Method for removing ethylene vinyl alcohol copolymer from waste polymer materials

Abstract

This paper describes a method for removing ethylene vinyl alcohol copolymer from waste polymer materials containing polyester and ethylene vinyl alcohol copolymer. The method includes providing the waste polymer material in shredded or cut form, contacting the shredded or cut waste polymer material with an alcohol-based solvent at a temperature of 80 to 170°C to at least partially dissolve the ethylene vinyl alcohol copolymer in the alcohol-based solvent while keeping the polyester substantially unaffected, separating the polyester from the solvent mixture containing the alcohol-based solvent and the vinyl alcohol copolymer dissolved therein by solid-liquid separation, precipitating the vinyl alcohol copolymer dissolved in the solvent mixture, and separating the precipitated vinyl alcohol copolymer from the solvent mixture to obtain the vinyl alcohol copolymer and the used alcohol-based solvent. A method for depolymerizing polyester derived from waste polymer multilayer articles is also described.

Description

[Technical Field]

[0001] This invention relates to the field of obtaining useful products from waste polymer materials. Specifically, this invention relates to a method for removing ethylene vinyl alcohol copolymer from a waste polymer multilayer article comprising polyester, ethylene vinyl alcohol copolymer, and optionally a third polymer, such as polyolefin. The method according to this invention uses a solvent, and since all solvents used in this method are recyclable, the method according to this invention has a low environmental impact. This invention also relates to a method for depolymerizing polyester from a waste polymer multilayer article. [Background technology]

[0002] Polymer materials are currently widely used in a variety of items, including carpets, clothing, coverings, bedding, textiles, building materials, and packaging materials. The reuse and disposal of used polymer materials are becoming increasingly complex due to the fact that these materials are increasingly composed of numerous different polymers, each contributing to specific desired properties. For example, multilayer packaging materials, such as packaging films used in food applications, have become very common in the packaging industry in recent years and can exhibit many different polymer combinations depending on the specific product requirements. Because of the wide variety of polymers present within multilayer packaging materials, their recyclability presents challenges, and industrially feasible solutions have yet to be provided.

[0003] Polymer multilayer articles are generally classified into three main categories: flexible non-metallic articles, flexible metallic articles, and rigid non-metallic articles. Flexible articles are also called multilayer films, while rigid non-metallic articles are called multilayer trays (MLTs), and their rigidity is usually derived from the presence of a relatively thick polyester (e.g., PET) body.

[0004] In multilayer tray (MLT) applications, ethylene vinyl alcohol copolymer (e.g., EVOH) is typically combined with polyolefins such as polyethylene (PE) and / or polypropylene (PP) and condensation polymers such as polyester, e.g., PET. A common type of MLT is a PE / EVOH / PET multilayer article, where each layer may have a different thickness.

[0005] Multilayer polymer articles are complex because they consist of different layers of heteropolymers such as polyolefins and polyesters, with each layer selected to provide specific properties advantageous to the article. For example, polyethylene (PE) is frequently used due to its flexibility and can function as a moisture barrier in packaging materials for medical products and consumer goods. Ethylene vinyl alcohol copolymer (EVOH) can function as an oxygen barrier widely used in food packaging materials, and polyethylene terephthalate (PET) can function as an effective gas and moisture barrier that imparts rigidity and strength. Further increasing the complexity of these multilayer polymer articles are numerous adhesion layers (e.g., ethylene vinyl acetate copolymer (EVA), adhesives and / or additives (e.g., TiO2)) that may be present in small amounts compared to the main polymer components or groups of components.

[0006] The versatility and affordability of multilayer polymer materials have created significant demand for them. Therefore, there is a large potential amount of waste multilayer materials that can be recovered and reused in their original intended applications.

[0007] It is highly desirable to provide a method for recycling waste polymer multilayer articles, which at least includes a method for depolymerizing the main polymer, for example, polyester in the multilayer article, into constituent units of the polymer for reuse as recycled raw materials in repolymerization. It is known that the quality of the recycled raw materials obtained by depolymerization, i.e., monomers, dimers, and oligomers obtained by such a process, largely depends on the removal of impurities present in the waste polymer article. These impurities typically include colorants and other additives that may be present in the polymer material, such as fillers and plasticizers. In multilayer articles, polymers other than the depolymerized polyester are also considered impurities, because the presence of such polymers in the depolymerization process and / or the recycled raw materials obtained from that process can have a significant impact on the quality of the raw materials. Naturally, this also negatively affects the quality of the repolymerized product.

[0008] Therefore, it is important to be able to selectively remove ethylene vinyl alcohol copolymer and optionally a third polymer, such as polyolefin, from waste polymer multilayer articles. In other words, in order to reuse the raw materials constituting waste polymer multilayer articles, it is necessary to effectively separate various polymers, and for this purpose, an appropriate separation method is required.

[0009] In this technical field, it has been proposed to decompose multilayer polymer films into their constituent polymers using a series of solvent washings based on thermodynamic calculations of polymer solubility. This known method is called solvent-targeted recovery and precipitation (STRAP), but it has the problem that different solvents and process conditions must be used for each soluble polymer in the multilayer polymer article. For example, Theodore W. Walker et al., 'Recycling of multilayer plastic packaging materials by solvent-targeted recovery and precipitation', Sci. Adv. 2020 (6), 2020 discloses a method for selectively dissolving polyethylene (PE) and EVOH in multilayer PET / EVOH / PE articles. This method involves selectively dissolving the PE fraction in toluene at 110°C, then separating this solubilized fraction from EVOH and PET by mechanical filtration, selectively dissolving this EVOH fraction in DMSO at 95°C, and then separating the solubilized fraction from the remaining PET.

[0010] International Publication No. 2022157928 provides a method for extracting EVOH from a multilayer resin molded article containing an EVOH layer. The EVOH extractant comprises a polar solvent with a solubility parameter of 9 to 13, such as DMSO, and a quaternary ammonium salt. Recovery of EVOH is performed by precipitation with water and separation by filtration or centrifugation.

[0011] Therefore, EVOH requires a polar solvent with a solubility parameter of 9-13, such as DMSO, which is an aprotic polar solvent, while PE requires toluene. Small amounts of each of these solvents may remain in the polyester, which significantly limits the reuse of such polyesters. Also, because the dissolution temperatures used are relatively high, it may not be possible to efficiently separate the dissolved polymer from the solvent. Therefore, the solvent is likely to contain impurities. This hinders the reuse of the solvent, which is undesirable from an environmental standpoint. [Overview of the Initiative] [Problems that the invention aims to solve]

[0012] Therefore, there is a need for an improved method for removing ethylene vinyl alcohol copolymer from a waste polymer multilayer article comprising polyester, ethylene vinyl alcohol copolymer, and optionally a third polymer, such as polyolefin, which does not have the drawbacks of the prior art or at least has reduced drawbacks.

[0013] Another object of the present invention is to provide an improved separation method that is more cost-effective, more robust, and does not generate further waste logistics.

[0014] Another objective is to provide an improved method for removing polymers other than the ethylene vinyl alcohol copolymer from waste polymer multilayer articles containing polyester and ethylene vinyl alcohol copolymers.

[0015] Another objective is to provide a method that combines removing the ethylene vinyl alcohol copolymer from a waste polymer multilayer article containing polyester and ethylene vinyl alcohol copolymer with depolymerizing the polyester under conditions for obtaining monomers and / or oligomers. [Means for solving the problem]

[0016] In a first aspect, the present invention provides a method as claimed in claim 1. According to the invention as claimed in the claims, a method for removing an ethylene vinyl alcohol copolymer from a waste polymer material containing a polyester and an ethylene vinyl alcohol copolymer, comprising: a) providing a waste polymer material in a reduced size form; b) contacting the waste polymer material in a reduced size form with an alcoholic solvent at a temperature of 90 to 170°C, thereby at least partially dissolving the ethylene vinyl alcohol copolymer in the alcoholic solvent while keeping the polyester substantially unaffected; c) separating the polyester by solid-liquid separation from a solvent mixture containing the alcoholic solvent and the vinyl alcohol copolymer dissolved in the solvent mixture; d) precipitating the vinyl alcohol copolymer dissolved in the solvent mixture; e) separating the precipitated vinyl alcohol copolymer from the solvent mixture to obtain the vinyl alcohol copolymer and the used alcoholic solvent. A method is provided which comprises the above steps.

