Method for recycling pet plastic waste
Patent Information
- Application Number
- CN202611478340.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-09-22
- Publication Date
- 2026-10-27
Smart Images
Figure CN122977955A_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of solid waste plastic treatment technology, and relates to a method for recycling and treating PET plastic waste. Background Technology
[0002] With the widespread and increasing use of non-biodegradable polymer materials, plastic and microplastic particulate pollution in terrestrial and aquatic ecosystems has recently garnered significant attention, posing one of the greatest challenges to sustainable development for human society. Polyethylene terephthalate (PET), a thermoplastic polyester made from repeating units of terephthalic acid and ethylene glycol, is primarily used in synthetic fibers and packaging materials due to its excellent properties such as light weight, non-toxicity, chemical resistance, and recyclability. Because PET is difficult to biodegrade, recycling PET plastic waste is crucial for reducing pollution and conserving resources given its widespread use.
[0003] Previously, PET was typically recycled through traditional landfill and incineration, which caused severe air pollution and wasted valuable land during the recycling process. From a sustainability perspective, researchers are exploring mechanical, biological, and chemical methods to recycle PET plastic waste.
[0004] Currently, mechanical recycling is the mainstream method for recycling PET plastic waste, but it still has the following limitations: On the one hand, PET is prone to thermal degradation and hydrolysis during repeated melting and mechanical shearing, leading to a decrease in molecular weight, intrinsic viscosity, and material properties; on the other hand, mechanical cleaning and sorting are difficult to effectively remove dyes, pigments, metal residues, additives, and other impurities tightly bound to the PET matrix, limiting the purity and quality of recycled PET. In addition, mechanical recycling has high requirements for the composition and cleanliness of raw materials. For PET / PE, PET / PVC, PET / PC composite films, and composite or blended materials that are difficult to physically separate, such as polyester / cotton and polyester / spandex, it is difficult to achieve effective separation and high-value recycling of each component.
[0005] For bio-recycling, only plastics with hydrolyzable ester or amide bonds in the main chain can be broken down into oligomers or monomers using this method.
[0006] Compared to mechanical and biological recycling methods, chemical recycling methods have gained more attention for their ability to selectively convert plastic waste into high-value products, including feedstocks for oil refining, fuels, and monomers. However, current chemical recycling methods have the following drawbacks: excessively high recycling temperatures or times, low recycling efficiency, and the use of expensive and environmentally unfriendly solvents.
[0007] Currently, some existing technologies utilize ethylene glycol to depolymerize PET plastic waste for PET recycling. The ethylene glycol depolymerization of PET is a typical solid-liquid heterogeneous reaction, limited by the interfacial effect between PET and ethylene glycol. To achieve a high BHET (bis(2-hydroxyethyl) terephthalate) yield without relying on conventional catalysts, high-temperature and high-pressure conditions above 245℃ and 1.1-15.3 MPa are required. Catalysis and microwave-assisted reactions are important means to reduce the harshness of the reaction. Current catalyst-based research can control the reaction temperature at 160-200℃ and the reaction time at 1-4 hours. Although this significantly shortens the reaction temperature and time compared to catalyst-free conditions, reducing the reaction temperature below 100℃ remains a significant challenge.
[0008] Therefore, in this field, there is a desire to develop a more environmentally friendly, milder recycling method for PET plastic waste with high recycling efficiency, and to obtain products with high yield and high purity. Summary of the Invention
[0009] To address the shortcomings of existing technologies, the purpose of this application is to provide a method for recycling and processing PET plastic waste. This application utilizes green solvents to achieve efficient dissolution and regeneration of PET plastic waste under normal pressure and mild conditions. Alternatively, solvent-assisted alcoholysis can be used to rapidly convert PET into monomers with low energy consumption, achieving closed-loop recycling and demonstrating significant environmental, social, and economic benefits.
[0010] To achieve this objective, the present application adopts the following technical solution: In a first aspect, this application provides a method for recycling PET plastic waste, the recycling method comprising the following steps: S1. PET plastic waste and 1,3-dimethylpropylene urea (DMPU, structural formula: Mix and dissolve to obtain a solution; S2-1. Add an anti-solvent to the solution obtained in step S1 to obtain recycled PET plastic; or... S2-2. Ethylene glycol and a catalyst are added to the solution obtained in step S1 to carry out an alcoholysis reaction to obtain bis(2-hydroxyethyl) terephthalate crystals.
