuring about 2x2 to 5x5 cm. 10 g of the fabric block was weighed on a dry matter basis and placed in a 250 ml round-bottom flask with 140 ml of DMAc solvent. The mixture was heated to 80°C in an oil bath using an Ika C-MAG HS 7 hot plate and maintained at this temperature for 4 hours with continuous mechanical stirring to decompose the polyurethane fibers and dissolve the polyurethane via solid-liquid extraction. After extraction, the remaining PET was filtered through a coarse filter and compressed to remove DMAc and dissolved polyurethane fibers via solid-liquid separation. To enhance the precipitation of polyurethane in the DMAc, boiling water was added at a 1:1 weight ratio to the initial amount of DMAc and stirred. The polyurethane precipitated in the 1:1 wt% DMAc / water solution was then filtered under reduced pressure through a Buchner filter equipped with a paper filter with a pore size of 12 to 15 µm. Most of the polyurethane precipitate is recovered from the paper filter, while the fine polyurethane precipitate passes through the paper filter, producing a turbid filtrate.

[0103] After removing as much DMAc as possible, an alcohol solvent (EG) is added to the textile at a weight ratio of 1:20. The EG is then heated to 150°C and held for 15 minutes to remove dyes, residual DMAc, and elastic fibers from the textile. The textile is then compressed again through a coarse filter to remove most of the EG and residual DMAc.

[0104] The above process results in the production of approximately 1 g of DMAc and approximately 0.005 g of elastic fibers in the reaction mixture containing polyester fabric. The weight of the reaction mixture is 320 g, and the amount of elastic fibers in the reaction mixture is 0.0015% by weight.

[0105] The resulting polyester fabric block was then depolymerized at 197°C for about 1 to 2 hours, and the generated BHET monomer was recovered from the reaction mixture by precipitation and crystallization.

[0106] Example 3-2: Extraction at 80°C for 4 hours, followed by treatment with ethylene glycol (EG).

[0107] Except for the uncompressed or squeezed washed polyester fabric (DMAc and EG treatment), the process described in Examples 3-1 was repeated. This process produced approximately 10 g of DMAc and approximately 0.05 g of elastic fibers in the reaction mixture containing the polyester fabric. The total weight of the reaction mixture was 288 g, and the amount of elastic fibers in the reaction mixture was 0.017% by weight.

[0108] BHET was obtained as described in Example 3-1 above.

[0109] Example 3-3: Extraction at 80°C for 4 hours without subsequent treatment with ethylene glycol (EG).

[0110] The process described in Example 3-1 was repeated, except that the polyester fabric was not washed with ethylene glycol (EG) at all. This process produced approximately 61 g of DMAc and approximately 0.3 g of elastic fibers in the reaction mixture containing the polyester fabric. The total weight of the reaction mixture was 349 g, and the amount of elastic fibers in the reaction mixture was 0.085% by weight.

[0111] BHET was obtained as described in Example 3-1 above.

[0112] Comparative Experiment A: Extraction was not performed at 80℃ for 4 hours, and no subsequent treatment with ethylene glycol (EG) was used.

[0113] The waste polyester fabric from Example 3-1 was used directly without any pretreatment. This produced 0 g of DMAc and approximately 1.5 to 2 g of elastic fibers in the reaction mixture containing the polyester fabric. The reaction mixture weighed 280 g, and the amount of elastic fibers in the reaction mixture was 0.5 to 0.7% by weight.

[0114] BHET was obtained as described in Example 3-1 above.

