A method for recycling waste polyester and polycarbonate to produce recycled polyarylate

Abstract

This invention discloses a method for preparing recycled polyarylate from waste polyester and polycarbonate. The recycling and reprocessing method includes the following steps: (1) Under a protective gas atmosphere, polyester and polycarbonate, along with a catalyst, are mixed uniformly in an alcohol solution, heated, and then catalytically alcoholyzed to obtain diester terephthalate and bisphenol A, respectively. (2) The diester terephthalate obtained from the alcoholysis of diester terephthalate is subjected to acyl chloride treatment to obtain the corresponding terephthaloyl chloride. (3) Finally, without separating the end-capping agent from the recycled monomers, terephthaloyl chloride and bisphenol A are co-polymerized and upgraded to polyarylate under mild conditions using interfacial polycondensation technology. This invention eliminates the need for additional purification techniques to remove the end-capping agent from the recycled monomers, simplifies the waste polymer recycling process, and achieves "upgraded recycling" of polyester and polycarbonate plastics, resulting in better economic benefits.

Description

Technical Field

[0001] This invention relates to the field of polymer materials, and specifically to a method for preparing recycled polyarylates from waste polyester and polycarbonate. Background Technology

[0002] Plastics are primarily derived from fossil fuels, and waste plastics are considered a serious waste of carbon resources and a major source of environmental pollution. Polyethylene terephthalate (PET) is the most widely used polyester globally, with consumption projected to exceed 65 million tons in 2021. Currently, PET is mainly recycled through mechanical processes. However, this leads to varying degrees of thermal and mechanical degradation of the polymer, limiting the number of primary and secondary recycling cycles. Furthermore, polycarbonate (PC) and PC / ABS blends are widely used engineering plastics. The motivation for recycling BPA-PC is clear: to reduce the environmental release of bisphenol A (BPA). Extensive evidence indicates that BPA is toxic. In many organisms, it has been shown to disrupt the thyroid and endocrine system, and to exhibit toxic, mutagenic, and carcinogenic effects.

[0003] Currently, there are various depolymerization strategies for PET and PC, namely chemical depolymerization in nucleophilic solvents (such as hydrolysis, glycolysis, aminohydrolysis, ammonolysis, and methanololysis). However, current processes suffer from many technical problems, including insufficient polymer properties, low depolymerization efficiency, and metal residues. Depolymerization processes often require multi-step processing to obtain monomers with high purity for subsequent production. Facing waste plastics in real-world applications presents even more complex challenges. The functionality of plastics, including their aesthetics, depends entirely on many other added components, including plasticizers, antioxidants, mildew inhibitors, deodorizers, and colorants. These additional compounds (often called additives) result in low purity products from alcoholysis, making it difficult to effectively recycle and reuse plastic materials. Therefore, the use of chemical recycling methods to recover polyester or polycarbonate and achieve closed-loop recycling or the preparation of high-value polymer materials has not yet been truly realized. Summary of the Invention

[0004] To address the lack of recycling technology for waste plastics and the obstacles posed by the complex components such as impurities in waste plastics to their upgrading and utilization, this invention provides a method for preparing recycled polyarylates from waste polyester and polycarbonate.

[0005] One objective of this invention is to provide a method for preparing recycled polyarylates from waste polyester and polycarbonate, comprising the following steps:

[0006] (1) In a protective gas atmosphere, polyester and polycarbonate and catalyst are mixed evenly in an alcohol solution, heated and catalytically alcoholyzed, and purified to obtain dimethyl terephthalate and bisphenol A, respectively.

[0007] (2) The dimethyl terephthalate obtained in step (1) was subjected to low-temperature alkaline hydrolysis with sodium hydroxide in a methanol / water mixture to obtain sodium terephthalate. After complete hydrolysis, the solution was neutralized with hydrochloric acid to obtain terephthalic acid precipitate, which was filtered, washed, and dried to obtain pure terephthalic acid. Subsequently, terephthalic acid and a certain amount of thionyl chloride were mixed, and catalytic amounts of pyridine and DMF were added. The mixture was then heated in a reflux reactor. The thionyl chloride was removed under reduced pressure and stored. The resulting light gray product was repeatedly extracted with petroleum ether at 80°C to obtain pure terephthaloyl chloride.

