CN115959984A - Polyester polymer degradation method - Google Patents

Abstract

The invention discloses a method for degrading polyester polymers, which utilizes organic acid as a solvent to mix the organic acid with waste polyester polymers, thus realizing depolymerization of the polymers; the waste polyester polymer comprises a polyester repeating unit formed by copolymerization of dicarboxylic acid and dihydric alcohol; the depolymerization product comprises dicarboxylic acid monomer and diol carboxylic ester, the dicarboxylic acid monomer is obtained by solid-liquid separation, and the diol carboxylic ester is obtained by distilling and recovering the solvent. In the product obtained by the invention, the dicarboxylic acid monomer can be used as a high-purity monomer for polyester repolymerization, and the micromolecular diol dicarboxylate can be used for other purposes through separation and purification, so that the economic benefit maximization of polymer degradation is facilitated.

Description

Polyester polymer degradation method

Technical Field

The invention relates to a degradation method of a polyester polymer, which can obtain a dicarboxylic acid polymerization monomer and diol dicarboxylate with high purity, and belongs to the field of organic chemistry.

Background

Polyesters are a generic name of polymers obtained by polycondensation of polyhydric alcohols and polybasic acids, mainly refer to polyethylene terephthalate (PET), and broadly include linear thermoplastic resins such as polybutylene terephthalate (PBT) and polyarylates, and are engineering plastics with excellent performance and wide applications. Specific varieties of polyesters are: polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene-2, 6-naphthalate (PEN), polyethylene furan dicarboxylate (PEF) and various modified polyester-based fibers, with PET polyester being the most widely used.

PET polyester is a polymer with important status in world plastics, is widely applied to the fields of various containers, packaging materials, films, engineering plastics and the like, and is increasingly replacing other synthetic materials. The waste PET material has no toxic or side effect, but the degradation period of the waste PET material in a natural environment is too long, and the waste PET also causes huge environmental pollution and resource waste due to the rapid increase of the yield and consumption of the PET polyester. Therefore, the degradation and recovery of PET can reduce the pollution to the environment and effectively utilize the energy in waste plastics.

The commercial recycling of the waste PET is mainly performed by a physical recycling method at present, but the method causes structural deterioration and performance degradation of the material, so that it can be processed only into low-value products such as textile fibers or low-grade resins and quickly and completely becomes waste. More than 80% of the uses of PET are as food packaging materials, and only in chemical recycling can contaminants bound to the polymer chain be removed by purification of monomers or oligomers, and only such materials can be reprocessed into PET articles for food contact applications. At present, the chemical circulation method of the waste PET mainly comprises an alcoholysis method, a glycolysis method, a hydrolysis method and the like.

The main depolymerization product of the alcoholysis method is dimethyl terephthalate (DMT), the alcoholysis usually needs to be carried out under harsher reaction conditions (temperature 200-350 ℃, pressure 10-20 MPa, nitrogen protection), and slight pollution of PET cannot be tolerated. The main depolymerization products of glycolysis are ethylene terephthalate (BHET) and some oligomers, and although the reaction conditions are mild, the glycolysis is not completely degraded, so that the cost of separation and purification of some oligomers is greatly increased. In all chemical recoveries, terephthalic acid (TPA) is only obtained by hydrolysis. At present, more than 75 percent of the total production capacity of PET in the world adopts high-purity terephthalic acid or medium-purity terephthalic acid as a polymerization raw material to be directly esterified with Ethylene Glycol (EG) and continuously polycondensed into PET polyester. Therefore, PET hydrolysis recovery processes are increasingly gaining attention.

The hydrolysis method can be classified into alkaline hydrolysis, neutral hydrolysis and acidic hydrolysis according to pH.

The neutral hydrolysis is that PET reacts under the condition of water or water vapor by adopting zinc acetate, manganese acetate and the like as catalysts, and hydrolysis products are EG and TPA. The neutral hydrolysis needs to be carried out at high temperature and high pressure, the requirement on equipment materials is high, the continuous operation is difficult, the purity of the product obtained by the neutral hydrolysis method is not high, the later purification process is complex, and the cost is high.

