A method for degrading polyesters and the resulting degradation products and uses

Abstract

The application discloses a method for degrading polyester, and a degraded product and application thereof. The method comprises the following steps: alcoholysis, impurity removal and crystallization treatment of the polyester in the presence of a titanium-containing catalyst to obtain a degraded product. The green and efficient titanium-containing catalyst has high catalytic efficiency, and the depolymerization rate reaches 100%. The polymerization degree of the oligomer in the alcoholysis product is only 1-3. Moreover, the green and efficient titanium-containing catalyst does not contain heavy metals, and is harmless to the environment and human bodies. The catalyst residual amount in the target product is low, and has no influence on the polyester regeneration.

Description

Technical Field

[0001] This invention belongs to the field of polyester chemical degradation technology, specifically relating to a method for degrading polyester and the resulting degradation products and their applications. Background Technology

[0002] Polyethylene terephthalate (PET) is widely used in fibers, films, and bottles due to its excellent performance and low price. Its production accounts for over 70% of the world's total output. This huge market has led to a growing accumulation of waste PET. Due to its stable chemical properties and significant resistance to microorganisms and atmospheric pollution, it cannot undergo effective natural degradation within a time span of 16 to 48 years. Traditional disposal methods such as incineration and landfill cause significant environmental damage. Therefore, effectively utilizing waste resources, alleviating energy shortages and environmental pollution problems, and effectively recycling waste PET are key issues for achieving sustainable development strategies in the polyester industry.

[0003] Waste PET polyester recycling methods are mainly divided into physical and chemical methods. Physical recycling involves melting waste PET and reshaping it. This method is simple, requires little investment, and has low costs, but it is difficult to improve the quality of recycled products, resulting in low added value, low resource utilization, and secondary pollution. Chemical recycling can achieve closed-loop recycling from "polymer-monomer-polymer," yielding high-value, multi-variety recycled products with good economic and social benefits. Currently, chemical recycling methods mainly include hydrolysis, methanol alcoholysis, ethylene glycol alcoholysis, and other chemical depolymerization methods.

[0004] In the chemical degradation of PET, hydrolysis is divided into neutral, acidic, and alkaline hydrolysis methods. While neutral hydrolysis does not use strong acids or bases as catalysts, it requires high pressure and high reaction temperature, placing strict demands on equipment design, control, and safety. Acidic or alkaline hydrolysis requires strong acids or bases as catalysts, resulting in waste liquid containing large amounts of concentrated acid or alkali, making post-treatment difficult. Alcohololysis technology is relatively mature compared to other methods, mainly including methanol alcoholysis and ethylene glycol alcoholysis. Methanol alcoholysis produces dimethyl terephthalate (DMT), which is easily vaporized, convenient to purify, and easy to operate continuously in production lines. However, since current PET polymerization processes are mostly direct esterification routes, existing polymerization equipment makes it difficult to integrate DMT polymerization into the production line. Ethylene glycol alcoholysis of PET has a simple reaction route, does not use corrosive catalysts such as strong acids or bases, has low requirements for temperature and pressure, a high safety factor, and can be used in conjunction with industrial PET polymerization equipment, making it suitable for industrial mass production, greatly improving economic efficiency and reducing equipment maintenance costs. However, this method also has certain problems. Since PET depolymerization and polymerization are an equilibrium reaction, it is difficult to achieve the ideal depolymerization yield. The depolymerization products contain a certain amount of oligomers, making the separation and purification process difficult and affecting the purity and yield of the target product. In addition, commonly used depolymerization catalysts such as zinc acetate will remain in the target product and are not easy to remove. High levels of residues will lead to severe thermal degradation of the recycled product, affecting the recycling of PET. Summary of the Invention

[0005] To overcome the problems existing in the prior art, namely the presence of heavy metal components in the catalyst, low catalytic activity, low depolymerization rate, high catalyst residue in the depolymerization product, and the trouble caused to polyester (e.g., PET) regeneration, the present invention provides a method for degrading polyester and the obtained degradation product, which has a high yield and purity of the target degradation product, aryl dialkyl acid dihydroxyalkyl ester (e.g., ethylene terephthalate BHET).

[0006] One of the objectives of this invention is to provide a method for degrading polyester, comprising: performing alcoholysis, impurity removal, and crystallization treatment on the polyester in the presence of a titanium-containing catalyst to obtain degradation products.

[0007] In a preferred embodiment, the polyester is selected from poly(p-aryldialkyl) glycol esters, preferably from at least one of poly(p-phenylene) glycol esters (e.g., poly(p-phenylene terephthalate), poly(p-naphthalene) glycol esters (e.g., poly(p-naphthalene) glycol esters), poly(furandialkyl) glycol esters (e.g., poly(furandicarboxylate) glycol esters), more preferably from at least one of PET, PBT, PETG, PCTG, PTT (polymethyl terephthalate), PEN (polyethylene naphthalate), PEF (polyethylene furanate) (e.g., PET), and most preferably the polyester is polyester waste, such as PET bottle material.

[0008] In this way, the waste can be degraded and reused.

[0009] For example, when the polyester is PET, the alcoholysis product is a mixture of BHET, BHET dimer, BHET trimer, diethylene glycol and ethylene glycol, etc., and the degree of polymerization of the oligomer in the alcoholysis product is 1 to 3.

[0010] In a preferred embodiment, the titanium-containing catalyst is selected from titanium-containing compounds.

[0011] In a further preferred embodiment, the titanium-containing catalyst is selected from at least one of diol-modified alkyl titanate, alkyl titanate, titanium diol, titanium phosphate, and organic-inorganic hybrid titanium.

