CN114907211A - A kind of degradation method of polyester - Google Patents

Abstract

The invention discloses a polyester degradation method. Specifically, the degradation method of the polyester disclosed by the invention comprises the following steps: degrading polyester under the action of carboxylic acid and a catalyst; the polyester comprises a repeating unit formed by dicarboxylic acid and dihydric alcohol; the catalyst is Lewis acid and/or sulfonic acid organic acid. The degradation method has wide application range, the obtained product dicarboxylic acid is simple to separate and can be used for resynthesis of polyester, and the catalyst can be recycled; the obtained product diol dicarboxylate can form carboxylic acid after hydrogenation reduction, and is repeatedly used for polyester degradation together with a catalyst in the degradation liquid, thereby being beneficial to realizing the maximization of the industrial benefit of polyester degradation.

Description

A kind of degradation method of polyester

technical field

The invention belongs to the field of organic chemistry and relates to a method for degrading polyester.

Background technique

Polyester is a general term for polymers obtained by polycondensation of polyols and polycarboxylic acids. It is a class of engineering plastics with excellent properties and wide applications. It can also be made into polyester fibers and polyester films. The specific varieties of polyester are: polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), poly-2,5-furan Ethylene diformate (PEF), and a variety of modified polyester-based fibers, of which PET polyester is the most widely used.

PET polyester is an excellent crystalline thermoplastic polyester material, which is widely used in food packaging, textiles, films, synthetic fibers, etc. However, because it is difficult to be degraded by microorganisms in the environment, with the rapid growth of PET polyester production and consumption, the disposal of waste PET polyester has become increasingly prominent. Recycling waste PET polyester can not only reduce environmental pollution, but also realize the recycling of resources. The recovery methods of PET polyester mainly include physical and chemical methods, in which the monomers or intermediates obtained by chemical degradation can be used as raw materials to re-produce high-performance polyester materials, which can realize efficient recycling of resources.

At present, the chemical degradation methods of PET polyester mainly include alcoholysis, hydrolysis and aminolysis. The alcoholysis method uses various alcohols such as methanol and ethylene glycol as the alcoholysis agent, and degrades PET polyester into terephthalate (DMT, BHET) and ethylene glycol through different processes. The product obtained by the alcoholysis method has high purity and relatively mild conditions, and it is easy to realize continuous industrial production, such as the low-pressure methanol alcoholysis process of PET polyester by DuPont. In this process, the PET polyester is first cut into pieces, and then put into a reaction vessel containing molten DMT, and the temperature of the reactor is controlled at 220 ° C, so that the PET polyester is completely dissolved in the solution; the obtained solution is poured into the reactor. In the reactor, methanol with a temperature in the range of 260-300° C. and a pressure in the range of 0.34-0.65 MPa is blown into the reactor, and a depolymerization reaction occurs with the PET polyester solution in the reactor. In addition, there are three-stage continuous methanol depolymerization PET polyester process adopted by EastmanKodak Company and so on. There are many researches on the alcoholysis method, and the process is relatively mature, which usually involves high temperature above 200 °C or various medium and high pressure controls. The hydrolysis method uses water as a solvent to catalyze the degradation of PET polyester, depolymerize it into monomers terephthalic acid (TPA) and ethylene glycol, and the obtained TPA monomer can be directly used for the reproduction of PET polyester. The neutral hydrolysis method is usually carried out in the temperature range of 245 to 300 ° C, and the pressure is usually controlled between 1 to 4 MPa. The process of supercritical water hydrolysis of PET developed by KobeSteel of Japan also belongs to this category. The alkaline hydrolysis method is usually carried out in an aqueous solution of sodium hydroxide and potassium hydroxide, and the usual conditions are that the reaction pressure is controlled between 1.4 and 2 MPa in the temperature range of 200 to 250 ° C, and the reaction is carried out for 3 to 5 hours. The main products obtained by this method are sodium terephthalate or potassium terephthalate and ethylene glycol, and high-purity terephthalic acid can be obtained through acidification, but the subsequent treatment of the waste liquid produced by the method is relatively complicated, and it is easy to pollute the environment . The aminolysis method is the aminolysis reaction of PET polyester with different kinds of amines to generate the corresponding benzamides. However, due to the slow aminolysis reaction of PET and many by-products, the aminolysis method of PET has not been industrialized so far.