[0011] The PET waste recycling method provided in this application can be divided into two paths. The first path is the dissolution and regeneration of PET. Non-PET components can be removed by filtering through the selective dissolution effect of 1,3-dimethylpropylene urea, and the addition of an anti-solvent allows the PET to be regenerated. The resulting recycled PET plastic has high yield and high purity, and excellent chemical and thermal stability. The second path involves adding a catalyst and the solvent ethylene glycol, using 1,3-dimethylpropylene urea to assist in the ethylene glycol alcoholysis of PET (i.e., 1,3-dimethylpropylene urea serves as a highly efficient co-solvent for the ethylene glycol alcoholysis reaction of PET), to obtain the PET monomer bis(2-hydroxyethyl) terephthalate. The obtained monomer has high yield and high purity. Compared with the recycling process in the prior art, both paths of this application have advantages in terms of temperature and time.
[0012] Specifically, this application constructs a dual-pathway recycling method for PET using 1,3-dimethylpropylene urea (DMPU) as a common medium. DMPU can be used as a selective solvent for PET or as a co-solvent for the glycol hydrolysis of PET. Depending on the quality of the raw materials or product requirements, it can selectively guide the generation of recycled PET plastic or bis(2-hydroxyethyl) terephthalate.
[0013] In the second pathway, 1,3-dimethylpropaneurea can improve the accessibility of PET ester groups and activate ethylene glycol. The catalyst activates ethylene glycol, and the two work together to promote the selective alcoholysis of PET to bis(2-hydroxyethyl) terephthalate.
[0014] In this application, the chemical reaction formula for the ethylene glycol alcoholysis of PET is as follows: .
[0015] In some embodiments, the PET plastic waste in step S1 includes any one or a combination of at least two of the following: PET waste plastics from fresh household waste, PET waste plastics from industrial and agricultural production, and PET waste plastics from aged waste.
[0016] In some embodiments, before mixing the PET plastic waste and 1,3-dimethylpropaneurea in step S1, the following steps are also included: PET plastic waste is crushed and screened to obtain PET plastic fragments.
[0017] In some embodiments, the sieve used for sieving is 20 to 200 mesh, such as 20 mesh, 40 mesh, 50 mesh, 60 mesh, 80 mesh, 100 mesh, 120 mesh, 140 mesh, 150 mesh, 160 mesh, 180 mesh, 200 mesh, etc.
[0018] In some embodiments, the dissolution step S1 is followed by a filtration step, the purpose of which is to remove insoluble impurities.
[0019] In some embodiments, the mass ratio of the PET plastic waste and 1,3-dimethylpropaneurea in step S1 is 1:(10~20), for example 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, etc.
[0020] In some embodiments, the dissolution described in step S1 is carried out under stirring conditions (specifically, continuous stirring), wherein the stirring temperature is 120~180℃, for example 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, etc., and the stirring time is 10~40min, for example 10min, 15min, 20min, 25min, 30min, 35min, 40min, etc.
[0021] In some embodiments, the antisolvent in step S2-1 includes ultrapure water.
[0022] In some embodiments, step S2-1 specifically includes: adding an antisolvent to the solution obtained in step S1 to regenerate the PET plastic, then performing solid-liquid separation to obtain recycled PET plastic, and then cleaning the recycled PET plastic.
[0023] In some embodiments, the solid-liquid separation is performed by vacuum filtration.
[0024] In some embodiments, the filtrate collected by the solid-liquid separation contains 1,3-dimethylpropylene urea, which can be recycled and reused to dissolve PET plastic waste.
[0025] In some embodiments, the cleaning of recycled PET plastic specifically includes: repeatedly washing the recycled PET plastic with ultrapure water to remove residual organic solvents on the solid surface.
[0026] In some embodiments, the mass ratio of ethylene glycol in step S2-2 to PET plastic waste in step S1 is (0.8~1.2):1, for example 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, etc.
[0027] In some embodiments, the catalyst in step S2-2 is a catalyst capable of catalyzing the transesterification of PET with ethylene glycol.
[0028] In some embodiments, the catalyst in step S2-2 includes any one or a combination of at least two of the following: metal salt catalyst, metal oxide catalyst, acid catalyst, basic catalyst, ionic liquid catalyst, deep eutectic solvent catalyst, and supported catalyst.