[0017] In a second aspect, the present invention provides a method as claimed in the claims, which further comprises: dispersing the polyester by adding a reactive solvent to obtain a dispersion; adding a depolymerization catalyst to the dispersion; and depolymerizing the polyester under conditions for obtaining monomers and / or oligomers dissolved in the reactive solvent, wherein the reactive solvent contains an alcoholic solvent, preferably at least a part of the used alcoholic solvent.

[0018] The inventors have surprisingly discovered that the EVOH polymer layer, which forms part of a waste multilayer polymer article, can be separated from the multilayer polymer article by dissolving it in an alcohol-based solvent, which is also commonly used as a reactive solvent when depolymerizing the polyester in the waste multilayer polymer article, at a temperature of 90 to 170°C. Furthermore, it was found that the EVOH polymer can be selectively separated from any third polymer, such as polyolefin, and that this third polymer can be separated from the solvent mixture by density separation, thereby eliminating the need to use a separate solvent for polyolefin.

[0019] EVOH dissolved in an alcohol-based solvent can be easily precipitated and separated from the alcohol-based solvent mixture, thereby obtaining a vinyl alcohol copolymer and a used alcohol-based solvent. In embodiments of the present invention, the used alcohol-based solvent can be reused for further dissolution of EVOH and / or reused as a reactive solvent when depolymerizing polyester.

[0020] Detailed description of the invention In the context of this disclosure, firstly, any scope disclosed shall include the numerical values ​​at both ends of that scope. Furthermore, as used herein, “substantially,” “essentially,” “consisting essentially of,” “essentially all,” and their equivalents, as well as “about,” have the usual meaning, unless otherwise specified, relating to composition or process steps, that deviations may occur in a composition or process step, but such deviations shall be limited to such extent that the essential characteristics and effects of the composition or process step are not significantly affected by the deviation. Furthermore, the verb “to comprise” and its conjugations are used in a non-restrictive sense, meaning that the matters described following the word are included, but not that matters not explicitly stated are excluded. Finally, references to elements with the indefinite article “a” or “an” do not exclude the possibility that there may be multiple elements unless the context explicitly requires that there be one or only one element. Thus, the indefinite article “a” or “an” usually means “at least one.”

[0021] multilayer article According to the present invention, waste polymer material is typically supplied as a reduced-size multilayer film or multilayer tray. Size reduction can be carried out, for example, by shredding, crushing, wet-grinding, or cutting the waste polymer material to obtain flakes or pellets of appropriate size. Other size reduction methods may also be suitable. Shredding involves crushing the waste polymer material in a shredder. This can produce fragments of a certain length, such as strips or ribbons. Crushing or wet-grinding usually provides smaller fragments. The waste polymer material can also be cut into smaller fragments with typical linear dimensions of 0.1 to 10 cm. In this embodiment, the waste polymer multilayer material may contain relatively small particles with typical linear dimensions of 0.1 to 10 cm, preferably 0.5 to 6 cm, and more preferably 0.8 to 4 cm. Suitable flakes, for example, have a square shape with typical dimensions of 1 × 1 cm to 2 × 2 cm. In one preferred embodiment, the waste polymer material is substantially dry and more preferably has a moisture content of less than 5% by weight, more preferably less than 3% by weight, and even more preferably less than 1% by weight of the waste polymer material.

[0022] The waste polymer material comprises polyester and ethylene vinyl alcohol copolymer (EVOH), preferably in the form of a separate layer in a multilayer polymer article. In any one embodiment, the waste polymer material may also comprise polyolefin, preferably polyethylene (PE), in the form of a separate layer.

[0023] EVOH copolymers suitable for use in the present invention may contain at least about 50 mol% and at most 80 mol% vinyl alcohol in their molecules. Preferred copolymers may contain about 60-75 mol% vinyl alcohol. The remaining portion of the EVOH molecule consists mainly of 20-50 mol%, preferably 40-25 mol%, ethylene. Since EVOH is usually produced by the hydrolysis of ethylene vinyl acetate copolymer, some residual vinyl acetate may be present. Typically, the amount of vinyl acetate that may be present in the EVOH molecule is less than about 3% by weight, preferably less than 1.5% by weight. Typically, EVOH copolymers have a concentration of about 1.1-1.2 g / dm³ 3 It has a density and its melting point is typically in the range of approximately 160°C to 190°C. EVOH is decomposable at temperatures above 230°C.

[0024] The waste polymer material further includes polyester. Among this class of condensed polymers, polyethylene terephthalate (PET) is a preferred polyester. As is known in the art, PET may contain further comonomers such as isophthalic acid, diethylene glycol (DEG), and cyclohexanedimethanol (CHDM) to improve its properties. However, other polyesters, such as polyethylene naphthalate (PEN) based on 2,6-naphthalenedicarboxylic acid and ethylene glycol, are not excluded. Other examples include so-called biodegradable polymers, such as polylactic acid (PLA), polybutylene terephthalate (PBT), polypropylene terephthalate, polypentaerythrityl terephthalate and their copolymers, such as ethylene terephthalate and polyglycols, such as copolymers of polyoxyethylene glycol and poly(tetramethylene glycol), as well as polycyclohexylene-2,5-flangecarboxylate (PCF), polybutylene adipate-co-terephthalate (PBAT), polybutylene sevacate-co-terephthalate (PBSeT), polybutylene succinate-co-terephthalate (PBST), and polybutylene 2,5-flangecarboxylate-co-succinate (PBSF). Examples include polybutylene 2,5-flange carboxylate-co-azipart (PBAF), polybutylene 2,5-flange carboxylate-co-azelate (PBAzF), polybutylene 2,5-flange carboxylate-co-sebacate (PBSeF), polybutylene 2,5-flange carboxylate-co-brazilate (PBBrF), polybutylene 2,5-flange carboxylate (PBF), polybutylene succinate (PBS), polybutylene azipart (PBA), polybutylene succinate-co-azipart (PBSA), polybutylene succinate-co-sebacate (PBSSe), polybutylene sebacate (PBSe), and copolymers thereof, such as copolymers with polylactic acid and / or PET.

[0025] The waste polymer material may optionally contain, in addition to polyester and EVOH, one or more of a separate third polymer, such as polyolefin, polyvinyl chloride, polyamide, and / or polystyrene. The polyolefin may include polyethylene, polypropylene, or a combination thereof. If the third polymer is a polyolefin, it can be melted at the temperature applied in step (b) of the method. If the third polymer is polyvinyl chloride and / or polystyrene, some grades thereof cannot be melted in step (b) of the method according to the present invention, nor can they be dissolved in an alcoholic solvent.

[0026] Waste polymer multilayer materials typically have the advantage of not containing fragments of inorganic solids, such as stone, glass, or metals, such as aluminum, steel, copper, brass, and nickel. While such materials may be present in other waste materials, they are rarely found in waste polymer multilayer articles. However, the present invention also allows for the treatment of inorganic solids and metals as needed.

[0027] Removal of EVOH According to step b) of the method according to the present invention, the waste polymer material in a reduced size form is brought into contact with an alcohol-based solvent at a temperature of 90 to 170°C, thereby at least partially dissolving the ethylene vinyl alcohol copolymer in the alcohol-based solvent while keeping the polyester substantially unaffected. The contact can be achieved, for example, by adding the alcohol-based solvent to the waste polymer material, or vice versa.

[0028] Alcoholic solvents can be selected from monoalcohols, dialcohols, and trialcohols. Preferably, non-halogenated alcohols are used. More preferably, polyols are used. Shorter chain alcohols, such as C6-C10 monoalcohols and similarly preferably C2-C10 dialcohols, and more preferably C2-C8 dialcohols, are preferred. Examples include 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, 1,4-be Examples include lenzendimethanol, ethylene glycol (1,2-ethanediol) 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. The preferred alcohol used in the second step in a suitable embodiment comprises a glycol, more preferably an alkylene glycol, which is selected from ethylene glycol (1,2-ethanediol), propylene glycol (1,3-propanediol), 1,4-butanediol, and 1,5-pentanediol.

