Recycling method of polyethylene glycol terephthalate waste plastics

Abstract

The invention relates to the technical field of plastic waste recycling, in particular to a method for recycling poly (glycol terephthalate) waste plastics, which comprises the following steps: catalyzing and depolymerizing poly (glycol terephthalate) or poly (glycol terephthalate) waste plastics in water in a hydrogen-containing atmosphere to produce 1, 2, 3-trimethyl-1, 3-pentanediol monoisobutyrate); the invention relates to a method for preparing 1, 4-cyclohexanedicarboxylic acid, dihydric alcohol and 4-methyl cyclohexanecarboxylic acid. The invention provides a method for pyrolyzing poly (ethylene terephthalate) or poly (ethylene terephthalate) waste plastics through hydrogenation series neutral water for the first time, and meanwhile, 1, 4-cyclohexanedicarboxylic acid, dihydric alcohol and 4-methyl cyclohexane formic acid are obtained from the poly (ethylene terephthalate). The degradation efficiency is high, and the product can be purified through a simple separation means to obtain a pure product. And under the same reaction system condition, the depolymerization of the polyethylene glycol terephthalate is completed again, and the method has very good polyethylene glycol terephthalate plastic eurytopic applicability.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling of plastic waste, and particularly relates to a method for recycling waste poly(ethylene terephthalate) plastics. Background Art

[0002] Poly(ethylene terephthalate) is a typical thermoplastic plastic, which has the advantages of non-toxicity, odorlessness, light weight, high transparency, good mechanical properties, etc., and is widely used in many fields such as fibers, packaging, and engineering plastics. As one of the most widely used commercial plastics. However, the recovery rate of waste poly(ethylene terephthalate) is very low, only 14%. A large amount of waste poly(ethylene terephthalate) is scattered in the natural environment, causing irreversible impacts and damage to the ecological environment and human health, and at the same time causing serious waste of resources.

[0003] At present, the efficient recovery and utilization of poly(ethylene terephthalate) has become one of the hot issues widely concerned at home and abroad. Common treatment methods for waste plastics include incineration, landfill, mechanical recycling, and chemical recycling. Chemical recycling is to depolymerize solid polymer materials into smaller molecules, intermediate raw materials, or directly into monomers, and the monomers can be further polymerized to form new polymers. Therefore, the chemical recycling method has become an important method for recycling poly(ethylene terephthalate).

[0004] Chemical recycling methods for depolymerizing poly(ethylene terephthalate) include methanol alcoholysis, ethylene glycol alcoholysis, hydrolysis, ammonolysis, etc., which can respectively produce different monomer raw materials. Among them, the hydrolysis method generally needs to be carried out under relatively high acidic or alkaline conditions, and a large amount of acid and alkali waste liquid will be generated after depolymerization, polluting the environment. At the same time, since the nucleophilicity of water is weaker than that of ethylene glycol and methanol, the hydrolysis process of poly(ethylene terephthalate) is relatively slow, and high temperature and high pressure conditions are often required, or phase transfer catalysts, solvents such as dioxane are added.

[0005] Therefore, a simpler method is needed to realize the recycling of poly(ethylene terephthalate). Summary of the Invention

[0006] The purpose of the present invention is to provide a method for recycling waste poly(ethylene terephthalate) plastics, which proposes a simpler method to realize the catalytic cracking of poly(ethylene terephthalate), and for the first time obtains 1,4-cyclohexanedicarboxylic acid products from poly(ethylene terephthalate) through hydrogenation tandem neutral hydrothermal depolymerization. At the same time, this method has good applicability to poly(ethylene terephthalate) plastics.

[0007] The solution adopted by the present invention to achieve the purpose is: a method for recycling poly (ethylene terephthalate) waste plastics, which uses poly (ethylene terephthalate) or poly (ethylene terephthalate) waste plastics to catalytically depolymerize in water under a hydrogen-containing atmosphere to produce 1,4-cyclohexanedicarboxylic acid, 4-methylcyclohexanecarboxylic acid and diol.

