Method for treating polyester-containing recycled material

Abstract

The invention provides a polyester-containing recycled material treatment method which comprises the following steps: providing a recycled material which comprises recycled polyester; performing a first stage depolymerization step, which comprises mixing the recovered polyester with oligomeric bis (2-hydroxyethyl) terephthalate (o-BHET) for extrusion depolymerization to at least obtain or produce poly (2-hydroxyethyl) terephthalate (p-BHET); and performing a second stage depolymerization step, which comprises mixing poly (bis (2-hydroxyethyl) terephthalate) (p-BHET) with a depolymerization solution to perform chemical depolymerization so as to at least obtain a monomer bis (2-hydroxyethyl) terephthalate (m-BHET).

Description

Technical Field

[0001] The invention relates to a method for processing recycled materials, in particular to a method for processing recycled materials containing polyester. Background Art

[0002] Polyester fiber fabrics are widely used in the market and in daily life. For example, polyester fiber can be woven with nylon fiber or spandex fiber, and then made into various kinds of fabrics such as cloth, clothes, shirts, sets, bags, quilts, hats, skirts, mattresses, pants, socks, etc. by the common methods used in the textile industry or garment industry. Therefore, with the rising awareness of environmental protection today, how to recycle the polyester in these waste fabrics and / or treat the recycled materials containing polyester has become a current research topic. Summary of the invention

[0003] The present invention is directed to a method for processing recycled materials containing polyester, which can improve the recovery rate of polyester and / or reduce the recovery cost of polyester.

[0004] According to an embodiment of the present invention, a method for processing recycled materials containing polyester includes the following steps: providing recycled materials, which include recycled polyester; performing a first depolymerization step, which includes mixing the recycled polyester with oligomeric bis(hydroxyethyl) terephthalate (o-BHET) and performing extrusion depolymerization to at least obtain or produce poly(hydroxyethyl) terephthalate) (p-BHET); and performing a second depolymerization step, which includes mixing poly(hydroxyethyl) terephthalate (p-BHET) with a depolymerization liquid and performing chemical depolymerization to at least obtain monomeric bis(hydroxyethyl) terephthalate (m-BHET).

[0005] According to an embodiment of the present invention, based on the total weight of the mixture in the first depolymerization step, the weight ratio of oligomeric bis(hydroxyethyl) terephthalate (o-BHET) is 5 wt % to 20 wt %.

[0006] According to one embodiment of the present invention, the first depolymerization step further comprises mixing the recovered polyester, oligomeric bis(hydroxyethyl) terephthalate (o-BHET) and a catalyst.

[0007] According to one embodiment of the present invention, the weight ratio of the catalyst is 0.2 wt % to 8 wt % based on the total weight of the mixture in the first depolymerization step.

[0008] According to one embodiment of the present invention, the extrusion depolymerization in the first stage of depolymerization step comprises heating to 200° C. to 280° C.

[0009] According to one embodiment of the present invention, the extrusion depolymerization in the first depolymerization step is performed for 1 minute to 10 minutes.

[0010] According to one embodiment of the present invention, the depolymerization liquid includes ethylene glycol, and the weight proportion of ethylene glycol is 30 wt % to 80 wt % based on the total weight of the mixture in the second depolymerization step.

[0011] According to one embodiment of the present invention, the chemical depolymerization in the second depolymerization step comprises heating to 190°C to 240°C.

[0012] According to one embodiment of the present invention, the chemical depolymerization in the second depolymerization step is carried out for 0.5 hour to 5 hours.

[0013] According to one embodiment of the present invention, the first depolymerization step is performed at least M times, and the second depolymerization step is performed at least N times, wherein M and N are both natural numbers, and M is greater than N. Furthermore, the oligomeric bis(hydroxyethyl) terephthalate (o-BHET) in the first depolymerization step performed for the Mth time includes that obtained by performing the second depolymerization step for the Nth time.

[0014] Based on the above, the polyester-containing recyclate processing method of the present invention can improve the polyester recovery rate and / or reduce the polyester recovery cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic flow chart of a method for processing recycled materials containing polyester according to an embodiment of the present invention.