[0012] After extensive experimental research, the inventors discovered that the catalytic effect of the diol-modified alkyl titanate is better than that of the unmodified alkyl titanate, and it is more conducive to the formation of aryl dialkyl acid dihydroxyalkyl esters (such as BHET or BHBT), that is, the depolymerization is more thorough.

[0013] In a further preferred embodiment, the alkyl titanate is selected from at least one of tetraethyl titanate, tetrabutyl titanate, tetraisopropyl titanate, and tetraisobutyl titanate; and / or, the diol titanium is titanium glycol; and / or, the organic-inorganic hybrid titanium can be any type of organic-inorganic hybrid titanium disclosed in the prior art.

[0014] In a preferred embodiment, the diol-modified alkyl titanate is obtained as follows: the alkyl titanate is mixed with a diol at 20–50°C, then heated to 70–100°C, and then cooled and filtered to obtain the modified alkyl titanate.

[0015] In the preparation of the modified alkyl titanate, the alkyl titanate is preferably at least one of tetraethyl titanate, tetrabutyl titanate, tetraisopropyl titanate, and tetraisobutyl titanate, and the diol is preferably at least one of ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,6-hexanediol, for example, ethylene glycol and / or 1,4-butanediol.

[0016] In a further preferred embodiment, in the preparation of the modified alkyl titanate, the molar ratio of the alkyl titanate to the diol is 1:(2-10), for example 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10.

[0017] In a further preferred embodiment, the mixing is carried out as follows: the alkyl titanate is mixed with a solvent to obtain an alkyl titanate solution, and the diol is added dropwise to the alkyl titanate solution at 20–50°C (e.g., 20°C, 30°C, 40°C, or 50°C).

[0018] Preferably, the solvent is selected from at least one of petroleum ether, isopropanol, cyclohexane, toluene, and tetrahydrofuran; the molar ratio of the alkyl titanate to the solvent is 1:1 to 1:50, for example, 1:2, 1:5, 1:8, 1:10, 1:12, 1:15, 1:18, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, or 1:50.

[0019] In a preferred embodiment, the amount of the titanium-containing catalyst is 0.1wt% to 0.8wt% based on 100wt% of the polyester, preferably 0.2wt% to 0.5wt%, for example 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, or 0.8wt%, or a range consisting of any two point values ​​(e.g., 0.2wt% to 0.8wt%, 0.2wt% to 0.6wt%, 0.3wt% to 0.8wt%, 0.3wt% to 0.7wt%, etc.).

[0020] Through extensive research, the inventors discovered that the amount of titanium-containing catalyst used cannot be too high. When it exceeds 0.8 wt%, although depolymerization can be achieved, it leads to a high content of oligomers (dimers and above) in the alcoholysis products and a low content of the target degradation product, p-aryl dialkyl acid dihydroxyalkyl esters (e.g., BHET or BHBT), resulting in a low yield of the target degradation product (e.g., BHET or BHBT) and a high catalyst residue. Conversely, the catalyst amount cannot be too low either, otherwise depolymerization will be incomplete. Therefore, the amount of titanium-containing catalyst should not be too high or too low, and should be 0.1 wt% to 0.8 wt% of the polyester weight, preferably 0.2 wt% to 0.5 wt%.

[0021] This invention uses a green and efficient titanium-containing catalyst as a catalyst for the alcoholysis of polyester. (1) The inventors unexpectedly discovered through experiments that, under the conditions of the process described in this invention, a small amount of titanium-containing catalyst can achieve high catalytic efficiency and a depolymerization rate of 100%. (2) The inventors found that when the titanium-containing catalyst is controlled within the scope of this invention, it can promote the generation of p-aryl dialkyl acid dihydroxyalkyl esters (i.e., the target degradation product) and increase the content of the target product in the alcoholysis product (>95%). (3) In addition, the green and efficient titanium-containing catalyst is harmless to the environment and human body, the catalyst residue in the target product is low, and the trace titanium residue has no effect on the regeneration of polyester (e.g., PET or PBT) (because the titanium-containing catalyst can be used as a commonly used polyester polymerization catalyst).

[0022] In a preferred embodiment, the alcoholysis is performed using a diol.

[0023] In a further preferred embodiment, the diol is selected from at least one of ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,6-hexanediol.

[0024] In a preferred embodiment, the weight ratio of the diol to the polyester is (2-8):1, preferably (3-5):1, for example 2:1, 3:1, 4:1, 5:1, 6:1, 7:1 or 8:1.

[0025] If too little diol is used, depolymerization will be incomplete, resulting in high oligomer content and difficulty in product separation; if too much diol is used, depolymerization costs will be high.

[0026] In a preferred embodiment, the alcoholysis temperature is 190–250°C; and / or, the alcoholysis pressure is 0.2–0.6 MPa; and / or, the alcoholysis time is 1–10 (preferably 2–5) hours.

[0027] For example, the alcoholysis temperature is 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, or 250°C; and / or, the alcoholysis pressure is 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, or 0.6 MPa; and / or, the alcoholysis time is 1, 2, 3, 4, 5, 6, 8, or 10 hours.

[0028] In a further preferred embodiment, the alcoholysis temperature is 200–230°C; and / or, the alcoholysis pressure is 0.35–0.5 MPa; and / or, the alcoholysis time is 3–4 hours.

[0029] In a preferred embodiment, the alcoholysis is carried out under a protective atmosphere, preferably under nitrogen.

