Feed purification of polyester waste for recycling processes

Abstract

Purified polyester for reuse is produced by pretreating waste polyester material with dichloromethane (DCM). The purified polyester can be recycled by any chemical or mechanical recycling process. In the case where the waste polyester material includes non-polyester contaminants, the DCM-treated polyester material produces a slurry including DCM, a solid component including a polyester monomer product for reuse, and a waste liquid component, wherein the non-polyester contaminants can be filtered from the top of the liquid component.

Description

Technical Field

[0001] This application is a divisional application of Chinese Patent Application 202180079910.1. The invention generally relates to recycling processes, and more specifically to a method for purifying waste polyester feedstock with dichloromethane (DCM) prior to initiating a recycling process. Background Technology

[0002] The presence of impurities in low-quality plastic waste raises questions about the efficiency and effectiveness of chemical and mechanical recycling of plastic waste. For example, small amounts of impurities in the monomer or polymer feed stream (such as dyes, pigments, dirt, and foreign or dissimilar polymers) can be highly detrimental to the quality of the incoming raw materials and lead to severe degradation of the mechanical, optical, and / or barrier properties of the reformed polymer.

[0003] Chemical recycling uses waste plastics or waste textiles as raw materials. The recycling process dissolves polymers and / or generates monomers for the preparation of new plastics. Very high purity (99%) is required for the monomers to produce new high-molecular-weight polyesters via step-growth / condensation polymerization. The ongoing challenge in chemical recycling is obtaining low-quality, compositionally inconsistent feedstocks and processing them through depolymerization and monomer purification to produce the final product (monomer) with the quality required for condensation (or step-growth) polymerization. Currently, purification is achieved post-reaction purification via treatment with activated carbon and ion exchange resins, involving decolorization and deionization. While these techniques, along with pre-reaction distillation, have largely succeeded in removing impurities, including color, the dirtier and more colored the input, the more frequently the regeneration of the purification medium must occur. Reactivation of used or contaminated activated carbon is typically pyrolytic (at temperatures in the 600-900°C range), resulting in high energy costs. Furthermore, ion exchange bed regeneration involving reflux washing with dilute acids or alkalis generates environmental waste and / or requires additional processing.

[0004] Mechanical recycling can only use colorless inputs that have been thoroughly cleaned. Because mechanical recycling has zero tolerance for foreign substances, a large amount of plastic is rejected during the sorting process. In the case of polyethylene terephthalate (PET) bottles, a batch of PET bottles with only 1% polyolefin (e.g., caps, rings, labels, etc.) is unqualified for mechanical recycling and will be rejected. Due to these limitations, mechanical recycling is a low-recycling process (57%). Summary of the Invention

[0005] In one aspect, the present invention relates to a method comprising: purifying a waste containing polyester by treating it with dichloromethane (DCM); and recovering the purified polyester from the DCM-treated waste for recycling.

[0006] In another aspect, the present invention relates to a method comprising: purifying waste containing polyester terephthalate (PET) by treating it with dichloromethane (DCM); and recovering the purified PET from the DCM-treated waste for recycling.

[0007] Further aspects and / or embodiments of the invention will be provided in the detailed description of the invention set forth below, without limitation.

[0008] This application also relates to the following implementation schemes:

[0009] 1. A method comprising:

[0010] The waste containing polyester was purified by treatment with dichloromethane (DCM); and

[0011] The purified polyester is recovered from the waste products of DCM treatment for recycling.

[0012] 2. The method according to embodiment 1, wherein the purified polyester comprises a solid component and a liquid component, wherein contaminants float to the surface of the liquid component and are removed by filtering the contaminants from the surface of the liquid component.

[0013] 3. The method according to embodiment 1, wherein the purified polyester comprises a solid component and a liquid component and contaminants are removed from the purified polyester sample by filtration.

[0014] 4. The method according to embodiment 1, wherein the waste further comprises a non-polyester polymer, wherein the non-polyester polymer is recycled for reuse.

[0015] 5. The method according to embodiment 4, wherein the non-polyester polymer is selected from polyolefins, polyurethanes, polyimides, polyamides, and combinations thereof.

