Method for efficiently depolymerizing, decolorizing and purifying colored waste polyester

Abstract

The invention relates to a method for efficiently depolymerizing, decoloring and purifying colored waste polyester, which is characterized by comprising the following steps of: (1) feeding waste polyester, a transition metal salt catalyst and ethylene glycol into a reactor, fully mixing and reacting to obtain a depolymerization solution; (2) adding deionized water into the obtained depolymerization liquid, and continuously stirring to ensure that the whole system still has better flowability at the temperature, so as to obtain a diluent of the depolymerization liquid at the temperature; (3) peroxysulfate is added into the diluent of the depolymerization liquid, and the system begins to be subjected to a decolorization reaction; and (4) recrystallizing the solution obtained after the decoloration reaction is finished, and filtering to obtain the recrystallized depolymerized monomer ethylene glycol terephthalate and recovered ethylene glycol. The depolymerization and decoloration purification method has the advantages of environmental protection, high efficiency and low cost.

Description

Technical Field

[0001] The invention relates to a polyethylene terephthalate (PET) recovery and treatment method, in particular to a method for depolymerization, decolorization and purification of polyethylene terephthalate. Background Art

[0002] Polyethylene terephthalate and other polyester materials derived from fossil energy have been mass-produced since their development in the 20th century due to their excellent properties and are widely used in packaging, textiles, building materials, home appliances, electronics and other fields. PET materials have a high content of aromatic rings and lack active hydrogen atoms, which makes them physically inert and chemically stable. However, this also makes it difficult for various waste polyester materials to degrade in the natural environment, which not only pollutes the environment but also causes a huge waste of resources.

[0003] At present, there are three main types of recycling methods being used for waste polyester PET materials of different types, sources, purity and composition:

[0004] 1. Energy recovery after incineration and oxidation: This method has a low recycling rate for the value of waste polyester and is prone to produce various harmful waste gases, so it is not an ideal recycling method.

[0005] 2. Physical recycling through sorting, cleaning, crushing, melting, regeneration, and mechanical blending. The physical recycling and regranulation process requires high temperature melting of polyester, which will cause molecular chain breakage and oxidation, and have adverse effects on the color value, viscosity, and mechanical properties of the recycled polyester particles. At the same time, this method cannot remove various additives such as dyes, stabilizers, flame retardants, antioxidants, and modifiers that are harmful to the quality of recycled polyester. Therefore, it cannot process low-quality waste polyester, has stricter requirements on raw materials, and limits its application areas.

[0006] 3. Biochemical recycling methods such as high-temperature depolymerization, chemical grafting modification, and enzyme-catalyzed enzymatic hydrolysis. Among them, the chemical recycling technology for waste polyester PET materials usually uses various depolymerization agents (such as water, methanol, ethanol, ethylene glycol, butanediol, etc.) to depolymerize and regenerate various monomers (such as terephthalic acid PTA, dimethyl terephthalate DMT, ethylene glycol terephthalate BHET, dibutyl terephthalate DBTP, etc.) under certain conditions, and then re-synthesize high-quality polyester. This method does not have the restrictive problem of quality reduction, so it has great development potential.

[0007] In the process of regenerating waste polyester, how to efficiently remove various dyes and colorants in order to obtain higher quality products has always been a key problem in realizing the reuse of post-consumer polyester. In the process of chemically recycling waste polyester, the product will exist in the form of monomers in the reaction solvent system, and various impurities such as dyes will also be released from the original waste polyester bulk phase into the solvent. Therefore, various physical and chemical methods can be used to remove these impurities at this stage.

[0008] However, among most existing physical decolorization methods, common ones such as physical adsorption methods (activated carbon adsorption, ion exchange resin adsorption) have problems such as easy saturation of adsorbent, dissolution pollution of adsorbent itself, difficulty in regeneration of adsorbent or environmentally unfriendly regeneration process. Physical extraction method has problems such as large toxicity or danger of extractant, large consumption of extractant, and residual extractant. In chemical decolorization, oxidants such as hypochlorous acid and hypochlorite, hydrogen peroxide, sodium dithionite, ozone, and chlorine are usually used. However, these oxidants have various problems, such as hydrogen peroxide itself is not stable enough and is easy to decompose, hypochlorous acid and hypochlorite will produce toxic and harmful gases during the decolorization reaction, ozone and chlorine are gases at room temperature, and the transportation and storage costs are high. Sodium dithionite itself is not stable enough and is prone to decomposition and self-explosion. The above physical and chemical decolorization methods have many problems in environmental protection, cost, safety, etc., which limit their large-scale application in industry.

[0009] Therefore, developing a waste polyester recycling process that can fully realize the efficient depolymerization of waste polyester and achieve economical, environmentally friendly, safe and efficient decolorization of the product is of great significance to achieving the full life cycle recycling of waste polyester. Summary of the invention

[0010] The first technical problem to be solved by the present invention is to provide a low-cost method for efficient depolymerization and decolorization and purification of colored waste polyester in view of the above-mentioned technical status quo.

