A method for directional high-value conversion of waste polyester products

Abstract

The invention discloses a method for directional high-value conversion of waste polyester products, belonging to the technical field of solid waste recycling. The method uses dimethyl carbonate as a methyl source, places waste polyester products containing only polyester, bromide and solvent in a pressure-resistant tube, or places waste polyester products containing polyester and brominated flame retardant and solvent in a pressure-resistant tube, and performs depolymerization reaction at 120-180° C. in a closed environment for 6 hours or longer, cools down after the reaction, and prepares bisphenol A dimethyl ether or carboxylate. The method is simple in process, easy to implement, and can realize the conversion of polyester, hydroxyl-containing compounds and the like in one pot. The method has broad application prospects in the treatment of waste polyester products, is green and environmentally friendly, and can realize high-value recovery of commercial plastics containing brominated flame retardants without the need for additional catalyst addition.

Description

Technical Field

[0001] The invention belongs to the technical field of solid waste recycling, and specifically relates to a method for directional high-value conversion of waste polyester products. Background Art

[0002] Halogens play an important role in industrial production and daily life, but the halogenated organic pollutants (HOCs) present in the products are environmentally persistent, difficult to degrade and biotoxic, posing a huge threat to human health and environmental safety. Various methods for degrading halogenated organic pollutants have been disclosed in the prior art, but the energy consumption and reagent costs are high. If the high-value utilization of halogen-containing waste can be achieved, waste can be turned into treasure, which is conducive to the advancement of the industry.

[0003] Bromine is a scarce non-renewable resource and one of the important chemical raw materials. There are more than 100 high value-added products related to bromine, among which the industry market size of brominated flame retardants is extremely large. There are more than 70 varieties of brominated flame retardants, among which the output of decabromodiphenyl ether, hexabromocyclododecane and tetrabromobisphenol A accounts for more than 50% of the total output of brominated flame retardants. However, decabromodiphenyl ether and hexabromocyclododecane are listed as persistent organic pollutants. Some studies have also shown that tetrabromobisphenol A is a potential endocrine disruptor, and new brominated flame retardants such as decabromodiphenyl ethane and brominated epoxy resin also have potential environmental risks and toxic effects. Despite this, based on the advantages of brominated flame retardants such as high flame retardant efficiency, good thermal stability and low cost, brominated flame retardants cannot be completely replaced by other flame retardants for the time being.

[0004] Brominated flame retardants are widely used in electronic products, building materials and the automotive industry. Among them, more than 30% are used in the production of electronic and electrical equipment. In recent years, technological advances have led to an increasing number of discarded electronic and electrical products. The brominated flame retardants (about 3% to 25%) contained in these electronic wastes may become potential toxic substances, causing serious secondary pollution. Traditional landfill and open-air incineration methods can cause the migration and accumulation of brominated flame retardants in soil and water, or release harmful substances such as polybrominated dibenzodioxins (PBDD) and polybrominated dibenzofurans (PBDF). In order to prevent secondary pollution of brominated organic pollutants, researchers have paid more and more attention to debromination methods of bromine-containing wastes, such as solvent decomposition and pyrolysis. However, most studies focus on how to improve the yield and quality of products after debromination, while relatively few studies have been conducted on bromine recovery and recycling.

[0005] A Chinese patent document with publication number CN115368627A discloses a method for recovering flame-retardant polyester. The method determines the flame-retardant polyester as polyester A or polyester B according to the type of flame retardant. Polyester A is a polyester whose flame retardant is one or more of decabromodiphenylethane, decabromodiphenyl ether, hexabromocyclododecane and brominated epoxy; polyester B is a polyester whose flame retardant is one or more of phosphate flame retardant, tetrabromobisphenol A, tetrabromobisphenol S and brominated polycarbonate, wherein polyester A is first subjected to microwave alcoholysis and then subjected to extraction treatment to recover the flame retardant; and polyester B is first subjected to extraction treatment to recover the flame retardant and then subjected to microwave alcoholysis to recover the polyester.