[0029] In some embodiments, the catalyst described in step S2-2 comprises 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD).
[0030] In some embodiments, the mass ratio of the catalyst in step S2-2 to the PET plastic waste in step S1 is (0.04~0.08):1, for example 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, etc.
[0031] In some embodiments, the temperature of the alcoholysis reaction in step S2-2 is 60~80℃, such as 60℃, 65℃, 70℃, 75℃, 80℃, etc., and the time of the alcoholysis reaction is 10~60min, such as 10min, 15min, 20min, 25min, 30min, 35min, 40min, 45min, 50min, 55min, 60min, etc.
[0032] In some embodiments, the alcoholysis reaction described in step S2-2 is carried out under stirring conditions.
[0033] In some embodiments, step S2-2 specifically includes: adding ethylene glycol and a catalyst to the solution obtained in step S1 to carry out an alcoholysis reaction, then adding water to precipitate oligomers, then performing solid-liquid separation to remove the oligomers, then refrigerating the filtrate, and collecting the bis(2-hydroxyethyl) terephthalate crystals that are insoluble in the system.
[0034] In some embodiments, the oligomers removed by the solid-liquid separation can be recycled and reused in the alcoholysis reaction.
[0035] In some embodiments, the refrigeration of the filtrate specifically includes: refrigerating the filtrate at 3~5℃ (e.g., 3℃, 4℃, 5℃, etc.) for 10~14h (e.g., 10h, 11h, 12h, 13h, 14h, etc.).
[0036] In some embodiments, the refrigeration of the filtrate further includes the following steps: The mixed solution obtained from refrigeration is subjected to vacuum distillation to recover water, ethylene glycol, catalyst, and 1,3-dimethylpropaneurea. Water can be used in the step of "adding water to precipitate oligomers", while ethylene glycol and catalyst can be used in the step of "alcoholysis reaction".
[0037] In some embodiments, the recycling method includes the following steps: S1. Crushing and screening PET plastic waste to obtain PET plastic fragments; PET plastic fragments and 1,3-dimethylpropaneurea were mixed and stirred at 120~180℃ for 10~40 min to dissolve. Then, the mixture was filtered to remove insoluble impurities to obtain a solution. S2-1. Add ultrapure water as a reverse solvent to the solution obtained in step S1 to regenerate the PET plastic. Then, achieve solid-liquid separation by vacuum filtration to obtain the regenerated PET plastic. Collect the filtrate, recover and reuse the 1,3-dimethylpropaneurea in the filtrate, and repeatedly wash the regenerated PET plastic with ultrapure water; or, S2-2. Add ethylene glycol and catalyst to the solution obtained in step S1, and perform alcoholysis reaction at 60~80℃ for 10~60 min. Then add water to precipitate oligomers, and then perform solid-liquid separation to remove oligomers. The removed oligomers can be recycled and reused in the alcoholysis reaction. Then, refrigerate the filtrate at 3~5℃ for 10~14 h to cool and crystallize. Collect the bis(2-hydroxyethyl) terephthalate crystals that are insoluble in the system. Perform vacuum distillation on the mixed solution obtained from the refrigeration to recover water, ethylene glycol, catalyst, and 1,3-dimethylpropaneurea. Water can be used in the step of "adding water to precipitate oligomers", and ethylene glycol and catalyst can be used in the step of "alcoholysis reaction".
[0038] Compared with the prior art, this application has the following advantages: 1. This application uses 1,3-dimethylpropaneurea as a selective solvent for PET, which can achieve rapid dissolution of PET at a temperature lower than the PET melting temperature. It eliminates the need for PET melting treatment or high-pressure reaction equipment, which helps to shorten the processing time, reduce heating energy consumption, and reduce PET degradation and discoloration caused by high-temperature treatment.
[0039] 2. After impurity removal and anti-solvent regeneration, the PET solution has a high PET recovery rate and high purity of recycled PET plastic (PET recovery rate: >81%, preferably >95%; purity of recycled PET plastic: >99%). Its main chemical structure and thermal properties are basically the same as those of pure PET. This shows that this application can effectively maintain the material properties while purifying PET.