[0016] 6. The method according to embodiment 5, wherein the polyolefin is polyethylene and / or polypropylene.

[0017] 7. The method according to embodiment 4, wherein the waste comprises aluminum and / or aluminum-containing membranes, and the aluminum and / or aluminum-containing membranes are recycled for reuse.

[0018] 8. The method according to embodiment 1, wherein the DCM removes impurities selected from non-ester polymers, physical contaminants and / or dirt, colorants, organic impurities, and metallic and ionic impurities.

[0019] 9. The method according to embodiment 1, wherein the polyester being treated comprises polyester sheets, polyester fabrics, and / or polyester fibers used as pre-cleaning polyester inputs in a recycling process.

[0020] 10. The method according to embodiment 9, wherein the recycling process is a chemical recycling process or a mechanical recycling process.

[0021] 11. The method according to embodiment 10, wherein the chemical recycling process is selected from solvent dissolution, alcoholysis, hydrolysis, acidolysis, phospholysis, ammonolysis, ammonolysis, and enzymatic hydrolysis.

[0022] 12. The method according to embodiment 10, wherein the chemical recycling process includes solvent dissolution.

[0023] 13. The method according to embodiment 10, wherein the chemical recycling process includes glycolysis depolymerization.

[0024] 14. A method comprising:

[0025] Waste containing polyester terephthalate (PET) is purified by treatment with dichloromethane (DCM); and

[0026] Purified PET is recovered from waste products of DCM treatment for recycling.

[0027] 15. The method according to embodiment 14, wherein the purified PET comprises a solid component and a liquid component, wherein contaminants float to the surface of the liquid component and are removed by filtering the contaminants from the surface of the liquid component.

[0028] 16. The method according to embodiment 14, wherein the purified PET comprises a solid component and a liquid component, and contaminants are removed from the purified PET sample by filtration.

[0029] 17. The method according to embodiment 14, wherein the waste further comprises non-polyester polymers, wherein these non-polyester polymers are recycled for reuse.

[0030] 18. The method according to embodiment 17, wherein the non-polyester polymer is selected from polyolefins, polyurethanes, polyimides, polyamides, and combinations thereof.

[0031] 19. The method according to embodiment 18, wherein the polyolefin is polyethylene and / or polypropylene.

[0032] 20. The method according to embodiment 14, wherein the waste comprises aluminum and / or an aluminum-containing membrane, and the aluminum and / or aluminum-containing membrane is recycled for reuse.

[0033] 21. The method according to embodiment 14, wherein the DCM removes impurities selected from non-ester polymers, physical contaminants and / or dirt, colorants, organic impurities, and metallic and ionic impurities.

[0034] 22. The method according to embodiment 14, wherein the polyester being treated comprises PET sheets used as pre-cleaned PET input in a recycling process.

[0035] 23. The method according to embodiment 22, wherein the recycling process is a chemical recycling process or a mechanical recycling process.

[0036] 24. The method according to embodiment 23, wherein the chemical recycling process includes solvent dissolution.

[0037] 25. The method according to embodiment 23, wherein the chemical recycling process includes glycolysis depolymerization. Attached Figure Description

[0038] This patent or application document contains at least one color drawing. A copy of this patent or application disclosure with color drawings will be provided by the office upon request and payment of the necessary fees.

[0039] Figure 1 The photograph shows the separated product generated from the pretreatment of PET waste mixture flakes with dichloromethane (DCM) for self-use (Example 1).

[0040] Figure 2 The photograph shows a comparison of incoming PET contaminant flakes and recycled clean PET products along with recycled removed polyolefins and contaminants removed using pretreatment with DCM (Example 2).

[0041] Figure 3A and 3B This is a photograph showing the product obtained from PET color films pretreated with DCM (Example 2).

[0042] Figure 4 These are photographs showing time-series DCM extracts obtained from DCM-treated PET color and dirt mixture sheets (Examples 1 and 2).

[0043] Figure 5 It is a real-time plotting of the color extracted from the DCM pre-processed PET cleaning color film (Example 2).

[0044] Figure 6 This is a photograph showing the decolorization of black polyester fabric using DCM pretreatment (Example 5).

