Methods for depolymerization of waste polymer materials and systems for their application

Abstract

A method for depolymerizing waste polymer material into monomers includes releasing at least a portion of the dye from the waste polymer material into an alcohol solvent, wherein the alcohol solvent is a polyol, without depolymerizing the condensate in the waste polymer material and under conditions preventing a reaction between at least one dye and the alcohol solvent. The alcohol solvent is added at a weight ratio of alcohol solvent to waste polymer material between 200:1 and 10:1. The waste polymer, which is then at least partially decolorized, is separated from the alcohol solvent, and the at least one dye is extracted from the alcohol solvent to regenerate the alcohol solvent, which is then sent to storage for reuse. The condensate is depolymerized in purified, recycled alcohol solvent using a catalyst. A reactor system for carrying out the method is also described.

Description

Technical Field

[0001] This invention relates to a method for depolymerizing waste polymer materials into monomers by catalytic depolymerization, the waste polymer materials comprising condensation polymers and at least one dye.

[0002] The present invention also relates to a system for implementing the depolymerization method. Background Technology

[0003] Such a method is known from WO2016 / 105198A1. According to this known method, colorants such as dyes and pigments are released from the condensation polymer after depolymerization. When water is added at the end of the depolymerization step, two phases are formed. The first phase is a liquid containing the monomer product in water and the alcohol solvent used in the depolymerization step. The second phase is a slurry containing the colorant, catalyst, any pigment, oligomers, and a portion of the alcohol solvent. The two phases can be separated from each other. Subsequently, the catalyst can be separated from the additives in a washing step using a detergent such as dichloromethane.

[0004] In other experiments, a color change has been observed that may occur during the depolymerization step. This change is usually obvious, indicating that the colorant has been transformed. It has been further observed that the transformed colorant cannot be removed from the first liquid phase containing the monomer product. The colorant then eventually enters the product during crystallization unless it is removed in an adsorption step, such as in an activated carbon tower, prior to crystallization. However, the used activated carbon tower would be disposed of as chemical waste, which is clearly undesirable from both an environmental and cost perspective.

[0005] According to WO2014 / 047620, it is also known to treat waste polymeric materials such as polyethylene terephthalate (PET) derived from bottles by applying decolorizing agents. Examples of decolorizing agents given are ethers such as 2-butoxyethanol and bleaching agents such as sodium hypochlorite. These agents are applied as aqueous solutions at temperatures of 82 to 100°C. According to the disclosure, these agents allow for the acquisition of completely decolorized PET material that can be recycled without any yellow residue. However, in the case of bis(2-hydroxyethyl) terephthalate monomers of PET to be recycled, the use of such aqueous solutions may lead to contamination. The erosion of the PET polymer by water leads to hydrolysis, which constitutes an alternative to glycolysis for obtaining BHET monomers. Furthermore, while decolorization may be effective for bottles that are reused without complete depolymerization, it is not suitable for waste polymeric materials derived from fabrics and other sources different from bottles. The pigment concentration in fabrics may be 2-10% by weight and is generally higher than the pigment concentration in bottles. Since colorants are typically organic compounds, they only dissolve successfully in aqueous solutions at limited color concentrations.

[0006] JP 2004217871A discloses a method for recovering components from colored raw materials that can be reused in the polymerization of polyesters using sodium carbonate catalysts. Typical recovered components include BHET or DMT. These methods do not aim to recover colorants as commercial products. In the disclosed methods, a solid-liquid separation step for separating residual alcohol solvents from the raw materials is essential. This is because the separation of colorants from the solvents used in prior art methods is incomplete. Known methods also require the application of a load to obtain the correct density for decolorization. Summary of the Invention

[0007] Therefore, one object of the present invention is to provide an improved depolymerization method in which the amount of colorant entering the monomer product stream is reduced, and which is particularly suitable for removing colorants from fabrics. The present invention can also be used to remove other impurities besides dyes, such as, for example, flame retardants.

[0008] Another object of the present invention is to provide a system that can implement the said depolymerization method.

[0009] According to a first aspect, the present invention provides a method for depolymerizing waste polymer material into monomers as described in claim 1, wherein the waste polymer material comprises a condensation polymer and at least one dye. The method includes the following steps:

[0010] - Without depolymerizing the condensate and under conditions that prevent a reaction between the dye and the alcohol solvent, at least a portion of the at least one dye is released from the waste polymer material into the alcohol solvent, wherein the alcohol solvent is a polyol;

[0011] - Separate at least partially decolorized waste polymer from the alcohol solvent;

[0012] - In the alcohol solvent separation step, the at least one dye is separated from the alcohol solvent in order to recover the alcohol solvent; and

[0013] - The condensate is depolymerized in an alcohol solvent by using a catalyst, wherein the alcohol solvent used in the depolymerization is substantially composed of the recovered alcohol solvent obtained in the alcohol solvent separation step.

[0014] Surprisingly, it was found that one or more dyes could be removed from the waste polymer material prior to depolymerization to prevent reaction between the dyes and the alcohol solvent. The alcohol solvent serves as a carrier for removing colorants such as dyes. The stream of alcohol solvent containing the colorant is specifically directed to an alcohol solvent separation stage to remove the colorant again from the alcohol solvent. Separation of one or more dyes from the alcohol solvent is essential for the ability to reuse the recovered and purified alcohol solvent for depolymerizing the condensate. In fact, colored pretreatment solvents such as ethylene glycol may slow down depolymerization to the extent that they become ineffective. In fact, colored dyes or other additives may interfere with the catalyst used in depolymerization. Some dyes, such as anthraquinone (AQ) dyes, may not affect depolymerization, while others, such as azo dyes, may.

[0015] Polycondensates such as polyesters are typically colored with disperse dyes. Such disperse dyes can include azo dyes and anthraquinone dyes. Other possible disperse dyes can include quinophtalene, amino ketones, methylene dyes, nitro / nitroso dyes, and coumarins. In addition to the dyes typically used for polyesters mentioned above, other types of dyes may be incorporated into the pretreatment solvent. This is because polyesters (e.g., in fabric form) can be combined with other materials such as cotton, nylon, and elastane. Dyes in the context of this invention may also include optical brighteners and / or fluorescent whitening agents. Among these, those based on piracene derivatives are preferred for use with, for example, polyester fabrics. An example of a suitable optical brightener is OB-1, given by the following formula:

[0016]

[0017] And blankophor B, given by the following formula:

[0018]

[0019] Waste polymers or waste polymer fabrics may also contain particulate brighteners such as titanium dioxide (TiO2). These are typically insoluble in solvents or only partially soluble in solvents, but do not appear to substantially affect depolymerization.

[0020] According to the present invention, decolorization is carried out for a sufficiently long period to avoid the need for a solid / liquid separation step, as described in JP2004217871A. In fact, a portion of the alcohol solvent in the colored polymer raw material is also the alcohol solvent required for the depolymerization of the condensation polymer itself.

[0021] Compared to the alcohol solvents used in the prior art, the method of the present invention is configured to use an increased amount of alcohol solvent to achieve a greater degree of substantially complete decolorization of the colored polymer feedstock. Preferably, "greater degree of decolorization" means achieving substantially complete decolorization of the colored polymer feedstock. At first glance, the increased amount of alcohol solvent may seem illogical due to the higher consumption of alcohol solvent. However, the benefits have proven to outweigh the drawbacks. The (almost) complete decolorization with the alcohol solvent overcomes the adverse effects of dyes and other impurities in the remaining processes. For example, the reaction kinetics of the depolymerization process using purified recycled alcohol solvent are substantially unaffected or remain at an acceptable level. Furthermore, separation devices such as activated carbon towers are less contaminated, and there is less risk of obtaining non-conforming monomers such as BHET. While there is a possibility of separating the dye from the resulting monomer mixture, this would result in the loss of monomers or other depolymerized components.

[0022] The steps of releasing at least a portion of at least one dye from the waste polymer material into the alcohol solvent and separating at least partially decolorized waste polymer from the alcohol solvent can be carried out in a first mixing chamber, in which the waste polymer material and the alcohol solvent are mixed, preferably under stirring, and at least one dye is released from the waste polymer material and absorbed by the alcohol solvent. The dye-depleted waste polymer material is then separated from the dye-containing alcohol solvent using a first separator.