The alkaline hydrolysis is generally carried out in an aqueous NaOH solution at a concentration of 4-20%, but the process is slow, the product TPA is not highly pure, terephthalic acid is obtained only by acid washing after the reaction is completed, and a large amount of waste salts and waste liquids are also generated in the process.

Acidic hydrolysis is generally carried out using concentrated sulfuric acid as catalyst. Pusztaszeri in 1982 issued a patent for recycling PET by acid-catalyzed hydrolysis using concentrated sulfuric acid (>14.5 mol/L) as catalyst, after hydrolysis was complete, the product was diluted with cold water and then NaOH solution was added to pH =11. In this case, the system is composed of ethylene glycol, sodium salt of TPA and Na ₂ SO ₄ Aqueous solution and insoluble impurities. Filtering, acidifying the filtrate to pH =1-3, precipitating solid TPA, filtering, and washing to obtain purity>99% TPA. The disadvantage of this process is that PE is present due to chemical equilibriumT is not completely depolymerized, some PET and oligomers thereof exist, so that the TPA purification process is complex, a large amount of concentrated acid and strong base consumed in the reaction are difficult to recycle, environmental pollution is easily caused, a large amount of waste salt is produced, the generated glycol is difficult to recover, and the atom economy is not high. And the concentration of the PET substrate in the method is less than 2wt%, and industrial production is difficult to realize.

Therefore, it is very important to develop a novel method for degrading waste PET, which has the advantages of thorough depolymerization, simple later purification, high yield and purity of terephthalic acid and atom economy.

Disclosure of Invention

The invention aims to provide a polyester polymer degradation method, organic acid is used as a solvent to carry out chemical depolymerization on waste PET, a dicarboxylic acid monomer obtained by degradation can be used as a high-purity monomer for polyester repolymerization, and an obtained micromolecular diol dicarboxylic acid ester is a high value-added chemical product, can be used for other purposes by separation and purification, and is beneficial to realizing the maximization of the economic benefit of polymer degradation.

The polyester polymer degradation method of the invention uses organic acid as solvent, and mixes the organic acid, catalyst and waste polyester polymer to realize depolymerization of the polymer. The waste polyester polymer comprises a polyester repeating unit formed by copolymerization of dicarboxylic acid and dihydric alcohol; the depolymerization product comprises dicarboxylic acid monomer and diol carboxylic ester; obtaining dicarboxylic acid monomer through solid-liquid separation, and obtaining diol carboxylic ester through distilling and recovering solvent.

The waste polyester polymer comprises the following repeated structural unit segments.

Wherein fragment A is an aromatic region fragment and fragment B is an aliphatic region fragment. After the polymer is degraded, the aromatic region segment can be separated to obtain a solid product of dicarboxylic acid monomer, and the fat region can be separated to obtain a liquid product of dihydric alcohol carboxylate.

Wherein n =2 to 6, preferably n =2 to 4.

Ar is an aromatic ring structure, preferably

The polymer may be present in any form other than a polyester structure, without affecting polyester degradation.

Preferably, the waste polyester polymer includes commercially available PET powder or pellets, and beverage bottles of PET material currently on the market are mainstream, including but not limited to: clear or colored PET beverage bottles such as a transparent mineral water bottle, a cola bottle, a sprite bottle, a pulsation bottle, a kvass bottle and the like; plastic trays, fruit boxes, lunch boxes and the like made of colorless or colored PET materials, and various non-woven fabrics made of PET materials which cannot be recycled.

The structure of the organic acid is shown below:

wherein R is hydrogen or C1-C6 linear, branched or cyclic alkyl.

Preferably, R of the organic acid is H or a linear alkyl group, most preferably methyl. The acetic acid has good effect and is cheap and easy to obtain.

The mass ratio of the volume of the organic acid solvent to the waste polyester polymer is 100-1mL:1g, preferably 20 to 10.

The catalyst comprises: h ₂ O、HBr、HCl、H ₂ SO ₄ 、HOTf、CF ₃ COOH、MeSO ₃ H. One or more of TsOH. Preferably, the catalyst is H ₂ O and CF ₃ COOH, most preferably not added.

