A method for preparing p-diphenic acid using polyester colored blended waste material
By depolymerizing and decolorizing waste polyester-containing colored blended textiles in a reactor, high-purity parabens were prepared, solving the problem of difficult recycling of waste polyester textiles and realizing the efficient recycling of resources.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- WEST ANHUI UNIV
- Filing Date
- 2025-12-22
- Publication Date
- 2026-06-02
Smart Images
Figure CN122127216A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of polyester waste recycling technology, and more specifically, to a method for preparing terephthalic acid from polyester-containing colored blended waste. Background Technology
[0002] The efficient recycling of polyester (PET) blended textile waste faces significant challenges. Globally, 200 billion pieces of discarded clothing and 150 million tons of textiles are generated annually, of which only 12% are recycled. Due to the strong chemical inertness of these textiles and their extremely long natural degradation time, the vast majority of waste ends up in landfills or incineration, leading to severe resource depletion and environmental pollution. Therefore, achieving a virtuous cycle of recycling and reuse of polyester-containing waste has become an unavoidable and urgent issue for current social development.
[0003] Polyethylene terephthalate (PET) in these textiles is a high-value polymer with enormous recycling potential. Upgrading waste polyester into high-value chemicals offers a sustainable and economically viable solution to the global blended textile waste crisis. While various methods for polyester depolymerization and purification have been reported, including alcoholysis, acid hydrolysis, alkaline hydrolysis, enzymatic treatment, hydrothermal methods, and ionic liquid dissolution, some of which have been industrialized, these methods are only suitable for plastic products with high PET content (such as beverage bottles), which have a simple composition, are easy to sort, wash, and have a single color, making them easy to purify and separate. However, the recycling rate of waste polyester textiles remains extremely low, mainly because these textiles have complex compositions and contain various dyes and colorants, lacking effective recycling technologies.
[0004] Therefore, developing an efficient depolymerization, decolorization, and purification process for colored blended waste to prepare high-purity PTA is of great significance for realizing the full life cycle recycling of waste polyester. Summary of the Invention
[0005] To address the aforementioned technical problems, this invention provides a method for preparing terephthalic acid from polyester-containing colored blended waste, comprising the following steps: Blended textile waste, sodium hydroxide, oxidant, ethanol, and water are added to a reactor. The temperature is controlled to rise to the reaction temperature of 80–90°C, stirred and refluxed, and allowed to fully react and decompose for 1–3 hours. Then, the ethanol is recovered by distillation, and the undecomposed solid impurities are removed by filtration to obtain a depolymerization solution. The amount of sodium hydroxide used is 30%–50% of the mass of the blended textile waste, the amount of oxidant used is 1%–5% of the mass of the waste polyester, and the amount of ethanol and water used is 2–10 times the mass of the blended textile waste. The volume ratio of ethanol to water is 80:20 to 20:80. The obtained depolymerization solution is adjusted to pH 8-10 with protic acid, and then washed with organic solvent A to remove some impurities and colored substances, thus obtaining a preliminary purified solution; the amount of organic solvent A is 0.5-4 times the mass of the blended waste material. Activated carbon was added to the preliminary purified solution, and the decolorization reaction was maintained at 80-90°C with stirring for 0.5-2 hours. The decolorized solution was obtained by hot filtration. The amount of activated carbon used was 1%-10% of the mass of the blended waste material. Organic solvent B was added to the solution obtained after the decolorization reaction, and then acidified under stirring at room temperature to precipitate crystals. The crystals were then filtered to obtain a white solid of p-benzoic acid. The amount of organic solvent B used was 0.5 to 4 times the mass of the blended waste material.
[0006] Preferably, the oxidant is a peroxide or hypochlorite. Preferably, the organic solvent A is one or more mixtures of n-butanol, toluene, ethyl acetate, dichloromethane, dichloroethane, and n-hexane.
[0007] Preferably, the organic solvent B is one or more of methanol, ethanol, n-butanol, toluene, ethyl acetate, dichloromethane, dichloroethane, and n-hexane.