[0011] The second technical problem to be solved by the present invention is to provide an environmentally friendly method for efficient depolymerization and decolorization and purification of colored waste polyester in view of the above-mentioned technical status quo.

[0012] The third technical problem to be solved by the present invention is to provide a method for efficient depolymerization and decolorization purification of colored waste polyester with good decolorization effect in view of the above-mentioned technical status quo.

[0013] The technical solution adopted by the present invention to solve the above technical problems is: a method for efficient depolymerization and decolorization and purification of colored waste polyester, characterized by comprising the following steps:

[0014] ① Add waste polyester, transition metal salt catalyst and ethylene glycol into a reactor, mix them thoroughly, and then control the temperature to rise to a reaction temperature of 200-240°C, react for 2-6 hours, and then lower the temperature to 120-150°C after the reaction is completed. Filter and remove the unreacted solid impurities to obtain a depolymerization liquid; the amount of the transition metal salt catalyst is 0.1%-5% of the mass of the waste polyester, and the amount of ethylene glycol is 2-10 times the mass of the waste polyester; the transition metal salt catalyst is a transition metal carboxylate;

[0015] ② Add deionized water to the obtained depolymerization solution, and continue stirring at a temperature of 40 to 80° C. to ensure that the system as a whole still has good fluidity at this temperature, and obtain a depolymerization solution dilution at this temperature;

[0016] ③ Add persulfate to the depolymerization liquid dilution, maintain the temperature at 40-80°C and keep stirring, the system begins to undergo a decolorization reaction, the reaction lasts for 0.5-2h, and the mass of the persulfate is 0.1%-5% of the waste polyester;

[0017] ④ After the decolorization reaction is completed, the solution obtained is recrystallized at a low temperature of 0 to 4°C, and then filtered to obtain the depolymerized monomer ethylene terephthalate and the recovered ethylene glycol. The Lab color value of the obtained BHET is measured to characterize the decolorization effect, and the characteristic peak absorbance of the ethylene glycol solution is measured by ultraviolet absorption spectroscopy to characterize the decolorization effect.

[0018] Preferably, the waste polyester is waste polyester PET bottle flakes, waste polyester PET film flakes, waste polyester PET fibers or waste polyester PET textiles.

[0019] Preferably, the transition metal salt catalyst is a transition metal acetate.

[0020] Preferably, the transition metal acetate is at least one of cobalt acetate, cobaltous acetate, zinc acetate, ferric acetate, ferrous acetate, cupric acetate, nickel acetate and hydrates thereof, with zinc acetate being the most preferred.

[0021] Preferably, the mass of the deionized water in step ② is 1 to 4 times that of the depolymerization solution.

[0022] Compared with the prior art, the present invention has the advantages that the cations of transition metal salts can coordinate with the carbonyl oxygen on the ester group in the polyester molecular chain, thereby reducing the electron cloud density of the carbonyl carbon, and finally catalyzing and promoting the solvent ethylene glycol in the reaction solution to attack the carbonyl carbon to produce an SN2 substitution reaction, and finally completing the depolymerization of the polyester chain segment. Therefore, the cations of transition metal salts can have a high catalytic effect on the depolymerization reaction of waste polyester.

[0023] The anion of the transition metal salt is a carboxylate group, which can form a hydrogen bond with the hydroxyl hydrogen on the ethylene glycol in the solvent. It is more preferred that the acetate group can form a stronger hydrogen bond, inducing an increase in the polarity of ethylene glycol, promoting the dissociation of the hydroxyl hydrogen on the ethylene glycol participating in the SN2 substitution reaction, and then enabling the hydroxyl oxygen on the ethylene glycol to attack the carbonyl carbon in the polyester chain segment, completing the alcoholysis of the polyester chain segment.

[0024] The use of salts whose cation composition is transition metal can not only play the role of catalytic depolymerization catalyst of waste polyester in the depolymerization stage, but also can further activate catalytic peroxysulfate (PMS) to produce active oxidizing species, which has a decolorizing effect on colored impurities such as dyes in the waste polyester, thereby obtaining higher quality depolymerized monomer ethylene terephthalate (BHET).

[0025] Persulfate (PMS) is used as an oxidant as the source of active oxidizing species. It has the advantages of being solid at room temperature, stable performance, safe storage, easy solubility in water, and a green, friendly and non-toxic aqueous solution. At the same time, it produces hydroxyl free radicals, superoxide free radicals, singlet oxygen and other active species with high reduction potential and long half-life through activation, which can effectively degrade various types of pollutants, so it has high industrial application value.

[0026] The present invention innovatively uses transition metal salts to successively depolymerize waste polyester segments and activate PMS to produce active oxidative species to treat colored impurities in waste polyester, thereby reducing the use of additional catalysts, reducing the steps of recycling waste polyester, and reducing the recycling cost of waste polyester. The entire process does not produce toxic and harmful gases, and the materials used are relatively stable at room temperature, which is of great significance for promoting the recycling of waste polyester throughout its life cycle. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below with reference to the embodiments.