[0029] Conventional techniques require the use of polar solvents with a solubility parameter of 9-13 and quaternary ammonium salts to dissolve EVOH. Surprisingly, the inventors have found that relatively unsuitable alcoholic solvents, such as ethylene glycol (EG), which have a much higher solubility parameter, can dissolve EVOH in waste polymer multilayer articles to a degree that allows for high-yield removal of EVOH from the articles.

[0030] While the use of alcohol-based solvents is essential to the present invention, the addition of other solvents, for example, in smaller amounts than the alcohol-based solvent, is not excluded, for example, up to 50% by weight, more preferably up to 30% by weight, even more preferably up to 20% by weight, and even more preferably up to 10% by weight relative to the amount of alcohol-based solvent. Most preferably, no solvents other than alcohol-based solvents are added to the solvent mixture. In some embodiments, an aprotic solvent can be added to the solvent mixture containing the alcohol-based solvent. Suitable aprotic polar solvents that can be added include, but are not limited to, dichloromethane (DCM), tetrahydrofuran (THF), ethyl acetate, acetonitrile, dimethylformamide (DMF), dimethylpropylene urea, dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), acetone, hexamethyl phosphate triamide (HMPT), pyridine, and sulfolane. Preferred aprotic polar solvents have a dielectric constant greater than 10, more preferably greater than 20, and most preferably greater than 30.

[0031] Step b) of this method also includes heating the solvent mixture to a temperature in the range of 90 to 170°C until the EVOH polymer is at least partially dissolved. Preferred temperatures are selected within the range of 100°C to 165°C, more preferably 110°C to 160°C, even more preferably 120°C to 155°C, and most preferably 130°C to 150°C. If the temperature is too low, the EVOH may not dissolve sufficiently in the alcoholic solvent, and if the temperature is too high, it may lead to premature depolymerization of the polyester. The indicated temperature range is further selected considering the optimal recovery of the EVOH polymer from the mixture. Heating is usually carried out for a period of 10 minutes to 8 hours or longer. The pressure during heating is usually 90 to 200 kPa, for example, atmospheric pressure. The heating step forms a slurry containing the polyester and dissolved EVOH. At least a portion of the EVOH dissolves at the selected dissolution temperature and duration, while the polyester remains substantially undissolved and substantially unaffected. It is preferable that the heating is carried out so that substantially all of the EVOH is dissolved. However, this is not considered necessary. Small amounts, for example, up to 10% by weight of the initial amount of EVOH, for example, up to 5% by weight, preferably up to 3% by weight, or even up to 1% by weight, may remain undissolved.

[0032] After the dissolution step b), the slurry is subjected to solid-liquid separation in step c) of this method. In this step, the polyester is separated from the solvent mixture containing the alcohol-based solvent and the dissolved EVOH. Any suitable solid-liquid separation method can be used, such as centrifugation, filtration, or a combination thereof. Typically, a filtration step is performed using a coarse filter, thereby forming a filtrate. In this case, the polyester remains on the filter, while the solvent mixture passes through the filter as a liquid, possibly in the form of small particles, thus separating the polyester from the solvent mixture. 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. Typically, the filtration step is performed using a filter with a mesh larger than 0.2 μm to form a filtrate.

[0033] After recovering the filtrate containing the solvent mixture, the EVOH present in the solvent mixture is precipitated in step d) of the method according to the present invention, and then separated from the solvent mixture in a further step e) of the method according to the present invention. The mesh size in the filtration separation can be selected so that the majority of the EVOH particles are retained. Preferably, the mesh is larger than 0.2 μm, and the upper limit of the mesh size may depend on the particle size of the EVOH particles, which in turn depends on many variables, including the concentration of EVOH in the alcoholic solvent, the cooling time, the temperature, and possibly the water content of the alcoholic solvent. A suitable upper limit of the mesh size can be easily selected by those skilled in the art and may be, for example, less than 20 μm. In addition to the mesh size, the pressure used may also have an effect, and usually, using a larger negative pressure allows for a smaller mesh size. This embodiment is appropriately carried out by providing the solvent mixture or slurry to a filter chamber containing a filter, and applying negative pressure to the filter at that time. The recovered EVOH can then be further processed as needed.

[0034] A particularly useful embodiment of the present invention provides a method further comprising the step of reusing, at least partially, the spent alcohol-based solvent obtained in step e) in step b). In other words, the alcohol-based solvent used to dissolve EVOH is reused, after separation, for further dissolution of EVOH. This can be carried out in a container, for example, a scrubber, into which the spent alcohol-based solvent is again supplied along with a fresh feed of waste polymer multilayer material. By reusing the alcohol-based solvent for dissolving the newly supplied EVOH, the concentration of EVOH in the solvent mixture provided in step b), i.e., during contact between the reduced-size form of waste polymer material and the alcohol-based solvent, is effectively increased. It has been found that exceeding a threshold concentration of EVOH in the solvent mixture promotes the precipitation of EVOH from this solution. The threshold concentration can depend on many factors but can be in the range of 20-30 mg / mL.

[0035] In another useful embodiment, a method is provided in which the precipitation of EVOH dissolved in the solvent mixture in step d) is performed by cooling the solvent mixture to a temperature in the range 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, under ambient pressure. In another embodiment, step d) may further include adding a poor solvent such as water to the solvent mixture, which, according to yet another embodiment, is cooled to a temperature below the contact temperature of step b) before, during, or after the addition of the poor solvent such as water. It is not excluded that water be added as an aqueous solution or as a mixture of alcohol and water.

[0036] In a further improved embodiment, the added water (or aqueous solution) has 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 under ambient pressure. It has been found that adding relatively low-temperature water to the solvent mixture significantly improves precipitation and subsequent separation of the precipitated EVOH.

[0037] To improve the reusability of spent alcohol-based solvents, one embodiment of the method is provided, in which the added water is separated from the spent alcohol-based solvent obtained in step e), and then optionally the alcohol-based solvent is reused according to step f). Since the boiling point of the added water is generally different from (and lower than) the boiling point of the alcohol-based solvent used in the method in most embodiments, this separation can be carried out simply by, for example, evaporation of the water.

[0038] The amount of impurities that may remain in the polyester after step c) (e.g., small amounts of any other solvent other than the alcohol-based solvent, or colorants, such as titanium dioxide) can be further reduced by one embodiment of the method, in which the polyester obtained in step c) is washed with a suitable washing liquid, such as water or polyalcohol. Washing or rinsing can be performed in one step or repeated over multiple steps by supplying the polyester to a washing tank. In one embodiment, washing may include washing by friction. Washing can be important because small amounts of impurities in the polyester may cause discoloration in further downstream processes, such as the process of depolymerizing the polyester to its monomers. Washing the polyester may also be advantageous when combined with embodiments that further include a step of reusing the used alcohol-based solvent obtained in step e) at least partially in step b). Reusing the alcohol-based solvent may increase the EVOH concentration in the solvent mixture as described above, and some EVOH may remain in the polyester. Washing the polyester effectively removes EVOH completely or to a smaller amount.

[0039] The waste polymer multilayer article may contain several polymer materials. In one preferred embodiment, a method is provided in which the waste polymer material comprises 85-99% by weight of polyester, 1-15% by weight of EVOH, and optionally polyolefin, the total of which is 100% by weight. According to one embodiment of the present invention, the waste polymer material further comprises polyolefin, preferably as a separate layer in the polymer multilayer article. The polyolefin preferably includes polyethylene. This embodiment is advantageous in that the polyolefin can be separated from the polyester by density separation. A suitable process for achieving this is disclosed, for example, in International Publication No. 2021089809, the entirety of which is incorporated herein by reference.