[0008] The beneficial effects of this invention are as follows: It has low requirements for the source of waste polyester raw materials, simple operation process, and is easy to scale up production. It yields PTA monomers with high purity and good color, and all solvents can be recycled and reused, significantly reducing energy consumption and costs. It breaks through the bottleneck of difficult decolorization and purification of colored blended waste polyester. It is of great significance and value for realizing true recycling of waste PET polyester. Attached Figure Description
[0009] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a diagram of the raw materials and the purified PTA product after decomposition in this invention; Figure 3 This is a comparison diagram of the decolorizing solutions under different conditions according to the present invention; Figure 4 This is a hydrogen nuclear magnetic resonance spectrum of a high-purity PTA monomer obtained as an example of the present invention; Figure 5 This is an HPLC analysis chromatogram of high-purity PTA monomer obtained as an example of the present invention. Detailed Implementation
[0010] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, some features described in the examples may be combined in other examples.
[0011] Example 1 This embodiment proposes a method for preparing terephthalic acid from polyester-containing colored blended waste, comprising the following steps: Blended textile waste, sodium hydroxide, oxidant, ethanol, and water are added to a reactor. The temperature is controlled to rise to the reaction temperature of 85°C, stirred and refluxed, and allowed to fully react and decompose for 2 hours. Then, the ethanol is recovered by distillation, and the undecomposed solid impurities are removed by filtration to obtain a depolymerization solution. The amount of sodium hydroxide used is 40% of the mass of the blended textile waste, the amount of oxidant is 3% of the mass of the waste polyester, and the amount of ethanol and water is 6 times the mass of the blended textile waste. The volume ratio of ethanol to water is 50:50. The obtained depolymerization solution was adjusted to pH 9 with protic acid, and then washed with organic solvent A to remove some impurities and colored substances, thus obtaining a preliminary purified solution; the amount of organic solvent A used was twice the mass of the blended waste material. Activated carbon was added to the preliminary purified solution, and the decolorization reaction was maintained at 85°C with stirring for 1 hour. The decolorized solution was obtained by hot filtration. The amount of activated carbon used was 5% of the mass of the blended waste material. Organic solvent B was added to the solution obtained after the decolorization reaction, and then acidified under stirring at room temperature to precipitate crystals. The crystals were then filtered to obtain a white solid of terephthalic acid. The amount of organic solvent B used was twice the mass of the blended waste material. in: The oxidizing agents are peroxides and hypochlorites; Organic solvent A is n-butanol; Organic solvent B is methanol.
[0012] Example 2 The difference between this embodiment and Embodiment 1 is that: Blended textile waste, sodium hydroxide, oxidant, ethanol, and water are added to a reactor. The temperature is controlled to rise to the reaction temperature of 80°C, stirred and refluxed, and allowed to fully react and decompose for 1 hour. Then, the ethanol is recovered by distillation, and the undecomposed solid impurities are removed by filtration to obtain a depolymerization solution. The amount of sodium hydroxide used is 30% of the mass of the blended textile waste, the amount of oxidant is 1% of the mass of the waste polyester, and the amount of ethanol and water is twice the mass of the blended textile waste. The volume ratio of ethanol to water is 80:20. The obtained depolymerization solution was adjusted to pH 8 with protic acid, and then washed with organic solvent A to remove some impurities and colored substances, thus obtaining a preliminary purified solution; the amount of organic solvent A used was 0.5 times the mass of the blended waste material. Activated carbon was added to the preliminary purified solution, and the decolorization reaction was maintained at 80°C with stirring for 0.5 h. The decolorized solution was obtained by hot filtration. The amount of activated carbon used was 1% of the mass of the blended waste material. Organic solvent B was added to the solution obtained after the decolorization reaction, and then acidified to precipitate crystals under stirring at room temperature. The crystals were then filtered to obtain a white solid of terephthalic acid. The amount of organic solvent B used was 0.5 times the mass of the blended waste material. Organic solvent A is toluene; Organic solvent B is ethanol.