[0115] According to well-known practice, with b The value is used to measure the color of the mother liquor and BHET, b The value is a measure of yellowness. The b value was measured on the mother liquor (ML) and the dried BHET obtained by separation from the mother liquor (dry BHET). value. Figure 1 Examples 3-1 to 3-3 are shown (in) Figure 1 The results of the color measurements of the mother liquor (ML) and the dried BHET were used in the experiments (referred to as low, medium, and high) and the comparative experiment A. Figure 2 Examples 3-1 to 3-3 and Comparative Experiment A (b) are shown. The correlation between the value and the amount of elastic fibers. (From...) Figure 1 and Figure 2It can be concluded that the amount of residual elastic fibers in the polyester fabric is the primary cause of any yellowing observed in the BHET obtained after depolymerization. Furthermore, pretreatment with EG is important, as it reduces yellowing. This is likely due to the evaporation of DMAc prior to actual depolymerization during the process, although other explanations cannot be ruled out.

[0116] To confirm the evaporation of DMAc, a mixture of DMAc and EG (1:1 wt%) was heated in a sealed container to prevent evaporation. This did indeed show yellowing in the mixture, with the EG retaining its yellow color when the DMAc was distilled off.

[0117] Example 4: Extraction at 80°C for 4 hours, with different amounts of cold water added.

[0118] In addition to selecting the amount of water, the process of Example 1 was repeated so that the DMAc / water weight ratio was from 90 / 10 to 50 / 50. The results showed that when the DMAc / water ratios were 50 / 50, 80 / 20, 66 / 33, and 90 / 10, the degree of polyurethane precipitation from the DMAc solvent (measured by the amount of precipitate after 15 minutes) decreased with decreasing water content. It should be noted that higher initial concentrations of polyurethane in waste fabrics may require less water or no water at all for precipitation.

[0119] Examples 5-6 and Comparative Experiment B: Extraction at different temperatures and times, with the addition of cold water to enhance precipitation.

[0120] Example 5

[0121] Example 1 was repeated except that the mixture was heated to 110°C in an oil bath using an Ika C-MAG HS 7 heating plate and held at that temperature for 2 hours under continuous mechanical stirring to decompose the polyurethane fibers and dissolve the polyurethane, and extracted by solid-liquid extraction.

[0122] Comparative Experiment B:

[0123] Example 1 was repeated except that the mixture was heated to 140°C in an oil bath using an Ika C-MAG HS 7 heating plate and maintained at that temperature for 30 minutes with continuous mechanical stirring to decompose the polyurethane fibers and dissolve the polyurethane, and extracted by solid-liquid extraction. The mixture was cooled to 80°C, and boiling water was added after cooling. As a result, the precipitation of polyurethane was much slower than in Example 1.

[0124] Example 6

[0125] Except for heating the mixture in an oil bath to 80°C using an Ika C-MAG HS 7 heating plate and maintaining that temperature for 1 hour under continuous mechanical stirring to decompose the polyurethane fibers and dissolve the polyurethane, and extracting it by solid-liquid extraction, Example 1 was repeated.

[0126] Example 7

[0127] Except for heating the mixture in an oil bath to 80°C using an Ika C-MAG HS 7 heating plate and maintaining that temperature for 2 hours under continuous mechanical stirring to decompose the polyurethane fibers and dissolve the polyurethane, and extracting it by solid-liquid extraction, Example 1 was repeated.

[0128] Example 8

[0129] Except for heating the mixture in an oil bath to 80°C using an Ika C-MAG HS 7 heating plate and maintaining that temperature for 3 hours under continuous mechanical stirring to decompose the polyurethane fibers, and dissolving the polyurethane through solid-liquid extraction, Example 1 was repeated.

[0130] The results of Examples 5 to 8 and Comparative Experiment B are as follows: Figures 3 to 5 As shown in Table 1 below.

[0131] Figure 3 A crucial finding was revealed: despite using shorter pretreatment times, the elastic fiber chains became shorter with increasing pretreatment temperature. Results showed that pretreatment with DMAc at 80°C for 4 hours yielded the longest elastic fiber chains while simultaneously removing almost all elastic fibers from the textile. These longer elastic fiber chains are considered essential for better sedimentation. Furthermore, from the perspective of recycling elastic fibers, longer elastic fiber chains are more valuable.

