Method for treating polyester-containing recyclate

Abstract

To provide a disposal method for a recyclable material containing polyester (recyclate).SOLUTION: A disposal method for recyclate comprises: providing a recyclable material containing polyester; performing a first depolymerization step, comprising mixing the recyclable material and oligo-bis(2-hydroxyethyl) terephthalate (o-BHET) for reaction and extrusion depolymerization to at least obtain or produce poly-bis(2-hydroxyethyl) terephthalate (p-BHET); and performing a second depolymerization step, comprising mixing the p-BHET and a depolymerization solution for chemically depolymerization to at least obtain or produce monomer-bis(2-hydroxyethyl) terephthalate (m-BHET).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for treating recycled PET bottles, and more particularly to a method for treating recycled PET bottles containing polyester.

Background Art

[0002] Polyester fibers are a commonly seen fabric in the market and daily life. For example, polyester fibers are woven together with nylon fibers and spandex fibers, and are made into various types of fabrics such as clothes, shirts, covers, bags, quilts, hats, skirts, mattresses, trousers, and socks using conventional methods in the fabric industry and the sewing industry. With the recent awakening of environmental awareness, research is underway to recycle the polyester in these fabrics and / or to treat polyester waste.

Summary of the Invention

Problems to be Solved by the Invention

[0003] Therefore, the present invention provides a method for treating recycled PET bottles containing polyester.

Means for Solving the Problems

[0004] In one embodiment, the present invention provides a method for treating recycled polyester, the method comprising: providing a recycled material containing polyester; mixing the renewable material with oligo-bis(2-hydroxyethyl) terephthalate (о-BHET) to perform reaction and extrusion depolymerization to obtain or generate at least poly-bis(2-hydroxyethyl) terephthalate (p-BHET); performing a first depolymerization step; mixing p-BHET with a depolymerization solution to perform chemical depolymerization to obtain or generate at least monomer Bis(2-HydroxyEthyl) Terephthalate (m-BHET); and performing a second depolymerization step.

Advantages of the Invention

[0005] Based on the above, the present invention can improve the overall recycling efficiency and / or recycling rate of polyester, and further reduce the recycling cost.

Brief Description of the Drawings

[0006] Attached drawings are included to provide a further understanding of the present invention, which are incorporated herein and constitute a part of this specification. The drawings represent exemplary embodiments of the present invention and are useful for explaining the principles of the present invention together with the specification.

[0007]

Figure 1

Modes for Carrying Out the Invention

[0008] In the following detailed description, in order to provide a thorough understanding of various principles of the present invention, exemplary embodiments representing specific details are described for purposes of illustration and not limitation. However, it will be apparent to those skilled in the art who benefit from the present invention that the present invention may be practiced in other embodiments that depart from the specific details described herein. In addition, descriptions of well-known devices, methods, and materials are omitted so as not to obscure the description of the various principles of the present invention.

[0009] As used herein, non-limiting terms (e.g., about, substantially, essentially, inherently, can, be able to, or other similar terms) refer to non-essential or optional implementation, inclusion, addition, or presence.

[0010] A range may here be expressed as "about" one particular value to "about" another particular value, and may also be expressed linearly with one particular value and / or another particular value. When expressing the range, another embodiment includes from and / or to one particular value. Similarly, when a value is expressed as an approximation using "about" preceding it, it is understood that the particular value forms another embodiment. Furthermore, it is understood that the endpoints of each range are clearly related to or independent of another endpoint.

[0011] All terms used herein (including technical and scientific terms) have the same meaning as the meaning in the general knowledge in the technical field to which the present invention belongs or the generally understood meaning, unless otherwise defined. Terms (such as those defined in commonly used dictionaries) should be described as having a meaning consistent with the meaning in the relevant technical context, and it should be understood that they should not be interpreted in an idealized or overly formal meaning, except when clearly defined herein.

[0012] [Recycled material containing polyester] A recycled material containing polyester (also referred to as a recyclate) is provided. In one embodiment, the recycled material containing polyester may be referred to as a polyester-containing recyclate.

[0013] In one embodiment, a method for obtaining a recycled material includes collecting various types of recycled materials or wastes containing polyester, and performing corresponding classification according to the documents, colors, and / or purposes of the above-mentioned recycled materials. The above-mentioned recycled materials include, for example, clothes, shirts, covers, bags, quilts, hats, skirts, mattresses, trousers, socks, but the present invention is not limited thereto. Generally, the label of ordinary clothes indicates the fiber components used.