[0013] Example 3 The difference between this embodiment and Embodiment 1 is that: Blended textile waste, sodium hydroxide, oxidant, ethanol, and water are added to a reactor. The temperature is controlled to rise to the reaction temperature of 90°C, stirred and refluxed, and allowed to fully react and decompose for 3 hours. Then, the ethanol is recovered by distillation, and the undecomposed solid impurities are removed by filtration to obtain a depolymerization solution. The amount of sodium hydroxide used is 50% of the mass of the blended textile waste, the amount of oxidant is 5% of the mass of the waste polyester, and the amount of ethanol and water is 10 times the mass of the blended textile waste. The volume ratio of ethanol to water is 20:80. The obtained depolymerization solution was adjusted to pH 10 with protic acid, and then washed with organic solvent A to remove some impurities and colored substances, thus obtaining a preliminary purified solution; the amount of organic solvent A used was 4 times the mass of the blended waste material. Activated carbon was added to the preliminary purified solution, and the decolorization reaction was maintained at 90°C with stirring for 2 hours. The decolorized solution was obtained by hot filtration. The amount of activated carbon used was 10% of the mass of the blended waste material. Organic solvent B was added to the solution obtained after the decolorization reaction, and then acidified under stirring at room temperature to precipitate crystals. The crystals were then filtered to obtain a white solid of terephthalic acid. The amount of organic solvent B used was four times the mass of the blended waste material. Organic solvent A is a mixture of n-butanol, toluene, ethyl acetate, dichloromethane, dichloroethane, and n-hexane; Organic solvent B is a mixture of methanol, ethanol, n-butanol, toluene, ethyl acetate, dichloromethane, dichloroethane, and n-hexane.
[0014] Example 4 The HPLC analysis conditions are as follows: An Agilent-1260 high-performance liquid chromatograph was used, with a Benetnach C18 column (5 μm, 4.6 x 150 mm), acetonitrile as the solvent, a detection wavelength of 254 nm, an acetonitrile-water-formic acid mobile phase (90:10:0.1, V / V / V), a flow rate of 1.0 mL / min, and an injection volume of 10 μL. The NMR analysis conditions were as follows: Bruker 400 NMR spectrometer, 400 MHz, was used to perform 1H NMR analysis on the product, and the sample was dissolved in DMSO-d6.
[0015] Example 1: Weigh 150 g of waste clothing and place it in a 2000 mL three-necked flask. Add 40 g of sodium hydroxide, 300 mL of 95% ethanol, 200 mL of water, and 3 mL of 30% hydrogen peroxide. Heat and stir under reflux for 2 hours. Replace the reflux apparatus with a distillation apparatus to recover the ethanol. Filter the residue to remove insoluble matter, and adjust the pH of the filtrate to approximately 9 with hydrochloric acid. Then add 200 mL of n-butanol, stir at room temperature for 30 minutes, allow to stand to separate the aqueous layer, and distill the organic layer under reduced pressure to recover the solvent. Add 6 g of activated carbon to the above aqueous solution, heat and stir at 80°C for 2 hours, and filter while hot. Add 200 mL of dichloromethane to the filtrate, stir at room temperature, and slowly add hydrochloric acid dropwise to adjust the pH to 4. A large amount of white solid precipitates; stir. Filter to obtain a white filter cake, and dry to obtain a white solid. Under these process conditions, the product purity is >99.5% and has good color.
[0016] Example 2: Weigh 150 g of waste clothing and place it in a 2000 mL three-necked flask. Add 40 g of sodium hydroxide, 300 mL of 95% ethanol, 200 mL of water, and 3 mL of 30% hydrogen peroxide. Heat and stir under reflux for 2 hours. Replace the reflux apparatus with a distillation apparatus to recover the ethanol. Filter the residue to remove insoluble matter, and adjust the pH of the filtrate to approximately 9 with hydrochloric acid. Then add 200 mL of n-butanol, stir at room temperature for 30 minutes, allow to stand to separate the aqueous layer, and distill the organic layer under reduced pressure to recover the solvent. Add 6 g of activated carbon to the above aqueous solution, heat and stir at 80°C for 2 hours, and filter while hot. Add 200 mL of dichloromethane to the filtrate, stir at room temperature, and slowly add hydrochloric acid dropwise to adjust the pH to 4. A large amount of white solid precipitates, which is then stirred. Filter to obtain a white filter cake, and dry to obtain a white solid. Under these process conditions, the product purity is >99.5% and has good color.