[0045] Figure 7 Photographs showing the depolymerization of black polyester fabrics with and without DCM pretreatment (Example 7).

[0046] Figure 8 This is a photograph showing the removal of red dye from a red 60 / 40 cotton / polyester fabric (Example 8). Invention Details

[0047] The following describes the preferred aspects and / or embodiments of the invention currently considered to be protected. Any substitutions or modifications in function, purpose, or structure are intended to be covered by the appended claims. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural indicators unless the context clearly specifies otherwise. The terms “comprise,” “comprised,” “comprises,” and / or “comprising” as used in the specification and the appended claims specify the presence of a explicitly stated component, element, feature, and / or step, but do not exclude the presence or addition of one or more other components, elements, features, and / or steps.

[0048] As used herein, the term "mechanical recycling" refers to a recycling process that preserves the molecular structure of waste polyester products by flaking and remelting and extruding recycled pellets, which are ready for remolding applications or directly formed into new commodities. Mechanical recycling requires uncontaminated, colorless waste streams, which necessitates thorough sorting and cleaning so that only similar materials are recycled together and have little or no color content.

[0049] As used herein, the term "chemical recycling" refers to a process by which a plastic polymer is chemically reduced to its original monomers so that it can be repolymerized and remade into new plastic materials. Through chemical recycling, plastic waste streams can be converted back into raw materials for further recycling. Unlike mechanical recycling, which requires sorting of single streams of plastic waste, chemical recycling can be used for mixed post-consumer plastic waste streams consisting of polyethylene (PE), polypropylene (PP), and polystyrene (PS). Chemical recycling is also more tolerant of colorant and contaminant content than mechanical recycling. Chemical recycling processes include, but are not limited to, solvent dissolution and depolymerization processes. Examples of depolymerization recycling reactions include, but are not limited to, alcoholysis (e.g., glycolysis and methanolysis), solvent decomposition, hydrolysis, acidolysis, phospholysis, ammonolysis, ammonialysis, enzymatic hydrolysis, and other exchange reactions that produce oligomers or monomers. Through clarification, in the context of polyester depolymerization, transesterification occurs via alcoholysis, where the alcohol groups cleave the ester bonds of the polymer.

[0050] As used herein, the term "glycolytic depolymerization" refers to a depolymerization recycling process in which a diol is inserted into a polymer chain, thereby breaking ester bonds and replacing them with hydroxyalkyl ends. Examples of diols used in glycolytic depolymerization include, but are not limited to, ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, cyclohexanediol, and dipropylene glycol.

[0051] As used herein, the term “solvent dissolution” refers to a chemical recycling process in which solvents are used to dissolve polymers and separate them from other materials.

[0052] As used herein, the term "filtration" is intended to include any process that separates solids from liquids. Examples of filtration processes include, but are not limited to, mechanical filtration (such as skimming), general filtration using gravity, vacuum filtration, cold filtration, hot filtration, and combinations thereof.

[0053] This document describes a method for simultaneously removing multiple impurities from a polyester waste sample (also referred to herein as the “raw material”) by treatment with dichloromethane (DCM). Examples of polyester raw materials include, but are not limited to, plastic waste and polyester fibers and / or fabrics as previously described herein, which may include clothing, yarns, pile, carpet, and rug fibers. As those skilled in the art will understand, polyester fibers and / or fabrics may include higher dye content than those found in plastic packaging waste. Once treated with DCM, the raw material can be used in any mechanical or chemical recycling process, including but not limited to solvent dissolution and glycolysis recycling processes. For the purposes of the following discussion, polyethylene terephthalate (PET) sheets will be referred to as an exemplary polyester raw material; however, it should be understood that the purification method described herein is applicable to any polyester raw material.