[0028] The present invention is described in detail below by way of examples.

[0029] Example 1: 25g of red waste polyester polyester cloth, 100g of ethylene glycol, and 0.2g of zinc acetate dihydrate were added to a 500mL round-bottom flask, and the flask was placed on a magnetic stirrer for continuous stirring. After the reaction was maintained at 205°C in an oil bath for 4 hours, the solid insoluble matter was removed by filtration at 120-150°C while hot and then transferred to another 500mL round-bottom flask. 125mL of normal temperature deionized water was added to the filtrate, and the temperature was maintained and stirred for 10min after the filtrate dropped to 80°C to ensure that the system was fully mixed. 0.2g of peroxysulfate PMS was added to the solution, and stirring was maintained at 80°C for 1h for decolorization reaction. After the decolorization reaction was completed, the solution was cooled and crystallized at 0-4°C for 12h, and then filtered to obtain depolymerized monomer ethylene terephthalate BHET and filtrate. The yield of the depolymerized monomer BHET was 95.7% obtained by liquid phase analysis test of the depolymerized liquid. The strongest absorption peak intensity of the depolymerized monomer was compared with the original blank undecolorized group to obtain a BHET solid phase decolorization rate of 98.7%. The strongest absorption peak intensity of the ethylene glycol filtrate after crystallization was compared with the original blank undecolorized group to obtain a liquid phase decolorization rate of 99.1%. Under the reaction conditions, the colored waste polyester has a high depolymerization rate, and has a good decolorization effect on the depolymerized monomer BHET and the filtrate EG, while having a more economical amount of solvent and decolorizer.

[0030] Example 2: Add 25g of red waste polyester polyester cloth, 100g of ethylene glycol, and 0.2g of zinc acetate dihydrate to a 500mL round-bottom flask, place the flask on a magnetic stirrer and continue stirring, keep the temperature at 205°C in an oil bath for 4 hours, filter and remove solid insolubles while hot at 120-150°C, and transfer to another 500mL round-bottom flask, add 125mL of room temperature deionized water to the filtrate, and maintain the temperature and continue stirring for 10min after the filtrate drops to 80°C to ensure that the system is fully mixed. In this group, no peroxysulfate PMS is added to the solution, and stirring is maintained at 80°C for 1h. When the reaction is finished, the solution is cooled and crystallized at 0-4°C for 12h, and then filtered to obtain the depolymerized monomer ethylene terephthalate BHET and the filtrate. The yield of the depolymerized monomer BHET was 95.4% obtained by liquid phase analysis test of the depolymerized liquid. The strongest absorption peak strength of the depolymerized monomer was tested by ultraviolet absorption. This data was used as the original blank undecolorized group data for the original reference of decolorization effect for other groups. The strongest absorption peak strength of the ultraviolet absorption test of the ethylene glycol filtrate after crystallization was tested. This data was used as the original blank undecolorized group data for the original reference of decolorization effect for other groups. Under this reaction condition, the colored waste polyester has a high depolymerization rate and no decolorization effect. The data is used as blank data for reference of other experimental groups.

[0031] Example 3: 25g of red waste polyester polyester cloth and 100g of ethylene glycol were added to a 500mL round-bottom flask. No transition metal salt catalyst was added to this group. The flask was placed on a magnetic stirrer for continuous stirring. After the reaction was maintained at 205°C in an oil bath for 4 hours, the solid insoluble matter was removed by filtration at 120-150°C while hot and then transferred to another 500mL round-bottom flask. 125mL of normal temperature deionized water was added to the filtrate. After the filtrate dropped to 80°C, the temperature was maintained and stirred for 10min to ensure that the system was fully mixed. 0.2g of peroxysulfate PMS was added to the solution, and stirring was maintained at 80°C for 1h for decolorization reaction. After the decolorization reaction was completed, the solution was cooled and crystallized at 0-4°C for 12h, and then filtered to obtain the depolymerized monomer ethylene terephthalate BHET and the filtrate. The yield of the depolymerized monomer BHET was 5.6% by liquid phase analysis test of the depolymerized liquid. The strongest absorption peak intensity of the depolymerized monomer was compared with the original blank undecolorized group to obtain a BHET solid phase decolorization rate of 22.3%. The strongest absorption peak intensity of the crystallized ethylene glycol filtrate was compared with the original blank undecolorized group to obtain a liquid phase decolorization rate of 24.1%. Under the reaction conditions, the depolymerization effect of the colored waste polyester was extremely low, and the PMS activation was insufficient, resulting in a poor decolorization effect.