[0023] However, according to a preferred embodiment of the invention, a method is provided in which the waste polymer material / alcohol solvent extraction and separation steps include extracting dye from the waste polymer material using an alcohol solvent, and separating the dye-depleted waste polymer material from the dye-containing alcohol solvent in the same method step. The extraction can be carried out in a continuous stirred tank reactor (CSTR) (also known as a mixed flow reactor (MFR)) or a series of such CSTRs. In another embodiment, the extraction can be carried out in an extractor, preferably using countercurrent and screw conveying. In the preferred countercurrent extraction, the polymer waste from which at least one dye is to be extracted is moved in one direction (optionally in sheet form) within an extraction device, such as a cylindrical extractor, via a conveying device (e.g., a conveying screw), where it comes into contact with an alcohol extraction solvent flowing countercurrently relative to the conveying direction. The further the starting material moves, the more concentrated the extract becomes.

[0024] In other preferred embodiments, the waste polymer material can be provided statically in the extraction device, and the alcohol solvent moves within or around the waste polymer material. In yet another embodiment, multiple extraction devices can be provided in series, wherein the alcohol solvent can be fed back from one extraction device to the previous extraction device. Such embodiments of the method include at least a first release step and a second release step, wherein the second release step uses the recovered alcohol solvent from the first release step. The number of release steps can be selected to obtain substantially discolored waste polymer, and can be at least 2, more preferably at least 3, even more preferably at least 4, even more preferably at least 5, even more preferably at least 6, and at most 10-15.

[0025] The alcohol solvent separation step, which separates the dye from the alcohol solvent prior to depolymerization, forms a seamless step with the remaining steps of the process. From the viewpoint of recovering dye from the polymer feedstock, performing alcohol separation in a single step is also advantageous. Such a step may involve a relatively large amount of alcohol solvent. However, the method of the present invention includes regenerating the alcohol solvent in purified form.

[0026] According to the present invention, a relatively large amount of alcohol solvent can be defined as parts by weight of alcohol solvent relative to the weight of the waste polymer material raw material. A suitable weight ratio of alcohol solvent to waste polymer material raw material can be between 200:1 and 10:1, more preferably between 150:1 and 20:1, even more preferably between 150:1 and 30:1, and even more preferably between 120:1 and 40:1. The same amount applies when recycled alcohol solvent is used in the release step. When recycled alcohol solvent is used in multiple subsequent release steps, the same amount applies in each release step.

[0027] Another advantage of using a relatively large amount of alcohol solvent is that impurities other than dyes can also be recovered from the waste polymer material raw materials and the purified alcohol solvent obtained by separation from the alcohol solvent. For example, flame retardants used in waste polymer materials can be substantially removed by the method and system of the present invention.

[0028] It should be understood that polyols such as glycols and glycerols have excellent performance as carriers: their polarity is higher than that of monohydric alcohols, which leads to reduced miscibility with many organic solvents such as halogenated alkanes and aromatic compounds (which are not entirely nonpolar). Secondly, while polyols can extract colorants such as dyes from condensation polymers, in alcohol solvent separation steps, such as through extraction steps, the dyes tend to transfer to solvents with lower polarity. Furthermore, polyols are not problematic from a health or environmental perspective. Therefore, the optional additional use of effective but more problematic solvents such as xylene or chloroform may be limited to certain steps, thereby reducing exposure and facilitating industrial operation. In a preferred embodiment of the method, the step of releasing at least a portion of at least one dye from the waste polymer is carried out without non-alcoholic or aromatic solvents such as xylene and / or chloroform. Another advantage is that the alcohol solvent selectively releases the dye rather than the pigment. Therefore, the pigment (if present) can be recovered in a later stage of the process. This makes it possible to separate the pigment and dye and promotes the regeneration of the alcohol solvent.

[0029] It should be noted that the recovered alcohol solvent can also be reused in other steps of the method besides the depolymerization step, such as in the release step.

[0030] Results have confirmed that, in the preferred embodiment, the method is characterized by an alcohol solvent separation step, such that the recovered alcohol solvent has a purity of at least 95% by weight, preferably at least 98% by weight, and more preferably at least 99% by weight. Suitable methods for achieving this are further disclosed below. The purity of the recovered alcohol solvent can be defined as the percentage by weight of the solvent relative to the total weight of the solvent and dye. Purity can be measured by weighing. Another suitable method is to determine the color of the recovered alcohol solvent using UV-vis.

[0031] The alcohol solvents used in the methods of this invention include polyols. Preferred embodiments include methods in which the alcohol solvent is a glycol, more preferably an alkylene glycol (or alkylene glycol), selected from ethylene glycol (1,2-ethylene glycol), propylene glycol (1,3-propanediol), 1,4-butanediol, and 1,5-pentanediol. Although each alkylene glycol solvent can be used to depolymerize any condensation polymer, ethylene glycol is particularly preferred when depolymerizing polyethylene terephthalate (PET) polymers, and 1,3-propanediol, for example, is particularly preferred when depolymerizing polypropylene terephthalate (PTT) polymers. When depolymerizing polybutylene terephthalate (PBT) polymers, alcohol solvents containing 1,4-butanediol may be particularly preferred.

[0032] In the alcohol solvent separation step, in principle, any separation method can be used to separate at least one dye from the alcohol solvent in order to recover the alcohol solvent. However, some methods have proven to be more efficient than others in separating at least one dye from the alcohol solvent. One of these methods may be preferred, depending on the solvent properties, such as, for example, the boiling point and solubility of the dye in the alcohol solvent. The separation methods according to the embodiments described below can also be combined in any combination.

[0033] According to one embodiment of the invention, a method is provided in which the alcohol solvent separation step includes the extraction of dye from the alcohol solvent. The extraction can be carried out in a continuous stirred tank reactor (CSTR) (also known as a mixed flow reactor (MFR)) or a series of such CSTRs. The extraction can also be carried out in an extractor, preferably using countercurrent and screw conveying. In the preferred countercurrent extraction, the material to be extracted moves in one direction (optionally in the form of a fine slurry of alcohol solvent) within a cylindrical extractor in contact with the extraction solvent. The farther the starting material moves, the more concentrated the extract becomes.

[0034] During the extraction process, a second solvent immiscible with the alcohol solvent can be used to extract the dye from the alcohol solvent. Suitable second solvents are selected from the group consisting of alkanes, cycloalkanes, esters, and ethers, excluding aromatics. Halogenated hydrocarbons can also be used, with preferred halogenated hydrocarbons including halogenated methane and ethane, and particularly chloromethane and ethane, such as dichloromethane, dichloroethane, and chloroform. Preferred ethers are immiscible with polyols and do not contain hydroxyl groups. More preferably, the ether is an aliphatic compound, such as methyl tert-butyl ether, diethyl ether, diisopropyl ether, tetrahydrofuran, and dimethyl ether. In a preferred embodiment, aromatic compounds such as toluene, xylene, benzene, ethylbenzene, chlorobenzene, and dichlorobenzene can also be used as the second solvent.

[0035] The extraction process is typically carried out at a temperature not exceeding the boiling point of the extraction solvent. Preferably, this temperature does not exceed 10°C below the boiling point of the extraction solvent to prevent or limit solvent evaporation. Extraction can be carried out at room temperature or even below room temperature.

[0036] Instead of using a single alcohol solvent, different solvents can be used in the first and second extraction processes. Depending on the choice of solvent and dye, the second extraction can be applied in exchange with the alcohol solvent and / or with the solvent from the first extraction. Using different extraction solvents facilitates the separation of different dyes from one another.

[0037] Another preferred embodiment provides a method in which the alcohol solvent separation step includes separating the dye from the alcohol solvent using a carbon adsorption device. The carbon adsorption device comprises activated carbon in the form of powdered or granular activated carbon. Typically, activated carbon is made in granular form as powder or fine particles with a size less than 1.0 mm (average diameter between 0.15 and 0.25 mm). Therefore, they represent a large surface area to volume ratio and a small diffusion distance. So-called PAC materials can also be used, and generally represent even finer materials composed of crushed or ground carbon particles. ASTM classifies particles passing through an 80-mesh sieve (0.177 mm) and smaller as PAC. Alternatively, granular activated carbon (GAC) can also be used. Compared to powdered activated carbon, GAC has a relatively large particle size and therefore presents a smaller external surface area. Extruded activated carbon (EAC), comprising powdered activated carbon fused together with a binder, can also be used. Polymer-coated activated carbon can also be used.