[0008] (3) Finally, the terephthaloyl chloride from step (2) and the bisphenol A recovered in step (1) were directly used for polymerization. At room temperature, the recovered bisphenol A, NaOH, and deionized water were added to the reactor and mixed. After stirring for a certain period, the catalyst was added. Then, a dichloromethane solution containing terephthaloyl chloride and isophthaloyl chloride was added dropwise at the reaction temperature. After the polymerization reaction was completed, the dichloromethane solvent was recovered and the crude product was solidified. The collected crude product was crushed, washed, and recycled polyarylate was obtained.

[0009] In a preferred embodiment of the present invention,

[0010] Step (1),

[0011] The polyester is polyethylene terephthalate (PET).

[0012] The alcohol is one of methanol, ethanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, and 1,4-butanediol; preferably methanol or ethylene glycol.

[0013] The catalyst is one or a combination of 1,5,7-triazabicyclo[4.4.0]decen-5-ene (TBD) acetate, 1,5,7-triazabicyclo[4.4.0]decen-5-ene (TBD) lactate, 1,8-diazobispirocyclo[5.4.0]undec-7-ene (DBU) acetate, 1,8-diazobispirocyclo[5.4.0]undec-7-ene (DBU) lactate, sodium acetate, magnesium acetate, potassium carbonate, potassium tert-butoxide, sodium ethoxide, tetrabutylammonium acetate, N,N-dimethylimidazolium carbamate, tetrabutylammonium hydroxide, potassium hydroxide, aluminum isopropoxide, and sodium carbonate.

[0014] The protective gas is nitrogen or carbon dioxide; nitrogen is preferred.

[0015] The mixing temperature of the reactants, catalyst, and alcohol is 0–60°C; preferably 25–40°C.

[0016] The catalytic alcoholysis temperature is 60–200°C; the reaction time is 0.5–24 h; preferably, the alcoholysis temperature is 100–180°C and the reaction time is 1–8 h.

[0017] The amount of the depolymerization catalyst is 0.2 to 20 wt% of the polymer; preferably 0.2 to 10 wt%.

[0018] The polymer content to alcohol content is 0.2–100 wt% by mass; preferably 20–100 wt%.

[0019] Step (2),

[0020] The volume ratio of the methanol and water mixture is 20-300%; preferably 20-200%.

[0021] The molar ratio of sodium hydroxide to terephthalic acid is 200-300%; preferably 200-250%.

[0022] The hydrolysis temperature is 40–100℃; preferably 60–80℃.

[0023] The molar ratio of terephthalic acid to thionyl chloride is 10–40%; preferably 10–20%.

[0024] The heating temperature is 60–130°C; the heating reaction time is 1–6 h; preferably, the heating temperature is 80–120°C and the reaction time is 3–6 h.

[0025] The molar ratio of pyridine to terephthalic acid is 1–50%; preferably 1–10%.

[0026] The mass ratio of DMF to terephthalic acid is 1–50 wt%; preferably 1–10%.

[0027] In step (3),

[0028] The molar ratio of sodium hydroxide to terephthalic acid is 200–300%; preferably 200–220%.

[0029] The volume ratio of deionized water to dichloromethane is 40–150%; preferably 40–100%.

[0030] The polymerization catalyst is 15-crown-5, 18-crown-6, sodium dioctyl succinate, sodium citrate, sodium tartrate, sodium gluconate, sodium triacetate, sodium sorbate, sodium ethylenediaminetetraacetate, sodium ethylenediaminetetramethylidene phosphate, sodium glycocholate, sodium terephthalate, sodium stearate, tetrabutylammonium bromide, tetrabutylammonium chloride, butyltrimethylammonium chloride, benzyltriethylammonium bromide, benzyltriethylammonium chloride, hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, sodium dodecylbenzenesulfonate, sodium benzenesulfonate, sodium p-methylbenzenesulfonate, sodium alginate, or dodecane.

[0031] The amount of polymerization catalyst used is 0.1–5 wt%; preferably 0.1–2 wt%.