[0016] Description of Reference Numerals

[0017] S11, S12, S20, S30, S40, S51, S52: steps. DETAILED DESCRIPTION

[0018] In the following detailed description, for the purpose of illustration and not limitation, exemplary embodiments that disclose specific details are set forth to provide a thorough understanding of the various principles of the present invention. However, it will be apparent to one of ordinary skill in the art that, with the benefit of this disclosure, the present invention may be practiced in other embodiments that depart from the specific details disclosed herein. In addition, descriptions of well-known devices, methods, and materials may be omitted to avoid obscuring the description of the various principles of the present invention.

[0019] Ranges may be expressed herein as from "about" one particular value to "about" another particular value, which may also be expressed directly as one particular value and / or to another particular value. When expressing the range, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when a value is expressed as an approximation by using the antecedent "about," it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each range may be expressly related to or independent of the other endpoint.

[0020] In this document, non-limiting terms (such as: may, can, for example or other similar terms) mean that implementation, inclusion, addition or existence are optional or necessary.

[0021] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. It will also be understood that terms (such as those defined in commonly used dictionaries) should be interpreted as having a meaning consistent with their meaning in the relevant technical context and should not be interpreted in an idealized or overly formal sense unless explicitly defined as such herein.

[0022] [Contains recycled polyester]

[0023] Providing recycled materials containing polyester.

[0024] In one embodiment, the method of obtaining recyclables includes, for example, collecting various types of recyclables or wastes containing polyester; and classifying the recyclables according to the type, color and / or purpose of use. The recyclables may include fabrics, but the present invention is not limited thereto. Fabrics may include cloth, clothes, shirts, sets, bags, quilts, hats, skirts, mattresses, pants, socks, etc., but the present invention is not limited thereto. Generally, regular fabric labels or product catalogs may indicate the fiber composition or proportion used.

[0025] In one embodiment, the recyclate containing polyester may be further subjected to one of the following pre-treatments (i.e., treatment before subsequent treatment; still recyclate in essence): removing objects on the recyclate (e.g., clips, fasteners, accessories, zippers, labels and / or other objects that are obviously not polyester-containing); performing preliminary cleaning of the recyclate (e.g., washing stains, shaking off impurities, etc., but not limited to); reducing the single size of the recyclate by quick or simple physical means (e.g., shearing, cutting, slicing or dicing, but not limited to); and / or drying the recyclate.

[0026] In one embodiment, the method of obtaining the recyclate may also include, for example, directly purchasing the processed recyclate containing polyester.

[0027] It should be noted that the term "polyester" herein includes polymers commonly referred to as polyesters, particularly aromatic polyesters, and particularly refers to polyesters derived from purified terephthalic acid (PTA) and ethylene glycol (EG) (i.e., polyethylene terephthalate (PET)).

[0028] In addition, the polyester herein may also be, for example, poly(trimethylene terephthalate), poly(butylene terephthalate), polyethylene naphthalate, or a combination thereof. In this embodiment, the polyester is preferably polyethylene terephthalate, poly(trimethylene terephthalate), or a combination thereof. In addition, copolymers may also be used, which particularly refer to copolymers that can be obtained by using two or more dicarboxylic acids and / or two or more diol components.

[0029] In one embodiment, the dyes used for fabrics are mostly organic dyes. For example, azo dyes (such as monoazo dyes or disazo dyes) are commonly used for dyeing polyester. Organic dyes usually have good adhesion to polymers. It is worth noting that the present invention does not limit the types of organic dyes.

[0030] In one embodiment, the dye used for the fabric does not include inorganic dyes. Most inorganic dyes contain heavy metal elements, which may easily cause allergies or discomfort to the human body.

[0031] In one embodiment, based on the total weight of the fabric, the weight proportion of the dye in the fabric is substantially less than 10 wt %.

[0032] In one embodiment, based on the total weight of the fabric, the weight ratio of the polyester in the fabric is substantially greater than or equal to 90 wt %.

[0033] [Pretreatment of recycled materials containing polyester]

[0034] In one embodiment, the recyclables of appropriate size can be selected by appropriate means (such as screening with a screen or air separation with an air separator, but not limited thereto) to carry out the subsequent reprocessing steps.

[0035] In one embodiment, the recyclables can be judged or confirmed to be of appropriate size by appropriate means (eg, weighing on a scale).

[0036] In one embodiment, taking a balance weighing method as an example, with approximately 2 grams as a unit, if the number of particles of the recyclables is greater than or approximately equal to 50, it can be determined that the recyclables are of an appropriate size.