[0054] Referring to the attached diagram, when PET sheets are treated with liquid DCM, a PET / DCM slurry is formed. PET (1.38 g / cm³) 3 ) and DCM (1.33g / cm 3 The density difference between the PET flakes and impurities is sufficient to cause the PET flakes to settle to the bottom of the slurry while impurities with lower density float there. These impurities can be filtered from the surface (e.g., by skimming), leaving a purified PET sample. Figure 1 When the PET input is stained, the DCM removes the dye and colorant from the sample (Figure 3-7). The DCM can also remove dirt and grime from the PET and carry it into a suspension, where it can be easily removed by filtration. Figure 2 Since contaminants and fouling are known to introduce metal and ionic impurities into the recycling process, the application of DCM can further purify the PET feedstock. Figure 1 , 2 Once purified, PET samples can proceed to a recycling process, and DCM can also be recycled through filtration and evaporation processes, such as low-energy distillation at 40°C.

[0055] Examples of impurities that can be removed from polyester raw materials using DCM treatment include, but are not limited to, non-ester polymers, physical contaminants and / or dirt, colorants, organic impurities, metallic and ionic impurities, and combinations thereof. Non-limiting examples of organic impurities are acetaldehyde or its acetal. Examples of metallic impurities include, but are not limited to, aluminum or aluminum-containing films, iron and copper as wires or powders. Examples of non-ester polymers present in polyester raw materials include, but are not limited to, polymers such as polyolefins (found in bottle caps), polyamides (e.g., nylon), polyimides, polyurethanes, and polyvinyl chloride, many of which have densities lower than those of PET and DCM. For example, polyolefin polyethylene (PE) has a density of 0.85 g / cm³ for amorphous PE. 3 The density is 1.0 g / cm³ for crystalline PE. 3 The density of polyolefin polypropylene (PP) is 0.895-0.92 g / cm³. 3 The density; and polyamide nylon has a density of 1.15 g / cm³. 3 The density.

[0056] Using DCM for purification of polyester feedstock offers numerous advantages. For example, DCM treatment minimizes or eliminates the need for costly, labor-intensive, and energy-intensive post-reaction and / or post-processing purification procedures currently used in polyester recycling processes, such as filtration, decolorization, and demetallization / deionization. Furthermore, using DCM for the removal of non-ester polymers from polyester feedstock minimizes or eliminates reactor fouling and the resulting downtime. Using DCM for the removal of contaminants and / or fouling from polyester feedstock also reduces the need for purification media (e.g., ion exchange). Therefore, the application of DCM reduces the need for regenerating ion exchange media, which generate their own undesirable waste streams. Using DCM for the removal of color from polyester feedstock further reduces the need for carbon bed regeneration, a labor-intensive and expensive process typically carried out at 900°C.

[0057] In contrast, the DCM recoverable from this polyester feedstock is infinitely reusable and does not generate any additional waste for the recycling process. Purification of the polyester feedstock sample with DCM removes impurities, resulting in a cleaner and more efficient recycling process. DCM can be recovered from the purified polymer by filtration at room temperature (Examples 1, 2, 5, 8) or optionally at elevated temperatures (Examples 3, 4, 6, 7). DCM recycling is carried out using distillation at approximately 40°C (i.e., the boiling point of DCM), rather than at much higher temperatures requiring activated carbon regeneration.

[0058] The DCM purification described herein can be used with any recycling process to increase product purity and reduce processing costs, time, waste, and complexity.

[0059] In one embodiment, DCM purification is used in the alcoholysis depolymerization recycling process. A non-limiting alcoholysis depolymerization recycling process is the volatile catalyst (VolCat) chemical recycling process described in US 9,255,194 B2 and US 9,914,816 B2 by Allen et al. In one embodiment, the VolCat process depolymerizes the polyester in a reactor at a temperature equal to or higher than the boiling point of the alcohol using an alcohol solvent and an organic catalyst. In another embodiment, the organic catalyst has a boiling point at least 50°C lower than the boiling point of the alcohol solvent, and depolymerization is carried out at a temperature higher than the boiling point of the alcohol solvent. In a further embodiment, the organic catalyst has a boiling point at least 50°C lower than the boiling point of the alcohol solvent, and depolymerization is carried out at a temperature higher than the boiling point of the organic catalyst. In another embodiment, the polyester input and alcohol solvent are heated to a reaction temperature of approximately 200-250°C before the introduction of the organic catalyst. The reaction products from the depolymerization of VolCat are monomers and / or oligomeric diesters from polyester, as well as recovered organic catalysts and excess alcohol solvents, the former intended to be reused in recycled polyester products and the latter also intended to be reused in subsequent depolymerization reactions.