The mass ratio of the catalyst to the waste polyester polymer is 1:250 to 1:2, preferably 1:100 to 1:50, most preferably none.

H ₂ O can be added as a catalyst, can improve the yield of TPA, but has an influence on the yield of ethylene glycol diacetate; preferably, the water content is 0 to 20And most preferably from 2 to 5wt%.

The depolymerization reaction is carried out in a flange type hydrothermal reaction kettle, the reaction temperature is 180-300 ℃, and the reaction time is 1-24 hours.

The depolymerization method of the invention is simple, the conversion rate of the polyester is high, the purity of the product is high, and the obtained product is simple to separate. In addition, the method degrades the polyester, can obtain the dicarboxylic acid monomer which is reused for polymerization after simple treatment, can also obtain the chemical raw material dihydric alcohol dicarboxylate with high value, and has more economic benefit.

The invention has simple operation: adding the polymer, the solvent and the catalyst into a high-pressure reaction kettle, and heating and stirring until the reaction is complete. The obtained product is simple to separate: after the reaction is finished, the dicarboxylic acid monomer product can be crystallized and separated out from the solvent, and the dicarboxylic acid product with high purity can be obtained by filtering, wherein the product is a layered crystal, and the crystal form is verified by SEM and XRD; the dihydric alcohol dicarboxylic ester exists in an organic acid solution, and the dihydric alcohol dicarboxylic ester and the organic acid solvent can be obtained by reduced pressure distillation.

The invention can degrade and convert the polymer containing the polyester repeating unit into dicarboxylic acid and dihydric alcohol dicarboxylate, and has the advantages of high conversion rate, single product and simple separation. The dicarboxylic acid can be directly used for the resynthesis of the polyester, and the dihydric alcohol dicarboxylic ester can be directly used in other chemical transformation as a chemical, thereby being beneficial to realizing the maximization of the economic benefit of the degradation of the polyester.

Drawings

FIG. 1 is a diagram of terephthalic acid obtained according to the process of the present invention ¹ H NMR spectrum.

FIG. 2 is a diagram of 2, 5-furandicarboxylic acid obtained according to the process of the present invention ¹ H NMR spectrum.

FIG. 3 is a drawing of 2, 6-naphthalenedicarboxylic acid obtained by the process according to the invention ¹ H NMR spectrum.

FIG. 4 is a schematic representation of the preparation of ethylene glycol diacetate obtained by the process according to the invention ¹ H NMR spectrum.

FIG. 5 is a schematic representation of the preparation of ethylene glycol monoacetate obtained according to the method of the invention ¹ H NMR spectrum.

FIG. 6 is a diagram of a method according to the inventionMethod for obtaining butanediol diacetate ¹ H NMR spectrum.

FIG. 7 is a 1H NMR spectrum of 1, 4-cyclohexanedimethanol diacetate obtained by the method of the invention.

Fig. 1-7 are spectra obtained on a Bruker Advance 400Spectrometer at ambient temperature.

Fig. 8 is an SEM image of a commercially available TPA powder.

Fig. 9 is an SEM image (150X) of TPA obtained by degrading PET chips.

Fig. 10 is an SEM image (500X) of TPA obtained by degrading PET chips.

FIG. 11 is an SEM image of a commercially available PET powder (50 μm).

Fig. 12 is an SEM image (200X) of TPA obtained from degradation of PET powder.

Fig. 13 is an SEM image (500X) of TPA obtained from degradation of PET powder.

Fig. 14 is an XRD pattern of TPA. a) TPA obtained by the process of the present invention; b) TPA obtained by alkaline hydrolysis; c) Standard PDF cards of TPA.

FIG. 15 is a photograph of terephthalic acid obtained in examples 1-8 with different catalysts.

FIG. 16 is a photograph of PET from different sources.

Figure 17 is a photograph of TPA obtained by degradation of PET from different sources.

FIG. 18 is a photograph of 2, 5-furandicarboxylic acid obtained by degradation of PEF polyester in example 38.

