Depolymerization method of polyethylene terephthalate by glycol decomposition

Abstract

The present invention relates to a process for depolymerization of a material comprising polyethylene terephthalate (PET) by glycolysis with ethylene glycol (EG), comprising reacting the material comprising PET with EG in the presence of at least one catalyst to obtain glycollysis products comprising bis(2-hydroxyethyl) terephthalate (BHET) and / or its oligomers, the catalyst comprising an acetate salt of a metal selected from calcium, magnesium, aluminum, and mixtures thereof. The catalyst can be prepared by in situ reaction of acetic acid with a compound comprising the metal.

Description

Technical Field

[0001] The present invention relates to a method for depolymerizing polyethylene terephthalate by glycolysis. Specifically, the method uses a catalyst that has a reduced impact on the environment and can be prepared from readily available raw materials.

Background Art

[0002] Polyethylene terephthalate (PET) is a semi-crystalline thermoplastic polyester having high strength and high transparency. PET is obtained by an esterification reaction of terephthalic acid (TPA) and ethylene glycol (EG), or a transesterification reaction of dimethyl terephthalate (DMT) and EG. Due to its physical and chemical properties, PET has many applications. Specifically, PET is used for the production of textile fibers and carpets (fiber grade PET), food containers (e.g., beverage bottles, bottle grade PET), and food packaging films (film grade PET).

[0003] Currently, worldwide PET production reaches amounts exceeding 80 million tons per year. From the viewpoints of the high consumption of PET and its non-biodegradability, there is a strong technical need to recycle this material in order to reduce the environmental impact of used products and the consumption of oil-derived raw materials for the production of new products.

[0004] The primary method of PET waste recycling is so-called "mechanical recycling." Mechanical recycling is based on the mechanical separation of polymers from impurities and subsequent re-granulation. Specifically, mechanical recycling involves sorting and separating PET waste, removing impurities, crushing, heat treatment, and extrusion into granules. This recycling technology is widely used but limited, and can only be used to recover PET from bottles, with relatively low impurity content (less than approximately 10% (by weight / weight)). In addition, the presence of dyes and other additives in PET waste, as well as the need for re-granulation to enable reintroduction into industrial manufacturing cycles, results in recycled polymers of lower quality than those obtained from virgin raw materials. Mechanical recycling also involves the accumulation of the aforementioned impurities in the polymer, leading to a degradation of polymer quality with each recycling.

[0005] The second method of PET waste recycling is so-called "chemical recycling." Chemical recycling is based on the chemical conversion (depolymerization) of PET polymer chains to their starting monomers or oligomers through solvolysis. The PET depolymerization product can be easily purified from contaminants and then used in new polymerization methods, thus overcoming the drawbacks associated with mechanical recycling methods. Chemical recycling has the added advantage of satisfying the criteria that support the concepts of a circular economy and sustainable development, as it makes it possible to obtain the original raw materials from the treatment of PET waste.

[0006] The PET depolymerization reaction can be carried out by several methods, as described below. • To produce monomer EG and TPA by hydrolysis (acidic, alkaline, or neutral). • DMT is produced by methanol decomposition, and then converted to PET by transesterification with EG. • To produce bis-2-hydroxyethyl terephthalate (BHET) by glycol decomposition, for example, by decomposition of polymer chains with EG.

[0007] Currently, depolymerization by glycol decomposition using EG is considered the most promising and advantageous recycling technology for development, as it yields products (compound BHET) that can be directly used as monomers in the synthesis of PET or other widely used polymers (e.g., unsaturated polyester resins for polyurethane production).

[0008] Depolymerization of PET by glycol decomposition using EG is generally carried out at temperatures in the range of 180°C to 250°C and atmospheric pressure, usually in the presence of a catalyst. During depolymerization, the polymer chains are transformed by solvolysis cleavage, resulting in monomers (BHET) by theoretical complete depolymerization or monomers together with oligomers by partial depolymerization.

[0009] A schematic diagram of the reaction process for the depolymerization of PET using EG is shown in Diagram 1 below. [ka]

[0010] BHET can be used as a monomer to produce various grades of PET (bottle grade, fiber grade, and film grade) that have characteristics and properties completely equivalent to those of PET obtained from virgin raw materials. Diagram 2 shows the polymerization reaction that results in the production of PET from BHET. [ka]

[0011] The polymerization of BHET releases 1 mole of EG, which can be recycled, for example, in a depolymerization method.

[0012] Depolymerization can be carried out in the presence or absence of a catalyst. However, non-catalytic depolymerization is not economically viable compared to catalytic glycol decomposition due to the low conversion yield of PET to BHET and the significantly longer reaction time.

[0013] The catalysts most commonly used for PET depolymerization are primarily based on metal salts, specifically salts of Zn, Ti, Pb, Mn, and Na. These metal salts are typically acetates, carbonates, bicarbonates, and hydrochlorides. In industrial methods, zinc acetate is by far the most widely used catalyst due to its high efficiency in terms of depolymerization rate and yield.

[0014] At the end of depolymerization, the metal introduced with the catalyst must be removed from the monomer before being used to produce further polymers, in order to prevent interference with the quality of the final product and to avoid accumulation in the polymer during subsequent recycling cycles.