[0038] Another preferred embodiment provides a method in which the alcohol solvent separation step includes treating the alcohol solvent in a distillation stage to deliver a distillate stream containing an output concentration of at least 95% by weight of the alcohol solvent.

[0039] In a fourth preferred embodiment of the method, the alcohol solvent separation step includes a nanofiltration step to separate the dye from the alcohol solvent. Nanofiltration essentially comprises a membrane filtration method that uses a membrane with nanoscale pores passing through it. Typically, the pore size of nanofiltration membranes is in the range of 1-10 nanometers, which is smaller than the pore size used in microfiltration and ultrafiltration. The membranes used are primarily made of polymer films or metals such as aluminum. The pore area density can range from 1 to over 100 pores / cm². 2 Within the range.

[0040] To substantially prevent any reaction between the alcohol solvent and one or more dyes, the release step is preferably carried out at a temperature of at most 160°C, more preferably at most 150°C, and even more preferably between 100 and 140°C. It is not considered necessary to decrease or increase the pressure. The reactions to be prevented are particularly esterification or transesterification reactions. Such reactions readily occur and result in color changes, for example, from blue to red. In the research leading to this invention, it has been found that when modifications such as esterification (transesterification) are prevented, the dye can be more easily removed from the polyol alcohol solvent. This is desirable to ensure that the polyol alcohol solvent can be purified and recycled.

[0041] In one embodiment, the second release step is performed after dye release has occurred and the alcohol solvent has separated from the waste polymer material. This second release step is suitably carried out at a higher temperature than the first release step to allow for further release of dye that may be present in the waste polymer material rather than on its surface. Preferably, this second release step is carried out in the same chamber as the first release step. This is done by redispersing the solid waste into a (fresh) alcohol solvent. Furthermore, the outlet of the separator is suitably closed during redispersing. More preferably, a combined reaction chamber and separator are used. This can be achieved, for example, by utilizing a centrifuge chamber.

[0042] Although the release step of the present invention is carried out using a polyol alcohol solvent, it is not excluded that the polyol alcohol solvent provided to the chamber for the release step further contains water. In such a case, the weight ratio of polyol to water is suitably at least 1, preferably at least 3 (75 wt% polyol, 25 wt% water), more preferably at least 8 or 9 (90 wt% polyol, 10 wt% water) or 19 or higher (95 wt% polyol, 5 wt% water). It has been proven that water is a highly suitable means of cooling polyols after the release step. Such cooling is desirable to increase the range of extraction solvents. Although water may be undesirable for depolymerization considering the risk of hydrolysis (rather than glycolysis), the presence of water during the dye release step has not been found to be problematic.

[0043] Condensation polymers are more specifically polyesters. A preferred example of polyester is PET, but other polyesters are not excluded. Examples include polylactic acid, polybutylene terephthalate (PBT), polypropylene terephthalate (PTT), polyethylene naphthalate (PEN), vectran (a condensation polymer of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), polyethylene adipate (PEA), polyhydroxybutyrate (PHB), polyhydroxyalkanoate (PHA), polycaprolactone (PCL), polyglycolic acid (PGA), polyethylene furanoate (PEF), polybutylene furanoate (PBF), and poly(cyclohexanediol terephthalate) (PCT). In textile fibers, PET, PTT, and PEN are currently the most common polyester materials. PEF and PBF are more recently introduced polyesters that can be produced from biomaterials. PET is currently used more than any other polyester.

[0044] Besides polyesters, polyamides can also be a component of waste polymer materials. It has been found that polyols can be used as alcohol solvents to remove dyes from both polyamides and polyesters. Nylons such as nylon-6 and nylon-6,6 are well-known examples of polyamides.

[0045] In another embodiment, the polyamide is separated from the polyester after the dye release step. The separation of the polyamide, and more specifically, nylon-6, from other materials is carried out in a heating step at a temperature above 150°C, for example, 155°C in a polyol (such as glycerol or ethylene glycol), as is known itself from WO98 / 35998. Thus, nylon-6 can be removed as a separate stream by means of filtration or centrifugation after heating to the desired temperature. In one embodiment, the removal of nylon-6 material by dissolution can be carried out in the same chamber as the release step. While this is not considered strictly necessary, its advantage is that the waste solid material does not need to be transferred from one chamber to another before it decomposes into a processable liquid stream rather than a mixture of discrete solid parts and liquid. This is particularly relevant if the polymer waste material originates from fabrics. While polyester from packaging materials (such as bottles) is typically pre-processed into sheets of limited dimensions, waste fabrics may have larger dimensions. Furthermore, fabrics are often based on fibers that can cause clogging.

[0046] In cases where nylon-6 and the dye ultimately enter the same stream, they can subsequently be separated, for example, by means of extraction. Alternatively, a cooling and separation step can be performed prior to extraction to cure the nylon material, which can then be separated, for example, by means of filtration.

[0047] In another step or embodiment, additional polyamide can be removed by dissolution by raising the temperature above 170°C, such as above 190°C. Filtration or centrifugation can then be reused. It has been observed that removing all the polyamide at once by heating to temperatures above 170°C, such as above 190°C, is feasible. However, in the latter case, the temperature may be too high for filtration. In one embodiment, the temperature of the mixture is lowered. For example, a heat exchanger, such as one in which the mixture exchanges heat with a stream of alcohol solvent, can be used. In an alternative embodiment, another solvent with a lower temperature can be added, such as, for example, hot water, more particularly water above 90°C, such as boiling water. While this may cause some precipitation of the polyamide, the polyester and polyamide can still be separated from each other using a filter with coarse mesh (suitably larger than 0.2 μm). The polyamide can then be removed from the solvent (i.e., a mixture of water and polyol such as ethylene glycol) on a second filter. It has been observed that the addition of such another solvent can occur downstream of the first separator used to separate the polyester from the polyamide, for example when the first separator is a high-temperature centrifuge.

[0048] After the optional removal of at least some of the polyamide, such as nylon-6, the method can proceed to the depolymerization of the polyester using a catalyst. Suitable catalysts for depolymerizing the condensate include functionalized magnetic particles with catalytic partial functionalization, such as those described in NL2018269 and PCT / NL2016 / 050920 in the name of the applicant, which are incorporated herein by reference. More particularly, depolymerization is carried out in an alcohol solvent using the catalyst at a temperature of at least 170°C, preferably at least 180°C. The catalyst concentration can vary. Preferably, the catalyst concentration is between 0.01 and 10 wt% relative to the amount of polyester, for example between 0.08 and 5 wt%. A mixture of catalysts can be used instead of a single catalyst. At the specified temperature, catalytic depolymerization by means of glycolysis is selective for polyester and more particularly for PET.

[0049] In the presence of polyamide in the depolymerized polymer waste, the polyamide will essentially not be depolymerized. The polymer and any oligomers can then be separated from the depolymerized monomer products. Advantageously, nylon-6,6 is only slightly soluble in boiling water and otherwise insoluble in water or water / alcohol mixtures. Therefore, after cooling and the addition of water at the end of the depolymerization step, any nylon-6,6 will enter the solid phase of the product, which also contains the catalyst but not the monomers containing the polyester. This solid phase can then be modified to remove its different components.

[0050] It was observed that the second phase obtained after adding water at the end of the depolymerization step typically contains pigments and / or dyes. Pigments tend to be less soluble in the alcohol solvent than dyes prior to depolymerization. Furthermore, it is not considered necessary to remove all dyes or other colorants from the waste polymer material prior to depolymerization. Pigments are typically removed from the aqueous phase by centrifugation. Where any pigment or dye remains in the aqueous phase, their concentration will be very low. They can be removed from it by adsorption, such as adsorption on an activated carbon column, without incurring excessive costs for the adsorption column.

[0051] In a further embodiment, the polyol solvent containing the released dye is cooled after its separation from the solid waste polymer material and before the solvent separation step. Suitably, cooling includes a step of heat exchange between the polyol solvent and another stream of polyol solvent directed to the first chamber. In a further option, the solvent extraction process can be arranged such that the first extraction solvent is also used to cool the polyol solvent. The first extraction solvent may have a boiling point of at least 100°C, and preferably at least 110°C or even at least 120°C. If desired, further extraction can then be carried out with a second extraction solvent having a lower boiling point (such as haloalkanes, for example chloroform, dichloromethane, dichloroethane, etc.).