[0006] A Chinese patent document with publication number CN102557883A discloses a method for converting bromine-containing plastics from waste electrical appliances into phenol in a subcritical fluid. The invention cleans and crushes waste electronic and electrical product plastics (containing brominated flame retardants) into powder, adds the powder and a solvent into a high-pressure reactor for heating and reaction, then separates the obtained solid-liquid mixture, collects the upper organic solvent extract, adds an extractant to the oil phase for liquid-liquid extraction to obtain an extract, separates the extract by rotary evaporation at 60-80°C and recycles it, and the liquid remaining at the bottom of the evaporator is phenol, which can be used as a chemical product after purification.

[0007] However, the above inventions only involve recycling methods, and do not develop strategies for the utilization of bromine wastes such as brominated flame retardants. The annual consumption of high molecular weight polyesters such as polyethylene terephthalate and polycarbonate is increasing year by year, and the waste polyesters produced are also increasing. These waste high molecular weight polyesters are also difficult to degrade quickly and naturally. If the high value utilization of waste polyesters and brominated flame retardants can be achieved, it will help reduce the pollution threat to the ecological environment and turn waste into treasure. Summary of the invention

[0008] In view of the deficiencies in the above-mentioned prior art, the present invention provides a method for targeted high-value conversion of waste polyester products. The method has a simple process, is easy to implement, and can achieve the conversion of polyester in one pot. The method can achieve high-value recovery of waste polyester and commercial plastics containing brominated flame retardants.

[0009] The specific technical solutions adopted are as follows:

[0010] The present invention provides a method for directional high-value conversion of waste polyester products, comprising the following steps:

[0011] When the waste polyester product contains only polyester, dimethyl carbonate is used as a methyl source, the waste polyester product, bromide and solvent are placed in a pressure-resistant tube, and a depolymerization reaction is carried out at 120-180° C. in a closed environment for 6 hours or longer, and the temperature is lowered after the reaction is completed to prepare bisphenol A dimethyl ether or carboxylate;

[0012] When the waste polyester product contains polyester and brominated flame retardant, dimethyl carbonate is used as a methyl source, the waste polyester product and the solvent are placed in a pressure-resistant tube, and a depolymerization reaction is carried out at 120-180° C. in a closed environment for ≥6 hours, and the temperature is lowered after the reaction is completed to prepare bisphenol A dimethyl ether or carboxylate;

[0013] The bromide is selected from n-butyl bromide, 3,3-dimethyl-1-bromobutane, 1,2-dibromoethane, bromostyrene, isopentyl bromide, 4-phenyl-1-butyl bromide, 1-bromo-2-methylpropane, sec-butyl bromide, cyclohexane bromide, 2-bromo-2-methylbutane, tert-butyl bromide or brominated flame retardant;

[0014] Brominated flame retardants include tris(2,3-dibromopropyl)isocyanurate, tetrabromobisphenol A-bis(2,3-dibromopropyl ether), hexabromocyclododecane, decabromodiphenyl ethane, polybrominated diphenyl ethers or tetrabromobisphenol A;

[0015] The structural formula is as follows:

[0016] .

[0017] The method of the present invention uses dimethyl carbonate as a methyl source and utilizes a specific bromide to catalyze the directional high-value conversion of polyester (i.e., the occurrence of polyester depolymerization reaction). The selection of bromide is necessary. When bromobenzene is selected, it cannot play a catalytic role. The method of the present invention can be used for the depolymerization and upgrading of various waste polyester materials.

[0018] Preferably, the waste polyester product is first crushed into centimeter-level pieces and then placed in a pressure-resistant tube for depolymerization reaction. The waste polyester product includes waste CDs, waste buckets, waste films or flame-retardant boards, etc.

[0019] The polyester includes polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyethylene furandicarboxylate, polyethylene succinate, polyethylene adipate or polylactic acid.

[0020] When the polyester is polycarbonate, the obtained product is bisphenol A dimethyl ether. When the polyester is polyethylene terephthalate, polybutylene terephthalate, polyethylene furandicarboxylate, polyethylene succinate, polyethylene adipate or polylactic acid, the obtained product is the corresponding carboxylate.