[0015] Catalytic depolymerization methods using metal salts as catalysts are described, for example, in European Patent Application Publication No. 0723951(A1) and International Publication No. 2017 / 087752(A1).

[0016] European Patent Application Publication No. 0723951(A1) describes a method for preparing high-purity BHET by depolymerizing PET from recycled post-consumer or industrial waste. Preferably, the depolymerization is catalyzed with catalysts based on zinc acetate, lath acetate, and ce acetate, or titanium butoxide (Ti(OBu)4). In the sole example of the method's implementation, zinc acetate is used as the catalyst at an amount of about 2.2 mmol / kg (PET+EG). European Patent Application Publication No. 0723951(A1) further mentions calcium acetate and other compounds among the catalysts tested, showing that calcium acetate is less effective compared to zinc acetate.

[0017] International Publication No. 2017 / 087752(A1) describes a chemical recycling method for PET in which the depolymerization reaction is assisted by microwaves. The reaction mixture includes a catalytic system comprising a catalyst and a microwave absorber. The catalyst is preferably a zinc salt, specifically zinc acetate. An alternative catalyst is magnesium acetate.

[0018] The metal catalysts currently used for PET depolymerization in state-of-the-art technology have several drawbacks. Firstly, the most effective catalysts are based on transition metals and heavy metals (e.g., Zn, Ti, Pb), i.e., elements with a significant environmental impact, and removing them from the BHET monomer at the end of depolymerization is quite difficult.

[0019] Secondly, since catalysts are used in relatively large quantities (the catalyst / PET ratio in the reaction mixture can be 4% to 6% (by weight) depending on the type of catalyst and reaction conditions), it is extremely important in industrial plants to ensure that a large amount of catalyst is always available in order to guarantee the continuity of the depolymerization method. This means that the plant must have appropriate storage space for the catalyst, and very often the catalyst must also be stored under controlled humidity and temperature conditions to prevent degradation (for example, alkali metal and alkaline earth metal acetates are hygroscopic).

[0020] Thirdly, since catalysts are synthetic compounds, their manufacturing costs are relatively high, significantly impacting the final cost of the resulting BHET.

[0021] From the perspective of the aforementioned shortcomings, it is clear that the latest technology clearly requires catalytic depolymerization methods using alternative catalysts to those of known technologies. Specifically, the catalyst must have a low environmental impact and be readily and inexpensively available.

[0022] A further drawback of PET recycling methods is the limited types of waste that can be depolymerized. Currently, PET waste recovered through depolymerization almost without exception originates from the separate collection of plastic containers, particularly bottles. Other types of waste, especially PET fibers from spinning processes or post-consumer carpet collection, are largely unused and end up in landfills due to the high levels of impurities they contain.

[0023] Carpets containing PET are composed of, for example, multilayer structures containing different types of materials, namely polymer materials and non-polymer materials, and there are various inorganic substances used as additives. Specifically, in carpets, polyester is used to produce the fiber part visible from the outside, the lower layer support cloth or lower layer support mesh (so-called primary base fabric) to which the fiber part is bonded, or the lining of the carpet (so-called secondary base fabric) that contacts the support surface. An intermediate layer of an adhesive or reinforcing material such as rubber latex and filler materials (e.g., calcium salts and magnesium salts, aluminum compounds) can be arranged between these layers. At the end of these life cycles, carpets containing PET are generally subjected to cutting and separation of the admixture fraction, resulting in a fibrous material having a cotton-like appearance (so-called fluff). The fluff contains PET together with a relatively large amount of admixture (about 20% by weight or less), and the most abundant admixtures are calcium carbonate and / or magnesium carbonate, dolomite minerals, aluminosilicates, and aluminum trihydroxide.

[0024] Together with the admixtures (e.g., adhesives) adsorbed during use, the specific structure and chemical composition of the carpet make the recovery of the PET contained therein quite complicated and economically unfeasible. However, PET waste from carpets is still a very interesting material source for recycling because it is available in large quantities. Therefore, it is desirable to develop a depolymerization method that can also effectively use this type of material.

Summary of the Invention

Problems to be Solved by the Invention

[0025] Therefore, from the perspective of the aforementioned prior art, the applicant faced the problem of providing a method for depolymerizing a material containing PET that overcomes the aforementioned drawbacks of the known art. Specifically, the applicant faced the problem of providing a depolymerization method that uses a catalyst with a reduced environmental impact and having an efficiency similar to that of known catalysts or even superior to known catalysts. In addition, the catalyst must be readily available or easily prepared from raw materials having these characteristics.

[0026] The applicant has further addressed the problem of providing a depolymerization method that can supply PET-containing materials derived from various types of waste and processing scraps, including PET-containing materials derived from waste containing a significant amount of contaminants such as post-consumer carpet recycling waste.

Means for Solving the Problems

[0027] It has been found that the above and other objects, further exemplified in the following description, can be achieved by a method for depolymerizing a material containing PET using calcium acetate, magnesium acetate, or aluminum acetate as a catalyst. These salts, although the metal components are not composed of heavy metals or transition metals but consist of alkaline earth metals (Ca and Mg) and amphoteric metals (Al), have been found to be similar to the most efficient catalysts known in the prior art such as zinc acetate while reducing the environmental impact, and may even have a higher efficiency than the said catalyst. Furthermore, these salts are readily available and relatively inexpensive, and can be easily removed from the BHET obtained at the end of the depolymerization even by simply washing with water.