[0030] The analysis of the products after alcoholysis revealed that, under the alcoholysis process of this invention, taking PET as an example, all PET was completely depolymerized, and the BHET content in the depolymerization products was >93%, while the total content of dimers and trimers was below 7%. Preferably, a modified titanium-based catalyst was used, resulting in a BHET content >95%, a BHET dimer content below 4.5%, and a trimer content below 0.5% in the depolymerization products, achieving excellent depolymerization results.

[0031] In a preferred embodiment, the impurity removal includes (a) filtration I treatment, (b) water addition and stirring, and (c) filtration II treatment to obtain a clear filtrate.

[0032] In a further preferred embodiment, the filtration I treatment in step (a) is carried out while hot at 80-140°C (preferably 90-130°C) to obtain a first filtrate; and / or, the stirring in step (b) is carried out at 60-100°C (preferably 70-85°C) (e.g., for 1-4 hours).

[0033] For example, the filtration I treatment described in step (a) is carried out while hot at 80°C, 90°C, 100°C, 110°C, 120°C, 130°C or 140°C; and / or, the stirring described in step (2) is carried out at 60°C, 70°C, 80°C or 90°C for 1, 2, 3 or 4 hours.

[0034] In a further preferred embodiment, in step (b), the weight ratio of water to the first filtrate is (2-10):1, preferably (2-5):1.

[0035] For example, the weight ratio of water to the first filtrate is 2:1, 3:1, 4:1, 5:1, 6:1, 8:1, or 10:1.

[0036] In this invention, vacuum distillation is not performed to remove the diol after the filtration I treatment described in step (a), because vacuum distillation would cause some of the depolymerization products to recombine into oligomers, resulting in a low content of the target product, p-aryl dialkyl acid dihydroxyalkyl ester monomer (e.g., BHET or BHBT). Furthermore, the inventors discovered through extensive experimentation that when water is added to the first filtrate, the p-aryl dialkyl acid dihydroxyalkyl ester monomer tends to be extracted into the aqueous phase. Thus, subsequent separation, cooling, and crystallization yield the p-aryl dialkyl acid dihydroxyalkyl ester monomer product.

[0037] In a preferred embodiment, the filtration II process described in step (c) is performed while hot at the stirring temperature described in step (b).

[0038] In a preferred embodiment, the crystallization process is carried out at 0–25°C for 2–24 hours.

[0039] In a further preferred embodiment, the crystallization process is carried out as follows: first crystallize at 15-30°C for 5-20 hours, and then crystallize at 0-5°C for 0.5-5 hours.

[0040] In a further preferred embodiment, the crystallization process is carried out as follows: first crystallize at 20-28°C for 10-15 hours, and then crystallize at 0-5°C for 1-3 hours.

[0041] For example, the crystallization process is carried out as follows: first crystallize at 15°C, 16°C, 18°C, 20°C, 22°C, 24°C, 26°C, 28°C or 30°C for 5, 6, 8, 10, 12, 14, 16, 18, or 20 hours, and then crystallize at 0°C, 1°C, 2°C, 3°C, 4°C or 5°C for 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5 hours.

[0042] Through extensive experimentation, the inventors discovered that cooled p-aryl dialkyl acid dihydroxyalkyl esters (e.g., BHET), p-aryl dialkyl acid dihydroxyalkyl ester dimers (e.g., BHET dimers), and p-aryl dialkyl acid dihydroxyalkyl ester trimers (e.g., BHET trimers) all crystallize and precipitate under conventional crystallization methods, resulting in a mixture that does not yield high-purity p-aryl dialkyl acid dihydroxyalkyl ester monomer products. This invention, through multi-stage crystallization, can obtain high-purity p-aryl dialkyl acid dihydroxyalkyl ester monomer products (e.g., BHET), with a purity >95%, and potentially approaching 99%.

[0043] In a preferred embodiment, the degradation product is obtained by filtration (e.g., vacuum filtration) and drying after the crystallization treatment.

[0044] In a further preferred embodiment, the drying is carried out at 50–90°C for 10–24 hours.

[0045] In a preferred embodiment, the method includes: adding treated waste polyester material (e.g., PET bottle material) and diol (e.g., ethylene glycol EG) to an alcoholysis reactor at a certain feeding ratio; adding a titanium-containing catalyst; replacing the air in the reactor with nitrogen; then introducing a certain amount of nitrogen to maintain a positive pressure in the reactor; reacting at 190–250°C and 0.2–0.6 MPa for 2–5 hours to obtain an alcoholysis product; filtering the alcoholysis product while hot at 80–140°C to obtain a first filtrate; adding water to the first filtrate; stirring at 60–100°C for 1–4 hours; filtering to obtain a clear filtrate; cooling the clear filtrate at 0–25°C to crystallize for 10–24 hours (preferably, first crystallizing at 15–25°C for 5–15 hours, then crystallizing at 0–5°C for 10–15 hours); filtering to obtain crystals (e.g., BHET); and drying in a vacuum oven to obtain the final product (e.g., BHET).

[0046] In this invention, the alcoholysis process, along with the impurity removal and crystallization process, can be used to obtain p-aryl dialkyl acid dihydroxyalkyl esters (instead of dimers, trimers, or other oligomers).

[0047] The degradation product obtained by the method described in this invention is a p-aryl dialkyl acid dihydroxyalkyl ester (e.g., BHET or BHBT).