[0037] In one embodiment, before the subsequent re-manufacturing steps are performed, the substrate may be physically sized (eg, sheared, trimmed, cut or diced, but not limited thereto).

[0038] [Recycling steps for recycled materials containing polyester]

[0039] Figure 1 FIG. 1 is a schematic flow chart of a method for processing recycled materials containing polyester according to an embodiment of the present invention. Figure 1As shown, the process of the method for processing polyester-containing recyclate may include the following steps.

[0040] Step S11: providing recycled material containing polyester or recycled polyester.

[0041] Step S12: providing oligo Bis(2-HydroxyEthyl)Terephthalate (o-BHET).

[0042] Step S20: First depolymerization step: Mix the polyester-containing recyclate or recycled polyester with oligomeric bis(2-HydroxyEthyl)Terephthalate to carry out reaction extrusion depolymerization, and at least obtain or produce poly(2-HydroxyEthyl)Terephthalate (p-BHET).

[0043] Step S30: at least obtaining or producing poly(bis(hydroxyethyl) terephthalate) (p-BHET).

[0044] Step S40: the second depolymerization step: chemically depolymerizing poly(bis(hydroxyethyl) terephthalate) (p-BHET).

[0045] Step S51: Obtain or produce monomer Bis(2-HydroxyEthyl)Terephthalate (m-BHET).

[0046] Step S52: Obtain or produce oligomeric bis(hydroxyethyl) terephthalate (o-BHET).

[0047] In addition, the oligomeric bis(hydroxyethyl) terephthalate (o-BHET) obtained or produced in step S52 can be used in the subsequent step S12.

[0048] Specifically, the steps of reprocessing the recycled material containing polyester may include a first depolymerization step and a second depolymerization step in sequence, which are described in detail as follows.

[0049] [First depolymerization step]

[0050] The recycled material or recycled polyester containing polyester may be fed into an extruder for extrusion to depolymerize the polyester therein by a reactive extrusion method.

[0051] The extruder is, for example, a commercially available single screw extruder (SSE), a twin screw extruder (TSE) or other similar screw extruders, but the present invention is not limited thereto. In addition, the present invention does not describe in detail the structure and / or operation of the commercially available screw extruders.

[0052] In one embodiment, oligomeric bis(hydroxyethyl) terephthalate (o-BHET) may be fed into an extruder to increase the depolymerization rate and / or quality of the polyester in the extruder.

[0053] In one embodiment, the aforementioned oligomeric bis(2-HydroxyEthyl) terephthalate (o-BHET) is, for example, a polymerization of 2 to 5 bis(2-HydroxyEthyl)Terephthalate (BHET) monomers. The number of monomers corresponding to the oligomeric bis(2-HydroxyEthyl) terephthalate (o-BHET) can be derived by an appropriate method (e.g., molecular weight estimation).

[0054] In one embodiment, bis(hydroxyethyl) terephthalate (BHET) may be one of the raw materials of polyester (e.g., polyethylene terephthalate (PET)). Therefore, the addition of BHET or its oligomers will not substantially affect the remanufacturing of recycled materials containing polyester (e.g., byproducts or impurities); or, the aforementioned effects may be reduced.

[0055] In one embodiment, oligomeric bis(hydroxyethyl) terephthalate (o-BHET) can be obtained through other or corresponding recovery steps.

[0056] In one embodiment, bis(hydroxyethyl) terephthalate or its oligomers can be obtained by esterification reaction of terephthalic acid (PTA) and ethylene glycol (EG).

[0057] In one embodiment, during the depolymerization of the polyester by reactive extrusion, substantially no ethylene glycol (EG) is added or fed into the extruder.

[0058] In one embodiment, since the boiling point of oligomeric bis(hydroxyethyl)terephthalate (o-BHET) is greater than the boiling point of bis(hydroxyethyl)terephthalate (BHET) and the boiling point of ethylene glycol (EG) (about 197° C.), feeding oligomeric bis(hydroxyethyl)terephthalate (o-BHET) into the extruder may be safer than feeding monomeric bis(hydroxyethyl)terephthalate (m-BHET) or ethylene glycol (EG) into the extruder, and / or the reprocessing steps and / or the corresponding equipment may be simpler. For example, compared to the method of feeding monomeric bis(hydroxyethyl)terephthalate (m-BHET) or ethylene glycol (EG), feeding oligomeric bis(hydroxyethyl)terephthalate (o-BHET) into the extruder may not require providing additional back pressure or reducing the back pressure of the extruder.