[0008] Preferably, the poly (ethylene terephthalate) is at least one of polyethylene terephthalate (PETE), polytrimethylene terephthalate (PTT), and polybutylene terephthalate (PBT). When it is polyethylene terephthalate, the diol is ethylene glycol; when it is polytrimethylene terephthalate, the diol is propylene glycol; when it is polybutylene terephthalate, the diol is butanediol.

[0009] Preferably, it includes the following steps:

[0010] (1) Mix the catalyst, water and poly (ethylene terephthalate) or poly (ethylene terephthalate) waste plastics, and carry out a depolymerization reaction under a hydrogen-containing atmosphere;

[0011] (2) After the reaction, a solid-liquid mixture is obtained. After solid-liquid separation, a solid and a liquid are obtained. The obtained solid is washed with a polar organic solvent, and the washing liquid and the liquid obtained by solid-liquid separation are combined;

[0012] (3) The total liquid obtained in step (2) is extracted with a polar organic solvent to obtain an aqueous phase and an organic phase I. The aqueous phase is concentrated to obtain a pure diol product. After the organic phase I is removed of the solvent, it is eluted with a low-polarity organic solvent to obtain an organic phase II and a crude product of solid 1,4-cyclohexanedicarboxylic acid. The crude product of solid 1,4-cyclohexanedicarboxylic acid is purified to obtain a pure product of 1,4-cyclohexanedicarboxylic acid. The organic phase II is removed of the solvent to obtain 4-methylcyclohexanecarboxylic acid.

[0013] The hydrogen-containing atmosphere used in the present invention can be pure hydrogen or a mixture of hydrogen and an inert gas (such as a gas mixture of hydrogen and nitrogen), etc. Preferably, the hydrogen-containing atmosphere is a pure hydrogen atmosphere.

[0014] Preferably, in step (1), the concentration of poly (ethylene terephthalate) or poly (ethylene terephthalate) waste plastics in the mixed system after mixing, calculated based on the terephthalate monomer contained therein, is 0.1–0.6 mol / L.

[0015] Preferably, in step (1), the catalyst includes at least one of palladium-based catalysts supported on different carriers, and the content of palladium in the catalyst accounts for 0.1%-5% of the molar concentration of the terephthalate monomer contained in the added poly (ethylene terephthalate) or poly (ethylene terephthalate) waste plastics.

[0016] Preferably, the catalyst support further contains other metals, including at least one of nickel, cobalt, copper, manganese, iron, and ruthenium. When the catalyst contains other metal supports, the content of palladium in the catalyst accounts for 0.05%-1% of the molar concentration of the terephthalic acid glycol ester monomer contained in the added polyethylene terephthalate or polyethylene terephthalate waste plastics.

[0017] By adding other metals to the catalyst in combination with palladium, the catalytic effect of palladium can be further enhanced, reducing the palladium content in the reaction system without affecting the reaction process and product yield, or further increasing the yield.

[0018] The catalyst includes, but is not limited to, one of palladium-based catalysts supported on different carriers such as Pd / C, Pd / Al2O3, Pd / BaSO4, Pd / SiO2, Pd / CNTs, Pd / CB, Pd / r-GO, Pd / TiO2, Pd@FAU, PdNi / C, PdNi / TiO2, etc.

[0019] Preferably, in step (1), the reaction conditions for the depolymerization reaction are: a hydrogen-containing atmosphere with a pressure of 1.0-4.0 MPa, a reaction temperature of 160-240 °C, and a reaction duration of 5-30 h.

[0020] Preferably, in step (2), the polar organic solvent includes at least one of ethyl acetate, chloroform, and dichloromethane.

[0021] Preferably, in step (3), the polar organic solvent includes at least one of ethyl acetate, chloroform, and dichloromethane.