FIG. 19 is a photograph showing the degradation of PEN polyester as a raw material in example 39 to obtain 2, 6-naphthalenedicarboxylic acid.

FIG. 20 is a photograph showing terephthalic acid obtained by degradation of a mixture of PET polyester and PP polymer in example 41.

FIG. 21 is a photograph showing terephthalic acid obtained by degrading a nonwoven fabric obtained by blending PET and polyethylene in example 42.

FIG. 22 is a photograph showing degradation of polyethylene terephthalate-1, 4-cyclohexanedimethanol ester (PETG) as a raw material to obtain terephthalic acid in example 44.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention can be made by those skilled in the art after reading the teaching of the present invention, and these equivalents also fall within the scope of the claims appended to the present application.

Examples 1 to 8 were prepared by using PET polyester as a template material and examining the effect of different catalysts on the yields of depolymerization products TPA and EGDA. Tables 9-14 show the effect of different water contents on the yields of the depolymerization products TPA and EGDA and EGMA using PET polyester as the template material. Examples 15 to 19 were prepared by examining the results of depolymerization reactions at different PET concentrations using PET polyester as a raw material. Examples 20 to 29 are the results of examining the depolymerization reaction of PET of different origin. Examples 30 and 31 are scale-up experiments to degrade PET polyester. Examples 32 and 33 are results of examining depolymerization of PET by different organic acid solvents. Examples 34 to 37 are the results of examining the degradation of PET chips at different temperatures. Examples 38 to 44 were made to examine the results of the acetolysis of other polyesters other than PET.

The structure of the solid product is represented by nuclear magnetic resonance in the depolymerization process, the obtained yield is the separation yield, and the product is obtained by the part 5 of the experimental method of Pure Terephthalic Acid (PTA) for industrial use, which is the national standard of the people's republic of China: the purity was determined by measuring the acid value (GB/T30921.5-2016). The structure of the liquid product was confirmed by NMR, and the yield was determined by gas chromatography.

The invention relates to a novel degradation method of waste PET, which has the core technology that acetic acid is used as a solvent to react with an acid catalyst, and depolymerization products are terephthalic acid (TPA), ethylene Glycol Diacetate (EGDA) and Ethylene Glycol Monoacetate (EGMA). A consumed Onhaha empty bottle is selected and cut into fragments, and reaction parameters of PET fragment degradation are inspected. Multiple experiments prove that the depolymerization products in the depolymerization reaction are mainly TPA and EGDA, and EGMA and the intermediate products which are not completely depolymerized are fewer. The reaction scheme is as follows:

the effect of different bronsted acids as catalysts on PET degradation was first investigated.

Examples 1 to 8:

2.5g of PET fragments, 25mL of glacial acetic acid and different acid catalysts (shown in table 1) in the table 1 are sequentially added into a 30mL flange type hydrothermal reaction kettle, the hydrothermal reaction kettle is sealed and then placed into a homogeneous phase synthesizer, the rotation speed of the homogeneous phase synthesizer is 10Hz, the hydrothermal reaction kettle is heated to 220 ℃, and depolymerization reaction is carried out for 10 hours under the condition that the constant temperature is 220 ℃. And after the reaction is finished, filtering to obtain a solid, namely the terephthalic acid. The filtrate contained EGDA and acetic acid, with butanediol diacetate as an internal standard, and was quantified by gas chromatography.

For examples 1-8, the degradation rate of the polyester was greater than 99.9% using different catalysts, and the reaction products TPA and EGDA were the highest in yield when trifluoromethanesulfonic acid and methanesulfonic acid were used as catalysts, but the color of the product was not good due to partial carbonization (FIG. 15). Therefore, relatively speaking, on the premise of ensuring the color of the product, the method has higher separation yield without adding a catalyst.

TABLE 1 Experimental parameters for different acids as catalysts

In the following experiments, the influence of different water contents on the monomer yield was examined using glacial acetic acid as solvent without addition of a catalyst.