[0032] Example 4: 25g of red waste polyester polyester cloth, 100g of ethylene glycol, and 0.1g of zinc acetate dihydrate were added to a 500mL round-bottom flask, and the flask was placed on a magnetic stirrer for continuous stirring. After the reaction was maintained at 205°C in an oil bath for 4 hours, the solid insoluble matter was removed by filtration at 120-150°C while hot and then transferred to another 500mL round-bottom flask. 125mL of normal temperature deionized water was added to the filtrate, and the temperature was maintained and stirred for 10min after the filtrate dropped to 80°C to ensure that the system was fully mixed. 0.2g of peroxysulfate PMS was added to the solution, and stirring was maintained at 80°C for 0.5h for decolorization reaction. After the decolorization reaction was completed, the solution was cooled and crystallized at 0-4°C for 12h, and then filtered to obtain the depolymerized monomer ethylene terephthalate BHET and the filtrate. The yield of the depolymerized monomer BHET was 78.4% obtained by liquid phase analysis of the depolymerized liquid. The strongest absorption peak intensity of the depolymerized monomer was compared with the original blank undecolorized group to obtain a BHET solid phase decolorization rate of 71.5%. The strongest absorption peak intensity of the crystallized ethylene glycol filtrate was compared with the original blank undecolorized group to obtain a liquid phase decolorization rate of 69.5%. Under the reaction conditions, the small amount of catalyst used has a low depolymerization rate for colored waste polyester, a short decolorization time, and a poor decolorization effect on the depolymerized monomer BHET and the filtrate EG.

[0033] Example 5: 25g of red waste polyester polyester cloth, 100g of ethylene glycol, and 0.2g of zinc acetate dihydrate were added to a 500mL round-bottom flask, and the flask was placed on a magnetic stirrer for continuous stirring. After the reaction was maintained at 205°C in an oil bath for 4 hours, the solid insoluble matter was removed by filtration at 120-150°C while hot and then transferred to another 500mL round-bottom flask. 125mL of normal temperature deionized water was added to the filtrate, and the temperature was maintained and stirred for 10min after the filtrate dropped to 80°C to ensure that the system was fully mixed. 0.5g of peroxysulfate PMS was added to the solution, and stirring was maintained at 80°C for 1h for decolorization reaction. After the decolorization reaction was completed, the solution was cooled and crystallized at 0-4°C for 12h, and then filtered to obtain the depolymerized monomer ethylene terephthalate BHET and the filtrate. The yield of the depolymerized monomer BHET was 95.8% obtained by liquid phase analysis of the depolymerized liquid. The strongest absorption peak intensity of the depolymerized monomer was compared with the original blank undecolorized group to obtain a BHET solid phase decolorization rate of 99.3%. The strongest absorption peak intensity of the ethylene glycol filtrate after crystallization was compared with the original blank undecolorized group to obtain a liquid phase decolorization rate of 99.6%. Under this reaction condition, the colored waste polyester has a high depolymerization rate, and has excellent decolorization effects on the depolymerized monomer BHET and the filtrate EG, but the amount of decolorizer used is relatively large, and the amount of PMS can be adjusted according to demand.

[0034] Example 6: 25g of red waste polyester polyester cloth, 100g of ethylene glycol, and 0.2g of zinc acetate dihydrate were added to a 500mL round-bottom flask, and the flask was placed on a magnetic stirrer for continuous stirring. After the reaction was maintained at 205°C in an oil bath for 4 hours, the solid insoluble matter was removed by filtration at 120-150°C while hot and then transferred to another 500mL round-bottom flask. 125mL of normal temperature deionized water was added to the filtrate, and the temperature was maintained and stirred for 10min after the filtrate dropped to 80°C to ensure that the system was fully mixed. 0.2g of peroxysulfate PMS was added to the solution, and stirring was maintained at 80°C for 2h for decolorization reaction. After the decolorization reaction was completed, the solution was cooled and crystallized at 0-4°C for 12h, and then filtered to obtain the depolymerized monomer ethylene terephthalate BHET and the filtrate. The yield of the depolymerized monomer BHET was 95.7% obtained by liquid phase analysis of the depolymerized liquid. The strongest absorption peak intensity of the depolymerized monomer was compared with the original blank undecolorized group to obtain a BHET solid phase decolorization rate of 98.7%. The strongest absorption peak intensity of the ethylene glycol filtrate after crystallization was compared with the original blank undecolorized group to obtain a liquid phase decolorization rate of 99.0%. Under this reaction condition, the colored waste polyester has a high depolymerization rate, and has a good decolorization effect on the depolymerized monomer BHET and the filtrate EG, but the decolorization treatment time is long, and the decolorization treatment time can be adjusted according to actual needs.