[0052] Optionally or additionally, water can be added as a cooling method. Essentially, the addition of water results in a mixture of polyol and water, which may be undesirable for depolymerization, given the risk of hydrolysis rather than glycolysis of the condensation polymer. However, the presence of water in the polyol is not considered harmful, provided the temperature of the release step is low enough to avoid depolymerization. Furthermore, the water concentration in the storage container can be controlled by adding fresh polyol. Additionally, the stream of the polyol / water mixture can be treated, for example, by distillation, to separate the water from the polyol.

[0053] According to a second aspect, the present invention provides a system for depolymerizing waste polymer materials containing condensation polymers and dyes, the system comprising:

[0054] (1) A heating device for heating alcohol solvents;

[0055] (2) A first chamber for mixing waste polymer material in an alcohol solvent, wherein the waste polymer material is heated by means of the alcohol solvent, the first chamber being provided with an inlet for the alcohol solvent and an inlet for the waste polymer material, wherein in use after heating the waste polymer material, the dye will at least partially be released from the waste polymer material and enter the alcohol solvent;

[0056] (3) A first separation section, optionally integrated with a first chamber, for separating waste polymer material in solid form from an alcohol solvent and having a first outlet for the alcohol solvent;

[0057] (4) Another separation section for separating the dye from the alcohol solvent to recover the alcohol solvent, said separation section being arranged downstream of the first outlet of the first separator;

[0058] (5) A storage container for recovering alcohol solvent, the storage container including an inlet connected to a separation section and an outlet connected to another chamber;

[0059] (6) The other chamber is provided for the depolymerization of the condensation polymer and is provided with a first inlet for the waste polymer material, optionally with another inlet for the depolymerization catalyst, and another inlet for the recovery of the alcohol solvent.

[0060] The reactor system of this invention enables efficient recycling and reuse of the alcohol solvent. A heating device is arranged herein to heat the alcohol solvent, and then the heat is transferred from the alcohol solvent to the waste polymer material. This is done to prevent uneven temperature distribution in the first chamber. The latter carries the risk that the temperature will locally (e.g., at the reactor walls) rise to the reaction temperature of the dye and the alcohol solvent.

[0061] One embodiment of the invention provides a system in which a first chamber and a first separation section are integrated and together constitute a mixing / separator unit, wherein waste polymer material can be retained (statically) in the first chamber and an alcohol solvent is fed into the first chamber and guided through or along the waste polymer material to extract the dye contained therein. The dye-containing alcohol solvent then exits the first chamber through an outlet. In this way, the first separator for separating solid waste polymer and alcohol solvent is not a separate component of the mixing / separator unit, and the separation is implicit.

[0062] In another embodiment, a system is provided in which a first chamber and a first separator are integrated and together constitute an extraction unit in which waste polymer is retained, or the extraction unit is propelled by a mechanical device (such as a conveyor screw) disposed within the first chamber, and an alcohol solvent is fed into the first chamber, preferably in a countercurrent flow relative to the conveying direction of the mechanical device. A tray or other separation device then acts as the first separator.

[0063] To ensure a substantially uniform temperature in the mixture of waste polymer material and alcohol solvent, dye release is preferably carried out in a rotating container. More specifically, the rotating container is configured to function as a centrifuge chamber. Rotating containers, such as those used in washing machines, are robust enough to withstand the load of waste polymer material. Furthermore, by limiting the temperature, no significant physical or chemical degradation occurs.

[0064] In one embodiment, after the release step, the waste polymer material can be mechanically conveyed to a subsequent container or reaction chamber. Tools, such as one or more grippers or other mechanical devices, can be provided for this purpose to move the solid material from one location to another. Conveyor belts can be used as auxiliary devices for movement.

[0065] Alternatively, the solid material can be redispersed in a liquid such as an alcohol solvent, which is not preferred. It can then be transported, for example, in the form of flakes or flake dispersions. One embodiment of the invention provides a system in which a first chamber and a first separator together constitute a centrifuge chamber, wherein at least one valve is provided to allow the alcohol solvent to be selectively retained in or removed from the centrifuge chamber.

[0066] Another embodiment relates to a system in which the release section includes an extraction device for extracting dye from an alcohol solvent, preferably using a second solvent that is immiscible with the alcohol solvent, the extraction device preferably being provided with an inlet for the second solvent.

[0067] Another embodiment provides a system in which the separation section includes a carbon absorption device for separating the dye from the alcohol solvent.

[0068] In another embodiment of the system of the present invention, the separation section includes a distillation device for delivering a distillate stream containing an alcohol solvent with an output concentration of at least 95% by weight.

[0069] According to yet another embodiment, the system is characterized in that the separation section includes a nanofiltration section for separating the dye from the alcohol solvent.

[0070] The reactor system also includes a separate chamber for depolymerization of the condensate, which is provided with a first inlet for the waste polymer material and another inlet for the catalyst, as well as another inlet, also optionally, for the alcohol solvent, and a separator for separating the catalyst from the monomer-containing solution after depolymerization of the condensate. An additional inlet for water may be present to allow precipitation of the oligomers and produce a first aqueous phase containing the monomer product and a second phase containing the catalyst, oligomers, and additives. An advantage of using the separate chamber for depolymerization is that it allows for simultaneous decolorization pretreatment and depolymerization treatment. Another advantage is that this separate chamber can be configured to add a significant amount of water and to separate the aqueous stream without the risk of contaminating the outlet line where some released dyes might remain. Furthermore, the use of a separate reactor where temperature control appears less critical allows for the installation of heating devices within the reactor. Additionally, specific designs for the reactor can be used. One example of such a reactor design is a combination of a heated vessel and one or more plug flow reactors, as disclosed in application WO2016 / 205200A1, which is incorporated herein by reference.

[0071] In a further embodiment, the alcohol solvent is heated to a predetermined temperature before entering a preferred rotating container in which the release takes place. Preheating the alcohol solvent, rather than heating it within the container, allows the temperature within the container to remain within a predetermined temperature limit. In one specific embodiment, dye release can also be carried out in a series of sequential steps, such as a first step and a second step. Each step can be carried out at a predetermined temperature and for a predetermined duration. This allows for selective release of dyes, for example, selective release of dyes that have already been added to fabrics by printing from dyes incorporated earlier in the manufacturing process. It also allows for selective release of dyes from the fabric material and subsequently, selective release of dyes from polyester bottles (e.g., PET bottles). Such selective release of dyes benefits downstream extraction processes, separating individual dyes that can be reused for coloring purposes without having to be disposed of as chemical waste.

[0072] In a further embodiment, the first chamber and the first separator are arranged relative to each other such that the separated solid waste polymer material can be redispersed in the first chamber by adding an alcohol solvent. This allows multiple steps to be performed in the first chamber without the need to transport the solid material. In one embodiment, the first chamber and the first separator together constitute a centrifuge chamber, wherein at least one valve is provided, allowing the alcohol solvent to be selectively retained in or removed from the centrifuge chamber.

[0073] In yet another embodiment, a filter is arranged downstream of the first outlet of the first separator for solid-liquid separation under conditions different from those in the first separator. Such a filter is considered suitable, for example, for the separation of polyamides. In a preferred embodiment, a cooling device is present upstream of the filter and downstream of the first outlet. One embodiment of the cooling device is a heat exchanger. An alternative embodiment of the cooling device is an inlet for a coolant such as water. The coolant is then mixed with a polyol alcohol solvent. A mixing device may be provided thereto. Such a mixing device may include a mixing chamber and / or a stirrer, as is known to those skilled in the art. In another embodiment, a bypass exists around the filter. This allows the filter to be integrated downstream of the first separator and upstream of the extraction device without requiring any solvent flow through the filter. Alternatively, the filter may be arranged in a separate circulation line, with or without any further extraction device for the filtrate downstream of the filter.

[0074] In an advantageous embodiment, a heating device is arranged downstream of the storage container and a heat exchanger is located upstream of the heating device for heat exchange between the alcohol solvent from the storage container and the stream containing the released dye originating from the first separator. This embodiment is energy-efficient.

[0075] In another embodiment, the heating device is equipped with a temperature sensor and a controller to specify the heating of the alcohol solvent to a predetermined temperature. The temperature sensor can be arranged in different locations, such as in the first chamber, downstream of the heating device, or upstream of the heating device. The number of temperature sensors can be selected as needed. Such implementations are known to those skilled in the art of reactor design. Attached Figure Description

[0076] These and other aspects will be further illustrated with reference to the accompanying drawings and embodiments, wherein:

[0077] Figure 1 This is a schematic layout diagram of the reactor system according to the first embodiment;

[0078] Figure 2 This is a schematic layout diagram of the reactor system according to the second embodiment;

[0079] Figure 3 This is a schematic layout diagram of the reactor system according to the third embodiment;

[0080] Figure 4 It is a schematic graph of relative absorbance relative to the number of pretreatment cycles;

[0081] Figure 5 This is a schematic graph showing the PET to BHET conversion (%) of fabrics after one pretreatment cycle and after six pretreatment cycles relative to depolymerization time.