Examples 9 to 14:

5.0g of PET fragments and 25mL of acetic acid aqueous solution are sequentially added into a 30mL flange type hydrothermal reaction kettle, the water content is shown in Table 2, the hydrothermal kettle is sealed and then placed into a homogeneous phase synthesizer, the rotating speed of the homogeneous phase synthesizer is 10Hz, the hydrothermal reaction kettle is heated to 220 ℃, and depolymerization reaction is carried out for 10 hours under the condition that the constant temperature is 220 ℃. And after the reaction is finished, filtering to obtain a solid, namely the terephthalic acid. The filtrate contained EGDA, EGMA and acetic acid, and was quantified by gas chromatography using butanediol diacetate as an internal standard.

TABLE 2 Effect of different Water content on PET polyester degradation

For examples 9-14, the degradation rate of the polyester with different water content was greater than 99.9% in the absence of the catalyst with glacial acetic acid as solvent, and it was found that the yield of EGDA gradually decreased with the increase of water content, the yield of EGMA gradually increased, the overall yield remained stable within a certain range, and the yields of TPA and glycol carboxylate were high with the water content of 0-20 wt%. Indicating that the degradation reaction of the polyester is strongly resistant to water under these conditions.

The following experiment examined the effect of different PET concentrations on monomer yield using an aqueous acetic acid solution containing 5wt% water as solvent without the addition of a catalyst.

Examples 15 to 19:

a certain amount of PET fragments (table 3) and 25mL of acetic acid aqueous solution with the water content of 5wt% are sequentially added into a 30mL flange-type hydrothermal reaction kettle, the hydrothermal kettle is sealed and then placed into a homogeneous phase synthesizer, the rotating speed of the homogeneous phase synthesizer is 10Hz, the hydrothermal reaction kettle is heated to 220 ℃, and depolymerization reaction is carried out for 10 hours under the condition that the constant temperature is 220 ℃. And after the reaction is finished, filtering to obtain a solid, namely the terephthalic acid. The filtrate contained EGDA, EGMA and acetic acid, and was quantified by gas chromatography using butanediol diacetate as an internal standard.

TABLE 3 Effect of different PET substrate concentrations on polyester degradation

In examples 14 to 19, the concentration of PET as a solvent in the aqueous acetic acid solution containing 5wt% of water was found to have a large influence on depolymerization without adding a catalyst, and when the mass ratio of PET to the aqueous acetic acid solution was 1/2, the yields of terephthalic acid and ester were significantly reduced, but when the mass ratio of PET to the aqueous acetic acid solution was 1/5, the depolymerization effect was the best.

In the following experiment, depolymerization of PET from different sources was examined using an aqueous acetic acid solution containing 5wt% water as a solvent without adding a catalyst.

Examples 20 to 29:

5.0g of PET fragments (shown in table 4) from different sources and 25mL of acetic acid aqueous solution with the water content of 5wt% are sequentially added into a 30mL flange type hydrothermal reaction kettle, the hydrothermal kettle is sealed and then placed into a homogeneous phase synthesizer, the rotation speed of the homogeneous phase synthesizer is 10Hz, the hydrothermal reaction kettle is heated to 220 ℃, and depolymerization reaction is carried out for 10 hours under the condition that the constant temperature is 220 ℃. And after the reaction is finished, filtering to obtain a solid, namely the terephthalic acid. The filtrate contained EGDA, EGMA and acetic acid, and was quantified by gas chromatography using butanediol diacetate as an internal standard.

TABLE 4 Effect of different sources of PET on polyester degradation

For examples 20 to 29, it can be seen that the depolymerization effect by the process of the present invention is very good for different sources of PET of different colors (fig. 16) (fig. 17), indicating that the present invention is very resistant to different sources of PET and is very advantageous for achieving a closed loop cycle of PET. The lower panel is a photograph of PET from different sources.