[0014] In one embodiment, a pretreatment (i.e., a treatment before subsequent treatment, essentially still a recycled material) may be further performed on the recycled material containing polyester. The pretreatment may include removing objects on the recycled material (e.g., clips, fasteners, ornaments, labels, and / or other objects that do not clearly contain other polyester), performing preliminary washing of the recycled material (e.g., washing stains, removing impurities, etc., but the present invention is not limited thereto), using physical methods to reduce the recycled material to a single size (e.g., including shearing, cutting, severing, or slitting, but the present invention is not limited thereto), and / or drying the recycled material.

[0015] In one embodiment, a method for obtaining a recycled material may include, for example, directly purchasing a processed polyester-containing recyclate.

[0016] The term "polyester" in this specification includes polymers generally called polyesters, particularly aromatic polyesters, and in particular refers to polyesters derived from purified terephthalic acid (PTA) and ethylene glycol (EG) (i.e., polyethylene terephthalate (PET)).

[0017] In addition, the polyester in this specification may be, for example, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, or a combination of the above materials. In an embodiment, the polyester is preferably polyethylene terephthalate, polytrimethylene terephthalate, or a combination thereof. In addition, a copolymer may be used, which particularly refers to a copolymer obtained using two or more dicarboxylic acids and / or two or more diol components.

[0018] In one embodiment, most of the dyes used in the fabric are organic dyes. For example, azo dyes (e.g., monoazo dyes or disazo dyes) are generally used to dye polyester. The adhesion of organic dyes to polymers is generally relatively good. It should be noted that the present invention does not limit the types of organic dyes.

[0019] In one embodiment, since most inorganic dyes contain heavy metal elements that are likely to cause allergies or discomfort to the human body, the dyes used in the fabric do not contain inorganic dyes.

[0020] In one embodiment, based on the total weight of the fabric, the weight ratio of the dye to the entire fabric is substantially less than 10% by weight.

[0021] In one embodiment, based on the total weight of the fabric, the weight ratio of the polyester to the entire fabric is higher than 90% by weight or substantially equal to 90% by weight.

[0022] [Pretreatment of Recycled Rate Containing Polyester] In one embodiment, the appropriate size of the recycled rate may be selected by an appropriate method for subsequent recycling steps (e.g., sieving by a sieve or classification by an air classifier, but the present invention is not limited thereto).

[0023] In one embodiment, the appropriate size of the recycled rate may be determined or confirmed by an appropriate method (e.g., weighing method such as a balance).

[0024] In one embodiment, the weighing method for determining or confirming the appropriate size of the recycled rate may include, for example, using 2 grams as a unit. When the number of particles of the recycled rate is 50 or more, it may be determined or confirmed as a recycled rate of an appropriate size.

[0025] In one embodiment, before proceeding to the subsequent recycling step, the recycled rate may be made into an appropriate size by a physical method (e.g., shearing, cutting, severing, or fracturing, but the present invention is not limited thereto).

[0026] [Recycling Step of Recycled Rate Containing Polyester] FIG. 1 is a flowchart of a method for treating a recycled rate containing polyester according to one embodiment of the present invention. As shown in FIG. 1, the process of the method for treating a recycled rate containing polyester may include the following steps.

[0027] Step S11: Provide a polyester-containing recycled rate or recycled polyester.

[0028] Step S12: Provide oligo-bis(2-hydroxyethyl) terephthalate (o-BHET).

[0029] Step S20: Execute the first depolymerization step. The first stage includes a process of mixing a polyester-containing recyclate or recycled polyester with о-BHET and performing reaction and extrusion depolymerization.

[0030] Step S30: At least poly-bis(2-hydroxyethyl) terephthalate (p-BHET) is obtained or generated.

[0031] Step S40: Execute the second depolymerization step. The first stage includes a process of performing chemical depolymerization of poly-bis(2-hydroxyethyl) terephthalate (p-BHET).

[0032] Step S51: Monomer-bis(2-hydroxyethyl) terephthalate (m-BHET) is obtained or generated.

[0033] Step S52: Oligo-bis(2-hydroxyethyl) terephthalate (о-BHET) is obtained or generated.

[0034] In one embodiment, the о-BHET obtained or generated in step S52 may be further used for subsequent steps that are the same as or similar to step S12.