[0035] Example 7: 25g of red waste polyester polyester cloth, 150g of ethylene glycol, and 0.3g of zinc acetate dihydrate were added to a 500mL round-bottom flask, and the flask was placed on a magnetic stirrer for continuous stirring. After the reaction was maintained at 205°C in an oil bath for 4 hours, the solid insoluble matter was removed by filtration at 120-150°C while hot and then transferred to another 500mL round-bottom flask. 125mL of normal temperature deionized water was added to the filtrate, and the temperature was maintained and stirred for 10min after the filtrate dropped to 80°C to ensure that the system was fully mixed. 0.2g of peroxysulfate PMS was added to the solution, and stirring was maintained at 80°C for 1h for decolorization reaction. After the decolorization reaction was completed, the solution was cooled and crystallized at 0-4°C for 12h, and then filtered to obtain the depolymerized monomer ethylene terephthalate BHET and the filtrate. The yield of the depolymerized monomer BHET was 98.1% obtained by liquid phase analysis of the depolymerized liquid. The strongest absorption peak intensity of the depolymerized monomer was compared with the original blank undecolorized group to obtain a solid phase decolorization rate of BHET of 63.3%. The strongest absorption peak intensity of the ethylene glycol filtrate after crystallization was compared with the original blank undecolorized group to obtain a liquid phase decolorization rate of 74.9%. Under this reaction condition, the depolymerization rate of colored waste polyester is extremely high, but the decolorization effect of the depolymerized monomer BHET and the filtrate EG is average due to the increase in the total mass of the system and the dilution of the oxidant concentration.

[0036] Example 8: 25g of red waste polyester polyester cloth, 150g of ethylene glycol, and 0.2g of zinc acetate dihydrate were added to a 500mL round-bottom flask, and the flask was placed on a magnetic stirrer for continuous stirring. After the reaction was maintained at 205°C in an oil bath for 4 hours, the solid insoluble matter was removed by filtration at 120-150°C while hot, and then transferred to another 500mL round-bottom flask. 125mL of normal temperature deionized water was added to the filtrate, and the temperature was maintained and stirred for 10min after the filtrate dropped to 80°C to ensure that the system was fully mixed. 0.5g of peroxysulfate PMS was added to the solution, and stirring was maintained at 80°C for 1h for decolorization reaction. After the decolorization reaction was completed, the solution was cooled and crystallized at 0-4°C for 12h, and then filtered to obtain the depolymerized monomer ethylene terephthalate BHET and the filtrate. The yield of the depolymerized monomer BHET was 94.5% obtained by liquid phase analysis of the depolymerized liquid. The strongest absorption peak intensity of the depolymerized monomer was compared with the original blank undecolorized group to obtain a BHET solid phase decolorization rate of 98.3%. The strongest absorption peak intensity of the ethylene glycol filtrate after crystallization was compared with the original blank undecolorized group to obtain a liquid phase decolorization rate of 97.8%. Under this reaction condition, the depolymerization rate of colored waste polyester is average, and the depolymerized monomer BHET and the filtrate EG have good decolorization effects, but the amount of solvent and decolorizer is large.

[0037] Example 9: 25g of red waste polyester polyester cloth, 100g of ethylene glycol, and 0.2g of zinc acetate dihydrate were added to a 500mL round-bottom flask, and the flask was placed on a magnetic stirrer for continuous stirring. After the reaction was maintained at 205°C in an oil bath for 4 hours, the solid insoluble matter was removed by filtration at 120-150°C while hot and then transferred to another 500mL round-bottom flask. 125mL of normal temperature deionized water was added to the filtrate, and the temperature was maintained and stirred for 10min after the filtrate dropped to 80°C to ensure that the system was fully mixed. 0.2g of peroxysulfate PMS was added to the solution, and the solution was stirred for 1h at 40°C for decolorization reaction. After the decolorization reaction was completed, the solution was cooled and crystallized at 0-4°C for 12h, and then filtered to obtain the depolymerized monomer ethylene terephthalate BHET and the filtrate. The yield of the depolymerized monomer BHET was 95.3% obtained by liquid phase analysis of the depolymerized liquid. The strongest absorption peak intensity of the depolymerized monomer was compared with the original blank undecolorized group to obtain a solid phase decolorization rate of BHET of 64.2%. The strongest absorption peak intensity of the ethylene glycol filtrate after crystallization was compared with the original blank undecolorized group to obtain a liquid phase decolorization rate of 79.03%. Under this reaction condition, the depolymerization rate of colored waste polyester is relatively high, but the decolorization temperature is relatively low, and the decolorization effect of the depolymerized monomer BHET and the filtrate EG is average.

[0038] Example 10: 25g of red waste polyester polyester cloth, 150g of ethylene glycol, and 0.3g of zinc acetate dihydrate were added to a 500mL round-bottom flask, and the flask was placed on a magnetic stirrer for continuous stirring. After the reaction was maintained at 205°C in an oil bath for 4 hours, the solid insoluble matter was removed by filtration at 120-150°C while hot and then transferred to another 500mL round-bottom flask. 125mL of normal temperature deionized water was added to the filtrate, and the temperature was maintained and stirred for 10min after the filtrate dropped to 80°C to ensure that the system was fully mixed. 0.2g of peroxysulfate PMS was added to the solution, and the solution was stirred for 1h at 60°C for decolorization reaction. After the decolorization reaction was completed, the solution was cooled and crystallized at 0-4°C for 12h, and then filtered to obtain the depolymerized monomer ethylene terephthalate BHET and the filtrate. The yield of the depolymerized monomer BHET was 92.2% obtained by liquid phase analysis of the depolymerized liquid. The strongest absorption peak intensity of the depolymerized monomer was compared with the original blank undecolorized group to obtain a solid phase decolorization rate of BHET of 79.2%. The strongest absorption peak intensity of the ethylene glycol filtrate after crystallization was compared with the original blank undecolorized group to obtain a liquid phase decolorization rate of 81.4%. Under this reaction condition, the depolymerization rate of colored waste polyester is relatively high, but due to the increase in the total reaction mass, the concentration of peroxysulfate is reduced, and the decolorization reaction temperature is reduced, the decolorization effect on the depolymerized monomer BHET and the filtrate EG is general.