[0022] Preferably, in step (3), the low-polarity solvent includes C5-C 18 alkane low-polarity organic solvents or aromatic ring low-polarity organic solvents.

[0023] Preferably, the C5-C 18 alkane low-polarity organic solvents include at least one of n-hexane, n-pentane, isopentane, petroleum ether, and kerosene, and the aromatic ring low-polarity organic solvents include at least one of toluene, p-xylene, and chlorobenzene.

[0024] Preferably, the recovery of the catalyst is further included, and the specific operation is: washing and drying the solid obtained in step (2) to obtain the recovered catalyst.

[0025] The present invention has the following advantages and beneficial effects:

[0026] The present invention first proposes a method for hydrogenation tandem neutral hydrothermal depolymerization of polyethylene terephthalate or polyethylene terephthalate waste plastics, and simultaneously obtains 1,4-cyclohexanedicarboxylic acid, diol and 4-methylcyclohexanecarboxylic acid from polyethylene terephthalate.

[0027] The method of the present invention has high degradation efficiency, and the products can be purified to obtain pure products by simple separation means. After the reaction, the catalyst can be recovered and the depolymerization of polyethylene terephthalate can be completed again under the conditions of the same reaction system.

[0028] The reaction conditions of this method are simple, green, cheap, and have good yields, and have good general applicability to polyethylene terephthalate plastics. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a flow chart of the present invention;

[0030] Figure 2 is a flow chart of Example 1 of the present invention;

[0031] Figure 3 is a product diagram prepared in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0032] For a better understanding of the present invention, the following examples further illustrate the present invention, but the content of the present invention is not limited to the following examples.

[0033] As Figure 1 shown, a method for recycling polyethylene terephthalate waste plastics of the present invention includes the following steps:

[0034] (1) Mix the catalyst, water and polyethylene terephthalate or polyethylene terephthalate waste plastics, and carry out a depolymerization reaction in a hydrogen-containing atmosphere;

[0035] (2) After the reaction, a solid-liquid mixture is obtained, which is filtered by suction. The products are all in the filtrate, and washed with at least one of polar organic solvents such as ethyl acetate, chloroform, dichloromethane, etc., and the washing liquid and the filtrate are combined;

[0036] (3) The total liquid obtained in step (2) (filtrate + washing liquid) can be purified by a certain treatment method to obtain 1,4-cyclohexanedicarboxylic acid, 4-methylcyclohexanecarboxylic acid and diol respectively;

[0037] The above certain treatment method is as follows: An organic solvent (including but not limited to large-polarity organic solvents such as ethyl acetate, dichloromethane, chloroform, etc.) is added to the total liquid for multiple extractions of the solution to obtain an aqueous phase and an organic phase I. The aqueous phase is concentrated by rotary evaporation to obtain pure diol. After the organic phase I is dried with anhydrous sodium sulfate, the solvent is removed by distillation under reduced pressure at low temperature. Petroleum ether or ether (boiling range: 30 - 60 °C) is added, and the crude product of 1,4-cyclohexanedicarboxylic acid is obtained by elution and the organic phase II is obtained. The organic phase II is distilled under reduced pressure to remove the solvent to obtain 4-methylcyclohexanecarboxylic acid; the crude product of 1,4-cyclohexanedicarboxylic acid is obtained by suction filtration and drying to obtain 1,4-cyclohexanedicarboxylic acid;

[0038] (4) The solid-phase filter cake obtained in step (2) is washed with ethyl acetate 2 - 3 times and then dried under vacuum at 40 °C to obtain the recovered catalyst.

[0039] The poly(ethylene terephthalate) is at least one of polyethylene terephthalate PETE, poly(trimethylene terephthalate) PTT, and poly(butylene terephthalate) PBT. When it is polyethylene terephthalate, the diol is ethylene glycol; when it is poly(trimethylene terephthalate), the diol is propylene glycol; when it is poly(butylene terephthalate), the diol is butylene glycol.