[0040] In another embodiment of this method, the waste polymer material may further contain small amounts of functional additives, such as colorants, usually titanium dioxide. In such embodiments, the functional additives are dissolved in an alcohol-based solvent and separated from the polyester together with the alcohol-based solvent in step d).

[0041] The weight ratio of alcohol-based solvent to waste polymer material is variable over a wide range, but preferably greater than 1:1. In a preferred embodiment, the weight ratio of waste polymer material to alcohol-based solvent is in the range of 1:2 to 1:40, more preferably 1:5 to 1:35, more preferably 1:10 to 1:25, and most preferably 1:15 to 1:20. Lower ratios are more preferable because they result in less solvent being used.

[0042] Depolymerization of polyester According to a second aspect of the present invention, a preferred method further comprises the steps of: dispersing the polyester recovered after step c) by adding a reactive solvent to obtain a dispersion; adding a depolymerization catalyst to the dispersion; and depolymerizing the polyester under conditions for obtaining monomers and / or oligomers dissolved in the reactive solvent, wherein the reactive solvent includes an alcohol-based solvent, and optionally, the alcohol-based solvent is obtained in step e) of the present method.

[0043] The depolymerization reaction is called solvolysis because it takes place in a reactive solvent in which the polyester is dissolved. The reactive solvent is selected as a solvent for the polyester and / or for the reaction products obtained from the polyester by depolymerization. Such reactive solvents are known to those skilled in the art. In the context of this invention, the term “reactive solvent” also includes mixtures of solvents that are reactive and non-reactive. Depolymerization of polyester by solvolysis is usually carried out in alcoholic solvents, typically in alkanols, alkanediols, alkanetriols, or combinations thereof. Non-limiting examples of alkanols, alkanediols, and alkanetriols are methanol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene-15 glycol, 1,4-butanediol, 1,5-pentanediol, and glycerol. Ethylene glycol has been found suitable in terms of its physical properties (such as its boiling point of about 200°C). In the depolymerization of PET, using ethylene glycol yields bis(2-hydroxyethyl) terephthalate (BHET) as the main depolymerization product. Dimers, trimers, and even oligomers can also be obtained.

[0044] For depolymerization, waste polymer material, which in this case substantially contains polyester, is preferably charged into the reaction vessel in a weight ratio with a reactive alcohol-based solvent in the range of 2:1 to 1:10, more preferably in the range of 1:2 to 1:9, and even more preferably in the range of 1:4 to 1:8. Note that a third polymer, such as polyolefin, polyamide, or polystyrene, may not be dissolved in step c) of this method and may still be present in the dispersion (also called the reaction mixture) in which depolymerization is carried out.

[0045] In one embodiment, waste polymer material, a reactive solvent, and optionally a catalyst are supplied to a reaction vessel. The reaction mixture is heated to a temperature of at least 150°C, during which the waste polymer material is heated as part of the reaction mixture, and any third polymer other than polyester may melt or remain substantially solid. This heating step serves to dissolve at least some of the polyester present in the waste material into the reactive solvent in order to initiate the depolymerization reaction. The heating step may cause any third polymer other than the polyester polymer to melt. In particular, polyolefins, such as polypropylene and polyethylene, typically have melting temperatures in the range of 100-140°C. Other third polymers, such as certain grades of polyamide or polystyrene, may partially dissolve or remain substantially solid. The third polymer can be removed from the reaction mixture by density separation.

[0046] Furthermore, waste polymer materials may contain relatively small amounts of chlorine-containing polymers. In fact, polyvinyl chloride (PVC) is sometimes used in multilayer articles for its mechanical stability and as a gas barrier, and polyvinylidene chloride (PVDC) may function as an oxygen and moisture barrier. The inventors have found that when the waste polymer material contains chlorine-containing polymers, it is advantageous to add a base such as sodium hydroxide (NaOH) in at least one of steps a) to e) of this method and / or in any depolymerization step.

[0047] Glycolysis is one preferred method of depolymerization, preferably using a catalyst. Typically, the preferred use of ethylene glycol may result in a reaction mixture containing at least one monomer, including bis(2-hydroxyethyl) terephthalate (BHET). The polymer concentration in the reaction mixture or dispersion before depolymerization is usually 1 to 30% by weight of the total weight of the reaction mixture, although concentrations outside this range may also be possible. An example of a suitable depolymerization by glycolysis is known from International Publication No. 2016 / 105200 in the name of the present applicant. According to this process, the terephthalate polymer is depolymerized by glycolysis in the presence of a specially designed catalyst. Water is added at the end of the depolymerization process, causing phase separation. This allows the first phase containing the BHET monomer to be separated from the second phase containing the catalyst, oligomer, and additives. The first phase may contain impurities in dissolved form and as dispersed particles. The BHET monomer can then be obtained by crystallization.

[0048] High purity is required for depolymerized raw materials to be reused in repolymerization. As is well known, any impurities can affect the subsequent polymerization reaction from the raw materials. Furthermore, since terephthalate polymers are used in medical applications as well as food applications, strict regulations are applied to prevent health problems. The present invention makes it possible to achieve such high purity.

[0049] The reaction mixture can be heated to a suitable temperature, which is 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 in the range of 160°C to 250°C. More preferably, the depolymerization step may include forming monomers at a temperature in the range of 185°C to 225°C. A suitable pressure in the depolymerization reactor is 1 to 5 bar, preferably higher than 1.0 bar, and more preferably less than 3.0 bar.

[0050] The average residence time of the polyester, as well as its monomers, dimers, and oligomers during the depolymerization step may be in the range of 30 seconds to 3 hours, or longer. The temperature can be lowered to 160°C or below to stop the depolymerization reaction and / or deactivate the catalyst, but it is preferable that it does not fall below 85°C.

[0051] Catalyst system The present invention can be carried out using any catalyst suitable for the purpose. Suitable catalysts include heterogeneous catalysts. In this case, in the depolymerization method according to one embodiment, the catalyst forms a dispersion in the reaction mixture. Other suitable catalysts include homogeneous catalysts. Homogeneous catalysts do not form a dispersion, but are usually dissolved in the reaction mixture.

[0052] Several possible heterogeneous depolymerization catalysts are based on ferromagnetic and / or ferrimagnetic materials. Antiferromagnetic materials, synthetic magnetic materials, paramagnetic materials, and superparamagnetic materials, such as those comprising at least one of Fe, Co, Ni, Gd, Dy, Mn, Nd, and Sm, and preferably at least one of O, B, C, and N, such as iron oxide, ferrite, magnetite, hematite, and maghemite, can also be used. Catalyst particles may include nanoparticles.

[0053] The catalyst particles catalyze the depolymerization reaction. In this depolymerization reaction, individual molecules of the condensed polymer are released from the solid polymer by the catalytic reaction. This solid polymer is, for example, semi-crystalline. As a result of this release, the polymer material is dispersed in the reactive solvent and / or the individual polymer molecules dissolve in the reactive solvent. It is believed that such dispersion or dissolution further promotes the depolymerization from the polymer to monomers and oligomers.

[0054] One suitable class of catalysts is transition metals, either in metallic or ionic form. Ionic forms include free ions in solution and in ionic or covalent bonds. Ionic bonds are formed when one atom donates one or more electrons to another. Covalent bonds are formed by interatomic bonds resulting from the sharing of one electron pair between two atoms. Transition metals can be selected from the first series of transition metals, also known as 3d orbital transition metals. More specifically, transition metals can be selected from iron, nickel, and cobalt. However, iron and nickel particles are most preferred because cobalt is undesirable from a health perspective, and iron and nickel particles can be formed in their pure form. Furthermore, alloys of individual transition metals can be used.

[0055] If the catalyst particles are made of metal, they may have an oxidized surface, which may further enhance the catalytic action. This oxidized surface can occur naturally through contact with air or water, or it may be intentionally created.

[0056] The most preferred method is the use of iron-containing particles. In addition to being magnetic, iron-containing particles catalyze the depolymerization of PET, and it has been found that the conversion rate to monomers can reach 70-90% within a maximum allowable reaction time of 6 hours, although this depends on the amount of catalyst charged and other process factors such as the PET / solvent ratio.