[0059] In one embodiment, the boiling point of oligomeric bis(hydroxyethyl) terephthalate (o-BHET) may be greater than about 250°C.

[0060] In one embodiment, based on the total weight of the material fed into the extruder, the weight ratio of oligomeric bis(hydroxyethyl) terephthalate (o-BHET) to the material fed into the extruder is substantially about 5 wt % to 20 wt %; preferably, about 10 wt % to 15 wt %.

[0061] In one embodiment, a corresponding catalyst may be introduced into the extruder to increase the depolymerization rate of the polyester in the extruder.

[0062] In one embodiment, the catalyst comprises organic metal.

[0063] In one embodiment, the organic metal used as the catalyst may include organic zinc (e.g., zinc acetate), organic cobalt (e.g., cobalt acetate), organic titanium (e.g., alkoxide titanium salt), organic antimony (e.g., antimony acetate), organic aluminum (e.g., aluminum formate, aluminum acetate, aluminum propionate, and other organic aluminum acids), or a combination thereof.

[0064] In one embodiment, based on the total weight of the material fed into the extruder, the weight ratio of the catalyst to the material fed into the extruder is substantially about 0.2wt% to 8wt%; preferably, about 0.5wt% to 5wt%.

[0065] In one embodiment, based on the total weight of the recycled material containing polyester, bis(hydroxyethyl) terephthalate (o-BHET) and the catalyst fed into the extruder, the weight ratio of bis(hydroxyethyl) terephthalate (o-BHET) to the above three materials fed into the extruder is substantially about 5wt% to 20wt%; preferably, about 10wt% to 15wt%.

[0066] In one embodiment, based on the total weight of the recycled polyester-containing material, oligomeric bis(hydroxyethyl) terephthalate (o-BHET) and the catalyst fed into the extruder, the weight ratio of the catalyst to the aforementioned three materials fed into the extruder is substantially about 0.2wt% to 8wt%; preferably, about 0.5wt% to 5wt%.

[0067] If the relative amount of the aforementioned oligomeric bis(hydroxyethyl) terephthalate (o-BHET) is too low (e.g., less than 5 wt%) and / or the relative amount of the catalyst is too low (e.g., less than 0.2 wt%), the depolymerization efficiency and / or depolymerization amount may be reduced, thereby reducing the subsequent treatment efficiency and / or recovery amount.

[0068] If the relative amount of the aforementioned oligomeric bis(hydroxyethyl) terephthalate (o-BHET) is too high (eg, greater than 20 wt%), the depolymerization ratio of the depolymerized product may be slightly increased, but the overall depolymerization amount may be reduced, thereby increasing the recycling cost.

[0069] If the relative amount of the aforementioned catalyst is too high (e.g., greater than 8 wt%), the depolymerization ratio of the depolymerized product may be slightly increased, but more catalyst must be used, the overall depolymerization amount is reduced, and / or the difficulty of subsequent catalyst treatment (e.g., separation of catalyst) is increased, thereby increasing the recycling cost.

[0070] In one embodiment, at least one feeder (e.g., side feeder) may be attached to the extruder. The feeder may be a loss-in-weight feeder equipped with a loss-in-weight meter. The aforementioned feeder is also a common commercially available device and / or optional accessory. In other words, the aforementioned components (e.g., recycled materials containing polyester; and oligomeric bis(hydroxyethyl) terephthalate (o-BHET) or catalyst) may be mixed before feeding; or, they may be fed into the extruder by different feeders and mixed in the extruder.

[0071] In one embodiment, the mixture in the extruder can substantially undergo a corresponding homogeneous reaction, thereby possibly reducing the corresponding mass transfer bottleneck.

[0072] In one embodiment, the extruder may have a heating zone. In this way, after the polyester-containing recyclate is fed into the extruder, the polyester-containing mixture in the extruder may be correspondingly extruded and heated to depolymerize by a hot extrusion reaction and then be extruded or extruded. In one embodiment, the heating temperature of the heating zone may be between about 200 and 280°C; preferably, about 220 to 260°C.

[0073] In one embodiment, the time for depolymerization of the polyester by the reactive extrusion method may be about 1 minute to 10 minutes; preferably, about 2 minutes to 5 minutes.