[0039] Example 11: 25g of red waste polyester polyester cloth, 100g of ethylene glycol, and 0.2g of tetrahydrated cobalt acetate were added to a 500mL round-bottom flask, and the flask was placed on a magnetic stirrer for continuous stirring. After the reaction was maintained at 205°C in an oil bath for 4 hours, the solid insoluble matter was removed by filtration at 120-150°C while hot, and then transferred to another 500mL round-bottom flask. 125mL of normal temperature deionized water was added to the filtrate, and the temperature was maintained and stirred for 10min after the filtrate dropped to 80°C to ensure that the system was fully mixed. 0.2g of peroxysulfate PMS was added to the solution, and stirring was maintained at 80°C for 1h for decolorization reaction. After the decolorization reaction was completed, the solution was cooled and crystallized at 0-4°C for 12h, and then filtered to obtain depolymerized monomer ethylene terephthalate BHET and filtrate. The yield of the depolymerized monomer BHET was 96.4% obtained by liquid phase analysis of the depolymerized liquid. The strongest absorption peak intensity of the depolymerized monomer was compared with the original blank undecolorized group to obtain a solid phase decolorization rate of BHET of 93.4%. The strongest absorption peak intensity of the ethylene glycol filtrate after crystallization was compared with the original blank undecolorized group to obtain a liquid phase decolorization rate of 94.3%. Under this reaction condition, the depolymerization rate of colored waste polyester is relatively high, and the decolorization effect of the depolymerized monomer BHET and the filtrate EG is good. At the same time, it has a relatively economical amount of solvent and decolorizer, but it is also necessary to consider that cobalt ions have certain physiological toxicity.

[0040] Example 12: 25g of red waste polyester polyester cloth, 100g of ethylene glycol, and 0.3g of tetrahydrated cobalt acetate were added to a 500mL round-bottom flask, and the flask was placed on a magnetic stirrer for continuous stirring. After the reaction was maintained at 205°C in an oil bath for 4 hours, the solid insoluble matter was removed by filtration at 120-150°C while hot and then transferred to another 500mL round-bottom flask. 125mL of normal temperature deionized water was added to the filtrate. After the filtrate dropped to 80°C, the temperature was maintained and stirred for 10min to ensure that the system was fully mixed. 0.2g of peroxysulfate PMS was added to the solution, and stirring was maintained at 80°C for 1h for decolorization reaction. After the decolorization reaction was completed, the solution was cooled and crystallized at 0-4°C for 12h, and then filtered to obtain depolymerized monomer ethylene terephthalate BHET and filtrate. The yield of the depolymerized monomer BHET was 97.6% obtained by liquid phase analysis of the depolymerized liquid. The strongest absorption peak intensity of the depolymerized monomer was compared with the original blank undecolorized group to obtain a solid phase decolorization rate of BHET of 94.1%. The strongest absorption peak intensity of the ethylene glycol filtrate after crystallization was compared with the original blank undecolorized group to obtain a liquid phase decolorization rate of 96.8%. Under this reaction condition, the depolymerization rate of colored waste polyester is extremely high, and the decolorization effect of the depolymerized monomer BHET and the filtrate EG is also good. At the same time, it has a more economical amount of solvent and decolorizer, but it is also necessary to consider that cobalt ions have certain physiological toxicity.

[0041] Example 13: 25g of red waste polyester polyester cloth, 100g of ethylene glycol, and 0.2g of cobaltous acetate were added to a 500mL round-bottom flask, and the flask was placed on a magnetic stirrer for continuous stirring. After the reaction was maintained at 205°C in an oil bath for 4 hours, the solid insoluble matter was removed by filtration at 120-150°C while hot, and then transferred to another 500mL round-bottom flask. 125mL of normal temperature deionized water was added to the filtrate, and the temperature was maintained and stirred for 10min after the filtrate dropped to 80°C to ensure that the system was fully mixed. 0.2g of peroxysulfate PMS was added to the solution, and stirring was maintained at 80°C for 1h for decolorization reaction. After the decolorization reaction was completed, the solution was cooled and crystallized at 0-4°C for 12h, and then filtered to obtain the depolymerized monomer ethylene terephthalate BHET and the filtrate. The yield of the depolymerized monomer BHET was 95.3% obtained by liquid phase analysis of the depolymerized liquid. The strongest absorption peak intensity of the depolymerized monomer was compared with the original blank undecolorized group to obtain a solid phase decolorization rate of BHET of 98.9%. The strongest absorption peak intensity of the ethylene glycol filtrate after crystallization was compared with the original blank undecolorized group to obtain a liquid phase decolorization rate of 99.7%. Under this reaction condition, the colored waste polyester has a high depolymerization rate, and has an excellent decolorization effect on the depolymerized monomer BHET and the filtrate EG. At the same time, it has a relatively economical amount of solvent and decolorizer, but it is also necessary to consider that cobalt ions have certain physiological toxicity.

