A method for recycling depolymerization products of a polyester-containing article

Abstract

The application discloses a method for recycling a polyester-containing product depolymerization product. The method is to heat the enzymatic hydrolysis liquid containing a dibasic ammonium salt and a dihydric alcohol, promote thermal decomposition of the dibasic ammonium salt, and directly recycle the ammonia separated out into reusable ammonia water through a condensing system. Meanwhile, the dibasic acid is crystallized in situ by using the characteristics that the solubility of the dibasic acid sharply decreases under specific conditions, and high-efficiency separation of the dibasic acid and the dihydric alcohol is realized through subsequent solid-liquid separation, so that technical bottlenecks such as acid and alkali consumption, salt-containing wastewater generation and low dihydric alcohol recovery rate in the traditional sodium salt process are fundamentally avoided.

Description

Technical Field

[0001] This invention relates to the field of degradation technology for polyester-containing products, and in particular to a method for recycling depolymerization products of polyester-containing products. Specifically, it is a method for removing ammonia from degradation products. Background Technology

[0002] Plastic and fiber products are widely used, but their large-scale disposal after use causes serious environmental problems and resource waste. Polyethylene terephthalate (PET), as the world's largest-produced synthetic polyester, faces increasingly serious disposal issues after its disposal. Waste textiles (PET waste textiles), in particular, are far more difficult to recycle than relatively pure PET bottle flakes due to their complex composition (often containing dyes, auxiliaries, and blends with other fibers). Among numerous recycling methods, bio-enzymatic degradation is considered one of the most promising green technologies due to its mild conditions and environmentally friendly characteristics. Relevant patents can be found in WO 2014 / 079844, WO 2015 / 097104, WO 2015 / 173265, and WO 2017 / 198786, etc.

[0003] However, the optimal pH for enzymatic degradation of PET, whether using cutinase or PETase, is typically neutral or slightly alkaline. The enzymatic hydrolysis process continuously releases acidic terephthalic acid (PTA), causing a rapid drop in the pH of the reaction system and severely inhibiting enzyme activity. To address this issue, existing technologies generally employ the addition of an alkali (such as sodium hydroxide) to the reaction system for neutralization, thereby maintaining pH stability and improving depolymerization efficiency.

[0004] After the reaction, the degradation solution rich in PTA and ethylene glycol (EG) requires further treatment to recover high-purity PTA. A common process involves adding excess strong acid (such as sulfuric acid or hydrochloric acid) to the system for "acid precipitation," causing PTA to redefine. While this classic "base neutralization-acid precipitation" route is effective, it has inherent drawbacks: ① The use of strong acids and bases leads to high chemical consumption and costs; ② It generates large amounts of high-salinity wastewater (such as sodium sulfate and sodium chloride), making subsequent treatment difficult and imposing a heavy environmental burden; ③ The PTA product obtained from acid precipitation is prone to contain inorganic salts, requiring multiple water washes to achieve polymerization-grade purity, increasing process complexity and energy consumption; ④ Due to the strong interaction between inorganic sodium salts (such as byproducts sodium acetate or sodium sulfate) and EG molecules, complete separation is difficult, resulting in low EG recovery rates, resource waste, and product contamination.

[0005] In the process of scaling up in practice, there is an urgent need to further develop a new process for deammoniation of dicarboxylic acid ammonium salts that is more efficient, energy-saving and suitable for industrial application, in order to further reduce the overall cost and energy consumption of the biological recycling of polyester, especially PET, and promote its large-scale commercial application. Summary of the Invention

[0006] To avoid the problem of acid and alkali consumption, this invention proposes a method for recycling depolymerization products containing polyester. This invention is an integrated process that simultaneously completes deammoniation, PTA crystallization, and EG enrichment and recovery within a single reaction system through heating. The process involves heating an enzymatic hydrolysate containing ammonium dicarboxylic acid salts (such as ammonium terephthalate) and diols (such as ethylene glycol) to promote the thermal decomposition of the ammonium dicarboxylic acid salts. The precipitated ammonia is directly recovered as reusable ammonia water via a condensation system. Simultaneously, utilizing the characteristic that the solubility of dicarboxylic acids (such as PTA) decreases sharply under specific conditions, it is crystallized in situ. Subsequent solid-liquid separation achieves efficient separation of the dicarboxylic acid and diol, fundamentally avoiding the technical bottlenecks of acid and alkali consumption, saline wastewater generation, and low diol recovery rates in traditional sodium salt processes.