[0082] Figure 6 It is a schematic layout diagram of the reactor system according to the fourth embodiment; and

[0083] Figure 7 This is a schematic layout diagram of a reactor system according to a fifth embodiment of the present invention;

[0084] Figure 8 This is a schematic graph showing the PET to BHET conversion rate (%) of fabrics with different solvent to waste polymer ratios relative to depolymerization time during the pretreatment cycle.

[0085] Figure 9 This is a schematic graph showing the PET to BHET conversion rate (%) of fabrics relative to depolymerization time for different solvent-to-waste polymer ratios and pretreatment cycle numbers; and

[0086] Figure 10 A bar graph showing the amount of phosphorus flame retardant after different pretreatments is presented. Detailed Implementation

[0087] The accompanying drawings are not drawn to scale, and the same reference numerals in different drawings represent the same or corresponding features.

[0088] Figure 1 A schematic layout of a reactor system according to a first embodiment of the invention is shown, which allows for the recycling of the alcohol solvent. The alcohol solvent according to the invention is a polyol, more preferably a diol, such as a C2-C5 diol, and more preferably ethylene glycol. The use of ethylene glycol is preferred because it can be used both as a solvent for dye release and as a solvent and reactant in depolymerization. Therefore, the use of ethylene glycol in the dye release step does not lead to polymer waste contamination in later stages of the process.

[0089] like Figure 1 The reactor system shown includes a first chamber 10, a first separation section or separator 11, another chamber 80, and another separator 81. Although the first chamber 10 and the first separator 11 are... Figure 1The components are shown as a single element 1, but they can be integrated, particularly in the form of centrifuge chambers, as schematically represented by the dashed lines between articles 10 and 11. The first chamber 10 and separator 11 are configured to mix waste polymer entering via inlet 14 with alcohol solvent entering via inlet 13, such that at least a portion of at least one dye is released from the waste polymer material into the alcohol solvent without depolymerizing the condensate and under conditions preventing reaction between the dye and the alcohol solvent; and to separate at least partially decolorized waste polymer from the alcohol solvent. The at least partially decolorized waste polymer exits the first chamber 10 through outlet 19, while the dye-containing alcohol solvent exits the first separator 11 through outlet 28.

[0090] like Figure 6 As shown, the mixing chamber / separator combination can also be embodied as extraction device 100. Extraction device 100 is a solid-liquid separator, in which solid flakes of waste polymer are introduced via a bottom inlet 14, while an alcohol solvent enters via an inlet 13 at the top of extraction device 100. The waste polymer flakes are conveyed upwards via a conveying device such as a conveying screw 102 in the direction of arrow 101. The waste polymer flakes are mixed with the downward-flowing alcohol solvent, which flows in the opposite direction to the conveying direction 101, to achieve the extraction of dye from the waste polymer into the alcohol solvent. The decolorized waste polymer flakes exit the extrusion device 100 at the top through outlet 19, while the bottom layer of alcohol solvent containing the extracted dye is removed via outlet 28.

[0091] The other chamber 80 and the other separator 81 configured for depolymerizing waste polymers can be separate or integrated. In one embodiment (not shown), the other chamber 80 may include a mixing vessel and one or more plug flow depolymerization reactors. The latter is considered advantageous because the residence time in such a plug flow reactor can be easily controlled. Furthermore, the plug flow reactor can be embodied as a longitudinally cylindrical reactor with a small cross-sectional area relative to the circumference. By insulating such a reactor and / or adding external heating elements such as wires, a constant temperature can be maintained, which is beneficial to the progress of depolymerization in such another reactor chamber 80. However, good results for depolymerization can also be achieved with reactors in the form of cylindrical vessels, which are known per se.

[0092] like Figure 1The illustrated reactor system also includes a separation section 40 for separating the dye from the alcohol solvent, and a storage container 20 for the alcohol solvent. In one embodiment, the separation section 40 may include an extraction device. In another embodiment, the separation section 40 may include a carbon absorption device, such as an activated carbon tower, for separating the dye from the alcohol solvent. In yet another embodiment, the separation section may include a distillation device for delivering a distillate stream containing an alcohol solvent with an output concentration of at least 95% by weight. In a fourth embodiment, the separation section 40 may include a nanofiltration section for separating the dye from the alcohol solvent. The separation section 40 may also include multiple embodiments arranged in series. The separation section 40 may also be provided as a combination of any of the disclosed embodiments.

[0093] In the illustrated embodiment, an additional mixing chamber 30 is provided, which has an inlet 31 for a coolant (preferably water or an aqueous solution). However, this mixing chamber 30 is optional. Furthermore, a heat exchanger 21 and a heater 22 are shown. The heater 22 can be embodied in any known form, for example as a heat exchanger with steam or as a heat exchanger with another liquid such as oil. Figure 1 The additional components shown in the embodiments are adsorption tower 90 and crystallization unit 95. Furthermore, it has been observed that there may be a higher... Figure 1 The diagram shows more heat exchangers, and the alcohol solvent can be distributed from storage container 20 to more locations within the reactor system. Alternatively, more than one storage container can be used, i.e., to ensure that the alcohol solvent with a higher purity than that in the first chamber 10 is fed into another chamber 80.

[0094] In operation, the alcohol solvent flows from storage container 20 via solvent line 29 to solvent inlet 13 of first chamber 10. Solvent line 29 is equipped with heat exchanger 21 and heating device 22 to heat the solvent to a desired temperature, for example in the range of 100-160°C, preferably 110-140°C. Atmospheric pressure is used in this embodiment, but other pressures are not excluded. The temperature of the solvent at solvent inlet 13 of first chamber 10 is controlled by means of a controller and one or more suitable sensors, as is known in the art itself.

[0095] In the first chamber 10, the solvent is mixed with waste polymer material supplied via inlet 14. In one example, the first chamber 10 is a batch reactor, which is filled with waste polymer material before the solvent is supplied via solvent inlet 13. It is not excluded that multiple chambers 10 may exist in parallel to enable simultaneous and semi-continuous processing. In another embodiment, multiple chambers 10 are arranged in series, such as... Figure 7As shown, two first chambers (10-1, 10-2) are arranged in series, wherein the decolorized waste polymer stream 19-1 exiting first chamber 10-1 is fed into the subsequent first chamber 10-2 for further decolorization. The further decolorized waste polymer exits the subsequent first chamber 10-2 as stream 19-2. The dye-containing alcohol solvent 13-1 exiting first chamber 10-1 is then fed into the subsequent first chamber 10-2 to absorb more dye from the decolorized waste polymer stream 19-1. The increased dye-containing alcohol solvent exits the other first chamber 10-2 as stream 13-2. If desired, more than two first chambers can be arranged in series.

[0096] like Figure 1 As shown, a mixer may be present in the first chamber 10. The mixer may be a mechanical agitator. Optionally, the first chamber 10 may be rotated as a whole. Mixing is desired to obtain a uniform temperature distribution. To prevent the temperature in the first chamber 10 from exceeding the predetermined operating temperature for the dye release step, it is preferable that the first chamber 10 does not contain any heating device, such as a heating device integrated into the wall of the first chamber 10. Instead, the heating of the waste polymer material is carried out by means of heat transfer from the solvent. If desired or necessary, the solvent can be refreshed during the treatment of the waste polymer material. The solvent can be removed via an outlet through the first separator 11. Figure 1 Valve 12 is shown to indicate that the solvent flow can be controlled to remove solvent from the first chamber 10. If desired, the solvent thus removed can be recirculated back into the first chamber via a shortcut circulation line.

[0097] Once the dye release step has been carried out in the first chamber at a predetermined temperature for a predetermined time period and at a predetermined concentration of waste polymer material relative to the alcohol solvent, the first chamber 10 is emptied into the first separator 11. It is certainly possible that the emptying involves the removal of the main liquid component. Instead of a centrifuge, the separator 11 can optionally be embodied as a filter, such as a coarse filter with a mesh size in the micrometer range. This is sufficient if the waste polymer material is provided in relatively large, discrete portions.