[0040] 3,1,3-Dimethylpropaneurea can also be used as a co-solvent for the ethylene glycol alcoholysis of PET. In the presence of a catalyst, it can enhance the transesterification reaction between PET and ethylene glycol, significantly reduce the reaction energy barrier of PET alcoholysis, and complete the depolymerization of PET at a lower temperature and in a shorter time.
[0041] 4. After oligomer separation and cooling crystallization, high-purity BHET can be obtained from the alcoholysis products of ethylene glycol. The chromatographic, spectral and thermal properties of the obtained BHET are basically consistent with those of the BHET standard and can be used as a raw material for PET repolymerization or other high-value utilization processes.
[0042] 5. During alcoholysis, 1,3-dimethylpropaneurea can promote the swelling or partial dissolution of PET, improve the transfer process of ethylene glycol and catalyst into the PET, increase the effective contact area between PET and the reaction medium, and promote the transesterification reaction by regulating the molecular interactions around ethylene glycol, thereby achieving low-temperature rapid ethylene glycol alcoholysis of PET.
[0043] 6. The recycling method provided in this application has good applicability to raw materials. It is not only applicable to waste PET textiles, but also to PET bottle flakes, films, sheets and colored PET products. For composite materials such as PET / PE, PET / PVC and PET / PC that are difficult to separate directly by mechanical methods, the PET components can also be recycled through selective dissolution and solid-liquid separation, thereby improving the resource utilization level of complex PET waste.
[0044] 7. The 1,3-dimethylpropaneurea of this application can be used as a good solvent for dissolving PET and can also assist in the alcoholysis of PET. It has multifunctional properties and is irreplaceable compared to other solvents. Attached Figure Description
[0045] Figure 1 This is a process flow diagram of the PET plastic waste recycling method provided in Example 1.
[0046] Figure 2 This is a process flow diagram of the PET plastic waste recycling method provided in Example 4.
[0047] Figure 3 The Fourier transform infrared spectra of the recycled PET plastic and pure PET obtained in Example 1 are shown.
[0048] Figure 4 The images show the hydrogen NMR spectra of the recycled PET plastic and pure PET obtained in Example 1.
[0049] Figure 5 The images show the 1H NMR spectra of the original DMPU and the recycled DMPU.
[0050] Figure 6 The Fourier transform infrared spectra of BHET and BHET standard recovered in Example 4 are shown.
[0051] Figure 7 The above are the 1H NMR spectra of BHET and BHET standards recovered in Example 4. Detailed Implementation
[0052] The technical solution of this application will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of this application and should not be construed as specific limitations thereof.
[0053] Example 1 This embodiment provides a method for recycling PET plastic waste, the recycling method comprising the following steps: S1. Crushing and screening of PET plastic waste: After crushing the PET plastic waste, it is passed through an 80-mesh sieve to obtain PET plastic fragments; Solution-treated PET: Weigh 0.5g of the above-obtained PET plastic fragments into a pressure-resistant bottle, then add 1,3-dimethylpropaneurea, and stir continuously at 160℃ for 20min to dissolve. Then filter to remove insoluble impurities to obtain the solution. The mass ratio of PET plastic fragments to 1,3-dimethylpropaneurea is 1:10. S2. Vacuum filtration to achieve solid-liquid two-phase separation: 10 mL of ultrapure water is added to the solution obtained in step S1 as a reverse solvent to regenerate the PET plastic. Then, the solution is filtered using a vacuum filtration device to achieve solid-liquid separation and obtain the regenerated PET plastic. The filtrate is collected and subjected to vacuum distillation to recover 1,3-dimethylpropylene urea. The recovered 1,3-dimethylpropylene urea can be used in the dissolution process in step S1. Finally, the regenerated PET plastic is repeatedly washed with ultrapure water to remove residual organic solvents on the solid phase surface.
[0054] The process flow diagram of the PET plastic waste recycling method provided in this embodiment is as follows: Figure 1 As shown.
[0055] Example 2 The only difference between this embodiment and Embodiment 1 is that in step S1, the mass ratio of PET plastic fragments to 1,3-dimethylpropaneurea is 1:15, the continuous stirring temperature is 120°C, and the continuous stirring time is 40 min.
[0056] Example 3 The only difference between this embodiment and Embodiment 1 is that in step S1, the mass ratio of PET plastic fragments to 1,3-dimethylpropaneurea is 1:20, the continuous stirring temperature is 180°C, and the continuous stirring time is 10 min.