[0017] Example 3: Weigh 150 g of waste clothing and place it in a 2000 mL three-necked flask. Add 40 g of sodium hydroxide, 300 mL of 95% ethanol, and 200 mL of water. Heat and stir under reflux for 2 hours. Replace the reflux apparatus with a distillation apparatus to recover the ethanol. Filter the residue to remove insoluble matter, and adjust the pH of the filtrate to approximately 9 with hydrochloric acid. Then add 200 mL of ethyl acetate, stir at room temperature for 30 minutes, allow to stand to separate the aqueous layer, and distill the organic layer under reduced pressure to recover the solvent. Add 12 g of activated carbon to the above aqueous solution, heat and stir at 80°C for 2 hours, and filter while hot. Add 200 mL of n-butanol to the filtrate, stir at room temperature, and slowly add hydrochloric acid to adjust the pH to 4. A large amount of white solid precipitates, which is then stirred. Filter to obtain a white filter cake, and dry to obtain a white solid. In this process, no oxidant was added for decolorization, and the amount of activated carbon was increased, resulting in a product with a slightly worse color than that in Example 1.
[0018] Example 4: Weigh 150 g of waste clothing and place it in a 2000 mL three-necked flask. Add 40 g of sodium hydroxide, 300 mL of 95% ethanol, 200 mL of water, and 3 mL of 30% hydrogen peroxide. Heat and stir under reflux for 2 hours. Replace the reflux apparatus with a distillation apparatus to recover the ethanol. Filter the residue to remove insoluble matter, and adjust the pH of the filtrate to approximately 9 with hydrochloric acid. Then add 200 mL of n-butanol, stir at room temperature for 30 minutes, and allow to stand to separate the aqueous layer. Add 200 mL of dichloromethane to the aqueous layer, stir at room temperature, and slowly add hydrochloric acid dropwise to adjust the pH to 4. A large amount of white solid precipitates; stir. Filter and dry to obtain a creamy-white solid. This process does not use activated carbon for decolorization, resulting in a product with poor color.
[0019] Example 5: Weigh 150 g of waste clothing and place it in a 2000 mL three-necked flask. Add 40 g of sodium hydroxide, 300 mL of 95% ethanol, and 200 mL of water. Heat and stir under reflux for 2 hours. Replace the reflux apparatus with a distillation apparatus to recover the ethanol. Filter the residue to remove insoluble matter, and adjust the pH of the filtrate to approximately 9 with hydrochloric acid. Then add 200 mL of n-butanol, stir at room temperature for 30 minutes, allow to stand to separate the aqueous layer, and distill the organic layer under reduced pressure to recover the solvent. Add 6 g of activated carbon to the above aqueous solution, heat and stir at 80°C for 2 hours, and filter while hot. Add 200 mL of dichloromethane to the filtrate, stir at room temperature, and slowly add hydrochloric acid to adjust the pH to 4. A large amount of white solid precipitates, which is then stirred. Filter to obtain a white filter cake, and dry to obtain a creamy white solid. This process does not use an oxidizing agent for decolorization, resulting in a product with poor color.