[0098] After removal from the first chamber 11, the solvent stream 28 containing the released dye typically has a temperature above 100°C. It typically requires cooling before being exchanged with the extraction solvent. Suitable halogenated alkanes have boiling points well below 100°C. Aromatic hydrocarbons such as xylene and toluene are also possible. In one embodiment, they can also be used as a coolant. To cool the solvent stream 28, it undergoes heat exchange with fresh solvent in the solvent line 29 in a heat exchanger 21. The heat exchanger 21 can be embodied as is known to those skilled in the art. Additional heat exchangers may be present if desired. For example, another heat exchanger can be provided to exchange heat with a liquid such as water. Water can be added as a coolant at different locations in the reactor system. To prevent excessive expansion, water is suitably added as hot water, i.e., water at least 70°C or even at least 90°C. Another intermediate heating liquid, such as oil, can also be used.

[0099] Downstream of one or more heat exchange steps, solvent stream 28 can be further cooled by adding coolant 31 to mixing chamber 30. As explained above, coolant 31 can be water. Alternatively, coolant 31 can be the extraction solvent. It is observed that this addition of coolant 31 to mixing chamber 30 is optional, if desired. Optionally, coolant 31 can be added based on the temperature in first chamber 10 and the flow rate of solvent in solvent stream 28. It should be understood that the addition of coolant is typically under the control of a controller and can be controlled according to a predetermined control protocol (e.g., embodied in software).

[0100] The cooled solvent stream 32 is fed into a separation section 40, which is provided with another inlet 41 for extracting the solvent. In one embodiment, the separation section 40 is embodied as an extraction device 40, which is a liquid-liquid separator in which two immiscible liquids are mixed to achieve the extraction of the dye from the alcohol solvent to the extraction solvent. It is not excluded that other types of extraction devices 40, as known to those skilled in the art, will be used. The extraction device 40 shown produces two layers of liquid. In the example shown, the bottom layer contains the extraction solvent containing the extracted dye, which is removed via outlet 49. The top layer contains the alcohol solvent, which is removed via solvent outlet 43. To ensure good cleanliness of the alcohol solvent, the solvent can be recycled back to the extraction device 40 via a recirculation line 44. Optionally, the recirculation line 44 can lead to a separate extraction chamber (not shown). It should also be understood that the solvent obtained at solvent outlet 43 or the dye-containing extraction solvent at outlet 49 can undergo further extraction and other processing. In particular, the dye-containing extraction solvent can be treated to obtain a separated dye at a higher concentration. Suitable purification and separation techniques, including chromatography, can be utilized. It should also be understood that multiple extraction devices 40 can be used in parallel. Color sensors can be used to direct the solvent flow to the color-specific extraction device to minimize color contamination. Furthermore, polymer waste can be pretreated and separated into different, color-specific materials. Even if single-color waste typically contains multiple dyes, color diversity is reduced.

[0101] In other embodiments, such as when separation section 40 includes an activated carbon tower, the purified or cleaned alcohol solvent is removed via solvent outlet 43, while the dye remains in the activated carbon bed and can be removed via outlet 49.

[0102] In other embodiments, such as when separation section 40 includes a nanofiltration section, purified or cleaned alcohol solvent is removed via solvent outlet 43, while dye can be removed via outlet 49.

[0103] Solvent stream from solvent outlet 43, which is not recirculated via circulation line 44, is introduced as clean solvent stream 45 into storage container 20. If quality control is required, the clean solvent stream 45 can be sensed before entering the storage container. If the solvent stream is not sufficiently clean, it can be introduced into a waste stream or a stream awaiting further processing. However, in the experiments leading to this invention, it has been found that when the released dye is not modified by reaction with the solvent during the dye release step, the released dye is more thoroughly removed from solvent stream 32.

[0104] After the solvent is removed from the first chamber 10, the polymer waste can be directed to another chamber 80. This can be done either in a substantially dry form or after redispersing in a fresh alcohol solvent. It is not excluded that the polymer waste undergoes several dye release steps in the alcohol solvent. These steps can occur at different temperatures, typically increasing from the first to the last step. Performing dye release in multiple steps at different temperatures has the advantage that dyes released more rapidly into the alcohol solvent will be separated from those released less rapidly. The rate of release may depend on the chemical composition of the dye and its arrangement within and / or on the surface of the waste. Representative dye materials are known to those skilled in the art. If multiple release steps are performed, they will... Figure 1 The example shown takes place in the same first chamber 10. Any desired temperature changes can be achieved by means of the heating device 22. If any separate treatment of the resulting dissolved stream 28 would be desired, this can be carried out downstream.

[0105] Another chamber 80 is specifically configured for the depolymerization of polyester in the waste polymer material, preferably but not exclusively polyethylene terephthalate. This other chamber 80 is provided with an inlet 82 for the depolymerization catalyst. Another inlet 86 is present for clean or purified recycled alcohol solvent from storage container 20. Inlet 86 is connected to storage container 20 via line 87. A heating device is present in reactor 80 or applied to the polymer waste stream 19 to reach the desired depolymerization temperature. Another separator 81 is provided with an inlet 83 for a reagent (more particularly water or an aqueous solution) to produce two distinct phases that can be separated in separator 81. The first aqueous phase exits separator 81 via outlet 85 and is carried to crystallization unit 95 via optional absorber 90. This produces monomer product 99 and an aqueous stream 98 that can be removed as waste. The second phase is a slurry or solid phase and contains oligomers, catalyst, and additives. This is removed from separator 81 via outlet 84 and reused, optionally after being treated as a catalyst composition and inserted into another chamber 80 via catalyst inlet. The optional treatment may involve a separation step to remove additives and pigments.

[0106] Figure 2 A second embodiment of the reactor system according to the present invention is shown. Figure 2 The reactor system in Figure 1The reactor system differs in that it includes a filter unit 50 with a filter outlet 59. This filter unit 50 is configured to remove polyamide from the solvent stream 28. The solvent stream 28 is thus diluted in the mixing chamber 30 with water from the inlet 31. This results in the precipitation of polyamides such as nylon 6 or nylon 6,6. The filter unit 50 separates the precipitated polyamide from the solvent stream 33. The remaining solvent stream 51, which may still contain any dye, is then directed to the extraction device 40. If the remaining solvent stream 51 is completely devoid of colorant or dye, it can be directly fed to the storage container 20. For clarity, it has been observed that polyamide removal requires heating to a temperature of at least 160°C. It is anticipated that polyamide separation occurs after the dye release step. As previously discussed, the first chamber is thus refilled with the alcohol solvent that entered the first chamber 10 via the solvent inlet 13. A bypass 32 may be present around the filter unit 50 so that the solvent stream 28 generated by one or more dye release steps does not need to pass through the filter unit 50. In cases where the waste polymer material contains more than one type of polyamide material, such as nylon 6,6 in addition to nylon 6, the temperature in the first chamber 10 during polyamide dissolution can be controlled to selectively dissolve nylon 6.

[0107] Figure 3 A third example of a reactor system according to the present invention is shown. Figure 3 The reactor system in Figure 2 The reactor system differs in that a separate chamber 70 with accompanying downstream treatment is provided for separating the polyamide from the polymer waste. This separate chamber 70 is provided with an inlet 73 for an alcohol solvent, which is preheated to a desired temperature by means of an additional heater 23. Another chamber additionally includes an inlet 72 for water. Typically, water is added after a predetermined period for polyamide dissolution. The water lowers the temperature in chamber 70, allowing the resulting mixture (typically a slurry of solid polyester in an alcohol solvent in which polyamide is dissolved) to be directed through a separator 71, such as a filter having a mesh size of at least 0.2 micrometers. The stream 79 of solid polyester (typically carrying some alcohol solvent, which may be fresh) is then directed to another chamber 80 for depolymerization. The solvent stream containing polyamide 74 is directed to filter unit 50 to remove nylon 6,6. Another polyamide, such as nylon 6, can be obtained by separating it from nylon 6,6 as stream 69 in a separate filter unit 60 using an aqueous solvent stream 51 as input. The remaining solvent stream 61 is fed back to the separation section 40.