[0040] In step (1), the concentration of the poly(ethylene terephthalate) or poly(ethylene terephthalate)-type waste plastics in the mixed system includes but is not limited to 0.1 - 0.6 mol / L (referring to the molar concentration of the terephthalic acid diol ester monomer contained in the poly(ethylene terephthalate)).

[0041] The catalyst includes but is not limited to palladium-based catalysts supported on different carriers such as Pd / C, Pd / Al2O3, Pd / BaSO4, Pd / SiO2, Pd / CNTs, Pd / CB, Pd / r-GO, Pd / TiO2, Pd@FAU, etc. The catalyst includes at least one of the palladium-based catalysts supported on different carriers, and the content of palladium in the catalyst accounts for 0.1% - 5% of the molar concentration of the terephthalic acid diol ester monomer contained in the added poly(ethylene terephthalate) or poly(ethylene terephthalate)-type waste plastics.

[0042] The reaction conditions for the depolymerization reaction: a hydrogen-containing atmosphere with a pressure of 1.0 - 4.0 MPa, a reaction temperature of 160 - 240 °C, and a reaction duration of 5 - 30 h.

[0043] In the present invention, the preferred temperature for catalytic hydrogenation degradation is 180 °C, the preferred pressure is 1.2 MPa, and the preferred reaction time is 15 - 30 h.

[0044] The used hydrogen-containing atmosphere can be pure hydrogen or a mixture of hydrogen and an inert gas (such as a gas mixture of hydrogen and nitrogen), etc. Preferably, the hydrogen-containing atmosphere is a pure hydrogen atmosphere.

[0045] In the present invention, the degradation substrates include, but are not limited to, pure poly(ethylene terephthalate), pure terephthalate copolymer, terephthalate and substituted ethylene terephthalate related polymers or other related product wastes.

[0046] The method of the present invention uses one of the palladium-based catalysts as the catalyst, uses water as the reaction solvent, and under the conditions of a temperature of 160 - 240 °C and a hydrogen-containing atmosphere pressure of 1.0 - 4.0 MPa, hydrogenation degrades poly(ethylene terephthalate) and its related product wastes to produce 1,4-cyclohexanedicarboxylic acid, diol, and 4-methylcyclohexanecarboxylic acid.

[0047] Example 1

[0048] As Figure 2 shown, a method for recycling waste poly(ethylene terephthalate) plastics includes the following steps: Add 180 mg of commercial poly(ethylene terephthalate) particles, 5 mg (0.0047 mmol) of palladium on carbon (10 wt.% loading), and 3 mL of water to a 500 mL high-pressure reaction kettle quartz reaction bottle. The content of palladium in the catalyst accounts for 0.5% of the molar concentration of the ethylene terephthalate monomer contained. Place the reaction bottle in the reaction kettle, introduce hydrogen until the pressure value in the reactor is 1.2 MPa, and carry out the degradation reaction under the reaction conditions of a temperature of 180 °C for 20 h. After the reaction is completed, carry out vacuum filtration, and wash the filter cake with ethyl acetate 2 - 3 times to separate the reaction solid and liquid. Use nuclear magnetic resonance hydrogen spectrum to determine the reaction yield, and the yield of 1,4-cyclohexanedicarboxylic acid is 94%, and the yield of ethylene glycol is 75%. Use gas chromatography to determine the reaction yield, and the yield of 4-methylcyclohexanecarboxylic acid is 1%. Use the separation method mentioned above to obtain the actual separation yield of the product. That is, add an organic solvent (including but not limited to large polar organic solvents such as ethyl acetate, dichloromethane, chloroform, etc.) to the filtrate to extract the solution three times to obtain an aqueous phase and an organic phase I. The aqueous phase is concentrated by rotary evaporation to obtain ethylene glycol. The organic phase I is dried with anhydrous sodium sulfate, and then the solvent is removed by low-temperature vacuum distillation and concentration. Add petroleum ether or ether (boiling range: 30 - 60 °C), and elute to obtain the crude product of 1,4-cyclohexanedicarboxylic acid and obtain an organic phase II. The organic phase II is distilled under reduced pressure to remove the solvent to obtain 4-methylcyclohexanecarboxylic acid; the crude product of 1,4-cyclohexanedicarboxylic acid is dried to obtain pure 1,4-cyclohexanedicarboxylic acid. The actual separation yield of 1,4-cyclohexanedicarboxylic acid is 96%.