[0032] The ratio of bisphenol A, terephthaloyl chloride and isophthaloyl chloride is 2:0.4 to 1:0.4 to 1; preferably 2:0.8 to 1:0.8 to 1.

[0033] The pre-stirring time is 0.5 to 3 hours; preferably 0.5 to 1 hour.

[0034] The polymerization reaction temperature is -20 to 60°C; the polymerization reaction time is 3 to 24 hours; preferably, the polymerization reaction temperature is 0 to 30°C and the reaction time is 5 to 12 hours.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] (1) This invention employs a strategy of metal-free alcoholysis and low-temperature interfacial polymerization to successfully upgrade and synthesize polyarylates from waste polyester and polycarbonate waste, thereby enhancing the greenness and resource utilization of the recycling process. The recycled polyarylates exhibit excellent performance, comparable to that of the existing commercial polyarylate U-100.

[0037] (2) Compared with traditional waste polymer recycling methods, this invention does not require the separation of end-capping agents in polyester and polycarbonate, saving product separation and purification costs. The synthesis route is carried out under mild conditions, which is simple and does not require high-end reaction equipment. It is more suitable for the current recycling and regeneration of real waste polyester and polycarbonate, and is more convenient for subsequent pilot-scale and industrial-scale production.

[0038] This invention uses recycled polyester and polycarbonate plastics to synthesize polyarylates via alcoholysis and repolymerization, achieving "upgraded recycling" of polyester plastics and polycarbonate. The "upgraded recycling" is mainly reflected in the production of a high-value-added material. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the process for upgrading and recycling polyarylates from polyester and polycarbonate in Example 1.

[0040] Figure 2 The 1H NMR spectrum of the regenerated polyarylate and the virgin polyarylate (U-100) in Example 2 is shown. 1 H-NMR spectrum.

[0041] Figure 3 This is a differential thermal analysis (DTA) graph of the recycled polyarylate from Example 4.

[0042] Figure 4 This is a photograph of the recycled polyarylate tablets from Example 4. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, specific embodiments are provided to illustrate the invention. It should be noted that these embodiments are intended to further illustrate the invention, but should not be construed as limiting the scope of protection of the invention.

[0044] Example 1

[0045] (1) Under nitrogen atmosphere, 192g of polyethylene terephthalate and 254g of polycarbonate were placed in two separate high-pressure reactors. 1g of 1,5,7-triazabicyclo[4.4.0]decen-5-ene (TBD) acetate and 1L of methanol were added to each reactor, and the mixtures were thoroughly mixed. The polyester and polycarbonate were catalytically alcoholyzed at 160°C for 3 hours. Excess methanol and volatile substances were removed by rotary distillation. Finally, the products were washed with a small amount of distilled water and dried in an oven to obtain 190g of dimethyl terephthalate and 220g of bisphenol A.

[0046] (2) The dimethyl terephthalate obtained in step (1) was added to a mixed solution of 300 ml methanol / 100 ml water, and the mixture was heated to 60 °C. 90 g of sodium hydroxide was added under continuous stirring until the solid was completely dissolved to obtain sodium terephthalate. After complete hydrolysis, the solution was neutralized to neutral with dilute hydrochloric acid to obtain terephthalic acid precipitate. After filtration, washing, and drying, pure terephthalic acid was obtained. Subsequently, terephthalic acid and 700 g of thionyl chloride were mixed, and 1.6 g of pyridine and 60 g of DMF were added. The mixture was then heated in a reflux reactor. The thionyl chloride was removed under reduced pressure and stored. The resulting light gray product was repeatedly extracted with petroleum ether at 80 °C to obtain 196 g of pure terephthaloyl chloride.

[0047] (3) Finally, the terephthaloyl chloride from step (2) and the bisphenol A recovered in step (1) were directly used for polymerization. At room temperature, the recovered bisphenol A (containing a capping agent), 90 g of sodium hydroxide, and 60 mL of deionized water were added to the reactor and mixed. After stirring for 1 h, 3 g of tetrabutylammonium chloride catalyst was added. Then, 50 mL of a dichloromethane solution containing 196 g of terephthaloyl chloride and 196 g of isophthaloyl chloride was added dropwise at the reaction temperature. Subsequently, the polymerization reaction was completed by heating at 20 °C for 8 h. Finally, the solvent dichloromethane was recovered and the crude product (polyarylate) was solidified. The collected crude product was crushed and washed to obtain approximately 670 g of recycled polyarylate. The above process flow is as follows: Figure 1 As shown.