[0021] Specifically, in the process of depolymerization, in addition to using recycled waste bromide, the corresponding pure bromide can also be used.

[0022] Optionally, the solvent is N -Methylpyrrolidone or N , N-dimethylformamide; based on the molar number of the polyester, the amount of the solvent added is 1 to 10 mL / g.

[0023] Preferably, the mass ratio of dimethyl carbonate to waste polyester product is 1 to 3:1, further 1.8:1; the solvent is N -Methylpyrrolidone.

[0024] Preferably, the depolymerization reaction temperature is 150-180° C., and the depolymerization reaction time is 8-24 h.

[0025] Preferably, the bromide is selected from n-butane bromide.

[0026] Under the above conditions, the reaction effect is better.

[0027] During the depolymerization reaction (theoretically), the amount of bromide added is 1 mol% to 10 mol% of the polyester based on the molar number of the polyester structural unit; when the added amount is 2 mol%, a 100% decomposition rate of the polyester and a 99% yield of bisphenol A dimethyl ether can be achieved.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The bromide used in the present invention can be recycled waste bromide or the corresponding pure bromide, which has the advantages of wide adaptability, high efficiency and wide sources, and can promote the depolymerization reaction of dimethyl carbonate in polyester and prepare high-purity bisphenol A dimethyl ether or carboxylic acid ester.

[0030] (2) The method developed in the present invention has the advantages of mild conditions and high catalytic efficiency. It can achieve complete conversion of polycarbonate under standard reaction conditions and can also be used for the depolymerization and upgrading of various waste polyester materials. It can efficiently complete the targeted upgrading and conversion of various types of PC waste CDs, PC waste buckets and PC waste films in a relatively short time.

[0031] (3) The method of the present invention is applicable to the conversion and upgrading of other types of waste polyesters (polyethylene terephthalate, polybutylene terephthalate, polyethylene furandicarboxylate, polyethylene succinate, polyethylene adipate and polylactic acid) and other types of hydroxyl-containing aromatic compounds. The products are high-value chemicals such as corresponding carboxylic acid esters and ethers, which to a certain extent shows the high applicability of the method and further broadens the scope of waste plastic treatment and product appreciation. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A roadmap for the depolymerization of polycarbonates catalyzed by bromide using dimethyl carbonate as the methyl source.

[0033] Figure 2The figure is the H NMR spectrum of bisphenol A dimethyl ether BPAME, the product obtained in Example.

[0034] Figure 3 The figure is the NMR carbon spectrum of bisphenol A dimethyl ether BPAME, the product obtained in Example. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with the examples and drawings. It should be understood that these examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. The operating methods in the following examples that do not specify specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturer. Contents not described in detail in this specification belong to prior art known to professionals and technicians in the field.

[0036] In the embodiment, the route of using dimethyl carbonate DMC as the methyl source and using bromide to catalyze the depolymerization reaction of polycarbonate PC to produce bisphenol A dimethyl ether BPAME is as follows: Figure 1 As shown, the NMR hydrogen spectrum and NMR carbon spectrum of the obtained product bisphenol A dimethyl ether BPAME are as follows: Figure 2 and Figure 3 shown.

[0037] Example 1

[0038] In a pressure tube reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.254 g of CR-pure polycarbonate (PC, Mn ~ 150,000) powder (1 mmol based on the molar number of polyester structural units), 0.72 g of dimethyl carbonate (8 mmol), n-butyl bromide (2 mol% based on the molar number of PC) and N -methyl pyrrolidone (2mL), after placing the pressure tube reactor, start stirring and heating, under normal pressure and closed environment, heat the reaction system to 150°C, and depolymerization reaction occurs in a closed environment at this temperature for 8 hours. After the reaction is completed, cool to room temperature, dilute the obtained mixed solution with ethyl acetate, and measure the yield of the diluted solution by GC. The results show that the decomposition rate of PC in this embodiment is 100%, and the yield of bisphenol A dimethyl ether is 99%.