[0074] In one embodiment, the time for depolymerization of polyester by heated reactive extrusion method can be about 1 minute to 10 minutes; preferably, about 2 minutes to 5 minutes; wherein, the heating temperature can be between about 200°C and 280°C; preferably, about 220°C to 260°C.

[0075] If the depolymerization time is too short (eg, less than 1 minute) and / or the heating temperature is too low (eg, less than 200° C.), the depolymerization efficiency and / or depolymerization amount may be reduced, thereby reducing the subsequent processing efficiency and / or recovery amount.

[0076] If the depolymerization time is too long (eg, greater than 10 minutes) and / or the heating temperature is too high (eg, greater than 280° C.), the proportion of other byproducts or impurities may be too high, thereby reducing the subsequent treatment efficiency and / or recovery amount.

[0077] In one embodiment, the first depolymerization step can depolymerize most of the polyester in the recyclate into poly(bis(hydroxyethyl) terephthalate) (p-BHET), which contains more BHET monomers than oligo(bis(hydroxyethyl) terephthalate) (o-BHET), but is substantially insufficient to form suitable fibers or polymers.

[0078] In one embodiment, the aforementioned poly(bis(2-HydroxyEthyl)terephthalate) (p-BHET) is, for example, a polymerization of about 10 to 100 bis(2-HydroxyEthyl)Terephthalate (BHET) monomers. The number of monomers corresponding to poly(bis(2-HydroxyEthyl)terephthalate) (p-BHET) can be derived by an appropriate method (e.g., molecular weight estimation).

[0079] [Second depolymerization step]

[0080] The second depolymerization step is performed after the first depolymerization step.

[0081] The second depolymerization step may include chemical depolymerization. For example, the p-BHET obtained in the first depolymerization step and the depolymerization liquid may be placed in a depolymerization tank for chemical depolymerization.

[0082] The chemical depolymerization liquid can basically break the chain of poly (bis (hydroxyethyl) terephthalate) (p-BHET), thereby achieving a further depolymerization effect. In addition, it is possible to obtain a polyester composition with a shorter molecular chain (i.e., oligomeric bis (hydroxyethyl) terephthalate (o-BHET)) and an ester monomer composed of a diacid unit and two diol units (e.g., monomeric bis (hydroxyethyl) terephthalate (m-BHET)). In other words, the average molecular weight of the mixture after chemical depolymerization is basically smaller than the average molecular weight of the mixture obtained in the first depolymerization step (mostly poly (bis (hydroxyethyl) terephthalate (p-BHET)).

[0083] In addition, the present invention does not limit the type of depolymerization liquid. For example, water can be used for hydrolysis. For another example, alcohol (such as methanol, ethanol, ethylene glycol, diethylene glycol or a mixture thereof) can be used for alcoholysis.

[0084] In one embodiment, alcohols are preferred as the depolymerization liquid. Ethylene glycol (EG) is a more suitable alcoholysis liquid. One of the reasons may be that EG can be a reactive monomer for producing virgin PET chips.

[0085] In one embodiment, based on the total weight of the reaction materials involved in the depolymerization (e.g., poly(bis(hydroxyethyl) terephthalate) (p-BHET) and ethylene glycol obtained in the first depolymerization step), the weight ratio of ethylene glycol (EG) is substantially about 30 wt % to 80 wt %; preferably, about 40 wt % to 70 wt %.

[0086] If the relative amount of the aforementioned ethylene glycol is too low (eg, less than 30 wt %), the depolymerization efficiency and / or depolymerization amount may be reduced, thereby reducing the subsequent treatment efficiency and / or recovery amount.

[0087] If the relative amount of the aforementioned ethylene glycol is too high (eg, greater than 80 wt%), the depolymerization ratio of the depolymerized product may be slightly increased, but more ethylene glycol must be used and / or the overall depolymerization amount is reduced, thereby increasing the recycling cost.

[0088] When the chemical depolymerization reaction is carried out, a heating step may be appropriately performed. Generally speaking, heating can accelerate the progress of the chemical reaction. For example, the poly(bis(hydroxyethyl) terephthalate) (p-BHET) obtained in the first depolymerization step and ethylene glycol may be put into a depolymerization tank, and then an alcoholysis reaction may be carried out at a temperature of 190° C. to 240° C. for about 0.5 to 5 hours; preferably, an alcoholysis reaction may be carried out at a temperature of 200° C. to 230° C. for about 1 to 3 hours.