[0035] Specifically, the process of the method for treating a recyclate containing polyester may subsequently include the first depolymerization step and the second depolymerization step, and the detailed description thereof is as follows.

[0036] [First Depolymerization Step] By feeding a polyester-containing recyclate or recycled polyester into an extruder for extrusion, the polyester therein is depolymerized by the reaction during extrusion. Thus, the depolymerization may be called reaction and extrusion depolymerization.

[0037] The extruder may be, for example, a commercially available single screw extruder (SSE), twin screw extruder (TSE), or other similar screw extruder, but the present invention is not limited thereto. In addition, the present invention does not detail the structure and / or operation of commercially available screw extruders.

[0038] In one embodiment, by supplying o-BHET to the extruder, the depolymerization and / or quality of the polyester supplied to the extruder may be improved.

[0039] In one embodiment, the above-described o-BHET may be, for example, a polymer of 2 to 5 bis(2-hydroxyethyl) terephthalate (BHET) monomers. The number of corresponding monomer units of o-BHET may be calculated or estimated by an appropriate method (e.g., calculated or estimated from the corresponding molecular weight).

[0040] In one embodiment, BHET may be one of the raw materials of the polyester (e.g., polyethylene terephthalate (PET)). Therefore, the addition of BHET or its oligomer basically does not affect the polyester recycled from the recyclate containing polyester (e.g., side reactants and / or impurities), or the side reactants and / or impurities can be reduced.

[0041] In one embodiment, o-BHET may be obtained or generated from other or corresponding recycling steps.

[0042] In one embodiment, BHET or its oligomer may be obtained or generated from the esterification reaction of terephthalic acid (PTA) and ethylene glycol (EG).

[0043] In one embodiment, during the process of depolymerizing the polyester by the reaction during extrusion, ethylene glycol (EG) is basically not added or supplied to the extruder.

[0044] The boiling point of o-BHET is higher than those of BHET and EG (about 197 °C or 387 °F). Therefore, in one embodiment, feeding o-BHET to an extruder can be simpler and / or safer for equipment (e.g., an extruder) corresponding to a recycling process (e.g., an extrusion process) compared to feeding m-BHET or EG to the extruder. For example, feeding o-BHET to an extruder can be done without the need to provide additional backpressure or with a reduced backpressure of the extruder compared to the method of feeding m-BHET or EG.

[0045] In one embodiment, the boiling point of o-BHET may be about 250 °C or 482 °F or higher.

[0046] In one embodiment, based on the total weight of the materials fed to the extruder, the weight ratio of o-BHET in the materials fed to the extruder is basically about 5 wt% to 20 wt%, preferably about 10 wt% to 15 wt%.

[0047] In one embodiment, a corresponding catalyst may be fed to the extruder to improve the depolymerization rate of the polyester fed to the extruder.

[0048] In one embodiment, the above-mentioned catalyst may include an organometallic compound.

[0049] In one embodiment, the organometallic compound as the above-mentioned catalyst may include organozinc (e.g., zinc acetate), organocobalt (e.g., cobalt acetate), organotitanium (e.g., alkoxide titanium salts), organoantimony (e.g., antimony acetate), organoaluminum (e.g., aluminum formate, aluminum acetate, aluminum propionate, and other organoaluminum compounds of organic acids), or combinations thereof.

[0050] In one embodiment, based on the total weight of the materials supplied to the extruder, the weight ratio of the catalyst in the materials supplied to the extruder is about 0.2 wt% to 8 wt%, preferably about 0.5 wt% to 5 wt%.

[0051] In one embodiment, based on the total weight of the recycled material containing polyester, о-BHET, and the catalyst supplied to the extruder, the weight ratio of о-BHET in the above three materials supplied to the extruder is basically about 5 wt% to 20 wt%, preferably about 10 wt% to 15 wt%.

[0052] In one embodiment, based on the total weight of the recycled material containing polyester, о-BHET, and the catalyst supplied to the extruder, the weight ratio of the catalyst in the above three materials supplied to the extruder is basically about 0.2 wt% to 8 wt%, preferably about 0.5 wt% to 5 wt%.

[0053] If the relative amount of the above-mentioned о-BHET is excessively low (for example, less than 5 wt%), and / or the relative amount of the catalyst is excessively low (for example, less than 0.2 wt%), the depolymerization efficiency and / or the amount of depolymerization may be reduced, thereby potentially reducing the subsequent treatment efficiency and / or the final relative recycling amount.