[0007] The technical solution of the present invention is as follows: The first objective of this invention is to provide a method for degrading polyester-containing articles, the method comprising the following steps: (a) contacting the polyester-containing articles with a degrading enzyme to carry out an enzymatic hydrolysis reaction, wherein ammonia water / ammonia gas / liquid ammonia / ammonium hydroxide is used as a pH adjuster in the enzymatic hydrolysis reaction, and a degradation solution containing ammonium salts of dibasic acids and diols is formed after the enzymatic hydrolysis reaction; (c) Heat treatment of the degradation solution.

[0008] In one embodiment of the present invention, before step (c) heats the degradation solution, step (b) is further included to increase the mass concentration of the diol in the degradation solution.

[0009] In one embodiment of the invention, step (b) increases the diol content by one or more of the following methods: ①Removing water by vacuum distillation; ② The degradation solution from step (a) can be reused for the degradation of polyester products.

[0010] In one embodiment of the present invention, step (b) involves removing water by vacuum distillation to increase the mass concentration of diol in the degradation solution.

[0011] In one embodiment of the invention, the mass concentration of the diol in step (b) is increased to a concentration sufficient to allow the dicarboxylic acid, a thermal decomposition product, to crystallize out in the subsequent step (c).

[0012] In one embodiment of the present invention, based on gas chromatography determination, the mass concentration of diol in the degradation solution of step (b) is increased to 50% or more, preferably 60% or more, and more preferably 70% or more.

[0013] In one embodiment of the present invention, based on gas chromatography determination, the mass concentration of diol in the degradation solution of step (b) is 50-90%, preferably 60-85%, and more preferably 70-80%.

[0014] In one embodiment of the present invention, the temperature of the heat treatment in step (c) is 110-190°C, preferably 120-180°C, and more preferably 130-170°C.

[0015] In one embodiment of the present invention, the heating treatment in step (c) is carried out under reduced pressure, preferably with a system pressure of -0.06 to -0.095 MPa, more preferably -0.07 to -0.09 MPa.

[0016] In one embodiment of the present invention, in step (c), the ammonia gas released during the heating process is condensed and recovered to generate an ammonia solution; preferably, an ammonia solution with a concentration of 15-25% is generated.

[0017] In one embodiment of the present invention, the recovered ammonia solution is reused for the enzymatic hydrolysis reaction in step (a) above.

[0018] In one embodiment of the present invention, the polyester-containing product is a polyester-containing plastic, film, or fiber fabric.

[0019] In one embodiment of the present invention, the polyester is selected from one or more of polyethylene terephthalate (PET), polyethylene terephthalate (PTT), polyethylene terephthalate (PBT), polyethylene isosorbide terephthalate (PEIT), polybutylene succinate (PBS), polybutylene adipate succinate (PBSA), polybutylene adipate terephthalate (PBAT), polyethylene furanate (PEF), poly(ethylene adipate) (PEA), polybutylene terephthalate succinate (PBST), and polyethylene succinate (PES), preferably polyethylene terephthalate (PET).