[0039] Example 2

[0040] In a pressure tube reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.254 g of CR-pure PC powder (1 mmol), 0.36 g of dimethyl carbonate (4 mmol), n-butyl bromide (based on the molar number of PC, the added amounts were set to 1, 2, 4, 6, 8, and 10 mol%, respectively) and N-methylpyrrolidone (2 mL), after placing the pressure tube reactor, start stirring and heating, and under normal pressure and closed environment, the reaction system is heated to 150 ° C, and the depolymerization reaction occurs in a closed environment at this temperature for 6 hours. After the reaction is completed, the temperature is cooled to room temperature, and the obtained mixed solution is diluted with ethyl acetate. The dilution is measured by GC to determine the yield. The results show that the yields of bisphenol A dimethyl ether are 11%, 88%, 87%, 87%, 87% and 88%, respectively.

[0041] Example 3

[0042] In a pressure tube reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.254 g of CR-pure PC powder (1 mmol), different masses of dimethyl carbonate (2, 4, 6, and 8 mmol, respectively), 0.0027 g of n-butyl bromide (2 mol% based on the molar number of PC) and N -methylpyrrolidone (2 mL), after placing the pressure tube reactor, start stirring and heating, the reaction system is heated to 150 ° C, and the depolymerization reaction occurs in a closed environment at this temperature for 6 hours. After the reaction is completed, the temperature is cooled to room temperature, and the obtained mixed solution is diluted with ethyl acetate. The dilution is measured by GC to determine the yield. The results show that the yields of bisphenol A dimethyl ether are 36%, 88%, 90% and 94%, respectively.

[0043] Example 4

[0044] Into a pressure tube reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller were added 0.254 g of CR-pure PC powder (1 mmol), 0.36 g of dimethyl carbonate (4 mmol), different bromides (n-butyl bromide, 3,3-dimethyl-1-bromobutane, 1,2-dibromoethane, bromostyrene, isopentyl bromide, 4-phenyl-1-butyl bromide, 1-bromo-2-methylpropane, sec-butyl bromide, cyclohexane bromide, 2-bromo-2-methylbutane, tert-butyl bromide) (based on the molar number of PC, the added amount was 2 mol%) and N -methylpyrrolidone (2 mL), after placing the pressure tube reactor, start stirring and heating, the reaction system is heated to 150 ° C, and the depolymerization reaction occurs in a closed environment at this temperature for 6 h. After the reaction is completed, the temperature is cooled to room temperature, and the obtained mixed solution is diluted with ethyl acetate. The dilution is measured by GC. The results show that the yields of bisphenol A dimethyl ether are 88%, 85%, 80%, 75%, 74%, 61%, 60%, 69%, 51%, 74% and 65%, respectively. Bromobenzene as a catalyst cannot catalyze the above depolymerization reaction.

[0045] Example 5

[0046] Into a pressure tube reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller were added 0.254 g of CR-pure PC powder (1 mmol), 0.72 g of dimethyl carbonate (8 mmol), different bromides (tris(2,3-dibromopropyl)isocyanurate, tetrabromobisphenol A-bis(2,3-dibromopropyl ether), hexabromocyclododecane, decabromodiphenylethane, decabromodiphenyl ether, tetrabromobisphenol A) (based on the molar number of PC, the added amount was 2 mol%) and N -methylpyrrolidone (2 mL), after placing the pressure tube reactor, start stirring and heating, the reaction system is heated to 150 ° C, and the depolymerization reaction occurs in a closed environment at this temperature for 8 h. After the reaction is completed, the temperature is lowered to room temperature, and the obtained mixed solution is diluted with ethyl acetate. The dilution is measured by GC to determine the yield. The results show that the yields of bisphenol A dimethyl ether are 99%, 98%, 96%, 92%, 92% and 30%, respectively.