[0049] The 1,4-cyclohexanedicarboxylic acid separated in this example 1 1H NMR data is as follows: 1,4-cyclohexanedicarboxylic acid

[0050]

[0051] (trans / cis = 7 / 10)

[0052] 1,4 - Cyclohexanedicarboxylic acid(1a): 1 H NMR(400MHz, DMSO - d6)δ12.08(s, trans + cis, 4.9H), 2.37(s, cis, 2.9H), 2.14(s, trans, 2H), 1.97 - 1.81(m, trans, 4H), 1.76 - 1.65(m, cis, 5.8H), 1.60 - 1.55(m, cis, 5.8H), 1.43 - 1.19(m, trans, 4H). 13 C NMR(100MHz, DMSO - d6)δ176.47, 176.17, 41.75, 27.76, 25.66。

[0053] 4 - Methylcyclohexanecarboxylic acid

[0054]

[0055] 4 - methyl - 1 - cyclohexanecarboxylic acid(2a): 1 H NMR(400MHz, DMSO - d6)δ10.72(s, 1H), 2.39(m, 1H), 1.86(m, 2H), 1.46(m, 4H), 1.29(m, 1H), 1.13(m, 2H), 0.85(d, 3H). 13 C NMR(100MHz, DMSO - d6)δ177.11, 176.37, 42.59, 34.00, 31.20, 28.89, 25.94, 22.51, 21.27。

[0056] Ethylene glycol

[0057]

[0058] Ethylene glycol(3a): 1 H NMR(400MHz, D2O)δ4.7(m, 2H), 3.57(t, 4H). 13 C NMR(100MHz, D2O)δ62.12。

[0059] Example 2

[0060] Replace the commercial polyethylene terephthalate in Example 1 with a PET film. The following steps are included: Add 2.0 g of PET film, 82.8 mg (0.08 mmol) of palladium on carbon (10% loading) and 90 mL of water into a 500 mL high-pressure reactor quartz reaction flask. The content of palladium in the catalyst accounts for 0.75% of the molar concentration of the ethylene terephthalate monomer contained. Place the reaction flask in the reactor, introduce hydrogen until the pressure value in the reactor is 4 MPa, and carry out the degradation reaction under the reaction conditions of a temperature of 240 °C for 30 h. After the reaction is completed, carry out vacuum filtration and wash the filter cake with ethyl acetate 2 - 3 times to separate the reaction solid and liquid. Use nuclear magnetic resonance hydrogen spectrum to determine the reaction yield. The yield of 1,4-cyclohexanedicarboxylic acid is 95%, and the yield of ethylene glycol is 99%. Use gas chromatography to determine the reaction yield. The yield of 4-methylcyclohexanecarboxylic acid is 4%. After the separation operation, the actual separation yield of 1,4-cyclohexanedicarboxylic acid is 94%, and the yield of ethylene glycol is 99%.

[0061] The physical picture of the product prepared in this example is as Figure 3 shown.

[0062] Example 3

[0063] The difference between this example and Example 1 is that: change the palladium on carbon (10% loading) in Example 1 to palladium / barium sulfate (10% loading), replace the hydrogen pressure with 1.0 Mpa, and the content of palladium in the catalyst accounts for 3% of the molar concentration of the ethylene terephthalate monomer contained. Use nuclear magnetic resonance hydrogen spectrum to determine the reaction yield. The yield of 1,4-cyclohexanedicarboxylic acid is 93%, and the yield of ethylene glycol is 86%. Use gas chromatography to determine the reaction yield. The yield of 4-methylcyclohexanecarboxylic acid is 1%. After the separation operation, the actual separation yield of 1,4-cyclohexanedicarboxylic acid is 93%.