[0020] A second object of the present invention is to provide a method for recovering monomers and / or degradation products from PET-containing articles, comprising the following steps: (a) The PET-containing product is brought into contact with a degradation enzyme to carry out an enzymatic hydrolysis reaction. Ammonia water / ammonia gas / liquid ammonia / ammonium hydroxide is used as a pH adjuster in the enzymatic hydrolysis reaction. After the enzymatic hydrolysis reaction, a degradation solution containing ammonium terephthalate and ethylene glycol is formed. (c) Heating treatment to simultaneously achieve deammoniation, terephthalic acid and ethylene glycol recovery.

[0021] In one embodiment of the present invention, before step (c) heats the degradation solution, step (b) is further included to increase the mass concentration of ethylene glycol in the degradation solution.

[0022] In one embodiment of the present invention, the relevant limitations, types of polyester products, types of polyester, etc. in steps (b) and (c) are as described in [3]-

[13] .

[0023] A third object of the present invention is to provide a method for recycling PET-containing articles, comprising the following steps: (a) The PET product is brought into contact with a degradation enzyme to carry out an enzymatic hydrolysis reaction. Ammonia water / ammonia gas / liquid ammonia / ammonium hydroxide is used as a pH adjuster in the enzymatic hydrolysis reaction. After the enzymatic hydrolysis reaction, a degradation solution containing ammonium terephthalate and ethylene glycol is formed. (c) Heating treatment to simultaneously achieve deammoniation, terephthalic acid and ethylene glycol recovery; (d) Optionally, the recovered terephthalic acid and / or ethylene glycol are purified, and (e) the recovered terephthalic acid and / or ethylene glycol are used in PET synthesis.

[0024] In one embodiment of the present invention, before step (c) heats the degradation solution, step (b) is further included to increase the mass concentration of ethylene glycol in the degradation solution.

[0025] In one embodiment of the present invention, the relevant limitations, types of polyester products, and types of polyester in steps (b) and (c) are as described above.

[0026] Beneficial effects: This invention is an enzyme-ammonia coupled aqueous phase degradation method, which uses ammonia water to replace sodium hydroxide. Ammonia water can not only adjust the pH, but also react with PTA to generate water-soluble ammonium terephthalate.

[0027] This invention couples the entire process of deammoniation, PTA, and EG recovery within a single reaction system. It utilizes heating to dehydrate and deammonize, allowing the ammonia gas generated from the decomposition of ammonium terephthalate to be directly recovered and reused in the upstream enzymatic hydrolysis process. Simultaneously, it leverages the solubility change of PTA in the reaction system to directly crystallize it out. After the reaction, solid-liquid separation yields high-purity PTA and an EG-rich liquid phase, achieving the goal of simultaneous ammonia recovery, PTA precipitation, and EG enrichment without the need for additional media or material transfer, fundamentally avoiding the problems of sodium salt introduction and acid / base consumption.

[0028] The present invention simplifies the process flow, integrates multiple steps into one system, and significantly reduces equipment investment and operating costs.

[0029] This invention significantly reduces energy consumption: it avoids the energy-intensive multiple evaporation and washing processes, reducing overall energy consumption by more than 30%.

[0030] The process of this invention is green and environmentally friendly: the entire process does not require the use of strong acids or alkalis, and no high-salt wastewater is generated, making it highly environmentally friendly. Detailed Implementation

[0031] The present invention will be further illustrated below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalents also fall within the scope defined by the appended claims.

[0032] In each embodiment, details such as undiscussed situations, type selection, and dosage selection can be referred to the relevant guidance of other embodiments, provided that the content does not conflict. For the sake of brevity, each embodiment has not been described in detail. Unless otherwise specified, "above," "below," "not higher than," "not lower than," and "A~B" in this invention all include the stated number.

[0033] In one embodiment, the present invention provides a method for degrading polyester-containing articles, the method comprising the following steps: (a) contacting the polyester-containing articles with a degrading enzyme to carry out an enzymatic hydrolysis reaction, wherein ammonia water / ammonia gas / liquid ammonia / ammonium hydroxide is used as a pH adjuster in the enzymatic hydrolysis reaction, and a degradation solution containing ammonium salt of dibasic acid and diol is formed after the enzymatic hydrolysis reaction; and (c) heating the degradation solution.