There are many studies on the degradation of PET polyester, and there are relatively mature processes. However, due to various conditions, there is still a lot of room for improvement in the recycling of PET polyester through chemical methods. In addition, with the continuous development of the polyester industry, various polyester materials with different structures and functions have emerged in recent years. The industrial production and use of these functional polyesters will inevitably face the problem of waste recycling.

In conclusion, it is of great significance to develop a new, general polyester degradation method with higher industrial added value.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to overcome the defects of the existing polyester degradation methods such as single type and narrow application range, and provide a polyester degradation method. Different from the traditional degradation method, the present invention adopts carboxylic acid to degrade polyester, and has wide application range. The product obtained by the degradation method of the present invention is simple to isolate. The degradation product dicarboxylate obtained in the present invention can be converted into diol by conventional methods for the resynthesis of polyester, or directly used as a chemical in other chemical conversions, the catalyst can be recycled and reused, or hydrogenated After reduction, a carboxylic acid is formed, which is used together with the catalyst in the degradation solution for the repeated degradation of polyester, which is conducive to maximizing the industrial benefit of polyester degradation.

The present invention solves the above technical problems through the following technical solutions.

The present invention provides a method for degrading polyester, which comprises the following steps: degrading the polyester under the action of carboxylic acid and a catalyst; that is, the polyester comprises a dicarboxylic acid and a dihydric alcohol to form The repeating unit; the catalyst is Lewis acid and/or sulfonic acid organic acid.

In certain embodiments of the present invention, the structure of the repeating unit can be shown in formula I:

Wherein, ring A is a C ₆ -C ₁₀ aromatic ring, or a 5-6 membered heteroaromatic ring with "heteroatoms selected from one or more of N, O and S, and the number of heteroatoms is 1-2";

n is an integer of 1-9.

)或萘环。In certain embodiments of the present invention, in Ring A, the C ₆ -C ₁₀ aromatic ring may be a benzene ring (eg

) or a naphthalene ring.

)。In some embodiments of the present invention, in Ring A, the "heteroatoms are selected from one or more of N, O and S, and the number of heteroatoms is 1-2" 5-6 membered heteroatoms The aromatic ring can be a 5-6 membered heteroaromatic ring with "the heteroatom is O and the number of heteroatoms is 1-2", or it can be a furan ring (for example,

).

In certain embodiments of the present invention, n can be an integer from 1 to 5, and can also be 1, 2, or 3.

In certain embodiments of the present invention, Ring A may be

In certain embodiments of the present invention, the structure of the repeating unit may be

In certain embodiments of the present invention, the repeating unit of the polyester can be the structure shown in formula I:

Wherein, the definitions of rings A and n are the same as those described above.

In certain embodiments of the present invention, the degradation products include dicarboxylic acids and glycol dicarboxylates.

In some embodiments of the present invention, the structure of the dicarboxylic acid can be as shown in formula P1,

Wherein, the definition of ring A is the same as above.

In certain embodiments of the present invention, the structure of the dicarboxylic acid can be

In some embodiments of the present invention, the structure of the diol dicarboxylate can be represented by formula P2,

Wherein, R ¹ is C ₁ -C ₆ alkyl;

The definition of n is the same as above.

In certain embodiments of the present invention, in R ¹ , C ₁ -C ₆ alkyl may be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl groups such as methyl, ethyl or n-propyl.

In some embodiments of the present invention, the structure of the diol dicarboxylate can be

In some embodiments of the present invention, the Lewis acid can be a perfluoroalkyl sulfonate M(C _m F _2m+1 SO ₃ ) _x , wherein M is Sc ion, Y ion, Ce ion, Yb ion, Lu ion, Ti ion, Zr ion, Hf ion, V ion, Nb ion, Ta ion, Mo ion, W ion, Cu ion, Al ion, Fe ion, Ga ion, In ion, Sn ion or Bi ion, m is an integer from 1 to 8, and x is an integer from 1 to 6;

Preferably, M is Sc ion, Hf ion, Zr ion, Al ion or Fe ion, more preferably Hf ion;

Preferably, m is 1, 2 or 3;

Preferably, x is 3 or 4;

Preferably, the Lewis acid is triflate M(CF ₃ SO ₃ ) _x , and the definitions of M and x are as described above;

Preferably, the triflate is Hf(OTf) ₄ , Al(OTf) ₃ , Fe(OTf) ₃ or Sc(OTf) ₃ , more preferably Hf(OTf) ₄ .

In certain embodiments of the present invention, the sulfonic acid-based organic acid may be perfluoroalkanesulfonic acid HC _m' F _2m'+1 SO ₃ , wherein m' is an integer of 1-8, preferably 1, 2 or 3, eg TfOH.