[0048] A second objective of this invention is to provide a p-aryl dialkyl acid dihydroxyalkyl ester obtained by the method described in one objective of this invention. Preferably, the p-aryl dialkyl acid dihydroxyalkyl ester is one or more of terephthalic acid diol ester, p-naphthyl dialkyl acid diol ester, and p-furan dialkyl acid diol ester. More preferably, the p-aryl dialkyl acid dihydroxyalkyl ester compound is one or more of ethylene terephthalate, 1,4-cyclohexanediethanol terephthalate, butylene terephthalate, ethylene naphthyl dimethyl acid, and ethylene p-furan dimethyl acid, for example, ethylene terephthalate (BHET) and / or butylene terephthalate (BHBT).

[0049] In a preferred embodiment, the purity of the p-aryldialkyl acid dihydroxyalkyl ester reaches 95% or higher.

[0050] Taking polyethylene terephthalate (BHET) as an example, currently, the purity of the product of this invention is higher than that of commercially available polyethylene terephthalate products.

[0051] In a preferred embodiment, the residual titanium content in the p-aryldialkyl acid dihydroxyalkyl ester is less than 500 mg / Kg, preferably less than 300 mg / Kg.

[0052] Although the p-aryl dialkyl acid dihydroxyalkyl esters obtained by the method described in this invention are recycled, they have almost the same or even higher quality (e.g., the same or higher purity) as the virgin products.

[0053] A third objective of this invention is to provide the application of p-aryl dialkyl acid dihydroxyalkyl esters obtained by the method described in one objective of this invention or p-aryl dialkyl acid dihydroxyalkyl esters described in another objective of this invention in polyester preparation, preferably polyesters prepared by polycondensation reaction.

[0054] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In the following, various technical solutions can, in principle, be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] (1) The present invention uses a green and efficient titanium-containing catalyst with high catalytic efficiency and a depolymerization rate of 100%. The degree of polymerization of the oligomers in the depolymerization products is only 1 to 3. Among them, the content of p-aryl dialkyl acid dihydroxyalkyl ester (e.g., BHET, BHBT) is >90%, preferably >95%.

[0057] (2) The green and efficient titanium-containing compound used in this invention is a catalyst. The catalyst does not contain heavy metals and is harmless to the environment and human body. The catalyst residue in the target product is low, only a few hundred mg / Kg, and has no effect on polyester regeneration.

[0058] (3) The present invention obtains high-purity p-aryl dialkyl acid dihydroxyalkyl ester products (e.g., BHET) by optimizing the separation and purification process of depolymerization products. The purity of the product (e.g., BHET) can reach more than 93%, preferably more than 95%, and the yield is 65-85% by nuclear magnetic resonance and high performance liquid chromatography.

[0059] (4) The high-purity p-aryl dialkyl acid dihydroxyalkyl ester products (e.g., BHET) prepared by the method of the present invention can be directly used to prepare polyester products. The recycled polyester has the same properties as the virgin polyester, and the waste polyester can be recycled in a closed loop. Attached Figure Description

[0060] Figure 1 The infrared spectrum of BHET in Example 1 is shown;

[0061] Figure 2 The 1H NMR spectrum of BHET in Example 1 is shown;

[0062] Figure 3 The DSC spectrum of BHET in Example 1 is shown;

[0063] Figure 4 The high-performance liquid chromatography (HPLC) chromatogram of BHET in Example 1 is shown.

[0064] Figure 4 In the text, the highest peak (with a retention time of 1.725 minutes) is marked with "1.725".

[0065] Figure 5 The 1H NMR spectrum of BHET in Example 2 is shown;

[0066] Figure 6 The HPLC chromatogram of BHET in Example 2 is shown;

[0067] Figure 6 In the text, the peak (highest peak) at the retention time of 1.722 minutes is labeled "Peak 1 - 1.722".

[0068] Figure 7The 1H NMR spectrum of BHET in Example 3 is shown;

[0069] Figure 8 The HPLC chromatogram of BHET in Example 3 is shown;

[0070] Figure 8 In the text, the highest peak (with a retention time of 1.720 minutes) is marked with "1.720", while the other peaks are marked with "2.022", "2.238", "2.371", and "2.672" from left to right.

[0071] Figure 9 The HPLC chromatogram of BHET in Example 4 is shown;

[0072] Figure 9 In the text, the highest peak (with a retention time of 1.725 minutes) is marked with "1.725".

[0073] Figure 10 The 1H NMR spectrum of BHET in Example 5 is shown;

[0074] Figure 11 The 1H NMR spectrum of BHET in Example 6 is shown;

[0075] Figure 12 The 1H NMR spectrum of BHET in Example 7 is shown;

[0076] Figure 13 The HPLC chromatogram of BHET in Example 7 is shown;

[0077] Figure 13 In the text, the peak (highest peak) at the retention time of 1.726 minutes is labeled "Peak 1 - 1.726";

[0078] Figure 14 The 1H NMR spectrum of BHET in Example 8 is shown;

[0079] Figure 15 The HPLC chromatogram of BHET in Example 8 is shown;

[0080] Figure 15 In the middle, the peak (highest peak) at the retention time of 1.721 minutes is written as "Peak 1 - 1.721";

[0081] Figure 16 The 1H NMR spectrum of BHET in Example 9 is shown;

[0082] Figure 17 The HPLC chromatogram of BHET in Example 9 is shown;

[0083] Figure 17In the middle, the peak (highest peak) at the retention time of 1.721 minutes is written as "Peak 1 - 1.721";

[0084] Figure 18 The 1H NMR spectrum of BHET in Example 10 is shown;

[0085] Figure 19 The HPLC chromatogram of BHET in Example 10 is shown;

[0086] Figure 19 In the text, the peak (highest peak) at the retention time of 1.725 minutes is labeled "Peak 1 - 1.725";

[0087] Figure 20 The HPLC chromatogram of BHET in Example 11 is shown;

[0088] Figure 20 In the text, the peak (highest peak) at the retention time of 1.720 minutes is labeled "Peak 1-1.720". Detailed Implementation

[0089] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0090] It should also be noted that the various specific technical features described in the following embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the various possible combinations will not be described separately in this invention.