[0034] For step (a), existing technology uses sodium hydroxide solution to neutralize the acidic substances produced by enzymatic hydrolysis, forming a sodium dicarboxylate solution (such as sodium terephthalate). However, subsequent acid precipitation (such as acetic acid, sulfuric acid, or hydrochloric acid) is required to precipitate the dicarboxylic acid (such as PTA). This process not only leads to the double consumption of acid and alkali reagents but also generates a large amount of saline wastewater. More importantly, the dicarboxylic acid and diol (such as EG) in this process need to be recovered through two separate processes: precipitation separation and distillation.

[0035] To avoid the problem of acid and alkali consumption, this invention proposes an enzyme-ammonia coupled aqueous phase degradation method, which uses ammonia water to replace sodium hydroxide. Ammonia water can not only adjust the pH, but also react with dicarboxylic acids such as PTA to generate water-soluble dicarboxylic acid ammonium salts.

[0036] For step (c), the ammonium dicarboxylic acid salt, the product of enzyme-ammonia coupled aqueous phase degradation, can be decomposed by heating to obtain a dicarboxylic acid. Taking advantage of the characteristic that the solubility of dicarboxylic acids such as PTA decreases sharply under specific temperature / pressure conditions, they are crystallized in situ. Subsequent solid-liquid separation achieves efficient separation of dicarboxylic acids such as PTA from diols such as EG, fundamentally avoiding acid and alkali consumption and the generation of saline wastewater in traditional sodium salt processes.

[0037] The heating temperature in step (c) is 110-190℃, preferably 120-180℃, and more preferably 130-170℃. For example, the heating temperatures are 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, and 190℃.

[0038] The heat treatment in step (c) is performed under reduced pressure. Further, the system pressure is -0.06 to -0.095 MPa, preferably -0.07 to -0.09 MPa. Examples of system pressures include -0.06 MPa, -0.065 MPa, -0.07 MPa, -0.075 MPa, -0.08 MPa, -0.085 MPa, -0.09 MPa, and -0.095 MPa.

[0039] The specific temperature and pressure mentioned above are conducive to the decomposition of dicarboxylic acid ammonium salts and the subsequent crystallization and precipitation of dicarboxylic acid products in the degradation solution.

[0040] Furthermore, before heating the degradation solution in step (c), step (b) is included to increase the mass concentration of the diol in the degradation solution. Increasing the mass concentration of the diol in the degradation solution helps to reduce the solubility of diacids such as PTA, making them easier to crystallize and precipitate.

[0041] Step (b) can increase the diol content in the degradation solution by one or more of the following methods: ① removing water by vacuum distillation, ② reusing the degradation solution from step (a) for the degradation of polyester products.

[0042] ① Vacuum distillation for dehydration refers to removing a certain proportion of water from the degradation solution under reduced pressure, thereby increasing the diol content in the degradation solution. Preferably, vacuum distillation is carried out at 50-90℃ and -0.07-0.09 MPa to remove approximately 50%-95% of the water, yielding a concentrated solution.

[0043] ② The degradation solution from step (a) is reused for the degradation of polyester-containing products because it contains a relatively high diol content. By directly recycling this solution into a new degradation process (a), the diol content in the system will gradually increase as the polyester decomposes. Through several cycles, the diol content in the final degradation solution will be effectively increased.

[0044] Any of the above methods can be used alone, or one or more methods can be used in combination to increase the diol content in the degradation solution. Most preferably, vacuum distillation is performed to remove some water (such as about 70%-90%) to obtain a concentrated solution.

[0045] Furthermore, in step (b), the mass concentration of the diol is increased to a concentration sufficient to allow the diacid, a thermal decomposition product, to crystallize out in the subsequent step (c). Preferably, the mass concentration of the diol is increased to 50% or more, more preferably 60% or more, and even more preferably 70% or more. For example, the mass concentration of the diol is increased to 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%. The above mass concentrations of the diol are obtained by gas chromatography.