[0064] Example 4

[0065] The difference between this example and Example 1 is that: replace the 1.2 MPa hydrogen pressure in Example 1 with 2.0 Mpa, replace the reaction temperature of 180 °C with 160 °C, and the content of palladium in the catalyst accounts for 5% of the molar concentration of the ethylene terephthalate monomer contained. Use nuclear magnetic resonance hydrogen spectrum to determine the reaction yield. The yield of 1,4-cyclohexanedicarboxylic acid is 95%, and the yield of ethylene glycol is 86%. Use gas chromatography to determine the reaction yield. The yield of 4-methylcyclohexanecarboxylic acid is 3%. After the separation operation, the actual separation yield of 1,4-cyclohexanedicarboxylic acid is 91%.

[0066] Example 5

[0067] The difference between this example and Example 1 is as follows: The commercial polyethylene terephthalate in Example 1 is replaced with a PET food tray, the reaction temperature is modified to 200 °C, and the catalyst dosage is modified to a loading of 0.1%. The reaction yields are determined using nuclear magnetic resonance hydrogen spectroscopy, and the yield of 1,4-cyclohexanedicarboxylic acid is 94%, and the yield of ethylene glycol is 83%. The reaction yields are determined using gas chromatography, and the yield of 4-methylcyclohexanecarboxylic acid is 2%. After separation operations, the actual separation yield of 1,4-cyclohexanedicarboxylic acid is 99%.

[0068] Example 6

[0069] The difference between this example and Example 1 is as follows: The commercial polyethylene terephthalate in Example 1 is replaced with polybutylene terephthalate. The reaction yields are determined using nuclear magnetic resonance hydrogen spectroscopy, and the yield of 1,4-cyclohexanedicarboxylic acid is 86%, and the yield of butanediol is 80%. The reaction yields are determined using gas chromatography, and the yield of 4-methylcyclohexanecarboxylic acid is 3%. After separation operations, the actual separation yield of 1,4-cyclohexanedicarboxylic acid is 85%.

[0070] Example 7

[0071] The difference between this example and Example 1 is as follows: The commercial polyethylene terephthalate in Example 1 is replaced with polypropylene terephthalate. The reaction yields are determined using nuclear magnetic resonance hydrogen spectroscopy, and the yield of 1,4-cyclohexanedicarboxylic acid is 90%, and the yield of propylene glycol is 82%. The reaction yields are determined using gas chromatography, and the yield of 4-methylcyclohexanecarboxylic acid is 3%. After separation operations, the actual separation yield of 1,4-cyclohexanedicarboxylic acid is 87%.

[0072] Example 8

[0073] The differences between this example and Example 1 are as follows: The catalyst in Example 1 was changed to 22 mg of PdNi / C (0.25 wt.% Pd, 2 wt.% Ni loading), 180 mg of commercial polyethylene terephthalate particles were changed to 45 mg of commercial polyethylene terephthalate particles, and the reaction time was changed to 15 h. The content of palladium in the catalyst accounted for 0.2% of the molar concentration of the terephthalic acid ethylene glycol monomer contained, and the content of nickel in the catalyst accounted for 3% of the molar concentration of the terephthalic acid ethylene glycol monomer contained. The reaction yields were determined by nuclear magnetic resonance hydrogen spectroscopy, and the yield of 1,4-cyclohexanedicarboxylic acid was 95%, and the yield of ethylene glycol was 90%. The reaction yields were determined by gas chromatography, and the yield of 4-methylcyclohexanecarboxylic acid was 1%. After separation, the actual separation yield of 1,4-cyclohexanedicarboxylic acid was 90%. Compared with the yield of Example 1, on the premise of reducing the content of palladium in the catalyst by nearly half, a yield better than that of Example 1 was still obtained, indicating that in this example, by reducing the content of the noble metal palladium and increasing the content of the inexpensive metal nickel, nickel metal can promote the catalytic effect of palladium, reducing the cost without weakening the degradation effect, and having good application prospects.