[0091] Furthermore, various embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention. The resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0092] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0093] Preparation of modified titanate catalyst A: Tetrabutyl titanate (57.2 g) and 80 ml tetrahydrofuran were stirred and dissolved. Ethylene glycol (52 g) was slowly added dropwise to the reaction system. The reaction temperature was 30 °C and the addition time was 2 hours. After the addition was completed, the temperature was slowly raised to 80 °C. After reacting for 2 hours, the heating was stopped. After cooling to room temperature, the mixture was filtered, washed with ethanol, and dried under vacuum to obtain modified titanate catalyst A.

[0094] Preparation of modified titanate catalyst B: Isopropyl titanate (23.9 g) and 30 ml isopropanol were stirred and dissolved. Ethylene glycol (13 g) was slowly added dropwise to the reaction system. The reaction temperature was 25 °C and the addition time was 1 hour. After the addition was completed, the temperature was slowly raised to 85 °C. After reacting for 1 hour, the heating was stopped. After cooling to room temperature, the mixture was filtered, washed with ethanol, and dried under vacuum to obtain modified titanate catalyst B.

[0095] Preparation of modified titanate catalyst C: Tetraethyl titanate (38.3 g) and 100 ml petroleum ether were stirred and dissolved. Ethylene glycol (72.9 g) was slowly added dropwise to the reaction system at a reaction temperature of 40 °C for 3 hours. After the addition was completed, the temperature was slowly raised to 90 °C. After reacting for 3 hours, the heating was stopped. After cooling to room temperature, the mixture was filtered, washed with acetone, and dried under vacuum to obtain modified titanate catalyst C3.

[0096] Taking waste PET as an example, the depolymerization rate of waste PET is shown in Equation (1), and the yield of product BHET is shown in Equation 2, wherein the molecular weight of BHET is 254 g / mol and the molecular weight of PET repeating unit is 192 g / mol.

[0097]

[0098]

[0099]

Example 1

[0100] Waste PET polyester bottle material and ethylene glycol were added to a reactor at a mass ratio of 1:4, along with 0.3 wt% (based on PET mass) of modified titanate catalyst A. The air inside the reactor was replaced with nitrogen to ensure airtightness. A certain amount of nitrogen was then introduced to bring the pressure inside the reactor to 0.4 MPa. Stirring was started, and the reactor temperature was set to 200℃. The reaction time was 3 hours after the reactor temperature reached the set temperature, yielding the depolymerization product. The depolymerization product was filtered hot at 120℃ to obtain the first filtrate. Deionized water was added at a ratio of 1:2 (first filtrate:water). After stirring in an 80℃ water bath for 2 hours, the mixture was filtered to obtain a clear filtrate. The clear filtrate was cooled and crystallized at 25℃ for 12 hours, then cooled again at 4℃ for 2 hours. The crystals were then filtered to obtain BHET crystals, which were dried in a vacuum oven at 80℃ for 10 hours and weighed to obtain the target product, BHET.

[0101] Figure 1 This is the infrared spectrum of BHET; the stretching vibration of -OH is at a wavenumber of 3444 cm⁻¹. -1 It appears at 2964 cm⁻¹, with a relatively strong absorption peak. -1 And 2881cm -1 The peak at 1714 cm⁻¹ belongs to the stretching vibration peak of -CH₂-.-1 The peak at 1504 cm⁻¹ corresponds to the stretching vibration of the carbonyl C=O bond. -1 and 1457cm -1 The nearby peak is also related to the C=C vibrational absorption peak of the benzene ring skeleton, 1278 cm⁻¹. -1 and 1132cm -1 The characteristic peak at 875 cm⁻¹ corresponds to the stretching vibration of the CO bond in the ester group. -1 The peak emitted is consistent with the CH peak of substituted benzene, indicating the presence of substitution at the para-C position on the benzene ring, 727 cm⁻¹. -1 The peak at that location corresponds to the in-plane bending vibration of the benzene ring, while the CH4 atoms attached to the benzene ring undergo out-of-plane bending vibration. Based on the above analysis, the measured PET alcoholysis product is BHET.

[0102] Figure 2 It's BHET's. 1 The ¹H NMR spectrum shows peak a at 4.98 ppm, representing the terminal hydroxyl hydrogen; peak b at 3.71–3.74 ppm, representing the hydrogen on the methylene group near the hydroxyl group; peak c near 4.33 ppm, representing the proton peak corresponding to the -COO-CH₂-methylene group; and peak f at 8.13 ppm, representing the four hydrogens on the benzene ring. The peak area ratio of peaks a, b, c, and f is 2:4:4:4, consistent with the hydrogen number ratio at each chemical position in the BHET structure. Furthermore, characteristic peaks of water (δ = 3.34 ppm) and solvent peaks of DMSO (δ = 2.51 ppm) are present. Therefore, NMR analysis further confirms that the product has a BHET structure.

[0103] Figure 3 The DSC spectrum of BHET shows only one melting peak at 109.7℃ with no other impurity peaks. The peak is sharp and falls within the theoretical melting point range of BHET (109~112℃), indicating that the product has high purity.