[0108] It was observed that, as a result of the addition of water during the process, for example in chambers 30 and 70, the return stream 45 to storage container 20 will contain water in addition to the alcohol solvent. Therefore, storage container 20 itself will also contain water. This is not considered problematic. Although the alcohol solvent can be separated from the water by distillation, relatively small amounts of water, such as up to 20% by weight, are not considered problematic for the dye release step. If the water concentration in the storage container would exceed a predetermined concentration, fresh alcohol solvent can be added, or return stream 45 can be rejected due to excessive water content.

[0109] Example

[0110] Example 1: Dye release from polyester fabric by high-temperature extraction

[0111] A 250 mL round-bottom flask was filled with 125 g of ethylene glycol (EG) and 1.7 g of polyester fabric to obtain a 1:75 PET:EG mass ratio. The mixture was stirred and heated in an oil bath to the extraction temperature. The reaction was allowed to proceed for 1 to 2 hours, with samples removed over time. Afterward, the hot reaction mixture was poured onto a sieve to separate the solid fabric fibers from the liquid stream of ethylene glycol. The solid fabric fibers were then rinsed with hot (120 °C) EG. The extracted colorant in the EG was monitored for color changes visually and by UV-VIS spectroscopy.

[0112] Experiments were conducted on polyester fabrics colored with yellow dye and polyester fabrics colored with blue dye. The observations for yellow and blue dyes are shown in Tables 1 and 2, respectively.

[0113]

[0114] Table 1 – Dye Release from Polyester Fabrics Colored Yellow

[0115]

[0116] Table 2 – Dye Release for Blue-Colored Polyester Fabrics

[0117] Example 2: Dye separation via solvent-solvent extraction

[0118] EG liquid stream was purified by liquid-liquid extraction, in which the dye was transferred from the EG phase to the extraction solvent phase. The colored EG stream was mixed with the extraction solvent at a 50:50 mass ratio. The extraction solvent was immiscible with EG. A two-phase system was obtained. In the system tested, the bottom phase was the extraction solvent containing the dye. Residual dye in the EG phase was removed by multiple extraction cycles. Extraction was performed at room temperature.

[0119] It was found that dichloromethane and chloroform solutions were feasible for dye release from yellow and blue polyesters to p-xylene, however, only for dyes that were not modified during extraction. Acetic acid and dimethylformamide, as second extraction solvents, were found to be miscible with ethylene glycol and unsuitable for extraction. For blue dyes, extraction in dichloromethane was preferred over extraction in chloroform.

[0120] Example 3: Dye release from PET bottle flakes via high-temperature extraction

[0121] The orange raw material, in flake form, from a PET bottle was used in the same process as in Example 1. The PET in the bottle was at least partially crystalline. High-temperature extraction was tested at different temperatures.

[0122] Table 3 – Dye Release from Orange Flakes from PET Bottles

[0123] As can be seen, for PET sheets, a temperature of 120°C is too low to achieve dye release beyond the margin. Most of the dye remains in the PET sheets and will be released during depolymerization. Higher temperatures are feasible to release the dye before degradation and to prevent the monomer-containing product from being contaminated by the dye (if the dye would dissolve into the aqueous phase). After extracting the dye with dichloromethane and chloroform as in Example 2, it proved more difficult to remove the dye from ethylene glycol than for the dyes released in Examples 1 and 2 that originated from textile waste polymers.

[0124] Example 4: Dye separation via activated carbon (AC)

[0125] As described in Example 1, adsorption extraction by activated carbon was performed after a first extraction by high-temperature mixing at 150°C. For reproducibility determination, each adsorption analysis was performed in duplicate. A colored extraction solvent produced by the optimal fabric extraction method was added to a round-bottom flask. Optionally, the solution was heated to a temperature representative of the industrial application of the method (80°C) before mixing with a certain amount of activated carbon to obtain a concentration of 400 to 800 mg / L. The solution was mixed at 120 rpm for 2 hours, and samples were taken out after 5, 10, 15, 20, 40, 60, 80, 100, and 120 minutes of mixing to determine the color removal rate over time. Each sample was processed immediately to separate the activated carbon and prevent additional reactions. Ethylene glycol and activated carbon were separated by centrifugation at 6000 rpm for 3 minutes, wherein the supernatant was (partially) decolorized ethylene glycol. The samples were analyzed using UV-Vis spectroscopy to determine the color removal rate and total color removal rate over time, showing that multiple cycles under optimal conditions (500 mg / L carbon dose, 80 °C) resulted in color removal rates ranging from 70% to 97%.

[0126] Example 5: Recovery of extraction solvent

[0127] 250 g of EG was mixed with 16.7 g of polyester fabric and heated to 150 °C using an oil bath. The EG was cooled to room temperature and separated from the polyester fabric by sieving. The separated EG was then distilled, and the fraction removed at 197 °C was collected as recovered EG. UV-Vis analysis was performed, and the results are shown in Table 4.

[0128] sample: The relative absorbance at 557 nm is [-]. Extraction begins 0.1 When the extraction reaches T=150℃ 7 When the extract has cooled to RT 5 Recycled extraction solvent 0.1 Residue after solvent recovery 240

[0129] Table 4 – Examples of Extraction Solvent Recovery

[0130] Example 6: Depolymerization of recovered alcohol solvent purified from activated carbon

[0131] 250 g of ethylene glycol was filled into a 1000 mL beaker, and the EG was stirred and heated to 150 °C using an oil bath. Then, 16.7 g of polyester fabric was added to the beaker to obtain a PET:EG mass ratio of approximately 1:15. Extraction was complete when 150 °C was reached. After this time, the hot (150 °C) reaction mixture was poured onto a (tea) sieve to separate the solid fabric fibers from the liquid stream of colored ethylene glycol. The beaker containing the colored EG was then filtered through a carbon filter cake (at 90 °C), and the filtrate was collected in a Buchner flask and then transferred to a 250 mL flask.

[0132] After separating the pretreated raw materials and colored EG and purifying the colored EG with activated carbon, as disclosed above, the purified EG is used for the depolymerization reaction of polyester.

[0133] The reference scale for laboratory depolymerization experiments was 125g ethylene glycol and 16.7g PET in a 250ml flask. Magnetic catalyst was added at a ratio of 0.01:10:75 catalyst:PET:EG (based on weight).

[0134] After removing the magnetic catalyst, the mixture was centrifuged and filtered at approximately 100°C. The filtrate was then placed in a crystallization dish and cooled to 20°C. The solid BHET crystals were then filtered through 12–15 micrometer filter paper and transferred again to the crystallization dish for further drying in a vacuum oven at 60°C and 200 mbar. The quality of the product was measured by HPLC, XRF, and colorimetry.

[0135] Example 7: Depolymerization using recovered alcohol solvent from distillation

[0136] The above experiment was repeated, but the separated colored EG was purified by distillation (97% of the EG was recovered, and 3% was retained as a residue). The purified EG was then used again for the depolymerization of the polyester, as described in Example 6 above.

[0137] The results are presented in Table 5. The BHET produced by depolymerization using recycled purified ethylene glycol as the reactive solvent met specifications in terms of b* value and iron ion content. The purity of the samples was above 93% by weight, and the indicative specifications for a* and L* were satisfactory.

[0138] experiment % by weight [Fe] b* A* L* Example 6 98.04 0.4 0.36 0.61 93.33 Example 7 93.73 0.5 1.49 -0.21 92.93

[0139] Table 5 – Properties of BHET obtained after depolymerization. UV-VIS results show that virtually all dyes have been separated from ethylene glycol; this is given in Table 6.

[0140] sample: Relative absorbance at 588 nm [-]: Recycled EG 0.121 Residue 6.66

[0141] Table 6 – Absorbance of UV-VIS dyes in recovered EG and residues

[0142] Example 8: Efficiency of Multiple Preprocessing Cycles

[0143] A 500 mL beaker was filled with 250 g of ethylene glycol, and the EG was stirred and heated to 150 °C. Then, 16.7 g of polyester fabric was added to the beaker to obtain a PET:EG mass ratio of approximately 1:15. Extraction was complete when the mixture was stirred at 150 °C for 10 minutes. After this time, the hot (150 °C) reaction mixture was poured onto a (tea) sieve to separate the solid fabric fibers from the liquid stream of colored ethylene glycol. The beaker containing the colored EG was then measured using UV-VIS, and the results were displayed... Figure 4 In the middle, the Figure 4 The relative absorbance of colored EG after each pretreatment cycle is shown. Partially decolorized fabrics were reused in subsequent cycles, where the ratio of PET:EG during the pretreatment mixture was always satisfied at 1:15.