In certain embodiments of the present invention, the carboxylic acid may be a C2 _{- C6} carboxylic acid, preferably acetic acid, n-propionic acid or n-butyric acid.

In some embodiments of the present invention, the molar ratio of the carboxylic acid to the dicarboxylic acid monomer contained in the polyester may be 2:1-30:1, preferably 5:1-15:1 , such as 6:1, 7:1, 11:1, or 13:1.

In some embodiments of the present invention, based on the amount of the dicarboxylic acid monomer contained in the polyester, the amount of the catalyst may be 0.1-20 mol%, preferably 1-10 mol%, For example 2 mol %, 5 mol % or 10 mol %.

In certain embodiments of the present invention, the degradation can be carried out with the participation of water. The amount of water is not particularly limited, as long as it does not affect the degradation of the polyester.

In certain embodiments of the present invention, the degradation may be carried out at a temperature of 140-180°C, eg, 150°C.

In certain embodiments of the present invention, the degree of degradation can be monitored by conventional means in the art (such as infrared spectroscopy, mass spectrometry, nuclear magnetic resonance, etc.), and the degradation time can be 8 to 24 hours, such as 8 hours ~12h.

In certain embodiments of the present invention, the post-treatment of the degradation may include the following steps: filtering, washing, and drying to obtain the dicarboxylic acid. The reagent used in the washing can be an alcoholic solvent (eg, ethanol).

The filtrate obtained by the filtration can be further subjected to the following operations: adding water and an organic solvent to the filtrate, extracting the organic phase, removing the solvent in the organic phase, and obtaining the glycol dicarboxylate. The organic solvent can be an ester solvent (eg, ethyl acetate). The organic phase can also be dried by drying reagents (eg, anhydrous sodium sulfate, anhydrous magnesium sulfate, etc.). The method for removing the solvent in the organic phase can be a conventional method in the art, such as concentration under reduced pressure, evaporation and the like.

In some embodiments of the present invention, the filtrate obtained by filtration can also be subjected to the following operation, which comprises: subjecting the filtrate obtained by filtration to catalytic hydrogenation with a hydrogen source under the action of a heterogeneous hydrogenation catalyst reaction.

Preferably, the heterogeneous hydrogenation catalyst is Pd/C.

Preferably, the hydrogen source is hydrogen.

Preferably, the material ratio of the heterogeneous hydrogenation catalyst to the catalyst described in the polyester degradation method is 1:5 to 1:15, for example, 1:10.

Preferably, the temperature of the catalytic hydrogenation reaction is 150-200°C, for example, 180°C.

In some embodiments of the present invention, the catalytic hydrogenation reaction may further include the following steps: after the catalytic hydrogenation reaction is completed, the reaction solution is filtered, and the filter cake and the filtrate are collected.

In the catalytic hydrogenation reaction, the filter cake containing the heterogeneous hydrogenation catalyst can be recovered and can be repeatedly used in the catalytic hydrogenation reaction, for example, in the catalytic hydrogenation reaction as described above.

In the catalytic hydrogenation reaction, the filtrate contains the aforementioned catalyst and carboxylic acid, which can be repeatedly used for the degradation of the aforementioned polyester.

Preferably, the catalytic hydrogenation reaction is the catalytic hydrogenation reaction shown below:

The definitions of R1, n and catalyst are as described above, wherein, the catalyst is the catalyst contained in the filtrate obtained by the filtration described above, and there is no need to add additionally; the catalyst is preferably the aforementioned Lewis Acids such as the aforementioned triflate M(CF ₃ SO ₃ ) _x , more such as Fe(OTf) ₃ .

In the present invention, the catalysts all refer to the catalysts in the aforementioned degradation reaction, which are different from the heterogeneous hydrogenation catalysts. The heterogeneous hydrogenation catalysts described in the present invention refer to the catalysts in the aforementioned catalytic hydrogenation reactions. Homogeneous hydrogenation catalyst.

Unless otherwise specified, the terms used in the present invention have the following meanings:

The term "polyester" refers to a polymer in which repeating units are linked by ester functional groups. The repeating unit of "polyester" may be an ester structure formed from a dicarboxylic acid and a dihydric alcohol.