[0089] If the depolymerization time is too short (eg, less than 0.5 hours) and / or the heating temperature is too low (eg, less than 190° C.), the depolymerization efficiency and / or depolymerization amount may be reduced, thereby reducing the subsequent processing efficiency and / or recovery amount.

[0090] If the depolymerization time is too long (e.g., greater than 5 hours) and / or the heating temperature is too high (e.g., greater than 240° C.), most of the p-BHET may be depolymerized to m-BHET. Although the depolymerization ratio of the depolymerized product may be slightly increased, more time or cost (e.g., heat energy) is required, thereby increasing the recycling cost.

[0091] [Separation of depolymerization products]

[0092] The depolymerization product after the second depolymerization step may include a polyester component with a shorter molecular chain (i.e., oligomeric bis(hydroxyethyl) terephthalate (o-BHET)) and an ester monomer composed of a diacid unit and two diol units (e.g., monomeric bis(hydroxyethyl) terephthalate (m-BHET)). The ester monomer composed of a diacid unit and two diol units may be separated from the polyester component with a shorter molecular chain by an appropriate purification method (e.g., crystallization, activated carbon adsorption, filtration and / or drying).

[0093] <Examples and Comparative Examples>

[0094] The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples at all.

[0095] <Example 1>

[0096] Take about 90 kilograms (kg) of recycled polyester (such as waste PET fabric). And, mix the recycled polyester with about 10 kilograms of oligomeric bis(hydroxyethyl) terephthalate (o-BHET) and about 0.3 kilograms of zinc acetate (which can be used as a catalyst), and then send it into a twin-screw extruder for extrusion pre-depolymerization. The extruder temperature is set to about 260°C. After extrusion, the poly(bis(hydroxyethyl) terephthalate) (p-BHET) enters the stirring tank again, and about 400 kilograms of ethylene glycol (EG) and about 0.2 kilograms of zinc acetate (which can be used as a catalyst) are added, and the reaction is continued for about 180 minutes at an atmosphere of about 190°C to 200°C (such as about 195°C to 198°C) to depolymerize into a crude product. The crude product comprises oligomeric bis(hydroxyethyl) terephthalate (o-BHET) and monomeric bis(hydroxyethyl) terephthalate (m-BHET).

[0097] After depolymerization, the crude product is cooled to about room temperature (e.g., 198↘25°C), and oligomeric bis(hydroxyethyl) terephthalate (o-BHET) and monomeric bis(hydroxyethyl) terephthalate (m-BHET) are crystallized and filtered. After that, after the aforementioned crystals are mixed with hot water at about 90°C, oligomeric bis(hydroxyethyl) terephthalate (o-BHET) is basically insoluble and can be filtered out to be recovered in the extrusion pre-depolymerization unit for reuse; in addition, monomeric bis(hydroxyethyl) terephthalate (m-BHET) which is basically soluble in hot water at about 90°C can be purified by activated carbon or other suitable adsorbent materials to remove impurities. Afterwards, the purified 90° C. solution containing the monomer bis(hydroxyethyl) terephthalate (m-BHET) is cooled to about 5° C. to allow the monomer bis(hydroxyethyl) terephthalate (m-BHET) dissolved therein to crystallize out, and the solution is filtered and dried to obtain the corresponding monomer bis(hydroxyethyl) terephthalate (m-BHET).

[0098] Finally, based on the weight of polyester in the recycled material containing polyester, the recovery rate of the product monomer bis(hydroxyethyl) terephthalate (m-BHET) was about 80.6 wt %.

[0099] In the aforementioned method, the extrusion pre-depolymerization of the recycled material containing polyester and oligomeric bis(hydroxyethyl) terephthalate (o-BHET) is a molten homogeneous reaction. Moreover, the poly(bis(hydroxyethyl) terephthalate) (p-BHET) after extrusion depolymerization is basically soluble in ethylene glycol (EG) at about 190°C to 200°C (e.g., 195°C to 198°C), so the reaction of poly(bis(hydroxyethyl) terephthalate) (p-BHET) and ethylene glycol (EG) is a liquid homogeneous reaction. By carrying out the corresponding reaction in a homogeneous state, it is possible to accelerate the depolymerization reaction and / or improve the recovery rate of polyester.