[0057] Non-porous metal particles, particularly transition metal particles, can be adequately prepared by the thermal decomposition of carbonyl complexes such as pentacarbonyl iron and tetracarbonyl nickel. Alternatively, iron oxide and nickel oxide can be prepared by exposing the metal to oxygen at high temperatures, such as above 400°C. Non-porous particles may be more suitable than porous particles because they may be exposed to alcohol less, and therefore less corroded, allowing them to be reused for catalytic activity more frequently. Furthermore, in the case of surface oxidation, the limited surface area may result in a reduction in the amount of metal ions, and consequently, a decrease in the level of ions present in the product stream as leached contaminants that need to be removed from the product stream.

[0058] Another class of suitable catalysts includes particles based on alkaline earth elements selected from beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba), and their oxides. A preferred alkaline earth metal oxide is magnesium oxide (MgO). Other suitable metals, but not limited to these, include titanium (Ti), zirconium (Zr), manganese (Mn), zinc (Zn), aluminum (Al), germanium (Ge), antimony (Sb), and their oxides and alloys. Noble metals such as palladium (Pd) and platinum (Pt) are also suitable. MgO and ZnO catalyze the depolymerization of PET, and conversion rates to monomers have been found to reach 70-90% within the allowable reaction time, although this depends on the amount of catalyst charged and other process factors such as the PET / solvent ratio. Suitable hydrotalcite-based catalysts are also possible.

[0059] Preferably, catalyst particles are selected so as to be substantially insoluble in (alcohol-based) reactive solvents even at temperatures exceeding 100°C. Oxides that tend to readily dissolve in alcohols such as ethylene glycol at high temperatures, such as amorphous SiO2, are unsuitable.

[0060] The preferred concentration of the catalyst is 1% by weight or less based on the amount of PET. Good results were also obtained when the charged amount of the catalyst was less than 0.2% by weight, and further less than 0.1% by weight, based on the amount of PET. Thus, the small charged amount of the catalyst is very beneficial, and the method according to the present invention makes it possible to increase the recovery amount of the nanoparticle catalyst.

[0061] The non-porous particles according to the present invention suitably have a surface area of less than 10 m 2 / g, more preferably at most 5 m 2 / g, even more preferably at most 1 m 2 / g. In another embodiment, the surface area is at least 3 m 2 / g. The porosity is suitably less than 10 -2 cm 3 / g, or for example at most 10 -3 cm 3 / g. Porous particles can also be used. Porous particles generally exhibit a larger surface area.

[0062] In the depolymerization method according to one embodiment, the catalyst forms a dispersion in the reaction mixture during mixing and / or depolymerization. A particularly preferred heterogeneous catalyst that can be used in the present invention is a catalyst complex comprising catalyst particles and a catalyst substance bound to the catalyst particles and connected to the catalyst particles via, for example, a linking group. The catalyst substance includes an ionic liquid containing a cationic moiety having a positive charge and an anionic moiety having a negative charge. The catalyst particles are preferably nanoparticles, more preferably magnetic particles, and the magnetic particles are preferably used in a method in which the recovery step of the catalyst is performed using the magnetic attraction between a magnet and the particles. The catalyst particles themselves may also exhibit catalytic activity.

[0063] The catalyst complex (ABC) comprises three distinguishable elements: (nano)particles (A), a bridging portion (B) containing linking groups chemically, for example, by covalent bonding, or physically, for example, by adsorption, to the particles, and a catalyst material (C) bonded to the particles (A), for example, by chemical bonding to the linking groups, for example, by covalent bonding. It is preferable that the linking groups do not completely cover the surface of the nanoparticles, as in core-shell particles. In the following disclosure, the catalyst may also be referred to as MF.

[0064] The particles of the catalyst composite described in the claims are preferably based on a ferromagnetic and / or ferrimagnetic material. Antiferromagnetic materials, synthetic magnetic materials, paramagnetic materials, and superparamagnetic materials, such as materials containing at least one of Fe, Co, Ni, Gd, Dy, Mn, Nd, and Sm, and preferably at least one of O, B, C, and N, such as iron oxide, ferrite, hematite (Fe2O3), magnetite (Fe3O4), and maghemite (Fe2O3, γ-Fe2O3), are also usable. From a cost standpoint, relatively inexpensive particles, such as iron (Fe)-containing particles, are preferred even when the catalyst composite is recovered completely or largely. A further advantage of iron particles or iron oxide particles is that they have a very high saturation magnetization, allowing them to be easily separated by a magnetic separator. More importantly, iron oxide (nano) particles have a favorable effect on the decomposition reaction. Iron oxides may further contain additional elements such as cobalt and / or manganese, for example, as in CoFe2O4.

[0065] The present invention allows for a protective coating to be applied to catalyst particles used in a catalyst complex, at least partially. This coating can further stabilize the catalyst by maintaining the particles in a suspended state. Therefore, at least a portion of the surface of the catalyst particles can be coated with materials such as polyethyleneimine (PEI), polyethylene glycol (PEG), silicone oil, fatty acids (e.g., oleic acid or stearic acid), silane, mineral oil, amino acids, polyacrylic acid, or polyvinylpyrrolidone (PVP). Carbon can also be used as a coating material. The coating can be removed before or during the catalytic reaction. Methods for removing the coating may include, for example, a separate solvent washing step before use in a reactor, or combustion in air. However, removal of the coating is not essential.

[0066] Preferably, catalyst particles are selected so as to be substantially insoluble in (alcohol-based) reactive solvents even at temperatures exceeding 100°C. Oxides that tend to readily dissolve in alcohols such as ethylene glycol at high temperatures, such as amorphous SiO2, are unsuitable.

[0067] It was found that the catalyst particles are preferably small enough so that the catalyst complex functions as a catalyst, breaking down the terephthalate polymer into smaller units, and the yield of these smaller units, particularly their monomers, is commercially viable. Furthermore, it was found that the nanoparticles are preferably large enough so that the catalyst complex can be reused by recovery. Suitable catalyst particles have an average diameter greater than 1 μm, ranging from 3 μm to larger. Suitable nanoparticles have an average diameter of 2 to 500 nm, and even larger, ranging from 1 μm.

[0068] In one example of this catalyst composite, 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 nm to 10 nm. For example, in terms of the yield and recovery of the catalyst composite, particles of a fairly small size of 5 nm to 10 nm have been found to be optimal. Note that the term "size" refers to the average diameter of the particles, and the actual diameter of the particles may vary somewhat depending on their properties. Furthermore, aggregates may form, for example, in solution. These aggregates typically have a size in the range of 50 nm to 200 nm, for example, 80 nm to 150 nm, for example, about 100 nm.

[0069] 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 complex method, usually applied to smaller particle sizes but equally applicable to larger sizes, involves taking representative electron microscope images and measuring the individual particle sizes on these images. The number mean can be used as the average particle size. Approximately, the size with the maximum number of particles, or the median size, can be used as the average.

[0070] This catalyst material comprises at least two parts. The first part relates to a positively charged part (cation). The second part relates to a negatively charged part (anion), which is usually a salt complex part. The negative and positive charges are usually balanced. The positively and negatively charged parts have been found to exhibit synergistic and enhancing effects in terms of conversion and selectivity in the decomposition process of waste terephthalate polymers.

[0071] The positively charged portion (cation) may be aromatic, aliphatic, and / or heterocyclic. The cationic portion may be aliphatic and preferably selected from guanidinium (carbamimidylazanium), ammonium, phosphonium, and sulfonium. The non-aromatic or aromatic heterocyclic portion preferably includes a heterocycle having at least one, preferably at least two heteroatoms. The heterocycle may have five or six atoms, preferably five atoms. The positively charged portion may be an aromatic portion, and the aromatic portion preferably stabilizes the positive charge. Typically, the cationic portion has a delocalized positive charge. The heteroatoms may 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, isoquinols, and viologen-type compounds (e.g., those having two bonded pyridine ring structures). Particularly preferred is the imidazole structure, which generates the imidazolium ion. Particularly suitable cationic moieties having N as a heteroatom include imidazolium (a five-membered ring with two Ns), piperidinium (a six-membered ring with one N), pyrrolidinium (a five-membered ring with one N), and pyridinium (a six-membered ring with one N). A preferred imidazolium cationic moiety is butylmethylimidazolium (bmim). + ) and dialkylimidazolium are included. Other suitable cationic moieties include, but are not limited to, triazolium (a five-membered ring with three nitrogen atoms), thiazolidinium (a five-membered ring with nitrogen and sulfur atoms), and (iso)quinolinium (a two-membered six-membered ring with nitrogen atoms (naphthalene)).