[0046] Furthermore, in step (c), the ammonia gas released during the heating process is condensed and recovered to generate an ammonia solution. Preferably, an ammonia solution with a concentration of 10-40% is generated, more preferably an ammonia solution with a concentration of 15-25%. For example, concentrations of 10%, 15%, 20%, 25%, 30%, 35%, and 40% are used.

[0047] Furthermore, the recovered ammonia solution is reused in the enzymatic hydrolysis reaction of step (a) above, that is, as a pH adjuster in the enzymatic hydrolysis reaction.

[0048] In one embodiment, the present invention provides a method for recovering monomers and / or degradation products from PET-containing products, comprising the following steps: (a) contacting the PET-containing products with a degradation enzyme to carry out an enzymatic hydrolysis reaction, wherein ammonia water / ammonia gas / liquid ammonia / ammonium hydroxide is used as a pH adjuster in the enzymatic hydrolysis reaction, and a degradation liquid containing ammonium terephthalate and ethylene glycol is formed after the enzymatic hydrolysis reaction; (c) heating treatment to simultaneously achieve deammoniation, terephthalic acid and ethylene glycol recovery.

[0049] The present invention is particularly suitable for the treatment of PET-containing products and the recovery of related monomers and / or degradation products, wherein the ammonium salt of the corresponding dicarboxylic acid is ammonium terephthalate. Ammonia, terephthalic acid, and ethylene glycol are simultaneously obtained after heat treatment.

[0050] The phrase "simultaneously achieving deammoniation, terephthalic acid, and ethylene glycol recovery" and "simultaneously obtaining ammonia, terephthalic acid, and ethylene glycol" refers to the thermal decomposition of ammonium terephthalate through heating treatment, releasing ammonia (which is directly recovered as reusable ammonia water via a condensation system). The distillate contains ethylene glycol, while PTA crystallizes in situ, leaving a small amount of ethylene glycol in the solution. In other words, ammonia, terephthalic acid, and ethylene glycol are obtained simultaneously. Compared to existing technologies that use sodium hydroxide solution to neutralize the acidic substances produced by enzymatic hydrolysis to form sodium terephthalate solution, where PTA and EG require separate precipitation and distillation processes for recovery, the "simultaneous" nature of this invention is relative to existing technologies.

[0051] Furthermore, before heating the degradation solution in step (c), step (b) is also included to increase the mass concentration of ethylene glycol in the degradation solution.

[0052] The relevant processes and parameters in steps (a), (b), and (c) can be referred to the relevant content in the previous embodiment, and will not be repeated here.

[0053] In one embodiment, the present invention provides a method for recycling PET-containing articles, comprising the following steps: (a) contacting the PET articles with a degrading enzyme to perform an enzymatic hydrolysis reaction, wherein ammonia water / ammonia gas / liquid ammonia / ammonium hydroxide is used as a pH adjuster in the enzymatic hydrolysis reaction, and a degradation solution containing ammonium terephthalate and ethylene glycol is formed after the enzymatic hydrolysis reaction; (c) heating treatment to simultaneously achieve deammoniation, terephthalic acid and ethylene glycol recovery; (d) optionally, purifying the recovered terephthalic acid and / or ethylene glycol; and (e) using the recovered terephthalic acid and / or ethylene glycol for PET synthesis.

[0054] Furthermore, before heating the degradation solution in step (c), step (b) is also included to increase the mass concentration of ethylene glycol in the degradation solution.

[0055] The relevant processes and parameters in steps (a), (b), and (c) can be referred to the relevant content in the previous embodiment, and will not be repeated here.