[0057] Example 4 This embodiment provides a method for recycling PET plastic waste, the recycling method comprising the following steps: S1. Crushing and screening of PET plastic waste: After crushing the PET plastic waste, it is passed through an 80-mesh sieve to obtain PET plastic fragments; Solution-treated PET: Weigh 0.5g of the above-obtained PET plastic fragments into a pressure-resistant bottle, then add 1,3-dimethylpropaneurea, and stir continuously at 160℃ for 20min to dissolve. Then filter to remove insoluble impurities to obtain the solution. The mass ratio of PET plastic fragments to 1,3-dimethylpropaneurea is 1:10. S2. Utilizing 1,3-dimethylpropylene urea to assist in the alcoholysis of PET plastic to generate bis(2-hydroxyethyl) terephthalate, achieving closed-loop recycling: The solution obtained in step S1 was placed in a two-necked flask, and then ethylene glycol and catalyst (1,5,7-triazabicyclo[4.4.0]dec-5-ene) were added. The alcoholysis reaction was carried out at 80°C for 60 min. After that, 20 mL of water was added to precipitate oligomers. Then, solid-liquid separation was performed to remove the oligomers. The removed oligomers could be recycled and reused in the alcoholysis reaction. The filtrate was then refrigerated at 4°C for 12 h to cool and crystallize. The bis(2-hydroxyethyl) terephthalate crystals that were insoluble in the system were collected. The mixed solution obtained after refrigeration was subjected to vacuum distillation to recover water, ethylene glycol, catalyst, and 1,3-dimethylpropaneurea. Water can be used in the step of "adding water to precipitate oligomers", and ethylene glycol and catalyst can be used in the step of "alcoholysis reaction". The mass ratio of PET plastic fragments, ethylene glycol, and catalyst is 1:1:0.06.
[0058] The process flow diagram of the PET plastic waste recycling method provided in this embodiment is as follows: Figure 2 As shown.
[0059] Example 5 The only difference between this embodiment and Example 4 is that in step S2, the mass ratio of PET plastic fragments, ethylene glycol, and catalyst is 1:1:0.06, the alcoholysis reaction temperature is 60°C, and the alcoholysis reaction time is 60 min.
[0060] Example 6 The only difference between this embodiment and Example 4 is that in step S2, the mass ratio of PET plastic fragments, ethylene glycol, and catalyst is 1:1:0.06, the alcoholysis reaction temperature is 70°C, and the alcoholysis reaction time is 10 min.
[0061] Comparative Example 1 This comparative example provides a method for recycling PET plastic waste, the method comprising the following steps: S1. Crushing and screening of PET plastic waste: After crushing the PET plastic waste, it is passed through an 80-mesh sieve to obtain PET plastic fragments; Solution-treated PET: Weigh 0.5g of the above-obtained PET plastic fragments into a pressure-resistant bottle, then add naphthalene, and stir continuously at 200℃ for 60min to dissolve. Then filter to remove insoluble impurities to obtain the solution. The mass ratio of PET plastic fragments to naphthalene is 1:10. S2. Vacuum filtration to achieve solid-liquid two-phase separation: Add 10 mL of ultrapure water to the solution obtained in step S1 as a reverse solvent to regenerate the PET plastic. Then, use a vacuum filtration device to perform filtration to achieve solid-liquid separation and obtain regenerated PET plastic. Finally, repeatedly wash the obtained regenerated PET plastic with ultrapure water to remove residual organic solvents on the solid phase surface.
[0062] Comparative Example 2 This comparative example provides a method for recycling PET plastic waste, the method comprising the following steps: S1. Crushing and screening of PET plastic waste: After crushing the PET plastic waste, it is passed through an 80-mesh sieve to obtain PET plastic fragments; Solution-treated PET: Weigh 0.5g of the above-obtained PET plastic fragments into a pressure-resistant bottle, then add 1-butyl-3-methylimidazolium chloride (BmimCl), and stir continuously at 180℃ for 8 hours to dissolve. Then filter to remove insoluble impurities to obtain the solution. The mass ratio of PET plastic fragments to 1-butyl-3-methylimidazolium chloride is 1:20. S2. Vacuum filtration to achieve solid-liquid two-phase separation: Add 10 mL of ultrapure water to the solution obtained in step S1 as a reverse solvent to regenerate the PET plastic. Then, use a vacuum filtration device to perform filtration to achieve solid-liquid separation and obtain regenerated PET plastic. Finally, repeatedly wash the obtained regenerated PET plastic with ultrapure water to remove residual organic solvents on the solid phase surface.