[0132] Figure 4 The results show that the Mw and Mn of the precipitated and extracted elastic fibers are slightly lower than those of the pretreated sample. This is likely due to the poor homogeneity of the solid sample. The results also indicate that very few elastic fibers can be obtained from the experiment at 140 °C (Comparative Experiment B). In fact, the filter tends to clog, and DMAc cannot be removed almost completely.

[0133] Figure 5 The final results showed kinetic samples pretreated at 80°C for 4 hours. Interestingly, these experiments did not show substantial changes in Mw and Mn over time, whereas other experiments have shown a decrease in Mw and Mn over time. It appears that the elastic fiber chains did not degrade, but 80°C is high enough to at least dissolve the elastic fibers and extract them from the textile. Figure 5The results also indicate that a shorter pretreatment time of 4 hours at 80°C is possible. Furthermore, these results suggest that DMAc pretreatment at 80°C does not cause excessive degradation of the elastic fibers, thus facilitating recycling.

[0134]

[0135] Table 1 Measurement of the molecular weight of polyurethane

[0136] Example 9

[0137] This embodiment demonstrates the beneficial effect of cutting the raw material (waste polymer textile material) into blocks rather than shredding it into blocks of approximately the same size.

[0138] Example 1 was repeated, in which 200 g of textile material was added to 4000 ml of DMAc (textile to solvent ratio 1:20). The mixture was pretreated at 80°C for 4 hours. The dissolved elastic fibers and DMAc were then separated from the PET using a coarse filter. In another step, the same 4000 ml of DMAc was used as the solvent, and 200 g of textile material was treated (making the effective textile to solvent ratio 1:10). Because the volume of the fibrous textile material was larger than that of the cut textile material, it was impossible to transfer all the fibrous textile material to the given amount of DMAc solvent, as all the solvent was absorbed by the fibrous textile material. Therefore, the extraction of polyurethane was not optimal. In contrast, the cut textile material was completely immersed in the given amount of DMAc solvent. This improved the extraction of polyurethane.

[0139] Therefore, the preferred method according to the invention comprises the following steps: Cutting the textile into pieces (e.g., 2x2 to 5x5 cm). Adding the cut textile to a container, such as a beaker or RBF. Adding an appropriate amount of a polar aprotic solvent, such as DMAc, to achieve a textile-to-solvent ratio of 20. Raising the temperature of the mixture to 80°C and stirring for approximately 4 hours. While the mixture is still hot, filtering the textile and solvent through a coarse filter. Pressing or squeezing the textile to remove as much residual DMAc as possible from the textile and collecting the solvent. Then performing another textile pretreatment with the solvent to produce an effective textile-to-solvent ratio of 1:10. Optionally washing the textile with water and then pretreatment with an alcohol solvent, such as EG. After removing as much DMAc as possible, adding the textile again to an alcohol solvent, such as EG, at a ratio of 1:20.

[0140] Now heat the EG to 150°C for 15 minutes and pretreat the textile to remove the dye and residual DMAc. The temperature of the EG should not be too high to prevent at least partial or substantial degradation of the DMAc. Filter the textile again through a coarse filter and press or squeeze it to remove most of the EG and residual DMAc. The textile is now ready for depolymerization. The EG used for pretreatment can be used again for the same pretreatment to achieve a textile-solvent ratio of 1:10 again.

[0141] To obtain the elastic fibers, the solution was cooled, and then cold water (1:1) was added to DMAc to allow the elastic fibers to precipitate for 15 minutes. After precipitation, the material was filtered through a 12 to 15 µm filter, and any remaining elastic fibers were washed with water or ethanol / acetone.

[0142] Comparative Experiment C:

[0143] Example 1 was repeated except that the mixture was heated to 160-165°C in an oil bath using an Ika C-MAG HS 7 heating plate and maintained at that temperature for 10 minutes with continuous mechanical stirring to decompose the polyurethane fibers, and the polyurethane was dissolved by solid-liquid extraction. As a result, some polyester fibers also began to dissolve at these temperatures, forming a slurry, which adversely affected the polyurethane extraction. Clearly, the loss of some polyester during pretreatment is undesirable.