[0056] In each embodiment, there are no particular limitations on the type of degrading enzyme; any enzyme with degrading activity against polyester, especially PET, is acceptable, such as PET hydrolase, keratinase, lipase, and esterase. Typically, the degrading enzyme is selected from one or more of the following: PET hydrolase, keratinase, lipase, carboxylesterase, p-nitrobenzyl esterase, esterase, PHA depolymerase, and PHB depolymerase.

[0057] The polyester-containing products described in this invention refer to plastics, films, or fiber fabrics containing polyester. Specifically, this includes plastic products such as plastic bottles, plastic trays, plastic packaging, soft plastics, hard plastics, injection molded parts (electronic casings / automotive parts), etc.; various film-type products; and fiber fabrics such as various fibers, various textiles, tires, etc. The method described in this invention can be used for the pretreatment, degradation, and recycling of the above-mentioned product waste. The polyester-containing products may contain other polymers, auxiliaries, additives, etc., and are preferably primarily composed of polyester. The polyester-containing products may optionally undergo various pretreatments to improve degradation efficiency.

[0058] The polyester described in this invention refers to a polymer containing ester functional groups in its main chain. Further, the polyester is selected from one or more of polyethylene terephthalate (PET), polypropylene terephthalate (PTT), polybutylene terephthalate (PBT), polyisosorbate terephthalate (PEIT), polybutylene succinate (PBS), polybutylene adipate succinate (PBSA), polybutylene adipate terephthalate (PBAT), polyethylene furanate (PEF), poly(ethylene adipate) (PEA), polybutylene terephthalate succinate (PBST), and polyethylene succinate (PES), preferably polyethylene terephthalate (PET).

[0059] Example 1 Take 500 mL of the aqueous reaction solution (mainly containing ammonium terephthalate and ethylene glycol) obtained by degrading PET waste textiles through a bio-enzyme-ammonia coupling system. First, perform vacuum distillation at 60℃ and -0.085 MPa to remove about 80% of the water, and obtain a concentrated solution (gas chromatography determination, ethylene glycol mass concentration is 80%). After stirring evenly, transfer it to a 500 mL reaction vessel and connect it to a condensation recovery system.

[0060] The reaction system was placed in an oil bath and reacted for 3 hours under reduced pressure conditions of 200 rpm stirring speed, 130℃ temperature, and -0.09 MPa system pressure. During the process, ammonium terephthalate gradually decomposed, and the released ammonia gas was collected by a condensation system to obtain an ammonia solution with a concentration of approximately 20%, which can be directly reused in the upstream enzymatic hydrolysis process. The distillate contained ethylene glycol and water (gas chromatography determination showed that the ethylene glycol mass concentration was approximately 95%).

[0061] Meanwhile, terephthalic acid (PTA), due to its extremely low solubility in ethylene glycol, gradually precipitates out, forming a suspension. After the reaction is complete, vacuum filtration is performed. The solid is washed three times with hot ethylene glycol at 80°C, and then vacuum dried for 6 hours to obtain a white powdery PTA product. The filtrate is distilled to recover the ethylene glycol.

[0062] Example 2 Take 500 mL of the aqueous reaction solution (mainly containing ammonium terephthalate and ethylene glycol) obtained by degrading PET waste textiles through a bio-enzyme-ammonia coupling system, and carry out vacuum distillation at 130℃ and -0.09 MPa. Terephthalic acid (PTA) gradually precipitates out, and the bottom liquid contains terephthalic acid and a small amount of ethylene glycol. The distillate contains ethylene glycol and water (gas chromatography determination, ethylene glycol mass concentration is 20-40%).

[0063] After the reaction was completed, the bottom liquid was vacuum filtered. The solid was washed three times with hot ethylene glycol at 80°C, and then vacuum dried for 6 hours to obtain a white powdery PTA product. The ethylene glycol was recovered by distillation of the filtrate.