Example 30:

60g of PET fragments and 300mL of acetic acid aqueous solution with the water content of 5wt% are sequentially added into a 500mL reaction kettle, the reaction kettle is sealed, mechanical stirring is started, and depolymerization reaction is carried out for 10 hours at the constant temperature of 220 ℃. After the reaction, 45.86g of terephthalic acid solid is obtained by filtration, and the separation yield is 88.40%. The filtrate contained EGDA, EGMA and acetic acid, and quantitative determination was performed by gas chromatography using butanediol diacetate as an internal standard, with a gas yield of 88.2% (ethylene glycol diacetate: ethylene glycol monoacetate =77%: 23%). The solvent acetic acid was recovered by distillation under reduced pressure, and 35.7g of a colorless liquid, in which EGDA amounted to 83.81% in the total amount of 29.41g (100Pa, 62 ℃ C.) of EGMA6.29g (100Pa, 68 ℃ C.) was obtained.

Example 31:

60g of PET fragments and 300mL of glacial acetic acid are sequentially added into a 500mL reaction kettle, the reaction kettle is sealed, mechanical stirring is started, the temperature is increased to 220 ℃, and depolymerization reaction is carried out for 10 hours under the condition of constant temperature of 220 ℃. After the reaction, the mixture was filtered to obtain 42.91g of a terephthalic acid solid, and the isolation yield was 76.20%. EGDA and acetic acid are contained in the filtrate, butanediol diacetate is taken as an internal standard, the quantification is carried out by gas chromatography, and the gas phase yield of the ethylene glycol diacetate is 77.3%. The solvent was recovered by distillation under reduced pressure to give EGDA33.7g (100Pa, 62 ℃ C.), and the separation yield amounted to 73.81%.

Example 32:

adding 1.0g of PET fragments and 5mL of n-valeric acid into 30mL of pressure-resistant pipe with a magnetic stirrer in sequence, sealing the pressure-resistant pipe, placing the sealed pressure-resistant pipe in high-temperature heat-conducting silicone oil, heating the pressure-resistant pipe to 220 ℃ at a magnetic stirring speed of 700rpm, and carrying out depolymerization reaction for 5 hours at a constant temperature of 220 ℃. After the reaction is finished, the solid obtained is the terephthalic acid (yield is 78%, purity is 99.30%).

Example 33:

sequentially adding 1.0g of PET fragments and 5mL of n-hexanoic acid into 30mL of pressure-resistant tube with a magnetic stirrer, sealing the pressure-resistant tube, placing the sealed pressure-resistant tube in high-temperature heat-conducting silicone oil, heating the pressure-resistant tube to 250 ℃ at a magnetic stirring speed of 700rpm, and carrying out depolymerization reaction for 3 hours at a constant temperature of 250 ℃. After the reaction is finished, the solid obtained is the terephthalic acid (the yield is 82 percent, and the purity is 99.18 percent).

Example 34:

5.0g of PET fragments and 25mL of acetic acid aqueous solution with the water content of 5wt% are sequentially added into a 30mL flange-type hydrothermal reaction kettle, the hydrothermal kettle is sealed and then placed into a homogeneous phase synthesizer, the rotating speed of the homogeneous phase synthesizer is 10Hz, and depolymerization reaction is carried out for 10 hours at the constant temperature of 180 ℃. After the reaction is finished, the solid obtained by filtration is the terephthalic acid (the yield is 30.2 percent, and the purity is 79.68 percent). EGDA (23.7%) and EGMA (5.9%) contained in the filtrate were detected by gas chromatography using butanediol diacetate as an internal standard.

Example 35:

5.0g of PET fragments and 25mL of acetic acid aqueous solution with the water content of 5wt% are sequentially added into a 30mL flange-type hydrothermal reaction kettle, the hydrothermal kettle is sealed and then placed into a homogeneous phase synthesizer, the rotating speed of the homogeneous phase synthesizer is 10Hz, and depolymerization reaction is carried out for 10 hours at the constant temperature of 250 ℃. After the reaction is finished, the solid obtained is the terephthalic acid (the yield is 93.8 percent, and the purity is 99.25 percent). EGDA (70.4%) and EGMA (17.7%) contained in the filtrate were detected by gas chromatography using butanediol diacetate as an internal standard.

