Method for chemically recovering polyethylene glycol terephthalate from deep eutectic solution
By using a deep eutectic solution composed of ethylene glycol and thymeol as a catalyst, the problem of insufficient swelling and nucleophilic capacity in chemical recovery of polyethylene terephthalate is solved, efficient degradation and recyclability are achieved, and the Catalyst residue improves product purity and recycling efficiency.
Patent Information
- Application Number
- CN202411225106.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-03
- Publication Date
- 2024-12-10
AI Technical Summary
In the existing chemical recycling methods, ethylene glycol has insufficient swelling capacity and weak nucleophilic capacity on polyethylene terephthalate, resulting in slow reaction rate and low activity, and metal-based deep eutectic solution during the separation of degradation products. It is prone to residues, causing product pollution and catalyst loss.
The deep eutectic solution composed of ethylene glycol and thymethol is used as a catalyst to improve the nucleophilic ability of ethylene glycol and the swelling degree of polyethylene terephthalate through hydrogen bonding, and recover through rotary evaporation and liquid separation. Ethylene glycol and thymeol achieve their recyclability and avoid residue.
Improve the degradation efficiency of polyethylene terephthalate, shorten the reaction time, reduce the reaction temperature, and the environmental protection and low toxicity and recyclability of the deep eutectic solution, avoid catalyst residue, improve product purity and Recycling efficiency.
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Figure CN119100921A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a method for chemically recycling plastics, in particular to a method for chemically recycling polyethylene terephthalate using a deep eutectic solution. Background Art
[0002] Polyethylene terephthalate (PET) is a petroleum-based thermoplastic material. Due to its excellent durability, high transparency and lightweight characteristics, it is widely used in the manufacture of disposable plastic bottles, fiber plastic materials, plastic films and other plastic products. However, due to the complex structure and high crystallinity of PET, it is difficult to degrade in the natural environment, which not only causes serious pollution to the ecological environment, but also poses a potential threat to human health. Therefore, the recycling and treatment of polyethylene terephthalate has become a research focus and technology development focus, aiming to effectively respond to and alleviate the environmental problems caused by it.
[0003] The recycling strategy of polyethylene terephthalate (PET) mainly covers two major approaches: physical recycling and chemical recycling. Although physical recycling is simple and easy, it can easily cause irreversible degradation of PET material performance, thereby affecting the quality of recycled products. In contrast, chemical recycling focuses on using degradants to efficiently convert PET into high-value monomers, which can be reused in polymer materials, thereby achieving the full life cycle cycle of PET.
[0004] Among the many methods of chemical recycling, glycol hydrolysis has attracted much attention due to its unique advantages. Its advantages are mainly reflected in the high homogeneity of the product, which is only bis(hydroxyethyl) terephthalate monomer (BHET), which greatly facilitates the separation and recovery of degradation products. However, the technical difficulties of this method are: (1) the slow reaction rate caused by the insufficient swelling ability of ethylene glycol on PET; (2) the low reaction activity caused by the weak nucleophilic ability of ethylene glycol. These problems still need further research and optimization.
[0005] Deep eutectic solvent (DES) is a new type of green solvent, which is prepared by mixing two or more different hydrogen bond acceptors and hydrogen bond donors in a specific molar ratio at a specific temperature. This solvent exhibits similar properties to ionic liquids, but the preparation process is simpler, the cost is low, and the toxicity is low. It is reported that metal-based deep eutectic solutions have been used as catalysts in the chemical recycling of PET. Rollo et al. successfully used DES composed of FeCl3·6H2O and methanesulfonic acid to catalyze the hydrolysis of PET (Chemical Engineering Journal, 2023, 456: 141092). In addition, DES composed of zinc chloride, zinc acetate, potassium carbonate and other components have also been shown to have the ability to catalyze the alcoholysis of PET ethylene glycol (Journal of Polymers and the Environment, 2022, 30: 333-343; Journal of Polymers and the Environment, 2019, 27: 2956-2962). The performance of DES in catalyzing PET degradation mostly comes from improving the nucleophilicity of ethylene glycol through hydrogen bonding. However, the high water solubility of metal salts makes it easy for metal-based deep eutectic solutions to remain in the separation process of degradation products and difficult to recover, thus causing product contamination and catalyst loss problems. Similarly, choline chloride-based DES with high water solubility also faces similar technical challenges. Therefore, it is necessary to develop a method for chemically recovering PET using a recyclable deep eutectic solution to address the technical challenges faced by such reagents in the chemical recovery of PET. Summary of the invention
[0006] The purpose of the present invention is to provide a method for chemically recovering polyethylene terephthalate using a deep eutectic solution in view of the technical challenges currently faced by polyethylene terephthalate in chemical recovery. The deep eutectic solution used in the method not only has the performance advantages of strengthening the nucleophilic ability of ethylene glycol and improving the swelling degree of PET, but also has the advantages of being recyclable and having no residue in the product.