[0054] If the relative amount of the above-mentioned о-BHET is excessively high (for example, more than 20 wt%), although the depolymerization rate of the target depolymerized material slightly increases, conversely, the overall amount of depolymerization is reduced, which may increase the recycling cost.

[0055] If the relative amount of the above-mentioned catalyst is excessively high (for example, more than 8 wt%), although the depolymerization rate of the target depolymerized material slightly increases, more catalyst is required, which may reduce the overall amount of depolymerization, and / or conversely, increase the difficulty of subsequent catalyst treatment (for example, catalyst separation), thereby potentially increasing the recycling cost.

[0056] In one embodiment, at least one feeder (e.g., a side feeder) may be attached to the extruder. The feeder described above may be a loss-in-weight feeder equipped with a weighing scale. The feeder described above may also be a general commercially available module and / or optional accessory. In other words, various materials (e.g., recycled materials containing polyester, and further о-BHET and / or catalyst) may be mixed before supply, or they may be supplied to the extruder through different feeders and mixed within the extruder.

[0057] In one embodiment, a substantially corresponding homogeneous reaction occurs in the mixture within the extruder. In this way, the bottleneck of the process or reaction caused by the corresponding mass transfer can be reduced.

[0058] In one embodiment, the extruder may have a heating zone. In this way, after the recycled material containing polyester is supplied to the extruder, the polyester-containing mixture within the extruder is correspondingly extruded and heated, and then depolymerized through thermal extrusion or hot pressing reaction, and then may be squeezed out or extruded. In one embodiment, the heating temperature of the heating zone is about 200 - 280 °C, and preferably about 220 - 260 °C.

[0059] In one embodiment, the polyester depolymerization reaction time (also referred to as the extrusion time) during extrusion may be about 1 minute to 10 minutes, and preferably about 2 minutes to 5 minutes.

[0060] In one embodiment, the thermal polyester depolymerization reaction time (also referred to as the extrusion time) during extrusion may be about 1 minute to 10 minutes, and preferably about 2 minutes to 5 minutes, and the heating temperature may be between about 200 °C and 280 °C, and preferably about 220 °C to 260 °C.

[0061] When the above-mentioned extrusion time is excessively short (for example, less than 1 minute), and / or when the heating temperature is excessively low (for example, less than 200 °C), the depolymerization efficiency and / or the relative depolymerization rate may decrease, thereby potentially reducing the subsequent processing efficiency and / or the final relative regeneration amount.

[0062] When the above-mentioned depolymerization time is excessively long (for example, longer than 10 minutes), and / or when the heating temperature is excessively high (for example, higher than 280 °C), the relative ratio of side reaction products or impurities may increase, thereby potentially reducing the subsequent processing efficiency and / or the final relative regeneration amount.

[0063] In one embodiment, the first depolymerization step can depolymerize most of the polyester in the recycled material into poly-bis(2-hydroxyethyl) terephthalate (p-BHET). Compared with o-BHET, p-BHET contains many BHET monomers, but p-BHET is substantially insufficient to form fibers or polymers suitable for appropriate applications.

[0064] In one embodiment, the above-mentioned p-BHET is, for example, a polymerization of about 10 to 100 BHET monomers (for example, 10 to 100 BHET monomer units). The number of monomer units of the corresponding p-BHET may be calculated or estimated by an appropriate method (for example, calculated or estimated from the corresponding molecular weight).

[0065] [Second Depolymerization Step] The second depolymerization step is performed after the first depolymerization step.

[0066] The second depolymerization step may include a chemical depolymerization process. For example, the p-BHET obtained in the first depolymerization step may be introduced into a depolymerization tank together with a depolymerization solution for chemical depolymerization.

[0067] The chemical depolymerization solution can basically perform further depolymerization by breaking the polymer chains of p-BHET. In this way, it is possible to obtain compounds having shorter polyester chains (for example, о-BHET) and ester monomers composed of dicarboxylic acid units and diols (for example, m-BHET). In other words, the average molecular weight of the mixture after chemical depolymerization is basically lower than the average molecular weight of the mixture obtained in the first depolymerization step (mostly p-BHET).