[0063] Comparative Example 3 This comparative example provides a method for recycling PET plastic waste, the method comprising the following steps: S1. Crushing and screening of PET plastic waste: After crushing the PET plastic waste, it is passed through an 80-mesh sieve to obtain PET plastic fragments; Solution-treated PET: Weigh 0.5g of the above-obtained PET plastic fragments into a pressure-resistant bottle, then add isosorbide dimethyl ether, stir continuously at 180℃ for 10min to dissolve, then filter to remove insoluble impurities to obtain the solution; The mass ratio of PET plastic fragments to isosorbide dimethyl ether is 1:10. S2. Using isosorbide dimethyl ether to assist in the alcoholysis of PET plastic to generate bis(2-hydroxyethyl) terephthalate, achieving closed-loop recycling: The solution obtained in step S1 was placed in a two-necked flask, and then ethylene glycol and catalyst (1,5,7-triazabicyclo[4.4.0]dec-5-ene) were added. The alcoholysis reaction was carried out at 120°C for 180 min. After that, 20 mL of water was added to precipitate oligomers. Then, solid-liquid separation was performed to remove the oligomers. The removed oligomers could be recycled and reused in the alcoholysis reaction. The filtrate was then refrigerated at 4°C for 12 h to cool and crystallize. The bis(2-hydroxyethyl) terephthalate crystals that were insoluble in the system were collected. The mixed solution obtained after refrigeration was subjected to vacuum distillation to recover water, ethylene glycol, catalyst, and isosorbide dimethyl ether. Water can be used in the step of "adding water to precipitate oligomers", and ethylene glycol and catalyst can be used in the step of "alcoholysis reaction". The mass ratio of PET plastic fragments, ethylene glycol, and catalyst is 1:1:0.1.
[0064] Comparative Example 4 This comparative example provides a method for recycling PET plastic waste, the method comprising the following steps: S1. Crushing and screening of PET plastic waste: After crushing the PET plastic waste, it is passed through an 80-mesh sieve to obtain PET plastic fragments; Solution-treated PET: Weigh 0.5g of the above-obtained PET plastic fragments into a pressure-resistant bottle, then add dihydro-L-glucanone, and stir continuously at 170℃ for 20min to dissolve. Then filter to remove insoluble impurities to obtain the solution. The mass ratio of PET plastic fragments to dihydro-L-glucanone is 1:10. S2. Utilizing dihydro-L-glucanone to assist in the alcoholysis of PET plastic to generate bis(2-hydroxyethyl) terephthalate, achieving closed-loop recycling: The solution obtained in step S1 was placed in a two-necked flask, and then ethylene glycol and catalyst (1,5,7-triazabicyclo[4.4.0]dec-5-ene) were added. The alcoholysis reaction was carried out at 120°C for 180 min. After that, 20 mL of water was added to precipitate oligomers. Then, solid-liquid separation was performed to remove the oligomers. The removed oligomers could be recycled and reused in the alcoholysis reaction. The filtrate was then refrigerated at 4°C for 12 h to cool and crystallize. The bis(2-hydroxyethyl) terephthalate crystals that were insoluble in the system were collected. The mixed solution obtained after refrigeration was subjected to vacuum distillation to recover water, ethylene glycol, catalyst, and dihydro-L-glucanone. Water can be used in the step of "adding water to precipitate oligomers", and ethylene glycol and catalyst can be used in the step of "alcoholysis reaction". The mass ratio of PET plastic fragments, ethylene glycol, and catalyst is 1:1:0.06.
[0065] The PET recycling rate (i.e., recycled PET plastic yield), PET conversion rate during alcoholysis, and BHET yield in the embodiments and comparative examples of this application are calculated using the following formulas: ; ; ; Among them, M BHET The molar mass of BHET is 254 g / mol; M PET The molar mass of the repeating PET unit is 192 g / mol.