[0104] Figure 4 This is the high performance liquid chromatography (HPLC) chromatogram of BHET. The elution time of BHET is 1.725 minutes, and the elution time of the dimer is 2.685 minutes. There is no trimer, indicating that the purity of the obtained alcoholysis product BHET is 97.6%.

[0105] In this embodiment, the waste polyester depolymerization rate is 100%, the BHET content in the depolymerization solution is 97.2%, the BHET yield of the depolymerized monomer is 73.1%, the BHET purity is 97.59%, and the residual titanium content of the catalyst in the BHET is 8.5 mg / Kg.

[0106] Based on this experiment, it can be seen that the titanium-based catalyst of the present invention has strong advantages in alcoholysis of waste PET bottle material, catalyst and reaction process. It not only has high depolymerization efficiency and product yield, but also extremely high BHET purity, extremely low catalyst residue, and excellent alcoholysis effect.

[0107]

Example 2

[0108] The process of Example 1 was repeated, except that: waste PET polyester bottle material and ethylene glycol were added to the reactor at a mass ratio of 1:4.5, and the filtration temperature in step (a) was 130°C. Everything else was the same as in Example 1.

[0109] In Example 2, the waste polyester depolymerization rate was 100%, the BHET content in the depolymerization solution was 98.0%, the BHET yield of the depolymerized monomer was 77.6%, and the BHET purity was 98.24%. Figure 5 The depolymerization product BHET in this embodiment 1 H NMR spectrum Figure 6 This is an HPLC chromatogram of the depolymerization product BHET in this embodiment. The elution time of BHET is 1.722 minutes, the elution time of the dimer is 2.671 minutes, and there is no trimer.

[0110]

Example 3

[0111] The process of Example 1 was repeated, except that: waste PET polyester bottle material and ethylene glycol were added to the reactor at a mass ratio of 1:3, and the filtration temperature in step (a) was 110°C. Everything else was the same as in Example 1.

[0112] In Example 3, the waste polyester depolymerization rate was 100%, the BHET content in the depolymerization solution was 95.8%, the BHET yield of the depolymerized monomer was 70.9%, and the BHET purity was 96.8%. Figure 7 The depolymerization product BHET in this embodiment 1 H NMR spectrum Figure 8 This is an HPLC chromatogram of the depolymerization product BHET in this embodiment. The elution time of BHET is 1.720 minutes, the elution time of the dimer is 2.672 minutes, and there is no trimer.

[0113]

Example 4

[0114] The process of Example 1 was repeated, except that: waste PET polyester bottle material and ethylene glycol were added to the reactor at a mass ratio of 1:2, and the alcoholysis catalyst was replaced with modified titanate catalyst C. Everything else was the same as in Example 1.

[0115] In Example 4, the waste polyester depolymerization rate was 100%, the BHET content in the depolymerization solution was 60.0%, the BHET yield of the depolymerized monomer was 58.0%, and the BHET purity was 95.3%. Figure 9 This is an HPLC chromatogram of the depolymerization product BHET in this embodiment. The elution time of BHET is 1.725 minutes, the elution time of the dimer is 2.686 minutes, and the elution time of the trimer is 5.844 minutes.

[0116]

Example 5

[0117] The process of Example 1 was repeated, except that the treated waste PET polyester bottle material and ethylene glycol were added to the reactor at a mass ratio of 1:4.5, and 0.4 wt% (based on the mass of PET) of isopropyl titanate was added. Everything else was the same as in Example 1.

[0118] In Example 5, the waste polyester depolymerization rate was 100%, the BHET content in the depolymerization solution was 93.3%, the BHET yield of the depolymerized monomer was 67.3%, the BHET purity was 95.2%, and the residual titanium catalyst content in the BHET was 258 mg / kg. Figure 10 The depolymerization product BHET in this embodiment 1 H NMR spectrum.

[0119]

Example 6

[0120] The process of Example 5 was repeated, except that 0.4 wt% (based on the mass of PET) of tetrabutyl titanate was added to the reactor as a depolymerization catalyst, and everything else was the same as in Example 5.

[0121] In Example 6, the waste polyester depolymerization rate was 100%, the BHET content in the depolymerization solution was 93.1%, the BHET yield of the depolymerized monomer was 66.8%, the BHET purity was 95.0%, and the titanium content of the residual catalyst in the BHET was 133 mg / Kg. Figure 11 The depolymerization product BHET in this embodiment 1 H NMR spectrum.

[0122]

Example 7

[0123] The process of Example 5 was repeated, except that 0.4 wt% (based on the mass of PET) of modified titanate catalyst B was added to the reactor, and the reaction pressure in the reactor was 0.6 MPa. Everything else was the same as in Example 5.

[0124] In Example 7, the waste polyester depolymerization rate was 100%, the BHET content in the depolymerization solution was 96.2%, the BHET yield of the depolymerized monomer was 79.0%, the BHET purity was 95.9%, and the titanium content of the residual catalyst in the BHET was 328 mg / Kg. Figure 12 The depolymerization product BHET in this embodiment 1 H NMR spectrum Figure 13 This is an HPLC chromatogram of the depolymerization product BHET in this embodiment. The elution time of BHET is 1.726 minutes, the elution time of the dimer is 2.681 minutes, and the elution time of the trimer is 5.812 minutes.

[0125]

Example 8

[0126] The process of Example 2 was repeated, except that 0.1 wt% (based on the mass of PET) of modified titanate catalyst A was added to the reactor. Otherwise, it was the same as in Example 2.