[0072] In a preferred method, the cationic moiety of the catalyst is selected from at least one of imidazolium, piperidinium, pyridinium, pyrrolidinium, sulfonium, ammonium, and phosphonium groups.

[0073] The aforementioned cationic moiety may have one or more substituents, which are preferably selected from the alkyl moiety. In certain examples, the aforementioned alkyl moiety has a length of C1 to C6, for example, C2 to C4. In certain examples, the aforementioned imidazolium group has two substituents R1 and R2, each bonded to one of two nitrogen atoms; the aforementioned piperidinium group has two substituents R1 and R2 bonded to its nitrogen atom; the aforementioned pyridinium group has two substituents R1 and R2, one of which is bonded to its nitrogen atom; the aforementioned pyrrolidinium group has two substituents R1 and R2 bonded to its nitrogen atom; the aforementioned sulfonium group has three substituents R1, R2, and R3 bonded to its sulfur atom; the aforementioned ammonium group has four substituents R1, R2, R3, and R4 bonded to its nitrogen atom; and the aforementioned phosphonium group has four substituents R1, R2, R3, and R4 bonded to its phosphorus atom.

[0074] The negatively charged portion (anion) may be associated with anionic complexes, but it may also be associated with simple ions such as halide ions. This may be associated with the salt complex portion, preferably Fe 3+ , Al 3+ Ca 2+ Zn 2+ Cu 2+ Positively charged metal ions such as divalent or trivalent, and for example, Cl - F - , Br - This may involve a metal salt complex moiety that has a negatively charged counterion, such as a halide ion. For example, the salt may be Fe 3+ The salt complex moiety contains, for example, a halide type, for example, FeCl4 - Furthermore, counterions that do not involve metal salt complexes, such as the halide ions which are known in themselves, can also be used.

[0075] The linking group may include a bridging portion for connecting the catalyst material to the catalyst particles. The catalyst material and the catalyst particles are combined by a bridging portion that connects the catalyst material to the catalyst particles. This connection usually involves a physical or chemical bond between the bridging portion and the combination of the catalyst material on the one hand and the catalyst particles on the other. In particular, multiple bridging portions are connected or bonded to the surface region of the catalyst particles. Suitable bridging portions include weak organic acids, silyl-containing groups, and silanols. More specifically, the bridging portion includes a functional group for bonding to the oxide of the particle and a second linking group for bonding to the catalyst material. The functional group is, for example, a carboxylic acid, alcohol, silicate 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 that connects to the cationic portion, and the alkyl chain is usually C l The compound is ~C6, for example, propyl and ethyl. The linking group can be attached to a cationic moiety, such as a preferred imidazolium moiety. In the linked state, the BC complex includes imidazolium having two alkyl groups, for example, butylmethylimidazolium (bmim+) or ethylmethylimidazolium.

[0076] The cross-linking portion is appropriately provided as a reactant in which the linking group is functionalized for chemical reaction with the catalyst. For example, appropriate functionalization of the linking group is provided as a substituted alkyl halide. For example, suitable reactants include 3-chloropropyltrialkoxysilane and 3-bromopropyltrialkoxysilane. The alkoxy group is preferably ethoxy, but methoxy and propoxy groups are not excluded. Trialkoxysilanes are preferred, but dialkyldialkoxysilanes and trialkylmonalkoxysilanes are not excluded. In the case of dialkyldialkoxysilanes and trialkylmonalkoxysilanes, the alkyl group is preferably a lower alkyl such as C1-C4. In that case, at least one alkyl group is functionalized with a halogen, for example, as described above.

[0077] The aforementioned reactants then react with a catalyst. Preferably, this reaction generates a positive charge on the cationic moiety, more specifically on the heteroatom, but mainly in a delocalized form, preferably on the heterocyclic cationic moiety. This reaction is, for example, a reaction between a (substituted) alkyl halide and a heteroatom, such as a nitrogen-containing cationic moiety, which results in a bond between the heteroatom and the alkyl group. As a result, the heteroatom becomes positively charged and the halide becomes negatively charged. The negatively charged halide can then be strengthened by the addition of a Lewis acid to form a metal salt complex. One example is the reaction of a chloride to FeCl4 - One example is the transformation to [this].

[0078] According to the present invention, the crosslinking portion and the catalyst material bonded thereto are 5 × 10 -6 ~0.1, preferably 1 × 10 -5 ~0.01, futuristically 2 × 10 -5 ~10 -3 For example, 4 x 10 -5 ~10 -4 It is supplied in the amount (moles of cross-linking portion / grams of magnetic particles). From the viewpoint of efficient recovery of the catalyst complex, it is preferable to have a relatively large amount available for use, but from the viewpoint of the amount of catalyst and its cost, a somewhat smaller amount may be preferable.

[0079] Furthermore, homogeneous catalysts are more difficult to recover from the product flow. In some cases, recovery of such catalysts is even impossible. However, it may be possible to recover homogeneous catalysts before crystallization of, for example, BHET monomers. However, this requires specific measures to overcome the problems. Therefore, in embodiments of the method of the present invention, the use of heterogeneous catalysts is preferred.

[0080] In preferred embodiments, the catalyst can be used in a proportion of 0.001 to 20% by weight, more preferably 0.01 to 10% by weight, and most preferably 0.01 to 5% by weight relative to the weight of the polymer.

[0081] conclusion The present invention provides a method for efficiently recovering EVOH and optionally other polymers such as polyolefins from waste multilayer polymer materials containing polyester such as PET and EVOH. This method is relatively robust, substantially unaffected by the presence of additives and impurities, and preferably uses only one solvent. Thus, this method is particularly suitable for waste multilayer polymer articles, such as MLT. Furthermore, the remaining polyester is ready for further processing, particularly depolymerization, because residual substances, such as polymers, decomposed polymers, and solvents, are effectively removed before such further processing.

[0082] In some embodiments, the present invention can also provide a BHET monomer of relatively high purity after depolymerization. In the context of the present invention, high purity may mean that there is a relatively small amount of impurities and / or a relatively small amount of EVOH polymer present in the BHET monomer after pretreatment and depolymerization.

[0083] The present invention will be further described by the following embodiments, which are illustrative and descriptive and do not limit the scope of the invention. It will be apparent to those skilled in the art that many modifications, whether obvious or not, can be conceived that fall within the scope of protection defined by the appended claims. [Brief explanation of the drawing]

[0084] [Figure 1] This figure schematically shows the particle size distribution of EVOH dissolved in ethylene glycol at different EVOH concentrations. [Figure 2] This figure schematically shows the particle size distribution of EVOH dissolved in ethylene glycol at different EVOH concentrations after settling for two days without stirring. [Figure 3] This figure schematically shows the particle size distribution of dissolved EVOH before and after adding water during precipitation, when the EVOH concentration in ethylene glycol is 25 mg / mL. [Examples]

[0085] Materials and methods Initial waste materials The laminated waste material (MLT) sample contained a PET outer layer, a PE outer layer, and an EVOH intermittent layer. The average thickness of the PET layer was 469 μm, the average thickness of the PE layer was 47 μm, and the average thickness of the EVOH layer was 8 μm, resulting in an average total thickness of 524 μm for this laminate. As a result, the composition of the MLT was as follows: PET 92.5 wt%, EVOH 1.3 wt%, and PE 6.2 wt%. The PET layer is intended to provide rigidity to the MLT, the PE is intended to provide a moisture barrier, and the EVOH is intended to provide an oxygen barrier to the MLT. During recycling, waste MLT is usually shredded in mechanical recycling equipment. This recycling equipment generates fragments and flakes of the cut material. Some fine fragments may also be present. Shredding does not usually promote the separation (delamination) of these separate layers because these separate layers tend to adhere to each other relatively strongly.