Example 36:

sequentially adding 5.0g of PET fragments and 25mL of acetic acid aqueous solution with the water content of 5wt% into a 30mL flange-type hydrothermal reaction kettle, sealing the hydrothermal reaction kettle, placing the hydrothermal reaction kettle in a homogeneous phase synthesizer, and carrying out depolymerization reaction for 2 hours at the constant temperature of 280 ℃ at the rotating speed of 10 Hz. After the reaction, the solid obtained was filtered to obtain terephthalic acid (yield 96.9%, purity 99.68%). EGDA (75.6%) and EGMA (18.9%) contained in the filtrate were detected by gas chromatography using butanediol diacetate as an internal standard.

Example 37:

5.0g of PET fragments and 25mL of glacial acetic acid are sequentially added into a 30mL flange-type hydrothermal reaction kettle, the hydrothermal kettle is sealed and then placed into a homogeneous phase synthesizer, the rotation speed of the homogeneous phase synthesizer is 10Hz, and depolymerization reaction is carried out for 2 hours at a constant temperature of 280 ℃. After the reaction is finished, the solid obtained is the terephthalic acid (the yield is 95.8 percent, and the purity is 99.72 percent). EGDA (95.3%) contained in the filtrate was detected by gas chromatography using butanediol diacetate as an internal standard.

Example 38:

a PEF polyester degradation method comprises the following specific steps:

adding 5.0g of PEF polyester (with the molecular weight of more than 30000) and 25mL of glacial acetic acid into a 30mL flange-type hydrothermal reaction kettle, sealing the hydrothermal kettle, placing the kettle in a homogeneous phase synthesizer at the rotating speed of 10Hz, heating to 220 ℃, and carrying out depolymerization reaction for 10 hours at the constant temperature of 220 ℃. After the reaction, the solid obtained was filtered to obtain 2, 5-furandicarboxylic acid (yield 84.3%, purity 99.32%). EGDA (85.1%) was detected in the filtrate by gas chromatography using butanediol diacetate as internal standard.

Example 39:

a degradation method of PEN polyester comprises the following specific steps:

5.0g of PEN polyester and 25mL of glacial acetic acid are sequentially added into a 30mL flange-type hydrothermal reaction kettle, the hydrothermal kettle is sealed and then placed into a homogeneous phase synthesizer, the rotation speed of the homogeneous phase synthesizer is 10Hz, the mixture is heated to 220 ℃, and depolymerization reaction is carried out for 10 hours at the constant temperature of 220 ℃. After the reaction, the solid obtained was filtered to obtain 2, 6-naphthalenedicarboxylic acid (yield 80.9%, purity 99.18%). EGDA (77.2%) in the filtrate was detected by gas chromatography using ethylene glycol diacetate as an internal standard.

Example 40:

a degradation method of PBT polyester comprises the following specific steps:

adding 5.0g of PBT polyester powder and 25mL of glacial acetic acid into a 30mL flange-type hydrothermal reaction kettle in sequence, sealing the hydrothermal kettle, placing the kettle in a homogeneous phase synthesizer at the rotation speed of 10Hz, heating to 220 ℃, and carrying out depolymerization reaction for 10 hours at the constant temperature of 220 ℃. After the reaction, the solid obtained was filtered to obtain terephthalic acid (yield 83.5%, purity 99.74%). BGDA (83.6%) in the filtrate was detected by gas chromatography using ethylene glycol diacetate as an internal standard.

Example 41:

a method for degrading a mixture of PET and Polypropylene (PP) comprises the following specific steps:

sequentially adding 4.5g of PET polyester, 0.5g of PP polymer fragments and 25mL of glacial acetic acid into a 30mL flange-type hydrothermal reaction kettle, sealing the hydrothermal kettle, placing the kettle in a homogeneous phase synthesizer at the rotating speed of 10Hz, heating to 220 ℃, and carrying out depolymerization reaction for 10 hours at the constant temperature of 220 ℃. After the reaction is finished, solid particles sink to the bottom, and the solid obtained by filtering is the terephthalic acid (the yield is 94.1 percent, and the purity is 99.34 percent). EGDA (99.8%) in the filtrate was detected by gas chromatography using ethylene glycol diacetate as an internal standard. Wherein the PP partially re-solidifies as a spherical solid floating above the system.