[0074] Example 9

[0075] The differences between this example and Example 1 are as follows: The catalyst in Example 1 was changed to 22 mg of PdNi / TiO2 (0.25 wt.% Pd, 2 wt.% Ni loading), 180 mg of commercial polyethylene terephthalate particles were changed to 90 mg of commercial polyethylene terephthalate particles, and the reaction time was changed to 15 h. The content of palladium in the catalyst accounted for 0.1% of the molar concentration of the terephthalic acid ethylene glycol monomer contained, and the content of nickel in the catalyst accounted for 1.5% of the molar concentration of the terephthalic acid ethylene glycol monomer contained. The reaction yields were determined by nuclear magnetic resonance hydrogen spectroscopy, and the yield of 1,4-cyclohexanedicarboxylic acid was 96%, and the yield of ethylene glycol was 88%. The reaction yields were determined by gas chromatography, and the yield of 4-methylcyclohexanecarboxylic acid was 1%. After separation, the actual separation yield of 1,4-cyclohexanedicarboxylic acid was 92%.

[0076] Example 10

[0077] The differences between this example and Example 1 are as follows: The catalyst in Example 1 was changed to 24 mg of PdNi / TiO2 (1 wt.% Pd and 1 wt.% Ni loading), 180 mg of commercial polyethylene terephthalate particles were changed to 45 mg of commercial polyethylene terephthalate particles, and the reaction time was changed to 15 h. The content of palladium in the catalyst accounted for 1% of the molar concentration of the ethylene terephthalate monomer contained, and the content of nickel in the catalyst accounted for 2% of the molar concentration of the ethylene terephthalate monomer contained. The reaction yields were determined by nuclear magnetic resonance hydrogen spectroscopy, and the yield of 1,4-cyclohexanedicarboxylic acid was 96% and the yield of ethylene glycol was 88%. The reaction yields were determined by gas chromatography, and the yield of 4-methylcyclohexanecarboxylic acid was 1%. After separation operation, the actual separation yield of 1,4-cyclohexanedicarboxylic acid was 92%.

[0078] Example 10

[0079] The Pd / C catalyst in Example 1 was replaced with the filter cake obtained by suction filtration and drying under the reaction conditions of Example 1, and all of it was put into the reaction as the recovered solid catalyst. The remaining dosages and experimental steps were the same as above. The reaction yields were determined by nuclear magnetic resonance hydrogen spectroscopy, and the yield of 1,4-cyclohexanedicarboxylic acid was 91% and the yield of ethylene glycol was 87%. The reaction yields were determined by gas chromatography, and the yield of 4-methylcyclohexanecarboxylic acid was 3%.

[0080] Comparative Example 1

[0081] The differences between this example and Example 8 are as follows: The catalyst in Example 8 was changed to 22 mg of Ni / C (2 wt.% Ni loading). The reaction products were detected by nuclear magnetic resonance hydrogen spectroscopy, and no reactants were produced, indicating that the addition of a single nickel metal catalyst could not make the reaction proceed, and the addition of a palladium-nickel bimetallic catalyst containing palladium could jointly promote the occurrence of the reaction.

[0082] The above are the preferred embodiments of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and changes can be made, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims

1. A method for recycling waste poly(ethylene terephthalate) plastics, characterized in that: Using polyethylene terephthalate or waste plastics of polyethylene terephthalate type to catalytically depolymerize in water under a hydrogen-containing atmosphere to produce 1,4-cyclohexanedicarboxylic acid, 4-methylcyclohexanecarboxylic acid and diol.