[0086] Additional materials used Ethylene glycol (EG), used as an alcohol-based solvent, was obtained from Sigma-Aldrich.

[0087] Poly(vinyl alcohol-co-ethylene) with CAS registry number 25067-34-9 was obtained from Sigma Aldrich.

[0088] A catalyst complex (also called an MF catalyst) comprising iron particles (A), a cross-linking portion (B) containing linking groups connected to the particles, and a catalytic substance (C) bound to the particles (A) was used in the depolymerization experiment.

[0089] Experiment on the solubility of EVOH To test the solubility of EVOH in EG, several mixtures of EG and EVOH at different concentrations were prepared. 200 mL, or 222 g, of EG was added to a 500 mL beaker. Concentrations of 0.5, 1, 5, 15, 25, or 50 mg / mL were produced by adding 100, 200, 1000, 3000, 5000, or 10000 mg of EVOH to the EG, depending on the desired concentration. These reaction mixtures were placed on a heater and heated to approximately 150°C while stirring with a magnetic stirrer bar. The EVOH particles slowly dissolved and became viscous. After 2-3 hours, substantially all of the EVOH particles had dissolved in the EG. The heating temperature of the heating plate should not exceed approximately 250°C to prevent thermal degradation of the EVOH particles as they adhere to the bottom of the beaker.

[0090] Mastersizer Measurement Mastersizer analysis was performed using a Malvern Mastersizer 3000 to measure the particle size of EVOH precipitated in the mixture. To prepare for the measurement, the measurement cell and circulation system were washed with EG and water. Then, 100 mL of EG was added to the circulation system and stirred at 2400 rpm for several minutes until all bubbles were removed. A background measurement was then performed to prepare the system for measurement. Once prepared, the EG / EVOH solution was added to the circulation system until an appropriate light shielding rate (approximately 8-12%) was achieved. The amount of sample added ranged from a few drops to a few mL, depending on the concentration of the sample. The particle size distribution of EVOH particles was obtained by performing measurements using standard settings (five measurements with blue and red lasers). After the measurement, the system was thoroughly washed with water and EG.

[0091] experiment Example 1: Effect of EVOH on the reaction kinetics of PET depolymerization In a 250 ml round-bottom flask, 125 g of EG, 16.7 g of PET shredded flakes obtained from the raw material of clear PET bottles, and 0.017 g of MF catalyst were added. Thus, a depolymerization reaction mixture was obtained in the ratio of 0.01 MF:1 PET:7.5 EG. To this reaction mixture, EVOH copolymer was added to the round-bottom flask at an amount of 10% by weight (relative to the amount of PET), i.e., 1.67 g of EVOH. Note that this amount may be much larger than the amount typically used in MLT, for example. EVOH is a copolymer in which the alcohol and ethylene parts have different ratios, as shown below. [ka]

[0092] This ratio affects the properties; generally, lower ethylene content may result in higher barrier properties, while generally, higher ethylene content is advantageous for extrusion molding at low temperatures. Although this invention is not limited to a specific type of EVOH, in this example, EVOH with y = 32 mol% was used. This grade is considered to be commonly used in MLT as well.

[0093] Next, the round-bottom flask was placed in a depolymerization apparatus equipped with a reflux condenser and heated to a reflux temperature of 197°C. The reaction mixture was stirred at 300 rpm and reacted for 4 hours. After the depolymerization of PET, the reaction mixture was cooled to 120-140°C and the residue was collected by pouring it into a tea strainer. Boiling water was added in a 50 / 50 wt% / wt% ratio, and the reaction mixture was centrifuged to remove at least some of the MF catalyst. Weighing of the precipitate revealed that not all EVOH was separated by centrifugation.

[0094] These results suggest that EVOH does not affect the PET depolymerization kinetics using MF catalysts. Furthermore, EVOH readily dissolved in high-temperature EG.

[0095] Because EVOH exhibits excellent solubility in EG, it may appear in further processes downstream of the glycolysis-based depolymerization process of PET, which is generally undesirable. This invention utilizes the observation that EVOH dissolves well in high-temperature EG to provide an efficient solution for removing EVOH from reaction mixtures. Details are provided below.

[0096] Example 2: Solubility of EVOH in EG and after addition of water EVOH is a polymer that partially dissolves and becomes sticky when in contact with water, which poses a serious problem in terms of process equipment fouling. Sticky behavior is generally undesirable in industrial processes because it can cause fouling in parts of the equipment used and may also lead to other problems. In Example 2, the solubility of EVOH in EG was experimented to predict the conditions under which EVOH can completely dissolve in EG. When substantially dissolved, stickiness is not a significant problem.

[0097] In Example 1, EVOH granules of the same type were dissolved in EG at a concentration of 10% by weight over different temperatures and durations. The results showed that EVOH dissolved relatively well in EG at temperatures above 120-130°C. When the EVOH / EG mixture was cooled to room temperature, a turbid mixture formed. This indicates that EVOH precipitated in this EVOH / EG mixture. In another experiment, demineralized water was added to the EVOH / EG mixture at a temperature of approximately 80-90°C in a 50 / 50% by weight ratio. After cooling this EVOH / EG mixture to room temperature, a turbid mixture formed. This indicates that EVOH precipitated in this mixture. These results confirm that EG is an excellent solvent for dissolving EVOH, while demineralized water acts as a poor solvent.

[0098] Example 3: Pretreatment of MLT consisting of PET / EVOH / PE The MLT disclosed in the "Initial Waste Material" section above was cut into flakes, and 5g of these flakes were added to 100ml of EG and treated for 4 hours with slow stirring at different temperatures (130°C, 150°C, and 170°C). Higher temperatures were not tested for pretreatment because PET may begin to depolymerize under those conditions. In one experiment, it was confirmed that the formed BHET was only 0.12% by weight after 5 hours of EVOH extraction at 170°C.

[0099] Delamination of the MLT flakes was observed at 130°C, and its degree increased in temperature tests at 150°C and 170°C. At all temperatures, clumps of PE formed and tended to float to the top of the mixture. Some PE was observed to accumulate around the stirrer. Since PE did not dissolve substantially in EG and tended to float to the top of the mixture due to its lower density, it was separated from the mixture.

[0100] When the EVOH / EG mixture was cooled to room temperature, a turbid mixture was formed. This indicates that EVOH precipitated in the mixture. In another experiment, water was added to the EVOH / EG mixture at a temperature of approximately 80-90°C in a 50 / 50 wt% ratio. After cooling to room temperature, a turbid mixture was obtained. These results confirm that EG is an excellent solvent for dissolving EVOH, while water acts as a poor solvent. In the presence of water, precipitation of EVOH was observed even after heating to 100°C.

[0101] PET flakes were obtained by solid-liquid separation (filtration) of the EVOH / PE / PET / EG mixture. The separated PET fraction, pretreated at 170°C, was subjected to DSC and FTIR measurements. The results showed that no EVOH remained, and only a small amount of PE remained on the curled PET flakes. The PE was observed floating on top of the EVOH / PE / PET / EG mixture. Since EVOH was not detected in the DSC and FTIR measurements, it was concluded that EVOH was substantially completely dissolved in EG.

[0102] Finally, it was found that some MLT flake samples warped significantly during pretreatment. This warping can prevent the PE from completely separating from the PET and EVOH layers. However, those skilled in the art can control the degree of warping to below a threshold by adjusting parameters such as flake type (different thicknesses), heating rate, flake size, stirring rate, and starting temperature through routine experiments.

[0103] Example 4: Recovery of EVOH from EG The method according to the present invention results in the precipitation of EVOH in the reaction mixture. Step e) of this method includes separating the precipitated EVOH (or vinyl alcohol copolymer in general) from EG (or solvent mixture in general) to obtain EVOH and spent EG solvent. To make the process economically viable, it is preferable to purify the EVOH-rich EG after extraction. In that case, the spent alcohol-based solvent can actually be reused in step b) of the method according to the present invention, at least partially.