[0100] <Example 2>, <Example 3> and <Example 4>

[0101] The methods of Example 2, Example 3 and Example 4 may be similar to those of Example 1, except that the ratio or amount of the pre-depolymerized oligomeric bis(hydroxyethyl) terephthalate (o-BHET) extruded, the ratio or amount of zinc acetate (which may be used as a catalyst), the ratio of the catalyst, and the corresponding adjustment of the temperature and / or time.

[0102] The corresponding adjustments and results of <Example 2>, <Example 3> and <Example 4> are shown in [Table 1].

[0103] [Table 1]

[0104]

[0105] <Comparative Example 1>

[0106] About 100 kg of recycled materials containing polyester (such as waste PET fabric) are taken. The waste PET fabric is reacted with about 0.5 kg of zinc acetate and about 400 kg of ethylene glycol (EG) at about 195° C. for about 180 minutes to depolymerize into a crude product, which includes oligomeric bis(hydroxyethyl) terephthalate (o-BHET) and monomeric bis(hydroxyethyl) terephthalate (m-BHET).

[0107] After depolymerization, the crude product is cooled to about room temperature (e.g., 198↘25°C), and oligomeric bis(hydroxyethyl) terephthalate (o-BHET) and monomeric bis(hydroxyethyl) terephthalate (m-BHET) are crystallized and filtered. After that, after the aforementioned crystals are mixed with hot water at about 90°C, oligomeric bis(hydroxyethyl) terephthalate (o-BHET) is basically insoluble and can be filtered out to be recovered in the extrusion pre-depolymerization unit for reuse; in addition, monomeric bis(hydroxyethyl) terephthalate (m-BHET) which is basically soluble in hot water at about 90°C can be purified by activated carbon or other suitable adsorbent materials to remove impurities. Afterwards, the purified solution containing the monomer bis(hydroxyethyl) terephthalate (m-BHET) at a temperature of about 90° C. is cooled to about 5° C. to allow the monomer bis(hydroxyethyl) terephthalate (m-BHET) dissolved therein to crystallize out, and the solution is filtered and dried to obtain the corresponding monomer bis(hydroxyethyl) terephthalate (m-BHET).

[0108] Finally, the recovery rate of the product monomer bis(hydroxyethyl) terephthalate (m-BHET) was about 67.4% based on the weight of polyester in the recycled material containing polyester.

[0109] In the aforementioned method, the recycled material containing polyester may be difficult or even insoluble in ethylene glycol (EG) at about 195° C. Therefore, the initial state of the corresponding depolymerization reaction is basically a solid-liquid heterogeneous reaction. As a result, the reaction rate and / or product ratio may be reduced.

[0110] <Comparative Example 2>, <Comparative Example 3>, and <Comparative Example 4>

[0111] The methods of <Comparative Example 2>, <Comparative Example 3> and <Comparative Example 4> can be similar to that of Comparative Example 1, and the difference may be: the ratio or amount of the pre-depolymerized oligomeric bis(hydroxyethyl) terephthalate (o-BHET) extruded, the ratio or amount of zinc acetate, and the corresponding adjustment of temperature and / or time.

[0112] The corresponding adjustments and results of <Comparative Example 2>, <Comparative Example 3> and <Comparative Example 4> are shown in Table 2.

[0113] [Table 2]

[0114]

[0115] [Utilization of depolymerization products]

[0116] The ester monomer composed of a diacid unit and two diol units (such as the monomer bis(hydroxyethyl) terephthalate (m-BHET)) can be obtained through the common methods of general polyester synthesis (such as esterification and polymerization reactions) to obtain the corresponding recycled polyester (recycle-PET, r-PET).

[0117] Polyester compositions with shorter molecular chains (e.g., oligomeric bis(hydroxyethyl) terephthalate (o-BHET)) can first be freed from impurities (e.g., dyes or their derivatives, salts, but not limited thereto) by appropriate means (e.g., crystallization, activated carbon adsorption, filtration, and / or drying); and then, can be used in subsequent steps of reprocessing the polyester-containing recyclate (e.g., the same or similar to the aforementioned first stage depolymerization step).