[0028] In some cases (e.g., calcium acetate), the catalyst according to the present invention exhibits a higher reaction rate than known catalysts even at a low weight concentration, enabling the depolymerization to be completed in a shorter time compared to known methods. This provides the advantage that a smaller volume reactor can be used for the same production capacity compared to what is required in state-of-the-art methods.

[0029] The applicant also found, surprisingly, that a depolymerization catalyst could be generated in situ in a reaction mixture of acetic acid and a compound containing a metal counterion, such as an oxide, hydroxide, carbonate, or bicarbonate of the aforementioned metal. By appropriately adding acetic acid and the metal-containing compound to the reaction mixture, it was possible to generate metal acetates capable of catalyzing the depolymerization reaction with efficiency in exactly the same way as the same compound prepared in-house (ex situ) and added to the reaction mixture, both in terms of reaction rate and conversion yield from PET to BHET.

[0030] The in situ generation of catalysts from readily available, low-cost, and environmentally friendly reagents makes it possible to overcome the disadvantages associated with the catalyst supply of the known technologies described above.

[0031] It has also been observed that catalysts can be prepared in situ by using calcium carbonate, a mixture of calcium carbonate and magnesium carbonate, or a metal compound present as an inclusion in PET-containing materials supplied for depolymerization, such as aluminum hydroxide, which is commonly found in materials derived from post-consumer carpet waste. This makes it possible to utilize a wide range of PET waste for the production of BHET, specifically post-consumer carpet waste and other materials that are currently mainly disposed of in landfills.

[0032] In addition, the in situ catalyst preparation methods described herein are not limited to Ca, Mg, and Al acetates. In fact, these methods can be advantageously used in the depolymerization of PET-containing materials by glycol decomposition in the presence of any metal acetate salt capable of efficiently acting as a depolymerization catalyst, such as zinc acetate, lead acetate, iron acetate, manganese acetate, and antimony acetate, which are known catalysts.

[0033] Accordingly, according to a first aspect, the present invention relates to a method for depolymerizing a material containing polyethylene terephthalate (PET) by glycol degradation using monoethylene glycol (EG), comprising reacting the material containing PET with EG in the presence of at least one catalyst to obtain a glycolized product containing bis(2-hydroxyethyl) terephthalate (BHET) and / or its oligomer, wherein the catalyst comprises an acetate of a metal selected from calcium, magnesium, aluminum, and mixtures thereof.

[0034] According to a second aspect, the present invention relates to a method for depolymerizing a material containing polyethylene terephthalate (PET) by glycol decomposition using ethylene glycol (EG), comprising reacting PET with EG in the presence of at least one catalyst containing a metal acetate to obtain a glycol decomposition product containing bis(2-hydroxyethyl) terephthalate (BHET) and / or its oligomer, wherein the catalyst is obtained in situ by the reaction of acetic acid with a compound containing the metal. [Brief explanation of the drawing]

[0035] [Figure 1] This figure shows the time-dependent trend of the total yield of the depolymerization reaction in Examples 1 to 3. [Figure 2] This figure shows the time-dependent trend of the total yield of the depolymerization reaction in Examples 4 and 5. [Figure 3] This figure shows the time-dependent trend of the total yield of the depolymerization reaction in Examples 6 and 7. [Figure 4] This figure shows the time-dependent trend of the total yield of the depolymerization reaction in Example 8. [Figure 5] This figure shows the time-dependent trend of the total yield of the depolymerization reaction in Examples 9 to 10. [Figure 6] This figure shows the time-dependent trend of the total yield of the depolymerization reaction in Example 12 compared to Example 13. [Figure 7]This figure shows the time-dependent trend of the total yield of the depolymerization reaction in Example 14. [Figure 8] This figure shows the time-dependent trend of the total yield of the depolymerization reaction in Example 15 compared to Example 3. [Figure 9] This figure shows the time-dependent trend of the total yield of the depolymerization reaction in Example 16 compared to Example 5. [Modes for carrying out the invention]

[0036] In general, the PET-containing material supplied to the depolymerization method according to the present invention may be any material containing PET in an amount of preferably 60% by weight or more, more preferably 70% by weight or more, and even more preferably 80% by weight or more. The material may contain impurities, i.e., compounds other than PET, in an amount of 40% by weight or less, preferably 30% by weight or less, and even more preferably 20% by weight or less.

[0037] Examples of inclusions commonly found in PET-containing materials derived from recovered waste include dyes, polyolefins (e.g., polyethylene or polypropylene), rubber latex, polyamides, polyvinyl alcohol (EVOH), polyvinyl acetate (EVA), UV absorbers; fillers (e.g., calcium carbonate, magnesium carbonate, aluminum hydroxide, titanium dioxide, carbon black, silica), metal particles (e.g., aluminum), and other inclusions resulting from the use of the article.

[0038] Preferably, the PET-containing material may include post-consumer PET waste and / or post-industrial PET waste, which may originate from a wide variety of products such as the following: • Clear and / or colored PET bottles for food products (e.g., water and soft drinks); • Multilayer PET articles, typically used in the food industry, in which a PET layer is bonded to a layer of other polymer or metallic material; Articles containing PET fibers, such as textiles and carpets.