[0047] Example 6

[0048] 0.254 g CR purity PC powder (1 mmol), 0.36 g dimethyl carbonate (4 mmol), 0.0027 g n-butyl bromide (2 mol% based on the molar number of PC) and different solvents ( N -Methylpyrrolidone, N , N -dimethylformamide) (2 mL), after placing the pressure tube reactor, start stirring and heating, the reaction system is heated to 140 ° C, and the depolymerization reaction occurs in a closed environment at this temperature for 6 h. After the reaction is completed, the temperature is cooled to room temperature, and the obtained mixed solution is diluted with ethyl acetate. The dilution is measured by GC. The results show that the yields of bisphenol A dimethyl ether are 88% and 27% respectively; the yield of bisphenol A dimethyl ether in the same reaction system using acetonitrile, tetrahydrofuran, dichloromethane, toluene, and cyclohexane as solvents is 0%.

[0049] Example 7

[0050] Two kinds of waste PC plastics (waste PC CDs and waste PC buckets) were crushed into centimeter-scale pieces in advance, and then 1 g (about 4 mmol) of the crushed materials, 1.8 g of dimethyl carbonate, 0.01 g of n-butyl bromide and N-Methyl pyrrolidone (2 mL) was placed in a pressure tube reactor. After the pressure tube reactor was placed, stirring and heating were turned on. The reaction system was heated to 150°C, and a depolymerization reaction occurred in a closed environment at this temperature for 8 h. After the reaction was completed, the temperature was cooled to room temperature, and the resulting mixed solution was the product. The mixed solution was diluted with ethyl acetate, and the dilution was measured for yield by GC. The results showed that the yields of bisphenol A dimethyl ether from PC waste optical discs and PC waste buckets in this embodiment were 99% and 97%, respectively.

[0051] Example 8

[0052] Different polyester materials (polyethylene terephthalate, polybutylene terephthalate, polyethylene furandicarboxylate, polyethylene succinate, polyethylene adipate, polylactic acid) (1 mmol), 0.72 g of dimethyl carbonate (8 mmol), 0.0027 g of n-butyl bromide (2 mol% based on the molar number of polyester) and N -methylpyrrolidone (2 mL), after placing the pressure tube reactor, start stirring and heating. The reaction system is heated to 150°C, and the depolymerization reaction occurs in a closed environment at this temperature for 8 hours. After the reaction is completed, the temperature is cooled to room temperature, and the resulting mixed solution is the product. The mixed solution is passed through 1 The yields were determined by H NMR. The results showed that the yields of the corresponding carboxylic acid esters in this example were 99% (dimethyl terephthalate), 56% (dimethyl terephthalate), 96% (dimethyl 2,5-furandicarboxylate), 99% (dimethyl succinate), 92% (dimethyl adipate) and 65% (methyl lactate).

[0053] Example 9

[0054] 1.0 g of PET mesh tube (containing polybrominated diphenyl ethers) broken into centimeter-sized pieces, 1.8 g of dimethyl carbonate and N -methylpyrrolidone (8 mL), after placing the pressure tube reactor, start stirring and heating, the reaction system is heated to 160 ° C, and the depolymerization reaction occurs in a closed environment at this temperature for 10 h. After the reaction is completed, the temperature is cooled to room temperature, and the resulting mixed solution is the product. The resulting mixed solution is passed through 1 The yield was determined by H NMR with trioxane as the internal standard. The results showed that the yield of dimethyl terephthalate (DMT) obtained in this example was 97%.

[0055] Example 10

[0056] In a pressure tube reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 1.0 g of PC flame retardant board (containing polybrominated diphenyl ether) broken into centimeter-sized pieces, 1.8 g of dimethyl carbonate (20 mmol) and N -methylpyrrolidone (8 mL), after placing the pressure tube reactor, start stirring and heating, the reaction system is heated to 180 ° C, and the depolymerization reaction occurs in a closed environment at this temperature for 24 h. After the reaction is completed, cool to room temperature, and the resulting mixed solution is the product. The resulting mixed solution is passed through 1 The yield was determined by H NMR with trioxane as the internal standard. The results showed that the yield of bisphenol A dimethyl ether BPAME obtained in this example was 95%.