[0066] The recycled PET plastics or BHET obtained in the embodiments and comparative examples of this application were tested using the following methods: The purity of BHET was determined by high performance liquid chromatography. A standard curve was established using BHET standards, and the mass percentage of BHET was calculated based on the measured concentration of BHET in the sample and the sample weight.
[0067] PET purity (i.e., the purity of recycled PET plastic) was determined using a complete hydrolysis-high performance liquid chromatography (HPLC) method. The specific method is as follows: A certain mass of PET sample was weighed and completely hydrolyzed to convert the PET into terephthalic acid (TPA). The TPA content in the hydrolysate was determined using HPLC. Based on the measured TPA content and the stoichiometric relationship between PET repeating structural units and TPA, the mass content of PET in the sample was calculated, and this mass content was used as the PET purity. The calculation formula is as follows: ; Among them, M PET The molar mass of the repeating PET unit is 192 g / mol. M TPA The molar mass of TPA is 166 g / mol. W TPA The TPA mass is measured after complete hydrolysis of recycled PET plastic.
[0068] The results are shown in Table 1.
[0069] Table 1
[0070] As shown in Table 1, the first path of the PET plastic waste recycling method provided in this application not only has a low recycling temperature and short processing time, but also produces recycled PET plastic with high yield (PET recovery rate: >81%, preferably >95%) and high purity (>99%). The second path of the PET plastic waste recycling method provided in this application allows for PET recycling at an alcoholysis temperature below 100°C, and produces BHET monomer with high yield (81.6%~85.1%) and high purity (98.5%~98.7%).
[0071] Compared with Example 1, Comparative Example 1 required a higher reaction temperature, Comparative Example 2 required a longer reaction time, and had a lower PET recovery rate.
[0072] Compared with Example 4, Comparative Example 3 had significantly lower PET conversion rate and BHET yield, and Comparative Example 4 had significantly lower PET conversion rate and BHET yield.
[0073] The Fourier transform infrared (FT-IR) spectra of recycled PET plastic and pure PET obtained in Example 1 of this application are as follows: Figure 3 As shown, the nuclear magnetic resonance (NMR) of the recycled PET plastic obtained in Example 1 of this application and that of pure PET is... 1 The hydrogen spectrum of H NMR is as follows: Figure 4 As shown, from Figure 3 and Figure 4 It can be seen that the patterns of recycled PET plastic are basically the same as those of pure PET.
[0074] The PET plastic waste recycling method provided in Examples 1-3 of this application allows for the recovery and recycling of 1,3-dimethylpropylene urea after PET regeneration via vacuum distillation. The 1,3-dimethylpropylene urea recovered in step S3 of Example 1 of this application is designated as the first recycled DMPU. This DMPU is then reused in the dissolution process to obtain the second through fifth recycled DMPU. The original DMPU and the recycled DMPU are subjected to 1H NMR spectroscopy, and the test results are as follows: Figure 5As shown, after 5 cycles, the purity and recovery rate of the recovered 1,3-dimethylpropylene urea reached 92.71% and 93.54%, respectively. That is, this application reduces the consumption of fresh solvent and the amount of waste liquid generated through solvent recovery and recycling, and has potential resource and environmental benefits.
[0075] The Fourier transform infrared spectra of the BHET and BHET standard recovered in Example 4 of this application are as follows: Figure 6 As shown, the 1H NMR spectra of BHET and BHET standards recovered in Example 4 of this application are as follows. Figure 7 As shown, from Figure 6 and Figure 7 It can be seen that the chromatograms of recycled BHET are basically consistent with those of BHET standard, and it can be used as a raw material for PET repolymerization or other high-value utilization processes.
[0076] The applicant declares that this application illustrates the PET plastic waste recycling method through the above embodiments, but this application is not limited to the above embodiments, that is, it does not mean that this application must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to this application, equivalent substitutions of the raw materials used in this application, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of this application.
Claims
1. A method for recycling and processing PET plastic waste, characterized in that, The recycling method includes the following steps: S1. Mix PET plastic waste and 1,3-dimethylpropaneurea, dissolve, and obtain a solution; S2-1. Add an anti-solvent to the solution obtained in step S1 to obtain recycled PET plastic; or... S2-2. Ethylene glycol and a catalyst are added to the solution obtained in step S1 to carry out alcoholysis reaction to obtain bis(2-hydroxyethyl) terephthalate crystals. The antisolvent in step S2-1 is ultrapure water, and the catalyst in step S2-2 is a catalyst capable of catalyzing the transesterification of PET and ethylene glycol.