[0039] In a particularly preferred embodiment, the depolymerized material includes post-consumer waste and / or post-industrial scrap containing PET, preferably post-consumer carpet waste containing PET.

[0040] PET-containing materials can be supplied to the depolymerization method in the form of granules, flakes, fibers, or fluff.

[0041] The depolymerization catalyst is present in the reaction mixture in an amount effective for depolymerizing the PET present in the reaction mixture. Preferably, the catalyst is present in the reaction mixture in an amount ranging from 0.1% to 5% by weight, more preferably from 0.4% to 2.0% by weight, relative to the weight of the PET contained in the material to be depolymerized.

[0042] Preferably, the catalyst is present in the reaction mixture in a proportion of more than 5 mmol, more preferably more than 15 mmol, and even more preferably more than 20 mmol per 1 kg (PET + EG), for example, in the range of 20 to 50 mmol, where "PET + EG" is the total weight of EG and PET present in the PET-containing material.

[0043] As described above, the catalyst can be prepared in a laboratory facility and added to the reaction mixture itself, or the catalyst can be prepared by an in situ reaction of acetic acid and a compound containing at least one metal that can produce an acetate of the metal with the acetic acid.

[0044] In this specification, the expression "metallic acetate" includes mixed salts, i.e., metal salts in which one or more counterions other than the acetate ion are present in addition to the acetate anion (hereinafter also referred to as "Ac"). An example of a mixed salt is calcium bicarbonate acetate (hereinafter also referred to as Ca(HCO3)Ac), which can be obtained from the reaction of acetic acid and calcium carbonate in appropriate stoichiometric ratios.

[0045] Preferably, the metal-containing compound is selected from oxides, hydroxides, carbonates, bicarbonates, chlorides, and mixtures thereof.

[0046] Preferably, the metal-containing compound is selected from calcium carbonate, calcium bicarbonate, calcium hydroxide, magnesium carbonate, magnesium bicarbonate, magnesium hydroxide, aluminum hydroxide, and aluminum trichloride.

[0047] As described above, when the catalyst is prepared in situ, it may contain acetates other than calcium acetate, magnesium acetate, and aluminum acetate. In such cases, the metal-containing compound includes at least one metal selected from zinc, iron, manganese, antimony, and mixtures thereof, and the aforementioned compound is in the form of an oxide, hydroxide, carbonate, bicarbonate, or chloride.

[0048] The reagents necessary to produce the in situ catalyst can be added together or separately to EG, or to a mixture containing EG and PET.

[0049] In a preferred embodiment, the PET-containing material further comprises a metal-containing compound in a catalytically effective amount, i.e., an amount sufficient to provide an acetate that can catalyze the depolymerization reaction by reacting with acetic acid. If the concentration of the metal-containing compound is not sufficient to obtain a catalytically effective amount of metal acetate, the metal compound can be intentionally added to the reaction mixture.

[0050] Preferably, acetic acid is added to the reaction mixture in an amount ranging from 0.01% to 5% by weight, more preferably from 0.03% to 1.5% by weight, and even more preferably from 0.1% to 1% by weight, relative to the material containing PET.

[0051] Preferably, the metal-containing compound is added to the reaction mixture in an amount ranging from 0.01% to 5% by weight, more preferably from 0.02% to 1.8% by weight, and even more preferably from 0.06% to 1.2% by weight, relative to the PET-containing material.

[0052] Preferably, the molar ratio of acetic acid to the metal compound is in the range of 1:1 to 1:10.

[0053] The applicant noted that the metal acetate formation reaction competes with the reaction of acetic acid and EG, which involves the formation of the corresponding ethylene glycol monoacetate polyester (EGMA) or ethylene glycol diacetate polyester (EGDA), and therefore may affect the yield of the acetate catalyst formation reaction. However, it was found that this can be overcome by adding acetic acid and a metal compound to EG, or a mixture of EG and PET, under appropriate conditions. Specifically, it is preferable to first mix acetic acid and a metal compound with a material containing EG and optionally PET at a relatively low temperature, preferably in the range of 20°C to 70°C, more preferably 20°C to 50°C, and even more preferably 20°C to 40°C, and then proceed by raising the temperature of the mixture to a temperature selected for the depolymerization reaction. Without referring to any particular theory, at low temperatures, the catalyst formation reaction is more favorable than the formation of EGMA and EGDA esters, and once the metal acetate is formed, the temperature of the reaction mixture can be raised to the depolymerization temperature without resulting in the formation of EGMA and EGDA esters.

[0054] If the material containing PET to be depolymerized contains a metal compound, the latter is preferably added to EG and acetic acid at a low temperature.

[0055] In particular, in one embodiment, the depolymerization method including in situ catalyst generation is a. Mix acetic acid, a metal-containing compound, and EG at a temperature in the range of 20°C to 70°C, preferably 20°C to 50°C; b. Heat the mixture obtained in step a to a temperature within the range of 170°C to 230°C; and c. A material containing PET is supplied to the mixture obtained in step b to obtain glycol decomposition products. Includes.