[0144] Example 9: The effect of multiple pretreatment cycles on depolymerization time

[0145] Post-consumer polyester fabric raw materials with various colorants and dyes were subjected to multiple pretreatment cycles, as described above for Example 8. Two samples were made with the same polyester fabric composition, but were pretreated using one or six cycles. After the pretreatment cycle, the polyester samples were depolymerized with a reaction mixture concentration of 0.01:10:75 catalyst:PET:EG, as described for Example 6.

[0146] The results of the depolymerization show Figure 5 In the middle, the Figure 5 The PET to BHET conversion rates of two polyester fabrics were specifically shown. The depolymerization of the two polyester fabrics exhibited different times to achieve high or low conversion rates. Clearly, the polyester fabric utilizing only one pretreatment cycle reacted the slowest. The experiments concluded that more pretreatment cycles resulted in faster depolymerization and higher conversion rates.

[0147] Example 10: Effect of PET:EG ratio

[0148] As described above with respect to Example 1, post-consumer polyester fabric raw materials containing a deep blue pigment and dye were subjected to dye release via high-temperature extraction. For Sample 1, an EG:PET ratio of 7.5:1 was used, which is outside the claimed range, while for Samples 2 and 3, the EG:PET ratio was 75:1, which is within the claimed range. The deep blue dye was then separated by solvent-solvent extraction according to the procedure of Example 2. Subsequently, the polyester samples were depolymerized using a reaction mixture concentration of 0.01:10:75 catalyst:PET:EG and using recovered EG solvent from the solvent-solvent extraction.

[0149] The results of the depolymerization show Figure 8 In the middle, the Figure 8The changes in PET to BHET conversion rates over time for samples 1-3 are shown. For a given conversion rate, the depolymerization of sample 1 showed a much longer reaction time. On the other hand, the depolymerization of samples 2 and 3 showed much faster conversion rates, and were in fact very similar to the depolymerization using fresh EG.

[0150] Color results are given in Table 7. The mother liquor (ML) and the BHET produced by depolymerization using recycled purified ethylene glycol as the reaction solvent showed very different color values ​​(exemplified by b* as a measure of yellowing) between samples 1 (comparison) and 2 (according to the claimed invention). The difference in mother liquor (ML) quality between samples 1 and 2 was particularly significant. This indicates that, as claimed, pretreatment using a relatively high EG:PET ratio significantly increases the overall quality. The improvement in overall quality is particularly seen and confirmed using the b* value.

[0151] sample b* 1 ml of sample 21.25 2ml of sample 3.36 Sample 1BHET 1.34 Sample 2BHET -0.76

[0152] Table 7 – Properties of Mother Liquor (ML) and BHET Obtained After Depolymerization

[0153] It turns out that the mother liquor (ML) of Sample 1 (comparison) was much darker (deep yellow) than the mother liquor (ML) of Sample 2 (according to the claimed invention). The latter was essentially colorless.

[0154] Example 11: Removal of other impurities such as flame retardants

[0155] Post-consumer polyester fabric raw materials with phosphorus flame retardants were provided and subjected to phosphoric acid release via high-temperature extraction as described above for Example 1. For Sample 1, no pretreatment was performed (comparative), while for Sample 2, an EG:PET ratio of 15:1 was used during phosphoric acid release, and for Sample 3, a two-step phosphoric acid release was used, utilizing an EG:PET ratio of 15:1 in each step. Phosphoric acid was then separated by solvent-solvent extraction according to the procedure of Example 2. Subsequently, the polyester samples were depolymerized using a reaction mixture concentration of 0.01:10:75 catalyst:PET:EG and using recovered EG solvent from the solvent-solvent extraction.

[0156] The results of the depolymerization show Figure 9 In the middle, the Figure 9 The changes in PET to BHET conversion rates over time for samples 1-3 are shown. Reference samples using fabric raw materials without any flame retardants are also included. For a given conversion rate, the depolymerization reaction time of sample 1 is significantly longer than that of samples 2 and 3. The depolymerization reaction of sample 3 shows a conversion rate very similar to that of the reference sample using no flame retardants in the raw material.

[0157] Figure 10Finally, the amount of phosphoric acid remaining in the reaction mixture after depolymerization of samples 1 to 3 is shown (from left to right in each group of bar graphs). The bar graphs in the middle group show the amount of phosphoric acid remaining in the mother liquor after crystallization, while the bar graphs in the right group show the amount of phosphoric acid remaining in the generated BHET. It should be noted that for sample 1 (without pretreatment), no BHET was generated, as shown. The results clearly demonstrate the beneficial effects of the release step, as claimed.

Claims

1. A method for depolymerizing waste polymer material into monomers, said waste polymer material comprising a condensation polymer and at least one dye, wherein said condensation polymer is a polyester, said method comprising the following steps: - Without depolymerizing the condensate and under conditions that prevent a reaction between the at least one dye and the alcohol solvent, at least a portion of the at least one dye is released from the waste polymer material into the alcohol solvent, wherein the alcohol solvent is a polyol and is added at a weight ratio of the alcohol solvent to the waste polymer material between 200:1 and 30:1, wherein the release of at least a portion of the at least one dye from the waste polymer material is carried out at a temperature of up to 160°C; - Separate at least partially decolorized waste polymer from the alcohol solvent; - In the alcohol solvent separation step, the at least one dye is separated from the alcohol solvent in order to recover the alcohol solvent; - The condensate is depolymerized in an alcohol solvent by using a catalyst, wherein the alcohol solvent is essentially a recycled alcohol solvent obtained in the alcohol solvent separation step.

2. The method according to claim 1, wherein the alcohol solvent is added at a weight ratio of the alcohol solvent to the waste polymer material between 150:1 and 30:

1.

3. The method according to claim 1 or 2, wherein the alcohol solvent separation step is performed such that the recovered alcohol solvent has a purity of at least 95% by weight.

4. The method of claim 1, wherein the step of releasing at least a portion of the at least one dye from the waste polymer is carried out without a non-alcoholic solvent.

5. The method of claim 1, wherein the alcohol solvent separation step comprises extracting the at least one dye from the alcohol solvent using a second solvent that is immiscible with the alcohol solvent.

6. The method of claim 1, wherein the alcohol solvent separation step comprises extracting the at least one dye from the alcohol solvent using a carbon absorption device.

7. The method of claim 1, wherein the alcohol solvent separation step comprises treating the alcohol solvent in a distillation stage to deliver a distillate stream containing an output concentration of at least 95% by weight of the alcohol solvent.

8. The method of claim 1, wherein the alcohol solvent separation step comprises a nanofiltration step to separate the at least one dye from the alcohol solvent.

9. The method according to claim 1, wherein the alcohol solvent has a boiling point of at least 160°C at atmospheric pressure.

10. The method of claim 5, wherein the second solvent has a lower polarity than the alcohol solvent.

11. The method of claim 1, wherein at least 30% by volume of the waste polymer material is derived from fabric.

12. The method of claim 1, wherein 50-100% by weight of the at least one dye is removed from the waste polymer material.

13. The method of claim 1, wherein the release step is performed in a rotating container.

14. The method of claim 13, wherein the alcohol solvent is heated to a predetermined temperature before entering the rotating container, the predetermined temperature being configured to release at least a portion of the at least one dye from the waste polymer material.

15. The method of claim 14, wherein the alcohol solvent is refreshed and treated to have the predetermined temperature during release.

16. The method of claim 13, wherein the release step comprises a first release step and a second release step, wherein the second release step uses the recovered alcohol solvent from the first release step, and / or wherein the second release step is performed at a higher temperature than the first release step.

17. The method of claim 16, wherein the first release step and the second release step are configured for the selective release of the first colorant and the second colorant.

18. The method of claim 1, wherein the waste polymer further comprises polyamide.

19. The method of claim 18, wherein the polyester and the polyamide are separated from each other after the waste polymer is separated from the alcohol solvent and before the catalytic depolymerization of the polyester.

20. The method of claim 1, wherein the catalyst for depolymerizing the condensate comprises functionalized magnetic particles with catalytic functionalization.

21. The method according to claim 1, wherein the alcohol solvent is a diol.

22. The method of claim 5, wherein the second solvent is selected from the group consisting of alkanes, cycloalkanes, esters and ethers, excluding aromatics.

23. The method of claim 1, wherein the reaction to be prevented is the esterification or transesterification reaction of the at least one dye with the alcohol solvent.

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