[0144] Comparative Experiment D:

[0145] Example 1 was repeated except that the mixture was heated to 140°C in an oil bath using an Ika C-MAG HS 7 heating plate and maintained at that temperature for 30 minutes with continuous mechanical stirring to decompose the polyurethane fibers, and the polyurethane was dissolved by solid-liquid extraction. The mixture was cooled to 80°C, and cold water was added after cooling. The result was that in Comparative Experiment D, the precipitation of polyurethane was quite slow, and therefore much slower than in Example 1.

[0146] Example 10

[0147] Example 1 was repeated using a polyacrylonitrile (PAN) fiber textile material, with the following differences. The mixture of textile material and DMAc was heated to 50°C in an oil bath using an Ika C-MAG HS 7 heating plate and maintained at this temperature for 4 hours with continuous mechanical stirring to decompose the PAN fibers and dissolve the PAN by solid-liquid extraction. After extraction, the remaining PET was filtered through a coarse filter to remove the DMAc and dissolved PAN fibers by solid-liquid separation.

[0148] The results showed that PAN was easily removed from the mixture during pretreatment with DMAc at 50°C. After washing with 25 ml of ethylene glycol (EG) and filtering under reduced pressure, PAN was essentially removed from the polyester fabric. The washing process was repeated once, followed by washing five times with an excess of deionized water (approximately 150 ml).

Claims

1. A method for recovering polyurethane polymer from waste polymeric textile material comprising polyester fibers and polyurethane fibers, the method comprising the following steps: a) providing the waste polymeric textile material in shredded or cut form; b) contacting the waste polymeric textile material in shredded or cut form with a polar aprotic solvent at a temperature of 25 to 125 °C to at least partially dissolve the polyurethane in the polar aprotic solvent while the polyester is essentially unaffected; c) separating the polyester from a solvent mixture comprising the polar aprotic solvent and the polyurethane dissolved therein by solid-liquid separation; d) precipitating the polyurethane dissolved in the solvent mixture; e) separating the precipitated polyurethane from the solvent mixture to obtain the polyurethane polymer and used polar aprotic solvent; f) optionally reusing the used polar aprotic solvent at least partially in step b).

2. The method according to claim 1, wherein precipitating the polyurethane dissolved in the solvent mixture in step d) comprises adding water to the solvent mixture, wherein the solvent mixture is optionally cooled to below the temperature of the contacting in step b) before, during or after adding the water.

3. The method according to claim 2, wherein the temperature of the added water is 1 to 100 °C at ambient pressure, more preferably 5 to 50 °C at ambient pressure, even more preferably 10 to 40 °C, and most preferably 15 to 30 °C at ambient pressure.

4. The method according to any one of the preceding claims, wherein the polyurethane polymer obtained in step e) has a Mn of at least 50000 Da.

5. The method according to any one of claims 2 to 4, wherein the added water is separated from the used polar aprotic solvent obtained in step e) before the optional reuse of the polar aprotic solvent according to step f).

6. The method according to any one of the preceding claims, wherein the polyester obtained in step c) is extruded and / or washed to further remove the polar aprotic solvent still present in the polyester, wherein the optional washing is preferably performed in counterflow.

7. The method according to any one of the preceding claims, further comprising the following steps: g) contacting the polyester obtained in step c) with a polyol solvent at a temperature of 50 to 200 °C to further dissolve possible remaining polyurethane in the polyol solvent and to evaporate the polar aprotic solvent while the polyester is essentially unaffected; and h) separating the polyester from a polyol solvent mixture comprising the polyol solvent, possible remaining polyurethane dissolved in the polyol solvent mixture and possible remaining polar aprotic solvent by solid-liquid separation.