[0048] Example 2

[0049] (1) Under nitrogen atmosphere, 192g of polyethylene terephthalate and 254g of polycarbonate were placed in two separate high-pressure reactors, with 2g of sodium carbonate and 1L of methanol added to each, and mixed thoroughly. The mixture was heated at 160°C for 3 hours to catalytically alcoholyze the polyester and polycarbonate. Excess methanol and volatile substances were removed by rotary distillation. Finally, the product was washed with a small amount of distilled water and dried in an oven to obtain 186g of dimethyl terephthalate and 220g of bisphenol A.

[0050] (2) The dimethyl terephthalate obtained in step (1) was added to a mixed solution of 200 mL methanol / 200 mL water, and the mixture was heated to 80 °C. 90 g of sodium hydroxide was added under continuous stirring until the solid was completely dissolved to obtain sodium terephthalate. After complete hydrolysis, the solution was neutralized with dilute hydrochloric acid to obtain terephthalic acid precipitate, which was filtered, washed, and dried to obtain pure terephthalic acid. Subsequently, the obtained terephthalic acid was mixed with 660 g of thionyl chloride, and 2 g of pyridine and 90 g of DMF were added. The mixture was then heated in a reflux reactor. The thionyl chloride was removed under reduced pressure and stored. The resulting light gray product was repeatedly extracted with petroleum ether at 80 °C to obtain 188 g of pure terephthaloyl chloride.

[0051] (3) Finally, the terephthaloyl chloride from step (2) and the bisphenol A recovered in step (1) were directly used for polymerization. At room temperature, the recovered bisphenol A (containing a capping agent), 90 g of sodium hydroxide, and 80 mL of deionized water were added to the reactor and mixed. After stirring for 1.5 h, 2 g of butyltrimethylammonium chloride catalyst was added. Then, 80 mL of a dichloromethane solution containing 188 g of terephthaloyl chloride and 188 g of isophthaloyl chloride was added dropwise at the reaction temperature. Subsequently, the polymerization reaction was completed by heating at 15 °C for 12 h. Finally, the solvent dichloromethane was recovered and the crude product (polyarylate) was solidified. The collected crude product was crushed and washed to obtain approximately 663 g of recycled polyarylate. The recycled polyester was tested on a 600 MHz Bruker spectrometer using deuterated chloroform (CDCl3) as a solvent. 1 H-NMR, the results are as follows Figure 2 As shown.

[0052] Example 3

[0053] (1) Under nitrogen atmosphere, 384 g of polyethylene terephthalate and 508 g of polycarbonate were placed in two separate high-pressure reactors, with 5 g of zinc carbonate and 4 L of methanol added to each, and mixed thoroughly. The mixture was heated at 190 °C for 2 h to catalytically alcoholyze the polyester and polycarbonate. Excess methanol and volatile substances were removed by rotary distillation. Finally, the product was washed with a small amount of distilled water and dried in an oven to obtain 380 g of dimethyl terephthalate and 450 g of bisphenol A.

[0054] (2) The dimethyl terephthalate obtained in step (1) was added to a mixed solution of 2 L methanol / 1.5 L water, and the mixture was heated to 60 °C. 200 g of sodium hydroxide was added under continuous stirring until the solid was completely dissolved to obtain sodium terephthalate. After complete hydrolysis, the solution was neutralized with dilute hydrochloric acid to obtain terephthalic acid precipitate, which was filtered, washed, and dried to obtain pure terephthalic acid. Subsequently, terephthalic acid and 1.5 kg of thionyl chloride were mixed, and 3 g of pyridine and 120 g of DMF were added. The mixture was then heated in a reflux reactor. The thionyl chloride was removed under reduced pressure and stored. The resulting light gray product was repeatedly extracted with petroleum ether at 80 °C to obtain 396 g of pure terephthaloyl chloride.