[0118] [Beneficial technical effects]

[0119] The method of the present invention firstly depolymerizes the polyester-containing recycled material or the recycled polyester into poly(bis(hydroxyethyl) terephthalate) (p-BHET) by the aforementioned first depolymerization step (including reaction extrusion depolymerization); and then depolymerizes the aforementioned poly(bis(hydroxyethyl) terephthalate) (p-BHET) into monomeric poly(bis(hydroxyethyl) terephthalate) (m-BHET) by the second depolymerization step (including chemical depolymerization). In this way, the recovery rate of polyester can be increased and / or the recovery cost of polyester can be reduced.

[0120] Compared with directly treating the polyester-containing recyclate or recycled polyester only by chemical depolymerization, the polyester recovery rate of the present invention can be higher and / or the polyester recovery cost can be lower. For example, directly treating the polyester-containing recyclate or recycled polyester only by chemical depolymerization may require a longer depolymerization time, require a larger amount of depolymerization liquid and / or may have more impurities, which may be caused by the polyester chain length of the directly treated polyester-containing recyclate or recycled polyester being longer and / or more difficult to dissolve.

[0121] In addition, if the polyester recycling process is performed multiple times by the method of the present invention, the oligomeric bis(hydroxyethyl) terephthalate (o-BHET) produced or obtained in the second stage depolymerization step of the previous time (not limited to the previous time; that is, it may include the previous time, the previous time or multiple times) can be used in the first stage depolymerization step of the next time (not limited to the next time; that is, it may include the next time, the next time or multiple times). In this way, the recovery rate of polyester can be improved and / or the recovery cost of polyester can be reduced.

[0122] [Practicality]

[0123] By using the method of the present invention, polyester in recycled materials (such as recycled fabrics) can be recycled. Furthermore, the recycled polyester can be reused. The reuse method includes, but is not limited to, the manufacture of fabrics, containers, plates, packaging materials, films and other polyester-containing objects.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for processing recycled materials containing polyester, characterized in that: include: providing recycled content, which includes recycled polyester; Performing a first depolymerization step, which includes mixing the recovered polyester with oligomeric bis(hydroxyethyl) terephthalate (o-BHET) for extrusion depolymerization to obtain or produce at least poly(bis(hydroxyethyl) terephthalate) (p-BHET); as well as The second depolymerization step includes mixing the poly(bis(hydroxyethyl) terephthalate) (p-BHET) with a depolymerization liquid to perform chemical depolymerization to obtain at least monomeric bis(hydroxyethyl) terephthalate (m-BHET).

2. The method for processing recycled materials containing polyester according to claim 1, characterized in that: Wherein, based on the total weight of the mixture in the first depolymerization step, the weight proportion of the oligomeric bis(hydroxyethyl) terephthalate (o-BHET) is 5 wt % to 20 wt %.

3. The method for processing recycled materials containing polyester according to claim 1, characterized in that: The first depolymerization step further comprises mixing the recycled polyester, the oligomeric bis(hydroxyethyl) terephthalate (o-BHET) and a catalyst.

4. The method for processing recycled materials containing polyester according to claim 3, characterized in that: Wherein, based on the total weight of the mixture in the first depolymerization step, the weight proportion of the catalyst is 0.2 wt % to 8 wt %.

5. The method for processing recycled materials containing polyester according to claim 1, characterized in that: The extrusion depolymerization in the first depolymerization step includes heating to 200°C to 280°C.

6. The method for processing recycled materials containing polyester according to claim 1, characterized in that: The extrusion depolymerization in the first depolymerization step is carried out for 1 minute to 10 minutes.

7. The method for processing recycled materials containing polyester according to claim 1, characterized in that: The depolymerization liquid comprises ethylene glycol, and the weight proportion of the ethylene glycol is 30wt% to 80wt% based on the total weight of the mixture in the second depolymerization step.

8. The method for processing recycled materials containing polyester according to claim 1, characterized in that: The chemical depolymerization in the second depolymerization step comprises heating to 190°C to 240°C.

9. The method for processing recycled materials containing polyester according to claim 1, characterized in that: The chemical depolymerization in the second depolymerization step is carried out for 0.5 to 5 hours.

10. The method for processing recycled materials containing polyester according to claim 1, characterized in that: in: The first deaggregation step is performed at least M times, and the second deaggregation step is performed at least N times, wherein M and N are both natural numbers, and M is greater than N; and The oligomeric bis(hydroxyethyl) terephthalate (o-BHET) in the first depolymerization step performed for the Mth time includes the oligomeric bis(hydroxyethyl) terephthalate (o-BHET) obtained by performing the second depolymerization step for the Nth time.

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