[0007] The present invention provides a method for chemically recovering polyethylene terephthalate from a deep eutectic solution, and the technical scheme adopted is as follows:
[0008] S1 prepares a deep eutectic solution consisting of ethylene glycol and thymol in a reactor;
[0009] S2: adding polyethylene terephthalate to the deep eutectic solution obtained in step S1 and reacting for a period of time;
[0010] S3: filtering the degradation liquid obtained in step S2, wherein the filter cake C1 is undegraded polyethylene terephthalate, and the filtrate L1 is a deep eutectic solution and degradation products;
[0011] S4: adding water to wash the filtrate L1 obtained in step S3, and then using a separatory funnel to separate the liquids, the solid phase is bis(hydroxyethyl) terephthalate dimer and oligomer, the aqueous phase L2 is ethylene glycol and bis(hydroxyethyl) terephthalate monomers, and the oil phase is thymol;
[0012] S5: concentrate the aqueous phase L2 obtained in step S4, and filter after recrystallization, and the solid filter cake C2 is bis(hydroxyethyl) terephthalate monomer;
[0013] S6: rotary evaporating the filtrate obtained in step S5 to recover ethylene glycol.
[0014] Preferably, in step S1, the molar ratio of ethylene glycol to thymol in preparing the deep eutectic solution is 10:1-25:1, the temperature is 50-90° C., and the time is 30-120 minutes.
[0015] Preferably, in step S2, the reaction heating method is oil bath heating or oven heating, the temperature is 150-210° C., and the time is 0.5-5 hours.
[0016] Preferably, in step S4, the temperature of the washing water is 60-100°C.
[0017] As a further improvement of the technical solution, in step S4 and step S6, the recovered thymol and ethylene glycol can be returned to step S1 for recycling after vacuum drying.
[0018] The principles and beneficial effects of the present invention are as follows:
[0019] (1) The deep eutectic solution used in the present invention directly uses ethylene glycol, a degradation agent of polyethylene terephthalate, as a hydrogen bond acceptor, and only needs to add thymol as a hydrogen bond acceptor. This not only utilizes the hydrogen bonding characteristics of the deep eutectic solution to enhance the nucleophilic ability of ethylene glycol, but also reduces the types of substances in the reaction system, making it easier to separate and purify.
[0020] (2) The thymol in the deep eutectic solution used in the present invention is a benzene-based substance, which has a high solubility in polyethylene terephthalate, can increase the swelling degree of polyethylene terephthalate in the reaction system, and accelerate the reaction rate.
[0021] (3) The ethylene glycol in the deep eutectic solution used in the present invention can be recovered by rotary evaporation, and thymol can be recovered by liquid separation, which is recyclable and not easy to remain in the product.
[0022] (4) The ethylene glycol and thymol in the deep eutectic solution used in the present invention are both environmentally friendly reagents, and compared with new solvents such as ionic liquids, they have significant advantages in environmental protection and low toxicity.