[0056] In situ preparation of the catalyst is particularly useful when the PET-containing material further contains one or more metal compounds that act as precursors for the in situ production of the catalyst by reaction with acetic acid. In fact, it is possible to determine the metal content of the material and then add acetic acid to the reaction mixture. When a relatively large amount of metal compounds are present in the PET-containing material, it is always possible to convert only a small portion of the metal compounds and add enough acetic acid to produce the required amount of catalyst. The remainder of the metal compounds present as impurities is then removed in the glycol decomposition product purification process. This is particularly true in the case of recycled PET derived from recovered carpet (fluff) that typically contains at least 3% to 5% by weight of calcium carbonate and / or aluminum hydroxide.

[0057] In particular, in one embodiment, the depolymerization method using in situ catalyst generation is a. Mixing EG, acetic acid, and the material containing PET, as well as the compound containing the metal, at a temperature in the range of 20°C to 70°C, preferably 20°C to 50°C; b. The mixture obtained in step a is heated to a temperature in the range of 170°C to 230°C to cause a reaction and obtain glycol decomposition products. Includes.

[0058] Preferably, the glycol decomposition reaction is carried out at a temperature in the range of 170°C to 230°C, more preferably in the range of 190°C to 210°C. The heating of the reaction mixture is not carried out by microwave irradiation.

[0059] In one embodiment, when the catalyst contains magnesium acetate, the heating of the reaction mixture is not performed by microwave irradiation.

[0060] In the glycol decomposition reaction, EG is used in a weight ratio of EG:PETm preferably in the range of 1:1 to 8:1, more preferably in the range of 1:1 to 4:1, and even more preferably in the range of 1:1 to 2:1, where PETm refers to a material containing PET.

[0061] The duration of the glycol decomposition reaction can vary widely depending on reaction conditions such as temperature, stirring, and type of reactor. Typically, the reaction time is 1 to 6 hours, preferably 1.5 to 4 hours. The reaction can be carried out in batch or continuous manner. The reaction pressure is usually atmospheric pressure, but reduced or increased pressure may be used.

[0062] Glycol decomposition reactions result in the purification of glycol decomposition products, including BHET and / or its oligomers. At the end of depolymerization, the glycol decomposition products typically also contain residual fractions of the material, including unreacted PET and other depolymerization products (e.g., water, EG-insoluble impurities, etc.).

[0063] BHET and / or its oligomers can be separated from glycol degradation products and purified using appropriate techniques of known technologies such as distillation, filtration, and crystallization.

[0064] BHET and / or its oligomers obtained by the methods described herein can be used as raw materials in new methods for producing polyester polymers and copolymers. For example, they can be polymerized to produce PET from recycled BHET alone or in combination with BHET produced from virgin raw materials.

[0065] The methods described herein can be carried out using equipment and apparatus known in the art for the production of polymers, specifically polyesters.

[0066] Advantageously, the depolymerization reaction can be carried out in an acid-resistant stainless steel reactor equipped with suitable inlets for adding liquid acetic acid and solid compounds for in situ catalyst generation. The reactor may be equipped with heating and mixing means for heating the reaction mixture to a desired temperature and maintaining agitation. [Examples]

[0067] The following embodiments are provided solely for illustrative purposes of the present invention and should not be considered to limit the scope of protection as defined by the accompanying claims.

[0068] In the examples, refer to the attached Figures 1 to 7, which illustrate the time-dependent trend of the total yield of the glycol decomposition reaction in Examples 1 to 14.

[0069] Examples 1. Depolymerization test The efficiency of the method described herein was verified by a series of catalytic depolymerization tests on waste containing different types of PET. The depolymerization tests were performed as follows:

[0070] The glycol decomposition reaction was carried out in a 1-liter round-bottom Pyrex glass reaction flask. The flask was heated using a heating mantle (isomantle). The reaction flask has four necks with the following functions: A thermocouple thermometer is inserted into the first port to detect the temperature of the liquid mixture during the reaction, and the temperature setting point can be digitally set by a heating mantle. A reflux condenser is inserted into the second port to condense the vapors generated during the reaction using a continuously supplied stream of cold water. The remaining two openings are used to supply materials containing monoethylene glycol (EG) and PET, and these two openings are kept closed with two frosted glass stoppers during the depolymerization reaction.

[0071] The reaction mixture was continuously stirred using a magnetic stirrer with a PTFE magnetic stirring rod, and the rotation speed of the stirring rod could be digitally set by an isomantler. The reaction temperature and rotation speed were set to 195°C and 1400 rpm, respectively.

[0072] EG and (if prepared in the laboratory) the catalyst are first added to the reaction flask. The mixture is then heated to the reaction temperature while maintaining stirring, recondensing the resulting vapor using a bubble condenser. When the glycol-catalyst mixture reaches the reaction temperature, the material containing PET (hereinafter simply referred to as "PET"), which has been preheated to 110°C, is introduced into the flask.

[0073] The moment when PET is added to the reaction flask is defined as reaction start time 0 (t0). Starting at t0, a sample of the glycol decomposition fluid is taken at regular intervals using a glass Pasteur pipette. The liquid is then transferred to a vial cooled with cold water to stop the reaction, and the content of BHET and its oligomers is determined by HPLC analysis.

[0074] The time required for complete dissolution of PET in glycol to be observed should also be noted.

[0075] At the end of the glycol decomposition, the contents of the flask are removed and the liquid is subjected to the final HPLC analysis.