[0057] Comparative Example 1

[0058] In a pressure tube reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, polyethylene terephthalate (1 mmol), 0.72 g of dimethyl carbonate (8 mmol), 0.01 g of ionic liquid catalyst [Bmim][Br] (based on the molar number of polyester, the added amount is about 5 mol%) and N -methylpyrrolidone (2 mL), after placing the pressure tube reactor, start stirring and heating. The reaction system is heated to 150°C, and the depolymerization reaction occurs in a closed environment at this temperature for 8 h. After the reaction is completed, the temperature is cooled to room temperature, and the resulting mixed solution is the product. The mixed solution is passed through 1 The yield was determined by H NMR, and the results showed that the yield of the corresponding carboxylic acid ester in this example was 80% (dimethyl terephthalate).

[0059] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for directional high-value treatment of waste polyester products, characterized in that: The following steps are involved: When the waste polyester product contains only polyester, dimethyl carbonate is used as a methyl source, the waste polyester product, bromide and solvent are placed in a pressure-resistant tube, and a depolymerization reaction is carried out at 120-180° C. in a closed environment for 6 hours or longer, and the temperature is lowered after the reaction is completed to prepare bisphenol A dimethyl ether or carboxylate; When the waste polyester product contains polyester and brominated flame retardant, dimethyl carbonate is used as a methyl source, the waste polyester product and the solvent are placed in a pressure-resistant tube, and a depolymerization reaction is carried out at 120-180° C. in a closed environment for 6 hours or more, and the temperature is lowered after the reaction is completed to prepare bisphenol A dimethyl ether or carboxylate; The solvent is N -Methylpyrrolidone or N , N - dimethylformamide; The bromide is selected from n-butyl bromide, 3,3-dimethyl-1-bromobutane, 1,2-dibromoethane, bromostyrene, isopentyl bromide, 4-phenyl-1-butyl bromide, 1-bromo-2-methylpropane, sec-butyl bromide, cyclohexane bromide, 2-bromo-2-methylbutane, tert-butyl bromide or brominated flame retardant; The brominated flame retardant is selected from tris(2,3-dibromopropyl)isocyanurate, tetrabromobisphenol A-bis(2,3-dibromopropyl ether), hexabromocyclododecane, decabromodiphenylethane, polybrominated diphenyl ether or tetrabromobisphenol A.

2. The method for directional high-value conversion of waste polyester products according to claim 1, characterized in that: The waste polyester product is first crushed into centimeter-level pieces and then placed in a pressure-resistant tube to undergo a depolymerization reaction.

3. The method for directional high-value conversion of waste polyester products according to claim 1, characterized in that: Waste polyester products include waste CDs, waste buckets, waste films or flame retardant boards.

4. The method for directional high-value conversion of waste polyester products according to claim 1, characterized in that: The polyester includes polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyethylene furandicarboxylate, polyethylene succinate, polyethylene adipate or polylactic acid.

5. The method for directional high-value conversion of waste polyester products according to claim 1, characterized in that: When the polyester is polycarbonate, the obtained product is bisphenol A dimethyl ether. When the polyester is polyethylene terephthalate, polybutylene terephthalate, polyethylene furandicarboxylate, polyethylene succinate, polyethylene adipate or polylactic acid, the obtained product is the corresponding carboxylate.

6. The method for directional high-value conversion of waste polyester products according to claim 1, characterized in that: Based on the mass of the waste polyester product, the amount of solvent added is 1 to 10 mL / g.

7. The method for directional high-value conversion of waste polyester products according to claim 1, characterized in that: The mass ratio of dimethyl carbonate to waste polyester product is 1 to 3:1, and the solvent is N- Methylpyrrolidone.

8. The method for directional high-value conversion of waste polyester products according to claim 1, characterized in that: The depolymerization reaction temperature is 150-180°C, and the depolymerization reaction time is 8-24 h.

9. The method for directional high-value conversion of waste polyester products according to claim 1, characterized in that: The bromide is selected from n-butane bromide.

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