[0042] Example 14: 25g of red waste polyester polyester cloth, 100g of ethylene glycol, and 0.2g of ferric acetate were added to a 500mL round-bottom flask, and the flask was placed on a magnetic stirrer for continuous stirring. After the reaction was maintained at 205°C in an oil bath for 4 hours, the solid insoluble matter was removed by filtration at 120-150°C while hot and then transferred to another 500mL round-bottom flask. 125mL of normal temperature deionized water was added to the filtrate, and the temperature was maintained and stirred for 10min after the filtrate dropped to 80°C to ensure that the system was fully mixed. 0.2g of peroxysulfate PMS was added to the solution, and the solution was stirred for 1h at 80°C for decolorization reaction. After the decolorization reaction was completed, the solution was cooled and crystallized at 0-4°C for 12h, and then filtered to obtain the depolymerized monomer ethylene terephthalate BHET and the filtrate. The yield of the depolymerized monomer BHET was 76.9% obtained by liquid phase analysis of the depolymerized liquid. The strongest absorption peak intensity of the depolymerized monomer was compared with the original blank undecolorized group to obtain a BHET solid phase decolorization rate of 86.3%. The strongest absorption peak intensity of the ultraviolet absorption test of the ethylene glycol filtrate after crystallization was compared with the original blank undecolorized group to obtain a liquid phase decolorization rate of 84.2%. Under the reaction conditions, ferric acetate was used for catalysis, and the depolymerization rate of the colored waste polyester was average, and the decolorization effect of the depolymerized monomer BHET and the filtrate EG was average.

[0043] Example 15: 25g of red waste polyester polyester cloth, 100g of ethylene glycol, and 0.2g of ferrous acetate were added to a 500mL round-bottom flask, and the flask was placed on a magnetic stirrer for continuous stirring. After the reaction was maintained at 205°C in an oil bath for 4 hours, the solid insoluble matter was removed by filtration at 120-150°C while hot, and then transferred to another 500mL round-bottom flask. 125mL of normal temperature deionized water was added to the filtrate, and the temperature was maintained and stirred for 10min after the filtrate dropped to 80°C to ensure that the system was fully mixed. 0.2g of peroxysulfate PMS was added to the solution, and stirring was maintained at 80°C for 1h for decolorization reaction. After the decolorization reaction was completed, the solution was cooled and crystallized at 0-4°C for 12h, and then filtered to obtain the depolymerized monomer ethylene terephthalate BHET and the filtrate. The yield of the depolymerized monomer BHET was 78.3% obtained by liquid phase analysis of the depolymerized liquid. The strongest absorption peak intensity of the depolymerized monomer was compared with the original blank undecolorized group to obtain a solid phase decolorization rate of BHET of 96.3%. The strongest absorption peak intensity of the ethylene glycol filtrate after crystallization was compared with the original blank undecolorized group to obtain a liquid phase decolorization rate of 96.1%. Under this reaction condition, the depolymerization rate of colored waste polyester is average, but the depolymerization monomer BHET and the filtrate EG have good decolorization effects.

[0044] Example 16: 25g of red waste polyester polyester cloth, 100g of ethylene glycol, and 0.2g of monohydrated copper acetate were added to a 500mL round-bottom flask, and the flask was placed on a magnetic stirrer for continuous stirring. After the reaction was maintained at 205°C in an oil bath for 4 hours, the solid insoluble matter was removed by filtration at 120-150°C while hot, and then transferred to another 500mL round-bottom flask. 125mL of normal temperature deionized water was added to the filtrate, and the temperature was maintained and stirred for 10min after the filtrate dropped to 80°C to ensure that the system was fully mixed. 0.2g of peroxysulfate PMS was added to the solution, and the solution was stirred for 1h at 80°C for decolorization reaction. After the decolorization reaction was completed, the solution was cooled and crystallized at 0-4°C for 12h, and then filtered to obtain the depolymerized monomer ethylene terephthalate BHET and the filtrate. The yield of the depolymerized monomer BHET was 71.5% by liquid phase analysis test of the depolymerized liquid. The strongest absorption peak intensity of the depolymerized monomer was compared with the original blank undecolorized group to obtain a BHET solid phase decolorization rate of 72.3%. The strongest absorption peak intensity of the ethylene glycol filtrate after crystallization was compared with the original blank undecolorized group to obtain a liquid phase decolorization rate of 74.2%. Under the reaction conditions, the depolymerization rate of colored waste polyester is average, and the decolorization effect of the depolymerized monomer BHET and the filtrate EG is average.