[0076] 2. Examples 1-3 (comparative) Catalyst: Zinc acetate (ZnAc2) Following the procedure described in Point 1, the depolymerization of granulated PET was carried out in the presence of zinc acetate, with catalysts added at different concentrations. The PET used was in a substantially pure form (approximately 100% purity). The composition of the reaction mixture, along with the analytical results of the reaction solutions collected at different reaction times, is shown in Tables 1 to 3.

[0077] The EG / PET weight ratio and the catalyst / PET weight ratio represent the weight ratio of EG and the weight ratio of the catalyst to the material containing PET, respectively.

[0078] The parameters "BHET yield," "dimer yield (of BHET)," and "total yield" represent the ratio of the amount of BHET, the ratio of the amount of BHT dimers, and the ratio of the total amount of "BHET + dimers" to the weight of the material containing PET, respectively, and are expressed as moles / moles (%).

[0079] [Table 1]

[0080] [Table 2]

[0081] [Table 3]

[0082] Figure 1 shows the time-dependent trend of the total yield of the depolymerization reaction.

[0083] 3. Examples 4-5 Catalyst: Calcium acetate (CaAc2) According to the method described in Point 1, fine-grained PET (100% purity) was depolymerized in the presence of calcium acetate added at 1% and 3% by weight of the PET added.

[0084] The composition of the reaction mixture, along with the analysis results of the reaction solutions collected at different reaction times, is shown in Tables 4 and 5.

[0085] [Table 4]

[0086] [Table 5]

[0087] Figure 2 shows the time-dependent trend of the total yield of the depolymerization reaction.

[0088] A comparison of the results from Examples 1-3 and Examples 4-5 shows that the CaAc2 catalyst has similar efficiency to ZnAc2 and exhibits a faster depolymerization reaction rate than ZnAc2 of the same weight of catalyst.

[0089] 4. Examples 6-7 Since the physical form of the PET-containing material can also affect the degree of the depolymerization reaction, the procedure described in Step 1 was carried out by supplying PET-containing waste consisting of spinning waste (purity approximately 97.5%) and using ZnAc2 and CaAc2 as catalysts.

[0090] The composition of the reaction mixture, along with the analysis results of reaction solutions collected at different reaction times, is shown in Tables 6 and 7.

[0091] [Table 6]

[0092] [Table 7]

[0093] Figure 3 shows the time-dependent trend of the total yield of the depolymerization reaction in Examples 6 and 7.

[0094] In these examples, we compare two different weight-based addition amounts, but it can be seen that these correspond to the same molar addition amount (approximately 5.5 mmol of catalyst).

[0095] The comparison of graphs in Figure 3 shows that CaAc2 is a depolymerization catalyst that achieves results almost identical to those of conventional ZnAc2, even at low weight concentrations. Reactions in the presence of CaAc2 complete faster than those using ZnAc2.

[0096] 5. Examples 8-10 Catalyst: Calcium acetate (CaAc2) The efficiency of the CaAc2 catalyst was tested in the depolymerization reaction of PET waste from carpet fluffs. The fluffs used had a PET content of 80% by weight.

[0097] The method described in Point 1 was carried out by supplying fluff to a reaction mixture containing CaAc2 as a catalyst.

[0098] In the fluff feeding test, at the end of the glycol decomposition reaction, the reaction mixture at 195°C still contained a fraction of suspended solids with a yellowish-brown appearance, which was removed by hot filtration of the reaction mixture (approximately 190°C). The insoluble residue separated by filtration, which amounted to approximately 10%–15% of the weight of the fluff fed in, was analyzed by DSC, TGA, and FT-IR. The analysis revealed the presence of a mixture of polypropylene, adhesives, and other inorganic substances, including calcium carbonate.

[0099] The composition of the reaction mixture, along with the analysis results of reaction solutions collected at different reaction times, is shown in Tables 8 to 10.

[0100] [Table 8]

[0101] [Table 9]

[0102] [Table 10]

[0103] Figure 4 shows the time-dependent trend of the total yield of the depolymerization reaction in Example 8, and Figure 5 shows the time-dependent trend of the total yield of the reactions in Examples 9 and 10.

[0104] Examples 9 and 10 demonstrate that, even when operated at relatively low CaAc2 catalyst concentrations and EG / PET ratios, conversion yields of PET to BHET and oligomers similar to those used in known glycol decomposition methods such as ZnAc2 are obtained at a higher EG / PET ratio.

[0105] 6. Examples 11-12 Catalyst: Acetic acid and calcium bicarbonate acetate (Ca(HCO3)Ac) produced in situ The following depolymerization test was performed according to the procedure described in Point 1. In Example 11 (comparative), the depolymerization test was performed using PET in fibrous form (purity approximately 97.5%) that was substantially free of impurities. To test the potential effect as a depolymerization catalyst, only acetic acid was added to the reaction mixture. Acetic acid was added to EG at 30°C, and the mixture was then heated to 195°C and maintained under reflux. At this temperature, PET fibers were added. After 3 hours of reaction, no dissolution of the fibers was observed, and HPLC analysis of the reaction mixture did not detect the presence of BHET.

[0106] Example 12 was carried out under the same conditions as Example 11, except that equimolar amounts of CaCO3 and acetic acid were added to EG at 30°C. The mixture was then heated to 195°C and maintained under reflux, and PET fibers were added. The reaction was continued until the fibers were completely dissolved. Thus, the data shown in Table 11 demonstrate that an active equivalent amount of catalyst Ca(HCO3)Ac was produced in the reaction mixture at a concentration of 2.66% by weight relative to the weight of the PET fibers.