[0060] In another embodiment, the VolCat reaction is carried out in a chemical reactor, which may be a pressure reactor, such as an autoclave or extrusion reactor, or a non-pressurized reactor, such as a round-bottom flask. In a further embodiment, the depolymerization reaction, which may be pressurized or non-pressurized, and one or more optional purification steps for the monomer product are carried out in a batch and / or continuous flow process. In another embodiment, a solvent having limited solubility for the monomer product can be used to purify the depolymerized polyester monomer product, whether obtained in a batch process or by continuous flow. Alcohols and / or water are non-limiting examples of such purification solvents. When an alcohol is used for purification, the alcohol may be an unreacted alcohol from the depolymerization reaction or a newly introduced clean alcohol. In a further embodiment, the recovered monomer product obtained from the VolCat reaction can be used to generate new polymer materials.

[0061] In another embodiment, the polyester is selected from polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polypropylene terephthalate (PTT), polyethylene furanate (PEF), and combinations thereof. In a further embodiment, the alcohol solvent is a diol and / or a glycol solvent. In another embodiment, the alcohol solvent is selected from 1,2-ethylene glycol (ethylene glycol, EG), 1,3-propanediol (trimethylene glycol), 1,4-butanediol (tetramethylene glycol), 1,5-pentanediol (pentanediol), and combinations thereof. In a further embodiment, the organic catalyst is an amine organic catalyst and / or its carboxylate. In another embodiment, the amine of the amine organic catalyst and / or its carboxylate is a tertiary amine. In a further embodiment, the amine organic catalyst and / or its carboxylate is selected from triethylamine (TEA), tetramethylethylenediamine (TMEDA), pentamethyldiethylenetriamine (PMDETA), trimethyltriazacyclononane (TACN), 4-(N,N-dimethylamino)pyridine (DMAP), 1,4-diazabicyclo[2.2.2]octane (DABCO), N-methylimidazole (NMI), and combinations thereof. In another embodiment, the amine organic catalyst and / or its carboxylate is TEA and / or its carboxylate. In a further embodiment, the polyester input comprises terephthalate and the recovered depolymerization product comprises terephthalate monomer. In another embodiment, the polyester input comprises PET and the recovered polyester monomer product is bis(2-hydroxyethyl) terephthalate (BHET). In a further embodiment, the polyester input comprises PET, the alcohol is EG, the amine organic catalyst is TEA and / or its carboxylate, and the recovered reaction product comprises unreacted EG, TEA, and BHET.

[0062] In another embodiment, the DCM purification can be combined with pre-reactive distillation, which removes water, residual DCM, and other volatile impurities from the polyester and enhances the efficiency of the VolCat recycling process. Applying DCM purification to the feedstock in the VolCat recycling process (with or without pre-reactive distillation) minimizes the use of decolorizing agents and the need for ion exchangers to purify the output product, thus reducing processing time and the cost of operating the VolCat recycling process.

[0063] Various aspects and / or embodiments of the invention have been described for illustrative purposes, but are not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein has been chosen in order to best explain the principles, practical application, or technical improvements of these aspects and / or embodiments that are superior to those found in the market, or to enable those skilled in the art to understand these aspects and / or embodiments disclosed herein.

[0064] experiment

[0065] The following embodiments are described to provide a complete disclosure to those skilled in the art on how to manufacture and use various aspects and embodiments of the invention as described herein. While efforts have been made to ensure accuracy regarding variables such as amounts, temperatures, etc., experimental errors and biases should be taken into account. Unless otherwise stated, parts are parts by weight, temperatures are degrees Celsius, and pressures are atmospheric pressure or near atmospheric pressure. Unless otherwise specified, all components are commercially available. Example 1