2. The recycling method of polyalkylene terephthalate waste plastics according to claim 1, characterized in that: The polyethylene terephthalate is at least one of polyethylene terephthalate glycol, polypropylene terephthalate glycol, and polybutylene terephthalate glycol. When it is polyethylene terephthalate glycol, the diol is ethylene glycol; when it is polypropylene terephthalate glycol, the diol is propylene glycol; when it is polybutylene terephthalate glycol, the diol is butylene glycol.

3. The method for recycling waste poly(ethylene terephthalate) plastics according to claim 1 or 2, characterized in that, It includes the following steps: (1) Mix the catalyst, water with polyethylene terephthalate or waste plastics of polyethylene terephthalate type, and carry out a depolymerization reaction under a hydrogen-containing atmosphere; (2) After the reaction, a solid-liquid mixture is obtained. After solid-liquid separation, a solid and a liquid are obtained. Wash the obtained solid with a polar organic solvent, and combine the washing liquid and the liquid obtained by solid-liquid separation; (3) Extract the total liquid obtained in step (2) with a polar organic solvent to obtain an aqueous phase and an organic phase I. The aqueous phase is concentrated to obtain pure diol. After removing the solvent from the organic phase I, elute it with a small-polarity organic solvent to obtain an organic phase II and a crude product of solid 1,4-cyclohexanedicarboxylic acid. After purifying the crude product of solid 1,4-cyclohexanedicarboxylic acid, pure 1,4-cyclohexanedicarboxylic acid is obtained. Remove the solvent from the organic phase II to obtain 4-methylcyclohexanecarboxylic acid.

4. The method for recycling poly(ethylene terephthalate) waste plastics according to claim 3, wherein: In step (1), the concentration of polyethylene terephthalate or waste plastics of polyethylene terephthalate type in the mixed system calculated based on the terephthalate glycol monomer contained therein is 0.1–0.6 mol / L.

5. The recycling method of poly(ethylene terephthalate) waste plastics according to claim 3, characterized in that: In step (1), the catalyst includes at least one of palladium-based catalysts supported on different carriers. The content of palladium in the catalyst accounts for 0.1%-5% of the molar concentration of the terephthalate glycol monomer contained in the added polyethylene terephthalate or waste plastics of polyethylene terephthalate type.

6. The method for recycling poly(ethylene terephthalate) waste plastics according to claim 5, wherein: The supported material of the catalyst also contains other metals, including at least one of nickel, cobalt, copper, manganese, iron, ruthenium. When the catalyst contains other metal supported materials, the content of palladium in the catalyst accounts for 0.05%-1% of the molar concentration of the terephthalate glycol monomer contained in the added polyethylene terephthalate or waste plastics of polyethylene terephthalate type.

7. The recycling method of polyalkylene terephthalate waste plastics according to claim 3, characterized in that: In step (1), the reaction conditions of the depolymerization reaction are: a hydrogen-containing atmosphere with a pressure of 1.0-4.0 MPa, a reaction temperature of 160-240 °C, and a reaction duration of 5-30 h.

8. The method for recycling waste poly(ethylene terephthalate) plastics according to claim 3, characterized in that: In step (2), the polar organic solvent includes at least one of ethyl acetate, chloroform, and dichloromethane.

9. The method for recycling poly(ethylene terephthalate) waste plastics according to claim 3, characterized in that: In step (3), the polar organic solvent includes at least one of ethyl acetate, chloroform, and dichloromethane, and the low-polarity solvent includes a low-polarity organic solvent of alkanes or aromatic ring type having C5-C 18 The low-polarity organic solvent of alkanes having C5-C 18 includes at least one of n-hexane, n-pentane, isopentane, petroleum ether, and kerosene, and the low-polarity organic solvent of aromatic ring type includes at least one of toluene, p-xylene, and chlorobenzene.

10. The method for recycling waste poly(ethylene terephthalate) plastics according to claim 3, characterized in that: It also includes the recovery of the catalyst. The specific operation is: wash and dry the solid obtained in step (2) to obtain the recovered catalyst.

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