[0064] Example 3 Ethylene glycol is further purified by distillation. The distillation is carried out at a controlled temperature of 160℃ and a pressure of -0.09MPa. The fraction is collected to obtain ethylene glycol with a mass fraction of more than 99.5%, which meets the polyester grade standard and can be reused in the polymerization reaction process.

[0065] Example 4 The obtained terephthalic acid and ethylene glycol were melt-polymerized at 280°C in the presence of a catalyst to obtain recycled PET.

[0066] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for degrading polyester-containing products, characterized in that, The method includes the following steps: (a) The polyester-containing product is brought into contact with a degradation enzyme to carry out an enzymatic hydrolysis reaction. Ammonia water / ammonia gas / liquid ammonia / ammonium hydroxide is used as a pH adjuster in the enzymatic hydrolysis reaction. After the enzymatic hydrolysis reaction, a degradation solution containing ammonium salts of dibasic acids and diols is formed. (c) Heat treatment of the degradation solution.

2. The method according to claim 1, characterized in that, Before step (c) heats the degradation solution, step (b) further includes increasing the mass concentration of the diol in the degradation solution.

3. The method according to claim 2, characterized in that, Step (b) increases the diol content by one or more of the following methods: ①Removing water by vacuum distillation; ② The degradation solution from step (a) can be reused for the degradation of polyester products.

4. The method according to claim 2, characterized in that, Based on gas chromatography determination, the mass concentration of diol in the degradation solution of step (b) is increased to more than 50%, preferably more than 60%.

5. The method according to claim 1, characterized in that, The temperature of the heat treatment in step (c) is 110-190°C, preferably 120-180°C, and more preferably 130-170°C; And / or, the heat treatment is carried out under reduced pressure, preferably with a system pressure of -0.06 to -0.095 MPa, more preferably -0.07 to -0.09 MPa.

6. The method according to claim 1, characterized in that, In step (c), the ammonia gas released during the heating process is condensed and recovered to generate an ammonia solution; preferably, an ammonia solution with a concentration of 15-25% is generated.

7. The method according to claim 6, characterized in that, The recovered ammonia solution is reused in the enzymatic hydrolysis reaction of step (a) above.

8. The method according to claim 1, characterized in that, The polyester-containing product is a polyester-containing plastic, film, or fiber fabric; And / or, the polyester is selected from one or more of polyethylene terephthalate, polyethylene terephthalate, polyethylene butylene terephthalate, polyethylene isosorbide terephthalate, polybutylene succinate, polybutylene adipate, polybutylene terephthalate, polyethylene furanate, polyethylene (ethylene adipate), polybutylene terephthalate, and polyethylene succinate, preferably polyethylene terephthalate.

9. A method for recovering monomers and / or degradation products from PET-containing products, characterized in that, Includes the following steps: (a) The PET-containing product is brought into contact with a degradation enzyme to carry out an enzymatic hydrolysis reaction. Ammonia water / ammonia gas / liquid ammonia / ammonium hydroxide is used as a pH adjuster in the enzymatic hydrolysis reaction. After the enzymatic hydrolysis reaction, a degradation solution containing ammonium terephthalate and ethylene glycol is formed. (c) The degradation liquid is heated to simultaneously achieve deammoniation, terephthalic acid and ethylene glycol recovery.

10. A method for recycling PET-containing articles, characterized in that, Includes the following steps: (a) The PET-containing product is brought into contact with a degradation enzyme to carry out an enzymatic hydrolysis reaction. Ammonia water / ammonia gas / liquid ammonia / ammonium hydroxide is used as a pH adjuster in the enzymatic hydrolysis reaction. After the enzymatic hydrolysis reaction, a degradation solution containing ammonium terephthalate and ethylene glycol is formed. (c) The degradation liquid is heated to simultaneously achieve deammoniation, terephthalic acid and ethylene glycol recovery; (d) Optionally, the recovered terephthalic acid and / or ethylene glycol may be purified; (e) Use the recovered terephthalic acid and / or ethylene glycol for PET synthesis.