[0066] DCM purification of PET sheets containing contaminated material

[0067] 2.5 kg of roadside mixed PET flakes were added to a 22 L glass reactor along with 12 L of DCM and gently stirred at room temperature. Even before stirring, the DCM immediately absorbed an astonishing amount of color. DCM samples were taken at 1, 2, and 3 hours, and the less dense material was skimmed off from the liquid surface, revealing it to be PE, PP, and aluminum-containing films. Most of the dirt and grime initially on or within the dirty PET was released into the DCM liquid and easily filtered out, leaving clean PET flakes that were easily recovered via subsequent filtration. Very little colored material was found in the resulting product as polyolefin or color retained in the PET. Figure 1 Panel 1 shows PET immersed in DCM (which has absorbed color), with polyolefin and aluminum foil floating in it. Figure 1 (Panel 2) illustrates the removal of floating material from the surface of DCM liquid and dirt / fouling using a wire mesh screen. Figure 1 (Panel 3) shows the dirt / fouling suspended in the remaining DCM liquid. Figure 1 Panel 4 shows the recovered and purified PET flakes. Figure 2 The image shows a PET sheet containing a mixture of roadside sludge as input (left), purified PET (top center), recycled polyolefins and aluminum (bottom center), and filtered sludge and dirt removed during the filtration process (right). Figure 4 (Right) shows three time-series samples of DCM solution.

[0068] Example 2

[0069] DCM purification of clean color PET flakes

[0070] 2.5 kg of clean colored PET flakes were added to a 22 L glass reactor along with 12 L of DCM and gently stirred at room temperature. Even before stirring, the DCM immediately turned dark. DCM samples were taken at 1, 2, 3, 4, 5, 6, and 24 hours, and the PET flakes were subsequently recovered by filtration. Figure 3A The image shows a portion of a clean colored PET sheet before (left) and after (right) DCM treatment, as well as a portion of the dye and other materials extracted after DCM evaporation (top, in the flask). Figure 3B The image shows clean color flakes before (left) and after (right) recovery from the DCM process. Most of the dye has been extracted from the treated material; the remaining blue colorant is mostly insoluble pigment, which is easily removed by filtration in subsequent recycling processes such as depolymerization. Figure 4 Seven DCM solution time-series samples are shown (left). Table 1 shows CIE color measurements of the cleaned color flake samples before (left) and after (right) DCM purification. As shown therein, DCM purification of the initial PET produced a resulting PET with improved optical properties, where L* increased from 45.12 to 49.23 and the color was significantly reduced, with a* decreasing from -9.22 to -2.6 (less green) and b* decreasing from +13.5 to +2.91 (less yellow).

[0071] Table 1

[0072] Before and after removing color from PET cleaning color flakes

[0073]

[0074] L* = Brightness from black (0) to white (100)

[0075] a* = Green (-) to Red (+)

[0076] b* = Blue (-) to Yellow (+)

[0077] SD = Standard Deviation

[0078] Table 2 shows the CIE color measurements of time-series aliquots of DCM liquid from the clean color PET sheet described herein and the PET sheet containing roadside sludge from Example 1. Figure 5 This is a graph plotting the color extraction data from the clean color PET sheets in Table 2. Table 2 and Figure 5The data shows that the discoloration occurred within two hours.

[0079] Table 2

[0080] Real-time color extraction (solution) time series

[0081]

[0082] Example 3

[0083] Depolymerization of untreated clean colored PET flakes by glycolysis (VOLCAT)

[0084] 1001 g of post-consumer clean-color PET flakes and 4501 g of EG were placed in a 2-gallon Parr pressure reactor and purged with nitrogen. The reactor was equipped with a stirrer, a condenser with a pressure regulator (separate from the reactor and equipped with a valve), a 300 mL outlet below the condenser, and a catalyst addition manifold. The reactor was sealed and the reaction mixture was heated to an internal temperature of approximately 220 °C with stirring (using a two-bladed impeller shaft at 200 rpm), at which point the internal pressure was observed to be 10 psi. Then, TEA (52.6 g) was added through the catalyst addition manifold by pressurizing the top space above the catalyst to approximately 30 psi and briefly opening the valve until the pressure began to rise in the reactor (at which point the valve was closed). The reaction was stirred at this temperature for 1 hour, during which time the condenser valve was opened and the reactor pressure was slowly reduced through the condenser regulator until ambient pressure was reached, while the distillate containing the catalyst was collected at ambient pressure until a temperature of 180 °C was reached. The reaction was then cooled to 90 °C, at which point the reaction was filtered through a polypropylene pad covered with a fine diatomaceous earth layer. After cooling the filtrate, BHET was recovered in ethylene glycol as a concentrated white slurry. The slurry was then vacuum filtered to recover solid BHET, which was compressed by applying a rubber barrier, washed with water, blotted dry, and subsequently dried in a vacuum oven at 65°C. The color of the precipitated slurry, the dried BHET product, and the recovered mother liquor obtained after filtering the BHET were measured.