[0023] (5) The deep eutectic solution used in the present invention can synergize with other heterogeneous catalysts to further improve the efficiency of PET degradation reaction. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] In order to more clearly illustrate the specific implementation of the present invention, the following is a brief introduction to the drawings required for use in the specific implementation:
[0025] Figure 1 The differential scanning calorimetry (DSC) curves of the deep eutectic solutions prepared in Examples 1 and 2 of the present invention;
[0026] Figure 2 This is a schematic diagram of the layers of the middle water phase and the top oil phase taken out from the separatory funnel in Example 1 of the present invention;
[0027] Figure 3 Liquid NMR hydrogen spectrum of the deep eutectic solution prepared in Example 2 of the present invention ( 1 H-NMR);
[0028] Figure 4 The liquid NMR hydrogen spectrum and carbon spectrum of the bis(hydroxyethyl) terephthalate monomer obtained in Example 2 of the present invention are ( 1 H-NMR and 13 C-NMR);
[0029] Figure 5 This is a comparison chart of the degradation efficiency of polyethylene terephthalate in Examples 1 and 2 of the present invention and Comparative Example 1. DETAILED DESCRIPTION
[0030] To make the technical solution of the present invention clearer, the technical solution in the embodiment of the present invention will be described below in conjunction with the accompanying drawings in the embodiment of the present invention. Obviously, the described embodiment is only a part of the embodiment of the present invention, not all of the embodiments. Based on the embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.
[0031] It should be noted that the polyethylene terephthalate described in the present invention can be used as laboratory reagents and plastic products from various sources such as beverages, food packaging, and cosmetics.
[0032] Example 1
[0033] 15.0 mL of ethylene glycol and 2.7 g of thymol were added to the flask and mixed at 80 °C for 1 hour to prepare a deep eutectic solution with a molar ratio of ethylene glycol to thymol of 15:1. The differential scanning calorimetry (DSC) curve showed that the melting point of the deep eutectic solution was significantly lower than the melting points of ethylene glycol and thymol (-13 °C and 48 °C, respectively). The deep eutectic solution was successfully prepared ( Figure 1 ).
[0034] After the obtained deep eutectic solution was heated to 196° C. in an oil bath, 2.6 g of polyethylene terephthalate was added, and the mixture was subjected to condensation reflux reaction for 2 hours at normal pressure and 196° C. After the reaction time was over, the degradation liquid was filtered, and the filter cake was the undegraded polyethylene terephthalate, which was dried and weighed. It was calculated that the degradation rate of polyethylene terephthalate in this Example 1 was 100%.
[0035] Add 600 mL of 80°C water to the filtrate for washing, and it can be seen that the water phase and the oil phase are clearly separated ( Figure 2 ). The bottom solid phase, the middle aqueous phase and the top oil phase were collected by a separatory funnel, wherein the oil phase was thymol. The collected aqueous phase was concentrated to 60 mL, recrystallized at 4°C for 12 hours, and then filtered. The filter cake was bis-hydroxyethyl terephthalate monomer, which was dried and weighed. The yield of bis-hydroxyethyl terephthalate in Example 1 was calculated to be 75.0%. The filtrate was rotary evaporated to recover ethylene glycol.
[0036] Figure 1 The differential scanning calorimetry (DSC) curves of the deep eutectic solutions prepared in Examples 1 and 2 are shown.
[0037] Figure 2 A schematic diagram showing the layering of the middle aqueous phase and the top oil phase taken out from the separatory funnel in Example 1.
[0038] Example 2
[0039] 10.0 mL of ethylene glycol and 1.1 g of thymol were added to the reactor and mixed at 60 °C for 1.5 hours to prepare a deep eutectic solution with a molar ratio of ethylene glycol to thymol of 25:1. The differential scanning calorimetry (DSC) curve showed that the deep eutectic solution was successfully prepared ( Figure 1 ). Liquid H NMR Spectrum ( 1 H-NMR, Figure 3 ) showed that compared with the pure ethylene glycol solution, the hydroxyl peak of ethylene glycol in the deep eutectic solution moved to the low field, and the nucleophilic ability of ethylene glycol was enhanced.
[0040] 1.5 g of polyethylene terephthalate was added to the obtained deep eutectic solution, and the mixture was heated to 180° C. in an oven and reacted for 5 hours. After the reaction time was over, the degradation solution was filtered, and the filter cake was undegraded polyethylene terephthalate, which was dried and weighed. It was calculated that the degradation rate of polyethylene terephthalate in Example 2 was 88.1%.