[0055] (3) Finally, the terephthaloyl chloride from step (2) and the bisphenol A recovered in step (1) were directly used for polymerization. At room temperature, the recovered bisphenol A (containing a capping agent), 180 g of sodium hydroxide, and 150 mL of deionized water were added to the reactor and mixed. After stirring for 3 h, 14 g of sodium p-toluenesulfonate catalyst was added. Then, 100 mL of a dichloromethane solution containing 396 g of terephthaloyl chloride and 396 g of isophthaloyl chloride was added dropwise at the reaction temperature. Subsequently, the polymerization reaction was completed by heating at 25 °C for 5 h. Finally, the solvent dichloromethane was recovered and the crude product (polyarylate) was solidified. The collected crude product was crushed and washed to obtain approximately 1.30 kg of recycled polyarylate.

[0056] Example 4

[0057] (1) Under nitrogen atmosphere, 1.9 kg of polyethylene terephthalate and 2.50 kg of polycarbonate were placed in two separate high-pressure reactors, with 3 g of magnesium acetate and 4 L of methanol added to each, and mixed thoroughly. The mixture was heated at 190 °C for 2 h to catalytically alcoholyze the polyester and polycarbonate. Excess methanol and volatile substances were removed by rotary distillation. Finally, the product was washed with a small amount of distilled water and dried in an oven to obtain 1.94 kg of dimethyl terephthalate and 2.22 kg of bisphenol A.

[0058] (2) The dimethyl terephthalate obtained in step (1) was added to a mixed solution of 3L methanol / 2L water, and the mixture was heated to 80°C. 0.9 kg of sodium hydroxide was added under continuous stirring until the solid was completely dissolved to obtain sodium terephthalate. After complete hydrolysis, the solution was neutralized with dilute hydrochloric acid to obtain terephthalic acid precipitate. After filtration, washing, and drying, pure terephthalic acid was obtained. Subsequently, terephthalic acid and 7 kg of thionyl chloride were mixed stepwise with stirring, and 20 g of pyridine and 500 g of DMF were added. The mixture was then heated in a reflux reactor. The thionyl chloride was removed under reduced pressure and stored. The resulting light gray product was repeatedly extracted with petroleum ether at 80°C to obtain 1.90 kg of pure terephthaloyl chloride.

[0059] (3) Finally, the terephthaloyl chloride from step (2) and the bisphenol A recovered in step (1) were directly used for polymerization. At room temperature, the recovered bisphenol A (containing a capping agent), 0.9 kg of sodium hydroxide, and 2 L of deionized water were added to the reactor and mixed. After stirring for 3 h, 10 g of butyltrimethylammonium chloride catalyst was added. Then, 5 L of a dichloromethane solution containing 1.90 kg of terephthaloyl chloride and 1.9 kg of isophthaloyl chloride was added dropwise at the reaction temperature. Subsequently, the polymerization reaction was completed by heating at 15 °C for 10 h. Finally, the solvent dichloromethane was recovered and the crude product (polyarylate) was solidified. The collected crude product was crushed and washed to obtain approximately 6.66 kg of recycled polyarylate. The recycled polyarylate was characterized by differential thermal analysis (DSC) using a Mettler Toledo DSC3 model differential thermal analyzer at a heating rate of 10 °C / min. The results are as follows. Figure 3 As shown. Recycled polyarylate powder is melt-pressed to obtain a thin film material, such as... Figure 4 As shown.