[0107] [Table 11]

[0108] Figure 6 shows the time-dependent trend of the total yield of the depolymerization reaction in Example 12 compared to Example 13.

[0109] 7. Example 13 Catalyst: Acetic acid and calcium bicarbonate acetate (Ca(HCO3)Ac) produced in situ Example 13 was carried out under the same conditions as Example 12, but acetic acid and PET fluff were added to EG at 30°C, and CaCO3 contained in the PET fluff (80% purity) was used. The CaCO3 content in the fluff was approximately 5% by weight relative to the weight of the fluff.

[0110] The composition of the reaction mixture, along with the analysis results of the reaction solutions collected at different reaction times, is shown in Table 12.

[0111] [Table 12]

[0112] Figure 6 shows the time-dependent trend of the total yield of the depolymerization reaction in Example 13. The results indicate that the PET glycol decomposition method in Example 13 proceeds to a similar extent as in Example 12, confirming that an effective depolymerization catalyst can be prepared in situ by utilizing metal compounds present as inclusions in recycled PET-containing materials.

[0113] 8. Example 14 Catalyst: Magnesium acetate (MgAc2) According to the method described in Point 1, fine-grained PET (100% purity) was depolymerized using magnesium acetate added with 0.45% by weight of MgAc2 relative to the weight of the PET added.

[0114] The composition of the reaction mixture, along with the analysis results of the reaction solutions collected at different reaction times, is shown in Table 13.

[0115] [Table 13]

[0116] Figure 7 shows the time-dependent trend of the total yield of the depolymerization reaction in Example 14. The results indicate that magnesium acetate is also an effective catalyst in PET depolymerization.

[0117] 9. Examples 15-18: Other catalysts produced in situ Examples 15 to 18 were carried out under the same conditions as Example 12, and each was performed as follows: In Example 15, acetic acid and zinc carbonate were used in a molar ratio of 2:1. In Example 16, acetic acid and calcium oxide were used in a molar ratio of 2:1. In Example 17, acetic acid and magnesium hydroxide were used in a molar ratio of 2:1. In Example 18, acetic acid and aluminum hydroxide were used in a molar ratio of 3:1. It was added to EG at 30°C.

[0118] Next, in both cases, the mixture was heated to 195°C, maintained under reflux, and PET granules were added.

[0119] The composition of the reaction mixture is shown in Tables 14 to 17, along with the analysis results of the reaction solutions collected at different reaction times.

[0120] [Table 14]

[0121] [Table 15]

[0122] [Table 16]

[0123] [Table 17]

[0124] Figures 8 and 9 show the time-dependent trend of the total yield of the depolymerization reaction in Examples 15 and 16 compared with Examples 3 and 5, respectively. The same catalyst was prepared in the laboratory and then added to the reaction mixture. The results indicate that the catalyst produced in situ is just as effective as the one produced in the laboratory.

[0125] 10. Examples 19-20: Recovery of BHET by evaporation and crystallization of EG In Examples 19 and 20, the focus was on separating BHET and its dimer using the same methods as in Examples 12 and 13, in order to obtain a material that can be polymerized into PET.

[0126] In this first step, the glycol decomposition residue was filtered to separate unconverted PET and other impurities from the glycol decomposition material. A portion of the glycol in the filtered product was evaporated by flash evaporation under vacuum.

[0127] At this point, a large excess of water (four times the weight of glycol) was added to precipitate the product. The latter was then filtered again, washed with water, and finally dried.

[0128] Next, the obtained materials were analyzed by HPLC, FT-IR, DSC, and NMR, and were confirmed to be BHET and its dimers.

[0129] As shown in Table 18, the properties of the separated products (content of COOH groups and diethylene glycol (DEG), melting point) are consistent with those typically required for the polymerized material.