8. The method according to claim 7, wherein the amount of polar aprotic solvent still present in the polyester after step h) is below 1 : 1 relative to the amount of alcoholic solvent.

9. The method according to any one of claims 7 and 8, wherein the waste polymeric textile material further comprises polyamide fibers, which are dissolved in step g) and then separated from the polyester in step h).

10. The process according to any one of the preceding claims, wherein the waste polymeric textile material further comprises acrylic polymer fibers, the acrylic polymers are dissolved in step b) and the dissolved acrylic polymers are separated from the first mixture in step d).

11. The process according to any one of the preceding claims, wherein the waste polymeric textile material further contains functional additives, such as dyes, and the functional additives are dissolved in the polar aprotic solvent and the functional additives are separated from the polyesters with the polar aprotic solvent in step d).

12. The process according to any one of the preceding claims, wherein the polar aprotic solvent comprises dimethylacetamide.

13. The process according to any one of claims 7 to 12, wherein the polyol solvent comprises a diol, more preferably an alkylene diol selected from the group consisting of ethylene glycol (1,2-ethanediol), propylene glycol (1,3-propanediol), 1,4-butanediol and 1,5-pentanediol.

14. The process according to any one of the preceding claims, wherein step b) is carried out at a temperature of 60 to 100 °C.

15. The process according to any one of claims 7 to 14, wherein step g) is carried out at a temperature of 110 to 190 °C, more preferably 120 to 170 °C, even more preferably 130 to 150 °C.

16. The process according to any one of the preceding claims, wherein the weight ratio of polar aprotic solvent to textile waste material is 1:2 to 1:

40.

17. The process according to any one of the preceding claims, wherein the polyesters comprise polyethylene terephthalate.

18. The process according to any one of the preceding claims, wherein the polyurethanes comprise polyether-polyurea copolymers, preferably spandex.

19. The process according to any one of claims 10 to 18, wherein the acrylic polymers comprise polyacrylonitrile.

20. The process according to any one of the preceding claims, wherein the waste polymeric material comprises 85 to 99 wt% of polyesters, 1 to 15 wt% of polyurethanes and optionally polyamides and / or acrylic polymers, the total being 100 wt%.

21. The process according to any one of the preceding claims, wherein step b) is carried out for 0.5 to 8 hours, more preferably 2 to 6 hours.

22. The process according to any one of claims 7 to 21, wherein step g) is carried out for 5 to 60 minutes, more preferably 10 to 40 minutes.

23. The process according to any one of the preceding claims, further comprising the steps of i) adding a reactive solvent to disperse the polyesters recovered after step h) and obtaining a dispersion; j) adding a depolymerization catalyst to the dispersion; k) depolymerizing the polyesters under reaction conditions to obtain monomers and / or oligomers dissolved in the reactive solvent; wherein the reactive solvent comprises a polyol, optionally the polyol obtained from step h).

24. The process according to claim 23, wherein the depolymerization is carried out at a temperature of at least 160 °C, preferably at least 180 °C, more preferably at least 190 °C, and even more preferably up to 250 °C. ​ 25. The method according to claim 23 or 24, wherein the catalyst for depolymerization of the polyester comprises functionalized magnetic particles, which are functionalized with catalytic moieties.

26. A BHET product, which is obtainable by or by the method according to any one of claims 23 to 25, and which has a total nitrogen content of below 1000 ppm, preferably below 800 ppm, even more preferably below 500 ppm, and most preferably below 300 ppm.

27. The BHET product according to claim 26, which has a total nitrogen content of above 0.06 ppm, preferably above 0.07 ppm, more preferably above 0.08 ppm, and even more preferably above 0.09 ppm.

28. The BHET product according to claim 26 or 27, which corresponds to a b value in the CIELAB color space lower than 2, for example lower than 1.5, lower than 1.0 or lower than 0.

5.

29. The BHET product according to any one of claims 26 to 28, which corresponds to a b value in the CIELAB color space higher than 0, for example higher than 0.05 or higher than 0.1.

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