[0085] Example 4

[0086] Pretreatment of clean colored PET sheets by glycolysis (VOLCAT) depolymerization

[0087] Pretreated clean-colored PET flakes (1004 g) and EG (4505 g) from Example 2 were placed in a 2-gallon Parr pressure reactor and purged with nitrogen. The reactor was equipped with a stirrer, a top-mounted condenser with a pressure regulator (separate from the reactor and equipped with a valve), a 300 mL outlet below the condenser, and a catalyst addition manifold. The reactor was sealed and the reaction mixture was heated to an internal temperature of approximately 220 °C with stirring (using a two-bladed impeller shaft at 200 rpm), at which point the internal pressure was observed to be 10 psi. Then, TEA (53.0 g) was added through the catalyst addition manifold by pressurizing the top space above the catalyst to approximately 30 psi and briefly opening the valve until the pressure began to rise in the reactor (at which point the valve was closed). The remaining process conditions as described in Example 3 were repeated. The color of the precipitated slurry, the dried BHET product, and the recovered mother liquor obtained after filtering the BHET were measured.

[0088] Table 3 compares the products obtained from the glycolytic depolymerization of untreated clean color flakes (Example 3) and the DCM-pretreated clean color flakes described herein. The products are: (i) a slurry containing BHET products in the EG mother liquor, (ii) separated solid BHET, and (iii) liquid mother liquor. As shown in Table 3, the DCM-pretreated fabric exhibits significant improvements in optical properties, with L* increasing from 71.98 to 93.88, a* decreasing from 16.34 to -0.73 (less red), and b* decreasing from 62.73 to 26.31 (less yellow).

[0089] Table 3

[0090] Comparison of products obtained from the depolymerization of clean colored flakes via glycolysis (VOLCAT)

[0091] With and without preprocessing

[0092]

[0093] Example 5

[0094] DCM purification of black polyester fabric

[0095] A slice of 50 g of black polyester fabric with polyurethane appliqué was stirred with 250 g of DCM in a 500 mL Erlenmeyer flask at room temperature. The liquid turned deep purple almost immediately. After 1 hour and 15 minutes, the sample was filtered, rinsed with DCM, and blotted dry; the fabric weighed 49.5 g at this point. The polyurethane appliqué was found to have lifted off the fabric, and the fabric had turned light blue. After evaporation of the DCM, the extractable from the reaction was deep black / purple, weighing 1.9 g (3.8%). Figure 6The image shows a black input polyester fabric (left), decolorized in DCM (center left), decolorized polyester fabric (center right), and dye recovered after evaporation in DCM (right).

[0096] Example 6

[0097] Volate depolymerization of untreated black polyester fabric

[0098] 50 g of black polyester fabric, 250 g of EG, and 3.6 mL of TEA were sealed in a 450 mL glass Parr reactor with stirring (impeller downwards). The reaction was heated to 220 °C with stirring. After 30 minutes, the reactor was cooled to 100 °C, filtered through a glass fiber mat, and treated with 10 g of activated carbon at 90 °C for 30 minutes. The solution was then re-filtered through diatomaceous earth and allowed to cool to room temperature, during which time crystals formed. The BHET crystals were vacuum filtered, compressed using a rubber barrier, rinsed with water, and first vacuum dried on the filter, then dried overnight in a vacuum oven at 65 °C.