Example 42:

a degradation method of non-woven fabric blended by PET and Polyethylene (PE) comprises the following specific steps:

5g of non-woven fabric fragments and 25mL of glacial acetic acid are added into a 30mL flange type hydrothermal reaction kettle, the hydrothermal kettle is sealed and then placed into a homogeneous phase synthesizer, the rotation speed of the homogeneous phase synthesizer is 10Hz, and depolymerization reaction is carried out for 10 hours at a constant temperature of 220 ℃. After the reaction, the solid particles settled at the bottom, and the solid obtained by filtering was terephthalic acid (yield 94.2%, purity 99.75%). EGDA (96.6%) in the filtrate was detected by gas chromatography using ethylene glycol diacetate as an internal standard. Wherein the PE part is separated from the non-woven fabric and is solidified into a spherical solid floating above the system again.

Example 43:

a degradation method of polyester cloth (the main component is PET) comprises the following specific steps:

adding 5g of polyester fabric fragments and 25mL of glacial acetic acid into a 30mL flange-type hydrothermal reaction kettle, sealing the hydrothermal kettle, placing the kettle in a homogeneous phase synthesizer, and performing depolymerization reaction for 10 hours at a constant temperature of 220 ℃ at a rotation speed of 10 Hz. After the reaction, the solid obtained by filtration was terephthalic acid (yield 89.4%, purity 97.38%). EGDA (85.1%) in the filtrate was detected by gas chromatography using ethylene glycol diacetate as an internal standard.

Example 44:

a method for degrading polyethylene glycol terephthalate-1, 4-cyclohexane dimethanol ester (PETG) comprises the following specific steps:

5g of PETG particles and 25mL of glacial acetic acid are added into a 30mL flange-type hydrothermal reaction kettle, the hydrothermal kettle is sealed and then placed into a homogeneous phase synthesizer, the rotation speed of the homogeneous phase synthesizer is 10Hz, and depolymerization reaction is carried out for 10 hours at a constant temperature of 220 ℃. After the reaction, solid particles settled at the bottom, and the solid obtained by filtering was terephthalic acid (yield 87.3%, purity 97.20%). EGDA and CHDMDA were detected by gas chromatography using ethylene glycol diacetate as an internal standard.

Claims (7)

1. A method for degrading a polyester polymer, comprising:

organic acid is used as a solvent, and the organic acid is mixed with the waste polyester polymer, so that the depolymerization of the polymer can be realized; the waste polyester polymer comprises a polyester repeating unit formed by copolymerization of dicarboxylic acid and dihydric alcohol; the depolymerization product comprises dicarboxylic acid monomer and diol carboxylic ester, the dicarboxylic acid monomer is obtained by solid-liquid separation, and the diol carboxylic ester is obtained by distilling and recovering the solvent.

2. A degradation process according to claim 1, characterized in that said waste polyester polymer comprises the following segments of recurring structural units:

wherein segment A is an aromatic region segment and segment B is an aliphatic region segment; n =2 to 6;

ar is an aromatic ring structure.

3. A degradation process according to claim 1, characterized in that the organic acid has the following structure:

wherein R is hydrogen or C1-C6 linear, branched or cyclic alkyl.

4. The degradation method according to claim 1, characterized in that:

the mass ratio of the volume of the organic acid to the waste polyester polymer is 100-1mL:1g.

5. The degradation method according to claim 1, characterized in that:

the depolymerization reaction system also comprises a catalyst which comprises H ₂ O、HBr、HCl、H ₂ SO ₄ 、HOTf、CF ₃ COOH、MeSO ₃ H. One or more of TsOH.

6. The degradation method according to claim 5, characterized in that:

the mass ratio of the catalyst to the waste polyester polymer is 1:250 to 1:2.

7. the degradation method according to claim 1, characterized in that:

the depolymerization reaction is carried out at 180-300 deg.C for 1-24 hr.

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