[0130] [Table 18] The embodiments of the present invention include the following: <1> A method for depolymerizing a material containing polyethylene terephthalate (PET) by glycol decomposition (glycolysis) using ethylene glycol (EG), The method includes reacting a PET-containing material with EG in the presence of at least one catalyst to obtain a glycol decomposition product containing bis(2-hydroxyethyl) terephthalate (BHET) and / or its oligomer, Here, the catalyst comprises an acetate of a metal selected from calcium, magnesium, aluminum, and mixtures thereof. method. <2> The catalyst is obtained by an in situ reaction of acetic acid with a compound containing the metal. <1> Methods used. <3> The metal-containing compound is selected from oxides, hydroxides, carbonates, bicarbonates, chlorides, and mixtures thereof. <2> Methods used. <4> The metal-containing compound is selected from calcium carbonate, calcium bicarbonate, calcium hydroxide, magnesium carbonate, magnesium bicarbonate, magnesium hydroxide, aluminum hydroxide, and aluminum trichloride. <2> or <3> Methods used. <5> The material containing the PET contains a compound containing the metal, <2> ~ <4> The method described in any one of the following ways. <6> a. Mix acetic acid, the compound containing the aforementioned metal, and EG at a temperature within the range of 20°C to 70°C; b. Heat the mixture obtained in step a to a temperature within the range of 170°C to 230°C; and c. To obtain glycol decomposition products, supply the PET-containing material to the mixture obtained in step b above. including, <2> ~ <5> The method described in any one of the following ways. <7> a. Mixing EG, acetic acid, and the material containing the PET, as well as the compound containing the metal, at a temperature within the range of 20°C to 70°C; and b. The mixture obtained in step a is heated to a temperature in the range of 170°C to 230°C to cause the reaction and obtain glycol decomposition products. including, <5> Methods used. <8> The aforementioned PET-containing material includes post-consumer waste and / or post-industrial scrap containing PET, preferably including post-consumer carpet waste containing PET. <1> ~ <7> The method described in any one of the following ways. <9> The PET-containing material is in the form of granules, flakes, fibers, or fluff. <1> ~ <8> The method described in any one of the following ways. <10> The weight ratio of EG to PETm (EG:PETm) is 1:1 to 8:1, preferably 1:1 to 4:1, and more preferably 1:1 to 2:1, where PETm refers to the material containing PET. <1> ~ <9> The method described in any one of the following ways. <11> If the catalyst contains magnesium acetate, the reaction mixture is not heated by microwave irradiation. <1> ~ <10> The method described in any one of the following ways. <12> A method for depolymerizing a material containing polyethylene terephthalate (PET) by glycol decomposition (glycolysis) using ethylene glycol (EG), The method involves reacting a PET-containing material with EG in the presence of at least one catalyst containing a metal acetate to obtain a glycol decomposition product containing bis(2-hydroxyethyl) terephthalate (BHET) and / or its oligomer. Here, the catalyst is obtained by an in situ reaction between acetic acid and a compound containing the metal. method. <13> The in situ reaction between acetic acid and the compound containing the metal is, a. Mix acetic acid, the compound containing the aforementioned metal, and EG at a temperature within the range of 20°C to 70°C; b. Heat the mixture obtained in step a to a temperature within the range of 170°C to 230°C; and c. To obtain the glycol decomposition product, supply the PET-containing material to the mixture obtained in step b. including, <12> Methods used. <14> The in situ reaction between acetic acid and the compound containing the metal is as follows: a. Mixing EG, acetic acid, and the material containing PET, as well as the compound containing the metal, at a temperature within the range of 20°C to 70°C; b. The mixture obtained in step a is heated to a temperature in the range of 170°C to 230°C to cause the reaction and obtain the glycol decomposition product. including, <12> Methods used.

Claims

1. A method for depolymerizing a material containing polyethylene terephthalate (PET) by glycol decomposition (glycolysis) using ethylene glycol (EG), The method involves reacting a PET-containing material with EG in the presence of at least one catalyst containing a metal acetate to obtain a glycol decomposition product containing bis(2-hydroxyethyl) terephthalate (BHET) and / or its oligomer, Here, the method includes the step of preparing the catalyst by an in situ reaction between acetic acid and a compound containing the metal, The material containing the PET contains a compound containing the metal, method.

2. The step of preparing the catalyst by the in situ reaction of acetic acid and a compound containing the metal is: a. Mix acetic acid, the metal-containing compound, and EG at a temperature in the range of 20°C to 70°C; b. Heating the mixture obtained in step a to a temperature in the range of 170°C to 230°C; and c. To obtain the glycol decomposition product, supply the PET-containing material to the mixture obtained in step b. The method according to claim 1, including the method described in claim 1.

3. The step of preparing the catalyst by the in situ reaction of acetic acid and a compound containing the metal is: a. Mixing EG, acetic acid, and the material containing PET, as well as the compound containing the metal, at a temperature in the range of 20°C to 70°C; b. The mixture obtained in step a is heated to a temperature in the range of 170°C to 230°C to cause the reaction and obtain the glycol decomposition product. The method according to claim 1, including the method described in claim 1.

4. The method according to any one of claims 1 to 3, wherein the acetate of the metal is selected from calcium acetate, magnesium acetate, aluminum acetate, zinc acetate, lead acetate, iron acetate, manganese acetate, antimony acetate, and mixtures thereof.

5. The method according to any one of claims 1 to 3, wherein the compound containing the metal is selected from oxides, hydroxides, carbonates, bicarbonates, chlorides, and mixtures thereof.

6. The method according to any one of claims 1 to 3, wherein the metal-containing compound is selected from calcium carbonate, calcium bicarbonate, calcium hydroxide, magnesium carbonate, magnesium bicarbonate, magnesium hydroxide, aluminum hydroxide, and aluminum trichloride.

7. The method according to any one of claims 1 to 3, wherein the PET-containing material includes post-consumer waste and / or post-industrial scrap containing PET.

8. The method according to any one of claims 1 to 3, wherein the PET-containing material includes post-consumer carpet waste containing PET.

9. The method according to any one of claims 1 to 3, wherein the PET-containing material is in the form of granules, flakes, fibers, or fluff.

10. The method according to any one of claims 1 to 3, wherein the weight ratio of EG to PETm (EG:PETm) is 1:1 to 8:1, where PETm represents the material containing PET.

11. The method according to any one of claims 1 to 3, wherein the weight ratio of EG to PETm (EG:PETm) is 1:1 to 4:1, where PETm represents the material containing PET.

12. The method according to any one of claims 1 to 3, wherein the weight ratio of EG to PETm (EG:PETm) is 1:1 to 2:1, where PETm represents the material containing PET.

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