[0104] The EG / EVOH mixture becomes turbid after cooling to room temperature, and this process is found to become even more pronounced with the addition of water. Therefore, inducing precipitation and / or aggregation, followed by size-based separation, is a preferred method for separation. This is preferable to the addition of water because EVOH can be precipitated in pure EG.

[0105] To investigate the temperature at which EVOH begins to dissolve in EG, or at which EVOH in EG begins to cause turbidity, various EG solutions with different concentrations of EVOH were prepared (concentrations of 1, 5, 10, 15, 20, and 25 mg / ml were used). After dissolving EVOH in EG at 150°C, the mixture was cooled in a first cycle, and the temperature at which turbidity was observed was recorded. The turbid mixture was heated again and became substantially clear at approximately 80°C. A second cooling cycle was then performed, and the temperature at which turbidity occurred was observed again. From these results, it was found that turbidity was observed at similar temperatures during cooling for all tested concentrations of EVOH in EG. From these experiments, it can also be concluded that the cooling temperature should preferably be below 30°C for significant precipitation to occur.

[0106] Therefore, separation of EVOH particles from an EVOH / EG mixture based on particle size is preferably carried out at temperatures below this level.

[0107] The particle size was measured using the Mastersizer described above. First, three concentrations were prepared as starting points for the Mastersizer. The three samples contained 1 mg / mL, 12.5 mg / mL, and 25 mg / mL of EVOH in EG, respectively. The initial particle size distributions for the three samples are shown in Figure 1.

[0108] Sedimentation of EVOH particles was observed in all samples, but was particularly noticeable in the 12.5 mg / mL and 25 mg / mL samples after being left undisturbed for two days. This is shown in Figure 2.

[0109] The sample was centrifuged at 4000 rpm for 3 minutes, and the precipitate was separated at concentrations of 12.5 mg / ml and 25 mg / ml. The sample was then centrifuged again under the same conditions after adding water (50 / 50 wt%). Figure 3 shows that the observed particle size increased with the addition of water. This result was also confirmed by optical spectroscopy.

[0110] The precipitated EVOH / EG solution was filtered using a Buchner apparatus with a 12-15 μm paper filter, then washed several times with water and dried. Filtration proved effective as a solid-liquid separation method, as evidenced by the easy formation of a cake on the filter. The resulting filtrate appeared clear. It was observed that, in addition to the concentration and time of EVOH precipitation, the cooling rate could also affect the precipitation.

[0111] Filtration efficiency test The filtration efficiency of 25 mg / mL EVOH in EG solution was measured using four different cooling methods. The amount of liquid poured into the filter and the amount of solid matter remaining on the filter after filtration were weighed. The results are shown in Table 1 below.

[0112] [Table 1]

[0113] Filtration efficiency reached approximately 75% to over 90%. It was observed that the highest filtration efficiency was achieved when the EVOH / EG solution was rapidly cooled, or when stirring was omitted or limited.

[0114] In another experiment, a solution containing 25 mg / mL of EVOH in EG was divided into two parts. One part was subjected to centrifugation and filtration, while the other part was filtered immediately. The solid material obtained after centrifugation and filtration was 85%, while the solid material obtained after immediate filtration was 98%. From this experiment, it is considered that filtration is more efficient than centrifugation, or a combination of centrifugation and filtration.

[0115] The present invention has been described with reference to the specific embodiments discussed above. It will be understood that these embodiments can take various modifications and alternative forms that are well known to those skilled in the art.

Claims

1. A method for removing an ethylene vinyl alcohol copolymer from a waste polymer material containing a polyester and an ethylene vinyl alcohol copolymer, a) A step of providing waste polymer material in a reduced size form, b) The step of contacting the waste polymer material in the reduced size form with an alcohol-based solvent at a temperature of 90 to 170°C, thereby dissolving the ethylene vinyl alcohol copolymer in the alcohol-based solvent at least partially while keeping the polyester substantially unaffected; c) A step of separating the polyester from the solvent mixture containing the alcohol-based solvent and the vinyl alcohol copolymer dissolved in the solvent mixture by solid-liquid separation, d) A step of precipitating the vinyl alcohol copolymer dissolved in the solvent mixture, e) Separating the precipitated vinyl alcohol copolymer from the solvent mixture to obtain the vinyl alcohol copolymer and the used alcohol-based solvent. Methods that include...

2. The method according to claim 1, further comprising the step of reusing, at least partially, the used alcohol-based solvent obtained in step e) in step b).

3. The method according to claim 1 or 2, wherein the precipitation of the vinyl alcohol copolymer dissolved in the solvent mixture in step d) is further comprising cooling the solvent mixture to a temperature in the range 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, under ambient pressure.

4. The method according to claim 3, wherein water is added to the solvent mixture in step d).

5. The method according to claim 4, wherein the added water has a temperature of 1 to 100°C under ambient pressure, more preferably 5 to 50°C under ambient pressure, even more preferably 10 to 40°C, and most preferably 15 to 30°C at ambient temperature.

6. The method according to claim 4 or 5, wherein the added water is separated from the used alcohol-based solvent obtained in step e), and then the alcohol-based solvent is optionally reused according to step f).

7. The method according to any one of claims 1 to 6, wherein the method further comprises: dispersing the polyester by adding a reactive solvent to obtain a dispersion; adding a depolymerization catalyst to the dispersion; and depolymerizing the polyester under conditions for obtaining monomers and / or oligomers dissolved in the reactive solvent, the reactive solvent comprising an alcohol-based solvent, preferably comprising at least a portion of the used alcohol-based solvent.

8. The method according to any one of claims 1 to 7, wherein the waste polymer material further comprises a chlorine-containing polymer, and a base is added to the solvent mixture in at least one of steps a) to e) and / or to the reaction mixture during the depolymerization of the polyester.

9. The method according to any one of claims 1 to 8, wherein the waste polymer material comprises a multilayer tray, and the multilayer tray optionally further comprises a polyolefin.

10. The method according to claim 9, wherein the polyolefin is separated from the polyester by density separation.

11. The method according to any one of claims 1 to 10, wherein the waste polymer material further comprises a functional additive, such as a colorant, and the functional additive is dissolved in the alcohol-based solvent and separated from the polyester together with the alcohol-based solvent in step c).

12. The method according to any one of claims 1 to 11, wherein the alcohol-based solvent comprises a glycol, more preferably an alkylene glycol, and the glycol is selected from ethylene glycol (1,2-ethanediol), propylene glycol (1,3-propanediol), 1,4-butanediol, and 1,5-pentanediol.

13. The method according to any one of claims 1 to 12, wherein step b) is carried out at a temperature of 100°C to 165°C, preferably 110°C to 160°C, more preferably 120°C to 155°C, and most preferably 130°C to 150°C.

14. The method according to any one of claims 1 to 13, wherein the weight ratio of the alcohol-based solvent to the waste polymer material is in the range of 1:2 to 1:

40.

15. The method according to any one of claims 1 to 14, wherein the polyester comprises polyethylene terephthalate.

16. The method according to any one of claims 1 to 15, wherein the ethylene vinyl alcohol copolymer comprises EVOH having 20 to 50 mol% ethylene.

17. The method according to any one of claims 1 to 16, wherein the waste polymer material comprises 85 to 99% by weight of polyester, 1 to 15% by weight of ethylene vinyl alcohol copolymer, and optionally polyolefin and / or chlorine-containing polymer, the total of which is 100% by weight.

18. The method according to any one of claims 1 to 17, wherein step b) is carried out for 0.5 to 8 hours, more preferably for 2 to 6 hours.

19. The method according to any one of claims 7 to 18, 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.

20. The method according to any one of claims 7 to 19, wherein the catalyst for the depolymerization of the polyester includes functionalized magnetic particles functionalized in the catalyst portion.

21. The method according to any one of claims 1 to 20, wherein the polyester obtained in step c) is washed with a suitable cleaning liquid, for example, water or polyalcohol, and the washing includes washing by friction.

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