[0060] Table 1

[0061]

[0062] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for recycling waste polyesters and polycarbonates to produce recycled polyarylate, characterized in that, Includes the following steps: (1) In a protective gas atmosphere, polyester and polycarbonate and catalyst are mixed evenly in an alcohol solution, heated and catalytically alcoholyzed, and purified to obtain dimethyl terephthalate and bisphenol A, respectively. (2) The dimethyl terephthalate obtained in step (1) was subjected to low-temperature alkaline hydrolysis with sodium hydroxide in a methanol / water mixed solution to obtain sodium terephthalate. After complete hydrolysis, the solution was neutralized to neutral with hydrochloric acid to obtain terephthalic acid precipitate, which was filtered, washed, and dried to obtain pure terephthalic acid; Subsequently, terephthalic acid and a certain amount of thionyl chloride were mixed, and catalytic amounts of pyridine and DMF were added. The mixture was then heated in a reflux reactor. The thionyl chloride was removed under reduced pressure and stored. The resulting light gray product was repeatedly extracted with petroleum ether at 80°C to obtain pure terephthaloyl chloride. (3) Finally, the terephthaloyl chloride from step (2) and the bisphenol A recovered in step (1) were directly used for polymerization. At room temperature, the recovered bisphenol A, NaOH, and deionized water were added to the reactor and mixed. After stirring for a certain period, the catalyst was added. Then, a dichloromethane solution containing terephthaloyl chloride and isophthaloyl chloride was added dropwise at the reaction temperature. After the polymerization reaction was completed, the dichloromethane solvent was recovered and the crude product was solidified. The collected crude product was crushed, washed, and recycled polyarylate was obtained.

2. The method of recycling waste polyesters and polycarbonates to produce recycled polyarylate according to claim 1, characterized in that In step (1), the polyester is polyethylene terephthalate (PET); the polycarbonate is bisphenol A type polycarbonate; the alcohol is one of methanol, ethanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, and 1,4-butanediol; and the catalyst is 1,5,7-triazabicyclo[4.4.0]decene-5-ene (TBD) acetate or 1,5,7-triazabicyclo[4.4.0]decene. -5-ene (TBD) lactate, 1,8-diazobisspirocyclic [5.4.0]undecyl-7-ene (DBU) acetate, 1,8-diazobisspirocyclic [5.4.0]undecyl-7-ene (DBU) lactate, sodium acetate, magnesium acetate, potassium carbonate, potassium tert-butoxide, sodium ethoxide, tetrabutylammonium acetate, N,N-dimethylimidazolium carboxylate, tetrabutylammonium hydroxide, potassium hydroxide, aluminum isopropoxide, sodium carbonate, or a combination thereof.

3. The method of recycling waste polyesters and polycarbonates to produce recycled polyarylate according to claim 1, characterized in that The protective gas in step (1) is nitrogen or carbon dioxide; the mixing temperature of the reactants, catalyst, and alcohol is 0-60°C; the catalytic alcoholysis temperature is 60-200°C; the amount of the depolymerization catalyst is 0.2-20 wt% of the polymer; the mass ratio of the polymer to the alcohol compound is 0.2-100 wt%; and the reaction time is 0.5-24 h.

4. The method of recycling waste polyesters and polycarbonates to produce recycled polyarylate according to claim 1, characterized in that The volume ratio of the methanol and water mixture in step (2) is 20-300%; the molar ratio of sodium hydroxide to terephthalic acid is 200-300%; and the hydrolysis temperature is 40-100℃.

5. The method of recycling waste polyesters and polycarbonates to produce recycled polyarylate according to claim 1, characterized in that In step (2), the molar ratio of terephthalic acid to thionyl chloride is 10-40%; the heating temperature is 60-130℃; the heating reaction time is 1-6h; the molar ratio of pyridine to terephthalic acid is 1-50%; and the mass ratio of DMF to terephthalic acid is 1-50wt%.

6. The method of recycling waste polyesters and polycarbonates to produce recycled polyarylate according to claim 1, characterized in that In step (3), the molar ratio of sodium hydroxide to bisphenol A is 100-150%; the volume ratio of deionized water to dichloromethane is 40-150%; the polymerization catalyst is butyltrimethylammonium chloride; the amount of polymerization catalyst is 0.1-5 wt%; and the molar ratio of bisphenol A, terephthaloyl chloride and isophthaloyl chloride is 2:0.4-1:0.4-1.

7. The method of recycling waste polyesters and polycarbonates to produce recycled polyarylate according to claim 1, characterized in that The pre-stirring time in step (3) is 0.5 to 3 hours; the polymerization reaction temperature is -20 to 60°C; and the polymerization reaction time is 3 to 24 hours.

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