[0041] Add 600 mL of 60°C water to the filtrate for washing, and then use a separatory funnel to collect the bottom solid phase, the middle water phase and the top oil phase, where the oil phase is thymol. Concentrate the collected water phase to 60 mL, recrystallize at 4°C for 12 hours, and then filter. Liquid nuclear magnetic resonance hydrogen and carbon spectra ( 1 H-NMR and 13 C-NMR, Figure 4 ) The structure of the filter cake product was characterized, and it was found that the product had a characteristic peak of bis-hydroxyethyl terephthalate monomer. The filter cake was dried and weighed, and the yield of bis-hydroxyethyl terephthalate in Example 2 was calculated to be 52.3%. The filtrate was rotary evaporated to recover ethylene glycol.
[0042] Figure 3 The liquid NMR hydrogen spectrum of the deep eutectic solution prepared in Example 2 is shown ( 1 H-NMR).
[0043] Figure 4 The liquid NMR hydrogen spectrum and carbon spectrum of the bis(hydroxyethyl) terephthalate monomer obtained in Example 2 are shown ( 1 H-NMR and 13 C-NMR).
[0044] Comparative Example 1
[0045] The difference from Example 1 is that thymol is not contained in this Comparative Example 1, and only ethylene glycol solution is used. The amounts of other reactants and reaction conditions remain unchanged and will not be described in detail here.
[0046] In this comparative example 1, the degradation rate of polyethylene terephthalate was 16.1%, and the yield of bis(hydroxyethyl) terephthalate was 2.6%.
[0047] The degradation rate of polyethylene terephthalate and the yield of polyethylene terephthalate obtained in Example 1, Example 2 and Comparative Example 1 were compared ( Figure 5 ), it can be seen that the method for chemically recovering polyethylene terephthalate from a deep eutectic solution provided by the present invention can improve the degradation efficiency, shorten the reaction time, and reduce the reaction temperature.
[0048] Figure 5 A comparison chart of the degradation efficiency of polyethylene terephthalate in Example 1, Example 2 and Comparative Example 1 is shown.
[0049] Please note that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only express several implementation methods of this application, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent.
Claims
1. A method for chemically recovering polyethylene terephthalate from a deep eutectic solution, characterized in that: The following steps are involved: S1 prepares a deep eutectic solution consisting of ethylene glycol and thymol in a reactor; S2: adding polyethylene terephthalate to the deep eutectic solution obtained in step S1 and reacting for a period of time; S3: filtering the degradation liquid obtained in step S2, wherein the filter cake C1 is undegraded polyethylene terephthalate, and the filtrate L1 is a deep eutectic solution and degradation products; S4: adding water to wash the filtrate L1 obtained in step S3, and then using a separatory funnel to separate the liquids, the solid phase is bis(hydroxyethyl) terephthalate dimer and oligomer, the aqueous phase L2 is ethylene glycol and bis(hydroxyethyl) terephthalate monomers, and the oil phase is thymol; S5: concentrate the aqueous phase L2 obtained in step S4, and filter after recrystallization, and the solid filter cake C2 is bis(hydroxyethyl) terephthalate monomer; S6: rotary evaporate the filtrate obtained in step S5 to recover ethylene glycol.
2. The method for chemically recovering polyethylene terephthalate from a deep eutectic solution according to claim 1, characterized in that: In step S1, the molar ratio of ethylene glycol to thymol in preparing the deep eutectic solution is 10:1-25:1, the temperature is 50-90° C., and the time is 30-120 minutes.
3. The method for chemically recovering polyethylene terephthalate from a deep eutectic solution according to claim 1, characterized in that: In step S2, the reaction heating method is oil bath heating or oven heating, the temperature is 150-210° C., and the time is 0.5-5 hours.
4. The method for chemically recovering polyethylene terephthalate from a deep eutectic solution according to claim 1, characterized in that: In step S4, the temperature of the washing water is 60-100°C.
5. The method for chemically recovering polyethylene terephthalate from a deep eutectic solution according to claim 1, characterized in that: In step S4 and step S6, the recovered thymol and ethylene glycol can be returned to step S1 for recycling after vacuum drying.