[0068] The present invention does not limit the type of the depolymerization solution. For example, hydrolysis may be carried out using water. For example, alcoholysis may be carried out by using an alcohol (for example, methanol, ethanol, ethylene glycol, diethylene glycol, or a mixture thereof). In one embodiment, the depolymerization solution is preferably an alcohol. More preferably, the depolymerization solution is EG, because EG can serve as a reaction monomer for producing virgin PET chips.

[0069] In one embodiment, based on the total weight of the reactants involved in the depolymerization reaction (for example, p-BHET obtained in the first depolymerization step and ethylene glycol for the chemical depolymerization step), the weight ratio of EG is basically about 30 wt% to 80 wt%, and about 40 wt% to 70 wt% is preferred.

[0070] When the relative amount of ethylene glycol is excessively low (for example, less than 30 wt%), the depolymerization efficiency and / or the amount of depolymerization may decrease, which may reduce the subsequent treatment efficiency and / or the final relative regeneration amount may decrease.

[0071] When the relative amount of ethylene glycol is excessive (e.g., more than 80% by weight), although the depolymerization rate of the target depolymerizable material may slightly increase, more ethylene glycol may be required, and / or conversely, the overall amount of depolymerization may be reduced, which may increase the recycling cost.

[0072] During the chemical depolymerization reaction, an appropriate heating step may be carried out. The increase in temperature typically accelerates the rate of the chemical reaction. For example, after introducing p-BHET and ethylene glycol obtained in the first depolymerization step into the depolymerization tank, alcoholysis may be carried out at a temperature of 190°C to 240°C for about 0.5 hours to 5 hours. Alcoholysis is preferably carried out at a temperature of 200°C to 230°C for 1 hour to 3 hours.

[0073] When the above-mentioned chemical depolymerization time is excessively short (e.g., less than 0.5 hours), and / or when the heating temperature is excessively low (e.g., less than 190°C), the depolymerization efficiency and / or the amount of depolymerization may decrease, which may reduce the subsequent treatment efficiency and / or the final relative recycling amount.

[0074] When the above-mentioned chemical depolymerization time is excessively long (e.g., longer than 5 hours), and / or when the heating temperature is excessively high (e.g., higher than 240°C), although the depolymerization rate may slightly increase, since most of the p-BHET has been depolymerized into m-BHET, more time or cost (e.g., thermal energy) is required.

[0075] [Separation of the product of the above-mentioned depolymerization step] The depolymerization product after performing the second depolymerization step may include a compound having a shorter polyester chain (e.g., о-BHET) and an ester monomer composed of a dicarboxylic acid unit and a diol (e.g., m-BHET). The ester monomer and the compound having a shorter polyester chain may be separated by an appropriate purification method (e.g., crystallization, activated carbon adsorption, filtration, and / or drying).

[0076] [Examples and Comparative Examples] Examples and comparative examples for explaining the present invention are shown below, but the present invention is not limited thereto.

[0077] <Example 1>

[0078] Provide about 90 kilograms (kg) of polyester-containing recyclate (e.g., waste PET fabric, “PET” in Table 1). Mix the above-described polyester-containing recyclate with about 10 kg of о-BHET and about 0.3 kg of zinc acetate (which may be referred to as a catalyst), and then supply it to a twin-screw extruder for extrusion and preliminary depolymerization. The heating temperature of the extruder is about 260°C. Then, the extruded p-BHET (“extrusion product” in Table 1) is introduced into a stirring tank, about 400 kg of additional EG and about 0.2 kg of zinc acetate (which may be referred to as a catalyst) are added, and the reaction is continued at about 190°C to 200°C (e.g., about 195°C to 198°C) for about 180 minutes to depolymerize the crude product. The crude product contains о-BHET and m-BHET.

[0079] After depolymerization, the crude product is cooled to approximately room temperature (e.g., represented as 198 → 25°C), and о-BHET and m-BHET are crystallized and filtered. Subsequently, the above-described filtered crystals are mixed with warm water at 90°C. о-BHET is basically insoluble and is filtered for reuse by extrusion and preliminary depolymerization. m-BHET, which is basically soluble in warm water at 90°C, is purified by removing impurities using activated carbon or other suitable adsorbents. Then, the purified 90°C solution containing m-BHET is cooled to about 5°C, dissolved to crystallize and precipitate m-BHET, and after filtration and drying, the corresponding m-BHET is obtained.

[0080] Finally, based on the weight of the original polyester-containing recyclate, the weight ratio of the m-BHET product is about 80.6% by weight. That is, the recycling rate of the polyester is about 80.6% by weight.