[0099] Example 7

[0100] Volate depolymerization of pretreated black polyester fabrics

[0101] 25 g of black polyester fabric, 250 g of EG, and 3.6 mL of TEA were sealed in a 450 mL glass Parr reactor (impeller facing down) with stirring. The reaction was heated to 220 °C with stirring. After 30 minutes, the reactor was cooled to 100 °C, filtered through a glass fiber mat, and treated with 10 g of activated carbon for 30 minutes. The solution was then re-filtered through diatomaceous earth and noted to have a lighter color than that of Example 4. After cooling to room temperature, crystals formed. The BHET crystals were vacuum filtered, compressed using a rubber barrier, rinsed with water, and first vacuum dried on a filter, then dried overnight in a vacuum oven at 65 °C. Figure 7 The diagram illustrates the VolCat depolymerization of (i) the untreated black polyester fabric of Example 4 (top image) and (ii) the pretreated black polyester fabric described herein (bottom image). The CIE color values ​​of the resulting BHET products are shown. Figure 7 The rightmost figure shows the following values ​​between untreated and pretreated fabric samples: improved whiteness of 91.5 to 95.7 (L*), red removal of 0.9 to -0.2 (a*), and a significant reduction in yellowness of 13.8 to 7.4 (b*).

[0102] Example 8

[0103] DCM purification of red 60 / 40 cotton / polyester fabric

[0104] At room temperature, 71.3 g of 60 / 40 red cotton / polyester fabric was agitated overnight in 750 g of DCM. The next morning, the fabric was filtered, wrung out to remove most of the DCM, and rinsed with two 75 mL volumes of additional DCM. The DCM was recovered on a rotary evaporator to obtain 1.0 g of red solids. The fabric was resuspended in the recovered DCM and agitated again overnight. The fabric was filtered again, wrung out to remove most of the DCM, and dried. The DCM was recovered using a rotary evaporator, yielding a total combined mass of 1.2 g of red solids. The dried fabric weighed 69.8 g, a loss of 1.5 g (2.1%). Figure 8 The image shows the received fabric (left), the dye extracted from the fabric using DCM treatment (center), and the fabric post-treatment (right).

Claims

1. A method comprising: (i) Purify the waste containing polyester terephthalate (PET) by treating it with dichloromethane (DCM); and (ii) Recycle purified PET from waste products of DCM treatment for recycling, wherein the treated PET includes polyester fabrics and / or polyester fibers used as pre-cleaned polyester inputs in the recycling process.

2. The method of claim 1, wherein the purified PET comprises solid and liquid components and contaminants are removed from the purified polyester sample by filtration.

3. The method of claim 2, wherein contaminants are removed by filtration after mixing with DCM for at least 1 hour.

4. The method of claim 2, wherein contaminants are removed by filtration after mixing with DCM for at least 2 hours.

5. The method of claim 1, wherein the DCM removes impurities selected from physical dirt and / or grime, colorants, organic impurities, and metallic and ionic impurities.

6. The method of claim 5, wherein the impurity is a colorant.

7. The method of claim 5, wherein the impurity is an organic impurity, including acetaldehyde or its acetal.

8. The method of claim 5, wherein the impurity is a metallic impurity, including iron or copper; optionally, wherein the copper is wire or powder.

9. The method of claim 1, wherein the waste further comprises a non-polyester polymer and wherein DCM removes impurities composed of the non-polyester polymer.

10. The method of claim 9, wherein the non-polyester polymer is selected from polyurethane, polyimide, polyamide, and combinations thereof.

11. The method of claim 1, wherein the recycling process is a chemical recycling process or a mechanical recycling process.

12. The method of claim 11, wherein the chemical recycling process is selected from solvent dissolution, alcoholysis, hydrolysis, acidolysis, phospholysis, ammonolysis, ammonolysis, and enzymatic hydrolysis.

13. The method of claim 12, wherein the chemical recycling process includes solvent dissolution.

14. The method of claim 12, wherein the chemical recycling process comprises glycolysis depolymerization.

15. The method according to any one of the preceding claims further includes removing DCM by pre-reaction distillation.

16. Purified PET recovered from the method according to any one of the preceding claims.

17. The purified PET of claim 16, wherein the purified PET comprises a solid component and a liquid component, wherein a contaminant floats to the surface of the liquid component and is removed by filtering the contaminant from the surface of the liquid component.

18. The purified PET of claim 16, wherein the purified PET comprises a solid component and a liquid component, and contaminants are removed from the purified PET sample by filtration.

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