Examples of "polyester" include, but are not limited to, polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polyterephthalate Ethylene glycol dicarboxylate co-isosorbide terephthalate (PEIT), polylactic acid (PLA), poly(L-lactic acid) (PLLA), poly(D-lactic acid) (PDLA), poly(D,L) -lactic acid) (PDLLA), PLA stereocomplex (scPLA), polyhydroxyalkanoate (PHA), poly(3-hydroxybutyrate) (P(3HB)/PHB), poly(3-hydroxyvaleric acid) ester) (P(3HV)/PHV), poly(3-hydroxycaproate) (P(3HHx)), poly(3-hydroxyoctanoate) (P(3HO)), poly(3-hydroxydecanoic acid) ester) (P(3HD)), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)/PHBV), poly(3-hydroxybutyrate-co- -3-hydroxyhexanoate) (P(3HB-co-3HHx)/(PHBHHx)), poly(3-hydroxybutyric acid-co-4-hydroxybutyric acid) (P(3HB-co-4HB)), Poly(3-hydroxybutyrate-co-5-hydroxyvalerate) (PHB5HV), Poly(3-hydroxybutyrate-co-3-hydroxypropionate) (PHB3HP), Polyhydroxybutyrate- Co-hydroxyoctanoate (PHBO), polyhydroxybutyrate-co-hydroxyoctadecate (PHBOd), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxyl) Butyrate) (P(3HB-co-3HV-co-4HB)), polybutylene succinate (PBS), polybutylene succinate co-butylene adipate (PBSA) , Polybutylene adipate co-butylene terephthalate (PBAT), polyethylene furandicarboxylate (PEF), polycaprolactone (PCL), poly(ethylene adipate) polyester) (PEA) and blends/mixtures of two or more of the above, also cover polyester segments in copolymers such as polyurethane (PU), unsaturated polyester resins, etc.

The term "polymer" refers to a macromolecule whose structure consists of a plurality of repeating units linked by covalent chemical bonds. In the context of the present invention, the term polymer encompasses natural and synthetic polymers composed of a single type of monomer (ie, homopolymers) or natural and synthetic polymers composed of two or more different types of monomers material (ie, copolymer).

The term "alkyl" refers to a straight or branched chain alkyl group having the specified number of carbon atoms (eg, _C1 - _C6 ). Alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, isobutyl, sec-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl Wait.

The term "aromatic ring" refers to a cyclic group consisting of only carbon atoms having a specified number of carbon atoms (eg C ₆ -C ₁₀ ), which is monocyclic or polycyclic, and at least one ring is aromatic ( complies with Huckel's rule). Aromatic rings are linked to other segments of the molecule through aromatic rings or non-aromatic rings. Aromatic rings include, but are not limited to, benzene rings, naphthalene rings, and the like.

The term "heteroaromatic ring" refers to a specified number of ring atoms (eg, 5-6 members), a specified number of heteroatoms (eg, 1 or 2), a specified heteroatom species (one of N, O, and S) (or more) cyclic groups, which are monocyclic or polycyclic, and at least one ring is aromatic (according to Huckel's rule). Heteroaromatic rings are linked to other segments of the molecule through aromatic or non-aromatic rings. Heteroaromatic rings include, but are not limited to, furan rings, pyrrole rings, thiophene rings, pyrazole rings, imidazole rings, oxazole rings, thiazole rings, pyridine rings, pyrimidine rings, and the like.

On the basis of conforming to common knowledge in the art, the above preferred conditions can be combined arbitrarily to obtain preferred examples of the present invention.

The reagents and raw materials used in the present invention are all commercially available.

The positive progressive effect of the present invention is:

(1) Different from traditional degradation methods, the present invention adopts carboxylic acid (such as acetic acid, propionic acid, n-butyric acid, etc.) to degrade polyester, and is suitable for various polyesters, such as PET polyester, PTT polyester, PBT Polyester, PEF polyester, etc., with a wide range of applications.

(2) The product obtained by the present invention is easy to separate.

(3) The degradation product diol dicarboxylate of the present invention can be converted into diol by conventional methods, and used for the resynthesis of polyester, and the catalyst can be recycled and reused, which is conducive to maximizing the industrial benefit of polyester degradation.

(4) The filtrate after the degradation solution of the present invention reclaims phthalic acid can also undergo further catalytic hydrogenation, so that the glycol dicarboxylate in it is converted into carboxylic acid, and continues to be used for polyester together with the catalyst in the degradation solution The degradation of the polyester, in which the catalyst in the catalytic hydrogenation reaction can also be recycled, which is conducive to maximizing the industrial benefit of polyester degradation.