[0081] In the above method, the depolymerization reaction (i.e., the first depolymerization step, which may be called the preliminary depolymerization step) between the recyclate containing polyester and o-BHET during extrusion is a homogeneous reaction in a substantially molten state. In addition, after the above-mentioned preliminary depolymerization step, the extruded p-BHET is basically soluble in EG at about 190°C to 200°C (for example, about 195°C to 198°C). Therefore, the chemical depolymerization process of p-BHET and EG (i.e., the second depolymerization step) is a homogeneous reaction of liquids. Through the corresponding reactions under the corresponding homogeneous reactions, the overall total recycling efficiency and / or recycling rate of polyester can be increased.

[0082] <Example 2>, <Example 3>, <Example 4>

[0083] Examples 2, 3, and 4 were carried out in a manner similar to Example 1. The obvious differences are the ratio of the amount of o-BHET in the preliminary depolymerization step, the ratio of the amount of zinc acetate in the corresponding depolymerization step ("ZnAc" in Table 1), the corresponding reaction temperature ("Temperature" in Table 1), and / or the corresponding reaction time ("Time" in Table 1).

[0084] The corresponding conditions / parameters and results of Examples 2, 3, and 4 are shown in Table 1.

[0085]

Table 1

[0086] <Comparative Example 1>

[0087] Provide a recyclate containing about 100 kilograms (kg) of polyester (for example, waste PET fabric, "PET" in Table 2). The recyclate containing the above-mentioned polyester is introduced into a stirring tank, about 400 kg of additional EG and about 0.5 kg of zinc acetate are added, and the reaction is continued at about 190°C to 200°C (for example, about 195°C to 198°C) for about 180 minutes to depolymerize into a crude product. The crude product contains o-BHET and m-BHET.

[0088] After depolymerization, the crude product is cooled to approximately room temperature (e.g., represented as 198 → 25°C), and о-BHET and m-BHET are crystallized and filtered. Subsequently, the above-mentioned filtered crystals are mixed with warm water at 90°C. о-BHET is basically insoluble and is filtered. m-BHET, which is basically soluble in warm water at 90°C, is purified by removing impurities using activated carbon or other suitable adsorbents. Thereafter, the purified solution of m-BHET at 90°C is cooled to approximately 5°C, and m-BHET is crystallized and precipitated by dissolving it, and after filtration and drying, the corresponding m-BHET is obtained.

[0089] Finally, based on the weight of the original polyester-containing recyclate, the weight ratio of the m-BHET product is approximately 67.4% by weight. That is, the recycling rate of the polyester is approximately 67.4% by weight.

[0090] In the method described above, it is difficult, and even impossible, for the recyclate containing polyester to melt in EG at approximately 190°C to 200°C (e.g., approximately 195°C to 198°C). For this reason, the initial reaction state of the corresponding depolymerization reaction is basically a solid-liquid heterogeneous reaction. As a result, the overall recycling efficiency and / or recycling rate decreases or drops.

[0091] <Comparative Example 2>, <Comparative Example 3>, <Comparative Example 4>

[0092] Comparative Example 2, Comparative Example 3, and Comparative Example 4 were carried out in a method similar to Comparative Example 1. The obvious differences are the ratio of the amount of zinc acetate (「ZnAc」 in Table 2) in the corresponding depolymerization step, the corresponding reaction temperature (「temperature」 in Table 2), and / or the corresponding reaction time (「time」 in Table 2).

[0093]

Table 2

[0094] [Utilization of the product after depolymerization] From the ester monomer (e.g., m-BHET) composed of a dicarboxylic acid unit and a diol obtained by the above-described treatment method, the corresponding recycled polyester (recycled PET, r-PET) can be obtained by a general synthesis method (e.g., esterification and / or polymerization reaction).

[0095] A compound with a shorter polyester chain (e.g., о-BHET) is purified by an appropriate method (e.g., crystallization, activated carbon adsorption, filtration, and / or drying) to remove impurities (e.g., dyes or their derivatives, salts, but not limited thereto), and then the purified compound with a shorter polyester chain can be used in subsequent regeneration steps (e.g., the same or similar to the above-described first depolymerization step) of the treatment method of the recyclate containing polyester.