[0020] Example 6: Weigh 150 g of waste clothing and place it in a 2000 mL three-necked flask. Add 40 g of sodium hydroxide, 300 mL of 95% ethanol, 200 mL of water, and 3 mL of 30% hydrogen peroxide. Heat and stir under reflux for 2 hours. Replace the reflux apparatus with a distillation apparatus to recover the ethanol. Filter the residue to remove insoluble matter, and adjust the pH of the filtrate to approximately 9 with hydrochloric acid. Add 6 g of activated carbon to the above aqueous solution, heat and stir at 80°C for 2 hours, and filter while hot. Add 200 mL of dichloromethane to the filtrate, stir at room temperature, and slowly add hydrochloric acid dropwise to adjust the pH to 4. A large amount of white solid precipitates; stir. Filter and dry to obtain a creamy-white solid.
[0021] The process conditions did not include solvent A for impurity removal, resulting in poor product quality and color.
[0022] Example 7: Weigh 150 g of waste clothing and place it in a 2000 mL three-necked flask. Add 40 g of sodium hydroxide, 300 mL of 95% ethanol, and 200 mL of water. Heat and stir under reflux for 2 hours. Replace the reflux apparatus with a distillation apparatus to recover the ethanol. Filter the residue to remove insoluble matter. Stir the filtrate at room temperature and slowly add hydrochloric acid to adjust the pH to 4. A large amount of brown solid precipitates; stir. Filter and dry to obtain a dark brown solid. The product obtained under these process conditions has very poor quality and color, serving as a control group.
[0023] Figure 1 This is a process flow diagram of the present invention; Figure 2 The diagram shows the raw materials and the purified PTA product after decomposition in this invention. Figure 3 This is a comparison diagram of the decolorizing solutions under different conditions according to the present invention; number 5 in the diagram is the decolorizing solution under the conditions of Example 1; Figure 4 The 1H NMR spectrum of the high-purity PTA monomer obtained in Example 1; Figure 5 The image shows the HPLC analysis spectrum of the high-purity PTA monomer obtained in Example 1; in the figure: the peak at a retention time of 10.751 min represents the PTA monomer; Figure 5 The statistical data is shown in the table below: The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.
Claims
1. A method for preparing terephthalic acid from polyester-containing colored blended waste, characterized in that, Includes the following steps: Blended textile waste, sodium hydroxide, oxidant, ethanol, and water are added to a reactor. The temperature is controlled to rise to the reaction temperature of 80–90°C, stirred and refluxed, and allowed to fully react and decompose for 1–3 hours. Then, the ethanol is recovered by distillation, and the undecomposed solid impurities are removed by filtration to obtain a depolymerization solution. The amount of sodium hydroxide used is 30%–50% of the mass of the blended textile waste, the amount of oxidant used is 1%–5% of the mass of the waste polyester, and the amount of ethanol and water used is 2–10 times the mass of the blended textile waste. The volume ratio of ethanol to water is 80:20 to 20:
80. The obtained depolymerization solution is adjusted to pH 8-10 with protic acid, and then washed with organic solvent A to remove some impurities and colored substances, thus obtaining a preliminary purified solution; the amount of organic solvent A is 0.5-4 times the mass of the blended waste material. Activated carbon is added to the preliminary purified solution, and the decolorization reaction is maintained at 80-90℃ with stirring for 0.5-2 hours. The decolorized solution is obtained by hot filtration. The amount of activated carbon used is 1%-10% of the mass of the blended waste material. Organic solvent B was added to the solution obtained after the decolorization reaction, and then acidified under stirring at room temperature to precipitate crystals. The crystals were then filtered to obtain a white solid of p-benzoic acid. The amount of organic solvent B used was 0.5 to 4 times the mass of the blended waste material.
2. The method for preparing terephthalic acid from polyester-containing colored blended waste according to claim 1, characterized in that, The oxidizing agent is a peroxide or hypochlorite.
3. The method for preparing terephthalic acid from polyester-containing colored blended waste according to claim 1, characterized in that, The organic solvent A is one or more of the following: n-butanol, toluene, ethyl acetate, dichloromethane, dichloroethane, and n-hexane.
4. The method for preparing terephthalic acid from polyester-containing colored blended waste according to claim 1, characterized in that, The organic solvent B is one or more of methanol, ethanol, n-butanol, toluene, ethyl acetate, dichloromethane, dichloroethane, and n-hexane.