[0127] In Example 8, the waste polyester depolymerization rate was 100%, the BHET content in the depolymerization solution was 73.8%, the BHET yield of the depolymerized monomer was 55.2%, the BHET purity was 95.5%, and the titanium content of the residual catalyst in the BHET was 304 mg / Kg. Figure 14 The depolymerization product BHET in this embodiment 1 H NMR spectrum Figure 15 This is an HPLC chromatogram of the depolymerization product BHET in this embodiment. The elution time of BHET is 1.721 minutes, the elution time of the dimer is 2.672 minutes, and there is no trimer.

[0128]

Example 9

[0129] The process of Example 2 was repeated, except that 0.2 wt% (based on the mass of PET) of modified titanate catalyst A was added to the reactor, and the filtration temperature in step (a) was 100°C. Everything else was the same as in Example 2.

[0130] In Example 9, the waste polyester depolymerization rate was 100%, the BHET content in the depolymerization solution was 96.3%, the BHET yield of the depolymerized monomer was 79.9%, the BHET purity was 96.7%, and the titanium content of the residual catalyst in the BHET was 336 mg / Kg. Figure 16 The depolymerization product BHET in this embodiment 1 H NMR spectrum Figure 17 This is an HPLC chromatogram of the depolymerization product BHET in this embodiment. The elution time of BHET is 1.721 minutes, the elution time of the dimer is 2.670 minutes, and the elution time of the trimer is 5.776 minutes.

[0131]

Example 10

[0132] The process of Example 2 was repeated, except that 0.4 wt% (based on the mass of PET) of modified titanate catalyst A was added to the reactor, and the filtration temperature in step (a) was 140°C. Everything else was the same as in Example 2.

[0133] In Example 10, the waste polyester depolymerization rate was 100%, the BHET content in the depolymerization solution was 97.3%, the BHET yield of the depolymerized monomer was 77.0%, the BHET purity was 96.9%, and the titanium content of the residual catalyst in the BHET was 37 mg / Kg. Figure 18 The depolymerization product BHET in this embodiment 1 H NMR spectrum Figure 19 This is an HPLC chromatogram of the depolymerization product BHET in this embodiment. The elution time of BHET is 1.725 minutes, the elution time of the dimer is 2.677 minutes, and there is no trimer.

[0134]

Example 11

[0135] The process of Example 2 was repeated, except that the reaction pressure in the reactor was 0.35 MPa, and everything else was the same as in Example 2.

[0136] In Example 11, the depolymerization rate of waste polyester was 100%, the yield of the depolymerized monomer BHET was 76.3%, and the purity of BHET was 97.7%. Figure 20 This is an HPLC chromatogram of the depolymerization product BHET in this embodiment. The elution time of BHET is 1.720 minutes, and the elution time of the dimer is 2.662 minutes. There is no trimer.

[0137]

Example 12

[0138] The process of Example 2 was repeated, except that the reaction pressure in the reactor was 0.3 MPa, and everything else was the same as in Example 2.

[0139] In Example 12, the waste polyester depolymerization rate was 100%, the depolymerized monomer BHET yield was 73.5%, and the BHET purity was 96.8%.

[0140]

Example 13

[0141] The process of Example 2 was repeated, except that the depolymerization reaction time was 2 hours, and everything else was the same as in Example 2.

[0142] In Example 13, the depolymerization rate of waste polyester was 100%, the yield of the depolymerized monomer BHET was 70.8%, and the purity of BHET was 97.7%.

[0143]

Example 14

[0144] The process of Example 2 was repeated, except that the reaction temperature in the depolymerization reactor was 210°C, and everything else was the same as in Example 2.

[0145] In Example 14, the waste polyester depolymerization rate was 100%, the depolymerized monomer BHET yield was 72.7%, and the BHET purity was 97.3%.

[0146]

Example 15

[0147] The process of Example 2 was repeated, except that: deionized water was added at a ratio of filtrate:water = 1:4, and the mixture was stirred in a 70°C water bath for 2 hours. The mixture was then filtered to obtain the filtrate. The clarified filtrate was crystallized at 27°C for 10 hours, and then crystallized at 5°C for 3 hours. The crystalline BHET was obtained by suction filtration. Everything else was the same as in Example 2.

[0148] In Example 15, the waste polyester depolymerization rate was 100%, the depolymerized monomer BHET yield was 75.7%, and the BHET purity was 98.5%.

[0149]

Example 16

[0150] The process of Example 2 was repeated, except that: deionized water was added at a ratio of filtrate:water = 1:5, and the mixture was stirred in a 70°C water bath for 2 hours. The mixture was then filtered to obtain the filtrate. The clarified filtrate was crystallized at 22°C for 15 hours, and then crystallized at 0°C for 1 hour. The crystalline BHET was obtained by suction filtration. Everything else was the same as in Example 2.

[0151] In Example 16, the waste polyester depolymerization rate was 100%, the depolymerized monomer BHET yield was 72.7%, and the BHET purity was 98.3%.

[0152]

Example 17

[0153] The process of Example 2 was repeated, except that the filtrate was cooled at 4°C for 14 hours and then filtered to obtain BHET crystals. Otherwise, it was the same as in Example 2.

[0154] In Example 17, the waste polyester depolymerization rate was 100%, the depolymerized monomer BHET yield was 77.8%, and the BHET purity was 96.7%.