Detailed ways

The present invention is further described below by way of examples, but the present invention is not limited to the scope of the described examples. The experimental methods that do not specify specific conditions in the following examples are selected according to conventional methods and conditions, or according to the product description.

In the following examples, the structure of the repeating unit of the polyester involved is as follows:

General steps:

Add 96 mg of PET polyester chips, 0.2 ml of glacial acetic acid (the molar ratio of raw materials to feed is about 1:6), add metal trifluoromethanesulfonate catalyst, seal and heat to 150 ° C in a 5 mL sample bottle, and stir the reaction properly. time. After the reaction is completed, filter, and the obtained solid is washed with a small amount of ethanol and dried, which is pure terephthalic acid P1-A. The filtrate can be re-added with PET chips and glacial acetic acid to carry out the degradation reaction again. After multiple reactions, ethylene glycol diacetate can be recovered by distillation or extraction.

Examples 1-8

The specific conditions and yields of the examples are shown in Table 1.

Table 1

The above examples 1-9 mainly obtained the degradation product terephthalic acid P1-A, ¹ H NMR (500MHz, DMSO) δ13.26 (s, 2H), 8.04 (s, 4H), HR-MS (ESI-TOF) C ₈ H ₇ O ₆ ⁺ [M+H] ⁺ calculated 167.0344, found 167.0337;

Ethylene glycol diacetate P2-A, ¹ H NMR(500MHz, CDCl ₃ )δ4.28(s,4H),2.09(s,6H),HR-MS(ESI-TOF)C ₆ H ₁₁ O ₄ ⁺ [M+H] ⁺ Calculated 147.0657, found 147.0653.

Example 10

96 mg of PET polyester flakes, 0.2 ml of glacial acetic acid (the molar ratio of raw materials and feeding amounts is about 1:6), and 18 mg of hafnium trifluoromethanesulfonate are added to a 5 ml sample bottle in sequence. The sample bottle was sealed and heated to 150°C, and the reaction was stirred for 8 to 12 hours. After the reaction was completed, the mixture was filtered, and the obtained solid was washed with a small amount of ethanol and dried to obtain 76.9 mg of terephthalic acid P1-A, with an isolated yield of 94%. To the obtained filtrate, 96 mg of PET was added again and 0.1 ml of glacial acetic acid was added, the seal was heated to 150 ° C, and the reaction was stirred for 8 to 12 hours. After filtration, washing the solid, and drying, 76.7 mg of terephthalic acid P1-A was obtained, and the isolated yield was 94%. Repeating again, 79.0 mg of terephthalic acid P1-A was isolated in 95% yield. Water and ethyl acetate were added to the filtrate obtained at last to separate the layers, the aqueous phase was extracted several times with ethyl acetate, the organic phases were combined and dried, and the solvent was evaporated to obtain ethylene glycol diacetate P2-A, and 190 mg were collected. , the yield was 87% of the total amount of the three additions.

Example 11

96 mg of PET polyester flakes, 0.5 ml of propionic acid (the molar ratio of the raw materials feeding amount is about 1:13), and 18 mg of hafnium trifluoromethanesulfonate are sequentially added to a 5 ml sample bottle. The seal was heated to 150°C, and the reaction was stirred for 8 to 12 hours. After the reaction was completed, it was filtered, and the obtained solid was washed with a small amount of ethanol and dried to obtain 71.4 mg of terephthalic acid P1-A with an isolated yield of 86%. Water and ethyl acetate were added to the obtained filtrate for separation, the aqueous phase was extracted several times with ethyl acetate, the organic phases were combined and dried, and then the solvent was evaporated to obtain ethylene glycol dipropionate P2-B, 76.9 mg were collected, Yield 89%.

Example 12

96 mg of PET polyester flakes, 0.5 ml of n-butyric acid (the molar ratio of the raw material feeding amount is about 1:11), and 18 mg of hafnium trifluoromethanesulfonate are sequentially added to a 5 ml sample bottle. The seal was heated to 150°C, and the reaction was stirred for 8 to 12 hours. After the reaction was completed, it was filtered, and the obtained solid was washed with a small amount of ethanol and dried to obtain 61.0 mg of terephthalic acid P1-A with an isolated yield of 74%. Water and ethyl acetate were added to the obtained filtrate for separation, the aqueous phase was extracted several times with ethyl acetate, the organic phases were combined and dried, and then the solvent was evaporated to obtain ethylene glycol di-n-butyrate P2-C, and 86.4 mg were collected. , the yield is 86%.