2. The recycling method according to claim 1, characterized in that, The PET plastic waste mentioned in step S1 includes any one or a combination of at least two of the following: PET waste plastics from fresh household waste, PET waste plastics from industrial and agricultural production, and PET waste plastics from aged waste. And / or, prior to mixing the PET plastic waste and 1,3-dimethylpropylene urea as described in step S1, the following steps are also included: PET plastic waste is crushed and sieved to obtain PET plastic fragments; And / or, the dissolution described in step S1 may be followed by a filtration step.
3. The recycling method according to claim 1, characterized in that, The mass ratio of PET plastic waste to 1,3-dimethylpropylene urea in step S1 is 1:(10~20); And / or, the dissolution described in step S1 is carried out under stirring conditions, wherein the stirring temperature is 120~180℃ and the stirring time is 10~40min.
4. The recycling method according to claim 1, characterized in that, Step S2-1 specifically includes: adding an antisolvent to the solution obtained in step S1 to regenerate the PET plastic, then performing solid-liquid separation to obtain recycled PET plastic, and then cleaning the recycled PET plastic; The filtrate collected by the solid-liquid separation contains 1,3-dimethylpropylene urea, which can be recycled and reused to dissolve PET plastic waste. The cleaning of recycled PET plastic specifically includes: repeatedly cleaning the recycled PET plastic with ultrapure water.
5. The recycling method according to claim 1, characterized in that, The mass ratio of ethylene glycol in step S2-2 to PET plastic waste in step S1 is (0.8~1.2):
1.
6. The recycling method according to claim 1, characterized in that, The mass ratio of the catalyst in step S2-2 to the PET plastic waste in step S1 is (0.04~0.08):
1.
7. The recycling method according to claim 1, characterized in that, The alcoholysis reaction in step S2-2 is carried out at a temperature of 60-80°C for 10-60 minutes.
8. The recycling method according to claim 1, characterized in that, Step S2-2 specifically includes: adding ethylene glycol and a catalyst to the solution obtained in step S1 to carry out an alcoholysis reaction, then adding water to precipitate oligomers, then performing solid-liquid separation to remove oligomers, then refrigerating the filtrate and collecting bis(2-hydroxyethyl) terephthalate crystals that are insoluble in the system.
9. The recycling method according to claim 8, characterized in that, The oligomers removed by the solid-liquid separation can be recycled and reused in the alcoholysis reaction; And / or, the refrigeration of the filtrate specifically includes: refrigerating the filtrate at 3~5℃ for 10~14h; And / or, the refrigeration of the filtrate further includes the following steps: The refrigerated mixture was subjected to vacuum distillation to recover water, ethylene glycol, catalyst, and 1,3-dimethylpropaneurea.
10. The recycling method according to any one of claims 1-9, characterized in that, The recycling method includes the following steps: S1. Crushing and screening PET plastic waste to obtain PET plastic fragments; PET plastic fragments and 1,3-dimethylpropaneurea were mixed and stirred at 120~180℃ for 10~40 min to dissolve. Then, the mixture was filtered to remove insoluble impurities to obtain a solution. S2-1. Add ultrapure water as a reverse solvent to the solution obtained in step S1 to regenerate the PET plastic. Then, achieve solid-liquid separation by vacuum filtration to obtain the regenerated PET plastic. Collect the filtrate, recover and reuse the 1,3-dimethylpropylene urea in the filtrate, and repeatedly wash the regenerated PET plastic with ultrapure water; or, S2-2. Add ethylene glycol and catalyst to the solution obtained in step S1, and perform alcoholysis reaction at 60~80℃ for 10~60 min. Then add water to precipitate oligomers, and then perform solid-liquid separation to remove oligomers. The removed oligomers can be recycled and reused in the alcoholysis reaction. Then, refrigerate the filtrate at 3~5℃ for 10~14 h to cool and crystallize. Collect the bis(2-hydroxyethyl) terephthalate crystals that are insoluble in the system. Perform vacuum distillation on the mixed solution obtained from the refrigeration to recover water, ethylene glycol, catalyst, and 1,3-dimethylpropaneurea.