[0155]

Example 18

[0156] The process of Example 2 was repeated, except that the filtrate was cooled and crystallized at 25°C for 14 hours, and then filtered to obtain BHET crystals. Otherwise, it was the same as in Example 2.

[0157] In Example 18, the waste polyester depolymerization rate was 100%, the depolymerized monomer BHET yield was 70.3%, and the BHET purity was 98.0%.

[0158]

Example 19

[0159] The process of Example 5 was repeated, except that the mixture of water and the first filtrate was stirred at 60°C for 1 hour.

[0160] In Example 19, the waste polyester depolymerization rate was 100%, the depolymerized monomer BHET yield was 50.8%, and the BHET purity was 93.9%.

[0161]

Example 20

[0162] The process of Example 5 was repeated, except that the mixture of water and the first filtrate was stirred at 80°C for 1 hour.

[0163] In Example 20, the waste polyester depolymerization rate was 100%, the depolymerized monomer BHET yield was 62.7%, and the BHET purity was 95.1%.

[0164]

Example 21

[0165] Repeat the process of Example 2, except that the alcoholysis time is 2 hours, and other conditions remain the same.

[0166] In Example 21, the waste polyester depolymerization rate was 100%, the depolymerized monomer BHET yield was 70.8%, and the BHET purity was 97.7%.

[0167]

Example 22

[0168] The process of Example 2 was repeated, except that the alcoholysis time was 5 hours, while other conditions remained unchanged.

[0169] In Example 22, the waste polyester depolymerization rate was 100%, the depolymerized monomer BHET yield was 77.6%, and the BHET purity was 98.2%.

[0170]

Example 23

[0171] The process of Example 2 was repeated, except that the alcoholysis temperature was 190°C, and all other conditions remained the same.

[0172] In Example 23, the waste polyester depolymerization rate was 100%, the depolymerized monomer BHET yield was 70.3%, and the BHET purity was 95.2%.

[0173]

Example 24

[0174] The process of Example 2 was repeated, except that the alcoholysis temperature was 230°C, and all other conditions remained the same.

[0175] In Example 24, the waste polyester depolymerization rate was 100%, the depolymerized monomer BHET yield was 72.8%, and the BHET purity was 96.0%.

[0176] Comparative Example 1

[0177] The process of Example 1 was repeated, except that 2 wt% (based on the mass of PET) of titanium-containing catalyst (modified titanate catalyst A) was added, while other conditions remained unchanged.

[0178] The depolymerization rate reached 100%, however, the BHET content in the alcoholysis products was 11.75 wt%, the dimer content was 81.3 wt%, and the trimer content was 6.56 wt%. The yield of the target product BHET was 8.7%.

[0179] Comparative Example 2

[0180] Repeat the process of Example 1, except that: deionized water is added at a ratio of 1:2 for the first filtrate to water, and the mixture is stirred at room temperature for 2 hours, while other conditions remain unchanged.

[0181] The purity of the target product was 97.0%, and the yield was 12.1%.

[0182]

Experimental Example

[0183] 83g of BHET monomer and 0.52g of tetrabutyl titanate obtained in Example 2 were added to a three-necked flask. The temperature was gradually increased to 190°C under a nitrogen atmosphere and the reaction was carried out for 1 hour. The vacuum distillation apparatus was then changed, and the temperature was increased to 280°C. The vacuum degree of the system was gradually adjusted to less than 300 Pa. After reacting for 2.5 hours, a PET product with a number average molecular weight of 19,000 g / mol was obtained.

[0184] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for degrading polyester, comprising: Polyester is subjected to alcoholysis, impurity removal, and crystallization in the presence of a titanium-containing catalyst to obtain polyester degradation products. The polyester is selected from poly(p-aryldialkyl) glycol ester, and the alcoholysis is carried out using a diol. The titanium-containing catalyst is selected from diol-modified alkyl titanate, which is obtained as follows: the alkyl titanate is mixed with a solvent to obtain an alkyl titanate solution, the diol is added dropwise to the alkyl titanate solution at 20-50°C, the solution is then heated to 70-100°C, and finally cooled and filtered. The modified alkyl titanate is obtained; the amount of titanium-containing catalyst is 0.3wt%~0.5wt% based on 100wt% of the polyester; the impurity removal includes (a) filtration I treatment, (b) water addition and stirring, and (c) filtration II treatment to obtain a clear filtrate; the crystallization treatment is carried out as follows: first crystallize at 20~28℃ for 10~15h, and then crystallize at 0~5℃ for 1~3h; in step (a), the filtration I treatment is carried out at 80~140℃ to obtain a first filtrate.

2. The method according to claim 1, characterized in that, The polyester is selected from at least one of poly(p-phenylene terephthalate), poly(p-naphthalene dialkylate), and poly(furan dialkylate).

3. The method according to claim 1, characterized in that, The diol is selected from at least one of ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,6-hexanediol.

4. The method according to claim 1, characterized in that, The weight ratio of the diol to the polyester is (2~8):

1.

5. The method according to claim 1, characterized in that, The alcoholysis temperature is 190~250℃; and / or, The pressure for the alcoholysis is 0.2~0.6 MPa; and / or, The alcoholysis time is 1-10 hours; and / or, The alcoholysis was carried out under a protective atmosphere.

6. The method according to claim 1, characterized in that, The alcoholysis was carried out under nitrogen atmosphere.

7. The method according to claim 1, characterized in that, In step (b), the weight ratio of water to the first filtrate is (2~10):

1.

8. The method according to any one of claims 1 to 7, characterized in that, After the crystallization process, the product is filtered and dried to obtain the degradation product.

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