Example 13

103 mg of PTT polyester flakes, 0.2 ml of glacial acetic acid (the molar ratio of raw materials and feeding amounts is about 1:6), and 18 mg of hafnium trifluoromethanesulfonate were sequentially added to a 5 ml sample bottle. The seal was heated to 150°C, and the reaction was stirred for 8 to 12 hours. After the reaction was completed, it was filtered, and the obtained solid was washed with a small amount of ethanol and dried to obtain 76.3 mg of terephthalic acid P1-A with an isolated yield of 92%. Water and ethyl acetate were added to the obtained filtrate for separation, the aqueous phase was extracted several times with ethyl acetate, the organic phases were combined and dried, and then the solvent was evaporated to obtain propylene glycol diacetate P2-D, which was collected 64.8 mg in a yield of 64.8 mg. 80%.

Example 14

110 mg of PBT polyester flakes, 0.2 ml of glacial acetic acid (the molar ratio of raw materials and feeding amounts is about 1:6), and 18 mg of hafnium trifluoromethanesulfonate were sequentially added to a 5 ml sample bottle. The seal was heated to 150°C, and the reaction was stirred for 8 to 12 hours. After the reaction was completed, the mixture was filtered, and the obtained solid was washed with a small amount of ethanol and dried to obtain 78.0 mg of terephthalic acid P1-A with an isolated yield of 94%. Water and ethyl acetate were added to the obtained filtrate for separation, the aqueous phase was extracted several times with ethyl acetate, the organic phases were combined and dried, and then the solvent was evaporated to obtain butanediol diacetate P2-E, 68.0 mg was collected, Yield 78%.

Example 15

92 mg of PEF polyester chips, 0.2 mL of acetic acid (the raw material dosage was fixed at 1:6), and 18 mg of hafnium trifluoromethanesulfonate were sequentially added to a 5-mL sample bottle. The seal was heated to 150°C, and the reaction was stirred for 8 to 12 hours. After the reaction was completed, the mixture was filtered, and the obtained solid was washed with a small amount of ethanol and dried to obtain 55.6 mg of 2,5-furandicarboxylic acid P1-B with an isolated yield of 67%. ¹ H NMR (500 MHz, DMSO) δ 13.53 (s, 2H), 7.28 (s, 2H). The filtrate can be reused and recovered ethylene glycol diacetate as previously described.

Example 16

Add 96 mg of PET polyester chips, 0.2 ml of glacial acetic acid (the molar ratio of the raw materials to the sample bottle is about 1:6), add Fe(OTf) ₃ (5mol%), seal and heat to 150 ° C, and stir the reaction in a 5 mL sample bottle. 8h. After the reaction is completed, filter, and the obtained solid is washed with a small amount of ethanol and dried to obtain pure terephthalic acid P1-A, and the isolated yield is 81%. About 3 mL of the reaction filtrate to be treated was placed in the reactor, 10% of the Pd/C (the molar ratio of Pd element and Fe(OTf) ₃ was about 1:10) was added, 15 bar of hydrogen was introduced, and the reaction was heated up after sealing. was heated to 180°C and reacted at 180°C for 2 hours. After the reaction was completed and lowered to room temperature, the reaction solution was filtered, and the collected solid was the recovered Pd/C powder, which could be repeatedly used in hydrogenation experiments after drying. The obtained filtrate is a mixed solution of Fe(OTf) ₃ , acetic acid and ethylene glycol diacetate, which can be repeatedly used for PET degradation. The acetic acid yield for this step can be determined by NMR internal standard quantification, and the typical yield is about 88%.

Example 17

Add 2mmol of n-hexanoic acid to a 5mL sample bottle, add Fe(OTf) ₃ to make the concentration in n-hexanoic acid reach about 0.125mol/L, and then add water to make the concentration in n-hexanoic acid reach about 0.5mol/L. Then, 96 mg of PET polyester (0.5 mmol) fragments were added, and the mixture was sealed and heated to 150° C., and the reaction was stirred for 8 h. After the reaction is completed, filter, and the obtained solid is washed with a small amount of ethanol and dried to obtain pure terephthalic acid P1-A, and the isolated yield is 95%. The reaction filtrate to be treated is placed in the reactor, and 10% loading of Pd/C (the molar ratio _of Pd element and Fe(OTf) is about 1:10) is added, 15bar hydrogen is introduced, and the reactor is heated to 180°C and react at 180°C for 2 hours. After the reaction was completed and lowered to room temperature, the reaction solution was filtered, and the collected solid was the recovered Pd/C powder, which could be repeatedly used in hydrogenation experiments after drying. The obtained filtrate is a mixed solution of Fe(OTf) ₃ , n-hexanoic acid and ethylene glycol dicaproate, which can be repeatedly used for PET degradation. The residual amount of hexanoic acid after this step can be determined by NMR internal standard quantitative method, and the typical content is about 95% of the initial added amount.