[0096] [Unexpected effect] The treatment method of the present invention includes the above-described first depolymerization step (including the reaction during extrusion) for depolymerizing the polyester-containing recyclate into p-BHET, and the above-described second depolymerization step (including a chemical depolymerization reaction) for depolymerizing the above-described p-BHET into m-BHET. In this way, the overall recycling efficiency and / or recycling rate of polyester can be increased, and further, the recycling cost can be reduced thereby.

[0097] Compared with the direct treatment method (e.g., only chemical depolymerization shown in the above-described comparative example), the overall recycling efficiency and / or recycling rate of the polyester of the present invention is high, and further, the recycling cost can be further reduced. For example, the treatment method of the recyclate containing polyester by only chemical depolymerization may require a longer depolymerization time, may require a larger amount of depolymerization solution, and / or may produce more impurities. The reason may be that the polyester chain length of the recyclate is longer and / or the long-chain polyester is difficult to dissolve in EG.

[0098] In addition, when the processing method of the present invention is executed in a plurality of cycles or a plurality of times, the о-BHET generated or obtained in the second depolymerization step in the previous cycle or the previous time (not limited to the previous cycle or the previous time, for example, it may include the previous cycle or the previous time, the previous cycle or the previous times, or a plurality of previous cycles or the previous time) can be used in the first depolymerization step of subsequent processing (not limited to the next cycle or the next time, for example, it may include the next cycle or the next time, the subsequent cycle or the subsequent times, or a plurality of subsequent cycles or the subsequent times). In this way, the overall recycling efficiency and / or recycling rate of the polyester can be increased, and furthermore, the overall recycling cost can be reduced thereby.

[0099] It will be apparent to those skilled in the art that various modifications and variations can be made to the described embodiments without departing from the scope or spirit of the present invention. In view of the above, the present invention is intended to embrace modifications and variations as long as they fall within the scope of the appended claims and their equivalents.

Industrial Applicability

[0100] By using the processing method of the present invention, the polyester in the recycled material (for example, recycled fabric) can be recycled. Furthermore, the recycled polyester can be reused. The reuse methods include, but are not limited to, the manufacture of fabrics, containers, sheets, packaging materials, films, and other polyester-containing products.

Explanation of Signs

[0101] S11, S12, S20, S30, S40, S51, S52: Steps

Claims

1. Providing a recycled material containing polyester, Mixing the recycled material with oligo-bis(2-hydroxyethyl) terephthalate (o-BHET) and performing reaction and extrusion depolymerization to obtain or generate at least poly-bis(2-hydroxyethyl) terephthalate (p-BHET), and executing a first depolymerization step, Mixing the p-BHET with a depolymerization solution and performing chemical depolymerization in which the reaction system is liquid in a depolymerization tank to obtain or generate a crude product containing at least monomer-bis(2-hydroxyethyl) terephthalate (m-BHET) and oligo-bis(2-hydroxyethyl) terephthalate (o-BHET), and executing a second depolymerization step, Cooling and crystallizing the crude product, filtering it, dissolving the filtered crystals in warm water, and obtaining a solution containing monomer-bis(2-hydroxyethyl) terephthalate (m-BHET), including, The depolymerization solution contains ethylene glycol, and the weight ratio of the ethylene glycol to the total weight of the mixture in the second depolymerization step is 30% by weight to 80% by weight, The first depolymerization step and the second depolymerization step further include mixing a catalyst, The extrusion depolymerization in the first depolymerization step includes heating to 200°C to 280°C, The chemical depolymerization in the second depolymerization step includes heating to 190°C to 240°C, a method for treating a recyclate.

2. The weight ratio of the o-BHET to the total weight of the mixture in the first depolymerization step is 5% by weight to 20% by weight. The method for treating a recyclate according to Claim 1.

3. The weight ratio of the catalyst to the total weight of the mixture in the first depolymerization step is 0.2% by weight to 8% by weight. The method for treating a recyclate according to Claim 1.

4. The first depolymerization step is executed for 1 minute to 10 minutes. The method for treating a recyclate according to Claim 1.

5. The second depolymerization step is executed for 0.5 hour to 5 hours. The method for treating a recyclate according to Claim 1.

6. The first depolymerization step is executed at least M times or M cycles, and the second depolymerization step is executed at least N times or N cycles. Both M and N are natural numbers, and M is greater than N. The method for treating the recycling rate according to claim 1, wherein the о-BHET used for mixing in the M-th or M-th cycle of the first depolymerization step includes the о-BHET obtained or generated in the N-th or N-th cycle of the second depolymerization step.

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