[0045] Example 17: 25g of red waste polyester polyester cloth, 100g of ethylene glycol, and 0.2g of nickel acetate were added to a 500mL round-bottom flask, and the flask was placed on a magnetic stirrer for continuous stirring. After the reaction was maintained at 205°C in an oil bath for 4 hours, the solid insoluble matter was removed by filtration at 120-150°C while hot, and then transferred to another 500mL round-bottom flask. 125mL of normal temperature deionized water was added to the filtrate, and the temperature was maintained and stirred for 10min after the filtrate dropped to 80°C to ensure that the system was fully mixed. 0.2g of peroxysulfate PMS was added to the solution, and the solution was stirred for 1h at 80°C for decolorization reaction. After the decolorization reaction was completed, the solution was cooled and crystallized at 0-4°C for 12h, and then filtered to obtain the depolymerized monomer ethylene terephthalate BHET and the filtrate. The yield of the depolymerized monomer BHET was 63.6% by liquid phase analysis test of the depolymerized liquid. The strongest absorption peak intensity of the depolymerized monomer was compared with the original blank undecolorized group to obtain a BHET solid phase decolorization rate of 61.2%. The strongest absorption peak intensity of the ethylene glycol filtrate after crystallization was compared with the original blank undecolorized group to obtain a liquid phase decolorization rate of 55.8%. Under this reaction condition, the depolymerization rate of colored waste polyester is average, and the decolorization effect of the depolymerized monomer BHET and the filtrate EG is average.

[0046] In the above-mentioned embodiment, in the depolymerization and decolorization purification treatment of colored waste polyester, the addition amount of transition metal acetate catalyst (zinc acetate, cobalt acetate, cobaltous acetate, ferrous acetate, ferrous acetate, cupric acetate and nickel acetate), the addition amount of decolorizing agent PMS, the decolorization treatment temperature and time and other main factors are controlled, and the depolymerization monomer BHET yield, the decolorization effect of the depolymerization monomer BHET and the decolorization effect of the filtrate EG are used as the optimization targets for regulation, and it is confirmed that Example 1, Example 12 and Example 13 all have good effects. After further considering the physiological toxicity and cost of the transition metal salt catalyst, it is finally confirmed that Example 1 is the best example. In Example 1, zinc acetate dihydrate (0.8%wt content in waste polyester) is used as a common catalyst for depolymerization and activation of PMS. After alcoholysis in ethylene glycol of 2 to 4 times the mass of waste polyester, PMS (0.8%wt content in waste polyester) is added for advanced oxidation decolorization treatment (reaction temperature 80°C, reaction time 1h), and finally recrystallization is used to obtain monomer BHET and filtrate EG. The depolymerization process has a high yield (>95%), and the depolymerization monomer BHET and the filtrate EG have a significant decolorization effect compared with the blank control group (decolorization rate>98.5%).

Claims

1. A method for efficient depolymerization and decolorization purification of colored waste polyester, characterized in that The steps include: ① Add waste polyester, transition metal salt catalyst and ethylene glycol into a reactor, mix them thoroughly, and then control the temperature to rise to a reaction temperature of 200-240°C, react for 2-6 hours, and then lower the temperature to 120-150°C after the reaction is completed. Filter and remove the unreacted solid impurities to obtain a depolymerization liquid; the amount of the transition metal salt catalyst is 0.1%-5% of the mass of the waste polyester, and the amount of ethylene glycol is 2-10 times the mass of the waste polyester; the transition metal salt catalyst is a transition metal carboxylate; ② Add deionized water to the obtained depolymerization solution, and continue stirring at a temperature of 40 to 80° C. to ensure that the system as a whole still has good fluidity at this temperature, and obtain a depolymerization solution dilution at this temperature; ③ Add persulfate to the depolymerization liquid dilution, maintain the temperature at 40-80°C and keep stirring, the system begins to undergo a decolorization reaction, the reaction lasts for 0.5-2h, and the mass of the persulfate is 0.1%-5% of the waste polyester; ④ After the decolorization reaction is completed, the solution obtained is recrystallized at a low temperature of 0 to 4°C, and then filtered to obtain the depolymerized monomer ethylene terephthalate and the recovered ethylene glycol after recrystallization.

2. The method for efficient depolymerization and decolorization and purification of colored waste polyester according to claim 1, characterized in that The waste polyester is waste polyester PET bottle flakes, waste polyester PET film flakes, waste polyester PET fibers or waste polyester PET textiles.

3. The method for efficient depolymerization and decolorization and purification of colored waste polyester according to claim 1, characterized in that The transition metal salt catalyst is transition metal acetate.

4. The method for efficient depolymerization and decolorization and purification of colored waste polyester according to claim 3, characterized in that The transition metal acetate is at least one of cobalt acetate, cobaltous acetate, zinc acetate, ferric acetate, ferrous acetate, cupric acetate, nickel acetate and hydrates thereof.

5. The method for efficient depolymerization and decolorization and purification of colored waste polyester according to claim 1, characterized in that The mass of the deionized water in step ② is 1 to 4 times that of the depolymerization solution.