The filtrate and Pd/C collected in the above steps were used for PET degradation again: 96 mg of PET polyester (0.5 mmol) fragments were added to the above filtrate, sealed and heated to 150° C., and the reaction was stirred for 8 h. After the reaction is completed, filter, and the obtained solid is washed with a small amount of ethanol and dried to obtain pure terephthalic acid P1-A, and the isolated yield is 88%. The reaction filtrate to be treated was placed in a reactor, the recovered Pd/C powder was added, 15 bar of hydrogen was introduced, and the reactor was heated to 180° C. after sealing, and reacted at 180° C. for 2 hours. After the reaction is completed and lowered to room temperature, the reaction solution is filtered, and the Pd/C powder and the degradation solution can be collected again. At this time, the n-hexanoic acid content is about 92% of the initial addition amount.

Comparative Example 1

In a 15 mL reaction flask were added 220 mg of PBT polyester chips, 183 mg of saccharin, 35 mg of hafnium triflate and 2 mL of toluene. The reaction bottle was sealed and heated to 150° C., and the reaction was carried out with stirring for 24 hours. There was no change in the PBT polyester fragments, and no degradation product was obtained.

Comparative Example 2

Add 96 mg of PET polyester flakes, 0.2 ml of glacial acetic acid (the molar ratio of raw materials to feed is about 1:6), and 0.2 ml of water into a 5 mL sample bottle in turn, then seal the bottle and heat it to 150°C. After stirring and reacting for 24 hours, the PET polyester Fragments are clearly visible, and there is no obvious change in shape. The solution was only slightly turbid, and the yields of degradation products P1-A and P2-A were below 5%.

Claims (14)

1. A method of degrading a polyester, comprising the steps of: degrading polyester under the action of carboxylic acid and a catalyst; the polyester comprises a repeating unit formed by dicarboxylic acid and dihydric alcohol; the catalyst is Lewis acid and/or sulfonic acid organic acid.

2. The method of degrading a polyester according to claim 1, wherein the repeating unit has a structure represented by formula I:

wherein ring A is C ₆ -C ₁₀ An aromatic ring, or a 5-6 membered heteroaromatic ring having one or more heteroatoms selected from N, O and S, and a heteroatom number of 1-2 ";

n is an integer of 1 to 9.

3. The method for degrading polyester according to claim 2, wherein in ring A, C is ₆ -C ₁₀ The aromatic ring is a benzene ring or a naphthalene ring;

and/or, in the ring A, the heteroatom is selected from one or more of N, O and S, the 5-6-membered heteroaromatic ring with 1-2 heteroatoms is a 5-6-membered heteroaromatic ring with 1-2 heteroatoms as the heteroatom, and can be a furan ring;

and/or n is an integer from 1 to 5, and may be 1, 2 or 3.

4. The method for degrading polyester according to claim 3, wherein ring A is

Preferably, the structure of the repeating unit is

5. The method for degrading a polyester according to any one of claims 1 to 4, wherein the product obtained by the degradation comprises dicarboxylic acid and diol dicarboxylate.

6. The method for degrading polyester according to claim 5, wherein the dicarboxylic acid has a structure represented by the formula P1,

wherein ring A is as defined in any one of claims 2 to 4;

and/or the structure of the diol dicarboxylate is shown as a formula P2,

wherein R is ¹ Is C ₁ -C ₆ An alkyl group;

n is as defined in claim 2 or 3.

7. The method for degrading polyester according to claim 6, wherein the dicarboxylic acid has a structure of

And/or, when the structure of the diol dicarboxylate is shown as formula P2, C ₁ -C ₆ Alkyl is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl, for example methyl, ethyl or n-propyl; preferably, the diol dicarboxylate has the structure

8. The method of degrading a polyester according to claim 1, wherein the repeating unit of the polyester has a structure represented by formula I:

wherein rings A and n are as defined in any one of claims 2 to 7.

9. The method for degrading polyester according to claim 1, wherein the Lewis acid is perfluoroalkylsulfonate M (C) _m F _2m+1 SO ₃ ) _x Wherein M is Sc ion, Y ion, Ce ion, Yb ion, Lu ion, Ti ion, Zr ion, Hf ion, V ion, Nb ion, Ta ion, Mo ion, W ion, Cu ion, Al ion, Fe ion, Ga ion, In ion, Sn ion or Bi ion, M is an integer of 1-8, and x is an integer of 1-6;

and/or the sulfonic acid organic acid is perfluoroalkyl sulfonic acid HC _m’ F _2m’+1 SO ₃ Wherein m' is an integer of 1 to 8;

and/or the carboxylic acid is C ₂ -C ₆ A carboxylic acid;

and/or the molar ratio of the dicarboxylic acid to dicarboxylic acid monomers contained in the polyester is 2: 1-30: 1;

and/or, the amount of the catalyst is 0.1-20 mol% based on the amount of dicarboxylic acid monomers contained in the polyester;

and/or, the degradation is carried out in the presence of water;

and/or the degradation is carried out at the temperature of 140-180 ℃;

and/or the degradation time is 8-24 h;

and/or the degradation post-treatment comprises the following steps: filtering, washing and drying to obtain the dicarboxylic acid.

10. The method for degrading polyester according to claim 9,

when the Lewis acid is perfluoroalkyl sulfonate M (C) _m F _2m+1 SO ₃ ) _x When M is Sc ion, Hf ion, Zr ion, Al ion or Fe ion, Hf ion is preferred;

and/or, when the Lewis acid is a perfluoroalkylsulfonate M (C) _m F _2m+1 SO ₃ ) _x When m is 1, 2 or 3;

and/or, when the Lewis acid is perfluoroalkyl sulfonate M (C) _m F _2m+1 SO ₃ ) _x When x is 3 or 4;

and/or, when the sulfonic acid organic acid is perfluoroalkyl sulfonic acid HC _m’ F _2m’+1 SO ₃ When m' is 1, 2 or 3;

and/or, the carboxylic acid is acetic acid, n-propionic acid or n-butyric acid;

and/or the molar ratio of the dicarboxylic acid to dicarboxylic acid monomers contained in the polyester is 5: 1-15: 1;

and/or the amount of the catalyst is 1-10 mol% based on the amount of dicarboxylic acid monomers contained in the polyester;

and/or the post-treatment of degradation comprises the following steps: filtering, washing and drying to obtain dicarboxylic acid; the filtrate obtained by filtering is subjected to the following operations: adding water and an organic solvent into the filtrate, extracting to obtain an organic phase, and removing the solvent in the organic phase to obtain the glycol dicarboxylate.

11. The degradation method according to claim 1, wherein the post-treatment of degradation comprises the steps of: filtering, washing and drying to obtain dicarboxylic acid; the filtrate obtained by the filtration is subjected to the following operation, and comprises the following steps: and carrying out catalytic hydrogenation reaction on the filtrate obtained by filtering and a hydrogen source under the action of a heterogeneous hydrogenation catalyst.

12. The degradation process according to claim 11, characterized in that it satisfies one or more of the following conditions:

(1) the hydrogen source is hydrogen;

(2) the heterogeneous hydrogenation catalyst is Pd/C;

(3) the mass ratio of the heterogeneous hydrogenation catalyst to the catalyst is 1: 5-1: 15, such as 1: 10;

(4) the temperature of the catalytic hydrogenation reaction is 150-200 ℃, for example 180 ℃;

(5) in the post-treatment of degradation, the catalytic hydrogenation reaction further comprises the following steps: after the catalytic hydrogenation reaction is finished, filtering the reaction solution, and collecting a filter cake and filtrate; said filter cake containing said heterogeneous hydrogenation catalyst is reusable for said catalytic hydrogenation reaction; and/or the filtrate contains the catalyst and carboxylic acid, and can be repeatedly used for degrading the polyester.

13. The degradation process of claim 12, wherein the catalytic hydrogenation reaction is a catalytic hydrogenation reaction as follows:

the R is ¹ Is defined as in claim 6 or 7, and n is defined as in claim 2 or 3.

14. The method of any one of claims 10 to 13The polyester degradation method, characterized in that the Lewis acid is trifluoromethanesulfonate M (CF) ₃ SO ₃ ) _x M and x are as defined in claim 8 or 9; preferably, the triflate is Hf (OTf) ₄ 、Al(OTf) ₃ 、Fe(OTf) ₃ Or Sc (OTf) ₃ More preferably Hf (OTf) ₄ ；

And/or the sulfonic acid organic acid is TfOH.